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TeV Gamma-Ray Observations of the Perseus and Abell 2029 Galaxy Clusters
Galaxy clusters might be sources of TeV gamma rays emitted byhigh-energy protons and electrons accelerated by large-scale structureformation shocks, galactic winds, or active galactic nuclei.Furthermore, gamma rays may be produced in dark matter particleannihilation processes at the cluster cores. We report on observationsof the galaxy clusters Perseus and A2029 using the 10 m Whipple Cerenkovtelescope during the 2003-2004 and 2004-2005 observing seasons. We applya two-dimensional analysis technique to scrutinize the clusters for TeVemission. In this paper we first determine flux upper limits on TeVgamma-ray emission from point sources within the clusters. Second, wederive upper limits on the extended cluster emission. We subsequentlycompare the flux upper limits with EGRET upper limits at 100 MeV andtheoretical models. Assuming that the gamma-ray surface brightnessprofile mimics that of the thermal X-ray emission and that the spectrumof cluster cosmic rays extends all the way from thermal energies tomulti-TeV energies with a differential spectral index of -2.1, ourresults imply that the cosmic-ray proton energy density is less than7.9% of the thermal energy density for the Perseus Cluster.
| RM-synthesis of the Perseus cluster
We present low frequency radio polarimetric observations of the Perseuscluster. The data were taken with the Westerbork Synthesis RadioTelescope (WSRT) between 315-360 MHz. We have discovered faint,extended, highly polarized emission that we associate with the Perseuscluster \citep{DeBruynBrentjens2005}. We propose that at least one ofthese structures is associated with large-scale structure formation gasinflow from the Perseus-Pisces supercluster. The extragalactic emissionis seen through a polarized Galactic synchrotron foreground screen. Thediscovery was made possible by a novel rotation measure analysistechnique, called Faraday Rotation Measure Synthesis, or RM-synthesisfor short \citep{BrentjensDeBruyn2005}.
| XMM-Newton Observation of IC 310 in the Outer Region of the Perseus Cluster of Galaxies
We present results from an XMM-Newton observation of the head-tail radiogalaxy IC 310 located in the southwest region of the Perseus cluster.The spectrum is well fitted by an absorbed power-law model with a photonindex of 2.50 ± 0.02 without significant absorption excess. TheX-ray image shows a point-like emission at IC 310 without any sign of astructure correlated with the radio halo tail. The temperature of theintracluster medium surrounding IC 310 declines as a function ofdistance from the cluster center, from kT 6 keV in the northeastcorner of the field of view to about 3keV in the southwest region.Although we do not find any sharp edges in the surface brightnessprofile, a brightness excess of about 20% over a smooth β model isseen. The temperature also rises by about 10% in the same region. Thisindicates that the IC 310 region is a subcluster probably infalling intothe Perseus cluster, and the gas in front of IC 310 towards the Perseuscluster is likely to be compressed by the large-scale motion, whichsupports the view that the IC 310 system is undergoing a merger.
| Diffuse polarized emission associated with the Perseus cluster
We report on full-polarization radio observations of the Perseus cluster(Abell 426) using the Westerbork Synthesis RadioTelescope (WSRT) at wavelengths from 81-95 cm. We detect faint, veryextended polarized emission throughout the cluster region. We haveemployed a novel technique, Rotation Measure synthesis (Brentjens &de Bruyn, 2005, A&A, 441, 1217) to unravel the polarizationproperties of the emission across the full field of view. We detectpolarized emission over a wide range of RM from about 0 to 90 radm-2. Low RM emission (RM < 15 rad m-2) isattributed to the local Galactic foreground. It has a chaotic structurewith smooth changes in polarization angle on scales of the order of10´-30´, not unlike those seen by Haverkorn et al. (2003a,A&A, 403, 1045) at the same frequencies. Emission at values of RM> 30 rad m-2 on the other hand, shows organized structureson scales up to a degree and displays rapidly fluctuating polarizationangles on scales of the synthesized beam. A Galactic foregroundinterpretation for the high RM emission can not be ruled out, butappears extremely implausible. WSRT observations at 21 cm of the RM of adozen discrete sources surrounding the Perseus cluster indicate a smoothlarge-scale gradient in the Galactic foreground RM. The diffusestructures have a clear excess RM of about 40 rad m-2relative to these distant radio galaxies. This excess Faraday depth, thegenerally good spatial association with the cluster and the differentmorphology of the high RM emission, compared to the genuine Galacticforeground emission, all point to an association of the high RM emissionwith the Perseus cluster. The polarized emission reaches typical surfacebrightness levels of 0.5-1 mJy per 2 arcmin×3 arcmin beam and mustbe rather highly polarized (20%). Due to dynamic range limitationsand lack of sensitivity to large-scale structure we have not yetdetected the corresponding total intensity. Most of the polarizedemission, located at distances of about 1° from the cluster centre,appears too bright, by about 1-2 orders of magnitude, to be explainableas Thomson scattered emission of the central radio source off thethermal electrons in the cluster. However, this remains a viableexplanation for the highly polarized 21 cm emission from the inner10´-20´and part of the 81-95 cm emission. The bulk of theemission associated with the Perseus cluster may instead be related tobuoyant bubbles of relativistic plasma, probably relics from stillactive or now dormant AGN within the cluster. A lenticular shapedstructure, referred to as the lens, and measuring 0.5-1 Mpc isstrikingly similar to the structures predicted b Enßlin et al.(1998, A&A, 332, 395). At the western edge of the cluster, we detectvery long, linear structures that may be related to shocks caused byinfall of gas into the Perseus cluster along the Perseus-Piscesfilamentary structure of the cosmic web.
