Friday.
1808.09974
Detecting the orbital motion of nearby supermassive black hole binaries with Gaia
D'Orazio, Loeb
Show that a 5yr Gaia mission could astrometrically detect the orbital motion of up to a hundred supermassive black hole binaries with sub-parsec separations in the hearts of nearby, bright active galactic nuclei (AGN). The AGN lie out to a redshift of z=0.1 and in the V-band magnitude range 12<m_V<16. The distribution of detectable binary masses peaks around 1e8 solar masses and is truncated above 1e9 Msun.
1808.10051
Improving Hickson-like compact group finders in redshift surveys: an implementation in the SDSS
Diaz-Gimenez et al
Present an algorithm to identify compact groups (CGs) that close follows Hickson's original aim and that improves the completeness of the samples of compact groups obtained from redshift surveys. Instead of identifying CGs in projection first and then checking a velocity concordance criterion, identify them directly in redshift space using Hickson-like criteria. The methodology was tested on a mock light cone of galaxies built from the outputs of a recent semi-analytic model of galaxy formation run on top of the Millennium Simulation I after scaling to represent the first-year Planck cosmology. The new algorithm identifies nearly twice as meany CGs, no longer missing CGs that failed the isolation criterion because of velocity outliers lying in the isolation annulus. The new CG sample picks up lower surface brightness groups, which are both looser and with fainter brightest galaxies, missed by the classic method. A new catalogue of compact groups from SDSS is the natural corollary of this study. The publicly available sample comprises 462 observational groups with four or more galaxy members, of which 406 clearly fulfill all the compact group requirements: compactness, isolation, and velocity concordance of all of their members. The remaining 56 groups need further redshift information of potentially contaminating sources. This constitutes the largest sample of groups that strictly satisfy all the Hickson's criteria in a survey with available spectroscopic information.
1808.10057
Forecasting gamma-ray bursts using gravitational waves
Akcay
Explore the intriguing possibility of employing future ground-based gravitational-wave interferometers to detect the inspired of binary neutron stars sufficiently early to alert EM observatories so that gamma-ray burst (GRB) can be observed in its entirety from its very beginning. Quantify the ability to predict a GRB by computing the time a binary neutron star (BNS) system takes to inspire from its moment of detection to its final merger. Define the moment of detection to be the instant at which the interferometer network accumulates a signal-to-noise ratio of 15. For the computations, specifically consider BNS systems at luminosity distances of (i) D<=200 Mpc for the 3-interferometer advanced LIGO-Virgo network of 2020, and (ii) D<=1000 Mpc for Einstein Telescope's B and C configurations. In the case of Advanced LIGO-Virgo, find that at best get a few minutes of warning time, thus expect no forecast of GRBs in the 2020s. On the other hand, Einstein Telescope will provide us with advance warning times of more than 5 hrs for D<=100 Mpc. Taking one hour as a benchmark advance warning time, obtain a corresponding range of roughly 600 Mpc for the Einstein Telescope C configurations. Using current BNS merger event rates within this volume, show that Einstein C will forecast >~O(1e2) GRBs in the 2030s. Reapply the warning-time computation to binary BH - NS inspires and find 1 to 3 tidal disruption events to be forecast by the same detector. This is a pedagogical introduction to gravitational-wave astronomy written at a level accessible to PhD students, advanced under graduates, and colleagues in astronomy/astrophysics who wish to learn more about the underlying physics. Though many of the results may be known to the experts, they might nonetheless find this article motivating and exciting.
Thursday, August 30, 2018
Wednesday, August 29, 2018
Day 1458
Thursday.
1808.09516
Magnification bias in the shear-ratio test: a viable mitigation strategy
Unruh, Schneider, Hilbert
Using the same lens galaxies, the ratios of tangential shears for different source galaxy redshifts is equal to the ratios of their corresponding angular-diameter distances. This is the so-called shear-ratio test (SRT) and it is valid when effects induced by the intervening large-scale structure (LSS) an be neglected. The dominant LSS effect is magnification bias which, on the one hand, induces an additional shear, and on the other hand, causes a magnification of the lens population. The objective is to quantify the magnification bias for the SRT and show an easy-to-apply mitigation strategy that does not rely on additional observations. Use ray-tracing data through the Millennium simulations to measure the influence of magnification on the SRT an test the mitigation strategy. Using the SRT as a null-test, find deviations from zero up to 10% for a flux-limited sample of lens galaxies, which is a strong function of lens redshift and the lens-source line-of-sight separation. Using the mitigation strategy can improve the null-test by a factor of ~100.
1808.09516
Magnification bias in the shear-ratio test: a viable mitigation strategy
Unruh, Schneider, Hilbert
Using the same lens galaxies, the ratios of tangential shears for different source galaxy redshifts is equal to the ratios of their corresponding angular-diameter distances. This is the so-called shear-ratio test (SRT) and it is valid when effects induced by the intervening large-scale structure (LSS) an be neglected. The dominant LSS effect is magnification bias which, on the one hand, induces an additional shear, and on the other hand, causes a magnification of the lens population. The objective is to quantify the magnification bias for the SRT and show an easy-to-apply mitigation strategy that does not rely on additional observations. Use ray-tracing data through the Millennium simulations to measure the influence of magnification on the SRT an test the mitigation strategy. Using the SRT as a null-test, find deviations from zero up to 10% for a flux-limited sample of lens galaxies, which is a strong function of lens redshift and the lens-source line-of-sight separation. Using the mitigation strategy can improve the null-test by a factor of ~100.
Day 1457
Friday. Monday. Tuesday. Wednesday.
1808.07464
Massive neutrinos leave fingerprints on cosmic voids
Kreisch, ..., Spergel, Wandelt, et al
Massive neutrinos uniquely affect cosmic voids. Explore their impact on void clustering using both the DEMNUni and MassiveNuS simulations. For voids, neutrino effects depend on the observed void tracers. As the neutrino mass increases, the number of small voids traced by cold dark matter particles increases and the number of large voids decreases. Surprisingly, when massive, highly biased haloes are used as tracers, find the opposite effect. How neutrinos impact the scale at which voids cluster and the void correlation is similarly sensitive to the tracers. This scale dependent trend is not due to simulation volume or halo density. The interplay of these signatures in the void abundance and clustering leaves a distinct fingerprint that could be detected with observations and potentially help break degeneracies between different cosmological parameters. This paper paves the way to exploit cosmic voids in future surveys to constrain the mass of neutrinos.
1808.07491
Weak lensing shear estimation beyond the shape-noise limit: a machine learning approach
Springer, Ofek, Weiss, Merten
Weak lensing shear estimation typically results in per galaxy statistical errors significantly larger than the gravitational signal of only a few percent. These statistical errors are mostly a result of shape-noise -- an estimation error due to the diverse (and a-priori unknown) morphology of individual background galaxies. These errors are inversely proportional to the limiting angular resolution at which localized objects, such as galaxy clusters, can be probed with weak lensing shear. In this work, report on the initial attempt to reduce statistical errors in weak lensing shear estimation using a machine learning approach -- training a multi-layered convolutional neural network to directly estimate the shear, given an observed background galaxy image. Train, calibrate and evaluate the performance and stability of the estimator using simulated galaxy images designed to mimic the distribution of HST observations of lensed background sources in the CLASH galaxy cluster survey. Using the trained estimator, produce weak lensing shear maps of the cores of 20 galaxy clusters in the CLASH survey, demonstrating an RMS scatter reduced by approximately 26% when compared to maps produced with a commonly used shape estimator. This is equivalent to a survey speed enhancement of approximately 60%. However, given the non-transparent nature of the machine learning approach, this results requires further testing and validation. Provide python code to train and test this estimator on both simulated and real galaxy cluster observations. Also provide updated weak lensing catalogues for the 20 CLASH galaxy clusters studied.
1808.07551
The Dark Universe - Exercises and proceedings form the German-Italian WE Heraeus Summer School held in 2017 in Heidelberg
Brems, et al
The Heroes Summer School series "Astronomy from four perspectives", funded by the WE Heraeus Foundation, draws together teachers and teacher students, astronomers, physicists and astronomy students from Germany and Italy. For each summer school, participants gather at one of the four participating nodes: Heidelberg, Padua, Jena, and Florence. The main goal of the series is to bring astronomy into schools, which is achieved by educating and training the teachers and teacher students. In this e-print, present the exercises, tutorials, and high-school classroom materials developed during the fifth summer school of the series, which took place at House der Astronomie in Heidelberg Aug. 26 -- Sep. 2, 2017. The tutorials were prepared beforehand for the participants of the Summer schools, and are suitable for use in teacher training. Classroom material were developed mainly during the summer school itself, and are suitable for high-school level teaching. They include question sheets for pupils, and some pointers on where to use the material in the German high school curriculum. Both sets of materials address the summer school's four main topics: Supernova cosmology, the viral theorem, rotation curves of galaxies, and the temperature of the cosmic microwave background (CMB).
1808.07772
Easily interpretable bulk flows: continuing tension with the standard cosmological model
Peery, Watkins, Feldman
Present an improved Minimal Variance (MV) method for using a radial peculiar velocity sample to estimate the average of the three-dimensional velocity field over a spherical volume, which leads to an easily interpretable bulk flow measurement. The only assumption required is that the velocity field is irrotational. The resulting bulk flow estimate is particularly insensitive to smaller scale flows. Also introduce a new constraint into the MV method that ensures that bulk flow estimates are independent of the value of the Hubble constant H_0; this is important given the tension between the locally measured H_0 and that obtained from the CMB observations. Apply the method to the Cosmic Flows-3 catalogues and find that, while the bulk flows for shallower spheres are consistent with the standard cosmological model, there is some tension between the bulk flow in a spherical volume with radius 150 hMpc and its expectations; find only a ~2% chance of obtaining a bulk flow as large or larger in the standard cosmological model with Planck parameters.
1808.08235
'Upper-limit lensing': constraining galaxy stellar masses with singly-imaged background sources
Smith, Lucey, Collier
Strong gravitational lensing can provide accurate measurements of the stellar mass-to-light ratio Upsilon in low-z (<~0.05) early-type galaxies, and hence probe for possible variations in the stellar initial mass function (IMF). However, true multiple imaging lens systems are rare, hindering the construction of large nearby lens samples. Here, present a method to derive upper limits on Upsilon in galaxies with single close-projected background sources, where where no counter-image is detected, down to some relative flux limit. Present a proof-of-principle applications to 3 galaxies with integral field observations from different instruments. in the first case study, only a weak constraint on Upsilon is obtained. In the second, the absence of a detectable counter-image excludes stellar masses higher than expected for a Salpeter IMF. In the 3rd system, the current observations do not yield a useful limit, but the analysis indicates that deeper observations should reveal a counter-image if the stellar mass is any larger than expected for a MW IMF. Discuss how this method can help enlarge the current samples of low-z galaxies with lensing constraints, both by adding upper limits on Upsilon and by guiding follow-up to promising single-image systems in search of fainter counter-images.
1808.08800
Discovery of strongly inverted metallicity gradients in dwarf galaxies at $z$$\sim$2
Wang, Jones, Treu, et al
Report the first sub-kiloparsec spatial resolution measurements of strongly inverted gas-phase metallicity gradients in two dwarf galaxies at z~2. The galaxies have stellar masses ~1e9 Msun, sSFR ~20 Gyr^{-1}, and global metallicity 12+log(O/H)~8.1 (1/4 solar). Their metallicity radial gradients are measured to be highly inverted, i.e., 0.122±).008 and 0.111±0.017 dex/kpc, which is hitherto unseen at such small masses in similar redshift ranges. From the HST observations of the source nebular emission and stellar continuum, present the 2-dimensional spatial maps of SFR surface density, stellar population age, and gas fraction, which show that the galaxies are currently undergoing rapid mass assembly via disk inside-out growth. More importantly, using a simple chemical evolution model, find that the gas fractions for different metallicity regions cannot be explained by pure gas accretion. The spatially resolved analysis based on a more advanced gas regulator model results in a spatial map of net gaseous outflows, triggered by active central starbursts, that potentially play a significant role in shaping the spatial distribution of metallicity by effectively transporting stellar nucleosynthesis yields outwards. The relation between wind mass loading factors and stellar surface densities measured in different regions of the galaxies shows that a single type of wind mechanism, driven by either energy or momentum conservation, cannot explain the entire galaxy. These sources present a unique constraint on the effects of gas flows on the early phase of disk growth from the perspective of spatially resolved chemical evolution within individual systems.
1808.08912
On the measurement of the local Hubble constant from the superlimninal motion of the jet launched in GW170817
Dado, Dar
The direction of the axis of the orbital motion of the merging binary neutron stars in the GW170817 event coincided with that of the apparent superluminal jet, which produced the short hard gamma ray burst (SHB) 170817A. It supports the local value of the Hubble constant provided by standard candle Type Ia SNe, H_0=73.24±1.74 km/s/Mpc, which differs by 3 sigma from the cosmic value H_0=67.74±0.46 km/s/Mpc obtained from the CMB radiation by Planck assuming the standard LCDM cosmology. The measured superluminal motion of the jet also allows critical tests of the assumed production mechanism of SHBs in general and of SHB170817A in particular.
1808.07464
Massive neutrinos leave fingerprints on cosmic voids
Kreisch, ..., Spergel, Wandelt, et al
Massive neutrinos uniquely affect cosmic voids. Explore their impact on void clustering using both the DEMNUni and MassiveNuS simulations. For voids, neutrino effects depend on the observed void tracers. As the neutrino mass increases, the number of small voids traced by cold dark matter particles increases and the number of large voids decreases. Surprisingly, when massive, highly biased haloes are used as tracers, find the opposite effect. How neutrinos impact the scale at which voids cluster and the void correlation is similarly sensitive to the tracers. This scale dependent trend is not due to simulation volume or halo density. The interplay of these signatures in the void abundance and clustering leaves a distinct fingerprint that could be detected with observations and potentially help break degeneracies between different cosmological parameters. This paper paves the way to exploit cosmic voids in future surveys to constrain the mass of neutrinos.
