We present the results of a ∼60-h multiband observational campaign with the Atacama Large Millimeter Array targeting a spectroscopically confirmed and lensed sub-
L
⋆
galaxy at
z
= 6.07, first ...identified during the ALMA Lensing Cluster Survey (ALCS). We sampled the dust continuum emission from rest frame 90–370 μm at six different frequencies and set constraining upper limits on the molecular gas line emission and content by targeting the CO (7 − 6) and C
I
(
3
P
2
−
3
P
1
) transitions in two lensed images with
μ
≳ 20. Complementing these submillimeter observations with deep optical and near-IR photometry and spectroscopy with JWST, we find this galaxy to form stars at a rate of SFR ∼ 7
M
⊙
yr
−1
, ∼50 − 70% of which is obscured by dust. This is consistent with what one would predict for a
M
⋆
∼ 7.5 × 10
8
M
⊙
object by extrapolating the relation between the fraction of the obscured star formation rate and stellar mass at
z
< 2.5 and with observations of IR-detected objects at 5 <
z
< 7. The light-weighted dust temperature of
T
dust
∼ 50 K is similar to that of more massive galaxies at similar redshifts, although with large uncertainties and with possible negative gradients. We measure a dust mass of
M
dust
∼ 1.5 × 10
6
M
⊙
and, by combining C
I
, C
II
, and a dynamical estimate, a gas mass of
M
gas
∼ 2 × 10
9
M
⊙
. Their ratio (
δ
DGR
) is in good agreement with predictions from models and empirical relations in the literature. The dust-to-stellar mass fraction of
f
dust
∼ 0.002 and the young stellar age (100 − 200 Myr) are consistent with efficient dust production via supernovae, as predicted by existing models and simulations of dust evolution. Also, the expected number density of galaxies with
M
dust
∼ 10
6
M
⊙
at
z
= 6 from a subset of these models is in agreement with the observational estimate that we set from the parent ALCS survey. The combination of gravitational lensing and deep multiwavelength observations allowed us to probe luminosity and mass regimes up to two orders of magnitude lower than what has been explored so far for field galaxies at similar redshifts. Our results serve as a benchmark for future observational endeavors of the high-redshift and faint sub-
L
⋆
galaxy population that might have driven the reionization of the Universe.
We present the results of a search for galaxy clusters in the Subaru–XMM Deep Field (SXDF). We reach a depth for a total cluster flux in the 0.5–2 keV band of 2 × 10−15 erg cm−2 s−1 over one of the ...widest XMM–Newton contiguous raster surveys, covering an area of 1.3 deg2. Cluster candidates are identified through a wavelet detection of extended X-ray emission. The red-sequence technique allows us to identify 57 cluster candidates. We report on the progress with the cluster spectroscopic follow-up and derive their properties based on the X-ray luminosity and cluster scaling relations. In addition, three sources are identified as X-ray counterparts of radio lobes, and in three further sources, an X-ray counterpart of the radio lobes provides a significant fraction of the total flux of the source. In the area covered by near-infrared data, our identification success rate achieves 86 per cent. We detect a number of radio galaxies within our groups, and for a luminosity-limited sample of radio galaxies we compute halo occupation statistics using a marked cluster mass function. We compare the cluster detection statistics in the SXDF with that in the literature and provide the modelling using the concordance cosmology combined with current knowledge of the X-ray cluster properties. The joint cluster log(N) − log(S) is overpredicted by the model, and an agreement can be achieved through a reduction of the concordance σ8 value by 5 per cent. Having considered the dn/dz and the X-ray luminosity function of clusters, we conclude that to pin down the origin of disagreement a much wider (50 deg2) survey is needed.
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.
Context. Multi-wavelength, optical to IR/submm observations of strongly lensed galaxies identified by the Herschel Lensing Survey are used to determine the physical properties of high-redshift ...star-forming galaxies close to or below the detection limits of blank fields. Aims. We aim to constrain theIR stellar and dust content, and to determine star formation rates and histories, dust attenuation and extinction laws, and other related properties. Methods. We studied a sample of seven galaxies with spectroscopic redshifts z ~ 1.5−3 that have been detected with precision thanks to gravitational lensing, and whose spectral energy distribution (SED) has been determined from the rest-frame UV to the IR/mm domain. For comparison, our sample includes two previously well-studied lensed galaxies, MS1512-cB58 and the Cosmic Eye, for which we also provide updated Herschel measurements. We performed SED fits of the full photometry of each object, and of the optical and infrared parts separately, exploring various star formation histories, using different extinction laws, and exploring the effects of nebular emission. The IR luminosity, in particular, is predicted consistently from the stellar population model. The IR observations and emission line measurements, where available, are used as a posteriori constraints on the models. We also explored energy conserving models, that we created by using the observed IR/UV ratio to estimate the extinction. Results. Among the models we have tested, models with exponentially declining star-forming histories including nebular emission and assuming the Calzetti attenuation law best fit most of the observables. Models assuming constant or rising star formation histories predict in most cases too much IR luminosity. The SMC extinction law underpredicts the IR luminosity in most cases, except for two out of seven galaxies, where we cannot distinguish between different extinction laws. Our sample has a median lensing-corrected IR luminosity ~3 × 1011L⊙, stellar masses between 2 × 109M⊙ and 2 × 1011M⊙, and IR/UV luminosity ratios spanning a wide range. The dust masses of our galaxies are in the range 2−17 × 107M⊙, extending previous studies at the same redshift down to lower masses. We do not find any particular trend of the dust temperature Tdust with LIR, suggesting an overall warmer dust regime at our redshift regardless of IR luminosity. Conclusions. Gravitational lensing enables us to study the detailed physical properties of individual IR-detected z ~ 1.5−3 galaxies up to a factor of ~10 fainter than achieved with deep blank field observations. We have in particular demonstrated that multi-wavelength observations combining stellar and dust emission can constrain star formation histories and extinction laws of star-forming galaxies, as proposed in an earlier paper. Fixing the extinction based on the IR/UV observations successfully breaks the age-extinction degeneracy often encountered in obscured galaxies.
