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Register a new userThe ionised gas outflow in the Circinus galaxy: kinematics and physical conditions
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Added by
Marcos Fonseca-Faria
Publication date
2021
fields
Physics
and research's language is
English
Authors
M. A. Fonseca-Faria
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We employ MUSE/VLT data to study the ionised and highly ionised gas phases of the feedback in Circinus, the closest Seyfert 2 galaxy to us. The analysis of the nebular emission allowed us to detect a remarkable high-ionisation gas outflow beyond the galaxy plane traced by the coronal lines [Fe VII] $lambda$6089 and [Fe X] $lambda$6374, extending up to 700 pc and 350 pc NW from the nucleus, respectively. This is the first time that the [Fe X] emission is observed at such distances from the central engine in an AGN. The gas kinematics reveals expanding gas shells with velocities of a few hundred km s$^{-1}$, spatially coincident with prominent hard X-ray emission detected by Chandra. Density and temperature sensitive line ratios show that the extended high-ionisation gas is characterized by a temperature reaching 25000 K and an electron density > 10$^2$ cm$^{-3}$. We found that local gas excitation by shocks produced by the passage of a radio jet leads to the spectacular high-ionisation emission in this object. This hypothesis is fully supported by photoionisation models that accounts for the combined effects of the central engine and shocks. They reproduce the observed emission line spectrum at different locations inside and outside of the NW ionisation cone. The energetic outflow produced by the radio jet is spatially located close to an extended molecular outflow recently reported using ALMA which suggests that they both represent different phases of the same feedback process acting on the AGN.
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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.
The most intensively star-forming galaxies are extremely luminous at far-infrared (FIR) wavelengths, highly obscured at optical and ultraviolet wavelengths, and lie at $zge 1-3$. We present a programme of ${it Herschel}$ FIR spectroscopic observations with the SPIRE FTS and photometric observations with PACS, both on board ${it Herschel}$, towards a sample of 45 gravitationally lensed, dusty starbursts across $zsim 1-3.6$. In total, we detected 27 individual lines down to 3-$sigma$, including nine $[rm C{small II}]$ 158-$mu$m lines with confirmed spectroscopic redshifts, five possible $[rm C{small II}]$ lines consistent with their far-infrared photometric redshifts, and in some individual sources a few $[rm O{small III}]$ 88-$mu$m, $[rm O{small III}]$ 52-$mu$m, $[rm O{small I}]$ 145-$mu$m, $[rm O{small I}]$ 63-$mu$m, $[rm N{small II}]$ 122-$mu$m, and OH 119-$mu$m (in absorption) lines. To derive the typical physical properties of the gas in the sample, we stack all spectra weighted by their intrinsic luminosity and by their 500-$mu$m flux densities, with the spectra scaled to a common redshift. In the stacked spectra, we detect emission lines of $[rm C{small II}]$ 158-$mu$m, $[rm N{small II}]$ 122-$mu$m, $[rm O{small III}]$ 88-$mu$m, $[rm O{small III}]$ 52-$mu$m, $[rm O{small I}]$ 63-$mu$m, and the absorption doublet of OH at 119-$mu$m, at high fidelity. We find that the average electron densities traced by the $[rm N{small II}]$ and $[rm O{small III}]$ lines are higher than the average values in local star-forming galaxies and ULIRGs, using the same tracers. From the $[rm N{small II}]/[rm C{small II}]$ and $[rm O{small I}]/[rm C{small II}]$ ratios, we find that the $[rm C{small II}]$ emission is likely dominated by the photo-dominated regions (PDR), instead of by ionised gas or large-scale shocks.
We present a detailed X-ray spectral analysis of the Circinus Galaxy using archival data obtained with the ASCA satellite. The spectrum shows numerous emission lines in the soft X-ray band from highly ionized ions, as well as Compton reflection and fluorescent lines from neutral or near-neutral matter. We analyze the spectrum in the context of a self-consistent recombination cascade model and find that a nearly flat differential emission measure (DEM) distribution in ionization parameter fits the data. For a fixed solid angle distribution of matter surrounding a point source, this corresponds to a run of electron density of the form, n(r) ~ r^(-3/2), which is suggestive of Bondi accretion onto a central compact mass. Using this density profile and comparing the resulting emission spectra with the ASCA data, the size of the X-ray emission line region is estimated to be < 1 kpc. We also show that the derived density as a function of radius is compatible with the X-ray recombination line emission region being the confining medium of the coronal line regions.
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.
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