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|The Araucaria Project .|
Results from a long-term observational project called the AraucariaProject are presented. Based on Wide Field optical monitoring of 8nearby galaxies, covering a large range of metallicities, more than 500Cepheids and a few hundred Blue Supergiant candidates were identified.From the analysis of Cepheid P-L relations of outstanding qualityderived from our data we conclude that the slope of these relations inthe I band and Wesenheit index are not dependent on metallicity.Comparing the I-band magnitudes of Cepheids of a period of ten days, ascomputed from our P-L relations, to the I-band magnitudes of the tip ofthe RGB, which is widely believed to be independent of populationeffects, we cannot see any obvious dependence of the zero point of theI-band P-L relation on metallicity. A preliminary analysis of IRfollow-up observations of sub-samples of the identified Cepheids invarious galaxies of the project show that the distances obtained fromthese data are systematically shorter by about of 0.1 mag than thosederived from the optical photometry. It is likely that this effect canbe attributed to the internal reddening in the program galaxies. Theselected Blue Supergiant candidates were observed spectroscopically with8m-class telescopes to determine their element abundances, and theirluminosities from the Flux-weighted Gravity-Luminosity Relationship.Results on this aspect of the Araucaria Project are presented in thereview of Kudritzki presented during this conference.
|The Disk and Extraplanar Environment of NGC 247|
The stellar content of the spiral galaxy NGC 247 is investigated usingdeep visible and near-infrared images. The main-sequence turnoff (MSTO)in the inner 12 kpc of the disk corresponds to an age of ~6 Myr. A meanstar formation rate (SFR) of 0.1 Msolar yr-1during the past 16 Myr is computed from star counts. The color of thered supergiant plume does not change with radius, suggesting that themean metallicity of young stars does not vary by more than ~0.1 dex. Thenumber of bright main-sequence stars per local stellar mass densityclimbs toward larger radii out to a distance of 12 kpc; the scalelengths that characterize the radial distributions of young and oldstars in the disk thus differ. The density of bright main-sequence starswith respect to projected H I mass gradually drops with increasingradius. The population of very young stars disappears in the outer disk;the MSTO at galactocentric radii between 12 and 15 kpc corresponds to~16 Myr, while between 15 and 18 kpc the age is >=40 Myr. Red giantbranch (RGB) stars are resolved at a projected minor-axis galactocentricdistance of ~12 kpc. There is a broad spread in metallicity among theRGB stars, with a mean [M/H]~-1.2. The RGB tip occurs ati'=24.5+/-0.1, indicating that the distance modulus is27.9+/-0.1. Luminous AGB stars with an age ~3 Gyr are also seen in thisfield.Based on observations obtained at the Gemini Observatory, which isoperated by the Association of Universities for Research in Astronomy,Inc., under a cooperative agreement with the NSF on behalf of the Geminipartnership: the National Science Foundation (United States), theParticle Physics and Astronomy Research Council (United Kingdom), theNational Research Council of Canada (Canada), CONICYT (Chile), theAustralian Research Council (Australia), CNPq (Brazil), and CONICET(Argentina).This publication makes use of data products from the Two Micron All SkySurvey, which is a joint project of the University of Massachusetts andthe Infrared Processing and Analysis Center/California Institute ofTechnology, funded by the National Aeronautics and Space Administrationand the National Science Foundation.
|Masses of the local group and of the M81 group estimated from distortions in the local velocity field|
Based on high precision measurements of the distances to nearby galaxieswith the Hubble telescope, we have determined the radii of the zerovelocity spheres for the local group, R0 =0.96±0.03Mpc, and for the group of galaxies around M 81/M 82,0.89±0.05Mpc. These yield estimates of MT =(1.29±0.14)· 1012 Mȯ and(1.03±0.17)· 1012 Mȯ,respectively, for the total masses of these groups. The R0method allows us to determine the mass ratios for the two brightestmembers in both groups, as well. By varying the position of the centerof mass between the two principal members of a group to obtain minimalscatter in the galaxies on a Hubble diagram, we find mass ratios of0.8:1.0 for our galaxy and Andromeda and 0.54:1.00 for the M82 and M81galaxies, in good agreement with the observed ratios of the luminositiesof these galaxies.
