Day 1113

Thursday.

1606.08847
The Dragonfly Nearby Galaxies Survey.  I.  Substantial variation in the diffuse stellar haloes around spiral galaxies
Merritt, van Dokkum, Abraham, Zhang

Galaxies are through to grow through accretion; as less massive galaxies are disrupted and merge over time, their debris results in diffuse, clumpy stellar halos enveloping the central galaxy.  Present a study of the variation in the stellar halos of galaxies, using data from the Dragonfly Nearby Galaxies Survey (DNGS).  The survey consists of wide field, deep (mu_g>31 mag/arcsec^2) optical imagine of nearby galaxies using the Dragonfly Telephoto Array.  The sample includes 8 spiral galaxies with stellar masses similar to that of the MW, inclinations of 16-90 degrees and distances between 7-18 Mpc.  Construct stellar mass surface density profiles from the observed g-band surface brightness in combination with the g-r color as a function of radius, and compute the halo fractions from the excess stellar mass (relative to a disk+bulge fit) beyond 8 half-mass radii.  Find a mean halo faction of 0.009±0.005 and a large RMS scatter of 1.10+0.9-0.26 dex.  The peak-to-peak scatter is a factor of >100 -- while some galaxies feature strongly structured halos resembling that of M31, three of the 8 have halos that are completely undetected in the data.  Conclude that spiral galaxies as a class exhibit a rich variety in stellar halo properties, implying that their assembly histories have been highly non-uniform.  Find no convincing evidence for an environmental or stellar mass dependence of the halo fraction in the sample.

1606.08862
Constraining stochastic gravitational wave background from weak lens gin of CMB B-modes
Shaikh, et al

A stochastic GW background (SGWB) will affect the CMB anisotropies via WL.  Unlike WL due to LSS which only deflects photon trajectories, a SGWB has an additional effect on rotating the polarization vector along the trajectory.  Study the relative importance of these two effects, deflection and rotation, specifically in the context of E-mode to B-mode power transfer caused by WL due to SGWB.  Using WL distortion of the CMB as a probe, derive constraints on the spectral energy density Omega_GW of the SGWB, sourced at different redshifts, without assuming any particular model for its origin.  Present these bounds on Omega_GW for different power-law models characterizing the SGWB, indicating the threshold above which observable imprints of SGWB must be present in CMB.


1606.09091
Constraint on neutrino masses from the lensing dispersion of Type Ia supernovae
Hada, Futamase

Investigate how accurate the total mass of neutrinos is constrained from the magnitude dispersion of Type Ia SNe due to the effects of gravitational lensing.  For this purpose, use the propagation equation of light bundles in a realistic inhomogeneous universe and propose a sample selection for SNe to avoid difficulties associated with small scale effects such as strong lensing or shear effects.  With a fitting formula for the NL matter PS taking account of the effects of massive neutrino, find that in the model it is possible to obtain the upper limit Sigma m_nu~1.0 eV for future optical imaging surveys: WFIRST and LSST.  Furthermore, discuss how far SNeIa need to be observed and to what extend the magnitude error must be reduced except for lensing in order to realize the current tightest limit Sigma M_nu < 0.2 eV.

Day 1112

Wednesday.

1606.08448
Relative likelihood for life a s function of cosmic time
Loeb, Batista, Sloan

Is life most likely to emerge at the preset cosmic time near a star like the Sun?  Address this question by calculating the relative formation probability per unit time of habitable Earth-like planets within a fixed comoving volume of the Universe, dP(t)/dt, starting from the first stars and continuing to the distant cosmic future.  Conservatively restrict the attention to the context of "life as we know it" and the standard cosmological model, LCDM.  Find that unless habitability around low mass stars is suppressed, life is most likely to exist near 0.1 Msun stars 10 trillion years from now.  Spectroscopic searches for biosignatures in the atmospheres of transiting Earth-mass planets around low mass stars will determine whether resent-day life is indeed premature or typical from a cosmic perspective.


