arXiv subjects

Mathilde Jauzac

Publications and source records attributed to Mathilde Jauzac.

At least 91 records · Page 5Linked to original sources

arXiv2018

Extreme magnification of a star at redshift 1.5 by a galaxy-cluster lens

Galaxy-cluster gravitational lenses can magnify background galaxies by a total factor of up to ~50. Here we report an image of an individual star at redshift z=1.49 (dubbed "MACS J1149 Lensed Star 1 (LS1)") magnified by >2000. A separate image, detected briefly 0.26 arcseconds from LS1, is likely a counterimage of the first star demagnified for multiple years by a >~3 solar-mass object in the cluster. For reasonable assumptions about the lensing system, microlensing fluctuations in the stars' light curves can yield evidence about the mass function of intracluster stars and compact objects, including binary fractions and specific stellar evolution and supernova models. Dark-matter subhalos or massive compact objects may help to account for the two images' long-term brightness ratio.

astro-ph.GA↗

arXiv2018

Dark matter under the microscope: Constraining compact dark matter with caustic crossing events

A galaxy cluster acts as a cosmic telescope over background galaxies but also as a cosmic microscope of the lens imperfections. The diverging magnification of lensing caustics enhances the microlensing effect of substructure present within the lensing mass. Fine-scale structure can be accessed as a moving background source brightens and disappears when crossing these caustics. The recent recognition of a distant lensed star near the Einstein radius of the galaxy cluster MACSJ1149.5+2223 (Kelly et al. 2017) allows the rare opportunity to reach subsolar mass microlensing through a super-critical column of cluster matter. Here we compare these observations with high-resolution ray-tracing simulations that include stellar microlensing set by the observed intracluster starlight and also primordial black holes that may be responsible for the recently observed LIGO events. We explore different scenarios with microlenses from the intracluster medium and black holes, including primordial ones, and examine strategies to exploit these unique alignments. We find that the best constraints on the fraction of compact dark matter in the small-mass regime can be obtained in regions of the cluster where the intracluster medium plays a negligible role. This new lensing phenomenon should be widespread and can be detected within modest-redshift lensed galaxies so that the luminosity distance is not prohibitive for detecting individual magnified stars. Continuous {\it Hubble Space Telescope} monitoring of several such optimal arcs will be rewarded by an unprecedented mass spectrum of compact objects that can contribute to uncovering the nature of dark matter.

astro-ph.CO↗

arXiv2018

What if LIGO's gravitational wave detections are strongly lensed by massive galaxy clusters?

Motivated by the preponderance of so-called "heavy black holes" in the binary black hole (BBH) gravitational wave (GW) detections to date, and the role that gravitational lensing continues to play in discovering new galaxy populations, we explore the possibility that the GWs are strongly-lensed by massive galaxy clusters. For example, if one of the GW sources were actually located at $z=1$, then the rest-frame mass of the associated BHs would be reduced by a factor $\sim2$. Based on the known populations of BBH GW sources and strong-lensing clusters, we estimate a conservative lower limit on the number of BBH mergers detected per detector year at LIGO/Virgo's current sensitivity that are multiply-imaged, of $R_{\rm detect}\simeq10^{-5}{\rm yr}^{-1}$. This is equivalent to rejecting the hypothesis that one of the BBH GWs detected to date was multiply-imaged at $<\sim4σ$. It is therefore unlikely but not impossible that one of the GWs is multiply-imaged. We identify three spectroscopically confirmed strong-lensing clusters with well constrained mass models within the $90\%$ credible sky localisations of the BBH GWs from LIGO's first observing run. In the event that one of these clusters multiply-imaged one of the BBH GWs, we predict that $20-60\%$ of the putative next appearances of the GWs would be detectable by LIGO, and that they would arrive at Earth within three years of first detection.

astro-ph.HE↗

arXiv2017

Dark matter dynamics in Abell 3827: new data consistent with standard Cold Dark Matter

