277 research outputs found
From Spitzer Galaxy Photometry to Tully-Fisher Distances
This paper involves a data release of the observational campaign: Cosmicflows
with Spitzer (CFS). Surface photometry of the 1270 galaxies constituting the
survey is presented. An additional ~ 400 galaxies from various other Spitzer
surveys are also analyzed. CFS complements the Spitzer Survey of Stellar
Structure in Galaxies, that provides photometry for an additional 2352
galaxies, by extending observations to low galactic latitudes (|b|<30 degrees).
Among these galaxies are calibrators, selected in K band, of the Tully-Fisher
relation. The addition of new calibrators demonstrate the robustness of the
previously released calibration. Our estimate of the Hubble constant using
supernova host galaxies is unchanged, H0 = 75.2 +/- 3.3 km/s/Mpc.
Distance-derived radial peculiar velocities, for the 1935 galaxies with all the
available parameters, will be incorporated into a new data release of the
Cosmicflows project. The size of the previous catalog will be increased by 20%,
including spatial regions close to the Zone of Avoidance.Comment: Accepted for publication in MNRAS, 16 pages, 14 figures, 6 table
Numerical action reconstruction of the dynamical history of dark matter haloes in N-body simulations
We test the ability of the numerical action method (NAM) to recover the
individual orbit histories of mass tracers in an expanding universe in a region
of radius 26Mpc/h, given the masses and redshift-space coordinates at the
present epoch. The mass tracers are represented by dark matter haloes
identified in a high resolution N-body simulation of the standard LCDM
cosmology. Since previous tests of NAM at this scale have traced the underlying
distribution of dark matter particles rather than extended haloes, our study
offers an assessment of the accuracy of NAM in a scenario which more closely
approximates the complex dynamics of actual galaxy haloes. We show that NAM can
recover present-day halo distances with typical errors of less than 3 per cent,
compared to 5 per cent errors assuming Hubble flow distances. The total halo
mass and the linear bias were both found to be constained at the 50 per cent
level. The accuracy of individual orbit reconstructions was limited by the
inability of NAM, in some instances, to correctly model the positions of haloes
at early times solely on the basis of the redshifts, angular positions, and
masses of the haloes at the present epoch. Improvements in the quality of NAM
reconstructions may be possible using the present-day three-dimensional halo
velocities and distances to further constrain the dynamics. This velocity data
is expected to become available for nearby galaxies in the coming generations
of observations by SIM and GAIA.Comment: 12 pages, 9 figures. submitted to MNRA
Our Peculiar Motion Away from the Local Void
The peculiar velocity of the Local Group of galaxies manifested in the Cosmic
Microwave Background dipole is found to decompose into three dominant
components. The three components are clearly separated because they arise on
distinct spatial scales and are fortuitously almost orthogonal in their
influences. The nearest, which is distinguished by a velocity discontinuity at
~7 Mpc, arises from the evacuation of the Local Void. We lie in the Local Sheet
that bounds the void. Random motions within the Local Sheet are small. Our
Galaxy participates in the bulk motion of the Local Sheet away from the Local
Void. The component of our motion on an intermediate scale is attributed to the
Virgo Cluster and its surroundings, 17 Mpc away. The third and largest
component is an attraction on scales larger than 3000 km/s and centered near
the direction of the Centaurus Cluster. The amplitudes of the three components
are 259, 185, and 455 km/s, respectively, adding collectively to 631 km/s in
the reference frame of the Local Sheet. Taking the nearby influences into
account causes the residual attributed to large scales to align with observed
concentrations of distant galaxies and reduces somewhat the amplitude of motion
attributed to their pull. On small scales, in addition to the motion of our
Local Sheet away from the Local Void, the nearest adjacent filament, the Leo
Spur, is seen to be moving in a direction that will lead to convergence with
our filament. Finally, a good distance to an isolated galaxy within the Local
Void reveals that this dwarf system has a motion of at least 230 km/s away from
the void center. Given the velocities expected from gravitational instability
theory in the standard cosmological paradigm, the distance to the center of the
Local Void must be at least 23 Mpc from our position. The Local Void is large!Comment: Tentatively scheduled for Astrophysical Journal, 676 (March 20),
2008. 18 figures, 3 tables including web link for 2 tables, web links to 2
video
Associations of Dwarf Galaxies
Hubble Space Telescope Advanced Cameras for Surveys has been used to
determine accurate distances for 20 galaxies from measurements of the
luminosity of the brightest red giant branch stars. Five associations of dwarf
galaxies that had originally been identified based on strong correlations on
the plane of the sky and in velocity are shown to be equally well correlated in
distance. Two more associations with similar properties have been discovered.
Another association is identified that is suggested to be unbound through tidal
disruption. The associations have the spatial and kinematic properties expected
of bound structures with 1 - 10 x 10^11 solar mass. However, these entities
have little light with the consequence that mass-to-light ratios are in the
range 100 - 1000 in solar units. Within a well surveyed volume extending to 3
Mpc, all but one known galaxy lies within one of the groups or associations
that have been identified.Comment: 50 pages, 2 tables, 15 encapsulated figures, 1 (3 part) jpg figure.
Submitted to Astronomical Journa
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