Type 1s Research Articles

The spectral energy distribution of the central parsecs of the nearest AGN

Spectral energy distributions (SEDs) of the central few tens of parsec region of some of the nearest, most well studied, active galactic nuclei (AGN) are presented. These genuine AGN-core SEDs, mostly from Seyfert galaxies, are characterised by two main features: an IR bump with the maximum in the 2-10 micron range, and an increasing X-ray spectrum in the 1 to ~200 keV region. These dominant features are common to Seyfert type 1 and 2 objects alike. Type 2 AGN exhibit a sharp drop shortward of 2 micron, with the optical to UV region being fully absorbed, while type 1s show instead a gentle 2 micron drop ensued by a secondary, partially-absorbed optical to UV emission bump. Assuming the bulk of optical to UV photons generated in these AGN are reprocessed by dust and re-emitted in the IR in an isotropic manner, the IR bump luminosity represents >70% of the total energy output in these objects while the high energies above 20 keV are the second energetically important contribution. Galaxies selected by their warm IR colours, i.e. presenting a relatively-flat flux distribution in the 12 to 60 micron range have often being classified as AGN. The results from these high spatial resolution SEDs question this criterion as a general rule. It is found that the intrinsic shape of the IR SED of an AGN and inferred bolometric luminosity largely depart from those derived from large aperture data. AGN luminosities can be overestimated by up to two orders of magnitude if relying on IR satellite data. We find these differences to be critical for AGN luminosities below or about 10^{44} erg/s. Above this limit, AGNs tend to dominate the light of their host galaxy regardless of the aperture size used. We tentatively mark this luminosity as a threshold to identify galaxy-light- vs AGN- dominated objects.

CALIBRATION OF [O IV] 26 μm AS A MEASURE OF INTRINSIC ACTIVE GALACTIC NUCLEUS LUMINOSITY

We compare [O IV] 25.89 μm emission line luminosities with very hard (10-200 keV) X-rays from Swift, INTEGRAL, and BeppoSAX for a complete sample of 89 Seyferts from the Revised Shapley-Ames sample. Using Seyfert 1s, we calibrate [O IV] as a measure of active galactic nucleus (AGN) intrinsic luminosity, for particular use in high-obscuration environments. With this calibration, we measure the average decrement in 14-195 keV X-ray to [O IV] luminosity ratio for Seyfert 2s compared to type 1s. We find a decrement of 3.1 ± 0.8 for Seyfert 2s, and a decrement of 5.0 ± 2.7 for known Compton-thick Seyfert 2s. These decrements imply column densities of approximately log NH = 24.6 cm–2 and 24.7 cm–2, respectively. Thus, we infer that the average Seyfert 2 is more highly obscured and intrinsically more luminous than would be inferred even from the very hard X-rays. We demonstrate two applications of the hard X-ray to [O IV] ratio. For the extremely obscured NGC 1068, we measure a column density of log NH = 25.3-25.4 cm–2. Finally, by comparing [O IV] luminosities to total infrared luminosities for 12 bright ultraluminous infrared galaxies, we find that four have substantial AGN contributions.

The X-ray emission of the most luminous 3CR radio sources

Context. Although many radio-loud quasars and galaxies have been observed in X-rays, systematic studies of well defined samples are rare. Aims. We investigate the X-ray properties of the most luminous radio sources in the 3CR catalogue, in order to assess whether they are similar to the most luminous radio-quiet quasars, for instance in the X-ray normalization with respect to the optical luminosity, or in the distribution of the absorption column density. Methods. We have selected the (optically identified) 3CR radio sources whose 178-MHz monochromatic luminosity lies in the highest factor-of-three bin. The 4 most luminous objects had already been observed in X-rays. Of the remaining 16, we observed 8 randomly chosen ones with XMM-Newton, with the only requirement that half were of type 1 and half of type 2 according to the optical identification. Results. All targets were detected. The optical-to-X-ray spectral index, $\alpha_{\rm ox}$, can be computed only for the type 1s and, in agreement with previous studies, is found to be flatter than in radio-quiet quasars of similar luminosity. However, the Compton-thin type 2s have an absorption-corrected X-ray luminosity systematically lower than the type 1s, by a factor which makes them consistent with the radio-quiet $\alpha_{\rm ox}$. Within the limited statistics, the Compton-thick objects seem to have a reflected component more luminous than the Compton-thin ones. Conclusions. The extra X-ray component observed in type 1 radio-loud quasars is beamed for intrinsic causes, and is not collimated by the absorbing torus as is the case for the (intrinsically isotropic) disk emission. The extra component can be associated with a relativistic outflow, provided that the flow opening angle and the Doppler beaming factor are ~$1/5$-$1/7$ radians.

