Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
The Millennium Galaxy Catalogue: 16 <=BMGC < 24 galaxy counts and the calibration of the local galaxy luminosity function
The Millennium Galaxy Catalogue (MGC) is a 37.5 deg2,medium-deep, B-band imaging survey along the celestial equator, takenwith the Wide Field Camera on the Isaac Newton Telescope. The surveyregion is contained within the regions of both the Two Degree FieldGalaxy Redshift Survey (2dFGRS) and the Sloan Digital Sky Survey EarlyData Release (SDSS-EDR). The survey has a uniform isophotal detectionlimit of 26 mag arcsec-2 and it provides a robust,well-defined catalogue of stars and galaxies in the range 16<=BMGC < 24 mag.Here we describe the survey strategy, the photometric and astrometriccalibration, source detection and analysis, and present the galaxynumber counts that connect the bright and faint galaxy populationswithin a single survey. We argue that these counts represent the stateof the art and use them to constrain the normalizations (φ*) of anumber of recent estimates of the local galaxy luminosity function. Wefind that the 2dFGRS, SDSS Commissioning Data (CD), ESO Slice Project,Century Survey, Durham/UKST, Mt Stromlo/APM, SSRS2 and NOG luminosityfunctions require a revision of their published φ* values by factorsof 1.05 +/- 0.05, 0.76 +/- 0.10, 1.02 +/- 0.22, 1.02 +/- 0.16, 1.16 +/-0.28, 1.75 +/- 0.37, 1.40 +/- 0.26 and 1.01 +/- 0.39, respectively.After renormalizing the galaxy luminosity functions we find a mean localbJ luminosity density of .1
| Period-luminosity relations of SX Phoenicis stars
We propose the following criteria to distinquish between fundamental (F)and first-overtone (H) pulsating SX Phoenicis variables: the (H)pulsators are SX Phe stars with nearly symmetrical light curves andlight amplitudes (total range) less than or equal to 0.29 m in V; the(F) pulsating stars have light amplitudes greater than or equal 0.25 min V and asymmetrical light curves. These criteria provide a separationof the stars into two groups that lead to two parallel P - L relationsthat are offset by 0.37m. This offset is in excellent agreement with theoffset, 0.36m predicted from the double-mode pulsating variable SX Phe.The (H) pulsating variables have shorter periods on average than the (F)pulsators as predicted by P1/ P0 = Q1/Q0 approximately equal 0.778. The mean periods of the SX Phestars in globular clusters are shown to be correlated with themetallicity (Fe/H) in the sense that the shortest period variables arefound in the most metal-poor clusters. The fundamental-mode SX Phe starsin the Carina dwarf galaxy give a distance modulus of 20.0 and (Fe/H) =-1.5.
| Kinematics and dynamics of the MKW/AWM poor clusters
We report 472 new redshifts for 416 galaxies in the regions of the 23poor clusters of galaxies originally identified by Morgan, Kayser, andWhite (MKW), and Albert, White, and Morgan (AWM). Eighteen of the poorclusters now have 10 or more available redshifts within 1.5/h Mpc of thecentral galaxy; 11 clusters have at least 20 available redshifts. Basedon the 21 clusters for which we have sufficient velocity information,the median velocity scale is 336 km/s, a factor of 2 smaller than foundfor rich clusters. Several of the poor clusters exhibit complex velocitydistributions due to the presence of nearby clumps of galaxies. We checkon the velocity of the dominant galaxy in each poor cluster relative tothe remaining cluster members. Significantly high relative velocities ofthe dominant galaxy are found in only 4 of 21 poor clusters, 3 of whichwe suspect are due to contamination of the parent velocity distribution.Several statistical tests indicate that the D/cD galaxies are at thekinematic centers of the parent poor cluster velocity distributions.Mass-to-light ratios for 13 of the 15 poor clusters for which we havethe required data are in the range 50 less than or = M/LB(0)less than or = 200 solar mass/solar luminosity. The complex nature ofthe regions surrounding many of the poor clusters suggests that thesegroupings may represent an early epoch of cluster formation. Forexample, the poor clusters MKW7 and MKWS are shown to be gravitationallybound and likely to merge to form a richer cluster within the nextseveral Gyrs. Eight of the nine other poor clusters for which simpletwo-body dynamical models can be carried out are consistent with beingbound to other clumps in their vicinity. Additional complex systems withmore than two gravitationally bound clumps are observed among the poorclusters.
| Galaxy redshifts in an equatorial field in Virgo and the spatial distribution of local Lyman alpha clouds
New redshifts are presented for 51 galaxies which lie in a narrow stripalong the celestial equator. The redshifts are derived from a mixture ofoptical and H I spectra; for the latter subset (37 galaxies) H I fluxesand line widths are also given. One of the two Ly-alpha clouds in theLocal Supercluster appears to be associated with a spiral galaxy,although the angular and physical separations (42 arcmin and 180 kpc)are large. The other nearby Ly-alpha cloud and the large H I cloudappear to be more isolated. None of the nine Ly-alpha clouds withvelocities between 5000-20,000 km/s are associated with any specificgalaxies, but most appear to fall within or near the large-scalestructures defined by the galaxies.
| Head-on binary collisions in globular clusters
Collision probabilities between identical binaries of three differentbinding energies are computed for binaries in the cores of globularclusters. The more tightly bound a binary is, the smaller the chance isthat it suffers a collision. It is found that a given binary in aglobular cluster core probably does not suffer more than a very fewcollisions. If it is not broken up into single stars, it will become sotightly bound that collisions involving it are very rare. Since it isfound that head-on collisions are so rare, the collisions which areprobably more important in affecting the evolution of the cluster coreare the long-range (large impact parameter) encounters.
| Double galaxies - Redshift measurements, error analysis, and mean mass/luminosity ratio
New radial velocities for 44 double galaxy systems are presented. Theratio k between the internal and external errors in the redshift data isestimated by comparing data from catalog galaxies with a sample fromWhite et al. (1983). This ratio is found to increase from 1.0 to 2.1from galaxies with strong emission lines to absorption-line objects. Thedisparity between the absolute and internal errors diminishes for theredshift differentials of pair components, because the individual errorsin the redshifts measured for the members of a given pair are observedto be positively correlated. The average value of k for the whole sampleis estimated by considering the values of the first four moments of themass/luminosity ratio as functions of k. The absolute error in theredshift differential is 1.4 times the internal error, bringing the meanratio of orbital mass to luminosity for 490 pairs into good agreementwith the values determined from the differential rotation of galaxies.
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
Каталог и designations:
|
