The total star formation budget of galaxies consists of the sum of the unobscured star formation, as observed in the rest-frame ultraviolet (UV), together with the obscured component that is absorbed ...and re-radiated by dust grains in the infrared. We explore how the fraction of obscured star formation depends on stellar mass for mass-complete samples of galaxies at . We combine GALEX and WISE photometry for SDSS-selected galaxies with the 3D-HST treasury program and Spitzer/MIPS 24 m photometry in the well-studied five extragalactic Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) fields. We find a strong dependence of the fraction of obscured star formation (fobscured = SFRIR/SFRUV+IR) on stellar mass, with remarkably little evolution in this fraction with redshift out to z = 2.5. 50% of star formation is obscured for galaxies with log(M/M ) = 9.4; although unobscured star formation dominates the budget at lower masses, there exists a tail of low-mass, extremely obscured star-forming galaxies at . For log(M/M ) > 10.5, >90% of star formation is obscured at all redshifts. We also show that at fixed total SFR, is lower at higher redshift. At fixed mass, high-redshift galaxies are observed to have more compact sizes and much higher star formation rates, gas fractions, and hence surface densities (implying higher dust obscuration), yet we observe no redshift evolution in with stellar mass. This poses a challenge to theoretical models, where the observed compact sizes at high redshift seem in tension with lower dust obscuration.
We examine the effects of pre-processing across the Coma Supercluster, including 3505 galaxies over ∼500 deg2, by quantifying the degree to which star-forming (SF) activity is quenched as a function ...of environment. We characterize environment using the complementary techniques of Voronoi Tessellation, to measure the density field, and the Minimal Spanning Tree, to define continuous structures, and so we measure SF activity as a function of local density and the type of environment (cluster, group, filament, and void), and quantify the degree to which environment contributes to quenching of SF activity. Our sample covers over two orders of magnitude in stellar mass (108.5-1011 M), and consequently, we trace the effects of environment on SF activity for dwarf and massive galaxies, distinguishing so-called mass quenching from environment quenching. Environmentally driven quenching of SF activity, measured relative to the void galaxies, occurs to progressively greater degrees in filaments, groups, and clusters, and this trend holds for dwarf and massive galaxies alike. A similar trend is found using g − r colours, but with a more significant disparity between galaxy mass bins driven by increased internal dust extinction in massive galaxies. The SFR distributions of massive SF galaxies have no significant environmental dependence, but the distributions for dwarf SF galaxies are found to be statistically distinct in most environments. Pre-processing plays a significant role at low redshift, as environmentally driven galaxy evolution affects nearly half of the galaxies in the group environment, and a significant fraction of the galaxies in the more diffuse filaments. Our study underscores the need for sensitivity to dwarf galaxies to separate mass-driven from environmentally driven effects, and the use of unbiased tracers of SF activity.
In a hierarchical Universe clusters grow via the accretion of galaxies from the field, groups and even other clusters. As this happens, galaxies can lose and/or consume their gas reservoirs via ...different mechanisms, eventually quenching their star formation. We explore the diverse environmental histories of galaxies through a multiwavelength study of the combined effect of ram-pressure stripping and group ‘processing’ in Abell 963, a massive growing cluster at z = 0.2 from the Blind Ultra Deep H i Environmental Survey (BUDHIES). We incorporate hundreds of new optical redshifts (giving a total of 566 cluster members), as well as Subaru and XMM–Newton data from LoCuSS, to identify substructures and evaluate galaxy morphology, star formation activity, and H i content (via H i deficiencies and stacking) out to 3 × R
200. We find that Abell 963 is being fed by at least seven groups, that contribute to the large number of passive galaxies outside the cluster core. More massive groups have a higher fraction of passive and H i-poor galaxies, while low-mass groups host younger (often interacting) galaxies. For cluster galaxies not associated with groups we corroborate our previous finding that H i gas (if any) is significantly stripped via ram-pressure during their first passage through the intracluster medium, and find mild evidence for a starburst associated with this event. In addition, we find an overabundance of morphologically peculiar and/or star-forming galaxies near the cluster core. We speculate that these arise from the effect of groups passing through the cluster (post-processing). Our study highlights the importance of environmental quenching and the complexity added by evolving environments.
