M. J. Jee

The Hubble Space Telescope Cluster Supernova Survey. V. Improving the Dark-energy Constraints above z > 1 and Building an Early-type-hosted Supernova Sample

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 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.

EVOLUTION OF THE COLOR-MAGNITUDE RELATION IN GALAXY CLUSTERS AT z ∼ 1 FROM THE ACS INTERMEDIATE REDSHIFT CLUSTER SURVEY

We apply detailed observations of the color-magnitude relation (CMR) with the Advanced Camera for Surveys on the Hubble Space Telescope to study galaxy evolution in eight clusters at z 1. The early-type red sequence is well defined and elliptical and lenticular galaxies lie on similar CMRs. We analyze CMR parameters—scatter, slope, and zero point—as a function of redshift, galaxy properties and cluster mass. For bright galaxies (MB – 21 mag). While the bright S0 population consistently shows larger scatter than the ellipticals, the scatter of the latter increases in the peripheral cluster regions. If we interpret these results as due to age differences, bright elliptical galaxies in cluster cores are, on average, older than S0 galaxies and peripheral elliptical galaxies (by about 0.5 Gyr, using a simple, single-burst solar metallicity stellar population model). The CMR zero point, slope, and scatter in the (U – B) z = 0 rest-frame show no significant evolution out to redshift z 1.3 or significant dependence on cluster mass. Two of our clusters display CMR zero points that are redder (by 2σ) than the average (U – B) z = 0 of our sample. We also analyze the fraction of morphological early-type and late-type galaxies on the red sequence. We find that, while in the majority of the clusters most (80% to 90%) of the CMR population is composed of early-type galaxies, in the highest-redshift, low-mass cluster of our sample, the CMR late-type/early-type fractions are similar (50%), with most of the late-type population composed of galaxies classified as S0/a. This trend is not correlated with the clusters X-ray luminosity, or with its velocity dispersion, and could be a real evolution with redshift.

Discovery of a Very Bright Strongly Lensed Galaxy Candidate at z ≈ 7.6*

Using Hubble Space Telescope (HST) and Spitzer IRAC imaging, we report the discovery of a very bright strongly lensed Lyman break galaxy (LBG) candidate at -->z ~ 7.6 in the field of the massive galaxy cluster Abell 1689 ( -->z = 0.18). The galaxy candidate, which we refer to as A1689-zD1, shows a strong -->z850 − J110 break of at least 2.2 mag and is completely undetected ( J110 − H160 and -->H160 − [ 4.5 μ m ] colors, are exactly the properties of an -->z ~ 7.6 LBG, and can only be reasonably fit by a star-forming galaxy at -->z = 7.6 ± 0.4 ( -->χ2ν = 1.1). Attempts to reproduce these properties with a model galaxy at -->z χ2ν ≥ 25). A1689-zD1 has an observed (lensed) magnitude of 24.7 AB (8 σ) in the NICMOS H160 band and is ~1.3 mag brighter than the brightest known z850-dropout galaxy. When corrected for the cluster magnification of ~9.3 at -->z ~ 7.6, the candidate has an intrinsic magnitude of -->H160 = 27.1 AB, or about an L* galaxy at -->z ~ 7.6. The source-plane deprojection shows that the star formation is occurring in compact knots of size 300 pc. The best-fit stellar population synthesis models yield a median redshift of 7.6, stellar masses -->(1.6–3.9) × 109 M☉, stellar ages 45-320 Myr, star formation rates 7.6 M☉ yr−1, and low reddening with -->AV ≤ 0.3. These properties are generally similar to those of LBGs found at -->z ~ 5–6. The inferred stellar ages suggest a formation redshift of -->z ~ 8–10 ( -->t 0.63 Gyr). A1689-zD1 is the brightest observed, highly reliable -->z > 7.0 galaxy candidate found to date.

