LOFAR discovery of rare large FR-I jets in low-luminosity radio galaxy NGC 5322

TL;DR

This paper reports the discovery of faint, large-scale FR-I radio jets in the nearby galaxy NGC 5322 using LOFAR, revealing a rare population of low-luminosity radio galaxies with unusually extensive jets.

Contribution

It presents the first detection of faint, large FR-I jets in NGC 5322 at 144 MHz, highlighting their large extent and low luminosity, and discusses their implications for galaxy evolution.

Findings

Jets extend about 350 kpc, larger than typical for similar luminosity.

Jets are faint outside the optical galaxy, only detectable with LOFAR.

NGC 5322's jets are unusually large for their low radio luminosity.

Abstract

The discovery of faint FR~I radio jets in the nearby elliptical galaxy NGC 5322 is reported here using 144 MHz LOFAR image. The jets have an angular extent of $\sim40$ arcmin or a projected physical extent of $\sim350$ kpc. The faint jets remain well collimated and disappear in the intergalactic medium, without any visible hotspot or radio lobes. The jets detected up to $\sim20$ kpc extent at higher frequencies are relatively bright within the optical extent of the galaxy but become faint abruptly outside, where detection is made only in the LOFAR image. The total radio luminosity of the galaxy at 144 MHz is estimated to be $3.7(\pm0.4)\times10^{22}$ W Hz$^{-1}$. The 144 MHz radio luminosity of the faint jets outside the optical extent is estimated to be $7.1(\pm2.0)\times10^{21}$ W Hz$^{-1}$. The extent of the jets for its radio luminosity is abnormally large when compared to the general population of radio galaxies. It makes NGC 5322 a member of a rare population of radio galaxies, previously not detected in other radio surveys. A combined effect of stellar core depletion and low-density environment around the jets, inferred from previous studies in other wave-bands, resulting into weak entrainment of surrounding material to the jets could be responsible for its large size despite a low radio luminosity.