Star Formation in Ram Pressure Stripped Tails

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.23). 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: 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.
    The Astrophysical Journal 03/2014; 792(1). DOI:10.1088/0004-637X/792/1/11 · 6.28 Impact Factor
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    ABSTRACT: One process affecting gas-rich cluster galaxies is ram pressure stripping (RPS), i.e., the removal of galactic gas through direct interaction with the intracluster medium (ICM). Galactic magnetic fields may have an important impact on the stripping rate and tail structure. We run the first magnetohydrodynamic (MHD) simulations of RPS that include a galactic magnetic field, using 159 pc resolution throughout our entire domain in order to resolve mixing throughout the tail. We find very little difference in the total amount of gas removed from the unmagnetized and magnetized galaxies, although a magnetic field with a radial component will initially accelerate stripped gas more quickly. In general, we find that magnetic fields in the disk lead to slower velocities in the stripped gas near the disk and faster velocities farther from the disk. We also find that magnetic fields in the galactic gas lead to larger unmixed structures in the tail. Finally, we discuss whether ram pressure stripped tails can magnetize the ICM. We find that the total magnetic energy density grows as the tail lengthens, likely through turbulence. There are μG-strength fields in the tail in all of our MHD runs, which survive to at least 100 kpc from the disk (the edge of our simulated region), indicating that the area-filling factor of magnetized tails in a cluster could be large.
    The Astrophysical Journal 10/2014; 795(2):148. DOI:10.1088/0004-637X/795/2/148 · 6.28 Impact Factor
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    ABSTRACT: We present the analysis of a deep Chandra observation of a ~2 L * late-type galaxy, ESO 137-002, in the closest rich cluster A3627. The Chandra data reveal a long (gsim40 kpc) and narrow tail with a nearly constant width (~3 kpc) to the southeast of the galaxy, and a leading edge ~1.5 kpc from the galaxy center on the upstream side of the tail. The tail is most likely caused by the nearly edge-on stripping of ESO 137-002's interstellar medium (ISM) by ram pressure, compared to the nearly face-on stripping of ESO 137-001 discussed in our previous work. Spectral analysis of individual regions along the tail shows that the gas throughout it has a rather constant temperature, ~1 keV, very close to the temperature of the tails of ESO 137-001, if the same atomic database is used. The derived gas abundance is low (~0.2 solar with the single-kT model), an indication of the multiphase nature of the gas in the tail. The mass of the X-ray tail is only a small fraction (<5%) of the initial ISM mass of the galaxy, suggesting that the stripping is most likely at an early stage. However, with any of the single-kT, double-kT, and multi-kT models we tried, the tail is always "over-pressured" relative to the surrounding intracluster medium (ICM), which could be due to the uncertainties in the abundance, thermal versus non-thermal X-ray emission, or magnetic support in the ICM. The Hα data from the Southern Observatory for Astrophysical Research show a ~21 kpc tail spatially coincident with the X-ray tail, as well as a secondary tail (~12 kpc long) to the east of the main tail diverging at an angle of ~23° and starting at a distance of ~7.5 kpc from the nucleus. At the position of the secondary Hα tail, the X-ray emission is also enhanced at the ~2σ level. We compare the tails of ESO 137-001 and ESO 137-002, and also compare the tails to simulations. Both the similarities and differences of the tails pose challenges to the simulations. Several implications are briefly discussed. Based on observations made with the Chandra X-Ray Observatory and the Southern Observatory for Astrophysical Research (SOAR) telescope.
    The Astrophysical Journal 11/2013; 777(2):122-. DOI:10.1088/0004-637X/777/2/122 · 6.28 Impact Factor

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