目录
图像
上传图像
DSS Images Other Images
相关文章
Gemini/GMOS spectra of globular clusters in the Leo group elliptical NGC 3379
The Leo group elliptical NGC 3379 is one of the few normal ellipticalgalaxies close enough to make possible observations of resolved stellarpopulations, deep globular cluster (GC) photometry and highsignal-to-noise ratio GC spectra. We have obtained Gemini/GMOS spectrafor 22 GCs associated with NGC 3379. We derive ages, metallicities andα-element abundance ratios from simple stellar population modelsusing the recent multi-index χ2 minimization method ofProctor & Sansom. All of these GCs are found to be consistent withold ages, i.e. >~10Gyr, with a wide range of metallicities. This iscomparable to the ages and metallicities that Gregg et al. found acouple of years ago for resolved stellar populations in the outerregions of this elliptical. A trend of decreasing α-elementabundance ratio with increasing metallicity is indicated.The projected velocity dispersion of the GC system is consistent withbeing constant with radius. Non-parametric, isotropic models require asignificant increase in the mass-to-light ratio at large radii. Thisresult is in contrast to that of Romanowsky et al., who recently found adecrease in the velocity dispersion profile as determined from planetarynebulae (PN). Our constant dispersion requires a normal-sized dark halo,although without anisotropic models we cannot rigorously determine thedark halo mass.A two-sided χ2 test over all radii gives a 2σdifference between the mass profile derived from our GCs compared to thePN-derived mass model of Romanowsky et al. However, if we restrict ouranalysis to radii beyond one effective radius and test if the GCvelocity dispersion is consistently higher, we determine a > 3σdifference between the mass models, and hence we favour the conclusionthat NGC 3379 does indeed have dark matter at large radii in its halo.
| The Cool ISM in S0 Galaxies. II. A Survey of Atomic Gas
The place of lenticular galaxies within the range of types of galaxiesremains unclear. We previously reported the mass of molecular hydrogenfor a volume-limited sample of lenticular galaxies, where we saw thatthe amount of gas was less than that predicted by the return of stellarmass to the interstellar medium. Here we report observations of atomichydrogen (H I) for the same sample. Detections in several galaxies makemore compelling the case presented in our earlier paper that the mass ofcool gas in S0 galaxies cuts off at ~10% of what is expected fromcurrent models of gas return from stellar evolution. The molecular andatomic phases of the gas in our sample galaxies appear to be separateand distinct, both spatially and in velocity space. We propose that themolecular gas arises mostly from the stellar mass returned to thegalaxy, while the atomic hydrogen is mainly accumulated from externalsources (infall, captured dwarfs, etc.). While this proposal fits mostof the observations, it makes the presence of the upper mass cutoff evenmore mysterious.
| Wide-field kinematics of globular clusters in the Leo I group
We present wide-field spectroscopy of globular clusters around theLeo I group galaxies NGC 3379 andNGC 3384 using the FLAMES multi-fibre instrument atthe VLT. We obtain accurate radial velocities for 42 globular clusters(GCs) in total, 30 for GCs around the elliptical NGC 3379, eight aroundthe lenticular NGC 3384, and four which may be associated with eithergalaxy. These data are notable for their large radial range extendingfrom 0.7 arcmin to 14.6 arcmin (2 to 42 kpc) from the centre of NGC3379, and small velocity uncertainties of about 10 km s-1. Wecombine our sample of 30 radial velocities for globular clusters aroundNGC 3379 with 8 additional GC velocities from the literature, and find aprojected velocity dispersion of σp =175+24-22 km s-1 at R < 5' andσp = 147+44-39 at R > 5'.These velocity dispersions are consistent with a dark matter halo aroundNGC 3379 with a concentration in the range expected from a ΛCDMcosmological model and a total mass of ≈ 6 × 1011~Mȯ. Such a model is also consistent with the stellarvelocity dispersion at small radii and the rotation of the H I ring atlarge radii, and has a (M/L)B that increases by a factor offive from several kpc to 100 kpc. Our velocity dispersion for theglobular cluster system of NGC 3379 is somewhat higher than that foundfor the planetary nebulae (PNe) in the inner region covered by the PNdata, and we discuss possible reasons for this difference. For NGC 3384,we find the GC system has a rotation signature broadly similar to thatseen in other kinematic probes of this SB0 galaxy. This suggests thatsignificant rotation may not be unusual in the GC systems of discgalaxies.
| Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis
X-ray observations have revealed in other galaxies a class ofextranuclear X-ray point sources with X-ray luminosities of1039-1041 ergs s-1, exceeding theEddington luminosity for stellar mass X-ray binaries. Theseultraluminous X-ray sources (ULXs) may be powered by intermediate-massblack holes of a few thousand Msolar or stellar mass blackholes with special radiation processes. In this paper, we present asurvey of ULXs in 313 nearby galaxies withD25>1' within 40 Mpc with 467 ROSAT HighResolution Imager (HRI) archival observations. The HRI observations arereduced with uniform procedures, refined by simulations that help definethe point source detection algorithm employed in this survey. A sampleof 562 extragalactic X-ray point sources withLX=1038-1043 ergs s-1 isextracted from 173 survey galaxies, including 106 ULX candidates withinthe D25 isophotes of 63 galaxies and 110 ULX candidatesbetween 1D25 and 2D25 of 64 galaxies, from which aclean sample of 109 ULXs is constructed to minimize the contaminationfrom foreground or background objects. The strong connection betweenULXs and star formation is confirmed based on the striking preference ofULXs to occur in late-type galaxies, especially in star-forming regionssuch as spiral arms. ULXs are variable on timescales over days to yearsand exhibit a variety of long term variability patterns. Theidentifications of ULXs in the clean sample show some ULXs identified assupernovae (remnants), H II regions/nebulae, or young massive stars instar-forming regions, and a few other ULXs identified as old globularclusters. In a subsequent paper, the statistic properties of the surveywill be studied to calculate the occurrence frequencies and luminosityfunctions for ULXs in different types of galaxies to shed light on thenature of these enigmatic sources.
| Gas and Stars in an H I-Selected Galaxy Sample
We present the results of a J-band study of the H I-selected AreciboDual-Beam Survey and Arecibo Slice Survey galaxy samples using TwoMicron All Sky Survey data. We find that these galaxies span a widerange of stellar and gas properties. However, despite the diversitywithin the samples, we find a very tight correlation between luminosityand size in the J band, similar to that found in a previous paper byRosenberg & Schneider between the H I mass and size. We also findthat the correlation between the baryonic mass and the J-band diameteris even tighter than that between the baryonic mass and the rotationalvelocity.
| A sample of X-ray emitting normal galaxies from the BMW-HRI Catalogue
We obtained a sample of 143 normal galaxies with X-ray luminosity in therange 1038{-}1043 erg s-1 from thecross-correlation of the ROSAT HRI Brera Multi-scale Wavelet (BMW-HRI)Catalogue with the Lyon-Meudon Extragalactic Database (LEDA). We findthat the average X-ray properties of this sample are in good agreementwith those of other samples of galaxies in the literature. We selected acomplete flux limited serendipitous sample of 32 galaxies from which wederived the log N-log S distribution of normal galaxies in the fluxrange 1.1{-} 110 × 10-14 erg cm-2s-1. The resulting distribution is consistent with theEuclidean -1.5 slope. Comparisons with other samples, such as theExtended Medium Sensitivity Survey, the ROSAT All Sky Survey, theXMM-Newton/2dF survey, and the Chandra Deep Field Survey indicate thatthe log N -log S distribution of normal galaxies is consistent with aEuclidean slope over a flux range of about 6 decades.
| Spectro-morphology of galaxies: A multi-wavelength (UV-R) classification method
We present a quantitative method to classify galaxies, based onmulti-wavelength data and constructed from the properties of nearbygalaxies. Our objective is to define an classification method that canbe used for low and high redshift objects. We estimate the concentrationof light (C) at the galaxy center and the 180° rotational asymmetry(A), computed at several wavelengths, from ultraviolet (UV) to I-band.The variation of the indices of concentration and asymmetry with thewavelength reflects the proportion and the distribution of young and oldstellar populations in galaxies. In general C is found to decrease, andA to increase from optical to UV: the patchy appearance of a galaxy inthe UV with no bulge is often very different from its counterpart atoptical wavelengths, with a prominent bulge and a more regular disk. Wequantify the variation of C and A with wavelength. In this way we areable to distinguish five types of galaxies that we callspectro-morphological types: compact, ringed, spiral, irregular andcentral-starburst galaxies, which can be differentiated by thedistribution of their stellar populations. We discuss in detail themorphology of the galaxies of the sample, and describe the morphologicalcharacteristics of each spectro-morphological type. We applyspectro-morphology to three objects at a redshift z1 in the HubbleDeep Field North, which gives encouraging results for applications tolarge samples of high-redshift galaxies. This method of morphologicalclassification could be used to study the evolution of the morphologywith redshift and is expected to put observational constraints onscenarios of galaxy evolution.
