120161267
An off-axis Hartmann sensor for the measurement of absorption-induced wavefront distortion in advanced gravitational wave interferometers
We describe a novel off-axis Hartmann wavefront sensor, developed for the measurement of wavefront distortions induced in the mirrors (test masses) of advanced gravitational wave interferometers by residual absorption of the circulating laser power.
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.
116908435
Cuspy No More: How Outflows Affect the Central Dark Matter and Baryon Distribution in Lambda CDM Galaxies
We examine the evolution of the inner dark matter (DM) and baryonic density profile of a new sample of simulated field galaxies using fully cosmological, Lambda CDM, high resolution SPH + N-Body simulations. These simulations include explicit H2 and metal cooling, star formation (SF) and supernovae (SNe) driven gas outflows. Starting at high redshift, rapid, repeated gas outflows following bursty SF transfer energy to the DM component and significantly flatten the originally `cuspy' central DM mass profile of galaxies with present day stellar masses in the 10^4.5 -- 10^9.8 Msolar range. At z=0, the central slope of the DM density profile of our galaxies (measured between 0.3 and 0.7 kpc from their centre) is well fitted by rhoDM propto r^alpha with alpha \simeq -0.5 + 0.35 log_10(Mstar/10^8Msolar) where Mstar is the stellar mass of the galaxy and 4 < log_10 Mstar < 9.4. These values imply DM profiles flatter than those obtained in DM--only simulations and in close agreement with those inferred in galaxies from the THINGS and LITTLE THINGS survey. Only in very small halos, where by z=0 star formation has converted less than ~ 0.03% of the original baryon abundance into stars, outflows do not flatten the original cuspy DM profile out to radii resolved by our simulations. The mass (DM and baryonic) measured within the inner 500 pc of each simulated galaxy remains nearly constant over four orders of magnitudes in stellar mass for Mstar 10^9 Msolar. This finding is consistent with estimates for faint Local Group dwarfs and field galaxies. These results address one of the outstanding problems faced by the CDM model, namely the strong discrepancy between the original predictions of cuspy DM profiles and the shallower central DM distribution observed in galaxies.
9242923
INTERPRETING THE EVOLUTION OF THE SIZE-LUMINOSITY RELATION FOR DISK GALAXIES FROM REDSHIFT 1 TO THE PRESENT
A sample of very high resolution cosmological disk galaxy simulations is used to investigate the evolution of galaxy disk sizes back to redshift 1 within the ΛCDM cosmology. Artificial images in the rest-frame B band are generated, allowing for a measurement of disk scale lengths using surface brightness profiles as observations would, and avoiding any assumption that light must follow mass as previous models have assumed. We demonstrate that these simulated disks are an excellent match to the observed magnitude-size relation for both local disks and for disks at z = 1 in the magnitude/mass range of overlap. We disentangle the evolution seen in the population as a whole from the evolution of individual disk galaxies. In agreement with observations, our simulated disks undergo roughly 1.5 mag arcsec^(–2) of surface brightness dimming since z = 1. We find evidence that evolution in the magnitude-size plane varies by mass, such that galaxies with M_* ≥ 10^9 M_⊙ undergo more evolution in size than luminosity, while dwarf galaxies tend to evolve potentially more in luminosity. The disks grow in such a way as to stay on roughly the same stellar-mass-size relation with time. Finally, due to an evolving stellar-mass-star-formation-rate (SFR) relation, a galaxy at a given stellar mass (or size) at z = 1 will reside in a more massive halo and have a higher SFR, and thus a higher luminosity, than a counterpart of the same stellar mass at z = 0.
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
119296134
Why Baryons Matter: The Kinematics of Dwarf Spheroidal Satellites
We use some of the highest resolution cosmological simulations ever produced of Milky Way-mass galaxies that include both baryons and dark matter to show that baryonic physics (energetic feedback from supernovae and subsequent tidal stripping) significantly reduces the dark matter mass in the central regions of luminous satellite galaxies. The reduced central masses of the simulated satellites reproduce the observed internal dynamics of Milky Way and M31 satellites as a function of luminosity. Including baryonic physics in Cold Dark Matter models naturally explains the observed low dark matter densities in the Milky Way’s dwarf spheroidal population. Our simulations therefore resolve the tension between kinematics predicted in Cold Dark Mater theory and observations of satellites, without invoking alternative forms of dark matter.
6345715
The scatter about the ‘Universal’ dwarf spheroidal mass profile: a kinematic study of the M31 satellites And V and And VI
While the satellites of the Milky Way (MW) have been shown to be largely consistent in terms of their mass contained within one half-light radius (M_half) with a ‘universal’ mass profile, a number of M31 satellites are found to be inconsistent with these relations, and seem kinematically colder in their central regions than their MW cousins. In this work, we present new kinematic and updated structural properties for two M31 dwarf spheroidals (dSph), And V and And VI, using data from the Keck Low Resolution Imaging Spectrograph (LRIS) and the DEep Imaging Multi-Object Spectrograph (DEIMOS) instruments and the Subaru Suprime-Cam imager. We measure systemic velocities of v_r=−393.1 ± 4.2 and −344.8 ± 2.5 km s^(−1), and dispersions of σ_v= 11.5^(+5.3)_(−4.4) and 9.4^(+3.2)_(−2.4) km s^(−1) for And V and And VI, respectively, meaning these two objects are consistent with the trends in σv and r_half set by their MW counterparts. We also investigate the nature of this scatter about the MW dSph mass profiles for the ‘classical’ (i.e. M_V < −8) MW and M31 dSph. When comparing both the ‘classical’ MW and M31 dSph to the best-fitting mass profiles in the size–velocity dispersion plane, we find general scatter in both the positive (i.e. hotter) and negative (i.e. colder) directions from these profiles. However, barring one exception (CVnI) only the M31 dSph are found to scatter towards a colder regime, and, excepting the And I dSph, only MW objects scatter to hotter dispersions. The scatter for the combined population is greater than expected from measurement errors alone. We assess this divide in the context of the differing disc-to-halo mass (i.e. stars and baryons to total virial mass) ratios of the two hosts and argue that the underlying mass profiles for dSph differ from galaxy to galaxy, and are modified by the baryonic component of the host.