Day 1506

Friday.  Monday.

1811.12374
The Ultraviolet detection of diffuse gas in galaxy groups
Stocke, et al

A small survey of the UV-absorbing gas in 12 low-z galaxy groups has been conducted using COS on-board HST.  Targets were selected from a large, homogeneously-selected sample of groups found in SDSS.  A critical selection criterion excluded sight line that pass close (<1.5 viral radii) to a group galaxy, to ensure absorber association with the group as a whole.  Deeper galaxy redshift observations are used both to search for closer galaxies and also to characterize these 1e13.5 to 1e14.5 Msun groups, the most massive of which are highly-virialized with numerous ETGs.  This sample also includes two spiral-rich groups, not yet fully virialized.  At group-centre impact parameters of 0.3-2 Mpc, these S/N=15-30 spectra detected HI absorption in 7 of 12 groups, high (OVI) and low (SiIII) ion metal lines are present in 2/3 of the absorption components.  None of the 3 most highly-virialized, ETG-doinated groups are detected in absorption.  Covering fractions >~50% are seen at all impact parameters probed, but do not require large filling factors despite an enormous extent.  Unlike halo clouds in individual galaxies, group absorbers have radial velocities which are too low to escape the group potential well without doubt.  This suggests that these groups are "closed boxes" for galactic evolution in the current epoch.  Evidence is presented that the cool and warm group absorbers are not a pervasive intra-group medium (IGrM), requiring a hotter (T~1e6 to 1e7 K) iGrM to be present to close the baryon accounting.


1811.12398
Cosmological filaments in the light of excursion set of saddle points
Fard, et al

The universe in large scales is structured as a network, called cosmic web.  Filaments are one of the structural components of this web, which can be introduced as a novel probe to study the formation and evolution of structures and as a probe to study the cosmo models and even to address the missing baryon problem.  The aim of this work is to introduce an analytical framework to study the statistics of filaments.  Plan to present an approach to obtain the length to mass relation of filaments and the number density of filaments per length and mass.  For this objective, model filaments as collapsed objects which have an extension in one direction, accordingly use the ellipsoidal collapse to study the evolution of an overdense region via gravitational instability.  In this context, the critical density of filament formation is obtained which will be a crucial parameter for number density count.  Also, find that the nonlinear density of filaments in the epoch of formation is almost mass independent and is in order of ~30 [units?].  A fitting function is presented for length-mass relation.  For the statistics of filaments propose a novel framework which is named as excursion set of saddle points.  In this approach, count the saddle points of the density field Hessian matrix, and relate it to the count of filaments.  In addition, address the filament in filament problem with up-crossing approximation.

Day 1505

Thursday.

1811.11491
The optical afterglow of GW170817 at one year post-merger
Lamb, et al

Present observations of the optical afterglow of GRB 170817A, made by HST, between Feb and Aug 2018, up to one year after the neutron star merger, GW170817.  The afterglow shows a rapid decline beyond 170 days, and confirms the jet origin for the observed outflow, in contrast to more slowly declining expectations for 'failed-jet' scenarios.  Show here that the broadband (radio, optical, X-ray) afterglow is consistent with a structured outflow where an ultra-relativistic jet, with Lorentz factor Gamma >~100, forms a narrow core (~5 deg) and is surrounded by a wider angular component that extends to ~15 deg, which is itself relativistic (Gamma >~5).  For a 2-component model of this structure, the late-time optical decline, where F~t^-alpha, is alpha=2.2±0.2, and for a Gaussian structure the decline is alpha=2.45±0.22.  Find the Gaussian model to be consistent with both the early ~10 days and late >~290 days data.  The agreement of the optical light curve with the evolution of the broadband spectral energy distribution, and its continued decline, indicates that the optical flux is arising primarily from the afterglow and not any underlying host system.  This provides the deepest limits on any host stellar cluster, with a luminosity <~4000 Sun~M_F606W >~ -4.5.

1811.11584
The effect on cosmological parameter estimation of a parameter dependent covariance matrix
Kodwani, Alonso, Ferreira

Cosmological large-scale structure analyses based on 2pt correlation functions often assume a Gaussian likelihood function with a fixed covariance matrix.  Study the impact on cosmological parameter estimation of ignoring the parameter dependence of this covariance matrix, focusing on the particular case of joint weak-lensing and galaxy clustering analyses.  Using a Fisher matrix formalism (calibrated against exact likelihood evolution in particular simple cases), quantify the effect of using a parameter dependent covariance matrix on both the bias and variance of the parameters.  Confirm that the approximation of a parameter-independent covariance matrix is exceptionally good in all realistic scenarios.  The information content in the covariance matrix (in comparison with the 2 pt function themselves) does not change with the fractional sky coverage.  Therefore the increase in information due to the parameter dependent covariance matrix becomes negligible as the number of modes increases.  Even for surveys covering less than 1% of the sky, this effect only causes a bias of up to O(10%) of the statistical uncertainties, with a misestimation of the parameter uncertainties at the same level or lower.  The effect will only be smaller with future large-area surveys.  Thus for most analyses the effect of a parameter-dependent covariance matrix can be ignored both in terms of the accuracy and precision of the recovered cosmological constraints.

Day 1504

Wednesday.

1811.10604

Astrophyiscs with radioactive isotopes

Diehl

Radioactivity was discovered as a by-product of searching for elements with suitable chemical properties.  Understanding its characteristics led to the development of nuclear physics, understanding that unstable configurations of nucleons transform into stable end products through radioactive decay.  In the universe, nuclear reactions create new nuclei under the energetic circumstances characterizing cosmic nucleosynthesis sites, such as the cores of stars and SN explosions.  Observing the radioactive decays of unstable nuclei which are by-products of such cosmic nucleosynthesis, is a special discipline of astronomy.  Understanding these special cosmic sites, their environments, their dynamics, and their physical processes, is the 'Astrophysics with Radioactivities' that makes the subject of this book.  Address the history, the candidate sites of nucleosynthesis, the different observational opportunities, and the tools of this field of astrophysics.


