121679938
Testing the suppression of opto-acoustic parametric interactions using optical feedback control
We report an investigation designed to suppress three-mode opto-acoustic parametric interactions in advanced gravitational-wave detectors, through optical feedback control. In this paper, we present our initial results on the control of parametric instability in a high-finesse Fabry–Perot cavity using low input laser power. We show that injection of an anti-phase TEM01 mode with appropriate power will optically interfere and suppress the excited high-order mode in the cavity within a few seconds.
15931132
Compensation of strong thermal lensing in high-optical-power cavities.
In an experiment to simulate the conditions in high optical power advanced gravitational wave detectors, we show for the first time that the time evolution of strong thermal lenses follows the predicted infinite sum of exponentials (approximated by a double exponential), and that such lenses can be compensated using an intracavity compensation plate heated on its cylindrical surface. We show that high finesse approximately 1400 can be achieved in cavities with internal compensation plates, and that mode matching can be maintained. The experiment achieves a wave front distortion similar to that expected for the input test mass substrate in the Advanced Laser Interferometer Gravitational Wave Observatory, and shows that thermal compensation schemes are viable. It is also shown that the measurements allow a direct measurement of substrate optical absorption in the test mass and the compensation plate.
118456248
Observation of three-mode parametric interactions in long optical cavities
C. Zhao, L. Ju, Y. Fan, S. Gras, B. J. J. Slagmolen, H. Miao, P. Barriga, and D. G. Blair, D. J. Hosken, A. F. Brooks, P. J. Veitch, D. Mudge, and J. Munch
121643265
The Science benefits and Preliminary Design of the Southern hemisphere Gravitational Wave Detector AIGO.
The proposed southern hemisphere gravitational wave detector AIGO increases the projected average baseline of the global array of ground based gravitational wave detectors by a factor ~4. This allows the world array to be substantially improved. The orientation of AIGO allows much better resolution of both wave polarisations. This enables better distance estimates for inspiral events, allowing unambiguous optical identification of host galaxies for about 25% of neutron star binary inspiral events. This can allow Hubble Law estimation without optical identification of an outburst, and can also allow deep exposure imaging with electromagnetic telescopes to search for weak afterglows. This allows independent estimates of cosmological acceleration and dark energy as well as improved understanding of the physics of neutron star and black hole coalescences. This paper reviews and summarises the science benefits of AIGO and presents a preliminary conceptual design.
144912
Multicolor cavity metrology.
Long-baseline laser interferometers used for gravitational-wave detection have proven to be very complicated to control. In order to have sufficient sensitivity to astrophysical gravitational waves, a set of multiple coupled optical cavities comprising the interferometer must be brought into resonance with the laser field. A set of multi-input, multi-output servos then lock these cavities into place via feedback control. This procedure, known as lock acquisition, has proven to be a vexing problem and has reduced greatly the reliability and duty factor of the past generation of laser interferometers. In this article, we describe a technique for bringing the interferometer from an uncontrolled state into resonance by using harmonically related external fields to provide a deterministic hierarchical control. This technique reduces the effect of the external seismic disturbances by 4 orders of magnitude and promises to greatly enhance the stability and reliability of the current generation of gravitational-wave detectors. The possibility for using multicolor techniques to overcome current quantum and thermal noise limits is also discussed.
9537968
The Origin and Evolution of the Mass-Metallicity Relationship for Galaxies: Results from Cosmological N-Body Simulations
We examine the origin and evolution of the mass-metallicity relationship (MZR, M*-Z) for galaxies using high-resolution cosmological smoothed particle hydrodynamics (SPH) + N-body simulations that include a physically motivated description of supernova feedback and subsequent metal enrichment. We discriminate between two sources that may contribute to the origin of the MZR: (1) metal and baryon loss due to gas outflow or (2) inefficient star formation at the lowest galaxy masses. Our simulated galaxies reproduce the observed MZR in shape and normalization at both z = 0 and 2. We find that baryon loss occurs due to UV heating before star formation turns on in galaxies with Mbar < 108 M☉, but that some gas loss due to supernova-induced winds is required to subsequently reproduce the low effective chemical yield observed in low-mass galaxies. Despite this, we show that low star formation efficiencies, regulated by supernova feedback, are primarily responsible for the lower metallicities of low-mass galaxies and the overall M*-Z trend. We find that the shape of the MZR is relatively constant with redshift but that its normalization increases with time. Simulations with no energy feedback from supernovae overproduce metals at low galaxy masses by rapidly transforming a large fraction of their gas into stars. Despite the fact that our low-mass galaxies have lost a majority of their baryons, they are still the most gas-rich objects in our simulations due to their low star formation efficiencies.
