J/ApJS/212/2 Giant molecular clouds in the 4th Galactic quadrant (Garcia+, 2014)
Giant molecular clouds and massive star formation in the southern Milky Way.
Garcia P., Bronfman L., Nyman L.-A., Dame T.M., Luna A.
<Astrophys. J. Suppl. Ser., 212, 2 (2014)>
=2014ApJS..212....2G 2014ApJS..212....2G
ADC_Keywords: Molecular clouds ; Milky Way ; Infrared sources ; H II regions
Keywords: galaxies: spiral; Galaxy: structure; ISM: clouds; stars: massive
Abstract:
The Columbia University-Universidad de Chile CO Survey of the southern
Milky Way is used to separate the CO(1-0) emission of the fourth
Galactic quadrant within the solar circle into its dominant
components, giant molecular clouds (GMCs). After the subtraction of an
axisymmetric model of the CO background emission in the inner southern
Galaxy, 92 GMCs are identified, and for 87 of them the twofold
distance ambiguity is solved. Their total molecular mass is
M(H2)=1.14±0.05x108M☉, accounting for around 40% of the
molecular mass estimated from an axisymmetric analysis of the H2
volume density in the Galactic disk, M(H2)disk=3.03x108M☉.
The large-scale spiral structure in the southern Galaxy, within the
solar circle, is traced by the GMCs in our catalog; three spiral arm
segments, the Centaurus, Norma, and 3 kpc expanding arm, are analyzed.
After fitting a logarithmic spiral arm model to the arms, tangent
directions at 310°, 330°, and 338°, respectively, are
found, consistent with previous values from the literature. A complete
CS(2-1) survey toward IRAS point-like sources with far-IR colors
characteristic of ultracompact H II regions is used to estimate the
massive star formation rate per unit H2 mass (MSFR) and the massive
star formation efficiency (ε) for GMCs. The average MSFR for
GMCs is 0.41±0.06L☉/M☉, and for the most massive clouds
in the Norma arm it is 0.58±0.09L☉/M☉. Massive star
formation efficiencies of GMCs are, on average, 3% of their available
molecular mass.
Description:
The data used are part of the Columbia-Universidad de Chile
12CO(J=1->0) surveys. These surveys provide us with the most
extensive and homogeneous observational data set of CO emission in the
Galactic disk (Grabelsky et al. 1987ApJ...315..122G 1987ApJ...315..122G; Bronfman et al.
1989ApJS...71..481B 1989ApJS...71..481B; Dame et al. 1986ApJ...305..892D 1986ApJ...305..892D; Luna et al.
2006ApJ...641..938L 2006ApJ...641..938L).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 58 92 Giant molecular clouds in the fourth Galactic
quadrant, within the solar circle
table4.dat 22 60 Far-IR luminosity and massive star formation
efficiency for giant molecular clouds (GMCs)
table5.dat 38 92 Peak antenna temperature and molecular mass derived
from the model subtracted data set (MSD) and GMCs
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See also:
VII/216 : H-alpha emission regions in Southern Milky Way (Rodgers+ 1960)
J/MNRAS/437/1791 : RMS survey: molecular observations (Urquhart+, 2014)
J/MNRAS/420/1656 : RMS compact HII regions distances (Urquhart+, 2012)
J/ApJ/699/1153 : Kinematic dist. to GRS molecular clouds (Roman-Duval+, 2009)
J/ApJ/699/1092 : Giant molecular clouds (SRBY) (Heyer+, 2009)
J/MNRAS/366/1096 : Kinematic distance ambiguity (Busfield+, 2006)
J/A+A/397/133 : Star-forming complexes in the Galaxy (Russeil+, 2003)
J/MNRAS/291/261 : Methanol maser of IRAS-selected sources (Walsh+ 1997)
J/A+AS/115/81 : A CS(2-1) survey of UC HII regions (Bronfman+, 1996)
J/A+A/275/67 : Velocity Field of the outer Galaxy (Brand+ 1993)
J/A+A/171/261 : RRLs of Southern HII Regions (Caswell+ 1987)
J/ApJS/63/821 : Inner Galaxy Molecular clouds & cloud cores (Scoville+, 1987)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq [1/92] Cloud running sequence number
4- 10 F7.3 deg GLON [302.1/347.3] Galactic longitude (1)
12- 17 F6.3 deg GLAT [-1.3/1.3] Galactic latitude (1)
19- 24 F6.1 km/s Vlsr [-129.3/-7.8] LSR velocity
26 A1 --- f_Vlsr [*] Flag on Vlsr (2)
28- 31 F4.1 km/s DV [4/18.4] Line width (ΔV(FWHM)) of the GMC
composite spectrum
33- 36 F4.1 kpc D [1.8/12.5]? Heliocentric kinematic distance (3)
38 A1 --- n_D Adopted distance (N=near, F=far, and T=tangent)
40- 44 A5 --- f_D Method(s) used for the distance estimation (4)
46- 48 I3 pc R [16/131]? Linear radius (5)
50- 53 F4.2 [Msun] Mvir [4.9/6.9]? Log virial mass (3)
55- 58 F4.2 [Msun] M(H2) [4.9/7]? Log molecular mass M(H2) (3)
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Note (1): The Galactic longitude l and Galactic latitude b of the CO peak
intensity in the spatial map of each GMC (as described in Figure 4).
