Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.9202p&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #92.02; Bulletin of the American Astronomical Society, Vol. 24, p.1266
Astronomy and Astrophysics
Astronomy
Scientific paper
We present a comparison of galaxy distances estimated via the Tully-Fisher relation and those estimated using supernovae. In the first case, we assume type Ia supernovae (SN Ia) are standard candles. By restricting the sample to those late-type galaxies which have had both well observed supernova events and which are also suitable for an application of the Tully-Fisher relation, the resulting sample should be essentially free of ``Malmquist-like'' effects. Consequently, the observed dispersion should only reflect that intrinsic in the two techniques and enable a fair assessment of the precision of the two methods. The sample (14 SN Ia) has an rms dispersion of only 0.4 mag, implying that both techniques are reasonably accurate indicators of extragalactic distances. The calibration of the Tully-Fisher relations obtained using local galaxies provides an absolute calibration for SN Ia of M_B = -18.69 +/- 0.19. Existing data on more distant SN Ia are used to derive a global estimate of the Hubble Constant, the result being H_deg = 87 +/- 12 km sec(-1) Mpc(-1) . Alternatively, if we force H_deg ~ 45 km sec(-1) Mpc(-1) , the Tully-Fisher relations would still have a small rms dispersion but must then have a discontinuous absolute calibration (delta m = 1.4 mag.) over a small range in distance, namely 4.0 < D < 6.5 Mpc. We also present a similar comparison using distances estimated via the method of modeling the expanding photospheres of type II supernovae (SN II). In this case, the rms dispersion for 6 SN II is 11% in distance, or equivalently 0.22 mag., implying both that this method is at least as reliable as assuming SN Ia are standard candles, and that the Tully-Fisher relations produce good distance estimates as well. That is, the distances estimated via these two methods are consistent within the stated internal errors. Consequently, discrepancies in the value of the Hubble Constant estimated using the SN II method and the TF relation are probably a result of differences in the Hubble flow within the samples themselves, and not an indication of inconsistent distance estimates.
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