Title Calibrating the I_CO to N(H_2) Conversion Factor in Nearby Galaxies Pi D. Meier Time 140 hrs 1. Name: Calibrating the I_CO to N(H_2) Conversion Factor in Nearby Galaxies --D. Meier, J. Turner et al. 2. One short paragraph with science goal(s): Directly or indirectly, the uncertainties in the validity of the conversion factor between I_co and N(H_2) (Xco) limits precision determinations of the molecular universe. Detailed spatially resolved observations of GMCs in galaxies other than our own are vital to investigations of the reliability of CO as a mass tracer under varying influences. Does Xco depend on the dynamics of the region, that is, are virialized GMCs a requirement for the applicability of Xco? Under virial conditions it is predicted that Xco depends on n^0.5/T. Is this relation observed and if so how much data must be observed in order to establish H_2 densities and temperatures accurately enough to correct the standard value? Is Xco dependent on observed sizescale as would be expected if internal cloud structure changes with size? Is Xco a function of galactocentric distance? Does Xco obtained in lower metallicity outer disks of spirals overlap Xco determined in similar metallicity dwarfs? Finally, since it is known that the higher J transitions of 12CO are susceptible to photospheric effects, can one directly establish a 12CO(2-1) or 12CO(3-2) "conversion factors", which will be more suitably to high redshift observations, and in general, the high sensitivity "workhorse" ALMA bands? We undertake a study of the lowest three CO lines in different isotopomers to model the CO behavior in the clouds in three different environments, nine lines in total with dust continuum, following Meier et al. 2001, ApJ, 551. 3. Number of sources: 3 nearby galaxies 4. Coordinates: 4.1. Possible targets M83 SBc galaxy, gas-rich, starburst nucleus 13:37, -30 NGC1068 02:42, 00 Circinus 14:13, -65 N6822 19:44, -15 4.2. Moving target: no 4.3. Time critical: no CO J=1-0 imaging: ----------------- 5. Spatial scales: 5.1. Angular resolution (arcsec): 1" 5.2. Range of spatial scales/FOV (arcsec): 10 distributed fields across each galaxy 5.3. Single dish total power data: yes 5.4. ACA: yes 5.5. Subarrays: no 6. Frequencies: 6.1. Receiver band: Band 3 6.2. Lines and Frequencies (GHz): 12CO(1-0) at 115 GHz 6.3. Spectral resolution (km/s): 3 km/s 6.4. Bandwidth or spectral coverage (km/s or GHz): 8. Line intensity: 8.1. Typical value (K or Jy): 10 K 8.2. Required rms per channel (K or Jy): 0.05 K 8.3. Spectral dynamic range: 200 9. Polarization: no 10. Integration time for each observing mode/receiver setting (hr): 2 hr per field per galaxy (observed simultaneously with 13CO(1-0) and C18O(1-0)) 13CO J=1-0 imaging: ----------------- 5. Spatial scales: 5.1. Angular resolution (arcsec): 1" 5.2. Range of spatial scales/FOV (arcsec): 10 distributed fields across each galaxy 5.3. Single dish total power data: yes 5.4. ACA: yes 5.5. Subarrays: no 6. Frequencies: 6.1. Receiver band: Band 3 6.2. Lines and Frequencies (GHz): 13CO(1-0) at 110.2 GHz 6.3. Spectral resolution (km/s): 3 km/s 6.4. Bandwidth or spectral coverage (km/s or GHz): 300 km/s max 8. Line intensity: 8.1. Typical value (K or Jy): 1.2 K 8.2. Required rms per channel (K or Jy): 0.04 K 8.3. Spectral dynamic range: 30 9. Polarization: no 10. Integration time for each observing mode/receiver setting (hr): 2 hr per field per galaxy (observed simultaneously with 12CO(1-0) and C18O(1-0)) C18O J=1-0 imaging: ----------------- 5. Spatial scales: 5.1. Angular resolution (arcsec): 1" 5.2. Range of spatial scales/FOV (arcsec): 10 distributed fields across each galaxy 5.3. Single dish total power data: yes 5.4. ACA: yes 5.5. Subarrays: no 6. Frequencies: 6.1. Receiver band: Band 3 6.2. Lines and Frequencies (GHz): C18O(1-0) at 109.7 GHz 6.3. Spectral resolution (km/s): 3 km/s 6.4. Bandwidth or spectral coverage (km/s or GHz): 300 km/s max 7. Continuum flux density: 7.1. Typical value: 0.1 mJy 7.2. Continuum peak value: 1 mJy 7.3. Required continuum rms: 0.006 mJy 7.4. Dynamic range in image: 17 8. Line intensity: 8.1. Typical value (K or Jy): 0.3 K 8.2. Required rms per channel (K or Jy): 0.04 K 8.3. Spectral dynamic range: 8 9. Polarization: no 10. Integration time for each observing mode/receiver setting (hr): 2 hr per field per galaxy (observed simultaneously with 