Open AccessExploring the selection of galaxy clusters and groups: an optical survey for X‐ray dark clusters
Author(s) -
Gilbank David G.,
Bower Richard G.,
Castander F. J.,
Ziegler B. L.
Publication year - 2004
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2004.07335.x
Subject(s) - physics , astrophysics , redshift , cluster (spacecraft) , galaxy cluster , galaxy , passband , galaxy groups and clusters , astronomy , selection (genetic algorithm) , optics , artificial intelligence , computer science , band pass filter , programming language
Data from a new, wide‐field, coincident optical and X‐ray survey, the X‐ray Dark Cluster Survey (XDCS), are presented. This survey comprises simultaneous and independent searches for clusters of galaxies in the optical and X‐ray passbands. Optical cluster detection algorithms implemented on the data are detailed. Two distinct optically selected catalogues are constructed, one based on I ‐band overdensity, the other on overdensities of colour‐selected galaxies. The superior accuracy of the colour‐selection technique over that of the single‐passband method is demonstrated, via internal consistency checks and comparison with external spectroscopic redshift information. This is compared with an X‐ray‐selected cluster catalogue. In terms of gross numbers, the survey yields 185 I ‐band‐selected, 290 colour‐selected and 15 X‐ray‐selected systems, residing in ∼11 deg 2 of optical + X‐ray imaging. The relationship between optical richness/luminosity and X‐ray luminosity is examined, by measuring X‐ray luminosities at the positions of our 290 colour‐selected systems. Power‐law correlations between the optical richness/luminosity and X‐ray luminosity are fitted, both exhibiting approximately 0.2 dex of intrinsic scatter. Interesting outliers in these correlations are discussed in greater detail. Spectroscopic follow‐up of a subsample of X‐ray underluminous systems confirms their reality.