We present new measurements of the evolution of the galaxy stellar mass functions (GSMF) and UV luminosity functions (UV LF) for galaxies from \(z=6-9\) within the Frontier Field cluster ...MACSJ0416.1-2403 and its parallel field. To obtain these results, we derive the stellar masses of our sample by fitting synthetic stellar population models to their observed spectral energy distribution with the inclusion of nebular emission lines. This is the deepest and farthest in distance mass function measured to date and probes down to a level of M\(_{*} = 10^{6.8}M_{\odot}\). The main result of this study is that the low-mass end of our GSMF to these limits and redshifts appears to become steeper from \(-1.98_{-0.07}^{+0.07}\) at \(z=6\) to \(-2.38_{-0.88}^{+0.72}\) at \(z=9\), steeper than previously observed mass functions at slightly lower redshifts, and we find no evidence of turnover in the mass range probed. We furthermore demonstrate that the UV LF for these system also appears to show a steepening at the highest redshifts, without any evidence of turnover in the luminosity range probed. Our \(M_{\mathrm{UV}}-M_{*}\) relation exhibit shallower slopes than previously observed and are in accordance with a constant mass-to-light ratio. Integrating our GSMF, we find that the stellar mass density increases by a factor of \(\sim15_{-6}^{+21}\) from \(z=9\) to \(z=6\). We estimate the dust-corrected star formation rates (SFRs) to calculate the specific star formation rates (\(\mathrm{sSFR}=\mathrm{SFR/M_{*}}\)) of our sample, and find that for a fixed stellar mass of \(5\times10^{9}M_{\odot}\), sSFR \(\propto(1+z)^{2.01\pm0.16}\). Finally, from our new measurements, we estimate the UV luminosity density (\(\rho_{\textrm{UV}}\)) and find that our results support a smooth decline of \(\rho_{\textrm{UV}}\) towards high redshifts.
We study a large sample of 625 low-redshift brightest cluster galaxies (BCGs) and link their morphologies to their structural properties. We derive visual morphologies and find that ~57% of the BCGs ...are cD galaxies, ~13% are ellipticals, and ~21% belong to the intermediate classes mostly between E and cD. There is a continuous distribution in the properties of the BCG's envelopes, ranging from undetected (E class) to clearly detected (cD class), with intermediate classes (E/cD and cD/E) showing the increasing degrees of the envelope presence. A minority (~7%) of BCGs have disk morphologies, with spirals and S0s in similar proportions, and the rest (~2%) are mergers. After carefully fitting the galaxies light distributions by using one-component (Sersic) and two-component (Sersic+Exponential) models, we find a clear link between the BCGs morphologies and their structures and conclude that a combination of the best-fit parameters derived from the fits can be used to separate cD galaxies from non-cD BCGs. In particular, cDs and non-cDs show very different distributions in the \(R_e\)--\(RFF\) plane, where \(R_e\) is the effective radius and \(RFF\) (the residual flux fraction) measures the proportion of the galaxy flux present in the residual images after subtracting the models. In general, cDs have larger \(R_e\) and \(RFF\) values than ellipticals. Therefore we find, in a statistically robust way, a boundary separating cD and non-cD BCGs in this parameter space. BCGs with cD morphology can be selected with reasonably high completeness (~75%) and low contamination (~20%). This automatic and objective technique can be applied to any current or future BCG sample with good quality images.
