From IAC: ” Galaxies that feed galaxies”


Giuseppina Battaglia

Instituto de Astrofísica de Canarias – IAC

Pan-STARRS1 map. Location of our overlapping objectives in an RGB representation of the distribution of stars in the halo of the Milky Way. Credit: Giuseppina Battaglia

Pann-STARS telescope, U Hawaii, Mauna Kea, Hawaii, USA, 4,207 m (13,802 ft) above sea level

Most of the information we have about the Milky Way stellar halo comes from its inner region, which we can observe close to the solar neighbourhood. However, for the first time the chemical properties of the external regions of the halo of our galaxy were explored with high resolution spectroscopy in the optical of a sample of 28 red giant stars at large distances from the Sun. The method that was used, i.e. a spectroscopic analysis, consists in separating the light of the stars in its different frequencies in order to obtain information on the star’s chemical composition. The analysis of the chemical properties of the stars can provide information on the characteristics of the environment in which they were born.

“The abundance of some chemical elements in the stars in the external regions of the Milky Way halo – explains Giuseppina Battaglia, astrophysicist at the IAC and first author of the article – was found to be surprisingly different from the information we had concerning the inner regions of the halo”. On the other hand, several similarities were discovered with the chemical composition observed for stars in nearby massive dwarf galaxies, such as Sagittarius and the Large Magellanic Cloud. These signatures tells us that the external regions of the stellar halo might contain the remains of one, or more, massive dwarf galaxy, devoured by the Milky Way.

Stellar haloes are a common component of galaxies like the Milky Way. “The theory explaining the formation of structure and galaxies in the Universe predicts that stellar haloes, and in particular their outer regions, consist mainly of the stellar component of destroyed, smaller galaxies.” G.Battaglia comments “Qualitatively this is in agreement with the observational findings of this study, where we found remnants of cannibalized dwarf galaxies around the Milky Way.”

For this study data from about 100 hours of telescope observing time were used, obtained on facilities in both the Northern and Southern hemisphere. Specifically, the team used the Very Large Telescope “Kueyen” (UT2) of the European Southern Observatory in Paranal and the Magellan telescope Clay in Las Campanas, both in Chile, as well as the Hobby Eberly Telescope, in Texas.

ESO/VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

Carnegie 6.5 meter Magellan Baade and Clay Telescopes located at Carnegie’s Las Campanas Observatory, Chile. over 2,500 m (8,200 ft) high

U Texas Austin McDonald Observatory Hobby-Eberly Telescope, Altitude 2,026 m (6,647 ft)

Science article:
What is the Milky Way outer halo made of? High resolution spectroscopy of distant red giants. Astronomy & Astrophysics

See the full article here.

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The Instituto de Astrofísica de Canarias(IAC) is an international research centre in Spain which comprises:

The Instituto de Astrofísica, the headquarters, which is in La Laguna (Tenerife).
The Centro de Astrofísica en La Palma (CALP)
The Observatorio del Teide (OT), in Izaña (Tenerife).
The Observatorio del Roque de los Muchachos (ORM), in Garafía (La Palma).

These centres, with all the facilities they bring together, make up the European Northern Observatory(ENO).

The IAC is constituted administratively as a Public Consortium, created by statute in 1982, with involvement from the Spanish Government, the Government of the Canary Islands, the University of La Laguna and Spain’s Science Research Council (CSIC).

The International Scientific Committee (CCI) manages participation in the observatories by institutions from other countries. A Time Allocation Committee (CAT) allocates the observing time reserved for Spain at the telescopes in the IAC’s observatories.

The exceptional quality of the sky over the Canaries for astronomical observations is protected by law. The IAC’s Sky Quality Protection Office (OTPC) regulates the application of the law and its Sky Quality Group continuously monitors the parameters that define observing quality at the IAC Observatories.

The IAC’s research programme includes astrophysical research and technological development projects.

The IAC is also involved in researcher training, university teaching and outreachactivities.

The IAC has devoted much energy to developing technology for the design and construction of a large 10.4 metre diameter telescope, the ( Gran Telescopio CANARIAS, GTC), which is sited at the Observatorio del Roque de los Muchachos.

Gran Telescopio Canarias at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, SpainGran Telescopio CANARIAS, GTC