J/ApJS/253/23 VLA 9GHz obs. of HII region candidates (Armentrout+, 2021)
A VLA census of the Galactic H II region population.
Armentrout W.P., Anderson L.D., Wenger T.V., Balser D.S., Bania T.M.
<Astrophys. J. Suppl. Ser., 253, 23 (2021)>
=2021ApJS..253...23A 2021ApJS..253...23A
ADC_Keywords: H II regions; Radio continuum; Infrared sources
Keywords: H II regions ; Very Large Array ; Star formation ; Massive stars ;
Interstellar medium ; Galaxy structure
Abstract:
The Milky Way contains thousands of HII region candidates identified
by their characteristic mid-infrared morphology, but lacking
detections of ionized gas tracers such as radio continuum or radio
recombination line emission. These targets thus remain unconfirmed as
HII regions. With only ∼2500 confirmed HII regions in the Milky Way,
Galactic surveys are deficient by several thousand nebulae when
compared to external galaxies with similar star formation rates. Using
sensitive 9 GHz radio continuum observations with the Karl G. Jansky
Very Large Array, we explore a sample of HII region candidates in
order to set observational limits on the actual total population of
Galactic HII regions. We target all infrared-identified "radio-quiet"
sources from the Wide-field Infrared Survey Explorer Catalog of
Galactic HII regions between 245°≥l≥90° with infrared
diameters less than 80". We detect radio continuum emission from 50%
of the targeted HII region candidates, providing strong evidence that
most of the radio-quiet candidates are bona fide HII regions. We
measure the peak and integrated radio flux densities and compare the
inferred Lyman continuum fluxes using models of OB stars. We conclude
that stars of approximately spectral type B2 and earlier are able to
create HII regions with similar infrared and radio continuum
morphologies as the more luminous HII regions created by O stars. From
our 50% detection rate of "radio-quiet" sources, we set a lower limit
of ∼7000 for the HII region population of the Galaxy. Thus the vast
majority of the Milky Way's HII regions remain to be discovered.
Description:
We observe the 9GHz (∼3cm) continuum emission from 146 compact
(infrared diameter <80") radio-quiet HII region candidates with the
VLA in D configuration (Project ID: VLA/16A-371). We follow the
observing procedures of Armentrout+ (2017ApJ...841..121A 2017ApJ...841..121A).
These observations were conducted between 2017 February and May, split
into 2hr scheduling blocks by source longitude.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 79 167 *VLA radio continuum parameters
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Note on tablea1.dat: Parameters in this table stem from the CASA routine
imstat with user-defined masks. Images were smoothed to a common
resolution of 15" with a boxcar filter before these parameters were
calculated. Null values correspond to no detections.
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See also:
VIII/58 : A Survey of Radio H II Regions in the Northern Sky (Lockman+ 1989)
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
J/A+A/171/261 : RRLs of Southern HII Regions (Caswell+ 1987)
J/AJ/127/1632 : UBVR(UIT) photometry of O and OB stars in SMC (Oey+, 2004)
J/ApJS/194/32 : The HII Region Discovery Survey (HRDS). II. (Anderson+, 2011)
J/MNRAS/424/1925 : Spectrocopic Binarity of O and B type stars (Chini+, 2012)
J/MNRAS/424/2442 : Catalog of bubbles from Milky Way Project (Simpson+, 2012)
J/ApJS/212/1 : The WISE catalog of Galactic HII regions (Anderson+, 2014)
J/ApJ/784/111 : Morphology of cand. intermediate-mass SFRs (Lundquist+, 2014)
J/ApJS/221/26 : Radio obs. of Galactic WISE HII regions (Anderson+, 2015)
J/ApJ/806/199 : RRL & continuum data of 21 Gal. H II regions (Balser+, 2015)
J/ApJ/799/153 : Yellowballs in Milky Way project (Kerton+, 2015)
J/A+A/588/A97 : Continuum sources from the THOR survey (Bihr+, 2016)
J/ApJS/234/33 : A GBT survey of large Galactic HII regions (Anderson+, 2018)
J/ApJ/870/32 : Kinematics in young star clusters & associations (Kuhn+, 2019)
J/A+A/627/A175 : GLOSTAR. Radio Source Catalogue I (Medina+ 2019)
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 A15 --- WISE WISE identifier (GLLL.lll+BB.bbb) from
Anderson+, 2014, J/ApJS/212/1
(<[ABB2014] WISE GLLL.ll+BB.bbb> in Simbad)
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- 29 A1 --- DE- Sign of the 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- 47 F7.3 mJy Sint [0.12/164.1]? Integrated flux density
49- 54 F6.3 mJy e_Sint [0.02/17.1]? Uncertainty in Sint
56- 60 F5.3 mJy/beam Speak [0.014/8]? peak flux density
62- 66 F5.3 mJy/beam e_Speak [0.003/2.4] Uncertainty (map RMS)
for Speak (1)
68- 72 I5 arcsec2 Area [370/27270]? Region area (2)
74- 75 I2 min Exp [4/16] Integration time
77- 79 I3 --- Fig4 Figure sub-number on Figure 4
(column added by the author) (3)
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Note (1): e_Speak corresponds to the map noise RMS.
Note (2): Areas were determined from hand drawn CASA masks for each detected
region.
Note (3): For the 21 sources with 16 minutes "Deep Integration", only the
16 minutes image is provided.
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Acknowledgements:
Will Armentrout [warmentr at nrao.edu]
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 05-May-2021