arXiv subjects

Víctor Villar

Publications and source records attributed to Víctor Villar.

5 recordsLinked to original sources

arXiv2016

Properties of galaxies at the faint end of the H$α$ luminosity function at $z\sim0.62$

Studies measuring the star formation rate density, luminosity function, and properties of star-forming galaxies are numerous. However, it exists a gap at $0.5<z<0.8$ in H$α$-based studies. Our main goal is to study the properties of a sample of faint H$α$ emitters at $z\sim0.62$. We focus on their contribution to the faint end of the luminosity function and derived star formation rate density, characterising their morphologies and basic photometric and spectroscopic properties. We use a narrow-band technique in the near-infrared, with a filter centred at 1.06 $μ$m. The data come from ultra-deep VLT/HAWK-I observations in the GOODS-S field with a total of 31.9 h in the narrow-band filter. We perform a visual classification of the sample and study their morphologies from structural parameters available in CANDELS. Our 28 H$α$-selected sample of faint star-forming galaxies reveals a robust faint-end slope of the luminosity function $α=-1.46_{-0.08}^{+0.16}$. The derived star formation rate density at $z\sim0.62$ is $ρ_\mathrm{SFR} = 0.036_{-0.008}^{+0.012} M_{\odot}~\mathrm{yr^{-1}~Mpc^{-3}}$. The sample is mainly composed of disks, but an important contribution of compact galaxies with Sérsic indexes $n\sim2$ display the highest specific star formation rates. The luminosity function at $z\sim0.62$ from our ultra-deep data points towards a steeper $α$ when an individual extinction correction for each object is applied. Compact galaxies are low-mass, low-luminosity, and starburst-dominated objects with a light profile in an intermediate stage from early to late types.

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arXiv2014

Recent stellar mass assembly of low-mass star-forming galaxies at redshifts 0.3 < z < 0.9

The epoch when low-mass star forming galaxies (LMSFGs) form the bulk of their stellar mass is uncertain. While some models predict an early formation, others favor a delayed scenario until later ages of the universe. We present constraints on the star formation histories (SFHs) of a sample of LMSFGs obtained through the analysis of their spectral energy distributions using a novel approach that (1) consistently combines photometric (broadband) and spectroscopic (equivalent widths of emission lines) data, and (2) uses physically motivated SFHs with non-uniform variations of the star formation rate (SFR) as a function of time. The sample includes 31 spectroscopically confirmed LMSFGs (7.3 < log M*/Msun < 8.0) at 0.3 < z_spec < 0.9 in the Extended-Chandra Deep Field-South field (E-CDF-S). Among them, 24 were selected with photometric stellar mass log M*/Msun < 8.0, 0.3 < z_phot < 1.0, and NB816 < 26 AB mag; the remaining 7 were selected as blue compact dwarfs (BCDs) within the same photometric redshift and magnitude ranges. We also study a secondary sample of 43 more massive spectroscopically confirmed galaxies (8.0 < log M*/Msun < 9.1), selected with the same criteria. The SFRs and stellar masses derived for both samples place our targets on the standard main sequence of star forming galaxies. The median SFH of LMSFGs at intermediate redshifts appears to form 90% of the median stellar mass inferred for the sample in the 0.5-1.8 Gyr immediately preceding the observation. These results suggest a recent stellar mass assembly for LMSFGs, consistent with the cosmological downsizing trends. We find similar median SFH timescales for the more massive secondary sample.

astro-ph.GA↗

arXiv2014

Selection of AGN candidates in the GOODS-South Field through SPITZER/MIPS 24 microns variability

We present a study of galaxies showing mid-infrared variability in the deepest Spitzer/MIPS 24 $μ$m surveys in the GOODS-South field. We divide the dataset in epochs and subepochs to study the long-term (months-years) and the short-term (days) variability. We use a $χ^2$-statistics method to select AGN candidates with a probability $\leq$ 1% that the observed variability is due to statistical errors alone. We find 39 (1.7% of the parent sample) sources that show long-term variability and 55 (2.2% of the parent sample) showing short-term variability. We compare our candidates with AGN selected in the X-ray and radio bands, and AGN candidates selected by their IR emission. Approximately, 50% of the MIPS 24 $μ$m variable sources would be identified as AGN with these other methods. Therefore, MIPS 24 $μ$m variability is a new method to identify AGN candidates, possibly dust obscured and low luminosity AGN that might be missed by other methods. However, the contribution of the MIPS 24 $μ$m variable identified AGN to the general AGN population is small ($\leq$ 13%) in GOODS-South.

astro-ph.GA↗

arXiv2014

Selection of AGN candidates in the GOODS-South Field through SPITZER/MIPS 24 $μ$m variability

We present a study of galaxies showing mid-infrared variability in data taken in the deepest Spitzer/MIPS 24 $μ$m surveys in the GOODS-South field. We divide the dataset in epochs and subepochs to study the long-term (months-years) and the short-term (days) variability. We use a $χ^2$-statistics method to select AGN candidates with a probability $\leq$ 1% that the observed variability is due to statistical errors alone. We find 39 (1.7% of the parent sample) sources that show long-term variability and 55 (2.2% of the parent sample) showing short-term variability. That is, 0.03 sources $\times$ arcmin$^{-2}$ for both, long-term and short-term variable sources. After removing the expected number of false positives inherent to the method, the estimated percentages are 1.0% and 1.4% of the parent sample for the long-term and short-term respectively. We compare our candidates with AGN selected in the X-ray and radio bands, and AGN candidates selected by their IR emission. Approximately, 50% of the MIPS 24 $μ$m variable sources would be identified as AGN with these other methods. Therefore, MIPS 24 $μ$m variability is a new method to identify AGN candidates, possibly dust obscured and low luminosity AGN, that might be missed by other methods. However, the contribution of the MIPS 24 $μ$m variable identified AGN to the general AGN population is small ($\leq$ 13%) in GOODS-South.

astro-ph.GA↗

arXiv2007

The Halpha-based Star Formation Rate Density of the Universe at z=0.84

We present the results of an Halpha near-infrared narrow-band survey searching for star-forming galaxies at redshift z=0.84. This work is an extension of our previous narrow-band studies in the optical at lower redshifts. After removal of stars and redshift interlopers (using spectroscopic and photometric redshifts), we build a complete sample of 165 Halpha emitters in the Extended Groth strip and GOODS-N fields with L(Halpha)>10^41 erg/s. We compute the Halpha luminosity function at z=0.84 after corrections for [NII] flux contamination, extinction, systematic errors, and incompleteness. Our sources present an average dust extinction of A(Halpha)=1.5 mag. Adopting Halpha as a surrogate for the instantaneous star formation rate (SFR), we measure a extinction-corrected SFR density of 0.17+-0.03 M_sun/yr/Mpc3. Combining this result to our prior measurements at z=0.02, 0.24, and 0.40, we derive an Halpha-based evolution of the SFR density proportional to (1+z)^beta with beta=3.8+-0.5. This evolution is consistent with that derived by other authors using different SFR tracers.

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