Recent independent results from numerical simulations and observations have shown that brightest cluster galaxies (BCGs) have increased their stellar mass by a factor of almost 2 between z ∼ 0.9 and ...z ∼ 0.2. The numerical simulations further suggest that more than half this mass is accreted through major mergers. Using a sample of 18 distant galaxy clusters with over 600 spectroscopically confirmed cluster members between them, we search for observational evidence that major mergers do play a significant role. We find a major merger rate of 0.38 ± 0.14 mergers per Gyr at z ∼ 1. While the uncertainties, which stem from the small size of our sample, are relatively large, our rate is consistent with the results that are derived from numerical simulations. If we assume that this rate continues to the present day and that half of the mass of the companion is accreted on to the BCG during these mergers, then we find that this rate can explain the growth in the stellar mass of the BCGs that is observed and predicted by simulations. Major mergers therefore appear to be playing an important role, perhaps even the dominant one, in the build up of stellar mass in these extraordinary galaxies.
We analyse the evolution of the red sequence in a sample of galaxy clusters at redshifts 0.8 < z < 1.5 taken from the HAWK-I Cluster Survey (HCS). The comparison with the low-redshift (0.04 < z < ...0.08) sample of the WIde-field Nearby Galaxy-cluster Survey (WINGS) and other literature results shows that the slope and intrinsic scatter of the cluster red sequence have undergone little evolution since z = 1.5. We find that the luminous-to-faint ratio and the slope of the faint end of the luminosity distribution of the HCS red sequence are consistent with those measured in WINGS, implying that there is no deficit of red galaxies at magnitudes fainter than
$M_V^{\ast }$
at high redshifts. We find that the most massive HCS clusters host a population of bright red sequence galaxies at M
V
< −22.0 mag, which are not observed in low-mass clusters. Interestingly, we also note the presence of a population of very bright (M
V
< −23.0 mag) and massive (log (M
*/M⊙) > 11.5) red sequence galaxies in the WINGS clusters, which do not include only the brightest cluster galaxies and which are not present in the HCS clusters, suggesting that they formed at epochs later than z = 0.8. The comparison with the luminosity distribution of a sample of passive red sequence galaxies drawn from the COSMOS/UltraVISTA field in the photometric redshift range 0.8 < z
phot < 1.5 shows that the red sequence in clusters is more developed at the faint end, suggesting that halo mass plays an important role in setting the time-scales for the build-up of the red sequence.
We present Advanced Camera for Surveys, NICMOS, and Keck adaptive-optics-assisted photometry of 20 Type Ia supernovae (SNe Ia) from the Hubble Space Telescope (HST) Cluster Supernova Survey. The SNe ...Ia were discovered over the redshift interval 0.623 < z < 1.415. Of these SNe Ia, 14 pass our strict selection cuts and are used in combination with the world's sample of SNe Ia to derive the best current constraints on dark energy. Of our new SNe Ia, 10 are beyond redshift z = 1, thereby nearly doubling the statistical weight of HST-discovered SNe Ia beyond this redshift. Our detailed analysis corrects for the recently identified correlation between SN Ia luminosity and host galaxy mass and corrects the NICMOS zero point at the count rates appropriate for very distant SNe Ia. Adding these SNe improves the best combined constraint on dark-energy density, rho sub(DE)(z), at redshifts 1.0 < z < 1.6 by 18% (including systematic errors). For a flat LAMBDACDM universe, we find ohm sub(Lambda) = 0.729 + or - 0.014 (68% confidence level (CL) including systematic errors). For a flat wCDM model, we measure a constant dark-energy equation-of-state parameter w = -1.013 super(+0.068) sub(-0.073) (68% CL). Curvature is constrained to ~0.7% in the owCDM model and to 2% in a model in which dark energy is allowed to vary with parameters w sub(0) and w sub(a). Further tightening the constraints on the time evolution of dark energy will require several improvements, including high-quality multi-passband photometry of a sample of several dozen z > 1 SNe Ia. We describe how such a sample could be efficiently obtained by targeting cluster fields with WFC3 on board HST. The updated supernova Union2.1 compilation of 580 SNe is available at http://supernova.lbl.gov/Union.
