Marc Postman - Profile on Academia.edu (original) (raw)
Papers by Marc Postman
Requirements for TA-DA, a general Tool for Astrophysical Data Analysis
We report on the development of TA-DA, a general Tool for Astrophysical Data Analysis. TA-DA is i... more We report on the development of TA-DA, a general Tool for Astrophysical Data Analysis. TA-DA is intended as a powerful, integrated web service to significantly simplify the process of comparing calibrated astrophyiscal data with theoretical stellar evolutionary models. It is built upon the Synphot (for synthetic photometry) and Chorizos (a Bayesian multi-parametric chi-squared fitting algorithm) packages. TA-DA will allow to
Requirements for TA-DA, a general Tool for Astrophysical Data Analysis
We report on the development of TA-DA, a general Tool for Astrophysical Data Analysis. TA-DA is i... more We report on the development of TA-DA, a general Tool for Astrophysical Data Analysis. TA-DA is intended as a powerful, integrated web service to significantly simplify the process of comparing calibrated astrophyiscal data with theoretical stellar evolutionary models. It is built upon the Synphot (for synthetic photometry) and Chorizos (a Bayesian multi-parametric chi-squared fitting algorithm) packages. TA-DA will allow to easily and reliably compute a variety of fundamental observables including synthetic photometry from theoretical spectral energy distributions, color corrections, and bandpass transformations. It will also support the cross-calibration of photometry from different archives, analysis of individual SEDs, statistical analysis of HR diagrams and self-consistent prediction of astronomical performance.
Observatory Operations to Optimize Scientific Return, 1998
ABSTRACT The Hubble Data Archive at the Space Telescope Science Institute contains over 4.3 TB of... more ABSTRACT The Hubble Data Archive at the Space Telescope Science Institute contains over 4.3 TB of data, primarily for the Hubble Space Telescope, but also from complementary space- based and ground-based facilities. We are in the process of upgrading and generalizing many of the HDA's component system, developing tools to provide more integrated access to the HDA holdings, and working with other major data providing organizations to implement global data location services for astronomy and other space science disciplines. This paper describes the key elements of our archiving and data distribution systems, including a planned transition to DVD media, data compression, data segregation, on-the-fly calibration, an engineering data warehouse, and distributed search and retrieval facilities.
Astrophysics. Multiple images of a highly magnified supernova formed by an early-type cluster galaxy lens
Science (New York, N.Y.), Jan 6, 2015
In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a stro... more In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a strong gravitational lens could be used to measure the rate of cosmic expansion. We report the discovery of such a system. In Hubble Space Telescope imaging, we have found four images of a single supernova forming an Einstein cross configuration around a redshift z = 0.54 elliptical galaxy in the MACS J1149.6+2223 cluster. The cluster's gravitational potential also creates multiple images of the z = 1.49 spiral supernova host galaxy, and a future appearance of the supernova elsewhere in the cluster field is expected. The magnifications and staggered arrivals of the supernova images probe the cosmic expansion rate, as well as the distribution of matter in the galaxy and cluster lenses.
The Concentration-Mass Relation from CLASH clusters using galaxy dynamics
ABSTRACT Galaxy clusters play a key role in testing cosmological models and in constraining the p... more ABSTRACT Galaxy clusters play a key role in testing cosmological models and in constraining the properties of dark matter. One of these key tests is the mass density profile of clusters - the concentration-mass relation. There is a reported tension between the observed concentration-mass relation and the one theoretically expected using simulated galaxy clusters, where the observed clusters appear to have higher concentration than simulated clusters of similar total mass. In The Cluster Lensing And Supernova survey with Hubble (CLASH), we use different and independent techniques to estimate the mass distribution in clusters. The comparison between different techniques offers an observational test of the techniques and understanding of the systematics. In this work, we estimate the concentration-mass relation for about 8 (at the 0.2< z &;lt; 0.6 redshift range) of the 20 X-ray selected CLASH clusters using galaxy dynamics. We use a unique spectroscopic data set with more than about 300 cluster members per cluster. Finally, we compare our results to the theoretical expected ones and to the estimations derived using the lensing technique.
