arXiv subjects

Felipe Andrade-Santos

Publications and source records attributed to Felipe Andrade-Santos.

53 records · Page 3Linked to original sources

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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arXiv2017

Probing the hot X-ray gas in the narrow-line region of Mrk 3

We study the prototypical Seyfert 2 galaxy, Markarian 3, based on imaging and high-resolution spectroscopy observations taken by the Chandra X-ray Observatory. We construct a deconvolved X-ray image, which reveals the S-shaped morphology of the hot gas in the narrow line region (NLR). While this morphology is similar to the radio and [O III] emission, the distribution of the X-ray gas is broader than that obtained at these other wavelengths. By mapping the density and temperature distribution of the hot gas in the NLR, we demonstrate the presence of shocks towards the west ($M=2.5^{+1.0}_{-0.6}$) and east ($M=1.5^{+1.0}_{-0.5}$). Moreover, we compute the flux ratios between the [O III] and $0.5-2$ keV band X-ray luminosity and show that it is non-uniform in the NLR with the western side of the NLR being more highly ionized. In addition, based on the Chandra grating data we investigate the line ratios of the Si XIII triplet, which are not consistent with pure photoionization. Based on these results, we suggest that in the NLR of Mrk 3 both photoionization and collisional ionization act as excitation mechanisms. We conclude that the canonical picture, in which photoionization is solely responsible for exciting the interstellar medium in the NLR of Seyfert galaxies, may be overly simplistic. Given that weak and small-scale radio jets are commonly detected in Seyfert galaxies, it is possible that shock heating plays a non-negligible role in the NLR of these galaxies.

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arXiv2017

X-Ray morphological analysis of the Planck ESZ clusters

X-ray observations show that galaxy clusters have a very large range of morphologies. The most disturbed systems which are good to study how clusters form and grow and to test physical models, may potentially complicate cosmological studies because the cluster mass determination becomes more challenging. Thus, we need to understand the cluster properties of our samples to reduce possible biases. This is complicated by the fact that different experiments may detect different cluster populations. For example, SZ selected cluster samples have been found to include a greater fraction of disturbed systems than X-ray selected samples. In this paper we determined eight morphological parameters for the Planck Early Sunyaev-Zeldovich (ESZ) objects observed with XMM-Newton. We found that two parameters, concentration and centroid-shift, are the best to distinguish between relaxed and disturbed systems. For each parameter we provide the values that allow one to select the most relaxed or most disturbed objects from a sample. We found that there is no mass dependence on the cluster dynamical state. By comparing our results with what was obtained with REXCESS clusters, we also confirm that indeed the ESZ clusters tend to be more disturbed, as found by previous studies.

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arXiv2017

The fraction of cool-core clusters in X-ray vs. SZ samples using Chandra observations

We derive and compare the fractions of cool-core clusters in the {\em Planck} Early Sunyaev-Zel'dovich sample of 164 clusters with $z \leq 0.35$ and in a flux-limited X-ray sample of 100 clusters with $z \leq 0.30$, using {\em Chandra} observations. We use four metrics to identify cool-core clusters: 1) the concentration parameter: the ratio of the integrated emissivity profile within 0.15 $r_{500}$ to that within $r_{500}$, and 2) the ratio of the integrated emissivity profile within 40 kpc to that within 400 kpc, 3) the cuspiness of the gas density profile: the negative of the logarithmic derivative of the gas density with respect to the radius, measured at 0.04 $r_{500}$, and 4) the central gas density, measured at 0.01 $r_{500}$. We find that the sample of X-ray selected clusters, as characterized by each of these metrics, contains a significantly larger fraction of cool-core clusters compared to the sample of SZ selected clusters (44$\pm$7\% vs. 28$\pm$4\% using the concentration parameter in the 0.15--1.0 $r_{500}$ range, 61$\pm$8\% vs. 36$\pm$5\% using the concentration parameter in the 40--400 kpc range, 64$\pm$8\% vs. 38$\pm$5\% using the cuspiness, and 53$\pm$7\% vs. 39$\pm$5\% using the central gas density). Qualitatively, cool-core clusters are more X-ray luminous at fixed mass. Hence, our X-ray flux-limited sample, compared to the approximately mass-limited SZ sample, is over-represented with cool-core clusters. We describe a simple quantitative model that uses the excess luminosity of cool-core clusters compared to non-cool-core clusters at fixed mass to successfully predict the observed fraction of cool-core clusters in X-ray selected samples.

