Andromeda IV, a solitary gas‐rich dwarf galaxy

Abstract

Observations are presented of the isolated dwarf irregular galaxy And IV made with the Hubble Space Telescope Advanced Camera for Surveys and the Giant Metrewave Radio Telescope in the 21 cm H i line. We determine the galaxy distance of 7.17±0.31 Mpc using the Tip of Red Giant Branch method. The galaxy has a total blue absolute magnitude of -12.81 mag, linear Holmberg diameter of 1.88 kpc, and an H i-disk extending to 8.4 times the optical Holmberg radius. The H i massto-blue luminosity ratio for And IV amounts 12.9 M /L . From the GMRT data we derive the rotation curve for the H i and fit it with different mass models. We find that the data are significantly better fit with an iso-thermal dark matter halo, than by an NFW halo. We also find that MOND rotation curve provides a very poor fit to the data. The fact that the isothermal dark matter halo provides the best fit to the data supports models in which star formation feedback results in the formation of a dark matter core in dwarf galaxies. The total mass-to-blue luminosity ratio of 162 M /L makes And IV among the darkest dIrr galaxies known. However, its baryonic-to-dark mass ratio (M gas + M * )/M T = 0.11 is close to the average cosmic baryon fraction of 0.15.

Galaxy Groups Within 3500 km s−1

“…Our group identification algorithm requires a good estimation of the mass of galaxies. Stars are the dominant baryonic component of 80% galaxies (Karachentsev et al 2016). Stellar luminosity can be used as a proxy for the total mass of a galaxy (Bell & de Jong 2001).…”

The universal rotation curve of dwarf disc galaxies

“…Furthermore, circular velocities of low mass galaxies, with Vmax 50 km/s, require to be checked for the pressure support correction, this can be done using the so-called "asymmetric drift correction" (Dalcanton & Stilp 2010). Therefore, most of the RCs in our sample either have the asymmetric drift correction applied (the ones taken from Oh et al 2011Oh et al , 2015Lelli et al 2014;Gentile et al 2010Gentile et al , 2012 or pressure support has been determined and is too small to affect the RC (the ones taking from Swaters et al 2009;Weldrake et al 2003;Karachentsev et al 2016). Despite that, we leave three galaxies (UGC1501, UGC5427 and UGC7861) for which circular velocities were not corrected.…”

Void galaxies in the nearby Universe – I. Sample description

“…We mention two known galaxies falling into the volume under consideration which are very gas-rich, low-metallicity objects, and, hence, are similar to many void galaxies. The first one is And IV (Karachentsev et al 2016;Pustilnik et al 2008) at D ∼7 Mpc falling in a minivoid with the total size of ∼7 Mpc. The second example is a very gas-rich pair of a metal-poor LSBD and an H i-cloud without visible optical counterpart, HI 1225+01 (Salzer et al 1991).…”