J/MNRAS/506/2232 SCORPIO field's study with ASKAP (Umana+, 2021)
A first glimpse at the Galactic plane with the ASKAP: the SCORPIO field.
Umana G., Trigilio C., Ingallinera A., Riggi S., Cavallaro F., Marvil J.,
Norris R.P., Hopkins A.M., Buemi C.S., Bufano F., Leto P., Loru S.,
Bordiu C., Bunton J.D., Collier J.D., Filipovic M., Franzen T.M.O.,
Thompson M.A., Andernach H., Carretti E., Dai S., Kapinska A.,
Koribalski B.S., Kothes R., Leahy D., McConnell D., Tothill N.,
Michalowski M.J.
<Mon. Not. R. Astron. Soc., 2232-2246 (2021)>
=2021MNRAS.506.2232U 2021MNRAS.506.2232U (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Planetary nebulae ; Supernova remnants ;
H II regions ; Galactic plane ; Radio sources ; Photometry
Keywords: techniques: image processing - techniques: interferometric - surveys -
stars: evolution - stars: formation - radio continuum: general
Abstract:
In the broad context of the Australian Square Kilometer Array
Pathfinder (ASKAP) early-science phase and preparation for the related
surveys, we report the first radio observations towards the Galactic
plane. The targeted field was chosen to encompass the entire SCORPIO
survey, one of the several pathfinder projects for the Evolutionary
Map of the Universe survey planned with the ASKAP. The observations
were carried out in 2018 January at a central frequency of 912 MHz,
with 15 operational antennas, and covered a total area of about 40
square degrees in three different pointings. The final image has a
resolution of 24.1 * 21.1 arcsec2 and a median rms of
541 µJy/beam. We were able to extract 3545 candidate sources, 75 per
cent of them point sources. For a preliminary validation, a comparison
with the 843 MHz Molonglo Galactic Plane Survey is presented. Although
the present observations were obtained with the ASKAP only partially
deployed, its unique capability to map complex sources, such as those
inhabiting the Galactic plane, at different angular scales, is
highlighted. Within the SCORPIO field all the previously classified
H II regions, Planetary Nebulae (PNe), and supernovae remnants (SNRs),
previously known to be radio sources, were detected. We also report
new radio detections from several H II regions previously classified
as 'candidates' or 'radio quiet' and from half of all the PNe in the
SCORPIO field with robust classification. Most notably, we find
numerous unclassified, extended sources which constitute a promising
sample of candidates H II regions and SNRs.
Description:
A new era in radio astronomy has finally arrived. The Square Kilometre
Array (SKA) precursors have started their early-science phase with
impressive results that foreshadow their full operation. In particular
the Australian SKA Array Pathfinder (ASKAP, Hotan et al.
2021PASA...38....9H 2021PASA...38....9H) is transforming the way in which large radio
surveys have been so far conducted. Due to the wide-field phased array
feed (PAF) system (Chippendale, Hayman & Hay 2014PASA...31...19C 2014PASA...31...19C)
mounted on each antenna, ASKAP is capable of a huge instantaneous field
of view.
A number of different regions of the sky were selected for testing the
array in this phase: among these, one is centred towards the same
field of the 'Stellar Continuum Originating from Radio Physics in
Ourgalaxy' (SCORPIO) project (Umana et al. 2015MNRAS.454..902U 2015MNRAS.454..902U, Cat.
J/MNRAS/454/902). We will refer to this targeted observation as to the
'ASKAP SCORPIO observations'.
The SCORPIO field was observed with the ASKAP in band 1 (from 792 to
1032 MHz) in 2018 January using 15 antennas (of the 36 in the
completed array) during the early-science phase. The array
configuration had a minimum baseline of 22.4 m and a maximum
baseline of 2.3 km. This implies that the observations, at the
central frequency of 912 MHz, are sensitive to a minimum and maximum
angular scale of 29.5 arcsec and 50 arcmin, respectively,
(see section 2.1 The ASKAP observations).
