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.
We present a comprehensive study of star-forming (SF) galaxies in the Hubble Space Telescope
(HST) Frontier Field recent cluster merger A2744 (z = 0.308). Wide-field, ultraviolet–infrared (UV–IR) ...imaging enables a direct constraint of the total star formation rate (SFR) for 53 cluster galaxies, with SFRUV+IR = 343 ± 10 M⊙ yr−1. Within the central 4 arcmin (1.1 Mpc) radius, the integrated SFR is complete, yielding a total SFRUV+IR = 201 ± 9 M⊙ yr−1. Focusing on obscured star formation, this core region exhibits a total SFRIR = 138 ± 8 M⊙ yr−1, a mass-normalized SFRIR of ΣSFR = 11.2 ± 0.7 M⊙ yr−1 per 1014 M⊙ and a fraction of IR-detected SF galaxies
$f_{\rm SF} = 0.080^{+0.010}_{-0.037}$
. Overall, the cluster population at z ∼ 0.3 exhibits significant intrinsic scatter in IR properties (total SFRIR, T
dust distribution) apparently unrelated to the dynamical state: A2744 is noticeably different to the merging Bullet cluster, but similar to several relaxed clusters. However, in A2744 we identify a trail of SF sources including jellyfish galaxies with substantial unobscured SF due to extreme stripping (SFRUV/SFRIR up to 3.3). The orientation of the trail, and of material stripped from constituent galaxies, indicates that the passing shock front of the cluster merger was the trigger. Constraints on star formation from both IR and UV are crucial for understanding galaxy evolution within the densest environments.
The galaxy cluster CLG0218.3-0510 at z = 1.62 is one of the most distant galaxy clusters known, with a rich multiwavelength data set that confirms a mature galaxy population already in place. Using ...very deep, wide-area (20 Mpc × 20 Mpc) imaging by Spitzer MIPS at 24 μm, in conjunction with Herschel five-band imaging from 100 to 500 μm, we investigate the dust-obscured, star formation properties in the cluster and its associated large-scale environment. Our galaxy sample of 693 galaxies at z ∼ 1.62 detected at 24 μm (10 spectroscopic and 683 photo-z) includes both cluster galaxies (i.e. within r < 1 Mpc projected cluster-centric radius) and field galaxies, defined as the region beyond a radius of 3 Mpc. The star formation rates (SFRs) derived from the measured infrared luminosity range from 18 to 2500 M yr−1, with a median of 55 M yr−1, over the entire radial range (10 Mpc). The cluster's brightest far-infrared galaxy, taken as the centre of the galaxy system, is vigorously forming stars at a rate of 256 ± 70 M yr−1, and the total cluster SFR enclosed in a circle of 1 Mpc is 1161 ± 96 M yr−1. We estimate a dust extinction of ∼3 mag by comparing the SFRs derived from O ii luminosity with the ones computed from the 24 μm fluxes. We find that the in-falling region (1-3 Mpc) is special: there is a significant decrement (3.5×) of passive relative to star-forming galaxies in this region, and the total SFR of the galaxies located in this region is lower (∼130 M yr−1 Mpc−2) than anywhere in the cluster or field, regardless of their stellar mass. In a complementary approach, we compute the local galaxy density, Σ5, and find no trend between SFR and Σ5. However, we measure an excess of star-forming galaxies in the cluster relative to the field by a factor of 1.7, that lends support to a reversal of SF-density relation in CLG0218.
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.
We present a complete census of all Herschel-detected sources within the six massive lensing clusters of the HST Frontier Fields (HFF). We provide a robust legacy catalogue of 263 sources with ...Herschel fluxes, primarily based on imaging from the Herschel Lensing Survey and PEP/HerMES Key Programmes. We optimally combine Herschel, Spitzer and WISE infrared (IR) photometry with data from HST, VLA and ground-based observatories, identifying counterparts to gain source redshifts. For each Herschel-detected source we also present magnification factor (μ), intrinsic IR luminosity and characteristic dust temperature, providing a comprehensive view of dust-obscured star formation within the HFF. We demonstrate the utility of our catalogues through an exploratory overview of the magnified population, including more than 20 background sub-LIRGs unreachable by Herschel without the assistance gravitational lensing.
