Wednesday. Thursday.
1807.03724
The quasi-linear nearby Universe
Hoffman, et al
The local Universe provides a unique opportunity for testing cosmology and theories of structure formation. To facilitate this opportunity, present a new method for the reconstruction of the quasi-linear matter density and velocity fields from galaxy peculiar velocities and apply it to the Cosmicflows-2 data. The method consists of constructing and ensemble of cosmological simulations, constrained by the standard cosmological model and the observational data. The quasi-linear density field is the geometric mean and variance of the fully non-linear density fields of the simulations. The main nearby clusters (Virgo, Centaurus, Coma), superclusters (Shapley, Perseus-Pisces) and voids (Dipole Repeller) are robustly reconstructed. Galaxies are born biased with respect to the underlying DM distribution. Using the quasi-linear framework, demonstrate that the luminosity-weighted density field derived from the 2M++ redshift compilations is non-linearly biased with respect to the matter density field. The bias diminishes in the linear regime.
1807.03789
Star cluster ages in the Gaia era
Choi, Conroy, et al
Use the framework developed as part of the MESA Isochrones and Stellar Tracks (MIST) project to assess the utility of several types of observables in jointly measuring the age and 1d stellar model parameters in star clusters. Begin with a pedagogical overview summarizing the effects of stellar model parameters, such as the He abundance, mass-loss efficiency, and the mixing length parameter, on observational diagnostics including the color-magnitude diagram, mass-radius relation, and surface abundances, amongst others. Find that these parameters and the stellar age influence observables in qualitatively distinctive, degeneracy-breaking ways. To assess the current state of affairs, use the recent Gaia DR2 along with data from the literature to investigate 3 well-studies old open clusters -- NGC6819, M67, NGC6791 -- as case studies. Although there is no obvious tension between the existing observations and the MIST models for NGC6819, there are interesting discrepancies in the cases of M67 and NGC6791. At this time, parallax zero point uncertainties in Gaia DR2 remain one of the limiting factors in the analysis of these clusters. With a combination of exquisite photometry, parallax distances, and cluster memberships from Gaia at the end of its mission, anticipate precise and accurate ages for these and other star clusters in the Galaxy.
1807.03793
EasyCritics II. Testing its efficiency: new gravitational lens candidates in CFHTLenS
Carrasco, et al
Report the results of EasyCritics, a fully automated algorithm for the efficient search of SL regions in wide-field surveys, applied to CFHTLenS. By using only the photometric information of the brightest elliptical galaxies distributed over a wide redshift range (0.2<~z<~0.9) and without requiring the identification of arcs, the algorithm produces a lensing potential models and catalogs of critical curves of the entire survey area. Explore several parameter set configurations in order to test the efficiency of the approach. In a specific configurations, EasyCritics generates only ~1200 possibly super-critical regions in the CFHTLS area, drastically reducing the effective area for inspection from 154 sq. deg to ~0.623 sq. deg, i.e. by more than 2 orders of magnitude. Among the pre-selected SL regions, identify 32 of the 44 previously known lenses on the group and cluster scale, and discover 9 new promising lens candidates. The detection rate can be easily improved to ~82% by a simple modification in the parameter set, but at the expense of increasing the total number of possible SL candidates. Note that EasyCritics is fully complementary to other arc-finders since we characterize lenses instead of directly identifying arcs. Although future comparisons against numerical simulations are required for fully assessing the efficiency of EasyCritics, the algorithm seems very promising for upcoming surveys covering 1e4 sq deg, such as the Euclid mission and LSST, where the pre-selection of candidates for any kind of SL analysis will be indispensable due to the expected enormous data volume.
