arXiv subjects

H. Ebeling

Publications and source records attributed to H. Ebeling.

At least 19 recordsLinked to original sources

arXiv2024

Beyond MACS: Physical properties of extremely X-ray luminous clusters at $z > 0.5$

We present a sample of over 100 highly X-ray luminous galaxy clusters at $z\sim$ 0.5-0.9, discovered by the extended Massive Cluster Survey (eMACS) in ROSAT All-Sky Survey (RASS) data. Follow-up observations of a subset at higher resolution and greater depth with the Chandra X-ray Observatory are used to map the gaseous intra-cluster medium, while strong-gravitational-lensing features identified in Hubble Space Telescope imaging allow us to constrain the total mass distribution. We present evidence of the exceptional gravitational-lensing power of these massive systems, search for substructure along the line of sight by mapping the radial velocities of cluster members obtained through extensive ground-based spectroscopy, and identify dramatic cases of galaxy evolution in high-density cluster environments. The available observations of the eMACS sample presented here provide a wealth of insights into the properties of very massive clusters ($\gtrsim 10^{15} M_\odot$) at $z > 0.5$, which act as powerful lenses to study galaxies in the very distant Universe. We also discuss the evolutionary state, galaxy population, and large-scale environment of eMACS clusters and release to the community all data and science products to further the understanding of the first generation of truly massive clusters to have formed in the Universe.

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arXiv2021

ALMA 1.3 mm Survey of Lensed Submillimeter Galaxies (SMGs) Selected by Herschel: Discovery of Spatially Extended SMGs and Implications

We present an ALMA 1.3 mm (Band 6) continuum survey of lensed submillimeter galaxies (SMGs) at $z=1.0\sim3.2$ with an angular resolution of $\sim0.2$". These galaxies were uncovered by the Herschel Lensing Survey (HLS), and feature exceptionally bright far-infrared continuum emission ($S_\mathrm{peak} \gtrsim 90$ mJy) owing to their lensing magnification. We detect 29 sources in 20 fields of massive galaxy clusters with ALMA. Using both the Spitzer/IRAC (3.6/4.5 $\mathrm{μm}$) and ALMA data, we have successfully modeled the surface brightness profiles of 26 sources in the rest-frame near- and far-infrared. Similar to previous studies, we find the median dust-to-stellar continuum size ratio to be small ($R_\mathrm{e,dust}/R_\mathrm{e,star} = 0.38\pm0.14$) for the observed SMGs, indicating that star formation is centrally concentrated. This is, however, not the case for two spatially extended main-sequence SMGs with a low surface brightness at 1.3 mm ($\lesssim 0.1$ mJy arcsec$^{-2}$), in which the star formation is distributed over the entire galaxy ($R_\mathrm{e,dust}/R_\mathrm{e,star}>1$). As a whole, our SMG sample shows a tight anti-correlation between ($R_\mathrm{e,dust}/R_\mathrm{e,star}$) and far-infrared surface brightness ($Σ_\mathrm{IR}$) over a factor of $\simeq$ 1000 in $Σ_\mathrm{IR}$. This indicates that SMGs with less vigorous star formation (i.e., lower $Σ_\mathrm{IR}$) lack central starburst and are likely to retain a broader spatial distribution of star formation over the whole galaxies (i.e., larger $R_\mathrm{e,dust}/R_\mathrm{e,star}$). The same trend can be reproduced with cosmological simulations as a result of central starburst and potentially subsequent "inside-out" quenching, which likely accounts for the emergence of compact quiescent galaxies at $z\sim2$.

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arXiv2020

Diffuse Radio Sources in a Statistically Complete Sample of High Redshift Galaxy Clusters

Non-thermal properties of galaxy clusters have been studied with detailed and deep radio images in comparison with X-ray data. While much progress has been made, most of the studied clusters are at a relatively low redshift (z < 0.3). We here investigate the evolutionary properties of the non-thermal cluster emission using two statistically complete samples at z > 0.3. We obtained short JVLA observations at L-band of the statistically complete sample of very X-ray luminous clusters from the Massive Cluster Survey (MACS) presented by Ebeling et al. (2010), and redshift range 0.3 - 0.5. We add to this list the complete sample of the 12 most distant MACS clusters (z > 0.5) presented in Ebeling et al. (2007). Most clusters show evidence of emission in the radio regime. We present the radio properties of all clusters in our sample and show images of newly detected diffuse sources. A radio halo is detected in 19 clusters, and five clusters contain a relic source. Most of the brightest cluster galaxies (BCG) in relaxed clusters show radio emission with powers typical of FRII radio galaxies, and some are surrounded by a radio mini-halo. The high frequency of radio emission from the BCG in relaxed clusters suggests that BCG feedback mechanisms are in place already at z about 0.6. The properties of radio halos and the small number of detected relics suggest redshift evolution in the properties of diffuse sources. The radio power (and size) of radio halos could be related to the number of past merger events in the history of the system. In this scenario, the presence of a giant and high-power radio halo is indicative of an evolved system with a large number of past major mergers.

