990 research outputs found
Distinguishing Mergers and Disks in High Redshift Observations of Galaxy Kinematics
The majority of massive star-forming galaxies at have velocity
gradients suggestive of rotation, in addition to large amounts of disordered
motions. In this paper, we demonstrate that it is challenging to distinguish
the regular rotation of a disk galaxy from the orbital motions of merging
galaxies with seeing-limited data. However, the merger fractions at
are likely too low for this to have a large effect on measurements of disk
fractions. To determine how often mergers pass for disks, we look to galaxy
formation simulations. We analyze 24000 synthetic images and kinematic
maps of 31 high-resolution simulations of isolated galaxies and mergers at
. We determine if the synthetic observations pass criteria commonly
used to identify disk galaxies, and whether the results are consistent with
their intrinsic dynamical states. Galaxies that are intrinsically mergers pass
the disk criteria for anywhere from 0 to 100 of sightlines. The exact
percentage depends strongly on the specific disk criteria adopted, and weakly
on the separation of the merging galaxies. Therefore, one cannot tell with
certainty whether observations of an individual galaxy indicate a merger or a
disk. To estimate the fraction of mergers passing as disks in current
kinematics samples, we combine the probability that a merger will pass as a
disk with theoretical merger fractions from a cosmological simulation. Taking
the latter at face-value, the observed disk fractions are overestimated by
small amounts: at most by at high stellar mass ( M)
and at low stellar mass ( M).Comment: 15 pages, 10 figures, accepted for publication in Ap
Characterizing Foreground for redshifted 21-cm radiation: 150 MHz GMRT observations
Foreground removal is a major challenge for detecting the redshifted 21-cm
neutral hydrogen (HI) signal from the Epoch of Reionization (EoR). We have used
150 MHz GMRT observations to characterize the statistical properties of the
foregrounds in four different fields of view. The measured multi-frequency
angular power spectrum C_l(Delta nu) is found to have values in the range 10^4
mK^2 to 2 x 10^4 mK^2 across 700 <= l <= 2 x 10^4 and Delta nu <= 2.5 MHz,
which is consistent with model predictions where point sources are the most
dominant foreground component. The measured C_l(Delta nu) does not show a
smooth Delta nu dependence, which poses a severe difficulty for foreground
removal using polynomial fitting.
The observational data was used to assess point source subtraction.
Considering the brightest source (~ 1 Jy) in each field, we find that the
residual artifacts are less than 1.5% in the most sensitive field (FIELD I). We
have used FIELD I, which has a rms noise of 1.3 mJy/Beam, to study the
properties of the radio source population to a limiting flux of 9 mJy. The
differential source count is well fitted with a single power law of slope -1.6.
We find there is no evidence for flattening of the source counts towards lower
flux densities which suggests that source population is dominated by the
classical radio-loud Active Galactic Nucleus (AGN).