During our Herschel Lensing Survey (HLS) of massive galaxy clusters, we have discovered an exceptionally bright source behind the z = 0.22 cluster Abell 773, which appears to be a strongly lensed ...submillimeter galaxy (SMG) at z = 5.2429. This source is unusual compared to most other lensed sources discovered by Herschel so far, because of its higher submm flux (~200 mJy at 500 μm) and its high redshift. The dominant lens is a foreground z = 0.63 galaxy, not the cluster itself. The source has a far-infrared (FIR) luminosity of LFIR = 1.1 × 1014/μ L , where μ is the magnification factor, likely ~11. We report here the redshift identification through CO lines with the IRAM-30 m, and the analysis of the gas excitation, based on CO(7-6), CO(6-5), CO(5-4) detected at IRAM and the CO(2-1) at the EVLA. All lines decompose into a wide and strong red component, and a narrower and weaker blue component, 540 km s-1 apart. Assuming the ultraluminous galaxy (ULIRG) CO-to-H2 conversion ratio, the H2 mass is 5.8 × 1011/μ M , of which one third is in a cool component. From the C I(3P2-3P1) line we derive a C I/H2 number abundance of 6 × 10-5 similar to that in other ULIRGs. The H2Op(2,0,2-1,1,1) line is strong only in the red velocity component, with an intensity ratio I(H2O)/I(CO) ~ 0.5, suggesting a strong local FIR radiation field, possibly from an active nucleus (AGN) component. We detect the NII205 μm line for the first time at high-z. It shows comparable blue and red components, with a strikingly broad blue one, suggesting strong ionized gas flows.
Aims. We present in this letter the first analysis of a z ~ 8 galaxy candidate found in the Hubble and Spitzer imaging data of Abell 2744 as part of the Hubble Frontier Fields legacy program. ...Methods. We applied the most commonly used methods to select exceptionally high-redshift galaxies by combining non-detection and color criteria using seven HST bands. We used GALFIT on IRAC images to fit and subtract contamination of bright nearby sources.The physical properties were inferred from spectral energy distribution-fitting using templates with and without nebular emission. Results. This letter is focused on the brightest candidate we found (mF160W = 26.2) over the 4.9 arcmin2 field of view covered by the WFC3. It is not detected in the ACS bands and at 3.6 μm, while it is clearly detected at 4.5 μm with rather similar depths. This break in the IRAC data might be explained by strong OIII+Hβ lines at z ~ 8 that contribute to the 4.5 μm photometry. The best photo-z is found at z ~ 8.0+0.2-0.5, although solutions at low-redshift (z ~ 1.9) cannot be completely excluded , but they are strongly disfavored by the SED-fitting. The amplification factor is relatively small at μ = 1.49 ± 0.02. The star formation rate in this object ranges from 8 to 60 M⊙ yr-1, the stellar mass is on the order of M⋆ = (2.5−10) × 109 M⊙, and the size is r ≈ 0.35 ± 0.15 kpc. Conclusions. This object is one of the first z ~ 8 Lyman break galaxy candidates showing a clear break between 3.6 μm and 4.5 μm, which is consistent with the IRAC properties of the first spectroscopically confirmed galaxy at a similar redshift. Due to its brightness, the redshift of this object could potentially be confirmed by near-infrared spectroscopy with current 8−10 m telescopes. The nature of this candidate will be revealed in the coming months with the arrival of new ACS and Spitzer data, increasing the depth at optical and near-infrared wavelengths.