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arXiv2018

Quantifying the suppression of the (un)-obscured star formation in galaxy cluster cores at 0.2$\lesssim$$z$$\lesssim$0.9

We quantify the star formation (SF) in the inner cores ($\mathcal{R}$/$R_{200}$$\leq$0.3) of 24 massive galaxy clusters at 0.2$\lesssim$$z$$\lesssim$0.9 observed by the $Herschel$ Lensing Survey and the Cluster Lensing and Supernova survey with $Hubble$. These programmes, covering the rest-frame ultraviolet to far-infrared regimes, allow us to accurately characterize stellar mass-limited ($\mathcal{M}_{*}$$>$$10^{10}$ $M_{\odot}$) samples of star-forming cluster members (not)-detected in the mid- and/or far-infrared. We release the catalogues with the photometry, photometric redshifts, and physical properties of these samples. We also quantify the SF displayed by comparable field samples from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. We find that in intermediate-$z$ cluster cores, the SF activity is suppressed with respect the field in terms of both the fraction ($\mathcal{F}$) of star-forming galaxies (SFG) and the rate at which they form stars ($\mathcal{SFR}$ and $s\mathcal{SFR} = \mathcal{SFR}/\mathcal{M}_{*}$). On average, the $\mathcal{F}$ of SFGs is a factor $\sim$$2$ smaller in cluster cores than in the field. Furthermore, SFGs present average $\mathcal{SFR}$ and $s\mathcal{SFR}$ typically $\sim$0.3 dex smaller in the clusters than in the field along the whole redshift range probed. Our results favour long time-scale quenching physical processes as the main driver of SF suppression in the inner cores of clusters since $z$$\sim$0.9, with shorter time-scale processes being very likely responsible for a fraction of the missing SFG population.

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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.

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arXiv2018

Thirty-fold: Extreme gravitational lensing of a quiescent galaxy at $z=1.6$

We report the discovery of eMACSJ1341-QG-1, a quiescent galaxy at $z=1.594$ located behind the massive galaxy cluster eMACSJ1341.9$-$2442 ($z=0.835$). The system was identified as a gravitationally lensed triple image in Hubble Space Telescope images obtained as part of a snapshot survey of the most X-ray luminous galaxy clusters at $z>0.5$ and spectroscopically confirmed in ground-based follow-up observations with the ESO/X-Shooter spectrograph. From the constraints provided by the triple image, we derive a first, crude model of the mass distribution of the cluster lens, which predicts a gravitational amplification of a factor of $\sim$30 for the primary image and a factor of $\sim$6 for the remaining two images of the source, making eMACSJ1341-QG-1 by far the most strongly amplified quiescent galaxy discovered to date. Our discovery underlines the power of SNAPshot observations of massive, X-ray selected galaxy clusters for lensing-assisted studies of faint background populations.

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arXiv2017

Molecular gas properties of a lensed star-forming galaxy at z~3.6: a case study

We report on the galaxy MACSJ0032-arc at z=3.6314 discovered during the Herschel Lensing snapshot Survey of massive galaxy clusters, and strongly lensed by the cluster MACSJ0032.1+1808. The successful detections of its rest-frame UV, optical, FIR, millimeter, and radio continua, and of its CO emission enable us to characterize, for the first time at such a high redshift, the stellar, dust, and molecular gas properties of a compact star-forming galaxy with a size smaller than 2.5 kpc, a fairly low stellar mass of 4.8x10^9 Msun, and a moderate IR luminosity of 4.8x10^11 Lsun. We find that the bulk of the molecular gas mass and star formation seems to be spatially decoupled from the rest-frame UV emission. About 90% of the total star formation rate is undetected at rest-frame UV wavelengths because of severe obscuration by dust, but is seen through the thermal FIR dust emission and the radio synchrotron radiation. The observed CO(4-3) and CO(6-5) lines demonstrate that high-J transitions, at least up to J=6, remain excited in this galaxy, whose CO spectral line energy distribution resembles that of high-redshift submm galaxies, even though the IR luminosity of MACSJ0032-arc is ten times lower. This high CO excitation is possibly due to the compactness of the galaxy. We find evidence that this high CO excitation has to be considered in the balance when estimating the CO-to-H2 conversion factor. The inferred depletion time of the molecular gas in MACSJ0032-arc supports the decrease in the gas depletion timescale of galaxies with redshift, although to a lesser degree than predicted by galaxy evolution models. Instead, the measured molecular gas fraction as high as 60-79% in MACSJ0032-arc favors the continued increase in the gas fraction of galaxies with redshift as expected, despite the plateau observed between z~1.5 and z~2.5.

