Day 1563

Tuesday.

1905.01336
Proxima Centauri b is not a transiting exoplanet
Jenkins, et al

We report Spitzer Space Telescope observations during predicted transits of the exoplanet Proxima Centauri b. As the nearest terrestrial habitable-zone planet we will ever discover, any potential transit of Proxima b would place strong constraints on its radius, bulk density, and atmosphere. Subsequent transmission spectroscopy and secondary-eclipse measurements could then probe the atmospheric chemistry, physical processes, and orbit, including a search for biosignatures. However, our photometric results rule out planetary transits at the 200~ppm level at 4.5$~{\mu}m$, yielding a 3$\sigma$ upper radius limit of 0.4~$R_\rm{\oplus}$ (Earth radii). Previous claims of possible transits from optical ground- and space-based photometry were likely correlated noise in the data from Proxima Centauri's frequent flaring. Follow-up observations should focus on planetary radio emission, phase curves, and direct imaging. Our study indicates dramatically reduced stellar activity at near-to-mid infrared wavelengths, compared to the optical. Proxima b is an ideal target for space-based infrared telescopes, if their instruments can be configured to handle Proxima's brightness.

1905.01433

Deep+Wide lensing surveys will provide exquisite measurements of the dark matter haloes of dwarf galaxies

Leauthaud, et al

The advent of new deep+wide photometric lensing surveys will open up the possibility of direct measurements of the dark matter halos of dwarf galaxies. The HSC wide survey will be the first with the statistical capability of measuring the lensing signal with high signal-to-noise at log(M*)=8. At this same mass scale, LSST will have the most overall constraining power with a predicted signal-to-noise for the galaxy-galaxy lensing signal around dwarfs of SN=200. WFIRST and LSST will have the greatest potential to push below the log(M*) = 7 mass scale thanks to the depth of their imaging data. Studies of the dark matter halos of dwarf galaxies at z=0.1 with gravitational lensing are soon within reach. However, further work will be required to develop optimized strategies for extracting dwarfs samples from these surveys, determining redshifts, and accurately measuring lensing on small radial scales. Dwarf lensing will be a new and powerful tool to constrain the halo masses and inner density slopes of dwarf galaxies and to distinguish between baryonic feedback and modified dark matter scenarios.

1905.01612

Modeling the tightest relation between galaxy properties and dark matter halo properties from hydrodynamical simulations of galaxy formation

He

We investigate how a property of a galaxy correlates most tightly with a property of its host dark matter halo, using state-of-the-art hydrodynamical simulations of galaxy formation EAGLE, Illustrius, and IllustrisTNG. Unlike most of the previous work, our analyses focus on all types of galaxies, including both central and satellite galaxies. We find that the stellar mass of a galaxy at the epoch of the peak circular velocity with an evolution correlation gives the tightest such correlation to the peak circular velocity $V_{\rm peak}$ of the galaxy's underlining dark matter halo. The evolution of galaxy stellar mass reduces rather than increases scatter in such a relation. We also find that one major source of scatter comes from stellar mass striping due to the strong interactions between galaxies. Even though, we show that the size of scatter predicted by hydrodynamical simulations has a negligible impact on the clustering of dense $V_{\rm peak}$-selected subhalo samples from simulations, which suggests that even the simplest subhalo abundance matching (SHAM), without scatter and any additional free parameter, can provide a robust prediction of galaxy clustering that can agree impressively well with the observations from the SDSS main galaxy survey.

1905.01710

The self similarity of weak lensing peaks

Davies, et al

We study the statistics of weak lensing convergence peaks, such as their abundance and two-point correlation function (2PCF), for a wide range of cosmological parameters $\Omega_m$ and $\sigma_8$ within the standard $\Lambda$CDM paradigm, focusing on intermediate-height peaks with signal-to-noise ratio (SNR) of $1.5$ to $3.5$. We find that the cosmology dependence of the peak abundance can be described by a one-parameter fitting formula that is accurate to within $\sim3\%$. The peak 2PCFs are shown to feature a self-similar behaviour: if the peak separation is rescaled by the mean inter-peak distance, catalogues with different minimum peak SNR values have identical clustering, which suggests that the peak abundance and clustering are closely interconnected. A simple fitting model for the rescaled 2PCF is given, which together with the peak abundance model above can predict peak 2PCFs with an accuracy better than $\sim5\%$. The abundance and 2PCFs for intermediate peaks have very different dependencies on $\Omega_m$ and $\sigma_8$, implying that their combination can be used to break the degeneracy between these two parameters.

1905.02078

Unequal time correlates and the Zeldovich approximation

Chisari, Pontzen

The modeling of cosmological observables is based on the statistics of the matter density, velocity and gravitational fields in the Universe as a function of time. Typically, calculations are restricted to equal time correlations, where any given fields are evaluated at the same redshift. For some applications, it is necessary to make accurate predictions of unequal time correlators, where the fields considered are evaluated at different redshifts. In this work, we show that the Zeldovich approximation provides an accurate analytical prescription to model unequal time correlators, which we validate against numerical N-body simulations. The Zeldovich approximation introduces a scale-dependent exponential suppression of unequal time correlators, which depends on cosmology and the redshifts of the fields considered. Comparing the Zeldovich case to previous approximations, we show that it can yield accurate predictions for wavenumbers that extend well into the nonlinear regime. However, we also show that correlations over such scales are typically suppressed by the geometry of the lightcone, and thus should normally be negligible for cosmology with galaxy surveys. We discuss potential exceptions, such as intrinsic galaxy alignments, where unequal time correlators could play a role in the modeling of the observables.

1905.02084

An excess of non-Gaussian fluctuations in the cosmic infrared background consistent with gravitational lensing

Feng, Holder

The cosmic infrared background (CIB) is gravitationally lensed. A quadratic-estimator technique that is inherited from lensing analyses of the cosmic microwave background (CMB) can be applied to detect the CIB lensing effects. However, the CIB fluctuations are intrinsically strongly non-Gaussian, making CIB lensing reconstruction highly biased. We perform numerical simulations to estimate the intrinsic non-Gaussianity and establish a cross-correlation approach to precisely extract the CIB lensing signal from raw data. We apply this technique to CIB data from the Planck satellite and cross-correlate the resulting lensing estimate with the CIB data, galaxy number counts and the CMB lensing potential. We detect an excess that is consistent with a lensing contribution at $>4\sigma$.