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Friday.
1507.08292
CMB lensing and scale dependent new physics
Hojjati, Linder
CMB lensing has become a new cosmological probe, carrying rich information on the matter power spectrum and distances over the redshift range z~1-4. Investigate the role of scale dependent new physics, such as from modified gravity, neutrino mass, and cold (low sound speed) dark energy, and its signature on CMB lensing. The distinction between different scale dependences, and the different redshift dependent weighting of the matter power spectrum entering into CMB lensing and other power spectra, imply that CMB lensing can probe simultaneously a diverse range of physics. Highlight the role of arc minute resolution polarization experiments for distinguishing between physical effects.
1507.08336
No galaxy left behind: accurate measurements with the faintest objects in the Dark Energy Survey
Suchyta, Huff, .. Melchir, ... Gaztanaga, ... Leistedt, Peiris, Ross, Rykoff, Sheldon, et al
Accurate statistical measurement with large imaging surveys has traditionally required throwing away a sizable fraction of the data. This is because most measurements have relied on selecting nearly complete samples, where variations in the composition of the galaxy population with seeing, depth, or other survey characteristics are small. Introduce a new measurement method that aims to minimize this wastage, allowing precision measurement for any class of stars or galaxies detectable in an imaging survey. Implement the proposal in Balrog, a software package which embeds fake objects in real imaging in order to accurately characterize measurement biases. Demonstrate this technique with an angular clustering measurement using DES data. First show that recovery of the injected galaxies depends on a wide variety of survey characteristics in the same way as the real data. Then construct a flux-limited sample of the faintest galaxies in DES, chosen specifically for their sensitivity to depth and seeing variations. Using the synthetic galaxies as randoms in the standard Lande-Szalay correlation function estimator suppresses the effects of variable survey selection by at least 2 orders of magnitude. With this correction, the measured angular clustering is found to be in excellent agreement with that of a matched sample drawn from much deeper, higher-resolution space-based COSMOS imaging; over angular scales of 0.004 deg<theta<0.2 deg; find a best-fit scaling amplitude between the DES and COSMOS measurements of 1.00±0.09. Expect this methodology to be broadly useful for extending the statistical reach of measurements in a wide variety of coming imaging surveys.
1507.08530
Observational signatures of self-destructive civilisations
Stevens, Forgan, O'Malley-James
Address the possibility that intelligent civilizations that destroy themselves could present signatures observable by humanity. Placing limits on the number of self-destroyed civilizations in the MW has strong implications for the final three terms in Drake's Equation, and would allow identification of which classes of solution to Fermi's paradox fit wit the evidence (or lack thereof). Using the Earth as an example, consider a variety of scenarios in which humans could extinguish their own technological civilization. Each scenario presents some form of observable signature that could be probed by astronomical campaigns to detect and chartreuse extrasolar planetary systems. Some observables are unlikely to be detected at interstellar distances, but some scenarios are likely to produce significant changes in atmospheric composition that could be detected serendipitously with next-generation telescopes. In some cases, the timing of the observation would prove crucial to detection, as the decay of signatures is rapid compared to humanity's communication lifetime. In others, the signatures persist on far longer timescales.
1507.08552
How astronomers view education and public outreach
Dang, Russo
Over the past few years, there have been a few studies on the development of an interest in science and scientists' views on public outreach. Yet, to date, there has been no global study regarding astronomers' views on these matters. Through the completion of the survey by 155 professional astronomers online and in person during the 28th IAU general assembly in 2012, explored the development of an interest for astronomy and their views on time constraints and budget restriction regarding public outreach activities. Find that astronomers develop an interest in astronomy between the ages of 4-6 but that the decision to undertake a career in astronomy often comes during late adolescence. Also discuss the claim that education and public outreach is regarded an optional task rather than a scientist's duty. The study revealed that many astronomers think there should be a larger percentage of their research that should be invested into outreach activities, calling for a change in grant policies.
Thursday.
1507.07694
Digital sky surveys from the ground: status and perspectives
Shanks
Review the status of Digital Sky Surveys. The focus will be on extragalactic surveys with an area of more than 100 sq.deg. The SDSS is the archetype of such imaging surveys and it is its great success that has prompted great activity in this field. The latest surveys explore wider, fainter and higher resolution and also a longer wavelength range than SDSS. Many of these surveys overlap particularly in the Southern Hemisphere where there are Pan-STARRS, DES and the ESO VST surveys, and the aim here is to compare their properties. Since there is no dedicated article on the VST ATLAS in this symposium, review the properties of this particular survey. This easily fits onto the other main focus which is the compare overlapping Southern Surveys and see how they best fit wit the available NIR imaging data. Conclude that the Southern Hemisphere will soon overtake the North in terms of multi wavelength imaging. However, note that the South has more limited opportunities for spectroscopic follow-up and this weakness will persist during the LSST era. Some new perspectives are offered on this and other aspects of survey astronomy.
1507.07937
Lens galaxies in the Illustris simulation: power-law models and the bias of the Hubble constant from time-delays
Xu, Sluse, Schneider, Springel, Vogelsberger, Nelson, Hernquist
The combination of dynamical and strong GL studies of massive galaxies shows that their total density profile in the central region (i.e., up to a few half-light rides) can be described by a power law, rho(r)~r^-gamma. Therefore, such a power-law model is employed for a large number of SL applications, including the so-called time-delay technique used to infer the Hubble constant H0. However, since the radial scale at which strong lensing features are formed (i.e., the Einstein radius) corresponds to the transition from the dominance of baryonic matter to dark matter, there is no known reason why galaxies should follow a power law in density. The assumption of a power law artificially breaks the mass-sheet degeneracy, a well-known invariance transformation in gravitational lensing which affects the product of Hubble constant and time delay and can therefore cause a bias in the determination of H0 from the time-delay technique. In this paper, use the Illustris hydro sims to estimate the amplitude of this bias, and to understand how it is related to observational properties of galaxies. Investigating a large sample of Illustris galaxies that have velocity dispersion sigma_SIE>160 km/s at redshifts below z=1, find that the bias on H0 introduced by the power-law assumption can reach 20-50%, with a scatter of 10-30 % (rms). However, find that by selecting galaxies with an inferred power-law model slope close to isothermal, it is possible to reduce the bias on H0 to <5%, and the scatter to <10%. This could potentially be used to form less biased statistical samples for H0 measurements in the upcoming large survey era.
1507.08031
Clustering and bias measurements of SDSS voids
Clampitt, Jain, Sánchez
Using a void catalog from the SDSS survey, present the first measurements of void clustering and the corresponding void bias. Over the range 30-200 Mpc/h the void auto-correlation is detected at 5-sigma significance for voids of radius 15-20 Mpc/h. Also measure the void-galaxy cross-correlation at higher S/N and compare the inferred void bias with the autocorrelation results. Void bias is constant with scale for voids of a given size, but its value falls from 5.6±1.0 to below zero as the void radius increases from 15-30 Mpc/h. The comparison of the measurements with carefully matched galaxy mock catalogs, with no free parameters related to the voids, shows that model predictions can be reliably made for void correlations. Study the dependence of void bias on tracer density and void size with a few to future applications. In combination with the previous lensing measurements of void mass profiles, these clustering measurements provide another step towards using voids as cosmo tracers.
Wednesday.
