Principal Investigator: Paul Goldsmith (Jet Propulsion Laboratory)
Title: Probing Stellar Feedback at cloud boundaries using [OI] observations in SOFIA Data Archive
Abstract: Here we propose to study stellar feedback at cloud boundaries through the kinematics and luminosity of [OI] emission and determine the gas-phase oxygen abundance in warm atomic/molecular regions. Observations of atomic oxygen fine structure line (hereafter [OI]) emission are invaluable in astronomy, since this emission traces exclusively stellar feedback to molecular clouds, which in turn regulates star formation and drives galaxy evolution. The [OI] lines also provide valuable information about the oxygen abundance in high-density regions, which controls the formation of water (Van Dishoeck, Herbst, & Neufeld 2013), an essential molecule for life. However, velocity-resolved [OI] observations are very rare compared to the observations of major atomic and molecular species, (e.g. CO and HI) since the [OI] emission is only observable using suborbital or space telescopes. To date, SOFIA observations of [OI] represent the largest body of velocity-resolved [OI] data. This large data set can make a significant impact on astronomical studies. The proposed program will study [OI] kinematics and the gas-phase oxygen abundance using the large set of SOFIA [OI] spectral maps. These data are all currently in the SOFIA Science Archive. We will focus on the bright star-forming regions observed in both [OI] 63 µm and 146 µm using the SOFIA GREAT and upGREAt instruments. To probe the stellar energy input to the surface of molecular clouds, we will compare the [OI] spectra to the [CII] and CO spectra. This will reveal the unique dynamics of the PDRs (turbulence and gas flows using the [OI] linewidth and skewness) and highlight processes such as photoevaporation and radiation stripping. We will also carry out PDR modeling and the model will provide a relation between thermal pressure Pth and the FUV flux G0, P_th∝ G_0^α, where α is a free parameter describing the relation and determined by the physics of the HII region and PDR.
Principal Investigator: Paul Goldsmith (Jet Propulsion Laboratory)
Title: Probing the ISM baryon cycle and the transition rates between different ISM phases using machine learning
Abstract: We propose to probe the baryon life cycle by estimating the transition rates between ISM phases in several high-mass star-forming regions, including Orion, Carina, NGC 6334, and 30 Doradus. We will also compare the resulting transition rates to theoretical simulations, where the rates are used as a free parameter to control the outcomes, and test the stellar feedback mechanisms implemented in the galaxy evolution theories. The baryon cycle of the ISM is a critical process in the Universe because it is the primary mechanism of galaxy evolution. Among many ISM properties, the transition rates between different ISM phases are the most critical parameters that directly connect observations with theories. However, the transition rates are rarely estimated due to lack of an efficient method to measure the essential ISM properties for calculating the transition rates such as spatial and density distributions of each ISM phases and FUV flux at a large spatial scale containing an entire star-forming region at an adequate resolution. In this study, we will develop a novel methodology using generative adversarial networks (GANs) that estimates the density structure and FUV flux across the entire observed regions pixel-by-pixel from SOFIA and ancillary observations. The trained GAN will take the emission intensities of observations (e.g., [CII], [OI], CO, Hα and dust continuum) as input variables and deliver the ISM phase types and their properties (column density and volume fractions) as outputs. Using the property maps, we will estimate the transition rates between ISM phases and test the stellar feedback mechanisms in ISM and galaxy evolution simulations. The proposed program will deliver an exclusively detailed view of the distribution of various ISM phases in star-forming regions and the transition rate between ISM phases to constrain galaxy evolution simulations.
