J/ApJ/841/121 HII region candidates in the OSC spiral arm (Armentrout+, 2017)
High-mass star formation in the Outer Scutum-Centaurus Arm.
Armentrout W.P., Anderson L.D., Balser D.S., Bania T.M., Dame T.M.,
Wenger T.V.
<Astrophys. J., 841, 121-121 (2017)>
=2017ApJ...841..121A 2017ApJ...841..121A (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way; H II regions; Radio lines; Infrared sources;
Molecular data
Keywords: Galaxy: structure; H II regions
Abstract:
The Outer Scutum-Centaurus (OSC) spiral arm is the most distant
molecular spiral arm in the Milky Way, but until recently little was
known about this structure. Discovered by Dame and Thaddeus, the OSC
lies ∼15kpc from the Galactic Center. Due to the Galactic warp, it
rises to nearly 4° above the Galactic Plane in the first Galactic
quadrant, leaving it unsampled by most Galactic plane surveys. Here we
observe HII region candidates spatially coincident with the OSC using
the Very Large Array to image radio continuum emission from 65 targets
and the Green Bank Telescope to search for ammonia and water maser
emission from 75 targets. This sample, drawn from the Wide-field
Infrared Survey Explorer Catalog of Galactic HII Regions, represents
every HII region candidate near the longitude-latitude (l,b) locus of
the OSC. Coupled with their characteristic mid-infrared morphologies,
detection of radio continuum emission strongly suggests that a target
is a bona fide HII region. Detections of associated ammonia or water
maser emission allow us to derive a kinematic distance and determine
if the velocity of the region is consistent with that of the OSC.
Nearly 60% of the observed sources were detected in radio continuum,
and more than 20% have ammonia or water maser detections. The
velocities of these sources mainly place them beyond the Solar orbit.
These very distant high-mass stars have stellar spectral types as
early as O4. We associate high-mass star formation at 2 new locations
with the OSC, increasing the total number of detected HII regions in
the OSC to 12.
Description:
We followed a two-tier observing strategy and observed both radio
continuum and molecular line emission of the Outer Scutum-Centaurus
(OSC) HII region targets. Our total sample included 75 HII region
candidates. We observed 65 of these candidates using the VLA (8-10GHz)
in the summer of 2014 ((VLA14A-194) and all 75 with the Green Bank
Telescope (GBT; H20 22.2351GHz, NH3 23.6945GHz, NH3 23.7226GHz,
NH3 23.8701GHz) spanning 2 years and included projects GBT13B-403 in
2015 January, GBT15B-232 in 2016 January-March, and GBT16B-414 in
2017 January).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 63 65 VLA radio continuum parameters
table3.dat 117 39 Molecular line parameters
--------------------------------------------------------------------------------
See also:
VII/20 : Catalogue of HII Regions (Sharpless 1959)
VIII/76 : Leiden/Argentine/Bonn (LAB) Survey of Galactic HI (Kalberla+ 2005)
J/A+A/275/67 : Velocity Field of the outer Galaxy (Brand+ 1993)
J/A+AS/103/541 : Arcetri Catalogue of H2O Maser Sources (Brand+ 1994)
J/A+AS/115/81 : A CS(2-1) survey of UC HII regions (Bronfman+, 1996)
J/PASJ/59/1185 : Water maser in galactic IRAS sources (Sunada+, 2007)
J/AJ/140/1194 : FUV/HI relations in nearby galaxies (Bigiel+, 2010)
J/ApJS/194/32 : The HII Region Discovery Survey (HRDS). II. (Anderson+, 2011)
J/ApJ/738/27 : Galactic HII regions RRL and continuum data (Balser+, 2011)
J/MNRAS/418/1689 : Red MSX water maser and ammonia emissions (Urquhart+, 2011)
J/ApJ/754/62 : HRDS III. HII region kinematic distances (Anderson+, 2012)
J/ApJS/208/11 : The Red MSX Source Survey: massive protostars (Lumsden+, 2013)
