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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Arlin Crotts (Columbia University)
for the LAMA Collaboration
full 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
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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Event 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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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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Williams et al. 2003: magnitudes of HZT SN Ia hosts (0.43 < z < 1.06)
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The 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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Universal 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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