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Long-slit optical emission-line spectra of the H2O megamaser galaxies ESO 103-G03, TXS 2226-184, and IC 1481 are evaluated in order to look for characteristics typical for water-megamaser galaxies. We present rotation curves, line ratios, electron densities, temperatures, and Hbeta luminosities. The successful line-profile decompositions rest on d-Lorentzians with an additional parameter d to adjust the wings, rather than Gaussians or Lorentzians as basic functions. No significant velocity gradient is found along the major axis in the innermost 2 kpc of TXS 2226-184. IC 1481 reveals a spectrum suggestive of a vigorous starburst in the central kiloparsec 10^8 years ago. None of the three galaxies shows any hints for outflows nor special features which could give clues to the presence of H2O megamaser emission. The galaxies are of normal Seyfert-2 (ESO 103-G035) or LINER (TXS 2226-184, IC 1481) type., Comment: 12 pages, 14 figures, accepted for publication in A&A, corrected typos

Winds and outflows in starburst galaxies and AGN provide important information on the physics of the "central engine", the presence and evolution of (nuclear) starbursts, and the metal enrichment of the nuclear environment and the intergalactic medium. Here, we concentrate on two examples, X-ray observations of the (U)LIRG NGC6240 and the BAL quasar APM08279+5255., Comment: 6 pages incl. 2 figures, to appear in "Recycling interstellar and intergalactic matter", IAU Symp. 217, P.-A. Duc et al. (eds); related papers available at http://www.xray.mpe.mpg.de/~skomossa/

We have observed the narrow-line regions (NLRs) of the seven brightest radio-quiet PG (or BQS) quasars (z < 0.5) with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope (HST). Linear-ramp filters were used to image the [OIII] lambda 5007 line emission with 0.0455-0.1 arcsec pixel resolution. We find that the NLRs are very compact with typical extents of 2-4 arcsec. Two quasars show compact filamentary structures similar to Seyfert NLRs. They may be related to radio outflows. Most interestingly, when including a sample of Seyfert galaxies observed with HST, we tentatively find that the size of the NLR is proportional to the square root of the [OIII] luminosity. This is comparable to the scaling found for the size of the broad-line region with continuum luminosity, which has been interpreted in terms of a constant photoionization parameter. The relation determined here connects the NLR of radio-quiet quasars and Seyferts over three orders of magnitude in [OIII] luminosity., Comment: 6 pages, 4 figures, accepted for publication in ApJ Letters

Recently Perlmutter et al. suggested a positive value of Einstein's cosmological constant Lambda on the basis of luminosity distances from type-Ia supernovae. However, Lambda world models had earlier been proposed by Hoell & Priester and Liebscher et al. on the basis of quasar absorption-line data. Employing more general repulsive fluids ("dark energy") encompassing the Lambda component we quantitatively compare both approaches with each other. Fitting the SN-data by a minimum-component model consisting of dark energy + dust yields a closed universe with a large amount of dust exceeding the baryonic content constrained by big-bang nucleosynthesis. The nature of the dark energy is hardly constrained. Only when enforcing a flat universe there is a clear tendency to a dark-energy Lambda fluid and the `canonical' value Omega_M = 0.3 for dust. Conversely, fitting the quasar-data by a minimum-component model yields a sharply defined, slightly closed model with a low dust density ruling out significant pressureless dark matter. The dark-energy component obtains an equation-of-state P = -0.96 epsilon close to that of a Lambda-fluid. Omega_M = 0.3 or a precisely flat spatial geometry are inconsistent with minimum-component models. It is found that quasar and supernova data sets cannot be reconciled with each other via (repulsive ideal fluid+dust+radiation)-world models. Compatibility could be reached by drastic expansion of the parameter space with at least two exotic fluids added to dust and radiation as world constituents. If considering such solutions as far-fetched one has to conclude that the quasar absorption line and the SN-Ia constraints are incompatible., Comment: 8 pages, 4 figures, latex, accepted for publication in A&A

