Research > Radio emission in quasars

Some highlight results on the radio emission in quasars

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Revealing the interplay of jets, winds and emission-line gas in type 2 quasars with radio polarization

Figure from Silpa, S. et al. (2022), MNRAS, 513, 4208, arXiv:2204.05613.

In this work we present results from a combined radio polarization and emission-line study of five type 2 targets, which demonstrates that the interplay of jets/winds and emission-line gas is most likely responsible for the nature of radio outflows in radio-quiet AGN. These five sources are known to exhibit close association between radio structures and ionized gas morphology and kinematics. Four sources show polarization in this new data. We detect 0.5−1 per cent fractional polarization in the radio cores and a high fractional polarization (10−30 per cent) in the lobes of these sources. The morphological, spectral, and polarization properties suggest a jet origin for radio emission in four targets whereas the current data cannot fully discern the origin of radio emission (jet or wind) in one target. An anticorrelation between various polarized knots in the radio and [O III] emission is observed in our sources, similar to that observed in some radio-loud AGN in the literature. This suggests that the radio emission is likely to be depolarized by the emission-line gas.

The Figure Shows, Left: VLA 5 GHz, total intensity contours in black for J1430+1339 with red superimposed electric polarization vectors. Right: gray-scale HST [O III] image. In the left panel, the length of the vectors are proportional to fractional polarization. In the right panel, the VLA 5 GHz A-array total intensity contours are in cyan with the polarization vectors proportional to polarised intensity. The radio structure follows the [O III] emitting gas; however, the location of the strongest radio polarization structures appear to be offset from the strongest [O III] emission, suggest depolarization by the emission-line gas.

Silpa, S. et al. 2022

Discovering hidden Radio-AGN and their connection to the host galaxy ionised gas

Figure from Jarvis et al. (2022), MNRAS, 503, 1780, arXiv:2103.00014

In this paper we present an overview of the survey and VLA images a medium resolution (MR: 1″/L-band/1.4GHz) and high resolution (HR: 0.3″/C-band/6GHz), for all 42 quasars. We also compare these to the low resolution (LR) FIRST images. Example images are show in the figure below which gives an overview of the range of morphologies that we observe. We find that 67% of the sample show extended radio structures on ~1-60 kpc scales. Furthermore, by using a range of criteria, we find a surprisingly high fraction of Radio-AGN in our sample of quasars. At least 57% harbour a Radio-AGN, despite the fact that only 9-21% would be classified as Radio-AGN by traditional criteria. The origin of the radio emission in the remainder of the sample remains ambiguous.

We also demonstrate a relationship between the radio emission and ionised gas properties (traced via [O III]). For example, we see a negative correlation between velocity width of the emission line and the size of the radio emission (see below). This has been observed previously in more powerful Radio-AGN, and is an indication that compact radio emission (either from jets or quasar winds) is having a dramatic impact on the host galaxy gas. Overall our paper shows the important or studying the radio emission at high spatial resolution to understand feedback from quasars – even for low radio luminosity (“radio quiet”) sources.

The Figure shows example VLA images to show the variety of morphologies seen across the different images: Low Resolution (LR; 1.4GHz, ~5″ resolution) images are overlaid with green contours, Medium Resolution (MR; 1.4GHz, ~1″ resolution) images are overlaid with blue contours and High Resolution (HR; 6GHz, ~0.3″ resolution) images are overlaid with black contours.

Jarvis et al. 2021


Prevalence of radio jets associated with quasars

Figure from Jarvis et al. 2019, MNRAS, 485, 2710, (arXiv:1902.07727).

Using the VLA radio interferometer we performed multi-resolution and multi-frequency observations of a sample of 10 quasars (i.e, the most rapidly growing black holes!) at redshift z<0.2. Despite these not being classified as "radio AGN" by most traditional methods, we found that the radio emission is dominated by the AGN (>~90%) in 9 of the 10 targets. Furthermore our high-resolution imaging revealed jet-like structures in at least 8 of these sources, indicating that radio jets are (perhaps surprisingly) prevalent in such systems. The figure shows the distribution of ionised gas ([O III] emission) in the background and the contours show the distribution of radio emission from our various observations.

Jarvis et al. 2019


Storm in a "Teacup"

Figure from Harrison et al. 2015, ApJ, 800, 45 (2015), (arXiv:1410.4198).

Using the VLA radio interferometer we performed multi-resolution and multi-frequency observations of the Teacup AGN; a z=0.1 radio-quiet quasar. The Teacup AGN was observed by us in 2014 to have a high-velocity gas component ~1kpc from the central core. This is seen in the high-velocity wing of the [O III] emission-line profile at this location (see the inset spectrum at the bottom of the image). Additionally, HST narrow-band imaging reveals a ~10kpc arc of ionised gas to the East (see image). Our new VLA data revealed that both the high-velocity outflow and ionised arc are associated with radio emission. Our interpretation of these results is that a radio jet (or possibly quasar wind) is interacting with the gas ~1kpc from the core and driving the high-velocity outflow. Additionally there are bi-polar radio bubbles being inflated by the central AGN that are interacting with the gas on ~10-12kpc scales. This AGN is "radio-quiet", which means that its radio luminosity is typical for its optical radio luminosity, and is therefore more representative of the overall population than radio-loud AGN. Our results show in the importance of radio observations for understanding AGN feedback for systems with low radio luminosities. This is the first object from a large sample to be presented in Jarvis+18 in prep.

Harrison et al. 2015