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CAS10 - An unbiased pilot survey for Galactic water masers

Short title: Caswell & Breen (2010)
Authors: Caswell, J. L.Breen, S. L.
Journal: Monthly Notices of the Royal Astronomical Society, Volume 407, Issue 4, pp. 2599-2610.
Bibcode:

Target type: Blind
Transitions: H2O_22,CH3OH_6(II)

Abstract
The Australia Telescope Compact Array has been used in a fast surveying mode to study the 22-GHz transition of water in two small sample regions of the southern Galactic plane. The observations allow an unbiased search for water masers, including any that may have no association with masers from other molecules (or indeed, no association with any other detectable celestial object). Positions with arcsecond accuracy were obtained from the original survey data for detected sources, and these were re-observed at an epoch more than two years later. Variability of the spectra between the epochs was considerable: our total of 32 masers comprises 24 detected at both epochs, two detected at only the first epoch and six detected at only the follow-up epoch. The success of our surveying mode shows it to be a practical strategy for the difficult task of extending unbiased water maser surveys to a large portion of the Galactic plane. Our results show quantitatively the effect of variability on the completeness of surveys conducted at a single epoch. Most of our maser detections are new discoveries. Only four had previously been detected (in searches towards interesting targets in the survey area). The high density of water masers from our unbiased survey supports earlier suggestions that they are the most populous maser species, and one of the most sensitive and reliable tracers of massive young stellar objects - newly forming massive young stars. The spectra of nine masers show high-velocity emission, and they show a striking preponderance of blueshifted high-velocity features. This is compatible with such blueshifts being a characteristic of populations dominated by masers at the earliest evolutionary stage of star formation, in some cases prior to the onset of methanol masers. Amongst the high-velocity emission sources there are two new examples where blueshifted high-velocity outflows dominate the total emission these substantially increase the previously known meagre population of five such objects and suggest that they may be surprisingly abundant.

Abstract

The Australia Telescope Compact Array has been used in a fast surveying mode to study the 22-GHz transition of water in two small sample regions of the southern Galactic plane. The observations allow an unbiased search for water masers, including any that may have no association with masers from other molecules (or indeed, no association with any other detectable celestial object). Positions with arcsecond accuracy were obtained from the original survey data for detected sources, and these were re-observed at an epoch more than two years later. Variability of the spectra between the epochs was considerable: our total of 32 masers comprises 24 detected at both epochs, two detected at only the first epoch and six detected at only the follow-up epoch. The success of our surveying mode shows it to be a practical strategy for the difficult task of extending unbiased water maser surveys to a large portion of the Galactic plane. Our results show quantitatively the effect of variability on the completeness of surveys conducted at a single epoch.

Most of our maser detections are new discoveries. Only four had previously been detected (in searches towards interesting targets in the survey area). The high density of water masers from our unbiased survey supports earlier suggestions that they are the most populous maser species, and one of the most sensitive and reliable tracers of massive young stellar objects - newly forming massive young stars. The spectra of nine masers show high-velocity emission, and they show a striking preponderance of blueshifted high-velocity features. This is compatible with such blueshifts being a characteristic of populations dominated by masers at the earliest evolutionary stage of star formation, in some cases prior to the onset of methanol masers. Amongst the high-velocity emission sources there are two new examples where blueshifted high-velocity outflows dominate the total emission these substantially increase the previously known meagre population of five such objects and suggest that they may be surprisingly abundant.

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Detection table from Caswell & Breen (2010)

