ABSTRACT
The Galaxy And Mass Assembly Survey (GAMA) covers five fields with highly complete spectroscopic coverage (>95 per cent) to intermediate depths (r < 19.8 or i < 19.0 mag), and collectively ...spans 250 deg2 of equatorial or southern sky. Four of the GAMA fields (G09, G12, G15, and G23) reside in the European Southern Observatory (ESO) VST KiDS and ESO VISTA VIKING survey footprints, which combined with our GALEX, WISE, and Herschel data provide deep uniform imaging in the $FUV/NUV/u/g/r/i/Z/Y/J/H/K_s/W1/W2/W3/W4/P100/P160/S250/S350/S500$ bands. Following the release of KiDS DR4, we describe the process by which we ingest the KiDS data into GAMA (replacing the SDSS data previously used for G09, G12, and G15), and redefine our core optical and near-infrared (NIR) catalogues to provide a complete and homogeneous data set. The source extraction and analysis is based on the new ProFound image analysis package, providing matched-segment photometry across all bands. The data are classified into stars, galaxies, artefacts, and ambiguous objects, and objects are linked to the GAMA spectroscopic target catalogue. Additionally, a new technique is employed utilizing ProFound to extract photometry in the unresolved MIR–FIR regime. The catalogues including the full FUV–FIR photometry are described and will be fully available as part of GAMA DR4. They are intended for both standalone science, selection for targeted follow-up with 4MOST, as well as an accompaniment to the upcoming and ongoing radio arrays now studying the GAMA 23h field.
We investigate the dynamical evolution of galaxies in groups with different formation epochs. Galaxy groups have been selected to be in different dynamical states, namely dynamically old and ...dynamically young, which reflect their early and late formation times, respectively, based on their halo mass assembly. The brightest galaxies in dynamically young groups have suffered their last major galaxy merger typically ∼2 Gyr more recently than their counterparts in dynamically old groups. Furthermore, we study the evolution of velocity dispersion in these two classes and compare them with the analytic models of isolated halos. The velocity dispersion of dwarf galaxies in high-mass, dynamically young groups increases slowly in time, while the analogous dispersion in dynamically old, high-mass groups is constant. In contrast, the velocity dispersion of giant galaxies in low-mass groups decreases rapidly at late times. This increasing velocity bias is caused by dynamical friction, and starts much earlier in the dynamically old groups. The recent Radio-SAGE model of galaxy formation suggests that radio luminosities of central galaxies, considered to be tracers of AGN activity, are enhanced in halos that assembled more recently, independent of the time since the last major merger.
ABSTRACT
We present a revised measurement of the optical extragalactic background light (EBL), based on the contribution of resolved galaxies to the integrated galaxy light (IGL). The cosmic optical ...background radiation (COB), encodes the light generated by star formation, and provides a wealth of information about the cosmic star formation history (CSFH). We combine wide and deep galaxy number counts from the Galaxy And Mass Assembly survey (GAMA) and Deep Extragalactic VIsible Legacy Survey (DEVILS), along with the Hubble Space Telescope (HST) archive and other deep survey data sets, in nine multiwavelength filters to measure the COB in the range from 0.35 μm to 2.2 μm. We derive the luminosity density in each band independently and show good agreement with recent and complementary estimates of the optical-EBL from very high-energy (VHE) experiments. Our error analysis suggests that the IGL and γ-ray measurements are now fully consistent to within $\sim 10{{\ \rm per\ cent}}$, suggesting little need for any additional source of diffuse light beyond the known galaxy population. We use our revised IGL measurements to constrain the CSFH, and place amplitude constraints on a number of recent estimates. As a consistency check, we can now demonstrate convincingly, that the CSFH, stellar mass growth, and the optical-EBL provide a fully consistent picture of galaxy evolution. We conclude that the peak of star formation rate lies in the range 0.066–0.076 M⊙ yr−1 Mpc−3 at a lookback time of 9.1 to 10.9 Gyr.
