arXiv subjects

D. Harvey

Publications and source records attributed to D. Harvey.

13 recordsLinked to original sources

arXiv2026

Non-spherical BUFFALOs: a weak lensing view of the Frontier Field clusters and associated systematics

Galaxy clusters are tracers of the large scale structures of the Universe, making the time evolution of their mass function dependent on key cosmological parameters, such as the cosmic matter density or the amplitude of density fluctuations $\sigma_8$. Accurate measurements of cluster's total masses are therefore essential, yet they can be challenging, particularly for clusters with complex morphologies, as simple mass profiles are often adopted to fit the measurements. In this work, we focus on the Frontier Fields galaxy clusters: a sample of six extremely massive systems, that, in most cases, exhibit highly complex mass distributions. The BUFFALO survey extended the Hubble Space Telescope observations for the Frontier Fields galaxy clusters, providing high-resolution multi-band imaging within a few Mpc. Combining this high-quality imaging dataset with ancillary spectroscopy, we produce weak-lensing catalogues with very high source densities, about 50 sources/arcmin$^2$. This allows us to robustly estimate the individual weak-lensing cluster masses and quantify the sensitivity of these measurements on different factors, such as the cluster centring, the uncertainty on the redshift distribution or the foreground contamination and boost factor correction. This provides a data-driven analysis of the different sources of systematics that can impact such measurements. We find that the largest sources of systematic bias arise for the most disturbed clusters, such as the multi-modal, merging galaxy cluster Abell 2744. This analysis sets a comprehensive framework for assessing the impact of systematics on the weak-lensing estimates of cluster masses, and in particular, in the case of unrelaxed clusters. This can play a key role in forthcoming cosmological analyses based on wide-field surveys such as Euclid and the Legacy Survey of Space and Time of the Rubin Observatory.

astro-ph.CO↗

arXiv2024

PSZ2 G282.28+49.94, a recently discovered analogue of the famous Bullet Cluster

We present a detailed study of the gas and galaxy properties of the cluster PSZ2 G282.28+49.94 detected in the Planck all-sky survey. The intracluster medium (ICM) of this object at z=0.56 exhibits a cometary-like shape. Combining Chandra and TNG observations, we characterised the spatially resolved thermodynamical properties of the gas and the spatial and velocity distribution of 73 galaxy members. The cluster structure is quite complex with an elongated core region containing the two brightest cluster galaxies and one dense group to the south-east. Since there is no velocity difference between the core and the south-east group, we suggest the presence of a merger along the plane of the sky. This structure is related to complex X-ray and radio features, and thus the merger has likely been caught during the post-merger phase. Comparing the distribution of the ICM and of member galaxies, we find a large offset of $\sim 350$ kpc between the position of the X-ray peak and the centre of a concentration of galaxies, preceding it in the likely direction of motion. This configuration is similar to the famous Bullet Cluster, leading us to dub PSZ2 G282.28+49.94 the "Planck bullet", and represents an ideal situation to provide astrophysical constraints to the self-interaction cross-section ($\sigma/m$) of dark matter particles. These results illustrate the power of a multi-wavelength approach to probe the merging scenario of such complex and distant systems.

astro-ph.CO↗

arXiv2024

Water-based Quantum Dots Liquid Scintillator for Particle Physics

Liquid scintillators are typically composed from organic compounds dissolved in organic solvents. However, usage of such material is often restricted due to fire safety and environmental reasons. Because of this, R\&D of water-based liquid scintillators is of extreme relevance; yet, no such scintillators have been made commercially available as yet. Here, we investigate an alternative, water-based quantum dots liquid scintillator. Pre-determined and controllable optical properties of the quantum dots, as well as the existence of large libraries of established protocols for their dispersion in aqueous solutions, make them an attractive option for nuclear and particle physics applications. We characterize the optical properties of water-based quantum dots liquid scintillator and find that most of its optical properties are preserved upon quantum dots' phase transfer into water, through the addition of an oleic acid hydrophilic layer. Using the developed scintillator, the time and charge responses from atmospheric muons are measured, highlighting the practical viability of water-based quantum dots liquid scintillators for nuclear and particle physics, special interest on neutrino physics.

physics.ins-det↗

arXiv2022

Constraints on dark matter self-interaction from the internal density profiles of X-COP galaxy clusters

