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  • 1602.07695v1

    Rights statement: This is an author-created, un-copyedited version of an article accepted for publication/published in The Astrophysical Journal. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at doi: 10.3847/0004-637X/823/2/74

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Lyman alpha signatures from direct collapse black holes

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Article number74
<mark>Journal publication date</mark>1/06/2016
<mark>Journal</mark>The Astrophysical Journal
Issue number2
Volume823
Number of pages14
Publication statusPublished
Early online date24/05/16
Original languageEnglish

Abstract

`Direct collapse black holes' (DCBHs) provide possible seeds for supermassive black holes that exist at redshifts as high as z~7. We study Lyman Alpha (Lya) radiative transfer through simplified representations of the DCBH-scenario. We find that gravitational heating of the collapsing cloud gives rise to a Lya cooling luminosity of up to ~ 1e38(M_gas/1e6 Msun)^2 erg/s. The Lya production rate can be significantly larger during the final stages of collapse, but collisional deexcitation efficiently suppresses the emerging Lya flux. Photoionization by a central source boosts the Lya luminosity to L~1e43(M_BH/1e6 M_sun) erg/s during specific evolutionary stages of the cloud, where M_BH denotes the mass of the black hole powering this source. We predict that the width and velocity off-set of the Lya spectral line range from a few tens to few thousands km/s, depending sensitively on the evolutionary state of the cloud. We also compare our predictions to observations of CR7 (Sobral et al. 2015), a luminous Lya emitter at z~7, which is potentially associated with a DCBH. If CR7 is powered by a black hole, then its Lya flux alone requires that M_BH> 1e7 M_sun, which exceeds the mass of DCBHs when they first form. The observed width of the Lya spectrum favors the presence of only a low column density of hydrogen, log [N_HI/cm^-2]~19-20. The shape of the Lya spectrum indicates that this gas is outflowing. These requirements imply that if CR7 harbors a DCBH, then the physical conditions that enabled its formation have been mostly erased, which is in agreement with theoretical expectations.

Bibliographic note

This is an author-created, un-copyedited version of an article accepted for publication/published in The Astrophysical Journal. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at doi: 10.3847/0004-637X/823/2/74