VLA observations of water masers towards 6.7 GHz methanol maser sources

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arXiv:1009.2334v1 [astro-ph.GA] 13 Sep 2010
Astronomy & Astrophysics manuscript no. bartkiewicz˙water˙final
September 14, 2010
c ? ESO 2010
VLA observations of water masers towards 6.7GHz methanol
maser sources
A. Bartkiewicz1, M. Szymczak1, Y.M. Pihlstr¨ om2,3, H.J. van Langevelde4,5, A. Brunthaler6, and M.J. Reid7
1Toru´ n Centre for Astronomy, Nicolaus Copernicus University, Gagarina 11, 87-100 Toru´ n, Poland
e-mail: annan@astro.uni.torun.pl
2Department of Physics and Astronomy, MSC07 4220, University of New Mexico, Albuquerque, NM 87131, USA
3National Radio Astronomy Observatory, 1003 Lopezville Road, Socorro, NM 87801, USA
4Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands
5Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands
6Max-Planck-Insitut f¨ ur Radioastronomie, Auf dem H¨ ugel 69, 53121 Bonn, Germany
7Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
Received 2010 June 18; accepted 2010 September 09
ABSTRACT
Context. 22GHz water and 6.7GHz methanol masers are usually thought as signposts of early stages of high-mass star formation but
little is known about their associations and the physical environments they occur in.
Aims. To obtain accurate positions and morphologies of the water maser emission and relate them to the methanol maser emission
recently mapped with Very Long Baseline Interferometry.
Methods. A sample of 31 methanol maser sources was searched for 22GHz water masers using the VLA and observed in the 6.7GHz
methanol maser line with the 32m Torun dish simultaneously.
Results. Water maser clusters were detected towards 27 sites finding 15 new sources. The detection rate of water maser emission
associated with methanol sources was as high as 71%. In a large number of objects (18/21) the structure of water maser is well
aligned withthat of theextended emissionat 4.5µmconfirming theoriginof water emission fromoutflows. Thesources withmethanol
emission with ring-like morphologies, which likely trace a circumstellar disk/torus, either do not show associated water masers or the
distribution of water maser spots is orthogonal to the major axis of the ring.
Conclusions. The two maser species are generally powered by the same high-mass young stellar object but probe different parts
of its environment. The morphology of water and methanol maser emission in a minority of sources is consistent with a scenario
that 6.7GHz methanol masers trace a disc/torus around a protostar while the associated 22GHz water masers arise in outflows. The
majority of sources in which methanol maser emission is associated with the water maser appears to trace outflows. The two types of
associations might be related to different evolutionary phases.
Key words. stars: formation – ISM: molecules – masers – techniques: interferometric
1. Introduction
Studies of high-mass star forming regions (HMSFRs) are dif-
ficult but important in astrophysics as they are responsible for
many of the energetic phenomena we see in galaxies. However,
their largedistances,heavy obscurationand rapidityofevolution
make observations challenging. Maser emission has become a
unique tool to study massive star formation. Methanol masers
at 6.7GHz as well as water masers at 22GHz have been rec-
ognized as tracers of massive star formation (e.g., Caswell et
al. 1995; Menten 1991; Sridharan et al. 2002; Urquhart et al.
2010). Moreover, both maser species are found associated with
the very early stage of a protostar, when it still accretes and be-
fore it begins to ionise the surrounding medium. These masers
are often detectable before an ultra–compact HII region is seen
at cm wavelengths.
Studies of maser emission at milliarcsecond scale, using
Very Long Baseline Interferometry (VLBI) techniques, reveal
a wide range of morphologies of 6.7GHz methanol masers.
They can form simple structures (a single spot), lie in linear
structures or arcs, or are distributed randomly without any ap-
parent regularity (e.g., Minier et al. 2000; Norris et al. 1998;
Phillips et al. 1998; Walsh et al. 1998). However, it is still un-
clear where and how they are produced. Are they related with
disks/tori around young massive protostars or found in outflows
or shocks? (e.g., Dodson et al. 2004; Minier et al. 2000; Walsh
et al. 1998). Detailed studies of particular sources reveal further
clues to the origin of methanol masers. Unfortunately, they are
not always consistent with one scenario.High angularresolution
mid-infrared (MIR) observations by De Buizer & Minier (2005)
revealedthatthe outflowscenariois moreplausiblein thecase of
NGC 7538IRS1, where the linear structure of methanol masers
had been suggested as originating in an edge-on Keplerian disc
(Pestalozzi et al. 2004). On the other hand, van der Walt et al.
(2007) argued that a simple Keplerian-like disc model was more
consistentwith theobservedkinematicsofmethanolmaser spots
in linear structures than the shock model proposed by Dodson et
al. (2004).
A relatively high detection rate of water masers to-
ward methanol masers is confirmed with single-dish stud-
ies. Szymczak et al. (2005) observed 79 targets with 6.7GHz
methanol maser emission and detected the 22GHz water line in
52% cases. Similarly, Sridharan et al. (2002) reported a detec-
tion rate of 42% for the sample of 69 HMSFRs. In interferomet-
ric investigations Beuther et al. (2002) obtained a 62% detection

