Title Nuclear Dense Gas in Active Galaxies Pi E. Schinnerer Time 256 hrs 1. Name of program and authors 1.5.3: Name -- Nuclear Dense Gas in Active Galaxies Authors: E. Schinnerer, S. Garcia-Burillo 2. Science goal: The polar molecule HCN is commonly used as a tracer of dense molecular gas. The correlation between the HCN luminosity and the far-infrared (FIR) luminosity is found to be tighter than the well-known correlation between the CO luminosity and the FIR luminosity, and more importantly, the HCN-FIR correlation remains linear to high FIR luminosity, unlike the CO-FIR correlation, which 'saturates' at high FIR luminosity. Since HCN is a dense gas tracer, likely associated with active star forming regions, the linear HCN-FIR correlation suggests that the FIR luminosity originates from star formation rather than AGN activity in IR luminous galaxies. However, the HCN to CO intensity ratio varies substantially among luminous galaxies, which may indicate variation of the star formation efficiency (= star formation rate/total molecular gas mass) as a function of IR luminosity. The excitation conditions for HCN can be met either in star forming regions, or in gas close to the nuclei of galaxies, where AGN may heat the gas and dust. Recently, the HCN to HCO+ ratio has been suggested as a good discriminator between excitation due to an AGN (X-ray dominated regions; collisional excitation) or due to star formation (IR pumping; non-collisional excitation). Therefore, we propose to simultaneously image HCN and HCO+ (their first 4 transitions) in a representative sample of starburst and AGN galaxies to identify the excitation source of both HCN and HCO+ and to test whether their ratios can indeed be used as discriminator indepedent of transition. Note that in the case of high-J transitions of both HCN and HCO+ IR pumping might indeed play a vital role. In addition, high angular resolution is vital to spatially resolve possible nuclear star forming regions and the AGN itself. A good understanding of the excitation conditions of HCN and HCO+ are also paramount for the interpretation of observations of dense molecular gas in galaxies at high redshifts (z > 4) which will be routinely done with ALMA using high-J transitions. 3. Number of sources: 4 4. Coordinates: 4.1. active galaxies at ~10 - 20 Mpc distance: 4.2. Moving target: no 4.3. Time critical: no 5. Spatial scales: 5.1. Angular resolution (arcsec): 0.1" 5.2. Range of spatial scales/FOV (arcsec): 0.1" to 15" 5.3. Required pointing accuracy: ~ 0.5" 6. Observational setup 6.1. Single dish total power data: no 6.2. Stand-alone ACA: no 6.3. Cross-correlation of 7m ACA and 12m baseline-ALMA antennas: no 6.4. Subarrays of 12m baseline-ALMA antennas: no 7. Frequencies: 7.1. Receiver band: 3,5,6,7 7.2. Lines and Frequencies (GHz): HCN/HCO+(1-0),(2-1),(3-2),(4-3): 88, 178, 266, 356 GHz multi-line 2 lines per setting per band 7.3. Spectral resolution (km/s): 20 km/s 7.4. Bandwidth or spectral coverage (km/s or GHz): ~ 1200 km/s per line; total bandwidth ~ 1.5-2 GHz (depends on line separation) 8. Continuum flux density: 8.1. Typical value (Jy): < 0.5 mJy/beam at 230 GHz 8.2. Required continuum rms (Jy or K): 8.3. Dynamic range within image: 8.4. Calibration requirements: absolute ( n/a ) repeatability ( n/a ) relative ( n/a ) 9. Line intensity: 9.1. Typical value (K or Jy): ~ 0.9 mJy/beam at 266 GHz 9.2. Required rms per channel (K or Jy): 0.15 mJy/beam 9.3. Spectral dynamic range: >5 9.4. Calibration requirements: absolute ( 5% ) repeatability ( 5% ) relative ( 5% ) 10. Polarization: no 11. Integration time for each observing mode/receiver setting (hr): 1 track (+/- 4hr) at 266 x 4 sources x 2 configurations x 4 frequency set-ups The assumption is that the line intensity and rms noise do roughly scale with frequency. 12. Total integration time for program (hr): 256 hr 13. Comments on observing strategy : (optional) ----------------------------------------------------------------------------- Revised version of drsp1_1.5.3.txt. The science goal has been up-dated and slightly modified thus some of the previous comments might not be relevant anymore. ************************************************************************* Comments: proposes to simultaneously image HCN and HCO+ in 5 transitions in a representative sample of AGn and starburst.. consisting of 4 sources. The proposal only discusses 4 transitions --> The abstract has been corrected to 4 transitions. I don't see why two sources, one AGN and one starburst would not be enough. this is a huge amount of time. --> Given that the HCN/HCO+ lines are of high interest in high redshift sources understanding their chemistry in local well defined counterparts is paramount. Given the fact that at the resolution ALMA will achieve source properties are basically unknown, a sample of having 2 AGN and 2 pure starbursts seems the best way to avoid misinterpretation of results in case one source might turn out to host both AGN and starburst. Also, this will help to sample a possible wider range in nuclear properties such as the ionization strength of the AGN and the age and SFR rate of nuclear starbursts. ************************************************************************* Previous comments: Review Jean Turner: HCN is an interesting molecule for starbursts. One issue is the one that Phil Solomon has pointed out, that HCN is better correlated with Lir than CO. This is worth pursuing with high spatial resolution. HCN could well trace the star formation much better than CO (and presumably these galaxies would all already have comparable CO maps). However, it seems to me premature to do 10 sources. HCN could be confusing. Especially in exotic objects, with a lot of mid-IR emission. With the high spatial resolution one can isolate the AGN to some degree and perhaps simplify the problem to learn interesting things about dense gas and HCN in these two different categories of systems. This project will be done by ALMA. I think the dust continuum will be exceedingly useful in helping out with where the gas is (this would potentially require band 3 to weed out the free-free contribution) Scope: I think this is an awful lot of time to devote to HCN. At the moment it is unclear how much one might learn, with potential excitation issues, particularly in AGN, but anywhere there is strong mid-IR emission. Ewine will know better about the mid-IR pumping of HCN. If there are SSCs forming, there is VERY strong and localized mid-IR. Ditto AGN. Two galaxies carefully chosen galaxies would be sufficient to reveal unusual HCN properties. Technical: High resolution is needed to separate AGN; however, too high is not good for molecules. They propose 0.1", this is a reasonable compromise. Integration time is fine per galaxy. Total time for project should be cut, to possibly 2 sources instead of 10, for a total of 32 hrs. Comment Ewine: Both collisions and mid-IR pumping can indeed affect the HCN excitation in these hot cores. Two sources seems too few to me to test any relation, so I propose to cut to 6 sources = 96 hrs