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HAR05 - A MERLIN survey of 4.7-GHz excited OH masers in star-forming regions

Interferometry data

Short title: Harvey-Smith & Cohen (2005)
Authors: Harvey-Smith, L.Cohen, R. J.
Journal: Monthly Notices of the Royal Astronomical Society, Volume 356, Issue 2, pp. 637-646.
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Target type: High_mass_SFR
Observations category: SF.general
Facility type: interferometer
Transitions: OH_4660,OH_4750,OH_4765

Abstract
Phase-referenced observations of 13 star-forming regions in the 2 1/2 , J = 1/2 transition of rotationally excited OH at 4765 MHz have been carried out using MERLIN. Two of the regions were also observed at 4750 MHz and one at 4660 MHz. There were 10 maser detections at 4765 MHz and three non-detections. There were no detections at 4750 and 4660 MHz. The 4765-MHz masers have brightness temperatures of ∼10 7 K at MERLIN resolution (∼50 mas). Several cases of 4765-MHz masers overlapping in position and velocity with 1720-and 1665-MHz masers are reported. There are also isolated 4765-MHz masers with peak flux densities 30 times that of any ground-state counterpart. Most of the 4.7-GHz maser spots are unresolved at 50-mas angular resolution, but in four of the nearest sources the maser spots are resolved, indicating a characteristic size for 4765-MHz maser regions of ∼100 au. In W3(OH) we discovered that 20 per cent of the 4765-MHz emission comes from a narrow low-brightness filament that stretches north-south for ∼1.0 arcec (∼2200 au) between two previously known 4765-MHz maser spots. The filament appears in projection against the H II region and has a brightness temperature of ∼4 × 10 5 K. There are matching absorption features in mainline transitions of highly excited OH. The filament may trace a shock front in a rotating disc.

Abstract

Phase-referenced observations of 13 star-forming regions in the 2 1/2 , J = 1/2 transition of rotationally excited OH at 4765 MHz have been carried out using MERLIN. Two of the regions were also observed at 4750 MHz and one at 4660 MHz. There were 10 maser detections at 4765 MHz and three non-detections. There were no detections at 4750 and 4660 MHz. The 4765-MHz masers have brightness temperatures of ∼10 7 K at MERLIN resolution (∼50 mas). Several cases of 4765-MHz masers overlapping in position and velocity with 1720-and 1665-MHz masers are reported. There are also isolated 4765-MHz masers with peak flux densities 30 times that of any ground-state counterpart. Most of the 4.7-GHz maser spots are unresolved at 50-mas angular resolution, but in four of the nearest sources the maser spots are resolved, indicating a characteristic size for 4765-MHz maser regions of ∼100 au. In W3(OH) we discovered that 20 per cent of the 4765-MHz emission comes from a narrow low-brightness filament that stretches north-south for ∼1.0 arcec (∼2200 au) between two previously known 4765-MHz maser spots. The filament appears in projection against the H II region and has a brightness temperature of ∼4 × 10 5 K. There are matching absorption features in mainline transitions of highly excited OH. The filament may trace a shock front in a rotating disc.

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Detection table from Harvey-Smith & Cohen (2005)

