Structure and stellar content of dwarf galaxies. III: B and R photometry of dwarf galaxies in the M101 group and the nearby field

TL;DR

This study presents detailed B and R band CCD photometry of 21 dwarf galaxies around the M101 group, providing key structural and stellar content data to explore their properties and potential stellar halos.

Contribution

It offers new photometric measurements and analysis of dwarf galaxies in the M101 group and nearby field, including surface brightness profiles and color gradients, enhancing understanding of their structure.

Findings

Some galaxies show luminosity excess suggesting extended stellar halos.

Photometric parameters will be used for comparative analysis with other dwarf galaxies.

Data indicates possible presence of old stellar populations in dwarf irregulars.

Abstract

We have carried out CCD photometry in the Cousins B and R bands of 21 dwarf galaxies in and around the M101 group. Eleven are members and suspected members of the group and ten are field galaxies in the projected vicinity of the group. We have derived total magnitudes, effective radii, effective surface brightnesses, as well as galaxy diameters at various isophotal levels in both colours. Best-fitting exponential parameters and colour gradients are also given for these galaxies. Some of the galaxies show a pronounced luminosity excess above the best-fitting exponential at large radii, or surface brightnesses fainter than approx 26 mag/sq_arcsec in R. This feature, while non-significant for a single case and technically difficult to interpret, might be an indication of the existence of an extended old stellar halo in dwarf irregulars. The photometric parameters of the galaxies presented here will be combined with previously published data for nearby dwarf galaxies and statistically analysed in a forthcoming paper.