The Velocity Field Around Groups of Galaxies
F.D.A.Hartwick
http://arxiv.org/abs/1104.1621v1 A statistical method is presented for determining the velocity field
in the immediate vicinity of groups of galaxies using only positional
and redshift information with the goal of studying the perturbation of
the Hubble flow around groups more distant than the Local Group. The
velocities are assumed to obey a Hubble-like expansion law, i.e.
$V=H_{exp}R$ where the expansion rate $H_{exp}$ is to be determined.
The method is applied to a large, representative group catalog and
evidence is found for a sub-Hubble expansion rate within two well
defined radii beyond the virial radii of the groups. This result is
consistent with that of Teerikorpi et al. (2008) who found a similar
expansion law around 3 nearby groups and extends it to a more
representative volume of space.
The Shape of Dark Matter Haloes in the Aquarius Simulations: Evolution
and Memory
Carlos A. Vera-Ciro, Laura V. Sales, Amina Helmi, Carlos S. Frenk,
Julio F. Navarro, Volker Springel, Mark Vogelsberger, Simon D.M. White
http://arxiv.org/abs/1104.1566v1
We use the high resolution cosmological N-body simulations from the
Aquarius project to investigate in detail the mechanisms that
determine the shape of Milky Way-type dark matter haloes. We find
that, when measured at the instantaneous virial radius, the shape of
individual haloes changes with time, evolving from a typically prolate
configuration at early stages to a more triaxial/oblate geometry at
the present day. This evolution in halo shape correlates well with the
distribution of the infalling material: prolate configurations arise
when haloes are fed through narrow filaments, which characterizes the
early epochs of halo assembly, whereas triaxial/oblate configurations
result as the accretion turns more isotropic at later times.
Interestingly, at redshift z=0, clear imprints of the past history of
each halo are recorded in their shapes at different radii, which also
exhibit a variation from prolate in the inner regions to
triaxial/oblate in the outskirts. Provided that the Aquarius haloes
are fair representatives of Milky Way-like 10^12 Msun objects, we
conclude that the shape of such dark matter haloes is a complex,
time-dependent property, with each radial shell retaining memory of
the conditions at the time of collapse.
SNLS3: Constraints on Dark Energy Combining the Supernova Legacy
Survey Three Year Data with Other Probes
M. Sullivan, J. Guy, A. Conley, N. Regnault, P. Astier, C. Balland, S.
Basa, R. G. Carlberg, D. Fouchez, D. Hardin, I. M. Hook, D. A. Howell,
R. Pain, N. Palanque-Delabrouille, K. M. Perrett, C. J. Pritchet, J.
Rich, V. Ruhlmann-Kleider, D. Balam, S. Baumont, R. S. Ellis, S.
Fabbro, H. K. Fakhouri, N. Fourmanoit, S. Gonzalez-Gaitan, M. L.
Graham, M. J. Hudson, E. Hsiao, T. Kronborg, C. Lidmam, A. M. Mourao,
J. D. Neill, S. Perlmutter, P. Ripoche, N. Suzuki, E. S. Walker
http://arxiv.org/abs/1104.1444v1
We present observational constraints on the nature of dark energy
using the Supernova Legacy Survey three year sample (SNLS3) of Guy et
al. (2010) and Conley et al. (2011). We use the 472 SNe Ia in this
sample, accounting for recently discovered correlations between SN Ia
luminosity and host galaxy properties, and include the effects of all
identified systematic uncertainties directly in the cosmological fits.
