Stellar populations of early-type galaxies in different environments - III. Line-strength gradients



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Sánchez Blázquez, Patricia and Gorgas García, Francisco Javier and Cardiel López, Nicolás (2006) Stellar populations of early-type galaxies in different environments - III. Line-strength gradients. Astronomy & Astrophysics, 457 (3). p. 823. ISSN 0004-6361

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Aims. This is the third paper of a series devoted to the study of the stellar content of early-type galaxies. The goal of the series is to set constraints on the evolutionary status of these objects. Methods. We present line-strength gradients for 22 spectral indices measured in a sample of 82 early-type galaxies in different environments, including the high-density cores of the Coma cluster, the Virgo cluster, poor groups, and isolated field galaxies. Using new evolutionary population synthesis models, we derive age and metallicity gradients, and compare the mean values with the predictions of different galaxy formation models. We explore the behaviour of individual chemical species by deriving the metallicity gradient with different indicators. Results. We find that the strength of the metallicity gradient inferred from stellar population models depends on the specific Lick index employed. In particular, metallicity gradients obtained with CN2 and C4668 combined with H beta are steeper than those measured using Ca4227 or Fe4383. The correlation of the metallicity gradients with other parameters also depends on the specific index employed. If the metallicity gradient is obtained using CN2 and Mgb, then it correlates with the central age of the galaxies. On the contrary, if Fe4383 or Ca4227 is used, the metallicity gradient correlates with the velocity dispersion gradient. Conclusions. This may suggest that several mechanisms have helped to set the age and metallicity gradients in early-type galaxies. While we do not find any correlation between the metallicity gradient and the central velocity dispersion for galaxies in low-density environments, we find a marginal correlation between the metallicity gradient and the mass for galaxies in the centre of the Coma cluster. We also find a trend for which galaxies in denser environments show a steeper metallicity gradient than galaxies in less dense environments. We interpret these results in light of the different mechanisms proposed to explain the observed changes between galaxies as a function of environment.

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© ESO 2006. We would like to thank the anonymous referee for very helpful comments. The WHT is operated on the island of La Palma by the Royal Greenwich Observatory at the Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. The Calar Alto Observatory is operated jointly by the Max-Planck Institute für Astronomie, Heidelberg, and the Spanish Instituto de Astrofísica de Andalucía (CSIC). This work was partially supported by the Spanish research project AYA 2003-01840 and by the Australian Research Council. We are grateful to the CATs for their generous allocations of telescope time.

Uncontrolled Keywords:CCD surface photometry; Elliptic galaxies; Metallicity gradients; Absorption features; Cluster galaxies; Radial gradients; Color gradients; Galactic winds; Coma cluster; Merger model
Subjects:Sciences > Physics > Astrophysics
Sciences > Physics > Astronomy
Sciences > Physics > Atmospheric physics
ID Code:28593
Deposited On:27 Feb 2015 11:05
Last Modified:10 Dec 2018 15:05

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