Who's Lurking in the Radio Glow of Galaxies? ⚡ экспресс
We present a catalog of 115 compact radio sources in galaxies NGC 5474, NGC 4631, and M51, obtained with the Karl G. Jansky Very Large Array in its most extended A configuration at 10 GHz frequency. For some sources, diffuse counterparts were previously known from high-resolution radio surveys. We identified compact counterparts to eight star-forming regions, four candidates for anomalous microwave emission sources, and one supernova remnant (SN 2011dh). Nine compact radio sources are associated with X-ray objects, most of which are background active galactic nuclei that fall within the D25 isophotal diameter of the host systems. Such active nuclei can be false positives in studies of X-ray binary populations, highlighting the importance of high-angular-resolution multiwavelength observations. This work demonstrates the broad range of scientific questions requiring next-generation sensitive radio instruments such as the Square Kilometre Array and the planned next generation Very Large Array.
Radio astronomers aimed the VLA telescope at three spiral galaxies – NGC 5474, NGC 4631, and M51 – and saw a scene resembling a city at night: 115 bright points, like streetlights and lit windows. The telescope worked in maximum resolution mode, capturing radio waves to which space is almost transparent.
The big surprise came when comparing with X-ray images. Nine sources coincided with X-ray dots. They were expected to be binary systems with black holes within galaxies, but almost all turned out to be distant quasars – their light piercing the disk of a neighboring galaxy like a searchlight through frosted glass. Worse, some of these "searchlights" had been wrongly labeled as local objects for decades. Without accounting for such impostors, astronomers risk overestimating the number of their own black holes many times over. That's why new giant radio telescopes are learning to separate native lights from background high beams.
🎯 The radio echo of supernova SN 2011dh, captured in this survey, resembles a slowly dissipating patch of fog that reveals an unexpected detail: before the explosion, the star shed a record amount of mass, hastening its end.