1606.08841
Cross-correlating Planck CMB lensing with SDSS: Lensing-lensing and galaxy-lensing cross-correlations
Singh, Mandelbaum, Brownstein

Present first results from cross-correlating Planck CMB lensing maps with SDSS galaxy lensing shape catalog and BOSS galaxy catalogs.  For galaxy position vs CMB lensing cross-correlations, measure the convergence signal around the galaxies in configuration space, using the BOSS LOWZ (z~0.40) and CMASS (z~0.57) samples.  With fixed Planck 2015 cosmology, doing a joint fit with the galaxy clustering measurement, for the LOWZ (CMASS) sample find a galaxy bias b_g=0.175±0.04 (1.95±0.02) and galaxy-matter cross-correlation coefficient r_cc=1.0±0.2 (0.8±0.1) using 20<r_p<70 Mpc/h, consistent with results from gg lensing.  Using the same scales and including the gglensing measurements, constrain Omega_m=0.284±0.024 and relative calibration bias between the CMB lensing and galaxy lensing to be b_gamma=0.82±0.15.  The combination of galaxy lensing and CMB lensing also allows to measure the cosmological distance ratios (with z_l~0.3, z_s~0.5) R= (D_s D_l,*) / (D_* D_L,s) = 2.68±0.29, consistent with predictions from the Planck 2015 cosmology (R=2.35).  Detect the galaxy position-CMB convergence cross-correlation at small scales, r_p<1 Mpc/h and find consistency with lensing by NFW halos of mass M_h~1e13 Msun/h.  Finally, measure the CMB lensing-galaxy shear cross-correlation, finding an amplitude of A=0.76±0.23 (z_eff=0.35, theta<2deg) with respect to Planck 2015 LCDM predictions (1sigma-level consistency).  Do not find evidence for relative systematics between the CMB and SDSS galaxy lensing.

Day 1111

Thursday.  Friday.  Monday.  Tuesday.

1606.07817
Constraints on assembly bias from galaxy clustering
Zentner, Hearing, van den Bosch, Lange, Villarreal

Constrain the newly-introduced decorated HOD model using SDSS DR7 measurements of projected galaxy clustering or r-band luminosity threshold samples.  The decorated HOD is a model for the galaxy-halo connection that augments the HOD by allowing for the possibility of galaxy assembly bias: galaxy luminosity may be correlated with DM halo properties besides mass, Mvir.  Demonstrate that it is not possible to rule out galaxy assembly bias using DR7 measurements of galaxy clustering alone.  Moreover, galaxy samples with Mr<-20 and Mr<-20.5 favor strong central galaxy assembly bias.  These samples prefer scenarios in which high-concentration are more likely to host a central galaxy relative to low-concentration halos of the same mass.  Exclude zero assembly bias with high significance for these samples.  Satellite galaxy assembly bias is significant for the faintest sample, Mr<-19.  Find no evidence for assembly bias in the Mr<-21 sample.  Assembly bias should be accounted for in galaxy clustering analysis or attempts to exploit galaxy clustering to constrain cosmology.  In addition to presenting the first constraints on HOD models that accommodate assembly bias, the analysis includes several improvements over previous analyses of these data.  Therefore, the inferences supersede previously-published results even in the case of a standard HOD analysis.


1606.07837
The systematic error test for PSF correction in weak gravitational lensing shear measurement bo the ERA Method by idealizing PSF
Okura, Futamase

Improve the ERA (Ellipticity of Re-smeared Artificial image) method of PSF correction in WL shear analysis in order to treat realistic shape of galaxies and PSF.  This is done by re-smearing PSF and the observed galaxy image smeared by a RSF (Re-Smearing Function), and allows use of a new PSF with a simple shape and to correct PSF effect without any approximations and assumptions.  Perform numerical test to show that the method applied for galaxies and PSF with some complicated shapes can correct PSF effect with systematic error less than 0.1%.  Also apply ERA method for real data of A1689 cluster to confirm that it is able to detect the systematic WL shear pattern.  The ERA method requires less than 0.1 or 1 second to correct PSF for each object in numerical test and real data analysis, respectively.

Day 1110

Monday.  Tuesday.  Wednesday.