| Radio and Far-Infrared Emission as Tracers of Star Formation and Active Galactic Nuclei in Nearby Cluster Galaxies
We have studied the radio and far-infrared (FIR) emission from 114galaxies in the seven nearest clusters (<100 Mpc) with prominentX-ray emission to investigate the impact of the cluster environment onthe star formation and active galactic nucleus (AGN) activity in themember galaxies. The X-ray selection criterion is adopted to focus onthe most massive and dynamically relaxed clusters. A large majority ofcluster galaxies show an excess in radio emission over that predictedfrom the radio-FIR correlation, the fraction of sources with radioexcess increases toward cluster cores, and the radial gradient in theFIR/radio flux ratio is a result of radio enhancement. Of theradio-excess sources, 70% are early-type galaxies, and the same fractionhost an AGN. The galaxy density drops by a factor of 10 from thecomposite cluster center out to 1.5 Mpc, yet galaxies show no change inFIR properties over this region and show no indication of masssegregation. We have examined in detail the physical mechanisms thatmight impact the FIR and radio emission of cluster galaxies. Whilecollisional heating of dust may be important for galaxies in clustercenters, it appears to have a negligible effect on the observed FIRemission for our sample galaxies. The correlations between radio and FIRluminosity and radius could be explained by magnetic compression fromthermal intracluster medium pressure. We also find that simple delayedharassment cannot fully account for the observed radio, FIR, and mid-IRproperties of cluster galaxies.
| Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data
We present central velocity dispersions and Mg2 line indicesfor an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984had no previous measures. This sample contains the largest set ofhomogeneous spectroscopic data for a uniform sample of ellipticalgalaxies in the nearby universe. These galaxies were observed as part ofthe ENEAR project, designed to study the peculiar motions and internalproperties of the local early-type galaxies. Using 523 repeatedobservations of 317 galaxies obtained during different runs, the dataare brought to a common zero point. These multiple observations, takenduring the many runs and different instrumental setups employed for thisproject, are used to derive statistical corrections to the data and arefound to be relatively small, typically <~5% of the velocitydispersion and 0.01 mag in the Mg2 line strength. Typicalerrors are about 8% in velocity dispersion and 0.01 mag inMg2, in good agreement with values published elsewhere.
| Line-of-Sight Reddening Predictions: Zero Points, Accuracies, the Interstellar Medium, and the Stellar Populations of Elliptical Galaxies
Revised (B-V)0-Mg2 data, which are used to testreddening predictions, are presented for 402 elliptical galaxies. Thesereddening predictions can tell us both what the intrinsic errors are inthis relationship among gE galaxy stellar populations as well as detailsof nearby structure in the interstellar medium (ISM) of our Galaxy, andof the intrinsic errors in reddening predictions. Using least-squaresfits, the explicit 1 σ errors in reddenings predicted by theBurstein-Heiles (BH) method and the Schlegel and coworkers (IR) methodare calculated, as well as the 1 σ observational error in the(B-V)0-Mg2 for gE galaxies. It is found that indirections with E(B-V)<0.100 mag (where most of these galaxies lie),1 σ errors in the IR reddening predictions are 0.006-0.009 mag inE(B-V), those for BH reddening predictions are 0.011 mag, and the 1σ agreement between the two reddening predictions is 0.007 mag.The IR predictions have an accuracy of 0.010-0.011 mag in directionswith E(B-V)>=0.100 mag, significantly better than those of the BHpredictions (0.024-0.025). Both methods yield good evidence thatgas-to-dust variations that vary by a factor of 3, both high and low,exist along many lines of sight in our Galaxy. Both methods also predictmany directions with E(B-V)<0.015 mag, despite the difference in zeropoint that each has assumed. The ~0.02 higher reddening zero point inE(B-V) previously determined by Schlegel and coworkers is confirmed,primarily at the Galactic poles. Independent evidence of reddening atthe north Galactic pole (NGP) is reviewed, with the conclusion thatdirections still exist at the NGP that have E(B-V)<<0.01. Twolines of evidence suggest that IR reddenings are overpredicted indirections with high gas-to-dust ratios. As high gas-to-dust directionsin the ISM also include the Galactic poles, this overprediction is thelikely cause of the E(B-V)~0.02 mag larger IR reddening zero pointrelative to that of BH.
| Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| Redshift-Distance Survey of Early-Type Galaxies. I. The ENEARc Cluster Sample
This paper presents data on the ENEARc subsample of the larger ENEARsurvey of nearby early-type galaxies. The ENEARc galaxies belong toclusters and were specifically chosen to be used for the construction ofa Dn-σ template. The ENEARc sample includes newmeasurements of spectroscopic and photometric parameters (redshift,velocity dispersion, line index Mg2, and the angular diameterdn), as well as data from the literature. New spectroscopicdata are given for 229 cluster early-type galaxies, and new photometryis presented for 348 objects. Repeat and overlap observations withexternal data sets are used to construct a final merged catalogconsisting of 640 early-type galaxies in 28 clusters. Objectivecriteria, based on catalogs of groups of galaxies derived from completeredshift surveys of the nearby universe, are used to assign galaxies toclusters. In a companion paper, these data are used to construct thetemplate Dn-σ distance relation for early-typegalaxies, which has been used to estimate galaxy distances and derivepeculiar velocities for the ENEAR all-sky sample. Based on observationsat Complejo Astronomico El Leoncito, operated under agreement betweenthe Consejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; Cerro Tololo Inter-American Observatory,National Optical Astronomical Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation; the EuropeanSouthern Observatory (ESO), partially under the ESO-ON agreement; theFred Lawrence Whipple Observatory; the Observatório do Pico dosDias, operated by the Laboratório Nacional de Astrofísicaand the MDM Observatory at Kitt Peak.
| ASCA Observations of the Temperature Structure and Metal Distribution in the Perseus Cluster of Galaxies
Large-scale distributions of hot-gas temperature and Fe abundance in thePerseus cluster have been studied with multi-pointing observations bythe GIS instrument onboard ASCA. Within a radius of 20' from the clustercenter, the energy spectra requires two temperature components, in whichthe cool component indicates kT ~ 2 keV and the hot-componenttemperature shows a significant decline from about 8 keV to 6 keV towardthe center. In the outer region of the cluster, the temperature shows afluctuation with an amplitude of about 2 keV, which suggest that awestern region at ~16' from the cluster center is relatively hotter. Asfor the Fe abundance, a significant decline with radius is detected from0.44 solar at the center to ~ 0.1 solar at a 50' offset region. If theobserved Fe-K line intensity within 4' from the center is suppressed bya factor of 2 due to the resonance scattering effect, the corrected Femass density follows the galaxy distribution. Finally, our results donot support the large-scale velocity gradients previously reported fromthe same GIS data.
| Particle injection and reacceleration in clusters of galaxies and the EUV excess: the case of Coma
We calculate the energy distribution of the relativistic particlesinjected in the ICM during a phase of reacceleration of the relativisticparticles in the cluster volume. We apply our results to the case of theComa cluster in which recent merging activity and the presence of aradio halo may suggest that reacceleration processes are efficient. Wefind that the electron population injected in the central part of thecluster by the head tail radio galaxy NGC 4869 may account for a largefraction, if not all, of the detected EUV excess via inverse Comptonscattering of the cosmic microwave background (CMB) photons. If radiohaloes are powered by reacceleration mechanisms active in the clustervolume, moderate non-thermal EUV excesses (of the order ~1-5X10^42 ergs^-1) should be a common feature of clusters containing powerful headtail radio galaxies and/or AGNs.
