GAMA+KiDS: Alignment of galaxies in galaxy groups and its dependence on galaxy scale. (arXiv:1905.00370v1 [astro-ph.CO])

GAMA+KiDS: Alignment of galaxies in galaxy groups and its dependence on galaxy scale. (arXiv:1905.00370v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Georgiou_C/0/1/0/all/0/1">Christos Georgiou</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chisari_N/0/1/0/all/0/1">Nora Elisa Chisari</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fortuna_M/0/1/0/all/0/1">Maria Cristina Fortuna</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hoekstra_H/0/1/0/all/0/1">Henk Hoekstra</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kuijken_K/0/1/0/all/0/1">Konrad Kuijken</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Joachimi_B/0/1/0/all/0/1">Benjamin Joachimi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vakili_M/0/1/0/all/0/1">Mohammadjavad Vakili</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bilicki_M/0/1/0/all/0/1">Maciej Bilicki</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dvornik_A/0/1/0/all/0/1">Andrej Dvornik</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Erben_T/0/1/0/all/0/1">Thomas Erben</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Giblin_B/0/1/0/all/0/1">Benjamin Giblin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Heymans_C/0/1/0/all/0/1">Catherine Heymans</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Napolitano_N/0/1/0/all/0/1">Nicola R. Napolitano</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shan_H/0/1/0/all/0/1">HuanYuan Shan</a>

Intrinsic galaxy alignments are a source of bias for weak lensing
measurements as well as a tool for understanding galaxy formation and
evolution. In this work, we measure the alignment of shapes of satellite
galaxies, in galaxy groups, with respect to the brightest group galaxy (BGG),
as well as alignments of the BGG shape with the satellite positions, using the
highly complete Galaxy And Mass Assembly (GAMA) spectroscopic survey and deep
imaging from the Kilo Degree Survey. We control systematic errors with
dedicated image simulations and measure accurate shapes using the DEIMOS shape
measurement method. We find a significant satellite radial alignment signal,
which vanishes at large separations from the BGG. We do not identify any strong
trends of the signal with galaxy absolute magnitude or group mass. The
alignment signal is dominated by red satellites. We also find that the outer
regions of galaxies are aligned more strongly than their inner regions, by
varying the radial weight employed during the shape measurement process. This
behaviour is evident for both red and blue satellites. BGGs are also found to
be aligned with satellite positions, with this alignment being stronger when
considering the innermost satellites, using red BGGs and the shape of the outer
region of the BGG. Lastly, we measure the global intrinsic alignment signal in
the GAMA sample for two different radial weight functions and find no
significant difference.

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