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|The Classification of Galaxies: Early History and Ongoing Developments|
"You ask what is the use of classification, arrangement,systematization. I answer you; order and simplification are the firststeps toward the mastery of a subject the actual enemy is the unknown."
|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.
|Companions of Bright Barred Shapley-Ames Galaxies|
Companion galaxy environment for a subset of 78 bright and nearby barredgalaxies from the Shapley-Ames Catalog is presented. Among the spiralbarred galaxies, there are Seyfert galaxies, galaxies with circumnuclearstructures, galaxies not associated with any large-scale galaxy cloudstructure, galaxies with peculiar disk morphology (crooked arms), andgalaxies with normal disk morphology; the list includes all Hubbletypes. The companion galaxy list includes the number of companiongalaxies within 20 diameters, their Hubble type, and projectedseparation distance. In addition, the companion environment was searchedfor four known active spiral galaxies, three of them are Seyfertgalaxies, namely, NGC 1068, NGC 1097, and NGC 5548, and one is astarburst galaxy, M82. Among the results obtained, it is noted that theonly spiral barred galaxy classified as Seyfert 1 in our list has nocompanions within a projected distance of 20 diameters; six out of 10Seyfert 2 bar galaxies have no companions within 10 diameters, six outof 10 Seyfert 2 galaxies have one or more companions at projectedseparation distances between 10 and 20 diameters; six out of 12 galaxieswith circumnuclear structures have two or more companions within 20diameters.
|The faint end of the galaxy luminosity function|
We present and discuss optical measurements of the faint end of thegalaxy luminosity function down to MR=-10 in five differentlocal environments of varying galaxy density and morphological content.The environments we studied, in order of decreasing galaxy density, arethe Virgo Cluster, the NGC 1407 Group, the Coma I Group, the Leo Groupand the NGC 1023 Group. Our results come from a deep wide-angle surveywith the National Astronomical Observatories of Japan Subaru 8-mTelescope on Mauna Kea and are sensitive down to very faintsurface-brightness levels. Galaxies were identified as group or clustermembers on the basis of their surface brightness and morphology. Thefaintest galaxies in our sample have R~ 22.5. There were thousands offainter galaxies but we cannot distinguish cluster members frombackground galaxies at these faint limits so do not attempt to determinea luminosity function fainter than MR=-1010. In all cases,there are far fewer dwarfs than the numbers of low-mass haloesanticipated by cold dark matter theory. The mean logarithmic slope ofthe luminosity function between MR=-1018 andMR=-1010 is α~=-1.2, far shallower than the cold darkmatter mass function slope of α~=-1.8. We would therefore need tobe missing about 90 per cent of the dwarfs at the faint end of oursample in all the environments we study to achieve consistency with CDMtheory. It is unlikely that such large numbers of dwarfs are missedbecause (i) the data are deep enough that we are sensitive to very lowsurface brightness galaxies, and (ii) the seeing is good enough that wecan have some confidence in our ability to distinguish high surfacebrightness dwarfs from background galaxies brighter than R= 22.5. Onecaveat is that we miss compact members taken to be background galaxies,but such objects (like M32) are thought to be rare.
|The UZC-SSRS2 Group Catalog|
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
|Redshifts for 2410 Galaxies in the Century Survey Region|
The Century Survey strip covers 102 deg2 within the limits8h5<=α<=16h5, 29.0d<=δ<=30.0d, equinoxB1950.0. The strip passes through the Corona Borealis supercluster andthe outer region of the Coma cluster. Within the Century Survey region,we have measured 2410 redshifts that constitute four overlappingcomplete redshift surveys: (1) 1728 galaxies with Kron-CousinsRph<=16.13 covering the entire strip, (2) 507 galaxieswith Rph<=16.4 in right ascension range8h32m<=α<=10h45m, equinox B1950.0, (3) 1251 galaxies withabsorption- and K-corrected RCCDc<=16.2 (where ``c''indicates ``corrected'') covering the right ascension range8h5<=α<=13h5, equinox B1950.0, and (4) 1255 galaxieswith absorption- and K-corrected VCCDc<=16.7 also coveringthe right ascension range 8h5<=α<=13h5, equinoxB1950.0. All these redshift samples are more than 98% complete to thespecified magnitude limit. We derived samples 1 and 2 from scans of thePOSS1 red (E) plates calibrated with CCD photometry. We derived samples3 and 4 from deep V and R CCD images covering the entire region. Weinclude coarse morphological types for all the galaxies in sample 1. Thedistribution of (V-R)CCD for each type correspondsappropriately with the classification. Work reported here is basedpartly on observations obtained at the Michigan-Dartmouth-MITObservatory.
|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.