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ID	Obs. RA	Obs. Dec	RA offset	Dec offset	l	b	Group id	#	Maser spot	Source name	Image	Descr.	Line	Frequency	V_peak	F_peak	Telescope	RMS	Beam	Detection	Class	Dist. (parallax)	Date
	(J2000)	(J2000)	(mas)	(mas)	(deg.)	(deg.)							OH	(MHz)	(km/s)	(Jy)		(mJy)	(arcsec)	Yes/No		(kpc)
1	+02 25 40.7716	+62 05 54.441			133.714956	1.21599	G133.715+1.215			W3-IRS5		Descr	4765 MHz;	4765	-38.95	0.609	MERLIN	4.000	50 x 40	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		26.02.1995
	+02 25 40.7716	+62 05 54.441	0 mas	0 mas	133.714956	1.215990		1		W3-IRS5					-38.95	0.609
2	+02 27 3.7129	+61 52 24.641			133.947136	1.064133	G133.947+1.064			W3(OH)	Image	Descr	4765 MHz;	4765	-45.01 .. -43.22	0.741 .. 72.218	MERLIN	7.000	50 x 40	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		15.03.1995
	+02 27 3.7129	+61 52 24.641	0 mas	0 mas	133.947136	1.064133		1	spot C	W3(OH)					-45.01	72.218
3	+06 07 47.8403	-06 22 56.576			213.704858	-12.596999	G213.705-12.597			Mon R2		Descr	4765 MHz;	4765	10.62	1.323 .. 7.722	MERLIN	15.000	190 x 50	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		25.02.1995
	+06 07 47.8403	-06 22 56.576	0 mas	0 mas	213.704858	-12.596999		1	A	Mon R2					10.62	7.722
	+06 07 47.835	-06 22 56.461	-81 mas	114.2 mas	213.704819	-12.597004		2	B	Mon R2					10.62	1.323
4	+19 10 13.5173	+09 06 13.911			43.166882	0.010914	G43.166+0.011			W49N		Descr	4765 MHz;	4765	2.3	0.354	MERLIN	6.000	100 x 40	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		25.02.1995
	+19 10 13.5173	+09 06 13.911	0 mas	0 mas	43.166882	0.010914		1		W49N					2.3	0.354
5	+19 10 10.943	+09 05 17.598			43.148117	0.013086	G43.166+0.011			W49SW			4765 MHz;	4765	8.55	0.637	MERLIN	9.000	90 x 40	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		25.02.1995
	+19 10 10.943	+09 05 17.598	0 mas	0 mas	43.148117	0.013086		1		W49SW					8.55	0.637
6	+19 23 43.914	+14 30 34.113			49.489667	-0.387555	G49.489-0.386			W51		Descr	4765 MHz;	4765	57.47	0.151	MERLIN	4.000	80 x 40	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		26.02.1995
	+19 23 43.914	+14 30 34.113	0 mas	0 mas	49.489667	-0.387555		1		W51					57.47	0.151
7	+20 01 45.7259	+33 32 44.97			70.293234	1.600354	G70.293+1.601			K3-50		Descr	4765 MHz;	4765	-20.31	1.535	MERLIN	55.000	140 x 80	+H₂O +CH₃OH I -CH₃OH II +OH	SFR_MIXED		28.02.1995
	+20 01 45.7259	+33 32 44.97	0 mas	0 mas	70.293234	1.600354		1		K3-50					-20.31	1.535
8	+20 39 0.3804	+42 24 37.169			81.744415	0.590947	G81.762+0.596			DR21(OH)N		Descr	4765 MHz;	4765	3.58 .. 5.04	0.206 .. 2.083	MERLIN	4.000	50	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		04.03.1995
	+20 39 0.3804	+42 24 37.169	0 mas	0 mas	81.744415	0.590947		1	A	DR21(OH)N					5.04	2.083
	+20 39 0.3827	+42 24 37.17	34.5 mas	0 mas	81.744420	0.590942		2	B	DR21(OH)N					3.88	0.206
	+20 39 0.3785	+42 24 37.247	-28.5 mas	77 mas	81.744429	0.590965		3	C	DR21(OH)N					3.58	0.642
9	+21 43 1.4382	+54 56 17.737			98.03585	1.445982	G98.035+1.446			21413+5442		Descr	4765 MHz;	4765	-62.1	0.48	MERLIN	9.000	50	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		22.02.1995
	+21 43 1.4382	+54 56 17.737	0 mas	0 mas	98.035850	1.445982		1		21413+5442					-62.1	0.48
10	+23 13 45.2778	+61 28 10.603			111.541982	0.777012	G111.542+0.769			NGC 7538-IRS 1	Image	Descr	4765 MHz;	4765	-59.03 .. -57.75	0.275 .. 0.492	MERLIN	5.000	100	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		04.03.1995
	+23 13 45.2778	+61 28 10.603	0 mas	0 mas	111.541982	0.777012		1	A	NGC 7538-IRS 1					-58.74	0.275
	+23 13 45.3501	+61 28 9.745	1086.3 mas	-858.2 mas	111.542029	0.776738		2	B	NGC 7538-IRS 1					-59.03	0.492
	+23 13 45.3781	+61 28 9.712	1506.3 mas	-891.2 mas	111.542077	0.776709		3	C	NGC 7538-IRS 1					-57.75	0.433

Non-detection table from Harvey-Smith & Cohen (2005)