1808.07491
Weak lensing shear estimation beyond the shape-noise limit: a machine learning approach
Springer, Ofek, Weiss, Merten
Weak lensing shear estimation typically results in per galaxy statistical errors significantly larger than the gravitational signal of only a few percent. These statistical errors are mostly a result of shape-noise -- an estimation error due to the diverse (and a-priori unknown) morphology of individual background galaxies. These errors are inversely proportional to the limiting angular resolution at which localized objects, such as galaxy clusters, can be probed with weak lensing shear. In this work, report on the initial attempt to reduce statistical errors in weak lensing shear estimation using a machine learning approach -- training a multi-layered convolutional neural network to directly estimate the shear, given an observed background galaxy image. Train, calibrate and evaluate the performance and stability of the estimator using simulated galaxy images designed to mimic the distribution of HST observations of lensed background sources in the CLASH galaxy cluster survey. Using the trained estimator, produce weak lensing shear maps of the cores of 20 galaxy clusters in the CLASH survey, demonstrating an RMS scatter reduced by approximately 26% when compared to maps produced with a commonly used shape estimator. This is equivalent to a survey speed enhancement of approximately 60%. However, given the non-transparent nature of the machine learning approach, this results requires further testing and validation. Provide python code to train and test this estimator on both simulated and real galaxy cluster observations. Also provide updated weak lensing catalogues for the 20 CLASH galaxy clusters studied.
1808.07551
The Dark Universe - Exercises and proceedings form the German-Italian WE Heraeus Summer School held in 2017 in Heidelberg
Brems, et al
The Heroes Summer School series "Astronomy from four perspectives", funded by the WE Heraeus Foundation, draws together teachers and teacher students, astronomers, physicists and astronomy students from Germany and Italy. For each summer school, participants gather at one of the four participating nodes: Heidelberg, Padua, Jena, and Florence. The main goal of the series is to bring astronomy into schools, which is achieved by educating and training the teachers and teacher students. In this e-print, present the exercises, tutorials, and high-school classroom materials developed during the fifth summer school of the series, which took place at House der Astronomie in Heidelberg Aug. 26 -- Sep. 2, 2017. The tutorials were prepared beforehand for the participants of the Summer schools, and are suitable for use in teacher training. Classroom material were developed mainly during the summer school itself, and are suitable for high-school level teaching. They include question sheets for pupils, and some pointers on where to use the material in the German high school curriculum. Both sets of materials address the summer school's four main topics: Supernova cosmology, the viral theorem, rotation curves of galaxies, and the temperature of the cosmic microwave background (CMB).
1808.07772
Easily interpretable bulk flows: continuing tension with the standard cosmological model
Peery, Watkins, Feldman
Present an improved Minimal Variance (MV) method for using a radial peculiar velocity sample to estimate the average of the three-dimensional velocity field over a spherical volume, which leads to an easily interpretable bulk flow measurement. The only assumption required is that the velocity field is irrotational. The resulting bulk flow estimate is particularly insensitive to smaller scale flows. Also introduce a new constraint into the MV method that ensures that bulk flow estimates are independent of the value of the Hubble constant H_0; this is important given the tension between the locally measured H_0 and that obtained from the CMB observations. Apply the method to the Cosmic Flows-3 catalogues and find that, while the bulk flows for shallower spheres are consistent with the standard cosmological model, there is some tension between the bulk flow in a spherical volume with radius 150 hMpc and its expectations; find only a ~2% chance of obtaining a bulk flow as large or larger in the standard cosmological model with Planck parameters.
1808.08235
'Upper-limit lensing': constraining galaxy stellar masses with singly-imaged background sources
Smith, Lucey, Collier
Strong gravitational lensing can provide accurate measurements of the stellar mass-to-light ratio Upsilon in low-z (<~0.05) early-type galaxies, and hence probe for possible variations in the stellar initial mass function (IMF). However, true multiple imaging lens systems are rare, hindering the construction of large nearby lens samples. Here, present a method to derive upper limits on Upsilon in galaxies with single close-projected background sources, where where no counter-image is detected, down to some relative flux limit. Present a proof-of-principle applications to 3 galaxies with integral field observations from different instruments. in the first case study, only a weak constraint on Upsilon is obtained. In the second, the absence of a detectable counter-image excludes stellar masses higher than expected for a Salpeter IMF. In the 3rd system, the current observations do not yield a useful limit, but the analysis indicates that deeper observations should reveal a counter-image if the stellar mass is any larger than expected for a MW IMF. Discuss how this method can help enlarge the current samples of low-z galaxies with lensing constraints, both by adding upper limits on Upsilon and by guiding follow-up to promising single-image systems in search of fainter counter-images.
1808.08800
Discovery of strongly inverted metallicity gradients in dwarf galaxies at $z$$\sim$2
Wang, Jones, Treu, et al
Report the first sub-kiloparsec spatial resolution measurements of strongly inverted gas-phase metallicity gradients in two dwarf galaxies at z~2. The galaxies have stellar masses ~1e9 Msun, sSFR ~20 Gyr^{-1}, and global metallicity 12+log(O/H)~8.1 (1/4 solar). Their metallicity radial gradients are measured to be highly inverted, i.e., 0.122±).008 and 0.111±0.017 dex/kpc, which is hitherto unseen at such small masses in similar redshift ranges. From the HST observations of the source nebular emission and stellar continuum, present the 2-dimensional spatial maps of SFR surface density, stellar population age, and gas fraction, which show that the galaxies are currently undergoing rapid mass assembly via disk inside-out growth. More importantly, using a simple chemical evolution model, find that the gas fractions for different metallicity regions cannot be explained by pure gas accretion. The spatially resolved analysis based on a more advanced gas regulator model results in a spatial map of net gaseous outflows, triggered by active central starbursts, that potentially play a significant role in shaping the spatial distribution of metallicity by effectively transporting stellar nucleosynthesis yields outwards. The relation between wind mass loading factors and stellar surface densities measured in different regions of the galaxies shows that a single type of wind mechanism, driven by either energy or momentum conservation, cannot explain the entire galaxy. These sources present a unique constraint on the effects of gas flows on the early phase of disk growth from the perspective of spatially resolved chemical evolution within individual systems.
1808.08912
On the measurement of the local Hubble constant from the superlimninal motion of the jet launched in GW170817
Dado, Dar
The direction of the axis of the orbital motion of the merging binary neutron stars in the GW170817 event coincided with that of the apparent superluminal jet, which produced the short hard gamma ray burst (SHB) 170817A. It supports the local value of the Hubble constant provided by standard candle Type Ia SNe, H_0=73.24±1.74 km/s/Mpc, which differs by 3 sigma from the cosmic value H_0=67.74±0.46 km/s/Mpc obtained from the CMB radiation by Planck assuming the standard LCDM cosmology. The measured superluminal motion of the jet also allows critical tests of the assumed production mechanism of SHBs in general and of SHB170817A in particular.
Wednesday, August 22, 2018
Day 1456
Thursday.
1808.07335
A unified analysis of four cosmic shear surveys
Chang, Wang, Dodelson, Eifler, Heymans, Jarvis, Jee, Joudaki, Krause, Malz, Mandelbaum, Mohammed, Schneider, Timet, Troxel, Zuntz
In the past few years, several independent collaborations have presented cosmological constraints from tomographic cosmic shear analyses. These analyses differ in many aspects: the datasets, the shear and photometric redshift estimation algorithms, the theory model assumptions, and they inference pipelines. To assess the robustness of the existing cosmic shear results, present in this paper a united analysis of four of the recent cosmic shear surveys: DLS, CFHTLenS, DES-SV, and KiDS-450. By using a unified pipeline, show how the cosmological constraints are sensitive to the various details of the pipeline. Identify several analysis choices that can shift the cosmological constraints by a significant fraction of the uncertainties. For the fiducial analysis choice, considering a Gaussian covariance, conservative scale cuts, assuming no baryonic feedback contamination, identical cosmological parameter priors and IA treatments, find the constraints (mean, 16% and 84% confidence intervals) on the parameter S_8==sigma_8 (Omega_m/0.3)^0.5 to be S_8=0.94_-0.045^+0.046 (DLS), 0.66-0.071+0.070 (CHFTLenS), 0.84-0.061+0.062 (DES-SV) and 0.76-0.049+0.048 (KiDS-450). From the goodness-of-fit and the Bayesian evidence ratio, determine that amongst the 4 surveys, the 2 more recent surveys, DES-SV and KiDS-450, have acceptable goodness-of-fit an are consistent with each other. The combined constraints are S_8=0.79+0.042-0.041, which is in good agreement with the first year of DES cosmic shear results and recent CMB constraints from the Planck satellite.
1808.07335
A unified analysis of four cosmic shear surveys
Chang, Wang, Dodelson, Eifler, Heymans, Jarvis, Jee, Joudaki, Krause, Malz, Mandelbaum, Mohammed, Schneider, Timet, Troxel, Zuntz
In the past few years, several independent collaborations have presented cosmological constraints from tomographic cosmic shear analyses. These analyses differ in many aspects: the datasets, the shear and photometric redshift estimation algorithms, the theory model assumptions, and they inference pipelines. To assess the robustness of the existing cosmic shear results, present in this paper a united analysis of four of the recent cosmic shear surveys: DLS, CFHTLenS, DES-SV, and KiDS-450. By using a unified pipeline, show how the cosmological constraints are sensitive to the various details of the pipeline. Identify several analysis choices that can shift the cosmological constraints by a significant fraction of the uncertainties. For the fiducial analysis choice, considering a Gaussian covariance, conservative scale cuts, assuming no baryonic feedback contamination, identical cosmological parameter priors and IA treatments, find the constraints (mean, 16% and 84% confidence intervals) on the parameter S_8==sigma_8 (Omega_m/0.3)^0.5 to be S_8=0.94_-0.045^+0.046 (DLS), 0.66-0.071+0.070 (CHFTLenS), 0.84-0.061+0.062 (DES-SV) and 0.76-0.049+0.048 (KiDS-450). From the goodness-of-fit and the Bayesian evidence ratio, determine that amongst the 4 surveys, the 2 more recent surveys, DES-SV and KiDS-450, have acceptable goodness-of-fit an are consistent with each other. The combined constraints are S_8=0.79+0.042-0.041, which is in good agreement with the first year of DES cosmic shear results and recent CMB constraints from the Planck satellite.
Tuesday, August 21, 2018
Day 1455
Wednesday.
1808.06615
Beyond the classical distance-redshift test: cross-correlating redshift-free standard candles and sirens with redshift surveys
Mukherjee, Wandelt
LSST will supply up to 1e6 SNe to constrain DE through the distance-redshift (D_L-z) test. Obtaining spectroscopic SN redshifts (spec-z's) is unfeasible; alternatives are suboptimal and may be biased. Propose a powerful multi-tracer generalization of the Alcock-Paczynski test that pairs redshift-free distance tracers and an overlapping galaxy redshift survey. Cross-correlating 5e4 redshift-free SNe with DESI or Euclid outperforms the classical D_L-z test with spec-zs for all SN. The method also applies to gravitational wave sirens or any z-free distance tracer.
Beyond the classical distance-redshift test: cross-correlating redshift-free standard candles and sirens with redshift surveys
Mukherjee, Wandelt
LSST will supply up to 1e6 SNe to constrain DE through the distance-redshift (D_L-z) test. Obtaining spectroscopic SN redshifts (spec-z's) is unfeasible; alternatives are suboptimal and may be biased. Propose a powerful multi-tracer generalization of the Alcock-Paczynski test that pairs redshift-free distance tracers and an overlapping galaxy redshift survey. Cross-correlating 5e4 redshift-free SNe with DESI or Euclid outperforms the classical D_L-z test with spec-zs for all SN. The method also applies to gravitational wave sirens or any z-free distance tracer.
Monday, August 20, 2018
Day 1454
Tuesday.
1808.05619
Testing the uniqueness of gravitational lens mass models
Wals, Williams
The positions of images produced by the gravitational lensing of background sources provide unique insight into galaxy-lens mass distribution. However, even quad images of extended sources are not able to fully characterize the central regions of the host galaxy. Most previous work has focused either on the radial density profile of the lenses or localized substructure clumps. Here, concentrate on the azimuthal mass asymmetries near the image circle. The motivation for considering such mass inhomogeneities is that the transition between the central stellar dominated region and the outer dark matter dominated region, though well represented by a power law density profile, is unlikely to be featureless, and encodes information about the dynamical state and assembly history of galaxies. It also happens to roughly coincide with the Einstein radius. Ask if galaxies that have mass asymmetries beyond ellipticity can be modeled with simpler lenses, i.e., can complex mass distributions masquerade as simple elliptical+shear lenses? The preliminary study indicates that for galaxies with elliptical stellar and dark matter distributions, but with no mass asymmetry, and an extended source filling the diamond caustic, an elliptical+shear lens model can reproduce the images well, thereby hiding the potential complexity of the actual mass distribution. For galaxies with non-zero mass asymmetry, the answer depends on the size and brightness distribution of the source, and its location within the diamond caustic. In roughly half of the cases considered, the mass asymmetries can easily evade detection.
1808.05695
Reconciling the diversity and uniformity of galactic rotation curves with self-interacting dark matter
Ren, Kwa, Kaplinghat, Yu
Galactic rotation curves exhibit diverse behavior in the inner regions, while obeying an organizing principle, i.e., they can be approximately described by a radial acceleration relation or the Modified Newtonian Dynamics phenomenology. Analyze the rotation curve data from the eSPARC sample, and explicitly demonstrate that both the diversity and uniformity are naturally reproduced in a hierarchical structure formation model with the addition of dark matter self-interactions. The required concentrations of the dark matter haloes are fully consistent with the concentration-mass relation predicted by the Planck cosmological model. The inferred stellar mass-to-light (3.6 um) ratios scatter around 0.5 Msun/Lsun, as expected from population synthesis models, leading to a tight radial acceleration relation and baryonic Tully-Fisher relation. The inferred stellar-halo mass relation is consistent with the expectations from abundance matching. These results indicate that the inner dark matter haloes of galaxies are thermalized due to the self-interactions of dark matter particles.
