The coordinates, apparent magnitudes and redshifts of the extragalactic objects are listed in Table 1. The projected impact parameters (Col. 6) range from 0.8 to about 4.7 h-1 Mpc, and therefore probe the cluster from the inner Abell radius all the way out to the low-density environment and large-scale filaments. The wavelength and flux calibrated 1-D spectra are displayed in Fig. 1. The mean signal-to-noise ratio has been computed as a function of wavelength from the photon statistics after subtraction of the spectral lines in the normalized spectrum.
Besides the stellar objects (which are dealt with in a separate paper), we discovered 16 new emission-line objects, a BL Lac candidate and an elliptical galaxy. We confirmed the redshift of the QSO US 370. The emission-line objects consist of 9 quasars, 3 Seyfert 1 and 4 HII-region galaxies (see below). We included HS 1309+2605 as a BL Lac candidate because none of the usual stellar absorption features could be detected in the slit spectrum (see Fig. 1). However there has been no radio detection ([Kim etal. 1994]; [Kim 1994]) and the signal-to-noise ratio in our optical spectrum is insufficient for a final decision. The normal galaxy HS 1312+2651 was originally classified as a "Narrow Emission" object according to the objective-prism spectrum, but the emission feature could not be confirmed.
Twelve emission-line objects show broad permitted emission lines and
should be quasars or Seyfert 1 galaxies. We adopt the definition by
[Véron-Cetty & Véron (1998)] of a quasar as a star-like object, or an object
with a star-like nucleus, brighter than the absolute B-band magnitude of
-21.5 . We have made a distinction between QSOs and Seyfert 1
galaxies on the basis of this definition, and calculated the absolute B-band
magnitude MB of all the objects in Table 1 (Col. 10). Note
that no K-correction was applied since it is usually of the same order as
the uncertainties in the photometry and/or it does not affect the
classification.
Among the Seyfert galaxies, we find several sub-types. RXJ1252.6+3002 belongs
to the class of narrow-line Seyfert 1 galaxies [(Boller etal. 1996)].
The intrinsic FWHM of H, around 1150 km s-1, is typical for such
objects, and it is only slightly larger than that of
[OIII]
500.7. Moreover, the flux ratio of
[OIII]
500.7 to H
is less than unity which rules out the
possibility that it is a Seyfert 2 [(Shuder & Osterbrock 1981)]. Additional
support for this classification comes from the detection of strong blends of
FeII lines in the regions around 457.0 nm and 519.0 nm
[(Koski 1978)]. HS 1302+2629 also shows relatively narrow lines,
but given its FWHM at H
of
km s-1, it has to be
classified as a classical Seyfert 1 galaxy. Although HS 1312+2735 is obviously
a Seyfert 1 galaxy, a Seyfert 1.5 type [(Netzer 1990)] is still
possible given the shape of the H
line.
The intrinsically faintest objects HS 1249+2620, HS 1257+2732, HS 1303+2908 and HS 1312+2644 only show narrow permitted emission lines. In Sect. 5 below, we show that these narrow emission-line galaxies (NELGs) are indeed HII region (i.e. starburst) galaxies.
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