Warm Molecular Gas in the Central Parsecs of the Buried Nucleus of NGC 4418 Traced with the Fundamental CO Rovibrational Absorptions

Ohyama, Youichi; Onishi, Shusuke; Matsumoto, K.; Isobe, Naoki; Shirahata, Mai; Baba, Shigeo; Sakamoto, Kazushi

doi:10.3847/1538-4357/acd692

Cited by 4 publications

(1 citation statement)

References 60 publications

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“…Rich et al (2023) previously reported the detection of the ν 2 14.0 μm band of HCN and the ν 5 13.7 μm band of C 2 H 2 in absorption toward the NE core in VV 114E. The fundamental band of CO at 4.67 μm, tracing transitions between the ground state and the first vibrationally excited state, has been observed in absorption toward several heavily obscured U/LIRGs from the ground (e.g., Spoon et al 2003;Geballe et al 2006;Shirahata et al 2013;Baba et al 2022;Ohyama et al 2023). Pereira-Santaella et al (2024) demonstrated JWST's capabilities for studying the CO band in emission.…”

Section: Introductionmentioning

confidence: 97%

GOALS-JWST: Mid-infrared Molecular Gas Excitation Probes the Local Conditions of Nuclear Star Clusters and the Active Galactic Nucleus in the LIRG VV 114

Buiten,

van der Werf,

Viti

et al. 2024

ApJ

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The enormous increase in mid-IR sensitivity and spatial and spectral resolution provided by the JWST spectrographs enables, for the first time, detailed extragalactic studies of molecular vibrational bands. This opens an entirely new window for the study of the molecular interstellar medium in luminous infrared galaxies (LIRGs). We present a detailed analysis of rovibrational bands of gas-phase CO, H2O, C2H2, and HCN toward the heavily obscured eastern nucleus of the LIRG VV 114, as observed by NIRSpec and the medium resolution spectrograph on the Mid-InfraRed Instrument (MIRI MRS). Spectra extracted from apertures of 130 pc in radius show a clear dichotomy between the obscured active galactic nucleus (AGN) and two intense starburst regions. We detect the 2.3 μm CO bandheads, characteristic of cool stellar atmospheres, in the star-forming regions, but not toward the AGN. Surprisingly, at 4.7 μm, we find highly excited CO (T ex ≈ 700–800 K out to at least rotational level J = 27) toward the star-forming regions, but only cooler gas (T ex ≈ 200 K) toward the AGN. We conclude that only mid-infrared pumping through the rovibrational lines can account for the equilibrium conditions found for CO and H2O in the deeply embedded starbursts. Here, the CO bands probe regions with an intense local radiation field inside dusty young massive star clusters or near the most massive young stars. The lack of high-excitation molecular gas toward the AGN is attributed to geometric dilution of the intense radiation from the bright point source. An overview of the relevant excitation and radiative transfer physics is provided in an appendix.

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Section: Introductionmentioning

confidence: 97%

GOALS-JWST: Mid-infrared Molecular Gas Excitation Probes the Local Conditions of Nuclear Star Clusters and the Active Galactic Nucleus in the LIRG VV 114

Buiten,

van der Werf,

Viti

et al. 2024

ApJ

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Double, double, toil, and trouble

Wethers,

Aalto,

Privon

et al. 2024

A&A

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Compact obscured nuclei (CONs) are an extremely obscured (N$_ H2 >$1025 cm$^ $) class of galaxy nuclei thought to exist in 20-40 per cent of nearby (ultra-)luminous infrared galaxies While they have been proposed to represent a key phase of the active galactic nucleus (AGN) feedback cycle, the nature of these CONs -- what powers them, their dynamics, and their impact on the host galaxy -- remains unknown. This work analyses the galaxy-scale optical properties of the local CON NGC\,4418 ($z$=0.00727). The key aims of the study are to understand the impact of nuclear outflows on the host galaxy and infer the power source of its CON. Through the mapping of the galaxy spectra and kinematics, we seek to identify new structures in NGC\,4418 to ultimately reveal more about the CON's history, its impact on the host, and, more generally, the role CONs play in galaxy evolution. We present new, targeted integral field unit observations of the galaxy with the Multi-Unit Spectroscopic Explorer (MUSE). For the first time, we mapped the ionised and neutral gas components of the galaxy, along with their dynamical structure, to reveal several previously unknown features of the galaxy. We confirm the presence of a previously postulated, blueshifted outflow along the minor axis of NGC\,4418. We find this outflow to be decelerating and, for the first time, show it to extend in both directions from the nucleus. We report the discovery of two further outflow structures: a redshifted southern outflow connected to a tail of ionised gas surrounding the galaxy and a blueshifted bubble to the north. In addition to these features, we find the iii emission reveals the presence of knots across the galaxy, which are consistent with regions of the galaxy that have been photoionised by an AGN. We identify several new features in NGC\,4418, including a bubble structure, a reddened outflow, and iii knot structures throughout the galaxy. We additionally confirm the presence of a bilateral blueshifted outflow along the minor axis. Based on the properties of these features, we conclude that the CON in NGC\,4418 is most likely powered by AGN activity.

