1301.1348
Reconstructing the initial density field of the local universe: method and test with mock catalogs
Wang, Mo, Yang, van den Bosch
Reconstruct an initial linear density field which follows the multivariate Gaussian distribution with variances given by the linear power spectrum of the current CDM model and evolves through gravitational instability to the present-day density field in the local Universe. Develop a Hamiltonian Markov Chain Monte Carlo (HMC) method to obtain the linear density field from a posterior probability function that consists of 2 components: a prior of a Gaussian density field with a given linear spectrum, and a likelihood term that is given by the current density field. The present-day density field can be reconstructed from galaxy groups using the method developed in Wang+(2009). Using a realistic mock SDSS DR7 based on Millennium sim with galaxies, show that this method can effectively and accurately recover both the amplitudes and phases of the initial, linear density field down to a scale of 2.8 Mpc/h. To examine the performance of this method in the highly NL regime, use N-body sims to evolve these reconstructed IC to the present day. The resimulatd density field thus obtained accurately matches the original density field of the Millennium simulation in the density range 0.3<rho/rho(mean)<20 without any significant bias. The Fourier phases of the resimulated density fields are tightly correlated with those of the original simulations down to a scale corresponding to a wavenumber of ~1 h/Mpc, much smaller than the translinear scale, which corresponds to a wavenumber of 0.15 h/Mpc.
1301.1474
Influence of the variation of fundamental constants on the primordial nucleosynthesis
Coc et al
The main influences come from the weak rates and the A=2, n(p,g)d, bottleneck reaction.
1301.1682
The relation between velocity dispersion and mass in simulated clusters of galaxies: dependence on the tracer and the baryonic physics
Munari, Biviano, Borgani, Murante, Fabjan
Present an analysis of the relation between the masses of cluster- and group-sized haloes, extracted from LCDM cosmological N-body and hydrodynamic simulations, and their velocity dispersions, at different redshifts from z=2 to z=0. The main purpose of this analysis: understand how the implementation of baryonic physics in simulations affects such relation, i.e., to what extent the use of the velocity dispersion as a proxy for cluster mass determination is hampered by the imperfect knowledge of the baryonic physics. Use several sets of simulations with different physics implemented. Velocity dispersions are determined using 3 different tracers: DM particles, sub haloes, and galaxies. Confirm that DM particles trace a relation that is fully consistent with the theoretical expectations based on the virial theorem and with previous results presented in the literature. Subhaloes and galaxies tracer steeper relations, and with larger values of the normalization. Such relations imply that galaxies and subhaloes have a ~10 per cent velocity bias relative to the DM particles, which can be either positive or negative, depending on the halo mass, redshift and physics implemented in the simulation. Explain these differences as due to dynamical processes, namely dynamical friction and tidal disruption, acting on substructures and galaxies, but not on DM particles. These processes appear to be more or less effective, depending on the halo masses and the importance of baryon cooling, and may create a non-trivial dependence of the velocity bias and the D-M relation [?] on the tracer, the halo mass and its redshift. These results are relevant in view of the application of velocity dispersion as a proxy for cluster masses in ongoing and future large redshift surveys.
1301.1684
Testing phenomenological and theoretical models of dark meter density profiles with galaxy clusters
Silva, Lima, Sodre
Use the stacked gravitational lensing mass profile of 4 high-mass (M>1e15 Msun) galaxy clusters around z~0.3 from Umetsu+ 2011 to fit density profiles of phenomenological (NFW, Einasto, Sersic, Stadel and Hernquist) and theoretical (non-singular isothermal sphere, DARKexp, Kang & He) models of the DM distribution. Account for large-scale structure effects, including a 2-halo term in the analysis. Find that the Stadel model provides the best fit to the data as measured by the reduced chisq. It is followed by the generalized NFW profile with a free inner slope and by the Einasto profile. The NFW model gives the best fit if the 2-halo term is neglected; in agreement with results from Umetsu. Among the theoretical profiles, the DARKexp model with a single form parameter has the best performance, almost identical to that of the Stadel profile. This may indicate a connection between this theoretical model and the phenomenology of dark matter haloes, shedding light on the dynamical basis of empirical profiles which emerge from numerical simulations.
