arXiv subjects

David Elbaz

Publications and source records attributed to David Elbaz.

At least 127 records · Page 7Linked to original sources

arXiv2009

A simple model to interpret the ultraviolet, optical and infrared SEDs of galaxies

We present a simple, largely empirical but physically motivated model, which is designed to interpret consistently multi-wavelength observations from large samples of galaxies in terms of physical parameters, such as star formation rate, stellar mass and dust content. Our model is both simple and versatile enough to allow the derivation of statistical constraints on the star formation histories and dust contents of large samples of galaxies using a wide range of ultraviolet, optical and infrared observations. We illustrate this by deriving median-likelihood estimates of a set of physical parameters describing the stellar and dust contents of local star-forming galaxies from the Spitzer Infrared Nearby Galaxy Sample (SINGS) and from a newly-matched sample of SDSS galaxies observed with GALEX, 2MASS, and IRAS. The model reproduces well the observed spectral energy distributions of these galaxies across the entire wavelength range from the far-ultraviolet to the far-infrared. We find important correlations between the physical parameters of galaxies which are useful to investigate the star formation activity and dust properties of galaxies. Our model can be straightforwardly applied to interpret observed ultraviolet-to-infrared spectral energy distributions (SEDs) from any galaxy sample.

astro-ph.CO↗

arXiv2009

Cosmic star-formation history from a non-parametric inversion of infrared galaxy counts

[Abridged] This paper aims at providing new conservative constraints to the cosmic star-formation history from the empirical modeling of mid- and far-infrared data. We perform a non-parametric inversion of galaxy counts at 15, 24, 70, 160, and 850 microns simultaneously. It is a "blind" search (no redshift information is required) of all possible evolutions of the infrared luminosity function of galaxies, from which the evolution of the star-formation rate density and its uncertainties are derived. The cosmic infrared background (CIRB) measurements are used a posteriori to tighten the range of solutions. The inversion relies only on two hypotheses: (1) the luminosity function remains smooth both in redshift and luminosity, (2) a set of infrared spectral energy distributions (SEDs) of galaxies must be assumed. The range of star-formation histories that we derive is well constrained and consistent with redshift-based measurements from deep surveys. The redshift decompositions of the counts are also recovered successfully. Therefore, multi-wavelength counts and CIRB (both projected observations) alone seem to contain enough information to recover the cosmic star-formation history with quantifiable errors. A peak of the SFRD at z~2 is preferred, although higher redshifts are not excluded. We also find a good consistency between the observed evolution of the stellar mass density and the prediction from our model. Finally, the inability of the inversion to model perfectly and simultaneously all the multi-wavelength infrared counts (especially at 160 microns where an excess is seen around 20 mJ) implies either (i) the existence of a sub-population of colder galaxies, (ii) a larger dispersion of dust temperatures among local galaxies than expected, (iii) or a redshift evolution of the infrared SEDs of galaxies.

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arXiv2009

The QSO HE0450-2958: Scantily dressed or heavily robed? A normal quasar as part of an unusual ULIRG

(Abridged) The luminous z=0.286 quasar HE0450-2958 is interacting with a companion galaxy at 6.5 kpc distance and the whole system is a ULIRG. A so far undetected host galaxy triggered the hypothesis of a mostly "naked" black hole (BH) ejected from the companion by three-body interaction. We present new HST/NICMOS 1.6micron imaging data at 0.1" resolution and VLT/VISIR 11.3micron images at 0.35" resolution that for the first time resolve the system in the near- and mid-infrared. We combine these with existing optical HST and CO maps. (i) At 1.6micron we find an extension N-E of the quasar nucleus that is likely a part of the host galaxy, though not its main body. If true, this places HE0450-2958 directly onto the M_BH-M_bulge-relation for nearby galaxies. (ii) HE0450-2958 is consistent with lying at the high-luminosity end of Narrow-Line Seyfert 1 Galaxies, and more exotic explanations like a "naked quasar" are unlikely. (iii) All 11.3micron radiation in the system is emitted by the quasar nucleus, which is radiating at super-Eddington rate, L/L_Edd=6.2+3.8-1.8, or 12 M_sun/yr. (iv) The companion galaxy is covered in optically thick dust and is not a collisional ring galaxy. It emits in the far infrared at ULIRG strength, powered by Arp220-like star formation (strong starburst-like). An M82-like SED is ruled out. (v) With its black hole accretion rate HE0450-2958 produces not enough new stars to maintain its position on the M_BH-M_bulge-relation, and star formation and black hole accretion are spatially disjoint; the bulge has to grow by redistribution of preexisting stars. (vi) Systems similar to HE0450-2958 with spatially disjoint ULIRG-strength star formation and quasar activity are rare. At z<0.43 we only find <4% (3/77) candidates for a similar configuration.

