Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
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.
| Impact of Dark Matter Subhalos on Extended H I Disks of Galaxies: Possible Formation of H I Fine Structures and Stars
Recent observations have discovered star formation activities in theextreme outer regions of disk galaxies. However, it remains unclear whatphysical mechanisms are responsible for triggering star formation insuch low-density gaseous environments of galaxies. In order tounderstand the origin of these outer star-forming regions, wenumerically investigate how the impact of dark matter subhalos orbitinga gas-rich disk galaxy embedded in a massive dark matter halo influencesthe dynamical evolution of the outer H I gas disk of the galaxy. We findthat if the masses of the subhalos (Msb) in a galaxy with anextended H I gas disk are as large as 10-3Mh,where Mh is the total mass of the galaxy's dark halo, localfine structures can be formed in the extended H I disk. We also findthat the gas densities of some apparently filamentary structures canexceed a threshold gas density for star formation and thus be likely tobe converted into new stars in the outer part of the H I disk in somemodels with larger Msb. These results thus imply that theimpact of dark matter subhalos (``dark impact'') can be important forbetter understanding the origin of recent star formation discovered inthe extreme outer regions of disk galaxies. We also suggest thatcharacteristic morphologies of local gaseous structures formed by thedark impact can indirectly prove the existence of dark matter subhalosin galaxies. We discuss the origin of giant H I holes observed in somegas-rich galaxies (e.g., NGC 6822) in the context of the dark impact.
| Massive HI clouds with no optical counterparts as high-density regions of intragroup HI rings and arcs
We present a new scenario in which massive intragroup HI clouds are thehigh-density parts of large HI rings/arcs formed by dynamicalinteraction between galaxy groups and gas-rich, low surface brightness(LSB) galaxies with extended gas discs. Our hydrodynamical simulationsdemonstrate that the group tidal field is very efficient at strippingthe outer HI gas of the disc if the gaseous disc of the LSB galaxyextends 2-5 times further than the stellar disc. We find that a massive,extended `leading stream' orbiting the centre of the group can form outof the stripped outer HI envelope, while the severely shrunken LSBgalaxy, whose stellar disc remains unaffected, continues on its path.The result is a relatively isolated, massive HI cloud with a ring- orarc-like shape, a very inhomogeneous density distribution(NHI~ 1.0 × 1017-1.1 × 1020atomcm-2), and, initially, no stellar content. Only thehigh-density peaks of the simulated intragroup HI ring/arc can bedetected in many current HI observations. These will appear asrelatively isolated `HI islands' near the group centre. We also findthat star formation can occur within the ring/arc, if the total gas masswithin the intragroup ring/arc is very large (~4 × 109Msolar). We discuss these results in terms of existingobservations of intragroup gas (e.g. the Leo Ring and HIPASS J0731-69)and intergalactic HII regions.
| A wide-field HI study of the NGC 1566 group
We report on neutral hydrogen observations of a ~ 5.5 × 5.5deg2 field around the NGC 1566 galaxy group with themultibeam narrow-band system on the 64-m Parkes Telescope. We detected13 HI sources in the field, including two galaxies not previously knownto be members of the group, bringing the total number of confirmedgalaxies in this group to 26. Each of the HI galaxies can be associatedwith an optically catalogued galaxy. No `intergalactic HI clouds' werefound to an HI mass limit of ~3.5 ×108Msolar. We have estimated the expected HIcontent of the late-type galaxies in this group and find that the totaldetected HI is consistent with our expectations. However, while noglobal HI deficiency is inferred for this group, two galaxies exhibitindividual HI deficiencies. Further observations are needed to determinethe gas removal mechanisms in these galaxies.
