Oct 16, 2008, SFIG, Zhiyu Zhang, Seminar 2008 Introduction of Radio Interferometry and the EVLA Zhiyu Zhang

Oct 16, 2008, SFIG, Zhiyu Zhang Introduction of interferometers Fundamental of interferometry Next generation radio interferometers Introduction of E-VLA Science cases Summary Outline

Oct 16, 2008, SFIG, Zhiyu Zhang Introduction of interferometers Real time m–cm: WSRT, GMRT, VLA, ATCA, etc. Mm: CARMA, PdBI, etc. Sub-mm: SMA etc. VLBI E-MERLIN, EVN, VLBA, LBA, Space-VLBI(VSOP) etc. Optical: VLT-I, and?

Oct 16, 2008, SFIG, Zhiyu Zhang Advantage and shortcoming Best resolution – VLBI ~10 -6 arcsec, Much better than single dish telescopes at the same band!!! Stable -- even part of it can work. Flat baseline – much better than single dish 3-D data cube -- 4-D information. position, intensity, and spectral line. Tracing position – Spacecrafts, asteroid, etc. Rapid response – Pulsar Very long time integration – more than one day, can be thousands of hours ____________________________________ Missing flux -- can be partly adjusted Expensive -- cost for correlators Deconvolution algorithm -- fast Fourier transition, not only one solution Complicated calibration – phase, flux, bandpass etc. Data reduction – hard to study

Oct 16, 2008, SFIG, Zhiyu Zhang Fundamental Angular resolution ~ λ/B & frequency Resolution -- depends on shortest & longest baseline Field of view (FOV) -- equal to single dish main beam UV-coverage -- depends on earth rotation, and configuration of antennas. interpolating & imaging quality Antenna configuration – beam response and better UV-coverage Phase Calibration -- calibration for position Bandpass calibration -- calibration for spectra Flux calibration -- calibration for flux De-convolve algorithm -- CLEAN, MEM, Hybrid, etc.

Oct 16, 2008, SFIG, Zhiyu Zhang D Single dish:  = /D B Interferometer:  = /B Scheme

Oct 16, 2008, SFIG, Zhiyu Zhang combine signals from two antennas separated by baseline vector b in a correlator; each sample is one “visibility” each visibility is a value of the spatial coherence function V (b) at coordinates u and v obtain sky brightness distribution by Fourier inversion: Visibility

Oct 16, 2008, SFIG, Zhiyu Zhang UV-Coverage ALMA snapshot Central hole

Oct 16, 2008, SFIG, Zhiyu Zhang Clean Imaging Weighting Self-calibration Resampling 3D-2D Algorithm: CLEAN MEM Hybrid

Oct 16, 2008, SFIG, Zhiyu Zhang Introduction of a few of next generation interferometers ATA EVLA ALMA LOFAR SKA 350x 6m 64 x 12m elements one square kilometer

Oct 16, 2008, SFIG, Zhiyu Zhang Introduction of the VLA Built 1970’s, dedicated 1980,27 x 25m diameter antennas Two-dimensional 3-armed array design Four scaled configurations, maximum baselines 35, 10, 3.5, 1.0 Km. Eight bands centered at 0.074, 0.327, 1.4, 4.6, 8.4, 15, 23, 45 GHz 100 MHz total IF bandwidth per polarization Full polarization in continuum modes. Digital correlator provides up to 512 total channels – but only 16 at maximum bandwidth. VLA in D-configuration (1 km maximum baseline)‏

Oct 16, 2008, SFIG, Zhiyu Zhang Introduction of the EVLA Sensitivity: Continuum sensitivity improvement over the VLA by factors of 5 to 20, to give point-source sensitivity better than 1 microJy between 2 and 40 GHz. Frequency Accessibility: Operation at any frequency between 1.0 and 50 GHz, with up to 8 GHz bandwidth per polarization. Spectral Capability: Full polarization (8 GHz bandwidth per polarization), with a minimum of 16,384 channels, frequency resolution to 1 Hz, and 128 independently tunable sub-bands. Resolution: Angular resolution up to 200 / (frequency in GHz) milliarcseconds with tens of Kelvin brightness temperature sensitivity at full resolution. Low-Brightness Capability: Fast, high fidelity imaging of extended low-brightness emission with tens of arcseond resolution and microKelvin brightness sensitivity. Imaging Capability: Spatial dynamic range greater than 10 6, frequency dynamic range greater than 105, image field of view greater than 109 with full spatial frequency samplng. Operations: Dynamic scheduling, based on weather, array configuration, and science requirements. "Default" images automatically produced, with all data products archived.

