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|Observing the Dark Matter Density Profile of Isolated Galaxies|
Using the Sloan Digital Sky Survey (SDSS), we probe the halo massdistribution by studying the velocities of satellites orbiting isolatedgalaxies. In a subsample that covers 2500 deg2 on the sky, wedetect about 3000 satellites with absolute blue magnitudes going down toMB=-14; most of the satellites have MB=-16 to -18,comparable to the magnitudes of M32 and the Magellanic Clouds. After acareful, model-independent removal of interlopers, we find that theline-of-sight velocity dispersion of satellites declines with distanceto the primary. For an L* galaxy the rms line-of-sightvelocity changes from ~120 km s-1 at 20 kpc to ~60 kms-1 at 350 kpc. This decline agrees remarkably well withtheoretical expectations, as all modern cosmological models predict thatthe density of dark matter in the peripheral parts of galaxies declinesas ρDM~r-3. Thus, for the first time we finddirect observational evidence of the density decline predicted bycosmological models; we also note that this result contradictsalternative theories of gravity such as modified Newtonian dynamics(MOND). We also find that the velocity dispersion of satellites within100 kpc scales with the absolute magnitude of the central galaxy asσ~L0.3 this is very close to the Tully-Fisher relationfor normal spiral galaxies.
|A Complete Redshift Survey to the Zwicky Catalog Limit in a 2^h X 15 deg Region around 3C 273|
We compile 1113 redshifts (648 new measurements, 465 from theliterature) for Zwicky catalog galaxies in the region (-3.5d <= delta<= 8.5d, 11h5 <= alpha <= 13h5). We include redshifts for 114component objects in 78 Zwicky catalog multiplets. The redshift surveyin this region is 99.5% complete to the Zwicky catalog limit, m_Zw =15.7. It is 99.9% complete to m_Zw = 15.5, the CfA Redshift Survey(CfA2) magnitude limit. The survey region is adjacent to the northernportion of CfA2, overlaps the northernmost slice of the Las CampanasRedshift Survey, includes the southern extent of the Virgo Cluster, andis roughly centered on the QSO 3C 273. As in other portions of theZwicky catalog, bright and faint galaxies trace the same large-scalestructure.
|An image database. II. Catalogue between δ=-30deg and δ=70deg.|
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
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