* Astronomy

Title: KK258, a new transition dwarf galaxy neighbouring the Local Group
Author: I. D. Karachentsev, L. N. Makarova, R. B. Tully, Po-Feng Wu, A. Y. Kniazev

Here we present observations with the Advanced Camera for Surveys on the Hubble Space Telescope of the nearby, transition-type dwarf galaxy KK258 = ESO468-020. We measure a distance of 2.23±0.05 Mpc using the Tip of Red Giant Branch method. We also detect H emission from this gas-poor dwarf transition galaxy at the velocity Vh = 92±5 km s-1 or VLG = 150 km s-1. With this distance and velocity, KK258 lies near the local Hubble flow locus with a peculiar velocity ~3 km s=1. We discuss the star formation history of KK258 derived from its colour-magnitude diagram. The specific star formation rate is estimated to be log[sSFR] = -2.64 and -2.84 (Gyr-1) from the FUV-flux and H-flux, respectively. KK258 has the absolute magnitude MB=-10.3 mag, the average surface brightness of 26.0 mag arcsec-2 and the hydrogen mass log(MHI)<5.75 solar masses. We compare KK258 with 29 other dTr- galaxies situated within 5 Mpc from us, and conclude that its properties are typical for transition dwarfs. However, KK258 resides 0.8 Mpc away from its significant neighbour, the Sdm galaxy NGC 55, and such a spatial isolation is unusual for the local transition dwarfs.

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