The following programs have data available for download and analysis by the astronomy community; some observation titles link to detailed information on the program and the results achieved. Data analysis tools are provided by the SOFIA Science Center, in addition to tutorials on using these tools to analyze SOFIA processed data. Information about the SOFIA data archive can be found here. 

• A Testbed for Starburst Activity: 30 Doradus
• The Multi-phase Envelope of NGC 7538 IRS1
• Exploring the CMZ: the Arches Cluster
• New [C II] Maps in Massive Star Formation Regions
• Organic Inventories in Young Stellar Objects and Disks with EXES
• Orion Molecular Cloud (OMC-1)
• Betelgeuse High Resolution 25 Micron Spectra 2015-2020
• Galactic Center Legacy Program
• [OI] and CO Maps of Pillars in the Carina Nebula
• [C II] Map of the M51 Galaxy
• 30 Doradus
• Horsehead Nebula [C II] Map
• SN 2014J Imaging and Spectroscopy

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A Testbed for Starburst Activity: 30 Doradus

30 Doradus (the Tarantula nebula) is a very wide HII region which hosts strong starburst activity. At its center lies a large cluster of massive stars, which powers extended PDR regions. Thanks to its location in the LMC, it is one of the best laboratories to study how local conditions -- thermal, kinematic, density and magnetic fields -- support starburst activity.

Hydrogen density and temperature fields can be retraced through the emission from atomic and ionized tracers’ lines (see Chevance et al., 2020), such as the wide [CII] and [OI] maps obtained with FIFI-LS (projects 75_0016 and 05_0100). The data also cover [NIII] and [OIII] transitions. In the densest regions, the effect of large optical depth makes the interpretation more uncertain -- using maps from isotopes such as [13CII] (GREAT, 83_0610) can alleviate that issue.

High spectral resolution mapping is the most direct technique to determine the kinematic field. With a velocity resolution of ~1km/s, GREAT maps of the bright [CII] line (project 06_0170) can be used to evaluate the contribution of stellar feedback to the whole region.

Finally, large polarization maps at 53, 89, 154, and 214 μm (HAWC+, project 76_0001) reveal the morphology of the magnetic field (see the corresponding 30Dor Cookbook recipe). Emission at the shorter wavelengths traces hot dust from the densest compact regions with high spatial resolution (5” at 53 μm).

All these datasets are publicly available from the IRSA archive.

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The Multi-phase Envelope of NGC 7538 IRS1

NGC 7538 IRS 1 is one of the many IR-bright, young stellar objects (YSO) within the HII region NGC 7538, in the Perseus’ arm of the Milky Way. IRS 1 is still actively accreting mass, offering one of the best perspectives into the very first stages of star formation. The composition of the protostar’s envelope can be used to retrace the early processing of gas, dust and PAHs by the UV radiation field, which should be strongly absorbed during this young phase. SOFIA extensively observed IRS 1 in the mid and far-IR, providing:

• photometric images at 7.7, 19.7, 25.3, 31.5 and 37.1 µm, which can be used to distinguish the infrared contributions from dust and PAHs, the latter being mainly constrained by the emission level at 7.7 µm (FORCAST, project 01_0034)
• spectrally-resolved images (R~600 and R~1000) covering 75-95 µm and 135-155 µm. The derived far-IR  photometry can refine the source’s SED and constrain the temperature, emissivity and size distribution of the colder dust component, as shown by Sandell et al., 2020 with mid-IR data. Gas-phase transitions for atomic, ionized and molecular species may also be detectable (FIFI-LS, project 03_0151)
• high-resolution spectra from 5.5 to 27 µm, covering ro-vibrational transitions of several gas-phase components - H2O, HCN, C2H2, CS, SO2, CH4, CH3, NH3. the availability of low and high-J transitions (across P, Q- R-branches) for CH4, HCN, H2O and SO2 can allow one to derive the abundance of these molecules in a comprehensive way, tracing both cold and warm gas components (EXES, projects 02_0104, 03_0080, 04_0120, 75_0024). Indriolo et al. 2015, 2020, demonstrate the analysis of similar EXES H2O data in protostars. 

All calibrated data are available from the IRSA SOFIA Archive.

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Exploring the CMZ: the Arches Cluster

The Arches Cluster, the densest star cluster in our galaxy, is located within the Galactic Center’s Central Molecular Zone (CMZ), just about 25 pc from Sagittarius A*. Named after the arch-shaped radio-bright structures in its line of sight, it is believed to be an important ionization source, powering the major star formation area in the CMZ (the Galactic Center bubble). The physical and dynamical characterization of the cluster’s environment is key to evaluating the stellar feedback from its hot young stars, and can in large part be derived from the analysis of publicly available archival SOFIA maps.

