arXiv subjects

A. Saintonge

Publications and source records attributed to A. Saintonge.

71 records · Page 4Linked to original sources

arXiv2010

The dust content of high-z submillimeter galaxies revealed by Herschel

We use deep observations taken with the Photodetector Array Camera and Spectrometer (PACS), on board the Herschel satellite as part of the PACS evolutionary probe (PEP) guaranteed project along with submm ground-based observations to measure the dust mass of a sample of high-z submillimeter galaxies (SMGs). We investigate their dust content relative to their stellar and gas masses, and compare them with local star-forming galaxies. High-z SMGs are dust rich, i.e. they have higher dust-to-stellar mass ratios compared to local spiral galaxies (by a factor of 30) and also compared to local ultraluminous infrared galaxies (ULIRGs, by a factor of 6). This indicates that the large masses of gas typically hosted in SMGs have already been highly enriched with metals and dust. Indeed, for those SMGs whose gas mass is measured, we infer dust-to-gas ratios similar or higher than local spirals and ULIRGs. However, similarly to other strongly star-forming galaxies in the local Universe and at high-z, SMGs are characterized by gas metalicities lower (by a factor of a few) than local spirals, as inferred from their optical nebular lines, which are generally ascribed to infall of metal-poor gas. This is in contrast with the large dust content inferred from the far-IR and submm data. In short, the metalicity inferred from the dust mass is much higher (by more than an order of magnitude) than that inferred from the optical nebular lines. We discuss the possible explanations of this discrepancy and the possible implications for the investigation of the metalicity evolution at high-z.

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arXiv2010

Herschel deep far-infrared counts through the Abell 2218 cluster-lens

Gravitational lensing by massive galaxy clusters allows study of the population of intrinsically faint infrared galaxies that lie below the sensitivity and confusion limits of current infrared and submillimeter telescopes. We present ultra-deep PACS 100 and 160 microns observations toward the cluster lens Abell 2218, to penetrate the Herschel confusion limit. We derive source counts down to a flux density of 1 mJy at 100 microns and 2 mJy at 160 microns, aided by strong gravitational lensing. At these levels, source densities are 20 and 10 beams/source in the two bands, approaching source density confusion at 160 microns. The slope of the counts below the turnover of the Euclidean-normalized differential curve is constrained in both bands and is consistent with most of the recent backwards evolutionary models. By integrating number counts over the flux range accessed by Abell 2218 lensing (0.94-35 mJy at 100 microns and 1.47-35 mJy at 160 microns, we retrieve a cosmic infrared background (CIB) surface brightness of ~8.0 and ~9.9 nW m^-2 sr^-1, in the respective bands. These values correspond to 55% (+/- 24%) and 77% (+/- 31%) of DIRBE direct measurements. Combining Abell 2218 results with wider/shallower fields, these figures increase to 62% (+/- 25%) and 88% (+/- 32%) CIB total fractions, resolved at 100 and 160 microns, disregarding the high uncertainties of DIRBE absolute values.

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arXiv2010

Herschel PEP: The star-formation rates of 1.5<z<2.5 massive galaxies

The star formation rate (SFR) is a key parameter in the study of galaxy evolution. The accuracy of SFR measurements at z~2 has been questioned following a disagreement between observations and theoretical models. The latter predict SFRs at this redshift that are typically a factor 4 or more lower than the measurements. We present star-formation rates based on calorimetric measurements of the far-infrared (FIR) luminosities for massive 1.5 12.2 L_sun. The SFGs and AGNs tend to exhibit the same 24 micron excess. The UV SFRs are in closer agreement with the FIR-based SFRs. Using a Calzetti UV extinction correction results in a mean excess of up to 0.3 dex and a scatter of 0.35 dex from the FIR SFRs. The previous UV SFRs are thus confirmed and the mean excess, while narrowing the gap, is insufficient to explain the discrepancy between the observed SFRs and simulation predictions.

