Day 865

Wednesday.  Thursday.  Friday.


1504.01384
Euclid astroseismology and Kuiper belt objects
Gould, Huber, Stello

Euclid, which is primarily a DE/cosmo mission, may have a microlensing component, consisting of perhaps 4 dedicated one-month campaigns aimed at the Galactic bulge.  Show that such a program would yield excellent auxilliary science, including astroseismology detections for about 100k giant stars, and detection of about 1k KBOs, down to 2-2.5 mag below the observed break in the KBO LF at I~26.  For the 400 KBOs below the break, Euclid will measure accurate orbits, with fraction period errors <~2.5%.


1504.01413
Detection of universality of dark matter profile from Subaru weak lensing measurements of 50 massive clusters
Niikura, Takada, Okabe, Martino, Takahashi

Develop a novel method of measuring the lensing distortion profiles of clusters with stacking the scaled amplitudes of BG galaxy ellipticities as a function of the scaled centric radius according to the NFW prediction of each cluster, based on the assumption that the different clusters in a sample follow the universal NFW profile.  First demonstrate the feasibility of this method using both the analytical NFW model and simulated haloes in high-resolution N-body simulations.  Then apply, as a proof of concept, this method to the Subaru WL data and the XMM/Chandra X-ray observables for a sample of 50 massive clusters in the range 0.15<z<0.3, where their halo masses range over an order of magnitude.  To estimate the NFW parameters of each cluster, use the halo mass proxy relation of X-ray observables, based on either the hydrostatic equilibrium or the gas mass, and then infer the halo concentration from the model c(M) relation.  Evaluate a performance of the NFW scaling analysis by measuring the scatters of 50 cluster lensing profiles relative to the NFW predictions over a range of radii, 0.14<R/[Mpc/h]<2.8.  Found a 4-6 sigma level evidence of the universal NFW profile in 50 clusters, for both the X-ray halo mass proxy relations, although the gas mass appears to be a better proxy of the underlying true mass.  By comparing the measurements with the simulations of cluster lensing taking into account the statistical errors of intrinsic galaxy shapes in the Subaru data, argue that additional halo mass errors or intrinsic scatters of sigma_lnM500c~0.2-0.3 could reconcile a difference between the measurements and the simulations.


1504.01421
Highly siderophile elements in the earth's mantle as a clock for the moon-forming impact
Jacobson, et al

According to the generally accepted scenario, the last giant impact on the Earth formed the Moon and initiated the final phase of core formation by melting the Earth's mantle.  Different ages have been proposed.  Show that a Moon-forming event at 40 Myr after condensation, or earlier, is ruled out at 99.9% CL.  Use a large number of N-body sims to demonstrate a relationship between the time of the last giant impact on an Earth-like planet and the amount of mass subsequently added during the era known as Late Accretion.  As the last giant impact is delayed, the late-accreted mass decreases in a predictable fasten.  This relationship exists within both the classical scenario and the Grand Tack scenario of terrestrial planet formation, and it holds across a wide range of disk conditions.  The concentration of highly siderophile elements (HSEs) in Earth's mantle constrains the mass of chondritic material added to Earth during Late Accretion.  Using HSE abundance measurements, determine a Moon-formation age of 95±32 Myr since condensation.  The possibility exists that some late projectiles were differentiated and left an incomplete HSE record in Earth's mantel.  Even in this case, various isotopic constraints strongly suggest that the late-accreted mass did not exceed 1% of Earth's mass, and so the HSE clock still robustly limits the timing of the Moon-forming event to significantly later than 40 My after condensation.


1504.01437
The unexpected diversity of dwarf galaxy rotation curves
Oman, Navarro, ... Frenk, ... White, Bower, ... Schaye et al

Elaine the circular velocity profiles of galaxies in LCDM cosmological hydrodynamical sims from the EAGLE and LOCAL GROUPS projects and compare them with a compilation of observed rotation curves of galaxies spanning a wide range in mass.  The shape of the circular velocity profiles of simulated galaxies varies systematically as a function of galaxy mass, but shows remarkably little variation at fixed maximum circular velocity.  This is especially true for low-mass DM-dominated systems, reflecting the expected similarity of the underlying CDM halos.  This is at odds with observed dwarf galaxies, which show a large diversity of rotation curve shapes, even at fixed maximum rotation speed.  Some dwarfs have rotation curves that agree well with simulations, others do not.  The latter are systems where the inferred mass enclosed in the inner regions is much lower than expected for CDM haloes and include many galaxies where previous work claims the presence of a constant density "core".  The "cusp vs core" issue is thus better characterized as an "inner mass deficit" problem than as a density slope mismatch.  For several galaxies the magnitude of this inner mass deficit is well in excess of that reported in recent simulations where cores result from baryon-induced fluctuations in the gravitational potential.  Conclude that one or more of the following statements must be true: (i) the DM is more complex than envisaged by any current model;  (ii) current simulations fail to reproduce the effects of baryons on the inner regions of dwarf galaxies; and/or (iii) the mass profiles of "inner mass deficit" galaxies inferred from kinematic data are incorrect.


