2,406 research outputs found
An Exploration of the Tully-Fisher Relation for Extreme Late-Type Spiral Galaxies
This paper explores the adherence of 47 extreme late-type galaxies to the B-
and V-band Tully-Fisher relations defined by a sample of local calibrators. In
both bands we find the mean luminosity at a given line width for extreme
late-type spirals to lie below that predicted by standard Tully-Fisher
relations. While many of the extreme late-type spirals do follow the
Tully-Fisher relation to within our observational uncertainties, most of these
galaxies lie below the normal, linear Tully-Fisher relation, and some are
underluminous by more than 2 sigma (i.e. >1.16 magnitudes in V). This suggests
a possible downward curvature of the Tully-Fisher relation for some of the
smallest and faintest rotationally supported disk galaxies. This may be a
consequence of the increasing prevalence of dark matter in these systems. We
find the deviation from the Tully-Fisher relation to increase with decreasing
luminosity and decreasing optical linear size in our sample, implying that the
physically smallest and faintest spirals may be a structurally and
kinematically distinct class of objects.Comment: 32 pages, 13 figures; to appear in the November A
Anomalous Evolution of the Dwarf Galaxy HIPASS J1321-31
We present HST/WFPC2 observations of the dwarf galaxy HIPASS J1321-31. This
unusual galaxy lies in the direction of the Centaurus A group of galaxies, and
has a color-magnitude diagram with a distinctive red plume of luminous stars.
This feature could arise from (a) a red giant branch if the galaxy were much
nearer than previously recognized, (b) a peculiar asymptotic giant branch, or,
(c) an ~1 Gigayear old population of intermediate mass red supergiants, which
we find to be the most likely explanation. However, the lack of equally
luminous blue stars requires that the star formation has dropped substantially
since these stars were formed. Evidently HIPASS J1321-31 experienced an episode
of enhanced star formation rather recently in its star formation history
followed by a period of relative quiescence which has led to the evolution of
the main sequence stars into the red supergiant branch. The stellar populations
in HIPASS J1321-31 reflect a star formation history that is uncommon in star
forming dwarf galaxies. This is the first time such a star formation history
has been noted, although the literature contains a small number of other dwarf
galaxies with similar color-magnitude diagrams. Therefore, HIPASS J1321-31 and
these other galaxies represent a different path of dwarf galaxy evolution that
has not been well-explored and an important probe into how dwarf galaxies
evolve.Comment: 5 pages, including 3 figures and 1 table, emulateapj5/apjfonts style.
Accepted by the Astrophysical Journal Letter
A search for resonant production of pairs in $4.8\ \rm{fb}^{-1}p\bar{p}\sqrt{s}=1.96\ \rm{TeV}$
We search for resonant production of tt pairs in 4.8 fb^{-1} integrated
luminosity of ppbar collision data at sqrt{s}=1.96 TeV in the lepton+jets decay
channel, where one top quark decays leptonically and the other hadronically. A
matrix element reconstruction technique is used; for each event a probability
density function (pdf) of the ttbar candidate invariant mass is sampled. These
pdfs are used to construct a likelihood function, whereby the cross section for
resonant ttbar production is estimated, given a hypothetical resonance mass and
width. The data indicate no evidence of resonant production of ttbar pairs. A
benchmark model of leptophobic Z \rightarrow ttbar is excluded with m_{Z'} <
900 GeV at 95% confidence level.Comment: accepted for publication in Physical Review D Sep 21, 201
Precision Top-Quark Mass Measurements at CDF
We present a precision measurement of the top-quark mass using the full
sample of Tevatron TeV proton-antiproton collisions collected
by the CDF II detector, corresponding to an integrated luminosity of 8.7
