We present a catalog of 182 galaxy clusters detected through the Sunyaev-Zel'dovich (SZ) effect by the Atacama Cosmology Telescope in a contiguous 987.5 deg2 field. The clusters were detected as SZ ...decrements by applying a matched filter to 148 GHz maps that combine the original ACT equatorial survey with data from the first two observing seasons using the ACTPol receiver. Optical/IR confirmation and redshift measurements come from a combination of large public surveys and our own follow-up observations. Where necessary, we measured photometric redshifts for clusters using a pipeline that achieves accuracy Δz/(1 + z) = 0.015 when tested on Sloan Digital Sky Survey data. Under the assumption that clusters can be described by the so-called universal pressure profile (UPP) and its associated mass scaling law, the full signal-to-noise ratio > 4 sample spans the mass range , with median . The sample covers the redshift range 0.1 < z < 1.4 (median z = 0.49), and 28 clusters are new discoveries (median z = 0.80). We compare our catalog with other overlapping cluster samples selected using the SZ, optical, and X-ray wavelengths. We find that the ratio of the UPP-based SZ mass to richness-based weak-lensing mass is . After applying this calibration, the mass distribution for clusters with M500c > 4 × 1014 M is consistent with the number of such clusters found in the South Pole Telescope SZ survey.
ABSTRACT
We report a significant detection of the hot intergalactic medium in the filamentary bridge connecting the galaxy clusters Abell 399 and Abell 401. This result is enabled by a low-noise, ...high-resolution map of the thermal Sunyaev–Zeldovich signal from the Atacama Cosmology Telescope (ACT) and Planck satellite. The ACT data provide the 1.65 arcmin resolution that allows us to clearly separate the profiles of the clusters, whose centres are separated by 37 arcmin, from the gas associated with the filament. A model that fits for only the two clusters is ruled out compared to one that includes a bridge component at >5σ. Using a gas temperature determined from Suzaku X-ray data, we infer a total mass of $(3.3\pm 0.7)\times 10^{14}\, \mathrm{M}_{\odot }$ associated with the filament, comprising about 8 per cent of the entire Abell 399–Abell 401 system. We fit two phenomenological models to the filamentary structure; the favoured model has a width transverse to the axis joining the clusters of ${\sim }1.9\, \mathrm{Mpc}$. When combined with the Suzaku data, we find a gas density of $(0.88\pm 0.24)\times 10^{-4}\, \mathrm{cm}^{-3}$, considerably lower than previously reported. We show that this can be fully explained by a geometry in which the axis joining Abell 399 and Abell 401 has a large component along the line of sight, such that the distance between the clusters is significantly greater than the $3.2\, \mathrm{Mpc}$ projected separation on the plane of the sky. Finally, we present initial results from higher resolution (12.7 arcsec effective) imaging of the bridge with the MUSTANG-2 receiver on the Green Bank Telescope.
Ecologists have long sought to understand the factors controlling the structure of savanna vegetation. Using data from 2154 sites in savannas across Africa, Australia, and South America, we found ...that increasing moisture availability drives increases in fire and tree basal area, whereas fire reduces tree basal area. However, among continents, the magnitude of these effects varied substantially, so that a single model cannot adequately represent savanna woody biomass across these regions. Historical and environmental differences drive the regional variation in the functional relationships between woody vegetation, fire, and climate. These same differences will determine the regional responses of vegetation to future climates, with implications for global carbon stocks.
We investigate the origin of halo assembly bias, the dependence of halo clustering on assembly history. We relate halo assembly to peak properties measured in the Lagrangian space of the initial ...linear Gaussian random density field and show how these same Lagrangian properties determine large- scale bias. We focus on the two regimes where assembly bias has been observed to be significant: at masses very large and very small compared to the nonlinear mass scale. At high masses, we show that assembly bias is expected from the statistics of the peaks of Gaussian random fluctuations, and we show that the extent of assembly bias found in N-body simulations of rare halos is in excellent agreement with our theoretical prediction. At low masses, we argue that assembly bias largely arises from a subpopulation of low-mass halos whose mass accretion has ceased. Due to their arrested development, these halos naturally become unbiased, in contrast to their antibiased peers. We show that a simple toy model incorporating these effects can roughly reproduce the bias trends found in N-body simulations.
