VLBI imaging of high-redshift galaxies and protoclusters at low radio frequencies with the International LOFAR Telescope

Abstract

It is generally known that luminous, ultra-steep spectrum radio sources are preferentially associated with massive galaxies at high redshifts. In this paper, we describe a pilot project directed at such objects to demonstrate the feasibility and importance of using the LOw-Frequency ARray (LOFAR) data to study the most distant massive galaxies undergoing formation and protoclusters. We successfully imaged four high-redshift (z > 2), high-luminosity radio galaxies with sub-arcsecond resolution, at 144 MHz, using the International LOFAR Telescope (ILT). Our targets were 4C 41.17, which we dubbed “the Anthill” galaxy (z = 3.8), as well as B2 0902+34 (z = 3.4), 4C 34.34 (z = 2.4), and 4C 43.15 (z = 2.5). We mapped their low-frequency morphologies and the spatial distributions of their low-frequency spectral indices and then compared these results with the available optical, infrared, and X-ray images. Both for the Anthill at z = 3.8 and B2 0902+34 at z = 3.4, the location of the steepest radio emission coincides with the Lyα–emitting ionized gas halo. Our pilot project demonstrates that thanks to its outstanding sensitivity and high angular resolution at low frequencies, the ILT is a unique facility for studying the co-evolution and interaction of massive galaxies, galaxy clusters, and supermassive black holes in the early Universe.

Absorption of Millimeter-band CO and CN in the Early Universe: Molecular Clouds in the Radio Galaxy B2 0902+34 at Redshift 3.4

“…The CO/CN values that we find in B2 0902+34 resemble those found in the low-z radio galaxies 4C 31.04 and 4C 52.37 by Morganti et al (2023;Figure 5). This could be consistent with the scenario that the radio source interacts with the surrounding gaseous medium (Cordun et al 2023; see Section 1).…”

“…Carilli (1995) described the radio/optical structure of this galaxy as "bizarre," with a bright northern radio lobe that shows a sharp (∼90°) bend and a flat-spectrum radio core located in a "valley" between two optical peaks. Recent 144 MHz imaging of the radio source with the Low Frequency Array (LOFAR) suggests that the complex radio structure is either the result of different episodes of AGN activity, or, more likely, due to interactions between the radio source and the surrounding halo gas (Cordun et al 2023). B2 0902+34 is surrounded by a rich circumgalactic medium (CGM) in the form of a giant Lyα nebula (Reuland et al 2003), and is thought to be a collapsing protogiant elliptical (Adams et al 2009).…”