Second Byurakan Survey (SBS)

The Second Byurakan Survey (SBS)
By Lidia Erastova

When publishing their last 15th list of the excessive UV continuum galaxies the authors of the First Byurakan Survey mentioned that the results of the First Survey were very inhomogeneous and for creation of samples of active galaxies of various types in 1978 they started systematic observations for the Second Survey. Really, after the preliminary study of objects of the First Survey, it was only possible to outline the whole variety of types of activity of extragalactic objects and make up a link from normal galaxies to quasars. The creation of samples of active extragalactic objects and their study aimed at understanding the phenomena of activity became the main goal. Due to the use of new emulsions with small grains, selection of active objects not only by excessive UV continuum but also by the emission lines became possible.

A total area of 991 square degrees of the Northern sky was covered by a set of 64 fields obtained on the Byurakan 1 m Schmidt telescope. This area is a continuous strip between 7h40m – 17h15m in right ascension and +49° – +61° in declination. Each field was covered typically by a set of about 10 plates with the use of three objective prisms in combination with different Schott filters. About 3600 objects were distinguished in these plates, including Markarian galaxies located in this area.

At present slit spectra for most of the Survey objects have been obtained with a dispersion of about 100A in the wavelength range from 3500A to 7000A, which allowed carrying out physical classification of active formations. The Second Survey showed that the known classification scheme encounters difficulties; remote galaxies often show complicated features proving that the nature of these objects itself is complicated and features of various type of activity is simultaneously present.

Nevertheless, the authors succeeded to build enough homogeneous new deep samples of all known types of active extragalactic objects. Note that the magnitude range allowed revealing in enough numbers objects of all activity types from absolutely faint BCDG to quasars. So far, the classification of more than 750 AGNs has been established as follows; 596 QSOs, 10 BLL, 155 Sy galaxies, as well as ~ 90 LINERs, ~560 SBN, 195 BCDG, and 150 HII galaxies and other emission line galaxies (Stepanian 2005). For the first time, samples of all extragalactic objects are being discussed and compared without a preliminary separation on stellar and diffuse ones.

It may happen that after further investigations, the classification of individual objects will be clarified and even revised due to the abovementioned classification difficulties and due to obtaining of new higher quality slit spectra.

Now the Survey presents large, homogeneous and new deep samples of bright QSOs, AGN, and faint star-forming galaxies in the Northern sky that were selected in a reasonably uniform way accompanied by complete sets of spectroscopic data. The volume of reliable investigation of AGN and some types of discovered objects extends out to a distance of about 500 Mpc, that is, more than 50 times deeper than in the FBS. Each sample requires an individual consideration for its completeness and other parameters. This is a subject for further studies of the Survey objects.

At present first results on samples of quasars (Chavushyan), Seyfert galaxies (Erastova), and blue dwarf galaxies (Petrosian) have been obtained, as well as results on the sample of blue degenerate stars (Balayan) which is a by-product of the Survey.

The complete sample of the SBS AGN might be used as a second layer to the complete sample of AGN originally compiled in the Markarian survey in order to compare AGN properties in the very local (z < 0.03) and local (or low­redshift z < 0.15) Universe. SBS AGN may also be useful as a low­redshift counterpart to compare with the galaxies and AGN population at higher redshifts.

The Seyfert galaxies of the Second Survey do not fit in the accepted separation into two types. By their parameters, they gradually fill in the gap between Seyfert galaxies of types 1 and 2; many intermediate types appear, which indicate on continuous change of the parameters when transiting from type 1 to type 2.

Thus, the majority of the SBS Sy galaxies may be classified by the use of classical definitions. However, nearly 20% of SBS Sy galaxies do not follow the classical definition for AGNs. They show very strong and broad (FWHM>3000kms-1) or relatively broad (FWHM>1000kms-1) Hα emission line, without any sign of presence of Hβ or [OIII]λ5007/4959. These objects might be heavily absorbed AGN. The other group shows low­contrast very weak broad (FWHM~1000-4000kms-1) Hα and/or Hβ emission lines with a narrow component (FWHM less than 200 kms-1).

The studied wavelength range allowed distinguishing a big number of objects that are either bright Seyferts and/or faint quasars, which exactly show that such separation is artificial and QSO and Seyfert type galaxies form a continuous sequence of objects of the same type. 290 AGN/QSOs with B < 17.5 were discovered. About 13% of star­like SBS objects with B < 17.0 and ~6% with B < 16.5 turn out to be QSOs. The lower limit to the cumulative surface density of bright QSOs in the redshift range 0.3 < z < 2.2 is set to 0.05 deg-2 for B < 17.0, and 0.15 deg-2 for B < 17.5, respectively.

The local (z < 0.15 and z < 0.3) AGN luminosity function (LF) derived from SBS provides a new accurate zero­point for studying AGN/QSO evolution. The SBS sample of low­redshift AGN might be used to test the nuclear luminosity function of AGN in the local Universe.

The existence of narrow­line QSOs (NLQSOs) objects with spectral characteristics similar to NLS1s but with quasar luminosities, has been established. There exists a smooth transition in all measured properties between SBS NLS1s and NLQSOs.