Antimicrobial peptides are small, cationic proteins that can induce lysis of bacterial cells through interaction with their membranes. Different mechanisms for cell lysis have been proposed, but ...these models tend to neglect the role of the chemical composition of the membrane, which differs between bacterial species and can be heterogeneous even within a single cell. Moreover, the cell envelope of Gram-negative bacteria such as E. coli contains two membranes with differing compositions. To this end, we report the first molecular dynamics simulation study of the interaction of the antimicrobial peptide, polymyxin B1 with complex models of both the inner and outer membranes of E. coli. The results of >16 microseconds of simulation predict that polymyxin B1 is likely to interact with the membranes via distinct mechanisms. The lipopeptides aggregate in the lipopolysaccharide headgroup region of the outer membrane with limited tendency for insertion within the lipid A tails. In contrast, the lipopeptides readily insert into the inner membrane core, and the concomitant increased hydration may be responsible for bilayer destabilization and antimicrobial function. Given the urgent need to develop novel, potent antibiotics, the results presented here reveal key mechanistic details that may be exploited for future rational drug development.
ABSTRACT Line-intensity mapping (LIM) experiments coming online now will survey fluctuations in aggregate emission in the C ii ionized carbon line from galaxies at the end of reionization. ...Experimental progress must be matched by theoretical reassessments of approaches to modelling and the information content of the signal. We present a new model for the halo–C ii connection, building upon results from the Feedback In Realistic Environments simulations suggesting that gas mass and metallicity most directly determine C ii luminosity. Applying our new model to an ensemble of peak-patch halo light-cones, we generate new predictions for the C ii LIM signal at z ≳ 6. We expect a baseline 4000-h LIM survey from the Cerro Chajnantor Atacama Telescope facility to have the fundamental sensitivity to detect the C ii power spectrum at a significance of 5σ at z ∼ 6, with an extended or successor Stage 2 experiment improving significance to 48σ at z ∼ 6 and achieving 11σ at z ∼ 7.5. Cross-correlation through stacking, simulated against a mock narrow-band Lyman-break galaxy survey, would yield a strong detection of the radial profile of cosmological C ii emission surrounding star-forming galaxies. We also analyse the role of a few of our model’s parameters through the pointwise relative entropy (PRE) of the distribution of C ii intensities. While the PRE signature of different model parameters can become degenerate or diminished after factoring in observational distortions, various parameters do imprint themselves differently on the one-point statistics of the intrinsic signal. Further work can pave the way to access this information and distinguish different sources of non-Gaussianity in the C ii LIM observation.
We construct cosmic microwave background lensing mass maps using data from
the 2014 and 2015 seasons of observations with the Atacama Cosmology Telescope
(ACT). These maps cover 2100 square degrees ...of sky and overlap with a wide variety
of optical surveys. The maps are signal dominated on large scales and have fidelity
such that their correlation with the cosmic infrared background is clearly visible by
eye. We also create lensing maps with thermal Sunyaev-Zel’dovich contamination
removed using a novel cleaning procedure that only slightly degrades the lensing
signal-to-noise ratio. The cross-spectrum between the cleaned lensing map and the
BOSS CMASS galaxy sample is detected at 10-σ significance, with an amplitude of
A = 1.02±0.10 relative to the Planck best-fit LCDM cosmological model with fiducial
linear galaxy bias. Our measurement lays the foundation for lensing cross-correlation
science with current ACT data and beyond.
Abstract
We report on the serendipitous discovery of three transient millimeter-wave sources using data from the Atacama Cosmology Telescope. The first, detected at R.A
.
= 273.8138, decl. = −49.4628 ...at ∼50
σ
total, brightened from less than 5 mJy to at least 1100 mJy at 150 GHz with an unknown rise time shorter than 13 days, during which the increase from 250 mJy to 1100 mJy took only 8 minutes. Maximum flux was observed on 2019 November 8. The source’s spectral index in flux between 90–150 GHz was positive,
α
= 1.5 ± 0.2. The second, detected at R.A. = 105.1584, decl
.
= −11.2434 at ∼20
σ
total, brightened from less than 20 mJy to at least 300 mJy at 150 GHz with an unknown rise time shorter than 8 days. Maximum flux was observed on 2019 December 15. Its spectral index was also positive,
α
= 1.8 ± 0.2. The third, detected at R.A
.
= 301.9952, decl. = 16.1652 at ∼40
σ
total, brightened from less than 8 mJy to at least 300 mJy at 150 GHz over a day or less but decayed over a few days. Maximum flux was observed on 2018 September 11. Its spectrum was approximately flat, with a spectral index of
α
= −0.2 ± 0.1. None of the sources were polarized to the limits of these measurements. The two rising-spectrum sources are coincident in position with M and K stars, while the third is coincident with a G star.
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