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3 D Map of the Milky Way with Gaia

3 D Map of the Milky Way with Gaia. C. Cacciari INAF - Osservatorio Astronomico, Bologna.

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3 D Map of the Milky Way with Gaia

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  1. 3D Map of the Milky Way with Gaia C. Cacciari INAF - Osservatorio Astronomico, Bologna The primary objective of Gaia is the Galaxy: to observe the physical characteristics, kinematics and distribution of stars over a large fraction of its volume, with the goal of achieving a full understanding of the MW dynamics and structure, and consequently its formation and history. (Concept and Technology Study Report, ESA-SCI(2000)4

  2. Gaia in a nutshell • all sky (i.e. ~ 40,000 deg2) survey complete to Vlim = 20 •  ~ one billion sources • high (μas) accuracy astrometry (parallaxes, positions, proper motions) • optical spectrophotometry (luminosities, astrophysical parameters) • spectroscopy (radial velocities, rotation, chemistry) to V = 16

  3. Satellite and System Launched on 19 December 2013 from Kourou (French Guiana) Launcher: Soyuz–Fregat ESA-only mission (Airbus DS contractor) Lifetime: 5 yr (+ 1yr possible extension) L2 (gravitational equilibrium 1.5 million km from Earth away from Sun ) Lissajous orbit around L2 Figure courtesy A. Buzzoni Figures courtesy EADS-Astrium

  4. Satellite and System Figures courtesy EADS-Astrium

  5. Payload and Telescope Basic angle monitoring system Rotation axis (6 h) Two SiC primary mirrors 1.45  0.50 m2 at 106.5° FoV 1.7° x 0.6° SiC toroidal structure (optical bench) Combined focal plane (CCDs) Superposition of two Fields of View (FoV)

  6. Sky Scanning Principle • Spin axis: 45o to Sun • Scan rate: 60 arcsec/s • Spin period: 6 hr • FoV-1: t0 • t0 + 6hr • FoV-2: t0 + 106.5m • t0 + 106.5m + 6hr • repeated 10-30 days later 29 revolutions of spin axis around solar direction in 5 yr :

  7. Transit maps Ecliptic coordinates Galactic coordinates End of mission (5 yr) sky-average numberof transits: ~ 70 (max  200 at = 45  10)

  8. Scanning the entire sky MOVIE

  9. R ~ 80 – 20 R ~ 90 – 70 Slitless spectroscopy on Ca triplet (847–870 nm) Resolution 11,500 The instruments

  10. Focal Plane 104.26cm Wave Front Sensor Red Photometer CCDs Blue Photometer CCDs 42.35cm Wave Front Sensor Radial-Velocity Spectrometer CCDs Basic Angle Monitor Basic Angle Monitor CCD X time = 4.4 s Sky Mapper CCDs Astrometric Field CCDs – Total FOV ~ 40x40 arcmin ~ 4.4 ‘ ~ 4.4 ' along-scan Sky mapper: - detects all objects to 20 mag - rejects cosmic-ray events - FoV discrimination Astrometry: - total detection noise: 6e- Total field: - active area: 0.75 deg2 - CCDs: 14 + 62 + 14 + 12 - each CCD: 4500x1966 px (TDI) - pixel size = 10 µm x 30 µm = 59 mas x 177 mas Photometry: - spectro-photometer - blue and red CCDs Spectroscopy: - high-resolution spectra - red CCDs

  11. Gaia spectro-photometric system Internal calibration External calibration ● same principle as for classical spectrophotometry ● much more complicated instrument model ● ~ 200 calibrators needed to model instrument response ● mmag internal accuracy, a few % external accuracy Figure courtesy A. Brown

  12. BP/RP first results Star HIP 86564 K5, V=6.64 ● BP and RP low resolution internally calibrated spectral energy distributions ● single transit ESA/Gaia/DPAC/Airbus

  13. Radial-Velocity Measurement Concept Courtesy David Katz CCD detectors RVS spectrograph Field of view Spectra of the star HIP 86564 Top: Gaia-RVS on FoV 0,  CCD row 4 strip 15  Bottom: Narval on 2-m Bernard Lyot Telescope (Pic du Midi), convolved to the nominal resolving power of the RVS: R=11500

  14. Parallax – Parsec Arcsecond = 1/60 arcmin = 1/3600 deg = 1/206265 radian = 1/1,296,000 circle 1˝ ≈ the angle subtended by a US dime coin (17.9 mm diameter) at a distance of 4 km Parsec (pc): distance at which the average Earth-Sun distance (1 AU=150 106 km) is seen under a parallactic angle (parallax) of 1˝ 1pc = 3.26ly parallax (˝) = 1/distance (pc)

  15. Astrometry: a historical perspective Hipparchos 1 degree 1 arcminute Tycho Brahe meridian circles 1 arcsecond Flamsteed Bessel 1 milli-arcsecond Hipparcos Gaia 1 micro-arcsecond ?? 1500 1600 1700 1800 1900 2000 2100 150 BC Year 1/60 Large-angle astrometry 1/60 1/1000 1/100 Small-angle astrometry Figure: Lennart Lindegren

  16. Scan width: 0.7° Sky scans (highest accuracy along scan) Astrometry: data reduction principles 1. Object matching in successive scans 2. Attitude and calibrations are updated 3. Objects positions etc. are solved 4. Higher terms are solved 5. More scans are added 6. System is iterated (Global Iterative Solution) Figure courtesy Michael Perryman

  17. FromHipparcosto Gaia

  18. Astrometric accuracy: the Hyadesd= 46 pc = 151 ly 1960 1990 Figure courtesy ESA 2020

  19. One billion stars in 5D (6D … 9D) will provide: in the Galaxy … distances, velocity distributions and astrophysical parameters (APs) of all stellarpopulations in the MW to unprecedented accuracy allowing to: • map the spatial and dynamical structure of bulge, disk(s) and halo(s) • derive formation and chemical history (e.g. accretion and/or interaction events) of the MW & star formation history throughout • obtain the trigonometric calibration of primary distance indicators (RR Lyraes, Cepheids) accurate and robust definition of the cosmic distance scale and beyond the Galaxy … • QSO detection and definition of rest frame • structure and stellar population studies in nearby (LG) galaxies

  20. Stellar populations of the MW: The Hertzprung-Russell diagram BRIGHT intrinsic luminosities need distances FAINT MOVIE HOT Temperatures from colours (spectrophotometry) COLD

  21. Gravitational light bending This is the dominating relativistic effect in Gaia astrometric measurements Accurate measures of γ of Parametrized Post-Newtonian (PPN) formulation of gravitational theories is of key importance in fundamental physics Gaia will measure  to ~ 5x10-7 (10-4 - 10-5 present)

  22. Data processing & distribution • Data Processing and Analysis Consortium (DPAC): more than • 500 people from 20 European countries and ESA • Final catalogue ~ 2020–22 • Intermediate data releases • Science alerts (e.g. SNe) data released immediately • No proprietary data rights

  23. more information on Gaia at http://www.cosmos.esa.int/web/gaia Thank you !

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