In order to examine the far-infrared (far-IR)/radio correlation at high redshift, we have studied the Spitzer70 μm/far-IR properties of sub-mJy radio sources from the 13HXMM–Newton/Chandra Deep Field ...by redshift and galaxy type: active galactic nucleus (AGN) or star-forming galaxy (SFG). We directly detect 70 μm counterparts (at >3σ significance) for 22.5 per cent (92/408) of the radio sources, while for the rest we perform stacking analysis by redshift and galaxy type. For the sources detected at 70 μm, we find that the median and scatter of the observed flux density ratio, q70, are similar to previous results in the literature, but with a slight decrease in q70 towards higher redshifts. Of the radio sources detected at 70 μm 8/92 were already classified as AGN, but two of which maybe SFGs. For the stacked sources, we obtain a detection for the SFGs at every redshift bin which implies they have mean flux densities a factor ∼5 below the original 70 μm detection limit. For the stacked AGN, we obtain a detection only in our highest redshift bin (1 ≤z≤ 5) where we may be sampling hot dust associated with the AGN at rest frame 12−35 μm. The combined observed mean value of q70 for the SFGs (detected and non-detected at 70 μm) decreases gradually with redshift, consistent with tracks derived from empirical spectral energy distributions (SEDs) of local SFGs. Upon closer inspection and when comparing with tracks of appropriate luminosity, the values of q70 broadly agree at low redshift. However, at z∼ 1, the observed q70for ultraluminous infrared galaxies (ULIRGs) is 2 σ below the value seen for local ULIRGs tracks, implying a difference in the SED between local and z∼ 1 ULIRGs. At higher redshifts, the convergence of the tracks and the higher uncertainties in q70 do not allow us to determine if such a difference persists.
Using Herschel Photodetector Array Camera (PACS) and Spectral and Photometric Imaging Receiver (SPIRE) observations of Lockman Hole-North and Great Observatories Origins Deep Survey-North (GOODS-N) ...as part of the Herschel Multi-tiered Extragalactic Survey (HerMES) project, we explore the far-infrared (IR) properties of a sample of mid-IR-selected starburst-dominated ultraluminous infrared galaxies (ULIRGs) at z∼ 2. The selection of the sample is based on the detection of the stellar bump that appears in the spectral energy distribution of star-forming galaxies at 1.6 μm. We derive robust estimates of infrared luminosities (LIR) and dust temperatures (Td) of the population and find that while the luminosities in our sample span less than an order of magnitude (12.24 ≤ log(LIR/L⊙) ≤ 12.94), they cover a wide range of dust temperatures (25 ≤Td≤ 62 K). Galaxies in our sample range from those that are as cold as high-z submillimetre galaxies (SMGs) to those that are as warm as optically faint radio galaxies (OFRGs) and local ULIRGs. Nevertheless, our sample has median Td= 42.3 K, filling the gap between SMGs and OFRGs, bridging the two populations. We demonstrate that a significant fraction of our sample would be missed from ground-based (sub)mm surveys (850–1200 μm), showing that the latter introduce a bias towards the detection of colder sources. We conclude that Herschel observations confirm the existence of high-z ULIRGs warmer than SMGs, show that the mid-IR selection of high-z ULIRGs is not Td dependent, reveal a large dispersion in Td of high-z ULIRGs and provide the means to characterize the bulk of the ULIRG population, free from selection biases introduced by ground-based (sub)mm surveys.
We have assembled a sample of five X-ray-absorbed and submm-luminous type 1 QSOs at z ∼ 2 which are simultaneously growing their central black holes through accretion and forming stars copiously. We ...present here the analysis of their rest-frame UV-to-submm spectral energy distributions (SEDs), including new Herschel data. Both AGN (direct and reprocessed) and star formation (SF) emission are needed to model their SEDs. From the SEDs and their UV–optical spectra we have estimated the masses of their black holes M
BH ∼ 109–1010 M⊙, their intrinsic AGN bolometric luminosities L
BOL ∼ (0.8–20) × 1013 L⊙, Eddington ratios L
BOL/L
Edd ∼ 0.1–1.1 and bolometric corrections
$L_{\rm BOL}/L_{\rm X,2{\rm -}10}\sim 30{-}500$
. These values are common among optically and X-ray-selected type 1 QSOs (except for RX J1249), except for the bolometric corrections, which are higher. These objects show very high far-infrared luminosities L
FIR ∼ (2–8) × 1012 M⊙ and star formation rates SFR ∼1000 M⊙ yr−1. From their L
FIR and the shape of their FIR–submm emission we have estimated star-forming dust masses of M
DUST ∼ 109 M⊙. We have found evidence of a tentative correlation between the gas column densities of the ionized absorbers detected in X-ray (
$N_{\rm H_{ion}}$
) and SFR. Our computed black hole masses are amongst the most massive known.
