J. Iglesias-Páramo

Dust attenuation in the nearby universe: a comparison between galaxies selected in the ultraviolet and in the far-infrared

We compare the dust attenuation properties of two samples of galaxies purely selected in the Galaxy Evolution Explorer (GALEX) near-ultraviolet band (NUV; 1750-2750 A, λmean = 2310 A) and in the far-infrared (FIR) at 60 μm. These samples are built using the GALEX and IRAS sky surveys over ~600 deg2. The NUV-selected sample contains 95 galaxies detected down to NUV = 16 mag (AB system). Eighty-three galaxies in this sample are spiral or irregular, and only two of them are not detected at 60 μm. The FIR-selected sample is built from the IRAS PSCz survey, which is complete down to 0.6 Jy. Among the 163 sources, we select 118 star-forming galaxies that are well measured by IRAS; all but one are detected in NUV, and 14 galaxies are not detected in the far-ultraviolet band (FUV; 1350-1750 A, λmean = 1530 A). The dust-to-ultraviolet (NUV and FUV) flux ratio is calibrated to estimate the dust attenuation at both wavelengths. The median value of the attenuation in NUV is found to be ~1 mag for the NUV-selected sample, versus ~2 mag for the FIR-selected one. Within both samples, the dust attenuation is found to correlate with the luminosity of the galaxies. Almost all the NUV-selected galaxies and two-thirds of the FIR-selected sample exhibit a lower dust attenuation than expected from the tight relation found previously for starburst galaxies between dust attenuation and the slope of the ultraviolet continuum. The situation is reversed for the remaining third of the FIR-selected galaxies: their extinction is higher than that deduced from their FUV - NUV color and the relation for starbursts.

Star formation and dust attenuation properties in galaxies from a statistical ultraviolet-to-far-infrared analysis

We study two galaxies samples selected in near-ultraviolet (NUV) and in far-infrared (FIR) for which the spectral energy distributions (SEDs) from the far-UV (FUV) to the FIR are available. We compared the observed SEDs to modelled SEDs with several star formation histories (SFHs; decaying star formation rate plus burst) and dust attenuation laws (power law + 2175 A bump). The Bayesian method allows one to estimate statistically the best parameters by comparing each observed SED to the full set of 82 800 models. We reach the conclusion that the UV dust attenuation cannot be estimated correctly from SED analysis if the FIR information is not used. The dispersion is larger than with the FIR data. The distribution is also not symmetrically distributed about zero: there is an overestimation for UV-selected galaxies and an underestimation for FIR-selected galaxies. The output from the analysis process suggests that UV-selected galaxies have attenuation laws in average similar to the Large Magellanic Cloud extinction law while FIR-selected galaxies attenuation laws resemble more the Milky Way extinction law. The dispersion about the average relation in the log (F dust /F FUV ) versus FUV-NUV diagram (once the main relation with FUV - NUV accounted for) is explained by two other parameters: the slope of the attenuation law and the instantaneous birthrate parameters b 0 for UV-selected galaxies and the same ones plus the strength of the bump for the FIR-selected galaxies. We propose a recipe to estimate the UV dust attenuation for UV galaxies only (that should only be used whenever the FIR information is not available because the resulting A FUV is poorly defined with an uncertainty of about 0.32): A FUV = 1.4168 (FUV - NUV) 2 + 0.3298 (NUV - I) 2 + 2.1207 (FUV - NUV) + 2.7465 (NUV - I) + 5.8408.

Star formation and dust attenuation properties in galaxies from a statistical UV-to-FIR analysis

We study two galaxies samples selected in near-ultraviolet (NUV) and in far-infrared (FIR) for which the spectral energy distributions (SEDs) from the far-UV (FUV) to the FIR are available. We compared the observed SEDs to modelled SEDs with several star formation histories (SFHs; decaying star formation rate plus burst) and dust attenuation laws (power law + 2175 A bump). The Bayesian method allows one to estimate statistically the best parameters by comparing each observed SED to the full set of 82 800 models. We reach the conclusion that the UV dust attenuation cannot be estimated correctly from SED analysis if the FIR information is not used. The dispersion is larger than with the FIR data. The distribution is also not symmetrically distributed about zero: there is an overestimation for UV-selected galaxies and an underestimation for FIR-selected galaxies. The output from the analysis process suggests that UV-selected galaxies have attenuation laws in average similar to the Large Magellanic Cloud extinction law while FIR-selected galaxies attenuation laws resemble more the Milky Way extinction law. The dispersion about the average relation in the log (F dust /F FUV ) versus FUV-NUV diagram (once the main relation with FUV - NUV accounted for) is explained by two other parameters: the slope of the attenuation law and the instantaneous birthrate parameters b 0 for UV-selected galaxies and the same ones plus the strength of the bump for the FIR-selected galaxies. We propose a recipe to estimate the UV dust attenuation for UV galaxies only (that should only be used whenever the FIR information is not available because the resulting A FUV is poorly defined with an uncertainty of about 0.32): A FUV = 1.4168 (FUV - NUV) 2 + 0.3298 (NUV - I) 2 + 2.1207 (FUV - NUV) + 2.7465 (NUV - I) + 5.8408.