| The Remnants of Intergalactic Supernovae
Intergalactic Type Ia supernovae (SNe) have been discovered recently inrich galaxy clusters. These SNe are likely the descendants of anintergalactic stellar population, which has been discovered in recentyears through a variety of tracers. We estimate the observationalsignatures of the associated SN remnants (SNRs) in the unusualintracluster medium (ICM) environment. We find that if Type Ia SNe stillhave a circumstellar medium (CSM) at the time of explosion, then theirremnants are visible in the optical for ~102-103yr, with properties similar to young galactic SNRs. In contrast withgalactic SNRs, in which the ejecta from the explosion interacts with theinterstellar medium (ISM), intracluster SNRs become undetectable in theoptical band once their ejecta passes beyond the CSM and enters the hotand tenuous ICM. If Type Ia SNe have a CSM, there should be ~150 youngSNRs in the nearby Virgo Cluster, with an Hα luminosity of~1035 ergs s-1 and an angular size of ~0.1". Weinvestigate the possibility that members of this SNR population may haverecently been detected but incorrectly identified as intergalactic H IIregions. Alternatively, if optical intergalactic SNRs do not exist inVirgo, this will constitute evidence that Type Ia SNe are devoid of aCSM, with implications for progenitor scenarios. Regardless of thepresence of a CSM, about 10 older SNRs per square degree should bedetectable in Virgo in the radio band, with fluxes of order 0.1 mJy at 1GHz. Their angular sizes (~1"), morphologies, and lack of opticalassociation with distant galaxies can distinguish them from the muchmore numerous background population. Their detection would provide anaccurate measurement of the intracluster SN rate. Deep pointedobservations toward the site of SN 1980I, a possibly intergalactic TypeIa event in Virgo, could test for the existence of a CSM by comparisonto our predictions for the early-time development of intergalactic SNRs.
| Nearby early-type galaxies with ionized gas. I. Line-strength indices of the underlying stellar population
With the aim of building a data-set of spectral properties of wellstudied early-type galaxies showing emission lines, we presentintermediate resolution spectra of 50 galaxies in the nearby Universe.The sample, which covers several of the E and S0 morphologicalsub-classes, is biased toward objects that might be expected to haveongoing and recent star formation, at least in small amounts, because ofthe presence of the emission lines. The emission is expected to comefrom the combination of active galactic nuclei and star formationregions within the galaxies. Sample galaxies are located in environmentscorresponding to a broad range of local galaxy densities, althoughpredominantly in low density environments. Our long-slit spectra coverthe 3700-7250 Å wavelength range with a spectral resolution of≈7.6 Å at 5550 Å. The specific aim of this paper, and ourfirst step in the investigation, is to map the underlying galaxy stellarpopulation by measuring, along the slit positioned along the galaxymajor axis, line-strength indices at several, homogeneousgalacto-centric distances. For each object we extracted 7luminosity-weighted apertures (with radii 1.5´´,2.5´´, 10´´, r_e/10, r_e/8, r_e/4 and r_e/2)corrected for the galaxy ellipticity and 4 gradients (0 ≤ r ≤r_e/16, r_e/16 ≤ r ≤ r_e/8, r_e/8 ≤ r ≤ r_e/4 and r_e/4≤ r ≤ r_e/2). For each aperture and gradient we measured 25line-strength indices: 21 of the set defined by the Lick-IDS“standard” system (Trager et al. [CITE], ApJS, 116, 1) and 4introduced by Worthey & Ottaviani ([CITE], ApJS, 111, 377).Line-strength indices have been transformed to the Lick-IDS system.Indices derived then include Hβ, Mg1, Mg2, Mgb, MgFe, Fe5270,Fe5335 commonly used in classic index-index diagrams. The paperintroduces the sample, presents the observations, describes the datareduction procedures, the extraction of apertures and gradients, thedetermination and correction of the line-strength indices, the procedureadopted to transform them into the Lick-IDS System and the proceduresadopted for the emission correction. We finally discuss the comparisonsbetween our dataset and line-strength indices available in theliterature. A significant fraction, about 60%, of galaxies in thepresent sample has one previous measurement in the Lick-IDS system butbasically restricted within the r_e/8 region. Line-strength measuresobtained both from apertures and gradients outside this area and withinthe r_e/8 region, with the present radial mapping, are completely new.Full appendix and Figs. 8 to 13 are only available in electronic form athttp://www.edpsciences.org Full Tables 6, 7, 9 and 10 are only availableat the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/433/497 Based onobservations obtained at the European Southern Observatory, La Silla,Chile (Programs Nr. 60.A-0647 and 61.A-0406).
| Discovery of Intergalactic H II Regions
We have discovered a number of very small isolated H II regions 20-30kpc from their nearest galaxy. The H II regions appear as tiny emissionline dots (ELdots) in narrow band images obtained by the NOAO Survey forIonization in Neutral Gas Galaxies (SINGG). We have spectroscopicconfirmation of 5 isolated H II regions in 3 systems. The Hαluminosities of the H II regions are equivalent to the ionizing flux ofonly 1 large or a few small OB stars each. These stars appear to haveformed in situ and represent atypical star formation in the low densityenvironment of galaxy outskirts. In situ star formation in theintergalactic medium offers an alternative to galactic wind models toexplain metal enrichment. In interacting systems (2 out of 3), isolatedH II regions could be a starting point for tidal dwarf galaxies.