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2Bartkiewicz et al.: VLA observations of water masers towards 6.7GHz methanol masers
rate of water masers toward methanolmasers. Recently,Breen et
al. (2010) searched 379 water masers and found methanol emis-
sion in ≈ 52% of the sources. Although different excitation con-
ditions are required for both molecules, their origin is in some
sense dependent and likely related to the same powering source.
There are few HMSFRs with detailed studies of methanol–
water maser associations. For example Pillai et al. (2006) ob-
served the HMSFR G11.11−0.12over a wide wavelength range.
They reported that methanol masers were associated with an
accretion disc driving an outflow traced by water maser emis-
sion. Moscadelli et al. (2007) explored HMSFR G24.78+0.08
andshowedthatwatermaserstraceafastexpandingshellclosely
surroundinga hyper-compactHII region.Methanolmasers were
proposed to have emerged in a rotating toroid lying radially out-
ward of the HII region. However, there is a lack of data for a
large sample of methanol and water masers at high angular res-
olution with a few mJy sensitivity to get better statistics on the
two types of associations.
We have recently completed a survey of 31 sources at
6.7GHzusingtheEuropeanVLBINetwork(EVN)(Bartkiewicz
et al. 2009). Due to the high angular and spectral resolution as
well as the high sensitivity we have discovered nine sources
(29% of the sample) with ring-like maser distributions (with a
typical major axis of 0.′′19). These ring-like structures strongly
suggesttheexistenceofacentralobject,andcouldprovideaclue
to its nature. Each source with ring-like morphology coincides
within 1′′with a MIR object (from the GLIMPSE survey) that
has an excess of 4.5µm emission, which is evidence for shocked
regions (e.g., Cyganowski et al. 2008). This suggests that even
ring-like structures can arise due to shock waves or in outflows.
In order to answer the question what are these structures?, we
initiated wide and detailed studies of that sample of methanol
maser sources. Here, we present the first results of our investi-
gation of the presence, position, and distribution of water maser
emission toward6.7GHz methanolmaseremission. We used the
NRAO Very Large Array (VLA) to search for water masers near
the locations of 6.7 GHz methanol masers and, if detected, to
compare the positions of the two masing species.
2. Observations and data reduction
2.1. VLA observations
To investigate the relationship between water and methanol
masers in HMSFRs, our sample of 31 methanol maser sources
(Table 1) was observed at 22.23508GHz using the VLA in CnB
configuration in two 12h runs on 2009 June 4 and 5 (the project
AB1324). A spectral line mode with a single IF and 6.25MHz
bandwidth divided into 128 spectral channels was used, yield-
ing a velocity coverage of 84kms−1and a channel spacing of
0.65kms−1. The pointing positions were defined as the coor-
dinates of the brightest 6.7GHz methanol maser component
(Table 1) and the bandpass was centred at the methanol maser
peak velocity taken from Bartkiewicz et al. (2009, their Table
5). 3C286 was used as the primary flux density calibrator for
all targets. We used two secondary calibrators (J1851+0035and
J1832−1035) to monitor changes in interferometer amplitude
and phase; these were selected from the VLA calibrator cata-
log to be near the targets (Table 1). We allocated 50 s for ob-
servation of the secondary calibrator, followed by 250s for the
maser source. These times included slew and on-source integra-
tion times. In total each targetwas observedfor35min, resulting
in about 29min on-source integration time.
The data reduction was carried out following the standard
recipes recommended in Appendix B of the AIPS cookbook1.
The amplitude and phase errors of 3C286 were corrected us-
ing the default source model and 3C286 was subsequently used
to derive the secondary-calibrator flux densities. The antenna
gains were calibrated using the secondary-calibratordata. A few
bad data points were flagged and images (512×512 pixels with
pixel size of 0.′′15) were created using natural weighting. The
noise levels in the maps and the synthesized beams are listed in
Table 1. The analysis of maser properties was carried out using
maps centred on the position of the brightest water maser spots.
We estimate that, with the relatively stable weather condi-
tions during our observations, position errors of water maser
spots are dominated by the errors of the secondary-calibrator
positions, which could be as large as 0.′′15 for these two calibra-
tors. However,the relative position uncertainties are much better
(≈10mas).
2.2. 32m dish observations
The same sample was observed in the 6.7GHz methanol maser
line using the Torun 32m telescope over 20 days in June 2009
nearly simultaneously with the VLA H2O observations. The
telescope characteristics and calibration procedures were de-
scribed in Szymczak et al. (2002). The spectra were taken in fre-
quencyswitchingmodewitharesultingspectralchannelspacing
of 0.04kms−1and sensitivity of ∼0.6Jy (3σ). The accuracy of
the absolute flux density calibration was better than 15%.
3. Results
The observational results are summarized in Table 2 and
Figure 1. Table 2 lists the coordinates of the brightest water
maser spot in each target, the LSR velocity (Vp), and the inten-
sity (Sp)as wellas thevelocityextentofthewateremission(∆V)
and the integrated flux density (Sint). In most cases the Galactic
names of the water maser sources are the same as those of the
methanol masers in Bartkiewicz et al. (2009). However, for five
watermasersourcesthenamesareupdated(markedby1)astheir
positions differ by more than 3.′′6 (0.◦001) from the methanol
maser positions. The two columns of Table 2, ∆wm, give the an-
gular separation of two nearest spots of both species and the cor-
responding difference in velocity. The last two columns, PAH2O
andPAMIR,list positionanglesofwatermaseremissionandMIR
counterpart if it exists (Sect. 3.3). PA is defined as East of North
in the whole paper.
In Figure 1, we present the spectra and angular distributions
of the water maser emission for the detected sources. The spec-
tra were extracted from the map data cubes using the AIPS task
ISPEC and represent the total flux density of maser emission
measured in the maps. All spots detected in each of the indi-
vidual channel maps are shown. Overlaid are the spectra and
distributions of the 6.7GHz methanol masers as obtained with
the EVN (Bartkiewicz et al. 2009). The parameters of all de-
tected water maser spots of each source are listed in Table 3.
Specifically, the position (∆RA, ∆Dec) relative to the brightest
6.7GHz methanol maser spot (as listed in Table 1), the LSR ve-
locity (VLSR) and the intensity (S) of the maser spots are given.
Due to the relatively poor spectral resolution of 0.65kms−1
of our water maser spectra we postpone an analysis of line pro-
files until follow up VLBI observations when a higher spectral
resolution will be used.
1See http://www.nrao.edu/aips/coobook.html

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Bartkiewicz et al.: VLA observations of water masers towards 6.7GHz methanol masers3
Fig.1. Spectra and maps of the 22GHz water (VLA) and 6.7GHz methanol (EVN) maser emission. The upper and lower panels
correspond to the water and methanol maser spectra, respectively. The thin bars under the spectra show the velocity ranges of the
displayed water maser spots. The thin grey lines represent the systemic velocities of sources (Table 4). Each square represents a
22GHz water maser spot observed in a single channel. Note, the typical absolute positional uncertainty of water emission is 0.′′15.
The circles represent the 6.7GHz methanol maser spots from Bartkiewicz et al. (2009) with the absolute positional accuracy of a
few mas. The colours of squares and circles relate to the LSR velocities as indicated in the spectra. The coordinates are relative
to the brightest spots of methanol emission (Table 1). Note, the source names are the Galactic coordinates of the brightest spot of
the methanol maser. The dotted lines correspond to the PAMIRof 4.5µm counterparts as listed in Table 2. The colour version is
available on-line.

