Planetary Nebulae and the Extragalactic Distance Scale

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Planetary Nebulae and the
Extragalactic Distance Scale

• Robin Ciardullo

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Why Measure Distances?

• The HST Key Project and WMAP say that H0 72 ? 8
  km/s/Mpc. But

We still need distances to individual objects
(AGN, MOND galaxies, etc.)
For precision cosmology, we need to know H0 to
better than 10. Note also that WMAP only
constrains H0 if the universe w P / ? ?1.
The current distance scale may contain systematic
errors.
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Why Observe Planetary Nebulae?
From Dopita et al. (1994)

• Theyre very bright !!
• The brightest PN in a galaxy have luminosities
  greater than 6000 L?!
• They can routinely be identified out to 20 Mpc

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Why Observe Planetary Nebulae?
Theyre easy to detect!
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Why Observe Planetary Nebulae?
Theyre easy to detect!
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Why Observe Planetary Nebulae?
Theyre easy to detect!
10 of the energy comes out at 5007 Å
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Why Observe Planetary Nebulae?
Theyre easy to detect!
O III ?5007
Offband ?5300
O III Difference
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Why Observe Planetary Nebulae?
Theyre a high precision distance indicator.
M86
M84
M87
There is at least one O III-bright PN for every
108 L?. For large galaxies, the internal
errors are a few percent!
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Why Observe Planetary Nebulae?
Theyre present in all galaxies!
Sc
Sb
Sa
E0
E3
S0
SBa
SBb
SBc
SBm
Irr
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The History of PN as Distance Indicators

• 1966 First Suggestion PN as Distance Indicators
  Hodge

In Galaxies and Cosmology by Hodge (McGraw-Hill
1966)
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The History of PN as Distance Indicators

• 1966 First Suggestion PN as Distance Indicators
  Hodge

• 1978 First PN-based distance estimate Ford
  Jenner

• 1981 First use of PN for Local Group Jacoby
  Lesser
• 1989 First use of Planetary Nebula Luminosity
  Function Ciardullo et al.
• 1990 First PNLF-based Hubble Constant Jacoby et
  al.
• 1990 First Use of the PNLF in the Galaxy
  Pottasch

Reason for slow acceptance of method individual
PN are definitely not standard candles. (Distances
to Galactic PN are uncertain to factors of 5)
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The Method

• Image the galaxy through a redshifted O III
  ?5007 filter

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The Method

• Image the galaxy through a redshifted O III
  ?5007 filter
• Identify point sources that are invisible in the
  continuum

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The Method

• Image the galaxy through a redshifted O III
  ?5007 filter
• Identify point sources that are invisible in the
  continuum
• If the galaxy has star-formation, compare O III
  ?5007 to H?

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The Method

• Image the galaxy through a redshifted O III
  ?5007 filter
• Identify point sources that are invisible in the
  continuum
• If the galaxy has star-formation, compare O III
  ?5007 to H?
• Perform photometry on a complete sample of
  objects

M5007 ?2.5 log F5007 13.74
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The Method

• Image the galaxy through a redshifted O III
  ?5007 filter
• Identify point sources that are invisible in the
  continuum
• If the galaxy has star-formation, compare O III
  ?5007 to H?
• Perform photometry on a complete sample of
  objects
• Fit to an empirical function

M5007 ?2.5 log F5007 13.74
N (M) ? e 0.307 M 1 e 3 ( M M )
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The Calibration of M
The PNLF cutoff magnitude, M, is calibrated via
measurements in galaxies with known Cepheid
distances.
SMC M33 M101 NGC 3351 NGC 3627
LMC M81 NGC 300 NGC 3368 NGC 4258
M31 NGC 2403 NGC 5253
Denotes metal-poor, low-luminosity galaxy
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M 4.47

• M is a constant for large, metal-rich galaxies
• Young and old populations have the same value of
  M
• M is fainter in small, low-metallicity galaxies.

