Day 1161

Thursday.

1609.08613
The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: higher correlations revealed by germ-grain Minkowski Functionals
Wiegland, Eisenstein

Probe the higher-order clustering of the galaxies in the final data release (DR12) of SDSS BOSS using the method of germ-grain Minkowski Functionals (MFs).  The sample consists of 410k BOSS galaxies from the northern Galactic cap in the redshift range 0.450-0.595.  Show the MFs to be sensitive to contributions up to the 6-pt correlation function for this data set.  Ensure with a custom angular mask that the results are more independent of boundary effects than in previous analyses of this type.  Extract the higher-order part of the MFs and quantify the difference to the case without higher-order correlations.  The resulting chi2 value of over 10,000 for a modest number of degrees of freedom, O(200), indicates a 100-sigma deviation and demonstrates that there is a highly significant signal of the non-Gaussian contributions to the galaxy distribution.  This statistical power can be useful in testing models with differing higher-order correlations.  Comparing the galaxy data to the QPM and MutiDark-Patchy mocks, find that the latter better describes the observed structure.  From an order-by-order decomposition it is expected that, for example, already a reduction of the amplitude of the MD-patchy mock power spectrum by 5% would remove the remaining tension.


1609.08632
A marked correlation function for constraining modified gravity models
White

Future large scale structure surveys will provide increasingly tight constraints on the cosmo model.  These surveys will report results on the distance scale and growth rate of perturbations through measurements of BAO and RSD.  It is interesting to ask: what further analyses should become routine, so as to test as-yet-unknown models of cosmic acceleration?  Models which aim to explain the accelerated expansion rate of the Universe by modifications to GR often invoke screening mechanisms which can imprint a non-standard density dependence on their predictions.  This suggests density-dependent clustering as a 'generic' constraint.  This paper argues that a density-marked correlation function provides a density-dependent statistic which is easy to compute and report and requires minimal additional infrastructure beyond what is routinely available to such survey analysis.  Give one realization of this idea and study it using low order perturbation theory.  Encourage groups developing modified gravity theories to see whether such statistics provide discriminatory power for their models.  


1609.00944
Lensing smoothing of BAO wiggles
Dio

Study non-perturbatively the effect of the deflection angle on the BAO wiggles of the matter power spectrum in real space.  Show that from z~2 this introduces a dispersion of roughly 1 Mpc at BAO scale, which corresponds approximately to a 1% effect.  The lensing effect induced by the deflection angle, which is completely geometrical and survey independent, smears out the BAO wiggles.  The effect on the power spectrum amplitude at BAO scale is about 0.1% for z~2 and 0.2% for z~4.  Compare the smoothing effects induced by the lensing potential and non-linear structure formation, showing that the two effects become comparable at z~4, while the lensing effect dominates for sources at higher redshifts.  Note that this effect is not accounted through BAO reconstruction techniques.

Day 1160

Wednesday.

1609.08167
Galaxy bias from galaxy-galaxy lensing in the DES science verification data
Prat et al

Present a measurement of GGL around a magnitude-limited (i_AB<22.5) sample of galaxies selected from the DES-SV data.  Split these lenses into 3 photometric-redshift bins from 0.2 to 0.8, and determine the product of the galaxy bias b and cross-correlation coefficient between the galaxy and DM overdensity fields r in each bin, using scales above 4 Mpc/h comoving, where the linear bias model is found to be valid given the current uncertainties.  Compare the galaxy bias results from GGL with those obtained from galaxy clustering (Crocce+2016) and CMB lensing (Giannantonio+ 2016) for the same sample of galaxies, and found the measurements to be in good agreement with those in Crocce+2016, while, in the lowest z bin (z~0.3), they show some tension with the findings in Giannantonio+2016.  The results are found to be rather insensitive to a large range of systematic effects.  Measure (b x r) to be 0.87±0.11, 1.12±0.16 and 1.24±0.23, respectively for the 3 redshift bins of width Delta z = 0.2 in the range 0.2<z<0.8, defined with the photo-z algorithm BPZ.  Using a different code to split the lens sample, TPZ, leads to changes in the measured biases at the 10-20% level, but it does not alter the main conclusion of this work: when comparing with Crocce+2016, do not find strong evidence for a cross-correlation parameter significantly below one in this galaxy sample, except possibly at the lowest redshift bin (z~0.3), where it is found r=0.71±0.11 when using TPZ, and 0.83±0.12 with BPZ, assuming the difference between the results from the 2 probes can be solely attributed to the cross-correlation parameter.

Day 1159

Tuesday.

