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Stefano Ettori

Publications and source records attributed to Stefano Ettori.

At least 91 records · Page 5Linked to original sources

Excess entropy and energy feedback from within cluster cores up to r$_{200}$

We estimate the "non-gravitational" entropy-injection profiles, $ΔK$, and the resultant energy feedback profiles, $ΔE$, of the intracluster medium for 17 clusters using their Planck SZ and ROSAT X-Ray observations, spanning a large radial range from $0.2r_{500}$ up to $r_{200}$. The feedback profiles are estimated by comparing the observed entropy, at fixed gas mass shells, with theoretical entropy profiles predicted from non-radiative hydrodynamic simulations. We include non-thermal pressure and gas clumping in our analysis. The inclusion of non-thermal pressure and clumping results in changing the estimates for $r_{500}$ and $r_{200}$ by 10\%-20\%. When clumpiness is not considered it leads to an under-estimation of $ΔK\approx300$ keV cm$^2$ at $r_{500}$ and $ΔK\approx1100$ keV cm$^2$ at $r_{200}$. On the other hand, neglecting non-thermal pressure results in an over-estimation of $ΔK\approx 100$ keV cm$^2$ at $r_{500}$ and under-estimation of $ΔK\approx450$ keV cm$^2$ at $r_{200}$. For the estimated feedback energy, we find that ignoring clumping leads to an under-estimation of energy per particle $ΔE\approx1$ keV at $r_{500}$ and $ΔE\approx1.5$ keV at $r_{200}$. Similarly, neglect of the non-thermal pressure results in an over-estimation of $ΔE\approx0.5$ keV at $r_{500}$ and under-estimation of $ΔE\approx0.25$ keV at $r_{200}$. We find entropy floor of $ΔK\approx300$ keV cm$^2$ is ruled out at $\approx3σ$ throughout the entire radial range and $ΔE\approx1$ keV at more than 3$σ$ beyond $r_{500}$, strongly constraining ICM pre-heating scenarios. We also demonstrate robustness of results w.r.t sample selection, X-Ray analysis procedures, entropy modeling etc.

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CoMaLit-V. Mass forecasting with proxies. Method and application to weak lensing calibrated samples

Mass measurements of astronomical objects are most wanted but still elusive. We need them to trace the formation and evolution of cosmic structure but we can get direct measurements only for a minority. This lack can be circumvented with a proxy and a scaling relation. The twofold goal of estimating the unbiased relation and finding the right proxy value to plug in can be hampered by systematics, selection effects, Eddington/Malmquist biases and time evolution. We present a Bayesian hierarchical method which deals with these issues. Masses to be predicted are treated as missing data in the regression and are estimated together with the scaling parameters. The calibration subsample with measured masses does not need to be representative of the full sample as far as it follows the same scaling relation. We apply the method to forecast weak lensing calibrated masses of the Planck, redMaPPer and MCXC clusters. Planck masses are biased low with respect to weak lensing calibrated masses, with a bias more pronounced for high redshift clusters. MCXC masses are under-estimated by ~20 per cent, which may be ascribed to hydrostatic bias. Packages and catalogs are made available with the paper.

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CLUMP-3D. Three dimensional lensing and multi-probe analysis of MACS J1206.2-0847, a remarkably regular cluster

Multi-wavelength techniques can probe the distribution and the physical properties of baryons and dark matter in galaxy clusters from the inner regions out to the peripheries. We present a full three-dimensional analysis combining strong and weak lensing, X-ray surface brightness and temperature, and the Sunyaev-Zel'dovich effect. The method is applied to MACS J1206.2-0847, a remarkably regular, face-on, massive, M_{200}=(1.1+-0.2)*10^{15}M_Sun/h, cluster at z=0.44. The measured concentration, c_{200}=6.3+-1.2, and the triaxial shape are common to halos formed in a LCDM scenario. The gas has settled in and follows the shape of the gravitational potential, which is evidence of pressure equilibrium via the shape theorem. There is no evidence for significant non-thermal pressure and the equilibrium is hydrostatic.

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Little evidence for entropy and energy excess beyond $r_{500}$ - An end to ICM preheating?

