Upload
barnard-moody
View
213
Download
0
Embed Size (px)
Citation preview
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