| Resolving the Stellar Population of the Standard Elliptical Galaxy NGC 3379
Using the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) onboard the Hubble Space Telescope, we have obtained F110W (~J) and F160W(~H) images of three fields in NGC 3379, a nearby normal giantelliptical galaxy. These images resolve individual red giant stars,yielding the first accurate color-magnitude diagrams for a normalluminous elliptical galaxy. The photometry reaches ~1 mag below the redgiant branch (RGB) tip with errors of <~0.2 mag in F110W-F160W. Astrong break in the luminosity function at F160W=23.68+/-0.06 isidentified as the tip of the red giant branch; comparison withtheoretical isochrones implies a distance of 10.8+/-0.6 Mpc, in goodagreement with a number of previous estimates using various techniques.The mean metallicity is close to solar, but there is an appreciablespread in abundance, from at least as metal-poor as [Fe/H]~-1.5 to ashigh as +0.8. There is a significant population of stars brighter thanthe RGB tip by up to ~1 mag. The observations of each field were splitover two epochs separated by 2-3 months, allowing the identification ofcandidate long-period variables; at least 40% of the stars brighter thanthe RGB tip are variable. Lacking period determinations, the exactnature of these variables remains uncertain, but the bright AGB starsand variables are similar to those found in metal-rich globular clustersand are not luminous enough to imply an intermediate-age population. Allof the evidence points to a stellar population in NGC 3379 that is verysimilar to the bulge of the Milky Way, or an assortment of Galacticglobular clusters covering a large metallicity spread.
| Properties of isolated disk galaxies
We present a new sample of northern isolated galaxies, which are definedby the physical criterion that they were not affected by other galaxiesin their evolution during the last few Gyr. To find them we used thelogarithmic ratio, f, between inner and tidal forces acting upon thecandidate galaxy by a possible perturber. The analysis of thedistribution of the f-values for the galaxies in the Coma cluster leadus to adopt the criterion f ≤ -4.5 for isolated galaxies. Thecandidates were chosen from the CfA catalog of galaxies within thevolume defined by cz ≤5000 km s-1, galactic latitudehigher than 40o and declination ≥-2.5o. Theselection of the sample, based on redshift values (when available),magnitudes and sizes of the candidate galaxies and possible perturberspresent in the same field is discussed. The final list of selectedisolated galaxies includes 203 objects from the initial 1706. The listcontains only truly isolated galaxies in the sense defined, but it is byno means complete, since all the galaxies with possible companions underthe f-criterion but with unknown redshift were discarded. We alsoselected a sample of perturbed galaxies comprised of all the diskgalaxies from the initial list with companions (with known redshift)satisfying f ≥ -2 and \Delta(cz) ≤500 km s-1; a totalof 130 objects. The statistical comparison of both samples showssignificant differences in morphology, sizes, masses, luminosities andcolor indices. Confirming previous results, we found that late spiral,Sc-type galaxies are, in particular, more frequent among isolatedgalaxies, whereas Lenticular galaxies are more abundant among perturbedgalaxies. Isolated systems appear to be smaller, less luminous and bluerthan interacting objects. We also found that bars are twice as frequentamong perturbed galaxies compared to isolated galaxies, in particularfor early Spirals and Lenticulars. The perturbed galaxies have higherLFIR/LB and Mmol/LB ratios,but the atomic gas content is similar for the two samples. The analysisof the luminosity-size and mass-luminosity relations shows similartrends for both families, the main difference being the almost totalabsence of big, bright and massive galaxies among the family of isolatedsystems, together with the almost total absence of small, faint and lowmass galaxies among the perturbed systems. All these aspects indicatethat the evolution induced by interactions with neighbors would proceedfrom late, small, faint and low mass Spirals to earlier, bigger, moreluminous and more massive spiral and lenticular galaxies, producing atthe same time a larger fraction of barred galaxies but preserving thesame relations between global parameters. The properties we found forour sample of isolated galaxies appear similar to those of high redshiftgalaxies, suggesting that the present-day isolated galaxies could bequietly evolved, unused building blocks surviving in low densityenvironments.Tables \ref{t1} and \ref{t2} are only available in electronic form athttp://www.edpsciences.org
| UBRI photometry of globular clusters in the Leo group galaxy NGC 3379
We present wide-area UBRI photometry for globular clusters around theLeo group galaxy NGC 3379. Globular cluster candidates are selected fromtheir B-band magnitudes and their (U-B)o versus(B-I)o colours. A colour-colour selection region was definedfrom photometry of the Milky Way and M31 globular cluster systems. Wedetect 133 globular cluster candidates, which supports previous claimsof a low specific frequency for NGC 3379.The Milky Way and M31 reveal blue and red subpopulations, with(U-B)o and (B-I)o colours indicating meanmetallicities similar to those expected based on previous spectroscopicwork. The stellar population models of Maraston and Brocato et al. areconsistent with both subpopulations being old, and with metallicities of[Fe/H]~-1.5 and -0.6 for the blue and red subpopulations, respectively.The models of Worthey do not reproduce the (U-B)o colours ofthe red (metal-rich) subpopulation for any modelled age.For NGC 3379 we detect a blue subpopulation with similar colours, andpresumably age/metallicity, to that of the Milky Way and M31 globularcluster systems. The red subpopulation is less well defined, perhaps dueto increased photometric errors, but indicates a mean metallicity of[Fe/H]~-0.6.
