arXiv subjects

Veronique Buat

Publications and source records attributed to Veronique Buat.

At least 37 records · Page 2Linked to original sources

arXiv2017

Photometric redshifts for the next generation of deep radio continuum surveys - I: Template fitting

We present a study of photometric redshift performance for galaxies and active galactic nuclei detected in deep radio continuum surveys. Using two multi-wavelength datasets, over the NOAO Deep Wide Field Survey Boötes and COSMOS fields, we assess photometric redshift (photo-z) performance for a sample of $\sim 4,500$ radio continuum sources with spectroscopic redshifts relative to those of $\sim 63,000$ non radio-detected sources in the same fields. We investigate the performance of three photometric redshift template sets as a function of redshift, radio luminosity and infrared/X-ray properties. We find that no single template library is able to provide the best performance across all subsets of the radio detected population, with variation in the optimum template set both between subsets and between fields. Through a hierarchical Bayesian combination of the photo-z estimates from all three template sets, we are able to produce a consensus photo-z estimate which equals or improves upon the performance of any individual template set.

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arXiv2016

Far-reaching Dust Distribution in Galaxy Disks

In most studies of dust in galaxies, dust is only detected from its emission to approximately the optical radius of the galaxy. By combining the signal of 110 spiral galaxies observed as part of the Herschel Reference Survey, we are able to improve our sensitivity by an order-of-magnitude over that for a single object. Here we report the direct detection of dust from its emission that extends out to at least twice the optical radius. We find that the distribution of dust is consistent with an exponential at all radii with a gradient of ~-1.7 dex R$_{25}^{-1}$. Our dust temperature declines linearly from ~25 K in the centre to 15 K at R$_{25}$ from where it remains constant out to ~2.0 R$_{25}$. The surface-density of dust declines with radius at a similar rate to the surface-density of stars but more slowly than the surface-density of the star-formation rate. Studies based on dust extinction and reddening of high-redshift quasars have concluded that there are substantial amounts of dust in intergalactic space. By combining our results with the number counts and angular correlation function from the SDSS, we show that with Milky Way type dust we can explain the reddening of the quasars by the dust within galactic disks alone. Given the uncertainties in the properties of any intergalactic dust, we cannot rule out its existence, but our results show that statistical investigations of the dust in galactic halos that use the reddening of high-redshift objects must take account of the dust in galactic disks.

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arXiv2015

Herschel Observations of Major Merger Pairs at z=0: Dust Mass and Star Formation

We present Herschel PACS $\&$ SPIRE far-infrared (FIR) and sub-mm imaging observations for a large K-band selected sample of 88 close major-merger pairs of galaxies (H-KPAIRs) in 6 photometric bands (70, 100, 160, 250, 350, and 500 $μm$). Among 132 spiral galaxies in the 44 spiral-spiral (S$+$S) pairs and 44 spiral-elliptical (S$+$E) pairs, 113 are detected in at least one Herschel band. Star formation rate (SFR) and dust mass ($M_{\rm dust}$) are derived from the IR SED fitting. Mass of total gas ($M_{\rm gas}$) is estimated by assuming a constant dust-to-gas mass ratio of 0.01. Star forming spiral galaxies (SFGs) in S$+$S pairs show significant enhancements in both specific star formation rate (sSFR) and star formation efficiency (SFE), while having nearly the same gas mass, compared to control galaxies. On the other hand, for SFGs in S$+$E pairs, there is no significant sSFR enhancement and the mean SFE enhancement is significantly lower than that of SFGs in S$+$S pairs. This suggests an important role for the disc-disc collision in the interaction induced star formation. The $M_{\rm gas}$ of SFGs in S$+$E pairs is marginally lower than that of their counterparts in both S$+$S pairs and the control sample. Paired galaxies with and without interaction signs do not differ significantly in their mean sSFR and SFE. As found in previous works, this much larger sample confirms the primary and secondary spirals in S+S pairs follow a Holmberg effect correlation on sSFR.

