EDP Sciences
Free access
Volume 424, Number 2, September III 2004
Page(s) 509 - 517
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20041210

A&A 424, 509-517 (2004)
DOI: 10.1051/0004-6361:20041210

Kinematics of two dwarf galaxies in the NGC 6946 group

A. Begum and J. N. Chengalur

National Centre for Radio Astrophysics, Post Bag 3, Ganeshkhind, Pune 411 007, India
    e-mail: [ayesha;chengalur]@ncra.tifr.res.in

(Received 1 May 2004 / Accepted 28 May 2004)

We present high velocity resolution (~ 1.6 km s -1) Giant Meterwave Radio Telescope (GMRT) HI 21 cm synthesis images of the dwarf galaxies KK98 250 and KK98 251, as well as optical broad band images of KK98 250. We find that, despite being faint ( $M_B \la -14$), both galaxies have regular velocity fields. In both cases the velocity fields are consistent with rigid body rotation. We derive rotation curves for the galaxies and fit mass models to them. For both galaxies, we find acceptable fits using isothermal halos while NFW halos provide a poor fit. Finally, we compile from literature a sample of galaxies with HI synthesis observations and  I band magnitudes. From this sample we find, in agreement with earlier studies (which used single dish HI data), that dwarf galaxies tend to lie below the I band Tully-Fisher relation defined by brighter galaxies.

Key words: galaxies: dwarf -- Galaxy: kinematics and dynamics -- galaxies: individual: KK98 250 -- galaxies: individual: KK98 251 -- radio lines: galaxies -- cosmology: dark matter

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