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STRUCTURE, MOTIONS AND COSMOLOGY FROM THE TAIPAN SURVEY

STRUCTURE, MOTIONS AND COSMOLOGY FROM THE TAIPAN SURVEY. Matthew Colless The Australian National University Melbourne, 19 July 2017. C osmological goals of Taipan.

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STRUCTURE, MOTIONS AND COSMOLOGY FROM THE TAIPAN SURVEY

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  1. STRUCTURE, MOTIONS AND COSMOLOGY FROM THE TAIPAN SURVEY Matthew Colless The Australian National University Melbourne, 19 July 2017

  2. Cosmological goals of Taipan • What is the current expansion rate of the universe?Aim to measure the local Hubble constant, H0, with 1% precision from the large-scale distribution of galaxies • What are the local universe density and velocity fields?Map the both density and velocity fields over a greater volume and with more galaxies than previous surveys • What is the correct theory of gravity on large scales?Test gravity models using both the peculiar velocities of galaxies and the redshift-space distortions of their large-scale distribution

  3. Why measure H0? (with emphasis on the ‘0’) • H0, the local (i.e. zero-redshift) expansion rate, is a fundamental cosmic parameter (⟹ universe age/scale) • For a flat LCDM universe, Planck CMB observations give H0 to ~1.5% – but this is a model-dependent result

  4. CMB H0 is model-dependent The H0 estimated from CMB observations is an extrapolation to low z of measurements at high z, and depends on other parameters of the cosmological model and on the nature of the model itself

  5. Why measure H0? • H0, the local (i.e. zero-redshift) expansion rate, is a fundamental cosmic parameter (⟹ universe age/scale) • For a flat LCDM universe, Planck CMB observations give H0 to ~1.5% – but this is a model-dependent result • An independent determination of H0 is a key prior that improves the constraints on other parameters (e.g. dark energy, neutrino numbers/mass)

  6. H0 is key prior for dark energy

  7. Why measure H0? • H0, the local (i.e. zero-redshift) expansion rate, is a fundamental cosmic parameter (⟹ universe age/scale) • For a flat LCDM universe, Planck CMB observations give H0 to ~1.5% – but this is a model-dependent result • An independent determination of H0 is a key prior that improves the constraints on other parameters (e.g. dark energy, neutrino numbers/mass) • Currently, there are systematic discrepancies between H0 determined from the CMB and local measurements (via Cepheids, masers, SNe) – tension at up to 3s level

  8. Local and CMB H0 are discrepant H0 from CMB H0 from Cepheids & SNe H0 from local BAO All local measures (except BAO) give higher H0 than CMB

  9. Local and CMB H0 are discrepant • Furthermore, the observational discrepancies in H0 have been sharpening up over time • These discrepancies could be… • systematic errors in the local or CMB measurements • a signature of non-LCDM physics in cosmological model • a signature of gravitational physics due to inhomogeneity and back-reaction

  10. UKST-TAIPAN instrument system • The Taipan survey will employ the new TAIPAN multi-fibre spectrograph on a rejuvenated UKST… • The 1.2-metre UK Schmidt Telescope at Siding Spring Observatory is being completely refurbished so that it can operate in an automated mode, substantially increasing efficiency while reducing operating costs • A new 150-fibre Starbugs positioner is being built by AAO to provide rapid automated reconfigurations (a prototype for the MANIFEST system on the Giant Magellan Telescope); a proposal to upgrade this to 300 fibres is under review • A new TAIPAN spectrograph is being built by AAO to provide high-throughput, fixed-format spectroscopy over the full visible range from 370nm to 870nm at R~2100

  11. The UK Schmidt Telescope (before)

  12. Starbug fibre positioner • Starbugs are piezoelectric micro-robots providing an elegant way to position fibres in telescope focal planes • The full 150-starbug TAIPAN system is now being commissioned on the UKST [LIEF proposal submitted for upgrade to 300 starbugs; if successful, the 300-starbug system could in operations by the start of 2019] • Starbugs will also be used in the MANIFEST fibre system that will feed spectrographs on the Giant Magellan Telescope

  13. Starbug fibre positioner

  14. TAIPAN spectrograph • The TAIPAN spectrograph is a two-channel, fixed format design • Covers 370–870nm at ⟨R⟩~2100 with 3.3” diameter input fibres Top view of TAIPAN spectrograph showing both blue & red channels

