scholarly journals H i absorption towards radio active galactic nuclei of different accretion modes

2020 ◽  
Vol 494 (4) ◽  
pp. 5161-5177
Author(s):  
Yogesh Chandola ◽  
D J Saikia ◽  
Di Li
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
High Excitation ◽  
Host Galaxies ◽  
Detection Rates ◽  
Systemic Velocity ◽  
Wide Range ◽  
Significant Difference ◽  
Absorption Experiment

ABSTRACT We present results of H i absorption experiment done using the Giant Metrewave Radio Telescope (GMRT) towards 27 low- and intermediate-luminosity ($P_{\rm 1.4 GHz}\, \sim 10^{23}$-1026 W Hz−1) radio active galactic nuclei (AGNs), classified as either low excitation radio galaxies (LERGs) or high excitation radio galaxies (HERGs) and with WISE colour W2[4.6 μm]−W3[12  μm]> 2. We report H i absorption detection towards seven radio AGNs, six of which are new. Combined with other sources from literature classified as LERGs or HERGs, we confirm our earlier result that compact radio AGNs with WISE colour W2−W3 > 2 have higher detection rates compared to those with W2−W3 < 2. We find that H i absorption detection rate is higher for HERGs (37.0$^{+15.8}_{-11.5}$ per cent) compared to LERGs (22.0$^{+3.9}_{-3.4}$ per cent), mainly due to a larger fraction of HERGs being gas and dust rich with a younger stellar population compared to LERGs. However, for similar compact radio structures and host galaxies with WISE colours W2−W3 > 2, we don’t find any significant difference in detection rates of two types of AGNs implying detection of H i gas may not necessarily mean high excitation mode AGN. We further analysed the kinematics towards these sources. We find that while LERGs show a wide range in the shift of centroid velocities ($\sim \, -$479 to +356 km s−1) relative to the optical systemic velocity, most of the HERGs have centroid velocity shift less than 200 km s−1, possibly due to differences in jet-interstellar medium interaction.

scholarly journals LoTSS DR1: Double-double radio galaxies in the HETDEX field

2019 ◽  
Vol 622 ◽  
pp. A13 ◽  
Author(s):  
V. H. Mahatma ◽  
M. J. Hardcastle ◽  
W. L. Williams ◽  
P. N. Best ◽  
J. H. Croston ◽  
...  
Keyword(s):  
Life Cycle ◽  
Active Galactic Nuclei ◽  
Galaxy Evolution ◽  
Control Sample ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Host Galaxy ◽  
Host Galaxies ◽  
Significant Difference ◽  
Double Radio Galaxies

Context. Double-double radio galaxies (DDRGs) represent a short but unique phase in the life-cycle of some of the most powerful radio-loud active galactic nuclei (RLAGN). These galaxies display large-scale remnant radio plasma in the intergalactic medium left behind by a past episode of active galactic nuclei (AGN) activity, and meanwhile, the radio jets have restarted in a new episode. The knowledge of what causes the jets to switch off and restart is crucial to our understanding of galaxy evolution, while it is important to know if DDRGs form a host galaxy dichotomy relative to RLAGN. Aims. The sensitivity and field of view of LOFAR enables the observation of DDRGs on a population basis rather than single-source observations. Using statistical comparisons with a control sample of RLAGN, we may obtain insights into the nature of DDRGs in the context of their host galaxies, where physical differences in their hosts compared to RLAGN as a population may allow us to infer the conditions that drive restarting jets. Methods. We utilised the LOFAR Two-Metre Sky Survey (LoTSS) DR1, using a visual identification method to compile a sample of morphologically selected candidate DDRGs, showing two pairs of radio lobes. To confirm the restarted nature in each of the candidate sources, we obtained follow-up observations with the Karl. G. Jansky Very Large Array (VLA) at higher resolution to observe the inner lobes or restarted jets, the confirmation of which created a robust sample of 33 DDRGs. We created a comparison sample of 777 RLAGN, matching the luminosity distribution of the DDRG sample, and compared the optical and infrared magnitudes and colours of their host galaxies. Results. We find that there is no statistically significant difference in the brightness of the host galaxies between double-doubles and single-cycle RLAGN. The DDRG and RLAGN samples also have similar distributions in WISE mid-infrared colours, indicating similar ages of stellar populations and dust levels in the hosts of DDRGs. We conclude that DDRGs and “normal” RLAGN are hosted by galaxies of the same type, and that DDRG activity is simply a normal part of the life cycle of RLAGN. Restarted jets, particularly for the class of low-excitation radio galaxies, rather than being a product of a particular event in the life of a host galaxy, must instead be caused by smaller scale changes, such as in the accretion system surrounding the black hole.

scholarly journals Recoiling Black Holes: Electromagnetic Signatures, Candidates, and Astrophysical Implications

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
S. Komossa
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Host Galaxies ◽  
Wide Range ◽  
Galaxy Cores ◽  
Galaxy Assembly ◽  
Anisotropic Emission

