Astron. Astrophys. Suppl. Ser. 145, 229-242

A search for LSB dwarf galaxies in the M81 group on digitally stacked Schmidt plates

D.Froebrich - H.Meusinger

Send offprint request: H. Meusinger

Thüringer Landessternwarte Tautenburg, Sternwarte 5, D-07778 Tautenburg, Germany
e-mail: frobrich@tls-tautenburg.de/meus@tls-tautenburg.de

Received December 21, 1999; accepted May 18, 2000

Abstract:

We present a search for low surface brightness (LSB) dwarf galaxies in a region of 10 square degrees around M 81. The survey is based on the digital co-addition of Schmidt plates where algorithms for sub-arcsecond co-centering, quality-weighting and sigma-clipping "bad pixel'' rejection are applied. The 3$\sigma$ surface brightness limit is $\mu_{\rm lim} = 25.6\,\mbox{mag/}\Box\hbox{$^{\prime\prime}$ }$. In a substantial fraction of the surveyed area, the detection of LSB objects is limited by "Galactic cirrus'' rather than by the limiting magnitude of the stacked image. Optimum search parameters for an automated detection of dwarf galaxies are derived from simulations. The final selection of LSB dwarf candidates relies on a combination of automated detection and visual inspection. We present six new dwarf galaxy candidates with $\mu_{B}(0) \ge 23\,\mbox{mag/}\Box\hbox{$^{\prime\prime}$ }$. Photometric data and best fitting parameters for the exponential model are derived both for the new candidates and for some previously known LSB dwarf galaxies in the field. For the most likely new dwarf member of the M81 group, a central surface brightness of $\mu_{B}(0) = 25.4\,\mbox{mag/}\Box\hbox{$^{\prime\prime}$ }$ and a scale-length of 0.3kpc are derived.

Key words: galaxies: clusters: individual: M81 group -- galaxies: general -- galaxies: photometry -- galaxies: fundamental parameters