We report the results of mid- to far-infrared spectroscopic observations of Galactic star-forming regions with ISO, Spitzer, and AKARI. Owing to the high sensitivity of the IRS onboard Spitzer, we detected [Si II] 35 μm, [Fe II] 26 μm, and [Fe III] 23 μm lines widely in low-density star-forming regions, and derived gas-phase Si and Fe abundances as 3–100% and <22%, respectively. With the FTS onboard AKARI, we obtained the spatial distribution ofthe [O III]  88 μm emission in two star-forming regions.

Observations using the HIFI and PACS instruments aboard the Herschelsatellite provide a unique way to study the chemical inventory,the dynamics, and the energy balance in dense interstellar clouds heated byUV radiation. We propose a comprehensive observing program to revealthe details of the interaction of massive young stars with theirparental molecular clouds.

What are the physical conditions in the nuclear region of Seyfert galaxies? Can we asses the predominant nuclear source of power starburst or AGN by using high density gas tracers? We have used SEST, JCMT, and IRAM 30 m telescopes to observe the J = 1–0, J = 3–2, and J = 4–3 transition lines of HNC and HCN in the Seyfert 2 galaxies NGC 1068 and NGC 3079. We model the excitatioon conditions of these molecules based on the observed 3–2/1–0 line intensity ratios. In these proceedings we show the line ratios and discuss the excitation conditions modeled. We summarize our results and conclusions as follows: in NGC 1068, the emission of HNC emerges from lower(< 105 cm-3) density gas than HCN (> 105 cm-3). Instead, the emission of HNC andHCN emerges from the same gas in NGC 3079. The observed HCN/HNC line ratios favor a PDR scenario rather than an XDR one. However, the N(HNC)/N(HCN) column density ratios obtained for NGC 3079 can be found only in XDR environments.

We present high-angular resolution (10 pc) sub-millimeter observations of the N159W region in the LMC obtained with the NANTEN2 telescope. We observed the 12CO J = 4 → 3, J = 7 → 6, 13CO J = 4 → 3 rotational and the [C i] 609 μm and [C i] 370 μm fine-structure transitions toward this region. We detected the [C i] 370 μm and 13CO J = 4 → 3 transitions for the first time in the LMC.

Recent improvements to the plasma simulation code Cloudy will allow the inclusion of model ions and molecules from third-party databases. These models will have important effects on Cloudy predictions at a wide variety of conditions and energies. Here we present a brief discussion of this work and highlight future goals.

For three prototypical galaxies (IC 342, M 82, Antennae), we successfully applied PDR models to explain observed CO line ratios simultaneously with atomic fine structure lines. The model well confines the physical parameters of the gas, which is extremely clumped to allow the UV radiation to penetrate through the molecular clouds over large distances.

We present spectral line observations towards the Monoceros PDR in Rosette in context with optical (DSS), far-infrared (C+, KAO), and mid-infrared (Spitzer) imaging of the region. The new data include maps in CO isotopomeric lines (IRAM 30 m, APEX, and NANTEN2) and cuts through the interface in a variety of chemical tracers and transitions: HCN, HNC, HCO+, CN, CCH, and CS, in some cases including rarer isotopomers (IRAM 30 m and APEX). Our goal is to study, and possibly resolve, the temperature, chemical, and density structure in the clumpy PDR/molecular cloud transition. As a first results, we do find evidence for a layered structure perpendicular to the impinging UV radiation in selected chemical and excitational tracers.

Following up on our previous low-resolution studies (Beuther et al. 2000; Mookerjea et al. 2006) in the nearby star forming region Cepheus B, we try to understand photo-induced chemistry of the photon dominated regions (PDRs) using the higher resolution data observed with the IRAM 30 m telescope at Pico Veleta. The aim of our study is to resolve the temperature, chemical, and excitation structure of the transition zone from the H ii region to the dense molecular cloud in a PDR which is subject only to moderately strong UV fields. We study two cuts running through the interfaces into the main cloud and thus allow to trace several interface regions. Particularly, we select two positions at the interface for a more detailed study. The studied frequency ranges from 85 GHz to 272 GHz and includes 21 transitions of 11 molecules such as HCN, HCO+, CN, CS, CCH, and CCS. Combined with the low – J CO maps in this region (Ungerechts et al. 2000), we calculate the integrated intensity distribution along the cuts and line ratios between different tracers and transitions. H2 column density along the cuts has been estimated under the Local Thermodynamic Equilibrium (LTE) assumption. The integrated line intensities present nice changes from the H ii region into the molecular clouds. There is an enhancement of all the tracers at the two interface positions.

Wepresent 12CO(J = 3–2) and 12CO(J = 1–0) observations of the supergiant Hii region NGC 604 in the nearest face-on spiral galaxy M 33 using the Atacama Submillimeter Telescope Experiment (ASTE) 10-m and the Nobeyama Radio Observatory (NRO) 45-m telescopes. We found high 12CO(J = 3–2)/12CO(J = 1–0) ratio gas with an arc-like distribution (“high-ratio gas arc”) surrounding the central star cluster of NGC 604. Our results suggest that dense gas formation and second-generation star formation occur in the surrounding gas compressed by the stellar wind and/or supernova of the first-generation stars of NGC 604, i.e., the central star cluster of NGC 604. Thus, NGC 604 is an example of large-scale sequential star formation.

In this paper we discuss our recent efforts to update the X-ray treatment of grains in the PDR modeling code Cloudy.

The CO N+ Deuterium Observations Receiver (CONDOR) is one of the very fewheterodyne receivers operational between 1.25 and 1.53 THz. It has successfullyobtained first-light observations on APEX and is currently being modified tofly as the low frequency channel of GREAT on SOFIA.