J/A+A/651/A98 M31 C-band (6.6GHz) Sardinia radio tel. map (Fatigoni+, 2021)
Study of the thermal and non-thermal emission components in M31:
the Sardinia Radio Telescope view at 6.6 GHz.
Fatigoni S., Radiconi F., Battistelli E.S., Murgia M., Carretti E.,
Castangia P., Concu R., de Bernardis P., Fritz J., Genova-Santos R.,
Govoni F., Guidi F., Lamagna L., Masi S., Melis A., Paladini R.,
Perez-Toledo F.M., Piacentini F., Poppi S., Rebolo R., Rubino-Martin J.A.,
Surcis G., Tarchi A., Vacca V.
<Astron. Astrophys. 651, A98 (2021)>
=2021A&A...651A..98F 2021A&A...651A..98F (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Galaxies, radio ; Radio continuum ;
Millimetric/submm sources
Keywords: galaxies: Individual: Messier 31 - radio continuum: galaxies -
ISM: general - radiation mechanisms: non-thermal -
radiation mechanisms: thermal
Abstract:
The Andromeda galaxy is the best known large galaxy besides our own
Milky Way. Several images and studies exist at all wavelengths from
radio to hard X-ray. Nevertheless, only few observations are available
in the microwave range where its average radio emission reaches the
minimum.
In this paper we want to study the radio morphology of the galaxy,
decouple thermal from non-thermal emission and extract the star
formation rate. We also aim to derive a complete catalogue of radio
sources for the mapped patch of sky. We have observed the Andromeda
galaxy with the Sardinia Radio Telescope at 6.6 GHz with very high
sensitivity and angular resolution, and an unprecedented sky coverage.
Using new 6.6GHz data and Effelsberg radio telescope ancillary data,
we confirm that, globally, the spectral index assumes a value of
∼0.7-0.8, while in the star forming regions it decreases to ∼0.5. By
disentangling (gas) thermal and non-thermal emission, we found that at
6.6GHz, thermal emission follows the distribution of HII regions
around the ring. Non-thermal emission, within the ring, appears to be
more uniform and smooth than thermal emission, due to the diffusion of
the cosmic ray electrons away from their birthplaces. Hence the
magnetic fields are nearly constant in intensity. Based on the thermal
emission map, we have calculated a star formation rate map.
Integrating within a radius of Rmax=15kpc, we obtained a total star
formation rate of 0.19±0.01M*/yr in agreement with previous results
in literature. Finally, we correlated our radio data with Infrared
images of the Andromeda galaxy. We found an unexpected high
correlation between non-thermal and MIR data in the central region,
with a correlation parameter r=0.93. Finally, by computing the
logarithmic 24um/21cm ratio q24um, we found a decreasing trend with
increasing galactocentric distance and an increasing dispersion. The
logarithmic FIR/radio ratio is found to be 2.41±0.04.
Description:
The 6.6GHz Map of M31 acquired with the Sardinia Radio Telescope
(SRT), with an angular resolution of FWHM=2.9'.
The map size is 2.4°x3.1°=7.4deg2, centred at
(RA; Dec)=(0:42:48;+41:16:48The final sensitivity is 0.43mJy/beam. A
catalogue containing all the point sources found in the sky region
covered by the map is also included.
Objects:
-------------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------------
00 42 44.33 +41 16 07.5 M31 = NAME Andromeda
-------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 86 93 Catalogue of point sources
list.dat 75 1 Information on fits image
fits/* . 1 fits image
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- N Source identification number
5- 31 A27 --- NObj Nearest NED object
33- 38 A6 --- Class NED Object Class
40- 44 F5.2 deg RAdeg Right Ascension (J2000)
46- 50 F5.2 deg DEdeg Declination (J2000)
52- 56 F5.3 Jy F6.6GHz Flux Density at 6.6GHz
58- 62 F5.3 Jy e_F6.6GHz Flux Density at 6.6GHz Error
64- 68 F5.3 --- A Model Amplitude
70- 74 F5.2 --- alphaMod Model 'spectral index'
76- 80 F5.2 --- k Model curvature
82- 86 F5.2 --- alpha Measured spectral index, alpha1.4GHz6.6GHz
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
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- 34 F7.5 GHz Freq Observed frequency
36- 38 I3 Kibyte size Size of FITS file
40- 57 A18 --- FileName Name of FITS file, in subdirectory fits
59- 75 A17 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
Federico Radiconi, federico.radiconi(at)roma1.infn.it
(End) S. Fatigoni, F. Radiconi [Rome, Italy], P. Vannier [CDS] 17-May-2021