J/MNRAS/490/832 Young stellar population of metal-poor NGC 6822 (Jones+, 2019)
The young stellar population of the metal-poor galaxy NGC 6822.
Jones O.C., Sharp M.J., Reiter M., Hirschauer A.S., Meixner M.,
Srinivasan S.
<Mon. Not. R. Astron. Soc., 490, 832-847 (2019)>
=2019MNRAS.490..832J 2019MNRAS.490..832J (SIMBAD/NED BibCode)
ADC_Keywords: YSOs ; Star Forming Region ; Stars, pre-main sequence ;
Galaxies, nearby ; Photometry, infrared ; Stars, diameters ;
Effective temperatures
Keywords: stars: formation - stars: pre-main-sequence
galaxies: individual: (NGC 6822) - Local Group -
galaxies: photometry - galaxies: stellar content
Abstract:
We present a comprehensive study of massive young stellar objects
(YSOs) in the metal-poor galaxy NGC 6822 using IRAC and MIPS data
obtained from the Spitzer Space Telescope. We find over 500 new YSO
candidates in seven massive star formation regions; these sources were
selected using six colour-magnitude cuts. Via spectral energy
distribution fitting to the data with YSO radiative transfer models we
refine this list, identifying 105 high-confidence and 88
medium-confidence YSO candidates. For these sources, we constrain
their evolutionary state and estimate their physical properties. The
majority of our YSO candidates are massive protostars with an
accreting envelope in the initial stages of formation. We fit the mass
distribution of the Stage I YSOs with a Kroupa initial mass function
and determine a global star formation rate of 0.039M☉/yr. This
is higher than star formation rate estimates based on integrated UV
fluxes. The new YSO candidates are preferentially located in clusters
which correspond to seven active high-mass star-formation regions
which are strongly correlated with the 8 and 24µm emission from
PAHs and warm dust. This analysis reveals an embedded high-mass star
formation region, Spitzer I, which hosts the highest number of massive
YSO candidates in NGC 6822. The properties of Spitzer I suggest it is
younger and more active than the other prominent HII and
star-formation regions in the galaxy.
Description:
There is excellent wide-field coverage of NGC 6822 in the optical to
mid-IR. We use these deep, uniform photometric catalogues to produce a
combined multiwavelength data set from which we identify YSO
candidates and assess potential contamination from other populations
of sources.
Near-IR JHK photometry covering an area of 3deg2 was taken from
Sibbons et al. (2012A&A...540A.135S 2012A&A...540A.135S, Cat. J/A+A/540/A135). They
observed NGC 6822 with the Wide Field CAMera (WFCAM) on the 3.8m
United Kingdom Infrared Telescope (UKIRT). This data is complete to a
depth of 19.5mag in the J band and 18.7 in K. In the mid-IR, NGC 6822
was observed with Spitzer Infrared Array Camera (IRAC) and Multiband
Imaging Photometer for Spitzer (MIPS) as part of the Spitzer Infrared
Nearby Galaxies Survey (SINGS; Kennicutt et al. 2003PASP..115..928K 2003PASP..115..928K).
Using six mid-IR colour-cuts we find over 500 YSO candidates in seven
massive star formation regions. This is the first catalogue of young
embedded stars in the process of formation identified in the galaxy.
