Extremely inverted peaked spectrum radio sources

TL;DR

This paper investigates extremely inverted spectrum radio sources with spectral index greater than +2.5, aiming to identify rare sources that challenge standard synchrotron models and explore alternative absorption mechanisms.

Contribution

The study focuses on identifying and analyzing radio galaxies with spectral indices >+2.5, testing the limits of synchrotron self-absorption theories and considering alternative absorption scenarios.

Findings

Extremely inverted spectrum sources are very rare.

Some sources may support alternative absorption models like free-free absorption.

Results could impact understanding of jet-ISM interactions in radio galaxy evolution.

Abstract

We report our ongoing search for extremely inverted spectrum compact radio galaxies, for which the defining feature in the radio spectrum is not the spectral peak, but instead the slope of the spectrum (alpha) in the high-opacity (i.e., lower frequency) part of the radio spectrum. Specifically, our focus is on the spectral regime with spectral index, alpha >+2.5. The motivation for our study is, firstly, extragalactic sources with such extreme spectral index are extremely rare, because of the unavailability of right combination of sensitivity and resolution over a range of low frequencies. The second reason is more physically motivated, since alpha = +2.5 is the maximum slope theoretically possible for a standard radio source emitting synchrotron radiation. Therefore such sources could be the test-bed for some already proposed alternative scenarios for synchrotron self-absorption (SSA), like the free-free absorption (FFA) highlighting the importance of jet-ISM interaction in the radio galaxy evolution.