Ultraluminous infrared galaxies (ULIRGs) are outstanding due to their huge luminosity output in the infrared, which is predominantly powered by super starbursts and/or hidden active galactic nuclei (AGN). NGC 6240 is one of the nearest ULIRGs and is considered a key representative of its class. Here, we report the first high-resolution imaging spectroscopy of NGC 6240 in X-rays. The observation, performed with the ACIS-S detector aboard the Chandra X-ray observatory, led to the discovery of two hard nuclei, coincident with the optical-IR nuclei of NGC 6240. The AGN character of both nuclei is revealed by the detection of absorbed hard, luminous X-ray emission and two strong neutral Fe Kα lines. In addition, extended X-ray emission components are present, changing their rich structure in dependence of energy. The close correlation of the extended emission with the optical Hα emission of NGC 6240, in combination with the softness of its spectrum, clearly indicates its relation to starburst-driven superwind activity.

We present the first systematic study of (non-radio-selected) radio-loud narrow-line Seyfert 1 (NLS1) galaxies. Cross-correlation of the `Catalogue of Quasars and Active Nuclei' with several radio and optical catalogues led to the identification of 11 radio-loud NLS1 candidates including 4 previously known ones. Most of the radio-loud NLS1s are compact, steep spectrum sources accreting close to, or above, the Eddington limit. The radio-loud NLS1s of our sample are remarkable in that they occupy a previously rarely populated regime in NLS1 multi-wavelength parameter space. While their [OIII]/H_beta and FeII/H_beta intensity ratios almost cover the whole range observed in NLS1 galaxies, their radio properties extend the range of radio-loud objects to those with small widths of the broad Balmer lines. Among the radio-detected NLS1 galaxies, the radio index R distributes quite smoothly up to the critical value of R ~ 10 and covers about 4 orders of magnitude in total. Statistics show that ~7% of the NLS1 galaxies are formally radio-loud while only 2.5% exceed a radio index R > 100. Several mechanisms are considered as explanations for the radio loudness of the NLS1 galaxies and for the lower frequency of radio-louds among NLS1s than quasars. While properties of most sources (with 2-3 exceptions) generally do not favor relativistic beaming, the combination of accretion mode and spin may explain the observations. (abbreviated)Comment: Astronomical Journal (first submitted in Dec. 2005); 45 pages incl. 1 colour figur

We report Swift observations of a sample of 92 bright soft X-ray selected active galactic nuclei (AGN). This sample represents the largest number of AGN observed to study the spectral energy distribution (SED) of AGN with simultaneous optical/UV and X-ray data. The principal motivation of this study is to understand the SEDs of AGN in the optical/UV to X-ray regime and to provide bolometric corrections which are important in determining the Eddington ratio L/L Edd . In particular, we rigorously explore the dependence of the UV-EUV contribution to the bolometric correction on the assumed EUV spectral shape. We find strong correlations of the spectral slopes α X and α UV with L/L Edd . Although Narrow-Line Seyfert 1 galaxies (NLS1s) have steeper α X and higher L/L Edd than Broad-Line Seyfert 1 galaxies (BLS1s), their optical/UV to X-ray spectral slopes α ox and optical/UV slopes α UV are very similar. The mean SED of NLS1s shows that in general this type of AGN appears to be fainter in the UV and at hard X-ray energies than BLS1s. We find a strong correlation between α X and α UV for AGN with X-ray spectral slopes α X <1.6. For AGN with steeper X-ray spectra, both this relation and the relation between α X and L/L Edd break down. At α X ≈1.6, L/L Edd reaches unity. We note an offset in the α UV -L/L Edd relation between NLS1s and BLS1s. We argue that α UV is a good estimator of L/L Edd and suggest that α UV can be used to estimate L/L Edd in high-redshift QSOs. Although NLS1s appear to be highly variable in X-rays they only vary marginally in the UV.

