119809223
Gingin High Optical Power Test Facility
The Australian Consortium for Gravitational Wave Astronomy (ACIGA) in collaboration with LIGO is developing a high optical power research facility at the AIGO site, Gingin, Western Australia. Research at the facility will provide solutions to the problems that advanced gravitational wave detectors will encounter with extremely high optical power. The problems include thermal lensing and parametric instabilities. This article will present the status of the facility and the plan for the future experiments.
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
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.
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.
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.
32479235
Hierarchical formation of bulgeless galaxies: why outflows have low angular momentum
Using high resolution, fully cosmological smoothed particle hydrodynamical simulations of dwarf galaxies in a Lambda cold dark matter Universe, we show how high redshift gas outflows can modify the baryon angular momentum distribution and allow pure disc galaxies to form. We outline how galactic outflows preferentially remove low angular momentum material due a combination of (a) star formation peaking at high redshift in shallow dark matter potentials, an epoch when accreted gas has relatively low angular momentum, (b) the existence of an extended reservoir of high angular momentum gas in the outer disc to provide material for prolonged SF at later times and (c) the tendency for outflows to follow the path of least resistance which is perpendicular to the disc. We also show that outflows are enhanced during mergers, thus expelling much of the gas which has lost its angular momentum during these events, and preventing the formation of ‘classical’, merger driven bulges in low-mass systems. Stars formed prior to such mergers form a diffuse, extended stellar halo component similar to those detected in nearby dwarfs.
16591772
THE DUAL ORIGIN OF STELLAR HALOS
We investigate the formation of the stellar halos of four simulated disk galaxies using high-resolution, cosmological SPH + N-body simulations. These simulations include a self-consistent treatment of all the major physical processes involved in galaxy formation. The simulated galaxies presented here each have a total mass of ~1012 M , but span a range of merger histories. These simulations allow us to study the competing importance of in situ star formation (stars formed in the primary galaxy) and accretion of stars from subhalos in the building of stellar halos in a ΛCDM universe. All four simulated galaxies are surrounded by a stellar halo, whose inner regions (r < 20 kpc) contain both accreted stars, and an in situ stellar population. The outer regions of the galaxies' halos were assembled through pure accretion and disruption of satellites. Most of the in situ halo stars formed at high redshift out of smoothly accreted cold gas in the inner 1 kpc of the galaxies' potential wells, possibly as part of their primordial disks. These stars were displaced from their central locations into the halos through a succession of major mergers. We find that the two galaxies with recently quiescent merger histories have a higher fraction of in situ stars (~20%-50%) in their inner halos than the two galaxies with many recent mergers (~5%-10% in situ fraction). Observational studies concentrating on stellar populations in the inner halo of the Milky Way will be the most affected by the presence of in situ stars with halo kinematics, as we find that their existence in the inner few tens of kpc is a generic feature of galaxy formation.
14106085
The nature of HI absorbers in GRB afterglows: clues from hydrodynamic simulations
In recent work, we have shown that it is possible to link quantitatively many aspects of damped Lyman alpha (DLA) absorbers in the spectra of quasars to high resolution simulations of galaxy formation. Using runs from the same series of hydrodynamic numerical studies, we consider the expected properties of intrinsic Lyman alpha absorbers seen in the spectra of high redshift (z > 2) gamma ray burst afterglows (GRB-DLAs). If GRBs are associated with the death of massive stars, their afterglows provide insights into otherwise unprobed regions of protogalactic objects, but detailed physical interpretations are currently embryonic. We find that median impact parameters (measured from the potential minimum) are approximately 1 kpc for GRBs compared with 4 kpc for QSO-DLAs. However, an equally important difference is that GRB-DLAs are predominantly associated with halos of mass 10 < Mvir/M < 10, an order of magnitude larger than the hosts of QSO-DLAs. Accordingly, there are differences in the stellar properties of hosts. For instance mean star formation rates are higher: 〈Ṁ?〉 ' 10 M yr−1 for GRB-DLAs compared with 〈Ṁ?〉 ' 1 M yr−1 for QSO-DLAs. Our simulations accurately predict the form of the GRB-DLA H I column density distribution, producing quantitative agreement for NHI > 10 cm−2, but they somewhat underpredict the incidence of low column densities NHI < 10 cm−2. This is reflected in our estimate of the ionizing photon escape fraction, fesc ' 1%, which is lower than the observational GRB-derived escape fraction (2%). Line-of-sight neutral gas metallicities predicted by our simulations (10−2 < Z/Z < 1) are consistent with the modest observational constraints. Because of large internal dispersions in gas metallicities, this agreement is not significantly compromised by imposing a cut-off on the metallicity of stars able to launch GRBs (Z? < Z /3), confounding claims that the observed metallicity of GRB-DLAs poses a severe challenge to current GRB models.
39151409
The cold gas content of bulgeless dwarf galaxies
We present an analysis of the neutral hydrogen (H i) properties of a fully cosmological hydrodynamical dwarf galaxy, run with varying simulation parameters. As reported by Governato et al., the high-resolution, high star formation density threshold version of this galaxy is the first simulation to result in the successful reproduction of a (dwarf) spiral galaxy without any associated stellar bulge. We have set out to compare in detail the H i distribution and kinematics of this simulated bulgeless disc with what is observed in a sample of nearby dwarfs. To do so, we extracted the radial gas density profiles, velocity dispersion (e.g. velocity ellipsoid and turbulence) and the power spectrum of structure within the cold interstellar medium (ISM) from the simulations. The highest resolution dwarf, when using a high-density star formation threshold comparable to densities of giant molecular clouds, possesses bulk characteristics consistent with those observed in nature, though the cold gas is not as radially extended as that observed in nearby dwarfs, resulting in somewhat excessive surface densities. The lines-of-sight velocity dispersion radial profiles have values that are in good agreement with the observed dwarf galaxies, but due to the fact that only the streaming velocities of particles are tracked, a correction to include the thermal velocities can lead to profiles that are quite flat. The ISM power spectra of the simulations appear to possess more power on smaller spatial scales than that of the Small Magellanic Cloud. We conclude that unavoidable limitations remain due to the unresolved physics of star formation and feedback within parsec-scale molecular clouds.
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.