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Galaxies

Nimisha G. Kantharia National Centre for Radio Astrophysics Tata Institute of FundamentalResearch Pune. Galaxies. Electromagnetic Spectrum. Radio frequencies. Accessible em bands on earth. Milky way in Infrared. Stellar distribution is traced in this map. Some Terminology.

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Galaxies

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  1. Nimisha G. Kantharia National Centre for Radio Astrophysics Tata Institute of FundamentalResearch Pune Galaxies

  2. Electromagnetic Spectrum Radio frequencies

  3. Accessible em bands on earth

  4. Milky way in Infrared • Stellar distribution is traced in this map.

  5. Some Terminology • Distance - light year: (3 x 10^5 ) km/s * (365 * 24 * 60 * 60) sec ~ 9.5 x 10^12 km ! compare with earth radius ~ 6400 km compare with galactic radius ~ 100,000 light yrs! • Distance in Solar system: Astronomical unit = 1.5 x 10^8 km (earth-sun distance) • Mass – solar mass: 1.9 x 10^30 kg !! • Luminosity – solar luminosity: 3.8 x 10^26 Watts

  6. GMRT Khodad

  7. Galaxies • Collection of stars and gas. ~10^11 stars. Gas ~ 2-3% of stellar mass. Many types. • http://imagine.gsfc.nasa.gov/

  8. Types of Galaxies • Hubble Tuning Fork diagram – evolutionary sequence? spirals – gas; ellipticals – less gas

  9. Spirals edge-on view • Andromeda galaxy • M31 www.noao.edu/image_gallery/galaxies.html

  10. Spirals face-on view • Whirlpool galaxy • M51 www.noao.edu/image_gallery/galaxies.html

  11. Types of Galaxies • Can you classify these galaxies?

  12. Galaxy Catalogues -Messier • Charles Messier gave Messier catalogue: M31, M33, M51 • Identified 'nebulous objects' while looking for comets in the 18th century • 110 objects catalogued – still widely used by astronomers

  13. Messier catalogue • 110 nebulous objects - supernova remnants, galaxies, HII regions. • http://www.seds.org/messier/

  14. New General Catalogue (NGC) • Compiled by J.L.E. Dreyer in 1888. • Galaxies, open clusters, globular clusters of stars, HII regions, supernova remnants • 47 Tucanae = NGC104 • http://www.seds.org

  15. NGC 253 – starbursthttp://www.seds.org

  16. Other catalogues • Catalogues have since been created by specific optical observatories e.g. UGC (using Palomar data), ESO and for specific objects e.g. Markarian (galaxies bright in uv), Arp (interacting galaxies). • What information is required to catalogue galaxies?

  17. How to locate galaxies in the sky? • To locate galaxies, stars etc on sky • Celestial sphere • Right ascension • Declination • Visible stars above horizon: ~ 3000 - all in Milkyway http://inkido.indiana.edu/a100/celestialsphere.html

  18. Rotation in Galaxies • Familiar with earth's revolution around sun • Stars, gas in galaxies differentially rotate around the centre.

  19. Rotation curves Rotation curve of a typical spiral galaxy: predicted (A) and observed (B). Dark matter can explain the velocity curve having a "flat" appearance out to large radii. (from wikipedia)

  20. Dark Matter in galaxies • Gravity balanced by centrifugal force • G Mm / R^2 = mv^2 / R • v = sqrt ( GM / R) • At R_max using observed v km/s, an estimate of mass of galaxy can be obtained. • ~ 96% mass in universe is dark

  21. GMRT – low radio frequencies • GMRT consists of 30 disk antennas over 25 km region and observes the universe at radio frequencies of 150, 240, 325, 610 and 1420 MHz.

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