1609.07937
Weak-lensing shear estimates with general adaptive moments, and studies of bias by pixellation, PSF distortions, and noise
Simon, Schneider

In WL, weighted quadrupole moments of the brightness profile in galaxy images are a common way to estimate gravitational shear.  Employ general adapt moments (GLAM) to study causes of shear bias on a fundamental level and for a practical definition of an image ellipticity.  For GLAM, the ellipticity is identical to that of isophotes of elliptical images, and this ellipticity is always an unbiased estimator of reduced shear.  The theoretical framework reiterates that moment-based techniques are similar to a model-based approach in the sense that they fit an elliptical profile to the image to obtain weighted moments.  As a result, moment-based estimates of ellipticities are prone to undercutting bias.  The estimation is fundamentally limited mainly by pixellation which destroys information on the original, pre-seeing image.  Give an optimized estimator for the pre-seeing GLAM ellipticity and its bias for noise-free images.  To deal with images where pixel noise is prominent, consider a likelihood model of GLAM parameters in the pre-seeing frame.  Similar to the noise-free case, this likelihood is biased in the presence of undercutting.   The bias does not vary with the overall noise level but it depends in detail on the correlation of pixel noise as well as the noise homogeneity over the image, which could be relevant for the calibration strategies of other methodologies.  Give an analytic expression for the undercutting bias and suggest means to reduce it.  Moreover, within a Bayesian framework of the GLAM ellipticity, noise-dependent bias emerges after marginalization of the likelihood over image size or centroid position, even in the absence of undercutting.  Therefore, a Bayesian approach to shape measurements does not necessarily mitigate noise bias although the tests show that it can be reduced.

Day 1158

Monday.

1609.07147

What galaxy masses perturb the local cosmic expansion?

Peñarrubia, Fattahi

Use 12 cosmo N-body sims of Local Group systems (Sawala+2016) to inspect the relation between the viral mass of the main halos (Mvir,1 and Mvir,2), the mass derived from the relative motion of the halo pair (Mtim), and that inferred from the local Hubble flow (Mlhf).  Show that within the Spherical Collapse Model (SCM), which provides an idealized description of structure formation in an expanding Universe, the correspondence between the 3 mass estimates is exact, i.e. Mlhf=Mtim=Mvir,1+Mvir,2.  However, comparison with Apostle sims reveals that, contrary to what the SCM states, a relative large fraction of the mass that perturbs the local Hubble flow and drives the relative trajectory of the main galaxies is not contained within Rvir, and that the amount of "extra-viral" mass tends to increase in galaxies with a slow accretion rate.  In addition, find that modeling the peculiar velocities around the Local Group returns an unbiased constraint on the viral mass ratio of the main galaxy pair (fm=M1/M2~Mvir1/Mvir2), as well as the individual masses of the main galaxies (M1 and M2) without a priori assumptions on the matter distribution nor the equilibrium state of these systems.  Adopting Deimer+Kravtsov (2014) outer halo profile, which scales as rho~R^-4 at R>~Rvir, indicates that M1 and M2 roughly correspond to the asymptotically-convergent (total) masses of the individual haloes.  In contrast, find that estimates of Mvir based on the dynamics of tracers at R>>Rvir require a prior information on the internal matter distribution and the growth rate of the main galaxies, both of which are typically difficult to quantify.

1609.07474

Scaling in global tidal dissipation of the Earth-Moon system

van Putten

The Moon migrated to r_leftmoon~3.8e10 cm over a characteristic time r/v=1e10 Gyr by tidal interaction with the Earth's oceans at a present velocity of v=3.8cm/yr.  Derive scaling of global dissipation that covers the entire history over the past 4.52 Gyr.  Off-resonance tidal interactions at relatively short tidal periods in the past reveal the need for scaling with amplitude.  The global properties of the complex spatio-temprial dynamics and dissipation in broad spectrum ocean waves is modeled by damping e=hF/(2Q0), where h is the tidal wave amplitude, F is the tidal frequency, and Q0 is the Q-factor at the present time.  It satisfies Q0~14 for consistency of migration time and age of the Moon consistent wth observations for a near-resonance state today.  It shows a startlingly fast eviction of the Moon from an unstable near-synchronous orbit close to the Roche limit, probably in a protolunar disk.  Rapid spin down of the Earth from an initial ~30% of break-up by the moon favored early formation of a clement global climate.  Our theory suggests moons may be similarly advantageous to potentially habitable exoplanets.

Day 1157

Friday.

