Astron. Astrophys. Suppl. Ser. 133, 181-196

CCD imaging of twenty nearby isolated irregular galaxies

L.N. Makarova and I.D. Karachentsev

Special Astrophysical Observatory, Russian Academy of Sciences, N. Arkhyz, KChR, Stavropolsky kraj 357147, Russia

Received April 7; accepted April 20, 1998

Abstract:

We present B, V and I CCD stellar photometry for a sample of 20 field irregular dwarf galaxies. Their corrected radial velocity is V₀ < 500 km s^-1. Most of them have been resolved into stars for the first time. Based on photometry of their brightest blue stars we have derived the following distances: 5.9 Mpc (UGC 685), 5.4 Mpc (UGC 1281), 7.2 Mpc (UGC 3303), 7.0 Mpc (UGC 3476), 7.3: Mpc (UGC 3600), 7.2: Mpc (UGC 3698), 7.9 Mpc (NGC 2337), 8.6 Mpc (UGC 3817), 5.7 Mpc (UGC 3860), 5.6 Mpc (UGC 4426), $\geq$7.9 Mpc (F 565-v1), 7.4: Mpc (UGC 5086), 7.1 Mpc (UGC 5272), 5.9 Mpc (UGC 5340), 7.1 Mpc (UGC 5427), 2.7: Mpc (UGC 5456), 6.6 Mpc (NGC 3274), 9.3 Mpc (UGC 5889), 5.2 Mpc (NGC 5238), and 8.0 Mpc (UGC 9405).

Our sample exhibits diverse morphological properties evidently caused by their different starburst activity. The galaxy sample has a median integral absolute magnitude M_B = -14.6 and a median integral colour $(B-V)\rm _T = +0.47$. One dwarf, UGC 5340, stands out by its very blue colour, $(B-V)\rm _T = +0.18$, and by its high M(HI)/L ratio, as expected for young galaxies. Four objects of the sample are IRAS sources.

Being well isolated systems, the considered galaxies may be used to estimate a local value of the Hubble parameter, H = V₀/D. For half of the sample galaxies their individual H- values are concentrated within [58-68] km s^-1/Mpc with a median of 65 km s^-1/Mpc.

Key words: galaxies: distances -- galaxies: stellar content -- galaxies: dwarf; irregular