Oct 16, 2008, SFIG, Zhiyu Zhang Ultrasensitive Array New Mexico Array VLA by 2012 Two Phases Ten new antennas Range up to 250 Km from EVLA + WIDAR Wideband Interferometric Digital ARchitecture Receivers PHASE I PHASE II Proposed

Oct 16, 2008, SFIG, Zhiyu Zhang EVLA Phase I - Key Science Examples Measuring the three-dimensional structure of the Sun's magnetic field Mapping the changing structure of the dynamic heliosphere Measuring the rotation speed of asteroids Observing ambipolar diffusion and thermal jet motions in young stellar objects Measuring three-dimensional motions of ionized gas and stars in the centre of the Galaxy Mapping the magnetic fields in individual galaxy clusters Conducting unbiased searches for redshifted atomic and molecular absorption Looking through the enshrouding dust to image the formation of high-redshift galaxies Disentangling starburst from black hole activity in the early universe Providing direct size and expansion estimates for up to 100 gamma-ray bursts every year Main Science Projects EVLA Phase II - Key Science Examples AU-scale imaging of local star forming regions and proto-planetary disks Resolving the dusty cores of galaxies to distinguish star formation from black hole accretion Imaging at the highest resolution at any wavelength of the earliest galaxies (z~30) Imaging of galaxy clusters with 50 kpc or better resolutions at arbitrary redshifts Imaging of thermal sources at milliarcsecond scales Resolving individual compact HII regions and supernova remnants in external galaxies as distant as M82 Tying together the optical and radio reference frames with sub-milliarcsecond precision Measuring accurate parallax distances and proper motions for hundreds of pulsars as distant as the Galactic Center Providing 50 pc or better resolution for galaxies at any redshift Monitoring and imaging the full evolution of the radio emission associated with X-ray and other transients

Oct 16, 2008, SFIG, Zhiyu Zhang Resolution vs. Frequency VLA vs. EVLA A key EVLA requirement is continuous frequency coverage from 1 to 50 GHz. This will be met with 8 frequency bands: Two existing (K, Q)‏ Four replaced (L, C, X, U)‏ Two new (S, A)‏ Existing meter-wavelength bands (P, 4) retained with no changes. Blue areas show existing coverage. Green areas show new coverage.

Oct 16, 2008, SFIG, Zhiyu Zhang Resolution vs. Frequency VLA vs. EVLA

Oct 16, 2008, SFIG, Zhiyu Zhang NOISE regimes

Oct 16, 2008, SFIG, Zhiyu Zhang ParameterVLAEVLAFactor Point Source Sensitivity (1- , 12 hours)10  Jy1  Jy10 Maximum BW in each polarization0.1 GHz 8 GHz80 Frequency channels at max. bandwidth1616, Maximum number of frequency channels5124,194, Coarsest frequency resolution50 MHz2 MHz25 Finest frequency resolution381 Hz0.12 Hz3180 (Log) Frequency Coverage (1 – 50 GHz)22%100%5 Sensitivity, Bandwidth & Frequency resolution

Oct 16, 2008, SFIG, Zhiyu Zhang 1δ, 12 h integration Sensitivity

Oct 16, 2008, SFIG, Zhiyu Zhang Continuum Sensitivity vs. Frequency VLA EVLA ALMA

Oct 16, 2008, SFIG, Zhiyu Zhang SKA will have A sensitivity of hundred times of the VLA Arp 220 as a template of High Z galaxies

Oct 16, 2008, SFIG, Zhiyu Zhang 4PLCXUKQ F (GHz) (cm) (′)(′) (″)(″) Flx(mJy, 10 min) T(K) Full Band Coverage 1 ‘continuum’ (maximum sensitivity) observations 2 spectral line surveys

