2. Quality of the data

   

Table 1: Comparison of galaxy velocities measured by us to those in the literature: QR = Quintana & Ramírez (1990), M = Malumuth et al. (1992)

Coordinates	QR	QR	QR	Our	Our	Our	Velocity	R
(2000.0)	velocity	error	number	velocity	error	reference	difference	magnitude
4 31 3.14-12 58 27.01	10457	33	QR32	10524	22	73	67	14.4
4 34 9.86-13 14 35.63	10044	38	QR358	9932	27	331	-112	16.6
Coordinates	M	M	M	Our	Our	Our	Velocity	R
(2000.0)	velocity	error	number	velocity	error	reference	difference	magnitude
4 31 23.63-13 04 12.39	9797	126	M3	9610	76	90	-187	15.5
4 31 43.06-13 07 09.70	10991	163	M5	11106	43	115	115	17.0
4 32 23.93-12 46 47.45	10700	30	M19	10140	23	164	-560	14.9
4 32 52.84-13 22 33.42	9665	80	M27	9594	21	189	-71	15.7
4 33 00.06-13 15 59.91	11063	51	M39	10967	19	204	-96	15.7
4 33 11.43-13 27 59.68	10689	170	M50	10670	19	218	-19	17.5
4 33 14.38-13 19 48.88	11802	74	M51	11860	27	219	58	17.3
4 33 28.34-13 27 18.83	9806	144	M74	10134	49	249	328	18.1
4 33 33.49-13 18 52.17	11773	56	M83	11754	31	262	-19	17.5
4 33 33.92-13 22 50.20	10235	45	M84	10288	20	264	53	16.5
4 33 38.40-13 02 39.49	16691	136	M93	16808	50	281	117	18.3
4 33 42.78-13 08 46.79	10495	50	M102	10546	58	295	51	17.9
4 33 56.88-13 19 18.75	9561	77	M114	9577	41	313	16	17.7
4 34 03.81-13 27 47.23	8305	42	M121	8316	58	323	11	15.8
4 34 07.25-13 15 14.45	9440	51	M123	9521	22	326	81	16.6
4 34 12.95-13 10 03.83	10836	64	M128	10894	58	335	58	17.3
4 34 35.72-13 21 19.38	10093	27	M139	10100	23	354	7	17.0
4 35 32.37-13 33 22.23	9867	112	M154	10121	23	395	254	15.5
Coordinates	CfA	CfA	CfA	Our	Our	Our	Velocity	R
(2000.0)	velocity	error	number	velocity	error	reference	difference	magnitude
4 31 03.22-12 58 26.12	10519	33	A0428-1304	10524	22	73	-5	14.4
4 31 16.57-12 27 18.90	9582	32	I 376	9224	23	85	-358	14.0
4 31 23.71-13 04 13.44	9797	126	A0429-1310	9610	76	90	-187	15.5
4 31 43.10-13 07 10.74	10991	163	A0430-1253A	11106	43	115	115	17.0
4 32 52.92-13 22 33.43	9581	28	A0430-1328A	9594	21	189	13	15.7
4 33 00.14-13 16 00.08	11062	34	A0430-1322B	10967	19	204	-95	15.7
4 33 14.43-13 19 49.28	11802	74	A0430-1326	11860	27	219	58	17.3
4 33 28.41-13 27 19.68	9806	144	A0431-1333A	10134	49	249	328	18.1
4 33 33.53-13 18 52.51	11773	56	A0431-1325C	11754	31	262	-19	17.5
4 33 33.92-13 22 50.71	10347	34	A0431-1329C	10288	20	264	-59	16.5
4 33 38.46-13 02 39.65	16691	136	A0431-1308A	16808	50	281	117	18.3
4 33 56.93-13 19 19.48	9561	77	A0431-1325E	9577	41	313	16	17.7
4 34 07.24-13 15 14.35	9513	47	A0431-1321H	9521	22	326	8	16.6
4 34 09.94-13 14 35.07	10101	38	A0431-1320D	9932	27	331	-169	16.6
4 34 13.05-13 10 04.09	10836	64	A0431-1316C	10894	58	335	58	17.3
4 34 35.72-13 21 19.45	10191	29	A0432-1327B	10100	23	354	-91	17.0
4 35 32.40-13 33 22.54	9867	112	A0433-1339	10121	23	395	254	15.5

Figure 2: Distribution of errors on velocities derived from absorption lines for the entire catalogue (full line) and for our data (dotted line)

