J/A+A/704/A295 ISM phases and abundances in the central parsec (Vermot+, 2025)
Interstellar medium phases and abundances in the central parsec.
A JWST MIRI/MRS view of the Galactic Center.
Vermot P., Ciurlo A., Rouan D., Morris M.R., Bron E., Le Bourlot J.,
Le Petit F., Qiu J., Togi A., Ghez A., Do T., Lu J.R.
<Astron. Astrophys. 704, A295 (2025)>
=2025A&A...704A.295V 2025A&A...704A.295V (SIMBAD/NED BibCode)
ADC_Keywords: Galactic center ; Spectroscopy ; Infrared
Keywords: methods: data analysis - techniques: spectroscopic -
ISM: abundances - Galaxy: center - infrared: ISM
Abstract:
The Galactic center (GC) is a unique and extreme astrophysical
laboratory for studying the interplay between gas, stars, and a
supermassive black hole (SMBH). In particular, the circumnuclear disk
(CND) and its central cavity (CC) present two contrasting environments
in terms of gas content, density, and stellar activity, making them
ideal regions in which to study the multiphase structure and chemical
composition of the interstellar medium (ISM).
We aim to determine the properties (temperature, density, abundances,
and spatial distribution) of the various phases of the ISM in the
central parsec of the GC, with particular attention in this paper to
the ionized medium.
We used newly obtained observations from the Mid-Infrared Instrument
(MIRI) equipped with the Medium Resolution Spectrometer (MRS) aboard
the James Webb Space Telescope (JWST) to extract spectra covering the
entire spectral range from 5 to 27um in the CND and in the CC. We
used the photoionization code CLOUDY to generate synthetic spectra
with the same spectral range and resolution, simulating a wide range
of gas phases and abundances. We then determined the contribution of
each phase to the spectra. Once the abundances and contribution from
each phase of the gas were determined, we identified four dominant
phases and performed a spatial analysis to determine their
contribution to each spaxel of the datacubes.
We find that in both the CND and the CC, the bulk of the emission
originates from warm ionized gas with temperatures of between 104 and
104.8 K. In the CND, molecular gas contributes significantly to the
flux and is spatially structured, while the CC shows minimal molecular
gas content, as is expected from these regions. Coronal gas is
detected in both regions at the interface between molecular and warm
ionized gas. The hottest coronal phase appears faint and patchy in the
CC, and has an elongated morphology in the CND. Abundance fitting (in
solar-normalized logarithmic units) is primarily constrained by
abundances: we measure a robust depletion of Fe relative to alpha
elements with log(Fe/alpha)=-0.78±0.20 (CC) and -0.84±0.26 (CND),
while CNO is only mildly enhanced relative to alpha,
log(CNO/alpha)=0.27±0.20 (CC) and 0.05±0.26 (CND). Absolute
abundances are supersolar but more degenerate; the best-fitting models
yield (log alpha, log CNO, log Fe) = (1.4, 1.4, 0.4) in the CC and
(2.0, 1.8, 1.2) in the CND.
The observed abundance pattern (enhanced CNO and alpha elements with
suppressed Fe) indicates a chemically young environment, recently
enriched by core-collapse supernovae and stellar winds, with a limited
contribution from older Type Ia supernovae. This favors a scenario of
massive, recent star formation rather than cumulative long-term
enrichment. Additionally, the projected orientation of the newly
identified CND elongated hot coronal feature, perpendicular to the
direction toward the SMBH, suggests the action of a large-scale shock
possibly resulting from past energetic outflows.
Description:
JWST/MIRI-MRS observations of the Galactic Center (Circum-Nuclear Disk
(CND) and Central Cavity (CC)). CND observed 2024-04-18; CC observed
2024-09-11; background at RA=17:44:46.647, Dec=-28:53:44.41 (J2000).
Coverage 5-27um at R∼3000-1500. Data cubes were background-subtracted,
continuum-removed via a 100-bin rolling median per spaxel, and
rebinned to Delta-lambda=0.04 um using fractional (integral-
preserving) rebinning. Model spectra include interstellar extinction
using the Chiar et al. (2006ApJ...651..268C 2006ApJ...651..268C) curve with AV=30. We
provide observed spectra (native and rebinned; MJy/sr), a CLOUDY-based
line list with unitless fractional contributions (sum=1.0), and FITS
cubes of phase maps (molecular, warm ionized, warm coronal, hot
coronal) with WCS coordinates.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
cnd_reb.dat 52 500 Circum-Nuclear Disk (CND) rebinned spectrum
cnd_hr.dat 24 27555 Circum-Nuclear Disk (CND) native spectrum
cnd_line.dat 37 90 Circum-Nuclear Disk (CND) CLOUDY line list
cc_reb.dat 52 500 Central Cavity (CC) rebinned spectrum
cc_hr.dat 24 27555 Central Cavity (CC) native spectrum
cc_line.dat 37 81 Central Cavity (CC) CLOUDY line list
list.dat 103 2 List of fits maps
fits/* . 2 Individual fits maps
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Byte-by-byte Description of file: cnd_reb.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.6 um lam Wavelength
12- 24 E13.6 MJy/sr Fobs Observed Inu (rebinned)
26- 38 E13.6 MJy/sr Fmod Model Inu (rebinned)
40- 52 E13.6 MJy/sr Resid Observed - Model Inu
--------------------------------------------------------------------------------
Byte-by-byte Description of file: cnd_hr.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.6 um lam Wavelength
12- 24 E13.6 MJy/sr Fobs Observed Inu (native)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: cnd_line.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Ion Species/ion
14- 23 F10.6 um lam Wavelength
25- 37 E13.6 --- Frac Fraction (unitless); sum=1.0 (1)
--------------------------------------------------------------------------------
Note (1): Column 'Frac' gives the unitless fractional contribution of each line;
the sum over the file is 1.0.
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Byte-by-byte Description of file: cc_reb.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.6 um lam Wavelength
12- 24 E13.6 MJy/sr Fobs Observed Inu (rebinned)
26- 38 E13.6 MJy/sr Fmod Model Inu (rebinned)
40- 52 E13.6 MJy/sr Resid Observed - Model Inu
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Byte-by-byte Description of file: cc_hr.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.6 um lam Wavelength
12- 24 E13.6 MJy/sr Fobs Observed Inu (native)
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Byte-by-byte Description of file: cc_line.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Ion Species/ion
14- 23 F10.6 um lam Wavelength
25- 37 E13.6 --- Frac Fraction (unitless); sum=1.0 (1)
--------------------------------------------------------------------------------
Note (1): Column 'Frac' gives the unitless fractional contribution of each line;
the sum over the file is 1.0.
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28 I1 --- Nz Number of slices
30- 32 I3 Kibyte size Size of FITS file
34- 46 A13 --- FileName Name of FITS file, in subdirectory fits
48-103 A56 --- Title Title of the FITS file
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Acknowledgements:
Pierre Vermot, pierre.vermot(at)obspm.fr
(End) Patricia Vannier [CDS] 15-Oct-2025