Description:
<jats:title>Abstract</jats:title>
<jats:p>As the largest, clearly defined building blocks of our universe, galaxy clusters are interesting astrophysical laboratories and important probes for cosmology. X-ray surveys for galaxy clusters provide one of the best ways to characterize the population of galaxy clusters. We provide a description of the construction of the <jats:sans-serif>NORAS II</jats:sans-serif> galaxy cluster survey based on X-ray data from the northern part of the <jats:sans-serif>ROSAT</jats:sans-serif> All-Sky Survey. <jats:sans-serif>NORAS II</jats:sans-serif> extends the <jats:sans-serif>NORAS</jats:sans-serif> survey down to a flux limit of 1.8 × 10<jats:sup>−12</jats:sup> erg s<jats:sup>−1</jats:sup> cm<jats:sup>−2</jats:sup> (0.1–2.4 keV), increasing the sample size by about a factor of two. The <jats:sans-serif>NORAS II</jats:sans-serif> cluster survey now reaches the same quality and depth as its counterpart, the southern <jats:sans-serif>REFLEX II</jats:sans-serif> survey, allowing us to combine the two complementary surveys. The paper provides information on the determination of the cluster X-ray parameters, the identification process of the X-ray sources, the statistics of the survey, and the construction of the survey selection function, which we provide in numerical format. Currently <jats:sans-serif>NORAS II</jats:sans-serif> contains 860 clusters with a median redshift of <jats:italic>z</jats:italic> = 0.102. We provide a number of statistical functions, including the log <jats:italic>N</jats:italic>–log <jats:italic>S</jats:italic> and the X-ray luminosity function and compare these to the results from the complementary <jats:sans-serif>REFLEX II</jats:sans-serif> survey. Using the <jats:sans-serif>NORAS II</jats:sans-serif> sample to constrain the cosmological parameters, <jats:italic>σ</jats:italic>
<jats:sub>8</jats:sub> and Ω<jats:sub>
<jats:italic>m</jats:italic>
</jats:sub>, yields results perfectly consistent with those of <jats:sans-serif>REFLEX II</jats:sans-serif>. Overall, the results show that the two hemisphere samples, <jats:sans-serif>NORAS II</jats:sans-serif> and <jats:sans-serif>REFLEX II</jats:sans-serif>, can be combined without problems into an all-sky sample, just excluding the zone of avoidance.</jats:p>