Letter to the Editor

Deep optical imaging of the dark galaxy candidate AGESVC1 282^⋆

¹ Université de Strasbourg, CNRS, Observatoire Astronomique de Strasbourg (ObAS), UMR 7550, 67000 Strasbourg, France
e-mail: bilek@astro.unistra.fr
² Astronomical Observatory, Volgina 7, 11060 Belgrade, Serbia
³ Astronomical Institute of the Czech Academy of Sciences, Boční II 1401/1a, 141 00 Praha 4, Czech Republic

Received: 13 August 2020
Accepted: 21 September 2020

Abstract

The blind H I 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 1.4 m Milanković Telescope. After observing it for 10.4 h 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 × 10⁷ L_⊙, giving a stellar mass below 1.4 × 10⁷ M_⊙ and a H I-to-stellar mass ratio above 3.1. By inspecting archival H I observations of the surrounding region, we found that none of the standard explanations for optically dark H I clouds fits the available constraints on this object.