We report the detection of CO(J = 5 -> 4), CO(J = 3 -> 2), and CO(J = 1 -> 0) emission in the strongly lensed, Herschel/SPIRE-selected submillimeter galaxy (SMG) HERMES J105751.1+573027 at z = 2.9574 ...? 0.0001, using the Plateau de Bure Interferometer, the Combined Array for Research in Millimeter-wave Astronomy, and the Green Bank Telescope. The observations spatially resolve the molecular gas into four lensed images with a maximum separation of ~9'' and reveal the internal gas dynamics in this system. We derive lensing-corrected CO line luminosities of L'CO(1-0) = (4.17 ? 0.41), L'CO(3-2) = (3.96 ? 0.20), and L'CO(5-4) = (3.45 ? 0.20) X 1010 ( Delta *mL/10.9)--1 K km s--1 pc2, corresponding to luminosity ratios of r 31 = 0.95 ? 0.10, r 53 = 0.87 ? 0.06, and r 51 = 0.83 ? 0.09. This suggests a total molecular gas mass of M gas = 3.3X1010 ( Delta *aCO/0.8) ( Delta *mL/10.9)--1 M . The gas mass, gas mass fraction, gas depletion timescale, star formation efficiency, and specific star formation rate are typical for an SMG. The velocity structure of the gas reservoir suggests that the brightest two lensed images are dynamically resolved projections of the same dust-obscured region in the galaxy that are kinematically offset from the unresolved fainter images. The resolved kinematics appear consistent with the complex velocity structure observed in major, 'wet' (i.e., gas-rich) mergers. Major mergers are commonly observed in SMGs and are likely to be responsible for fueling their intense starbursts at high gas consumption rates. This study demonstrates the level of detail to which galaxies in the early universe can be studied by utilizing the increase in effective spatial resolution and sensitivity provided by gravitational lensing.
We separate the extragalactic radio source population above ∼50 μJy into active galactic nuclei (AGN) and star-forming sources. The primary method of our approach is to fit the infrared spectral ...energy distributions (SEDs), constructed using Spitzer/IRAC (Infrared Array Camera) and Multiband Imaging Photometer for Spitzer (MIPS) and Herschel/SPIRE photometry, of 380 radio sources in the Extended Chandra Deep Field-South. From the fitted SEDs, we determine the relative AGN and star-forming contributions to their infrared emission. With the inclusion of other AGN diagnostics such as X-ray luminosity, Spitzer/IRAC colours, radio spectral index and the ratio of star-forming total infrared flux to k-corrected 1.4 GHz flux density, q
IR, we determine whether the radio emission in these sources is powered by star formation or by an AGN. The majority of these radio sources (60 per cent) show the signature of an AGN at some wavelength. Of the sources with AGN signatures, 58 per cent are hybrid systems for which the radio emission is being powered by star formation. This implies that radio sources which have likely been selected on their star formation have a high AGN fraction. Below a 1.4 GHz flux density of 1 mJy, along with finding a strong contribution to the source counts from pure star-forming sources, we find that hybrid sources constitute 20–65 per cent of the sources. This result suggests that hybrid sources have a significant contribution, along with sources that do not host a detectable AGN, to the observed flattening of the source counts at ∼1 mJy for the extragalactic radio source population.
