Delfin++ (Delaunay Edge Void Finder) is a simple and time-efficient algorithm, with a single input variable, designed to find cosmological voids within a 3-dimensional distribution of galaxies by characterizing them as polyhedral regions from a Delaunay tessellation. Two density metrics are defined and used to search for density minima and construct polyhedra that represent the underdense zones. A density threshold is used to define the limit above which a galaxy will not be considered part of a void. This threshold is commonly defined as 0.2n̄, where n̄ is the mean point density of the sample, whereas the values used in this work range from 0.2n̄ to 0.33n̄. The algorithm is applied to artificial data, with different density contrasts, as well as to galaxy data from SDSS DR10. The detected voids are compared with voids that have been produced through the application of vide. Our algorithm detects roundish underdense regions in the galaxy samples, with differences and overlaps compared to the vide algorithm's results. Closer agreement is revealed when the edge length density metric is used over large galaxy samples, allowing for the detection of up to 90% of the largest vide voids. We measure ellipticities of Delfin++ detected voids and find that their distribution is shifted towards smaller values in comparison with vide's distribution, and with predictions from an analytical model. The voids found with Delfin++ are not intended to generate a catalog, but rather represent a proof of concept of a simpler algorithm or with fewer rules for further calibration and future production of a final catalog. Delfin++ performance tests suggest that enhanced characterization of voids can be achieved through (i) choice of other density threshold values, and (ii) early recognition and rejection of deformed polyhedra induced by missing data.

We study dynamical dark energy models within Einstein's theory by means of matter perturbations and the growth index γ. Within four-dimensional General Relativity, we assume that dark energy does not cluster, and we adopt a linear ansatz for the growth index to investigate its impact on the deceleration parameter, q, and on the dark energy equation-of-state parameter, w. Following this approach, we identify a relationship between q_0 (today's value of q) and γ, which to the best of our knowledge is new. For w(z), we find that in most of the cases considered it crosses the -1 line (quintom) ending at a present day value w_0 > -1. Furthermore, we show that an analytic expression for w(z) may be obtained in the form of order (4,4) (or higher) Padé parameterizations.

Besides their causal connection with long and short-term magnetic variability, solar bipolar magnetic regions are our chief source of insight into the location, size, and properties of large-scale toroidal magnetic structures in the solar interior. The great majority of these regions (≈95%) follow a systematic east–west polarity orientation (Hale’s law) that reverses in opposite hemispheres and across even and odd cycles. These regions also present a systematic north–south polarity orientation (Joy’s law) that helps build the poloidal field that seeds the new cycle. Exceptions to Hale’s law are rare and difficult to study due to their low numbers. Here, we present a statistical analysis of the inclination (tilt) with respect to the equator of Hale versus anti-Hale regions spanning four solar cycles, considering two complementary tilt definitions adopted in previous studies. Our results show that anti-Hale regions belong to a separate population than Hale regions, suggesting a different originating mechanism. However, we find that anti-Hale region tilts present similar systematic tilt properties and similar latitudinal distributions to Hale regions, implying a strong connection between the two. We see this as evidence that they belong to a common toroidal flux system. We speculate that anti-Hale regions originate from poloidal field sheared and strengthened on the spot after the emergence of Hale regions with very strong poloidal contribution. Thus, they are not in contradiction with the idea of largely coherent toroidal flux systems inside the solar interior.

We present the temperature and polarization angular power spectra of the CMB measured by the Atacama Cosmology Telescope (ACT) from 5400 deg2of the 2013–2016 survey, which covers >15000 deg2at 98 and 150 GHz. For this analysis we adopt a blinding strategy to help avoid confirmation bias and, related to this, show numerous checks for systematic error done before unblinding. Using the likelihood for the cosmological analysis we constrain secondary sources of anisotropy and foreground emission, and derive a “CMB-only” spectrum that extends to ℓ=4000. At large angular scales, foreground emission at 150 GHz is ∼1% of TT and EE within our selected regions and consistent with that found byPlanck. Using the same likelihood, we obtain the cosmological parameters for ΛCDM for the ACT data alone with a prior on the optical depth of τ=0.065±0.015. ΛCDM is a good fit. The best-fit model has a reduced χ2of 1.07 (PTE=0.07) withH0=67.9±1.5 km/s/Mpc. We show that the lensing BB signal is consistent with ΛCDM and limit the celestial EB polarization angle to ψP =−0.07̂±0.09̂. We directly cross correlate ACT withPlanckand observe generally good agreement but with some discrepancies in TE. All data on which this analysis is based will be publicly released.