1301.0624
The X-ray/SZ view of the virial region. II. Gas mass fraction
Eckert, Ettori, Molendi, Vazza, Paltani
Using hot gas fraction of galaxy clusters as standard ruler relies on the assumption that the baryon fraction in clusters agrees with the cosmic value, and does not differ from one system to another. Test this hypothesis by measuring the gas mass fraction over the entire cluster volume in a sample of local clusters. Combining the SZ thermal pressure from Planck and the X-ray gas density from ROSAT, measure for the first time the average gas fraction out to the virial radius and beyond in a large sample of clusters. Also obtain azimuthally-averaged measurements of the gas fraction for 18 individual systems, which were used to compute the scatter of f_gas around the mean value at different radii and its dependence on the cluster's temperature. THe gas mass fraction increases with radius and reaches the cosmic baryon fraction close to R200. At R200, measure f_gas,200 = 0.176pm0.009. Find significant differences between the baryon fraction of relaxed, CC systems and unrelaxed, non-cool core (NCC) clusters in the outer regions. On average, the gas fraction in NCC clusters slightly exceeds the cosmic baryon fraction, while in CC systems the gas fraction converges to the expected value when accounting for the stellar content, without any evidence for variations from one system to another. Find that f_gas estimates in NCC systems slightly disagree with the cosmic value approaching R200. This result could be explained either by a violation of the assumption of hydrostatic equilibrium or bay an inhomogeneous distribution of the gas mass. Conversely, CC clusters are found to provide reliable constraints on f_gas at overdensities >200, which makes them suitable for cosmological studies.
1301.1688
PRIMUS: constraints on star formation quenching and galaxy merging, and the evolution of the stellar mass function from z=0-1
Moustakas, Coil, Aird, Blanton, Cool, Eisenstein, ... et al
Measure the evolution of the stellar mass function (SMF) of 0<z<1 using PRIMUS and SDSS. From PRIMUS construct an i<23 flux-liited sample of 40 galaxies at 0.2<z<1.0 over 5 fields totaling 5.5 degsq, and from SDSS select 170k galaxies at 0.01<z<0.2 that are analyzed consistently wrt PRIMUS to minimize systematic errors in evolutionary measurements. Find that the SMF of all galaxies evolves relatively little since z=1, although there is evidence for mass assembly downsizing; measure a ~30% increase in the number density of 1e10 Msun galaxies since z~0.6, and a <10% change in the number density of all >1e11 Msun galaxies since z~1. Dividing the sample into SF and quiescent using an evolving cut in specific SFR, find that the number density of ~1e10Msun SF galaxies stays relatively constant since z~0.6, whereas the space-density of >1e11 Msun SF galaxies decreases by ~50% in 0<z<1. Meanwhile, the number density of ~1e10Msun quiescent galaxies increases steeply towards low redshift, by a factor of ~2-3 since z~0.6, while the number of massive quiescent galaxies remains approximately constant since z~1. These results suggest that the rate at which SF galaxies are quenched increases with decreasing stellar mass, but taht the bulk of the stellar mass buildup within the quiescent population occurs around 1e10.8Msun. In addition, conclude that mergers do not appear to be a dominant channel for the stellar mass buildup of galaxies at z<1, even among massive (1e11 Msun) quiescent galaxies.
