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GOM17 - A Search for Water Maser Emission from Brown Dwarfs and Low-luminosity Young Stellar Objects

Short title: Gomez et al. (2017)
Authors: Gomez, Jose F.Palau, AinaUscanga, LuceroManjarrez, GuillermoBarrado, David
Journal: The Astronomical Journal, Volume 153, Issue 5, article id. 221, 7 pp. (2017).
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Target type: YSO,Other
Observations category: SF.general
Facility type: mixed

Abstract
We present a survey for water maser emission toward a sample of 44 low-luminosity young objects, comprising (proto-)brown dwarfs, first hydrostatic cores (FHCs), and other young stellar objects (YSOs) with bolometric luminosities lower than 0.4 L _sun. Water maser emission is a good tracer of energetic processes, such as mass-loss and/or accretion, and is a useful tool to study these processes with very high angular resolution. This type of emission has been confirmed in objects with L _bol > 1 L _sun. Objects with lower luminosities also undergo mass-loss and accretion, and thus, are prospective sites of maser emission. Our sensitive single-dish observations provided a single detection when pointing toward the FHC L1448 IRS 2E. However, follow-up interferometric observations showed water maser emission associated with the nearby YSO L1448 IRS 2 (a Class 0 protostar of L _bol ~ 3.6-5.3 L _sun) and did not find any emission toward L1448 IRS 2E. The upper limits for water maser emission determined by our observations are one order of magnitude lower than expected from the correlation between water maser luminosities and bolometric luminosities found for YSOs. This suggests that this correlation does not hold at the lower end of the (sub)stellar mass spectrum. Possible reasons are that the slope of this correlation is steeper at L _bol <= 1 L _sun or that there is an absolute luminosity threshold below which water maser emission cannot be produced. Alternatively, if the correlation still stands at low luminosity, the detection rates of masers would be significantly lower than the values obtained in higher-luminosity Class 0 protostars.

Abstract

We present a survey for water maser emission toward a sample of 44 low-luminosity young objects, comprising (proto-)brown dwarfs, first hydrostatic cores (FHCs), and other young stellar objects (YSOs) with bolometric luminosities lower than 0.4 L _sun. Water maser emission is a good tracer of energetic processes, such as mass-loss and/or accretion, and is a useful tool to study these processes with very high angular resolution. This type of emission has been confirmed in objects with L _bol > 1 L _sun. Objects with lower luminosities also undergo mass-loss and accretion, and thus, are prospective sites of maser emission. Our sensitive single-dish observations provided a single detection when pointing toward the FHC L1448 IRS 2E. However, follow-up interferometric observations showed water maser emission associated with the nearby YSO L1448 IRS 2 (a Class 0 protostar of L _bol ~ 3.6-5.3 L _sun) and did not find any emission toward L1448 IRS 2E. The upper limits for water maser emission determined by our observations are one order of magnitude lower than expected from the correlation between water maser luminosities and bolometric luminosities found for YSOs. This suggests that this correlation does not hold at the lower end of the (sub)stellar mass spectrum. Possible reasons are that the slope of this correlation is steeper at L _bol <= 1 L _sun or that there is an absolute luminosity threshold below which water maser emission cannot be produced. Alternatively, if the correlation still stands at low luminosity, the detection rates of masers would be significantly lower than the values obtained in higher-luminosity Class 0 protostars.

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Detection table from Gomez et al. (2017)

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ID	Obs. RA	Obs. Dec	l	b	Group id	grpv	Source name	Other name	Image	Line	V_peak	F_peak	Telescope	V_step	RMS	Beam	Detection	Class	Dist. (parallax)	Date
	(J2000)	(J2000)	(deg.)	(deg.)				Typea		H₂O	(km/s)	(Jy)		(km/s)	(Jy)	(arcsec)	Yes/No		(kpc)
1	03 25 25.5	+30 45 2.5	158.0110	-21.4361	G158.000-21.441	G158.0110-21.4361	L1448 IRS 2E	FHC	Image	22 GHz;	0.08 (0.03)	-2.3	EFF	0.047	16.000	39	+H₂O -CH₃OH II	SFR		2015 Sep 29
2	03 25 22.3	+30 45 13.1	157.9993	-21.4404	G158.000-21.441	G157.9999-21.4407	L1448 IRS 2		Image	22 GHz;	0.46 (0.03)	-1.19	EFF	0.047		3.4 x 3.1	+H₂O -CH₃OH II	SFR		2015 October 14

Non-detection table from Gomez et al. (2017)