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Thursday, November 30

  1. page LCDM edited ... lower median redshift. To get an overestimated shear value you need, for example, coherent ta…
    ...
    lower median redshift. To get an overestimated shear value you need, for
    example, coherent tangential residual PSF contamination. This is usually picked
    ...
    histogram introduces some
    some
    uncertainty just
    ...
    small field. I
    I
    don't know
    ...

    I also redidre-did the analysis
    by the simulators when deriving their predicted concentrations from their synthetic clusters.
    Since the substructure is offset from the optic axis we see the second effect predicted by
    ...
    and Corless, iei.e. that the
    clump analysis value. With the fiducial critical density I get c=16[+5/-3]; with the higher critical
    density (z=0.9, or 14% understimated shear) I get c=12[+3/-2].
    (view changes)
    11:24 pm
  2. page LCDM edited ... In general one would expect shear to be underestimated: PSF roundening, and catalogue dilutio…
    ...
    In general one would expect shear to be underestimated: PSF roundening, and
    catalogue dilution by foreground and cluster members both do it. More subtly,
    catalogue dilution meanswould mean that we overestimated
    ...
    a lower background number density
    ...
    a shallower depthadepth and
    lower
    ...
    get an overetsimatedoverestimated shear value
    example, coherent tangential residual PSF contamination. This is usually picked
    up on... It has been suggested that using the HDF redshift histogram introduces some uncertainty just due to the cosmic variance associated with such a small field. I don't know which way it goes though.
    I also redid the analysis using just a single mass component, as would be done
    ...
    their predicted concentrations. Sinceconcentrations from their synthetic clusters.
    Since
    the
    substructure
    substructure is offset
    ...
    and Corless, ie that the
    ...
    clump) concentration decreases.is lower than the double
    clump analysis value.
    With
    the
    the fiducial critical
    density (z=0.9, or 14% understimated shear) I get c=12[+3/-2].
    ...
    of all thiosthis we have
    ...
    et al (2002) that there
    significant line of sight mass structure, which would lead to a higher projected
    concentration than would be measured by a simulator.
    (view changes)
    11:21 pm
  3. page LCDM edited ... up to c~10 or so, even for halos at 10^14 Msun/h. I'm not sure how overcooled that simulation …
    ...
    up to c~10 or so, even for halos at 10^14 Msun/h. I'm not sure how overcooled that simulation was, so it's
    unclear whether the simple estimate above would be consistent with their simulation.
    Possible explanations for the Ultra-High concentration in Cl0024+52
    [Phil]
    In Kneib et al (2003) we analysed a large, sparse mosaic of WFPC2 images,
    extending to a radius of 11 arcmin or so, covering the field of the merging
    cluster Cl0024+52. In the weak lensing mass map you can clearly see a secondary
    mass clump to the North West of the main cluster component. The ellipticity
    catalogue was masked within the central 100 arcsec as the contamination by
    bright cluster members is very high here - not so much their own ellipticity but
    rather the lensing and masking effects the bright members have on the backgound
    galaxies. The HST mosai was single filter: the weak lensing sources were
    selected using their faint magnitudes alone. The HDF redshift distribution was
    used to estimate the median redshift of background galaxies in images of the
    given depth - this was determined to be z=1.1.
    We fitted two mass components to the ellipticity data, allowing positions,
    masses and concentrations to vary. To the central clump we applied a strong
    lensing prior, anchoring the position of the clump to that found in the strong
    lensing analysis and constraining the Einstein radius to be that of the strong
    lens model (within a Gaussian prior defined by the error bar). There is not much
    more strong lensing information than this - there seems to be just one dominant
    multiple image system forming a broken Einstein ring.
    The concentration of the central clump was found to be 22{+9/-5}. The second
    clump (comprising some 30% of the total cluster mass) was found to have a lower
    concentration (~4).
    With the paucity of weak lensing data in the central region, and the lack of any
    further strong lensing information, the central component of Cl0024+52 is
    somewhat under-constrained, and I guess susceptible to systematic errors. To
    address some of these I re-did the analysis using critical densities for the
    weak lensing catalogue that were 8% lower and 14% higher than the fiducial value
    - these correspond to source plane redshifts of 1.3 and 0.9 respectively. Using
    a different critical density is equivalent to applying a shear calibration
    factor to the data, of the kind often needed in weak lensing analyses (see the
    STEP papers for examples - 5-10% is not unheard of).
    The higher critical density (z=0.9, or 14% understimated shear) gave a lower
    concentration value: 14[+5/-3]. Similarly, the lower critical density gave a
    higher concentration.
    In general one would expect shear to be underestimated: PSF roundening, and
    catalogue dilution by foreground and cluster members both do it. More subtly,
    catalogue dilution means we overestimated the number density of background
    galaxies, and a lower number density is indicative of a shallower deptha and
    lower median redshift. To get an overetsimated shear value you need, for
    example, coherent tangential residual PSF contamination. This is usually picked
    up on...
    I also redid the analysis using just a single mass component, as would be done
    by the simulators when deriving their predicted concentrations. Since the
    substructure is offset from the optic axis we see the second effect predicted by
    King and Corless, that the inferred (single clump) concentration decreases. With
    the fiducial critical density I get c=16[+5/-3]; with the higher critical
    density (z=0.9, or 14% understimated shear) I get c=12[+3/-2].
    On top of all thios we have the observation of Czoske et al that there is
    significant line of sight mass structure, which would lead to a higher projected
    concentration than would be measured by a simulator.
    I conclude that we may well be seeing a collection of effects in this cluster
    all of which combine to increase the inferred concentration. The concentration
    corresonding to that predicted from simulations may well be less than 12 and so
    pose no "problem."