1609.06719
Anisotropy in the all-sky distribution of galaxy morphological types
Javanmardi, Kroupa

Present the first study of the isotropy of the distribution of morphological types of galaxies in the Local Universe out to around 200 Mpc using more than 60k galaxies from the HyperLeda database.  Divide the sky into two opposite hemispheres and compare the abundance distribution of the morphological types, T, using the Kolmogorov-Smirnov (KS) test.  This is repeated for different directions in the sky and the KS statistic as function of sky coordinates is obtained.  For 3 samples of galaxies within around 100, 150 and 200 Mpc, find a significant hemispherical asymmetry with a vanishingly small chance of occurring in an isotropic distribution.  Astonishingly, regardless of this extreme significance, the hemispherical asymmetry is aligned with the Celestial Equator at the 97.1-99.8% and with the Ecliptic at the 94.6-97.6% confidence levels, estimated using a Monte Carlo analysis.  Shifting T values randomly within their uncertainties has a negligible effect on this result.  When a magnitude limit of B<=15mag is applied, the sample within 100 Mpc shows no significant anisotropy after random shifting of T.  However, the direction of the asymmetry in the samples within 150 and 200 Mpc and B<=15 mag is found to be within an angular separation of 32 degrees from (l,b)=(123.7,24.6) with 97.2% and 99.9% confidence levels, respectively.  This direction is only 2.6 degrees away from the Celestial North Poles.  Unless the Local Universe has a significant anisotropic distribution of galaxy types aligned with the orientation or the orbit of the Earth (which would be a challenge for the Cosmological Principle), the results show that there seems to be a systematic bias in the classification of galaxy morphological types between the data from the Northern and the Southern Equatorial sky.  Further studies are absolutely needed to find out the exact source of this anisotropy.


1609.06903
The universal rotation curve of dwarf disk galaxies
Karukes, Salucci

Use the concept of the spiral rotation curves universality (Parsic+1996) to investigate the luminous and DM properties of the dwarf disk galaxies in the local volume (size ~11 Mpc).  The sample includes 36 objects with rotation curves carefully selected from the literature.  Find that, despite the large variations of the sample in luminosities (~2 of dex), the rotation curves in specifically normalized units look all alike and lead to the lower-mass version of the universal rotation curve of spiral galaxies found in Parsic+1996.  Mass model V(R/R_opt)/V_opt, the double normalized universal rotation curve of dwarf disk galaxies: the results show that these systems are totally dominated by DM whose density shows a core size between 2 and 3 stellar disk scale lengths.  Similar to galaxies of different Hubble types and luminosities, the core radius r_0 and the central density rho_0 of the DM halo of these objects are related by rho_0 r_0~100 M_sun/pc^2.  The structural properties of the dark and luminous matter emerge try well correlated.  In addition, to describe these relations, need to introduce a new parameter, measuring the compactness of light distribution of a (dwarf) disk galaxy.  These structural properties also indicate that there is no evidence of abrupt decline at the faint end of the baryonic to halo mass relation.  Finally, find that the distributions of the stellar disk and its dark matter halo are closely related.

Day 1156

Wednesday.  Thursday.

1609.06348
The minimum halo mass for star formation at z=6-8
Finlator, et al

Recent analysis of strongly-lensed sources in the Hubble Frontier Fields indicates that the rest-frame UV LF of galaxies at z=6--8 rises as a power law down to M_UV=-15, and possibly as faint as -12.5.  Use predictions from a cosmo radiation hydro sim to map these luminosities onto physical space, constraining the minimum DM halo mass and stellar mass that the FFs probe.  While previously-published theoretical studies have suggested or assumed that early SF was suppressed in haloes less massive than 1e9--1e11 Msun, find that recent observations demand vigorous SF in haloes at least as massive as (3.1, 5.6, 10.5)e9 Msun at z=(6,7,8).  Likewise, find that FF observations probe down to stellar masses of (8.1, 18, 32)e6 Msun; that is, they are observing the likely progenitors of analogues to Local Group dwarfs such as Pegasus and M32.  The sims yield somewhat different constraints than two complementary models that have been invoked in similar analyses, emphasizing the need for further observations constraints on the galaxy-halo connection.

Day 1155

Tuesday.

