Perpustakaan Digital ITB

Peculiar velocity analysis is currently a growing field due to the advent of new data from various surveys. One statistic that can be derived from peculiar velocity analyses is the bulk flow within the survey volume, which is closely related to the cosmological model and so can be used to test theories. To measure the bulk flow accurately, a sky coverage as complete as possible is needed to disentangle the dipole from the monopole component of the velocity field. In this work, we use the Fundamental Plane (FP) relation for early-type galaxies to measure distances by combining the velocity dispersion measurements from the 6dFGS, SDSS, and LAMOST spectroscopic surveys. Our sample has a sky coverage of ?3.0? steradians out to redshift z ? 0.055. We use near-infrared J-band photometry from the 2MASS Extended Source Catalog to make our sample as homogeneous as possible. We fit the FP with a 3D Gaussian using a maximum likelihood method. We measure peculiar velocities as the logarithmic ratio of the distances inferred from observed redshifts and comoving distances derived from the FP. Our final peculiar velocity sample consists of 15525 individual galaxies. We measure the bulk flow within the survey volume directly from the log-distance ratio measurements using a maximum likelihood method. We find bulk flow amplitudes of 236 ± 62, 248 ± 50, 296 ± 41, and 262 ± 41 km s?1 at scales 46, 56, 68, and 77 h?1 Mpc, respectively. These amplitudes are consistent at 1? with the root-mean-square bulk motions expected in a standard ?CDM cosmology. The direction of the bulk flow we measure is consistent with both previous measurements and the direction of the cosmic microwave background (CMB) dipole motion.