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arXiv2017

Gas sloshing in Abell 2204: Constraining the properties of the magnetized intracluster medium

The rich galaxy cluster Abell 2204 exhibits edges in its X-ray surface brightness at $\sim 65$ and $35 {\rm~ kpc}$ west and east of its center, respectively. The presence of these edges, which were interpreted as sloshing cold fronts, implies that the intracluster medium was recently disturbed. We analyze the properties of the intracluster medium using multiple Chandra observations of Abell 2204. We find a density ratio $n_{\rm in}/n_{\rm out} = 2.05\pm0.05$ and a temperature ratio $T_{\rm out}/T_{\rm in} = 1.91\pm0.27$ (projected, or $1.87\pm0.56$ deprojected) across the western edge, and correspondingly $n_{\rm in}/n_{\rm out} = 1.96\pm0.05$ and $T_{\rm out}/T_{\rm in} =1.45\pm0.15$ (projected, or $1.25\pm0.26$ deprojected) across the eastern edge. These values are typical of cold fronts in galaxy clusters. This, together with the spiral pattern observed in the cluster core, supports the sloshing scenario for Abell 2204. No Kelvin-Helmholtz eddies are observed along the cold front surfaces, indicating that they are effectively suppressed by some physical mechanism. We argue that the suppression is likely facilitated by the magnetic fields amplified in the sloshing motion, and deduce from the measured gas properties that the magnetic field strength should be greater than $24\pm6$ $μ$G and $32\pm8$ $μ$G along the west and east cold fronts, respectively.

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arXiv2017

The Case for Electron Re-Acceleration at Galaxy Cluster Shocks

On the largest scales, the Universe consists of voids and filaments making up the cosmic web. Galaxy clusters are located at the knots in this web, at the intersection of filaments. Clusters grow through accretion from these large-scale filaments and by mergers with other clusters and groups. In a growing number of galaxy clusters, elongated Mpc-size radio sources have been found, so-called radio relics. These relics are thought to trace relativistic electrons in the intracluster plasma accelerated by low-Mach number collisionless shocks generated by cluster-cluster merger events. A long-standing problem is how low-Mach number shocks can accelerate electrons so efficiently to explain the observed radio relics. Here we report on the discovery of a direct connection between a radio relic and a radio galaxy in the merging galaxy cluster Abell 3411-3412. This discovery indicates that fossil relativistic electrons from active galactic nuclei are re-accelerated at cluster shocks. It also implies that radio galaxies play an important role in governing the non-thermal component of the intracluster medium in merging clusters.

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arXiv2017

The Double Galaxy Cluster Abell 2465 III. X-ray and Weak-lensing Observations

We report Chandra X-ray observations and optical weak-lensing measurements from Subaru/Suprime-Cam images of the double galaxy cluster Abell 2465 (z=0.245). The X-ray brightness data are fit to a beta-model to obtain the radial gas density profiles of the northeast (NE) and southwest (SW) sub-components, which are seen to differ in structure. We determine core radii, central temperatures, the gas masses within $r_{500c}$, and the total masses for the broader NE and sharper SW components assuming hydrostatic equilibrium. The central entropy of the NE clump is about two times higher than the SW. Along with its structural properties, this suggests that it has undergone merging on its own. The weak-lensing analysis gives virial masses for each substructure, which compare well with earlier dynamical results. The derived outer mass contours of the SW sub-component from weak lensing are more irregular and extended than those of the NE. Although there is a weak enhancement and small offsets between X-ray gas and mass centers from weak lensing, the lack of large amounts of gas between the two sub-clusters indicates that Abell 2465 is in a pre-merger state. A dynamical model that is consistent with the observed cluster data, based on the FLASH program and the radial infall model, is constructed, where the subclusters currently separated by ~1.2Mpc are approaching each other at ~2000km/s and will meet in ~0.4Gyr.