Various classification schemes exist for homogeneous and isotropic (CP) world models, which include pressureless matter (so-called dust) and Einstein's cosmological constant Lambda. We here classify the solutions of more general world models consisting of up to four non-interacting fluids, each with pressure P, energy density epsilon and an equation of state P = (gamma - 1) epsilon with 0 <= gamma <= 2. In addition to repulsive fluids with negative pressure and positive energy density, which generalize the classical repulsive (positive) Lambda component, we consider fluids with negative energy density as well. The latter generalize a negative Lambda component. This renders possible new types of models that do not occur among the classical classifications of world models. Singularity-free periodic solutions as well as further `hill-type', `hollow-type' and `shifting-type' models are feasible. However, if one only allows for three components (dust, radiation and one repulsive component) in a spatially flat universe the repulsive classical Lambda fluid (with Lambda > 0) tends to yield the smoothest fits of the Supernova Ia data from Perlmutter et al. (1999). Adopting the SN Ia constraints, exotic negative energy density components can be fittingly included only if the universe consists of four or more fluids., Comment: 12 pages, 11 figures, latex, A&A in press

We review theoretical and observational arguments favoring a scenario in which a typical massive black hole (MBH) is formed in the merger core of colliding disk systems at high z during the build-up of a spheroid. Low-mass (~ 10^{5-6} M_sun) seed black holes are assumed to have been formed earlier. The most massive black holes giving rise to the most luminous active galactic nuclei (AGN) in active phases are expected to grow in violent mergers of large disk-plus-bulge systems that lead to giant elliptical galaxies, the typical hosts of radio galaxies and quasars. We consider current ultraluminous infrared galaxies (ULIRG) as systems closely resembling the predecessors of early formed massive ellipticals. As an example, we discuss the evidence for an AGN in the merging system NGC 6240 which we advertize as a prototypical active ULIRG, obscured in X-rays by a high column density absorber., Comment: 18 pages incl. 2 figures (needs cl2emult.cls). Contribution to the proceedings of the workshop on "Trends in Astrophysics and Cosmology" (Bad Honnef, August 24-28, 1998). To appear in Lecture Notes in Physics (W. Kundt, C. v.d.Bruck, eds). Preprint and related papers available at http://www.xray.mpe.mpg.de/~skomossa/

We briefly review and extend our discussion of the ROSAT detection of the extraordinarily luminous (> 10^{42} erg/s) partly extended (> 30 kpc diameter) X-ray emission from the ultraluminous infrared galaxy NGC 6240. The `standard'-model of starburst outflow is contrasted with alternatives and a comparison with the X-ray properties of ellipticals is performed., Comment: 6 pages incl. 2 figures, uses crckapb.sty. To appear in the proc. of the Ringberg workshop on "Ultraluminous Galaxies: Monsters or Babies" (Ringberg castle, Sept. 1998), Ap&SS, in press; preprint and related papers also available at http://www.xray.mpe.mpg.de/~skomossa/

We present an X-ray spectral and spatial analysis of the composite starburst/Seyfert galaxy NGC 1365. Excellent fits of the ROSAT PSPC spectrum are obtained by combining a soft thermal component with a hard powerlaw. The hard component may be either seen directly or can be explained by scattering of the AGN powerlaw at circumnuclear warm high-column-density gas. A compilation of the multi-wavelength properties of NGC 1365 and comparison with hard X-ray selected AGNs shows that the hard component of NGC 1365 is too faint compared to its broad Balmer line components challenging simple unified models. According to analytical estimates, supernova driven outflow can fully account for the X-ray luminosity in the Raymond-Smith component if the observed IR emission is mainly provided by the central starburst. We do not find obvious optical counterparts for three faint PSPC sources south of the nucleus. In particular, there is no coincidence with the two supernovae reported in NGC 1365. With the ROSAT HRI data, we have precisely located the extraordinary southwest X-ray source NGC1365-X1 which falls on one of the subordinate spiral arms. The source is found to be highly variable (a factor about 10) on the timescale of months. Intrinsic to NGC 1365, its huge luminosity makes it exceptional among stellar X-ray sources. At present, the most likely interpretation seems to be an ultra-powerful X-ray binary., Comment: 11 pages incl. 5 figures; A&A, in press (scheduled for vol. 339, November 1998)

