Contents
Images
Upload your image
DSS Images Other Images
Related articles
Kinematics of the local universe. VII. New 21-cm line measurements of 2112 galaxies
This paper presents 2112 new 21-cm neutral hydrogen line measurementscarried out with the meridian transit Nan\c cay radiotelescope. Amongthese data we give also 213 new radial velocities which complement thoselisted in three previous papers of this series. These new measurements,together with the HI data collected in LEDA, put to 6 700 the number ofgalaxies with 21-cm line width, radial velocity, and apparent diameterin the so-called KLUN sample. Figure 5 and Appendices A and B forcorresponding comments are available in electronic form at thehttp://www.edpsciences.com
| CCD calibration of the magnitude scale for the SSRS2 sample: The equatorial region
In this paper we continue our investigation on the isophotal nature,accuracy, and uniformity of the magnitude system adopted in the SouthernSky Redshift Survey extension (SSRS2). Extending our earlier work, weexamine galaxies in the equatorial region, primarily in the declinationrange delta greater than or equal to -17.5 deg and less than or equal to0 deg, over a large range of right ascension, covering the southern andnorthern Galactic caps. For this purpose, we have obtained CCD isophotalmagnitudes in the B and R bands for 265 galaxies of differentmorphological types. Using the larger sample we confirm our earlierclaim that the mSSRS2 magnitudes are very nearly themagnitude measured within the isophote muB = 26 mag/sqarcsec, with a dispersion of about 0.30 mag. The relative zero-pointoffset between our mSSRS2 magnitudes and the CCD photometryis -0.02 mag from all data we have obtained. However, we detect avariation of the zero-point across different regions of the sky of +/-0.10 mag for regions at large angular separations. We also estimate thatthe zero-point offset between the mSSRS2 and Zwicky systemsis relatively small (approximately 0.10 mag), which should allow us tocombine the data from the SSRS2 and the CfA2 Redshift Survey.
| Evolutionary models for disk galaxies
The evolution of disk galaxies is studied within the framework of a gasturbulence energy balance between the supernovae input energy and theturbulence collisional dissipation. The initial mass, the angularmomentum, and the gas accretion rate determine the evolution of themodels. We predict the present gas content and the star formationhistory of a galaxy. The role of gas accretion is discussed. Thecomparison between models and observations shows that gas accretion maybe very important to explain the high gas content of the dwarf irregulargalaxies. A Schmidt's law with a star formation rate per surface unitproportional to the square of the gas surface density provides a goodagreement with the models at the Hubble time as well as during theirevolution.
| Nitrogen and oxygen evolution in dwarf irregular galaxies
In the present computation of numerical chemical evolution models for asample of 40 dwarf irregular galaxies, assuming bursts of star formationand taking account of galactic winds, N and O evolution is followed upin light of the most recent results on stellar evolution. The N and Oabundances observed are well reproduced by theoretical models with suchimplications as the ability to explain the N/O vs O diagrams of dwarfirregulars, as well as those of halo stars in the Galaxy, by means of aprimary fraction of N ranging from 30 to 50 percent. A Salpeter (1955)initial mass function is applicable to all these galaxies, whilefunctions strongly varying with metallicity do not yield the observeddata.
| A statistical analysis of the Einstein normal galaxy sample. I - Spiral and irregular galaxies
The results of a statistical analysis of 48 spiral and irregulargalaxies observed with the Einstein Observatory are reported. It isfound that the X-ray luminosity is not directly correlated with the massof the galaxies, but is strongly correlated with the blue luminosity.This suggests that most X-ray sources, including low-mass binaries, arebinary systems belonging to both old disk and young arm Population Icomponents. A real bulge population of X-ray sources exists that cancontribute significantly to the X-ray luminosity of early-type spirals.The X-ray emission from a sample of 29 relatively isolated, normalelliptical and S0 galaxies is also studied, and the results are comparedto those for the above sample to investigate the origin of the X-rayemission in early-type galaxies and the possible emission mechanisms.The influence of a powerful radio source and the onset of nuclearactivity are also examined.
| Stochastic star formation and chemical evolution of dwarf irregular galaxies
The Gerola et al. (1980) stochastic self-propagating star formationmodel is the basis of the present discussion of the observationalproperties of a sample of magellanic and dwarf irregular galaxies.One-zone model galaxies are presented which take into account both thebursting mode of star formation and the inflow of unenriched gas, wherethe rate of star formation is assumed to depend on both a stochasticterm representing the fraction of active cells in the Gerola model andthe current fractionary mass of gas. Models for the SMC and LMC are usedin choosing among different solutions and in fixing an efficiency factorin the star formation rate, the underlying initial mass function, andthe time scale of mass accretion. It is found that the high dispersionrate of observed dwarf irregular galaxy properties cannot be explainedby means of the stochastic star formation mechanism alone.
| Structure and dynamics of barred spiral galaxies, in particular of the Magellanic type
Not Available
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
NEWS@SKY (Science&Space News)
