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Register a new userThe emission line properties of the 3CR radio galaxies at redshift one: shocks, evolution, and the alignment effect
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P. N. Best
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The results of a deep spectroscopic campaign on powerful radio galaxies with redshifts z ~ 1, to investigate in detail their emission line gas properties, are presented. Both the 2-dimensional velocity structure of the [OII] 3727 emission line and the ionisation state of the gas are found to be strongly dependent upon the linear size (age) of the radio source in a manner indicative of the emission line properties of small (young) radio sources being dominated by the passage of the radio source shocks. The consequences of this evolution throughout the few times 10-to-the-7 year lifetime of the radio source are discussed, particularly with relation to the alignment of the UV--optical continuum emission of these objects along their radio axis, the nature of which shows similar evolution.
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An analysis of the kinematics and ionisation state of the emission line gas of a sample of 14 3CR radio galaxies with redshifts z~1 is carried out. The data used for these studies, deep long--slit spectroscopic exposures from the WHT, are presented in an accompanying paper. It is found that radio sources with small linear sizes (<150 kpc) have lower ionisation states, higher emission line fluxes and broader line widths than larger radio sources. The emission line ratios of small radio sources are in agreement with theoretical shock ionisation predictions and their velocity profiles are distorted. Together with the other emission line properties this indicates that shocks associated with the radio source dominate the kinematics and ionisation of the emission line gas during the period that the radio source is expanding through the ISM. Gas clouds are accelerated by the shocks, giving rise to the irregular velocity structures observed, whilst shock compression of the clouds and the presence of the ionising photons associated with the shocks combine to lower the ionisation state of the emission line gas. By contrast, in larger sources the shock fronts have passed well beyond the emission line regions; their emission line gas has much more settled kinematical properties, indicative of rotation, and emission line ratios consistent with the dominant source of ionising photons being the active galactic nucleus. (Abridged)
We present HST/WFPC2 Linear Ramp Filter images of high surface brightness emission lines (either [OII], [OIII], or H-alpha+[NII]) in 80 3CR radio sources. We overlay the emission line images on high resolution VLA radio images (eight of which are new reductions of archival data) in order to examine the spatial relationship between the optical and radio emission. We confirm that the radio and optical emission line structures are consistent with weak alignment at low redshift (z < 0.6) except in the Compact Steep Spectrum (CSS) radio galaxies where both the radio source and the emission line nebulae are on galactic scales and strong alignment is seen at all redshifts. There are weak trends for the aligned emission line nebulae to be more luminous, and for the emission line nebula size to increase with redshift and/or radio power. The combination of these results suggests that there is a limited but real capacity for the radio source to influence the properties of the emission line nebulae at these low redshifts (z < 0.6). Our results are consistent with previous suggestions that both mechanical and radiant energy are responsible for generating alignment between the radio source and emission line gas.
We analyze Chandra observations of diffuse soft X-ray emission associated with a complete sample of 3CR radio galaxies at z < 0.3. In this paper we focus on the properties of the spectroscopic sub-classes of high excitation galaxies (HEGs) and broad line objects (BLOs). Among the 33 HEGs we detect extended (or possibly extended) emission in about 40% of the sources; the fraction is even higher (8/10) restricting the analysis to the objects with exposure times larger than 10 ks. In the 18 BLOs, extended emission is seen only in 2 objects; this lower detection rate can be ascribed to the presence of their bright X-ray nuclei that easily outshine any genuine diffuse emission. A very close correspondence between the soft X-ray and optical line morphology emerges. We also find that the ratio between [O III] and extended soft X-ray luminosity is confined within a factor of 2 around a median value of 5. Both results are similar to what is seen in Seyfert galaxies. We discuss different processes that could explain the soft X-ray emission and conclude that the photoionization of extended gas, coincident with the narrow line region, is the favored mechanism.
We present basic properties of $sim$3,300 emission line galaxies detected by the FastSound survey, which are mostly H$alpha$ emitters at $z sim$ 1.2-1.5 in the total area of about 20 deg$^2$, with the H$alpha$ flux sensitivity limit of $sim 1.6 times 10^{-16} rm erg cm^{-2} s^{-1}$ at 4.5 sigma. This paper presents the catalogs of the FastSound emission lines and galaxies, which will be open to the public in the near future. We also present basic properties of typical FastSound H$alpha$ emitters, which have H$alpha$ luminosities of $10^{41.8}$-$10^{43.3}$ erg/s, SFRs of 20--500 $M_odot$/yr, and stellar masses of $10^{10.0}$--$10^{11.3}$ $M_odot$. The 3D distribution maps for the four fields of CFHTLS W1--4 are presented, clearly showing large scale clustering of galaxies at the scale of $sim$ 100--600 comoving Mpc. Based on 1,105 galaxies with detections of multiple emission lines, we estimate that contamination of non-H$alpha$ lines is about 4% in the single-line emission galaxies, which are mostly [OIII]$lambda$5007. This contamination fraction is also confirmed by the stacked spectrum of all the FastSound spectra, in which H$alpha$, [NII]$lambda lambda$6548,6583, [SII]$lambda lambda$6717, 6731, and [OI]$lambda lambda$6300,6364 are seen.
Powerful radio galaxies often display enhanced optical/UV continuum emission and extended emission line regions, elongated and aligned with the radio jet axis. The expansion of the radio source strongly affects the gas clouds in the surrounding IGM, and the kinematic and ionization properties of the extended emission line regions display considerable variation over the lifetime of individual sources, as well as with cosmic epoch. We present the results of deep rest-frame UV and optical imaging and UV spectroscopy of high redshift 6C radio galaxies. The interdependence of the host galaxy and radio source properties are discussed, considering: (i) the relative contribution of shocks associated with the expanding radio source to the observed emission line gas kinematics, and their effect on the ionization state of the gas; (ii) the similarities and differences between the morphologies of the host galaxies and aligned emission for a range of radio source powers; and (iii) the influence of radio power on the strength of the observed alignment effect.
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