The BeppoSAX X-ray view of reflection-dominated Seyfert Galaxies

We present new results from BeppoSAX observations of reflection-dominated Seyfert galaxies, and namely: 1) the Compton-thick Seyfert 2s NGC1068 and Circinus Galaxy; 2) the Seyfert 1 NGC4051, whose nucleus was observed on May 1998 to have switched off, leaving only a residual reflection component as an echo of its past activity. Our main focus in this paper is on the soft X-ray continuum properties and on the X-ray line spectroscopy.Comment: 6 Latex pages, 5 figures, Accepted for publication in Advances in Space Research, Proceedings of 32nd Sci. Ass. of COSPA

Suzaku Observations of the Circinus galaxy

We report Suzaku observations of the active, Compton-thick Circinus galaxy. Observations were obtained with both the X-ray Imaging spectrometer (XIS) and the Hard X-ray Detector (HXD). Below 10 keV, the nuclear spectrum is dominated by radiation reflected from cold dense gas of high column density, while above 13 keV the radiation is directly transmitted nuclear emission seen through a column density of $~ 4 x 10^{24} cm^-2. In the 0.2--10 keV band, the XIS spectrum is contaminated at 5% level by the brightest off-nuclear source in Circinus (CG X-1), but drops to 1% in the 5-10 keV and is negligible at higher energies. We find no significant evidence for variability in the hard (>12 keV) emission. The Circinus is marginally detected with the HXD/GSO in the 50--100 keV band at 2.5\sigma level. We model the 3-70 keV band XIS+PIN spectra with a four components: the Compton transmitted nuclear emission, the reflected nuclear emission, a soft power law (representing a combination of scattered nuclear emission, extended emission and contamination by sources in the galaxy below a few keV). The hard nuclear power-law is found to have a photon index Gamma_h ~= 1.6, very similar to the soft power-law. The high energy cut-off is E_C ~= 49 keV. These results agree with those from BeppoSax. An extrapolation of this model up to the GSO band shows good agreement with the GSO spectrum and supports our detection of the Circinus up to ~= 100keV.Comment: ApJ accepte

Brain Age from the Electroencephalogram of Sleep

The human electroencephalogram (EEG) of sleep undergoes profound changes with age. These changes can be conceptualized as "brain age", which can be compared to an age norm to reflect the deviation from normal aging process. Here, we develop an interpretable machine learning model to predict brain age based on two large sleep EEG datasets: the Massachusetts General Hospital sleep lab dataset (MGH, N = 2,621) covering age 18 to 80; and the Sleep Hearth Health Study (SHHS, N = 3,520) covering age 40 to 80. The model obtains a mean absolute deviation of 8.1 years between brain age and chronological age in the healthy participants in the MGH dataset. As validation, we analyze a subset of SHHS containing longitudinal EEGs 5 years apart, which shows a 5.5 years difference in brain age. Participants with neurological and psychiatric diseases, as well as diabetes and hypertension medications show an older brain age compared to chronological age. The findings raise the prospect of using sleep EEG as a biomarker for healthy brain aging

The final verdict by XMM-Newton: the X-ray obscured Seyfert galaxy NGC5506 has a broad Fe K-alpha line

We present the first unambiguous evidence of a broad (Gaussian width ~330 eV) component of the iron K-alpha fluorescent emission line in the X-ray obscured Narrow Line Seyfert 1 Galaxy NGC5506. This is the main results of a spectroscopic monitoring campaign on this source performed with the XMM-Newton observatory between February 2001 and January 2009. The broad line lacks extreme redwards skewness. If modelled with a relativistic component, the profile of the line is consistent with a flat emissivity radial dependence (alpha~1.9). The disk inclination (~40 degrees) is nominally larger then typically observed in unobscured AGN, in agreement with most measurements of broadened iron lines in Seyfert 2 galaxies. The quality of the data allows us to decompose the full iron emission line complex, and to study its long-term (timescales of weeks to years) variability pattern. The intensity of the neutral and narrow iron K-alpha core remains constant during the monitoring campaign. This indicates that the optically thick gas responsible for the non-relativistic reprocessing of the primary AGN continuum in NGC5506 is probably located in the torus rather than in the optical Broad Line Region.Comment: 11 pages, 8 figures, accepted for publication in MNRA

Discovery of a nuclear gas bar feeding the active nucleus in Circinus

We report the discovery of gas inflow motions towards the active nucleus of the Circinus galaxy caused by the non-axisymmetric potential of a nuclear gas bar. Evidence for dust associated with the bar comes from the HST/NICMOS H-K color map, whereas the streaming motions along the gas bar are seen in the velocity field of the H2 S(1)(1-0) emission line. The gas bar is about 100 pc long with a visual extinction in excess of 10 mag. Indication for the gaseous nature of this bar comes from the lack of a stellar counterpart even in the K band where the extinction is greatly reduced. We also use the NICMOS emission line images (Pa-alpha, [SiVI], and [FeII]) to study the innermost region of the ionization cones and the nuclear star forming activity. We discuss the possible relationship of these components with the gaseous bar.Comment: 14 pages, 7 figures (3 color plates), accepted for publication in Ap

Resolving the complex structure of the dust torus in the active nucleus of the Circinus galaxy

