We present evidence that the mid infrared (MIR) is a good tracer of the total
infrared luminosity, L(IR), and star formation rate (SFR), of galaxies up to z
1.3. We use deep MIR images from the ...Infrared Space Observatory (ISO) and the
Spitzer Space Telescope in the Northern field of the Great Observatories
Origins Deep Survey (GOODS-N) together with VLA radio data to compute three
independant estimates of L(IR). The L(IR,MIR) derived from the observed 15
and/or 24 um flux densities using a library of template SEDs, and L(IR,radio),
derived from the radio (1.4 and/or 8.5 GHz) using the radio-far infrared
correlation, agree with a 1-sigma dispersion of 40 %. We use the k-correction
as a tool to probe different parts of the MIR spectral energy distribution
(SED) of galaxies as a function of their redshift and find that on average
distant galaxies present MIR SEDs very similar to local ones. However, in the
redshift range z= 0.4-1.2, L(IR,24um) is in better agreement with L(IR,radio)
than L(IR,15 um) by 20 %, suggesting that the warm dust continuum is a better
tracer of the SFR than the broad emission features due to polycyclic aromatic
hydrocarbons (PAHs). We find marginal evidence for an evolution with redshift
of the MIR SEDs: two thirds of the distant galaxies exhibit rest-frame MIR
colors (L(12 um)/L(7 um) and L(10 um)/L(15 um) luminosity ratios) below the
median value measured for local galaxies. Possible explanations are examined
but these results are not sufficient to constrain the physics of the emitting
regions. We compare three commonly used SED libraries which reproduce the
color-luminosity correlations of local galaxies with our data and discuss
possible refinements to the relative intensities of PAHs, warm dust continuum
and silicate absorption.
The TIR and FUV luminosity functions of galaxies and the related luminosity
densities rho(TIR) and rho(FUV) are known to evolve from z=0 to z~1 but with a
different rate: the galaxy populations ...appear brighter in the past at both
wavelengths but the evolution in TIR is larger than in FUV. It leads to an
increase of the ratio of TIR to FUV luminosity densities rho(TIR)/rho(FUV)
which can be interpreted as a global increase of the dust attenuation from z=0
to z~1. Our aim is to understand the origin of this increase. We focus on
infrared galaxies with L(TIR>10^{11} Lsun at z~0.7 observed by SPITZER/MIPS and
we measure their UV emission at 2310 A from GALEX. These Luminous InfraRed
Galaxies (LIRGs) represent the bulk of the TIR luminosity density at
intermediate redshift. Some evolution of L(TIR)/L(FUV) and therefore of dust
attenuation is found for these galaxies: LIRGs at z=0.7 span a larger range of
L(TIR)/L(FUV) ratios than at z=0 and their mean dust attenuation at FUV is
found ~0.5 mag lower than for their local counterparts. The decrease of dust
attenuation is found lower than that reported in other studies for bright
galaxies selected in UV rest-frame at z=1 and 2. From a semi-quantitative
analysis we find that the slight decrease of dust attenuation for LIRGs at
z=0.7 remains consistent with the increase of rho(TIR)/rho(FUV) with redshift.
