ABSTRACT
The infrared (IR) spectral energy distributions (SEDs) of main-sequence galaxies in the early Universe (z > 4) is currently unconstrained as IR continuum observations are time-consuming and ...not feasible for large samples. We present Atacama Large Millimetre Array Band 8 observations of four main-sequence galaxies at z ∼ 5.5 to study their IR SED shape in detail. Our continuum data (rest-frame 110 $\rm \mu m$, close to the peak of IR emission) allows us to constrain luminosity-weighted dust temperatures and total IR luminosities. With data at longer wavelengths, we measure for the first time the emissivity index at these redshifts to provide more robust estimates of molecular gas masses based on dust continuum. The Band 8 observations of three out of four galaxies can only be reconciled with optically thin emission redward of rest-frame $100\, {\rm \mu m}$. The derived dust peak temperatures at z ∼ 5.5 ($30\!-\!43\, {\rm K}$) are elevated compared to average local galaxies, however, $\sim 10\, {\rm K}$ below what would be predicted from an extrapolation of the trend at z < 4. This behaviour can be explained by decreasing dust abundance (or density) towards high redshifts, which would cause the IR SED at the peak to be more optically thin, making hot dust more visible to the external observer. From the $850{\hbox{-}}{\rm \mu m}$ dust continuum, we derive molecular gas masses between 1010 and $10^{11}\, {\rm M_{\odot }}$ and gas fractions (gas over total mass) of $30\!-\!80{{\ \rm per\ cent}}$ (gas depletion times of $100\!-\!220\, {\rm Myr}$). All in all, our results provide a first measured benchmark SED to interpret future millimetre observations of normal, main-sequence galaxies in the early Universe.
We investigate Ly , O iii λ5007, H , and C ii 158 m emission from 1124 galaxies at z = 4.9-7.0. Our sample is composed of 1092 Ly emitters (LAEs) at z = 4.9, 5.7, 6.6, and 7.0 identified by ...Subaru/Hyper-Suprime-Cam (HSC) narrowband surveys covered by Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH) and 34 galaxies at z = 5.148-7.508 with deep ALMA C ii 158 m data in the literature. Fluxes of strong rest-frame optical lines of O iii and H (Hβ) are constrained by significant excesses found in the SPLASH 3.6 and 4.5 m photometry. At z = 4.9, we find that the rest-frame H equivalent width and the Ly escape fraction fLy positively correlate with the rest-frame Ly equivalent width . The correlation is similarly found at z ∼ 0-2, suggesting no evolution of the correlation over z 0-5. The typical ionizing photon production efficiency of LAEs is log( ion/Hz erg−1) 25.5, significantly (60%-100%) higher than those of LBGs at a given UV magnitude. At z = 5.7-7.0, there exists an interesting turnover trend that the O iii/H flux ratio increases in and then decreases out to . We also identify an anticorrelation between a ratio of C ii luminosity to star formation rate (LC ii/SFR) and at the >99% confidence level.. We carefully investigate physical origins of the correlations with stellar-synthesis and photoionization models and find that a simple anticorrelation between and metallicity explains self-consistently all of the correlations of Ly , H , O iii/H , and C ii identified in our study, indicating detections of metal-poor (∼0.03 Z ) galaxies with .
ABSTRACT We investigate morphological properties of 61 Ly emitters (LAEs) at z = 4.86 identified in the COSMOS field, based on Hubble Space Telescope Advanced Camera for Surveys (ACS) imaging data in ...the F814W band. Out of the 61 LAEs, we find the ACS counterparts for 54 LAEs. Eight LAEs show double-component structures with a mean projected separation of 0 63 (∼4.0 kpc at z = 4.86). Considering the faintness of these ACS sources, we carefully evaluate their morphological properties, that is, size and ellipticity. While some of them are compact and indistinguishable from the point-spread function (PSF) half-light radius of 0 07 (∼0.45 kpc), the others are clearly larger than the PSF size and spatially extended up to 0 3 (∼1.9 kpc). We find that the ACS sources show a positive correlation between ellipticity and size and that the ACS sources with large size and round shape are absent. Our Monte Carlo simulation suggests that the correlation can be explained by (1) the deformation effects via PSF broadening and shot noise or (2) the source blending in which two or more sources with small separation are blended in our ACS image and detected as a single elongated source. Therefore, the 46 single-component LAEs could contain the sources that consist of double (or multiple) components with small spatial separation (i.e., 0 3 or 1.9 kpc). Further observation with high angular resolution at longer wavelengths (e.g., rest-frame wavelengths of 4000 Å) is inevitable to decipher which interpretation is adequate for our LAE sample.
