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Astronomy 423 at UNM Radio Astronomy
Radio Astronomy Intro, part 2 Greg Taylor University of New Mexico Jan 24, 2011
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G. Taylor, Astr 423 at UNM
Announcements
• Observing proposals for EVLA and VLBA time due tomorrow, Jan 25 by 3pm MT. Just one paragraph (references optional) – I want at least one from everybody (can use today’s suggestions) – Strongly advise against “detection experiments”
• Graduate credit for properly enrolled Graduate students should happen automatically. If not, then turn in green card to OGS
Astronomy 423 at UNM Radio Astronomy
More Science with the EVLA Some Possible EVLA Observing Projects
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G. Taylor, Astr 423 at UNM
What are the benefits to doing radio astronomy?
1. can do it easily from the ground, day and night!
2. some objects/processes are easier to detect in the radio compared to other wavelengths
cheap, easy to repair, upgrade round the clock observations – efficient observatories
- some distant, active galaxies are dominated by radio emission
- jets from accretion onto a black hole
- interstellar gas clouds between interacting galaxies - magnetic fields
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G. Taylor, Astr 423 at UNM
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G. Taylor, Astr 423 at UNM
Name that planet observed in the radio with the VLA
detection of the magnetic belts around Jupiter
synchrotron emission from energetic particles in magnetic fields
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G. Taylor, Astr 423 at UNM
Solar activity in the radio 8
G. Taylor, Astr 423 at UNM
What are the benefits to doing radio astronomy?
3. radio waves can propagate (fairly easily, sometimes affected) through the interstellar medium
unprecedented views of distant parts of our Galaxy reveal details of visibly obscured regions – star formation
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G. Taylor, Astr 423 at UNM
• Our Galactic center (GC) is 25,000 ly away (8000 pc) • GC lies behind 30 visual magnitudes of dust and gas
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G. Taylor, Astr 423 at UNM
VLA image at λ=90 cm
~45” resolution inner few degrees
of the Galaxy
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G. Taylor, Astr 423 at UNM
“Mini-spiral” of gas spiraling around (and onto) the central supermassive (~4 x 106 Mo black hole), SgrA*
6 cm VLA image (Ekers et al. 1983)
10’=25 pc
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G. Taylor, Astr 423 at UNM
VLA 20 cm Lang, Morris & Echevarria 1999
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G. Taylor, Astr 423 at UNM
Possible VLA project #1
• Look at 21cm observations of some compact galaxies – Look at rotation curves to learn about kinematics – Measure the HI content of some galaxy or group of galaxies – Look for HI deficiency in clusters of galaxies
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G. Taylor, Astr 423 at UNM
What are the benefits to doing radio astronomy?
4. radio emission provides a wide variety of quantitative physical information about the source
radio continuum emission - spectral index (flux as a fxn. of frequency) = energetics - brightness/flux = density, strength of magnetic field number of illuminating stars
radio spectral line emission - width, amplitude of the line = temperature, density - velocity = kinematic motions of gas, distance
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G. Taylor, Astr 423 at UNM
0218+35
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G. Taylor, Astr 423 at UNM
Possible VLA project #2
• Look at new transitions (5 GHz OH, lines ~30 GHz) – Look at a Gravitational Lens to study ISM of distant galaxy – Look at a star forming region in our own galaxy
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G. Taylor, Astr 423 at UNM
Differences between optical and radio observing
Optical
direct detection via CCD of the cosmic photon, strikes CCD DETECTION
Radio
- radio wave (cosmic signal) is so weak that it needs to be amplified in order to be processed radio hardware
- measure the wave properties of the radio wave, then reconstruct radio signal
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G. Taylor, Astr 423 at UNM
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G. Taylor, Astr 423 at UNM
Parkes 64-m in New South Wales, Australia
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G. Taylor, Astr 423 at UNM
Arecibo Radio Telescope, Puerto Rico
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G. Taylor, Astr 423 at UNM
• Frequencies ranging from 330 MHz to 86 GHz
• Angular resolution to 100 microarcseconds at highest frequency
Very Long Baseline Array (VLBA)
Dedicated in 1993
10 antennas recording to tape
Correlator in Socorro, NM
Combinable with Global Arrays
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G. Taylor, Astr 423 at UNM
VLBA Time Lapse Movie
courtesy Enno Middelberg and the NRAO site Techs
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G. Taylor, Astr 423 at UNM
Primary Beam
l=sin(θ), D = antenna diameter in contours: at factors of 3 increments wavelengths dB = 10log(power ratio) For VLA: θ3dB = 1.02/D, First null = 1.22/D
πDl
Antenna Performance Parameters
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G. Taylor, Astr 423 at UNM
The VLBA 10 antennas each 25 m in diameter
Synthesised aperature over 8 hours.
