1,180 research outputs found
Redshifts and Velocity Dispersions of Galaxy Clusters in the Horologium-Reticulum Supercluster
We present 118 new optical redshifts for galaxies in 12 clusters in the
Horologium-Reticulum supercluster (HRS) of galaxies. For 76 galaxies, the data
were obtained with the Dual Beam Spectrograph on the 2.3m telescope of the
Australian National University at Siding Spring Observatory. After combining 42
previously unpublished redshifts with our new sample, we determine mean
redshifts and velocity dispersions for 13 clusters, in which previous
observational data were sparse. In six of the 13 clusters, the newly determined
mean redshifts differ by more than 750 km/s from the published values. In the
case of three clusters, A3047, A3109, and A3120, the redshift data indicate the
presence of multiple components along the line of sight. The new cluster
redshifts, when combined with other reliable mean redshifts for clusters in the
HRS, are found to be distinctly bi-modal. Furthermore, the two redshift
components are consistent with the bi-modal redshift distribution found for the
inter-cluster galaxies in the HRS by Fleenor et al. (2005).Comment: 13 pages, 3 figures, Accepted to A
Limits on spacetime foam
Plausibly spacetime is "foamy" on small distance scales, due to quantum fluctuations. We elaborate on the proposal to detect spacetime foam by looking for seeing disks in the images of distant quasars and AGNs. This is a null test in the sense that the continued presence of unresolved "point" sources at the milli-arc second level in samples of distant compact sources puts severe constraints on theories of quantized spacetime foam at the Planckian level. We discuss the geometry of foamy spacetime, and the appropriate distance measure for calculating the expected angular broadening. We then deal with recent data and the constraints they put on spacetime foam models. While time lags from distant pulsed sources such as GRBs have been posited as a possible test of spacetime foam models, we demonstrate that the time-lag effect is rather smaller than has been calculated, due to the equal probability of positive and negative fluctuations in the speed of light inherent in such models. Thus far, images of high-redshift quasars from the Hubble Ultra-Deep Field (UDF) provide the most stringent test of spacetime foam theories. While random walk models () have already been ruled out, the holographic () model remains viable. Here parametrizes the different spacetime foam models according to which the fluctuation of a distance is given by with being the Planck length. Indeed, we see a slight wavelength-dependent blurring in the UDF images selected for this study. Using existing data in the {\it Hubble Space Telescope (HST)} archive we find it is impossible to rule out the model, but exclude all models with . By comparison, current GRB time lag observations only exclude models with
Multiple Merging Events in the Double Cluster A3128/A3125
Multi-fiber spectroscopy has been obtained for 335 galaxies in the field of
the double cluster A3128/A3125, using the 2dF multi-fiber positioner on the
AAT. A total of 532 objects in the double cluster now have known redshifts. We
have also obtained a 20 ks Chandra ACIS-I image of A3128 and radio imaging with
the MOST and the ATCA. The spatial-kinematic distribution of redshifts in the
field of A3128/A3125, when combined with the Chandra image of A3128, reveals a
variety of substructures present in the galaxy distribution and in the hot ICM.
The most striking large-scale feature in the galaxy distribution is an
underpopulated redshift zone ~4000 km/s on either side of the cluster velocity
at ~17500 km/s. We attribute this depletion zone to the effect of the extensive
Horologium-Reticulum Supercluster (HRS), within which A3128/A3125 is embedded.