1507.07554
Deriving star formation histories from photometry using energy balance spectral energy distribution modelling
Smith, Hayward
Panchromatic SED fitting is a critical tool for determining the physical properties of distant galaxies, such as their stellar mass and SFR. One widely used method is the publicly available MAGPHYS code. Build on the previous analysis (Hayward & Smith 2015) by presenting some modifications which enable MAGPHYS to automatically estimate galaxy SFHs, including uncertainties, based on UV to FIR photometry. Use state-of-the-art synthetic photometry derived by performing 3d dust radiative transfer on hydro sims of isolated disc and merging galaxies to test how well the modified MAGPHYS is able to recover SFHs under idealized conditions, where the true SFH is known. Find that while the SFH of the model with the best fit to the synthetic photometry is a poor representation of the true SFH (showing large variations with the line-of-sight to the galaxy and spurious bursts of SF), median-likelihood SFHs generated by marginalizing over the default MAGPHYS libraries produce robust estimates of the smoothly-varying isolated disk simulation SFHs. This preference for the median-likelihood SFH is quantitatively underlined by the estimates of chi2_SFH (analogous to the chi2 goodness-of-it estimator) and Delta M/M (the integrated absolute mass discrepancy between the model and true SFH) that strongly prefer the median-likelihood SFHs over those that best fit the UV-to-far-IR photometry. In contrast, unable to derive a good estimate of the SFH for the merger simulations (either best-fit or median-likelihood) despite being able to obtain a reasonable fit to the simulated photometry, likely because the analytic SFHs with bursts superposed in the standard MAGPHYS library are insufficiently general/realistic.
1507.07560
Probing the isotropy of cosmic acceleration traced by Type Ia supernovae
Javanmardi, Porciani, Kroupa, Pflamm-Altenburg
Present a method to test the isotropy of the magnitude-redshift relation of SNe Ia and single out the most discrepant direction (in terms of the S/N ratio) with respect to the all-sky data. The technique accounts for possible directional variations of the correction for SNe Ia and yields all-sky maps of the best-fit cosmological parameters with arbitrary angular resolution. To show its potential, apply the method to the recent Union2.1 compilation, building maps with 3 different angular resolution. Use a MC method to estimate the statistical significance with which can reject the null hypothesis that the magnitude-redshift relation is isotropic based on the properties of the observed most discrepant directions. Find that, based on pure S/N arguments, the null hypothesis cannot be rejected at any meaningful CL. However, if one considers that the strongest deviations in the Union 2.1 sample closely align with the dipole temperature anisotropy of the CMB, find that the null hypothesis should be rejected at the 95-99% CL, slightly depending on the angular resolution of the study. If this result is not due to a statistical fluke, it might either indicate that the SN data have not been cleaned from all possible systematics or even point towards new physics. Finally discuss future perspectives in the field for achieving larger and more uniform data sets that will vastly improve the quality of the results and optimally exploit the method.
1507.07642
Extreme value statistics of CMB lensing deflection angles
Merkel, Schaefer
The smaller the angular scales on which the anisotropies of the CMB are probed, the more important their distortion due to GL becomes. Investigate the maxima and minima of the CMB lensing deflection field using general extreme value statistics. Since general extreme value statistics applies to uncorrelated data in first place, consider appropriately low-pass filtered defection maps. Besides the suppression of correlations filtering is required for another reason: The lensing field itself is not directly observable but needs to be (statistically) reconstructed from the lensed CMB by means of a quadratic estimator. This reconstruction, though, is noise dominated and therefore requires smoothing, too. In idealized Gaussian realization as well as in realistically reconstructed data, find that both maxima and minima of the deflection angle components follow consistently a general extreme value distribution of Weibull-type. However, its shape, location and scale parameters vary significantly between different realizations. The statistics' potential power to constrain cosmological models appears therefore rather limited.
1507.07843
Intrinsic alignments of galaxies in the Horizon-AGN cosmological hydrodynamical simulation
Chisari, ... Miller, ... Benabed, et al
The IA of galaxies are recognised as a contaminant to WL measurements. In this work, study the alignment of galaxy shape and spins at z~0.5 in Hirozon-AGN, an adaptive-mesh-refinement hydro cosmo sim box of 100 Mpc/h a side with AGN feedback implementation. Find that spheroidal galaxies in the simulation show a tendency to be aligned radially towards over-densities in the DM density field and other spheroidal. This trend is in agreement with observations, but the amplitude of the signal depends strongly on how shapes are measured and how galaxies are selected in the sim. Disc galaxies show a tendency to be oriented tangentially around spheroidals in 3d. While this signal seems suppressed in projection, this does not guarantee that disc alignments can be safely ignored in future WL surveys. The shape alignments of luminous galaxies in Horizon-AGN are in agreement with observations and other simulation works, but find less alignment for lower luminosity populations. Also characterize the systematics of galaxy shapes in the simulation and how that they can be safely neglected when measuring the correlation of the density field and galaxy ellipticities.
Tuesday.
1507.06996
Intrinsic alignments of galaxies in the EAGLE and cosmo-OWLS simulations
Velliscig, Cacciato, Schaye, Hoekstra, ... et al
Report results for the alignments of galaxies in the EAGLE and cosmos-OWLS simulations as a function of galaxy separation and halo mass. The combination of these hydro-cosmo sims enables to span four orders of magnitude in halo mass (10.7<log10[M200/(Msun/h)]<15) and a large range of separations (-1<log10(r/[Mpc/h]<2). Focus on two classes of alignments: the orientations of galaxies with respect to either the directions to, or the orientations of, surrounding galaxies. Find that the strength of the alignment is a strongly decreasing function of the distance between galaxies. The orientation-direction alignment can remain significant up to ~100 Mpc, for galaxies hosted by the most massive haloes in the simulations. Galaxies hosted by more massive sub haloes show stronger alignment. At a fixed halo mass, more aspherical or prolate galaxies exhibit stronger alignments. The spatial distribution of satellites is anisotropic and significantly aligned with the major axis of the main host halo. The major axis of satellite galaxies, when all stars are considered, are preferentially aligned towards the center of the main host halo. The predicted projected direction-orientation alignment, epsilon_g+(r_p), is in broad agreement with recent observations when only stars within the typical observable extent of galaxy are used to define galaxy orientations. Find that the orientation-orientation alignment is weaker than the orientation-direction alignment on all scales. Overall, the strength of galaxy alignments depends strongly on the subset of stars that are used to measure the orientations of galaxies and it is always weaker than the alignment of the DM haloes. Thus, alignment models that use halo orientation as a direct proxy for galaxy orientation will overestimate the impact of intrinsic alignments on weak lensing analyses.
