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| Hamburg/SAO Survey (HSS) for Emission-Line Galaxies - New Wide-Angle Search for Blue Compact Galaxies (BCG) |
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Sky positions of known BCGs from the Northern Sample, drawn from the SBS,
HSS and Case survey, where
SBS BCGs marked as crosses (x), HSS BCGs as open circles and Case BCGs
as crosses (+).
Get PostScript file of this picture
All so far available prism surveys demonstrated clearly their
desicive role in providing with effective wide-angle search for
emission-line objects.
The creation and study of the Blue Compact Galaxy (BCG) sample basing on
the Second Byurakan Survey (SBS) during the previous decade
gave many interesting results and caused certain
progress in understanding many related cosmogony and cosmology topics.
New project named Hamburg/SAO Survey extends study of blue compact galaxies
to new large wide-angle sample based on digitized objective-prism
photoplates of the Hamburg Quasar Survey (HQS).
The main goals of the project are:
creation of joined "BCG Northern Sample" assembling together
the three BCG samples from SBS, HSS and Case survey
search for the most metal-deficient galaxies
The most metal-deficient galaxies are very appropriate objects to deal with such important cosmological and cosmogonical problems as:
estimate of primordial helium abundance - a crucial parameter for
check the Standard Big Bang nucleosynthesis (SBBN) theory
understanding of basic processes determining the chemical evolution
of galaxies
constraints on models of stellar nucleosynthesis
determination of the stellar initial mass function
BCGs as dwarf galaxies experiencing intense star formation, have in their optical spectra strong enough emission lines and give the advantage to detect representative dwarf galaxy population at the distances well beyond the Local Supercluster. Thus they serve as good objects to study:
spatial distribution of low-mass galaxies and test
cosmological theories of origin and development of large-scale
structure of the Universe
However all the existing samples of BCGs are located either in small sky areas or in narrow bands. Hence, strong boundary effects can take place for any statistical analysis. The important role of the Hamburg/SAO Survey is not only in providing a new large BCG sample in large region of sky, but also in filling the gap between areas of two other large BCG samples from SBS and Case survey. As a result these three samples will be joined into one the large "Northern Sample" with total area about 3000 square degrees. Moreover it is designed to overlap partly with the previous surveys and will therefore allow to derive common selection functions which will greatly improve the validity of all statistical results.
The selection semi-automated procedure developed at the Hamburg observatory for quasar search was a little adopted for search of emission-line galaxies. During selection of candidates were used digitized (PDS 1010G microdensitometer) objective prism (1.7 deg.) plates (Kodak IIIa-J) obtained at the 80/120 cm Schmidt telescope (Calar Alto, Spain) during the Hamburg Quasar Survey. The size of plates is 24x24 cm, each plate covers field of 5.5x5.5 square degrees.
The wavelength range enables emission-line galaxies search within 3400 - 5400 Angstroms. Reached redshift limit of detectable emission-line galaxies is z < 0.08.
The preliminary selection was made according to presense of blue enough continuum for objects with the survey B-magnitudes = 16 -19.5. The consequent search used as the main selection criteria the indication on the presence of prominent [OIII] 4959,5007AA emission lines in the range 5000- 5400 A.
The first selection of candidates was carried out at the Hamburg observatory during October-December 1994. Fields were analyzed in the regions:
Right Ascension: 8h00m - 15h30m, Declination: +40 deg. - +45 deg.
The number of selected candidates exceeds 1000.
The second selection was done in December 1995 - January 1996 to complete both strips within:
The third selection was done in January 1997 to improve coverage of the zone above with new good quality plates. About 100 new good candidates was found, mainly in the strip +40 deg. - +45 deg.
The forth selection was done in January - March 1998 in new strip to cover the gap between two first HSS strips and the zone of the Case objective prism survey. 335 ELG first priority candidates are separated, and about 600 more second priority candidates. The sample of BCGs in this new strip is a subject of INTAS project No. 96-0500.
Usually the mode of fast (snapshot) observations is used with the aim to detect strong enough emission lines, estimate redshifts, make preliminary classification of ELG type and get a first guess on chemical abundances.
| Period | Telescope | Wavelength | Spectra Number |
|---|---|---|---|
| January-April 1995 | 6m, IPCS, Russia | 3700 - 5500 AA | 186 |
| December 1995 | 6m, CCD, Russia | 3700 - 8000 AA | 89 |
| February 1996 | 6m, CCD, Russia | 3700 - 5500 AA | 6 |
| June 1996 | MMT, CCD, USA | 3700 - 8000 AA | 8 |
BCGs compose major part (>60%) of observed emission-line objects
in accordance to the idea of use objective-prism wide-field
surveys as favorable technique to search for narrow emission-line galaxies
preliminary estimates of oxygen abundance:
about 30 new BCGs are expected with Oxygen abundance in the range
12+log(O/H) = 7.6-8.0 which need confirmation with higher signal-to-noise
ratio spectra; there were no (in 1997) new galaxies with extremely low metallicity
forming sample includes emission-line galaxies with the
similar physical properties as from the Second Byurakan Survey and Case
Survey;
this result confirms that the HSS is not biased relative
to other objective-prism surveys and can be used in the same manner for
wide-angle search for emission-line galaxies up to z < 0.05 (0.08)
3 October 2005