1808.05978
Larve Covariance Matrices: Accurate models without mocks
O'Connell, Eisenstein
Covariance matrix estimation is a persistent challenge for cosmology. Focus on a class of model covariance matrices that can be generated with high accuracy and precision, using a tiny fraction of the computational resources that would be required to achieve comparably precise covariance matrices using mock catalogues. In previous work, the free parameters in these models were determined using sample covariance matrices computed using a large number of mocks, but demonstrate that those parameters can be estimated consistently and with good precision by applying jackknife methods to a single survey volume. This enables model covariance matrices that are calibrated from data alone, with no reference to mocks.
1808.05619
Testing the uniqueness of gravitational lens mass models
Wals, Williams
The positions of images produced by the gravitational lensing of background sources provide unique insight into galaxy-lens mass distribution. However, even quad images of extended sources are not able to fully characterize the central regions of the host galaxy. Most previous work has focused either on the radial density profile of the lenses or localized substructure clumps. Here, concentrate on the azimuthal mass asymmetries near the image circle. The motivation for considering such mass inhomogeneities is that the transition between the central stellar dominated region and the outer dark matter dominated region, though well represented by a power law density profile, is unlikely to be featureless, and encodes information about the dynamical state and assembly history of galaxies. It also happens to roughly coincide with the Einstein radius. Ask if galaxies that have mass asymmetries beyond ellipticity can be modeled with simpler lenses, i.e., can complex mass distributions masquerade as simple elliptical+shear lenses? The preliminary study indicates that for galaxies with elliptical stellar and dark matter distributions, but with no mass asymmetry, and an extended source filling the diamond caustic, an elliptical+shear lens model can reproduce the images well, thereby hiding the potential complexity of the actual mass distribution. For galaxies with non-zero mass asymmetry, the answer depends on the size and brightness distribution of the source, and its location within the diamond caustic. In roughly half of the cases considered, the mass asymmetries can easily evade detection.
1808.05695
Reconciling the diversity and uniformity of galactic rotation curves with self-interacting dark matter
Ren, Kwa, Kaplinghat, Yu
Galactic rotation curves exhibit diverse behavior in the inner regions, while obeying an organizing principle, i.e., they can be approximately described by a radial acceleration relation or the Modified Newtonian Dynamics phenomenology. Analyze the rotation curve data from the eSPARC sample, and explicitly demonstrate that both the diversity and uniformity are naturally reproduced in a hierarchical structure formation model with the addition of dark matter self-interactions. The required concentrations of the dark matter haloes are fully consistent with the concentration-mass relation predicted by the Planck cosmological model. The inferred stellar mass-to-light (3.6 um) ratios scatter around 0.5 Msun/Lsun, as expected from population synthesis models, leading to a tight radial acceleration relation and baryonic Tully-Fisher relation. The inferred stellar-halo mass relation is consistent with the expectations from abundance matching. These results indicate that the inner dark matter haloes of galaxies are thermalized due to the self-interactions of dark matter particles.
1808.05978
Larve Covariance Matrices: Accurate models without mocks
O'Connell, Eisenstein
Covariance matrix estimation is a persistent challenge for cosmology. Focus on a class of model covariance matrices that can be generated with high accuracy and precision, using a tiny fraction of the computational resources that would be required to achieve comparably precise covariance matrices using mock catalogues. In previous work, the free parameters in these models were determined using sample covariance matrices computed using a large number of mocks, but demonstrate that those parameters can be estimated consistently and with good precision by applying jackknife methods to a single survey volume. This enables model covariance matrices that are calibrated from data alone, with no reference to mocks.
Sunday, August 19, 2018
Day 1453
Monday.
1808.05552
Least squares two-point function estimation
Tessore
The standard estimator for the 2pt function of a homogeneous and isotropic random field is a special case of a larger class of least squares estimators that interpolate the function values. Using a different interpolation scheme, 2pt function values can be estimated at specific distances, instead of the binned averages.
1808.05886
The lensing time delay between gravitational and electromagnetic waves
Cremonese, Mörtsell
The recent detection of gravitational waves (GWs) and EM waves originating from the same source makes the start of a new multi-messenger era in astronomy. The arrival time difference between the GW and EM signal can be used to constrain differences in their propagation speed, and thus gravitational theories. Study to what extent a non-zero time delay can be explained by gravitational lensing when the line of sight to the source passes near a massive object. For galaxy scale lenses, this delay becomes relevant for GWs with frequencies between 1e-6 and 1e-9 Hz, sourced by super massive binary black-holes. In addition to GWs detectable by Pulsar Timing Arrays (PTAs), expect to find also a unique and recognizable EM signal. Show that the delay between the GW and EM signal can be of the order of days to months; within reach of future observations. The effect may become important in future multi-messenger astronomy probing of gravitational propagation and interactions.
1808.05552
Least squares two-point function estimation
Tessore
The standard estimator for the 2pt function of a homogeneous and isotropic random field is a special case of a larger class of least squares estimators that interpolate the function values. Using a different interpolation scheme, 2pt function values can be estimated at specific distances, instead of the binned averages.
1808.05886
The lensing time delay between gravitational and electromagnetic waves
Cremonese, Mörtsell
The recent detection of gravitational waves (GWs) and EM waves originating from the same source makes the start of a new multi-messenger era in astronomy. The arrival time difference between the GW and EM signal can be used to constrain differences in their propagation speed, and thus gravitational theories. Study to what extent a non-zero time delay can be explained by gravitational lensing when the line of sight to the source passes near a massive object. For galaxy scale lenses, this delay becomes relevant for GWs with frequencies between 1e-6 and 1e-9 Hz, sourced by super massive binary black-holes. In addition to GWs detectable by Pulsar Timing Arrays (PTAs), expect to find also a unique and recognizable EM signal. Show that the delay between the GW and EM signal can be of the order of days to months; within reach of future observations. The effect may become important in future multi-messenger astronomy probing of gravitational propagation and interactions.
Thursday, August 16, 2018
Day 1452
Friday.
1808.05208
The evolution of the UV-to-mm extragalactic background light: evidence for a top-heavy initial mass function?
Cowley et al
Present predictions for the UV-to-mm extragalactic background light (EBL) from the GALFORM SAM of galaxy formation. Combine GALFORM with the GRASIL radiative transfer code for computing fully self-consistent UV-to-mm SEDs for each simulated galaxy, accounting for the absorption and re-emission of stellar radiation by interstellar dust. The predicted EBL is in near-perfect agreement with recent observations over the whole UV-to-mm spectrum, as is the evolution of the cosmic SED over the z range for which observations are available (z<~1). Show that approximately 90% of the EBL is produced at z<2 although this shifts to higher z for sub-mm wavelengths. Assess whether one of the more controversial aspects of the model, a top-heavy IMF for galaxies undergoing dynamically-triggered bursts of SF, is necessary in order to reproduce the EBL, and find that variant models with a universal solar-neighborhood IMF cannot produce as good agreement with EBL observations over the whole UV-to-mm spectrum.
1808.05223
Galaxy ellipticity measurements n the near-infrared for weak lensing
Lee, Chary, Wright
Investigate the value of the NIR imaging from upcoming surveys for constraining the ellipticities of galaxies. Select galaxies between 0.5<z<3 that are brighter than expected Euclid sensitivity limits from the GOODS-S and N fields in CANDELS. The co-added CANDELS/HST V+I and J+H imagine are degraded in resolution and sensitivity to simulate Euclid-quality optical and NIR images. Then run GALFIT on these simulated images and find that optical and NIR provide similar performance in measuring galaxy ellipticities at 0.5<z<3. At z>1.0, the NIR-selected source density is higher by a factor of 1.4 and therefore the scatter in NIR-derived ellipticities is about 30% smaller, implying a more precise ellipticity measurement. The good performance of the NIR is mainly because galaxies have an intrinsically smoother light distribution in the NIR bands than in the optical, the latter tracing the clumpy SF regions. In addition, the NIR bands have a higher surface brightness per pixel than the optical images, while being less affected by dust attenuation. Despite the worse spatial sampling and resolution of Euclid NIR compared to optical, the NIR approach yields equivalent or more precise galaxy ellipticity measurements. If systematics that affect shape such as dithering strategy and PSF under sampling can be mitigated, inclusion of the NIR can improve galaxy ellipticity measurements over all redshifts. This is particularly important for upcoming weak lensing surveys, such as with Euclid and WFIRST.
1808.05422
Accurate prediction of H$_3$O$^+$ and D$_3$O$^+$ sensitivity coefficients to probe a variable proton-to-electron mass ratio
Owens, et al
The mass sensitivity of the vibration-rotation-inversion transitions of H_3 ^16O^+, H_3 ^18O^+, and D_3 ^16O^+ is investigated variationally using the nuclear motion program TROVE. The calculations utilize new high-level ab initio potential energy and dipole moment surfaces. Along with the mass dependence, frequency data and Einstein A coefficients are computed for all transitions probed. Particular attention is paid to the Delta|k|=3 and Delta|k-l|=3 transitions comprising the accidentally coinciding |J,K=0, v_2=0^+> and |J,K=3, v_2=0^-> rotation-inversion energy levels. The newly computed probes exhibit sensitivities comparable to their ammonia and methanol counterparts, thus demonstrating their potential for testing the cosmological stability of the proton-to-electron mass ratio. The theoretical TROVE results are in close agreement with sensitivities obtained using the nonrigid and rigid inverter approximate models, confirming that the ab initio theory used in the present study is adequate.
1808.05208
The evolution of the UV-to-mm extragalactic background light: evidence for a top-heavy initial mass function?
Cowley et al
Present predictions for the UV-to-mm extragalactic background light (EBL) from the GALFORM SAM of galaxy formation. Combine GALFORM with the GRASIL radiative transfer code for computing fully self-consistent UV-to-mm SEDs for each simulated galaxy, accounting for the absorption and re-emission of stellar radiation by interstellar dust. The predicted EBL is in near-perfect agreement with recent observations over the whole UV-to-mm spectrum, as is the evolution of the cosmic SED over the z range for which observations are available (z<~1). Show that approximately 90% of the EBL is produced at z<2 although this shifts to higher z for sub-mm wavelengths. Assess whether one of the more controversial aspects of the model, a top-heavy IMF for galaxies undergoing dynamically-triggered bursts of SF, is necessary in order to reproduce the EBL, and find that variant models with a universal solar-neighborhood IMF cannot produce as good agreement with EBL observations over the whole UV-to-mm spectrum.
1808.05223
Galaxy ellipticity measurements n the near-infrared for weak lensing
Lee, Chary, Wright
Investigate the value of the NIR imaging from upcoming surveys for constraining the ellipticities of galaxies. Select galaxies between 0.5<z<3 that are brighter than expected Euclid sensitivity limits from the GOODS-S and N fields in CANDELS. The co-added CANDELS/HST V+I and J+H imagine are degraded in resolution and sensitivity to simulate Euclid-quality optical and NIR images. Then run GALFIT on these simulated images and find that optical and NIR provide similar performance in measuring galaxy ellipticities at 0.5<z<3. At z>1.0, the NIR-selected source density is higher by a factor of 1.4 and therefore the scatter in NIR-derived ellipticities is about 30% smaller, implying a more precise ellipticity measurement. The good performance of the NIR is mainly because galaxies have an intrinsically smoother light distribution in the NIR bands than in the optical, the latter tracing the clumpy SF regions. In addition, the NIR bands have a higher surface brightness per pixel than the optical images, while being less affected by dust attenuation. Despite the worse spatial sampling and resolution of Euclid NIR compared to optical, the NIR approach yields equivalent or more precise galaxy ellipticity measurements. If systematics that affect shape such as dithering strategy and PSF under sampling can be mitigated, inclusion of the NIR can improve galaxy ellipticity measurements over all redshifts. This is particularly important for upcoming weak lensing surveys, such as with Euclid and WFIRST.
1808.05422
Accurate prediction of H$_3$O$^+$ and D$_3$O$^+$ sensitivity coefficients to probe a variable proton-to-electron mass ratio
Owens, et al
The mass sensitivity of the vibration-rotation-inversion transitions of H_3 ^16O^+, H_3 ^18O^+, and D_3 ^16O^+ is investigated variationally using the nuclear motion program TROVE. The calculations utilize new high-level ab initio potential energy and dipole moment surfaces. Along with the mass dependence, frequency data and Einstein A coefficients are computed for all transitions probed. Particular attention is paid to the Delta|k|=3 and Delta|k-l|=3 transitions comprising the accidentally coinciding |J,K=0, v_2=0^+> and |J,K=3, v_2=0^-> rotation-inversion energy levels. The newly computed probes exhibit sensitivities comparable to their ammonia and methanol counterparts, thus demonstrating their potential for testing the cosmological stability of the proton-to-electron mass ratio. The theoretical TROVE results are in close agreement with sensitivities obtained using the nonrigid and rigid inverter approximate models, confirming that the ab initio theory used in the present study is adequate.
Wednesday, August 15, 2018
Day 1451
Thursday.
