1212.1717
Simulations of the galaxy population constrained by observations from z=3 to the present day: implications for galactic winds and the fate of their ejecta
Henriques, White, ... Springel
LS simulations of galaxy formation in LCDM, models on Millennium and Millennium-II simulations. Fast sampling techniques, allows observed galaxy abundances over M* = 1e7-1e12 Msun and 0<z<3 to be used as simultaneous constraints in the MCMC analysis. With only z=0 constraints, no single set of parameters can reproduce observed galaxy abundances at all z simultaneously (low mass galaxies form too early and thus are overabundant at high z). Data require the efficiency with which galactic wind eject are re-accreted to vary with redshift and halo mass quite differently than previously assumed, but in a similar way as in some recent hydro sims of galaxy formation. This produces an evolving galaxy population which fits observed abundances as a function of stellar mass, B- and K-band luminosity at all redshifts simultaneously. Also produces a significant improvement in two other areas where previous models were deficient. Leads to present day dwarf galaxy populations which are younger, bluer, more strongly SF and more weakly clustered on small scales than before, although the passive fraction of faint dwarfs remains too high.
1212.1721
CosmoHammer: cosmological parameter estimation with the MCMC Hammer
Akeret, Seehars, Amara, Refregier, Csillaghy
Study the benefits and limits of parallelised MCMC sampling in cosmology, but it takes a long time to run. To achieve greater speed through parallelisation, algorithms need to have short auto-correlation times and minimal overheads caused by tuning and burn-in. In order to efficiently distribute the MCMC sampling over thousands of cores on modern cloud computing infrastructure, develop a Python framework (CosmoHammer) which embeds emcee (affine invariant ensemble sampler). Test the performance for cosmo parameter estimation from CMB. While Metropolis-Hastings is constrained by overheads, CosmoHammer is able to accelerate the sampling process from a wall time of 30 hours on a single machine to 16 minutes by the efficient use of 2048 cores.
1212.1799
Mediatrix method for filamentation of objects in images: application to gravitational arcsBom, Makler, Albuquerque
An iterative procedure that decomposes elongated objects in filaments along their main direction over their intensity peak. From this decomposition, the method meausres the object's length and thickness. THis technique is applied in preliminary tests to arc-shaped objects (simulated gravitational arcs) to recover their curvature center.
1212.1915
Bring out your codes! Bring out your codes! (increasing software visibility and re-use)
Allen et al
Many codes still remain hidden from public view. Astrophysics source code library (ASCL) now indexed by ADS & a new journal Astronomy & Computing focused on astrophysics software, and the increasing success of education efforts such as Software Carpentry and SciCoder, the community has the opportunity to set a higher standard for its science by encouraging the release of SW for examination and possible reuse. Present issues inhibiting code release and sought suggestions for tackling these factors (by panel). Algorithms should be readily available, code used to produce published scientific results should be made available; there should be discovery mechanisms to allow these to be found easily. With increased use of resources such as GitHub, ASCL and a stated strong preference from the new journal for code release, expected to see additional progress over the next few years.
1212.1916
Astrophysics source code library
Allen et al
ASCL founded in 1999 is a free on-line registry for source codes of interest to astronomers and astrophysicists, accessed at http://ascl.net. Currently has >500 code entries, records citable and indexed by ADS.
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