| 1. |
- Aharonian, Felix, et al.
(författare)
-
Hitomi observation of radio galaxy NGC 1275 : The first X-ray microcalorimeter spectroscopy of Fe-K alpha line emission from an active galactic nucleus
- 2018
-
Ingår i: Publications of the Astronomical Society of Japan. - : Oxford University Press (OUP). - 0004-6264 .- 2053-051X. ; 70:2
-
Tidskriftsartikel (refereegranskat)abstract
- The origin of the narrow Fe-K alpha fluorescence line at 6.4 keV from active galactic nuclei has long been under debate; some of the possible sites are the outer accretion disk, the broad line region, a molecular torus, or interstellar/intracluster media. In 2016 February-March, we performed the first X-ray microcalorimeter spectroscopy with the Soft X-ray Spectrometer (SXS) on board the Hitomi satellite of the Fanaroff-Riley type I radio galaxy NGC 1275 at the center of the Perseus cluster of galaxies. With the high-energy resolution of similar to 5 eV at 6 keV achieved by Hitomi/SXS, we detected the Fe-K alpha line with similar to 5.4 sigma significance. The velocity width is constrained to be 500-1600 km s(-1) (FWHM for Gaussian models) at 90% confidence. The SXS also constrains the continuum level from the NGC 1275 nucleus up to similar to 20 keV, giving an equivalent width of similar to 20 eV for the 6.4 keV line. Because the velocity width is narrower than that of the broad H alpha line of similar to 2750 km s(-1), we can exclude a large contribution to the line flux from the accretion disk and the broad line region. Furthermore, we performed pixel map analyses on the Hitomi/SXS data and image analyses on the Chandra archival data, and revealed that the Fe-K alpha line comes from a region within similar to 1.6 kpc of the NGC 1275 core, where an active galactic nucleus emission dominates, rather than that from intracluster media. Therefore, we suggest that the source of the Fe-K alpha line from NGC 1275 is likely a low-covering-fraction molecular torus or a rotating molecular disk which probably extends from a parsec to hundreds of parsecs scale in the active galactic nucleus system.
|
|
| 2. |
- Kawamuro, Taiki, et al.
(författare)
-
AGN X-Ray Irradiation of CO Gas in NGC 2110 Revealed by Chandra and ALMA
- 2020
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 895:2
-
Tidskriftsartikel (refereegranskat)abstract
- We report spatial distributions of the Fe-K alpha line at 6.4 keV and the CO(J = 2-1) line at 230.538 GHz in NGC 2110, which are, respectively, revealed by Chandra and Atacama Large Millimeter/submillimeter Array (ALMA) at 05. A Chandra 6.2-6.5 keV to 3.0-6.0 keV image suggests that the Fe-K alpha emission extends preferentially in a northwest to southeast direction out to 3 '', or similar to 500 pc, on each side. Spatially resolved spectral analyses support this by finding significant Fe-K alpha emission lines only in the northwest and southeast regions. Moreover, their equivalent widths are found to be similar to 1.5 keV, indicative for the fluorescence by nuclear X-ray irradiation as the physical origin. By contrast, CO(J = 2-1) emission is weak therein. For quantitative discussion, we derive ionization parameters by following an X-ray dominated region (XDR) model. We then find them high enough to interpret the weakness as the result of X-ray dissociation of CO and/or H-2. Another possibility also remains that CO molecules follow a superthermal distribution, resulting in brighter emission in higher-J lines. Further follow-up observations are encouraged to draw a conclusion on what predominantly changes the interstellar matter properties and whether the X-ray irradiation eventually affects the surrounding star formation as active galactic nucleus (AGN) feedback.
|
|
| 3. |
- Kawamuro, Taiki, et al.
