arXiv subjects

Kyle Finner

Publications and source records attributed to Kyle Finner.

32 records · Page 2Linked to original sources

arXiv2023

A New Galaxy Cluster Merger Capable of Probing Dark Matter: Abell 56

We report the discovery of a binary galaxy cluster merger via a search of the redMaPPer optical cluster catalog, with a projected separation of 535 kpc between the BCGs. Archival XMM-Newton spectro-imaging reveals a gas peak between the BCGs, suggesting a recent pericenter passage. We conduct a galaxy redshift survey to quantify the line-of-sight velocity difference ($153\pm281$ km/s) between the two subclusters. We present weak lensing mass maps from archival HST/ACS imaging, revealing masses of $M_{200}=4.5\pm0.8\times10^{14}$ and $2.8\pm0.7\times10^{14}$ M$_\odot$ associated with the southern and northern galaxy subclusters respectively. We also present deep GMRT 650 MHz data revealing extended emission, 420 kpc long, which may be an AGN tail but is potentially also a candidate radio relic. We draw from cosmological n-body simulations to find analog systems, which imply that this system is observed fairly soon (60-271 Myr) after pericenter, and that the subcluster separation vector is within 22$^\circ$ of the plane of the sky, making it suitable for an estimate of the dark matter scattering cross section. We find $σ_{\rm DM}=1.1\pm0.6$ cm$^2$/g, suggesting that further study of this system could support interestingly tight constraints.

astro-ph.CO↗

arXiv2023

A New Dissociative Galaxy Cluster Merger: RM J150822.0+575515.2

Galaxy cluster mergers that exhibit clear dissociation between their dark matter, intracluster gas, and stellar components are great laboratories for probing dark matter properties. Mergers that are binary and in the plane of the sky have the additional advantage of being simpler to model, allowing for a better understanding of the merger dynamics. We report the discovery of a galaxy cluster merger with all these characteristics and present a multiwavelength analysis of the system, which was found via a search in the redMaPPer optical cluster catalog. We perform a galaxy redshift survey to confirm the two subclusters are at the same redshift (0.541, with $368\pm519$ km s$^{-1}$ line-of-sight velocity difference between them). The X-ray morphology shows two surface-brightness peaks between the BCGs. We construct weak lensing mass maps that reveal a mass peak associated with each subcluster. Fitting NFW profiles to the lensing data, we find masses of $M_{\rm 200c}=36\pm11\times10^{13}$ and $38\pm11\times10^{13}$ M$_\odot/h$ for the southern and northern subclusters respectively. From the mass maps, we infer that the two mass peaks are separated by $520^{+162}_{-125}$ kpc along the merger axis, whereas the two BCGs are separated by 697 kpc. We also present deep GMRT 650 MHz data to search for a radio relic or halo, and find none. Using the observed merger parameters, we find analog systems in cosmological n-body simulations and infer that this system is observed between 96-236 Myr after pericenter, with the merger axis within $28^{\circ}$ of the plane of the sky.

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arXiv2023

The First Weak-lensing Analysis with the James Webb Space Telescope: SMACS J0723.3-7327

Utilizing the James Webb Space Telescope Early Release NIRCam Observations, we perform a weak-lensing analysis of the massive galaxy cluster SMACS J0723.3-7327 ($z=0.39$). We investigate the spatial variation of the PSF from the stars in the mosaic image. Our measurements show that the PSF for both modules has very small spatial and temporal variation with average complex ellipticity components of $e_1=0.007\pm0.001$ and $e_2=0.029\pm0.001$ in the observed north-up reference frame. We create PSF models through a principal component analysis of the stars and show that they properly account for the ellipticity of the PSF with residual shapes of $e_1=(0.3\pm3.5)\times10^{-4}$ and $e_2=(1.8\pm4.0)\times10^{-4}$. We select background galaxies by their photometric redshift and measure galaxy shapes by model fitting. Our weak-lensing source catalog achieves 215 galaxies arcmin$^{-2}$. We map the projected mass density of SMACSJ0723 and detect the cluster with a peak significance of $12.2σ$. The mass distribution is found to elongate in the east-west direction with an extension to the northeast edge of the field of view where a candidate substructure is found in the Chandra X-ray imaging. We fit the tangential shear with a Navarro-Frenk-White model and estimate the mass of the cluster to be $M_{500}=7.9\pm1.1\times10^{14}$ M$_{\odot}$ ($M_{200}=11.4\pm1.5\times10^{14}$ M$_\odot$ ), which agrees with existing mass estimates. Combining the multiwavelength evidence from literature with our weak-lensing analysis, we hypothesize that SMACSJ0723 is observed near first pericenter passage and we identify candidate radio relics.

