100 deg2^2 Mock Galaxy Cone for HI Surveys with the Early SKA

We distribute an easy-to-use mock catalog of galaxies with detailed neutral atomic hydrogen (HI) and auxiliary molecular and optical properties. The catalog covers a field of 10-by-10 degrees and a redshift range of z=0-1.2. It contains galaxies with 21cm peak flux densities down to 1uJy and is, within this flux limit, complete for HI masses above 10^8 solar masses. Five random realisations of the catalog in ASCII format (~4GB/file) and subtables with HI flux limits of 10u Jy (~500MB/file) and 100uJy$ (~30MB/file) can be downloaded at http://ict.icrar.org/store/staff/do/s3sax.Comment: 3 pages, 1 table, 2 figure

Rebounds of deformed cavitation bubbles

Presented here are experiments clarifying how the deformation of cavitation bubbles affects their rebound. Rebound bubbles carry the remaining energy of a bubble following its initial collapse, which dissipates energy mainly through shock waves, jets, and heat. The rebound bubble undergoes its own collapse, generating such violent events anew, which can be even more damaging or effective than at first bubble collapse. However, modeling rebound bubbles is an ongoing challenge because of the lack of knowledge on the exact factors affecting their formation. Here we use single-laser-induced cavitation bubbles and deform them by variable gravity or by a neighboring free surface to quantify the effect of bubble deformation on the rebound bubbles. Within a wide range of deformations, the energy of the rebound bubble follows a logarithmic increase with the bubble's initial dipole deformation, regardless of the origin of this deformation

Evolution of the Milky Way in Semi-Analytic Models: Detecting Cold Gas at z=3 with ALMA and SKA

We forecast the abilities of the Atacama Large Millimeter/submillimeter Array (ALMA) and the Square Kilometer Array (SKA) to detect CO and HI emission lines in galaxies at redshift z=3. A particular focus is set on Milky Way (MW) progenitors at z=3 for their detection within 24 h constitutes a key science goal of ALMA. The analysis relies on a semi-analytic model, which permits the construction of a MW progenitor sample by backtracking the cosmic history of all simulated present-day galaxies similar to the real MW. Results: (i) ALMA can best observe a MW at z=3 by looking at CO(3-2) emission. The probability of detecting a random model MW at 3-sigma in 24 h using 75 km/s channels is roughly 50%, and these odds can be increased by co-adding the CO(3-2) and CO(4-3) lines. These lines fall into ALMA band 3, which therefore represents the optimal choice towards MW detections at z=3. (ii) Higher CO transitions contained in the ALMA bands geq6 will be invisible, unless the considered MW progenitor coincidentally hosts a major starburst or an active black hole. (iii) The high-frequency array of SKA, fitted with 28.8 GHz receivers, would be a powerful instrument for observing CO(1-0) at z=3, able to detect nearly all simulated MWs in 24 h. (iv) HI detections in MWs at z=3 using the low-frequency array of SKA will be impossible in any reasonable observing time. (v) SKA will nonetheless be a supreme ha survey instrument through its enormous instantaneous field-of-view (FoV). A one year pointed HI survey with an assumed FoV of 410 sqdeg would reveal at least 10^5 galaxies at z=2.95-3.05. (vi) If the positions and redshifts of those galaxies are known from an optical/infrared spectroscopic survey, stacking allows the detection of HI at z=3 in less than 24 h.Comment: 14 pages, 5 figures, 5 table

Three-point phase correlations: A new measure of non-linear large-scale structure

We derive an analytical expression for a novel large-scale structure observable: the line correlation function. The line correlation function, which is constructed from the three-point correlation function of the phase of the density field, is a robust statistical measure allowing the extraction of information in the non-linear and non-Gaussian regime. We show that, in perturbation theory, the line correlation is sensitive to the coupling kernel F_2, which governs the non-linear gravitational evolution of the density field. We compare our analytical expression with results from numerical simulations and find a 1-sigma agreement for separations r<30 Mpc/h. Fitting formulae for the power spectrum and the non-linear coupling kernel at small scales allow us to extend our prediction into the strongly non-linear regime where we find a 1-sigma agreement with the simulations for r<2 Mpc/h. We discuss the advantages of the line correlation relative to standard statistical measures like the bispectrum. Unlike the latter, the line correlation is independent of the bias, in the regime where the bias is local and linear. Furthermore, the variance of the line correlation is independent of the Gaussian variance on the modulus of the density field. This suggests that the line correlation can probe more precisely the non-linear regime of gravity, with less contamination from the power spectrum variance.Comment: 11 pages, 5 figures. v2: replacement of the low resolution simulations, more precise quantification of the agreement with simulations, references added. Matches published version. Our code to calculate the line correlation is available at http://blue-shift.ch/phas