Non-gravitational feedback affects the nature of the intra-cluster medium (ICM). X-ray cooling of the ICM and in situ energy feedback from AGN's and SNe as well as {\it preheating} of the gas at epochs preceding the formation of clusters are proposed mechanisms for such feedback. While cooling and AGN feedbacks are dominant in cluster cores, the signatures of a preheated ICM are expected to be present even at large radii. To estimate the degree of preheating, with minimum confusion from AGN feedback/cooling, we study the excess entropy and non-gravitational energy profiles upto $r_{200}$ for a sample of 17 galaxy clusters using joint data sets of {\it Planck} SZ pressure and {\it ROSAT/PSPC} gas density profiles. The canonical value of preheating entropy floor of $\gtrsim 300$ keV cm$^2$, needed in order to match cluster scalings, is ruled out at $\approx 3σ$. We also show that the feedback energy of 1 keV/particle is ruled out at 5.2$σ$ beyond $r_{500}$. Our analysis takes both non-thermal pressure and clumping into account which can be important in outer regions. Our results based on the direct probe of the ICM in the outermost regions do not support any significant preheating.

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The relation between mass and concentration in X-ray galaxy clusters at high redshift

Galaxy clusters are the most recent, gravitationally-bound products of the hierarchical mass accretion over cosmological scales. How the mass is concentrated is predicted to correlate with the total mass in the cluster's halo, with systems at higher mass being less concentrated at given redshift and for any given mass, systems with lower concentration are found at higher redshifts. Through a spatial and spectral X-ray analysis, we reconstruct the total mass profile of 47 galaxy clusters observed with Chandra in the redshift range $0.4 0.4$, and is well suited to provide the first constraint on the concentration--mass relation at $z>0.7$ from X-ray analysis. Under the assumptions that the distribution of the X-ray emitting gas is spherically symmetric and in hydrostatic equilibrium, we combine the deprojected gas density and spectral temperature profiles through the hydrostatic equilibrium equation to recover the parameters that describe a NFW total mass distribution. The comparison with results from weak lensing analysis reveals a very good agreement both for masses and concentrations. Uncertainties are however too large to make any robust conclusion on the hydrostatic bias of these systems. The relation is well described by the form $c \propto M^B (1+z)^C$, with $B=-0.50 \pm 0.20$, $C=0.12 \pm 0.61$ (at 68.3\% confidence), it is slightly steeper than the one predicted by numerical simulations ($B\sim-0.1$) and does not show any evident redshift evolution. We obtain the first constraints on the properties of the concentration--mass relation at $z > 0.7$ from X-ray data, showing a reasonable good agreement with recent numerical predictions.

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The Morphologies and Alignments of Gas, Mass, and the Central Galaxies of CLASH Clusters of Galaxies

Morphology is often used to infer the state of relaxation of galaxy clusters. The regularity, symmetry, and degree to which a cluster is centrally concentrated inform quantitative measures of cluster morphology. The Cluster Lensing and Supernova survey with Hubble Space Telescope (CLASH) used weak and strong lensing to measure the distribution of matter within a sample of 25 clusters, 20 of which were deemed to be relaxed based on their X-ray morphology and alignment of the X-ray emission with the BCG. Towards a quantitative characterization of this important sample of clusters, we present uniformly estimated X-ray morphological statistics for all 25 CLASH clusters. We compare X-ray morphologies of CLASH clusters with those identically measured for a large sample of simulated clusters from the MUSIC-2 simulations, selected by mass. We confirm a threshold in X-ray surface brightness concentration of C>0.4 for cool-core clusters, where C is the ratio of X-ray emission inside 100 kpc/h70 compared to inside 500 kpc/h70. We report and compare morphologies of these clusters inferred from Sunyaev-Zeldovich Effect (SZE) maps of the hot gas and in from projected mass maps based on strong and weak lensing. We find a strong agreement in alignments of the orientation of major axes for the lensing, X-ray, and SZE maps of nearly all of the CLASH clusters at radii of 500 kpc (approximately 0.5R500 for these clusters). We also find a striking alignment of clusters shapes at the 500 kpc scale, as measured with X-ray, SZE, and lensing, with that of the near-infrared stellar light at 10 kpc scales for the 20 "relaxed" clusters. This strong alignment indicates a powerful coupling between the cluster- and galaxy-scale galaxy formation processes.