(författare)
-
Hard X-Ray Irradiation Potentially Drives Negative AGN Feedback by Altering Molecular Gas Properties
- 2021
-
Ingår i: Astrophysical Journal, Supplement Series. - : American Astronomical Society. - 1538-4365 .- 0067-0049. ; 257:2
-
Tidskriftsartikel (refereegranskat)abstract
- To investigate the role of active galactic nucleus (AGN) X-ray irradiation on the interstellar medium (ISM), we systematically analyzed Chandra and Atacama Large Millimeter/submillimeter Array CO (J = 2-1) data for 26 hard X-ray (>10 keV) selected AGNs at redshifts below 0.05. While Chandra unveils the distribution of X-ray-irradiated gas via Fe-K alpha emission, the CO (J = 2-1) observations reveal that of cold molecular gas. At high resolutions less than or similar to 1 '', we derive Fe-K alpha and CO (J = 2-1) maps for the nuclear 2 '' region and for the external annular region of 2 ''-4 '', where 2 '' is similar to 100-600 pc for most of our AGNs. First, focusing on the external regions, we find the Fe-K alpha emission for six AGNs above 2 sigma. Their large equivalent widths (greater than or similar to 1 keV) suggest a fluorescent process as their origin. Moreover, by comparing the 6-7 keV/3-6 keV ratio, as a proxy of Fe-K alpha, and CO (J = 2-1) images for three AGNs with the highest significant Fe-K alpha detections, we find a possible spatial separation. These suggest the presence of X-ray-irradiated ISM and the change in the ISM properties. Next, examining the nuclear regions, we find that (1) the 20-50 keV luminosity increases with the CO (J = 2-1) luminosity; (2) the ratio of CO (J = 2-1)/HCN (J = 1-0) luminosities increases with 20-50 keV luminosity, suggesting a decrease in the dense gas fraction with X-ray luminosity; and (3) the Fe-K alpha-to-X-ray continuum luminosity ratio decreases with the molecular gas mass. This may be explained by a negative AGN feedback scenario: the mass accretion rate increases with gas mass, and simultaneously, the AGN evaporates a portion of the gas, which possibly affects star formation.
|
|
| 4. |
- Ricci, C., et al.
(författare)
-
A Tight Correlation between Millimeter and X-Ray Emission in Accreting Massive Black Holes from
- 2023
-
Ingår i: Astrophysical Journal Letters. - 2041-8213 .- 2041-8205. ; 952:2
-
Tidskriftsartikel (refereegranskat)abstract
- Recent studies have proposed that the nuclear millimeter continuum emission observed in nearby active galactic nuclei (AGNs) could be created by the same population of electrons that gives rise to the X-ray emission that is ubiquitously observed in accreting black holes. We present the results of a dedicated high-spatial-resolution (∼60-100 mas) Atacama Large Millimeter/submillimeter Array (ALMA) campaign on a volume-limited (<50 Mpc) sample of 26 hard X-ray (>10 keV) selected radio-quiet AGNs. We find an extremely high detection rate (25/26 or 94 − 6 + 3 % ), which shows that nuclear emission at millimeter wavelengths is nearly ubiquitous in accreting SMBHs. Our high-resolution observations show a tight correlation between the nuclear (1-23 pc) 100 GHz and the intrinsic X-ray emission (1σ scatter of 0.22 dex). The ratio between the 100 GHz continuum and the X-ray emission does not show any correlation with column density, black hole mass, Eddington ratio, or star formation rate, which suggests that the 100 GHz emission can be used as a proxy of SMBH accretion over a very broad range of these parameters. The strong correlation between 100 GHz and X-ray emission in radio-quiet AGNs could be used to estimate the column density based on the ratio between the observed 2-10 keV ( F 2 - 10 keV obs ) and 100 GHz (F 100 GHz) fluxes. Specifically, a ratio log ( F 2 - 10 keV obs / F 100 GHz ) ≤ 3.5 strongly suggests that a source is heavily obscured ( log ( N H / cm − 2 ) ≳ 23.8 ). Our work shows the potential of ALMA continuum observations to detect heavily obscured AGNs (up to an optical depth of one at 100 GHz, i.e., N H ≃ 1027 cm−2), and to identify binary SMBHs with separations <100 pc, which cannot be probed by current X-ray facilities.
|
|
