J/ApJ/785/162 YSO candidates in the Magellanic Bridge (Chen+, 2014)
Spitzer view of massive star formation in the tidally stripped
Magellanic Bridge.
Chen C.-H.R., Indebetouw R., Muller E., Kawamura A., Gordon K.D.,
Sewilo M., Whitney B.A., Fukui Y., Madden S.C., Meade M.R., Meixner M.,
Oliveira J.M., Robitaille T.P., Seale J.P., Shiao B., van Loon J.TH.
<Astrophys. J., 785, 162 (2014)>
=2014ApJ...785..162C 2014ApJ...785..162C (SIMBAD/NED BibCode)
ADC_Keywords: YSOs ; Magellanic Clouds ; Photometry, UBVRIJKLMNH ;
Stars, masses ; Stars, ages ; Extinction
Keywords: infrared: stars - Magellanic Clouds - stars: formation -
stars: pre-main sequence
Abstract:
The Magellanic Bridge is the nearest low-metallicity, tidally stripped
environment, offering a unique high-resolution view of physical
conditions in merging and forming galaxies. In this paper, we present
an analysis of candidate massive young stellar objects (YSOs), i.e.,
in situ, current massive star formation (MSF) in the Bridge using
Spitzer mid-IR and complementary optical and near-IR photometry. While
we definitely find YSOs in the Bridge, the most massive are
∼10 M☉≪45 M☉ found in the LMC. The intensity of MSF in
the Bridge also appears to be decreasing, as the most massive YSOs are
less massive than those formed in the past. To investigate
environmental effects on MSF, we have compared properties of massive
YSOs in the Bridge to those in the LMC. First, YSOs in the Bridge are
apparently less embedded than in the LMC: 81% of Bridge YSOs show
optical counterparts, compared to only 56% of LMC sources with the
same range of mass, circumstellar dust mass, and line-of-sight
extinction. Circumstellar envelopes are evidently more porous or
clumpy in the Bridge's low-metallicity environment. Second, we have
used whole samples of YSOs in the LMC and the Bridge to estimate the
probability of finding YSOs at a given H I column density, N(H I). We
found that the LMC has ∼3xhigher probability than the Bridge for
N(H I)>12x1020/cm2, but the trend reverses at lower N(H I).
Investigating whether this lower efficiency relative to H I is due to
less efficient molecular cloud formation or to less efficient cloud
collapse, or to both, will require sensitive molecular gas observations.
Description:
The Spitzer observations of the Bridge were obtained as part of the
Legacy Program "Surveying the Agents of Galaxy Evolution in the
Tidally-Stripped, Low-Metallicity Small Magellanic Cloud" (SAGE-SMC;
Gordon et al. 2011AJ....142..102G 2011AJ....142..102G). These observations included images
taken at 3.6, 4.5, 5.8, and 8.0 um bands with the InfraRed Array
Camera (IRAC) and at 24, 70, and 160 um bands with the Multiband
Imaging Photometer for Spitzer (MIPS). The details of data processing
are given in Gordon et al. (2011AJ....142..102G 2011AJ....142..102G). To construct
multi-wavelength SEDs for sources in the Spitzer catalog, we have
expanded it by adding photometry from optical and NIR surveys covering
the Bridge, i.e., BRI photometry from the Super COSMOS Sky Surveys
(SSS; Hambly et al. 2001MNRAS.326.1279H 2001MNRAS.326.1279H) and JHKs photometry from the
Two Micron All Sky Survey (2MASS; Skrutskie et al. 2006AJ....131.1163S 2006AJ....131.1163S,
Cat. VII/233).
Objects:
------------------------------------------------------------------------
RA (ICRS) DE Designation(s)
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03 11 -77.5 Magellanic Bridge = NAME Magellanic Bridge
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 99 60 Multi-wavelength Photometry for lambda>3 mum
of YSO Candidates Selected from CMD Criteria
table2.dat 101 60 Multi-wavelength Photometry for lambda<3 mum
of YSO Candidates Selected from CMD Criteria
table3.dat 134 26 Inferred Physical Parameters from SED Fits
to YSOs
table4.dat 121 83 Inferred Physical Parameters from SED Fits
to Fainter YSO Candidates
table5.dat 121 96 Inferred Physical Parameters from SED Fits
to HAeBe Candidates
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See also:
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
J/ApJS/101/41 : SMC and Bridge extended catalog (Bica+ 1995)
J/A+A/551/A78 : The Magellanic Bridge Catalogue of Stars - MBCS
(Bagheri+, 2013)
J/ApJ/795/108 : Stellar populations in the Magellanic bridge (Skowron+, 2014)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 20 A20 --- Name Source name (JHHMMSS.ss+DDMMSS.ss)
22- 23 I2 --- Rank [1/60] Ranking of the brightness at 8 micron
