J/ApJS/244/35 VLA observations of the Central Molecular Zone (Lu+, 2019)
A census of early-phase high-mass star formation in the Central Molecular Zone.
Lu X., Mills E.A.C., Ginsburg A., Walker D.L., Barnes A.T., Butterfield N.,
Henshaw J.D., Battersby C., Kruijssen J.M.D., Longmore S.N., Zhang Q.,
Bally J., Kauffmann J., Ott J., Rickert M., Wang K.
<Astrophys. J. Suppl. Ser., 244, 35 (2019)>
=2019ApJS..244...35L 2019ApJS..244...35L
ADC_Keywords: Galactic center; Star Forming Region; H II regions; Masers;
Radio continuum
Keywords: Star formation ; Galactic center ; H II regions ; Astrophysical masers
Abstract:
We present new observations of the C-band continuum emission and
masers to assess high-mass (>8M☉) star formation at early
evolutionary phases in the inner 200pc of the Central Molecular Zone
(CMZ) of the Galaxy. The continuum observation is complete to
free-free emission from stars above 10-11M☉ in 91% of the
covered area. We identify 104 compact sources in the continuum
emission, among which five are confirmed ultracompact HII regions, 12
are candidates of ultracompact HII regions, and the remaining 87
sources are mostly massive stars in clusters, field stars, evolved
stars, pulsars, extragalactic sources, or of unknown nature that is to
be investigated. We detect class II CH3OH masers at 23 positions,
among which six are new detections. We confirm six known H2CO masers
in two high-mass star-forming regions and detect two new H2CO masers
toward the Sgr C cloud, making it the ninth region in the Galaxy that
contains masers of this type. In spite of these detections, we find
that current high-mass star formation in the inner CMZ is only taking
place in seven isolated clouds. The results suggest that star
formation at early evolutionary phases in the CMZ is about 10 times
less efficient than expected from the dense gas star formation
relation, which is in line with previous studies that focus on more
evolved phases of star formation. This means that if there will be any
impending, next burst of star formation in the CMZ, it has not yet begun.
Description:
The VLA observations were carried out in the B configuration in 2016
August-October with the project code 16A-173. We targeted the inner
200pc of the Central Molecular Zone (CMZ) of the Galaxy. A total of 31
fields were observed (see Figure 1).
The C-band receiver was used to cover six lines, including two CH3OH
lines at the rest frequencies of 6.668GHz and 5.005GHz, a radio
recombination line H(111)α at the rest frequency of 4.744GHz,
and three formaldehyde isotopolog lines H2CO, H213CO, and
H2C18O between rest frequencies of 4.389 and 4.830GHz. For each
line, a velocity range of ±200km/s was covered. In addition to the
lines, a total of 16 wideband spectral windows were used to cover a
2GHz wide continuum between 4.2 and 6.9GHz, but owing to strong radio
frequency interference (RFI), the available bandwidth for continuum
imaging is less, with a typical value of 1.7GHz.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 176 104 Properties of compact sources in C-band continuum
table4.dat 92 23 Properties of CH3OH masers
table5.dat 58 8 Properties of H2CO masers
table6.dat 148 7 Summary of high-mass star formation indicators
refs.dat 69 29 References
fits/* . 24 Individual continuum images in FITS format for
the four tiles Sgr A, Dust Ridge, Sgr C and Sgr B2
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
VIII/96 : 6-GHz methanol multibeam maser catalogue (Caswell+, 2010-12)
J/ApJS/74/181 : Small-diameter radiosources catalogue (Zoonematkermani+, 1990)
J/ApJS/91/347 : A 5-GHz VLA Survey of the Galactic Plane (Becker+ 1994)
J/MNRAS/321/77 : Large-amplitude variables near the GC (Glass+, 2001)