|Objective Classification of Spiral Galaxies Having Extended Rotation Curves Beyond the Optical Radius|
We carry out an objective classification of four samples of spiralgalaxies having extended rotation curves beyond the optical radius. Amultivariate statistical analysis (viz., principal component analysis[PCA]) shows that about 96% of the total variation is due to twocomponents, one being the combination of absolute blue magnitude andmaximum rotational velocity beyond the optical region and the otherbeing the central density of the halo. On the basis of PCA a fundamentalplane has been constructed that reduces the scatter in the Tully-Fisherrelation up to a maximum of 16%. A multiple stepwise regression analysisof the variation of the overall shape of the rotation curves shows thatit is mainly determined by the central surface brightness, while theshape purely in the outer part of the galaxy (beyond the optical radius)is mainly determined by the size of the galactic disk.
|Advanced Camera for Surveys Imaging of 25 Galaxies in Nearby Groups and in the Field|
We present Hubble Space Telescope Advanced Camera for Surveys images andcolor-magnitude diagrams for 25 nearby galaxies with radial velocitiesVLG<500 km s-1. Distances are determined basedon the luminosities of stars at the tip of the red giant branch thatrange from 2 to 12 Mpc. Two of the galaxies, NGC 4163 and IC 4662, arefound to be the nearest known representatives of blue compact dwarfobjects. Using high-quality data on distances and radial velocities of110 nearby field galaxies, we derive their mean Hubble ratio to be 68 kms-1 Mpc-1 with a standard deviation of 15 kms-1 Mpc-1. Peculiar velocities of most of thegalaxies, Vpec=VLG-68D, follow a Gaussiandistribution with σv=63 km s-1 but with atail toward high negative values. Our data display the known correlationbetween peculiar velocity and galaxy elevation above the LocalSupercluster plane. The small observed fraction of galaxies with highpeculiar velocities, Vpec<-500 km s-1, may beunderstood as objects associated with nearby groups (Coma I, Eridanus)outside the local volume.
|The Second Kiso Survey for ultraviolet-excess galaxies. V.|
The catalogue list and the identification chart of ultraviolet(UV)-excess galaxies, which have been detected on two or three-colorKiso Schmidt plates, are presented for 10 Schmidt fields. Catalogued are127 objects, down to the photographic magnitude ~17.5 in the sky area ofsome 300 square degrees. The number of KUGs detected in this paper ismuch smaller than that of the high galactic area, and the total numberof KUGs newly detected in the second survey reaches up to 1,954.
|Measuring improved distances to nearby galaxies: Thae Araucaria project.|
|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.
|Halos of Spiral Galaxies. III. Metallicity Distributions|
We report results of a campaign to image the stellar populations in thehalos of highly inclined spiral galaxies, with the fields roughly 10 kpc(projected) from the nuclei. We use the F814W (I) and F606W (V) filtersin the Wide Field Planetary Camera 2 on board the Hubble SpaceTelescope. We unambiguously resolve the stellar halos 1 to 2 mag fainterthan the tip of the red giant branch. Extended halo populations aredetected in all galaxies. The color-magnitude diagrams appear to becompletely dominated by giant branch stars, with no evidence for thepresence of young stellar populations in any of the fields. Themetallicity distribution function for the galaxy sample is derived frominterpolation within an extensive grid of red giant branch loci. Theseloci are derived from theoretical sequences that are calibrated usingthe Galactic globular clusters and from empirical sequences formetal-rich stellar populations. We find that the metallicitydistribution functions are dominated by metal-rich populations, with atail extending toward the metal-poor end. To first order, the overallshapes of the metallicity distribution functions are similar to what ispredicted by a simple, single-component model of chemical evolution withthe effective yields increasing with galaxy luminosity. However,metallicity distributions significantly narrower than the simple modelare observed for a few of the most luminous galaxies in the sample. Thediscrepancies are similar to those previously observed for NGC 5128, thehalo of M31, and the Galactic bulge. Our observations can be used tohelp distinguish between models for the formation of spiral galaxies. Itappears that more luminous spiral galaxies also have more metal-richstellar halos. The increasingly significant departures from theclosed-box model for the more luminous galaxies indicate that aparameter in addition to a single yield is required to describe chemicalevolution. This parameter, which could be related to gas infall oroutflow either in situ or in progenitor dwarf galaxies that later mergeto form the stellar halo, tends to make the metallicity distributionsnarrower at high metallicity.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
|Halos of Spiral Galaxies. II. Halo Metallicity-Luminosity Relation|
Using the Hubble Space Telescope, we have resolved individual red giantbranch stars in the halos of eight nearby spiral galaxies. The fieldslie at projected distances between 2 and 13 kpc along the galaxies'minor axes. The data set allows a first look at the systematic trends inhalo stellar populations. We have found that bright galaxies tend tohave broad red giant branch star color distributions with redder meancolors, suggesting that the heavy-element abundance spread increaseswith the parent galaxy luminosity. The mean metallicity of the stellarhalo, estimated using the mean colors of red giant branch stars,correlates with the parent galaxy luminosity. The metallicity of theMilky Way halo falls nearly 1 dex below this luminosity-metallicityrelation, suggesting that the halo of the Galaxy is more the exceptionthan the rule for spiral galaxies; i.e., massive spirals with metal-poorhalos are unusual. The luminosity-halo stellar abundance relation isconsistent with the scaling relation expected for stellar systemsembedded in dominant halos, suggesting that the bulk of the halo stellarpopulation may have formed in situ.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
