OzDES Reverberation Mapping Program: CIV lags from six years of data

Abstract

We present 29 successfully recovered CIV time lags in Active Galactic Nuclei from the complete Dark Energy Survey Reverberation Mapping campaign. The AGN in this sample span a redshift range of 1.9<z<3.5. We successfully measure the velocity dispersion from the CIV spectral linewidth for 25 of these 29 sources, and use these to calculate new high-redshift black hole mass estimates, finding masses between 0.8 and 1.3 billion solar masses. We also identify a selection effect due to the duration of the survey that can impact the radius-luminosity relation derived from this and other (high-redshift) data. This paper represents the culmination of the OzDES CIV campaign.

Figures (8)

• Figure 1: An example of gold rated source, DES J022620.86-045946.48. In the photometric and spectroscopic lightcurves we can see that there is a long term smooth variation that is present in both lightcurves. This is an important feature in most high quality lag measurements. This leads to a posterior for the lag (top right) with a sharp peak in both JAVELIN and ICCF. The smaller broader peaks at $\sim$180 days and $\sim$540 days correspond to seasonal gaps and are likely caused by aliasing.
• Figure 2: An example of silver rated source, DES J002959.21-434835.24. In the original photometric and spectroscopic lightcurves we can see that there is a long term variation present in the photometric lightcurve, however in this case there is a less obvious signal in the spectroscopic lightcurve. This leads to a posterior for the lag with a sharp peak in both JAVELIN and ICCF accompanied by many smaller peaks. These smaller peaks are likely caused by aliasing given their location, however, since there is much more of the probability contained within them, this example is rated as having a lower quality lag measurement than the example shown in \ref{['fig:goldexample']}.
• Figure 3: An example of bronze rated source, DES J032703.62-274425.27. In the photometric and spectroscopic lightcurves we can see that there is a variation in both lightcurves, however, with a generally lower signal-to-noise than seen in \ref{['fig:goldexample', 'fig:silverexample']}, and very little temporal overlap due to seasonal gaps. This leads to a posterior for the lag with multiple sharp peaks in both JAVELIN and ICCF, however, the most prominent peak in both are the same, giving credibility to this measurement, albeit at lower confidence than the silver and gold samples.
• Figure 4: Spectra for all successfully recovered Civ sources. Note that the OzDES spectrum spans the wavelength range 3800-8800Å, however, for visibility the plotting range has been restricted to 3800-7500Å. The Civ line appears at $\sim$4537Å in the lowest redshift source and progresses toward the right as redshift increases (darker red indicates higher redshift). Some spectra show absorption features in the Civ line, which were severe enough in four sources to prevent an accurate linewidth measurement (see Table \ref{['tab:BHM_results']}).
• Figure 5: The distribution of recovered rest frame lags and redshifts compared to the expected distribution of the OzDES sample based on historic $R-L$ relation estimates Grier2019. Note that it appears to be difficult to recover lags above a redshift $z=2.8$, with only one recovery out of a possible $\sim$30, with no gold measurements above $z=2.35$. This is likely due to low intrinsic variability of high-luminosity sources, the low signal-to-noise of high-redshift measurements, and time limit due to the maximum survey duration.