Supermassive black holes (SMBHs) may not always reside right at the centers of their host galaxies. This is a prediction of numerical relativity simulations, which imply that the newly formed single SMBH, after binary coalescence in a galaxy merger, can receive kick velocities up to several 1000 km/s due to anisotropic emission of gravitational waves. Long-lived oscillations of the SMBHs in galaxy cores, and in rare cases even SMBH ejections from their host galaxies, are the consequence. Observationally, accreting recoiling SMBHs would appear as quasars spatially and/or kinematically offset from their host galaxies. The presence of the “kicks” has a wide range of astrophysical implications which only now are beginning to be explored, including consequences for black hole and galaxy assembly at the epoch of structure formation, black hole feeding, and unified models of active galactic nuclei (AGN). Here, we review the observational signatures of recoiling SMBHs and the properties of the first candidates which have emerged, including follow-up studies of the candidate recoiling SMBH of SDSSJ092712.65+294344.0.

scholarly journals The Origin and Evolution of Giant Radio Galaxies

2022 ◽  
Vol 8 ◽  
Author(s):  
David Garofalo
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Spiral Galaxies ◽  
Radio Galaxy ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
High Excitation ◽  
Origin And Evolution ◽  
Black Hole Spin ◽  
Upper Limit

Giant radio galaxies are arguably the least understood of jetted active galactic nuclei (AGN). We propose that radio galaxies are the product of large mergers that do not involve radio galaxies or radio quasars, such as in merging spiral galaxies, while giant radio galaxies emerge from a merger involving a parent that in the not-too-distant past harbored a radio galaxy. Predictions following from this are an upper limit to the number fraction of giant radio galaxies to radio galaxies, lower average redshift for giant radio galaxies, a higher incidence of high excitation for giant radio galaxies compared with radio galaxies, and lower average prograde black hole spin values for giant radio galaxies compared to radio galaxies and to bright radio quiet quasars.

scholarly journals Multiwavelength surveys for Active Galactic Nuclei

2019 ◽  
Vol 15 (S356) ◽  
pp. 11-11
Author(s):  
William Nielsen Brandt
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Future Prospects ◽  
Host Galaxies ◽  
General Survey ◽  
Anisotropic Emission

AbstractMost of what we know about active galactic nuclei (AGNs) has been driven, or at least strongly shaped, by our methods for finding them, and multiwavelength AGN surveys have achieved remarkable successes in recent decades. I will present a broad, and thus necessarily shallow, review of such multiwavelength AGN surveys. I will first present some brief introductory points on, e.g., general survey approaches, AGN luminosities, host galaxies, and anisotropic emission/obscuration. I will then review many of the key current surveys and their results, separating these into ground-based and space-based surveys. Finally, I will discuss some future prospects including essential remaining questions and “discovery space” considerations.

scholarly journals Probing the cool ISM in galaxies via 21 cm H i absorption

2012 ◽  
Vol 8 (S292) ◽  
pp. 188-188
Author(s):  
J. R. Allison ◽  
E. M. Sadler ◽  
S. J. Curran ◽  
S. N. Reeves
Keyword(s):  
Spectral Line ◽  
Active Galactic Nuclei ◽  
Large Scale ◽  
Galactic Nuclei ◽  
Host Galaxies ◽  
The Galaxy ◽  
Early Type Galaxy ◽  
Finding Method ◽  
Compact Array ◽  
Cold Gas

AbstractRecent targeted studies of associated H i absorption in radio galaxies are starting to map out the location, and potential cosmological evolution, of the cold gas in the host galaxies of Active Galactic Nuclei (AGN). The observed 21 cm absorption profiles often show two distinct spectral-line components: narrow, deep lines arising from cold gas in the extended disc of the galaxy, and broad, shallow lines from cold gas close to the AGN (e.g. Morganti et al. 2011). Here, we present results from a targeted search for associated H i absorption in the youngest and most recently-triggered radio AGN in the local universe (Allison et al. 2012b). So far, by using the recently commissioned Australia Telescope Compact Array Broadband Backend (CABB; Wilson et al. 2011), we have detected two new absorbers and one previously-known system. While two of these show both a broad, shallow component and a narrow, deep component (see Fig. 1), one of the new detections has only a single broad, shallow component. Interestingly, the host galaxies of the first two detections are classified as gas-rich spirals, while the latter is an early-type galaxy. These detections were obtained using a spectral-line finding method, based on Bayesian inference, developed for future large-scale absorption surveys (Allison et al. 2012a).