  15. TAIPAN technical specifications TAIPAN throughput Blue arm Red arm Dichroic split

  16. The UK Schmidt Telescope (with TAIPAN)

  17. Taipan survey components & phases • The Taipan galaxy survey has three components: • BAO survey – large-volume z-survey optimized for cosmology • Peculiar velocity survey – Fundamental Plane survey optimized for nearby early-type galaxies and measuring peculiar motions • Legacy survey – an i-band magnitude-limited sample optimized for high completeness and legacy value • The survey will be carried out in two phases: • Taipan Phase 1 (first ~15 months) will be based on 2MASS (BAO survey), 6dFGS (PV survey) & KiDS-S (i-band survey); these are the best available sources at the survey outset • Taipan Final (next ~3 years) will be based on SkyMapper and PanSTARRS (all surveys); best sources available by end 2018

  18. Taipan Phase 1 & Taipan Final • Taipan galaxy survey – Phase 1 & Final…

  19. Taipan & FunnelWeb • Taipan galaxy survey… • FunnelWeb stellar survey…3x106 stars with 5.7<V<12.5 and d < +30º targeted in future exoplanet searches (e.g. TESS) • expands on legacy of RAVE (Steinmetz+ 2006, Siebert+ 2011) which observed ~0.5x106 stars with lower R and ll coverage • requires the rapid fibre positioning of the Starbugs technology to acquire an average of 5 fields/hour (a spectrum every 2s + reconfiguration time!)

  20. Taipan compared to other surveys

  21. Taipan redshift sample N(z)

  22. Taipan velocity sample N(z)

  23. Example field configurations

  24. Simulation of Taipan survey observations BAO sample: 2MASS LRGs and JVega<15.4; PV sample: 6dFGS, Taipan; Legacy sample: i<17

  25. Taipan Live Data Reduction (TLDR)

  26. Taipan & WALLABY • WALLABY is an all-sky HI survey that will measure redshifts for ~500,000 HI galaxies using the Australian SKA Pathfinder: b≈ 0.7, <z>≈0.04, Veff≈0.35Gpc3 • WALLABY will also obtain HI Tully-Fisher distances & peculiar velocities for a large sample of spirals • WALLABY TF peculiar velocities for spirals will complement the Taipan FP peculiar velocities for early-types, sampling more densely the nearer half of the Taipan survey volume

  27. Taipan–WALLABY overlaps

  28. A combined all-sky survey • Strong arguments for an all-sky survey of local universe: • to completely characterize the local velocity field, especially the monopole (local Hubble constant) and dipole terms • to map the foreground large-scale structure for cross-correlation with deeper observations (particularly all-sky CMB surveys) • to make a definitive database of optical spectra for local galaxies • This can be achieved by combining the SDSS, Taipan and LAMOST surveys into an all-sky (|b|>10) survey to r≈17.5 • Taipan will cover southern hemisphere and north to +15º • SDSS/BOSS cover ⪞π steradians of north (with some overlap in south) • LAMOST could cover the remaining ⪝π steradians of north • All surveys can provide good S/N spectra to r≈17.6 at R~2000 • Need consistent selection criteria (pre-/post-selection of sample) based on SDSS + SkyMapper+ Pan-STARRs imaging

  29. Measuring H0 with BAO • Baryon acoustic oscillations (BAO) imprint co-moving scale of 146 Mpcon matter distribution (calibrated to 0.3% by Planck) • BAO scale is well within the linear regime of gravitationally growing fluctuations, so is a standard ruler seen at all redshifts that allows mapping of cosmic distances and geometry • First detected in z-surveys by by 2dFGRS (Cole+2005) & SDSS (Eisenstein+2005) • Key application of BAO in low-redshift surveys is is measuring H0

  30. Existing low-z BAO H0 measurement

  31. Hubble constant from 6dFGS At low z, distance measurements only constrain H0– but are model-independent! Beutler+ 2011 (6dFGS, BAO) H0 = 67 ± 3.2 km/s/Mpc Riess+ 2016 (Cepheids, SNe) H0 = 73.0 ± 1.8 km/s/Mpc Planck 2015 (CMB, BAO) H0 = 67.3 ± 0.7 km/s/Mpc (model-dependent) low-z (BAO) (WMAP7) high-z

  32. Taipan BAO distance determinations

  33. Hubble constant from Taipan • With ~2,000,000 galaxies at <z> ≈ 0.17 over Veff ≈ 1.3 Gpc3, simulations show Taipan Final will measure H0 to 0.9% precision (2.1% precision in Phase 1) • This is 5x better than 6dFGS: • Gain ~2.5x from larger sample size and volume of Taipan cf. 6dFGS • Gain another ~2x from better BAO reconstruction