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4Bartkiewicz et al.: VLA observations of water masers towards 6.7GHz methanol masers
Table 1. 6.7GHz methanol maser sites searched for the 22GHz water maser emission
Source∗
Gll.lll±bb.bbb
G21.407−00.254
G22.335−00.155
G22.357+00.066
G23.207−00.377
G23.389+00.185
G23.657−00.127
G23.707−00.198
G23.966−00.109
G24.148−00.009
G24.541+00.312
G24.634−00.324
G25.411+00.105
G26.598−00.024
G27.221+00.136
G28.817+00.365
G30.318+00.070
G30.400−00.296
G31.047+00.356
G31.581+00.077
G32.992+00.034
G33.641−00.228
G33.980−00.019
G34.751−00.093
G35.793−00.175
G36.115+00.552
G36.705+00.096
G37.030−00.039
G37.598+00.425
G38.038−00.300
G38.203−00.067
G39.100+00.491
∗The Galactic coordinates of the brightest 6.7GHz methanol maser spots (Bartkiewicz et al. 2009)
Position of 6.7GHz masers
RA(h m s)
18 31 06.33794
18 32 29.40704
18 31 44.12055
18 34 55.21212
18 33 14.32477
18 34 51.56482
18 35 12.36600
18 35 22.21469
18 35 20.94266
18 34 55.72152
18 37 22.71271
18 37 16.92106
18 39 55.92567
18 40 30.54608
18 42 37.34797
18 46 25.02621
18 47 52.29976
18 46 43.85506
18 48 41.94108
18 51 25.58288
18 53 32.563
18 53 25.01833
18 55 05.22296
18 57 16.894
18 55 16.79345
18 57 59.12288
18 59 03.64233
18 58 26.79772
19 01 50.46947
19 01 18.73235
19 00 58.04036
Vp
Secondary calibrator
calibrator
J1832−1035
J1832−1035
J1832−1035
J1832−1035
J1832−1035
J1832−1035
J1832−1035
J1832−1035
J1832−1035
J1832−1035
J1832−1035
J1832−1035
J1832−1035
J1832−1035
J1851+0035
J1851+0035
J1851+0035
J1851+0035
J1851+0035
J1851+0035
J1851+0035
J1851+0035
J1851+0035
J1851+0035
J1851+0035
J1851+0035
J1851+0035
J1851+0035
J1851+0035
J1851+0035
J1851+0035
Synthesized beam
maj, min; PA (′′,′′;o)
1.19, 0.49;+61
1.07, 0.72;+48
1.36, 0.73;+39
1.05, 0.85;+2
0.88, 0.84;+83
1.03, 0.55;−77.5
1.22, 0.84;−37
1.70, 0.72;−44
1.65, 0.52;−60
1.89, 0.74;−48
2.82, 0.60;+42
0.35, 0.35;+45
3.38, 0.65;−46
1.20, 0.89;+47
4.56, 0.62;+41
1.48, 0.71;+38
1.36, 0.64;+45
1.02, 0.82;+44
0.96, 0.88;+50
0.92, 0.82;−39
1.01, 0.83;−57
1.03, 0.80;−58
1.02, 0.81;−60
1.15, 0.80;−53
1.46, 0.70;−51
2.09, 0.65;−48
2.05, 0.72;+42
2.36, 0.64;+42
2.74, 0.65;−48
2.11, 0.78;−47
2.24, 0.77;−46
Rms noise
Dec(◦ ′ ′′)
−10 21 37.4108
−09 29 29.6840
−09 22 12.3129
−08 49 14.8926
−08 23 57.4723
−08 18 21.3045
−08 17 39.3577
−08 01 22.4698
−07 48 55.6745
−07 19 06.6504
−07 31 42.1439
−06 38 30.5017
−05 38 44.6424
−05 01 05.3947
−03 29 40.9216
−02 17 40.7539
−02 23 16.0539
−01 30 54.1551
−01 10 02.5281
+00 04 08.3330
+00 31 39.180
+00 55 25.9760
+01 34 36.2612
+02 27 57.910
+03 05 05.4140
+03 24 06.1124
+03 37 45.0861
+04 20 45.4570
+04 24 18.9559
+04 39 34.2938
+05 42 43.9214
(kms−1)
89.0
35.6
79.7
77.1
75.4
82.6
79.2
70.9
17.8
105.7
35.4
97.3
24.2
118.8
90.7
36.1
98.5
80.7
95.6
91.8
58.8
58.9
52.7
60.7
73.0
53.1
78.6
85.8
55.7
79.6
15.3
per channel (mJybeam−1)
2
4
3
4
3
3
4
5
4
6
3
3
3
5
4
3
4
3
2
3
5
4
5
4
5
3
6
6
5
10
11
3.1. Association of water and methanol masers
In the VLA cubes of size 77′′×77′′, water masers were detected
in 27 out of 31 cases, out of which 15 are new detections.A total
of 339 distinct maser spots were detected. To define the detec-
tion rate of water masers actually associated with the methanol
masers, we need to determine their relative separation in physi-
cal coordinates. The near-far distance ambiguity is not well re-
solved for our sources, but it has been argued that the near kine-
matic distances are more likely (Szymczak et al. 2005). Recent
measurements of trigonometric parallaxes of several methanol
sources (Reid et al.2009; Rygl et al.2010) strongly support this
assumption.Inthefollowingwethereforeuseonlythenearkine-
matic distance estimates, and we calculated them following the
prescription given by Reid et al.(2009). The systemic veloci-
ties, Vsys, were taken either from the observations of optically
thin thermal lines (Szymczak et al.2007) or from the mid-range
velocity of methanol maser features (Bartkiewicz et al.2009).
The projected linear separation, ∆wmdist(pc), between the nearest
spots of the water and methanol emission were then calculated
using the angular separation from Table 2. The near kinematic
distances for all 31 objects and the linear separations are listed
in Table 4.
For the majority of the detections (22 of 27), the methanol
emission is displaced by less than 0.026pc with a median value
of 0.0017pc (Table 4, Fig. 2). In these sources the velocity dif-
ference between the nearest spots of both masers ranges from
0.7 to 13.9kms−1, with a median value of 1.95kms−1. The
intrinsic separation of the water and methanol spots may be
Fig.2. Histogram of linear separations between the water and
methanol masers for the sample. The inset is the enlargement of
the histogram for the first bin.
slightly different because the position uncertainty of 0.′′15 re-
sults in 0.002−0.005pc displacement for our sources and there
is likely an additional spatial offset along the line of sight not
accounted for using only the projected separation. It is striking
that the largest linear separation of 0.026pc, for the objects con-
sidered to have associated methanol and water masers, is con-

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Bartkiewicz et al.: VLA observations of water masers towards 6.7GHz methanol masers5
Fig.1. continued. The radio continuum emission at the level of 3σrmsdetected toward G24.148−00.009is also indicated by a black
contour (Bartkiewicz et al. 2009).
sistent with the mean separation of ∼0.03pc between the stel-
lar objects observed in the Orion Nebula Cluster (McCaughrean
& Stauffer1994) while the median separation of 0.0017pc well
agreeswithmeanseparationof0.002pcbetweenprotostellarob-
jects predicted by the merging model of massive star formation
(Stahler et al.2000). Those above suggest an association of wa-
ter and methanol masing regions with the same protostellar ob-
ject in 22 sources. The emissions of both maser species for the
remaining five sources shows a separation >0.1pc (see Table 4,

