6.1.5 New Objective-Prism Surveys in Progress
Evidently, the quest for finding more metal-poor galaxies is not over. The KISS (KPNO International Spectroscopic Survey, see Salzer 1999) is a CCD based objective prism survey. It selects candidates from their H emission, an advantage in searching for low metallicity systems. However an H survey produces not only BCGs, but also AGN etc. The real advantage is the usage of CCD detectors which enables a more than fivefold increase in limiting distance compared to photographic surveys. KISS finds on average 17 emission line galaxies per square degree (i.e. 170 times more than the original Markarian survey). Follow-up spectroscopy to investigate low metallicity candidates is under way (Salzer, private communication).
In an attempt to detect low metallicity galaxies, the Calan-Tololo survey plates have been searched by eye for objects without visible continuum, but with strong emission lines (Maza et al. 1999, in preparation). Interesting candidates are selected for spectroscopic follow up. More than two dozen galaxies with oxygen abundance of 1/10 Z or less have been found so far, and of these 8 are around 1/20 Z (Masegosa and Maza, private communication).
The HSS (Hamburg/SAO Survey) selects emission line dwarf galaxy candidates from the Hamburg quasar survey plates. The HSS has already yielded many new emission line dwarf galaxies (Ugruymov et al. 1999, Pustilnik et al. 1999a), and the follow-up study is well in progress. The dwarf (MB = -12.6) HS 0822+3542 was recently found to have an oxygen abundance of only 12 + log(O/H) = 7.35 (Merlino et al. 1999, Kniazev et al. 1999), i.e. not far from that of SBS 0335-052 (see also Table 3).
Other recent work includes the UCM (Universidad Complutense Madrid) survey, based on an H selection, yielding objects from tiny BCGs to AGN, but mainly relatively luminous ones (cf. Gallego et al. 1997). For a recent review of surveys for star forming galaxies, see Comte (1998).
Whereas objective prism and UV-excess surveys are good at picking up high surface brightness dwarfs with emission lines, we have shown that very metal-poor galaxies also come in other brands. In particular, since metallicity, luminosity and surface brightness are positively correlated we expect the existence of very metal-poor LSB dwarfs, like dEs and LSBGs. Surveys for such galaxies could be rewarding in the hunt for the ``most metal-poor galaxies'', although abundances will be more difficult to determine, especially for dEs lacking H II regions. New dEs are still found in the Local Group and its vicinity, and several surveys for LSBGs in the local Universe have been undertaken, and should strongly benefit from new wide field CCD cameras and projects like the Sloan Digital Sky Survey. To get a picture about work in progress, see the recent conference volume ``The low surface brightness universe'' by Davies et al. (1999).