We present new arcminute-resolution maps of the Cosmic Microwave Background temperature and polarization anisotropy from the Atacama Cosmology Telescope, using data taken from 2013–2016 at 98 and 150 GHz. The maps cover more than 17,000 deg2, the deepest 600 deg2 with noise levels below 10μK-arcmin. We use the power spectrum derived from almost 6,000 deg2 of these maps to constrain cosmology. The ACT data enable a measurement of the angular scale of features in both the divergence-like polarization and the temperature anisotropy, tracing both the velocity and density at last-scattering. From these one can derive the distance to the last-scattering surface and thus infer the local expansion rate, H0. By combining ACT data with large-scale information from WMAP we measure H0=67.6± 1.1 km/s/Mpc, at 68% confidence, in excellent agreement with the independently-measured Planck satellite estimate (from ACT alone we find H0=67.9± 1.5 km/s/Mpc). The ΛCDM model provides a good fit to the ACT data, and we find no evidence for deviations: both the spatial curvature, and the departure from the standard lensing signal in the spectrum, are zero to within 1σ; the number of relativistic species, the primordial Helium fraction, and the running of the spectral index are consistent with ΛCDM predictions to within 1.5–2.2σ. We compare ACT, WMAP, and Planck at the parameter level and find good consistency; we investigate how the constraints on the correlated spectral index and baryon density parameters readjust when adding CMB large-scale information that ACT does not measure. The DR4 products presented here will be publicly released on the NASA Legacy Archive for Microwave Background Data Analysis.

Luis E. Campusano, Gabriel Marinello, Roger G. Clowes, Christopher P. Haines , Sebastián Pereira, Daniel Pizarro, Nancy Hitschfeld-Kahler, and Ilona K. Söchting 1 Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile; luis@das.uchile.cl 2 Joint ALMA Observatory, Avenida Alonso de Córdova 3107, Vitacura 7630355, Santiago, Chile 3 Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK 4 INAF—Osservatorio Astronomico di Brera, via Brera 28, I-20121, Milano, Italy 5 Departamento de Ciencias de la Computación, Universidad de Chile, Casilla 2777, Santiago, Chile 6 INRIA Chile, Av. Apoquindo 2827, Las Condes, Santiago, Chile 7 Wärtsilä Corporation, P.O. Box 196, Helsinki, Finland Received 2019 December 17; published 2020 February 14

We identify 1901 galaxy clusters (Ng…2) with the VoML+G algorithm (Paper I) on the Two-Degree Field Galaxy Redshift Survey. We present the 341 clusters with at least 10 galaxies that are within 0.009<z<0.14 (the Catalog), of which 254 (∼75%) have counterparts in the literature (NED), with the remainder (87) plausibly “new” because of incompleteness of previous searches or unusual galaxy contents. The 207 clusters within z = 0.04–0.09 are used to study the properties of the galaxy systems in the nearby universe, including their galaxy contents parameterized by the late-type galaxy fractions ( fL). For this nearly complete cluster subsample, we find the following: (i) 63% are dominated by early-type galaxies (i.e., the late-type-poor clusters, fL<0.5) with corresponding mean multiplicity and logarithmic virial mass (in units of Me) of 22±1 and 12.91±0.04, respectively; and (ii) 37% are dominated by late-type galaxies (i.e., the late-type-rich clusters, fL…0.5) with corresponding mean multiplicity and logarithmic virial mass (in units of Me) of 15.7±0.9 and 12.66±0.07, respectively. The statistical analysis of the late-type fraction distribution supports, with a 3σ confidence level, the presence of two population components. It is suggested that the late-type-poor galaxy systems reflect and extend the class of Abell-APM-EDCC clusters and that the late-type-rich systems (∼one-third of the total) belong to a new, previously unappreciated class. The late-type-rich clusters, on average high mass-to-light ratio systems, appear to be more clustered on large scales than the late-type-poor clusters. A class of late-type-rich clusters is not predicted by current theory.

