1 Introduction

Objective prism surveys for emission-line galaxies (ELGs) are the main source of large samples of both AGNs and galaxies with enhanced star formation (SF) activity. Several large samples of ELGs were published since the end of the 1980s. They include the samples of the University of Michigan (UM) survey (Salzer & MacAlpine [1988]; Salzer [1989]; Salzer et al. [1989]) near the equator, the Tololo and Cálan-Tololo survey samples (Terlevich et al. [1991]; Maza et al. [1991]) and the recent Marseille Schmidt survey (Surace & Comte [1998]) of the Southern sky.

In the Northern sky, large samples of ELGs have appeared during the last decade thanks to such objective prism surveys as the First and the Second Byurakan (SBS) surveys (Markarian et al. [1983]; Izotov et al. [1993a]; Stepanian [1994]; Pustilnik et al. [1995]), the Case survey (Pesch et al. [1995]; Salzer et al. [1995]; Ugryumov et al. [1998]), and the Heidelberg void survey (Popescu et al. [1996], [1997], [1998]). All these projects employed detection of strong emission lines on blue-sensitive photoplates. A complementary approach was based on the search of strong H$\alpha$-emission on red objective prism plates as e.g. in the Universidad Complutense de Madrid (UCM) survey (Zamorano et al. [1994]; Zamorano et al. [1996]; Gallego et al. [1997]), and the MBC (Montreal) survey (Coziol et al. [1993], [1994]).

 

 

Table 1: Journal of observations

Date	Telescope	Instrument	Grating	Wavelength	Dispersion	Observed
			[Å/mm]	range [Å]	[Å/pixel]	number
(1)	(2)	(3)	(4)	(5)	(6)	(7)
22.05-25.05.1998	2.1 m KPNO	GoldCam	165	3600-7400	2.7	69
27.05-01.06.1998	2.2 m CAHA	CAFOS	187	3700-8100	8.9	44

Despite the large effort to establish the above mentioned surveys, they yielded only relatively small complete samples on the order of 10² blue compact galaxies (BCGs hereafter, e.g. Thuan et al. 1999). This is related to the relatively low surface density of the objects in the surveys of about 0.2-0.3 per sq deg (e.g. Popescu et al. [1997]). But only complete samples of sufficient size will allow studying the distribution of the inherent physical parameters of BCGs. The experience of all these surveys can be summarized as follows. To push progress in statistical studies of low-mass galaxies with star formation bursts, a reasonably large volume has to be surveyed and the selection has to be done by well understood selection procedures. Especially for BCGs of extremely low chemical abundances, which seem to be very rare objects in the local universe after all we have learned so far, a coverage of several 10³ square degrees down to the technical limits of the surveys is essential. These limits are at magnitudes as faint as $m_{\rm b}$ = 18- 19 mag. To derive a statistically robust sample of sufficient sizes from a very large field survey, objective selection procedures for the ELGs have to be applied.

With the data described below and in Papers I and II (Ugryumov et al. [1999]; Pustilnik et al. [1999]) of this series, the authors pursue the goal of creating a new large sample of H II galaxies, or BCGs in a zone with a total area of the order 1500 square degrees. This region will fill the gap between the zones of the SBS and the region covered by the Case survey. The SBS is situated at $\alpha = 7^{\rm h} 40^{\rm m} \div 17^{\rm h} 20^{\rm m}$, $\delta = +49\hbox{$^\circ$ }\div +61\hbox{$^\circ$ }$, while the Case covers $\alpha = 8^{\rm h} 00^{\rm m} \div 16^{\rm h} 20^{\rm m}$, $\delta = +29\hbox{$^\circ$ } \div +38\hbox{$^\circ$ }$. For a description of the BCGs found in these two surveys, see Izotov et al. ([1993a], [1993b]), Thuan et al. ([1994]) and Pustilnik et al. ([1995]) for the SBS and Salzer et al. ([1995]), Ugryumov ([1997]), Ugryumov et al. ([1998]) for the Case survey which is still in progress.

Thus, the new Hamburg/SAO Survey (HSS) for emission-line galaxies leads, firstly, to the creation of a new BCG/H II galaxy sample in a large sky region with the boundaries $7^{\rm h} 20^{\rm m}$ to $17^{\rm h} 40^{\rm m}$ in right ascension and $+35\hbox{$^\circ$ }$ to $+50\hbox{$^\circ$ }$ in declination. Secondly, after combining the three BCG samples in the SBS, the Case and the HSS zones, a large Northern BCG sample covering about 3000 square degrees will be available. The main goal of the project is the search for emission-line galaxies (ELG) in order to create a new deep sample of blue compact/H II galaxies (BCG) in a large area of the sky. Another important goal of this work is to search for new extremely low-metallicity galaxies.

This is the third article of a series devoted to follow-up spectroscopy results of HSS ELG candidates. It deals with 113 candidates selected in the band between $+35\hbox{$^\circ$ }$ and $+40\hbox{$^\circ$ }$ in declination which is complementary to the zone +40$^{\circ}$$\div$+50$^{\circ}$ studied in our previous papers. The basic ideas of the HSS and its selection methods of ELG candidates are described along with the first results of the follow-up spectroscopy in Ugryumov et al. ([1999]) (Paper I). The final selection was slightly modified to improve significantly the detection rate of ELGs in follow-up spectroscopy as described in Paper II. In short, the ELG candidate selection criteria applied are a blue or flat continuum (near $\lambda$ 4000 Å) and the presence of strong or moderate [O III] $\lambda\lambda$4959, 5007 Å emission lines recognized on digitized prism spectra. Candidates accepted are restricted to the B-magnitude range $16^{\rm m} - 19\hbox{$.\!\!^{\rm m}$ }5$.

The article is organized as follows. In Sect. 2 we give the details of the spectroscopic observations and of the data reduction. In Sect. 3 the results of the observations are presented in several tables. Along with general parameters for the emission-line galaxies and several quasars, the parameters of the strongest emission lines of the ELGs are summarized in a separate table. The information on two non-emission-line galaxies is presented as well. In Sect. 4 we briefly discuss the new data and summarize the current state of the Hamburg/SAO survey. Throughout this paper a Hubble constant H₀ = 75 km$\,$s^-1 Mpc^-1 is used.