Papers for Friday, Sep 17 2021

We present the first results of the LBT Imaging of Galaxy Haloes and Tidal Structures (LIGHTS) survey. LIGHTS is an ongoing observational campaign with the 2x8.4m Large Binocular Telescope (LBT) aiming to explore the stellar haloes and the low surface brightness population of satellites down to a depth of muV~31 mag/arcsec^2 (3 sigma in 10"x10" boxes) of nearby galaxies. We simultaneously collected deep imaging in the g and r Sloan filters using the Large Binocular Cameras (LBCs). The resulting images are 60 times (i.e. ~4.5 mag) deeper than those from the Sloan Digital Sky Survey (SDSS), and they have characteristics comparable (in depth and spatial resolution) to the ones expected from the future Legacy Survey of Space and Time (LSST). Here we show the first results of our pilot programme targeting NGC1042 (an M33 analogue at a distance of 13.5 Mpc) and its surroundings. The depth of the images allowed us to detect an asymmetric stellar halo in the outskirts of this galaxy whose mass (1.4+-0.4x10^8 Msun) is in agreement with the Lambda Cold Dark Matter (LambdaCDM) expectations. Additionally, we show that deep imaging from the LBT reveals low mass satellites (a few times 10^5 Msun) with very faint central surface brightness muV(0)~27 mag/arcsec^2 (i.e. similar to Local Group dwarf spheroidals, such as Andromeda XIV or Sextans, but at distances well beyond the local volume). The depth and spatial resolution provided by the LIGHTS survey open up a unique opportunity to explore the `missing satellites' problem in a large variety of galaxies beyond our Local Group down to masses where the difference between the theory and observation (if any) should be significant.

We present observations of the extremely luminous but ambiguous nuclear transient (ANT) ASASSN-17jz, spanning roughly 1200 days of the object's evolution. ASASSN-17jz was discovered by the All-Sky Automated Survey for Supernovae (ASAS-SN) in the galaxy SDSS J171955.84+414049.4 on UT 2017 July 27. The transient peaked at an absolute $B$-band magnitude of $M_{B,{\rm peak}}=-22.81$, corresponding to a bolometric luminosity of $L_{\rm bol,peak}=8.3\times10^{44}$ ergs s$^{-1}$, and exhibited late-time ultraviolet emission with a total emitted energy of $E_{\rm tot}=(1.36\pm0.08)\times10^{52}$ ergs. This late-time light is accompanied by increasing X-ray emission that becomes softer as it brightens. ASASSN-17jz exhibited a large number of spectral emission lines most commonly seen in active galactic nuclei (AGNs) with little evidence of evolution, except for the Balmer lines, which became fainter and broader over time. We consider various physical scenarios for the origin of the transient, including those involving supernovae (SNe), tidal disruption event (TDEs), AGN outbursts, and ANTs. We find that the most likely explanation is that ASASSN-17jz was an SN IIn occurring in or near the disk of an existing AGN, and that the late-time emission is caused by the AGN transitioning to a more active state.

The origin and fate of magnetars (young, extremely magnetized neutron stars, NSs) remain unsolved. Probing their evolution is therefore crucial for investigating possible links to other species of isolated NSs, such as the X-ray dim NSs (XDINSs) and rotating radio transients (RRATs). Here we investigate the spin evolution of magnetars. Two avenues of evolution are considered: one with exponentially decaying B-fields, the other with sub- and super-exponential decay. Using Monte Carlo methods, we synthesize magnetar populations using different input distributions and physical parameters, such as for the initial spin period, its time derivative and the B-field decay timescale. Additionally, we introduce a fade-away procedure that can account for the fading of old magnetars, and we briefly discuss the effect of alignment of the B-field and spin axes. Imposing the Galactic core-collapse supernova rate of ~20 kyr^-1 as a strict upper limit on the magnetar birthrate and comparing the synthetic populations to the observed one using both manual and automatic optimization algorithms for our input parameter study, we find that the B-field must decay exponentially or super-exponentially with a characteristic decay timescale of 0.5-10 kyr (with a best value of ~4 kyr). In addition, the initial spin period must be less than 2 sec. If these constraints are kept, we conclude that there are multiple choices of input physics that can reproduce the observed magnetar population reasonably well. We also conclude that magnetars may well be evolutionary linked to the population of XDINSs, whereas they are in general unlikely to evolve into RRATs.

The behavior of the shock wave in the atmosphere of the non-fundamental mode RR Lyrae pulsator remains a mystery. In this work, we firstly report a blueshifted Mg triplet emission in continuous spectroscopic observations for a non-Blazhko RRc pulsator (Catalina-1104058050978) with LAMOST medium resolution spectra. We analyse the photometric observations from Catalina Sky Survey of this RRc pulsator with pre-whitening sequence method and provide the ephemeris and phases. An additional frequency signal with $P_1/P_x = 0.69841$ is detected and discussed. The redshift and radial velocity of the spectra are provided by fitting process with $S\acute{e}rsic$ functions and cross-correlation method. Moreover, we plot the variation of H$\alpha$ and Mg lines in a system comoving with the pulsation. Clear evolution of comoving blueshifted hydrogen and Mg emission is observed, which further confirms the existence of shock waves in RRc pulsators. The shock-triggered emission lasts over $15\%$ of the pulsation cycle, which is much longer than the previous observations.

Recent observational and theoretical studies of the Local Group (LG) dwarf galaxies have highlighted their unique star formation history, stellar metallicity, gas content, and kinematics. We investigate the commonality of these tantalizing features by comparing constrained LG and field central dwarf halo simulations in the NIHAO project. For the first time, constrained LG simulations performed with NIHAO hydrodynamics which track the evolution of MW and M31 along with ~100 dwarfs in the Local Group are presented. The total gas mass and stellar properties (velocity dispersion, evolution history, etc.) of present-day LG dwarfs are found to be similar to field systems. Overall, the simulated LG dwarfs show representative stellar properties to other dwarfs in the Universe. However, relative to fields, LG dwarfs have more cold gas in their central parts and more metal-rich gas in the halo stemming from interactions with MW/M31 and/or feedback. The larger gas metal content in LG dwarfs results in early star formation events that lead to strong feedback and subsequent quenching. We also test for the impact of metal diffusion on the chemical evolution of LG dwarfs, and find that metal diffusion does not affect the stellar or gaseous content of LG relative to field dwarfs; the largest differences are found with the gas metallicity (~0.1 dex). Our results show that properties from LG dwarfs may be used as general constraints for studying the overall dwarf population in the Universe, providing a powerful local laboratory for galaxy formation tests and comparisons.

The physical processes behind the transfer of mass from parsec-scale clumps to massive-star-forming cores remain elusive. We investigate the relation between the clump morphology and the mass fraction that ends up in its most massive core (MMC) as a function of infrared brightness, i.e. a clump evolutionary tracer. Using ALMA 12 m and ACA we surveyed 6 infrared-dark hubs in 2.9mm continuum at $\sim$3" resolution. To put our sample into context, we also re-analysed published ALMA data from a sample of 29 high mass-surface density ATLASGAL sources. We characterise the size, mass, morphology, and infrared brightness of the clumps using Herschel and Spitzer data. Within the 6 newly observed hubs, we identify 67 cores, and find that the MMCs have masses between 15-911 $\mathrm{M}_{\odot}$ within a radius of 0.018-0.156 pc. The MMC of each hub contains 3-24% of the clump mass ($f_\mathrm{MMC}$), becoming 5-36% once core masses are normalised to the median core radius. Across the 35 clumps, we find no significant difference in the median $f_\mathrm{MMC}$ values of hub and non-hub systems, likely the consequence of a sample bias. However, we find that $f_\mathrm{MMC}$ is $\sim$7.9 times larger for infrared-dark clumps compared to infrared-bright ones. This factor increases up to $\sim$14.5 when comparing our sample of 6 infrared-dark hubs to infrared-bright clumps. We speculate that hub-filament systems efficiently concentrate mass within their MMC early on during its evolution. As clumps evolve, they grow in mass, but such growth does not lead to the formation of more massive MMCs.

Using the Reduced Relativistic Gas (RRG) model, we analytically determine the matter power spectrum for Warm Dark Matter (WDM) on small scales, $k>1\ h\text{/Mpc}$. The RRG is a simplified model for the ideal relativistic gas, but very accurate in the cosmological context. In another work, we have shown that, for typical allowed masses for dark matter particles, $m>5\ \text{keV}$, the higher order multipoles, $\ell>2$, in the Einstein-Boltzmann system of equations are negligible on scales $k<10\ h\text{/Mpc}$. Hence, we can follow the perturbations of WDM using the ideal fluid framework, with equation of state and sound speed of perturbations given by the RRG model. We derive a M\'esz\'aros like equation for WDM and solve it analytically in radiation, matter and dark energy dominated eras. Joining these solutions, we get an expression that determines the value of WDM perturbations as a function of redshift and wavenumber. Then we construct the matter power spectrum and transfer function of WDM on small scales and compare it to some results coming from Lyman-$\alpha$ forest observations. Besides being a clear and pedagogical analytical development to understand the evolution of WDM perturbations, our power spectrum results are consistent with the observations considered and the other determinations of the degree of warmness of dark matter particles.

