scholarly journals The Hubble Constant and the Deceleration Parameter

1974 ◽  
Vol 63 ◽  
pp. 47-59
Author(s):  
G. A. Tammann
Keyword(s):  
Velocity Field ◽  
Deceleration Parameter ◽  
Preliminary Report ◽  
Hubble Constant ◽  
Intrinsic Properties ◽  
Local Anisotropy ◽  
A Chain ◽  
Distance Indicators ◽  
Luminosity Evolution ◽  
Parent Galaxy

A preliminary report is given of recent work with A. Sandage on the Hubble constant. Through a chain of distance indicators in Sc and Ir galaxies (cepheids, brightest stars, H iiregions, and luminosity classes) the distance scale is carried beyond any possible local anisotropy of the velocity field. Special care is taken to allow for the dependence of the intrinsic properties of the distance indicators on the size of the parent galaxy, and for the effect of the Malmquist correction. H0 is found to be 55 ± 7 km s-1 Mpc-1; within the errors no systematic changes with distance were found.A formal value of the deceleration constant q0 = 1 ± 1 was recently derived by Sandage (1972a) and Sandage and Hardy (1973). The most important correction to this value is probably the luminosity evolution of galaxies, which tends to push q0 below 0.5. The ensuing evidence for an open universe is also favored by independent arguments.

scholarly journals Peculiar Red Giants in External Galaxies

1989 ◽  
Vol 106 ◽  
pp. 35-50 ◽  
Author(s):  
Harvey B. Richer
Keyword(s):  
Star Formation ◽  
Stellar Evolution ◽  
Hubble Constant ◽  
Red Giants ◽  
Stellar Content ◽  
Late Type ◽  
External Galaxies ◽  
Distance Indicators ◽  
Luminosity Evolution ◽  
Local Value

AbstractStudy of the late-type stellar content in external galaxies provides numerous clues for the theory of stellar evolution, for star-formation scenarios in galaxies, and for proper models of the luminosity evolution of galaxies which are then used in cosmological studies. In addition, these late-type stars can be used as distance indicators themselves and yield a local value of the Hubble constant consistent with recent Cepheid determinations.

scholarly journals The effects of peculiar velocities in SN Ia environments on the local H0 measurement

2020 ◽  
Vol 500 (3) ◽  
pp. 3728-3742
Author(s):  
Thomas M Sedgwick ◽  
Chris A Collins ◽  
Ivan K Baldry ◽  
Philip A James
Keyword(s):  
Hubble Constant ◽  
Density Parameter ◽  
Host Galaxies ◽  
Peculiar Velocities ◽  
Standard Candle ◽  
Modern Cosmology ◽  
Type Ia ◽  
The Difference ◽  
Ia Supernovae ◽  
Distance Indicators

ABSTRACT The discrepancy between estimates of the Hubble constant (H0) measured from local (z ≲  0.1) scales and from scales of the sound horizon is a crucial problem in modern cosmology. Peculiar velocities (vpec) of standard candle distance indicators can systematically affect local H0 measurements. We here use 2MRS galaxies to measure the local galaxy density field, finding a notable z  <  0.05 underdensity in the SGC-6dFGS region of 27  ±  2 per cent. However, no strong evidence for a ‘Local Void’ pertaining to the full 2MRS sky coverage is found. Galaxy densities are used to measure a density parameter, Δϕ+−, which we introduce as a proxy for vpec that quantifies density gradients along a supernova (SN) line of sight. Δϕ+− is found to correlate with local H0 estimates from 88 Pantheon Type Ia supernovae (SNe Ia; 0.02  <  z  <  0.05). Density structures on scales of ∼50 Mpc are found to correlate strongest with H0 estimates in both the observational data and in mock data from the MDPL2-Galacticus simulation. Using trends of H0 with Δϕ+−, we can correct for the effects of density structure on local H0 estimates, even in the presence of biased vpec. However, the difference in the inferred H0 estimate with and without the peculiar velocity correction is limited to < 0.1  per cent. We conclude that accounting for environmentally induced peculiar velocities of SN Ia host galaxies does not resolve the tension between local and CMB-derived H0 estimates.

scholarly journals Distance Indicators in the Magellanic Clouds

1983 ◽  
Vol 6 ◽  
pp. 209-216 ◽  
Author(s):  
J.A. Graham
Keyword(s):  
Chemical Evolution ◽  
Comparative Studies ◽  
Hubble Constant ◽  
Magellanic Clouds ◽  
Distance Scale ◽  
Stellar Systems ◽  
Age Range ◽  
Distance Indicators ◽  
The Universe

In talking about the overall distance scale of the Universe and the Hubble Constant, the Magellanic Clouds are good places to start. They are stellar systems large enough to contain stars, clusters and nebulae of all types, covering a wide age range. With modern telescopes and detectors, we are able to observe stars from the very bright down to those fainter intrinsically than our own Sun. From comparative studies, we may thus establish our basic calibrations of bright objects before moving out to measure the Universe at large. At the same time, the fact that both Magellanic Clouds are independently evolving galaxies, enables us to separate the effects of stellar age and chemical evolution on the calibrations that we make.