1606.06291
A high stellar velocity dispersion and ~100 globular clusters for the ultra diffuse galaxy dragonfly 44
van Dokkum, et al

Recently a population of large, very low surface brightness, spheroidal galaxies was identified in the Coma cluster.  The apparent survival of these UDGs (ultra-diffuse galaxies) in a rich cluster suggests that they have very high masses.  Present the stellar kinematics of Dragonfly 44, one of the largest Coma UDGs, using a 33.5 hr integration with DEIMOS on the Kick II telescope.  Find a velocity dispersion of 47 km/s, which implies a dynamical mass of M_dyn=0.7e10Msun within its reprojected half-light radius of r_1/2=4.6 kpc.  The M/L ratio is 48 Msun/Lsun, and the DM fraction is 98 % within the HLR.  The high mass of Dragonfly 44 is accompanies by a large globular cluster population.  From deep Gemini imaging taken in 0.4" seeing, infer that Dragonfly 44 has 94 globular clusters, similar to the counts for other galaxies in this mass range.  Results add to other recent evidence that many UDGs are "failed" galaxies, with the sizes, DM content, and globular cluster systems of much more luminous objects.  Estimate the total dark halo mass of Dragonfly 44 by comparing the amount of DM within r=4.6 kpc to enclosed mass profiles of NFW haloes.  The enclosed mass suggests a total mass of 1e12 Msun, similar to the mass of the MW.  The existence of nearly-dark objects with this mass was unexpected, as galaxy formation was thought to be maximally-efficient in this regime.

Day 1109

Friday.

1606.04947
Models of low-mass helium white dwarfs including gravitational settling, thermal and chemical diffusion, and rotational mixing
Istrate, et al

A large number of extremely low-mass He white dwarfs (ELM WDs) have been discovered n recent years.  The majority of them are found in close binary systems suggesting they are formed either through a common-envelope phase or via stable mass transfer in a low-mass X-ray binary (LMXB) or a cataclysmic variable (CV) system.  Here, investigate the formation of these objects through the LMXB channel with emphasis on the proto-WD evolution in environments with different metallicities.  Study the combined effects of rotational mixing and element diffusion (e.g. gravitational settling, thermal and chemical diffusion) on the evolution of proto-WDs and on the cooling properties of the resulting WDs.  Present state-of-the-art binary stellar evolution models computed with MESA for metallicities between Z=0.0002 and Z=0.02, producing WDs with masses between 0.16-0.45 Msun.  The results confirm that element diffusion plays a significant role in the evolution of proto-WDs that experience H shell flashes.  The occurrence of these flashes produces a clear dichotomy in the cooling timescales of ELM WDs, which has important consequences e.g. for the age determination of binary millisecond pulsars.  Rotational mixing is found to counteract the effect of gravitational settling in the surface layers of young, bloated ELM proto-WDs and therefore plays a key role in determining their surface chemical abundances.  Predict that these proto-WDs have He-rich envelopes through a significant part of their lifetime, a crucial ingredient for understanding the newly observed ELM proto-WD pulsators.  The H envelope at detachment, although small compared to the total mass of the WD, contains enough angular momentum such that the spin frequency of the resulting WD on the cooling track is well above the orbital frequency.


1606.05309
Absorption line spectroscopy of gravitationally-lensed galaxies: further evidence for an increased escape fraction of ionizing photons at high redshift
Leethochawalit et al

The fraction of ionizing photos that escape from high z SF galaxies remains a key obstacle in evaluating whether galaxies were the primary agents of cosmic reionization.  In an earlier work, proposed using the covering fraction of low ionization gas, measured via deep absorption line spectroscopy, as a proxy.  Present a significant update using this method, sampling seven gravitationally-lensed sources in the redshift range 4<z<6.  Show the absorbing gas in the sources is spatially inhomogeneous with a median covering fraction of 66%.  Correcting for reddening according to a dust-in-cloud model, estimate this implies an absolute escape fraction of ~19±6%.  Recognizing this is higher than independent estimates based on recombination rate suites of the IGM from QSO absorption lines, quantify possible biases and uncertainties.  Collectively find the average escape fraction could be reduced to no less than 11%, excluding the effect of spatial variations.  For one of the lensed sources, have sufficient S/N to demonstrate the presence of such spatial variations as well as scatter in its dependence on the Lya equivalent width consistent with recent simulations.  If this source is typical, the lower limit to the escape fraction could be reduced by a further factor ~2.  Across the sample, find a modest anti-correlation between the inferred escape fraction and the local star formation rate consistent with a time delay between a burst and leaking LyC photons.  The analysis demonstrates considerable variations in the proportion of ionizing photons that can escape consistent with being governed by the small scale behavior of star-forming regions which fluctuate in their activities over short timescales.  This supports the suggestion that the escape fraction may increase toward the reionization era when star formation becomes more energetic and burst-like.


