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  1. OA@INAF
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  3. 1 CONTRIBUTI IN RIVISTE (Journal articles)
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Please use this identifier to cite or link to this item: http://hdl.handle.net/20.500.12386/28938
Title: Setting the Stage for Cosmic Chronometers. I. Assessing the Impact of Young Stellar Populations on Hubble Parameter Measurements
Authors: Moresco, Michele
Jimenez, Raul
Verde, Licia
POZZETTI, Lucia 
CIMATTI, ANDREA
Citro, Annalisa
Issue Date: 2018
Journal: THE ASTROPHYSICAL JOURNAL 
Number: 868
Issue: 2
First Page: 84
Abstract: The expansion history of the universe can be constrained in a cosmology-independent way by measuring the differential age evolution of cosmic chronometers. This yields a measurement of the Hubble parameter H(z) as a function of redshift. The most reliable cosmic chronometers known so far are extremely massive and passively evolving galaxies. Age-dating these galaxies is, however, a difficult task, and even a small contribution of an underlying young stellar population could, in principle, affect the age estimate and its cosmological interpretation. We present several spectral indicators to detect, quantify, and constrain such contamination in old galaxies and study how their combination can be used to maximize the purity of cosmic chronometers selection. In particular, we analyze the Ca II H/K ratio, the presence (or absence) of Hα and [O II] emission lines, higher-order Balmer absorption lines, and UV flux; each indicator is especially sensitive to a particular age range, allowing us to detect young components ranging between 10 Myr and 1 Gyr. The combination of these indicators minimizes the contamination to a level below 1% in the case of ideal data. More importantly, it offers a way to control the systematic error on H(z) as a function of the contamination by young stellar populations. We show that for our previous measurements of the Hubble parameter, the possible bias induced by the presence of a younger component is well below the current errors. We envision that these indicators will be instrumental in paving the road for a robust and reliable dating of the old population and its cosmological interpretation.
URI: http://hdl.handle.net/20.500.12386/28938
URL: https://iopscience.iop.org/article/10.3847/1538-4357/aae829
ISSN: 0004-637X
DOI: 10.3847/1538-4357/aae829
Bibcode ADS: 2018ApJ...868...84M
Fulltext: open
Appears in Collections:1.01 Articoli in rivista

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