J/MNRAS/461/4022 JCMT Gould Belt Survey: Southern Orion A (Mairs+, 2016)
The JCMT Gould Belt Survey: a first look at Southern Orion A with SCUBA-2.
Mairs S., Johnstone D., Kirk H., Buckle J., Berry D.S.,
Broekhoven-Fiene H., Currie M.J., Fich M., Graves S., Hatchell J.,
Jenness T., Mottram J.C., Nutter D., Pattle K., Pineda J.E., Salji C.,
Di Francesco J., Hogerheijde M.R., Ward-Thompson D., Bastien P.,
Bresnahan D., Butner H., Chen M., Chrysostomou A., Coude S., Davis C.J.,
Drabek-Maunder E., Duarte-Cabral A., Fiege J., Friberg P., Friesen R.,
Fuller G.A., Greaves J., Gregson J., Holland W., Joncas G., Kirk J.M.,
Knee L.B.G., Marsh K., Matthews B.C., Moriarty-Schieven G., Mowat C.,
Rawlings J., Richer J., Robertson D., Rosolowsky E., Rumble D., Sadavoy S.,
Thomas H., Tothill N., Viti S., White G.J., Wouterloot J., Yates J., Zhu M.
<Mon. Not. R. Astron. Soc., 461, 4022-4048 (2016)>
=2016MNRAS.461.4022M 2016MNRAS.461.4022M (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Millimetric/submm sources
Keywords: stars: formation - stars: protostars - ISM: structure -
submillimetre: general - submillimetre: ISM
Abstract:
We present the JCMT Gould Belt Survey's first look results of the
southern extent of the Orion A Molecular Cloud (δ≤-5:31:27.5).
Employing a two-step structure identification process, we construct
individual catalogues for large-scale regions of significant emission
labelled as islands and smaller-scale subregions called fragments
using the 850µm continuum maps obtained using SCUBA-2. We calculate
object masses, sizes, column densities, and concentrations. We discuss
fragmentation in terms of a Jeans instability analysis and highlight
interesting structures as candidates for follow-up studies.
Furthermore, we associate the detected emission with young stellar
objects (YSOs) identified by Spitzer and Herschel. We find that
although the population of active star-forming regions contains a wide
variety of sizes and morphologies, there is a strong positive
correlation between the concentration of an emission region and its
calculated Jeans instability. There are, however, a number of highly
unstable subregions in dense areas of the map that show no evidence of
star formation. We find that only ∼72 per cent of the YSOs defined as
Class 0+I and flat-spectrum protostars coincide with dense 850µm
emission structures (column densities >3.7x1021cm-2). The
remaining 28 per cent of these objects, which are expected to be
embedded in dust and gas, may be misclassified. Finally, we suggest
that there is an evolution in the velocity dispersion of YSOs such
that sources which are more evolved are associated with higher
velocities.
Description:
The observations presented throughout this paper were performed using
the SCUBA-2 instrument (Holland et al., 2013MNRAS.430.2513H 2013MNRAS.430.2513H) as part
of the JCMT Gould Belt Survey (Ward-Thompson et al.,
2007PASP..119..855W 2007PASP..119..855W). This instrument has provided continuum coverage
at both 850um and 450um simultaneously at effective beam sizes of
14.1-arcsec and 9.6-arcsec, respectively (Dempsey et al.,
2013MNRAS.430.2534D 2013MNRAS.430.2534D). In this work, we present Southern Orion A in
both wavelengths, but focus mainly on the 850um data for analysis. All
of the observations were taken in the PONG1800 mapping mode, yielding
circular maps ('PONGs') of 0.5° in diameter. There are 17 0.5°
subregions across the Orion A Molecular Cloud, 13 of which cover
Southern Orion A. These locations were individually observed four to
six times throughout 2012 February to 2015 January, and were then
co-added (once co-added, these structures are referred to as 'tiles')
and mosaicked to form the final map.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 80 359 Observed parameters corresponding to the
850um-identified islands
table3.dat 51 359 850um-identified islands and their properties
table4.dat 93 431 850um-identified fragments and their properties
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See also:
VIII/12 : Orion A Emission-Line Surveys (Jewell+ 1989)
J/A+A/392/239 : IR survey of outflows in Orion A (Stanke+, 2002)
J/ApJ/653/383 : SCUBA obs. in Orion A South region (Johnstone+, 2006)
J/ApJ/665/1194 : Dense cores in the Orion A cloud survey (Ikeda+, 2007)
J/A+A/496/153 : Molecular hydrogen flows along Ori A cloud (Davis+, 2009)
J/AJ/144/192 : Spitzer survey of Orion A & B. YSO catalog (Megeath+, 2012)
J/A+A/564/A29 : Optical and near-infrared phot. in Orion A (Bouy+, 2014)
J/A+A/564/A68 : Orion A GMC 13CO and C18O maps (Shimajiri+, 2014)
J/ApJ/764/114 : BVRI photometry of stars in Orion A (Hsu+, 2013)
J/ApJ/768/99 : X-ray survey of YSOs in Orion A (Pillitteri+, 2013)
J/ApJ/769/149 : IR spectroscopy in Orion A: transitional disks (Kim+, 2013)
J/ApJ/790/49 : Gould's Belt VLA survey. III. Orion region (Kounkel+, 2014)
J/ApJS/217/7 : Orion A dense cores based on 1.1mm and C18O
(Shimajiri+, 2015)
J/MNRAS/449/1769 : Orion A North prestellar core properties (Salji+, 2015)
J/A+A/587/A153 : VISION I. VISTA Orion A Survey (Meingast+, 2016)
J/ApJS/226/8 : Orion A Class II objects Spitzer/IRS survey (Kim+, 2016)
J/A+A/600/A141 : Orion A integral shaped filament image (Kainulainen+, 2017)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- MJLSG Source name (JHHMMSS.s+DDMMSSI) (1)
19- 21 I3 --- IslandID [1/359] Island identification number
23- 24 I2 h RAh Right ascension (J2000) (2)
26- 27 I2 min RAm Right ascension (J2000) (2)
29- 33 F5.2 s RAs [] Right ascension (J2000) (2)
35 A1 --- DE- Declination sign (J2000) (2)
36- 37 I2 deg DEd Declination (J2000) (2)
39- 40 I2 arcmin DEm Declination (J2000) (2)
42- 46 F5.2 arcsec DEs Declination (J2000) (2)
48- 56 F9.2 arcsec+2 Area Total area of an island
58- 63 F6.2 Jy S850 Total 850um flux observed within the
island's boundaries
65- 68 F4.2 Jy/beam F850peak Maximum 850um flux value within the
island's boundaries
70- 75 F6.2 Jy S450 Total 450um flux observed within the
island's boundaries
77- 80 F4.2 Jy/beam F450peak Maximum 450um flux value within the
island's boundaries
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Note (1): The source name is based on the coordinates of the peak emission
location of each object in right ascension and declination: Jhhmmss.s+ddmmss.