| A catalogue and analysis of X-ray luminosities of early-type galaxies
We present a catalogue of X-ray luminosities for 401 early-typegalaxies, of which 136 are based on newly analysed ROSAT PSPC pointedobservations. The remaining luminosities are taken from the literatureand converted to a common energy band, spectral model and distancescale. Using this sample we fit the LX:LB relationfor early-type galaxies and find a best-fit slope for the catalogue of~2.2. We demonstrate the influence of group-dominant galaxies on the fitand present evidence that the relation is not well modelled by a singlepower-law fit. We also derive estimates of the contribution to galaxyX-ray luminosities from discrete-sources and conclude that they provideLdscr/LB~=29.5ergs-1LBsolar-1. Wecompare this result with luminosities from our catalogue. Lastly, weexamine the influence of environment on galaxy X-ray luminosity and onthe form of the LX:LB relation. We conclude thatalthough environment undoubtedly affects the X-ray properties ofindividual galaxies, particularly those in the centres of groups andclusters, it does not change the nature of whole populations.
| The Radio Galaxy Populations of Nearby Northern Abell Clusters
We report on the use of the NRAO VLA Sky Survey (NVSS) to identify radiogalaxies in 18 nearby Abell clusters. The listings extend from the coresof the clusters out to radii of 3 h-175 Mpc, whichcorresponds to 1.5 Abell radii and approximately 4 orders of magnitudein galaxy density. To create a truly useful catalog, we have collectedoptical spectra for nearly all of the galaxies lacking public velocitymeasurements. Consequently, we are able to discriminate between thoseradio galaxies seen in projection on the cluster and those that are inactuality cluster members. The resulting catalog consists of 329 clusterradio galaxies plus 138 galaxies deemed foreground or backgroundobjects, and new velocity measurements are reported for 273 of theseradio galaxies. The motivation for the catalog is the study of galaxyevolution in the cluster environment. The radio luminosity function is apowerful tool in the identification of active galaxies, as it isdominated by star-forming galaxies at intermediate luminosities andactive galactic nuclei (AGNs) at higher luminosities. The flux limit ofthe NVSS allows us to identify AGNs and star-forming galaxies down tostar formation rates less than 1 Msolar yr-1. Thissensitivity, coupled with the all-sky nature of the NVSS, allows us toproduce a catalog of considerable depth and breadth. In addition tothese data, we report detected infrared fluxes and upper limits obtainedfrom IRAS data. It is hoped that this database will prove useful in anumber of potential studies of the effect of environment on galaxyevolution. Based in part on observations obtained with the Apache PointObservatory 3.5 m telescope, which is owned and operated by theAstrophysical Research Consortium (ARC).
| Temperature Map of the Perseus Cluster of Galaxies Observed with ASCA
We present a two-dimensional temperature map of the Perseus Clusterbased on multipointing observations with the ASCA Gas ImagingSpectrometer, covering a region with a diameter of ~2°. Bycorrecting for the effect of the X-ray telescope response, thetemperatures were estimated from hardness ratios, and the completetemperature structure of the cluster with a spatial resolution of about100 kpc was obtained for the first time. There is an extended coolregion with a diameter of ~20' and kT~5 keV about 20' east of thecluster center. This region also shows higher surface brightness and issurrounded by a large ringlike hot region with kT>~7 keV and islikely to be a remnant of a merger with a poor cluster. Another extendedcool region is extending outward from the IC 310 subcluster. Thesefeatures and the presence of several other hot and cool blobs suggestthat this rich cluster has been formed as the result of a repetition ofmany subcluster mergers.
| The LX-σ Relation for Galaxies and Clusters of Galaxies
We demonstrate that individual elliptical galaxies and clusters ofgalaxies form a continuous X-ray luminosity-velocity dispersion(LX-σ) relation. Our samples of 280 clusters and 57galaxies have LX~σ4.4 andLX~σ10, respectively. This unifiedLX-σ relation spans 8 orders of magnitude inLX and is fully consistent with the observed and theoreticalluminosity-temperature scaling laws. Our results support the notion thatgalaxies and clusters of galaxies are the luminous tracers of similardark matter halos.
