News

Sydney University astronomers granted observing time on the Hubble Space Telescope



17 June 2013

Two astronomers, Professors Geraint Lewis and Joss Bland-Hawthorn, from the Sydney Institute for Astronomy, located in the School of Physics, have been awarded observing time on one of the world's premier observing facilities, the Hubble Space Telescope. Obtaining observations with this unparalleled telescope is extremely competitive, and this award has demonstrated that their research is world-leading.

As part of an international team, Professor Lewis has secured 28 Primary Spacecraft Orbits and 28 parallel spacecraft orbits in Cycle 21 of the Hubble Space Telescope (HST) program due to begin in October this year. In addition, Professor Bland-Hawthorn has been awarded 50 Primary Spacecraft Orbits in the same cycle.

Globular Clusters

Professor Lewis' team will use the allotted time on the telescope to observe globular clusters in the halo of galaxy M31. Globular Clusters are fossil relics from which we can obtain critical insights into events that underlie galaxy assembly.

Image of the PAndAS survey. The colour is the number of stars at each point, with black being the main Andromeda and Triangulum galaxies. The yellow at the edge of Andromeda and the faint blue spread around are the tidal debris of smaller galaxies ripped apart by the strong tidal forces. Credit: Mike Irwin
Image of the PAndAS survey. The colour is the number of stars at each point, with black being the main Andromeda and Triangulum galaxies. The yellow at the edge of Andromeda and the faint blue spread around are the tidal debris of smaller galaxies ripped apart by the strong tidal forces. Credit: Mike Irwin

As part of the major Pan-Andromeda Archaeological Survey (PAndAS) the team have discovered two groups of Globular Clusters that closely trace narrow stellar debris streams in the halo of galaxy M31. With the time on the HST, the team will image 14 Globular Clusters spanning these two accreted families, allowing measurements of the stellar populations, distance, and structural parameters of each object.

"This imaging provides a unique opportunity for the study within a single galactic halo of two different Globular Cluster sub-groups that we know to be accreted. This novel approach opens a new angle of attack on long-standing questions in the field," Said Professor Lewis.

The team will, for the first time, quantify the typical properties of accreted Globular Clusters in the M31 halo as well as the degree of variation amongst them, and how closely they correspond to the suspected accreted Globular Clusters population in the Milky Way.

"Observing these globulars is like delving into the past, a true cosmological archaeologist" said Professor Lewis

Combined with new radial velocity measurements for the Globular Clusters, the observations will allow the team to trace the orbits of the two streams within the M31 halo, and thus break the main degeneracies that plague numerical models designed to probe the gravitational potential and distribution of dark mass.

Galactic wind

Professor Bland-Hawthorn's proposal is to follow up his discovery in 2003 of a huge wind blowing out from the centre of the Galaxy. The Hubble observations are to make comprehensive, high resolution spectral observations of six distant halo stars in the Milky Way. The light from these stars is used as a background source to "see through" the Galactic wind.

Illustration of the Fermi gamma-ray bubbles extending ~10 kpc or ~50 degrees above and below the GC, as viewed from outside the Galaxy (courtesy NASA/GSFC). Superimposed (in yellow) are four of our AGN sight lines, which bracket the vertical extent of the Fermi bubbles, and (in red) two of the halo-star sightlines, which probe the inner halo.
Illustration of the Fermi gamma-ray bubbles extending ~10 kpc or ~50 degrees above and below the GC, as viewed from outside the Galaxy (courtesy NASA/GSFC). Superimposed (in yellow) are four of our AGN sight lines, which bracket the vertical extent of the Fermi bubbles, and (in red) two of the halo-star sightlines, which probe the inner halo.

"Like other spiral galaxies, the Milky Way has highly concentrated galactic wind extending out to the top and bottom from the centre of the Galaxy, the nuclear wind is thought to be powered by either the central black hole or active star formation in the galaxy," said Professor Bland-Hawthorn.

Professor Bland-Hawthorn's Hubble time will reveal the relationship between the different components of the wind, which will aid the understanding of outflows from other galaxies and our own Galaxy nucleus.


Contact: Tom Gordon

Phone: 02 93513201

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