The remnant radio galaxy associated with NGC 1534

Abstract

We present new observations of the large-scale radio emission surrounding the lenticular galaxy NGC 1534 with the Australia Telescope Compact Array and Murchison Widefield Array. We find no significant compact emission from the nucleus of NGC 1534 to suggest an active core, and instead find lowpower radio emission tracing its star-formation history with a radio-derived star-formation rate of 0.38 ± 0.03 M yr −1 . The spectral energy distribution of the extended emission is well-fit by a continuous injection model with an 'off' component, consistent with dead radio galaxies. We find the spectral age of the emission to be 203 Myr, having been active for 44 Myr. Polarimetric analysis points to both a large-scale magneto-ionic Galactic foreground at +33 rad m −2 and a component associated with the northern lobe of the radio emission at −153 rad m −2 . The magnetic field of the northern lobe shows an unusual circular pattern of unknown origin. While such remnant sources are rare, combined low-and high-frequency radio surveys with high surface-brightness sensitivities are expected to greatly increase their numbers in the coming decade, and combined with new optical and infrared surveys should provide a wealth of information on the hosts of the emission.

Remnant Radio Galaxy Candidates of Small Angular Sizes

“…We point out that the bias towards the remnants of large powerful radio galaxies continues to exist even in case of individual RRGs reported in the literature. In fact, individual RRGs were discovered primarily owing to their peculiar radio morphology that appeared extended, amorphous, and lacked compact features (e.g., [11][12][13][14]). Individual RRGs such as blob1 [12], NGC 1534 [14], J021659-044920 [11], B2 0924+30 [13,15,16] were identified based on their unusual amorphous-shaped large-scale radio morphology of low-surface-brightness emission at low-frequencies (≤325 MHz).…”

“…In fact, individual RRGs were discovered primarily owing to their peculiar radio morphology that appeared extended, amorphous, and lacked compact features (e.g., [11][12][13][14]). Individual RRGs such as blob1 [12], NGC 1534 [14], J021659-044920 [11], B2 0924+30 [13,15,16] were identified based on their unusual amorphous-shaped large-scale radio morphology of low-surface-brightness emission at low-frequencies (≤325 MHz). Considering the biases and limitations introduced by the angular size cutoff we attempt to search and characterize the nature of RRGs of small angular sizes (LAS < 30 ) that have remained unexplored, hitherto.…”

Combining LOFAR and Apertif Data for Understanding the Life Cycle of Radio Galaxies

“…An other useful addition is the information on polarisation for characterising the conditions of the radio plasma. This information is, at present, limited to a small number of remnant and restarted radio galaxies (see, e.g., [50][51][52][53]), but it is expected to rapidly expand in the near future, as part of the deliverable of the new large radio surveys.…”

Murchison Widefield Array detection of steep-spectrum, diffuse, non-thermal radio emission within Abell 1127

“…An alternative explanation is that of remnant (non-re-accelerated) electrons from a long-dead radio galaxyconfirmation of this would require, at the least, access to a higher-frequency detection of the emission to confirm spectral steepening (see e.g., Murgia et al 2011;Duchesne & Johnston-Hollitt 2019). Potential hosts for such a scenario are sources 'B' (the BCG) or 'E', with 'E' the most likely candidate based on existing detected emission at 1.4 GHz.…”