Tracing satellite planes in the Sculptor group: II. Discovery of five faint dwarf galaxies in the DESI Legacy Survey

TL;DR

This paper reports the discovery of five faint dwarf galaxies around NGC 253 using deep imaging surveys, contributing new data to the study of satellite galaxy distributions and their consistency with Lambda-CDM models.

Contribution

It presents the first systematic search for faint dwarf satellites around NGC 253, revealing five new candidates and analyzing their spatial distribution in relation to cosmological expectations.

Findings

Discovered five new dwarf galaxy candidates near NGC 253.

The satellite distribution is less flattened and more consistent with Lambda-CDM.

The overall satellite system appears lopsided, but conclusions are limited by lack of distance and velocity data.

Abstract

Although substantial progress has been made in reconciling LCDM simulations with the observed abundance and distribution of satellite galaxies, important tensions persist. Studying satellite systems around spiral galaxies thus remains key in addressing these tensions. In this series of papers we report the first results of an on-going systematic survey of faint dwarf spheroidal galaxies in the vicinity of the bright late-type spiral NGC 253 galaxy, the brightest member of the Sculptor filament located at a distance of 3.7 Mpc. We performed a new NGC 253 satellite search by means of visual inspection using co-added image cutouts reprocessed in the DESI Legacy image surveys, reaching a very low surface brightness regime (28.0--29.0 mag arcsec-2). Five new dwarf galaxy candidates have been discovered in the vicinity of NGC 253, that we named them Do V, Do VI, Do VII, Do VIII and Do IX. Assuming they are associated to NGC 253, their total absolute V-magnitudes fall in the -7 to -9 mag range, which is typical for dwarf satellites in the local Universe. The central surface brightness tend to be extremely low for all the discovered dwarfs and fall roughly in the range of 25--26 mag arcsec-2 in g-band. We present a new list of galaxies located around the giant spiral NGC 253. With the inclusion of these additional satellite candidates, the overall spatial distribution of the system becomes less flattened and is now broadly consistent with analogs drawn from Lambda-CDM expectations. Interestingly, the distribution appears to be rather lopsided. Yet, firm conclusions on the presence of absence of a correlated satellite structure are hampered since distance information is lacking, the census of observed dwarfs in the system remains far from complete, and spectroscopic velocities are not even available for most known satellites.