T. Nikola

FIRST SCIENCE OBSERVATIONS WITH SOFIA/FORCAST: THE FORCAST MID-INFRARED CAMERA

The Stratospheric Observatory For Infrared Astronomy (SOFIA) completed its first light flight in May of 2010 using the facility mid-infrared instrument FORCAST. Since then, FORCAST has successfully completed 13 science flights on SOFIA. In this Letter, we describe the design, operation, and performance of FORCAST as it relates to the initial three Short Science flights. FORCAST was able to achieve near-diffraction-limited images for λ > 30 μm allowing unique science results from the start with SOFIA. We also describe ongoing and future modifications that will improve overall capabilities and performance of FORCAST.

A 205 μm [N II] MAP OF THE CARINA NEBULA

We present the results of a � 250 arcmin 2 mapping of the 205 �m [NII] fine-structure emission over the northern Carina Nebula, including the Car I and Car II HII regions. Spectra were obtained using the South Pole Imaging Fabry-Perot Interferometer (SPIFI) at the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) at South Pole. We supplement the 205 �m data with new reductions of far-IR fine-structure spectra from the Infrared Space Observatory (ISO) Long Wavelength Spectrometer (LWS) in 63 �m [OI], 122 �m [NII], 146 �m [OI], and 158 �m [CII]; the 146 �m [OI] data include 90 raster positions which have not been previously published. Morphological comparisons are made with optical, radio continuum and CO maps. The 122/205 line ratio is used to probe the density of the low-ionization gas, and the 158/205 line ratio is used to probe the fraction of C + arising from photodissociation regions (PDRs). The [OI] and [CII] lines are used to construct a PDR model of Carina. When the PDR properties are compared with other sources, Carina is found to be more akin to 30 Doradus than galactic star-forming regions such as Orion, M17, or W49; this is consistent with the view of Carina as a more evolved region, where much of the parent molecular cloud has been ionized or swept away. These data constitute the first ground-based detection of the 205 �m [NII] line, and the third detection overall since those of the COBE FIRAS and the KAO in the early 1990s. Subject headings: HII regions — infrared: ISM — ISM: individual (Carina nebula) — ISM: lines and bands — photon-dominated region (PDR) — submillimeter: ISM

First detection of the [O III] 88 μm line at high redshifts: characterizing the starburst and narrow-line regions in extreme luminosity systems

We have made the first detections of the 88 ?m [O III] line from galaxies in the early universe, detecting the line from the lensed active galactic nucleus (AGN)/starburst composite systems APM?08279+5255 at z = 3.911 and SMM?J02399-0136 at z = 2.8076. The line is exceptionally bright from both systems, with apparent (lensed) luminosities ~1011 L ?. For APM?08279, the [O III] line flux can be modeled in a star formation paradigm, with the stellar radiation field dominated by stars with effective temperatures, T eff > 36,000?K, similar to the starburst found in M82. The model implies ~35% of the total far-IR luminosity of the system is generated by the starburst, with the remainder arising from dust heated by the AGN. The 88 ?m line can also be generated in the narrow-line region of the AGN if gas densities are around a few 1000 cm?3. For SMM?J02399, the [O III] line likely arises from H II regions formed by hot (T eff > 40,000?K) young stars in a massive starburst that dominates the far-IR luminosity of the system. The present work demonstrates the utility of the [O III] line for characterizing starbursts and AGN within galaxies in the early universe. These are the first detections of this astrophysically important line from galaxies beyond a redshift of 0.05.

MID-J CO EMISSION FROM NGC 891: MICROTURBULENT MOLECULAR SHOCKS IN NORMAL STAR-FORMING GALAXIES

We have detected the CO(6-5), CO(7-6), and [C I] 370 μm lines from the nuclear region of NGC 891 with our submillimeter grating spectrometer ZEUS on the Caltech Submillimeter Observatory. These lines provide constraints on photodissociation region (PDR) and shock models that have been invoked to explain the H2 S(0), S(1), and S(2) lines observed with Spitzer. We analyze our data together with the H2 lines, CO(3-2), and infrared continuum from the literature using a combined PDR/shock model. We find that the mid-J CO originates almost entirely from shock-excited warm molecular gas; contributions from PDRs are negligible. Also, almost all of the H2 S(2) line and half of the S(1) line are predicted to emerge from shocks. Shocks with a pre-shock density of 2 × 104 cm–3 and velocities of 10 km s–1 and 20 km s–1 for C-shocks and J-shocks, respectively, provide the best fit. In contrast, the [C I] line emission arises exclusively from the PDR component, which is best parameterized by a density of 3.2 × 103 cm–3 and a far-ultraviolet field of Go = 100 for both PDR/shock-type combinations. Our mid-J CO observations show that turbulence is a very important heating source in molecular clouds, even in normal quiescent galaxies. The most likely energy sources for the shocks are supernovae or outflows from young stellar objects. The energetics of these shock sources favor C-shock excitation of the lines.

CO-Dark Star Formation and Black Hole Activity in 3C 368 at z = 1.131: Coeval Growth of Stellar and Supermassive Black Hole Masses* **

We present the detection of four far-infrared fine-structure oxygen lines, as well as strong upper limits for the CO(2–1) and [N ii] 205 μm lines, in 3C 368, a well-studied radio-loud galaxy at z = 1.131. These new oxygen lines, taken in conjunction with previously observed neon and carbon fine-structure lines, suggest a powerful active galactic nucleus (AGN), accompanied by vigorous and extended star formation. A starburst dominated by O8 stars, with an age of ~6.5 Myr, provides a good fit to the fine-structure line data. This estimated age of the starburst makes it nearly concurrent with the latest episode of AGN activity, suggesting a link between the growth of the supermassive black hole and stellar population in this source. We do not detect the CO(2–1) line, down to a level twelve times lower than the expected value for star-forming galaxies. This lack of CO line emission is consistent with recent star formation activity if the star-forming molecular gas has low metallicity, is highly fractionated (such that CO is photodissociated throughout much of the clouds), or is chemically very young (such that CO has not yet had time to form). It is also possible, although we argue it is unlikely, that the ensemble of fine-structure lines is emitted from the region heated by the AGN.

CO (J = 7 → 6) Observations of NGC 253: Exited Molecular Gas in the Nucleus

We report observations of the CO J = 7 → 6 transition toward the starburst nucleus of NGC 253. This is the highest-excitation CO measurement in this source to date, and allows an estimate of the molecular gas excitation conditions. We find that the bulk of the 2-5×107 M⊙ of molecular gas in the central 180 pc is highly excited. The inferred mass of warm, dense molecular gas is 10-30 times the atomic gas mass as traced through its [C II] and [O I] line emission. This large mass ratio is inconsistent with photodissociation region models where the gas is heated by far-UV starlight. It is also not likely that the gas is heated by shocks in outflows or cloud-cloud collisions given the lack of evidence for substantial heating in fast shocks. We propose two mechanisms for heating the molecular gas: cosmic rays ionization and dissipation of supersonic turbulence, both of which which provide a natural means of uniformly heating the full volume of molecular clouds, and provide a good match to the cooling observed in the CO lines.