1507.07340
The mass distribution in an assembling super galaxy group at $z=0.37$
Smit, Schrabback, Valender, Kuijken, Gonzalez, Moustakas, Tran
Present a WL analysis of supergroup SG1120-1202, consisting of four distinct X-ray luminous groups, that will merge to form a cluster comparable in mass to Coma at z=0. These groups lie within a projected separation of 1 to 4 Mpc and within Delta nu=550 km/s and form a unique protocluster to study the matter distribution in a coalescing system. Using high-resolution HST/ACS imaging, combined with an extensive spectroscopic and imaging data set, study the WL distortion of background galaxy images by the matter distribution in the supergroup. Compare the reconstructed projected density field with the distribution of galaxies and hot X-ray emitting gas in the system and derive halo parameters for the individual density peaks. Show that the projected mass distribution closely follows the locations of the X-ray peaks and associated brightest group galaxies. One of the groups that lies at slightly lower redshift (z~0.35) than the other 3 groups (z~0.37) is X-ray luminous, but is barely detected in the WL signal. The other 3 groups show a significant detection (up to 5 sigma in mass), with velocity dispersions between 355±60 and 530±50 km/s and masses between 0.8±0.4e14 and 1.6±0.5e15 Msun/h, consistent with independent measurements. These groups are associated with peaks in the galaxy and gas density in a relatively straightforward manner. Since the groups show no visible signs of interaction, this supports the picture that these are groups just before they merge into a cluster.
Monday.
1507.06646
Beyond six parameters: extending $\Lambda$ CDM
Di Valentino, Melchiorri, Silk
Cosmological constraints are usually derived under the assumption of a 6 parameters LCDM theoretical framework or simple one-parameter extensions. In this paper, present for the first time cosmo constraints in a significantly extended scenario, varying up to 12 cosmo parameters simultaneously, including the sum of neutrino masses, the neutrino effective number, the DE EoS, the gravitational waves background and the running of the spectral index of primordial perturbations. Using the latest Planck 2015 data release (with polarization) find no significant indication for extensions to the standard LCDM scenario, with the notable exception of the angular power spectrum lensing amplitude, A_lens that is larger than the expected value at more than 2 std. dev. even when combining the Planck data with BAO and SNIa external datasets. In the extended cosmo framework, find that a combined Planck+BAO analysis constrains the value of the r.m.s. density fluctuation parameter to sigma8=0.781±0.065 at 95% c.l., helping to relieve the possible tensions with the CFHTLenS cosmic shear survey. Also find a lower value for the reionization optical depth tau=0.058±0.040 at 95% c.l. respect to the one derived under the assumption of LCDM. The scalar spectral index n_s is now compatible with Harrison-Zeldovich spectrum to within 2.5 std. dev. Combining the Planck data set with the HST prior on the Hubble constant provides a value for the EoS w<-1 at more than 2 std deviations while the neutrino effective number is fully compatible with the expectations of the standard 3 neutrino framework.
Thursday. Friday.
1507.05966
Can life survive Gamma-ray bursts in the high-redshift universe?
Li, Zhang
Nearby GRBs have been proposed as a possible cause of mass extinctions on Earth. Due to the higher event rate of GRBs at higher redshifts, it has been speculated that life as we know it may not survive above a certain redshift (z>0.5). Examine the duty cycle of lethal GRBs in the solar neighborhood, in the SDSS galaxies and GRB host galaxies, with the dependence of the long GRB rate on SF and metallicity properly taken into account. Find that the number of lethal GRBs attacking Earth within the past 500 Myr (~epoch of the Ordovician mass extinction) is 0.93. The number of lethal GRBs hitting a certain planet increases with redshift, thanks to the increasing SFR and decreasing metallicity in high-z galaxies. Taking 1 per 500 Myr as a conservative duty cycle for life to survive, as evidenced by the existence, find that there are still a good fraction of SDSS galaxies beyond z=0.5 where the GRB rate at high-mass radius is lower than this value. Derive the fraction of such benign galaxies as a function of redshift through MC simulations, and find that the fraction is ~50% at z~1.5 and ~10% even at z~3. The mass distribution of benign galaxies is dominated by MW-like ones, thanks to their commonness, relatively large mass, and low SFR. GRB host galaxies are among the most dangerous ones.
1507.05969
Estimates for the number of visible galaxy-spanning civilizations and the cosmological expansion of life
Olson
...the distance to the nearest visible Kardaschev type III (galaxy-spanning) civilizations is cosmological.
1507.05977
Cross-correlation cosmic shear with the SDSS and VLA FIRST surveys
Demetroullas, Brown
Measure the cosmic shear power spectrum on large angular scales by cross-correlating the shapes of ~9 million galaxies measure in the optical SDSS survey with the shapes of ~2.7e5 radio galaxies measured by the overlapping VLA-FIRST survey. The measurements span the multipole range 10<l<130, corresponding to angular scales 2deg<theta<20 deg. On these scales, the shear maps from both surveys suffer from significant systematic effects that prohibit a measurement of the shear power spectrum from either survey alone. Conversely, demonstrate that a power spectrum measured by cross-correlating the two surveys is unbiased. Measure an E-mode power spectrum from the data that is inconsistent with zero signal at the 99% CL (~2.7 sigma). The odd-parity B-mode signal and the EB cross-correlation are both found to be consistent with zero (within 1 sigma). These constraints are obtained after a careful error analysis that accounts for uncertainties due to cosmic variance, random galaxy shape noise and shape measurement errors, as well as additional errors associated with the observed large-scale systematic effects in the two surveys. Constraints are consistent wit the expected signal in the concordance cosmological model assuming recent estimates of the cosmological parameters from the Planck satellite, and literature values for the median redshifts of the SDSS and FIRST galaxy populations. The cross-power spectrum approach described in this paper represents a powerful technique for mitigating shear systematics and will be ideal for extracting robust results, with the exquisite control of systematics required, from further cosmic shear surveys wit the SKA, LSST, Euclid and WFIRST-AFTA.
1507.06140
How environment drives galaxy evolution: lessons learnt from satellite galaxies
Pasquali
Galaxy evolution is driven by intrinsic and environmental processes, bot contributing to shape the observed properties of galaxies. A number of early studies, both observational and theoretical, have shown that the SF activity of galaxies depends n their environmental local density and also on galaxy hierarchy, i.e. centrals vs. satellite. In fact, contrary to their central (most massive) galaxy of a group cluster, satellite galaxies are stripped of their gas and stars, and have their star formation quenched by their environment. Large galaxy surveys like SDSS now permit us to investigate in detail environment-driven transformation processes by comparing centrals and satellites. In this paper, summarize what have been learnt about environmental effects by analyzing the observed properties of local central and satellite galaxies in SDSS, as a function of their stellar mass and the DM matter mass of their host group/cluster.
1507.06270
At what distance ac the human eye detect a candle flame?
Krisciunas, Carona
Using CCD observations of a candle flame situated at a distance of 338m and calibrated with observations of Vega, show that a candle flame situated at ~2.6 km (1.6 miles) is comparable in brightness to a 6th magnitude star with the spectral energy distribution of Vega. The human eye cannot detect a candle flame at 10 miles or further, as some statements on the web suggest.
1507.06300
A quantitative criterion for defining planets
Margot
A simple metric can be used to determine whether a planet or exoplanet can clear its orbital zone during a characteristic time scale, such as the lifetime of the host star on the main sequence. This criterion requires only estimates of star mass, planet mass, and orbital period, making it possible to immediately classify 99% of all known exoplanets. All 8 planets and all classifiable exoplanets satisfy the criterion. This metric may be useful in generalizing and simplifying the definition of a planet.
1507.06639
SKA engineering change proposal: gridded visibilities to enable precision cosmology with radio weak lensing
Harrison, Brown
Submitted document as supporting material to an engineering change proposal (ECP) for the SKA. This ECP requests gridded visilbities as an extra imaging data product from the SKA, in order to enable bespoke analysis techniques to measure source morphologies to the carry necessary for precision cosmology with radio weak lensing. Also discuss the properties of an SKA weak lensing data set and potential overlaps with other cosmology science goals.
