2014ApJ...791L..30M -
Astrophys. J., 791, L30 (2014/August-3)
HST-COS spectroscopy of the cooling flow in A1795–Evidence for inefficient star formation in condensing intracluster gas.
McDONALD M., ROEDIGER J., VEILLEUX S. and EHLERT S.
Abstract (from CDS):
We present far-UV spectroscopy from the Cosmic Origins Spectrograph on the Hubble Space Telescope of a cool, star-forming filament in the core of A1795. These data, which span 1025 Å < λrest< 1700 Å, allow for the simultaneous modeling of the young stellar populations and the intermediate-temperature (105.5 K) gas in this filament, which is far removed (∼30 kpc) from the direct influence of the central active galactic nucleus. Using a combination of UV absorption line indices and stellar population synthesis modeling, we find evidence for ongoing star formation, with the youngest stars having ages of 7.5–2.0+2.5 Myr and metallicities of 0.4–0.1+0.2 Z☉. The latter is consistent with the local metallicity of the intracluster medium. We detect the O VI λ1038 line, measuring a flux of f_ O VI, 1038_= 4.0±0.9x10–17 erg/s/cm2. The O VI λ1032 line is redshifted such that it is coincident with a strong Galactic H2absorption feature, and is not detected. The measured O VI λ1038 flux corresponds to a cooling rate of 0.85±0.2 (stat)±0.15 (sys) M☉/yr at ∼105.5 K, assuming that the cooling proceeds isochorically, which is consistent with the classical X-ray luminosity-derived cooling rate in the same region. We measure a star formation rate of 0.11±0.02 M☉/yr from the UV continuum, suggesting that star formation is proceeding at 13–2+3% efficiency in this filament. We propose that this inefficient star formation represents a significant contribution to the larger-scale cooling flow problem.
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Journal keyword(s):
galaxies: clusters: individual: A1795 - galaxies: clusters: intracluster medium - galaxies: star formation - galaxies: stellar content
Simbad objects:
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