1811.10607
Formation of ultra-diffuse galaxies in the field and in galaxy groups
Jian, Dekel, et al

Study UDGs in zoom in cosmo sims, seeing the origins of UDGs in the field versus galaxy groups.  Find that while field UDGs arise from dwarfs in a characteristic mass range by multiple episodes of SN feedback, group UDGs may also form by tidal puffing up and they become quiescent by ram-pressure stripping.  The field and group UDGs share similar properties, independent of distance from the group centre.  Their DM haloes have ordinary spin parameters and centrally dominant DM cores.  Their stellar component tend to have a prolate shape with a Sersic index n~1 but no significant rotation.  Ram pressure removes the gas from the group UDGs when they are at pericentre, quenching SF in them and making them redder.  This generates a color/SFR gradient with distance from the center, as observed in clusters.  Find that ~20% of the field UDGs that fall into a massive halo survive as satellite UDGs.  In addition, normal field dwarfs on highly eccentric orbits can become UDGs near pericentre due to tidal puffing up, contributing about half of the group-UDG pupation.  Interpret the findings using simple toy models, showing that gas stripping is mostly due to ram pressure than tides.  Estimate that the energy deposited by tides in the bound component of a satellite over one orbit can cause significant puffing up provided that the orbit is sufficiently eccentric.

Day 1503

Tuesday.

1811.10596
Dark energy survey year 1: an independent E/B-mode cosmic shear analysis
Asgari, Heymans

Present an independent cosmic shear analysis of the non-cosmological B-mode distortions within the public first year data from DES.  Find no significant detection of B-modes in a full tomographic analysis of the primary METACALIBRATION shear catalog.  This is in contrast to the secondary IM3SHAPE shear catalogue, where B-modes are detected at a significance of ~3 sigma with a pattern that is consistent with the B-mode signature of a repeating additive shear bias across the survey.  Use the COSEBIs statistic to cleanly separate the B-modes from the gravitational lensing signal (E-modes).  Find good agreement between the measured E-modes and their theoretical expectation given the DES cosmological parameter constraints.

Day 1502

Wednesday.  Thursday.  (Friday.)  Monday.

1811.09070
The dark matter deficit galaxies in hydrodynamical simulations
Jing, et al

Low mass galaxies are expected to be DM dominated even with their centrals.  Recently two observations reported two dwarf galaxies in group environment with very little dark matter in their centrals.  Explore the population and origins of DM deficit galaxies (DMDGs) in 2 state-of-the-art hydro sims, the EAGLE and Illustris projects.  For all satellite galaxies with M*>1e9 Msun in groups with M200>1e13 Msun, find that about 5.0% of them in the EAGLE, and 3.2 % in the Illlustris are DMDGs with DM fractions below 50% inside 2x half-stellar-mass radii.  Demonstrate the DMDGs are highly tidal disrupted galaxies; and because DM has higher binding energy than stars, mass loss of the DM is much more rapid than stars in DMDGs during tidal interactions.  If DMDGs were confirmed in observations, they are expected in current galaxy formation models.


1811.09598
KiDS+GAMA: intrinsic alignment model constraints for current and future weak lensing cosmology
Johnston, et al

Directly constrain the NLA model of galaxy IA, analyzing the most representative and compete flux-limited sample of spectroscopic galaxies available for cosmic shear surveys.  Measure the projected galaxy position-intrinsic shear correlations and the projected galaxy clustering signal using high- resolution imaging from KiDS overlapping with GAMA, and data from SDSS.  Separating samples by color, make no significant detection of blue galaxy alignments, constraining the blue galaxy NLA amplitude A_IA^B=0.2±0.4 to be consistent with zero.  Make robust detections (~9sigma) for red galaxies, with A_IA^R=3.4±0.5, corresponding to a net radial alignment with the galaxy density field.  Provide informative priors for current and future WL surveys, and improvement over de facto wide priors that allow for unrealistic levels of IA contamination.  For a color-split cosmic shear analysis of the final KiDS survey area, forecast that the priors will improve the constraining power on S_8 and the DE equation of state w_0, by up to 62% and 51%, respectively.  The results indicate, however, that the modeling of red/blue-split galaxy alignments may be insufficient to describe samples with variable central/satellite galaxy fractions.

Day 1501

Tuesday.

1811.06989
Dark energy survey year 1 results: constraints on intrinsic alignments and their colour dependence from galaxy clustering and weak lensing

Samuroff, et al

Perform a joint analysis of intrinsic alignments and cosmology using tomographic weak lensing ,galaxy clustering and gg lensing measurements from Y1 of DES.  Define ealry- and late-type subsamples, which are found to pass a series of systematics tests, including for spurious photometric redshift error and point spread function correlations.  Analyse these spit data alongside the fiducial mixed Y1 sample using a range of IA models.  In a fiducial NL Alignment (NLA) analysis, assuming a flat LCDM cosmology, find a significant difference in IA amplitude, with early-type galaxies favoring A_IA=2.38+0.32-0.31 and late-type galaxies consistent with no IA at 0.05+0.10-0.09.  Find weak evidence of a diminishing alignment amplitude at higher z in the early-type sample.  The analysis is repeated using a number of extended model spaces, including a physically motivated model that includes both tidal torquing and tidal alignment mechanisms.  In multi probe likelihood chains in which cosmology, IA in both galaxy samples and all other relevant systematics are varied simultaneously, find the tidal alignment and tidal torquing parts of the IA signal have amplitudes A_1=2.7±0.7, A_2=-2.9±1.9, respectively, for early-type galaxies and A_1=0.6±0.4, A_2=-2.3±1.3 for late-type galaxies.  In the full (mixed Y1 sample the best constraints are A_1=0.7±0.4, A_2=-1.4+1.0-1.4.  For all galaxy splits and IA models considered, report cosmological parameter constraints that are consistent with the results of Troxel+2017 and DES 2017.


1811.07135
An orbital window into the ancient Sun's mass
Spalding, Fischer, Laughlin

Models of the Sun's long-term evolution suggest that its luminosity was substantial reduced 2-4 billion years ago, which is inconsistent with substantial evidence for warm and wet conditions in the geological records of both ancient Earth and Mars.  Typical solutions to this co-called "faint young Sun paradox" consider changes in the atmospheric composition of Earth and Mars, and while attractive, geological verification of these ideas is generally lacking -- particularly for Mars.  One possible under-explored solution to the faint young Sun paradox is that the Sun has simply lost a few percent of its mass during its lifetime.  If correct, this would slow, or potentially even offset the increase in luminosity expected from a constant-mass model.  However, this hypothesis is challenging to test.  Here, propose a novel observational proxy of the Sun's ancient mass that may be readily measured from accumulation patterns in sedimentary rocks on Earth and Mars.  Show that the orbital parameters of the Solar system planets undergo quasi-cyclic oscillations at a frequency, given by secular mode g_2-g_5, that scales approximately linearly with the Sun's mass.  Thus by examining the cadence of sediment accumulation in ancient basins, it is possible to distinguish between the cases of a constant mass Sun and a more massive ancient Sun to a precision of greater than about 1%.  This approach provide and avenue toward verification, or of falsification, of the massive early Sun hypothesis.