. Using a sample of candidate events decaying into the
lepton+jets channel, we obtain distributions of the top-quark masses and the
invariant mass of two jets from the boson decays from data. We then compare
these distributions to templates derived from signal and background samples to
extract the top-quark mass and the energy scale of the calorimeter jets with
{\it in situ} calibration. The likelihood fit of the templates from signal and
background events to the data yields the single most-precise measurement of the
top-quark mass, \mtop = 172.85 \pm\pmComment: submitted to Phys. Rev. Let
Measurement of and Production in Collisions at = 1.96 TeV
The Standard Model predictions for and production are
tested using an integrated luminosity of 200 pb of \ppbar collision data
collected at the Collider Detector at Fermilab. The cross sections are measured
selecting leptonic decays of the and bosons, and photons with
transverse energy GeV that are well separated from leptons. The
production cross sections and kinematic distributions for the and
are compared to SM predictions.Comment: 7 pages, 4 figures, submitted to PR
Combined search for the standard model Higgs boson decaying to a bb pair using the full CDF data set
We combine the results of searches for the standard model Higgs boson based
on the full CDF Run II data set obtained from sqrt(s) = 1.96 TeV p-pbar
collisions at the Fermilab Tevatron corresponding to an integrated luminosity
of 9.45/fb. The searches are conducted for Higgs bosons that are produced in
association with a W or Z boson, have masses in the range 90-150 GeV/c^2, and
decay into bb pairs. An excess of data is present that is inconsistent with the
background prediction at the level of 2.5 standard deviations (the most
significant local excess is 2.7 standard deviations).Comment: To be published in Phys. Rev. Lett (v2 contains minor updates based
on comments from PRL
Measurements of branching fraction ratios and CP-asymmetries in suppressed B^- -> D(-> K^+ pi^-)K^- and B^- -> D(-> K^+ pi^-)pi^- decays
We report the first reconstruction in hadron collisions of the suppressed
decays B^- -> D(-> K^+ pi^-)K^- and B^- -> D(-> K^+ pi^-)pi^-, sensitive to the
CKM phase gamma, using data from 7 fb^-1 of integrated luminosity collected by
the CDF II detector at the Tevatron collider. We reconstruct a signal for the
B^- -> D(-> K^+ pi^-)K^- suppressed mode with a significance of 3.2 standard
deviations, and measure the ratios of the suppressed to favored branching
fractions R(K) = [22.0 \pm 8.6(stat)\pm 2.6(syst)]\times 10^-3, R^+(K) =
[42.6\pm 13.7(stat)\pm 2.8(syst)]\times 10^-3, R^-(K)= [3.8\pm 10.3(stat)\pm
2.7(syst]\times 10^-3, as well as the direct CP-violating asymmetry A(K) =
-0.82\pm 0.44(stat)\pm 0.09(syst) of this mode. Corresponding quantities for
B^- -> D(-> K^+ pi^-)pi^- decay are also reported.Comment: 8 pages, 1 figure, accepted by Phys.Rev.D Rapid Communications for
Publicatio
Measurement of branching ratio and Bs0 lifetime in the decay Bs0 -> J/psi f0(980) at CDF
We present a study of Bs0 decays to the CP-odd final state J/psi f0(980) with
J/psi -> mu+ mu- and f0(980) -> pi+ pi-. Using ppbar collision data with an
integrated luminosity of 3.8/fb collected by the CDF II detector at the
Tevatron we measure a Bs0 lifetime of tau(Bs0 -> J/psi f0(980)) = 1.70
-0.11+0.12(stat) +-0.03(syst) ps. This is the first measurement of the Bs0
lifetime in a decay to a CP eigenstate and corresponds in the standard model to
the lifetime of the heavy Bs0 eigenstate. We also measure the product of
branching fractions of Bs0 -> J/psi f0(980) and f0(980) -> pi+ pi- relative to
the product of branching fractions of Bs0 -> J/psi phi and phi -> K+ K- to be
R_f0/phi = 0.257 +_0.020(stat) +-0.014(syst), which is the most precise
determination of this quantity to date.Comment: accepted by Phys. Rev.
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