We present integral field spectroscopy of galaxy cluster Abell 3827, using ALMA and VLT/MUSE. It reveals an unusual configuration of strong gravitational lensing in the cluster core, with at least seven lensed images of a single background spiral galaxy. Lens modelling based on HST imaging had suggested that the dark matter associated with one of the cluster's central galaxies may be offset. The new spectroscopic data enable better subtraction of foreground light, and better identification of multiple background images. The inferred distribution of dark matter is consistent with being centered on the galaxies, as expected by LCDM. Each galaxy's dark matter also appears to be symmetric. Whilst we do not find an offset between mass and light (suggestive of self-interacting dark matter) as previously reported, the numerical simulations that have been performed to calibrate Abell 3827 indicate that offsets and asymmetry are still worth looking for in collisions with particular geometries. Meanwhile, ALMA proves exceptionally useful for strong lens image identifications.

astro-ph.CO↗

arXiv2017

Hubble Frontier Fields: systematic errors in strong lensing models of galaxy clusters - Implications for cosmography

Strong gravitational lensing by galaxy clusters is a fundamental tool to study dark matter and constrain the geometry of the Universe. Recently, the Hubble Space Telescope Frontier Fields programme has allowed a significant improvement of mass and magnification measurements but lensing models still have a residual root mean square between 0.2 arcsec and few arcsec- onds, not yet completely understood. Systematic errors have to be better understood and treated in order to use strong lensing clusters as reliable cosmological probes. We have analysed two simulated Hubble-Frontier-Fields-like clusters from the Hubble Frontier Fields Comparison Challenge, Ares and Hera. We use several estimators (relative bias on magnification, den- sity profiles, ellipticity and orientation) to quantify the goodness of our reconstructions by comparing our multiple models, optimized with the parametric software LENSTOOL , with the input models. We have quantified the impact of systematic errors arising, first, from the choice of different density profiles and configurations and, secondly, from the availability of con- straints (spectroscopic or photometric redshifts, redshift ranges of the background sources) in the parametric modelling of strong lensing galaxy clusters and therefore on the retrieval of cosmological parameters. We find that substructures in the outskirts have a significant im- pact on the position of the multiple images, yielding tighter cosmological contours. The need for wide-field imaging around massive clusters is thus reinforced. We show that competitive cosmological constraints can be obtained also with complex multimodal clusters and that photometric redshifts improve the constraints on cosmological parameters when considering a narrow range of (spectroscopic) redshifts for the sources.

astro-ph.CO↗

arXiv2017

A test for skewed distributions of dark matter and a possible detection in galaxy cluster Abell 3827

Simulations of self-interacting dark matter (SIDM) predict that dark matter should lag behind galaxies during a collision. If the interaction is mediated by a high-mass force carrier, the distribution of dark matter can also develop asymmetric dark matter tails. To search for this asymmetry, we compute the gravitational lensing properties of a mass distribution with a free {\em skewness} parameter. We apply this to the dark matter around the four central galaxies in cluster Abell~3827. In the galaxy whose dark matter peak has previously been found to be offset, we tentatively measure a skewness $s=0.23^{+0.05}_{-0.22}$ in the same direction as the peak offset. Our method may be useful in future gravitational lensing analyses of colliding galaxy clusters and merging galaxies.

astro-ph.CO↗

arXiv2017

Mapping substructure in the HST Frontier Fields cluster lenses and in cosmological simulations

We map the lensing-inferred substructure in the first three clusters observed by the Hubble Space Telescope Frontier Fields Initiative (HSTFF): Abell 2744 (z = 0.308), MACSJ0416, (z = 0.396) and MACSJ1149 (z = 0.543). Statistically resolving dark-matter subhaloes down to ~10^{9.5} solar masses, we compare the derived subhalo mass functions (SHMFs) to theoretical predictions from analytical models and with numerical simulations in a Lambda Cold Dark Matter (LCDM) cosmology. Mimicking our observational cluster member selection criteria in the HSTFF, we report excellent agreement in both amplitude and shape of the SHMF over four decades in subhalo mass (10^{9-13} solar masses). Projection effects do not appear to introduce significant errors in the determination of SHMFs from simulations. We do not find evidence for a substructure crisis, analogous to the missing satellite problem in the Local Group, on cluster scales, but rather excellent agreement of the count-matched HSTFF SHMF down to M_{sub halo}/M_{halo} ~ 10^{-5}. However, we do find discrepancies in the radial distribution of sub haloes inferred from HSTFF cluster lenses compared to determinations from simulated clusters. This suggests that although the selected simulated clusters match the HSTFF sample in mass, they do not adequately capture the dynamical properties and complex merging morphologies of these observed cluster lenses. Therefore, HSTFF clusters are likely observed in a transient evolutionary stage that is presently insufficiently sampled in cosmological simulations. The abundance and mass function of dark matter substructure in cluster lenses continues to offer an important test of the LCDM paradigm, and at present we find no tension between model predictions and observations.

