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G. A. Tammann

Publications and source records attributed to G. A. Tammann.

38 records · Page 3Linked to original sources
arXiv1996

Focussing in on H_0

Six independent methods yield a Virgo cluster modulus of (m-M)=31.66+/- 0.08. This inserted into the Hubble diagram of clusters, whose relative distances to the Virgo cluster are known, gives H_0=54+/-4. The result is independent of any observed or inferred velocity of the Virgo cluster and holds out 10 000 km/s. An analogous use of the Fornax cluster is not yet possible because of its unknown structure in space and its poorly understood distance relative to other clusters. Field galaxies, corrected for Malmquist bias, give H_0=53+/-3. The results of purely physical distance determinations cluster around H_0=55+/-10. These results may be compared with the high-weight determination of H_0=58.5+/-3 from Cepheid-calibrated SNe Ia and their Hubble diagram out to 30 000 km/s (Saha 1996). The agreement of the independent methods suggests that the external error of an adopted value of H_0=58 is equal or less than 13%.

astro-ph↗
arXiv1996

H_0 from HST

HST has so far provided Cepheid distances to nine galaxies. Although not sufficient yet to determine the distance of the extended Virgo cluster, they are decisive for the distance scale in two ways. (1) Seven of the galaxies contribute to a much improved calibration of the Tully-Fisher relation. Applying this to a complete sample of Virgo spirals one obtains a cluster distance of (m-M)=31.79 +/- 0.09. Other distance indicators support this value. The adopted linear distance of 22.0 +/- 0.8 Mpc combined with the cluster velocity of 1178 +/- 32 km s^-1 (in the CMB frame) gives H_0=54 +/- 2 (internal error). (2) Six of the galaxies have been the site of seven SNe Ia with well observed maxima. Their resulting calibration in absolute magnitudes gives M_B(max)=-19.53 +/- 0.07 and M_V(max)=-19.49 +/- 0.07 with negligible intrinsic scatter. If this calibration is used to determine the distances of all distant SNe Ia with known maxima and with 1100 < v < 30'000 km s^-1, H_0 becomes 56 +/- 3 (internal error). Systematic errors tend to make this an upper limit; in particular the case H_0 >= 70 can be excluded. The conclusion is that the large-scale value of the Hubble constant is H_0=55 +/- 10 (external error).

astro-ph↗