ABSTRACT
We present a complete structural analysis of the ellipticals (E), diffuse bulges (dB), compact bulges (cB), and discs (D) within a redshift range 0 < z < 1, and stellar mass log10(M*/M⊙) ≥ ...9.5 volume-limited sample drawn from the combined DEVILS and HST-COSMOS region. We use the profit code to profile over ∼35 000 galaxies for which visual classification into single or double component was pre-defined in Paper-I. Over this redshift range, we see a growth in the total stellar mass density (SMD) of a factor of 1.5. At all epochs we find that the dominant structure, contributing to the total SMD, is the disc, and holds a fairly constant share of $\sim 60{{\ \rm per\ cent}}$ of the total SMD from z = 0.8 to z = 0.2, dropping to $\sim 30{{\ \rm per\ cent}}$ at z = 0.0 (representing $\sim 33{{\ \rm per\ cent}}$ decline in the total disc SMD). Other classes (E, dB, and cB) show steady growth in their numbers and integrated stellar mass densities. By number, the most dramatic change across the full mass range is in the growth of diffuse bulges. In terms of total SMD, the biggest gain is an increase in massive elliptical systems, rising from 20 per cent at z = 0.8 to equal that of discs at z = 0.0 (30 per cent) representing an absolute mass growth of a factor of 2.5. Overall, we see a clear picture of the emergence and growth of all three classes of spheroids over the past 8 Gyr, and infer that in the later half of the Universe’s timeline spheroid-forming processes and pathways (secular evolution, mass-accretion, and mergers) appear to dominate mass transformation over quiescent disc growth.
ABSTRACT
Using high-resolution Hubble Space Telescope imaging data, we perform a visual morphological classification of ∼36 000 galaxies at z < 1 in the deep extragalactic visible legacy ...survey/cosmological evolution survey region. As the main goal of this study, we derive the stellar mass function (SMF) and stellar mass density (SMD) sub-divided by morphological types. We find that visual morphological classification using optical imaging is increasingly difficult at z > 1 as the fraction of irregular galaxies and merger systems (when observed at rest-frame UV/blue wavelengths) dramatically increases. We determine that roughly two-thirds of the total stellar mass of the Universe today was in place by z ∼ 1. Double-component galaxies dominate the SMD at all epochs and increase in their contribution to the stellar mass budget to the present day. Elliptical galaxies are the second most dominant morphological type and increase their SMD by ∼2.5 times, while by contrast, the pure-disc population significantly decreases by $\sim 85{{\ \rm per\ cent}}$. According to the evolution of both high- and low-mass ends of the SMF, we find that mergers and in situ evolution in discs are both present at z < 1, and conclude that double-component galaxies are predominantly being built by the in situ evolution in discs (apparent as the growth of the low-mass end with time), while mergers are likely responsible for the growth of ellipticals (apparent as the increase of intermediate/high-mass end).
Abstract
Using a sample of 472 local Universe (z < 0.06) galaxies in the stellar mass range $10.25\,\,{<}\,\,\log \boldsymbol {\mathcal {M}}_{\star }/\boldsymbol {\mathcal {M}}_{{\odot }}\,\,{<}\,\, ...10.75$, we explore the variation in galaxy structure as a function of morphology and galaxy colour. Our sample of galaxies is subdivided into red, green, and blue colour groups and into elliptical and non-elliptical (disk-type) morphologies. Using Kilo-Degree Survey (KiDS) and Visible and Infrared Survey Telescope for Astronomy (VISTA) Kilo-Degree Infrared Galaxy Survey (VIKING) derived postage stamp images, a group of eight volunteers visually classified bars, rings, morphological lenses, tidal streams, shells, and signs of merger activity for all systems. We find a significant surplus of rings (2.3σ) and lenses (2.9σ) in disk-type galaxies as they transition across the green valley. Combined, this implies a joint ring/lens green valley surplus significance of 3.3σ relative to equivalent disk-types within either the blue cloud or the red sequence. We recover a bar fraction of ${\sim }44\hbox{ per cent}$ which remains flat with colour, however, we find that the presence of a bar acts to modulate the incidence of rings and (to a lesser extent) lenses, with rings in barred disk-type galaxies more common by ∼20–30 percentage points relative to their unbarred counterparts, regardless of colour. Additionally, green valley disk-type galaxies with a bar exhibit a significant 3.0σ surplus of lenses relative to their blue/red analogues. The existence of such structures rules out violent transformative events as the primary end-of-life evolutionary mechanism, with a more passive scenario the favoured candidate for the majority of galaxies rapidly transitioning across the green valley.
