Spectral Properties of Heavily Obscured Seyfert Galaxies from the INTEGRAL All-Sky Survey

Astronomy Letters - We have investigated the X-ray spectral properties of the ten heavily obscured nearby (z < 0.1) active galactic nuclei (AGNs) IGR J00256+6821, NGC 1194, CGCG...     

Weighing black holes with warm absorbers

We present a new technique for determining an upper limit for the mass of the black hole in active galactic nuclei showing warm absorption features. The method relies on the balance of radiative and gravitational forces acting on outflowing warm absorber clouds. It has been applied to six objects: five Seyfert 1 galaxies: IC 4329a, MCG-6-30-15, NGC 3516, NGC 4051 and NGC 5548; and one radio-quiet quasar: MR 2251-178. We discuss our result in comparison with other methods. The procedure could also be applied to any other radiatively driven optically thin outflow in which the spectral band covering the major absorption is directly observed.     

Numerical studies on the structure of the cosmic ray electron halo in starburst galaxies

The structure of the cosmic ray electron halo of a starburst galaxy depends strongly on the nature of galactic wind and the configuration of the magnetic field. We have investigated these dependencies by solving numerically the propagation of electrons originating in starburst galaxies, most likely in supernova remnants. The calculations are made for several models for the galactic winds and for the configuration of the magnetic fields for comparison with observations. Our simulation of a quasi-radio halo reproduces both the extended structure of ∼9 kpc and the subtle hollow structure near the polar region of the radio halo that are observed in the starburst galaxy NGC 253. These findings suggest the existence of strong galactic wind in NGC 253.      

Photometric study of the OB star clusters NGC 1502 and NGC 2169 and mass estimation of their members at the University Observatory Jena

In this work we present detailed photometric results of the trapezium like galactic nearby OB clusters NGC 1502 and NGC 2169 carried out at the University Observatory Jena. We determined absolute BVRI magnitudes of the mostly resolved components using Landolt standard stars. This multi colour photometry enables us to estimate spectral type and absorption as well as the masses of the components, which were not available for most of the cluster members in the literature so far, using models of stellar evolution. Furthermore, we investigated the optical spectrum of the components ADS 2984A and SZ Cam of the sextuple system in NGC 1502. Our spectra clearly confirm the multiplicity of these components, which is the first investigation of this kind at the University Observatory Jena (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Do LINER 2 galaxies harbour low-luminosity active galactic nuclei?

We use ROSAT HRI spatial data and ASCA spectral measurements for a sample of seven nearby, early-type spiral galaxies, to address the question of whether a low-luminosity active galactic nucleus (LLAGN) is present in galaxies that have a LINER 2 classification. The brightest discrete X-ray source in the ROSAT HRI observations is invariably found to be positionally coincident with the optical galactic nucleus, and in most cases its flux dominates the X-ray emission from the central region of the galaxy. All seven galaxies have X-ray spectra consistent with a two-component, soft thermal plus hard power-law, spectral form. If we exclude the two galaxies with relatively hard X-ray spectra, NGC 3628 and NGC 4594, for which there is supporting evidence for a LLAGN (or alternatively in the case of NGC 3628 a dominant ultraluminous X-ray binary), then the remaining galaxies show surprisingly similar X-ray spectral properties. Specifically the flux ratio F _X(0.5–1)/ F _X(2–5) , which measures the relative strengths of the thermal and non-thermal emission components, shows little scatter about a mean of 0.66, a value very similar to that measured in the classic starburst galaxy NGC 253. As there is no obvious reason why the luminosity of the hard power-law continuum emanating from a putative LLAGN should be very closely correlated with the thermal emission of the surrounding region, this suggests that that the broad-band (0.5–5 keV) X-ray emission from these LINER 2 galaxies may originate in a common set of processes probably associated with the starburst phenomenon. Conversely, it appears that in many LINER 2 galaxies and perhaps the majority, the nuclear X-ray luminosity does not derive directly from the presence of a LLAGN.     