|Halos of Spiral Galaxies. I. The Tip of the Red Giant Branch as a Distance Indicator|
We have imaged the halo populations of a sample of nearby spiralgalaxies using the Wide Field Planetary Camera 2 on board the HubbleSpace Telescope with the aim of studying the stellar populationproperties and relating them to those of the host galaxies. In fourgalaxies, the red giant branch is sufficiently well populated to measurethe magnitude of the tip of the red giant branch (TRGB), a well-knowndistance indicator. Using both the Sobel edge-detection technique andmaximum likelihood analysis to measure the I-band magnitude of the TRGB,we determine distances to four nearby galaxies: NGC 253, NGC 4244, NGC4945, and NGC 4258. For the first three galaxies, the TRGB distance ishere determined more directly, and is likely to be more accurate, thanprevious distance estimates. In the case of NGC 4258, our TRGB distanceis in good agreement with the geometrical maser distance, supporting theLarge Magellanic Cloud distance modulus (m-M)0=18.50 that isgenerally adopted in recent estimates of the Hubble constant.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
|The Baryonic Tully-Fisher Relation of Galaxies with Extended Rotation Curves and the Stellar Mass of Rotating Galaxies|
I investigate the baryonic Tully-Fisher relation for a sample ofgalaxies with extended 21 cm rotation curves spanning the range 20 kms-1<~Vf<=300 km s-1. A variety ofscalings of the stellar mass-to-light ratio Υ* areconsidered. For each prescription for Υ*, I give fitsof the form Md=AVxf.Presumably, the prescription that comes closest to the correct valuewill minimize the scatter in the relation. The fit with minimum scatterhas A=50 Msolar km-4 s4 andx=4. This relation holds over five decades in mass. Galaxy color,stellar fraction, and Υ* are correlated with eachother and with Md, in the sense that more massivegalaxies tend to be more evolved. There is a systematic dependence ofthe degree of maximality of disks on surface brightness. High surfacebrightness galaxies typically have Υ*~3/4 of themaximum disk value, while low surface brightness galaxies typicallyattain ~1/4 of this amount.
|The Disk and Extraplanar Regions of NGC 55|
The stellar content of the nearby SB(s)m galaxy NGC 55 is investigatedusing images obtained with the Gemini South and Canada-France-Hawaiitelescopes. The (K, H-K) and (K, J-K) color-magnitude diagrams (CMDs) ofstars near the plane of the disk reveal signatures of large-scale starformation during recent and intermediate epochs in the form of redsupergiants (RSGs) with MK=-11.5, and an asymptotic giantbranch (AGB) that peaks near MK=-10. Comparisons with stellarevolution models suggest that the brightest RSGs have an age near 8 Myr.A well-defined plume, which stellar evolution models suggest containsstars with masses near the RSG-AGB transition, is detected in CMDsconstructed both from infrared and visible wavelength observations. Itis concluded that star formation in the thin disk of NGC 55 has occurredat a significant rate for at least the past 0.1-0.2 Gyr, and this isconsistent with other indicators. The near-infrared spectral energydistribution of the integrated light near the center of the galaxy isconsistent with that in other Magellanic irregular galaxies, indicatingthat the star-forming history of NGC 55, when averaged over timescalesof 0.1-1 Gyr, has likely not been peculiar when compared with otherlate-type systems. Evidence is also presented that the disk contains alarge population of old [log(tyr)~10] stars, and it is arguedthat a stable disk has been in place in NGC 55 for a significantfraction of the age of the universe. At projected distances in excess of2 kpc off of the disk plane, the brightest AGB stars have ages10+3-2 Gyr. Thus, despite indications that dustand gas are present in the envelope surrounding the NGC 55 disk, the AGBcontent suggests that recently formed stars do not occur in largenumbers in the extraplanar region. The (r'-i')colors of the RGB in the extraplanar region are consistent with [Fe/H]between -2.2 and -0.7, with the majority of stars having [Fe/H]>-1.2,and the mean metallicity inferred from the RGB color does not changewith distance above the disk plane. Thus, the stellar component in theextraplanar envelope is well mixed, at least in terms of metallicity.The mean metallicity of RGB stars is in excellent agreement with thatmeasured in the extraplanar H II regions EHR 1 and 2, suggesting thatthe age-metallicity relation in this part of NGC 55 has been flat for atleast a few Gyr. Finally, the RGB tip occurs near i'=23.1 inthe extraplanar region, and a distance modulus of 26.5 is computed fromthis feature.Based on observations obtained at the Gemini Observatory, which isoperated by the Association of Universities for Research in Astronomy,Inc., under a cooperative agreement with the NSF on behalf of the Geminipartnership: the National Science Foundation (United States), theParticle Physics and Astronomy Research Council (United Kingdom), theNational Research Council of Canada (Canada), CONICYT (Chile), theAustralian Research Council (Australia), CNPq (Brazil), and CONICET(Argentina).This publication makes use of data products from the Two Micron All SkySurvey, which is a joint project of the University of Massachusetts andthe Infrared Processing and Analysis Center/California Institute ofTechnology, funded by the National Aeronautics and Space Administrationand the National Science Foundation.
