The EVLA and SKA pathfinder surveys Jim Condon NRAO, Charlottesville

The EVLA recycles VLA infrastructure The VLA is a 1960’s design 27 x 25-meter VLA parabaloids – Off-axis Cassegrain optics for > 1 GHz Many km of railroad tracks: – 4 scaled arrays, 1 ‒ 36 km – Selectable resolution and brightness sensitivity – Good imaging with nearly natural weighting – Multiwavelength spectra at constant angular resolution Leiden 2011 Feb 24

The EVLA recycles VLA infrastructure VLA was designed in the 1960’s Advantages: – Already exists and paid for! – Works well 1 to 50 GHz – Sensitive and flexible Disadvantages: – Small field of view – Many competing users Leiden 2011 Feb 24

What’s new? 1. Receivers and feeds for continuous coverage from 1 to 50 GHz Band (GHz) T sys /  (best weather) 1-2L S C X Ku K Ka Q L K Q Ka X C S Ku Feed Heaters

What’s new? 2. The ‘WIDAR’ correlator The key element of the EVLA is its `WIDAR’ correlator – a 10 petaflop computer Major capabilities: – 8 GHz/polarization maximum instantaneous bandwidth – Spectral dynamic range up to 58 dB – Extensive special modes – 64 independently tunable full polarization ‘spectral windows’, each of which effectively forms an independent ‘sub-correlator’ Leiden 2011 Feb 24

Summary of wideband coverage: Freq.IF BWSW Width # SWP Freq. Res. Vel. Res. Nch per NchData rate* GHz MHzkHzkm/sspctrmtotalMB/s L1— S2— C4— X8— U12— K18— A26.5— Q For dual (RR,LL) polarization, with recirculation For full polarization, spectral channels are 2 x wider. * With 10 second averaging Leiden 2011 Feb 24

EVLA sensitivity The table gives the 1-hour, 1-  point-source sensitivities, in continuum and line (1 km/sec) BandCodeEffectiveB W SEFD  (cont)  (line) GHz Jy  Jy mJy 1 – 2L – 4S – 8C – 12X – 18Ku – 27K – 40Ka Q

How can the EVLA contribute? The EVLA already exists, so it can be used now to develop imaging techniques on real data: 1.Wideband imaging 2.High-fidelity imaging The EVLA can support other surveys with 1.Reference fields 2.High-frequency survey? 3.CO spectroscopy 4.Continuum spectral indices 5.High angular resolution and position accuracy

Wideband imaging The EVLA will often be operating in ‘wideband’ mode, with large fractional bandwidths:  ~ 1. Source structures change significantly over this range – cannot simply grid all channels on one transform plane. The primary telescope beam scales with -1 – introducing a ‘false’ spectral index. Deconvolving all background sources – even beyond the main beam – is necessary to achieve full sensitivity. Leiden 2011 Feb 24

High-fidelity imaging The super-linear design of the EVLA should enable much higher DR imaging than before, so DR will be limited at virtually all bands by various primary-beam issues: – Systematic pointing offsets – Unsteady tracking – Noncircular beams (alt-az mount telescopes) – Polarization beams (special case of above). Leiden 2011 Feb 24

3C147 deep 1440 MHz Detailed testing underway with 12-station, full polarization, 4 subband initial configuration. Most demanding testing is at L- band, short spacings. 12 antennas, 110 MHz, 6 hours integration Best image so far: 400,000:1 DR for 3C147. (850,000:1 to noise in corners). Some artifacts visible – due to noncircular primary beams. RMS noise in corners ~ 1 millionth of the peak. First Null 50% power Leiden 2011 Feb 24

3C147 field at L-Band with the EVLA Only 12 antennas used Bandwidth: 128 MHz ~7 hr. integration Dynamic range: ~700,000:1 3C147: Residual errors in the full field Smearing and W-Term errors Errors due to PB pointing Errors due to PB sidelobes Leiden 2011 Feb 24

High-Fidelity Imaging – Cygnus A Cygnus A, observed with WIDAR last year at X band (3.6 cm), self- calibrated and imaged with the best modern methods, provided an image: – No better than that which Rick Perley made 25 years ago with the VLA – A noise level 1000 times the thermal noise! Leiden 2011 Feb 24

What Went Wrong? What is wrong with Cyg A? Clearly associated with imaging/self-calibration. Many ideas – little progress… Important problem that must be solved. Image of the calibrator for Cygnus A DR is ~650,000:1 Noise is 6  Jy (thermal) 0.004% of peak! Leiden 2011 Feb 24

CO in submm galaxies Leiden 2011 Feb 24 Low-excitation molecular gas in active star forming galaxies at z~2, during the ‘epoch of galaxy assembly.’ These observations show more total gas, by a factor 2, than previously derived from higher order transitions and indicate that the gas is extended on scales ~ 16 kpc. They challenge many preconceptions on massive galaxy formation at high z. (Ivison et al 2011, MNRAS, in press).

Molecular gas in lensed LBGs The Ka band has performed the first imaging of molecular gas in normal star forming galaxies at high redshift (LBGs) Two strongly lensed were detected in CO1-0. The gas masses, gas fractions, moderate CO excitation, and star formation efficiencies are comparable to low-redshift star-forming galaxies 16 Riechers et al., 2011, ApJ,724, L153

CO in the most distant starburst galaxy at z = 5.3 The EVLA and the PdBI found CO emission from the most distant known submm galaxy at z=5.3. These observations show the cold gas that fuels the star formation, implying extreme amounts (>10 10 M ☉ ) of dense gas in this forming elliptical galaxy. (Riechers et al. 2010, ApJ, 720, L131)

4.051 z= mJy CO2-1 46GHz 0.4mJy 1000 km/s 0.3mJy SFR ~ 10 3 M o /year M gas ~ M o Early, clustered massive galaxy formation GN20 molecule-rich proto-cluster at z=4 (Daddi) CO 2-1 in 3 submm galaxies, all in 256 MHz band Evolving Universe Leiden 2011 Feb 24

EVLA as SKA pathfinder: counts of very faint sources Local visibility function ϕ (L) = L 5/2 ρ (L) yields counts normalized by static Euclidean counts ∆ log(L) ~ 1.2 evolution for all radio sources ~ 0.8, ∆ log(z) ~ 0.5 over wide flux range (more sensitive survey ≠ “deeper” survey) stars AGN stars

Simple model counts ≈ Wilner et al. (2008)

The EVLA as an SKA pathfinder: deeper knowledge through confusion

Ultimate limits for radio continuum surveys confusion:  c ~.03 K at 1.4 GHz) instrumental natural field of view Ω dynamic range noise 

Summary: Examples of possible EVLA contributions CO J=1-0 spectra of high-z galaxies, clusters, and quasars Continuum radio spectra of individual sources and fields All-sky 6 cm NVSS for spectra of stronger (more luminous) AGN Sky density of faint sources “Reference” field with higher resolution and sensitivity than EMU/WODAN surveys Leiden 2011 Feb 24