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The Universe of Galaxies The Universe o Galaxies Ajit Kembhavi IUCAA
Galaxies: Stars: ~10 11 Mass: ~10 11 M Sun Contain stars, gas and dust, possibly a supermassive black hole at the centre. Much of the mass is in the form of dark matter.
The Milky Way Galaxy
Spitzer Near-IR Central 900 light years
The Milky Way Galaxy COBE-DIRBE composite near-ir image, 1.25, 2.2 and 3.5 m. Emission is dominated by relatively cool giant K stars in the disk and bulge. Dust obscuration is weak in the near-ir. Cosmic Background Explorer-Diffuse IR Background Experiment
The Milky Way Galaxy
The halo is thought to be spherical in shape and consists of metal poor (old) globular clusters and filed stars. The stars have high proper motion. The mass of the halo is ~10 9 M Sun. In addition there is a The disk dark consists matter of halo flattened which system could contain of stars, as gas much as and dust 90 with percent a variety of the of mass structures of the galaxy. like spiral arms and bars. There is substantial star formation and a mix of old and new stars. The Classically disk is supported a bulge consists by of old rotation. About 95 percent of stars the stars and is are supported in a thin by random disk with scale height of ~300 motions pc, the of other stars 5 rather percent than rotation. are in a thick disk with scale But height there ~1000 are pseudobulges pc. The in some stellar mass of the disk is ~6x10 galaxies 10 M Sun which and the are more disk like in luminosity is ~2x10 10 L Sun. The nature. Sun The completes bulge of one the Galaxy has orbit in ~250x10 6 yr. a mass of ~2x10 10 M Sun and the luminosity is ~5x10 9 M Sun. Spark & Gallagher Galaxies in the Universe
illustration October 2010 1-10 GeV map from Fermi Gamma Ray Space Observatory all sky data
The Content of the Milky Way Galaxy
Stars and masses Radius Radius 700,000 700,000 km km 25-50 R SUN 0.1-10 R SUN ~1000 R SUN Planet and White Dwarf
Swan Nebula Omega Nebula, M 17, NGC 6618 in Lyra 5000-6000 light years away, ~15 light years diameter, HII region Embedded open cluster of 35 stars ionizes surrounding gas due to radiation from hot young stars.
Bok Globule B68 Distance 125 pc Size ~10 4 AU ~ Oort cloud size Close to collapse, Mass ~2M Sun
Planetary Nebula Ring Nebula, M57, NGC 6720 in Lyra 8.8 mag, ~2300 light years away Torus of light emitting material, surrounding a central star, which is a white dwarf Ring expands at ~1 arcsec/century, so age is ~6000-8000 years.
Supernova Remnant Crab Nebula in Taurus, M1, NGC 1952 First Observed April 4, 1054 AD 8.4 mag, distance 6300 light years Diametre 10 light years Expansion velocity 1800 km/s Radio pulsar at the centre
The Crab Pulsar
ISM Phases Gas and dust are generally well mixed in the ISM.
Globular Cluster 47 Tuc NGC 104, massive globular cluster containing millions of stars, 20 light years across and at a distance of 13.4 thousand light years. Contains many exotic pulsars.
The Galactic Centre
VLA 1m radio image
Galactic Centre Chandra X-ray Images [B] 10 light years
SgrA* Keck 2 micron HKL Composite
Star Closest to Galactic Centre NTT, Gemini, VLT Schodel et.al 2003 Bound, highly eccentric (0.87) orbit, period 15.2yr, pericentre distance 17 light hours (0.5mpc), semi-major axis 4.54mpc Best fit central point mass 3.7x10 6 M Sun
The Shape of the Milky Way Galaxy
Herschel s Milky Way A model of the Milky Way Galaxy by William Herschel based on his own observations in the 19 th century
Jan Oort
Spiral structure of the Milky War from HI observations
External Galaxies
Andromeda Galaxy M31, NGC 224 2.5 million light years M32 M 101
M 51 Distance ~31 Mly First object to be recognized as a spiral, by Lord Ross 1845.
Elliptical Galaxy M 87 Largest and brightest galaxy in the Virgo Cluster, distance 55 Mlyr
Ellipsoidal Galaxies
Niel Brandt Hubble s Tuning Fork
Sudhanshu Barway 2007
Surface Brightness Distribution
NGC 661 V
Surface Brightness Profile
Bulge Disk Decomposition 2 = (O i -m i ) 2 / i 2 UGC 1250
Bulge-Disk Decomposition
The Fundamental Plane
Log r e = A*log + B*log I e + const
Photometric Plane Ellipticals and Early Type Bulges
Hubble Deep Field Deep exposure of a region in Ursa major 7 sq arcmin in four filters. 30.3 hr at 606 nm. Most of the ~3000 objects in the field are galaxies.
Coma Cluster NGC 4889 NGC 4874 Rich cluster containing ~1000 identified galaxies. Distance 99 Mpc
Large Scale Structure 2DF Galaxy Redshift Survey
Centaurus A Lenticular galaxy, closest radio galaxy to Earth, distance ~11 Mly
Radio Galaxy Cen A VLA 6 cm A
M87
Radio Galaxy M87 One-sided jet. Bulk relativistic motion. Superluminal motion.
The Jet in M87
Quasars
Emission Lines, Rapid Variability
Quasar Host Galaxies
Unification
Supermassive Black Hole
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Coma Cluster
Black Hole Mass
Gravitational Lens
Butterfly Nebula
Horsehead Nebula
Structures in the Universe
The Milky Way Galaxy
No foreground stars because cloud is a short distance away. Alves, Lada & Lada, Nature 2001
Four Component ISM Gas Phase Temp T(K) Density nt Covering n cm -3 factor Cold H 2 ~15 >10 2 1.5x10 3 <0.01 Molecular The covering factors sum to unity, if Cool atomic H I all phases ~18 are known. ~30 5.4x10 3 ~0.03 The volume of the ISM is mostly Warm H I, filled by ~8000 tenuous ~0.3 hot plasma, 2.4x10 but 3 ~0.2-0.5 H II the mass is dominated by the Hot ionized H II cooler atomic ~5x10 5 and ~5x10 molecular -3 2.5x10 3 ~0.5-0.8 clouds.