astro-ph.GA↗

arXiv2016

The Evolution Of The Faint End Of The UV Luminosity Function During The Peak Epoch Of Star Formation (1<z<3)

[Abridged] We present a robust measurement of the rest-frame UV luminosity function (LF) and its evolution during the peak epoch of cosmic star formation at 1 50% completeness in order to minimize these systematics, we still find that the faint-end slope is steep and getting steeper with redshift, though with slightly shallower (less negative) values ($α=-1.55\pm0.06$, $-1.69\pm0.07$ and $-1.79\pm0.08$ for $z\sim1.3$, 1.9 and 2.6, respectively). Finally, we conclude that the faint star-forming galaxies with UV magnitudes of $-18.5<M_{UV}<-12.5$ covered in this study, produce the majority (55%-60%) of the unobscured UV luminosity density at 1<z<3.

astro-ph.GA↗

arXiv2016

A shock front at the radio relic of Abell 2744

Radio relics are Mpc-scale diffuse radio sources at the peripheries of galaxy clusters which are thought to trace outgoing merger shocks. We present XMM-Newton and Suzaku observations of the galaxy cluster Abell 2744 (z=0.306), which reveal the presence of a shock front 1.5 Mpc East of the cluster core. The surface-brightness jump coincides with the position of a known radio relic. Although the surface-brightness jump indicates a weak shock with a Mach number $\mathcal{M}=1.7_{-0.3}^{+0.5}$, the plasma in the post-shock region has been heated to a very high temperature ($\sim13$ keV) by the passage of the shock wave. The low acceleration efficiency expected from such a weak shock suggests that mildly relativistic electrons have been re-accelerated by the passage of the shock front.

astro-ph.HE↗

arXiv2016

[CII] emission in z ~ 6 strongly lensed, star-forming galaxies

The far-infrared fine-structure line [CII] at 1900.5\,GHz is known to be one of the brightest cooling lines in local galaxies, and therefore it has been suggested to be an efficient tracer for star-formation in very high-redshift galaxies. However, recent results for galaxies at $z>6$ have yielded numerous non-detections in star-forming galaxies, except for quasars and submillimeter galaxies. We report the results of ALMA observations of two lensed, star-forming galaxies at $z = 6.029$ and $z=6.703$. The galaxy A383-5.1 (star formation rate [SFR] of 3.2 M$_\odot$ yr$^{-1}$ and magnification of $μ= 11.4\pm1.9$) shows a line detection with $L_{\rm [CII]} = 8.9\times10^{6}$ L$_\odot$, making it the lowest $L_{\rm [CII]}$ detection at $z>6$. For MS0451-H (SFR = 0.4 M$_\odot$ yr$^{-1}$ and $μ= 100\pm20$) we provide an upper limit of $L_{\rm [CII]} < 3\times10^{5}$ L$_\odot$, which is 1\,dex below the local SFR-$L_{\rm [CII]}$ relations. The results are consistent with predictions for low-metallicity galaxies at $z>6$, however, other effects could also play a role in terms of decreasing $L_{\rm [CII]}$. The detection of A383-5.1 is encouraging and suggests that detections are possible, but much fainter than initially predicted.

astro-ph.GA↗

arXiv2016

Systematic or Signal? How dark matter misalignments can bias strong lensing models of galaxy clusters