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We have conducted a multiwavelength survey of 42 radio loud narrow-1ine Seyfert 1 galaxies (RLNLS1s), selected by searching among all the known sources of this type and omitting those with steep radio spectra. We analyse data from radio frequencies to X-rays, and supplement these with information available from online catalogues and the literature in order to cover the full electromagnetic spectrum. This is the largest known multiwavelength survey for this type of source. We detected 90% of the sources in X-rays and found 17% at γ rays. Extreme variability at high energies was also found, down to timescales as short as hours. In some sources, dramatic spectral and flux changes suggest interplay between a relativistic jet and the accretion disk. The estimated masses of the central black holes are in the range ∼ 10 6−8 M ⊙ , lower than those of blazars, while the accretion luminosities span a range from ∼ 0.01 to ∼ 0.49 times the Eddington limit, with an outlier at 0.003, similar to those of quasars. The distribution of the calculated jet power spans a range from ∼ 10 42.6 to ∼ 10 45.6 erg s −1 , generally lower than quasars and BL Lac objects, but partially overlapping with the latter. Once normalised by the mass of the central black holes, the jet power of the three types of active galactic nuclei are consistent with each other, indicating that the jets are similar and the observational differences are due to scaling factors. Despite the observational differences, the central engine of RLNLS1s is apparently quite similar to that of blazars. The historical difficulties in finding radio-loud narrow-line Seyfert 1 galaxies might be due to their low power and to intermittent jet activity.

Blazars with strong emission lines were found to be associated mostly with broad-line type 1 Active Galactic Nuclei (AGN). Hitherto, evidence for blazars identified with Narrow Line Seyfert 1 (NLS1) AGN was limited to very few individual cases. Here we present a comprehensive study of a sample of 23 genuine radio-loud NLS1 galaxies which have the radio-loudness parameters, the ratio of radio (21 cm) to optical (4400Å) luminosity, greater than 100. The sample, drawn from the SDSS and FIRST, is homogeneous and the largest of this kind. A significant fraction of the sample objects show interesting radio to X-ray properties that are unusual to most of the previously known radio-loud NLS1 AGN, but are reminiscent of blazars. These include flat radio spectra, large amplitude flux and spectral variability, compact VLBI cores, very high brightness temperatures (10 11−14 K) derived from variability, enhanced optical emission in excess of the normal ionising continuum, flat X-ray spectra, and blazar-like SEDs. We interpret them as evidence for the postulated blazar nature of these very radio-loud NLS1 AGN, which might possess at least moderately relativistic jets. We suggest that those steep spectrum radio-loud NLS1 AGN in the sample are of the same population but with their radio jets aligned at large angles to the lines-of-sight. Intrinsically, some of the objects have relatively low radio power and would have been classified as radio-intermediate AGN.The black hole masses, estimated from the broad Balmer line width and luminosity, are within 10 6−8 M ⊙ , and the inferred Eddington ratios are around unity. Unless the black hole masses are largely under-estimated, our result stretches the low mass end of the black holes of luminous, fast accreting radio-loud AGN to a smaller mass regime (the order of 10 6 M ⊙ ) in the black hole mass-radio-loudness space where other normal AGN are seldom found. The results imply that radio-loud AGN may be powered by black holes with moderate masses (∼ 10 6−7 M ⊙ ) accreting at high rates (Eddington ratios up to unity or higher). The host galaxies of a few nearby objects appear to be disk-like or merger; and some of the objects show imprints of young stellar populations in their SDSS spectra. We find that some of the objects, despite having strong emission lines, resemble high-energy peaked BL Lacs in their SED with the synchrotron component peaked at around the UV; such objects constitute an intriguingly high fraction of the sample. The radio sources of the sample are ubiquitously compact. They are smaller than at most several tens of kilo-parsecs, suggesting a possible link with compact steep-spectrum radio sources. Given the peculiarities of blazar-like NLS1 galaxies, questions arise as to whether they are plain downsizing extensions of normal radio-loud AGN, or whether they form a previously unrecognised population.

