Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
Stellar population gradient in lenticular galaxies: NGC 1023, NGC 3115 and NGC 4203
We investigate the stellar population content in the lenticular galaxiesNGC 1023, NGC 3115 and NGC 4203 applying a population synthesis methodbased on a seven component spectral basis with different ages -2.5*E6, 10*E6, 25*E6, 75*E6,200*E6, 1.2*E9 and older than 1010years, and metallicity in the range -1.3<= [Z/Zsun]<=-0.2. This study employs two-dimensional STIS spectra in the rangelambda lambda 2900-5700 Å, obtained from the Hubble SpaceTelescope public archives. We extracted one-dimensional spectra inadjacent windows 100 pc wide (projected distance) from the nuclearregions up to 300-400 pc. The largest contribution, both in lambda 5870Å flux and mass fraction, comes from old stars (age>1010 years). We verified the possible existence ofcircumnuclear bursts (CNBs) in NGC 3115 and NGC 4203.
| A search for Low Surface Brightness galaxies in the near-infrared. I. Selection of the sample
A sample of about 3800 Low Surface Brightness (LSB) galaxies wasselected using the all-sky near-infrared (J, H and Ks-band)2MASS survey. The selected objects have a mean central surfacebrightness within a 5'' radius around their centre fainter than 18 magarcsec-2 in the Ks band, making them the lowestsurface brightness galaxies detected by 2MASS. A description is given ofthe relevant properties of the 2MASS survey and the LSB galaxy selectionprocedure, as well as of basic photometric properties of the selectedobjects. The latter properties are compared to those of other samples ofgalaxies, of both LSBs and ``classical'' high surface brightness (HSB)objects, which were selected in the optical. The 2MASS LSBs have aBT_c-KT colour which is on average 0.9 mag bluerthan that of HSBs from the NGC. The 2MASS sample does not appear tocontain a significant population of red objects.All tables and Figs. 2a-c are only available in electronic form athttp://www.edpsciences.org
| The faint end of the galaxy luminosity function
We present and discuss optical measurements of the faint end of thegalaxy luminosity function down to MR=-10 in five differentlocal environments of varying galaxy density and morphological content.The environments we studied, in order of decreasing galaxy density, arethe Virgo Cluster, the NGC 1407 Group, the Coma I Group, the Leo Groupand the NGC 1023 Group. Our results come from a deep wide-angle surveywith the National Astronomical Observatories of Japan Subaru 8-mTelescope on Mauna Kea and are sensitive down to very faintsurface-brightness levels. Galaxies were identified as group or clustermembers on the basis of their surface brightness and morphology. Thefaintest galaxies in our sample have R~ 22.5. There were thousands offainter galaxies but we cannot distinguish cluster members frombackground galaxies at these faint limits so do not attempt to determinea luminosity function fainter than MR=-1010. In all cases,there are far fewer dwarfs than the numbers of low-mass haloesanticipated by cold dark matter theory. The mean logarithmic slope ofthe luminosity function between MR=-1018 andMR=-1010 is α~=-1.2, far shallower than the cold darkmatter mass function slope of α~=-1.8. We would therefore need tobe missing about 90 per cent of the dwarfs at the faint end of oursample in all the environments we study to achieve consistency with CDMtheory. It is unlikely that such large numbers of dwarfs are missedbecause (i) the data are deep enough that we are sensitive to very lowsurface brightness galaxies, and (ii) the seeing is good enough that wecan have some confidence in our ability to distinguish high surfacebrightness dwarfs from background galaxies brighter than R= 22.5. Onecaveat is that we miss compact members taken to be background galaxies,but such objects (like M32) are thought to be rare.
| A fast bar in the post-interaction galaxy NGC 1023
We measured the bar pattern speed, Ωp , of the SB0galaxy NGC 1023 using the Tremaine-Weinberg method withstellar-absorption slit spectroscopy. The morphology and kinematics ofthe Hi gas outside NGC 1023 suggest it suffered a tidal interaction,sometime in the past, with one of its dwarf companions. At present,however, the optical disc is relaxed. If the disc had been stabilized bya massive dark matter halo and formed its bar in the interaction, thenthe bar would have to be slow. We found Ωp=5.0+/-1.8kms-1 arcsec-1 , so that the bar endsnear its corotation radius. It is therefore rotating rapidly and musthave a maximum disc.
