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