General Research Interests

My research interests lie in the intersection of new cameras and telescopes that operate at millimeter and submillimeter wavelengths and the science that is enabled by these new facilities. More than 98\% of the photons in the universe fall within the mm/submm portion of the electromagnetic spectrum. This emission is due to a source population that spans all spatial scales and the entire observable history of our universe. Consequently, the mm/submm portion of the spectrum is rich with evidence of how structure forms and evolves. These are exciting times to be working in this part of the spectrum. The confluence of recent innovations in sensitive mm-wavelength detectors along with the commissioning of the Large Millimeter Telescope (LMT) and first-science with the Atacama Large Millimeter/submillimeter Array (ALMA) - two new and fundamentally transformative facilities in astronomy - now offers unprecedented potential for new scientific discovery in the coming decade.

Studies of starbursting galaxies

Distant galaxies are the repository of most of the luminous matter in the Universe, and as such, they serve as important observables for many fundamental questions about its history, fate, and composition. In the last twenty years, sensitive observations at millimeter and submillimeter (submm) wavelengths have revealed a population of optically obscured galaxies at high redshift. This dust-obscurred galaxy population has a number density which is 10--50 times higher than that expected from galaxies whose luminosity does not evolve with time. These galaxies are believed to be massive young galaxies seen during their formation and rapid-growth phases, with an inferred star formation rate exceeding about 1000 times that of the Milky Way. Unfortunately, the combination of their faintness at nearly all wavelengths (particularly in the rest-frame UV--optical) and, until recently, the low signal/noise of the existing mm/submm data has greatly hampered both the identification of sources and follow-up investigations.

Over the past decade we have made immense progress in understanding this critical population of galaxies through detailed investigations with ALMA, SCUBA-2, and our own AzTEC instrument. During this time I led a collaboration of 12 scientists from four countries (US, UK, Mexico, Korea) working closely with another team of astronomers from Japan in an effort to observationally constrain models of galaxy evolution and structure formation as traced by the SMG population. Our group's primary goals have been to:

  • Test the evolution of bias of massive (elliptical) galaxies and clusters in the high-z universe, with respect to the underlying matter distribution;
  • Combine the angular-distribution of SMGs with spectroscopic redshifts (derived from CO molecular-line observations using the redshift-receiver on the Large Millimeter Telescope) to constrain the 3-dimensional distribution of large-scale structure in the high-z ($z \gg 1$) universe;
  • Quantitatively characterize extreme star formation in galaxies found in the field as well as in clusters and proto-clusters;
  • robustly characterize the statistics of the faintest galaxies in the SMG population, taking advantage of the lensing associated with massive clusters;
  • Determine the degree of (point-source) mm-wavelength galaxy contamination as a function of redshift to low resolution, lower frequency, SZE/dark-energy experiments; and
  • Understand the formation and evolution of massive starbursting systems in clusters and how this differs from evolution in an un-biased environment.

Clusters and large scale structure

On larger scales, clusters of galaxies represent the most massive quasi-virialized structures in the Universe today and, as a result, offer an impressive laboratory (and set of test particles) where we may test our paradigm of cosmology, structure formation and evolution. This is most evident in two ways. First, since clusters started forming before the Universe became dominated by dark-energy, their number density as a function of mass is a key probe of the universe's equation of state. Second, it is well known that star formation rates are suppressed in galaxies in low-redshift clusters, however at high redshifts, where both galaxy merger rates are higher and the available gas reservoirs are larger, we expect just the opposite -- an overdensity of luminous, dusty starburst galaxies centered on the regions of dark matter overdensity. This expectation is supported by some mm and submm observations, although with insufficient statistics to trace the evolution of the SMG overdensity as a function of redshift or environment.

We have been working on both sets of questions with the AzTEC camera. However, a limited mapping speed - that is, the rate at which we can map the sky to interesting levels of sensitivity - have hampered our progress. This will radically change with our upcoming TolTEC camera. TolTEC will offer unique views of the Sunyaev-Zeldovich effect (both kinetic and thermal) in clusters along with the dust-obscurred galaxy populations both in and behind the clusters.

Star formation in the Milky Way

Recently, working closely with star formation folks at UMass, my graduate student Yuping Tang and I have embarked on a project to measure the dust temperature and density in our Milky Way's galactic center. This has turned out to be a very interesting project with many surprises. In fact, Yuping has had to invent entirely new techniques in order to interpret the CMZ data. This project has just gotten off the ground but it has seeded an entirely new set of interests in my regarding the physics of how clouds of gas turn into stars.

Research Projects

I have been fortunate to have been involved with some great and rewarding research projects over my career. Here are a few that I am actively involved with right now.

The TolTEC Project

I lead the TolTEC Project - a program funded by the National Science Foundation to build a new large-format camera for the Large Millimeter Telescope. With TolTEC we will, for the first time, image tens to hundreds of square degrees of sky with sufficient depth to provide radically new views of galaxy formation, the formation of dust and metals in our Universe, and star formation in the Milky Way and in nearby galaxies. Take a look at our project website and consider getting involved.

At UMass we are leading the project, developing all the cryogenic infrastructure for the camera, leading the development of the data analysis pipeline, and helping to manage the four initial public surveys that we will do with the instrument.

The Large Millimeter Telescope

The LMT is a 50-meter diameter millimeter wavelength telescope located on Sierra Negra in Mexico. Along with being an active user of the telescope I am also the Principal Investigator of its initial continuum imaging camera, AzTEC.

While I am mostly known as an extragalactic astronomer who studies the ultra-massive and prolific starburst galaxy population, some of my favorite projects on the LMT have involved much more local phenomena, such as observations of the Circum Galactic Zone (CMZ) in the Milky Way's center with my student, Yuping Tang and my colleague Daniel Wang, and also some beautiful imaging of the debris disk around Epsilon Eridani. This is the beauty of observing at millimeter wavelengths - you can see nearby objects just as well as objects at high redshifts.