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G. H. Jacoby, T.E. Armandroff (KPNO/NOAO), J.E. Davies (JHU)
We will present our 4-m discovery images of And VI, a new Local Group dwarf galaxy near M31 identified using a digital filter technique applied to the digitized POSS-II sky survey. Based on deep follow-up B-, V-, and I- band imaging at the 3.5-m WIYN telescope, we will report our estimates for the distance, mean metallicity and age, and spread in metallicity and age for the stars in And VI.
The non-detection of sources in our 4-m H\alpha images, combined with IRAS flux limits, argues against the presence of significant star forming regions that would indicate this galaxy is a dwarf irregular. Rather, the resemblance of And VI to other dwarf spheroidals in the vicinity of M31 (And I, II, III, and V) argues that And VI also is a dwarf spheroidal.
And VI was independently reported by Karachentsev & Karachentseva (1998) but designated as Pegasus Dw; an initial V-I CMD has been presented by Grebel & Guhathakurta (ApJL, submitted) that indicates a physical association with M31. Here, we refine the results of that study, both in regard to distance and metallicity.
At a projected distance of 271 kpc from M31, And VI is nearly twice as far from M31 as the next most distant dwarf spheroidal previously known (And II). This extreme distance, combined with And VI's close proximity to a bright star, probably explains its delayed discovery. Our (not yet completed) survey extends somewhat beyond the projected distance of And VI, and when completed may reveal additional dwarfs. However, it may be necessary to extend surveys for M31 dwarfs to even greater projected radii to ensure completeness. Our technique, using the digitized POSS-II, provides a quick and effective approach to finding very low surface brightness dwarf galaxies.
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The author(s) of this abstract have provided an email address for comments about the abstract: gjacoby@noao.edu