High-Resolution Radio Observations of Five Optically Selected Type 2 Quasars

Máté Krezinger,Roger Deane,Zsolt Paragi,Sándor Frey

doi:10.3390/sym12040527

Abstract

Many low-luminosity active galactic nuclei (AGNs) contain a compact radio core which can be observed with high angular resolution using very long baseline interferometry (VLBI). Combining arcsec-scale structural information with milliarcsec-resolution VLBI imaging is a useful way to characterise the objects and to find compact cores on parsec scales. VLBI imaging could also be employed to look for dual AGNs when the sources show kpc-scale double symmetric structure with flat or inverted radio spectra. We observed five such sources at redshifts 0.36 < z < 0.58 taken from an optically selected sample of Type 2 quasars with the European VLBI Network (EVN) at 1.7 and 5 GHz. Out of the five sources, only one (SDSS J1026–0042) shows a confidently detected compact VLBI core at both frequencies. The other four sources are marginally detected at 1.7 GHz only, indicating resolved-out radio structure and steep spectra. Using first-epoch data from the ongoing Karl G. Jansky Very Large Array Sky Survey, we confirm that indeed all four of these sources have steep radio spectra on arcsec scale, contrary to the inverted spectra reported earlier in the literature. However, the VLBI-detected source, SDSS J1026−0042, has a flat integrated spectrum. Radio AGNs that show kpc-scale symmetric structures with truly flat or inverted spectra could still be promising candidates of dual AGNs, to be targeted with VLBI observations in the future.

Highlights

Despite decades of detailed investigation, the true nature of the low-luminosity active galactic nuclei (LLAGNs, e.g., Seyferts and LINERs) is still under debate
We report on the observations of five LLAGNs with the European VLBI Network (EVN) at two frequencies, 1.7 and 5 GHz
From the five targeted LLAGN sources, only SDSS J1026−0042 was firmly detected with the EVN

Summary

Introduction

Despite decades of detailed investigation, the true nature of the low-luminosity active galactic nuclei (LLAGNs, e.g., Seyferts and LINERs) is still under debate. Universe contain LLAGN [1] Since they are much fainter (with bolometric luminosity Lbol < 1038 W and radio power P1.4GHz < 1035 W Hz−1 ) than the radio-loud AGNs and typically lack prominent, extended jets, it is more difficult to observe them. As with all AGNs, these sources are powered by accretion onto a supermassive black hole, but with a lower accretion rate. They appear as “downscaled” AGNs (e.g., [2]). These sources show mostly low ionization state optical emission lines in their spectra [1], and have low accretion rates (

Results

Discussion

Conclusion