1808.04597
Apparent cosmic acceleration due to local bulk flow
Colin, et al
Recent observations reveal a bulk flow in the local Universe which is faster and extends to larger scales than is expected around a typical observer in the standard LCDM cosmology. The deceleration parameter q_0 derived from local observations is then expected to show a scale-dependent dipolar modulation. From a maximum likelihood analysis of the Joint Lightcurve Analysis catalogue of Type Ia SNe, find such a dipole in q_0 extending out to z~0.2, with a magnitude comparable to its monopole. Although not statistically significant in current data, such a dipole must be allowed for, especially in analyzing surveys with incomplete sky coverage such as JLA and its successor Pantheon; out of 740 (1048) SNe Ia in the JLA (Pantheon) catalogues, 632 (890) are in the hemisphere opposite to the direction of bulk flow for which their redshifts have been corrected. However the monopole component of q_0, which has been widely ascribed to a cosmological constant (dark energy), drops in statistical significance and becomes consistent with zero at 2 sigma (95% CL). This suggests that the apparent acceleration of the expansion rate deduced from supernovae may be an artifact of the bulk flow.
1808.04977
CPz: Classification-aided photometric-redshift estimation
Fotopoulou, Paltani
Broadband photometry offers a time and cost effective method to reconstruct the continuum emission of celestial objects. Thus, photometric redshift estimation has supported the scientific exploitation of extragalactic multi wavelength surveys for more than twenty years. in the era of precision cosmology, with the upcoming Euclid and LSST surveys, very tight constraints are put on the expected performance of photometric redshift estimation using broadband photometry, thus new methods have to be developed in order to reach the required performance. Present a novel automatic method of optimizing photometric z performance, the classification-aided photometric redshift estimation (CPz). The main feature of CPz is the unified treatment of all classes of objects detected in extragalactic surveys: galaxies of any type (passive, star forming and starbursts), AGN, QSO, stars and also include the identification of potential photometric z catastrophic outliers. The method operates in 3 stages. First, the photometric catalog is confronted with star, galaxy and QSO model templates by means of SED fitting. Second, 3 machine-learning classifiers are used to identify 1) the probability of each source to be a star, 2) the optimal photo-z model library set-up for each source and 3) the probability to be a photo-z catastrophic outlier. Lastly, the final sample is assembled by identifying the probability thresholds to be applied on the outcome of each of the 3 classifiers. Apply the method to the near-IR VISTA public surveys, matched with optical photometry from CFHTLS, KIDS and SDSS, mid-infrared WISE photometry. Show that CPz offers improved photometric z performance for both normal galaxies and AGN without the need for extra X-ray information.
1808.05099
Astroid mining with small spacecraft and its economic feasibility
Calla, Fries, Welch
Asteroid mining offers the possibility to revolutionize supply and availability of many resources vital for human civilization. Analysis suggests that Near-Earth Asteroids (NEA) contain enough volatile and high value minerals to make the mining process economically feasible. Considering possible applications, specifically the mining of water in space has become a major focus for near-term options. Most proposed projects for asteroid mining, however, involve spacecraft based on traditional designs resulting in large, monolithic and expensive systems. An alternative approach is presented in this paper, basing the asteroid mining process on multiple small spacecraft, i.e. a decentralized architecture. To the best knowledge of the authors, limited thorough analysis of the astroid mining capability of small spacecraft has been conducted. This paper explores the lower limit of spacecraft size for asteroid mining operations. After defining a feasible miniaturized spacecraft design, capable of extracting water from astroids and transporting it to an appropriate orbit, a high-level economic analysis is performed. This analysis reveals several key constraints in making near-term asteroid mining financially sustainable under the assumptions given in this study.
1808.04597
Apparent cosmic acceleration due to local bulk flow
Colin, et al
Recent observations reveal a bulk flow in the local Universe which is faster and extends to larger scales than is expected around a typical observer in the standard LCDM cosmology. The deceleration parameter q_0 derived from local observations is then expected to show a scale-dependent dipolar modulation. From a maximum likelihood analysis of the Joint Lightcurve Analysis catalogue of Type Ia SNe, find such a dipole in q_0 extending out to z~0.2, with a magnitude comparable to its monopole. Although not statistically significant in current data, such a dipole must be allowed for, especially in analyzing surveys with incomplete sky coverage such as JLA and its successor Pantheon; out of 740 (1048) SNe Ia in the JLA (Pantheon) catalogues, 632 (890) are in the hemisphere opposite to the direction of bulk flow for which their redshifts have been corrected. However the monopole component of q_0, which has been widely ascribed to a cosmological constant (dark energy), drops in statistical significance and becomes consistent with zero at 2 sigma (95% CL). This suggests that the apparent acceleration of the expansion rate deduced from supernovae may be an artifact of the bulk flow.
1808.04977
CPz: Classification-aided photometric-redshift estimation
Fotopoulou, Paltani
Broadband photometry offers a time and cost effective method to reconstruct the continuum emission of celestial objects. Thus, photometric redshift estimation has supported the scientific exploitation of extragalactic multi wavelength surveys for more than twenty years. in the era of precision cosmology, with the upcoming Euclid and LSST surveys, very tight constraints are put on the expected performance of photometric redshift estimation using broadband photometry, thus new methods have to be developed in order to reach the required performance. Present a novel automatic method of optimizing photometric z performance, the classification-aided photometric redshift estimation (CPz). The main feature of CPz is the unified treatment of all classes of objects detected in extragalactic surveys: galaxies of any type (passive, star forming and starbursts), AGN, QSO, stars and also include the identification of potential photometric z catastrophic outliers. The method operates in 3 stages. First, the photometric catalog is confronted with star, galaxy and QSO model templates by means of SED fitting. Second, 3 machine-learning classifiers are used to identify 1) the probability of each source to be a star, 2) the optimal photo-z model library set-up for each source and 3) the probability to be a photo-z catastrophic outlier. Lastly, the final sample is assembled by identifying the probability thresholds to be applied on the outcome of each of the 3 classifiers. Apply the method to the near-IR VISTA public surveys, matched with optical photometry from CFHTLS, KIDS and SDSS, mid-infrared WISE photometry. Show that CPz offers improved photometric z performance for both normal galaxies and AGN without the need for extra X-ray information.
1808.05099
Astroid mining with small spacecraft and its economic feasibility
Calla, Fries, Welch
Asteroid mining offers the possibility to revolutionize supply and availability of many resources vital for human civilization. Analysis suggests that Near-Earth Asteroids (NEA) contain enough volatile and high value minerals to make the mining process economically feasible. Considering possible applications, specifically the mining of water in space has become a major focus for near-term options. Most proposed projects for asteroid mining, however, involve spacecraft based on traditional designs resulting in large, monolithic and expensive systems. An alternative approach is presented in this paper, basing the asteroid mining process on multiple small spacecraft, i.e. a decentralized architecture. To the best knowledge of the authors, limited thorough analysis of the astroid mining capability of small spacecraft has been conducted. This paper explores the lower limit of spacecraft size for asteroid mining operations. After defining a feasible miniaturized spacecraft design, capable of extracting water from astroids and transporting it to an appropriate orbit, a high-level economic analysis is performed. This analysis reveals several key constraints in making near-term asteroid mining financially sustainable under the assumptions given in this study.
Day 1450
Wednesday.
1808.03654
How low does it go? Too few Galactic satellites with standard reionization quenching
Graus, et al
A standard prediction of galaxy formation theory is that the ionizing background suppresses galaxy formation in haloes with peak circular velocities smaller than V_peak ~20 km/s, rendering the majority of haloes below this scale completely dark. Use a suite of cosmological zoom simulations of MW-like haloes that include central MW disk galaxy potentials to investigate the relationship between sub haloes and ultra faint galaxies. Find that there are far too few sub haloes within 50 kpc of the MW that had V_peak > 20 km/s to account for the number of ultra faint galaxies already known within that volume today. In order to match the observed count, must populate sub haloes down to V_peak~6 km/s with ultra faint dwarfs. The required haloes have peak viral temperatures as low as 1500 K, well below the atomic H cooling limit of 1e4 K. Allowing for the possibility that the LMC contributes several of the satellites within 50 kpc could potentially raise this threshold to 10 km/s (4000 K), still below the atomic cooling limit and for below the nominal reioinization threshold.
1808.04083
Measuring the duration of last scattering
Hadzhiyska, Spergel
The CMB fluctuations effectively measure the basic properties of the universe during the recombination epoch. CMB measurements fix the distance to the surface of last scatter, the sound horizon of the baryon-photon fluid and the fraction of the energy density in relativistic species. Show that the microwave background observations can also very effectively constrain the thickness of the last scattering surface, which is directly related to the ratio of the small-scale E_mode polarization signal to the small-scale temperature signal. The current cosmological data enables a 0.1% measurement of the thickness of the surface of fast scatter: 19±0.065 Mpc. This constraint is relatively model-independent, so it can provide a new metric for systematic errors and an independent test of the LCDM model. On the other hand, it is sensitive to models which affect the reionization history of the universe such as models with annihilating dark matter and varying fundamental constants (e.g., the fine-structure constant, alpha_EM, and electron rest mass, m_e) and as such can be used as a viable tool to constrain them.
1808.04367
New constraints one IGM thermal evolution from the Ly{\alpha} forest power spectrum
Walther, et al
Determine the thermal evolution of the IGM over 3 Gyr of cosmic time 1.8<z<5.4 by comparing measurements of the Ly_alpha forest power spectrum to a suite of ~70 hydro sims. Conduct Bayesian inference of IGM thermal parameters using an end-to-end forward modeling framework whereby mock spectra generated form the simulation grid are used to build a custom emulator which interpolates the PS between thermal grid points. The temperature at mean density T0 rises steadily from T0 ~ 6000 K at z=5.4, peaks at 14000 K at z~3.4, and decreases at lower z reading T0 ~ 7000K by z~1.8. This evolution provides conclusive evidence for photoionization heating resulting from the reioinization of He II, as well as the subsequent cooling of the IGM due to the expansion of the Universe after all reioinization events are complete. The results are broadly consistent with previous measurements of thermal evolution based on a variety of approaches, but the sensitivity of the PS, the combination of high precision BOSS measurements of large-scale modes (k <~ 0.02 s/km) with the recent determination of the small-scale power, the large grid of models, and the careful statistical analysis allow breaking of the well known degeneracy between the temperature at mean density T0 and the slope of the temperature density relation gamma that has plagued previous analyses. At the highest redshifts z>=5, infer lower temperatures than expected from the standard picture of IGM thermal evolution leaving little room for additional smoothing of the Ly_alpha forest by free streaming of warm dark matter.
1808.04384
The impact of wrong assumptions in BAO reconstruction
Sherwin, White
The process of density field reconstruction enhances the statistical power of distance scale measurements using BAO. During the process a fiducial cosmology is assumed in order to convert sky coordinates and redshifts into distances; fiducial bias and z-space-distortion parameters are also assumed in the procedure. Analytically assess the impact of incorrect cosmology and bias assumptions on the post-reconstruction PS using low-order Lagrangian perturbation theory, deriving general expressions for the incorrectly reconstructed spectra. Find that the BAO peak location appears to shift only by a negligible amount due to wrong assumptions made during reconstruction. However, the shape of the BAO peak and the quadrupole amplitude can be affected by such errors (at the percet- and five-percet-level respectively), which potentially could cause small biases in parameter inference for future surveys; outline solutions to such complications.
How low does it go? Too few Galactic satellites with standard reionization quenching
Graus, et al
A standard prediction of galaxy formation theory is that the ionizing background suppresses galaxy formation in haloes with peak circular velocities smaller than V_peak ~20 km/s, rendering the majority of haloes below this scale completely dark. Use a suite of cosmological zoom simulations of MW-like haloes that include central MW disk galaxy potentials to investigate the relationship between sub haloes and ultra faint galaxies. Find that there are far too few sub haloes within 50 kpc of the MW that had V_peak > 20 km/s to account for the number of ultra faint galaxies already known within that volume today. In order to match the observed count, must populate sub haloes down to V_peak~6 km/s with ultra faint dwarfs. The required haloes have peak viral temperatures as low as 1500 K, well below the atomic H cooling limit of 1e4 K. Allowing for the possibility that the LMC contributes several of the satellites within 50 kpc could potentially raise this threshold to 10 km/s (4000 K), still below the atomic cooling limit and for below the nominal reioinization threshold.
1808.04083
Measuring the duration of last scattering
Hadzhiyska, Spergel
The CMB fluctuations effectively measure the basic properties of the universe during the recombination epoch. CMB measurements fix the distance to the surface of last scatter, the sound horizon of the baryon-photon fluid and the fraction of the energy density in relativistic species. Show that the microwave background observations can also very effectively constrain the thickness of the last scattering surface, which is directly related to the ratio of the small-scale E_mode polarization signal to the small-scale temperature signal. The current cosmological data enables a 0.1% measurement of the thickness of the surface of fast scatter: 19±0.065 Mpc. This constraint is relatively model-independent, so it can provide a new metric for systematic errors and an independent test of the LCDM model. On the other hand, it is sensitive to models which affect the reionization history of the universe such as models with annihilating dark matter and varying fundamental constants (e.g., the fine-structure constant, alpha_EM, and electron rest mass, m_e) and as such can be used as a viable tool to constrain them.
1808.04367
New constraints one IGM thermal evolution from the Ly{\alpha} forest power spectrum
Walther, et al
Determine the thermal evolution of the IGM over 3 Gyr of cosmic time 1.8<z<5.4 by comparing measurements of the Ly_alpha forest power spectrum to a suite of ~70 hydro sims. Conduct Bayesian inference of IGM thermal parameters using an end-to-end forward modeling framework whereby mock spectra generated form the simulation grid are used to build a custom emulator which interpolates the PS between thermal grid points. The temperature at mean density T0 rises steadily from T0 ~ 6000 K at z=5.4, peaks at 14000 K at z~3.4, and decreases at lower z reading T0 ~ 7000K by z~1.8. This evolution provides conclusive evidence for photoionization heating resulting from the reioinization of He II, as well as the subsequent cooling of the IGM due to the expansion of the Universe after all reioinization events are complete. The results are broadly consistent with previous measurements of thermal evolution based on a variety of approaches, but the sensitivity of the PS, the combination of high precision BOSS measurements of large-scale modes (k <~ 0.02 s/km) with the recent determination of the small-scale power, the large grid of models, and the careful statistical analysis allow breaking of the well known degeneracy between the temperature at mean density T0 and the slope of the temperature density relation gamma that has plagued previous analyses. At the highest redshifts z>=5, infer lower temperatures than expected from the standard picture of IGM thermal evolution leaving little room for additional smoothing of the Ly_alpha forest by free streaming of warm dark matter.