OB associations play an important role in Galactic evolution, though their origins and dynamics remain poorly studied, with only a small number of systems analysed in detail. In this paper we revisit the existence and membership of the Cygnus OB associations. We find that of the historical OB associations only Cyg OB2 and OB3 stand out as real groups. We search for new OB stars using a combination of photometry, astrometry, evolutionary models and an SED fitting process, identifying 4680 probable OB stars with a reliability of $>$90\%. From this sample we search for OB associations using a new and flexible clustering technique, identifying 6 new OB associations. Two of these are similar to the associations Cyg OB2 and OB3, though the others bear no relationship to any existing systems. We characterize the properties of the new associations, including their velocity dispersions and total stellar masses, all of which are consistent with typical values for OB associations. We search for evidence of expansion and find that all are expanding, albeit anistropically, with stronger and more significant expansion in the direction of Galactic longitude. We also identify two large-scale (160 pc and 25 km s$^{-1}$) kinematic expansion patterns across the Cygnus region, each including three of our new associations, and attribute this to the effects of feedback from a previous generation of stars. This work highlights the need to revisit the existence and membership of the historical OB associations, if they are to be used to study their properties and dynamics.

The gravitational potentials of realistic galaxy models are in general non-integrable, in the sense that they admit orbits that do not have three independent isolating integrals of motion and are therefore chaotic. However, if chaotic orbits are a small minority in a stellar system, it is expected that they have negligible impact on the main dynamical properties of the system. In this paper we address the question of quantifying the importance of chaotic orbits in a stellar system, focusing, for simplicity, on axisymmetric systems. Chaotic orbits have been found in essentially all (non-St\"ackel) axisymmetric gravitational potentials in which they have been looked for. Based on the analysis of the surfaces of section, we add new examples to those in the literature, finding chaotic orbits, as well as resonantly trapped orbits among regular orbits, in Miyamoto-Nagai, flattened logarithmic and shifted Plummer axisymmetric potentials. We define the fractional contributions in mass of chaotic ($\xi_{\rm c}$) and resonantly trapped ($\xi_{\rm t}$) orbits to a stellar system of given distribution function, which are very useful quantities, for instance in the study of the dispersal of stellar streams of galaxy satellites. As a case study, we measure $\xi_{\rm c}$ and $\xi_{\rm t}$ in two axisymmetric stellar systems obtained by populating flattened logarithmic potentials with the Evans ergodic distribution function, finding $\xi_{\rm c}\sim 10^{-4}-10^{-3}$ and $\xi_{\rm t}\sim 10^{-2}-10^{-1}$.

The Cepheus Flare region consists of a group of dark cloud complexes that are currently active in star formation. The aim of this work is to estimate the motion of four clouds, L1147/1158, L1172/1174, L1228 and L1251 located at relatively high Galactic latitude (b $\gt$ 14$^{\circ}$) in the Cepheus Flare region. We study the relationship between the motion of the cloud with respect to the magnetic field and the clump orientations with respect to both the magnetic field and the motion. We estimated the motion of the molecular clouds using the proper motion and the distance estimates of the young stellar objects (YSOs) associated with them using the Gaia EDR3 data. By assuming that the YSOs are associated with the clouds and share the same velocity, the projected direction of motion of the clouds are estimated. We estimated a distance of 371$\pm$22 pc for L1228 and 340$\pm$ 7 pc for L1251 implying that all four complexes are located at almost the same distance. Assuming that both the clouds and YSOs are kinematically coupled, we estimated the projected direction of motion of the clouds using the proper motions of the YSOs. All the clouds in motion are making an offset of $\sim$ 30$^{\circ}$ with respect to the ambient magnetic fields except in L1172/1174 where the offset is $\sim$ 45$^{\circ}$. In L1147/1158, the starless clumps are found to be oriented predominantly parallel to the magnetic fields while prestellar clumps show random distribution. In L1172/1174, L1228 and L1251,the clumps are oriented randomly with respect to magnetic field. With respect to the motion of the clouds, there is a marginal trend that the starless clumps are oriented more parallel in L1147/1158 and L1172/1174. In L1228, the clumps major axis are oriented more randomly. In L1251, we find a bimodal trend in case of starless clumps.

The observational appearance of black holes in X-ray binary systems depends on their masses, spins, accretion rate and the misalignment angle between the black hole spin and the orbital angular momentum. We used high-precision optical polarimetric observations to constrain the position angle of the orbital axis of the black hole X-ray binary MAXI J1820+070. Together with previously obtained orientation of the relativistic jet and the inclination of the orbit this allowed us to determine a lower limit of 40 degrees on the misalignment angle. Such a large misalignment challenges the models of quasi-periodic oscillations observed in black hole X-ray binaries, puts strong constraints on the black hole formation mechanisms, and has to be accounted for when measuring black hole masses and spins from the X-ray data.

Binary stars can inflate the observed velocity dispersion of stars in dark matter dominated systems such as ultra-faint dwarf galaxies (UFDs). However, the population of binaries in UFDs is poorly constrained by observations, with preferred binary fractions for individual galaxies ranging from a few percent to nearly unity. Searching for wide binaries through nearest neighbor (NN) statistics (or the two-point correlation function) has been suggested in the literature, and we apply this method for the first time to detect wide binaries in a UFD. By analyzing the positions of stars in Reticulum~II (Ret~II) from Hubble Space Telescope images, we search for angularly resolved wide binaries in Ret~II. We find that the distribution of their NN distances shows an enhancement at projected separations of $\lesssim8$ arc seconds relative to a model containing no binaries. We show that such an enhancement can be explained by a binary fraction of $f_b\approx0.07^{+0.04}_{-0.03}$, with modest evidence for a smaller mean separation than is seen in the solar neighborhood. We also use the observed magnitude distribution of stars in Ret~II to constrain the initial mass function over the mass range $0.34-0.78~M_{\odot}$, finding that a shallow power-law slope of $\alpha = 1.10^{+0.30}_{-0.09}$ matches the data.

While radio emission in quasars can be contributed to by a variety of processes (involving star forming regions, accretion disk coronas and winds, and jets), the powering of the radio loudest quasars must involve very strong jets, presumably launched by the Blandford-Znajek mechanism incorporating the magnetically arrested disk (MAD) scenario. We focus on the latter and investigate the dependence of their fraction on redshift. We also examine the dependence of the radio-loud fraction (RLF) on BH mass ($M_{\rm BH}$) and Eddington ratio ($\lambda_{\rm Edd}$) while excluding the redshift bias by narrowing its range. In both these investigations we remove the bias associated with: (1) the diversity of source selection by constructing two well-defined, homogeneous samples of quasars (first within $0.7 \leq z < 1.9$, second within $0.5 \leq z < 0.7$); (2) a strong drop in the RLF of quasars at smaller BH masses by choosing those with BH masses larger than $10^{8.5} M_{\odot}$. We confirm some previous results showing the increase in the fraction of radio-loud quasars with cosmic time and that this trend can be even steeper if we account for the bias introduced by the dependence of the RLF on BH mass whereas the bias introduced by the dependence of the RLF on Eddington ratio is shown to be negligible. Assuming that quasar activities are triggered by galaxy mergers we argue that such an increase can result from the slower drop with cosmic time of mixed mergers than of wet mergers.

We present comprehensive orbital analyses and dynamical masses for the substellar companions Gl~229~B, Gl~758~B, HD~13724~B, HD~19467~B, HD~33632~Ab, and HD~72946~B. Our dynamical fits incorporate radial velocities, relative astrometry, and most importantly calibrated Hipparcos-Gaia EDR3 accelerations. For HD~33632~A and HD~72946 we perform three-body fits that account for their outer stellar companions. We present new relative astrometry of Gl~229~B with Keck/NIRC2, extending its observed baseline to 25 years. We obtain a $<$1\% mass measurement of $71.4 \pm 0.6\,M_{\rm Jup}$ for the first T dwarf Gl~229~B and a 1.2\% mass measurement of its host star ($0.579 \pm 0.007\,M_{\odot}$) that agrees with the high-mass-end of the M dwarf mass-luminosity relation. We perform a homogeneous analysis of the host stars' ages and use them, along with the companions' measured masses and luminosities, to test substellar evolutionary models. Gl~229~B is the most discrepant, as models predict that an object this massive cannot cool to such a low luminosity within a Hubble time, implying that it may be an unresolved binary. The other companions are generally consistent with models, except for HD~13724~B that has a host-star activity age 3.8$\sigma$ older than its substellar cooling age. Examining our results in context with other mass-age-luminosity benchmarks, we find no trend with spectral type but instead note that younger or lower-mass brown dwarfs are over-luminous compared to models, while older or higher-mass brown dwarfs are under-luminous. The presented mass measurements for some companions are so precise that the stellar host ages, not the masses, limit the analysis.