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arXiv2016

New Constraints on Spatial Variations of the Fine Structure Constant from Clusters of Galaxies

We have constrained the spatial variation of the fine structure constant using multi-frequency measurements of the thermal Sunyaev-Zeldovich effect of 618 X-ray selected clusters. Although our results are not competitive with the ones from quasar absorption lines, we improved by a factor 10 and ~2.5 previous results from Cosmic Microwave Background power spectrum and from galaxy clusters, respectively.

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arXiv2016

Hiding in Plain Sight - Recovering Clusters of Galaxies with the Strongest AGN in Their Cores

A key challenge in understanding the feedback mechanism of AGN in Brightest Cluster Galaxies (BCGs) is the inherent rarity of catching an AGN during its strong outburst phase. This is exacerbated by the ambiguity of differentiating between AGN and clusters in X-ray observations. If there is evidence for an AGN then the X-ray emission is commonly assumed to be dominated by the AGN emission, introducing a selection effect against the detection of AGN in BCGs. In order to recover these 'missing' clusters, we systematically investigate the colour-magnitude relation around some ~3500 ROSAT All Sky Survey selected AGN, looking for signs of a cluster red sequence. Amongst our 22 candidate systems, we independently rediscover several confirmed systems, where a strong AGN resides in a central galaxy. We compare the X-ray luminosity to red sequence richness distribution of our AGN candidate systems with that of a similarly selected comparison sample of ~1000 confirmed clusters and identify seven 'best' candidates (all of which are BL Lac objects), where the X-ray flux is likely to be a comparable mix between cluster and AGN emission. We confirm that the colours of the red sequence are consistent with the redshift of the AGN, that the colours of the AGN host galaxy are consistent with AGN, and, by comparing their luminosities with those from our comparison clusters, confirm that the AGN hosts are consistent with BCGs.

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arXiv2016

Constraining spatial variations of the fine structure constant using clusters of galaxies and Planck data

We propose an improved methodology to constrain spatial variations of the fine structure constant using clusters of galaxies. We use the {\it Planck} 2013 data to measure the thermal Sunyaev-Zeldovich effect at the location of 618 X-ray selected clusters. We then use a Monte Carlo Markov Chain algorithm to obtain the temperature of the Cosmic Microwave Background at the location of each galaxy cluster. When fitting three different phenomenological parameterizations allowing for monopole and dipole amplitudes in the value of the fine structure constant we improve the results of earlier analysis involving clusters and the CMB power spectrum, and we also found that the best-fit direction of a hypothetical dipole is compatible with the direction of other known anomalies. Although the constraining power of our current datasets do not allow us to test the indications of a fine-structure constant dipole obtained though high-resolution optical/UV spectroscopy, our results do highlight that clusters of galaxies will be a very powerful tool to probe fundamental physics at low redshift.

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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).

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arXiv2016

A Multi-Wavelength Photometric Census of AGN and Star Formation Activity in the Brightest Cluster Galaxies of X-ray Selected Clusters

Despite their reputation as being "red and dead", the unique environment inhabited by Brightest Cluster Galaxies (BCGs) can often lead to a self-regulated feedback cycle between radiatively cooling intracluster gas and star formation and AGN activity in the BCG. However the prevalence of "active" BCGs, and details of the feedback involved, are still uncertain. We have performed an optical, UV and Mid-IR photometric analysis of the BCGs in 981 clusters at 0.03 < z < 0.5, selected from the ROSAT All Sky Survey. Using Pan-STARRS PS1 3pi, GALEX and WISE survey data we look for BCGs with photometric colours which deviate from that of the bulk population of passive BCGs - indicative of AGN and/or star formation activity within the BCG. We find that whilst the majority of BCGs are consistent with being passive, at least 14% of our BCGs show a significant colour offset from passivity in at least one colour index. And, where available, supplementary spectroscopy reveals the majority of these particular BCGs show strong optical emission lines. On comparing BCG "activity" with the X-ray luminosity of the host cluster, we find that BCGs showing a colour offset are preferentially found in the more X-ray luminous clusters, indicative of the connection between BCG "activity" and the intracluster medium.

