### Abstract

Many measurements in cosmology depend on the use of integrated distances or time, but galaxies evolving passively on a timescale much longer than their age difference allow us to determine the expansion rate H(z) solely as a function of the redshift-time derivative dz/dt. These model-independent "cosmic chronometers" can therefore be powerful discriminators for testing different cosmologies. In previous applications, the available sources strongly disfavored models (such as ΛCDM) predicting a variable acceleration, preferring instead a steady expansion rate over the redshift range 0 ≲ z ≲ 2. A more recent catalog of 30 objects appears to suggest non-steady expansion. In this paper, we show that such a result is entirely due to the inclusion of a high, locally inferred value of the Hubble constant H_{0} as an additional datum in a set of otherwise pure cosmic-chronometer measurements. This H_{0}, however, is not the same as the background Hubble constant if the local expansion rate is influenced by a Hubble Bubble. Used on their own, the cosmic chronometers completely reverse this conclusion, favoring instead a constant expansion rate out to z ∼ 2.

Original language | English (US) |
---|---|

Article number | 270 |

Journal | Astrophysical Journal |

Volume | 835 |

Issue number | 2 |

DOIs | |

State | Published - Feb 1 2017 |

### Fingerprint

### Keywords

- cosmological parameters
- cosmology: observations
- cosmology: theory
- distance scale
- galaxies: evolution
- galaxies: general

### ASJC Scopus subject areas

- Astronomy and Astrophysics
- Space and Planetary Science

### Cite this

_{0}on the Interpretation of Cosmic-chronometer Data.

*Astrophysical Journal*,

*835*(2), [270]. https://doi.org/10.3847/1538-4357/835/2/270

**Impact of a Locally Measured H _{0} on the Interpretation of Cosmic-chronometer Data.** / Wei, Jun Jie; Melia, Fulvio; Wu, Xue Feng.

Research output: Contribution to journal › Article

_{0}on the Interpretation of Cosmic-chronometer Data',

*Astrophysical Journal*, vol. 835, no. 2, 270. https://doi.org/10.3847/1538-4357/835/2/270

_{0}on the Interpretation of Cosmic-chronometer Data. Astrophysical Journal. 2017 Feb 1;835(2). 270. https://doi.org/10.3847/1538-4357/835/2/270

}

TY - JOUR

T1 - Impact of a Locally Measured H0 on the Interpretation of Cosmic-chronometer Data

AU - Wei, Jun Jie

AU - Melia, Fulvio

AU - Wu, Xue Feng

PY - 2017/2/1

Y1 - 2017/2/1

N2 - Many measurements in cosmology depend on the use of integrated distances or time, but galaxies evolving passively on a timescale much longer than their age difference allow us to determine the expansion rate H(z) solely as a function of the redshift-time derivative dz/dt. These model-independent "cosmic chronometers" can therefore be powerful discriminators for testing different cosmologies. In previous applications, the available sources strongly disfavored models (such as ΛCDM) predicting a variable acceleration, preferring instead a steady expansion rate over the redshift range 0 ≲ z ≲ 2. A more recent catalog of 30 objects appears to suggest non-steady expansion. In this paper, we show that such a result is entirely due to the inclusion of a high, locally inferred value of the Hubble constant H0 as an additional datum in a set of otherwise pure cosmic-chronometer measurements. This H0, however, is not the same as the background Hubble constant if the local expansion rate is influenced by a Hubble Bubble. Used on their own, the cosmic chronometers completely reverse this conclusion, favoring instead a constant expansion rate out to z ∼ 2.

AB - Many measurements in cosmology depend on the use of integrated distances or time, but galaxies evolving passively on a timescale much longer than their age difference allow us to determine the expansion rate H(z) solely as a function of the redshift-time derivative dz/dt. These model-independent "cosmic chronometers" can therefore be powerful discriminators for testing different cosmologies. In previous applications, the available sources strongly disfavored models (such as ΛCDM) predicting a variable acceleration, preferring instead a steady expansion rate over the redshift range 0 ≲ z ≲ 2. A more recent catalog of 30 objects appears to suggest non-steady expansion. In this paper, we show that such a result is entirely due to the inclusion of a high, locally inferred value of the Hubble constant H0 as an additional datum in a set of otherwise pure cosmic-chronometer measurements. This H0, however, is not the same as the background Hubble constant if the local expansion rate is influenced by a Hubble Bubble. Used on their own, the cosmic chronometers completely reverse this conclusion, favoring instead a constant expansion rate out to z ∼ 2.

KW - cosmological parameters

KW - cosmology: observations

KW - cosmology: theory

KW - distance scale

KW - galaxies: evolution

KW - galaxies: general

UR - http://www.scopus.com/inward/record.url?scp=85011985249&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85011985249&partnerID=8YFLogxK

U2 - 10.3847/1538-4357/835/2/270

DO - 10.3847/1538-4357/835/2/270

M3 - Article

AN - SCOPUS:85011985249

VL - 835

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2

M1 - 270

ER -