To extend the molecular gas measurements to more typical star-forming galaxies (SFGs) with star formation rates SFR< 40 M⊙ yr-1 and stellar masses M∗< 2.5 × 1010M⊙ at z ~ 1.5−3, we have observed CO ...emission with the IRAM Plateau de Bure Interferometer and the IRAM 30 m telescope for five strongly lensed galaxies, selected from the Herschel Lensing Survey. These observations are combined with a compilation of CO measurements from the literature. From this, we infer the CO luminosity correction factors r2,1 = 0.81 ± 0.20 and r3,1 = 0.57 ± 0.15 for the J = 2 and J = 3 CO transitions, respectively, valid for SFGs at z> 1. The combined sample of CO-detected SFGs at z> 1 shows a large spread in star formation efficiency (SFE) with a dispersion of 0.33 dex, such that the SFE extends well beyond the low values of local spirals and overlaps the distribution of z> 1 submm galaxies. We find that the spread in SFE (or equivalently in molecular gas depletion timescale) is due to the variations of several physical parameters, primarily the specific star formation rate, and also stellar mass and redshift. The dependence of SFE on the offset from the main sequence and the compactness of the starburst is less clear. The possible increase of the molecular gas depletion timescale with stellar mass, now revealed by low M∗ SFGs at z> 1 and also observed at z = 0, contrasts with the generally acknowledged constant molecular gas depletion timescale and refutes the linearity of the Kennicutt-Schmidt relation. A net rise of the molecular gas fraction (fgas) is observed from z ~ 0.2 to z ~ 1.2, followed by a very mild increase toward higher redshifts, as found in earlier studies. At each redshift the molecular gas fraction shows a large dispersion, mainly due to the dependence of fgas on stellar mass, producing a gradient of increasing fgas with decreasing M∗. We provide the first measurement of the molecular gas fraction of z> 1 SFGs at the low-M∗ end between 109.4<M∗/M⊙< 109.9, reaching a mean ⟨ fgas ⟩ = 0.69 ± 0.18, which shows a clear fgas upturn at these lower stellar masses. Finally, we find evidence for a nonuniversal dust-to-gas ratio among high-redshift SFGs, high-redshift submm galaxies, local spirals, and local ultraluminous IR galaxies with near-solar metallicities, as inferred from a homogeneous analysis of their rest-frame 850 μm luminosity per unit gas mass. The SFGs with z> 1 show a trend for a lower Lν(850 μm) /Mgas mean by 0.33 dex compared to the other galaxy populations.
We report on the galaxy MACSJ0032-arc at zCO = 3.6314 discovered during the Herschel Lensing snapshot Survey of massive galaxy clusters, and strongly lensed by the cluster MACS J0032.1+1808. The ...successful detections of its rest-frame ultraviolet (UV), optical, far-infrared (FIR), millimeter, and radio continua, and of its CO emission enable us to characterize, for the first time at such a high redshift, the stellar, dust, and molecular gas properties of a compact star-forming galaxy with a size smaller than 2.5 kpc, a fairly low stellar mass of 4.8+ 0.5-1.0 × 109M⊙, and a moderate IR luminosity of 4.8+ 1.2-0.6 × 1011L⊙. By combining the stretching effect of the lens with the high angular resolution imaging of the CO(1–0) line emission and the radio continuum at 5 GHz, we find that the bulk of the molecular gas mass and star formation seems to be spatially decoupled from the rest-frame UV emission. About 90% of the total star formation rate is undetected at rest-frame UV wavelengths because of severe obscuration by dust, but is seen through the thermal FIR dust emission and the radio synchrotron radiation. The observed CO(4–3) and CO(6–5) lines demonstrate that high-J transitions, at least up to J = 6, remain excited in this galaxy, whose CO spectral line energy distribution resembles that of high-redshift submm galaxies, even though the IR luminosity of MACSJ0032-arc is ten times lower. This high CO excitation is possibly due to the compactness of the galaxy. We find evidence that this high CO excitation has to be considered in the balance when estimating the CO-to-H2 conversion factor. Indeed, the respective CO-to-H2 conversion factors as derived from the correlation with metallicity and the FIR dust continuum can only be reconciled if excitation is accounted for. The inferred depletion time of the molecular gas in MACSJ0032-arc supports the decrease in the gas depletion timescale of galaxies with redshift, although to a lesser degree than predicted by galaxy evolution models. Instead, the measured molecular gas fraction as high as 60–79% in MACSJ0032-arc favors the continued increase in the gas fraction of galaxies with redshift as expected, despite the plateau observed between z ~ 1.5 and z ~ 2.5.
