1. Extragalactic Science
Jim Condon
Extragalactic science with radio aperture-synthesis interferometers. Note the large number N of telescopes. High-sensitivity, high dynamic range aperture-synthesis interferometry is unique to radio wavelengths because of quantum noise in coherent amplifiers; optical interferometers must divide signals from each telescope and correlate before amplification so sensitivity falls as N grows.

2. Eleventh Synthesis Imaging Workshop, June 10-17, 2008
Why Synthesis Imaging?
Angular resolution can be specified by the observer (to reduce “confusion,” match angular scales of the source or multiwavelength data -- but trade off surface-brightness sensitivity)
Extremely accurate absolute astrometry
(high angular resolution, clocks instead of rulers, no plane-parallel refraction)
High dynamic range via deconvolution and self-calibration “fixing” telescope
High sensitivity via long integrations, suppression of “baseline” errors and RFI
(Figures from Brunthaler et al. 2005, Science, 307, 1440)
Angular resolution (beats confusion, tradeoff with surface-brightness sensitivity, highest at “longest” radio wavelengths) and high astrometric accuracy. Compared with single dish, interferometer uses time delay (time measured very accurately) and not physical pointing (hard to measure accurately), no dependence on plane-parallel refraction. Sensitivity: Multiplying interferometer minimizes “baseline” errors from gain fluctuations and allows long integrations. Fringe switching and decorrrelation reduce interference. VLA just “works well” compared with most single dishes. Past interferometer limitations on frequency coverage, bandwidth, and spectral resolution are disappearing with EVLA and ALMA.
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

3. Eleventh Synthesis Imaging Workshop, June 10-17, 2008
Extragalactic Science: The radio continuum sky at 45 arcsec resolution  Where’s our Galaxy?
The continuum radio sky varies slowly with wavelength, so the 1.4 GHz NVSS and FLS/VLA surveys (show the FLS poster ~ 120 MHz LOFAR field to rms ~150 microJy) predict what the LOFAR surveys will look like. Nearly all (1.4 GHz) radio sources are extragalactic, and even the strongest fewX10^4 are so distant that they are smoothly distributed on the sky. (In a sensitive high-resolution survey, most discrete sources in the Galaxy are planetary nebulae, not SNRs and HII regions.) At dec > 0 deg, the Galaxy is nearly invisible at 45 arcsec resolution, even less visible at 6.3 arcsec LOFAR 120 MHz resolution.
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

4. “It’s turtles all the way down”
The high-latitude sky is quite uniform at the 2.5 mJy sensitivity limit of the NVSS, even though most sources are AGN and as correlated as massive elliptical galaxies, because the sources have a high median redshift <z> ~ 0.8 and thus a low space density. Angular clustering signals are WEAK so uniform survey sensitivity, resolution, and calibration are essential to extract the signals. High dynamic range is important so sidelobes of strong sources don’t obliterate the areas of sky around them. Negligible anisotropy is introduced by dust extinction in the ISM and by contamination by foreground stars, unlike other wavebands (keep “cosmic windows” of SWIRE in mind). Data quality is needed to make use of data quantity (Lesson 2).
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

5. Flux density versus luminosity of radio sources
Evolution 10X in luminosity  few nearby sources, <z> ~ 1
“shell”  L  S
AGNs at high L, S
Star-forming galaxies at low L, S
< 1% of extragalactic radio sources at any flux density are in UGC catalog of brightest ~ 10^4 galaxies.
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

6. High Luminosity: Relativistic Jets and Lobes from AGN
Centaurus A at
radio (purple),
optical, and X-ray
wavelengths
Their high radio luminosities (Lradio ~ 10^{45} ergs/s) make radio galaxies easily visible anywhere in the universe. This led to Ryle’s discovery of
cosmological evolution ruling out the steady-state universe before the discovery of the CMB, the discovery of first quasar (3C 273), and the recognition that there must be supermassive black holes in the centers of galaxies. There is still a strong X-ray/radio connection for studying the energetics of these jets.
VLBI first measured “superluminal” motions in the relativistic jets (but no WYSIWYG makes interpretation harder).
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