1301.1863
CFHTLenS: Higher-order galaxy-mass correlations probed by galaxy-galaxy-galaxy lensing
Simon, Erben, Schneider, Heymans, Hildebrandt, Hoekstra, Kitching, Mellier, Van Waerbeke, ... Kuijken, Rowe, Schrabback, Semboloni, Velander et al
First direct measurement of the galaxy-matter bispectrum as a function galaxy luminosity, stellar mass, and SED type. Use G3L technique on angular scales between 9 and 50 arcmin, to quantify (i) the excess surface mass density around galaxy pairs ("excess mass"), (ii) the excess shear-shear correlations around single galaxies, both of which yield a measure of two types of galaxy-matter bispectra. Apply method to the state-of-theart CFHTLenS, spanning 154 sq.deg. This survey allows us to detect a significant change of the bispectra with lens properties. Measurements for lens populations with distinct redshift distributions become comparable by a newly devised normalization technique. That will also aid future comparison to other surveys or simulations. A significant dependence of the normalized G3L statistics on luminosity within -23<M_r<-18 and stellar mass within 5e9Msun<M_star<2e11Msun is found. Both bispectra exhibit a stronger signal for more luminous lenses or higher stellar mass lenses for the excess mass. Importantly, find the excess mass to be very sensitive to galaxy type as recently predicted with SAM: luminous (M_r<-21) late-type galaxies show no detectable signal, while all excess mass detected for luminous galaxies seems to be associated with early-type galaxies. Also present the first observational constraints on 3rd-order stochastic galaxy biasing parameters.
1301.2009
On the abundances of noble and biologically relevant gases in lake Vostok, Antarctica
Mousis, Lakhlifi, Picaoud, Pasek, Chassefiere
Investigate the composition of clathrates (molecules trapped in crystal structure) that are expected to form in this environment from the air supplied to the lake by melting ice. Determine the fugacities of the different volatiles present in the lake by defining a "pseudo" pure substance dissolved in water owning the average properties of the mixture and by using the Redlich-Kwong equation of state to mimic its thermodynamic behavior. Irrespective of the clathrate structure considered in the model, find that Xe and Kr are strongly impoverished in the lake water compared to their atmospheric abundances. Ar and CH4 are also found depleted in the Lake Vostok water by 1/2-1/3-95% ranges, compared to atmospheric abundances. On the other hand, the CO abundance is found substantially enriched in the lake water compared to atmospheric abundance (by x1.6-x5). The comparison of the predictions of the CO2 and CH4 mole fractions in Lake Vostok with future in situ measurements will allow disentangling between the possible supply sources. [what is their prediction based on? Atmospheric composition in the past?]
1301.2067
The star-forming progenitors of massive red galaxies
Cattaneo, Woo, Dekel, Faber
Link between massive red galaxies at z=0 and SF galaxies at high z investigated with SAM that is successful in explaining the galaxy color-magnitude bimodality, and the stellar mass-age relation for red-sequence galaxies. Model used to explore the processes that drive SF in different types of galaxies as a function of stellar mass and redshift. Find that most 2<z<4 SF galaxies with M*>1e10 Msun evolve into red-sequence galaxies. Also, most of the massive galaxies on the red-sequence today have passed through a phase of intense SF at z>2. Specifically, ~90% of today's red galaxies with M*>1e11 Msun were fed during this phase by cold streams including minor mergers. Gas-rich major mergers are rare and the effects of merger-driven SB are ephemeral. On the other hand, major mergers are important in powering the most extreme SBs. Gas-rich mergers also explain the tail of intermediate-mass red galaxies that form relatively late, after the epoch of peak SF. In 2/3 of the currently red galaxies that had an intense SF event at z<1, this event was triggered by a merger.
1301.2119
Modeling the history of astronomy: Ptolemy, Copernicus and Tycho
Timberlake
A series of activities in which students investigate and use the models of planetary motion introduced by Ptolemy, Copernicus, and Brahe. The activities involve the use of open source software to help students discover important observational facts, learn from necessary vocabulary, understand the fundamental properties of different theoretical models, and relate the theoretical models to observational data. Once they understand the observations and models, students complete a series of projects in which they observe and model a fictitious solar system with 4 planets orbiting in circles around a central star.
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