Galactic Radio Science Cornelia C Lang University of
- Slides: 25
Galactic Radio Science Cornelia C. Lang University of Iowa Eleventh Synthesis Imaging Workshop Socorro, NM, June 10 -17, 2008
Outline • Radio Emission: what can we learn? – Thermal and non-thermal continuum emission – Spectral line radiation – The radio spectrum & interferometers • A Radio Tour of the Milky Way – – Star birth and death in the ISM Stellar radio sources Interstellar gas: ionized & atomic clouds Exotic radio sources • An Unusual Place: Galactic Center 2
Radio Emission Mechanisms 3 • Synchrotron radiation - continuum • Energetic charged particles accelerating along magnetic field lines (non-thermal) • What can we learn? • particle energy • strength of magnetic field • polarization • orientation of magnetic field
Radio Emission Mechanisms 4 • Thermal emission - continuum • Blackbody radiation for objects with T~3 -30 K • Brehmsstralung “free-free” radiation: charged particles interacting in a plasma at T; e- accelerated by ion • What can we learn? H image • mass of ionized gas • optical depth • density of electrons in plasma • rate of ionizing photons Courtesy of Dana Balser
Radio Emission Mechanisms • What we measure from radio continuum • Radio flux or flux density at different frequencies Flux or Flux Density • Spectral index , where S ~ Spectral index across a SNR thermal no n- th = -0. 1 er m al = -0 . 7 From T. Delaney Frequency 5
Radio Emission Mechanisms 6 • Spectral line emission - Discrete transitions in atoms and molecules Atomic Hydrogen “spin-flip” transition 21 cm Molecular Lines CO, CS, H 20, Si. O, etc. ! Recombination Lines outer transitions of H H 166 , H 92 , H 41 • What can we learn? (1. 4, 8. 3 GHz, 98 GHz) • gas physical conditions (n, T) • kinematics (Doppler Effect)
Also a wide variety of instruments! ATA CA, USA 7 VLA/EVLA NM, USA ATCA, Australia Millimeter > 15 GHz < 10 mm Low-Frequency < 1. 4 GHz >1 m Centimeter 1. 4 MHz - 15 GHz 20 cm – 1 cm ALMA, Chile Pd. B, France CARMA, CA, USA SMA, Hawaii, USA GMRT, India LOWFAR, NL LWA, NM, USA
Tour of the Galaxy: Interstellar 8 • Low Mass Star Formation - obscured regions of the Galaxy with high resolution - collimated outflows powered by protostar – 10000 s AU Chandler & Richer 2001 Zapata et al. 2005 VLA 7 mm spectral line (Si. O) – 0. 5” SMA 1 mm spectral line (CO 2 -1) – 1”
Tour of the Galaxy: Interstellar 9 • Probing massive stars in formation - tend to be forming in clusters; confusion! go to high frequencies (sub-mm) - “hot molecular cores” (100 -300 K) around protostars; complex chemistry Ceph A-East d=725 pc; black=SMA 875 m; green=VLA 3 cm; lines=sub-mm species Spatial resolutions of <1” (where 1”~0. 004 pc or ~750 AU) from Brogan et al. (2007)
Tour of the Galaxy: Interstellar 10 • High Mass Stars in HII Regions - high resolution shows objects forming of size ~1000 s AU! - ultra-compact HIIs are < 0. 1 pc with densities n > 104 cm-3 W 49 VLA 7 mm continuum De. Pree et al. (2004)
Tour of the Galaxy: Interstellar 11 • HII regions: ionization & kinematics - continuum Lyman photons = # stars - continuum density, mass of ionized H - RRLs kinematics, physical conditions H 92 a velocity distribution Sickle HII region Quintuplet Pistol Nebula (Lang, Goss & Wood 1997) +20 to -60 km/s (Lang, Goss & Morris 2001)
Tour of the Galaxy: Stellar Sources • Stars: Middle Age and Evolving “Radio H-R Diagram” from Stephen White 12
Tour of the Galaxy: Stellar Sources 13 • Stars: Very low mass and brown dwarfs - some M+L type dwarfs, brown dwarfs show quiescent and flaring nonthermal emission (Berger et al. 2001 -7; Hallinan et al. (2006, 2008) <-- magnetic activity at the poles: electrons interact with dwarf’s magnetic field to produce radio waves that then are amplified by masers OFF ON