|The Nature of Accreting Black Holes in Nearby Galaxy Nuclei|
We have found compact X-ray sources in the center of 21 (54%) of 39nearby face-on spiral and elliptical galaxies with available ROSAT HRIdata. ROSAT X-ray luminosities (0.2-2.4 keV) of these compact X-raysources are ~10^37-10^40 ergs s^-1 (with a mean of 3x10^39 ergs s^-1).The mean displacement between the location of the compact X-ray sourceand the optical photometric center of the galaxy is ~390 pc. The factthat compact nuclear sources were found in nearly all (five of six)galaxies with previous evidence for a black hole or an active galacticnucleus (AGN) indicates that at least some of the X-ray sources areaccreting supermassive black holes. ASCA spectra of six of the 21galaxies show the presence of a hard component with relatively steep(Gamma~2.5) spectral slope. A multicolor disk blackbody model fits thedata from the spiral galaxies well, suggesting that the X-ray object inthese galaxies may be similar to a black hole candidate in its soft(high) state. ASCA data from the elliptical galaxies indicate that hot(kT~0.7 keV) gas dominates the emission. The fact that (for both spiraland elliptical galaxies) the spectral slope is steeper than in normaltype 1 AGNs and that relatively low absorbing columns (N_H~10^21 cm^-2)were found to the power-law component indicates that these objects aresomehow geometrically and/or physically different from AGNs in normalactive galaxies. The X-ray sources in the spiral and elliptical galaxiesmay be black hole X-ray binaries, low-luminosity AGNs, or possibly youngX-ray luminous supernovae. Assuming the sources in the spiral galaxiesare accreting black holes in their soft state, we estimate black holemasses ~10^2-10^4 M_solar.
|Evolutionary Status of Dwarf ``Transition'' Galaxies|
We present deep B-band, R-band, and Hα imaging of three dwarfgalaxies: NGC 3377A, NGC 4286, and IC 3475. Based on previous broadbandimaging and H I studies, these mixed morphology galaxies have beenproposed to be, respectively, a gas-rich low surface brightness Imdwarf, a nucleated dwarf that has lost most of its gas and is intransition from Im to dS0, N, and the prototypical example of a gas-poor``huge low surface brightness'' early-type galaxy. From the combinationof our broadband and Hα imaging with the published information onthe neutral gas content of these three galaxies, we find that (1) NGC3377A is a dwarf spiral, similar to those found by Schombert andcoworkers and Matthews & Gallagher; (2) both NGC 3377A and NGC 4286have comparable amounts of ongoing star formation, as indicated by theirHα emission, while IC 3475 has no detected H II regions to a verylow limit; (3) the global star formation rates are at least a factor of20 below those of 30 Doradus for NGC 3377A and NGC 4286; (4) while theamount of star formation is comparable, the distribution of star-formingregions is very different between NGC 3377A and NGC 4286, with Hαemission scattered over most of the optical face of NGC 3377A and allcontained within the inner half of the optical disk of NGC 4286; (5)given their current star formation rates and gas contents, both NGC3377A and NGC 4286 can continue to form stars for more than a Hubbletime; (6) both NGC 3377A and NGC 4286 have integrated total B-R colorsthat are redder than the integrated total B-R color for IC 3475 and thusit is unlikely that either galaxy will ever evolve into an IC 3475counterpart; and (7) IC 3475 is too blue to be a dE. We thus concludethat we have not identified potential precursors to galaxies such as IC3475, and unless significant changes occur in the star formation rates,neither NGC 3377A nor NGC 4286 will evolve into a dwarf elliptical ordwarf spheroidal within a Hubble time. Furthermore, optical morphology,even when coupled with the knowledge of the neutral gas content of adwarf galaxy, is not sufficient to determine its evolutionary phase. Theevolutionary states of NGC 3377A and NGC 4286 are thus unclear and morecomplicated than might be inferred from either previous broadbandimaging or H I content alone.