We present a new analysis of the ionizing emissivity (\(\dot{N}_{\rm{ion}}\), s\(^{-1}\) Mpc\(^{-3}\)) for galaxies during the epoch of reionization and their potential for completing and maintaining ...reionization. We use extensive SED modelling -- incorporating two plausible mechanisms for the escape of Lyman continuum photon -- to explore the range and evolution of ionizing efficiencies consistent with new results on galaxy colours (\(\beta\)) during this epoch. We estimate \(\dot{N}_{\rm{ion}}\) for the latest observations of the luminosity and star-formation rate density at \(z<10\), outlining the range of emissivity histories consistent with our new model. Given the growing observational evidence for a UV colour-magnitude relation in high-redshift galaxies, we find that for any plausible evolution in galaxy properties, red (brighter) galaxies are less efficient at producing ionizing photons than their blue (fainter) counterparts. The assumption of a redshift and luminosity evolution in \(\beta\) leads to two important conclusions. Firstly, the ionizing efficiency of galaxies naturally increases with redshift. Secondly, for a luminosity dependent ionizing efficiency, we find that galaxies down to a rest-frame magnitude of \(M_{\rm{UV}} \approx -15\) alone can potentially produce sufficient numbers of ionizing photons to maintain reionization as early as \(z\sim8\) for a clumping factor of \(C_{\rm{H {\small II}}} \leq 3\).
We present a multi-component structural analysis of the internal structure of
$1074$ high redshift massive galaxies at $1<z<3$ from the CANDELS HST Survey.
In particular we examine galaxies best-fit ...by two structural components, and
thus likely forming discs and bulges. We examine the stellar mass, star
formation rates, and colours of both the inner `bulge' and outer `disc'
components for these systems using SED information from the resolved ACS+WFC3
HST imaging. We find that the majority of both inner and outer components lie
in the star-forming region of UVJ space ($68$ and $90$ per cent respectively).
However, the inner portions, or the likely forming bulges, are dominated by
dusty star formation. Furthermore, we show that the outer components of these
systems have a higher star formation rate than their inner regions, and the
ratio of star formation rate between `disc' and `bulge' increases at lower
redshifts. Despite the higher star formation rate of the outer component, the
stellar mass ratio of inner to outer component remains constant through this
epoch. This suggests that there is mass transfer from the outer to inner
components for typical two component forming systems, thus building bulges from
disks. Finally, using Chandra data we find that the presence of an AGN is more
common in both $1$-component spheroid-like galaxies and $2$-component systems
($13\pm3$ and $11\pm2$ per cent) than in $1$-component disc-like galaxies
($3\pm1$ per cent), demonstrating that the formation of a central
inner-component likely triggers the formation of central massive black holes in
these galaxies.
We analyze an extremely deep 450-$\mu$m image
($1\sigma=0.56$\,mJy\,beam$^{-1}$) of a $\simeq 300$\,arcmin$^{2}$ area in the
CANDELS/COSMOS field as part of the SCUBA-2 Ultra Deep Imaging EAO Survey
...(STUDIES). We select a robust (signal-to-noise ratio $\geqslant 4$) and
flux-limited ($\geqslant 4$\,mJy) sample of 164 sub-millimeter galaxies (SMGs)
at 450-$\mu$m that have $K$-band counterparts in the COSMOS2015 catalog
identified from radio or mid-infrared imaging. Utilizing this SMG sample and
the 4705 $K$-band-selected non-SMGs that reside within the noise level
$\leqslant 1$\,mJy\,beam$^{-1}$ region of the 450-$\mu$m image as a training
set, we develop a machine-learning classifier using $K$-band magnitude and
color-color pairs based on the thirteen-band photometry available in this
field. We apply the trained machine-learning classifier to the wider COSMOS
field (1.6\,deg$^{2}$) using the same COSMOS2015 catalog and identify a sample
of 6182 450-$\mu$m SMG candidates with similar colors. The number density,
radio and/or mid-infrared detection rates, redshift and stellar mass
distributions, and the stacked 450-$\mu$m fluxes of these SMG candidates, from
the S2COSMOS observations of the wide field, agree with the measurements made
in the much smaller CANDELS field, supporting the effectiveness of the
classifier. Using this 450-$\mu$m SMG candidate sample, we measure the
two-point autocorrelation functions from $z=3$ down to $z=0.5$. We find that
the 450-$\mu$m SMG candidates reside in halos with masses of $\simeq
(2.0\pm0.5) \times10^{13}\,h^{-1}\,\rm M_{\odot}$ across this redshift range.
We do not find evidence of downsizing that has been suggested by other recent
observational studies.
