HII Galaxies - Galaxies with intense current bursts of star formation:
The heavy element abundances of gas-rich galaxies and their
gas-mass fractions are the main parameters characterizing their global
evolution. These can be related to both the global properties of galaxies
and the membership of galaxies in various elements of the large-scale
The knowledge of the metallicity for large homogeneously selected galaxy
samples would allow us to address various issues of galaxy chemical evolution
on a good statistical basis.
My research related to this topic have been concentrated on
collaborative projects aimed at creating
new samples of such objects, determination of their
element abundances as well as the detailed study of some interesting
objects from these new samples.
I was and/or I am still involved in the following projects:
(i) BCGs from the First and Second Byurakan Surveys.
This work was based on the objective-prism photoplates of the
(ii) A new digital KPNO International Spectral Survey (KISS)
aimed at creating a deep sample of emission-line galaxies.
The technique we employed for this project combines the benefits of a
traditional photographic survey with the advantages of using new CCD detectors
in astronomy. The spectral range for objective-prism spectra covered
4800-5500 A; was restricted by a specially
designed filter that transmits from rest-frame H to just shortward of
the strong night-sky line at 5577 A; and this greatly reduces the sky
(iii) The Hamburg/SAO Survey of Emission-Line Galaxies (HSS-ELG)
was based on the digitized photographic objective-prism database of the
Hamburg Quasar Survey. The main goal of the HSS-ELG
was to search for emission-line galaxies with HII-type spectra
in order to create a new deep sample of BCGs in an area of
about 3000 of the sky. Another important goal
of this work was to search for new extremely low-metallicity galaxies.
(iv) Hamburg/SAO Survey for Low Metallicity Galaxies (HSS-LM) is
devoted to the search for extremely metal-deficient BCGs
and to the creation of a well selected large BCG sample with strong
emission lines and oxygen abundance measured with classic T method,
in an area of about 3500 of the sky
not covered with previous searches.
I was involved in the observations, reduction and analysis of
spectral and photometrical data for these projects. New created
samples from these projects were used for
various follow-up studies
and some of them were done with my participation, namely:
(a) The studies of the environment of low-mass galaxies with
active starformation (SF hereafter) and a possible trigger of SF bursts due to
Finally we concluded that in 80%
(or more) BCGs from the studied sample, the SF bursts are triggered
either by tidal action of various strengths
from other galaxies, or due to mergers of low-mass galaxies.
(b) Searches for and detailed studies of Wolf-Rayet features and
broad components of strong emission lines.
They are the signatures of collective effects of massive star winds
and supernova explosions
on to interstellar medium of host galaxies of various metallicities.
(c) Heavy element abundance
patterns and the metallicity distribution of BCGs.
(d) Structural parameters and morphology of BCGs.
One of the main results of all these projects was
the discovery of new extremely metal-poor galaxies
(XMPGs; with 12 + log O/H 7.6 or Z 1/20 solar) in the nearby Universe.
These galaxies have received much attention, since some of these objects
may be primeval galaxies that are now experiencing their first major
burst of star formation and they are local counterparts of high-redshift
just formed dwarf galaxies.
The first such object discovered in our
projects, was the galaxy SBS 0335-052, which is almost
as metal-poor as the well-known
metal-poor galaxy I Zw 18. I was in the team that discovered this object
and analysed spectral and photometric data for SBS 0335-052
and its western companion 0335-052W, also discovered by our team.
It was shown that 0335-052W has the same redshift as that of
SBS 0335-052 and has an extremely low oxygen abundance.
It was argued that both these
galaxies are likely to be nearby young dwarf galaxies and the
properties of these galaxies were compared with theoretical predictions
and properties of
high-redshift galaxies which are often considered as primeval galaxies.
Different XMPGs can have differing evolution scenarios, and therefore
quite different observational properties.
To understand the nature of XMPGs we need to carefully
study the group properties of sufficiently large number of such galaxies with
reliable estimates of O/H.
As a first step of such a project we planed to form the
sufficiently large sample of XMPGs.
The systematical searches for XMPGs were conducted and, as a result,
many new such galaxies were found.
At the same time we checked
a half-dozen of previously-claimed XMPGs and found that
majority of them were not
real XMPGs but had poor observational spectral data and should be
rejected from the final sample.
For some new discovered XMPGs (additionally to studies of SBS 0335-052 system)
we started detailed multi-wavelength
studies where we found that
SF bursts were triggered by tidal actions with local environment
and studied XMPGs are located within voids.
Deep multi-band photometry was
performed for some of those galaxies with
1.5m (Calar Alto, Spain) and 2.5m (La Silla, Chile) telescopes
as well as integrated HI in the 21-cm line radio observations
and infrared observations with NTT and VLT telescopes.
Part of the data is reduced and some new data are still being reduced.
The Sloan Digital Sky Survey (SDSS) is an ambitious international
survey project that will ultimately cover one quarter of the sky
through deep, 5-color photometry and spectroscopy.
I have begun a systematic search of XMPGs using the spectroscopic
database of SDSS.
Eight new objects were identified after
the analysis of 250,000 galaxy
spectra within an area of 3000 deg on the sky.
Our oxygen abundance determinations have an
accuracy of 0.1 dex and are based on the temperature-sensitive
[OIII] 4363 A; line and on the direct calculation
of the electron temperature.
For that I developed a new method of oxygen abundance determination
using the [OII] 7319,7330 A; lines, which is particularly
useful for SDSS emission-line spectra with redshifts 0.024 since the
[OII] 3727 A; emission line falls outside of the
SDSS wavelength range.
In parallel, I started a project to create
the SDSS HII-galaxies
with Oxygen abundances Catalog (SHOC),
which is a listing of strong emission-line galaxies
from SDSS Data Release I.
One of the goal for both projects is to create a sample XMPGs and reference
sample of ELGs for a comparative study of their properties.