1,033 research outputs found
REPORT OF THE WESTERN EXTENSION PUBLIC AFFAIRS COMMITTEE
Teaching/Communication/Extension/Profession,
The First Detailed X-ray Observations of High-Redshift, Optically-Selected Clusters: XMM-Newton Results for Cl 1324+3011 at z = 0.76 and Cl 1604+4304 at z = 0.90
We present the first detailed X-ray observations of optically-selected
clusters at high redshift. Two clusters, Cl 1324+3011 at z = 0.76 and Cl
1604+4304 at z = 0.90, were observed with XMM-Newton. The optical center of
each cluster is coincident with an extended X-ray source whose emission is
detected out to a radius of 0.5 Mpc. The emission from each cluster appears
reasonably circular, with some indication of asymmetries and more complex
morphologies. Similarly to other optically-selected clusters at redshifts of z
> 0.4, both clusters are modest X-ray emitters with bolometric luminosities of
only Lx = 1.4 - 2.0 x 10^(44) erg/s. We measure gas temperatures of T = 2.88
(+0.71/-0.49) keV for Cl 1324+3011 and 2.51 (+1.05/-0.69) keV for Cl 1604+4304.
The X-ray properties of both clusters are consistent with the high-redshift
Lx-T relation measured from X-ray-selected samples at z > 0.5. However, based
on the local relations, their X-ray luminosities and temperatures are low for
their measured velocity dispersions (sigma). The clusters are cooler by a
factor of 2 - 9 compared to the local sigma-T relation. We briefly discuss the
possible explanations for these results.Comment: 14 pages, 4 figures; accepted for publication in Astrophysical
Journal Letters; version with full resolution figures available at
http://bubba.ucdavis.edu/~lubin/xmm.pd
The GEEC2 spectroscopic survey of Galaxy Groups at
We present the data release of the Gemini-South GMOS spectroscopy in the
fields of 11 galaxy groups at , within the COSMOS field. This forms
the basis of the Galaxy Environment Evolution Collaboration 2 (GEEC2) project
to study galaxy evolution in haloes with across cosmic
time. The final sample includes spectroscopically--confirmed members with
per cent complete for galaxies within the virial
radius, and with stellar mass . Including
galaxies with photometric redshifts we have an effective sample size of galaxies within the virial radii of these groups. We present group
velocity dispersions, dynamical and stellar masses. Combining with the GCLASS
sample of more massive clusters at the same redshift we find the total stellar
mass is strongly correlated with the dynamical mass, with
. This stellar
fraction of per cent is lower than predicted by some halo occupation
distribution models, though the weak dependence on halo mass is in good
agreement. Most groups have an easily identifiable most massive galaxy (MMG)
near the centre of the galaxy distribution, and we present the spectroscopic
properties and surface brightness fits to these galaxies. The total stellar
mass distribution in the groups, excluding the MMG, compares well with an NFW
profile with concentration , for galaxies beyond . This is
more concentrated than the number density distribution, demonstrating that
there is some mass segregation.Comment: Accepted for publication in MNRAS. The appendix is omitted due to
large figures. The full version will be available from the MNRAS website and
from http://quixote.uwaterloo.ca/~mbalogh/papers/GEEC2_data.pdf. Long data
tables are available from MNRAS or by contacting the first autho
The slope of the black-hole mass versus velocity dispersion correlation
Observations of nearby galaxies reveal a strong correlation between the mass
of the central dark object M and the velocity dispersion sigma of the host
galaxy, of the form log(M/M_sun) = a + b*log(sigma/sigma_0); however, published
estimates of the slope b span a wide range (3.75 to 5.3). Merritt & Ferrarese
have argued that low slopes (<4) arise because of neglect of random measurement
errors in the dispersions and an incorrect choice for the dispersion of the
Milky Way Galaxy. We show that these explanations account for at most a small
part of the slope range. Instead, the range of slopes arises mostly because of
systematic differences in the velocity dispersions used by different groups for
the same galaxies. The origin of these differences remains unclear, but we
suggest that one significant component of the difference results from Ferrarese
& Merritt's extrapolation of central velocity dispersions to r_e/8 (r_e is the
effective radius) using an empirical formula. Another component may arise from
dispersion-dependent systematic errors in the measurements. A new determination
of the slope using 31 galaxies yields b=4.02 +/- 0.32, a=8.13 +/- 0.06, for
sigma_0=200 km/s. The M-sigma relation has an intrinsic dispersion in log M
that is no larger than 0.3 dex. In an Appendix, we present a simple model for
the velocity-dispersion profile of the Galactic bulge.Comment: 37 pages, 9 figure
A Very Hot, High Redshift Cluster of Galaxies: More Trouble for Omega_0 = 1
We have observed the most distant (z=0.829) cluster of galaxies in the
Einstein Extended Medium Sensitivity Survey, with the ASCA and ROSAT
satellites. We find an X-ray temperature of 12.3 +3.1/-2.2 keV for this
cluster, and the ROSAT map reveals significant substructure. The high
temperature of MS1054-0321 is consistent with both its approximate velocity
dispersion, based on the redshifts of 12 cluster members we have obtained at
the Keck and the Canada-France-Hawaii telescopes, and with its weak lensing
signature. The X-ray temperature of this cluster implies a virial mass ~ 7.4 x
10^14 h^-1 solar masses, if the mean matter density in the universe equals the
critical value, or larger if Omega_0 < 1. Finding such a hot, massive cluster
in the EMSS is extremely improbable if clusters grew from Gaussian
perturbations in an Omega_0 = 1 universe. Combining the assumptions that
Omega_0 = 1 and that the intial perturbations were Gaussian with the observed
