Spatially Resolved Metal Loss from M31. (arXiv:1811.02589v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Telford_O/0/1/0/all/0/1">O. Grace Telford</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Werk_J/0/1/0/all/0/1">Jessica K. Werk</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dalcanton_J/0/1/0/all/0/1">Julianne J. Dalcanton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Williams_B/0/1/0/all/0/1">Benjamin F. Williams</a>
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 $1.8times10^9 , M_odot$ 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.
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 $1.8times10^9 , M_odot$ 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.
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