arXiv subjects

M. Brodwin

Publications and source records attributed to M. Brodwin.

At least 19 recordsLinked to original sources

arXiv2026

The Massive and Distant Clusters of WISE Survey 2: Detection of splashback radii in galaxy cluster total light stacks

The splashback radius, the radius of the apocenter of the first orbit of infalling material, is a measurable quantity marking the boundary between a galaxy cluster and its infalling region. We report detections of splashback radii in total light stacks, i.e. image stacks centered on the cores of galaxy clusters. Our analysis uses Wide-field Infrared Survey Explorer (WISE) W1 and W2 images of 83,345 candidate clusters at $0.5 \lesssim z \lesssim 1.9$ from the Massive and Distant Clusters of WISE Survey 2 (MaDCoWS2). The clusters are organized in stacks by redshift and signal-to-noise ($S\slash N$) ratios. We adopt a statistical approach, using 1000 bootstrap realizations to determine the median projected splashback radius and its confidence interval in a given bin. We compare our splashback radii with the measurements made by K. Thongkham et al. on a similar sample of MaDCoWS2 clusters using galaxy-cluster cross-correlation and find that they are consistent, although our method yields larger error bars. Our main systematic error is the accuracy of the background subtraction, but its impact remains small: the consistency of K. Thongkham et al. and our results suggests that neither method suffers from large systematics. The sensitivity of total light stacking to the contribution of faint galaxies can be advantageous to locate splashback radii when only the brightest galaxies are detected in individual images, such as at high redshifts. We present a potential application of this new technique to probe the evolution of the stellar mass in cluster infalling regions.

astro-ph.CO↗

arXiv2024

The Massive and Distant Clusters of WISE Survey 2: A Stacking Analysis Investigating the Evolution of Star Formation Rates and Stellar Masses in Groups and Clusters

The evolution of galaxies depends on their masses and local environments; understanding when and how environmental quenching starts to operate remains a challenge. Furthermore, studies of the high-redshift regime have been limited to massive cluster members, owing to sensitivity limits or small fields of views when the sensitivity is sufficient, intrinsically biasing the picture of cluster evolution. In this work, we use stacking to investigate the average star formation history of more than 10,000 groups and clusters drawn from the Massive and Distant Clusters of WISE Survey 2 (MaDCoWS2). Our analysis covers near ultraviolet to far infrared wavelengths, for galaxy overdensities at $0.5 \lesssim z \lesssim 2.54$. We employ SED fitting to measure the specific star formation rates (sSFR) in four annular apertures with radii between 0 and 1000 kpc. At $z \gtrsim 1.6$, the average sSFR evolves similarly to the field in both the core and the cluster outskirts. Between $\overline{z} = 1.60$ and $\overline{z} = 1.35$, the sSFR in the core drops sharply, and continues to fall relative to the field sSFR at lower redshifts. We interpret this change as evidence that the impact of environmental quenching dramatically increases at $z \sim 1.5$, with the short time span of the transition suggesting that the environmental quenching mechanism dominant at this redshift operates on a rapid timescale. We find indications that the sSFR may decrease with increasing host halo mass, but lower-scatter mass tracers than the signal-to-noise ratio (S/N) are needed to confirm this relationship.

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arXiv2024

SPT Clusters with DES and HST Weak Lensing. II. Cosmological Constraints from the Abundance of Massive Halos

