The rest-frame ultraviolet properties of galaxies during the first three billion years of cosmic time (redshift z > 4) indicate a rapid evolution in the dust obscuration of such galaxies. This ...evolution implies a change in the average properties of the interstellar medium, but the measurements are systematically uncertain owing to untested assumptions and the inability to detect heavily obscured regions of the galaxies. Previous attempts to measure the interstellar medium directly in normal galaxies at these redshifts have failed for a number of reasons, with two notable exceptions. Here we report measurements of the forbidden C ii emission (that is, C II) from gas, and the far-infrared emission from dust, in nine typical star-forming galaxies about one billion years after the Big Bang (z ≈ 5-6). We find that these galaxies have thermal emission that is less than 1/12 that of similar systems about two billion years later, and enhanced C II emission relative to the far-infrared continuum, confirming a strong evolution in the properties of the interstellar medium in the early Universe. The gas is distributed over scales of one to eight kiloparsecs, and shows diverse dynamics within the sample. These results are consistent with early galaxies having significantly less dust than typical galaxies seen at z < 3 and being comparable in dust content to local low-metallicity systems.
ABSTRACT The observed evolution of the gas fraction and its associated depletion time in main-sequence (MS) galaxies provides insights on how star formation proceeds over cosmic time. We report ALMA ...detections of the rest-frame ∼300 m continuum observed at 240 GHz for 45 massive ( ), normal star-forming ( ), i.e., MS, galaxies at in the COSMOS field. From an empirical calibration between cold neutral, i.e., molecular and atomic, gas mass and monochromatic (rest-frame) infrared luminosity, the gas mass for this sample is derived. Combined with stellar mass and star formation rate (SFR) estimates (from MagPhys fits) we obtain a median gas fraction of and a median gas depletion time correction for the location on the MS will only slightly change the values. The reported uncertainties are the error on the median. Our results are fully consistent with the expected flattening of the redshift evolution from the 2-SFM (2 star formation mode) framework which empirically prescribes the evolution assuming a universal, log-linear relation between SFR and gas mass coupled to the redshift evolution of the specific star formation rate (sSFR) of MS galaxies. While shows only a mild dependence on location within the MS, a clear trend of increasing across the MS is observed (as known from previous studies). Further, we comment on trends within the MS and (in)consistencies with other studies.
The Cosmic Evolution Survey (COSMOS) is designed to probe the correlated evolution of galaxies, star formation, active galactic nuclei (AGNs), and dark matter (DM) with large-scale structure (LSS) ...over the redshift range z > 0.5-6. The survey includes multiwavelength imaging and spectroscopy from X-ray-to-radio wavelengths covering a 2 deg super(2) area, including HST imaging. Given the very high sensitivity and resolution of these data sets, COSMOS also provides unprecedented samples of objects at high redshift with greatly reduced cosmic variance, compared to earlier surveys. Here we provide a brief overview of the survey strategy, the characteristics of the major COSMOS data sets, and a summary the science goals.
We present imaging data and photometry for the COSMOS survey in 15 photometric bands between 0.3 and 2.4 mu m. These include data taken on the Subaru 8.3 m telescope, the KPNO and CTIO 4 m ...telescopes, and the CFHT 3.6 m telescope. Special techniques are used to ensure that the relative photometric calibration is better than 1% across the field of view. The absolute photometric accuracy from standard-star measurements is found to be 6%. The absolute calibration is corrected using galaxy spectra, providing colors accurate to 2% or better. Stellar and galaxy colors and counts agree well with the expected values. Finally, as the first step in the scientific analysis of these data we construct panchromatic number counts which confirm that both the geometry of the universe and the galaxy population are evolving.
COSMOS: Hubble Space Telescope Observations Scoville, N; Abraham, R. G; Aussel, H ...
The Astrophysical journal. Supplement series,
09/2007, Letnik:
172, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The Cosmic Evolution Survey (COSMOS) was Initiated with an extensive allocation (590 orbits in Cycles 12-13) using the Hubble Space Telescope (HST) for high-resolution imaging. Here we review the ...characteristics of the HST imaging with the Advanced Camera for Surveys (ACS) and parallel observations with NICMOS and WFPC2. A square field (1.8 deg super(2)) has been imaged with single-orbit ACS I-band F814W exposures with 50% completeness for sources 0.5" in diameter at I sub(AB) = 26.0 mag. The ACS is a key part of the COSMOS survey, providing very high sensitivity and high-resolution (0.09" FWHM and 0.05" pixels) imaging and detecting a million objects. These images yield resolved morphologies for several hundred thousand galaxies. The small HST PSF also provides greatly enhanced sensitivity for weak-lensing investigations of the dark matter distribution.
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.
Photometric Redshifts of Galaxies in COSMOS Mobasher, B; Capak, P; Scoville, N. Z ...
