Filament Hunting: Integrated HI 21cm Emission From Filaments Inferred by Galaxy Surveys

Large scale filaments, with lengths that can reach tens of Mpc, are the most prominent features in the cosmic web. These filaments have only been observed indirectly through the positions of galaxies in large galaxy surveys or through absorption features in the spectra of high redshift sources. In this study we propose to go one step further and directly detect intergalactic medium filaments through their emission in the HI 21cm line. We make use of high resolution cosmological simulations to estimate the intensity of this emission in low redshift filaments and use it to make predictions for the direct detectability of specific filaments previously inferred from galaxy surveys, in particular the Sloan Digital Sky Survey. Given the expected signal of these filaments our study shows that HI emission from large filaments can be observed by current and next generation radio telescopes. We estimate that gas in filaments of length $l \gtrsim$ 15 $h^{-1}$Mpc with relatively small inclinations to the line of sight ($\lesssim 10^\circ$) can be observed in $\sim40-100$ hours with telescopes such as GMRT or EVLA, potentially providing large improvements over our knowledge of the astrophysical properties of these filaments. Due to their large field of view and sufficiently long integration times, upcoming HI surveys with the Apertif and ASKAP instruments will be able to detect large filaments independently of their orientation and curvature. Furthermore, our estimates indicate that a more powerful future radio telescope like SKA-2 can be used to map most of these filaments, which will allow them to be used as a strong cosmological probe.Comment: 16 pages, 11 figures, Accepted for publication in MNRA

Complete Positivity for Mixed Unitary Categories

In this article we generalize the \CP^\infty-construction of dagger monoidal categories to mixed unitary categories. Mixed unitary categories provide a setting, which generalizes (compact) dagger monoidal categories and in which one may study quantum processes of arbitrary (infinite) dimensions. We show that the existing results for the \CP^\infty-construction hold in this more general setting. In particular, we generalize the notion of environment structures to mixed unitary categories and show that the \CP^\infty-construction on mixed unitary categories is characterized by this generalized environment structure.Comment: Lots of figure

Faint star counts in the near-infrared

We discuss near-infrared star counts at the Galactic pole with a view to guiding the NGST and ground-based NIR cameras. Star counts from deep K-band images from the CFHT are presented, and compared with results from the 2MASS survey and some Galaxy models. With appropriate corrections for detector artifacts and galaxies, the data agree with the models down to K~18, but indicate a larger population of fainter red stars. There is also a significant population of compact galaxies that extend to the observational faint limit of K=20.5. Recent Galaxy models agree well down to K$\sim$19, but diverge at fainter magnitudes.Comment: 14 pages and 4 diagrams; to appear in PAS

Massively parallel approximate Gaussian process regression

We explore how the big-three computing paradigms -- symmetric multi-processor (SMC), graphical processing units (GPUs), and cluster computing -- can together be brought to bare on large-data Gaussian processes (GP) regression problems via a careful implementation of a newly developed local approximation scheme. Our methodological contribution focuses primarily on GPU computation, as this requires the most care and also provides the largest performance boost. However, in our empirical work we study the relative merits of all three paradigms to determine how best to combine them. The paper concludes with two case studies. One is a real data fluid-dynamics computer experiment which benefits from the local nature of our approximation; the second is a synthetic data example designed to find the largest design for which (accurate) GP emulation can performed on a commensurate predictive set under an hour.Comment: 24 pages, 6 figures, 1 tabl

Logarithmic coarsening and glassy behavior in a polymer model with mass-dependent diffusion

We present a model of polymer growth and diffusion with frustration mechanisms for density increase and with diffusion rates of Arrhenius form with mass-dependent energy barriers Gamma(m) ~ (m-1)^gamma. It shows non-universal logarithmic coarsening involving the exponent gamma. Strong-glass behavior is found in the typical times for disappearance of all polymers up to a given length, without reference to the equilibrium states of the macroscopic system. These features are predicted by numerical simulations, scaling theories and an analytic solution of the master equation within an independent interval approximation, which also provides the cluster size distribution.Comment: 16 pages, including 7 figures. To be published in Phys. Rev.