MMA Imaging and Calibration Group

Agenda for meeting Mon, 8 March 1999 at 4pm EST.

Date: Mon, 8 March 1999

Time: 4:00 pm EST (2:00 pm Socorro, 2:00 pm Tucson)

Phone: (804)296-7082 (CV SoundStation Premier Conference phone).

Past minutes, etc on MMA Imaging and Calibration Division Page

Agenda

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European Meeting

Bob has issued a report.

Antenna RFP Meeting 5 Mar -- Mangum

Antenna Polarization Issues -- Crutcher, Wootten

After the discussion at the Euro meeting, I asked Dick Crutcher about requirements for polarization. Here is his response:

While having all MMA receivers linear probably makes sense from the technical perspective of building them, it does have an unfortunate implication. We have a single linear feed at Hat Creek, and observe linear polarization by putting a quarter-wave plate at 45 deg. in front of the feed to convert to circular polarization. Then rotating this plate by 90 degrees converts from right (say) to left. Cross-correlating circular polarization responses then gives directly the sum and difference of the Stokes Q and U linear polarization Stokes parameters, without having to subtract two quantities dominated by Stokes I. This works well, and appears to be the proposed system for the MMA. The only defects are that the quarter wave transmission plates are narrow band and add non-negligible noise. As I understand it, the MMA polarization system for observing linear polarization will work like this and have these disadvantages. I suspect most polarization work with the MMA will be linear rather than circular, so unless there is something I'm missing the MMA will not be optimized for its dominant polarization mode.

To derive circular polarization with such a system, you take the measured RR = I + V and LL = I - V and subtract them to get Stokes V; this is very subject to error since you are subtracting two big numbers to get a small number. If you really want to measure circular polarization, it is best to have half-wave plates so you can rotate the linear feed responses, and cross-correlate the linears to derive circular without having to subtract two big numbers. We built such half wave plates for Hat Creek at 113 GHz. But perhaps the MMA feeds are rotatable (?), so a half-wave plate is unnecessary. If they are not planned to be rotatable, consideration should be given to making them so.

I personally would have preferred intrinsically circularly polarized feeds, so one could derive linear polarization from RL and LR without the loss, narrow bands, and hassle that plates introduce.

Configurations - Kogan

Leonia has produced some 64 x 12m configurations:

I have carried out the optimization of the compact configuration with 64 antennas. I have the original configuration (three circles) and the optimum configurations for the circle areas of optimization with radius 10 and 20 synthesized beams. The plots of relevant beams are available also. The primary beam of the 12 meter antenna should have the 0.5 double width 11" at the used wavelength 0.85mm.

The minimum spacing 15m used as a constraint on the optimization.

Optimization of the compact configuration with 64 antennas. The beams shape shows the optimization in the predicted area. Original configuration has sidelobes 13%. Here we have the configuration. Optimization of the compact configuration with 64 antennas, showing the beam shape.

The optimum configuration for the small area (10 synthesized beam) gives sidelobes better 1%. Here we have the configuration. The optimum configuration for the small area (10 synthesized beam), showing the beam shape.

The optimum configuration for the big area (20 synthesized beam) gives sidelobes better 4%. Here we have the configuration. The optimum configuration for the big area (20 synthesized beam), showing the beam shape.

PR - Wootten

Let's discuss the simulation of the HDF some more. Examples are collected at: the zlines page . Avery has questioned Blitz's contention that SKA will provide a better instrument with which to measure CO at z>3.6. Let's evaluate that claim. Lorne says:
This is the note I'm sending to Ralph Pudritz, chair of our Long Range Planning Panel. I haven't done any modeling - just tried to do some scaling with z of a reduced (by 10 times) IRAS 10214 CO spectrum. When the LRPP was in Victoria, you asked me to submit a summary of the capabilities of the LSA/MMA for high-z CO line observations. This request grew out of our discussion of your statement at the Town Hall meeting that "the LSA/MMA would permit observations of CO out to z=4 "where the SKA would take over for sources at higher z".

The CO spectrum consists of regularly spaced lines at intervals of 115 GHz with the CO 1-0 line at 115.3 GHz being the lowest frequency. The wide bandwidth coverage proposed for the LSA/MMA means that, for any z from 0 to at least 20, there will be at least 6 CO transitions observable (up to ~12 at higher z). Such broad coverage is important for excitation studies.

Below I have estimated the time required to detect some of these CO lines as a function of z. I've taken the LSA/MMA sensitivities for a 60 x 12m array from Table 1 of MMA Memo 177 by Mark Holdaway. The tabulated times are for a 5-sigma detection of a galaxy with excitation conditions similar to IRAS10214+4724 but with 1/10th the observed CO luminosity found by Solomon et al ApJ 398,L29, 1992. This reduced luminosity is comparable to that of brighter Sb and Sc galaxies and less than that modeled by Silk & Spaans (ApJ 488,L79,1997) for high-z starbursting galaxies.

I haven't had time to extend the calculations beyond the 6-5 line, but the models indicate that, for starburst galaxies at high z (where Tbg is also high), the CO lines up to J~12-11 will be efficiently excited.

Table 1.The time, t, for a 5-sigma detection with the LSA/MMA of a compact galaxy with CO line luminosity 10% that of IRAS10214+4724. The blank entries in the time columns indicate that the observed frequency falls below 30 GHz. S is the flux.

