1112.4408 (J. Rosdahl et al.)
J. Rosdahl, J. Blaizot
{Abridged} We investigate the observability of cold accretion streams at
redshift 3 via Lyman-alpha radiation and the feasibility of cold accretion as
the main driver behind giant Lya blobs (LABs). We run cosmological zoom
simulations focusing on 3 halos spanning two orders of magnitude in mass, from
10^11 to 10^13 solar masses. We use a version of the AMR code Ramses that
includes radiative transfer of UV photons, and we employ a refinement strategy
that allows us to resolve accretion streams in their natural environment to an
unprecedented level. For the first time, we self-consistently model
self-shielding in the cold streams from the cosmological UV background, which
enables us to accurately predict their temperatures, ionization states and Lya
luminosities. We find the efficiency of gravitational heating in cold streams
in a ~10^11 solar mass halo is around 10-20% throughout most of the halo but
reaching much higher values close to the center. As a result most of the Lya
luminosity comes from the circumgalactic gas which is concentrated at the
central 20% of the halo radius, leading to Lya emission which is not extended.
In more massive halos, of >10^12 solar masses, cold accretion is complex and
disrupted, and gravitational heating does not happen as a steady process. The
cold accretion in these massive halos can easily produce those observed giant
blobs that have stellar continuum counterparts. Our simulations largely agree
with LAB observations, though we slightly and systematically over-predict LAB
abundances, perhaps hinting that the interplay of Lya scattering, local UV
enhancement and SNe feedback may have a negative net effect on the Lya
luminosity and extent. We predict that a factor of a few increase in
sensitivity from the current observational limits should unambiguously reveal
continuum-free accretion streams around massive galaxies at z=3.
View original:
http://arxiv.org/abs/1112.4408
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