내용
사진
사진 업로드
DSS Images Other Images
관련 글
The Survey for Ionization in Neutral Gas Galaxies. I. Description and Initial Results
We introduce the Survey for Ionization in Neutral Gas Galaxies (SINGG),a census of star formation in H I-selected galaxies. The survey consistsof Hα and R-band imaging of a sample of 468 galaxies selected fromthe H I Parkes All Sky Survey (HIPASS). The sample spans three decadesin H I mass and is free of many of the biases that affect otherstar-forming galaxy samples. We present the criteria for sampleselection, list the entire sample, discuss our observational techniques,and describe the data reduction and calibration methods. This paperfocuses on 93 SINGG targets whose observations have been fully reducedand analyzed to date. The majority of these show a single emission linegalaxy (ELG). We see multiple ELGs in 13 fields, with up to four ELGs ina single field. All of the targets in this sample are detected inHα, indicating that dormant (non-star-forming) galaxies withMHI>~3×107 Msolar are veryrare. A database of the measured global properties of the ELGs ispresented. The ELG sample spans 4 orders of magnitude in luminosity(Hα and R band), and Hα surface brightness, nearly 3 ordersof magnitude in R surface brightness and nearly 2 orders of magnitude inHα equivalent width (EW). The surface brightness distribution ofour sample is broader than that of the Sloan Digital Sky Survey (SDSS)spectroscopic sample, the EW distribution is broader than prism-selectedsamples, and the morphologies found include all common types ofstar-forming galaxies (e.g., irregular, spiral, blue compact dwarf,starbursts, merging and colliding systems, and even residual starformation in S0 and Sa spirals). Thus, SINGG presents a superior censusof star formation in the local universe suitable for further studiesranging from the analysis of H II regions to determination of the localcosmic star formation rate density.
| 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.
| 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.
| The 1000 Brightest HIPASS Galaxies: H I Properties
We present the HIPASS Bright Galaxy Catalog (BGC), which contains the1000 H I brightest galaxies in the southern sky as obtained from the H IParkes All-Sky Survey (HIPASS). The selection of the brightest sourcesis based on their H I peak flux density (Speak>~116 mJy)as measured from the spatially integrated HIPASS spectrum. The derived HI masses range from ~107 to 4×1010Msolar. While the BGC (z<0.03) is complete inSpeak, only a subset of ~500 sources can be consideredcomplete in integrated H I flux density (FHI>~25 Jy kms-1). The HIPASS BGC contains a total of 158 new redshifts.These belong to 91 new sources for which no optical or infraredcounterparts have previously been cataloged, an additional 51 galaxiesfor which no redshifts were previously known, and 16 galaxies for whichthe cataloged optical velocities disagree. Of the 91 newly cataloged BGCsources, only four are definite H I clouds: while three are likelyMagellanic debris with velocities around 400 km s-1, one is atidal cloud associated with the NGC 2442 galaxy group. The remaining 87new BGC sources, the majority of which lie in the zone of avoidance,appear to be galaxies. We identified optical counterparts to all but oneof the 30 new galaxies at Galactic latitudes |b|>10deg.Therefore, the BGC yields no evidence for a population of``free-floating'' intergalactic H I clouds without associated opticalcounterparts. HIPASS provides a clear view of the local large-scalestructure. The dominant features in the sky distribution of the BGC arethe Supergalactic Plane and the Local Void. In addition, one can clearlysee the Centaurus Wall, which connects via the Hydra and Antlia Clustersto the Puppis Filament. Some previously hardly noticable galaxy groupsstand out quite distinctly in the H I sky distribution. Several newstructures, including some not behind the Milky Way, are seen for thefirst time.
| 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.
| Globular Clusters as Candidates for Gravitational Lenses to Explain Quasar-Galaxy Associations
We argue that globular clusters (GCs) are good candidates forgravitational lenses in explaining quasar-galaxy associations. Thecatalog of associations (Bukhmastova 2001) compiled from the LEDAcatalog of galaxies (Paturel 1997) and from the catalog of quasars(Veron-Cetty and Veron 1998) is used. Based on the new catalog, we showthat one might expect an increased number of GCs around irregulargalaxies of types 9 and 10 from the hypothesis that distant compactsources are gravitationally lensed by GCs in the halos of foregroundgalaxies. The King model is used to determine the central surfacedensities of 135 GCs in the Milky Way. The distribution of GCs incentral surface density was found to be lognormal.
