Studies of the M81 Group: Tidal Star Formation and Spitzer
John Feldmeier
CWRU/NOAO
Collaborators: Robin Ciardullo (PSU), Pat Durrell (YSU),
Megan De Cesar (PSU), George Jacoby (WIYN), Denise
Hurley-Keller(CWRU), Chris Mihos (CWRU)
Galaxies are Fat
• Size of a Star = 7 x 10^8 m• Distance between Stars = 3 x 10^16 m Ratio = 4 x 10^7 – Unlikely
• Size of a large Galaxy = 9 x 10^20 m• Distance Between Galaxies = 3 x 10^22 m Ratio = 33 – 1,000,000 times more
common!
Movie Time!
• So, galaxy collisions can be common. What are their effects on galaxies and their environment?
• Programs for galaxy crashes are available at http://burro.astr.cwru.edu/JavaLab/index.html
The M81 Group
Yun, Ho, & Lo (1994)
D = 3.1 Mpc
Interaction is believed to have occurred 220 – 290 Myr ago
IPN observations from KPNO 4-m (PI: Feldmeier)
IRG observations from CFHT (PI: Durrell)
Loose Limit (4 PN): < 5.3%
Strict Limit (1 PN): < 1.3%
1 +/- 0.4 RGB stars per sq arcmin - < 2%
Blue objects are all sources with (V-I) colors bluer than 0.4 (at most 10% contamination). Objects are 34 and 37 kpc away from M81 (Durrell et al. 2004)
Evidence for extra-tidal star formation in the M81 group – well after the collision