Principal Investigator: Archana Soam (USRA)
Title: Investigation on gas kinematics and dynamics of the Carina Pillars: Origin of flows and estimation of physical properties
Abstract: The interaction of newly formed stars with their natal clouds give a rise to a number of dynamical and chemical effects, forming HII regions, injecting energy in the surrounding ISM, and forming PDRs. These provide valuable laboratories of radiation driven dynamics and physical/chemical evolution of the gas and dust. Because of their high spectral resolution, SOFIA/GREAT data provide detailed information on star-formation, gas flows, turbulent motions and constraints models of radiation driven cloud evolution and the chemistry and physics of PDRs. For this purpose, we propose to work on SOFIA archival data of the Carina nebula under project 75_0038. This project contains a sufficient amount of mid- and high-J CO lines with [OI] 63 um data on four Carina pillars irradiated by eta-Carina. We already started analyzing data on one of the pillars, G287.76-0.87. Our preliminary results shows that the head of this pillar is moving toward us more slowly than eta-Carina, so in the rest frame of this star, the pillar is moving away from us. If the pillars form part of an expanding complex, then this velocity would mean that the pillar is on the far side, i.e., more distant than eta-Carina. We want to extend our investigation in other two pillars, namely G287.722-0.59 and G287.926-0.1. The Carina nebula has also been studied by ALMA, APEX, SIRPOL, BLASTPol etc. Therefore, available SOFIA archival data will be combined with these other available datasets to perform a multiwavelength analysis of gas flows and physical properties of the pillars in Carina. One paper on kinematics of a single pillar is under preparation. We expect two more papers, one gas and dust emissions and other with gas flows and magnetic field orientations. Therefore, we request for one year of SARP funding for the completion of this project.
Principal Investigator: Loren Anderson (West Virginia University)
Title: Expansion of HII Regions, Stellar Feedback, and the Implications for Triggered Star Formation
Abstract: As HII regions expand, they may cause the collapse of condensations on their peripheries. This process is known as triggered star formation, and is one example of "positive" stellar feedback. We do not know the importance or timescale for triggered star formation, in large part because until recently it was very difficult to measure HII region expansion. SOFIA maps of the [CII] line, however, have proven to be exceptional tracers of HII region expansion. The SOFIA archive contains ~30 [CII] maps of individual Galactic HII regions, a map of the Galactic center that covers many HII regions, and ~10 maps of HII regions in the Large and Small Magellanic Clouds. These HII regions span a wide range of sizes and luminosities, and provide a representative sample of high mass star formation regions. We will investigate the expansion of all suitable HII regions and explore the implications for stellar feedback and triggered star formation. We will then determine the dependence of the expansion rates on HII region and ionizing source properties. SOFIA is the only observatory that can provide the needed spatial and spectral resolution in [CII] mapped over entire HII regions. These observations will allow us to determine expansion rates in a large sample of HII regions and determine if the expansion is related to HII region or stellar properties. This work will result in knowledge of how quickly triggered star formation must proceed, and the importance of stellar feedback in the evolution of HII regions.
Principal Investigator: Fiorella Polles (USRA)
Title: Investigating the electron density distribution in low-metallicity environment with multiple diagnostics
Abstract: The study of the galaxies up to the Epoch of Reionization through the investigation of the [OIII] 88μm/[CII] 158μm ratio is now possible with ALMA. However, often overlooked in both the high-z and nearby galaxy studies is the electron density diagnostic capability of the line ratio [OIII]88μm/[OIII]52μm, also available at high-z with ALMA, and with SOFIA in the local universe. As valuable as this ratio is to investigate the structure of these objects, alone it does not provide the complete picture of the inhomogeneous ionized gas distribution. A combination of several ratios, probing densities of different gas phases, is necessary to tell the full story. While a rich set of tracers is not yet possible at high-z, the 'chemically-young' environment that characterizes the high-z galaxies can be found in the nearby low-metallicity dwarf galaxies. This archival project will investigate the electron density distribution in low metallicity environments, bring clarity to the use of different density diagnostics, and deliver advice on the usefulness of the [OIII]88μm/[OIII]52μm ratio. With these lines, combined with other available optical, mid- and far-infrared electron density diagnostics, we will perform this pilot study on three dwarf galaxies: NGC1140, NGC1569 and NGC5253. We will develop multi-component models using Cloudy and compare observables with synthetic spectra produced by Cloudy with a density distribution of clouds. This method will allow us to identify the relation between observables and the associated density structure. The models and the observables will be combined using a new in-hand Bayesian code that computes the probability density function of the physical parameters from a suite of observables and mitigates issues related to the χ2 method. We aim to provide interpretive tools to draw reliable conclusions on the properties of ionized gas phases in galaxies.
