Graduate student Kevin Hall and I carried out deep integral-field spectroscopic observations of a unique conjunction of an early massive dusty starburst galaxy and two quasars in its background with the 10-meter Keck telescope on Mauna Kea, Hawaii. All three massive galaxies are at redshifts greater than 2.5 (corresponding to a very young universe, about 18% of its current age).

Previous high-resolution quasar absorption-line spectroscopy has revealed high neutral hydrogen column density, extremely metal-poor (about 1% solar) gas streams in the circumgalactic medium of the starburst. Here, with 2 hours of integration time, we detect a filamentary hydrogen Lyman-α nebula stretching 180 kiloparsec from the starburst. The filament intercepts both quasar sightlines, implying that we are seeing the same gas stream in both emission and in absorption.

The starburst-quasar conjunction also multiplies the efficiency of the Keck observations, allowing a direct comparison of the extended nebulae in two distinct environments: starburst vs. quasar. We find that the nebula around the quasars are much brighter and show steeper surface brightness profiles than the one around the dusty starburst. This is consistent with the additional photoionization and photon scattering provided by the quasars.

Bibliography: Hall, K. and Fu, H., ApJ, in press (2024) “HI Ly-α Emission from a Metal-Poor Cool Stream Fueling an Early Dusty Starburst” The analysis Python notebooks and the coadded datacubes are shared on Github.

stream data Above: Optimally extracted HI Lyman-α surface brightness maps. Extended nebulae are detected around all three early massive galaxies, with diverse morphologies. The filamentary nebula around the starburst (yellow cross) intercepts the directions towards both background QSOs (red and yellow stars).

stream data Above: Azimuthally averaged HI Lyman-α surface brightness profiles. The nebulae around quasars (labelled QSO1 and QSO2) are clearly brighter than that around the starburst (labelled SMG) in the central 100 kpc.

Acknowledgement

The research benefited from the excellent data from the W. M. Keck Observatory on Mauna Kea, Hawaii. The work at Iowa was generously supported by the National Science Foundation (NSF) under grant AST-2103251.