Astrophysics of Galaxies (astro-ph.GA)

Abstract: Supermassive black holes (SMBHs) and nuclear star clusters (NSCs) co-exist in many galaxies. While the formation history of the black hole is essentially lost, NSCs preserve their evolutionary history imprinted onto their stellar populations and kinematics. Studying SMBHs and NSCs in tandem might help us to ultimately reveal the build-up of galaxy centres. In this study, we combine large-scale VLT/MUSE and high-resolution adaptive-optics-assisted VLT/SINFONI observations of the early-type galaxy FCC 47 with the goal being to assess the effect of a spatially (non-)variable initial mass function (IMF) on the determination of the mass of the putative SMBH in this galaxy. We achieve this by performing DYNAMITE Schwarzschild orbit-superposition modelling of the galaxy and its NSC. In order to properly take account of the stellar mass contribution to the galaxy potential, we create mass maps using a varying stellar mass-to-light ratio derived from single stellar population models with fixed and with spatially varying IMFs. Using the two mass maps, we estimate black hole masses of $(7.1^{+0.8}_{-1.1})\times 10^7\,M_{\odot}$ and $(4.4^{+1.2}_{-2.1}) \times 10^7\,M_{\odot}$ at $3\sigma$ signifance, respectively. Compared to models with constant stellar-mass-to-light ratio, the black hole masses decrease by 15% and 48%, respectively. Therefore, a varying IMF, both in its functional form and spatially across the galaxy, has a non-negligible effect on the SMBH mass estimate. Furthermore, we find that the SMBH in FCC 47 has probably not grown over-massive compared to its very over-massive NSC.

Abstract: We have performed experimental investigations of methanol formation via the reactions of low energy $CH_{3}^{+}$ ions with an amorphous solid water (ASW) surface around 10 K. A newly developed experimental apparatus enabled irradiation of the ASW surface by several eV ions and detection of trace amounts of reaction products on the surface. It was found that methanol molecules were produced by low-energy $CH_{3}^{+}$ irradiation of the ASW surface and that hydroxy groups in produced methanol originated from water molecules in ASW, as predicted in a previous theoretical study. Little temperature dependence of observed methanol intensity is apparent in the temperature range 12 - 60 K. Ab-initio molecular dynamics simulations under constant temperature conditions of 10 K suggested that this reaction spontaneously produced a methanol molecule and an $H_{3}O^{+}$ ion, regardless of the contact point of $CH_{3}^{+}$ on the ASW surface. We have performed simulation with an astrochemical model under molecular-cloud conditions, where the reaction between $CH_{3}^{+}$ and $H_{2}O$ ice, leading to methanol formation, was included. We found that the impact of the reaction on methanol abundance was limited only at the edge of the molecular cloud (< 1 mag) because of the low abundance of $CH_{3}^{+}$ in the gas phase, whereas the reaction between the abundant molecular ion $HCO^{+}$ and $H_{2}O$ ice, which has not yet been confirmed experimentally, can considerably affect the abundance of a complex organic molecule. This work sheds light on a new type of reaction between molecular ions and ice surfaces that should be included in astrochemical models.

Abstract: We estimated the angular momentum, $J$, of $720$ galaxies in the Local Volume with distances $r < 12$ Mpc. The distribution of the average angular momentum along the Hubble sequence has a maximum at the morphological type $T= 4$ (Sbc), while the dispersion of the $J$-values for galaxies is minimal. Among the Local Volume population, 27 elite spiral galaxies stand out, with an angular momentum greater than 0.15 of the Milky Way, $J > 0.15 J_{MW}$, making the main contribution ($ > 90\%$) to the total angular momentum of galaxies in the considered volume. Using observational data on the kinematics and structure of these galaxies, we determined the direction of their spins. We present the first map of the distribution of the spins of 27 nearby massive spiral galaxies in the sky and note that their pattern does not exhibit significant alignment with respect to the Local Sheet plane. The relationship between the magnitude of the angular momentum and stellar mass of the local galaxies is well represented by a power law with an exponent of ($5/3$) over an interval of $6$ orders of magnitude of the mass of galaxies.