Figure 3: Distribution of errors on velocities derived from emission lines (our data only)

Figure 4: Distribution of the Tonry & Davis R parameter given by the cross-correlation measure on absorption lines (our data)

Figure 5: Relation between the Tonry & Davis R parameter and the errors on velocities derived from absorption lines (our data)

For galaxies with absorption lines, two velocity standard stars from the Maurice et al. (1984) list were observed each night in order to check the intrinsic quality of our velocity measurements. The errors, derived by cross-correlating the star spectra to the spectrum of M31, range (from night to night) from $\pm$16 to $\pm 23$ km s^-1 for HD 24331, and from $\pm$17 to $\pm 43$ km s^-1 for HD 48381. The mean internal error on velocities derived from the rms in the mean wavelength calibration is 66 km s^-1.

For emission line measurements, the errors on velocities were estimated from the dispersion of the velocities derived from the various emission lines present. When only one emission line was present we averaged the emission and absorption line redshifts whenever possible; if no reliable absorption line redshift was available, we estimated the internal error on a single emission line to be the intrinsic value of 66 km s^-1. The number of redshifts obtained from emission lines is 85.

The distributions of errors on all the velocities in the catalogue are displayed in Figs. 2 and 3 for absorption and emission line measurements respectively. For the 220 galaxies with absorption lines taken from our observations, the histogram of the Tonry & Davis signal to noise parameter R given by the cross-correlation measure is displayed in Fig. 4 (this quantity is not given in previously published catalogues). The corresponding correlation between the Tonry & Davis R parameter and the error on the velocity is shown in Fig. 5.

In order to check the quality of our redshifts, we also reobserved 2 galaxies from Quintana & Ramírez (1990) and 18 from Malumuth et al. (1992). The results are shown in Table 1. For galaxies observed twice, we chose to give in our final catalogue the redshift with the smallest error (usually our data). The mean absolute difference between our measurements and those of Malumuth et al. (18 galaxies) is 117 km s^-1, with a dispersion of 137 km s^-1, implying that the general agreement is good. Note that the difference between our velocities and those of the literature does not tend to be larger for fainter magnitudes. The agreement with the two galaxies in common with Quintana & Ramírez (1990) is satisfactory but cannot be tested statistically. A comparison with 17 galaxies in common with the CfA redshift catalogue (Huchra et al. 1992) gives a mean absolute difference of 115 km s^-1 with a dispersion of 107 km s^-1. Notice that there are many galaxies in common in the Malumuth and CfA samples.

The final redshifts derived from our observations given in the catalogue are those derived from the cross-correlation with M31, since this template gave the best results. A correction was applied to correct for the velocity of M31 (-300 km s^-1) and to obtain heliocentric velocities.

Figure 6: Velocity histogram of all the galaxies in the catalogue

The histogram of all the velocities in the catalogue is displayed in Fig. 6. It will be discussed in detail in a companion paper (Durret et al. in preparation).

   

Table 2: Completeness of the redshift catalogue for different field diameters and for various limiting magnitudes in the R band. Numbers in parentheses indicate the absolute numbers of galaxies with and without redshifts respectively. Note that for galaxies belonging to the cluster 1800'' correspond to 1.732 Mpc with H₀=50 km s^-1 Mpc^-1

Limiting	1800	2400	3600	5400
radius ('')
R magnitude
16.0	100.0% (64/64)	98.7% (77/78)	80.7% (96/119)	62.3% (114/183)
16.5	84.3% (75/89)	74.6% (94/126)	65.1% (123/189)	52.1% (146/280)
17.0	81.7% (98/120)	72.3% (128/177)	61.4% (178/290)	51.1% (216/423)
17.5	85.5% (124/145)	74.0% (165/223)	62.0% (230/371)	50.4% (289/573)
18.0	80.6% (158/196)	70.5% (206/292)	57.3% (283/494)	46.0% (354/769)
18.5	78.7% (196/249)	69.1% (250/362)	52.7% (336/638)	40.5% (415/1024)
19.0	62.6% (206/329)	55.5% (263/474)	40.6% (353/869)	30.6% (435/1421)

We have estimated the completeness of the final spectroscopic catalogue presented here by comparing the number of galaxies with redshifts to the total number of galaxies from our photographic plate catalogue in the same area. Results are shown in Table 2. Note that the 17 galaxies in our redshift catalogue which do not have magnitudes (see Sect. 3) have been excluded from these statistics, and therefore the catalogue completeness may be slightly larger than estimated in the table.