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Investigating the nature of narrow-line Seyfert 1 galaxies with high-energy spectral complexity
With the commissioning of XMM-Newton came the discovery of 2.5-10keVspectral complexity in some narrow-line Seyfert 1 galaxies (NLS1). Thishigh-energy complexity can be manifested as sharp, spectral drops orgradual curvature in the spectrum. Models which are normally consideredare ionized reflection and partial covering. In this work, we define twosamples of NLS1: a complex sample whose members exhibit high-energycomplexity (C sample), and a general sample of NLS1 whose 2.5-10keVspectra do not strongly deviate from a simple power law (S sample). Wethan compare multiwavelength parameters of these two samples todetermine if there are any distinguishing characteristics in the complexNLS1. Considering historical light curves of each object, we find thatthe C sample is representative of NLS1 in a low X-ray flux state,whereas the members of the S sample appear to be in a typical fluxstate. Moreover, from measurements of αox withcontemporaneous ultraviolet (UV)/X-ray data, we find that the C sampleof NLS1 appear X-ray weaker at the time of the observation. For two NLS1in the C sample multi-epoch measurements of αox areavailable and suggest that αox approaches more normalvalues as the complexity between 2.5 and 10keV diminishes. This impliesthat a source could transit from one sample to the other as its X-rayflux varies. Secondly, there are indications that the C sample sources,on average, exhibit stronger optical FeII emission, with the three mostextreme (FeII/Hβ > 1.8) FeII emitters all displaying complexityin the 2.5-10keV band. It is an intriguing possibility that we may beable to identify X-ray complex NLS1 based on the extreme strength of themore easily observable optical FeII emission. However, it is not clearif the possible connection between FeII strength and spectral complexityis due to the FeII producing mechanism or because strong FeII emittersmay exhibit the greatest variability and consequently more likely to becaught in an extreme (low) flux state. Based on the current analysis, wecannot straightforwardly dismiss absorption or reflection as the causeof the X-ray complexity; by considering the multiple UV/X-rayobservations of 1H 0707-495 (a C sample member), we discuss a possiblemethod of distinguishing the two models provided further UV/X-rayobservations.
| 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-upsnapshot observations with XMM-Newton. The typical exposure was between5 and 10ks. The objects were primarily selected on the bases of X-raybrightness and not on hardness ratio; thus the sample cannot be strictlydefined as a `soft'sample. One of the main outcomes from the XMM-Newtonobservations was that all of the AGN, including 11 type 1.8-2 objects,required low levels of intrinsic absorption (NH<~1021cm-2). The low absorption in type 2 systems isa challenge to account for in the standard orientation-based unificationmodel, and we discuss possible physical and geometrical models whichcould elucidate the problem. Moreover, there does not appear to be anyrelation between the strength and shape of the soft excess, and thespectral classification of the AGN in this sample. We further identify anumber of AGN which deserve deeper observations or further analysis: forexample, the low-ionization nuclear emission regions (LINERs) NGC 5005and NGC 7331, where optically thin thermal and extended emission isdetected, and the narrow-line Seyfert 1 II Zw 177, which shows a broademission feature at ~ 5.8keV.
| The Seyfert Population in the Local Universe
The magnitude-limited catalog of the Southern Sky Redshift Survey(SSRS2) is used to characterize the properties of galaxies hostingactive galactic nuclei (AGNs). Using emission-line ratios, we identify atotal of 162 (3%) Seyfert galaxies out of the parent sample with 5399galaxies. The sample contains 121 Seyfert 2 galaxies and 41 Seyfert 1galaxies. The SSRS2 Seyfert galaxies are predominantly in spirals oftypes Sb and earlier or in galaxies with perturbed appearance as theresult of strong interactions or mergers. Seyfert galaxies in thissample are twice as common in barred hosts as the non-Seyfert galaxies.By assigning galaxies to groups using a percolation algorithm, we findthat the Seyfert galaxies in the SSRS2 are more likely to be found inbinary systems when compared with galaxies in the SSRS2 parent sample.However, there is no statistically significant difference between theSeyfert and SSRS2 parent sample when systems with more than two galaxiesare considered. The analysis of the present sample suggests that thereis a stronger correlation between the presence of the AGN phenomenonwith internal properties of galaxies (morphology, presence of bar,luminosity) than with environmental effects (local galaxy density, groupvelocity dispersion, nearest neighbor distance).Partly based on observations at European Southern Observatory (ESO),under the ESO-ON agreement to operate the 1.52 m telescope.