| Galaxy identifications in the ROSAT All-Sky Survey
In a correlation study of the ROSAT All-Sky Survey Bright SourceCatalogue (RASS-BSC) with the Catalogue of Principal Galaxies (PGC) 904X-ray sources were found that possess possible extragalacticcounterparts within a search radius of 100 arcsec. A visual screeningprocess was applied to classify the reliability of the correlations. 547correlations have been quoted as reliable identifications. From these,349 sources are known as active galaxies. Although for the other sourcesno hints for activity were found in the literature, 69% of those forwhich we have distances show X-ray luminosities exceeding those ofnormal galaxies, a clear sign that these galaxies also own hithertounreported X-ray active components. Some objects are located inside orin the direction of a known group or cluster of galaxies. Their X-rayflux may therefore be in part affected by hot gas emission. Luminosityand log N-log S distributions are used to characterize differentsubsamples. Nuclei that are both optically and X-ray active are foundpredominantly in spirals. Two special source samples are defined, onewith candidates for X-ray emission from hitherto unknown groups orclusters of galaxies, and one with high X-ray luminosity sources, thatare likely candidates to possess hitherto unreported active galacticnuclei. Besides a compilation of X-ray and optical parameters, alsoX-ray overlays on optical images for all the objects are supplied aspart of this work. Full data set (Table 1) and the 904 overlay imagesare only available at CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/378/30
| Luminosity versus Phase-Space-Density Relation of Galaxies Revisited
We reexamined the correlation between the BTmagnitude and the phase-space-density parameterw=(D225vc)-1 of galaxies forthe Virgo, the Coma, the Fornax, and the Perseus clusters in an effortto better understand the physical underpinning of the fundamental plane.A tight correlation (BT=alog w+b) common to differentmorphological types of galaxies (E, S0, S) was found for the Virgo andthe Coma clusters, with a=1.87+/-0.10 and 1.33+/-0.11, respectively. Aninvestigation using only E galaxies was made for the four clusters. Theresults indicated that the empirical linear relation might be commonamong the Coma, the Fornax, and the Perseus clusters, with the VirgoCluster showing deviation. This relation, which is another way toproject the fundamental plane, has an expression insensitive to themorphology and may be suitable for treating galaxies of differentmorphological types collectively.
| The Properties of the X-Ray-selected EMSS Sample of BL Lacertae Objects
We present updated and complete radio, optical, and X-ray data for BLLac objects in the Einstein Medium Sensitivity Survey (EMSS). Thecomplete ``M91'' sample first presented in Morris et al. is updated toinclude 26 BL Lac objects in total, and we define a new, virtuallycomplete sample consisting of 41 EMSS BL Lac objects (the ``D40''sample). New high signal-to-noise ratio, arcsecond-resolution VLAobservations are also presented for 11 EMSS BL Lac objects, completingVLA observations of the M91 sample. The addition of four new objects, aswell as updated X-ray flux and redshift information, has increased the value for the M91 sample to0.399+/-0.057 and =0.427+/-0.045 forthe newly defined D40 sample. In conjunction with other studies ofX-ray-selected BL Lac (XBL) samples, these results solidify negativeevolution for XBLs, especially for more extreme high-energy-peaked BLLac objects, for which we find=0.271+/-0.077. The observed, spectral, and radio properties ofXBLs are completely consistent with being the beamed population oflow-luminosity, FR-1 radio galaxies. However, our VLA observations doconfirm that XBLs are too core dominated to be consistent with a beamedpopulation of FR-1's seen at intermediate angles, as suggested by theunified model, if XBLs have moderate outflow velocities (γ~5).
