Lyman Alpha Blobs as an Observational Signature of Cold Accretion Streams into Galaxies

TL;DR

This paper proposes that Lyman Alpha blobs are observational signatures of cold gas streams accreting into galaxies, supported by hydrodynamic simulations matching observed properties and morphologies.

Contribution

It demonstrates that cold accretion streams can produce Lyman Alpha blobs with realistic luminosities and structures, linking them to galaxy formation processes.

Findings

Cold flows produce Lyman Alpha emission consistent with observed blobs.

Filamentary cold streams explain diverse blob morphologies.

Lyman Alpha blobs are linked to galaxy cold accretion in dense environments.

Abstract

Recent hydrodynamic simulations of galaxy formation reveal streams of cold (T ~ 1e4 K) gas flowing into the centers of dark matter halos as massive as 1e12-1e13.5 M_sun at redshifts z~1-3. In this paper we show that if > 20% of the gravitational binding energy of the gas is radiated away, then the simulated cold flows are spatially extended Lyman Alpha (Lya) sources with luminosities, Lya line widths, and number densities that are comparable to those of observed Lya blobs. Furthermore, the filamentary structure of the cold flows can explain the wide range of observed Lya blob morphologies. Since the most massive halos form in dense environments, the association of Lya blobs with overdense regions arise naturally. We argue that Lya blobs - even those which are clearly associated with starburst galaxies or quasars - provide direct observational support for the cold accretion mode of galaxies. We discuss various testable predictions of this association.