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1. The Computational Complexity of Feasibility Analysis for Conditional DAG Tasks

   https://doi.org/10.1145/3606342  

   Baruah, Sanjoy; Marchetti-Spaccamela, Alberto (September 2023, ACM Transactions on Parallel Computing)

   The Conditional DAG (CDAG) task model is used for modeling multiprocessor real-time systems containing conditional expressions for which outcomes are not known prior to their evaluation. Feasibility analysis for CDAG tasks upon multiprocessor platforms is shown to be complete for the complexity classpspace; assumingnp≠pspace, this result rules out the use of Integer Linear Programming solvers for solving this problem efficiently. It is further shown that there can be no pseudo-polynomial time algorithm that solves this problem unlessp=pspace. 

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2. Tracing the Ionization Structure of the Shocked Filaments of NGC 6240

   https://doi.org/10.3847/1538-4357/ac2ebb  

   Medling, Anne M.; Kewley, Lisa J.; Calzetti, Daniela; Privon, George C.; Larson, Kirsten; Rich, Jeffrey A.; Armus, Lee; Allen, Mark G.; Bicknell, Geoffrey V.; Díaz-Santos, Tanio; et al (December 2021, The Astrophysical Journal)

   Abstract We study the ionization and excitation structure of the interstellar medium in the late-stage gas-rich galaxy merger NGC 6240 using a suite of emission-line maps at ∼25 pc resolution from the Hubble Space Telescope, Keck/NIRC2 with Adaptive Optics, and the Atacama Large Millimeter/submillimeter Array (ALMA). NGC 6240 hosts a superwind driven by intense star formation and/or one or both of two active nuclei; the outflows produce bubbles and filaments seen in shock tracers from warm molecular gas (H₂2.12μm) to optical ionized gas ([Oiii], [Nii], [Sii], and [Oi]) and hot plasma (FeXXV). In the most distinct bubble, we see a clear shock front traced by high [Oiii]/Hβand [Oiii]/[Oi]. Cool molecular gas (CO(2−1)) is only present near the base of the bubble, toward the nuclei launching the outflow. We interpret the lack of molecular gas outside the bubble to mean that the shock front is not responsible for dissociating molecular gas, and conclude that the molecular clouds are partly shielded and either entrained briefly in the outflow, or left undisturbed while the hot wind flows around them. Elsewhere in the galaxy, shock-excited H₂extends at least ∼4 kpc from the nuclei, tracing molecular gas even warmer than that between the nuclei, where the two galaxies’ interstellar media are colliding. A ridgeline of high [Oiii]/Hβemission along the eastern arm aligns with the southern nucleus’ stellar disk minor axis; optical integral field spectroscopy from WiFeS suggests this highly ionized gas is centered at systemic velocity and likely photoionized by direct line of sight to the southern active galactic nucleus. 

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3. New Observations of the IR Emission Corona from the 2019 July 2 Eclipse Flight of the Airborne Infrared Spectrometer

   https://doi.org/10.3847/1538-4357/ac6ce8  

   Samra, Jenna E.; Madsen, Chad A.; Cheimets, Peter; DeLuca, Edward E.; Golub, Leon; Marquez, Vanessa; Reyes, Naylynn Tañón (July 2022, The Astrophysical Journal)

   Abstract The Airborne Infrared Spectrometer (AIR-Spec) was commissioned during the 2017 total solar eclipse, when it observed five infrared coronal emission lines from a Gulfstream V research jet owned by the National Science Foundation and operated by the National Center for Atmospheric Research. The second AIR-Spec research flight took place during the 2019 July 2 total solar eclipse across the south Pacific. The 2019 eclipse flight resulted in seven minutes of observations, during which the instrument measured all four of its target emission lines: Sxi1.393μm, Six1.431μm, Sxi1.921μm, and Feix2.853μm. The 1.393μm Sxiline was detected for the first time, and probable first detections were made of Sixi1.934μm and Fex1.947μm. The 2017 AIR-Spec detection of Feixwas confirmed and the first observations were made of the Feixline intensity as a function of solar radius. Telluric absorption features were used to calibrate the wavelength mapping, instrumental broadening, and throughput of the instrument. AIR-Spec underwent significant upgrades in preparation for the 2019 eclipse observation. The thermal background was reduced by a factor of 30, providing a 5.5× improvement in signal-to-noise ratio, and the postprocessed pointing stability was improved by a factor of 5 to <10″ rms. In addition, two imaging artifacts were identified and resolved, improving the spectral resolution and making the 2019 data easier to interpret. 

