Abstract
Dwarf galaxies are key objects for small-scale cosmological tests like the abundance problems or the planes-of-satellites problem. A crucial task is therefore to get accurate information for as many nearby dwarf galaxies as possible. Using extremely deep, ground-based V and i-band Subaru Suprime Cam photometry with a completeness of i = 27 mag, we measure the distance of the dwarf galaxy [TT2009] 25 using the tip of the red giant branch as a standard candle. This dwarf resides in the field around the Milky Way-analog NGC 891. Using a Bayesian approach, we measure a distance of 10.28−1.73+1.17 Mpc, which is consistent with the distance of NGC 891, and thus confirm it as a member of NGC 891. The dwarf galaxy follows the scaling relations defined by the Local Group dwarfs. We do not find an extended stellar halo around [TT2009] 25. In the small field of view of 100 kpc covered by the survey, only one bright dwarf galaxy and the giant stream are apparent. This is comparable to the Milky Way, where one bright dwarf resides in the same volume, as well as the Sagittarius stream – excluding satellites which are farther away but would be projected in the line-of-sight. It is thus imperative to survey for additional dwarf galaxies in a larger area around NGC 891 to test the abundance of dwarf galaxies and compare this to the number of satellites around the Milky Way.
Highlights
In the ΛCDM universe, structure is built up through hierarchical merging in a bottom-up scenario
Using extremely deep, groundbased V and i-band Subaru Suprime Cam photometry with a completeness of i = 27 mag, we measure the distance of the dwarf galaxy [TT2009] 25 using the tip of the red giant branch as a standard candle
Using extremely deep V and i band images taken with the Subaru Suprime Cam we resolved the upper part of the RGB of the dwarf galaxy [TT2009] 25
Summary
In the ΛCDM universe, structure is built up through hierarchical merging in a bottom-up scenario (e.g., the review by Frenk & White 2012). We present a TRGB distance measurement for the dwarf galaxy [TT2009] 25, discovered by Trentham & Tully (2009) in a wide-field MegaCam-based survey of the region around NGC 1023, and close to the Milky Way analog NGC 891. This latter galaxy has been targeted to resolve its stellar halo and search for streams through detection of individual RGB stars (Mouhcine et al 2010) with ground-based Subaru data, accompanied by data from the Hubble space telescope (Rejkuba et al 2009).
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