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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."
| 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.
| 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.
| 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.
| The Magellanic Stream, High-Velocity Clouds, and the Sculptor Group
The Magellanic Stream is a 100deg×10degfilament of gas that lies within the Galactic halo and contains~2×108 Msolar of neutral hydrogen. In thispaper we present data from the H I Parkes All Sky Survey (HIPASS) in thefirst complete survey of the entire Magellanic Stream and itssurroundings. We also present a summary of the reprocessing techniquesused to recover large-scale structure in the Stream. The substantialimprovement in spatial resolution and angular coverage compared toprevious surveys reveals a variety of prominent features, includingbifurcation along the main Stream filament; dense, isolated clouds thatfollow the entire length of the Stream; head-tail structures; and acomplex filamentary web at the head of the Stream where gas is beingfreshly stripped away from the Small Magellanic Cloud and the Bridge.Debris that appears to be of Magellanic origin extends out to 20°from the main Stream filaments. The Magellanic Stream has a velocitygradient of 700 km s-1 from the Clouds to the tail of theStream, ~390 km s-1 greater than that due to Galacticrotation alone, therefore implying a noncircular orbit. The dualfilaments comprising the Stream are likely to be relics from gasstripped separately from the Magellanic Bridge and the SMC. This impliesthat (1) the Bridge is somewhat older than conventionally assumed; and(2) the Clouds have been bound together for at least one or two orbits.The transverse velocity gradient of the Stream also appears to supportlong-term binary motion of the Clouds. A significant number of the mostelongated cataloged Stream clouds (containing ~1% of the Stream mass)have position angles aligned along the Stream. This suggests thepresence of shearing motions within the Stream, arising from tidalforces or interaction with the tenuous Galactic halo. As previouslynoted, clouds within one region of the Stream, along the sight line tothe less distant half (southern half on the sky) of the Sculptor Group,show anomalous properties. There are more clouds along this sight linethan any other part of the Stream, and their velocity distributionsignificantly deviates from the gradient along the Stream. We argue thatthis deviation could be due to a combination of halo material, and notto distant Sculptor clouds, based on a spatial and kinematic comparisonbetween the Sculptor Group galaxies and the anomalous clouds and thelack of cloud detection in the northern half of the group. This resulthas significant implications for the hypothesis that there might existdistant, massive high-velocity clouds within the Local Group. Catalogedclouds within the Magellanic Stream do not have a preferred scale size.Their mass spectrum f(MHI)~M-2.0HI andcolumn density spectrum f(NHI)~N-2.8HIare steep compared with Lyα absorbers and galaxies, and similar tothe anomalous clouds along the Sculptor Group sight line.
| Star Formation in Sculptor Group Dwarf Irregular Galaxies and the Nature of ``Transition'' Galaxies
We present new Hα narrowband imaging of the H II regions in eightSculptor group dwarf irregular (dI) galaxies. The Hα luminositiesof the detected H II regions range from some of the faintest detected inextragalactic H II regions (~1035 ergs s-1 in SC24) to some of the most luminous (~1040 ergs s-1in NGC 625). The total Hα luminosities are converted into currentstar formation rates (SFRs). Comparing the Sculptor group dI's to theLocal Group dI's, we find that the Sculptor group dI's have, on average,lower values of SFR when normalized to either galaxy luminosity or gasmass (although there is considerable overlap between the two samples).The range for both the Sculptor group and Local Group samples is largewhen compared with that seen for the sample of gas-rich, quiescent, lowsurface brightness (LSB) dI's from van Zee et al. (published in 1997)and the sample of isolated dI's from van Zee (from 2000 and 2001). Thisis probably best understood as a selection effect since the nearby groupsamples have a much larger fraction of extremely low luminosity galaxiesand the smaller galaxies are much more liable to large relativevariations in current SFRs. The Sculptor group and LSB samples are verysimilar with regard to mean values of both τgas andτform, and the Local Group and isolated dI samples arealso similar to each other in these two quantities. Currently, theSculptor group lacks dI galaxies with elevated normalized current SFRsas high as the Local Group dI's IC 10 and GR 8. The properties of``transition'' (dSph/dIrr) galaxies in Sculptor and the Local Group arealso compared and found to be similar. The transition galaxies aretypically among the lowest luminosities of the gas-rich dwarf galaxies.Relative to the dwarf irregular galaxies, the transition galaxies arefound preferentially nearer to spiral galaxies and are found nearer tothe center of the mass distribution in the local cloud. While most ofthese systems are consistent with normal dI galaxies, exhibitingtemporarily interrupted star formation, the observed density-morphologyrelationship (which is weaker than that observed for the dwarfspheroidal galaxies) indicates that environmental processes such as``tidal stirring'' may play a role in causing their lower SFRs.