X-ray spectral evolution in an X-ray changing-look AGN NGC 1365 with variable column density

X-ray changing-look active galactic nuclei(CL AGNs) are a subpopulation of AGNs, whose lineof-sight column densities increase/decrease within several years. The physical mechanism for the variation of column density is unclear. We reduce the X-ray data from XMM-Newton and Nu STAR observations for a CL AGN NGC 1365 with strong variation of column densities. The X-ray spectrum quickly softens as the X-ray luminosity increases and optical-to-X-ray spectral index also increases as increasing of optical luminosity. These results support that NGC 1365 also undergoes strong spectral evolution as that recently suggested for the optically selected CL AGNs with reappearance/disappearance of broad emission lines.Therefore, the variation of column density may be driven by the variable disk winds during the strong evolution of disk/corona.     

NGC 3310 and its tidal debris: remnants of galaxy evolution

NGC 3310 is a local galaxy with an intense, ongoing starburst thought to result from a merger with a companion galaxy. It has several known tidal features in the northwest and southern regions around the main galactic disc, as well as a closed, tidal loop emerging from the eastern side of the disc and rejoining in the north. This loop appears to be distinct from the rest of the shells surrounding NGC 3310 and is the first of its kind to be detected in a starburst galaxy. In this work, we present U BV R photometry to faint surface brightness levels of this debris network, and we explore various strategies for modelling NGC 3310's disc and subtracting its contribution from each region of debris. We then compare these photometric results with the GALaxy EVolution (GALEV) spectral synthesis models, and find possible material from the intruder galaxy, suggesting that the recent accretion of several small galaxies is driving the evolution of NGC 3310.     

A new superwind galaxy: XMM–Newton observations of NGC 6810

We present the first imaging X-ray observation of the highly inclined  ( i = 78°)  Sab Seyfert 2 galaxy NGC 6810 using XMM–Newton , which reveals soft X-ray emission that extends out to a projected height of ∼7 kpc away from the plane of the galaxy. The soft X-ray emission beyond the optical disc of the galaxy is most plausibly extraplanar, although it could instead come from large galactic radius. This extended X-ray emission is spatially associated with diffuse Hα emission, in particular with a prominent 5-kpc-long Hα filament on the north-west of the disc. A fraction ≲35 per cent of the total soft X-ray emission of the galaxy arises from projected heights  | z | ≥ 2 kpc  . Within the optical disc of the galaxy the soft X-ray emission is associated with the star-forming regions visible in ground-based Hα and XMM–Newton optical monitor near-UV imaging. The temperature, supersolar α-element-to-iron abundance ratio, soft X-ray/Hα correlation, and X-ray to far-infrared (FIR) flux ratio of NGC 6810 are all consistent with local starbursts with winds, although the large base radius of the outflow would make NGC 6810 one of the few 'disc-wide' superwinds currently known. Hard X-ray emission from NGC 6810 is weak, and the total   E = 2–10 keV  luminosity and spectral shape are consistent with the expected level of X-ray binary emission from the old and young stellar populations. The X-ray observations provide no evidence of any active galactic nucleus activity. We find that the optical, IR and radio properties of NGC 6810 are all consistent with a starburst galaxy, and that the old classification of this galaxy as a Seyfert 2 galaxy is probably incorrect.     

The formerly X-ray reflection-dominated Seyfert 2 galaxy NGC 6300

In this paper, a BeppoSAX observation of the bright Seyfert 2 galaxy NGC 6300 is presented. The rapidly variable emission from the active nucleus is seen through a Compton-thin     absorber. A Compton-reflection component with an unusually high reflection fraction     , and the comparison with a reflection-dominated spectrum measured by RXTE two and half years earlier suggest that NGC 6300 belongs to the class of 'transient' active galactic nucleus, undergoing long and repeated periods of low activity. The spectral transition provides support to the idea that Compton-thick and Compton-thin X-ray absorbers in Seyfert 2 galaxies are decoupled, the former being most likely associated with the 'torus', whereas the latter is probably located at much larger distances.     

