Stellar population analysis from broad-band colours

Abstract

We have developed an analytical method to investigate the stellar populations in a galaxy using the broad‐band colours. The method enables us to determine the relative contribution, spatial distribution and age for different stellar populations and gives a hint about the dust distribution in a galaxy. We apply this method to the irregular galaxy NGC 3077, using CCD images in U, B, V and R filters.

Molecular Gas and Star Formation in NGC 3077

“…Despite the ambiguity in the source of the neutral gas surrounding NGC 3077, all simulations of the M81ÈM82È NGC 3077 group agree that the strongest interaction between NGC 3077 and M81 occurred 300È600 Myr ago (Cottrell 1976 ;van der Hulst 1979 ;Brouillet et al 1991 ;Yun et al 1994 ;Yun 1998). The strength of the starburst estimated from the 2.6 mm continuum, the superbubble sizes (Martin 1998), and the UV colors (Benacchio & Galletta 1981 ;Price & Gullixson 1989 ;Abdel-Hamid & Notni 2000a, 2000bSakai & Madore 2001) all suggest that the current burst of star formation is Myr old. While the [10 star formation of the outer parts of NGC 3077 and its halo object, "" Garland,ÏÏ appears to be Myr old, more con-[150 sistent with a direct trigger by the interaction (Sakai & Madore 2001), the central burst appears too young to have been triggered directly.…”

“…These clusters that are not embedded in molecular gas are probably somewhat older than those seen at the interface of GMCs B and D. Optical/UV observation of these clusters suggests that they are D10È100 Myr old, with the older age stars increasingly dominating as one proceeds away from the center (Benacchio & Galletta 1981 ;Price & Gullixson 1989 ;Abdel-Hamid & Notni 2000a, 2000bSakai & Madore 2001).…”

“…If NGC 3077 did have a large disk of gas as suggested by Yun et al (Yun et al 1994 ;Yun 1998), the above points suggest that a burst of star formation starting a few hundred million years ago could have been driven. There are indications for this somewhat older stellar population (Abdel-Hamid & Notni 2000a, 2000bSakai & Madore 2001). This might provide hints that the gas around NGC 3077 has been stripped from NGC 3077 itself ; however, this cannot be taken as proof.…”