We present the first study of the far-infrared (FIR) properties of high-redshift, radio-selected ultraluminous infrared galaxies (ULIRGs) using deep observations obtained with the Spectral and ...Photometric Imaging Receiver (SPIRE) from the Herschel Multi-tiered Extragalactic Survey (HerMES). These galaxies span a large range of 850-μm fluxes from submillimetre-luminous ∼10 mJy sources (SCUBA galaxies) to ∼1.5 mJy from stacked SCUBA non-detections, thus likely representing a complete distribution of ULIRG spectral energy distributions (SEDs). From Keck spectroscopic surveys in the Lockman-North field we identified a sample of 31 submillimetre galaxies (SMGs) and 37 submillimetre-faint, optically faint radio galaxies (OFRGs), all with radio-inferred IR luminosities >1012 L⊙. These galaxies were cross-identified with SPIRE 250-, 350- and 500-μm catalogues based on fluxes extracted at 24-μm positions in the SWIRE survey, yielding a sample of more than half of the galaxies well detected in at least two of the SPIRE bandpasses. By fitting greybody dust models to the SPIRE photometry together with SCUBA 850-μm measurements (for OFRGs, only 850- upper limits), we infer dust temperatures and FIR luminosities. The OFRGs detected by SPIRE have median 〈Td〉= 41 ± 5 K and the SMGs have 〈Td〉= 34 ± 5 K, both in reasonable agreement with previous (pre-Herschel) estimates, reaffirming that the local FIR/radio correlation holds (at least for this subset of high-z ULIRGs) at high redshift (we measure 〈qIR〉= 2.43 ± 0.21 using SIR derived from greybody fit coupled with a power-law extrapolation to the 24 μm). Our observations first confirm that a substantial fraction of OFRGs exhibits large infrared luminosities corresponding to SFRs of ∼400 M⊙ yr−1. The SPIRE observations secondly confirm the higher dust temperatures for these OFRGs than similarly selected SMGs, consistent with early predictions of the submillimetre-faint radio populations. Our observations also clearly confirm the large infrared luminosities of most SMGs selected with S850 μm > 5 mJy and radio and strong 24-μm detections, corresponding to SFRs of ∼700 M⊙ yr−1.
Abstract
We investigate the properties (e.g. star formation rate, dust attenuation, stellar mass and metallicity) of a sample of infrared (IR) luminous galaxies at z ∼ 1 via near-IR spectroscopy with ...Subaru-FMOS. Our sample consists of Herschel SPIRE and Spitzer MIPS selected sources in the COSMOS field with photometric redshifts in the range of 0.7 < z
phot < 1.8, which have been targeted in two pointings (0.5 deg2) with FMOS. We find a modest success rate for emission-line detections, with candidate Hα emission lines detected for 57 of 168 SPIRE sources (34 per cent). By stacking the near-IR spectra we directly measure the mean Balmer decrement for the Hα and Hβ lines, finding a value of 〈E(B − V)〉 = 0.51 ± 0.27 for 〈L
IR〉 = 1012 L⊙ sources at 〈z〉 = 1.36. By comparing star formation rates estimated from the IR and from the dust-uncorrected Hα line we find a strong relationship between dust attenuation and star formation rate. This relation is broadly consistent with that previously seen in star-forming galaxies at z ∼ 0.1. Finally, we investigate the metallicity via the N2 ratio, finding that z ∼ 1 IR-selected sources are indistinguishable from the local mass-metallicity relation. We also find a strong correlation between dust attenuation and metallicity, with the most metal-rich IR sources experiencing the largest levels of dust attenuation.
We present strong empirical evidence for a physical connection between the occurrence of a starburst (SB) and a luminous active galactic nucleus (AGN) phase. Drawing infrared (IR), X-ray and ...optically selected samples from COSMOS, we find that the locus of type II AGN hosts in the optical colour-magnitude (U − V/V) and colour-colour (U − V/V − J) space significantly overlaps with that of IR-luminous (L
IR > 1010 L) galaxies. Based on our observations, we propose that, when simultaneously building their black hole and stellar masses, type II AGN hosts are located in the same part of colour-colour space as dusty star-forming galaxies. In fact, our results show that IR-luminous galaxies at z < 1.5 are on average three times more likely to host a type II AGN (L
X > 1042 erg s−1) than would be expected serendipitously, if AGN and star-formation events were unrelated. In addition, the optical and IR properties of the AGN/SB hybrid systems tentatively suggest that the AGN phase might be coeval with a particularly active phase in a galaxy's star-formation history. Interestingly, we also find a significant fraction of type II AGN hosts offset from the dusty galaxy sequence in colour-colour space, possibly representing a transitional or post-SB phase in galaxy evolution. Our findings are consistent with a scenario whereby AGN play a role in the termination of star formation in massive galaxies.
