Star Formation in Ram Pressure Stripped Tails

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.52). 03/2012; 422(2). DOI: 10.1111/j.1365-2966.2012.20737.x
Source: arXiv

ABSTRACT We investigate the impact of star formation and feedback on ram pressure
stripping using high-resolution adaptive mesh simulations, building on a
previous series of papers that systematically investigated stripping using a
realistic model for the interstellar medium, but without star formation. We
find that star formation does not significantly affect the rate at which
stripping occurs, and only has a slight impact on the density and temperature
distribution of the stripped gas, indicating that our previous (gas-only)
results are unaffected. For our chosen (moderate) ram pressure strength,
stripping acts to truncate star formation in the disk over a few hundred
million years, and does not lead to a burst of star formation. Star formation
in the bulge is slightly enhanced, but the resulting change in the
bulge-to-disk ratio is insignificant. We find that stars do form in the tail,
primarily from gas that is ablated from the disk and the cools and condenses in
the turbulent wake. The star formation rate in the tail is low, and any
contribution to the intracluster light is likely to be very small. We argue
that star formation in the tail depends primarily on the pressure in the
intracluster medium, rather than the ram pressure strength. Finally, we compare
to observations of star formation in stripped tails, finding that many of the
discrepancies between our simulation and observed wakes can be accounted for by
different intracluster medium pressures.

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    ABSTRACT: In a 5 hour Halpha exposure of the N-W region of the Coma cluster with the 2.1m telescope at SPM (Mx) we discovered a 65 kpc cometary emission of ionized gas trailing behind the SBab galaxy NGC 4848. The tail points in the opposite direction of the cluster center, in the same direction where stripped HI has been detected in previous observations. The galaxy shows bright HII regions in an inner ring-like pattern, where the star formation takes place at the prodigious rate of 8.9 Msun/yr. From the morphology of the galaxy and of the trailing material, we infer that the galaxy is suffering from ram pressure due to its high velocity motion through the cluster IGM. We estimate that 4 x 10^9 Msun of gas is swept out from the galaxy forming the tail. Given the ambient conditions in the Coma cluster (rho = 6.3 x 10^-27 g/cm^3; sigma_vel = 940 km/s) simulations predict that the ram pressure mechanism is able to remove such an amount of gas in less than 200 Myr. This, combined with the geometry of the interaction, indicating radial infall into the cluster, leads to the conclusion that NGC 4848 is caught in its first passage through the dense cluster environment.
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    ABSTRACT: Context: Several galaxies in the Virgo cluster are known to have large HI gas tails related to a recent ram-pressure stripping event. The Virgo cluster has been extensively observed at 1539 A in the far-ultraviolet for the GALEX Ultraviolet Virgo Cluster Survey (GUViCS), and in the optical for the Next Generation Virgo Survey (NGVS), allowing a study of the stellar emission potentially associated with the gas tails of 8 cluster members. On the theoretical side, models of ram-pressure stripping events have started to include the physics of star formation. Aim: We aim to provide quantitative constraints on the amount of star formation taking place in the ram-pressure stripped gas, mainly on the basis of the far-UV emission found in the GUViCS images in relation with the gas content of the tails. Methods: We have performed three comparisons of the young stars emission with the gas column density: visual, pixel-by-pixel and global. We have compared our results to other observational and theoretical studies. Results: We find that the level of star formation taking place in the gas stripped from galaxies by ram-pressure is low with respect to the available amount of gas. Star formation is lower by at least a factor 10 compared to the predictions of the Schmidt Law as determined in regular spiral galaxy disks. It is also lower than measured in dwarfs galaxies and the outer regions of spirals, and than predicted by some numerical simulations. We provide constraints on the star formation efficiency in the ram-pressure stripped gas tails, and compare these with current models.
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