Black Holes in Nearby Galaxies

1. Black Holes in Nearby Galaxies Claire Max NGAO Team Meeting March 7, 2007

2. Outline • General principles of black hole mass measurements • Potential benefits of NGAO, and science requirements (first cut)

3. General Principles • Equate kinetic energy of rotation with gravitational potential energy: • Spatial resolution matters: need to resolve R’s as small as possible. Width of PSF gives an upper limit on black hole mass (can’t “see” any closer). • PSF stability matters: R must be well determined

4. Estimate radius of black hole’s “gravitational sphere of influence” • Equate kinetic energy, gravitational potential energy • Example: 200 km/sec, 2 x 108 solar masses, aBH= 50 pc • Within this distance from the black hole, gas and stars “feel” the black hole’s gravity • To measure the black hole’s mass, must be able to resolve aBH • Keck AO today resolves 30 pc at z = 0.02, 50 pc at z = 0.05. • NGAO will resolve even smaller distances (e.g. using Ca triplet at 8498 Å, 8542 Å, 8662 Å).

5. Two general types of measurements:1) Keplerian circular velocities • Assume material is in isotropic, circular Keplerian rotation around the black hole. Measure radial velocities (component of velocity in and out of plane of the sky). • Examples: water masers in NGC 4258 (mm wave); orbits of individual stars in Galactic Center

6. Two general types of measurements:2) Velocity dispersions • Measure velocity dispersion as function of position (e.g. Sauron IFU) • Issues: • Stellar velocity dispersions in elliptical galaxies: velocities are not isotropic. Need to model the orbits in some detail. Challenging. • Gas velocity dispersions: gas velocity fields are often quite disordered due to non-gravitational forces. • Increased spatial resolution helps in both cases. Ca triplet helps a lot. NGC 3377, Sauron IFU

7. Additional Considerations • May need to use IFU together with set of long-slit spectra, to unravel gravitational field of the larger scale galaxy • Alternatively, can use a wider field mode of the IFU • Necessary for non-ideal galaxies: • Kinematically decoupled cores • Bars • Warps • Merger remnants 40 arc sec

8. NGAO benefits and science requirements • Benefits of using Calcium Triplet (8500 - 8660 Å) with decent wavefront error • At a given distance from us, can measure lower black hole masses • At given black hole mass, can detect BH in more distant galaxies • Key performance metrics: • Low wavefront error • Operation at 8500 Å • Stable PSFs

9. Science and Instrument Requirements • AO system: • Wavefront error low enough to give “good” performance at I band (needs to be quantified in simulations, work is in progress) • Stable PSF in near IR (needs to be quantified further) • Instruments: single IFUs • I band out to K band • Field of view: Narrow mode (a few arc sec) to resolve gravitational sphere of influence. Possibly a wide mode as well (up to 30 arc sec) to map galaxy kinematics on larger scales. • Velocity resolution not a key driver: a few 10’s of km/sec (OSIRIS today can do this). (Need to quantify requirement.) • Instruments: long slit spectroscopy • Key if wide field mode of IFU is not available • Slit length up to 30 arc sec, configurable at arbitrary angles