1606.05337
Calibration of weak-lensing shear in the Kilo-Degree Survey
Fenech Conti, Herbonnet, Hoekstra, Merten, Miller, Viola

Describe and test the pipeline used to measure the WL shear signal from KiDS.  It includes a novel method of 'self-calibration' that partially corrects for the effect of noise bias.  Also discuss the 'weight bias' that may arise in optimally-weighted measurements, and present a scheme to mitigate that bias. To study the residual biases arising from both galaxy selection and shear measurement, and to derive an empirical correction to reduce the shear biases to <~1%, create a suite of simulated images whose properties are close to those of the KIDS surveys observations.  Find that the use of 'self-calibration' reduces the additive and multiplicative shear biases significantly, although further correction via a calibration scheme is required, which also corrects for a dependence of the bias on galaxy properties.  Find that the calibration relation itself is biased by the use of noisy, measured galaxy properties, which may limit the final accuracy that can be achieved.  Assess the accuracy of the calibration in the tomographic bins used for the KiDS cosmic shear analysis, testing in particular the effect of possible variations in the uncertain distributions of galaxy size, magnitude and ellipticity, and conclude that the calibration procedure is accurate at the level of multiplicative bias <~1% required for the KiDS cosmic shear analysis.


1606.05338
KiDS-450: Cosmological parameter constraints from tomographic weak gravitational lensing
Hildebrandt, Viola, Heymans, Joudaki, Kuijken, et al

Present cosmological parameter constraints from a tomographic WL analysis of ~450 deg^2 of imaging data from KiDS.  For a flat LCDM cosmo with a prior on H0 that encompasses the most recent direct measurements, find S8=sigma_8 (Omega_m/0.3)^{1/2} = 0.745±0.039.  This result is in good agreement with other low z probes of large scale structure, including recent cosmic shear results, along with pre-Planck cosmic microwave background constraints.  A 2.3-sigma tension in S8 and 'substantial discordance' in the full parameter space is found with respect to the Planck 2015 results.  Use shear measurements for nearly 15M galaxies, determined with a new improved 'self-calibrating' version of lensfit validated using an extensive suite of image simulations.  Four-band ugri photometric redshifts are calibrated directly with deep spectroscopic surveys.  The redshift calibration is confirmed using two independent techniques based on angular cross-correlations and the properties of the photometric redshift probability distributions.  The covariance matrix is determined using an analytical approach, verified numerically with large mock galaxy catalogues.  Account for uncertainties in the modeling of intrinsic galaxy alignments and their impact of baryon feedback on the shape of the non-linear matter power spectrum, in addition to the small residual uncertainties in the shear and redshift calibration.  The cosmology analysis was performed blind.  The high-level data products, including shear correlation functions, covariance matrices, redshift distributions, and MCMC chains are available at kids.strw.leidenuniv.nl.

Day 1108

Wednesday.  Thursday.

1606.04321
Ambiguities in gravitational lens models: the density field from the source position transformation
Unruh, Schneider, Sluse