We examine the prospects for measurement of the Hubble parameter $H_0$ via observation of the secular parallax of other galaxies due to our own motion relative to the cosmic microwave background rest frame. Peculiar velocities make distance measurements to individual galaxies highly uncertain, but a survey sampling many galaxies can still yield a precise $H_0$ measurement. We use both a Fisher information formalism and simulations to forecast errors in $H_0$ from such surveys, marginalizing over the unknown peculiar velocities. The optimum survey observes $\sim 10^2$ galaxies within a redshift $z_\mathrm{max}=0.05$. The required errors on proper motion are comparable to those that can be achieved by Gaia and future astrometric instruments. A measurement of $H_0$ via parallax has the potential to shed light on the tension between different measurements of $H_0$.

Disc-halo decomposition on rotationally supported star-forming galaxies (SFGs) at $z>1$ are often limited to massive galaxies ($M_\star>10^{10}~M_\odot$) and rely on either deep Integral Field Spectroscopy data or stacking analyses. We present a study of the dark matter (DM) content of 9 $z\approx1$ SFGs selected Using the brightest [OII] emitters in the deepest Multi-Unit Spectrograph Explorer (MUSE) field to date, namely the 140hr MUSE Extremely Deep Field, we perform disk-halo decompositions on 9 low-mass SFGs (with $10^{8.5}<M_\star<10^{10.5}~M_\odot$) using a novel 3D modeling approach, which together with the exquisite S/N allows us to measure individual rotation curves to $3\times R_e$. The DM component primarily uses the generalized $\alpha,\beta,\gamma$ profile from Di Cintio et al., or a Navarro-Frenk-White (NFW) profile. The disk stellar masses $M_\star$ obtained from the [OII] disk-halo decomposition agree with the values inferred from the spectral energy distributions. While the rotation curves show diverse shapes, ranging from rising to declining at large radii, the DM fractions within the half-light radius $f_{\rm DM}(<R_e)$ are found to be 60\% to 95\%, extending to lower masses (densities) the results of Genzel et al., who found low DM fractions in SFGs with $M_\star>10^{10}~M_\odot$. The DM halos show constant surface densities of $\sim100~M_\odot$ pc$^{-2}$. Half of the sample shows a strong preference for cored over cuspy DM profiles. The presence of DM cores appears to be related to galaxies with stellar-to-halo mass $\log M_\star/M_{\rm vir}\approx-2.5$. In addition, the cuspiness of the DM profiles is found to be a strong function of the recent star-formation activity. Both of these results are interpreted as evidence for feedback-induced core formation in the Cold Dark Matter context.

Context. Due to our increasing knowledge on the Galactic and stellar neighborhood of the Solar System, modern long-period comet motion studies have to take into account both stellar perturbations and the overall Galactic potential. Aims. Our aim is to propose algorithms and methods to perform numerical integration of a Solar System small body equations of motion much faster and at the same time with greater precision. Methods. We propose a new formulation of the equations of motion formulated in the Solar System barycentric frame but accurately accounting for the differential perturbations caused by the Galactic potential. To use these equations effectively we provide numerical ephemerides of the Galactic positions of the Sun and a set of potential stellar perturbers. Results. The proposed methods offer the precision higher by several orders of magnitude and simultaneously greatly reduce the necessary CPU time. The application of this approach is presented with the example of a detailed dynamical study of the past motion of comet C/2015 XY1.

The redshift distribution of fast radio bursts (FRBs) is not well constrained. The association of the Galactic FRB 200428 with the young magnetar SGR 1935+2154 raises the working hypothesis that FRB sources track the star formation history of the universe. The discovery of FRB 20200120E in association with a globular cluster in the nearby galaxy M81, on the other hand, casts doubts on such an assumption. We apply the Monte Carlo method developed in a previous work to test different FRB redshift distribution models against the recently released first CHIME FRB catalog in terms of their distributions in specific fluence, inferred isotropic energy, and external dispersion measure ($\rm DM_E$). Our results clearly show that the hypothesis that all FRBs track the star formation history of the universe is ruled out. The hypothesis that all FRBs track the accumulated stars throughout history describes the data better but still cannot pass both the energy and $\rm DM_E$ criteria. The data seem to be better modeled with either a redshift distribution model invoking a significant delay with respect to star formation or a hybrid model invoking both a dominant delayed population and an insignificant star formation population. We discuss the implications of this finding for FRB source models.

Gravitational waves (GWs) from inspiralling neutron stars afford us a unique opportunity to infer the as-of-yet unknown equation of state of cold hadronic matter at supranuclear densities. The dominant matter effects are due to the star's response to their companion's tidal field, leaving a characteristic imprint in the emitted GW signal. This unique signature allows us to constrain the neutron star equation of state. At GW frequencies above $\gtrsim 800$Hz, however, subdominant tidal effects known as dynamical tides become important. In this letter, we demonstrate that neglecting dynamical tidal effects associated with the fundamental ($f$-) mode leads to large systematic biases in the measured tidal deformability of the stars and hence in the inferred neutron star equation of state. Importantly, we find that $f$-mode dynamical tides will already be relevant for Advanced LIGO's and Virgo's fifth observing run ($\sim 2025$) -- neglecting dynamical tides can lead to errors on the neutron radius of $\mathcal{O}(1{\rm km})$, with dramatic implications for the measurement of the equation of state. Our results demonstrate that the accurate modelling of subdominant tidal effects beyond the adiabatic limit will be crucial to perform accurate measurements of the neutron star equation of state in upcoming GW observations.

As part of an All-Sky Automated Survey for SuperNovae (ASAS-SN) search for sources with large flux decrements, we discovered a transient where the quiescent, stellar source, ASASSN-V J192114.84+624950.8, rapidly decreased in flux by $\sim55\%$ ($\sim0.9$ mag) in the g-band. The \textit{TESS} light curve revealed that the source is a highly eccentric, eclipsing binary. Fits to the light curve using \textsc{phoebe} find the binary orbit to have $e=0.79$, $P_{\rm orb}=18.462~\text{days}$, and $i=88.6^{\circ}$ and the ratios of the stellar radii and temperatures to be $R_2/R_1 = 0.71$ and $T_{e,2}/T_{e,1} = 0.82$. Both stars are chromospherically active, allowing us to determine their rotational periods of $P_1=1.52$ days and $P_2=1.79$ days, respectively. A LBT/MODS spectrum shows that the primary is a late-G or early-K type dwarf. Fits to the SED show that the luminosities and temperatures of the two stars are $L_1 = 0.48~L_{\sun}$, $T_1= 5050~K$, $L_2 = 0.12~L_{\sun}$, and $T_{2} = 4190~K$. We conclude that ASASSN-V J192114.84+624950.8 consists of two chromospherically active, rotational variable stars in a highly elliptical eclipsing orbit.

The Fermi Gamma-ray Space Telescope has revealed a diffuse $\gamma$-ray background at energies from 0.1 GeV to 1 TeV, which can be separated into Galactic emission and an isotropic, extragalactic component. Previous efforts to understand the latter have been hampered by the lack of physical models capable of predicting the $\gamma$-ray emission produced by the many candidate sources, primarily active galactic nuclei and star-forming galaxies, leaving their contributions poorly constrained. Here we present a calculation of the contribution of star-forming galaxies to the $\gamma$-ray background that does not rely on empirical scalings, and is instead based on a physical model for the $\gamma$-ray emission produced when cosmic rays accelerated in supernova remnants interact with the interstellar medium. After validating the model against local observations, we apply it to the observed cosmological star-forming galaxy population and recover an excellent match to both the total intensity and the spectral slope of the $\gamma$-ray background, demonstrating that star-forming galaxies alone can explain the full diffuse, isotropic $\gamma$-ray background.

We report on a timing programme of 74 young pulsars that have been observed by the Parkes 64-m radio telescope over the past decade. Using modern Bayesian timing techniques, we have measured the properties of 124 glitches in 52 of these pulsars, of which 74 are new. We demonstrate that the glitch sample is complete to fractional increases in spin-frequency greater than $\Delta\nu^{90\%}_{g}/\nu \approx 9.3 \times 10^{-9}$. We measure values of the braking index, $n$, in 33 pulsars. In most of these pulsars, their rotational evolution is dominated by episodes of spin-down with $n > 10$, punctuated by step changes in the spin-down rate at the time of a large glitch. The step changes are such that, averaged over the glitches, the long-term $n$ is small. We find a near one-to-one relationship between the inter-glitch value of $n$ and the change in spin-down of the previous glitch divided by the inter-glitch time interval. We discuss the results in the context of a range of physical models.