Principal Investigator: Sarah Nickerson (Bay Area Environmental Research Institute)
Title: Building the Mid-Infrared Molecular Inventory in Star Forming Regions
Abstract: The mid-infrared (MIR) provides the only access to rovibrational transitions and molecules with no permanent dipole moment. Compared to longer wavelengths in the radio, sub-mm and far-infrared, the MIR uniquely probes hot core material closest to embedded protostars. Nonetheless, the MIR has historically been underutilized in analogous astrochemical studies for reasons including atmospheric interference and low available spectral resolution from previous space missions. Most high spectral resolution line surveys have been limited to the radio, sub-mm and far-infrared wavelengths. Accordingly, the model chemical networks require testing and refinement in the MIR regime. SOFIA/EXES is presently is only spectrograph that both accesses nearly the entire the MIR and can resolve individual molecular transitions. We will compile the first large-scale study of hot cores in the MIR, comparing the six hot cores with extensive data in the SOFIA archive. We will analyze the rich, unpublished spectra and species we have found in the archive and combine these findings with published data in order to compare the presence of species and their relative abundances across these hot cores. In order to accomplish this, we are near completion of a suite of analysis tools for the EXES spectra. Unlike other spectral analysis codes, ours is tuned for the MIR. We intend to publish and make our code publicly available for the community to aid other groups' research. Our work will yield unique insights into the interplay between a massive protostar's age and environment, and the molecular signatures in the hot core that envelops it. Comparison to chemical models will confirm existing theory and reveal new relationships between species. This comprehensive data set will serve as an invaluable, and first of its kind, reference for the astrochemical scientific communities.
Principal Investigator: Jonathan Tan (University of Virginia)
Title: Massive Protostars Across the Galaxy
Abstract: We propose to carry out the most comprehensive radiative transfer (RT) and spectral energy distribution (SED) modeling study to date of high- and intermediate-mass protostars via analysis of FORCAST and HAWC+ archival data of such sources in a variety of environments across the Galaxy. This project will yield the information needed to make fundamental tests of massive star formation theories. In addition to simple SED fitting, which is prone to having degeneracies in derived parameters, detailed analyses of the image morphologies, e.g., brightness distributions along outflow axes, will also be carried out to further constrain protostellar properties. In this way we will obtain the most accurate and broadest census of massive protostars as a function of environmental conditions. We will then be able to examine if there is a critical density for forming the most massive stars and assess the clustering properties of high- and intermediate-mass protostars in different regions. By comparison with IRAS and other datasets, we will also search for accretion burst driven variability. This project is highly synergistic with a number of other methods of studying massive protostars, since SED and RT modeling of thermal dust emission is one of the best ways to measure basic physical properties of these systems, which are crucial inputs to models of their outflows, ionization structures and astrochemistry.
Principal Investigator: Tommy Wiklind (Catholic University of America)
Title: Far-Infrared Diagnostic Emission Lines: Probing Metallicity Across Cosmic Time
Abstract: Far-infrared atomic fine-structure lines can be used to derive gas density, ionization parameter and gas-phase metallicity in both local and high-z galaxies. In contrast to optical/UV diagnostic lines, they are not affected by extinction. However, these lines have only recently become available, thanks to Herschel/PACS and now SOFIA/FIFI-LS. Their usefulness in characterizing the interstellar gas needs to be verified through comparison with established optical/UV diagnostics. With this SOFIA archival proposal we aim to analyze a large set of far-infrared fine-structure lines observed with SOFIA in nearby low-metallicity dwarf galaxies. The SOFIA archive contains 62 data-sets, spread over 21 low-metallicity dwarf galaxies. Combined with complementary spectroscopic data from Herschel, the SOFIA/FIFI-LS data comprises an impressive suite of fine-structure lines that can be used to characterize the gas, and compare with optical/UV diagnostics. Theoretical ionization models suggest that the ratio ([OIII]52+[OIII]88)/[NIII]57 is a gas-phase metallicity diagnostic, useful down to ~0.2Zo. We will test the validity of these model results. We will also test other combinations of far-infrared fine-structure line ratios and their diagnostic values for characterizing the gas. In particular, we will apply the results from our local metal-poor galaxies with recent ALMA observations of high redshift systems. ALMA is providing a growing number of fine-structure line observations at high-z, but due to atmospheric absorption, only a limited set of far-infrared lines are accessible at a given redshift. Hence, several 'secondary' diagnostics are needed for high-z galaxies. One caveat with using a O/N diagnostic is the complicated production of nitrogen. The O/N ratio has been proposed to depend on the star formation history. We will investigate this by deriving non-parametric star formation histories for galaxies in our sample using a state-of-the-art SED-fitting across UV-FIR wavelengths.