Wednesday.
1507.05614
Statistical signatures of Panspermia in Exoplanet surveys
Lin, Loeb
A fundamental astrobiological question is whether life arose spontaneously on earth or was transported here from an extrasolar system. Propose a new strategy to answer this question based on the principle that life which arose via spreading will exhibit more clustering than life which arose spontaneously. Develop simple statistical models of panspermia to illustrate observable consequences of these excess correlations. Future searches for biosignatures in the atmospheres of exoplanets could test these predictions: panspermia predicts large regions in the MW where life saturates its environment interspersed with voids where life is very uncommon. In a favorable scenario, detection of as few as ~25 biologically active exoplanets could yield a 5 sigma detection of panspermia.
1507.05618
Antisymmetric galaxy cross-correlations as a cosmological probe
Dai, Kamionkowski, et al
The auto-correlation between two members of a galaxy population is symmetric under the interchange of the 2 galaxies being correlated. The cross-correlation between two different types of galaxies, separated by a vector r, is not necessarily the same as that for a pair separated by -r. Local anisotropies in the 2pt x-correlation function may thus indicate a specific direction which when mapped as a function of position trace out a vector field. This vector field can then be decomposed into longitudinal and transverse components, and those transverse components written as positive- and negative-helicity components. A locally asymmetric x-correlation of the longitudinal type arises naturally in halo clustering, even with Gaussian ICs, and could be enhanced with local-type non-Gaussianity. Early-Universe scenarios that introduce a vector field may also give rise to such effects. These antisymmetric cross-correlations also provide a new possibility to seek a preferred cosmic direction correlated with the hemispherical power asymmetry in the cosmic microwave background and to seek a preferred location associated with the CMB cold spot. New ways to seek cosmic parity breaking are also possible.
1507.05627
The universality of the viral halo mass function and models for non-universality of other halo definitions
Despali, Giocoli, Angulo, Tormen, Sheth, Baso, Moscardini
The abundance of galaxy clusters can constrain both the geometry and structure growth in the Universe. However, this probe could be significantly complicated by recent claims of non universality -- non-trivial dependencies with respect to the cosmological model and redshift. In this work, analyse the dependence of the mass function on the way haloes are identified and establish if this can cause departures from universality. In order to explore this dependance, use a set of different DM only cosmological simulations, with the latest cosmo parameters from Planck; this first suite of simulations is followed by a lower resolution set carried out with different cosmo parameters. Identify DM haloes using a Spherical Overdensity algorithm with varying overdensity thresholds (viral, 2000 rho_c, 1000 rho_c, 500 rho_c, 200 rho_c and 200 rho_b) at all redshifts. Notice that, when expressed in terms of the rescaled variable nu, the mass function for viral haloes can be considered universal as a function of redshift and cosmology, while this is clearly no the case for the other considered over densities. Provide fitting functions for the halo mass function parameters as a function of density, that allow to predict, with a few percent accuracy, the halo mass function for a wide range of halo definitions, redshifts and cosmo models. Then present how the departures from universality associated with other halo definitions can be derived by combining the universality of the viral definition with the expected shape of the density profile of haloes.
1507.05647
Mapping ad simulating systematics due to spatially-varying observing conditions in DES Science Verification data
Leistedt, Peiris, et al
Spatially-varying depth and characteristics of observing conditions, such as seeing, airmass, or sky background, are major sources of systematic uncertainties in modern galaxy survey analyses, in particular in deep multi-epoch surveys. Present a framework to extract and project these sources of systematics onto the sky, and apply it to DES to map the observing conditions of the SV data. The resulting distributions and maps of sources of systematics are used in several analysis of DES SV to perform detailed null tests with the data, and also to incorporate systematics in survey simulations. Illustrate the complementarity of these 2 approaches by comparing the SV data with the BCC-UFig, a synthetic sky catalogue generated by forward-modeling of the DES SV images. Analyse the BCC-UFig simulation to construct galaxy samples mimicking those used in SV galaxy clustering studies. Show that the spatially-varying survey depth imprinted in the observed galaxy densities and the redshift distributions of the SV data are successfully reproduced by the simulation and well-captured by the maps of observing conditions. The combined use of the maps, the SV data and the BCC-Fig simulation allows to quantify the impact of spatial systematics on N(z), the redshift distributions inferred using photo-z. Conclude that spatial systematics in the SV data are mainly due to seeing fluctuations and are under control in current clustering and WL analyses. The framework presented here is relevant to all multi-epoch surveys, and will be essential for exploiting future surveys such as LSST, which will require detailed null-tests and realistic end-to-end simulations to correctly interpret the deep-, high-cadence observations of the sky.
1507.05823
Gone without a bang: an archival HST survey for disappearing massive stars
Reynolds, Fraser, Gilmore
Find one candidate between 1994 and 2013 which is consistent with a 25-30 Msun yellow suppressant which has undergone an optically dark core-collapse.
1507.05909
Redshift distribuions of galaxies in the DES science verification shear catalog and implications for weak lensing
Bonnett, et al
Present photometric z estimates for galaxies used in WL analysis of DES SV data. Four model- or machine learning-based photo-z methods - ANNZ2, BPZ calibrated against BCC-fig simulations, SkyNet, and TPZ - are analyzed. For training, calibration, and testing of these methods, construct a catalogue of spectroscopically confirmed galaxies matched against DES SV data. The performance of the methods is evaluated against the matched spectroscopic catalogue, focusing on metrics relevant for WL analysis, with additional validation against COSMOS photo-zs. From the galaxies in the DES SV shear catalogue, which have mean redshift 0.72±0.01 over the range 0.3<z<1.3, construct 3 tomographic bins with means of z={0.45,0.67,1.00}. These bins each have systematic uncertainties delta z<~0.05 in the mean of the fiducial SkyNet photo-z n(z). Propagate the errors in the z distributions through to their impact on cosmological parameters estimated with cosmic shear, and find that they cause shifts in the value of sigma_8 of approx 3%. This shift is within the one sigma statistical errors on sigma8 for the DES SV shear catalog. Further study the potential impact of systematic differences on the critical surface density Sigma_crit, finding levels of bias safely less than the statistical power of DES SV data. Recommend a final Gaussian prior for the photo-z bias in the man of n(z) of width 0.05 for each of the 3 tomographic bins, and show that this is a sufficient bias model for the corresponding cosmology analysis.
Tuesday. DES Paper day.
1507.05090
Weak lensing by galaxy troughs in DES science verification data
Gruen et al
Measure the radial alignment of BG galaxies around galaxy "troughs", under densities in projections of the foreground galaxy field over a wide range of redshift in SV data from DES. Detection of the shear signal is highly significant (10 to 15 sigma for the smallest angular scales) for troughs with 0.2<z<0.5 of the projected galaxy field and angular diameters of 10' to 1 deg. These measurements probe the connection between the galaxy, matter density, and convergence fields. By assuming galaxies are biased tracers of the matter density with Poissonian noise, find agreement of the measurements with predictions in a fiducial LCDM model. The prediction for the lensing signal on large trough scales is virtually independent of the details of the underling model for the connection of galaxies and matter. The comparison of the shear around toughs with that around cylinders with large galaxy counts is consistent with a symmetry between galaxy and matter over- and under densities. In addition, measure the 2 point angular correlation of troughs with galaxies which, in contrast to the lensing signal, is sensitive to galaxy bias on all scales. The lensing signal of troughs and their clustering with galaxies is therefore a promising probe of the statistical properties of matter under densities and their connection to the galaxy field.