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arXiv2010

Herschel unveils a puzzling uniformity of distant dusty galaxies

The Herschel Space Observatory enables us to accurately measure the bolometric output of starburst galaxies and active galactic nuclei (AGN) by directly sampling the peak of their far-infrared (IR) emission. Here we examine whether the spectral energy distribution (SED) and dust temperature of galaxies have strongly evolved since z~2.5. We use Herschel deep extragalactic surveys from 100 to 500um to compute total IR luminosities in galaxies down to the faintest levels, using PACS and SPIRE in the GOODS-North field (PEP and HerMES key programs). We show that measurements in the SPIRE bands can be used below the statistical confusion limit if information at higher spatial resolution is used to identify isolated galaxies whose flux is not boosted by bright neighbors. Below z~1.5, mid-IR extrapolations are correct for star-forming galaxies with a dispersion of only 40% (0.15dex), therefore similar to z~0 galaxies. This narrow distribution is puzzling when considering the range of physical processes that could have affected the SED of these galaxies. Extrapolations from only one of the 160um, 250um or 350um bands alone tend to overestimate the total IR luminosity. This may be explained by the lack of far-IR constraints around and above ~150um (rest-frame) on local templates. We also note that the dust temperature of luminous IR galaxies around z~1 is mildly colder by 10-15% than their local analogs and up to 20% for ULIRGs at z~1.6. Above z=1.5, distant galaxies are found to exhibit a substantially larger mid- over far-IR ratio, which could either result from stronger broad emission lines or warm dust continuum heated by a hidden AGN. Two thirds of the AGNs identified in the field with a measured redshift exhibit the same behavior as purely star-forming galaxies. Hence a large fraction of AGNs harbor star formation at very high SFR and in conditions similar to purely star-forming galaxies.

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arXiv2010

Star formation in AGN hosts in GOODS-N

Sensitive Herschel far-infrared observations can break degeneracies that were inherent to previous studies of star formation in high-z AGN hosts. Combining PACS 100 and 160um observations of the GOODS-N field with 2Msec Chandra data, we detect ~20% of X-ray AGN individually at >3sig. The host far-infrared luminosity of AGN with L2-10~10^43erg/s increases with redshift by an order of magnitude from z=0 to z~1. In contrast, there is little dependence of far-infrared luminosity on AGN luminosity, for L2-10<~10^44erg/s AGN at z>~1. We do not find a dependence of far-infrared luminosity on X-ray obscuring column, for our sample which is dominated by L2-10<10^44erg/s AGN. In conjunction with properties of local and luminous high-z AGN, we interpret these results as reflecting the interplay between two paths of AGN/host coevolution. A correlation of AGN luminosity and host star formation is traced locally over a wide range of luminosities and also extends to luminous high z AGN. This correlation reflects an evolutionary connection, likely via merging. For lower AGN luminosities, star formation is similar to that in non-active massive galaxies and shows little dependence on AGN luminosity. The level of this secular, non-merger driven star formation increasingly dominates over the correlation at increasing redshift.

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arXiv2010

PEP: first Herschel probe of dusty galaxy evolution up to z~3

We exploit the deepest existing far-infrared (FIR) data obtained so far by Herschel at 100 and 160 um in the GOODS-N, as part of the PACS Evolutionary Probe (PEP) survey, to derive for the first time the evolution of the rest-frame 60-um, 90-um, and total IR luminosity functions (LFs) of galaxies and AGNs from z=0 to unprecedented high redshifts (z~2-3). The PEP LFs were computed using the 1/Vmax method. The FIR sources were classified by means of a detailed broad- band SED-fitting analysis and spectral characterisation. Based on the best-fit model results, k-correction and total IR (8-1000 um) luminosity were obtained for each source. LFs (monochromatic and total) were then derived for various IR populations separately in different redshift bins and compared to backward evolution model predictions. We detect strong evolution in the LF to at least z~2. Objects with SEDs similar to local spiral galaxies are the major contributors to the star formation density (SFD) at z< 0.3, then, as redshift increases, moderate SF galaxies - most likely containing a low-luminosity AGN - start dominating up to z ~= 1.5. At >1.5 the SFD is dominated by the contributions of starburst galaxies. In agreement with previous findings, the comoving IR LD derived from our data evolves approximately as (1 + z)^(3.8+/-0.3) up to z~1, there being some evidence of flattening up to z~2.

