| 1. |
- Fathi, Kambiz, et al.
(författare)
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ALMA FOLLOWS STREAMING OF DENSE GAS DOWN TO 40 PC FROM THE SUPERMASSIVE BLACKHOLE IN NGC 1097
- 2013
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Ingår i: Astrophysical Journal Letters. - 2041-8205. ; 770:2, s. L27-
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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.
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| 2. |
- Izumi, Takuma, et al.
(författare)
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ALMA OBSERVATIONS OF THE SUBMILLIMETER DENSE MOLECULAR GAS TRACERS IN THE LUMINOUS TYPE-1 ACTIVE NUCLEUS OF NGC 7469
- 2015
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 811:1
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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.
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| 3. |
- Izumi, Takuma, et al.
(författare)
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Submillimeter ALMA Observations of the Dense Gas in the Low-Luminosity Type-1 Active Nucleus of NGC 1097
- 2013
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Ingår i: Publications of the Astronomical society of Japan. - : Oxford University Press (OUP). - 0004-6264 .- 2053-051X. ; 65:5
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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.
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| 4. |
- Izumi, Takuma, et al.
(författare)
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SUBMILLIMETER-HCN DIAGRAM FOR ENERGY DIAGNOSTICS IN THE CENTERS OF GALAXIES
- 2016
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 818:1
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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.
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