Research

My research is focussed on understanding the formation and evolution of galaxies.

Galaxies are some of the most fascinating objects in our Universe, and understanding their formation and evolution is an important problem for modern astrophysics. Not so long ago, at the beginning of the 20th Century, all galaxies were thought to be nebulae within our own Galaxy, which in turn was considered to be the entire Universe. It is now known that these nebulae are in fact vast, gravitationally-bound systems of stars, gas, dust and dark matter, some lying at unimaginably large distances from us.

The galaxies we observe have a wide range of properties and are generally (and historically) classified in terms of their morphology or shape. Spiral galaxies, like our own Milky Way, are flattened disks that are actively forming stars, compared to elliptical galaxies, which formed the bulk of their stars long ago and have evolved passively since. Understanding the different evolutionary paths which produces these two types of system and disentangling whether internal properties or the environment drives evolution (is it "nature or nurture"?), is one of the primary goals in extragalactic astronomy. By studying the different matter components in galaxies in different environments, I hope to constrain models of how they form and evolve.

Main Interests

The growth of the red sequence; the link between AGN feedback and star formation

Processes regulating star formation and chemical evolution

Dust content in nearby galaxies

The physical conditions in the multiphase interstellar medium

Spectroscopic techniques in extragalactic astronomy (particularly IFU spectroscopy)

Research Highlights

The growth of the red sequence: migration of nearby spirals

The diagram below shows galaxy colour versus the mass of stars. As galaxy colour is a proxy for star formation, the plot divides "blue and new" star-forming spirals from "red and dead" ellipticals. I am interested in the properties of galaxies falling between the two sequences: what mechanism quenches star formation in spiral galaxies, driving them from the blue cloud to the red sequence? Does the migration of spirals we see today account for the growth of the red sequence during the evolution of the universe?


We used a complete volume-limited sample of nearby galaxies in different environments (from isolated galaxies to Virgo cluster members), to study the migration of spirals from the blue to the red sequence. Although our analysis confirms that, in the transition region between the two sequences, a high fraction of spirals host active galactic nuclei (AGN), it clearly shows that late-types with quenched star formation are mainly HI deficient galaxies preferentially found in the Virgo cluster. This suggests that environmental effects could play a significant role in driving the migration of local galaxies from the blue sequence. However, since AGN activity, gas content of galaxies, and the properties of large scale structure evolve with the age of the Universe, the dominant mechanism driving the quenching probably varies with redshift.

The role of cold gas in chemical evolution

Galaxies can be thought of as factories which convert gas into stars, which in turn produce the heavy elements or metals. Understanding the processes driving star formation and chemical evolution is another important area of research. The observed correlation between the mass of stars in galaxies and the abundance of metals, the stellar mass - metallicity relation (pictured below), provides a valuable constraint to current theoretical models of galaxy evolution, because numerical simulations are now able to reproduce the relation.


However, because there are large discrepancies in the metallicity measurements derived using different methods, the exact shape of the relation is difficult to constrain, and so the underlying cause of the relation is debateable. In addition, the cause of the scatter around the relation is still unclear. What process causes the shape and scatter in the stellar mass - metallicity relation? In my recent work, using newly reduced optical spectroscopy of the Herschel Reference Survey, I found a clear correlation between the HI gas content and metallicity, and also linked gas content to the scatter in the mass - metallicity relation.

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Contact me

Address: Instituto de Física y Astronomía
         Universidad de Valparaíso
         Av. Gran Bretaña 1111
         Valparaíso, Chile

        

Telephone: +56 9 9901 3258
FAX: +56 32 2508230
Skype: txhughes
E-mail: thomas.hughes (at) uv.cl