We present ultra-deep mid-IR spectra of 48 infrared-luminous galaxies in the GOODS-South field obtained with the InfraRed Spectrograph (IRS) on the Spitzer Space Telescope. These galaxies are ...selected among faint infrared sources (0.14 - 0.5 mJy at 24 um) in two redshift bins (0.76-1.05 and 1.75-2.4) to sample the major contributors to the cosmic infrared background at the most active epochs. We estimate redshifts for 92% of the sample using PAH and Si absorption features. Only few of these galaxies (5% at z~1 and 12% at z~2) have their total infrared luminosity dominated by emission from AGN. The averaged mid-IR spectra of the z~1 LIRGs and of the z~2 ULIRGs are very similar to the averaged spectrum of local starbursts and HII-like ULIRGs, respectively. We find that 6.2um PAH equivalent widths reach a plateau of ~1 um for L(24 mu) < 1E11 L(sun). At higher luminosities, EW (6.2 mu) anti-correlates with L(24 um). Intriguingly, high-z ULIRGs and SMG lie above the local EW (6.2 um) - L(24 um) relationship suggesting that, at a given luminosity, high-z ULIRGs have AGN contributions to their dust emission lower than those of local counterparts. A quantitative analysis of their morphology shows that most of the luminous IR galaxies have morphologies similar to those of IR-quiet galaxies at the same redshift. All z~2 ULIRGs of our sample are IR-excess BzK galaxies and most of them have L(FIR)/L(1600A) ratios higher than those of starburst galaxies at a given UV slope. The ``IR excess'' (Daddi et al. 2007) is mostly due to strong 7.7 um PAH emission and under-estimation of UV dust extinction. On the basis of the AGN-powered L (6 um) continuum measured directly from the mid-IR spectra, we estimate an average intrinsic X-ray AGN luminosity of L(2-10 keV) = (0.1 +/- 0.6) 1E43 erg/s, a value substantially lower than the prediction by Daddi et al. (2007).
We have observed the cluster RX J0152.7-1357 (z\(\sim\)0.83) at 24\(\mu\)m with the Multiband Imaging Photometer for Spitzer (MIPS). We detected twenty-two sources associated with spectroscopically ...confirmed cluster members, while ten more have photometric redshifts compatible with membership. Two of the 32 likely cluster members contain obvious active nuclei while the others are associated with dusty star formation. The median IR-determined star formation rate among the remaining galaxies is estimated at 22 M$_\odot$$ \(yr\)^{-1}$, significantly higher than in previous estimates from optical data. Most of the MIR-emitting galaxies also have optical emission lines, but a few do not and hence have completely hidden bursts of star formation or AGN activity. An excess of MIR-emitting galaxies is seen in the cluster in comparison to the field at the same redshift. The MIR cluster members are more associated with previously detected infalling late type galaxies rather than triggered by the ongoing merging of bigger X-ray clumps. Rough estimates also show that ram pressure may not be capable of stripping the gas away from cluster outskirt galaxies but it may disturb the gas enough to trigger the star formation activity. Harassment can also play a role if for example these galaxies belong to poor galaxy groups. Thus, bursts of star formation occur in the cluster environment and could also help consume the galaxy gas content in addition to ram pressure, harassment or galaxy-galaxy strong interactions.
We investigate whether the mean star formation activity of star-forming galaxies from z=0 to z=0.7 in the GOODS-S field can be reproduced by simple evolution models of these systems. In this case, ...such models might be used as first order references for studies at higher z to decipher when and to what extent a secular evolution is sufficient to explain the star formation history in galaxies. We selected star-forming galaxies at z=0 and at z=0.7 in IR and in UV to have access to all the recent star formation. We focused on galaxies with a stellar mass ranging between 10^{10} and 10^{11} M_sun for which the results are not biased by the selections. We compared the data to chemical evolution models developed for spiral galaxies and originally built to reproduce the main characteristics of the Milky Way and nearby spirals without fine-tuning them for the present analysis. We find a shallow decrease in the specific star formation rate (SSFR) when the stellar mass increases. The evolution of the SSFR characterizing both UV and IR selected galaxies from z=0 to z=0.7 is consistent with the models built to reproduce the present spiral galaxies. There is no need to strongly modify of the physical conditions in galaxies to explain the average evolution of their star formation from z=0 to z=0.7. We use the models to predict the evolution of the star formation rate and the metallicity on a wider range of redshift and we compare these predictions with the results of semi-analytical models.
