1303.0835
Impact of systematic uncertainties in N-body simulations on the precision cosmology from galaxy clustering
Wu, Huterer
DM N-body sims a tool to model galaxy clustering, and help interpret results of galaxy z-surveys; but the galaxy properties from sims are not necessarily represnetative of the observed galaxy populations (e.g., absence of baryons). Assess how the uncertainties in N-body simulations impact the cosmo parameters inferred from galaxy z surveys. Apply halo model, find that the velocity bias of galaxies in modeling the z-space distortions is likely to be the predominant source of systematic bias. z-space distortions in wide&deep survey like BigBOSS: 10% uncertainty in velocity bias limit k_max to 0.14 h/Mpc. In contrast, find that the uncertainties related to the density profiles and the galaxy occupation statistics lead to relatively insignificant systematic biases. The ability to calibrate the velocity bias accurately---from observations as well as simulations --- will likely set the ultimate limit on the smallest length scale that can be used to infer cosmological information from galaxy clustering.
1303.0839
Halo mass function and the free streaming scale
Schneider, Smith, Reed
Nature of structure formation around particle free streaming scale is not well understood. Particle-based sims of hot/warm/cold DM with free-streaming cut-off all suffer from spurious structure formation at scales below their respective free streaming scales, i.e., where the physics of halo formation is most affected by free streaming. Perform a series of high-res sims of different WDM, and develop an approximate method to subtract artificial structures in the measured halo mass function. The corrected measurements are then used to construct and calibrate an extended Press-Schechter model with a sharp-k window function and adequate mass assignment. [subtract artificial structures?! do hydro-sims not have artificial structure problem?] The EPS model gives accurate predictions for the low-z halo mass function of CDM and WDM models, but it significantly under-predicts the halo abundance at high z. Taking into account the ellipticity of the initial patches and connect the characteristic filter scale to the smallest ellipsoidal axis, eliminates this inconsistency and obtain and accurate MF over all z and all DM particle masses covered by the sim. As and additional application, use model to predict the microhalo abundance of the standard neutralino-CDM scenario and give the first quantitative prediction of the MF over the full range of scales of CDM structure formation.
1303.0928
Dwarf galaxy populations in present-day galaxy clusters - II. the history of early-type and late-type dwarfs
Lisker, Weinmann, Janz, Meyer
How did the dwarf galaxy population of present-day galaxy clusters form and grow over time? Analyze the history of DM subhaloes in Millennium-II sim. Use SAM to link to observations. Argue: a reasonable analogue to early morphological types or red-sequence dwarf galaxies are those subhaloes that experienced strong mass loss, or alternatively those that have spent a long time in massive haloes. This approach reproduces the observed morhphology-distance relation of dwarf galaxies in Virgo and Coma clusters, and thus provides insight into their history. Over their lifetime, present-day late types have experienced an amount of environmental influence similar to what the progenitors of dwarf ellipticals had already experienced at z>2. Therefore, dwarf ellipticals are more likely to be a result of early and continuous environmental influence in group- and cluster-size haloes, rather than a recent transformation product. The observed morphological sequences of late-type and early-type galaxies have developed in parallel, not consecutively. Consequently, the characteristics of today's late-type galaxies are not necessarily representative for the progenitors of today's dwarf ellipticals. Studies aiming to reproduce the present-day dwarf population thus need to start at early epochs, model the influence of various environments, and also take into account the evolution of the environments themselves.
1303.0952
Reanalysis of the gravitational microlensing event MACHO-97-BLG-41 based on combined data
Jung, Han, Gould, Maoz
Reanalysis shows that it's a binary lens (no planet).
1303.1024detection baryon acoustic oscillations by 3d weak lensing
Grassi, Schaefer
BAO inaccessible even to WL tomography because of wide LoS weighting functions and require a specialized approach via 3d shear estimates. Quantify uncertainty of estimating the matter PS amplitude at the BAO vector by Fisher-matrix approach with a fixed cosmology and show in this way that future WL surveys such as EUCLID and DES are able to pick up the first four wiggles, with EUCLID giving a better precision. Also provide a detailed investigation of the correlation existing between errors and of their scaling behavior with respect to survey parameters such as median redshift, error on redshift, error on the galaxy shape measurement, sky coverage, and wrt the number of wiggles one is trying to determine.
1303.1055
A first look at creating mock catalogs with machine learning techniques
Xu, Ho, Trac, Schneider, Poczos, Ntampaka
Investigate ML techniques for predicting the number of galaxies N_gal that occupy a halo, given the halo's properties. These types of mappings are crucial for constructing the mock galaxy catalogs necessary for analysis of large-scale structure. ML techniques different from regular HOD modeling, as they do not assume a prescribed relationship between halo properties and N_gal; ML techniques only dependent on parent halo properties (advantageous over subhalo-based approaches, since subhalo id is difficult). Test 2 algorithms: SVM and k-nearest neighbor (kNN) regression. Take galaxies and haloes from Millennium and predict N_gal by training over 6 numbers: number of particles, M_200, sigma_v, v_max, half-mass radius, and spin. Predictions match the overall distribution of haloes reasonably well, and the galaxy correlation function at large scales to 5-10%. In addition, demonstrate a feature selection algorithm to isolate the halo parameters that are most predictive, a useful technique for understanding the mapping between halo properties and N_gal. [so which one was the most useful param?] Also use ML for different galaxy sub-populations (blue/red/high M*/low M*). Given its non-parameteric nature as well as its powerful predictive and feature selection capabilities, ML offers an interesting alternative for creating mock catalogs. [but you're training it off someone else's mock catalog!]
1303.1100
Transmitting signals over interstellar distances: three approaches compared in the context of the Drake equation
Arnold
As the title says: 3 methods are radio, laser and artificial transits. Quantitative comparison based on: energy cost and transmitting time L. Radio transmitters are the most energy-effective, while macro-engineered planetary-sized objects producing artificial transits seem effective on the long term to transmit an attention-getting signal for a time that might be much longer than the lifetime of the civilization that produced the artifact. [eep!]
1303.1147
Kepler photometry of four radio-loud AGN in 2010-2012
Wehrle, Wiita, .. .et al
As the title says. Timescale from minutes to months, comparable to the light crossing time of the accretion disk around the central SMBH or the base of the relativistic jet. Kepler's almost continuous observations provide much better temporal coverage than is possible from ground-based observations. Construct power spectral densities using 8 Kepler quarters of long-cadence (30 min) data for 3 AGN, 6 quarters for one AGN and 2 quarters of short-cadence (1-minute) data for all 4 AGN . On timescales longer than about 0.2-0.6 dat, find red noise with mean power-law slopes ranging from -1.8 to -1.2, consistent with the variability originating in turbulence either behind a shock or within an accretion disk. Each AGN has a range of red noise slopes which vary slightly by month and quarther of observations. No quasi-periodic oscillations of astrophyiscal origin were detected. Detected several days-long flares when brightness increased by 3-7% in two objects. No flares on timescales of minutes to hours were detected. Observations imply that the duty cycle for enhanced activity in these radio-loud AGN is small. These well-sampled AGN light curves provide an impetus to develop more detailed models of turbulence in jets and instabilities in accretion disks.
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