1807.03938
Production of Silicon on Mass increasing white dwarfs -- possible origin of high-velocity-features in type Ia supernovae
Kato, Saio, Hachisu
SNe Ia often show high-velocity absorption features (HVFs) in their early phase spectra; however the origin of the HVSs is unknown. Show that a near-Chandrasekhar-mass WD develops a Si-rich layer on a carbon-oxygen (CO) core before it explodes as an SNIa. Calculate the nuclear yield in successive He shell flashes for 1.0 Msun, 1.2 Msun, and 1.35 Msun CO Was accreting He-rich matter with several mass-accretion rates ranging from 1e-7 Msun/yr to 7.5e-7 Msun/yr. For the 1.35 Msun WD with the accretion rate of 1.6e-7 Msun/yr, the surface layer developed as He burning ash and consisted of 40% 24Mg, 33%12C, 23% 28Si, and a few percent of 20Ne by weight. For a higher mass accretion rate of 7.5e-7 Msun/yr, the surface layer consisted of 58%12C, 31%24Mg, and 0.43% 28Si. For the 1.2 Msun WDs, Si is produced only for lower mass accretion rates (2% for 1.6e-7 Msun/yr). No substantial Si (<0.07%) is produced on the 1.0 Msun WD independently of the mass-accretion rate. If the Si-rich surface layer is the origin of Si II HVFs, its characteristics are consistent with that of mass increasing WDs. Also discuss possible Ca production on very massive Was (>~1.38 Msun).
1807.04194
Aerogel scattering filters for cosmic microwave background observations
Essinger-Hileman, Bennett, et al
Present the design and performance of broadband and tunable IR-blocking filters for millimeter and sub-millimeter astronomy composed of small scattering particles embedded in a aerogel substrate. The ultra-low-density (<100 mg/cm^3) aerogel substrate provides an index of refraction as low as 1.05, removing the need for anti-reflection coatings and allowing for broad band operation from DC to above 1THz. The size distribution of the scattering particles can be tuned to provide a variable cutoff frequency. Aerogel filters with embedded high-resistivity Si powder are being produced at 40cm diameter to enable large-aperture cryogenic receivers for CMB polarimeters, which require large arrays of sub-Kelvin detectors in their search for the signature of an inflationary gravitational-wave background.
1807.04215
GridSPT: Grid-based calculation for perturbation theory of large-scale structure
Taruya, Nishimichi, Jeong
PT (perturbation theory) calculation of large-scale structure has been used to interpret the observed NL statistics of large-scale structure at the quasi-linear regime. In particular, the so-called standard perturbation theory (SPT) provides a basis for the analytical computation of the higher-order quantities of large-scale structure. Here, present a novel, grid-based algorithm for the SPT calculation, hence named GridSPT, to generate the higher-order density and velocity fields from a given linear power spectrum. Taking advantage of the Fast Fourier Transform, the GridSPT quickly generates the NL density fields at each order, from where the statistical quantities such as NL PS and bispectrum are calculated. Comparing the density yields (to fifth order) from GridSPT with those from the full N-body simulations in the configuration space, find that GridSPT accurately reproduces the N-body result on large scales. The agreement worsens with smaller smoothing radius, particularly for the under-dense regions where it is found that 2LPT (second-order Lagrangian perturbation theory) algorithm performs well.
1807.04266
Accurate cosmic shear errors: do we need ensembles of simulations?
Barreira, Krause, Schmidt
Accurate inference of cosmology from WL shear requires an accurate shear PS covariance matrix. Here, investigate the accuracy requirement and quantify the relative importance of the Gaussian (G), SSC and connected non-Gaussian (cNG) contributions to the covariance. Specifically, forecast cosmological parameter constraints for future wide-field surveys and study how different covariance matrix components affect parameter bounds. The main results is that the cNG term represents only a small and potentially negligible contribution to statistical parameter errors: the errors obtained using the G+SSC subset are within <~5% of those obtained with the full G+SSC+cNG matrix for a Euclid-like survey. This result also holds for the shear correlation function, variations in survey specifications and for different analytical prescriptions of the cNG term. The cNG term is that which is often tackled using numerical expensive ensembles of survey realizations. The results suggest however that the accuracy of analytical or approximate numerical methods to compute the cNG term is likely to be sufficient for cosmic shear inference from the next generation of surveys.