The four directly imaged planets orbiting the star HR 8799 are an ideal laboratory to probe atmospheric physics and formation models. We present more than a decade's worth of Keck/OSIRIS observations of these planets, which represent the most detailed look at their atmospheres to-date by its resolution and signal to noise ratio. We present the first direct detection of HR 8799 d, the second-closest known planet to the star, at moderate spectral resolution with Keck/OSIRIS (K-band; R~4,000). Additionally, we uniformly analyze new and archival OSIRIS data (H and K band) of HR 8799 b, c, and d. First, we show detections of water (H2O) and carbon monoxide (CO) in the three planets and discuss the ambiguous case of methane (CH4) in the atmosphere of HR 8799b. Then, we report radial velocity (RV) measurements for each of the three planets. The RV measurement of HR 8799 d is consistent with predictions made assuming coplanarity and orbital stability of the HR 8799 planetary system. Finally, we perform a uniform atmospheric analysis on the OSIRIS data, published photometric points, and low resolution spectra. We do not infer any significant deviation from to the stellar value of the carbon to oxygen ratio (C/O) of the three planets, which therefore does not yet yield definitive information about the location or method of formation. However, constraining the C/O ratio for all the HR 8799 planets is a milestone for any multiplanet system, and particularly important for large, widely separated gas giants with uncertain formation processes.

Accreting millisecond X-ray pulsars are known to provide a wealth of physical information during their successive states of outburst and quiescence. Based on the observed spin-up and spin-down rates of these objects it is possible, among other things, to infer the stellar magnetic field strength and test models of accretion disc flow. In this paper we consider the three accreting X-ray pulsars (XTE J1751-305, IGR J00291+5934, and SAX J1808.4-3658) with the best available timing data, and model their observed spin-up rates with the help of a collection of standard torque models that describe a magnetically-threaded accretion disc truncated at the magnetospheric radius. Whilst none of these models are able to explain the observational data, we find that the inclusion of the physically motivated phenomenological parameter $\xi$, which controls the uncertainty in the location of the magnetospheric radius, leads to an enhanced disc-integrated accretion torque. These 'new' torque models are compatible with the observed spin-up rates as well as the inferred magnetic fields of these objects provided that $\xi \approx 0.1-0.5$. Our results are supplemented with a discussion of the relevance of additional physics effects that include the presence of a multipolar magnetic field and general-relativistic gravity.

The fragmentation process in massive star-forming regions is one of the contemporary problems in astrophysics, and several physical processes have been proposed to control the fragmentation including turbulence, magnetic field, rotation, stellar feedback, and gravity. However, the fragmentation process has been poorly studied at small spatial scales well below 1000 AU. We aim to use ALMA (Atacama Large Millimeter and Submillimeter Array) high angular resolution data to identify the fragments in W51 IRS2 and to study the fragmentation properties on a spatial scale of 200 AU. We used ALMA data of W51 IRS2 from three projects, which give an angular resolution of 0.028$^{\prime\prime}$ (144 AU) at millimeter wavelengths. We identified compact fragments by using {\it uv}-range constrained 1.3 mm continuum data. A Mean Surface Density of Companions (MSDC) analysis has been performed to study the separations between fragments. A total number of 33 continuum sources are identified and 29 out of them are defined as fragments in the surveyed region.The MSDC analysis reveals two breaks corresponding to spatial sales of 1845 AU and 7346 AU, indicative of a two-level clustering phenomenon, along with a linear regime below 1845 AU, mostly associated with W51 North, whose slope is consistent with the slope for the clustering regime of other cluster-like regions in the Galaxy. The typical masses and separations of the fragments as well as the relation between density and number of fragments can be explained through a thermal Jeans process operating at high temperatures of 200--400 K, consistent with previous measurements of the temperature in the region, and produced by the nearby massive stars. Therefore, although W51 IRS2 seems to be undergoing a thermally inhibited fragmentation phase, this does not seem to prevent the formation of a protocluster associated with W51 North.

Dust grains are aligned with the interstellar magnetic field and drift through the interstellar medium (ISM). Evolution of interstellar dust is driven by grain motion. In this paper, we study the effect of grain alignment with magnetic fields and grain motion on grain growth in molecular clouds. We first discuss characteristic timescales of internal alignment (i.e., alignment of the grain axis with its angular momentum, ${\bf J}$) and external alignment (i.e., alignment of ${\bf J}$ with the magnetic field) and find the range of grain sizes that have efficient alignment. Then, we study grain growth for such aligned grains drifting though the gas. Due to the motion of aligned grains along the magnetic field, gas accretion would increase the grain elongation rather than decrease, as in the case of random orientation. Grain coagulation also gradually increases grain elongation, leading to the increase of elongation with the grain size. The coagulation of aligned grains can form dust aggregates that contain the elongated binaries comprising a pair of grains with parallel short axes. The presence of superparamagnetic iron clusters within dust grains enhances internal alignment and thus increases the maximum size of aligned grains from $\sim 2$ to $\sim 10\mu m$ for dense clouds of $n_{\rm H}\sim 10^{5}\rm cm^{-3}$. Determining the size of such aligned grains with parallel axes within a dust aggregate would be important to constrain the location of grain growth and the level of iron inclusions. We find that grains within dust aggregates in 67P/Churyumov-Gerasimenko obtained by {\it Rosetta} have the grain elongation increasing with the grain radius, which is not expected from coagulation by Brownian motion but consistent with the grain growth from aligned grains.

The prompt emission of most gamma-ray bursts (GRBs) typically exhibits a non-thermal Band component. The synchrotron radiation in the popular internal shock model is generally put forward to explain such a non-thermal component. However, the low-energy photon index $\alpha \sim -1.5$ predicted by the synchrotron radiation is inconsistent with the observed value $\alpha \sim -1$. Here, we investigate the evolution of a magnetic field during propagation of internal shocks within an ultrarelativistic outflow, and revisit the fast cooling of shock-accelerated electrons via synchrotron radiation for this evolutional magnetic field. We find that the magnetic field is first nearly constant and then decays as $B'\propto t^{-1}$, which leads to a reasonable range of the low-energy photon index, $-3/2 < \alpha < -2/3$. In addition, if a rising electron injection rate during a GRB is introduced, we find that $\alpha$ reaches $-2/3$ more easily. We thus fit the prompt emission spectra of GRB 080916c and GRB~080825c.

We studied the harmonics of the millihertz quasi-periodic oscillations (mHz QPOs) in the neutron-star low-mass X-ray binary 4U 1636-53 using the Rossi X-ray Timing Explorer observations. We detected the harmonics of the mHz QPOs in 73 data intervals, with most of them in the transitional spectra state. We found that the ratio between the rms amplitude of the harmonic and that of the fundamental remains constant in a wide range of the fundamental frequency. More importantly, we studied, for the first time, the rms amplitude of the harmonics vs. energy in 4U 1636-53 in the 2-5 keV range. We found that the rms amplitude of both the harmonic and the fundamental shows a decreasing trend as the energy increases, which is different from the behaviors reported in QPOs in certain black hole systems. Furthermore, our results suggest that not all observations with mHz QPOs have the harmonic component, although the reason behind this is still unclear.

We extend previous work on gamma-ray burst (GRB) afterglows involving hot thermal electrons at the base of a shock-accelerated tail. Using a physically-motivated electron distribution based on first-principles simulations, we compute broadband emission from radio to TeV gamma-rays. For the first time, we present the effects of a thermal distribution of electrons on synchrotron self-Compton (SSC) emission. The presence of thermal electrons causes temporal and spectral structure across the entire observable afterglow, which is substantively different from models that assume a pure power-law distribution for the electrons. We show that early-time TeV emission is enhanced by more than an order of magnitude for our fiducial parameters, with a time-varying spectral index that does not occur for a pure power law of electrons. We further show that the X-ray "closure relations" take a very different, also time-dependent, form when thermal electrons are present; the shape traced out by the X-ray afterglows is a qualitative match to observations of the traditional decay phase.

GRB 060505 was the first well-known nearby (at redshift 0.089) "hybrid" gamma-ray burst that has a duration longer than 2 seconds but without the association of a supernova down to very stringent limits. The prompt $\gamma-$ray flash lasting $\sim 4$ sec could consist of an intrinsic short burst and its tail emission, but the sizable temporal lag ($\sim 0.35$ sec) as well as the environment properties led to the widely-accepted classification of a long duration gamma-ray burst originated from the collapse of a massive star. Here for the $ first$ time we report the convincing evidence for a thermal-like optical radiation component in the spectral energy distribution of the early afterglow emission. In comparison to AT2017gfo, the thermal radiation is $\sim 2$ times brighter and the temperature is comparable at similar epochs. The optical decline is much quicker than that in X-rays, which is also at odds with the fireball afterglow model but quite natural for the presence of a blue kilonova. Our finding reveals a neutron star merger origin of the hybrid GRB 060505 and strongly supports the theoretical speculation that some binary neutron stars can merge ultra-quickly (within $\sim 1$ Myr) after their formation when the surrounding region is still highly star-forming and the metallicity remains low. Gravitational wave and electromagnetic jointed observations are expected to confirm such scenarios in the near future.