Combining the SNLS3 data with the full WMAP7 power spectrum, the Sloan
Digital Sky Survey luminous red galaxy power spectrum, and a prior on
the Hubble constant H0 from SHOES, in a flat universe we find
omega_m=0.269+/-0.015 and w=-1.061+0.069-0.068 -- a 6.5% measure of
the dark energy equation-of-state parameter w. The statistical and
systematic uncertainties are approximately equal, with the systematic
uncertainties dominated by the photometric calibration of the SN Ia
fluxes -- without these calibration effects, systematics contribute
only a ~2% error in w. When relaxing the assumption of flatness, we
find omega_m=0.271+/-0.015, omega_k=-0.002+/-0.006, and
w=-1.069+0.091-0.092. Parameterizing the time evolution of w as
w(a)=w_0+w_a(1-a), gives w_0=-0.905+/-0.196, w_a=-0.984+1.094-1.097 in
a flat universe. All of our results are consistent with a flat, w=-1
universe. The size of the SNLS3 sample allows various tests to be
performed with the SNe segregated according to their light curve and
host galaxy properties. We find that the cosmological constraints
derived from these different sub-samples are consistent. There is
evidence that the coefficient, beta, relating SN Ia luminosity and
color, varies with host parameters at >4sigma significance (in
addition to the known SN luminosity--host relation); however this has
only a small effect on the cosmological results and is currently a
sub-dominant systematic.
Supernova Constraints and Systematic Uncertainties from the First 3
Years of the Supernova Legacy Survey
A. Conley, J. Guy, M. Sullivan, N. Regnault, P. Astier, C. Balland, S.
Basa, R.G. Carlberg, D. Fouchez, D. Hardin, I.M. Hook, D.A. Howell, R.
Pain, N. Palanque-Delabrouille, K.M. Perrett, C.J. Pritchet, J. Rich,
V. Ruhlmann-Kleider, D. Balam, S. Baumont, R.S. Ellis, S. Fabbro, H.K.
Fakhouri, N. Fourmanoit, S. Gonzalez-Gaitan, M.L. Graham, M.J. Hudson,
E. Hsiao, T. Kronborg, C. Lidman, A.M. Mourao, J.D. Neill, S.
Perlmutter, P. Ripoche, N. Suzuki, E.S. Walker
http://arxiv.org/abs/1104.1443v1
We combine high redshift Type Ia supernovae from the first 3 years of
the Supernova Legacy Survey (SNLS) with other supernova (SN) samples,
primarily at lower redshifts, to form a high-quality joint sample of
472 SNe (123 low-$z$, 93 SDSS, 242 SNLS, and 14 {\it Hubble Space
Telescope}). SN data alone require cosmic acceleration at >99.9%
confidence, including systematic effects. For the dark energy equation
of state parameter (assumed constant out to at least $z=1.4$) in a
flat universe, we find $w = -0.91^{+0.16}_{-0.20}(\mathrm{stat})
^{+0.07}_{-0.14} (\mathrm{sys})$ from SNe only, consistent with a
cosmological constant. Our fits include a correction for the recently
discovered relationship between host-galaxy mass and SN absolute
brightness. We pay particular attention to systematic uncertainties,
characterizing them using a systematics covariance matrix that
incorporates the redshift dependence of these effects, as well as the
shape-luminosity and color-luminosity relationships. Unlike previous
work, we include the effects of systematic terms on the empirical
light-curve models. The total systematic uncertainty is dominated by
calibration terms. We describe how the systematic uncertainties can be
reduced with soon to be available improved nearby and
intermediate-redshift samples, particularly those calibrated onto
USNO/SDSS-like systems.
Cosmology with Hypervelocity Stars
Abraham Loeb (Harvard)
http://arxiv.org/abs/1102.0007v2
In the standard cosmological model, the merger remnant of the Milky
Way and Andromeda (Milkomeda) will be the only galaxy remaining within
our event horizon once the Universe has aged by another factor of ten,
~10^{11} years after the Big Bang. After that time, the only
extragalactic sources of light in the observable cosmic volume will be
hypervelocity stars being ejected continuously from Milkomeda.
Spectroscopic detection of the velocity-distance relation or the
evolution in the Doppler shifts of these stars will allow a precise
measurement of the vacuum mass density as well as the local matter
distribution. Already in the near future, the next generation of large
telescopes will allow photometric detection of individual stars out to
the edge of the Local Group, and may target the ~10^{5+-1}
hypervelocity stars that originated in it as cosmological tracers.
