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Appendix F: Report of the Panel on the Interstellar Medium and Star and Planet Formation
Pages 305-324

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From page 305...
... In this complex, turbulent, and dynamic environment, clouds of dense molecular gas are produced that are the sites of star formation. Within these molecular clouds, dense cores form that eventually gravitationally collapse and often fragment further to form stars with a wide range of masses.
From page 306...
... Shifting to local studies of Milky Way molecular clouds, there have been substantial developments in our understanding of the many relevant physical scales and processes associated with star formation. Surveys of local star-forming regions with Spitzer provided the first complete censuses of their low-mass protostars and analyzed their spatial distributions relative to the cloud structures.
From page 307...
... Laboratory experiments, including microgravity studies of dust particle collisions, chemical measurements of ice mantle formation and sublimation, and analyses of meteorites, provide critical inputs for both theoretical models and the interpretation of astronomical data. Building on these many achievements over the past decade, this appendix discusses the opportunities for making further progress in characterizing and understanding the state of the ISM in the Milky Way and nearby galaxies, star formation, and planet formation, greatly assisted and informed by the contributions of more than 150 science white papers from the broader community.
From page 308...
... Imaging cold neutral gas structures in emission is also critical to uncover the cold gas dynamics, organization, and connection to star formation. Our view of the Milky Way's ISM has been hampered by seeing it in projection.
From page 309...
... Enabling the full diagnostic potential of these lines requires high-velocity resolution farIR observations coupled with matched resolution diagnostics of the ionized, atomic, and molecular gas phases (e.g., Hα, HI, and CO) to separate the emission arising from various phases.
From page 310...
... High-resolution UV spectroscopy can provide measurements of the depletion of heavy elements in the MW and nearby galaxies; low-resolution UV through mid-IR spectroscopy can trace the extinction curve; and mid-IR spectroscopy with JWST will better characterize the silicate absorption bands and other features. X rays can provide detailed information on dust mineralogy and dust-to-gas ratio, via measurements of absorption edges and scattering halos.
From page 311...
... The densest gas, in which stars form, generally comprises only a few percent of the total cloud mass, leading to low global star formation efficiencies. An observational census of the dense gas as a function of interstellar environment, and understanding how dense structures form and evolve, has important implications for understanding galactic-scale star formation.
From page 312...
... , is needed to distinguish heating by turbulent dissipation, stellar radiation and/or cosmic rays. To address the role of magnetic fields in cloud structure and dynamics, high-resolution (<0.1 pc, ~10" to resolve filaments in MW clouds)
From page 313...
... radio and mm spectroscopy of large samples of nearby galaxies to detect HCN, HCO+, CO isotopologues, and different excitation lines (>10× fainter than CO) are crucial to measuring the physical state of dense gas, then relate that to environment and the star formation efficiency.
From page 314...
... will provide complementary data on rarer, high-amplitude variability like FU Orionis star outbursts, PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION F-10
From page 315...
... The form of the stellar initial mass function (IMF) , provides a fundamental test of star formation theories and is crucial to the interpretation of the composite spectra of distant galaxies.
From page 316...
... That hypothesis would falsify the classical planet formation models that predict very slow time scales in the outer regions of disks, and point instead to more efficient mechanisms to assemble giant planets with (at least initially) long orbital periods (perhaps employing rapid planetesimal formation and pebble accretion)
From page 317...
... The most promising options for determining the temperature, density, chemical, and dynamical structure PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION F-13
From page 318...
... , and the origins and evolution of both the solar system and the exoplanet population. Observations of dynamically cleared gaps in circumstellar disks may point to a population of young giant planets with masses ~ 10 M⊕ to 10 PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION F-14
From page 319...
... The physical conditions, spatial structures, and dynamics of CPDs are controlled by the combined gravitational potential of the protoplanet and host star, the local heating, and the mechanics of mass transfer from the circumstellar disk reservoir. Direct imaging measurements of the CPD spectral energy distribution (SED)
From page 320...
... Then, by empirically characterizing how these planets perturb their disks as a function of their mass, we could extrapolate to indirectly infer constraints on the mass function into the super-Earth regime by measuring more subtle disk substructures. These young planetary architectures could then be compared with their more evolved counterparts around main-sequence hosts found from microlensing surveys and direct imaging campaigns.
From page 321...
... The ISM, star formation, and planet formation also involve key physical processes that are less commonly encountered elsewhere, including nonideal MHD and multiple-fluid effects, complex timedependent chemistry and dust evolution, and planetary growth processes (F-Q1, F-Q2, F-Q3, F-Q4)
From page 322...
... F-Q2b: What is the origin and prevalence of high density structures in molecular clouds, and what role do they play in star formation? F-Q2c: What generates the observed chemical complexity of molecular gas?
From page 323...
... (F-Q3) Laboratory and other F-Q1, F-Q2, Existing laboratories Properties of dust at X-ray through mm PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION F-19
From page 324...
... ; ices, spectroscopy, cross gas/surface chemistry, dust properties sections, physical and growth (F-Q1, F-Q2, F-Q4) properties of grain materials, plasma astrophysics PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION F-20


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