Broadband radio continuum and host galaxy properties of extremely inverted spectrum compact radio galaxies
Abstract
We present broadband radio continuum spectra spanning 0.15-8 GHz for a sample of ten Extremely Inverted Spectrum Extragalactic Radio Sources (EISERS), selected from narrowband, low-frequency surveys below 1.4 GHz. In these surveys, EISERS show unusually steep low-frequency spectral indices, approaching or exceeding the synchrotron self-absorption (SSA) limit of α= +2.5, expected for homogeneous synchrotron sources. We have 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 EISERS in 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 through flux-scale offsets, intrinsic variability of these compact sources and diverse angular resolutions between surveys. We modelled the broadband radio spectra as synchrotron emission affected by synchrotron self-absorption 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 and thermal electron densities are similar to the general class of peak spectrum sources, with BSSA spanning over a large range of values from 20 mG to 8 G and ne ∼ 29−128cm−3. Optical and infrared analysis further indicates that the EISERS are preferentially associated with dusty starburst galaxies, composite starburst-AGN systems, or obscured AGN embedded in dense circumnuclear environments, supporting a scenario in which at least a fraction of these sources represent young or environmentally confined radio AGN.
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BibTeX
@misc{mhaskey2026broadband,
title = {{Broadband radio continuum and host galaxy properties of extremely inverted spectrum compact radio galaxies}},
author = {Mukul Mhaskey and Barenya Dev and Aritra Basu and Helmut Meusinger and Surajit Paul and Matthias Hoeft},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.06222},
eprint = {2610.06222},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.06222},
note = {CC BY-NC-SA 4.0},
}
RIS
TY - UNPB
TI - Broadband radio continuum and host galaxy properties of extremely inverted spectrum compact radio galaxies
AU - Mukul Mhaskey
AU - Barenya Dev
AU - Aritra Basu
AU - Helmut Meusinger
AU - Surajit Paul
AU - Matthias Hoeft
PY - 2026
DA - 2026/10/05
PB - arXiv
DO - 10.48550/arxiv.2610.06222
UR - https://arxiv.org/abs/2610.06222
AB - We present broadband radio continuum spectra spanning 0.15-8 GHz for a sample of ten Extremely Inverted Spectrum Extragalactic Radio Sources (EISERS), selected from narrowband, low-frequency surveys below 1.4 GHz. In these surveys, EISERS show unusually steep low-frequency spectral indices, approaching or exceeding the synchrotron self-absorption (SSA) limit of α= +2.5, expected for homogeneous synchrotron sources. We have 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 EISERS in 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 through flux-scale offsets, intrinsic variability of these compact sources and diverse angular resolutions between surveys. We modelled the broadband radio spectra as synchrotron emission affected by synchrotron self-absorption 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 and thermal electron densities are similar to the general class of peak spectrum sources, with B_SSA spanning over a large range of values from 20 mG to 8 G and n_e ∼ 29−128cm^−3. Optical and infrared analysis further indicates that the EISERS are preferentially associated with dusty starburst galaxies, composite starburst-AGN systems, or obscured AGN embedded in dense circumnuclear environments, supporting a scenario in which at least a fraction of these sources represent young or environmentally confined radio AGN.
ER -