47 research outputs found
The LX-sigma Relation for Galaxies and Clusters of Galaxies
We demonstrate that individual elliptical galaxies and clusters of galaxies
form a continuous X-ray luminosity---velocity dispersion (LX-sigma) relation.
Our samples of 280 clusters and 57 galaxies have LX ~ sigma^4.4 and LX ~
sigma^10, respectively. This unified LX - sigma relation spans 8 orders of
magnitude in LX and is fully consistent with the observed and theoretical
luminosity---temperature scaling laws. Our results support the notion that
galaxies and clusters of galaxies are the luminous tracers of similar dark
matter halos.Comment: 11 pages, including 2 tables and 2 figures. Accepted for publication
in The Astrophysical Journal Letters; the Letters version excludes Table 1,
which is available in ASCII format at http://tdc-www.harvard.edu/lxsigm
Dwarf galaxies in the Dynamically Evolved NGC 1407 Group
The NGC 1407 Group stands out among nearby structures by its properties that
suggest it is massive and evolved. It shares properties with entities that have
been called fossil groups: the 1.4 magnitude differential between the dominant
elliptical galaxy and the second brightest galaxy comes close to satisfying the
definition that has been used to define the fossil class. There are few
intermediate luminosity galaxies, but a large number of dwarfs in the group. We
estimate there are 250 group members to the depth of our survey. The slope of
the faint end of the luminosity function (reaching M_R = -12) is alpha = -1.35.
Velocities for 35 galaxies demonstrate that this group with one dominant galaxy
has a mass of 7 X 10^13 M_sun and M/L_R = 340. Two galaxies in close proximity
to NGC 1407 have very large blueshifts. The most notable is the second
brightest galaxy, NGC 1400, with a velocity of -1072 km/s with respect to the
group mean. We report the detection of X-ray emission from this galaxy and from
the group.Comment: final version to appear in MNRAS, URL for data include
The Cluster LX-sigma Relation Has Implications for Scale-Free Cosmologies
I show that the cluster LX-sigma relation should be sensitive to cosmologies
with a scale-free power spectrum of initial density fluctuations, P(k) ~ k^n. I
derive the dependence, and argue that a conservative interpretation of current
observations implies n < -2.0 and n < -1.1 at the one-sided 90% and 99%
confidence levels, respectively. This result, which agrees with constraints on
n from the x-ray cluster temperature function, should be roughly independent of
the value of Omega or Lambda.Comment: 4 pages, including 1 figure. To appear in the Astrophysical Journal
Letter
The NGC 5846 Group: Dynamics and the Luminosity Function to M_R=-12
We conduct a photometric and spectroscopic survey of a 10 sq. deg. region
surrounding the nearby NGC 5846 group of galaxies, using the
Canada-France-Hawaii and Keck I telescopes to study the population of dwarf
galaxies as faint as M_R=-10. Candidates are identified on the basis of
quantitative surface brightness and qualitative morphological criteria.
Spectroscopic follow up and a spatial correlation analysis provide the basis
for affirming group memberships. Altogether, 324 candidates are identified and
83 have spectroscopic membership confirmation. We argue on statistical grounds
that a total 251 +/- 10 galaxies in our sample are group members. The
observations, together with archival Sloan Digital Sky Survey, ROSAT,
XMM-Newton, and ASCA data, suggest that the giant ellipticals NGC 5846 and NGC
5813 are the dominant components of subgroups separated by 600 kpc in
projection and embedded in a 1.6 Mpc diameter dynamically evolved halo. The
galaxy population is overwhelmingly early type. The group velocity dispersion
is 322 km/s, its virial mass is 8.4 x 10^13 M_sun, and M/L_R = 320 M_sun/L_sun.
The ratio of dwarfs to giants is large compared with other environments in the
Local Supercluster studied and, correspondingly, the luminosity function is
relatively steep, with a faint end Schechter function slope of \alpha_d = -1.3
+/- 0.1 (statistical) +/- 0.1 (systematic) at our completeness limit of M_R =
-12.Comment: 17 pages; accepted for publication in the Astronomical Journa
The Canadian Cluster Comparison Project: detailed study of systematics and updated weak lensing masses
Masses of clusters of galaxies from weak gravitational lensing analyses of
ever larger samples are increasingly used as the reference to which baryonic
scaling relations are compared. In this paper we revisit the analysis of a
sample of 50 clusters studied as part of the Canadian Cluster Comparison
Project. We examine the key sources of systematic error in cluster masses. We
quantify the robustness of our shape measurements and calibrate our algorithm
empirically using extensive image simulations. The source redshift distribution
is revised using the latest state-of-the-art photometric redshift catalogs that
include new deep near-infrared observations. Nonetheless we find that the
uncertainty in the determination of photometric redshifts is the largest source
of systematic error for our mass estimates. We use our updated masses to
determine b, the bias in the hydrostatic mass, for the clusters detected by
Planck. Our results suggest 1-b=0.76+-0.05(stat)}+-0.06(syst)}, which does not
resolve the tension with the measurements from the primary cosmic microwave
background.Comment: resubmitted to MNRAS after review by refere
The Orbital Structure of Dark Matter Halos with Gas
With the success of the Chandra and XMM missions and the maturation of
gravitational lensing techniques, powerful constraints on the orbital structure
of cluster dark matter halos are possible. I show that the X-ray emissivity and
mass of a galaxy cluster uniquely specify the anisotropy and velocity
dispersion profiles of its dark matter halo. I consider hydrostatic as well as
cooling flow scenarios, and apply the formalism to the lensing cluster
CL0024+16 and the cooling flow cluster Abell 2199. In both cases, the model
predicts a parameter-free velocity dispersion profile that is consistent with
independent optical redshift surveys of the clusters.Comment: 17 pages, 12 figures; to appear in the Astrophysical Journa
An updated determination of \alpha_s from tau decays
Employing our previous framework to treat non-perturbative effects
self-consistently, including duality violations, we update the determination of
the strong coupling, \alpha_s, using a modified version of the 1998 OPAL data,
updated to reflect current values of exclusive mode hadronic \tau decay
branching fractions. Our best n_f=3 values from the updated OPAL data are
\alpha_s(m^2_\tau)=0.325+-0.018 and \alpha_s(m^2_\tau)=0.347+-0.025 in
fixed-order and contour-improved perturbation theory, respectively.
To account for non-perturbative effects, non-linear, multi-parameter fits are
necessary. We have, therefore, investigated the posterior probability
distribution of the model parameters underlying our fits in more detail. We
find that OPAL data alone provide only weak constraints on some of the
parameters needed to model duality violations, especially in the case of fits
involving axial vector channel data, making additional prior assumptions on the
expected size of these parameters necessary at present. We provide evidence
that this situation could be greatly improved if hadronic spectral functions
based on the high-statistics BaBar and Belle data were to be made available.Comment: 26 pages, 6 figure