122904515
Status of the Australian Consortium for Interferometric Gravitational Astronomy
We report the status of research and development being undertaken by the members of the Australian Consortium for Interferometric Gravitational Astronomy.
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.
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.
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.
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.
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
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.
14399224
The Formation of Polar Disk Galaxies
Polar ring galaxies, such as NGC 4650A, are a class of galaxies that have two kinematically distinct components that are inclined by almost 90° to each other. These striking galaxies challenge our understanding of how galaxies form; the origin of their distinct components has remained uncertain and is the subject of much debate. We use high-resolution cosmological simulations of galaxy formation to show that polar ring galaxies are simply an extreme example of the misalignment of angular momentum that occurs during the hierarchical structure formation characteristic of a cold dark matter cosmology. In our model, polar ring galaxies form through the continuous accretion of gas whose angular momentum is misaligned with the central galaxy.
118510988
A BARYONIC SOLUTION TO THE MISSING SATELLITES PROBLEM
It has been demonstrated that the inclusion of baryonic physics can alter the dark matter densities in the centers of low-mass galaxies, making the central dark matter slope more shallow than predicted in pure cold dark matter simulations. This flattening of the dark matter profile can occur in the most luminous subhalos around Milky Way mass galaxies. Zolotov et al. have suggested a correction to be applied to the central masses of dark matter-only satellites in order to mimic the affect of (1) the flattening of the dark matter cusp due to supernova feedback in luminous satellites and (2) enhanced tidal stripping due to the presence of a baryonic disk. In this paper, we apply this correction to the z = 0 subhalo masses from the high resolution, dark matter-only Via Lactea II (VL2) simulation, and find that the number of massive subhalos is dramatically reduced. After adopting a stellar mass to halo mass relationship for the VL2 halos, and identifying subhalos that are (1) likely to be destroyed by stripping and (2) likely to have star formation suppressed by photo-heating, we find that the number of massive, luminous satellites around a Milky Way mass galaxy is in agreement with the number of observed satellites around the Milky Way or M31. We conclude that baryonic processes have the potential to solve the missing satellites problem.
11918007
At the heart of the matter: the origin of bulgeless dwarf galaxies and Dark Matter cores
Astronomy Department, University of Washington, Seattle, WA 98195, US 2 Peremiah Horrocks Institute, University of Central Lancashire, Preston, Lancashire,PR1 2HE, UK Institute for Theoretical Physics, University of Zurich, Winterthurestrasse 190, CH-8057 Zürich. 4 Theoretical Astrophysics, California Institute of Technology, MC 350-17, Pasadena, CA, 91125 US Department of Physics and Astronomy, University of Nevada, Las Vegas, NV US Department of Physics and Astronomy, McMaster University, Hamilton, ON, L8S 4M1, Canada 7 Institute of Particle Physics, UCSC, Santa Cruz, CA 95064, US Haverford College, Department of Astronomy 370 Lancaster Ave, Haverford, PA 19041 Department of Astronomy and Astrophysics. University of California, Santa Cruz, CA 95064 US
4805930
Testing rotational mixing predictions with new boron abundances in main-sequence B-type stars
New boron abundances for seven main-sequence B-type stars are determined from HST STIS spectroscopy around the B III 2066 A line. Boron abundances provide a unique and critical test of stellar evolution models that include rotational mixing, since boron is destroyed in the surface layers of stars through shallow mixing long before other elements are mixed from the stellar interior through deep mixing. The stars in this study are all on or near the main sequence and are members of young Galactic clusters. They show no evidence of mixing with gas from H-burning layers from their CNO abundances. Boron abundances range from 12 + log(B/H) ≤ 1.0 to 2.2. The boron abundances are compared to the published values of the stellar nitrogen abundances [all have 12 + log(N/H) ≤ 7.8] and to their host cluster ages (4-16 Myr) to investigate the predictions from models of massive star evolution with rotational mixing effects. We find that the variations in boron and nitrogen are generally within the range of the predictions from the stellar evolution models with rotation (where predictions for models with rotation rates from 0 to 450 km s-1 and μ-barriers are examined), especially given their age and mass ranges. Three stars (of 34 B-type stars with detailed boron abundance determinations) deviate from the model predictions, showing either much larger boron depletions than can be explained by the rotating model predictions or a spectroscopic mass that is lower than expected, given the rotating model predictions for its age and abundances. The results from these three stars suggest that rotational mixing could be more efficient than that currently modeled at the highest rotation rates.