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6 Bartkiewicz et al.: VLA observations of water masers towards 6.7GHz methanol masers
Fig.1. continued. The radio continuum emission at the levels of 3, 10 and 30 × σrms detected towards G26.598−00.024 and
G28.817+00.365are indicated by black contour lines (Bartkiewicz et al. 2009).
Fig. 2), suggesting the two species are associated with separate
young stellar objects within a cluster.
We conclude that at least 71% (22/31) methanol maser
sources in the sample have associated water masers. This can
be explained that both maser species being excited by the same
underlying central object or closely associated objects. This de-
tection rate is higher than the 52% inferred from the 100m dish
observation of a much larger sample (Szymczak et al.2005).
However,we note that the 100m dish survey was about 60 times
less sensitive than the VLA observations. Considering the VLA

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Bartkiewicz et al.: VLA observations of water masers towards 6.7GHz methanol masers7
Fig.1. continued.
data above a flux of 0.45Jy (the mean rms noise value of ob-
servations using the Effelsberg antenna) we obtain a detection
rate of 55%. Our analysis demonstrating an intrinsic association
of both methanol and water masers with the same underlying
object or closely projected objects suggests that the two maser
species share a common stage in the early evolution of massive
star.
An inspection of the water and methanol maser spectra for
the22objects(Fig.1),forwhichbothtypesofmasersareexcited
by the same underlying central star, reveals that in about two-
thirds of the sources the water emission does not appear at the

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8Bartkiewicz et al.: VLA observations of water masers towards 6.7GHz methanol masers
Fig.1. continued.
same velocities as the methanol emission. In G22.335−0.155,
G23.207−0.377,G23.389+0.185,G31.581+0.077,G34.475−
−0.093, G38.038−0.300,G38.203−0.067only a few features of
both maser species coincide in velocity. Furthermore, the veloc-
ity spread of the water masers is 2−15 times larger than that
of the methanol masers with the exception of G23.389+0.185,
G23.707−00.198,G33.980−00.019,G36.705+0.096,G39.100+
+00.491. That was also found in a larger sample observed us-
ing ATCA by Breen et al. (2010). This implies that the wa-
ter and methanol masers emerge from different portions of the
gas surrounding the protostar. It is consistent with theoreti-
cal models which propose that radiative pumping of CH3OH

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Bartkiewicz et al.: VLA observations of water masers towards 6.7GHz methanol masers9
Fig.1. continued. The radio continuum emission at the levels of 3 and 6 × σrmsdetected toward G36.115+00.552 is indicated by
black contour lines (Bartkiewicz et al. 2009).
moleculeoccurs at temperaturesless than 150K and density less
than 108cm−3(e.g., Cragg et al.2005 and references therein),
but the collisional pumping of H2O molecules occurs in dense
(>108cm−3) and hot (400K) shocked gas (Elitzur et al.1989).
3.2. Methanol sources without water emission
Towards
G25.411+0.105, G27.221+0.136, no water emission was
detected above a 5σ level of 15−25mJy (Table 2). Three of
foursources,G23.657−0.127,G24.634−0.324,

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10Bartkiewicz et al.: VLA observations of water masers towards 6.7GHz methanol masers
Fig.1. continued.
them (G23.657−0.127, G24.634−0.324 and G25.411+0.105)
show a ring-like structure of the 6.7GHz methanol maser
emission (Bartkiewicz et al.2009). Such morphologies have
been found recently in at least nine out 31 sources (Bartkiewicz
et al.2009) and was the reason for these follow-up observations.
In addition there are five methanol sources (G24.148−00.009,
G24.541+00.312,
G38.038−00.300) where the water masers seem to be unas-
sociated since the linear distance between both masers is
above 0.1pc (Table 4). Their methanol masers have linear,
arched, complex/ring, ring and complex structures, respectively
(Bartkiewicz et al.2009). For the clarity we list the morpho-
G30.400−00.296,G31.047+00.356and

