Volume 530, June 2011
|Number of page(s)||4|
|Published online||05 May 2011|
Letters to the Editor
Can evidence for cosmological accretion be observed in the Hα emission from galaxies at z ~ 2?⋆
GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
2 Institut d’Astrophysique Spatiale, UMR 8617, CNRS, Université Paris-Sud, Bâtiment 121, 91405 Orsay Cedex, France
Received: 24 January 2011
Accepted: 22 April 2011
In previous studies, it has been shown that the large line widths observed in high surface brightness Hα emitters at low and high redshifts are likely due to the mechanical energy injected by intense star formation. Here we discuss the possibility that the high surface brightnesses observed are not due to star formation, but due to cosmological gas accretion. We assume that all of the accretion energy is dissipated as shocks from the accreting gas. We show that in order to explain the high surface brightnesses both the mass accretion rate and energy would have to be much higher than expected from simulations or from equating the star formation with the accretion rate. We also investigate scaling relations between the surface brightness expected from accretion and for star formation through mechanical heating and photo-ionization, trying to identify a regime where such accretion may become evident in galaxies. Unfortunately, the surface brightness necessary to detect the gas in optical line emission is about an order of magnitude lower than what has currently been achieved with near-infrared observations of distant galaxies.
Key words: cosmology: observations / galaxies: evolution / galaxies: formation / galaxies: kinematics and dynamics / infrared: galaxies
© ESO, 2011
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