1510.07621
CONCEPT - The COsmological $N$-body CodE in PyThon
Dakin
CONCEPT is a free and open-source code for cosmological N-body sims on massively parallel computers with distributed memory. Collisionless dark matter is the only implemented particle species. Gravity can be computed using the PP, PM or the P3M algorithm. The goal of CONCEPT is tot make it pleasant to work with cosmological N-body simulations - for the cosmologist as well as for the source code developer. This is the user guide. The source code and additional documentation can be found at github.
1510. 07657
The imprint of rapid star formation quenching on the spectral energy distributions of galaxies
Ciesla, et al
In high density environment, the gas content of galaxies is stripped, leading to a rapid quenching of their SF activity. This dramatic environmental effect is generally not taken into account in the SFHs usually assumed to perform SED fitting of these galaxies, yielding to a poor fit of their stellar emission and, consequently, a biased estimate of the SFR. Aim at reproducing the SFH of galaxies that underwent a rapid SF quenching using a truncated delayed SFH that is implemented in the SED fitting code CIGALE. Show that the ratio between the instantaneous SFR and the SFR just before the quenching (r_SFR) is well constrained as long as rest frame UV data are available. This SED modeling is applied to the Herschel Reference Survey (HRS) containing isolated galaxies and sources falling in the dense environment of the Virgo cluster. The latter are HI-deficient due to ram pressure stripping. Show that the truncated delayed SFH successfully reproduces their SED while typical SFH assumptions fail. A good correlation is found between r_SFR and HI-def, the parameter quantifying the gas deficiency of cluster galaxies, meaning that SED fitting results can be used to provide a tentative estimate of the gas deficiency of galaxies for which HI observations are not available. The HRS galaxies are place on the SFR-M* diagram showing that the HI-deficient sources lie in the quiescent region confirming previous studies. Using the r_SFR parameter, derive the SFR of these sources before quenching and show that they were previously on the main sequence relation. Show that the r_SFR parameter is also well recovered for deeply obscured high redshift sources, as well as in absence of IR data. SED fitting is thus a powerful tool to identify galaxies that underwent a rapid star formation quenching.
1510.07702
The massive end of the luminosity and stellar mass functions and clustering from CMASS to SDSS: evidence for and against passive evolution
Bernardi, et al
Describe the LF, based on Sersic fits to the light profiles, of CMASS galaxies at z~0.55. Compared to previous estimates, the Sersic-based reductions imply more luminous, massive galaxies, consistent with the effects of Sersic rather than Petrosian or deVaucouleur-based photometry on SDSS main galaxy sample at z~0.1. This implies a significant revision of the high mass end of the correlation between stellar and halo mass. Inferences about the evolution of the luminosity and stellar mass functions depend strongly on the assumed, and uncertain, k+e corrections. In turn, these depend on the assumed age of the population. Applying k+e corrections taken from fitting the models of Marston et al (2009) to the colors of both SDSS and CMASS galaxies, the evolution of the luminosity and stellar MFs appears impressively passive, provided that the fits are required to return old ages. However, when matched in comoving number- or luminosity-density, the SDSS galaxies are less strongly clustered compared to their counterparts in CMASS. This rules out the passive evolution scenario, and, indeed, any minor merger scenarios which preserve the rank ordering in stellar mass of the population. Potential incompletenesses in the CMASS sample would further enhance this mismatch. The analysis highlights the virtue of combining clustering measurements with number counts.
1510.07704
The Pluto system: initial results from its exploration by New Horizons
Stern et al
The Pluto system was recently explored by NASA's New Horizons spacecraft, making closest approach on 14 July 2015. Pluto's surface displays diverse landforms, terming ages, albedos, colors, and composition gradients. Evidence is found for a water-ice crust, geologically young surface units, surface ice convection, wind streaks, volatile transport, and glacial flow. Pluto's atmosphere is highly extended, with trace hydrocarbons, a global haze layer, and a surface pressure near 10 micro-bars. Pluto's diverse surface geology and long-term activity raise fundamental questions about how small planets remain active many billions of years after formation. Pluto's large moon Charon displays tectonics and evidence for a heterogeneous crustal composition, its N pole displays puzzling dark terrain. Small satellites Hydra and Nix have higher albedos than expected.
1510.08073
Deriving Photometric redshifts using fuzzy archetypes and self-organizing maps. I. Methodology
Speagle, Eisenstein
Propose a method to substantially increase the flexibility and power of template fitting-based photometric redshifts by transforming a large number of galaxy spectral templates into a corresponding collection of "fuzzy archetypes" using a suitable set of perturbative priors designed to account for empirical variation in dust attenuation and emission line strengths. To bypass widely separated degeneracies in parameter space (e.g., the redshift-reddening degeneracy), train self-organizing maps (SOMs) on a large "model catalogs" generated from appropriate MC sampling of the fuzzy archetypes to cluster the predicted observables in a topologically smooth fashion. Subsequent sampling over the SOM then allows full reconstruction of the relevant PDFs using the associated set of inverse mappings from the SOM to the underlying model parameters. This combined approach enables the multi-modal exploration of known variation among galaxy SEDs using a large number of archetypes with minimal modeling assumptions. Demonstrate the power of this approach to recover full redshift PDFs using a discrete MCMC sampling method combined with SOMs constructed from model catalogs based on LSST ugrizY and Euclid YJH mock photometry.
1510.08076
How to measure metallicity from five-band photometry with supervised machine learning algorithms
Acquaviva
Demonstrate that it is possible to measure metallicity from SDSS 5-band photometry to better than 0.1 dex using supervised machine learning algorithms. [...] All the routines to reproduce the results and to apply them to other data sets are made available.
1510.08080
Deriving photometric redshifts using fuzzy archetypes and self-organizing maps. II. Comparing sampling techniques using mock data
Speagle, Eisenstein
Investigate the performance of several sampling approaches that build on the general idea (of fuzzy archetypes and SOMs) using a mock catalog designed to approximately simulate LSST and Euclid data from z=0-6 at fixed LSST Y=24 mag. Test 8 different approaches: 2 brute-force methods, 2 MCMC-based methods, 2 hierarchical sampling methods, and 2 "quick-search" methods based on quantities derived during the initial SOM training process. Find most methods perform reasonably well with small catastrophic outlier fractions and are able to robustly identify redshift probability distribution functions that are multi-model and/or poorly constrained. Once these insecure objects are removed, the results are generally in good agreement wit the strict accuracy requirements necessary to meet Euclid WL goals for most redshifts above z~0.8. These results demonstrate the utility of the data clustering-based approach and highlight its effectiveness to derive quick and accurate photo-z's using large numbers of templates.
1510.08193
Mass--concentration relation of clusters of galaxies from CFHTLenS
Du, et al
Extract the M-c relation by measuring the density profiles of individual clusters instead of using stacked WL signals. Results show that within error bars, the derived M-c relation for redMaPper clusters is in agreement with simulation predictions.
1510.08837
A new empirical constraint on the Prevalence of technological species in the Universe
Frank, Sullivan
Recent advances in exoplanet studies provide strong constraints on all astrophysical terms in the Drake Equation. Using these and modifying the form and intent of the Drake equation, show that a firm lower bound on the probability that one or more additional technological species have evolved anywhere and at any time in the history of the observable Universe. As long as the probability that a habitable zone planet develops a technological species is larger than ~1e-24, then humanity is not the only time technological intelligence has evolved.
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