SL is regarded as the most precise technique to measure the mass in the inner region of galaxies or galaxy clusters.  In particular, the mass within one Einstein radius can be determined with an accuracy of order of a few percent or better, depending on the image configurations.  For other radii, however, degeneracies exist between galaxy density profiles, precluding an accurate determination of the enclosed mass.  The source position transformation (SPT), which includes the well-known mass-sheet transformation (MST) as a special case, describes this degeneracy of the lensing observables in a more general way.  In this paper, explore properties of an SPT, removing the MST to leading order, i.e., consider degeneracies which have not been described before.  The deflection field alpha-hat(theta) resulting from an SPT is not curl-free in general, and thus not a deflection that can be obtained from a lensing mass distribution.  Starting from a variational principle, construct lensing potentials that give rise to a deflection field alpha, which differs from alpha hat by less than an observationally motivated upper limit.  The corresponding mass distributions from these 'valid' SPTs are studied: their radial profiles are modified relative to the original mass distribution in a significant and non-trivial way, and originally axisymmetric mass distributions can obtain a finite ellipticity.  These results indicate a significant effect of the SPT on quantitative analyses of lens systems.  Show that the mass inside the Einstein radius of the original mass distribution is conserved by the SPT; hence, as is the case for the MST, the SPT does not affect the mass determination as the Einstein radius.

Day 1107

Thursday.  Friday.  Monday.  Tuesday.

1606.03092
Consistency of the growth rate in different environments with the 6dF galaxy survey: measurement of the void-galaxy & galaxy-galaxy correlation functions
Achitouv, Blake

Present a new test of gravitational physics by comparing the growth rate of cosmic structure measured around voids with that measured around galaxies in the same large-scale structure dataset, the low-redshift 6-degree Field Galaxy Survey.  By fitting a self-consistent RSD model to the 2d g-g and void-galaxy correlation functions, recover growth rate values f\sigma_8=0.36±0.06 and 0.39±0.11, respectively.  The environmental-dependence of cosmo statistics can potentially discriminate between modified-gravity scenarios which modulate the growth rate as a function of scale or environment and test the underlying assumptions of homogeneity and isotropy.


1606.03216
Intrinsic alignments in the Illustris simulation
Hilbert, Xu, Schneider, Springer, Vogelsberger, Hernquist

Study IA of galaxy image shapes within Illustris.  Investigate how IA correlations depend on observable galaxy properties such as stellar mass, apparent magnitude, redshift, and photometric type, and on the employed shape measurement method.  The correlations considered include the matter density-intrinsic ellipticity (mI), galaxy density-intrinsic ellipticity (dI), gravitational shear-intrinsic ellipticity (GI), and intrinsic ellipticity-intrinsic ellipticity (II) correlations.  Find stronger correlations for more massive and more luminous galaxies, as well as for earlier photometric types, in agreement with observations.  Moreover, shape measurement methods that down-weight the outer parts of galaxy images produce much weaker IA signals on intermediate and large scales than method employing flat radial weights. Thus, the expected contribution of IA to the observed ellipticity correlation in tomographic cosmic shear surveys may be below one percent or several percent of the full signal depending on the details of the shape measurement method.  A comparison of the results to a tidal alignment model indicates that such a model is able to reproduce the IA correlations well on intermediate and large scales, provided the effect of varying galaxy density is correctly taken into account.  Also find that the GI contributions to the observed ellipticity correlations could be inferred directly from measurements of galaxy density-intrinsic ellipticity correlations, expect on small scales, where systematic differences between mI and dI correlations are large.


1606.03399
Improving photometric redshifts with Ly$\alpha$ tomography
Schmittfull, White

Forming a 3D view of the Universe is a long-standing goal of astronomical observations, and one that becomes increasingly difficult at high z.  Discuss how tomography of the IGM at z~2.5 can be used to estimate the z of massive galaxies in a large volume of the Universe based on spectra of galaxies in their background.  The method is based on the fact that hierarchical structure formation leads to a strong dependence of the halo density on LS environment.  A map of the latter can thus be used to refine the knowledge of the redshifts of haloes and the galaxies and AGN which they host.  Show that tomographic maps of the IGM at a resolution of 2.5 Mpc/h can determine the redshifts of more than 90% of massive galaxies with uncertainty of delta(z)/(1+z) = 0.01.  Higher resolution maps allow such redshift estimation for lower mass galaxies and haloes.