| A search for Low Surface Brightness galaxies in the near-infrared. III. Nançay H I line observations
A total of 334 Low Surface Brightness galaxies detected in the 2MASSall-sky near-infrared survey have been observed in the 21 cm H I lineusing the Nançay telescope. All have a Ks-band meancentral surface brightness, measured within a 5'' radius, fainter than18 mag arcsec-2 and a Ks-band isophotal radius atthe 20 mag arcsec-2 level larger than 20''. We present globalH I line parameters for the 171 clearly detected objects and the 23marginal detections, as well as upper limits for the undetected objects.The 171 clear detections comprise 50 previously uncatalogued objects and41 objects with a PGC entry only.Tables 3-5 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/408/465Figures 1 and 2 are only available in electronic form athttp://www.edpsciences.org
| A search for Low Surface Brightness galaxies in the near-infrared. I. Selection of the sample
A sample of about 3800 Low Surface Brightness (LSB) galaxies wasselected using the all-sky near-infrared (J, H and Ks-band)2MASS survey. The selected objects have a mean central surfacebrightness within a 5'' radius around their centre fainter than 18 magarcsec-2 in the Ks band, making them the lowestsurface brightness galaxies detected by 2MASS. A description is given ofthe relevant properties of the 2MASS survey and the LSB galaxy selectionprocedure, as well as of basic photometric properties of the selectedobjects. The latter properties are compared to those of other samples ofgalaxies, of both LSBs and ``classical'' high surface brightness (HSB)objects, which were selected in the optical. The 2MASS LSBs have aBT_c-KT colour which is on average 0.9 mag bluerthan that of HSBs from the NGC. The 2MASS sample does not appear tocontain a significant population of red objects.All tables and Figs. 2a-c are only available in electronic form athttp://www.edpsciences.org
| The Luminosity Function of Star Clusters in Spiral Galaxies
Star clusters in six nearby spiral galaxies are examined using archiveimages from the Wide Field Planetary Camera 2 (WFPC2) on board theHubble Space Telescope (HST). The galaxies have previously been studiedfrom the ground and some of them are known to possess rich populationsof ``young massive clusters.'' Comparison with the HST images indicatesa success rate of ~75% for the ground-based cluster detections, withtypical contaminants being blends or loose groupings of several stars incrowded regions. The luminosity functions (LFs) of cluster candidatesidentified on the HST images are analyzed and compared with existingdata for the Milky Way and the LMC. The LFs are well approximated bypower laws of the form dN(L)/dL~Lα, with slopes in therange -2.4<~α<~-2.0. The steeper slopes tend to be foundamong fits covering brighter magnitude intervals, although direct hintsof a variation in the LF slope with magnitude are seen only at lowsignificance in two galaxies. The surface density of star clusters at areference magnitude of MV=-8,Σ-8cl, scales with the mean star formationrate (SFR) per unit area, ΣSFR. Assuming that the LFcan be generally expressed asdN(L)/dL=cAΣγSFRLα,where A is the galaxy area, γ~1.0-1.4, α=-2.4, and thenormalization constant c is determined from the WFPC2 data analyzedhere, the maximum cluster luminosity expected in a galaxy from randomsampling of the LF is estimated as a function of ΣSFRand A. The predictions agree well with existing observations of galaxiesspanning a wide range of ΣSFR values, suggesting thatsampling statistics play an important role in determining the maximumobserved luminosities of star clusters in galaxies. Based onobservations obtained 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.
| Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
| HIPASS High-Velocity Clouds: Properties of the Compact and Extended Populations
A catalog of southern anomalous-velocity H I clouds at decl. <+2° is presented. This catalog is based on data from the H I ParkesAll-Sky Survey (HIPASS) reprocessed with the MINMED5 procedure andsearched with a new high-velocity cloud-finding algorithm. The improvedsensitivity (5 σ: ΔTB= 0.04 K), resolution(15.5′), and velocity range (-500 kms-1
| Local velocity field from sosie galaxies. I. The Peebles' model
Pratton et al. (1997) showed that the velocity field around clusterscould generate an apparent distortion that appears as tangentialstructures or radial filaments. In the present paper we determine theparameters of the Peebles' model (1976) describing infall of galaxiesonto clusters with the aim of testing quantitatively the amplitude ofthis distortion. The distances are determined from the concept of sosiegalaxies (Paturel 1984) using 21 calibrators for which the distanceswere recently calculated from two independent Cepheid calibrations. Weuse both B and I-band magnitudes. The Spaenhauer diagram method is usedto correct for the Malmquist bias. We give the equations for theconstruction of this diagram. We analyze the apparent Hubble constant indifferent regions around Virgo and obtain simultaneously the Local Groupinfall and the unperturbed Hubble constant. We found:[VLG-infall = 208 ± 9 km s-1] [\log H =1.82 ± 0.04 (H ≈ 66 ± 6 km s-1Mpc-1).] The front side and backside infalls can be seenaround Virgo and Fornax. In the direction of Virgo the comparison ismade with the Peebles' model. We obtain: [vinfall} =CVirgo/r0.9 ± 0.2] withCVirgo=2800 for Virgo and CFornax=1350 for Fornax,with the adopted units (km s-1 and Mpc). We obtain thefollowing mean distance moduli: [μVirgo=31.3 ± 0.2(r=18 Mpc )] [μFornax=31.7 ± 0.3 (r=22 Mpc). ] Allthese quantities form an accurate and coherent system. Full Table 2 isonly available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/57
| The Hi Parkes All Sky Survey: southern observations, calibration and robust imaging
The acquisition of Hi Parkes All Sky Survey (HIPASS) southern sky datacommenced at the Australia Telescope National Facility's Parkes 64-mtelescope in 1997 February, and was completed in 2000 March. HIPASS isthe deepest Hi survey yet of the sky south of declination +2°, andis sensitive to emission out to 170 h 75 -1Mpc. The characteristic rootmean square noise in the survey images is 13.3mJy. This paper describesthe survey observations, which comprise 23020 eight-degree scans of9-min duration, and details the techniques used to calibrate and imagethe data. The processing algorithms are successfully designed to bestatistically robust to the presence of interference signals, and areparticular to imaging point (or nearly point) sources. Specifically, amajor improvement in image quality is obtained by designing amedian-gridding algorithm which uses the median estimator in place ofthe mean estimator.
| X-ray emission from the Sculptor galaxy NGC 300
We report here the results of a full analysis of all the ROSAT PSPCspectral imaging observations and all the ROSAT HRI high resolutionimaging observations of the very nearby (D=2.1 Mpc) Sculptor galaxy, NGC300. Many point sources are detected within the field, several of themshowing evidence for variability, and we present full source listsdetailing their X-ray properties, and attempt to classify them on thebasis of their temporal, spectral and multi-wavelength characteristics.A black hole X-ray binary candidate, a supersoft source and severalsupernova remnants and H ii regions are detected in X-rays, as isunresolved, possibly diffuse emission, accounting for perhaps ~ 20% ofthe total NGC 300 X-ray (0.1-2.4 keV) luminosity (5.8*E38 ergs-1). We compare the X-ray source luminosity distribution ofNGC 300 with that of other nearby galaxies, and we also compare NGC 300with its Sculptor neighbours, concluding that it is a quite anunremarkable system, showing no unusual X-ray (or othermulti-wavelength) properties. It may be one of the best examples of acompletely typical normal quiescent late-type spiral galaxy.
| Tip of the red giant branch distance for the Sculptor group dwarf ESO 540-032
We present the first VI CCD photometry for the Sculptor group galaxy ESO540-032 obtained at the Very Large Telescope UT1+FORS1. The (I, V-I)colour-magnitude diagram indicates that this intermediate-type dwarfgalaxy is dominated by old, metal-poor ([Fe/H]~ -1.7 dex) stars, with asmall population of slightly more metal-rich ([Fe/H]~ -1.3 dex), young(age 150-500 Myr) stars. A discontinuity in the I-band luminosityfunction is detected at I0 = 23.44+/- 0.09 mag. Interpretingthis feature as the tip of the red giant branch and adoptingMI = -4.20+/- 0.10 mag for its absolute magnitude, we havedetermined a Population II distance modulus of (m - M)0 =27.64 +/- 0.14 mag (3.4 +/- 0.2 Mpc). This distance confirms ESO 540-032as a member of the nearby Sculptor group but is significantly largerthan a previously reported value based on the Surface BrightnessFluctuation (SBF) method. The results from stellar population synthesismodels suggest that the application of the SBF technique on dwarfgalaxies with mixed morphology requires a detailed knowledge of theunderlying stellar composition and thus offers no advantage over adirect distance measurement using the tip of the red giant branch asdistance indicator. We produce the surface brightness profiles for ESO540-032 and derive the photometric and structural parameters. The globalproperties follow closely the relations between metallicity and bothabsolute magnitude and central surface brightness defined by dwarfelliptical galaxies in the Local Group. Finally, we identify and discussa non-stellar object near the galaxy center which may resemble aglobular cluster. Based on observations collected at the EuropeanSouthern Observatory (ESO 64.N-0069).
