J/ApJ/923/263 VLA 1.3 & 5cm observations of 9 EGOs in the MW (Towner+, 2021)
VLA observations of nine Extended Green Objects in the Milky Way: ubiquitous
weak, compact continuum emission, and multi-epoch emission from methanol, water,
and ammonia masers.
Towner A.P.M., Brogan C.L., Hunter T.R., Cyganowski C.J.
<Astrophys. J., 923, 263 (2021)>
=2021ApJ...923..263T 2021ApJ...923..263T
ADC_Keywords: Radio continuum; Star Forming Region; Masers; Radio lines
Keywords: Star formation ; Star forming regions ; Radio interferometry ;
Astrophysical masers ; Protoclusters ; Massive stars ;
Radio continuum emission ; Water masers ; Radio jets ;
Compact H II region ; Very Large Array
Abstract:
We have observed a sample of nine Extended Green Objects (EGOs) at
1.3 and 5cm with the Very Large Array (VLA) with subarcsecond
resolution and ∼7-14µJy/beam-sensitivities in order to characterize
centimeter continuum emission as it first appears in these massive
protoclusters. We find an EGO-associated continu um emission --within
1" of the extended 4.5µm emission-- in every field, which is
typically faint (order 101-102µJy) and compact (unresolved at
0.3"-0.5"). The derived spectral indices of our 36 total detections
are consistent with a wide array of physical processes, including both
non-thermal (19% of detections) and thermal free-free processes (e.g.,
ionized jets and compact HII regions, 78% of sample) and warm dust
(1 source). We also find an EGO-associated 6.7GHz CH3OH and 22GHz
H2O maser emission in 100% of the sample and a NH3(3,3) masers in
∼45%; we do not detect any NH3(6,6) masers at ∼5.6mJy/beam
sensitivity. We find statistically-significant correlations between
Lradio and Lbol at two physical scales and three frequencies,
consistent with thermal emission from ionized jets, but no correlation
between LH2O and Lradio for our sample. From these data, we
conclude that EGOs likely host multiple different centimeter
continuum-producing processes simultaneously. Additionally, at our
∼1000au resolution, we find that all EGOs except G18.89-0.47 contain
1∼2 massive sources based on the presence of CH3OH maser groups,
which is consistent with our previous work suggesting that these are
typical massive protoclusters, in which only one to a few of the young
stellar objects are massive.
Description:
We used the Karl G. Jansky Very Large Array to observe our sample of
nine Extended Green Objects (EGOs) at 1.3cm (22GHz, K-band) and 5cm
(6GHz, C-band) under projects 17B-323 and 18A-249. These observations
include continuum data at 1.3 and 5cm and line data for the 22GHz H2O,
23, and 25GHz NH3(3,3) & (6,6), and 6.7GHz Class II CH3OH maser species.
