SPIDER – I. Sample and galaxy parameters in the grizYJHK wavebands

Depto de Astrofísica, Universidad de La Laguna (ULL), E-38206 La Laguna, Tenerife, Spain
Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 10/2010; 408(3):1313 - 1334. DOI: 10.1111/j.1365-2966.2010.16850.x
Source: arXiv


This is the first paper of a series presenting the Spheroids Panchromatic Investigation in Different Environmental Regions (SPIDER). The sample of spheroids consists of 5080 bright (Mr < −20) early-type galaxies (ETGs), in the redshift range of 0.05 to 0.095, with optical (griz) photometry and spectroscopy from the Sloan Digital Sky Survey Data Release 6 (SDSS-DR6) and near-infrared (YJHK) photometry from the UKIRT Infrared Deep Sky Survey-Large Area Survey (UKIDSS-LAS) (DR4). We describe how homogeneous photometric parameters (galaxy colours and structural parameters) are derived using grizYJHK wavebands. We find no systematic steepening of the colour–magnitude relation when probing the baseline from g−r to g−K, implying that internal colour gradients drive most of the mass–metallicity relation in ETGs. As far as structural parameters are concerned we find that the mean effective radius of ETGs smoothly decreases, by 30 per cent, from g through K, while no significant dependence on waveband is detected for the axial ratio, Sersic index and a4 parameters. Furthermore, velocity dispersions are remeasured for all the ETGs using starlight and compared to those obtained by SDSS. The velocity dispersions are rederived using a combination of simple stellar population models as templates, hence accounting for the kinematics of different galaxy stellar components. We compare our (2dphot) measurements of total magnitude, effective radius and mean surface brightness with those obtained as part of the SDSS pipeline (photo). Significant differences are found and reported, including comparisons with a third and independent part. A full characterization of the sample completeness in all wavebands is presented, establishing the limits of application of the characteristic parameters presented here for the analysis of the global scaling relations of ETGs.

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    ABSTRACT: We analyse the Fundamental Plane (FP) relation of $39,993$ early-type galaxies (ETGs) in the optical (griz) and $5,080$ ETGs in the Near-Infrared (YJHK) wavebands, forming an optical$+$NIR sample of $4,589$ galaxies. We focus on the analysis of the FP as a function of the environment where galaxies reside. We characterise the environment using the largest group catalogue, based on 3D data, generated from SDSS at low redshift ($z < 0.1$). We find that the intercept $``c''$ of the FP decreases smoothly from high to low density regions, implying that galaxies at low density have on average lower mass-to-light ratios than their high-density counterparts. The $``c''$ also decreases as a function of the mean characteristic mass of the parent galaxy group. However, this trend is weak and completely accounted for by the variation of $``c''$ with local density. The variation of the FP offset is the same in all wavebands, implying that ETGs at low density have younger luminosity-weighted ages than cluster galaxies, consistent with the expectations of semi-analytical models of galaxy formation. We measure an age variation of $\sim 0.048$~dex ($\sim 11\%$) per decade of local galaxy density. This implies an age difference of about $32 \%$ ($\sim 3 \, Gyr$) between galaxies in the regions of highest density and the field. We find the metallicity decreasing, at $\sim 2$~$\sigma$, from low to high density. We also find $2.5 \, \sigma$ evidence that the variation in age per decade of local density augments, up to a factor of two, for galaxies residing in massive relative to poor groups. (abridged) Comment: 29 pages, 28 figures, accepted to MNRAS
    Monthly Notices of the Royal Astronomical Society 03/2010; 408(3). DOI:10.1111/j.1365-2966.2010.17273.x · 5.11 Impact Factor
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    ABSTRACT: We analyze the dependence of the Fundamental Plane (FP) relation on the environment where galaxies reside, for a sample of 39, 993 early-type galaxies (ETGs) in the optical (griz) and Near-Infrared (YJHK) wavebands. The intercept “c” of the FP decreases from high- to low-density regions, implying that galaxies at low density have on average lower mass-to-light ratios than their high-density counterparts. Since the variation of “c” is the same at all wavebands, we conclude that ETGs at low density have younger luminosity-weighted ages (and higher metallicity) than cluster ETGs. The velocity dispersion slope of the FP, “a”, is smaller for groups relative to field ETGs, independent of the waveband. The surface brightness slope, “b”, does not change with waveband for group galaxies, while exhibits a small, but significant increase from g through K for the field sample. We interpret these trends as the result of a different variation of dark-matter fraction and stellar population properties with galaxy mass for high-density relative to low-density environments.
    04/2011: pages 79-84;
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    ABSTRACT: [Abridged] We present ground-based MDM V-band and Spitzer/IRAC 3.6um-band photometric observations of the 72 representative galaxies of the SAURON Survey. In combination with the SAURON stellar velocity dispersion measured within an effective radius (se), this allows us to explore the location of our galaxies in the main scaling relations. We investigate the dependence of these relations on our recent kinematical classification of early-type galaxies (i.e. Slow/Fast Rotators) and the stellar populations. Slow Rotator and Fast Rotator E/S0 galaxies do not populate distinct locations in the scaling relations, although Slow Rotators display a smaller intrinsic scatter. Surprisingly, extremely young objects do not display the bluest (V-[3.6]) colours in our sample, as is usually the case in optical colours. This can be understood in the context of the large contribution of TP-AGB stars to the infrared, even for young populations, resulting in a very tight (V-[3.6]) - se relation that in turn allows us to define a strong correlation between metallicity and velocity dispersion. Many Sa galaxies appear to follow the Fundamental Plane defined by E/S0 galaxies. Galaxies that appear offset from the relations correspond mostly to objects with extremely young populations, with signs of on-going, extended star formation. We correct for this effect in the Fundamental Plane, by replacing luminosity with stellar mass using an estimate of the stellar mass-to-light ratio, so that all galaxies are part of a tight, single relation. The new estimated coefficients are consistent in both photometric bands and suggest that differences in stellar populations account for about half of the observed tilt with respect to the virial prediction. After these corrections, the Slow Rotator family shows almost no intrinsic scatter around the best-fit Fundamental Plane.
    Monthly Notices of the Royal Astronomical Society 07/2011; 417(3). DOI:10.1111/j.1365-2966.2011.19372.x · 5.11 Impact Factor
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