|Light and Motion in the Local Volume|
Using high-quality data on 149 galaxies within 10 Mpc, I find nocorrelation between luminosity and peculiar velocity at all. There is nounequivocal sign on scales of 1-2 Mpc of the expected gravitationaleffect of the brightest galaxies, in particular infall toward groups, orof infall toward the supergalactic plane on any scale. Either darkmatter is not distributed in the same way as luminous matter in thisregion, or peculiar velocities are not due to fluctuations in mass. Thesensitivity of peculiar velocity studies to the background model ishighlighted.
|Detection of Neutral Hydrogen in Early-Type Dwarf Galaxies of the Sculptor Group|
We present results of deep 21 cm neutral hydrogen (H I) lineobservations of five early- and mixed-type dwarf galaxies in the nearbySculptor group using the Australia Telescope National Facility 64 mParkes Radio Telescope. Four of these objects, ESO 294-G010, 410-G005,540-G030, and 540-G032, were detected in H I with neutral hydrogenmasses in the range (2-9)×105 Msolar(MHI/LB=0.08, 0.13, 0.16, and 0.18Msolar L-1solar, respectively). These HI masses are consistent with the gas mass expected from stellar outflowsover a large period of time. Higher spatial resolution H I data from theAustralia Telescope Compact Array interferometer were further analyzedto measure more accurate positions and the distribution of the H I gas.In the cases of the dwarfs ESO 294-G010 and ESO 540-G030, we findsignificant offsets of 290 and 460 pc, respectively, between theposition of the H I peak flux and the center of the stellar component.These offsets are likely to have internal causes such as the winds fromstar-forming regions. The fifth object, the spatially isolated dwarfelliptical galaxy Scl-dE1, remains undetected at our 3 σ limit of22.5 mJy km s-1 and thus must contain less than105 Msolar of neutral hydrogen. This leavesScl-dE1 as the only Sculptor group galaxy known in which no interstellarmedium has been found to date. The object joins a list of similarsystems, including the Local Group dwarfs Tucana and Cetus, that do notfit into the global picture of the morphology-density relation in whichgas-rich dwarf irregular galaxies are in relative isolation andgas-deficient dwarf elliptical galaxies are satellites of more luminousgalaxies.
|The Local Group and Other Neighboring Galaxy Groups|
Over the last few years, rapid progress has been made in distancemeasurements for nearby galaxies based on the magnitude of stars on thetip of the red giant branch. Current CCD surveys with the Hubble SpaceTelescope (HST) and large ground-based telescopes bring ~10% accuratedistances for roughly a hundred galaxies within 5 Mpc. The new data ondistances to galaxies situated in (and around) the nearest groups-theLocal Group, M81 Group, Cen A/M83 Group, IC 342/Maffei Group, Sculptorfilament, and Canes Venatici cloud-allowed us to determine their totalmass from the radius of the zero-velocity surface, R0, whichseparates a group as bound against the homogeneous cosmic expansion. Thevalues of R0 for the virialized groups turn out to be closeeach other, in the range of 0.9-1.3 Mpc. As a result, the total massesof the groups are close to each other, as well, yielding total mass toblue luminosity ratios of 10-40 MsolarL-1solar. The new total mass estimates are 3-5times lower than old virial mass estimates of these groups. Becauseabout half of galaxies in the Local volume belong to such loose groups,the revision of the amount of dark matter (DM) leads to a low localdensity of matter, Ωm~=0.04, which is comparable withthe global baryonic fraction Ωb but much lower than theglobal density of matter, Ωm=0.27. To remove thediscrepancy between the global and local quantities ofΩm, we assume the existence of two different DMcomponents: (1) compact dark halos around individual galaxies and (2) anonbaryonic dark matter ``ocean'' with ΩDM1~=0.07 andΩDM2~=0.20, respectively.Based in part on observations made with the NASA/ESA Hubble SpaceTelescope, obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555.