In addition, numerous smaller groups of galaxies are identified, particularly
in the underpopulated region within +-4000 km/s of the cluster redshift. Due to
the large gravitational influence of the HRS, these groups arrive at A3128 with
a very high (hypersonic) infall velocity. Two of these groups appear as
elongated filaments in position-velocity diagrams, indicating that they are
tidally distended groups which have been disrupted after a close passage
through A3128. We have identified a primary NE-SW merger axis connecting A3128
with A3125, along which the filaments are also oriented. In addition, the
Chandra image reveals that the X-ray emission is split into two components,
each with very small core radii, that are separated by ~1 Mpc along the NE-SW
axis. We propose that the complex X-ray morphology is likely the result of the
hypersonic infall of a relatively small group into A3128. The group produces a
major disruption in the ICM due to its high infall velocity.Comment: 52 pages, 27 figures, accepted for publication in the Astronomical
Journal. A more easily down-loaded version with full resolution figures is
available at http://www.physics.unc.edu/~jim/a3128/LANL
Large-Scale Velocity Structures in the Horologium-Reticulum Supercluster
We present 547 optical redshifts obtained for galaxies in the region of the
Horologium-Reticulum Supercluster (HRS) using the 6dF multi-fiber spectrograph
on the UK Schmidt Telescope at the Anglo Australian Observatory. The HRS covers
an area of more than 12deg x 12deg on the sky centered at approximately RA =
03h19m, DEC = -50deg 02amin. Our 6dF observations concentrate upon the
inter-cluster regions of the HRS, from which we describe four primary results.
First, the HRS spans at least the redshift range from 17,000 to 22,500 km s^-1.
Second, the overdensity of galaxies in the inter-cluster regions of the HRS in
this redshift range is estimated to be 2.4, or del rho/ rho ~ 1.4. Third, we
find a systematic trend of increasing redshift along a Southeast-Northwest
(SE-NW) spatial axis in the HRS, in that the mean redshift of HRS members
increases by more than 1500 km s^-1 from SE to NW over a 12 deg region. Fourth,
the HRS is bi-modal in redshift with a separation of ~ 2500 km s^-1 (35 Mpc)
between the higher and lower redshift peaks. This fact is particularly evident
if the above spatial-redshift trend is fitted and removed. In short, the HRS
appears to consist of two components in redshift space, each one exhibiting a
similar systematic spatial-redshift trend along a SE-NW axis. Lastly, we
compare these results from the HRS with the Shapley supercluster and find
similar properties and large-scale features.Comment: 20 pages, 9 figures, accepted to A
USU Teaching Documentation: Dossiers from the Mentoring Program
The nation\u27s land grant institutions were founded on the principle of access for the general public to the knowledge gained through research and creative activity fostered in higher education. Central to our access mission is our dedication to teaching and learning that is informed by research and discovery, both of which must result, at least in part, from our engagement with our external constituents. That teaching and learning informs our research and vice versa; our research informs and aids in our teaching mission.
This work, compiled by Professors Maria Luisa Spicer-Escalante and Cathy Ferrand Bullock, is focused on how the best, highly informed teaching is accomplished when done in an intentional manner. That intentional process helps the best university educators thoughtfully build their teaching story in an organized manner. Educators think about how they can successfully reach and engage their appropriate student audiences (or mentees), what they hope to accomplish, and how they intend to accomplish their goals. Further, as learning outcomes are identified and established, first-rate methods for course design, content inclusion, and continuous improvement can be outlined.
Those of us who follow these intentional principles may then detail our growth and success along the way as teachers in the development of documents that tell our stories. Undoubtedly, the ability to clearly document and articulate that story will help academic personnel add to their tenure and promotion preparation in a very meaningful way. But as or even more important is the opportunity to describe these journeys with all the efforts, large and small, of improving their product in terms of learning outcomes and student growth and success.
The nuggets of wisdom compiled by Professors Spicer-Escalante and Bullock, in USU Teaching Documentation: Dossiers from the Mentoring Program, will help teachers across the board from the new lecturer or assistant professor to the experienced professor dive into their teaching programs and find ways to continuously experiment and refine their approaches to our critically important student audiences.
Good luck, teach on, and successfully document some of the most important work you all do!
