Age-dating Stellar Populations of Luminous Red Galaxies

AbstractWe investigate the possibility of using Luminous Red Galaxies (LRGs) as “Cosmic chronometers” to measure the expansion rate of the universe to 3% over a redshift range 0.1 < z < 1.0. In this method, H(z) is directly measured by using the ages of passively evolving galaxies to determine dz/dt. We first present results from our study of LRGs in simulations Crawford et al. where we explore the impact of extended star formation histories on the measurements of the Hubble parameter. We then extract a carefully selected sample of LRGs taken from Sloan Digital Sky Survey (SDSS) Data Released Seven (DR7), stack spectra in redshift bins to increase the signal-to-noise, and use the Lick index modelling presented in Thomas et al. to age-date the sample. We discuss the implications for expansion rate measurements and outline a proposal to observe LRGs with the Southern African Large Telescope (SALT).

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Studying Luminous Red Galaxies to probe H(z) at high redshift

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313004729 ◽

2012 ◽

Vol 8 (S295) ◽

pp. 185-185

Author(s):

A. Ratsimbazafy ◽

C. Cress ◽

S. Crawford ◽

Keyword(s):

High Redshift ◽

Sloan Digital Sky Survey ◽

Age Dating ◽

Time Interval ◽

Spectral Fitting ◽

Luminous Red Galaxies ◽

Sky Survey ◽

Intense Burst ◽

Red Galaxies ◽

The Universe

AbstractLuminous Red Galaxies (LRGs) have old, red stellar populations often interpreted as evidence of a formation scenario in which these galaxies form in a single intense burst of star formation at high redshift. By measuring the average age of LRGs at two different redshifts, one can potentially measure the redshift interval corresponding to a time interval and thus measure the Hubble parameter H(z) ≈ −(1 + z)−1 Δ z/Δt (as in Jimenez & Loeb). The goal of this project is to measure directly the expansion rate of the universe at the redshift range 0.1 < z < 1.0 within 3% precision. We explore the age-dating of Sloan Digital Sky Survey LRGs using the stellar population models of Lick absorption line indices after stacking spectra in redshift bins to increase the signal-to-noise. We also use the method of full spectral fitting to measure the ages of LRGs observed with the Southern Africa Large Telescope (SALT).

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Stellar populations in Luminous Red Galaxies: cosmic chronometers?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310003480 ◽

2009 ◽

Vol 5 (S262) ◽

pp. 414-415

Author(s):

A. L. Ratsimbazafy ◽

C. M. Cress ◽

S. L. Blyth ◽

S. M. Crawford ◽

E. A. Olivier ◽

...

Keyword(s):

Stellar Population ◽

Spectral Synthesis ◽

Stellar Populations ◽

Age Dating ◽

Population Modelling ◽

Large Telescope ◽

Luminous Red Galaxies ◽

Red Galaxies ◽

Star Formation Histories ◽

The Universe

AbstractThe expansion rate of the Universe can potentially be measured using age-dating of Luminous Red Galaxies (LRGs). Here, we explore the validity of the assumptions implicit in this method using LRGs identified in the Millenium Simulation (MS). We use stellar population modelling and spectral synthesis to estimate the errors on ages that can be expected and discuss optimization of such an experiment. We find that H(z) using simulated galaxies from MS can be recovered with high accuracy. Using single stellar populations (SSPs) to age-date LRGs is not sufficient but if the MS star formation histories of galaxies are used, accurate ages are obtainable. We discuss an observing program to carry out this experiment using SALT (Southern African Large Telescope).

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