|Discovery of a Solitary Dwarf Galaxy in the APPLES Survey|
During the APPLES parallel campaign, the Hubble Space Telescope (HST)Advanced Camera for Surveys has resolved a distant stellar system, whichappears to be an isolated dwarf galaxy. It is characterized by acircularly symmetric distribution of stars with an integrated magnitudemF775W=20.13+/-0.02, a central surface brightnessμF775W~=21.33+/-0.18 mag arcsec-2, and ahalf-light radius of ~=1.8". The ACS and VLT spectra show no evidence ofionized gas and appear to be dominated by a 3 Gyr old stellarpopulation. The OB spectral type derived for two resolved stars in thegrism data and the systemic radial velocity (Vhel~=670 kms-1) measured from the VLT data give a fiducial distance of~=9+/-2 Mpc. These findings, with the support of the spatial morphology,would classify the system among the dwarf spheroidal (dSph) galaxies.Following IAU rules, we have named this newly discovered galaxy APPLES1. An intriguing peculiarity of APPLES 1 is that the properties (age andmetallicity) of the stellar content so far detected are similar to thoseof dSph galaxies in the Local Group, where star formation is thought tobe driven by galaxy interactions and mergers. Yet, APPLES 1 seems not tobe associated with a major group or cluster of galaxies. Therefore,APPLES 1 could be the first example of a field dSph galaxy withself-sustained and regulated star formation, and therefore would make aninteresting test case for studies of the formation and evolution ofunperturbed dSph galaxies.
|New light on the formation and evolution of M 31 and its globular cluster system|
We present spectroscopic ages, metallicities, and [ α/Fe] ratiosfor 70 globular clusters in M 31 that were derived from Lick line-indexmeasurements. A new interpolation technique of age-metallicity andα/Fe-diagnostic grids is used to account for changes in indexstrength as a response to abundance-ratio variations, in particular forall of the Balmer-line Lick indices. In addition to a population of old(>10 Gyr) globular clusters with a wide range of metallicities, fromabout -2.0 dex to solar values, we find evidence for a population ofintermediate-age globular clusters with ages between ~5 and 8 Gyr and amean metallicity [Z/H] ≈ -0.6. We also confirm the presence of youngM 31 globular clusters that were recently identified by Beasley et al.(2004, AJ, 128, 1623), which have ages 1 Gyr and relatively highmetallicities around -0.4 dex. The M 31 globular cluster system has aclearly super-solar mean [ α/Fe] = 0.14 ± 0.04 dex.Intermediate-age and young objects show roughly solar abundance ratios.We find evidence for an age-[ α/Fe] relation in the sense thatyounger clusters have smaller mean [ α/Fe] ratios. From acomparison of indices, mostly sensitive to carbon and/or nitrogenabundance, with SSP model predictions for nitrogen-enhanced stellarpopulations, we find a dichotomy in nitrogen enhancement between youngand old M 31 globular clusters. The indices of objects older than 5 Gyrare consistent with a factor of three or higher in nitrogen enhancementcompared to their younger counterparts. Using kinematical data fromMorrison et al. (2004, ApJ, 603, 87) we find that the globular clustersub-population with halo kinematics is old (9 Gyr), has a bimodalmetallicity distribution, and super-solar [ α/Fe] . Disk globularclusters have a wider range of ages, are on average more metal-rich, andhave a slightly smaller mean [ α/Fe] ratio. A cross-correlation ofstructural parameters for M 31 globular clusters with spectroscopicallyderived ages, metallicities, and [ α/Fe] ratios shows acorrelation between half-light/tidal radius and metallicity, which ismost likely due to the correlation of half-light/tidal radius andgalactocentric distance. We compare our results for M 31 globularclusters with those obtained with the same technique for globularclusters in the Milky Way, Large Magellanic Cloud, M 81, and otherspiral galaxies in the Sculptor group. Finally, we compare the globularcluster systems of the two Local Group spirals, M 31 and Milky Way, withtheir integrated bulge light.