| Neutral Hydrogen Mapping of Virgo Cluster Blue Compact Dwarf Galaxies
A new installment of neutral hydrogen mappings of blue compact dwarf(BCD) galaxies, as defined by optical morphology, in and near the VirgoCluster is presented. The primary motivation was to search for outlyingclouds of H I as potential interactive triggers of enhanced starformation, and therefore the mapped galaxies were selected for large H Imass, large optical diameter, and large velocity profile width.Approximately half the sample proved to have one or more small, lowcolumn density, star-free companion clouds, either detached or appearingas an appendage in our maps, at a resolution on the order of 4 kpc.Comparison is made with a sample of similarly mapped field BCD galaxiesdrawn from the literature; however, the Virgo Cluster sample of mappedBCDs is still too small for conclusive comparisons to be made. We found,on the one hand, little or no evidence for ram-pressure stripping nor,on the other, for extremely extended low column density H I envelopes.The H I rotation curves in most cases rise approximately linearly andslowly, as far out as we can trace the gas.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| A Search for Active Galactic Nuclei in Sc Galaxies with H II Spectra
We have searched for nuclear radio emission from a statisticallycomplete sample of 40 Sc galaxies within 30 Mpc that are opticallyclassified as star-forming objects, in order to determine whether weakactive galactic nuclei might be present. Only three nuclear radiosources were detected, in NGC 864, NGC 4123, and NGC 4535. Thesegalaxies have peak 6 cm radio powers of ~1020 WHz-1 at arcsecond resolution, while upper limits of thenondetected galaxies typically range from 1018.4 to1020 W Hz-1. The three nuclear radio sources areall resolved and appear to have diffuse morphologies, with linear sizesof ~300 pc. This strongly indicates that circumnuclear star formationhas been detected in these three H II galaxies. Comparisons withprevious 20 cm Very Large Array (VLA) results for the detected galaxiesshow that the extended nuclear radio emission has a flat spectrum in twoobjects and is almost certainly generated by thermal emission from gasionized by young stars in the centers of those galaxies. The 6 cm radiopowers are comparable to predictions for thermal emission that are basedon the nuclear Hα luminosities and imply nuclear star formationrates of 0.08-0.8 Msolar yr-1, while thelow-resolution NRAO VLA Sky Survey implies galaxy-wide star formationrates of 0.3-1.0 Msolar yr-1 in stars above 5Msolar. In a few of the undetected galaxies, the upper limitsto the radio power are lower than predicted from the Hαluminosity, possibly because of overresolution of central star-formingregions. Although the presence of active nuclei powered by massive blackholes cannot be definitively ruled out, the present results suggest thatthey are likely to be rare in these late-type galaxies with H IIspectra.
| Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
| Local velocity field from sosie galaxies. I. The Peebles' model
Pratton et al. (1997) showed that the velocity field around clusterscould generate an apparent distortion that appears as tangentialstructures or radial filaments. In the present paper we determine theparameters of the Peebles' model (1976) describing infall of galaxiesonto clusters with the aim of testing quantitatively the amplitude ofthis distortion. The distances are determined from the concept of sosiegalaxies (Paturel 1984) using 21 calibrators for which the distanceswere recently calculated from two independent Cepheid calibrations. Weuse both B and I-band magnitudes. The Spaenhauer diagram method is usedto correct for the Malmquist bias. We give the equations for theconstruction of this diagram. We analyze the apparent Hubble constant indifferent regions around Virgo and obtain simultaneously the Local Groupinfall and the unperturbed Hubble constant. We found:[VLG-infall = 208 ± 9 km s-1] [\log H =1.82 ± 0.04 (H ≈ 66 ± 6 km s-1Mpc-1).] The front side and backside infalls can be seenaround Virgo and Fornax. In the direction of Virgo the comparison ismade with the Peebles' model. We obtain: [vinfall} =CVirgo/r0.9 ± 0.2] withCVirgo=2800 for Virgo and CFornax=1350 for Fornax,with the adopted units (km s-1 and Mpc). We obtain thefollowing mean distance moduli: [μVirgo=31.3 ± 0.2(r=18 Mpc )] [μFornax=31.7 ± 0.3 (r=22 Mpc). ] Allthese quantities form an accurate and coherent system. Full Table 2 isonly available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/57
| Supernovae in isolated galaxies, in pairs and in groups of galaxies
In order to investigate the influence of environment on supernova (SN)production, we have performed a statistical investigation of the SNediscovered in isolated galaxies, in pairs and in groups of galaxies. 22SNe in 18 isolated galaxies, 48 SNe in 40 galaxy members of 37 pairs and211 SNe in 170 galaxy members of 116 groups have been selected andstudied. We found that the radial distributions of core-collapse SNe ingalaxies located in different environments are similar, and consistentwith those reported by Bartunov, Makarova & Tsvetkov. SNe discoveredin pairs do not favour a particular direction with respect to thecompanion galaxy. Also, the azimuthal distributions inside the hostmembers of galaxy groups are consistent with being isotropics. The factthat SNe are more frequent in the brighter components of the pairs andgroups is expected from the dependence of the SN rates on the galaxyluminosity. There is an indication that the SN rate is higher in galaxypairs compared with that in groups. This can be related to the enhancedstar formation rate in strongly interacting systems. It is concludedthat, with the possible exception of strongly interacting systems, theparent galaxy environment has no direct influence on SN production.
| A Comparison of Ultraviolet Imaging Telescope Far-Ultraviolet and Hα Star Formation Rates
We have used archival ultraviolet (UV) imaging of 50 nearby star-forminggalaxies obtained with the Ultraviolet Imaging Telescope (UIT) to deriveintegrated near-UV and far-UV magnitudes, and have combined these datawith Hα, far-infrared, and thermal radio continuum measurements toexplore the consistency of UV and Hα star formation rates (SFRs).In agreement with previous studies, we find that the UV and HαSFRs are qualitatively consistent, even before corrections forextinction are applied. The uncorrected UV SFRs are systematically lowerby a factor of 1.5 (with a factor of 2 scatter) among luminous galaxieswith SFR>~1 Msolar yr-1, indicating a highereffective attenuation of the far-UV radiation. Among less luminousgalaxies there is no significant offset between the Hα and far-UVSFR scales. This behavior is consistent with that of higher redshiftsamples observed by Sullivan et al., Glazebrook et al., and Yan et al.for comparable ranges of galaxy luminosities and absolute SFRs.Far-infrared and thermal radio continuum data available for a subset ofour sample allow us to estimate the attenuation in the UV and atHα independently. The UV and Hα attenuations appear to becorrelated, and confirm systematically higher attenuations in the UV.Although the galaxies in our sample show modest levels of attenuation(with median values of 0.9 mag at Hα and 1.4 mag at 1550 Å),the range across the sample is large, ~4 mag for Hα and >~5 magin the far-UV (1550 Å). This indicates that the application of asingle characteristic extinction correction to Hα or UV SFRs isonly realistic for large, well-defined and well-studied galaxy samples,and that extinction bias may be important for UV oremission-line-selected samples of star-forming galaxies.
