Title The Molecular ISM in Low Surface Brightness Galaxies Pi Turner Time 96 hrs 1. Name: The Molecular ISM in Low Surface Brightness Galaxies --Turner et al. 2. One short paragraph with science goal(s): LSB are low surface brightness, low star formation, metal-poor galaxies which make up the most ubiquitous class of galaxies in the universe. Suppressed star formation in LSBs must stem from different physical conditions of the ISM. Detection of molecular gas in these galaxies are at the current limit of technology (O'Neil et al. 2003). Are LSBs weak in CO because they have very little molecular gas or because CO fails to trace H_2 in the low metallicity galaxies? Does the molecular ISM follow the light distribution as is HSB galaxies? Is the interstellar pressure large enough to maintain a multi-phase ISM? Can GMCs exist in such low surface density (yet rotationally massive) LSB disks, and if so are they gravitationally bound? If the molecular ISM is present and significantly clumped like in HSBs, the very low interstellar radiation field (ISRF) implies that CO photodissociation is irrelevant and that CO's weakness likely stems from molecular gas being very cold. If the ISM is not clumped then the molecular gas must be warm, very diffuse and stable against collapse. Determinations of the structure and physical conditions in LSBs will aid in separating the two possibilities. Studies of local LSBs may also provide insights into the nature of Lyman-alpha absorbers at high-z, given their apparent similarity. Moreover, the very low ISRF in LSBs will provide a complimentary dataset to local, low metallicity star forming galaxies for constraining the effects of UV photons on CO at low metallicity. Finally, constraints of the NFW cold dark matter density profiles may be obtained for these dark matter dominated galaxies. 3. Number of sources: 10, A sample distributed between massive LSB disks and small LSB dwarfs. 4. Coordinates: 4.1. distributed across the sky. 4.2. Moving target: no 4.3. Time critical: no CO J=1-0 imaging: ---------------- 5. Spatial scales: 5.1. Angular resolution (arcsec): 1" (50 - 100 pc @ 10 - 20 Mpc) 5.2. Range of spatial scales/FOV (arcsec): single pointing 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), 114.7 GHz (20 Mpc and Ho=70) 6.3. Spectral resolution (km/s): 5 km/s 6.4. Bandwidth or spectral coverage (km/s or GHz): 500 km/s max 7. Continuum flux density: 7.1. Typical value: 0.05 mJy 7.2. Continuum peak value: 0.05 mJy 7.3. Required continuum rms: 0.004 mJy 7.4. Dynamic range in image: 12 8. Line intensity: 8.1. Typical value (K or Jy): 5 mJy 8.2. Required rms per channel (K or Jy): 0.4 mJy 8.3. Spectral dynamic range: 12 9. Polarization: no 10. Integration time for each observing mode/receiver setting (hr): 5 hrs per galaxy CO J=3-2 imaging: ---------------- 5. Spatial scales: 5.1. Angular resolution (arcsec): 1" (50 - 100 pc @ 10 - 20 Mpc) 5.2. Range of spatial scales/FOV (arcsec): small mosaic (~4 pointing) 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), 344.2 GHz (20 Mpc and Ho=70) 6.3. Spectral resolution (km/s): 5 km/s 6.4. Bandwidth or spectral coverage (km/s or GHz): 300 km/s max 7. Continuum flux density: 7.1. Typical value: 0.2 mJy 7.2. Continuum peak value: 0.8 mJy 7.3. Required continuum rms: 0.05 mJy 7.4. Dynamic range in image: 15 8. Line intensity: 8.1. Typical value (K or Jy): 45 mJy 8.2. Required rms per channel (K or Jy): 1.9 mJy 8.3. Spectral dynamic range: 24 9. Polarization: no 10. Integration time for each observing mode/receiver setting (hr): 0.25 hr per pointing per galaxy 13CO J=3-2 imaging: ---------------- 5. Spatial scales: 5.1. Angular resolution (arcsec): 1" (50 - 100 pc @ 10 - 20 Mpc) 5.2. Range of spatial scales/FOV (arcsec): 1 field (towards brightest GMCs in the 4 brightest sources) 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), 329.0 GHz (20 Mpc and Ho=70) 6.3. Spectral resolution (km/s): 5 km/s 6.4. Bandwidth or spectral coverage (km/s or GHz): 300 km/s max 7. Continuum flux density: 7.1. Typical value: 1 mJy 7.2. Continuum peak value: 1 mJy 7.3. Required continuum rms: 0.009 mJy 7.4. Dynamic range in image: 100 8. Line intensity: 8.1. Typical value (K or Jy): 6 mJy 8.2. Required rms per channel (K or Jy): 0.6 mJy 8.3. Spectral dynamic range: 10 9. Polarization: no 10. Integration time for each observing mode/receiver setting (hr): 9 hrs per galaxy 11. Total integration time for program (hr): (5 + 1)*10 + 9*4 = 96 hrs = ~7 % of sub-theme. 12. Comments on observing strategy (e.g. line surveys, Target of Opportunity, Sun, ...): (optional) Sensitivity calculations for the CO(1-0) line emission are based on 1/4 the intensity of the brightest LSBs detected in O'Neil et al. 2003. Sensitivities for the three brightest galaxies is assumed to be equal to the brightest galaxies in the O'Neil et al. 2003 survey. Targets will be chosen at distances between 10 - 20 Mpc, as a compromise between sensitivity, areal coverage and maintaining resolution close to the individual GMC scale. 12CO(1-0) will be used to map the ISM over the central 3-6 Kpc (10 - 20 Mpc). 12CO(3-2) will be observed towards the detections as a minimum establishment of gas excitation. Towards the three brightest sources an attempt to detect 13CO(2-1) will be included for constraints on gas density and/or the CO isotopic ratio. 3mm continuum for tracing free-free emission associated with star formation will be obtained for free, simultaneously with the 12CO(1-0) data. In the 5 hrs per galaxy at 115 GHz, a 115 GHz continuum rms of 0.004 mJy or the ionizing flux of a few O7V stars. Likewise 0.8 mm continuum for tracing cool dust associated with the molecular gas will be obtained for free, simultaneously with the 12CO(3-2) and 13CO(3-2) data. In the 0.25 hrs per galaxy at 345 GHz, a 345 GHz continuum rms of 0.05 mJy or GMCs with M(H_2)>~3x10^5 Mo (at 10 Mpc) will be detected. Towards the four brightest sources the deep continuum observation simultaneous with 13CO(3-2) will provide 330 GHz continuum rms of 0.009 mJy or GMCs with M(H_2)>~5x10^4 Mo (at 10 Mpc) of dust will be detected. **************************************************************** Review Chris Carilli: OK -------------------------------------------------- Review v2.0: The molecular ISM in LSB... Turner et al. The substantial change in DRSP2 is to modify the expected continuum level down in these targets. In contrast with the other proposals sharing some/all investigators, maybe LSBs are getting more coverage as a class of galaxy? (This is intended as an encouragement to up-size the other programs more than to down-size this one). Is the ACA going to be much help for single pointings?