J/A+A/563/A68 CH3OH and H2O Galactic center masers (Chambers+, 2014)
Star formation sites toward the Galactic Center region. The correlation of
CH3OH masers, H2O masers, and near-IR green sources.
Chambers E.T., Yusef-Zadeh F., Ott J.
<Astron. Astrophys., 563, A68-68 (2014)>
=2014A&A...563A..68C 2014A&A...563A..68C
ADC_Keywords: Masers; Radio lines
Keywords: ISM: clouds - ISM: molecules - stars: formation - Galaxy: center
Abstract:
We present a study of star formation in the central molecular zone
(CMZ) of our Galaxy through the association of three star formation
indicators: 6.7GHz CH3OH masers, 22GHz H2O masers, and enhanced
4.5µm emission ('green') sources. We explore how star formation in
the CMZ (|l|<1.3°, |b|<10') compares with that of the Galactic
disk (6°>l>345°, |b|<2°). Using an automated algorithm, we
search for green sources toward 6.7GHz CH3OH masers detected in the
Parkes Methanol Multibeam Survey. We combine these results with lists
of 22GHz H2O masers, including our Mopra survey of the CMZ. We find
that the correlation of CH3OH masers with green sources is a
function of Galactic latitude, with a minimum close to b=0 and
increasing with |b| (toward the central part of the Galaxy,
6°>l>345°, |b|<2°). We find no significant difference
between the correlation rate of CH3OH masers with green sources in
the CMZ and the disk. This suggests that although the physical
conditions of the gas are different in the CMZ from that of the
Galactic disk, once gravitational instability sets in at sufficiently
high densities, signatures of star formation appear to be similar in
both regions. Moreover, the detection of green sources, even at the
distance of the Galactic center, shows that our technique can easily
identify the early stages of star formation, especially in
low-extinction regions of the Galaxy. Through the association of H2O
and CH3OH masers, we identify 15 star-forming sites in the CMZ. We
find a higher correlation rate of coincident H2O and CH3OH masers
within the CMZ compared to the Galactic disk, indicating a difference
in the maser evolutionary sequence for star-forming cores in these two
regions.
Description:
The 6.7GHz CH3OH masers we use in our analysis were identified by C10
(Caswell et al., 2010MNRAS.404.1029C 2010MNRAS.404.1029C, Cat. VIII/96) as part of the
Parkes Methanol Multibeam Survey. Initial detections of the 6.7GHz
CH3OH masers were made with the Parkes Observatory, and subsequent
follow-up observations with the Australia Telescope Compact Array to
pinpoint the maser locations to 0.4" accuracy.
We observed the Galactic center region with the CSIRO/CASS Mopra
telescope in the period 2006 Sep. 13 to 2006 Oct. 15 and 2007 July 24
to September 17. Data were taken in the on-the-fly mode, dumping data
every 2s with the then newly installed 12mm receiver, dual
polarization.
To identify enhanced 4.5µm sources, we use data obtained with the
Spitzer Space Telescope using the Infrared Array Camera (IRAC)
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 33 37 H2O masers in the survey region
tableb1.dat 70 175 Association of green sources with CH3OH masers
tableb2.dat 55 131 Association of H2O masers with CH3OH masers
tableb3.dat 55 113 CH3OH masers not associated with H2O masers
tableb4.dat 48 114 H2O masers not associated with CH3OH masers
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See also:
VIII/96 : 6-GHz methanol multibeam maser catalogue (Caswell+, 2010-12)
J/MNRAS/416/1764 : H2O Southern Galactic Plane Survey (HOPS) (Walsh+, 2011)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- H2O [1/37] H2O maser sequential number
4- 9 F6.3 deg GLON [-2/2] Galactic longitude (1)
11- 16 F6.3 deg GLAT Galactic latitude (1)
18- 23 F6.1 km/s V Velocity of peak maser emission (1)
25- 28 F4.2 K Tpeak Peak intensity of the maser
30- 33 I4 --- Nvo Number of voxels in the source
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Note (1): Values of GLON, GLAT and V are extracted from the Mopra data cube,
which has a pixel size of 0.5' and a channel width of ∼3.6km/s.