Principal Investigator: Michael Kuhn (California Institute of Technology)
Title: Why do young embedded clusters disperse? Connecting stellar dynamics to H II region expansion
Abstract: Most star-forming regions produce stars that disperse after formation rather than remaining together as a bound cluster. This is thought to be a consequence of stellar feedback that expels remaining molecular gas, and this mass loss, in turn, leaves the stars gravitationally unbound. However, theoretical models make differing predictions about the strength of this effect and mechanism by which gas expulsion disrupts clusters. It has recently become possible to observe both processes - gas expulsion and star cluster disruption - simultaneously, with [CII] data cubes revealing expanding HII bubbles around massive clusters and Gaia astrometry showing the expansion of those clusters. We propose to perform a joint analysis of archival 158 micron [CII] observations from the SOFIA/GREAT FEEDBACK legacy program together with publicly available Gaia EDR3 astrometry of stars for two massive star-forming regions, M16 and M17. In this analysis, we will connect the patterns seen in stellar velocities to signs of expansion seen in the gas. We will estimate expansion velocities for the bubbles and stellar groups, examine differences in stellar velocities for stars projected inside and outside the bubbles, and estimate bubble expansion timescales and trace-back times for stars. We will determine whether the results are consistent with a cause-effect relationship between bubble and cluster expansion, we will examine whether the bubble properties affect cluster expansion, and we will compare these results to expectations from theoretical models.
Principal Investigator: David Chuss (Villanova University)
Title: Testing the Predictions of RAT Theory in Star Forming Clouds
Abstract: We propose to use multiwavelength HAWC+ observations for exploring correlations between the polarization fraction, slope of the polarization spectrum, polarization dispersion and environmental variables including column density and temperature across an ensemble of sources of high mass star formation within the HAWC+ archival catalog. This investigation will test RAT grain alignment theory. The improved understanding of the environmental constraints on grain alignment will serve to enhance the efficacy of statistical methods such as the polarization dispersion analysis (PDA) and histogram of relative orientation (HRO) techniques that are increasingly important in understanding the role of magnetic fields in star formation.
Principal Investigator: Jordan Guerra (Villanova University)
Title: Statistical Study of the Magnetic Field Structure in Molecular Clouds of the Gould Belt
Abstract: We propose an statistical study of the magnetic field strength and orientation in molecular clouds of the Gould Belt (GB). The Davis-Chandrasekhar-Fermi (DCF) method will be used within circular kernels to calculate local values of the POS magnetic field strength and thus construct maps. For the DCF method we will use angular dispersion measured from HAWC+/SOFIA polarimetric observations of GB clouds, column density maps from Herschel and velocity dispersion maps from the Green Bank Observatory Ammonia survey. Maps of the POS magnetic field will be used to create maps of the mass-to-flux ratio with angular resolution of up to ten times higher than that of Planck data. Histograms of relative orientation (HRO) will be constructed using the mass-to-flux ratio maps to observationally test the alignment of magnetic fields with filamentary structures at subparsec scales and compare with results from magnetohydrodynamical (MHD) simulations of molecular clouds and star formation.
