Advisor: Robin Ciardullo George Jacoby, John Feldmeier, Pat Durrell Kimberly Herrmann July 2 nd, 2005 Penn State Planetary Nebula Studies of Face-On Spiral Galaxies: Is the Disk Mass-to-Light Ratio Constant? W. Keel, KPNO, 4-m Mayall Telescope N. King, KPNO, NOAO, NSF, 4-m Mayall Telescope 1/15

HALO DISK (Modified from Carroll & Ostlie 1996) Why study Disk Mass-to-Light Ratios? Assume a constant Disk Mass-to-Light Ratio Disk Distribution of Mass (Astronomy Today, Chaisson & McMillan) Dark Matter Halos 2/15

Our Project: PNe kinematics & Disk Mass The orbits of old disk stars will oscillate in z according to  z = the velocity dispersion in z  (R) = the disk mass surface density z 0 = the disk scale height VLT ANTU + FORS1, ESO Since a)a disk’s surface brightness declines exponentially with radius, R b)spiral disks are supposed to have a constant M/L  z should decline exponentially with R 3/15

Why use PNe to study Spiral Disks? PNe are found in outer regions Easier than absorption line spectroscopy Representative of old galactic disk Easy to find ([O III] 5007 emission) –1 st step: Photometry –PNLF gives distance Precise spectroscopic velocities ( ~ 2 km s -1 ) –2 nd step: Spectroscopy HALO DISK (Modified from Carroll & Ostlie 1996) 4/15

How do we find PNe? Image the galaxy in several filters: [O III] 5007 (50 Å FWHM) H  + [N II] (75 Å FWHM) Harris V 5/15

How do we find PNe? Image the galaxy in several filters: Blinking Method –Find objects clearly on-band but not off-band Eliminate H II region, SN contaminants Determine locations (RA & dec) & magnitudes Need follow-up spectroscopy to get velocities 5/15

Candidate PNe 152 candidates in M33 6/15

242 candidates in M83 6/15

65 candidates in M101 6/15

PNe Spectroscopy Observations –Use HYDRA with WIYN (or 4 m at CTIO) –Multiple setups with min exposures –Target as many PNe as many times as possible –Also target the blank sky, some miscellaneous objects, and random positions Typical Spectral Reduction –Using IRAF: dohydra, bias subtraction, flat fielding, wavelength calibration, sky subtraction, combining multiple setups, barycentric & systemic velocity corrections –Extra concentration on wavelength calibration 7/15

Resulting Velocities 140 velocities in M33 8/15

-66.6> v > -110km/s -33.3> v > -66.6km/s 0> v > -33.3km/s 33.3> v > 0km/s 66.6> v > 33.3km/s 131> v > 66.6km/s ~190 velocities in M83 8/15

47 velocities in M101 (so far) 8/15

Subtracting out Rotation 9/15

Velocity Dispersion 10/15

Velocity Ellipsoid Epicyclic Approximation –Separate rotation from perpendicular oscillations Maximum Likelihood Method –Determine which combinations of  z &  R are most likely Toomre stability –A thin disk is stable against axisymmetric perturbations Morosov stability –A thin disk is stable against the formation of a bar 11/15

M33 Results Scale length > twice the K band scale length! M/L V increases by a factor of 5 through the disk (not constant!)  R must turn down in center- otherwise  R > v R  z /  R (R) agrees with numerical models 12/15

Possible Problems Possible H II region contaminants Wrong value of scale height, z 0 Radial gradient in the scale height Systematic extinction due to dust Breakdown of isothermal disk approximation at large radii Breakdown in stability arguments (Mostly because of a sample of one) 13/15

Conclusions PNe are useful for studying galactic dynamics They are easy to find & have good spectroscopic precision Dispersion needs to be decomposed Velocity dispersion in z (  z ) shows exponential decay For M33: the disk mass-to-light ratio is not constant throughout the disk Need more spiral galaxies… 14/15

Stay Tuned! VLT ANTU + FORS1, ESO King, KPNO/NOAO/NSF, Mayall Teles J. Cuillandre. CFHT A. Block, NOAO/AURA/NSF T. Rector, Gemini/AURA GMOS Team, Gemini M33: Done! M83: Finishing spectral analysis M101: Finishing spectral analysis M94: Images obtained NGC 6946: Images obtained M74: Granted time for imaging in Nov 15/15

Eliminating H II Regions

Velocity Ellipsoid Epicyclic Approximation: Maximum Likelihood Method –Determine probability for every combination of possible  z and  R –0 <  z < 100 km s -1, 0.25 <  z /  R < 1.0 Toomre (Morosov) stability

Maximum Likelihood Method Determine probability for every combination of possible  z and  R 0 <  z < 100 km s -1, 0.25 <  z /  R < 1.0 For each bin: –Consider a  z and a  R –For each PN in the bin determine  2 rot and  2 res P(PN)

Toomre/Morosov Stability A thin stellar disk is stable against axisymmetric perturbations if where  (the epicyclic frequency) is The disk is stable against non-axisymmetric perturbations if The isothermal approximation can be used to show this is

Epicyclic Frequency

Epicyclic Approximation Collisionless Boltzmann Equation with Jeans Equation & symmetry & small asymmetric drift