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The XXL Survey IV. Mass-temperature relation of the bright cluster sample

The XXL survey is the largest survey carried out by XMM-Newton. Covering an area of 50deg$^2$, the survey contains $\sim450$ galaxy clusters out to a redshift $\sim$2 and to an X-ray flux limit of $\sim5\times10^{-15}erg\,s^{-1}cm^{-2}$. This paper is part of the first release of XXL results focussed on the bright cluster sample. We investigate the scaling relation between weak-lensing mass and X-ray temperature for the brightest clusters in XXL. The scaling relation is used to estimate the mass of all 100 clusters in XXL-100-GC. Based on a subsample of 38 objects that lie within the intersection of the northern XXL field and the publicly available CFHTLenS catalog, we derive the $M_{WL}$ of each system with careful considerations of the systematics. The clusters lie at $0.1<z<0.6$ and span a range of $ T\simeq1-5keV$. We combine our sample with 58 clusters from the literature, increasing the range out to 10keV. To date, this is the largest sample of clusters with $M_{WL}$ measurements that has been used to study the mass-temperature relation. The fit ($M\propto T^b$) to the XXL clusters returns a slope $b=1.78^{+0.37}_{-0.32}$ and intrinsic scatter $σ_{\ln M|T}\simeq0.53$; the scatter is dominated by disturbed clusters. The fit to the combined sample of 96 clusters is in tension with self-similarity, $b=1.67\pm0.12$ and $σ_{\ln M|T}\simeq0.41$. Overall our results demonstrate the feasibility of ground-based weak-lensing scaling relation studies down to cool systems of $\sim1keV$ temperature and highlight that the current data and samples are a limit to our statistical precision. As such we are unable to determine whether the validity of hydrostatic equilibrium is a function of halo mass. An enlarged sample of cool systems, deeper weak-lensing data, and robust modelling of the selection function will help to explore these issues further.

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The X-ray/SZ view of the virial region. I. Thermodynamic properties

We measure the thermodynamic properties of cluster outer regions to provide constraints on the processes that rule the formation of large scale structures. We derived the thermodynamic properties of the intracluster gas (temperature, entropy) by combining the SZ thermal pressure from Planck and the X-ray gas density from ROSAT. This method allowed us to reconstruct for the first time temperature and entropy profiles out to the virial radius and beyond in a large sample of objects. At variance with several recent Suzaku studies, we find that the entropy rises steadily with radius, albeit at at a somewhat lower rate than predicted by self-similar expectations. We note significant differences between relaxed, cool-core systems and unrelaxed clusters in the outer regions. Relaxed systems appear to follow the self-similar expectations more closely than perturbed objects. Our results indicate that the well-known entropy excess observed in cluster cores extends well beyond the central regions. When correcting for the gas depletion, the observed entropy profiles agree with the prediction from gravitational collapse only, especially for cool-core clusters.

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The X-ray/SZ view of the virial region. II. Gas mass fraction

Several recent studies used the hot gas fraction of galaxy clusters as a standard ruler to constrain dark energy, which provides competitive results compared to other techniques. This method, however, relies on the assumption that the baryon fraction in clusters agrees with the cosmic value Omega_b/Omega_m, and does not differ from one system to another. We test this hypothesis by measuring the gas mass fraction over the entire cluster volume in a sample of local clusters. Combining the SZ thermal pressure from Planck and the X-ray gas density from ROSAT, we measured for the first time the average gas fraction (fgas) out to the virial radius and beyond in a large sample of clusters. We also obtained azimuthally-averaged measurements of the gas fraction for 18 individual systems, which we used to compute the scatter of fgas around the mean value at different radii and its dependence on the cluster's temperature. The gas mass fraction increases with radius and reaches the cosmic baryon fraction close to R200. At R200, we measure fgas,200=0.176+/-0.009. We find significant differences between the baryon fraction of relaxed, cool-core (CC) systems and unrelaxed, non-cool core (NCC) clusters in the outer regions. In average, the gas fraction in NCC clusters slightly exceeds the cosmic baryon fraction, while in CC systems the gas fraction converges to the expected value when accounting for the stellar content, without any evidence for variations from one system to another. We find that fgas estimates in NCC systems slightly disagree with the cosmic value approaching R200. This result could be explained either by a violation of the assumption of hydrostatic equilibrium or by an inhomogeneous distribution of the gas mass. Conversely, cool-core clusters are found to provide reliable constraints on fgas at overdensities >200, which makes them suitable for cosmological studies.

