The Gas-phase Metallicity Profiles of Star-forming Galaxies in the Modified Accretion Disk Framework. (arXiv:2201.04151v2 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Wang_E/0/1/0/all/0/1">Enci Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lilly_S/0/1/0/all/0/1">Simon J. Lilly</a>
Simulations indicate that the inflow of gas of star-forming galaxies is
almost co-planar and co-rotating with the gas disk, and that the outflow of gas
driven by stellar winds and/or supernova explosions is preferentially
perpendicular to the disk. This indicates that the galactic gas disk can be
treated as a modified accretion disk. In this work, we focus on the metal
enhancement in galactic disks in this scenario of gas accretion. Assuming that
the star formation rate surface density ($Sigma_{rm SFR}$) is of exponential
form, we obtain the analytic solution of gas-phase metallicity with only three
free parameters: the scalelength of $Sigma_{rm SFR}$ ($h_{rm R}$), the
metallicity of the inflowing gas and the mass-loading factor defined as the
wind-driven outflow rate surface density per $Sigma_{rm SFR}$. According to
this simple model, the negative gradient of gas-phase metallicity is a natural
consequence of the radial inflow of cold gas which is continuously enriched by
in-situ star formation as it moves towards the disk center. We fit the model to
the observed metallicity profiles for six nearby galaxies chosen to have
well-measured metallicity profiles extending to very large radii. Our model can
well characterize the overall features of the observed metallicity profiles.
The observed profiles usually show a floor at the outer regions of the disk,
corresponding to the metallicity of inflow gas. Furthermore, we find the
$h_{rm R}$ of $Sigma_{rm SFR}$ inferred from these fits agree well with
independent estimates from $Sigma_{rm SFR}$ profiles, supporting the basic
model.
Simulations indicate that the inflow of gas of star-forming galaxies is
almost co-planar and co-rotating with the gas disk, and that the outflow of gas
driven by stellar winds and/or supernova explosions is preferentially
perpendicular to the disk. This indicates that the galactic gas disk can be
treated as a modified accretion disk. In this work, we focus on the metal
enhancement in galactic disks in this scenario of gas accretion. Assuming that
the star formation rate surface density ($Sigma_{rm SFR}$) is of exponential
form, we obtain the analytic solution of gas-phase metallicity with only three
free parameters: the scalelength of $Sigma_{rm SFR}$ ($h_{rm R}$), the
metallicity of the inflowing gas and the mass-loading factor defined as the
wind-driven outflow rate surface density per $Sigma_{rm SFR}$. According to
this simple model, the negative gradient of gas-phase metallicity is a natural
consequence of the radial inflow of cold gas which is continuously enriched by
in-situ star formation as it moves towards the disk center. We fit the model to
the observed metallicity profiles for six nearby galaxies chosen to have
well-measured metallicity profiles extending to very large radii. Our model can
well characterize the overall features of the observed metallicity profiles.
The observed profiles usually show a floor at the outer regions of the disk,
corresponding to the metallicity of inflow gas. Furthermore, we find the
$h_{rm R}$ of $Sigma_{rm SFR}$ inferred from these fits agree well with
independent estimates from $Sigma_{rm SFR}$ profiles, supporting the basic
model.
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