Radio bubbles and superwind outflow in NGC 6764 (original) (raw)
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The Astrophysical Journal, 2012
We report the detection of far-IR CO rotational emission from the prototypical Seyfert 2 galaxy NGC 1068. Using Herschel-PACS, we have detected 11 transitions in the J upper = 14-30 (E upper /k B = 580-2565 K) range, all of which are consistent with arising from within the central 10 (700 pc). The detected transitions are modeled as arising from two different components: a moderate-excitation (ME) component close to the galaxy systemic velocity and a high-excitation (HE) component that is blueshifted by ∼80 km s −1. We employ a large velocity gradient model and derive n H2 ∼ 10 5.6 cm −3 , T kin ∼ 170 K, and M H2 ∼ 10 6.7 M for the ME component and n H2 ∼ 10 6.4 cm −3 , T kin ∼ 570 K, and M H2 ∼ 10 5.6 M for the HE component, although for both components the uncertainties in the density and mass are ±(0.6-0.9) dex. Both components arise from denser and possibly warmer gas than traced by low-J CO transitions, and the ME component likely makes a significant contribution to the mass budget in the nuclear region. We compare the CO line profiles with those of other molecular tracers observed at higher spatial and spectral resolution and find that the ME transitions are consistent with these lines arising in the ∼200 pc diameter ring of material traced by H 2 1-0 S(1) observations. The blueshift of the HE lines may also be consistent with the bluest regions of this H 2 ring, but a better kinematic match is found with a clump of infalling gas ∼40 pc north of the active galactic nucleus (AGN). We consider potential heating mechanisms and conclude that X-ray-or shock heating of both components is viable, while far-UV heating is unlikely. We discuss the prospects of placing the HE component near the AGN and conclude that while the moderate thermal pressure precludes an association with the ∼1 pc radius H 2 O maser disk, the HE component could potentially be located only a few parsecs more distant from the AGN and might then provide the N H ∼ 10 25 cm −2 column obscuring the nuclear hard X-rays. Finally, we also report sensitive upper limits extending up to J upper = 50, which place constraints on a previous model prediction for the CO emission from the X-ray obscuring torus.
Molecular gas in NUclei of GAlaxies (NUGA)
Astronomy and Astrophysics, 2009
We present CO(1-0) and CO(2-1) maps of the LINER galaxy NGC 7217, obtained with the IRAM interferometer, at 2.4 ′′ ×1.9 ′′ and 1.2 ′′ ×0.8 ′′ resolution respectively. The nuclear ring (at r = 12 ′′ = 0.8kpc) dominates the CO maps, and has a remarkable sharp surface density gradient at its inner edge. The latter is the site of the stellar/Hα ring, while the CO emission ring extends farther or is broader (500-600pc). This means that the star formation has been more intense toward the inner edge of the CO ring, in a thin layer, just at the location of the high gas density gradient. The CO(2-1)/CO(1-0) ratio is close to 1, typical of warm optically thick gas with high density. The overall morphology of the ring is quite circular, with no evidence of non-circular velocities. In the CO(2-1) map, a central concentration might be associated with the circumnuclear ionized gas detected inside r=3" and interpreted as a polar ring in the literature. The CO(2-1) emission inside 3" coincides with a spiral dust lane, clearly seen in the HST V − I color image. N-body simulations including gas dissipation and star formation are performed to better understand the nature of the nuclear ring observed. The observed rotation curve of NGC 7217 allows two possibilities, according to the adopted mass for the disk:
Molecular gas in NUclei of GAlaxies (NUGA) XIII. The interacting Seyfert 2/LINER galaxy NGC 5953
Astronomy and Astrophysics, 2010
