Structure and stellar content of dwarf galaxies - I. B and R photometry of dwarf galaxies in the M 81 group
September
Structure and stellar content of dwarf galaxies?
T. Bremnes 1 2
B. Binggeli 1 2
P. Prugniel 0 1
0 Observatoire de Lyon , F-64561 St. Genis-Laval Cedex , France
1 Send o print requests to: T. Bremnes
2 Astronomical Institute, University of Basel , Venusstrasse 7, CH-4102 Binningen , Switzerland
We have carried out CCD photometry in the is a gap of data and knowledge between LG and cluster Cousins B and R bands of 25 dwarf galaxy members and dwarfs. ttrsobftsooiahiuenfravrrloisulegiplstaIendehpheneszvutaceioent(tsmrtswftloueaeesoutasdamogaistnlnaaehlaemlopslotpabtam,peewlphoxalrmeyatee-sisashenrgbrwausandesp.nrvieuirifhnTtcdelsaplueorhctpaoBsadteheolsfgeweebm−desgtme,drhaameiRetdelgteabaanirhxMsirctiwtnecciayongcurilbjeh8dtlosyolais1tsiuvusabnnpretrmgedeoahngrsbspeireoasr.naejtaulneBterd)pdpeca,.rierritsitiseo,sponutanfri-rettPnelegsetvtasatoeeaatphldcfirrawneeti,eaxoirgeavsiuacIoeleellohsIsuuxsIna.iotspssvgohuBtoogeef-rwpnaireftvhseadiaihnetencoesihndget-s-- ittrapPTOeohanoarsumeopmcrioTvu\oenmbegot1lmanseon0aetrpcaebnirsMealoavrnrnrf(iiipoedsbOns(crygg1ttHoehCo9tfgPphe7artdrm(e9)ohtoise,)au.eegre,tlwpi.rooLvu,dsagieGdptwmuahodaaenmlaal"lrsedl-ntfyexisoednrs,tidfesth)oattelgefehitmbantveiyghlngataaeVhatntxSndeitetiiccerarehmrsgOtisgampmaoaeolbedapifaoscdgi,enntKeatirrdlntovrwdt&egaaphF,eatheboobonBofrryhdi-introdgKawoeadlwhvlmoxaretedaarrrnecretfwtefle(surgsi1wtHgnisasa9caetaglr9laageutpa2nroxexta&s)dndye--.. corner of the M 81 group and show the luminosity function of its presently known members. This paper is the rst in a series dedicated to this purpose. A more detailed account of the scienti c background and motivation of our project will be given in a
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Dwarf galaxies are by now widely recognized as prime
laboratories for the study of many key issues of astronomy,
such as structure formation, galaxy evolution, star
formation, and dark matter
(e.g., Meylan & Prugniel 1994;
Ferguson & Binggeli 1994)
. Up to the present, studies
of dwarf galaxies have concentrated either on clusters of
galaxies, such as Virgo and Fornax, or the Local Group
(LG). The clusters, although rich in dwarfs, are relatively
distant. The LG dwarfs can be studied in great detail, but
there are only a few of them and these are much fainter,
intrinsically, than the known cluster dwarfs. Hence there
In our rst observing campaign we did B and R
imaging for essentially all ( 35) known dwarf
members from Bo¨rngen et al.'s list. Paper II will present deep
B; V; R; I photometry for a subsample of non-resolved
(early-type) dwarfs. However, for the purpose of
completeness we use here part of the material from Paper II,
so that the principal data on the group members can
be found in the present paper, including a CCD picture
gallery which supplements/supersedes the photographic
atlas of
Karachentseva et al. (1985)
. The photometric
data, i.e. surface brightness pro les and colour gradients
presented here and in Paper II will be interpreted in
Paper III, which is to appear in the main journal of A&A.
Kar 52
DDO 53
UGC 4483
Kar 54
UGC 4998
NGC 2976
BK 2N
Kar 59
BK 3N
T. Bremnes et al.: Structure and stellar content of dwarf galaxies. I.
A952+69 Kar 61
Ho IX BK 5N
DDO 71 UGC 5423
UGC 5658
IC 2574
DDO 82
BK 6N
DDO 87
Kar 73
Kar 74
In Appendix A we discuss the possible nature of an
unusual clustering of low-surface brightness objects in the
south-east corner of the M 81 group. While the case for
extra-galactic objects (Bo¨rngen et al. 1984) remains
viable, we argue in favour of a galactic nature (cirrus clouds)
for at least some of the cases.
In Appendix B we show the luminosity function for
M 81 group galaxies.
2. The sample
In Table 1 we give a complete list of the presently known
members and possible members of the M 81 group,
including also some galaxies in the near background which
had been classi ed as dwarf members before a velocity
became available. This list was prepared by Binggeli (Van
Driel et al. 1998) based on Bo¨rngen et al. (1982, 1984) and
Karachentseva et al. (1985)
. A map showing the
distribution of these objects on the sky can be found in Van Driel
et al. (1998). The observational status of the dwarfs with
respect to the photometry of both the present Paper I
and the upcoming Paper II is given in the Cols. 11{14 of
Table 1. A gallery of our best images, in terms of depth,
seeing, and morphological detail, is given in Fig. 1. As the
images from Paper II are usually superior due to a longer
exposure time, we show them here instead of the
somewhat less deep images from the rst observing campaign.
Deep R exposures of the objects suspected to be galactic
cirrus clouds are presented in Figs. A1, A2 and A3.
The present photometry is based on the images of 32
objects which were taken on three nights in December
1992 and seven nights in March 1993 on the 1:2 m
telescope of the OHP by P. Prugniel. They are 40 minute
Cousins B and 20 minute Cousins R exposures. The
camera used was the n 2 Tektronix 512 512 CCD (...truncated)