The Future of the Past
Harvard University Astronomy 218 Concluding Lecture, May 4, 2000
"Radio" Observations of the Redshifted Universe: c. 2000
1000 100 10 1 0.1
OVRO, BIMA, PdB 30-m,14-m, 12-m JCMT, CSO, HHT
Wavelength [cm]
VLA, Arecibo
0.01 0.001 1
2
3
4
5
6
7 8 9
2
Redshift
10
"Radio" Observations of the Redshifted Universe: Recent Additions by ~2009 LOFAR
1000
100
Wavelength [cm]
VLA+, GBT
10
1
GBT LMT
0.1
0.01
SMA
0.001
1
2
3
4
5
6
7 8 9
2
Redshift
10
"Radio" Observations of the Redshifted Universe: c. 2015 LOFAR
1000
100
Wavelength [cm]
SKA
10
1
ALMA
0.1
0.01
0.001
1
2
3
4
5
6
7 8 9
2
Redshift
10
The Atacama Large Millimeter Array (ALMA)
• No less than 64 12-meter antennas located at an elevation of 16,400 feet in Llano de Chajnantor, Chile • Imaging instrument in all atmospheric windows between 1 cm and 350 microns • Array configurations from approximately 150 meters to 10 km • Spatial resolution of 10 milliarcseconds, 10 times better than the VLA and the Hubble Space Telescope • Able to image sources arcminutes to degrees across at one arcsecond resolution • Velocity resolution under 0.05 km/s • Faster and more flexible imaging instrument than the VLA • Largest and most sensitive instrument in the world at millimeter and submillimeter wavelengths • Point source detection sensitivity 20 times better than the VLA
Sample SKA Design Specifications
Aeff /Tsys: 2 x 104 m2 K-1 (or 0.003ha-1 Jy K-1) Total Frequency Range: 0.15 - 20 GHz Imaging Field Of View: 1º @ 1.4 GHz Instantaneous Pencil Beams: 100 Separation of Beams: 100º (low n); 1º (middling n ) • Number of Spatial Pixels: 108 • Angular Resolution: 0.1” @ 1.4 GHz • Continuum Surface Brightness Sensitivity:
– 1 K @ 0.1” (continuum)
• • • • •
Instr. Aeff/Tsys 70m 145 GBT 285 VLA 280 Arec 1,414 ALMA 98 1HT 193 DSNarr 3,547 SKA 20,000
• • • • •
Instantaneous Bandwidth : 0.5 + n/5 GHz Number of Spectral Channels: 104 Number of IF bands: 2 Clean Beam Dynamic Range: 106 @ 1.4 GHz Polarization Purity: -40 dB
SKA Scheme for Distribution of Antennas
Processor
SKA H I Redshift Surveys
Number of detected galaxies and volume sampled for a number of recent large galaxy redshift survey projects. Optical surveys are shown in blue and HI(HIPASS) surveys in red. The SKA would sample to greater depths than presently possible, and would sample galaxies in atomic hydrogen, thereby viewing galaxian masses independent of stellar content or star formation history
Techniques for the Future
• On-the-fly mapping • Multi-beam arrays • Snapshot aperture synthesis (no reliance on Earth rotation) • Massive mosaicing • Improved "corrections" for short-spacing hole • Remote observing • Orbiting elements in VLBI