1811.07136
Accurate redshift determination of standard sirens by the luminosity distance space-redshift space large scale structure cross correlation
Zhang

Point out a new possibility to determine the average redshift distribution of a large sample of gravitational wave standard sirens, without spectroscopic follow-ups.  It is based on the X-correlation between the luminosity-distance space LSS traced by standard sirens, and the z space LSS traced by galaxies in preexisting EM wave observations.  Construct an unbiased and model independent estimator E_z to realize this possibility.  Demonstrate with BBO and Euclid that, 0.1% accuracy in z determination can be achieved.  This method can significantly alleviate the need of spectroscopic follow-up of standard sirens, and enhance their cosmological applications.

Day 1500

Monday.

1811.06081
Measurement of splash back feature around SZ-selected galaxy clusters with DES, PST and ACT
Shin, et al

Present a detection of the splash back feature around galaxy clusters selected sing they rSZ signal.  Recent measurements of the splash back feature around optically selected galaxy clusters have found that the splash back radius, r_sp, is smaller than predicted by N-body simulations.  A possible explanation for this discrepancy is that r_sp inferred from the observed radial distrubiton of galaxies is affected by selection effects related to the optical cluster-finding algorithms.  Test this possibility by measuring the splash back feature in clusters selected via the SZ effect in data from the SPT SZ survey and ACT Polarimeter survey.  The measurement is accomplished by correlating these clusters with galaxies detected int the DES Y3 data.  The SZ observable used to select clusters in this analysis is expected to have a twitter correlation with halo mass and to be more immune to projection effects and aperture-induced biases than optically selected clusters.  Find that the measured r_sp for SZ-selected clusters is consistent with the expectations from simulations, although the small number of SZ-selected clusters make s a precise comparison difficult.  In agreement with previous work, when using optically selected redMaPPer clusters, r_sp is ~2 sigma smaller than in the simulations.  These results motivate detailed investigations of selection biases in optically selected cluster catalogs and exploration of the splash back feature as a function of galaxy color, finding that blue galaxies have profiles close to a power law with no discernible splashback feature, which is consistent with them being on their first infall into the cluster.


1811.06556
Biases in inferring dark matter profiles from dynamical and lensing measurements
Scibelli, Perna, Keeton

The degeneracy between disk and halo contributions in spiral galaxy rotation curves makes it difficult to obtain a full understanding of the distribution of baryons and DM in disc galaxies like our own MW.  Using mock data, study how constraints on DM profiles obtained from kinematics, strong lensing, or a combination of the two are affected by assumptions about the halo model.  Compare 4 different models: spherical isothermal and NFW haloes, along with spherical and elliptical Burkert haloes. For both kinematics and lensing, find examples where different models fit the data well but give enclosed masses that are inconsistent with the true (i.e., input) values.  This is especially notable when the input and fit models differ in having cored or cusp profiles (such as fitting an NFW model when the underlying DM distribution follows a different profiles).  Find that mass biases are more pronounced with lensing than with kinematics, and using both methods can help reduce the bias and provide stronger constraints on the DM distributions.


1811.06844
Paleo-detectors: searching for Dark Matter with Ancient Minerals
Drukier, et al

Thanks to the large integration time of paleo-detectors, relative small target masses suffice to obtain exposures, i.e. the product of integration time and target mass, much larger than what is feasible in the conventional direct detection approach.  Discuss the paleo-detector proposal in detail, in particular, a range of background sources.  For low-mass WIMPs with masses m_chi <~ 10 GeV, the largest contribution to the background budget comes for nuclear recoils induced by coherent scattering of solar neutrinos.  For heavier WIMPs, the largest background source is nuclear recoils induced by fast neutrons created by heavy radioactive contaminants, particularly ^238U; neutrons can arise in spontaneous fission or from alpha-particles created in ^238U decays.  Also discuss the challenges of mineral optimization, specifically the determination of readily available minerals from rocks in deep boreholes which are able to record persistent damage from nuclear recoils.  In order to suppress backgrounds induced by radioactive contaminants, propose to use minerals found in marine evaporites or in ultra-basic rocks.  Estimate the sensitivity of paleo-detectors to spin-independent and spin-dependent WIMP-nucleus interactions.  In all interaction cases considered here, the sensitivity of low-mass WIMPs with masses m_chi<~10GeV extends to WIMP-nucelaon cross sections many orders of magnitude smaller than current upper limits.  For heavier WIMPs with masses m_chi>~30 GeV cross elections a factor of few to ~100 smaller than current upper limits can be probed by paleo-detectors.

Day 1499

Friday.

1811.05982
The shapes of the rotation curves of star-forming galaxies over the last $\approx$ 10 Gyr
Tiley, et al

Analyse maps of the spatially-resolved nebular emission of ~1500 SF galaxies at z~0.6-2.2 from deep KMOS and MUSE observations to measure the average shape of their rotation curves.  Use these to test claims for declining rotation curves at large radii and galaxies at z~1-2 that have been interpreted as evidence for an absence of dark matter.  Show that the shape of the average rotation curves, and the extend to which they decline beyond their peak velocities, depends upon the normalization prescription used to construct the average curve.  Normalising in size by the galaxy stellar disk-scale length R_d, construct stacked position-velocity diagrams that trace the average galaxy rotation curve out to 6R_d (~13 kpc, on average).  Combining these curves with average HI rotation curves for local systems, investigate how the shapes of galaxy rotation curves evolve over ~10 Gyr.  The average rotation curve for galaxies binned in stellar mass, stellar surface mass density and/or redshift is approximately flat, or continues to rise, out to at least 6R_d.  Find a correlation between the outer slopes of galaxies' rotation curves and their stellar mass surface densities, with the higher surface density systems exhibiting flatter or less steeply rising rotation curves.  Drawing comparisons with hydro sims, show that the average shapes of the rotation curves for the sample of massive, SF galaxies at z~0-2.2 are consistent with those expected from LCDM theory an imply DM fractions within 6R_d of at least 60%.


