Setting the Stage for Cosmic Chronometers. II. Impact of Stellar Population Synthesis Models Systematics and Full Covariance Matrix. (arXiv:2003.07362v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Moresco_M/0/1/0/all/0/1">Michele Moresco</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jimenez_R/0/1/0/all/0/1">Raul Jimenez</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Verde_L/0/1/0/all/0/1">Licia Verde</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cimatti_A/0/1/0/all/0/1">Andrea Cimatti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pozzetti_L/0/1/0/all/0/1">Lucia Pozzetti</a>
The evolution of differential ages of passive galaxies at different redshifts
(cosmic chronometers) has been proved to be a method potentially able to
constrain the Hubble parameter in a cosmology-independent way, but the
systematic uncertainties must be carefully evaluated. In this paper, we compute
the contribution to the full covariance matrix of systematic uncertainties due
to the choice of initial mass function, stellar library, and metallicity,
exploring a variety of stellar population synthesis models; the effect of a
residual young component and star formation history was discussed elsewhere.
Through simulations in the redshift range 0<z<1.5 we find that the choice of
the stellar population synthesis model dominates the total error budget on
H(z), with contributions at ~4.5% level, discarding the most discordant model.
The contribution due to the choice of initial mass function is <0.5%, while
that due to the stellar library is ~6.6% on average. In parallel, we also
assess the impact of an uncertainty in the determination of the stellar
metallicity, finding that an error of ~10% (5%) on the stellar metallicity
propagates to a 9% (4%) error on H(z). These results are used to provide the
combined contribution of these systematic effects on the error budget. For
current H(z) measurements, where the uncertainties due to metallicity and star
formation history were already included, we show that, using the more modern
stellar libraries, the additional systematic uncertainty is between 5.4% (at
z=0.2) and 2.3% (at z=1.5). To reach the goal of keeping the systematic error
budget below the 1% level we discuss that efforts needed to obtain higher
resolution and signal-to-noise spectra and improvements in the modeling of
stellar population synthesis.
The evolution of differential ages of passive galaxies at different redshifts
(cosmic chronometers) has been proved to be a method potentially able to
constrain the Hubble parameter in a cosmology-independent way, but the
systematic uncertainties must be carefully evaluated. In this paper, we compute
the contribution to the full covariance matrix of systematic uncertainties due
to the choice of initial mass function, stellar library, and metallicity,
exploring a variety of stellar population synthesis models; the effect of a
residual young component and star formation history was discussed elsewhere.
Through simulations in the redshift range 0<z<1.5 we find that the choice of
the stellar population synthesis model dominates the total error budget on
H(z), with contributions at ~4.5% level, discarding the most discordant model.
The contribution due to the choice of initial mass function is <0.5%, while
that due to the stellar library is ~6.6% on average. In parallel, we also
assess the impact of an uncertainty in the determination of the stellar
metallicity, finding that an error of ~10% (5%) on the stellar metallicity
propagates to a 9% (4%) error on H(z). These results are used to provide the
combined contribution of these systematic effects on the error budget. For
current H(z) measurements, where the uncertainties due to metallicity and star
formation history were already included, we show that, using the more modern
stellar libraries, the additional systematic uncertainty is between 5.4% (at
z=0.2) and 2.3% (at z=1.5). To reach the goal of keeping the systematic error
budget below the 1% level we discuss that efforts needed to obtain higher
resolution and signal-to-noise spectra and improvements in the modeling of
stellar population synthesis.
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