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ELL04 - Discovery of new 19.9-GHz methanol masers in star-forming regions

Short title: Ellingsen et al. (2004)
Authors: Ellingsen, S. P.Cragg, D. M.Lovell, J. E. J.Sobolev, A. M.Ramsdale, P. D.Godfrey, P. D.
Journal: Monthly Notices of the Royal Astronomical Society, Volume 354, Issue 2, pp. 401-413.
Bibcode:

Target type: Known_Class_II
Transitions: CH3OH_19(II)

Abstract
We have used the NASA Tidbinbilla 70-m antenna to search for emission from the 2₁-3₀ E (19.9-GHz) transition of methanol. The search was targeted towards 22 star formation regions that exhibit maser emission in the 107.0-GHz 3₁-4₀ A⁺ methanol transition, and in the 6.6-GHz 5₁-6₀ A⁺ transition characteristic of class II methanol maser sources. A total of seven sources were detected in the 2₁-3₀ E transition, six of these being new detections. Many of the new detections are weak (~0.5 Jy), however, they appear to be weak masers rather than thermal or quasi-thermal emission. We find a strong correlation between sources that exhibit 19.9-GHz methanol masers and those that both have the class II methanol masers projected against radio continuum emission and have associated 6035-MHz OH masers. This suggests that the 19.9-GHz methanol masers arise in very specific physical conditions, probably associated with a particular evolutionary phase. In the model of Cragg, Sobolev & Godfrey these observations are consistent with gas temperatures of 50 K, dust temperatures of 150-200 K and gas densities of 10^6.5-10^7.5 cm^-3.

Abstract

We have used the NASA Tidbinbilla 70-m antenna to search for emission from the 2₁-3₀ E (19.9-GHz) transition of methanol. The search was targeted towards 22 star formation regions that exhibit maser emission in the 107.0-GHz 3₁-4₀ A⁺ methanol transition, and in the 6.6-GHz 5₁-6₀ A⁺ transition characteristic of class II methanol maser sources. A total of seven sources were detected in the 2₁-3₀ E transition, six of these being new detections. Many of the new detections are weak (~0.5 Jy), however, they appear to be weak masers rather than thermal or quasi-thermal emission.

We find a strong correlation between sources that exhibit 19.9-GHz methanol masers and those that both have the class II methanol masers projected against radio continuum emission and have associated 6035-MHz OH masers. This suggests that the 19.9-GHz methanol masers arise in very specific physical conditions, probably associated with a particular evolutionary phase. In the model of Cragg, Sobolev & Godfrey these observations are consistent with gas temperatures of 50 K, dust temperatures of 150-200 K and gas densities of 10^6.5-10^7.5 cm^-3.

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Detection table from Ellingsen et al. (2004)

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ID	Obs. RA	Obs. Dec	l	b	Group id	Source name	Image	Descr.	Line	V_peak	FWHM	F_peak	Telescope	RMS	Beam	Detection	Class	Dist. (parallax)	Date
	(J2000)	(J2000)	(deg.)	(deg.)					CH₃OH (class II)	(km/s)	(km/s)	(Jy)		(Jy)	(arcsec)	Yes/No		(kpc)
1	15 31 45.5	-56 30 50	323.7402	-0.2627	G323.740-0.263	323.740-0.263	Image	Descr	19 GHz (II);	-51.4	3.1	0.15	TID	0.100	53	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		2003 Apr-Nov
2	15 55 48.5	-52 43 07	328.8084	0.6329	G328.809+0.633	328.808+0.633	Image	Descr	19 GHz (II);	-43.7	0.9	0.79	TID	0.100	53	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2003 Apr-Nov
3	16 52 4.7	-46 08 34	339.8841	-1.2588	G339.884-1.259	339.884-1.259	Image	Descr	19 GHz (II);	-36.2	0.4	9.8	TID	0.100	53	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2003 Apr-Nov
	16 52 4.7	-46 08 34	339.8841	-1.2588	G339.884-1.259	339.884-1.259			19 GHz (II);	-36.8	0.4	1.5	TID	0.100	53	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2003 Apr-Nov
5	17 05 10.9	-41 29 06	345.0030	-0.2235	G345.003-0.223	345.003-0.223	Image	Descr	19 GHz (II);	-27.4	3.4	0.22	TID	0.100	53	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2003 Apr-Nov
6	16 56 47.6	-40 14 26	345.0095	1.7923	G345.010+1.792	345.010+1.792	Image	Descr	19 GHz (II);	-17.6	1.5	0.21	TID	0.100	53	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2003 Apr-Nov
7	17 20 53.4	-35 47 01	351.4170	0.6452	G351.417+0.645	NGC 6334F	Image	Descr	19 GHz (II);	-10.4	0.3	146.7	TID	0.100	53	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		2003 Apr-Nov
	17 20 53.4	-35 47 01	351.4170	0.6452	G351.417+0.645	NGC 6334F			19 GHz (II);	-11	0.3	26.8	TID	0.100	53	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		2003 Apr-Nov
	17 20 53.4	-35 47 01	351.4170	0.6452	G351.417+0.645	NGC 6334F			19 GHz (II);	-9.6	0.4	1.9	TID	0.100	53	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		2003 Apr-Nov
10	17 30 26.2	-34 41 46	353.4097	-0.3603	G353.410-0.360	353.410-0.360	Image	Descr	19 GHz (II);	-20.5	1.8	0.33	TID	0.100	53	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2003 Apr-Nov

Non-detection table from Ellingsen et al. (2004)