| Recycling of Ghost Galaxies: the Origin of giant HI Ring around NGC 1533
We propose that the giant HI ring recently discovered by HIPASS for S0galaxy NGC 1533 is formed by unequal-mass merging between gas-rich LSB(low surface brightness: ``ghost'') galaxies and HSB disks. The NGC 1533progenitor HSB spiral is transformed into a barred S0 during merging andthe outer HI gas disk of the LSB is transformed into the giant HI ring.We also discuss two different possibilities for the origin of isolatedstar-forming regions (``ELdot'' objects) in the giant gas ring.
| HI Tidal Tails, Bridges and Clouds
There is plenty of intergalactic H I gas without any obvious stellarcontent ranging from (1) extended gas envelopes around some normal andpeculiar galaxies, (2) tidal tails/bridges in interacting or merginggalaxy systems, (3) large-scale rings around early type galaxies, and(4) detached clouds at varying distances from associated galaxies, butthere are few or no isolated H I clouds.The HIPASS Bright Galaxy Catalog, which covers the whole southern sky,contains only one definite extragalactic H I cloud which is locatedclose to the galaxy NGC 2442 whereas it is sensitive to isolated H Iclouds with MHI > 106 × D2Mȯ. The space density of H I clouds is therefore about1/1000th that of galaxies with the same MHI.
| Intergalactic H II Regions Discovered in SINGG
A number of very small isolated H II regions have been discovered atprojected distances up to 30 kpc from their nearest galaxy. These H IIregions appear as tiny emission-line objects in narrowband imagesobtained by the NOAO Survey for Ionization in Neutral Gas Galaxies(SINGG). We present spectroscopic confirmation of four isolated H IIregions in two systems; both systems have tidal H I features. Theresults are consistent with stars forming in interactive debris as aresult of cloud-cloud collisions. The Hα luminosities of theisolated H II regions are equivalent to the ionizing flux of only a fewO stars each. They are most likely ionized by stars formed in situ andrepresent atypical star formation in the low-density environment of theouter parts of galaxies. A small but finite intergalactic star formationrate will enrich and ionize the surrounding medium. In one system, NGC1533, we calculate a star formation rate of 1.5×10-3Msolar yr-1, resulting in a metal enrichment of~1×10-3 solar for the continuous formation of stars.Such systems may have been more common in the past and a similarenrichment level is measured for the ``metallicity floor'' in dampedLyα absorption systems.
| 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.
| Redshift-Distance Survey of Early-Type Galaxies. I. The ENEARc Cluster Sample
This paper presents data on the ENEARc subsample of the larger ENEARsurvey of nearby early-type galaxies. The ENEARc galaxies belong toclusters and were specifically chosen to be used for the construction ofa Dn-σ template. The ENEARc sample includes newmeasurements of spectroscopic and photometric parameters (redshift,velocity dispersion, line index Mg2, and the angular diameterdn), as well as data from the literature. New spectroscopicdata are given for 229 cluster early-type galaxies, and new photometryis presented for 348 objects. Repeat and overlap observations withexternal data sets are used to construct a final merged catalogconsisting of 640 early-type galaxies in 28 clusters. Objectivecriteria, based on catalogs of groups of galaxies derived from completeredshift surveys of the nearby universe, are used to assign galaxies toclusters. In a companion paper, these data are used to construct thetemplate Dn-σ distance relation for early-typegalaxies, which has been used to estimate galaxy distances and derivepeculiar velocities for the ENEAR all-sky sample. Based on observationsat Complejo Astronomico El Leoncito, operated under agreement betweenthe Consejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; Cerro Tololo Inter-American Observatory,National Optical Astronomical Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation; the EuropeanSouthern Observatory (ESO), partially under the ESO-ON agreement; theFred Lawrence Whipple Observatory; the Observatório do Pico dosDias, operated by the Laboratório Nacional de Astrofísicaand the MDM Observatory at Kitt Peak.
