The CALIFA survey across the Hubble sequence

Abstract

Various different physical processes contribute to the star formation and stellar mass assembly histories of galaxies. One important approach to understanding the significance of these different processes on galaxy evolution is the study of the stellar population content of today's galaxies in a spatially resolved manner. The aim of this paper is to characterize in detail the radial structure of stellar population properties of galaxies in the nearby universe, based on a uniquely large galaxy sample, considering the quality and coverage of the data. The sample under study was drawn from the CALIFA survey and contains 300 galaxies observed with integral field spectroscopy. These cover a wide range of Hubble types, from spheroids to spiral galaxies, while stellar masses range from M ∼ 10 9 to 7 × 10 11 M . We apply the fossil record method based on spectral synthesis techniques to recover the following physical properties for each spatial resolution element in our target galaxies: the stellar mass surface density (µ ), stellar extinction (A V ), light-weighted and mass-weighted ages ( log age L , log age M ), and mass-weighted metallicity ( log Z M ). To study mean trends with overall galaxy properties, the individual radial profiles are stacked in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd). We confirm that more massive galaxies are more compact, older, more metal rich, and less reddened by dust. Additionally, we find that these trends are preserved spatially with the radial distance to the nucleus. Deviations from these relations appear correlated with Hubble type: earlier types are more compact, older, and more metal rich for a given M , which is evidence that quenching is related to morphology, but not driven by mass. Negative gradients of log age L are consistent with an inside-out growth of galaxies, with the largest log age L gradients in Sb-Sbc galaxies. Further, the mean stellar ages of disks and bulges are correlated and with disks covering a wider range of ages, and late-type spirals hosting younger disks. However, age gradients are only mildly negative or flat beyond R ∼ 2 HLR (half light radius), indicating that star formation is more uniformly distributed or that stellar migration is important at these distances. The gradients in stellar mass surface density depend mostly on stellar mass, in the sense that more massive galaxies are more centrally concentrated. Whatever sets the concentration indices of galaxies obviously depends less on quenching/morphology than on the depth of the potential well. There is a secondary correlation in the sense that at the same M early-type galaxies have steeper gradients. The µ gradients outside 1 HLR show no dependence on Hubble type. We find mildly negative log Z M gradients, which are shallower than predicted from models of galaxy evolution in isolation. In general, metallicity gradients depend on stellar mass, and less on morphology, hinting that metallicity is affected by both -the depth of the potential well and morphology/quenching....

THE SPATIALLY RESOLVED NUV–r COLOR OF LOCAL STAR-FORMING GALAXIES AND CLUES FOR QUENCHING

“…Beyond R 1 kpc , dust attenuation does not vary much. The findings of González Delgado et al (2015) and Nelson et al (2015b) indicate that in the galaxy scale, the dust attenuation is not a strong function of radius. A similar conclusion is also reached by Iglesias-Páramo et al (2013).…”

“…For this work, understanding the dust maps of galaxies will be helpful in interpreting the presented results. González Delgado et al (2015) explore the two-dimensional properties of ∼300 galaxies using the CALIFA IFS data. They find that the stacked A V profile shows a significant negative gradient in the innermost regions of galaxies.…”

The Evolution of Star Formation Histories of Quiescent Galaxies

“…Another method is to infer galaxy star formation histories (SFHs) from the fossil record of their past stellar populations (e.g., Panter et al 2003Panter et al , 2007Thomas et al 2005;González Delgado et al 2014;McDermid et al 2015;Citro et al 2016;Fumagalli et al 2016), sampling wide ranges of stellar masses and redshifts. For example, McDermid et al (2015) and Citro et al (2016) measure the SFHs of massive early-type galaxies and find that these systems are very old, forming the bulk of their mass in the first 1-2 Gyr.…”

The CALIFA Survey: Exploring the Oxygen Abundance in the Local Universe

“…We found solid evidence that mass assembly in typical galaxies happens from inside-out [17]. The SFH and chemical enrichment of bulges and early-type galaxies are fundamentally related to the total stellar mass, while for disk galaxies, it is more related to the local stellar mass density [18,19]; negative age gradients indicate that the quenching is progressing outwards in massive galaxies [18], and age and metallicity gradients suggest that galaxy bars have not significantly altered the SFH of spirals [20]; finally, we explore the spatially-resolved stellar populations across the Hubble sequence [19] and how mergers influence the assembly of blue elliptical galaxies [21]. (ii) We explore the origin of the low intensity, LINER -like, ionized gas in galaxies.…”

“…The second criticism is that the calibrators using the direct method hardly derive oxygen abundances above solar, in contrast with the metallicity-derived for the stellar populations using different methods, e.g., [19,52], not only in the Local Universe, but at larger redshifts. In the naive perception that chemical enrichment follows an instant recycling and a closed-box model, gas and stellar metallicity should be tightly linked, and they can only increase with time; therefore, the oxygen abundances derived using the direct method should be biases, since they cannot reproduce the supra-solar metallicities observed in some stellar populations.…”