We present in this paper one of the largest galaxy morphological classification catalogues to date, including over 20 million of galaxies, using the Dark Energy Survey (DES) Year 3 data based on ...Convolutional Neural Networks (CNN). Monochromatic \(i\)-band DES images with linear, logarithmic, and gradient scales, matched with debiased visual classifications from the Galaxy Zoo 1 (GZ1) catalogue, are used to train our CNN models. With a training set including bright galaxies (\(16\le{i}<18\)) at low redshift (\(z<0.25\)), we furthermore investigate the limit of the accuracy of our predictions applied to galaxies at fainter magnitude and at higher redshifts. Our final catalogue covers magnitudes \(16\le{i}<21\), and redshifts \(z<1.0\), and provides predicted probabilities to two galaxy types -- Ellipticals and Spirals (disk galaxies). Our CNN classifications reveal an accuracy of over 99\% for bright galaxies when comparing with the GZ1 classifications (\(i<18\)). For fainter galaxies, the visual classification carried out by three of the co-authors shows that the CNN classifier correctly categorises disky galaxies with rounder and blurred features, which humans often incorrectly visually classify as Ellipticals. As a part of the validation, we carry out one of the largest examination of non-parametric methods, including \(\sim\)100,000 galaxies with the same coverage of magnitude and redshift as the training set from our catalogue. We find that the Gini coefficient is the best single parameter discriminator between Ellipticals and Spirals for this data set.
We present a study on the clustering of a stellar mass selected sample of galaxies with stellar masses M*>10^10Msol at redshifts 0.4<z<2.0, taken from the Palomar Observatory Wide-field Infrared ...Survey. We examine the clustering properties of these stellar mass selected samples as a function of redshift and stellar mass, and find that galaxies with high stellar masses have a progressively higher clustering strength than galaxies with lower stellar masses. We also find that galaxies within a fixed stellar mass range have a higher clustering strength at higher redshifts. We further estimate the average total masses of the dark matter haloes hosting these stellar-mass selected galaxies. For all galaxies in our sample the stellar-mass-to-total-mass ratio is always lower than the universal baryonic mass fraction and the stellar-mass-to-total-mass ratio is strongly correlated with the halo masses for central galaxies, such that more massive haloes contain a lower fraction of their mass in the form of stars. The remaining baryonic mass is included partially in stars within satellite galaxies in these haloes, and as diffuse hot and warm gas. We also find that, at a fixed stellar mass, the stellar-to-total-mass ratio increases at lower redshifts. This suggests that galaxies at a fixed stellar mass form later in lower mass dark matter haloes, and earlier in massive haloes. We interpret this as a `halo downsizing' effect.
Evolutionary studies that compare galaxy structure as a function of redshift are complicated by the fact that any particular galaxy's appearance depends in part on the rest-frame wavelength of the ...observation. This leads to the necessity for a "morphological k-correction" between different pass-bands, especially when comparing the rest-frame optical or infrared (IR) to the ultraviolet (UV). This is of particular concern for high redshift studies that are conducted in the rest-frame UV. We investigate the effects of this "band-pass shifting" out of the UV by quantifying nearby galaxy structure via "CAS parameters" (concentration, asymmetry, and clumpiness). For this study we combine pan-chromatic data from the UV through the near-IR with GALEX (Galaxy Evolution Explorer) data of 2073 nearby galaxies in the "NUV" (~230 nm) and 1127 in the "FUV" (~150 nm), providing the largest study of this kind in the mid- to far-UV. We find a relationship between the CAS parameters and observed rest-frame wavelength that make galaxies appear more late-type at shorter wavelengths, particularly in the UV. The effect is strongest for E/S0 galaxies in the far-UV, which have concentrations and asymmetries that more resemble those of spiral and peculiar/merging galaxies in the optical. This may be explained by extended disks containing recent star formation. Here we also release the CAS values of the galaxies imaged in GALEX NUV and FUV for use in comparisons with deep HST imaging and JWST in the future.
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