We explore how assuming that mass traces light in strong gravitational lensing models can lead to systematic errors in the predicted position of multiple images. Using a model based on the galaxy cluster MACSJ0416 (z = 0.397) from the Hubble Frontier Fields, we split each galactic halo into a baryonic and dark matter component. We then shift the dark matter halo such that it no longer aligns with the baryonic halo and investigate how this affects the resulting position of multiple images. We find for physically motivated misalignments in dark halo position, ellipticity, position angle and density profile, that multiple images can move on average by more than 0.2" with individual images moving greater than 1". We finally estimate the full error induced by assuming that light traces mass and find that this assumption leads to an expected RMS error of 0.5", almost the entire error budget observed in the Frontier Fields. Given the large potential contribution from the assumption that light traces mass to the error budget in mass reconstructions, we predict that it should be possible to make a first significant detection and characterisation of dark halo misalignments in the Hubble Frontier Fields with strong lensing. Finally, we find that it may be possible to detect ~1kpc offsets between dark matter and baryons, the smoking gun for self-interacting dark matter, should the correct alignment of multiple images be observed.

astro-ph.CO↗

arXiv2015

Warm-hot baryons comprise 5-10 per cent of filaments in the cosmic web

Observations of the cosmic microwave background indicate that baryons account for 5% of the Universe's total energy content. In the local Universe, the census of all observed baryons falls short of this estimate by a factor of two. Cosmological simulations indicate that the missing baryons might not have condensed into virialized haloes, but reside throughout the filaments of the cosmic web (where matter density is larger than average) as a low-density plasma at temperatures of $10^5-10^7$ kelvin, known as the warm-hot intergalactic medium. There have been previous claims of the detection of warm baryons along the line of sight to distant blazars and of hot gas between interacting clusters. These observations were, however, unable to trace the large-scale filamentary structure, or to estimate the total amount of warm baryons in a representative volume of the Universe. Here we report X-ray observations of filamentary structures of gas at $10^7$ kelvin associated with the galaxy cluster Abell 2744. Previous observations of this cluster were unable to resolve and remove coincidental X-ray point sources. After subtracting these, we reveal hot gas structures that are coherent over scales of 8 mergaparsecs. The filaments coincide with over-densities of galaxies and dark matter, with 5-10% of their mass in baryonic gas. This gas has been heated up by the cluster's gravitational pull and is now feeding its core. Our findings strengthen evidence for a picture of the Universe in which a large fraction of the missing baryons reside in the filaments of the cosmic web.

astro-ph.CO↗

arXiv2015

Are Ultra-faint Galaxies at z=6-8 Responsible for Cosmic Reionization ? Combined Constraints from the Hubble Frontier Fields Clusters and Parallels

We use deep Hubble Space Telescope imaging of the Frontier Fields to accurately measure the galaxy rest-frame ultraviolet luminosity function (UV LF) in the redshift range $z \sim 6-8$. We combine observations in three lensing clusters A2744, MACS0416, MACS0717 and their associated parallels fields to select high-redshift dropout candidates. We use the latest lensing models to estimate the flux magnification and the effective survey volume in combination with completeness simulations performed in the source plane. We report the detection of 227 galaxy candidates at $z=6-7$ and 25 candidates at $z \sim 8$. While the total survey area is about 4 arcmin$^{2}$ in each parallel field, it drops to about 0.6 to 1 arcmin$^{2}$ in the cluster core fields because of the strong lensing. We compute the UV luminosity function at $z \sim 7$ using the combined galaxy sample and perform Monte Carlo simulations to determine the best fit Schechter parameters. We are able to reliably constrain the LF down to an absolute magnitude of $M_{UV}=-15.25$, which corresponds to 0.005$L^{\star}$. More importantly, we find that the faint-end slope remains steep down to this magnitude limit with $α=-2.04_{-0.17}^{+0.13}$. Our results confirm the most recent results in deep blank fields but extend the LF measurements more than two magnitudes deeper. The UV LF at $z \sim 8$ is not very well constrained below $M_{UV}=-18$ due to the small number statistics and incompleteness uncertainties. To assess the contribution of galaxies to cosmic reionization we derive the UV luminosity density at $z\sim7$ by integrating the UV LF down to an observationally constrained limit of $M_{UV} = -15$. We show that our determination of Log($ρ_{UV}$)=$26.2\pm0.13$ (erg s$^{-1}$ Hz$^{-1}$ Mpc$^{-3}$) can be sufficient to maintain the IGM ionized.

