Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
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.
| Oxygen and Nitrogen in Leo A and GR 8
We present elemental abundances for multiple H II regions in Leo A andGR 8 obtained from long-slit optical spectroscopy of these two nearbylow-luminosity dwarf irregular galaxies. As expected from theirluminosities, and in agreement with previous observations, the derivedoxygen abundances are extremely low in both galaxies. Highsignal-to-noise ratio (S/N) observations of a planetary nebula in Leo Ayield 12+log(O/H)=7.30+/-0.05 semiempirical calculations of the oxygenabundance in four H II regions in Leo A indicate12+log(O/H)=7.38+/-0.10. These results confirm that Leo A has one of thelowest ISM metal abundances of known nearby galaxies. Based on resultsfrom two H II regions with high S/N measurements of the weak [O III]λ4363 line, the mean oxygen abundance of GR 8 is12+log(O/H)=7.65+/-0.06 using ``empirical'' and ``semiempirical''methods, similar abundances are derived for six other GR 8 H II regions.Similar to previous results in other low-metallicity galaxies, the meanlog(N/O)=-1.53+/-0.09 for Leo A and -1.51+/-0.07 for GR 8. There is noevidence of significant variations in either O/H or N/O in the H IIregions. The metallicity-luminosity relation for nearby (D<5 Mpc)dwarf irregular galaxies with measured oxygen abundances has a meancorrelation of 12+log(O/H)=5.67MB-0.151MB, with adispersion in oxygen about the relationship of σ=0.21. Theseobservations confirm that gas-rich, low-luminosity galaxies haveextremely low elemental abundances in the ionized gas phase of theirinterstellar media. Although Leo A has one of the lowest metalabundances of known nearby galaxies, detection of tracers of an olderstellar population (RR Lyrae variable stars, horizontal branch stars,and a well-populated red giant branch) indicate that it is not a newlyformed galaxy, as has been proposed for some other similarlow-metallicity star-forming galaxies.
| The K Luminosity-Metallicity Relation for Dwarf Galaxies and the Tidal Dwarf Galaxies in the Tails of HCG 31
We determine a K-band luminosity-metallicity (L-Z) relation for dwarfirregular galaxies over a large range of magnitudes,-20.5
| Infrared Properties of Star-forming Dwarf Galaxies. I. Dwarf Irregular Galaxies in the Local Volume
A sample of 34 dwarf irregular galaxies (dIs) in the Local Volume, mostnearer than 5 Mpc, has been imaged in the near-infrared (NIR) in J andKs at the Canada-France-Hawaii Telescope (CFHT) in Hawaii andthe Observatorio Astronómico Nacional in the Sierra San PedroMártir, in Mexico. Absolute magnitudes in Ks rangefrom -14 to -18. In the CFHT images, stars brighter thanMKs~-7.5 were resolved. We show that the resolvedcomponent comprises more than 50% of the light from star formationbursts within the last 3 Gyr. In most cases, the resolved populationdown to MKs=-7.5 represents less than 5% of thetotal NIR flux in Ks, with fractions in J being 1.5-2 timeslarger. Thus, the NIR light of dIs can be considered to be predominantlycontributed by stars older than about 4 Gyr. Although exponential atlarge radii, surface brightness profiles for the unresolved componentflatten in the centers. They can be fitted across the whole range ofradii with a hyperbolic secant (sech) defined as a function of twoparameters: the central surface brightness and the scale length of theexponential. With respect to this model, only two galaxies (NGC 1569 andNGC 3738) show an excess of flux in the center, both of which arehosting starbursts. Isophotal, total, and fitted sech magnitudes havebeen calculated for all galaxies for which the unresolved component wasdetected, along with semimajor axes at μJ=23 magarcsec-2 and μKs=22 magarcsec-2. The scale length and the semimajor axes correlatelinearly with absolute isophotal magnitude. The same is true for colorsand the central brightness. More luminous dIs tend to be larger, redder,and brighter in the center. The fraction of light contributed by youngstars is independent of both luminosity and central surface brightness.The Tully-Fisher relation shows considerable scatter, but residuals aretied to surface brightness. The galaxies appear to lie in a``fundamental plane'' defined by the sech absolute magnitude, the sechcentral surface brightness, and the H I line width. The rms of residualsin MK is only 0.4 mag, which implies that the plane can beused to evaluate the distances of star-forming dwarfs. Corrections fortilt do not reduce the residuals, so line widths must be governedpredominantly by random motions. Color-magnitude diagrams (CMDs) arepresented for 29 galaxies in which stars were resolved. Most show afinger centered around J-Ks=1 mag. In some cases, there is ared tail extending to J-Ks=2.5 mag. Most color profilesconstructed for the unresolved component show a remarkably constantJ-Ks=0.8-1.0 mag, matching the color of the finger in theCMDs.Based on observations obtained at the Canada-France-Hawaii Telescope,which is operated by the National Research Council of Canada, the CentreNational de la Recherche Scientifique de France, and the University ofHawaii; also based on data acquired at OAN-SPM in Mexico.