Abstract: Luminous infrared galaxies at high redshifts ($z$>4) include extreme starbursts that build their stellar mass over short periods of time (>100 Myr). These galaxies are considered to be the progenitors of massive quiescent galaxies at intermediate redshifts ($z\sim$2) but their stellar structure and buildup is unknown. Here, we present the first spatially resolved near-infrared imaging of GN20, one of the most luminous dusty star-forming galaxies known to date, observed at an epoch when the Universe was only 1.5 Gyr old. The 5.6$\mu$m image taken with the JWST Mid-Infrared Instrument (MIRI/JWST) shows that GN20 is a very luminous galaxy (M$_\mathrm{1.1\mu m,AB}$=$-$25.01), with a stellar structure composed of a conspicuous central source and an extended envelope. The central source is an unresolved nucleus that carries 9% of the total flux. The nucleus is co-aligned with the peak of the cold dust emission, and offset by 3.9 kpc from the ultraviolet stellar emission. The diffuse stellar envelope is similar in size to the clumpy CO molecular gas distribution. The centroid of the stellar envelope is offset by 1 kpc from the unresolved nucleus, suggesting GN20 is involved in an interaction or merger event supported by its location as the brightest galaxy in a proto-cluster. The stellar size of GN20 is larger by a factor of about 3-5 than known spheroids, disks, and irregulars at $z\sim$4, while its size and low S\'ersic index are similar to those measured in dusty, infrared luminous galaxies at $z\sim$2 of the same mass. GN20 has all the ingredients necessary for evolving into a massive spheroidal quiescent galaxy at intermediate $z$: it is a large, luminous galaxy at $z$=4.05 involved in a short and massive starburst centred in the stellar nucleus and extended over the entire galaxy, out to radii of 4 kpc, and likely induced by the interaction or merger with a member of the proto-cluster.

Abstract: Since the mid 70ies it is known that the dwarf galaxies around the Milky Way are arranged in a thin, polar structure. The arrangement and motion within this structure has been identified as a severe challenge to the standard model of cosmology, dubbed as the plane of satellites problem. More observational evidence for such structures has been put forward around other galaxies, such as the Andromeda galaxy, Cen\,A or NGC\,253, among others, adding to the previously identified tensions. Solutions to the plane of satellite problem should therefore not only be tailored to the Milky Way, but need to explain all these different observed systems and environments.

Abstract: Mergers between galaxy clusters are an important stage in the formation of the large-scale structure of the Universe. Some of the mergers show a spectacular bow shock that formed as a result of recent passage of a smaller cluster through a bigger one, the classic example of this being the so-called bullet cluster. In this paper, I describe ten examples of interacting clusters identified among 200 of the most massive objects, with total masses above $1.4 \times 10^{14}$ M$_{\odot}$, from the IllustrisTNG300 simulation by searching for prominent bow shocks in their temperature maps. Despite different mass ratios of the two merging clusters, the events are remarkably similar in many respects. In all cases, the companion cluster passed close to the main one only once, between 0.9 and 0.3 Gyr ago, with the pericenter distance of 100-530 kpc and a velocity of up to 3400 km s$^{-1}$. The subcluster, typically an order of magnitude smaller in mass than the main cluster before the interaction, loses most of its dark matter and gas in the process. The displacement between the collisionless part of the remnant and the bow shock is such that the remnant typically lags behind the shock or coincides with it, with a single exception of the merger occurring with the largest velocity. Usually about 1% of the gas cells in the merging clusters are shocked, and the median Mach numbers of these gas cells are around two. Due to the relatively small size of the simulation box, no close analog of the bullet cluster was found, but I identified one case that is similar in terms of mass, velocity, and displacement. The presented cases bear more resemblance to less extreme observed interacting clusters such as A520 and Coma.