We present a spectral and spatial analysis of the nuclear and circumnuclear X-ray emission of the prominent southern starburst/Seyfert galaxy NGC 1365. To describe the X-ray spectrum of the core source, we favour a two-component model consisting of about equally strong contributions from a Raymond-Smith plasma (with ~cosmic abundances) and a powerlaw. The origin of both components is discussed, and a detailed comparison of the X-ray properties with multi-wavelength observations of NGC 1365 and a large sample of type-I AGNs is performed. Among the surrounding X-ray sources we focus on an analysis of the enigmatic source NGC 1365-X1, which is one of the most luminous and most highly variable off-nuclear X-ray sources known so far. Positions of further X-ray sources in the field of view are derived and it is briefly pointed out that all HRI sources (except one) are `aligned' relative to the central source., Comment: 4 pages (modified aa style using xray_symp.cls) incl. 3 figures, to appear in the proc. of "Highlights in X-ray Astronomy" (Garching, June 1998), B Aschenbach et al. (eds); MPE preprint 448

We briefly review and extend our discussion of the ROSAT detection of the extraordinarily luminous (>10^{42} erg/s) partly extended (> 30 kpc diameter) X-ray emission from the double-nucleus ultraluminous infrared galaxy NGC 6240. The ROSAT spectrum can be well fit by emission from two components in roughly equal proportions: a thermal optically thin plasma with kT \sim 0.6 keV and a hard component that can be represented by a canonical AGN powerlaw. Source counts appear to have dropped by 30% within a year. Altogether, these findings can be well explained by a contribution of radiation from an AGN essentially hidden at other wavelengths. Fits of ASCA spectra, conducted by various groups, corroborate this result, revealing a high-equivalent width FeK blend which again is straightforwardly interpreted by scattered AGN light. If radiating at the Eddington limit, the central black hole mass does not exceed 10^7 M_sun. We discuss implications for the formation of this AGN. However, the luminosity in the remaining extended thermal component is still at the limits of a pure starburst-wind-induced source. We suggest that the deeply buried starburst has switched to a partially dormant phase so that heating of the outflow is diminished and a cooling flow could have been established. This flow may account for the extended shock heating traced by LINER-like emission line ratios and the extremely luminous H_2 emission from the central region of this galaxy. Next-generation X-ray telescopes will be able to test this proposal., Comment: to appear in the proc. of "Highlights in X-ray Astronomy" (Garching, June 1998); B Aschenbach et al. (eds)

We report the detection of luminous extended X-ray emission in NGC 6240 on the basis of ROSAT HRI observations of this ultraluminous IR galaxy. The spatial structure and temporal behavior of the X-ray source were analyzed. We find that >= 70% of the soft X-ray emission is extended beyond a radius of 5 arcsec. Strong emission can be traced out to a radius of 20 arcsec and weaker emission extends out to 50 arcsec. With a luminosity of at least 10^{42} erg/s this makes NGC 6240 one of the most luminous X-ray emitters in extended emission known. Evidence for a nuclear compact variable component is indicated by a drop of 32% in the HRI count rate as compared to the PSPC data taken one year earlier. No short-timescale variability is detected. The HRI data, which represent the first high-resolution study of the X-ray emission from NGC 6240, complement previous spectral fits to ROSAT PSPC data (astro-ph/9710098; A&A 330, 823) that suggested a two-component model consisting of thermal emission from shocked gas immersed in a starburst wind plus a powerlaw source attributed to scattered light from an obscured AGN. We discuss several models to account for the extended and compact emission. Although pushed to its limits the starburst outflow model is tenable for the essential part of the extended emission. For the AGN-type component we propose a model consisting of a near-nuclear `warm scatterer' that explains the apparent fading of the X-ray flux within a year as well as the strong FeKalpha complex seen in an ASCA spectrum., Comment: 8 pages incl. 5 figures, A&A in press; preprint incl. 2 colour figures available as MPE Preprint 435

