Attila Kovacs

Galaxy Formation and Evolution

My main scientific goal is to gain insight into the physical processes that power galaxies, and how these evolve with the universe. Galaxies form through the gravitational collapse of gas, and grow through merging and by the accretion of material from their halos. These processes release of vast gravitational potentials, which can ignite starbursts or fuel an active galactic nucleus (AGN).

The most active starburst galaxies (and AGNs) are heavily obscured by dust at optical and UV wavelengths making them difficult to observe with conventional telescopes. Most of their light is re-emitted as cold (~40K) thermal radiation in the far-infrared and submillimeter bands. As a result, we must use the cold dust continuum (and the associated cold molecular gas) emission to best study such luminous objects.

Submillimeter Galaxy (SMG) Populations

The substructure of an SMG from a deconvolved image at 350um.

Kovacs et al. 2010

SMG number counts can be powerful cosmological constraints.

Weiss et al. 2009

The need for dust studies is helped by the fact that a dusty galaxy would appear equally bright, regardless of distance, at (sub)millimeter wavelengths. This makes unbiased studies possible across much of the volume of the universe. Since the discovery of the submillimeter galaxy (SMG) population in 1996, we now have tens of thousands of such galaxies from a combination of ground-based surveys and from the Herschel space telescope.

However, the interpretation of these surveys is hindered by the difficulty of associating counterparts to SMGs at other wavelengths, or determining their distances (redshifts). Furthermore, because of the limited spatial resolution of most (sub)millimeter telescopes, we do not know their close clustering properties, which is necessary to determine number counts (vs. brightness) with confidence. Such counts could provide direct constraints for cosmological models.

To overcome these difficulties, my main goals are:

• Pioneer new ways to obtain redshifts for at least a representative sample of SMGs. (Currently, we can do this only for a very small, biased subsample.)

• Discover the small angle (<20 arcsec) clustering properties of SMGs, and with these determine their true number counts (vs. their brightness).

• Improve our theoretical/empirical understanding of dust spectral energy distributions (SEDs) such that we can extract more physical information about the processes that heat the ISM.

• Better understand the cross-band properties of SMGs, such that we can more confidently identify counterparts at other wavelengths. Some of the relevant understanding may come from the detailed studies of local starburst (and other) galaxies.

Data Reduction and Imaging for Bolometer Arrays

NGC253 at 850um. Understanding local galaxies can help interpret distant SMGs.

Weiss et al. 2009

A second component to my research is to pioneer new ways to collect and reduce data from ground-based bolometer arrays (and background-limited instruments in general). The main problem is that strongly varying atmospheric and instrumental signals can be orders of magnitude brighter than the faint objects we seek to observe. Detecting a sub-mm galaxy at 350um is analogous to trying to see a 17th magnitude star during broad daylight.

Getting around the problem involves a combination of innovative observing strategies and a novel data reduction approach. Starting from my PhD at Caltech, I have become a leader in both these fields. The Lissajous observing pattern, which I originally introduced at the CSO, is now used at most major sub-mm telescopes (e.g. APEX, IRAM, ASTE etc.).

My data reduction software CRUSH is the de facto standard for the new generation of large bolometer arrays. It is currently used for 8 different instruments at 4 telescopes. Others have copied its ideas to build custom pipelines, like MPIfR's BoA package, or the official SCUBA-2 data reduction software (SMURF).