Abstract
The study of galaxy morphology is fundamental to understand the physical processes driving the structural evolution of galaxies. It has long been known that dense environments host high ...fractions of early-type galaxies and low fractions of late-type galaxies, indicating that the environment affects the structural evolution of galaxies. In this paper, we present an analysis of the morphological composition of red sequence galaxies in a sample of nine galaxy clusters at 0.8 < z < 1.5 drawn from the HAWK-I Cluster Survey (HCS), with the aim of investigating the evolutionary paths of galaxies with different morphologies. We classify galaxies according to their apparent bulge-to-total light ratio and compare with red sequence galaxies from the lower redshift WIde-field Nearby Galaxy-cluster Survey (WINGS) and ESO Distant Cluster Survey (EDisCS). We find that, while the HCS red sequence is dominated by elliptical galaxies at all luminosities and stellar masses, the WINGS red sequence is dominated by elliptical galaxies only at its bright end (M
V < −21.0 mag), while S0s become the most frequent class at fainter luminosities. Disc-dominated galaxies comprise 10–14 per cent of the red sequence population in the low (WINGS) and high (HCS) redshift samples, although their fraction increases up to 40 per cent at 0.4 < z < 0.8 (EDisCS). We find a 20 per cent increase in the fraction of S0 galaxies from z ∼ 1.5 to 0.05 on the red sequence. These results suggest that elliptical and S0 galaxies follow different evolutionary histories and, in particular, that S0 galaxies result, at least at intermediate luminosities (−22.0 < M
V < −20.0), from the morphological transformation of quiescent spiral galaxies.
ABSTRACT
We use spatially resolved spectroscopy of a distant giant gravitational arc to test orientation effects on Mg ii absorption equivalent width (EW) and covering fraction (〈κ〉) in the ...circumgalactic medium of a foreground star-forming galaxy (G1) at z ∼ 0.77. Forty-two spatially-binned arc positions uniformly sample impact parameters (D) to G1 between 10 and 30 kpc and azimuthal angles α between 30° and 90° (minor axis). We find an EW-D anticorrelation, akin to that observed statistically in quasar absorber studies, and an apparent correlation of both EW and 〈κ〉 with α, revealing a non-isotropic gas distribution. In line with our previous results on Mg ii kinematics suggesting the presence of outflows in G1, at minimum a simple 3D static double-cone model (to represent the trace of bipolar outflows) is required to recreate the EW spatial distribution. The D and α values probed by the arc cannot confirm the presence of a disc, but the data highly disfavour a disc alone. Our results support the interpretation that the EW-α correlation observed statistically using other extant probes is partly shaped by bipolar metal-rich winds.
ABSTRACT
We present spatially resolved Echelle spectroscopy of an intervening Mg ii–Fe ii–Mg i absorption-line system detected at zabs = 0.73379 towards the giant gravitational arc PSZ1 ...G311.65–18.48. The absorbing gas is associated with an inclined disc-like star-forming galaxy, whose major axis is aligned with the two arc-segments reported here. We probe in absorption the galaxy’s extended disc continuously, at ≈3 kpc sampling, from its inner region out to 15× the optical radius. We detect strong ($W_0^{2796}\gt 0.3$Å) coherent absorption along 13 independent positions at impact parameters D = 0–29 kpc on one side of the galaxy, and no absorption at D = 28–57 kpc on the opposite side (all de-lensed distances at zabs). We show that (1) the gas distribution is anisotropic; (2) $W_0^{2796}$, $W_0^{2600}$, $W_0^{2852}$, and the ratio $W_0^{2600}\!/W_0^{2796}$, all anticorrelate with D; (3) the $W_0^{2796}$–D relation is not cuspy and exhibits significantly less scatter than the quasar-absorber statistics; (4) the absorbing gas is co-rotating with the galaxy out to D ≲ 20 kpc, resembling a ‘flat’ rotation curve, but at D ≳ 20 kpc velocities decline below the expectations from a 3D disc-model extrapolated from the nebular O ii emission. These signatures constitute unambiguous evidence for rotating extra-planar diffuse gas, possibly also undergoing enriched accretion at its edge. Arguably, we are witnessing some of the long-sought processes of the baryon cycle in a single distant galaxy expected to be representative of such phenomena.