astro-ph.GA↗

arXiv2015

Illuminating a Dark Lens : A Type Ia Supernova Magnified by the Frontier Fields Galaxy Cluster Abell 2744

SN HFF14Tom is a Type Ia Supernova (SN) discovered at z = 1.3457 +- 0.0001 behind the galaxy cluster Abell 2744 (z = 0.308). In a cosmology-independent analysis, we find that HFF14Tom is 0.77 +- 0.15 magnitudes brighter than unlensed Type Ia SNe at similar redshift, implying a lensing magnification of mu_obs = 2.03 +- 0.29. This observed magnification provides a rare opportunity for a direct empirical test of galaxy cluster lens models. Here we test 17 lens models, 13 of which were generated before the SN magnification was known, qualifying as pure "blind tests". The models are collectively fairly accurate: 8 of the models deliver median magnifications that are consistent with the measured mu to within 1-sigma. However, there is a subtle systematic bias: the significant disagreements all involve models overpredicting the magnification. We evaluate possible causes for this mild bias, and find no single physical or methodological explanation to account for it. We do find that model accuracy can be improved to some extent with stringent quality cuts on multiply-imaged systems, such as requiring that a large fraction have spectroscopic redshifts. In addition to testing model accuracies as we have done here, Type Ia SN magnifications could also be used as inputs for future lens models of Abell 2744 and other clusters, providing valuable constraints in regions where traditional strong- and weak-lensing information is unavailable.

astro-ph.CO↗

arXiv2015

Hubble Frontier Fields : A High-Precision Strong-Lensing Mass Model of the Massive Galaxy Cluster Abell 2744 using 180 Multiple Images

We present a high-precision mass model of galaxy cluster Abell 2744, based on a strong-gravitational-lensing analysis of the \emph{Hubble Space Telescope Frontier Fields} (HFF) imaging data, which now include both \emph{Advanced Camera for Surveys} and \emph{Wide-Field Camera 3} observations to the final depth. Taking advantage of the unprecedented depth of the visible and near-infrared data, we identify 34 new multiply imaged galaxies, bringing the total to 61, comprising 181 individual lensed images. In the process, we correct previous erroneous identifications and positions of multiple systems in the northern part of the cluster core. With the \textsc{Lenstool} software and the new sets of multiple images, we model the cluster using two cluster-scale dark matter halos plus galaxy-scale halos for the cluster members. Our best-fit model predicts image positions with an \emph{RMS} error of 0.69$\arcsec$, which constitutes an improvement by almost a factor of two over previous parametric models of this cluster. We measure the total projected mass inside a 200~kpc aperture as ($2.162\pm 0.005$)$\times 10^{14}M_{\odot}$, thus reaching 1\% level precision for the second time, following the recent HFF measurement of MACSJ0416.1-2403. Importantly, the higher quality of the mass model translates into an overall improvement by a factor of 4 of the derived magnification factor. % for the high-redshift lensed background galaxies. Together with our previous HFF gravitational lensing analysis, this work demonstrates that the HFF data enables high-precision mass measurements for massive galaxy clusters and the derivation of robust magnification maps to probe the early Universe.

astro-ph.CO↗

arXiv2015

The behaviour of dark matter associated with 4 bright cluster galaxies in the 10kpc core of Abell 3827