Data for project 17B-323 were taken between 2017 December 30 and
2018 February 13, which we will refer to as observing epoch 2018.1.
All observations for project 17B-323 were taken at 1.3cm. 5cm data for
project 18A-249 were taken in May and June of 2018 (observing epoch
2018.4), and 1.3cm data for 18A-249 were taken in 2019 July (observing
epoch 2019.6).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 81 9 Extended Green Object (EGO) source properties
table4.dat 128 36 Properties of centimeter continuum sources
table5.dat 88 5 Extended centimeter continuum sources: flux density
not recoverable in one or both bands
table6.dat 115 83 Summary of maser emission
table7.dat 108 2106 2D Gaussian fit results
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See also:
J/ApJ/463/205 : CS and NH3 Survey of H2O Maser Emission (Anglada+ 1996)
J/A+A/403/1095 : Methanol masers survey of low-mass YSO (Minier+, 2003)
J/AJ/136/2391 : GLIMPSE Extended Green Objects catalog (Cyganowski+, 2008)
J/ApJ/702/1615 : CH3OH maser survey of EGOs (Cyganowski+, 2009)
J/MNRAS/418/1689 : Red MSX water maser and ammonia emissions (Urquhart+, 2011)
J/AN/333/634 : Torun methanol source catalogue (Szymczak+, 2012)
J/ApJ/764/61 : Water maser & NH3 survey of GLIMPSE EGOs (Cyganowski+, 2013)
J/ApJ/783/130 : Parallaxes of high mass star forming regions (Reid+, 2014)
J/A+A/568/A41 : ATLASGAL Compact Source Catalog: 280<l<60 (Urquhart+, 2014)
J/ApJ/832/187 : ALMA & VLA radio continuum obs. of NGC 6334I (Brogan+, 2016)
J/ApJS/227/25 : Deep VLA obs. toward 58 high-mass SFRs (Rosero+, 2016)
J/A+A/602/A77 : HOBYS: 46 MDCs found in NGC 6334 (Tige+, 2017)
J/MNRAS/474/219 : 6.7 GHz methanol masers observations (Szymczak+, 2018)
J/MNRAS/473/1059 : Complete sample of Gal. clump properties (Urquhart+, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- EGO EGO source name
13- 14 I2 h RAh [18] Hour of right ascension (J2000)
16- 17 I2 min RAm [8/44] Minute of right ascension (J2000)
19- 22 F4.1 s RAs Second of right ascension (J2000)
24 A1 --- DE- [-] Sign of declination (J2000)
25- 26 I2 deg DEd [3/20] Degree of declination (J2000)
28- 29 I2 arcmin DEm Arcminute of declination (J2000)
31- 32 I2 arcsec DEs Arcsecond of declination (J2000)
34- 35 I2 km/s Vlsr [12/87] Local Standard of Rest velocity (1)
37- 39 F3.1 kpc Dist [1.6/4.8] Distance (2)
41- 43 F3.1 kpc e_Dist [0.2/0.7] Dist uncertainty
45- 48 F4.2 mas plx [1.13/1.83]? Parallax distance (3)
50- 53 F4.2 mas e_plx [0.07/0.11]? plx lower uncertainty
55- 58 F4.2 mas E_plx [0.08/0.14]? plx upper uncertainty
60- 62 I3 Msun Mcl [59/806] Clump mass (4)
64- 65 I2 K Tdust [22/29] Dust temperature (5)
67 I1 K e_Tdust [1/2] Tdust uncertainty
69- 73 F5.2 Lsun Lbol [1.29/28.1] Bolometric luminosity (6)
75- 78 F4.2 Lsun e_Lbol [0.26/4.1] Lbol median absolute deviation
80- 81 I2 Lsun/Msun Lbol/Mcl [3/35] Lbol to Mclump ratio
--------------------------------------------------------------------------------
Note (1): Local Standard of Rest Kinematic (LSRK) velocities are derived from
single-component fits to NH3 (1,1) emission and originally published
in Cyganowski+ (2013, J/ApJ/764/61 ; see their Table 3).
Note (2): Distances are estimated from the LSRK velocity and the Galactic
rotation curve parameters from Reid+ (2014, J/ApJ/783/130) for all sources
except G14.33-0.64 and G14.63-0.58. All kinematic distances are the
near distance, and the uncertainty on each assumed to be 15%, as in
Towner+ (2019ApJ...875..135T 2019ApJ...875..135T).
Note (3): Parallax distances (with their uncertainties) are given for
G14.33-0.64 and G14.63-0.58 from Reid+ (2014, J/ApJ/783/130) and
references therein, with the kinematic distances given for comparison.
Note (4): Masses are the average of the graybody-derived and NH3
temperature-derived masses presented in Towner+ (2019ApJ...875..135T 2019ApJ...875..135T);
see their Table 8 for values and their Section 4.1 for procedure. We
have compared these distances to those returned by the Monte-Carlo tool
presented in Wenger+ (2018ApJ...856...52W 2018ApJ...856...52W) and found that this tool
returns distances that agree with our current values within errors, with
similar error magnitudes.