25- 29 F5.2 mag 3.6mag ? Spitzer/IRAC 3.6 micron band magnitude
31- 34 F4.2 mag e_3.6mag ? Error in 3.6mag (G1)
36- 40 F5.2 mag 4.5mag Spitzer/IRAC 4.5 micron band magnitude
42- 45 F4.2 mag e_4.5mag Error in 4.5mag (G1)
47- 51 F5.2 mag 5.8mag ? Spitzer/IRAC 5.8 micron band magnitude
53- 56 F4.2 mag e_5.8mag ? Error in 5.8mag (G1)
58- 62 F5.2 mag 8.0mag Spitzer/IRAC 8.0 micron band magnitude
64- 67 F4.2 mag e_8.0mag Error in 8.0mag (G1)
69- 72 F4.2 mag 24mag ? Spitzer/MIPS 24 micron band magnitude
74- 77 F4.2 mag e_24mag ? Error in 24mag (G1)
79- 83 F5.2 mag 70mag ? Spitzer/MIPS 70 micron band magnitude
85- 88 F4.2 mag e_70mag ? Error in 70mag (G1)
90- 95 A6 --- Class Classification (G2)
97- 99 A3 --- Remark Remark (G3)
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 20 A20 --- Name Source name (JHHMMSS.ss+DDMMSS.ss)
22- 23 I2 --- Rank [1/60] Ranking of the brightness at 8 micron
25- 29 F5.2 mag Bmag ? SSS B band magnitude
31- 34 F4.2 mag e_Bmag ? Error in Bmag (G1)
36- 40 F5.2 mag Rmag ? SSS R band magnitude
42- 45 F4.2 mag e_Rmag ? Error in Rmag (G1)
47- 52 F6.2 mag Imag ? SSS I band magnitude
54- 57 F4.2 mag e_Imag ? Error in Imag (G1)
59- 63 F5.2 mag Jmag ? 2MASS J band magnitude
65- 68 F4.2 mag e_Jmag ? Error in Jmag (G1)
70- 74 F5.2 mag Hmag ? 2MASS H band magnitude
76- 79 F4.2 mag e_Hmag ? Error in Hmag (G1)
81- 85 F5.2 mag Ksmag ? 2MASS KS band magnitude
87- 90 F4.2 mag e_Ksmag ? Error in Ksmag (G1)
92- 97 A6 --- Class Classification (G2)
99-101 A3 --- Remark Remark (G3)
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 20 A20 --- Name Source name (JHHMMSS.ss+DDMMSS.ss)
22- 26 F5.2 mag 8.0mag Spitzer/IRAC 8.0 micron band magnitude
28- 33 A6 --- Type YSO type (G2)
35- 37 F3.1 --- SR Stage range (G4)
39- 41 F3.1 --- e_SR Error in SR
43- 46 F4.1 Msun M* Central stellar mass
48- 50 F3.1 Msun e_M* Error in M*
52- 58 E7.2 Lsun L Total luminosity
60- 66 E7.2 Lsun e_L Error in L
68- 74 E7.2 Msun/yr Menv Envelope accretion rate
76- 82 E7.2 Msun/yr e_Menv Error in Menv
84- 90 E7.2 Rsun Mdisk Disk mass
92- 98 E7.2 Rsun e_Mdisk Error in Mdisk
100-106 E7.2 yr Age Central stellar age
108-114 E7.2 yr e_Age Error in Age
116-119 F4.1 mag AV Foreground extinction
121-124 F4.1 mag e_AV Error in AV
126-129 F4.1 deg Inc Inclination angle
131-134 F4.1 deg e_Inc Error in Inc
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Byte-by-byte Description of file: table4.dat table5.dat
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Bytes Format Units Label Explanations
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1- 20 A20 --- Name Source name (JHHMMSS.ss+DDMMSS.ss)
22- 25 F4.1 Msun M* Central stellar mass
27- 29 F3.1 Msun e_M* ? Uncertainty in M* (1)
31- 37 E7.1 Lsun L Total luminosity
39- 45 E7.1 Lsun e_L ? Uncertainty in L (1)
47- 53 E7.1 Msun/yr Menv Envelope accretion rate
55- 61 E7.1 Msun/yr e_Menv ? Uncertainty in Menv (1)
63- 69 E7.1 Msun Mdisk Disk mass
71- 77 E7.1 Msun e_Mdisk ? Uncertainty in Mdisk (1)
79- 81 F3.1 --- SR Stage range (G4)
83- 85 F3.1 --- e_SR ? Uncertainty in SR (1)
87- 93 E7.1 yr Age Central stellar age
95-101 E7.1 yr e_Age ? Uncertainty in Age (1)
103-106 F4.1 mag AV Foreground extinction
108-111 F4.1 mag e_AV ? Uncertainty in AV (1)
113-116 F4.1 deg Inc Inclination angle
118-121 F4.1 deg e_Inc ? Uncertainty in Inc (1)
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Note (1): The uncertainties are calculated as the weighted standard deviation
of these quantities of all of the acceptable YSO models. In cases
where there is only one acceptable model for a given source, an
uncertainty cannot be calculated this way so the corresponding space
is left blank.
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Global notes:
Note (G1): The uncertainties listed here are only errors in measurements and do
not include errors in flux calibration, i.e., 5% in 3.6, 4.5, 5.8, and
8.0 mum, 10% in 24 mum, 20% in 70 mum, and 10% in BRIJHKs. Thus, the total
uncertainty of a flux is the quadratic sum of the measurement error and
the calibration error.
Note (G2): Classification as follows:
G = Background galaxy;
I/II/III = Type I/II/III YSO;
mul = Multiple.
Note (G3): Remark as follows:
mul = Multiple;
ext = Extended source.
Note (G4): Stage Range is the weighted standard deviation of the stages
determined from each of the acceptable models for a YSO.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 15-Jun-2017