We have continued the program of spectroscopic follow up observations of objects from the Second
Byurakan Survey (SBS). The Survey contains  more than 1300 galaxies and 1700 starlike objects with m_{pg}<19.5  Our work is directed towards the construction of a complete sample of  faint
Markarian galaxies. Here we present results of 122 SBS galaxies  observed with the Cananea GHO 2.1m telescope during 1996-1998. Among them,  10 new Seyfert galaxies and one LINER were discovered. In the sample  reported here, another 107 emission-line and 4 absorption-line
galaxies  were spectroscopically confirmed. The apparent magnitude and redshift  distributions,
as well as examples of slit spectra for diferent types of emission-line galaxies are presented.

In order to construct a complete sample of emission-line galaxies down to m_{pg}<17.5 contained in the Second Byurakan Survey sample (Markarian \& Stepanian 1983, 1984a, b; Markarian, Stepanian \& Erastova 1985, 1986; Stepanian, Lipovetsky \& Erastova 1988, 1990, Stepanian 1994), a follow-up spectral study of the selected objects is required. This work is aimed towards this goal.

The SBS is a low resolution objective prism survey. Those observations were carried out with the 40-52" Schmidt camera of the Byurakan Observatory equipped with 1.5, 3 and 4 degrees objective prisms. The selection of objects was done by visual inspection of the plates. The selection criteria were the following: the presence of a strong UV continuum, the presence of emission lines and/or an observed peculiar energy distribution in the spectra.

The main goal of the SBS was the selection of peculiar objects belonging to the following classes: galaxies with UV-excess continuum radiation, emission line galaxies with or without appreciable UV-excess continuum, as well as  QSOs and AGN candidates, white dwarfs, subdwarfs, and other
types of objects that possess strong UV continuum radiation.

Between 1974 and 1991 a total area of 1000 square degrees of the sky was observed down to the limiting magnitude 19.5. This area is confined within the strip defined by  7h 40m < \alpha < 17h 15m, and  +49 \deg < \delta < +61 \deg. A selection of more than 1300 galaxies and about 1700 stellar-like objects with an excess ultraviolet emission is the main result of the SBS survey.

While high resolution spectral observations of faint objects are beingcarried out primarily with the 6m telescope at SAO in Russia (Stepanian \etal  1993 and references therein), observations of relatively brighter objects are being carried out with  the 2.1m telescope of the Guillermo Haro Observatory (GHO) (Carrasco \etal 1997, 1998 ) located in northern Mexico. So far, hundreds of QSOs, Seyfert galaxies, Emission-Line Galaxies (ELGs), Blue Compact Dwarf Galaxies (BCDGs), as well as some peculiar stars have already been found in the SBS sample.

There have been several attempts to produce complete samples of AGN or UVX galaxies. Naturally, every selection method of AGNs -- optical, radio, IR, X-Ray or any other -- is biased. The question is then, which one of them is capable to produce the most complete AGN sample, where the term
``complete'' means that we have selected the most significant part of all objects, down to a certain flux limit. As it was shown in the Markarian galaxy survey, the UVX criteria produces a more complete AGN sample than any other method. Of course the combination of several selection
techniques will eventually produce a real complete flux-limited sample. It has been known that our primary source of Seyfert type galaxies was the First Byurakan  Survey (FBS). The SBS provides us with objects fainter by two magnitudes in comparision to the FBS. On the other hand it has been shown, that the spectroscopic classification of galaxies in a magnitude-limited redshift survey provided the most complete sample of low-luminosity AGNs available today (Huchra \& Burg  1992). Our long term project shall allow us to compile the first complete sample of faint (m_{pg}<17.5) Seyfert and AGN galaxies. Such a sample, shall also allow us to construct a Luminosity Function (hereafter LF) of AGN and UVX galaxies out to a distance of about
500 Mpc.

Here we report on the results of the follow-up spectroscopic observations of 122 relatively bright galaxies (15.0-17.5) from the SBS sample. These observations constitute a part of an ongoing effort to obtain the data required by the scientific goals outlined above. There is also a general interest in increasing the sample of known Seyfert and AGN galaxies.
 
 

OBSERVATIONS AND DATA REDUCTION

Three observing runs in 1996, 1997 and 1998 were allocated for our project, at the GHO telescope in Cananea, Mexico. Observations were carried out with the 2.1m telescope and the LFOSC spectrophotometer equipped with a 600 x 400 pixel CCD. The read out noise of the detector is 8 $e^-$. A set up covering the spectral range of 4000-7100 \AA\  with a dispersion of 5.3 \AA /pixel was adopted. The effective instrumental spectral resolution was about 11 \AA.

The usual data reduction procedures -- bias and flat field corrections, cosmic rays removal, wavelength linearization, background subtraction, and flux calibration -- were carried out with the IRAF reduction package and software packages developed at the Special Astrophysical Observatory, Russia (Vlasyuk 1993).