| 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.
| 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.
| The column density distribution function at z= 0 from HI selected galaxies
We have measured the column density distribution function, f(NHI), at z= 0 using 21-cm HI emission from galaxies selected from ablind HI survey. f(NH I) is found to be smaller and flatterat z= 0 than indicated by high-redshift measurements of damped Lymanα (DLA) systems, consistent with the predictions of hierarchicalgalaxy formation. The derived DLA number density per unit redshift,dNDLA/dz= 0.058, is in moderate agreement with valuescalculated from low-redshift QSO absorption line studies. We use twodifferent methods to determine the types of galaxies which contributemost to the DLA cross-section: comparing the power-law slope off(NH I) to theoretical predictions and analysingcontributions to dNDLA/dz. We find that comparison of thepower-law slope cannot rule out spiral discs as the dominant galaxy typeresponsible for DLA systems. Analysis of dNDLA/dz however, ismuch more discriminating. We find that galaxies with log MHI< 9.0 make up 34 per cent of dNDLA/dz Irregular andMagellanic types contribute 25 per cent; galaxies with surfacebrightness account for 22 per cent and sub-L* galaxiescontribute 45 per cent to dNDLA/dz. We conclude that a largerange of galaxy types give rise to DLA systems, not just large spiralgalaxies as previously speculated.
| FLASH redshift survey - I. Observations and catalogue
The FLAIR Shapley-Hydra (FLASH) redshift survey catalogue consists of4613 galaxies brighter than bJ= 16.7 (corrected for Galacticextinction) over a 700-deg2 region of sky in the generaldirection of the Local Group motion. The survey region is a70°× 10° strip spanning the sky from the ShapleySupercluster to the Hydra cluster, and contains 3141 galaxies withmeasured redshifts. Designed to explore the effect of the galaxyconcentrations in this direction (in particular the Supergalactic planeand the Shapley Supercluster) upon the Local Group motion, the 68 percent completeness allows us to sample the large-scale structure betterthan similar sparsely-sampled surveys. The survey region does notoverlap with the areas covered by ongoing wide-angle (Sloan or 2dF)complete redshift surveys. In this paper, the first in a series, wedescribe the observation and data reduction procedures, the analysis forthe redshift errors and survey completeness, and present the surveydata.
| Nebular abundances of nearby southern dwarf galaxies
The results of optical spectroscopy of H II regions in a sample ofsouthern dwarf irregulars consisting of five dwarf galaxies in theCentaurus A group, four dwarfs in the Sculptor group, and eightadditional dwarf galaxies are presented. Oxygen abundances are derivedusing the direct method where [O III]lambda 4363 is detected;otherwise, abundances are derived with the bright-line method using theMcGaugh and the Pilyugin calibrations. ESO358-G060 has the lowest oxygenabundance (12+log(O/H) = 7.32) in the sample, which is comparable to thevalue for the second most metal-poor galaxy known (SBS 0335-052). Inall, new oxygen abundances are reported for nine dwarf galaxies; updatedvalues are presented for the remaining galaxies. Derived oxygenabundances are in the range from 3% to 26% of the solar value. Oxygenabundances for dwarfs in the southern sample are consistent with themetallicity-luminosity relationship defined by a control sample of dwarfirregulars with [O III]lambda 4363 abundances and well-measureddistances. However, NGC 5264 appears to have an (upper branch) oxygenabundance approximately two to three times higher than other dwarfs atsimilar luminosities. Nitrogen-to-oxygen and neon-to-oxygen abundanceratios are also reported; in particular, IC 1613 and IC 5152 showelevated nitrogen-to-oxygen ratios for their oxygen abundances.
| 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
| Astrophysics in 2001
During the year, astronomers provided explanations for solar topicsranging from the multiple personality disorder of neutrinos tocannibalism of CMEs (coronal mass ejections) and extra-solar topicsincluding quivering stars, out-of-phase gaseous media, black holes ofall sizes (too large, too small, and too medium), and the existence ofthe universe. Some of these explanations are probably possibly true,though the authors are not betting large sums on any one. The data oughtto remain true forever, though this requires a careful definition of``data'' (think of the Martian canals).