We present cosmological constraints from the abundance of galaxy clusters selected via the thermal Sunyaev-Zel'dovich (SZ) effect in South Pole Telescope (SPT) data with a simultaneous mass calibration using weak gravitational lensing data from the Dark Energy Survey (DES) and the Hubble Space Telescope (HST). The cluster sample is constructed from the combined SPT-SZ, SPTpol ECS, and SPTpol 500d surveys, and comprises 1,005 confirmed clusters in the redshift range $0.25-1.78$ over a total sky area of 5,200 deg$^2$. We use DES Year 3 weak-lensing data for 688 clusters with redshifts $z<0.95$ and HST weak-lensing data for 39 clusters with $0.6<z<1.7$. The weak-lensing measurements enable robust mass measurements of sample clusters and allow us to empirically constrain the SZ observable--mass relation. For a flat $\Lambda$CDM cosmology, and marginalizing over the sum of massive neutrinos, we measure $\Omega_\mathrm{m}=0.286\pm0.032$, $\sigma_8=0.817\pm0.026$, and the parameter combination $\sigma_8\,(\Omega_\mathrm{m}/0.3)^{0.25}=0.805\pm0.016$. Our measurement of $S_8\equiv\sigma_8\,\sqrt{\Omega_\mathrm{m}/0.3}=0.795\pm0.029$ and the constraint from Planck CMB anisotropies (2018 TT,TE,EE+lowE) differ by $1.1\sigma$. In combination with that Planck dataset, we place a 95% upper limit on the sum of neutrino masses $\sum m_\nu<0.18$ eV. When additionally allowing the dark energy equation of state parameter $w$ to vary, we obtain $w=-1.45\pm0.31$ from our cluster-based analysis. In combination with Planck data, we measure $w=-1.34^{+0.22}_{-0.15}$, or a $2.2\sigma$ difference with a cosmological constant. We use the cluster abundance to measure $\sigma_8$ in five redshift bins between 0.25 and 1.8, and we find the results to be consistent with structure growth as predicted by the $\Lambda$CDM model fit to Planck primary CMB data.

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arXiv2023

SPT Clusters with DES and HST Weak Lensing. I. Cluster Lensing and Bayesian Population Modeling of Multi-Wavelength Cluster Datasets

We present a Bayesian population modeling method to analyze the abundance of galaxy clusters identified by the South Pole Telescope (SPT) with a simultaneous mass calibration using weak gravitational lensing data from the Dark Energy Survey (DES) and the Hubble Space Telescope (HST). We discuss and validate the modeling choices with a particular focus on a robust, weak-lensing-based mass calibration using DES data. For the DES Year 3 data, we report a systematic uncertainty in weak-lensing mass calibration that increases from 1% at $z=0.25$ to 10% at $z=0.95$, to which we add 2% in quadrature to account for uncertainties in the impact of baryonic effects. We implement an analysis pipeline that joins the cluster abundance likelihood with a multi-observable likelihood for the Sunyaev-Zel'dovich effect, optical richness, and weak-lensing measurements for each individual cluster. We validate that our analysis pipeline can recover unbiased cosmological constraints by analyzing mocks that closely resemble the cluster sample extracted from the SPT-SZ, SPTpol ECS, and SPTpol 500d surveys and the DES Year 3 and HST-39 weak-lensing datasets. This work represents a crucial prerequisite for the subsequent cosmological analysis of the real dataset.

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arXiv2023

SPT-SZ MCMF: An extension of the SPT-SZ catalog over the DES region

We present an extension to a Sunyaev-Zel'dovich Effect (SZE) selected cluster catalog based on observations from the South Pole Telescope (SPT); this catalog extends to lower signal-to-noise than the previous SPT-SZ catalog and therefore includes lower mass clusters. Optically derived redshifts, centers, richnesses and morphological parameters together with catalog contamination and completeness statistics are extracted using the multi-component matched filter algorithm (MCMF) applied to the S/N>4 SPT-SZ candidate list and the Dark Energy Survey (DES) photometric galaxy catalog. The main catalog contains 811 sources above S/N=4, has 91% purity and is 95% complete with respect to the original SZE selection. It contains 50% more total clusters and twice as many clusters above z=0.8 in comparison to the original SPT-SZ sample. The MCMF algorithm allows us to define subsamples of the desired purity with traceable impact on catalog completeness. As an example, we provide two subsamples with S/N>4.25 and S/N>4.5 for which the sample contamination and cleaning-induced incompleteness are both as low as the expected Poisson noise for samples of their size. The subsample with S/N>4.5 has 98% purity and 96% completeness, and will be included in a combined SPT cluster and DES weak-lensing cosmological analysis. We measure the number of false detections in the SPT-SZ candidate list as function of S/N, finding that it follows that expected from assuming Gaussian noise, but with a lower amplitude compared to previous estimates from simulations.