|A catalogue of ultraluminous X-ray sources in external galaxies|
We present a catalogue of ultraluminous X-ray sources (ULXs) in externalgalaxies. The aim of this catalogue is to provide easy access to theproperties of ULXs, their possible counterparts at other wavelengths(optical, IR, and radio), and their host galaxies. The cataloguecontains 229 ULXs reported in the literature until April 2004. Most ULXsare stellar-mass-black hole X-ray binaries, but it is not excluded thatsome ULXs could be intermediate-mass black holes. A small fraction ofthe candidate ULXs may be background Active Galactic Nuclei (AGN) andSupernova Remnants (SNRs). ULXs with luminosity above 1040ergs s-1 are found in both starburst galaxies and in thehalos of early-type galaxies.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/429/1125
|Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies|
Published mass models fitted to galaxy rotation curves are used to studythe systematic properties of dark matter (DM) halos in late-type anddwarf spheroidal (dSph) galaxies. Halo parameters are derived by fittingnon-singular isothermals to (V^2 - Vvis^2)1/2,where V(r) is the observed rotation curve and Vvis is therotation curve of the visible matter. The latter is calculated from thesurface brightness assuming that the mass-to-light ratio M/L is constantwith radius. ``Maximum disk'' values of M/L are adjusted to fit as muchof the inner rotation curve as possible without making the halo have ahollow core. Rotation curve decomposition becomes impossible fainterthan absolute magnitude M_B ≃ -14, where V becomes comparable tothe velocity dispersion of the gas. To increase the luminosity rangefurther, we include dSph galaxies, which are physically related tospiral and irregular galaxies. Combining the data, we find that DM halossatisfy well defined scaling laws analogous to the ``fundamental plane''relations for elliptical galaxies. Halos in less luminous galaxies havesmaller core radii r_c, higher central densities ρ_0, and smallercentral velocity dispersions σ. Scaling laws provide new anddetailed constraints on the nature of DM and on galaxy formation andevolution. Some simple implications include:1 -- A single, continuous physical sequence of increasing mass extendsfrom dSph galaxies with M_B ≃ -7.6 to Sc I galaxies with M_B≃ -22.4.2 -- The high DM densities in dSph galaxies are normal for such tinygalaxies. Since virialised density depends on collapse redshiftzcoll, ρ_0 ∝ (1 + zcoll)^3, the smallestdwarfs formed at least Δ zcoll ≃ 7 earlier thanthe biggest spirals.3 -- The high DM densities of dSphs implies that they are real galaxiesformed from primordial density fluctuations. They are not tidalfragments. Tidal dwarfs cannot retain even the low DM densities of theirgiant-galaxy progenitors. In contrast, dSphs have higher DM densitiesthan do giant-galaxy progenitors.4 -- The fact that, as luminosity decreases, dwarf galaxies become muchmore numerous and also more nearly dominated by DM raises thepossibility that there exists a large population of objects that arecompletely dark. Such objects are a canonical prediction of cold DMtheory. If they exist, ``empty halos'' are likely to be small and dense-- that is, darker versions of Draco and UMi.5 -- The slopes of the DM parameter correlations provide a measure ongalactic mass scales of the slope n of the power spectrum|δk|2 ∝ k^n of primordial densityfluctuations. Our preliminary results, not yet corrected for baryoniccompression of DM, give n ≃ -1.9 ± 0.2. This is consistentwith cold DM theory.
|Dark Matter in Galaxies: Observational overview|
I review the observational side of the present state of the debate aboutthe dark matter in galaxies, with emphasis on the core/cusp problem inlow surface brightness galaxies, and the question of maximum /sub-maximum disks in spiral galaxies. Some remarks are made about thedwarf spheroidals around the Milky Way, and about elliptical galaxies.
|UBVI Surface Photometry of the Spiral Galaxy NGC 300 in the Sculptor Group|
We present UBVI surface photometry over a 20.5' × 20.5' area ofthe late-type spiral galaxy NGC 300. We have derived isophotal maps,surface brightness profiles, ellipticity profiles, position angleprofiles, and color profiles. By merging our I-band measurements withthose of Böker et al. based on Hubble Space Telescope observations,we have obtained combined I-band surface brightness profiles for theregion 0.02'' < r < 500'' and have decomposed the profiles intothree components: a nucleus, a bulge, and an exponential disk.
|On the Origin of Nuclear Star Clusters in Late-Type Spiral Galaxies|
A large fraction of bulgeless disk galaxies contain young compactstellar systems at their centers, in spite of the local gravitationalstability of these disks. We evaluate two contrasting hypotheses for theorigin of the nuclear star clusters in late-type disk galaxies. Theclusters could not have migrated from distant eccentric locations in thedisk. Instead they must have formed in situ, requiring radial transportof gas toward the center of the disk. This transport could be aconsequence of the development of the magnetorotational instability inthe differentially rotating warm neutral medium. We evaluate the rate ofgas transport into the disk center and find that it is sufficient tosupport continuous star formation in that location. Enhanced stellarsurface brightness in the inner few hundred parsecs and the formation ofa compact stellar system in the central few parsecs are unavoidable indark matter halos with divergent density profiles. We illustrate ourconclusions on a model of the nearest late-type disk galaxy M33.
