Letter to the Editor

Deep silence: Radio properties of little red dots

¹ Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences, Konkoly-Thege Miklós út 15-17, 1121 Budapest, Hungary
² CSFK, MTA Centre of Excellence, Konkoly-Thege Miklós út 15-17, 1121 Budapest, Hungary
³ Institute of Physics and Astronomy, ELTE Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
⁴ Department of Astronomy, Institute of Physics and Astronomy, ELTE Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
⁵ HUN-REN–ELTE Extragalactic Astrophysics Research Group, ELTE Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary

^⋆ Corresponding author; perger.krisztina@csfk.org

Received: 30 September 2024
Accepted: 28 November 2024

Abstract

To investigate the radio properties of the recently found high-redshift population, we collected a sample of 919 little red dots (LRDs) from the literature. By cross-matching their co-ordinates with the radio catalogues based on the first- and second-epoch observations of the Very Large Array Sky Survey (VLASS) and the Faint Images of the Radio Sky at Twenty-centimeters (FIRST) survey, we found no radio counterparts coinciding with any of the LRDs. To uncover possible sub-milli-Jansky-level weak radio emission, we performed mean and median image stacking analyses of empty-field ‘quick look’ VLASS and FIRST image cutouts centred on the LRD positions. We found no radio emission above 3σ noise levels (∼11 and ∼18 μJy beam⁻¹ for the VLASS and FIRST maps, respectively) in either of the stacked images for the LRD sample, while the noise levels of the single-epoch images are comparable to those found earlier in the stacking of high-redshift radio-quiet active galactic nuclei (AGNs). The non-detection of radio emission in LRDs suggests that these sources host weaker (or no) radio AGNs.