We report on the redshift measurement and CO line excitation of HERMES J105751.1+573027 (HLSW-01), a strongly lensed submillimeter galaxy discovered in Herschel/SPIRE observations as part of the ...Herschel Multi-tiered Extragalactic Survey (HerMES). HLSW-01 is an ultra-luminous galaxy with an intrinsic far-infrared luminosity of L FIR = 1.4 X 1013 L , and is lensed by a massive group of galaxies into at least four images with a total magnification of Delta *m = 10.9 ? 0.7. With the 100 GHz instantaneous bandwidth of the Z-Spec instrument on the Caltech Submillimeter Observatory, we robustly identify a redshift of z = 2.958 ? 0.007 for this source, using the simultaneous detection of four CO emission lines (J = 7 -> 6, J = 8 -> 7, J = 9 -> 8, and J = 10 -> 9). Combining the measured line fluxes for these high-J transitions with the J = 1 -> 0, J = 3 -> 2, and J = 5 -> 4 line fluxes measured with the Green Bank Telescope, the Combined Array for Research in Millimeter Astronomy, and the Plateau de Bure Interferometer, respectively, we model the physical properties of the molecular gas in this galaxy. We find that the full CO spectral line energy distribution is described well by warm, moderate-density gas with T kin = 86-235 K and cm--3. However, it is possible that the highest-J transitions are tracing a small fraction of very dense gas in molecular cloud cores, and two-component models that include a warm/dense molecular gas phase with T kin ~ 200 K, cm--3 are also consistent with these data. Higher signal-to-noise measurements of the J up >= 7 transitions with high spectral resolution, combined with high spatial resolution CO maps, are needed to improve our understanding of the gas excitation, morphology, and dynamics of this interesting high-redshift galaxy.
Dust-obscured galaxies (DOGs) are an ultraviolet-faint, infrared-bright galaxy population that reside at z ~ 2 and are believed to be in a phase of dusty star-forming and active galactic nucleus ...(AGN) activity. We present far-infrared (far-IR) observations of a complete sample of DOGs in the 2 deg super(2) of the Cosmic Evolution Survey. The 3077 DOGs have left angle bracketzright angle bracket= 1.9 + or - 0.3 and are selected from 24 mu m and r super(+) observations using a color cut of r super(+) - 24 > or =, slanted 7.5 (AB mag) and S sub(24) > or =, slanted 100 mu Jy. Based on the near-IR spectral energy distributions, 47% are bump DOGs (star formation dominated) and 10% are power-law DOGs (AGN-dominated). We use SPIRE far-IR photometry from the Herschel Multi-tiered Extragalactic Survey to calculate the IR luminosity and characteristic dust temperature for the 1572 (51%) DOGs that are detected at 250 mu m (> or =, slanted3sigma). For the remaining 1505 (49%) that are undetected, we perform a median stacking analysis to probe fainter luminosities. Herschel-detected and undetected DOGs have average luminosities of (2.8 + or - 0.4) x 10 super(12) L sub(middot in circle) and (0.77 + or - 0.08) x 10 super(12) L sub(middot in circle), and dust temperatures of (33 + or - 7) K and (37 + or - 5) K, respectively. The IR luminosity function for DOGs with S sub(24) > or =, slanted 100 mu Jy is calculated, using far-IR observations and stacking. DOGs contribute 10%-30% to the total star formation rate (SFR) density of the universe at z = 1.5-2.5, dominated by 250 mu m detected and bump DOGs. For comparison, DOGs contribute 30% to the SFR density for all z = 1.5-2.5 galaxies with S sub(24) > or =, slanted 100 mu Jy. DOGs have a large scatter about the star formation main sequence and their specific SFRs show that the observed phase of star formation could be responsible for their total observed stellar mass at z ~ 2.
PDF
