|Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis|
X-ray observations have revealed in other galaxies a class ofextranuclear X-ray point sources with X-ray luminosities of1039-1041 ergs s-1, exceeding theEddington luminosity for stellar mass X-ray binaries. Theseultraluminous X-ray sources (ULXs) may be powered by intermediate-massblack holes of a few thousand Msolar or stellar mass blackholes with special radiation processes. In this paper, we present asurvey of ULXs in 313 nearby galaxies withD25>1' within 40 Mpc with 467 ROSAT HighResolution Imager (HRI) archival observations. The HRI observations arereduced with uniform procedures, refined by simulations that help definethe point source detection algorithm employed in this survey. A sampleof 562 extragalactic X-ray point sources withLX=1038-1043 ergs s-1 isextracted from 173 survey galaxies, including 106 ULX candidates withinthe D25 isophotes of 63 galaxies and 110 ULX candidatesbetween 1D25 and 2D25 of 64 galaxies, from which aclean sample of 109 ULXs is constructed to minimize the contaminationfrom foreground or background objects. The strong connection betweenULXs and star formation is confirmed based on the striking preference ofULXs to occur in late-type galaxies, especially in star-forming regionssuch as spiral arms. ULXs are variable on timescales over days to yearsand exhibit a variety of long term variability patterns. Theidentifications of ULXs in the clean sample show some ULXs identified assupernovae (remnants), H II regions/nebulae, or young massive stars instar-forming regions, and a few other ULXs identified as old globularclusters. In a subsequent paper, the statistic properties of the surveywill be studied to calculate the occurrence frequencies and luminosityfunctions for ULXs in different types of galaxies to shed light on thenature of these enigmatic sources.
|Toward the Secondary Bar: Gas Morphology and Dynamics in NGC 4303|
We report on the molecular gas properties in the central kiloparsec ofthe almost face-on double-barred galaxy NGC 4303 (M61), using the12CO 1-0 line emission observed with the Owens Valley RadioObservatory (OVRO) millimeter interferometer. The bulk of the molecularline emission comes from two straight gas lanes that run north-southalong the leading sides of the large-scale primary bar. Velocitydeviations of up to 90 km s-1 from the mean rotationalvelocity are associated with these gas lanes. Inside a radius of ~5"(~400 pc) the molecular gas forms a spiral pattern that, for thenorthern arm, can be traced to the nucleus. The high angular resolutionof our OVRO data (2''~150 pc), together with archival HubbleSpace Telescope (HST) data, allows for a comparison with dynamicalmodels of gas flow in the inner kiloparsec of single- and double-barredgalaxies. We find that the observed global properties of the moleculargas are in agreement with models for the gas flow in a strong,large-scale bar, and the two-arm spiral structure seen in12CO in the inner kiloparsec can already be explained by adensity wave initiated by the potential of that bar. Only a weakcorrelation between the molecular gas distribution and the extinctionseen in the HST V-H map is found in the inner 400 pc of NGC 4303: Theinnermost part of one arm of the nuclear 12CO spiralcorrelates with a weak dust filament in the color map, while the overalldust distribution follows a ring or single-arm spiral pattern wellcorrelated with the UV continuum. This complicated nuclear geometry ofthe stellar and gaseous components allows for two scenarios: (1) Aself-gravitating m=1 mode is present, forming the spiral structure seenin the UV continuum. In this case, the gas kinematics would beunaffected by the small (~4") inner bar. (2) The UV continuum traces acomplete ring that is heavily extincted north of the nucleus. Such aring forms in hydrodynamic models of double bars, but the models cannotaccount for the UV emission observed on the leading side of the innerbar. Comparison with other starburst ring galaxies where the moleculargas emission and the star-forming clusters form a ring or tightly woundspiral structure suggests that the starburst ring in NGC 4303 is in anearly stage of formation.
|ROSAT X-Ray Observations of Central Galactic Starbursts|
We present spatial and spectral results of ROSAT observations of twogalaxies: NGC 4569 and NGC 4303. Both objects are members of the VirgoCluster and have nearby smaller companions with which they have probablygone through an encounter. Both soft X-ray spectra (0.1-2.4 keV) can befitted with a two-component model consisting of a power-law componentfrom a non-thermal emission of a compact active nucleus and aRaymond-Smith model for a hot thin thermal plasma originating fromstarbursts. The X-ray luminosities are in the range of 1040erg s-1. The central source of NGC 4569 is very compact andcan not be resolved with the ROSAT HRI detector, while there is extendedsoft X-ray emission in the galactic disk as well as above it. NGC 4303is dominated by the active nucleus in the X-ray. But several additionaldisk sources associated with H II regions can be observed.
