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

• Published in: Astronomy and astrophysics (Berlin) Vol. 676; p. A29
• Main Authors: Cordun, C. M., Timmerman, R., Miley, G. K., van Weeren, R. J., Sweijen, F., Morabito, L. K., Röttgering, H. J. A.
• Format: Journal Article
• Language: English
• Published: Heidelberg EDP Sciences 01.08.2023
• Subjects: Angular resolution; Galactic clusters; Infrared imagery; LOFAR; Luminosity; Pilot projects; Radio astronomy; Radio emission; Radio frequency; Radio galaxies; Radio sources (astronomy); Red shift; Spatial distribution; Stars & galaxies; Supermassive black holes
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/202346320

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 Ly α –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.