J/ApJS/155/421 : Survey of Galactic Center region at 20cm (Yusef-Zadeh+, 2004)
J/AJ/129/348 : Radio compact HII regions in the Milky Way (Giveon+, 2005)
J/ApJS/165/173 : Chandra sources in Galaxy central 150pc (Muno+, 2006)
J/AJ/136/2391 : GLIMPSE Extended Green Objects catalog (Cyganowski+, 2008)
J/ApJS/174/481 : 2LC Compact Radio Sources in the GC (Lazio+, 2008)
J/other/PASA/26.454 : Precise positions of methanol masers (Caswell, 2009)
J/ApJS/181/110 : Galactic center X-ray sources (Muno+, 2009)
J/ApJ/702/178 : YSOs in the central 400pc of the Galaxy (Yusef-Zadeh+, 2009)
J/ApJ/699/186 : VLA observations of the Galactic center (Zhao+, 2009)
J/ApJ/736/133 : Spitzer-IRS study of massive YSOs in the GC (An+, 2011)
J/MNRAS/417/114 : HST/NICMOS Galactic Center survey catalogue (Dong+, 2011)
J/MNRAS/416/1764 : H2O Southern Galactic Plane Survey (HOPS) (Walsh+, 2011)
J/ApJ/766/114 : Water & methanol masers in G75.78+0.34 (Sanchez-Monge+, 2013)
J/ApJS/212/1 : The WISE catalog of Galactic HII regions (Anderson+, 2014)
J/A+A/563/A68 : CH3OH and H2O Galactic center masers (Chambers+, 2014)
J/ApJ/799/53 : YSO/MS star models in the CMZ (Koepferl+, 2015)
J/A+A/588/A97 : Continuum sources from the THOR survey (Bihr+, 2016)
J/ApJS/227/10 : CH3OH & OH line emission from the GC (Cotton+, 2016)
J/A+A/586/A50 : Central Molecular Zone H2CO temperature maps (Ginsburg+, 2016)
J/ApJ/853/171 : mm point sources in extended Sgr B2 cloud (Ginsburg+, 2018)
J/A+A/619/A124 : THOR survey in northern Galactic plane (Wang+, 2018)
J/ApJS/235/26 : Ultradeep cat. of X-ray point sources in the GC (Zhu+, 2018)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- ID Continuum source identification (CNNN
with NNN from 1 to 104)
6- 7 I2 h RAh Hour of right ascension (J2000)
9- 10 I2 min RAm Minute of right ascension (J2000)
12- 16 F5.2 s RAs Second of right ascension (J2000)
18 A1 --- DE- Sign of declination (J2000)
19- 20 I2 deg DEd Degree of declination (J2000)
22- 23 I2 arcmin DEm Arcminute of declination (J2000)
25- 29 F5.2 arcsec DEs Arcsecond of declination (J2000)
31- 34 F4.2 pc Reff ? Effective radius
35- 36 A2 --- f_Reff UR: Unresolved source
38- 42 F5.2 mJy/beam Ipeak [0.1/27.4] Peak intensity corrected for
primary-beam response
44- 47 F4.2 mJy/beam e_Ipeak [0.03/1.6] Ipeak uncertainty
49- 53 F5.2 mJy Fint [0.1/64.2] Integrated flux corrected for
primary-beam response
55- 58 F4.2 mJy e_Fint [0.03/3.4] Fint uncertainty
60- 64 F5.2 --- alpha [-4.4/2.2] Spectral index corrected for
primary-beam response
66- 69 F4.2 --- e_alpha [0.01/3.4] alpha uncertainty (1)
71 A1 --- HST HST Paschen-α survey
(Wang+ 2010MNRAS.402..895W 2010MNRAS.402..895W)
73- 87 A15 --- HII WISE HII regions
(Anderson+ 2014, J/ApJS/212/1)
89-108 A20 --- YSOs Spitzer YSOs
(Yusef-Zadeh+, 2009, J/ApJ/702/178 and
An+, 2011, J/ApJ/736/133)
110 A1 --- NH2 Herschel N(H2) data
from Battersby+ 2011A&A...535A.128B 2011A&A...535A.128B
112-131 A20 --- OID Counterparts against UC HII (2)
133-172 A40 --- Det Identifiers of previous detections of
compact radio continuum emission using
radio interferometers (see refs.dat file)
174-176 A3 --- Note Remarks (3)
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Note (1): The systematic uncertainty in spectral indices of 0.05 is not listed.
Note (2): Counterparts that would argue against UC HII regions, with references
in parentheses (see refs.dat file). The object types generally follow the
abbreviation convention of SIMBAD:
X = X-ray sources;
Mi* = Mira variable stars;
F*? = possible field stars;
WR* = Wolf-Rayet stars;
PN = planetary nebula.
Note (3): Ultracompact (UC) HII candidates and confirmed UC HII regions are
labeled with "UC?" and "UC," respectively.
