We present a new near-infrared survey covering the 2 deg2 COSMOS field conducted using WIRCam at the Canada-France-Hawaii Telescope. By combining our near-infrared data with Subaru B and z images, we ...construct a deep, wide-field optical-infrared catalog. At K s < 23 (AB magnitudes), our survey completeness is greater than 90% and 70% for stars and galaxies, respectively, and contains 143,466 galaxies and 13,254 stars. Using the BzK diagram, we divide our galaxy catalog into quiescent and star-forming galaxy candidates. At z ~ 2, our catalogs contain 3931 quiescent and 25,757 star-forming galaxies representing the largest and most secure sample at these depths and redshifts to date. Our counts of quiescent galaxies turns over at K s ~ 22, an effect that we demonstrate cannot be due to sample incompleteness. Both the number of faint and bright quiescent objects in our catalogs exceed the predictions of a recent semi-analytic model of galaxy formation, indicating potentially the need for further refinements in the amount of merging and active galactic nucleus feedback at z ~ 2 in these models. We measure the angular correlation function for each sample and find that the slope of the field galaxy correlation function flattens to 1.5 by K s ~ 23. At small angular scales, the angular correlation function for passive BzK galaxies is considerably in excess of the clustering of dark matter. We use precise 30-band photometric redshifts to derive the spatial correlation length and the redshift distributions for each object class. At K s < 22, we find r Delta *g/1.8 0 = 7.0 +/- 0.5h -1 Mpc for the passive BzK candidates and 4.7 +/- 0.8 h -1 Mpc for the star-forming BzK galaxies. Our pBzK galaxies have an average photometric redshift of zp ~ 1.4, in approximate agreement with the limited spectroscopic information currently available. The stacked K s image will be made publicly available from IRSA.
We present the results of a search for galaxy dusters in the first 36 XMM-Newton pointings on the Cosmic Evolution Survey (COSMOS) field. We reach a depth for a total cluster flux in the 0.5-2 keV ...band of 3 x 10 super(-15) ergs cm sub(-2) s sub(-1), having one of the widest XMM-Newton contiguous raster surveys, covering an area of 2.1 deg super(2). Cluster candidates are identified through a wavelet detection of extended X-ray emission. Verification of the cluster candidates is done based on a galaxy concentration analysis in redshift slices of thickness 0.1-0.2 in redshift, using the multiband photometric catalog of the COSMOS field and restricting the search to z < 1.3 and i sub(AB) < 25. We identify 72 clusters and derive their properties based on the X-ray cluster scaling relations. A statistical description of the survey in terms of the cumulative log (N > S) - logS distribution compares well with previous results, although yielding a somewhat higher number of clusters at similar fluxes. The X-ray luminosity function of COSMOS clusters matches well the results of nearby surveys, providing a comparably tight constraint on the faint-end slope of alpha = 1.03 plus or minus 0.04. For the probed luminosity range of (8 x 10 super(42))-(2 x 10 super(44)) ergs s sub(-1), our survey is In agreement with and adds significantly to the existing data on the cluster luminosity function at high redshifts and implies no substantial evolution at these luminosities to z = 1.3.
We present photometric redshifts and spectral energy distribution (SED) classifications for a sample of 1542 optically identified sources detected with XMM in the COSMOS field. Our template fitting ...classifies 46 sources as stars and 464 as nonactive galaxies, while the remaining 1032 require templates with an active galactic nucleus (AGN) contribution. High accuracy in the derived photometric redshifts was accomplished as the result of (1) photometry in up to 30 bands with high-significance detections, (2) a new set of SED templates, including 18 hybrids covering the far-UV to mid-infrared, which have been constructed by the combination of AGNs and nonactive galaxies templates, and (3) multiepoch observations that have been used to correct for variability (most important for type 1 AGNs). The reliability of the photometric redshifts is evaluated using the subsample of 442 sources with measured spectroscopic redshifts. We achieved an accuracy of for i* AB < 22.5 ( for i* AB < 24.5). The high accuracies were accomplished for both type 2 (where the SED is often dominated by the host galaxy) and type 1 AGNs and QSOs out to z = 4.5. The number of outliers is a large improvement over previous photometric redshift estimates for X-ray-selected sources (4.0% and 4.8% outliers for i* AB < 22.5 and i* AB < 24.5, respectively). We show that the intermediate band photometry is vital to achieving accurate photometric redshifts for AGNs, whereas the broad SED coverage provided by mid-infrared (Spitzer/IRAC) bands is important to reduce the number of outliers for normal galaxies.
