High-redshift obscured quasars: radio emission at sub-kiloparsec scales

Abstract

The radio properties of 11 obscured `radio-intermediate' quasars at redshifts z>~2 have been investigated using the European Very-Long-Baseline-Interferometry Network (EVN) at 1.66 GHz. A sensitivity of ~25 micro Jy per 14x17 mas2 beam was achieved, and in 7 out of 11 sources unresolved radio emission was securely detected. The detected radio emission of each source accounts for ~30-100 % of the total source flux density. The physical extent of this emission is ~<150 pc, and the derived properties indicate that this emission originates from an active galactic nucleus (AGN). The missing flux density is difficult to account for by star-formation alone, so radio components associated with jets of physical size >~150 pc, and ~< 40 kpc are likely to be present in most of the sources. Amongst the observed sample steep, flat, gigahertz-peaked and compact-steep spectrum sources are all present. Hence, as well as extended and compact jets, examples of beamed jets are also inferred, suggesting that in these sources, the obscuration must be due to dust in the host galaxy, rather than the torus invoked by the unified schemes. Comparing the total to core (~< 150 pc) radio luminosities of this sample with different types of AGN suggests that this sample of z >~2 radio-intermediate obscured quasars shows radio properties that are more similar to those of the high-radio-luminosity end of the low-redshift radio-quiet quasar population than those of FR I radio galaxies. This conclusion may reflect intrinsic differences, but could be strongly influenced by the increasing effect of inverse-Compton cooling of extended radio jets at high redshift.

14 pages, 7 figures, 4 tables, accepted for publication in MNRAS

References in corpus (6)

• A Survey of Kiloparsec-Scale Radio Outflows in Radio-Quiet Active Galactic Nuclei
• A population of high-redshift type-2 quasars-I. Selection Criteria and Optical Spectra
• The prevalence of FRI radio quasars
• Mid-infrared spectroscopy of high-redshift obscured quasars
• An 80-kpc Lyman-alpha halo around a high redshift type-2 QSO
• A population of high-redshift type-2 quasars-II. Radio Properties

Cited by in corpus (11)

• Observational constraints on the spin of the most massive black holes from radio observations
• The radio loudness of SDSS quasars from the LOFAR Two-metre Sky Survey: ubiquitous jet activity and constraints on star formation
• Millimetre observations of a sample of high-redshift obscured quasars
• VLBI Observations of a sample of Palomar-Green quasars I: parsec-scale morphology
• Gas and dust in a z=2.8 obscured quasar
• The preferentially magnified active nucleus in IRAS F10214+4724 - III. VLBI observations of the radio core
• The Quasar Feedback Survey: zooming into the origin of radio emission with e-MERLIN
• Probing the nature of compact ultra-steep spectrum radio sources with the e-EVN and e-MERLIN
• The ATESP 5 GHz radio survey. III. 4.8, 8.6 and 19 GHz follow-up observations of radio galaxies
• Revealing faint compact radio jets at redshifts above 5 with very long baseline interferometry
• Radio-FIR correlation- A probe into cosmic ray propagation in the nearby galaxy IC 342