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arXiv2023

Weak-lensing mass bias in merging galaxy clusters

Although weak lensing (WL) is a powerful method to estimate a galaxy cluster mass without any dynamical assumptions, a model bias can arise when the cluster density profile departs from the assumed model profile. In a merging system, the bias is expected to become most severe because the constituent halos undergo significant structural changes. In this study, we investigate WL mass bias in binary cluster mergers using a suite of idealized hydrodynamical simulations. Realistic WL shear catalogs are generated by matching the source galaxy properties, such as intrinsic shape dispersion, measurement noise, source densities, etc., to those from Subaru and {\it Hubble Space Telescope} observations. We find that, with the typical mass-concentration ($M$-$c$) relation and the Navarro-Frenk-White (NFW) profile, the halo mass bias depends on the time since the first pericenter passage and increases with the mass of the companion cluster. The time evolution of the mass bias is similar to that of the concentration, indicating that, to first order, the mass bias is modulated by the concentration change. For a collision between two $\sim10^{15}~M_{\odot}$ clusters, the maximum bias amounts to $\sim60\%$. This suggests that previous WL studies may have significantly overestimated the mass of the clusters in some of the most massive mergers. Finally, we apply our results to three merger cases: Abell 2034, MACS J1752.0+4440, and ZwCl 1856.8+6616, and report their mass biases at the observed epoch, as well as their pre-merger masses, utilizing their merger shock locations as tracers of the merger phases.

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arXiv2022

HST and HSC Weak-lensing Study of the Equal-mass Dissociative Merger CIZA J0107.7+5408

A dissociative merger is formed by the interplay of ram pressure and gravitational forces, which can lead to a spatial displacement of the dark matter and baryonic components of the recently collided subclusters. CIZA J0107.7+5408 is a nearby (z=0.105) dissociative merger that hosts two X-ray brightness peaks and a bimodal galaxy distribution. Analyzing MMT/Hectospec observations, we investigate the line-of-sight and spatial distribution of cluster galaxies. Utilizing deep, high-resolution Hubble Space Telescope Advanced Camera for Surveys imaging and large field-of-view Subaru Hyper-Suprime-Cam observations, we perform a weak-lensing analysis of CIZA J0107.7+5408. Our weak-lensing analysis detects a bimodal mass distribution that is spatially consistent with the cluster galaxies but significantly offset from the X-ray brightness peaks. Fitting two NFW halos to the lensing signal, we find an equal-mass merger with subcluster masses of $M_{200,NE}=2.8^{+1.1}_{-1.1}\times10^{14}$ M$_\odot$ and $M_{200,SW}=3.1^{+1.2}_{-1.2}\times10^{14}$ M$_\odot$. Moreover, the mass-to-light ratios of the subclusters, $(M/L)_{NE}=571^{+89}_{-91}$ $M_\odot/L_{\odot,B}$ and $(M/L)_{SW}=564^{+87}_{-89}$ $M_\odot/L_{\odot,B}$, are found to be consistent with each other and within the range of mass-to-light ratios found for galaxy clusters.

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arXiv2021

Multiwavelength Analysis of A1240, the Double Radio Relic Merging Galaxy Cluster Embedded in a ~80 Mpc-long Cosmic Filament

We present a multiwavelength study of the double radio relic cluster A1240 at z=0.195. Our Subaru-based weak lensing analysis detects three mass clumps forming a ~4 Mpc filamentary structure elongated in the north-south orientation. The northern ($M_{200}=2.61_{-0.60}^{+0.51}\times10^{14} M_{\odot}$) and middle ($M_{200}=1.09_{-0.43}^{+0.34}\times10^{14} M_{\odot}$) mass clumps separated by ~1.3 Mpc are associated with A1240 and co-located with the X-ray peaks and cluster galaxy overdensities revealed by Chandra and MMT/Hectospec observations, respectively. The southern mass clump ($M_{200}=1.78_{-0.55}^{+0.44}\times10^{14} M_{\odot}$), ~1.5 Mpc to the south of the middle clump, coincides with the galaxy overdensity in A1237, the A1240 companion cluster at z=0.194. Considering the positions, orientations, and polarization fractions of the double radio relics measured by the LOFAR study, we suggest that A1240 is a post-merger binary system in the returning phase with the time-since-collision ~1.7 Gyr. With the SDSS DR16 data analysis, we also find that A1240 is embedded in the much larger-scale (~80 Mpc) filamentary structure whose orientation is in remarkable agreement with the hypothesized merger axis of A1240.