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arXiv2021

Mapping the intracluster medium temperature in the era of NIKA2 and MUSTANG-2

We present preliminary results from an on-going program that aims at mapping the intracluster medium (ICM) temperature of high redshift galaxy clusters from the MaDCoWS sample using a joint analysis of shallow X-ray data obtained by $Chandra$ and high angular resolution Sunyaev-Zel'dovich (SZ) observations realized with the NIKA2 and MUSTANG-2 cameras. We also present preliminary results from an on-going Open Time program within the NIKA2 collaboration that aims at mapping the ICM temperature of a galaxy cluster at $z=0.45$ from the resolved detection of the relativistic corrections to the SZ spectrum. These studies demonstrate how high angular resolution SZ observations will play a major role in the coming decade to push the investigation of ICM dynamics and non-gravitational processes to high redshift before the next generation X-ray observatories come into play.

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arXiv2020

Euclid preparation: X. The Euclid photometric-redshift challenge

Forthcoming large photometric surveys for cosmology require precise and accurate photometric redshift (photo-z) measurements for the success of their main science objectives. However, to date, no method has been able to produce photo-$z$s at the required accuracy using only the broad-band photometry that those surveys will provide. An assessment of the strengths and weaknesses of current methods is a crucial step in the eventual development of an approach to meet this challenge. We report on the performance of 13 photometric redshift code single value redshift estimates and redshift probability distributions (PDZs) on a common set of data, focusing particularly on the 0.2--2.6 redshift range that the Euclid mission will probe. We design a challenge using emulated Euclid data drawn from three photometric surveys of the COSMOS field. The data are divided into two samples: one calibration sample for which photometry and redshifts are provided to the participants; and the validation sample, containing only the photometry, to ensure a blinded test of the methods. Participants were invited to provide a redshift single value estimate and a PDZ for each source in the validation sample, along with a rejection flag that indicates sources they consider unfit for use in cosmological analyses. The performance of each method is assessed through a set of informative metrics, using cross-matched spectroscopic and highly-accurate photometric redshifts as the ground truth. We show that the rejection criteria set by participants are efficient in removing strong outliers, sources for which the photo-z deviates by more than 0.15(1+z) from the spectroscopic-redshift (spec-z). We also show that, while all methods are able to provide reliable single value estimates, several machine-learning methods do not manage to produce useful PDZs. [abridged]

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arXiv2020

The Chandra Deep Wide-Field Survey: A New Chandra Legacy Survey in the Boötes Field I. X-ray Point Source Catalog, Number Counts and Multi-Wavelength Counterparts

We present a new, ambitious survey performed with the Chandra X-ray Observatory of the 9.3 deg$^2$ Boötes field of the NOAO Deep Wide-Field Survey. The wide field probes a statistically representative volume of the Universe at high redshift. The Chandra Deep Wide-Field Survey exploits the excellent sensitivity and angular resolution of Chandra over a wide area, combining 281 observations spanning 15 years, for a total exposure time of 3.4 Ms, and detects 6891 X-ray point sources down to limiting fluxes of $4.7\times10^{-16}$, $1.5\times10^{-16}$, and $9\times10^{-16}$ erg cm$^{-2}$ s$^{-1}$, in the $0.5-7$ keV, $0.5-2$ keV, and $2-7$ keV bands, respectively. The robustness and reliability of the detection strategy is validated through extensive, state-of-the-art simulations of the whole field. Accurate number counts, in good agreement with previous X-ray surveys, are derived thanks to the uniquely large number of point sources detected, which resolve $65.0 \pm 12.8\%$ of the cosmic X-ray background between $0.5-2$ keV and $81.0 \pm 11.5\%$ between $2-7$ keV. Exploiting the wealth of multi-wavelength data available on the field, we assign redshifts to $\sim 94\%$ of the X-ray sources, estimate their obscuration and derive absorption-corrected luminosities. We provide an electronic catalog containing all the relevant quantities needed for future investigations.