Application of the global modal approach to the spiral galaxies

We have tested the applicability of the global modal approach in the density wave theory of spiral structure for a sample of spiral galaxies with measured axisymmetric background properties. We report here the results of the simulations for four galaxies: NGC 488, NGC 628, NGC 1566, and NGC 3938. Using the observed radial distributions for the stellar velocity dispersions and the rotation velocities we have constructed the equilibrium models for the galactic disks in each galaxy and implemented two kinds of stability analyses - the linear global analysis and 2D-nonlinear simulations. In general, the global modal approach is able to reproduce the observed properties of the spiral arms in the galactic disks. The growth of spirals in the galactic disks can be physically understood in terms of amplification by over-reflection at the corotation resonance. Our results support the global modal approach as a theoretical explanation of spiral structure in galaxies. This revised version was published online in August 2006 with corrections to the Cover Date.     

XMM–Newton observations of bright ROSAT selected active galactic nuclei with low intrinsic absorption

We present a sample of 21 ROSAT bright active galactic nuclei (AGNs), representing a range of spectral classes, and selected for follow-up snapshot observations with XMM–Newton . The typical exposure was between 5 and 10 ks. The objects were primarily selected on the bases of X-ray brightness and not on hardness ratio; thus the sample cannot be strictly defined as a 'soft'sample. One of the main outcomes from the XMM–Newton observations was that all of the AGN, including 11 type 1.8–2 objects, required low levels of intrinsic absorption  ( N _H≲ 10²¹ cm⁻²)  . The low absorption in type 2 systems is a challenge to account for in the standard orientation-based unification model, and we discuss possible physical and geometrical models which could elucidate the problem. Moreover, there does not appear to be any relation between the strength and shape of the soft excess, and the spectral classification of the AGN in this sample. We further identify a number of AGN which deserve deeper observations or further analysis: for example, the low-ionization nuclear emission regions (LINERs) NGC 5005 and NGC 7331, where optically thin thermal and extended emission is detected, and the narrow-line Seyfert 1 II Zw 177, which shows a broad emission feature at ∼ 5.8 keV.     

The period–luminosity relation for type II Cepheids in globular clusters

We report the result of our near-infrared observations ( JHK _s) for type II Cepheids (including possible RV Tau stars) in galactic globular clusters. We detected variations of 46 variables in 26 clusters (10 new discoveries in seven clusters) and present their light curves. Their periods range from 1.2 d to over 80 d. They show a well-defined period–luminosity relation at each wavelength. Two type II Cepheids in NGC 6441 also obey the relation if we assume the horizontal branch stars in NGC 6441 are as bright as those in metal-poor globular clusters in spite of the high metallicity of the cluster. This result supports the high luminosity which has been suggested for the RR Lyr variables in this cluster. The period–luminosity relation can be reproduced using the pulsation equation     assuming that all the stars have the same mass. Cluster RR Lyr variables were found to lie on an extrapolation of the period–luminosity relation. These results provide important constraints on the parameters of the variable stars.
Using Two Micron All-Sky Survey (2MASS) data, we show that the type II Cepheids in the Large Magellanic Cloud (LMC) fit our period–luminosity relation within the expected scatter at the shorter periods. However, at long periods (   P > 40  d, i.e. in the RV Tau star range) the LMC field variables are brighter by about one magnitude than those of similar periods in galactic globular clusters. The long-period cluster stars also differ from both these LMC stars and galactic field RV Tau stars in a colour–colour diagram. The reasons for these differences are discussed.     