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arXiv2015

Evolution of mid-infrared galaxy luminosity functions from the entire AKARI NEP-Deep field with new CFHT photometry

We present infrared galaxy luminosity functions (LFs) in the AKARI North Ecliptic Pole (NEP) deep field using recently-obtained, wider CFHT optical/near-IR images. AKARI has obtained deep images in the mid-infrared (IR), covering 0.6 deg$^2$ of the NEP deep field. However, our previous work was limited to the central area of 0.25 deg$^2$ due to the lack of optical coverage of the full AKARI NEP survey. To rectify the situation, we recently obtained CFHT optical and near-IR images over the entire AKARI NEP deep field. These new CFHT images are used to derive accurate photometric redshifts, allowing us to fully exploit the whole AKARI NEP deep field. AKARI's deep, continuous filter coverage in the mid-IR wavelengths (2.4, 3.2, 4.1, 7, 9, 11, 15, 18, and 24$μ$m) exists nowhere else, due to filter gaps of other space telescopes. It allows us to estimate restframe 8$μ$m and 12$μ$m luminosities without using a large extrapolation based on spectral energy distribution (SED) fitting, which was the largest uncertainty in previous studies. Total infrared luminosity (TIR) is also obtained more reliably due to the superior filter coverage. The resulting restframe 8$μ$m, 12$μ$m, and TIR LFs at $0.15<z<2.2$ are consistent with previous works, but with reduced uncertainties, especially at the high luminosity-end, thanks to the wide field coverage. In terms of cosmic infrared luminosity density ($Ω_{\mathrm{IR}}$), we found that the $Ω_{\mathrm{IR}}$ evolves as $\propto (1+z)^{4.2\pm 0.4}$.

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arXiv2015

GOODS-HERSCHEL: star formation, dust attenuation and the FIR-radio correlation on the Main Sequence of star-forming galaxies up to z~4

We use deep panchromatic datasets in the GOODS-N field, from GALEX to the deepest Herschel far-infrared and VLA radio continuum imaging, to explore, using mass-complete samples, the evolution of the star formation activity and dust attenuation of star-forming galaxies to z~4. Our main results can be summarized as follows: i) the slope of the SFR-M correlation is consistent with being constant, and equal to ~0.8 at least up to z~1.5, while its normalization keeps increasing with redshift; ii) for the first time here we are able to explore the FIR-radio correlation for a mass-selected sample of star-forming galaxies: the correlation does not evolve up to z~4; iii) we confirm that galaxy stellar mass is a robust proxy for UV dust attenuation in star-forming galaxies, with more massive galaxies being more dust attenuated, strikingly we find that this attenuation relation evolves very weakly with redshift, the amount of dust attenuation increasing by less than 0.3 magnitudes over the redshift range [0.5-4] for a fixed stellar mass, as opposed to a tenfold increase of star formation rate; iv) the correlation between dust attenuation and the UV spectral slope evolves in redshift, with the median UV spectral slope of star-forming galaxies becoming bluer with redshift. By z~3, typical UV slopes are inconsistent, given the measured dust attenuation, with the predictions of commonly used empirical laws. Finally, building on existing results, we show that gas reddening is marginally larger (by a factor of around 1.3) than stellar reddening at all redshifts probed, and also that the amount of dust attenuation at a fixed ISM metallicity increases with redshift. We speculate that our results support evolving ISM conditions of typical star-forming galaxies such that at z~1.5 Main Sequence galaxies have ISM conditions getting closer to those of local starbursts.

