A MULTIWAVELENGTH STUDY OF A SAMPLE OF 70 mu m SELECTED GALAXIES IN THE COSMOS FIELD. I. SPECTRAL ENERGY DISTRIBUTIONS AND LUMINOSITIES

2010
Article

Résumé

We present a large robust sample of 1503 reliable and unconfused 70 mu m selected sources from the multiwavelength data set of the Cosmic Evolution Survey. Using the Spitzer IRAC and MIPS photometry, we estimate the total infrared (IR) luminosity, L-IR (8-1000 mu m), by finding the best-fit template from several different template libraries. The long-wavelength 70 and 160 mu m data allow us to obtain a reliable estimate of L-IR, accurate to within 0.2 and 0.05 dex, respectively. The 70 mu m data point enables a significant improvement over the luminosity estimates possible with only a 24 mu m detection. The full sample spans a wide range in IR luminosity, L-IR approximate to 10(8)-10(14) L-circle dot, with a median luminosity of 10(11.4) L-circle dot. We identify a total of 687 luminous, 303 ultraluminous, and 31 hyperluminous infrared galaxies (LIRGs, ULIRGs, and HyLIRGs) over the redshift range 0.01 < z < 3.5 with a median redshift of 0.5. Presented here are the full spectral energy distributions (SEDs) for each of the sources compiled from the extensive multiwavelength data set from the ultraviolet (UV) to the far-infrared. A catalog of the general properties of the sample (including the photometry, redshifts, and L-IR) is included with this paper. We find that the overall shape of the SED and trends with L-IR (e.g., IR color temperatures and optical-IR ratios) are similar to what has been seen in studies of local objects; however, our large sample allows us to see the extreme spread in UV to near-infrared colors spanning nearly 3 orders of magnitude. In addition, using SED fits we find possible evidence for a subset of cooler ultraluminous objects than observed locally. However, until direct observations at longer wavelengths are obtained, the peak of emission and the dust temperature cannot be well constrained. We use these SEDs, along with the deep radio and X-ray coverage of the field, to identify a large sample of candidate active galactic nuclei (AGNs). We find that the fraction of AGNs increases strongly with L-IR, as it does in the local universe, and that nearly 70% of ULIRGs and all HyLIRGs likely host a powerful AGN.

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2010
Article

Résumé

Official source

https://infoscience.epfl.ch/record/172908?ln=fr

À propos de ce résultat

Concepts associés (18)

Concepts associés

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Publications associées (35)

Publications associées

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Theory predicts that galaxies are not randomly distributed in the Universe. They form a complex network of filamentary structures, the Cosmic Web, divided in clusters, groups, filaments and walls. This picture has been confirmed by the large galaxy redshift surveys. Galaxy properties like morphology and star formation rates are strongly influenced by their environment. The most radical transformations are observed in galaxy clusters, located at the intersection of filaments. Nevertheless, the location where the environment starts to play a role and the main physical phenomenon responsible for these changes are still unknown. The aim of this thesis is to determine where and how galaxies are affected by the environment, at local and global scales. We gathered high quality photometry in the 5 optical bands

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with MegaCam on the Canada-France-Hawaii Telescope for 3 medium mass galaxy clusters at intermediate redshift, with a spatial extent on the sky plane reaching 8 to 13 times the cluster virial radii. These clusters were selected to represent as much as possible progenitors of clusters in the local Universe. The core of these clusters have rich ancillary data from the ESO Distant Cluster Survey. The redshift and mass ranges of these clusters, combined to the wide field of the observations make this study unique. We computed photometric redshifts to map the galaxy distribution around the clusters. We were able to identify overdense regions forming groups and filaments, unveiling for the first time the large scale structures in such details for this type of clusters. We studied the fraction of galaxies in the red sequence in different environments, namely in the field, filaments and groups. We find that significant quenching processes are already at work in filaments, even at large cluster-centric distances. We also show that the local neighborhood of galaxies has a stronger impact on galaxy colors than the global environment. An optical spectroscopic follow-up with the VIsible MultiObject Spectrograph on the Very Large Telescope confirms our photometric results. In particular, the fraction of galaxies with detected \otwo emission line is smaller with increasing density. We also find that the star formation rate, determined from [OII], is in average weaker in groups and clusters than in lower density environments. This thesis opens new perspectives to study the way galaxies populate the Cosmic Web. Combined to weak-lensing analysis and cosmological simulations, it will allow a deeper understanding of the structure formation and their baryonic content. It is a first step before extending the results to much larger samples, with the help of the upcoming all-sky cosmological surveys such as Euclid or the Square Kilometer Array.

EPFL2015

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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 10(13) less than or similar to M-200c/M-circle dot less than or similar to 10(14) 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 0.5 R-200c. 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 similar to 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.

2011

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Context. Though Ly alpha emission is one of the most used tracers of massive star formation at high redshift, it is strongly affected by neutral gas radiation transfer effects. A correct understanding of these effects is required to properly quantify the star formation rate along the history of the Universe. Aims. We aim to parameterize the escape of Ly alpha photons as a function of the galaxy properties, in order to properly calibrate the Ly alpha luminosity as a tracer of star formation intensity at any age of the Universe. Methods. We have embarked on a program to study the properties of the Ly alpha emission (spectral profile, spatial distribution, relation to Balmer lines intensity,...) in a number of starburst galaxies in the Local Universe. The study is based on Hubble Space Telescope spectroscopic and imaging observations at various wavelengths, X-ray data, and ground-based spectroscopy, complemented with the use of evolutionary population synthesis models. Results. We present here the results obtained for one of those sources, IRAS 08339+6517, a strong Ly alpha emitter in the Local Universe, which is undergoing an intense episode of massive star formation. We have characterized the properties of the starburst, which transformed 1.4 x 10(8) M-circle dot of gas into stars around 5-6 Myr ago. The mechanical energy released by the central super stellar cluster (SSC), located in the core of the starburst, has created a cavity devoid of gas and dust around it, leaving a clean path through which the UV continuum of the SSC is observed, with almost no extinction. While the average extinction affecting the stellar continuum is significantly larger out of the cavity, with E(B - V) = 0.15 on average, we have not found any evidence for regions with very large extinctions, which could be hiding some young, massive stars not contributing to the global UV continuum. The observed soft and hard X-ray emissions are consistent with this scenario, being originated by the interstellar medium heated by the release of mechanical energy in the first case, and by a large number of active high-mass X-ray binaries (HMXBs) in the second. In addition to the central compact emission blob, we have identified a diffuse Ly alpha emission component smoothly distributed over the whole central area of IRAS 08339+6517. This diffuse emission is spatially decoupled from the UV continuum, the H alpha emission, or the H alpha/H beta ratio. Both locally and globally, the Ly alpha/H alpha ratio is lower than the Case B predictions, even after reddening correction, with an overall Ly alpha escape fraction of only 4%. Conclusions. We conclude that in IRAS 08339+6517 the Ly alpha photons resonantly scattered by an outflowing shell of neutral gas are being smoothly redistributed over the whole central area of the galaxy. Their increased probability of being destroyed by dust would explain the low Ly alpha escape fraction measured. In any case, in the regions where the diffuse Ly alpha emission shows the largest Ly alpha/H alpha ratios, no additional sources of Ly alpha emission are required, like ionization by hot plasma as proposed for Haro 2, another galaxy in our sample. These results stress again the importance of a proper correction of scattering and transfer effects when using Ly alpha to derive the star formation rate in high-redshift galaxies.

EDP Sciences2014

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EPFL2015

EDP Sciences2014