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**TITLE**
ASP Conference Series, Vol. **VOLUME***, **YEAR OF PUBLICATION**
**NAMES OF EDITORS**
H i Rotation of Dwarf Galaxies with Unusually High H i
Mass­to­Light Ratios
Bradley E. Warren & Helmut Jerjen
Research School of Astronomy and Astrophysics, Australian National
University, Mount Stromlo Observatory, Cotter Road, Weston ACT
2611, Australia
B¨arbel S. Koribalski
Australia Telescope National Facility, CSIRO, PO Box 76, Epping NSW
1710, Australia
Abstract. We present here preliminary results of a multi­wavelength
investigation into high H i mass­to­light ratio dwarf galaxies identified
in the HIPASS Bright Galaxy Catalog. Here we focus on the rotational
properties of some of the galaxies.
One way to investigate aspects of star formation and galaxy evolution is to
look at galaxies which appear to have done little of either, those with excessive
quantities of neutral hydrogen compared to their stellar content. How could such
galaxies, generally low luminosity dwarf galaxies, maintain such a high relative
proportion of gas, where as others have processed most of their gas into stars?
Could the star formation have been impaired or halted in some way? Could
their dark matter properties have affected their evolution?
One of the first products of the H i Parkes All­Sky Survey (HIPASS) is the
HIPASS Bright Galaxy Catalog (BGC, Koribalski et al. 2003, AJ submitted)
listing the 1000 apparently strongest extragalactic HI sources in the southern
hemisphere. A comparison of the BGC H i data with preliminary optical prop­
erties (from LEDA, the Lyon­Meudon Extragalactic Database, Paturel et al.
1997, A&AS, 124, 109) of the BGC galaxies (Jerjen et al. 2003 in preparation)
revealed numerous sources, mostly intrinsically faint dwarf galaxies, with high
H i mass­to­light ratios; 68 galaxies have M HI =LB – 3 M fi =L fi .
In Warren et al. (2003, IAU Symposium 217) we presented some preliminary
results from multi­wavelength observations of a sample of 20 high and 20 low
M HI =LB dwarf galaxies, including optical and radio properties for three high
M HI =LB galaxies (ESO215--G?009, ESO348--G009 and MCG--04--02--003). Only
one of these galaxies, ESO215--G?009, retained a high M HI =LB after accurate
CCD photometry was obtained. Here we look at the rotational properties of
the H i component of these three galaxies, obtained from observations with the
Australia Telescope Compact Array (ATCA), in particular ESO215--G?009 (see
Warren, Jerjen, and Koribalski 2003 in preparation).
By assuming a spherical mass distribution, the dynamical mass for the
galaxies was calculated from the H i rotational properties. For ESO348--G009
and MCG--04--02--003 rough estimates of this value have been made from H i
position­velocity slices at position angles of ¸250 ffi and ¸10 ffi . The angular H i
1

2 Warren, Jerjen and Koribalski
Figure 1. (left) H i velocity field of ESO215--G?009. The cross marks
the dynamical centre of the galaxy. Contour levels are at 567, 573, 579,
585, 591, 597, 603, 609, 615, 621, and 627 km s \Gamma1 . (right) Preliminary
H i rotation curve derived from the velocity field of ESO215--G?009
assuming an inclination of 36 ffi \Sigma 2 ffi .
radii of the two galaxies are approximately 2.5 0 and 4.0 0 , respectively, which at
their estimated distances (8.4 Mpc and 9.5 Mpc from the BGC Local Group
velocity with H 0 = 75 km s \Gamma1 Mpc \Gamma1 ) gives the galaxies H i radii at ¸6 kpc
and ¸11 kpc. The line of sight rotational velocities at the outer radius are
about 40 km s \Gamma1 and 50 km s \Gamma1 , respectively, although for both galaxies the
rotation curves are only just starting to turn over at the point where this is
measured. Using estimates of the inclination from B band optical images (¸90 ffi
and ¸60 ffi ), the approximate dynamical masses are 2.3 \Theta10 9 M fi for ESO348--
G009 and 8.3 \Theta10 9 M fi for MCG--04--02--003. These compare to the H i masses
of these galaxies of 2.2 \Theta10 8 M fi and 3.4 \Theta10 8 M fi , respectively.
Fig. 1 (left) shows the H i velocity field of ESO215--G?009, which has M HI =LB
= 21.3 \Sigma 1.4 M fi =L fi (Warren et al. 2003). A rotation curve was fit to this
field using a tilted ring model in AIPS over both sides of the galaxy. The rota­
tion curve with the best fitting inclination angle of 36 ffi \Sigma 2 ffi is shown in Fig. 1
(right). At the last point of the curve (368 00 \Sigma 18 00 ) the rotational velocity is
51 \Sigma 3 km s \Gamma1 (inclination corrected). At the estimated distance of 4.2 Mpc,
the radius of the disk is 7.5 \Sigma 0.4 kpc. This gives a dynamical mass of 4.5 \Sigma
0.8 \Theta10 9 M fi , which compares to the H i mass of 4.3 \Theta10 8 M fi (BGC). The
dynamical mass to H i mass ratio is therefore ¸10, and the dynamical mass­to­
light ratio is ¸220 M fi =L fi . This indicates that the stellar component is an
extremely small fraction of the total galaxy mass.