Reporting a Deficit of Intrinsic NV Absorbers in Core-dominated, Radio-loud Quasars

TL;DR

This study investigates the scarcity of intrinsic NV absorption systems in core-dominated, radio-loud quasars compared to radio-quiet ones, suggesting orientation effects influence the detection of these systems.

Contribution

It provides the first statistical evidence of a deficit of intrinsic NV absorbers in radio-loud quasars and links this to orientation effects based on radio morphology.

Findings

Significant lower incidence of NV systems in radio-loud quasars (6%) compared to radio-quiet (29%).

Radio morphology indicates face-on orientation for most radio-loud quasars, affecting NV absorption detection.

Orientation effects likely cause the observed deficit of NV absorbers in radio-loud quasars.

Abstract

We searched the Hubble Space Telescope Cosmic Origins Spectrograph archive for ultraviolet spectra of 428 AGN to identify intrinsic NV absorption systems. We filtered out Type 2 AGN, blazars, and spectra that do not cover at least part of the velocity window from 5000 km/s blueward to 5000 km/s redward (hereafter, the ``associated'' region) of the NV emission line. This yielded 175 Type 1 quasars, 34 radio-loud, 133 radio-quiet, and eight unconstrained. Our survey uncovered 77 associated NV systems in the spectra of 48 of these low-redshift quasars. We consider the incidence of intrinsic absorbers as a function of quasar properties (optical, radio and X-ray). We find a statistically significant dearth of intrinsic NV systems in the spectra of the 34 radio-loud quasars (6%), compared to 29% of the 133 radio-quiet quasars containing at least one intrinsic system. Assuming intrinsic systems are equally likely to occur in radio-loud and radio-quiet quasars and the orientations of the two subsamples are comparable, there is a 0.1% probability of such a deficit occurring by chance in the radio-loud population. We propose that this deficit of systems is caused by orientation effects. FIRST radio images are available for 14 of the 33 radio-loud quasars. These show that only three of the 14 radio-loud quasars have lobe-dominated morphologies, whereas 11 of the 14 radio-loud quasars have compact radio morphologies, implying that these quasars are face on, and suggesting that clouds that produce NV absorption are rarely found along the polar axis.