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arXiv2014

Impact of star formation history on the measurement of star formation rates

Context. Measuring star formation across the Universe is key to constrain models of galaxy formation and evolution. Yet, determining the SFR (star formation rate) of galaxies remains a challenge. Aims. In this paper we investigate in isolation the impact of a variable star formation history on the measurement of the SFR. Methods. We combine 23 state-of-the-art hydrodynamical simulations of 1<z<2 galaxies on the main sequence with the cigale spectral energy distribution modelling code. This allows us to generate synthetic spectra every 1 Myr for each simulation, taking the stellar populations and the nebular emission into account. Using these spectra, we estimate the SFR from classical estimators which we compare with the true SFR we know from the simulations. Results. We find that except for the Lyman continuum, classical SFR estimators calibrated over 100 Myr overestimate the SFR from ~25% in the FUV band to ~65% in the U band. Such biases are due 1) to the contribution of stars living longer than 100 Myr, and 2) to variations of the SFR on timescales longer than a few tens of Myr. Rapid variations of the SFR increase the uncertainty on the determination of the instantaneous SFR but have no long term effect. Conclusions. The discrepancies between the true and estimated SFR may explain at least part of the tension between the integral of the star formation rate density and the stellar mass density at a given redshift. To reduce possible biases, we suggest to use SFR estimators calibrated over 1 Gyr rather than the usually adopted 100 Myr timescales.

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arXiv2013

A new HST/Herschel deep field at the North Ecliptic Pole: preparing the way for JWST, SPICA and Euclid

We propose a co-ordinated multi-observatory survey at the North Ecliptic Pole. This field is the natural extragalactic deep field location for most space observatories (e.g. containing the deepest Planck, WISE and eROSITA data), is in the continuous viewing zones for e.g. Herschel, HST, JWST, and is a natural high-visibility field for the L2 halo orbit of SPICA with deep and wide-field legacy surveys already planned. The field is also a likely deep survey location for the forthcoming Euclid mission. It is already a multi-wavelength legacy field in its own right (e.g. AKARI, LOFAR, SCUBA-2): the outstanding and unparalleled continuous mid-IR photometric coverage in this field and nowhere else enables a wide range of galaxy evolution diagnostics unachievable in any other survey field, by spanning the wavelengths of redshifted PAH and silicate features and the peak energy output of AGN hot dust. We argue from the science needs of Euclid and JWST, and from the comparative multiwavelength depths, that the logical approach is (1) a deep (H-UDF) UV/optical tile in the NEP over ~10 square arcminutes, and (2) an overlapping wide-field UV/optical HST survey tier covering >100 square arcminutes, with co-ordinated submm SPIRE mapping up to or beyond the submm point source confusion limit over a wider area and PACS data over the shallower HST tier.

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arXiv2012

GOODS-Herschel: Impact of Active Galactic Nuclei and Star Formation Activity on Infrared Spectral Energy Distributions at High Redshift

We explore the effects of active galactic nuclei (AGN) and star formation activity on the infrared (0.3-1000 microns) spectral energy distributions of luminous infrared galaxies from z = 0.5 to 4.0. We have compiled a large sample of 151 galaxies selected at 24 microns (S24 > 100 uJy) in the GOODS-N and ECDFS fields for which we have deep Spitzer IRS spectroscopy, allowing us to decompose the mid-IR spectrum into contributions from star formation and AGN activity. A significant portion (~25%) of our sample is dominated by an AGN in the mid-IR. Based on the mid-IR classification, we divide our full sample into four sub-samples: z~1 star-forming (SF) sources; z~2 SF sources; AGN with clear 9.7 micron silicate absorption; and AGN with featureless mid-IR spectra. From our large spectroscopic sample and wealth of multi-wavelength data, including deep Herschel imaging at 100, 160, 250, 350, and 500 microns, we use 95 galaxies with complete spectral coverage to create a composite spectral energy distribution (SED) for each sub-sample. We then fit a two-temperature component modified blackbody to the SEDs. We find that the IR SEDs have similar cold dust temperatures, regardless of the mid-IR power source, but display a marked difference in the warmer dust temperatures. We calculate the average effective temperature of the dust in each sub-sample and find a significant (~20 K) difference between the SF and AGN systems. We compare our composite SEDs to local templates and find that local templates do not accurately reproduce the mid-IR features and dust temperatures of our high redshift systems. High redshift IR luminous galaxies contain significantly more cool dust than their local counterparts. We find that a full suite of photometry spanning the IR peak is necessary to accurately account for the dominant dust temperature components in high redshift IR luminous galaxies.