Note (5): Dust temperatures come from Table 8 of Towner+ (2019ApJ...875..135T 2019ApJ...875..135T).
In Towner+ (2019), temperatures are derived from single-component
graybody fits to far-IR (70, 160, & 870um) data.
Note (6): Towner+ (2019ApJ...875..135T 2019ApJ...875..135T) derive four luminosities for each EGO:
one using single-component graybody fitting (see their Table 8) and
three using radiative-transfer modeling packages (see their Table 9).
In this work, we adopt as Lbol for each EGO the median of these four
values.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- EGO EGO Source Name
13- 16 A4 --- Name Source Name (1)
18- 19 I2 h RAh [18] Hour of Right Ascension (J2000) (2)
21- 22 I2 min RAm [8/44] Minute of Right Ascension (J2000) (2)
24- 31 F8.5 s RAs Second of Right Ascension (J2000) (2)
33- 39 F7.5 s e_RAs [4e-05/0.004] Uncertainty in RAs (2)
41- 41 A1 --- DE- [-] Sign of the Declination (J2000) (2)
42- 43 I2 deg DEd [3/20] Degree of Declination (J2000) (2)
45- 46 I2 arcmin DEm Arcminute of Declination (J2000) (2)
48- 54 F7.4 arcsec DEs Arcsecond of Declination (J2000) (2)
56- 61 F6.4 arcsec e_DEs [0.0005/0.1] Uncertainty in DEs (2)
63- 63 A1 --- l_F1.3cm Limit flag on F1.3cm
65- 68 I4 uJy F1.3cm [41/2633] 1.3cm Flux
70- 72 I3 uJy e_F1.3cm [11/133]? Uncertainty in F1.3cm
74- 74 A1 --- f_S1.3cm Resolved flag on S1.3cm (3)
76- 76 A1 --- l_S1.3cm Limit flag on S1.3cm
78- 81 I4 mas S1.3cm-a [69/5500]? 1.3cm Size, major axis
83- 85 I3 mas S1.3cm-b [34/440]? 1.3cm Size, minor axis
87- 89 I3 deg S1.3cm-pa [34/179]? 1.3cm Size, position angle
91- 91 A1 --- l_F5cm Limit flag on F5cm
93- 96 I4 uJy F5cm [22/2147] 5cm Flux
98- 99 I2 uJy e_F5cm [5/77]? Uncertainty in F5cm
101-101 A1 --- f_S5cm Resolved flag on S5cm (3)
103-103 A1 --- l_S5cm Limit flag on S5cm
105-108 I4 mas S5cm-a [73/5600]? 5cm Size, major axis
110-111 I2 mas S5cm-b [47/47]? 5cm Size, minor axis
113-115 I3 deg S5cm-pa [155/155]? 5cm Size, position angle
117-117 A1 --- l_alpha Limit flag on alpha
119-123 F5.2 --- alpha [-0.42/2.25] Spectral index
125-128 F4.2 --- e_alpha [0.05/0.3]? Uncertainty in alpha
--------------------------------------------------------------------------------
Note (1): For each EGO, the numbering order in Table 4 is determined by the
1.3cm integrated flux density of each detection. The brightest 1.3cm
source in an EGO is CM1, the second-brightest is CM2, etc. Sources
which are detected only at 5cm and not at 1.3cm are numbered after
all 1.3cm sources, in decreasing order of 5cm flux density.
See Section 3.1.2.
Note (2): All positions are derived from the 1.3cm data, unless the source
is not detected at 1.3cm, in which case the 5cm position is used. For
fitted sources, the position and position uncertainty are those returned
by imfit; for aperture-photometry sources, the position is that of the
peak intensity and position uncertainty is the cell size.
