http://arxiv.org/abs/1904.03930
The role of gas accretion in galaxy evolution is still a matter of debate. The presence of inflows of metal-poor gas that trigger star formation bursts of low metallicity has been proposed as an explanation for the local anti-correlation between star formation rate (SFR) and gas-phase metallicity ($\rm Z_g$) found in the literature. In the present study, we show how the anti-correlation is also present as part of a diversified range of behaviours for a sample of more than 700 nearby spiral galaxies from the SDSS IV MaNGA survey. We have characterized the local relation between SFR and $\rm Z_g$ after subtracting the azimuthally averaged radial profiles of both quantities. $60\%$ of the analyzed galaxies display a $\rm SFR-Z_g$ anti-correlation, with the remaining $40\%$ showing no correlation ($19\%$) or positive correlation ($21\%$). Applying a Random Forest machine-learning algorithm, we obtain that the slope of the correlation is mainly determined by the average gas-phase metallicity of the galaxy. Galaxy mass, $g-r$ colors, stellar age, and mass density seem to play a less significant role. This result is supported by the performed 2nd-order polynomial regression analysis. Thus, the local $\rm SFR-Z_g$ slope varies with the average metallicity, with the more metal-poor galaxies presenting the lowest slopes (i.e., the strongest $\rm SFR-Z_g$ anti-correlations), and reversing the relation for more metal-rich systems. The dependence seems to flatten in the metal-poor regime, hinting at a single slope for low-metallicity galaxies. Our results suggest that external gas accretion fuels star-formation in metal-poor galaxies, whereas in metal-rich systems the gas comes from previous star formation episodes.
L. Sánchez-Menguiano, J. Almeida, C. Muñoz-Tuñón, et. al.
Tue, 9 Apr 19
10/105
Comments: 22 pages, 11 figures. Submitted to ApJ
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