CALIFA, the Calar Alto Legacy Integral Field Area survey

We present the Calar Alto Legacy Integral Field Area survey (CALIFA). CALIFAs main aim is to obtain spatially resolved spectroscopic information for ~600 galaxies of all Hubble types in the Local Universe (0.005< z <0.03). The survey has been designed to allow three key measurements to be made: (a) Two-dimensional maps of stellar populations (star formation histories, chemical elements); (b) The distribution of the excitation mechanism and element abundances of the ionized gas; and (c) Kinematic properties (velocity ?elds, velocity dispersion), both from emission and from absorption lines. To cover the full optical extension of the target galaxies (i.e. out to a 3sigma depth of ~23 mag/arcsec2), CALIFA uses the exceptionally large ?eld of view of the PPAK/PMAS IFU at the 3.5m telescope of the Calar Alto observatory. We use two grating setups, one covering the wavelength range between 3700 and 5000 AA at a spectral resolution R~1650, and the other covering 4300 to 7000 AA at R~850. The survey was allocated 210 dark nights, distributed in 6 semesters and starting in July 2010 and is carried out by the CALIFA collaboration, comprising ~70 astronomers from 8 di?erent countries. As a legacy survey, the fully reduced data will be made publically available, once their quality has been veri?ed. We showcase here early results obtained from the data taken so far (21 galaxies).

Mass-metallicity relation explored with CALIFA - I. Is there a dependence on the star-formation rate?

We studied the global and local ℳ-Z relation based on the first data available from the CALIFA survey (150 galaxies). This survey provides integral field spectroscopy of the complete optical extent of each galaxy (up to 2−3 effective radii), with a resolution high enough to separate individual H II regions and/or aggregations. About 3000 individual H II regions have been detected. The spectra cover the wavelength range between [OII]3727 and [SII]6731, with a sufficient signal-to-noise ratio to derive the oxygen abundance and star-formation rate associated with each region. In addition, we computed the integrated and spatially resolved stellar masses (and surface densities) based on SDSS photometric data. We explore the relations between the stellar mass, oxygen abundance and star-formation rate using this dataset. We derive a tight relation between the integrated stellar mass and the gas-phase abundance, with a dispersion lower than the one already reported in the literature (σ_Δlog (O/H) = 0.07 dex). Indeed, this dispersion is only slightly higher than the typical error derived for our oxygen abundances. However, we found no secondary relation with the star-formation rate other than the one induced by the primary relation of this quantity with the stellar mass. The analysis for our sample of ~3000 individual H II regions confirms (i) a local mass-metallicity relation and (ii) the lack of a secondary relation with the star-formation rate. The same analysis was performed with similar results for the specific star-formation rate. Our results agree with the scenario in which gas recycling in galaxies, both locally and globally, is much faster than other typical timescales, such like that of gas accretion by inflow and/or metal loss due to outflows. In essence, late-type/disk-dominated galaxies seem to be in a quasi-steady situation, with a behavior similar to the one expected from an instantaneous recycling/closed-box model.

Star Formation in the Nearby Universe: The Ultraviolet and Infrared Points of View

This work presents the main ultraviolet (UV) and far-infrared (FIR) properties of two samples of nearby galaxies selected from the GALEX (λ = 2315 A, hereafter NUV) and IRAS (λ = 60 μm) surveys, respectively. They are built in order to obtain detection at both wavelengths for most of the galaxies. Star formation rate (SFR) estimators based on the UV and FIR emissions are compared. Systematic differences are found between the SFR estimators for individual galaxies based on the NUV fluxes corrected for dust attenuation and on the total IR luminosity. A combined estimator based on NUV and IR luminosities seems to be the best proxy over the whole range of values of SFR. Although both samples present similar average values of the birthrate parameter b, their star-formation-related properties are substantially different: NUV-selected galaxies tend to show larger values of b for lower masses, SFRs, and dust attenuation, supporting previous scenarios of star formation history (SFH). Conversely, about 20% of the FIR-selected galaxies show high values of b, SFR, and NUV attenuation. These galaxies, most of them being LIRGs and ULIRGs, break down the downsizing picture of SFH; however, their relative contribution per unit volume is small in the local universe. Finally, the cosmic SFR density of the local universe is estimated in a consistent way from the NUV and IR luminosities.

