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Gravity-Driven Lyman-Alpha Blobs from Cold Streams into Galaxies | | T. Goerdt
; A. Dekel
; A. Sternberg
; D. Ceverino
; R. Teyssier
; J. R. Primack
; | | Date: |
30 Nov 2009 | | Abstract: | We use high-res cosmological hydro AMR simulations to predict the hydrogen
Lalpha emission from the cold gas streams that fed galaxies in massive haloes
at high z. The local emissivities due to collisional excitation are calculated
from the simulated gas properties, while photoionization is less important. The
Lalpha surface density is mapped assuming that 85% of the Lalpha photons are
observed. Typical haloes of mass Mv~10^{12-13}Msun at z ~ 3 emit as Lalpha
blobs (LABs) with luminosities 10^{43-44} erg/s and 50-100kpc extent. Most of
the Lalpha comes from the extended, narrow, partly clumpy, inflowing, cold
streams of (1-5)*10^4K that feed the galaxy. Dust absorption is negligible in
the streams. The predicted LAB morphology is irregular, with dense clumps and
elongated extensions. The area contained within isophotes with surface
brightnesses of 2.2*10^{-18} erg s^{-1} cm^{-2} arcsec^{-2} is ~20-200
arcsec^2. The linewidth is expected to range from a few hundreds to above 1000
km/s with a large variance. The typical Lalpha surface brightness profile is
proportional to r^{-1.2}. The Lalpha emission in our simulations is powered by
the gravitational energy gained by the streaming into the halo potential well,
while the UV background contributes <20%. A toy model of gravitational heating
explains the simulated results. The simulated LABs are similar in luminosity,
morphology and extent to the observed LABs, and they have distinct kinematic
features. The predicted luminosity function is consistent with observations,
and the predicted areas and linewidths reproduce the observed scaling
relations. The LABs can be regarded as direct detections of the cold streams
that drive galaxy evolution at high z. This mechanism for producing LABs
appears inevitable in most high-z galaxies. | | Source: | arXiv, 0911.5566 | | Services: | Forum | Review | PDF | Favorites | |
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