The data reduction process used the ASKAPSOFT package, based on
CASACORE and specifically optimized for managing the ASKAP data
(Guzman et al. 2019ascl.soft12003G). The data reduction procedure is
managed by a pipeline that configures and launches a series of jobs
running on the Galaxy supercomputer at the Pawsey facility in Perth,
(see section 2.2 Data reduction).
The last step of the askapsoft pipeline processing is an application
of the source finder algorithm selavy (Whiting & Humphrey
2012PASA...29..371W 2012PASA...29..371W) to create a compact source catalogue. SELAVY
provides, for each fitted component, the peak and integrated flux
densities, with their errors, the position angle, and the major and
the minor FWHMs of the Gaussian component, indicating both the fit and
its deconvolved value, given the image's restoring beam,
(see section 3.1 Compact source extraction and preliminary validation).
The H II regions are found in star-forming sites, in the vicinity of
high-mass stars, where the gas is ionized by ultraviolet photons from
the central object. They are tracers of the current epoch star
formation and their continuum radio emission is due to thermal
Bremsstrahlung radiation. As anticipated (see section 3.3 Known
Galactic sources), we produce the table2.dat for the 112 sources
detected by visual inspection and extracted by SELAVY,
(see section 3.3.1 H II regions).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 85 112 *H II regions and H II regions candidates
detected and extracted with SELAVY
--------------------------------------------------------------------------------
Note on table2.dat: we produce a catalogue for the 112 sources detected by
visual inspection and extracted by SELAVY which is the last step of the
ASKAPSOFT pipeline processing is an application of the source finder algorithm
SELAVY (Whiting & Humphrey 2012PASA...29..371W 2012PASA...29..371W) to create a compact source
catalogue, (see section 3.1 Compact source extraction and preliminary
validation).
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See also:
J/ApJS/212/1 : The WISE catalog of Galactic HII regions (Anderson+, 2014)
J/MNRAS/454/902 : SCORPIO 1 catalogue of compact radio sources (Umana+, 2015)
J/ApJS/117/361 : PNe in NRAO VLA Sky Survey (Condon+ 1998)
J/AJ/131/2525 : MAGPIS 20cm survey (Helfand+, 2006)
J/A+A/619/A124 : THOR survey in northern Galactic plane (Wang+, 2018)
J/MNRAS/490/5063 : Extended sources in SCORPIO at 2.1GHz (Ingallinera+, 2019)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 16 A16 --- Source Source identifier name construct
as JDDD.ddd+DD.dddd (SourceID)
18- 32 A15 --- WISE WISE identifier as GLLL.lll+BB.bbb
([ABB2014] WISE GLLL.lll+BB.bbb in Simbad) (1)
34- 35 I2 h RAh Right ascension (J2000)
37- 38 I2 min RAm Right ascension (J2000)
40- 43 F4.1 s RAs Right ascension (J2000)
45 A1 --- DE- Sign of declination (J2000)
46- 47 I2 deg DEd Declination (J2000)
49- 50 I2 arcmin DEm Declination (J2000)
52- 53 I2 arcsec DEs Declination (J2000)
55 A1 --- Cl Classification of HII region (C) (2)
57- 64 F8.2 mJy S912 The integrated flux density
at 912 MHz (S912) (3)
66- 71 F6.2 mJy e_S912 Mean error of S912 (err)
73- 78 F6.2 arcsec MajAxis FWHM of the major axes (θdmax) (4)
80- 85 F6.2 arcsec MinAxis FWHM of the minor axes ((θdmin) (4)
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Note (1): WISE identifier as Anderson et al.
(2014ApJS..212....1A 2014ApJS..212....1A, Cat. J/ApJS/212/1).
Note (2): Following the classification made by Anderson et al.
(2014ApJS..212....1A 2014ApJS..212....1A, Cat. J/ApJS/212/1).
Galactic HII region classification as follows:
K = Known
G = Group
C = Candidate
Q = radio Quiet
? = no radio data
Note (3): From the ASKAP images of the SCORPIO field at 912 MHz.
Note (4): The angular dimensions of the source as determined by the Gaussian fit
during the data reduction (see section 2.2 Data reduction)
deconvolved by the synthesized beam.
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 21-Jun-2024