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arXiv2012

Evidence for a wide range of UV obscuration in z ~ 2 dusty galaxies from the GOODS-Herschel survey

Dusty galaxies at z ~ 2 span a wide range of relative brightness between rest-frame mid-infrared (8um) and ultraviolet wavelengths. We attempt to determine the physical mechanism responsible for this diversity. Dust-obscured galaxies (DOGs), which have rest-frame mid-IR to UV flux density ratios > 1000, might be abnormally bright in the mid-IR, perhaps due to prominent AGN and/or PAH emission, or abnormally faint in the UV. We use far-infrared data from the GOODS-Herschel survey to show that most DOGs with 10^12 L_Sun < L_IR < 10^13 L_Sun are not abnormally bright in the mid-IR when compared to other dusty galaxies with similar IR (8--1000um) luminosities. We observe a relation between the median IR to UV luminosity ratios and the median UV continuum power-law indices for these galaxies, and we find that only 24% have specific star formation rates which indicate the dominance of compact star-forming regions. This circumstantial evidence supports the idea that the UV- and IR-emitting regions in these galaxies are spatially coincident, which implies a connection between the abnormal UV faintness of DOGs and dust obscuration. We conclude that the range in rest-frame mid-IR to UV flux density ratios spanned by dusty galaxies at z ~ 2 is due to differing amounts of UV obscuration. Of galaxies with these IR luminosities, DOGs are the most obscured. We attribute differences in UV obscuration to either: 1) differences in the degree of alignment between the spatial distributions of dust and massive stars, or 2) differences in the total dust content.

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arXiv2012

Far-Ultraviolet and Far-Infrared Bivariate Luminosity Function of Galaxies: Complex Relation between Stellar and Dust Emission

Far-ultraviolet (FUV) and far-infrared (FIR) luminosity functions (LFs) of galaxies show a strong evolution from $z = 0$ to $z = 1$, but the FIR LF evolves much stronger than the FUV one. The FUV is dominantly radiated from newly formed short-lived OB stars, while the FIR is emitted by dust grains heated by the FUV radiation field. It is known that dust is always associated with star formation activity. Thus, both FUV and FIR are tightly related to the star formation in galaxies, but in a very complicated manner. In order to disentangle the relation between FUV and FIR emissions, we estimate the UV-IR bivariate LF (BLF) of galaxies with {\sl GALEX} and {\sl AKARI} All-Sky Survey datasets. Recently we invented a new mathematical method to construct the BLF with given marginals and prescribed correlation coefficient. This method makes use of a tool from mathematical statistics, so called "copula". The copula enables us to construct a bivariate distribution function from given marginal distributions with prescribed correlation and/or dependence structure. With this new formulation and FUV and FIR univariate LFs, we analyze various FUV and FIR data with {\sl GALEX}, {\sl Spitzer}, and {\sl AKARI} to estimate the UV-IR BLF. The obtained BLFs naturally explain the nonlinear complicated relation between FUV and FIR emission from star-forming galaxies. Though the faint-end of the BLF was not well constrained for high-$z$ samples, the estimated linear correlation coefficient $ρ$ was found to be very high, and is remarkably stable with redshifts (from 0.95 at $z = 0$ to 0.85 at $z = 1.0$). This implies the evolution of the UV-IR BLF is mainly due to the different evolution of the univariate LFs, and may not be controlled by the dependence structure.

