# Radiative age mapping of the remnant radio galaxy B2 0924+30: the LOFAR perspective

## TL;DR

This study uses LOFAR radio observations to map the spectral ages of the remnant radio galaxy B2 0924+30, revealing detailed age distribution and signs of past AGN activity cessation around 50 million years ago.

## Contribution

It demonstrates the effectiveness of low-frequency LOFAR data in spatially resolving and dating the oldest regions of a radio galaxy remnant, advancing spectral age mapping techniques.

## Key findings

- AGN activity ceased ~50 Myr ago
- Outer lobes are younger than inner regions
- LOFAR data enables detailed age mapping of old source regions

## Abstract

We have observed the steep spectrum radio source B2 0924+30 using the LOw Frequency ARray (LOFAR) telescope. Hosted by a z=0.026 elliptical galaxy, it has a relatively large angular size of 12' (corresponding to 360 kpc projected linear size) and a morphology reminiscent of a remnant Fanaroff-Riley type II (FRII) radio galaxy. We combine LOFAR and archival images to study the spectral properties at a spatial resolution of 1'. We derive low frequency spectral index maps and use synchrotron ageing models to infer ages for different regions of the source. Using radiative ageing model fitting we show that the AGN activity ceased around 50 Myr ago. We note that the outer regions of the lobes are younger than the inner regions which is interpreted as a sign that those regions are remnant hotspots. We demonstrate the usefulness of maps of AGN radio remnants taken at low frequencies and suggest caution over the interpretation of spectral ages derived from integrated flux density measurements versus age mapping. The spectral index properties as well as the derived ages of B2 0924+30 are consistent with it being an FRII AGN radio remnant. LOFAR data are proving to be instrumental in extending our studies to the lowest radio frequencies and enabling analysis of the oldest source regions.