| Spectroscopy of globular cluster candidates in the Sculptor group galaxies NGC 253 and 55
We have obtained spectra for 103 published globular cluster candidatesin the Sculptor group galaxies NGC 253 and 55. On the basis of radialvelocities and digitized plate images, 14 globular clusters areidentified in NGC 253 and one probable globular cluster is identified inNGC 55. The majority of the objects in the sample appear to bebackground galaxies. We have obtained and analysed COSMOS plate scans ofNGC 253 and 55 and use these along with the spectroscopically identifiedclusters to define new samples of globular cluster candidates in the twogalaxies which should have reduced contamination.
| 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.
| Seeing Galaxies through Thick and Thin. I. Optical Opacity Measures in Overlapping Galaxies
We describe the use of partially overlapping galaxies to provide directmeasurements of the effective absorption in galaxy disks, independent ofassumptions about internal disk structure. The nonoverlapping parts ofthe galaxies and symmetry considerations are used to reconstruct, viadifferential photometry, how much background galaxy light is lost inpassing through the foreground disks. Extensive catalog searches andfollow-up imaging yield ~15-25 nearby galaxy pairs suitable for varyingdegrees of our analysis; 11 of the best such examples are presentedhere. From these pairs, we find that interarm extinction is modest,declining from AB~1 mag at 0.3RB25 toessentially zero by RB25; the interarm dust has ascale length consistent with that of the disk starlight. In contrast,dust in spiral arms and resonance rings may be optically thick(AB>2) at virtually any radius. Some disks have flatterextinction curves than the Galaxy, with AB/AI~1.6this is probably the signature of clumpy dust distributions. Even thoughtypical spirals are not optically thick throughout their disks, wherethey are optically thick is correlated with where they are mostluminous: in spiral arms and inner disks. This correlation betweenabsorption and emission regions may account for their apparent surfacebrightness being only mildly dependent on inclination, erroneouslyindicating that spirals are generally optically thick. Taken as anensemble, the opacities of spiral galaxies may be just great enough tosignificantly affect QSO counts, though not enough to cause theirhigh-redshift cutoff. Based in part on archival observations with theNASA/ESA Hubble Space Telescope (HST) obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS5-26555.
| Surface BR Photometry of Newly Discovered Dwarf Elliptical Galaxies in the Nearby Sculptor and Centaurus A Groups
Prompted by the recent finding of a large number of gas-rich dwarfirregular galaxies in the nearby southern galaxy groups Sculptor (Scl)and Centaurus A (Cen A) we carried out a complementary survey to searchfor members of the gas-poor dwarf elliptical (dE) galaxy family. Intotal 18 dE candidates were identified on SRC Sky Survey films coveringthe group regions. For five dE's in the Scl group and five in the Cen Agroup, membership information is available from surface brightnessfluctuations distance measurements; two dEs in each group also haveindependent redshift measurements. The remaining eight galaxies havebeen associated to the groups based on their morphology. We acquireddeep B- and R-band CCD images for all galaxies and determined theirphotometric and structural parameters. According to the magnitude rangecovered, -14
| Young massive star clusters in nearby spiral galaxies. III. Correlations between cluster populations and host galaxy properties
We present an analysis of correlations between integrated properties ofgalaxies and their populations of young massive star clusters. Data for21 nearby galaxies presented by Larsen & Richtler (\cite{lr99}) areused together with literature data for 10 additional galaxies, spanninga range in specific U-band cluster luminosity T_L(U) from 0 to 15. Wefind that T_L(U) correlates with several observable host galaxyparameters, in particular the ratio of Far-Infrared (FIR) tomBox{B-band} flux and the surface brightness. Taking the FIRluminosity as an indicator of the star formation rate (SFR), it is foundthat T_L(U) correlates very well with the SFR per unit area. A similarcorrelation is seen between T_L(U) and the atomic hydrogen surfacedensity. The cluster formation efficiency seems to depend on the SFR ina continuous way, rather than being related to any particularly violentmode of star formation. We discuss fundamental features of possiblescenarios for cluster formation. One possibility is that the correlationbetween T_L(U) and SFR is due to a common controlling parameter, mostprobably the high density of the ISM. Another scenario conceives a highT_L(U) as resulting from the energy input from many massive stars incase of a high SFR. Based on observations made with the Nordic OpticalTelescope, operated on the island of La Palma jointly by Denmark,Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio delRoque de los Muchachos of the Instituto de Astrofisica de Canarias, andwith the Danish 1.5-m telescope at ESO, La Silla, Chile.