J/ApJ/783/130 : Parallaxes of high mass star forming regions (Reid+, 2014)
J/ApJS/212/1 : The WISE catalog of Galactic HII regions (Anderson+, 2014)
J/ApJ/798/L27 : CO obs. of molecular clouds in the 2nd quadrant (Sun+, 2015)
J/ApJ/806/199 : RRL and continuum data of 21 Gal. H II regions (Balser+, 2015)
J/ApJS/221/26 : Radio obs. of Galactic WISE HII regions (Anderson+, 2015)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 A15 --- Name Target name (GLLL.lll+bb.bbb) (G1)
17- 18 I2 h RAh Hour of right ascension (J2000)
20- 21 I2 min RAm Minute of right ascension (J2000)
23- 27 F5.2 s RAs Second of right ascension (J2000)
29 A1 --- DE- Sign of declination (J2000)
30- 31 I2 deg DEd Degree of declination (J2000)
33- 34 I2 arcmin DEm Arcminute of declination (J2000)
36- 39 F4.1 arcsec DEs Arcsecond of declination (J2000)
41- 46 F6.2 mJy Sint [0.6/601.2]? Integrated flux
48- 52 F5.2 mJy/beam Spk [0.09/48.7]? Peak flux, Speak
54- 57 F4.2 mJy/beam e_Spk [0.02/0.7] rms noise, σSpeak
59- 63 I5 arcsec2 Area [120/21830]? Area of each mask
--------------------------------------------------------------------------------
Byte-by-byte Description of file:table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 A15 --- Name Target name (GLLL.lll+bb.bbb) (G1)
17- 18 I2 h RAh Hour of right ascension (J2000)
20- 21 I2 min RAm Minute of right ascension (J2000)
23- 27 F5.2 s RAs Second of right ascension (J2000)
29 A1 --- DE- Sign of declination (J2000)
30- 31 I2 deg DEd Degree of declination (J2000)
33- 34 I2 arcmin DEm Arcminute of declination (J2000)
36- 39 F4.1 arcsec DEs Arcsecond of declination (J2000)
41- 66 A26 --- Trans Transition (1)
68- 72 I5 mK TL [15/14505] Line intensity (2)
74- 75 I2 mK e_TL [1/11]? TL uncertainty
77- 86 A10 km/s DelV FWHM line width, ΔV
88- 91 F4.2 km/s e_DelV [0.03/1.33]? DelV uncertainty (3)
93- 98 F6.2 km/s VLSR [-69.16/61.97] Local Standard of Rest peak
velocity
100- 103 F4.2 km/s e_VLSR [0.01/0.39]? VLSR uncertainty
105- 106 I2 mK rms [7/40]? rms baseline noise
108- 117 A10 --- Note Note(s) on previous detections (4)
--------------------------------------------------------------------------------
Note (1): Transitions reported are the three lowest energy ammonia inversion
transitions (i.e., (1, 1), (2, 2), and (3, 3)), their hyperfine lines,
and water maser emission, where detected. Ammonia's hyperfine lines
are labeled according to their transition, shown in Figure 3.
Note (2): For ammonia detections, values reported are the result of Gaussian
fits to each component. For water maser detections, peak and center
velocities are read directly from the data and rounded to the nearest
0.5km/s.
Note (3): Water maser velocities are given as the range over which emission
rises 3σ above the noise.
Note (4): The note column indicates previous line detections at comparable
velocities, including maser species. Code as follows:
1a = H2O; Sunada et al. 2007, J/PASJ/59/1185
1b = Urquhart et al. 2012, J/MNRAS/418/168
2 = ammonia; Urquhart et al. 2012, J/MNRAS/418/168
3a = radio recombination line; Anderson et al. 2011, J/ApJS/194/32
3b = radio recombination line; Anderson et al. 2015, J/ApJS/221/26
4 = CS; Bronfman et al. 1996, J/A+AS/115/81
5a = CO; Lundquist et al. 2015ApJ...806...40L 2015ApJ...806...40L
5b = CO; Ao et al. 2004AJ....128.1716A 2004AJ....128.1716A
--------------------------------------------------------------------------------
Global notes:
Note (G1): Targets for these observations were taken from the WISE Catalog of
Galactic HII Regions (see Anderson+ 2014, J/ApJS/212/1 ;
<[ABB2014] WISE GLLL.lll+BB.bbb> in Simbad).
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 22-Sep-2023