The GREAT map of the fine structure [C II] line at 158 µm offers the high spectral resolution necessary to identify distinct gas components along the line of sight, and to map out the region’s kinematics (project 05_0076, strip map 5A). Wide FIFI-LS maps of that same [C II] line as well as the [N III] line at 57 µm trace the distribution of dense gas on a larger spatial scale, and can be used to derive the temperature field (project 04_0032). Finally, thermal dust emission and compact IR-bright sources, including candidate young stellar objects, can be located from the 25 µm and 37 µm FORCAST maps, part of the Galactic Center Legacy program (project 07_0189). All these datasets are publicly available from the IRSA archive.

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New [C II] Maps in Massive Star Formation Regions

Massive stars strongly influence the chemistry, dynamics, morphology and thermal structure of their natal environment through a variety of processes globally described as stellar feedback. Feedback is significantly altering these environments, affecting star formation in them, and eventually regulating the evolution of galaxies. To facilitate the identification of driving feedback mechanisms such as stellar wind, radiation pressure and thermal expansion, co-PIs Alexander Tielens (Leiden Observatory) and Nicola Schneider (University of Cologne) are leading the FEEDBACK legacy program on SOFIA.

Across a diverse selection of massive star formation regions (including HII regions of different geometries, single stars, small groups and star clusters), [C II] and [O I] maps will be used to characterize the kinematic and physical properties over large spatial scales. Schneider et al., 2020 presents in detail the scientific context and the observation plans. The Maryland team’s website gives detailed information on the sources and provides links to the PDR analysis tools, while the Cologne team’s website informs about the current observations status. FEEDBACK observations with GREAT started in 2019, and will eventually produce large spectrally-resolved maps of [C II] and [O I] emission on 11 sources.

Preliminary data have been released for the sources RCW79, RCW49, RCW36, RCW120, NGC7538, NGC6334, the Cygnus X region, W40, M16 and M17, corresponding to FITS data cubes of the observations to date. The data are publicly available for download at the SOFIA Archive under program ID 07_0077. While all maps have varying number of missing spatial fields (see completion rates), the observed fields are already fully sampled for [C II]. These maps will be completed after missing fields are observed during the remainder of Cycle 8.

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Organic Inventories in Young Stellar Objects and Disks with EXES

The 5.5-8 microns spectral region is rich in vibrational and rovibrational transitions of organic molecules and their isotopologues, including pre-biotic molecules. Spectral signatures from water (in particular the ground state v2 vibrational band), formaldehyde, methane, ammonia, CH3, HCN, and more complex organics can be emitted from warm and hot regions around young stellar objects, as well as the inner regions (<a few AU) of protoplanetary disks. High resolution mid-IR spectra are hence an important tool to understand the mechanics of dust grain evaporation in stellar environments, and eventually to retrace chemical evolution during planet formation.

While the 5.5-8 microns region is inaccessible from the ground, it is observable with the EXES instrument aboard SOFIA. Thanks to its high spectral resolution modes up to R~90000, much higher than what Spitzer IRS could offer, profiles of blended and individual transitions can be analyzed to estimate molecular abundances and excitation temperatures. In addition, measurements of the gas velocity through Doppler-shifts can help to identify the source region for each molecule.

Over the past several years, EXES observations have contributed to a rich inventory of mid-IR spectra from YSOs and protoplanetary disks. The available public database includes sources such as: GV Tau's disk (project 05_0097, Carr et al., in prep), and massive protostars AFGL 2136, AFGL 2591 (projects 04_0120/05_0041 - Barr et al. 2020, 2018, Indriolo et al. 2020), Orion IRc2 (project 05_0043/06_0061, Nickerson et al. in prep) and high-mass YSOs NGC 7538 IRS 1 and IRS 9 (project 75_0024).All calibrated data is available from the IRSA SOFIA Archive.

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Orion Molecular Cloud (OMC-1)

Combined analysis of mid- and far-IR spectroscopic and photometric data is key to the study of the chemistry, kinetics and thermal structure of star forming regions, probing warm dust as well as ionized and molecular gas. One of the nearest massive star forming regions, OMC-1, is situated just behind the Orion Nebula and has been extensively observed with all SOFIA instruments.

Through the SOFIA public data archive, anyone can access a large number of infrared high-quality infrared maps and spectra of OMC-1. Some of those datasets explore previously never-observed wavelengths, and many cover regions of interest such as the Orion Bar, considered to be the prototypical photon dominated region. These datasets include:

• HAWC+ photometric and polarization maps at 53, 89, 154, and 214 microns (proposal ID: 70_0609). Chuss et al. (2019) derived the large-scale polarization structure of OMC-1, confirming the global hour-glass shape of its magnetic field. With a spatial resolution of 5-19”, the Orion Bar and other sub-structures can also be clearly resolved. See also Astrobites piece.
• GREAT ionized carbon [CII] velocity-resolved map at 158 microns (proposal ID: 04_0066): this wide maps provide unique information on ISM kinematics near massive stars. Pabst et al. (2019) focused their analysis on the region of the stellar wind-bubble associated to the Orion Veil.
• FORCAST and FLITECAM imaging of the Orion Bar at 3.3 and 11.2 microns  (proposal ID: 04_0058), targeting PAH's emission signatures and diagnostic of PAH’s size and abundance.
• FIFI-LS maps of mid-J CO lines between 69 and 200 microns (proposal ID: 03_0044), which can trace the thermal structure of shocked gas.