HARMONI view of the host galaxies of active galactic nuclei around cosmic noon. Resolved stellar morpho-kinematics and the MBH-sigma* relation

2021 ◽  
Author(s):  
B. García-Lorenzo ◽  
A. Monreal-Ibero ◽  
M. Pereira-Santaella ◽  
N. Thatte ◽  
C. Ramos Almeida ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Host Galaxies

scholarly journals Disentangling AGN and starburst activities in NGC 6240 from an X-ray perspective

2014 ◽  
Vol 10 (S312) ◽  
pp. 36-38
Author(s):  
Junfeng Wang
Keyword(s):  
Active Galactic Nuclei ◽  
Large Scale ◽  
Imaging Spectroscopy ◽  
Galactic Nuclei ◽  
Resolving Power ◽  
High Excitation ◽  
X Ray ◽  
Supermassive Black Hole ◽  
X Ray Imaging ◽  
High Temperature Gas

AbstractThe circum-nuclear region in an active galaxy is often complex with presence of high excitation gas, collimated radio outflow, and star formation activities, besides the actively accreting supermassive black hole. The unique spatial resolving power of Chandra X-ray imaging spectroscopy enables more investigations to disentangle the active galactic nuclei and starburst activities. For galaxies in the throes of a violent merging event such as NGC6240, we were able to resolve the high temperature gas surrounding its binary active black holes and discovered a large scale soft X-ray halo.

scholarly journals A Systematic Search for Dual AGNs in Merging Galaxies (Astro-daring): III: Results from the SDSS Spectroscopic Surveys

2021 ◽  
Vol 162 (6) ◽  
pp. 276
Author(s):  
Yang-Wei Zhang ◽  
Yang Huang ◽  
Jin-Ming Bai ◽  
Xiao-Wei Liu ◽  
Jian-guo Wang ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Angular Separation ◽  
Careful Analysis ◽  
Emission Lines ◽  
Host Galaxies ◽  
Merging Galaxies ◽  
The Third ◽  
First Time ◽  
Consistent Approach

Abstract As the third installment in a series systematically searching dual active galactic nuclei (AGN) among merging galaxies, we present the results of 20 dual AGNs found by using the SDSS fiber spectra. To reduce the flux contamination from both the fiber aperture and seeing effects, the angular separation of two cores in our merging galaxy pairs sample is restricted at least larger than 3″. By careful analysis of the emission lines, 20 dual AGNs are identified from 61 merging galaxies with their two cores both observed by the SDSS spectroscopic surveys. 15 of them are identified for the first time. The identification efficiency is about 32.79% (20/61), comparable to our former results (16 dual AGNs identified from 41 merging galaxies) based on the long-slit spectroscopy. Interestingly, two of the 20 dual AGNs show two prominent cores in radio images and their radio powers show they as the radio-excess AGNs. So far, 31 dual AGNs are found by our project and this is the current largest dual AGN sample, ever constructed with a consistent approach. This sample, together with more candidates from ongoing observations, is of vital importance to study the AGN physics and the coevolution between the supermassive black holes and their host galaxies.

scholarly journals AGN polarization modeling with Stokes

2006 ◽  
Vol 2 (S238) ◽  
pp. 375-376 ◽  
Author(s):  
René W. Goosmann ◽  
C. Martin Gaskell ◽  
Masatoshi Shoji
Keyword(s):  
Monte Carlo ◽  
Radiative Transfer ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Dust Grains ◽  
Free Electrons ◽  
Wide Range ◽  
Polarization Spectra

AbstractWe introduce a new, publicly available Monte Carlo radiative transfer code, Stokes, which has been developed to model polarization induced by scattering of free electrons and dust grains. It can be used in a wide range of astrophysical applications. Here, we apply it to model the polarization produced by the equatorial obscuring and scattering tori assumed to exist in active galactic nuclei (AGNs). We present optical/UV modeling of dusty tori with a curved inner shape and for two different dust types. The polarization spectra enable us to clearly distinguish between the two dust compositions. The Stokes code and its documentation can be freely downloaded from http://www.stokes-program.info/.

scholarly journals Luminosity Correlation of the X-ray Selected Radio-Loud AGNs

1999 ◽  
Vol 194 ◽  
pp. 306-310
Author(s):  
Q. Yuan ◽  
J. Wu ◽  
K. Huang
Keyword(s):  
Active Galactic Nuclei ◽  
Broad Band ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Spectral Indices ◽  
Strong Correlations ◽  
Band Energy ◽  
X Ray ◽  
Sky Survey ◽  
Bl Lacs

This paper presents a test of the luminosity correlation of the X-ray selected radio-loud Active Galactic Nuclei (AGNs), based on a large sample constructed by combining our cross-identification of southern sky sources with the radio-loud sources in the northern hemisphere given by Brinkmann et al. (1995). All sources were detected both by the ROSAT All-Sky Survey and the radio surveys at 4.85 GHz. The broad band energy distribution confirms the presence of strong correlations between luminosities in the radio, optical, and X-ray bands which differ for quasars, seyferts, BL Lacs, and radio galaxies. The tight correlations between spectral indices αox and monochromatic luminosities at 5500 Å and 4.85 GHz are also shown.

Sign in / Sign up

Export Citation Format

Share Document