A characteristic oxygen abundance gradient in galaxy disks unveiled with CALIFA

Abstract

We present the largest and most homogeneous catalog of H ii regions and associations compiled so far. The catalog comprises more than 7000 ionized regions, extracted from 306 galaxies observed by the CALIFA survey. We describe the procedures used to detect, select, and analyze the spectroscopic properties of these ionized regions. In the current study we focus on characterizing of the radial gradient of the oxygen abundance in the ionized gas, based on the study of the deprojected distribution of H ii regions. We found that all galaxies without clear evidence of an interaction present a common gradient in the oxygen abundance, with a characteristic slope of α O/H = −0.1 dex/r e between 0.3 and 2 disk effective radii (r e ), and a scatter compatible with random fluctuations around this value, when the gradient is normalized to the disk effective radius. The slope is independent of morphology, the incidence of bars, absolute magnitude, or mass. Only those galaxies with evidence of interactions and/or clear merging systems present a significantly shallower gradient, consistent with previous results. The majority of the 94 galaxies with H ii regions detected beyond two disk effective radii present a flattening in the oxygen abundance. The flattening is statistically significant. We cannot provide a conclusive answer regarding the origin of this flattening. However, our results indicate that its origin is most probably related to the secular evolution of galaxies. Finally, we find a drop/truncation of the oxygen abundance in the inner regions for 26 of the galaxies. All of them are non-interacting, mostly unbarred Sb/Sbc galaxies. This feature is associated with a central star-forming ring, which suggests that both features are produced by radial gas flows induced by resonance processes. Our result suggests that galaxy disks grow inside-out, with metal enrichment driven by the local star formation history and with a small variation galaxy-by-galaxy. At a certain galactocentric distance, the oxygen abundance seems to be correlated well with the stellar mass density and total stellar mass of the galaxies, independently of other properties of the galaxies. Other processes, such as radial mixing and inflows/outflows seem to have a limited effect on shaping of the radial distribution of oxygen abundances, although they are not ruled out.

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

“…We repeated the analysis restricting the selection to those spaxels with an EW(Hα) > 20Å without any significant variation in the results. Figure 4 illustrates these results, showing the common abundance gradient (left panel), very similar to the one reported in [44], and the different shapes in the abundance profile at different masses (right panel), where the three regimes described before are evident. For this particular case, the O3N2 calibrator proposed by [49] was adopted (12 + log(O/H) = 8.50 − 0.22 log(O3N2)).…”

“…In [44], we used the updated CALIFA catalog of ∼7000 H II regions, extracted from 306 individual galaxies, to study the radial oxygen abundance gradient up to 3-4 disk effective radii. We confirmed that the abundance gradients present a common slope up to ∼2 effective radii, with a distribution compatible with being produced by random fluctuations, for all galaxies when normalized to the disk effective radius of α O/H = −0.1 dex/r e (using the O3N2 calibrator by [42]).…”

The 13th Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-IV Survey Mapping Nearby Galaxies at Apache Point Observatory

“…Cano-Díaz et al (2016) showed that the relationship between star formation rate (SFR) and stellar mass that held for entire star-forming galaxies was also true for spatially resolved regions within a galaxy. In another intriguing clue to the relation between small and large scales, Sánchez et al (2014) found that the H II regions in 306 CALIFA galaxies have a characteristic disk oxygen abundance gradient when scaled to its effective radius.…”

Gas-Phase Oxygen Abundances and Radial Metallicity Gradients in the Two Nearby Spiral Galaxies NGC 7793 and NGC 4945

“…The gas-phase metallicity has been studied in the Milky Way and nearby spiral galaxies through abundance analysis of H II regions (e.g., Vila-Costas & Edmunds 1992; Sánchez et al 2014), disclosing that a radial metallicity gradient across the galactic disk is almost invariably negative (i.e., higher abundances near the galactic center). The oxygen metallicity gradient is a key constraint to models of chemical evolution.…”