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arXiv2021

Discovery of a double radio relic in ZwCl1447.2+2619: A rare testbed for shock acceleration models with a peculiar surface brightness ratio

We report a discovery of a double radio relic in the cluster merger ZwCl1447.2+2619 ($z=0.376$) with uGMRT observations at $420\rm~MHz$ and $700\rm~MHz$. The linear sizes of the northern and southern relics are $\sim0.3~$Mpc and $\sim1.2~$Mpc, respectively, which is consistent with the theoretical expectation that a larger relic is produced in the less massive subcluster side. However, ZwCl1447.2+2619 is unlike other known double radio relic systems, where the larger relics are much more luminous by several factors. In this merger the higher surface brightness of the smaller northern relic makes its total radio luminosity comparable to that of the much larger southern relic. The surface brightness ratio $\sim0.1$ between the two radio relics differs significantly from the relation observed in other double radio relic systems. From our radio spectral analysis, we find that both relics signify similar weak shocks with Mach numbers of $2.9\pm0.8$ and $2.0\pm0.7$ for the northern and southern relics, respectively. Moreover, the northern relic is connected to a discrete radio source with an optical counterpart, which indicates the possible presence of cosmic ray injection and re-acceleration. Therefore, we propose that this atypical surface brightness ratio can be explained with the particle acceleration efficiency precipitously dropping in the weak shock regime and/or with re-acceleration of fossil cosmic rays. Our multi-wavelength analysis and numerical simulation suggest that ZwCl1447.2+2619 is a post-merger, which has experienced a near head-on collision $\sim0.7\rm~Gyr$ ago.

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arXiv2021

Exemplary Merging Clusters: Weak-lensing and X-ray Analysis of the Double Radio Relic Merging Galaxy Clusters MACS 1752.0+4440 and ZWCL 1856.8+6616

The investigation of merging galaxy clusters that exhibit radio relics is strengthening our understanding of the formation and evolution of galaxy clusters, the nature of dark matter, the intracluster medium, and astrophysical particle acceleration. Each merging cluster provides only a single view of the cluster formation process and the variety of merging clusters is vast. Clusters hosting double radio relics are rare and extremely important because they allow tight constraints on the merger scenario. We present a weak-lensing and X-ray analysis of MACSJ1752.0+4440 ($z$=0.365) and ZWCL1856.8+6616 ($z$=0.304), two double radio relic clusters. Our weak-lensing mass estimates show that each cluster is a major merger with approximately 1:1 mass ratio. The total mass of MACSJ1752.0+4440 (ZWCL1856.8+6616) is $M_{200}=14.7^{+3.8}_{-3.3}\times10^{14}\ $M$_\odot$ ($M_{200}=2.4^{+0.9}_{-0.7}\times10^{14}\ $M$_\odot$). We find that these two clusters have comparable features in their weak-lensing and gas distributions, even though the systems have vastly different total masses. From the likeness of the X-ray morphologies and the remarkable symmetry of the radio relics, we propose that both systems underwent nearly head-on collisions. However, revelations from the hot-gas features and our multiwavelength data analysis suggest that ZWCL1856.8+6618 is likely at a later merger phase than MACSJ1752.0+4440. We postulate that the SW radio relic in MACSJ1752.0+4440 is a result of particle re-acceleration.