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ID	Obs. RA	Obs. Dec	l	b	Group id	Source name	Image	Descr.	Line	V_range	V_peak	F_peak	Telescope	Configuration	V_step	RMS	Beam	Detection	Class	Dist. (parallax)	Date
	(J2000)	(J2000)	(deg.)	(deg.)					H₂O	(km/s)	(km/s)	(Jy)			(km/s)	(Jy)	(arcsec)	Yes/No		(kpc)
1	13 10 39.4	-62 52 39.6	305.1202	-0.0876	G305.120-0.088	305.120-0.087	Image	Descr	22 GHz;	-41;-17	-35	1.2	ATCA	H75	0.84	0.170	25	+H₂O	SFR		2007 October 9
	13 10 39.4	-62 52 39.6	305.1202	-0.0876	G305.120-0.088	305.120-0.087			22 GHz;	-41;-17	-33	3.1	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O	SFR		2004 July 30
3	13 10 41.2	-62 43 5.9	305.1357	0.0710	G305.137+0.068	305.136+0.071			22 GHz;	51;53	52	1.3	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O	SFR		2004 July 30
4	13 10 42.7	-62 43 19.5	305.1381	0.0671	G305.137+0.068	305.138+0.067	Image	Descr	22 GHz;	-42;-36	-38	1.6	ATCA	H75	0.84	0.170	25	+H₂O	SFR		2007 October 9
5	13 11 13.6	-62 47 25.5	305.1917	-0.0055	G305.200+0.019	305.191-0.006	Image	Descr	22 GHz;	-60;40	33	23	ATCA	H75	0.84	0.170	25	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		2007 October 9
	13 11 13.6	-62 47 25.5	305.1917	-0.0055	G305.200+0.019	305.191-0.006			22 GHz;	-60;40	32	6.1	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		2004 July 30
7	13 11 16.9	-62 46 36.1	305.1991	0.0077	G305.200+0.019	305.198+0.007	Image	Descr	22 GHz;	-42;-24	-40	7	ATCA	H75	0.84	0.170	25	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		2007 October 9
	13 11 16.9	-62 46 36.1	305.1991	0.0077	G305.200+0.019	305.198+0.007			22 GHz;	-42;-24	-34	4.2	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		2004 July 30
9	13 11 13.7	-62 34 40.6	305.2084	0.2063	G305.208+0.206	305.208+0.207	Image	Descr	22 GHz;	-45;-34	-35	135	ATCA	H75	0.84	0.170	25	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2007 October 9
	13 11 13.7	-62 34 40.6	305.2084	0.2063	G305.208+0.206	305.208+0.207			22 GHz;	-45;-34	-38	70	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2004 July 30
11	13 11 53.8	-62 46 55.6	305.2688	-0.0032	G305.270-0.005	305.269-0.003	Image	Descr	22 GHz;	-83;-53	-60	0.8	ATCA	H75	0.84	0.170	25	+H₂O	GALAXY		2007 October 9
12	13 11 54.9	-62 47 10.7	305.2706	-0.0076	G305.270-0.005	305.271-0.007	Image	Descr	22 GHz;	-40;-24	-35	3.3	ATCA	H75	0.84	0.170	25	+H₂O	GALAXY		2007 October 9
	13 11 54.9	-62 47 10.7	305.2706	-0.0076	G305.270-0.005	305.271-0.007			22 GHz;	-40;-24	-33	8.2	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O	GALAXY		2004 July 30
14	13 12 05	-62 51 41.6	305.2838	-0.0841	G305.284-0.084	305.284-0.084	Image	Descr	22 GHz;	-20;-11	-16	1.2	ATCA	H75	0.84	0.170	25	+H₂O			2007 October 9
	13 12 05	-62 51 41.6	305.2838	-0.0841	G305.284-0.084	305.284-0.084			22 GHz;	-20;-11	-17	0.9	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O			2004 July 30
16	13 12 18.4	-62 42 17.1	305.3217	0.0701	G305.320+0.070	305.322+0.070	Image	Descr	22 GHz;	-96;-11	-30	258	ATCA	H75	0.84	0.170	25	+H₂O -OH	SFR		2007 October 9
	13 12 18.4	-62 42 17.1	305.3217	0.0701	G305.320+0.070	305.322+0.070			22 GHz;	-96;-11	-32	160	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O -OH	SFR		2004 July 30