Aims. We exploit deep observations of the GOODS-N field taken with PACS, the Photodetector Array Camera and Spectrometer, onboard of Herschel, as part of the PACS evolutionary probe guaranteed time ...(PEP), to study the link between star formation and stellar mass in galaxies to z ~ 2. Methods. Starting from a stellar mass – selected sample of ~4500 galaxies with mag4.5 µm < 23.0 (AB), we identify ~350 objects with a PACS detection at 100 or 160 ~1500 with only Spitzer 24 μm counterpart. Stellar masses and total IR luminosities (LIR) are estimated by fitting the spectral energy distributions (SEDs). Results. Consistently with other Herschel results, we find that LIR based only on 24 μm data is overestimated by a median factor ~1.8 at z ~ 2, whereas it is underestimated (with our approach) up to a factor ~1.6 at 0.5 < z < 1.0. We then exploit this calibration to correct LIR based on the MIPS/Spitzer fluxes. These results clearly show how Herschel is fundamental to constrain LIR, and hence the star formation rate (SFR), of high redshift galaxies. Using the galaxies detected with PACS (and/or MIPS), we investigate the existence and evolution of the relations between the SFR, the specific star formation rate (SSFR=SFR/mass) and the stellar mass. Moreover, in order to avoid selection effects, we also repeat this study through a stacking analysis on the PACS images to fully exploit the far-IR information also for the Herschel and Spitzer undetected subsamples. We find that the SSFR-mass relation steepens with redshift, being almost flat at z < 1.0 and reaching a slope of α = -0.50+0.13-0.16 at z ~ 2, at odds with recent works based on radio-stacking analysis at the same redshift. The mean SSFR of galaxies increases with redshift, by a factor ~15 for massive M > 1011 $M_{\odot}$ galaxies from z = 0 to z = 2, and seems to flatten at z > 1.5 in this mass range. Moreover, the most massive galaxies have the lowest SSFR at any z, implying that they have formed their stars earlier and more rapidly than their low mass counterparts (downsizing).
Models of galaxy evolution assume some connection between the AGN and star formation activity in galaxies. We use the multi-wavelength information of the CDFS to assess this issue. We select the AGNs ...from the 3 Ms XMM-Newton survey and measure the star-formation rates of their hosts using data that probe rest-frame wavelengths longward of 20 μm, predominantly from deep 100 μm and 160 μm Herschel observations, but also from Spitzer-MIPS-70 μm. Star-formation rates are obtained from spectral energy distribution fits, identifying and subtracting an AGN component. Our sample consists of sources in the z ≈ 0.5−4 redshift range, with star-formation rates SFR ≈ 101−103 M⊙ yr-1 and stellar masses M⋆ ≈ 1010−1011.5 M⊙. We divide the star-formation rates by the stellar masses of the hosts to derive specific star-formation rates (sSFR) and find evidence for a positive correlation between the AGN activity (proxied by the X-ray luminosity) and the sSFR for themost active systems with X-ray luminosities exceeding Lx ≃ 1043 erg s-1 and redshifts z ≳ 1. We do not find evidence for such a correlation for lower luminosity systems or those at lower redshifts, consistent with previous studies. We do not find any correlation between the SFR (or the sSFR) and the X-ray absorption derived from high-quality XMM-Newton spectra either, showing that the absorption is likely to be linked to the nuclear region rather than the host, while the star-formation is not nuclear. Comparing the sSFR of the hosts to the characteristic sSFR of star-forming galaxies at the same redshift (the so-called “main sequence”) we find that the AGNs reside mostly in main-sequence and starburst hosts, reflecting the AGN-sSFR connection; however the infrared selection might bias this result. Limiting our analysis to the highest X-ray luminosity AGNs (X-ray QSOs with Lx > 1044 erg s-1), we find that the highest-redshift QSOs (with z ≳ 2) reside predominantly in starburst hosts, with an average sSFR more than double that of the “main sequence”, and we find a few cases of QSOs at z ≈ 1.5 with specific star-formation rates compatible with the main-sequence, or even in the “quiescent” region. Finally, we test the reliability of the colour–magnitude diagram (plotting the rest-frame optical colours against the stellar mass) in assessing host properties, and find a significant correlation between rest-frame colour (without any correction for AGN contribution or dust extinction) and sSFR excess relative to the “main sequence” at a given redshift. This means that the most “starbursty” objects have the bluest rest-frame colours.
