http://arxiv.org/abs/1811.02589
As galaxies evolve, they must enrich and exchange gas with the intergalactic medium, but the mechanisms driving these processes remain poorly understood. In this work, we leverage missing metals as tracers of past gas flows to constrain the history of metal ejection and redistribution in M31. This is a unique case of a roughly $L*$ galaxy where spatially resolved measurements of the gas-phase and stellar metallicity, dust extinction, and neutral ISM gas content are available, enabling a census of the metal mass present in stars, gas, and dust. We combine spatially resolved star formation histories from the Panchromatic Hubble Andromeda Treasury survey with a model of metal production by Type II SNe, Type Ia SNe, and AGB stars to calculate the history of metal production in M31. We find that $1.8\times10^9 \, M_\odot$ of metals, or 62% of the metal mass formed within $r < 19 \,\mathrm{kpc}$, is missing from the disk in our fiducial model, implying that the M31 disk has experienced significant gaseous outflows over its lifetime. This fiducial missing metal mass is over a factor of 100 larger than the observational estimate of the metal content of M31’s circumgalactic medium (CGM). If all of this missing metal mass resides in M31’s CGM, we show that either the hydrogen mass in the CGM must exceed the stellar mass in M31, or the CGM must have super-solar metallicity. We find that no net metal loss is required in the past 1.5 Gyr, but some metal mass produced since then in the central $\sim5 \,\mathrm{kpc}$ has likely been redistributed farther out in the disk.
O. Telford, J. Werk, J. Dalcanton, et. al.
Thu, 8 Nov 18
15/72
Comments: Submitted to ApJ, comments welcome! Figure 6 shows key result
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