18	13 12 35.8	-62 37 19.2	305.3617	0.1499	G305.362+0.150	305.361+0.150	Image	Descr	22 GHz;	-45;-31	-35	313	ATCA	H75	0.84	0.170	25	+H₂O +CH₃OH II +OH	SFR		2007 October 9
	13 12 35.8	-62 37 19.2	305.3617	0.1499	G305.362+0.150	305.361+0.150			22 GHz;	-45;-31	-36	105	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O +CH₃OH II +OH	SFR		2004 July 30
20	13 13 45.7	-62 51 27.8	305.4748	-0.0962	G305.475-0.096	305.475-0.096	Image	Descr	22 GHz;	-91;-50	-85	3.3	ATCA	H75	0.84	0.170	25	+H₂O +CH₃OH I +CH₃OH II	SFR		2007 October 9
	13 13 45.7	-62 51 27.8	305.4748	-0.0962	G305.475-0.096	305.475-0.096			22 GHz;	-91;-50	-83	0.7	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O +CH₃OH I +CH₃OH II	SFR		2004 July 30
22	13 14 22.8	-62 45 59.8	305.5531	-0.0117	G305.558+0.013	305.553-0.012	Image	Descr	22 GHz;	-45;-30	-35	4.5	ATCA	H75	0.84	0.170	25	+H₂O -CH₃OH I +CH₃OH II	SFR		2007 October 9
23	13 14 25.7	-62 44 30	305.5608	0.0127	G305.558+0.013	305.561+0.013	Image	Descr	22 GHz;	-48;-38	-42	0.7	ATCA	H75	0.84	0.170	25	+H₂O -CH₃OH I +CH₃OH II	SFR		2007 October 9
	13 14 25.7	-62 44 30	305.5608	0.0127	G305.558+0.013	305.561+0.013			22 GHz;	-48;-38	-41	4.9	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O -CH₃OH I +CH₃OH II	SFR		2004 July 30
25	13 14 27.3	-62 44 30.9	305.5638	0.0122	G305.558+0.013	305.564+0.012	Image	Descr	22 GHz;	-36;-34	-35	1.1	ATCA	H75	0.84	0.170	25	+H₂O -CH₃OH I +CH₃OH II	SFR		2007 October 9
26	13 15 26.4	-62 51 2.8	305.6660	-0.1065	G305.666-0.106	305.666-0.106	Image		22 GHz;	-77;-59	-69	6.5	ATCA	H75	0.84	0.170	25	+H₂O	SFR		2007 October 9
27	13 15 26.4	-62 51 2.8	305.6660	-0.1065	G305.666-0.106	305.666-0.107		Descr	22 GHz;	-77;-59	-63	0.9	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O	SFR		2004 July 30
28	13 15 48.5	-62 39 25.4	305.7262	0.0824	G305.726+0.082	305.726+0.082	Image	Descr	22 GHz;	-55;-32	-44	6.2	ATCA	H75	0.84	0.170	25	+H₂O	EVOLVED		2007 October 9
	13 15 48.5	-62 39 25.4	305.7262	0.0824	G305.726+0.082	305.726+0.082			22 GHz;	-55;-32	-44	5.3	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O	EVOLVED		2004 July 30
30	13 16 45.5	-62 50 22.2	305.8169	-0.1097	G305.822-0.114	305.817-0.110	Image	Descr	22 GHz;	-105;-40	-55	1.3	ATCA	H75	0.84	0.170	25	+H₂O +CH₃OH I +CH₃OH II	SFR		2007 October 9
	13 16 45.5	-62 50 22.2	305.8169	-0.1097	G305.822-0.114	305.817-0.110			22 GHz;	-105;-40	-51	4.3	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O +CH₃OH I +CH₃OH II	SFR		2004 July 30
32	13 16 48.6	-62 50 39	305.8222	-0.1149	G305.822-0.114	305.822-0.115	Image	Descr	22 GHz;	-45;-36	-38	4.8	ATCA	H75	0.84	0.170	25	+H₂O +CH₃OH I +CH₃OH II	SFR		2007 October 9
33	13 16 52.9	-62 48 37.2	305.8338	-0.0820	G305.834-0.082	305.834-0.082	Image	Descr	22 GHz;	-125;29	-113	23	ATCA	H75	0.84	0.170	25	+H₂O	SFR		2007 October 9
	13 16 52.9	-62 48 37.2	305.8338	-0.0820	G305.834-0.082	305.834-0.082			22 GHz;	-125;29	-110	10.5	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O	SFR		2004 July 30
35	13 17 15.7	-62 42 23.3	305.8873	0.0170	G305.887+0.017	305.887+0.017	Image	Descr	22 GHz;	-107;-24	-29	27	ATCA	H75	0.84	0.170	25	+H₂O +CH₃OH I +CH₃OH II	SFR_MIXED		2007 October 9
	13 17 15.7	-62 42 23.3	305.8873	0.0170	G305.887+0.017	305.887+0.017			22 GHz;	-107;-24	-28	22.5	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O +CH₃OH I +CH₃OH II	SFR_MIXED		2004 July 30