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arXiv2010

Far-infrared properties of submillimeter and optically faint radio galaxies

We use deep observations obtained with the Photodetector Array Camera and Spectrometer (PACS) onboard the Herschel space observatory to study the far-infrared (FIR) properties of submm and optically faint radio galaxies (SMGs and OFRGs). From literature we compiled a sample of 35 securely identified SMGs and nine OFRGs located in the GOODS-N and the A2218 fields. This sample is cross-matched with our PACS 100 um and 160 um multi-wavelength catalogs. About half of the galaxies in our sample are detected with PACS. The dust temperatures and the infrared luminosities of our galaxies are derived by fitting their PACS and SCUBA 850 um (only the upper limits for the OFRGs) flux densities with a single modified (beta=1.5) black body function. The median dust temperature of our SMG sample is T=36+/-8K while for our OFRG sample it is T=47+/-3K. For both samples, median dust temperatures derived from Herschel data agree well with previous estimates. In particular, Chapman et al. (2005) found a dust temperature of T=36+/-7K for a large sample of SMGs assuming the validity of the FIR/radio correlation. The agreement between our studies confirms that the local FIR/radio correlation effectively holds at high redshift even though we find =2.17+/-0.19, a slightly lower value than that observed in local systems. The median IR luminosities of SMGs and OFRGs are 4.6*10^12 Lsun and 2.6*10^12 Lsun, respectively. We note that for both samples the IR luminosity estimates from the radio part of the spectral energy distribution are accurate, while estimates from the mid-IR are considerably (x3) more uncertain. Our observations confirm the remarkably high luminosities of SMGs and thus imply median star-formation rates of 960Msun yr^-1 for SMGs with S(850um)>5mJy and 460Msun yr^-1 for SMGs with S(850um)>2mJy, assuming a Chabrier IMF and no dominant AGN contribution to the far-infrared luminosity.

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arXiv2010

The far-infrared/radio correlation as probed by Herschel

We set out to determine the ratio, q(IR), of rest-frame 8-1000um flux, S(IR), to monochromatic radio flux, S(1.4GHz), for galaxies selected at far-IR and radio wavelengths, to search for signs that the ratio evolves with redshift, luminosity or dust temperature, and to identify any far-IR-bright outliers - useful laboratories for exploring why the far-IR/radio correlation is generally so tight when the prevailing theory suggests variations are almost inevitable. We use flux-limited 250-um and 1.4-GHz samples, obtained in GOODS-N using Herschel (HerMES; PEP) and the VLA. We determine bolometric IR output using ten bands spanning 24-1250um, exploiting data from PACS and SPIRE, as well as Spitzer, SCUBA, AzTEC and MAMBO. We also explore the properties of an L(IR)-matched sample, designed to reveal evolution of q(IR) with z, spanning log L(IR) = 11-12 L(sun) and z=0-2, by stacking into the radio and far-IR images. For 1.4-GHz-selected galaxies, we see tentative evidence of a break in the flux ratio, q(IR), at L(1.4GHz) ~ 10^22.7 W/Hz, where AGN are starting to dominate the radio power density, and of weaker correlations with z and T(d). From our 250-um-selected sample we identify a small number of far-IR-bright outliers, and see trends of q(IR) with L(1.4GHz), L(IR), T(d) and z, noting that some of these are inter-related. For our L(IR)-matched sample, there is no evidence that q(IR) changes significantly as we move back into the epoch of galaxy formation: we find q(IR) goes as (1+z)^gamma, where gamma = -0.04 +/- 0.03 at z=0-2; however, discounting the least reliable data at z<0.5 we find gamma = -0.26 +/- 0.07, modest evolution which may be related to the radio background seen by ARCADE2, perhaps driven by <10uJy radio activity amongst ordinary star-forming galaxies at z>1.