Cluster galaxies in XMMU J2235-2557: galaxy population properties in most massive environments at z ∼1.4

We present a multi-wavelength study of galaxy populations in the core of the massive, X-ray luminous cluster XMMU J2235 at z=1.39, based on high quality VLT and HST photometry at optical and near-infrared wavelengths. We derive luminosity functions in the z, H, and Ks bands, approximately corresponding to restframe U, R and z band. These show a faint-end slope consistent with being flat, and a character istic magnitude Mclose to passive evolution predictions of Mof local massive clusters, with a formation redshift z> 2. The color-magnitude and color-mass diagrams show evidence of a tight red sequence (intrinsic scatter . 0: 08) of massive galaxies already in place, with overall old stellar populations and g enerally early-type morphology. Beside the red colors, these massive (> 6� 10 10 M�) galaxies typically show early-type spectral features, an d rest-frame far-UV emission consistent with very low star formation rates (SFR< 0: 2M�/yr). Star forming spectroscopic members, with SFR of up to� 100M�/yr, are all located at clustercentric distances &250kpc, with the central cluster region already appearing effectively quenched. Most part of the cluster galaxies more massive than 6� 10 10 Mwithin the studied area do not appear to host significant levels of st ar formation. The high-mass end galaxy populations in the core of this cluster appear to be in a very advanced evolutionary stage, not only in terms of formation of the stellar populations, but also of the asse mbly of the stellar mass. The high-mass end of the galaxy stellar mass function is essentially already in place. The stellar mass f raction estimated within r500 (�1%, Kroupa IMF) is already similar to that of local massive clusters. On the other hand, surface brightness distribution modeling of the massive red sequence galaxies may suggest that their size is often smaller than expected based on the local stellar mass vs size relation. An evolution of the stellar mass vs size relation m ight imply that, in spite of the overall early assembly of these sources , their evolution is not complete, and processes like minor ( and likely dry) merging might still shape the structural properties of thes e objects to resemble those of their local counterparts, wit hout substantially affecting their stellar mass or host stellar populations. None theless, a definite conclusion on the actual relevance of siz e evolution for the studied early-type sample is precluded by possible systematics and biases.

BRIGHT STRONGLY LENSED GALAXIES AT REDSHIFT z ∼ 6-7 BEHIND THE CLUSTERS ABELL 1703 AND CL0024+16*

We report on the discovery of three bright, strongly lensed objects behind Abell 1703 and CL0024+16 from a dropout search over 25 arcmin2 of deep NICMOS data, with deep ACS optical coverage. They are undetected in the deep ACS images below 8500 A and have clear detections in the J and H bands. Fits to the ACS, NICMOS, and IRAC data yield robust photometric redshifts in the range z ~ 6-7 and largely rule out the possibility that they are low-redshift interlopers. All three objects are extended, and resolved into a pair of bright knots. The bright i-band dropout in Abell 1703 has an H-band AB magnitude of 23.9, which makes it one of the brightest known galaxy candidates at z > 5.5. Our model fits suggest a young, massive galaxy only ~60 million years old with a mass of ~1010 M ☉. The dropout galaxy candidates behind CL0024+16 are separated by 25 (~2 kpc in the source plane), and have H-band AB magnitudes of 25.0 and 25.6. Lensing models of CL0024+16 suggest that the objects have comparable intrinsic magnitudes of AB ~27.3, approximately one magnitude fainter than L* at z ~ 6.5. Their similar redshifts, spectral energy distribution, and luminosities, coupled with their very close proximity on the sky, suggest that they are spatially associated, and plausibly are physically bound. Combining this sample with two previously reported, similarly magnified galaxy candidates at z ~ 6-8, we find that complex systems with dual nuclei may be a common feature of high-redshift galaxies.