Oct 16, 2008, SFIG, Zhiyu Zhang FIRST A. Faint Images of the Radio Sky at Twenty-centimeters B. Flux limit = 1mJy C. Resolution limit = 5″ D. ~90/sq degree E. Coincide with SDSS NVSS ( ) A. NRAO VLA Sky Survey B. Configuration D and DnC C. F = 1.4 GHz D.  >-40° E. Completeness limit ~ 2.5 mJy F. Resolution  ~ 45″ G. 1.8  10 6 sources Survey Speed EVLAVLA

Oct 16, 2008, SFIG, Zhiyu Zhang Arp 220, Z=8? High Z CO survey

Oct 16, 2008, SFIG, Zhiyu Zhang K-band spectra, in Massive SFR, One tuning pair (4 pairs totally)

Oct 16, 2008, SFIG, Zhiyu Zhang 64 Spectral Lines, with Full Polarization, and different spectral resolution with 4-bit Re-Quantization GHz which covers 3 RRL + 1 Mol, 12 sub-band pairs (SBP) free GHz which covers 2 RRL + 3 Mol, 11 SBP free GHz which covers 2 RRL + 14 Mol, all SBP used GHz which covers 1 RRL + 14 Mol, 1 SBP free 24 SBP 40 SBP Continuum Spectra

Oct 16, 2008, SFIG, Zhiyu Zhang Ideas 1. super-fine spectral resolution observation towards molecular clouds – get the information of each clump. ( High performance in spectral observation) 2. RRL observation – Broad line region in AGNs? (High sensitivity and very broad bandwidth, and later high resolution to resolve) 3. H 2 CO maser survey in the Galaxy? (Hi sensitivity, fast survey speed, without confusion from surrounding absorption) 4. Weak molecular absorption lines towards continuum sources like SNR or quasar, as dense gas tracer. 5. I am still thinking about some interesting attempts.

Oct 16, 2008, SFIG, Zhiyu Zhang Thank You!

Oct 16, 2008, SFIG, Zhiyu Zhang Backup Slides

Oct 16, 2008, SFIG, Zhiyu Zhang Now w points to the source, u to the east, and v toward the North. The direction cosines l and m ( on the celestial sphere plane) increase to the east and the north respectively. UV-plane

Oct 16, 2008, SFIG, Zhiyu Zhang Assume small frequency width (Δν) and no motion of the source. Now consider radiation from a small solid angle dΩ from direction S Stationary, Monochromatic, Two element Interferometer It is multiply but not plus because of lower noise.

Oct 16, 2008, SFIG, Zhiyu Zhang Making a SIN Correlator

Oct 16, 2008, SFIG, Zhiyu Zhang Adding a time delay Change the spatial resolution to the resolution of time (much easier to handle)

Oct 16, 2008, SFIG, Zhiyu Zhang Visibility We now define a complex function, V, from the two independent correlator outputs: This gives us a beautiful and useful relationship between the source brightness, and the response of an interferometer:

Oct 16, 2008, SFIG, Zhiyu Zhang A Schematic Illustration 1 The correlator can be thought of ‘casting’ a sinusoidal coherence pattern, of angular scale λ/b radians, onto the sky. 2 The correlator multiplies the source brightness by this coherence pattern, and integrates (sums) the result over the sky. 3 Fringe separation set by baseline length and wavelength Long baseline gives close- packed fringes. Short baseline gives widely- separated fringes.

Oct 16, 2008, SFIG, Zhiyu Zhang Can’t be sampled, missing flux

Oct 16, 2008, SFIG, Zhiyu Zhang UV Coverage of the VLA/EVLA Missing flux

Oct 16, 2008, SFIG, Zhiyu Zhang

Dirty beam

Oct 16, 2008, SFIG, Zhiyu Zhang Software Newstar :WSRT, Nobeyama, etc. GILDAS(MIRA) :IRAM PdBI MIRIAD :WSRT, ATCA, CARMA, SMA etc. AIPS :VLA, VLBA, etc. MIR :SMA AIPS++ => CASA :ALMA, EVLA, PdBI, etc. Uniform, convenience, good at imaging Powerful, complicated, good at calibration and specific usage Powerful, Uniform, Convenience, Still in programming

Oct 16, 2008, SFIG, Zhiyu Zhang H71  H70  H69  H68  H67  H66  H65  H64  H63  H62  K-band spectra line excitation temperature?