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Weak gravitational lensing provides a potentially powerful method for the detection of clusters. In addition to cluster candidates, a large number of objects with possibly no optical or X-ray component have been detected in shear-selected samples. We develop an analytic model to investigate the claim of Weinberg & Kamionkowski (2002) that unvirialised protoclusters account for a significant number of these so-called dark lenses. In our model, a protocluster consists of a small virialised region surrounded by in-falling matter. We find that, in order for a protocluster to simultaneously escape X-ray detection and create a detectable weak lensing signal, it must have a small virial mass (~10^{13} Msun) and large total mass (~ 10^{15} Msun), with a relatively flat density profile outside of the virial radius. Such objects would be characterized by rising tangential shear profiles well beyond the virial radius. We use a semi-analytic approach based on the excursion set formalism to estimate the abundance of lensing protoclusters with a low probability of X-ray detection. We find that they are extremely rare, accounting for less than 0.4 per cent of the total lenses in a survey with background galaxy density n = 30 arcmin^{-2} and an intrinsic ellipticity dispersion of 0.3. We conclude that lensing protoclusters with undetectable X-Ray luminosities are too rare to account for a significant number of dark lenses.
The study of galaxy protoclusters is beginning to fill in unknown details of the important phase of the assembly of clusters and cluster galaxies. This review describes the current status of this field and highlights promising recent findings related
[Abridged] We present the results of a large program conducted with the Very Large Telescope and Keck telescope to search for forming clusters of galaxies near powerful radio galaxies at 2.0 < z < 5.2. We obtained narrow- and broad-band images of nin
We constrain the scaling relation between optical richness ($lambda$) and halo mass ($M$) for a sample of SDSS redMaPPer galaxy clusters within the context of the {it Planck} cosmological model. We use a forward modeling approach where we model the p
The possibility that primordial black holes (PBHs) form a part of dark matter has been considered over a wide mass range from the Planck mass ($10^{-5}~rm g$) to the level of the supermassive black hole in the center of the galaxy. Primordial origin
We report the results of a submillimeter dust continuum survey of the protoclusters NGC 2068 and NGC 2071 in Orion B carried out at 850 microns and 450 microns with SCUBA on JCMT. The mapped region is ~ 32 x 18 in size (~ 4 pc x 2 pc) and consists of