Hubble Space Telescope/Advanced Camera for Surveys Confirmation of the Dark Substructure in A520

We present the results from a weak gravitational lensing study of the merging cluster A520 based on the analysis of Hubble Space Telescope/Advanced Camera for Surveys (ACS) data. The excellent data quality allows us to reach a mean number density of source galaxies of ~109 per sq. arcmin, which improves both resolution and significance of the mass reconstruction compared to a previous study based on Wide Field Planetary Camera 2 (WFPC2) images. We take care in removing instrumental effects such as the trailing of charge due to radiation damage of the ACS detector and the position-dependent point spread function (PSF). This new ACS analysis confirms the previous claims that a substantial amount of dark mass is present between two luminous subclusters. We examine the distribution of cluster galaxies and observe very little light at this location. We find that the centroid of the dark peak in the current ACS analysis is offset to the southwest by ~1 arcmin with respect to the centroid from the WFPC2 analysis. Interestingly, this new centroid is in better spatial agreement with the location where the X-ray emission is strongest, and the mass-to-light ratio estimated with this centroid is much higher 813+-78 M_sun/L_Rsun than the previous value; the aperture mass based on the WFPC2 centroid provides a slightly lower, but consistent mass. Although we cannot provide a definite explanation for the presence of the dark peak, we discuss a revised scenario, wherein dark matter with a more conventional range sigma_DM/m_DM < 1 cm^2/g of self-interacting cross-section can lead to the detection of this dark substructure. If supported by detailed numerical simulations, this hypothesis opens up the possibility that the A520 system can be used to establish a lower limit of the self-interacting cross-section of dark matter.

Early-type Galaxies at z = 1.3. I. The Lynx Supercluster: Cluster and Groups at z = 1.3. Morphology and Color-Magnitude Relation

We confirm the detection of three groups in the Lynx supercluster, at z ≈ 1.3, through spectroscopic follow-up and X-ray imaging, and we give estimates for their redshifts and masses. We study the properties of the group galaxies compared to the two central clusters, RX J0849+4452 and RX J0848+4453. Using spectroscopic follow-up and multi-wavelength photometric redshifts, we select 89 galaxies in the clusters, of which 41 are spectroscopically confirmed, and 74 galaxies in the groups, of which 25 are spectroscopically confirmed. We morphologically classify galaxies by visual inspection, noting that our early-type galaxy (ETG) sample would have been contaminated at the 30%-40% level by simple automated classification methods (e.g., based on Sersic index). In luminosity-selected samples, both clusters and groups show high fractions of bulge-dominated galaxies with a diffuse component that we visually identified as a disk and which we classified as bulge-dominated spirals, e.g., Sas. The ETG fractions never rise above ≈50% in the clusters, which is low compared to the fractions observed in other massive clusters at z ≈ 1. In the groups, ETG fractions never exceed ≈25%. However, overall bulge-dominated galaxy fractions (ETG plus Sas) are similar to those observed for ETGs in clusters at z ~ 1. Bulge-dominated galaxies visually classified as spirals might also be ETGs with tidal features or merger remnants. They are mainly red and passive, and span a large range in luminosity. Their star formation seems to have been quenched before experiencing a morphological transformation. Because their fraction is smaller at lower redshifts, they might be the spiral population that evolves into ETGs. For mass-selected samples of galaxies with masses M > 10^(10.6) M_☉ within Σ > 500 Mpc^(–2), the ETG and overall bulge-dominated galaxy fractions show no significant evolution with respect to local clusters, suggesting that morphological transformations might occur at lower masses and densities. The ETG mass-size relation shows evolution toward smaller sizes at higher redshift in both clusters and groups, while the late-type mass-size relation matches that observed locally. When compared to the clusters, the group ETG red sequence shows lower zero points (at ~2σ) and larger scatters, both expected to be an indication of a younger galaxy population. However, we show that any allowed difference between the age in groups and clusters would be small when compared to the differences in age in galaxies of different masses.