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arXiv2016

Frontier Fields Clusters: Deep Chandra Observations of the Complex Merger MACS J1149.6+2223

The HST Frontier Fields cluster MACS J1149.6+2223 is one of the most complex merging clusters, believed to consist of four dark matter halos. We present results from deep (365 ks) Chandra observations of the cluster, which reveal the most distant cold front (z=0.544) discovered to date. In the cluster outskirts, we also detect hints of a surface brightness edge that could be the bow shock preceding the cold front. The substructure analysis of the cluster identified several components with large relative radial velocities, thus indicating that at least some collisions occur almost along the line of sight. The inclination of the mergers with respect to the plane of the sky poses significant observational challenges at X-ray wavelengths. MACS J1149.6+2223 possibly hosts a steep-spectrum radio halo. If the steepness of the radio halo is confirmed, then the radio spectrum, combined with the relatively regular ICM morphology, could indicate that MACS J1149.6+2223 is an old merging cluster.

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arXiv2016

Strong-Lensing Analysis of MACS,J0717.5+3745 from Hubble Frontier Fields observations: How well can the mass distribution be constrained?

[abridged] We present a strong-lensing analysis of MACSJ0717.5+3745, based on the full depth of the Hubble Frontier Field (HFF) observations, which brings the number of multiply imaged systems to 61, ten of which are spectroscopically confirmed. The total number of images comprised in these systems rises to 165. Our analysis uses a parametric mass reconstruction technique, as implemented in the Lenstool software, to constrain a mass distribution composed of four large-scale mass components + galaxy-scale perturbers. We find a superposition of cored isothermal mass components to provide a good fit to the observational constraints, resulting in a very shallow mass distribution for the smooth (large-scale) component. Given the implications of such a flat mass profile, we investigate whether a model composed of "peaky" non-cored mass components can also reproduce the observational constraints. We find that such a non-cored mass model reproduces the observational constraints equally well. Although the total mass distributions of both models are consistent, as well as the integrated two dimensional mass profiles, we find that the smooth and the galaxy-scale components are very different. We conclude that, even in the HFF era, the generic degeneracy between smooth and galaxy-scale components is not broken, in particular in such a complex galaxy cluster. Consequently, insights into the mass distribution of MACS J0717 remain limited, underlining the need for additional probes beyond strong lensing. Our findings also have implications for estimates of the lensing magnification: we show that the amplification difference between the two models is larger than the error associated with either model. This uncertainty decreases the area of the image plane where we can reliably study the high-redshift Universe by 50 to 70%.

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arXiv2015

Hubble Frontier Fields: Predictions for the Return of SN Refsdal with the MUSE and GMOS Spectrographs

We present a high-precision mass model of the galaxy cluster MACSJ1149.6+2223, based on a strong-gravitational-lensing analysis of Hubble Space Telescope Frontier Fields (HFF) imaging data and spectroscopic follow-up with Gemini/GMOS and VLT/MUSE. Our model includes 12 new multiply imaged galaxies, bringing the total to 22, comprised of 65 individual lensed images. Unlike the first two HFF clusters, Abell 2744 and MACSJ0416.1-2403, MACSJ1149 does not reveal as many multiple images in the HFF data. Using the Lenstool software package and the new sets of multiple images, we model the cluster with several cluster-scale dark-matter halos and additional galaxy-scale halos for the cluster members. Consistent with previous analyses, we find the system to be complex, composed of five cluster-scale halos. Their spatial distribution and lower mass, however, makes MACSJ1149 a less powerful lens. Our best-fit model predicts image positions with an RMS of 0.91". We measure the total projected mass inside a 200~kpc aperture as ($1.840\pm 0.006$)$\times 10^{14}$M$_{\odot}$, thus reaching again 1% precision, following our previous HFF analyses of MACSJ0416.1-2403 and Abell 2744. In light of the discovery of the first resolved quadruply lensed supernova, SN Refsdal, in one of the multiply imaged galaxies identified in MACSJ1149, we use our revised mass model to investigate the time delays and predict the rise of the next image between November 2015 and January 2016.