THE IMPOSSIBLY EARLY GALAXY PROBLEM Steinhardt, Charles. L.; Capak, Peter; Masters, Dan ...
Astrophysical journal/The Astrophysical journal,
06/2016, Letnik:
824, Številka:
1
Journal Article
Recenzirano
Odprti dostop
ABSTRACT The current hierarchical merging paradigm and ΛCDM predict that the universe should be a time in which the most massive galaxies are transitioning from their initial halo assembly to the ...later baryonic evolution seen in star-forming galaxies and quasars. However, no evidence of this transition has been found in many high-redshift galaxy surveys including CFHTLS, Cosmic Assembly Near-infrared Deep Extragalactic Survey (CANDELS), and Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH), which were the first studies to probe the high-mass end at these redshifts. Indeed, if halo mass to stellar mass ratios estimated at lower-redshift continue to , CANDELS and SPLASH report several orders of magnitude more halos than is possible to have been formed by those redshifts, implying that these massive galaxies formed impossibly early. We consider various systematics in the stellar synthesis models used to estimate physical parameters and possible galaxy formation scenarios in an effort to reconcile observation with theory. Although known uncertainties can greatly reduce the disparity between recent observations and cold dark matter merger simulations, there remains considerable tension with current theory even if taking the most conservative view of the observations.
Imaging of NGC 5907's stellar stream Laine, Seppo; Grillmair, Carl J.; Martínez–Delgado, David ...
Proceedings of the International Astronomical Union,
08/2015, Letnik:
11, Številka:
S317
Journal Article
Recenzirano
Odprti dostop
We have obtained deep g, r, and i-band Subaru and ultra-deep 3.6 μm IRAC images of parts of the multiply-wrapped stellar stream around the nearby edge-on galaxy NGC 5907. We have fitted the surface ...brightness measurements of the stream with FSPS stellar population synthesis models to derive the metallicity and age of the brightest parts of the stream. The resulting relatively high metallicity (Fe/H = −0.3) is consistent with a major merger scenario but a satellite accretion event cannot be ruled out.
We report interferometric imaging of CII ( super(2)P sub(3/2) arrow right super(2)P sub(1/2)) and OH ( super(2)Pi sub(1/2) J = 3/2 arrow right 1/2) emission toward the center of the galaxy ...protocluster associated with the z = 5.3 submillimeter galaxy (SMG) AzTEC-3, using the Atacama Large (sub) Millimeter Array (ALMA). We detect strong CII, OH, and rest-frame 157.7 mu m continuum emission toward the SMG. The CII( super(2)P sub(3/2) arrow right super(2)P sub(1/2)) emission is distributed over a scale of 3.9 kpc, implying a dynamical mass of 9.7 x 10 super(10)M sub(middot in circle), and a star formation rate (SFR) surface density of capital sigma sub(SFR) = 530 M sub(middot in circle) yr super(-1) kpc super(-2). This suggests that AzTEC-3 forms stars at capital sigma sub(SFR) approaching the Eddington limit for radiation pressure supported disks. We find that the OH emission is slightly blueshifted relative to the CII line, which may indicate a molecular outflow associated with the peak phase of the starburst. We also detect and dynamically resolve CII ( super(2)P sub(3/2) arrow right super(2)P sub(1/2)) emission over a scale of 7.5 kpc toward a triplet of Lyman-break galaxies with moderate UV-based SFRs in the protocluster at ~95 kpc projected distance from the SMG. These galaxies are not detected in the continuum, suggesting far-infrared SFRs of <18- 54 M sub(middot in circle) yr super(-1), consistent with a UV-based estimate of 22 M sub(middot in circle) yr super(-1). The spectral energy distribution of these galaxies is inconsistent with nearby spiral and starburst galaxies, but resembles those of dwarf galaxies. This is consistent with expectations for young starbursts without significant older stellar populations. This suggests that these galaxies are significantly metal-enriched, but not heavily dust-obscured, "normal" star-forming galaxies at z > 5, showing that ALMA can detect the interstellar medium in "typical" galaxies in the very early universe.