This thesis makes use of the imaging data from the Advanced Camera for Surveys (ACS) of the Hubble Space Telescope (HST) in the Cosmic Evolution Survey (COSMOS) and the Deep Extragalactic VIsible ...Legacy Survey (DEVILS) field. We provide visual morphological classifications of 44,000 galaxies out to redshift \(z = 1\) and above a stellar mass of \(10^{9.5} M_\odot\) (D10/ACS sample). We perform a robust Bayesian bulge-disk decomposition analysis of the D10/ACS sample. This study forms one of the largest morphological classification and structural analyses catalogues in this field to date. Using these catalogues, we explore the evolution of the stellar mass function (SMF) and the stellar mass density (SMD) together with the stellar mass-size relations (\(M_*-R_e\)) of galaxies as a function of morphological type as well as for disks and bulges, separately. We quantify that one-third of the current stellar mass of the Universe was formed during the last 8 Gyr. We find that the moderate growth of the high-mass end of the SMF is dominated by the growth of elliptical systems and that the vast majority of the stellar mass of the Universe is locked up in disk+bulge systems at all epochs and that they increase their contribution to the total SMD with time. The contribution of the pure-disk morphology gradually decreases with time (\(\sim40\%\)), while ellipticals increase their contribution by a factor of \(1.7\) since \(z = 1\). By decomposing galaxies into disks and bulges we quantify that on average \(\sim50\%\) of the total stellar mass of the Universe at all epochs is in disk structures with this contribution relatively unchanged since \(z \sim 0.6\). With this comes more rapid growth of pseudo-bulges and spheroids (bulges and ellipticals) in mass. Furthermore, while the cosmic star-formation history is declining the Universe is transitioning from a disk dominated era to ...
We explore the evolution of the stellar mass-size relation of galaxies of different morphological types and specifically bulge and disk components. We use a sample of \(\sim35,000\) galaxies within a ...redshift range \(0 < z < 1\), and stellar mass \(\log_{10}(\mathrm{M}_*/\mathrm{M}_\odot) \geq 9.5\) volume-limited sample drawn from the combined DEVILS and HST-COSMOS region for which we presented a morphological classification into sub-classes of double-component (BD), pure-disk (pD), elliptical (E), and compact (C) in Paper-I and a structural decomposition into disk (D), diffuse bulge (dB), and compact bulge (cB) in Paper-II. We find that compared to disks, ellipticals and bulges follow steeper \(M_*-R_e\) relations, likely indicating distinct evolutionary mechanisms. Ellipticals and disk structures follow consistently unchanged slopes of \(\sim0.5\) and \(\sim0.3\), respectively, at all redshifts. We quantify that disks follow a redshift independent \(M_*-R_e\) slope regardless of the presence or absence of a bulge component (i.e., BD or pD) suggesting a similar origin and evolutionary pathway for all disks. Since \(z = 1\) compact-bulges present a steepening relation which do not follow that of Es whilst diffuse-bulges experience a modest flattening. Overall, we find a close-to-no variation in the \(M_*-R_e\) relations over the last \(\sim8\) Gyr suggesting that despite ongoing although declining star-formation, mass evolution, morphological transitions and mergers, evolution moves galaxies along their \(M_*-R_e\) trails. This seems to be consistent with an inside-out growth and evolution picture in which galaxies grow in size as they do in stellar mass. Besides, minor mergers are likely to be responsible for the growth of Es, at least in \(z < 1\).
Classification of galactic morphologies is a crucial task in galactic astronomy, and identifying fine structures of galaxies (e.g., spiral arms, bars, and clumps) is an essential ingredient in such a ...classification task. However, seeing effects can cause images we obtain to appear blurry, making it difficult for astronomers to derive galaxies' physical properties and, in particular, distant galaxies. Here, we present a method that converts blurred images obtained by the ground-based Subaru Telescope into quasi Hubble Space Telescope (HST) images via machine learning. Using an existing deep learning method called generative adversarial networks (GANs), we can eliminate seeing effects, effectively resulting in an image similar to an image taken by the HST. Using multiple Subaru telescope image and HST telescope image pairs, we demonstrate that our model can augment fine structures present in the blurred images in aid for better and more precise galactic classification. Using our first of its kind machine learning-based deblurring technique on space images, we can obtain up to 18% improvement in terms of CW-SSIM (Complex Wavelet Structural Similarity Index) score when comparing the Subaru-HST pair versus SeeingGAN-HST pair. With this model, we can generate HST-like images from relatively less capable telescopes, making space exploration more accessible to the broader astronomy community. Furthermore, this model can be used not only in professional morphological classification studies of galaxies but in all citizen science for galaxy classifications.
PDF
