Evidence for shock-heated gas in the Taffy Galaxies and Bridge from Optical Emission-Line IFU spectroscopy. (arXiv:1812.07743v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Joshi_B/0/1/0/all/0/1">Bhavin A. Joshi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Appleton_P/0/1/0/all/0/1">Philip N. Appleton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Blanc_G/0/1/0/all/0/1">Guillermo A. Blanc</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Guillard_P/0/1/0/all/0/1">Pierre Guillard</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rich_J/0/1/0/all/0/1">Jeffrey Rich</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Struck_C/0/1/0/all/0/1">Curtis Struck</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Freeland_E/0/1/0/all/0/1">Emily E. Freeland</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Peterson_B/0/1/0/all/0/1">Bradley W. Peterson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Helou_G/0/1/0/all/0/1">George Helou</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Alatalo_K/0/1/0/all/0/1">Katherine Alatalo</a>
We present optical IFU observations of the Taffy system (UGC 12914/15); so
named because of the radio emission that stretches between the two galaxies.
Given that these gas rich galaxies are believed to have recently collided
head-on, the pair exhibits a surprisingly normal total (sub-LIRG) IR luminosity
($mathrm{L_{FIR} sim 4.5 times 10^{10}}$ L$_odot$). Previous observations
have demonstrated that a large quantity of molecular and neutral gas have been
drawn out of the galaxies into a massive multi-phase bridge, consistent with
numerical models of the near face-on, counter-rotating collision. We present,
for the first time, spatially resolved spectroscopy of the ionized gas in the
system. The results show that the ionized gas is highly disturbed
kinematically, with gas spread in two main filaments between the two galaxies.
The line profiles exhibit widespread double components found in both the bridge
and parts of the disks of the galaxies. Deep Balmer absorption (perhaps a
post-starburst relic of the collision) is also seen in the outer ring of UGC
12914, and over part of the main disk of UGC 12915. We have investigated the
spatial distribution of the excitation properties of the ionized gas using
emission-line diagnostic diagrams, and conclude that large quantities (up to
40$%$) of the emission from the entire system is consistent with gas heated in
$sim$200 km s$^{-1}$ shocks. While the shocked gas is mainly associated with
regions in the bridge, there is a significant amount of shocked gas associated
with both galaxies. The results confirm other multi-wavelength indicators that
suggest that the effects of shocks and turbulence can continue to be felt in a
high-speed galaxy collision long after the collision has occurred. The
persistence of shocks in the Taffy system may explain the relatively low
current star formation rates in the system as a whole.
We present optical IFU observations of the Taffy system (UGC 12914/15); so
named because of the radio emission that stretches between the two galaxies.
Given that these gas rich galaxies are believed to have recently collided
head-on, the pair exhibits a surprisingly normal total (sub-LIRG) IR luminosity
($mathrm{L_{FIR} sim 4.5 times 10^{10}}$ L$_odot$). Previous observations
have demonstrated that a large quantity of molecular and neutral gas have been
drawn out of the galaxies into a massive multi-phase bridge, consistent with
numerical models of the near face-on, counter-rotating collision. We present,
for the first time, spatially resolved spectroscopy of the ionized gas in the
system. The results show that the ionized gas is highly disturbed
kinematically, with gas spread in two main filaments between the two galaxies.
The line profiles exhibit widespread double components found in both the bridge
and parts of the disks of the galaxies. Deep Balmer absorption (perhaps a
post-starburst relic of the collision) is also seen in the outer ring of UGC
12914, and over part of the main disk of UGC 12915. We have investigated the
spatial distribution of the excitation properties of the ionized gas using
emission-line diagnostic diagrams, and conclude that large quantities (up to
40$%$) of the emission from the entire system is consistent with gas heated in
$sim$200 km s$^{-1}$ shocks. While the shocked gas is mainly associated with
regions in the bridge, there is a significant amount of shocked gas associated
with both galaxies. The results confirm other multi-wavelength indicators that
suggest that the effects of shocks and turbulence can continue to be felt in a
high-speed galaxy collision long after the collision has occurred. The
persistence of shocks in the Taffy system may explain the relatively low
current star formation rates in the system as a whole.
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