I investigate the nature of the transient nebulous companions to the sungrazing comet C/1882 R1, known as the Great September Comet. The features were located several degrees to the southwest of the comet's head and reported independently by four observers, including J. F. J. Schmidt and E. E. Barnard, over a period of ten days nearly one month after perihelion, when the comet was 0.7 AU to 1 AU from the Sun. I conclude that none of the nebulous companions was ever sighted more than once and that, contrary to his belief, Schmidt observed unrelated objects on the four consecutive mornings. Each nebulous companion is proposed to have been triggered by a fragment at most a few tens of meters across, released from the comet's nucleus after perihelion and seen only because it happened to be caught in the brief terminal outburst, when its mass was suddenly shattered into a cloud of mostly microscopic debris due possibly to rotational bursting triggered by sublimation torques. The fragment's motion was affected by a strong outgassing-driven nongravitational acceleration with a significant out-of-plane component. Although fragmentation events were common, only a small fraction of nebulous companions was detected because of their transient nature. The observed brightness of the nebulous companions is proposed to have been due mainly to C2 emissions, with a contribution from scattering of sunlight by the microscopic dust. By their nature, the fragments responsible for the nebulous companions bear a strong resemblance to the dwarf Kreutz sungrazers detected with the coronagraphs aboard the SOHO space probe. Only their fragmentation histories are different and the latter display no terminal outburst, a consequence of extremely short lifetimes of the sublimating icy and refractory material in the Sun's corona.

We report the discovery of MAGAZ3NE J095924+022537, a spectroscopically-confirmed protocluster at $z = 3.3665^{+0.0009}_{-0.0012}$ around a spectroscopically-confirmed $UVJ$-quiescent ultra-massive galaxy (UMG; $M_{\star}=2.34^{+0.23}_{-0.34}\times10^{11} {\rm M}_\odot$) in the COSMOS UltraVISTA field. We present a total of 38 protocluster members (14 spectroscopic and 24 photometric), including the UMG. Notably, and in marked contrast to protoclusters previously reported at this epoch which have been found to contain predominantly star-forming members, we measure an elevated fraction of quiescent galaxies relative to the coeval field ($73.3^{+26.7}_{-16.9}\%$ versus $11.6^{+7.1}_{-4.9}\%$ for galaxies with stellar mass $M_{\star} \geq 10^{11} {\rm M}_\odot$). This high quenched fraction provides a striking and important counterexample to the seeming ubiquitousness of star-forming galaxies in protoclusters at $z>2$ and suggests, rather, that protoclusters exist in a diversity of evolutionary states in the early Universe. We discuss the possibility that we might be observing either "early mass quenching" or non-classical "environmental quenching." We also present the discovery of MAGAZ3NE J100028+023349, a second spectroscopically-confirmed protocluster, at a very similar redshift of $z = 3.3801^{+0.0213}_{-0.0281}$. We present a total of 20 protocluster members, 12 of which are photometric and 8 spectroscopic including a post-starburst UMG ($M_{\star}=2.95^{+0.21}_{-0.20}\times10^{11} {\rm M}_\odot$). Protoclusters MAGAZ3NE J0959 and MAGAZ3NE J1000 are separated by 18 arcminutes on the sky (35 comoving Mpc), in good agreement with predictions from simulations for the size of "Coma"-type cluster progenitors at this epoch. It is highly likely that the two UMGs are the progenitors of Brightest Cluster Galaxies (BCGs) seen in massive virialized clusters at lower redshift.

Galaxy evolution is generally affected by tidal interactions. Firstly, in this series, we reported several effects which suggest that tidal interactions contribute to regulating star formation (SF). To confirm that so, we now compare stellar mass assembly histories and SF look-back time annular profiles between CALIFA survey tidally and non-tidally perturbed galaxies. We pair their respective star-forming regions at the closest stellar mass surface densities to reduce the influence of stellar mass. The assembly histories and annular profiles show statistically significant differences so that higher star formation rates characterize regions in tidally perturbed galaxies. These regions underwent a more intense (re)activation of SF in the last 1 Gyr. Varying shapes of the annular profiles also reflect fluctuations between suppression and (re)activation of SF. Since gas-phase abundances use to be lower in more actively than in less actively star-forming galaxies, we further explore the plausible presence of metal-poor gas inflows able to dilute such abundances. The resolved relations of oxygen (O) abundance, with stellar mass density and with total gas fraction, show slightly lower O abundances for regions in tidally perturbed galaxies. The single distributions of O abundances statistically validate that so. Moreover, from a metallicity model based on stellar feedback, the mass rate differentials (inflows$-$outflows) show statistically valid higher values for regions in tidally perturbed galaxies. These differentials, and the metal fractions from the population synthesis, suggest dominant gas inflows in these galaxies. This dominance, and the differences in SF through time, confirm the previously reported effects of tidal interactions on SF.

Our galaxy is full with planets. We now know that planets and planetary systems are diverse and come with different sizes, masses and compositions, as well as various orbital architectures. Although there has been great progress in understanding planet formation in the last couple of decades, both observationally and theoretically, several fundamental questions remain unsolved. This might not be surprising given the complexity of the process that includes various physical and chemical processes, and spans huge ranges of length-scales, masses, and timescales. In addition, planet formation cannot be directly observed but has to be inferred by gluing together different pieces of information into one consistent picture. "How do planets form?" remains a fundamental question in modern astrophysics. In this review we list some of the key open questions in planet formation theory as well as the challenges and upcoming opportunities.

We analyze the observations of EUV loop evolution associated with the filament eruption located at the border of an active region. The event SOL2013-03-16T14:00 was observed with a large difference of view point by the Solar Dynamics Observatory and Solar Terrestrial Relations Observatory --A spacecraft. The filament height is fitted with the sum of a linear and exponential function. These two phases point to different physical mechanisms such as: tether-cutting reconnection and a magnetic instability. While no X-ray emission is reported, this event presents the classical eruption features like: separation of double ribbons and the growth of flare loops. We report the migration of the southern foot of the erupting filament flux rope due to the interchange reconnection with encountered magnetic loops of a neighbouring AR. Parallel to the erupting filament, a stable filament remains in the core of active region. The specificity of this eruption is that coronal loops, located above the nearly joining ends of the two filaments, first contract in phase, then expand and reach a new stable configuration close to the one present at the eruption onset. Both contraction and expansion phases last around 20 min. The main difference with previous cases is that the PIL bent about 180 deg around the end of the erupting filament because the magnetic configuration is at least tri-polar. These observations are challenging for models which interpreted previous cases of loop contraction within a bipolar configuration. New simulations are required to broaden the complexity of the configurations studied.

We present high-sensitivity CH 9 cm ON/OFF observations toward 18 extra-galactic continuum sources that have been detected with OH 18 cm absorption in the Millennium survey with the Arecibo telescope. CH emission was detected toward six of eighteen sources. The excitation temperature of CH has been derived directly through analyzing all detected ON and OFF velocity components. The excitation temperature of CH 3335 MHz transition ranges from $-54.5$ to $-0.4$ K and roughly follows a log-normal distribution peaking within [$-$5, 0] K, which implies overestimation by 20% to more than ten times during calculating CH column density by assuming the conventional value of $-60$ or $-10$ K. Furthermore, the column density of CH would be underestimated by a factor of $1.32\pm 0.03$ when adopting local thermal equilibrium (LTE) assumption instead of using the CH three hyperfine transitions. We found a correlation between the column density of CH and OH following log$N$(CH) = (1.80$\pm$ 0.49) log$N$(OH) $-11.59 \pm 6.87$. The linear correlation between the column density of CH and H$_2$ is consistent with that derived from visible wavelengths studies, confirming that CH is one of the best tracers of H$_2$ component in diffuse molecular gas.

Star-forming regions have been proposed as potential Galactic cosmic-ray accelerators for decades. Cosmic ray acceleration can be probed through observations of gamma-rays produced in inelastic proton-proton collisions, at GeV and TeV energies. We analyze more than 11 years of Fermi-LAT data from the direction of Westerlund 2, one of the most massive and best-studied star-forming regions in our Galaxy. The spectral and morphological characteristics of the LAT source agree with the ones in the TeV regime (HESS J1023-575), allowing the description of the gamma-ray source from a few hundreds of MeV to a few tens of TeVs. We will present the results and discuss the implications of the identification with the stellar cluster and the radiation mechanism involved.

We present the composite optical spectrum for the largest sample of giant radio quasars (GRQs). They represent a rare subclass of radio quasars due to their large projected linear sizes of radio structures, which exceed 0.7 Mpc. To construct the composite spectrum, we combined 216 GRQ's optical spectra from Sloan Digital Sky Survey (SDSS). As a result, we obtained the composite spectrum covering the wavelength range from 1400 {\AA} to 7000 {\AA}. We calculated the power-law spectral slope for GRQ's composite, obtaining $\alpha_{\lambda}=-1.25$ and compared it with that of the smaller-sized radio quasars, as well as with the quasar composite spectrum obtained for large sample of SDSS quasars. We obtained that the GRQ's continuum is flatter (redder) than the continuum of comparison quasar samples. We also show that the continuum slope depends on core and total radio luminosity at 1.4 GHz, being steeper for higher radio luminosity bin. Moreover, we found the flattening of the continuum with an increase of the projected linear size of radio quasar. We show that $\alpha_{\lambda}$ is orientation-dependent, being steeper for a higher radio core-to-lobe flux density ratio which is consistent with AGN unified model predictions. For two GRQs, we fit the spectral energy distribution using X-CIGALE code to compare the consistency of results obtained in the optical part of the electromagnetic spectrum with broad-band emission. The parameters obtained from the SED fitting confirmed the larger dust luminosity for the redder optical continuum.