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arXiv2011

CIGALEMC: Galaxy Parameter Estimation using a Markov Chain Monte Carlo Approach with Cigale

We introduce a fast Markov Chain Monte Carlo (MCMC) exploration of the astrophysical parameter space using a modified version of the publicly available code CIGALE (Code Investigating GALaxy emission). The original CIGALE builds a grid of theoretical Spectral Energy Distribution (SED) models and fits to photometric fluxes from Ultraviolet (UV) to Infrared (IR) to put contraints on parameters related to both formation and evolution of galaxies. Such a grid-based method can lead to a long and challenging parameter extraction since the computation time increases exponentially with the number of parameters considered and results can be dependent on the density of sampling points, which must be chosen in advance for each parameter. Markov Chain Monte Carlo methods, on the other hand, scale approximately linearly with the number of parameters, allowing a faster and more accurate exploration of the parameter space by using a smaller number of efficiently chosen samples. We test our MCMC version of the code CIGALE (called CIGALEMC) with simulated data. After checking the ability of the code to retrieve the input parameters used to build the mock sample, we fit theoretical SEDs to real data from the well known and studied SINGS sample. We discuss constraints on the parameters and show the advantages of our MCMC sampling method in terms of accuracy of the results and optimization of CPU time.

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arXiv2010

Dust Attenuation in UV-selected Starbursts at High Redshift and their Local Counterparts: Implications for the Cosmic Star Formation Rate Density

We present a new analysis of the dust obscuration in starburst galaxies at low and high redshift. This study is motivated by our unique sample of the most extreme UV-selected starburst galaxies in the nearby universe (z<0.3), found to be good analogs of high-redshift Lyman Break Galaxies (LBGs) in most of their physical properties. We find that the dust properties of the Lyman Break Analogs (LBAs) are consistent with the relation derived previously by Meurer et al. (M99) that is commonly used to dust-correct star formation rate measurements at a very wide range of redshifts. We directly compare our results with high redshift samples (LBGs, BzK, and sub-mm galaxies at z=2-3) having IR data either from Spitzer or Herschel. The attenuation in typical LBGs at z=2-3 and LBAs is very similar. Because LBAs are much better analogs to LBGs compared to previous local star-forming samples, including M99, the practice of dust-correcting the SFRs of high redshift galaxies based on the local calibration is now placed on a much more solid ground. We illustrate the importance of this result by showing how the locally calibrated relation between UV measurements and extinction is used to estimate the integrated, dust-corrected star formation rate density at z=2-6.

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arXiv2010

The Herschel-SPIRE Legacy Survey (HSLS): the scientific goals of a shallow and wide submillimeter imaging survey with SPIRE

A large sub-mm survey with Herschel will enable many exciting science opportunities, especially in an era of wide-field optical and radio surveys and high resolution cosmic microwave background experiments. The Herschel-SPIRE Legacy Survey (HSLS), will lead to imaging data over 4000 sq. degrees at 250, 350, and 500 micron. Major Goals of HSLS are: (a) produce a catalog of 2.5 to 3 million galaxies down to 26, 27 and 33 mJy (50% completeness; 5 sigma confusion noise) at 250, 350 and 500 micron, respectively, in the southern hemisphere (3000 sq. degrees) and in an equatorial strip (1000 sq. degrees), areas which have extensive multi-wavelength coverage and are easily accessible from ALMA. Two thirds of the of the sources are expected to be at z > 1, one third at z > 2 and about a 1000 at z > 5. (b) Remove point source confusion in secondary anisotropy studies with Planck and ground-based CMB data. (c) Find at least 1200 strongly lensed bright sub-mm sources leading to a 2% test of general relativity. (d) Identify 200 proto-cluster regions at z of 2 and perform an unbiased study of the environmental dependence of star formation. (e) Perform an unbiased survey for star formation and dust at high Galactic latitude and make a census of debris disks and dust around AGB stars and white dwarfs.