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Bartkiewicz et al.: VLA observations of water masers towards 6.7GHz methanol masers 11
Table 2. Results of H2O observations
RA(J2000)
(h m s)
18 31 06.3380
18 32 29.4070
18 31 44.1210
18 34 55.2019
18 33 14.3250
Dec(J2000)
(◦′′′)
−10 21 37.460
−09 29 29.734
−09 22 12.362
−08 49 14.943
−08 23 57.522
Vp
∆VSp
Sint
∆wm
(kms−1)
PAH2O
PAMIR
Gll.lll±bb.bbb
G21.407−00.2542
G22.335−00.1552
G22.357+00.066
G23.207−00.377
G23.389+00.185
G23.657−00.127
G23.707−00.1982
G23.966−00.109
G24.155−00.0101,2
G24.534+00.3191
G24.634−00.324
G25.411+00.105
G26.598−00.024
G27.221+00.136
G28.817+00.365
G30.318+00.070
G30.403−00.2971,2
G31.047+00.3571,2
G31.581+00.0772
G32.992+00.0342
G33.641−00.228
G33.980−00.0192
G34.751−00.0932
G35.793−00.1752
G36.115+00.552
G36.705+00.0962
G37.030−00.0392
G37.598+00.425
G38.041−00.2981,2
G38.203−00.0672
G39.100+00.491
1The position of the H2O maser differs by more than 3.′′6 from that of CH3OH maser (Bartkiewicz et al. 2009) and its name is updated.
2New detection.
(kms−1)
92.9
29.0
88.3
73.2
78.0
(kms−1)
7.9
7.2
30.2
29.0
2.6
(Jyb−1)
0.68
0.76
3.14
11.46
0.15
<0.015
0.91
1.12
0.17
0.19
<0.015
<0.015
1.09
<0.025
13.07
2.81
0.08
0.67
12.55
1.61
5.12
0.40
0.53
2.39
4.91
0.55
0.27
2.91
0.15
0.63
0.64
(Jykms−1)
1.57
1.12
7.75
55.8
0.28
(′′)
0.03
0.01
0.04
0.06
0.03
(◦)(◦)
2.2
−27
12
−29
57
90
−30
22
−2.6
1.5
1.2
−0.9
8
52
−80
18 35 12.4165
18 35 22.2150
18 35 21.9019
18 34 53.4636
−08 17 39.108
−08 01 22.520
−07 48 34.575
−07 19 19.000
72.6
48.9
24.4
101.1
13.8
42.7
24.4
2.0
0.57
5.98
0.20
0.18
0.77
0.03
25.5
35.8
−1.3
1.8
5.3
−2.7
64
−69
−12
−13
18 39 55.9561
−05 38 44.692 22.27.30.540.14
−3.7
−76
−71
18 42 37.2368
18 46 25.0260
18 47 52.9295
18 46 43.5549
18 48 41.9510
18 51 25.5820
18 53 32.5630
18 53 25.0180
18 55 05.2220
18 57 16.8840
18 55 16.7830
18 57 59.1320
18 59 03.6420
18 58 26.7970
19 01 50.4088
19 01 18.7320
19 00 58.0601
−03 29 41.121
−02 17 40.954
−02 23 11.303
−01 30 52.855
−01 10 02.578
+00 04 07.233
+00 31 39.130
+00 55 26.076
+01 34 36.361
+02 27 57.950
+03 05 05.514
+03 24 06.062
+03 37 45.086
+04 20 45.407
+04 24 32.705
+04 39 34.243
+05 42 44.321
88.1
49.9
125.5
77.4
99.5
76.0
56.8
62.2
52.7
58.7
78.3
56.4
81.2
100.9
62.3
90.1
23.9
66.5
20.4
7.9
27.0
13.8
20.4
30.9
3.3
36.8
15.1
39.5
12.5
10.5
40.2
17.8
11.9
2.0
34.76
9.99
0.17
1.89
2.22
0.54
15.4
0.49
2.51
3.53
10.24
0.71
0.78
11.69
0.28
1.54
1.32
0.37
0.20
10.5
4.64
0.11
1.06
0.10
0.25
0.10
0.16
0.09
0.15
0.01
0.05
13.8
0.05
0.35
−2.7
−4.2
19.8
14.8
1.8
−3.8
0.7
2.6
−4.6
1.3
−2.1
0.9
−1.3
13.9
2.6
0.7
8.6
−89
−56
−88
−67
−53
90
−60
−66
180
15
27
35
57
26
36
72
−64
−80
42
39
−45
−48
−35
−41
logical classification of all methanol masers in the last column
in Table 4. It is interesting that towards G38.038−0.300 two
distinct water masers were detected, but both were offset about
15”, corresponding to 0.2pc separation for the near kinematic
distance.
We note that emission from the 22GHz water transition of-
ten exhibits significant temporal variability on time scales of a
few months (Brand et al.2003). Therefore we may expect that
a number of non-detections in our sample can be different at
otherepoch.However,our non-detectionswere also not detected
by the single dish study (Szymczak et al.2005), when observed
with a sensitivity of ∼1.5Jy. Thus, the water emission in these
sources may be relatively weak if present at all.
3.3. Maser luminosity
We have calculated the maser luminosities using the VLA data
for the water maser emission and the 32m dish observations for
the methanol maser emission (Table 4). They were observed al-
most simultaneously(Sect. 2.2).In oursample, the isotropic wa-
ter maser luminosity ranges from 10−7.4to 10−4.6L⊙. The me-
dian luminosity for the whole sample is 10−6L⊙. We note, that
all but one, G23.207−00.377,sources with the ring morphology
of methanol emission have water maser luminosities lower than
10−6L⊙(Fig. 3). This suggests that these sources are associated
with young massive stellar objects, in which water masers are
less luminous thanin the methanolsources of othermorphology.
The water masers detected in our survey that are not associ-
ated with methanolmasers havea medianH2O maserluminosity
of 10−6.9L⊙(Fig. 3). Thus they do not significantly differ from
the luminosityof water masers that are associated with methanol
sources. The median luminosity of methanol maser emission,
estimated from single dish data, is 10−5.7L⊙, somewhat higher
than that of the water maser emission (Fig. 3). We relate this
difference to the extremely high sensitivity of the VLA observa-
tions, about 60 times better than that reported in Szymczak et al.
(2005).We donotnoticeanycorrelationbetweenluminositiesof
methanol and water masers. Xu et al. (2008) found a correlation
betweenthese bothvalues,howevertheyclaimedthatsincethere
were no physical connections between both lines, it might be a
distance squared effect, as suggested by Palla et al. (1991). The
two maser species require different excitation conditions and,
even if they are related to the same YSO (Sect. 3.1), may arise
in different subregionssuch as discs and outflows. Further, Xu et
al. (2008) found water maser luminosities were higher than the
methanol maser luminosities, a finding that is not supported by
our data.
4. Discussion
4.1. Morphologies of masers and MIR counterparts
Weareinterestedinstudyingthemorphologyofthemasersinre-
lationto that of the dust.So, we searchedformid-infrared(MIR)
emission toward the detected water masers using the Spitzer