Numerical modelling of the vertical structure and dark halo parameters in disc galaxies

The non‐linear dynamics of bending instability and vertical structure of a galactic stellar disc embedded into a spherical halo are studied with N‐body numerical modelling. Development of the bending instability in stellar galactic disc is considered as the main factor that increases the disc thickness. Correlation between the disc vertical scale height and the halo‐to‐disc mass ratio is predicted from the simulations. The method of assessment of the spherical‐to‐disc mass ratio for edge‐on spiral galaxies with a small bulge is considered. Modelling of eight edge‐on galaxies: NGC 891, NGC 4738, NGC 5170, UGC 6080, UGC 7321, UGC 8286, UGC 9422 and UGC 9556 is performed. Parameters of stellar discs, dark haloes and bulges are estimated. The lower limit of the dark‐to‐luminous mass ratio in our galaxies is of the order of one within the limits of their stellar discs. The dark haloes dominate by mass in the galaxies with very thin stellar discs (NGC 5170, UGC 7321 and UGC 8286) (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A search for H I in nine southern galactic clusters

The results of a search for H I features in nine galactic clusters are reported. In six of the clusters the earliest spectral types represented are in the range B0–B9. On the whole, twelve H I features (nine maxima and three minima) were detected, of which seven were disregarded as they were not related to any cluster. The conclusion is that at least in six clusters (Cr 121, Cr 140, Cr 132a, b, Ru 3 and Ru 106) no related H I could be detected. For the remainder (NGC 5460, Cr 135 and Cr 394), the evidence was inconclusive. Our results are in agreement with the qualitative conclusion from earlier work that interstellar H I should be expected only in relatively young clusters.Participated only in the observations and study of the clusters Cr 394, Ru 106 and NGC 5460.     

Timing evidence in determining the accretion state of the Seyfert galaxy NGC 3783

Previous observations with the Rossi X-ray Timing Explorer ( RXTE ) have suggested that the power spectral density (PSD) of NGC 3783 flattens to a slope near zero at low frequencies, in a similar manner to that of Galactic black hole X-ray binary systems (GBHs) in the 'hard' state. The low radio flux emitted by this object, however, is inconsistent with a hard state interpretation. The accretion rate of NGC 3783 (∼7 per cent of the Eddington rate) is similar to that of other active galactic nuclei (AGN) with 'soft'-state PSDs and higher than that at which the GBH Cyg X-1, with which AGN are often compared, changes between 'hard' and 'soft' states (∼2 per cent of the Eddington rate). If NGC 3783 really does have a 'hard'-state PSD, it would be quite unusual and would indicate that AGN and GBHs are not quite as similar as we currently believe. Here we present an improved X-ray PSD of NGC 3783, spanning from ∼10⁻⁸ to ∼10⁻³ Hz, based on considerably extended (5.5 yr) RXTE observations combined with two orbits of continuous observation by XMM–Newton . We show that this PSD is, in fact, well fitted by a 'soft' state model which has only one break, at high frequencies. Although a 'hard'-state model can also fit the data, the improvement in fit by adding a second break at low frequency is not significant. Thus NGC 3783 is not unusual. These results leave Arakelian 564 as the only AGN which shows a second break at low frequencies, although in that case the very high accretion rate implies a 'very high', rather than 'hard' state PSD. The break frequency found in NGC 3783 is consistent with the expectation based on comparisons with other AGN and GBHs, given its black hole mass and accretion rate.     

The thermal and non-thermal components of sixteen nebular complexes

The nature of the fine structure of sixteen galactic nebular complexes is investigated by producing their radio spectra. The complexes are: W31, W33, W35, K39, W42, W40, W43, W48, W47, W49, K47, W51, W3, Carina, NGC 6334 and NGC 6357. Various physical parameters of the thermal components are derived by adopting a homogeneous, optically thin, spherical model. The variations of the physical parameters derived from the model as a function of the electron temperature and distance are investigated. A discussion about the thermal and non-thermal spectra is included. Some simple statistics on the physical parameters of the thermal sources (diameter, density, mass) are also presented by employing a sample of sixty-seven thermal components.     