Removing known contaminants and through multiwavelength SED fitting to
the data with the Robitaille et al. (2006ApJS..167..256R 2006ApJS..167..256R) and
Robitaille (2017A&A...600A..11R 2017A&A...600A..11R) models, we compile a robust inventory
of 105 high-confidence and 88 medium-confidence YSO candidates (see
Tables 2 and 3). The majority of these sources are Stage I YSOs with
an accreting envelope in the initial stages of formation. For these
sources, we also determine the YSO mass and bolometric luminosity from
the effective temperature and radius (Table 8).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 126 105 Table of photometry for the high-confidence
YSO Candidates
table3.dat 126 88 Table of photometry for the medium-confidence
YSO Candidates
table4.dat 126 588 Magnitudes and uncertainties for the possible
YSO Candidates
table7.dat 52 103 Physical Parameters of YSO Candidates fit with
the Robitaille et al. (2006ApJS..167..256R 2006ApJS..167..256R)
models
table8.dat 64 103 Physical Parameters of YSO Candidates fit with
the Robitaille (2017A&A...600A..11R 2017A&A...600A..11R) models
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See also:
J/A+A/540/A135 : AGB population of NGC 6822 (Sibbons+, 2012)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID [10/578] Source identifier
5- 12 F8.4 deg RAdeg Right ascension (J2000)
14- 20 F7.3 deg DEdeg Declination (J2000)
22- 27 F6.2 mag Jmag ?=-99.99 WFCAM J-band magnitude
29- 34 F6.2 mag e_Jmag ?=-99.99 Error on Jmag
36- 41 F6.2 mag Hmag ?=-99.99 WFCAM H-band magnitude
43- 48 F6.2 mag e_Hmag ?=-99.99 Error on Hmag
50- 55 F6.2 mag Kmag ?=-99.99 WFCAM K-band magnitude
57- 62 F6.2 mag e_Kmag ?=-99.99 Error on Kmag
64- 68 F5.2 mag 3.6mag Spitzer/IRAC 3.6um band magnitude
70- 73 F4.2 mag e_3.6mag Error on 3.6mag
75- 79 F5.2 mag 4.5mag Spitzer/IRAC 4.5um band magnitude
81- 84 F4.2 mag e_4.5mag Error on 4.5mag
86- 90 F5.2 mag 5.8mag Spitzer/IRAC 5.8um band magnitude
92- 95 F4.2 mag e_5.8mag Error on 5.8mag
97-101 F5.2 mag 8.0mag Spitzer/IRAC 8.0um band magnitude
103-106 F4.2 mag e_8.0mag Error on 8.0mag
108-112 F5.2 mag 24mag Spitzer/MIPS 24um band magnitude
114-117 F4.2 mag e_24mag Error on 24mag
119 I1 --- CMD [3-6] CMD score (1)
121 A1 --- PAH [01] PAH flag (2)
123 A1 --- Photosph [01] Stellar Photosphere flag (3)
125-126 I2 --- Cluster [-1/6] Cluster Membership flag (4)
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Note (1): CMD score as follows:
3 = Reliable YSO candidate, the object meets the YSO colour-criteria in 3
of the 6 mid-IR CMDs used to select YSO candidates (17/105)
4 = Reliable YSO candidate, the object meets the YSO colour-criteria in 4
of the 6 mid-IR CMDs used to select YSO candidates (20/105)
5 = Reliable YSO candidate, the object meets the YSO colour-criteria in 5
of the 6 mid-IR CMDs used to select YSO candidates (11/105)
6 = Reliable YSO candidate, the object meets the YSO colour-criteria in 6
of the 6 mid-IR CMDs used to select YSO candidates (57/105)
Note (2): PAH flag as follows:
0 = No PAH enhancement (23/105)
1 = Strong PAH emission (82/105)
Note (3): Stellar Photosphere flag as follows:
0 = Stellar photosphere not present (96/105)
1 = Possible presence of a stellar photosphere (9/105)
Note (4): Cluster membership as follows:
