Deep Chandra Observations of HCG 16 - I. Active Nuclei, Star formation and Galactic Winds

TL;DR

This study uses deep X-ray and radio observations of HCG 16 to analyze nuclear activity, star formation, and galactic winds, revealing variable active nuclei, starburst dominance, and properties of superwinds in the group.

Contribution

First detailed multi-wavelength analysis of HCG 16 revealing nuclear activity, star formation history, and galactic wind properties in a compact galaxy group.

Findings

Confirmed obscured active nuclei in NGC 833 and NGC 835.

Detected Fe-Kα emission line in NGC 835's spectrum.

Identified starburst dominance and declining star formation in NGC 838 and NGC 839.

Abstract

We present new, deep Chandra X-ray and Giant Metrewave Radio Telescope 610~MHz observations of the spiral-galaxy-rich compact group HCG 16, which we use to examine nuclear activity, star formation and the high luminosity X-ray binary populations in the major galaxies. We confirm the presence of obscured active nuclei in NGC 833 and NGC 835, and identify a previously unrecognized nuclear source in NGC 838. All three nuclei are variable on timescales of months to years, and for NGC 833 and NGC 835 this is most likely caused by changes in accretion rate. The deep Chandra observations allow us to detect for the first time an Fe-K$\alpha$ emission line in the spectrum of the Seyfert 2 nucleus of NGC 835. We find that NGC 838 and NGC 839 are both starburst-dominated systems, with only weak nuclear activity, in agreement with previous optical studies. We estimate the star formation rates in the two galaxies from their X-ray and radio emission, and compare these results with estimates from the infra-red and ultra-violet bands to confirm that star formation in both galaxies is probably declining after galaxy-wide starbursts were triggered ~400-500 Myr ago. We examine the physical properties of their galactic superwinds, and find that both have temperatures of ~0.8 keV. We also examine the X-ray and radio properties of NGC 848, the fifth largest galaxy in the group, and show that it is dominated by emission from its starburst.