| 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
| New distances to galaxies in the Centaurus A group
We present Hubble Space Telescope/WFPC2 images of seventeen dwarfgalaxies in the Centaurus A group. Their distances derived from themagnitudes of the tip of the red giant branch are 5.2 Mpc (KK112), 3.2Mpc (ESO 321-014), 3.5 Mpc (KK179), 3.4 Mpc (NGC 5102), 4.6 Mpc (KK200),3.7 Mpc (ESO 324-024), 4.7 Mpc (KK208), 4.6 Mpc (ESO 444-084), 4.4 Mpc(IC 4316), 4.5 Mpc (NGC 5264), 3.6 Mpc (KK211), 3.6 Mpc (KK213), 3.4 Mpc(ESO 325-011), 3.8 Mpc (KK217), 4.0 Mpc (KK221), 4.8 Mpc (NGC 5408), and3.6 Mpc (PGC 51659). The galaxies are concentrated in two spatiallyseparated groups around NGC 5128 = Cen A and NGC 5236 = M 83. The Cen Agroup itself has a mean distance of 3.63+/- 0.07 Mpc, a velocitydispersion of 89 km s-1, a mean projected radius of 263 kpc,an estimated orbital mass of 2.1x 1012 Msun, andan orbital mass-to-blue luminosity ratio of 64Msun/Lsun. For the M 83 group we derived a meandistance of 4.57+/- 0.05 Mpc, a velocity dispersion of 62 kms-1, a mean projected radius of 142 kpc, an estimated orbitalmass of 0.8x 1012 Msun, andMorb/LB = 37 Msun/Lsun. TheM 83 group moves away from the Cen A group, which yields a radius of thezero-velocity surface of the Cen A group of R0 < 1.26 Mpc.The total mass within R0, M0 < 2.7x1012 Msun, agrees with the orbital mass estimate.The centroids of both the groups have very small peculiar velocities,(+18+/- 24) km s-1 (Cen A) and (-17+/-27) km s-1(M 83) with respect to the local Hubble flow with H0 = 70 kms-1 Mpc-1. Based on observations made with theNASA/ESA Hubble Space Telescope. The Space Telescope Science Instituteis operated by the Association of Universities for Research inAstronomy, Inc. under NASA contract NAS 5-26555. Figure 3 is onlyavailable in electronic form at http://www.edpsciences.org
| An H I survey of the Centaurus and Sculptor groups. Constraints on the space density of low mass galaxies
We present results of two 21-cm H I surveys performed with the AustraliaTelescope Compact Array in the nearby Centaurus A and Sculptor galaxygroups. These surveys are sensitive to compact H I clouds and galaxieswith H I masses as low as ~ 3 x 106 Msun, and aretherefore among the most sensitive extragalactic H I surveys to date.The surveys consist of sparsely spaced pointings that sampleapproximately 2% of the groups' area on the sky. We detected previouslyknown group members, but we found no new H I clouds or galaxies down tothe sensitivity limit of the surveys. If the H I mass function had afaint end slope of alpha = 1.5 below Mion {Hi} =107.5 Msun in these groups, we would have expected~ 3 new objects. Cold dark matter theories of galaxy formation predictthe existence of a large number low mass dark matter sub-halos thatmight appear as tiny satellites in galaxy groups. Our results supportand extend similar conclusions derived from previous H I surveys that aH I rich population of these satellites does not exist.
| 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.
| A Comparative Study of Star-forming and Quiescent Dwarf Galaxies
We present the results from a comparative study of the atomic hydrogen(H I) and optical properties of a sample of 16 dwarf galaxies, chosen toinvestigate the effects of star formation on the properties of low-masssystems. The violent star formation bursts believed to occur in theselow-mass systems suggest a possible connection between the activelystar-forming blue compact dwarfs (BCDs), and the quiescent low surfacebrightness dwarfs (LSBDs). It has been suggested that LSBDs, uponundergoing a burst of star formation, will evolve into BCDs and thenback into LSBDs when the star formation slows or stops as the H I columndensity falls below the critical threshold necessary to support it. Wehave examined the location and kinematics of H I in eight BCDs and eightLSBDs of similar H I masses and a range of color indices to investigatethis ``evolutionary'' sequence. The starburst episodes in these low-massgalaxies should lead to (1) a dispersal/depletion of the H I seen in theeight LSB dwarfs and (2) more centrally concentrated and agitated H I inthe eight BCDs. The results of this project indicate that the quiescentLSBD galaxies have more diffuse H I distributions and often show aringlike structure, while the active galaxies have more highly centrallyconcentrated H I reservoirs. The bluer, more recently active systems ofboth types also have higher internal H I velocity dispersions,indicating that energy has been pumped into the interstellar medium ofthese galaxies. These observations are consistent with an evolutionaryscheme wherein the H I reservoirs in these galaxies take on differentcharacteristics depending upon their star formation histories.