The eFEDS survey is a proof-of-concept mini-survey designed to demonstrate the survey science capabilities of SRG/eROSITA. It covers an area of 140 square degrees where 542 galaxy clusters have been detected out to a redshift of 1.3. The eFEDS field is partly embedded in the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) S19A data release, which covers 510 square degrees, containing approximately 36 million galaxies. This galaxy catalogue is used to construct a sample of 180 shear-selected galaxy clusters. In the common area to both surveys, about 90 square degrees, we investigate the effects of selection methods in the galaxy cluster detection by comparing the X-ray selected, eFEDS, and the shear-selected, HSC-SSP S19A, galaxy cluster samples. There are 25 shear-selected clusters in the eFEDS footprint. The relation between X-ray bolometric luminosity and weak-lensing mass is investigated, and it is found that the normalization of the bolometric luminosity and mass relation of the X-ray selected and shear-selected samples is consistent within $1\sigma$. Moreover, we found that the dynamical state and merger fraction of the shear-selected clusters is not different from the X-ray selected ones. Four shear-selected clusters are undetected in X-rays. A close inspection reveals that one is the result of projection effects, while the other three have an X-ray flux below the ultimate eROSITA detection limit. Finally, 43% of the shear-selected clusters lie in superclusters. Our results indicate that the scaling relation between X-ray bolometric luminosity and true cluster mass of the shear-selected cluster sample is consistent with the eFEDS sample. There is no significant population of X-ray underluminous clusters, indicating that X-ray selected cluster samples are complete and can be used as an accurate cosmological probe.

Narrow-line Seyfert 1 (NLS1) galaxies are believed to be active galactic nuclei (AGN) in the early stages of their evolution. Some dozens of them have been found to host relativistic jets, whilst the majority has not even been detected in radio, emphasising the heterogeneity of the class in this band. In this paper, our aim is to determine the predominant source of radio emission in a sample of 44 NLS1s, selected based on their extended kpc-scale radio morphologies at 5.2 GHz. We accomplish this by analysing their spatially resolved radio spectral index maps, centred at 5.2 GHz. In addition, we utilise several diagnostics based on mid-infrared emission to estimate the star formation activity of their host galaxies. These data are complemented by archival data to draw a more complete picture of each source. We find an extraordinary diversity among our sample. Approximately equal fractions of our sources can be identified as AGN-dominated, composite, and host-dominated. Among the AGN-dominated sources are a few NLS1s with very extended jets, reaching distances of tens of kpc from the nucleus. One of these, J0814+5609, hosts the most extended jets found in an NLS1 so far. We also identify five NLS1s that could be classified as compact steep-spectrum sources. We further conclude that due to the variety seen in NLS1s simple proxies, such as the star formation diagnostics also employed in this paper, and the radio loudness parameter, are not ideal tools for characterising NLS1s. We emphasise the necessity of examining NLS1s as individuals, instead of making assumptions based on their classification. When these issues are properly taken into account, NLS1s offer an exceptional environment to study the interplay of the host galaxy and several AGN-related phenomena, such as jets and outflows. [Abstract abridged.]

Cosmic ray propagation is determined by the properties of interstellar turbulence. The multiphase nature of interstellar medium (ISM) and diversity of driving mechanisms give rise to spatial variation of turbulence properties. Meanwhile, precision astroparticle experiments pose challenges to the conventional picture of homogeneous and isotropic transport of cosmic rays (CRs). We are beginning a new chapter of CR propagation research when studies of particle transport and interstellar turbulence confront each other. Here we review our recent developement on understandings of magnetohydrodynamic (MHD) turbulence and its connection to the fundamental processes governing cosmic ray propagation, different regimes of particle transport, that are augmented with observational discovery and analysis from multi-wavelength observations.

Local metal-poor galaxies are ideal analogues of primordial galaxies with the interstellar medium (ISM) barely being enriched with metals. However, it is unclear whether carbon monoxide remains a good tracer and coolant of molecular gas at low metallicity. Based on the observation with the upgraded Northern Extended Millimeter Array (NOEMA), we report a marginal detection of CO $J$=2-1 emission in IZw18, pushing the detection limit down to $L^\prime_{\rm CO(2-1)}$=3.99$\times$10$^3$ K km$^{-1}$pc$^{-2}$, which is at least 40 times lower than previous studies. As one of the most metal-poor galaxies, IZw18 shows extremely low CO content despite its vigorous star formation activity. Such low CO content relative to its infrared luminosity, star formation rate, and [CII] luminosity, compared with other galaxies, indicates a significant change in the ISM properties at a few percent of the Solar metallicity. In particular, the high [CII] luminosity relative to CO implies a larger molecular reservoir than the CO emitter in IZw18. We also obtain an upper limit of the 1.3mm continuum, which excludes a sub-millimetre excess in IZw18.

With the remarkable advent of gravitational-wave astronomy, we have shed light on previously shrouded events: compact binary coalescences. Neutron stars are promising (and confirmed) sources of gravitational radiation and it proves timely to consider the ways in which these stars can be deformed. Gravitational waves provide a unique window through which to examine neutron-star interiors and learn more about the equation of state of ultra-dense nuclear matter. In this work, we study two relevant scenarios for gravitational-wave emission: neutron stars that host (non-axially symmetric) mountains and neutron stars deformed by the tidal field of a binary partner. Although they have yet to be seen with gravitational waves, rotating neutron stars have long been considered potential sources. By considering the observed spin distribution of accreting neutron stars with a phenomenological model for the spin evolution, we find evidence for gravitational radiation in these systems. We study how mountains are modelled in both Newtonian and relativistic gravity and introduce a new scheme to resolve issues with previous approaches to this problem. The crucial component of this scheme is the deforming force that gives the star its non-spherical shape. We find that the force (which is a proxy for the star's formation history), as well as the equation of state, plays a pivotal role in supporting the mountains. Considering a scenario that has been observed with gravitational waves, we calculate the structure of tidally deformed neutron stars, focusing on the impact of the crust. We find that the effect on the tidal deformability is negligible, but the crust will remain largely intact up until merger.

During the last decades there is a continuing international endeavor in developing realistic space weather prediction tools aiming to forecast the conditions on the Sun and in the interplanetary environment. These efforts have led to the need of developing appropriate metrics in order to assess the performance of those tools. Metrics are necessary for validating models, comparing different models and monitoring adjustments or improvements of a certain model over time. In this work, we introduce the Dynamic Time Warping (DTW) as an alternative way to validate models and, in particular, to quantify differences between observed and synthetic (modeled) time series for space weather purposes. We present the advantages and drawbacks of this method as well as applications on WIND observations and EUHFORIA modeled output at L1. We show that DTW is a useful tool that permits the evaluation of both the fast and slow solar wind. Its distinctive characteristic is that it warps sequences in time, aiming to align them with the minimum cost by using dynamic programming. It can be applied in two different ways for the evaluation of modeled solar wind time series. The first way calculates the so-called sequence similarity factor (SSF), a number that provides a quantification of how good the forecast is, compared to a best and a worst case prediction scenarios. The second way quantifies the time and amplitude differences between the points that are best matched between the two sequences. As a result, it can serve as a hybrid metric between continuous measurements (such as, e.g., the correlation coefficient) and point-by-point comparisons. We conclude that DTW is a promising technique for the assessment of solar wind profiles offering functions that other metrics do not, so that it can give at once the most complete evaluation profile of a model.

Little is known about the chemistry of isocyanates (compounds with the functional group R-N=C=O) in the interstellar medium, as only four of them have been detected so far: isocyanate radical (NCO), isocyanic acid (HNCO), N-protonated isocyanic acid (H$_2$NCO$^+$) and methyl isocyanate (CH$_3$NCO). The molecular cloud G+0.693-0.027, located in the Galactic Centre, represents an excellent candidate to search for new isocyanates since it exhibits high abundances of the simplest ones, HNCO and CH$_3$NCO. After CH$_3$NCO, the next complex isocyanates are ethyl isocyanate (C$_2$H$_5$NCO) and vinyl isocyanate (C$_2$H$_3$NCO). Their detection in the ISM would enhance our understanding of the formation of these compounds in space. We have detected C$_2$H$_5$NCO and H$_2$NCO$^+$ towards G+0.693-0.027 (the former for the first time in the interstellar medium) with molecular abundances of (4.7$-$7.3)$\times$10$^{-11}$ and (1.0$-$1.5)$\times$10$^{-11}$, respectively. A ratio CH$_3$NCO / C$_2$H$_5$NCO = 8$\pm$1 is obtained; therefore the relative abundance determined for HNCO:CH$_3$NCO:C$_2$H$_5$NCO is 1:1/55:1/447, which implies a decrease by more than one order of magnitude going progressively from HNCO to CH$_3$NCO and to C$_2$H$_5$NCO. This is similar to what has been found for e.g. alcohols and thiols and suggests that C$_2$H$_5$NCO is likely formed on the surface of dust grains. In addition, we have obtained column density ratios of HNCO / NCO > 269, HNCO / H$_2$NCO$^+$ $\sim$ 2100 and C$_2$H$_3$NCO / C$_2$H$_5$NCO~<~4. A comparison of the Methyl~/~Ethyl ratios for isocyanates (-NCO), alcohols (-OH), formiates (HCOO-), nitriles (-CN) and thiols (-SH) is performed and shows that ethyl-derivatives may be formed more efficiently for the N-bearing molecules than for the O- and S-bearing molecules.

