SwePub
Sök i SwePub databas

  Utökad sökning

Träfflista för sökning "WFRF:(Imanishi Masatoshi) "

Sökning: WFRF:(Imanishi Masatoshi)

  • Resultat 1-8 av 8
Sortera/gruppera träfflistan
   
NumreringReferensOmslagsbildHitta
1.
  • Fathi, Kambiz, et al. (författare)
  • LOCAL INSTABILITY SIGNATURES IN ALMA OBSERVATIONS OF DENSE GAS IN NGC 7469
  • 2015
  • Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213 .- 1538-4357 .- 0004-637X. ; 806:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We present an unprecedented measurement of the disk stability and local instability scales in the luminous infrared Seyfert 1 host, NGC 7469, based on ALMA observations of dense gas tracers and with a synthesized beam of 165 x 132 pc. While we confirm that non-circular motions are not significant in redistributing the dense interstellar gas in this galaxy, we find compelling evidence that the dense gas is a suitable tracer for studying the origin of its intensely high-mass star-forming ringlike structure. Our derived disk stability parameter Q accounts for a thick disk structure, and its value falls below unity at the radii in which intense star formation is found. Furthermore, we derive the characteristic instability scale lambda(c) and find a striking agreement between our measured scale of similar to 180 pc and the typical sizes of individual complexes of young and massive star clusters seen in high-resolution images.
  •  
2.
  • Fathi, Kambiz, et al. (författare)
  • ALMA FOLLOWS STREAMING OF DENSE GAS DOWN TO 40 PC FROM THE SUPERMASSIVE BLACKHOLE IN NGC 1097
  • 2013
  • Ingår i: Astrophysical Journal Letters. - 2041-8205. ; 770:2, s. L27-
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a kinematic analysis of the dense gas in the central 200 parsecs of thenearby galaxy NGC1097, based on Cycle 0 observations with the Atacama LargeMillimeter/sub-millimeter Array (ALMA). We use the HCN(4-3) line to trace the densest interstellar molecular gas (nH2 ~ 10^8 cm-3), and quantify its kinematics by means of Fourier decomposition. We find a striking similarity between the ALMA kinematic data and the analytic spiral in ow model that we have previously constructed based onionized gas velocity fields on larger scales. We are able to follow dense gas streamingdown to 40 pc distance from the supermassive black hole in this Seyfert 1 galaxy. In order to fulll marginal stability, we deduce that the dense gas is conned to a very thin disc, with 6.0+2.2-2.7 10^6 Msun dynamical mass inside a radius of 40 pc. Finally, we derive a dense gas in ow rate of 0.09Msun yr-1 at 40 pc radius. Combined with previous valuesfrom the H and CO gas, we calculate a combined molecular and ionized gas in ow rateof 0.2Msun yr-1 at 40 pc distance from the central supermassive black hole of NGC1097.
  •  
3.
  • Imanishi, Masatoshi, et al. (författare)
  • ALMA 002 Resolution Observations Reveal HCN-abundance-enhanced Counter-rotating and Outflowing Dense Molecular Gas at the NGC 1068 Nucleus
  • 2020
  • Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 902:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We present ALMA similar to 002 resolution observations of the nucleus of the nearby (similar to 14 Mpc) type 2 active galactic nucleus NGC 1068 at HCN/HCO+/HNCJ = 3-2 lines, as well as at their(13)C isotopologue and vibrationally excited lines, to scrutinize the morphological, dynamical, chemical, and physical properties of dense molecular gas in the putative dusty molecular torus around a mass-accreting supermassive black hole. We confirm almost east-west-oriented dense molecular gas emission both morphologically and dynamically, which we regard as coming from the torus. Bright emission is compact (less than or similar to 3 pc), and low-surface-brightness emission extends out to 5-7 pc. These dense molecular gas properties are not symmetric between the eastern and western torus. The HCNJ = 3-2 emission is stronger than the HCO(+)J = 3-2 emission within the similar to 7 pc torus region, with an estimated dense molecular mass of (0.4-1.0) x 10(6)M. We interpret that HCN abundance is enhanced in the torus. We detect signatures of outflowing dense molecular gas and a vibrationally excited HCNJ = 3-2 line. Finally, we find that in the innermost (less than or similar to 1 pc) part of the torus, the dense molecular line rotation velocity, relative to the systemic velocity, is the opposite of that in the outer (greater than or similar to 2 pc) part, in both the eastern and western torus. We prefer a scenario of counter-rotating dense molecular gas with innermost almost Keplerian rotation and outer slowly rotating (far below Keplerian) components. Our high-spatial-resolution dense molecular line data reveal that torus properties of NGC 1068 are much more complicated than the simple axisymmetrically rotating torus picture in the classical active galactic nucleus unification paradigm.
  •  
4.
  • Izumi, Takuma, et al. (författare)
  • ALMA OBSERVATIONS OF THE SUBMILLIMETER DENSE MOLECULAR GAS TRACERS IN THE LUMINOUS TYPE-1 ACTIVE NUCLEUS OF NGC 7469
  • 2015
