2 Sample selection

A large fraction of presently known HzRGs have been found by selecting ultra steep spectrum (USS) radio sources. Various groups have been involved in the search using this technique (Röttgering et al. 1994; Chambers et al. 1996; Blundell et al. 1998). At present there are about 150 radio galaxies know with z > 2 (de Breuck et al. in preparation) of which 25 have z > 3, 5 greater than 4 and 1 has a redshift greater than 5. About 60$\%$ of all HzRGs have been found with the USS technique and this percentage increases with redshift (e.g. de Breuck et al. 1998).

The observations presented in this paper are an extension of the sample observed by Carilli et al. (1997). We selected the present sample from the $\sim$110 radio galaxies that were known at the time (1997). Of these 110 about 50 (most of the optically bright ones) had already been observed at high resolution (VLA in A configuration) at several frequencies (mostly by Carilli et al. 1997; few others by Carilli et al. 1994 and Athreya et al. 1997). From the remaining list we selected all the radio galaxies having total (estimated) flux density at 4.5 GHz greater than 25 $\mu$Jy, which allowed a reasonable detection of the polarized flux, even in sources with only $\sim$0.5$\%$ percentage polarization. The final selection to reduce the sample to 27 objects was done randomly. Three sources at z < 2, 0152-209, 1017-220 and 2224-273 (respectively at z=1.89, 1.77 and 1.68) from the MRC catalogue (McCarthy et al. 1996), were added, since they are part of a sample of high redshift radio galaxies observed with HST/NICMOS (Pentericci 1999) and the VLA was needed to match the resolution of the near infrared images. Compared to the previous sample, the galaxies observed in this sample have, on average, slightly lower optical magnitudes.

In Table 1 we report the radio and optical properties of our sample: for each radio galaxy we list the radio catalogue from which it was originally taken, the redshift (usually determined from the Ly$\alpha$ emission line), and the optical magnitude of the host galaxies. In a number of cases no optical magnitude was available, either because the sources were identified by observations in a different band (e.g. K band) or because they have not been measured. We also report the total flux densities at 1.4, 4.5 and 8.2 GHz (the first value is taken from published radio catalogues listed in the table, the others are determined from the present observations), and the total extent (in arcseconds) measured from the 8.2 GHz images for all radio sources. In the last column we list the references for the optical identification and redshift determination.

 

Table 1: Source parameters

Source			R	Size	F1.4	F4.7	F8.2
(B1950)	z	Catalog	(mag)	(arcsec)	(mJy)	(mJy)	(mJy)	Ref.
(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)
0011-023	2.080	PKS	23.5	<0.2	347$^{\it a}$	161	95	1
0152-209	1.89	MRC	21.9	2.2	453$^{\it b}$	109	47	2
0930+389	2.395	6C	--	4.2	215$^{\it c}$	73	33	3
1017-220	1.77	MRC	21.6	<0.2	583$^{\it d}$	257	148	2
J1019+053	2.765	MG	23.7	2.2	454$^{\it a}$	120	59	4
1031+34	2.1	6C	21.4	41.2	478$^{\it a}$	128	56	3
1039+681	2.530	8C	--	16.6	268$^{\it a}$	61	25	5
1056+39	2.171	B2	23.6	14.2	264$^{\it a}$	71	34	3
1132+37	2.88	B2	--	<0.2	637$^{\it c}$	227	127	3
1134+369	2.120	6C	--	14.0	235$^{\it a}$	61	26	3
1202+527	2.73	TX	--	5.3	441$^{\it a}$	188	162	6
1204+401	2.066	B3	23.0	2.5	237$^{\it c}$	60	28	7
J1338-19	4.11	TN	22.0	5.2	--	23	9	8
1339+35	2.772	FW	--	13.0	124$^{\it c}$	21	9	9
1357+007	2.671	PKS	23.7	2.7	296$^{\it a}$	59	32	10
1425-148	2.355	PKS	22.0	11.6	413$^{\it d}$	120	53	9
1558-003	2.520	TX	23.4	9.2	375$^{\it a}$	91	38	10
1647+100	2.509	TX	23.5	23.4	298$^{\it a}$	44	18	9
J1747+182	2.281	MG	23.0	7.3	1095$^{\it a}$	329	166	11
1908+722	3.537	6C	21.4	15.4	259$^{\it a}$	49	16	12
2034+027	2.129	TX	24	3.9	243$^{\it a}$	61	26	2
2048-272	2.06	MRC	>24	6.7	457$^{\it e}$	90	35	2
2052-253	2.630	MRC	23.8	20.0	219$^{\it e}$	49	22	2
2104-242	2.49	MRC	22.7	23.7	297$^{\it e}$	58	21	2
2211-251	2.508	MRC	23.4	3.5	836$^{\it d}$	227	112	2
2224-273	1.68	MRC	22.5	<0.2	233$^{\it e}$	48	19	2
2319+223	2.554	TX	--	8.9	284$^{\it a}$	44	17	9