1609.05476
Cosmological constraints from the redshift dependence of the Alcock-Paczynski effect: application to the SDSS-III BOSS DR12 galaxies
Li, et al

Apply the methodology developed in Li 2014, 2015 to BOSS DR12 galaxies and derive cosmo constraints from the redshift dependence of the AP effect.  The apparent anisotropy in distribution of observed galaxies arise from two main sources, RSD due to galaxy peculiar velocities, and the geometric distortion when incorrect cosmological models are assumed for transforming redshift to comoving distance, known as the AP effect.  Anisotropies produced by RSD are, although large, maintains a nearly uniform magnitude over a large range of redshift, while the degree of anisotropies from the AP effect varies with redshift by much larger magnitude.  Split the DR12 galaxies into 6 z bins, measure the 2pt correlation function in each bin, and assess the redshift evolution of anisotropies.  Obtain constraints of Omega_m=0.290±0.053, w=-1.07±0.15, which are comparable with the current constraints from other cosmo probes such as SNe Ia, CMB, and BAO.  Combining these cosmo probes with this method yield tight constraints for Omega_m=0.301±0.006, w=-1.054±0.025.  This method is complementary to the other LSS probes like BAO and topology.  Expect this technique will play an important role in deriving cosmo constraints from LSS surveys.

Day 1154

Monday.

1609.04822
A free-form lensing model of A370 revealing stellar mass dominated BCGs, in Hubble Frontier Fields images
Diego, et al

Derive a free-form mass distribution for the unrelaxed cluster A370 (z=0.375), using the latest HFF images and GLASS spectroscopy.  Staring from a reliable set of 10 multiply lensed systems, produce a free-form model that identifies ~80 multiple-images.  Good consistency is found between models using independent subsamples and these lensed systems, with detailed agreement for the well resolved arcs.  The mass distribution has two very similar concentrations centered on the two prominent BCGs, with mass profiles that are accurately constrained by a uniquely useful system of long radially lensed images centered on both BCGs.  Show that the lensing mass profiles of these BCGs are mainly accounted for by their stellar mass profiles, with a modest contribution from dark matter within r<100 kpc of each BCG.  This conclusion may favor a cooled cluster gas origin for BCGs, rather than via mergers of normal galaxies for which DM should dominate over stars.  Growth via merging between BCGs is, however, consistent with this finding, so that stars still dominated over dark matter.


1609.05175
A test of Gaia Data Release 1 parallaxes: implications for the local distance scale
Casertano, Riess, Bucciarelli, Lattanzi

Present a comparison of Gaia DR1 parallaxes with photometric parallaxes for a sample of 212 Galactic Cepheids at a median distance of 2 kpc, and explore their implications on the distance scale and the local value of the Hubble constant H0.  The Cepheid distances are estimated from a recent calibration of the NIR Period-Luminosity P-L relation.  The comparison is carried out in parallax space, where the DR1 parallax errors, with a median value of half the median parallax, are expected to be well-behaved.  With the exception of one outlier, the DR1 parallaxes are in remarkably good global agreement with the reductions, and the published errors may be conservatively overestimated by about 20%.  The parallaxes of 9 Cepheids brighter than G=6 may be systematically underestimated, trigonometric parallaxes measured with the HST FGS for three of these objects confirm this trend.  If interpreted as an independent calibration of the Cepheid luminosities and assumed to be otherwise free of systematic uncertainties, DR1 parallaxes would imply a decrease of 0.3% in the current estimate of the local Hubble constant, well within their statistical uncertainty, and corresponding to a value 2.5 sigma (3.5 sigma if the errors are scaled) higher than the value inferred from Planck CMB data used in conjunction with LCDM.  Also test for zero point error in Gaia parallaxes and find none to a precision of ~20 mas.  Caution however that with this early release, the complete systematic properties of the measurements may not be fully understood at the statistical level of the Cepheid sample mean, a level an order of magnitude below the individual uncertainties.  The early results from DR1 demonstrate again the enormous impact that the full mission with likely have on fundamental questions in astrophysics and cosmology.

Day 1153

Friday.

1609.04398
Star formation quenching timescale of central galaxies in a hierarchical universe
Hahn, Tinker, Wetzel

Central galaxies make up the majority of the galaxy population, including the majority of the quiescent population at M*>1e10 Msun.  Thus, the mechanisms(s) responsible for quenching central galaxies plays a crucial rote in galaxy evolution as a whole.  Combine a high resolution cosmo N-body sim with observed evolutionary trends of the "star formation main sequence," quiescent fraction, and stellar mass function at z<1 to construct a model that statistically tracks the SFHs and quenching of central galaxies.  Comparing this model to the distribution of central galaxy star formation rates in a group catalog of SDSS DR7, constrain the timescales over which physical processes cease SF in central galaxies.  Over the stellar mass range 1e9.5 to 1e11 Msun, infer quenching e-folding times that span 1.5 to 0.5 Gyr with more massive central galaxies quenching faster.  For M*=1e10.5 Msun, this implies a total migration time of ~4 Gyrs from the SF MS to quiescence.  Compared to satellites, central galaxies take ~2 Gyrs long er to quench their SF, suggesting that different mechanisms are responsible for quenching centrals versus satellites.  The central galaxy quenching timescale inferred provides key constraints for proposed SF quenching mechanisms.  The timescale is generally consistent with gas depletion timescales predicted by quenching through strangulation.  However, the exact physical mechanism(s) responsible for this still remain unclear.

