T. D. Rawle

Stellar population gradients in early-type cluster galaxies★

We present a study of internal stellar population gradients in early-type cluster galaxies. Using the Very Large Telescope (VLT) Visible Multi-Object Spectrograph (VIMOS) integral field unit, we observed 19 galaxies in the core of the Shapley supercluster (z = 0.048). The radial trends in nine absorption lines (HδF to Fe5406) were measured to the effective radius for 14 galaxies, from which we derived the gradients in age, total metallicity and α-element overabundance. We combine these with results from 11 galaxies studied in our previous VIMOS work. We observe a mean metallicity gradient of —0.13 ± 0.04dex -1 and, in common with the findings of previous studies, galaxies with log σ ≳ 2.1 have a sizeable intrinsic scatter in metallicity gradient. The mean log(age/Gyr) gradient is —0.02 ± 0.06 dex -1 , although several galaxies have significant positive or negative age gradients. The mean gradient in α-element enhancement is —0.10 ± 0.04 dex -1 . We find that stellar population gradients are primarily related to the central metallicity: early-type galaxies with supersolar centres have steep negative metallicity gradients and positive age gradients; those with solar metallicity centres have negligible [Z/H] gradients and negative age gradients. There is a strong observed anticorrelation between the gradients in age and metallicity. While a part of this trend can be attributed to the correlation of measurement errors, we demonstrate that there is an underlying intrinsic relation. For the Shapley galaxies, B - R colour gradients predicted from spectroscopic age and metallicity generally agree well with those measured directly from photometry.

Molecular gas content in strongly lensed z similar to 1.5-3 star-forming galaxies with low infrared luminosities

To extend the molecular gas measurements to more typical star-forming galaxies (SFGs) with star formation rates SFR textless 40 M-circle dot yr(-1) and stellar masses M-* textless 2.5 x 10(10) M-circle dot at z similar to 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 r(2,1) = 0.81 +/- 0.20 and r(3,1) = 0.57 +/- 0.15 for the J = 2 and J = 3 CO transitions, respectively, valid for SFGs at z textgreater 1. The combined sample of CO-detected SFGs at z textgreater 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 textgreater 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 textgreater 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 (f(gas)) is observed from z similar to 0.2 to z similar to 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 f(gas) on stellar mass, producing a gradient of increasing f(gas) with decreasing M-*. We provide the first measurement of the molecular gas fraction of z textgreater 1 SFGs at the low-M-* end between 10(9.4) textless M-*/M-circle dot textless 10(9.9), reaching a mean af(gas)o = 0.69 +/- 0.18, which shows a clear f(gas) 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 mu m luminosity per unit gas mass. The SFGs with z textgreater 1 show a trend for a lower L-nu(850 mu m)/M-gas mean by 0.33 dex compared to the other galaxy populations.

Dust-obscured star formation in the outskirts of XMMU J2235.3−2557, a massive galaxy cluster at z = 1.4

Star formation (SF) in the galaxy populations of local massive clusters is reduced with respect to field galaxies, and tends to be suppressed in the core region. Indications of a reversal of the SF–density relation have been observed in a few z > 1.4 clusters. Using deep imaging from 100–500u2009μm from Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging REceiver (SPIRE) onboard Herschel, we investigate infrared properties of spectroscopic and photo-z cluster members, and of Hα emitters in XMMU J2235.3−2557, one of the most massive, distant, X-ray selected clusters known. Our analysis is based mostly on fitting of the galaxies spectral energy distribution (SED) in the rest-frame 8–1000u2009μm. We measure total IR luminosity, deriving star formation rates (SFRs) ranging from 89 to 463u2009M⊙u2009yr−1 for 13 galaxies individually detected by Herschel, all located beyond the core region (r >250u2009kpc). We perform a stacking analysis of nine star-forming members not detected by PACS, yielding a detection with SFR = 48 ± 16u2009M⊙u2009yr−1. Using a colour criterion based on a star-forming galaxy SED at the cluster redshift, we select 41 PACS sources as candidate star-forming cluster members. We characterize a population of highly obscured SF galaxies in the outskirts of XMMU J2235.3−2557. We do not find evidence for a reversal of the SF–density relation in this massive, distant cluster.

Star formation in the cluster CLG0218.3-0510 at z = 1.62 and its large-scale environment: the infrared perspective

The galaxy cluster CLG0218.3-0510 at z=1.62 is one of the most distant galaxy clusters known, with a rich muti-wavelength data set that confirms a mature galaxy population already in place. Using very deep, wide area (20x20 Mpc) imaging by Spitzer/MIPS at 24um, in conjunction with Herschel 5-band imaging from 100-500um, 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 24um (10 spectroscopic and 683 photo-z) includes both cluster galaxies (i.e. within r <1 Mpc projected clustercentric 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 Ms/yr, with a median of 55 Ms/yr, over the entire radial range (10 Mpc). The cluster brightest FIR galaxy, taken as the centre of the galaxy system, is vigorously forming stars at a rate of 256

Early Science with the Large Millimeter Telescope: observations of dust continuum and CO emission lines of cluster-lensed submillimetre galaxies at z=2.0–4.7

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An extended Herschel drop-out source in the center of AS1063: a normal dusty galaxy at z=6.1 or SZ substructures?

70 Ms/yr, and the total cluster SFR enclosed in a circle of 1 Mpc is 1479

S0 galaxies in the Coma cluster: environmental dependence of the S0 offset from the Tully–Fisher relation

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Star formation in the massive cluster merger Abell 2744

122 Ms/yr/Mpc2. We estimate a dust extinction of about 3 magnitudes by comparing the SFRs derived from [OII] luminosity with the ones computed from the 24um fluxes. We find that the in-falling region (1-3 Mpc) is special: there is a significant decrement (3.5x) of passive relative to star-forming galaxies in this region, and the total SFR of the galaxies located in this region is lower (130 Ms/yr/Mpc2) than anywhere in the cluster or field, regardless of their stellar mass. In a complementary approach we compute the local galaxy density, Sigma5, and find no trend between SFR and Sigma5. However, we measure an excess of star-forming galaxies in the cluster relative to the field by a factor 1.7, that lends support to a reversal of the SF-density relation in CLG0218.

Serendipitous detection of an overdensity of Herschel-SPIRE 250 μm sources south of MRC 1138−26

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 (Jup = 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) × 1011u2009M⊙/μ, and the mean dust mass is (2.0 ± 0.2) × 109u2009M⊙/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′CO–LFIR correlation observed for local luminous and ultraluminous infrared galaxies to higher far-infrared and CO luminosities.

ALMA detection of [C ii] 158 μm emission from a strongly lensed z = 2.013 star-forming galaxy

In the course of our 870 μm APEX/LABOCA follow-up of the Herschel Lensing Survey we have detected a source in AS1063 (RXC J2248.7-4431) that has no counterparts in any of the Herschel PACS/SPIRE bands, it is a Herschel drop-out with S870=S500 ≥ 0:5. The 870 μm emission is extended and centered on the brightest cluster galaxy, suggesting either a multiply imaged background source or substructure in the Sunyaev-Zeldovich increment due to inhomogeneities in the hot cluster gas of this merging cluster. We discuss both interpretations with emphasis on the putative lensed source. Based on the observed properties and on our lens model we find that this source may be the first submillimeter galaxy (SMG) with a moderate far-infrared (FIR) luminosity (LFIR.