The performance of photometric reverberation mapping at high redshift and the reliability of damped random walk models

S C Read,D J B Smith,M J Jarvis,G Gürkan

doi:10.1093/mnras/stz3574

Abstract

ABSTRACT Accurate methods for reverberation mapping using photometry are highly sought after since they are inherently less resource intensive than spectroscopic techniques. However, the effectiveness of photometric reverberation mapping for estimating black hole masses is sparsely investigated at redshifts higher than z ≈ 0.04. Furthermore, photometric methods frequently assume a damped random walk (DRW) model, which may not be universally applicable. We perform photometric reverberation mapping using the javelin photometric DRW model for the QSO SDSS-J144645.44+625304.0 at z = 0.351 and estimate the Hβ lag of $65^{+6}_{-1}$ d and black hole mass of $10^{8.22^{+0.13}_{-0.15}}\, \mathrm{M_{\odot }}$. An analysis of the reliability of photometric reverberation mapping, conducted using many thousands of simulated CARMA process light curves, shows that we can recover the input lag to within 6 per cent on average given our target’s observed signal-to-noise of &gt;20 and average cadence of 14 d (even when DRW is not applicable). Furthermore, we use our suite of simulated light curves to deconvolve aliases and artefacts from our QSO’s posterior probability distribution, increasing the signal-to-noise on the lag by a factor of ∼2.2. We exceed the signal-to-noise of the Sloan Digital Sky Survey Reverberation Mapping Project (SDSS-RM) campaign with a quarter of the observing time per object, resulting in a ∼200 per cent increase in signal-to-noise efficiency over SDSS-RM.

Highlights

All active galactic nuclei (AGNs) are believed to be powered by an accretion disc around a central supermassive black hole (SMBH), which is itself surrounded by a broad-line region (BLR; Antonucci 1993; Urry & Padovani 1995; Ho 2008; Heckman & Best 2014)
The first observation we can make is that JAVELIN does perform worse when the input light curve is not a damped random walk (DRW) process, as JAVELIN assumes
We see that the model-independent Von Neumann estimator recovers lags with an accuracy very similar to that of JAVELIN (4 per cent), when not assuming DRW

Summary

Introduction

All active galactic nuclei (AGNs) are believed to be powered by an accretion disc around a central supermassive black hole (SMBH), which is itself surrounded by a broad-line region (BLR; Antonucci 1993; Urry & Padovani 1995; Ho 2008; Heckman & Best 2014). In the absence of a direct black hole mass measurement, there exist scaling relations based on emission line widths (e.g. Hβ: Wandel, Peterson & Malkan 1999 and Mg II: McLure & Jarvis 2002) and luminosity at 5100 Å (e.g. Bentz et al 2013) These relations are typically calibrated at low redshift and have not been extended to high redshift 2017) despite widespread extrapolated use at high redshift (McLure & Dunlop 2004; Vestergaard 2004; Vestergaard & Peterson 2006; Netzer et al 2007; Runnoe et al 2013; Feng, Shen & Li 2014; Mejıa-Restrepo et al 2016) It is for the purposes of validating these scaling relations that more black hole mass measurements at higher redshifts are needed. Assuming that the BLR is gravitationally dominated by the SMBH, it is possible to estimate the black hole mass from the time delay between continuum emission from the accretion disc and the reprocessed emission from the BLR, known as the ‘lag’, from the Keplerian motion equation

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Conclusion