| The Mass of the Centaurus A Group of Galaxies
The mass M and the radius Rh of the Centaurus A group areestimated from the positions and radial velocities of 30 probablecluster members. For an assumed distance of 3.9 Mpc, it is found thatRh~640 kpc. The velocity dispersion in the Cen A group is114+/-21 km s-1. From this value and Rh=640 kpc,the virial theorem yields a total mass of 1.4x1013Msolar for the Cen A group. The projected mass method gives amass of 1.8x1013 Msolar. These values suggest thatthe Cen A group is about 7 times as massive as the Local Group. The CenA mass-to-light ratio is found to be M/LB=155-200(M/L)solar. The cluster has a zero-velocity radiusR0=2.3 Mpc.
| New Galaxies Discovered in the First Blind H I Survey of the Centaurus A Group
We have commenced a 21 cm survey of the entire southern sky(δ<0^deg, -1200 km s^-1-13.0), low surface brightness dwarf galaxies with H I profileline-widths suggestive of dynamics dominated by dark matter. The newgroup members add approximately 6% to the H I mass of the group and 4%to its light. The H I mass function, derived from all the known groupgalaxies in the interval 10^7 M_solar
| 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
| 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.
| 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
| HI halos of dwarf galaxies in the Centaurus Group.
Not Available
| The Galaxy Motion Relative to Nearby Galaxies and the Local Velocity Field
We consider a sample of 103 galaxies with radial velocities V_0_ <500 km s^-1^ and distances obtained by means of photometric distanceindicators: Cepheids (n = 17), brightest stars (n = 69), and galaxymembership in the nearby bound groups (n = 17). Ranking the galaxieswith their distance R we determine a running apex for the Sun, theGalaxy, and the Local Group as a function of R. For the solar apex withrespect to the LG galaxies we obtain the parameters: {l_sun_ =93^deg^+/-2^deg^, b_sun_ = -4^deg^+/- 2^deg^, V_sun_ = 316+/-5 kms^-1^}. That corresponds to a Galaxy center apex {l = 107^deg^, b =-18^deg^, v = 90 km s^-1^}, pointing at ~14^deg^ from M31. When theconsidered volume depth increases from 1.0-1.5 Mpc up to 4-8 Mpc, thesolar apex drifts to {l_sun_ = 91^deg^, b_sun_ = 0^deg^, V_sun_ = 334 kms^-1^}, while the LG centroid apex shows a complicate wandering in aregion {l = [40^deg^, 100^deg^], b = [0^deg^, +60^deg^]) with velocityincreasing from 0 up to 40 km s^-1^, The running value for the localHubble parameter, H(R), reaches the maximum (90+/-5) km s^-1^ Mpc^-1^ atR ~ 2 Mpc, and then decreases down to (70-65) km s^-1^ Mpc^- 1^. Whenboth the Hubble component and the apex velocity are removed, theresidual velocity field shows clear signs of anisotropy. Within theLocal Supergalactic plane there is a prevalence of negative peculiarvelocities towards the "+SGY" direction. This feature perhaps has thesame origin as the "Local Velocity Anomaly" (LVA) known to exist over ascale of 10-30 Mpc. Besides the LVA, an excess of negative peculiarvelocities is seen also along the SGZ axis and can be interpreted as ifthe expansion of the local pancake proceeds about 30% slower in thedirection perpendicular to the symmetry plane than in the plane itself.Inside the Local Volume, galaxies possess a peculiar velocity dispersionof (72+/-2) km s^-1^ independent on the assumed volume depth. This valueis almost the same for dwarf and giant galaxies: a behavior which has nosimple explanations. The use of more precise solar apex parameters andthe correction for the local anisotropy improves the use of radialvelocities of nearby galaxies as distance indicators and allows to builda more accurate 3D map of the LV which reveals more "fine grain"structure details than Tully's catalog data.
| The Local Group in comparison with other nearby groups of galaxies.
