October 24, 2020

A galaxy with a quasar-like luminosity discovered


Artist’s impression of the BOSS-EUVLG1.
The day

An international scientific team, led by researchers from the Centro de Astrobiología (CAB, CSIC-INTA) and with the participation of the Instituto de Astrofísica de Canarias (IAC), has discovered the galaxy BOSS-EUVLG1. It is the most luminous star-forming galaxy with hardly any dust known to date and its discovery has been possible thanks to observations made with the Gran Telescopio Canarias (GTC), installed at the Roque de los Muchachos Observatory (Garafía, La Palma), and with the Atacama Large Millimeter / submillimeter Array (ALMA), in Chile. The discovery was published recently in the Monthly Notices of the Royal Astronomical Society Letters.

The galaxy, named BOSS-EUVLG1, has a redshift value of 2.47. This value represents a measure of the “redness” of the light coming from the galaxy and indicates its distance from us and its age. The greater this displacement, the farther the galaxy is. In the case of BOSS-EUVLG1, the value of 2.47 means that we observed the galaxy when the age of the Universe was approximately 2.7 billion years, that is, 20% of its current age.

The values ​​of BOSS-EUVLG1 redshift and luminosity caused it to be classified by the Baryon Oscillation Spectroscopic Survey (BOSS) project as a quasar. However, based on observations made with the GTC’s OSIRIS and EMIR instruments and with the ALMA radio telescope, the researchers have been able to show that it is not a quasar, but that it is actually a galaxy with extreme and exceptional properties. .

A quasar is a distant object that emits large amounts of energy, with radiation similar to that of stars, but hundreds of billions of times brighter than stars. The word quasar is an acronym for quasi stellar radio source.

As the study points out, the high luminosity that BOSS-EUVLG1 presents in the ultraviolet range and in the Lyman Alpha emission line is due to the large number of young and massive stars it has. ANDThis high luminosity, much greater than that of other galaxies, led to the initial thought that it was a quasar. However, in quasars the high luminosity is due to the activity of supermassive black holes in the nuclei and not to the formation of stars.

“BOSS-EUVLG1 appears to be dominated byr a very massive and young star formation outbreak, with hardly any dust and with a very low metal content, indicates Rui Marques Chaves, a CAB researcher, formerly a doctoral student at the Instituto de Astrofísica de Canarias and the University of La Laguna (ULL), and lead author of the study.

The rate of star formation in this galaxy is very high, about a thousand solar masses a year. This value is about a thousand times greater than that of the Milky Way, although it is a galaxy 30 times smaller than ours. “This rate of star formation is only comparable to that of the most luminous infrared galaxies known, but the absence of dust in BOSS-EUVLG1 allows its ultraviolet and visible emission to reach us with hardly any attenuation “, explains Ismael Pérez Fournon, a researcher at the IAC and the University of La Laguna and co-author of the study.

Massive galaxies

Thus, the results of the study suggest that BOSS-EUVLG1 constitutes an example of the initial phases of the formation of massive galaxies. Despite its high luminosity and star formation rate, its low metallicity indicates that the galaxy has barely had time to enrich the interstellar medium with dust and new metals. However, “the galaxy will evolve towards a more dusty phase, similar to that of infrared galaxies, -says Camilo E. Jiménez Ángel, IAC doctoral student and study co-author. Furthermore, its high luminosity in the ultraviolet will last only about 100 million years, a very short time in the evolution of galaxies. “This would explain why other similar galaxies have not been discovered, says Claudio Dalla Vecchia, IAC researcher and co-author. BOSS-EUVLG1 was discovered thanks to the analysis of half a million spectra of galaxies and quasars of the BOSS project of the Sloan Digital Sky Survey (SDSS)

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