Frank Galey
Executive Vice President and Provost
Utah State University 2019https://digitalcommons.usu.edu/ua_faculty/1000/thumbnail.jp
Search for right-handed W bosons in top quark decay
We present a measurement of the fraction f+ of right-handed W bosons produced
in top quark decays, based on a candidate sample of events in the
lepton+jets decay mode. These data correspond to an integrated luminosity of
230pb^-1, collected by the DO detector at the Fermilab Tevatron
Collider at sqrt(s)=1.96 TeV. We use a constrained fit to reconstruct the
kinematics of the and decay products, which allows for the
measurement of the leptonic decay angle for each event. By comparing
the distribution from the data with those for the expected
background and signal for various values of f+, we find
f+=0.00+-0.13(stat)+-0.07(syst). This measurement is consistent with the
standard model prediction of f+=3.6x10^-4.Comment: Submitted to Physical Review D Rapid Communications 7 pages, 3
figure
Measurement of Semileptonic Branching Fractions of B Mesons to Narrow D** States
Using the data accumulated in 2002-2004 with the DO detector in
proton-antiproton collisions at the Fermilab Tevatron collider with
centre-of-mass energy 1.96 TeV, the branching fractions of the decays B ->
\bar{D}_1^0(2420) \mu^+ \nu_\mu X and B -> \bar{D}_2^{*0}(2460) \mu^+ \nu_\mu X
and their ratio have been measured: BR(\bar{b}->B) \cdot BR(B-> \bar{D}_1^0
\mu^+ \nu_\mu X) \cdot BR(\bar{D}_1^0 -> D*- pi+) =
(0.087+-0.007(stat)+-0.014(syst))%; BR(\bar{b}->B)\cdot BR(B->D_2^{*0} \mu^+
\nu_\mu X) \cdot BR(\bar{D}_2^{*0} -> D*- \pi^+) =
(0.035+-0.007(stat)+-0.008(syst))%; and (BR(B -> \bar{D}_2^{*0} \mu^+ \nu_\mu
X)BR(D2*0->D*- pi+)) / (BR(B -> \bar{D}_1^{0} \mu^+ \nu_\mu X)\cdot
BR(\bar{D}_1^{0}->D*- \pi^+)) = 0.39+-0.09(stat)+-0.12(syst), where the charge
conjugated states are always implied.Comment: submitted to Phys. Rev. Let
Measurement of the Lifetime Difference in the B_s^0 System
We present a study of the decay B_s^0 -> J/psi phi We obtain the CP-odd
fraction in the final state at time zero, R_perp = 0.16 +/- 0.10 (stat) +/-
0.02 (syst), the average lifetime of the (B_s, B_sbar) system, tau (B_s^0)
=1.39^{+0.13}_{-0.16} (stat) ^{+0.01}_{-0.02} (syst) ps, and the relative width
difference between the heavy and light mass eigenstates, Delta Gamma/Gamma =
(Gamma_L - Gamma_H)/Gamma =0.24^{+0.28}_{-0.38} (stat) ^{+0.03}_{-0.04} (syst).
With the additional constraint from the world average of the B_s^0$lifetime
measurements using semileptonic decays, we find tau (B_s^0)= 1.39 +/- 0.06 ~ps
and Delta Gamma/\Gamma = 0.25^{+0.14}_{-0.15}. For the ratio of the B_s^0 and
B^0 lifetimes we obtain tau(B_s^0)/tau(B^0)} = 0.91 +/- 0.09 (stat) +/- 0.003
(syst).Comment: submitted to Phys. Rev. Lett. FERMILAB-PUB-05-324-
Search for Large Extra Spatial Dimensions in Dimuon Production with the D0 Detector
We present the results of a search for the effects of large extra spatial
dimensions in collisions at 1.96 TeV in events
containing a pair of energetic muons. The data correspond to 246 \ipb of
integrated luminosity collected by the \D0 experiment at the Fermilab Tevatron
Collider. Good agreement with the expected background was found, yielding no
evidence for large extra dimensions. We set 95% C.L. lower limits on the
fundamental Planck scale between 0.85 TeV and 1.27 TeV within several
formalisms. These are the most stringent limits achieved in the dimuon channel
to date.Comment: 8 pages, 3 figures, 1 table. Published in Phys. Rev. Lett. Minor
changes in v2 to match the published versio
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