Context. Dust attenuation curves in external galaxies are useful for studying their dust properties as well as interpreting their intrinsic spectral energy distributions. These functions are not very ...well known in the UV range whether at low or high redshift. In particular, the presence or absence of a UV bump at 2175 Å remains an open issue that has consequences on the interpretation of broad band colours of galaxies involving the UV range. Aims. We want to study the dust attenuation curve in the UV range at z > 1 where the UV is redshifted into the visible and with Herschel data to constrain dust emission and a global dust attenuation. In particular, we search for a UV bump and related implications for dust attenuation determinations. Methods. We use deep photometric data of the Chandra Deep Field South obtained with intermediate and broad band filters by the MUSYC project to sample the UV rest frame of galaxies with 1 < z < 2. Herschel/PACS and Spitzer/MIPS data are used to measure the dust emission. We select 30 galaxies with high S/N in all bands. Their SEDs from the UV to the far-IR are fitted using the CIGALE code and the characteristics of the dust attenuation curves obtained as Bayesian outputs of the SED fitting process. Results. The mean dust attenuation curve we derive exhibits a significant UV bump at 2175 Å whose amplitude corresponds to 35% (76%) that of the Milky Way (Large Magellanic Cloud: LMC2 supershell) extinction curve. An analytical expression of the average attenuation curve (A(λ)/AV) is given and found to be slightly steeper than the Calzetti et al. one, although at a 1σ level. Our galaxy sample is used to study the derivation of the slopes of the UV continuum from broad band colours, including the rest frame GALEX FUV − NUV colour. Systematic errors induced by the presence of the bump are quantified. We compare dust attenuation factors measured with CIGALE to the slope of the UV continuum and find that there is a large scatter around the relation valid for local starbursts (~0.7 mag). The uncertainties on the determination of the UV slope lead to an extra systematic error in a range of 0.3 to 0.7 mag on dust attenuation when a filter overlaps the UV bump.
We present deep optical imaging observations of 2 square degree area, covered by the Cosmic Evolution Survey (COSMOS), made by the prime-focus camera (Supreme-Cam) on the 8.2 m Subaru Telescope. ...Observations were done in six broadband B (4459.7 AA), g' (4723.1 AA), V (5483.8 AA), r' (6213.0 AA), i' (7640.8 AA), z' (8855.0 AA) and one narrowband (NB 816) filters. A total of 10 super(6) galaxies were detected to r' similar to 26.5 mag. These data, combined with observations at u* and K-band are used to construct the photometric catalogs for the COSMOS, to measure their photometric redshifts, multiband spectral energy distributions, and stellar masses, and to identify high-redshift candidates. This catalog provides multi-wave band data for scientific analysis of the COSMOS survey.
Context. In the past decade, sensitive, resolved Sunyaev-Zel’dovich (SZ) studies of galaxy clusters have become common. Whereas many previous SZ studies have parameterized the pressure profiles of ...galaxy clusters, non-parametric reconstructions will provide insights into the thermodynamic state of the intracluster medium. Aim. We seek to recover the non-parametric pressure profiles of the high redshift (z = 0.89) galaxy cluster CLJ 1226.9+3332 as inferred from SZ data from the MUSTANG, NIKA, Bolocam, and Planck instruments, which all probe different angular scales. Methods. Our non-parametric algorithm makes use of logarithmic interpolation, which under the assumption of ellipsoidal symmetry is analytically integrable. For MUSTANG, NIKA, and Bolocam we derive a non-parametric pressure profile independently and find good agreement among the instruments. In particular, we find that the non-parametric profiles are consistent with a fitted generalized Navaro-Frenk-White (gNFW) profile. Given the ability of Planck to constrain the total signal, we include a prior on the integrated Compton Y parameter as determined by Planck. Results. For a given instrument, constraints on the pressure profile diminish rapidly beyond the field of view. The overlap in spatial scales probed by these four datasets is therefore critical in checking for consistency between instruments. By using multiple instruments, our analysis of CLJ 1226.9+3332 covers a large radial range, from the central regions to the cluster outskirts: 0.05 R500 < r < 1.1 R500. This is a wider range of spatial scales than is typically recovered by SZ instruments. Similar analyses will be possible with the new generation of SZ instruments such as NIKA2 and MUSTANG2.