1811.06408
SDSS-IV MaNGA: Signatures of halo assembly in kinematically misaligned galaxies
Duckworth, et al

Investigate the relationship of kinematically misaligned galaxies with their large-scale environment, in the context of halo assembly bias.  According to numerical simulations, halo age at fixed halo mass is intrinsically linked to the large-scale tidal environment created by the cosmic web.  Investigate the relationship between distances to various cosmic web features and present-time gas accretion rate.  Select a sub-sample of ~900 central galaxies from the MaNGA survey with defined global position angles (PA; angle at which velocity change is greatest) for their stellar and Alpha gas components up to a minimum of 1.5 R_eff.  Split the sample by misalignment between the gas and stars as defined by the difference in their PA.  For each central galaxy, find its distance to nodes and filaments within the cosmic web, and estimate the host halo's age using the central stellar mass to total halo mass ratio M*/Mh.  Also construct halo occupation distributions using a background subtraction technique for galaxy groups split using the central galaxy's kinematic misalignment.  Find, at fixed halo mass, no statistical difference in these properties between the kinematically aligned and misaligned galaxies.  Suggest that the lack of correlation could be indicative of cooling flows from the hot halo playing a far larger role than 'cold mode' accretion from the cosmic web or a demonstration that the spatial extent of current large-scale internal field unit (IFU) surveys hold little information about large-scale environment extractable through this method.


1811.06499
Cosmological constraints from galaxy-lensing cross correlations using BOSS galaxies with SDSS and CMB lensing
Singh, Mandelbaum, Seljak, Rodriquez-Torres, Solar

Present cosmological parameter constraints based on a joint modeling of galaxy-lensing cross correlations and galaxy clustering measurements in the SDSS, marginalizing over small-scale modeling uncertainties using mock galaxy catalogs, without explicit modeling of galaxy bias.  Show that the modeling method is robust to the impact of different choices for how galaxies occupy DM haloes and to the impact of baryonic physics (at the ~2% level in cosmo params) and test for the impact of covariance on the likelihood analysis and of the survey window function on the theory computations.  Applying the results to the measurements using galaxy sample from BOSS and lensing measurements using shear from SDSS galaxies and CMB lensing from Planck, with conservative scale cuts, obtain S_8==(sigma8/0.8228)^0.8 (Omega_m/0.307)^0.6=0.85±0.05 (stat) using LOWZ x SDSS galaxy lensing, and S_8=0.91±0.1 (stat) using combination of LOWZ and CMASS x Planck CMB lensing.  Estimate the systematic uncertainty in the gg lensing measurements to be ~6% (dominated by photometric z uncertainties) and in the galaxy-CMB lensing measurements to be ~3%, from small scale modeling uncertainties including baryonic physics.

Day 1498

Tuesday.  Wednesday.  Thursday.

1811.04083
Early dark energy can resolve the Hubble tension
Poulin, Smith, Karwal, Kamionkowski

Early dark energy (EDE) that behaves like cosmological constant at early times (z>~3000) and then decays away like radiation or faster at later times can solve the Hubble tension.  In these models, the sound horizon at decoupling is reduced resulting in a larger value of the Hubble parameter H0 inferred from the CMB.  Consider 2 physical models for this EDE, one involving an oscillating scalar field and another a slowly-rolling field.  Perform a detailed calculation of the evolution of perturbations in these models.  A MCMC search of the parameter space for the EDE parameters, in conjunction with the standard cosmological parameters, identifies regions in which H0 inferred from Planck CMB data agrees with the SH0ES local measurement.  In these cosmologies, current BAO and SN data are described as successfully as in LCDM while the fit to Planck data is slightly improved.  Future CMB and large-scale-structure surveys will further probe this scenario.


1811.04098
Systematically measuring Ultra Diffuse Galaxies (SMUDGes).  I.  Survey description and first results in the Coma galaxy cluster and environs
Zaritsky, et al

Present a homogeneous catalog of 275 large (effective radius >~5.3 arcsec) UDG candidates lying within an ~290 sq deg region surrounding the Coma cluster.  The catalog results from the automated post processing of data from the Legacy Surveys, a 3-band imaging survey covering 14000 sq deg of the extragalactic sky.  Describe a pipeline that identifies UDGs and provides their basic parameters.  The survey is as complete in these large UDGs as previously published UDG surveys of the central region of the Coma cluster.  Conclude that the majority of the detections are at roughly the distance of the Coma cluster, implying effective radii >=2.5 kpc, and that the sample contains a significant number of analogs of DF44, where the effective radius exceeds 4 kpc, both within the cluster and in the surrounding field.  The g-z color of the UDGs spans a large range, suggesting that even large UDGs may reflect a range of formation histories.  A majority of the UDGs are consistent with being lower stellar mass analogs of red sequence galaxies, but find both red and blue UDG candidates in the vicinity of the Coma cluster and a relative overabundance of blue UDG candidates in the lower density environments and the field.  The eventual processing the full Legacy Surveys data will produce the largest, most homogeneous sample of large UDGs.


1811.04714
The stellar halo of isolated central galaxies in the Hyper Suprime-Cam imaging survey
Wang, et al

Study the faint stellar halo of isolated central galaxies, by stacking galaxy images in the HSC survey and accounting for the residual sky background sampled with random points.  The surface brightness profiles in HSC r-band are measured up to 120 kpc from the galaxy center for a wide range of galaxy stellar mass (9.2<log_10(M*/Msun)<11.4), and down to a surface brightness of about 32.8 mag/arcsec^2, which an indication of signals to even large scales and fainter magnitudes.  Failing to account for the outer stellar halo below the noise level of individual images will lead to underestimates of the total luminosity by <=20%.  Splitting galaxies according to the concentration parameter of their light distributions, find that the surface brightness profiles of low concentration galaxies drop faster between 20 kpc and 100 kpc and are more extended beyond 100 kpc than those of high concentration galaxies.  The profile of low concentration galaxies persist out to the average halo viral radius.  Albeit the large galaxy-to-galaxy scatter, find a strong self-similarity of the stellar halo profiles.  They show unified forms once the projected distance is scaled by the halo viral radius.  The color of the stellar halo is redder in the center and bluer outside, with high concentration galaxies having redder and flatter color profiles.  Such a color gradient persists to about 80 kpc for galaxies more massive than 1e10.2 Msun, whereas for galaxies with 9.2<log_10(M*/Msun)<10.2, the gradient is consistent with being flat between 10 and 30 kpc.


