1705.10852
Resolving the era of river-forming climates on Mars using stratigraphic logs of river-deposit dimensions
Kite, Howard, Lucas, Lewis
River deposits are one of the main lines of evidence that tell us that Mars once had a climate different from today, and so changes in river deposits with time tell us something about how Mars climate changed with time. In this study, focus in on one sedimentary basin - Aeolis Dorsa - which contains an exceptionally high number of exceptionally well-preserved river deposits that appear to have formed over an interval of >0.5 Myr. Use changes in the river deposits' scale with stratigraphic elevation as a proxy for changes in river paloedischarge. Meander wavelengths tighten upwards and channel widths narrow upwards, and there is some evidence for a return to wide large-wavelength channels higher in the stratigraphy. Meander wavelength and channel width covary with stratigraphic elevation. The factor of 1.5-2 variations in paleochannel dimensions with stratigraphic elevation correspond to ~2.6-fold variability in bank-forming discharge (using standard wavelength-discharge scalings and width-discharge scalings). Taken together with evidence from a marker bed for discharge variability at ~10m stratigraphic distances, the variation in the scale of river deposits indicates that bank-forming discharge varied at both 10m stratigraphic (1e2-1e6 yr) and ~100m stratigraphic (1e3 - 1e9 yr) scales. Changing sediment input leading to a change in characteristic slopes and/or drainage area could be responsible, and another possibility is changing climate (±50 W/m^2 in peak energy available for snow/ice melt).
1705.11167
The ellipticity of galaxy cluster halos from satellite galaxies and weak lensing
Shin, Clampitt, Jain, Bernstein, Neil, Rozo, Rykoff
Study the ellipticity of galaxy cluster halos as characterized by the distribution of cluster galaxies and as measured with weak lensing. Use monte-carol sims of projected, elliptical cluster density profiles to estimate and correct for several biases that arise in using cluster satellite galaxies. The primary biases are Poisson noise bias (due to the finite number of satellites), edge bias (due to the cluster edge) and projection effects. Correct these biases for clusters with different richness. Apply the methodology to 10,428 SDSS clusters identified by the redMaPPer algorithm with richness above 20. Find a mean ellipticity = 0.265±0.002 (stat) ±0.031 (syst.) corresponding to an axis ratio = 0.580±0.02(stat)±0.040(syst). The dominant contribution to the systematic uncertainty comes from the uncertainty in the number of interlopers in the redMaPPer cluster sample. Compare this ellipticity of the satellites to the halo shape, through a stacked lensing measurement using optimal estimators of the lensing quadrupole based on Clampitt and Jain (2016). Find a best-fit axis ratio of 0.55±0.09, consistent with the satellite ellipticity. Thus cluster galaxies trace the shape of the DM halo to within the estimated uncertainties. Finally, restack the satellite and lensing ellipticity measurements along the major axis of the cluster central galaxy's light distribution. From the lensing measurements, infer a misalignment angle with an RMS of 30 deg when stacking on the central galaxy. Discuss applications of halo shape measurements to test the effects of the baryonic gas and AGN feedback, as well as DM and gravity. The major improvements in S/N expected with the ongoing DES and future surveys from LSST, Euclid and WFIRST will make halo shapes a useful probe of these effects.
Resolving the era of river-forming climates on Mars using stratigraphic logs of river-deposit dimensions
Kite, Howard, Lucas, Lewis
River deposits are one of the main lines of evidence that tell us that Mars once had a climate different from today, and so changes in river deposits with time tell us something about how Mars climate changed with time. In this study, focus in on one sedimentary basin - Aeolis Dorsa - which contains an exceptionally high number of exceptionally well-preserved river deposits that appear to have formed over an interval of >0.5 Myr. Use changes in the river deposits' scale with stratigraphic elevation as a proxy for changes in river paloedischarge. Meander wavelengths tighten upwards and channel widths narrow upwards, and there is some evidence for a return to wide large-wavelength channels higher in the stratigraphy. Meander wavelength and channel width covary with stratigraphic elevation. The factor of 1.5-2 variations in paleochannel dimensions with stratigraphic elevation correspond to ~2.6-fold variability in bank-forming discharge (using standard wavelength-discharge scalings and width-discharge scalings). Taken together with evidence from a marker bed for discharge variability at ~10m stratigraphic distances, the variation in the scale of river deposits indicates that bank-forming discharge varied at both 10m stratigraphic (1e2-1e6 yr) and ~100m stratigraphic (1e3 - 1e9 yr) scales. Changing sediment input leading to a change in characteristic slopes and/or drainage area could be responsible, and another possibility is changing climate (±50 W/m^2 in peak energy available for snow/ice melt).
1705.11167
The ellipticity of galaxy cluster halos from satellite galaxies and weak lensing
Shin, Clampitt, Jain, Bernstein, Neil, Rozo, Rykoff
Study the ellipticity of galaxy cluster halos as characterized by the distribution of cluster galaxies and as measured with weak lensing. Use monte-carol sims of projected, elliptical cluster density profiles to estimate and correct for several biases that arise in using cluster satellite galaxies. The primary biases are Poisson noise bias (due to the finite number of satellites), edge bias (due to the cluster edge) and projection effects. Correct these biases for clusters with different richness. Apply the methodology to 10,428 SDSS clusters identified by the redMaPPer algorithm with richness above 20. Find a mean ellipticity = 0.265±0.002 (stat) ±0.031 (syst.) corresponding to an axis ratio = 0.580±0.02(stat)±0.040(syst). The dominant contribution to the systematic uncertainty comes from the uncertainty in the number of interlopers in the redMaPPer cluster sample. Compare this ellipticity of the satellites to the halo shape, through a stacked lensing measurement using optimal estimators of the lensing quadrupole based on Clampitt and Jain (2016). Find a best-fit axis ratio of 0.55±0.09, consistent with the satellite ellipticity. Thus cluster galaxies trace the shape of the DM halo to within the estimated uncertainties. Finally, restack the satellite and lensing ellipticity measurements along the major axis of the cluster central galaxy's light distribution. From the lensing measurements, infer a misalignment angle with an RMS of 30 deg when stacking on the central galaxy. Discuss applications of halo shape measurements to test the effects of the baryonic gas and AGN feedback, as well as DM and gravity. The major improvements in S/N expected with the ongoing DES and future surveys from LSST, Euclid and WFIRST will make halo shapes a useful probe of these effects.
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