J/A+A/691/A121 HCN and star formation at 260pc in NGC 4321 (Neumann+, 2024)
A 260 pc resolution ALMA map of HCN(1-0) in the galaxy NGC 4321.
Neumann L., Bigiel F., Barnes A.T., Gallagher M.J., Leroy A., Usero A.,
Rosolowsky E., Beslic, I., Boquien M., Cao Y., Chevance M., Colombo D.,
Dale D.A., Eibensteiner C., Grasha K., Henshaw J.D., Jimenez-Donaire M.J.,
Meidt S., Menon S.H., Murphy E.J., Pan H.-A., Querejeta M., Saito T.,
Schinnerer E., Stuber S.K., Teng Y.-H., Williams T.G.
<Astron. Astrophys. 691, A121 (2024)>
=2024A&A...691A.121N 2024A&A...691A.121N (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Interstellar medium ; Radio lines
Keywords: ISM: molecules - galaxies: ISM - galaxies: individual: NGC 4321 -
galaxies: star formation
Abstract:
The property of star formation rate (SFR) is tightly connected to the
amount of dense gas in molecular clouds. However, it is not fully
understood how the relationship between dense molecular gas and star
formation varies within galaxies and in different morphological
environments. Most previous studies have typically been limited to
kiloparsec-scale resolution such that different environments could not
be resolved.
In this work, we present new ALMA observations of HCN(1-0) at 260pc
scale to test how the amount of dense gas and its ability to form
stars varies with environmental properties. Combined with existing
CO(2-1) observations from ALMA and Hα from MUSE, we measured
the HCN/CO line ratio, a proxy for the dense gas fraction, and
SFR/HCN, a proxy for the star formation efficiency of the dense gas.
We find a systematic >1dex increase (decreases) of HCN/CO (SFR/HCN)
towards the centre of the galaxy, and roughly flat trends of these
ratios (average variations <0.3dex) throughout the disc. While spiral
arms, interarm regions, and bar ends show similar HCN/CO and SFR/HCN,
on the bar, there is a significantly lower SFR/HCN at a similar
HCN/CO.
The strong environmental influence on dense gas and star formation in
the centre of NGC 4321, suggests either that clouds couple strongly to
the surrounding pressure or that HCN emission traces more of the bulk
molecular gas that is less efficiently converted into stars. Across
the disc, where the ISM pressure is typically low, SFR/HCN is more
constant, indicating a decoupling of the clouds from their surrounding
environment. The low SFR/HCN on the bar suggests that gas dynamics
(e.g. shear and streaming motions) can have a large effect on the
efficiency with which dense gas is converted into stars. In addition,
we show that HCN/CO is a good predictor of the mean molecular gas
surface density at 260pc scales across environments and physical
conditions.
Description:
HCN(1-0) and HCO+(1-0) data cubes from ALMA, processed through the
PHANGS-ALMA pipeline.
Objects:
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RA (2000) DE Designation(s)
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12 22 54.92 +15 49 20.2 NGC 4321 = M 100
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 122 2 List of fits datacubes
fits/* . 2 Individual fits datacubes
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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- 30 I3 --- Nz Number of slices
32- 38 I7 m/s bVRAD Lower value of VRAD interval
40- 46 I7 m/s BVRAD Upper value of VRAD interval
48- 54 F7.2 m/s dVRAD VRAD resolution
56- 60 I5 Kibyte size Size of FITS file
62- 75 A14 --- FileName Name of FITS file, in subdirectory fits
77-122 A46 --- Title Title of the FITS file
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Acknowledgements:
Lukas Neumann, lukas.neumann.astro(at)gmail.com
(End) L. Neumann [AIfA, Bonn Univ., Germany], P. Vannier [CDS] 09-Jul-2024