SARP Selected Proposal Abstracts

Proposal ID: 09_0511

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.

Proposal ID: 09_0512

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.

Proposal ID: 09_0520

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.

Proposal ID: 09_0523

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.

Proposal ID: 09_0524

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.

Proposal ID: 09_0530

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.

Proposal ID: 09_0533

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.

Proposal ID: 09_0534

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.

Proposal ID: 09_0535

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.

Proposal ID: 09_0537

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.

Proposal ID: 09_0540

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.

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