We present 12 CO(1-0) and 12 CO(2-1) maps of the interacting Seyfert 2/LINER galaxy NGC 5953 obtained with the IRAM interferometer at resolutions of 2. ′′ 1 × 1. ′′ 4 and 1. ′′ 1 × 0. ′′ 7, respectively. We also present single-dish IRAM 30 m observations of the central region of NGC 5953 for the 12 CO(1-0), 12 CO(2-1), and HCN(1-0) transitions at resolutions of 22 ′′ , 12 ′′ , and 29 ′′ , respectively. The CO emission is distributed over a disk of diameter ∼16 ′′ (∼2.2 kpc), within which are several, randomly distributed peaks. The strongest peak does not coincide with the nucleus, but is instead offset from the center, ∼2-3 ′′ (∼340 pc) toward the west/southwest. The kinematics of the molecular component are quite regular, as is typical of a rotating disk. We also compared the 12 CO distribution of NGC 5953 with observations at other wavelengths in order to study correlations between different tracers of the interstellar medium. The HST/F606W WFPC2 images show flocculent spiral structures and an "S-shape" feature > ∼ 60 pc in radius, possibly associated with a nuclear bar or with the radio jet. A two-dimensional bulge/disk decomposition of the H-band (HST/F160W) and 3.6 µm (Spitzer/IRAC) images reveals a circumnuclear "ring" ∼10-14 ′′ in diameter, roughly coincident in size with the CO disk and with a star-forming ring previously identified in ionized gas. This ring is not present in the near-infrared (NIR) J − K color image, nor is it present in the "dust-only" image constructed from the 8 µm IRAC map. The implication is that the excess residual ring is stellar, with colors similar to the surrounding disk. We interpret this ring, visible in ionized gas, which appears as stars in the NIR, and with no sign of hot dust, as due to a red super giant population at least 10-15 Myr old. However, star formation is still ongoing in the disk and in the ring itself. Using NIR images, we computed the gravity torques exerted by the stellar potential on the gas. The torques are predominantly positive in both 12 CO(1-0) and 12 CO(2-1), suggesting that gas is not flowing into the center, and less than 5% of the gas angular momentum is exchanged in each rotation. This comes from the regular and almost axisymmetric total mass and gas distributions in the center of the galaxy. In NGC 5953, the AGN is apparently not being actively fueled in the current epoch.
CO Observations of NGC 2359: The Molecular Clouds Revisited
The Astronomical Journal, 2001
Based on CO (2È1) observations obtained with the Swedish-ESO Submillimeter Telescope, the distribution of molecular material associated with the Wolf-Rayet ring nebula NGC 2359 has been determined. The angular resolution is 22A, and the velocity resolution is 0.33 km s~1. Three molecular components are detected in the direction of the nebula. The bulk of the molecular gas is observed at 54 km s~1 and follows the southeastern border of the nebula. Adopting a distance d \ 5 kpc for NGC 2359, an mass of about 1200^500 appears to be related to the southern part of the nebula, H 2 M _ while 140^50 are linked to the Ðlamentary windblown bubble. The volume density of the molecu-M _ lar gas related to the southern bar is º103 molecules cm~3, while lower densities were estimated for H 2 the material associated with the Ðlamentary windblown bubble. From the present data, it is not clear if the molecular gas at 37 km s~1 (^380^120 d \ 5 kpc) is associated with the nebula, but the M _ , molecular material observed at 67 km s~1 (^70^25 d \ 5 kpc) seems to be unconnected. The M _ , comparison between ionized, H I, and molecular distributions indicates that the H I Ðlament detected with the Very Large Array is located at the interface between the ionized and molecular material, and that the H I Ðlament at 54 km s~1 has originated in the photodissociation of the Most of the molec-H 2. ular gas associated with the Ðlamentary bubble seems to be interstellar in origin. The dynamics of the nebula is reanalyzed based on these new molecular results. It is consistent with either momentum conservation or an intermediate stage between energy and momentum conservation.