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Three-dimensional Multi-probe Analysis of the Galaxy Cluster A1689

We perform a 3D multi-probe analysis of the rich galaxy cluster A1689 by combining improved weak-lensing data from new BVRi'z' Subaru/Suprime-Cam observations with strong-lensing, X-ray, and Sunyaev-Zel'dovich effect (SZE) data sets. We reconstruct the projected matter distribution from a joint weak-lensing analysis of 2D shear and azimuthally integrated magnification constraints, the combination of which allows us to break the mass-sheet degeneracy. The resulting mass distribution reveals elongation with axis ratio ~0.7 in projection. When assuming a spherical halo, our full weak-lensing analysis yields a projected concentration of $c_{200c}^{2D}=8.9\pm 1.1$ ($c_{vir}^{2D}\sim 11$), consistent with and improved from earlier weak-lensing work. We find excellent consistency between weak and strong lensing in the region of overlap. In a parametric triaxial framework, we constrain the intrinsic structure and geometry of the matter and gas distributions, by combining weak/strong lensing and X-ray/SZE data with minimal geometric assumptions. We show that the data favor a triaxial geometry with minor-major axis ratio 0.39+/-0.15 and major axis closely aligned with the line of sight (22+/-10 deg). We obtain $M_{200c}=(1.2\pm 0.2)\times 10^{15} M_{\odot}/h$ and $c_{200c}=8.4\pm 1.3$, which overlaps with the $>1σ$ tail of the predicted distribution. The shape of the gas is rounder than the underlying matter but quite elongated with minor-major axis ratio 0.60+/-0.14. The gas mass fraction within 0.9Mpc is 10^{+3}_{-2}%. The thermal gas pressure contributes to ~60% of the equilibrium pressure, indicating a significant level of non-thermal pressure support. When compared to Planck's hydrostatic mass estimate, our lensing measurements yield a spherical mass ratio of $M_{Planck}/M_{GL}=0.70\pm 0.15$ and $0.58\pm 0.10$ with and without corrections for lensing projection effects, respectively.

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CoMaLit-IV. Evolution and self-similarity of scaling relations with the galaxy cluster mass

The scaling of observable properties of galaxy clusters with mass evolves with time. Assessing the role of the evolution is crucial to study the formation and evolution of massive halos and to avoid biases in the calibration. We present a general method to infer the mass and the redshift dependence, and the time-evolving intrinsic scatter of the mass-observable relations. The procedure self-calibrates the redshift dependent completeness function of the sample. The intrinsic scatter in the mass estimates used to calibrate the relation is considered too. We apply the method to the scaling of mass M_Delta versus line of sight galaxy velocity dispersion sigma_v, optical richness, X-ray luminosity, L_X, and Sunyaev-Zel'dovich signal. Masses were calibrated with weak lensing measurements. The measured relations are in good agreement with time and mass dependencies predicted in the self-similar scenario of structure formation. The lone exception is the L_X-M_Delta relation whose time evolution is negative in agreement with formation scenarios with additional radiative cooling and uniform preheating at high redshift. The intrinsic scatter in the sigma_v-M_Delta relation is notably small, of order of 14 per cent. Robust predictions on the observed properties of the galaxy clusters in the CLASH sample are provided as cases of study. Catalogs and scripts are publicly available at http://pico.bo.astro.it/~sereno/CoMaLit/.

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CoMaLit - II. The scaling relation between mass and Sunyaev-Zel'dovich signal for Planck selected galaxy clusters

We discuss the scaling relation between mass and integrated Compton parameter of a sample of galaxy clusters from the all-sky {\it Planck} Sunyaev-Zel'dovich catalogue. Masses were measured with either weak lensing, caustics techniques, or assuming hydrostatic equilibrium. The retrieved $Y_{500}$-$M_{500}$ relation does not strongly depend on the calibration sample. We found a slope of 1.4-1.9, in agreement with self-similar predictions, with an intrinsic scatter of $20\pm10$ per cent. The absolute calibration of the relation can not be ascertained due to systematic differences of $\sim$20-40 per cent in mass estimates reported by distinct groups. Due to the scatter, the slope of the conditional scaling relation, to be used in cosmological studies of number counts, is shallower, $\sim$1.1-1.6. The regression methods employed account for intrinsic scatter in the mass measurements too. We found that Planck mass estimates suffer from a mass dependent bias.

