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Gravity-driven Lyα blobs from cold streams into galaxies


Goerdt, T; Dekel, A; Sternberg, A; Ceverino, D; Teyssier, R; Primack, J R (2010). Gravity-driven Lyα blobs from cold streams into galaxies. Monthly Notices of the Royal Astronomical Society, 407(1):613-631.

Abstract

We use high-resolution cosmological hydrodynamical adaptive mesh refinement (AMR) simulations to predict the characteristics of Lyα emission from the cold gas streams that fed galaxies in massive haloes at high redshift. The Lyα luminosity in our simulations is powered by the release of gravitational energy as gas flows from the intergalactic medium into the halo potential wells. The ultraviolet UV background contributes only <20per cent to the gas heating. The Lyα emissivity is due primarily to electron-impact excitation cooling radiation in gas at ~2 × 104 K. We calculate the Lyα emissivities assuming collisional ionization equilibrium at all gas temperatures. The simulated streams are self-shielded against the UV background, so photoionization and recombination contribute negligibly to the Lyα line formation. We produce theoretical maps of the Lyα surface brightnesses, assuming that ~85per cent of the Lyα photons are directly observable. We do not consider transfer of the Lyα radiation, nor do we include the possible effects of internal sources of photoionization such as star-forming regions. Dust absorption is expected to obscure a small fraction of the luminosity in the streams. We find that typical haloes of mass Mv ~ 1012-1013Msolar at z ~ 3 emit as Lyα blobs (LABs) with luminosities 1043-1044ergs-1. Most of the Lyα comes from the extended (50-100kpc) narrow, partly clumpy, inflowing, cold streams of (1-5) × 104K that feed the growing galaxies. The predicted LAB morphology is therefore irregular, with dense clumps and elongated extensions. The integrated area contained within surface brightness isophotes of 2 × 10-18ergs-1cm-2arcsec-2 is ~2-100arcsec2, consistent with observations. The linewidth is expected to range from 102 to more than 103kms-1 with a large variance. The typical Lyα surface brightness profile is ~ r-1.2 where r is the distance from the halo centre. Our simulated LABs are similar in luminosity, morphology and extent to the observed LABs, with distinct kinematic features. The predicted Lyα luminosity function is consistent with observations, and the predicted areas and linewidths roughly recover the observed scaling relations. This mechanism for producing LABs appears inevitable in many high-z galaxies, though it may work in parallel with other mechanisms. Some of the LABs may thus be regarded as direct detections of the cold streams that drove galaxy evolution at high z.

We use high-resolution cosmological hydrodynamical adaptive mesh refinement (AMR) simulations to predict the characteristics of Lyα emission from the cold gas streams that fed galaxies in massive haloes at high redshift. The Lyα luminosity in our simulations is powered by the release of gravitational energy as gas flows from the intergalactic medium into the halo potential wells. The ultraviolet UV background contributes only <20per cent to the gas heating. The Lyα emissivity is due primarily to electron-impact excitation cooling radiation in gas at ~2 × 104 K. We calculate the Lyα emissivities assuming collisional ionization equilibrium at all gas temperatures. The simulated streams are self-shielded against the UV background, so photoionization and recombination contribute negligibly to the Lyα line formation. We produce theoretical maps of the Lyα surface brightnesses, assuming that ~85per cent of the Lyα photons are directly observable. We do not consider transfer of the Lyα radiation, nor do we include the possible effects of internal sources of photoionization such as star-forming regions. Dust absorption is expected to obscure a small fraction of the luminosity in the streams. We find that typical haloes of mass Mv ~ 1012-1013Msolar at z ~ 3 emit as Lyα blobs (LABs) with luminosities 1043-1044ergs-1. Most of the Lyα comes from the extended (50-100kpc) narrow, partly clumpy, inflowing, cold streams of (1-5) × 104K that feed the growing galaxies. The predicted LAB morphology is therefore irregular, with dense clumps and elongated extensions. The integrated area contained within surface brightness isophotes of 2 × 10-18ergs-1cm-2arcsec-2 is ~2-100arcsec2, consistent with observations. The linewidth is expected to range from 102 to more than 103kms-1 with a large variance. The typical Lyα surface brightness profile is ~ r-1.2 where r is the distance from the halo centre. Our simulated LABs are similar in luminosity, morphology and extent to the observed LABs, with distinct kinematic features. The predicted Lyα luminosity function is consistent with observations, and the predicted areas and linewidths roughly recover the observed scaling relations. This mechanism for producing LABs appears inevitable in many high-z galaxies, though it may work in parallel with other mechanisms. Some of the LABs may thus be regarded as direct detections of the cold streams that drove galaxy evolution at high z.

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Additional indexing

Other titles:Gravity-driven Lyman-alpha blobs from cold streams into galaxies
Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute for Computational Science
Dewey Decimal Classification:530 Physics
Language:English
Date:September 2010
Deposited On:02 Mar 2011 14:23
Last Modified:05 Apr 2016 14:33
Publisher:Wiley-Blackwell
ISSN:0035-8711
Additional Information:The definitive version is available at www.blackwell-synergy.com
Publisher DOI:10.1111/j.1365-2966.2010.16941.x
Related URLs:http://arxiv.org/abs/0911.5566
Permanent URL: http://doi.org/10.5167/uzh-41748

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