Day 1152

Thursday.

1609.04010
Constraining the frequency of free-floating planets from a synthesis of microlensing, radial velocity, and direct imaging survey results
Clinton, Gaudi

A microlensing survey by Sumi+2011 exhibits an overabundance of short-timescale events (STEs; t_E<2 days) relative to what is expected from known stellar populations and a smooth power-law extrapolation down to the brown dwarf regime.  This excess has been interpreted as a population of ~Jupiter-mass objects that outnumber MS stars by nearly 2x; however the microlensing data alone cannot distinguish between events due to wide-separation (a>~10AU) and free-floating planets.  Assuming these STEs are indeed due to planetary-mass objects, aim to constrain the fraction of these events that can be explained by bound by wide-separation planets.  Fit the observed timescale distribution with a lens mass function comprised of brown dwarfs, MS stars, and stellar remnants, finding and thus corroborating the initial identification of an excess of STEs.  Then include population of bound planets that are expected not to show signatures of the primary lens (host) in their microlensing light curves and that are also consistent with results from representative microlensing, radial velocity, and direct imaging surveys.  Find that bound planets alone cannot explain the entire STE excess without violating the constraints from the surveys considered and thus some fraction of these events must be due to free-floating planets, if the model for bound planets holds.  Estimate a median fraction of STEs due to free-floating planets to be f=0.67 (0.23-0.85 at 95% confidence) when assuming "hot-start" planet evolutionary models and f=0.58 ().14-0.83 at 95% confidence) for "cold-start" models.  Assuming a delta-function distribution of free-floating planets of mass m_p=2 M_Jup yields a number of free-floating planets per MS star of N=1.4 (0.48-1.8 at 95% confidence) in the "hot-start" use and N=1.2 (0.29-1.8 at 95% confidence) in the "cold-start" case.


1609.04303
Gaia Data Release 1: Astrometry - one billion positions, two million proper motions and parallaxes
Lindgren et al

Gaia DR1 contains astrometric results for more than 1 billion stars with m<20.7 based on observations collected by the Gaia satellite during the first 14 months of its operational phase.  Give a brief overview of the astrometric content of the data release and of the model assumptions, data processing, and validation of the results.  For stars in common with the Hipparcos and Tycho-2 catalogues, complete astrometric single-star solutions are obtained by incorporating positional information from the earlier catalogues.  For other stars only their positions are obtained by neglecting their proper motions and parallaxes.  The results are validated by an analysis of the residuals, through special validation runs, and by comparison with external data.  Results.  For about 22 million of the brighter stars (down to m~11.5) obtain positions, parallaxes, and proper motions to Hipparcos-type precision or better.  For these stars, systematic errors depending e.g. on position and color are at a level of 0.3 mas.  For the remaining stars, obtain positions at epoch J2015.0 accurate to ~10mas.  Positions and proper motions are given in a reference fame that is aligned with the International Celecitial Reference Frame (ICRF) to better than 0.1 mas at epoch J2015.0, and non-rotating with respect to ICRF to within 0.03 mas/yr.  The Hipparcos reference frame is found to rotate with respect to the Gia DR1 frame at a rate of 0.24 mas/yr.  Based on less than a quarter of the nominal mission length and on very provisional and incomplete calibrations, the quality and completeness of the astrometric data in Gaia DR1 are far from what is expected for the final mission products.  The results nevertheless represent a huge improvement n the available fundamental stellar data and practical definition of the optical reference frame.

Day 1151

Wednesday.

