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Register a new userAn HI absorbing circumnuclear disk in Cygnus A
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We present Very Long Baseline Array (VLBA) HI absorption observations of the core region of the powerful radio galaxy Cygnus A. These data show both broad (FWHM = 231 pm 21 km/s) and narrow (FWHM <30 km/s) velocity width absorption components. The broad velocity absorption shows high opacity on the counter jet, low opacity against the core and no absorption on the jet side. We argue that these results are most naturally explained by a circumnuclear HI absorbing disk orientated roughly perpendicular to the jet axis. We estimate that the HI absorbing gas lies at a radius of ~80 pc has a scale height of about 20 pc, density n > 10^{4} cm^{-3} and total column density in the range 10^{23}-10^{24} cm^{-2}. Models in which the HI absorption is primarily from an atomic or a molecular gas phase can both fit our data. Modelling taking into account the effective beam shows that the broad HI absorbing gas component does not cover the radio core in Cygnus A and therefore does not contribute to the gas column that blocks our view of the hidden quasar nucleus. If however Cygnus A were observed from a different direction, disk gas on ~100 pc radius scales would contribute significantly to the nuclear column density, implying that in some radio galaxies gas on these scales may contribute to the obscuration of the central engine. We argue that the circumnuclear torus in Cygnus A contains too little mass to power the AGN over > 10^{7} yr but that material in the outer HI absorbing gas disk can provide a reservoir to fuel the AGN and replenish torus clouds. The second narrow HI absorption component is significantly redshifted (by 186km/s) with respect to the systemic velocity and probably traces infalling gas which will ultimately fuel the source. [abridged]
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We report on the detection of three strong HI absorbers originating in the outskirts (i.e., impact parameter, $rho_{rm cl} approx (1.6-4.7) r_{500}$) of three massive ($M_{500}sim3times10^{14} M_{odot}$) clusters of galaxies at redshift $z_{rm cl} approx 0.46$, in the $Hubble Space Telescope$ Cosmic Origins Spectrograph ($HST$/COS) spectra of 3 background UV-bright quasars. These clusters were discovered by the 2500 deg$^2$ South Pole Telescope Sunyaev$-$Zeldovich (SZ) effect survey. All three COS spectra show partial Lyman limit absorber with $N(HI) > 10^{16.5} rm cm^{-2}$ near the photometric redshifts ($|Delta z/(1+z)| approx 0.03$) of the clusters. The compound probability of random occurrence of all three absorbers is $<0.02$%, indicating that the absorbers are most likely related to the targeted clusters. We find that the outskirts of these SZ-selected clusters are remarkably rich in cool gas compared to existing observations of other clusters in the literature. The effective Doppler parameters of the Lyman series lines, obtained using single cloud curve-of-growth (COG) analysis, suggest a non-thermal/turbulent velocity of a few $times10 rm km s^{-1}$ in the absorbing gas. We emphasize the need for uniform galaxy surveys around these fields and for more UV observations of QSO-cluster pairs in general in order to improve the statistics and gain further insights into the unexplored territory of the largest collapsed cosmic structures.
We present the results of the latest NuSTAR monitoring campaign of the Compton-thick Seyfert 2 galaxy NGC 1068, composed of four $sim$50 ks observations performed between July 2017 and February 2018 to search for flux and spectral variability on timescales from 1 to 6 months. We detect one unveiling and one eclipsing event with timescales less than 27 and 91 days, respectively, ascribed to Compton-thick material with $N_H=(1.8pm0.8)times10^{24}$ cm$^{-2}$ and $N_Hgeq(2.4pm0.5)times10^{24}$ cm$^{-2}$ moving across our line of sight. This gas is likely located in the innermost part of the torus or even further inward, thus providing further evidence of the clumpy structure of the circumnuclear matter in this source. Taking advantage of simultaneous Swift-XRT observations, we also detected a new flaring ULX, at a distance $dsim$30 (i.e. $sim$2 kpc) from the nuclear region of NGC 1068, with a peak X-ray intrinsic luminosity of $(3.0pm0.4)times10^{40}$ erg s$^{-1}$ in the 2-10 keV band.
We study the particle energy distribution in the cocoon surrounding Cygnus A, using radio images between 151 MHz and 15 GHz and a 200 ks Chandra ACIS-I image. We show that the excess low frequency emission in the the lobe further from Earth cannot be explained by absorption or excess adiabatic expansion of the lobe or a combination of both. We show that this excess emission is consistent with emission from a relic counterlobe and a relic counterjet that are being re-energized by compression from the current lobe. We detect hints of a relic hotspot at the end of the relic X-ray jet in the more distant lobe. We do not detect relic emission in the lobe nearer to Earth as expected from light travel-time effects assuming intrinsic symmetry. We determine that the duration of the previous jet activity phase was slightly less than that of the current jet-active phase. Further, we explain some features observed at 5 and 15 GHz as due to the presence of a relic jet.
We present the images and kinematics of circumnuclear molecular gas from 100 pc scale down to 10 pc scale in nearby active galactic nuclei (AGNs) using the Submillimeter Array (SMA) and the Plateau de Bure Interferometer (PdBI). We have observed several nearby galaxies that host AGNs, such as the nearest radio galaxy Centaurus A (NGC 5128), the Seyfert 2 galaxy M51 (NGC 5194), the Seyfert 2 galaxy NGC 1068, the Seyfert 1 galaxy NGC 1097, and the Seyfert 2 / starburst composite galaxy NGC 4945, in CO lines to see whether the molecular gas distribution, kinematics, and physical conditions at 10 - 100 pc scale follows the AGN unified model or not. In 100 pc scale, most of the circumnuclear molecular gas shows smooth velocity gradient, suggesting a regular rotating feature, and also shows abnormal line ratios, suggesting the existence of active sources to make the circumnuclear molecular gas dense and/or warm conditions or abnormal chemical compositions. In 10 pc scale, on the other hand, the molecular gas kinematics shows various characteristics, some shows very disturbed kinematics such as a jet-entrained feature in the galaxies that have jets, but some still shows regular rotation feature in a galaxy that does not have obvious jets. These results indicate that the kinematics and physical/chemical conditions of the circumnuclear molecular gas at the scale less than 100 pc is highly affected by the AGN activities, and at this scale, there is no clear evidence of any unified feature seen in the circumnuclear molecular gas.
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