Many attempts have been made to predict the position of antigenic sites in proteins from certain features of their primary structure. Parameters such as the hydrophilicity, static accessibility and ...mobility of short segments of polypeptide chains have been correlated with the location of continuous epitopes in proteins. Relative scales describing the structural propensity of each of the 20 amino acids have been derived and these are commonly used for constructing structural prediction profiles and for locating the position of epitopes. The predictive value of algorithms based on eight such scales has been compared in the present study, using as antigenicity data base the location of 29 continuous epitopes in four model proteins. A chi 2 statistical analysis showed that a segmental mobility scale and a hydrophilicity scale based on peptide retention times during chromatography gave the highest level of correct predictions.
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.
Oxygen abundances 12+log(O/H) in the interstellar medium of a large sample
of distant (z>0.4) luminous infrared galaxies (LIRGs) were estimated from their
extinction corrected emission-line ratios, ...on the basis of the VLT/FORS2
spectra with good S/N and moderate resolution. These LIRGs were selected from
ISOCAM deep survey fields (CFRS, UDSR, UDSF). They show oxygen abundances
ranging from 8.36 to 8.93, with a median value of 8.67, which is 0.5 lower than
that of the local bright disks (i.e., L*) at the given magnitude. A significant
fraction of distant large disks are indeed LIRGs. Such massive disks could have
formed ~50% of their metals and stellar masses since z~1.
We constrain the past star formation histories of a sample of 25 distant
(z~0.7) luminous infrared galaxies (LIRGs) detected with the mid infrared
cameras ISOCAM and MIPS onboard the ISO and Spitzer ...satellites.
We use high resolution VLT-FORS2 spectroscopy in addition to a comprehensive
library of 200,000 model optical spectra to derive Bayesian likelihood
estimates of the star formation histories of these galaxies based on the
analysis of Balmer absorption lines and the 4000 A break.
The locus of distant LIRGs in the diagram defined by Hdelta_A and D4000 is
roughly comparable to that of local LIRGs observed with IRAS, suggesting that
no trend for an evolution is detected between the local and distant LIRGs. We
obtain similar results when using either the H8 or the H$\delta_A$ Balmer
absorption-line indices in combination with D4000.
We compute a birthrate parameter (b=SFR/) of 4\pm1, confirming that the
distant LIRGs are currently experiencing a major phase of star formation. The
most likely duration of the bursts is 0.10 Gyr, during which the LIRGs produce
5-10 % of their current stellar mass. No evidence is found for successive
starbursts on the scale of a few times $10^7$ yr, such as those predicted by
some numerical simulations of major mergers. However, the large number density
of those galaxies suggest that they could experience between two and four LIRG
phases until the present epoch.
We show that measures of star formation rates (SFRs) for infrared galaxies using either single-band 24 um or extinction-corrected Paschen-alpha luminosities are consistent in the total infrared ...luminosity = L(TIR) ~ 10^10 L_sun range. MIPS 24 micron photometry can yield star formation rates accurately from this luminosity upward: SFR(M_sun/yr) = 7.8 x 10^-10 L(24 um, L_sun) from L(TIR) = 5 x 10^9 L_sun to 10^11 L_sun, and SFR = 7.8 x 10^-10 L(24 um, L_sun) x (7.76 x 10^-11 L(24))^0.048 for higher L(TIR). For galaxies with L(TIR) >= 10^10 L_sun, these new expressions should provide SFRs to within 0.2 dex. For L(TIR) >= 10^11 L_sun, we find that the SFR of infrared galaxies is significantly underestimated using extinction-corrected Pa-alpha (and presumably using any other optical or near infrared recombination lines). As a part of this work, we constructed spectral energy distribution (SED) templates for eleven luminous and ultraluminous purely star forming infrared galaxies (LIRGs and ULIRGs) and over the spectral range 0.4 microns to 30 cm. We use these templates and the SINGS data to construct average templates from 5 microns to 30 cm for infrared galaxies with L(TIR) = 5 x 10^9 to 10^13 L_sun. All of these templates are made available on line.
