Danail Obreschkow

A semi-empirical simulation of the extragalactic radio continuum sky for next generation radio telescopes

We have developed a semi-empirical simulation of the extragalactic radio continuum sky suitable for aiding the design of next generation radio interferometers such as the Square Kilometre Array (SKA). The emphasis is on modelling the large-scale cosmological distribution of radio sources rather than the internal structure of individual galaxies. Here we provide a description of the simulation to accompany the online release of a catalogue of similar or equal to 320 million simulated radio sources. The simulation covers a sky area of 20x20 deg^2 - a plausible upper limit to the instantaneous field of view attainable with future (e.g. SKA) aperture array technologies - out to a cosmological redshift of z=20, and down to flux density limits of 10 nJy at 151, 610 MHz, 1.4, 4.86 and 18 GHz. Five distinct source types are included: radio-quiet active galactic nuclei (AGN), radio-loud AGN of the Fanaroff-Riley type I (FR I) and FR II structural classes, and star-forming galaxies, the latter split into Populations of quiescent and starbursting galaxies.

Simulation of the Cosmic Evolution of Atomic and Molecular Hydrogen in Galaxies

We present a simulation of the cosmic evolution of the atomic and molecular phases of the cold hydrogen gas in about 3x10^7 galaxies, obtained by postprocessing the virtual galaxy catalog produced by De Lucia & Blaizot on the Millennium Simulation of cosmic structure. Our method uses a set of physical prescriptions to assign neutral atomic hydrogen (HI) and molecular hydrogen (H2) to galaxies, based on their total cold gas masses and a few additional galaxy properties. These prescriptions are specially designed for large cosmological simulations, where, given current computational limitations, individual galaxies can only be represented by simplistic model objects with a few global properties. Our recipes allow us to (1) split total cold gas masses between HI, H2, and helium, (2) assign realistic sizes to both the HI and H2 disks, and (3) evaluate the corresponding velocity profiles and shapes of the characteristic radio emission lines. The results presented in this paper include the local HI and H2 mass functions, the CO luminosity function, the cold gas mass-diameter relation, and the Tully-Fisher relation (TFR), which all match recent observational data from the local universe. We also present high-redshift predictions of cold gas diameters and the TFR, both of which appear to evolve markedly with redshift.This poster presents first-order semi-analytic pretictions of the cosmic evolution of atomic and molecular hydrogen.

Understanding the H2/H i ratio in galaxies

We revisit the mass ratio R between molecular hydrogen (H2) and atomic hydrogen (HI) in different galaxies from a phenomenological and theoretical viewpoint. First, the local H2 mass function (MF) is estimated from the local CO luminosity function (LF) of the FCRAO Extragalactic CO-Survey, adopting a variable CO-to-H2 conversion fitted to nearby observations. This implies an average H2-density Omega(H2)=(6.9±2.7)x10^(-5)/h and Omega(H2)/Omega(HI)=0.26±0.11 the local Universe. Secondly, we investigate the correlations between R and global galaxy properties in a sample of 245 local galaxies. Based on these correlations we introduce four phenomenological models for R, which we apply to estimate H2 masses for each HI galaxy in the HIPASS catalogue. The resulting H2-MFs (one for each model for R) are compared to the reference H2-MF derived from the CO LF, thus allowing us to determine the Bayesian evidence of each model and to identify a clear best model, in which, for spiral galaxies, R negatively correlates with both galaxy Hubble type and total gas mass. Thirdly, we derive a theoretical model for R for regular galaxies based on an expression for their axially symmetric pressure profile dictating the degree of molecularization. This model is quantitatively similar to the best phenomenological one at redshift z=0, and hence represents a consistent generalization while providing a physical explanation for the dependence of R on global galaxy properties. Applying the best phenomenological model for R to the HIPASS sample, we derive the first integral cold gas MF(HI+H2+helium) of the local universe.

THE COSMIC DECLINE IN THE H2/HI-RATIO IN GALAXIES

We use a pressure-based model for splitting cold hydrogen into its atomic (HI) and molecular (H2) components to tackle the co-evolution of HI, H2, and star formation rates (SFR) in 3x10^7 simulated galaxies in the Millennium simulation. The main prediction is that galaxies contained similar amounts of HI at redshift z=1.5 than today, but substantially more H2, in quantitative agreement with the strong molecular line emission already detected in a few high-redshift galaxies and approximately consistent with inferences from studies of the damped Lyman-alpha absorbers seen in the spectra of quasars. The cosmic H2/HI ratio, i.e. Omega(H2)/Omega(HI), is predicted to evolve monotonically as (1+z)^1.6. This decline of the H2/HI ratio as a function of cosmic time is driven by the growth of galactic disks and the progressive reduction of the mean cold gas pressure. Finally, a comparison between the evolutions of HI, H2, and SFRs reveals two distinct cosmic epochs of star formation: an early epoch (z>3), driven by the evolution of Omega(HI+H2)(z), and a late epoch (z<3), driven by the evolution of Omega(H2)(z)/Omega(HI)(z).

