نتایج جستجو برای: galaxies size
تعداد نتایج: 599707 فیلتر نتایج به سال:
We study the variation of the dark matter mass fraction of elliptical galaxies as a function of their luminosity, stellar mass, and size using a sample of 29,469 elliptical galaxies culled from the Sloan Digital Sky Survey. We model ellipticals as a stellar Hernquist profile embedded in an adiabatically compressed dark matter halo. This model allows us to estimate a dynamical mass (Mdynm) at th...
We give a summary of our recent studies of spatial and velocity biases of galaxy-size halos in cosmological models. Recent progress in numerical techniques made it possible to simulate halos in large volumes with a such accuracy that halos survive in dense environments of groups and clusters of galaxies. While the very central parts of clusters still may have been affected by numerical effects,...
and – 2 – ABSTRACT Observations of ultraluminous infrared galaxies (ULIRGs) with an achieved resolution approaching the diffraction limit in the mid-infrared from 8-25 µm using the Keck Telescopes are reported. We find extremely compact structures, with spatial scales of < 0.3 ′′ (diameter) in six of the seven ULIRGs observed. These compact sources emit between 30% and 100% of the mid-infrared ...
The radio counterparts to the IRAS Redshift Survey galaxies are identified in the NRAO VLA Sky Survey (NVSS) catalog. Our new catalog of the infrared flux-limited (S60μm ≥ 2 Jy) complete sample of 1809 galaxies lists accurate radio positions, redshifts, and 1.4 GHz radio and IRAS fluxes. This sample is six times larger in size and five times deeper in redshift coverage (to z ≈ 0.15) compared wi...
The radio counterparts to the IRAS Redshift Survey galaxies are identified in the NRAO VLA Sky Survey (NVSS) catalog. Our new catalog of the infrared flux-limited (S60μm ≥ 2 Jy) complete sample of 1809 galaxies lists accurate radio positions, redshifts, and 1.4 GHz radio and IRAS fluxes. This sample is six times larger in size and five times deeper in redshift coverage (to z ≈ 0.15) compared wi...
The dramatic size evolution of early-type galaxies from z ∼ 2 to 0 poses a new challenge in the theory of galaxy formation, which may not be explained by the standard picture. It is shown here that the size evolution can be explained if the non-baryonic cold dark matter is composed of compact objects having a mass scale of ∼ 10M⊙. This form of dark matter is consistent with or only weakly const...
We have used deep images from the Hubble Space Telescope to study the evolution in the morphologies, sizes, stellar–masses, colors, and internal color dispersion of galaxies in the Hubble Deep Field North. We selected two galaxy samples at 0.7 ≤ z ≤ 1.4 and 1.9 ≤ z ≤ 3.0 from a near–infrared, flux–limited catalog with complete photometric and spectroscopic redshift information. At z ∼ 1 the maj...
We investigate the evolution in the distribution of surface brightness, as a function of size, for elliptical and S0 galaxies in the two clusters RDCS J1252.9-2927, z = 1.237 and RX J0152.7-1357, z = 0.837. We use multi-color imaging with the Advanced Camera for Surveys on the Hubble Space Telescope to determine these sizes and surface brightnesses. Using three different estimates of the surfac...
In this paper we discuss the demographics of the radio blazar population: (i) what are their parent ('unbeamed') sources and (ii) what magnitude and/or type of evolution have they undergone ? The discussion is based on models of radio source evolution and beaming based on a 'dual population' unification paradigm. These models, developed from radio blazar properties in bright samples, predict bl...
The recently discovered population of ultra-faint extended line emitters, with fluxes of a few times 10 erg s cm at z ∼ 3, can account for the majority of the incidence rate of Damped Lyα systems (DLAs) at this redshift if the line emission is interpreted as Lyα. We show here that a model similar to that proposed by Haehnelt, Steinmetz, & Rauch (2000), which explains the incidence rate and kine...
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