1997A&A...323...21V


Query : 1997A&A...323...21V

1997A&A...323...21V - Astronomy and Astrophysics, volume 323, 21-30 (1997/7-1)

The ionization mechanism of the extended gas in high redshift radio galaxies: shocks or AGN photoionization?

VILLAR-MARTIN M., TADHUNTER C. and CLARK N.

Abstract (from CDS):

We have compared the UV line ratios of a sample of very high redshift radio galaxies (HZRG, z>1.7) with shock and active galactic nuclei (AGN) photoionization models, with the goal of determining the balance between jet-induced shocks and AGN illumination in the extended emission line regions (EELR). We find that the UV line ratios cannot be explained in terms of photoionization of solar abundance gas by the classical power law of index α=-1.5, which successfully reproduces the general trends defined by the optical line ratios of low redshift radio galaxies. Pure shock models also provide a poor fit to the data. However, photoionization by a power law of index -1.0 provides an excellent fit to the UV line ratios. This suggests that the ionizing continuum spectral shape may depend on radio luminosity and/or redshift, such that it becomes harder as the radio power and/or redshift increase. However, an alternative possibility is that we are seeing the first signs of chemical evolution in these objects, since a power-law of index -1.5 with low metallicity also provides a very good fit to the data. For the high ionization conditions found in the the HZRG, we show that the power-law photoionization models provide a better fit to the data than the shock models. However, such is the complexity of the shock models that we cannot rule out the possibility that a different combination of input parameters can reproduce the observed spectra. We further show that the UV line ratios provide a sensitive test of the ionization mechanism for the lower ionization conditions prevalent in some low redshift jet-cloud interaction candidates. For high ionization parameter this discrimination is difficult due to the overlap of shock and power law photoionization models.

Abstract Copyright:

Journal keyword(s): galaxies: active - galaxies: jets - galaxies: ISM - ultraviolet: galaxies

CDS comments: Table 1: Object 0529-549 = PKS 0529-549, others are [RLM94]

Simbad objects: 24

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Number of rows : 24
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 NVSS J020242+014910 rG 02 02 43.0 +01 49 09           ~ 33 1
2 PMN J0214-1158 rG 02 14 17.4 -11 58 47           ~ 58 1
3 NVSS J021725+183704 rG 02 17 25.78 +18 37 04.7           ~ 17 1
4 [RLM94] 0355-037 rG 03 58 -03.6           ~ 8 0
5 NVSS J045114+091430 rG 04 51 14.47 +09 14 30.9           ~ 16 1
6 LEDA 2824392 QSO 05 30 25.4 -54 54 23           ~ 43 2
7 NVSS J075101+131923 rG 07 51 01.3 +13 19 19           ~ 18 1
8 NVSS J083053+191314 rG 08 30 53.44 +19 13 15.7           ~ 68 1
9 PMN J0945-2429 rG 09 45 32.7 -24 28 49           ~ 93 1
10 3C 239 rG 10 11 45.6 +46 28 20   22.5       ~ 148 1
11 [VV96] J102434.5+470911 Sy1 10 24 34.5 +47 09 11     20.5     ~ 477 0
12 3C 256 rG 11 20 43.022 +23 27 55.21   21.5       ~ 118 0
13 NAME Spiderweb Galaxy AGN 11 40 48.3 -26 29 09     22.00     ~ 264 1
14 4C 26.38 rG 12 32 23.63 +26 04 07.0           ~ 21 1
15 3C 294 rG 14 06 44.00 +34 11 25.0           ~ 222 1
16 4C -00.54 rG 14 13 15.2 -00 23 01           ~ 46 0
17 3C 326.1 G 15 56 10.0 +20 04 21     20.0     ~ 113 1
18 4C -00.62 rG 16 01 17.5 -00 28 47           ~ 64 1
19 3C 372 rG 18 10 55.70 +40 45 23.6   22.1       ~ 66 1
20 4C 48.48 rG 19 33 05.27 +48 11 41.8           ~ 39 1
21 4C 23.56 rG 21 07 15.080 +23 31 43.71           ~ 103 0
22 LEDA 2831507 Sy2 22 53 03.1 -40 57 46     20.0     ~ 98 1
23 PKS J2253-0840 rG 22 53 40.4 -08 40 44           ~ 13 1
24 4C 28.58 rG 23 51 59.23 +29 10 29.0           ~ 41 1

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2022.05.24-01:16:55

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