| Determination of Distances to Galaxies of the NGC 1023 Group. The Hubble Constant
On the basis of photographs from the 6 m Large Azimuthal Telescope andthe Hubble Space Telescope, VRI photometry of stars in 11 galaxies inthe NGC 1023 group has been carried out. The distances to these galaxieswere determined by the method of brightest stars. The distances to NGC925 and NGC 1023 were determined from the position of the top of the redgiant branch (the TRGB method). From the calculated average androot-mean-square distances to the NGC 1023 group (10.3 ± 2.2 Mpcand 9.7 ± 0.5 Mpc) the Hubble constant in this direction wasdetermined: H 0R = 75 ± 8 km·sec-1·Mpc-1 and H 0M =81 ± 5 km ·sec-1·Mpc-1.
| Keck Spectroscopy of Young and Old Star Clusters in NGC 1023
We present Keck/LRIS spectra for 11 old globular clusters in the S0-typegalaxy NGC 1023 and two young blue clusters in the nearby companion NGC1023A. Analysis of the spectra of seven old clusters with sufficientsignal-to-noise ratio shows generally good agreement betweenspectroscopic and previous photometric metallicity estimates, but theintegrated colors of two clusters are too blue for their spectroscopicmetallicities. Although the cluster ages are not well constrained, theyare most likely similar to those of Milky Way globular clusters andcertainly older than ~5 Gyr. The brightest globular cluster in thesample shows enhanced cyanogen, possibly indicating an abundance anomalysimilar to that observed in some M31 globular clusters. For the two blueclusters in NGC 1023A we estimate ages between 125 and 500 Myr on thebasis of their strong Balmer lines. The total masses are about8×104 Msolar and 6×104Msolar for a Miller-Scalo initial mass function and Z=0.004,making these objects similar to the young populous clusters in the LargeMagellanic Cloud. It is suggested that the two young clusters might haveformed during a period of enhanced star formation activity in NGC 1023A,stimulated by a close encounter with NGC 1023. Based on data obtained atthe W. M. Keck Observatory, which is operated as a scientificpartnership among the California Institute of Technology, the Universityof California and the National Aeronautics and Space Administration.
| 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.
| Hubble Space Telescope Observations of Star Clusters in NGC 1023: Evidence for Three Cluster Populations?
Using Hubble Space Telescope images we have carried out a study ofcluster populations in the nearby S0 galaxy NGC 1023. In two WFPC2pointings we have identified 221 cluster candidates. The small distance(~9 Mpc) combined with deep F555W and F814W images allows us to reachabout 2 mag below the expected turnover of the globular clusterluminosity function. NGC 1023 appears to contain at least threeidentifiable cluster populations: the brighter clusters show a clearlybimodal color distribution with peaks at (V-I)0=0.92 and at(V-I)0=1.15, and in addition there are a number of fainter,more extended objects with predominantly red colors. Among the brighterclusters, we find that the blue clusters have somewhat larger sizes thanthe red ones with mean effective radii of Re~2 andRe~1.7 pc, respectively. These clusters have luminosityfunctions (LFs) and sizes consistent with what is observed for globularclusters in other galaxies. Fitting Gaussians to the LFs of the blue andred compact clusters, we find turnover magnitudes ofMTO(blue)=-7.58-7.72-7.36 andMTO(red)=-7.37-7.50-7.09 in V anddispersions ofσV(blue)=1.121.331.03 andσV(red)=0.971.250.89. Thefainter, more extended clusters have effective radii up toRe~10-15 pc, and their LF appears to rise at least down toMV~-6, few of them being brighter than MV=-7. Wesuggest that these fainter objects may have a formation history distinctfrom that of the brighter GCs. Based on observations with the NASA/ESAHubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc. under NASA contract No. NAS5-26555.
| Catalogue of HI maps of galaxies. I.
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic 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.
| A catalogue of spatially resolved kinematics of galaxies: Bibliography
We present a catalogue of galaxies for which spatially resolved data ontheir internal kinematics have been published; there is no a priorirestriction regarding their morphological type. The catalogue lists thereferences to the articles where the data are published, as well as acoded description of these data: observed emission or absorption lines,velocity or velocity dispersion, radial profile or 2D field, positionangle. Tables 1, 2, and 3 are proposed in electronic form only, and areavailable from the CDS, via anonymous ftp to cdsarc.u-strasbg.fr (to130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| Line-strength gradients in the bulge components of NGC 3190 and 1023.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.271...39S&db_key=AST
| 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.
| Is NGC 1023/1023A an interacting system?
Recent medium dispersion spectra of the central regions of NGC 1023 andNGC 1023A analyzed to determine the source of the nearby neutralhydrogen cloud. A radial velocity in the range of 712-772 km/sec isderived, which coincides with the H I condensation extending from NGC1023 to NGC 1023A. The possibility of a tidal interaction between thetwo galaxies is discussed. The interaction would account for theobserved lack of structures and star formation regions in NGC 1023A.Persisting problems with the model are also considered.
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
Каталог и designations:
|
