Subaru Telescope | National Astronomical Observatory of Japan | 2015 Aug 04
[img3="Pseudo-color images from HSC observation which contains M81, M82, and NGC 3077. Diameter of the FOV is 1.5 degrees. (Credit: NAOJ/HSC Project)"]http://subarutelescope.org/Pressrelease ... 1group.jpg[/img3][hr][/hr]Astronomers using the Subaru Telescope's Hyper Suprime-Cam prime-focus camera recently observed the nearby large spiral galaxy M81, together with its two brightest neighbors, M82 and NGC3077. The results of their observations are deep, super wide-field images of the galaxies and their populations of young stars. As part of a Galactic Archaeology study, the team discovered that the spatial distribution of the young stars around these galaxies follows very closely that of their distribution of neutral hydrogen. "This is the first endeavor beyond the Local Group of galaxies to demonstrate the hierarchical galaxy assembly process on galactic scales," said team member Dr. Sakurako Okamoto (Shanghai Astronomical Observatory).
Cosmological archaeological studies such as this one help astronomers refine their understanding of galaxy formation and evolution. The currently favored cosmological galaxy models are based on the idea of hierarchical structure formation: that structures in the universe such as galaxies develop from small "overdensities" to become large-scale objects. For example, the Milky Way and M81 first formed as part of a local over-density in the primordial matter distribution – that is, the earliest accumulations of matter in the young universe. They grew over time via the agglomeration of numerous smaller building blocks, some of which may have survived later mergers to become present-day dwarf satellite galaxies. Establishing the presence and nature of these satellites, and determining the large-scale structure and stellar content of halos in spiral galaxies, is essential to understand and explain the physics of hierarchical galaxy assembly.
Over the last decade, astronomers doing large photometric surveys (that is, measuring the light intensities of celestial objects) have found a number of new satellite galaxies, stellar streams, and over-densities around the Milky Way and the Andromeda galaxies. The detailed properties of stars in these systems are studied to reconstruct the stellar contents of galaxies in the early stage, which is called "Galactic Archeology" or "near-field cosmology". For the Galactic Archeology study, it is necessary to resolve individual stars in a galaxy, and observe across a good fraction of the galaxy's radius.
Until now, the outskirts of the Milky Way and Andromeda are the only places that have been surveyed to sufficiently faint depths to enable detailed tests of hierarchical galaxy assembly process across wide scales. ...
Galaxies show appetite for growth
University of Edinburgh | 2015 Aug 04
A Hyper Suprime-Cam View of the Interacting Galaxies of the M81 Group - Sakurako Okamoto et al
- Astrophysical Journal Letters 809(1) L1 (10 Aug 2015) DOI: 10.1088/2041-8205/809/1/L1
arXiv.org > astro-ph > arXiv:1507.04889 > 17 Jul 2015