Each source is also designated an 'I' to signify it is an island as opposed
to a fragment.
Note (2): The 850um map location of the brightest pixel in the island.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- IslandID [1/359] Island identification number
5- 12 E8.3 cm-2 Npeak Peak column density (1)
14- 19 F6.2 Msun Mass Mass (2)
21- 24 F4.2 pc Rad Effective radius (3)
26- 30 F5.2 --- M/MJ Mass in Jeans mass unit (4)
32- 35 F4.2 --- C Concentration (calculated using equation (4))
37- 40 F4.2 --- AR Aspect ratio of the source (5)
42- 45 F4.2 mag Ak Average K-band extinction value (6)
47- 48 I2 --- Nfrags Number of fragments associated with the island
50- 51 I2 --- Nproto Number of protostars identified by Megeath
et al. (2012, Cat. J/AJ/144/192) and
Stutz et al. (2013, Cat. J/ApJ/767/36)
within the island's boundaries
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Note (1): Peak column density calculated by using the flux density of the
brightest pixel in the island (f850,peak) in equation (2) (using the values
shown in the text).
Note (2): Mass calculated by using the total flux of the island (S850) in
equation (1) (using the standard values shown).
Note (3): Effective radius that represents the radius of a circular projection
having the same area, A, as the island: R =(A/π)0.5.
Note (4): Jeans mass calculated using the radius of the island in equation (3)
(using the standard values shown).
Note (5): It is defined as the length of the horizontal dimension divided by
the length of the vertical dimension.
Note (6): taken directly from the extinction map provided by M. Lombardi
(private communication, 2015 July 18) of each source footprint. The extinction
can be converted to column density using equation (5).
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 17 A17 --- MJLSG Source name (JHHMMSS.s+DDMMSSF) (1)
19- 21 I3 --- FragID [1/431] Fragment identification number
23- 25 I3 --- IslandID [1/356]?=- Island number
28- 29 I2 h RAh Right ascension (J2000) (2)
31- 32 I2 min RAm Right ascension (J2000) (2)
34- 38 F5.2 s RAs [] Right ascension (J2000) (2)
40 A1 --- DE- Declination sign (J2000) (2)
41- 42 I2 deg DEd Declination (J2000) (2)
44- 45 I2 arcmin DEm Declination (J2000) (2)
47- 51 F5.2 arcsec DEs Declination (J2000) (2)
53- 60 E8.3 cm-2 Npeak Peak column density (3)
62- 66 F5.2 Msun Mass Mass (4)
68- 71 F4.2 pc Rad Effective radius (5)
73- 76 F4.2 --- M/MJ Mass in Jeans mass unit (6)
78- 81 F4.2 --- C Concentration (calculated using equation (4))
83- 86 F4.2 --- AR Aspect ratio of the source (7)
88- 91 F4.2 mag Ak Average K-band extinction value (8)
93 I1 --- Nproto Number of protostars identified by Megeath et
al. (2012, Cat. J/AJ/144/192) and
Stutz et al. (2013, Cat. J/ApJ/767/36)
within the fragment's boundaries
--------------------------------------------------------------------------------
Note (1): The source name is based on the coordinates of the peak emission
location of each object in right ascension and declination: Jhhmmss.s+ddmmss.
Each source is also designated an 'F' to signify it is an fragment as
opposed to an island.
Note (2): The 850um map location of the brightest pixel in the fragment.
Note (3): peak column density is calculated by using the flux density of the
brightest pixel in the fragment (f850, peak) in equation (2) (using the
values shown in the text).
Note (4): Mass is calculated by using the total flux of the fragment (S850) in
equation (1) (using the standard values shown).
Note (5): Effective radius that represents the radius of a circular projection
having the same area, A, as the island: R =(A/π)0.5.
Note (6): The Jeans mass is calculated using the radius of the fragment in
equation (3) (using the standard values shown).
Note (7): It is defined as the length of the horizontal dimension divided by
the length of the vertical dimension.
Note (8): taken directly from the extinction map provided by M. Lombardi
(private communication, 2015 July 18) of each source footprint.
The extinction can be converted to column density using equation (5).
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 11-Dec-2017