|New Reference Galaxy Standards for H I Emission Observations|
We have taken advantage of the improved baselines and higher sensitivityavailable with the upgraded Arecibo 305 m telescope to create a new H Ispectral line catalog of disk galaxies that can be used as a referencecatalog for anyone interested in 21 cm spectral line work. In all 108galaxies were observed, covering 24 hr of the sky at declinationsbetween 0° and 36° and velocities between 0 and 25,000 kms-1. The majority of the galaxies were observed at least twotimes on different nights to avoid problems with radio frequencyinterference, baseline fluctuations, etc. Comparing our measured valueswith all those available in the literature shows that although largeindividual variations may exist, the average difference between themeasurements is zero. In all we have considerable confidence in ourmeasurements, and the resulting catalog should be extremely useful as awell-defined reference catalog for anyone interested in 21 cm spectralline work.
|The Globular Cluster Systems of the Sculptor Group|
We use CTIO 4 m Mosaic II images taken with the Washington CM and HarrisR filters to identify candidate globular clusters in the six majorgalaxies of the Sculptor group: NGC 45, 55, 247, 254, 300, and 7793.From follow-up spectroscopy with Hydra-CTIO, we find 19 new globularclusters in NGC 55, 247, 253, and 300, bringing the total number ofknown Sculptor group globular clusters to 36. The newly discoveredclusters have spectroscopic ages consistent with those of old Milky Wayglobular clusters, and the majority are metal-poor. Their luminosityfunction closely resembles that of the Milky Way's globular clusters;their metallicity distribution is somewhat more metal-rich, but this maybe the result of our color selection of candidates. The mean[α/Fe] ratio in the clusters is -0.2+/-0.3, which is lower thanthe Milky Way average. The specific frequencies SN aresimilar to those of other late-type galaxies. However, if we calculatethe specific frequency using the K-band total magnitudes of the hostgalaxies, we find values that are more than a factor of 2 higher. Thekinematics of the globular cluster systems are consistent with rotationwith the H I disk in each of the four galaxies; however, only in NGC 253is this result based on more than seven objects. We suggest that theSculptor group galaxies add to evidence indicating that many of thefirst-generation globular clusters formed in disks, not halos.
|A Catalog of Neighboring Galaxies|
We present an all-sky catalog of 451 nearby galaxies, each having anindividual distance estimate D<~10 Mpc or a radial velocityVLG<550 km s-1. The catalog contains data onbasic optical and H I properties of the galaxies, in particular, theirdiameters, absolute magnitudes, morphological types, circumnuclearregion types, optical and H I surface brightnesses, rotationalvelocities, and indicative mass-to-luminosity and H I mass-to-luminosityratios, as well as a so-called tidal index, which quantifies the galaxyenvironment. We expect the catalog completeness to be roughly 70%-80%within 8 Mpc. About 85% of the Local Volume population are dwarf (dIr,dIm, and dSph) galaxies with MB>-17.0, which contributeabout 4% to the local luminosity density, and roughly 10%-15% to thelocal H I mass density. The H I mass-to-luminosity and the H Imass-to-total (indicative) mass ratios increase systematically fromgiant galaxies toward dwarfs, reaching maximum values about 5 in solarunits for the most tiny objects. For the Local Volume disklike galaxies,their H I masses and angular momentum follow Zasov's linear relation,expected for rotating gaseous disks being near the threshold ofgravitational instability, favorable for active star formation. We foundthat the mean local luminosity density exceeds 1.7-2.0 times the globaldensity, in spite of the presence of the Tully void and the absence ofrich clusters in the Local Volume. The mean local H I density is 1.4times its ``global'' value derived from the H I Parkes Sky Survey.However, the mean local baryon densityΩb(<8Mpc)=2.3% consists of only a half of the globalbaryon density, Ωb=(4.7+/-0.6)% (Spergel et al.,published in 2003). The mean-square pairwise difference of radialvelocities is about 100 km s-1 for spatial separations within1 Mpc, increasing to ~300 km s-1 on a scale of ~3 Mpc. alsoWe calculated the integral area of the sky occupied by the neighboringgalaxies. Assuming the H I size of spiral and irregular galaxies to be2.5 times their standard optical diameter and ignoring any evolutioneffect, we obtain the expected number of the line-of-sight intersectionswith the H I galaxy images to be dn/dz~0.4, which does not contradictthe observed number of absorptions in QSO spectra.