Other available data include high resolution spectra of dust obscured compact sources observed with EXES, and large mid-IR photometric maps obtained with FORCAST.

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Betelgeuse High Resolution 25 Micron Spectra 2015-2020

An observing program was executed close to the Betelgeuse's V-band minimum in February 2020 under several Director's Discretionary Time (DDT) programs.

These observations obtained with the EXES instrument were focused on high-spectral resolution spectra around 25 microns, encompassing forbidden [Fe II], [S I] and two water absorption features. Similar data were already obtained in 2015 and 2017, allowing evaluations of variations in line flux and width over time, with sufficient resolution (R~50000) to identify gas velocity changes.

Preliminary data appear to show that the water features at 25.24 microns are significantly deeper in 2020 compared to 2017. However, modeling is needed to confirm the celestial origin of the variation of the water features.

Graham Harper, University of Colorado Boulder, and his team demonstrated that [Fe II] and [S I] emission lines, originating from circumstellar regions well above the photosphere, display no significant change from 2015 to 2020 (paper published in ApJL). Their results suggest that while dust heating can be very sensitive to photometric variations, circumstellar gas in the regions probed by [Fe II] and [S I] lines may not be significantly heated by dust.

All EXES Betelgeuse calibrated data, including from 2020 observations, are publicly available on the IRSA archive under program IDs 75_0051, 05_0073, and 02_004.

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Galactic Center Legacy Program

The inaugural Legacy Program used the FORCAST instrument to observe the Galactic Center using the 25-micron and 37-micron bands. The data have unprecedented spatial resolution – six times higher than past observations — resulting in a vastly improved view of warm dust in the center of the galaxy and revealing signatures of star formation in exquisite detail.

FORCAST created high-quality mosaics of the most active star forming portions of the inner ~200 pc of the galaxy with an angular resolution of 2.3" and 3.4" for the 25 and 37 μm observations, respectively. They cover more than 99% of the hard saturated area in the corresponding Spitzer/MIPS mosaic. An overview paper meant to accompany the first survey data release has recently been published in ApJ. The data are available publicly available in the archive under project ID 07_0189 for further research. The composite image shows SOFIA data taken at 25 and 37 μm in blue and green, data from Herschel in red (70 μm), and the Spitzer Space Telescope in white (8 μm).

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[OI] and CO Maps of Pillars in the Carina Nebula

The Carina Nebula is home to several massive star clusters and more than 65 O stars. The Trumpler 16 cluster, including its famous member eta Carina, is thought to power the winds and radiation responsible for carving out the complex structures seen in Figure 1. Based on the morphology of these structures, this region of the Carina Nebula known as the South Pillars. Because these pillars are likely formed by the strong winds and radiation of massive stars, they are ideal places to investigate the interaction between this stellar feedback and dense molecular gas. Using the fully-sampled and velocity-resolved GREAT maps of these pillars, scientists can probe the kinematics, morphology, and physical conditions within these interesting regions.

The data are available publicly available in the archive under project ID 75_0038 for further research.

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[C II] Map of the M51 Galaxy

The entire galaxy M51 was imaged using both FIFI-LS and GREAT. The FIFI-LS observations took only 7 hr of observatory (wall-clock) time. The image is shown with a surface brightness scale in units of erg/s/cm2/sr. Read more here.

The data are available publicly available in the archive under project ID 04_0116 for further research.

“A SOFIA Survey of [C II] in the Galaxy M51. I. [C II] as a Tracer of Star Formation”
J.L.Pineda et al (2018), ApJL, 869, L30

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30 Doradus

Polarization maps of the star-forming region 30 Doradus in the Large Magellanic Cloud using HAWC+. The maps were taken at 53, 89, 154, and 214 μm, revealing dust emission between 10-100 K and allowing for an inferred morphology study of the magnetic field. Read more here.

The data are available publicly available in the archive under project ID 76_0001 for further research.

"SOFIA Community Science I: HAWC+ Polarimetry of 30 Doradus"
Gordon, et al, 2018, arXiv:1811.03100.

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Horsehead Nebula [C II] Map

Velocity resolved map of the Horsehead Nebula—a dark nebula and photodissociation region in the Orion Molecular Cloud Complex—using GREAT. The map was taken in the [C II] line at 158 μm. Read more here.

The data are available publicly available in the archive under project ID 75_0015 for further research.

"Kinematics of the Horsehead Nebula and IC 434 Ionization Front in CO and C+"
Bally, John, et al., 2018, AJ, 155, 80.
 

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SN 2014J Imaging and Spectroscopy

Imaging and grism spectroscopic data to probe the ejecta and surroundings of the bright Type Ia Supernova, SN 2014J, in M82. The observations were taken using FORCAST and the now retired instruments FLITECAM and HIPO. Read more here.

"Observations of Type Ia Supernova 2014J with FLITECAM/SOFIA"
Vacca, W. D., et al., 2015, ApJ, 804, 66.

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