TThe fundamental properties of the postulated dark matter (DM) affect the internal structure of gravitationally-bound structures. In the cold dark matter paradigm, DM particles interact only via gravity. Their distribution is well represented by an Einasto profile with shape parameter $α\approx0.18$, in the smallest dwarf galaxies or the most massive galaxy clusters alike. Conversely, if dark matter particles self-interact via additional forces, we expect the mass density profiles of DM halos to flatten in their central regions, thereby increasing the Einasto shape parameter. We measure the structural properties of the 12 massive X-COP galaxy clusters from observations of their hot gaseous atmosphere using the X-ray observatory XMM-Newton, and of the Sunyaev-Zeldovich effect using the Planck all-sky survey. After removing morphologically disturbed systems, we measure Einasto shape parameters with mean $\langleα\rangle = 0.19 \pm 0.03$ and intrinsic scatter $σ_α=0.06$, in close agreement with the prediction of the cold dark matter paradigm. We use cosmological hydrodynamical simulations of cluster formation with self-interacting DM (BAHAMAS-SIDM) to determine how the Einasto shape parameter depends on the self-interaction cross section. We use the fitted relation to turn our measurements of $α$ into constraints on the self-interaction cross section, which imply $σ/m < 0.19$ cm$^2$/g (95% confidence level) at collision velocity $v_\mathrm{DM-DM}\sim1,000$ km/s. This is lower than the interaction cross-section required for dark matter self-interactions to solve the core-cusp problem in dwarf spheroidal galaxies, unless the cross section is a strong function of velocity.

astro-ph.CO↗

arXiv2020

H0LiCOW XI. A weak lensing measurement of the external convergence in the field of the lensed quasar B1608+656 using HST and Subaru deep imaging

We investigate the environment and line of sight of the H0LiCOW lens B1608+656 using Subaru Suprime-Cam and the Hubble Space Telescope (HST) to perform a weak lensing analysis. We compare three different methods to reconstruct the mass map of the field, i.e. the standard Kaiser-Squires inversion coupled with inpainting and Gaussian or wavelet filtering, and $\tt{Glimpse}$ a method based on sparse regularization of the shear field. We find no substantial difference between the 2D mass reconstructions, but we find that the ground-based data is less sensitive to small-scale structures than the space-based observations. Marginalising over the results obtained with all the reconstruction techniques applied to the two available HST filters F606W and F814W, we estimate the external convergence, $κ_{\rm ext}$ at the position of B1608+656 is $κ_{\rm ext} = 0.11^{+0.06}_{-0.04}$, where the error bars corresponds respectively to the 16th and 84th quartiles. This result is compatible with previous estimates using the number-counts technique, suggesting that B1608+656 resides in an over-dense line of sight, but with a completely different technique. Using our mass reconstructions, we also compare the convergence at the position of several groups of galaxies in the field of B1608+656 with the mass measurements using various analytical mass profiles, and find that the weak lensing results favor truncated halo models.

astro-ph.GA↗

arXiv2018

Growing a `Cosmic Beast': Observations and Simulations of MACS J0717.5+3745

We present a gravitational lensing and X-ray analysis of a massive galaxy cluster and its surroundings. The core of MACS\,J0717.5+3745 ($M(R<1\,{\rm Mpc})\sim$\,$2$$\times$$10^{15}\,\msun$, $z$=$0.54$) is already known to contain four merging components. We show that this is surrounded by at least seven additional substructures with masses ranging from $3.8-6.5\times10^{13}\,\msun$, at projected radii $1.6$ to $4.9$\,Mpc. We compare MACS\,J0717 to mock lensing and X-ray observations of similarly rich clusters in cosmological simulations. The low gas fraction of substructures predicted by simulations turns out to match our observed values of $1$--$4\%$. Comparing our data to three similar simulated halos, we infer a typical growth rate and substructure infall velocity. That suggests MACS\,J0717 could evolve into a system similar to, but more massive than, Abell\,2744 by $z=0.31$, and into a $\sim$\,$10^{16}\,\msun$ supercluster by $z=0$. The radial distribution of infalling substructure suggests that merger events are strongly episodic; however we find that the smooth accretion of surrounding material remains the main source of mass growth even for such massive clusters.

astro-ph.CO↗

arXiv2018

The shape of galaxy dark matter halos in massive galaxy clusters: Insights from strong gravitational lensing