| The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances
We report data for I-band surface brightness fluctuation (SBF)magnitudes, (V-I) colors, and distance moduli for 300 galaxies. Thesurvey contains E, S0, and early-type spiral galaxies in the proportionsof 49:42:9 and is essentially complete for E galaxies to Hubblevelocities of 2000 km s-1, with a substantial sampling of Egalaxies out to 4000 km s-1. The median error in distancemodulus is 0.22 mag. We also present two new results from the survey.(1) We compare the mean peculiar flow velocity (bulk flow) implied byour distances with predictions of typical cold dark matter transferfunctions as a function of scale, and we find very good agreement withcold, dark matter cosmologies if the transfer function scale parameterΓ and the power spectrum normalization σ8 arerelated by σ8Γ-0.5~2+/-0.5. Deriveddirectly from velocities, this result is independent of the distributionof galaxies or models for biasing. This modest bulk flow contradictsreports of large-scale, large-amplitude flows in the ~200 Mpc diametervolume surrounding our survey volume. (2) We present adistance-independent measure of absolute galaxy luminosity, N and showhow it correlates with galaxy properties such as color and velocitydispersion, demonstrating its utility for measuring galaxy distancesthrough large and unknown extinction. Observations in part from theMichigan-Dartmouth-MIT (MDM) Observatory.
| The Dwarf Galaxy Population of the Dorado Group Down to MV~-11
We present V and I CCD photometry of suspected low surface brightnessdwarf galaxies detected in a survey covering ~2.4 deg2 aroundthe central region of the Dorado group of galaxies. The low surfacebrightness galaxies were chosen based on their sizes and magnitudes atthe limiting isophote of 26 Vμ. The selected galaxies have magnitudesbrighter than V~20 (MV~-11 for an assumed distance to thegroup of 17.2 Mpc), with central surface brightnessesμ0>22.5 V mag arcsec-2, scale lengths h>2", anddiameters >=14" at the limiting isophote. Using these criteria, weidentified 69 dwarf galaxy candidates. Four of them are large very lowsurface brightness galaxies that were detected on a smoothed image,after masking high surface brightness objects. Monte Carlo simulationsperformed to estimate completeness, photometric uncertainties and toevaluate our ability to detect extended low surface brightness galaxiesshow that the completeness fraction is, on average, >80% for dwarfgalaxies with -17=14"). The V-I colors of the dwarfcandidates vary from -0.3 to 2.3 with a peak on V-I=0.98, suggesting arange of different stellar populations in these galaxies. The projectedsurface density of the dwarf galaxies shows a concentration toward thegroup center similar in extent to that found around five X-ray groupsand the elliptical galaxy NGC 1132 studied by Mulchaey & Zabludoff,suggesting that the dwarf galaxies in Dorado are probably physicallyassociated with the overall potential well of the group. Based on thedata collected at the Cerro Tololo Inter-American Observatory (CTIO) andLas Campanas Observatory, Chile.
| 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.
| Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
| A catalogue of Mg_2 indices of galaxies and globular clusters
We present a catalogue of published absorption-line Mg_2 indices ofgalaxies and globular clusters. The catalogue is maintained up-to-datein the HYPERCAT database. The measurements are listed together with thereferences to the articles where the data were published. A codeddescription of the observations is provided. The catalogue gathers 3541measurements for 1491 objects (galaxies or globular clusters) from 55datasets. Compiled raw data for 1060 galaxies are zero-point correctedand transformed to a homogeneous system. Tables 1, 3, and 4 areavailable in electronic form only at the CDS, Strasbourg, via anonymousftp 130.79.128.5. Table 2 is available both in text and electronic form.
| 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.