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arXiv2010

Dissecting the cosmic infra-red background with Herschel/PEP

The constituents of the cosmic IR background (CIB) are studied at its peak wavelengths (100 and 160 um) by exploiting Herschel/PACS observations of the GOODS-N, Lockman Hole, and COSMOS fields in the PACS Evolutionary Probe (PEP) guaranteed-time survey. The GOODS-N data reach 3 sigma depths of ~3.0 mJy at 100 um and ~5.7 mJy at 160 um. At these levels, source densities are 40 and 18 beams/source, respectively, thus hitting the confusion limit at 160 um. Differential number counts extend from a few mJy up to 100-200 mJy, and are approximated as a double power law, with the break lying between 5 and 10 mJy. The available ancillary information allows us to split number counts into redshift bins. At z<=0.5 we isolate a class of luminous sources (L(IR)~1e11 Lsun), whose SEDs resemble late-spiral galaxies, peaking at ~130 um restframe and significantly colder than what is expected on the basis of pre-Herschel models. By integrating number counts over the whole covered flux range, we obtain a surface brightness of 6.36 +/- 1.67 and 6.58 +/-1.62 [nW m^-2 sr^-1] at 100 and 160 um, resolving ~45% and ~52% of the CIB, respectively. When stacking 24 um sources, the inferred CIB lies within 1.1 sigma and 0.5 sigma from direct measurements in the two bands, and fractions increase to 50% and 75%.Most of this resolved CIB fraction was radiated at z<=1.0, with 160 um sources found at higher redshift than 100 um ones.

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arXiv2010

The first Herschel view of the mass-SFR link in high-z galaxies

We exploit deep observations of the GOODS-N field taken with PACS, on board of Herschel, as part of the PEP guaranteed time, to study the link between star formation and stellar mass in galaxies to z~2. Starting from a stellar mass-selected sample of ~4500 galaxies with mag[4.5mu]<23 (AB), we identify ~350 objects with a PACS detection at 100 or 160mu and ~1500 with only Spitzer 24 mu counterpart. Stellar masses and total IR luminosities (LIR) are estimated by fitting the SEDs. Consistently with other Herschel results, we find that LIR based only on 24 mu 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 10^(11) (M_sun) 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.

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arXiv2009

The Arecibo Legacy Fast ALFA Survey: IX. The Leo Region HI Catalog, Group Membership and the HI Mass Function for the Leo I Group

We present the catalog of HI sources extracted from the ongoing Arecibo Legacy Fast ALFA (ALFALFA) extragalactic HI line survey, found within the sky region bounded by 9h36m < RA < 11h36m and +08deg < DEC < +12deg. The HI catalog presented here for this 118-deg^2 region is combined with ones derived from surrounding regions also covered by the ALFALFA survey to examine the large scale structure in the complex Leo region. Because of the combination of wide sky coverage and superior sensitivity, spatial and spectral resolution, the ALFALFA HI catalog of the Leo region improves significantly on the numbers of low HI mass sources as compared with those found in previous HI surveys. The HI mass function of the Leo I group presented here is dominated by low-mass objects: 45 of the 65 Leo I members have M_HI < 10^8 Msun, yielding tight constraints on the low-mass slope of the Leo I HI mass function. The best-fit slope is alpha < -1.41 + 0.2 - 0.1. A direct comparison between the ALFALFA HI line detections and an optical search of the Leo I region proves the advantage of the ALFALFA strategy in finding low mass, gas-rich dwarfs. These results suggest the existence of a significant population of low surface brightness, gas-rich, yet still very low HI mass galaxies, and may reflect the same type of morphological segregation as is seen in the Local Group. While the low mass end slope of the Leo I HI mass function is steeper than that determined for luminosity functions of the group, the slope still falls short of the values predicted by simulations of structure formation in the LCDM paradigm.

