Deep optical imaging of the dark galaxy candidate AGESVC1 282

TL;DR

This study used deep optical imaging to investigate a dark galaxy candidate in the Virgo cluster, finding no optical counterpart and constraining its stellar content, suggesting it may be a true dark galaxy without stars.

Contribution

First deep optical imaging of the dark galaxy candidate AGESVC1 282, providing constraints on its stellar content and challenging standard explanations for dark HI clouds.

Findings

No optical counterpart detected down to surface brightness limit of 29.1 mag arcsec$^{-2}$

Upper limit on V-band luminosity is $1.1\times10^7 L_\odot$

HI-to-stellar mass ratio is above 3.1

Abstract

The blind HI survey Arecibo Galaxy Environment Survey (AGES) detected several unresolved sources in the Virgo cluster, which do not have optical counterparts in the Sloan Digital Sky Survey. The origin of these dark clouds is unknown. They might be crucial objects since they could be the so-called dark galaxies, that is, the dark matter halos without stellar content that are expected from cosmological simulations. In order to reveal the nature of the dark clouds, we took a deep optical image of one them, AGESVC1 282, with the newly-commissioned 1.4m Milankovi\'c Telescope. After observing it for 10.4h in the $L$-filter, the image reached a surface-brightness limit of about 29.1 mag arcsec$^{-2}$ in $V$. No optical counterpart was detected. We placed an upper limit on the $V$-band luminosity of the object of $1.1\times10^7\,L_\odot$, giving a stellar mass below $1.4\times10^7\,M_\odot$ and a HI-to-stellar mass ratio above 3.1. By inspecting archival HI observations of the surrounding region, we found that none of the standard explanations for optically dark HI clouds fits the available constraints on this object.