A Sub-Damped Lyman Alpha Absorber with Unusual Abundances: Evidence of Gas Recycling in a Low-Redshift Galaxy Group. (arXiv:1901.08147v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Frye_B/0/1/0/all/0/1">Brenda Frye</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bowen_D/0/1/0/all/0/1">David V. Bowen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tripp_T/0/1/0/all/0/1">Todd M. Tripp</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jenkins_E/0/1/0/all/0/1">Ed Jenkins</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pettini_M/0/1/0/all/0/1">Max Pettini</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ellison_S/0/1/0/all/0/1">Sara L. Ellison</a>

Using HST/STIS G140M spectroscopy, we investigate an absorption line system
at $z$=0.07489 in the spectrum of QSO PG1543+489 ($z_{QSO}$=0.401). The
sightline passes within $rho$ = 66 kpc of an edge-on $2L^*$ disk galaxy at a
similar redshift, but the galaxy belongs to a group with 4 other galaxies
within $rho =160$ kpc. We detect [log $N$(H I/$cm^{-2}$) = 19.12$pm$0.04] as
well as N I, Mg II, Si II, and Si III, from which we measure a gas-phase
abundance of [N/H] = $-1.0pm 0.1$. Photoionization models indicate that the
nitrogen-to-silicon relative abundance is solar, yet magnesium is underabundant
by a factor of $approx$ 2. We also report spatially-resolved emission-line
spectroscopy of the nearby galaxy, and we extract its rotation curve. The
galaxy’s metallicity is $approx 8 times$ higher than [N/H] in the absorber,
and interestingly, the absorber velocities suggest that the gas at $rho =$ 66
kpc is corotating with the galaxy’s stellar disk, possibly with an inflow
component. These characteristics could indicate that this sub-DLA system arises
in a “cold-accretion” flow. However, the absorber abundance patterns are
peculiar. We hypothesize that the gas was ejected from its galaxy of origin
(or, perhaps is a result of tidal debris from interactions between the group
galaxies) with a solar nitrogen abundance, but that subsequently mixed with
(and was diluted by) gas in the circumgalactic medium (CGM) or group. If the
gas is bound to the nearby galaxy, this system may be an example of the gas
“recycling” predicted by theoretical galaxy simulations. Our hypothesis is
testable with future observations.

Using HST/STIS G140M spectroscopy, we investigate an absorption line system
at $z$=0.07489 in the spectrum of QSO PG1543+489 ($z_{QSO}$=0.401). The
sightline passes within $rho$ = 66 kpc of an edge-on $2L^*$ disk galaxy at a
similar redshift, but the galaxy belongs to a group with 4 other galaxies
within $rho =160$ kpc. We detect [log $N$(H I/$cm^{-2}$) = 19.12$pm$0.04] as
well as N I, Mg II, Si II, and Si III, from which we measure a gas-phase
abundance of [N/H] = $-1.0pm 0.1$. Photoionization models indicate that the
nitrogen-to-silicon relative abundance is solar, yet magnesium is underabundant
by a factor of $approx$ 2. We also report spatially-resolved emission-line
spectroscopy of the nearby galaxy, and we extract its rotation curve. The
galaxy’s metallicity is $approx 8 times$ higher than [N/H] in the absorber,
and interestingly, the absorber velocities suggest that the gas at $rho =$ 66
kpc is corotating with the galaxy’s stellar disk, possibly with an inflow
component. These characteristics could indicate that this sub-DLA system arises
in a “cold-accretion” flow. However, the absorber abundance patterns are
peculiar. We hypothesize that the gas was ejected from its galaxy of origin
(or, perhaps is a result of tidal debris from interactions between the group
galaxies) with a solar nitrogen abundance, but that subsequently mixed with
(and was diluted by) gas in the circumgalactic medium (CGM) or group. If the
gas is bound to the nearby galaxy, this system may be an example of the gas
“recycling” predicted by theoretical galaxy simulations. Our hypothesis is
testable with future observations.

http://arxiv.org/icons/sfx.gif