1807.03724
The quasi-linear nearby Universe
Hoffman, et al
The local Universe provides a unique opportunity for testing cosmology and theories of structure formation. To facilitate this opportunity, present a new method for the reconstruction of the quasi-linear matter density and velocity fields from galaxy peculiar velocities and apply it to the Cosmicflows-2 data. The method consists of constructing and ensemble of cosmological simulations, constrained by the standard cosmological model and the observational data. The quasi-linear density field is the geometric mean and variance of the fully non-linear density fields of the simulations. The main nearby clusters (Virgo, Centaurus, Coma), superclusters (Shapley, Perseus-Pisces) and voids (Dipole Repeller) are robustly reconstructed. Galaxies are born biased with respect to the underlying DM distribution. Using the quasi-linear framework, demonstrate that the luminosity-weighted density field derived from the 2M++ redshift compilations is non-linearly biased with respect to the matter density field. The bias diminishes in the linear regime.
1807.03789
Star cluster ages in the Gaia era
Choi, Conroy, et al
Use the framework developed as part of the MESA Isochrones and Stellar Tracks (MIST) project to assess the utility of several types of observables in jointly measuring the age and 1d stellar model parameters in star clusters. Begin with a pedagogical overview summarizing the effects of stellar model parameters, such as the He abundance, mass-loss efficiency, and the mixing length parameter, on observational diagnostics including the color-magnitude diagram, mass-radius relation, and surface abundances, amongst others. Find that these parameters and the stellar age influence observables in qualitatively distinctive, degeneracy-breaking ways. To assess the current state of affairs, use the recent Gaia DR2 along with data from the literature to investigate 3 well-studies old open clusters -- NGC6819, M67, NGC6791 -- as case studies. Although there is no obvious tension between the existing observations and the MIST models for NGC6819, there are interesting discrepancies in the cases of M67 and NGC6791. At this time, parallax zero point uncertainties in Gaia DR2 remain one of the limiting factors in the analysis of these clusters. With a combination of exquisite photometry, parallax distances, and cluster memberships from Gaia at the end of its mission, anticipate precise and accurate ages for these and other star clusters in the Galaxy.
1807.03793
EasyCritics II. Testing its efficiency: new gravitational lens candidates in CFHTLenS
Carrasco, et al
Report the results of EasyCritics, a fully automated algorithm for the efficient search of SL regions in wide-field surveys, applied to CFHTLenS. By using only the photometric information of the brightest elliptical galaxies distributed over a wide redshift range (0.2<~z<~0.9) and without requiring the identification of arcs, the algorithm produces a lensing potential models and catalogs of critical curves of the entire survey area. Explore several parameter set configurations in order to test the efficiency of the approach. In a specific configurations, EasyCritics generates only ~1200 possibly super-critical regions in the CFHTLS area, drastically reducing the effective area for inspection from 154 sq. deg to ~0.623 sq. deg, i.e. by more than 2 orders of magnitude. Among the pre-selected SL regions, identify 32 of the 44 previously known lenses on the group and cluster scale, and discover 9 new promising lens candidates. The detection rate can be easily improved to ~82% by a simple modification in the parameter set, but at the expense of increasing the total number of possible SL candidates. Note that EasyCritics is fully complementary to other arc-finders since we characterize lenses instead of directly identifying arcs. Although future comparisons against numerical simulations are required for fully assessing the efficiency of EasyCritics, the algorithm seems very promising for upcoming surveys covering 1e4 sq deg, such as the Euclid mission and LSST, where the pre-selection of candidates for any kind of SL analysis will be indispensable due to the expected enormous data volume.
