The Mass-Metallicity relation explored with CALIFA: I. Is there a dependence on the star formation rate? (1304.2158v1)

Abstract: We present the results on the study of 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 enough resolution to separate individual HII regions and/or aggregations. Nearly $\sim$3000 individual HII regions have been detected. The spectra cover the wavelength range between [OII]3727 and [SII]6731, with a sufficient signal-to-noise to derive the oxygen abundance and star-formation rate associated with each region. In addition, we have computed the integrated and spatially resolved stellar masses (and surface densities), based on SDSS photometric data. We explore the relations between the stellar mass, oxygen abundance and star-formation rate using this dataset. We derive a tight relation between the integrated stellar mass and the gas-phase abundance, with a dispersion smaller than the one already reported in the literature ($\sigma_{\Delta{\rm log(O/H)}}=$0.07 dex). Indeed, this dispersion is only slightly larger than the typical error derived for our oxygen abundances. However, we do not find any secondary relation with the star-formation rate, other than the one induced due to the primary relation of this quantity with the stellar mass. We confirm the result using the $\sim$3000 individual HII regions, for the corresponding local relations. Our results agree with the scenario in which gas recycling in galaxies, both locally and globally, is much faster than other typical timescales, 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.

An Analysis of the Mass-Metallicity Relation Using CALIFA Data

The paper presents an elaborate paper of the mass-metallicity (M-Z) relation derived from the CALIFA survey, which provides integral field spectroscopy data for 150 galaxies. This paper specifically examines whether the star formation rate (SFR) influences this mass-metallicity relation.

Key Findings and Analysis

The authors analyze a sample containing approximately 3000 individual H II regions, which are detected within a wavelength range including prominent lines such as [OII]3727 and [SII]6731. With this dataset, the authors estimate the oxygen abundance and star-formation rate, in addition to computing integrated and spatially resolved stellar masses using SDSS photometric data.

1. Tight M-Z Relation: They confirm a strong correlation between the integrated stellar mass and the gas-phase oxygen abundance, observing a dispersion ($\sigma_{\Delta{\rm log(O/H)}}$) of only 0.07 dex. This is just slightly broader than the error margin for their oxygen abundance measurements, indicating a robust correlation.
2. Lack of Secondary Dependence on SFR: Contrary to some earlier findings, the analysis shows no secondary dependence of the M-Z relation on the SFR beyond its primary association with stellar mass. This is observed both globally and in local H II regions, demonstrating consistency at different scales within galaxies.
3. Implication of Gas Recycling: The authors suggest that gas recycling within galaxies operates at a much faster timescale compared to events such as gas inflow and metal outflow. This could imply that disk galaxies are close to a quasi-steady state, appropriate for a closed-box model of enrichment.

The paper challenges the so-called "fundamental plane" concept, where the relationship among stellar mass, metallicity, and SFR implies complex interdependencies. Instead, the paper's findings support simpler models of galaxy evolution in which stellar mass primarily dictates metal content, consistent with a rapid recycling scenario.

Theoretical and Practical Implications

The findings have pivotal implications for theoretical models of galaxy evolution. The assertion that galaxies exhibit a quasi-static behavior, with gas recycling governing metallicity contributions, suggests straightforward theoretical models may adequately describe the chemical enrichment of disk galaxies. This understanding can refine models of galactic chemical evolution, potentially simplifying the complex interplay typically described in multi-dimensional spaces.

Practically, these results improve our understanding of galaxy formation processes and the influence of different feedback and accretion mechanisms, informing the strategies for future spectroscopic surveys and the analysis of galactic ecosystems in various environments.

Future Considerations

Future surveys and analyses could provide more significant insights by expanding the sample size or the redshift range, possibly integrating data from other regions such as high-density cluster environments. Additionally, investigating low-mass galaxies which are underrepresented in this paper could determine whether the M-Z relationship remains consistent across the full spectrum of galactic mass. Moreover, high-resolution simulations including feedback processes and gas dynamics may offer a deeper understanding of how these relationships operate in diverse cosmic contexts.

In conclusion, this paper presents a detailed examination of the mass-metallicity relation that challenges existing paradigms by emphasizing a model grounded on rapid gas recycling, providing a solid foundation for both observational and theoretical advancements in the field of astronomy.