| A Test for Large-Scale Systematic Errors in Maps of Galactic Reddening
Accurate maps of Galactic reddening are important for a number ofapplications, such as mapping the peculiar velocity field in the nearbyuniverse. Of particular concern are systematic errors which vary slowlyas a function of position on the sky, as these would induce spuriousbulk flow. We have compared the reddenings of Burstein & Heiles (BH)and those of Schlegel, Finkbeiner, & Davis (SFD) to independentestimates of the reddening, for Galactic latitudes |b|>10^deg. Ourprimary source of Galactic reddening estimates comes from comparing thedifference between the observed B-V colors of early-type galaxies, andthe predicted B-V color determined from the B-V-Mg_2 relation. We havefitted a dipole to the residuals in order to look for large-scalesystematic deviations. There is marginal evidence for a dipolar residualin the comparison between the SFD maps and the observed early-typegalaxy reddenings. If this is due to an error in the SFD maps, then itcan be corrected with a small (13%) multiplicative dipole term. Weargue, however, that this difference is more likely to be due to a small(0.01 mag) systematic error in the measured B-V colors of the early-typegalaxies. This interpretation is supported by a smaller, independentdata set (globular cluster and RR Lyrae stars), which yields a resultinconsistent with the early-type galaxy residual dipole. BH reddeningsare found to have no significant systematic residuals, apart from theknown problem in the region 230^deg
| X-ray luminosities for a magnitude-limited sample of early-type galaxies from the ROSAT All-Sky Survey
For a magnitude-limited optical sample (B_T <= 13.5 mag) ofearly-type galaxies, we have derived X-ray luminosities from the ROSATAll-Sky Survey. The results are 101 detections and 192 useful upperlimits in the range from 10^36 to 10^44 erg s^-1. For most of thegalaxies no X-ray data have been available until now. On the basis ofthis sample with its full sky coverage, we find no galaxy with anunusually low flux from discrete emitters. Below log (L_B) ~ 9.2L_⊗ the X-ray emission is compatible with being entirely due todiscrete sources. Above log (L_B) ~ 11.2 L_osolar no galaxy with onlydiscrete emission is found. We further confirm earlier findings that L_xis strongly correlated with L_B. Over the entire data range the slope isfound to be 2.23 (+/- 0.12). We also find a luminosity dependence ofthis correlation. Below log L_x = 40.5 erg s^-1 it is consistent with aslope of 1, as expected from discrete emission. Above this value theslope is close to 2, as expected from gaseous emission. Comparing thedistribution of X-ray luminosities with the models of Ciotti et al.leads to the conclusion that the vast majority of early-type galaxiesare in the wind or outflow phase. Some of the galaxies may have alreadyexperienced the transition to the inflow phase. They show X-rayluminosities in excess of the value predicted by cooling flow modelswith the largest plausible standard supernova rates. A possibleexplanation for these super X-ray-luminous galaxies is suggested by thesmooth transition in the L_x--L_B plane from galaxies to clusters ofgalaxies. Gas connected to the group environment might cause the X-rayoverluminosity.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| An X-Ray Spectral Survey of Radio-loud Active Galactic Nuclei with ASCA
We present a uniform and systematic analysis of the 0.6-10 keV X-rayspectra of radio-loud active galactic nuclei (AGNs) observed by ASCA.The sample, which is not statistically complete, includes 10 broad-lineradio galaxies (BLRGs), five radio-loud quasars (QSRs), nine narrow-lineradio galaxies (NLRGs), and 10 radio galaxies (RGs) of mixed FR I and FRII types. For several sources the ASCA data are presented here for thefirst time. The exposure times of the observations and the fluxes of theobjects vary over a wide range; as a result, so does the signal-to-noiseratio of the individual X-ray spectra. At soft X-rays, about 50% ofNLRGs and 100% of RGs exhibit thermal plasma emission components, withbimodal distributions of temperatures and luminosities. This indicatesthat the emission in such an object arises in hot gas either in asurrounding cluster or loose group or in a hot corona, consistent withprevious ROSAT and optical results. At energies above 2 keV, a hardpower-law component (photon index Γ~1.7-1.8) is detected in 90% ofcases. The power-law photon indices and luminosities in BLRGs, QSRs, andNLRGs are similar. This is consistent with simple orientation-basedunification schemes for lobe-dominated radio-loud sources in whichBLRGs, QSRs, and NLRGs harbor the same type of central engine. Moreover,excess cold absorption in the range 1021-1024cm-2 is detected in most (but not all) NLRGs, consistent withabsorption by obscuring tori, as postulated by unification scenarios.The ASCA data provide initial evidence that the immediate gaseousenvironment of the X-ray source of BLRGs may be different than inSeyfert 1 galaxies: absorption edges of ionized oxygen, common in thelatter, are detected in only one BLRG. Instead we detect large columnsof cold gas in a fraction (~44%-60%) of BLRGs and QSRs, comparable tothe columns detected in NLRGs, which is puzzling. This difference hintsat different physical and/or geometrical properties of the medium aroundthe X-ray source in radio-loud AGNs compared to their radio-quietcounterparts, properties that can be explored further with future X-rayobservations. For the full sample, the nuclear X-ray luminosity iscorrelated with the luminosity of the [O III] emission line, the FIRemission at 12 μm, and the lobe radio power at 5 GHz. The Fe Kαline is detected in 50% of BLRGs and in one QSR, with a large range ofintrinsic widths and equivalent widths. In the handful of NLRGs where itis detected, the line is generally unresolved. Comparing the averagepower-law photon indices of the various classes of radio-loud AGNs totheir radio-quiet counterparts from the literature, we find only a weakindication that the ASCA 2-10 keV spectra of BLRGs are flatter thanthose of Seyfert 1 galaxies of comparable X-ray luminosity. This resultis at odds with evidence from samples studied by other authorssuggesting that radio-loud AGNs have flatter spectra than radio-quietones. Rather, it supports the idea that a beamed synchrotronself-Compton component related to the radio source (jet) is responsiblefor the flatter slopes in those radio-loud AGNs. We argue that, becauseof the way those samples were constructed, beamed X-ray emission fromthe radio jets probably contributed to the observed X-ray spectra. Thesample studied here includes six weak-line radio galaxies (WLRGs),powerful radio galaxies characterized by [O III] 4569 and 5007 Åof unusually low luminosity and by unusually high [O II]/[O III] lineratios. The ASCA spectra of WLRGs can be generally decomposed into asoft thermal component with kT~1 keV, plus a hard component, describedeither by a flat (<Γ>=1.5) absorbed power law or by a veryhot (kT~100 keV) thermal bremsstrahlung model. Their intrinsicluminosities are in the rangeL2-10keV~1040-1042 ergs s-1,2 orders of magnitude lower than in other sources in our sample. If thehard X-ray emission is attributed to a low-luminosity AGN, aninteresting possibility is that WLRGs represent an extreme population ofradio galaxies in which the central black hole is accreting at a ratewell below the Eddington rate.