-1 = No cluster membership (42/105)
0 = Hubble I/III star-forming cluster (9/105)
1 = Spitzer III star-forming cluster (5/105)
2 = Hubble IV star-forming cluster (14/105)
3 = Hubble V star-forming cluster (12/105)
4 = Spitzer I star-forming cluster (12/105)
5 = Hubble X star-forming cluster (7/105)
6 = Spitzer II star-forming cluster (4/105)
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID [1/583] Source identifier
5- 12 F8.4 deg RAdeg Right ascension (J2000)
14- 20 F7.3 deg DEdeg Declination (J2000)
22- 27 F6.2 mag Jmag ?=-99.99 WFCAM J-band magnitude
29- 34 F6.2 mag e_Jmag ?=-99.99 Error on Jmag
36- 41 F6.2 mag Hmag ?=-99.99 WFCAM H-band magnitude
43- 48 F6.2 mag e_Hmag ?=-99.99 Error on Hmag
50- 55 F6.2 mag Kmag ?=-99.99 WFCAM K-band magnitude
57- 62 F6.2 mag e_Kmag ?=-99.99 Error on Kmag
64- 68 F5.2 mag 3.6mag Spitzer/IRAC 3.6um band magnitude
70- 73 F4.2 mag e_3.6mag Error on 3.6mag
75- 79 F5.2 mag 4.5mag Spitzer/IRAC 4.5um band magnitude
81- 84 F4.2 mag e_4.5mag Error on 4.5mag
86- 90 F5.2 mag 5.8mag Spitzer/IRAC 5.8um band magnitude
92- 95 F4.2 mag e_5.8mag Error on 5.8mag
97-101 F5.2 mag 8.0mag Spitzer/IRAC 8.0um band magnitude
103-106 F4.2 mag e_8.0mag Error on 8.0mag
108-112 F5.2 mag 24mag Spitzer/MIPS 24um band magnitude
114-117 F4.2 mag e_24mag Error on 24mag
119 I1 --- CMD [3-6] CMD score (1)
121 A1 --- PAH [01] PAH flag (2)
123 A1 --- Photosph [01] Stellar Photosphere flag (3)
125-126 I2 --- Cluster [-1/6] Cluster Membership flag (4)
--------------------------------------------------------------------------------
Note (1): CMD score as follows:
3 = Reliable YSO candidate, the object meets the YSO colour-criteria in 3
of the 6 mid-IR CMDs used to select YSO candidates (11/88)
4 = Reliable YSO candidate, the object meets the YSO colour-criteria in 4
of the 6 mid-IR CMDs used to select YSO candidates (18/88)
5 = Reliable YSO candidate, the object meets the YSO colour-criteria in 5
of the 6 mid-IR CMDs used to select YSO candidates (15/88)
6 = Reliable YSO candidate, the object meets the YSO colour-criteria in 6
of the 6 mid-IR CMDs used to select YSO candidates (44/88)
Note (2): PAH flag as follows:
0 = No PAH enhancement (53/88)
1 = Strong PAH emission (35/88)
Note (3): Stellar Photosphere flag as follows:
0 = Stellar photosphere not present (68/88)
1 = Possible presence of a stellar photosphere (20/88)
Note (4): Cluster membership as follows:
-1 = No cluster membership (54/88)
0 = Hubble I/III star-forming cluster (6/88)
1 = Spitzer III star-forming cluster (2/88)
2 = Hubble IV star-forming cluster (8/88)
3 = Hubble V star-forming cluster (2/88)
4 = Spitzer I star-forming cluster (12/88)
5 = Hubble X star-forming cluster (1/105)
6 = Spitzer II star-forming cluster (3/105)
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Byte-by-byte Description of file:table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.4 deg RAdeg Right ascension (J2000)
10- 17 F8.4 deg DEdeg Declination (J2000)
19- 24 F6.2 mag Jmag ?=-99.99 WFCAM J-band magnitude
26- 31 F6.2 mag e_Jmag ?=-99.99 Error on Jmag
33- 38 F6.2 mag Hmag ?=-99.99 WFCAM H-band magnitude
40- 45 F6.2 mag e_Hmag ?=-99.99 Error on Hmag
47- 52 F6.2 mag Kmag ?=-99.99 WFCAM K-band magnitude
54- 59 F6.2 mag e_Kmag ?=-99.99 Error on Kmag
61- 65 F5.2 mag 3.6mag Spitzer/IRAC 3.6um band magnitude