We assess how much unused strong lensing information is available in the deep \emph{Hubble Space Telescope} imaging and VLT/MUSE spectroscopy of the \emph{Frontier Field} clusters. As a pilot study, we analyse galaxy cluster MACS\,J0416.1-2403 ($z$$=$$0.397$, $M(R<200\,{\rm kpc})$$=$$1.6$$\times$$10^{14}\msun$), which has 141 multiple images with spectroscopic redshifts. We find that many additional parameters in a cluster mass model can be constrained, and that adding even small amounts of extra freedom to a model can dramatically improve its figures of merit. We use this information to constrain the distribution of dark matter around cluster member galaxies, simultaneously with the cluster's large-scale mass distribution. We find tentative evidence that some galaxies' dark matter has surprisingly similar ellipticity to their stars (unlike in the field, where it is more spherical), but that its orientation is often misaligned. When non-coincident dark matter and baryonic halos are allowed, the model improves by 35\%. This technique may provide a new way to investigate the processes and timescales on which dark matter is stripped from galaxies as they fall into a massive cluster. Our preliminary conclusions will be made more robust by analysing the remaining five \emph{Frontier Field} clusters.

astro-ph.CO↗

arXiv2017

H0LiCOW VIII. A weak lensing measurement of the external convergence in the field of the lensed quasar HE$\,$0435$-$1223

We present a weak gravitational lensing measurement of the external convergence along the line of sight to the quadruply lensed quasar HE$\,$0435$-$1223. Using deep r-band images from Subaru-Suprime-Cam we observe galaxies down to a 3$σ$ limiting magnitude of $\sim 26$ mags resulting in a source galaxy density of 14 galaxies / arcmin$^2$ after redshift-based cuts. Using an inpainting technique and Multi-Scale Entropy filtering algorithm, we find that the region in close proximity to the lens has an estimated external convergence of $κ=-0.012^{+0.020}_{-0.013}$ and is hence marginally under-dense. We also rule out the presence of any halo with a mass greater than $M_{\rm vir}=1.6\times10^{14}h^{-1}M_\odot$ (68$\%$ confidence limit). Our results, consistent with previous studies of this lens, confirm that the intervening mass along the line of sight to HE$\,$0435$-$1223 does not affect significantly the cosmological results inferred from the time delay measurements of that specific object.

astro-ph.CO↗

arXiv2017

A Potential Recoiling Supermassive Black Hole CXO J101527.2+625911

We have carried out a systematic search for recoiling supermassive black holes (rSMBH) using the Chandra Source and SDSS Cross Matched Catalog. From the survey, we have detected a potential rSMBH, 'CXO J101527.2+625911' at z=0.3504. The CXO J101527.2+625911 has a spatially offset (1.26$\pm$0.05 kpc) active SMBH and kinematically offset broad emission lines (175$\pm$25 km s$^{\rm -1}$ relative to systemic velocity). The observed spatial and velocity offsets suggest this galaxy could be a rSMBH, but we also have considered a possibility of dual SMBH scenario. The column density towards the galaxy center was found to be Compton thin, but no X-ray source was detected. The non-detection of the X-ray source in the nucleus suggests either there is no obscured actively accreting SMBH, or there exists an SMBH but has a low accretion rate (i.e. low-luminosity AGN (LLAGN)). The possibility of the LLAGN was investigated and found to be unlikely based on the H$α$ luminosity, radio power, and kinematic arguments. This, along with the null detection of X-ray source in the nucleus supports our hypothesis that the CXO J101527.2+625911 is a rSMBH. Our GALFIT analysis shows the host galaxy to be a bulge-dominated elliptical. The weak morphological disturbance and small spatial and velocity offsets suggest that CXO J101527.2+625911 could be in the final stage of merging process and about to turn into a normal elliptical galaxy.

astro-ph.GA↗

arXiv2017

Abell 2744: Too much substructure for Lambda CDM?

The massive substructures found in Abell 2744 by Jauzac et al. (2016) present a challenge to the cold dark matter paradigm due to their number and proximity to the cluster centre. We use one of the biggest N-body simulations, the Millennium XXL, to investigate the substructure in a large sample of massive dark matter haloes. A range of effects which influence the comparison with the observations is considered, extending the preliminary evaluation carried out by Jauzac et al. (2016). There are many tens of haloes in the simulation with a total mass comparable with or larger than that of Abell 2744. However, we find no haloes with a number and distribution of massive substructures (> 5 10^13 Msun) that is close to that inferred from the observations of Abell 2744. The application of extreme value statistics suggests that we would need a simulation of at least ten times the volume of the Millennium XXL to find a single dark matter halo with a similar internal structure to Abell 2744. Explaining the distribution of massive substructures in clusters is a new hurdle for hierarchical models to negotiate, which is not weakened by appeals to baryonic physics or uncertainty over the nature of the dark matter particle.