CO 1-0 CO 2-1 CO 3-2 CO 4-3 CO 6-5
z S(mJy) t S(mJy) t S(mJy) t S(mJy) t S(mJy) t
1 0.88 5.2min 3.5 10sec 7.9 2s 14.1 1s 18.1 1s
2 0.28 77m 0.98 3.1m 2.6 19s 4.5 5s 5.8 3s
3 0.15 -- 0.61 10.8m 1.4 1.5m 2.4 21s 3.1 8s
5 0.072 -- 0.29 73.5m 0.65 9.5m 1.2 2.3m 1.5 1m
10 0.028 -- 0.11 -- 0.25 117m 0.45 27.3m 0.58 11m
20 0.012 -- 0.047 -- 0.11 -- 0.19 -- 0.24 121m

Note that, for a given z, the flux in the line increases with increases frequency. For the starburst models of Silk & Spaans, the peak flux occurs near the J= 7-6 line, with a rest frequency of 807 GHz. It's also worth noting that all the important cooling lines of [CI] (809GHz), [NII](1460 GHz), [CII](1901 GHz) and N[II](2459 GHz), which were observed by COBE to be of much higher luminosity in the Milky Way than the CO lines, will be accessible with the LSA/MMA for z>~1.5.

I have prepared a plot of the above observing times vs z.
Lorne Avery's plot of observing time for various CO transitions versus z.

Harvey has examined the question of the relative strengths of the CO lines:

Below is a ... figure illustrating what happens to the brightness temperature emerging from various characteristic Milky Way molecular gas lines of sight when the local cmb temperature varies as (1+z). There's no attempt to simulate cloud evolution, that is definitely not the point.

(a) at upper left is a typical dark cloud line of sight through a gas column with 5 magnitudes of extinction, constant density 1280 H2/cc (there isn't enough atomic gas left to matter). The thermodynamics are included; the kinetic temperature varies from a few 10's of K at the edge to 9.5 K inside.

This is the kind of cloud which makes up the bulk of the emission from surveys of the galactic plane, as judged by the J=1-0 and J=2-1 lines. I didn't want to be too pessimitic about the effect of z on the J=1-0 line so this model has a J=2-1/J=1-0 intensity ratio of ~ 0.7 at z = 0 whereas I (1993 Ap J 411 720) saw a ratio more like 0.5 in the real MW.

(b) is an example of a really mild PDR in which a moderate-extinction gas column exposed to the interstellar far uv is dense enough to make lots of CO. The J=2-1/J=1-0 ratio is too high and the J=1-0 lines are too bright for this model to be characteristic of the MW galactic plane survey gas.

(c) is a strong PDR in which the far-uv field is taken to be 250 x normal and the density is jacked up to 10^5. Note that the ordinate here is linear. The change in intensity is due solely to the rayleigh- jeans correction.

regards, Harvey

Harvey Liszt's figure showing the excitation of CO in various cloud types.

Also see emails from Simon, Min and Bryan further from Harvey. See also: F. Combes, R. Maoli, and A. Omont, CO lines in high redshift galaxies: perspective for future mm instruments, accepted in A&A

which you can get off the astro-ph web site (xxx.lanl.gov/archive/astro-ph) as astro-ph/9902286

I updated the MMA history, which I put at our site. Any comments? I will abstract some points from this for a history slide.

Fall 99 Meeting - Wootten

Note that the 12m '30th birthday meeting' will be of substantial interest to our group:

6- 9 Jun 'Imaging at Radio through Submillimeter Wavelengths' meeting in Tucson

As you may know, a meeting of U. S. and European scientists is being planned for the Fall of 1999 in Washington, D. C. The goal of the meeting is to review the scientific program planned for the joint array and how that program interacts with the science goals of other astronomical facilities expected to be operational at the time that the MMA/LSA becomes operational.

Please comment upon the proto schedule for the Science With A Large Millimeter Array meeting at:

LMA99

Science topics for this suggestion were drawn from those identified by the 1997 Thaddeus committee (Task Group on Space Astronomy and Astrophysics, Committee on Astronomy and Astrophysics, Board on Physics and Astronomy, Space Studies Board, Commission on Physical Sciences, Mathematics and Applications, National Research Council) report A New Science Strategy for Space Astronomy and Astrophysics", or by McKee:

McKEE's PROPOSED DRAFT SCIENCE PRIORITIES (12/98)

  • PRIMARY
  • -The large scale structure of the Universe
  • -The formation and evolution of galaxies
  • -The formation and evolution of stars
  • -The formation and evolution of planets, particularly habitable planets
  • SECONDARY
  • -The impact of the astronomical environment on the Earth
  • -The nature of dark matter
  • -The origin of the elements
  • -The formation and evolution of black holes
  • -The origin of high energy particles and photons
  • -The origin and evolution of magnetic fields

We might further limit them to those for which we thought that the MMA would provide deep impact. Modifications and suggestions are welcome.

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Action Items 8Mar99

UPCOMING REVIEW: On or before 31 May 1999 we review results from the OVRO and BIMA phase correction systems.

REVIEW: 5 Mar 99 Antenna RFP review. Mangum to represent MMA ImCal. DECISION: 183 GHz or 22 GHz phase correction?

DECISION: Is a nutating secondary necessary?

DECISION: What is the effect of 1/f noise in the HEMT amplifiers of SIS receivers upon our ability to combine total power and interferometric images into a faithful representation of the sky?

MEETINGS: MAC meeting 17 Mar 1999 at noon. ------

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Travel

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T. Helfer:

A. Wootten: 12-13 April 43m observing 22-30 May househubby 9 - 13 Jun CSO

J. Mangum:

M. Yun:

B. Butler:

S. Radford: