The Imprint of Cosmic Reionization on the Luminosity Function of Galaxies

The (re)ionization of hydrogen in the early universe has a profound effect on the formation of the first galaxies: by raising the gas temperature and pressure, it prevents gas from cooling into small halos, thus affecting the abundance of present-day small galaxies. Using the Galform semi-analytic model of galaxy formation, we show that two key aspects of the reionization process—when reionization takes place and the characteristic scale below which it suppresses galaxy formation—are imprinted in the luminosity function of dwarf galaxies. We focus on the luminosity function of satellites of galaxies like the Milky Way and the LMC, which is easier to measure than the luminosity function of the dwarf population as a whole. Our results show that the details of these two characteristic properties of reionization determine the shape of the luminosity distribution of satellites in a unique way, and are largely independent of the other details of the galaxy formation model. Our models generically predict a bimodality in the distribution of satellites as a function of luminosity: a population of faint satellites and population of bright satellites separated by a "valley" forged by reionization. We show that this bimodal distribution is present at high statistical significance in the combined satellite luminosity function of the Milky Way and M31. We make predictions for the expected number of satellites around LMC-mass dwarfs where the bimodality may also be measurable in future observational programs. Our preferred model predicts a total of 26 ± 10 (68% confidence) satellites brighter than M V = 0 in LMC-mass systems

Dynamic Holographic Lock-In Imaging of Ultrasonic Waves

ABSTRACT A laser imaging approach is presented that utilizes the adaptive property of photorefractive materials to produce a real-time measurement of ultrasonic traveling wave surface displacement and phase in all planar directions simultaneously without scanning. The imaging method performs optical lockin operation. A single antisymmetric Lamb wave mode image produces direct quantitative determination of the phase velocity in all planar directions showing plate stiffness anisotropy. Excellent agreement was obtained with modeling calculations of the phase velocity in all planar directions for an anisotropic sheet material. The approach functions with diffusely scattering surfaces, subnanometer motions and at frequencies from Hz to GHz

Robust Mapping of Incoherent Fiber-Optic Bundles

A method and apparatus for mapping between the positions of fibers at opposite ends of incoherent fiber-optic bundles have been invented to enable the use of such bundles to transmit images in visible or infrared light. The method is robust in the sense that it provides useful mapping even for a bundle that contains thousands of narrow, irregularly packed fibers, some of which may be defective. In a coherent fiber-optic bundle, the input and output ends of each fiber lie at identical positions in the input and output planes; therefore, the bundle can be used to transmit images without further modification. Unfortunately, the fabrication of coherent fiber-optic bundles is too labor-intensive and expensive for many applications. An incoherent fiber-optic bundle can be fabricated more easily and at lower cost, but it produces a scrambled image because the position of the end of each fiber in the input plane is generally different from the end of the same fiber in the output plane. However, the image transmitted by an incoherent fiber-optic bundle can be unscrambled (or, from a different perspective, decoded) by digital processing of the output image if the mapping between the input and output fiber-end positions is known. Thus, the present invention enables the use of relatively inexpensive fiber-optic bundles to transmit images

Dynamic Holographic Lock-In Imaging of Ultrasonic Waves

A laser imaging approach is presented that utilizes the adaptive property of photorefractive materials to produce a real-time measurement of ultrasonic traveling wave surface displacement and phase in all planar directions simultaneously without scanning. The imaging method performs optical lock-in operation. A single antisymmetric Lamb wave mode image produces direct quantitative determination of the phase velocity in all planar directions showing plate stiffness anisotropy. Excellent agreement was obtained with modeling calculations of the phase velocity in all planar directions for an anisotropic sheet material. The approach functions with diffusely scattering surfaces, subnanometer motions and at frequencies from Hz to GHz

The star formation history of the Sagittarius stream

We present the first detailed quantitative study of the stellar populations of the Sagittarius (Sgr) streams within the Stripe 82 region, using photometric and spectroscopic observations from the Sloan Digital Sky Survey (SDSS). The star formation history (SFH) is determined separately for the bright and faint Sgr streams, to establish whether both components consist of a similar stellar population mix or have a distinct origin. Best fit SFH solutions are characterised by a well-defined, tight sequence in age-metallicity space, indicating that star formation occurred within a well-mixed, homogeneously enriched medium. Star formation rates dropped sharply at an age of ~5-7 Gyr, possibly related to the accretion of Sgr by the MW. Finally, the Sgr sequence displays a change of slope in age-metallicity space at an age between 11-13 Gyr consistent with the Sgr alpha-element knee, indicating that supernovae type Ia started contributing to the abundance pattern ~1-3 Gyr after the start of star formation. Results for both streams are consistent with being drawn from the parent Sgr population mix, but at different epochs. The SFH of the bright stream starts from old, metal-poor populations and extends to a metallicity of [Fe/H]~-0.7, with peaks at ~7 and 11 Gyr. The faint SFH samples the older, more metal-poor part of the Sgr sequence, with a peak at ancient ages and stars mostly with [Fe/H]9 Gyr. Therefore, we argue in favour of a scenario where the faint stream consists of material stripped i) earlier, and ii) from the outskirts of the Sgr dwarf.Comment: 15 pages, 12 figures. ccepted for publication in MNRA