Of Marching Bands and Interstellar Clouds Lorne Avery Nov. 6, 2002 Some slides courtesy Wayne Holland, UKATC

Courtesy W. Holland

Courtesy W. Holland

peak =0.3/Temp Courtesy W. Holland

Properties of Interstellar Clouds Cloud masses 10 6 M O Density 100 – 10 8 molecules/cm 3 Why important? – birthplaces of stars, planets Opaque in visible and UV light 99% of mass is gas 1% is dust and Gas? Interstellar gas and dust Courtesy W. Holland

Courtesy W. Holland

Properties of Marching Bands Big Parade Musical virtuosos Many varied instruments – e.g. up to 76 trombones, 110 cornets, bassoons, etc. Occasionally mounted cannons Majorettes

Rotating Batons Rotational energy is quantized E J = hBJ(J+1) h is Plank’s Constant J= 0,1,2,3… is rotational quantum number B  1/Moment of Inertia + - J=0 J=1 J=2 J=3 J=4 EJEJ Jumps emit e/m radiation if charged Freq =  E/h => spectral lines

Frequencies of Rotational Emission 100 gms 10 cm I=  M i r i 2, B  1/I E J =hBJ(J+1) J=0 J=1 J=2 J=3 J=4 EJEJ Freq = (E J+1 -E J )/h Freq J=1-0 =8.4 x GHz or Wavelength = 1.6 x Universe diameters!

Frequencies of an Interstellar Molecule M(C) = 2 x gms, M(O) = 2 x gms B(CO) = 57.5 GHz Freq(  J=1-0) = 115 GHz Freq(  J=2-1) = 230 GHz Etc Each type of molecule has unique set of line frequencies CO 0.7Å 0.4Å

What Spectral Lines Tell Us – cont’d Cloud velocity and internal motions Chemical Composition Isotopic Abundances – e.g.12C,13C Distances – Galactic Distances to early galaxies Cloud Temperature Cloud density => mass

What Spectral Lines Tell Us Line Doppler shift – bulk motion of gas shapes – internal cloud motions Doppler Shift:  Freq = Rest Freq x source velocity/speed of light CO  J = 3-2 in OMC-1 Sound speed = 0.5 –1 km/sec

Chemistry B.E. Turner, ApJ Supp, 70, 539, 1989

Redshift Z Observing Frequency GHz CO Lines in ALMA Observing Windows CO Day 1 Upgrade For Z = 0.5,1,2,3,4 Age of Universe is 55%,35%,19%,12%,9%

Gas Density & Temperature from Spectral Lines Lower J CO population ratios “thermalized” – i.e. line intensity same as that of a Black Body at temperature T, indep of n(H 2 ) Hence: CO gives Temperature J=0 J=1 J=2 J=3 J=4 EJEJ CO Energy Levels But generally intensity depends on n(H 2 ), Temp Intensity(J+1,J) =f{n(J+1),n(J)} where all n(J) depend upon n(H 2 ), T Calculate n(H 2 ) required to produce n(J) values that yield observed intensities => cloud mass

Outflow rates depend on contents of buckets Pump rates depend upon depth of reservoir In Equilibrium: Inflow rate = Outflow rate for each bucket Solve system of equations for contents of each bucket Calculating Contents of Leaky Buckets

Courtesy W. Holland

Black Body and Dust Emission For interstellar clouds peak is at mm wavelengths Position of peak => Temperature Dust emission approximates Black Body – i.e. F( ) = B(,T)Q( ) Dust emission spectrum => Temperature from peak, dust mass from flux Emission wideband; Sensitivity  [Bandwidth] 1/2 Planck Function, B(,T) Courtesy W. Holland

Courtesy W. Holland

Courtesy W. Holland

B  Polarization vector Dust Grain Emission Reveals Magnetic Field Direction Grains rotate due collisions Long axis  magnetic field Emission polarized  magnetic field direction in IS Clouds

Summary Millimetre astronomers study cold universe Cold clouds consist of 99% gas, 1% dust Dust is optically opaque => “Dark” clouds Gases emit spectral lines, dust continuum Millimetre astronomy – origin of stars, planets, earliest galaxies Planets, satellites, comets, asteroids Chemistry, kinematics, temperature, mass, distance Key Aspects of Millimetre Astronomy

Summary Band 3’s Importance for ALMA Pointing (Day 1) Phase calibration (Day 1) Holographic panel adjustment (Day 1) Useful under all weather conditions Will always be on; used for all projects Astronomically important; many science uses Will be most commonly used band – essential for successful technical and scientific ALMA operations