The Astrophysical Journal, 2015
We utilize the CLASH (Cluster Lensing And Supernova survey with Hubble) observations of 25 cluste... more We utilize the CLASH (Cluster Lensing And Supernova survey with Hubble) observations of 25 clusters to search for extreme emission-line galaxies (EELGs). The selections are carried out in two central bands: F105W (Y 105 ) and F125W (J 125 ), as the flux of the central bands could be enhanced by the presence of [O III] λλ4959, 5007 at redshift of ∼ 0.93 − 1.14 and 1.57 − 1.79, respectively. The multi-band observations help to constrain the equivalent widths of emission lines. Thanks to cluster lensing, we are able to identify 52 candidates down to an intrinsic limiting magnitude of 28.5 and to a rest-frame [O III] λλ4959, 5007 equivalent width of 3737Å. Our samples include a number of EELGs at lower luminosities that are missed in other surveys, and the extremely high equivalent width can be only found in such faint galaxies. These EELGs can mimic the dropout feature similar to that of high redshift galaxies and contaminate the color-color selection of high redshift galaxies when the S/N ratio is limited or the band coverage is incomplete. We predict that the fraction of EELGs in the future high redshift galaxy selections cannot be neglected.
A new paradigm for space astrophysics mission design
Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave, 2014
Astronomy & Astrophysics, 2014
Context. The study of the galaxy stellar mass function (SMF) in relation to the galaxy environmen... more Context. The study of the galaxy stellar mass function (SMF) in relation to the galaxy environment and the stellar mass density profile, ρ ⋆ (r),is a powerful tool to constrain models of galaxy evolution. Aims. We determine the SMF of the z=0.44 cluster of galaxies MACS J1206.2-0847 separately for passive and star-forming (SF) galaxies, in different regions of the cluster, from the center out to approximately 2 virial radii. We also determine ρ ⋆ (r) to compare it to the number density and total mass density profiles. Methods. We use the dataset from the CLASH-VLT survey. Stellar masses are obtained by spectral energy distribution fitting with the MAGPHYS technique on 5-band photometric data obtained at the Subaru telescope. We identify 1363 cluster members down to a stellar mass of 10 9.5 M ⊙ , selected on the basis of their spectroscopic (∼ 1/3 of the total) and photometric redshifts. We correct our sample for incompleteness and contamination by non members. Cluster member environments are defined using either the clustercentric radius or the local galaxy number density. Results. The whole cluster SMF is well fitted by a double Schechter function, which is the sum of the two Schechter functions that provide good fits to the SMFs of, separately, the passive and SF cluster populations. The SMF of SF galaxies is significantly steeper than the SMF of passive galaxies at the faint end. The SMF of the SF cluster galaxies does not depend on the environment. The SMF of the passive cluster galaxies has a significantly smaller slope (in absolute value) in the innermost (≤ 0.50 Mpc, i.e., ∼ 0.25 virial radii), and in the highest density cluster region than in more external, lower density regions. The number ratio of giant/subgiant galaxies is maximum in this innermost region and minimum in the adjacent region, but then gently increases again toward the cluster outskirts. This is also reflected in a decreasing radial trend of the average stellar mass per cluster galaxy. On the other hand, the stellar mass fraction, i.e., the ratio of stellar to total cluster mass, does not show any significant radial trend. Conclusions. Our results appear consistent with a scenario in which SF galaxies evolve into passive galaxies due to density-dependent environmental processes, and eventually get destroyed very near the cluster center to become part of a diffuse intracluster medium. Dynamical friction, on the other hand, does not seem to play an important role. Future investigations of other clusters of the CLASH-VLT sample will allow us to confirm our interpretation.
