Multiwavelength telescopesand surveys

SAMSI Tutorial #3Eric Feigelson (Penn State)

Over the past 50 years, an increasing fraction of astronomical observations are made at non-visible wavelengths. We thus learn the basics of multiwavelength astronomy.

Over the past 20 years, an increasing fraction of astronomical observations are based on carefully designed wide-field surveys. The resulting megadatasets require statistical interpretation more than small-sample studies. We thus learn some of the major astronomical surveys

Motivation

The electromagnetic spectrum (= light)

but most wavelengths of light don’t penetrate air(only optical & radio telescopes are ground-based)

Radio telescopes

Single dish

Green Bank Telescope (WV)

Interferometer

Very Large Array (NM)

Radio telescopes see ionized gas around hot stars in theMilky Way (thermal bremsstrahlung) and relativistic electrons spiralling around magnetic fields (nonthermalsynchrotron). These are produced only in very energeticenvironments (supernova shocks, black hole jets, …)

Top: Cyg ABot: M87Left: 3C288

2-6 cm

Radio galaxies imagedwith the VLA

Interferometric data are the Fouriertransform of the image. Statistical image restoration techniques includeleast squares (CLEAN) & maximum entropy.

SubMillimeter Array (Mauna Kea HI)

Wilkinson Microwave Anisotropy Probe

2001 --

Cosmic microwavebackground (CMB)radiation

Fluctuations in the cosmic microwave background

Infrared Astronomical Satellite (IRAS)

Early 1980s350,000 mid-IR sources inall-sky survey (12-100 µm)0.2 Jy sensitivity

Spitzer Space Telescope

2003-20070.001 Jy sensitivity (3-50 µm)3” resolution, spectroscopy

Cryogenically cooled bolometersSees mostly interstellar dust (soot, rock, ices)

Two-Micron All Sky Survey (2MASS)

Early 2000s300,000,000 stars and galaxies

Gemini North & South 8-m telescopesMauna Kea Hawaii & Chilean Andes

2000s0.3-0.9 µm (visible)1-10 µm (near-IR)

Visible light is mainly produced by thermal gases at 3-50,000 K(stellar photospheres).

Sloan Digital Sky Survey(SDSS)

2000s100,000,000 visual bandstars and galaxies plus1,000,000 spectra

ROSAT All-Sky Survey(RASS)

100,000 X-ray sources plus diffuse emission

Chandra X-ray Observatory

1999 —0.5-8 keV

X-rays produced mainlyby thermal gases at1-100 MK

Top: Tycho’s supernova remnantBot: Crab pulsar, jet & torusLeft: Galactic Center

INTEGRAL

2002 –Gamma-ray observatory20 keV—10 MeV

Astronomical databases & resourcesPerhaps more than any other scientific field, astronomicalresults are available online:

• Astrophysics Data System: nearly-complete, searchablefull-text (w/ subscription) research literatureadsabs.harvard.edu/abstract_service.html

• SIMBAD and NED: Databases of >10 million Galactic and extragalactic objects with images & referencessimbad.u-strasbg.fr ned.ipac.caltech.edu

• Vizier: Searchable library of >5000 published astronomical catalogs, N~tens to billions vizier.u-strasbg.fr

• NASA archive & mission science centersarchive.stsci.edu/sites.html

• Virtual Observatory: Developing resource for searching widely distributed mega-datasets www.us-vo.org