To test the dust torus model for active galactic nuclei directly, we study the extent and morphology of the nuclear dust distribution in the Circinus galaxy using high resolution interferometric observations in the mid-infrared with the MIDI instrument at the Very Large Telescope Interferometer. We find that the dust distribution in the nucleus of Circinus can be explained by two components, a dense and warm disk-like component of 0.4 pc size and a slightly cooler, geometrically thick torus component with a size of 2.0 pc. The disk component is oriented perpendicular to the ionisation cone and outflow and seems to show the silicate feature at 10 micron in emission. It coincides with a nuclear maser disk in orientation and size. From the energy needed to heat the dust, we infer a luminosity of the accretion disk corresponding to 20% of the Eddington luminosity of the nuclear black hole. We find that the interferometric data are inconsistent with a simple, smooth and axisymmetric dust emission. The irregular behaviour of the visibilities and the shallow decrease of the dust temperature with radius provide strong evidence for a clumpy or filamentary dust structure. We see no evidence for dust reprocessing, as the silicate absorption profile is consistent with that of standard galactic dust. We argue that the collimation of the ionising radiation must originate in the geometrically thick torus component. Our findings confirm the presence of a geometrically thick, torus-like dust distribution in the nucleus of Circinus, as required in unified schemes of Seyfert galaxies. Several aspects of our data require that this torus is irregular, or "clumpy".Comment: 20 pages, 16 figures, accepted for publication by A&

Obscuration of Active Galactic Nuclei by Circumnuclear Starbursts

We examine the possibility of the active galactic nucleus (AGN) obscuration by dusty gas clouds that spurt out from circumnuclear starburst regions. For the purpose, the dynamical evolution of gas clouds is pursued, including the effects of radiation forces by an AGN as well as a starburst. Here, we solve the radiative transfer equations for clouds, taking into consideration the growth of clouds by inelastic cloud-cloud collisions and the resultant change in optical depth. As a result, it is shown that if the starburst is more luminous than the AGN, gas clouds are distributed extensively above a galactic disk with the assistance of radiation pressure from the starburst. The total covering factor of gas clouds reaches a maximum of around 20%. After several $10^{7}$yr, gas clouds with larger optical depth form by cloud-cloud collisions and thereafter the clouds fall back due to weakened radiation pressure. The larger clouds undergo runaway growth and are eventually distributed around the equatorial plane on the inner sides of circumnuclear starburst regions. These clouds have an optical depth of several tens. The result is qualitatively consistent with the putative tendency that Seyfert 2 galaxies appear more frequently associated with starbursts than Seyfert 1s. On the other hand, if the AGN luminosity overwhelms that of the starburst, almost all clouds are ejected from the galaxy due to the radiation pressure from the AGN, resulting in the formation of a quasar-like object. The origin of obscuration of AGNs is discussed with relevant observations.Comment: 10 pages, 8 figure, accepted for publication in ApJ; Fig. 3 and Fig . 7 are available at http://www.rccp.tsukuba.ac.jp/Astro/watabe

Multicolour Optical Imaging of IR-Warm Seyfert Galaxies. V. Morphologies and Interactions. Challenging the Orientation Model

This paper is the last in a series, investigating the optical properties of a sample of mid-IR Warm Seyfert galaxies and of a control sample of mid-IR cold galaxies. In the present paper we parametrize the morphologies and interaction properties of the host galaxies and combine these with the major conclusions in our previous papers. Our results confirm that nuclear activity is linked to galactic interactions. We suggest an alternative view for the simple orientation-obscuration model postulated for Seyfert types 1 and 2, that takes into account the time evolution of their environmental and morphological properties. Within this view, an evolutionary link between starburst-dominated and AGN-dominated IR emission is also suggested, to account for the observational discriminator (mid-IR excess) between our Warm and Cold samples.Comment: 24 pages, including 6 figures and 3 tables (figure 5 included as independent file), Submitted to Ap

On the nature of X-ray absorption in Seyfert 2 galaxies

We have studied the correlation among X-ray absorption, optical reddening and nuclear dust morphology in Seyfert 2 galaxies. Two main conclusions emerge: a) the Balmer decrement and the amount of X-ray absorption are anticorrelated on a wide range of column density: 10^{21} < N_H < 10^{24} atoms/cm/cm. The correlation does no longer apply to Compton-thick objects (N_H < 10^{24} atoms/cm/cm), although they span a comparable range in Balmer decrement; b) Compton-thin Seyfert 2s seem to prefer nuclear environments, which are rich of dust on scales of the hundreds parsecs. On the other hand, Compton-thick Seyferts exhibit indifferently ``dust-poor'' and ``dust-rich'' environments. These results support an extension of the Seyfert unification scenario (as recently proposed by Matt, 2000), where Compton-thick Seyfert 2s are observed through compact ``torii'', whereas Compton-thin ones are obscured by dust on much larger scalesComment: 7 Latex pages, 6 figures, Accepted for publication in Monthly Notices of the Royal Astonomical Societ

A Chandra Observation of the Circinus Galaxy

We report on a recent Chandra ACIS-S observation of the Circinus galaxy. These observations confirm that the nuclear spectrum results from reflection of a hard X-ray continuum by ``neutral'' matter. The nuclear X-ray emission is extended by \sim 60 pc in the general direction of the optical ``ionization cone''. An image in the Fe K\alpha line has been made and shows that this emission extends up to 200 pc from the nucleus. There is also large-scale X-ray emission both along and perpendicular to the galaxy disk. Thermal plasma models for this extended gas indicate temperatures kT \sim 0.6 keV, though cooler photoionized gas is also possible. The X-ray emission from gas in the disk is probably associated with the starburst ring of radius 150--250 pc. The gas extending \sim 600 pc perpendicular to the disk is closely correlated with the high-excitation optical-line emission. In addition to its soft X-ray emission, we tentatively detect a hard component from the gas above the plane; this hard emission may represent nuclear X-rays scattered into our line of sight by electrons in the outflowing wind. Ten compact sources are found in the central kpc of the galaxy. The most luminous has an X-ray luminosity of \simeq 10^{40} erg s^{-1} and seems to be an X-ray binary in the Circinus galaxy with a black-hole mass exceeding 80 M_{\odot}.Comment: 25 pages, 13 figures. Accepted for publication in The Astrophysical Journa