Structure and stellar content of dwarf galaxies - I. B and R photometry of dwarf galaxies in the M 81 group

Astronomy and Astrophysics Supplement Series, Jul 2018

We have carried out CCD photometry in the Cousins B and R bands of 25 dwarf galaxy members and suspected members of the M 81 group of galaxies. Based on azimuthally averaged brightness profiles we have derived total magnitudes, effective radii, effective surface brightnesses, as well as galaxy diameters at various isophotal levels in both photometric bands. Best-fitting exponential parameters and colour gradients are also given for these galaxies. The data will be interpreted, along with those of another supplementary paper, in Paper III of this series (to appear in the main journal). In two appendices we discuss the nature of a clustering of unusual low-surface brightness objects in the south-east corner of the M 81 group and show the luminosity function of its presently known members.

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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 - 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)


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T. Bremnes, B. Binggeli, P. Prugniel. Structure and stellar content of dwarf galaxies - I. B and R photometry of dwarf galaxies in the M 81 group, Astronomy and Astrophysics Supplement Series, pp. 313-328, Volume 129, Issue 2, DOI: 10.1051/aas:1998398