We present an analysis of the levels and evolution of star formation activity in a representative sample of 30 massive galaxy clusters at 0.15 < z < 0.30 from the Local Cluster Substructure Survey, ...combining wide-field Spitzer/MIPS 24 mum data with extensive spectroscopy of cluster members. The specific SFRs of massive (M > ~ 10 super(10) M sub(middot in circle)) star-forming cluster galaxies within r sub(200) are found to be systematically ~28% lower than their counterparts in the field at fixed stellar mass and redshift, a difference significant at the 8.7sigma level. This is the unambiguous signature of star formation in most (and possibly all) massive star-forming galaxies being slowly quenched upon accretion into massive clusters, their star formation rates (SFRs) declining exponentially on quenching timescales in the range 0.7-2.0 Gyr. We measure the mid-infrared Butcher-Oemler effect over the redshift range 0.0-0.4, finding rapid evolution in the fraction (functionof sub(SF)) of massive (M sub(K) < - 23.1) cluster galaxies within r sub(200) with SFRs > 3 M sub(middot in circle) yr super(-1), of the form functionof sub(SF) alpha (1 + z) super(7.6 + or - 1.1). We dissect the origins of the Butcher-Oemler effect, revealing it to be due to the combination of a ~3 x decline in the mean specific SFRs of star-forming cluster galaxies since z ~ 0.3 with a ~1.5 x decrease in number density. Two-thirds of this reduction in the specific SFRs of star-forming cluster galaxies is due to the steady cosmic decline in the specific SFRs among those field galaxies accreted into the clusters. The remaining one-third reflects an accelerated decline in the star formation activity of galaxies within clusters. The slow quenching of star formation in cluster galaxies is consistent with a gradual shut down of star formation in infalling spiral galaxies as they interact with the intracluster medium via ram-pressure stripping or starvation mechanisms. The observed sharp decline in star formation activity among cluster galaxies since z ~ 0.4 likely reflects the increased susceptibility of low-redshift spiral galaxies to gas removal mechanisms as their gas surface densities decrease with time. We find no evidence for the build-up of cluster S0 bulges via major nuclear starburst episodes.
ABSTRACT We present a study of the spatial distribution and kinematics of star-forming galaxies in 30 massive clusters at 0.15 < z < 0.30, combining wide-field Spitzer 24 m and GALEX near-ultraviolet ...imaging with highly complete spectroscopy of cluster members. The fraction (fSF) of star-forming cluster galaxies rises steadily with cluster-centric radius, increasing fivefold by 2r200, but remains well below field values even at 3r200. This suppression of star formation at large radii cannot be reproduced by models in which star formation is quenched in infalling field galaxies only once they pass within r200 of the cluster, but is consistent with some of them being first pre-processed within galaxy groups. Despite the increasing fSF-radius trend, the surface density of star-forming galaxies actually declines steadily with radius, falling ∼15× from the core to 2r200. This requires star formation to survive within recently accreted spirals for 2-3 Gyr to build up the apparent over-density of star-forming galaxies within clusters. The velocity dispersion profile of the star-forming galaxy population shows a sharp peak of 1.44 at 0.3r500, and is 10%-35% higher than that of the inactive cluster members at all cluster-centric radii, while their velocity distribution shows a flat, top-hat profile within r500. All of these results are consistent with star-forming cluster galaxies being an infalling population, but one that must also survive ∼0.5-2 Gyr beyond passing within r200. By comparing the observed distribution of star-forming galaxies in the stacked caustic diagram with predictions from the Millennium simulation, we obtain a best-fit model in which star formation rates decline exponentially on quenching timescales of 1.73 0.25 Gyr upon accretion into the cluster.
Abstract
We report direct evidence of pre-processing of the galaxies residing in galaxy groups falling into galaxy clusters drawn from the Local Cluster Substructure Survey (LoCuSS). 34 groups have ...been identified via their X-ray emission in the infall regions of 23 massive (〈M200〉 = 1015 M⊙) clusters at 0.15 < z < 0.3. Highly complete spectroscopic coverage combined with 24 μm imaging from Spitzer allows us to make a consistent and robust selection of cluster and group members including star-forming galaxies down to a stellar mass limit of M⋆ = 2 × 1010 M⊙. The fraction fSF of star-forming galaxies in infalling groups is lower and with a flatter trend with respect to clustercentric radius when compared to the rest of the cluster galaxy population. At R ≈ 1.3 r200, the fraction of star-forming galaxies in infalling groups is half that in the cluster galaxy population. This is direct evidence that star-formation quenching is effective in galaxies already prior to them settling in the cluster potential, and that groups are favourable locations for this process.
