1. M101 Group Dave Riebel & Justice Bruursema 12 Februrary 2007

2. Basic Info Located in the Ursa Major constellation Part of the Virgo supercluster Brightest member, M101 is the pinwheel galaxy Main members consist of about 5-8 companion galaxies as defined by NGC Fouque et al. survey Lyons Groups of Galaxies Catalog Giuricin et al. Nearby Optical Galaxy survey

3. Group Members NameTypeRedshift* (km/s)mV*mV* M101SAB(rs)cd 241  2 8.3 NGC 5204SA(s)m 201  1 11.7 NGC 5474SA(s)cd pec 273  9 11.3 NGC 5477SA(s)m 304  5 14.4 NGC 5585SAB(s)d 305  3 11.2 UGC 8837IB(s)m 144  3 13.8 UGC 9405Im 222  6 17 *data gathered from NED **other possible members are NGC 5238 & UGC 8508

4. Image from www.nightsky.at/Photo/Gal/M101_wide_APO.html

5. Comparing Galaxy Groups Table from Karachentsev 1996 There have been no dwarf spheroidal galaxies with a diameter larger than 1 kpc detected in the NGC 5236 & M101 groups

6. M101 or NGC 5457 Very large, bright, nearly face on late-type spiral Bulgeless, extremely thin disk 28.8 arcmin x 26.9 arcmin = 1/5 the area of a full moon ~52 kpc = 2X the size of the Milky Way about 7.7 Mpc away, as determined by: Cepheid distances (Kelson et al. 1996) Planetary Nebulae distances (Feldmeier et al. 1996) Red Supergiant Var Stars (Jurcevic 2006) Mass is uncertain, often cited as 1.1·10 11 M o Problem is probably due to low surface brightness Studying dynamics of HII regions should help, although Puerari et al. only got 9.8·10 10 within 10kpc in 2004

7. More on M101 Gyser in nucleus (Moody et al. 1995) Intermediate mass black hole HII Regions – GHRs Home of SSCs ~1000 O stars, M101 has GHRs 2 orders of magnitude bigger than Milky Way’s X-ray binaries (recently found a 32.69hr eclipsing binary) ULX sources and UL-SSS (Also found in NGC 5204) possible intermediate mass black holes Hypernova – NGC 5471B, 5·10 52 ergs (Chen, R. et al., 2002) Super Novae observed (1909, 1951, 1970*) Not symmetric (in outer regions), core displaced from center of disk Perhaps distorted by near collision (NGC 5474)

8. NGC 5474 2 nd closest companion to M 101 Z velocity consistent with other studies (6-9 km/s) Bulge not coincident with kinematic center – Background?

9. Unanswered Questions Better mass estimates for M101 Photometry for NGC 5474 to understand star formation history What is the mechanism for the formation of GHR’s? (related to efficiency of molecular gas clouds to make new stars?) Can we use M101 and NGC 5204 to put better mass constraints on the BH’s of ULXs? (Vierdayanti et al. 2006)

10. References Chen, R., et al., 2002, A Critical Examination of Hypernova Remnant Candidates in M101, AJ, 123, 2462. Feldmeier, J., et al., 1996, The Planetary Nebulae Distance to M101,ApJ, 461, L25. Kelson, DD, et al., 1996, The Extragalactic Distance Scale Key Project. III…, ApJ, 463, 26. Karachentsev, I., 1996, The Local Group in comparison with other nearby groups of galaxies, A&A, 305, 33. Kong, A., Di Stefano, R., 2006, Ultra Luminous Supersoft X-Ray Sources in Nearby Galaxies. Liu, J., et al., 2006, Discovery of an eclipsing binary with a 32.69hr period in M101…, ApJ, 653, 602. Moody, J., et al., 1995, Evidence for mass outflow from the nucleus of M101: Knots, Rings and a Geyser, AJ 110, 2088. Rownd B. K., et al. H I distribution and kinematics in the peculiar spiral galaxy NGC 5474, AJ 108, 1638. Vierdayanti, K., et al., 2006, Do ULX Sources Really Contain Intermediate-Mass Black Holes?, PASJ, 58, 915. Thanks to http://hubblesite.org/newscenter/archive/releases/2006/10/ for the M101 picture and current distance/ size info.