Cooling lines as probes of the formation and buildup of galaxies and black holes

We discuss the use of SPICA to study the cosmic history of star formation and accretion by supermassive black holes. The cooling lines, in particular the high-J rotational lines of CO, provide a clear-cut and unique diagnostic for separating the contributions of star formation and AGN accretion to the total infrared luminosity of active, gas-rich galaxies. We briefly review existing efforts for studying high-J CO emission from galaxies at low and high redshift. We finally comment on the detectability of cooling radiation from primordial (very low metallicity) galaxies containing an accreting supermassive black hole with SPICA/SAFARI.Comment: to appear in the proceedings of "The Space Infrared Telescope for Cosmology & Astrophysics: Revealing the Origins of Planets and Galaxies", Oxford, July 2-8, 200

Using deuterated H3+ and other molecular species to understand the formation of stars and planets

The H3+ ion plays a key role in the chemistry of dense interstellar gas clouds where stars and planets are forming. The low temperatures and high extinctions of such clouds make direct observations of H3+ impossible, but lead to large abundances of H2D+ and D2H+ which are very useful probes of the early stages of star and planet formation. Maps of H2D+ and D2H+ pure rotational line emission toward star-forming regions show that the strong deuteration of H3+ is the result of near-complete molecular depletion of CNO-bearing molecules onto grain surfaces, which quickly disappears as cores warm up after stars have formed. In the warmer parts of interstellar gas clouds, H3+ transfers its proton to other neutrals such as CO and N2, leading to a rich ionic chemistry. The abundances of such species are useful tracers of physical conditions such as the radiation field and the electron fraction. Recent observations of HF line emission toward the Orion Bar imply a high electron fraction, and we suggest that observations of OH+ and H2O+ emission may be used to probe the electron density in the nuclei of external galaxies.Comment: Proceedings of the H3+ centennial symposium, to be published in RSPTA (editor: T. Oka

A Submillimeter Selected Quasar in the Field of Abell 478

We report the discovery of a z=2.83 quasar in the field of the cooling flow galaxy cluster Abell 478. This quasar was first detected in a submm survey of star forming galaxies at high redshifts, as the brightest source. We discuss the optical spectrum and far-IR spectral energy distribution (SED) of this object.Comment: 4 pages, 3 figures, in "Deep Millimeter Surveys: Implications for Galaxy Formation and Evolution", ed. J. Lowenthal and D. Hughes, World Scientific Publisher

The excitation of near-infrared H2 emission in NGC 253

Because of its large angular size and proximity to the Milky Way, NGC 253, an archetypal starburst galaxy, provides an excellent laboratory to study the intricacies of this intense episode of star formation. We aim to characterize the excitation mechanisms driving the emission in NGC 253. Specifically we aim to distinguish between shock excitation and UV excitation as the dominant driving mechanism, using Br\gamma, H_2 and [FeII] as diagnostic emission line tracers. Using SINFONI observations, we create linemaps of Br\gamma, [FeII]_{1.64}, and all detected H_2 transitions. By using symmetry arguments of the gas and stellar gas velocity field, we find a kinematic center in agreement with previous determinations. The ratio of the 2-1 S(1) to 1-0 S(1) H_2 transitions can be used as a diagnostic to discriminate between shock and fluorescent excitation. Using the 1-0 S(1)/2-1 S(1) line ratio as well as several other H_2 line ratios and the morphological comparison between H_2 and Br\gamma and [FeII], we find that excitation from UV photons is the dominant excitation mechanisms throughout NGC 253. We employ a diagnostic energy level diagram to quantitatively differentiate between mechanisms. We compare the observed energy level diagrams to PDR and shock models and find that in most regions and over the galaxy as a whole, fluorescent excitation is the dominant mechanism exciting the H_2 gas. We also place an upper limit of the percentage of shock excited H_2 at 29%. We find that UV radiation is the dominant excitation mechanism for the H_2 emission. The H_2 emission does not correlate well with Br\gamma but closely traces the PAH emission, showing that not only is H_2 fluorescently excited, but it is predominately excited by slightly lower mass stars than O stars which excite Br\gamma, such as B stars