Direct imaging and spectroscopy of habitable planets using JWST and a starshade
Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave, 2010
The Astrophysical Journal, 2014
We present the supernova (SN) sample and Type-Ia SN (SN Ia) rates from the Cluster Lensing And Su... more We present the supernova (SN) sample and Type-Ia SN (SN Ia) rates from the Cluster Lensing And Supernova survey with Hubble (CLASH). Using the Advanced Camera for Surveys and the Wide Field Camera 3 on the Hubble Space Telescope (HST), we have imaged 25 galaxy-cluster fields and parallel fields of non-cluster galaxies. We report a sample of 27 SNe discovered in the parallel fields. Of these SNe, ∼ 13 are classified as SN Ia candidates, including four SN Ia candidates at redshifts z > 1.2. We measure volumetric SN Ia rates to redshift 1.8 and add the first upper limit on the SN Ia rate in the range 1.8 < z < 2.4. The results are consistent with the rates measured by the HST/GOODS and Subaru Deep Field SN surveys. We model these results together with previous measurements at z < 1 from the literature. The best-fitting SN Ia delay-time distribution (DTD; the distribution of times that elapse between a short burst of star formation and subsequent SN Ia explosions) is a power law with an index of −1.00 +0.06(0.09) −0.06(0.10) (statistical) +0.12 −0.08 (systematic), where the statistical uncertainty is a result of the 68% and 95% (in parentheses) statistical uncertainties reported for the various SN Ia rates (from this work and from the literature), and the systematic uncertainty reflects the range of possible cosmic star-formation histories. We also test DTD models produced by an assortment of published binary population synthesis (BPS) simulations. The shapes of all BPS double-degenerate DTDs are consistent with the volumetric SN Ia measurements, when the DTD models are scaled up by factors of 3-9. In contrast, all BPS single-degenerate DTDs are ruled out by the measurements at > 99% significance level.
The Astrophysical Journal, 2012
We present a strong-lensing analysis of the galaxy cluster MACS J1206.2-0847 (z=0.44) using UV, O... more We present a strong-lensing analysis of the galaxy cluster MACS J1206.2-0847 (z=0.44) using UV, Optical, and IR, HST/ACS/WFC3 data taken as part of the CLASH multi-cycle treasury program, with VLT/VIMOS spectroscopy for some of the multiply-lensed arcs. The CLASH observations, combined with our mass-model, allow us to identify 47 new multiply-lensed images of 12 distant sources. These images, along with the previously known arc, span the redshift range 1 z 5.5, and thus enable us to derive a detailed mass distribution and to accurately constrain, for the first time, the inner mass-profile of this cluster. We find an inner profile slope of d log Σ/d log θ −0.55 ± 0.1 (in the range [1 ,53 ], or 5 r 300 kpc), as commonly found for relaxed and well-concentrated clusters. Using the many systems uncovered here we derive credible critical curves and Einstein radii for different source redshifts. For a source at z s 2.5, the critical curve encloses a large area with an effective Einstein radius of θ E = 28 ± 3 , and a projected mass of 1.34 ± 0.15 × 10 14 M . From the current understanding of structure formation in concordance cosmology, these values are relatively high for clusters at z ∼ 0.5, so that detailed studies of the inner mass distribution of clusters such as MACS J1206.2-0847 can provide stringent tests of the ΛCDM paradigm.
The Hubble Deep Field South: Formulation of the Observing Campaign
The Astronomical Journal, 2000
The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for an 8-meter to 16... more The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for an 8-meter to 16-meter UVOIR space observatory for launch in the 2025-2030 era. ATLAST will allow astronomers to answer fundamental questions at the forefront of modern astronphysics, including "Is there life elsewhere in the Galaxy?" We present a range of science drivers that define the main performance requirements for
SDSS Image Processing II: The Photo Pipelines
astro.princeton.edu
2Department of Astronomy, University of Washington, Seattle, WA 98195; ivezic@astro.washington.ed... more 2Department of Astronomy, University of Washington, Seattle, WA 98195; ivezic@astro.washington.edu ... 3University League Nursery School, Princeton, NJ 08544, USA ... 42555 NE 85th Street, Seattle, WA 98115, USA ... A description of the SDSS image ...