Early-type galaxies at z ~ 1.3 - IV. Scaling relations in different environments

We present the Kormendy and mass-size relations (MSR) for early-type galaxies (ETGs) as a function of environment at z ~ 1.3. Our sample includes 76 visually classified ETGs with masses 10^(10) < M/M_☉ < 10^(11.5), selected in the Lynx supercluster and in the Great Observatories Origins Deep Survey/Chandra Deep Field South field; 31 ETGs in clusters, 18 in groups, and 27 in the field, all with multi-wavelength photometry and Hubble Space Telescope/Advanced Camera for Surveys observations. The Kormendy relation, in place at z ~ 1.3, does not depend on the environment. The MSR reveals that ETGs overall appear to be more compact in denser environments: cluster ETGs have sizes on average around 30%-50% smaller than those of the local universe and a distribution with a smaller scatter, whereas field ETGs show an MSR with a similar distribution to the local one. Our results imply that (1) the MSR in the field did not evolve overall from z ~ 1.3 to present; this is interesting and in contrast to the trend found at higher masses from previous works; (2) in denser environments, either ETGs have increased in size by 30%-50% on average and spread their distributions, or more ETGs have been formed within the dense environment from non-ETG progenitors, or larger galaxies have been accreted to a pristine compact population to reproduce the MSR observed in the local universe. Our results are driven by galaxies with masses M lsim 2 × 10^(11) M_☉ and those with masses M ~ 10^(11) M_☉ follow the same trends as that of the entire sample. Following the Valentinuzzi et al. definition of superdense ETGs, ~35%-45% of our cluster sample is made up of superdense ETGs.

The rich globular cluster system of Abell 1689 and the radial dependence of the globular cluster formation efficiency

We study the rich globular cluster (GC) system in the center of the massive cluster of galaxies Abell 1689 (z = 0.18), one of the most powerful gravitational lenses known. With 28 Hubble Space Telescope/Advanced Camera for Surveys orbits in the F814W bandpass, we reach a magnitude I814 = 29 with 90% completeness and sample the brightest ∼5% of the GC system. Assuming the well-known Gaussian form of the GC luminosity function (GCLF), we estimate a total population of N total GC = 162,850 +75,450 −51,310 GCs within a projected radius of 400 kpc. As many as half of the GCs may comprise an intracluster component. Even with the sizable uncertainties, which mainly result from the uncertain GCLF parameters, this system is by far the largest GC population studied to date. The specific frequency SN is high, but not uncommon for central galaxies in massive clusters, rising from SN ≈ 5 near the center to ∼12 at large radii. Passive galaxy fading would increase SN by ∼20% at z = 0. We construct the radial mass profiles of the GCs, stars, intracluster gas, and lensing-derived total mass, and we compare the mass fractions as a function of radius. The estimated mass in GCs, M total = 3.9 × 10 10 M� , is comparable to ∼80% of the total stellar mass of the Milky Way. The shape of the GC mass profile appears intermediate between those of the stellar light and total cluster mass. Despite the extreme nature of this system, the ratios of the GC mass to the baryonic and total masses, and thus the GC formation efficiency, are typical of those in other rich clusters when comparing at the same physical radii. The GC formation efficiency is not constant, but varies with radius, in a manner that appears similar for different clusters; we speculate on the reasons for this similarity in profile.

Early-Type galaxies at z ~ 1.3. III. On the dependence of Formation Epochs and Star Formation Histories on Stellar Mass and Environment

We study the environmental dependence of stellar population properties at z ~ 1.3. We derive galaxy properties (stellar masses, ages, and star formation histories) for samples of massive, red, passive early-type galaxies (ETGs) in two high-redshift clusters, RXJ0849+4452 and RXJ0848+4453 (with redshifts of z = 1.26 and 1.27, respectively), and compare them with those measured for the RDCS1252.9–2927 cluster at z = 1.24 and with those measured for a similarly mass-selected sample of field contemporaries drawn from the GOODS-South field. Robust estimates of the aforementioned parameters have been obtained by comparing a large grid of composite stellar population models with extensive 8- to 10-band photometric coverage, from the rest-frame far-ultraviolet to the infrared. We find no variations of the overall stellar population properties among the different samples of cluster ETGs. However, when comparing cluster versus field stellar population properties we find that, even if the ages are similar and depend only on galaxy mass, the ones in the field do employ longer timescales to assemble their final mass. We find that, approximately 1 Gyr after the onset of star formation, the majority (75%) of cluster galaxies have already assembled most (>80%) of their final mass, while, by the same time, fewer (35%) field ETGs have. Thus, we conclude that while galaxy mass regulates the timing of galaxy formation, the environment regulates the timescale of their star formation histories.