3 Results

The velocity measurements obtained in this work are listed in Table 2 (Virgo) and 3 (Coma) as follow:
Column 1: the CGCG (Zwicky et al. 1961-68) or VCC (Binggeli et al. 1985) designation.
Columns 2, 3: (B1950) celestial coordinates, measured with few arcsec uncertainty.
Column 4: morphological type as given in the VCC.
Column 5: photographic magnitude.
Columns 6, 7: observed recessional velocity with uncertainty derived in this work. The latter quantity includes only statistical errors. The global uncertainty can be derived by adding in quadrature the systematic error of 50  $\rm km~ s^{-1}$due to the uncertainty in the absolute wavelength calibration. Several absorption line spectra have statistical errors up to 900  $\rm km~ s^{-1}$, reflecting a lack of strong features. These redshifts, however, are sufficient to derive a membership.
Column 8: type of lines (A = absorption; E = emission).
Column 9: observing run (L99 = Loiano 1999, L00 = Loiano 2000, Can = Cananea 2000, OHP = OHP 1999).
Column 10: old membership as given in the VCC (bk = background, m = member, - = possible member) (only for Table 2).
Column 10a: new membership.
Columns 11, 12: previously available redshift, with reference.

Figure 1 gives a representation in celestial coordinates of 639 galaxies in the VCC region with redshift $V\leq 3000$  $\rm km~ s^{-1}$(panel a) and a wedge diagram (in the same velocity window) is given in panel b. Small symbols mark galaxies taken from the literature, filled circles mark the measurements obtained in this work. Figure 2 gives a representation in celestial coordinates of 913 galaxies in the VCC region with redshift $\leq 24\, 000$  $\rm km~ s^{-1}$(panel a) and a wedge diagram is given in panel b. Figure 3 gives a representation in celestial coordinates of 1109 galaxies in the Coma region with measured redshift (top) and a wedge diagram is given (bottom). (Same use of symbols as in Figs. 1 and 2).

3.1 Redshift completeness

The VCC catalogue contains 2096 galaxies brighter than $B_{\rm T}=20.0$. Of these only 913 have a redshift measurement so far. Even at brighter levels the redshift information is far from complete (see Table 4 for details). For example among the 849 galaxies with $B_{\rm T}<16.0$ there are still 69 with no spectra available. It is not surprising, though, that such relatively bright objects remain unmeasured because, given the vicinity of the Virgo cluster, galaxies in this magnitude range have low luminosities ( $M_{\rm p}>-15.0$). Given the known inverse proportionality between the luminosity and the surface brightness, they all correspond with extremely low surface brightness galaxies, which are much more difficult to observe spectroscopically than objects of similar magnitude which are further away. Furthermore, galaxies with missing spectra are almost entirely dEs, thus with featureless spectra. During the spectroscopical runs described in the present paper we have tried, unsuccesfully, to measure several of these objects: VCC 236 (dE), 452 (dE), 816 (dE), 1417 (dE), 1497 (dE), 1503 (dE), 1571 (dE), 1649 (dE), 1755 (dE), 1825 (dIm/dE), 1945 (dE), 1991 (dE), 2083 (dS0) with integration time $\sim$ 30 min. We point out to those observers who wish to obtain succesfull spectra at 2 m class telescopes to try with much longer exposures.

 

 

Table 4: Redshift completeness in the Virgo cluster

mag	tot	with z	%
$\leq$15.0	549	546	99
$\leq$16.0	849	780	92
$\leq$17.0	1064	864	81
$\leq$18.0	1323	903	68
$\leq$19.0	1704	913	53
$\leq$20.0	2096	916	43

The redshift completeness is far better in the Coma-region, limited however to a brighter magnitude. Of the 1127 CGCG galaxies listed in the Coma region, 1082 have $B_{\rm T}\le15.7$. Another 45 belong to multiple systems which were split in their individual components, each of them fainter than the catalogue limiting magnitude 15.7. Only 2/1082 galaxies with $B_{\rm T}\le15.7$ and 18/1127 with $B_{\rm T}\le16.5$ remain with unknown redshift, thus the sample is 98% complete.

An interesting example of a strong emission-line object in the background of the Coma supercluster is CGCG 127-057N which was observed at Cananea. The spectrum of this galaxy (see Fig. 4) shows strong Balmer and [OIII] lines and weak [NII] and [SII]. The corresponding metallicity derived from [OIII]/H$\beta$, as prescribed by Edmunds & Pagel (1984) is: 12 + log(O/H) = 8.16.

3.2 membership

Figure 4: The emission-line spectrum of 127-057N

The membership to the Virgo cluster given in the VCC (members, possible-members, background) was estimatied on purely morphological grounds (mostly on the surface brightness) by Binggeli et al. (1985). The new redshifts presented in this paper, in conjunction with two other recent sets of Virgo velocity measurements (Magri 1994 and GGH98), can be used to reassess this issue. We find that all objects listed in the VCC as "members" are confirmed as such (V<3000  $\rm km~ s^{-1}$), stressing the high success-rate of the morphological estimate. "Possible members" are found with V<3000  $\rm km~ s^{-1}$ in 67% of cases, the remaining being background objects. We have noticed that out of the 13 "Possible members" which are in fact high redshift objects, 10 were classified as possible BCDs (BCD?). These appear to be systematically emission-line blue giant objects, not dwarfs, nor compact galaxies (see Table 2).

As an example we give in Fig. 5 the rotation curve of one of them: VCC 1849, which has a total rotational velocity up to 300   $\rm km~ s^{-1}$, not typical of a dwarf galaxy. The rotation curve was derived at intermediate dispersion during the Loiano 2000 run with the slit oriented along the galaxy major axis. All objects classified as "Background" in the VCC are confirmed as such.

Figure 5: The H$\alpha$ rotation curve of VCC 1849

In summary, we obtained 76 new redshift measurements of galaxies, 48 of which are projected onto the Virgo cluster and 28 in the direction of the Coma-A1367 supercluster. With these new data, the redshift completeness in the VCC region remains 92% for $B_{\rm T}\leq16.0$ and 68% for $B_{\rm T}\leq18.0$. All membership estimates, as given in the VCC, are confirmed. We remark that a large fraction of the possible members classified as BCDs?, are found to be giant emission-line galaxies well beyond the Virgo cluster.

The redshift completeness of CGCG galaxies in the direction of the Coma-A1367 supercluster is now 98%.

Acknowledgements

We wish to thank the TACS of the Loiano, Cananea and OHP telescopes for the generous amounts of time allocated to this project. G.G. wishes to thank his students for their contribution during the observations and the data reduction. This work could not be completed without the use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, Caltech under contract with NASA. L.C. has had support from CONACYT (Mexico) research grant No. G-28586E.