astro-ph.CO↗

arXiv2016

The Extraordinary Amount of Substructure in the Hubble Frontier Fields Cluster Abell 2744

We present a joint optical/X-ray analysis of the massive galaxy cluster Abell 2744 (z=0.308). Our strong- and weak-lensing analysis within the central region of the cluster, i.e., at R<1Mpc from the brightest cluster galaxy, reveals eight substructures, including the main core. All of these dark-matter halos are detected with a significance of at least 5sigma and feature masses ranging from 0.5 to 1.4x10^{14}Msun within R<150kpc. Merten et al. (2011) and Medezinski et al. (2016) substructures are also detected by us. We measure a slightly higher mass for the main core component than reported previously and attribute the discrepancy to the inclusion of our tightly constrained strong-lensing mass model built on Hubble Frontier Fields data. X-ray data obtained by XMM-Newton reveal four remnant cores, one of them a new detection, and three shocks. Unlike Merten et al. (2011), we find all cores to have both dark and luminous counterparts. A comparison with clusters of similar mass in the MXXL simulations yields no objects with as many massive substructures as observed in Abell 2744, confirming that Abell 2744 is an extreme system. We stress that these properties still do not constitute a challenge to $Λ$CDM, as caveats apply to both the simulation and the observations: for instance, the projected mass measurements from gravitational lensing and the limited resolution of the sub-haloes finders. We discuss implications of Abell 2744 for the plausibility of different dark-matter candidates and, finally, measure a new upper limit on the self-interaction cross-section of dark matter of sigma_{DM}<1.28cm2/g(68\% CL), in good agreement with previous results from Harvey et al. (2015).

astro-ph.CO↗

arXiv2003

Superhumps in Cataclysmic Binaries. XXIV. Twenty More Dwarf Novae

We report precise measures of the orbital and superhump period in twenty more dwarf novae. For ten stars, we report new and confirmed spectroscopic periods - signifying the orbital period P_o - as well as the superhump period P_sh. These are GX Cas, HO Del, HS Vir, BC UMa, RZ Leo, KV Dra, KS UMa, TU Crt, QW Ser, and RZ Sge. For the remaining ten, we report a medley of P_o and P_sh measurements from photometry; most are new, with some confirmations of previous values. These are KV And, LL And, WX Cet, MM Hya, AO Oct, V2051 Oph, NY Ser, KK Tel, HV Vir, and RX J1155.4-5641. Periods, as usual, can be measured to high accuracy, and these are of special interest since they carry dynamical information about the binary. We still have not quite learned how to read the music, but a few things are clear. The fractional superhump excess epsilon [=(P_sh-P_o)/P_o] varies smoothly with P_o. The scatter of the points about that smooth curve is quite low, and can be used to limit the intrinsic scatter in M_1, the white dwarf mass, and the mass-radius relation of the secondary. The dispersion in M_1 does not exceed 24%, and the secondary-star radii scatter by no more than 11% from a fixed mass-radius relation. For the well-behaved part of epsilon(P_o) space, we estimate from superhump theory that the secondaries are 18+-6% larger than theoretical ZAMS stars. This affects some other testable predictions about the secondaries: at a fixed P_o, it suggests that the secondaries are (compared with ZAMS predictions) 40+-14% less massive, 12+-4% smaller, 19+-6% cooler, and less luminous by a factor 2.5(7). The presence of a well-defined mass-radius relation, reflected in a well-defined epsilon(P_o) relation, strongly limits effects of nuclear evolution in the secondaries.

astro-ph↗

arXiv2003

FS Aur - a new class of Cataclysmic Variables or the missing link between Intermediate Polars and SW Sex objects?

FS Aur is a known dwarf nova with an orbital period of about 85.7 minutes. It has been assumed to be a member of the SU UMa subclass of cataclysmic variables (CVs), but previous searches for superhumps and superoutburst have been unsuccessful. We conducted a series of photometric and spectroscopic observations of FS Aur during quiescence. We confirmed its short orbital period from radial velocity measurements. However, the long-term photometry revealed an unexpected result: the system also shows a distinct 0.24 mag modulation in the BVR photometric bands with a period of 205.5 min, which is 2.4 times longer than the orbital period. We discuss various possible causes for such a peculiar behavior.

astro-ph↗