Virtual Observatories (Proceedings Volume)
The Cluster Lensing And Supernova survey with Hubble (CLASH) is a 524-orbit multi-cycle treasury ... more The Cluster Lensing And Supernova survey with Hubble (CLASH) is a 524-orbit multi-cycle treasury program to use the gravitational lensing properties of 25 galaxy clusters to accurately constrain their mass distributions. The survey, described in detail in this paper, will definitively establish the degree of concentration of dark matter in the cluster cores, a key prediction of CDM. The CLASH
Requirements for TA-DA, a general Tool for Astrophysical Data Analysis
We report on the development of TA-DA, a general Tool for Astrophysical Data Analysis. TA-DA is i... more We report on the development of TA-DA, a general Tool for Astrophysical Data Analysis. TA-DA is intended as a powerful, integrated web service to significantly simplify the process of comparing calibrated astrophyiscal data with theoretical stellar evolutionary models. It is built upon the Synphot (for synthetic photometry) and Chorizos (a Bayesian multi-parametric chi-squared fitting algorithm) packages. TA-DA will allow to
Requirements for TA-DA, a general Tool for Astrophysical Data Analysis
We report on the development of TA-DA, a general Tool for Astrophysical Data Analysis. TA-DA is i... more We report on the development of TA-DA, a general Tool for Astrophysical Data Analysis. TA-DA is intended as a powerful, integrated web service to significantly simplify the process of comparing calibrated astrophyiscal data with theoretical stellar evolutionary models. It is built upon the Synphot (for synthetic photometry) and Chorizos (a Bayesian multi-parametric chi-squared fitting algorithm) packages. TA-DA will allow to easily and reliably compute a variety of fundamental observables including synthetic photometry from theoretical spectral energy distributions, color corrections, and bandpass transformations. It will also support the cross-calibration of photometry from different archives, analysis of individual SEDs, statistical analysis of HR diagrams and self-consistent prediction of astronomical performance.
Observatory Operations to Optimize Scientific Return, 1998
ABSTRACT The Hubble Data Archive at the Space Telescope Science Institute contains over 4.3 TB of... more ABSTRACT The Hubble Data Archive at the Space Telescope Science Institute contains over 4.3 TB of data, primarily for the Hubble Space Telescope, but also from complementary space- based and ground-based facilities. We are in the process of upgrading and generalizing many of the HDA's component system, developing tools to provide more integrated access to the HDA holdings, and working with other major data providing organizations to implement global data location services for astronomy and other space science disciplines. This paper describes the key elements of our archiving and data distribution systems, including a planned transition to DVD media, data compression, data segregation, on-the-fly calibration, an engineering data warehouse, and distributed search and retrieval facilities.
Astrophysics. Multiple images of a highly magnified supernova formed by an early-type cluster galaxy lens
Science (New York, N.Y.), Jan 6, 2015
In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a stro... more In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a strong gravitational lens could be used to measure the rate of cosmic expansion. We report the discovery of such a system. In Hubble Space Telescope imaging, we have found four images of a single supernova forming an Einstein cross configuration around a redshift z = 0.54 elliptical galaxy in the MACS J1149.6+2223 cluster. The cluster's gravitational potential also creates multiple images of the z = 1.49 spiral supernova host galaxy, and a future appearance of the supernova elsewhere in the cluster field is expected. The magnifications and staggered arrivals of the supernova images probe the cosmic expansion rate, as well as the distribution of matter in the galaxy and cluster lenses.
The Concentration-Mass Relation from CLASH clusters using galaxy dynamics
ABSTRACT Galaxy clusters play a key role in testing cosmological models and in constraining the p... more ABSTRACT Galaxy clusters play a key role in testing cosmological models and in constraining the properties of dark matter. One of these key tests is the mass density profile of clusters - the concentration-mass relation. There is a reported tension between the observed concentration-mass relation and the one theoretically expected using simulated galaxy clusters, where the observed clusters appear to have higher concentration than simulated clusters of similar total mass. In The Cluster Lensing And Supernova survey with Hubble (CLASH), we use different and independent techniques to estimate the mass distribution in clusters. The comparison between different techniques offers an observational test of the techniques and understanding of the systematics. In this work, we estimate the concentration-mass relation for about 8 (at the 0.2< z &;lt; 0.6 redshift range) of the 20 X-ray selected CLASH clusters using galaxy dynamics. We use a unique spectroscopic data set with more than about 300 cluster members per cluster. Finally, we compare our results to the theoretical expected ones and to the estimations derived using the lensing technique.