Gravitationally Lensed HI with MeerKAT

The SKA era is set to revolutionize our understanding of neutral hydrogen (HI) in individual galaxies out to redshifts of z~0.8; and in the z > 6 intergalactic medium through the detection and imaging of cosmic reionization. Direct HI number density constraints will, nonetheless, remain relatively weak out to cosmic noon (z~2) - the epoch of peak star formation and black hole accretion - and beyond. However, as was demonstrated from the 1990s with molecular line observations, this can be overcome by utilising the natural amplification afforded by strong gravitational lensing, which results in an effective increase in integration time by the square of the total magnification (\mu^2) for an unresolved source. Here we outline how a dedicated lensed HI survey will leverage MeerKAT's high sensitivity, frequency coverage, large instantaneous bandwidth, and high dynamic range imaging to enable a lasting legacy of high-redshift HI emission detections well into the SKA era. This survey will not only provide high-impact, rapid-turnaround MeerKAT science commissioning results, but also unveil Milky Way-like systems towards cosmic noon which is not possible with any other SKA precursors/pathfinders. An ambitious lensed HI survey will therefore make a significant impact from MeerKAT commissioning all the way through to the full SKA era, and provide a more complete picture of the HI history of the Universe.Comment: 15 pages, 3 figures, accepted for publication, Proceedings of Science, workshop on "MeerKAT Science: On the Pathway to the SKA", held in Stellenbosch 25-27 May 2016. Comments welcom

Angular Momentum Regulates Atomic Gas Fractions of Galactic Disks

We show that the mass fraction f_atm = 1.35*MHI/M of neutral atomic gas (HI and He) in isolated local disk galaxies of baryonic mass M is well described by a straightforward stability model for flat exponential disks. In the outer disk parts, where gas at the characteristic dispersion of the warm neutral medium is stable in the sense of Toomre (1964), the disk consists of neutral atomic gas; conversely the inner part where this medium would be Toomre-unstable, is dominated by stars and molecules. Within this model, f_atm only depends on a global stability parameter q=j*sigma/(GM), where j is the baryonic specific angular momentum of the disk and sigma the velocity dispersion of the atomic gas. The analytically derived first-order solution f_atm = min{1,2.5q^1.12} provides a good fit to all plausible rotation curves. This model, with no free parameters, agrees remarkably well (+-0.2 dex) with measurements of f_atm in isolated local disk galaxies, even with galaxies that are extremely HI-rich or HI-poor for their mass. The finding that f_atm increases monotonically with q for pure stability reasons offers a powerful intuitive explanation for the mean variation of f_atm with M: in a cold dark matter universe galaxies are expected to follow j~M^(2/3), which implies the average scaling q~M^(-1/3) and hence f_atm~M^(-0.37), in agreement with observations.Comment: 5 pages, 3 figure

Theory of Polaron States in Pyramidal GaAs/AlGaAs Quantum Dots

In this thesis we address the subject of strong electron-phonon coupling in pyramidal quantum dots and pursue detailed physical, analytical and numerical investigations. The strong coupling polaron states in a pyramidal GaAs/AlGaAs quantum dot are computed numerically with an enhanced matrix diagonalization method that accounts for the particular structure of the Hamiltonian and uses an irregular reciprocal space discretization. Electron-electron interactions and multiple phonon interactions are neglected. We study quantum dots with either three or four confined electron states associated with two or three electron levels, respectively. Further, we develop a set of analytical tools to predict and interpret the polaron states of a more general model of quantum dots. Applying these tools to the particular case allows a complete classification of the polaron states and reveals new physical insight