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arXiv2009

A New Era in Extragalactic Background Light Measurements: The Cosmic History of Accretion, Nucleosynthesis and Reionization

(Brief Summary) What is the total radiative content of the Universe since the epoch of recombination? The extragalactic background light (EBL) spectrum captures the redshifted energy released from the first stellar objects, protogalaxies, and galaxies throughout cosmic history. Yet, we have not determined the brightness of the extragalactic sky from UV/optical to far-infrared wavelengths with sufficient accuracy to establish the radiative content of the Universe to better than an order of magnitude. Among many science topics, an accurate measurement of the EBL spectrum from optical to far-IR wavelengths, will address: What is the total energy released by stellar nucleosynthesis over cosmic history? Was significant energy released by non-stellar processes? Is there a diffuse component to the EBL anywhere from optical to sub-millimeter? When did first stars appear and how luminous was the reionization epoch? Absolute optical to mid-IR EBL spectrum to an astrophysically interesting accuracy can be established by wide field imagingat a distance of 5 AU or above the ecliptic plane where the zodiacal foreground is reduced by more than two orders of magnitude.

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arXiv2008

A simple model to interpret the ultraviolet, optical and infrared emission from galaxies

We present a simple, largely empirical but physically motivated model to interpret the mid- and far-infrared spectral energy distributions of galaxies consistently with the emission at ultraviolet, optical and near-infrared wavelengths. Our model relies on an existing angle-averaged prescription to compute the absorption of starlight by dust in stellar birth clouds and in the ambient ISM in galaxies. We compute the spectral energy distribution of the power reradiated by dust in stellar birth clouds as the sum of three components: a component of PAHs; a mid-IR continuum characterising the emission from hot grains; and a component of warm grains in thermal equilibrium with adjustable temperature. In the ambient ISM, we fix for simplicity the relative proportions of these three components to reproduce the spectral shape of diffuse cirrus emission in the Milky Way, and we include a component of cold grains in thermal equilibrium with adjustable temperature. Our model can be used to derive statistical constraints on the star formation histories and dust contents of large samples of galaxies using UV, optical and IR observations. We illustrate this by deriving median-likelihood estimates of the star formation rates, stellar masses, effective dust optical depths, dust masses, and relative strengths of different dust components of 66 well-studied nearby star- forming galaxies from the Spitzer Infrared Nearby Galaxy Survey (SINGS). From this analysis, we conclude that the mid- and far-IR colours of galaxies correlate strongly with the specific star formation rate, as well as with other galaxy-wide quantities connected to this parameter. Our model can be straightforwardly applied to interpret UV, optical and IR spectral energy distributions from any galaxy sample. [abridged]

