|
Current Research
Last updated: Fall 2010
A section of the GOODS-North field.
Galaxies and the dark matter haloes in which they reside are the gravitational building blocks of the universe, and my research encompasses the study of their formation, properties, and evolution in a wide range of different environments using a combination of observational and numerical techniques. Below are brief descriptions of a few particular recent or ongoing projects:
Spatially Resolved Properties of High-Redshift Starforming Galaxies
While the LCDM framework has provided a broadly consistent picture of galaxy formation via the hierarchical growth of dark matter halos, much debate remains concerning the more complicated baryonic physics of star formation, gas accretion, and feedback processes. It is of particular interest to study these processes in the young universe (redshift z ~ 2-3) when the majority of the cosmic star formation was occurring.
In collaboration with Chuck Steidel, Dawn Erb, and others I have led an observational program to map the kinematics of ionized gas in actively star-forming galaxies at z~2. This work uses integral-field spectroscopy paired with laser-guided adaptive optics to probe kinematics on kiloparsec scales using the Keck/OSIRIS spectrograph. Such high angular resolution spectroscopy represents a critical advance in observational techniques by allowing full use of the diffraction limit of large-aperture telescopes, and will be a key component in next-generation telescope facilities. We have found that, unlike typical local galaxies, starforming galaxies in the young universe have high velocity dispersions ~ 80 km/s which are in many cases comparable to or greater than their velocity shear about a preferred kinematic axis. The v/sigma of these galaxies appears to be related to their gas fraction (or stellar mass), suggesting that galaxies dominated by gas may not have formed gravitationally relaxed stellar structures. Read more about our results in Law et al. 2007a and 2009b.
There is evidence that these high-redshift starburst galaxies may have kinematic properties extremely similar to supercompact UV luminous galaxies at lower redshifts z ~ 0.2, as detailed by Basu-Zych et al. 2009 and Gonçalves et al. (in prep).
I am also leading a Cycle 17 program using the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope (HST) to survey the rest-frame optical morphologies of starforming galaxies at redshifts z=1.5-3. This survey is the largest to date, covering ~ 65 sq. arcmin along the line of sight to bright background QSOs to a depth of 27.9 AB. In contrast to earlier results using rest-frame UV imaging (Law et al. 2007b), we are able to extend the mass-radius relation for star forming galaxies at these epochs down to 10^9 Msun. Data are currently being acquired, early results will be published in Nagy et al. (in prep) and Law et al. (in prep).
Using a combination of HST/WFC3 imaging and Keck/OSIRIS integral-field spectroscopy, we have also used the high spatial resolution of these instruments to suppress emission from the central AGN of high redshift QSOs in order to isolate and study their host galaxies. By deriving the star formation properties of these host galaxies it will be possible to help relate the AGN phase to the global picture of galaxy evolution (Law et al., in prep).
|
A section of one of our WFC3 pointings |
Dynamics and Stellar Populations in the Local Group
One of the best laboratories for testing cosmological structure formation models is the Local Group (LG), consisting primarily of the Milky Way, Andromeda, and associated dwarf galaxies. I am actively involved with multiple projects to study the dynamics, stellar populations, and mass distribution within LG galaxies.
|
With the advent of deep photometric surveys, it has become apparent that galactic haloes (including that of the Milky Way) are threaded with the phase-mixed detritus of multiple generations of dwarf satellites that have been destroyed by the inexorable tides of their hosts' gravitational potential. In collaboration with Steve Majewski and Kathryn Johnston, my primary work in this field has centered around developing numerical models of the tidal disruption of the Sagittarius (Sgr) dwarf spheroidal galaxy in the potential of the Milky Way. By constraining these models to fit observational data from 2MASS and SDSS, we have been able to construct mass maps of the Milky Way and its cold dark matter halo (see Johnston et al. 2005, Law et al. 2005, Law & Majewski 2010a). This recent work suggests (Law et al. 2009a) that the Milky Way may have a significant non-axisymmetric component to its gravitational potential. Click here to see a movie of how we think the Milky Way --- Sgr system may have evolved, here to read our latest press release, or see our online Sgr web resource. |
Diagram of the Sgr --- Milky Way system. |
Using our model of the Sgr --- Milky Way system, we have been able to statistically determine the likely origins of a number of Galactic globular clusters. By dynamically associating specific clusters with the Sgr system, we have determined that the strength of the second-parameter effect on the horizontal branch morphology of clusters may be uniquely tied to their subhalo of origin (see discussion in Law & Majewski 2010b).
Diagram of age-metallicity relation and horizontal branch type (HBR) for Sgr clusters (from Law & Majewski 2010b).
These numerical models have direct application to not only the Sgr dwarf, but also to efforts to determine the origins of other satellites orbiting in the Milky Way's Galactic gravitational potential. Some collaborative efforts with which I have been associated are described by Geha et al. 2009, Lokas et al. 2010, Frichaboy et al. (in prep), and Siegel et al. (in prep).
|
|