| Stellar populations of cluster E and S0 galaxies
Spectral line index data for a sample of 290 E and S0 galaxies are usedto investigate the stellar populations of these galaxies. 250 of thegalaxies are members of 11 nearby clusters (cz_CMB<11500 km s^-1). Westudy how the stellar populations of the galaxies are related to thevelocity dispersions, the masses of the galaxies, and the clusterenvironment. This is done by establishing relations between theseparameters and the line indices Mg_2, and Hβ_G. Thedifference between the slope of the Mg_2-sigma relation and the slope ofthe -sigma relation indicates that the abundance ratio [Mg/Fe]is 0.3-0.4 dex higher for galaxies with velocity dispersions of 250 kms^-1 compared to galaxies with velocity dispersions of 100 km s^-1. Thisis in agreement with previous estimates by Worthey et al. The index is more strongly correlated with the projected cluster surfacedensity, rho_cluster, than with the galactic mass or the velocitydispersion. Earlier we found that the residuals for the Mg_2-sigmarelation depend on the cluster environment. Here we determine how boththe Mg_2 index and the index depend on the velocitydispersion and rho_cluster. Alternative explanations that could create aspurious environment dependence are discussed. No obvious alternativesare found. The environment dependence of the Mg_2-sigma relation issupported by data from Faber et al. The dependence on the environmentimplies that [Mg/Fe] decreases with increasing density, rho_cluster. Thedecrease in [Mg/Fe] is 0.1 dex over 2.5 dex in rho_cluster. We have alsostudied the extent to which the mass-to-light (M/L) ratios of thegalaxies are determined by the stellar populations. The M/L ratios arestrongly correlated with the indices Mg_2 and Hβ_G, while the index is only weakly correlated with the M/L ratio. Based oncurrent stellar population models, we find that it is not yet possibleto derive unique physical parameters (mean age, mean abundances, meanIMF, and fraction of dark matter) from the observables (line indices,velocity dispersion, mass, M/L ratio).
| An Einstein X-Ray Survey of Optically Selected Galaxies. I. Data
We present the results of a complete Einstein imaging proportionalcounter X-ray survey of optically selected galaxies from theShapley-Ames Catalog, the Uppsala General Catalogue, and the EuropeanSouthern Observatory Catalog. Well-defined optical criteria are used toselect the galaxies, and X-ray fluxes are measured at the opticallydefined positions. The result is a comprehensive list of X-ray detectionand upper limit measurements for 1018 galaxies. Of these, 827 haveeither independent distance estimates or radial velocities. Associatedoptical, redshift, and distance data have been assembled for thesegalaxies, and their distances come from a combination of directlypredicted distances and those predicted from the Faber-Burstein GreatAttractor/Virgocentric infall model. The accuracy of the X-ray fluxeshas been checked in three different ways; all are consistent with thederived X-ray fluxes being of <=0.1 dex accuracy. In particular,there is agreement with previously published X-ray fluxes for galaxiesin common with a 1991 study by Roberts et al. and a 1992 study byFabbiano et al. The data presented here will be used in further studiesto characterize the X-ray output of galaxies of various morphologicaltypes and thus to enable the determination of the major sourcescontributing to the X-ray emission from galaxies.
| The APM Bright Galaxy Catalogue
The APM Bright Galaxy Catalogue lists positions, magnitudes, shapes andmorphological types for 14681 galaxies brighter than b_J magnitude16.44, over a 4180 deg^2 area of the southern sky. Galaxy and stellarimages have been located from glass copy plates of the United KingdomSchmidt Telescope (UKST) IIIaJ sky survey using the automatedphotographic measuring (APM) facility in Cambridge, England. Themajority of stellar images are rejected by the regularity of their imagesurface brightness profiles. Remaining images are inspected by eye onfilm copies of the survey material and classed as stellar, multiplestellar, galaxy, merger or noise. Galaxies are further classified aselliptical, lenticular, spiral, irregular or uncertain. The 180 surveyfields are put on to a uniform photometric system by comparing themagnitudes of galaxies in the overlap regions between neighbouringplates. The magnitude zero-point, photometric uniformity andphotographic saturation are checked with CCD photometry. Finally, thecompleteness and reliability of the catalogue are assessed by usingvarious internal tests and by comparison with several independentlyconstructed galaxy catalogues.
| Ultraviolet properties of early-type galaxies.
We analyse the UV properties of early-type galaxies from their UVspectra in the IUE library, including both normal and active nuclei. Weco-added the spectra, and hence the objects into groups of similarspectral properties in the UV, also taking into account their propertiesin the visible/near-infrared ranges. Although, owing to the presence ofa residual fixed pattern noise, IUE data cannot be improved byco-addition as expected for spectra containing only random noise, thisprocedure still provided spectra of higher signal/noise ratio than inprevious studies, often based on individual spectra and therefromderived colour indices. Thanks to the co-adding procedure, informationon spectral features can now be assessed. The red stellar populationgroups exhibit a far-UV flux at different levels. The higher ones denotethe presence of the UV turnup, which possibly exhibits absorptionfeatures, at least as detected through the IUE aperture. As to the bluestellar population groups and/or AGNs, we have carried out simplesyntheses with UV star cluster templates and galaxy spectra in order toinfer the properties such as burst ages and contamination by an activenucleus. It has been possible to derive information on the extinctionlaw affecting some internally reddened galaxies; there are cases wherethe presence of the λ2200 A absorption feature suggests areddening law similar to the Galactic one, and others without theλ2200A feature, suggesting that it is rather an SMC type lawwhich applies, then.