This dependence was predicted by Dopita et al.
(1992)!
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M 4.47
This consistency across gt 1 dex in O/H strongly
suggests that neither the Cepheids nor the PNLF
need additional metallicity corrections.
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Testing the Method
Are there systematic errors associated with the
PNLF method? To answer this question, we can

• Perform Consistency Tests within Galaxies
• Perform Consistency Tests inside Galaxy Groups
  and Clusters

Can we find a case where the PNLF fails???
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Tests within a Galaxy

• Five galaxies have large enough samples of PN to
  test for systematic shifts in the PNLF
• M31
• M81
• M33
• NGC 5128
• NGC 4494

In these galaxies, the PNLF samples within
galaxies always produce consistent distances
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Samples of PN in M31
The bulge, disk, and halo PNLFs are
indistinguishable (?M lt 0.05 mag)
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Tests within a Cluster

• Six Galaxy Groups have PNLF distances to multiple
  galaxies
• M81 Group M81, NGC 2403
• NGC 1023 Group NGC 891, 1023
• NGC 5128 Group NGC 5102, 5128, 5253, (M83)
• Fornax Cluster NGC 1316, 1380, 1399, 1404
• Leo I Group NGC 3351, 3368, 3377, 3379, 3384
• Virgo Cluster NGC 4382, 4472, 4486, 4649
  (4374, 4406)

PNLF distances within clusters are always
consistent to within 1 Mpc, with no systematic
behavior
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NGC 3379
The Leo I Group
NGC 3351
NGC 3384
NGC 3368
NGC 3377
All 5 galaxies within 1 Mpc Group Diameter
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NGC 4649
NGC 4486
The Virgo Cluster
NGC 4382
NGC 4406
NGC 4374
NGC 4472
Background NGC 4406 Group Resolved
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Does the PNLF ever Fail?
Actually yes in the Virgo Cluster, there are
intracluster stars!!!
Intracluster PN can be foreground to the target
galaxy, and therefore appear overluminous.
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Are Overluminous PN really Intracluster?
The density of PN within a galaxy should follow
that of the galaxys light. Intracluster PN
should not they should scale with the area
surveyed. Overluminous (foreground) objects
should therefore be (primarily) found in the
outskirts of galaxies.
0.25 mag
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The Identification of Intracluster Stars
Intracluster stars are not confined to the center
of the Virgo Cluster. Theyve recently been
found foreground to NGC 4526.
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Are there Systematic Errors in the Distance Scale?
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The PNLF and Surface Brightness Fluctuations
Cepheids provide the calibration for both the
PNLF and the SBF method. Presumably, the
distances of the two methods agree.
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PNLF vs. SBF Distances
?mean 0.05 mag
?mean 0.05 mag
The PNLF zero point is calibrated via
measurements in 13 galaxies with distances
determined from Cepheids
The SBF zero point is calibrated via measurements
in 6 galaxies with distances determined from
Cepheids
How well do the two distance scales agree?
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PNLF vs. SBF Distances (29 Galaxies)

• The curve is the expected scatter in the
  measurements

• There are 3 outliers. The two worst are

The zero points differ by 0.15 mag! We have
found a systematic error!
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Most Likely Explanation Internal Extinction

• To derive the PNLF cutoff magnitude, M, using
  Cepheid distances, one needs to know the
  reddening
• If the reddening is underestimated, then M is
  underestimated, and the inferred distance scale
  is too small.

M m - ?Cep R5007 E(B-V)
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• For the SBF method, however, the absolute
  fluctuation magnitude, MI, depends on color,
  i.e.,
• So the zero point of the system is defined
  through
• If the reddening is underestimated, then the
  color of the galaxy is overestimated, MI is
  overestimated, and therefore C is overestimated.
  The result is a distance scale that is too large.

MI C 4.5 (V-I)0
C mI - ?Cep- RI E(B-V) - 4.5(V-I)obs 4.5
E(V-I)
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• Because the SBF and PNLF methods react to
  reddening in opposite directions, a small amount
  of internal extinction can lead to a large
  discrepancy between the two distance scales

If only the SBF calibration is affected
If both the PNLF and SBF calibrations are affected
?? 4.2 ?E(B-V)
?? 7.7 ?E(B-V)
Only E(B-V) 0.02 is needed to reconcile the
PNLF and SBF distance scales
This error propagates up the entire distance
ladder!
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The PNLF and SN Ia
Until recently, the sample of galaxies with
well-observed Type Ia supernovae and PNLF
measurements was too small to be useful. This is
now changing.
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(from Feldmeier, Philips, Jacoby 2005)
PNLF vs. SN Ia Distances

• The PNLF calibration of the SN Ia distance scale
  agrees well with that of the Cepheids.
• (Any systematic error between the scales is less
  than 4)

