Stefano Cristiani Stefano Cristiani INAF- INAF -Observatory of Trieste Observatory of Trieste for the CODEX team for the CODEX team 1
Relativistic Big Bang Cosmology Universal Expansion
Relativistic Big Bang Cosmology Expansion Cosmic Abundance Structure Microwave of light formation Background elements
Which of the solutions of the Friedmann equation corresponds to reality? Or in other words: What is the stress-energy tensor of the universe? For each mass/energy component i, what is Ω i , w i ? Density parameter Equation of state parameter How can these be measured? � Dynamics Both determined by gravity in GR � Geometry � Clustering (the universe is not homogeneous on small scales!)
Which of the solutions of the Friedmann equation corresponds to reality? Answers have already been provided by: •Cosmic Microwave Cosmic Microwave • Background Background •Supernovae type Ia Supernovae type Ia • •Large scale structure of Large scale structure of • galaxies and intergalactic galaxies and intergalactic medium medium •Galaxy clusters Galaxy clusters • •Weak lensing Weak lensing • Tegmark et al. (2004)
Standard Model With the assumptions of homogeneity and isotropy, the concordance model finds a FRW metric with a non zero cosmological constant ρ λ We do not know what ρ is and We do not know what λ is and how it evolves. how it evolves. Dynamics has never been Dynamics has never been measured. . measured All other experiments, such as All other experiments, such as High Z SNae SNae search and CMB search and CMB High Z Measurements of the Measurements of the measure geometry geometry: : measure dynamics of the Universe dynamics of the Universe dimming of magnitudes and dimming of magnitudes and can be compared to basic can be compared to basic scattering at the recombination scattering at the recombination experiments such as the test experiments such as the test surface and clustering clustering (growth of (growth of surface and of the equivalence principle of the equivalence principle structure). structure). Inertial - - Gravitational Gravitational Inertial mass… mass…
Can we measure the history of the expansion directly? a(t) Goal is to measure or reconstruct the unknown function a(t). t
Can we measure the history of the expansion directly? a(t) H Δ a t Δ t Yes: Measure a(z), da/dt(z) → a(t) Need to measure H(z) using the dynamics!
Can we measure the history of the expansion directly? a(t) H Δ a t Δ t Yes: Measure a(z), da/dt(z) → a(t) Need to measure H(z) using the dynamics!
Can we measure the history of the expansion directly? a(t) H Δ a t Δ t Yes: Measure a(z), da/dt(z) → a(t) Need to measure H(z) using the dynamics!
Measuring H(z) a(t) H 0 a(t 0 + Δ t 0 ) a(t 0 ) H(z) a(t e + Δ t e ) a(t e ) t e t e + Δ t e t 0 t 0 + Δ t 0 t z(t 0 + Δ t 0 ) - z(t 0 ) z dz 1 (t e ) z H 0 H z Δ t 0 t 0 dt 0
The Signal is SMALL! The change in sign is the signature of the non zero cosmological constant
How to Measure this signal? Masers : in principle very good candidates: lines are very narrow and measurements accurate: however they sit at the center of huge potential wells: large peculiar accelerations , larger than the Cosmic Signal are expected Molecular Lines with ALMA: as for Masers, local motions of the emitters are real killers. Few radio galaxies so far observed show variability at a level much higher than the signal we should like to detect α forest Ly α : Absorption from the many intervening lines in front of forest : Ly high-z QSOs are the most promising candidates. Simulations, observations and analysis all concur in indicating that Ly α forest and associated metal lines are produced by systems sitting in a warm IGM following beautifully the Hubble flow !
The Lyman Forest The Lyman Forest Today and … Today and … … years after … years after
Observing dz/dt in the Ly- α Forest
Observing dz/dt in the Ly- α Forest
Observing dz/dt in the Ly- α Forest Δ t = 10 6 years!
Observing dz/dt in the Ly- α Forest Δ t = 10 years: Δ Trans ~ 10 -6
The European Extremely Large Telescope 42 m aperture � ~900 1.45m mirror segments � NIR/optical � First light 2017? � See http://www.eso.org/public/ astronomy/projects/e- elt.html � for details
O-C < 80 cm/sec The HARPS Experience Th-Th < 10 cm/sec
HARPS: it is possible! • Exoplanets (HARPS) long term accuracy 1m/s, short term (hours) 0.1m/s (and largely understood) • ELT !! LOT OF PHOTONS (we need them!!)