| The Relationship between Stellar Light Distributions of Galaxies and Their Formation Histories
A major problem in extragalactic astronomy is the inability todistinguish in a robust, physical, and model-independent way how galaxypopulations are physically related to each other and to their formationhistories. A similar, but distinct, and also long-standing question iswhether the structural appearances of galaxies, as seen through theirstellar light distributions, contain enough physical information tooffer this classification. We argue through the use of 240 images ofnearby galaxies that three model-independent parameters measured on asingle galaxy image reveal its major ongoing and past formation modesand can be used as a robust classification system. These parametersquantitatively measure: the concentration (C), asymmetry (A), andclumpiness (S) of a galaxy's stellar light distribution. When combinedinto a three-dimensional ``CAS'' volume all major classes of galaxies invarious phases of evolution are cleanly distinguished. We argue thatthese three parameters correlate with important modes of galaxyevolution: star formation and major merging activity. This is arguedthrough the strong correlation of Hα equivalent width andbroadband colors with the clumpiness parameter S, the uniquely largeasymmetries of 66 galaxies undergoing mergers, and the correlation ofbulge to total light ratios, and stellar masses, with the concentrationindex. As an obvious goal is to use this system at high redshifts totrace evolution, we demonstrate that these parameters can be measured,within a reasonable and quantifiable uncertainty with available data outto z~3 using the Hubble Space Telescope GOODS ACS and Hubble Deep Fieldimages.
| New insights to the photometric structure of Blue Compact Dwarf galaxies from deep Near-Infrared studies. I. Observations, surface photometry and decomposition of surface brightness profiles
We have analyzed deep Near Infrared (NIR) broad band images for a sampleof Blue Compact Dwarf Galaxies (BCDs), observed with the ESO NTT andCalar Alto 3.6 m telescopes. The data presented here allows for thedetection and quantitative study of the extended stellar low-surfacebrightness (LSB) host galaxy in all sample BCDs. NIR surface brightnessprofiles (SBPs) of the LSB host galaxies agree at large galactocentricradii with those from optical studies, showing also an exponentialintensity decrease and compatible scale lengths. At small tointermediate radii (within 1-3 exponential scale lengths), however, theNIR data reveals for more than one half of our sample BCDs evidence fora significant flattening of the exponential profile of the LSBcomponent. Such profiles (type V SBPs, Binggeli & Cameron\cite{binggeli91}) have rarely been detected in the LSB component ofBCDs at optical wavelengths, where the relative flux contribution of thestarburst, being stronger than in the NIR, can readily hide a possiblecentral intensity depression in the underlying LSB host. The structuralproperties, frequency and physical origin of type V LSB profiles in BCDsand dwarf galaxies in general have not yet been subject to systematicstudies. Nevertheless, the occurrence of such profiles in an appreciablefraction of BCDs would impose important new observational constraints tothe radial mass distribution of the stellar LSB component, as well as tothe photometric fading of these systems after the termination ofstar-forming activities. We test the suitability of two empiricalfitting functions, a modified exponential distribution (Papaderos et al.\cite{papaderos96a}) and the Sérsic law, for the systematizationof the structural properties of BCD host galaxies which show a type Vintensity distribution. Either function has been found to satisfactorilyfit a type V distribution. However, it is argued that the practicalapplicability of Sérsic fits to the LSB emission of BCDs islimited by the extreme sensitivity of the achieved solutions to, e.g.,small uncertainties in the sky subtraction and SBP derivation. We findthat most of the sample BCDs show in their stellar LSB host galaxyoptical-NIR colors indicative of an evolved stellar population withsubsolar metallicity. Unsharp-masked NIR maps reveal numerousmorphological details and indicate in some cases, in combination withoptical data, appreciable non-uniform dust absorption on a spatial scaleas large as ~ 1 kpc.European Southern Observatory, program ID 65.N-0318(A).German-Spanish Astronomical Center, Calar Alto, operated by theMax-Planck-Institute for Astronomy, Heidelberg, jointly with the SpanishNational Commission for Astronomy.