| The ROSAT Bright Survey: II. Catalogue of all high-galactic latitude RASS sources with PSPC countrate CR > 0.2 s-1
We present a summary of an identification program of the more than 2000X-ray sources detected during the ROSAT All-Sky Survey (Voges et al.1999) at high galactic latitude, |b| > 30degr , with countrate above0.2 s-1. This program, termed the ROSAT Bright Survey RBS, isto more than 99.5% complete. A sub-sample of 931 sources with countrateabove 0.2 s-1 in the hard spectral band between 0.5 and 2.0keV is to 100% identified. The total survey area comprises 20391deg2 at a flux limit of 2.4 x 10-12 ergcm-2 s-1 in the 0.5 - 2.0 keV band. About 1500sources of the complete sample could be identified by correlating theRBS with SIMBAD and the NED. The remaining ~ 500 sources were identifiedby low-resolution optical spectroscopy and CCD imaging utilizingtelescopes at La Silla, Calar Alto, Zelenchukskaya and Mauna Kea. Apartfrom completely untouched sources, catalogued clusters and galaxieswithout published redshift as well as catalogued galaxies with unusualhigh X-ray luminosity were included in the spectroscopic identificationprogram. Details of the observations with an on-line presentation of thefinding charts and the optical spectra will be published separately.Here we summarize our identifications in a table which contains opticaland X-ray information for each source. As a result we present the mostmassive complete sample of X-ray selected AGNs with a total of 669members and a well populated X-ray selected sample of 302 clusters ofgalaxies with redshifts up to 0.70. Three fields studied by us remainwithout optical counterpart (RBS0378, RBS1223, RBS1556). While the firstis a possible X-ray transient, the two latter are isolated neutron starcandidates (Motch et al. 1999, Schwope et al. 1999).
| The Southern Sky Redshift Survey
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
| New active galactic nuclei detected in ROSAT All Sky Survey galaxies. I. Verification of selection strategy
We present the first results of a program to identify so far unknownactive nuclei (AGN) in galaxies. Candidate galactic nuclei have beenselected for optical spectroscopy from a cross-correlation of the ROSATAll Sky Survey (RASS) bright source catalog with optical galaxycatalogs. A high X-ray flux has been used as pointer to galaxies with ahigh probability to contain active nuclei. Only galaxies have beenaccepted for the program for which no activity was noted in NED. Formany of the galaxies no radial velocity was reported before. The opticalspectra demonstrate that the galaxies cover a redshift range of 0.014 to0.13 and that most of them host active nuclei. For 75% of the 33candidates the X-ray emission is caused by the AGN. In addition severalof the remaining candidates host Seyfert 2/LINER nuclei that, however,most certainly cannot explain the X-ray emission alone. Three BL Lacobjects have been detected serendipitously in galaxy fields that havebeen followed up by short ROSAT HRI observations to confirm the X-raygalaxy identification with improved position accuracy and point responsefunction. The sources show X-ray to radio flux ratios typical for X-rayselected BL Lac objects. The results presented in the paper prove theselection strategy as very successful to detect previously unknown AGNof all Seyfert 1 types in nearby galaxies encouraging the extension ofthis program. The detection of new nearby AGN will be used to initiate adetailed investigation of their multi-wavelength properties and acomparison with the more distant AGN population. based partially onobservations collected at the European Southern Observatory, La Silla,Chile
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
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