Constraints On Duty Cycles Of Quasars At Z $\sim$ 6

TL;DR

This study investigates the duty cycle and beaming angles of quasars at redshift around 6 by analyzing CII line observations, revealing that current constraints are highly sensitive to assumptions about cold gas dynamics.

Contribution

It introduces a method to constrain quasar duty cycles and beaming angles at high redshift using CII line data, highlighting the importance of cold gas dynamics.

Findings

Most likely quasar duty cycle is less than 1%.

Constraints are highly sensitive to cold gas velocity assumptions.

A second solution with full duty cycle appears under certain priors.

Abstract

We study the mass of quasar-hosting dark matter halos at z $\sim$ 6 and further constrain the fraction of dark matter halos hosting an active quasar $f_{on}$ and the quasar beaming angle $i_{\rm max}$ using observations of CII lines in the literature. We make assumptions that (1) more massive halos host brighter quasars, (2) a fraction of the halos host active quasars with a certain beaming angle, (3) cold gas in galaxies has rotational velocity $V_{\rm circ}=\alpha V_{\rm max}$, and that (4) quasars point randomly on the sky. We find that for a choice of specific $\alpha \gtrsim 1$, the most likely solution has $f_{\rm on} < 0.01$, corresponding to a small duty cycle of quasar activity. However, if we marginalize over $\alpha$, for some choices of a prior a second solution with $f_{\rm on}=1$ appears. Overall, our the constraints are highly sensitive to $\alpha$ and hence inconclusive. Stronger constraints on $f_{\rm on}$ can be made if we better understand the dynamics of cold gas in these galaxies.