4,706 research outputs found
Dust Abundance Variations in the Magellanic Clouds: Probing the Lifecycle of Metals with All-Sky Surveys
Observations and modeling suggest that the dust abundance (gas-to-dust ratio,
G/D) depends on (surface) density. The variations of the G/D provide
constraints on the timescales for the different processes involved in the
lifecycle of metals in galaxies. Recent G/D measurements based on Herschel data
suggest a factor 5---10 decrease in the dust abundance between the dense and
diffuse interstellar medium (ISM) in the Magellanic Clouds. However, the
relative nature of the Herschel measurements precludes definitive conclusions
on the magnitude of those variations. We investigate the variations of the dust
abundance in the LMC and SMC using all-sky far-infrared surveys, which do not
suffer from the limitations of Herschel on their zero-point calibration. We
stack the dust spectral energy distribution (SED) at 100, 350, 550, and 850
microns from IRAS and Planck in intervals of gas surface density, model the
stacked SEDs to derive the dust surface density, and constrain the relation
between G/D and gas surface density in the range 10---100 \Msu pc on
80 pc scales. We find that G/D decreases by factors of 3 (from 1500 to
500) in the LMC and 7 (from 1.5 to 2000) in the SMC between the
diffuse and dense ISM. The surface density dependence of G/D is consistent with
elemental depletions and with simple modeling of the accretion of gas-phase
metals onto dust grains. This result has important implications for the
sub-grid modeling of galaxy evolution, and for the calibration of dust-based
gas mass estimates, both locally and at high-redshift.Comment: 20 pages, 14 figure
An improved method for statistical studies of the internal kinematics of HII regions: the case of M 83
We present the integrated Halpha emission line profile for 157 HII regions in
the central 3.4' x 3.4' of the galaxy M 83 (NGC 5236). Using the Fabry-Perot
interferometer GHaFaS, on the 4.2 m William Herschel on La Palma, we show the
importance of a good characterization of the instrumental response function for
the study of line profile shapes. The luminosity-velocity dispersion relation
is also studied, and in the log(L)-log(sigma) plane we do not find a linear
relation, but an upper envelope with equation log(L)=0.9 *log(sigma)+38.1. For
the adopted distance of 4.5 Mpc, the upper envelope appears at the luminosity
L=10^38.5 ergs, in full agreement with previous studies of other galaxies,
reinforcing the idea of using HII regions as standard candles.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Machine-learning nonstationary noise out of gravitational-wave detectors
Signal extraction out of background noise is a common challenge in high-precision physics experiments, where the measurement output is often a continuous data stream. To improve the signal-to-noise ratio of the detection, witness sensors are often used to independently measure background noises and subtract them from the main signal. If the noise coupling is linear and stationary, optimal techniques already exist and are routinely implemented in many experiments. However, when the noise coupling is nonstationary, linear techniques often fail or are suboptimal. Inspired by the properties of the background noise in gravitational wave detectors, this work develops a novel algorithm to efficiently characterize and remove nonstationary noise couplings, provided there exist witnesses of the noise source and of the modulation. In this work, the algorithm is described in its most general formulation, and its efficiency is demonstrated with examples from the data of the Advanced LIGO gravitational-wave observatory, where we could obtain an improvement of the detector gravitational-wave reach without introducing any bias on the source parameter estimation
Nanophotonic waveguide enhanced Raman spectroscopy of biological submonolayers
Characterizing a monolayer of biological molecules has been a major
challenge. We demonstrate nanophotonic wave-guide enhanced Raman spectroscopy
(NWERS) of monolayers in the near-infrared region, enabling real-time
measurements of the hybridization of DNA strands and the density of
sub-monolayers of biotin-streptavidin complex immobilized on top of a photonics
chip. NWERS is based on enhanced evanescent excitation and collection of
spontaneous Raman scattering near nanophotonic waveguides, which for a one
centimeter silicon nitride waveguide delivers a signal that is more than four
orders of magnitude higher in comparison to a confocal Raman microscope. The
reduced acquisition time and specificity of the signal allows for a
quantitative and real-time characterization of surface species, hitherto not
possible using Raman spectroscopy. NWERS provides a direct analytic tool for
monolayer research and also opens a route to compact microscope-less
lab-on-a-chip devices with integrated sources, spectrometers and detectors
fabricated using a mass-producible CMOS technology platform
The Sloan Lens ACS Survey. I. A Large Spectroscopically Selected Sample of Massive Early-Type Lens Galaxies
The Sloan Lens ACS (SLACS) Survey is an efficient Hubble Space Telescope
Snapshot imaging survey for new galaxy-scale strong gravitational lenses. The
targeted lens candidates are selected spectroscopically from within the Sloan
Digital Sky Survey (SDSS) database of galaxy spectra for having multiple
nebular emission lines at a redshift significantly higher than that of the SDSS
target galaxy. In this paper, we present a catalog of 19 newly discovered
gravitational lenses, along with 9 other observed candidate systems that are
either possible lenses, non-lenses, or non-detections. The survey efficiency is
thus >=68%. We also present Gemini and Magellan IFU data for 9 of the SLACS
targets, which further support the lensing interpretation. A new method for the
effective subtraction of foreground galaxy images to reveal faint background
features is presented. We show that the SLACS lens galaxies have colors and
ellipticities typical of the spectroscopic parent sample from which they are
drawn (SDSS luminous red galaxies and quiescent main-sample galaxies), but are
somewhat brighter and more centrally concentrated. Several explanations for the
latter bias are suggested. The SLACS survey provides the first statistically
significant and homogeneously selected sample of bright early-type lens
galaxies, furnishing a powerful probe of the structure of early-type galaxies
within the half-light radius. The high confirmation rate of lenses in the SLACS
survey suggests consideration of spectroscopic lens discovery as an explicit
science goal of future spectroscopic galaxy surveys (abridged).Comment: ApJ, in press. 20 pages, numerous figures, uses emulateapj. Replaced
to include full-resolution spectro figures. Version with full-resolution
imaging figures available at
http://www.cfa.harvard.edu/~abolton/slacs1_hires.pdf (PDF) or at
http://www.cfa.harvard.edu/~abolton/slacs1_hires.ps.gz (PS). Additional SLACS
survey info at http://www.slacs.or
Investigation of top mass measurements with the ATLAS detector at LHC
Several methods for the determination of the mass of the top quark with the
ATLAS detector at the LHC are presented. All dominant decay channels of the top
quark can be explored. The measurements are in most cases dominated by
systematic uncertainties. New methods have been developed to control those
related to the detector. The results indicate that a total error on the top
mass at the level of 1 GeV should be achievable.Comment: 47 pages, 40 figure
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