J/A+A/709/A1 M99 dust properties and photometry with NIKA2 (Pantoni+, 2026)
Spatially-resolved interstellar dust properties in the face-on spiral galaxy
M99 as observed by NIKA2.
Pantoni L., Galliano F., Madden S.C., Adam R., Ade P., Ajeddig H., Andre P.,
Artis E., Aussel H., Baes M., Beelen A., Benoit A., Berta S., Bing L.,
Bourrion O., Calvo M., Casasola V., Catalano A., Chang I-D., De Looze I.,
De Petris M., Desert F.-X., Doyle S., Driessen E.F.C., Ejlali G., Gomez A.,
Goupy J., Jones A.P., Hanser C., Hughes A., Katsioli S., Keruzore F.,
Koch E.W., Kramer C., Ladjelate B., Lagache G., Leclercq S., Lestrade J.-F.,
Macias-Perez J.F., Maury A., Mauskopf P., Mayet F., Monfardini A.,
Moyer-Anin A., Munoz-Echeverria M., Nersesian A., Paradis D., Perotto L.,
Pisano G., Ponthieu N., Reveret V., Rigby A.J., Ritacco A., Romero C.,
Roussel H., Ruppin F., Schuster K., Sievers A., Smith M.W.L.,
Tabatabaei F.S., Tedros J., Tucker C., Ysard N., Xilouris E.M., Zylka R.
<Astron. Astrophys. 709, A1 (2026)>
=2026A&A...709A...1P 2026A&A...709A...1P (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Photometry, infrared ;
Photometry, millimetric/submm ; Radio sources
Keywords: galaxies: ISM - galaxies: individual: M99 - galaxies: spiral
Abstract:
Large dust grains in thermal equilibrium dominate the far-infrared
emission of star-forming galaxies and contribute substantially to
their millimetre continuum. Constraining dust properties in this
regime is challenging due to contamination from free-free and
synchrotron emission.
We investigate spatial variations in the dust spectral index, dust
mass, and grain size and composition in the nearby face-on spiral
galaxy M 99. To this end, we use new 1.15 and 2mm continuum
observations obtained with NIKA2 on the IRAM 30m telescope as part of
the IMEGIN Guaranteed Time Large Programme, combined with ancillary
data spanning ultraviolet to radio wavelengths.
We decompose the infrared-to-radio spectral energy distribution of
M 99 into dust, free-free, and synchrotron components using the
hierarchical Bayesian SED-fitting HerBIE. Dust emission is modelled
using both a modified blackbody (MBB) with a variable millimetre
spectral index beta and the THEMIS dust model with a fixed beta. Our
spatially resolved analysis is performed on ∼1.75kpc (25")
scales, encompassing the galaxy centre, spiral arms, and inter-arm
regions. From the MBB modelling, we find significant spatial
variations in beta, ranging from ∼1.6-1.7 in diffuse regions to
∼2.3-2.5 in denser, star-forming environments. These variations likely
reflect dust grain evolution driven by coagulation and changes in the
silicate-to-carbonaceous grain abundance. Dust masses inferred with
variable beta are up to a factor of ∼4 higher than those derived
assuming a fixed beta (1.6 on average). Variable-beta models recover
expected correlations with dust-to-stellar and dust-to-gas ratios,
whereas fixed-beta models systematically bias these quantities. The
small grain fraction increases from ∼10% in the centre to ∼15% in the
diffuse disc and is anti-correlated with the interstellar radiation
field intensity, while gas-phase metallicity plays only a minor role
within the central 8kpc. The synchrotron spectral index varies from
∼0.6-0.7 in star-forming regions to ∼1.2 in the diffuse medium,
consistent with cosmic-ray electron ageing.
Description:
We provide the integrated photometry for the galaxy as a whole and for
its three morphological components (disc, spiral arms, and central
region). We also report the results of the integrated SED fitting
performed using modified blackbody (MBB) and THEMIS dust models.
Objects:
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RA (2000) DE Designation(s)
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12 18 49.62 +14 24 59.3 NGC 4254 = M 99
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 48 17 Integrated multi-band photometry
table6.dat 52 11 Best fit parameters
table7.dat 94 14 Integrated photometry (arms, disc and centre)
table8.dat 60 27 Best fit parameters (arms, disc and centre)
list.dat 90 22 List of fits images
fits/* . 22 Individual fits images
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Inst Instrument
10- 17 F8.1 um lambda Central wavelength
19- 28 E10.4 Lsun Lum Luminosity
29- 35 F7.3 Jy Flux Flux
37- 41 F5.3 Jy e_Flux Uncertainty on flux
43- 48 F6.2 mJy rms rms
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Param Parameters
12- 15 A4 --- Unit Units
18- 25 E8.3 --- valTHEMIS Value, THEMIS
27- 34 E8.3 --- e_valTHEMIS ? Uncertainty on value, THEMIS
36- 43 E8.3 --- valMBB ? Value, MBB
45- 52 E8.3 --- e_valMBB ? Uncertainty on value, MBB
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Inst Instrument
10- 17 F8.1 um lambda Central wavelength
19- 25 F7.3 Jy Farms Flux, spiral arms
27- 31 F5.3 Jy e_Farms Uncertainty on Farms
33- 37 F5.2 mJy rmsarms rms, spiral arms
39- 45 F7.4 Jy Fdisc Flux, disc
47- 52 F6.4 Jy e_Fdisc Uncertainty on Fdisc
54- 58 F5.2 mJy rmsdisc rms, disc
60- 65 F6.4 Jy Fcentre Flux, centre
67- 72 F6.4 Jy e_Fcentre Uncertainty on Fcentre
74- 80 F7.4 mJy rmscentre rms, centre
82- 88 F7.3 Jy Ftot Flux, sum
90- 94 F5.3 Jy e_Ftot Uncertainty on Ftot
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Byte-by-byte Description of file: table8.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Param Parameters
12- 15 A4 --- Unit Units
17- 22 A6 --- Comp Morphological comp: disc, arms, centre
25- 32 E8.3 --- valTHEMIS Value, THEMIS
34- 41 E8.3 --- e_valTHEMIS ? Uncertainty on value, THEMIS
43- 51 E9.4 --- valMBB ? Value, MBB
53- 60 E8.3 --- e_valMBB ? Uncertainty on value, MBB
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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- 32 I5 Kibyte size Size of FITS file
34- 66 A33 --- FileName Name of FITS file, in subdirectory fits
68- 90 A23 --- Title Title of the FITS file
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Acknowledgements:
Lara Pantoni, lara.pantoni(at)ugent.be
(End) Lara Pantoni [Univ. Ghent], Patricia Vannier [CDS] 24-Feb-2026