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MEH97 - 44 GHz Methanol Masers and Quasi-Thermal Emission in Sagittarius B2

Interferometry data

Short title: Mehringer & Menten (1997)
Authors: Mehringer, David M. Menten, Karl M.
Journal: The Astrophysical Journal, Volume 474, Issue 1, pp. 346-361.
Bibcode:

Non-detection table: Show non-detection table
Detection table: Show detection table (1 detection)
Target type: Galaxy_center
Transitions: CH3OH_44(I),CH3OH_95(I),CH3OH_6(II),CH3OH_12(II),CH3OH_108(II),CH3OH_157(II)

Abstract
The Very Large Array has been used to obtain ~3'' resolution observations on the 44 GHz 7₀ --> 6₁A⁺ transition of CH₃OH (methanol) in the Sgr B2 massive star-forming complex. A total of 18 compact regions showing maser emission are found, which are spread over 2.1 pc � 4.3 pc (alpha � delta) region. Many of these are offset far from known molecular cores and ultracompact H II regions and may trace the interaction region of a cloud-cloud collision. There is no spatial coincidence between 44 GHz and 6.7 GHz CH₃OH masers in this region, as expected, because the pumping mechanisms for these two transitions are different. Isotropic maser luminosities range between 1 � 10^-6 and 2.1 � 10^-5 L_&sun. In addition, 17 regions with broad line width quasi-thermal 44 GHz CH₃OH emission are identified, many of which are close to known molecular hot cores, in particular those associated with the Sgr B2(N) and Sgr B2(M) continuum sources. In Sgr B2(N), quasi-thermal emission appears to be associated with two 10'' diameter ionized shells. These ionized shells may have swept up and shocked molecular material as they expanded. Also, a quasi-thermal core is observed to be coincident with a source of continuum emission from dust and emission from more complex species. In Sgr B2(M), CH₃OH quasi-thermal emission arises predominantly from the western portion of this region. The CH₃OH fractional abundance in most of the quasi-thermal cores appears to be quite high at ~10^-6. It is argued that grain-surface chemistry is responsible for this high abundance.	Comments: Only maser emission is included with only one intensity peak in each maser spot.

Abstract

The Very Large Array has been used to obtain ~3'' resolution observations on the 44 GHz 7₀ --> 6₁A⁺ transition of CH₃OH (methanol) in the Sgr B2 massive star-forming complex. A total of 18 compact regions showing maser emission are found, which are spread over 2.1 pc � 4.3 pc (alpha � delta) region. Many of these are offset far from known molecular cores and ultracompact H II regions and may trace the interaction region of a cloud-cloud collision. There is no spatial coincidence between 44 GHz and 6.7 GHz CH₃OH masers in this region, as expected, because the pumping mechanisms for these two transitions are different. Isotropic maser luminosities range between 1 � 10^-6 and 2.1 � 10^-5 L_&sun. In addition, 17 regions with broad line width quasi-thermal 44 GHz CH₃OH emission are identified, many of which are close to known molecular hot cores, in particular those associated with the Sgr B2(N) and Sgr B2(M) continuum sources. In Sgr B2(N), quasi-thermal emission appears to be associated with two 10'' diameter ionized shells. These ionized shells may have swept up and shocked molecular material as they expanded. Also, a quasi-thermal core is observed to be coincident with a source of continuum emission from dust and emission from more complex species. In Sgr B2(M), CH₃OH quasi-thermal emission arises predominantly from the western portion of this region. The CH₃OH fractional abundance in most of the quasi-thermal cores appears to be quite high at ~10^-6. It is argued that grain-surface chemistry is responsible for this high abundance.

Comments:
Only maser emission is included with only one intensity peak in each maser spot.