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arXiv2007

Mid-Infrared Spectral Diagnosis of Submillimeter Galaxies

We present deep mid-infrared spectroscopy with the Spitzer Space Telescope of 13 submillimeter galaxies (SMGs) in the Great Observatories Origins Deep Survey North (GOODS-N) field. We find strong polycyclic aromatic hydrocarbon (PAH) emission in all of our targets which allows us to measure mid-IR spectroscopic redshifts and place constraints on the contribution from star formation and active galactic nuclei (AGN) activity to the mid-IR emission. In the high signal-to-noise ratio composite spectrum of SMGs, we find that the hot dust continuum from an AGN contributes at most 30% of the mid-IR luminosity. We find that the mid-IR properties of SMGs are distinct from those of 24 micron -selected ULIRGs at z~2; the former are predominantly dominated by star formation while the latter are a more heterogeneous sample with many showing significant AGN activity. We fit the IRS spectrum and the mid-IR to radio photometry of SMGs with template spectral energy distributions to determine the best estimate of the total infrared luminosity from star formation. While many SMGs contain an AGN as evinced by their X-ray properties, our multi-wavelength analysis shows that the total infrared luminosity, LIR, in SMGs, is dominated by star formation and not AGN activity. We find that high redshift SMGs lie on the relation between LIR and LPAH6.2 (or LPAH7.7 or LPAH11.3) that has been established for local starburst galaxies. This suggests that PAH luminosity can be used as a proxy for the star formation rate in SMGs. SMGs are consistent with being a short lived cool phase in a massive merger. Although there appears to be an AGN present in many SMGs, it does not appear to have become strong enough to heat the dust and dominate the mid- or far-infrared emission.

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arXiv2006

The infrared compactness-temperature relation for quiescent and starburst galaxies

IRAS observations show the existence of a correlation between the infrared luminosity Lir and dust temperature Td in star-forming galaxies, in which larger Lir leads to higher dust temperature. The Lir-Td relation is commonly seen as reflecting the increase in dust temperature in galaxies with higher star formation rate. Even though the correlation shows a significant amount of dispersion, a unique relation has been commonly used to construct spectral energy distributions of galaxies in distant universe studies, such as source number counting or photometric redshift determination. In this work, we introduce a new parameter, namely the size of the star-forming region Rir and lay out the empirical and modelled relation between the global parameters Lir, Td and Rir of IR-bright non-AGN galaxies. IRAS 60-to-100um color is used as a proxy for the dust temperature and the 1.4GHz radio contiuum emission for the infrared spatial distribution. The analysis has been carried out on two samples. The first one is made of the galaxies from the 60um flux-limited IRAS Revised Bright Galaxy Samples which have a reliable RC size estimate from the VLA follow-ups of the IRAS Bright Galaxy Samples. The second is made of the sources from the 170um ISOPHOT Serendipity Sky Survey which are resolved by the NVSS or FIRST surveys. We show that the dispersion in the Lir-Td diagram can be reduced to a relation between the infrared surface brightness and the dust temperature, a relation that spans 5 orders of magnitude in surface brightness. We explored the physical processes giving rise to the Sir-Td relation, and show that it can be derived from the Schmidt law, which relates the star formation rate to the gas surface density.

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arXiv2005

Understanding galaxy formation with ISO deep surveys

We present the results obtained through the various ISO extragalactic deep surveys. While IRAS revealed the existence of galaxies forming stars at a rate of a few tens (LIRGs) or even hundreds (ULIRGs) solar masses in the local universe, ISO not only discovered that these galaxies were already in place at redshift one, but also that they are not the extreme objects that we once believed them to be. Instead they appear to play a dominant role in shaping present-day galaxies as reflected by their role in the cosmic history of star formation and in producing the cosmic infrared background detected by the COBE satellite in the far infrared to sub-millimeter range.

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arXiv2004

ISOCAM observations in the Lockman Hole - I The 14.3 micron shallow survey: data reduction, catalogue, and optical identifications

We present the image and catalogue of the 14.3 micron shallow survey of 0.55 square degrees in the region of the Lockman Hole (10h52m03s +57d21m46s, J2000) with the Infrared Space Observatory (ISO). The data have been analyzed with the recent algorithm by Lari et al. (2001) conceived to exploit ISO data in an optimal way, especially in the case of shallow surveys with low redundancy. Photometry has been accurately evaluated through extensive simulations and also the absolute calibration has been checked using a set of 21 stars detected at 14.3 micron, optical, and near-IR bands. On the basis of simulations, we evaluate that the survey is 80%, 50%, and 20% complete at 0.8, 0.6, and 0.45 mJy, respectively. Below the 20% completeness limit, fluxes are generally overestimated since the sources are preferentially detected if their positions correspond to positive oscillations of the noise. Moreover, from a comparison with the deep survey, we estimate that only sources brighter than 0.45 mJy are highly reliable. Only 5% of these sources do not have optical counterparts down to r'=25. Since none of the Spitzer imaging bands cover the 14.3 micron wavelength range, this data set will remain unique until the advent of the James Webb Space Telescope.

