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Magnetic field morphology and evolution in the Central Molecular Zone and its effect on gas dynamics
(EDP Sciences, 2024-11-22) Tress, Robin; Sormani, Mattia Carlo; Girichidis, P.; Glover, Simon; Klessen, Ralf Stephan; Smith, Rowan; Sobacchi, E.; Armillotta, Lucia; Barnes, A. T.; Battersby, C.; Bogue, Kamran R. J.; Brucy, Noé; Colzi, Laura; Federrath, C.; García, Pablo; Ginsburg, A.; Göller, Junia Aletta Beatrix; Hatchfield, H. P.; Henkel, C.; Hennebelle, P.; Henshaw, J. D.; Hirschmann, M.; Hu, Y.; Kauffmann, J.; Kruijssen, J. M. D.; Lazarian, A.; Lipman, Dani R.; Longmore, S. N.; Morris, Mark; Nogueras Lara, Francisco; Petkova, Maya A.; Pillai, Thushara; Rivilla, Victor M.; Sanchez-Monge, Alvaro; Soler, Juan Diego; Whitworth, David; Zhang, Qizhou; European Research Council (ERC); Royal Society; National Science Foundation (NSF); Consejo Superior de Investigaciones Científicas (CSIC); European Commission (EC); Deutsche Forschungsgemeinschaft (DFG); Ministerio de Ciencia e Innovación (MICINN); Agencia Estatal de Investigación (AEI); Chinese Academy of Science (CAS); Consejo Nacional de Ciencia y Tecnología (CONACyT); Unidad de Excelencia Científica María de Maeztu INSTITUTO DE CIENCIAS DEL ESPACIO, CEX2020-001058-M
The interstellar medium in the Milky Way’s Central Molecular Zone (CMZ) is known to be strongly magnetised, but its large-scale morphology and impact on the gas dynamics are not well understood. We explore the impact and properties of magnetic fields in the CMZ using three-dimensional non-self gravitating magnetohydrodynamical simulations of gas flow in an external Milky Way barred potential. We find that: (1) The magnetic field is conveniently decomposed into a regular time-averaged component and an irregular turbulent component. The regular component aligns well with the velocity vectors of the gas everywhere, including within the bar lanes. (2) The field geometry transitions from parallel to the Galactic plane near ɀ = 0 to poloidal away from the plane. (3) The magneto-rotational instability (MRI) causes an in-plane inflow of matter from the CMZ gas ring towards the central few parsecs of 0.01−0.1 M⊙ yr−1 that is absent in the unmagnetised simulations. However, the magnetic fields have no significant effect on the larger-scale bar-driven inflow that brings the gas from the Galactic disc into the CMZ. (4) A combination of bar inflow and MRI-driven turbulence can sustain a turbulent vertical velocity dispersion of σɀ = 5 km s−1 on scales of 20 pc in the CMZ ring. The MRI alone sustains a velocity dispersion of σɀ ≃ 3 km s−1. Both these numbers are lower than the observed velocity dispersion of gas in the CMZ, suggesting that other processes such as stellar feedback are necessary to explain the observations. (5) Dynamo action driven by differential rotation and the MRI amplifies the magnetic fields in the CMZ ring until they saturate at a value that scales with the average local density as B ≃ 102 (n/103 cm−3)0.33 µG. Finally, we discuss the implications of our results within the observational context in the CMZ.
The Galaxy Activity, Torus, and Outflow Survey (GATOS) V. Unveiling PAH survival and resilience in the circumnuclear regions of AGNs with JWST
(EDP Sciences, 2024-09-09) García-Bernete, Ismael; Rigopoulou, D.; Donnan, Fergus; Alonso-Herrero, Almudena; Pereira-Santaella, Miguel; Shimizu, T. Taro; Davies, Richard; Roche, P. F.; García-Burillo, Santiago; Labiano, Alvaro; Hermosa Muñoz, Laura; Zhang, Lulu; Audibert, A.; Bellocchi, Enrica; Bunker, A.; Combes, Francoise; Delaney, D.; Esparza-Arredondo, D.; Gandhi, P.; González-Martín, O.; Hönig, Sebastian; Imanishi, Masatoshi; Hicks, Erin K. S.; Fuller, L.; Leist, Mason Tanner; Levenson, N. A.; López-Rodríguez, E.; Packham, Christopher; Ramos Almeida, Cristina; Ricci, C.; Stalevski, Marko; Villar Martín, M.; Ward, M. J.; Science and Technology Facilities Council (STFC); Comunidad de Madrid; European Commission (EC); European Space Agency (ESA); Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT); Ministerio de Ciencia e Innovación (MICINN); National Aeronautics and Space Administration (NASA); Space Telescope Science Institute (STScI); Universidad Nacional Autónoma de México (UNAM)
