The star formation history of CALIFA galaxies: Radial structures^⋆

¹ Instituto de Astrofísica de Andalucía (CSIC), PO Box 3004, 18080 Granada, Spain
e-mail: rosa@iaa.es
² Departamento de Física, Universidade Federal de Santa Catarina, PO Box 476, 88040-900 Florianópolis, SC, Brazil
³ Centro Astronómico Hispano Alemán, Calar Alto, (CSIC-MPG), C/ Jesús Durbán Remón 2-2, 04004 Almería, Spain
⁴ Leibniz-Institut für Astrophysik Potsdam, innoFSPEC Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁵ Depto. de Física Teórica, Universidad Autnoma de Madrid, 28049 Madrid, Spain
⁶ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
⁷ Depto. Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
⁸ INAF − Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
⁹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹⁰ University of Vienna, Turkenschanzstrasse 17, 1180 Vienna, Austria
¹¹ Sydney Institute for Astronomy, The University of Sydney, Sydney NSW 2006, Australia
¹² University of Cambridge, Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UK
¹³ Departamento de Investigación Básica, CIEMAT, Avda. Complutense 40, 28040 Madrid, Spain
¹⁴ CEI Campus Moncloa, UCM-UPM, Departamento de Astrofísica y CC. de la Atmósfera, Facultad de CC<italic>.</italic> Físicas, Universidad Complutense de Madrid, Avda. Complutense s/n, 28040 Madrid, Spain
¹⁵ Landessternwarte, Zentrum fur Astronomie der Universitat Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
¹⁶ Dark Cosmology center, Niels Bohr Institute, University of Copenhagen, Juliane Mariesvej 30, 2100 Copenhagen, Denmark

Received: 3 June 2013
Accepted: 21 October 2013

Abstract

We have studied the radial structure of the stellar mass surface density (μ_∗) and stellar population age as a function of the total stellar mass and morphology for a sample of 107 galaxies from the CALIFA survey. We applied the fossil record method based on spectral synthesis techniques to recover the star formation history (SFH), resolved in space and time, in spheroidal and disk dominated galaxies with masses from 10⁹ to 10¹² M_⊙. We derived the half-mass radius, and we found that galaxies are on average 15% more compact in mass than in light. The ratio of half-mass radius to half-light radius (HLR) shows a dual dependence with galaxy stellar mass; it decreases with increasing mass for disk galaxies, but is almost constant in spheroidal galaxies. In terms of integrated versus spatially resolved properties, we find that the galaxy-averaged stellar population age, stellar extinction, and μ_∗ are well represented by their values at 1 HLR. Negative radial gradients of the stellar population ages are present in most of the galaxies, supporting an inside-out formation. The larger inner (≤1 HLR) age gradients occur in the most massive (10¹¹ M_⊙) disk galaxies that have the most prominent bulges; shallower age gradients are obtained in spheroids of similar mass. Disk and spheroidal galaxies show negative μ_∗ gradients that steepen with stellar mass. In spheroidal galaxies, μ_∗ saturates at a critical value (~7 × 10² M_⊙/pc² at 1 HLR) that is independent of the galaxy mass. Thus, all the massive spheroidal galaxies have similar local μ_∗ at the same distance (in HLR units) from the nucleus. The SFH of the regions beyond 1 HLR are well correlated with their local μ_∗, and follow the same relation as the galaxy-averaged age and μ_∗; this suggests that local stellar mass surface density preserves the SFH of disks. The SFH of bulges are, however, more fundamentally related to the total stellar mass, since the radial structure of the stellar age changes with galaxy mass even though all the spheroid dominated galaxies have similar radial structure in μ_∗. Thus, galaxy mass is a more fundamental property in spheroidal systems, while the local stellar mass surface density is more important in disks.