7. Jet Energy via Radio Bubbles in Hot Cluster Gas
1.4 GHz VLA contours over Chandra X-ray images. X-ray brightness gives pressure, energy = work to evacuate bubbles = pressure X volume.
This reduces the long-standing “cooling flow” problem, demonstrates “AGN feedback”.
6 X 1061 ergs ~ 3 X 107 solar masses X c2 (McNamara et al. 2005, Nature, 433, 45)
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

8. Resolution and Surface-brightness Sensitivity
Match observations to phenomena over orders-of-magnitude in angular/linear size and in frequency.
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

9. Superluminal Motion in Compact Jets
First major VLBI discovery: apparent superluminal motion, implying compact jets moving highly relativisitically. No WYSIWYG makes interpretation harder. Can trace deflections by interstellar clouds, probe free-free absorption in circumnuclear ISM. Comment on radio sensitivity to plasma propagation phenomena such as free-free absorption, interstellar scintillation.
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

10. Eleventh Synthesis Imaging Workshop, June 10-17, 2008
Resolving the circumnuclear disk in NGC 4258 and directly measuring the black-hole mass
NGC 4258
NGC 4258 r
Advantages of H2O “parallaxes”: speed ~ 900 km/s >> 30 km/s, period > 1000 years, relative position accuracy ~ 10 microarcsec with phase-coherent interferometry. Also directly measures SMBH masses (use for SMBH M / bulge sigma_v correlation, estimating Eddington ratio), observe accretion disks with sub-pc linear resolution, sub km/s velocity resolution. N4258 M= X10^6 MSun. Also, proper motions ~30 microarcsec/yr for LOS component of N Acceleration ~10 km/s/yr for N Enclosed density > 10^9 MSun/pc^3. 
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

11. Eleventh Synthesis Imaging Workshop, June 10-17, 2008
Beating Confusion
1.4 GHz image made with the 300-foot telescope. Ring shows area in next slide.
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

12. NVSS (45 arcsec) grayscale under GB 300-ft (12 arcmin) contours
“RMS” confusion
c  0.2 -0.7 2
where
is in mJy/beam,
is in GHz, and
 is in arcmin
Note multiple NVSS sources contributing to one GB “source”, effect on GB positions and angular sizes. Single dishes are badly confusion limited at cm wavelengths, so interferometers are needed for sensitive continuum observations. Still a problem with GBT observers not understanding this.
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

13. Eleventh Synthesis Imaging Workshop, June 10-17, 2008
Low Luminosity: AGN+Starbursts  = 5 arcsec  = 23 mJy/beam (c ~ 1 mJy/beam)
Distant sources: need deeper surveys but can cover smaller solid angles. VLA/Spitzer FLS rms confusion is only about 1 microJy/beam. Luminosity of 100 microJy source with alpha = -0.7 at z ~ 0.8 is ~ 2.5 X 10^{23} W Hz at 1.4 GHz in source frame. Angular size of galaxies < beam, so faint radio sources mostly will be unresolved, which is good for flux-limited completeness, which is limited by surface brightness sensitivity. Sources are a mixture of “woofly” FRI AGN and starbursts.
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

14. Low Luminosity: Star-forming Galaxies
synchrotron
dust
Ubiquitous spectrum of M82 yields miraculous FIR/radio correlation, which lets radio luminosity be used as an (extinction-free) indicator of
star-formation rate. Radio is small (10^{-5}) tail of dog.
free-free
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

15. Eleventh Synthesis Imaging Workshop, June 10-17, 2008
SNe and GRBs
SNe are the ultimate energy source of most synchrotron CRs in “normal” galaxies, although discrete SNRs account for only about 10% of the synchrotron
luminosity. Individual SNe study circumstellar environment and hence pre-explosion winds. z = GRB scintillation implies size at one month ~ 3 micro arcsec ~ 10^{17} cm implies superluminal expansion with gamma ~ a few. Relativistic to nonrelativistic, calorimetry of burst energy. Get geometry: lack of VLBA proper motion rejects “cannonball” model in favor of “fireball” model. Get circumburst density. Frail, Waxman, & Kulkarni (2000).
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