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arXiv2016

A Spectacular Bow Shock in the 11 keV Galaxy Cluster Around 3C 438

We present results of deep 153 ks Chandra observations of the hot, 11 keV, galaxy cluster associated with the radio galaxy 3C 438. By mapping the morphology of the hot gas and analyzing its surface brightness and temperature distributions, we demonstrate the presence of a merger bow shock. We identify the presence of two jumps in surface brightness and in density located at $\sim$400 kpc and $\sim$800 kpc from the cluster's core. At the position of the inner jump, we detect a factor of $2.3\pm 0.2$ density jump, while at the location of the outer jump, we detect a density drop of a factor of $3.5 \pm 0.7$. Combining this with the temperature distribution within the cluster, we establish that the pressure of the hot gas is continuous at the 400 kpc jump, while there is a factor of $6.2 \pm 2.8$ pressure discontinuity at 800 kpc jump. From the magnitude of the outer pressure discontinuity, using the Rankine-Hugoniot jump conditions, we determine that the sub-cluster is moving at $M = 2.3\pm 0.5$, or approximately $2600\pm 565$ km/s through the surrounding intracluster medium, creating the conditions for a bow shock. Based on these findings, we conclude that the pressure discontinuity is likely the result of an ongoing major merger between two massive clusters. Since few observations of bow shocks in clusters have been made, this detection can contribute to the study of the dynamics of cluster mergers, which offers insight on how the most massive clusters may have formed.

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arXiv2016

Binary Black Holes, Gas Sloshing, and Cold Fronts in the X-ray Halo Hosting 4C+37.11

We analyzed deep $Chandra$ ACIS-I exposures of the cluster-scale X-ray halo surrounding the radio source 4C+37.11. This remarkable system hosts the closest resolved pair of super-massive black hole and an exceptionally luminous elliptical galaxy, the likely product of a series of past mergers. We characterize the halo with $r_{500} = 0.95$ Mpc, $M_{500} = (2.5 \pm 0.2) \times 10^{14} \ M_{\rm{\odot}}$, $ kT = 4.6\pm 0.2$ keV, and a gas mass of $M_{\rm g,500} = (2.2 \pm 0.1) \times 10^{13} M_\odot$. The gas mass fraction within $r_{500}$ is $f_{\rm g} = 0.09 \pm 0.01$. The entropy profile shows large non-gravitational heating in the central regions. We see several surface brightness jumps, associated with substantial temperature and density changes, but approximate pressure equilibrium, implying that these are sloshing structures driven by a recent merger. A residual intensity image shows core spiral structure closely matching that seen for the Perseus cluster, although at $z=0.055$ the spiral pattern is less distinct. We infer the most recent merger occurred $1-2$ Gyr ago and that the event that brought the two observed super-massive black holes to the system core is even older. Under that interpretation, this black hole binary pair has, unusually, remained at pc-scale separation for more than 2 Gyr.

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arXiv2016

Probing the Outskirts of the Early Stage Galaxy Cluster Merger A1750

We present results from recent Suzaku and Chandra X-ray, and MMT optical observations of the strongly merging "double cluster" A1750 out to its virial radius, both along and perpendicular to a putative large-scale structure filament. Some previous studies of individual clusters have found evidence for ICM entropy profiles that flatten at large cluster radii, as compared with the self-similar prediction based on purely gravitational models of hierarchical cluster formation, and gas fractions that rise above the mean cosmic value. Weakening accretion shocks and the presence of unresolved cool gas clumps, both of which are expected to correlate with large scale structure filaments, have been invoked to explain these results. In the outskirts of A1750, we find entropy profiles that are consistent with self-similar expectations, and gas fractions that are consistent with the mean cosmic value, both along and perpendicular to the putative large scale filament. Thus, we find no evidence for gas clumping in the outskirts of A1750, in either direction. This may indicate that gas clumping is less common in lower temperature (kT~4keV), less massive systems, consistent with some (but not all) previous studies of low mass clusters and groups. Cluster mass may therefore play a more important role in gas clumping than dynamical state. Finally, we find evidence for diffuse, cool (<1 keV) gas at large cluster radii (R200) along the filament, which is consistent with the expected properties of the denser, hotter phase of the WHIM.

