NASA | GSFC | STScI | HubbleSite | 2020 Feb 20
Surprising new data from NASA's Hubble Space Telescope suggests the smooth, settled "brim" of the Sombrero galaxy's disk may be concealing a turbulent past. Hubble's sharpness and sensitivity resolves tens of thousands of individual stars in the Sombrero's vast, extended halo, the region beyond a galaxy's central portion, typically made of older stars. These latest observations of the Sombrero are turning conventional theory on its head, showing only a tiny fraction of older, metal-poor stars in the halo, plus an unexpected abundance of metal-rich stars typically found only in a galaxy's disk, and the central bulge. Past major galaxy mergers are a possible explanation, though the stately Sombrero shows none of the messy evidence of a recent merger of massive galaxies. ...On the left is an image of the Sombrero galaxy (M104) that includes a portion of the
much fainter halo far outside its bright disk and bulge. Hubble photographed two
regions in the halo (one of which is shown by the white box). The images on the right
zoom in to show the level of detail Hubble captured. The orange box, a small subset of
Hubble's view, contains myriad halo stars. The stellar population increases in density
closer to the galaxy's disk (bottom blue box). Credits: NASA/Digitized Sky Survey/
P. Goudfrooij (STScI)/The Hubble Heritage Team (STScI/AURA)
Long a favorite of astronomers and amateur sky watchers alike for its bright beauty and curious structure, the Sombrero Galaxy (M104) now has a new chapter in its strange story — an extended halo of metal-rich stars with barely a sign of the expected metal-poor stars that have been observed in the halos of other galaxies. Researchers, puzzling over the data from Hubble, turned to sophisticated computer models to suggest explanations for the perplexing inversion of conventional galactic theory. Those results suggest the equally surprising possibility of major mergers in the galaxy's past, though the Sombrero's majestic structure bears no evidence of recent disruption. ...
The results also defied expectations, indicating that the unperturbed Sombrero had undergone major accretion, or merger, events billions of years ago. Unlike our Milky Way galaxy, which is thought to have swallowed up many small satellite galaxies in so-called "minor" accretions over billions of years, a major accretion is the merger of two or more similarly massive galaxies that are rich in later-generation, higher-metallicity stars. ...
The Strikingly Metal-Rich Halo of the Sombrero Galaxy ~ Roger E. Cohen et al
- Astrophysical Journal 890(1):52 (2020 Feb 10) DOI: 10.3847/1538-4357/ab64e9
- arXiv.org > astro-ph > arXiv:2001.01670 > 06 Jan 2020 (v1), 07 Jan 2020 (v2)