We present ROSAT observations of the starburst galaxy NGC 2782 (HRI plus a weak PSPC frame) and the ultraluminous infrared galaxy NGC 6240 (PSPC). The (0.1-2.4) keV spectra of both objects appear similar. However, due to better sampling spectral modeling is only warranted in case of NGC 6240 for which both a single thermal Raymond-Smith model (kT = 0.44) or a hybrid model consisting of 80% power-law with the canonical photon index -1.9 plus 20% Raymond-Smith contribution (kT = 0.63) lead to good fits. However, the single thermal model turns out to be unlikely because it yields a luminosity of 3.8 10^{43} erg/s, which is hard to reach in a starburst superwind-scenario. The hybrid model leads to a more moderate luminosity of 5.2 10^{42} erg/s, of which 1.0 10^{42} erg/s can be attributed to shocked superwind gas. We link the remaining 4.2 10^{42} erg/s powerlaw to an AGN component because the alternative of inverse-compton scattering of the FIR radiation leads to a too low flux when estimated with available data. The result appears to be consistent with preliminarily announced ASCA observations. For NGC 2782 we find L_x = 4 10^{41} erg/s which can be explained by emission from a shocked superwind region with a high preshock density in agreement with earlier optical evidence for an outflowing supershell., Comment: 10 pages incl. 6 figures, to appear in A&A

We present multi-component photoionization models allowing for local density inhomogeneities in the NLR to interpret the emission line spectra of Seyfert 2 galaxies. This approach leads to a successful match of a large set of line intensities from the UV to the NIR. In particular, the hitherto elusive NIR features [SIII]9062+9531 as well as high-ionization lines like [FeVII] are consistently fitted. The predictions of CIII] and CIV are considerably improved. From the detailed analysis of single-component photoionization models we derive the minimal radial extent of the NLR and the necessary span in density. Furthermore, we determine constraints on suggestions made about the role of matter-bounded clouds, and on proposed explanations for large [OIII]4363/5007 ratios (the so-called `temperature problem'), and assess the usability of some emission-line ratios as indicators of the ionization parameter. We find that a systematic variation of the cloud column densities in a population of matter-bounded clouds is inconsistent with the trends and correlations exhibited by the emission lines in the diagnostic diagrams. Concerning the temperature problem, the only possibility that leads to an overall consistency with the strengths of all other observed emission lines is subsolar metal abundances (as compared to e.g. the presence of dust, the existence of a high-density component, or matter-bounded clouds). In addition, the consequences of the presence of (Galactic-ISM-like) dust internal to the clouds were investigated. These models alleviate the [OIII]-ratio problem but did not lead to overall consistent fits. In our final model series, the NLR is composed of a mixture of metal-depleted (0.5 x solar) clouds with a radius-independent range in densities (10^2 to 10^5 cm^-3) distributed over a range of distances from the nucleus (galactocentric radii from at least $\sim$ 10^{20} cm to 10^{21.5} cm, for $Q_{tot} = 10^{54}$ s^{-1}). In order to encompass the observed range of each line intensity relative to H$\beta$, it turns out to be necessary to vary the spectral energy distribution incident on the clouds, qualitatively confirming the findings of Ho et al. (1993). We found a successful continuum sequence by adding an increasing contribution of a hot black body ($T \approx 200000$ K) to a steep powerlaw ($\alpha_{uv-x} \approx -2$). These continua imply that low and high-excitation objects differ in the strength but not in the basic shape of the EUV bump., Comment: 17 pages, paper copies of the 10 figures available upon request, accepted by A&A; MPE preprint 383 (1996)