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Search for distant radio galaxies in SAO

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Search for distant radio galaxies in SAO

The search for distant objects which can be both galaxies and quasars is one of the most important problems of observational astrphysics, because it allows one to determine cosmological parameters connected with the time of appearence and evolution of stellar systems, large scale structure of the Universe. Discoveries of 1998 yr show the galaxies (i.e. objects with the stellar population) are the most distant objects. They can have redshifts Z up to 7. And theoretical models give for galaxies formation epoch Z up to 17. One of the most interesting problems in this direction is a search for distant radio galaxies, i.e. extended objects having radio emission and being to the current moment the eldest objects of the radio Universe after microwave background radiation. This problem (the search for distant radio galaxies) is a part of the project "Early Universe", which is described in SAO (Nizhnij Arkhyz): <click here> , and in St.Petersburg: <click here>.

Radio galaxies are important objects to be studied because they are sources of infrared-optical-ultraviolet continuum, emission lines and continual radio emission. Since all the components of their radiation have an extended structure, these objects can be investigated by the ground based telescopes. Fanaroff and Riley in 1974 identified 2 types of radio galaxies depending on their structure which are named now as FRI and FRII. Radio galaxies of the first type have radio emission decreasing to the sides of a radio source, radio galaxies of the second type have distribution of radio emission mostly concentrating in sidelobes, so called "hot spots". Radio galaxies are, generally, identified with elliptical galaxies. Radio galaxies in cluseters are identified with giant elliptical galaxies or cD-galaxies being the most powerful radio sources in clusters of galaxies and formed, apparantly, by the spiral galaxies merging. Some radio galaxies are identified with N-galaxies.
The diatant radio galaxies(Z>1) are especially interesting because they are probers of the epoch of galaxy formation in protoclusters (or in cluseters). Besides, the detection of Ly in surrounding matter can help to investigate neutral gas at high redshifts and to check the galaxy formation models.

A team of atronomers searches for and studys distant radio galaxies for several years in the Special astrophysical observatory . This team is headed by Prof. Yurij Parijskij and Prof. Natalia Soboleva. The main optical observer of the team is Dr. Alexander Kopylov. The following people are also work in this team: Dr. Adelina Temirova (analysis of radio and optical data), Olga Zhelenkova (data reduction in MIDAS, radio sources identification on the optical images), Dr. Oleg Verkhodanov (software design, operation with SED (Spectral Energy Distribution) curves, ages estimation and observations). The project of the SAO for the serach for distant radio galaxies, called "Big Trio" (because it unifies 3 big telescopes RATAN-600 - VLA - BTA), allows one to penetrate into "the Dark ages" with redshifts 7<Z<30 from the "low" values.

The project of the study of distant radio galaxies consists of several steps:

  1. selection of radio sources with steep spectra (spectral index < 1) mostly with flux densities from 10 till 100 mJy in the centimeter wavelength range at RATAN-600. The catalog "Cold". is used for this goal.
  2. Defenition of a sources structure with the radio interferometer VLA.
  3. Selection of double radio sources (radio galaxies) having a structure of the FRII type.
  4. Observations at 6m telescope of SAO RAS to identify objects and to obtain multicolor photometry and redshift.
  5. Estimaition of ages of the stellar population of elliptical galaxies and measurement/estimation of redshifts of identified objects in various evolutional models.
One may read about results of the "Big Trio" project in the following papers:
Some results for 1998:
RC 0105+0501(Russian KOI8)

vo@sao.ru
 (Oleg Verkhodanov)