A variety of projects are available for incoming graduate students to collaborate with faculty members on. Possibilities include:
with Paul Harding
How biased is the Sloan Digital Sky Survey Halo K giant sample?
Morrison, Harding, and Ma are using a sample of K giants from SDSS/SEGUE to study the halo of our galaxy. This sample is more than ten times larger than any previous sample and will provide important constraints on the formation of the outer halo. However to fully make use the SDSS K giant sample we need to understand how the properties of the K giants in the SEGUE sample are biased via their photometric selection, and spectroscopic observations.
We plan to observe a subsample of the SEGUE fields using Washington photometry on our Schmidt telescope on Kitt Peak. The reason for using Washington photometry is that its K giant selection biases are opposite of those of the SDSS ugriz photometry. This project will involve approximately a weeks observing at the Burrell Schmidt, processing of the data through to calibrated photometry. The properties of the K giants selected from the Washington photometry will then be compared to the sample of giants observed by SDSS in the same fields. This will allow us to test our existing bias correction techniques, and improve them if necessary.
with Earle Luck
Solar spectral synthesis
Spectrum synthesis is a basic tool for the determination of stellar abundances. Accurate syntheses require significant amounts of atomic and molecular data, much of which is inadequately known. Because of this requirement, detailed syntheses usually consider only limited wavelength regions. What is needed now is an order of magnitude increase in the number of accurately determined laboratory oscillator strengths and damping coefficients. This is not a realistic expectation in the near (5 year) term. What can be done is to exploit the Sun as a standard source. This project will re-determine solar line strengths from the Delbouille Solar Atlas and attempt to match the observed spectrum using the newly determined depths with the oscillator strength as the free parameter. A successful match will allow relative abundances to be determined for stars like the Sun from these newly matched regions.
with Stacy McGaugh
The dynamics of dwarf and spiral galaxies
The masses of galaxies are fundamental quantities. We seek to constrain the stellar and dark mass of spiral galaxies with rotation curve data. We further seek to understand the strong coupling between luminous and dark matter components of galaxies, as exemplified by the Baryonic Tull-Fisher Relation and the Radial Acceleration Relation. In addition to this empirical work, we will consider various dark matter halo models and compute the effects of adiabatic contraction on the dark matter halo.
with Chris Mihos
Modeling the dynamical history of galaxies
Through a combination of our own deep imaging data and archival data from astronomical satellites, we have built up a comprehensive multiwavelength picture of several nearby galaxies, including the giant spiral galaxy M101 and the Virgo elliptical M49. However, understanding this data in an overall evolutionary context is necessary. This project would develop computer simulations of galaxy interactions to build dynamical models of galaxies subject to constraints from the multiwavelength datasets. There would also be potential for 3D visualization aspects to the project.
Deep imaging of nearby galaxies
Using CWRU’s Burrell Schmidt telescope, we have developed techniques for very deep, wide-field surface photometry which we have used to study the outskirts of nearby galaxies as well as the diffuse intracluster starlight in the Virgo Cluster. We use broadband and narrowband filters to study both stars and gas. A variety of projects have probed the nature of extended star formation in galaxies, the evolution of the Virgo Cluster, the interaction history of the famous spiral galaxies M101 and M51, and the accretion of gas and stars onto galaxies today.
with Heather Morrison
Measuring the size and shape of the thick disk
We have known that the Milky Way has a thick disk since the 1980s, but it has been quite hard to estimate reliable parameters for its spatial distribution. Previously astronomers used star counts, with the result that various parameters (like local density and scale height) are correlated and thus impossible to estimates separately. SEGUE now has a large sample of spectra, and the ability to accurately relate the properties of the stars with spectra to the entire sample of stars in the galaxy. For the first time, we can estimate properties like the scale height of the thick disk by using the spectroscopic results, and tie these into predictions for the formation of the thick disk.
Substructure in the Milky Way halo
We think that much of the Milky Way’s halo was formed by accretion and subsequent destruction of satellites, but do not know whether there is also a part of the halo that formed ‘in situ’ at early times. We can use the velocity structure of halo stars to test this, as the ‘in situ’ halo should have a smooth distribution, while the accreted part will retain substructure, particularly in velocity. The SDSS/SEGUE survey has produced a sample of many thousands of halo giants spread out to more than 100 kpc, a unique sample. In this project we will explore a number of different approaches of measuring velocity substructure and apply it to the new enlarged sample of halo giants.
with Heather Morrison and Paul Harding
Downsizing the Milky Way
Recent developments in computational power have given us the ability to model the structure of stars much more realistically than before, using 3D models to treat convection properly, and NLTE models to discard other assumptions that we were forced to make. The new models, however, predict that giant branch and horizontal branch stars are significantly fainter than our previous assumptions. If this is true, it will have profound effects on our estimates of the mass of the Milky Way. This project will involve a literature search to find how the known satellites of our Galaxy had distances measured, plus checks on the distance scale for horizontal branch stars, to see if this idea holds up. If it does, it could lead to a collaboration with an astronomer expert in measuring the mass of the Milky Way.
with Idit Zehavi
The relation between galaxies and dark matter halos
Large galaxy surveys such as the SDSS have greatly improved our understanding of large-scale structure and enable detailed studies of the clustering of galaxies and their implications for cosmology, galaxy formation and evolution, and the relation between galaxies and dark matter halos. We aim to explore the galaxy-halo connection using simulations of physical models in order to extend the current empirical approach and build better models to describe the data. Related projects at the interface of theory and observations will explore the role of the large-scale environment in shaping the galaxy content of dark matter halos, their physical properties and galaxy clustering. These will utilize state-of-the-art galaxy formation simulations as well as the SDSS and preparatory work for upcoming surveys.