MULTIBAND ANALYSIS OF A SAMPLE OF BLUE COMPACT DWARF GALAXIES. I. SURFACE BRIGHTNESS DISTRIBUTION, MORPHOLOGY, AND STRUCTURAL PARAMETERS

Broadband observations in B, V, R, and I have been performed for a sample of 28 galaxies cataloged as blue compact dwarf galaxies (BCDs). Our deep imaging, reaching surface brightness levels of a few percent of the sky brightness, has allowed the detection of underlying emission or low surface brightness features for a substantial fraction of the sample. In this paper we present the first results of the program: deep contour maps in the B band, surface brightness profiles, and color profiles for all the galaxies. The information derived for this sample of galaxies has allowed us to analyze the morphology and the structural components of BCDs. Over 70% of the galaxies show complex profiles that preclude fitting by a single standard law, with extra structure at high to intermediate intensity levels. In 21 galaxies of the sample, an underlying low surface brightness component has been detected.

75 Kiloparsec Trails of Ionized Gas behind Two Irregular Galaxies in A1367

In a 6 hr Hα exposure of the northwest region of the cluster of galaxies A1367, we discovered a 75 kpc cometary emission of ionized gas trailing behind two Irr galaxies. The Hα trails correspond in position and length with tails of syncrotron radiation. At the galaxy side opposite to the tails, the two galaxies show bright H II regions aligned along arcs, where the star formation takes place at the prodigious rate of ~1 M⊙ yr-1. From the morphology of the galaxies and of the trailing material, we infer that the two galaxies are suffering from ram pressure due to their high-velocity motion through the cluster intergalactic medium. We estimate that ~109 M⊙ of gas, probably ionized in the giant H II regions, is swept out, forming the tails. The tails cross each other at some 100 kpc from the present galaxy location, indicating that a major tidal event occurred some ~5 × 107 yr ago. We exclude that mutual harassment produced the observed morphology, and we show with numerical simulations that it could have marginally aided ram pressure stripping by loosening the potential well of the galaxies.

The CALIFA survey across the Hubble sequence: Spatially resolved stellar population properties in galaxies

Various different physical processes contribute to the star formation and stellar mass assembly histories of galaxies. One important approach to understanding the significance of these different processes on galaxy evolution is the study of the stellar population content of todays galaxies in a spatially resolved manner. The aim of this paper is to characterize in detail the radial structure of stellar population properties of galaxies in the nearby universe, based on a uniquely large galaxy sample, considering the quality and coverage of the data. The sample under study was drawn from the CALIFA survey and contains 300 galaxies observed with integral field spectroscopy. These cover a wide range of Hubble types, from spheroids to spiral galaxies, while stellar masses range from M_* ∼ 10^9 to 7 x 10^11 M_⨀. We apply the fossil record method based on spectral synthesis techniques to recover the following physical properties for each spatial resolution element in our target galaxies: the stellar mass surface density (μ_*), stellar extinction (A_V), light-weighted and mass-weighted ages ( _L, _M), and mass-weighted metallicity ( _M). To study mean trends with overall galaxy properties, the individual radial profiles are stacked in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd). We confirm that more massive galaxies are more compact, older, more metal rich, and less reddened by dust. Additionally, we find that these trends are preserved spatially with the radial distance to the nucleus. Deviations from these relations appear correlated with Hubble type: earlier types are more compact, older, and more metal rich for a given M-star, which is evidence that quenching is related to morphology, but not driven by mass. Negative gradients of _L are consistent with an inside-out growth of galaxies, with the largest _L gradients in Sb-Sbc galaxies. Further, the mean stellar ages of disks and bulges are correlated and with disks covering a wider range of ages, and late-type spirals hosting younger disks. However, age gradients are only mildly negative or flat beyond R∼2 HLR (half light radius), indicating that star formation is more uniformly distributed or that stellar migration is important at these distances. The gradients in stellar mass surface density depend mostly on stellar mass, in the sense that more massive galaxies are more centrally concentrated. Whatever sets the concentration indices of galaxies obviously depends less on quenching/morphology than on the depth of the potential well. There is a secondary correlation in the sense that at the same M_* early-type galaxies have steeper gradients. The μ_* gradients outside 1 HLR show no dependence on Hubble type. We find mildly negative _M gradients, which are shallower than predicted from models of galaxy evolution in isolation. In general, metallicity gradients depend on stellar mass, and less on morphology, hinting that metallicity is affected by both - the depth of the potential well and morphology/quenching. Thus, the largest _M gradients occur in Milky Way-like Sb-Sbc galaxies, and are similar to those measured above the Galactic disk. Sc spirals show flatter _M gradients, possibly indicating a larger contribution from secular evolution in disks. The galaxies from the sample have decreasing-outward stellar extinction; all spirals show similar radial profiles, independent from the stellar mass, but redder than E and S0. Overall, we conclude that quenching processes act in manners that are independent of mass, while metallicity and galaxy structure are influenced by mass-dependent processes.

Integral field spectroscopy of a sample of nearby galaxies - II. Properties of the H ii regions

This is an electronic version of an article published in Astronomy and Astrophysics. Sanchez, S.F. et al. Integral field spectroscopy of a sample of nearby galaxies. II. Properties of the H II regions. Astronomy and Astrophysics 546 (2012): A2