Tour of the Galaxy: Stellar Sources 14 • Stars: Middle Age and Evolving Cyg. OB 2 #5– stellar wind emission Contreras et al. (1996) • Binary system with two O 7 I stars • Mass loss ~ 4 -5 x 10 -5 Mo year-1 WR 140 Dougherty et al. (2005) • WR star and O-star binary • Nonthermal, varying emission traces wind-wind collision
Tour of the Galaxy: Interstellar • Supernova Remnants Rudnick et al. Cassiopeia A SNR VLA 6 cm image d = 3 kpc Cassiopeia Gaensler & Frail G 5. 4 -1. 2 and PSR B 1757 -24 d = 5 kpc Sagittarius PSR moving 1, 000 miles/sec 15
Tour of the Galaxy: Interstellar 16 • Star Death: Pulsar Wind Nebulae Chandra X-ray Image G 54 VLA B-field Chandra X-ray Image 2. 5’ @ d=2 kpc ~ 1. 4 pc 2. 7’ @ d=5 kpc ~ 3. 8 pc G 54. 1+0. 3 VLA 6 cm Lang, Clubb, Wang & Lu, in prep. Crab radio studies: particle energies, polarization, magnetic field orientation VLA/VLBA pulsar proper motion can be combined with spin-axis orientation (X-ray) Pulsar timing and discovery done with single dish radio telescopes – Parkes, GBT
17 Tour of the Galaxy: Interstellar • HI absorption against bright sources - Interferometer resolves out Galactic HI emission features, allows the study of small-scale features Local bubble ~100 pc Cold HI scale height (2 z) ~200 pc From C. Brogan ~500 pc 3 c 138
Tour of the Galaxy: Interstellar 18 • HI absorption toward 3 c 138 VLBA: ‘ 95, ‘ 99, 2002 Resolution: 20 mas = 10 AU at 500 pc Changes in t indicate changes in density of Galactic atomic gas Sizescale of features ~ 25 AU! Brogan et al. (2005)
19 Tour of the Galaxy: Exotic • LS I+61 303 : A pulsar comet around a hot star? - well known radio, X-, ray, source - high mass X-ray binary with 12 solar mass Be star and NS Orbital Phase -----10 AU - radio emission models: (a) accretion-powered jet or (b) rotation powered pulsar -VLBA data support pulsar model in which particles are shockaccelerated in their interaction with the Be star wind/disk environment VLBA 3. 6 cm; 3 days apart! Note shift of centroid around orbit Astrometry is good to rms = 0. 2 AU (Dhawan, Mioduszewski & Rupen 2006)
Tour of the Galaxy: Exotic • LS I+61 303 : A pulsar comet around a hot star? Orbit greatly exaggerated VLBA emission vs. orbital phase Be star (with wind/disk) Dhawan, Mioduszewski & Rupen (2006) 20
Tour of the Galaxy: The Galactic Center • Our Galactic center (GC) is 25, 000 ly away (8000 pc) • GC lies behind 30 visual magnitudes of dust and gas 21
Center of our Galaxy VLA 20 cm VLA 1. 3 cm VLA 3. 6 cm Sgr. A* - 4 milliion Mo black hole source Credits: Lang, Morris, Roberts, Yusef-Zadeh, Goss, Zhao 22
Tour of the Galaxy: The Galactic Center • Magnetic Field: Pervasive vs. Local? VLA 90 cm VLA 3. 6 & 6 cm polarization B-field Nord et al. 2004 Lang & Anantharamaiah, in prep. 23
Tour of the Galaxy: The Galactic Center 24 Galactic Center Survey Numerous new compact and shell-like sources (massive star formation) D and C array - 4. 9 GHz Full polarization ~1 hour per pointing First high-resolution VLA polarimetric study on large scales! Preliminary results <----- C-array (Lang, Drout, Lazio and Golap, in prep. )
25 Summary • Radio Interferometry: a powerful tool – Physical insight into many different processes – Spatial scales comparable or better than at other wavelengths: multi-wavelength approach • A great time for students & interferometry! – Amazing science opportunities with new tools CARMA ATA EVLA LOFAR ALMA LWA
- Galactic center radio transients
- Trunked radio vs conventional radio
- Galactic address
- Hoyt sector model
- Starwars combine
- City structure model
- Galactic city model
- Reverberation
- Galactic habitable zone
- Active galactic nuclei
- Galactic phonics ure
- Galactic cap review
- Galactic plane
- Galactic habitable zone
- Active galactic nuclei
- Galactic
- Favorite subject is science
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