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arXiv2015

Chandra and XMM-Newton Observations of the Bimodal Planck SZ-detected Cluster PLCKG345.40-39.34 (A3716) with High and Low Entropy Subcluster Cores

We present results from Chandra, XMM-Newton, and ROSAT observations of the Planck SZ-detected cluster A3716 (PLCKG345.40-39.34 - G345). We show that G345 is, in fact, two subclusters separated on the sky by 400 kpc. We measure the subclusters' gas temperatures (~ 2-3 keV), total (~ 1-2 x 10^14 solar masses) and gas (~ 1-2 x 10^13 solar masses) masses, gas mass fraction within r500, entropy profiles, and X-ray luminosities (~ 10^43 erg/s). Using the gas density and temperature profiles for both subclusters, we show that there is good (0.8 sigma) agreement between the expected Sunyaev-Zel'dovich signal predicted from the X-ray data and that measured from the Planck mission, and better agreement within 0.6 sigma when we re-computed the Planck value assuming a two component cluster model, with relative amplitudes fixed based on the X-ray data. Dynamical analysis shows that the two galaxy subclusters are very likely (> 97% probability) gravitationally bound, and in the most likely scenario, the subclusters will undergo core passage in 500 +- 200 Myr. The northern subcluster is centrally peaked and has a low entropy core, while the southern subcluster has a high central entropy. The high central entropy in the southern subcluster can be explained either by the mergers of several groups, as suggested by the presence of five giant ellipticals or by AGN energy injection, as suggested by the presence of a strong radio source in one of its massive elliptical galaxies, or by a combination of both processes.

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arXiv2014

X-ray Selected Galaxy Groups in Boötes

We present the X-ray and optical properties of the galaxy groups selected in the Chandra X-Boötes survey. Our final sample comprises 32 systems at \textbf{$z<1.75$}, with 14 below $z = 0.35$. For these 14 systems we estimate velocity dispersions ($σ_{gr}$) and perform a virial analysis to obtain the radii ($R_{200}$ and $R_{500}$) and total masses ($M_{200}$ and $M_{500}$) for groups with at least five galaxy members. We use the Chandra X-ray observations to derive the X-ray luminosity ($L_X$). We examine the performance of the group properties $σ_{gr}$, $L_{opt}$ and $L_X$, as proxies for the group mass. Understanding how well these observables measure the total mass is important to estimate how precisely the cluster/group mass function is determined. Exploring the scaling relations built with the X-Boötes sample and comparing these with samples from the literature, we find a break in the $L_X$-$M_{500}$ relation at approximately $M_{500} = 5\times10^{13}$ M$_\odot$ (for $M_{500} > 5\times10^{13}$ M$_\odot$, $M_{500} \propto L_X^{0.61\pm0.02}$, while for $M_{500} \leq 5\times10^{13}$ M$_\odot$, $M_{500} \propto L_X^{0.44\pm0.05}$). Thus, the mass-luminosity relation for galaxy groups cannot be described by the same power law as galaxy clusters. A possible explanation for this break is the dynamical friction, tidal interactions and projection effects which reduce the velocity dispersion values of the galaxy groups. By extending the cluster luminosity function to the group regime, we predict the number of groups that new X-ray surveys, particularly eROSITA, will detect. Based on our cluster/group luminosity function estimates, eROSITA will identify $\sim$1800 groups ($L_X = 10^{41}-10^{43}$ ergs s$^{-1}$) within a distance of 200 Mpc. Since groups lie in large scale filaments, this group sample will map the large scale structure of the local universe.

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arXiv2014

Merger Signatures in the Galaxy Cluster Abell 98

We present results from Chandra and XMM-Newton observations of Abell 98 (A98), a galaxy cluster with three major components: a relatively bright subcluster to the north (A98N), a disturbed subcluster to the south (A98S), and a fainter subcluster to the far south (A98SS). We find evidence for surface brightness and temperature asymmetries in A98N consistent with a shock-heated region to the south, which could be created by an early stage merger between A98N and A98S. Deeper observations are required to confirm this result. We also find that A98S has an asymmetric core temperature structure, likely due to a separate ongoing merger. Evidence for this is also seen in optical data. A98S hosts a wide-angle tail (WAT) radio source powered by a central active galactic nucleus (AGN). We find evidence for a cavity in the intracluster medium (ICM) that has been evacuated by one of the radio lobes, suggesting that AGN feedback is operating in this system. Examples of cavities in non-cool core clusters are relatively rare. The three subclusters lie along a line in projection, suggesting the presence of a large-scale filament. We observe emission along the filament between A98N and A98S, and a surface brightness profile shows emission consistent with the overlap of the subcluster extended gas haloes. We find the temperature of this region is consistent with the temperature of the gas at similar radii outside this bridge region. Lastly, we examine the cluster dynamics using optical data. We conclude A98N and A98S are likely bound to one another, with a 67% probability, while A98S and A98SS are not bound at a high level of significance.

