[Paper Review] The Mass-Metallicity relation explored with CALIFA: I. Is there a dependence on the star formation rate?

S. F. Sánchez, F. F. Rosales-Ortega+41 more|DIGITAL.CSIC (Spanish National Research Council (CSIC))|Apr 8, 2013

Galaxies: Formation, Evolution, PhenomenaPhysics and Astronomy88 references134 citations

TL;DR

This study investigates the dependence of the mass-metallicity (M-Z) relation on star formation rate (SFR) using integral field spectroscopy from the CALIFA survey. It finds no significant correlation between SFR and metallicity at fixed stellar mass, suggesting the M-Z relation is primarily governed by stellar mass rather than current star formation activity.

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$3000 individual HII regions have been detected. The spectra cover the wavelength range between [OII]3727 and [SII]6731, with a sufficient signal-to-noise to derive the oxygen abundance and star-formation rate associated with each region. In addition, we have computed the integrated and spatially resolved stellar masses (and surface densities), based on SDSS photometric data. We explore the relations between the stellar mass, oxygen abundance and star-formation rate using this dataset. We derive a tight relation between the integrated stellar mass and the gas-phase abundance, with a dispersion smaller than the one already reported in the literature ($σ_{Δ{ m 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.

Motivation & Objective

• To test whether the mass-metallicity (M-Z) relation in galaxies exhibits a dependence on star formation rate (SFR) beyond stellar mass.
• To resolve conflicting results in the literature regarding the role of SFR in shaping the M-Z relation.
• To use high-resolution spatially resolved spectroscopy from the CALIFA survey to measure metallicity gradients and SFR across individual galaxies.
• To determine whether SFR acts as a secondary parameter in the M-Z relation or if stellar mass alone dominates metallicity trends.
• To clarify the physical mechanisms driving galaxy chemical evolution by isolating the influence of SFR from mass and other structural parameters.

Proposed method

• Utilizes spatially resolved spectroscopic data from the CALIFA survey, covering 600+ galaxies with high signal-to-noise in emission lines.
• Measures gas-phase metallicities using strong-line methods (e.g., N2, O3N2, R23) calibrated with photoionization models.
• Computes total stellar masses from stellar population synthesis modeling using the full spectral energy distribution.
• Estimates SFRs via Hα luminosity corrected for dust extinction using Balmer decrement (Hα/Hβ).
• Applies aperture photometry and spatial binning to derive radial metallicity gradients and integrated galaxy properties.
• Performs statistical analysis (e.g., linear and non-linear regression) to test for SFR dependence in the M-Z relation after controlling for stellar mass.

Experimental results

Research questions

• RQ1 Is the mass-metallicity relation in galaxies dependent on the current star formation rate, beyond the primary dependence on stellar mass?
• RQ2 Does the SFR influence metallicity at fixed stellar mass, or is the M-Z relation primarily governed by mass alone?
• RQ3 How do metallicity gradients vary with SFR across different galaxy types and morphologies?
• RQ4 Are there systematic differences in the M-Z relation when SFR is included as a secondary parameter in regression models?
• RQ5 What is the relative importance of SFR versus mass in explaining the scatter in the M-Z relation?

Key findings

• No significant dependence of metallicity on SFR is found at fixed stellar mass, indicating that SFR does not act as a secondary parameter in the M-Z relation.
• The M-Z relation remains tight and well-defined even after controlling for SFR, with the majority of scatter explained by stellar mass alone.
• Metallicity gradients are consistent across galaxies with different SFRs, suggesting that star formation rate does not alter the radial distribution of metals.
• The correlation between SFR and metallicity observed in some previous studies is likely driven by mass-SFR correlations rather than a direct physical link.
• The CALIFA data show that the M-Z relation is robustly described by stellar mass, with SFR contributing negligibly to the explanation of metallicity dispersion.
• The results support a scenario in which the M-Z relation is primarily shaped by the balance between gas inflows, outflows, and mass-loading factors, rather than current SFR.