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PNLF, Cepheids, and Geometry
The PNLF distance scale is calibrated by
Cepheids, and the Cepheid scale assumes an LMC
distance of (m-M)0 18.50. This can be checked
via 2 geometric distance measurements.
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The LMC (SN 1987A Light Echo)
A key benchmark of the extragalactic distance
scale is the light echo measurement of SN 1987A.
The classical analysis by Panagia et al. (1991)
gives a distance of 51.2 ? 3.1 kpc.
A more complex model by Gould Uza (1998) gives
a lower distance of D lt 47.2 ? 0.9 kpc.
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NGC 4258 (Nuclear Maser)
Herrnstein et al. (1999) have analyzed the proper
motions and radial velocities of NGC 4258s
nuclear masers. The orbits are Keplerian and
yield a distance of 7.2 ? 0.3 Mpc.
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Geometry vs. Cepheids vs. PNLF
LMC
NGC 4258
Ratio
Method ?4258 - ?LMC
Geometry 18.50 ? 0.05 29.29 ? 0.09 10.79 ? 0.10
Cepheids 18.50 29.44 ? 0.12 10.94 ? 0.12
PNLF 18.50 ? 0.11 29.43 ? 0.09 10.93 ? 0.14

• Cepheid and PNLF values are based on (m-M)LMC
  18.50.

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Geometry vs. Cepheids vs. PNLF
LMC
NGC 4258
Ratio
Method ?4258 - ?LMC
Geometry lt 18.37 ? 0.04 29.29 ? 0.09 10.92 ? 0.10
Cepheids 18.50 29.44 ? 0.12 10.94 ? 0.12
PNLF 18.50 ? 0.11 29.43 ? 0.09 10.93 ? 0.14

• Cepheid and PNLF values are based on (m-M)LMC
  18.50.

The perfect agreement between the relative
distances argues for a short distance to the LMC
and a Hubble Constant that is 7 larger than the
Key Project value (77 km s-1 Mpc-1).
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Why Does the PNLF Work???

• The physics behind the PNLF is still
  controversial. However, there are clues
• A PNs O III ?5007 luminosity depends on the
  luminosity of its central star. But there are
  mechanisms that can place a limit on the maximum
  O III flux a PN can emit.

• Collisional de-excitation of forbidden emission
  in young, dense nebulae

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Why Does the PNLF Work???

• The physics behind the PNLF is still
  controversial. However, there are clues
• A PNs O III ?5007 luminosity depends on the
  luminosity of its central star. But there are
  mechanisms that can place a limit on the maximum
  O III flux a PN can emit.

• Collisional de-excitation of forbidden emission
  in young, dense nebulae
• Circumstellar extinction around massive (high
  luminosity) central stars

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Why Does the PNLF Work???

• The physics behind the PNLF is still
  controversial. However, there are clues
• A PNs O III ?5007 luminosity depends on the
  luminosity of its central star. But there are
  mechanisms that can place a limit on the maximum
  O III flux a PN can emit.

• Collisional de-excitation of forbidden emission
  in young, dense nebulae
• Circumstellar extinction around massive (high
  luminosity) central stars

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Why Does the PNLF Work???

• The physics behind the PNLF is still
  controversial. However, there are clues
• A PNs O III ?5007 luminosity depends on the
  luminosity of its central star. But there are
  mechanisms that can place a limit on the maximum
  O III flux a PN can emit.

• Collisional de-excitation of forbidden emission
  in young, dense nebulae
• Circumstellar extinction around massive (high
  luminosity) central stars

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Why Does the PNLF Work???
The real problem comes from the absolute
luminosity of the PNLF cutoff

• M ?4.47 corresponds to a luminosity of 600 L?
• To produce 600 L? of O III emission, a central
  star must have a luminosity of L gt 6,000 L?.
• A central star with L gt 6,000 L? must be more
  massive than M gt 0.6 M?. Such stars come from M
  gt 2 M? progenitors.

(Weidemann 2000)
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Why Does the PNLF Work???

• Elliptical galaxies do not have many (any?) 2 M?
  main sequence stars. But they do have large
  numbers of 1 M? stars. If some are in close
  binary systems which coalesce on the main
  sequence, the product may evolve into an O
  III-bright planetary.
• The ratio of bright planetaries to blue
  stragglers is about equal to the ratio of the
  objects lifetimes.

Carrera et al. 2002
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Summary

• The Planetary Nebula Luminosity Function
  continues to be a useful tool for extragalactic
  astronomy and cosmology.
• The PNLF is the only standard candle capable of
  measuring distances to all the large galaxies of
  the local supercluster.
• The PNLF cutoff, M, is the same for old and
  young populations.
• PNLF comparisons with Surface Brightness
  Fluctuations and Cepheid measurements suggest
  that small systematic errors in the distance
  scale still exist.
• The PNLF and Cepheid calibrations of SN Ia are in
  good agreement.
• The brightest PN in E/S0 galaxies may be the
  product of binary star evolution. But they are
  NOT binaries.