This study analyses JWST MIRI/MRS observations of the infrared (IR) polycyclic aromatic hydrocarbon (PAH) bands in the nuclear (∼0.4″ at 11 μm; ∼75 pc) and circumnuclear regions (inner ∼kpc) of local active galactic nuclei (AGNs) from the Galactic Activity, Torus, and Outflow Survey (GATOS). We examine the PAH properties in the circumnuclear regions of AGNs and the projected direction of AGN-outflows and compare them to those in star-forming regions and the innermost regions of AGNs. This study employs 4.9–28.1 μm sub-arcsecond angular resolution data to investigate the properties of PAHs in three nearby sources (DL ∼ 30 − 40 Mpc). Our findings are aligned with previous JWST studies, demonstrating that the central regions of AGNs display a larger fraction of neutral PAH molecules (i.e. elevated 11.3/6.2 and 11.3/7.7 μm PAH ratios) in comparison to star-forming galaxies. We find that AGNs might affect not only the PAH population in the innermost region, but also in the extended regions up to ∼kpc scales. By comparing our observations to PAH diagnostic diagrams, we find that, in general, regions located in the projected direction of the AGN-outflow occupy similar positions on the PAH diagnostic diagrams as those of the innermost regions of AGNs. Star-forming regions that are not affected by the AGNs in these galaxies share the same part of the diagram as star-forming galaxies. We also examined the potential of the PAH-H2 diagram to disentangle AGN-versus-star-forming activity. Our results suggest that in Seyfert-like AGNs, the illumination and feedback from the AGN might affect the PAH population at nuclear and kpc scales, particularly with respect to the ionisation state of the PAH grains. However, PAH molecular sizes are rather similar. The carriers of the ionised PAH bands (6.2 and 7.7 μm) are less resilient than those of neutral PAH bands (11.3 μm), which might be particularly important for strongly AGN-host coupled systems. Therefore, caution must be applied when using PAH bands as star-formation rate indicators in these systems even at kpc scales, with the effects of the AGN being more important for ionised ones.
Polycyclic aromatic hydrocarbon emission in galaxies as seen with JWST
(Royal Astronomical Society, 2024-08-01) Rigopoulou, D.; Donnan, F. R.; García-Bernete, I.; Pereira Santaella, Miguel; Alonso-Herrero, Almudena; Davies, R.; Hunt, L. K.; Roche, P. F.; Shimizu, T.; Ministerio de Ciencia e Innovación (MICINN); Science and Technology Facilities Council (STFC)
We present a systematic study of mid-infrared spectra of galaxies including star-forming galaxies and active galactic nuclei observed with JWST MIRI-MRS and NIRSpec-IFU. We focus on the relative variations of the 3.3, 6.2, 7.7, 11.3, 12.7, and 17 m polycyclic aromatic hydrocarbon (PAH) features within spatially resolved regions of galaxies including NGC 3256, NGC 7469, VV 114, II Zw96, and NGC 5728. Using theoretical PAH models and extending our earlier work, we introduce a new PAH diagnostic involving the 17 m PAH feature. To determine the drivers of PAH band variations in galaxies, we compare observed PAH spectral bands to predictions from theoretical PAH models. We consider extinction, dehydrogenation, and PAH size and charge as possible drivers of PAH band variations. We find a surprising uniformity in PAH size distribution among the spatially resolved regions of the galaxies studied here, with no evidence for preferential destruction of the smallest grains, contrary to earlier findings. Neither extinction nor dehydrogenation play a crucial role in setting the observed PAH bands. Instead, we find that PAH charge plays a significant role in PAH inter-band variations. We find a tight relation between PAH charge and the intensity of the radiation field as traced by the [Ne iii][Ne ii] maps. In agreement with recent JWST results, we find a predominance of neutral PAH molecules in the nuclei of active galaxies and their outflows. Ionized PAHs are the dominant population in star-forming galaxies. We discuss the implications of our findings for the use of PAHs as ISM tracers in high redshift galaxies.
Synthesis and Spectroscopic Characterization of Interstellar Candidate Ethynyl Thiocyanate: HCCSCN
(IOP Publishing, 2024-11-14) Alonso, Elena R.; Insausti, Aran; Kolesniková, Lucie; León, Iker; McGuire, Brett A.; Shingledecker, Christopher N.; Agúndez, Marcelino; Cernicharo, José; Rivilla, Victor M.; Cabezas, Carlos; Jimenez-Serra, Izaskun; Martín-Pintado, Jesús; Guillemin, Jean Claude; National Science Foundation (NSF); Junta de Castilla y León; European Commission (EC); El Consejo Superior de Investigaciones Científicas (CSIC); Centre National de la Recherche Scientifique (CNRS); Ministerio de Ciencia e Innovación (MICINN)
This work aims to spectroscopically characterize and provide for the first time direct experimental frequencies of the ground vibrational state and two excited states of the simplest alkynyl thiocyanate (HCCSCN) for astrophysical use. Both microwave (8-16 GHz) and millimeter-wave regions (50-120 GHz) of the spectrum have been measured and analyzed in terms of Watson’s semirigid rotor Hamiltonian. A total of 314 transitions were assigned to the ground state of HCCSCN, and a first set of spectroscopic constants have been accurately determined. Spectral features of the molecule were then searched for in Sgr B2(N), NGC 6334I, G+0.693−0.027, and TMC-1 molecular clouds. Upper limits to the column density are provided.