1811.04798
From globular clusters to the disc: the dual life of our Galaxy
Recio-Blanco

The halo and disc globular cluster population can be used as a tracer of the primordial epochs of the MW formation.  In this work, literature data of globular clusters ages, chemical abundances, and structural parameters are studied, explicitly focussing on the origin of the known split in the age-metallicity relation of globular clusters.  When the alpha-element abundances, which are less strongly affected by the internal light-element spread of globular clusters (Si, Ca), are considered, a very low observational scatter among metal-poor clusters is observed.  A plateau at [SiCa/Fe]~0.35 dex, with a dispersion of only 0.05 dex is observed up to a metallicity of about -0.75 dex.  Only a few metal-poor clusters in this metallicity interval present low [SiCa/Fe] abundances.  Moreover, metal-rich globular clusters show a knee in the [alpha/Fe] versus [Fe/H] plane around [Fe/H] -0.75 dex.  As a consequence, if a substantial fraction of galactic globular clusters has an external origin, they have to be mainly formed either in galaxies that are massive enough to ensure high levels of [alpha/Fe] element abundances even at intermediate metallicity, or in lower mass dwarf galaxies accreted by the MW in their early phases of formation.  Finally, clusters in the metal-poor branch of the AMR present an anti-correlation of [SiCa/Fe] with the total cluster magnitude, while this is not the case for metal-rich branch clusters.  In addition, this lack of faint high-alpha clusters in the young metal-poor population is in contrast with what is observed for old and more metal-poor clusters, possibly reflecting a higher heterogeneity of formation environments at lower metallicity, accretion of high-mass satellites, as a major contribution to the current MW globular cluster system both in the metal-poor and the metal-intermediate regime is compatible with the observations.


1811.04934
An HSC view of the CMASS galaxy sample.  Halo mass as a function of stellar mass, size and S\'ersic index
Sonnenfeld, Wang, Bahcall

Aim: to determine the distribution of DM halo masses as a function of the stellar mass and the stellar mass profile, for massive galaxies in the BOSS CMASS sample.  Methods: use grimy photometry from HSC to obtain Sersic fits and stellar masses of CMASS galaxies for which HSC weak lensing data is available, visually selected to have spheroidal morphology.  Apply a cut in stellar mass, log(M*/Msun) > 11.0, selecting ~10k objects.  Using a Bayesian hierarchical inference method, first investigate the distribution of Sersic index and size as a function of stellar mass.  Then, making use of shear measurements from HSC, measure the distribution of halo mass as a function of stellar mass, size and Sersic index.  Results: the data reveals a steep stellar mass-size relation R_e ~ M*^beta_R, with beta_R larger than unity, and positive correlation between Sersic index and stellar mass: n~M*^0.46.  Halo mass scales approximately with the 1.7 power of the stellar mass.  Do not find evidence for an additional dependence of halo mass on size of Sersic index at fixed stellar mass. Conclusions: the results disfavor galaxy evolution models that predict significant differences in the size growth efficiency of galaxies living in low and high mass haloes.


1811.04940
Weak lensing analysis of galaxy pairs using CS82 data
Gonzalez, et al

Analyze a sample of close galaxies pairs (relative projected separation <25/h kpc and relative radial velocities <350 km/s) using a WL analysis based on the CFHT Stripe 82 survey.  Determine halo masses for the Total sample of pairs as well as for Interacting, Red and Higher luminosity pair subsamples with ~3 sigma confidence.  The derived lensing signal for the total sample can be fitted either by a singular isothermal sphere with sigma_V=223±24 km/s for a NFW profile with R_200=0.30±0.03 h^{-1} Mpc.  The pair total masses and total r band luminosities imply an average mass-to-light ratio of ~200 h Msun/Lsun.  On the other hand, Red pairs which include a large fraction of elliptical galaxies, show a large mass-to-light ratio of ~345 h Msun/Lsun.  Derived lensing masses were compared to a proxy of the dynamical mass, obtaining a good correlation.  However, there is a large discrepancy between lensing masses and the dynamical mass estimates, which could be accounted by astrophysical processes such as dynamical friction, by the inclusion of unbound pairs, and by significant deviations of the density distribution from a SIS and NFW profiles in the inner regions.  Also compared lensing masses with group mass estimates obtained from the Yang+ galaxy group catalog, finding a very good agreement with the sample of groups with 2 members.  Red and Blue pairs show large differences between group and lensing masses, which is likely due to the single mass-to-light ratio adopted to compute the group masses.


1811.04942
Satellite galaxies in the Illustris-1 simulation: anisotropic locations around relatively isolated hosts
Brainerd, Yamamoto

Investigate the locations of luminous satellite galaxies in the z=0 slice of the hydro sim Illustris-1.  As expected from previous studies, the satellites are distributed anisotropically in the plane of the sky, with a preference for being located near the major axes of their hosts.  Due to misalignment of mass and light within the hosts, the degree of anisotropy is considerably less when the mean satellite location is measured with respect to the hosts' stellar surface mass density then when it is measured with respect to the hosts' DM surface mass density.  When measured with respect to the hosts' dark matter surface mass density, the mean satellite location depends strongly on host stellar mass and luminosity, with the satellites of the faintest, least massive hosts showing the greatest anisotropy.  This is caused by a strong correlation between the degree of anisotropy in the plane of the sky and host-satellite proximity in 3d.  The satellites of the faintest, least massive hosts are dominated by objects that are close to their hosts in 3d, whereas the satellites of the brightness, most massive hosts are dominated by objects that are far from their hosts in 3d.  When measured with respect to the hosts' stellar surface mass density, the mean satellite location is essentially independent of host stellar mass and luminosity.  The satellite locations are, however, dependent upon the stellar masses of the satellites, with the most massive satellites having the most anisotropic distributions.