The diffuse Galactic emission is revealed after the point sources are
subtracted out from FIELD I . We find C_l \propto l^{-2.34} for 253 <= l <= 800
which is characteristic of the Galactic synchrotron radiation measured at
higher frequencies and larger angular scales. We estimate the fluctuations in
the Galactic synchrotron emission to be sqrt{l(l+1)C_l/2 pi} ~ 10 K at l=800
(theta > 10'). The measured C_l is dominated by the residual point sources and
artifacts at smaller angular scales where C_l ~ 10^3 mK^2 for l > 800.Comment: 22 pages, 17 figures, 5 tables, accepted to MNRAS for publicatio
DIFFERENTIATION BETWEEN Nocardia spp. AND Mycobacterium spp.: CRITICAL ASPECTS FOR BACTERIOLOGICAL DIAGNOSIS
New methodologies were developed for the identification of Nocardia but the initial diagnosis still requires a fast and accurate method, mainly due to the similarity to Mycobacterium, both clinical and bacteriologically. Growth on Löwenstein-Jensen (LJ) medium, presence of acid-fast bacilli through Ziehl-Neelsen staining, and colony morphology can be confusing aspects between Nocardia and Mycobacterium. This study describes the occurrence of Nocardia spp. in a mycobacterial-reference laboratory, observing the main difficulties in differentiating Nocardia spp. from Mycobacterium spp., and correlating isolates with nocardiosis cases. Laboratory records for the period between 2008 and 2012 were analyzed, and the isolates identified as Nocardia sp. or as non-acid-fast filamentous bacilli were selected. Epidemiological and bacteriological data were analyzed as well. Thirty-three isolates identified as Nocardia sp. and 22 as non-acid-fast bacilli were selected for this study, and represented 0.12% of isolates during the study period. The presumptive identification was based on macroscopic and microscopic morphology, resistance to lysozyme and restriction profiles using the PRA-hsp65 method. Nocardia spp. can grow on media for mycobacteria isolation (LJ and BBL MGIT™) and microscopy and colony morphology are very similar to some mycobacteria species. Seventeen patients (54.8%) were reported and treated for tuberculosis, but presented signs and symptoms of nocardiosis. It was concluded that the occurrence of Nocardia sp. during the study period was 0.12%. Isolates with characteristics of filamentous bacilli, forming aerial hyphae, with colonies that may be pigmented, rough and without the BstEII digestion pattern in PRA-hsp65 method are suggestive of Nocardia spp. For a mycobacterial routine laboratory, a flow for the presumptive identification of Nocardia is essential, allowing the use of more accurate techniques for the correct identification, proper treatment and better quality of life for patients
Investigating the Effect of Galaxy Interactions on Star Formation at 0.5<z<3.0
Observations and simulations of interacting galaxies and mergers in the local
universe have shown that interactions can significantly enhance the star
formation rates (SFR) and fueling of Active Galactic Nuclei (AGN). However, at
higher redshift, some simulations suggest that the level of star formation
enhancement induced by interactions is lower due to the higher gas fractions
and already increased SFRs in these galaxies. To test this, we measure the SFR
enhancement in a total of 2351 (1327) massive () major
() spectroscopic galaxy pairs at 0.5<z<3.0 with
km s (1000 km s) and projected separation <150 kpc selected from
the extensive spectroscopic coverage in the COSMOS and CANDELS fields. We find
that the highest level of SFR enhancement is a factor of 1.23
in the closest projected separation bin (<25 kpc) relative to a stellar mass-,
redshift-, and environment-matched control sample of isolated galaxies. We find
that the level of SFR enhancement is a factor of higher at 0.5<z<1
than at 1<z<3 in the closest projected separation bin. Among a sample of
visually identified mergers, we find an enhancement of a factor of
1.86 for coalesced systems. For this visually identified
sample, we see a clear trend of increased SFR enhancement with decreasing
projected separation (2.40 vs.\ 1.58 for
0.5<z<1.6 and 1.6<z<3.0, respectively). The SFR enhancement seen in our
interactions and mergers are all lower than the level seen in local samples at
the same separation, suggesting that the level of interaction-induced star
formation evolves significantly over this time period.Comment: 23 pages, 13 figures, Accepted for publication in Ap
Azimuthal anisotropy and correlations in p+p, d+Au and Au+Au collisions at 200 GeV
We present the first measurement of directed flow () at RHIC. is
found to be consistent with zero at pseudorapidities from -1.2 to 1.2,
then rises to the level of a couple of percent over the range . The latter observation is similar to data from NA49 if the SPS rapidities
are shifted by the difference in beam rapidity between RHIC and SPS.
