Discovery of Faint Double-peak Hα Emission in the Halo of Low Redshift Galaxies

Abstract

Aimed at the detection of cosmological gas being accreted onto galaxies in the local universe, we examined the H α emission in the halo of 164 galaxies in the field of view of the Multi-Unit Spectroscopic Explorer Wide survey (MUSE-Wide) with observable H α (redshift <0.42). An exhaustive screening of the corresponding H α images led us to select 118 reliable H α emitting gas clouds. The signals are faint, with a surface brightness of 10 − 17.3 ± 0.3 erg s − 1 cm − 2 arcsec − 2 . Through statistical tests and other arguments, we ruled out that they are created by instrumental artifacts, telluric line residuals, or high-redshift interlopers. Around 38% of the time, the H α line profile shows a double peak with the drop in intensity at the rest frame of the central galaxy, and with a typical peak-to-peak separation of the order of ±200 km s −1 . Most line emission clumps are spatially unresolved. The mass of emitting gas is estimated to be between 1 and 10 −3 times the stellar mass of the central galaxy. The signals are not isotropically distributed; their azimuth tends to be aligned with the major axis of the corresponding galaxy. The distances to the central galaxies are not random either. The counts drop at a distance >50 galaxy radii, which roughly corresponds to the virial radius of the central galaxy. We explore several physical scenarios to explain this H α emission, among which accretion disks around rogue intermediate-mass black holes fit the observations best.