| Distances to nearby galaxies in Sculptor
We present an analysis of Hubble Space Telescope/WFPC2 images of ninenearby galaxies in Sculptor. We derive their distances from theluminosity of the tip of the red giant branch stars with a typicalaccuracy of ~ 12%. Their distances are 4.21 Mpc (Sc 22), 4.92 Mpc (DDO226), 3.94 Mpc (NGC 253), 3.40 Mpc (KDG 2), 3.34 Mpc (DDO 6), 3.42 Mpc(ESO 540-030), 4.43 Mpc (ESO 245-05), 4.27 Mpc (UGCA 442), and 3.91 Mpc(NGC 7793). The galaxies are concentrated in several spatially separatedloose groups around NGC 300, NGC 253, and NGC 7793. The Sculptor galaxycomplex together with the CVn I cloud and the Local Group form a 10 Mpcfilament, apparently driven by the free Hubble flow.Based on observations made with the NASA/ESA Hubble Space Telescope. TheSpace Telescope Science Institute is operated by the Association ofUniversities for Research in Astronomy, Inc. under NASA contract NAS5-26555.
| The metallicity-luminosity relationship of dwarf irregular galaxies. II. A new approach
The nature of a possible correlation between metallicity and luminosityfor dwarf irregular galaxies, including those with the highestluminosities, has been explored using simple chemical evolutionarymodels. Our models depend on a set of free parameters in order toinclude infall and outflows of gas and covering a broad variety ofphysical situations. Given a fixed set of parameters, a non-linearcorrelation between the oxygen abundance and the luminosity may beestablished. This would be the case if an effective self-regulatingmechanism between the accretion of mass and the wind energized by thestar formation could lead to the same parameters for all the dwarfirregular galaxies. In the case that these parameters were distributedin a random manner from galaxy to galaxy, a significant scatter in themetallicity-luminosity diagram is expected. Comparing with observations,we show that only variations of the stellar mass-to-light ratio aresufficient to explain the observed scattering and, therefore, the actionof a mechanism of self-regulation cannot be ruled out. The possibleorigin of discrepancies in the metallicity-luminosity correlation foundby different authors is discussed.
| Local galaxy flows within 5 Mpc
We present Hubble Space Telescope/WFPC2 images of sixteen dwarf galaxiesas part of our snapshot survey of nearby galaxy candidates. We derivetheir distances from the luminosity of the tip of the red giant branchstars with a typical accuracy of ~ 12%. The resulting distances are4.26 Mpc (KKH 5), 4.74 Mpc (KK 16), 4.72 Mpc (KK 17), 4.66 Mpc (ESO115-021), 4.43 Mpc (KKH 18), 3.98 Mpc (KK 27), 4.61 Mpc (KKH 34), 4.99Mpc (KK 54), 4.23 Mpc (ESO 490-017), 4.90 Mpc (FG 202), 5.22 Mpc (UGC3755), 5.18 Mpc (UGC 3974), 4.51 Mpc (KK 65), 5.49 Mpc (UGC 4115), 3.78Mpc (NGC 2915), and 5.27 Mpc (NGC 6503). Based on distances and radialvelocities of 156 nearby galaxies, we plot the local velocity-distancerelation, which has a slope of H0 = 73 km s-1Mpc-1 and a radial velocity dispersion of 85 kms-1. When members of the M81 and Cen A groups are removed,and distance errors are taken into account, the radial velocitydispersion drops to sigmav = 41 km s-1. The localHubble flow within 5 Mpc exhibits a significant anisotropy, with twoinfall peculiar velocity regions directed towards the Supergalacticpoles. However, two observed regions of outflow peculiar velocity,situated on the Supergalactic equator, are far away ( ~ 50degr ) fromthe Virgo/anti-Virgo direction, which disagrees with a sphericallysymmetric Virgo-centric flow. About 63% of galaxies within 5 Mpc belongto known compact and loose groups. Apart from them, we found six newprobable groups, consisting entirely of dwarf galaxies.Based on observations made with the NASA/ESA Hubble Space Telescope. TheSpace Telescope Science Institute is operated by the Association ofUniversities for Research in Astronomy, Inc. under NASA contract NAS5-26555.}\fnmsep\thanks{Table 2, and Figs. 1 and 2, are only availablein electronic form at http://www.edpsciences.org
| 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
| The Evolutionary Status of Isolated Dwarf Irregular Galaxies. II. Star Formation Histories and Gas Depletion