astro-ph↗

arXiv2004

Luminous Infrared Starbursts in a Cluster of Galaxies

Analysing mid--infrared ISOCAM images of the cluster of galaxies J1888.16CL, we identified among its members several particularly active galaxies with total infrared luminosities well above 10^{11} Lsun. If powered by dust enshrouded starbursts, as suggested by their optical spectra, these Luminous Infrared Galaxies would exhibit star formation rates surprisingly high in the cluster environment. The triggering mechanism is unclear but could be tidal collisions within sub-structures or infalling groups.

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arXiv2004

The cosmic infrared background (CIRB) and the role of the "local environment of galaxies" in the origin of present-day stars

A combination of evidence is presented suggesting that the majority of the stars in today's galaxies were born during a luminous infrared phase (LIRP) triggered by the local environment of galaxies. The CIRB is a fossil record of these LIRPs and therefore reflects the influence of triggered star formation through galaxy-galaxy interactions, including non merging tidal encounters. This scenario, in which galaxies experienced several LIRPs in their history, is consistent with the measured redshift evolution of the cosmic density of star formation rates and of stellar masses of galaxies.

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arXiv2004

Dusty Starbursts and the Growth of Cosmic Structure

Dusty starbursts were more numerous around z~1 than today and appear to be responsible for the majority of cosmic star formation over the Hubble time. We suggest that they represent a common phase within galaxies in general which is triggered by the growth of cosmic structure. We discuss the origin of the luminosity of luminous infrared galaxies at z~1. Are these galaxies dominated by star formation or nuclear activity ? What is triggering their strong activity ? Is it triggered by external interactions or did it happen naturally within isolated galaxies ? We present HST-ACS high resolution optical images of luminous infrared galaxies at z~0.7 showing the evolution of the morphology of these galaxies as a function of infrared luminosity, or star formation rate, and discuss the effect of the environment on their activity.

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arXiv2004

Galaxy formation and evolution since z=1

Determination of the star formation rate can be done using mid-IR photometry or Balmer line luminosity after a proper correction for extinction effects. Both methods show convergent results while those based on UV or on [OII]3727 luminosities underestimate the SFR by factors ranging from 5 to 40 for starbursts and for luminous IR galaxies, respectively. Most of the evolution of the cosmic star formation density is related to the evolution of luminous compact galaxies and to luminous IR galaxies. Because they were metal deficient and were forming stars at very high rates (40 to 100 solar mass per year), it is probable that these (massive) galaxies were actively forming the bulk of their stellar/metal content at z < 1.

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arXiv2003

A Fossil Record of Galaxy Encounters

The cosmic infrared background (CIRB) is a record of a large fraction of the emission of light by stars and galaxies over time. The bulk of this emission has been resolved by the Infrared Space Observatory camera. The dominant contributors are bright starburst galaxies with redshift z ~ 0.8; that is, in the same redshift range as the active galactic nuclei responsible for the bulk of the x-ray background. At the longest wavelengths, sources of redshift z>2 tend to dominate the CIRB. It appears that the majority of present-day stars have been formed in dusty starbursts triggered by galaxy-galaxy interactions and the build-up of large-scale structures.