1807.03938
Production of Silicon on Mass increasing white dwarfs -- possible origin of high-velocity-features in type Ia supernovae
Kato, Saio, Hachisu
SNe Ia often show high-velocity absorption features (HVFs) in their early phase spectra; however the origin of the HVSs is unknown. Show that a near-Chandrasekhar-mass WD develops a Si-rich layer on a carbon-oxygen (CO) core before it explodes as an SNIa. Calculate the nuclear yield in successive He shell flashes for 1.0 Msun, 1.2 Msun, and 1.35 Msun CO Was accreting He-rich matter with several mass-accretion rates ranging from 1e-7 Msun/yr to 7.5e-7 Msun/yr. For the 1.35 Msun WD with the accretion rate of 1.6e-7 Msun/yr, the surface layer developed as He burning ash and consisted of 40% 24Mg, 33%12C, 23% 28Si, and a few percent of 20Ne by weight. For a higher mass accretion rate of 7.5e-7 Msun/yr, the surface layer consisted of 58%12C, 31%24Mg, and 0.43% 28Si. For the 1.2 Msun WDs, Si is produced only for lower mass accretion rates (2% for 1.6e-7 Msun/yr). No substantial Si (<0.07%) is produced on the 1.0 Msun WD independently of the mass-accretion rate. If the Si-rich surface layer is the origin of Si II HVFs, its characteristics are consistent with that of mass increasing WDs. Also discuss possible Ca production on very massive Was (>~1.38 Msun).
1807.04194
Aerogel scattering filters for cosmic microwave background observations
Essinger-Hileman, Bennett, et al
Present the design and performance of broadband and tunable IR-blocking filters for millimeter and sub-millimeter astronomy composed of small scattering particles embedded in a aerogel substrate. The ultra-low-density (<100 mg/cm^3) aerogel substrate provides an index of refraction as low as 1.05, removing the need for anti-reflection coatings and allowing for broad band operation from DC to above 1THz. The size distribution of the scattering particles can be tuned to provide a variable cutoff frequency. Aerogel filters with embedded high-resistivity Si powder are being produced at 40cm diameter to enable large-aperture cryogenic receivers for CMB polarimeters, which require large arrays of sub-Kelvin detectors in their search for the signature of an inflationary gravitational-wave background.
1807.04215
GridSPT: Grid-based calculation for perturbation theory of large-scale structure
Taruya, Nishimichi, Jeong
PT (perturbation theory) calculation of large-scale structure has been used to interpret the observed NL statistics of large-scale structure at the quasi-linear regime. In particular, the so-called standard perturbation theory (SPT) provides a basis for the analytical computation of the higher-order quantities of large-scale structure. Here, present a novel, grid-based algorithm for the SPT calculation, hence named GridSPT, to generate the higher-order density and velocity fields from a given linear power spectrum. Taking advantage of the Fast Fourier Transform, the GridSPT quickly generates the NL density fields at each order, from where the statistical quantities such as NL PS and bispectrum are calculated. Comparing the density yields (to fifth order) from GridSPT with those from the full N-body simulations in the configuration space, find that GridSPT accurately reproduces the N-body result on large scales. The agreement worsens with smaller smoothing radius, particularly for the under-dense regions where it is found that 2LPT (second-order Lagrangian perturbation theory) algorithm performs well.
1807.04266
Accurate cosmic shear errors: do we need ensembles of simulations?
Barreira, Krause, Schmidt
Accurate inference of cosmology from WL shear requires an accurate shear PS covariance matrix. Here, investigate the accuracy requirement and quantify the relative importance of the Gaussian (G), SSC and connected non-Gaussian (cNG) contributions to the covariance. Specifically, forecast cosmological parameter constraints for future wide-field surveys and study how different covariance matrix components affect parameter bounds. The main results is that the cNG term represents only a small and potentially negligible contribution to statistical parameter errors: the errors obtained using the G+SSC subset are within <~5% of those obtained with the full G+SSC+cNG matrix for a Euclid-like survey. This result also holds for the shear correlation function, variations in survey specifications and for different analytical prescriptions of the cNG term. The cNG term is that which is often tackled using numerical expensive ensembles of survey realizations. The results suggest however that the accuracy of analytical or approximate numerical methods to compute the cNG term is likely to be sufficient for cosmic shear inference from the next generation of surveys.
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