The results of UBV and Hα imaging of a large sample of isolateddwarf irregular galaxies are interpreted in the context of compositestellar population models. The observed optical colors are best fittedby composite stellar populations that have had approximately constantstar formation rates for at least 10 Gyr. The galaxies span a range ofcentral surface brightness, from 20.5 to 25.0 mag arcsec-2there is no correlation between surface brightness and star formationhistory. Although the current star formation rates are low, it ispossible to reproduce the observed luminosities without a majorstarburst episode. The derived gas depletion timescales are long,typically ~20 Gyr. These results indicate that dwarf irregular galaxies(dI's) will be able to continue with their slow, but constant, starformation activity for at least another Hubble time. The sample ofisolated dI's is compared with a sample of starbursting dwarf galaxiestaken from the literature. The starbursting dwarf galaxies have manysimilar properties; the main difference between these two types ofgas-rich dwarf galaxies is that the current star formation isconcentrated in the center of the starbursting systems, while it is muchmore distributed in the quiescent dI's. This results in pronounced colorgradients for the starbursting dwarf galaxies, while the majority of thequiescent dwarf irregular galaxies have minor or nonexistent colorgradients. Thus, the combination of low current star formation rates,blue colors, and the lack of significant color gradients indicates thatstar formation percolates slowly across the disks of normal dwarfgalaxies in a quasi-continuous manner.
| 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).
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| The Evolutionary Status of Isolated Dwarf Irregular Galaxies. I. UBV and Hα Imaging Observations
The results of UBV and Hα imaging of a large sample of gas-rich,isolated, dwarf irregular galaxies are presented. The majority of thelow-luminosity systems in this sample have no known neighbors within200-400 kpc and thus are unlikely to have had significant interactionswithin the last several gigayears. The new observations confirm thatdwarf irregular galaxies are blue systems, with median values for thesample of 0.42+/-0.040.05 in B-V and-0.22+/-0.040.07 in U-B. Analysis of the derivedsurface photometry indicates that most of these systems can be wellfitted by single exponential disks and have only minor color gradients.Furthermore, the observed H II regions are distributed sparsely acrossthe optical disk. H II region luminosity functions were constructed forthose systems with a sufficient number of H II regions; the derivedpower-law indices are generally shallow, with a median value of-1.61+/-0.310.24.
| HI properties of nearby galaxies from a volume-limited sample
We consider global HI and optical properties of about three hundrednearby galaxies with V_0 < 500 km s(-1) . The majority of them haveindividual photometric distance estimates. The galaxy sample parametersshow some known and some new correlations implying a meaningful dynamicexplanation: 1) In the whole range of diameters, 1 - 40 Kpc, the galaxystandard diameter and rotational velocity follows a nearly linearTully-Fisher relation, lg A25~(0.99+/-0.06)lg V_m. 2) The HImass-to-luminosity ratio and the HI mass-to-``total" mass (inside thestandard optical diameter) ratio increase systematically from giantgalaxies towards dwarfs, reaching maximum values 5 ;M_ȯ/L_ȯand 3, respectively. 3) For all the Local Volume galaxies their totalmass-to-luminosity ratio lies within a range of [0.2-16]M_ȯ/L_ȯ with a median of 3.0 ;M_ȯ/L_ȯ. TheM25/L ratio decreases slightly from giant towards dwarfgalaxies. 4) The M_HI/L and M25/L ratios for the samplegalaxies correlate with their mean optical surface brightness, which maybe caused by star formation activity in the galaxies. 5) The M_HI/L andM25/L ratios are practically independent of the local massdensity of surrounding galaxies within the range of densities of aboutsix orders of magnitude. 6) For the LV galaxies their HI mass andangular momentum follow a nearly linear relation: lgM_HI~(0.99+/-0.04)lg (V_m* A25), expected for rotatinggaseous disks being near the threshold of gravitational instability,favourable for active star formation. Table in the Appendix is availableonly in electronic form at the CDS via anonymous ftp 130.79.128.5 orhttp//cdsweb.u-strasbg.fr/Abstract.html
| 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.