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arXiv2014

Structure in galaxy clusters

We will discuss here how structures observed in clusters of galaxies can provide us insight on the formation and evolution of these objects. We will focus primarily on X-ray observations and results from hydrodynamical $N$-body simulations. This paper is based on a talk given at the School of Cosmology Jose Plinio Baptista -- `Cosmological perturbations and Structure Formation' in Ubu/ES, Brazil.

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arXiv2013

Dark Matter Subhalos and the X-ray Morphology of the Coma Cluster

Structure formation models predict that clusters of galaxies contain numerous massive subhalos. The gravity of a subhalo in a cluster compresses the surrounding intracluster gas and enhances its X-ray emission. We present a simple model, which treats subhalos as slow moving and gasless, for computing this effect. Recent weak lensing measurements by Okabe et al. have determined masses of ~ 10^13 solar masses for three mass concentrations projected within 300 kpc of the center of the Coma Cluster, two of which are centered on the giant elliptical galaxies NGC 4889 and NGC 4874. Adopting a smooth spheroidal beta-model for the gas distribution in the unperturbed cluster, we model the effect of these subhalos on the X-ray morphology of the Coma Cluster, comparing our results to Chandra and XMM-Newton X-ray data. The agreement between the models and the X-ray morphology of the central Coma Cluster is striking. With subhalo parameters from the lensing measurements, the distances of the three subhalos from the Coma Cluster midplane along our line of sight are all tightly constrained. Using the model to fit the subhalo masses for NGC 4889 and NGC 4874 gives 9.1 x 10^12 and 7.6 x 10^12 solar masses, respectively, in good agreement with the lensing masses. These results lend strong support to the argument that NGC 4889 and NGC 4874 are each associated with a subhalo that resides near the center of the Coma Cluster. In addition to constraining the masses and 3-d location of subhalos, the X-ray data show promise as a means of probing the structure of central subhalos.

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arXiv2012

A New Method to Quantify X-ray Substructures in Clusters of Galaxies

We present a new method to quantify substructures in clusters of galaxies, based on the analysis of the intensity of structures. This analysis is done in a residual image that is the result of the subtraction of a surface brightness model, obtained by fitting a two-dimensional analytical model (beta-model or Sérsic profile) with elliptical symmetry, from the X-ray image. Our method is applied to 34 clusters observed by the Chandra Space Telescope that are in the redshift range 0.02<z<0.2 and have a signal-to-noise ratio greater than 100. We present the calibration of the method and the relations between the substructure level with physical quantities, such as the mass, X-ray luminosity, temperature, and cluster redshift. We use our method to separate the clusters in two sub-samples of high and low substructure levels. We conclude, using Monte Carlo simulations, that the method recuperates very well the true amount of substructure for small angular core radii clusters (with respect to the whole image size) and good signal-to-noise observations. We find no evidence of correlation between the substructure level and physical properties of the clusters such as mass, gas temperature, X-ray luminosity and redshift. The scaling relations for the two sub-samples (high and low substructure level clusters) are different (they present an off-set, i.e., given a fixed mass or temperature, low substructure clusters tend to be more X-ray luminous), which is an important result for cosmological tests using the mass-luminosity relation to obtain the cluster mass function, since they rely on the assumption that clusters do not present different scaling relations according to their dynamical state.

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arXiv2009

Spiral-like structure in nearby clusters of galaxies

X-ray data analysis have found that fairly complex structures at cluster centres are more common than expected. Many of these structures have similar morphologies, which exhibit spiral-like substructure. It is not yet well known how these structures formed or are maintained. Understanding the origin of these spiral-like features at the centre of some clusters is the major motivation behind this work. We analyse deep \textit{Chandra} observations of 15 nearby galaxy clusters (0.01 $ < z < $ 0.06), and use X-ray temperature and substructure maps to detect small features at the cores of the clusters. We detect spiral-like features at the centre of 7 clusters: A85, A426, A496, Hydra A cluster, Centaurus, Ophiuchus, and A4059. These patterns are similar to those found in numerical hydrodynamic simulations of cluster mergers with non-zero impact parameter. In some clusters of our sample, a strong radio source also occupies the inner region of the cluster, which indicates a possible connection between the two. Our investigation implies that these spiral-like structures may be caused by off-axis minor mergers. Since these features occur in regions of high density, they may confine radio emission from the central galaxy producing, in some cases, unusual radio morphology.

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