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arXiv2020

Toward Solving the Puzzle: Dissecting the Complex Merger A521 with Multi-wavelength Data

A521 has been a subject of extensive panchromatic studies from X-ray to radio. The cluster possesses a number of remarkable features including a bright radio relic with a steep spectrum, more than three distinct galaxy groups forming a filament, and two disturbed X-ray peaks at odds with the distant position and tilted orientation of the radio relic. These several lines of evidence indicate a complex merger. In this paper, we present a multi-wavelength study of A521 based on Subaru optical, Hubble Space Telescope infrared, Chandra X-ray, GMRT radio, and MMT optical spectroscopic observations. Our weak-lensing (WL) analysis with improved systematics control reveals that A521 is mainly composed of three substructures aligned in the northwest to southeast orientation. These WL mass substructures are remarkably well-aligned with the cluster optical luminosity distribution constructed from our new enhanced cluster member catalog. These individual substructure masses are determined by simultaneously fitting three NFW profiles. We find that the total mass of A521 modeled by the superposition of the three halos is $13.0_{-1.3}^{+1.0} \times 10^{14}M_{\odot}$, a factor of two higher than the previous WL measurement. With these WL mass constraints combined with X-ray and radio features, we consider two merging scenarios, carry out the corresponding numerical simulations, and discuss strengths and weaknesses of each case.

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arXiv2020

Discovery of a Radio Relic in the Massive Merging Cluster SPT-CL 2023-5535 from the ASKAP-EMU PILOT SURVEY

The ASKAP-EMU survey is a deep wide-field radio continuum survey designed to cover the entire southern sky and a significant fraction of the northern sky up to $+30^{\circ}$. Here, we report a discovery of a radio relic in the merging cluster SPT-CL 2023-5535 at z=0.23 from the ASKAP-EMU pilot 300 sq. deg survey (800-1088 MHz). The deep high-resolution data reveal a $\sim2$ Mpc-scale radio halo elongated in the east-west direction, coincident with the intracluster gas. The radio relic is located at the western edge of this radio halo stretched $\sim0.5$ Mpc in the north-south orientation. The integrated spectral index of the radio relic within the narrow bandwidth is $α^{\scriptstyle \rm 1088~MHz}_{\scriptstyle \rm 800~MHz}=-0.76 \pm 0.06$. Our weak-lensing analysis shows that the system is massive ($M_{200}=1.04\pm0.36\times 10^{15} M_{\odot}$) and composed of at least three subclusters. We suggest a scenario, wherein the radio features arise from the collision between the eastern and middle subclusters. Our discovery illustrates the effectiveness of the ASKAP-EMU survey in detecting diffuse emissions in galaxy clusters and when completed, the survey will greatly increase the number of merging cluster detections with diffuse radio emissions.

astro-ph.HE↗

arXiv2020

Constraining the Mass of the Emerging Galaxy Cluster SpARCS1049+56 at z=1.71 with Infrared Weak Lensing

In the hierarchical structure formation model of the universe, galaxy clusters are assembled through a series of mergers. Accordingly, it is expected that galaxy clusters in the early universe are actively forming and dynamically young. Located at a high redshift of z=1.71, SpARCS1049+56 offers a unique look into the galaxy cluster formation process. This cluster has been shown to be rich in cluster galaxies and to have intense star formation. Its high redshift pushes a weak-lensing analysis beyond the regime of the optical spectrum into that of the infrared. Equipped with deep Hubble Space Telescope Wide Field Camera 3 UVIS and IR observations, we present a weak-lensing characterization of SpARCS1049+56. As few IR weak-lensing studies have been performed, we discuss the details of PSF modeling and galaxy shape measurement for an IR weak-lensing procedure and the systematics that come with the territory. It will be critical to understand these systematics in future weak-lensing studies in the IR with the next generation space telescopes such as JWST, Euclid, and WFIRST. Through a careful analysis, the mass distribution of this young galaxy cluster is mapped and the convergence peak is detected at a 3.3 sigma level. The weak-lensing mass of the cluster is estimated to be $3.5\pm1.2\times10^{14}\ \text{M}_\odot$ and is consistent with the mass derived from a mass-richness scaling relation. This mass is extreme for a cluster at such a high redshift and suggests that SpARCS1049+56 is rare in the standard $Λ$CDM universe.