|Bias Properties of Extragalactic Distance Indicators. VII. Correlation of Absolute Luminosity and Rotational Velocity for SC Galaxies over the Range of Luminosity Class from I to III-IV|
A distance-limited subset of the complete flux-limited sample of Scgalaxies in the Revised Shapley-Ames Catalog of Bright Galaxies isisolated by means of separate Spaenhauer diagrams for six individual vanden Bergh luminosity class intervals from Sc I+I.2,.3 to Sc III-IV. Thedistribution functions of kinematic absolute B^0,i_T(220,50) magnitudesand 21 cm line widths, W_20, corrected to edge-on orientation, have beendetermined for the same six bins of luminosity class. The individualluminosity functions for each luminosity class are bounded on both thebright and faint ends, showing that the present sample includes no dwarfSc spirals fainter than M(B_T)(220,50)=-18 belonging to luminosityclasses I to III-IV, as defined by the regularity of the spiral pattern.Star-forming galaxies with spiral structures as regular as the onesfound in these luminosity classes have absolute magnitudes brighter thanM_B(H=50)=-18 and 21 cm line widths larger thanW_20/sini=2v_rot(max)=165 km s^-1. Furthermore, the 21 cm line-widthdistributions move toward smaller rotational velocities as theluminosity classes change from I to III, showing that rotation is aprincipal parameter determining the regularity of the spiral pattern.Whether it is the only parameter awaits a similar investigation forspirals of all luminosity classes along the complete Hubble sequence. Inparticular, it has not yet been proved that all Im and Sm galaxies,where, by definition, the spiral arms are either lacking or aresemichaotic, have absolute magnitudes that are fainter than M_B=-18 andwhose 21 cm LWs are smaller than ~165 km s^-1, presumably because ofsmaller mass than the high-luminosity, regular spirals. The Teerikorpi``cluster population incompleteness bias'' is demonstrated again. Here,however, as in Papers II-IV of this series, we use field galaxies toshow that the slope and zero point of the Tully-Fisher (T-F) relationare systematically incorrect for flux-limited samples, the errorincreasing with redshift. The data also support the possibility that thezero point of the T-F relation for Sc galaxies, even in thedistance-limited sample, is a function of luminosity class, varying by0.42 mag between Sc I+I.2,.3 and Sc III galaxies if the slope of the T-Frelation for each class is taken to be that of the fundamentalcalibrating galaxies with Cepheid distances. If true, this is presumablydue to differences in the mass distribution and, therefore, in theresulting rotational velocity field as a function of luminosity classeven within a fixed Hubble type.
|Galaxies with a low gas content in the Coma I cloud of galaxies.|
We have observed the CO emission of six galaxies belonging to a smalldense group: NGC 4245, NGC 4251, NGC 4274, the elliptical NGC 4278, NGC4286 and NGC 4310. CO(1-0) and (2-1) lines have been detected and mappedin three galaxies. We present a comparison of the amount of molecularand atomic hydrogen in these galaxies with the expected amounts drawnfrom samples found in the literature. It is clear that most of the groupgalaxies have lower than average total gas masses, due to a largedeficiency of atomic hydrogen. Despite the large dispersion present inthe CO emission of galaxies, their content of molecular gas lies in theexpected range given their rather early types. This study shows thatgalaxies strongly deficient in HI do not exclusively belong to clusters,but can be found also in dense galaxy groups. The CO emission of thegalaxies, hence presumably their H_2_ content, is however not affectedby the environment; this conclusion holds for the group galaxies as wellas for the spirals previously studied in the Virgo and Coma clusters.
|The Im/dE,N mixed morphology dwarf ESO 359-G29 as a probe of a massive halo in NGC 1532|
Red and yellow images were made to determine the properties of ESO359-G29. The optical morphology of ESO 359-G29 in the yellow and red isthat of a nucleated dwarf E or dS0 galaxy, similar to those found inVirgo, Fornax, and Coma Clusters, in the rich and sparse groups, and ascompanions to single massive parents. The optical morphology in the blueshows a small rate of recent star formation. The H I content of ESO359-G29 is normal in all comparisons with the unbiased distance-limitedsample of Virgo Cluster dwarfs. The H I emission from NGC 1532 extends60 kpc south and 40 kpc north of the center of the galaxy and extendsnearly 4 times the radius of the galaxy disk. The total H I mass is 2.7x 10 exp 10 solar masses. The rotation curve, determined from the H Iemission, extends over 10 arcmin radius from the galaxy. Thejuxtaposition of NGC 1532 and ESO 359-G29 shows that ESO 359-G29 liesnear the minor axis of NGC 1532, about 82 kpc away.
|A small drift scan survey for galaxies in the northern sky|
CCD photometry has been obtained for 1054 galaxies to a limitingmagnitude rW = 18.0 in a narrow strip of the sky 12 arcmin wide by 60deg long. The data are being used to calibrate photographic photometryas part of a parallel redshift survey, but can also be used to study theprojected distribution of galaxies on large angular scales free fromsystematic effects that are present in photographic surveys.Fluctuations in the number density of order 20 percent are seen onangular scales of 5 deg and apparently correlate with the distributionof Abell Clusters that lie within 2 deg of the strip.
