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Planetary Nebulae and the Extragalactic Distance Scale

Planetary Nebulae and the Extragalactic Distance Scale. Robin Ciardullo. Why Measure Distances?. We still need distances to individual objects (AGN, MOND galaxies, etc.). The HST Key Project and WMAP say that H 0 = 72  8 km/s/Mpc . But ….

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Planetary Nebulae and the Extragalactic Distance Scale

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  1. Planetary Nebulae and the Extragalactic Distance Scale Robin Ciardullo

  2. Why Measure Distances? We still need distances to individual objects (AGN, MOND galaxies, etc.) The HST Key Project and WMAP say that H0 = 72  8 km/s/Mpc. But … For precision cosmology, we need to know H0 to better than 10%. Note also that WMAP only constrains H0if the universe w = P /  = 1. The current distance scale may contain systematic errors.

  3. Why Observe Planetary Nebulae? From Dopita et al. (1994) They’re very bright !! The brightest PN in a galaxy have luminosities greater than 6000 L! They can routinely be identified out to ~ 20 Mpc

  4. Why Observe Planetary Nebulae? They’re easy to detect!

  5. Why Observe Planetary Nebulae? They’re easy to detect!

  6. Why Observe Planetary Nebulae? They’re easy to detect! 10% of the energy comes out at 5007 Å

  7. Why Observe Planetary Nebulae? They’re easy to detect! [O III] 5007 [O III] Difference Offband 5300

  8. Why Observe Planetary Nebulae? They’re 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!

  9. Why Observe Planetary Nebulae? They’re present in all galaxies! Sc Sb Sa E0 E3 S0 SBa SBb SBc SBm Irr

  10. The History of PN as Distance Indicators • 1966: First Suggestion PN as Distance Indicators [Hodge] In “Galaxies and Cosmology” by Hodge (McGraw-Hill 1966)

  11. The History of PN as Distance Indicators • 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] • 1966: First Suggestion PN as Distance Indicators [Hodge] Reason for slow acceptance of method: individual PN are definitely not standard candles. (Distances to Galactic PN are uncertain to factors of ~ 5)

  12. The Method • Image the galaxy through a redshifted [O III] 5007 filter

  13. The Method • Image the galaxy through a redshifted [O III] 5007 filter • Identify point sources that are invisible in the continuum

  14. 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

  15. The Method M5007 = 2.5 log F5007 – 13.74 • 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

  16. The Method M5007 = 2.5 log F5007 – 13.74 • 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 N (M)  e 0.307M {1 – e 3 ( M* – M ) }

  17. The Calibration of M* The PNLF cutoff magnitude, M*, is calibrated via measurements in galaxies with known Cepheid distances. * Denotes metal-poor, low-luminosity galaxy

  18. 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)!

  19. M* = – 4.47 This consistency across > 1 dex in O/H strongly suggests that neither the Cepheids nor the PNLF need additional metallicity corrections.

  20. 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???

  21. 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

  22. Samples of PN in M31 The bulge, disk, and halo PNLFs are indistinguishable (M* < 0.05 mag)

  23. 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

  24. NGC 3379 The Leo I Group NGC 3351 NGC 3384 NGC 3368 NGC 3377 All 5 galaxies within 1 Mpc Group Diameter

  25. NGC 4649 NGC 4486 The Virgo Cluster NGC 4382 NGC 4406 NGC 4374 NGC 4472 Background NGC 4406 Group Resolved

  26. 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”.

  27. Are Overluminous PN really Intracluster? The density of PN within a galaxy should follow that of the galaxy’s 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

  28. The Identification of Intracluster Stars Intracluster stars are not confined to the center of the Virgo Cluster. They’ve recently been found foreground to NGC 4526.

  29. Are there Systematic Errors in the Distance Scale?

  30. 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.

  31. 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?

  32. PNLF vs. SBFDistances (29Galaxies) • 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!

  33. 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)

  34. MI = C + 4.5(V-I)0 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. C = mI- Cep- RI E(B-V) - 4.5(V-I)obs + 4.5 E(V-I)

  35. 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) OnlyE(B-V) ~ 0.02 is neededto reconcile the PNLF and SBF distance scales This error propagates up the entire distance ladder!

  36. 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.

  37. (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%)

  38. 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.

  39. 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 < 47.2  0.9 kpc.

  40. NGC 4258 (Nuclear Maser) Herrnstein et al. (1999) have analyzed the proper motions and radial velocities of NGC 4258’s nuclear masers. The orbits are Keplerian and yield a distance of 7.2  0.3 Mpc.

  41. *Cepheid and PNLF values are based on (m-M)LMC = 18.50. Geometry vs.Cepheidsvs.PNLF LMC NGC 4258 Ratio

  42. *Cepheid and PNLF values are based on (m-M)LMC = 18.50. Geometry vs.Cepheidsvs.PNLF LMC NGC 4258 Ratio 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).

  43. Why Does the PNLF Work??? The physics behind the PNLF is still controversial. However, there are clues … • A PN’s [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

  44. Why Does the PNLF Work??? The physics behind the PNLF is still controversial. However, there are clues … • A PN’s [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

  45. Why Does the PNLF Work??? The physics behind the PNLF is still controversial. However, there are clues … • A PN’s [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

  46. Why Does the PNLF Work??? The physics behind the PNLF is still controversial. However, there are clues … • A PN’s [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

  47. 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 > 6,000 L. • A central star with L > 6,000 L must be more massive than M > 0.6 M. Such stars come from M > 2 M progenitors. (Weidemann 2000)

  48. 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

  49. 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.

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