  34. Stress test • How Taipan will test the apparent tension in H0 measurements between high-z CMB and low-z distance ladder estimates: • 2017 status: the Planck CMB and SNe distance ladder estimates are in 2.8s tension • How Taipan will test the apparent tension in H0 measurements between high-z CMB and low-z distance ladder estimates: • 2017 status: the Planck CMB and SNe distance ladder estimates are in 2.8s tension • Case A: Taipan supports the Planck CMB estimate with a BAO-derived local 1% H0 measurement...… • How will Taipan test the apparent tension in H0 measurements between high-z CMB and low-z distance ladder estimates? • 2017 status: the Planck CMB and SNe distance ladder estimates are in 2.8s tension • Case A: Taipan supports the Planck CMB estimate with a BAO-derived local 1% H0 measurement... • Case B: Taipan supports the distance ladder estimate with a BAO-derived local 1% H0 measurement…

  35. Cosmology from velocities – 6dFGS • For parameters that are degenerate in Pgg(k), analysis of the peculiar velocity power spectrum Pvv(k) & Pgv(k) provides additional constraints • 6dFGS has measured Pvv(k) and the growth rate of structure fs8: • The growth rate is scale-independent for scales <300 Mpc/h • Overall growth rate at z~0 from Pvv(k) is consistent with higher-z estimates from RSD, and with Planck/WMAP LCDM models 6dFGS peculiar velocity power spectrum (Johnson et al. 2014) Rate of growth of structure (Johnson et al. 2014) Pvv(k) Planck WMAP RSD

  36. Taipan velocity power spectrum

  37. Joint fits to density & velocity fields • The density fluctuations source the large-scale velocity field, so sample variance cancels • Combining z & v tightens constraints on b= f/b = 𝛺𝛾/b • If b varies on large scales, implies non-standard physics such as non-Gaussianity or modified gravity • Combining z & v reduces degeneracy due to galaxy bias • Burkey+Taylor(2004), Koda+(2014) & Howlett+(2016) provide full density & velocity Fisher matrix forecasts for Taipan, both alone & combined with other surveys(incl. effects of primordial non-Gaussianity, scale-dependent density/velocity biases, & zero-point offsets)

  38. Growth rate of structure constraints Peculiar velocities Combined Redshifts

  39. Growth rate of structure constraints • The Taipan velocity survey improves on the 6dFGS v-survey by having… • ~4x the volume • ~5x sample size • smaller peculiar velocity errors • Combining RSD & Pvv(k), Taipan Final will constrain fs8 at z~0 to 2.7% (and 4.5% in Taipan Phase 1) • Can distinguish models of gravity with fs8~Ω(z)g and |g – gGR|> 0.05 at >3s

  40. Taipan and WALLABY jointly provide significantly improved constraints on the growth rate of structure parameter The combination of the two surveys can measure fs8 to <2% precision The low redshifts of the WALLABY and Taipan samples allow for a much more stringent test of deviations from GR, as it is at low z where differing g produce the largest changes in fs8 Growth rate of structure constraints Taipan WALLABY Howlett+2016

  41. Taipan survey – summary The Taipan galaxy survey is a multi-object spectroscopic survey starting in 2017 that will cover 2π steradians over the southern sky and obtain optical spectra for about 2 million galaxies out to a redshift z=0.4. It will use the refurbished 1.2-metre UK Schmidt Telescope at Siding Spring Observatory with the new TAIPAN instrument, comprising an innovative ‘Starbugs’ positioning system capable of rapidly and simultaneously deploying 150 fibres over the 6º diameter focal plane, and a purpose-built high-performance, fixed-format spectrograph. The main scientific goals of Taipan are: • to measure the distance scale of the universe (mainly governed by the local expansion rate, H0) to 1% precision, and the structure growth rate of structure to 5%; • to make the most extensive map yet constructed of the mass distribution and motions in the local universe, using peculiar velocities based on improved Fundamental Plane distances, which will enable sensitive tests of gravitational physics; and • to deliver a legacy sample of low-redshift galaxies as a unique laboratory for studying galaxy evolution as a function of mass and environment. The Taipan survey will be the primary redshift and optical spectroscopic reference catalogue for the local universe over the southern sky. See the Taipan White Paper for a complete description: https://arxiv.org/abs/1706.01246

  42. Forecast constraints Predictions from Fisher matrix analysis by Howlett+(2016) for results from combining various redshift and velocity surveys…

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