In the construction of an X-ray selected sample of galaxy clusters for cosmological studies, we have assembled a sample of 495 X-ray sources found to show extended X-ray emission in the first processing of the ROSAT All-Sky Survey. The sample covers the celestial region with declination δ ≥ 0 • and galactic latitude |b II | ≥ 20 • and comprises sources with a count rate ≥ 0.06 counts s −1 and a source extent likelihood of 7. In an optical follow-up identification program we find 378 (76%) of these sources to be clusters of galaxies.It was necessary to reanalyse the sources in this sample with a new X-ray source characterization technique to provide more precise values for the X-ray flux and source extent than obtained from the standard processing. This new method, termed growth curve analysis (GCA), has the advantage over previous methods to be robust, easy to model and to integrate into simulations, to provide diagnostic plots for visual inspection, and to make extensive use of the X-ray data. The source parameters obtained assist the source identification and provide more precise X-ray fluxes. This reanalysis is based on data from the more recent second processing of the ROSAT Survey. We present a catalogue of the cluster sources with the X-ray properties obtained as well as a list of the previously flagged extended sources which are found to have a non-cluster counterpart. We discuss the process of source identification from the combination of optical and X-ray data.To investigate the overall completeness of the cluster sample as a function of the X-ray flux limit, we extent the search for X-ray cluster sources to the data of the second processing of the ROSAT Survey for the northern sky region between 9 h and 14 h in right ascension. We include the search for X-ray emission of known clusters as well as a new investigation of extended X-ray sources. In the course of this search we find X-ray emission from additional 85 Abell clusters and 56 very probable cluster candidates among the newly found extended sources. A comparison of the X-ray cluster number counts of the NORAS sample with the REFLEX Cluster Survey results leads to an estimate of the completeness of the NORAS sample of RASS I extended clusters of about 50% at an X-ray flux of F x (0.1 − 2.4keV) = 3 × 10 −12 erg s −1 cm −2 . The estimated completeness achieved by adding the supplementary sample in the study area amounts to about 82% in comparison to REFLEX. The low completeness introduces an uncertainty in the use of the sample for cosmological statistical studies which will be cured with the completion of the continuing Northern ROSAT All-Sky -3 -(NORAS) cluster survey project.

We have studied the properties of Seyfert galaxies with high [OIII]5007 blueshifts ("blue outliers"), originally identified because of their strong deviation from the M BH − σ relation of normal, narrowline Seyfert 1 (NLS1) and broad-line Seyfert 1 (BLS1) galaxies. These blue outliers turn out to be important test-beds for models of the narrow-line region (NLR), for mechanisms of driving large-scale outflows, for links between NLS1 galaxies and radio galaxies, and for orientation-dependent NLS1 models. We report the detection of a strong correlation of line blueshift with ionization potential in each galaxy, including the measurement of coronal lines with radial velocities up to 500-1000 km s −1 , and we confirm a strong correlation between [OIII] blueshift and line width. All [OIII] blue outliers have narrow widths of their broad Balmer lines and high Eddington ratios. While the presence of nonshifted low-ionization lines signifies the presence of a classical outer quiescent NLR in blue outliers, we also report the absence of any second, non-blueshifted [OIII] component from a classical inner NLR. These results place tight constraints on NLR models. We favor a scenario in which the NLR clouds are entrained in a decelerating wind which explains the strong stratification and the absence of a zero-blueshift inner NLR of blue outliers. The origin of the wind remains speculative at this time (collimated radio plasma, thermal winds, radiatively accelerated clouds). It is perhaps linked to the high Eddington ratios of blue outliers. Similar, less powerful winds could be present in all Seyfert galaxies, but would generally only affect the coronal line region (CLR), or level off even before reaching the CLR. Similarities between blue outliers in NLS1 galaxies and (compact) radio sources are briefly discussed.