Using Quasars as Standard Candles for Studying Dark Energy
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Using Quasars as Standard Candles for Studying Dark Energy. / Denney, Kelly D.; Vestergaard, Marianne; Watson, D.; Davis, T.
I: American Astronomical Society, AAS Meeting #219, #440.20, Bind 219, 01.01.2012.Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning
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TY - JOUR
T1 - Using Quasars as Standard Candles for Studying Dark Energy
AU - Denney, Kelly D.
AU - Vestergaard, Marianne
AU - Watson, D.
AU - Davis, T.
PY - 2012/1/1
Y1 - 2012/1/1
N2 - We have recently demonstrated (Watson et al. 2011, ApJ, 740, L49) that quasars, or more generally active galactic nuclei (AGNs), can be used as standard candles for measuring distances in the universe, similar to Type Ia supernovae (SNe). Here, we present the initial findings of this new method, which relies on the technique of reverberation mapping to measure time delays between the quasar continuum and emission line variability signatures. Measuring this time delay effectively measures the radius between the central source and the emission-line gas. The emission line gas is photo-ionized by the continuum photons, and the radius to this emission-line region scales tightly with the nuclear luminosity - a consequence of the photoionization physics responsible for regulating the production of line-emitting photons. Hence, measuring the radius of the emission-line gas provides a measure of the intrinsic luminosity of the AGN, allowing for the determination of the AGN distance. Since AGNs are luminous and the emission line spectrum is easily visible at high redshifts (e.g., out to z 4), AGN-based distances can be used to extend the distance ladder past the SNe cutoff (z 1.5). This regime is where the power to distinguish the possible time dependence of the dark energy equation of state lies. We present our initial discovery AGN Hubble diagram of nearby reverberation mapped sources and discuss ways (1) to extend this in redshift and (2) to reduce the current scatter. We also present simulated forecasts demonstrating the power this method can have over, e.g., SNe, to constrain dark energy parameters by extending to higher redshifts than can currently be probed with any other technique.
AB - We have recently demonstrated (Watson et al. 2011, ApJ, 740, L49) that quasars, or more generally active galactic nuclei (AGNs), can be used as standard candles for measuring distances in the universe, similar to Type Ia supernovae (SNe). Here, we present the initial findings of this new method, which relies on the technique of reverberation mapping to measure time delays between the quasar continuum and emission line variability signatures. Measuring this time delay effectively measures the radius between the central source and the emission-line gas. The emission line gas is photo-ionized by the continuum photons, and the radius to this emission-line region scales tightly with the nuclear luminosity - a consequence of the photoionization physics responsible for regulating the production of line-emitting photons. Hence, measuring the radius of the emission-line gas provides a measure of the intrinsic luminosity of the AGN, allowing for the determination of the AGN distance. Since AGNs are luminous and the emission line spectrum is easily visible at high redshifts (e.g., out to z 4), AGN-based distances can be used to extend the distance ladder past the SNe cutoff (z 1.5). This regime is where the power to distinguish the possible time dependence of the dark energy equation of state lies. We present our initial discovery AGN Hubble diagram of nearby reverberation mapped sources and discuss ways (1) to extend this in redshift and (2) to reduce the current scatter. We also present simulated forecasts demonstrating the power this method can have over, e.g., SNe, to constrain dark energy parameters by extending to higher redshifts than can currently be probed with any other technique.
M3 - Journal article
VL - 219
JO - American Astronomical Society. Bulletin
JF - American Astronomical Society. Bulletin
SN - 0002-7537
ER -
ID: 44200573