MUSE Spectroscopic Identifications of Ultra-Faint Emission Line Galaxies with M$_{\mathrm{UV}}\sim$ -15

TL;DR

This study uses ultra-deep MUSE spectroscopy to identify and confirm the existence of extremely faint galaxies at high redshifts, providing insights into the sources that may have contributed to cosmic reionization.

Contribution

First spectroscopic confirmation of ultra-faint emission line galaxies at z=2.9-6.7 with magnitudes around -15, expanding understanding of early universe galaxy populations.

Findings

Detected 102 ultra-faint Lyman-alpha emitters at high redshift.

Confirmed faint UV continua and 1216 Angstrom-breaks through stacking.

Results suggest these galaxies are part of the high-EW tail of the Lyman-alpha population.

Abstract

Using an ultra-deep blind survey with the MUSE integral field spectrograph on the ESO Very Large Telescope, we obtain spectroscopic redshifts to a depth never explored before: galaxies with observed magnitudes m > 30 - 32. Specifically, we detect objects via Lyman-alpha emission at 2.9 < z < 6.7 without individual continuum counterparts in areas covered by the deepest optical/near-infrared imaging taken by the Hubble Space Telescope, the Hubble Ultra Deep Field. In total, we find 102 such objects in 9 square arcminutes at these redshifts. Detailed stacking analyses confirm the Lyman-alpha emission as well as the 1216 Angstrom-breaks and faint UV continua (M_UV ~ -15). This makes them the faintest spectroscopically-confirmed objects at these redshifts, similar to the sources believed to reionize the universe. A simple model for the expected fraction of detected/undetected Lyman-alpha emitters as a function of luminosity is consistent with these objects being the high-equivalent width tail of the normal Lyman-alpha-emitter population at these redshifts.