1808.04384
The impact of wrong assumptions in BAO reconstruction
Sherwin, White
The process of density field reconstruction enhances the statistical power of distance scale measurements using BAO. During the process a fiducial cosmology is assumed in order to convert sky coordinates and redshifts into distances; fiducial bias and z-space-distortion parameters are also assumed in the procedure. Analytically assess the impact of incorrect cosmology and bias assumptions on the post-reconstruction PS using low-order Lagrangian perturbation theory, deriving general expressions for the incorrectly reconstructed spectra. Find that the BAO peak location appears to shift only by a negligible amount due to wrong assumptions made during reconstruction. However, the shape of the BAO peak and the quadrupole amplitude can be affected by such errors (at the percet- and five-percet-level respectively), which potentially could cause small biases in parameter inference for future surveys; outline solutions to such complications.
Monday, August 13, 2018
Day 1449
Thursday. Friday. Monday. Tuesday.
1808.02525
Angular momentum and galaxy formation revisited: scaling relations for disks and bulges
Fall, Romanowsky
Show that the stellar specific angular momentum j*, mass M* and bulge fraction beta* of normal galaxies of all morphological types are consistent with a simple model based on a linear superposition of independent disks and bulges. In this model, disks and bulges follow scaling relations of the form j*, d~M*, d^alpha and j*, b~M*, b^alpha with alpha=0.67±0.07 but offset from each other by a factor 8±3, over the mass range 8.9 <= log(M*/M_sun)<=11.8. Separate fits for disks and bulges alone give apha=0.58±0.10 and alpha=0.83±0.16, respectively. This model correctly predicts that galaxies follow a curved 2d surface in the 3d space of j*, M*, and beta*. Find no statistical significant indication that galaxies with classical and pseudo bulges follow different relations in this space, although some differences are permitted within the observed scatter and the inherent uncertainties in decomposing galaxies into disks and bulges. As a byproduct of this analysis, show that the j*-M* scaling relations for disk-dominated galaxies from several previous studies are in excellent agreement with each other. In addition, resolve some conflicting claims about the beta*-dependence of the j*-M* scaling relations. The results presented here reinforce and extend the earlier suggestion path the distribution of galaxies with different beta* in the j*-M* diagram constitutes an objective, physically-motivated alternative to subjective classification schemes such as the Hubble sequence.
1808.02532
Predictions for the sky-averaged depth of the 21cm absorption signal at high redshift in cosmologies with and without non-baryonic cold dark matter
McGaugh
Consider the 21cm absorption signal expected at high z in cosmologies with and without non-baryonic cold dark matter. The expansion of the early universe decelerates strongly with dark matter, but approximately coasts without it. This results in a different path length across the epochs when absorption is expected, with the consequence that the absorption is predicted to be a factor of ~2 greater without dark matter than with it. Observation of such a signal would motivate consideration of extended theories of gravity in lieu of dark matter.
1808.02593
Testing shear recovery with field distortion
Zhang, et al
The tilt, rotation, or offset of each CCD with respect to the focal plane, as well as the distortion of the focal plane itself, cause shape distortions to the observed objects, an effect typically known as field distortion (FD). Point out that FD provides a unique way of quantifying the accuracy of cosmic shear measurement. The idea is to stack the shear estimators from galaxies that share similar FD-induced shape distortions. Given that the latter can be calculated with parameters from astrometric calibrations, the accuracy of the shear estimator can be directly tested on real images. It provides a way to calibrate the multiplicative and additive shear recovery biases within the scientific data itself, without incurring simulations or any external data sets. Use the CFHTLenS images to demonstrate the accuracy of the Fourier+Quad shear recovery method. Highlight some details in the image processing pipeline, including background removal, source identification and deblending, astrometric calibration, star selection for PSF reconstruction, noise reduction, etc. Show that in the shear ranges of -0.005 < g1 < 0.005 and -0.008 < g2 < 0.008, there are no visible multiplicative biases on the order of 0.04. Slight additive biases on the order of 5e-4 (6 sigma) are identified for sources provided by the official CFHTLenS catalog (not using its shear catalog), but are minor (4 sigma) for source catalog generated by the Fourier_Quad pipeline.
1808.02828
The 'Cosmic Seagull': a highly magnified disk-like galaxy at z~2.8 behind the Bullet Cluster
Motta, et al
Present Atacama Large Millimeter/submillimeter Array measurements of the 'Cosmic Seagull', a strongly magnified galaxy at z=2.7779 behind the Bullet Cluster. Report CO(3-2) and continuum 344 um (rest-frame) data at one of the highest differential magnifications ever recorded at sub millimeter wavelengths (mu up to ~50), facilitating a characterization of the kinematics of a rotational curve in great detail (at ~620 pc resolution in the source plane). Find no evidence for a decreasing rotation curve, from which a dynamical mass of (6.3±0.7)e10 Msun within r=2.6±0.1 kpc is derived. The discovery of a third, unpredicted, image provides key information for a future improvement of the lensing modeling of the Bullet Cluster and allows a measure of the stellar mass, 1.6+1.9-0.86e10 Msun, unaffected by strong differential magnification. The baryonic mass is expected to be dominated by the molecular gas content (f_gas=80±20%) based on an M_H2 mass estimated from the difference between dynamical and stellar masses. The star formation rate is estimated via the spectral energy distribution (SFR=190±10 Msun/yr), implying a molecular gas depletion time of 0.25±0.08 Gyr.
1808.02573
Investigation of the orientation of galaxies in clusters: the importance, methods and results of research
Pajowska, et al
Various models of structure formation can account for various aspects of the galaxy formation process on different scales, as well as for various observational features of structures. Thus, the investigation of galaxies orientation constitute a standard test of galaxies formation scenarios since observed variations in angular momentum represent fundamental constraints for any model of galaxy formation. Improve upon the method of analysis of the alignment of galaxies in clusters. The method allows analysis of both position angles of galaxy major axes and two angles describing the spatial orientation of galaxies. The distributions of analyzed angles were tested for isotropy by applying different statistical tests. For the sample of analyzed clusters, compute the mean values of analyzed statistics, checking whether they are the same as the expected ones in the case of random distribution of analyzed angles. The detailed discussion of this method has been performed. Show how to proceed in many particular cases in order to improve the statistical reasoning when analyzing the distribution of the angles in the observational data. Separately, compare these new results with those obtained from numerical simulations. Show the power of the method on the example of galaxy orientation analysis in 247 Abell rich galaxy clusters. Find that the orientations of galaxies in analyzed clusters are not random. This confirms an existence of the alignment of galaxies in rich Abells' galaxy clusters. This result is independent for the clusters of Bautz-Morgan types.
1808.02896
The evolution of assembly bias
Contreras, Zehavi, et al
Examine the evolution of assembly bias using a semi-analytical model of galaxy formation implemented in the Millennium-WMAP7 N-body sim. Consider fixed number density galaxy samples ranked by stellar mass or SFR. Investigate how the clustering of haloes and their galaxy content depend on halo formation time and concentration, and how these relationships evolve with redshift. At z=0 the dependencies of halo clustering on halo concentration and formation time are similar. However, at higher redshift, halo assembly bias weakens for haloes selected by age, and reverses and increases for haloes selected by concentration. The variation of the halo occupation with concentration and formation time is also similar at z=0 and changes at higher redshifts. In this case, the occupancy variation with halo age stays mostly constant with redshift but decreases for concentration. Finally, look at the evolution of assembly bias reflected in the galaxy distribution by examining the galaxy correlation functions relative to those of shuffled galaxy samples which remove the occupancy variation. This correlation functions ratio monotonically decreases with larger redshift and for lower number density samples, going below unity in some cases, leading to reduced galaxy clustering. While the halo occupation functions themselves vary, the assembly bias trends are similar whether selecting galaxies by stellar mass or SFR. The results provide further insight into the origin and evolution of assembly bias. The extensive occupation function measurements and fits are publicly available and can be used to create realistic mock catalogues.
1808.03088
The central cusps in dark matter haloes: fact or fiction?
Bauschev, Pilipenko
Investigate the reliability of standard N-body simulations by modeling of the well-known Hernquist halo with the help of GADGET-2 code (which uses the tree algorithm to calculate the gravitational force) and ph4 code (which uses the direct summation). Comparing the results, find that the core formation in the halo center (which is conventionally considered as the first sign of numerical effects, to be specific, of the collisional relaxation) has nothing to do with the collisional relaxation, being defined by the properties of the tree algorithm. This result cases doubts on the universally adopted criteria of the simulation reliability in the halo center. Though a halo model is used, which is theoretically proved to be stationary and stable, a sort of numerical 'violent relaxation' occurs. Its properties suggest that this effect is highly likely responsible for the central cusp formation in cosmological modeling of the large-scale structure, and then the 'core-cusp problem' is no more than a technical problem of N-body simulations.
1808.03294
Extragalactic imprinted in galactic dust maps
Chiang, Ménard
Extragalactic astronomy relies on the accurate estimation of source photometry corrected for Milky Way dust extinction. This has motivated the creation of a number of "Galactic" dust maps. Investigate whether these maps are contaminated by extragalactic signals using the so-called clustering redshift technique, i.e., by measuring a set of angular cross-correlations with spectroscopic galaxies and quasars as a function of redshift. The tomographic analysis reveals imprints of extragalactic large-scale structure patterns in 9 (out of 10) Galactic dust maps, including all infrared-based maps as well as "stellar" reddening maps. When such maps are used for extinction corrections, this extragalactic contamination introduces redshift- and scale-dependent biases in photometric estimates at the milli-magnitude level. It can affect both object-based analyses such as the estimation of the Hubble diagram with SNe as well as spatial statistics. The bias can be appreciable when measuring angular correlation functions with low amplitudes such as lensing-induced correlations or angular correlations for sources distributed over a broad redshift range. As expected, do not detect any extragalactic contamination for the dust map inferred from the distribution of HI from 21 cm observations. Such a map provides an alternative to widely used IR-based maps but relies on the assumption of a constant dust-to-gas ratio. Note that using the WISE 12 um map sensitive to Polycyclic Aromatic Hydrocarbons (PAH), an indirect dust tracer, detect the diffuse extragalactic PAH background up to z~2. For precision cosmology experiments using optical photometry, recommend to test the robustness of the final results against different dust maps used. Finally, provide a procedure to correct for or decrease the level of biased magnitude corrections in maps with extragalactic imprints.
1808.03410
The missing satellite problem outside of the Local Group: I -- Pilot observation
Tanaka, et al
Present results from a pilot observation of nearby (~20 Mpc) galaxies with mass similar to that of the MW to address the missing satellite problem. This is the first paper from an on-gong project to address the problem with a statistical sample of galaxies outside of the LG without employing an assumption that the LG is a typical halo in the Universe. Thanks to the close distances of the targets, dwarf galaxies around them can be identified as extended, diffuse galaxies. By applying a surface brightness cut tighter with a careful visual screening to remove artifacts and background contamination, construct a sample of dwarf galaxies. The luminosity function (LF) of one of the targets is broadly consistent with that of the MW, but the other has a more abundant dwarf population. Numerical simulations by Okamoto (2013) seem to over predict the number of dwarfs on average, while more recent predictions from Copernius Complexio are in a better agreement. In both observations and simulations there is a large diversity in the LFs, demonstrating the importance of addressing the missing satellite problem with a statistically representative sample. Also characterize the projected spatial distributions of the satellites and do not observe strong evidence for alignments around the central galaxies. Based on this successful pilot observation, carry out further observations to increase the sample of nearby galaxies, which is planned to be reported in future paper(s).
1808.03501
Quantifying the power spectrum of small-scale structure in semi-analytic galaxies
Brennan, et al
In the CDM picture of structure formation, galaxy mass distributions are predicted to have a considerable amount of structure on small scales. Strong gravitational lensing has proven to be a useful tool for studying this small-scale structure. Much of the attention has been given to detecting individual DM sub haloes through lens modeling, but recent work has suggested that the full population of sub haloes could be probed using a power spectrum analysis. In this paper, quantify the PS of small-scale structure in simulated galaxies, with the goal of understanding theoretical predictions and setting the stage for using measurements of the PS to test DM models. Use a sample of simulated galaxies generated from the Galactic semi-analytic model to determine the PS distribution first in the CDM paradigm and then in a warm dark matter scenario. Find that a measurement of the slope and amplitude of the power spectrum on galaxy strong lensing scales (k~1kpc^{-1}) could be used to distinguish between CDM and alternate DM models, especially if the most massive sub haloes can be directly detected via gravitational imaging.
1808.03940
Measurements and implications of cosmic ray anisotropies from TeV to trans-EeV energies
Deligny
Important observational results have been recently reported on the angular distributions of cosmic rays at all energies, calling into question the perception of CRs a decade ago. These results together with their in-progress interpretations are summarized in this review paper, covering both large-scale and small-scale anisotropies from TeV energies to the highest ones. While the magnetic field in the Galaxy has long been considered as an external data imprinting a quasi-random walk to particles and thus shaping the angular distributions of Galactic cosmic rays through the induced average density gradient, the information encompassed in the angular distributions in the TeV-PeV energy range appear today as a promising tool to infer some properties of the local magnetic field environments. At the highest energies, the extragalactic origin of the particles has been recently determined observationally. While no discrete source of ultrahigh-energy cosmic rays has been identified so far, the noose is tightening around nearby extragalactic objets, and some prospects are discussed.
