M101 Group

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 *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 • There have been no dwarf spheroidal galaxies with a diameter larger than 1 kpc detected in the NGC 5236 & M101 groups Table from Karachentsev 1996

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 1.1·1011 Mo • Problem is probably due to low surface brightness • Studying dynamics of HII regions should help, although Puerari et al. only got 9.8·1010 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, 5·1052 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. 2nd closest companion to M 101 Z velocity consistent with other studies (6-9 km/s) Bulge not coincident with kinematic center – Background? NGC 5474

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.