The luminosity function of relatively bright SBS QSOs shows that one of the most important results obtained on the basis of the complete sample of SBS QSOs is that the zero-point of the logN­B relationship, which is basic to any AGN evolution model, may be corrected. The logN­B relationship for SBS bright QSOs in the magnitude range 15.0 < B < 17.5 and redshift interval 0.3 < z < 2.2 reaches the value of 0.67±0.03. From this we conclude that the apparent evolution of the luminosity function is most likely the result of selection effects, rather than an indication of fast cosmological evolution.

The luminosity functions of SBS UVX galaxies allow us to conclude the following: within the survey area and up to a distance of ~500 Mpc, the SBS UVX galaxies comprise about 12% of field galaxies. The proportion of AGN among the UVX galaxies is no less than 15%, which is the highest amongst similar surveys up to date. About 1.8% of field galaxies with z < 0.1 are Seyfert galaxies. This value is nearly twice larger than the value of 1% previously obtained for the local Universe. In addition to the 90 LINERs, the percentage of AGNs is no less than 3% for field galaxies in a volume of 0.5 Gpc. The proportion of emission line galaxies without UV­excess is a little less than the proportion of UVX galaxies. Together they bring the number of relatively strong emission line galaxies to at least 20$\%$ of field galaxies.

The spatial distribution of SBS galaxies shows that the large­scale structure of the Universe is reliably mapped out to a scale of about 500 Mpc within the SBS sky area. A few nearby voids with a mean size of about 40 Mpc have been found.

UVX and star forming ELG do not show major differences in their magnitude, redshift, morphological type, and other properties.

The largest homogenous known sample of blue compact galaxies (~350 objects) selected from the Northern hemisphere has been compiled. The space density of BCG and blue compact dwarf galaxies (BCDG) have been estimated. BCG comprise of ~4% of field galaxies and nearly 20% of the total sample of SBS galaxies. More than half of BCGs (195) are blue compact dwarf galaxies (BCDG) and their space density is about ~2% of field galaxies.

Special searches showed that only one star­forming galaxy comparable to Mkn 116 (IZw 18) was found, SBS 0335-052. These are extremely rare objects. Further searches for such objects in SDSS confirmed this conclusion.

A large gap in the BCDG metallicity distribution between Z(Sun) /15 and Z(Sun) /50 has now been filled as a result of the compilation of a reasonably large sample of low metallically (Z/Z(Sun) ≤ 1/10) galaxies discovered among the SBS BCDG and whose metallicities are close to that of IZw 18. Nearly ~20% of observed SBS BCDG turned out to be metal deficient galaxies with 12+log(O/H) < 8.3. More than 55% of all known extremely metal­poor galaxies with 12 + log(O/H) < 7.49 were discovered owing to the SBS survey. The proportion of metal­deficient dwarf galaxies with 12 + log(O/H) < 8.3 reaches about 0.2% of the field galaxies.

A dozen of luminous -18.4 > MB > -19.9 BCGs are found with subsolar oxygen abundances. It is not excluded, in contrast to the metallicity­luminosity relationship, that metalpoorness is not the reserved privilege of blue compact dwarf galaxies. The majority of SBS BCGs, as well as BCDGs, have not yet been investigated. Investigation of the total sample of the SBS BCGs, and BCDGs may significantly improve our knowledge of the evolutionary state of star­forming and metal­deficient galaxies.

Examination of objects in various databases shows that some 1000 survey objects have also been observed as FIRST, IRAS, and X-rays sources. Many of them also appear to be found in other catalogs in radio, IR, UV, and X-ray ranges. This opens big possibilities for investigation of individual objects in all wavelength range. The multiwavelength studies using the SBS sample should lead to new insights into the nature of the activity present in these galaxies.

A comparison with other galaxy and quasar surveys shows that the SBS survey is one of the most powerful surveys of low and high­redshifted bright AGN, QSO, star­forming galaxies and other objects. SBS spans the bridge between the well known bright QSO surveys like BQS, MBQS, HQS, HBQS, and the relatively faint surveys like LBQS, AAT, 2dF, SDSS, et al.

The use of the combined UV excess and emission­line (EL) technique put forward by the SBS has led to discovery of active and star­forming galaxies with a range of observed and derived parameters broader than in other surveys based on a single selection technique. The UVX technique covers a larger space in redshifts than does the EL technique.

A sample of very rare extragalactic and Galactic objects was discovered. SBS 0035­052, one of the most metal poor BCDG, the second known so far; SBS 1425+606, one of the most luminous QSO in the Universe, at z = 3.165 with B = 15.83, M(B) = -31.5. The first radio quiet QSO with redshift greater than z > 3 amongst the brightest X­ray QSOs; SBS 1520+530, a new gravitational lens; SBS 0909+531, two binary systems of QSOs; SBS 1150+599 = PGN 135.9+55.9 is the most metal poor Galactic halo planetary nebula; SBS 1349+545, a rare magnetic white dwarf with an equivalent polar field strength amongst the strongest found in white dwarfs, at 760 MGauss; SBS 1517+503, one of the very rare type of dwarf carbon stars having DA white dwarf companion, the second known so far.

