1812.02749
Be it therefore resolved: Cosmological simulations of dwarf galaxies with extreme resolution
Wheeler, Hopkins, et al
Study a suite of extremely high-resolution cosmological FIRE simulations of dwarf galaxies (M_halo <~1e10 Msun), run to z=0 with 30 Msun resolution, sufficient (for the first time) to resolve the internal structure of individual supernovae remnants within the cooling radius. Every halo with M_halo >~1e8.6 Msun is populated by a resolved stellar galaxy, suggesting very low-mass dwarfs may be ubiquitous in the field. The ultra-faint dwarfs (UFDs; M*<1e5 Msun) have their star formation truncated early (z>~2), likely by deionization, while classical dwarfs (M*>1d5 Msun) continue forming stars to z<0.5. The systems have bursty SF histories, forming most of their stars in periods of elevated SF strongly clustered in both space and time. This allows the dwarf with M*/Mhalo>1e-4 to form a dark matter core >200 pc, while lower-mass UFDs exhibit cusps down to <~100pc, as expected from energetic arguments. The dwarfs with M*>1e4 Msun have half-mass radii (R_1/2) in agreement with Local Group (LG) dwarfs; dynamical mass vs R_1/2 and the degree of rotational support also resemble observations. The lowest-mass UFDs are below surface brightness limits of current surveys but are potentially visible in next-generation surveys (LSST). The stellar metallicities are lower than in LG dwarfs; this may reflect pre-enrichment of the LG by the massive hosts or Pop-III stars. Consistency with lower resolution studies implies that the simulations are numerically robust (for a given physical model).
1812.03167
Transverse velocities with the moving lens effect
Hotinli, et al
Gravitational potentials with change in time induce fluctuations in the observed CMB temperature. Cosmological structure moving transverse to the line of sight provides a specific example known as the moving lens effect. Here, explore how the observed CMB temperature fluctuations combined with the observed matter over-density can be used to infer the transverse velocity of cosmological structure on large scales. Show that near-future CMB surveys and galaxy surveys will have the statistical power to make a first detection of the moving lens effect. Discuss applications for the reconstructed transverse velocity.
1812.03248
An overview of the LSST image processing pipelines
Bosch, et al
LSST is an ambitious astronomical survey with a similarly ambitious Data Management component. Data Management for LSST includes processing on both nightly and yearly cadences to generate transient alerts, deep catalogs of the static sky, and forced photometry light-curves for billions of objects at hundreds of epoch, spanning at least a decade. The algorithms running in these pipelines are individually sophisticated and interact in subtle ways. This paper provides an overview of these pipelines, focusing more on those interactions than the details of any individual algorithm.
1812.03983
Towards emulating cosmic shear data: revisiting the calibration f the shear measurements for the Kilo-Degree Survey
Kannawadi, Hoekstra, et al
Exploiting the full statistical power of future cosmic shear surveys will necessitate improvements to the accuracy with which the gravitational lensing signal is measured. Present a framework for calibrating shear and image simulations that demonstrates the importance of including realistic correlations between galaxy morphology, size and more importantly, photometric redshifts. This realism is essential so that selection and shape measurement biases can be calibrated accurately for a tomographic cosmic shear analysis. Emulate KiDS observations of the COSMIS field using morphological information from HST imaging, faithfully reproducing the measured galaxy properties from KiDS observations of the same field. Calibrate the shear measurements from lensfit, and find through a range of sensitivity test that lensfit is robust and unbiased within the allowed 2% tolerance of the study. Results show that the calibration has to be performed by selecting the tomographic samples in the simulations, consistent with the actual cosmic shear analysis, because the joint distributions of galaxy properties are found to vary with redshift. Ignoring this redshift variations could result in misestimating the shear bias by an amout that exceeds the allowed tolerance. To improve the calibration for future cosmic shear analyses, it will be essential to also correctly account for the measurement of photometric redshifts, which requires simulating multi-band observations.
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