119238202
Toward the Formation of Realistic Galaxy Disks
In this review I demonstrate that a realistic model for the formation of galaxy disks depends on a proper treatment of the gas in galaxies. Historically, cosmological simulations of disk galaxy formation have suffered from a lack of resolution and a physically motivated feedback prescription. Recent computational progress has allowed for unprecedented resolution, which in turn allows for a more realistic treatment of feedback. These advances have led to a new examination of gas accretion, evolution, and loss in the formation of galaxy disks. Here I highlight the role that gas inflows, the regulation of gas by feedback, and gas outflows play in achieving simulated disk galaxies that better match observational results as a function of redshift.
119042953
Boron in the Small Magellanic Cloud: A Novel Test of Light-Element Production*
Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS) observations of the B III resonance line at λ2066 have been obtained and analyzed for two Small Magellanic Cloud (SMC) B-type stars. While boron is not detected in either star, upper limits to the boron abundance are set, with 12 + log(B/H) ≤ 1.6 for both AV 304 and NGC 346-637. The upper limits are consistent with the relationship between boron and oxygen previously reported for Galactic disk stars. The SMC upper limits are discussed in light of that galaxy's star formation history, present oxygen abundance, and present cosmic-ray flux. The UV spectrum has also been used to determine the iron-group abundances in the SMC stars. For AV 304, [Fe/H] =-0.6 ± 0.2, from both an absolute and a differential analysis (with respect to the Galactic B-type star HD 36591). This is consistent with results from A-F supergiants in the SMC. A lower iron abundance is found for NGC 346-637, [Fe/H] =-1.0 ± 0.3, but this is in good agreement with the supergiant iron abundances in NGC 330, another young SMC cluster. We propose that NGC 346-637 might be an unrecognized binary, however, which complicates its spectral analysis.
16780728
The UV, Optical, and IR Properties of SDSS Sources Detected by GALEX
We discuss the ultraviolet, optical, and infrared properties of the Sloan Digital Sky Survey (SDSS) sources detected by the Galaxy Evolution Explorer (GALEX) as part of its All–sky Imaging Survey (AIS) Early Release Observations (ERO). Virtually all (> 99%) of the GALEX sources in the overlap region are detected by SDSS; those without an SDSS counterpart within our 6 search radius are mostly unflagged GALEX artifacts. GALEX sources represent ∼2.5% of all SDSS sources within these fields and about half are optically unresolved. Most unresolved GALEX/SDSS sources are bright (r < 18) blue turn–off thick disk stars and are typically detected only in the GALEX near–UV band. The remaining unresolved sources include low–redshift quasars (z < 2.2), white dwarfs, and white dwarf/M dwarf pairs, and these dominate the optically unresolved sources detected in both GALEX bands. Almost all the resolved SDSS sources detected by GALEX are fainter than the SDSS “main” spectroscopic limit (conversely, of the SDSS galaxies in the “main” spectroscopic sample, about 40% are detected in at least one GALEX band). These sources have colors consistent with those of blue (spiral) galaxies (u − r < 2.2), and most are detected in both GALEX bands. Measurements of Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 NASA Harriett G. Jenkins Predoctoral Fellow; agueros@astro.washington.edu Kapteyn Institute, Postbus 800, Groningen 9700 AV, The Netherlands Department of Astronomy, 610 Space Sciences Building, Cornell University, Ithaca, NY 14853 Department of Physics & Astronomy, University of Pittsburgh, 3941 O’Hara Street, Pittsburgh, PA 15260 Princeton University Observatory, Princeton, NJ 08544
8132532
Forming a large disc galaxy from a z < 1 major merger
Using high-resolution SPH simulations in a fully cosmological Λ cold dark matter context, we study the formation of a bright disc-dominated galaxy that originates from a 'wet' major merger at z = 0.8 . The progenitors of the disc galaxy are themselves disc galaxies that formed from early major mergers between galaxies with blue colours. A substantial thin stellar disc grows rapidly following the last major merger and the present-day properties of the final remnant are typical of early-type spiral galaxies, with an i-band bulge-to-disc ratio ~0.65, a disc scalelength of 7.2 kpc, g−r = 0.5 mag , an HI linewidth (W_(20)/2) of 238 km s^(−1) and total magnitude i = −22.4. The key ingredients for the formation of a dominant stellar disc component after a major merger are (i) substantial and rapid accretion of gas through cold flows followed at late times by cooling of gas from the hot phase, (ii) supernova feedback that is able to partially suppress star formation during mergers and (iii) relative fading of the spheroidal component. The gas fraction of the progenitors' discs does not exceed 25 per cent at z < 3 , emphasizing that the continuous supply of gas from the local environment plays a major role in the regrowth of discs and in keeping the galaxies blue. The results of this simulation alleviate the problem posed for the existence of disc galaxies by the high likelihood of interactions and mergers for galaxy-sized haloes at relatively low z.