1808.02525
Angular momentum and galaxy formation revisited: scaling relations for disks and bulges
Fall, Romanowsky
Show that the stellar specific angular momentum j*, mass M* and bulge fraction beta* of normal galaxies of all morphological types are consistent with a simple model based on a linear superposition of independent disks and bulges. In this model, disks and bulges follow scaling relations of the form j*, d~M*, d^alpha and j*, b~M*, b^alpha with alpha=0.67±0.07 but offset from each other by a factor 8±3, over the mass range 8.9 <= log(M*/M_sun)<=11.8. Separate fits for disks and bulges alone give apha=0.58±0.10 and alpha=0.83±0.16, respectively. This model correctly predicts that galaxies follow a curved 2d surface in the 3d space of j*, M*, and beta*. Find no statistical significant indication that galaxies with classical and pseudo bulges follow different relations in this space, although some differences are permitted within the observed scatter and the inherent uncertainties in decomposing galaxies into disks and bulges. As a byproduct of this analysis, show that the j*-M* scaling relations for disk-dominated galaxies from several previous studies are in excellent agreement with each other. In addition, resolve some conflicting claims about the beta*-dependence of the j*-M* scaling relations. The results presented here reinforce and extend the earlier suggestion path the distribution of galaxies with different beta* in the j*-M* diagram constitutes an objective, physically-motivated alternative to subjective classification schemes such as the Hubble sequence.
1808.02532
Predictions for the sky-averaged depth of the 21cm absorption signal at high redshift in cosmologies with and without non-baryonic cold dark matter
McGaugh
Consider the 21cm absorption signal expected at high z in cosmologies with and without non-baryonic cold dark matter. The expansion of the early universe decelerates strongly with dark matter, but approximately coasts without it. This results in a different path length across the epochs when absorption is expected, with the consequence that the absorption is predicted to be a factor of ~2 greater without dark matter than with it. Observation of such a signal would motivate consideration of extended theories of gravity in lieu of dark matter.
1808.02593
Testing shear recovery with field distortion
Zhang, et al
The tilt, rotation, or offset of each CCD with respect to the focal plane, as well as the distortion of the focal plane itself, cause shape distortions to the observed objects, an effect typically known as field distortion (FD). Point out that FD provides a unique way of quantifying the accuracy of cosmic shear measurement. The idea is to stack the shear estimators from galaxies that share similar FD-induced shape distortions. Given that the latter can be calculated with parameters from astrometric calibrations, the accuracy of the shear estimator can be directly tested on real images. It provides a way to calibrate the multiplicative and additive shear recovery biases within the scientific data itself, without incurring simulations or any external data sets. Use the CFHTLenS images to demonstrate the accuracy of the Fourier+Quad shear recovery method. Highlight some details in the image processing pipeline, including background removal, source identification and deblending, astrometric calibration, star selection for PSF reconstruction, noise reduction, etc. Show that in the shear ranges of -0.005 < g1 < 0.005 and -0.008 < g2 < 0.008, there are no visible multiplicative biases on the order of 0.04. Slight additive biases on the order of 5e-4 (6 sigma) are identified for sources provided by the official CFHTLenS catalog (not using its shear catalog), but are minor (4 sigma) for source catalog generated by the Fourier_Quad pipeline.
1808.02828
The 'Cosmic Seagull': a highly magnified disk-like galaxy at z~2.8 behind the Bullet Cluster
Motta, et al
Present Atacama Large Millimeter/submillimeter Array measurements of the 'Cosmic Seagull', a strongly magnified galaxy at z=2.7779 behind the Bullet Cluster. Report CO(3-2) and continuum 344 um (rest-frame) data at one of the highest differential magnifications ever recorded at sub millimeter wavelengths (mu up to ~50), facilitating a characterization of the kinematics of a rotational curve in great detail (at ~620 pc resolution in the source plane). Find no evidence for a decreasing rotation curve, from which a dynamical mass of (6.3±0.7)e10 Msun within r=2.6±0.1 kpc is derived. The discovery of a third, unpredicted, image provides key information for a future improvement of the lensing modeling of the Bullet Cluster and allows a measure of the stellar mass, 1.6+1.9-0.86e10 Msun, unaffected by strong differential magnification. The baryonic mass is expected to be dominated by the molecular gas content (f_gas=80±20%) based on an M_H2 mass estimated from the difference between dynamical and stellar masses. The star formation rate is estimated via the spectral energy distribution (SFR=190±10 Msun/yr), implying a molecular gas depletion time of 0.25±0.08 Gyr.
1808.02573
Investigation of the orientation of galaxies in clusters: the importance, methods and results of research
Pajowska, et al
Various models of structure formation can account for various aspects of the galaxy formation process on different scales, as well as for various observational features of structures. Thus, the investigation of galaxies orientation constitute a standard test of galaxies formation scenarios since observed variations in angular momentum represent fundamental constraints for any model of galaxy formation. Improve upon the method of analysis of the alignment of galaxies in clusters. The method allows analysis of both position angles of galaxy major axes and two angles describing the spatial orientation of galaxies. The distributions of analyzed angles were tested for isotropy by applying different statistical tests. For the sample of analyzed clusters, compute the mean values of analyzed statistics, checking whether they are the same as the expected ones in the case of random distribution of analyzed angles. The detailed discussion of this method has been performed. Show how to proceed in many particular cases in order to improve the statistical reasoning when analyzing the distribution of the angles in the observational data. Separately, compare these new results with those obtained from numerical simulations. Show the power of the method on the example of galaxy orientation analysis in 247 Abell rich galaxy clusters. Find that the orientations of galaxies in analyzed clusters are not random. This confirms an existence of the alignment of galaxies in rich Abells' galaxy clusters. This result is independent for the clusters of Bautz-Morgan types.
1808.02896
The evolution of assembly bias
Contreras, Zehavi, et al
Examine the evolution of assembly bias using a semi-analytical model of galaxy formation implemented in the Millennium-WMAP7 N-body sim. Consider fixed number density galaxy samples ranked by stellar mass or SFR. Investigate how the clustering of haloes and their galaxy content depend on halo formation time and concentration, and how these relationships evolve with redshift. At z=0 the dependencies of halo clustering on halo concentration and formation time are similar. However, at higher redshift, halo assembly bias weakens for haloes selected by age, and reverses and increases for haloes selected by concentration. The variation of the halo occupation with concentration and formation time is also similar at z=0 and changes at higher redshifts. In this case, the occupancy variation with halo age stays mostly constant with redshift but decreases for concentration. Finally, look at the evolution of assembly bias reflected in the galaxy distribution by examining the galaxy correlation functions relative to those of shuffled galaxy samples which remove the occupancy variation. This correlation functions ratio monotonically decreases with larger redshift and for lower number density samples, going below unity in some cases, leading to reduced galaxy clustering. While the halo occupation functions themselves vary, the assembly bias trends are similar whether selecting galaxies by stellar mass or SFR. The results provide further insight into the origin and evolution of assembly bias. The extensive occupation function measurements and fits are publicly available and can be used to create realistic mock catalogues.
1808.03088
The central cusps in dark matter haloes: fact or fiction?
Bauschev, Pilipenko
Investigate the reliability of standard N-body simulations by modeling of the well-known Hernquist halo with the help of GADGET-2 code (which uses the tree algorithm to calculate the gravitational force) and ph4 code (which uses the direct summation). Comparing the results, find that the core formation in the halo center (which is conventionally considered as the first sign of numerical effects, to be specific, of the collisional relaxation) has nothing to do with the collisional relaxation, being defined by the properties of the tree algorithm. This result cases doubts on the universally adopted criteria of the simulation reliability in the halo center. Though a halo model is used, which is theoretically proved to be stationary and stable, a sort of numerical 'violent relaxation' occurs. Its properties suggest that this effect is highly likely responsible for the central cusp formation in cosmological modeling of the large-scale structure, and then the 'core-cusp problem' is no more than a technical problem of N-body simulations.
1808.03294
Extragalactic imprinted in galactic dust maps
Chiang, Ménard
Extragalactic astronomy relies on the accurate estimation of source photometry corrected for Milky Way dust extinction. This has motivated the creation of a number of "Galactic" dust maps. Investigate whether these maps are contaminated by extragalactic signals using the so-called clustering redshift technique, i.e., by measuring a set of angular cross-correlations with spectroscopic galaxies and quasars as a function of redshift. The tomographic analysis reveals imprints of extragalactic large-scale structure patterns in 9 (out of 10) Galactic dust maps, including all infrared-based maps as well as "stellar" reddening maps. When such maps are used for extinction corrections, this extragalactic contamination introduces redshift- and scale-dependent biases in photometric estimates at the milli-magnitude level. It can affect both object-based analyses such as the estimation of the Hubble diagram with SNe as well as spatial statistics. The bias can be appreciable when measuring angular correlation functions with low amplitudes such as lensing-induced correlations or angular correlations for sources distributed over a broad redshift range. As expected, do not detect any extragalactic contamination for the dust map inferred from the distribution of HI from 21 cm observations. Such a map provides an alternative to widely used IR-based maps but relies on the assumption of a constant dust-to-gas ratio. Note that using the WISE 12 um map sensitive to Polycyclic Aromatic Hydrocarbons (PAH), an indirect dust tracer, detect the diffuse extragalactic PAH background up to z~2. For precision cosmology experiments using optical photometry, recommend to test the robustness of the final results against different dust maps used. Finally, provide a procedure to correct for or decrease the level of biased magnitude corrections in maps with extragalactic imprints.
1808.03410
The missing satellite problem outside of the Local Group: I -- Pilot observation
Tanaka, et al
Present results from a pilot observation of nearby (~20 Mpc) galaxies with mass similar to that of the MW to address the missing satellite problem. This is the first paper from an on-gong project to address the problem with a statistical sample of galaxies outside of the LG without employing an assumption that the LG is a typical halo in the Universe. Thanks to the close distances of the targets, dwarf galaxies around them can be identified as extended, diffuse galaxies. By applying a surface brightness cut tighter with a careful visual screening to remove artifacts and background contamination, construct a sample of dwarf galaxies. The luminosity function (LF) of one of the targets is broadly consistent with that of the MW, but the other has a more abundant dwarf population. Numerical simulations by Okamoto (2013) seem to over predict the number of dwarfs on average, while more recent predictions from Copernius Complexio are in a better agreement. In both observations and simulations there is a large diversity in the LFs, demonstrating the importance of addressing the missing satellite problem with a statistically representative sample. Also characterize the projected spatial distributions of the satellites and do not observe strong evidence for alignments around the central galaxies. Based on this successful pilot observation, carry out further observations to increase the sample of nearby galaxies, which is planned to be reported in future paper(s).
1808.03501
Quantifying the power spectrum of small-scale structure in semi-analytic galaxies
Brennan, et al
In the CDM picture of structure formation, galaxy mass distributions are predicted to have a considerable amount of structure on small scales. Strong gravitational lensing has proven to be a useful tool for studying this small-scale structure. Much of the attention has been given to detecting individual DM sub haloes through lens modeling, but recent work has suggested that the full population of sub haloes could be probed using a power spectrum analysis. In this paper, quantify the PS of small-scale structure in simulated galaxies, with the goal of understanding theoretical predictions and setting the stage for using measurements of the PS to test DM models. Use a sample of simulated galaxies generated from the Galactic semi-analytic model to determine the PS distribution first in the CDM paradigm and then in a warm dark matter scenario. Find that a measurement of the slope and amplitude of the power spectrum on galaxy strong lensing scales (k~1kpc^{-1}) could be used to distinguish between CDM and alternate DM models, especially if the most massive sub haloes can be directly detected via gravitational imaging.
1808.03940
Measurements and implications of cosmic ray anisotropies from TeV to trans-EeV energies
Deligny
Important observational results have been recently reported on the angular distributions of cosmic rays at all energies, calling into question the perception of CRs a decade ago. These results together with their in-progress interpretations are summarized in this review paper, covering both large-scale and small-scale anisotropies from TeV energies to the highest ones. While the magnetic field in the Galaxy has long been considered as an external data imprinting a quasi-random walk to particles and thus shaping the angular distributions of Galactic cosmic rays through the induced average density gradient, the information encompassed in the angular distributions in the TeV-PeV energy range appear today as a promising tool to infer some properties of the local magnetic field environments. At the highest energies, the extragalactic origin of the particles has been recently determined observationally. While no discrete source of ultrahigh-energy cosmic rays has been identified so far, the noose is tightening around nearby extragalactic objets, and some prospects are discussed.
Wednesday, August 8, 2018
Day 1448
Wednesday.
1808.01740
Apparent evidence for Hawking points in the CMB sky
An, et al
Present powerful observational evidence of anomalous individual points in the very early universe that appear to be sources of vast amounts of energy, revealed as specific signals found in the CMB sky. Though seemingly problematic for cosmic inflation, the existence of such anomalous points is an implication of conformal cyclic cosmology (CCC), as what could be the Hawking points of the theory, these being the effects of the final Hawking evaporation of supermassive black holes in the aeon prior to ours. Although of extremely low temperature at emission, in CCC this radiation is enormously concentrated by the conformal compression of the entire future of the black hole, resulting in a single point at the crossover into the current aeon, with the emission of vast numbers of particles, whose effects appear to be seen as the observed anomalous points. The B-mode location found by BICEP2 is at one of these anomalous points.