The Astrophysical Journal, 2015
We utilize the CLASH (Cluster Lensing And Supernova survey with Hubble) observations of 25 cluste... more We utilize the CLASH (Cluster Lensing And Supernova survey with Hubble) observations of 25 clusters to search for extreme emission-line galaxies (EELGs). The selections are carried out in two central bands: F105W (Y 105 ) and F125W (J 125 ), as the flux of the central bands could be enhanced by the presence of [O III] λλ4959, 5007 at redshift of ∼ 0.93 − 1.14 and 1.57 − 1.79, respectively. The multi-band observations help to constrain the equivalent widths of emission lines. Thanks to cluster lensing, we are able to identify 52 candidates down to an intrinsic limiting magnitude of 28.5 and to a rest-frame [O III] λλ4959, 5007 equivalent width of 3737Å. Our samples include a number of EELGs at lower luminosities that are missed in other surveys, and the extremely high equivalent width can be only found in such faint galaxies. These EELGs can mimic the dropout feature similar to that of high redshift galaxies and contaminate the color-color selection of high redshift galaxies when the S/N ratio is limited or the band coverage is incomplete. We predict that the fraction of EELGs in the future high redshift galaxy selections cannot be neglected.
A new paradigm for space astrophysics mission design
Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave, 2014
Astronomy & Astrophysics, 2014
Context. The study of the galaxy stellar mass function (SMF) in relation to the galaxy environmen... more Context. The study of the galaxy stellar mass function (SMF) in relation to the galaxy environment and the stellar mass density profile, ρ ⋆ (r),is a powerful tool to constrain models of galaxy evolution. Aims. We determine the SMF of the z=0.44 cluster of galaxies MACS J1206.2-0847 separately for passive and star-forming (SF) galaxies, in different regions of the cluster, from the center out to approximately 2 virial radii. We also determine ρ ⋆ (r) to compare it to the number density and total mass density profiles. Methods. We use the dataset from the CLASH-VLT survey. Stellar masses are obtained by spectral energy distribution fitting with the MAGPHYS technique on 5-band photometric data obtained at the Subaru telescope. We identify 1363 cluster members down to a stellar mass of 10 9.5 M ⊙ , selected on the basis of their spectroscopic (∼ 1/3 of the total) and photometric redshifts. We correct our sample for incompleteness and contamination by non members. Cluster member environments are defined using either the clustercentric radius or the local galaxy number density. Results. The whole cluster SMF is well fitted by a double Schechter function, which is the sum of the two Schechter functions that provide good fits to the SMFs of, separately, the passive and SF cluster populations. The SMF of SF galaxies is significantly steeper than the SMF of passive galaxies at the faint end. The SMF of the SF cluster galaxies does not depend on the environment. The SMF of the passive cluster galaxies has a significantly smaller slope (in absolute value) in the innermost (≤ 0.50 Mpc, i.e., ∼ 0.25 virial radii), and in the highest density cluster region than in more external, lower density regions. The number ratio of giant/subgiant galaxies is maximum in this innermost region and minimum in the adjacent region, but then gently increases again toward the cluster outskirts. This is also reflected in a decreasing radial trend of the average stellar mass per cluster galaxy. On the other hand, the stellar mass fraction, i.e., the ratio of stellar to total cluster mass, does not show any significant radial trend. Conclusions. Our results appear consistent with a scenario in which SF galaxies evolve into passive galaxies due to density-dependent environmental processes, and eventually get destroyed very near the cluster center to become part of a diffuse intracluster medium. Dynamical friction, on the other hand, does not seem to play an important role. Future investigations of other clusters of the CLASH-VLT sample will allow us to confirm our interpretation.