A new type of dihydroorotate dehydrogenase, type 1S, from the thermoacidophilic archaeon Sulfolobus solfataricus.

Dihydroorotate dehydrogenase (DHOD) (EC 1.3.3.1) from the thermoacidophilic archaeon Sulfolobus solfataricus P2 (DSM 1617) was partially purified 3,158-fold, characterized, and the encoding genes identified. Based on enzymological as well as phylogenetic methods, dihydroorotate dehydrogenase from S. solfataricus (DHODS) represents a new type of DHOD, type 1S. Furthermore, it is unable to use any of the (type-specific) natural electron acceptors employed by all other presently known DHODs. DHODS shows optimal activity at 70 degrees C in the pH range 7-8.5. It is capable of using ferricyanide, 2,6-dichlorophenolindophenol (DCIP), Q(0), and molecular oxygen as electron acceptor. Kinetic studies employing ferricyanide indicate a two-site ping-pong mechanism with K(M) values of 44.2+/-1.9 microM for the substrate dihydroorotate and 344+/-21 microM for the electron acceptor ferricyanide, as well as competitive product inhibition with a K(i) of 23.7+/-3.4 microM for the product orotate (OA). The specific activity, as determined from a partially purified sample, is approximately 20 micromol mg(-1) min(-1). DHODS is a heteromeric enzyme comprising a catalytic subunit encoded by pyrD (291 aa; MW=31.1 kDa) and an electron acceptor subunit (208 aa; MW=23.6 kDa), encoded by orf1. DHODS employs a serine as catalytic base, which is unique for a cytosolic DHOD. To our knowledge, this work represents not only the first study on an archaeal DHOD but the first on a nonmesophilic DHOD as well.

Identification of environmental Serratia plymuthica strains with the new combo panels type 1S.

Automated systems are required when numerous samples need to be processed, offering both high through put and test of a multiple simultaneously. This study was performed to compare the MicroScan WalkAway automated identification system in conjunction with the new MicroScan Combo Neg Panels Type 1S with conventional biochemical methods for identifying ten environmental Serratia plymuthica strains. High correlation between both methods were observed for all the 21 tests evaluated, and the MicroScan system was found capable of correctly identifying all S. plymuthica strains tested. In all tests, the percentage of correlation was 100%, except in raffinose test (91%).

Identification of motile Aeromonas strains with the MicroScan WalkAway system in conjunction with the combo negative type 1S panels.

This study was performed to compare the MicroScan WalkAway automated identification system in conjunction with the new MicroScan Combo Negative type 1S panels with conventional biochemical methods for identifying 85 environmental, clinical, and reference strains of eight Aeromonas species.

Identification of Hafnia alvei with the MicroScan WalkAway system.

Hafnia alvei is a gram-negative facultatively anaerobic bacillus that belongs to the family Enterobacteriaceae. This organism is a causative agent of intestinal disorders and is found in different environments. H. alvei has received increased clinical attention as a cause of different infections in humans. This study was performed to compare the MicroScan WalkAway automated identification system in conjunction with the new MicroScan Combo Negative type 1S panels with conventional biochemical methods for identification of 21 H. alvei strains. The MicroScan WalkAway system was found capable of correctly identifying 20 of the 21 strains tested.

Strong Relativistic Effects and Natural Linewidths Observed in Dielectronic Recombination of Lithiumlike Carbon

