1806.07430
Direct measurement of the intra-pixel response function of Kepler Space TElescope's CCDs
Vorobiev, et al
Space missions designed for high precision photometric monitoring of stars often under-sample the point-spread function, with much of the light landing within a single pixel. Missions like MOST, Kepler, BRITE, and TESS, do this to avoid uncertainties due to pixel-to-pixel response non uniformity. This approach has worked remarkable well. However, individual pixels also exhibit response non uniformity. Typically, pixels are most sensitive near their centers and less sensitive near the edges, with a difference in response of as much as 50%. The exact shape of this fall-off, and its dependence on the wavelength of light, is the intra-pixel response function (IPRF). A direct measurement of the IPRF can be used to improve the photometric uncertainties, leading to improved photometry and astrometry of under-sampled systems. Using the spot-scan technique, measure the IPRF of a flight spare e2v CCD90 imaging sensor, which is used in the Kepler focal plane. The spot scanner generates spots with a FWHM of <~5 um across the range of 400-900 nm. Find that Kepler's CCD shows similar IPRF behavior to other back-illuminated devices, with a decrease in responsively near th e edges of a pixel by ~50%. The IPRF also depends on wavelength, exhibiting a large amount of diffusion at shorter wavelengths and becoming much more defined by the gate structure in the near-IR. This method can also be used to measure the IPRF of the CCDs used for TESS, which borrows much from the Kepler mission.
1806.07752
The halo masses of galaxies to $z\sim 3$: a hybrid observational and theoretical approach
Conselice, et al
Use a hybrid observational/theoretical approach to study the relation between galaxy kinematics and the derived stellar and halo masses of galaxies up to z=3 as a function of M*, z and morphology. The observational sample consists of a concatenation of 1125 galaxies with kinematic measurements at 0.4<z<3 from long-slit and integral-field studies. Investigate several ways to measure halo masses from observations based on results from SAMs, showing that galaxy halo masses can be retrieved with a scatter of ~0.4 dex by using only stellar masses. Discover a third parameter, relating to the time of the formation of the halo, which reduces the scatter in the relation between the stellar and halo masses, such that systems forming earlier have a higher stellar mass to halo mass ratio, which is also found observationally. Find that this scatter correlates with morphology, such that early-type, or older stellar systems, have higher M*/Mhalo ratios. Furthermore show using this approach and through WL and abundance matching, that the ratio of stellar to halo mass does not significantly evolve with redshift at 1<z<3. This is evidence for the regulated hierarchical assembly of galaxies such that the ratio of stellar to DM mass remains approximately constant since z=2. Use these results to show that the DM accretion rate evolves from dM_halo/dt ~ 4000 Msun/yr at z~2.5, to a few 100 Msun/yr by z~0.5.
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