| Spectroscopy for E and S0 galaxies in nine clusters
Central velocity dispersions, Mg_2 line indices and radial velocitiesfor 220 E and S0 galaxies are derived on the basis of intermediateresolution spectroscopy. Galaxies in the following clusters have beenobserved: Abell 194, Abell 539, Abell 3381, Abell 3574, S639, S753,Doradus, HydraI (Abell 1060) and Grm 15. For 151 of the galaxies, thevelocity dispersion has not previously been measured. 134 of the Mg_2determinations are for galaxies with no previous measurement. Thespectra cover either 500 or 1000A, centred on the magnesium triplet at5177A. The observations were obtained with the Boller & Chivensspectrograph at the ESO 1.5-m telescope and with the OPTOPUS, amulti-object fibre-fed B&C spectrograph, at the ESO 3.6-m telescope.The data are part of our ongoing study of the large-scale motions in theUniverse and the physical background for the Fundamental Plane. TheFourier fitting method was used to derive the velocity dispersions andradial velocities. The velocity dispersions have been corrected for theeffect of the size of the aperture. The correction was established onthe basis of velocity dispersion profiles available in the literature. Acomparison with results from Davies et al. shows that the derivedcentral velocity dispersions have an rms error of 0.036 in logsigma.There is no offset relative to the velocity dispersions from Davies etal. The offset relative to data from Lucey & Carter is-0.017+/-0.011 in logsigma, with our velocity dispersions being thesmallest. The velocity dispersions derived from the B&C and theOPTOPUS observations, as well as the velocity dispersions published byDavies et al., Dressler, Lucey & Carter and Lucey et al., can bebrought on a system consistent within 3 per cent. The Mg_2 line indiceshave been corrected for the size of the apertures, transformed to theLick system, and corrected for the effect of the velocity dispersion.From comparison with data from Davies et al. and from Faber, we findthat the rms error of Mg_2 is 0.013. Comparisons of the radialvelocities with data from the literature show that our determinationsare accurate to within ~=35 km s^-1. The accuracies reached for theseobservations are adequate for the study of the large-scale motions inthe Universe and for investigations of the Fundamental Plane.
| Multicolour CCD surface photometry for E and S0 galaxies in 10 clusters
CCD surface photometry for 232 E and S0 galaxies is presented. Thegalaxies are observed in Gunn r and Johnson B, or Gunn r and g. For 48of the galaxies surface photometry in Johnson U is also presented.Aperture magnitudes in Gunn nu are derived for half of the galaxies.Galaxies in the following clusters have been observed: Abell 194, Abell539, Abell 3381, Abell 3574, Abell S639, Abell S753, HydraI (Abell1060), DC2345-28, Doradus and Grm15. The data are part of our ongoingstudy of the large-scale motions in the Universe and the physicalbackground for the fundamental plane. We use a full model fittingtechnique for analysing the CCD images. This gives radial profiles oflocal surface brightness, colour, ellipticity and position angle. Theresiduals relative to the elliptical isophotes are describedquantitatively by Fourier expansions. Effective radius, mean surfacebrightness and total magnitude are derived by fitting a de Vaucouleursr^¼ growth curve. We have derived a characteristic radius r_nsimilar to the diameter D_n introduced by Dressler et al. The derivationof the effective parameters and of r_n takes the seeing into account. Weconfirm the results by Saglia et al. that the effects of the seeing canbe substantial. Seeing-corrected values of the effective parameters andr_n are also presented for 147 E and S0 galaxies in the Coma cluster.Colours, colour gradients and geometrical parameters are derived. Thephotometry is internally consistent within 0.016 mag. Comparison withthe photoelectric aperture photometry from Burstein et al. shows a meanoffset of 0.010 mag with an rms scatter of 0.034 mag. The globalphotometric parameters are compared with data from Faber et al., Luceyet al. and Lucey & Carter. These comparisons imply that the typicalrms errors are as follows - log r_n:+/-0.015 log r_e:+/-0.045m_T:+/-0.09 mag; _e:+/-0.16 mag. The rms error on thecombination log r_e-0.35_e which enters the fundamental planeis +/-0.020. Also, comparisons with data from Saglia et al. arepresented. The accuracy of the absolute photometry, as well as thederived parameters, makes the data suitable for our investigations ofthe fundamental plane and of the large-scale motions in the Universe.