In order to allow for a comparison with the measurements from other antenna systems, the voltage power spectral density measured by the Radio and Plasma waves receiver (RPW) on board Solar Orbiter needs to be converted into physical quantities that depend on the intrinsic properties of the radiation itself.The main goal of this study is to perform a calibration of the RPW dipole antenna system that allows for the conversion of the voltage power spectral density measured at the receiver's input into the incoming flux density. We used space observations from the Thermal Noise Receiver (TNR) and the High Frequency Receiver (HFR) to perform the calibration of the RPW dipole antenna system. Observations of type III bursts by the Wind spacecraft are used to obtain a reference radio flux density for cross-calibrating the RPW dipole antennas. The analysis of a large sample of HFR observations (over about ten months), carried out jointly with an analysis of TNR-HFR data and prior to the antennas' deployment, allowed us to estimate the reference system noise of the TNR-HFR receivers. We obtained the effective length of the RPW dipoles and the reference system noise of TNR-HFR in space, where the antennas and pre-amplifiers are embedded in the solar wind plasma. The obtained $l_{eff}$ values are in agreement with the simulation and measurements performed on the ground. By investigating the radio flux intensities of 35 type III bursts simultaneously observed by Solar Orbiter and Wind, we found that while the scaling of the decay time as a function of the frequency is the same for the Waves and RPW instruments, their median values are higher for the former. This provides the first observational evidence that Type III radio waves still undergo density scattering, even when they propagate from the source, in a medium with a plasma frequency that is well below their own emission frequency.

Galaxy clusters grow primarily through the continuous accretion of group-scale haloes. Group galaxies experience preprocessing during their journey into clusters. A star-bursting compact group, the Blue Infalling Group (BIG), is plunging into the nearby cluster A1367. Previous optical observations reveal rich tidal features in the BIG members, and a long H$\alpha$ trail behind. Here we report the discovery of a projected $\sim 250$ kpc X-ray tail behind the BIG using Chandra and XMM-Newton observations. The total hot gas mass in the tail is $\sim 7\times 10^{10}\ {\rm M}_\odot$ with an X-ray bolometric luminosity of $\sim 3.8\times 10^{41}$ erg s$^{-1}$. The temperature along the tail is $\sim 1$ keV, but the apparent metallicity is very low, an indication of the multi-$T$ nature of the gas. The X-ray and H$\alpha$ surface brightnesses in the front part of the BIG tail follow the tight correlation established from a sample of stripped tails in nearby clusters, which suggests the multiphase gas originates from the mixing of the stripped interstellar medium (ISM) with the hot intracluster medium (ICM). Because thermal conduction and hydrodynamic instabilities are significantly suppressed, the stripped ISM can be long lived and produce ICM clumps. The BIG provides us a rare laboratory to study galaxy transformation and preprocessing.

Hubble Space Telescope photometry of $\eta$ Carinae spans 23 years, including five spectroscopic events. The rapid brightening rate decreased after 2010, and the spectroscopic events in 2014 and 2020 had light curves different from their predecessors. Together with other indicators, these developments probably foretell the conclusion of $\eta$ Car's change of state.

We introduce a novel statistic to probe the statistics of phases of Fourier modes in two-dimensions (2D) for weak lensing convergence field $\kappa$. This statistic contains completely independent information compared to that contained in observed power spectrum. We compare our results against state-of-the-art numerical simulations as a function of source redshift and find good agreement with theoretical predictions. We show that our estimator can achieve better signal-to-noise compared to the commonly employed statistics known as the line correlation function (LCF). Being a two-point statistics, our estimator is also easy to implement in the presence of complicated noise and mask, and can also be generalised to higher-order. While applying this estimator for the study of lensed CMB maps, we show that it is important to include post-Born corrections in the study of statistics of phase.

Observations of the Sun's surface suggest a nonuniform radiated flux as related to the presence of bright active regions and darker coronal holes. The variations of the FUV/EUV source radiation can be expected to affect the Lyman-alpha backscatter glow measured by spaceborne instruments. In particular, inferring the heliolatitudinal structure of the solar wind from helioglow variations in the sky can be quite challenging if the heliolatitudinal structure of the solar FUV/EUV radiation is not properly included in the modeling of the heliospheric glow. We present results of analysis of the heliolatitudinal structure of the solar Lyman-alpha radiation as inferred from comparison of SOHO/SWAN satellite observations of the helioglow intensity with modeling results obtained from the recently-developed WawHelioGlow model. We find that in addition to time-dependent heliolatitudinal anisotropy of the solar wind, also time-dependent heliolatitudinal variations of the intensity of the solar Lyman-alpha and photoionizing emissions must be taken into account to reproduce the observed helioglow modulation in the sky. We present a particular latitudinal and temporal dependence of the solar Lyman-alpha flux obtained as a result of our analysis. We analyze also differences between polar-equatorial anisotropies close to the solar surface and seen by an observer located far from the Sun. We discuss the implications of these findings for the interpretation of heliospheric-glow observations.

Optical observations of a sample of 12 $\gamma$-ray bright blazars from four optical data archives, AAVSO, SMARTS, Catalina, and Steward Observatory, are compiled to create densely sampled light curves spanning more than a decade. As a part of the blazar multi-wavelength studies, several methods of analyses, e. g., flux distribution and RMS-flux relation, are performed on the observations with an aim to compare the results with the similar ones in the \gama-ray band presented in Bhatta & Dhital 2020. It is found that, similar to $\gamma$-ray band, blazars display significant variability in the optical band that can be characterized with log-normal flux distribution and a power-law dependence of RMS on flux. It could be an indication of possible inherent linear RMS-flux relation, yet the scatter in the data does not allow to rule out other possibilities. When comparing variability properties in the two bands, the blazars in the \gama-rays are found to exhibit stronger variability with steeper possible linear RMS-flux relation and the flux distribution that is more skewed towards higher fluxes. The cross-correlation study shows that except for the source 3C 273, the overall optical and the $\gamma$-ray emission in the sources are highly correlated, suggesting a co-spatial existence of the particles responsible for both the optical and $\gamma$-ray emission. Moreover, the sources S5 0716+714, Mrk 421, Mrk 501, PKS 1424-418 and PKS 2155-304 revealed possible evidence for quasi-periodic oscillations in the optical emission with the characteristic timescales, which are comparable to those in the $\gamma$-ray band detected in our previous work.

We study the evolution of the Universe at early stages, we discuss also preheating in the framework of hybrid braneworld inflation by setting conditions on the coupling constants $\lambda $ and $g$\ for effective production of $\chi$-particles. Considering the phase between the time observable CMB scales crossed the horizon and the present time, we write reheating and preheating parameters $N_{re}$, $T_{re}$ and $N_{pre}$ in terms of the scalar spectral index $n_{s}$, and prove that, unlike the reheating case, the preheating duration does not depend on the values of the equation of state $\omega ^{\ast }$. We apply the slow-roll approximation in the high energy limit to constrain the parameters of D-term hybrid potential. We show also that some inflationary parameters, in particular, the spectral index $n_{s}$ demand that the potential parameter $\alpha$ is bounded as $\alpha \geq 1$ to be consistent with $Planck$'s data, while the ratio $r$ is in agreement with observation for $ \alpha \leq 1 $ considering high inflationary e-folds. We also propose an investigation of the brane tension effect on the reheating temperature. Comparing our results to recent CMB measurements, we study preheating and reheating parameters $N_{re}$, $T_{re}$ and $N_{pre}$ in the Hybrid D-term inflation model in the range $0.8\leq \alpha\leq 1.1$\, and conclude that $T_{re}$ and $N_{re}$ require $\alpha \leq 1$, while for $N_{pre}$ the condition $\alpha \leq 0.9$ must be satisfied, to be compatible with $Planck$'s results.

Recently a series of studies on high energy gamma-ray burst~(GRB) photons suggest a light speed variation with linear energy dependence at the Lorentz violation scale of $3.6 \times 10^{17}~\mathrm{GeV}$, with subluminal propagation of high energy photons in cosmological space. We propose stringy space-time foam as a possible interpretation for this light speed variation. In such a string-inspired scenario, bosonic photon open-string travels \textit{in vacuo} at an infraluminal speed with an energy dependence suppressed by a single power of the string mass scale, due to the foamy structure of space-time at small scales, as described by D-brane objects in string theory. We present a derivation of this deformed propagation speed of the photon field in the infrared (IR) regime. We show that the light speed variation, revealed in the previous studies on GRBs time-delay data, can be well described within such a string approach towards space-time foam. We also derive the value of the effective quantum-gravity mass in this framework, and give a qualitative study on the theory-dependent coefficients. We comment that stringent constraints on Lorentz violation in the photon sector from complementary astrophysical observations can also be explained and understood in the space-time foam context.

