Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
Structure of Disk-dominated Galaxies. I. Bulge/Disk Parameters, Simulations, and Secular Evolution
A robust analysis of galaxy structural parameters, based on the modelingof bulge and disk brightnesses in the BVRH bandpasses, is presented for121 face-on and moderately inclined late-type spirals. Each surfacebrightness (SB) profile is decomposed into a sum of a generalizedSérsic bulge and an exponential disk. The reliability andlimitations of our bulge-to-disk (B/D) decompositions are tested withextensive simulations of galaxy brightness profiles (one-dimensional)and images (two-dimensional). We have used repeat observations to testthe consistency of our decompositions. The average systematic modelerrors are <~20% and <~5% for the bulge and disk components,respectively. The final set of galaxy parameters is studied forvariations and correlations in the context of profile type differencesand wavelength dependencies. Galaxy types are divided into three classesaccording to their SB profile shapes: Freeman type I, type II, and athird ``transition'' class for galaxies whose profiles change from typeII in the optical to type I in the infrared. Roughly 43%, 44%, and 13%of type I, type II, and transition galaxies, respectively, comprise oursample. Only type I galaxies, with their fully exponential disks, areadequately modeled by our two-component decompositions, and our mainresults focus on these profiles. We discuss possible interpretations ofFreeman type II profiles. The Sérsic bulge shape parameter fornearby type I late-type spirals shows a range between n=0.1 and 2, but,on average, the underlying surface density profile for the bulge anddisk of these galaxies is adequately described by a double-exponentialdistribution. The distribution of disk scale lengths shows a decreasingtrend with increasing wavelength, consistent with a higher concentrationof old stars or dust (or both) in the central regions relative to theouter disk. We confirm a coupling between the bulge and disk with ascale length ratio =0.22+/-0.09, or=0.13+/-0.06 for late-typespirals, in agreement with recent N-body simulations of disk formation.This ratio increases from ~0.20 for late-type spirals to ~0.24 forearlier types. These observations are consistent with bulges oflate-type spiral galaxies being more deeply embedded in their host diskthan earlier type bulges. Bulges and disks can thus preserve a nearlyconstant re/h but show a great range of SB for any giveneffective radius. The similar scaling relations for early- and late-typespirals suggest comparable formation and/or evolution scenarios for diskgalaxies of all Hubble types. In the spirit of Courteau, de Jong, &Broeils but using our new, more extensive database, we interpret thisresult as further evidence for regulated bulge formation byredistribution of disk material to the galaxy center, in agreement withmodels of secular evolution of the disk.
| A Near-Infrared Photometric Study of the Low-Latitude Globular Clusters Liller 1, Djorgovski 1, HP 1, and NGC 6528
Images recorded through J,H,Ks,2.2 μm continuum, and 2.3 μm COfilters are used to investigate the stellar contents of the low Galacticlatitude globular clusters NGC 6528, Liller 1, Djorgovski 1, and HP 1,as well as surrounding bulge fields. Metallicities are estimated for thelatter three clusters by comparing the colors and CO indexes of giantbranch stars with those in other clusters and the bulge, whilereddenings are estimated from the colors of bright bulge stars in thesurrounding fields. In some cases the metallicities and reddenings aresignificantly different from previous estimates. The horizontal branch(HB) in NGC 6528 occurs at K=13.2, and the K luminosity function of HBstars in this cluster is not significantly different from those in themoderately metal-rich clusters NGC 6304 and NGC 6316. R', the ratio ofHB to bright red giant branch (RGB) and asymptotic giant branch (AGB)stars, is 1.25+/-0.25, in good agreement with its value in otherglobular clusters. The RGB bump in NGC 6528 is detected at K=13.8, andthe relative brightness of this feature with respect to the HB isconsistent with the cluster being very metal rich. The HB in Liller 1occurs at K=14.4. Stars in Liller 1 have smaller J-K colors and COindexes than bulge giants with the same brightness, and a comparisonbetween the Liller 1 and NGC 6528 sequences on the (K, J-K), and (K,CO)color-magnitude diagrams (CMDs) indicates that Liller 1 has