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arXiv2020

Galaxy Clusters Selected via the Sunyaev-Zel'dovich Effect in the SPTpol 100-Square-Degree Survey

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-Zel'dovich 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 $μ$K-arcmin at 95 and 150 GHz, respectively) makes it possible to find more galaxy clusters at high redshift and lower mass.

astro-ph.CO↗

arXiv2019

The SPTpol Extended Cluster Survey

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-Zel'dovich (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 $ξ\ge 5$ and an additional 204 systems at $4<ξ<5$. 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 $ξ>4$ 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 ($λ-M$) 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 $σ$ level---with the relations intersecting at $λ=60$ . 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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arXiv2019

Mapping the gas thermodynamic properties of the massive cluster merger MOO J1142$+$1527 at z = 1.2

We present the results of the analysis of the very massive cluster MOO J1142$+$1527 at a redshift $z = 1.2$ based on high angular resolution NIKA2 Sunyaev-Zel'dovich (SZ) and $Chandra$ X-ray data. This multi-wavelength analysis enables us to estimate the shape of the temperature profile with unprecedented precision at this redshift and to obtain a map of the gas entropy distribution averaged along the line of sight. The comparison between the cluster morphological properties observed in the NIKA2 and $Chandra$ maps together with the analysis of the entropy map allows us to conclude that MOO J1142$+$1527 is an on-going merger hosting a cool-core at the position of the X-ray peak. This work demonstrates how the addition of spatially-resolved SZ observations to low signal-to-noise X-ray data can bring valuable insights on the intracluster medium thermodynamic properties at $z>1$.

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arXiv2019

Unveiling the merger dynamics of the most massive MaDCoWS cluster at $z = 1.2$ from a multi-wavelength mapping of its intracluster medium properties

The characterization of the Intra-Cluster Medium (ICM) properties of high-redshift galaxy clusters is fundamental to our understanding of large-scale structure formation processes. We present the results of a multi-wavelength analysis of the very massive cluster MOO J1142$+$1527 at a redshift $z = 1.2$ discovered as part of the Massive and Distant Clusters of WISE Survey (MaDCoWS). This analysis is based on high angular resolution $Chandra$ X-ray and NIKA2 Sunyaev-Zel'dovich (SZ) data. Although the X-ray data have only about 1700 counts, we are able to determine the ICM thermodynamic radial profiles, namely temperature, entropy, and hydrostatic mass. These have been obtained with unprecedented precision at this redshift and up to $0.7R_{500}$, thanks to the combination of high-resolution X-ray and SZ data. The comparison between the galaxy distribution mapped in infrared by $Spitzer$ and the morphological properties of the ICM derived from the combined analysis of the $Chandra$ and NIKA2 data leads us to the conclusion that the cluster is an on-going merger. We measure the hydrostatic mass profile of the cluster in four angular sectors centered on the large-scale X-ray centroid. This allows us to estimate a systematic uncertainty on the cluster total mass that characterizes both the impact of the observed deviations from spherical symmetry and of the core dynamics on the mass profile. We further combine the X-ray and SZ data at the pixel level to obtain maps of the temperature and entropy distributions averaged along the line of sight. We find a relatively low entropy core at the position of the X-ray peak and high temperature regions located on its south and west sides. The increase in ICM temperature at the location of the SZ peak is expected given the merger dynamics. (abridged)

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arXiv2019

The High-Redshift Clusters Occupied by Bent Radio AGN (COBRA) Survey: Follow-Up Optical Imaging

Here we present new red sequence overdensity measurements for 77 fields in the high-$z$ Clusters Occupied by Bent Radio AGN (COBRA) survey, based on $r$- and $i$-band imaging taken with Lowell Observatory's Discovery Channel Telescope. We observe 38 COBRA fields in $r$-band and 90 COBRA fields in $i$-band. By combining the $r$- and $i$-band photometry with our 3.6$μ$m and 4.5$μ$m $Spitzer$ IRAC observations, we identify 39 red sequence cluster candidates that host a strong overdensity of galaxies when measuring the excess of red sequence galaxies relative to a background field. We initially treat the radio host as the cluster center and then determine a new cluster center based on the surface density of red sequence sources. Using our color selection, we identify which COBRA cluster candidates have strong red sequence populations. By removing foreground and background contaminants, we more securely determine which fields include cluster candidates with a higher significance than our single-band observations. Additionally, of the 77 fields we analyze with a redshift estimate, 26 include newly estimated photometric redshifts.