| A Search for Low-Luminosity BL Lacertae Objects
Many properties of BL Lacs have become explicable in terms of the``relativistic beaming'' hypothesis, whereby BL Lacs are FR 1 radiogalaxies viewed nearly along the jet axis. However, a possible problemwith this model is that a transition population between beamed BL Lacsand unbeamed FR 1 galaxies has not been detected. A transitionpopulation of ``low-luminosity BL Lacs'' was predicted to exist inabundance in X-ray-selected samples such as the Einstein Extended MediumSensitivity Survey (EMSS) by Browne & Marcha. However, these BL Lacsmay have been misidentified as clusters of galaxies. We have conducted asearch for such objects in the EMSS with the ROSAT High-ResolutionImager (HRI) here we present ROSAT HRI images, optical spectra, and VLAradio maps for a small number of BL Lacs that were previouslymisidentified in the EMSS catalog as clusters of galaxies. While theseobjects are slightly lower in luminosity than other EMSS BL Lacs, theirproperties are too similar to the other BL Lacs in the EMSS sample to``bridge the gap'' between BL Lacs and FR 1 radio galaxies. Also, thenumber of new BL Lacs found is too low to alter significantly the X-rayluminosity function or value for the X-ray-selected EMSSBL Lac sample. Thus, these observations do not explain fully the discrepancy between the X-ray- and radio-selected BL Lacsamples.
| The galaxy cluster Abell 426 (Perseus). A catalogue of 660 galaxy positions, isophotal magnitudes and morphological types
We present a homogeneous catalogue of galaxies in the field of thenearby galaxy cluster A 426 (Perseus) based on a survey of digitisedSchmidt plates taken with the Tautenburg 2 m telescope in the B band.Accurate positions, morphological types, B25 isophotalmagnitudes, angular radii and position angles are given for 660 galaxieswithin a field of about 10 square-degrees, centred on alpha = 3() h 21()min, delta = 41degr 33' (J2000). When available, the radial velocity andthe most common name taken from NED or PGC are included. The cataloguecomprises galaxies brighter than B25~19.5. The estimatedlimit of completeness is B25~18. Two thirds of the galaxiesare published for the first time. The galaxy positions are measured witha mean accuracy of 0farcs5 , the photometric accuracy is of the order of0.1 to 0.2 mag depending on image crowding and galaxy shape.Morphological properties were evaluated from the visual inspections ofboth deep images obtained from the digital co-addition of a large numberof plates and higher-resolution images from single plates taken undergood seeing conditions. The superimposed images unveil faint structuresdown to mu_B ~ 27 mag arcsec(-2) . The catalogue is applied to a studyof statistical properties of the galaxies in A 426: projecteddistribution of morphological types, segregation of morphological types,position of the cluster centre, distribution of galaxy position angles,type-dependent luminosity functions, and total B-luminosity of the thecluster. In agreement with previous studies, we find a relativespiral-deficiency in the central region (r <~ 30'). The percentage ofidentified S+Irr increases, however, increases from 30% in the centre tomore than 50% in the outer parts. The projected distributions of early-and late-type galaxies are not co-centred. The total luminosity of allsupposed member galaxies in the surveyed area is estimated to(6.5+/-0.9)\ 10(12) x h50(-2) blue solar luminosities. We donot analyse in detail possible substructures in the projecteddistribution of galaxies. However, we found a pronounced clump ofgalaxies at alpha (J2000.0) = 3() h20fm4 , delta (J2000.0) = 43degr4 ',which is shown to be a background cluster at z~ 0.050. The catalogue isonly available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html } \fnmsep \thanks{ Based onobservations made with the 2\,m telescope of the ThüringerLandessternwarte Tautenburg, Germany, and with the 2.2\,m telescope ofthe German-Spanish Astronomical Centre, Calar Alto, Spain.