1811.05790
Prestige Bias on Time Allocation Committees?
Greaves

The TAC-serving boost in getting proposals accepted supports the hypothesis of a bias in operation.  The magnitude of the effect is remarkable, and not readily explained in a fair scenario.  Alternative models include TAC-members being mainly driven to proposed while serving, but this seems doubtful for applications to a highly-sought facility.  Or, TAC-members could gain expertise at the meetings, and so start to apply more successfully (itself, perhaps "unequal access"), but N(TAC) fell back substantially afterwards, contrary to such a model.

Day 1497

Tuesday.  Wednesday.  Thursday.  Friday.  Monday.

1811.00605
The nature of fast radio bursts
Pen

Physical constraints on the sources of fast radio bursts are few, and therefore viable theoretical models are many.  However, no one model can match all the available observational characteristics, meaning that these radio bursts remain one of the most mysterious phenomena in astrophysics.


1811.00637
Constraining the mass density of free-floating black holes using razor-thin lensing arcs
Banik, van den Bosch, et al

SL of AGNs in the radio can result in razor-thin arcs, with a thickness of less than a milli-arcsecond, if observed at the resolution achievable with very-long baseline interferometry (VLBI).  Such razor-thin arcs provide a unique window on the coarseness of the matter distribution between source and observer.  In this paper, investigate to what extent such razor-thin arcs can constrain the number density and mass function of 'free-floating' black holes, defined as black holes that do not, or no longer, reside at the center of a galaxy.  These can be either primordial in origin or arise as by-products of the evolution of super-massive black holes in galactic nuclei.  When sufficiently close to the line-of-siight, free-floating BHs cause kink-like distortions in the arcs, which are detectable by eye in the VLBI images as longs the BH mass exceeds ~1000 Msun.  Using a crude estimate for the detectability of such distortions, analytically compute constraints on the matter density of free-floating BHs resulting from null-detections of distortions along a realistic, fiducial arc, and find them to be comparable to those from quasar milli-lensing.  Also use predictions from a large hydrodynamical simulation for the demographics of free-floating BHs that are not primordial in origin, and show that their predicted mass density is roughly four orders of magnitude below the constraints achievable with a single razor-thin arc.


1811.01139
Weak lensing reveals a tight connection between dark matter halo mass and the distribution of stellar mass in massive galaxies
Huang, Leauthaud, Hearin, Behroozi, et al

Using deep images from HSC survey and taking advantage of its unprecedented weak lensing capabilities, reveal a remarkably tight connection between the stellar mass distribution of massive central galaxies and their host dark matter halo mass.  Massive galaxies with more extended stellar mass distributions tend to live in more massive dark matter haloes.  Explain this connection with a phenomenological model that assumes, (1) a tight relation between the halo mass and the total stellar content in the halo, (2) that the fraction of in-situ and ex-situ mass at r<10 kpc depends on halo mass.  This model provides an excellent description of the SMF of total stellar mass M_star^Max and stellar mass within inner 10 kpc (Mstar^10) and also reproduces the HSC WL signals of massive galaxies with different stellar mass distributions.  The best-fit model shows that halo mass varies significantly at fixed total stellar mass (as much as 0.4 dex) with a clear dependence on M_star^10.  The two-parameter Mstar^Max - MStar^10 description provides a more accurate picture of the galaxy-halo connection at the high-mass end than the simple stellar-halo mass relation (SHMR) and opens a new window to connect the assembly history of haloes with those of central galaxies.  The model also predicts that the ex-situ component dominates the mass profiles of galaxies at r<10 kpc for log Mstar >= 11.7.  The code used for this paper is available online: https://github.com/dr-guangtou/asap.


1811.01679
Magnifications of paired micro-images emerging from a micro-lensing critical curve: breakdown of the inverse square root approximation
Weisenbach, Schlechter, Wambsganss

Studies of the inner regions of micro-lensed AGN during caustic crossing events have often relied upon the approximation that the magnification near a fold caustic is inversely proportional to the square root of the source-caustic distance.  Examine here the behavior of the magnifications of individual micro-images, specifically micro-minima, for a point source near fold caustics.  Find that there are often already noticeable deviations between actual magnifications and approximation at distances (rendered dimensionless by the 'flux factor', or caustic strength) of 0.1.  Present some statistics on the behavior of the magnifications of the micro-minima examined.  Additionally, provide statistics on values of the caustic strength for images C and D of WSO 2237+0305.  Finally, suggest an alternative approximation for the magnification near fold caustics and show how it alters the magnification profile of a uniform disc from that of the standard approximation.


1811.01809
Brightest cluster galaxy alignments in merging clusters
Wittman, Foote, Golovich

The orientations of brightest cluster galaxies (BCGs) and their host clusters then to be aligned, but the mechanism driving this is not clear.  To probe the role of cluster mergers in this process, quantify alignments of BCGs in clusters undergoing major mergers (up to ~1 Gyr after first pericenter).  Find alignments entirely consistent with those of clusters in general.  This suggests that alignments are robust against major cluster mergers.  If, conversely, major mergers actually help orient the BCG, such a process is acting quickly because the orientation is in place within ~1 Gyr after fist pericenter.


1811.01962
Revisiting the size-luminosity relation the era of ultra diffuse galaxies
Danieli, van Dokkum

Galaxies are generally found to follow a relation between their size and luminosity, such that luminous galaxies typically have large sizes.  The recent identification of a significant population of galaxies with large sizes but low luminosities ('ultra diffuse galaxies', or UDGs) raises the question whether the inverse is also true, thetas, whether large galaxies typically have high luminosities.  Here, address this question by studying a size-limited sample of galaxies in the Coma cluster.  Sleect red cluster galaxies with sizes r_eff>2kpc down to M_g~-13 mag in an area of 9 deg^2, using carefully-filtered CHFT images.  The sample is complete to a central surface brightness of mu_g,0 ~ 25.0 mag arcsec^{-2} and includes 90% of Dragonfly-discovered UDGs brighter than this limit.  Unexpectedly, find that red, large galaxies have a fairly uniform distribution in the size-luminosity plane: there is no peak at the absolute magnitude implied by the canonical size-luminosity relation.  The number of galaxies within ±0.5 magnitudes of the canonical peak (M_g=-19.69 for 2<r_eff<3 kpc) is a factor of ~9 smaller than the number of fainter galaxies with -19<M_g<-13.  Large, faint galaxies such as UDGs are far more common than large galaxies that are on the size-luminosity relation.  An implication is that, for large galaxies, size is not an indicator of halo mass.  Finally, show that the structure of faint large galaxies is different from that of bright large galaxies: at fixed large size, the Sersic index decreases with magnitude following the relation log10 n ~ -0.067 M_g - 0.989.


