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24 April 2024 |
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Article overview
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A Robust Measurement of the Mass Outflow Rate of the Galactic Outflow from NGC 6090 | | John Chisholm
; Christy A. Tremonti
; Claus Leitherer
; Yanmei Chen
; | | Date: |
19 May 2016 | | Abstract: | To evaluate the impact of stellar feedback, it is critical to estimate the
mass outflow rates of galaxies. Past estimates have been plagued by uncertain
assumptions about the outflow geometry, metallicity, and ionization fraction.
Here we use Hubble Space Telescope ultraviolet spectroscopic observations of
the nearby starburst NGC 6090 to demonstrate that many of these quantities can
be constrained by the data. We use the Si~{sc IV} absorption lines to
calculate the scaling of velocity (v), covering fraction (C$_f$), and density
with distance from the starburst (r), assuming the Sobolev optical depth and a
velocity law of the form: $v propto(1 -R_i/r )^eta$ (were R$_i$ is the inner
outflow radius). We find that the velocity ($eta$=0.43) is consistent with an
outflow driven by an r$^{-2}$ force, while the scaling of the covering fraction
($C_f propto r^{-0.82}$) suggests that cool clouds in the outflow are in
pressure equilibrium with an adiabatically expanding medium. We use the column
densities of four weak metal lines and CLOUDY photoionization models to
determine the outflow metallicity, the ionization correction, and the initial
density of the outflow. Combining these values with the profile fitting, we
find R$_i$ = 63 pc, with all of the mass within 300~pc of the starburst.
Finally, we find that the maximum mass outflow rate is 2.3~M$_odot$ yr$^{-1}$
and the mass loading factor (outflow divided by star formation rate) is 0.09, a
factor of 10 lower than value calculated using common assumptions for the
geometry, metallicity and ionization structure of the outflow. | | Source: | arXiv, 1605.5769 | | Services: | Forum | Review | PDF | Favorites | |
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