Deep extragalactic surveys with ISOCAM revealed the presence of a large density of faint mid-infrared (MIR) sources. We have computed the 15 μm integrated galaxy light produced by these galaxies ...above a sensitivity limit of 50 μJy. It sets a lower limit to the 15 μm extragalactic background light of ($2.4 \pm 0.5$) nW m-2 sr-1. The redshift distribution of the ISOCAM galaxies is inferred from the spectroscopically complete sample of galaxies in the Hubble Deep Field North (HDFN). It peaks around $z\sim$ 0.8 in agreement with studies in other fields. The rest-frame 15 μm and bolometric infrared (8–1000 μm) luminosities of ISOCAM galaxies are computed using the correlations that we establish between the 6.75, 12, 15 μm and infrared (IR) luminosities of local galaxies. The resulting IR luminosities were double-checked using radio (1.4 GHz) flux densities from the ultra-deep VLA and WSRT surveys of the HDFN on a sample of 24 galaxies as well as on a sample of 109 local galaxies in common between ISOCAM and the NRAO VLA Sky Survey (NVSS). This comparison shows for the first time that MIR and radio luminosities correlate up to $z\sim$ 1. This result validates the bolometric IR luminosities derived from MIR luminosities unless both the radio-far infrared (FIR) and the MIR-FIR correlations become invalid around $z\sim$ 1. The fraction of IR light produced by active nuclei was computed from the cross-correlation with the deepest X-ray surveys from the Chandra and XMM-Newton observatories in the HDFN and Lockman Hole respectively. We find that at most 20% of the 15 μm integrated galaxy light is due to active galactic nuclei (AGNs) unless a large population of AGNs was missed by Chandra and XMM-Newton. About 75% of the ISOCAM galaxies are found to belong to the class of luminous infrared galaxies (LIR ≥ 1011 $L_{\odot}$). They exhibit star formation rates of the order of ~100 $M_{\odot}$ yr-1. The comoving density of infrared light due to these luminous IR galaxies was more than 40 times larger at $z\sim1$ than today. The contribution of ISOCAM galaxies to the peak of the cosmic infrared background (CIRB) at 140 μm was computed from the MIR-FIR correlations for star forming galaxies and from the spectral energy distribution of the Seyfert 2, NGC 1068, for AGNs. We find that the galaxies unveiled by ISOCAM surveys are responsible for the bulk of the CIRB, i.e. ($16 \pm 5$) nW m-2 sr-1 as compared to the (25 ± 7) nW m-2 sr-1 measured with the COBE satellite, with less than 10% due to AGNs. Since the CIRB contains most of the light radiated over the history of star formation in the universe, this means that a large fraction of present-day stars must have formed during a dusty starburst event similar to those revealed by ISOCAM.
We report the spectroscopic confirmation of a submillimeter galaxy (SMG) at s = 4.547 with an estimated L sub(IR) = (0.5-2.0) x 10 super(13) L. The spectra, mid-IR, and X-ray properties indicate the ...bolometric luminosity is dominated by star formation at a rate of >1000 M Yr super(-1). Multiple, spatially separated components are visible in the Lya line with an observed velocity difference of up to 380 km s super(-1) and the object morphology indicates a merger. The best-fit spectral energy distribution and spectral line indicators suggest the object is 2-8 Myr old and contains >10 super(10) M of stellar mass. This object is a likely progenitor for the massive early-type systems seen at z similar to 2.
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