Abstract
For the first time, we reveal large amounts of cold molecular gas in a ram
pressure stripped tail, out to a large, intracluster distance from the galaxy.
With the ESO APEX telescope we have detected 12CO(2-1) emission corresponding
to more than 10^9 Msun of molecular gas (assuming a Galactic value of the
CO-to-H_2 conversion factor) in three Ha bright regions along the tail of the
Norma cluster ram pressure stripped galaxy ESO137-001, out to a projected
distance of 40 kpc from the disk. The amount of 1.5x10^8 Msun of H_2 found in
the most distant region is similar to molecular masses of tidal dwarf galaxies.
We speculate that a ram pressure dwarf galaxy (RPDG) could be forming in this
location. Along the tail, the amount of molecular gas was found to drop, while
masses of the X-ray emitting and diffuse ionized components stay roughly
constant. Moreover, the amounts of hot and cold gas are large and similar, and
together nearly account for the missing gas from the disk. We find a very low
star formation efficiency (tau>10^10 yr) in the stripped gas in ESO~137-001 and
suggest that this is due to a low average gas density in the tail, or turbulent
heating of the interstellar medium that is induced by a ram pressure shock. By
means of simple numerical modeling, we suggest that ESO137-001 may be at a high
orbital velocity of about 3000 km/s in the Norma cluster, in order to be
consistent with a first infall scenario. The corresponding strong ram pressure
would then be able to strip denser gas than is usual in other known ram
pressure stripped galaxies. Such a dense component in the tail is more able to
quickly transform into molecular gas than stripped diffuse gas. The
unprecedented bulk of observed molecular gas in the ESO137-001 tail also
suggests that some stripped gas may survive ram pressure stripping in the
molecular phase.
Description
[1403.2328] Abundant molecular gas and inefficient star formation in intracluster regions: Ram pressure stripped tail of the Norma galaxy ESO137-001
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