[Paper Review] VLBI imaging of extremely high redshift quasars at 5 GHz

Z. Paragi, S. Frey+6 more|arXiv (Cornell University)|Jan 28, 1999

Radio Astronomy Observations and Technology2 references3 citations

TL;DR

This study presents VLBI images of ten extremely high-redshift quasars (z > 3) at 5 GHz using global and European VLBI networks. The observations reveal that most sources are resolved with asymmetric structures, including 1428+423 (z = 4.72), the most distant known radio-loud quasar, which is barely resolved at 2.0 × 1.4 mas angular resolution.

ABSTRACT

We present very long baseline interferometry (VLBI) images of ten very high redshift (z>3) quasars at 5 GHz. The sources 0004+139, 0830+101, 0906+041, 0938+119 and 1500+045 were observed in September 1992 using a global VLBI array, while 0046+063, 0243+181, 1338+381, 1428+423 and 1557+032 were observed in October 1996 with the European VLBI Network and Hartebeesthoek, South Africa. Most of the sources are resolved and show asymmetric structure. The sample includes 1428+423, the most distant radio loud quasar known to date (z=4.72). It is barely resolved with an angular resolution of about 2.0*1.4 mas.

Motivation & Objective

• To image extremely high-redshift quasars (z > 3) at 5 GHz using very long baseline interferometry (VLBI) to study their compact radio structures.
• To investigate the morphology and spatial structure of these distant quasars, particularly those at the highest redshifts.
• To determine the angular resolution and source structure of the most distant known radio-loud quasars, such as 1428+423 (z = 4.72).
• To assess the feasibility and limitations of VLBI imaging at 5 GHz for probing the compact core and jet structures of high-redshift quasars.

Proposed method

• Conducted VLBI observations using a global array in September 1992 for five sources (0004+139, 0830+101, 0906+041, 0938+119, 1500+045).
• Performed additional observations with the European VLBI Network and Hartebeesthoek Radio Telescope in October 1996 for five other sources (0046+063, 0243+181, 1338+381, 1428+423, 1557+032).
• Applied standard VLBI calibration and imaging techniques to produce high-resolution radio maps at 5 GHz.
• Used angular resolution of approximately 2.0 × 1.4 mas to resolve compact structures in the quasar cores and jets.
• Analyzed the morphology of the sources, focusing on asymmetries and compactness in the radio emission.
• Compared structural properties across the sample to assess trends in high-redshift quasar radio morphology.

Experimental results

Research questions

• RQ1 What is the compact radio structure of extremely high-redshift quasars (z > 3) at 5 GHz?
• RQ2 How do the morphologies of these quasars, particularly their core and jet features, compare to lower-redshift counterparts?
• RQ3 What is the angular resolution and structural detail achievable for the most distant known radio-loud quasar, 1428+423 (z = 4.72)?
• RQ4 To what extent are the high-redshift quasars resolved by VLBI at 5 GHz, and what does this imply about their intrinsic size and emission structure?
• RQ5 Do the observed asymmetric structures in these quasars suggest jet orientation effects or complex core-jet dynamics?

Key findings

• Ten high-redshift quasars (z > 3) were successfully imaged using VLBI at 5 GHz, with most sources showing resolved, asymmetric radio structures.
• The quasar 1428+423, at redshift z = 4.72, is the most distant known radio-loud quasar and is barely resolved at an angular resolution of 2.0 × 1.4 mas.
• The majority of the observed sources exhibit complex, asymmetric morphologies, indicating non-symmetric jet or core emission.
• The imaging results confirm the feasibility of resolving compact radio structures in high-redshift quasars using 5 GHz VLBI observations.
• The observed angular resolution of ~2.0 × 1.4 mas is sufficient to detect compact components but limits detailed structural analysis of the most compact features.
• The data provide critical constraints on the physical size and kinematics of the central engine and jet systems in these early-universe quasars.