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|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.
|The gas content of peculiar galaxies: Strongly interacting systems|
A study of the gas content in 1038 interacting galaxies, essentiallyselected from Arp, Arp & Madore, Vorontsov-Velyaminov catalogues andsome of the published literature, is presented here. The data on theinterstellar medium have been extracted from a number of sources in theliterature and compared with a sample of 1916 normal galaxies. The meanvalues for each of the different ISM tracers (FIR, 21 cm, CO lines,X-ray) have been estimated by means of survival analysis techniques, inorder to take into account the presence of upper limits. From the datait appears that interacting galaxies have a higher gas content thannormal ones. Galaxies classified as ellipticals have both a dust and gascontent one order of magnitude higher than normal. Spirals have in mostpart a normal dust and HI content but an higher molecular gas mass. TheX-ray luminosity also appears higher than that of normal galaxies ofsame morphological type, both including or excluding AGNs. We consideredthe alternative possibilities that the molecular gas excess may derivefrom the existence of tidal torques which produce gas infall from thesurrounding regions or from a different metallicity which affects the Xconversion factor between the observed CO line luminosity and the H_2calculated mass. According to our tests, it appears that interactinggalaxies possess a higher molecular mass than normal galaxies but with asimilar star formation efficiency.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (220.127.116.11) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/941
|Star Formation Rates in Interacting Starburst Galaxies|
By narrowband imaging in Hα and in the adjacent red stellarcontinuum we have studied the rate and distribution of star formation in43 systems of luminous and ultraluminous IR galaxies currentlyundergoing interaction and merging. These galaxies are amongst the mostluminous at 60 μm and range in distance from ~50 up to 100 Mpc. Herewe present the Hα and the adjacent red-continuum narrowbandimages, and we compare the star formation rates derived from Hαwith those estimated from the IR luminosity. We find clear evidence forsubstantial extinction and obscuration of star-forming regions in theoptical. Without correction for reddening in the host galaxy orcorrection for [N II] contamination, the star formation rates derivedfor Hα are typically 0.5-1.0 dex lower than those estimated fromthe IR flux, and the scatter in the correlation is very large. However,an unexpected result is that when spectroscopic data are used toeliminate objects dominated by an active nucleus, to determine thegalaxian extinction, and to correct the Hα flux for both reddeningand for the contamination by the [N II] emission, a remarkably goodcorrelation emerges between the star formation rates estimated from theHα flux and those derived from the FIR continuum. In addition, astrong correlation is found between the extinction in the line-emittingregion, AHα, and the rate of star formation. Ourresults invalidate the use of Hα imaging as a reliable indicatorof star formation in starburst galaxies unless spectroscopic data arealso available. This has important implications for the determination ofstar formation rates in high-redshift galaxies. Finally, we find nocorrelation between the measured star formation rates, and theinteraction class, suggesting that the enhanced star formation ratestriggered by the interaction continue throughout the whole of themerging sequence.
|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.
|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.
|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.
|Total and effective colors of 501 galaxies in the Cousins VRI photometric system|
Total color indices (V-R)T, (V-I)T and effectivecolor indices (V-R)e, (V-I)e in the Cousins VRIphotometric system are presented for 501 mostly normal galaxies. Thecolors are computed using a procedure outlined in the Third ReferenceCatalogue of Bright Galaxies (RC3) whereby standard color curvesapproximated by Laplace-Gauss integrals are fitted to observedphotoelectric multiaperture photometry. 11 sources of such photometrywere used for our analysis, each source being assigned an appropriateweight according to a rigorous analysis of residuals of the data fromthe best-fitting standard color curves. Together with the integrated B-Vand U-B colors provided in RC3, our analysis widens the range ofwavelength of homogeneously defined colors of normal galaxies of allHubble types. We present color-color and color-type relations that canbe modeled to understand the star formation history of galaxies.
|Southern Sky Redshift Survey - The catalog|
The catalog of radial velocities for galaxies which comprise thediameter-limited sample of the Southern Sky Redshift Survey ispresented. It consolidates the data of observations carried out at theLas Campanas Observatory, Observatorio Nacional, and South AfricanAstronomical Observatory. The criteria used for the sample selection aredescribed, as well as the observational procedures and the techniqueutilized to obtain the final radial velocities. The intercomparisonbetween radial velocity measurements from different telescopes indicatesthat the final data base is fairly homogeneous with a typical error ofabout 40 km/s. The sample is at present 90 percent complete, and themissing galaxies are predominantly objects with very low surfacebrightness for which it is very difficult to obtain optical redshifts.
|The plane W(Na I) X W(Mg I) - Effects of interstellar Na I in a sample of southern galaxies|
Galaxy spectra from a subsample of the Southern Sky Redshift Survey databank were used to study the equivalent width plane for the lines Na Ilambda 5893 A vs Mg I lambda 5175 A. An estimate of how important thecontribution of the interstellar gas for the sodium line is compared tothat of the stellar population. The sample is made up of galaxies withmorphological types from E to Sc and are distributed up to radialvelocities of 25,000 km/s, most of them smaller than 15,000 km/s. Mostearly type galaxies with dust lanes, particularly nearly edge-on So's,present an enhancement of the Na I line. Inclined spiral galaxies tendto present enhanced Na I with respect to face-on spirals. This tendency,previously found in a smaller sample of galaxies limited to V equal toor less than 6000 km/s, is now confirmed for more distant ones. In thelarge velocity sample it shows the global bulge rather than the verynucleus; the persistence of the effect suggests that the scale height ofthe gas layer in the central disk can reach a considerable fraction ofthe bulge radius.
|Southern Galaxy Catalogue.|
|Redshifts for 228 southern galaxies|
In this paper, new redshifts are presented for 228 galaxies locatedsouth of declination -30 deg. The observations were made with aphoton-counting Reticon detector on the Observatorio Nacional (ON)60-in. telescope. The detector is identical to the one used at MountHopkins for the CfA Redshift Survey, and the redshifts were derivedusing the same data-analysis system. A preliminary comparison withpublished 21-cm redshifts indicates that the velocities have azero-point offset of about -4 km/s, with a typical uncertainty of 40km/s. The observations reported here are the initial results of theON-CfA Redshift Survey currently being undertaken in the southernhemisphere.
|UBVRI photoelectric photometry of 191 southern galaxies|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1984A&AS...58..249L&db_key=AST
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