The artistic impression of a black hole. Photo credits: Internationales Twin Observatory / NOIRLab / NSF / AURA / P. Marenfeld
A galactic bar is the roughly linear structure of stars and gas that extends across the inner regions of some galaxies. The rod extends from an inner spiral arm across the core region to an arm on the other side. Found in about half of the spiral galaxies, including the Milky WayBeams are believed to channel large amounts of gas into the core regions, with profound consequences for the region, including spurts of star formation and the rapid growth of the super massive black hole downtown. Quasars, for example, have been suggested as a result of this type of activity. Ultimately, however, the feedback from such energetic events (e.g. supernovae) stops the influx and blocks the growth of the black hole.
How bars and gas inflows form and evolve are not known exactly – it is believed that galaxy mergers play a role – nor is the physical properties of galactic nuclei, which are still actively accumulating gas. A serious difficulty is that dust in the dense material around the core is opaque to optical radiation and, depending in part on the geometry, can obscure observations. Infrared and sub-millimeter wavelength measurements that can peer through the dust offer the best way forward.
A near-infrared Hubble image of the glowing, barred spiral galaxy ESO320-G030. Infrared observations and modeling of over a dozen molecular species at their center show massive gas inflows into a core region that is undergoing a star formation spurt and is dominated by three components, a small warm core, a disk, and an outer shell. Photo credit: NASA / HST; Alonso-Herrero et al.
The glowing, barred galaxy ESO 320-G030 is approximately one hundred and fifty thousand light years away and shows no signs of fusion. However, this galaxy has one bar nearly sixty thousand light years long and a second bar about ten times smaller perpendicular to it. This galaxy shows high star formation activity in the core region, but no clear evidence of an active core, possibly due to the high extinction. The galaxy is also seen with gas inflowing (and evidence of outflows at the same time), making it a nearby prototype of isolated, rapidly evolving galaxies powered by its bars.
CfA Astronomers Eduardo Gonzalez-Alfonso, Matt Ashby, and Howard Smith directed a program on Herschel far infrared spectroscopy of this object in conjunction with ALMA Submillimeter observations of the gas. By carefully modeling the shapes of the infrared absorption lines of water and several of its ionized and isotopic variations with fifteen other molecular species, including ammonia, OH, and NH, they conclude that there is a nuclear starburst of about twenty solar masses of stars per year due to short gas influx Lifespan (20 million years).
You will find evidence of three structural components: an envelope about five hundred light years in diameter, a dense circular disk about one hundred and twenty light years in radius, and a compact core or torus forty light years in size that is distinguished by its very warm dust . These three components are responsible for about 70% of the galaxy’s luminosity.
Although ESO 320-G030 is an exceptional example in that it is both bright and close by, the results suggest that similar complex core structures with inflows and outflows in luminous galaxies in the more distant Universe, including those during its most active stellar epoch , often are formation.
Reference: “A proto-pseudo bulge in ESO 320-G030 fed by a massive molecular influx driven by a core rod” by E. González-Alfonso, M. Pereira-Santaella, J. Fischer, S. García- Burillo, C. Yang A. Alonso-Herrero, L. Colina, MLN Ashby, HA Smith, F. Rico-Villas, J. Martín-Pintado, S. Cazzoli and KP Stewart, accepted October 27, 2020, Astronomy & Astrophysics.
DOI: 10.1051 / 0004-6361 / 202039047
arXiv: 2011.00347