Ensembles of probable physical companions around nearby massive galaxieswith V_0_<500km/s and M>3x10^11^Msun_ are derived.Recent estimates of distances for galaxies, a new criterion ofmembership, and also special searches for diffuse ("spheroidal") dwarfobjects have been used for this purpose. Under such an approach theMilky Way has thirteen companions, M31 eleven, M81 fifteen, NGC5128 ten,NGC5236 five, and M101 has seven. According to linear dimension(140kpc), radial velocity dispersion (68km/s), and morphological content(62 percent of E+Sph) the Local Group appears a common one among othersystems. Some properties of structure and kinematics of the nearbygroups are noted in relation to the luminosity ratio of their twobrightest members. The dynamical status of the 6 nearby groups can beexplained also without invoking significant amounts of Dark Matterbeyond 2-3 standard radii of the principal galaxies.
| The Peculiar HI Kinematics of the Wolf-Rayet Starburst Galaxy NGC 5253
We report the discovery of a peculiar H I velocity field in the nearbyamorphous dwarf starburst galaxy NGC 5253 which indicates that the bulkof the neutral atomic gas rotates about the galaxy's optical major axis.There is also weak evidence for a second H I dynamical componentrotating about the optical minor axis. We estimate the dynamical mass at3 x 108/sin2 i Mȯ. The gasdynamics in NGC 5253 are vaguelyreminiscent of what is seen in polar ring galaxies and dust laneellipticals, but the large gas mass fraction (~0.6 for i = 50 deg),young starburst population, irregular optical morphology, lack of astellar ring, and lack of stellar rotation (<= 7 km s-1) areinconsistent with either type of object. NGC 5253's unique gasdynamicsand current star formation activity may be either (1) the result of aninteraction with the nearby spiral M83 ~109 yr ago or (2) due to thedisruption and accretion of a gas-rich companion on a highly inclinedorbit. A combination of wide-field, high-sensitivity H I mapping and newoptical spectra measuring the stellar kinematics along the minor axiscould discriminate between these two possible interaction scenarios andconstrain the original, preinteraction nature of NGC 5253. It ispossible that NGC 5253 will later develop into a polar ring galaxy andthat we are observing it during its period of ring formation.
| Integrated photoelectric magnitudes and color indices of bright galaxies in the Johnson UBV system
The photoelectric total magnitudes and color indices published in theThird Reference Catalogue of Bright Galaxies (RC3) are based on ananalysis of approximately equals 26,000 B, 25,000 B-V, and 17,000 U-Bmultiaperture measurements available up to mid 1987 from nearly 350sources. This paper provides the full details of the analysis andestimates of internal and external errors in the parameters. Thederivation of the parameters is based on techniques described by theVaucouleurs & Corwin (1977) whereby photoelectric multiaperture dataare fitted by mean Hubble-type-dependent curves which describe theintegral of the B-band flux and the typical B-V and U-B integrated colorgradients. A sophisticated analysis of the residuals of thesemeasurements from the curves was made to allow for the random andsystematic errors that effect such data. The result is a homogeneous setof total magnitudes BTA total colors(B-V)T and (U-B)T, and effective colors(B-V)e and (U-B)e for more than 3000 brightgalaxies in RC3.
| 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.
| Ultraviolet observations of galaxies with the FAUST experiment
We have used the set of point sources detected by the Far UltravioletSpace Telescope (FAUST) instrument to identify galaxies and study thetotal galaxy flux in a 250 A wide band peaking at 1650 A. A sample of144 galaxies has been obtained after cross-reference with the RC3catalog, elimination of objects confused with stars and variouscorrections for the photometry. The UV-B color dispersion is found toincrease while the galaxies get redder from late to early types. Theirregular galaxies appear on average redder and the Sbc galaxies bluerthan indicated by the spectral energy distributions currently used forthe calculations of K-corrections. Various arguments lead us to make theassumption of a constant dust extinction within each galaxy. The UV fluxper unit area decreases on average from late to early type spirals. Wefind a weak correlation between the UV and far infra-red emission whilethe infra-red to UV flux ratio gets lower when galaxies get bluer (asmeasured by the UV to B flux ratio). The UV flux per unit areacorrelates with the HI gas surface density and the total gas surfacedensity when this quantity is available. The correlation with themolecular gas alone is weak. In the Virgo cluster, the UV flux per unitarea does not decrease in direct proportion to the HI deficiency. Galaxycounts per square degree and per magnitude interval have been obtainedat high-galactic latitudes. Combined with data at fainter magnitudes,they show a variation as a function of magnitude with a near-euclideanslope over a range of 8 magnitudes.
| 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.
| 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.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
Kataloglar ve belirtme:
|