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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- 3 A3 --- ID CH3OH maser identifier (MNN
with NN from 1 to 23)
5- 37 A33 --- Assoc Class II CH3OH masers spatially associated
with known UC/HC HII regions
(Reference in parentheses; see refs.dat file);
column added by CDS from Note on Table 6
39- 40 I2 h RAh Hour of right ascension (J2000)
42- 43 I2 min RAm Minute of right ascension (J2000)
45- 49 F5.2 s RAs Second of right ascension (J2000)
51 A1 --- DE- Sign of declination (J2000)
52- 53 I2 deg DEd Degree of declination (J2000)
55- 56 I2 arcmin DEm Arcminute of declination (J2000)
58- 62 F5.2 arcsec DEs Arcsecond of declination (J2000)
64- 69 F6.2 km/s nuPk [-57/73.5] νpeak value (G1)
71- 75 F5.2 Jy Fpk [0.05/64] Peak flux corrected for primary
beam response (Jy per channel) (G1)
77- 82 F6.2 Jy.km/s Fint [0.1/102.2] Integrated flux corrected for
primary beam response
84- 92 A9 --- Ref References (see refs.dat file)
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 A2 --- ID H2CO maser identifier (FN with N from 1 to 8)
4- 5 I2 h RAh Hour of right ascension (J2000)
7- 8 I2 min RAm Minute of right ascension (J2000)
10- 14 F5.2 s RAs Second of right ascension (J2000)
16 A1 --- DE- Sign of declination (J2000)
17- 18 I2 deg DEd Degree of declination (J2000)
20- 21 I2 arcmin DEm Arcminute of declination (J2000)
23- 27 F5.2 arcsec DEs Arcsecond of declination (J2000)
29- 34 F6.2 km/s nuPk [-54.2/75.2] νpeak value (G1)
36- 39 F4.2 Jy Fpk [0.09/1.2] Peak flux corrected for primary
beam response (Jy per channel) (G1)
41 A1 --- l_Fpk [c] Limit flag on Fpk (1)
43- 46 F4.2 Jy.km/s Fint [0.1/1.6] Integrated flux corrected for
primary beam response
48 A1 --- l_Fint [c] Limit flag on Fint (1)
50- 58 A9 --- Ref References (see refs.dat file)
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Note (1): Significant absorption is superimposed with maser emission (Figure 7);
therefore, reported fluxes are lower limits.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- Reg Region name (1)
20- 20 I1 --- Fig [2/5]? Figure number; column added by CDS
22- 23 I2 --- Nc [0/47] Number of UC/HC HII regions
25- 43 A19 --- Ref Reference(s) for UC/HC HII regions
(see refs.dat file)
45- 46 I2 --- Nm [0/20] Number of Class II Ch3OH masers
48- 49 I2 --- Nu [1/58] Number of unique indicators (2)
51- 54 F4.1 10-3Msun/yr SFR [0.4/25] Star forming rate (3)
56- 98 A43 --- File1 Name of the FITS file in subdirectory "fits"
for the Stokes-I PB-uncorrected image
(central frequency at 5.56GHz);
column added by CDS
100-148 A49 --- File2 Name of the FITS file in subdirectory "fits"
for the Stokes-I primary-beam-corrected
image; column added by CDS
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Note (1): Spatial coverage of the VLA observations is shown in Figure 1.
Note (2): Class II CH3OH masers spatially associated with known UC/HC HII
regions are excluded (see col. "Assoc" in Table 4).
Note (3): We assume each unique high-mass star formation indicator corresponds
to a high-mass protostar of >10M☉, thus representing a total
stellar mass of 129M☉ (see Appendix D of Lu+ 2019ApJ...872..171L 2019ApJ...872..171L).
The SFR is derived by dividing the total stellar mass in the
considered region by the characteristic timescale of 0.3Myr.
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Byte-by-byte Description of file: refs.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- Ref Reference code
5- 23 A19 --- BibCode Bibcode of the reference
25- 44 A20 --- Auth First author's name(s)
46- 69 A24 --- Cat VizieR catalogue reference
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Global notes:
Note (G1): For masers with multiple velocity components along the line of sight,
Vlsr, and the flux of the strongest peak is listed.
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History:
From electronic version of the journal for Tables 3-6
FITS continuum images downloaded at:
http://zenodo.org/record/3361116#.XmIG-kN7n8E
(End) Emmanuelle Perret [CDS] 06-Mar-2020