ASKAP discovery of a 30 kpc bipolar outflow from the edge-on disk of the nearby spiral galaxy ESO 130-G012

TL;DR

Using ASKAP EMU 944 MHz data, we report the discovery of a large-scale, hourglass-shaped bipolar outflow from the edge-on spiral ESO 130-G012, extending to at least $30\ \mathrm{kpc}$ above and below the disk. The outflow is hollow and limb-brightened, with a $\sim$10 kpc waist and an opening angle near $30^{\circ}$, likely originating from the full star-forming disk rather than a central AGN. Multiwavelength data (optical, IR, X-ray, HI) indicate a modest SFR of $\sim$0.1–0.6 M$_{\odot}$ yr$^{-1}$ and no canonical jet activity, suggesting a disk-wide stellar wind/Cosmic Ray-driven origin, though a past low-luminosity AGN remains a possibility. Energetics show that the observed lobes can be inflated by sustained star formation on $\sim$ tens of Myr timescales, with CRs contributing but not uniquely powering the outflow; this system thus provides a rare nearby example of a disk-wide wind that illuminates disk–halo feedback processes. The results motivate follow-up observations to quantify hot gas content, magnetic fields, and detailed gas kinematics across the halo.

Abstract

We present the discovery of a large-scale, limb-brightened outflow, extending at least 30 kpc above and below the star-forming disk of the edge-on galaxy ESO 130-G012 (D = 16.9 Mpc). Partially obscured by Galactic foreground stars and dust, this optically unremarkable, low-mass galaxy reveals one of the largest known hourglass-shaped outflows from the full extent of its bright stellar disk. The outflow was discovered in 944 MHz radio continuum images from the Australian Square Kilometre Array Pathfinder (ASKAP) obtained as part of the "Evolutionary Map of the Universe" (EMU) project. Its height is at least 3x that of the stellar disk diameter (~10 kpc), while its shape and size most resemble the large biconical, edge-brightened FUV and X-ray outflows in the nearby starburst galaxy NGC 3079. The large-scale, hourglass-shaped outflow of ESO 130-G012 appears to be hollow and originates from the star-forming disk, expanding into the halo with speeds close to the escape velocity before likely returning to the disk. Given ESO 130-G012's modest star formation rate, the height of the outflow is surprising and unusual, likely made possible by the galaxy's relatively low gravitational potential. Follow-up observations are expected to detect hot gas inside the bipolar outflow cones and magnetic fields along the X-shaped outflow wings. Neutral gas may also be lifted above the inner disk by the outflow.

Figures (11)

• Figure 1: Optical DECaPS colour-composite image of ESO 130-G012. The stellar disk clearly stands out despite the high density of foreground stars from the Milky Way Galactic Plane, and a curved dust lane is just visible against the bright galaxy bulge, suggesting a disk inclination of $\sim$80$^\circ$. The ESO $B_{\rm 25.5mag}$-band diameter of the stellar disk is $\sim$1.8 arcmin corresponding to 8.8 kpc for a distance of $D$ = 16.9 Mpc. --- North is up and East to the left.
• Figure 2: ASKAP EMU 944 MHz radio continuum image of the spectacular outflow from the edge-on galaxy ESO 130-G012. At the galaxy distance of 16.9 Mpc, the detected outflow height of at least 6$'$ corresponds to $\sim$30 kpc (see also Figure \ref{['fig:bubble-overlays']}). The ASKAP resolution of 15$"$ is indicated in the bottom left corner.
• Figure 3: ASKAP EMU 944 MHz radio continuum images of the bipolar outflow from the galaxy ESO 130-G012, rotated such that the flow is approximately along the y-axis. -- Left pair: Total intensity images at 15$"$ resolution. -- Right pair: Clean residual images smoothed to 20$"$ resolution. The contour levels are 30, 60, 150 and 300 $\mu$Jy beam$^{-1}$. The yellow ellipse indicates the approximate size of the stellar disk. Orange circles are drawn at radii of 60$"$, 150$"$, 300$"$ and 600$"$. At the galaxy distance of 16.9 Mpc, 60$"$ corresponds to $\sim$5 kpc. The blue ellipses have sizes of 560$"$$\times$ 340$"$ (46 kpc $\times$ 28 kpc).
• Figure 4: Zoom-in of the ESO 130-G012 outflow, here shown to a height of $\sim$160$"$ ($\sim$13 kpc). --- DECaPS $zrg$-band optical image overlaid with ASKAP EMU 944 MHz radio continuum contours. -- Left: Total intensity contours (yellow, 15$"$ resolution). -- Right: Clean residual contours (orange, 20$"$ resolution). The levels are 0.06, 0.09, 0.12, 0.15, 0.20, 0.25, 0.3, 0.4, 0.5, 0.6, 0.8 and 1.2 mJy beam$^{-1}$ (yellow / orange) plus 0.5, 1, 1.4, and 1.8 mJy beam$^{-1}$ (black, 8$"$ resolution).
• Figure 5: The inner ring and disk of ESO 130-G012. VPHAS+ H$\alpha$ image (left), overlaid with ASKAP EMU 944 MHz radio continuum contours at $\sim$8$"$ resolution (middle), and a zoom-in VPHAS+ continuum subtracted (H$\alpha$-$r$) image (right). Contours in the middle image are at 0.3, 0.4, 0.6 (red), 1.0, 1.2, 1.4, 1.6 and 2.1 mJy beam$^{-1}$ (yellow).