16. VLBA/HSA Image of the Starburst Nuclei in Arp 220
Arp 220 = ultraluminous starbursts in nuclei of two merging galaxies. This VLBA/HSA image clearly shows that the radio sources are multiple SN3,
not an AGN. Note ~ 1000 mag of visual extinction, angular resolution possible only with aperture synthesis.
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

17. Evolution of star formation
Radio “Madau diagram”
Free from dust extinction
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

18. Star Formation at High Redshift
Arp 220 spectra at high redshifts. Note small “K” correction at frequency ~ 300 GHz favors seeing the most luminous starburst galaxies, nearly independent of distance.
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

19. Primordial Starbursts
Technique pioneered with SCUBA on the single-dish JCMT, although VLA positions are needed to make reliable optical identifications of individual galaxies and obtain redshifts. ALMA will revolutionize this field. The sky will be filled with high-redshift star-forming galaxies, and ALMA will see those having low-enough luminosities that they will account for the bulk of the star formation throughout the universe.
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

20. Radio Spectral Lines: Cold Gas
HI and cold (10s of K) molecular gas are both most visible at radio wavelengths. HI extends beyond the galaxy of stars and is an excellent tracer of
mass and galaxy dynamics. Flat HI rotation curves implied dark-matter halos of galaxies. HI data indicate galaxy distances via the Tully-Fisher relation, map out the large-scale structure of the “local” universe, and sensitively trace the debris of galaxy-galaxy and galaxy-cluster interactions. HI only probe of “dark ages” and EOR. Molecular gas (e.g., CO, HCN,..) traces dense molecular clouds where stars form.
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

21. Eleventh Synthesis Imaging Workshop, June 10-17, 2008
Crash Forensics
NGC 4038/9 and UGC 813/6. Blue = HI, white = optical, red = radio continuum. HI, CO, radio continuum are long-lived records (~ 10^8 yr)
records for reconstructing galaxy collisions.
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

22. Eleventh Synthesis Imaging Workshop, June 10-17, 2008
EVLA and ALMA
Continuous frequency coverage from 1 GHz to 50 GHz
Detect CO at almost any redshift
Study excitation of star-forming gas in distant galaxies
VLA for low-excitation temps (low J) lines of CO, HCN at high z, and massive molecules in cold molecular clouds at low z.
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

23. The Most Distant Quasar
Walter et al. 2003
Optical Image
VLA image of CO (4-3) from the first known star formation
Redshifted to 46 GHz
Artist’s conception of disk of molecules and dust
z = 6.4 source in EOR, high mass of molecular gas and supermassive black hole only ~ 700 Myr after big bang.
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

24. Geometric Distances, H0, and Dark Energy
Preliminary
Properties of UGC 3789 Maser Disk
R ~ pc ( mas)
V ~ km/s
Mbh ~ 1.2 x 107 Msun
a ~ 3.6 km s-1 yr-1 (mean value)
D ~ 51 Mpc (15%)
H0 ~ 64 km s-1 Mpc-1
Cosmology (H0 and dark energy) exploiting the strengths of radio synthesis observations: penetrating dusty edge-on circumnuclear disk, measuring tiny accelerations (few km/s/year) of individual maser lines with high accuracy (frequency/time, not wavelength), 300 microarcsec resolution, differential astrometry with 10 microarcsec accuracy to measure geometric distances to galaxies up to ~ 100 Mpc, determine Hubble constant without the systematic errors associated with distance ladders based on standard candles, and thereby constrain the dark-energy equation of state.
Eleventh Synthesis Imaging Workshop, June 10-17, 2008

25. Eleventh Synthesis Imaging Workshop, June 10-17, 2008
The End...
End of talk. End of workshop. But not the end of synthesis imaging. Use what you have learned as a beginning to write a great proposal to make great observations with the E/VLA, VLBA, and ALMA and do great astronomy.
...NOT!
Eleventh Synthesis Imaging Workshop, June 10-17, 2008