12CO(1-0) and 13CO(1-0)) 12CO J=2-1 imaging: ----------------- 5. Spatial scales: 5.1. Angular resolution (arcsec): 0.5" 5.2. Range of spatial scales/FOV (arcsec): 15 distributed fields across each galaxy 5.3. Single dish total power data: yes 5.4. ACA: yes 5.5. Subarrays: no 6. Frequencies: 6.1. Receiver band: Band 6 6.2. Lines and Frequencies (GHz): 12CO(2-1) at 230 GHz 6.3. Spectral resolution (km/s): 3 km/s 6.4. Bandwidth or spectral coverage (km/s or GHz): 300 km/s max 8. Line intensity: 8.1. Typical value (K or Jy): 12 K 8.2. Required rms per channel (K or Jy): 0.02 K 8.3. Spectral dynamic range: 60 9. Polarization: no 10. Integration time for each observing mode/receiver setting (hr): 45 minutes per field per galaxy 13CO J=2-1 imaging: ----------------- 5. Spatial scales: 5.1. Angular resolution (arcsec): 1" 5.2. Range of spatial scales/FOV (arcsec): 15 distributed fields across each galaxy 5.3. Single dish total power data: yes 5.4. ACA: yes 5.5. Subarrays: no 6. Frequencies: 6.1. Receiver band: Band 6 6.2. Lines and Frequencies (GHz): 13CO(2-1) at 220.4 GHz 6.3. Spectral resolution (km/s): 3 km/s 6.4. Bandwidth or spectral coverage (km/s or GHz): 300 km/s max 8. Line intensity: 8.1. Typical value (K or Jy): 1.6 K 8.2. Required rms per channel (K or Jy): 0.02 K 8.3. Spectral dynamic range: 80 9. Polarization: no 10. Integration time for each observing mode/receiver setting (hr): 45 minutes per field per galaxy (simultaneous with C18O(2-1)) C18O J=2-1 imaging: ----------------- 5. Spatial scales: 5.1. Angular resolution (arcsec): 1" 5.2. Range of spatial scales/FOV (arcsec): 15 distributed fields across each galaxy 5.3. Single dish total power data: yes 5.4. ACA: yes 5.5. Subarrays: no 6. Frequencies: 6.1. Receiver band: Band 6 6.2. Lines and Frequencies (GHz): C18O(2-1) at 219 GHz 6.3. Spectral resolution (km/s): 3 km/s 6.4. Bandwidth or spectral coverage (km/s or GHz): 300 km/s max 7. Continuum flux density: 7.1. Typical value: 0.15 mJy 7.2. Continuum peak value: 2 mJy 7.3. Required continuum rms: 0.013 mJy 7.4. Dynamic range in image: 390 8. Line intensity: 8.1. Typical value (K or Jy): 0.4 K 8.2. Required rms per channel (K or Jy): 0.02 K 8.3. Spectral dynamic range: 20 9. Polarization: no 10. Integration time for each observing mode/receiver setting (hr): 45 minutes per field per galaxy (simultaneous with 13CO(2-1)) 12CO J=3-2 imaging: ----------------- 5. Spatial scales: 5.1. Angular resolution (arcsec): 0.5" 5.2. Range of spatial scales/FOV (arcsec): 20 distributed fields across each galaxy 5.3. Single dish total power data: yes 5.4. ACA: yes 5.5. Subarrays: no 6. Frequencies: 6.1. Receiver band: Band 7 6.2. Lines and Frequencies (GHz): 12CO(3-2) at 345 GHz 6.3. Spectral resolution (km/s): 3 km/s 6.4. Bandwidth or spectral coverage (km/s or GHz): 300 km/s max 8. Line intensity: 8.1. Typical value (K or Jy): 10 K 8.2. Required rms per channel (K or Jy): 0.2 K 8.3. Spectral dynamic range: 50 9. Polarization: no 10. Integration time for each observing mode/receiver setting (hr): 3 minutes per field per galaxy 13CO J=3-2 imaging: ----------------- 5. Spatial scales: 5.1. Angular resolution (arcsec): 1" 5.2. Range of spatial scales/FOV (arcsec): 20 distributed fields across each galaxy 5.3. Single dish total power data: yes 5.4. ACA: yes 5.5. Subarrays: no 6. Frequencies: 6.1. Receiver band: Band 7 6.2. Lines and Frequencies (GHz): 13CO(3-2) at 330.6 GHz 6.3. Spectral resolution (km/s): 3 km/s 6.4. Bandwidth or spectral coverage (km/s or GHz): 300 km/s max 8. Line intensity: 8.1. Typical value (K or Jy): 1.2 K 8.2. Required rms per channel (K or Jy): 0.02 K 8.3. Spectral dynamic range: 34 9. Polarization: no 10. Integration time for each observing mode/receiver setting (hr): 45 min per field per galaxy (simultaneous with C18O(3-2)) C18O J=3-2 imaging: ----------------- 5. Spatial scales: 5.1. Angular resolution (arcsec): 1" 5.2. Range of spatial scales/FOV (arcsec): 20 distributed fields across each galaxy 5.3. Single dish total power data: yes 5.4. ACA: yes 5.5. Subarrays: no 6. Frequencies: 6.1. Receiver band: Band 7 6.2. Lines and Frequencies (GHz): C18O(3-2) at 329 GHz 6.3. Spectral resolution (km/s): 3 km/s 6.4. Bandwidth or spectral coverage (km/s or GHz): 300 km/s max 7. Continuum flux density: 7.1. Typical value: 0.3 mJy 7.2. Continuum peak value: 3 mJy 7.3. Required continuum