PI: Erik Tollerud (etollerud@stsci.edu, http://www.stsci.edu/~etollerud/)
Project Duration:
1yr rotation with potential for thesis project
Project Abstract:
The SAGA Survey (http://sagasurvey.org, Geha et al. 2017) is a large effort to identify satellite galaxies like those known in the Local Group (the Milky Way and M31's dwarf satellites), but at distances of ~50 Mpc. This allows studies of satellite systems and the attendant field of "near-field cosmology" to be extended from a sample of 2 to a sample of 100. While the core part of the survey - identifying a handful of satellites among hundreds if not thousands of candidates per host - is well underway, many key science questions depend on more detailed follow-up observations of the satellites identified by the main survey. This project will initially focus on one of two areas:
- The SAGA-COS program, which will observe QSOs with sightlines that pass through SAGA hosts. This approved HST program for the coming cycle will require significant analysis to identify possible absorption features indicating the presence of Circum-galactic gas (i.e., tenuous metal-enriched gas far beyond the visible extent of the galaxy but within its dark matter halo), and correlating those features with both the satellites and the SAGA host. Additional stages of this project potentially include comparison with hydrodynamic simulations by the FIRE and/or CLOUDY team, as well as abundance analysis of absorption features strong enough to allow it, and associated comparison to the SAGA galaxies themselves.
- Optical spectroscopic follow-up to characterize the rotation curves and dark matter content of the SAGA satellites. This is a multi-year program, with several steps likely necessary. The starting point is to publish existing follow-up, focused primarily on emission line spectroscopy of the brighter satellites from SAGA Phase I. Once this proof-of-concept is complete, additional follow-up observations will be necessary for the fainter, primarily pressure-supported dwarfs. In both cases, significant Bayesian kinematical modeling will be necessary to determine the mass profiles of the satellites. For those where the data allow it, further work will enable comparison between these observations and simulations of satellites to determine of the SAGA satellites are consistent with the dark matter halo properties known from the Local Group galaxies. This work therefore has the potential to confirm or deny many of the long standing small-scale puzzles in galaxy formation by expanding them to statistical samples instead of the limited scope currently available only in the Local Group.
As an example, the plot below shows some of the broad-brush comparisons available from just the core survey Phase I (from Geha et al. 2017). These aforementioned projects would expand from these "one point per galaxy" plots to more thoroughly characterize individual satellites and expand the scope of the observations from primarily-imaging to more thorough characterization and comparison with the wealth of data in the Local Group.
The work you imagine having the graduate student do:
Both of the projects mentioned above have potential for at least one paper which the graduate student can lead. The second may require significant data reduction - reduction of the raw observations for the optical follow-up project, whereas the first will involve collaboration with a current postdoc who has already reduced the data. Depending on the student's interests, these projects have several potential directions that could lead to a thesis, either through a deep-diving in modeling of the follow-up observations, or through a more shallow but broad set of projects that focus on particular relatively straightforward (i.e. high S/N) targets.