The cosmological evolution can modify the dark matter (DM) properties in the early Universe to be vastly different from the properties today. Therefore, the relation between the relic abundance and the DM constraints today needs to be revisited. We propose novel \textit{transient} annihilations of DM which helps to alleviate the pressure from DM null detection results. As a concrete example, we consider the vector portal DM and focus on the mass evolution of the dark photon. When the Universe cools down, the gauge boson mass can increase monotonically and go across several important thresholds; opening new transient annihilation channels in the early Universe. Those channels are either forbidden or weakened at the late Universe which helps to evade the indirect searches. In particular, the transient resonant channel can survive direct detection (DD) without tuning the DM to be half of the dark photon mass and can be soon tested by future DD or collider experiments. A feature of the scenario is the existence of a light dark scalar.

Using 2-dimensional (2D) magnetohydrodynamics (MHD) simulations, we show that Petschek-type magnetic reconnection can be induced using a simple resistivity gradient in the reconnection outflow direction, revealing the key ingredient of steady fast reconnection in the collisional limit. We find that the diffusion region self-adjusts its half-length to fit the given gradient scale of resistivity. The induced reconnection x-line and flow stagnation point always reside within the resistivity transition region closer to the higher resistivity end. The opening of one exhaust by this resistivity gradient will lead to the opening of the other exhaust located on the other side of the x-line, within the region of uniform resistivity. Potential applications of this setup to reconnection-based thrusters and solar spicules are discussed. In a separate set of numerical experiments, we explore the maximum plausible reconnection rate using a large and spatially localized resistivity right at the x-line. Interestingly, the resulting current density at the x-line drops significantly so that the normalized reconnection rate remains bounded by the value $\simeq 0.2$, consistent with the theoretical prediction.

We investigate a recently proposed method for measuring the Hubble constant from gravitational wave detections of binary black hole coalescences without electromagnetic counterparts. In the absence of a direct redshift measurement, the missing information on the left-hand side of the Hubble-Lema\^itre law is provided by the statistical knowledge on the redshift distribution of sources. We assume that source distribution in redshift depends on just one unknown hyper-parameter, modeling our ignorance of the astrophysical binary black hole distribution. With tens of thousands of these "black sirens" -- a realistic figure for the third generation detectors Einstein Telescope and Cosmic Explorer -- an observational constraint on the value of the Hubble parameter at percent level can be obtained. This method has the advantage of not relying on electromagnetic counterparts, which accompany a very small fraction of gravitational wave detections, nor on often unavailable or incomplete galaxy catalogs.

Over the past two decades scientists have achieved a significant improvement of our understanding of the transport of energetic particles across a mean magnetic field. Due to test-particle simulations as well as powerful non-linear analytical tools our understanding of this type of transport is almost complete. However, previously developed non-linear analytical theories do not always agree perfectly with simulations. Therefore, a correction factor $a^2$ was incorporated into such theories with the aim to balance out inaccuracies. In this paper a new analytical theory for perpendicular transport is presented. This theory contains the previously developed unified non-linear transport theory, the most advanced theory to date, in the limit of small Kubo number turbulence. For two-dimensional turbulence new results are obtained. In this case the new theory describes perpendicular diffusion as a process which is sub-diffusive while particles follow magnetic field lines. Diffusion is restored as soon as the turbulence transverse complexity becomes important. For long parallel mean free paths one finds that the perpendicular diffusion coefficient is a reduced field line random walk limit. For short parallel mean free paths, on the other hand, one gets a hybrid diffusion coefficient which is a mixture of collisionless Rechester & Rosenbluth and fluid limits. Overall the new analytical theory developed in the current paper is in agreement with heuristic arguments. Furthermore, the new theory agrees almost perfectly with previously performed test-particle simulations without the need of the aforementioned correction factor $a^2$ or any other free parameter.

Pulsar timing experiments are currently searching for gravitational waves, and this dissertation focuses on the development and study of the pulsar timing residual models used for continuous wave searches. The first goal of this work is to re-present much of the fundamental physics and mathematics concepts behind the calculations and theory used in pulsar timing. While there exist many reference sources in the literature, I try to offer a fully self-contained explanation of the fundamentals of this research which I hope the reader will find helpful. The next goal broadly speaking has been to further develop the mathematics behind the currently used pulsar timing models for detecting gravitational waves with pulsar timing experiments. I classify four regimes of interest, governed by frequency evolution and wavefront curvature effects incorporated into the timing residual models. Of these four regimes the plane-wave models are well established in previous literature. I add a new regime which I label "Fresnel," as I show it becomes important for significant Fresnel numbers describing the curvature of the gravitational wavefront. Then I give two in-depth studies. The first forecasts the ability of future pulsar timing experiments to probe and measure these Fresnel effects. The second further generalizes the models to a cosmologically expanding universe, and I show how the Hubble constant can be measured directly in the most generalized pulsar timing residual model. This offers future pulsar timing experiments the possibility of being able to procure a purely gravitational wave-based measurement of the Hubble constant. The final chapter shows the initial steps taken to extend this work in the future toward Doppler tracking experiments.

The detection of gravitational waves from compact binary coalescence by Advanced LIGO and Advanced Virgo provides an opportunity to study the strong-field, highly-relativistic regime of gravity. Gravitational-wave tests of General Relativity (GR) typically assume Gaussian and stationary detector noise, thus do not account for non-Gaussian, transient noise features (glitches). We present the results obtained by performing parameterized gravitational-wave tests on simulated signals from binary-black-hole coalescence overlapped with three classes of frequently occurring instrumental glitches with distinctly different morphologies. We then review and apply three glitch mitigation methods and evaluate their effects on reducing false deviations from GR. By considering 9 cases of glitches overlapping with simulated signals, we show that the short-duration, broadband blip and tomte glitches under consideration introduce false violations of GR, and using an inpainting filter and glitch model subtraction can consistently eliminate such false violations without introducing additional effects.

We present here a provenance management system adapted to astronomical projects needs. We collected use cases from various astronomy projects and defined a data model in the ecosystem developed by the IVOA (International Virtual Observatory Alliance). From those use cases, we observed that some projects already have data collections generated and archived, from which the provenance has to be extracted (provenance "on top"), and some projects are building complex pipelines that automatically capture provenance information during the data processing (capture "inside"). Different tools and prototypes have been developed and tested to capture, store, access and visualize the provenance information, which participate to the shaping of a full provenance management system able to handle detailed provenance information.

Ultrahigh-energy photons up to 1.4 peta-electronvolts have been observed by new cosmic-ray telescope in China -- a hint that Lorentz invariance might break down at the Planck-scale level.

Lorentz Invariance Violation in Quantum Gravity (QG) models or a non-zero photon mass, $m_\gamma$, would lead to an energy-dependent propagation speed for photons, such that photons of different energies from a distant source would arrive at different times, even if they were emitted simultaneously. By developing source-by-source, Monte Carlo-based forward models for such time delays from Gamma Ray Bursts, and marginalising over empirical noise models describing other contributions to the time delay, we derive constraints on $m_\gamma$ and the QG length scale, $\ell_{\rm QG}$, using spectral lag data from the BATSE satellite. We find $m_\gamma < 4.0 \times 10^{-5} \, h \, {\rm eV}/c^2$ and $\ell_{\rm QG} < 5.3 \times 10^{-18} \, h \, {\rm \, GeV^{-1}}$ at 95% confidence, and demonstrate that these constraints are robust to the choice of noise model. The QG constraint is among the tightest from studies which consider multiple Gamma Ray Bursts and the constraint on $m_\gamma$, although weaker than from using radio data, provides an independent constraint which is less sensitive to the effects of dispersion by electrons.

Ground vibrations couple to the longitudinal and angular motion of the aLIGO test masses and limit the observatory sensitivity below 30\,Hz. Novel inertial sensors have the potential to improve the aLIGO sensitivity in this band and simplify the lock acquisition of the detectors. In this paper, we experimentally study a compact 6D seismometer that consists of a mass suspended by a single wire. The position of the mass is interferometrically read out relative to the platform that supports the seismometer. We present the experimental results, discuss limitations of our metallic prototype, and show that a compact 6D seismometer made out of fused silica and suspended with a fused silica fibre has the potential to improve the aLIGO low frequency noise.

We perform a new dark matter hot spot analysis using ten years of public IceCube data. In this analysis we assume dark matter self-annihilates to neutrino pairs and treat the production sites as discrete point sources. For neutrino telescopes these sites will appear as hot spots in the sky, possibly outshining other standard model neutrino sources. Comparing to galactic center analyses, we show that this approach is a powerful tool and capable of setting the highest neutrino detector limits for dark matter masses between 10 TeV and 100 PeV. This is due to the inclusion of spatial information in addition to the typically used energy deposition in the analysis.