Distance and mass of the NGC 253 galaxy group

TL;DR

This study measures the distances and total mass of the NGC 253 galaxy group using Hubble observations, revealing a low mass-to-luminosity ratio and a declined rotation curve, similar to other luminous spirals in the Local Volume.

Contribution

It provides new distance measurements for dwarf galaxies near NGC 253 and estimates the group's total mass, highlighting its unique rotation curve and mass-to-luminosity ratio compared to other galaxies.

Findings

Distances of dwarf galaxies are consistent with group membership.

Estimated total mass of NGC 253 is approximately 8.1×10^{11} solar masses.

NGC 253 has a declined rotation curve and a low mass-to-luminosity ratio.

Abstract

Two dwarf galaxies: WOC2017-07 and PGC 704814 located in the vicinity of the nearby luminous spiral galaxy NGC 253 were observed with the Advanced Camera for Surveys on the Hubble Space Telescope. Their distances of 3.62$\pm$0.18 Mpc and 3.66$\pm$0.18 Mpc were derived using the tip of the red giant branch method. These distances are consistent with the dwarf galaxies being members of the NGC 253 group. Based on the radial velocities and projected separations of seven assumed dwarf companions, we estimated the total mass of NGC 253 to be $(8.1\pm2.6) 10^{11} M_{\odot}$, giving a total-mass-to-$K$-luminosity ratio $M_{\rm orb}/L_K = (8.5\pm2.7) M_{\odot}/L_{\odot}$. A notable property of NGC 253 is its declined rotation curve. NGC 253 joins four other luminous spiral galaxies in the Local Volume with declined rotation curves (NGC 2683, NGC 2903, NGC 3521 and NGC 5055) that together have the low average total-mass-to-luminosity ratio, $M_{\rm orb}/L_K = (5.5\pm1.1) M_{\odot}/L_{\odot}$. This value is only $\sim$1/5 of the corresponding ratio for the Milky Way and M 31.