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arXiv2015

Flash Spectroscopy: Emission Lines from the Ionized Circumstellar Material around $<10$-Day-Old Type II Supernovae

Supernovae (SNe) embedded in dense circumstellar material (CSM) may show prominent emission lines in their early-time spectra ($\leq 10$ days after the explosion), owing to recombination of the CSM ionized by the shock-breakout flash. From such spectra ("flash spectroscopy"), we can measure various physical properties of the CSM, as well as the mass-loss rate of the progenitor during the year prior to its explosion. Searching through the Palomar Transient Factory (PTF and iPTF) SN spectroscopy databases from 2009 through 2014, we found 12 Type II SNe showing flash-ionized (FI) signatures in their first spectra. All are younger than 10 days. These events constitute 14\% of all 84 SNe in our sample having a spectrum within 10 days from explosion, and 18\% of SNe~II observed at ages $<5$ days, thereby setting lower limits on the fraction of FI events. We classified as "blue/featureless" (BF) those events having a first spectrum which is similar to that of a black body, without any emission or absorption signatures. It is possible that some BF events had FI signatures at an earlier phase than observed, or that they lack dense CSM around the progenitor. Within 2 days after explosion, 8 out of 11 SNe in our sample are either BF events or show FI signatures. Interestingly, we found that 19 out of 21 SNe brighter than an absolute magnitude $M_R=-18.2$ belong to the FI or BF groups, and that all FI events peaked above $M_R=-17.6$ mag, significantly brighter than average SNe~II.

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arXiv2015

Radio halos in SZ-selected clusters of galaxies: the making of a halo?

Radio halos are synchrotron radio sources detected in some massive galaxy clusters. Their Mpc-size indicates that (re)acceleration processes are taking place in the host cluster. X-ray catalogues of galaxy clusters have been used in the past to search for radio halos and to understand their connection with cluster-cluster mergers and with the thermal component of the intra-cluster medium. More recently, the Sunyaev-Zel'dovich effect has been proven to be a better route to search for massive clusters in a wider redshift range. With the aim of discovering new radio halos and understanding their connection with cluster-cluster mergers, we have selected from the Planck Early source catalog the most massive clusters, and we have observed with the Giant Metrewave Radio Telescope at 323 MHz those objects for which deep observations were not available. We have discovered new peculiar radio emission in three of the observed clusters finding: (i) a radio halo in the cluster RXCJ0949.8+1708; (ii) extended emission in Abell 1443 that we classify as a radio halo plus a radio relic, with a bright filament embedded in the radio halo; (iii) low-power radio emission is found in CIZA J1938.3+5409 which is ten times below the radio - X-ray correlation, and represents the first direct detection of the radio emission in the "upper-limit" region of the radio - X-ray diagram. We discuss the properties of these new radio halos in the framework of theoretical models for the radio emission.

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arXiv2015

Cosmology and astrophysics from relaxed galaxy clusters - IV: Robustly calibrating hydrostatic masses with weak lensing

This is the fourth in a series of papers studying the astrophysics and cosmology of massive, dynamically relaxed galaxy clusters. Here, we use measurements of weak gravitational lensing from the Weighing the Giants project to calibrate Chandra X-ray measurements of total mass that rely on the assumption of hydrostatic equilibrium. This comparison of X-ray and lensing masses provides a measurement of the combined bias of X-ray hydrostatic masses due to both astrophysical and instrumental sources. Assuming a fixed cosmology, and within a characteristic radius (r_2500) determined from the X-ray data, we measure a lensing to X-ray mass ratio of 0.96 +/- 9% (stat) +/- 9% (sys). We find no significant trends of this ratio with mass, redshift or the morphological indicators used to select the sample. In accordance with predictions from hydro simulations for the most massive, relaxed clusters, our results disfavor strong, tens-of-percent departures from hydrostatic equilibrium at these radii. In addition, we find a mean concentration of the sample measured from lensing data of c_200 = $3.0_{-1.8}^{+4.4}$. Anticipated short-term improvements in lensing systematics, and a modest expansion of the relaxed lensing sample, can easily increase the measurement precision by 30--50%, leading to similar improvements in cosmological constraints that employ X-ray hydrostatic mass estimates, such as on Omega_m from the cluster gas mass fraction.

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