2,283,333 research outputs found
MOND mass-to-light ratios for galaxy groups
I estimate MOND M/L values for nine galaxy groups that were recently studied
by Tully et al.. Instead of the large M/L values that they find with Newtonian
dynamics (up to 1200 solar units) the MOND estimates cluster around 1 solar
unit. Tully et al. find a systematic and significant difference between the M/L
values of groups that do not contain luminous galaxies and those that do:
Dwarfs-only groups have larger M/L values (by a factor of about 5). The MOND
M/L values do not show this trend; the Newtonian disparity is traced back to
the dwarfs-only groups having systematically smaller intrinsic accelerations
(similar sizes, but rather smaller velocity dispersions).Comment: 7 pages, Astrophys. J. Lett., in pres
Dynamical Models of Elliptical Galaxies in z=0.5 Clusters: II. Mass-to-Light Ratio Evolution without Fundamental Plane Assumptions
We study M/L evolution of early-type galaxies using dynamical modeling of
resolved internal kinematics. This makes fewer assumptions than Fundamental
Plane (FP) studies and provides a powerful new approach for studying galaxy
evolution. We focus on the sample of 25 galaxies in clusters at z=0.5 modeled
in Paper I. For comparison we compile and homogenize M/L literature data for 60
nearby galaxies that were modeled in comparable detail. The nearby sample obeys
log(M/L)_B = Z + S log(sigma_eff/[200 km/s]), with Z = 0.896 +/- 0.010, S =
0.992 +/- 0.054, and sigma_eff the effective velocity dispersion. The z=0.5
sample follows a similar relation but with lower zeropoint. The implied M/L
evolution is Delta log(M/L) / Delta z = -0.457 +/- 0.046(random) +/-
0.078(systematic), consistent with passive evolution following high-redshift
formation. This agrees with the FP results for this sample by van Dokkum & van
der Marel. This confirms that FP evolution tracks M/L evolution, which is an
important verification of the assumptions that underly FP studies. However,
while we find more FP evolution for galaxies of low sigma_eff (or low mass),
the dynamical M/L evolution instead shows little trend with sigma_eff. We argue
that this difference can be plausibly attributed to a combination of two
effects: (a) evolution in structural galaxy properties other than M/L; and (b)
the neglect of rotational support in studies of FP evolution. The results leave
the question open whether the low-mass galaxies in the sample have younger
population ages than the high-mass galaxies. This highlights the general
importance in the study of population ages for complementing dynamical
measurements with broad-band colors or spectroscopic population diagnostics.Comment: ApJ, submitted; 17 pages formatted with emulateap
On the Mass-to-Light Ratio of Large Scale Structure
We examine the dependence of the mass-to-light (M/L) ratio of large-scale
structure on cosmological parameters, in models that are constrained to match
observations of the projected galaxy correlation function w(rp). For a sequence
of cosmological models with a fixed P(k) shape and increasing normalization
\sig8, we find parameters of the galaxy halo occupation distribution (HOD) that
reproduce SDSS measurements of w(rp) as a function of luminosity. Using these
HOD models we calculate mean M/L ratios as a function of halo mass and populate
halos of N-body simulations to compute M/L in larger scale environments,
including cluster infall regions. For all cosmological models, the M/L ratio in
high mass halos or high density regions is approximately independent of halo
mass or smoothing scale. However, the "plateau" value of M/L depends on \sig8
as well as \Omega_m, and it represents the universal mass-to-light ratio
only for models in which the galaxy correlation function is approximately
unbiased, i.e., with \sig8 ~ \sig8_gal. Our results for cluster mass halos
follow the trend M/L = 577(\Omega_m/0.3)(\sig8/0.9)^{1.7} h Msun/Lsun. Combined
with Carlberg et al.'s (1996) mean M/L ratio of CNOC galaxy clusters, this
relation implies (\sig8/0.9)(\Omega_m/0.3)^{0.6} = 0.75 +/- 0.06. M/L ratios of
clusters from the SDSS and CAIRNS surveys yield similar results. This
constraint is inconsistent with parameter values \Omega_m ~ 0.3, \sig8 ~ 0.9
favored by recent joint analyses of CMB measurements and other large-scale
structure data. We discuss possible resolutions, none of which seems entirely
satisfactory. Appendices present an improved formula for halo bias factors and
an improved analytic technique for calculating the galaxy correlation function
from a given cosmological model and HOD. (Abridged)Comment: Accepted to ApJ (v 630, no 2). Replaced with accepted versio
Colors and Mass-to-Light Ratios of Bulges and Disks of Nearby Spiral Galaxies
We investigate colors and mass-to-light ratios (s) of the bulges and
disks for 28 nearby spiral galaxies with various morphological types of Sab to
Scd, using images in optical and near-infrared (, , and ) bands and
published rotation curves. It is shown that the observed colors and s
generally agree with the galaxy formation model with an exponentially declining
star formation rate and shallow slope (ex. Scalo) initial mass function (IMF)
for both the bulges and the disks. We find that the bulge is generally
higher than the disk and that the galaxies with larger bulge-to-total
luminosity ratio tend to have a smaller bulge . The fact indicates that
the luminosity-weighted average age of bulges for early-type spirals is younger
than that of later-type spirals. These results support a formation scenario
that produces young stars for the bulges of middle-type and early-type spirals.Comment: 33 pages, 24 figures, PASJ accepte
Identifying Borrowings between Eastern Mediterranean Cults:A Methodology Based on a Comparison of Cultic Practices for Ištar and Meter
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