|Nearby Optical Galaxies: Selection of the Sample and Identification of Groups|
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
|X-rays from the barred galaxy NGC 4303|
The late-type galaxy NGC 4303 (M61) is one of the most intensivelystudied barred galaxies in the Virgo Cluster. Its prominent enhancedstar formation throughout large areas of the disk can be nicely studieddue to its low inclination of about 27̂. We present observations ofNGC 4303 with the ROSAT PSPC and HRI in the soft X-ray (0.1-2.4 keV).The bulk of the X-ray emission is located at the nuclear region. Itcontributes more than 80% to the total observed soft X-ray flux. Theextension of the central X-ray source and theLX/LHα ratio point to a low luminous AGN(LINER) with a circumnuclear star-forming region. Several separate disksources can be distinguished with the HRI, coinciding spatially withsome of the most luminous H II regions outside the nucleus of NGC 4303.The total star formation rate amounts to 1-2 Msolaryr-1. The X-ray structure follows the distribution of starformation with enhancement at the bar-typical patterns. The bestspectral fit consists of a power-law component (AGN and HMXBs) and athermal plasma component of hot gas from supernova remnants andsuperbubbles. The total 0.1-2.4 keV luminosity of NGC 4303 amounts to5×1040 erg s-1, consistent with comparablegalaxies, like e.g. NGC 4569.
|Investigation of Barred Galaxies. V. Surroundings of SB and SA Galaxies|
|Groups of galaxies. III. Some empirical characteristics.|
|Catalogue of HI maps of galaxies. I.|
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 22.214.171.124 orhttp://cdsweb.u-strasbg.fr/Abstract.html
|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.
|Complex Mg II Absorption in the Outer Disk of M61|
The increasing availability of high-quality spectra of QSOabsorption-line systems at resolutions of only a few kilometers persecond is expected to facilitate the translation of the kinematics ofcomponents comprising the lines into the spatial distribution of gasaround an absorbing galaxy. In this Letter we present Hubble SpaceTelescope (HST) spectra of Q1219+047, a QSO whose line of sight passes21 h-1 kpc from the center of M61, through the outer regions of anextended H I disk. We detect complex Mg II absorption, spanning avelocity range of ~300 km s-1, and strong C IV absorption; these are thefirst UV observations of a QSO absorption-line system arising in theoutskirts of a disk of a nearby galaxy at low inclination. Ourobservations are at odds with models of galaxies in which absorbingclouds corotate with a galaxy's disk, because M61's low inclinationshould give rise to only a few Mg II components spread over a smallvelocity range in such a model. Hence our results throw doubt on whetherabsorption-line profiles can be used to infer the spatial distributionof gas around absorbing galaxies.
|New aperture photometry for 217 galaxies in the Virgo and Fornax clusters.|
We present photo electric multi-aperture photometry in UBVRI of 171 and46 galaxies in the Virgo and Fornax clusters, respectively. Many of thegalaxies have not been observed in at least one of these passbandsbefore. We discuss the reduction and transformation into the Cousinsphotometric system as well as the extinction coefficients obtainedbetween 1990 and 1993.
|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.
|The UV properties of normal galaxies. III. Standard luminosity profiles and total magnitudes.|
In the previous papers of this series we collected and reduced to thesame system all the available photometric data obtained in theultraviolet (UV) range for normal (i.e. non active) galaxies. Here weuse these data to derive standard UV luminosity profiles for threemorphological bins (E/S0; Sa/Sb; Sc/Sd) and extrapolated totalmagnitudes for almost 400 galaxies. We find that: 1) the UV growthcurves are well matched by the B-band revised standard luminosityprofiles, once a proper shift in the effective radius is applied, and 2)the UV light in early-type galaxies is more centrally concentrated thanthe visible light.
|Distribution of the spin vectors of the disk galaxies of the Virgo cluster. I. The catalogue of 310 disk galaxies in the Virgo area.|
|A revised catalog of CfA1 galaxy groups in the Virgo/Great Attractor flow field|
A new identification of groups and clusters in the CfA1 Catalog ofHuchra et al. is presented, using a percolation algorithm to identifydensity enhancements. It is shown that in the resulting catalog,contamination by interlopers is significantly reduced. The Schechterluminosity function is redetermined, including the Malmquist bias.