We investigate the nature of a sample of 92 Spitzer MIPS 24 km-selected galaxies in the CDF-S, showing power-law-like emission in the Spitzer IRAC 3.6-8 km bands. The main goal is to determine ...whether the galaxies not detected in X-rays (47% of the sample) are part of the hypothetical population of obscured AGNs not detected even in deep X-ray surveys. The majority of the IR power-law galaxies are ULIRGs at z > 1, and those with LIRG-like IR luminosities are usually detected in X-rays. The optical-to-IR SEDs of the X-ray-detected galaxies are almost equally divided between a BLAGN SED class (similar to an optically selected QSO) and an NLAGN SED (similar to the BLAGN SED but with an obscured UV/optical continuum). A small fraction of SEDs resemble warm ULIRGs (e.g., Mrk 231). Most galaxies not detected in X-rays have SEDs in the NLAGN+ULIRG class as they tend to be optically fainter and possibly more obscured. Moreover, the IR power-law galaxies have SEDs significantly different from those of high-z (z sub(sp) > 1) IR (24 km) selected and optically bright (VVDS I sub(AB) , 24) star-forming galaxies whose SEDs show a very prominent stellar bump at 1.6 km. The galaxies detected in X-rays have 2-8 keV rest-frame luminosities typical of AGNs. The galaxies not detected in X-rays have global X-ray-to-mid-IR SED properties that make them good candidates to contain IR-bright X-ray-absorbed AGNs. If all these sources are actually obscured AGNs, we would observe a ratio of obscured to unobscured 24 km-detected AGNs of 2:1, whereas models predict a ratio of up to 3:1. Additional studies using Spitzer to detect X-ray-quiet AGNs are likely to find more such obscured sources.
Abstract
The Astronomical Thermal Emission Camera (AzTEC) 1.1 mm survey of the two SCUBA HAlf Degree Extragalactic Survey (SHADES) fields is the largest (0.7 deg2) blank-field millimetre-wavelength ...(mm-wavelength) survey undertaken to date at a resolution of ≃18 arcsec and a depth of ≃1 mJy. We have used the deep optical to radio multiwavelength data in the SHADES Lockman Hole East and SXDF/UDS fields to obtain galaxy identifications for ≃64 per cent (≃80 per cent including tentative identifications) of the 148 AzTEC-SHADES 1.1 mm sources reported by Austermann et al., exploiting deep radio and 24 μm data complemented by methods based on 8 μm flux density and red optical-infrared (i − K) colour. This unusually high identification rate can be attributed to the relatively bright mm-wavelength flux density threshold, combined with the relatively deep supporting multifrequency data now available in these two well-studied fields. We have further exploited the optical-mid-infrared-radio data to derive an ≃60 per cent (≃75 per cent including tentative identifications) complete redshift distribution for the AzTEC-SHADES sources, yielding a median redshift of z ≃ 2.2, with a high-redshift tail extending to at least z ≃ 4. Despite the larger area probed by the AzTEC survey relative to the original SCUBA-SHADES imaging, the redshift distribution of the AzTEC sources is consistent with that displayed by the SCUBA sources, and reinforces tentative evidence that the redshift distribution of mm/submm sources in the Lockman Hole field is significantly different from that found in the SXDF/UDS field. Comparison with simulated surveys of similar scale extracted from semi-analytic models based on the Millennium simulation indicates that this is as expected if the mm/submm sources are massive (M > 1011 M⊙) star-forming galaxies tracing large-scale structures over scales of 10-20 Mpc. This confirms the importance of surveys covering several deg2 (as now underway with SCUBA2) to obtain representative samples of bright (sub)mm-selected galaxies. This work provides a foundation for the further exploitation of the Spitzer and Herschel data in the SHADES fields in the study of the stellar masses and specific star formation rates of the most active star-forming galaxies in cosmic history.
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 a search for the C II 158 {mu}m fine structure line (a main cooling line of the interstellar medium) and the underlying far-infrared (FIR) continuum in three high-redshift (6.6 < z < 8.2) ...star-forming galaxies using the IRAM Plateau de Bure Interferometer. We targeted two Ly{alpha}-selected galaxies (Ly{alpha} emitters, LAEs) with moderate UV-based star formation rates (SFRs {approx} 20 M{sub Sun} yr{sup -1}; Himiko at z = 6.6 and IOK-1 at z = 7.0) and a gamma-ray burst (GRB) host galaxy (GRB 090423 at z {approx} 8.2). Based on our 3{sigma} rest-frame FIR continuum limits, previous (rest-frame) UV continuum measurements and spectral energy distribution (SED) fitting, we rule out SED shapes similar to highly obscured galaxies (e.g., Arp 220, M 82) and less extreme dust-rich nearby spiral galaxies (e.g., M 51) for the LAEs. Conservatively assuming an SED shape typical of local spiral galaxies we derive upper limits for the FIR-based star formation rates (SFRs) of {approx}70 M{sub Sun} yr{sup -1}, {approx}50 M{sub Sun} yr{sup -1}, and {approx}40 M{sub Sun} yr{sup -1} for Himiko, IOK-1, and GRB 090423, respectively. For the LAEs these limits are only a factor {approx}3 higher than the published UV-based SFRs (uncorrected for extinction). This indicates that the dust obscuration in the z > 6 LAEs studied here is lower by a factor of a few than what has recently been found in some LAEs at lower redshift (2 < z < 3.5) with similar UV-based SFRs. A low obscuration in our z > 6 LAE sample is consistent with recent rest-frame UV studies of z {approx} 7 Lyman break galaxies.
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