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arXiv2008

HI clouds in the proximity of M33

Neutral hydrogen clouds are found in the Milky Way and Andromeda halo both as large complexes and smaller isolated clouds. Here we present a search for Hi clouds in the halo of M33, the third spiral galaxy of the Local Group. We have used two complementary data sets: a 3^o x 3^o map of the area provided by the Arecibo Legacy Fast ALFA (ALFALFA) survey and deeper pointed observations carried out with the Arecibo telescope in two fields that permit sampling of the north eastern and south-western edges of the HI disc. The total amount of Hi around M33 detected by our survey is $\sim 10^7$ M$_{\odot}$. At least 50% of this mass is made of HI clouds that are related both in space and velocity to the galaxy. We discuss several scenarios for the origin of these clouds focusing on the two most interesting ones: $(a)$ dark-matter dominated gaseous satellites, $(b)$ debris from filaments flowing into M33 from the intergalactic medium or generated by a previous interaction with M31. Both scenarios seem to fit with the observed cloud properties. Some structures are found at anomalous velocities, particularly an extended HI complex previously detected by Thilker et al. (2002). Even though the ALFALFA observations seem to indicate that this cloud is possibly connected to M33 by a faint gas bridge, we cannot firmly establish its extragalactic nature or its relation to M33. Taking into account that the clouds associated with M33 are likely to be highly ionised by the extragalactic UV radiation, we predict that the total gas mass associated with them is > 5 x 10^7 M$_{\odot}$. If the gas is steadily falling towards the M33 disc it can provide the fuel needed to sustain a current star formation rate of 0.5 M$_{\odot}$ yr$^{-1}$.

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arXiv2007

Geometrical tests of cosmological models. I. Probing dark energy using the kinematics of high-redshift galaxies

We suggest to use the observationally measured and theoretically justified correlation between size and rotational velocity of galactic discs as a viable method to select a set of high redshift standard rods which may be used to explore the dark energy content of the universe via the classical angular-diameter test. Here we explore a new strategy for an optimal implementation of this test. We propose to use the rotation speed of high redshift galaxies as a standard size indicator and show how high resolution multi-object spectroscopy and ACS/HST high quality spatial images, may be combined to measure the amplitude of the dark energy density parameter, or to constrain the cosmic equation of state parameter for a smooth dark energy component. We evaluate how systematics may affect the proposed tests, and find that a linear standard rod evolution, causing galaxy dimensions to be up to 30% smaller at z=1.5, can be uniquely diagnosed, and will minimally bias the confidence level contours in the [Omega_Q, w] plane. Finally, we show how to derive, without a priori knowing the specific functional form of disc evolution, a cosmology-evolution diagram with which it is possible to establish a mapping between different cosmological models and the amount of galaxy disc/luminosity evolution expected at a given redshift.

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arXiv2007

Geometrical tests of cosmological models. II. Calibration of rotational widths and disc scaling relations

This series of papers is dedicated to a new technique to select galaxies that can act as standard rods and standard candles in order to perform geometrical tests on large samples of high redshift galaxies to constrain different cosmological parameters. The goals of this paper are (1) to compare different rotation indicators in order to understand the relation between rotation velocities extracted from observations of the Halpha line and the [OII]3727 line, and (2) determine the scaling relations between physical size, surface brightness and magnitude of galaxies and their rotation velocity using the SFI++, a large catalog of nearby galaxies observed at I-band. A good correlation is observed between the rotation curve-derived velocities of the Halpha and [OII] observations, as well as between those calculated from velocity histograms, justifying the direct comparison of velocities measured from Halpha rotation curves in nearby galaxies and from [OII] line widths at higher redshifts. To provide calibration for the geometrical tests, we give expressions for the different scaling relations between properties of galaxies (size, surface brightness, magnitude) and their rotation speeds. Apart from the Tully-Fisher relation, we derive the size-rotation velocity and surface brightness-rotation velocity relations with unprecedentedly small scatters. We show how the best size-rotation velocity relation is derived when size is estimated not from disc scale lengths but from the isophotal diameter r23.5, once these have been corrected for inclination and extinction effects.

