Discovery of an extremely gas-rich dwarf triplet near the center of the Lynx-Cancer void

TL;DR

This paper reports the discovery of a unique triplet of extremely gas-rich dwarf galaxies near the center of the Lynx-Cancer void, challenging existing models of galaxy formation and baryon distribution.

Contribution

It presents the first detailed observations of a gas-rich dwarf triplet in a cosmic void, highlighting their deviation from standard galaxy relations and implications for galaxy formation theories.

Findings

The triplet galaxies are among the most gas-rich known.

They deviate from the Tully-Fisher relation but follow the baryonic Tully-Fisher relation.

Their baryon fractions are significantly below the cosmic average.

Abstract

Giant Metrewave Radio Telescope (GMRT) HI observations, done as part of an ongoing study of dwarf galaxies in the Lynx-Cancer void, resulted in the discovery of a triplet of extremely gas rich galaxies located near the centre of the void.The triplet members SDSS J0723+3621, J0723+3622 and J0723+3624 have absolute magnitudes M_B of -14.2, -11.9 and -9.7 and M(HI)/L_B of \sim 2.9, ~10 and ~25, respectively. The gas mass fractions, as derived from the SDSS photometry and the GMRT data are 0.93, 0.997, 0.997 respectively. The faintest member of this triplet SDSS J0723+3624 is one of the most gas rich galaxies known. We find that all three galaxies deviate significantly from the Tully-Fisher relation, but follow the baryonic Tully-Fisher relation. All three galaxies also have a baryon fraction that is significantly smaller than the cosmic baryon fraction. For the largest galaxy in the triplet, this is in contradiction to numerical simulations. The discovery of this very unique dwarf triplet lends support to the idea that the void environment is conducive to the formation of galaxies with unusual properties. These observations also provide further motivation to do deep searches of voids for a "hidden" very gas-rich galaxy population with M_B > -11.