Input tables: Table 2
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Detection table from Mehringer & Menten (1997)

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ID	Obs. RA	Obs. Dec	RA offset	Dec offset	l	b	Group id	#	Maser spot	Source name	Image	Line	V_peak	F_peak	Telescope	Beam	Detection	Class	Dist. (parallax)
	(J2000)	(J2000)	(mas)	(mas)	(deg.)	(deg.)						CH₃OH (class I)	(km/s)	(Jy)		(arcsec)	Yes/No		(kpc)
1	+17 47 19.7879	-28 22 17.2996			0.677384	-0.027155	G0.6554-0.0340			Sgr B2(N)	Image	44 GHz (I);	46 .. 77.3	0.71 .. 9.3	NRAOVLA	1.4 x 2.4	+CH₃OH I	SFR
	+17 47 20.1921	-28 22 3.17002	6061.44 mas	14129.2 mas	0.681509	-0.026389		1	A	Sgr B2(N)			55.3	0.79
	+17 47 18.804	-28 22 8.27108	-14760.3 mas	9028.12 mas	0.677661	-0.022770		2	B	Sgr B2(N)			67.5	0.88
	+17 47 18.7145	-28 22 9.47761	-16103 mas	7821.59 mas	0.677204	-0.022663		3	C	Sgr B2(N)			70.1	0.84
	+17 47 19.7147	-28 22 9.50485	-1100.16 mas	7794.35 mas	0.679097	-0.025803		4	D	Sgr B2(N)			69.1	1.97
	+17 47 19.7347	-28 22 9.60339	-799.494 mas	7695.81 mas	0.679112	-0.025880		5	E	Sgr B2(N)			65.5	1.03
	+17 47 19.3851	-28 22 10.7288	-6043.38 mas	6570.36 mas	0.678181	-0.024946		6	F	Sgr B2(N)			65.5	3.44
	+17 47 17.4318	-28 22 27.6712	-35342.5 mas	-10372 mas	0.670446	-0.021258		7	G	Sgr B2(N)			61.8	3.06
	+17 47 17.3961	-28 22 37.974	-35878.1 mas	-20674.8 mas	0.667930	-0.022629		8	H	Sgr B2(N)			72.7	1.38
	+17 47 17.5395	-28 22 45.9637	-33727.6 mas	-28664.5 mas	0.666304	-0.024228		9	I	Sgr B2(N)			75	1.12
	+17 47 18.1109	-28 22 49.0221	-25156.9 mas	-31722.9 mas	0.666662	-0.026460		10	J	Sgr B2(N)			77	0.85
	+17 47 15.9811	-28 22 50.4771	-57103.5 mas	-33177.9 mas	0.662272	-0.019991		11	K	Sgr B2(N)			73.7	3.3
	+17 47 18.3317	-28 22 50.8061	-21845.2 mas	-33506.9 mas	0.666658	-0.027409		12	L	Sgr B2(N)			77.3	0.86
	+17 47 18.4437	-28 22 55.698	-20164.2 mas	-38398.8 mas	0.665708	-0.028464		13	M	Sgr B2(N)			72.7	0.74
	+17 47 18.8361	-28 23 1.16958	-14278.9 mas	-43870.4 mas	0.665153	-0.030482		14	N	Sgr B2(N)			64.2	0.74
	+17 47 18.8476	-28 23 4.7688	-14106.3 mas	-47469.6 mas	0.664320	-0.031036		15	O	Sgr B2(N)			67.2	0.79
	+17 47 17.3877	-28 23 5.67502	-36004.5 mas	-48375.8 mas	0.661332	-0.026589		16	P	Sgr B2(N)			46	0.71
	+17 47 17.8301	-28 23 11.1429	-29369.1 mas	-53843.7 mas	0.660873	-0.028763		17	Q	Sgr B2(N)			57.2	1.15
	+17 47 18.4328	-28 23 41.2995	-20328.5 mas	-84000.3 mas	0.654852	-0.034992		18	R	Sgr B2(N)			71.4	9.3

Distribution of sources in all sky (l,b)

Distribution of sources in all sky using Aladin

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Distribution of sources in IRAS color-color diagram

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Original color diagram is taken form van der Veen & Habing (1987)

Type	Description
I	Oxygen-rich non-variable stars without circumstellar shells
II	Variable stars with "young" O-rich circumstellar shells
IIIa	Variable stars with more evolved O-rich circumstellar shells
IIIb	Variable stars with thick O-rich circumstellar shells
IV	Variable stars with very thick O-rich circumstellar shells
V	Planetary nebulae and non- variable stars with very cool circumstellar shells
VIa	Variable stars with relatively cold dust at large distances; a significant part of the stars is carbon-rich
VIb	Variable stars with relatively hot dust close to the star and relatively cold dust at large distances; Some of the objects have proven to be O-rich
VII	Variable stars with more evolved C-rich circumstellar shells
VIII	Different sort of objects

Distribution of the detection velocities versus galactic longitude from MEH97

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