EMU Radio Observations of Barred Spiral Galaxy NGC 5938 (Araish)

TL;DR

This work investigates the origin of radio emission in the barred spiral NGC 5938 by combining EMU ASKAP radio data with DECaPS2 optical/NIR, WISE infrared, and eROSITA X-ray observations. It uncovers a kpc-scale AGN jet, extending about $8.2\ \mathrm{kpc}$ out of a disk-dominated host, with a steep jet spectrum $\alpha \approx -1.2$, alongside ongoing star formation traced by infrared emission. The X-ray data reveal diffuse, jet-adjacent gas that appears to confine and shape the radio jet, suggesting jet–halo interactions and possible channelling by the X-ray gas, while the nucleus remains radio-weak and soft X-ray–bright, consistent with a low-luminosity or obscured core. Overall, NGC 5938 emerges as a rare spiral DRAGN, illustrating the complex coexistence of AGN feedback and disk galaxy evolution and highlighting the power of EMU for discovering such systems in the nearby universe.

Abstract

We present multi-wavelength observations of the nearby spiral galaxy NGC 5938 (Araish) to investigate the origin of its radio emission, specifically the contribution from active galactic nucleus (AGN) activity and star formation. Using Evolutionary Map of the Universe (EMU) data, we detect extended radio emission extending outwards to the galactic axis, with a steep non-thermal spectral index ($α= -1.2 \pm 0.2$) indicative of synchrotron radiation from an AGN jet. The jet has a physical extent of $\approx 8.2\,kpc$ (angular length of $64^{\prime\prime}$). Multi-wavelength data from The Dark Energy Camera Plane Survey 2 (DECaPS2), Wide-field Infrared Survey Explorer (WISE), and extended Roentgen Survey with an Imaging Telescope Array (eROSITA) provide further support for this interpretation. The colour-colour diagram presenting WISE infrared observations suggests the presence of dust and young stars that trace the galaxy's disk structure. Our analysis reveals a radio jet, alongside star formation traced by infrared emission, demonstrating the complex interplay of AGN activity and star formation in this well-resolved galaxy. Intriguingly, the spatial relationship reveals the brighter X-ray emission to be largely adjacent to and enveloping the extended radio emission. This suggests that the radio jet, while extending at a significant angle to the galactic disk, is confined by the larger X-ray gas halo, similar to other systems (i.e., ESO 295-IG022, Centaurus A) and may indicate jet collimation and channelling effects.

Figures (7)

• Figure 1: Radio and NIR observations of NGC 5938 (Araish). The top row (from left to right) shows the EMU Hi-Res image, the EMU Convolved Image, and the DECaPS2 optical z-band image. The bottom row shows the RACS Low, RACS Mid, and RACS High band images with the EMU Hi-Res contours overlaid at 3, 6, 9, 12, 15, 25, 50, and 75 $\sigma$ on all panels, where $\sigma$ = $65\mu$Jy beam$^{-1}$.
• Figure 2: Multi-wavelength observations of the spiral galaxy NGC 5938 (Araish) a: Radio continuum image from EMU 944 MHz tile SB62461, Convolved Image has the beam size of $15\hbox{$^{\prime\prime}$}$, at PA = 0$^{\circ}$, with an EMU Hi-Res inset image showing finer structures of the nucleus. b: DECaPS2 optical/NIR GRZ (475 nm, 644 nm, 926 nm) bands composite image represented by Blue, Green and Red colours respectively, with inset showing Hi-Res radio contours overlaid on the DECaPS2 z-band image, highlighting jet–ISM cavity overlap. c: WISE Band-3. d: eROSITA X-ray Observation: 0.2--5.0 keV, Gaussian smoothing at FWHM=$3\hbox{$^{\prime\prime}$}$, with inset showing Hi-Res radio contours overlaid on X-ray image, highlighting radio jet and X-ray adjoining. The EMU convolved radio contours are applied on all base images at 3, 9, 15, 25, and 50 $\sigma$, where $\sigma$ = $75\mu$Jy beam$^{-1}$. The radio emission from the jet region is encompassed by the $25\sigma$ radio contour.
• Figure 3: Infrared observations of NGC 5938 a: WISE Band W1, b: Band W2, c: Band W3, d: Band W4 images. 3, 9, 15, 25, and 50 $\sigma$ contours applied from EMU convolved radio observations, where $\sigma$ = $75\mu$Jy beam$^{-1}$.
• Figure 4: Top: WISE colour-colour diagram showing NGC 5938's position relative to stellar-dominated, dusty star-forming, SFMS, warm/AGN, and Quasar/AGN regions. The dashed curves mark template tracks from Jarrett_2023. The location of NGC 5938 (black dot) near the dusty star-forming / warm–AGN boundary indicates the presence of significant dust. Bottom: Star Formation Main Sequence diagram plotting mid-infrared–corrected star formation rate (SFR$_{\mathrm{MIRcor}}$) derived from WISE 12 $\mu$m luminosity following 2024MNRAS.529.3210B versus stellar mass. The contours represent the distribution of nearby galaxies from the combined 2MRS+S4G sample from Jarrett_2023, while the solid magenta line shows the SFMS fit from 2024MNRAS.529.3210B. The dashed grey line corresponds to a specific star formation rate of log(sSFR) = –11 yr$^{-1}$. NGC 5938 located on the SFMS, consistent with active star formation.
• Figure 5: RGB WISE Red-W4, Green-W3, and Blue-W1. W1 colour indicates excess hot dust emission from an AGN while W3 and W4 luminosity is sensitive to star formation. Radio Contours 3, 9, 15, 25, and 50 $\sigma$ applied from EMU radio observations.