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Register a new userGas and Dust Emission from the Nuclear Region of the Circinus Galaxy
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Simultaneous modeling of the line and continuum emission from the nuclear region of the Circinus galaxy is presented. Composite models which include the combined effect of shocks and photoionization from the active center and from the circumnuclear star forming region are considered. The effects of dust reradiation, bremsstrahlung from the gas and synchrotron radiation are treated consistently. The proposed model accounts for two important observational features. First, the high obscuration of Circinus central source is produced by high velocity and dense clouds with characteristic high dust-to-gas ratios. Their large velocities, up to 1500 kms, place them very close to the active center. Second, the derived size of the line emitting region is well in agreement with the observed limits for the coronal and narrow line region of Circinus.
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We report the first characterization of an extended outflow of high ionized gas in the Circinus Galaxy by means of the coronal line [FeVII] $lambda$6087 AA. This emission is located within the ionization cone already detected in the [OIII] $lambda$5007 AA line and is found to extend up to a distance of 700 pc from the AGN. The gas distribution appears clumpy, with several knots of emission. Its kinematics is complex, with split profiles and line centroids shifted from the systemic velocity. The physical conditions of the gas show that the extended coronal emission is likely the remnants of shells inflated by the passage of a radio-jet. This scenario is supported by extended X-ray emission, which is spatially coincident with the morphology and extension of the [FeVII] $lambda$6087~AA gas in the NW side of the galaxy. The extension of the coronal gas in the Circinus galaxy is unique among active galaxies and demonstrates the usefulness of coronal lines for tracing the shock ionization component in these objects.
We present a detailed study of the Circinus Galaxy, investigating its star formation, dust and gas properties both in the inner and outer disk. To achieve this, we obtained high-resolution Spitzer mid-infrared images with the IRAC (3.6, 5.8, 4.5, 8.0 micron) and MIPS (24 and 70 micron) instruments and sensitive HI data from the Australia Telescope Compact Array (ATCA) and the 64-m Parkes telescope. These were supplemented by CO maps from the Swedish-ESO Submillimetre Telescope (SEST). Because Circinus is hidden behind the Galactic Plane, we demonstrate the careful removal of foreground stars as well as large- and small-scale Galactic emission from the Spitzer images. We derive a visual extinction of Av = 2.1 mag from the Spectral Energy Distribution of the Circinus Galaxy and total stellar and gas masses of 9.5 x 10^{10} Msun and 9 x 10^9 Msun, respectively. Using various wavelength calibrations, we find obscured global star formation rates between 3 and 8 Msun yr^{-1}. Star forming regions in the inner spiral arms of Circinus, which are rich in HI, are beautifully unveiled in the Spitzer 8 micron image. The latter is dominated by polycyclic aromatic hydrocarbon (PAH) emission from heated interstellar dust. We find a good correlation between the 8 micron emission in the arms and regions of dense HI gas. The (PAH 8 micron) / 24 micron surface brightness ratio shows significant variations across the disk of Circinus.
In some AGN, nuclear dust lanes connected to kpc-scale dust structures provide all the extinction required to obscure the nucleus, challenging the role of the dusty torus proposed by the Unified Model. In this letter we show the pc-scale dust and ionized gas maps of Circinus constructed using sub-arcsec-accuracy registration of infrared VLT AO images with optical textit{Hubble Space Telescope} images. We find that the collimation of the ionized gas does not require a torus but is caused by the distribution of dust lanes of the host galaxy on $sim$10 pc scales. This finding questions the presumed torus morphology and its role at parsec scales, as one of its main attributes is to collimate the nuclear radiation, and is in line with interferometric observations which show that most of the pc-scale dust is in the polar direction. We estimate that the nuclear dust lane in Circinus provides $1/3$ of the extinction required to obscure the nucleus. This constitutes a conservative lower limit to the obscuration at the central parsecs, where the dust filaments might get optically thicker if they are the channels that transport material from $sim$100 pc scales to the centre.
We have used the ATCA and the SEST to map the large-scale atomic and molecular gas in the nearby Circinus galaxy. The HI mosaic of Circinus exhibits the warps in position angle and inclination revealed in the single-pointing image, both of which appear to settle beyond the inner 30 kpc which was previously imaged. The molecular gas has been mapped in both the CO transitions, where we derive a total molecular gas mass of ~2e9 Mo. Within a radius of 3 kpc, i.e. where CO was clearly detected, the molecular fraction climbs steeply from ~0.7 to unity with proximity to the nucleus. Our HI mosaic gives an atomic gas mass of ~6e9 Mo which is 70% of the fully mapped single dish value. The total neutral gas mass to dynamical mass ratio is therefore 3%, consistent with the SAS3 classification of Circinus. The high (molecular) gas mass fraction found previously, only occurs close to the central ~0.5 kpc and falls to < 10% within and outwith this region, allaying previous concerns regarding the validity of applying the Galactic conversion ratio to Circinus. The rotation curve, as traced by both the HI and CO, exhibits a steep dip at ~1 kpc, the edge of the atomic/molecular ring, within which the star-burst is occurring. We find the atomic and molecular gases to trace different kinematical features and believe that the fastest part of the sub-kpc ring consists overwhelmingly of molecular gas. Beyond the inner kpc, the velocity climbs to settle into a solid body rotation at >10 kpc. Most of the starlight emanates from within this radius and so much of the dynamical mass, which remains climbing to the limit of our data (>50 kpc), must be due to the dark matter halo.
We present an imaging and spectral analysis of the nuclear region of the ULIRG merger Arp 220, using deep textit{Chandra}-ACIS observations summing up to (sim 300mbox{ ks}). Narrow-band imaging with sub-pixel resolution of the innermost nuclear region reveals two distinct Fe-K emitting sources, coincident with the infrared and radio nuclear clusters. These sources are separated by 1 ((sim 380) pc). The X-ray emission is extended and elongated in the eastern nucleus, like the disk emission observed in millimeter radio images, suggesting starburst dominance in this region. We estimate Fe-K equivalent width (gtrsim 1) keV for both sources, and observed 2-10 keV luminosities (sim 2times{10}^{40}mbox{ erg}mbox{ s}^{-1}) (W) and (sim 3 times {10}^{40}mbox{ erg}mbox{ s}^{-1}) (E). In the 6-7 keV band the emission from these regions is dominated by the 6.7 keV Fe textsc{xxv} line, suggesting contribution from collisionally ionized gas. The thermal energy content of this gas is consistent with kinetic energy injection in the interstellar medium by Type II SNe. However, nuclear winds from hidden AGN ((varvsim 2000 mbox{ km}mbox{ s}^{-1})) cannot be excluded. The (3sigma) upper limits on the neutral Fe-K(alpha) flux of the nuclear regions correspond to intrinsic AGN 2-10 keV luminosities (< 1times {10}^{42}mbox{ erg}mbox{ s}^{-1}) (W) and (< 0.4times {10}^{42}mbox{ erg}mbox{ s}^{-1}) (E). For typical AGN SEDs the bolometric luminosities are (< 3times {10}^{43}mbox{ erg}mbox{ s}^{-1}) (W) and (< 8times {10}^{43}mbox{ erg}mbox{ s}^{-1}) (E), and black hole masses (<1times{10}^5 M_{astrosun}) (W) and (< 5times{10}^5 M_{astrosun}) (E) for Eddington limited AGNs with a standard 10% efficiency.
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