The Big BOSS BAO Survey Nikhil Padmanabhan Yale

The Big. BOSS BAO Survey Nikhil Padmanabhan Yale University 1

Big. BOSS is a Stage IV BAO Expt. • Questions : — Are the scientific goals compelling and attainable? — Are they justified in relation to other existing and planned experiments? • Status report on Baryon Oscillations as a DE probe — Theory — Observations • The Big. BOSS BAO science goals are attainable • The Big. BOSS experiment is a Stage IV DE experiment — Big. BOSS is compelling and justified Nikhil Padmanabhan Talk P 4 BAO Survey 2

Two Approaches to Dark Energy • Theoretical — A new energy component — Modifications to gravity on cosmological scales • Observational — Geometry (Homogeneous) — Growth of structure (Inhomogeneous) • Big. BOSS does both of these — Baryon Acoustic Oscillations (Expansion) – this talk — Redshift Space Distortions (Growth) – next talk Nikhil Padmanabhan Talk P 4 BAO Survey 3

A Standard Ruler Nikhil Padmanabhan Talk P 4 BAO Survey • Standard rulers analogous to standard candles • Sound waves frozen in the Early Universe • Characteristic scale ~ sound horizon • 100 Mpc/h for concordance cosmologies • Scale imprinted on density fluctuations • Constrained by the CMB 4

Calibrated by the CMB WMAP Science Team Nikhil Padmanabhan Talk P 4 BAO Survey 5

Two point correlations Wiggles in the power spectrum Nikhil Padmanabhan Talk P 4 BAO Survey Bump in the correlation function 6

Measuring d. A(z) and H(z) Nikhil Padmanabhan Talk P 4 BAO Survey 7

Measuring d. A(z) and H(z) • Transverse scale measures angular diameter distance • Radial scale measures the Hubble constant • Internal consistency tests • H(z) unique amongst dark energy probes • H(z) important to constrain dark energy at high redshifts Nikhil Padmanabhan Talk P 4 BAO Survey 8

Measuring the BAO feature • Use galaxies to trace the matter distribution with galaxy redshift surveys • First detection of BAO using the SDSS-II and 2 d. F galaxy surveys • Stage III surveys include BOSS, Wiggle. Z, HETDEX Nikhil Padmanabhan Talk P 4 BAO Survey 9

Measuring the BAO feature • Use the neutral gas as a tracer – the Lymanalpha forest • Probe in absorption by backlighting with quasars • SDSS-III first attempt to measure this • First detections of 3 D correlations in the Lyman-alpha forest Nikhil Padmanabhan Talk P 4 BAO Survey 10

What sets the BAO accuracy? • Volume • Number densities • Redshift precision — Define requirements for the Big. BOSS survey • Systematic effects — Is the BAO ruler robust? — Yes! • Nonlinear evolution — Washes out the BAO feature — Can be undone : reconstruction Nikhil Padmanabhan Talk P 4 BAO Survey 11

BAO is Robust • Three possible systematics — Nonlinear evolution — Galaxy bias — Redshift space distortions • Scale separation — BAO feature is at 100 Mpc/h — Effects above at ~10 Mpc/h — Expect effects to be small • Studied using perturbation theory/ numerical simulations — Substantial body of literature today — Effects ~ 0. 5% in distance at z=0, decrease at higher redshift — Can be corrected to < 0. 1% — Can be calculated using perturbation theory — Calibrated using numerical simulations Nikhil Padmanabhan Talk P 4 BAO Survey 12

Nonlinear evolution BAO feature smoothed by a Gaussian of width ~ 8 Mpc/h Worse along line of sight due to redshift space distortions Nikhil Padmanabhan Talk P 4 BAO Survey 13

Nonlinear Evolution Nikhil Padmanabhan Talk P 4 BAO Survey 14

Nonlinear evolution • Smoothing caused by bulk flows ~ 20 Mpc • Can be understood within perturbation theory • Effects included in forecasts • Can be undone reconstruction Nikhil Padmanabhan Talk P 4 BAO Survey 15

Reconstruction • • BAO smearing dominated by large scale flows These flows give rise to the observed density field Invert density field to get flow field Move galaxies back to their original positions — Removes the systematic effects of redshift space distortions in the BAO measurement Nikhil Padmanabhan Talk P 4 BAO Survey 16

Reconstruction : II Nikhil Padmanabhan Talk P 4 BAO Survey 17

Reconstruction : III Nikhil Padmanabhan Talk P 4 BAO Survey 18

DR 7 correlations - before 3. 3σ Nikhil Padmanabhan Talk P 4 BAO Survey NP et al, in prep 19