| The Catalog of Southern Ringed Galaxies
The Catalog of Southern Ringed Galaxies (CSRG) is a comprehensivecompilation of diameters, axis ratios, relative bar position angles, andmorphologies of inner and outer rings, pseudorings, and lenses in 3692galaxies south of declination -17 deg. The purpose of the catalog is toevaluate the idea that these ring phenomena are related to orbitalresonances with a bar or oval in galaxy potentials. The catalog is basedon visual inspection of most of the 606 fields of the Science ResearchCouncil (SRC) IIIa-J southern sky survey, with the ESO-B, ESO-R, andPalomar Sky surveys used as auxiliaries when needed for overexposed coreregions. The catalog is most complete for SRC fields 1-303 (mostly southof declination -42 deg). In addition to ringed galaxies, a list of 859mostly nonringed galaxies intended for comparison with other catalogs isprovided. Other findings from the CSRG that are not based on statisticsare the identification of intrinsic bar/ring misalignment; bars whichunderfill inner rings; dimpling of R'1pseudorings; pointy, rectangular, or hexagonal inner or outer ringshapes; a peculiar polar-ring-related system; and other extreme examplesof spiral structure and ring morphology.
| Total and effective colors of 501 galaxies in the Cousins VRI photometric system
Total color indices (V-R)T, (V-I)T and effectivecolor indices (V-R)e, (V-I)e in the Cousins VRIphotometric system are presented for 501 mostly normal galaxies. Thecolors are computed using a procedure outlined in the Third ReferenceCatalogue of Bright Galaxies (RC3) whereby standard color curvesapproximated by Laplace-Gauss integrals are fitted to observedphotoelectric multiaperture photometry. 11 sources of such photometrywere used for our analysis, each source being assigned an appropriateweight according to a rigorous analysis of residuals of the data fromthe best-fitting standard color curves. Together with the integrated B-Vand U-B colors provided in RC3, our analysis widens the range ofwavelength of homogeneously defined colors of normal galaxies of allHubble types. We present color-color and color-type relations that canbe modeled to understand the star formation history of galaxies.
| 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.
| Photometrically distinct nuclei in elliptical and early-type disks galaxies.
Not Available
| S0's and the lower limit of star-formation rates in disk galaxies
As an extension of our study of star formation and H II regions in Sagalaxies, we have observed eight disk galaxies classified S0-S0/Sa. Wehave detected discrete H II regions in three of these, all classifiedS0/Sa because their faint star-forming regions are visible on broadbandimages. Each of these galaxies has about 15 H II regions, with a totalluminosity in H-alpha between L = 1038.3 and1037.7 ergs/s. The star-formation rate in these galaxiesimplied by the H-alpha luminosity is less than 0.004 solar mass/yr, ascomparted to greater than 0.1 solar mass/yr in Sa galaxies. We concludethat normal star formation in disk galaxies can occur in exceedinglysmall amounts.
| The dependence of the cool matter content on galaxy morphology in galaxies of types E/S0, S0, and SA
Using the material assembled in earlier papers, we examine the manner inwhich the interstellar matter content varies along the Hubble sequencefrom S0 galaxies to Sa galaxies selected from the RSA2 compilation. Forthis we make use of a new and more detailed classification which isdescribed here as applied to these early disk/spiral galaxies. Theprominence of the disk in S0's and the visibility of features (H IIregions) in the Sa's serve as the basis for the subtypes. Three S0categories: subtle, intermediate, and pronounced, and four Sadescriptors: very early, early, intermediate, and late are assigned tothe galaxies. It is found that the total amount of hydrogen (H I + H2)is a function of subtype, being low in the S0's and rising smoothly fromthe early Sa's to the later Sa's. The average surface density ofhydrogen exceeds 3 solar masses/pc-squared only in the latest subtypesof the Sa's. We conclude that the prominence of the disk of a galaxyclosely follows the amount of cool gas which the disk contains.
|
Enviar un nuevo artículo
Enlaces relacionados
- - No se han encontrado enlaces -
En viar un nuevo enlace
Miembro de los siguientes grupos:
|
Datos observacionales y astrométricos
Catálogos y designaciones:
|