We identify 1901 galaxy clusters (Ng ≥ 2) with the VoML+G algorithm (Paper I) on the Two-Degree Field Galaxy Redshift Survey. We present the 341 clusters with at least 10 galaxies that are within 0.009 < z < 0.14 (the Catalog), of which 254 (∼75%) have counterparts in the literature (NED), with the remainder (87) plausibly “new” because of incompleteness of previous searches or unusual galaxy contents. The 207 clusters within z = 0.04–0.09 are used to study the properties of the galaxy systems in the nearby universe, including their galaxy contents parameterized by the late-type galaxy fractions (fL). For this nearly complete cluster subsample, we find the following: (i) 63% are dominated by early-type galaxies (i.e., the late-type-poor clusters, fL < 0.5) with corresponding mean multiplicity and logarithmic virial mass (in units of M⊙) of 22 ± 1 and 12.91 ± 0.04, respectively; and (ii) 37% are dominated by late-type galaxies (i.e., the late-type-rich clusters, fL ≥ 0.5) with corresponding mean multiplicity and logarithmic virial mass (in units of M⊙) of 15.7 ± 0.9 and 12.66 ± 0.07, respectively. The statistical analysis of the late-type fraction distribution supports, with a 3σ confidence level, the presence of two population components. It is suggested that the late-type-poor galaxy systems reflect and extend the class of Abell-APM-EDCC clusters and that the late-type-rich systems (∼one-third of the total) belong to a new, previously unappreciated class. The late-type-rich clusters, on average high mass-to-light ratio systems, appear to be more clustered on large scales than the late-type-poor clusters. A class of late-type-rich clusters is not predicted by current theory.

The Atacama B-mode Search is an experiment designed to measure the cosmic microwave background polarization at large angular scales (0ℓ>4). It observes at 145 GHz from a site at 5,190 m elevation in northern Chile. The noise equivalent polarization temperature, or NEQ, is 41 μK√s. One of the unique features of ABS is its use of a rapidly rotating ambient-temperature half-wave plate (HWP) {as the first optical element}. {The HWP spins} at 2.55 Hz to modulate the incident polarized signal at frequencies above where instrument white noise dominates over atmospheric fluctuations and other sources of low-frequency noise. We report here on the analysis of data from a 2,400 deg2 region of sky. We perform a blind analysis to reduce potential bias. After unblinding, we find agreement with the Planck TE and EE measurements on the same region of sky, {with a derived calibration factor of 00.89 ± 0.1}. We marginally detect polarized dust emission {(at 3.2 σ for EE and 2.2 σ for BB)} and give an upper limit on the tensor-to-scalar ratio of r<2.3 (95% confidence level) with the equivalent of 100 on-sky days of observation. We also present a new measurement of the polarization of Tau A and introduce new methods for calibration and data analysis associated with HWP-based observations.

Galaxy clusters are expected to form hierarchically in a Lambda cold dark matter (Lambda CDM) universe, growing primarily through mergers with lower mass clusters and the continual accretion of group-mass haloes. Galaxy clusters assemble late, doubling their masses since z similar to 0.5, and so the outer regions of clusters should be replete with accreting group-mass systems. We present an XMM-Newton survey to search for X-ray groups in the infall regions of 23 massive galaxy clusters (< M-200 > similar to 10(15)M(circle dot)) at z similar to 0.2, identifying 39 X-ray groups that have been spectroscopically confirmed to lie at the cluster redshift. These groups have mass estimates in the range 2 x 10(13)-7 x 10(14)M(circle dot), and group-to-cluster mass ratios as low as 0.02. The comoving number density of X-ray groups in the infall regions is similar to 25x higher than that seen for isolated X-ray groups from the XXL survey. The average mass per cluster contained within these X-ray groups is 2.2 x 10(14)M(circle dot), or 19 +/- 5 per cent of the mass within the primary cluster itself. We estimate that similar to 10(15)M(circle dot) clusters increase their masses by 16 +/- 4 per cent between z = 0.223 and the present day due to the accretion of groups with M-200 >= 10(13.2)M(circle dot). This represents about half of the expected mass growth rate of clusters at these late epochs. The other half is likely to come from smooth accretion of matter not bound within haloes. The mass function of the infalling X-ray groups appears significantly top heavy with respect to that of 'field' X-ray systems, consistent with expectations from numerical simulations, and the basic consequences of collapsed massive dark matter haloes being biased tracers of the underlying large-scale density distribution.

This paper presents a new algorithm to find under-dense regions called voids inside a 2D point set. The algorithm starts from terminal-edges (local longest-edges) in a Delaunay triangulation and builds the largest possible low density terminal-edge regions around them. A terminal-edge region can represent either an entire void or part of a void (subvoid). Using artificial data sets, the case of voids that are detected as several adjacent subvoids is analyzed and four subvoid joining criteria are proposed and evaluated. Since this work is inspired on searches of a more robust, effective and efficient algorithm to find 3D cosmological voids the evaluation of the joining criteria considers this context. However, the design of the algorithm permits its adaption to the requirements of any similar application.