We present far-infrared (FIR) analysis of 68 brightest cluster galaxies (BCGs) at 0.08 < z < 1.0. Deriving total infrared luminosities directly from Spitzer and Herschel photometry spanning the peak ...of the dust component (24-500 mu m), we calculate the obscured star formation rate (SFR). 22 super(+6.2) sub(-5.3)% of the BCGs are detected in the far-infrared, with SFR = 1-150 M sub(middot in circle) yr super(-1). The infrared luminosity is highly correlated with cluster X-ray gas cooling times for cool-core clusters (gas cooling time <1 Gyr), strongly suggesting that the star formation in these BCGs is influenced by the cluster-scale cooling process. The occurrence of the molecular gas tracing H alpha emission is also correlated with obscured star formation. For all but the most luminous BCGs (L sub(TIR) > 2 x 10 super(11) L sub(middot in circle)), only a small (<, ~0.4 mag) reddening correction is required for SFR(H alpha ) to agree with SFR sub(FIR). The relatively low H alpha extinction (dust obscuration), compared to values reported for the general star-forming population, lends further weight to an alternate (external) origin for the cold gas. Finally, we use a stacking analysis of non-cool-core clusters to show that the majority of the fuel for star formation in the FIR-bright BCGs is unlikely to originate from normal stellar mass loss.
We present Early Science observations with the Large Millimeter Telescope, AzTEC 1.1 mm continuum images and wide bandwidth spectra (73–111 GHz) acquired with the Redshift Search Receiver, towards ...four bright lensed submillimetre galaxies identified through the Herschel Lensing Survey-snapshot and the Submillimetre Common-User Bolometer Array-2 Cluster Snapshot Survey. This pilot project studies the star formation history and the physical properties of the molecular gas and dust content of the highest redshift galaxies identified through the benefits of gravitational magnification. We robustly detect dust continuum emission for the full sample and CO emission lines for three of the targets. We find that one source shows spectroscopic multiplicity and is a blend of three galaxies at different redshifts (z = 2.040, 3.252, and 4.680), reminiscent of previous high-resolution imaging follow-up of unlensed submillimetre galaxies, but with a completely different search method, that confirm recent theoretical predictions of physically unassociated blended galaxies. Identifying the detected lines as 12CO (J
up = 2–5) we derive spectroscopic redshifts, molecular gas masses, and dust masses from the continuum emission. The mean H2 gas mass of the full sample is (2.0 ± 0.2) × 1011 M⊙/μ, and the mean dust mass is (2.0 ± 0.2) × 109 M⊙/μ, where μ ≈ 2–5 is the expected lens amplification. Using these independent estimations we infer a gas-to-dust ratio of δGDR ≈ 55–75, in agreement with other measurements of submillimetre galaxies. Our magnified high-luminosity galaxies fall on the same locus as other high-redshift submillimetre galaxies, extending the
$L^{\prime }_{\rm CO}$
–L
FIR correlation observed for local luminous and ultraluminous infrared galaxies to higher far-infrared and CO luminosities.
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