J/ApJ/833/229 Star forming cloud-giant molecular cloud complexes (Lee+, 2016)
Observational evidence of dynamic star formation rate in Milky Way giant
molecular clouds.
Lee E.J., Miville-Deschenes M.-A., Murray N.W.
<Astrophys. J., 833, 229-229 (2016)>
=2016ApJ...833..229L 2016ApJ...833..229L (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Velocity dispersion ; Carbon monoxide ;
Interstellar medium
Keywords: galaxies: star formation; ISM: clouds
Abstract:
Star formation on galactic scales is known to be a slow process, but
whether it is slow on smaller scales is uncertain. We cross-correlate
5469 giant molecular clouds (GMCs) from a new all-sky catalog with 256
star-forming complexes (SFCs) to build a sample of 191 SFC-GMC
complexes-collections of multiple clouds each matched to 191 SFCs. The
total mass in stars harbored by these clouds is inferred from WMAP
free-free fluxes. We measure the GMC mass, the virial parameter, the
star formation efficiency ε and the star formation rate per
freefall time εff. Both ε and εff range
over 3-4 orders of magnitude. We find that 68.3% of the clouds fall
within σlogε=0.79±0.22dex and
σlogεff=0.91±0.22dex about the median. Compared to
these observed scatters, a simple model with a time-independent
εff that depends on the host GMC properties predicts
σlogεff=0.12-0.24. Allowing for a time-variable
εff, we can recover the large dispersion in the rate of star
formation. This strongly suggests that star formation in the Milky Way
is a dynamic process on GMC scales. We also show that the surface star
formation rate profile of the Milky Way correlates well with the
molecular gas surface density profile.
Description:
We cross-correlate the star-forming complexes (SFCs) in Lee+ (2012,
J/ApJ/752/146) with the catalog of giant molecular clouds (GMCs)
Miville-Deschenes+ (MML16; 2017, J/ApJ/834/57).
See section 2 for the explanations.
The result is 191 unique SFCs matched to 389 unique GMCs, recovering
93.5% of the total SFC free-free luminosity, 83.8% of the total SFC
free-free flux, and 9% of the total GMC gas mass.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 103 389 *MML16-SFC match (sorted by SFC luminosities)
table2.dat 75 191 SFC-GMC complexes (sorted by luminosities)
table3.dat 82 191 Star formation properties of SFC-GMC complexes
and unmatched clouds more massive than
104.75Msun (sorted by ionizing luminosities)
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Note on table1.dat: MML16 = Miville-Deschenes+ (2017, J/ApJ/834/57);
star-forming complexes (SFCs) from Lee+ (2012, J/ApJ/752/146).
See section 2 for further explanations.
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See also:
J/ApJ/834/57 : MW molecular clouds from 12CO (Miville-Deschenes+, 2017)
J/ApJ/831/73 : Galactic MCs associated with HII reg. (Vutisalchavakul+, 2016)
J/MNRAS/458/3479 : SVM selection of WISE YSO Candidates (Marton+, 2016)
J/A+A/588/A29 : Star formation in massive clumps in Milky Way (Heyer+, 2016)
J/ApJS/212/2 : GMCs in the 4th Galactic quadrant (Garcia+, 2014)
J/ApJ/779/113 : IR photometry of YSOs in the W40 region (Mallick+, 2013)
J/A+A/560/A76 : Stellar clusters in the inner Galaxy (Morales+, 2013)
J/ApJ/752/146 : Star forming complexes in Galactic WMAP sources (Lee+, 2012)
J/ApJ/748/14 : ONC population data from WFI observations (Da Rio+, 2012)
J/ApJS/194/12 : Trumpler 16 in the CCCP (Wolk+, 2011)
J/ApJ/723/1019 : Galactic SFR and gas surface densities (Heiderman+, 2010)
J/ApJ/719/1104 : Massive star forming complexes in GLIMPSE (Rahman+, 2010)
J/ApJ/709/424 : HII regions identified with WMAPS and GLIMPSE (Murray+, 2010)
J/ApJ/699/1092 : Giant molecular clouds (SRBY) (Heyer+, 2009)
J/ApJS/181/321 : Properties of Spitzer c2d dark clouds (Evans+, 2009)
J/ApJ/688/1142 : Star formation in W5: Spitzer observations (Koenig+, 2008)
J/A+A/404/223 : 2MASS IR star clusters in the Galaxy (Bica+, 2003)
J/ApJ/428/693 : Rosette Nebula and Maddalena Cloud structures (Williams+ 1994)
J/A+A/275/67 : Velocity Field of the outer Galaxy (Brand+ 1993)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 I5 -- GMCno [13/19689] GMC record number (1)