Page 12

12Bartkiewicz et al.: VLA observations of water masers towards 6.7GHz methanol masers
Table 4. Characteristic parameters of the sources observed.
Source
Gll.lll±bb.bbb
G21.407−00.254
G22.335−00.155
G22.357+00.066
G23.207−00.377
G23.389+00.185
G23.657−00.127
G23.707−00.198
G23.966−00.109
G24.148−00.009
G24.541+00.312
G24.634−00.324
G25.411+00.105
G26.598−00.024
G27.221+00.136
G28.817+00.365
G30.318+00.070
G30.400−00.296
G31.047+00.356
G31.581+00.077
G32.992+00.034
G33.641−00.228
G33.980−00.019
G34.751−00.093
G35.793−00.175
G36.115+00.552
G36.705+00.096
G37.030−00.039
G37.598+00.425
G38.038−00.300
G38.203−00.067
G39.100+00.491
1Class of morphology of methanol masers: S – simple, L – linear, R – ring, C – complex, A – arched,
P -pair (Bartkiewicz et al.2009).
2Distance based on the trigonometric parallax (Bartkiewicz et al.2008).
aLuminosity of water maser associated with the methanol source. In a few cases (e.g., G22.357+00.066)
only some spots lie in close surrounding of methanol emission (Fig. 1).
bThe upper limit is marked by symbol ↓. It means we did not register the water maser spots coinciding
with methanol masers.
cLuminosity of water maser unassociated or likely unassociated with methanol source.
Vsys
Dnear
(kpc)
5.12
2.47
4.86
4.63
4.47
3.192
4.22
4.37
1.92
5.70
3.00
5.25
1.85
6.04
4.90
2.97
5.76
4.51
5.49
4.88
3.77
3.75
3.24
3.83
4.66
3.75
5.02
6.36
3.66
5.31
1.70
∆wmdist
(pc)
0.00074
0.00012
0.00094
0.00135
0.00065
log(LH2O)a,b
(L⊙)
−6.02
−6.79
−5.37
−4.56
−6.89
−8.15↓
−6.63
−5.57
−8.22↓
−8.30↓
−8.22↓
−7.70↓
−7.42
−7.40↓
−4.72
−5.74
−8.30↓
−6.05
−4.70
−6.53
−5.30
−6.80
−6.22
−5.56
−5.29
−6.64
−6.34
−4.96
−8.00↓
−6.00
−7.06
log(LH2O)c
(L⊙)
log(LCH3OH)
(L⊙)
−5.34
−6.04
−5.58
−5.05
−5.14
−5.60
−5.13
−5.74
−7.23
−5.17
−6.48
−5.70
−6.54
−5.21
−6.34
−6.77
−5.80
−6.16
−5.82
−5.75
−4.88
−6.35
−6.35
−5.53
−5.29
−6.40
−5.47
−5.26
−5.96
−5.66
−6.29
Class1
(kms−1)
90.7
30.9
84.2
78.9
74.8
82.4
68.9
72.7
23.1
107.8
42.7
96.0
23.3
112.6
87.0
45.3
102.4
77.6
96.0
83.4
61.5
61.1
51.1
61.9
76.0
59.8
80.1
90.0
57.5
81.3
23.1
C
L
C
R
R
R
A
L
L
A
R
R
R
C
−7.03
0.01575
0.00063
0.23736
0.98931
−6.34
−7.77
−6.92
0.00126
0.00879
0.00288
0.29322
0.10145
0.00293
0.02508
0.00183
0.00455
0.00157
0.00297
0.00203
0.00273
0.00024
0.00154
0.24487
0.00129
0.00288
A/R
L
C/R
R
A/R
C
A
R
R
L
P
C
S
C
C
C
C
−6.89
−5.44
−6.30
−6.51
−7.47; −7.10
IRAC maps2. In total we found that 21 out 27 sources of wa-
ter maser emission have MIR counterparts within 1.′′2 arcsec-
onds on the sky (Table 2). To clarify the nature of the studied
sources we compare the morphology of the water maser and
MIR emission from maps at 4.5µm of pixel size of 0.′′6 (Fazio
et al.2004). The position angle of water maser clusters associ-
ated with the methanol source, PAH2O, was determined using a
least square fit to the maser spot distribution. For sources with a
single water maser cluster the PAH2Owas assumed to be a posi-
tion angle of the direction between the water maser cluster and
the flux-weighted centre of the 6.7GHz methanol maser distri-
bution observed with the EVN (Bartkiewicz et al.2009). The
PAMIRwas estimated using 4.5µm emission maps and by fit-
ting two-dimensional Gaussian components. For several objects
these estimates are veryuncertain, and instead we used the maps
of the 4.5µm−3.6µm excess. The values of PAH2Oand PAMIR
are listed in the two last columns of Table 2. The entries with
an error of about 10−15◦are given in italic. For the remaining
sources errors in PAMIRand PAH2Oare smaller than 6◦and 3◦,
respectively.
2http://irsa.ipac.caltech.edu/
Fig. 4 shows the distribution of the position angle differ-
ences. In 18 out of 21 sources the water maser structure is
aligned within less than 20◦with the extended emission at
4.5µm. For the remaining sources the position angle differ-
ences are less than 47◦. As the 4.5µm emission is interpreted as
tracer of shocked H2in the outflow (Smith et al.2006; Davis et
al.2007; Cyganowski et al.2008, 2009, and references therein)
our finding of tight alignment of the spatial extent of these two
tracers strongly suggests that the H2O masers originate in out-
flows. It is fully consistent with the theoretical model that H2O
masersareexcitedduetocollisionalpumpingwithH2molecules
in shocks associated with outflows (Elitzur et al.1989).
Comparison of the H2O maser morphology taken with the
VLA-CnB with that of 6.7GHz CH3OH maser seen with the
EVN (Bartkiewicz et al.2009) is difficult because of larger
positional uncertainty in the VLA 22 GHz data, and because
a significant fraction of the 6.7GHz flux may be missed in
the milliarcsecond (mas) resolution observations. The case of
G39.100+0.491 is instructive in this context; this relatively
nearby source (distance 1.7kpc) observed at 6.7GHz with the
5×15mas2EVN beam appeared as an irregular cluster of size
of 0.′′18×0.′′04 (Bartkiewicz et al.2009). However, using the

Page 13

Bartkiewicz et al.: VLA observations of water masers towards 6.7GHz methanol masers 13
Fig.3. a) Histogram of the water maser luminosity in the
6.7GHz methanolmaser sample (Table 4. The dashed bars mark
sources with the upper luminosity limits (non detections). b)
Same as in a) but for the sources with ring-like distribution of
methanol emission. c) Same as in a) but for the water maser
sources not associated with the methanol masers. d) Histograms
of methanol maser luminosity in the sample.
Fig.4. Histogram of the differencesin the position angles of ma-
jor axes of water maser distribution and 4.5µm emission excess
for the studied objects. The sources with small errors of PAMIR
are marked solid.
2.′′4×1.′′3 VLA beam, a much richer structure of methanol maser
emission was revealed: two bright clusters separated by ∼0.′′7 at
PA of −50◦and diffuse emission between them (Cyganowski et
al.2009). The 6.7GHz maser emission is clearly extended along
the same position angle as the 4.5µm emission in the Spitzer
maps, as well as the H2O maser emission observed here.
However,forsources with a ring-likedistributionof 6.7GHz
maser emission seen at mas resolution, the comparison with the
structure of water emission obtained with arcsecond resolution
is still useful. In four out of five rings, where a methanol-water
maser association exists, the major axis of the methanol ring is
crudely orthogonal to the main axis of the water maser struc-
ture. G23.207−0.377 is likely the best example. The part of
methanol masers form a ring-like structure with the PA of the
major axis of −60◦, and with a velocity range of 13.20kms−1,
the rest likely trace an outflow (Bartkiewicz et al.2009). The
water maser emission is distributed over a region of 1.′′5×1.′′5
and with the wider velocity range of 29kms−1. The linear size
of water maser is 0.04pc, while the methanol ring has diameter
of only 0.006pc. As the methanol emission in ring-like struc-
ture likely traces a disc or torus around a massive stellar object
(Bartkiewiczetal.2009)thewatermaseremissionalongthenor-
mal to the disc implies the outflow. This is supported by MIR
counterpart which shows PA of 52◦(Table 2). The other three
sources, G23.389+0.185, G33.980−0.019 and G34.751−0.093
are possible cases with a similar scenario.
We conclude that the water masers in our sample generally
coincide with the MIR counterpart sources. The majority of the
sources show a water maser structure aligned with the extension
direction of the 4.5µm emission, while in particular for some of
the objects, where the methanol masers are tracing circumstellar
discs/tori, the water masers appear in the orthogonal direction.
In general this is consistent with previous observations showing
that MIR emission is indeed associated with water masers, and
their relative distributions indicate that water masers originate in
outflows (e.g., De Buizer et al.2005).
Assuming that the methanol emission arises close to the
protostar, while H2O masers trace outflows further from the
central object, the size of the outflows can be estimated in
the case of 22 sources where a methanol–water maser as-
sociation exists. Our data imply size scales for the outflows
from 0.0006 to 0.13pc with a median and mean values of
0.01 and 0.022pc, respectively. We note, that three sources:
G22.335−0.155, G30.400−0.296 and G33.980−00.019 are un-
resolved with a 1.′′4×0.′′8 beam. Their velocity extents are from
3.3 to 7.9kms−1(Table 3). That also may suggest the presence
of outflows along the line of sight. However, we need to verify
that hypothesis with VLBI observations.
4.2. Signposts of multiple active centres
Towards 12 of the methanol targets, water maser emission
was detected in distinct clusters separated from methanol
maser spots by >0.1pc. In two objects, G37.030−00.039 and
G38.038−00.300,eventwowaterclusterssignificantlydisplaced
wereseen.Therefore,intotal14watermaserclusterswerefound
in our sample lying significantly further from methanol maser
spots (Table 5). Such characteristic was also noticed in studies
by Breen et al. (2010) using ATCA.
For these objects we also inspected Spitzer IRAC maps to
search for MIR counterparts of the water maser clusters. The
results are summarized in Table 5. We found that 10 of the
14 clusters have MIR counterparts which, within measurement
uncertainty, do not coincide with the methanol maser clusters
and their MIR counterparts that were reported in Bartkiewicz
et al. (2009). Therefore, we conclude that in these 10 cases
both masers, methanol and water, are not associated with the
same MIR object. It is possible that both masers are asso-
ciated with the same molecular cloud where star formation
takes place, but do not trace the environment of the same pro-