VLBA Synthesised Aperture 26
G. Taylor, Astr 423 at UNM
image courtesy Lincoln Greenhill (see Miyoshi et al 1995 Herrnstein et al 1999)
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G. Taylor, Astr 423 at UNM (Peck et al 2003) (today…)
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G. Taylor, Astr 423 at UNM
(Peck et al 2003)
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G. Taylor, Astr 423 at UNM
Possible EVLA/VLBA project #3
• Search for water masers – In the galactic center or in star forming regions – Measure line widths, kinematics – Consider physical conditions for any detected masers
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G. Taylor, Astr 423 at UNM
Hydra A
Taylor (1996)
core:
τ ~ 0.8
FWHM = 80 km/s
NH = 1 x 1024 cm-2
for Tspin = 8000 K
Virial Mass
M ~ R v2 / G
M ~ 2 x 107 Msun for r=50 pc
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G. Taylor, Astr 423 at UNM
HI absorption in PKS 2322-123
Taylor et al. (2000)
core:
τ ~ 0.26 FWHM = 735 km/s NH = 3 x 1024 cm-2
for Tspin = 8000 K
M ~ 109 Msun for r=50 pc
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G. Taylor, Astr 423 at UNM
Gas in 4C31.04
size pc67 1−h
Perlman et al
2001
HST imaging
4C31.04
Z=0.06
Conway 1996
VLBA 1.4GHz
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G. Taylor, Astr 423 at UNM
HI absorption in 1946+708
Peck & Taylor (2001)
“Global” VLBI observations
core:
τ ~ 0.2 FWHM = 350 km/s NH = 3 x 1023 cm-2
for Tspin = 8000 K
M ~ 108 Msun
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G. Taylor, Astr 423 at UNM
0402+379
Rodriguez et al. 2006
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G. Taylor, Astr 423 at UNM
0402+379
v ~ 600 km/s r ~ 7 pc
M(C2) ~ 7 x 108 Msun
Rodriguez et al. 2009
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G. Taylor, Astr 423 at UNM
Possible VLA project #4
• Measure large scale HI in 0402+379 – Determine extent of HI absorption in space/velocity – Measure line widths, kinematics
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G. Taylor, Astr 423 at UNM
Peck & Taylor (2001)
Spectral index map from 1.3/5 GHz VLBI observations
free-free optical depth:
τff ~ T-3/2 ne2ν-2 d
Ne ~ 3 x 1022 cm-2
ionization ~ 10%
Free-free absorption in 1946+708
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G. Taylor, Astr 423 at UNM
Centaurus A – a peculiar galaxy with extensive radio lobes
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G. Taylor, Astr 423 at UNM
(Peck 1999)
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G. Taylor, Astr 423 at UNM
Possible VLA project #5
• Search for HI absorption against newly discovered CSOs – Determine extent of HI absorption in space/velocity – Measure line widths, kinematics
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Further Reading 46
G. Taylor, Astr 423 at UNM
Blackbody Radiation
• Next class: To the chalk board