We present our measurements of the Hα, OIII, and O II luminosity functions as part of the Lyman Alpha Galaxies at Epoch of Reionization (LAGER) survey using our samples of 1577 z=0.47Hα-, 3933 z=0.93 ...O III-, and 5367 z=1.59 O II-selected emission line galaxies in a 3 deg2 single, CTIO/Blanco DECam pointing of the COSMOS field. Our observations reach 5σ depths of 8.2 × 10−18 erg s−1 cm−2 and comoving volumes of (1−7) × 105 Mpc3 making our survey one of the deepest narrow-band surveys. We select our emission line galaxies via spectroscopic confirmation, photometric redshifts, and colour–colour selections. We measure the observed luminosity functions for each sample and find best fits of φ* = 10−3.16+0.09 −0.09 Mpc−3and L* = 1041.72+0.09 −0.09 erg s−1 for Hα, φ* = 10−2.16+0.10−0.12 Mpc−3 and L* = 1041.38+0.07 −0.06 erg s−1 for
O III, and φ* = 10−1.97+0.07−0.07 Mpc−3 and L* = 1041.66+0.03−0.03 erg s−1 for OII, with α fixed to −1.75, −1.6, and −1.3, respectively. An excess of bright >1042 erg s−1 O III emitters is observed and may be due to active galactic nucleus (AGN) contamination. Corrections for dust attenuation are applied assuming AHα = 1 mag. We also design our own empirical restframe g − r calibration using SDSS DR12 data, test it against our z = 0.47 Hα emitters with zCOSMOS 1D spectra, and calibrate it for (g − r) between −0.8 and 1.3 mag. Dust and AGN corrected star formation rate densities (SFRDs) are measured as log10ρSFR/(Msun yr−1 Mpc−3)=−1.63 ± 0.04, −1.07 ± 0.06, and −0.90 ± 0.10 for Hα, OIII, and O II, respectively. We find our O III and O II samples fully trace cosmic star formation activity at their respective redshifts in comparison to multiwavelength SFRDs, while the Hα sample traces ∼70 per cent of the total z = 0.47 SFRD.
ABSTRACT
The H α equivalent width (EW) is an observational proxy for specific star formation rate (sSFR) and a tracer of episodic, bursty star-formation activity. Previous assessments show that the H ...α EW strongly anticorrelates with stellar mass as M−0.25 similar to the sSFR – stellar mass relation. However, such a correlation could be driven or even formed by selection effects. In this study, we investigate how H α EW distributions correlate with physical properties of galaxies and how selection biases could alter such correlations using a z = 0.47 narrow-band-selected sample of 1572 H α emitters from the Ly α Galaxies in the Epoch of Reionization (LAGER) survey as our observational case study. The sample covers a 3 deg2 area of COSMOS with a survey comoving volume of 1.1 × 105 Mpc3. We assume an intrinsic EW distribution to form mock samples of H α emitters and propagate the selection criteria to match observations, giving us control on how selection biases can affect the underlying results. We find that H α EW intrinsically correlates with stellar mass as W0∝M−0.16 ± 0.03 and decreases by a factor of ∼3 from 107 M⊙ to 1010 M⊙, while not correcting for selection effects steepens the correlation as M−0.25 ± 0.04. We find low-mass H α emitters to be ∼320 times more likely to have rest-frame EW>200 Å compared to high-mass H α emitters. Combining the intrinsic W0–stellar mass correlation with an observed stellar mass function correctly reproduces the observed H α luminosity function, while not correcting for selection effects underestimates the number of bright emitters. This suggests that the W0–stellar mass correlation when corrected for selection effects is physically significant and reproduces three statistical distributions of galaxy populations (line luminosity function, stellar mass function, EW distribution). At lower stellar masses, we find there are more high-EW outliers compared to high stellar masses, even after we take into account selection effects. Our results suggest that high sSFR outliers indicative of bursty star formation activity are intrinsically more prevalent in low-mass H α emitters and not a byproduct of selection effects.
We studied the clustering properties and multiwavelength spectral energy distributions of a complete sample of 162 Ly alpha -emitting (LAE) galaxies at z unk 3.1 discovered in deep narrowband MUSYC ...imaging of the Extended Chandra Deep Field-South. LAEs were selected to have observed frame equivalent widths >80 AAA and emission line fluxes >1.5 x 10 super(-17) ergs cm super(-2) s super(-1). Only 1% of our LAE sample appears to host AGNs. The LAEs exhibit a moderate spatial correlation length of unk = unk Mpc, corresponding to a bias factor b = unk, which implies median dark matter halo masses of log sub(10)M unk = unk M unk. Comparing the number density of LAEs, 1.5 plus or minus 0.3 x 10 super(-3) Mpc super(-3), with the number density of these halos finds a mean halo occupation similar to 1%-10%. The evolution of galaxy bias with redshift implies that most z = 3.1 LAEs evolve into present-day galaxies with unk, whereas other z > 3 galaxy populations typically evolve into more massive galaxies. Halo merger trees show that z = 0 descendants occupy halos with a wide range of masses, with a median descendant mass close to that of unk. Only 30% of LAEs have sufficient stellar mass (> similar to 3 x unk M unk) to yield detections in deep Spitzer IRAC imaging. A two-population SED fit to the stacked UBVRIzJK+3.6, 4.5, 5.6, 8.0 mu m fluxes of the IRAC-undetected objects finds that the typical LAE has low stellar mass ( unk x unk M unk), moderate star formation rate (2 plus or minus 1 M unk yr super(-1)), a young component age of unk Myr, and little dust (Av < 0.2). The best-fit model has 20% of the mass in the young stellar component, but models without evolved stars are also allowed.
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