| The Extraordinary ``Superthin'' Spiral Galaxy UGC 7321. I. Disk Color Gradients and Global Properties from Multiwavelength Observations
We present B- and R-band optical imaging and photometry, Hαnarrowband imaging, near-infrared H-band imaging, and H I 21 cmspectroscopy of the nearby (Vh=407 km s-1), Sdspiral galaxy UGC 7321. UGC 7321 exhibits a remarkably thin stellar diskwith no discernible bulge component. The galaxy has a very diffuse, lowsurface brightness disk, which appears to suffer relatively littleinternal extinction in spite of its nearly edge-on geometry(i~88deg). If seen face-on, UGC 7321 would have an observedcentral B-band surface brightness of only ~23.4 mag arcsec-2.The UGC 7321 disk shows significant B-R color gradients in both theradial and vertical directions: Δ(B-R)>=0.80 mag along thegalaxy major axis, and Δ(B-R) as large as 0.45 mag is observedparallel to the galaxy minor axis. These color gradients cannot beexplained solely by dust and are indicative of changes in the mix ofstellar ages and/or metallicity as a function of both radius and heightabove the galaxy plane. The outer regions of the UGC 7321 disk are tooblue to be explained by low metallicity alone (B-R<=0.6) and must berelatively young. However, the galaxy also contains stellar populationswith B-R>1.1, indicating it is not a young or recently formed galaxy.The disk of UGC 7321 is not a simple exponential but exhibits a lightexcess at small radii, as well as distinct surface brightness zones.Despite its organized disk structure, many of the global properties ofUGC 7321 (MB=-17.0 MHI=1.1x109MHI/LB=1.1 Msolar/LsolarW20=233 km s-1 hr=2.1 kpc) arereminiscent of a dwarf galaxy. Together the properties of UGC 7321 implythat it is an underevolved galaxy in both a dynamical and in a starformation sense.
| Star-forming Complexes in a Sample of Spiral and Irregular Galaxies
Over 300 star-forming complexes in 11 intermediate- and late-type spiraland irregular galaxies have been observed in the B, I, and Hαbands to determine their luminosity functions, ages, sizes, and masses.The total Hα luminosity from complexes compared with the totalgalaxy Hα luminosity ranges from 20% to 70%, but the percentage isnearly constant at 7% in the B band for most galaxies. A comparison ofthe colors and luminosities of the complexes with published clusterevolutionary models suggests that the complexes range in age from a fewtimes 10^6 yr to nearly 10^9 yr; the majority have ages of less than 1to 2x10^7 yr. The complex masses range from 10^4 to 10^7 M_solar. Theluminosity functions for the complexes follow a power law with anexponent of approximately -2 late-type galaxies have slightly shallowerslopes than intermediate-type galaxies. The sizes of the largestcomplexes in each galaxy scale approximately with the square root of thegalaxy luminosity, confirming previous studies. The complexes may have afractal size distribution that is consistent with values predicted bytheoretical turbulence models of the interstellar medium.
| Angular Momentum in the Sculptor Group
The spins of the major galaxies in the nearby Sculptor Group agree withthose calculated to be produced by tidal interactions among themselves.The agreement is closer than would be expected from publisheduncertainties in distances, indicating either that these uncertaintiesare smaller than calculated or that they are correlated. Three pairs ofgalaxies (NGC 55 and 300, 247 and 253, and 45 and 7793) are inapproximate two-body orbits; the direction of orbital angular momentumfor the first two pairs is derived.
