1802.09526
About 30% of Sun-like stars have Kepler-like planetary systems: a study of their Intrinsic architecture
Zhu, et al
Constrain the intrinsic architecture of Kepler planetary systems by modeling the observed multiplicities of the transiting planets (tranets) and their transit time variations (TTVs). Robustly determine that the fraction of Sun-like stars with Kepler-like planets, eta_Kepler, is 30±3%. Here Kepler-like planets are planets that have radii R_p >~ R_Earth and orbital periods P<400 days. Also find that the dispersion in orbital inclinations of planets within a given planetary system, sigma_i,k is a steep function of its number of planets, k. This can be parameterized as sigma_i,k ~ k^alpha and find that -4<alpha<-2 at 2-sigma level. Such a distribution well describes the observed multiplicities of both truants and TTVs with no excess of single truants. Therefore do not find evidence supporting the so-called "Kepler dichotomy." Together with a previous study on orbital eccentricities, now have a consistent picture: the fewer planets in a system, the hotter it is dynamically. Discuss briefly possible scenarios that lead to such a trend. Despite the Solar system not belonging to the Kepler club, it is interesting to notice that the Solar system also has three planets within 400 days and that the inclination dispersion is similar to Kepler systems of the same multiplicity.
1802.09696
Stacked lensing estimators and their covariance matrices: excess surface mass density vs. lensing shear
Shirasaki, Takada
Stacked lensing is a powerful means of measuring the average mass distribution around large-scale structure tracers. There are two stacked lensing estimators used in the literature, denoted as DeltaSigma and gamma_+, which are related as DeltaSigma=Sigma_cr gamma_+ on each lens-source pair basis, where Sigma_cr(z_l,z_s) is the critical surface mass density for lens and source at redshifts z_l and z_s, respectively. In this paper, derive a formula for the covariance matrix of DeltaSigma-estimator focusing on "weight" function to improve the S/N, where we assume that the lensing fields and the distribution of lensing objects obey the Gaussian statistics. Within this formula, show that, if background galaxy shapes are weighted by an about of Sigma_cr^-2(z_l,z_s), the DeltaSigma-estimator is optimal (it maximizes the S/N) in the shot noise limited regime. Validate the covariance formula by using numerical simulations. Show that the DeltaSigma-estimator with the weight Sigma_cr^-2 gives a greater (S/N)^2 than that of the gamma_+-estimator by about 5-25% for lensing objects at redshifts comparable with or higher than the median of source galaxy redshifts for hypothetical Subaru HSC and DES surveys. However, for low-z lenses such as z_l<0.3, the gamma_+-estimator has higher (S/N)^2 than DeltaSigma. Also discuss that the (S/N)^2 for DeltaSigma at large separations in the sample variance limited regime can be boosted, by up to a factor of 1.5, if one adopts a weight of Sigma_cr^-alpha with alpha>2. The formula allows one to explore how the combination of the different estimators can approach an optimal estimator in all regimes of redshifts and separation scales.
1802.10094
Insights on Dark Matter form Hydrogen during Cosmic Dawn
Muñoz, Loeb
The origin and composition of the cosmological DM remain a mystery. However, upcoming 21-cm measurements during cosmic dawn, the period of the first stellar formation, can provide new clues on the nature of DM. During this era, the baryon-DM fluid his the slowest it will ever be, making it ideal to search for DM elastically scattering with baryons through massless mediators, such as the photon. Here, explore whether DM particles with an electric "mini charge" can significantly alter the baryonic temperature and, thus, affect 21-cm observations. Find that the entirety of the DM cannot be mini charged at a significant level, lest it interferes with Galactic and extragalactic magnetic fields. However, if mini charged particles comprise a sub percent fraction of the DM, and have charges epsilon~1e-6 (in units of the electron charge) and masses m_chi ~ 1-60 MeV, they can significantly cool down the baryonic fluid, and be discovered in 21-cm experiments. Show how this scenario can explain the recent result by the EDGES collaboration, which requires a lower baryonic temperature than possible within the standard model, while remaining consistent with all current observations.