| CO Emission in Low-Luminosity, H I-rich Galaxies
We present ^12CO 1 --> 0 observations of 11 low-luminosity (M_B >-18), H I-rich dwarf galaxies. Only the three most metal-rich galaxies,with 12 + log (O/H) ~ 8.2, are detected. Very deep CO spectra of sixextremely metal-poor systems [12 + log (O/H) <= 7.5] yield only lowupper limits on the CO surface brightness, I_CO < 0.1 K km s^-1.Three of these six have never before been observed in a CO line, whilethe others now have much more stringent upper limits. For the very lowmetallicity galaxy Leo A, we do not confirm a previously reporteddetection in CO, and the limits are consistent with another recentnondetection. We combine these new observations with data from theliterature to form a sample of dwarf galaxies that all have COobservations and measured oxygen abundances. No known galaxies with 12 +log (O/H) < 7.9 (Z < 0.1 Z_ȯ) have been detected in CO. Mostof the star-forming galaxies with higher [12 + log (O/H) > 8.1]metallicities are detected at similar or higher I_CO surfacebrightnesses. The data are consistent with a strong dependence of theI_CO/M_H_2=X_CO conversion factor on ambient metallicity. The strikinglylow upper limits on some metal-poor galaxies lead us to predict that theconversion factor is nonlinear, increasing sharply below ~1/10 of thesolar metallicity [12 + log (O/H) <= 7.9].
| The Southern Sky Redshift Survey
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| The Z-L relationship of dwarf irregular galaxies. I. First results
{We have revisited the stated relation between the metallicity and theluminosity for nearby dwarf irregular galaxies. A sample based on theabsolute magnitude and the radius of the galaxies as observable criteriawas selected. New and better distance determinations from the literaturewere used and the metallicities were recalculated from publishedspectra. The derived distribution of dwarf galaxies in the Z-L plane isdifferent from the ones previously obtained. A factor which could havebearing on the Z-L relation is the different environment where thegalaxies reside. This was investigated using the selected sample but nofirm conclusion could be drawn and a more elaborate study should be madeusing a larger= sample. The two parameters mostly used for determiningthe metallicity and the luminosity are the oxygen abundance and theabsolute blue magnitude. In this analysis it is suggested that thenitrogen abundance and the near-infrared absolute magnitude should beused instead. These are less affected by the recent star formationhistory of the galaxy.}
| Discovery of Numerous Dwarf Galaxies in the Two Nearest Groups of Galaxies.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1313C&db_key=AST
| The Star Formation Histories of Sculptor Group Dwarf Galaxies. I. Current Star Formation Rates and Oxygen Abundances
We present Hα and [O III] imaging and nebular spectroscopy of H IIregions in Sculptor Group dwarf galaxies. Of the eight galaxies in thesample, only two, E471 -006 and A143, have detected H II regions. The HII region luminosity and size distributions for A143 are consistent withthose seen in other dwarf galaxies. Electron densities, filling factorsand emission measures are similar to those measured in other galaxies atsimilar distances but vary significantly from compact H II regions inthe Magellanic clouds. Oxygen line ratios are used to determine theoxygen abundances and ionization parameters. The oxygen abundances aretypically ~0.1 solar and are consistent with the O/H, M_B_ relation.Comparison of the star formation timescales in Sculptor, M81, and LocalGroups shows that the higher density M81 Group has many more galaxiesforming stars at an above average rate. This is evidence that localgalaxy density can have a measurable effect on current star formation.However, a single O/H, M_B_ relation seems to hold for all environments,so galaxy mass still appears to be the primary factor governing agalaxy's chemical evolution.
