WFPC2 LRF Imaging of Emission Line Nebulae in 3CR Radio Galaxies

TL;DR

This study uses HST imaging to analyze the spatial relationship between optical emission lines and radio structures in 3CR radio galaxies, revealing weak alignment at low redshift and strong alignment in CSS galaxies, with implications for radio influence on nebulae.

Contribution

First detailed imaging study comparing optical emission line structures with radio emissions across a large sample of 3CR galaxies, highlighting the influence of radio sources on nebulae.

Findings

Weak optical-radio alignment at low redshift.

Strong alignment in CSS radio galaxies.

Emission line nebulae tend to be more luminous and larger at higher redshifts or radio powers.

Abstract

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.