Mass-metallicity relation explored with CALIFA

Abstract

We studied the global and local M-Z relation based on the first data available from the CALIFA survey (150 galaxies). This survey provides integral field spectroscopy of the complete optical extent of each galaxy (up to 2−3 effective radii), with a resolution high enough to separate individual H ii regions and/or aggregations. About 3000 individual H ii regions have been detected. The spectra cover the wavelength range between [OII]3727 and [SII]6731, with a sufficient signal-to-noise ratio to derive the oxygen abundance and star-formation rate associated with each region. In addition, we computed the integrated and spatially resolved stellar masses (and surface densities) based on SDSS photometric data. We explore the relations between the stellar mass, oxygen abundance and star-formation rate using this dataset. We derive a tight relation between the integrated stellar mass and the gas-phase abundance, with a dispersion lower than the one already reported in the literature (σ Δlog (O/H) = 0.07 dex). Indeed, this dispersion is only slightly higher than the typical error derived for our oxygen abundances. However, we found no secondary relation with the star-formation rate other than the one induced by the primary relation of this quantity with the stellar mass. The analysis for our sample of ∼3000 individual H ii regions confirms (i) a local mass-metallicity relation and (ii) the lack of a secondary relation with the star-formation rate. The same analysis was performed with similar results for the specific star-formation rate. Our results agree with the scenario in which gas recycling in galaxies, both locally and globally, is much faster than other typical timescales, such like that of gas accretion by inflow and/or metal loss due to outflows. In essence, late-type/disk-dominated galaxies seem to be in a quasi-steady situation, with a behavior similar to the one expected from an instantaneous recycling/closed-box model.

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

“…Figure 3 shows the most recently-derived Σ-Z relation using the ∼9000 H II regions detected in the 492 CALIFA galaxies described before. The dispersion around the average relation is ∼0.08 dex, just slightly larger than the one reported for the global M-Z relation, in agreement with the results presented in [8,46]. In addition, we derived the same relation using a spaxel-by-spaxel selection of the star-forming regions, presented in [53], that comprise a total of nearly one million regions.…”

“…Once subtracting the best fitted function to the M-Z relation, the residuals of the abundance do not present any evident secondary relation to the SFR (right panel). Thus, the results presented in [46] are confirmed with a sample of galaxies enlarged by almost a factor of two. We tested the results using different calibrators for the oxygen abundance, including the O3N2 and N2 of both [42,49], the ONS by [50] and the counter-method by [51], without significant qualitative results.…”

“…The yellow solid points indicate the average abundance for a set of successive bins of 0.2 dex in stellar mass density, with the error bars indicating the standard deviation of the abundance distribution for each bin (with a typical value of ∼0.08 dex). Right panel: this shows the same distribution of the ∼1 million spaxels extracted from the same CALIFA galaxies for which ionization conditions is dominated by star formation, following the criteria outlined in [46]. Image and contours present the same density distribution.…”

“…To further explore these issues, we applied the same procedure to the IFS data provided by the CALIFA survey. In [46], we presented the first results based on the catalog of H II regions extracted from an enlarged sample of galaxies (∼100). We studied the dependence of the M-Z relation on the star formation rate.…”

“…Figure 2 presents an updated version of these results, including the last list of galaxies analyzed until January 2015 (271 galaxies from the CALIFA sample together with 31 galaxies from the CALIFA pilot studies). This sample of galaxies comprises all galaxies observed up to November 2014 (492 objects), for which we have at least five H II regions/aggregations within a range between 0.5 and 2.1 r e of galactocentric distances, thus those galaxies for which we have a well-defined oxygen abundance at the effective radius as defined in [46]. In total, the current sample is three-times larger than the one presented in our previous studies, with a much better coverage of the mass range.…”