The Circumnuclear Molecular Gas in the Seyfert Galaxy NGC 4945
The Astrophysical Journal, 2007
We have mapped the central region of NGC 4945 in the J = 2 → 1 transition of 12 CO, 13 CO, and C 18 O, as well as the continuum at 1.3 mm, at an angular resolution of 5 ′′ × 3 ′′ with the Submillimeter Array. The relative proximity of NGC 4945 (distance of only 3.8 Mpc) permits a detailed study of the circumnuclear molecular gas and dust in a galaxy exhibiting both an AGN (classified as a Seyfert 2) and a circumnuclear starburst in an inclined ring with radius ∼2. ′′ 5 (∼50 pc). We infer the systemic velocity ∼585 km s −1 from channel maps and PV-diagrams. We find that all three molecular lines trace an inclined rotating disk with major axis aligned with that of the starburst ring and large-scale galactic disk, and which exhibits solid-body rotation within a radius of ∼5 ′′ (∼95 pc). The rotation curve flattens beyond this radius, and the isovelocity contours exhibit an S-shaped asymmetry suggestive of a highly inclined bar as has been invoked to produce a similar asymmetry observed on larger scales. We infer an inclination for the nuclear disk of 62 • ±2 • , somewhat smaller than the inclination of the large-scale galactic disk of ∼78 •. The continuum emission at 1.3 mm also extends beyond the starburst ring, and is dominated by thermal emission from dust. If it traces the same dust emitting in the far-infrared, then the bulk of this dust must be heated by star-formation activity rather than the AGN. We discover a kinematically-decoupled component at the center of the disk with a radius smaller than 1. ′′ 4 (27 pc), but which spans approximately the same range of velocities as the surrounding disk. This component has a higher density than its surroundings, and is a promising candidate for the circumnuclear molecular torus invoked by AGN unification models.
Monthly Notices of the Royal Astronomical Society, 2015
We report the discovery of a new 21 cm H I absorption system using commissioning data from the Boolardy Engineering Test Array (BETA) of the Australian Square Kilometre Array Pathfinder (ASKAP). Using the 711.5 -1015.5 MHz band of ASKAP we were able to conduct a blind search for the 21 cm line in a continuous redshift range between z = 0.4 -1.0, which has, until now, remained largely unexplored. The absorption line, detected at z = 0.44 towards the GHz-peaked spectrum radio source PKS B1740−517, is confirmed by optical spectroscopy, using the Gemini South telescope, to be intrinsic to the early-type host galaxy. We detect a broad component at 0.2 per cent of the continuum, demonstrating ASKAP's excellent capability for performing a future wide-field survey for H I absorption at these redshifts. The [O III] and [O I] emission lines in the Gemini spectrum are broad and have double-peaked structures, pointing to outflowing ionised gas. Archival data from the XMM-Newton satellite exhibit an absorbed X-ray spectrum that is consistent with a high column density obscuring medium around the AGN. The absorption profile is complex, with four distinct components ranging in width from 5 -300 km s −1 and fractional depths from 0.2 -20 per cent. In addition to systemic H I gas, likely in a regular disc or ring structure, we find evidence for one or two blue shifted clouds and a broad outflow of neutral gas moving at a radial velocity of v ∼ 300 km s −1 . We infer that the expanding young radio source (t age ≈ 2500 yr) is driving surrounding neutral gas in an outflow of ∼ 1 M yr −1 .
Astronomy and Astrophysics, 2007
Context. Several studies of nearby active galaxies indicate significantly higher HCN-to-CO intensity ratios in AGN (e.g., NGC 1068) than in starburst (e.g., M82) environments. HCN enhancement can be caused by many different effects, such as higher gas densities and/or temperatures, UV/X-ray radiation, and non-collisional excitation. As active galaxies often exhibit intense circumnuclear star formation, high angular resolution/high sensitivity observations are of paramount importance to disentangling the influence of star formation from that of nuclear activity on the chemistry of the surrounding molecular gas. The tight relation of HCN enhancement and nuclear activity may qualify HCN as an ideal tracer of molecular gas close to the AGN, providing complementary and additional information to that gained via CO. Aims. NGC 6951 houses nuclear and starburst activity, making it an ideal testbed in which to study the effects of different excitation conditions on the molecular gas. Previous lower angular resolution/sensitivity observations of HCN(1-0) carried out with the Nobeyama Millimeter array by Kohno et al. (1999a) led to the detection of the starburst ring but no central emission has been found. Our aim was to search for nuclear HCN emission and, if successful, for differences of the gas properties of the starburst ring and the nucleus. Methods. We used the new A, B, C and D configurations of the IRAM PdBI array to observe HCN(1-0) in NGC 6951 at high angular resolution (1 ′′ ≡96 pc) and sensitivity. Results. We detect very compact (≤50pc) HCN emission in the nucleus of NGC 6951, supporting previous hints of nuclear gas structure. Our observations also reveal HCN emission in the starburst ring and resolve it into several peaks, leading to a higher coincidence between the HCN and CO distributions than previously reported by Kohno et al. (1999a). Conclusions. We find a significantly higher HCN-to-CO intensity ratio (≥0.4) in the nucleus than in the starburst ring (0.02-0.05). As for NGC 1068, this might result from a higher HCN abundance in the centre due to an X-ray dominated gas chemistry, but a higher gas density/temperature or additional non-collisional excitation of HCN cannot be entirely ruled out, based on these observations. The compact HCN emission is associated with rotating gas in a circumnuclear disk/torus.