1609.03973
Do dark matter haloes explain lensing peaks?
Matilla, Haiman, Hsu, Gupta, Petri

Investigate a recently proposed halo-based model Camelus for predicting WL peak counts, and compared its results over a collection of 12 cosmologies with those from N-body sims.  While counts from both models agree for peaks with S/N>1 (where S/N is the ratio of the park height to the rms shape noise), find ~50% fewer counts for peaks near S/N=0 and significantly higher counts in the negative S/N tail.    Adding shape noise reduces the differences to within 20% for all cosmologies.  Also found larger covariances that are more sensitive to cosmo parameters.  As a result, credibility regions in the (Omega_m, sigma8) are ~30% larger.  Even though the credible contours are commensurate, each model draws its predictive power from different types of peaks.  Low peaks, especially those with 2<S/N<3, convey important cosmo information in N-body data, as shown in DeitrichHartlap, Kratochivil10, but Camelus constrains cosmology almost exclusively from high significance peaks (S/N>3).  The results confirm the importance of using a cosmology-dependent covariance with at least a 14% improvement in parameter constraints.  Identify the covariance estimation as the main driver behind differences in inference, and suggest possible ways to make Camelus even more useful as a highly accurate peak count emulator.  

Day 1150

Monday.  Tuesday.

1609.02924
The effects of physically unrelated near neighbors on the galaxy-galaxy lensing signal
Brainerd

The effects of near neighbors on the gg lensing signal are investigated using a suite of Monte Carlo sims.  The redshifts, luminosities, and relative coordinates for the simulated lenses were obtained from a set of galaxies with known spectroscopic redshifts and known luminosities.  As expected, when all lenses are assigned a single, fixed redshift, the mean tangential shear is identically equal to the excess surface mass density, scaled by the critical surface mass density: gamma_T=DeltaSigma / Sigma_c.  When the lenses are assigned their observed redshifts and Sigma_c is taken to be the critical surface mass density of the central lens, the relationship gamma_T=DeltaSigma/Sigma_c is violated because >~90% of the near neighbors are located at redshifts significantly different from the central lenses.  For a given central lens, physically unrelated near neighbors give rise to a ratio of gamma_T to DelaSigma/Sigma_c that spans a wide range of ~0.5 to ~1.5 at projected distances rp~1 Mpc.  The magnitude and sense of the discrepancy between gamma_T and DeltaSigma/Sigma_c are functions of both rp and the velocity dispersions of the central lenses, sigma_nu.  At large rp, the difference between gamma_T and DeltaSigma/Sigma_c is, on average, much greater for low-sigma_nu central lenses that it is for high-sigma_nu central lenses.


1609.03281
A study of the sensitivity of shape measurements to the input parameters of weak lensing image simulations
Hoeksta, Viola, Herbonnet

Improvements in the accuracy of shape measurements are essential to exploit the statistical power of planned imaging surveys that aim to constrain cosmo parameters using WL by LSS.  Although a range of tests can be performed using the measurements, the performance of the algorithm can only be quantified using simulated images.  This yields, however, only meaningful results if the simulated images resemble the real observations sufficiently well.  In this paper, explore the sensitivity of the multiplicative bias to the input parameters of Euclid-like image sims.  Find that algorithms will need to account for the local density of sources.  In particular the impact of galaxies below the detection limit warrants further study, because magnification changes their number density, resulting in correlations between the lensing signal and multiplicative bias.  Although achieving sub-percent accuracy will require further study, estimate that sufficient archival HST data are available to create realistic population of galaxies.


1609.03388
Halo histories vs. galaxy properties at z=0, I: the quenching of star formation
Tinker, Wentzel, Conroy, Mao

Test whether halo age and galaxy age are correlated at fixed halo and galaxy mass.  The formation histories, and thus ages, of DM haloes correlate with their large-scale density rho, an effect known as assembly bias.  Test whether this correlation extends to galaxies by measuring the dependence of galaxy stellar age on rho.  To clarify the comparison between theory and observation, and to remove the strong environmental effects on satellites, use galaxy group catalogs to identify central galaxies and measure their quenched fraction, f_Q, as a function of LS environment.  Models that match halo age to central galaxy age predict a strong positive correlation between f_Q and rho.  However, show that the amplitude of this effect depends on the definition of halo age: assembly bias is significantly reduced when removing the effects of splash back haloes ---  those halos that are central but have passed through a larger halo or experienced strong tidal encounters.  Defining age using halo mass at its peak value rather than current mass removes these effects.  In SDSS data, at M_gal>~1e10.0 Msun/h^2, there is a ~5% increase in f_Q from low to high densities, which is in agreement with predictions of DM haloes using peak halo mass.  At lower stellar mass there is little to no correlation of f_Q with rho.  For these galaxies, age-matching is inconsistent with the data across the wide range the halo formation metrics that we tested.  This implies that halo formation history has a small but statistically significant impact on quenching of star formation at high masses, while the quenching process in low-mass central galaxies is uncorrelated with halo formation history.  

Day 1149

Friday.