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arXiv2019

Multi-wavelength Analysis of the Merging Galaxy Cluster A115

A115 is a merging galaxy cluster at $z\sim0.2$ with a number of remarkable features including a giant ($\sim2.5$ Mpc) radio relic, two asymmetric X-ray peaks with trailing tails, and a peculiar line-of-sight velocity structure. We present a multi-wavelength study of A115 using optical imaging data from Subaru, X-ray data from $Chandra$, and spectroscopic data from the Keck/DEIMOS and MMT/Hectospec instruments. Our weak-lensing analysis shows that the cluster is comprised of two subclusters whose mass centroids are in excellent agreement with the two BCG positions ($\lesssim10$"). By modeling A115 with a superposition of two Navarro-Frenk-White halos, we determine the masses of the northern and southern subclusters to be $M_{200}=1.58_{-0.49}^{+0.56}\times 10^{14} \text{M}_{\odot}$ and $3.15_{-0.71}^{+0.79}\times 10^{14} \text{M}_{\odot}$, respectively. Combining the two halos, we estimate the total cluster mass to be $M_{200}=6.41_{-1.04}^{+1.08}\times10^{14} \text{M}_{\odot}$ at $R_{200}=1.67_{-0.09}^{+0.10}$ Mpc. These weak-lensing masses are significantly (a factor of 3-10) lower than what is implied by the X-ray and optical spectroscopic data. We attribute the difference to the gravitational and hydrodynamic disruption caused by the collision between the two subclusters.

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arXiv2017

MC$^2$: Subaru and Hubble Space Telescope Weak-Lensing Analysis of the Double Radio Relic Galaxy Cluster PLCK G287.0+32.9

The second most significant detection of the Planck Sunyaev Zel'dovich survey, PLCK~G287.0+32.9 ($z=0.385$) boasts two similarly bright radio relics and a radio halo. One radio relic is located $\sim 400$ kpc northwest of the X-ray peak and the other $\sim 2.8$ Mpc to the southeast. This large difference suggests that a complex merging scenario is required. A key missing puzzle for the merging scenario reconstruction is the underlying dark matter distribution in high resolution. We present a joint Subaru Telescope and {\it Hubble Space Telescope} weak-lensing analysis of the cluster. Our analysis shows that the mass distribution features four significant substructures. Of the substructures, a primary cluster of mass $M_{200\text{c}}=1.59^{+0.25}_{-0.22}\times 10^{15} \ h^{-1}_{70} \ \text{M}_{\odot}$ dominates the weak-lensing signal. This cluster is likely to be undergoing a merger with one (or more) subcluster whose mass is approximately a factor of 10 lower. One candidate is the subcluster of mass $M_{200\text{c}}=1.16^{+0.15}_{-0.13}\times 10^{14} \ h^{-1}_{70} \ \text{M}_{\odot}$ located $\sim 400$ kpc to the southeast. The location of this subcluster suggests that its interaction with the primary cluster could be the source of the NW radio relic. Another subcluster is detected $\sim 2$ Mpc to the SE of the X-ray peak with mass $M_{200\text{c}}=1.68^{+0.22}_{-0.20}\times 10^{14} \ h^{-1}_{70} \ \text{M}_{\odot}$. This SE subcluster is in the vicinity of the SE radio relic and may have created the SE radio relic during a past merger with the primary cluster. The fourth subcluster, $M_{200\text{c}}=1.87^{+0.24}_{-0.22}\times 10^{14} \ h^{-1}_{70} \ \text{M}_{\odot}$, is northwest of the X-ray peak and beyond the NW radio relic.

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arXiv2017

Merging Cluster Collaboration: Optical and Spectroscopic Survey of a Radio-Selected Sample of Twenty Nine Merging Galaxy Clusters

Multi-band photometric and multi-object spectroscopic surveys of merging galaxy clusters allow for the characterization of the distributions of constituent dark matter and galaxy populations, constraints on the dynamics of the merging subclusters, and an understanding of galaxy evolution of member galaxies. We present deep photometric observations from Subaru/SuprimeCam and a catalog of $\sim$5400 spectroscopic cluster members from Keck/DEIMOS across 29 merging galaxy clusters ranging in redshift from $z=0.07$ to $0.55$. The ensemble is compiled based on the presence of radio relics, which highlight cluster scale collisionless shocks in the intra-cluster medium. Together with the spectroscopic and photometric information, the velocities, timescales, and geometries of the respective merging events may be tightly constrained. In this preliminary analysis, the velocity distributions of 28 of the 29 clusters are shown to be well fit by single Gaussians. This indicates that radio relic mergers largely occur transverse to the line of sight and/or near apocenter. In this paper, we present our optical and spectroscopic surveys, preliminary results, and a discussion of the value of radio relic mergers for developing accurate dynamical models of each system.

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