The Astrophysical journal. Supplement series,
09/2007, Letnik:
172, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present photometric redshifts for the COSMOS survey derived from a new code, optimized to yield accurate and reliable redshifts and spectral types of galaxies down to faint magnitudes and ...redshifts out to z similar to 1.2. The technique uses X super(2) template fitting, combined with luminosity function priors and with the option to estimate the Internal extinction or E(B - V). The median most probable redshift, best-fit spectral type and reddening, absolute magnitude, and stellar mass are derived in addition to the full redshift probability distributions. Using simulations with sampling and noise similar to those in COSMOS, the accuracy and reliability is estimated for the photometric redshifts as a function of the magnitude limits of the sample, S/N ratios, and the number of bands used. We find from the simulations that the ratio of derived 95% confidence interval in the X super(2) probability distribution to the estimated photometric redshift (D95) can be used to identify and exclude the catastrophic failures In the photometric redshift estimates. To evaluate the reliability of the photometric redshifts, we compare the derived redshifts with high-reliability spectroscopic redshifts for a sample of 868 normal galaxies with z < 1.2 from zCOSMOS. Considering different scenarios, depending on using prior, no prior, and/or extinction, we compare the photometric and spectroscopic redshifts for this sample. The rms scatter between the estimated photometric redshifts and known spectroscopic redshifts is sigma ( Delta (z)) = 0.031, where Delta (z) = (z sub(pbot) -- z sub(apot))/(1 + z unk) with a small fraction of outliers (<2.5%) outliers are defined as objects with A(z) > 3 sigma ( Delta (z)), where sigma ( Delta (z)) is the rms scatter in Delta (z). We also find good agreement sigma Delta (z)) = 0.10 between photometric and spectroscopic redshifts for type II AGNs. We compare results from our photometric redshift procedure with three other independent codes and find them in excellent agreement. We show preliminary results, based on photometric redshifts for the entire COSMOS sample (to i < 25 mag).
Context. Counting clusters is one of the methods to constrain cosmological parameters, but has been limited up to now both by the redshift range and by the relatively small sizes of the homogeneously ...surveyed areas. Aims. In order to enlarge publicly available optical cluster catalogs, in particular at high redshift, we have performed a systematic search for clusters of galaxies in the Canada France Hawaii Telescope Legacy Survey (CFHTLS). Methods. We considered the deep 2, 3 and 4 CFHTLS Deep fields (each 1 $\times$ 1 deg2), as well as the wide 1, 3 and 4 CFHTLS Wide fields. We used the Le Phare photometric redshifts for the galaxies detected in these fields with magnitude limits of i'=25 and 23 for the Deep and Wide fields respectively. We then constructed galaxy density maps in photometric redshift bins of 0.1 based on an adaptive kernel technique and detected structures with SExtractor at various detection levels. In order to assess the validity of our cluster detection rates, we applied a similar procedure to galaxies in Millennium simulations. We measured the correlation function of our cluster candidates. We analyzed large scale properties and substructures, including filaments, by applying a minimal spanning tree algorithm both to our data and to the Millennium simulations. Results. We detected 1200 candidate clusters with various masses (minimal masses between 1.0 $\times$ 1013 and 5.5 $\times$ 1013 and mean masses between 1.3 $\times$ 1014 and 12.6 $\times$ 10$^{14}~M_\odot$) in the CFHTLS Deep and Wide fields, thus notably increasing the number of known high redshift cluster candidates. We found a correlation function for these objects comparable to that obtained for high redshift cluster surveys. We also show that the CFHTLS deep survey is able to trace the large scale structure of the universe up to $z \geq 1$. Our detections are fully consistent with those made in various CFHTLS analyses with other methods. We now need accurate mass determinations of these structures to constrain cosmological parameters. Conclusions. We have shown that a search for galaxy clusters based on density maps built from galaxy catalogs in photometric redshift bins is successful and gives results comparable to or better than those obtained with other methods. By applying this technique to the CFHTLS survey we have increased the number of known optical high redshift cluster candidates by a large factor, an important step towards using cluster counts to measure cosmological parameters.
Context. XMM and Chandra opened a new area for the study of clusters of galaxies not only for cluster physics, but also for the detection of faint and distant clusters that were inaccessible with ...previous missions. Aims. This article presents 66 spectroscopically confirmed clusters (0.05 ≤ z ≤ 1.5) within an area of 6 deg2 enclosed in the XMM-LSS survey. Almost two thirds have been confirmed with dedicated spectroscopy only and 10% have been confirmed with dedicated spectroscopy supplemented by literature redshifts. Methods. Sub-samples, or classes, of extended-sources are defined in a two-dimensional X-ray parameter space allowing for various degrees of completeness and contamination. We describe the procedure developed to assess the reality of these cluster candidates using the CFHTLS photometric data and spectroscopic information from our own follow-up campaigns. Results. Most of these objects are low-mass clusters, hence constituting a still poorly studied population. In a second step, we quantify the correlations between the optical properties such as richness or velocity dispersion and the cluster X-ray luminosities. We examine the relation of the clusters to the cosmic web. Finally, we review peculiar compact structures in the surveyed area such as very distant clusters and fossil groups.
PDF
