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RISS 인기검색어
- 검색키워드
- 저자 : Seljak, Uroš (검색결과 4 건)
- 무료
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Precision cluster mass determination from weak lensing
Mandelbaum, Rachel,Seljak, Uroš,Baldauf, Tobias,Smith, Robert E. Blackwell Publishing Ltd 2010 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.405 No.3
<P>ABSTRACT</P><P>Weak gravitational lensing has been used extensively in the past decade to constrain the masses of galaxy clusters, and is the most promising observational technique for providing the mass calibration necessary for precision cosmology with clusters. There are several challenges in estimating cluster masses, particularly (a) the sensitivity to astrophysical effects and observational systematics that modify the signal relative to the theoretical expectations, and (b) biases that can arise due to assumptions in the mass estimation method, such as the assumed radial profile of the cluster. All of these challenges are more problematic in the inner regions of the cluster, suggesting that their influence would ideally be suppressed for the purpose of mass estimation. However, at any given radius the differential surface density measured by lensing is sensitive to all mass within that radius, and the corrupted signal from the inner parts is spread out to all scales. We develop a new statistic ϒ(<I>R</I>; <I>R</I><SUB>0</SUB>) that is ideal for estimation of cluster masses because it completely eliminates mass contributions below a chosen scale (which we suggest should be about 20 per cent of the virial radius), and thus reduces sensitivity to systematic and astrophysical effects. We use simulated and analytical profiles including shape noise to quantify systematic biases on the estimated masses for several standard methods of mass estimation, finding that these can lead to significant mass biases that range from 10 to over 50 per cent. The mass uncertainties when using the new statistic ϒ(<I>R</I>; <I>R</I><SUB>0</SUB>) are reduced by up to a factor of 10 relative to the standard methods, while only moderately increasing the statistical errors. This new method of mass estimation will enable a higher level of precision in future science work with weak lensing mass estimates for galaxy clusters.</P>
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Photometric redshift requirements for lens galaxies in galaxy–galaxy lensing analyses
Nakajima, R.,Mandelbaum, R.,Seljak, U.,Cohn, J. D.,Reyes, R.,Cool, R. Blackwell Publishing Ltd 2012 Monthly notices of the Royal Astronomical Society Vol.420 No.4
<P><B>ABSTRACT</B></P><P>Weak gravitational lensing is a valuable probe of galaxy formation and cosmology. Here we quantify the effects of using photometric redshifts (photo‐<I>z</I>) in galaxy–galaxy lensing, for both sources and lenses, both for the immediate goal of using galaxies with photo‐<I>z</I> as lenses in the Sloan Digital Sky Survey (SDSS) and as a demonstration of methodology for large, upcoming weak lensing surveys that will by necessity be dominated by lens samples with photo‐<I>z</I>. We calculate the bias in the lensing mass calibration as well as consequences for absolute magnitude (i.e. <I>k</I>‐corrections) and stellar mass estimates for a large sample of SDSS Data Release 8 (DR8) galaxies. The redshifts are obtained with the template‐based photo‐<I>z</I> code <SMALL>zebra</SMALL> on the SDSS DR8 <I>ugriz</I> photometry. We assemble and characterize the calibration samples (∼9000 spectroscopic redshifts from four surveys) to obtain photometric redshift errors and lensing biases corresponding to our full SDSS DR8 lens and source catalogues. Our tests of the calibration sample also highlight the impact of observing conditions in the imaging survey when the spectroscopic calibration covers a small fraction of its footprint; atypical imaging conditions in calibration fields can lead to incorrect conclusions regarding the photo‐<I>z</I> of the full survey.</P><P>For the SDSS DR8 catalogue, we find σ<SUB>Δ<I>z</I>/(1+<I>z</I>)</SUB>= 0.096 and 0.113 for the lens and source catalogues, with flux limits of <I>r</I>= 21 and 21.8, respectively. The photo‐<I>z</I> bias and scatter is a function of photo‐<I>z</I> and template types, which we exploit to apply photo‐<I>z</I> quality cuts. By using photo‐<I>z</I> rather than spectroscopy for lenses, dim blue galaxies and <I>L</I><SUB>*</SUB> galaxies up to <I>z</I>∼ 0.4 can be used as lenses, thus expanding into unexplored areas of parameter space. We also explore the systematic uncertainty in the lensing signal calibration when using source photo‐<I>z</I>, and both lens and source photo‐<I>z</I>; given the size of existing training samples, we can constrain the lensing signal calibration (and therefore the normalization of the surface mass density) to within 2 and 4 per cent, respectively.</P>
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