(1) Most common name in B1950 notation (except when there is a J); (2) redshift; (3) Radio catalogue: MRC Molonglo reference catalogue; TX Texas; PKS Parkes; MG MIT-Greenbank; 6C/8C Cambridge; B2 Second Bologna; (4) R-band magnitude of the host galaxies (when available); (5) Total angular extent of the radio source; (6) Total flux density at 1.4 GHz: $^{\it a}$ Green Bank 1.4 GHz, White and Becker 1992; $^{\it b}$ NVSS, Condon et al. 1998; $^{\it c}$ FIRST, Becker et al. 1995; $^{\it d}$ extrapolated from the 408 MHz flux of the PKSCAT90, Wright and Otrupcek (Eds) 1990; $^{\it e}$ extrapolated from the 408 MHz flux of the MRC Catalogue, Lange et al. 1981; (7) Total flux density at 4.7 GHz; (8) Total flux density at 8.2 GHz; (9) Reference for redshift: 1. Dunlop et al. 1989; 2. McCarthy et al. 1996; 3. Eales and Rawlings 1996; 4. Dey et al. 1995; 5. Lacy, Ph.D. Thesis; 6. Owen et al. 1995; 7. Thompson et al. 1994; 8. Rawlings and Lacy 1996; 9. De Breuck et al. in preparation; 10. Röttgering et al. 1997; 11. Eales and Rawlings 1993; 12. Dey et al. 1998.

 

Table 2: Core parameters

Source	Core Position(J2000)	F8.2	$\alpha_{4.7}^{8.2}$	CF20
	RA Dec	(mJy beam-1)		(%)
(1)	(2)	(3)	(4)	(5)
0011-023	00 14 25.54 - 02 05 55.1	88.4	-0.9	100.0
0152-209	...	...	...	...
0930+389	09 33 06.94 + 38 41 50.8	0.29	-0.8	0.8
1017-220	10 19 49.02 - 22 19 59.8	144.7	-1.0	100.0
1019+053J	10 19 33.42 + 05 34 34.8	X2.06	-1.0	4.7
1031+34	10 34 34.61 + 33 49 27.3	0.38	-0.3	0.6
1039+681	...	...	...	<0.23
1056+39	...	...	...	<0.13
1132+37	11 35 05.93 + 37 08 40.8	123.9	-1.0	100.0
1134+369	...	...	...	<0.16
1202+527	...	...	...	<0.04
1204+401	12 07 06.27 + 39 54 39.0	0.66	-0.5	2.1
1338-19J	13 38 26.23 - 19 42 33.6	0.16	-1.0	1.9
1339+35	...	...	...	<0.44
1357+007	14 00 21.26 + 00 30 20.7	10.3	-0.4	27.0
1425-148	14 28 41.72 - 15 02 28.4	0.35	-0.7	0.5
1558-003	16 01 17.36 - 00 28 46.3	0.97	-0.3	1.6
1647+100	...	...	...	<0.17
1747+182J	...	...	...	<0.28
1908+722	19 09 09.74 + 72 15 15.3	1.2	-1.3	4.8
2034+027	20 36 34.78 + 02 56 54.4	1.7	-1.2	6.1
2048-272	...	...	...	<0.18
2052-253	...	...	...	<2.3
2104-242	21 06 58.27 - 24 05 09.1	0.19	-1.6	0.7
2211-251	...	...	...	<0.04
2224-273	22 27 43.27 - 27 05 01.7	17.8	-1.6	100.0
2319+223	...	...	...	<0.25

(1) Source name, (2) position of the radio core in J2000 coordinates; (3) core surface brightness in mJy beam^-1, measured on the 8.2 GHz map, convolved to the resolution of the 4.7 GHz image, unless preceeded by an "X"; (4) core spectral index between 4.5 GHz and 8.2 GHz; (5) percentage core fractions calculated at a rest frame frequency of 20 GHz, with upper limits for the undetected cores.