Back-to-back jets emitted out-of-plane are found to be suppressed more if
compared to those emitted in-plane, which is consistent with {\it jet
quenching}. Using the scalar product method, we systematically compared
azimuthal correlations from p+p, d+Au and Au+Au collisions. Flow and non-flow
from these three different collision systems are discussed.Comment: Quark Matter 2004 proceeding, 4 pages, 3 figure
Azimuthal anisotropy: the higher harmonics
We report the first observations of the fourth harmonic (v_4) in the
azimuthal distribution of particles at RHIC. The measurement was done taking
advantage of the large elliptic flow generated at RHIC. The integrated v_4 is
about a factor of 10 smaller than v_2. For the sixth (v_6) and eighth (v_8)
harmonics upper limits on the magnitudes are reported.Comment: 4 pages, 6 figures, contribution to the Quark Matter 2004 proceeding
Plasma Wakefield Acceleration with a Modulated Proton Bunch
The plasma wakefield amplitudes which could be achieved via the modulation of
a long proton bunch are investigated. We find that in the limit of long bunches
compared to the plasma wavelength, the strength of the accelerating fields is
directly proportional to the number of particles in the drive bunch and
inversely proportional to the square of the transverse bunch size. The scaling
laws were tested and verified in detailed simulations using parameters of
existing proton accelerators, and large electric fields were achieved, reaching
1 GV/m for LHC bunches. Energy gains for test electrons beyond 6 TeV were found
in this case.Comment: 9 pages, 7 figure
All-optical switching and strong coupling using tunable whispering-gallery-mode microresonators
We review our recent work on tunable, ultrahigh quality factor
whispering-gallery-mode bottle microresonators and highlight their applications
in nonlinear optics and in quantum optics experiments. Our resonators combine
ultra-high quality factors of up to Q = 3.6 \times 10^8, a small mode volume,
and near-lossless fiber coupling, with a simple and customizable mode structure
enabling full tunability. We study, theoretically and experimentally, nonlinear
all-optical switching via the Kerr effect when the resonator is operated in an
add-drop configuration. This allows us to optically route a single-wavelength
cw optical signal between two fiber ports with high efficiency. Finally, we
report on progress towards strong coupling of single rubidium atoms to an
ultra-high Q mode of an actively stabilized bottle microresonator.Comment: 20 pages, 24 figures. Accepted for publication in Applied Physics B.
Changes according to referee suggestions: minor corrections to some figures
and captions, clarification of some points in the text, added references,
added new paragraph with results on atom-resonator interactio
Strange Resonance Production in p+p and Au+Au Collisions at RHIC Energies
Resonance yields and spectra from elementary p+p and Au+Au collisions at
200 GeV from the STAR experiment at RHIC are presented
and discussed in terms of chemical and thermal freeze-out conditions. Thermal
models do not adequately describe the yields of the resonance production in
central Au+Au collisions. The approach to include elastic hadronic interactions
between chemical freeze-out and thermal freeze-out suggests a time of 5 fm/c.Comment: 4 pages, 7 figures, proceedings of the Quark Matter 2004, in Oakland,
California, to be published in Journal of Physics G: Nuclear and Particle
Physic
Identified particles at large transverse momenta in STAR in Au+Au collisions @ sqrt(s_NN) = 200 GeV
We report measurements of the ratios of identified hadrons (pi,K,p,Lambda) in
Au+Au collisions at sqrt(s_NN) = 200 GeV as a function of both collision
centrality and transverse momentum (p_T). Ratios of anti-baryon to baryon
yields are independent of p_T within 2<p_T <6 GeV/c indicating that, for such a
range, our measurements are inconsistent with theoretical pQCD calculations
predicting a decrease due to a stronger contribution from valence quark
scattering. For both strange and non-strange species, a strong baryon
enhancement relative to meson yields is observed as a function of collision
centrality in this intermediate p_T region, leading to p/pi and Lambda/K ratios
greater than unity. The nuclear modification factor, R_cp (central relative to
peripheral collisions), is used to illustrate the interplay between jet
quenching and hadron production. The physics implications of these measurements
are discussed with reference to different theoretical models.Comment: 5 pages, 4 figures. Proceedings of Quark Matter 2004 Conference, Jan
2004, Oakland, USA. Submitted to Journal of Physics
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