Note (2):
* = The CO radial velocity of the cloud was corrected by +12.2km/s in order to
take into account the unusual velocity excess toward terminal velocities
up to galactocentric longitude 312° reported by Alvarez
et al. (1990ApJ...348..495A 1990ApJ...348..495A).
Note (3): Blank values indicate that the two-fold distance ambiguity could not
be removed for these clouds.
Note (4): The letters represent the method in which the two-fold distance
ambiguity was removed as follows:
a = Spatial association with optical objects from the RCW catalog (Rodgers
et al. 1960, Cat. VII/216) or visual optical counterparts
(Caswell & Haynes 1987, Cat. J/A+A/171/261).
b = IRAS/CS source associated to the cloud with distance ambiguity already
removed.
c = Observational size-to-linewidth relationship (Larson's Law).
d = Latitude criterion.
e = CO radial velocity of the cloud close (|v|<10km/s) to the tangential
velocity.
f = Presence or absence of absorption features from species like H2CO or
OH against the Hα continuum emission from HII regions, or cold
(10-30K) HI absorption against the warm (100-104K) HI continuum background.
g = Continuity of spiral arm.
Note (5): Radius for each GMC, defined as R=RangxD, with Rang being the
effective angular radius defined as πRang2=Aang and Aang
being the angular area. See section 2.3.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq [1/88] Cloud running sequence number
4- 5 I2 --- N [1/14] Number of UC HII associated with the
cloud
7- 12 I6 Lsun/kpc2 Firas [254/218249] Total FIR flux FIRAS of the
massive-star-forming regions associated
with the GMC (7)
14- 17 F4.2 [Lsun] Liras [3.24/6.81]? log FIR luminosity
(LFIR=FIRASD2; log(L/L☉))
19- 22 F4.1 % SFE [0/10.7]? Massive star formation efficiency (8)
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Note (7): The FIR flux of each UC HII region was derived directly from the
fluxes reported in the four bands of the IRAS point-like catalog
(version 1) as: FIRAS=4πΣ(νFν) (equation 12).
Note (8): The massive star formation efficiency ε is defined
in section 4.2:
ε = τOB(dM/dt)/MGMC, where
τOB = 108yr (ifetime for an OB star)
dM/dt = massive star formation rate (in M_☉/yr)
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq [1/92] Cloud running sequence number
4- 10 F7.3 deg GLON [302.1/347.3] Galactic longitude
12- 17 F6.3 deg GLAT [-1.3/1.3] Galactic latitude
19- 22 F4.2 K Tp(MSD) [0.1/8.5] Model subtracted data (MSD) peak
temperature (KΔlΔb) (6)
24- 27 F4.2 [Msun] MH2(MSD) [4.5/6.7]? MSD molecular mass M(H2) (6)
29- 33 F5.2 K Tp(GMC) [0.2/17.6] GMC peak temperature
(KΔlΔb)
35- 38 F4.2 [Msun] MH2(GMC) [4.9/7]? GMC molecular mass M(H2)
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Note (6): See Appendix A for further explanation about the Model Subtraction.
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Nomenclature Notes:
The GMCs are <[GBN2014] NN> = <[GBN2014] GMC GLLL.lll+BB.bbb> in Simbad.
History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 03-Jun-2014