| ROSATPSPC observations of the outer regions of the Perseus cluster of galaxies
We present an analysis of four off-axis ROSAT Position SensitiveProportional Counter (PSPC) observations of the Perseus cluster ofgalaxies (Abell 426). We detect the surface brightness profile to aradius of 80 arcmin (~2.4h^-1_50 Mpc) from the X-ray peak. The profileis measured in various sectors and in three different energy bands.First, a colour analysis highlights a slight variation of N_H over theregion, and cool components in the core and in the eastern sector. Weapply the beta-model to the profiles from different sectors and presenta solution to the, so-called, beta-problem. The residuals from anazimuthally-averaged profile highlight extended emission both in theeast and in the west, with estimated luminosities of about 8 and 1x10^43erg s^-1, respectively. We fit several models to the surfacebrightness profile, including the one obtained from the Navarro, Frenk& White potential. We obtain the best fit with the gas distributiondescribed by a power law in the inner, cooling region and a beta-modelfor the extended emission. Through the best-fitting results and theconstraints from the deprojection of the surface brightness profiles, wedefine the radius where the overdensity inside the cluster is 200 timesthe critical value, r_200, at 2.7h^-1_50 Mpc. Within 2.3 h^-1_50 Mpc(0.85r_200), the total mass in the Perseus cluster is 1.2x10^15M_solarand its gas fraction is about 30 per cent.
| Old Stellar Populations. VI. Absorption-Line Spectra of Galaxy Nuclei and Globular Clusters
We present absorption-line strengths on the Lick/IDS line-strengthsystem of 381 galaxies and 38 globular clusters in the 4000-6400Angstroms region. All galaxies were observed at Lick Observatory between1972 and 1984 with the Cassegrain Image Dissector Scanner spectrograph,which makes this study one of the largest homogeneous collections ofgalaxy spectral line data to date. We also present a catalog of nuclearvelocity dispersions used to correct the absorption-line strengths ontothe stellar Lick/IDS system. Extensive discussion of both random andsystematic errors of the Lick/IDS system is provided. Indices are seento fall into three families: alpha -element-like indices (including CN,Mg, Na D, and TiO2) that correlate positively with velocity dispersion;Fe-like indices (including Ca, the G band, TiO1, and all Fe indices)that correlate only weakly with velocity dispersion and the alphaindices; and H beta that anticorrelates with both velocity dispersionand the alpha indices. C24668 seems to be intermediate between the alphaand Fe groups. These groupings probably represent different elementabundance families with different nucleosynthesis histories.
| The Faint End of the Galaxy Luminosity Function in Abell 426 and 539
We derive I-band luminosity functions for galaxies in Abell 426 (Perseusand Abell 539, two rich, low Galactic latitude clusters at moderateredshift. Cluster members are selected via the color-magnitude relationfor bright galaxies. We find alpha = -1.56 +/- 0.07 for Perseus over therange -19.4 < M_I < -13.4 (15 < I < 21) and alpha = -1.42+/- 0.14 for -18.5 < M_I < -14 (17 < I < 21.5) for A539.These luminosity functions are similar to those derived in Virgo andFornax, weakly supporting claims for the existence of a universalluminosity function for galaxies in clusters.
| A catalogue of Mg_2 indices of galaxies and globular clusters
We present a catalogue of published absorption-line Mg_2 indices ofgalaxies and globular clusters. The catalogue is maintained up-to-datein the HYPERCAT database. The measurements are listed together with thereferences to the articles where the data were published. A codeddescription of the observations is provided. The catalogue gathers 3541measurements for 1491 objects (galaxies or globular clusters) from 55datasets. Compiled raw data for 1060 galaxies are zero-point correctedand transformed to a homogeneous system. Tables 1, 3, and 4 areavailable in electronic form only at the CDS, Strasbourg, via anonymousftp 130.79.128.5. Table 2 is available both in text and electronic form.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
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