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Comparing Masses in Literature (CoMaLit)-I. Bias and scatter in weak lensing and X-ray mass estimates of clusters

The first building block to use galaxy clusters in astrophysics and cosmology is the accurate determination of their mass. Two of the most well regarded direct mass estimators are based on weak lensing (WL) determinations or X-ray analyses assuming hydrostatic equilibrium (HE). By comparing these two mass measurements in samples of rich clusters, we determined the intrinsic scatters, $σ_\mathrm{WL}\sim$15 per cent for WL masses and $σ_\mathrm{HE}\sim$25 per cent for HE masses. The certain assessment of the bias is hampered by differences as large as $\sim$40 per cent in either WL or HE mass estimates reported by different groups. If the intrinsic scatter in the mass estimate is not considered, the slope of any scaling relation `observable--mass' is biased towards shallower values, whereas the intrinsic scatter of the scaling is over-estimated.

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CLASH-X: A Comparison of Lensing and X-ray Techniques for Measuring the Mass Profiles of Galaxy Clusters

We present profiles of temperature (Tx), gas mass, and hydrostatic mass estimated from new and archival X-ray observations of CLASH clusters. We compare measurements derived from XMM and Chandra observations with one another and compare both to gravitational lensing mass profiles derived with CLASH HST and ground-based lensing data. Radial profiles of Chandra and XMM electron density and enclosed gas mass are nearly identical, indicating that differences in hydrostatic masses inferred from X-ray observations arise from differences in Tx measurements. Encouragingly, cluster Txs are consistent with one another at ~100-200 kpc radii but XMM Tx systematically decline relative to Chandra Tx at larger radii. The angular dependence of the discrepancy suggests additional investigation on systematics such as the XMM point spread function correction, vignetting and off-axis responses. We present the CLASH-X mass-profile comparisons in the form of cosmology-independent and redshift-independent circular-velocity profiles. Ratios of Chandra HSE mass profiles to CLASH lensing profiles show no obvious radial dependence in the 0.3-0.8 Mpc range. However, the mean mass biases inferred from the WL and SaWLens data are different. e.g., the weighted-mean value at 0.5 Mpc is = 0.12 for the WL comparison and = -0.11 for the SaWLens comparison. The ratios of XMM HSE mass profiles to CLASH lensing profiles show a pronounced radial dependence in the 0.3-1.0 Mpc range, with a weighted mean mass bias of value rising to ~0.3 at ~1 Mpc for the WL comparison and of 0.25 for SaWLens comparison. The enclosed gas mass profiles from both Chandra and XMM rise to a value 1/8 times the total-mass profiles inferred from lensing at 0.5 Mpc and remain constant outside of that radius, suggesting that [8xMgas] profiles may be an excellent proxy for total-mass profiles at >0.5 Mpc in massive galaxy clusters.

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The mass-concentration relation in lensing clusters: the role of statistical biases and selection effects

The relation between mass and concentration of galaxy clusters traces their formation and evolution. Massive lensing clusters were observed to be over-concentrated and following a steep scaling in tension with predictions from the concordance $Λ$CDM paradigm. We critically revise the relation in the CLASH, the SGAS, the LOCUSS, and the high-redshift samples of weak lensing clusters. Measurements of mass and concentration are anti-correlated, which can bias the observed relation towards steeper values. We corrected for this bias and compared the measured relation to theoretical predictions accounting for halo triaxiality, adiabatic contraction of the halo, presence of a dominant BCG and, mostly, selection effects in the observed sample. The normalisation, the slope and the scatter of the expected relation are strongly sample-dependent. For the considered samples, the predicted slope is much steeper than that of the underlying relation characterising dark-matter only clusters. We found that the correction for statistical and selection biases in observed relations mostly solve the tension with the $Λ$CDM model.