Direct imaging and spectroscopy of habitable planets using JWST and a starshade
Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave, 2010
The Astrophysical Journal, 2014
We present the supernova (SN) sample and Type-Ia SN (SN Ia) rates from the Cluster Lensing And Su... more We present the supernova (SN) sample and Type-Ia SN (SN Ia) rates from the Cluster Lensing And Supernova survey with Hubble (CLASH). Using the Advanced Camera for Surveys and the Wide Field Camera 3 on the Hubble Space Telescope (HST), we have imaged 25 galaxy-cluster fields and parallel fields of non-cluster galaxies. We report a sample of 27 SNe discovered in the parallel fields. Of these SNe, ∼ 13 are classified as SN Ia candidates, including four SN Ia candidates at redshifts z > 1.2. We measure volumetric SN Ia rates to redshift 1.8 and add the first upper limit on the SN Ia rate in the range 1.8 < z < 2.4. The results are consistent with the rates measured by the HST/GOODS and Subaru Deep Field SN surveys. We model these results together with previous measurements at z < 1 from the literature. The best-fitting SN Ia delay-time distribution (DTD; the distribution of times that elapse between a short burst of star formation and subsequent SN Ia explosions) is a power law with an index of −1.00 +0.06(0.09) −0.06(0.10) (statistical) +0.12 −0.08 (systematic), where the statistical uncertainty is a result of the 68% and 95% (in parentheses) statistical uncertainties reported for the various SN Ia rates (from this work and from the literature), and the systematic uncertainty reflects the range of possible cosmic star-formation histories. We also test DTD models produced by an assortment of published binary population synthesis (BPS) simulations. The shapes of all BPS double-degenerate DTDs are consistent with the volumetric SN Ia measurements, when the DTD models are scaled up by factors of 3-9. In contrast, all BPS single-degenerate DTDs are ruled out by the measurements at > 99% significance level.
The Astrophysical Journal, 2012
We present a strong-lensing analysis of the galaxy cluster MACS J1206.2-0847 (z=0.44) using UV, O... more We present a strong-lensing analysis of the galaxy cluster MACS J1206.2-0847 (z=0.44) using UV, Optical, and IR, HST/ACS/WFC3 data taken as part of the CLASH multi-cycle treasury program, with VLT/VIMOS spectroscopy for some of the multiply-lensed arcs. The CLASH observations, combined with our mass-model, allow us to identify 47 new multiply-lensed images of 12 distant sources. These images, along with the previously known arc, span the redshift range 1 z 5.5, and thus enable us to derive a detailed mass distribution and to accurately constrain, for the first time, the inner mass-profile of this cluster. We find an inner profile slope of d log Σ/d log θ −0.55 ± 0.1 (in the range [1 ,53 ], or 5 r 300 kpc), as commonly found for relaxed and well-concentrated clusters. Using the many systems uncovered here we derive credible critical curves and Einstein radii for different source redshifts. For a source at z s 2.5, the critical curve encloses a large area with an effective Einstein radius of θ E = 28 ± 3 , and a projected mass of 1.34 ± 0.15 × 10 14 M . From the current understanding of structure formation in concordance cosmology, these values are relatively high for clusters at z ∼ 0.5, so that detailed studies of the inner mass distribution of clusters such as MACS J1206.2-0847 can provide stringent tests of the ΛCDM paradigm.
The Hubble Deep Field South: Formulation of the Observing Campaign
The Astronomical Journal, 2000
The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for an 8-meter to 16... more The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for an 8-meter to 16-meter UVOIR space observatory for launch in the 2025-2030 era. ATLAST will allow astronomers to answer fundamental questions at the forefront of modern astronphysics, including "Is there life elsewhere in the Galaxy?" We present a range of science drivers that define the main performance requirements for
SDSS Image Processing II: The Photo Pipelines
astro.princeton.edu
2Department of Astronomy, University of Washington, Seattle, WA 98195; ivezic@astro.washington.ed... more 2Department of Astronomy, University of Washington, Seattle, WA 98195; ivezic@astro.washington.edu ... 3University League Nursery School, Princeton, NJ 08544, USA ... 42555 NE 85th Street, Seattle, WA 98115, USA ... A description of the SDSS image ...
Virtual Observatories (Proceedings Volume)
The Cluster Lensing And Supernova survey with Hubble (CLASH) is a 524-orbit multi-cycle treasury ... more The Cluster Lensing And Supernova survey with Hubble (CLASH) is a 524-orbit multi-cycle treasury program to use the gravitational lensing properties of 25 galaxy clusters to accurately constrain their mass distributions. The survey, described in detail in this paper, will definitively establish the degree of concentration of dark matter in the cluster cores, a key prediction of CDM. The CLASH