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 A15 --- CH3OH CH3OH maser name (GLLL.lll+B.bbbn) (1)
17- 22 F6.1 km/s Vpeak Velocity of peak maser emission (1)
23 A1 --- n_Vpeak [c] Note on Vpeak (2)
25- 32 F8.4 deg GLON Galactic longitude from R peak (3)
34- 40 F7.4 deg GLAT Galactic latitude from R peak (3)
42- 46 F5.3 --- Value Value of the green pixel in each green
source candidate
48- 52 F5.3 --- Rbg Background green value near each green source
candidate
54- 58 F5.3 --- Rcut Green value used to define the boundary of
the green source candidate
60- 64 F5.3 --- Rtresh Average green value for the pixels within the
green source candidate
66- 68 I3 --- Npix Number of pixel in the green source candidate
70 A1 --- Green [Y/N] Is the green source associated with a
CH3OH maser ?
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Note (1): From C10, Caswell et al. (2010MNRAS.404.1029C 2010MNRAS.404.1029C, Cat. VIII/96)
Note (2): c: For CH3OH masers not detected in the C10 (2010MNRAS.404.1029C 2010MNRAS.404.1029C,
Cat. VIII/96) follow-up data, we use their survey cube data or the value
they list from Houghton & Whiteoak (1995MNRAS.273.1033H 1995MNRAS.273.1033H).
Note (3): Derived from IRAC data, which have a pixel size of 1.2".
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Byte-by-byte Description of file: tableb2.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- CH3OH CH3OH maser name (LLL.333+B.bbb)
15- 20 F6.1 km/s Vlow Lower velocity limit of the CH3OH maser (1)
22- 27 F6.1 km/s Vhigh Higher velocity limit of the CH3OH maser (1)
29- 35 F7.3 deg GLON H2O maser Galactic longitude
37- 42 F6.3 deg GLAT H2O maser Galactic latitude
44- 48 F5.1 km/s VH2O Velocity of the H2O peak emission
50 I1 --- r_VH2O Reference for VH2O (2)
52- 53 I2 arcsec Sep [1/70] Angular separation between the
associated CH3OH and H2O masers
55 A1 --- Green [Y/N] Is the CH3OH maser associated with
a green source ?
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Note (1): For easier comparison with the H2O masers, here we list the upper
and lower bounds of the CH3OH maser emission, as listed by C10
(2010MNRAS.404.1029C 2010MNRAS.404.1029C, Cat. VIII/96)
Note (2): Catalog from which the maser was identified as follows:
1 = this work (Mopra survey)
2 = Caswell et al. (2011MNRAS.410.1283C 2011MNRAS.410.1283C)
3 = Walsh et al. (2011MNRAS.416.1764W 2011MNRAS.416.1764W, Cat. J/MNRAS/416/1764)
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Byte-by-byte Description of file: tableb3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 A14 --- CH3OH CH3OH maser name (LLL.lll+B.bbbn)
16- 22 F7.3 deg GLON CH3OH maser Galactic longitude
24- 29 F6.3 deg GLAT CH3OH maser Galactic latitude
31- 36 F6.1 km/s Vlow Lower velocity limit of the CH3OH maser (1)
38- 43 F6.1 km/s Vhigh Higher velocity limit of the CH3OH maser (1)
45 A1 --- l_Speak Limit flag on Speak
46- 52 F7.2 Jy Speak Peak intensity of CH3OH maser emission
53 A1 --- n_Speak [b] Note on Speak (2)
55 A1 --- Green [Y/N] Is the CH3OH maser is associated with
a green source?
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Note (1): For easier comparison with the H2O masers, here we list the upper
and lower bounds of the CH3OH maser emission, as listed by C10
(2010MNRAS.404.1029C 2010MNRAS.404.1029C, Cat. VIII/96)
Note (2): For CH3OH masers not detected in the C10 (2010MNRAS.404.1029C 2010MNRAS.404.1029C,
Cat. VIII/96) follow-up data, we use their survey cube data or the value
they list from Houghton & Whiteoak (1995MNRAS.273.1033H 1995MNRAS.273.1033H).
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Byte-by-byte Description of file: tableb4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 A1 --- r_H2O Reference for H2O maser name (1)
3- 15 A13 --- H2O H2O maser name or number
17- 23 F7.3 deg GLON H2O maser Galactic longitude
25- 30 F6.3 deg GLAT H2O maser Galactic latitude
32- 37 F6.1 km/s VH2O Velocity of the H2O peak emission of the maser
39- 42 F4.2 K Tpeak ? Peak emission of the maser (in K)
43- 48 F6.2 Jy Fpeak ? Peak emission of the maser (in Jy)
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Note (1): References as follows:
a = H2O masers from Mopra data (this work)
b = H2O masers from Caswell et al. (2011MNRAS.410.1283C 2011MNRAS.410.1283C)
c = H2O masers from Walsh et al. (2011MNRAS.416.1764W 2011MNRAS.416.1764W, Cat. J/MNRAS/416/1764)
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 20-May-2014