ABSTRACT We present a detailed, multi-wavelength study of star formation (SF) and active galactic nucleus (AGN) activity in 11 near-infrared (IR) selected, spectroscopically confirmed massive ( 1014 ...M ) galaxy clusters at 1 < z < 1.75. Using new deep Herschel/PACS imaging, we characterize the optical to far-IR spectral energy distributions (SEDs) for IR-luminous cluster galaxies, finding that they can, on average, be well described by field galaxy templates. Identification and decomposition of AGNs through SED fittings allows us to include the contribution to cluster SF from AGN host galaxies. We quantify the star-forming fraction, dust-obscured SF rates (SFRs) and specific SFRs for cluster galaxies as a function of cluster-centric radius and redshift. In good agreement with previous studies, we find that SF in cluster galaxies at z 1.4 is largely consistent with field galaxies at similar epochs, indicating an era before significant quenching in the cluster cores (r < 0.5 Mpc). This is followed by a transition to lower SF activity as environmental quenching dominates by z ∼ 1. Enhanced SFRs are found in lower mass ( ) cluster galaxies. We find significant variation in SF from cluster to cluster within our uniformly selected sample, indicating that caution should be taken when evaluating individual clusters. We examine AGNs in clusters from z = 0.5-2, finding an excess AGN fraction at z 1, suggesting environmental triggering of AGNs during this epoch. We argue that our results-a transition from field-like to quenched SF, enhanced SF in lower mass galaxies in the cluster cores, and excess AGNs-are consistent with a co-evolution between SF and AGNs in clusters and an increased merger rate in massive halos at high redshift.
We report the detection of CO(2-1) emission coincident with the brightest cluster galaxy (BCG) of the high-redshift galaxy cluster SpARCS1049+56, with the Redshift Search Receiver (RSR) on the Large ...Millimeter Telescope (LMT). We confirm a spectroscopic redshift for the gas of z = 1.7091 0.0004, which is consistent with the systemic redshift of the cluster galaxies of z = 1.709. The line is well fit by a single-component Gaussian with an RSR-resolution-corrected FWHM of 569 63 km s−1. We see no evidence for multiple velocity components in the gas, as might be expected from the multiple image components seen in near-infrared imaging with the Hubble Space Telescope. We measure the integrated flux of the line to be 3.6 0.3 Jy km s−1, and using = 0.8 M (K km s−1 pc2)−1, we estimate a total molecular gas mass of 1.1 0.1 × 1011 M and a MH2/M ∼ 0.4. This is the largest gas reservoir detected in a BCG above z > 1 to date. Given the infrared-estimated star formation rate of 860 130 M yr−1, this corresponds to a gas depletion timescale of ∼0.1 Gyr. We discuss several possible mechanisms for depositing such a large gas reservoir to the cluster center-e.g., a cooling flow, a major galaxy-galaxy merger, or the stripping of gas from several galaxies-but conclude that these LMT data are not sufficient to differentiate between them.
The IRAC mapping of the NMBS-II fields program is an imaging survey at 3.6 and 4.5 m with the Spitzer Infrared Array Camera (IRAC). The observations cover three Canada-France-Hawaii Telescope Legacy ...Survey Deep (CFHTLS-D) fields, including one also imaged by AEGIS, and two MUSYC fields. These are then combined with archival data from all previous programs into deep mosaics. The resulting imaging covers a combined area of about 3 deg2, with at least ∼2 hr integration time for each field. In this work, we present our data reduction techniques and document the resulting coverage maps at 3.6 and 4.5 m. All of the images are W-registered to the reference image, which is either the z-band stack image of the 25% best-seeing images from the CFHTLS-D for CFHTLS-D1, CFHTLS-D3, and CFHTLS-D4, or the K-band images obtained at the Blanco 4-m telescope at CTIO for MUSYC1030 and MUSYC1255. We make all images and coverage maps described here publicly available via the Spitzer Science Center.
An understanding of the mass build-up in galaxies over time necessitates tracing the evolution of cold gas (molecular and atomic) in galaxies. To that end, we have conducted a pilot study called CO ...Observations with the LMT of the Blind Ultra-Deep H I Environment Survey (COOL BUDHIES). We have observed 23 galaxies in and around the two clusters Abell 2192 (z = 0.188) and Abell 963 (z = 0.206), where 12 are cluster members and 11 are slightly in the foreground or background, using about 28 total hours on the Redshift Search Receiver on the Large Millimeter Telescope (LMT) to measure the sub( 12)COJ = 1 ... 0 emission line and obtain molecular gas masses. These new observations provide a unique opportunity to probe both the molecular and atomic components of galaxies as a function of environment beyond the local Universe. For our sample of 23 galaxies, nine have reliable detections (S/N = 3.6) of the super( 12)COline, and another six have marginal detections (2.0 < S/N < 3.6). For the remaining eight targets we can place upper limits on molecular gas masses roughly between 10 super( 9) and 10 super( 10) M... Comparing our results to other studies of molecular gas, we find that our sample is significantly more abundant in molecular gas overall, when compared to the stellar and the atomic gas component, and our median molecular gas fraction lies about 1s above the upper limits of proposed redshift evolution in earlier studies. We discuss possible reasons for this discrepancy, with the most likely conclusion being target selection and Eddington bias. (ProQuest: ... denotes formulae/symbols omitted.)