Note (3): Sources flagged as 'unres' (u), or 'fixed' (f) were fit with
imfit; sources with an upper limit were measured using aperture
photometry.
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- EGO EGO Source Name
13- 18 A6 --- Name Source Name (1)
20- 21 I2 h RAh [18]? 1.3cm Hour of Right Ascension
(J2000) (2)
23- 24 I2 min RAm [8/9]? 1.3cm Minute of Right Ascension
(J2000) (2)
26- 27 I2 s RAs ? 1.3cm Second of Right Ascension (J2000) (2)
29 A1 --- DE- [-] 1.3cm Sign of the Declination (J2000) (2)
30- 31 I2 deg DEd [20]? 1.3cm Degree of Declination (J2000) (2)
33- 34 I2 arcmin DEm [3/6]? 1.3cm Arcminute of Declination
(J2000) (2)
36- 37 I2 arcsec DEs ? 1.3cm Arcsecond of Declination (J2000) (2)
39- 40 I2 arcsec S1.3cm-a [7/48]? 1.3cm Size, major axis
42- 43 I2 arcsec S1.3cm-b [4/24]? 1.3cm Size, minor axis
45- 46 I2 h RA5h [18]? 5cm Hour of Right Ascension (J2000) (2)
48- 49 I2 min RA5m [8/44]? 5cm Minute of Right Ascension
(J2000) (2)
51- 52 I2 s RA5s ? 5cm Second of Right Ascension (J2000) (2)
54 A1 --- DE5- [-] 5cm Sign of the Declination (J2000) (2)
55- 56 I2 deg DE5d [3/20]? 5cm Degree of Declination (J2000) (2)
58- 59 I2 arcmin DE5m ? 5cm Arcminute of Declination (J2000) (2)
61- 62 I2 arcsec DE5s ? 5cm Arcsecond of Declination (J2000) (2)
64- 65 I2 arcsec S5cm-a [7/58]? 5cm Size, major axis
67- 68 I2 arcsec S5cm-b [3/31]? 5cm Size, minor axis
70- 88 A19 --- Ref ADS bibcode of reference (3)
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Note (1): Sources are listed here as "NR-CM1, NR-CM2, etc." to indicate
that their flux density is not fully recoverable from our data. As we
cannot fully recover their flux density or morphology, we do not analyze
these sources further in this paper
Note (2): Positions reported are for the peak intensity in each band. Sizes
are based on the apparent morphology of the source in our data, and are
measured from the polygonal aperture used to define that morphology.
They may therefore be underestimates in one or more directions due to
spatial filtering, and should be treated as approximate.
Note (3): Representative reference for previous detection within our
estimated size for each source. This list is not comprehensive;
interested readers should consult references in and to these
publications for additional information.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- EGO EGO Source Name
13- 17 A5 --- Maser Maser species (1)
19- 24 F6.1 --- Epoch [2018.1/2019.6] Observational epoch (2)
26- 31 A6 --- Group Group name (3)
33- 34 I2 h RAh [18]? Hour of Right Ascension (J2000) (4)
36- 37 I2 min RAm [8/44]? Minute of Right Ascension (J2000) (4)
39- 44 F6.3 s RAs ? Second of Right Ascension (J2000) (4)
46- 50 F5.3 arcsec e_RAs [0.001/2.7]? Uncertainty in RAs (4)
52 A1 --- DE- [- ] Sign of the Declination (J2000) (4)
53- 54 I2 deg DEd [3/20]? Degree of Declination (J2000) (4)
56- 57 I2 arcmin DEm ? Arcminute of Declination (J2000) (4)
59- 64 F6.3 arcsec DEs ? Arcsecond of Declination (J2000) (4)
66- 70 F5.3 arcsec e_DEs [0.001/2.4]? Uncertainty in DEs (4)
72- 76 F5.3 arcsec dRA [0.001/3.41]? Angular spread, right ascension (5)
78- 82 F5.3 arcsec dDE [0.002/2.8]? Angular spread, declination (5)
84- 89 F6.2 km/s Vmin [-34.3/87.8]? Minimum velocity, >4σ maser
emission detected
91- 96 F6.2 km/s Vmax [-4/101.8]? Maximum velocity, >4σ maser
emission detected
98-102 F5.2 km/s Vpeak [-5.8/87.8]? Velocity at which the brightest
maser spot in each group appears (6)
104-109 F6.3 Jy Speak [0.02/61.4]? Integrated flux density of the
brightest maser spot in each group (6)
111-115 F5.3 Jy e_Speak [0.005/0.1]? Uncertainty in Speak (6)
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Note (1): The molecular species of the maser emission. Emission denoted
NH3 refers exclusively to the NH3 (3,3) metastable state, as we
did not detect any NH3 (6,6) emission with these observations.
