Contributed Talk - Splinter AGN
Galaxy overdensities around
3C radio galaxies and
quasars at 1 < z < 2.5 revealed by \it Spitzer
3.6 / 4.5 \mum and Pan-STARRS
Z. Ghaffari1, Ch. Westhues1, M. Haas1, R. Chini1, S. P. Willner2, M.L.N. Ashby2, B. J. Wilkes2
1 Astronomisches Institut, Ruhr-Universität Bochum,
Universitätsstra\sse 150, 44801 Bochum, Germany
2 Harvard-Smithsonian Center for Astrophysics, 60 Garden St.,
Cambridge, MA 02138, USA
Luminous radio sources are thought to reside in galaxy clusters or
proto-clusters. To confirm this idea , it is necessary to identify possible companion galaxies around RGs at the same redshift. Taking the advantage of the impressive and complete sample of 64 high-redshift 3C sources at 1 which
has been mapped by the
\it Spitzer Space Telescope.
The IRAC 3.6 \mum and 4.5 \mum 5-\sigma detection limit of
4 \muJy (22.4 AB mag) allows us to search for the brightest candidate cluster member galaxies associated with the 3C sources.
To remove the
contamination of foreground
stars and galaxies along the lines of sight toward the
we apply color cuts:
removed sources satisfy
either the IRAC1/2 cut %criterion
[3.6] - [4.5] < -0.3 or the Pan-STARRS/IRAC cut
i - [4.5] < 0.5 if
detected by Pan-STARRS.
For both selection methods,
about half of the 3C radio sources show significant overdensities
within 30\arcsec (\sim250 kpc) projected distance
from the radio source compared to the surrounding galaxy densities
measured in the 50\arcsec-120\arcsec annulus.
The Pan-STARRS/IRAC cut reveals higher average overdensities than
the IRAC1/2 cut.
To infer the nature of the cluster members, we rerun the analysis
using a stronger IRAC1/2 cut [3.6] - [4.5] < -0.1 which removes
1 passive ellipticals but not star-forming galaxies. For the strong cut, the
overdensities, on average, completely disappear at 1.
We therefore suggest that the 4.5 \mum detected cluster member
galaxies are mainly passive ellipticals.