Molecular Gas in NUclei of GAlaxies (NUGA) I.The counter-rotating LINER NGC4826
2003
We present new high-resolution observations of the nucleus of the counter-rotating LINER NGC4826, made in the J=1-0 and J=2-1 lines of 12CO with the IRAM Plateau de Bure mm-interferometer(PdBI).The CO maps, which achieve 0.8''(16pc) resolution in the 2-1 line, fully resolve an inner molecular gas disk which is truncated at an outer radius of 700pc. The total molecular gas mass is distributed in a lopsided nuclear disk of 40pc radius and two one-arm spirals, which develop at different radii in the disk. The distribution and kinematics of molecular gas in the inner 1kpc of NGC4826 show the prevalence of different types of m=1 perturbations in the gas. Although dominated by rotation, the gas kinematics are perturbed by streaming motions related to the m=1 instabilities. The non-circular motions associated with the inner m=1 perturbations agree qualitatively with the pattern expected for a trailing wave developed outside corotation ('fast' wave). In contrast, the streami...
The Astrophysical Journal, 1999
We present high resolution (3-5) observations of CO(J=1−0) and HCN(J=1−0) emission from the circumnuclear star forming ring in the barred spiral galaxy NGC 6951, a host of a type-2 Seyfert nucleus, using the Nobeyama Millimeter Array and the Nobeyama 45 m telescope. We find that the distribution of the HCN emission is different from that of CO in the circumnuclear region of NGC 6951; it is confirmed that CO emission is dominated by "twin peaks" morphology with two spiral arms, which are connected to the dust lanes, as reported by Kenney et al. (1992). On the other hand, although the HCN emission also shows a twin peaks morphology, the HCN peaks are spatially shifted downstream compared with the CO peaks. Most of the HCN emission is associated with the circumnuclear ring, where vigorous star formation occurs. The HCN to CO integrated intensity ratio in the brightness temperature scale, R HCN/CO , is also enhanced in the star forming ring. The peak value of the R HCN/CO is about 0.16-0.18, which is comparable to the R HCN/CO in the starburst regions of NGC 253 and M82. Consequently, the HCN emission spatially correlates better with the massive star forming regions than the CO emission in the circumnuclear region of NGC 6951. The formation mechanism of dense molecular gas has been investigated. No significant enhancement of R HCN/CO is observed at the CO peaks, which are interpreted as x 1 /x 2 orbit crowding regions. This suggests that the shocks along the orbit crowding do not promote the formation of dense molecular gas effectively but enhance the presence of low density GMCs in NGC 6951. Instead, gravitational instability can account for the dense molecular gas formation in the circumnuclear star forming ring because Toomre's Q value is below unity there. The R HCN/CO toward the type-2 Seyfert nucleus of NGC 6951 is 0.086 averaged over central r < 120 pc region. This is a rather normal value compared with non-active galaxies such as the Milky Way, and quite different from other type-2 Seyfert galaxies NGC 1068 and M51 where extremely high R HCN/CO of ∼ 0.5 have been reported. The variety of R HCN/CO values in these Seyfert nuclei would be attributed to the different physical conditions of the molecular gas around the nuclei.