3.2.2 Selection of the Photometric Sample

The HydraI photometric sample was selected from the catalog of Richter (1989). The catalog lists for each galaxy a number (throughout this thesis referred to with an `R' prepended, e.g. R269), V₂₅ (from Smyth 1980), a morphological type, and the heliocentric velocity ( $cz_{\rm hel}$) where known. The catalog is supposedly complete to $V_{25} = 16\hbox{$.\!\!^{\rm m}$ }65$ within a radius of $2^\circ$ from the cluster center, i.e. covering all our observed fields.

The sample selection procedure was as follows:

1.

All galaxies with $V_{25} \leq 16\hbox{$.\!\!^{\rm m}$ }5$ in our 43 DFOSC fields were selected. This was 87 galaxies.

2.

All galaxies with classifications of E, Ep, E/S0, S0p, S0/a, SB0, SB0p, and SB0/a were selected. The classifications listed by Richter (1989) were used. This left 70 galaxies.

3.

All galaxies known to be cluster members from the spectroscopy or galaxies without spectroscopy were selected. Since HydraI is clearly isolated in redshift space, cf. Fig.  (p. ), membership determination is straightforward. Redshifts were compiled as follows. Heliocentric velocities were compiled from 5 sources: Richter (1989), JFK95b, DFOSC, Lucey & Carter (1988), and Stein (1996)^3.1. In addition, an error-weighted mean of JFK95b and DFOSC was formed. An ``adopted'' value was chosen as the value from JFK95b+DFOSC, Lucey & Carter, Stein, and Richter, in that order of preference. The data are listed in Table .

Of the 70 galaxies, 62 had a measured redshift from one of the 5 sources. The redshift histogram is shown in Figure . HydraI is clearly isolated in redshift space. All galaxies with $cz_{\rm hel} > 7000$ km/s were taken to be in the background. That was 6 galaxies, leaving 64 galaxies in the sample, of which 56 are spectroscopically confirmed cluster members. These 64 galaxies are listed in Table .

The magnitude limit $V_{25} = 16\hbox{$.\!\!^{\rm m}$ }5$ was chosen since for galaxies fainter than this reliable surface photometric profiles could not be derived. This limit corresponds on the average to ${m_{\rm r_T}}= 15\hbox{$.\!\!^{\rm m}$ }75$, where ${m_{\rm r_T}}$ is fully corrected total Gunn r magnitude. This is based on the relation

$${m_{\rm r_T}}= V_{25} - 0.75 \, ; \quad {\rm rms} = 0.32 \enspace ,$$ (3.1)

which is established for the 64 galaxies in the photometric sample. The above magnitude limit corresponds to ${M_{\rm r_T}}= -18\hbox{$.\!\!^{\rm m}$ }85$ (for $H_0 = 50\,{\rm km}\,{\rm s}^{-1}\,{\rm Mpc}^{-1}$, cf. Sect. , p. ).

 