X-ray temperature function at low redshift, we show that the probability of
this cluster occurring in the volume sampled by the EMSS is less than a few
times 10^{-5}. Nor is MS1054-0321 the only hot cluster at high redshift; the
only two other EMSS clusters already observed with ASCA also have
temperatures exceeding 8 keV. Assuming again that the initial perturbations
were Gaussian and Omega_0 = 1, we find that each one is improbable at the <
10^{-2} level. These observations, along with the fact that these luminosities
and temperatures of the high- clusters all agree with the low-z L_X-T_X
relation, argue strongly that Omega_0 < 1. Otherwise, the initial perturbations
must be non-Gaussian, if these clusters' temperatures do indeed reflect their
gravitational potentials.Comment: 20 pages, 4 figures, To appear in 1 Aug 1998 ApJ (heavily revised
version of original preprint
A VLBI Resolution of the Pleiades Distance Controversy
Because of its proximity and its youth, the Pleiades open cluster of stars
has been extensively studied and serves as a cornerstone for our understanding
of the physical properties of young stars. This role is called into question by
the "Pleiades distance controversy" wherein the cluster distance of 120.2+/-1.5
pc as measured by the optical space astrometry mission Hipparcos is
significantly different from the distance of 133.5+/-1.2 pc derived with other
techniques. We present an absolute trigonometric parallax distance measurement
to the Pleiades cluster that uses very long baseline radio interferometry. This
distance of 136.2+/-1.2 pc is the most accurate and precise yet presented for
the cluster and is incompatible with the Hipparcos distance determination. Our
results cement existing astrophysical models for Pleiades-age stars.Comment: Cover-story article of the August 29th edition of Science. 22 pages,
2 figures, 6 tables; includes Supplementary materia
GPAQ-R: development and psychometric properties of a version of the general practice assessment questionnaire for use for revalidation by general practitioners in the UK.
BACKGROUND: The General Practice Assessment Questionnaire (GPAQ) has been widely used to assess patient experience in general practice in the UK since 2004. In 2013, new regulations were introduced by the General Medical Council (GMC) requiring UK doctors to undertake periodic revalidation, which includes assessment of patient experience for individual doctors. We describe the development of a new version of GPAQ - GPAQ-R which addresses the GMC's requirements for revalidation as well as additional NHS requirements for surveys that GPs may need to carry out in their own practices. METHODS: Questionnaires were given out by doctors or practice staff after routine consultations in line with the guidance given by the General Medical Council for surveys to be used for revalidation. Data analysis and practice reports were provided independently. RESULTS: Data were analysed for questionnaires from 7258 patients relating to 164 GPs in 29 general practices. Levels of missing data were generally low (typically 4.5-6%). The number of returned questionnaires required to achieve reliability of 0.7 were around 35 for individual doctor communication items and 29 for a composite score based on doctor communication items. This suggests that the responses to GPAQ-R had similar reliability to the GMC's own questionnaire and we recommend 30 completed GPAQ-R questionnaires are sufficient for revalidation purposes. However, where an initial screen raises concern, the survey might be repeated with 50 completed questionnaires in order to increase reliability. CONCLUSIONS: GPAQ-R is a development of a well-established patient experience questionnaire used in general practice in the UK since 2004. This new version can be recommended for use in order to meet the UK General Medical Council's requirements for surveys to be used in revalidation of doctors. It also meets the needs of GPs to ask about patient experience relating to aspects of practice care that are not specific to individual general practitioners (e.g. receptionists, telephone access) which meet other survey requirements of the National Health Service in England. Use of GPAQ-R has the potential to reduce the number of surveys that GPs need to carry out in their practices to meet the various regulatory requirements which they face
A Stellar Dynamical Measurement of the Black Hole Mass in the Maser Galaxy NGC 4258
We determine the mass of the black hole at the center of the spiral galaxy
NGC 4258 by constructing axisymmetric dynamical models of the galaxy. These
models are constrained by high spatial resolution imaging and long-slit
spectroscopy of the nuclear region obtained with the {\em Hubble Space
Telescope}, complemented by ground-based observations extending to larger
radii. Our best mass estimate is \MBH = (3.3 \pm 0.2) \times 10^7 \MSun for
a distance of 7.28 Mpc (statistical errors only). This is within 15% of
(3.82\pm 0.01) \times 10^7 \MSun, the mass determined from the kinematics of
water masers (rescaled to the same distance) assuming they are in Keplerian
rotation in a warped disk. The construction of accurate dynamical models of NGC
4258 is somewhat compromised by an unresolved active nucleus and color
gradients, the latter caused by variations in the stellar population and/or
obscuring dust. These problems are not present in the other black
hole mass determinations from stellar dynamics that have been published by us
and other groups; thus, the relatively close agreement between the stellar
dynamical mass and the maser mass in NGC 4258 enhances our confidence in the
black hole masses determined in other galaxies from stellar dynamics using
similar methods and data of comparable quality.Comment: 58 pages, submitted to ApJ. Some figures excluded due to size. The
entire paper is at http://www.noao.edu/noao/staff/lauer/nuker_papers.htm
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