The nature of galaxy structures on large scales is a key observational prediction for current models of galaxy formation. The Sloan Digital Sky Survey (SDSS) and the 2dF galaxy survey have revealed a number of structures on 40–150 h−1 Mpc scales at low redshifts, and some even larger ones. To constrain galaxy number densities, luminosities, and stellar populations in large structures at higher redshift, we have investigated two sheet-like structures of galaxies at z = 0.8 and 1.3 spanning 150 h−1 comoving Mpc embedded in large quasar groups (LQGs) extending over at least 200 h−1 Mpc. We present first results of an analysis of these sheet-like structures using two contiguous 1 deg Galaxy Evolution Explorer (GALEX) fields (FUV and NUV) cross-correlated with optical data from the SDSS. We derive a sample of 462 Lyman break galaxy (LBG) candidates coincident with the sheets. Using the GALEX and SDSS data, we show that the overall average spectral energy distribution of a LBG galaxy at z ∼ 1 is flat (in fλ) in the rest-frame wavelength range from 1500 Å to 4000 Å, implying evolved populations of stars in the LBGs. From the luminosity functions we get indications for overdensities in the two LQGs compared to their foreground regions. Similar conclusions come from the calculation of the 2-point correlation function, showing a 2σ overdensity for the LBGs in the z ∼ 0.8 LQG on scales of 1.6 to 4.8 Mpc, indicating similar correlation scales for our LBG sample as their z ∼ 3 counterparts.

Galaxy observations and N-body cosmological simulations produce conflicting dark matter halo density pro files for galaxy central regions. While simulations suggest a cuspy and universal density pro file (UDP) of this region, the majority of observations favor variable profiles with a core in the center. In this paper, we investigate the convergency of standard N-body simulations, especially in the cusp region, following the approach proposed by [1]. We simulate the well known Hernquist model using the SPH code Gadget-3 and consider the full array of dynamical parameters of the particles. We find that, although the cuspy pro file is stable, all integrals of motion characterizing individual particles suffer strong unphysical variations along the whole halo, revealing an effective interaction between the test bodies. This result casts doubts on the reliability of the velocity distribution function obtained in the simulations. Moreover, we find unphysical Fokker-Planck streams of particles in the cusp region. The same streams should appear in cosmological N-body simulations, being strong enough to change the shape of the cusp or even to create it. Our analysis, based on the Hernquist model and the standard SPH code, strongly suggests that the UDPs generally found by the cosmological N-body simulations may be a consequence of numerical effects. A much better understanding of the N-body simulation convergency is necessary before a 'core-cusp problem' can properly be used to question the validity of the CDM model.

This paper is the first in a series, presenting a new galaxy cluster finder based on a three-dimensional Voronoi Tesselation plus a maximum likelihood estimator, followed by gapping-filtering in radial velocity(VoML+G). The scientific aim of the series is a reassessment of the diversity of optical clusters in the local universe. A mock galaxy database mimicking the southern strip of the magnitude(blue)-limited 2dF Galaxy Redshift Survey (2dFGRS), for the redshift range 0.009 < z < 0.22, is built on the basis of the Millennium Simulation of the LCDM cosmology and a reference catalog of “Millennium clusters,” spannning across the 1.0 × 1012–1.0 × 1015 M⊙ h−1 dark matter (DM) halo mass range, is recorded. The validation of VoML+G is performed through its application to the mock data and the ensuing determination of the completeness and purity of the cluster detections by comparison with the reference catalog. The execution of VoML+G over the 2dFGRS mock data identified 1614 clusters, 22% with Ng ≥ 10, 64 percent with 10 > Ng ≥ 5, and 14% with Ng < 5. The ensemble of VoML+G clusters has a ∼59% completeness and a ∼66% purity, whereas the subsample with Ng ≥ 10, to z ∼ 0.14, has greatly improved mean rates of ∼75% and ∼90%, respectively. The VoML+G cluster velocity dispersions are found to be compatible with those corresponding to “Millennium clusters” over the 300–1000 km s−1 interval, i.e., for cluster halo masses in excess of ∼3.0 × 1013 M⊙ h−1.

We present an axially symmetric formula to calculate the probability of finding gravitational arcs in galaxy clusters, being induced by their massive dark matter haloes, as a function of clusters redshifts and virial masses. The formula includes the ellipticity of the clusters dark matter potential by using a pseudo-elliptical approximation. The probabilities are calculated and compared for two dark matter halo profiles, the Navarro, Frenk and White (NFW) and the non-singular- isothermal-sphere (NSIS). We demonstrate the power of our formulation through a Kolmogorov-Smirnov (KS) test on the strong lensing statistics of an X-ray bright sample of low-redshift Abell clusters. This KS test allows us to establish limits on the values of the concentration parameter for the NFW profile (c(Delta)) and the core radius for the NSIS profile (r(c)), which are related to the lowest cluster redshift (z(cut)) where strong arcs can be observed. For NFW dark matter profiles, we infer cluster haloes with concentrations that are consistent to those predicted by Lambda CDM simulations. As for NSIS dark matter profiles, we find only upper limits for the clusters core radii and thus do not rule out a purely SIS model. For alternative mass profiles, our formulation provides constraints through zcut on the parameters that control the concentration of mass in the inner region of the clusters haloes. We find that zcut is expected to lie in the 0.0-0.2 redshift, highlighting the need to include very low-z clusters in samples to study the clusters mass profiles.