1606.03407
Weighing the giants V: Galaxy cluster scaling relations
Mantz, et al

Present constraints on the scaling relations of galaxy cluster X-ray luminosity, temperature and gas mass (and derived quantities) with mass and redshift, employing masses from robust WL measurements.  These are the first such results obtained from an analysis that simultaneously accounts for selection effects and the underlying mass function, and directly incorporates lensing data to constrain total masses.  Constraints on the scaling relations and their intrinsic scatters are in good agreement with previous studies, and reinforce a picture in which departure from self-similar scaling laws are primarily limited to cluster cores.  However, the data are beginning to reveal new features that have implications for cluster astrophysics and provide new tests for hydrodynamical simulations.  Find a positive correlation the intrinsic scatters of luminosity and temperature at fixed mass, which is related to the dynamical state of the clusters.  While the evolution of the nominal scaling relations is consistent with self similarity, find tentative evidence that the luminosity and temperature scatters respectively decrease and increase with redshift.  Physically, this likely related to the development of cool cores and the rate of major mergers.  Also examine the scaling relations of redMaPPer richness and Compton Y from Planck.  While the richness--mass relation is in excellent agreement with recent work, the measured Y--mass relation departs strongly from that assumed in the Planck cluster cosmology analysis.  The latter result is consistent with easier comparisons of lensing and Planck scaling-relation-derived masses.


1606.03892
Higher order moments of lensing convergence - I. Estimate from simulations
Vicinanza, et al

Large area lensing surveys are expected to make it possible to use cosmic shear tomography as a tool to severely constrain cosmo parameters.  To this end, one typically relies on second order statistics such as the two-point correlation function and its Fourier counterpart, the power spectrum.  Moving a step forward, wonder whether and to which extent higher order statistics can improve the lensing FoM.  In this first paper of a series, investigate how second, third and fourth order lensing convergence moments can be measured and use as probe of the underlying cosmo model.  Use simulated data and investigate the impact on moments estimate of the map reconstruction procedure, the cosmic variance, and the intrinsic ellipticity noise.  Demonstrate that, under realistic assumptions, it is indeed possible to use higher order moments as a further lensing probe.

Day 1106

Tuesday.  Wednesday.

1606.01318
The origin of weak lensing convergence peaks
Liu, Haiman

WL convergence peaks are a promising tool to probe nonlinear structure evolution at late teams, providing additional cosmo info beyond second-order statistics.  Previous theoretical and observational studies have shown that the cosmo constraints on Omega_m and sigma_8 are improved by a factor of up to ~2 when peak counts are second-order statistics are combined, compared to using the latter alone.  Study the origin of lensing peaks using observational data from the 154 deg2 CFHTLS.  Find that while high peaks (with height kappa > 3.5 sigma_kappa, where sigma_kappa is the rms of the convergence kappa) are typically due to one single massive halo of ~1e15 Msun, low peaks (kappa<~sigma_kappa) are associated with constellations of 2-8 smaller haloes (<~1e13 Msun).  In addition, halos responsible for forming low peaks are found to be significantly offset from the LoS towards the peak center (impact parameter >~ their viral radii), compared with ~0.25 viral radii for haloes linked with high peaks, hinting that low peaks are more immune to baryonic processes whose impact is confined to the inner regions of the DM haloes.  Findings are in good agreement with results from the simulation work by Yang+2011.


1606.01516
The lopsided distribution of satellite galaxies
Libeskind, et al

The distribution of smaller satellite galaxies around large central galaxies has attracted attention because peculiar spatial and kinematic configurations have been detected in some systems.  A particularly striking example of such behavior is seen in the satellite system of Andromeda, where around 80% are on the nearside of that galaxy, facing the MW.  Motivated by this departure from anisotropy, examine the spatial distribution of satellites around pairs of galaxies in the SDSS.  By stacking tens of thousands of satellites around galaxy pairs, find that satellites tend to bulge towards the other central galaxy, preferably occupying the space between the pair, rather than being spherically or axis-symmetrically distributed around each host.  The bulging is a function of the opening angle examined, and is fairly strong -- there are up to ~10% more satellite in the space between the pair than expected from uniform.  Consequently, it is a statistically very strong signal, being inconsistent with a uniform distribution at the 5 sigma level.  The possibility that the observed signal is the result of the overlap of two haloes with extended satellite distributions, is ruled out by testing this hypothesis by performing the same test on isolated galaxies (and their satellites) artificially placed at similar separations.  These findings highlight the unrelaxed and interacting nature of galaxies in pairs.