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arXiv2019

An X-ray Detection of Star Formation In a Highly Magnified Giant Arc

In the past decade, our understanding of how stars and galaxies formed during the first 5 billion years after the Big Bang has been revolutionized by observations that leverage gravitational lensing by intervening masses, which act as natural cosmic telescopes to magnify background sources. Previous studies have harnessed this effect to probe the distant universe at ultraviolet, optical, infrared and millimeter wavelengths. However, strong lensing studies of young, star-forming galaxies have never extended into X-ray wavelengths, which uniquely trace high-energy phenomena. Here we report an X-ray detection of star formation in a highly magnified, strongly lensed galaxy. This lensed galaxy, seen during the first third of the history of the Universe, is a low--mass, low--metallicity starburst with elevated X-ray emission, and is a likely analog to the first generation of galaxies. Our measurements yield insight into the role that X-ray emission from stellar populations in the first generation of galaxies may play in re-ionizing the Universe. This observation paves the way for future strong lensing-assisted X-ray studies of distant galaxies reaching orders of magnitude below the detection limits of current deep fields, and previews the depths that will be attainable with future X-ray observatories.

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arXiv2019

Euclid preparation III. Galaxy cluster detection in the wide photometric survey, performance and algorithm selection

Galaxy cluster counts in bins of mass and redshift have been shown to be a competitive probe to test cosmological models. This method requires an efficient blind detection of clusters from surveys with a well-known selection function and robust mass estimates. The Euclid wide survey will cover 15000 deg$^2$ of the sky in the optical and near-infrared bands, down to magnitude 24 in the $H$-band. The resulting data will make it possible to detect a large number of galaxy clusters spanning a wide-range of masses up to redshift $\sim 2$. This paper presents the final results of the Euclid Cluster Finder Challenge (CFC). The objective of these challenges was to select the cluster detection algorithms that best meet the requirements of the Euclid mission. The final CFC included six independent detection algorithms, based on different techniques, such as photometric redshift tomography, optimal filtering, hierarchical approach, wavelet and friend-of-friends algorithms. These algorithms were blindly applied to a mock galaxy catalog with representative Euclid-like properties. The relative performance of the algorithms was assessed by matching the resulting detections to known clusters in the simulations. Several matching procedures were tested, thus making it possible to estimate the associated systematic effects on completeness to $<3$%. All the tested algorithms are very competitive in terms of performance, with three of them reaching $>80$% completeness for a mean purity of 80% down to masses of $10^{14}$ M$_{\odot}$ and up to redshift $z=2$. Based on these results, two algorithms were selected to be implemented in the Euclid pipeline, the AMICO code, based on matched filtering, and the PZWav code, based on an adaptive wavelet approach. [abridged]

astro-ph.CO↗

arXiv2019

Measurement of the Splashback Feature around SZ-selected Galaxy Clusters with DES, SPT and ACT

We present a detection of the splashback feature around galaxy clusters selected using their Sunyaev-Zel'dovich (SZ) signal. Recent measurements of the splashback feature around optically selected galaxy clusters have found that the splashback radius, $r_{\rm sp}$, is smaller than predicted by N-body simulations. A possible explanation for this discrepancy is that $r_{\rm sp}$ inferred from the observed radial distribution of galaxies is affected by selection effects related to the optical cluster-finding algorithms. We test this possibility by measuring the splashback feature in clusters selected via the SZ effect in data from the South Pole Telescope SZ survey and the Atacama Cosmology Telescope Polarimeter survey. The measurement is accomplished by correlating these clusters with galaxies detected in the Dark Energy Survey Year 3 data. The SZ observable used to select clusters in this analysis is expected to have a tighter correlation with halo mass and to be more immune to projection effects and aperture-induced biases than optically selected clusters. We find that the measured $r_{\rm sp}$ for SZ-selected clusters is consistent with the expectations from simulations, although the small number of SZ-selected clusters makes a precise comparison difficult. In agreement with previous work, when using optically selected redMaPPer clusters, $r_{\rm sp}$ is $\sim$ $2σ$ smaller than in the simulations. These results motivate detailed investigations of selection biases in optically selected cluster catalogs and exploration of the splashback feature around larger samples of SZ-selected clusters. Additionally, we investigate trends in the galaxy profile and splashback feature as a function of galaxy color, finding that blue galaxies have profiles close to a power law with no discernible splashback feature, which is consistent with them being on their first infall into the cluster.