1811.02368
The PAU Survey: Operation and orchestration of multi-band survey data
Tonello, et al

The Physics of the Accelerating Universe (PAU) Survey is an international project for the study of cosmological parameters associated with Dark Energy.  PAU's 18-CCD camera (PAUCam), installed at the prime focus on the Willam Herschel Telescope at the Roque de los Muchachos Observatory (La Palma, canary Islands), scans parts of the northern sky, to collect low resolution spectral information of millions of galaxies with its unique set of 40 narrow-band filters in the optical range from 450 nm to 850 nm, and a set of 6 standard board band filters.  The PAU data management (PAUdm) team is in charge of treating the data, including at a transfer from the observatory to the PAU Survey data center, hosted at Port d'Informació Clientífica (PIC).  PAUdm is also in charge of the storage, data reduction and, finally, of making the results available to the scientific community.  Describe the technical solutions adopted to cover different aspects of the PAU Survey data management, from the computing infrastructure to support the operations, to the software tools and web services for the data process orchestration and exploration.  In particular, focus on the PAU database, developed for the coordination of the different PAUdm tasks, and to preserve and guarantee the consistence of data and metadata.


1811.02374
First cosmology results using Type Ia Spernovae from the Dark Energy Survey: Constraints on cosmological parameters
Abbott, et al

Present the first cosmological parameter constraints using measurements of SNe Ia from DES Supernova Program (DES-SN).  The analysis uses a subsample of 207 spectroscopically confirmed SNe Ia from the first 3 years of DES-SN, combined with a low-redshift same of 122 SNe from the literature.  The "DES-SN3YR" result from these 329 SNe Ia is based on a series of companion analyses covering SN Ia discovery, spectroscopic selection, photometry, calibration, distance bias corrections, and evaluation of systematic uncertainties.  For a flat LCDM model, find a matter density Omega_m=0.331±0.038.  For a flat wCDM model, and combining the SNIa constraints with those form the CMB, find a dark energy equation of state w=-0.978±0.059, and Omega_m=0.321±0.018.  Fo a flat w0waCDM model, and combining probes from SN Ia, CMB and BAO, find w0=-0.885±0.114 and wa=0.387±0.430.  These results are in agreement with a cosmological constant and with previous constraints using SNe Ia (Pantheon, JLA).


1811.02375
Cosmological constraints from multiple probes in the Dark Energy Survey
DES collaboration, et al

The combination of multiple observational probes has long been advocated as a powerful way to constrain cosmological parameters, in particular DE.  DES has measured 207 spectroscopically-confirmed Type Ia SN lighcurves; the BAO feature; WL; and galaxy clustering.  Present combined results from these probes, deriving constraints on the equation of state, w, of DE and its energy density in the Universe.  Independently of other experiments, such as those that measure the CMB, the probes from this single photometric survey rule out a Universe with no dark energy, finding w=-0.80+0.09-0.11.  The geometry is shown to be consistent with a spatially flat Universe, and report a constrain on the baryon density of Omega_b=0.069+0.009-0.012 that is independent of early Universe measurements.  These results demonstrate the potential power of large multi-probe photometric surveys and pave the way for order of magnitude advances in the constraints on properties of DE and cosmology over the next decade.

1811.02376
First cosmological results using Type Ia Supernovae from the Dark Energy Survey: measurement of the Hubble Constant
Macaulay, et al

Present an improved measurement of H0 using the 'inverse distance ladder' method, which adds the information from 207 SNe Ia from DES at 0.018<z<0.85 to existing distance measurements of 122 low-z (<0.07) SNe Ia (Low-z) and measurements of BAOs.  Whereas traditional measurements of H0 with SNe Ia use a distance ladder of parallax and Cepheid variable stars, the inverse distance ladder relies on absolute distance measurements from the BAOs to calibrate the intrinsic magnitude of the SNe Ia.  Find H0=67.77±.13 km/s/Mpc (statistics and systematic uncertainties, 68% confidence).  The measurement makes minimal assumptions about the underlying cosmological model, and the analysis was blinded to reduce confirmation bias.  Examine possible systematic uncertainties and all are presently below the statistical uncertainties.  The H0 value is consistent with estimate derived from CMB assuming a LCDM universe (Planck+2018).


1811.02518
Luminous red galaxies in the Kilo Degree Survey: Selection with broad-band photometry and weak lensing measurements
Vakili, et al

Use the overlap between multi band photometry of the KiDS and spectroscopic data based on SDSS and GAMA to infer the color-magnitude relation of red-sequence galaxies.  Use this inferred relation to select LRGs in the range 0.1<z<0.7 over the entire KiDS DR3 footprint.  Construct two samples of galaxies with different constant comoving densities and different luminosity thresholds.  The selected red galaxies have photometric redshifts with typical photo-z errors of sigma_z~0.014 (1+z) that are nearly uniform with respect to observational systematics.  This makes them an ideal set of galaxies for lensing and clustering studies.  As an example, use the KiDS-450 cosmic shear catalogue to measure the mean tangential shear signal around the selected LERGs.  Detect a significant WL signal for lenses out to z~0.7.


1811.02862
Atlas of cosmic ray-induced astrochemistry
Albertsson, Kaufmann, Menten

Cosmic-rays are the primary initiators of interstellar chemistry, and getting a better understanding of the varying impact they have on the chemistry of interstellar clouds throughout the MW will not only expand the understanding of interstellar medium chemistry in our own galaxy, but also aid in extra-galactic studies.  This work uses the ALCHEMIC astrochemical modeling code to perform numerical simulations of chemistry for a range of ionization rates.  Study the impact of variations in the cosmic ray ionization rate on molecular abundances under idealized conditions, given by constant temperatures and a fixed density of 1e4 cm^{-3}.  As part of this study, examine whether observations of molecular abundances can be used to infer the cosmic ray ionization rate in such a simplified case.  Find that intense cosmic-ray ionization results in molecules, in particular the large and complex ones, being largely dissociated, and the medium becoming increasingly atomic.  Individual species have limitations in their use as probes of the cosmic ray ionization rate.  At early time (<1 Myrs) ions such as N2H+ and HOC+ make the best probes, while at later times, neutral species such as HNCO and SO stand out, in particular due to their large abundance variations.  It is however by combining species into pairs that the best probes are found.  Molecular ions such as N2H+ combined with different neutral species can provide probe candidates that outmatch individual species, in particular N2H+/C4H, N2H+/C2H, HOC+/O and HOC+/HNCO.  These still have limitations to their functional range, but are more functional as probes than individual species previously used.