Page 14

14Bartkiewicz et al.: VLA observations of water masers towards 6.7GHz methanol masers
tostar. They likely trace different protostars as most of them
have MIR properties typical of embedded young massive ob-
jects and show a 4.5µm−3.6µm excess that is an indicator of
shocked material in outflows (e.g., Cyganowski et al.2008).
The remaining four water maser clusters lying 0.1–0.3pc from
the methanol maser spots (G23.966−00.109, G31.581+00.077,
G37.598+00.425and tentativelyG31.047+00.356)(Table 5) are
likely associated with the same MIR objects as the methanol
emission.
4.3. Association and non-association with HII regions
In our previous VLA project we searched for the 8.4GHz con-
tinuum emission toward the presented methanol masers with the
sensitivity level of 0.15mJybeam−1(Bartkiewicz et al.2009). In
total, we detected eight sources toward the sample. Only in four
cases the continuum emission was associated with the methanol
sources. Concerning the project presented in this paper we note
that in three of these four objects the methanol structures are
also associated with the distribution of water masers (Fig. 1).
Therefore, both masers are likely physically connected with ra-
dio continuum emission. One example is G28.817+0.365where
methanolspots are distributed alonga PA of +45◦. Theyare pro-
jected on the central part of a HII region. Water masers are dis-
tributed along a PA of −89◦and are spread in the SW direction
from the radio continuum source. Such a distribution of masers
may indicate an outflow scenario for both masers. But proper
motion studies are needed to verify that scenario as for exam-
ple presented for 12GHz methanol masers in Moscadelli et al.
(2002). We note that the MIR counterpart is aligned with PA of
−88◦(Table 2) and supports the outflow hypothesis.
Two other sources with detected HII regions, G26.598−00.024
and G36.115+00.552, show similar characteristic. Here, the
overall distributions of methanol and water masers are crudely
aligned in the same direction as the MIR counterparts (Table 2).
In these cases masers are displaced from the centres of the ra-
dio continuum sources by 0.007 and 0.02pc, respectively. We
suggest that these three objects support the hypothesis that we
have HMSFRs at different evolutionary stage in our sample.
Beuther & Shepherd (2005) presented a scenario for the evo-
lution of massive outflows. When a B star forms via accretion
through a disk and the HII region is not yet formed, the disk-
outflow interaction produces a collimated outflow. With time a
hyper-compactHII region forms and the wind from the massive
youngstar producesa less collimatedoutflow.Thediskbeginsto
be destroyed and an outflow with a small degree of collimation
dominates the system. In sources with methanol maser rings, we
either did not detected water maser emission or relatively weak
one. In sources with HII counterparts the methanol maser mor-
phology is less regular (although G26.598−00.024 was classi-
fied as ring, we note it consists only three cluster of masers), and
water-methanol maser spot distributions can also be consistent
with an outflow scenario (Fig. 1).
In eight out nine objects, where no water was found
(Sect. 3.2), no continuum emission at 8.4GHz above
∼0.15mJybeam−1
wasdetected.
G24.148−00.009 which has weak and compact emission
(Sp=1.05mJybeam−1; Sint=1mJy; Bartkiewicz et al.2009).
We also note, that towards that source we did not detect any
water maser within 0.24pc. That is opposite to the result
obtained by Beuther et al. (2002), where methanol masers are
associated with cm emission only if there are nearby water
masers. However, as noted by these authors, in the archetypical
star forming region W3(OH) a situation similar to that of
Theoneexception is
G24.148−00.009 exists, where the methanol masers are associ-
ated with an ultracompact HII region and the water masers are
offset significantly and associated with a different young star
(Menten 1996).
The absence of continuum emission and water masers may
lend support to the hypothesis that 6.7GHz methanol masers
trace an earlier evolutionary phase than water masers where no
outflows have started yet (e.g., Ellingsen et al.2007). For the
(≈50%of)methanolmasersnotassociatedwithHIIregions(and
water emission) that show ring-like structures, we suggest that
they trace circumstellar discs/tori, probably at an early stage of
evolution. A less regular methanol morphology would appear in
later stages and could be related with outflows traced by wa-
ter masers. Comparative studies of water and methanol masers
in the giant molecular cloud G333.6−0.2 have suggested a sim-
ilar conclusion that 6.7GHz methanol masers trace an earlier
evolutionary phase of high-mass star formation than do lumi-
nous water masers (Breen et al.2007; Ellingsen et al.2007). It
is interesting that in four of five ring-like methanol sources, the
associated water masers are weaker than the methanol masers.
This supports the above mentioned scenario about an early evo-
lutionary stage for these sources, as they may be examples
where the outflows have just begun. Only one ring-like source
(G23.207−0.377) does not follow this trend, since its methanol
emission is much weaker than the water emission. However,
we note that in the distribution of methanol maser spots in this
source one can see components that may belong to the outflow
parttracedalso bywater emission(Fig. 1). Therefore,thatobject
is likely more evolved. We present this source in more details in
Sect. 3.4.
The aforementioned interpretation of evolutionary stage re-
lies basically on the lack of detectable continuum at cen-
timeter wavelengths. This may be misleading since only the
most compact continuum emission was mapped. We note, that
in a case of G22.357+0.066 observations with the VLA at
8.4GHz with a synthesized beam of 2.′′3 and a sensitivity of
0.3mJybeam−1, revealed a complex and extended source with
a peak flux of 1.02mJybeam−1which is 3σ detection (van
der Walt et al.2003). However, no emission was found at the
same frequency with a beam of 0.′′35×0.′′25 and a sensitivity of
0.15mJybeam−1(Bartkiewicz et al.2009). The methanol emis-
sion is offset by ∼15′′from the radio continuum peak, corre-
sponding to a projected linear distance of 0.35pc. We therefore
suggest that further sensitive searches for millimeter and cen-
timeter continuum counterparts of ring-like methanol sources
will be important to understand their nature.
5. Conclusions
High sensitivity VLA observations of the 22GHz water maser
line towards 31 methanol maser objects have yielded 27 detec-
tions, out of which 15 were detected for the first time. Most
(71%) of the methanol sources have water masers with a pro-
jectedseparationofless than0.026pc.Theyareeitherexcitedby
the same underlying central object or come from different, but
closely projected YSOs. We identified MIR counterparts of 21
water masers from Spitzer IRAC maps. The water maser struc-
tures are well aligned with the extended emission at 4.5µm for
a large fraction (18/21)of the studied objects. This confirms that
the water masers originate in outflows.
A distinct group of sources with ring-like methanol maser
distribution, likely tracing circumstellar disc/torus around high-
mass young stellar objects, show either no associated water
masers at all (4 out 9), or a water maser distribution which