Principal Investigator: H Perry Hatchfield (University of Connecticut)
Title: IGNITES: Investigating Galactic Nuclear Infrared Thermal Evolution of young Stars
Abstract: We propose the production of a census of evolutionary properties of star formation in the Milky Way's Galactic Center using 25.2 and 37.1um SOFIA's FORCAST instrument observations. The Central Molecular Zone (CMZ) provides a unique testbed for environmentally dependent theories of star formation which are vital for our interpretation of unresolved extragalactic observations. The CMZoom survey, a ~550 hour legacy program of the Submillimeter Array (SMA), produced a catalog of ~99% of possible sites of future high mass star formation in the CMZ. SOFIA's FORCAST instrument has recently produced high resolution maps of many key molecular clouds observed by CMZoom. By combining these two legacy program data sets, along with 8, 70, 160 and 250um data from Spitzer and Herschel, we will fit dust emission models for all CMZoom catalog objects. By studying this unbiased sample of dense substructure, we will characterize the distribution of thermal evolutionary states across the CMZ. We will then identify all deeply embedded star-forming sources and prepare more specific spectral models to further parametrize the star formation state. Additionally, we will consider the presence of other star formation tracers and evolutionary markers such as outflow signatures, H_2O and CH_3OH maser populations, and young stellar objects cataloged by previous surveys. By combining all of these readily available datasets, we will construct a census of evolutionary states for massive star forming regions across the Galactic Center and determine an accurate star formation rate for the CMZ. These products will be powerful resources for the study of environmentally dependent star formation and massive star formation, impacting how we understand spatially unresolved star formation throughout the more distant universe.
Principal Investigator: Jens Kauffmann (Haystack Observatory, Massachusetts Institute of Technology)
Title: Feedback and the Gao & Solomon Relation seen through [CII] and HCN
Abstract: Emission in the [CII] line accessible to SOFIA is observed to correlate with the star formation rate in galaxies. Emission in this line essentially probes how feedback from high-mass stars affects molecular clouds. The star formation rate in galaxies is also observed to correlate with the luminosity of the HCN (1-0) transition at 89 GHz (i.e., Gao-Solomon relation). This radiation originates in the denser sections of molecular clouds, and it provides an overall measure of the cloud material available for star formation. These well-established correlations imply a close connection between [CII] and HCN emission — which to our best knowledge has not been explored to date. This is regrettable, since investigations of the connections between [CII] and HCN emission allow to explore a hitherto relatively unexplored aspect of cloud structure. Specifically, the [CII]–to–HCN line ratio should provide information on the extent to which dense gas is affected by feedback. Constraints on the connection between dense gas and feedback are important for progress in astrophysics: the star formation rate per free–fall–time in galaxies is surprisingly low, and models of feedback–regulated star formation argue that this is the case because dense gas is disrupted by feedback. This investigation will deliver a new method that can in future be used to deliver rich new constraints on feedback–regulated star formation. We will study a sample of at least 6 molecular clouds in the Milky Way to investigate how the [CII]–to–HCN line ratio is influenced by cloud substructure and cloud evolution. We will also study at least two nearby galaxies to understand how the connection between dense gas and feedback might depend on the galactic environment. The observational work is complemented by a review of theoretical constraints on the connection between the emission in the [CII] and HCN (1–0) lines. All of the required maps in the [CII] and HCN (1–0) lines exist in science–ready format.
Principal Investigator: Glenn Orton (Jet Propulsion Laboratory)
Title: Analysis of Spectroscopy and Photometry of Uranus and Neptune at 17 - 37 microns
Abstract: This proposal will address photometric and spectroscopic observations of Uranus and Neptune from 17 to 37 microns using the FORCAST instrument in Cycle 3. This spectral region includes wavelengths falling between the limits of ISO Short-Wavelength Spectrometer and Spitzer IRS infrared observations. The analysis of these observations will advance our knowledge of the radiative and convective processes shaping the atmospheric dynamics of these two "Ice Giants". They will also determine the extent of para vs. ortho H2 disequilibrium in the upper tropospheres of both planets, improving constraints on the He/H2 ratio. The latter is a crucial value required to elucidate differences in formation mechanisms that distinguish them from the gas giants, Jupiter and Saturn. The proposed observations are also vital for ongoing efforts to develop models for the spectra of both planets as key components of an absolute calibration system used by Herschel spacecraft instruments and long-wavelength Earth-based observations. The observations made in 2015 will provide an assessment of the longer-term, but sub-seasonal, variability of atmospheric temperatures when compared with anticipated JWST Uranus and Neptune observations.