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arXiv2010

Stellar Mass and Velocity Functions of Galaxies: Backward evolution and the fate of Milky Way siblings

We attempt in this paper to check the consistency of the observed Stellar Mass Function (SMF), SFR functions and the cosmic star formation rate density with simple backward evolutionary models. Starting from observed SMF for star-forming galaxies, we use backwards models to predict the evolution of a number of quantities, such as the SFR function, the cosmic SFR density and the Velocity Function. The velocity being a parameter attached to a galaxy during its history (contrary to the stellar mass), this approach allows us to quantify the number density evolution of galaxies of a given velocity, e.g. of the Milky Way siblings. Observations suggest that the SMF of star forming galaxies is constant between redshift 0 and 1. In order to reproduce this result, we must quench star formation in a number of star forming galaxies. The SMF of these quenched galaxies is consistent with available data concerning the increase in the population of quiescent galaxies in the same redshift interval. The SMF of quiescent galaxies is then mainly determined by the distribution of active galaxies that must stop star formation, with a modest mass redistribution during mergers. The cosmic SFR density, and the evolution of the SFR functions are relatively well recovered, although they provide some clue for a small evolution of the SMF of star forming galaxies at the lowest redshifts. We thus consider that we have obtained in a simple way a relatively consistent picture of the evolution of galaxies at intermediate redshifts. We note that if this picture is correct, 50 percent of the Milky-Way sisters (galaxies with the same velocity as our Galaxy, i.e. 220 km/s) have quenched their star formation since redshift 1 (and an even larger fraction for larger velocities). We discuss the processes that might be responsible for this transformation.

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arXiv2008

Deep 15um AKARI observations in the CDFS: estimating dust luminosities for a MIR-selected sample and for Lyman Break Galaxies and the evolution of L(dust)/L(UV) with the redshift

Deep observations of the CDFS have been secured at 15um with AKARI/IRC infrared space telescope (ESA open time). From these observations, we define a sample of MIR-selected galaxies at 15um and we also obtain 15um flux densities for a sample of LBGs at z=1 already observed at 24um with Spitzer/MIPS. Number counts for the MIR-selected sample show a bump around a 15um flux density of 0.2mJy that can be attributed to galaxies at z>0.4 and at z>0.8 for the fainter part of the bump. This bump seems to be shifted as compared to other works and a possible origin can be the Cosmic variance. Thanks to this dataset, we have tested, on the two above samples at z=1, the validity of the conversions from monochromatic luminosities nu.f(nu) at a rest-frame wavelength of 8um by a comparison with total dust luminosities estimated from Spitzer rest-frame 12um data that we use as a reference. We find that the 8um dust luminosities are not all consistent and that some of them are better when compared to L(dust) evaluated from longer wavelength luminosities. We also find that the rest-frame 8um luminosities provide globally good estimates of L(dust). By comparing our data for the two samples to several libraries of SEDs, we find that models can explain the diversity of the observed f(24)/f(15) ratio quite reasonably for the MIR-selected sample and better for the LBG sample which are less dispersed than the MIR selection. However, when we analyse the luminosity dependence of this ratio, we find important discrepancies. Finally, we revisit the evolution of L(dust)/L(UV) ratio with the redshift z by re-calibrating previous L(dust) at z=2 based on our results and added new data points at higher redshifts. The decreasing trend is amplified as compared to the previous estimate.

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arXiv2007

IR and UV Galaxies at z=0.6 -- Evolution of Dust Attenuation and Stellar Mass as Revealed by SWIRE and GALEX