scholarly journals SNe Ia Redshift in a Nonadiabatic Universe

Universe ◽  
2018 ◽  
Vol 4 (10) ◽  
pp. 104 ◽  
Author(s):  
Rajendra Gupta
Keyword(s):  
Cosmological Constant ◽  
Deceleration Parameter ◽  
Hubble Constant ◽  
Cosmological Models ◽  
Single Parameter ◽  
New Approach ◽  
Cosmological Principle ◽  
Flat Universe ◽  
Λcdm Model ◽  
Two Parameters

By relaxing the constraint of adiabatic universe used in most cosmological models, we have shown that the new approach provides a better fit to the supernovae Ia redshift data with a single parameter, the Hubble constant H0, than the standard ΛCDM model with two parameters, H0 and the cosmological constant Λ related density, ΩΛ. The new approach is compliant with the cosmological principle. It yields the H0 = 68.28 (±0.53) km s−1 Mpc−1 with an analytical value of the deceleration parameter q0 = −0.4. The analysis presented is for a matter-only, flat universe. The cosmological constant Λ may thus be considered as a manifestation of a nonadiabatic universe that is treated as an adiabatic universe.

scholarly journals Redshifts and Large Scale Structures

1983 ◽  
Vol 104 ◽  
pp. 159-165
Author(s):  
G. Chincarini
Keyword(s):  
Deceleration Parameter ◽  
Large Scale ◽  
Hubble Constant ◽  
Large Scale Structures ◽  
Classical Paper ◽  
Scale Structures

The effort to measure the geometry of space by experiment, that is, the determination of the Hubble Constant, Ho, and of the deceleration parameter, qo, led toward the end of the first half of the century, to the classical paper by Humason, Mayall, and Sandage (1956). Their catalogue contains 920 redshifts collected over a twenty-year period (1935–1955). Further redshifts of galaxies were measured to refine such determinations and to study the dynamics of clusters (Zwicky 1933).

scholarly journals Cosmological Information from Galaxies and Radio Galaxies

1972 ◽  
Vol 44 ◽  
pp. 314-340 ◽  
Author(s):  
J. V. Peach
Keyword(s):  
Deceleration Parameter ◽  
Hubble Parameter ◽  
Radio Galaxies ◽  
Local Anisotropy ◽  
Cluster Galaxies ◽  
Recent Developments

An account is given of recent developments in the derivation of the value of the Hubble parameter applicable to regions beyond the local anisotropy. Recent observations relevant to interpretations of the magnitude-redshift diagram for cluster galaxies are discussed, in an attempt to assess uncertainties in the value of the deceleration parameter.

scholarly journals Theoretical Light Curves for Type Ia Supernovae and Determination of the Hubble Constant

1999 ◽  
Vol 183 ◽  
pp. 68-68
Author(s):  
Koichi Iwamoto ◽  
Ken'Ichi Nomoto
Keyword(s):  
Hubble Constant ◽  
Light Curves ◽  
Type Ia Supernovae ◽  
Maximum Brightness ◽  
Decline Rate ◽  
Type Ia ◽  
Error Bars ◽  
Ia Supernovae ◽  
Distance Indicators

The large luminosity (MV ≈ −19 ∼ −20) and the homogeneity in light curves and spectra of Type Ia supernovae(SNe Ia) have led to their use as distance indicators ultimately to determine the Hubble constant (H0). However, an increasing number of the observed samples from intermediate- and high-z (z ∼ 0.1 − 1) SN Ia survey projects(Hamuy et al. 1996, Perlmutter et al. 1997) have shown that there is a significant dispersion in the maximum brightness (∼ 0.4 mag) and the brighter-slower correlation between the brightness and the postmaximum decline rate, which was first pointed out by Phillips(1993). By taking the correlation into account, Hamuy et al.(1996) gave an estimate of H0 within the error bars half as much as previous ones.

scholarly journals The dark sector cosmology

2020 ◽  
Vol 29 (14) ◽  
pp. 2030014
Author(s):  
Elcio Abdalla ◽  
Alessandro Marins
Keyword(s):  
Dark Energy ◽  
Cosmological Parameters ◽  
Hubble Constant ◽  
Acoustic Oscillations ◽  
Dark Sector ◽  
Fundamental Physics ◽  
Observational Techniques ◽  
Distance Indicators ◽  
The Universe ◽  
Theoretical Developments

The most important problem in fundamental physics is the description of the contents of the Universe. Today, we know that 95% thereof is totally unknown. Two thirds of that amount is the mysterious Dark Energy described in an interesting and important review [E. J. Copeland, M. Sami and S. Tsujikawa, Int. J. Mod. Phys. D 15 (2006) 1753]. We briefly extend here the ideas contained in that review including the more general Dark Sector, that is, Dark Matter and Dark Energy, eventually composing a new physical Sector. Understanding the Dark Sector with precision is paramount for us to be able to understand all the other cosmological parameters comprehensively as modifications of the modeling could lead to potential biases of inferred parameters of the model, such as measurements of the Hubble constant and distance indicators such as the Baryon Acoustic Oscillations. We discuss several modern methods of observation that can disentangle the different possible descriptions of the Dark Sector. The possible applications of some theoretical developments are also included in this paper as well as a more thorough evaluation of new observational techniques at lower frequencies and gravitational waves.

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