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We describe the observations and resultant galaxy cluster catalog from the 2770 deg$^2$ SPTpol Extended Cluster Survey (SPT-ECS). Clusters are identified via the Sunyaev-Zeldovich (SZ) effect, and confirmed with a combination of archival and targeted follow-up data, making particular use of data from the Dark Energy Survey (DES). With incomplete followup we have confirmed as clusters 244 of 266 candidates at a detection significance $xi ge 5$ and an additional 204 systems at $4<xi<5$. The confirmed sample has a median mass of $M_{500c} sim {4.4 times 10^{14} M_odot h_{70}^{-1}}$, a median redshift of $z=0.49$, and we have identified 44 strong gravitational lenses in the sample thus far. Radio data are used to characterize contamination to the SZ signal; the median contamination for confirmed clusters is predicted to be $sim$1% of the SZ signal at the $xi>4$ threshold, and $<4%$ of clusters have a predicted contamination $>10% $ of their measured SZ flux. We associate SZ-selected clusters, from both SPT-ECS and the SPT-SZ survey, with clusters from the DES redMaPPer sample, and find an offset distribution between the SZ center and central galaxy in general agreement with previous work, though with a larger fraction of clusters with significant offsets. Adopting a fixed Planck-like cosmology, we measure the optical richness-to-SZ-mass ($lambda-M$) relation and find it to be 28% shallower than that from a weak-lensing analysis of the DES data---a difference significant at the 4 $sigma$ level---with the relations intersecting at $lambda=60$ . The SPT-ECS cluster sample will be particularly useful for studying the evolution of massive clusters and, in combination with DES lensing observations and the SPT-SZ cluster sample, will be an important component of future cosmological analyses.
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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 characterise the population of galaxy clusters. We provide a description of the construction of the NORAS II galaxy cluster survey based on X-ray data from the northern part of the ROSAT All-Sky Survey. NORAS II extends the NORAS survey down to a flux limit of 1.8 x 10^(-12) erg s^-1 cm^-2 (0.1 - 2.4 keV) increasing the sample size by about a factor of two. The NORAS II cluster survey now reaches the same quality and depth of its counterpart, the Southern REFLEX II 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 NORAS II contains 860 clusters with a median redshift of z = 0.102. We provide a number of statistical functions including the logN-logS and the X-ray luminosity function and compare these to the results from the complementary REFLEX II survey. Using the NORAS II sample to constrain the cosmological parameters, sigma_8 and Omega_m, yields results perfectly consistent with those of REFLEX II. Overall, the results show that the two hemisphere samples, NORAS II and REFLEX II, can be combined without problems to an all-sky sample, just excluding the Zone-of-Avoidance.
We study the polarisation properties of extragalactic sources at 95 and 150 GHz in the SPTpol 500 deg$^2$ survey. We estimate the polarised power by stacking maps at known source positions, and correct for noise bias by subtracting the mean polarised power at random positions in the maps. We show that the method is unbiased using a set of simulated maps with similar noise properties to the real SPTpol maps. We find a flux-weighted mean-squared polarisation fraction $langle p^2 rangle= [8.9pm1.1] times 10^{-4}$ at 95 GHz and $[6.9pm1.1] times 10^{-4}$ at 150~GHz for the full sample. This is consistent with the values obtained for a sub-sample of active galactic nuclei. For dusty sources, we find 95 per cent upper limits of $langle p^2 rangle_{rm 95}<16.9 times 10^{-3}$ and $langle p^2 rangle_{rm 150}<2.6 times 10^{-3}$. We find no evidence that the polarisation fraction depends on the source flux or observing frequency. The 1-$sigma$ upper limit on measured mean squared polarisation fraction at 150 GHz implies that extragalactic foregrounds will be subdominant to the CMB E and B mode polarisation power spectra out to at least $elllesssim5700$ ($elllesssim4700$) and $elllesssim5300$ ($elllesssim3600$), respectively at 95 (150) GHz.