1507.05092
Interloper bias in future large-scale structure surveys
Pullen, Hirata, Dore, Raccanelli
LSS of observable universe with emission line galaxies: next generation spectroscopic surveys. Interloping emission lines can masquerade as the survey's intended emission line at different redshifts. Interloping lines from galaxies that are not removed can contaminate the power spectrum measurement, mixing correlations from various redshifts and diluting the true signal. Assess the potential for power spectrum contamination, finding that an interloper fraction worse than 0.2% could bias PS measurements for future surveys by more than 10% of statistical errors, while also biasing inferences biased on the PS. Also construct a formalism for predicting biases for cosmo parameter measurements, and demonstrate that a 0.3% interloper fraction could bias measurements of the growth rate by more than 10% of the error, which can affect constraints from upcoming surveys on gravity. Use COSMOS mock catalog (CMC), with the emission lines re-scalesd to better reproduce recent data, to predict potential interloper fractions for the PFS and WFIRST. Find that secondary line identification, or confirming galaxy redshifts by finding correlated emission liens, is able to remove interloping emission lines in PFS. For WFIRST, use the CMC to predict that the 0.2% target can be reached for the WFIRST Ha survey, but sensitive optical and NIR photometry will be required. For the WFIRST [OIII] survey, the predicted interloper fractions reach several percent and their effects will have to be estimated and removed statistically (e.g. with deep training samples).
1507.05137
The difference imaging pipeline for the transient search in the Dark Energy Survey
Kessler, et al
DiffImg pipeline used to detect transients in deep images from DES-SN program in its first observing season from Aug 2013 to Feb 2014. Search for transients in 10 x 3-deg^2 fields are repeatedly observed in the griz passbands with a cadence of about 1 week. The observing strategy has been optimized to measure high-quality light curves and redshifts for thousands of SN Ia with the goal of measuring DE parameters. The essential DiffImg functions are to align each search image to a deep reference image, do a pixel-by-pixel subtraction and then examine the subtracted image for significant positive detections of point-source objects. The vast majority of detections are subtraction artifacts, but after selection requirements and image filtering with an automated scanning program, there are 130 detections per deg^2 per observation in each band, of which only 25% are artifacts. Of the 7500 transients discovered by DES-SN in its first observing season, each requiring a detection on atlas 2 separate nights, MC simulations predict that 27% are expected to be SN. Another 30% of the transients are artifacts, and most of the remaining transients are AGN and variable stars. Fake SNe Ia are overlaid onto the images to rigorously evaluate detection efficiencies, and to understand the DiffImg performance. The DiffImg efficiency measured with fake SNe agrees well with expectations from MC sims that uses analytical calculates of the fluxes and their uncertainties. In the 8 "shallow" fields with single-epoch 50% completeness depth 23.5, the SN Ia efficiency falls to 1/2 at z~0.7, in the 2 "deep" fields with mag-depth 24.5, the efficiency falls to 1/2 at z~1.1.
1507.05177
Observation of two new L4 Neptune Trojans in the Dark Energy Survey Supernova fields
Gerdes, et al
Report the discovery of the 8th and 9th known Trojans in stable orbits around Neptune's leading Lagrange point, L4. Both are in high-inclination orbits (18.8 and 19.4 deg, respectively). With an eccentricity of 0.104, 2014 QOK_441 has the most eccentric orbit of the 11 known stable Neptune Trojans. Describe the search procedure and investigate the object's long-term dynamical stability and physical properties.
1507.05334
On scale-dependent cosmic shear systematic effects
Kitching, Taylor, Cropper, Hoekstra, Hood, Massey, Niemi
Investigate the impact that realistic scale-dependence systematic effects may have on cosmic shear tomography. Model spatially varying residual ellipticity and size variations in WL measurements and propagate these thorough to predicted changes in the uncertainty and bias of cosmo parameters. Show that the survey strategy - whether it is regular or randomized - is an important factor in determining the impact of a systematic effect: a purely randomized survey strategy produces the smallest biases, at the expense of larger parameter uncertainties, and a very regularized survey strategy produces large biases, but unaffected uncertainties. However, by removing, or modeling, the affected scales (l-modes) in the regular cases the biases are reduced to negligible levels. Find that the integral of the systematic PS is not a good metric for dark energy performance, and advocate that systematic effects should be modeled accurately in real space, where they enter the measurement process, and their effect subsequently propagated into power spectrum contributions.
1507.05339
Path-integral evidence
Kitching, Taylor
Present a Bayesian formalism for the goodness-of-fit that is the evidence for a fixed functional form over the evidence for all functions that are a general perturbation about this form. This is done under the assumption that the statistical properties of the data can be modeled by a multivariate Gaussian distribution. Use this to show how one can optimize an experiment to find evidence for a fixed function over perturbations about this function. Apply this formalism to an illustrative problem of measuring perturbations in the dark energy EoS about a cosmological constant.
1507.05360
Galaxy clustering, photometric redshifts and diagnosis of systematics in the DES science verification data
Crocce, et al
Study the clustering of galaxies detected at i<22.5 in the SV observations of DES. 2PCFs are measured using 2.3e6 galaxies over a contiguous 116 deg^2 region in 5 bins of photo-z width Delta z=0.2 in the range 0.2<z<1.2. The impact of photo-z errors are assessed by comparing results using a template-based photo-z algorithm (BPZ) to a machine-learning algorithm (TPZ). A companion paper (Leistedt + 2015) presents maps of several observational variables (e.g. seeing, sky brightness) which could modulate the galaxy density. Characterize and mitigate systematic errors on the measured clustering which arise from these observational variables, in addition to others such as Galactic dust and stellar contamination. After correcting for systematic effects measured galaxy bias over a broad range of linear scales relative to mass clustering predicted from the Planck LCDM models, finding agreement with CFHTLS measurements with chi^2 of 4.0(8.7) with 5 degrees of freedom for the TPZ (BPZ) redshifts. Test a "near bias" model, in which the galaxy clustering is a fixed multiple of the predicted NL DM clustering. The precision of the data allow determination that the linear bias model describes the observed galaxy clustering to 2.5% accuracy down to scales at least 4 to 10x smaller than those on which linear theory is expected to be sufficient.
1507.05460
redMaGiC: selecting luminous red galaxies from the DES Science Verification Data
Rozo, et al
Introduce redMaGiC, an automated algorithm for selecting LRGs. The algorithm was specifically developed to minimize photometric redshift uncertainties in photometric LSS studies. redMaGiC achieves this by self-training the color-cuts necessary to produce a luminosity-thresholded LRG sample of constant comoving density. Demonstrate that redMaGiC photo-zs are very nearly as accurate as the best machine-learning based methods, yet they require minimal spectroscopic training, do not suffer from extrapolation biases, and are very nearly Gaussian. Apply the algorithm to DES SV data to produce a redMaGiC catalog sampling the z range 0.2<z<0.8. The fiducial sample has a comoving space density of 1e-3 (Mpc/h)^3, and a median photo-z bias (z_spec-z_photo) and scatter (sigma_z/(1+z)) of 0.005 and 0.017 respectively. The corresponding 5 sigma outlier fraction is 1.4%. Also test the algorithm with SDSS DR8 and Stripe 82 data, and discuss how spectroscopic training can be used to control photo-z biases at the 0.1% level.
