Cross-correlating Planck with VST ATLAS LRGs: a new test for the ISW
  effect in the Southern Hemisphere
  The Integrated Sachs-Wolfe (ISW) effect probes the late-time expansion
history of the universe, offering direct constraints on dark energy. Here we
present our measurements of the ISW signal at redshifts of $\bar{z}=0.35$,
$0.55$ and $0.68$, using the cross-correlation of the Planck CMB temperature
map with $\sim0.5$ million Luminous Red Galaxies (LRGs) selected from the VST
ATLAS survey. We then combine these with previous measurements based on WMAP
and similar SDSS LRG samples, providing a total sample of $\sim2.1$ million
LRGs covering $\sim12000$ deg$^2$ of sky. At $\bar{z}=0.35$ and $\bar{z}=0.55$
we detect the ISW signal at $1.2\sigma$ and $2.3\sigma$ (or $2.6\sigma$
combined), in agreement with the predictions of $\Lambda$CDM. We verify these
results by repeating the measurements using the BOSS LOWZ and CMASS,
spectroscopically confirmed LRG samples. We also detect the ISW effect in three
magnitude limited ATLAS+SDSS galaxy samples extending to $z\approx0.4$ at
$\sim2\sigma$ per sample. However, we do not detect the ISW signal at
$\bar{z}=0.68$ when combining the ATLAS and SDSS results. Further tests using
spectroscopically confirmed eBOSS LRGs at this redshift remain inconclusive due
to the current low sky coverage of the survey. If the ISW signal is shown to be
redshift dependent in a manner inconsistent with the predictions of
$\Lambda$CDM, it could open the door to alternative theories such as modified
gravity. It is therefore important to repeat the high redshift ISW measurement
using the completed eBOSS sample, as well as deeper upcoming surveys such as
DESI and LSST.