|General study of group membership. II - Determination of nearby groups|
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
|Investigations of the Local Supercluster velocity field. I - Observations close to Virgo, using Tully-Fisher distances and the Tolman-Bondi expanding sphere|
Results are presented of an investigation of the velocity-distancerelation close to the direction of the Virgo cluster, with distancesfrom the Tully-Fisher relation, and with attention to the Malmquistbias. For Theta greater than 8 deg, a behavior is revealed which is asexpected Tolman-Bondi solutions for an expanding spherical massdistribution. Various density distributions, constrained by the massinside the Local Group distance, agree with the observations, but onlyif the mass within the Virgo 6 deg region is close to or larger than thestandard Virgo virial mass values. It is inferred that the central6-degree mass has the standard M (virial) as a rough lower limit. Fromthis it follows, together with the light ratios within the localsupercluster and the light enhancement relative to the general field,that light does not trace mass. Background contamination produces anasymmetrical distribution of velocities behind r(Vir).
|Abell 154 and Virgo - Pilot study for H I observations of distant clusters of galaxies|
As a test of procedures required to study the H I contents of spiralgalaxies in distant clusters of galaxies, the cluster Abell 154 has beenobserved from Arecibo. Fourteen candidate detections were found in tworegions of the cluster comprising about 10 percent of the cluster area.These results are compared in detail with those expected for theexhaustively studied Virgo cluster displaced to the distance of A 154.Most of the candidate detections are likely to be the combined profilesof two or more spiral galaxies, many of them too faint to appear on thelist of morphological types classified by Dressler (1980). Any attemptto identify these H I signals with known bright spirals is problematicat best. The A 154 profiles are systematically broader than expected forVirgo, but a crude application of the Tully-Fisher correlation indicatesthat they are still consistent with available photometric data. Whilethe H I deficiency in Virgo would still be apparent at the A 154distance, no significant evidence is found for H I deficiency in A 154.
|Does the Central Depression of Stellar Disks Occur in Late Type Galaxies|
|Continuum radio emission from Virgo galaxies|
The paper presents single-antenna measurements of radio emission from120 galaxies in the Virgo cluster at 2380 MHz using a 2.6 arc min beam(half-power beam width). It also presents interferometric measurementsat the same frequency for 48 galaxies with less than or equal to 1 arcsec resolution. The relative concentration of the radio emission forthese galaxies, particularly the emission from the galactic diskcompared with that from the nucleus is discussed. It is found that thedisk emission dominates in most cases. Some indications that the fluxconcentration is greater in elliptical and lenticular galaxies than itis in spirals are also found.
|Ultraviolet observations and star-formation rate in galaxies|
The present 149 galaxies, essentially of spiral and irregular types wereobserved at about 2000 A in a survey using a balloon-borne imagingtelescope. Total ultraviolet fluxes in an about 125-A wide bandpass havebeen obtained by comparison with field stars. On average, the m(2000)-Bcolor gets redder from late to early morphological types. For a giventype, this color exhibits a large scatter which increases from late toearly types. As expected, the galaxies show a relation between them(2000)-B and B-V colors. After a correction for dust extinction basedon the neutral hydrogen content of each galaxy, the observed fluxes areused to obtain quantitative estimates of the current star formation rate(SFR). A good correlation is found between the SFR and the total gascontent. A weak correlation observed between the SFR per unit area andthe average gas surface density might be compatible with the existenceof a power-law relation of exponent 1, between birthrate and gasdensity. The SFR per unit gas mass shows both a significant dispersionand a decrease toward later types. Implications in terms of starformation history are discussed.
|Studies of the Virgo cluster. IV - an Atlas of Virgo cluster spiral galaxies: The luminosity range within a given spiral type|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985AJ.....90..395S&db_key=AST
|Supplement to the detailed bibliography on the surface photometry of galaxies|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985A&AS...60..517P&db_key=AST
|Digital surface photometry of galaxies toward a quantitative classification. III - A mean concentration index as a parameter representing the luminosity distribution|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1984ApJ...280....7O&db_key=AST
|A survey of galaxy redshifts. IV - The data|
The complete list of the best available radial velocities for the 2401galaxies in the merged Zwicky-Nilson catalog brighter than 14.5mz and with b (II) above +40 deg or below -30 deg ispresented. Almost 60 percent of the redshifts are from the CfA surveyand are accurate to typically 35 km/s.