COsmic CO Dynamics The Team EXperiment D EX ESO: G. Avila, B. Delabre, H. Dekker, S. D’Odorico, J. Liske, A.Manescau, L. Pasquini, P. Shaver Observatoire Geneve : M.Dessauges-Zavadsky, M. Fleury, C. Lovis, M. Mayor, D.Megevand, F. Pepe, D. Queloz, S. Udry INAF-Trieste P. Bonifacio, S. Cristiani, I.Coretti, V. D’Odorico, P. Di Marcantonio, P. Molaro, P.Santin, E.Vanzella, M.Viel Institute of Astronomy Cambridge: M. Haehnelt, R.Carswell, M. Murphy IAC: R. García López, J.M.Herreros, G.Israelian, A.Manchado, E. Martin, J. Perez, R. Rebolo, J. Sanchez Béjar, M.R.Zapatero OTHERS: F. Bouchy (Marseille), S. Borgani (DAUT-Ts), A. Grazian (INAF-OAR), S. Levshakov (St-Petersburg), L. Moscardini (UNIBo), S. Zucker (Tel Aviv), P.Spano (INAF-Brear), T. Wilklind (ESA), F.Zerbi (INAF-Brera)
What S/N do we need to detect dz/dt? What radial velocity accuracy can we achieve using the Ly α forest? How does the sensitivity depend on redshift? Real absorption line lists: derived from high- resolution, high-S/N UVES/VLT spectra (Kim, Cristiani & D’Odorico. 2002) .
What S/N do we need to detect dz/dt? What radial velocity accuracy can we achieve using the Ly α forest? How does the sensitivity depend on redshift? 1 1.7 0.9 1 1 z QSO N QSO S N 2 2 cm s 1450 30 5 v 2370 where the S/N is per 0.0125 Å pixel (4 pixel per resolution element at R = 100 000). Assumed 2 epochs Liske et al. 2007
A simulated measurement ~2 nights ~2 nights /month over /month over 15 years will 15 years will deliver any deliver any Not observable from the ground! one of these of these one sets of sets of points. points.
Are there enough photons in the sky? Yes! 20 known QSOs QSOs with with Yes! 20 known 2< z < 5 are bright enough 2< z < 5 are bright enough to achieve a radial velocity to achieve a radial velocity accuracy of 3 cm/s with accuracy of 3 cm/s with 3200 hours on a 42- -m ELT. m ELT. 3200 hours on a 42 and more will come (SDSS, GAIA...)
CODEX – The Instrument Basic spectrograph requirements (wish list): Spectral range: Want to span as large a redshift range as possible. Beyond z ~ 4-5 the Ly α forest “saturates” . Cannot observe below ~300 nm from ground. Ideal range = 300 – 680 nm. Resolution: Ly α lines have typical widths of 20-30 km/s. R = 50,000 would suffice. But higher resolution is required by metal lines and wavelength calibration. R ~ 150,000 Long term stability: ~1 cm/s over ~10 years.
Cross disperser 10 x VPHG 1500 l/mm 15 x 15 cm Camera 10 x F/1.4-2.8 CCD 10 x ~8K x 8K (15 µm pixels) 360 Mpix or 810 cm 2 Light enters here Cross-disperser Pupil slicer Anamorphic collimator Camera VPHG Echelle mosaic 20x160 cm Delabre & Dekker (ESO) Main disperser 5 x R4 echelle 42 l/mm 160 x 20 cm
CODEX underground laboratory floor plan Underground hall 20x30x8 m 1K Instrument room 10x20x5 m 0.1K Instrument tanks 2.5x4 m Instrument tanks 2.5x4 m Optical bench and 0.01K 0.01K detector 0.001K Control room and auxiliary equipment 1K
Potential Problems Changes in absorber ionisation structure (e.g. winds in the IGM) QSO continuum variability Weak lensing Wavelength calibration Wavelength calibration Fibre throughput Heliocentric correction (GAIA...) Temperature control Guiding accuracy None of these are currently believed to be show-stoppers.
Wavelength Calibration Classical method: ThAr comparison spectra. Problems: Long-term stability? Low line density in some parts of the optical spectrum. Alternative: Observe object spectrum through an iodine cell. Problems: Long-term stability? Loss of flux System pursued for CODEX: Optical or NIR laser producing a train of monochromatic femtosecond light pulses. Pulse repetition rate is controlled by an atomic clock. Produces a spectrum of evenly spaced δ -functions (frequency comb) whose absolute wavelengths are known to a precision limited only by the atomic clock. Current problem: comb is too dense, would need R=600,000 to resolve it.
Laser Comb Thomas Udem (MPQ) Train of femtosecond light pulses Frequency comb � Zero offset and line spacing known with absolute precision (limit = atomic clock.)
Immediate Science (first epoch data) • Cosmological variation of the fine structure Cosmological variation of the fine structure • constant constant – Accuracy in Δα / α ~ 10 -8
Recommend
More recommend
