RAS: HERON Survey Fishes Out Details in Ghostly Galaxy Outskirts

bystander · Post by **bystander** » Tue Oct 15, 2019 5:56 pm

HERON Survey Fishes Out Details in Ghostly Galaxy Outskirts
Royal Astronomical Society | 2019 Oct 15

An image of a dwarf elliptical galaxy satellite of the spiral galaxy NGC 7331, a galaxy similar to the Milky Way’s companion, the great Andromeda galaxy M31. This image shows the same exposure, but with increasing emphasis on very faint features. This study reveals for the first time that this galaxy is 50,000 light-years across (half the size of the Milky Way), and may be in the process of dissolving into the halo of NGC 7331 as its stars are stripped by gravitational tides. If one end of this galaxy were placed at the centre of the Milky Way, the other end would reach nearly to the edge of our galaxy’s disc, well past the location of the Sun. Credit: R. Michael Rich, UCLA
Astronomers have completed the largest survey to date of the faint outskirts of nearby galaxies, successfully testing a low-cost system for exploring these local stellar systems. R. Michael Rich ... led an international team carrying out a survey for the Haloes and Environments of Nearby Galaxies (HERON) collaboration ... The team find that the diameters of the galactic outskirts – the haloes - appear to correlate with the brightness and type of galaxy.

The outer regions of galaxies contain ancient stars ejected in collisions with other galaxies, as well as stars that were among the first to form in the galaxy’s history. Understanding these regions helps trace the invisible dark matter structures enmeshed with the visible stars and gas that make up the most obvious component of a galaxy. ...

These very faint, distant stars may trace the extent of dark matter associated with these galaxies, a possibility that the team plans to explore in the future. The team had sought a connection between evidence of a galaxy collision and the amount of star formation observed in a galaxy, but none is seen: old, red and dead galaxies are as likely to have visible collisions as a disc galaxy with a youthful burst of star formation; instead, collisions are mostly found to have occurred in any galaxy more luminous than the Milky Way. “Previously a study like this would examine a handful of galaxies; a sample of this size is unprecedented”, said Mosenkov. ...

The Halos and Environments of Nearby Galaxies (HERON) I:
Imaging, Sample Characteristics, and Envelope Diameters ~ R. Michael Rich et al

Monthly Notices of the RAS 490(2):1539 (Dec 2019) DOI: 10.1093/mnras/stz2106
arXiv.org > astro-ph > arXiv:1907.10706 > 24 Jul 2019 (v1), 11 Sep 2019 (v3)