Science Case for ALPACA. Arlin Crotts (Columbia University) for the LAMA Collaboration. . Proto-ALPACA imaging focal plane. 0.86 deg diameter field 6 CCDs, 7 arcmin square, 2048x2048 E2V 1 CCD for u,b,i,z; 2 r CCDs
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Science Case for ALPACAArlin Crotts (Columbia University)
for the LAMA Collaboration
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Proto-ALPACA imaging focal planefull ALPACA imaging focal plane
3 deg diameter field
240 CCDs, 8 arcmin square, 2048x2048 Fairchild
deep strip, 8 columns with 6 rows of u, 4 b, and 2 each r, i, z
wide strip, 8 more columns with 4 u, and 2 each b, r, i, z
NEO “ears”: 4 more columns of 2 each of r, i
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ALPACASurveyProducts(P. 1)Project ReviewALPACA Science Case 2005-07-15 Page 4
ALPACASurveyProducts(cont.)Density on sky (in ecliptic coordinates) of asteroids weighted by Earth impact
hazard (contours increase proportional to density), from Kaiser et al. 2001.
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Microlensing follow-up groups (PLANET, FUN, MOA) want to pick the ~100 best
of these lightcurves in terms of early planet-like deviations in microlensing fit.
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The distance modulus (m – M) is cosmology dependent; distance at given z depends on expansion (de)acceleration and spatial curvature. SN Ia standard candle relation puts constraint on ~(demwhereas CMB anisotropy first acoustic peak constrains tot, which together currently constrain dem the level of a few percent. Similar constraints are found by comparing cosmic microwave background constraints with m from cluster masses. Gives reasonable cosmic ages.
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of SNe Ia is from Riess et al. 1995, ApJ, 438, L17.
* MB m15(B) 1.1] (Altavista 2003, PhD thesis)
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Parameters affecting SN Ia LuminositiesEvent width (m15) can predict SN Ia luminosity to ~15% r.m.s., including color measures
(CMAGIC, C12) reduce this to 7-10% r.m.s. Are the residual errors due to measurement
error? Intrinsic processes? Extrinsic? Fundamentally stochastic? Possible factors include
(some treated in publications, with disagreement on nature, size – even sign – of effects):
Simulated Proto-ALPACA SN Ia lightcurves including realistic
effects of weather & instrument (checked against Gemini ETC).
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Reddening
Star = SNe Ia
Circle = I bc
Triangle = II P
Square = II b
Diamond = II N
Number labels = int (10*z)
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Number label = days after max.
Evolution of color over SN peak easily breaks the degeneracy between z=1 SNe Ia and z=0.3 SNe I bc (and further separates SNe Ia from others)
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SNe Ia tend to be closely associated with prominent host galaxy. (SNe II sometimes associated with disconnected star formation knots.)
Sullivan et al. 2003
Tonry et al. 2003
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Accuracy and Reliability of Photo z’sProject ReviewALPACA Science Case 2005-07-15 Page 15
Plan for Proto-ALPACA SN Ia StudiesWilliams et al. 2003: magnitudes of HZT SN Ia hosts (0.43 < z < 1.06)
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Improving SN Ia Standard Candle RelationThe primary challenge is likely to be control of systematic errors. One method of dealing with this might be to split the sample of 100,000 well-sampled light curves into redshift bins (~0.1) small enough that residual error in cosmological parameters are insignificant (see next slide), then perform a principle component analysis on the subsamples of ~10,000, and compare the results from different subsamples to gauge evolution. The quality of the data might allow us to explore 10-20 parameters. By finding the covariance of luminosity in a single bin with this parameter set we should be able to reduce the scatter significantly by producing a detailed luminosity model, or at least discard outriggers.
Behavior of dark energy can be parameterized by its pressure-like versus mass density w = p/(w=0: “normal matter,” w= 1/3: cosmic strings, wquintessence, w=1: cosmological constant). Current limits combining CMB anisotropies, LSS and SN Ia constraints limit w at the 0.1 level subject to limits on our uncertainty regarding the SN Ia standard candle assumption.
c.f. Lewis & Bridle 2002, Phys Rev D, 66, 103511
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2000 SNe with r.m.s m = 0.2, sampled in z via deep, ground-based imaging. Get maximal discrimination in dark energy density f at redshifts 0.3 < z < 0.8. This is true of most dark energy models, in this case quintessence (scalar field potential with slow-roll) versus k-essence (similar but with coupling to kinetic energy term) as might help explain why de ~ m
Wang & Garnavich 2001, ApJ, 552 445
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Standard candle apparent brightness at moderate
redshifts for different models of dark energy:
(baseline) de=0.7 cosmological constant – value of
0.6 or 0.8 varies by about 0.13 in mag at z=1, (thick)
pseudo Nambu-Goldstone boson, (thin) supergravity,
(long dashed) pure exponential, (thick dotted) inverse
tracker, (short dashed) periodic potential (Weller &
Albrecht 2001, PhysRevLet, 86, 1939)
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Cosmological Measures of Dark EnergyUniversal equation of state w=p/ describes expansion’s dynamics and therefore H(z).
What we actually observe are measures of H(z) and redshift integrals* over H(z), the
angle distance and luminosity distance:
Supernovae as standard candles:
luminosity distances dL(zi)
Baryon acoustic oscillation as standard ruler:
cosmic expansion rate H(zi)
angular diameter distance dA(zi)
Weak lensing cosmography:
ratios of dA(zi)/dA(zj)
*Comoving distance is related to expansion rate H(z):
and the observed distances (in flat Universe) dL = R0 r (1+z), dA = R0 r / (1+z)
The three independent methods will provide a powerful cross-check, and allow ALPACA to
place precise constraints on dark energy (+growth of structure via cluster counts+strong
lens delay timings+large-scale structure Alcock-Paczynski+cluster integrated Sachs-Wolfe…)
0 Spatial frequency k (h/Mpc) 0.5
The simplest dark energy investigation method sensitivities to estimate are SN Ia standard candles, weak lensing shear and baryon oscillations. To express dark energy dynamics, we use w = w0+ wa a = w0 + wa /(1+z), where wa describes the redshift change in w. A few points:
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