1507.05551
CMB lensing tomography with the DES science verification galaxies
Giannantonio, et al
Measure the cross-correlation between the galaxy density in DES SV data and the lensing of the CMB as reconstructed with Planck and SPT. When using the DES main galaxy sample over the full z range 0.2<z<1.2, a cross-correlation signal is detected at 6sigma and 4sigma with SPT and Planck, respectively. Then divide the DES galaxies into 5 photo-z bins, finding significant (>2sigma) detections in all bins. Comparing to the fiducial Planck cosmology, find the z evolution of the signal matches expectation, although the amplitude is consistently lower than predicted across redshift bins. Test for possible systematics that could affect the realist and find no evidence for significant contamination. Finally, demonstrate how these measurements can be used to constrain the growth of structure across cosmic time. Find the data are fit by a model in which the amplitude of structure in z<1.2 universe is 0.73±0.16 times as large as predicted in the LCDM Planck cosmology, a 1.7sigma deviation.
1507.05552
Cosmology from cosmic shear with DES Science Verification data
The Dark Energy Survey Collaboration, et al
Present the first constraints on cosmology from DES, using WL measurements from preliminary SV data. Use 139 sq deg of SV data, <3% of the full DES survey area. Using cosmic shear 2 point measurements over 3 z bins, find sigma8(Omega_m/0.3)^0.5=0.81±0.06 (68% CL), after marginalizing over 7 systematics parameters and 3 other cosmological parameters. Examine the robustness of the results to the choice of data vector and systematics assumed, and find them to be stable. About 20% of the error bar comes from marginalizing over shear and photo-z calibration uncertainties. The current state-of-the-art cosmic shear measurements from CFHTLenS are mildly discrepant with the cosmological constraints from Planck CMB data; the DES results are consistent with both datasets. The uncertainties are ~30% larger than those from CFHTLenS when carrying out a comparable analysis of the two datasets, which is attributed largely to the lower number density of the shear catalog. Investigate constraints on DE and find that, with this small fraction of the full survey, the DES SV constraints make negligible impact on the Planck constraints. The moderate disagreement between the CFHTLenS and Planck values of sigma8(Omega_m/0.3)^0.5 is present regardless of the value of w.
1507.05598
Cosmic shear measurements with DES Science Verification data
Becker et al
Present measurements of WL lensing cosmic shear 2pt statistics using DES SV data. Demonstrate that the results are robust to the choice of shear measurement pipeline, either ngmix or im3shape, and robust to the choice of 2pt statistic, including both real and Fourier-space statistics. The results pass a suite of null tests including tests for B-mode contamination and direct tests for any dependence of the 2pt functions on a set of 16 observing conditions and galaxy properties, such as seeing, airmass, galaxy color, galaxy magnitude, etc. Furthermore use a large suite of simulation to compute the covariance matrix of cosmic shear measurements and assign statistical significance to the null tests. Find that the covariance matrix is consistent with the halo model prediction, indicating that it has the appropriate level of halo sample variance. Compare the same jackknife procedure applied to the data and the simulations in order to search for additional sources of noise no capture by the simulations. Find no statistically significant extra sources of noise in the data. The overall detection significance with tomography for the highest source density catalog is 9.7 sigma. Cosmological constrains from the measurements in this work are presented in a companion paper.
1507.05603
The DES Science Verification weak lensing shear catalogs
Jarvis, Sheldon, Zuntz, Kacprzak, Bridle, et al
Present WL shear catalogs for DES SV from DECam. Describe object detection, PSF estimation and shear measurement procedures using 2 independent shear pipelines, IM3HSAPE and NGMIX, which produce catalogs of 2.12 M and 3.44 M galaxies, respectively. Detail a set of null tests for the shear measurements and find that they pass the requirements for systematic errors at the level necessary for WL science applications using the SV data. Also discuss some of the planned algorithmic improvements that will be necessary to produce sufficiently accurate shear catalogs for the full 5-yr DES, which is expected to cover 5000 sq deg.
Monday.
1507.04752
The Stripe 82 Massive galaxy project II: stellar mass completeness of spectroscopic galaxy samples from the Baryon Oscillation Spectroscopic survey
Leauthaud, et al
BOSS: >1e6 galaxies at 1.5<z<0.7 over a volume of 15.3 Gpc^3 (9376 deg^2) -- providing an opportunity to study the most massive galaxy populations with vanishing sample variance. However, BOSS samples are selected via complex color cuts that are optimized for cosmology studies, not galaxy science. Supplement BOSS samples with photo-z from Stripe 82 Massive Galaxy Catalog and measure the total galaxy stellar mass function (SMF) at z~0.3 and z~0.55. With the total SMF in hand, characterize the stellar mass completeness of BOSS samples. The high-redshift CMASS ("constant mass") sample is significantly impacted by mass imcompeteness and is 80% complete at log10(M*/Msun)>11.6 only in the narrow redshift range z=[0.51,0.61]. The low redshift LOWZ sample is 80% complete at log10(M*/Msun)>11.6 for z=[0.15,0.43]. To construct mass complete samples at lower masses, spectroscopic samples nee to be significantly supplemented by photo-z. This work will enable future studies to better utilize the BOSS samples for galaxy-formation science.
1507.04862
Enhancing the cosmic shear power spectrum
Simpson, Harnois-Déraps, Heymans, Jiminez, Verde
Applying a transformation to a non-Gaussian field can enhance the information content of the resulting PS, by reducing the correlations between Fourier modes. In the context of WL, it has been shown that this gain in information content is significant compromised by the presence of shape noise. Apply clipping to mock convergence fields, a technique which is known to be robust in the presence of noise and has been successfully applied to galaxy number density fields. When analyzed in isolation the resulting convergence PS returns degraded constraints on cosmo parameters. However, substantial gains can be achieved by performing a combined analysis of the PS derived from both the original and transformed fields. Even in the presence of realistic levels of shape noise, demonstrate that this approach is capable of reducing the area of likelihood contours within the Omega_m-sigma8 plane by more than a factor of 3.
Friday.
1507.04353
Detection of satellite remnants in the Galactic halo with Gaia III. Detection limits for Ultra Faint Dwarf Galaxies
Antoja, et al
Present a method to identify UFDG candidates in the halo of the MW using the future Gaia catalogue and explore its detection limits and completeness. The method is based on the Wavelet Transform and searches for over-densities in the combined space of sky coordinates and proper motions, using kinematics in the search for the first time. Test the method with a Gaia mock catalogue that has the Gaia Universe Model Snapshot (GUMS) as a background, and use a library of around 30k UFDGs simulated as Plummer spheres with a single stellar population. For the UFDGs, use a wide range of structural and orbital parameters that go beyond the range spanned by real systems, where some UFDGs may remain undetected. Characterize the detection limits as function of the number of observable stars by Gaia in the UFDGs with respect to that of the background and their apparent sizes in the sky and proper motion planes. Find that the addition of proper motions in the search improved considerably the detections compared to a photometric survey at the same magnitude limit. The experiments suggest that Gaia will be able to detect UFDGs that are similar to some of the known UFDGs even if the limit of Gaia is around 2 mags brighter than that of SDSS, with the advantage of having full-sky catalogue. Also see that Gaia could even find some UFDGs that have lower surface brightness than the SDSS limit.