| Young massive star clusters in nearby galaxies . I. Identification and general properties of the cluster systems
Using ground-based UBVRIHα CCD photometry we have been carryingout a search for young massive star clusters (YMCs) in a sampleconsisting of 21 nearby spiral galaxies. We find a large varietyconcerning the richness of the cluster systems, with some galaxiescontaining no YMCs at all and others hosting very large numbers of YMCs.Examples of galaxies with poor cluster systems are NGC 300 and NGC 4395,while the richest cluster systems are found in the galaxies NGC 5236 (M83), NGC 2997 and NGC 1313. The age distributions of clusters in thesegalaxies show no obvious peaks, indicating that massive clusters areformed as an ongoing process rather than in bursts. This is in contrastto what is observed in starbursts and merger galaxies. The radialdistributions of clusters follow the Hα surface brightnesses. Forthe galaxies in our sample there is no correlation between themorphological type and the presence of YMCs. Based on observations madewith the Nordic Optical Telescope, operated on the island of La Palmajointly by Denmark, Finland, Iceland, Norway, and Sweden, in the SpanishObservatorio del Roque de los Muchachos of the Instituto de Astrofisicade Canarias, and with the Danish 1.5-m telescope at ESO, La Silla,Chile.
| ROSAT observations of the Sculptor galaxy NGC 7793
We report here the results of spectral imaging observations with theROSAT PSPC of the field surrounding the very nearby (D=3.38 Mpc)Sculptor galaxy, NGC 7793. Many point sources are detected within thefield, several of them showing evidence for variability. Seven sourcesare seen to lie within the optical confines of the system, the brightest(LX ~ 9*E(38) erg s(-1) ), lying to the southern edge of NGC7793. This source, also observed to be variable, is seen now, not to beassociated with a z=0.071 redshift QSO, as was previously thought. Anumber of the other sources within the NGC 7793 disc are likely to bedue to X-ray binaries, supernova remnants or superbubbles within thegalaxy itself. Other sources may be associated with background AGN. Inaddition to the point source emission, rather uniform unresolvedemission is detected in and around NGC 7793 extending to a radius ofperhaps 4 kpc. This emission is likely to be contaminated to some degreeby unresolved point sources, as its temperature (kT~1 keV) is ratherhotter than is seen for the diffuse gas components in other nearbyspiral galaxies. Comparing the X-ray properties of NGC 7793 with thoseof the remaining Sculptor group members, suggests that it may, in termsof activity, lie somewhere between its quiescent and starburstneighbours.
| Surface Brightness Fluctuation Distances to Dwarf Elliptical Galaxies in the Sculptor Group
As part of an ongoing search for dwarf elliptical galaxies (dE's) in thevicinity of the Local Group (Jerjen et al.), we acquired deep B- andR-band images for five dE candidates identified on morphologicalcriteria in the Sculptor (Scl) group region. We carried out a surfacebrightness fluctuation (SBF) analysis on the R-band images to measurethe apparent fluctuation magnitude m_R for each dE. Using predictionsfrom stellar population synthesis models (Worthey) giving M_R values inthe narrow range between -1.17 and -1.13, the galaxy distances weredetermined. All of these dE candidates turned out to be satellites ofScl group major members. A redshift measurement of the dE candidate ESO294-010 yielded an independent confirmation of its group membership: the[O III] and Hα emission lines from a small H II region gave aheliocentric velocity of 117 (+/-5) km s^-1, in close agreement with thevelocity of its parent galaxy NGC 55 (v_ȯ = 125 km s^-1). Theprecision of the SBF distances (5%-10%) contributes to delineating thecigar-like distribution of the Scl group members, which extend overdistances from 1.7 to 4.4 Mpc and are concentrated in three, possiblyfour subclumps. The Hubble diagram for nine Scl galaxies, including twoof our dE's, exhibits a tight linear velocity-distance relation with asteep slope of 119 km s^-1 Mpc^-1. The results indicate thatgravitational interaction among the Scl group members plays only a minorrole in the dynamics of the group. However, the Hubble flow of theentire system appears strongly disturbed by the large masses of ourGalaxy and M31, which leads to the observed shearing motion. From thedistances and velocities of 49 galaxies located in the Local Group andtoward the Scl group, we illustrate the continuity of the galaxydistribution, which strongly supports the view that the two groups forma single supergalactic structure.
| 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.
| 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 130.79.128.5 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.
| A catalogue of spatially resolved kinematics of galaxies: Bibliography
We present a catalogue of galaxies for which spatially resolved data ontheir internal kinematics have been published; there is no a priorirestriction regarding their morphological type. The catalogue lists thereferences to the articles where the data are published, as well as acoded description of these data: observed emission or absorption lines,velocity or velocity dispersion, radial profile or 2D field, positionangle. Tables 1, 2, and 3 are proposed in electronic form only, and areavailable from the CDS, via anonymous ftp to cdsarc.u-strasbg.fr (to130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
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