The Evolution of the Interstellar Medium over Cosmic Time

C23 UV spectroscopy of the PG1159-type star NGC7094 C26 Variations of the radio synchrotron spectral index in the interstellar medium of M33 C38 Angular Momentum Evolution of Young Brown Dwarfs and Low Mass Stars C48 The radio halo of the nearby starburst galaxy NGC 253 C95 Signatures of early metal enrichment in Damped-Lyman Alpha systems C113 CO 4 → 3 and [CI] 1 → 0 in the centers of NGC4945 and Circinus C115 Ratio of atomic and molecular gas and gravitational stabilty in the disk of M51 C130 The Interstellar Mediumat Early Cosmic Times: Molecular Gas in Distant Quasar Host Galaxies C188 Probing the interstellar medium in distant galaxies with SPICA/ESI C191 The evolution of spectral energy distributions of galaxies over cosmic times C197 Observations of 60Fe in the Galaxy with INTEGRAL/SPI C204 Evolution of Interstellar Clouds in a hot Gas Environment C205 The effect of clouds in a galactic wind on the evolution of gas-rich dwarf galaxies C206 Energy and element deposit into the interstellar medium during the lives of massive stars C209 The distribution and kinematics of massive stars in the inner Galaxy mapped with SPI/INTEGRAL 26Al 1.8 MeV line observations C213 PDR modelling of the Galactic FIR line emission C239 Towards a complete picture of the molecular ISM in local Luminous Infrared Galaxies: first results from the JCMT/IRAM line survey C242 The Search for the Very High-redshift Tail of Submillimeter Galaxies     

Cosmic ray propagation and the star formation history of NGC 1961

We present new radio continuum data at four frequencies for the supermassive, peculiar galaxy NGC 1961. These observations allow us to separate the thermal and non-thermal radio emission and to determine the non-thermal spectral index distribution. This spectral index distribution in the galactic disc is unusual: at the maxima of the radio emission the synchrotron spectrum is very steep, indicating aged cosmic ray electrons. Away from the maxima the spectrum is much flatter. The steep spectrum of the synchrotron emission at the maxima indicates that a strong decline of the star formation rate has taken place at these sites. The extended radio emission is a sign of recent cosmic ray acceleration, probably by recent star formation. We suggest that a violent event in the past, most likely a merger or a collision with an intergalactic gas cloud, has caused the various unusual features of the galaxy.     

General relativistic dynamics applied to the rotation curves of galaxies

We extend our general relativistic analysis of galactic rotation curves (see Cooperstock and Tieu in Int. J. Mod. Phys. A 22:2293, 2007) with galaxies NGC 2841, NGC 2903 and NGC 5033. As before, we employ the solution of the Einstein field equations of general relativity with an expansion in Bessel functions. As in our earlier studies, the fits to the data are found to be very precise and the calculated baryonic masses are lower than those based upon Newtonian gravity. Also as in our previous studies, the galactic radii at which the optical luminosities terminate are seen to correlate with densities near 10^−21.75 kg m⁻³. This concordance lends further support to the correctness of the procedure as well as providing a potentially valuable piece of information in the understanding of galactic evolution.     

NGC 7468: A galaxy with an inner polar disk

We present our spectroscopic observations of the galaxy NGC 7468 performed at the 6-m Special Astrophysical Observatory telescope using the UAGS long-slit spectrograph, the MPFS multi-pupil fiber spectrograph, and the IFP scanning Fabry-Perot interferometer. We found no significant deviations from the circular rotation of the galactic disk in the velocity field in the regions of brightness excess along the major axis of the galaxy (the putative polar ring). Thus, these features are either tidal structures or weakly developed spiral arms. However, we detected a gaseous disk at the center of the galaxy whose rotation plane is almost perpendicular to the plane of the galactic disk. The central collision of NGC 7468 with a gas-rich dwarf galaxy and their subsequent merging seem to be responsible for the formation of this disk.