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The SKA view of cool-core clusters: evolution of radio mini-halos and AGN feedback

In about 70% of the population of relaxed, cool-core galaxy clusters, the brightest cluster galaxy (BCG) is radio loud, showing non-thermal radio jets and lobes ejected by the central active galactic nucleus (AGN). In recent years such relativistic plasma has been unambiguously shown to interact with the surrounding thermal intra-cluster medium (ICM) thanks to spectacular images where the lobe radio emission is observed to fill the cavities in the X-ray-emitting gas. This `radio feedback' phenomenon is widespread and is critical to understand the physics of the inner regions of galaxy clusters and the properties of the central BCG. At the same time, mechanically-powerful AGN are likely to drive turbulence in the central ICM which may also play a role for the origin of non-thermal emission on cluster-scales. Diffuse non-thermal emission has been observed in a number of cool-core clusters in the form of a radio mini-halo surrounding the radio-loud BCG on scales comparable to that of the cooling region. Large mini-halo samples are necessary to establish their origin and connection with the cluster thermal properties and dynamics, especially in light of future X-ray characterization of the cluster cores as it is expected by Athena-XIFU. We show that All-Sky reference survey at Band 2 with SKA1 at confusion limit (rms ~2 μJy per beam) has the potential to detect up to ~620 mini-halos at redshift z<0.6, whereas Deep Tier reference surveys at Band 1/2 with SKA1 at sub-arcsec resolution (rms ~0.2 μJy per beam) will allow a complete census of the radio-loud BCGs at any redshift down to a 1.4 GHz power of 10^{22} W/Hz. We further anticipate that SKA2 might detect up to ~1900 new mini-halos at redshift z<0.6 and characterize the radio-mode AGN feedback in every cluster and group up to redshift z ~1.7 (the highest-z where virialized clusters are currently detected).

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Mass and Concentration estimates from Weak and Strong Gravitational Lensing: a Systematic Study

We study how well halo properties of galaxy clusters, like mass and concentration, are recovered using lensing data. In order to generate a large sample of systems at different redshifts we use the code MOKA. We measure halo mass and concentration using weak lensing data alone (WL), fitting to an NFW profile the reduced tangential shear profile, or by combining weak and strong lensing data, by adding information about the size of the Einstein radius (WL+SL). For different redshifts, we measure the mass and the concentration biases and find that these are mainly caused by the random orientation of the halo ellipsoid with respect to the line-of-sight. Since our simulations account for the presence of a bright central galaxy, we perform mass and concentration measurements using a generalized NFW profile which allows for a free inner slope. This reduces both the mass and the concentration biases. We discuss how the mass function and the concentration mass relation change when using WL and WL+SL estimates. We investigate how selection effects impact the measured concentration-mass relation showing that strong lens clusters may have a concentration 20-30% higher than the average, at fixed mass, considering also the particular case of strong lensing selected samples of relaxed clusters. Finally, we notice that selecting a sample of relaxed galaxy clusters, as is done in some cluster surveys, explain the concentration-mass relation biases.

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CLASH-VLT: Constraints on the Dark Matter Equation of State from Accurate Measurements of Galaxy Cluster Mass Profiles

A pressureless scenario for the Dark Matter (DM) fluid is a widely adopted hypothesis, despite the absence of a direct observational evidence. According to general relativity, the total mass-energy content of a system shapes the gravitational potential well, but different test particles perceive this potential in different ways depending on their properties. Cluster galaxy velocities, being $\ll$c, depend solely on the gravitational potential, whereas photon trajectories reflect the contributions from the gravitational potential plus a relativistic-pressure term that depends on the cluster mass. We exploit this phenomenon to constrain the Equation of State (EoS) parameter of the fluid, primarily DM, contained in galaxy clusters. We use the complementary information provided by the kinematic and lensing mass profiles of the galaxy cluster MACS 1206.2-0847 at $z=0.44$, as obtained in an extensive imaging and spectroscopic campaign within the CLASH survey. The unprecedented high quality of our data-set and the properties of this cluster are well suited to determine the EoS parameter of the cluster fluid. Since baryons contribute at most $15\%$ to the total mass in clusters and their pressure is negligible, the EoS parameter we derive describes the behavior of the DM fluid. We obtain the most stringent constraint on the DM EoS parameter to date, $w=(p_r+2\,p_t)/(3\,c^2ρ)=0.00\pm0.15\mathrm{(stat)}\pm0.08\mathrm{(syst)}$, averaged over the radial range $0.5\,\mathrm{Mpc}\leq$$r$$\leq$$r_{200}$, where $p_r$ and $p_t$ are the radial and tangential pressure, and $ρ$ is the density. We plan to further improve our constraint by applying the same procedure to all clusters from the ongoing CLASH-VLT program.

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