The Hubble parameter

Abstract

Distance determinations to individual galaxies, groups, and clusters are critically reviewed. All modern distance determinations have been reduced to a common and internally consistent system. These distances are then used to discuss the present status of the extragalactic distance scale and of the Hubble Parameter, H Q . It is shown that the classical distance-scale "problem" starts quite abruptly at D £ 3 Mpc. It is emphasized that the reasons for this discrepancy are entirely independent of difficulties associated with large-scale deviations from a smooth Hubble flow. From eight different techniques the mean distance modulus of the Virgo cluster is found to be (m-Af) 0 =31.0±0.15 (Z>=15.8±1.1 Mpc). Twelve determinations of the difference between the distance moduli of the Coma and Virgo clusters yield A(ra-Af) 0 =3.71 ±0.05 mag and hence a Coma distance modulus (m-M) Q = 34.71 ±0.16 (Z>=87±6 Mpc). Combining this distance with the Coma cluster's cosmological velocity of 7210 kms' 1 yields a value i/ 0 (local) = 83 ±6 km s -1 Mpc -1 . From the velocity-distance relation for the brightest galaxies in clusters of Bautz-Morgan types I and I-II it is found that H q (global)/H Q {local) =0.92±0.08, in which "local" refers to northern clusters with V Q < 10,000 km s -1 . In other words, the cluster data do not show a statistically significant difference between the local and global values of the Hubble parameter. If one nevertheless adopts H Q (global)/H 0 {local) =0.92±0.08 then one obtains i/ 0 ( global) -76±9 km s -1 Mpc -1 . This observed value of H Q differs at the -3cr level from that predicted by theories of stellar evolution in conjunction with canonical models of the Universe with íl= 1 and A=0.

Beryllium detection in the very fast nova ASASSN-16kt (V407 Lupi)

“…For ASASSN-16kt we have that the observed V-band magnitude at 15 days is V 15 = 9.6 mag, then we obtain a distance of d V,15 = 11.2 ± 2.0 kpc, in agreement with our previous estimate. At galactic coordinates of l = 330.0938°and b = 9.573°, we obtain a height above the galactic plane of h = 1700 ± 300 pc, which is typical for bulge novae (della Valle & Livio 1998). We also report that the position of the nova is 0.5 distant from a GAIA DR1 source (ID 5999691733347769472) with a still unknown parallax and a magnitude of G = 18.95.…”

“…Moreover, the late spectra show it is a ONe nova, due to the presence of very bright [Ne iii] and [Ne v] lines and from the Ne abundance value derived from their analysis. Given its height above the galactic plane (h = 1.7 kpc), it is also a bulge nova, according to della Valle & Livio (1998). However, bulge novae are characterized by distinct properties, such as being slower and fainter than ASASSN-16kt, and are usually characterized by a typical Fe ii spectral class.…”

Determination of the Hubble constant from observations of Cepheid variables in the galaxy M96

“…Various methods for Virgo to Coma Four methods give distance to core Virgo Cluster (3,4,5,36) Weighted mean and adopted uncertainty for Leo-I to Virgo…”

“…Most published values fall in the range 40 < H 0 < 100kms 1 Mpc 1 , often with formal uncertainties of less than 10% (refs. 3,4,5). The intense interest in this debate stems from the fact that a value for H 0 greater than 75 kms 1 Mpc 1 corresponds to an age for the universe of less than 8:7 10 9 years in the favoured Einstein{de Sitter model.…”

The volume expansion rate and the age of the Universe

“…Recent observations of Cepheid variables in NGC4571 (Pierce et al 1994) and M100 (Freedman et al 1994) suggest that the Hubble parameter (H 0 ) is ∼ 80km/s/Mpc (Fukugita et al 1993;Jacoby et al 1992;van den Bergh 1992). Such a high value of H 0 may contradict the age estimate of our universe using, for example, globular clusters (Demanqul et al 1991;Renzini 1991) so that H 0 t 0 > 1.…”