With a primary goal of conducting precision weak-lensing measurements from space, the COSMOS survey has imaged the largest contiguous area observed by Hubble Space Telescope to date, using the ...Advanced Camera for Surveys (ACS). This is the first paper in a series in which we describe our strategy for addressing the various technical challenges in the production of weak-lensing measurements from COSMOS data. We first construct a source catalog from 575 ACS/WFC tiles (1.64 deg super(2)) subsampled at a pixel scale of 0.03". Defects and diffraction spikes are carefully removed, leaving a total of 1.2 x 10 super(6) objects to a limiting magnitude of F814W = 26.5. This catalog is made publicly available. Multiwavelength follow-up observations of the COSMOS field provide photometric redshifts for 73% of the source galaxies in the lensing catalog. We analyze and discuss the COSMOS redshift distribution and show broad agreement with other surveys to z similar to 1. Our next step is to measure the shapes of galaxies and correct them for the distortion induced by the time-varying ACS point-spread function and for charge transfer efficiency (CTE) effects. Simulated images are used to derive the shear susceptibility factors that are necessary in transforming shape measurements into unbiased shear estimators. For every galaxy we derive a shape measurement error and utilize this quantity to extract the intrinsic shape noise of the galaxy sample. Interestingly, our results indicate that intrinsic shape noise varies little with size, magnitude, or redshift. Representing a number density of 66 galaxies per arcmin super(2), the final COSMOS weak-lensing catalog contains 3.9 x 10 super(5) galaxies with accurate shape measurements. The properties of the COSMOS weak-lensing catalog described throughout this paper will provide key input numbers for the preparation and design of next-generation wide field space missions.
We present the Zurich Extragalactic Bayesian Redshift Analyzer (zebra). The current version of zebra combines and extends several of the classical approaches to produce accurate photometric redshifts ...down to faint magnitudes. In particular, zebra uses the template-fitting approach to produce Maximum Likelihood and Bayesian redshift estimates based on the following points.
An automatic iterative technique to correct the original set of galaxy templates to best represent the Spectral Energy Distributions (SEDs) of real galaxies at different redshifts.
A training set of spectroscopic redshifts for a small fraction of the photometric sample to improve the robustness of the photometric redshift estimates.
An iterative technique for Bayesian redshift estimates, which extracts the full two-dimensional redshift and template probability function for each galaxy.
We demonstrate the performance of zebra by applying it to a sample of 866 I
AB
≤ 22.5 COSMOS galaxies with available u*, B, V, g′, r′, i′, z′ and K
s
photometry and zCOSMOS spectroscopic redshifts in the range 0 < z < 1.3. Adopting a 5σ clipping that excludes ≤10 galaxies, both the Maximum Likelihood and Bayesian zebra estimates for this sample have an accuracy σΔz/(1+z) smaller than 0.03. Similar accuracies are recovered using mock galaxies.
zebra is made available at http://www.exp-astro.phys.ethz.ch/ZEBRA.
Understanding the mechanisms that lead dense environments to host galaxies with redder colors, more spheroidal morphologies, and lower star formation rates than field populations remains an important ...problem. As most candidate processes ultimately depend on host halo mass, accurate characterizations of the local environment, ideally tied to halo mass estimates and spanning a range in halo mass and redshift, are needed. In this work, we present and test a rigorous, probabilistic method for assigning galaxies to groups based on precise photometric redshifts and X-ray-selected groups drawn from the COSMOS field. The groups have masses in the range 1013 M 200c/M 1014 and span redshifts 0 < z < 1. We characterize our selection algorithm via tests on spectroscopic subsamples, including new data obtained at the Very Large Telescope, and by applying our method to detailed mock catalogs. We find that our group member galaxy sample has a purity of 84% and completeness of 92% within . We measure the impact of uncertainties in redshifts and group centering on the quality of the member selection with simulations based on current data as well as future imaging and spectroscopic surveys. As a first application of our new group member catalog which will be made publicly available, we show that member galaxies exhibit a higher quenched fraction compared to the field at fixed stellar mass out to z ~ 1, indicating a significant relationship between star formation and environment at group scales. We also address the suggestion that dusty star-forming galaxies in such groups may impact the high-l power spectrum of the cosmic microwave background and find that such a population cannot explain the low power seen in recent Sunyaev-Zel'dovich measurements.
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.
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