1808.02136
Correlations between the dark matter and baryonic properties of CLASH galaxy clusters
Del Popolo, Umetsu, Le Delliou, Lee
Study the total and DM density profiles as well as their correlations for a sample of 15 high-mass galaxy clusters by extending the previous work on several clusters from Newman+. The analysis focuses on 15 CLASH X-ray-selected clusters that have high-quality weak- and strong-lensing measurements from combined Subaru and HST observations. The total density profiles derived from lensing are interpreted based on the 2-phase scenario of cluster formation. In this context, the BCG forms in the first dissipative phase, followed by a dissipation less phase where baryonic physics flattens the inner DM distribution. This results in the formation of clusters with modified DM distribution and several correlations between characteristic quantities of the clusters. Find that the central DM density profiles of the clusters are strongly influenced by baryonic physics as found in earlier works. The inner slope of the DM density for the CLASH clusters is found to be flatter than the NFW profile, ranging from alpha=0.30 to 0.79. Examine correlations of the DM density slope alpha with the effective radius R_e and stellar mass M_e of the BCG, finding that these quantities are anti-correlated with a Spearman correlation coefficient of ~-0.6. Also study the correlation between R_e and the cluster halo mass M_500, and the correlation between the total masses inside 5 kpc and 100 kpc. Find that these quantities are correlated with Spearman coefficients of 0.68 and 0.64, respectively. These observed correlations are in support of the physical picture proposed by Newman+.
1808.0248
Cosmic-ray anisotropy from large scale structure and the effect of magnetic horizons
Globus, et al
Motivated by the ~7% dipole anisotropy in the distribution of ultra-high energy cosmic-rays (UHECRs) above 8 EeV, explore the anisotropy induced by the large scale structure, using constrained simulations of the local Universe and taking into account the effect of magnetic fields. The value of the intergalactic magnetic field (IGMF) is critical as it determines the UHECR cosmic horizon. Calculate the UHECR sky maps for different values of the IGMF variance and show the effect of the UHECR horizon on the observed anisotropy. The footprint of the local (<~350 Mpc) Universe on the UHECR background, a small angular scale enhancement in the Northern Hemisphere, is seen. At 11.5 EeV (the median value of the energy bin at which the dipole has been reported), the LSS-indiced dipole amplitude is A_1~10%, for IGMF in the range [0.3-3] nG for protons, Helium and Nitrogen, compatible with the rms value derived from the cosmic power spectrum. However at these energies the UHECRs are also influenced by the galactic magnetic field (GMF); discuss its effect on the LSS-indiced anisotropy.
1808.01740
Apparent evidence for Hawking points in the CMB sky
An, et al
Present powerful observational evidence of anomalous individual points in the very early universe that appear to be sources of vast amounts of energy, revealed as specific signals found in the CMB sky. Though seemingly problematic for cosmic inflation, the existence of such anomalous points is an implication of conformal cyclic cosmology (CCC), as what could be the Hawking points of the theory, these being the effects of the final Hawking evaporation of supermassive black holes in the aeon prior to ours. Although of extremely low temperature at emission, in CCC this radiation is enormously concentrated by the conformal compression of the entire future of the black hole, resulting in a single point at the crossover into the current aeon, with the emission of vast numbers of particles, whose effects appear to be seen as the observed anomalous points. The B-mode location found by BICEP2 is at one of these anomalous points.
1808.02136
Correlations between the dark matter and baryonic properties of CLASH galaxy clusters
Del Popolo, Umetsu, Le Delliou, Lee
Study the total and DM density profiles as well as their correlations for a sample of 15 high-mass galaxy clusters by extending the previous work on several clusters from Newman+. The analysis focuses on 15 CLASH X-ray-selected clusters that have high-quality weak- and strong-lensing measurements from combined Subaru and HST observations. The total density profiles derived from lensing are interpreted based on the 2-phase scenario of cluster formation. In this context, the BCG forms in the first dissipative phase, followed by a dissipation less phase where baryonic physics flattens the inner DM distribution. This results in the formation of clusters with modified DM distribution and several correlations between characteristic quantities of the clusters. Find that the central DM density profiles of the clusters are strongly influenced by baryonic physics as found in earlier works. The inner slope of the DM density for the CLASH clusters is found to be flatter than the NFW profile, ranging from alpha=0.30 to 0.79. Examine correlations of the DM density slope alpha with the effective radius R_e and stellar mass M_e of the BCG, finding that these quantities are anti-correlated with a Spearman correlation coefficient of ~-0.6. Also study the correlation between R_e and the cluster halo mass M_500, and the correlation between the total masses inside 5 kpc and 100 kpc. Find that these quantities are correlated with Spearman coefficients of 0.68 and 0.64, respectively. These observed correlations are in support of the physical picture proposed by Newman+.
1808.0248
Cosmic-ray anisotropy from large scale structure and the effect of magnetic horizons
Globus, et al
Motivated by the ~7% dipole anisotropy in the distribution of ultra-high energy cosmic-rays (UHECRs) above 8 EeV, explore the anisotropy induced by the large scale structure, using constrained simulations of the local Universe and taking into account the effect of magnetic fields. The value of the intergalactic magnetic field (IGMF) is critical as it determines the UHECR cosmic horizon. Calculate the UHECR sky maps for different values of the IGMF variance and show the effect of the UHECR horizon on the observed anisotropy. The footprint of the local (<~350 Mpc) Universe on the UHECR background, a small angular scale enhancement in the Northern Hemisphere, is seen. At 11.5 EeV (the median value of the energy bin at which the dipole has been reported), the LSS-indiced dipole amplitude is A_1~10%, for IGMF in the range [0.3-3] nG for protons, Helium and Nitrogen, compatible with the rms value derived from the cosmic power spectrum. However at these energies the UHECRs are also influenced by the galactic magnetic field (GMF); discuss its effect on the LSS-indiced anisotropy.
Tuesday, August 7, 2018
Day 1447
Tuesday.
1808.00969
The fast, luminous ultraviolet transient AT2018cow: Extreme supernova, or disruption of a star by a n intermediate-mass black hole?
Perley, et al
Wide-field optical surveys have begun to uncover large samples of fast (t_rise<5d), luminous (M_peak<-18), blue transients. While commonly attributed to the breakout of supernova shock into a dense wind, the great distances to the transients of this class found so far have hampered a detailed investigation of their properties until now. Present photometry and spectroscopy from a comprehensive worldwide campaign to observe AT2018cow (ATLAS18qqn), the first fast-luminous optical transient to be found in real time at low z. The first spectra (< 2days after discovery) are entirely featureless. A very broad absorption feature suggestive of near-relativistic velocities develops between 3-8 days, then disappears. Broad emission features of H and He develop after >10 days. The spectrum remains extremely hot throughout its evolution, and the photospheric radius contracts with time (receding below R<1e14 cm after 1 month). This behavior does not match that of any known supernova, although a relativistic jet within a fallback supernova could explain some of the observed features. Alternatively, the transient could originate from the disruption of a star by an intermediate-mass BH, although this would require long-lasting emission of highly super-Eddington thermal radiation. In either case, AT 2018cow suggests that the population of fast luminous transients represents a new class of astrophysical event. Intensive follow-up of this event in its late phases, and of any future events found at comparable distance, will be essential to better constrain their origins.
1808.01753
GAMA/G10-COSMOS/3D-HST: evolution of the galaxy stellar mass function over 12.5 Gyrs
Wright, Driver, Robotham
Using a combined and consistently analysed GAMA, G10-COSMOS, ad 3D-HST dataset, explore the evolution of the galaxy stellar-mass function over lookback times t_L in [0.2,12.5] h^{-1}_70 Gyr. Use a series of volume limited samples to fit Schechter functions in bins of ~constant lookback time and explore the evolution of the best-fit parameters in both single and two-component cases. In all cases, employ a fitting procedure that is robust to the effects of Eddington bias and sample variance. Surprisingly, when fitting a two-component Schechter function, find essentially no evidence of temporal evolution in M_star, the two alpha slope parameters, or the normalization of the low-mass component. Instead, the fits suggest that the various shape parameters have been exceptionally stable over cosmic time, as has the normalization of the low-mass component, and that the evolution of the stellar-mass function is well described by a simple build up of the high-mass component over time. When fitting a single component Schechter function, there is an observed evolution in both M_star and alpha, however this is interpreted as being an artifact. Finally, find that the evolution of the stellar-mass function, and the observed stellar mass density, can be well described by a simple model of constant growth in the high-mass source density over the last 11 h^{-1}_70 Gyrs.
1808.00969
The fast, luminous ultraviolet transient AT2018cow: Extreme supernova, or disruption of a star by a n intermediate-mass black hole?
Perley, et al
Wide-field optical surveys have begun to uncover large samples of fast (t_rise<5d), luminous (M_peak<-18), blue transients. While commonly attributed to the breakout of supernova shock into a dense wind, the great distances to the transients of this class found so far have hampered a detailed investigation of their properties until now. Present photometry and spectroscopy from a comprehensive worldwide campaign to observe AT2018cow (ATLAS18qqn), the first fast-luminous optical transient to be found in real time at low z. The first spectra (< 2days after discovery) are entirely featureless. A very broad absorption feature suggestive of near-relativistic velocities develops between 3-8 days, then disappears. Broad emission features of H and He develop after >10 days. The spectrum remains extremely hot throughout its evolution, and the photospheric radius contracts with time (receding below R<1e14 cm after 1 month). This behavior does not match that of any known supernova, although a relativistic jet within a fallback supernova could explain some of the observed features. Alternatively, the transient could originate from the disruption of a star by an intermediate-mass BH, although this would require long-lasting emission of highly super-Eddington thermal radiation. In either case, AT 2018cow suggests that the population of fast luminous transients represents a new class of astrophysical event. Intensive follow-up of this event in its late phases, and of any future events found at comparable distance, will be essential to better constrain their origins.
1808.01753
GAMA/G10-COSMOS/3D-HST: evolution of the galaxy stellar mass function over 12.5 Gyrs
Wright, Driver, Robotham
Using a combined and consistently analysed GAMA, G10-COSMOS, ad 3D-HST dataset, explore the evolution of the galaxy stellar-mass function over lookback times t_L in [0.2,12.5] h^{-1}_70 Gyr. Use a series of volume limited samples to fit Schechter functions in bins of ~constant lookback time and explore the evolution of the best-fit parameters in both single and two-component cases. In all cases, employ a fitting procedure that is robust to the effects of Eddington bias and sample variance. Surprisingly, when fitting a two-component Schechter function, find essentially no evidence of temporal evolution in M_star, the two alpha slope parameters, or the normalization of the low-mass component. Instead, the fits suggest that the various shape parameters have been exceptionally stable over cosmic time, as has the normalization of the low-mass component, and that the evolution of the stellar-mass function is well described by a simple build up of the high-mass component over time. When fitting a single component Schechter function, there is an observed evolution in both M_star and alpha, however this is interpreted as being an artifact. Finally, find that the evolution of the stellar-mass function, and the observed stellar mass density, can be well described by a simple model of constant growth in the high-mass source density over the last 11 h^{-1}_70 Gyrs.
Monday, August 6, 2018
Day 1446
Monday. Tuesday. Wednesday. Thursday. Friday. Monday.
1807.11075
The theory of inflation
Martin
This article contains a concise review of the theory of inflation. Discuss its main theoretical aspects as well as its observational predictions. Also explain how the most recent astrophysical observations constrain the inflationary scenario.
1807.11461
3D cosmic shear: numerical challenges, 3d lensing random fields generation and Minkowski functionals for cosmological inference
Mancini, et al
Cosmic shear - the weak gravitational lensing effect generated by fluctuations of the gravitational tidal fields of the large-scale structure - is one of the most promising tools for current and future cosmological analyses. The spherical-Bessel decomposition of the cosmic shear field ("3D cosmic shear") is one way to maximize the amount of redshift information in a lensing analysis and therefore provides a powerful tool to investigate in particular the growth of cosmic structure that is crucial for dark energy studies. However, the computation of simulated 3D cosmic shear covariance matrices presents numerical difficulties, due to the required integrations over highly oscillatory functions. Present and compare two numerical methods and relative implementations to perform these integrations. Then show how to generate 3D Gaussian random fields in spherical coordinates, starting from 3D cosmic shear covariances. To validate the field-generation procedure, calculate the Minkowski functionals associated with the random fields, compare them with the known expectation values for the Gaussian case and demonstrate parameter inference from Minkowski functions from a cosmic shear survey. This is a first step towards producing fully 3D Minkowski functionals for a lognormal field in 3D to extract Gaussian and non-Gaussian information from the cosmic shear field, as well as towards the use of Minkowski functionals as a probe of cosmology beyond the commonly used 2pt statistics.
1807.11077
Prediction of astrometric microlensing events from Gaia DR2 proper motions
Klüter, et al
Astrometric gravitational microlensing is an excellent tool to determine the mass of stellar objects. Using precise astrometric measurements of the lensed position of a background source in combination with accurate predictions of the positions of lens and unlensed source it is possible to determine the mass of the lens with an accuracy of a few percent. Making use of the recently published Gaia DR2 catalogue, predict astrometric microlensing events by foreground stars with higher proper motion passing a background source in the next decades. Select roughly 148k high-proper-motion stars from Gaia DR2 with mu_tot>150 mas/yr as potential lenses. Then search for background sources close to their paths. Using the astrometric parameters of Gaia DR2, calculate the future positions of source and lens. With a nested-intervals algorithm, determine the date and separation of the closest approach. Using Gaia DR2 photometry, determine an approximate mass of the lens, which is used to calculate the expected microlensing effects. Predict 3914 microlensing events by 2875 different lenses between 2010 and 2065 with expected shifts larger than 0.1 mas between the lensed and unlicensed positions of the source. 513 of those are expected to happen between 2014.5-2026.5 and might be measured by Gaia. For 127 events, also expect a magnification between 1 mag and 3 mag.
