Surveys of Cosmic Popula ons: Overview
Eric Feigelson (Astronomy & Astrophysics, Penn State)
Statistical Modeling of Cosmic Populations Penn State Summer School June 2014 Astronomical Surveys
Astronomers have been conducting all-sky (or at least, wide-field) surveys of the celestial sphere for centuries:
• 2nd c BC: 41 constellations, Hipparchus (Greece) • 2nd c: Almagest, ~1K stars, Ptolemy (Egypt) • 8th c: Dunhuang Star Chart, Tang Dynasty China • 10th c: Book of Fixed Stars, al-Sufi (Persia) • 17th c: Uranometria, Bayer (Germany) • 18th c: Atlas Coelestis, ~3K stars, Flamsteed (England) • 19th c: Bonner Durchmusterung, ~300K (Germany) • 19th c: Carte du Ciel, ~5M stars (France) • 20th c: USNO-B1.0, ~1G stars (USA)
• 1770s: 103 nebulae, Messier (France) • 1880s: ~8K nebulae, NGC catalog, Dreyer (Ireland) • 1990s: 20K galaxies, 3rd Ref Cat, de Vaucouleurs (USA) 2nd century Roman statue • 2000s: ~1G, Sloan Digital Sky Survey, Gunn et al. (USA) `Farnese Atlas) showing Hipparchus’ star catalog Faint Images of the Radio Sky at Twenty-centimeters (FIRST)
811,000 radio sources 1990s Infrared Astronomical Satellite (IRAS)
Early 1980s 350,000 mid-IR sources in all-sky survey Two-Micron All Sky Survey (2MASS)
Early 2000s 300,000,000 stars and galaxies ROSAT All-Sky Survey (RASS)
100,000 X-ray sources plus diffuse emission
eROSITA survey 2015-19 ~4M sources expected gal clusters, AGN, stars Large Area Telescope Fermi Observatory
20 MeV – 300 GeV
1,873 sources 2011 Star counts: The first flux limited surveys
For a uniform population of objects distributed randomly in transparent space: S = L / 4 π D2 V = 4/3 π D3 Num obj ~ V ~ S-3/2 logN ~ -1.5 logS
William Herschel (1785) used deviations from this prediction to infer that the Universe (now known as our Milky Way Galaxy) is limited in extent (~1 kpc) and is elongated in shape. Star counts at different Galactic latitudes
halo
disk
The Galaxy has multiple components with different spatial distributions producing strong deviations from the logN~-1.5 logS law.
Bahcall & Soneira 1980 The universe at faint magnitudes. I - Models for the galaxy and the predicted star counts But, near the Galac c plane, space is very opaque due to interstellar dust. Thus, Herschel’s galaxy is ~20 mes too small, which was not appreciated un l the 1930s.
Big effort in 1910-50s to address the “Fundamental equa on of stellar sta s cs” to simultaneously establish the distribu on of stellar luminosi es and their spa al distribu onin the Galac c disk:
A (S,l,b) = [D(r,l,b) F(L,Abs(r,l,b)) r2 dr
A = number of stars/deg-2 in flux interval around S towards direc on (l,b). (Star count data) D = number of stars/pc-3 at distance r from Earth towards (l,b) F = normalized distribu on of stellar luminosi es (LF) corrected for spa ally-dependent absorp on
Fredholm Type 1 integral equa on solved by Taylor expansion, Fourier transform, numerical integra on. This effort essen ally failed in the disk due to the patchy absorp on, but func ons reasonably well towards the Galac c poles (b=90o).
Trumpler & Weaver “Sta s cal Astronomy” 1953 Stellar populations & kinematics in the Galaxy New catalogs with 4-6 dimensions of phase space: (α,δ) Location in the sky π Parallax giving distance (µα, µδ) Proper motion across the sky Vr Radial velocity
50,000 stars have all 6 values measured, 100,000 have 5 values, 30M have 4 values (Hipparcos, UCAC2, Gen-Cop, RAVE,…). GAIA will revolutionize Galactic astrometry (~2017).
Fascinating structure: • Thin disk, thick disk, halo components of Galaxy • Trace star formation around Sun • Halo streams & cannibalized galaxies
Little sophisticated statistical work has been performed on these catalogs (e.g. mixture models, wavelet analysis) Milky Way halo ~ star streams from cannibalized dwarf galaxies
Model results
Observations of the Sagittarius dwarf galaxy streams
Monaco et al 2007 Some contemporary cosmology surveys
Galaxy/quasar spectroscopic survey (clustering, BAO, gal evolu on, AGN feedback) • WiggleZ: WiggeZ Dark Energy Survey (Australia) • GAMA: Galaxy & Mass Assembly (St Andrews/ESO/… consor um) • DEEP2: DEEP2 Galaxy Redshi Survey (large consor um) • J-PAS: Javalambre-PAU Astrophysical Survey (Mexico) • LAMOST: LArge-sky-area Mul Object Spectroscopic Telescope (China) • HETDEX: Hobby-Eberly Telescope Dark Energy Experiment (Univ Texas) • (e)BOSS: Baryon Oscilla on Spectroscopic Survey (SDSS consor um) • VIPERS: VIMOS Public Extragalac c Redshi Survey (ESO)
Mul -epoch photometric surveys (SN Ia, AGNs) • DES: Dark Energy Survey (FNAL/OSU/UPenn/… consor um) • Pan-STARRS: Panoramic Survey Telescope & Rapid Response System (Hawaii) • CRTS: Catalina Real-Time Transient Survey (Caltech) • SkyMapper: SkyMapper (ANU) • DES: Dark Energy Survey (FNAL/OSU/UPenn/… consor um) Cosmic micowave background survey (era of recombina on, infla on, cosmological models, Dark Energy, grav waves, nucleosynthesis, …) • BICEP: Robinson Gravita onal Wave Background Telescope (Caltech/JPL) • Planck: Planck satellite (ESA) • SPT: South Pole Telescope (Chicago/UCB/CWRU consor um)
21-cm surveys (Hi during era of reioniza on) • LOFAR: LOw-Frequency Array (Netherlands) • MeerKAT: Karoo Array Telescope (South Africa) • ASKAP: Australian SKA Pathfinder (Australia)
Mul wavelength pencil-beam surveys (gal forma on & evolu on, AGN, dust) • GOODS: Great Observatories Origins Deep Surveys (HST/Chandra/Spitzer/Herschel/VLA/Keck/VLT • CANDELS: Cosmic Assembly Near-infrared Deep Extragalac c Legacy Survey Astrophysical Simula ons: Surveys without observa on
z=18.3
z=5.7
z=0.0
Millennium Simulation Springel et al. 2005 Common observa onal challenges in surveys
• Data cleaning (cosmic rays, detector noise, bad pixels, …) • Flux calibra on, bright object satura on • Noise characteriza on • Faint source detec on • Source characteriza on (flux, extent, variability, color/SED, class)
• Survey coverage in RA/Dec • Survey coverage in flux sensi vity • Volume limited survey? • Edge effects (RA/Dec, velocity, distance, …) • Astrometry & catalog cross-matching • Data processing & database management • Data release, documenta on & promulga on (reproducibility)
Summary
Astronomers have been surveying the sky since an quity, cataloguing, classifying & characterizing vast numbers of celes al objects.
In the 21st century, due in part to the spectacular scien fic success of the Sloan Survey, tremendous resources are being placed on the development of new surveys.
Surveys place new demands on the astronomical community to develop high levels of skill in statistical and computational methodology, to complement our existing skills in astronomy and astrophysics.