ALMA observations of Lyman-alpha Blob 1: halo sub-structure illuminated from within

TL;DR

This study uses ALMA and HST observations combined with cosmological simulations to reveal that the extended Ly-alpha emission in a high-redshift LAB is caused by resonant scattering in neutral hydrogen associated with halo substructure.

Contribution

It provides the first detailed model linking halo substructure and Ly-alpha scattering to the observed morphology of giant LABs at high redshift.

Findings

ALMA resolves the LAB into three submillimeter sources with high star formation rates.

Spectroscopic confirmation of a satellite galaxy near one of the submillimeter sources.

Simulations show Ly-alpha photons scatter in neutral hydrogen within halo substructure, producing extended emission similar to observations.

Abstract

We present new Atacama Large Millimeter/Submillimeter Array (ALMA) 850um continuum observations of the original Lyman-alpha Blob (LAB) in the SSA22 field at z=3.1 (SSA22-LAB01). The ALMA map resolves the previously identified submillimeter source into three components with total flux density S_850 = 1.68+/-0.06 mJy, corresponding to a star formation rate of ~150 M_sun/yr. The submillimeter sources are associated with several faint (m~27 mag) rest-frame ultraviolet sources identified in Hubble Space Telescope Imaging Spectrograph (STIS) clear filter imaging (~5850A). One of these companions is spectroscopically confirmed with Keck MOSFIRE to lie within 20 projected kpc and 250 km/s of one of the ALMA components. We postulate that some of these STIS sources represent a population of low-mass star-forming satellites surrounding the central submillimeter sources, potentially contributing to their growth and activity through accretion. Using a high resolution cosmological zoom simulation of a 10^13 M_sun halo at z=3, including stellar, dust and Ly-alpha radiative transfer, we can model the ALMA+STIS observations and demonstrate that Ly-alpha photons escaping from the central submillimeter sources are expected to resonantly scatter in neutral hydrogen, the majority of which is predicted to be associated with halo substructure. We show how this process gives rise to extended Ly-alpha emission with similar surface brightness and morphology to observed giant LABs.