Advisor: Robin Ciardullo

George Jacoby, John Feldmeier, Pat Durrell

Kimberly Herrmann

July 2nd, 2005Penn State

Planetary Nebula Studies of Face-On Spiral Galaxies:

Is the Disk Mass-to-Light Ratio Constant?

W. Keel, KPNO, 4-m Mayall Telescope

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 starswill oscillate in z according to

02 )( zRGz

z = the velocity dispersion in

z(R) = the disk mass surface densityz0 = the disk scale height

VLT ANTU + FORS1, ESO

VLT ANTU + FORS1, ESO

Sincea)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)

– 1st step: Photometry– PNLF gives distance

• Precise spectroscopic velocities (~2 km s-

1)– 2nd 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 PNe152 candidatesin M33

6/15

242 candidatesin M83

6/15

65 candidatesin M101

6/15

PNe Spectroscopy• Observations

– Use HYDRA with WIYN (or 4 m at CTIO)– Multiple setups with 30-45 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 Velocities140 velocitiesin M33

8/15

-66.6 > v > -110 km/s

-33.3 > v > -66.6 km/s

0 > v > -33.3 km/s

33.3 > v > 0 km/s

66.6 > v > 33.3 km/s

131 > v > 66.6 km/s

~190 velocitiesin M83

8/15

47 velocities in M101(so far)

8/15

Subtracting out Rotation

9/15

ivivivv zRrotlos cossinsincossin

Velocity Dispersion0

2 )( zRGz

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

2222222222 cossinsinsincos measzRrotres iii

11/15

M33 Results• Scale length > twice the K band

scale length!• M/LV increases by a factor of 5

through the disk (not constant!)• R must turn down in center-

otherwise R > vR • z/ R(R) agrees with numerical

models

12/15

Possible Problems• Possible H II region contaminants

• Wrong value of scale height, z0

• 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, ESOKing, 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:

2222222222 cossinsinsincos measzRrotres iii

• 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

R

VcRrot ln

ln

2

1

2

122

• Toomre (Morosov) stability

36.30

Rz

z

c

Rz V

Rz

72.60

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 2rot and 2

res

R

VcRrot ln

ln

2

1

2

122 2222222222 cossinsinsincos measzRrotres iii

P(PN)

2

2

2 2exp

2

1

res

res

res

v

2

22 )2ln(

2

1)ln(

res

resres

vP

Toomre/Morosov StabilityA 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

G

R

36.3

R

V

R

V cc

ln

ln22

R

VG cR

236.3

.72.60

c

Rz V

Rz

0

2 )()(

Gz

RR z

Epicyclic Frequency

xx 2

m

eff

R

2

22

2

2

2),(

R

JzR z

eff

mR

c

m

z

R

V

R

J

R

2

3

2

R

V

R

V cc

ln

ln22

Epicyclic Approximation

• Collisionless Boltzmann Equation with Jeans Equation & symmetry & small asymmetric drift

BA

BRrot22

02

1

R

cc

dR

dV

R

VA

02

1

R

cc

dR

dV

R

VB

R

VcRrot ln

ln

2

1

2

122