67- 70 F4.2 mag e_3.6mag Error on 3.6mag
72- 76 F5.2 mag 4.5mag Spitzer/IRAC 4.5um band magnitude
78- 81 F4.2 mag e_4.5mag Error on 4.5mag
83- 87 F5.2 mag 5.8mag Spitzer/IRAC 5.8um band magnitude
89- 94 F6.2 mag e_5.8mag ?=-99.99 Error on 5.8mag
96-100 F5.2 mag 8.0mag Spitzer/IRAC 8.0um band magnitude
102-107 F6.2 mag e_8.0mag ?=-99.99 Error on 8.0mag
109-113 F5.2 mag 24mag Spitzer/MIPS 24um band magnitude
115-120 F6.2 mag e_24mag ?=-99.99 Error on 24mag
122 A1 --- CMD [0-6] CMD score (1)
124 A1 --- PAH [01] PAH flag (2)
126 A1 --- Photosph [01] Stellar Photosphere flag (3)
--------------------------------------------------------------------------------
Note (1): CMD score as follows:
0 = The object meets the YSO colour-criteria in none of the 6 mid-IR CMDs
used to select YSO candidates (6/588)
2 = Possible YSO candidate, the object meets the YSO colour-criteria in 2
of the 6 mid-IR CMDs used to select YSO candidates (220/588)
3 = Reliable YSO candidate, the object meets the YSO colour-criteria in 3
of the 6 mid-IR CMDs used to select YSO candidates (109/588)
4 = Reliable YSO candidate, the object meets the YSO colour-criteria in 4
of the 6 mid-IR CMDs used to select YSO candidates (149/588)
5 = Reliable YSO candidate, the object meets the YSO colour-criteria in 5
of the 6 mid-IR CMDs used to select YSO candidates (29/588)
6 = Reliable YSO candidate, the object meets the YSO colour-criteria in 6
of the 6 mid-IR CMDs used to select YSO candidates (75/588)
Note (2): PAH flag as follows:
0 = No PAH enhancement (472/588)
1 = Strong PAH emission (116/588)
Note (3): Stellar Photosphere flag as follows:
0 = Stellar photosphere not present (126/588)
1 = Possible presence of a stellar photosphere (236/588)
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Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID [10/578] Source identifier
5- 12 F8.4 deg RAdeg Right ascension (J2000)
14- 20 F7.3 deg DEdeg Declination (J2000)
22- 25 F4.2 --- chi2 Chi-squared of the fit
27- 30 I4 --- nfits Number of well-fitting models
32- 33 I2 Msun M* Best fit YSO candidate mass
35- 36 I2 Msun e_M* Error on M*
38- 43 I6 Lsun L* Best fit YSO candidate total luminosity
45- 50 I6 Lsun e_L* Error on L*
52 I1 --- Stage [1/3] Evolutionary stage (1)
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Note (1): Stage as follows:
1 = Stage I YSO dMenv/dt>10-6M*/yr (89/103)
2 = Stage II YSO dMenv/dt<10-6M*/yr and Mdisc/M*>10-6 (3/103)
3 = Stage III YSO Mdisc/M*<10-6 and dMenv/dt<10-6M*/yr (11/103)
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Byte-by-byte Description of file: table8.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID [10/578] Source identifier
5- 12 F8.4 deg RAdeg Right ascension (J2000)
14- 20 F7.3 deg DEdeg Declination (J2000)
22- 28 A7 --- modset Best Robitaille (2017A&A...600A..11R 2017A&A...600A..11R) model
set
30- 32 I3 --- nfits Number of best-fitting models from the
most-likely model set
34- 35 I2 Rsun R* Best fit YSO candidate radius
37- 38 I2 Rsun e_R* Error on R*
40- 44 I5 K Teff Best fit YSO candidate effective temperature
46- 50 I5 K e_Teff Error on Teff
52- 57 I6 Lsun L* Best fit YSO candidate total luminosity
59- 64 I6 Lsun e_L* Error on L*
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 25-Jan-2023