ametallicity comparable to, and perhaps even slightly lower than, that ofNGC 6528. Stars in Liller 1 and NGC 6528 occupy the same region of the(J-H, H-K) two-color diagram as bulge giants, which is consistent withthese clusters forming as part of the bulge. Stars in Djorgovski 1 andHP 1 have significantly smaller CO indexes than stars with the samebrightness in the surrounding bulge fields, and CMDs for these clustersare constructed by selecting objects according to CO index. Afteradjusting for differences in distance and reddening, the Djorgovski 1giant branch on the (K, J-K) CMD is well matched by that of the[Fe/H]=-2.2 cluster M92, while the giant branch of HP 1 follows that ofthe [Fe/H]=-1.6 globular cluster M13. The metallicities inferred forboth clusters are consistent with integrated J-K colors and CO indexesmeasured through moderately large (~35"-45") apertures. Based on thebrightness of the RGB tip, it is concluded that Djorgovski 1 has adistance modulus μ0=15.4, while the distance modulus of HP1 is μ0=14.7. The brightest stars in the fieldssurrounding Liller 1, Djorgovski 1, and HP 1 follow the same relationbetween MK and CO index as M giants in Baade's window. Starsas faint as the HB have been detected in the field surrounding HP 1, andthe relative numbers of HB and upper giant branch stars indicate thatR'=1.14+/-0.11. This relatively low value reinforces earlierstudies, which found that R', and hence the helium abundance, likelydoes not vary with radius in the innermost regions of the Galacticbulge.
| 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.
| 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.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| General study of group membership. II - Determination of nearby groups
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
| A list of some corrections to Zwicky's Catalogue of Galaxies and Clusters of Galaxies
Not Available
| A 21 CM survey of the Pisces-Perseus supercluster. III - The region north of +38 degrees
As part of a comprehensive survey of galaxies in the region of thePisces-Perseus supercluster and its surroundings, 21-cm lineobservations obtained with the NRAO 91-m telescope are presented for 383galaxies in the right ascension range from 22 to 10 hr and north of +38deg declination. Recent improvements to the Green Bank receiver/feedsystem have dramatically raised detection rates at the distance ofPisces-Perseus (cz = +5000 km/s). The present study has contributed todouble the number of known redshifts outside rich clusters in thissection of the sky. The H I content of the current sample, as expressedin terms of the H I mass expected for a galaxy of the same optical sizeand morphology, matches the standard of normalcy established forisolated galaxies.
| The large-scale distribution of galaxies in the Linx-Gemini region
A redshift distribution study of a sample of 283 bright galaxies in an1800 square degree area in the Linx-Gemini region, including newredshifts for 59 galaxies, provides evidence for the existence ofseveral large scale structures. The Linx-Ursa supercluster with meanvelocity of 3500 km/s, a large cloud of galaxies extending for at least50/h Mpc around Abell 569, a low density filament in Gemini composedmainly of spirals, and a possible outstanding structure containing thecluster Abell 779, are found. The Abell 569 cloud is suggested as thestructure most likely connected with the Perseus supercluster across thegalactic dimming region.
| KISO survey for ultraviolet-excess galaxies. I
Lists and identification charts of the ultraviolet-excess galaxies whichhave been detected on the multi-color plates taken with the Kiso Schmidttelescope are presented for the first 10 survey fields. Catalogued are573 objects, down to the photographic magnitude of about 17, in the skyarea of some 300 square degrees.
| A morphological study of ultraviolet-excess galaxies
A number of ultraviolet-excess galaxies have been detected during thecourse of surveys using the Kiso Schmidt telescope. In this paper, aclassification scheme is proposed for 142 selected objects on the basisof their morphological features, and the relation between themorphological type and the degree of ultraviolet excess is presented. Ingeneral, irregular galaxies with conspicuous H II regions and pairgalaxies tend to show higher degree of ultraviolet excess, while thedegree in spiral galaxies appears to range widely.
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
Каталог и designations:
|