The integrated emission line fluxes were determined with the help of the spectral analysis software package developed by Vlasyuk (private communication) at the Special Astrophysical Observatory. This software determines the best-fit Gaussian profile for every line and is capable of deblending closely spaced lines, as is the case of $\rm H\alpha$~6563 \AA\ and the [NII]~6548, 6584 \AA\ lines. In our case, this blending is due to the combined effects of the spectral instrumental resolution  and
the intrinsic width of the emission lines of the objects. In order to publish data of some relevance, we report measurements only for the strong emission lines. Flux corrections for telluric B band absorption were applied when necessary. This was done through dividing by a standard normalized
absorption profile until no apparent telluric absorption remained.

For every galaxy in our sample, the value of the dust reddening coefficient c(H{beta}) was determined from the observed ratio of I({Halpha})/I(H{beta}), assuming that the intrinsic ratio of F(H{alpha})/F(H{beta}) is given by:
 
 

F(H{alpha})/F(H{beta})  =  I(H{alpha})/I(H{beta}) x 10^{c(Hbeta)f(lambda)}

where {f(lambda)} is listed by Kaler (1976) for a standard galactic reddening law (Whitford 1958).

The values of c(H{beta}) were computed by assuming that the intrinsic ratio of FH{alpha})/F(H{beta}) is equal to 2.85 for narrow line emission galaxies, and is equal to 3.1 for Sy2 and for narrow line components of Sy1.5 (Veilleux \& Osterbrock, 1987).
 
 

RESULTS

The magnitude and redshift distributions of the entire sample of SBS galaxies observed in Cananea, are presented in Figures 1 and 2 respectively.

In the sample studied here, 10 galaxies show broad emission lines, typical for Seyfert galaxies. Seven galaxies show [OI] 6300 \AA\ emission line and one shows strong He I 5876 \AA\ in emission.  Four galaxies show only absorption lines such as Mg I b and Na I d.  We also found a probable triple system and three physical pairs of galaxies.

 SBS 1620+545 -- has a spectrum rather typical of Seyfert 2 type galaxies. Two other galaxies, SBS~1205+556 and  SBS~1344+527 most likely are also of this type. The spectrum of SBS 1436+597 has [NII]~6584 / H\alpha > 1. Other emission lines in the spectrum of this object are not evident, suggesting that it is a LINER.

For detailed information see Carrasco \etal 1997, 1998.

The Seyfert 1 galaxy SBS 1343+544 falls in the apparent luminosity gap between Seyfert galaxies and low-redshift QSOs. It is worth noticing that the optical QSO surveys discriminate against objects of extended morphology, causing some incompleteness at low redshifts. Meanwhile galaxy surveys dedicated to the investigation of the LF of Seyfert 1s (Cheng \etal 1985, Huchra \& Burg  1992) are incomplete at high nuclear luminosities. These surveys tend to miss those objects in which the active nucleus outshines the surrounding host galaxy and thus the corresponding object is not classified as such. The boundary in luminosity between QSOs and Sy 1s is probably not physically justified. However, there is an apparent deficiency in the number of Seyfert galaxies at the high luminosity end, probably due to selection effects. For this reason, the SBS was designed to avoid, as much as possible, the above mentioned selection biases, in order to bridge the gap and to gain further insight into the continuity of the properties of the high-luminosity QSOs and the lower luminosity Seyfert nuclei. As a result of the efforts of the SBS, the number of known intermediate QSO/Sy1 type of objects, has increased significantly during the last decade (see Martel \& Osterbrock 1994). As a consequence, we can now establish that there is a \Red{continuity} of physical properties between these two types of objects.  So far, the SBS sample has more than ten objects of this type.

The diagnostic classification diagrams for the studied objects, based on emission line ratios (Veilleux and Osterbrock  1987), are presented in Figures 3(a) and 3(b).

Examples of the LFOSC spectra of different types of emission-line galaxies are presented in
Figure 4.

CONCLUSIONS

The results of the spectrophotometric observations of 122 SBS galaxies carried out with the Cananea GHO 2.1m telescope in 1997-1998 are presented. Among the observed objects, {10 new Seyfert}galaxies and {one LINER} were found. These are {three Seyfert 1}, {one Seyfert 1.5} and
{six Seyfert 2} galaxies. The galaxy SBS 1343+544, being a Seyfert 1 object, has a luminosity and a spectrum that resemble those of QSOs, providing further evidence and support to the idea that Seyferts and QSOs are similar phenomena mainly differing in total luminosity.

In total, 118 emission-line galaxies and four absorption-line galaxies were spectroscopically confirmed. Spectral classification, redshifts, and relative intensities of the prominent emission lines were determined for all emission-line galaxies.

Since the observations reported here were made, the spectral date for relatively faint (m_{pg}<17.5) SBS galaxies have been obtained for about 80% of the sample. For producing a complete sample of SBS  galaxies, brighter than m_{pg}<17.5, we still require spectroscopic observations for nearly 200 objects.
 
 

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