Britt Lundgren’s research group studies the evolution of galaxies over billions of years by analyzing:

  1. the stellar populations and star formation histories of high-redshift galaxies directly through deep infrared imaging, and
  2. the evolution of the gas and dust content of galaxies and the intergalactic medium throughout cosmic history, as revealed by absorption in the spectra of background quasars.

Complete list of publications.

Using quasar spectra to detect gas around distant galaxies:

Quasars are actively accreting supermassive black holes in the centers of distant galaxies.  This activity in the galactic nucleus produces luminosities 100-1000 times greater than normal galaxies, allowing quasars to be observed from the distant Universe.

Left: The 2.5m Sloan Telescope at Apache Point Observatory. Top Right: A cartoon diagram (not to scale) of light from a distant quasar passing through large-scale structures of galaxies and intergalactic gas, before being detected on Earth; Bottom Right: the spectrum of a quasar, indicating absorption from neutral Hydrogen and some heavier elements, imprinted by the intervening cosmic web.

Absorption lines in quasar spectra probe gas and dust from galaxies and the intergalactic medium along the sight.  A cartoon depiction of absorption lines in the spectrum of a high-redshift quasar is shown above.  The colorful simulated image of large-scale structure (i.e., the spatial distribution of gas and galaxies in the cosmic web) was produced by John Healy (Durham University).  Beneath the image is an example of how absorption from clouds and filaments of neutral Hydrogen might appear in a quasar spectrum, as observed by a telescope on Earth.  At wavelengths greater than the quasar’s rest-frame Lyman-alpha emission, intervening absorption features from heavier elements (“metals”; Mg, Fe, C, etc.,) can be more clearly seen. 

It has been well-established that absorption lines detected in quasar spectra probe gas and dust associated with intervening galaxies, but the physical origin and distribution of the absorption in and around individual galaxies is not yet well understood.  While some absorbers may be caused by tidally stripped and/or virialized gas in the extended galaxy halos, others may be tracers of large-scale winds driven by star formation or active galactic nuclei.  Comparing the spatial distributions of quasar absorption lines to those of better-understood observable galaxies allows us to gain more information about their environments and their relationship to large scale structure in the Universe.

Left: A photograph of NASA’s Hubble Space Telescope, taken on the fifth servicing mission to the observatory in 2009 (Credit: NASA); Right: Infrared Hubble Space Telescope imaging of a distant quasar (“QSO”) with four detected foreground galaxies, studied in Lundgren et al. (2012). Shown in the top right is an equivalent image using the ground-based Keck Telescope from Wirth et al. (2004). As demonstrated here, the higher sensitivity and resolution of Hubble imaging is critical for resolving the sizes and shapes of intervening galaxies in high-redshift studies like this one.

By mining the vast spectroscopic quasar sample from the Sloan Digital Sky Survey in an effort led by Donald York (University of Chicago), we have identified tens of thousands of these gaseous tracers of foreground galaxies. Using the Hubble Space Telescope, we are now working to directly image the richest known quasar foreground fields. By identifying and analyzing a large sample of intervening galaxies matched to gas absorption, we can better understand how galaxies grow and evolve over billions of years of cosmic time through the consumption and expulsion of gas.

Studying galaxy evolution from early times with the Hubble Space Telescope:

The Hubble eXtreme Ultra-Deep Field
Credit:NASA, ESA, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University), and the HUDF09 Team

The successful final servicing of the Hubble Space Telescope in 2009 enabled new deepest-ever views of the high-redshift Universe using the infrared WFC3/IR camera.  Read about the evolution of 1500 galaxies extracted from the Hubble Ultra-Deep Field imaging here.