187 research outputs found
A 12 μm ISOCAM survey of the ESO-Sculptor field
We present a detailed reduction of a mid-infrared 12 μm (LW10 filter) ISOCAM open time observation performed on the ESOSculptor
Survey field (Arnouts et al. 1997, A&AS, 124, 163). A complete catalogue of 142 sources (120 galaxies and 22 stars),
detected with high significance (equivalent to 5σ), is presented above an integrated flux density of 0.24 mJy. Star/galaxy separation
is performed by a detailed study of colour-colour diagrams. The catalogue is complete to 1 mJy and, below this flux density, the
incompleteness is corrected using two independent methods. The first method uses stars and the second uses optical counterparts of
the ISOCAM galaxies; these methods yield consistent results. We also apply an empirical flux density calibration using stars in the
field. For each star, the 12 μm flux density is derived by fitting optical colours from a multi-band χ^2 to stellar templates (BaSel-2.0)
and using empirical optical-IR colour-colour relations. This article is a companion analysis to our 2007 paper (Rocca-Volmerange
et al. 2007, A&A, 475, 801) where the 12 μm faint galaxy counts are presented and analysed per galaxy type with the evolutionary
code PÉGASE.3
The 12 μm ISO-ESO-Sculptor and 24 μm Spitzer faint counts reveal a population of ULIRGs as dusty massive ellipticals: Evolution by types and cosmic star formation
Context. Multi-wavelength galaxy number counts provide clues to the nature of galaxy evolution. The interpretation per galaxy type of
the mid-IR faint counts obtained with ISO and Spitzer, consistent with the analysis of deep UV-optical-near IR galaxy counts, provide
new constraints on the dust and stellar emission. Discovering the nature of new populations, such as high redshift ultra-luminous
(≥10^(12) L_⊙) infrared galaxies (ULIRGs), is also crucial for understanding galaxy evolution at high redshifts.
Aims. We first present the faint galaxy counts at 12 μm from the catalogue of the ISO-ESO-Sculptor Survey (ISO-ESS) published in a
companion article (Seymour et al. 2007a, A&A, 475, 791). They go down to 0.31 mJy after corrections for incompleteness. We verify
the consistency with the existing ISO number counts at 15 μm. Then we analyse the 12 μm (ISO-ESS) and the 24 μm (Spitzer) faint
counts, to constrain the nature of ULIRGs, the cosmic star formation history and time scales for mass buildup.
Methods. We show that the “normal” scenarios in our evolutionary code PÉGASE, which had previously fitted the deep UV-opticalnear
IR counts, are unsuccessful at 12 μm and 24 μm. We thus propose a new ULIRG scenario adjusted to the observed cumulative
and differential 12 μm and 24 μm counts and based on observed 12 μm and 25 μm IRAS luminosity functions and evolutionary
optical/mid-IR colours from PÉGASE.
Results. We succeed in simultaneously modelling the typical excess observed at 12 μm, 15 μm (ISO), and 24 μm (Spitzer) in the
cumulative and differential counts by only changing 9% of normal galaxies (1/3 of the ellipticals) into ultra-bright dusty galaxies
evolving as ellipticals, and interpreted as distant ULIRGs. These objects present similarities with the population of radio-galaxy hosts
at high redshift. No number density evolution is included in our models even if minor starbursts due to galaxy interactions remain
compatible with our results.
Conclusions. Higher spectral and spatial resolution in the mid-IR, together with submillimeter observations using the future Herschel
observatory, will be useful to confirm these results
The 12 μm ISO-ESO-Sculptor and 24 μm Spitzer faint counts reveal a population of ULIRGs as dusty massive ellipticals: Evolution by types and cosmic star formation
Context. Multi-wavelength galaxy number counts provide clues to the nature of galaxy evolution. The interpretation per galaxy type of
the mid-IR faint counts obtained with ISO and Spitzer, consistent with the analysis of deep UV-optical-near IR galaxy counts, provide
new constraints on the dust and stellar emission. Discovering the nature of new populations, such as high redshift ultra-luminous
(≥10^(12) L_⊙) infrared galaxies (ULIRGs), is also crucial for understanding galaxy evolution at high redshifts.
Aims. We first present the faint galaxy counts at 12 μm from the catalogue of the ISO-ESO-Sculptor Survey (ISO-ESS) published in a
companion article (Seymour et al. 2007a, A&A, 475, 791). They go down to 0.31 mJy after corrections for incompleteness. We verify
the consistency with the existing ISO number counts at 15 μm. Then we analyse the 12 μm (ISO-ESS) and the 24 μm (Spitzer) faint
counts, to constrain the nature of ULIRGs, the cosmic star formation history and time scales for mass buildup.