In the Survey 14 very luminous QSOs with -29.5 > M(B) > -31.5; 13 BALQSOs; and 5 DLAQSOs were also found.

More than 1000 peculiar Galactic stars were identified. The vast majority (67%) of stellar objects selected in the SBS are DA white dwarfs (40%) and sdB subdwarfs (27%). The surface density of DA WD with B < 16.5 and B < 17.0 corresponds to 0.1 and 0.14 deg-2, respectively.

In fact, studies of individual samples of the Second Survey, as well as studies of its individual objects, just starts, thereupon often we have to come back to the Survey plates. Therefore, digitization of the low-dispersion survey plates will significantly facilitate the further work on the Survey.

SBS lists
The Second Byurakan Survey (SBS), a deeper and higher resolution large area (965 sq. deg.) sky survey for UV-excess and emission-line galaxies and QSOs, and blue stars. Objects filling the gap between Local Universe AGNs and distant QSOs were revealed

Markarian, B. E.; Lipovetskii, V. A.; Stepanian, J. A. – Second Byurakan spectral sky survey. I. Quasistellar and Seyfert objects // Ap, 19, 14-25, 1983
Markarian, B. E.; Stepanian, J. A. – Second Byurakan spectral sky survey. I - Results for region centered on α=11h30m, δ=+59°00´ // Ap, 19, 354-368, 1984
Markarian, B. E.; Stepanian, J. A. – Second Byurakan spectral sky survey. II - Results for region centered on α=09h50m, δ=+55°00´ // Ap, 20, 10-23, 1984
Markarian, B. E.; Stepanian, J. A. – Second Byurakan spectral sky survey. III - Results for region centered on α=08h00m, δ=+59°00´ // Ap, 20, 278-289, 1984
Markarian, B. E.; Stepanian, J. A.; Erastova, L. K. – Second Byurakan spectral sky survey. IV. Results for region centered on α=12h22m, δ=+55°00´ // Ap, 23, 623-633, 1986
Markarian, B. E.; Stepanian, J. A.; Erastova, L. K. – Second Byurakan Sky Survey. V - Results for region centered on α=15h30m, δ=+59°00´ // Ap, 25, 551-562, 1987

SBS objects spectroscopy

Markarian, B. E.; Lipovetskii, V. A.; Stepanian, J. A. – Slit spectra of objects of the second Byurakan survey. I // Ap, 20, 113-117, 1984
Markarian, B. E.; Lipovetskii, V. A.; Stepanian, J. A. – Slit spectra of galaxies of the Second Byurakan Survey. II // Ap, 21, 371-375, 1985

SBS new quasars

Markarian, B. E.; Erastova, L. K.; Stepanian, J. A.; Lipovetskii, V. A.; Shapovalova, A. I. – New Quasistellar Objects // Astron. Letters, 13, 1, 1987
Markarian, B. E.; Stepanian, J. A.; Lipovetskii, V. A. – New Quasistellar Objects. I // Astron. Circular, 1141, 1-3, 1980 (in Russian)
Markarian, B. E.; Stepanian, J. A.; Lipovetskii, V. A. – New Quasistellar Objects. II // Astron. Circular, 1142, 1-3, 1980 (in Russian)
Markarian, B. E.; Stepanian, J. A.; Lipovetskii, V. A. – New quasi-stellar objects. III // Astron. Circular, 1233, 2-4, 1982 (in Russian)
Markarian, B. E.; Stepanian, J. A.; Lipovetskii, V. A. – New Quasistellar Objects. III 944+540 1220+567 1221+545 1220+559 // Astron. Circular, 1237, 1, 1982 (in Russian)
Markarian, B. E.; Stepanian, J. A.; Lipovetskii, V. A. – New Quasistellar Objects. IV // Astron. Circular, 1265, 1-3, 1983 (in Russian)
Markarian, B. E.; Stepanian, J. A.; Lipovetskii, V. A. – New quasi-stellar objects. V // Astron. Circular, 1346, 7-8, 1984 (in Russian)
Markarian, B. E.; Erastova, L. K.; Stepanian, J. A.; Lipovetsky, V. A.; Shapovalova, A. I. – New Quasistellar Objects. VI // Astron. Circular, 1381, 5-6, 1985 (in Russian)

Quasars in FBS and SBS

Markarian, B. E.; Erastova, L. K.; Lipovetskii, V. A.; Stepanian, J. A.; Shapovalova, A. I. – Quasars and stellar objects in the Byurakan surveys // Ap, 26, 7-15, 1987

SBS general

Markarian, B. E.; Stepanian, J. A.; Erastova, L. K. – The Second Byurakan Spectral Sky Survey // Proc. IAU S121: Observational Evidence of Activity in Galaxies, held in Byurakan, Armenia, USSR, 3-7 June 1986. Eds. E.Ye. Khachikian, K.J. Fricke & J. Melnick. Kluwer Academic Publishers, Dordrecht, p. 25, 1987