The growth of galaxies is one of the key problems in understanding the structure and evolution of the universe and its constituents. Galaxies can grow their stellar mass by accretion of halo or intergalactic gas clouds, or by merging with smaller or similar mass galaxies. The gas available translates into a rate of star formation, which controls the generation of metals in the universe. The spatially resolved history of their stellar mass assembly has not been obtained so far for any given galaxy beyond the Local Group. Here we demonstrate how massive galaxies grow their stellar mass inside-out. We report the results from the analysis of the first 105 galaxies of the largest to date three-dimensional spectroscopic survey of galaxies in the local universe (CALIFA). We apply the fossil record method of stellar population spectral synthesis to recover the spatially and time resolved star formation history of each galaxy. We show, for the first time, that the signal of downsizing is spatially preserved, with both inner and outer regions growing faster for more massive galaxies. Further, we show that the relative growth rate of the spheroidal component, nucleus and inner galaxy, that happened 5-7 Gyr ago, shows a maximum at a critical stellar mass ∼ 7×10 10 M ⊙ . We also find that galaxies less massive than ∼ 10 10 M ⊙ show a transition to outside-in growth, thus connecting with results from resolved studies of the growth of low mass galaxies.

While studies of gas-phase metallicity gradients in disc galaxies are common, very little has been done towards the acquisition of stellar abundance gradients in the same regions. We present here a comparative study of the stellar metallicity and age distributions in a sample of 62 nearly face-on, spiral galaxies with and without bars, using data from the CALIFA survey. We measure the slopes of the gradients and study their relation with other properties of the galaxies. We find that the mean stellar age and metallicity gradients in the disc are shallow and negative. Furthermore, when normalized to the effective radius of the disc, the slope of the stellar population gradients does not correlate with the mass or with the morphological type of the galaxies. In contrast to this, the values of both age and metallicity at ∼2.5 scale lengths correlate with the central velocity dispersion in a similar manner to the central values of the bulges, although bulges show, on average, older ages and higher metallicities than the discs. One of the goals of the present paper is to test the theoretical prediction that non-linear coupling between the bar and the spiral arms is an efficient mechanism for producing radial migrations across significant distances within discs. The process of radial migration should flatten the stellar metallicity gradient with time and, therefore, we would expect flatter stellar metallicity gradients in barred galaxies. However, we do not find any difference in the metallicity or age gradients between galaxies with and without bars. We discuss possible scenarios that can lead to this lack of difference.

Aims. Fossil record methods based on spectral synthesis techniques have matured during the past decade, and their application to integrated galaxy spectra has fostered substantial advances in the understanding of galaxies and their evolution. Yet, because of the lack of spatial resolution, these studies are limited to a global view, providing no information about the internal physics of galaxies. Methods. Motivated by the CALIFA survey, which is gathering integral field spectroscopy (IFS) over the full optical extent of 600 galaxies, we have developed an end-to-end pipeline that: (i) partitions the observed datacube into Voronoi zones in order to, when necessary and taking due account of correlated errors, increase the signal-to-noise ratio; (ii) extracts rest-framed spectra, including propagated errors and bad-pixel flags; (iii) feeds the spectra into the starlight spectral synthesis code; (iv) packs the results for all galaxy zones into a single FITS or HDF5 file; (v) performs a series of post-processing operations, including zone-topixel image reconstruction and unpacking the spectral and stellar population properties derived by starlight into multidimensional time, metallicity, and spatial coordinates. This paper provides an illustrated description of the whole pipeline and its many products. Using data for the nearby spiral NGC 2916 as a showcase, we go through each of the steps involved and present a series of ways of visualizing and analyzing this manifold. These include 2D maps of properties such as the velocity field, stellar extinction, mean ages and metallicities, mass surface densities, and star formation rates on different time scales and normalized in different ways, as well as 1D averages in the temporal and spatial dimensions, which lead to evolutionary curves and radial profiles of physical properties. Projections of the stellar light and mass growth onto radius-age diagrams are introduced as a means of visualizing galaxy evolution in time and space simultaneously, something which can also be achieved in 3D with snapshot cuts through the (x, y, t) cubes. Results. The results vividly illustrate the richness both of the combination of IFS data with spectral synthesis and of the insights on galaxy physics provided by the variety of diagnostics and semi-empirical constraints obtained. Additionally, they give a glimpse of what is to come from CALIFA and future IFS surveys.

We use spatially resolved spectroscopy from the Calar Alto Legacy Integral Field Area (CALIFA) survey to study the nature of the line emitting gas in galaxies of different Hubble types, focusing on the separation of star-forming (SF) regions from those better characterized as diffuse ionized gas (DIG). The diagnosis is carried out in terms of the equivalent width of Hα (W Hα ). Three nebular regimes are identified. Regions where W Hα < 3Å define what we call the hDIG, the component of the DIG where photoionization is dominated by hot, low-mass, evolved stars. Regions where W Hα > 14Å trace SF complexes. W Hα values in the intermediate 3-14Å range reflect a mixed regime (mDIG) where more than one process contributes.This three-tier scheme is inspired both by theoretical and empirical considerations. Its application to CALIFA galaxies of different types and inclinations leads to the following results: (i) the hDIG component is prevalent throughout ellipticals and S0's as well as in bulges, and explains the strongly bimodal distribution of W Hα both among and within galaxies. (ii) Earlytype spirals have some hDIG in their discs, but this component becomes progressively less relevant for later Hubble types. (iii) hDIG emission is also present above and below galactic discs, as seen in several edge-on spirals in our sample. (iv) The SF/mDIG proportion grows steadily from early-to late-type spirals, and from inner to outer radii. (v) Besides circumventing basic inconsistencies in conventional DIG/SF separation criteria based on the Hα surface brightness, our W Hα -based method produces results in agreement with a classical excitation diagram analysis.

This paper describes the Second Public Data Release (DR2) of the Calar Alto Legacy Integral Field Area (CALIFA) survey. The data for 200 objects are made public, including the 100 galaxies of the First Public Data Release (DR1). Data were obtained with the integral-field spectrograph PMAS/PPak mounted on the 3.5 m telescope at the Calar Alto observatory. Two different spectral setups are available for each galaxy, (i) a lowresolution V500 setup covering the wavelength range 3745-7500 Å with a spectral resolution of 6.0 Å (FWHM); and (ii) a medium-resolution V1200 setup covering the wavelength range 3650-4840 Å with a spectral resolution of 2.3 Å (FWHM). The sample covers a redshift range between 0.005 and 0.03, with a wide range of properties in the color-magnitude diagram, stellar mass, ionization conditions, and morphological types. All the cubes in the data release were reduced with the latest pipeline, which includes improved spectrophotometric calibration, spatial registration, and spatial resolution. The spectrophotometric calibration is better than 6% and the median spatial resolution is 2. 4. In total, the second data release contains over 1.5 million spectra.