Few-electron systems of light elements are usually very well described in terms of LS coupling. Selection rules for atomic processes like radiative transitions, photoionization, and autoionization can be expressed in terms of L and S. For instance, in an electric dipole transition DS › 0, DL › 61 or 0 while parity is changed, and for Coulombic autoionization S, L, and parity are all conserved. It is well known that intercombination transitions, i.e., spinforbidden radiative transitions sDS fi 0d, are extremely weak for light elements. The extent to which such selection rules are obeyed indicates in some sense the validity of LS coupling. Dielectronic recombination is a process in which an electron is recombined with an ion through interaction with the electrons of the ion. The first step of the process is the reversal of autoionization; i.e., a free electron interacts with the bound electrons to form a doubly excited state. This state can decay by autoionization, but it can also relax by a radiative transition to a bound state. In the latter case, dielectronic recombination is completed. In the present work, dielectronic recombination (DR) has been used as a tool to gain spectroscopic information on autoionizing states of the displaced system of berylliumlike carbon. For a Be-like system there are two ionization limits present: 1s 2 2s 2 S and 1s 2 2p 2 P. In Be-like carbon (i.e., C 21 ), these two thresholds are separated by 8 eV. Separate Rydberg series run toward these limits. Consequently there will exist levels of the type 1s 2 2pn, 1,3 L which are energetically degenerate with continuum states 1s 2 2s«, 1,3 L. If the states of the former type have

Double electron capture by He-like ions: Collision energy dependence of the reaction window

Double electron capture by the He-like ions C 4+, N 5+, O 6+, Ne 8+ from the two electron targets H 2 and He is studied by spectroscopy of the autoionization electrons emitted after capture into excited states. Electron spectra are measured in a collision velocity range from 0.18 to 0.55 atomic units. The spectra are found to be due to decay of states of the type (1s 2 3 ln′ l′ and (1s 24 ln′ l′) into the continua (1s 22 l + e and (1s 2 3 l + e. respectively. It is found that only states lying, within a certain reaction window are populated. Energy position and dependence of the width of this window on the collision velocity are discussed and compared with predictions of the classical model for multiple electron capture.

Two-electron-one-photon transitions following double K-shell ionization in symmetric collisions of N, O and Ne

Cross sections for two-electron-one-photon transitions following double K-shell ionization in 200 keV collisions of N++NH3, O++H2O and Ne++Ne are reported. These transitions are of the type (1s)-2 to (2s)-1(2p)-1.

An expansion method for calculating atomic properties. VIII. Transitions in the Hartree-Fock approximation

According to Brillouin’s theorem, diagonal matrix elements of one-electron operators are given correct to first order by the Hartree-Fock approximation. Transition matrix elements of one-electron operators are not given correct to first order because of the contributions from virtual excitations involving a change in the azimuthal quantum number of the active electron but no change in the principal quantum number. The electric dipole matrix elements connecting the 1 s 2 s 1,3 S states of helium to the 1 s 2 p 1,3 P states are calculated exactly to first order in inverse powers of the nuclear charge and the differences from the Hartree-Fock approximation are shown explicitly to correspond to virtual transitions of the inner shell 1 s electron of the type 1 s — np . A generalization of the Hartree-Fock approximation is discussed which eliminates most of the first order error.

Treatment of the H 2 + -ion by means of one-, two- and three-center wave functions

The ground state energy of H 2 + is calculated with one- and multi-center wave functions by means of the variational method. By using hydrogen-like one-center wave functions a bound state is found even with Is function if it is centered-near one of the nuclei. Results can be improved by taking the linear combination of two or three of the one-center wave functions of the type 1s, 2s, 2p 2, 3d 2. By varying the position of the center we get the best results when the center is either located in one of the nuclei or in the middle point between the nuclei. A better approximation can be obtained with the two-center linear combination of 1s type wave functions centered on the two nuclei. The results can be essentially improved with the three-center wave function which is a linear combination of 1s wave functions centered on the two nuclei and on the middle point. In this case the energy and the internuclear distance areE = −0.5972e 2/a 0 andR = 2a 0, respectively, corresponding to the exact values − 0.60263e 2/a 0 and 2a 0.

An Asymptotic Expansion for

In the theory of the specific heats of gases of diatomic molecules the functionplays a well-known and important part. The rotational specific heat Crot of a diatomic molecule, which is susceptible of representation as a rigid body with two equal principal moments of inertia, without spin about the other principal axis, is given bywhere R is the gram-molecular gas-constant andthe pair of equal moments of inertia being equal to A. Whether such a model is or is not an adequate representation is a matter for determination by a detailed study of the structure of the band spectrum, particularly of the nature of the normal electronic and vibrational state. It is known to be applicable to normal molecules of the halogen hydrides, to CO and other molecules which have a normal state of type 1S including (but for a certain special feature) H2.