Proceedings of the Workshop
"The Magellanic Clouds and Other Dwarf Galaxies"
of the Bonn/Bochum-Graduiertenkolleg

H I Properties of new nearby Dwarf Galaxies

from the Karachentsev Catalog

W.K. Huchtmeier

Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Received 06th March 1998
Abstract. We present preliminary results from an H I-survey of 214 dwarf galaxies from the Karachentsev catalog of new nearby dwarf galaxies. Observations were performed with the Effelsberg 100 m radiotelescope, the Nançay radiotelescope, and the compact array of the Australia telescope. The detection rate was about 60%. The aim of this project is to improve our knowledge of the local luminosity function of galaxies and to find nearby dwarf galaxies for detailed studies. The relative content of H I (MH I/LB) of the galaxies in our survey is comparable to that of the sample of nearby galaxies for the same range in luminosity and morphological type.

1. Introduction

Galaxy catalogs generally are magnitude limited, e.g. the Revised Shapley-Ames catalog to mB≤13.0 (Sandage and Tammann 1987), or diameter limited samples, e.g. the Uppsala catalog to D(0)≥1.0' (Nilson 1973) or both (e.g. RC3, de Vaucouleurs et al. 1991). They are reasonably complete for bright galaxies but are increasingly incomplete for fainter galaxies. The best luminosity functions so far have been derived from deep surveys of galaxy clusters where all galaxies are at the same distance and where the volume contains large numbers of all types of galaxies. Deep surveys are available for the Virgo (Binggeli et al. 1985), the Fornax (Ferguson 1989) and the Centaurus cluster (Jerjen & Dressler 1997).

The situation for the Local volume is much more critical as an all sky survey is needed. In the zone of avoidance completeness will never be reached. Since the data compilation of Kraan-Korteweg and Tammann (1979, KKT hereafter) of all known galaxies with v0≤500 km s-1 to the most recent update of this sample (Karachentsev 1994) the number of known galaxies within the Local volume (i.e. the KKT sample) increased from 179 to 215 mainly by H I observations of the radial velocity of nearby dwarf galaxies. Recently Karachentseva & Karachentsev (1998) inspected the Palomar survey (POSS-II) and the ESO/SERC films to a limiting diameter of 0.5' instead of 1' used for many galaxy catalogs in the neigbourhood of all known galaxy groups within the Local volume. This survey covers about 25% of the whole sky. From a total of 260 nearby dwarf galaxy candidates 139 objects were not cataloged so far.

2. Observations

We performed H I-observations of these galaxies in order to measure their H I content and their radial velocity as a check for membership in the Local volume. Our search list of 214 galaxies contained these 'new' dwarf galaxies and among other undetected and marginal detected galaxies a certain overlap with detected objects. Observations were performed using the 100 m radiotelescope at Effelsberg which has a half power beam width of 9.3' at the wavelength of 21 cm for all galaxies north of declination -31°, the Nançay radiotelescope (HPBW 4' × 22') for the declination range from -31° to -38°, and the compact array of the ATNF (synthesized beam of the order of 50 arcsec) for objects south of -38°. We observed 159, 15, and 40 galaxies and detected 106, 9, and 19 galaxies respectively in these declination zones with a detection rate of 62%. Single dish observations were performed in the standard OFF - ON method where integrations of a few minutes were made alternatively on the source and a reference field on the sky not very far away. These two fields were combined to derive the actual profile. In general half an hour to one hour observing time was spent on source. The search range for the single dish telescopes was about 4200 km s-1 and 3000 km s-1 for the ATNF observations yielding a channel separation of 5 and 6 km s-1, respectively.

[Click here to see Fig. 1!]

3. Data

We present a selection of typical H I profiles observed with the 100 m radiotelescope in Fig. 1. Local H I-emission around 0 km s-1 has been cut out as it is much stronger than the weak extragalactic emission lines. A 0143+1426 is a background source outside the search range of this survey. Its radial velocity was known before. The spike at 3480 km s-1 in the spectrum of A 0147+2840 is due to interference. Many of the observed profiles are narrow - the signature of dwarf galaxies. The faintest object in this sample, A 0143+2633 [MBT0,i = -11.4, L10 in Fig. 2], has an optical extension of 0.6 × 0.18 arcmin2. Its relative H I content, MH I/LB = 1.6, is within the range of expected values for this morphological type and luminosity. The brightest object in Fig. 1, A 0338+6806 or L29 in Fig. 2 [MBT0,i = -17.3] is a low surface brightness object. The H I emission shows two different profiles close together. The stronger high velocity profile (vH I = 1328±5 km s-1) is due to UGC 2826 about 4 arcmin away. The relative H I content of A 0338+6806 (vH I = 1140±8 km s-1), MH I/LB = 0.15, is very low for its morphological type and luminosity. The small distance to UGC 2826 suggests that gravitational interaction between both galaxies could be a reason of the low gas content of A 0338+6806.

[Click here to see Fig. 2!]

4. Discussion

From the radial velocities of the galaxies given in Fig. 1 we derive that there are four new galaxies within the Local volume. The relativ H I content (MH I/LB) for all galaxies in Fig. 1 is shown in Fig. 3 together with the corresponding values (by a full line) for the KKT sample (from Huchtmeier and Richter 1988). The agreement is reasonable. However the scatter seems greater than expected from the observational errors. The discussion of A 0338+6806 demonstrates the possibility of confusion and environmental influences.

[Click here to see Fig. 3!]

References

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First version: 16thJuly,1998
Last update: 10thOctober,1998
Jochen M. Braun   &   Tom Richtler
 (E-Mail: jbraun|richtler@astro.uni-bonn.de)