1609.02358
The HI content of extremely metal-deficient blue compact dwarf galaxies
Thuan, Goehring, Hubbard, Izotov, Hunt

Obtained HI observations with the 100m GBT for a sample of 29 extremely metal-deficient star-forming Blue Compact Dwarf (BCD) galaxies, selected from SDSS spectral database to be extremely metal-deficient (12+logO/H<7.6).  Neutral hydrogen was detected in 28 galaxies, a 97% detection rate.  Combining the HI data with SDSS optical spectra for the BCD sample and adding complementary galaxy samples from the literature to extend the metallicity and mass ranges, study how the HI content of a galaxy varies with various global galaxian properties.  There is a clear trend of increasing gas mass fraction with decreasing metallicity, mass and luminosity.  Obtain the relation M(HI)/L(g)~L(g)^-0.3, in agreement with previous studies based on samples with a smaller luminosity range.  The median gas mass fraction f(gas) for the GBT sample is equal to 0.94 while the mean gas mass fraction is 0.90±0.15, with a lower limit of ~0.65.  The HI depletion time is independent of metallicity, with a large scatter around the median value of 3.4 Gyr.  The ratio of the baryonic mass to the dynamical mass of the metal-deficient BCDs varies from 0.05 to 0.80, with a median value of ~0.2.  About 65% of the BCDs in the sample have an effective yield larger than the true yield, implying that the neutral gas envelope in BCDs is more metal-deficient by a factor of 1.5-20, as compared to the ionized gas.

Day 1148

Wednesday.  Thursday.

1609.01283
The search for failed supernovae with the large binocular telescope: confirmation of a disappearing star
Adams, Kochanik, Gerke, Stank, Dai

Present HST imaging confirming the optical disappearance of the failed SN candidate identified by Gerke+2015.  This ~25 Msun red supergiant experienced a weak ~1e6 Lsun optical outburst in 2009 and is now at least 5 magnitudes faster than the progenitor in the optical.  The mid-IR flux has slowly decreased to the lowest levels since the first measurements in 2004.  There is faint (2000-3000 Lsun) NIR emission likely associated with the source.  Find the late-time evolution of the source to be inconsistent with obscuration from an ejected, dusty shell. Models of the spectral energy distribution indicate that the remaining bolometric luminosity is >6 times fainter than that of the progenitor and is decreasing as ~t^-4/3.  Conclude that the transient is unlikely to be a SN imposter or stellar merger.  The event is consistent with the ejection of the envelope of a red supergiant in a failed SN and the late-time emission could be powered by fallback accretion onto a newly-formed black hole.  Future IR and X-ray observations are needed to confirm this interpretation of the fate for the star.


1609.01714
The effect of fiber collisions on the galaxy power spectrum multipole
Hahn, Scoccimarro, Blanton, Tinker ,Rodriguez-Torres

Fiber-Fed muti-object spectroscopic surveys, with their ability to collect an unprecedented number of redshifts, currently dominate LSS studies.  However, physical constraints limit these surveys from successfully collecting redshifts from galaxies too close to each other on the focal plane.  This ultimately leads to significant systematic effects on galaxy clustering measurements.  Using simulated mock catalogs, demonstrate that fiber collisions have a significant impact on the power spectrum, P(k), monopole and quadrupole that exceeds the sample variance at scales smaller than k~0.1 h/Mpc.  Present two methods to account for fiber collisions in the power spectrum.  The first statistically reconstruct the clustering of fiber collided galaxy pairs by modeling the distribution of the LoS displacements between them.  It also property accounts for fiber collisions i the shot-noise corruption term of the P(k) estimator.  Using this method, recover the true P(k) monopole of the mock catalogs with residuals of <0.5% at k=0.3 h/Mpc and <4% at k=0.83 h/Mpc -- a significant improvement over existing correction methods.  The quadrupole, however, does not improve significantly.  The second method models the effect of fiber collisions on the power spectrum as a convolution with a configuration space top-hat function that depends on the physical scale of fiber collisions.  It directly computes theoretical predictions of the fiber-collided P(k) multipoles and reduce the influence of smaller scales to a set of nuisance parameters.  Using this method, reliably model the effect of fiber collisions on the monopole and quadrupole down to the scale limits of theoretical predictions.  The methods presented in this paper will allow robust analysis of galaxy power spectrum multipole measurements to much smaller scales than previously possible.

Day 1147

Monday.  Tuesday.

