scholarly journals Broad He i 1.08-µm absorption from the obscurer in the active galaxy NGC 5548

2020 ◽  
Vol 500 (2) ◽  
pp. 2063-2075
Author(s):  
Conor Wildy ◽  
Hermine Landt ◽  
Martin J Ward ◽  
Bożena Czerny ◽  
Daniel Kynoch

ABSTRACT The nucleus of the active galaxy NGC 5548 was the target of two intensive spectroscopic monitoring campaigns at X-ray, ultraviolet (UV), and optical frequencies in 2013/2014. These campaigns detected the presence of a massive obscuration event. In 2016/2017, Landt et al. conducted a near-IR spectroscopic monitoring campaign on NGC 5548 and discovered He i  1.08-μm absorption. Here, we decompose this absorption into its components and study its time variability. We attribute the narrow He  i absorption lines to the warm absorber (WA) and, as for the newly appeared low-ionization WA lines in the UV, their presence is most likely due to a reduction in ionization parameter caused by the obscurer. The observed variability of the narrow He i absorption is consistent with what is expected for the WA. Most importantly, we also detect fast, broad He i absorption, which we attribute to the obscurer. This He i broad absorption, which is indicative of a high column density gas, is unsaturated and variable on time-scales of a few months. The observed variability of the obscurer is mainly due to changes in ionization, although density changes also play a role. We test the physical cycle model of Dehghanian et al. which proposes that helium recombination can account for how the obscurer influences the physics of the WA gas. Our results support their model, but also indicate that the reality might be more complex.

2003 ◽  
Vol 212 ◽  
pp. 253-254
Author(s):  
Watson P. Varricatt ◽  
Peredur M. Williams ◽  
Nagarhalli M. Ashok

The near-IR spectrum of the periodic dust making WCpd+O4-5 binary WR 140 was monitored to cover the 2001 periastron passage and maximum colliding-wind activity. The He i λ1.083μm emission-line profile showed the appearence of a subpeak on epochs close to periastron passage. The evolution of the subpeak was consistent with the motion of the stars and the colliding wind region. The appearance and evolution of the emission subpeak suggests that the theoretical 1/r dependence of X-ray flux does not hold, so that there is no need to change the values of eccentricity and epoch of periastron passage derived from the RV orbit. JHK spectra show variations of the continuum and and dilution of the emission lines, in agreement with the production and cooling of dust.


1995 ◽  
Vol 10 ◽  
pp. 629-630 ◽  
Author(s):  
R. Schulz ◽  
Th. Encrenaz ◽  
J.A. Stüwe ◽  
G. Wiedemann

2001 ◽  
Vol 368 (1) ◽  
pp. 44-51 ◽  
Author(s):  
P. Severgnini ◽  
G. Risaliti ◽  
A. Marconi ◽  
R. Maiolino ◽  
M. Salvati

2020 ◽  
Vol 15 (S359) ◽  
pp. 17-21
Author(s):  
Karín Menéndez-Delmestre ◽  
Laurie Riguccini ◽  
Ezequiel Treister

AbstractThe coexistence of star formation and AGN activity has geared much attention to dusty galaxies at high redshifts, in the interest of understanding the origin of the Magorrian relation observed locally, where the mass of the stellar bulk in a galaxy appears to be tied to the mass of the underlying supermassive black hole. We exploit the combined use of far-infrared (IR) Herschel data and deep Chandra ˜160 ksec depth X-ray imaging of the COSMOS field to probe for AGN signatures in a large sample of >100 Dust-Obscured Galaxies (DOGs). Only a handful (˜20%) present individual X-ray detections pointing to the presence of significant AGN activity, while X-ray stacking analysis on the X-ray undetected DOGs points to a mix between AGN activity and star formation. Together, they are typically found on the main sequence of star-forming galaxies or below it, suggesting that they are either still undergoing significant build up of the stellar bulk or have started quenching. We find only ˜30% (6) Compton-thick AGN candidates (NH > 1024 cm–2), which is the same frequency found within other soft- and hard-X-ray selected AGN populations. This suggests that the large column densities responsible for the obscuration in Compton-thick AGNs must be nuclear and have little to do with the dust obscuration of the host galaxy. We find that DOGs identified to have an AGN share similar near-IR and mid-to-far-IR colors, independently of whether they are individually detected or not in the X-ray. The main difference between the X-ray detected and the X-ray undetected populations appears to be in their redshift distributions, with the X-ray undetected ones being typically found at larger distances. This strongly underlines the critical need for multiwavelength studies in order to obtain a more complete census of the obscured AGN population out to higher redshifts. For more details, we refer the reader to Riguccini et al. (2019).


Nature ◽  
1987 ◽  
Vol 325 (6106) ◽  
pp. 696-698 ◽  
Author(s):  
Ian McHardy ◽  
Bozena Czerny

2012 ◽  
Vol 08 ◽  
pp. 151-162 ◽  
Author(s):  
ALAN P. MARSCHER

Relativistic jets in blazars on parsec scales can now be explored with direct imaging at radio wavelengths as well as observations of time variability of flux and linear polarization at various wavebands. The results thus far suggest that the millimeter-wave "core" is usually a standing, conical shock and that the jet plasma is turbulent. Disturbances and turbulent plasma crossing the standing shock can explain much of the observed variability, as well as the appearance of bright knots moving down the jet at superluminal apparent speeds. The core, located parsecs downstream of the central engine, appears to be the site of many of the outbursts observed at optical, X-ray, and γ-ray energies. Rotations in the optical polarization position angle prior to the passage of a knot through the millimeter-wave core provide evidence for helical magnetic fields that accelerate and collimate the jet before turbulence tangles the fields.


Author(s):  
W.N. Brandt ◽  
D.M. Alexander ◽  
F.E. Bauer ◽  
C. Vignali
Keyword(s):  
X Ray ◽  

Sign in / Sign up

Export Citation Format

Share Document