37	13 17 44.1	-62 41 21.4	305.9431	0.0286	G305.943+0.029	305.943+0.028	Image		22 GHz;	-49;-27	-41	4.8	ATCA	H75	0.84	0.170	25	+H₂O -OH	EVOLVED		2007 October 9
38	13 17 44.1	-62 41 21.4	305.9431	0.0286	G305.943+0.029	305.943+0.029		Descr	22 GHz;	-49;-27	-41	2.7	ATCA	H168	1.68	0.170	12.2 x 10.7	+H₂O -OH	EVOLVED		2004 July 30
39	13 18 47	-62 44 52.2	306.0564	-0.0421	G306.056-0.042	306.056-0.042	Image	Descr	22 GHz;	-35;-20	-34	0.37	ATCA	H75	0.84	0.170	25	+H₂O -CH₃OH II	SFR		2007 October 9
	13 18 47	-62 44 52.2	306.0564	-0.0421	G306.056-0.042	306.056-0.042			22 GHz;	-35;-20	-28	3.5	ATCA	H168	1.68	0.170	13.3 x 9.9	+H₂O -CH₃OH II	SFR		2005 May 24
41	14 02 27.5	-61 45 14.3	311.2298	-0.0318	G311.230-0.032	311.230-0.032	Image	Descr	22 GHz;	15;40	29	20	ATCA	H75	0.84	0.170	25	+H₂O +CH₃OH II	EVOLVED		2007 October 9
	14 02 27.5	-61 45 14.3	311.2298	-0.0318	G311.230-0.032	311.230-0.032			22 GHz;	15;40	28.5	59	ATCA	H168	1.68	0.170	13.3 x 9.9	+H₂O +CH₃OH II	EVOLVED		2005 May 24
43	14 06 9.1	-61 42 17.8	311.6634	-0.1063	G311.663-0.106	311.663-0.106	Image	Descr	22 GHz;	-66;-30	-65	0.26	ATCA	H75	0.84	0.170	25	+H₂O	SFR		2007 October 9
	14 06 9.1	-61 42 17.8	311.6634	-0.1063	G311.663-0.106	311.663-0.106			22 GHz;	-66;-30	-36	0.8	ATCA	H168	1.68	0.170	13.3 x 9.9	+H₂O	SFR		2005 May 24
45	14 07 17.6	-61 38 38.8	311.8107	-0.0870	G311.811-0.087	311.811-0.087	Image	Descr	22 GHz;	-60;-37	-58	0.2	ATCA	H75	0.84	0.170	25	+H₂O	EVOLVED		2007 October 9
	14 07 17.6	-61 38 38.8	311.8107	-0.0870	G311.811-0.087	311.811-0.087			22 GHz;	-60;-37	-55	1.8	ATCA	H168	1.68	0.170	13.3 x 9.9	+H₂O	EVOLVED		2005 May 24
47	14 06 54.5	-61 25 52	311.8282	0.1302	G311.833+0.129	311.828+0.130	Image	Descr	22 GHz;	-117;-5	-109	1.6	ATCA	H75	0.84	0.170	25	+H₂O	SFR		2007 October 9
	14 06 54.5	-61 25 52	311.8282	0.1302	G311.833+0.129	311.828+0.130			22 GHz;	-117;-5	-114	1.2	ATCA	H168	1.68	0.170	13.3 x 9.9	+H₂O	SFR		2005 May 24
49	14 06 59.4	-61 25 47.7	311.8378	0.1286	G311.833+0.129	311.838+0.129	Image	Descr	22 GHz;	-49;-45	-48	1.2	ATCA	H75	0.84	0.170	25	+H₂O	SFR		2007 October 9
50	14 08 47.7	-61 32 8.6	312.0132	-0.0355	G312.013-0.035	312.013-0.035			22 GHz;	16;21	17	0.9	ATCA	H168	1.68	0.170	13.3 x 9.9	+H₂O	SFR		2005 May 24
51	14 08 58.3	-61 24 24.2	312.0714	0.0816	G312.071+0.082	312.071+0.082	Image	Descr	22 GHz;	-65;-15	-32	27	ATCA	H75	0.84	0.170	25	+H₂O +CH₃OH II	SFR		2007 October 9
	14 08 58.3	-61 24 24.2	312.0714	0.0816	G312.071+0.082	312.071+0.082			22 GHz;	-65;-15	-32	23.2	ATCA	H168	1.68	0.170	13.3 x 9.9	+H₂O +CH₃OH II	SFR		2005 May 24
53	14 09 10.1	-61 24 24.9	312.0938	0.0745	G312.094+0.074	312.094+0.074	Image	Descr	22 GHz;	-92;-39	-49	7.5	ATCA	H75	0.84	0.170	25	+H₂O	SFR		2007 October 9
	14 09 10.1	-61 24 24.9	312.0938	0.0745	G312.094+0.074	312.094+0.074			22 GHz;	-92;-39	-40	2.1	ATCA	H168	1.68	0.170	13.3 x 9.9	+H₂O	SFR		2005 May 24
55	14 09 29.3	-61 27 49.7	312.1135	0.0088	G312.113+0.009	312.114+0.009	Image		22 GHz;	-55;-27	-42	9.8	ATCA	H75	0.84	0.170	25	+H₂O	EVOLVED		2007 October 9
	14 09 29.3	-61 27 49.7	312.1135	0.0088	G312.113+0.009	312.114+0.009			22 GHz;	-55;-27	-47	8.8	ATCA	H168	1.68	0.170	13.3 x 9.9	+H₂O	EVOLVED		2005 May 24

Non-detection table from Caswell & Breen (2010)