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The CO-to-H₂ conversion factor of molecular outflows

Pereira-Santaella,

González-Alfonso,

García-Bernete

et al. 2024

A&A

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We analyze NIRSpec observations of the CO rovibrational $v$=1--0 band at sim 4.67 around the dust-embedded southern active galactic nucleus (AGN) of NGC 3256 ($d$=40\,Mpc; IR $\,$L_ We classify the CO $v$=1--0 spectra into three categories based on the behavior of P- and R-branches of the band: (a) both branches in absorption toward the nucleus; (b) P-R asymmetry (P-branch in emission and R-branch in absorption) along the disk of the galaxy; and (c) both branches in emission in the outflow region above and below the disk. In this paper, we focus on the outflow. The CO $v$=1--0 emission can be explained by the vibrational excitation of CO in the molecular outflow by the bright mid-IR sim 4.7 continuum from the AGN up to $r$sim 250\,pc. We model the ratios between the P($J$+2) and R($J$) transitions of the band to derive the physical properties (column density, kinetic temperature, and CO-to-H$_2$ conversion factor, $ CO $) of the outflowing gas. We find that the 12CO $v$=1--0 emission is optically thick for $J$<4, while the 13CO $v$=1--0 emission remains optically thin. From the P(2) R(0) ratio, we identify a temperature gradient in the outflow from $>$40\,K in the central 100\,pc to $<$15\,K at 250\,pc, sampling the cooling of the molecular gas in the outflow. We used three methods to derive $ CO $ in eight 100\,pc (0 apertures in the outflow by fitting the P($J$+2) R($J$) ratios with nonlocal thermodynamic equilibrium (NLTE) models. We obtain low median $ CO $ factors (0.40--0.61)$ CO H_2 $\,$M_ (K $ in the outflow regions. This implies that outflow rates and energetics might be overestimated if a 1.3--2 times larger ultraluminous infrared galaxy (ULIRG) like $ CO $ is assumed. The reduced $ CO $ can be explained if the outflowing molecular clouds are not virialized. We also report the first extragalactic detection of a broad (sigma =0.0091 spectral feature at 4.645 associated with aliphatic deuterium on polycyclic aromatic hydrocarbons (D$_n$-PAHs).

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Warm Molecular Gas in the Central Parsecs of the Buried Nucleus of NGC 4418 Traced with the Fundamental CO Rovibrational Absorptions

Cited by 4 publications

References 60 publications

GOALS-JWST: Mid-infrared Molecular Gas Excitation Probes the Local Conditions of Nuclear Star Clusters and the Active Galactic Nucleus in the LIRG VV 114

GOALS-JWST: Mid-infrared Molecular Gas Excitation Probes the Local Conditions of Nuclear Star Clusters and the Active Galactic Nucleus in the LIRG VV 114

Double, double, toil, and trouble

The CO-to-H₂ conversion factor of molecular outflows

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Warm Molecular Gas in the Central Parsecs of the Buried Nucleus of NGC 4418 Traced with the Fundamental CO Rovibrational Absorptions

Cited by 4 publications

References 60 publications

GOALS-JWST: Mid-infrared Molecular Gas Excitation Probes the Local Conditions of Nuclear Star Clusters and the Active Galactic Nucleus in the LIRG VV 114

GOALS-JWST: Mid-infrared Molecular Gas Excitation Probes the Local Conditions of Nuclear Star Clusters and the Active Galactic Nucleus in the LIRG VV 114

Double, double, toil, and trouble

The CO-to-H2 conversion factor of molecular outflows

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The CO-to-H₂ conversion factor of molecular outflows