Table: HydraI Redshift Data from Five Sources

ID	Name	Seq	$cz_{\rm hel}$ [km/s]
			Richter	JFK95b	DFOSC	JFK95b+DFOSC	LC88	Stein	Adopted	Ref.
R112	E501G13	-	3504	3520	-	3520	-	-	3520	JFK95b+DFOSC
R120	-	-	-	-	-	-	-	-	-	-
R129	-	-	3371	-	-	-	-	-	3371	Richter
R138	-	-	3768	-	-	-	-	-	3768	Richter
R166	E501G20	-	4306	-	4353	4353	-	-	4353	JFK95b+DFOSC
R185	-	-	-	-	-	-	-	-	-	-
R188	E501G21	-	4554	-	4575	4575	4592	-	4575	JFK95b+DFOSC
R193	E501G26	-	-	-	-	-	-	-	-	-
R194	-	-	4424	-	-	-	-	-	4424	Richter
R202	-	-	2453	-	-	-	-	-	2453	Richter
R209	-	4	-	-	-	-	-	4155	4155	Stein
R211	-	7	-	-	-	-	-	3707	3707	Stein
R212	E501G27	8	3204	3230	-	3230	3207	3175	3230	JFK95b+DFOSC
R213	-	-	3610	3583	-	3583	3562	-	3583	JFK95b+DFOSC
R214	-	9	-	-	-	-	-	4069	4069	Stein
R216	A1033-27	-	2378	2286	-	2286	2277	-	2286	JFK95b+DFOSC
R217	-	-	4875	4895	-	4895	4890	-	4895	JFK95b+DFOSC
R218	N3305	11	3978	3976	3976	3976	3975	3927	3976	JFK95b+DFOSC
R219	-	12	4377	4188	-	4188	4196	4179	4188	JFK95b+DFOSC
R224	N3307	16	3897	3764	3762	3762	-	3808	3762	JFK95b+DFOSC
R225	-	17	3732	3522	-	3522	3551	3581	3522	JFK95b+DFOSC
R226	-	-	-	-	-	-	-	-	-	-
R228	-	18	-	-	-	-	-	28629	28629	Stein
R231	-	19	3619	3685	-	3685	3687	3633	3685	JFK95b+DFOSC
R234	N3308	21	3598	3568	3540	3547	3545	3532	3547	JFK95b+DFOSC
R237	-	24	2895	3006	-	3006	3004	2973	3006	JFK95b+DFOSC
R238	E501G35	25	4156	4181	4191	4190	-	4177	4190	JFK95b+DFOSC
R239	I629	26	2742	2822	2793	2796	2816	2781	2796	JFK95b+DFOSC
R241	-	-	-	-	-	-	-	-	-	-
R243	-	27	3297	3441	3342	3357	3379	3300	3357	JFK95b+DFOSC
R245	-	-	4756	4789	4782	4783	4776	-	4783	JFK95b+DFOSC
R246	-	29	11650	-	-	-	-	11647	11647	Stein
R249	-	31	10716	-	-	-	-	10647	10647	Stein
R250	E437G08	-	4333	-	4392	4392	-	-	4392	JFK95b+DFOSC
R252	E437G09	-	3807	-	3681	3681	-	-	3681	JFK95b+DFOSC
R253	-	32	4782	4686	-	4686	-	4682	4686	JFK95b+DFOSC
R254	-	33	4659	4662	-	4662	-	4640	4662	JFK95b+DFOSC
R255	-	34	8529*	-	-	-	3193	3154	3193	LC88
R256	N3309	35	4079	4094	4084	4086	4079	4055	4086	JFK95b+DFOSC
R258	-	36	-	-	-	-	-	10427	10427	Stein
R261	-	38	-	3807	-	3807	-	3834	3807	JFK95b+DFOSC
R266	A1034-27A	-	4698	4739	4760	4759	4768	-	4759	JFK95b+DFOSC
R268	-	43	-	-	-	-	-	3640	3640	Stein
R269	N3311	-	3725	3868	-	3868	3833	-	3868	JFK95b+DFOSC
R273	-	44	2772	2687	2749	2731	2703	2745	2731	JFK95b+DFOSC
R278	-	46	4450	-	-	-	4478	4462	4478	LC88
R283	E437G11	48	4745	4938	4871	4897	-	4831	4897	JFK95b+DFOSC
R286	-	50	-	-	-	-	-	5626	5626	Stein
R288	E437G13	52	3610	3499	3571	3561	-	3534	3561	JFK95b+DFOSC
R290	-	55	-	-	-	-	-	11689	11689	Stein
R293	-	56	-	4482	-	4482	-	4439	4482	JFK95b+DFOSC
R295	E437G15	-	2743	-	2725	2725	-	-	2725	JFK95b+DFOSC
R305	-	58	4048	-	4033	4033	-	3983	4033	JFK95b+DFOSC
R307	-	-	3924	-	-	-	-	-	3924	Richter
R308	-	60	4084	4103	-	4103	4115	4105	4103	JFK95b+DFOSC
R316	E501G47	63	4841	4838	-	4838	4820	4805	4838	JFK95b+DFOSC
R317	N3315	64	3840	3793	3776	3779	3785	3754	3779	JFK95b+DFOSC
R319	-	65	-	4460	-	4460	4412	4387	4460	JFK95b+DFOSC
R322	E501G49	66	4112	4063	-	4063	4014	4028	4063	JFK95b+DFOSC
R327	-	67	4302	4213	-	4213	-	4191	4213	JFK95b+DFOSC
R334	E501G52	-	-	-	-	-	-	-	-	-
R336	N3316	68	3979	3876	3975	3962	3940	3937	3962	JFK95b+DFOSC
R337	-	-	-	-	-	-	-	-	-	-
R338	-	-	4203*	3075	-	3075	-	-	3075	JFK95b+DFOSC
R340	-	-	-	-	-	-	-	-	-	-
R343	-	69	3045*	4372	-	4372	-	4361	4372	JFK95b+DFOSC
R347	I2597	-	3014	2971	2985	2983	-	-	2983	JFK95b+DFOSC
R359	-	-	5157	-	-	-	5247	-	5247	LC88
R389	-	-	3432	-	-	-	-	-	3432	Richter
R445	-	-	10637	-	-	-	-	-	10637	Richter