1507.04356
Clustering properties of $g$-selected galaxies at $z\sim0.8$
Favole, et al
Current and future large redshift surveys, as SDSS IV eBOSS or DESI, will use emission line galaxies (ELG) to probe cosmological models by mapping the LSS of the universe in 0.6<z<1.7. With current data, explore the halo-galaxy connection by measuring 3 clustering properties of g-selected ELGs as matter tracers in the range 0.6<z<1: (i) the z-space 2PCF using spectroscopic redshifts from the BOSS ELG sample and VIPERS; (ii) the angular 2PCF on the footprint of the CFHT-LS; (iii) the gg lensing signal around the ELGs using the CFHTLenS. Interpret these observations by mapping them onto the latest high-resolution MultiDark Planck N-body simulation, using a novel (Sub)Halo-Abundance Matching technique that accounts for the ELG incompleteness. ELGs at z~0.8 live in halos of (1±0.5)e12Msun/h and 22.5±2.5% of them are satellites belonging to a larger halo. The halo occupation distribution of ELGs indicates that the sampled galaxies are those in which stars form in the most efficient way, according to their stellar-to-halo mass ratio.
1507.04362
An origin for multi-phase gas in galactic winds and halos
Thompson, Quataert, Zhang, Weinberg
The origin of high velocity cool gas seen in galactic winds remains unknown. Following Wang 1995, argue that rapid radiative cooing in initially host (1e7-8 K) thermally-driven outflows can produce fast neutral atomic and photoionzed cool gas. Outflows with hot gas mass-loading factor relative to star formation rate of beta>0.5 cool on scales ranging form the size of the host to tens of kpc. Provide scalings for the cooling radius r_cool, density, column density, emission measure, radiative efficiency, and cool gas velocity. At r_cool, the gas produces X-ray and then UV/optical line emission at velocities of hundreds to thousands of km/s with a total power bounded from above by the energy injection rate 0.01 L_star if the flow is powered by steady-state star formation with luminosity L_star. The wind is thermally and convectively unstable at and beyond r_cool. Thermal instability can amplify density fluctuations by a factor of ~100, potentially leading to a multi-phase medium. Cooled winds can decelerate in the extended gravitational potential of galaxies and may explain the prevalence of cool gas in galactic halos. Forward a picture of winds whereby cool clouds are initially accelerated from the host by ram pressure of the hot flow, but are rapidly shredded and incorporated into the hot flow by the Kelvin-Helmholtz instability. This increases the hot wind mass loading, seeding radiative and thermal instability and cool gas rebirth. Show that if the cooled wind re-shocks as it sweeps up the circumgalactic medium that its cooling time is short, thus depositing cool gas far out into the halo. Finally, show that conduction can dominate energy transport in low-beta hot galactic winds, leading to much flatter temperature profiles compared to the nominal expectation from adabaticity, potentially consistent with X-ray observations of some local starbursts (Abridged)
1507.04363
Probing cosmology and gravity with redshift-space distortions around voids
Hamaus, Sutter, Laaux, Wandelt
Cosmic voids in the LSS of the universe affect the peculiar motions of objects in their vicinity. Although these motions are difficult to observe directly, the clustering pattern of their surrounding tracers in z space is influenced in a unique way. This allows to investigate the interplay between densities and velocities around voids, which is solely dictated by the laws of gravity. With the help of N-body simulations and derived mock-galaxy catalogs, calculate the average density fluctuations inside and outside voids identified with a watershed algorithm in z-space and compare the results with the expectation from general relativity and the LCDM model of cosmology. Find that simple linear-theory predictions work remarkably well in describing the dynamics of voids even on relatively small scales. Adopting a Bayesian inference framework, determine the full posterior probability distribution of the model parameters and forecast the achievable accuracy on measurements of the growth rate of structure and the geometric distortion through the Alcock-Paczynski effect. Their relative uncertainties in galaxy surveys with number densities comparable to the SDSS MAIN (CMASS) sample that probe a volume of 1(Gpc/h)^3 yield sigma_f/b/(f/b)~40%(60%) and sigma_DAH/D_AH ~ 5% (8%), respectively. The presented method is highly model independent; its viability lies in the underlying assumption of statistical isotropy of the universe.
1507.04365
What is the optimal way to measure the galaxy power spectrum?
Smith, Marian
Measurements of the galaxy power spectrum contain a wealth of information about the Universe. Its optimal extraction is vital if we are to truly understand the micro-physical nature of DM and DE. In Smith&Marian2015, they generalized the PS methodology of Feldman+94 to take into account the key tenets of galaxy formation: galaxies form and reside exclusively in DM haloes; a given DM halo may host galaxies of various luminosities; galaxies inherit the LS bias associated with their host halo. In this paradigm, derive the optimal weighting and reconstruction scheme for maximizing the S/N on a given band power estimate. For a future all-sky flux-limited galaxy redshift survey of depth b_J~22, now demonstrate that the optimal weighting scheme does indeed provide improved S/N at the level of ~20% when compared to Feldman+94 and ~60% relative to Percival+2003, for scales of order k~0.5 Mpc/h [inverse?]. Using a Fisher matrix approach, show that the cosmological information yield is also increased relative to these alternate methods - especially the primordial PS amplitude and dark energy equation of state.
1507.04376
LoCuSS: exploring the selection of faint blue background galaxies for cluster weak-lensing
Ziparo, Smith, Okabe, Haines, Pereira, Egami
Cosmological constraints from galaxy clusters rely on accurate measurements of mass and internal structure of clusters. An important source of systematic uncertainty in cluster mass and structure measurements is the secure selection of background galaxies that are gravitationally lensed by clusters. This issue has been shown to be particularly severe for faint blue galaxies. Therefore explore the selection of faint blue background galaxies, by reference to photometric redshift catalogs derived from the COSMOS survey and the observations of massive galaxy clusters at z~0.2. Show that methods relying on photometric redshifts of galaxies in/behind clusters based on observations through five filters, and on deep 30-band COSMOS photometric redshifts are both inadequate to identify safely faint blue background galaxies. This is due to the small number of filters used by the former, and absence of massive galaxy clusters at redshifts of interest in the latter. Therefore develop a pragmatic method to combine both sets of photometric redshifts to select a population of blue galaxies based purely on photometric analysis. This sample yields stacked WL results consistent with the previously published results based on red galaxies. Also show that the stacked cluster centric number density profile of these faint blue galaxies is consistent with expectation from consideration of the lens magnification signal of the clusters. Indeed, the observed number density of blue background galaxies changes by ~10-30% across the radial range over which other surveys assume it to be flat.