1504.01594
The star formation history of galaxies: the role of galaxy mass, morphology and environment
Guglielmo, et al

Analyze the SFH of galaxies as a function of present-day environment, galaxy stellar mass and morphology.  The SFH is derived by means of a non-parametric spectrophotometric model applied to individual galaxies at z~0.04-0.1 in the WINGS clusters and the PM2GC field.  The field reconstructed evolution of the SFR density follows the values observed at each z (Madau+Dickinson 2014), except at z>2 where the estimate is ~1.7x higher than the high-z observed value.  The slope of the SFRD decline with time gets progressively steeper going from low mass to high mass haloes.  The decrease of the SFRD since z=2 is due to 1) quenching - 50% of the SFRD in the field and 75% in clusters at z>2 originated in galaxies that are passive today - and 2) the fact that the average SFR of today's SF galaxies has decreased with time.  Quantify the contribution to the SFRD(z) of galaxies of today's different masses and morphologies.   The current morphology correlates with the current SF activity but is irrelevant for the past stellar history.  The average SFH depends on galaxy mass, but galaxies of a given mass have different histories depending on their environment.  Conclude that the variation of the SFRD(z) with environment is not driven by different distributions of galaxy masses and morphologies in clusters and field, and must be due to an accelerated formation in high mass haloes compared to low mass ones even for galaxies that will end up having the same galaxy mass today.


** 1504.01676
Cosmological ensemble and directional averages of observables
Bonvin, et al

Show that at second order ensemble averages of observables and directional averages do not commute due to gravitational lensing.  In principle this non-commutativity is significant for a variety of quantities often used as observables.  Derive the relation between the ensemble average and the directional average of an observable, at second-order in perturbation theory.  Discuss the relevant of these two types of averages for making predictions of cosmological observables, focussing on observables related to distances and magnitudes.  In particular, show that the ensemble average of the distance is increased by gravitation lensing, whereas the directional averages of the distance is decreased.  Show that for a generic observable, there exists a particular function of the observable that is invariant under second-order lensing perturbations.


1504.02097
The origin and evolution of the galaxy mass-metallicity relation
Ma, Hopkins, ... et al

Use high-resolution cosmo zoom-in sims from the FIRE project to study the galaxy mass-metallicity relations (MZR) from z=0-6.  These simulations include explicit models of the multi-phase ISM, SF, and stellar feedback.  The simulations cover halo masses Mhalo=1e9-13 Msun and stellar mass Mstar-1e4-11 Msun at z=0 and have been shown to produce many observed galaxy properties from z=0-6.  For the first time, the simulations agree reasonably well with the observed mass-metallicity relations at z=0-3 for a broad range of galaxy masses. Predict the evolution of the MZR from z=0-6 as log(Zgas/Zsun)=12+log(O/H)-0.9=0.35[log(Mstar/Msun)-10]+0.93 exp(-0.43 z)-1.05 and log(Zgas/Zsun)=[Fe/H]-0.2=0.4[log(Mstar/Msun)-10]+0.67 exp(-0.50 z)-1.04, for gas-phase and stellar metallicity, respectively.  The simulations suggest that the evolution of MZR is associated with the evolution of stellar/gas mass fractions at different redshifts, indicating the existence of a universal metallicity relation between stellar mass, gas mass, and metallicities.  In the simulations, galaxies above Mstar=1e6 Msun are able to retain a large fraction of their metals inside the halo, because metal-rich winds fail to escape completely and are recycled into the galaxy.  This resolved a long-standing discrepancy between "sub-grid' wind models (and SAMs) and observations, where common sub-grid models cannot simultaneously reproduce the MZR and the stellar mass functions.


1504.02135
Geometric biases in power-spectrum measurements
Samushia, Branchini, Percival

The observed distribution of galaxies has local transverse isotropy around the LoS with respect to the observer.  The difference in the statistical clustering signal along and across the LoS encodes important information about the geometry of the Universe, its expansion rate and the rate of growth of structure within it.  Because the LoS varies across the survey, the standard FFT based methods of measuring the anisotropic power spectrum (APS) cannot be used for surveys with wide observational footprint, other than to measure the monopole moment.  Derive a simple analytic formula to quantify the bias for higher-order Legendre moments and demonstrate that it is scale independent for a simple survey model, and depends only on the observed area.  Derive a similar numerical correlation formula for recently proposed alternative estimators of the APS that are based on summing over galaxies rather than using an FFT, and can therefore incorporate a varying LoS.  Demonstrate that their bias depends on scale but not on the observed area.  For a quadrupole the bias is always less than 1% for k>0.01 h/Mpc at z>0.32. For a hexadecapole the bias is below 5% for k>0.05h/Mpc at z>0.32.