J/A+A/625/A148 12 molecular clouds of M31 spectra (Dassa-Terrier+, 2019)
M31 circum-nuclear region: A molecular survey with the IRAM interferometer.
Dassa-Terrier J., Melchior A.-L., Combes F.
<Astron. Astrophys. 625, A148 (2019)>
=2019A&A...625A.148D 2019A&A...625A.148D (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Molecular clouds ; Spectra, millimetric/submm
Keywords: galaxies: individual: M31 - galaxies: kinematics and dynamics -
submillimeter: ISM - molecular data
Abstract:
We analyse molecular observations performed at IRAM interferometer in
CO(1-0) of the circum-nuclear region (within 250pc) of Andromeda, with
2. arcsec=11pc resolution. We detect 12 molecular clumps in this
region, corresponding to a total molecular mass of (8.4+/
0.4)x104M☉. They follow the Larson's mass-size relation, but
lie well above the velocity-size relation. We discuss that these
clumps are probably not virialised, but transient agglomerations of
smaller entities that might be virialised. Three of these clumps have
been detected in CO(2-1) in a previous work, and we find temperature
line ratio below 0.5. With a RADEX analysis, we show that this gas is
in non local thermal equilibrium with a low excitation temperature
(Tex=5-9K). We find a surface beam filling factor of order 5 percent
and a gas density in the range 60-650cm-3, well below the critical
density. With a gas-to-stellar mass fraction of 4x10-4 and
dust-to-gas ratio of 0.01, this quiescent region has exhausted his gas
budget. Its spectral energy distribution is compatible with passive
templates assembled from elliptical galaxies. While weak dust emission
is present in the region, we show that no star formation is present
and support the previous results that the dust is heated by the old
and intermediate stellar population.
We study that this region lies formally in the low-density part of the
Kennicutt-Schmidt law, in a regime where the SFR estimators are not
completely reliable. We confirm the quiescence of the inner part of
this galaxy known to lie on the green valley.
Description:
We present the integrated spectrum for the 12 molecular clouds
detected within the circum-nuclear region of M31, following the same
numbering as in Figure 6, Table 3 and Table 4. Integration was
performed over twice the beam size, centered on the pixel with peak
flux. The uncertainty was estimated by adding the rms flux of the
noise to the variation of flux of the signal for an integration
surface varying between 1.8 beam and 2.2 beam size.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 36 12 Offset of each spectrum
sp/* . 12 Individual spectra
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Id [1/12] Spectrum number
6- 10 F5.1 arcsec offX X offset (1)
14- 18 F5.1 arcsec offY Y offset (1)
22- 36 A15 --- FileName Name of spectrum file in subdirectory sp
--------------------------------------------------------------------------------
Note (1): the offsets are computed with respect to the center of M31
00:42:44.37+41:16:08.34 (J2000).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: sp/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
3- 11 F9.1 m/s Vel Velocity
15- 21 F7.4 Jy Flux Flux
26- 31 F6.4 Jy e_Flux Uncertainty on flux
--------------------------------------------------------------------------------
Acknowledgements:
Julien Dassa-Terrier, julien.Dassa-Terrier(at)obspm.fr
(End) Julien Dassa-Terrier [LERMA, France], Patricia Vannier [CDS] 22-May-2019