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TOPIC: HCG 16

Blobrana

L

Posts: 131433

Date: Jun 18 16:51 2015

RE: HCG 16	Permalink

Hubble views a bizarre cosmic quartet This new NASA/ESA Hubble Space Telescope image shows a gathering of four cosmic companions. This quartet forms part of a group of galaxies known as the Hickson Compact Group 16, or HCG 16 - a galaxy group bursting with dramatic star formation, tidal tails, galactic mergers and black holes. This quartet is composed of (from left to right) NGC 839, NGC 838, NGC 835, and NGC 833 - four of the seven galaxies that make up the entire group. They shine brightly with their glowing golden centres and wispy tails of gas, set against a background dotted with much more distant galaxies. Read more __________________

Blobrana

L

Posts: 131433

Date: Sep 29 05:46 2014

Hickson Compact Group 16	Permalink

Title: Deep Chandra Observations of HCG 16 - II. The Development of the Intra-group Medium in a Spiral-Rich Group Author: E. O'Sullivan, J.M. Vrtilek, L.P. David, S. Giacintucci, A. Zezas, T.J. Ponman, G.A. Mamon, P. Nulsen, S. Raychaudhury We use a combination of deep Chandra X-ray observations and radio continuum imaging to investigate the origin and current state of the intra-group medium in the spiral-rich compact group HCG 16. We confirm the presence of a faint (L_X,bolo=1.87+1.03-0.66 x 10⁴¹ erg/s), low temperature (0.30+0.07-0.05 keV) intra-group medium (IGM) extending throughout the ACIS-S3 field of view, with a ridge linking the four original group members and extending to the southeast, as suggested by previous Rosat and XMM-Newton observations. This ridge contains 6.6+3.9-3.3 x 10⁹ solar masses of hot gas and is at least partly coincident with a large-scale HI tidal filament, indicating that the IGM in the inner part of the group is highly multi-phase. We present evidence that the group is not yet virialised, and show that gas has probably been transported from the starburst winds of NGC 838 and NGC 839 into the surrounding IGM. Considering the possible origin of the IGM, we argue that material ejected by galactic winds may have played a significant role, contributing 20-40% of the observed hot gas in the system. Read more (350kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Sep 29 05:45 2014

HCG 16	Permalink

Title: Deep Chandra Observations of HCG 16 - I. Active Nuclei, Star formation and Galactic Winds Author: E. O'Sullivan, A. Zezas, J.M. Vrtilek, S. Giacintucci, M. Trevisan, L.P. David, T.J. Ponman, G.A. Mamon, S. Raychaudhury 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-Kalpha 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. Read more (424kb, PDF) __________________

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