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arXiv2001

The AGN contribution to mid-infrared surveys

We provide constraints on the AGN contribution to the mid-IR extragalactic background light from a correlation analysis of deep X-ray and mid-IR observations in two regions centred on the Lockman Hole (LH) and Hubble Deep Field North (HDFN). Among the 76 galaxies detected by XMM in the LH area (200 square arcminutes), 24 show mid-IR emission, but the relative percentage of X-ray sources with mid-IR counterparts increases with the band energy: from 30% of the 0.5-2 keV sources up to 63% of the 5-10 keV sources. In contrast, only a small fraction of the mid-IR sources (around 10%) show X-ray emission. In the region centred on the HDFN (24 square arcminutes), 25% of the mid-IR sources are detected in the X-ray, while 30-40% of the X-ray sources show mid-IR emission. Under the conservative assumption that all XMM sources are AGN-dominated, AGNs contribute 15% of the total mid-IR flux in the LH. For the HDFN we have assumed that AGN-dominated sources are luminous X-ray sources with radio to X-ray SEDs typical of local AGNs, in which case we find that 18% of the mid-IR flux are due to AGN emission. If we put together all the existing information from the deepest HDFN data to the shallow large-area BeppoSAX observations in the ELAIS S1 region using the median mid-IR to X-ray spectral indices as a function of the X-ray flux, we find an AGN contribution to the 15um background of 17%. We conclude that the population of IR luminous galaxies detected in the ISOCAM deep surveys are mainly constituted by dust-obscured starbursts.

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arXiv2001

ISO investigates the nature of extremely-red hard X-ray sources responsible for the X-ray background

We analyse very deep X-ray and mid-IR surveys in common areas of the Lockman Hole and the HDF North to study the sources of the X-ray background (XRB) and to test the standard obscured accretion paradigm. We detect with ISO a rich population of X-ray luminous sources with red optical colours, including a fraction identified with Extremely Red Objects (R-K > 5) and galaxies with SEDs typical of normal massive ellipticals or spirals at z ~ 1. The high 0.5-10 keV X-ray luminosities of these objects (1E43-1E45 erg/s) indicate that the ultimate energy source is gravitational accretion, while the X-ray to IR flux ratios and the X-ray spectral hardness show evidence of photoelectric absorption at low X-ray energies. An important hint on the physics comes from the mid-IR data at 6.7 and 15 um, well reproduced by model spectra of completely obscured quasars under standard assumptions and l.o.s. optical depths tau ~ 30-40. Other predictions of the standard XRB picture, like the distributions of intrinsic bolometric luminosities and the relative fractions of type-I and -II objects (1:3), are also consistent with our results. Obscured gravitational accretion is then confirmed as being responsible for the bulk of the X-ray background, since we detect in the IR the down-graded energy photoelectrically absorbed in X-rays: 63% of the faint 5-10 keV XMM sources are detected in the mid-IR by Fadda et al. (2001). However, although as much as 90% of the X-ray energy production could be converted to IR photons, no more than 20% of the Cosmic IR Background can be attributed to X-ray loud AGNs.

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arXiv2001

ISOCAM Mid-InfraRed Detection of HR 10: A Distant Clone of Arp 220 at z=1.44

We report the detection of the extremely red object (ERO), HR 10 (I-K= 6.5, z=1.44), at 4.9 and 6.1 microns (rest-frame) with ISOCAM, the mid-infrared (MIR) camera onboard the Infrared Space Observatory (ISO). HR 10 is the first ERO spectroscopically identified to be associated with an ultra-luminous IR galaxy (ULIG) detected in the radio, MIR and sub-millimeter. The rest-frame spectral energy distribution (SED) of HR 10 is amazingly similar to the one of Arp 220, scaled by a factor 3.8+/-1.3. The corresponding 8-1000 microns luminosity (~ 7x10^12 h70^{-2} Lsol) translates into a star formation rate of about 1200 h70^{-2} Msol/yr if HR 10 is mostly powered by star formation. We address the key issue of the origin of the powerful luminosity of HR 10, i.e. starburst versus active galactic nucleus (AGN), by using the similarity with its closeby clone, Arp 220.

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arXiv1999

Mid and Far Infrared Surveys with ISO

We present the results of the extragalactic surveys performed at 15 and 175 microns using the ISOCAM and ISOPHOT instruments on-board the Infrared Space Observatory (ISO). The number counts at both wavelengths present a strong evolution. The preliminary study of the individual galaxies responsible for this evolution suggest that more star formation was hidden by dust at redshifts around z=1-2 and imply that the population of luminous IR galaxies detected by IRAS in the local universe must have played a major role in the formation and evolution of galaxies and cannot be considered anymore as extreme and rare cases.

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