| Corrections and additions to the third reference catalogue of bright galaxies
List of corrections and additions to the Third Reference Catalogue ofBright Galaxies (RC3) are given. The corrected version of the catalogue(RC3.9b), dated April 1994, is currently available through the nationaldata centers.
| Global properties of dwarf galaxies. I. Galaxy sample and IRAS infrared flux-densities
We have selected a sample of 278 dwarf galaxies for which at least Bmagnitudes and preferably also optical colour information are available.For those galaxies that have no previously published IRAS fluxes, wehave used the IRAS database to extract fluxes or upper limits tosensitivity levels significantly better than those of the IRAS PointSource Catalog. New IRAS data include 79 galaxies detected in at leastone band, and 66 galaxies with good upper limits. In total, about 60% ofall dwarf galaxies in the sample now have been detected at 60/100μm.
| Global properties of dwarf galaxies II. Colours and luminosities
We have used a previously determined sample of 278 dwarf galaxies formost of which B magnitudes, optical colours, HI fluxes and IRASflux-densities are known, in order to derive luminosities, colours andsurface brightnesses. Dwarf galaxy properties are compared to those of acontrol sample of 228 larger spiral galaxies. The dwarf galaxies have onaverage higher 60/100μm flux ratios and lower 12/25μm flux ratiosthan the spiral galaxies, indicating that the contribution of `cirrus'to the infrared emission from dwarf galaxies is relativelyinsignificant. In the dwarf galaxies, the 60/100μm flux ratioincreases with increasing optical blueness; spiral galaxies show theopposite. Dwarf galaxies with a low optical surface brightness have low100μm/HI ratios, but the converse is not true. Galaxies with high100μm/HI ratios (indicative of high dust-to-gas ratios) also havehigh FIR/B ratios as well as high 60/100μm flux-density ratios.Although this is true for both spiral and dwarf galaxies, at given100μm/HI ratios the dwarf galaxies have both a lower FIR/B ratio anda higher 60/100μm flux-density ratio. This result is of importance inthe interpretation of FIR/B - 60/100μm diagrams in terms of starformation activity.
| Nearby galaxies. I - The catalogue
The data of 289 nearby galaxies have been compiled. The inclusion of agalaxy into the catalog depends on its redshift as in the catalogue ofKraan-Korteweg and Tammann (1979) or on the fact that the objects areknown to be certain or probable members of nearby groups. The galaxiesin the sample form the Local Group with 51 certain and probable membersand several additional groups. One third of the galaxies in the catalog(96 objects) does not seem to belong to any group. The main emphasis isto get a distance-limited sample of galaxies, especially of dwarfobjects.
| Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members
This paper gives a catalog of the groups and associations obtained bymeans of a revised hierarchical algorithm applied to a sample of 4143galaxies with diameters larger than 100 arcsec and redshifts smallerthan 6000 km/s. The 264 groups of galaxies obtained in this way (andwhich contain at least three sample galaxies) are listed, with the looseassociations surrounding them and the individual members of eachaggregate as well; moreover, the location of every entity among 13regions corresponding roughly to superclusters is specified. Finally,1729 galaxies belong to the groups, and 466 to the associations, i.e.,the total fraction of galaxies within the various aggregates amounts to53 percent.
| Comparisons between 21 CM data from Effelsberg and Greenbank
Comparison of 21-cm data from the Effelsberg 100-m and NRAO Greenbank91-m telescopes are used to find the limiting precision for redshiftmeasurement. At SNR levels of 10 or above, the random uncertaintyactually achieved in a single redshift measurement is demonstrated to be0.85 km/s at a bandwidth of 6.25 MHz. Uncertainty in other bands scalesas the square root of the bandwidth relative to 6.25 MHz. Random erroris also found to be independent of which telescope or software is usedas long as the SNR is large. At low SNR the choice of software affectsprecision. Substantial systematic errors are shown to be present in someexisting systems or software, due to errors in specifying the locationof the center frequency. Such errors can easily be eliminated withstandardized intercomparisons.
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