DR 7 correlations - after 4. 1σ Nikhil Padmanabhan Talk P 4 BAO Survey NP et al, in prep 20

DR 7 Distance Measurements Nikhil Padmanabhan Talk P 4 BAO Survey NP et al, in prep 21

Implications • Reconstructing the DR 7 correlation function — First applications of reconstruction on data — 1. 9% distance measurement — 4. 1 sigma BAO detection — Equivalent to tripling the SDSS volume • Big. BOSS — Reconstruction works on real data, samples similar to the Big. BOSS sample — Reconstruction works as well as forecast (smoothing scale reduced from 8. 1 to 4. 4 Mpc/h, close to 50%) • Close to theoretical expectations Nikhil Padmanabhan Talk P 4 BAO Survey 22

Current BAO surveys • Stage II — SDSS-II (completed) (z ~ 0. 35) • Stage III — Wiggle. Z (completed) (z ~ 0. 6) — BOSS (see Martin White’s talk) • Galaxies (z < 0. 7) • Lyman-alpha forest (z ~ 2 -3) — HETDEX (under construction, z ~ 2 -4) Nikhil Padmanabhan Talk P 4 BAO Survey 23

A Hubble Diagram Nikhil Padmanabhan Talk P 4 BAO Survey 24 Daniel Eisenstein

The Big. BOSS BAO Survey • Stage IV dark energy experiment • Map dark energy between 0 < z < 3. 5 • Survey specifics — 14, 000 sq. deg. — Four tracers • • Luminous Red Galaxies (0. 5 < z < 1) Emission line galaxies (0. 5 < z < 1. 6) Quasars (0. 5 < z < 3. 5) Lyman-alpha forest (2. 2 < z < 3. 5) Nikhil Padmanabhan Talk P 4 BAO Survey 25

The Big. BOSS BAO Survey Nikhil Padmanabhan Talk P 4 BAO Survey 26

The Big. BOSS BAO Survey Nikhil Padmanabhan Talk P 4 BAO Survey 27

Redshift accuracy requirements Current large photo-z samples • Degrade d. A errors • Erase all H(z) information • Important at high z • Impossible to do reconstruction • Cannot be mitigated by dense sampling • Cannot be done with photo-z’s Nikhil Padmanabhan Talk P 4 BAO Survey 28

Big. BOSS tracers Nikhil Padmanabhan Talk P 4 BAO Survey 29

Big. BOSS S/N as a function of z • Big. BOSS S/N > 1 between 0 < z < 1. 5 Nikhil Padmanabhan Talk P 4 BAO Survey 30

Distance constraints • Isotropic dilation factor • Big. BOSS has < 1% distance errors over the widest redshift range • Probe the expansion history over the widest redshift range Nikhil Padmanabhan Talk P 4 BAO Survey 31

The impact of Big. BOSS : Fo. M Current BAO + SN + CMB Fo. M : 10 Nikhil Padmanabhan Talk P 4 BAO Survey 32

Questions from the Schmidt committee • How robust are the predictions for the galaxy BAO to number density degradations? • What information does the Lyman-alpha forest add to the galaxy distance constraints? — How well does the Lyman-alpha constraint work? Nikhil Padmanabhan Talk P 4 BAO Survey 33

Robustness of Big. BOSS performance is robust to degradations in the sample selection Nikhil Padmanabhan Talk P 4 BAO Survey 34

Lyman-alpha improve Fo. M Even in the Big. BOSS era, Lyman-alpha measurements improve constraints Nikhil Padmanabhan Talk P 4 BAO Survey 35

Lyman-alpha improves z coverage • Lyman-alpha increases redshift coverage from 1. 5 to 3. 5 Nikhil Padmanabhan Talk P 4 BAO Survey 36

BOSS Lyman-alpha measurements Nikhil Padmanabhan Talk P 4 BAO Survey 37

Big. BOSS is a Stage IV experiment For BAO only, assuming Planck prior and H 0 Assumes 14 K sq. deg Big. BOSS is competitive with space missions Nikhil Padmanabhan Talk P 4 BAO Survey 38

Conclusions • Status report on Baryon Oscillations as a DE probe — Theory • Theory well understood using perturbation theory, simulations — Observations • SDSS-II yields 1. 9% distance measurement in one bin using reconstruction • The Big. BOSS experiment is a Stage IV DE experiment — Big. BOSS is significant improvement over Stage III — Big. BOSS is competitive with space BAO missions — Big. BOSS is a unique ground based Stage IV BAO survey Nikhil Padmanabhan Talk P 4 BAO Survey 39