| The Frequency of Active and Quiescent Galaxies with Companions: Implications for the Feeding of the Nucleus
We analyze the idea that nuclear activity, either active galactic nuclei(AGNs) or star formation, can be triggered by interactions by studyingthe percentage of active, H II, and quiescent galaxies with companions.Our sample was selected from the Palomar survey and avoids selectionbiases faced by previous studies. This sample was split into fivedifferent groups, Seyfert galaxies, LINERs, transition galaxies, H IIgalaxies, and absorption-line galaxies. The comparison between the localgalaxy density distributions of the different groups showed that in mostcases there is no statistically significant difference among galaxies ofdifferent activity types, with the exception that absorption-linegalaxies are seen in higher density environments, since most of them arein the Virgo Cluster. The comparison of the percentage of galaxies withnearby companions showed that there is a higher percentage of LINERs,transition galaxies, and absorption-line galaxies with companions thanSeyfert and H II galaxies. However, we find that when we consider onlygalaxies of similar morphological types (elliptical or spiral), there isno difference in the percentage of galaxies with companions amongdifferent activity types, indicating that the former result was due tothe morphology-density effect. In addition, only small differences arefound when we consider galaxies with similar Hα luminosities. Thecomparison between H II galaxies of different Hα luminositiesshows that there is a significantly higher percentage of galaxies withcompanions among H II galaxies with L(Hα)>1039 ergss-1 than among those with L(Hα)<=1039ergs s-1, indicating that interactions increase the amount ofcircumnuclear star formation, in agreement with previous results. Thefact that we find that galaxies of different activity types have thesame percentage of companions suggests that interactions betweengalaxies is not a necessary condition to trigger the nuclear activity inAGNs. We compare our results with previous ones and discuss theirimplications.
| Quantitative Morphology of Galaxies Observed in the Ultraviolet
We present a quantitative study of the far-ultraviolet (FUV) and opticalmorphology in 32 nearby galaxies and estimate the ``morphologicalk-correction'' expected if these objects were observed unevolved at highredshift. Using the common indices of central concentration (C) androtational asymmetry (A) to quantify morphology, we considerindependently two phenomena that give rise to this k-correction.Bandshifting, the decrease in the rest-frame wavelength of lightobserved through optical filters, is explored by measuring these indicesin several passbands for each galaxy, and it is found to be the primarydriver of changes in C and A. In general, the optical trend found fordecreasing C and increasing A when going to shorter wavelengths extendsto the FUV. However, the patchy nature of recent star formation inlate-type galaxies, which is accentuated in the FUV, results in poorquantitative correspondence between morphologies determined in theoptical and FUV. We then artificially redshift our FUV images into theHubble Deep Field (HDF) filters to simulate various cosmologicaldistance effects, such as surface brightness dimming and loss of spatialresolution. Hubble types of many galaxies in our sample are not readilyidentifiable at redshifts beyond z~1, and the galaxies themselves aredifficult to detect beyond z~3. Because only features of the highestsurface brightness remain visible at cosmological distances, the changein C and A between simulated high-z galaxies and their unredshiftedcounterparts depends on whether their irregular features are primarilybright or faint. Our simulations suggest that k-corrections alone areindeed capable of producing the peculiar morphologies observed at highredshift; for example, several spiral galaxies have C and A indicestypical of irregular or peculiar HDF objects viewed at z>=2. Webriefly discuss some elements of a scheme to classify rest-frame UVimages, mergers, protogalaxies, and other objects for which classicalHubble types do not adequately encompass the existing morphology.
| A ROSAT High Resolution Imager survey of bright nearby galaxies
We use the extensive public archive of ROSAT High Resolution Imager(HRI) observations to carry out a statistical investigation of the X-rayproperties of nearby galaxies. Specifically we focus on the sample of486 bright (BT<=12.5) northern galaxies studied by Ho,Filippenko and Sargent (HFS) in the context of their exploration of theoptical spectroscopic properties of nearby galactic nuclei. Over 20percent of HFS galaxies are encompassed in ROSAT HRI fields of reasonable(>=10ks) exposure. The X-ray sources detected within the opticalextent of each galaxy are categorized as either nuclear or non-nuclear,depending on whether the source is positioned within or outside a25-arcsec radius circle centred on the optical nucleus. A nuclear X-raysource is detected in over 70per cent of the galaxies harbouring eithera Seyfert or LINER nucleus, compared with a detection rate of only~40per cent in less active systems. The correlation of the Hαluminosity with nuclear X-ray luminosity previously observed in QSOs andbright Seyfert 1 galaxies appears to extend down into the regime ofultra-low luminosity(LX~1038-1040ergs-1) activegalactic nuclei (AGN). The inferred accretion rates for this sample oflow-luminosity AGN are significantly sub-Eddington. In total, 142non-nuclear sources were detected. In combination with published datafor M31, this leads to a luminosity distribution (normalized to anoptical blue luminosity of 1010Lsolar) for thediscrete X-ray source population in spiral galaxies of the formdN/dL38 = (1.0 ± 0.2)L-1.838where L38 is the X-ray luminosity in units of1038ergs-1. The implied LXLBratio is ~1.1×1039ergs-1(1010Lsolar)-1. The nature ofthe substantial number of `superluminous' non-nuclear objects detectedin the survey is discussed.