Abstract: Photodissociation regions (PDRs), where the (far-)ultraviolet light from hot young stars interact with the gas in surrounding molecular clouds, provide laboratories for understanding the nature and role of feedback by star formation on the interstellar medium. While the general nature of PDRs is well understood - at least under simplified conditions - the detailed dynamics and chemistry of these regions, including gas clumping, evolution over time etc. can be very complex. We present interferometric observations of the 21 cm atomic hydrogen line, combined with [CII] 158 $\mu$m observations, towards the nearby reflection nebula IC 63. We find a clumpy HI structure in the PDR, and a ring morphology for the HI emission at the tip of IC 63. We further unveil kinematic substructure, of the order of 1~km~s$^{-1}$, in the PDR layers and several legs that will disperse IC 63 in $<$0.5 Myr. We find that the dynamics in the PDR explain the observed clumpy HI distribution and lack of a well-defined HI/H$_{2}$ transition front. However, it is currently not possible to conclude whether HI self-absorption (HISA) and non-equilibrium chemistry also contribute to this clumpy morphology and missing HI/H$_{2}$ transition front.

Abstract: Aims. We investigate dust attenuation of 122 heavily dust-obscured galaxies detected with the Atacama Large Millimeter Array (ALMA) and Herschel in the COSMOS field. We search for correlations between dust attenuation recipes and the variation of physical parameters, mainly the effective radii of galaxies, their star formation rates (SFR), and stellar masses, and aim to understand which of the commonly used laws best describes dust attenuation in dusty star-forming galaxies at high redshift. Methods. We make use of the extensive photometric coverage of the COSMOS data combined with highly-resolved dust continuum maps from ALMA. We use CIGALE to estimate various physical properties of these dusty objects, mainly their SFR, their stellar masses and their attenuation. We infer galaxy effective radii (Re) using GALFIT in the Y band of HSC and ALMA continuum maps. We use these radii to investigate the relative compactness of the dust continuum and the extension of the rest-frame UV/optical Re(y)/Re(ALMA). Results. We find that the physical parameters calculated from our models strongly depend on the assumption of dust attenuation curve. As expected, the most impacted parameter is the stellar mass, which leads to a change in the "starburstiness" of the objects. We find that taking into account the relative compactness of star-to-dust emission prior to SED fitting is crucial, especially when studying dust attenuation of dusty star-forming galaxies. Shallower attenuation curves did not show a clear preference of compactness with attenuation, while the Calzetti attenuation curve preferred comparable spatial extent of unattenuated stellar light and dust emission. The evolution of the Re(UV)/Re(ALMA) ratio with redshift peeks around the cosmic noon in our sample of DSFGs, showing that this compactness is correlated with the cosmic SFR density of these dusty sources.

Abstract: We present an analysis of the ultraviolet luminosity function (UV LF) and star formation rate density of distant galaxies ($7.5 < z < 13.5$) in the `blank' fields of the Prime Extragalactic Areas for Reionization Science (PEARLS) survey combined with Early Release Science (ERS) data from the CEERS, GLASS and NGDEEP surveys/fields. We use a combination of SED fitting tools and quality cuts to obtain a reliable selection and characterisation of high-redshift ($z>6.5$) galaxies from a consistently processed set of deep, near-infrared imaging. Within an area of 110 arcmin$^{2}$, we identify 214 candidate galaxies at redshifts $z>6.5$ and we use this sample to study the ultraviolet luminosity function (UV LF) in four redshift bins between $7.5<z<13.5$. The measured number density of galaxies at $z=8$ and $z=9$ match those of past observations undertaken by the em Hubble Space Telescope (HST). However, towards higher redshifts we find that the evolution of the UV LF is mild, resulting in higher measured number densities of UV luminous galaxies at $z=10.5$ and $z=12.5$ compared to predictions from simulations and past HST observations. When examining the star formation rate density of galaxies at this time period, our observations are still consistent with a constant star formation efficiency, are slightly lower than previous early estimations using JWST and support galaxy driven reionization at $z\sim8$.