Previous | Session 69 | Next
G. Jacoby (WIYN), M. Phillips (LCO), J. Feldmeier (NOAO)
Calibrating SN Type Ia in Early-Type Galaxies using the Planetary Nebulae Luminosity Function
Although seemingly passe, determining the Hubble constant directly and accurately is still vital to cosmological models. While results from WMAP imply a Hubble constant roughly equal to that found from direct distance indicators (~0), this result depends on the adopted equation of state (w=-1). If other equations of state are assumed, the WMAP results are consistent with a broad range of Hubble constants (Spergel et al 2003).
SN Type Ia have been found to make excellent distance indicators to great cosmological distances, provided that the relationship between maximum magnitude and decline rate is taken into account (Phillips et al 1999). However, it has been historically difficult to calibrate the zero point for this distance indicator, and has only been performed for a handful of well-observed SN Ia in star-forming galaxies.
Using the high precision [O III] \lambda 5007 Planetary Nebulae Luminosity Function distance indicator, and the Magellan Clay telescope, we can add more direct distances to nearby Type Ia SN, and improve the zero point calibration. By comparing the luminosities of SN Ia in the old populations of ellipticals and S0s with SN Ia in spirals, we can also test for evolutionary effects that may enter into dark energy measurements.
We report new (preliminary) PNLF distance moduli for the three early-type galaxies NGC 1316 (SN 1980N), 1380 (SN 1992A), and 524 (SN 2000cx) of 31.34 ± 0.15, 31.10 ± 0.20, and a lower limit of \mu > 31.8, respectively. All have well-observed Type~Ia SN. From these, and distances to three other well-observed SN~Ia having PNLF distances, we derive a revised Hubble constant of 77. The Hubble constant derived from Cepheid distances to these (or same-group) galaxies is 75.
Previous | Session 69 | Next
Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.