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 811:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 1 observations of the central kiloparsec region of the luminous type. 1 Seyfert galaxy NGC 7469 with unprecedented high resolution (0.'' 5x0.'' 4 = 165 x 132 pc) at submillimeter wavelengths. Utilizing the wide. bandwidth of ALMA, we simultaneously obtained HCN(4-3), HCO+(4-3), CS(7-6), and partially CO(3-2) line maps, as well as the 860 mu m continuum. The region consists of the central similar to 1 '' component and the surrounding starburst ring with a radius of similar to 1.'' 5-2.'' 5. Several structures connect these components. Except for CO(3-2), these dense gas tracers are significantly concentrated toward the central similar to 1 '', suggesting their suitability to probe the nuclear regions of galaxies. Their spatial distribution resembles well those of centimeter and mid-infrared continuum emissions, but it is anticorrelated with the optical one, indicating the existence of dust-obscured star formation. The integrated intensity ratios of HCN(4-3)/HCO+(4-3) and HCN(4-3)/CS(7-6) are higher at the active galactic nucleus (AGN) position than at the starburst ring, which is consistent with our previous findings (submillimeter-HCN enhancement). However, the HCN(4-3)/HCO+(4-3) ratio at the AGN position of NGC 7469 (1.11 +/- 0.06) is almost half of the corresponding value of the low-luminosity type. 1 Seyfert galaxy NGC 1097 (2.0 +/- 0.2), despite the more than two orders of magnitude higher X-ray luminosity of NGC 7469. But the ratio is comparable to that of the close vicinity of the AGN of NGC 1068 (similar to 1.5). Based on these results, we speculate that some heating mechanisms other than X-ray (e.g., mechanical heating due to an AGN jet) can contribute significantly for shaping the chemical composition in NGC 1097.
  •  
5.
  • Izumi, Takuma, et al. (författare)
  • Submillimeter ALMA Observations of the Dense Gas in the Low-Luminosity Type-1 Active Nucleus of NGC 1097
  • 2013
  • Ingår i: Publications of the Astronomical society of Japan. - 0004-6264 .- 2053-051X. ; 65:5
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the first 100 pc scale view of the dense molecular gas in the central similar to 1.3 kpc of the type-1 Seyfert NGC 1097, traced by HCN (J = 4-3) and HCO+ (J = 4-3) lines afforded with ALMA band 7. This galaxy shows significant HCN enhancement with respect to HCO+ and CO in the low-J transitions, which seems to be a common characteristic in AGN environments. Using the ALMA data, we consider the characteristics of the dense gas around this AGN, and search for the mechanism of HCN enhancement. We find a high HCN (J = 4-3) to HCO+ (J = 4-3) line ratio in the nucleus. The upper limit of the brightness temperature ratio of HCN (nu(2) = 1(1f), J = 4-3) to HCN (J = 4-3) is 0.08, which indicates that IR pumping does not significantly affect the pure rotational population in this nucleus. We also find a higher HCN (J = 4-3) to CS (J = 7-6) line ratio in NGC 1097 than in starburst galaxies, which is more than 12.7 on the brightness temperature scale. Combined with similar observations from other galaxies, we tentatively suggest that this ratio appears to be higher in AGN-host galaxies than in pure starburst ones, similar to the widely used HCN to HCO+ ratio. LTE and non-LTE modeling of the observed HCN and HCO+ lines using J = 4-3 and 1-0 data from ALMA, and J = 3-2 data from SMA, reveals a high HCN to HCO+ abundance ratio (5 <= [HCN]/[HCO+] <= 20: non-LTE analysis) in the nucleus, and that the high-J lines (J = 4-3 and 3-2) are emitted from dense (10(4.5) cm(-3) <= n(H2) <= 10(6) cm(-3)), hot (70 K <= T-kin <= 550 K) regions. Finally we propose that high-temperature chemistry is more plausible to explain the observed enhanced HCN emission in NGC 1097 than pure gas-phase PDR/XDR chemistry.
  •  
6.
  • Izumi, Takuma, et al. (författare)
  • SUBMILLIMETER-HCN DIAGRAM FOR ENERGY DIAGNOSTICS IN THE CENTERS OF GALAXIES
  • 2016
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 818:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Compiling data from literature and the Atacama Large Millimeter/submillimeter Array archive, we show enhanced HCN(4-3)/HCO+(4-3) and/or HCN(4-3)/CS(7-6) integrated intensity ratios in circumnuclear molecular gas around active galactic nuclei (AGNs) compared to those in starburst (SB) galaxies (submillimeter HCN. enhancement). The number of sample galaxies is significantly increased from our previous work. We expect that this feature could potentially be an extinction-free energy diagnostic tool of nuclear regions of galaxies. Non-LTE radiative transfer modelings of the above molecular emission lines involving both collisional and radiative excitation, as well as a photon trapping effect, were conducted to investigate the cause of the high line ratios in AGNs. As a result, we found that enhanced abundance ratios of HCN to HCO+ and HCN to CS in AGNs as compared to SB galaxies by a factor of a few to even greater than or similar to 10 are a plausible explanation for the submillimeter HCN. enhancement. However, a counterargument of a systematically higher gas density in AGNs than in SB galaxies can also be a plausible scenario. Although we cannot fully distinguish. these two scenarios at this moment owing to an insufficient amount of multi-transition, multi-species data, the former scenario is indicative of abnormal chemical composition in AGNs. Regarding the actual mechanism to realize the composition, we suggest that it is difficult with conventional gas-phase X-ray-dominated region ionization models to reproduce the observed high line ratios. We might have to take into account other mechanisms such as neutral-neutral reactions that are efficiently activated in high-temperature environments and/or mechanically heated regions to further understand the high line ratios in AGNs.
  •  
7.
  • 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. - 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.
  •  
8.
  • 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. - 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.
  •  
Skapa referenser, mejla, bekava och länka
  • Resultat 1-8 av 8

Kungliga biblioteket hanterar dina personuppgifter i enlighet med EU:s dataskyddsförordning (2018), GDPR. Läs mer om hur det funkar här.
Så här hanterar KB dina uppgifter vid användning av denna tjänst.

 
pil uppåt Stäng

Kopiera och spara länken för att återkomma till aktuell vy