astro-ph.CO↗

arXiv2019

Cluster Cosmology Constraints from the 2500 deg$^2$ SPT-SZ Survey: Inclusion of Weak Gravitational Lensing Data from Magellan and the Hubble Space Telescope

We derive cosmological constraints using a galaxy cluster sample selected from the 2500~deg$^2$ SPT-SZ survey. The sample spans the redshift range $0.25< z<1.75$ and contains 343 clusters with SZ detection significance $ξ>5$. The sample is supplemented with optical weak gravitational lensing measurements of 32 clusters with $0.29<z<1.13$ (from Magellan and HST) and X-ray measurements of 89 clusters with $0.25<z<1.75$ (from Chandra). We rely on minimal modeling assumptions: i) weak lensing provides an accurate means of measuring halo masses, ii) the mean SZ and X-ray observables are related to the true halo mass through power-law relations in mass and dimensionless Hubble parameter $E(z)$ with a-priori unknown parameters, iii) there is (correlated, lognormal) intrinsic scatter and measurement noise relating these observables to their mean relations. We simultaneously fit for these astrophysical modeling parameters and for cosmology. Assuming a flat $νΛ$CDM model, in which the sum of neutrino masses is a free parameter, we measure $Ω_\mathrm{m}=0.276\pm0.047$, $σ_8=0.781\pm0.037$, and $σ_8(Ω_\mathrm{m}/0.3)^{0.2}=0.766\pm0.025$. The redshift evolution of the X-ray $Y_\mathrm{X}$-mass and $M_\mathrm{gas}$-mass relations are both consistent with self-similar evolution to within $1σ$. The mass-slope of the $Y_\mathrm{X}$-mass relation shows a $2.3σ$ deviation from self-similarity. Similarly, the mass-slope of the $M_\mathrm{gas}$-mass relation is steeper than self-similarity at the $2.5σ$ level. In a $νw$CDM cosmology, we measure the dark energy equation of state parameter $w=-1.55\pm0.41$ from the cluster data. We perform a measurement of the growth of structure since redshift $z\sim1.7$ and find no evidence for tension with the prediction from General Relativity. We provide updated redshift and mass estimates for the SPT sample. (abridged)

astro-ph.CO↗

arXiv2019

Anatomy of a Cooling Flow: The Feedback Response to Pure Cooling in the Core of the Phoenix Cluster

We present new, deep observations of the Phoenix cluster from the Chandra X-ray Observatory, the Hubble Space Telescope, and the Karl Jansky Very Large Array. These data provide an order of magnitude improvement in depth and/or angular resolution at X-ray, optical, and radio wavelengths, yielding an unprecedented view of the core of the Phoenix cluster. We find that the one-dimensional temperature and entropy profiles are consistent with expectations for pure-cooling hydrodynamic simulations and analytic descriptions of homogeneous, steady-state cooling flow models. In the inner ~10 kpc, the cooling time is shorter by an order of magnitude than any other known cluster, while the ratio of the cooling time to freefall time approaches unity, signaling that the ICM is unable to resist multiphase condensation on kpc scales. When we consider the thermodynamic profiles in two dimensions, we find that the cooling is highly asymmetric. The bulk of the cooling in the inner ~20 kpc is confined to a low-entropy filament extending northward from the central galaxy. We detect a substantial reservoir of cool (10^4 K) gas (as traced by the [OII] doublet), which is coincident with the low-entropy filament. The bulk of this cool gas is draped around and behind a pair of X-ray cavities, presumably bubbles that have been inflated by radio jets, which are detected for the first time on kpc scales. These data support a picture in which AGN feedback is promoting the formation of a multiphase medium via a combination of ordered buoyant uplift and locally enhanced turbulence. These processes ought to counteract the tendency for buoyancy to suppress condensation, leading to rapid cooling along the jet axis. The recent mechanical outburst has sufficient energy to offset cooling, and appears to be coupling to the ICM via a cocoon shock, raising the entropy in the direction orthogonal to the radio jets.

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