Discovery of a Damped Ly$alpha$ System in a Low-z Galaxy Group: Possible Evidence for Gas Inflow and Nuclear Star Formation. (arXiv:1812.01632v1 [astro-ph.GA])

Discovery of a Damped Ly$alpha$ System in a Low-z Galaxy Group: Possible Evidence for Gas Inflow and Nuclear Star Formation. (arXiv:1812.01632v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Borthakur_S/0/1/0/all/0/1">Sanchayeeta Borthakur</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Momjian_E/0/1/0/all/0/1">Emmanuel Momjian</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Heckman_T/0/1/0/all/0/1">Timothy M. Heckman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Catinella_B/0/1/0/all/0/1">Barbara Catinella</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vogt_F/0/1/0/all/0/1">Frederic P. A. Vogt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tumlinson_J/0/1/0/all/0/1">Jason Tumlinson</a>

We present a low-redshift (z=0.029) Damped Lyman$alpha$ (DLA) system in the
spectrum of a background Quasi-Stellar Object (QSO). The DLA is associated with
an interacting galaxy pair within a galaxy group. We detected weak
Lyman$alpha$ emission centered at the absorption trough of the DLA. The
emission was likely tracing the neutral HI reservoir around the galaxies in the
interacting pair, which scattered the Lyman$alpha$ generated by star formation
within those galaxies. We also found that the interacting pair is enveloped by
a large HI cloud with $rm M(HI)=2times 10^{10}M_{odot}$. We discovered
blueshifted 21~cm HI emission, corresponding to M(HI)=$rm
2times10^{9}~M_{odot}$, associated with J151225.15$+$012950.4 – one of the
galaxies in the interacting pair. The blueshifted HI was tracing gas flowing
into the galaxy from behind and towards us. Gas at similar blueshifted
velocities was seen in the QSO sightline thus suggesting the presence of a
filamentary structure of the order of 100~kpc feeding the galaxy. We estimated
a mass inflow rate of $ rm 2 M_{odot}~yr^{-1}$ into the galaxy, which matches
the star formation rate estimated from H$alpha$ emission. It is likely that
the inflow of enormous amounts of gas has triggered star formation in this
galaxy. The sudden acquisition of cold gas may lead to a starburst in this
galaxy like those commonly seen in simulations.

We present a low-redshift (z=0.029) Damped Lyman$alpha$ (DLA) system in the
spectrum of a background Quasi-Stellar Object (QSO). The DLA is associated with
an interacting galaxy pair within a galaxy group. We detected weak
Lyman$alpha$ emission centered at the absorption trough of the DLA. The
emission was likely tracing the neutral HI reservoir around the galaxies in the
interacting pair, which scattered the Lyman$alpha$ generated by star formation
within those galaxies. We also found that the interacting pair is enveloped by
a large HI cloud with $rm M(HI)=2times 10^{10}M_{odot}$. We discovered
blueshifted 21~cm HI emission, corresponding to M(HI)=$rm
2times10^{9}~M_{odot}$, associated with J151225.15$+$012950.4 – one of the
galaxies in the interacting pair. The blueshifted HI was tracing gas flowing
into the galaxy from behind and towards us. Gas at similar blueshifted
velocities was seen in the QSO sightline thus suggesting the presence of a
filamentary structure of the order of 100~kpc feeding the galaxy. We estimated
a mass inflow rate of $ rm 2 M_{odot}~yr^{-1}$ into the galaxy, which matches
the star formation rate estimated from H$alpha$ emission. It is likely that
the inflow of enormous amounts of gas has triggered star formation in this
galaxy. The sudden acquisition of cold gas may lead to a starburst in this
galaxy like those commonly seen in simulations.

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