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

TL;DR

Using HST/COS UV spectra of 428 AGN and focusing on intrinsic NV absorbers within $|v_{ ext{offset}}|\, ext{≤}\,5000\, ext{km s}^{-1}$ of the NV emission line, the study assembles a Type 1 quasar subsample of 175 with partial coverage, including 34 radio-loud and 133 radio-quiet objects. They detect 77 NV NALs and 1 BAL across these quasars, with $~27\%$ of objects hosting at least one intrinsic NV system; importantly, the incidence in radio-loud quasars is only $\sim6\%$ compared to $\sim29\%$ in radio-quiet quasars, a deficit with probability $<0.1\%$ under an equal-likelihood assumption. FIRST imaging reveals that most radio-loud sources are core-dominated, implying sightlines near the poles, which supports orientation-based explanations for the NV deficit. The authors discuss archive biases and propose physical scenarios in which jet-driven ionization and wind geometry reduce the visibility of NV absorbers along polar lines of sight, with implications for quasar wind structure and feedback models.

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.

Figures (40)

• Figure 1: Distribution of optical ($3000$$\hbox{\AA}$), radio (5 GHz), and X-ray (2 keV) luminosities, and the radio-loudness parameter for the 428 quasars. The unshaded regions represent radio-loud quasars. The red shaded regions represent radio-quiet quasars. The blue shaded regions represent quasars that did not have a radio detection, and so only have an upper limit on $L_{\nu }$(5 GHz). The three regions are not cumulative. The combination of the three regions represents all quasars.
• Figure 3: Distribution of optical ($3000$$\hbox{\AA}$), radio (5 GHz), and X-ray (2 keV) luminosities, and the radio-loudness parameter for quasars whose spectra at least partially cover the N v associated region. These quasars form our subsample. The unshaded regions represent radio-loud quasars. The red shaded regions represent radio-quiet quasars. The blue shaded regions represent quasars that did not have a radio detection, and so only have an upper limit on $L_{\nu }$(5 GHz). The three regions are not cumulative. The combination of the three regions represents all quasars.
• Figure 4: Comparison of the properties of the intrinsic systems ($EW$ and $v_{offset}$) vs the properties of the host quasars ($z_{Em}$, $L(2$ keV), $L(3000$$\hbox{\AA}$), $L(5$ GHz), $\mathcal{R}$). Blue points represent quasars that have a radio detection, while red points represents quasars that did not, and so only have an upper limit for the radio luminosity.
• Figure 5: A pair plot of quasar properties ($z_{Em}$, $L(X-ray)$, $L(optical)$, $L(radio)$, $\mathcal{R}$) in the survey. The blue points represent quasars without an intrinsic NAL, and the red points represent those quasars containing at least one intrinsic system. All quasars within our sample that have an intrinsic NAL present in their spectra are radio-quiet quasars.
• Figure 6: Distribution of the radio-loudness parameter, $\mathcal{R}$, for the quasars in our subsample. The black shaded region corresponds to the quasars with one or more intrinsic N v systems, while the non-shaded region corresponds to quasars without an intrinsic N v system. The delimiter between radio-loud quasars and radio-quiet quasars is $\mathcal{R}=10$, denoted in the figure with a dashed red vertical line. Only two radio-loud quasars feature an intrinsic N v system.