rms: 0.062 mJy 7.4. Dynamic range in image: 50 8. Line intensity: 8.1. Typical value (K or Jy): 0.3 K 8.2. Required rms per channel (K or Jy): 0.02 K 8.3. Spectral dynamic range: 15 9. Polarization: no 10. Integration time for each observing mode/receiver setting (hr): 45 min per field per galaxy (simultaneous with 13CO(3-2)) 11. Total integration time for program (hr): ( 10 fields * (2 hr per field) +15 fields * (.5 hr per field) +20 fields * (.45 hr per field) ) * 3 galaxies = 140 hrs ~= 10% of sub-theme time 12. Comments on observing strategy (e.g. line surveys, Target of Opportunity, Sun, ...): (optional) Three spiral galaxies will be selected from across the Hubble sequence. Targets will be chosen at distances of ~5 Mpc, as a compromise between areal coverage and resolution necessary to resolve individual GMC scale (0.5" = 12 pc @ 5 Mpc). Ten fields distributed across different galactocentric radii in each galaxy. 15 and 20 fields distributed over the regions observed in CO(1-0) will also be observed. 12CO(1-0), 13CO(1-0) and C18O(1-0) will be observed simultaneously, while each of 13CO(2-1) and C18O(2-1), and 13CO(3-2) and C18O(3-2) will be observed simultaneously. The three lowest J transitions of the three most abundant isotopomers will be used to determine the gas physical conditions robustly. Having 13CO and C18O transitions will aid in determining CO opacities as well as locating potential sites of isotope abundance anomalies. C18O emission will undoubtedly be optically thin in all clouds providing a good N(H_2) for comparison with Ico. The observing times are driven by the weakest lines, which are the C18O lines, since the CO, 13CO, and C18O lines will be observed simultaneously. 45 minutes are necessary to get >10:1 signal to noise in these lines for typical line intensities expected. In Band 3 we cannot achieve these sensitivities, but with integrations of 2 hours, we are within a factor of 2, and can detect the expected signals from C18O(1-0). (The longer integrations at Band 3 are somewhat compensated for with the bigger primary beam) The number of fields per galaxy is based on preliminary maps made at CO(1-0) and followed up at CO(2-1) and CO(3-2); we assume that there is a nonunity filling factor (true outside the nuclear region) and so one does not need to map 4x the area at Band 6, and 9x the area at Band 7. We will need matching beams at the 3 Bands. 3mm continuum, 1 mm continuum and 0.8mm continuum will be observed simultaneously with the deep isotopic line integrations. 3mm continuum will trace free-free emission associated with star formation. The sensitivity achieved at 110 GHz is equivalent to the ionizing flux of one O7V star. Dust masses will be traced with the 220 GHz and 329 GHz continuum emission. The deep integrations will allow the detection of GMCs down to M(H_2)>~2x10^4 Mo (at 5 Mpc). Observations of 3 mm, 1mm and 0.8mm continuum provides good constraints on the SED in mm/submm for reliable separation of free-free and thermal dust emission. *********************************************************************** Review Chris Carilli: OK. I get sensitivity in 1 hr at 3 km/s res at 330 GHz at 1'' res of 0.02 K. they quote a required value of 0.035, so perhaps they need a little less time? Jean Turner: Chris is right; however, to get good sensitivity for the C18O(1-0) line we actually need 2 hours rather than the 1 given in the original DSRP, and even then the rms at Band 3 is a factor of 2 higher than the other bands. I've modified the DSRP with new integration times, 2 hours at Band 3, and 45 minutes per position for Bands 6 and 7. The total comes, coincidentally, to 140 hrs (I did not plan this! It's how it worked out), which is the original value. I've also included a note as to how we chose the observing times/sensitivities for these matched line observations in Section 12. If one wants to trim time, I would suggest trimming positions rather than observing time per line. -------------------------------------------------- Review v2.0: Calibrating the I_CO... Meier, Turner et al. Seems to be a carefully argued program. Again, a less modest proposal might be justified? Will the ACA be necessary? Any gain in analysing the results on a target from `The GMC scale...' proposal localgal_1? Note also that there's a similar kind of thing from Tatematsu et al. (Was 1.7.3).