Note (2): The epoch in which the listed observations were taken. Exact dates
for each observation can be found in Tables 2 & 3.
Note (3): Maser groups are named for the centimeter continuum source with
which they are associated, and for their maser species. If a maser group
is not associated with any centimeter continuum emission, it is named
"NC" (for "no centimeter continuum") and the maser species. The
"NC" numbering scheme is separate for each species and increases with
increasing Right Ascension within a given EGO. Maser groups with null
values in the data columns were non-detections in that epoch.
Note (4): The intensity-weighted position of each maser group. Uncertainties
are the standard deviation of the difference between the maser spots in
each group and the centroid position, weighted by flux density.
Uncertainties are in arcseconds for both RA and Dec.
Note (5): A measure of the physical extent of the maser group. Each RA, Dec
value is the standard deviation of the unweighted differences between
each individual maser spot and the centroid position for the maser group.
Note (6): As determined by its 2D Gaussian fit.
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- EGO EGO Source Name
13- 17 A5 --- Maser Maser species
19- 29 A11 "Y/M/D" Epoch Date of first observation
31- 33 I3 --- N [1/570] Running number for fit (1)
35- 40 A6 --- Group Group name (2)
42- 47 F6.2 km/s Vel [-34.3/96.8] Velocity fit channel (3)
49- 50 I2 h RAh [18] Hour of Right Ascension (J2000) (4)
52- 53 I2 min RAm [8/44] Minute of Right Ascension (J2000) (4)
55- 61 F7.4 s RAs Second of Right Ascension (J2000) (4)
63- 69 F7.5 arcsec e_RAs [0/0.2] Uncertainty in RAs (4)
71- 71 A1 --- DE- [-] Sign of the Declination (J2000) (4)
72- 73 I2 deg DEd [3/20] Degree of Declination (J2000) (4)
75- 76 I2 arcmin DEm Arcminute of Declination (J2000) (4)
78- 83 F6.3 arcsec DEs Arcsecond of Declination (J2000) (4)
85- 90 F6.4 arcsec e_DEs [0/0.3] Uncertainty in DEs (4)
92- 99 F8.5 Jy Flux [-0.03/61.6] Integrated flux density of
maser spot
101-108 F8.5 Jy e_Flux [-0.02/0.1] Uncertainty in Flux
--------------------------------------------------------------------------------
Note (1): Fits are listed on a per-channel basis. If a channel has three
maser spots, all three spots for that channel will be listed before any
spots for the next channel. See N=8-10 in this table: there are three
masers (NC-W1, CM1-W1, and NC-W4) at +6.50km/s, so all three masers
are listed before any maser data for +6.75km/s.
Note (2): The name of the maser group with which each maser is associated.
See text for naming convention.
Note (3): The velocity of the channel in which the fit was performed. If
multiple maser spots were fit within the same channel, the fit for each
spot is listed separately, in order of increasing RA.
Note (4): J2000 coordinates of each maser spot, as returned by imfit.
Uncertainties are those returned by imfit, in arcseconds for both RA and Dec.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 05-Jun-2023