School of Physics and Astronomy

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Dr Stuart L Lumsden

Astrophysics Group

Contact details

Room: 9.77
Tel: +44 (0)113 3436691
Email: s.l.lumsden @ leeds.ac.uk

Keywords

Starburst galaxies
Galaxy evolution
Massive star formation
Active galaxies

Research interests

My current research lies mostly in the field of observational massive star formation, specialising in infrared, sub-mm and radio astronomy.

Massive Star Formation

The world leading Red MSX Source (RMS) Survey is aimed at detecting and characterising all the massive young stellar objects in our galaxy. Massive stars are relatively rare, and hence typically lie at greater distances from us than more typical Solar mass stars. Massive protostars are even rarer since they exist for a very brief time before the star emerges from its natal molecular cloud to become an ordinary visible hot star.

Evidence (including our own) suggests massive stars accrete most of their mass once the star is already in the protostellar phase, and they therefore are the best probe of star formation models. Protostars are deeply embedded within their molecular clouds and therefore have to be studied at infrared or longer wavelengths. I have been co-leading the RMS Survey since 2001, using Galaxy wide infrared data from the MSX satellite in order to define a potential sample of massive protostars in this phase. We successfully obtained many hundreds of nights (and days) of time on facilities including the AAT, ATCA, CARMA, ESO (both La Silla and Paranal), Gemini, IRTF, JCMT, SMA, Subaru, UKIRT and the VLA in order to fully characterise our sample.

Key results to date are: limits on the star formation rate and accretion rate history for young massive stars showing just how brief the phase is (about 100000 years) and when the accrete their mass (mostly near the very end); clear evidence that in the earliest stages massive stars behave essentially the same as low mass stars (eg there is evidence that their outer envelopes must be convective); fundamentally proving the key importance of disc accretion as the major means by which even the most massive stars form (as opposed to, eg,collisional models); being able to show how differing aspects of the star formation process (outflows, accretion disks) evolve with time, so that both disks and outflows gradually fade away.

Active Galaxies

Active galaxies are largely powered by supermassive black holes that lie at their cores. These black holes, with masses ranging from a million to a billion times the mass of the sun, can completely dominate the energy output of a galaxy when they are actively accreting mass. Various observational classes of active galaxy are believed to be related to each other intrinsically by a very few fundamental underlying parameters. I have been actively involved in studies of such "unified models", ranging from: searching for direct evidence for the fast moving gas in the accretion disks of black holes even where the centre of the galaxy itself is hidden from our line of sight using scattered light spectroscopy, as well as the near infrared (where we penetrate the dust more easily); consideration of the accretion rates and black hole masses of nearby AGN to show that cosmic downsizing as seen quasars in the Sloan survey is still ongoing and occurs at lower luminosities as well; studying the circumnuclear molecular environment of nearby AGN to determine if the gas reservoir is a major factor in determining current accretion rates; and finally, studying the dust and moelcular gas emission from quasars early in their lives, at a redshift ~2, when their activity seems to peak, to look for evidence of "blow-out" of the free gas, consistent with the fact that nearby massive galaxies, although they contain massive black holes, have little neutral or molecular gas and are not remotely active.

Useful links

The Red MSX Source Survey website