Heidelberg
HIROCS
Clusters of
galaxies as the largest bound entities are one of the corner stones for our
understanding of the evolution of structure in the universe and of galaxies themselves:
Comparison of local and high-redshift space densities of clusters provides a
powerful tool to constrain models of structure formation and cosmology. On the
other hand clusters are unique laboratories to study the evolution of galaxies
both as a function of time and local density. As such, unbiased samples of
clusters over a wide range in redshift and density are a vital step towards
these goals. Currently there are only a handful of clusters known with
redshifts above unity and they come from heterogeneous sources. In order to
attack the above mentioned topics we have started a survey tailored for the
detection of high-redshift clusters ( z up to 1.5 ) based on multi-colour
photometry to be obtained with wide-field cameras in the optical (LAICA) and
near-infrared (OMEGA2000).
HIROCS as MANOS-wide is part of MANOS,
the extragalactic keyproject at MPIA.
HIROCS
fields
The field sizes
have been cut to 2°x1° in order to finish HIROCS within a reasonable time
frame.
First candidate found visually
During data reduction we found a first rich, high-redshift cluster
candidate as an excess of faint galaxies in an H-band
image. A colour image (blue=B, green=R,
red=H) shows the cluster as a cloud of red galaxies at lower centre. Note the
even distribution of the galaxies and the lack of a bright central cD galaxy.
The two bright stars just above the centre to the lower left and lower right of
the faint blue spiral are about 3’ apart. The colour-magnitude
diagram (lower center) and redshift distribution (lower left) of red
galaxies give a cluster redshift of 0.666 ± 0.006. Some representative spectra from the multi-colour classification give an
idea of the accuracy of the photometric redshifts.
Data acquisition finished in September 2008
The full data sets for all 3 HIROCS fields (except COSMOS) are now
available for 2 square degrees each.
First analysis of 03hA-field
End of January 2009 we finished the final analysis of the first full
data set for 1 square degree in the 3h-field. In all tiles the limiting magnitude is better than
originally planned. As described in the MANOS proposal, we measure the local
overdensity for each object. Plotting all
objects with overdensities above 3s, we clearly see the candidate
mentioned above at X=1200, Y=-700. One of the richest candidates at higher redshift is at z =
1.28 ± 0.03. The colour composit shows red
and blue cluster members (SEDs). One of the highest redshift candidates is at a
redshift of 1.634 ± 0.023.
We now hope to verify these candidates e.g. with LUCIFER at the LBT.
First candidates found in the COSMOS field
The HIROCS 10h field includes the COSMOS field. Using the public COSMOS
data in u, B, g, V, r, i, NB816, z and K (preliminary data set is shallow and
with bad seeing) together with the proprietary H-band imaging obtained with
OMEGA2000, we were able to conduct a cluster search in this field. The
redshifts of the candidates in this field reach out to z = 1.55. These results
(12 candidates in the redshift range 1.23 < z < 1.55) are described in a
letter to A&A (see http://arxiv.org/abs/0709.0411).
Internal information MPIAphot
manual
HIROCS
team:
Hermann-Josef
Röser (P.I., MPIA staff member)
Kris
Blindert (MPIA, postdoc)
Siegfried
Falter (now Böblingen)
Hans
Hippelein (MPIA staff member, retired)
Sadegh
Khochfar (MPE, Garching)
Christian
Wolf (
Michael
Zatloukal (MPIA, postdoc)
Hermann-Josef
Röser
Last
changes: February 3rd 2009