| Comparing Galaxy Morphology at Ultraviolet and Optical Wavelengths
We have undertaken an imaging survey of 34 nearby galaxies infar-ultraviolet (FUV, ~1500 Å) and optical (UBVRI) passbands tocharacterize galaxy morphology as a function of wavelength. This sample,which includes a range of classical Hubble types from elliptical toirregular, with emphasis on spirals at low inclination angle, provides avaluable database for comparison with images of high-z galaxies whoseFUV light is redshifted into the optical and near-infrared bands.Ultraviolet data are from the Ultraviolet Imaging Telescope (UIT)Astro-2 mission. We present images and surface brightness profiles foreach galaxy, and we discuss the wavelength dependence of morphology fordifferent Hubble types in the context of understanding high-z objects.In general, the dominance of young stars in the FUV produces the patchyappearance of a morphological type later than that inferred from opticalimages. Prominent rings and circumnuclear star formation regions areclearly evident in FUV images of spirals, while bulges, bars, and old,red stellar disks are faint to invisible at these short wavelengths.However, the magnitude of the change in apparent morphology ranges fromdramatic in early-type spirals with prominent optical bulges to slightin late-type spirals and irregulars, in which young stars dominate boththe UV and optical emission. Starburst galaxies with centrallyconcentrated, symmetric bursts display an apparent ``E/S0'' structure inthe FUV, while starbursts associated with rings or mergers produce apeculiar morphology. We briefly discuss the inadequacy of the opticallydefined Hubble sequence in describing FUV galaxy images and estimatingmorphological k-corrections, and we suggest some directions for futureresearch with this data set.
| The Arecibo Dual-Beam Survey: Arecibo and VLA Observations
The Arecibo Dual-Beam Survey is a ``blind'' 21 cm search for galaxiescovering ~430 deg2 of sky. We present the data from thedetection survey as well as from the follow-up observations to confirmdetections and improve positions and flux measurements. We find 265galaxies, many of which are extremely low surface brightness. Some ofthese previously uncataloged galaxies lie within the zone of avoidance,where they are obscured by the gas and dust in our Galaxy. Eighty-one ofthese sources are not previously cataloged optically, and there are 11galaxies that have no associated optical counterpart or are onlytentatively associated with faint wisps of nebulosity on the DigitizedSky Survey images. We discuss the properties of the survey, and inparticular we make direct determinations of the completeness andreliability of the sample. The behavior of the completeness and itsdependencies is essential for determining the H I mass function. Weleave the discussion of the mass function for a later paper, but do notethat we find many low surface brightness galaxies and seven sources withMHI<108 Msolar. The AreciboObservatory is part of the National Astronomy and Ionosphere Center,which is operated by Cornell University under cooperative agreement withthe National Science Foundation. in Puerto Rico.
| 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.
| Supernova Type Ia Luminosities, Their Dependence on Second Parameters, and the Value of H0
A sample of 35 Type Ia supernovae (SNe Ia) with good to excellentphotometry in B and V, minimum internal absorption, and1200
| A neutral hydrogen survey of polar ring galaxies. III. Nançay observations and comparison with published data
A total of 50 optically selected polar ring galaxies, polar ring galaxycandidates and related objects were observed in the 21-cm H i line withthe Nançay decimetric radio telescope and 31 were detected. Theobjects, selected by their optical morphology, are all north ofdeclination -39o, and generally relatively nearby (V< 8000km s-1) and/or bright (mB< 15.5). The H i linedata are presented for all 74 galaxies observed for the survey with theEffelsberg, Green Bank or Nanç radio telescopes, as well as allother published H i line parameters of these objects. Three objects wereobserved and detected by us at Parkes. A total of 59 objects weredetected. For each object a brief description is given based on aliterature search.
