Spirals

• M31. Has broad metallicity distribution in halo. Some 5-10 Gyr stars indicated by deep HST ACS imaging (Brown et al). Sarajedini finds evidence of even more metal-rich population (-0.21) in field and suggests thick disk component (but could it just be the disk?), with ages predominantly older than 1.5 Gyr . Williams also suggests relatively low recent star formation rate. No evidence of bursts in (relatively shallow) data. Ferguson and Johnson suggest very old population exists in far outer disk (could it be halo?).