Methods. We show that the “normal” scenarios in our evolutionary code PÉGASE, which had previously fitted the deep UV-opticalnear
IR counts, are unsuccessful at 12 μm and 24 μm. We thus propose a new ULIRG scenario adjusted to the observed cumulative
and differential 12 μm and 24 μm counts and based on observed 12 μm and 25 μm IRAS luminosity functions and evolutionary
optical/mid-IR colours from PÉGASE.
Results. We succeed in simultaneously modelling the typical excess observed at 12 μm, 15 μm (ISO), and 24 μm (Spitzer) in the
cumulative and differential counts by only changing 9% of normal galaxies (1/3 of the ellipticals) into ultra-bright dusty galaxies
evolving as ellipticals, and interpreted as distant ULIRGs. These objects present similarities with the population of radio-galaxy hosts
at high redshift. No number density evolution is included in our models even if minor starbursts due to galaxy interactions remain
compatible with our results.
Conclusions. Higher spectral and spatial resolution in the mid-IR, together with submillimeter observations using the future Herschel
observatory, will be useful to confirm these results
Gamma Ray Burst Host Galaxies Have `Normal' Luminosities
The galactic environment of Gamma Ray Bursts can provide good evidence about
the nature of the progenitor system, with two old arguments implying that the
burst host galaxies are significantly subluminous. New data and new analysis
have now reversed this picture: (A) Even though the first two known host
galaxies are indeed greatly subluminous, the next eight hosts have absolute
magnitudes typical for a population of field galaxies. A detailed analysis of
the 16 known hosts (ten with red shifts) shows them to be consistent with a
Schechter luminosity function with as expected for
normal galaxies. (B) Bright bursts from the Interplanetary Network are
typically 18 times brighter than the faint bursts with red shifts, however the
bright bursts do not have galaxies inside their error boxes to limits deeper
than expected based on the luminosities for the two samples being identical. A
new solution to this dilemma is that a broad burst luminosity function along
with a burst number density varying as the star formation rate will require the
average luminosity of the bright sample (
or ) to be much greater than the
average luminosity of the faint sample ( or ). This places the bright bursts at distances
for which host galaxies with a normal luminosity will not violate the observed
limits. In conclusion, all current evidence points to GRB host galaxies being
normal in luminosity.Comment: 18 pages, 3 figures, Submitted to ApJLet
Evolution of photoionization and star formation in starbursts and HII galaxies
We analyze the stellar and nebular energy distributions of starbursts using our evolutionary synthesis model PEGASE coupled to the photoionization code CLOUDY. The originality of this study is to relate the evolution and the metallicity of the starburst to the past star formation history of the host galaxy.We compare our model predictions to an observed sample of ~750 starbursts. the most striking feature from line ratio fitting is the decreasing spread in ionization parameter U at high metallicity Z. The best fits of emission line ratios are obtained with a combination of a high- and a low-ionization components. No additional source of ionizing photons --shocks or hidden AGN -- is needed. Colors and equivalent widths are fitted in coherency with emission line ratios. An underlying population is needed, even for small-aperture observations. This evolved population not only reddens the continuum and dilutes the equivalent width of the emission lines, but also participates in the ionization process. Its main effect on line ratios is to maintain a high level of excitation when the burst stops. Models combining underlying populations typical of Hubble sequence galaxies and instantaneous starbursts with ages between 0 and 8 Myr agree satisfactorily with all the data
Deepest Near-IR Surface Photometry of Galaxies in the Local Sphere of Influence
We present near-IR, deep (4 mag deeper than 2MASS) imaging of 56 Local Volume
galaxies. Global parameters such as total magnitudes and stellar masses have
been derived and the new near-IR data combined with existing 21cm and optical
B-band data. We present multiwavelength relations such as the HI mass-to-light
ratio and investigate the maximum total baryonic mass a galaxy can have.Comment: 4 pages, 3 figures, To be published in the proceedings of "Galaxies
in the Local Volume", ed. B. Koribalski, H. Jerje
Severe New Limits on the Host Galaxies of Gamma Ray Bursts
The nature of Gamma Ray Bursts (GRBs) remains a complete mystery, despite the
recent breakthrough discovery of low energy counterparts, although it is now
generally believed that at least most GRBs are at cosmological distances.
Virtually all proposed cosmological models require bursters to reside in
ordinary galaxies. This can be tested by looking inside the smallest GRB error
boxes to see if ordinary galaxies appear at the expected brightness levels.
This letter reports on an analysis of the contents of 26 of the smallest
regions, many from the brightest bursts. These events will have and
small uncertainties about luminosity functions, K corrections and galaxy
evolutions; whereas the recent events with optical transients are much fainter
and hence have high redshifts and grave difficulties in interpretation. This
analysis strongly rejects the many models with peak luminosities of as deduced from the curve with no evolution.
Indeed, the lower limit on acceptable luminosities is . The only possible solution is to either place GRBs at
unexpectedly large distances (with for the faint BATSE bursts) or to
require bursters to be far outside any normal host galaxy.Comment: 17 pages, to be published by ApJ
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