A strategy to measure the dark energy equation of state using the H ii galaxy Hubble function and X-ray active galactic nuclei clustering: preliminary results

Abstract

We explore the possibility of setting stringent constraints to the dark energy equation of state using alternative cosmic tracers like (a) the Hubble relation using H ii galaxies, which can be observed at much higher redshifts (z≲ 3.5) than those currently traced by Type Ia supernovae (SNeIa) samples, and (b) the large‐scale structure using the clustering of X‐ray selected active galactic nuclei (AGN), which have a redshift distribution peaking at z∼ 1. In this paper we use extensive Monte Carlo simulations to define the optimal strategy for the recovery of the dark energy equation of state using the high‐redshift (z≳ 2) Hubble relation, but accounting also for the effects of gravitational lensing, which for such high redshifts can significantly affect the derived cosmological constraints. We investigate the size of the sample of high‐z H ii galaxies needed to provide useful constraints in the dark energy equation of state. Based on a ‘figure of merit’ analysis, we provide estimates for the number of 2 ≲z≲ 3.5 tracers needed to reduce the cosmological solution space, presently provided by the Constitution SNIa set, by a desired factor. The analysis is given for any level of rms distance modulus uncertainty and we find that an expected reduction (i.e. by ∼20–40 per cent) of the current level of H ii‐galaxy‐based distance modulus uncertainty does not provide a significant improvement in the derived cosmological constraints. It is much more efficient to increase the number of tracers than to reduce their individual uncertainties. Finally, we propose a framework to put constraints on the dark energy equation of state by using the joint likelihood of the X‐ray AGN clustering and of the Hubble relation cosmological analyses. A preliminary joint analysis using the X‐ray AGN clustering of the 2XMM survey and the Hubble relation of the Constitution SNIa set provide Ωm= 0.31 ± 0.01 and w=−1.06 ± 0.05. We also find that the joint SNIa–2XMM analysis provides significantly more stringent cosmological constraints, increasing the figure of merit by a factor of ∼2, with respect to that of the joint SNIa–baryonic acoustic oscillation analysis.

The environment of HII galaxies revisited

“…L(Hβ) and the ionized gas velocity dispersion σ (see Terlevich & Melnick 1981;Melnick et al 1988;Fuentes-Masip et al 2000;Telles et al 2001;Bosch et al 2002;Siegel et al 2005;Bordalo & Telles 2011) renders them alternative cosmological distance probes. In Plionis et al (2011) we presented a thorough investigation of the viability of using HII galaxies to constrain the dark energy equation of state and they indeed appear to be a prominent cosmological probe (see also Melnick et al 2000;Siegel et al 2005). This was clearly verified by using them to estimate the Hubble constant, finding a value H 0 = 74.3 ± 4.3 km s −1 Mpc −1 (Chávez et al 2012), in excellent agreement with, and independently confirming, the most recent SNIa based results (Riess et al 2011;Freedman et al 2012).…”

Direct measurement of lensing amplification in Abell S1063 using a strongly lensed high redshift HII galaxy

“…The L − σ relation spans more than three orders of magnitude in luminosity, which allows us to observe a significant number of objects at large redshifts without recourse to gravitational telescopes; hence this accounts for the power of the relation as a cosmological probe (Plionis et al 2011;Terlevich et al 2015;Chávez et al 2016). But, of course, only the most luminous HII galaxies can be observed at higher redshifts with the current generation of 8−10 m telescopes, so gravitationally amplified objects such as ID11 provide us with the unique chance to verify that at high redshift the correlation holds also for low luminosity and possibly low metallicity HII galaxies.…”

A two-point diagnostic for the H ii galaxy Hubble diagram

“…More recently, Plionis et al (2011) and Terlevich et al (2015) demonstrated that the L(Hβ) − σ correlation is a viable high-z tracer, and used a compilation of 156 combined sources, including 24 GEHRs, 107 local HIIGx, and 25 high-z HIIGx, to constrain the parameters in ΛCDM, producing results consistent with Type Ia SNe. Most recently, we (Wei et al 2017) extended this very promising work even further by demonstrating that GEHRs and HIIGx may be utilized, not only to refine and confirm the parameters in the standard model but-perhaps more importantly-to compare and test the predictions of competing cosmologies, such as ΛCDM and the R h = ct universe (Melia 2003(Melia , 2007(Melia , 2013a(Melia , 2016(Melia , 2017aMelia & Abdelqader 2009;Melia & Shevchuk 2012).…”

“…The exact cause of the correlation between the luminosity L(Hβ) in Hβ and the ionized gas velocity dispersion σ is not yet fully understood, though an explanation may be found in the fact that the gas dynamics is almost certainly dominated by the gravitational potential of the ionizing star and its surrounding environment (Terlevich & Melnick 1981). These sources may therefore function as standard candles because the scatter in the L(Hβ) versus σ relation appears to be small enough for HIIGx and GEHRs to probe the cosmic distance scale independently of z (Melnick et al 1987 Melnick et al 2000;Bosch et al 2002;Telles 2003;Siegel et al 2005;Bordalo & Telles 2011;Plionis et al 2011;Mania & Ratra 2012;Chávez et al 2012Chávez et al , 2014Terlevich et al 2015).…”