We report the first detection of gravitational lensing due to galaxy clusters using only the polarization of the cosmic microwave background (CMB). The lensing signal is obtained using a new estimator that extracts the lensing dipole signature from stacked images formed by rotating the cluster-centered Stokes $Q/U$ map cutouts along the direction of the locally measured background CMB polarization gradient. Using data from the SPTpol 500 deg$^{2}$ survey at the locations of roughly 18,000 clusters with richness $lambda ge 10$ from the Dark Energy Survey (DES) Year-3 full galaxy cluster catalog, we detect lensing at $4.8sigma$. The mean stacked mass of the selected sample is found to be $(1.43 pm 0.4) times 10^{14} {rm M_{odot}}$ which is in good agreement with optical weak lensing based estimates using DES data and CMB-lensing based estimates using SPTpol temperature data. This measurement is a key first step for cluster cosmology with future low-noise CMB surveys, like CMB-S4, for which CMB polarization will be the primary channel for cluster lensing measurements.
We present a catalog of galaxy cluster candidates detected in 100 square degrees surveyed with the SPTpol receiver on the South Pole Telescope. The catalog contains 89 candidates detected with a signal-to-noise ratio greater than 4.6. The candidates are selected using the Sunyaev-Zeldovich effect at 95 and 150 GHz. Using both space- and ground-based optical and infrared telescopes, we have confirmed 81 candidates as galaxy clusters. We use these follow-up images and archival images to estimate photometric redshifts for 66 galaxy clusters and spectroscopic observations to obtain redshifts for 13 systems. An additional 2 galaxy clusters are confirmed using the overdensity of near-infrared galaxies only, and are presented without redshifts. We find that 15 candidates (18% of the total sample) are at redshift of $z geq 1.0$, with a maximum confirmed redshift of $z_{rm{max}} = 1.38 pm 0.10$. We expect this catalog to contain every galaxy cluster with $M_{500c} > 2.6 times 10^{14} M_odot h^{-1}_{70}$ and $z > 0.25$ in the survey area. The mass threshold is approximately constant above $z = 0.25$, and the complete catalog has a median mass of approximately $ M_{500c} = 2.7 times 10^{14} M_odot h^{-1}_{70}$. Compared to previous SPT works, the increased depth of the millimeter-wave data (11.2 and 6.5 $mu$K-arcmin at 95 and 150 GHz, respectively) makes it possible to find more galaxy clusters at high redshift and lower mass.
This paper presents 52 X-ray bright galaxy clusters selected within the 11 deg$^2$ XMM-LSS survey. 51 of them have spectroscopic redshifts ($0.05<z<1.06$), one is identified at $z_{rm phot}=1.9$, and all together make the high-purity Class 1 (C1) cluster sample of the XMM-LSS, the highest density sample of X-ray selected clusters with a monitored selection function. Their X-ray fluxes, averaged gas temperatures (median $T_X=2$ keV), luminosities (median $L_{X,500}=5times10^{43}$ ergs/s) and total mass estimates (median $5times10^{13} h^{-1} M_{odot}$) are measured, adapting to the specific signal-to-noise regime of XMM-LSS observations. The redshift distribution of clusters shows a deficit of sources when compared to the cosmological expectations, regardless of whether WMAP-9 or Planck-2013 CMB parameters are assumed. This lack of sources is particularly noticeable at $0.4 lesssim z lesssim 0.9$. However, after quantifying uncertainties due to small number statistics and sample variance we are not able to put firm (i.e. $>3 sigma$) constraints on the presence of a large void in the cluster distribution. We work out alternative hypotheses and demonstrate that a negative redshift evolution in the normalization of the $L_{X}-T_X$ relation (with respect to a self-similar evolution) is a plausible explanation for the observed deficit. We confirm this evolutionary trend by directly studying how C1 clusters populate the $L_{X}-T_X-z$ space, properly accounting for selection biases. We point out that a systematically evolving, unresolved, central component in clusters and groups (AGN contamination or cool core) can impact the classification as extended sources and be partly responsible for the observed redshift distribution.[abridged]
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