Page 15

Bartkiewicz et al.: VLA observations of water masers towards 6.7GHz methanol masers 15
Table 5. List of methanol maser sources with the water maser emission of linear offset greater than 0.1pc. The two first columns
list the galactic coordinates of methanol and water masers, respectively. ∆wmdistis the angular (Col. 3) and linear (Col. 4) separation
of H2O maser emission from the methanol source. ∆Vminis the minimum and ∆Vmaxis the maximum differences between the LSR
velocity of water maser spot from the analysed group and the systemic velocity (Table 4). The name of MIR source nearby to the
H2O maser emission and angular separation between them, ∆(MIR−H2O), are given.
CH3OH source
Gll.lll±bb.bbb
G22.357+00.066
G23.707−00.198
G23.966−00.109
G24.148−00.009
G24.541+00.312
G30.400−00.296
G31.047+00.356
G31.581+00.077
G32.992+00.034
G37.030−00.039
H2O emission
Gll.lll±bb.bbb
G22.351+0.068
G23.706−0.200
G23.965−0.110
G24.155−0.010
G24.534+0.319
G30.403−0.297
G31.047+0.357
G31.581+0.078
G32.996+0.041
G37.039−0.035
G37.039−0.034
G37.597+0.424
G38.038−0.305
G38.041−0.298
∆wmdist
∆Vmin
(km s−1)
22.3
3.1
4.5∗
0.6
6.7
21.8
0.2
1.7
0.2
2.8
4.8
1.6
4.1
0.8∗
∆Vmax
(km s−1)
22.9
5.0
MIR source
∆(MIR−H2O)
(arcsec)
3.22
1.32
0.62
7.34
5.13
7.92
5
2.31
0.32
1.62
6.12
4.11
1.62
5.22
(arcsec)
20.05
6.13
5.58
25.48
35.90
10.57
6.91
4.92
30.58
33.73
37.36
3.34
16.06
13.78
(pc)
0.47
0.13
0.12
0.24
0.99
0.29
0.11
0.13
0.72
0.82
0.91
0.10
0.28
0.24
G022.3506+00.0678
G023.7057-00.1999
G023.9649-00.1104
G024.1550-00.0119
G024.5351+00.3190
G030.4010-00.2960
G031.0467+00.3574
G031.5813+00.0788
G032.9962+00.0414
G037.0385-00.0350
G037.0385-00.0350
G037.5978+00.4253
G038.0384-00.3042
G038.0409-00.2968
23.1
8.7
29.7
20.2
4.9
17.9
8.7
6.1
2.2
18.6
G37.598+00.425
G38.038−00.300
1H2O maser emission is associated with the same MIR source as CH3OH maser emission.
2H2O maser emission is not associated with the same MIR source as CH3OH maser emission.
3H2O maser emission is not associated with the same MIR source as CH3OH maser emission, instead it lies in a cluster of three MIR sources.
4H2O maser emission is likely not associated with the same MIR source as CH3OH maser emission but with MIR object in the region
of diffuse (∼10′′) excess of 4.5µm emission seen in the IRAC Spitzer maps.
The name of the strongest MIR counterpart is given.
5H2O maser emission is tentatively associated with the same MIR source as CH3OH maser emission, laying at edge of diffuse excess of
4.5µm emission from possible cluster of MIR sources.
∗When single maser spot was observed only ∆Vminis given.
is orthogonal to the major axis of the methanol ring (4 out
9). Moreover, the majority of this group of objects (8 out 9)
does not show detectable continuum emission at 8.4GHz and
may represent an early phase of evolution. One methanol ring,
G26.598−00.024,lies at the edge of a HII region and is aligned
with associated water masers. Both masers water and methanol
masers likely form in outflows.
We suggest that massive star forming regions that contain
methanol masers with ring-like morphologies are at the earliest
evolutionarystates when the youngstar is still forming, possibly
via accretion througha disk. When winds begin to dominate, the
regular ring-like structure is destroyed and methanol and water
masers appear to be associated with the outflow. Further deep
observations of these sources in the radio continuum as well as
in the infrared range are required to explain their nature.
Acknowledgements. A.B. and M.S. acknowledge support by the Polish Ministry
of Science and Higher Education through grant N N203 386937. A.B. acknowl-
edges support by the Nicolaus Copernicus University grant 364-A (2009).
The Very Large Array (VLA) of the National Radio Astronomy Observatory
is a facility of the National Science Foundation operated under cooperative
agreement by Associated Universities, Inc. This research has made use of the
NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion
Laboratory, California Institute of Technology, under contract with the National
Aeronautics and Space Administration.
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