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Дата изменения: Tue Feb 8 09:57:25 2000 Дата индексирования: Sat Sep 11 20:33:04 2010 Кодировка: Поисковые слова: extreme ultraviolet |
Objective prism surveys for emission-line galaxies (ELGs) are the main source of large samples of both, AGNs and galaxies with enhanced star formation (SF) activity. Several large samples of ELGs were published since the end of 1980s. They include the samples of the University of Michigan (UM) survey (Salzer & MacAlpine [1988]; Salzer [1989]; Salzer et al. [1989]) near the equator, the Tololo and Cálan-Tololo survey samples (Terlevich et al. [1991]; Maza et al. [1991]) and the recent Marseille Schmidt survey (Surace & Comte [1998]) at the Southern sky.
In the Northern sky, large samples of ELGs have appeared during the
last decade thanks to such objective prism surveys as the First and
the Second Byurakan (SBS) surveys (Markarian et
al. [1983], Izotov et al. [1993a],
Stepanian [1994], Pustilnik et al. [1995]),
the Case survey (Pesch et al. [1995], Salzer et al.
[1995], Ugryumov et al. [1998]), and the
Heidelberg void survey (Popescu et al. [1996],
[1997], [1998]). All these projects employed
detection of strong emission lines on blue-sensitive photoplates. A
complementary approach was based on the search of strong
H-emission on red objective prism plates as e.g. in the
Universidad Complutense de Madrid (UCM)
survey (Zamorano et al. [1994], Zamorano et
al. [1996], Gallego et al. [1997]), and the MBC
(Montreal) survey (Coziol et al. [1993], [1994]).
Despite the large effort to establish the above mentioned surveys,
they yielded only relatively small complete samples in the order
of 102 blue compact galaxies (BCGs hereafter, e.g. Thuan et al., 1999). This is related to the
relatively low surface density of the objects in the surveys of about
0.2-0.3 per sq. deg. (e.g. Popescu et al. [1997]). But only
complete samples of sufficient size will allow to study the
distribution of the inherent physical parameters of BCGs. The
experience of all these surveys can be summarized as follows. To push
progress in statistical studies of low-mass galaxies with star
formation bursts, a reasonable large volume has to be surveyed and the
selection has to be done by well understood selection
procedures. Especially for BCGs of extremely low chemical abundances which seems
to be very rare objects in the local universe after all we
learned so far, a coverage of several 103 square degrees down to the
technical limits of the surveys is essential. These limits are at
magnitudes as faint as m
= 18 - 19 mag. To derive a statistical
robust sample of sufficient sample sizes from a very large field
survey, objective selection procedures for the ELGs have to be
applied.
With the data described below and in papers I and II
(Ugryumov et al. [1999], Pustilnik et al. [1999])
of this series, the authors pursue the goal of creating a new large
sample of H II-galaxies, or BCGs in a
zone with a total area of the order 1500 square degrees.
This region will fill the gap between the zones of the SBS and the
region covered by the Case survey. The SBS is situated at
,
,
while the
Case covers
,
.
For a description of the BCGs found in these two
surveys, see Izotov et al. ([1993a], [1993b]), Thuan
et al. ([1994]) and Pustilnik et al. ([1995]) for
the SBS and Salzer et al. ([1995]), Ugryumov
([1997]), Ugryumov et al. ([1998]) for the Case
survey which is still in progress.
Thus, the new Hamburg/SAO Survey (HSS) for emission-line galaxies leads,
firstly, to the creation of a new BCG/H II galaxy sample in a
large sky region with the boundaries 7h 20m to 17h 40m in
right ascension and
to
in declination.
Secondly, after combining the three BCG samples in the SBS, the Case
and the HSS zones, a large Northern BCG sample covering about 3000
square degrees will be available. The main goal of the project is the search for
emission-line galaxies (ELG) in order to create a new deep sample of
blue compact/H II galaxies (BCG) in a large area of the
sky. Another important goal of this work is to search for new
extremely low-metallicity galaxies.
This is the third article of a series devoted to follow-up
spectroscopy results of HSS ELG candidates. It
deals with 113 candidates selected in the band between and
in declination which is complementary to the zone
+40
+50
studied in our previous papers.
The basic ideas of the HSS
and its selection methods of ELG candidates are described along with
the first results of the follow-up spectroscopy in Ugryumov et
al. ([1999]) (Paper I). The final selection was slightly modified
to improve significantly the detection rate of ELGs in follow-up
spectroscopy as described in Paper II. In short, the
ELG candidate selection criteria applied are a blue or flat continuum
(near
4000 Å) and the presence of strong or moderate
[O III]
4959,5007 Å emission lines
recognized on digitized prism spectra. Candidates accepted
are restricted to the B-magnitude range
.
The article is organized as follows. In section 2 we give the details
of the spectroscopic observations and of the data reduction. In
section 3 the results of the observations are presented in several
tables. Along with general parameters for the emission-line galaxies
and several quasars, the parameters of the strongest emission lines of the
ELGs are summarized in a separate table. The information on two
non-emission-line galaxies is presented as well. In section 4 we
briefly discuss the new data and summarize the current state of the
Hamburg/SAO survey. Throughout this paper a Hubble constant H0 = 75
kms-1 Mpc-1 is used.