Work

Broadband radio continuum and host galaxy properties of extremely inverted spectrum compact radio galaxies

Year: 2026

Type: article

Abstract: We present broadband radio continuum spectra spanning 0.15–8 GHz for a sample of ten extremely inverted spectrum extragalactic radio sources (EISERSs) selected from narrowband, low-frequency surveys (below 1.4 GHz). In these surveys, EISERSs show unusually steep low-frequency spectral indices, approaching or exceeding the synchrotron self-absorption (SSA) limit of α ≈ +2.5 ( S ν ∝ ν α ) expected for homogeneous synchrotron sources. We performed follow-up quasi-simultaneous radio observations of these sources using uGMRT (0.150–1.4 GHz) and VLA (1.0–8.0 GHz). The new observations provide improved frequency coverage and consistent flux calibration across both the optically thick and optically thin spectral regimes. We find that the spectral slopes of EISERSs in the optically thick regime are flatter than the two-frequency spectral indices obtained using TGSS and WENSS and lie in the range +1.6 to +3, suggesting that heterogeneous survey data can introduce biases due to flux-scale offsets, the intrinsic variability of these compact sources, and the diverse angular resolutions of different surveys. We modelled the broadband radio spectra as synchrotron emission affected by SSA and subsequently modified by free–free absorption in an external ionised medium. The estimated physical parameters based on the best fits indicate that the magnetic fields ( B SSA ) and thermal electron densities ( n e ) are similar to the general class of peak spectrum sources, with B SSA spanning a large range, from 20 mG to 8 G, and n e from ∼29 − 128 cm −3 . Optical and IR analysis further indicates that the EISERSs are preferentially associated with dusty starburst galaxies, composite starburst–active galactic nucleus (AGN) systems, or obscured AGNs embedded in dense circumnuclear environments. This is consistent with a scenario in which at least a fraction of these sources represent young or environmentally confined radio AGNs.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202661248

Authors: Mukul Mhaskey, Barenya Dev, Aritra Basu, Helmut Meusinger, Surajit Paul, Matthias Hoeft