2 New steps in search for dwarf galaxy candidates

The Second Palomar Sky Survey (=POSS-II) covering the northern hemisphere, [ $0\hbox{$^\circ$ }< D < +90\hbox{$^\circ$ }$], together with the SERC Equatorial survey , [ $0\hbox{$^\circ$ }< D < -18\hbox{$^\circ$ }$], and the ESO/SERC survey, [ $-90\hbox{$^\circ$ }< D < -18\hbox{$^\circ$ }$], provide a unique opportunity to search systematically for LSB dwarfs on the homogeneous photographic material over the entire sky. This has already resulted in a recent discovery of the Andromeda dwarf satellites (Armandroff et al. 1998; Armandroff et al. 1999; Karachentsev & Karachentseva 1999), and the Local Group dwarf galaxy Cetus (Whiting et al. 1999).

Figure 1: Digital Sky Survey $5\hbox {$^\prime $ }\times 5\hbox {$^\prime $ }$ images of 50 dwarf galaxy candidates (continued in Figs. 2-5). North is up, and East is to the left

Figure 2: Digital Sky Survey images of 50 dwarf galaxy candidates (continued from Fig. 1)

Figure 3: Digital Sky Survey images of 50 dwarf galaxy candidates (continued from Fig. 1)

Figure 4: Digital Sky Survey images of 50 dwarf galaxy candidates (continued from Fig. 1)

Figure 5: Digital Sky Survey images of 50 dwarf galaxy candidates (continued from Fig. 1)

One of the tasks to be performed on the new sky surveys has been a compilation of a complete and representative volume-limited sample of galaxies. To this end Karachentseva & Karachentsev (2000) have undertaken a search on the POSS-II and the ESO/SERC copies for LSB dwarf galaxy candidates with angular diameters $a \geq 0\hbox{$.\mkern-4mu^\prime$ }5$ around all the Local Volume (=LV) galaxies. The LV galaxies with corrected radial velocities V₀ < 500 km s^-1were taken from the list by Karachentsev (1994), which is an up-dated version of Kraan-Korteweg & Tammann's (1979) and Schmidt & Boller's (1992) catalogues of nearby galaxies. Altogether 260 nearby dwarf galaxy candidates have been found (henceforth referred to as kk-objects or kk-galaxies), more than a half of them previously uncatalogued.

HI observations of the kk-objects with the 100-m Effelsberg radio telescope (Huchtmeier et al. 1997, 2000) have shown that:

1.

the HI detection rate is about 60% (a rather high value taking into account that the kk-list contains a large number of dSphs);

2.

the median radial velocity in the sample is about 1200 km s^-1, indicating that the kk-objects are mainly real dwarf galaxies;

3.

there are 40 kk-galaxies with V₀ < 500 km s^-1, which essentially increases the LV sample.

The next steps involved the following:

1.

A search for dwarf galaxy candidates in the Tully Local Void region, covering $\sim6000 \ifmmode\hbox{\rlap{$\sqcap$ }$\sqcup$ }\else{\unskip\nobreak\hfil \pe... ... }$\sqcup$ } \parfillskip=0pt\finalhyphendemerits=0\endgraf}\fi\hbox{$^\circ$ }$ area around {RA = $18^{\rm h}38^{\rm m}$, $D = +18\hbox{$^\circ$ }$}, yielded new 78 objects (Karachentseva et al. 1999);

2.

An overall search in the ESO/SERC sky region resulted in 81 dwarf galaxy candidates (Karachentseva & Karachentsev 2000);

3.

An overall search on the POSS-II, the northern hemisphere (except the Virgo cluster region and the Local Void area), yielded 101 dwarf galaxy candidates (Karachentsev et al. 2000). Many of them have been observed by W. Huchtmeier with the Effelsberg radio telescope.