Galaxy Structure

A broad range of galaxy research benefits from knowledge of a galaxy's structural components (e.g., disk, bulge, bar, rings, etc.), including understanding how galaxies formed, the connection with their central massive black hole, and more effectively using them to explore the large-scale structure of our Universe.    

We apply our in-house software to optical and infrared data from the Hubble Space Telescope, the Spitzer Space Telescope, and hopefully soon the James Webb Space Telescope, plus an array of ground-based facilities.

The Andromeda Galaxy (Credit and copyright: Robert Gendler)

We discovered a galaxy (LEDA 074886) shaped like an emerald-cut diamond, with an embedded, intermediate-scale, stellar disk. LEDA 2108986 is another such "ellicular" ES galaxy, but with its disk orientated face-on to us. Discovered after the Jeans-Hubble "tuning fork" was established, ES galaxies are still poorly recognised within the profession. Possibly set to rewrite the textbooks, they may represent a missing-link, a stepping-stone, in the evolution of distant, compact galaxies in the young universe which might have accreted or grown disks to become today's "lenticular" galaxies with large-scale disks. 

Left: Galaxy LEDA 074886 (the emerald cut galaxy) Right: Galaxy LEDA 2108986 (Credit and copyright: Alister Graham)

The centres of galaxies can be both crowded places, housing million-strong star clusters around a central black hole, or rather empty if a pair of massive black holes have got in there and caused damage. We use highly resolved images from satellites to measure these excesses and depletions, and study the connections with gravitational radiation.

Using Fourier harmonics to carefully model a galaxy's isophotes, and then subtracting our smooth representation of the galaxy, we can discover faint, previously hidden sources left behind, such as the glow around "intermediate mass" black holes.

The flattened disks of galaxies can form bar-like structures which wobble and buckle, creating unusual (peanut shell) shapes. We developed software to detect these features, along with the more extended bar, and thereby quantify the length and strength of such unusual, perturbed, stellar orbits.

By better appreciating galaxies, through simply knowing how big they are to identifying their components, astronomers can do a lot. For example, this information is helping to derive improved (redshift-independent) galaxy distances from which we can determine the large-scale flows of galaxies above and beyond that expected from the Big Bang expansion, thereby helping to constrain the dark matter content of the Universe and our origins on the grandest of scales.