Principal Investigator: Laura Lenkic (USRA)
Title: Investigating Gas Heating Efficiencies at Low Metallicity in the Magellanic Clouds
Abstract: Feedback from massive, in the form of energy deposited into the interstellar medium via stellar winds, supernova explosions, and photo-ionization shapes the surrounding environment, and can both inhibit and promote the formation of new stars. To understand galaxy evolution across cosmic time, it is necessary to study the interaction of massive stars with their surrounding ISM in a range of galactic environments, particularly at low metallicity which more closely resembles the early Universe. Owing to their proximity (50-60 kpc) and low-metallicity (0.2-0.5x solar metallicity), the Large and Small Magellanic Clouds are ideal targets to study the interaction between massive stars and their surrounding gas. We propose to use unpublished SOFIA GREAT observations of the 157.7 um fine-structure line [CII] in 14 star-forming regions across the Magellanic Clouds to study the coupling efficiency between far-ultraviolet photons and the interstellar medium. We will combine SOFIA observations with data from Spitzer and Herschel to derive the [CII]/FIR ratio; a measure of gas heating efficiency, and investigate how variations in heating efficiency are related to the presence of known massive, young stars. This work will provide a sample that can be combined with results from the SOFIA FEEDBACK legacy survey to study the effects of metallicity.
Principal Investigator: Uma Gorti (SETI Institute)
Title: Investigating warm outflows from protoplanetary disks with [OI]
Abstract: Accretion in disks is currently believed to be mediated by magnetic fields under non-ideal MHD conditions, and mass and angular momentum transport in the disk are achieved via winds and outflows, manifest as fast 100 km/s jets close to the star. Jets and hot (T~5000-10000K) winds are both observed from accreting stars at optical wavelengths. There is scant evidence for winds at radii greater than a few au, with the exception of cold (T~10-100K) molecular outflows seen in some disks. The latter originate at tens of au, and could be entrained cloud material in young embedded sources or photoevaporative thermal winds in more evolved objects. How material in the disk gets transported over the full radial extent of the disk, including across the planet-forming regions, is still uncertain. We propose to analyze archival SOFIA observations of the [OI]63um line from young protoplanetary disks. [OI] emission can probe gas over a wide range of temperatures from a few 100 K to a few thousand K, therefore the disk surface and outflow regions are both expected to be luminous in [OI]. We will use theoretical models combined with high spectral resolution GREAT archival data and ancillary line emission data at other wavelengths that arise from both the disk and outflow regions, and disentangle the relative [OI] contributions from each. Our goal is to determine the presence (or absence) of a warm wind and its radial extent from the velocity resolved line profile. The presence of even a weak wind will establish the existence of a contiguous outflow that transports mass and angular momentum all through the disk, and will provide much-needed constraints to theoretical studies of accretion and magnetic field-driven evolution of disks.
Principal Investigator: Anicia Arredondo (SOFIA)
Title: Investigating the thermal evolution of large asteroids using FORCAST calibrator targets
Abstract: Context: SOFIA+FORCAST regularly obtains mid-infrared (MIR) spectra of large asteroids as calibrators for other observations. This previously unused dataset represents a remarkable long-baseline series of observations of several objects, and can be used to investigate the thermal histories of these bodies and how thermal and compositional properties may change over time. Aims: We will analyze the long-base line spectra of three asteroids traditionally used as calibrators: (1) Ceres, (2) Pallas and (4) Vesta. These objects have been regularly observed over a period from 2014- 2022. This study will search for effects on the spectra caused by viewing geometry, seasons/orbital parameters as well as changes over time in thermophysical properties and composition. Methods: SOFIA is one of the only observatories capable of observing asteroids at the wavelengths in which their thermal emission peaks (10-20 μm). We will fit these spectra with a variety of thermal models to determine if the thermal and physical properties change over time. Compositional differences will be investigated as well as the effects of viewing geometry on these objects. We will characterize any spectral features found, compare the spectra with laboratory mineral data, and see how the physical properties and mineralogy changes over time. Synergies: This dataset will allow the asteroid community to contextualize JWST observations of these objects and other main belt asteroids. This work will also be compared to the results of the Dawn Mission which orbited both Ceres and Vesta but did not have a MIR instrument. Anticipated results: This is the first long-baseline MIR dataset that has been observed. This work will provide the first ever investigation of thermophysical properties and composition over time, as well as the effects viewing geometry on MIR spectra. This work will support asteroid science moving into the next decade with upcoming asteroid missions and JWST observations.