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arXiv2007

Geometrical tests of cosmological models. III. The cosmology-evolution diagram at z=1

The rotational velocity of distant galaxies, when interpreted as a size (luminosity) indicator, may be used as a tool to select high redshift standard rods (candles) and probe world models and galaxy evolution via the classical angular diameter-redshift or Hubble diagram tests. We implement the proposed testing strategy using a sample of 30 rotators spanning the redshift range 0.2<z<1 with high resolution spectra and images obtained by the VIMOS/VLT Deep Redshift Survey (VVDS) and the Great Observatories Origins Deep Survey (GOODs). We show that by applying at the same time the angular diameter-redshift and Hubble diagrams to the same sample of objects (i.e. velocity selected galactic discs) one can derive a characteristic chart, the cosmology-evolution diagram, mapping the relation between global cosmological parameters and local structural parameters of discs such as size and luminosity. This chart allows to put constraints on cosmological parameters when general prior information about discs evolution is available. In particular, by assuming that equally rotating large discs cannot be less luminous at z=1 than at present (M(z=1) < M(0)), we find that a flat matter dominated cosmology (Omega_m=1) is excluded at a confidence level of 2sigma and an open cosmology with low mass density (Omega_m = 0.3) and no dark energy contribution is excluded at a confidence level greater than 1 sigma. Inversely, by assuming prior knowledge about the cosmological model, the cosmology-evolution diagram can be used to gain useful insights about the redshift evolution of the structural parameters of baryonic discs hosted in dark matter halos of nearly equal masses.

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arXiv2007

The Arecibo Legacy Fast ALFA Survey: III. HI Source Catalog of the Northern Virgo Cluster Region

We present the first installment of HI sources extracted from the Arecibo Legacy Fast ALFA (ALFALFA) extragalactic survey, initiated in 2005. Sources have been extracted from 3-D spectral data cubes and then examined interactively to yield global HI parameters. A total of 730 HI detections are catalogued within the solid angle 11h44m < R.A.(J2000) < 14h00m and +12deg < Dec.(J2000) < +16deg, and redshift range -1600 \kms < cz < 18000 \kms. In comparison, the HI Parkes All-Sky Survey (HIPASS) detected 40 HI signals in the same region. Optical counterparts are assigned via examination of digital optical imaging databases. ALFALFA HI detections are reported for three distinct classes of signals: (a) detections, typically with S/N > 6.5; (b) high velocity clouds in the Milky Way or its periphery; and (c) signals of lower S/N (to ~ 4.5) which coincide spatially with an optical object of known similar redshift. Although this region of the sky has been heavily surveyed by previous targeted observations based on optical flux-- or size-- limited samples, 69% of the extracted sources are newly reported HI detections. The resultant positional accuracy of HI sources is 20" (median). The median redshift of the sample is ~7000 \kms and its distribution reflects the known local large scale structure including the Virgo cluster. Several extended HI features are found in the vicinity of the Virgo cluster. A small percentage (6%) of HI detections have no identifiable optical counterpart, more than half of which are high velocity clouds in the Milky Way vicinity; the remaining 17 objects do not appear connected to or associated with any known galaxy.

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arXiv2002

Galaxy morphology in the rich cluster Abell 2390

We have analysed images of the field of A2390 obtained with the CFHT and HST. The analysis fits models to bulge and disk components to several hundred galaxies, with about equal samples from the cluster and field. We also have assessed and graded asymmetries in the images. The cluster galaxies are compared in different cluster locations and also compared with field galaxies. We find that the central old population galaxies are bulge-dominated, while disk systems have young populations and are found predominantly in the outer cluster. S0 and bulgy disk galaxies are found throughout, but concentrate in regions of substructure. Disks of cluster blue galaxies are generally brighter and smaller than those in the field. We find that the cluster members have a higher proportion of interacting galaxies than the field sample. Interactions in the cluster and in the field, as well as cluster infall, appear to inhibit star-formation in galaxies.

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