7- 14 F8.4 deg GLONg Galactic longitude of GMC
16- 21 F6.4 deg Sigl [0.08/0.7] RMS dispersion in galactic longitude
of GMC (σl)
23- 29 F7.4 deg GLATg Galactic latitude of GMC
31- 36 F6.4 deg Sigb [0.08/0.6] RMS dispersion in galactic latitude
of GMC (σb)
38- 44 F7.2 km/s Vlsrg [-122/113] LSR velocity centroid of GMC
46- 50 F5.2 km/s SigV [0.8/16] RMS velocity dispersion of GMC
(σV)
52- 56 F5.2 kpc Distg [0.4/16] Kinematic distance to GMC
58- 60 I3 -- SFCno [0/277] Matched SFC record number (1)
62- 69 F8.4 deg GLONs Galactic longitude of SFC
71- 77 F7.4 deg GLATs Galactic latitude of SFC
79- 82 F4.2 deg Rad [0.01/2.2] Geometric mean radius of SFC
84- 90 F7.2 km/s Vlsrs [-122/112] LSR mean velocity of SFC
92- 96 F5.2 km/s ExpV [2.7/49] Expansion velocity of SFC
98-103 F6.3 kpc Dists [0.4/16] Kinematic distance to SFC
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Note (1): Coordinates and velocities of star-forming complexes (SFCs;
Lee+, 2012, J/ApJ/752/146) and MML16
(Miville-Deschenes+ 2017, J/ApJ/834/57) giant molecular clouds (GMCs)
matched to each other.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 -- SFCno [0/277] SFC record number (1)
5- 10 F6.2 deg GLON Mass-weighted mean galactic longitude
12- 16 F5.2 deg GLAT Mass-weighted mean galactic latitude
18- 24 F7.2 km/s Vmean [-122/110] Mass-weighted mean velocity
26- 30 F5.2 km/s SigV [1.2/22.2] Mass-weighted velocity dispersion
32- 35 F4.2 deg Rang [0.1/1] Geometric mean angular radius (Rang) (2)
37- 40 F4.2 deg MaxAxis [0.2/1.3] Maximum eigenvalue of
moment of inertia matrix (Rmax)
42- 45 F4.2 deg MinAxis [0.1/1] Minimum eigenvalue of
moment of inertia matrix (Rmin)
47- 51 F5.2 kpc Rgal [0.02/18] Mass-weighted mean galactocentric
radius (3)
53- 57 F5.2 kpc Dist [0.4/16] Mass-weighted mean kinematic distance (3)
59- 66 E8.3 K.km/s Wco [23.9/9640] Total CO flux
68- 75 E8.3 Msun Mgas [1580/] Total gas mass
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Note (1): The order of SFCno appear shuffled compared to Table 1 because we
adopt the mass-weighted distances of matched GMCs for each SFC here.
Note (2): The geometric mean angular radius is defined as
(MaxAxis*MinAxis2){1/3}
Note (3): We detail the calculations of the mass-weighted parameters in
Section 2.4.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 I3 -- SFCno [0/277] SFC record number (SFC-GMC complex)
5- 9 F5.2 km/s SigV [1/22.2] Velocity dispersion
11- 15 F5.2 kpc Dist [0.4/16] Kinematic distance
17- 22 F6.2 pc Rad [2/166] Physical radius (1)
24- 31 E8.3 s-1 Q Ionizing luminosity
33- 40 E8.3 Msun Mgas [1580/] Gas mass
42- 49 E8.3 Msun/pc2 Sigma [4/696] Gas column density (Σg) (2)
51- 58 E8.3 -- SFEbr [/0.4] Star formation efficiency
(εbr) (3)
60- 67 E8.3 -- SFRbr [0.0001/1.3] Star formation rate per
free-fall time (εff,br) (3)
69- 73 F5.2 10+6yr tff [1.4/40] Free-fall time ((3π/32Gρ)0.5)
75- 82 E8.3 -- aVir [0.2/26] Virial parameter (αvir) (4)
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Note (1): The physical radius is defined as Dist*tan(Rang).
The angular radius is defined in Section 2.4.
Note (2): The gas surface density (Σg) is defined as
Mgas/(Dist(π*MaxAxis*MinAxis))2
where MaxAxis and MinAxis are the maximum and minimum eigenvalues of
the moment of inertia matrix for each cloud (see Section 2.4).
Note (3): Star formation efficiency ε is defined as the ratio of the
mass in protostars to the total mass in a given star-forming region is
defined in Equation (1) as ε=M*/(Mgas+M*) where the
star-forming region may be a GMC or a smaller sub-region of a GMC.
The star formation rate per freefall time epsilonff is defined in
Equation (2): εff=ε*(tff/τ*) where τ* is
the lifetime of the (proto-)stellar object in question, and tff is
the freefall time of the star-forming region (a GMC or its
sub-region), which is assumed to have a mean density ρ.
The subscript "br" stands for bremsstrahlung (see Figure 3).
Note (4): The virial parameter is defined as 5*SigV2*Rad/G*Mgas where
G is the gravitational constant.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 03-May-2017