We directly detect dust emission in an optically detected, multiply imaged galaxy lensed by the Frontier Fields cluster MACSJ0717.5+3745. We detect two images of the same galaxy at 1.1 mm with the ...AzTEC camera on the Large Millimeter Telescope leaving no ambiguity in the counterpart identification. This galaxy, MACS0717_Az9, is at z > 4 and the strong lensing model ( = 7.5) allows us to calculate an intrinsic IR luminosity of 9.7 × 1010 L and an obscured star formation rate of 14.6 4.5 M yr−1. The unobscured star formation rate from the UV is only 4.1 0.3 M yr−1, which means the total star formation rate (18.7 4.5 M yr−1) is dominated (75%-80%) by the obscured component. With an intrinsic stellar mass of only 6.9 × 109 M , MACS0717_Az9 is one of only a handful of z > 4 galaxies at these lower masses that is detected in dust emission. This galaxy lies close to the estimated star formation sequence at this epoch. However, it does not lie on the dust obscuration relation (IRX-β) for local starburst galaxies and is instead consistent with the Small Magellanic Cloud attenuation law. This remarkable lower mass galaxy, showing signs of both low metallicity and high dust content, may challenge our picture of dust production in the early universe.
We present 12CO (J = 1 → 0) observations of a sample of local galaxies (0.04 < z < 0.08) with a large neutral hydrogen reservoir, or ‘H i monsters’. The data were obtained using the redshift search ...receiver on the five college radio astronomy observatory (FCRAO) 14 m telescope. The sample consists of 20 H i-massive galaxies with M
H i
> 3 × 1010 M⊙ from the Arecibo Legacy Fast ALFA (ALFALFA) survey and 8 low surface brightness galaxies (LSBs) with a comparable M
H i
(>1.5 × 1010 M⊙). Our sample selection is purely based on the amount of neutral hydrogen, thereby providing a chance to study how atomic and molecular gas relate to each other in these H i-massive systems. We have detected CO in 15 out of 20 ALFALFA selected galaxies and 4 out of 8 LSBs with molecular gas mass M
H2 of (1–11)× 109 M⊙. Their total cold gas masses of (2–7) × 1010 M⊙ make them some of the most gas-massive galaxies identified to date in the Local Universe. Observed trends associated with H i, H2, and stellar properties of the H i massive galaxies and the field comparison sample are analysed in the context of theoretical models of galaxy cold gas content and evolution, and the importance of total gas content and improved recipes for handling spatially differentiated behaviours of disc and halo gas are identified as potential areas of improvement for the modelling.
On the Clustering of Submillimeter Galaxies Williams, Christina C; Giavalisco, Mauro; Porciani, Cristiano ...
The Astrophysical journal,
06/2011, Letnik:
733, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We measure the angular two-point correlation function of submillimeter galaxies (SMGs) from 1.1 mm imaging of the COSMOS field with the AzTEC camera and ASTE 10 m telescope. These data yield one of ...the largest contiguous samples of SMGs to date, covering an area of 0.72 deg2 down to a 1.26 mJy beam--1 (1 Delta *s) limit, including 189 (328) sources with S/N >=3.5 (3). We can only set upper limits to the correlation length r 0, modeling the correlation function as a power law with pre-assigned slope. Assuming existing redshift distributions, we derive 68.3% confidence level upper limits of r 0 6-8h --1 Mpc at 3.7 mJy and r 0 11-12 h --1 Mpc at 4.2 mJy. Although consistent with most previous estimates, these upper limits imply that the real r 0 is likely smaller. This casts doubts on the robustness of claims that SMGs are characterized by significantly stronger spatial clustering (and thus larger mass) than differently selected galaxies at high redshift. Using Monte Carlo simulations we show that even strongly clustered distributions of galaxies can appear unclustered when sampled with limited sensitivity and coarse angular resolution common to current submillimeter surveys. The simulations, however, also show that unclustered distributions can appear strongly clustered under these circumstances. From the simulations, we predict that at our survey depth, a mapped area of 2 deg2 is needed to reconstruct the correlation function, assuming smaller beam sizes of future surveys (e.g., the Large Millimeter Telescope's 6'' beam size). At present, robust measures of the clustering strength of bright SMGs appear to be below the reach of most observations.
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