Spatially-resolved star formation histories of CALIFA galaxies

Implications for galaxy formation

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 Instituto de Astronomía,Universidad Nacional Autonóma de México, A.P. 70-264, 04510 México D.F., Mexico
⁴ Institut d’Astrophysique de Paris, UMR 7095, CNRS, Université Pierre et Marie Curie, 98bis boulevard Arago, 75014 Paris, France
⁵ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany

Received: 28 March 2017
Accepted: 13 June 2017

Abstract

This paper presents the spatially resolved star formation history (SFH) of nearby galaxies with the aim of furthering our understanding of the different processes involved in the formation and evolution of galaxies. To this end, we apply the fossil record method of stellar population synthesis to a rich and diverse data set of 436 galaxies observed with integral field spectroscopy in the CALIFA survey. The sample covers a wide range of Hubble types, with stellar masses ranging from M_⋆ ~ 10⁹ to 7 × 10¹¹ M_⊙. Spectral synthesis techniques are applied to the datacubes to retrieve the spatially resolved time evolution of the star formation rate (SFR), its intensity (Σ_SFR), and other descriptors of the 2D SFH in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd) and five bins of stellar mass. Our main results are that (a) galaxies form very fast independently of their current stellar mass, with the peak of star formation at high redshift (z > 2). Subsequent star formation is driven by M_⋆ and morphology, with less massive and later type spirals showing more prolonged periods of star formation. (b) At any epoch in the past, the SFR is proportional to M_⋆, with most massive galaxies having the highest absolute (but lowest specific) SFRs. (c) While today, the Σ_SFR is similar for all spirals and significantly lower in early-type galaxies (ETG), in the past, the Σ_SFR scales well with morphology. The central regions of today’s ETGs are where the Σ_SFR reached the highest values (> 10³ M_⊙ Gyr^-1 pc^-2), similar to those measured in high-redshift star-forming galaxies. (d) The evolution of Σ_SFR in Sbc systems matches that of models for Milky Way-like galaxies, suggesting that the formation of a thick disk may be a common phase in spirals at early epochs. (e) The SFR and Σ_SFR in outer regions of E and S0 galaxies show that they have undergone an extended phase of growth in mass between z = 2 and 0.4. The mass assembled in this phase is in agreement with the two-phase scenario proposed for the formation of ETGs. (f) Evidence of an early and fast quenching is found only in the most massive (M_⋆ > 2 × 10¹¹ M_⊙) E galaxies of the sample, but not in spirals of similar mass, suggesting that halo quenching is not the main mechanism for the shut down of star formation in galaxies. Less massive E and disk galaxies show more extended SFHs and a slow quenching. (g) Evidence of fast quenching is also found in the nuclei of ETG and early spirals, with SFR and Σ_SFR indicating that they can be the relic of the “red nuggets” detected at high redshift.