| Broad band properties of medium and low Lx/Lb early type galaxies
We have measured the spectral properties of five galaxies of low tointermediate Lx/Lb ratios with BeppoSAX and ASCA.A hard component (kT ~ 4-10 keV) is observed in all galaxies. In NGC1553 the BeppoSAX data show that this component is extended, and suggestan origin for the emission in the evolved stellar population. In NGC3115, a point-like source appears embedded in an extended componentmorphologically similar to the stellar body, suggesting an almost equalcontribution from the nuclear region and the binary population. A largecentral mass concentration and low level optical activity in NGC 3379argue for a contribution from the nucleus also in this object. However,for both NGC 3115 and NGC 3379, the nuclear emission is at a level wellbelow that observed in other galaxies who host similar nuclear blackholes. A second soft (kT ~ 0.3- 0.7 keV) spectral component is needed tofit the data of NGC 1407, NGC 1553 and NGC 4125 over the entire energyrange probed ( ~ 0.2-10 keV), best represented by a thermal componentwith line emission. We discuss possible interpretations of the origin ofthis component, which however will be better defined only with higherquality data.
| Investigations of the Local Supercluster velocity field. III. Tracing the backside infall with distance moduli from the direct Tully-Fisher relation
We have extended the discussion of Paper II (Ekholm et al.\cite{Ekholm99a}) to cover also the backside of the Local Supercluster(LSC) by using 96 galaxies within Theta <30degr from the adoptedcentre of LSC and with distance moduli from the direct B-bandTully-Fisher relation. In order to minimize the influence of theMalmquist bias we required log Vmax>2.1 and sigmaB_T<0.2mag. We found out that ifRVirgo<20 Mpc this sample fails to follow the expecteddynamical pattern from the Tolman-Bondi (TB) model. When we compared ourresults with the Virgo core galaxies given by Federspiel et al.(\cite{Federspiel98}) we were able to constrain the distance to Virgo:RVirgo=20-24 Mpc. When analyzing the TB-behaviour of thesample as seen from the origin of the metric as well as that withdistances from the extragalactic Cepheid PL-relation we found additionalsupport to the estimate RVirgo= 21 Mpc given in Paper II.Using a two-component mass-model we found a Virgo mass estimateMVirgo=(1.5 - 2)x Mvirial, whereMvirial=9.375*E14Msun forRVirgo= 21 Mpc. This estimate agrees with the conclusion inPaper I (Teerikorpi et al. \cite{Teerikorpi92}). Our results indicatethat the density distribution of luminous matter is shallower than thatof the total gravitating matter when q0<= 0.5. Thepreferred exponent in the density power law, alpha ~2.5, agrees withrecent theoretical work on the universal density profile of dark matterclustering in an Einstein-deSitter universe (Tittley & Couchman\cite{Tittley99}).
| A new HI ring: LGG 138
A complete ring of neutral hydrogen gas (HI) in the LGG 138 group ofgalaxies has been found. The HI mass of the ring is greater than 10^9solar masses, and the gas appears to be rotating with a projectedcircular speed of about 200 km per sec. Two bright galaxies are enclosedby the ring, both having radial velocities consistent with membership ofthe group. Faint stellar emission extends to the radial distance of theHI ring, where a small but distinct colour discontinuity of between 0.05and 0.20 magnitudes is detected. Three simple models for the formationof the system are briefly described, the most likely appearing to be apast gas-sweeping collision between one of the two bright galaxies andan outside intruder, with the colour break being partly due to anexpanding density wave that is triggering star formation, and partly toa different stellar population that has been collected from theoutskirts of the intruder.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| The I-Band Tully-Fisher Relation for SC Galaxies: 21 Centimeter H I Line Data
A compilation of 21 cm line spectral parameters specifically designedfor application of the Tully-Fisher (TF) distance method is presentedfor 1201 spiral galaxies, primarily field Sc galaxies, for which opticalI-band photometric imaging is also available. New H I line spectra havebeen obtained for 881 galaxies. For an additional 320 galaxies, spectraavailable in a digital archive have been reexamined to allow applicationof a single algorithm for the derivation of the TF velocity widthparameter. A velocity width algorithm is used that provides a robustmeasurement of rotational velocity and permits an estimate of the erroron that width taking into account the effects of instrumental broadeningand signal-to-noise. The digital data are used to establish regressionrelations between measurements of velocity widths using other commonprescriptions so that comparable widths can be derived throughconversion of values published in the literature. The uniform H I linewidths presented here provide the rotational velocity measurement to beused in deriving peculiar velocities via the TF method.
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