Galaxy cluster Abell 3827 hosts the stellar remnants of four almost equally bright elliptical galaxies within a core of radius 10kpc. Such corrugation of the stellar distribution is very rare, and suggests recent formation by several simultaneous mergers. We map the distribution of associated dark matter, using new Hubble Space Telescope imaging and VLT/MUSE integral field spectroscopy of a gravitationally lensed system threaded through the cluster core. We find that each of the central galaxies retains a dark matter halo, but that (at least) one of these is spatially offset from its stars. The best-constrained offset is 1.62+/-0.48kpc, where the 68% confidence limit includes both statistical error and systematic biases in mass modelling. Such offsets are not seen in field galaxies, but are predicted during the long infall to a cluster, if dark matter self-interactions generate an extra drag force. With such a small physical separation, it is difficult to definitively rule out astrophysical effects operating exclusively in dense cluster core environments - but if interpreted solely as evidence for self-interacting dark matter, this offset implies a cross-section sigma/m=(1.7+/-0.7)x10^{-4}cm^2/g x (t/10^9yrs)^{-2}, where t is the infall duration.

astro-ph.CO↗

arXiv2014

Hubble Frontier Fields: The Geometry and Dynamics of the Massive Galaxy Cluster Merger MACSJ0416.1-2403

We use a joint optical/X-ray analysis to constrain the geometry and history of the ongoing merging event in the massive galaxy cluster MACSJ0416.1-2403 (z=0.397). Our investigation of cluster substructure rests primarily on a combined strong- and weak-lensing mass reconstruction based on the deep, high-resolution images obtained for the Hubble Frontier Fields initiative. To reveal the system's dynamics, we complement this lensing analysis with a study of the intra-cluster gas using shallow Chandra data, and a three-dimensional model of the distribution and motions of cluster galaxies derived from over 100 spectroscopic redshifts. The multi-scale grid model obtained from our combined lensing analysis extends the high-precision strong-lensing mass reconstruction recently performed to cluster-centric distances of almost 1 Mpc. Our analysis detects the two well known mass concentrations in the cluster core. A pronounced offset between collisional and collisionless matter is only observed for the SW cluster component, while excellent alignment is found for the NE cluster. Both the lensing analysis and the distribution of cluster light strongly suggest the presence of a third massive structure, almost 2 arcmin SW of the cluster centre. Since no X-ray emission is detected in this region, we conclude that this structure is non-virialised and speculate that it might be part of a large-scale filament almost aligned with our line of sight. Combining all evidence from the distribution of dark and luminous matter, we propose two alternative scenarios for the trajectories of the components of MACSJ0416.1-2403. Upcoming deep X-ray observations that allow the detection of shock fronts, cold cores, and sloshing gas (all key diagnostics for studies of cluster collisions) will allow us to test, and distinguish between these two scenarios.

astro-ph.CO↗

arXiv2014

New Constraints on the Faint-end of the UV Luminosity Function at z~7-8 using the Gravitational Lensing of the Hubble Frontier Fields Cluster A2744

Exploiting the power of gravitational lensing, the Hubble Frontier Fields (HFF) program aims at observing six massive galaxy clusters to explore the distant Universe far beyond the depth limits of blank field surveys. Using the complete Hubble Space Telescope observations of the first HFF cluster Abell 2744, we report the detection of 50 galaxy candidates at $z \sim 7$ and eight candidates at $z \sim 8$ in a total survey area of 0.96 arcmin$^{2}$ in the source plane. Three of these galaxies are multiply-imaged by the lensing cluster. Using an updated model of the mass distribution in the cluster we were able to calculate the magnification factor and the effective survey volume for each galaxy in order to compute the ultraviolet galaxy luminosity function at both redshifts 7 and 8. Our new measurements extend the $z \sim 7$ UV LF down to an absolute magnitude of $M_{UV} \sim -15.5$. We find a characteristic magnitude of $M^{\star}_{UV}=-20.63^{+0.69}_{-0.56}$ mag and a faint-end slope $α= -1.88^{+0.17}_{-0.20}$ close to previous determinations in blank fields. We show here for the first time that this slope remains steep down to very faint luminosities of 0.01$L^{\star}$. Although prone to large uncertainties, our results at $z \sim 8$ also seem to confirm a steep faint-end slope below 0.1$L^{\star}$. The HFF program is therefore providing an extremely efficient way to study the faintest galaxy populations at $z > 7$ that would otherwise be inaccessible with current instrumentation. The full sample of six galaxy clusters will provide yet better constraints on the build-up of galaxies at early epochs and their contribution to cosmic reionization.

astro-ph.GA↗