J/A+A/633/A106 36GHz methanol lines from nearby galaxies (Humire+, 2020)
36 GHz methanol lines from nearby galaxies: maser or quasi-thermal emission?
Humire P.K., Henkel C., Gong Y., Leurini S., Mauersberger R.,
Levshakov S.A., Winkel B., Tarchi A., Castangia P., Malawi A., Asiri H.,
Ellingsen S.P., McCarthy T.P., Chen X., Tang X.
<Astron. Astrophys. 633, A106 (2020)>
=2020A&A...633A.106H 2020A&A...633A.106H (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Masers
Keywords: masers - galaxies: spiral - galaxies: individual: IC 342 -
galaxies: individual: Maffei 2 - galaxies: ISM - radio lines: galaxies
Abstract:
Methanol (CH3OH) is one of the most abundant interstellar molecules,
offering a vast number of transitions to be studied, including many
maser lines. However, while the strongest Galactic CH3OH lines, the
so-called class II masers, show no indications for the presence of
superluminous counterparts in external galaxies, the less luminous
Galactic class I sources appear to be different. Here we report
class I 36GHz (λ~=0.8cm) CH3OH 4-1 --> 30 E line emission
from the nearby galaxies Maffei 2 (D~=6Mpc) and IC 342 (D~=3.5Mpc),
measured with the 100m telescope at Effelsberg at three different
epochs within a time span of about five weeks. The 36GHz methanol line
of Maffei 2 is the second most luminous among the sources detected
with certainty outside the Local Group of galaxies. This is not
matched by the moderate infrared luminosity of Maffei 2.
Higher-resolution data are required to check whether this is related
to its prominent bar and associated shocks. Upper limits for M 82,
NGC 4388, NGC 5728 and Arp 220 are also presented. The previously
reported detection of 36GHz maser emission in Arp 220 is not
confirmed. Nondetections are reported from the related class I 44GHz
(λ~=0.7cm) methanol transition towards Maffei 2 and IC 342,
indicating that this line is not stronger than its 36GHz counterpart.
In contrast to the previously detected 36GHz CH3OH emission in NGC 253
and NGC 4945, our 36GHz profiles towards Maffei 2 and IC 342 are
similar to those of previously detected nonmasing lines from other
molecular species. However, by analogy to our Galactic center region,
it may well be possible that the 36GHz methanol lines in Maffei 2 and
IC 342 are composed of a large number of faint and narrow maser
features that remain spatially unresolved. In view of this, a search
for a weak broad 36GHz line component would also be desirable in
NGC 253 and NGC 4945.
Description:
The 36GHz measurements were carried out with the 100m
telescope at Effelsberg1 near Bonn, Germany, in early January and
early February 2019. Complementary 44GHz observations were taken in
late March 2019.
Objects:
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RA (2000) DE Designation(s)
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05 35 17.3 -05 23 28 Orion = M 42
03 46 48.51 +68 05 46.0 IC 342 = UGC 2847
02 41 55.09 +59 36 14.7 Maffei 2 = UGCA 39
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 149 13 List of fits spectra
fits/* . 13 Individual fits spectra
files/* . 3 Individual files in CLASS
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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- 24 I5 --- Nx Number of pixels along X-axis
26- 48 A23 "datime" Obs.date Observation date
50- 61 E12.6 Hz bFreq Lower value of relative frequency interval
63- 73 E11.6 Hz BFreq Upper value of relative frequency interval
75- 81 F7.2 Hz dFreq Frequency resolution
83- 85 I3 Kibyte size Size of FITS file
87-106 A20 --- FileName Name of FITS file, in subdirectory fits
108-149 A42 --- Title Title of the FITS file
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Acknowledgements:
Christian Henkel, chenkel(at)mpifr-bonn.mpg.de
(End) Patricia Vannier [CDS] 13-Jan-2020