We present a high-precision mass model of galaxy cluster Abell 2744, based on a strong gravitational-lensing analysis of the Hubble Space Telescope Frontier Fields (HFF) imaging data, which now ...include both Advanced Camera for Surveys and Wide Field Camera 3 observations to the final depth. Taking advantage of the unprecedented depth of the visible and near-infrared data, we identify 34 new multiply imaged galaxies, bringing the total to 61, comprising 181 individual lensed images. In the process, we correct previous erroneous identifications and positions of multiple systems in the northern part of the cluster core. With the lenstool software and the new sets of multiple images, we model the cluster using two cluster-scale dark matter haloes plus galaxy-scale haloes for the cluster members. Our best-fitting model predicts image positions with an rms error of 0.79 arcsec, which constitutes an improvement by almost a factor of 2 over previous parametric models of this cluster. We measure the total projected mass inside a 200 kpc aperture as (2.162 ± 0.005) × 1014 M⊙, thus reaching 1 per cent level precision for the second time, following the recent HFF measurement of MACSJ0416.1−2403. Importantly, the higher quality of the mass model translates into an overall improvement by a factor of 4 of the derived magnification factor. Together with our previous HFF gravitational lensing analysis, this work demonstrates that the HFF data enables high-precision mass measurements for massive galaxy clusters and the derivation of robust magnification maps to probe the early Universe.
ABSTRACT
We report the discovery of an intrinsically faint, quintuply-imaged, dusty galaxy MACS0600-z6 at a redshift z = 6.07 viewed through the cluster MACSJ0600.1–2008 (z = 0.46). A ≃ 4σ dust ...detection is seen at 1.2mm as part of the ALMA Lensing Cluster Survey (ALCS), an on-going ALMA Large programme, and the redshift is secured via C ii 158 μm emission described in a companion paper. In addition, spectroscopic follow-up with GMOS/Gemini-North shows a break in the galaxy’s spectrum, consistent with the Lyman break at that redshift. We use a detailed mass model of the cluster and infer a magnification μ ≳ 30 for the most magnified image of this galaxy, which provides an unprecedented opportunity to probe the physical properties of a sub-luminous galaxy at the end of cosmic reionization. Based on the spectral energy distribution, we infer lensing-corrected stellar and dust masses of $\rm {2.9^{+11.5}_{-2.3}\times 10^9}$ and $\rm {4.8^{+4.5}_{-3.4}\times 10^6}$$\rm {M_{\odot }}$, respectively, a star formation rate of $\rm {9.7^{+22.0}_{-6.6} \, M_{\odot } \, yr^{-1}}$, an intrinsic size of $\rm {0.54^{+0.26}_{-0.14}}$ kpc, and a luminosity-weighted age of 200 ± 100 Myr. Strikingly, the dust production rate in this relatively young galaxy appears to be larger than that observed for equivalent, lower redshift sources. We discuss if this implies that early supernovae are more efficient dust producers and the consequences for using dust mass as a probe of earlier star formation.
We present a high-precision mass model of the galaxy cluster MACSJ0416.1-2403, based on a strong-gravitational-lensing analysis of the recently acquired Hubble Space Telescope Frontier Fields (HFF) ...imaging data. Taking advantage of the unprecedented depth provided by HST/Advanced Camera for Survey observations in three passbands, we identify 51 new multiply imaged galaxies, quadrupling the previous census and bringing the grand total to 68, comprising 194 individual lensed images. Having selected a subset of the 57 most securely identified multiply imaged galaxies, we use the lenstool software package to constrain a lens model comprised of two cluster-scale dark-matter haloes and 98 galaxy-scale haloes. Our best-fitting model predicts image positions with an rms error of 0.68 arcsec, which constitutes an improvement of almost a factor of 2 over previous, pre-HFF models of this cluster. We find the total projected mass inside a 200 kpc aperture to be (1.60 ± 0.01) x 10^sup 14^ M.., a measurement that offers a three-fold improvement in precision, reaching the per cent level for the first time in any cluster. Finally, we quantify the increase in precision of the derived gravitational magnification of high-redshift galaxies and find an improvement by a factor of ~2.5 in the statistical uncertainty. Our findings impressively confirm that HFF imaging has indeed opened the domain of high-precision mass measurements for massive clusters of galaxies.(ProQuest: ... denotes formulae/symbols omitted.)