A VIRTUAL SKY WITH EXTRAGALACTIC H I AND CO LINES FOR THE SQUARE KILOMETRE ARRAY AND THE ATACAMA LARGE MILLIMETER/SUBMILLIMETER ARRAY*

We present a sky simulation of the atomic HI-emission line and the first 10 rotational CO emission lines of molecular gas in galaxies beyond the Milky Way. The simulated sky field has a comoving diameter of 500 Mpc/h; hence, the actual field-of-view depends on the (user-defined) maximal redshift zmax; e. g., for zmax=10, the field of view yields 4x4 deg^2. For all galaxies, we estimate the line fluxes, line profiles, and angular sizes of the Hi and CO-emission lines. The galaxy sample is complete for galaxies with cold hydrogen masses above 10^8 Msun. This sky simulation builds on a semi-analytic model of the cosmic evolution of galaxies in a Lambda-cold dark matter (Lambda CDM) cosmology. The evolving CDM distribution was adopted from the Millennium Simulation, an N-body CDM-simulation in a cubic box with a side length of 500 Mpc/h. This side length limits the coherence scale of our sky simulation: it is long enough to allow the extraction of the baryon acoustic oscillations in the galaxy power spectrum, yet the position and amplitude of the first acoustic peak will be imperfectly defined. This sky simulation is a tangible aid to the design and operation of future telescopes, such as the Square Kilometre Array, Large Millimeter Telescope, and Atacama Large Millimeter/submillimeter Array. The results presented in this paper have been restricted to a graphical representation of the simulated sky and fundamental dN/dz-analyses for peak flux density limited and total flux limited surveys of Hi and CO. A key prediction is that HI will be harder to detect at redshifts z>2 than predicted by a no-evolution model. The future verification or falsification of this prediction will allow us to qualify the semi-analytic models.We present a sky simulation of the atomic HI emission line and the first ten CO rotational emission lines of molecular gas in galaxies beyond the Milky Way. The simulated sky field has a comoving diameter of 500/h Mpc, hence the actual field-of-view depends on the (user-defined) maximal redshift zmax; e.g. for zmax=10, the field of view yields ~4x4 sqdeg. For all galaxies, we estimate the line fluxes, line profiles, and angular sizes of the HI and CO emission lines. The galaxy sample is complete for galaxies with cold hydrogen masses above 10^8 Msun. This sky simulation builds on a semi-analytic model of the cosmic evolution of galaxies in a Lambda-cold dark matter (LCDM) cosmology. The evolving CDM-distribution was adopted from the Millennium Simulation, an N-body CDM-simulation in a cubic box with a side length of 500/h Mpc. This side length limits the coherence scale of our sky simulation: it is long enough to allow the extraction of the baryon acoustic oscillations (BAOs) in the galaxy power spectrum, yet the position and amplitude of the first acoustic peak will be imperfectly defined. This sky simulation is a tangible aid to the design and operation of future telescopes, such the SKA, the LMT, and ALMA. The results presented in this paper have been restricted to a graphical representation of the simulated sky and fundamental dN/dz-analyzes for peak flux density limited and total flux limited surveys of HI and CO. A key prediction is that HI will be harder to detect at redshifts z>2 than predicted by a no-evolution model. The future verification or falsification of this prediction will allow us to qualify the semi-analytic models.

Hyper-Fit: Fitting Linear Models to Multidimensional Data with Multivariate Gaussian Uncertainties

Astronomical data is often uncertain with errors that are heteroscedastic (different for each data point) and covariant between different dimensions. Assuming that a set of D-dimensional data points can be described by a (D - 1)-dimensional plane with intrinsic scatter, we derive the general likelihood function to be maximised to recover the best fitting model. Alongside the mathematical description, we also release the hyper-fit package for the R statistical language (github.com/asgr/hyper.fit) and a user-friendly web interface for online fitting (hyperfit.icrar.org). The hyper-fit package offers access to a large number of fitting routines, includes visualisation tools, and is fully documented in an extensive user manual. Most of the hyper-fit functionality is accessible via the web interface. In this paper we include applications to toy examples and to real astronomical data from the literature: the mass-size, Tully-Fisher, Fundamental Plane, and mass-spin-morphology relations. In most cases the hyper-fit solutions are in good agreement with published values, but uncover more information regarding the fitted model.

Surface wave dynamics in orbital shaken cylindrical containers

Be it to aerate a glass of wine before tasting, to accelerate a chemical reaction, or to cultivate cells in suspension, the “swirling” (or orbital shaking) of a container ensures good mixing and gas exchange in an efficient and simple way. Despite being used in a large range of applications this intuitive motion is far from being understood and presents a richness of patterns and behaviors which has not yet been reported. The present research charts the evolution of the waves with the operating parameters identifying a large variety of patterns, ranging from single and multiple crested waves to breaking waves. Free surface and velocity fields measurements are compared to a potential sloshing model, highlighting the existence of various flow regimes. Our research assesses the importance of the modal response of the shaken liquids, laying the foundations for a rigorous mixing optimization of the orbital agitation in its applications.

DYNAMO-HST survey: clumps in nearby massive turbulent discs and the effects of clump clustering on kiloparsec scale measurements of clumps

We present

Analytical approximations for the collapse of an empty spherical bubble

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

100 pc resolution Hubble Space Telescope H