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Дата изменения: Tue Nov 24 21:18:57 1998 Дата индексирования: Sat Sep 11 22:06:56 2010 Кодировка: |
The main ELG candidate selection criteria applied here are a blue continuum
(near
4000 Å) and the presence of strong or moderate
[O III]
4959,5007 Å emission lines recognized
in digitized prism spectra with magnitudes in the range
B =
.
Figure 5 shows the equivalent widths of
the [O III]
5007 Å line versus the apparent and absolute
blue magnitudes. It is evident from Fig. 5a that the detection
limit of the HSS for BCGs based on this strongest emission line
is EW([O III]
5007 Å)
15 Å.
There is a clear trend of increase of equivalent
widths (EW) with apparent magnitude, and even more noticeable
anticorrelation between EWs and absolute magnitudes, if not only
BCGs but all ELGs are taken into account.
Similar trends were noticed for the UM ELGs by Salzer et al.
([1989a], [1989b]).
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In analogy to the UM ELGs, the anticorrelation evident in Fig. 5b
is caused by two effects. First, because of the
brightness limit imposed by the
plates we miss low-luminosity ELGs with weak emission lines. The galaxies
would populate the lower left corner of the Fig. 5b. Second, the
region of avoidance in the upper right corner is most likely caused by
metallicity effects.
In general HII regions in bright galaxies have
larger heavy element abundance, and, therefore, they are cooler with lower
EW([O III]5007 Å).