1802.10257
The correlation of extragalactic $\gamma$-rays with cosmic matter density distributions from weak-gravitational lensing
Shirasaki, et al
The extragalactic gamma-ray background (EGB) arises from accumulation [of] gamma-ray emissions from resolved and unresolved extragalactic sources as well as diffuse processes. It is important to understand the origin of the EGB in the context of cosmological structure formation. Known astrophysical gamma-ray sources such as blazers, star-forming galaxies, and radio galaxies are expected to trace the underlying cosmic matter density distribution. Explore the correlation of the EGB from Fermi-LAT data with the large-scale matter density distribution from the Subaru HSC SSP survey. Reconstruct an unbiased surface matter density distribution kappa at z<1 by applying WL analysis to the first-year HSC data. Then calculate the kappa-gamma cross-correlation. The measurement suggests overall weak correlation at angular scales of 30-60 arcmin. The result is essentially consistent with a null detection, and allows to derive constraints on the statistical relationships between astrophysical gamma-ray sources and DM haloes. Make forecasts for the detectability of the cross-correlation in the final HSC data. Detection with a ~3sigma confidence can be achieved with the full survey covering 1400 square degrees planned for HSC SSP.
1802.10282
Weak lensing study in VOICE survey I: Shear measurement
Fu, et al
The VST Optical Imaging of the CDFS and ES1 fields (VOICE) Survey is a VST INAF guaranteed time program proposed to provide deep optical imaging covering two 4 deg^2 cosmic windows. Present the cosmic shear measurement over four 1 deg^2 fields in the CDFS region in the r-band using LensFit. Each tile has more than one hundred exposures to reach deep imaging. More than 50 exposures of each tile passed image quality selection criteria for WL study. The r-band co-added image reaches 5 sigma limiting magnitude r=26.1 for point sources, which is 1.2 mag deeper than KiDS. The photometric redshifts are estimated using the VOICE ugri together with near-infrared VIDEO data YJHK_s, which is nearly double of that of KiDS. The performance of LensFit on deep imaging was calibrated using VOICE-ike simulation (Liu+2018). Furthermore, analyse the reliability of the shear catalogue by calculating the star-galaxy cross-correlations, the tomographic shear correlations of 2 redshift bins and the contaminations of the blended galaxies. As a further sanity check, constrain cosmological parameters by exploring the parameter space with Population Montecarlo sampling. For a flat LCDM model, obtain Sigma8=sigma8(Omega_m/0.3)^0.5 = 0.68+0.11-0.15.
1802.10283
Weak lensing study in VOICE survey II: shear bias calibrations
Liu, et al
The VST Optical Imaging of the CDFS and ES1 fields (VOICE) Survey is proposed to obtain deep optical ugri imaging of the CDFS and ES1 fields using VST. At present, the observations for the CDFS fields have been completed, and comprise in total about 4.9 deg^2 down to r_AB~26 mag. WL shear is measured in a companion paper for r-band images with seeing <~0.9". In this work, perform imaging simulations to calibrate possible biases of the measured shear signals. Statistically, the properties of the simulated PSF and galaxies show good agreement with those of observations. The multiplicative bias is calibrated to reach an accuracy of 3.0%. Study the bias sensitivities to undetected faint galaxies and to the existence of neighboring galaxies. Find that undetected galaxies contribute to 0.3% multiplicative bias. Further analysis shows that galaxies with lower S/N suffer from more significant impact due to the skewed background noise caused by undetected galaxies. Meanwhile, find that although most of the neighbors have been rejected in the shape measurement procedure, about one third of them still remain in the final shear sample. They show larger ellipticity dispersion and contribute to 0.2% multiplicative bias. Simply rejecting these galaxies can reduce the effective number density of galaxies for deep surveys, such as VOICE. Therefore efficient methods should be developed for future WL surveys in order to decompose their overlapped surface brightness distributions.
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