|Decreasing diameter of a molecular ring|
The nuclear region of the barred spiral galaxy NGC 4314 has been mappedat high angular resolution in CO (J = 1-0) with the Nobeyama millimeterarray. This galaxy presents a nuclear ring of hot spots at a radius ofabout 7 arcsec from the center. The CO emission is concentrated in theinner 10 arcsec and associated with the dust patches located inside thenuclear hot spots. The molecular ring is located inside the ring ofcontinuum emission, suggesting that nuclear molecular rings evolveslowly, reducing their radius due to friction exerted by the backgroundstars on the giant molecular clouds.
|Discovery of a cyclotron resonance feature at 30 keV from the transient X-ray pulsar Cepheus X-4|
From Ginga observations of the transient X-ray pulsar Cep X-4, aspectral line feature attributable to electron cyclotron resonance wasdiscovered at about 30 keV in the 1.2-37 keV X-ray spectrum. Thedetection, a fifth firm example of cyclotron resonance from X-raypulsars, implies a surface magnetic field of about 2.6 x 10 to the 12th(1 + z) G for this pulsar, where z is the gravitational redshift.Throughout the 66.25 s pulses, the cyclotron feature appears inabsorption, with at most + or - 5 percent variation in the resonancecenter energy around the mean value of 30.5 + or - 0.4 keV. Theresonance profile depends significantly on the pulse phase in such a waythat it is deepest on the decay slope of the leading peak of thedouble-peaked pulse profile.
|NGC 4286 and NGC 3377A - Galaxies with mixed morphologies between the dwarf Im and dE/dSO types|
Optical and radio data for the nucleated dwarf galaxy NGC 4286 show amixed morphology between a star-forming Im type and a gas-poor dSO, Nearly-type dwarf. The Im dwarf NGC 3377A shows no gas depletion, but itsmorphology and size are similar to the 'huge, very low surfacebrightness' gas-poor galaxies recently identified in the Virgo cluster.The morphology of NGC 4286 is interpreted as an original Im system thathas transformed itself (speciation along the dwarf sequence) into agas-poor dSO, N by losing most (but not all) of its original gas throughan internal supergalactic wind that was generated earlier by asuperluminous star cluster. The remnant of this cluster has now sunk tothe center by dynamical friction to form the observed unresolved brightnucleus. Such star clusters and superwinds are known to exist in manypresent-day starburst Sm and amorphous galaxies such as NGC 1569 and NGC1705.
|Atomic Hydrogen in the Elliptical Galaxy NGC 4278|
|Groups of galaxies in the Center for Astrophysics redshift survey|
By applying the Huchra and Geller (1982) objective group identificationalgorithm to the Center for Astrophysics' redshift survey, a catalog of128 groups with three or more members is extracted, and 92 of these areused as a statistical sample. A comparison of the distribution of groupcenters with the distribution of all galaxies in the survey indicatesqualitatively that groups trace the large-scale structure of the region.The physical properties of groups may be related to the details oflarge-scale structure, and it is concluded that differences among groupcatalogs may be due to the properties of large-scale structures andtheir location relative to the survey limits.
|Velocity measurements in the Coma filament of galaxies|
58 new velocity measurements of galaxies located in the Coma filamentcarried out with the 2.5-m Issac Newton telescope at La Palma arepresented. These optical observations complete a sample of 21-cm lineobservations in the same region up to the 15.0th magnitude.
|Radio continuum survey of the Coma/A1367 supercluster. II - 1.5 GHz observations of 396 CGCG galaxies|
1.5 GHz VLA radio continuum observations of 396 relatively isolated CGCGgalaxies in the Coma/A1367 supercluster yielded the detection of 95objects. These observations, added to the ones presented in previouspapers, form a complete sample of optically selected objects with m(p)equal to or less than 15.3. Two wide-angle-tailed sources have beenfound in smaller groups within the supercluster.
|KISO survey for ultraviolet-excess galaxies. III|
Presented here are the third list and identification charts of theultraviolet-excess galaxies which have been detected on the multicolorplates taken with the Kiso Schmidt telescope for 10 survey fields. Inthe sky area of some 300 square degrees 712 objects are catalogued downto the photographic magnitude of about 17.5.
|Observations of galaxies with an ultraviolet continuum at a frequency of 102 MHz. II|
A radio survey was carried out at 102 MHz to study the UV continuum of67 galaxies. The objects included 58 Seyfert galaxies and two BL Lacobjects. Data on the total flux, the flux of the scintillatingcomponent, the angular diameter of the scintillating component, thesolar elongation and the type of the galaxy are provided for the 11sources of 102 MHz emission detected. Radio spectra are also tabulatedin terms of the scintillating, central, northern, southern and easternradio components for the galaxies NGC 1068, 4151 and 5548. Variousdetails observed in the galaxies which featured 102 MHz emissions arebriefly discussed.
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