 

Notes: References: Richter = Richter (1989); LC88 = Lucey & Carter (1988); Stein = Stein (1996). ``ID'' is the number listed by Richter. ``Seq'' is the sequential ID listed by Stein. ``Ref.'' is the reference for the adopted $cz_{\rm hel}$ value. A ``*'' denotes a value which is probably in error - this concerns the Richter values for R255, R338, and R343. Note, that the values given in the JFK95b paper for R338 and R343 should be switched, as done here (I. Jørgensen and P. Stein, private communication, 1996).

 

Table: The HydraI Surface Photometry Sample

ID	Name	RA (1950)	DEC (1950)	V25 [mag]	Type	$cz_{\rm hel}$ [km/s]	Ref.
R112	E501G13	10:31:08.9	-26:38:20	13.19	S0(4)	3520	JFK95b+DFOSC
R120	-	10:31:20.0	-26:42:28	16.01	S0/a	-	-
R129	-	10:31:38.8	-27:11:35	14.72	S0(5)	3371	Richter
R138	-	10:31:53.6	-27:24:01	14.81	S0(5)	3768	Richter
R166	E501G20	10:32:26.6	-26:57:19	13.92	SB0(2)	4353	JFK95b+DFOSC
R185	-	10:32:50.9	-26:54:37	15.27	S0	-	-
R188	E501G21	10:32:59.4	-27:06:09	13.81	S0(6)pec	4575	JFK95b+DFOSC
R193	E501G26	10:33:03.7	-27:13:22	14.53	S0(6)	-	-
R194	-	10:33:09.9	-27:07:17	15.22	S0/a(r)	4424	Richter
R202	-	10:33:23.3	-26:44:26	15.02	S0	2453	Richter
R209	-	10:33:32.7	-27:06:47	15.83	E3/S0(3)	4155	Stein
R211	-	10:33:34.4	-26:58:39	16.09	S0	3707	Stein
R212	E501G27	10:33:36.6	-27:03:35	14.61	E6/S0	3230	JFK95b+DFOSC
R213	-	10:33:37.1	-27:18:10	14.71	S0(6)	3583	JFK95b+DFOSC
R214	-	10:33:40.9	-27:25:32	16.13	S0	4069	Stein
R216	A1033-27	10:33:43.2	-27:14:58	14.47	E2	2286	JFK95b+DFOSC
R217	-	10:33:49.9	-27:11:41	14.90	S0(6)	4895	JFK95b+DFOSC
R218	N3305	10:33:50.4	-26:54:10	12.91	E1	3976	JFK95b+DFOSC
R219	-	10:33:52.0	-27:25:43	14.67	S0(4)	4188	JFK95b+DFOSC
R224	N3307	10:33:56.2	-27:16:12	14.27	S0(5)/a(rs)	3762	JFK95b+DFOSC
R225	-	10:33:58.0	-27:27:43	15.03	SB(r)0(1)	3522	JFK95b+DFOSC
R226	-	10:33:58.3	-27:13:13	16.21	E	-	-
R231	-	10:33:59.6	-26:54:24	15.71	S0	3685	JFK95b+DFOSC
R234	N3308	10:34:01.3	-27:10:43	12.13	SB0(2)	3547	JFK95b+DFOSC
R237	-	10:34:01.8	-27:05:41	14.41	S0(3)	3006	JFK95b+DFOSC
R238	E501G35	10:34:03.5	-26:44:23	13.46	S0(6)/a	4190	JFK95b+DFOSC
R239	I629	10:34:03.9	-27:19:19	14.16	E2/S0	2796	JFK95b+DFOSC
R241	-	10:34:05.5	-27:07:50	16.20	S0	-	-