We report our analysis of MACS J0717.5+3745 using 140 and 268 GHz Bolocam data collected at the Caltech Submillimeter Observatory. We detect extended Sunyaev-Zel'dovich (SZ) effect signal at high ...significance in both Bolocam bands, and we employ Herschel-SPIRE observations to subtract the signal from dusty background galaxies in the 268 GHz data. We constrain the two-band SZ surface brightness toward two of the sub-clusters of MACS J0717.5+3745; the main sub-cluster (named C), and a sub-cluster identified in spectroscopic optical data to have a line-of-sight velocity of +3200 km s super(-l) (named B). We determine the surface brightness in two separate ways: via fits of parametric models and via direct integration of the images. For both sub-clusters, we find consistent surface brightnesses from both analysis methods. We constrain spectral templates consisting of relativistically corrected thermal and kinetic SZ signals, using a jointly-derived electron temperature from Chandra and XMM-Newton under the assumption that each sub-cluster is isothermal. The data show no evidence for a kinetic SZ signal toward sub-cluster C, but they do indicate a significant kinetic SZ signal toward sub-cluster B. The model-derived surface brightnesses for sub-cluster B yield a best-fit, line-of-sight velocity of v sub(z) = +3450 + or - 900 km s super(-1), with (1 - Probv sub(2) > or =, slanted 0) = 1.3 x 10 super(-5) (4.2sigma away from 0 for a Gaussian distribution). The directly integrated sub-cluster B SZ surface brightnesses provide a best-fit v sub(z) = +2550 + or - 1050 km s super(-l), with (1 - Probv sub(2) > or =, slanted 0) = 2.2 x 10 super(-3) (2.9sigma).
Abstract
Galaxy clusters are expected to form hierarchically in a Λ cold dark matter (ΛCDM) universe, growing primarily through mergers with lower mass clusters and the continual accretion of ...group-mass haloes. Galaxy clusters assemble late, doubling their masses since z ∼ 0.5, and so the outer regions of clusters should be replete with accreting group-mass systems. We present an XMM–Newton survey to search for X-ray groups in the infall regions of 23 massive galaxy clusters (〈M200〉 ∼ 1015 M⊙) at z ∼ 0.2, identifying 39 X-ray groups that have been spectroscopically confirmed to lie at the cluster redshift. These groups have mass estimates in the range 2 × 1013–7 × 1014 M⊙, and group-to-cluster mass ratios as low as 0.02. The comoving number density of X-ray groups in the infall regions is ∼25× higher than that seen for isolated X-ray groups from the XXL survey. The average mass per cluster contained within these X-ray groups is 2.2 × 1014 M⊙, or 19 ± 5 per cent of the mass within the primary cluster itself. We estimate that ∼1015 M⊙ clusters increase their masses by 16 ± 4 per cent between z = 0.223 and the present day due to the accretion of groups with M200 ≥ 1013.2 M⊙. This represents about half of the expected mass growth rate of clusters at these late epochs. The other half is likely to come from smooth accretion of matter not bound within haloes. The mass function of the infalling X-ray groups appears significantly top heavy with respect to that of ‘field’ X-ray systems, consistent with expectations from numerical simulations, and the basic consequences of collapsed massive dark matter haloes being biased tracers of the underlying large-scale density distribution.
ABSTRACT The Spitzer-Cosmic Assembly Deep Near-infrared Extragalactic Legacy Survey (S-CANDELS; PI G.Fazio) is a Cycle 8 Exploration Program designed to detect galaxies at very high redshifts ( ). To ...mitigate the effects of cosmic variance and also to take advantage of deep coextensive coverage in multiple bands by the Hubble Space Telescope (HST) Multi-cycle Treasury Program CANDELS, S-CANDELS was carried out within five widely separated extragalactic fields: the UKIDSS Ultra-deep Survey, the Extended Chandra Deep Field South, COSMOS, the HST Deep Field North, and the Extended Groth Strip. S-CANDELS builds upon the existing coverage of these fields from the Spitzer Extended Deep Survey (SEDS), a Cycle 6 Exploration Program, by increasing the integration time from SEDS' 12 hr to a total of 50 hr but within a smaller area, 0.16 deg2. The additional depth significantly increases the survey completeness at faint magnitudes. This paper describes the S-CANDELS survey design, processing, and publicly available data products. We present Infrared Array Camera (IRAC) dual-band catalogs reaching to a depth of 26.5 AB mag. Deep IRAC counts for the roughly 135,000 galaxies detected by S-CANDELS are consistent with models based on known galaxy populations. The increase in depth beyond earlier Spitzer/IRAC surveys does not reveal a significant additional contribution from discrete sources to the diffuse Cosmic Infrared Background (CIB). Thus it remains true that only roughly half of the estimated CIB flux from COBE/DIRBE is resolved.
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