|Characterizing the Dense Molecular Gas in M82 and NGC 1068: Star Formation versus AGN
|We propose to use HIFI to observe high-J rotational transitions of HCN, HNC and HCO+ in M82 and NGC 1068. These molecules are excellent tracers of dense molecular star-forming gas. Their high-J transitions (&amp;gt; J = 4-3), which have never been observed before, trace the densest and warmest regions of the molecular clouds, and their detection is only possible with Herschel. M82, a starburst galaxy with no detectable AGN, and NGC 1068, which harbors a luminous AGN, are ideally suited to test models that discriminate between the energy inputs from star-formation versus X-ray radiation from an AGN. The two sources produce significant differences in the gas physics and chemistry in the interstellar medium, and hence can be distinguished by deriving the physical properties of the molecular gas, and looking at diagnostic line ratios. These two galaxies are also important templates for understanding the physical processes in luminous star-forming and supermassive black hole-forming galaxies at high redshifts, which are too faint and highly obscured by dust. In 4.4 hours, we can obtain a total of 22 spectral lines for these molecules for the two galaxies. Combining these high-J observations with low-J measurements from the ground will provide at least 16 lines per galaxy for non-LTE modeling -- an unprecedented number that will put tight constraints on the physical parameters such as gas kinetic temperature, density, column density and mass. The models will also produce line optical depths, excitation temperature, and level populations providing insight into the excitation mechanism. We will use the line ratios of these molecules in the two galaxies to distinguish between excitation from a starburst and AGN by comparing them to the predictions from models in the literature. These two galaxies are also being observed as a part of the VNGS guaranteed time key project with SPIRE-FTS. The CO lines from FTS will probe ...and characterize the diffuse molecular gas, and will powerfully complement the results of this proposal.
|Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
|Publisher And Registrant
|European Space Agency
|European Space Agency, 2013, OT1_nrangwal_1, SPG v14.1.0. https://doi.org/10.5270/esa-ops6xko