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4. The Baryonic Content of Galaxies Mapped by MaNGA and the Gas Around Them

   https://doi.org/10.3847/1538-4357/ace329  

   Klimenko, Viacheslav_V; Kulkarni, Varsha; Wake, David_A; Poudel, Suraj; Bershady, Matthew_A; Péroux, Celine; Lundgren, Britt (August 2023, The Astrophysical Journal)

   Abstract We analyze the cool gas in and around 14 nearby galaxies (atz< 0.1) mapped with the Sloan Digital Sky Survey IV MaNGA survey by measuring absorption lines produced by gas in spectra of background quasars/active galactic nuclei at impact parameters of 0–25 effective radii from the galactic centers. Using Hubble Space Telescope/Cosmic Origins Spectrograph, we detect absorption at the galactic redshift and measure or constrain column densities of neutral (Hi, Ni, Oi, and Ari), low-ionization (Siii, Sii, Cii, Nii, and Feii), and high-ionization (Siiii, Feiii, Nv, and Ovi) species for 11 galaxies. We derive the ionization parameter and ionization-corrected metallicity usingcloudyphotoionization models. The Hicolumn density ranges from ∼10¹³to ∼10²⁰cm⁻²and decreases with impact parameter forr≳R_e. Galaxies with higher stellar mass have weaker Hiabsorption. Comparing absorption velocities with MaNGA radial velocity maps of ionized gas line emissions in galactic disks, we find that the neutral gas seen in absorption corotates with the disk out to ∼10R_e. Sight lines with lower elevation angles show lower metallicities, consistent with the metallicity gradient in the disk derived from MaNGA maps. Higher-elevation angle sight lines show higher ionization, lower Hicolumn density, supersolar metallicity, and velocities consistent with the direction of galactic outflow. Our data offer the first detailed comparisons of circumgalactic medium (CGM) properties (kinematics and metallicity) with extrapolations of detailed galaxy maps from integral field spectroscopy; similar studies for larger samples are needed to more fully understand how galaxies interact with their CGM. 

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5. A Rapid Ionization Change in the Nebular-phase Spectra of the Type Ia SN 2011fe

   https://doi.org/10.3847/2041-8213/ac4fbd  

   Tucker, M. A.; Ashall, C.; Shappee, B. J.; Kochanek, C. S.; Stanek, K. Z.; Garnavich, P. (February 2022, The Astrophysical Journal Letters)

   Abstract We present three new spectra of the nearby Type Ia supernova (SN Ia) 2011fe covering ≈480–850 days after maximum light and show that the ejecta undergoes a rapid ionization shift at ∼500 days after explosion. The prominent Feiiiemission lines at ≈4600 Å are replaced with Fei+Feiiblends at ∼4400 Å and ∼5400 Å. The ≈7300 Å feature, which is produced by [Feii]+[Niii] at ≲400 days after explosion, is replaced by broad (≈±15,000 km s⁻¹) symmetric [Caii] emission. Models predict this ionization transition occurring ∼100 days later than what is observed, which we attribute to clumping in the ejecta. Finally, we use the nebular-phase spectra to test several proposed progenitor scenarios for SN 2011fe. Nondetections of H and He exclude nearby nondegenerate companions, [Oi] nondetections disfavor the violent merger of two white dwarfs, and the symmetric emission-line profiles favor a symmetric explosion. 

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