R243	-	10:34:06.3	-27:03:33	14.16	S0(4)	3357	JFK95b+DFOSC
R245	-	10:34:08.0	-27:13:28	14.01	SB(rs)0(0)	4783	JFK95b+DFOSC
R250	E437G08	10:34:11.5	-27:48:10	13.92	S0(6)	4392	JFK95b+DFOSC
R252	E437G09	10:34:13.8	-27:57:16	14.03	E4/S0	3681	JFK95b+DFOSC
R253	-	10:34:13.9	-27:13:09	14.36	S(rs)0(1)	4686	JFK95b+DFOSC
R254	-	10:34:14.2	-26:53:21	15.47	E3	4662	JFK95b+DFOSC
R255	-	10:34:14.4	-27:12:38	15.46	E3	3193	LC88
R256	N3309	10:34:14.7	-27:15:29	11.50	E1	4086	JFK95b+DFOSC
R261	-	10:34:16.5	-27:27:27	15.07	S0	3807	JFK95b+DFOSC
R266	A1034-27A	10:34:20.0	-27:18:04	13.61	E7/S0	4759	JFK95b+DFOSC
R268	-	10:34:21.6	-27:19:33	16.05	S0	3640	Stein
R269	N3311	10:34:21.6	-27:16:04	10.65	S0(2)	3868	JFK95b+DFOSC
R273	-	10:34:23.9	-27:12:33	13.99	E1	2731	JFK95b+DFOSC
R278	-	10:34:27.7	-27:07:44	15.76	E1	4478	LC88
R283	E437G11	10:34:29.6	-27:39:35	13.41	S0(4)	4897	JFK95b+DFOSC
R286	-	10:34:31.3	-27:16:40	16.25	E	5626	Stein
R288	E437G13	10:34:33.0	-27:39:28	13.69	S0(5)pec	3561	JFK95b+DFOSC
R293	-	10:34:35.8	-27:18:29	15.98	E2	4482	JFK95b+DFOSC
R295	E437G15	10:34:37.2	-27:54:57	13.05	S0(7)	2725	JFK95b+DFOSC
R305	-	10:34:44.2	-27:43:30	14.07	SB(r)0(1)	4033	JFK95b+DFOSC
R307	-	10:34:47.0	-26:31:37	15.45	E2	3924	Richter
R308	-	10:34:48.5	-27:23:51	15.32	E3/S0	4103	JFK95b+DFOSC
R316	E501G47	10:34:55.7	-27:12:32	13.58	S0(5)	4838	JFK95b+DFOSC
R317	N3315	10:34:57.7	-26:55:54	12.93	SB0(0)	3779	JFK95b+DFOSC
R319	-	10:34:58.1	-27:00:48	15.40	S0	4460	JFK95b+DFOSC
R322	E501G49	10:34:59.2	-27:17:48	14.28	SB(s)0(6)	4063	JFK95b+DFOSC
R327	-	10:35:03.6	-27:36:50	14.82	SB(r)0(3)	4213	JFK95b+DFOSC
R334	E501G52	10:35:15.4	-27:07:36	13.95	S0(5)/a	-	-
R336	N3316	10:35:16.1	-27:20:02	12.85	SB0(1)	3962	JFK95b+DFOSC
R337	-	10:35:16.9	-27:20:24	16.00	E/S0	-	-
R338	-	10:35:18.9	-26:47:51	14.65	S0(5)	3075	JFK95b+DFOSC
R340	-	10:35:19.4	-27:14:11	16.17	E	-	-
R343	-	10:35:20.0	-26:47:02	15.11	S0(2)	4372	JFK95b+DFOSC
R347	I2597	10:35:25.7	-26:49:16	11.83	E3/S0	2983	JFK95b+DFOSC
R359	-	10:35:39.7	-27:11:27	15.19	SB(r)0(5)	5247	LC88
R389	-	10:36:11.4	-26:32:01	15.14	S0(5)	3432	Richter

 

Notes: All data are from Richter (1989), except for cz_hel, which is from ``Ref.'' (cf. the caption to Table ).