Bibcode
La Barbera, F.; De Carvalho, R. R.; de la Rosa, I. G.; Gal, R. R.; Swindle, R.; Lopes, P. A. A.
Bibliographical reference
The Astronomical Journal, Volume 140, Issue 5, pp. 1528-1556 (2010).
Advertised on:
11
2010
Citations
52
Refereed citations
50
Description
We present an analysis of stellar population gradients in 4546
early-type galaxies (ETGs) with photometry in grizYHJK along with
optical spectroscopy. ETGs were selected as bulge-dominated systems,
displaying passive spectra within the SDSS fibers. A new approach is
described which utilizes color information to constrain age and
metallicity gradients. Defining an effective color gradient,
∇sstarf, which incorporates all of the available color
indices, we investigate how ∇sstarf varies with galaxy
mass proxies, i.e., velocity dispersion, stellar (M sstarf)
and dynamical (M dyn) masses, as well as age, metallicity,
and [α/Fe]. ETGs with M dyn larger than 8.5 ×
1010 M sun have increasing age gradients and
decreasing metallicity gradients with respect to mass, metallicity, and
enhancement. We find that velocity dispersion and [α/Fe] are the
main drivers of these correlations. ETGs with 2.5 ×
1010 M sun <= M dyn <= 8.5
× 1010 M sun show no correlation of age,
metallicity, and color gradients with respect to mass, although color
gradients still correlate with stellar population parameters, and these
correlations are independent of each other. In both mass regimes, the
striking anti-correlation between color gradient and α-enhancement
is significant at ~5σ and results from the fact that metallicity
gradient decreases with [α/Fe]. This anti-correlation may reflect
the fact that star formation and metallicity enrichment are regulated by
the interplay between the energy input from supernovae, and the
temperature and pressure of the hot X-ray gas in ETGs. For all mass
ranges, positive age gradients are associated with old galaxies (>5-7
Gyr). For galaxies younger than ~5 Gyr, mostly at low mass, the age
gradient tends to be anti-correlated with the Age parameter, with more
positive gradients at younger ages.