The ALMA-QUARKS Survey: Evidence of an Explosive Molecular Outflow in IRAS 15520--5234

Abstract

We present a study of the massive protocluster IRAS 15520$-$5234, which displays evidence of an explosive molecular outflow that unleashed a kinetic energy of at least 10$^{48}$ erg. The protocluster contains 16 dense cores detected in the ALMA band 6 continuum emission maps, having masses in the range from 0.2 to 11.0 M$_{\odot}$. Our analysis of CO $(2-1)$ emission reveals 28 well collimated outflow fingers, the majority of which follow a Hubble-Lemaître velocity law. The outflow fingers show no preferred orientation in the plane of sky and emerge from a common center of origin. We estimate the total mass, momentum, and kinetic energy of the outflow fingers and find that the values are at least one order of magnitude higher than the typical bipolar outflows associated with massive protostars. The morphology and kinematics of the outflow fingers suggest that the outflow associated with IRAS 15520$-$5234 is explosive in nature. We calculate the dynamical age of the explosive event to be approximately 6550 years. Additionally, we estimate the frequency of such explosive outflows in the Galaxy, which is one event every 83 years. Finally, we speculate that the rearrangement of masses within the massive protocluster and the dynamical interaction among the massive cores may result in the formation of such an energetic event.

Figures (11)

• Figure 1: ALMA 1.3 mm continuum emission in the region I15520. The black ellipses represent the cores identified by yang2025 using the getsf algorithm. The cores are labeled numerically (in red) in the order they were identified in getsf. The beam is shown in the bottom-left corner, and the scale bar is shown in the bottom-right corner.
• Figure 2: (Top) ALMA CO moment-0 (left) and moment-1 (right) maps of the region I15520. In each panel, the identified continuum cores are marked with black ellipses. The velocity range of integration is mentioned in the top right corner of the CO moment-0 map. (Bottom) Normalized CO spectrum integrated over the ALMA field of view (black). The blue and red hatched regions indicate blue- and red-shifted wing emissions, respectively.
• Figure 3: The CO blue-shifted (left) and red-shifted (right) wing emission maps. The cyan and red lines represent the blue-shifted and red-shifted outflow fingers, respectively. The blue (in left) and red (in right) contours are drawn at the levels of [5, 8, 10, 15, 20, 50]$\times\sigma$, where $\sigma= 0.15$ and 0.25 Jy beam$^{-1}$ km s$^{-1}$ for the blue- and red-shifted wing emission maps, respectively. The velocity ranges of the wing emission maps are given in the top left corner of each figure. The black dashed rectangle represents the region of interest from where the explosive event is possibly originating.
• Figure 4: The Position-Velocity (PV) diagram of the CO outflow fingers associated with I15520. The blue and red lines represent the PV of the blue-shifted and red-shifted fingers, respectively. The radial velocities are given with respect to the cloud velocity. The projected distances are the distances measured from the explosive center. The gray lines represent a linear relationship between the radial velocity and the projected distances.
• Figure 5: (Left) Spitzer ratio Map Ch2(4.5$\mu$m)/Ch1(3.6$\mu$m) of I15520. The cyan contours represent the CORNISH 5.5 GHz radio continuum emission at the levels of [10, 20, 30, 50, 100]$\times\sigma$, where $\sigma=0.2$ mJy/beam. The blue and red lines represent the blue and red-shifted outflow fingers, respectively. The center of explosion is marked with a black rectangle. The green dashed circle represents the ALMA-QUARKS field of view. A scalebar is shown in the bottom right corner. (Right) H$_{30\alpha}$ emission from the center of the protocluster I15520. The 1.3 mm continuum cores are marked as black ellipses. The magenta diamonds represent the two radio continuum peaks identified in the observations of Garay2006 using the ATCA.