    Draft Proceeding LCDM {King}
    (view changes)
    11:14 pm
  4. page LCDM edited ... This interesting preprint by Lindsay King and Virginia Corless looks at the effect of large su…
    ...
    This interesting preprint by Lindsay King and Virginia Corless looks at the effect of large substructures on
    concentrations. They find that substructures that are 10-20% of the total mass of the cluster can, when aligned along the optical axis, increase the inferred concentration from 5 to up to 10 or so. If the same substructure is placed in the plane of the sky, the inferred concentration goes down (but only by a unit or so). Here are the two important figures:
    {King Corless2006-figure2.jpg} {http://www.slac.stanford.edu/~pjm/King%20Corless2006-figure2.jpg} {King Corless2006-figure2.jpg} {http://www.slac.stanford.edu/~pjm/King%20Corless2006-figure3a.jpg}{KingCorless2006-figure2.jpg} {KingCorless2006-figure3a.jpg}
    The "high" concentration of MS2137-23; a test case
    [Raphael]
    ...
    up to c~10 or so, even for halos at 10^14 Msun/h. I'm not sure how overcooled that simulation was, so it's
    unclear whether the simple estimate above would be consistent with their simulation.
    ...
    Proceeding LCDM {King Corless2006-figure2.jpg}{King}
    (view changes)
    10:34 pm
  5. page LCDM edited ... This interesting preprint by Lindsay King and Virginia Corless looks at the effect of large su…
    ...
    This interesting preprint by Lindsay King and Virginia Corless looks at the effect of large substructures on
    concentrations. They find that substructures that are 10-20% of the total mass of the cluster can, when aligned along the optical axis, increase the inferred concentration from 5 to up to 10 or so. If the same substructure is placed in the plane of the sky, the inferred concentration goes down (but only by a unit or so). Here are the two important figures:
    {King Corless2006-figure2.jpg} {http://www.slac.stanford.edu/~pjm/King%20Corless2006-figure2.jpg} {King Corless2006-figure2.jpg} {http://www.slac.stanford.edu/~pjm/King%20Corless2006-figure3a.jpg}
    The "high" concentration of MS2137-23; a test case
    [Raphael]
    ...
    up to c~10 or so, even for halos at 10^14 Msun/h. I'm not sure how overcooled that simulation was, so it's
    unclear whether the simple estimate above would be consistent with their simulation.
    ...
    Proceeding LCDM {King Corless2006-figure2.jpg}
    (view changes)
    10:29 pm
  6. page LCDM edited ... The effect of substructure on the lensing-inferred concentration [Phil] Note there is an T…
    ...
    The effect of substructure on the lensing-inferred concentration
    [Phil]
    Note there is anThis interesting preprint
    ...
    Lindsay King and Virginia Corless looks at the effect of large substructures on astro-ph discussing
    concentrations. They find that substructures that are 10-20% of the total mass of the cluster can, when aligned along the optical axis, increase the inferred concentration from 5 to up to 10 or so. If the same substructure is placed in the plane of the sky, the inferred concentration goes down (but only by a unit or so). Here are the two important figures:
    The "high" concentration of MS2137-23; a test case
    [Raphael]
    (view changes)
    10:22 pm

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