|Galaxy Formation: Clues from the Milky Way|
Stellar Populations are the fossil record of Galactic evolution.Interpretation of this record in the Local Group allows one to determinereliably the dominant physics controlling the evolution of thosegalaxies which are typical of the luminosity in the Universe, and is anessential prerequisite to understanding necessarily limited data at highredshifts. In our Galaxy, the key issues are the places and times offormation and merger of the oldest stellar populations : the halo, thickdisk and bulge - and their overlaps and evolutionary relationships, ifany. New results on studies of the stellar initial mass function at highredshift, the stellar populations of the Galactic bulge, and the mergerhistory of the Galactic disk are reviewed.
|Formation of bulges in very late-type galaxies from super star clusters|
The dynamical evolution of super star clusters (SSCs) moving in thebackground of a dark matter halo has been investigated as a possibleevent responsible for the formation of bulges in late-type spirals. Theunderlying physical processes include sinking of SSCs due to thedynamical friction and stripping of SSCs on their way to the centre. Ourmodel calculations show that only sinking of circumnuclear SSCscontributes to the formation of galactic bulges at the early stage.Based on the assumption of a universal density profile for the darkmatter halo, and an isothermal model for the SSCs, our simulations haveyielded bulges that are similar in many aspects to the observationalones. In particular, the derived surface density profiles can be wellfitted by an exponential structure with nuclear cusps, which isconsistent with Hubble Space Telescope observations.
|Infrared stellar populations in the central parts of the Milky Way galaxy|
Near- and mid-IR survey data from DENIS and ISOGAL are used toinvestigate the structure and formation history of the inner 10°(1.4 kpc) of the Milky Way galaxy. Synthetic bolometric corrections andextinction coefficients in the near- and mid-infrared (mid-IR) arederived for stars of different spectral types, to allow thetransformation of theoretical isochrones into observablecolour-magnitude diagrams. The observed IR colour-magnitude diagrams areused to derive the extinction, metallicity and age for individual stars.The inner galaxy is dominated by an old population (>~7 Gyr). Inaddition, an intermediate-age population (~200 Myr-7 Gyr) is detected,which is consistent with the presence of a few hundred asymptotic giantbranch stars with heavy mass loss. Furthermore, young stars (<~200Myr) are found across the inner bulge. The metallicities of thesestellar population components are discussed. These results can beinterpreted in terms of an early epoch of intense star formation andchemical enrichment that shaped the bulk of the bulge and nucleus, and amore continuous star formation history that gradually shaped the discfrom the accretion of subsolar metallicity gas from the halo. A possibleincrease in star formation ~200 Myr ago might have been triggered by aminor merger. Ever since the formation of the first stars, mechanismshave been at play that mix the populations from the nucleus, bulge anddisc. Luminosity functions across the inner Galactic plane indicate thepresence of an inclined (bar) structure at >~1 kpc from the GalacticCentre, near the inner Lindblad resonance. The innermost part of thebulge, within ~1 kpc from the Galactic Centre, seems azimuthallysymmetric.
|A Deep Chandra X-Ray Observation of NGC 1637|
We present a deep (168 ks) Chandra observation of the nearby face-onspiral galaxy NGC 1637 and study the X-ray source population. A total of32 X-ray sources are detected within the D25 ellipse of NGC1637, each of which is found to be variable during the 629 day periodcovered by the observations. Deep Hubble Space Telescope WFPC2observations of NGC 1637, nearly simultaneous with the Chandra data,were used to search for optical counterparts to the X-ray sources. Anultraluminous (LX=2.2×1039 ergss-1 0.3-7 keV) and variable (factor of 1.4) X-ray source isfound to positionally coincide with an optical faint and extended (~25pc FWHM) counterpart in the HST images (mV~22.8 mag,mI~21.1 mag). Given the multiband properties of this source,it likely represents a stellar-mass (~8 Msolar) black holecandidate located in an OB association in an outer spiral arm of NGC1637. Our analysis further reveals large amounts of diffuse emissionfilling the entire extent of the galaxy. The spectrum of the inner<~300 pc region is best described by a two-temperature thermal plasmaemission, with a low-temperature/low-absorption component(kTlow~0.3 keV) and a high-temperature/high-absorptioncomponent (kThigh~0.7-0.8 keV), likely associated with anoutflow of hot gas into the halo of NGC 1637. Comparison of themultiwavelength properties of a number of nearby galaxies shows that NGC1637 has remarkably high LX/LFIR andLX/LB ratios, suggesting a recent epoch with anenhanced star formation rate.
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