arXiv subjects

Rodrigo Stancioli

Publications and source records attributed to Rodrigo Stancioli.

6 recordsLinked to original sources

arXiv2026

X-SORTER (X-ray Survey Of meRging clusTErs in Redmapper): X-ray and Spectroscopic Characterization of 12 Optically Selected Galaxy Cluster Merger Candidates

Merging galaxy clusters offer a unique probe of dark matter (DM) interactions through the spatial offsets between galaxies, the intracluster medium, and the DM halo. Systems that are binary, near the plane of the sky, and observed shortly after first pericenter provide the cleanest constraints on the DM self-interaction cross-section. The X-SORTER (X-ray Survey Of meRging clusTErs in redMaPPer) program aims to systematically identify such mergers using optical indicators of binarity in the redMaPPer cluster catalog and to follow up promising candidates with X-ray and spectroscopic observations. We select massive clusters where the top redMaPPer brightest cluster galaxy (BCG) probability is below 0.98, the top two BCGs are separated by at least 0.95 arcmin, and the optical richness exceeds $\lambda = 120$. We present XMM and Keck/DEIMOS observations of twelve clusters with no previous XMM-Newton or Chandra archival data meeting these criteria. The X-ray data reveal that most targets are morphologically disturbed, with several clear post-pericenter, dissociative systems exhibiting X-ray peaks between the BCGs. Spectroscopy confirms cluster membership and rules out foreground or background contamination. Together, these results demonstrate that optical BCG properties provide an efficient means of identifying dynamically active clusters, including clean dissociative mergers suitable for detailed, multi-wavelength studies of dark matter and cluster evolution.

astro-ph.CO↗

arXiv2025

A Very Rich Bimodal Galaxy Cluster Merger: RXC J0032.1+1808

The galaxy cluster RXC J0032.1+1808 has been well-studied with optical imaging and gravitational lensing mass maps, both of which reveal an elongated morphology in the north-south direction. We find that its X-ray morphology is bimodal, suggesting that it is in the process of merging; combined with a previously reported detection of a radio relic, we suggest that the system is seen after first pericenter. We extract the global X-ray temperature and unabsorbed luminosity from archival XMM-Newton data, finding $T_X=8.5^{+1.1}_{-0.9}$ keV and $L_X=1.04 \pm 0.03 \times 10^{45}$ erg s$^{-1}$ at 90\% confidence in the $0.5$--$10.0$ keV energy range. We conduct a redshift survey of member galaxies and find that the line-of-sight relative velocity between the two subclusters is $76\pm364$ km/s. We use publicly available hydrodynamic simulations to show that it cannot be a head-on merger, that it is observed ${\approx}395$--560 Myr after pericenter, and that the viewing angle must be one that foreshortens the apparent subcluster separation by a factor ${\approx}2$.

astro-ph.HE↗

arXiv2025

Discovery and Multi-Wavelength Analysis of a New Dissociative Galaxy Merger: The Champagne Cluster

We report the discovery of a new binary galaxy cluster merger, the Champagne Cluster (RM J130558.9+263048.4), using a detection method that identifies dynamically active clusters in the redMaPPer SDSS DR8 photometric galaxy cluster catalog. The Champagne Cluster exhibits the classic X-ray morphology of a post-pericenter dissociative galaxy cluster merger: an X-ray peak located between two galaxy overdensities at the same redshift. We conducted a Keck/DEIMOS survey and obtained redshifts for {\bfseries 102} member galaxies. The redshift analysis indicates a relative velocity of 411 $\pm$ 180 km/s between the two subclusters, which suggests that the merger is happening near the plane of the sky. We estimated the bulk temperature (8.20 $\pm 1.2$ keV) and total X-ray luminosity (7.29 $\pm$ 0.19 $\times$ $10^{44}$ erg $\times$ $s^{-1}$) of the intracluster medium using $\textit{Chandra}$ archival data. We used the $\textit{ClusterPyXT}$ software to make a temperature map, and we compared it to hydrodynamic simulations to constrain the time since pericenter (TSP), the impact parameter, and the mass ratio. We found two scenarios that matched our data: a returning system with an impact parameter of 0 and TSP of 2.2 Gyr, and an outbound system with an impact parameter of 500 kpc and TSP of 0.4 Gyr. Both scenarios have a mass ratio of 1:10.

astro-ph.CO↗

arXiv2024

Line of Sight Bias in Dark Matter Inferences from Galaxy Cluster Mergers

In collisions of galaxy clusters, the lack of displacement between dark matter and galaxies suggests that the dark matter scattering depth is small. This yields an upper limit on the dark matter cross section if the dark matter column density is known. We investigate a bias in such constraints: the measured column density (along the line of sight, using gravitational lensing) is lower than that experienced by a dark matter particle, as follows. Dark matter halos are triaxial and generally collide along their major axes, yielding a high scattering column density -- but the merger is obvious only to observers whose line of sight is nearly perpendicular to that axis, yielding a low observed column density. We trace lines of sight through merging halos from the BigMDPL n-body simulation, both with and without mock observational effects. We find that a hypothetical skewer through the center of the halo along the merger axis (more precisely, along the current separation vector of the two halos) has nearly twice the column density of a typical line of sight. With weak lensing measurements, which involve some spatial averaging, this ratio is reduced to 1.25, suggesting that existing constraints on the scattering cross section are biased high by about 25%.

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.

astro-ph.CO↗

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 $\sigma_{\rm DM}=1.1\pm0.6$ cm$^2$/g, suggesting that further study of this system could support interestingly tight constraints.

astro-ph.CO↗