1811.02976
Failures of Halofit model for computation of Fisher matrices
Reimberg, Bernaudeau, Nishimichi, Rizzato

Use a simple cosmo model with two parameters (A_s, n_s) to illustrate the impact of using Halofit on error forecast based on Fisher information matrix for a h^{-3} Gpc^3 volume survey.  Show that Halofit fails to reproduce well the derivatives of the power spectrum with respect to the cosmo parameters despite the good fit produced for its amplitude.  Argue that the poor performance on the derivatives prediction is a general feature of this model and exhibit the response function for th Halofit to show how it compares with the same quantity measured on simulations.  The analytic structure of the Halofit response function points towards the origin of its weak performance at reproducing the derivatives of the non-linear power spectrum, which translate into unreliable Fisher information matrices.


1811.03095
Constraints on the existence of dark matter haloes by the M81 group and the Hickson compact groups of galaxies
Oehm, Kroupa

According to the standard model of cosmology the visible, baryonic matter of galaxies is embedded in DM haloes, thus extending the mass and the size of galaxies by one or two orders of magnitude.  Taking into account dynamical friction between the DM haloes, the nearby located M81 group of galaxies as well as the Hickson compact groups of galaxies are here investigated with regard to their dynamical behavior.  The results of the employment of the Markov Chain Monte Carlo method and the genetic algorithm show statistically substantial merger rates between galaxies, and long living constellations without merging galaxies comprise - apart from very few instances - initially unbound systems only.  This results is derived based on three- and four-body calculations for model of rigid Navaroo-Frenk-White profiles for the DM haloes, but verified by the comparison to randomly chosen individual solutions for the M81 galaxy group with high-resolution simulations of live self-consistent systems (N-body calculations).  In consequence, the observed compact confirmations of major galaxies are a very unlikely occurrence if DM haloes exist.


1811.03624
Inferences of $H_0$ in presence of a non-standard recombination
Chiang, Slosar

Measurements of the Hubble parameter from the distance ladder are in tension with indirect measurements based on the CMB data and the inverse distance ladder measurements at 3-4 sigma level.  Consider phenomenological modification to the timing and width of the recombination process and show that they can significantly affect this tension.  This possibility is appealing, because such modification affects both the distance to the last scattering surface and the calibration of the BAO ruler.  Moreover, because only a very small fraction of the most energetic photons keep the early universe in the plasma state, it is possible that such modification could occur without affecting the energy density budget of the universe or being incompatible with the era tight limits on the departure from the black-body spectrum of CMB.  In particular, find that under this simplified model, with a conservative subset of Planck data alone, H0=73.44-6.77+5.50 km/s/Mpc and in combination with BAO data H0=68.86-1.35+1.31 km/s/Mpc, decreasing the tension to ~2 sigma level.  However, when combined with Planck lensing reconstruction and high-ell polarization data, the tension climbs back to ~2.7 sigma, despite the uncertainty on non-ladder H0 measurement more than doubling.


1811.03625
Observational determination of the galaxy bias from cosmic variance with a random pointing survey: clustering of z~2 galaxies from Hubble's BoRG survey
Cameron, Trenti, Livermore, van der Velden

Gravitational clustering broadens the count-in-cells distribution of galaxies for surveys along uncorrelated (well-separated) lines of sight beyond Poisson noise.  A number of methods have proposed to measure this excess "cosmic" variance to constrain the galaxy bias (i.e. the strength of clustering) independently of the 2pt correlation function.  Here, present an observational application of these methods using data from 141 uncorrelated fields (~700 arcmin^2 total) from Hubble's Brightest of Reionizing Galaxies (BoRG) survey.  Use BoRG's broad-band imaging in optical and near infrared to identify N~1000 photometric candidates at z~2 through a combination of color selection and photometric z determination, building a magnitude-limited sample with m_AB<=24.5 in F160W.  Detect a clear excess in the variance of the galaxy number counts distribution compared to Poisson expectations, from which galaxy bias b~3.63±0.57 is estimated.  When divided by SED-fit classification into ~400 early-type and ~600 late-type candidates, estimate biases of b_early~4.06±0.67 and b_late~2.98±0.98 respectively.  These estimates are consistent with previous measurements of the bias from the 2pt correlation function, and demonstrate that with N>~100 sight-lines, each containing N>~5 objects, the count-in-cell analysis provides a robust measurement of the bias.  This implies that the method can be applied effectively to determine clustering properties (and characteristic dark-matter halo masses) of z~6-9 galaxies from a pure-parallel JWST survey similar in design to Hubble's BoRG survey.


1811.03631
The Spur and the Gap in GD-1: Dynamical evidence for a dark substructure in the Milky Way halo
Bonaca, Hogg, Price-Whelan, Conroy

Present a model for they interaction of the GD-1 stellar stream with a massive perturber that naturally explains many of the observed stream features, including a gap and an off-stream spur of stars.  The model involves an impulse by a fast encounter, after which the stream grows a loop of stars at different orbital energies.  At specific viewing angles, this loop appears offset from the stream track.  The configuration-space observations are sensitive to the mass, age, impact parameter, and total velocity of the encounter, and future velocity observations will constrain the full velocity vector of the perturber.  A quantitative comparison of the spur and gap features prefers models where the perturber is in the mass range of 1e6 Msun to 1e8 Msun.  Orbital integrations back in time show that the stream encounter could not have been caused by any known globular cluster or dwarf galaxy, and mass, size and impact-parameter arguments show that it could not have been caused by a DM substructure, like those predicted to populate galactic haloes in LCDM cosmology.  However, the expected densities of LCDM sub haloes in this mass range and in this part of the MW are 2-3 sigma lower than the inferred high density of the GD-1 perturber.  This observation opens up the possibility that detailed observations of streams could measure the mass spectrum of DM substructures and even identify individual substructures and their orbits in the Galactic halo.