1609.00730
Constrained simulations and excursion sets: understanding the risks and benefits of 'genetically modified' haloes
Porciani

Constrained realizations of Gaussian random fields are used in cosmology to design special initial conditions for numerical sims.  Review this approach and its application to density peaks providing several worked-out examples.  Then critically discuss the recent proposal to use constrained realizations to modify the linear density field within and around the Lagrangian patches that form DM haloes.  The ambitious concept is to forge 'genetically modified' halos with some desired properties after the non-linear evolution.  Demonstrate that the original implementation of this method is not exact but approximate because it tacitly assumes that protohaloes sample a set of random points with a fixed mean overdensity.  Show that carrying out a full genetic modification is a formidable and daunting task requiring a mathematical understanding of what determines the biased locations of protohaloes in the linear density field.  Discuss approximate solutions based on educated guesses regarding the nature of protohaloes.  Illustrate how the excursion-set method can be adapted to predict the non-linear evolution of the modified patches and this fine tune the constraints that are necessary to obtain preselected halo properties.  This technique allows exploration of the freedom around the original algorithm for genetic modification.  Find that the quantity which is most sensitive to changes is the halo mass-accretion rate at the mass scale on which the constraints are set.  Finally, discuss constraints based on the protohalo angular momenta.


1609.01041
The new world atlas of artificial night sky brightness
Falchi et al

Artificial lights raise night sky luminance, creating the most visible effect of light pollution-artificial sky glow.  Despite the increasing interest among scientists in fields such as ecology, astronomy, health care, and land-use planning, light pollution lacks a current quantification of its magnitude on a global scale.  To overcome this, present the world atlas of artificial sky luminance, computed with the light pollution propagation software using new high-resolution satellite data and new precision sky brightness measurements.  This atlas shows that more than 80% of the world and more than 99% of the U.S. and European populations live under light-polluted skies.  The Milky Way is hidden from more than 1/3 of humanity,, including 60% of Europeans and nearly 80% of North Americans.  Moreover, 23% of the world's land surfaces between 75 deg N and 60 deg S, 88% of Europe, and almost half of the United States experience light-polluted nights.


1609.01162
Galaxy and mass assembly (GAMA): detection of low-surface-brightness galaxies from SDSS data
Williams, Baldry et al

Report on a search for new LSBGs using SDSS data within the GAMA equatorial fields.  The search method consisted of masking objects detected with SDSS photo, combining grip images weighted to maximize the expected SNR, and smoothing the images.  The processed images were then run through a detect algorithm that finds all pixels above a set threshold and groups them based on their proximity to one another.  The list of detections was cleaned of contaminants such as diffraction spikes and the faint wings of masked objects.  From these, selecting potentially the brightest in terms of total flux, a list of 343 LSBGs was produced having been confirmed using VIKING imaging.  The photometry of this sample was refined using the deeper VIKING Z band as the aperture-defining band.  Measuring their g-i and J-K colors shows that most are consistent with being at redshifts less than 0.2.  The photometry is carried out using an AUTO aperture for each detection giving surface brightnesses of mu_r>=25 mag/arcsec2 and magnitudes of r>19.8 mag.  None of these galaxies are bright enough to be within the GAMA main survey limit, but could be part of future deeper surveys to measure the low-mass end of the galaxy stellar mass function.

Day 1146

Friday.

1609.00301
The lensing and temperature imprints of voids on the cosmic microwave background
Cai, et al

Seared for the signature of cosmic voids in the CMB, in both the Planck temperature and lensing-convergence maps; voids should give decrements in both.  Use zobov voids from DR12 SDSS CMASS sample.  Base the analysis on N-body sims to avoid a posteriori bias.  For the first time, detected the signature of voids in CMB lensing: the significance is 4.0 sigma, close to LCDM in both amplitude and projected density-profile shape.  A temperature dip is also seen, at models significance (1.6 sigma), with amplitude about 6 times the prediction.  This temperature signal is induced mostly by voids with radius between 100 and 150 Mpc/h, while the lensing signal is mostly contributed by smaller voids -- as expected; lensing relates directly to density, while ISW depends on gravitational potential.  The void abundance in observations and simulations agree as well.  Also repeated the analysis excluding lower-significance voids: no lensing signal is detected, with an upper limit of about 2x the LCDM prediction.  But the mean temperature decrement now becomes non-zero at the 3.4 sigma level (similar to that found by Granett+) with amplitude about 20x the prediction.  However, the observed dependence of temperature on void size is in poor agreement with simulations, whereas the lensing results are consistent with LCDM theory.  Thus, the overall tension between theory and observations does not favor non-standard theories of gravity, despite the hints of an enhanced amplitude for the ISW effect from voids.