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Дата изменения: Sat Nov 25 17:34:13 2000
Дата индексирования: Sat Sep 11 20:32:36 2010
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Поисковые слова: arp 220

   
The APM selected sample

To improve the efficiency for the selection of BCGs among the second priority candidates we introduced additional selection criteria using the APM (Irwin [1998]) database. An analysis of the spectroscopic classifications of all objects from the random subsample resulted in the following conclusions:

• The second priority candidates classified as BCG/H II based on their slit spectra all have rather blue colours according to the APM database (APM $(B-R) \le 1\fm0$). In this colour range BCGs constitute about 33% of all second priority objects classified by APM as galaxies (Figure 1),
• Most of the ELGs of other types are redder than BCGs,
• One BCG of the four newly found is classified in the APM as stellar. Possibly at faint magnitudes some fraction of very compact BCGs are not distinguished by the APM from blue stars. Therefore also the APM information is of no help to discriminate the very compact faint BCGs from blue stars at the faint end of the second priority candidates.

Therefore, having in mind to develop a strategy to pick up as many as possible low-mass BCG/H II-galaxies in the HSS region, but accounting as well for a high enough detection rate, we created an subsample of second priority BCG candidates, which fulfill the following additional criteria:

• APM non-stellar classification, and
• a blue colour ( $(B-R)< 1\fm0$) on the APM

Of 633 objects from the second priority list in the strip $\delta$=35-40 80 candidates were selected by these criteria. Eleven candidates from this additional list were observed by snap-shot spectroscopy. All of them have turned out to be ELGs of various types. 3 of them are certain BCGs, and 4 more are probable BCG/H II-galaxies. They are listed in Table 3 and are marked with $\ddagger$.