ABSTRACT We evaluate the dry merger activity in the Coma cluster, using a spectroscopically complete sample of 70 red-sequence (RS) galaxies, most of which (∼75%) are located within 0.2R 200 (∼0.5 Mpc) from the cluster center, with data from the Coma Treasury Survey obtained with the Hubble Space Telescope. The fraction of close galaxy pairs in the sample is the proxy employed for the estimation of the merger activity. We identify 5 pairs and 1 triplet, enclosing a total of 13 galaxies, based on limits on projected separation and line-of-sight velocity difference. Of these systems, none show signs of ongoing interaction, and therefore we do not find any true mergers in our sample. This negative result sets a 1σ upper limit of 1.5% per Gyr for the major dry merger rate, consistent with the low rates expected in present-day clusters. Detailed examination of the images of all the RS galaxies in the sample reveals only one with low surface brightness features identifiable as the remnant of a past merger or interaction, implying a post-merger fraction below 2%.

We investigate the strength of ultraviolet Fe ii emission in fainter quasars compared with brighter quasars for 1.0 a parts per thousand currency sign z a parts per thousand currency sign 1.8, using the Sloan Digital Sky Survey (SDSS) DR7QSO catalogue and spectra of Schneider et al., and the SDSS Faint Quasar Survey (SFQS) catalogue and spectra of Jiang et al. We quantify the strength of the UV Fe ii emission using the W2400 equivalent width of Weymann et al., which is defined between two rest-frame continuum windows at 2240-2255 and 2665-2695 . The main results are the following. (1) We find that for W2400 a parts per thousand(3) 25 there is a universal (i.e. for quasars in general) strengthening of W2400 with decreasing intrinsic luminosity, L3000. (2) In conjunction with previous work by Clowes et al., we find that there is a further, differential, strengthening of W2400 with decreasing L3000 for those quasars that are members of Large Quasar Groups (LQGs). (3) We find that increasingly strong W2400 tends to be associated with decreasing full width at half maximum (FWHM) of the neighbouring Mg ii lambda 2798 broad emission line. (4) We suggest that the dependence of W2400 on L3000 arises from Ly alpha fluorescence. (5) We find that stronger W2400 tends to be associated with smaller virial estimates from Shen et al. of the mass of the central black hole, by a factor of similar to 2 between the ultrastrong emitters and the weak. Stronger W2400 emission would correspond to smaller black holes that are still growing. The differential effect for LQG members might then arise from preferentially younger quasars in the LQG environments.

We present the catalogue of the Mg  II absorption systems detected at a high significance level using an automated search algorithm in the spectra of quasars from the 12th data release of the Sloan Digital Sky Survey. A total of 266,433 background quasars were searched for the presence of absorption systems in their spectra. The continuum modelling for the quasar spectra was performed using a mean filter. A pseudo-continuum derived using a median filter was used to trace the emission lines. The absorption system catalogue contains 39,694 Mg  II systems detected at a 6.0, 3.0σ level respectively for the two lines of the doublet. The catalogue was constrained to an absorption line redshift of 0.35 ≤ z2796 ≤ 2.3. The rest-frame equivalent width of the λ2796 line ranges between 0.2 ≤ Wr ≤ 6.2 A. Using Gaussian noise-only simulations, we estimate a false positive rate of 7.7 per cent in the catalogue. We measured the number density ∂N^(2796)/∂z of Mg II absorbers and find evidence for steeper evolution of the systems with Wr ≥ 1.2 A at low redshifts (z2796 ≤ 1.0), consistent with other earlier studies. A suite of null tests over the redshift range 0.5 ≤ z2796 ≤ 1.5 was used to study the presence of systematics and selection effects like the dependence of the number density evolution of the absorption systems on the properties of the background quasar spectra. The null tests do not indicate the presence of any selection effects in the absorption catalogue if the quasars with spectral signal-to-noise level less than 5.0 are removed. The resultant catalogue contains 36,981 absorption systems. The Mg  II absorption catalogue is publicly available and can be downloaded from the link http://srini.ph.unimelb.edu.au/mgii.php.