1507.04385
CLASH: joint analysis of strong-lensing, weak-lensing shear and magnification data for 20 galaxy clusters
Umetsu, Zitrin, Gruen, Merten, Donahue, Postman
Present a comprehensive analysis of SL, WL shear and magnification data for a sample of 16 X-ray-regular and 4 high-magnification galaxy clusters selected form the CLASH survey. The analysis combines constraints from 16-band HST observations and wide-field multi-color imaging taken primarily with Subaru/Suprime-Cam. Reconstruct surface mass density profiles of individual clusters from a joint analysis of the full lensing constraints, and determine masses and concentrations for all clusters. Find internal consistency of the ensemble mass calibration to be <5±6% by comparison with the CLASH WL-only measurements of Umetsu+. For the X-ray selected subsample, examine the concentration-mass relation and its intrinsic scatter using a Bayesian regression approach. The model yields a mean concentration of c(z=0.34)=3.95±0.35 at M_200c~14e14Msun and an intrinsic scatter of sigma(ln c_200c) = 0.13±0.06, in excellent agreement with LCDM predictions when the CLASH selection function based on X-ray morphological regularity and the projection effects are taken into account. Also derive an ensemble-averaged surface mass density profile for the X-ray selected subsample by stacking their individual profiles. The stacked mass profile is well described by a family of density profiles predicted for cusp DM-dominated halos, namely, the NFW, Einasto, and DARKexp models, whereas the single power-law, cored isothermal and Burkert density profiles are disfavored by the data. Show that cusp halo models that include the two-halo term provide improved agreement with the data. For the NFW halo model, measure a mean concentration of c_200c=3.79±0.30 at M_200c=14.1±1.0e14 Msun, demonstrating robust consistency between complementary analysis methods.
1507.04493
LoCuSS: weak-lensing mass calibration of galaxy clusters
Okabe, Smith
Present WL mass measurements of 50 X-ray luminous galaxy clusters at 0.15<z<0.3, based on high quality observations with Suprime-Cam counted on the 8.2m Subaru telescope. Pay close attention to possible systematic biases, aiming to control them at the <4% level. The dominant source of systematic bias in WL measurements of the mass of individual galaxy clusters is contamination of background galaxy catalogues by faint cluster and foreground galaxies. Extend the conservative method for selecting background galaxies with (V-i') colors redder than the red sequence of cluster members to use a color-cut that depends on cluster-centric radius. This allows definition of background galaxy samples that suffer <1% contamination, and comprise 13 galaxies per square arc minute. Thanks to the purity of the background galaxy catalogue, the largest systematic in the measurement is a shape measurement bias of 3%, that using custom-made simulations that probe weak shears up to g=0.3. The individual cutler mass and concentration measurements are in excellent agreement with predictions of the mass-concentration relation. Equally, the stacked shear profile is in excellent agreement with the NFW profile. The new LoCuSS mass measurements are consistent with the CCCP and CLASH surveys, and in tension with the Weighing the Giants (WtG) at ~2sigma significance.
Thursday.
1507.03988
Observational consequences of turbulent pressure in the envelopes of massive stars
Grassitelli, Fossati, Simon-Diaz, Langer, Castro, Sanyal
The major mass fraction of the envelope of hot luminous stars is radiatively stable. However, the partial ionization of H, He and Fe gives rise to extended sub-surface convection zones in all of them. In this work, investigate the effect of the pressure induced by the turbulent motion in these zones based on the mixing length theory, and search for observable consequences. Find that the turbulent pressure fraction can amount up to ~5% in OB supergiants, and to ~30% in cooler supergiants. The resulting structural changes are, however, not significantly affecting the evolutionary tracks compared to previous calculations. Instead, a comparison of macro turbulent velocities derived from high quality spectra of OB stars with the turbulent pressure fraction obtained in corresponding stellar models reveals a strong correlation of these two quantities. Discuss a possible physical connection, and conclude that turbulent pressure fluctuations may drive high-order oscillations, which - as conjectured earlier - manifest themselves as macro turbulence in the photospheres of hot luminous stars.
1507.03992
Frontier Fields: Subary weak-lensing analysis of the merging galaxy cluster A2744
Medezinski, Umetsu, Okabe, Nonino, Molnar, Massey, Dupke, Merten
Present a WL analysis of the merging FF cluster A2744 using Suprime-cam imaging. The wide-field lensing mass distribution reveals this cluster is comprised of 4 distinct substructures. Simultaneously modeling the 2d reduced shear field using a combination of NFW model for the main core and truncated NFW models for the sub haloes, determine their masses and locations. The total mass of the system is constrained as M_200c=2.06±0.42e15 Msun. The most massive clump is the southern component with M_200c=7.7±3.4e14 Msun, followed by the western substructure M_200c=4.5±2.0e14 Msun and 2 smaller substructures to the NE M_200c=2.8±1.6e14Msun, and NW M_200c=1.9±1.2e14 Msun. The presence of the 4 substructures supports the picture of multiple mergers. Using a composite of hydrodynamical binary simulations explain this complicated system without the need for a "slingshot" effect to produce the northwest X-ray interloper, as previously proposed. The locations of the substructures appear to be offset from both the gas (87+34-28 arctic, 90%CL) and the galaxies (72+34-53 arctic, 90%CL) in the case of the NW and W subhalos. To confirm or refute these findings, high resolution space-based observations extending beyond the current FF limited coverage to the W and NW area are essential.
1507.04301
CFHTLenS: weak lensing constraints on the ellipticity of galaxy-scale matter haloes and the galaxy-halo misalignment
Schrabback, Hilbert, Hoekstra, Simon, van Uitert, Erben, Heymans, Hildebrandt, Kitching, Mellier, Miller, Van Waerbeke, Bett, Coupon, Fu, Hudson, Joachimi, Kilbinger, Kuijken
Present WL constrains on the ellipticity of galaxy-scale matter haloes and the galaxy-halo misalignment. Using data from CFHTLenS, measure the weighted-average ratio of the aligned projected ellipticity components of galaxy matter halos and their embedded galaxies, f_h, split by galaxy type. Then compare the observations to measurements taken from Millennium Sims, assuming different models of galaxy-halo misalignment. Using Millennium Sims verify that the statistical estimator used removes contamination from cosmic shear. Also detect an additional signal in the simulations, which is interpreted as the impact of inartistic shape-shear alignments between the lenses and their large-scale substructure environment. These alignments are likely to have caused some of the previous observational constraints on f_h to be biased high. From CFHTLenS, find f_h=-0.04±0.25 for early-type galaxies, which is consistent with current models for the galaxy-halo misalignment predicting f_h~0.20. For late-type galaxies, measure f_h=0.69±0.36 from CFHTLenS. This can be compared to the simulated results which yield f_h~0.02 for misaligned late-type models.
1507.04338
Analytical model for non-thermal pressure in galaxy clusters - II. removing the hydrostatic mass bias
Shi, Komatsu, Nagai, Lau
Non-thermal pressure in galaxy clusters leads to underestimation of the mass of galaxy clusters based on hydrostatic equilibrium with thermal gas pressure. This occurs even for dynamically relaxed clusters that are used for calibrating the mass-observable scaling relations. Show that the analytical model for non-thermal pressure developed in Shi+Komatsu 2014 can correct for this so-called 'hydrostatic mass bias', if most of the non-thermal pressure comes from bulk and turbulent motions of gas in the ICM. The correction works for the sample average irrespective of the mass estimation method, or the dynamical state of the clusters. This makes it possible to correct for the bias in the hydrostatic mass estimates from X-ray surface brightness and the SZ observations that will be available for clusters in a wide range of redshifts and dynamical states.