We study dust attenuation and stellar mass of $\rm z\sim 0.6$ star-forming galaxies using new SWIRE observations in IR and GALEX observations in UV. Two samples are selected from the SWIRE and GALEX source catalogs in the SWIRE/GALEX field ELAIS-N1-00 ($Ω= 0.8$ deg$^2$). The UV selected sample has 600 galaxies with photometric redshift (hereafter photo-z) $0.5 \leq z \leq 0.7$ and NUV$\leq 23.5$ (corresponding to $\rm L_{FUV} \geq 10^{9.6} L_\sun$). The IR selected sample contains 430 galaxies with $f_{24μm} \geq 0.2$ mJy ($\rm L_{dust} \geq 10^{10.8} L_\sun$) in the same photo-z range. It is found that the mean $\rm L_{dust}/L_{FUV}$ ratios of the z=0.6 UV galaxies are consistent with that of their z=0 counterparts of the same $\rm L_{FUV}$. For IR galaxies, the mean $\rm L_{dust}/L_{FUV}$ ratios of the z=0.6 LIRGs ($\rm L_{dust} \sim 10^{11} L_\sun$) are about a factor of 2 lower than local LIRGs, whereas z=0.6 ULIRGs ($\rm L_{dust} \sim 10^{12} L_\sun$) have the same mean $\rm L_{dust}/L_{FUV}$ ratios as their local counterparts. This is consistent with the hypothesis that the dominant component of LIRG population has changed from large, gas rich spirals at z$>0.5$ to major-mergers at z=0. The stellar mass of z=0.6 UV galaxies of $\rm L_{FUV} \leq 10^{10.2} L_\sun$ is about a factor 2 less than their local counterparts of the same luminosity, indicating growth of these galaxies. The mass of z=0.6 UV lunmous galaxies (UVLGs: $\rm L_{FUV} > 10^{10.2} L_\sun$) and IR selected galaxies, which are nearly exclusively LIRGs and ULIRGs, is the same as their local counterparts.

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arXiv2006

The Evolution of the Visible and Hidden Star Formation in the Universe: Implication from the Luminosity Functions at FUV and FIR

Based on GALEX and IRAS/Spitzer datasets, we have found that both FUV and FIR luminosity functions (LFs) show a strong evolution from z=0 to z=1, but the FIR LF evolves much stronger than the FUV one. Consequently, the FIR/FUV luminosity density ratio increases from 4 (z=0) to 15 (z=1). It means that more than 80% of the star-forming activity in the Universe is hidden by dust at z=1. To explore this issue further, we have performed a combined analysis of the galaxy sample in FUV and FIR. For the Local Universe we used GALEX-IRAS sample, whereas at z=1 we used the Lyman-break galaxy sample selected by GALEX bands constructed by Burgarella et al. (2005), which is known to be representative of visible (i.e., non-obscured) star-forming galaxies at z=1. From these datasets, we constructed the LFs of the FUV-selected galaxies by the survival analysis to, take into account the upper-limit data properly. We discovered that the FIR LF of the Lyman-break galaxies show a significant evolution comparing with the local FIR LF, but it is a factor of 2-3 lower than the global FIR LF (Le Floc'h et al. 2005). This indicates that the evolution of visible galaxies is not strong enough to explain the drastic evolution of the FIR LF. Namely, a FIR-luminous, rapidly diminishing population of galaxies is required.

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arXiv2006

Radial variation of attenuation and star formation in the largest late-type disks observed with GALEX

For a sample of 43 nearby, late-type galaxies, we have investigated the radial variation of both the current star formation rate and the dust-induced UV light attenuation. To do this we have cross-correlated IRAS images and GALEX observations for each of these galaxies, and compiled observations of the gas (CO and HI) and metal-abundance gradients found in the literature. We find that attenuation correlates with metallicity. We then use the UV profiles, corrected for attenuation, to study several variants of the Schmidt law and conclude that our results are compatible with a simple law similar to the one of Kennicutt but extending smoothly to lower surface densities, but with considerable scatter. We do not detect an abrupt break in the UV light at the threshold radius derived from H-alpha data (at which the H-alpha profile shows a break and beyond which only a few HII regions are usually found). We interpret the H-alpha sudden break not as a change in the star formation regime (as often suggested) but as the vanishingly small number of ionizing stars corresponding to low levels of star formation.

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