Both Caltech and Non-Caltech students will be considered

Project Title:

High Resolution Imaging of the Galactic Center in the Thermal Infrared

Project Description:


This project will involve analysis of infrared images of the centeral regions of our Galaxy, to be obtained at the Palomar Observatory this spring. The primary scientific objective will be to search at wavelengths around 10um for an infrared counterpart to the peculiar radio source at the Galactic Center, Sgr A*, which may be a black hole.
The observations will be done with the 10um camera, MIRLIN, developed at JPL for use at the Palomar 5-m telescope. The analysis below presents the scientific background and demonstrates the scientific viability of the proposed observations. The observing time for the 10um observations has already been allocated at Mt. Palomar, and the observations will be made prior to the start of the SURF project. The SURF student will have primary responsibility for the analysis of these data, working with Dr. Werner and other members of the MIRLIN team.

Background Information:

The Galactic Center has been a continuous source of astrophysical challenge and insight since it was first identified in the infrared by Becklin and Neugebauer in the 1960 s. The most singular of the many objects it contains is the peculiar non-thermal radio source Sgr A*, which has a flat spectrum, a brightness temperature > 1e+7 K, and an intrinsic size less than 0.1 a.u. The very small proper motion of Sgr A* suggests that it is a massive object (> ~20 solar masses) located quite close to the dynamic center of the Galaxy. The nature of this object is unknown, but it is natural to identify it with the putative 1e+6 solar mass black hole whose presence at the Galactic Center is inferred from studies of the kinematics of the gas and the star in the central parsec of the Galaxy. In any case, it is clear that any new data which can constrain the properties of Sgr A* are potentially of great scientific significance.
Recently, Eckart et al (ApJ, 445, L23 - 1995) have produced extremely high resolution images of the Galactic Center region at 2.2um [= K] and find evidence for a small cluster of faint stars centered at Sgr A*, which they identify as a local clustering of moderately luminous stars with [K] = -3. They suggest that these stars may signal a central cusp in the density distribution, perhaps further supporting the identification of Sgr A* as a massive black hole.
Apart from these recent K band observations, no infrared observations reported to date have identified an infrared counterpart to Sgr A*. One of the reasons for this is that Sgr A* lies in a bright region of the Galactic Center complex, and any emission from Sgr A* must be teased out from a bright and somewhat spatially variable background. MIRLIN, which can achieve sub-arcsecond images at 10um on the 5-m, can obtain higher resolution images of the Galactic Center at 10um than any hitherto available and provide the best possible look for Sgr A*,
It can also be shown that MIRLIN can achieve interesting flux levels in this search. Taking our cue from Eckart et al, we assume that the central arcsecond around Sgr A* contains the equivalent of five [K] = -3 stars. Disregarding interstellar extinction, this group of stars would produce a total flux at the Earth of ~80mJy, taking the distance to the Galactic Center to be 8.5Kpc. Because the measured sensitivity of MIRLIN [1- sigma] is 6-7 mJy in 600 second, it is clear that MIRLIN could detect the 10um emission from these objects if they have a flat spectrum. If in fact they are stars, an upper limit from MIRLIN could set limits on any circumstellar material or other peculiar emission which might be associated with their proximity to the black hole. Finally, although the models for Sgr A* are quite uncertain in this wavelength region, the ~100mJy limit achievable from MIRLIN is in the range of the flux predicted in several of the cases presented by Zylka et al (1992, A&A,261, 119).

Literature references or articles that may provide more information on the project:

Eckart et al, Astrophysics Journal, v.445, p. L23 - May 20, 1995
Zylka et al, Astronomy and Astrophysics, v.261, p,119, 1992
Genzel et al, Rep. Progr. Physics, v.57, p.417, 1994

Requirements (skills, specific coursework, academic major, year in school, etc.):

Student should be major in physics, astronomy, or computer sciences, with good background in computing and data analysis. Ability to work independently is essential. Year in school is not a major factor.

Research Sponsor Name: Michael Werner
E-Mail: mww@ipac.caltech.edu
Division: JPL - Earth & Space Sciences
Telephone: (818) 354-0146
Address: M/C 233-303

For further information contact Dr. Werner

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