1807.11940
Real-space computation of $E$/$B$-mode maps I: Formalism, compact kernels, and polarized filaments
Rotti, Huffenberger
Derive full-sky, real-space operators that convert between polarization Stokes Q/U parameters and the coordinate-independent scalar E/B modes that are widely used in CMB and cosmic shear analysis. Also derive real space operators that decompose the measured Stokes parameters into those corresponding to E-modes and B-modes respectively, without ever evaluating the scalar fields themselves. For all these real space operators, show that the kernels split naturally into angular and radial parts and show explicitly how the radial extent of these kernels depends on the targeted band-limit. The kernels can be interpreted either as a complex convolving beam or as a Green's function when they are expressed in terms of the forward or inverse rotation Euler angles. Show that an arbitrary radial function can produce E/B-like maps, provided it vanishes at the origin and the antipodal point. These maps are simply filtered versions of the standard E/B maps. Argue that it is possible to compute E/B maps in real space with a compactly-supported kernel, an approach that can guarantee the avoidance of known foreground regions and could be employed in a massively-parallel scheme at high-resolution. Show that the spin raising and lowering operators eth^2/\bar{eth}^2 are special cases of these generalized radial functions, and present their band limited version. The spatial structure of the real space operators provides great intuition of the E/B structure of polarized, filamentary galactic foregrounds. Predict a non-zero B-mode signature that is expected from polorized filaments in the sky. This paper is the first part in a series of papers that explore real-space computation of polarization modes and their applications.
1807.11488
Intracluster light: a luminous tracer for dark matter in clusters of galaxies
Montes, Trujillo
The bulk of stars in galaxy clusters are confined within their constituent galaxies Those stars do not trace the extended distribution of dark matter well as they are located in the central regions of the cluster's dark matter sub-haloes. A small fraction of stars is expected, however, to follow the global DM shape of the cluster. These are the stars whose extended spatial distribution results from the merging activity of galaxies and form the intracluster light (ICL). In this work, compare the bi-directional distribution of DM in massive galaxy clusters (as traced by gravitational lensing models) with the distribution of the ICL. To do that, use the exquisite data from the Hubble Frontier Fields Initiative. Using the Modified Hausdorff distance (MHD) as a way of quantifying the similarities between the mass and ICL distributions, find an excellent agreement (MHD~25 kpc) between the two components. This result shows that the ICL exquisitely follows the global DM distribution, providing an accurate luminous tracer of DM. This finding opens up the possibility of exploring the distribution of DM in galaxy clusters in detail using only deep imaging observations.
1808.00015
Detection of the milky way spiral arms in dust from 3d mapping
Rasaei Kh., Bailer-Jones, Hogg, Schultheis
Large stellar surveys are sensitive to interstellar dust through the effects of reddening. Using extinctions measured from photometry and spectroscopy, together with 3d positions of individual stars, it is possible to construct a 3d dust map. Present the first continuous map of the list distribution in the Galactic disk out to 7 kpc within 100 pc of the Galactic mid plane, using red clump and giant stars from SDSS APOGEE DR14. Use a non-parametric method based on Gaussian Processes to map the dust density, which is the local property of the ISM rather than an integrated quantity. This method models the dust correlation between points in 3d space and can capture arbitrary variations, unconstrained by a pre-specified functional form. This produces a continuous map without line-of-sight artifacts. The resulting map traces some features of the local Galactic spiral arms, even though the model contains no prior suggestion of spiral arms, nor any underlying model for the Galactic structure. This is the first time that such evident arm structures have been captured by a dust density map in the MW. The resulting map also traces some of the known giant molecular clouds in the Galaxy and puts some constraints on their distances, some of which were hitherto relatively uncertain.
1808.00357
Effects of neutrino mass and asymmetry on cosmological structure formation
Zeng, Yeung, Chu
Light but massive cosmological neutrinos do not cluster significantly on small scales, due to their high thermal velocities. With finite masses, cosmological neutrinos become part of the total matter field and contribute to its smoothing Structure formation in the presence of massive neutrinos is therefore impeded compared to that in the standard LCDM cosmology with massless neutrinos. Neutrinos' masses also distort the anisotropy power spectrum of CMB. Furthermore, a finite chemical potential mu for cosmological neutrinos, still allowed by current data, would have a nonn-neigligible impact on CMB and structure formation. Consistently evaluate effects of neutrino masses and chemical potentials on the matter PS by use of a neutrino-involved N-body sim, with cosmo parameters obtained from a MCMC refitting of CMB data. The results show that while a finite averaged neutrino mass m_nu tends to suppress the matter power spectrum in a range of wave numbers, the neutrino degeneracy parameters xi_i == mu_i/T (i=1,2,3) enhance the latter, leading to a large parameter degeneracy between m_nu and xi_i. Provide an empirical formula for the effects on the matter power spectrum in a selected range of wave numbers induced by m_nu and eta == set (sum_i xi^2_i. Observing a strong correlation between m_nu and eta, propose a single z-independent parameter m_nu - (4/3)eta^2 to characterize the neutrino effects on the matter power spectrum.
1808.00464
First constraints on fuzzy dark matter from the dynamics of stellar streams in the Milky Way
Amorisco, Loeb
Present a novel method to constrain the mass of ultra-light bosons as the DM using stellar streams formed by disrupting Globular Clusters in the Milky Way. The turbulent density field of Fuzzy Dark Matter (FDM) haloes results in perturbations and dynamical heating of thin streams. Using numerical simulations based on an effective model, explore the magnitude of this phenomenon and show that this is observable for the range of axion masses m_a that is interesting for alleviating the 'small-scale problems' of LCDM. Derive an analytical model for the thickening of thin stellar streams and obtain an early conservative lower limit for the boson mass of m_a>1.5e-22 eV, using pre-Gaia literature data for six MW streams and after marginalizing over physical parameters. This demonstrates the great promise for using this novel dynamical method as a full independent probe of FDM, to complement results based on Lyman-alpha forest data.
1807.11075
The theory of inflation
Martin
This article contains a concise review of the theory of inflation. Discuss its main theoretical aspects as well as its observational predictions. Also explain how the most recent astrophysical observations constrain the inflationary scenario.
1807.11461
3D cosmic shear: numerical challenges, 3d lensing random fields generation and Minkowski functionals for cosmological inference
Mancini, et al
Cosmic shear - the weak gravitational lensing effect generated by fluctuations of the gravitational tidal fields of the large-scale structure - is one of the most promising tools for current and future cosmological analyses. The spherical-Bessel decomposition of the cosmic shear field ("3D cosmic shear") is one way to maximize the amount of redshift information in a lensing analysis and therefore provides a powerful tool to investigate in particular the growth of cosmic structure that is crucial for dark energy studies. However, the computation of simulated 3D cosmic shear covariance matrices presents numerical difficulties, due to the required integrations over highly oscillatory functions. Present and compare two numerical methods and relative implementations to perform these integrations. Then show how to generate 3D Gaussian random fields in spherical coordinates, starting from 3D cosmic shear covariances. To validate the field-generation procedure, calculate the Minkowski functionals associated with the random fields, compare them with the known expectation values for the Gaussian case and demonstrate parameter inference from Minkowski functions from a cosmic shear survey. This is a first step towards producing fully 3D Minkowski functionals for a lognormal field in 3D to extract Gaussian and non-Gaussian information from the cosmic shear field, as well as towards the use of Minkowski functionals as a probe of cosmology beyond the commonly used 2pt statistics.
1807.11077
Prediction of astrometric microlensing events from Gaia DR2 proper motions
Klüter, et al
Astrometric gravitational microlensing is an excellent tool to determine the mass of stellar objects. Using precise astrometric measurements of the lensed position of a background source in combination with accurate predictions of the positions of lens and unlensed source it is possible to determine the mass of the lens with an accuracy of a few percent. Making use of the recently published Gaia DR2 catalogue, predict astrometric microlensing events by foreground stars with higher proper motion passing a background source in the next decades. Select roughly 148k high-proper-motion stars from Gaia DR2 with mu_tot>150 mas/yr as potential lenses. Then search for background sources close to their paths. Using the astrometric parameters of Gaia DR2, calculate the future positions of source and lens. With a nested-intervals algorithm, determine the date and separation of the closest approach. Using Gaia DR2 photometry, determine an approximate mass of the lens, which is used to calculate the expected microlensing effects. Predict 3914 microlensing events by 2875 different lenses between 2010 and 2065 with expected shifts larger than 0.1 mas between the lensed and unlicensed positions of the source. 513 of those are expected to happen between 2014.5-2026.5 and might be measured by Gaia. For 127 events, also expect a magnification between 1 mag and 3 mag.
1807.11940
Real-space computation of $E$/$B$-mode maps I: Formalism, compact kernels, and polarized filaments
Rotti, Huffenberger
Derive full-sky, real-space operators that convert between polarization Stokes Q/U parameters and the coordinate-independent scalar E/B modes that are widely used in CMB and cosmic shear analysis. Also derive real space operators that decompose the measured Stokes parameters into those corresponding to E-modes and B-modes respectively, without ever evaluating the scalar fields themselves. For all these real space operators, show that the kernels split naturally into angular and radial parts and show explicitly how the radial extent of these kernels depends on the targeted band-limit. The kernels can be interpreted either as a complex convolving beam or as a Green's function when they are expressed in terms of the forward or inverse rotation Euler angles. Show that an arbitrary radial function can produce E/B-like maps, provided it vanishes at the origin and the antipodal point. These maps are simply filtered versions of the standard E/B maps. Argue that it is possible to compute E/B maps in real space with a compactly-supported kernel, an approach that can guarantee the avoidance of known foreground regions and could be employed in a massively-parallel scheme at high-resolution. Show that the spin raising and lowering operators eth^2/\bar{eth}^2 are special cases of these generalized radial functions, and present their band limited version. The spatial structure of the real space operators provides great intuition of the E/B structure of polarized, filamentary galactic foregrounds. Predict a non-zero B-mode signature that is expected from polorized filaments in the sky. This paper is the first part in a series of papers that explore real-space computation of polarization modes and their applications.
1807.11488
Intracluster light: a luminous tracer for dark matter in clusters of galaxies
Montes, Trujillo
The bulk of stars in galaxy clusters are confined within their constituent galaxies Those stars do not trace the extended distribution of dark matter well as they are located in the central regions of the cluster's dark matter sub-haloes. A small fraction of stars is expected, however, to follow the global DM shape of the cluster. These are the stars whose extended spatial distribution results from the merging activity of galaxies and form the intracluster light (ICL). In this work, compare the bi-directional distribution of DM in massive galaxy clusters (as traced by gravitational lensing models) with the distribution of the ICL. To do that, use the exquisite data from the Hubble Frontier Fields Initiative. Using the Modified Hausdorff distance (MHD) as a way of quantifying the similarities between the mass and ICL distributions, find an excellent agreement (MHD~25 kpc) between the two components. This result shows that the ICL exquisitely follows the global DM distribution, providing an accurate luminous tracer of DM. This finding opens up the possibility of exploring the distribution of DM in galaxy clusters in detail using only deep imaging observations.
1808.00015
Detection of the milky way spiral arms in dust from 3d mapping
Rasaei Kh., Bailer-Jones, Hogg, Schultheis
Large stellar surveys are sensitive to interstellar dust through the effects of reddening. Using extinctions measured from photometry and spectroscopy, together with 3d positions of individual stars, it is possible to construct a 3d dust map. Present the first continuous map of the list distribution in the Galactic disk out to 7 kpc within 100 pc of the Galactic mid plane, using red clump and giant stars from SDSS APOGEE DR14. Use a non-parametric method based on Gaussian Processes to map the dust density, which is the local property of the ISM rather than an integrated quantity. This method models the dust correlation between points in 3d space and can capture arbitrary variations, unconstrained by a pre-specified functional form. This produces a continuous map without line-of-sight artifacts. The resulting map traces some features of the local Galactic spiral arms, even though the model contains no prior suggestion of spiral arms, nor any underlying model for the Galactic structure. This is the first time that such evident arm structures have been captured by a dust density map in the MW. The resulting map also traces some of the known giant molecular clouds in the Galaxy and puts some constraints on their distances, some of which were hitherto relatively uncertain.
1808.00357
Effects of neutrino mass and asymmetry on cosmological structure formation
Zeng, Yeung, Chu
Light but massive cosmological neutrinos do not cluster significantly on small scales, due to their high thermal velocities. With finite masses, cosmological neutrinos become part of the total matter field and contribute to its smoothing Structure formation in the presence of massive neutrinos is therefore impeded compared to that in the standard LCDM cosmology with massless neutrinos. Neutrinos' masses also distort the anisotropy power spectrum of CMB. Furthermore, a finite chemical potential mu for cosmological neutrinos, still allowed by current data, would have a nonn-neigligible impact on CMB and structure formation. Consistently evaluate effects of neutrino masses and chemical potentials on the matter PS by use of a neutrino-involved N-body sim, with cosmo parameters obtained from a MCMC refitting of CMB data. The results show that while a finite averaged neutrino mass m_nu tends to suppress the matter power spectrum in a range of wave numbers, the neutrino degeneracy parameters xi_i == mu_i/T (i=1,2,3) enhance the latter, leading to a large parameter degeneracy between m_nu and xi_i. Provide an empirical formula for the effects on the matter power spectrum in a selected range of wave numbers induced by m_nu and eta == set (sum_i xi^2_i. Observing a strong correlation between m_nu and eta, propose a single z-independent parameter m_nu - (4/3)eta^2 to characterize the neutrino effects on the matter power spectrum.
1808.00464
First constraints on fuzzy dark matter from the dynamics of stellar streams in the Milky Way
Amorisco, Loeb
Present a novel method to constrain the mass of ultra-light bosons as the DM using stellar streams formed by disrupting Globular Clusters in the Milky Way. The turbulent density field of Fuzzy Dark Matter (FDM) haloes results in perturbations and dynamical heating of thin streams. Using numerical simulations based on an effective model, explore the magnitude of this phenomenon and show that this is observable for the range of axion masses m_a that is interesting for alleviating the 'small-scale problems' of LCDM. Derive an analytical model for the thickening of thin stellar streams and obtain an early conservative lower limit for the boson mass of m_a>1.5e-22 eV, using pre-Gaia literature data for six MW streams and after marginalizing over physical parameters. This demonstrates the great promise for using this novel dynamical method as a full independent probe of FDM, to complement results based on Lyman-alpha forest data.
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