J/AJ/144/173 YSOs from SED fitting in six HII regions (Dirienzo+, 2012)
Testing triggered star formation in six H II regions.
Dirienzo W.J., Indebetouw R., Brogan C., Cyganowski C.J., Churchwell E.,
Friesen R.K.
<Astron. J., 144, 173 (2012)>
=2012AJ....144..173D 2012AJ....144..173D
ADC_Keywords: H II regions ; YSOs ; Stars, masses ; Radial velocities ;
Velocity dispersion
Keywords: H II regions - ISM: bubbles - stars: formation - stars: protostars
Abstract:
We investigated six HII regions with infrared, bright rimmed bubble or
cometary morphology, in search of quantitative evidence for triggered
star formation, both collect and collapse and radiatively driven
implosion (RDI). We identified and classified 458 young stellar
objects (YSOs) in and around the HII regions. YSOs were determined by
fitting a collection of radiative transfer model spectral energy
distributions to infrared photometry for a large sample of point
sources. We determined areas where there exist enhanced populations of
relatively unevolved YSOs on the bright rims of these regions,
suggesting that star formation has been triggered there. We further
investigated the physical properties of the regions by using radio
continuum emission as a proxy for ionizing flux powering the HII
regions, and 13CO(1-0) observations to measure masses and
gravitational stability of molecular clumps. We used an analytical
model of collect and collapse triggered star formation, as well as a
simulation of RDI, and thus we compare the observed properties of the
molecular gas with those predicted in the triggering scenarios.
Notably, those regions in our sample that show evidence of cometary,
or "blister", morphology are more likely to show evidence of
triggering.
Description:
We have performed SED fitting on a large number of infrared point
sources around several HII regions, using 2MASS and Spitzer near-to
mid-infrared photometry. Spitzer Space Telescope is operated by the
Jet Propulsion Laboratory, California Institute of Technology. The
Infrared Array Camera (IRAC) and Multiband Imaging Photometer for
Spitzer (MIPS) instruments, together with the ground-based Two Micron
All Sky Survey (2MASS; II/246), provide the wide wavelength coverage
important for reliable identification and classification of Young
Stellar Objects (YSOs).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 71 8 HII region sample
table4.dat 74 458 Young Stellar Objects (YSOs) identified by SED
fitting
table6.dat 57 168 Molecular gas clump parameters
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See also:
II/293 : GLIMPSE Source Catalog (I + II + 3D) (IPAC 2008)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
VIII/58 : A Survey of Radio H II Regions in the Northern Sky (Lockman+ 1989)
J/MNRAS/424/2442 : Catalog of bubbles from Milky Way Project (Simpson+, 2012)
J/ApJ/741/110 : The BGPS. VII. Massive star-forming regions (Dunham+, 2011)
J/ApJ/690/706 : Distances of Galactic HII regions (Anderson+, 2009)
J/A+A/501/539 : RMS survey. 6cm observations of YSOs (Urquhart+, 2009
J/AJ/136/2391 : GLIMPSE Extended Green Objects catalog (Cyganowski+, 2008)
J/ApJ/688/1142 : Star formation in W5: Spitzer observations (Koenig+, 2008)
J/ApJ/670/428 : Bubbles in the galactic disk. II. (Churchwell+, 2007)
J/ApJ/649/759 : Bubbles in the galactic disk (Churchwell+, 2006)
J/AJ/131/2525 : MAGPIS 20cm survey (Helfand+, 2006)
J/MNRAS/301/640 : Ultracompact H II regions studies. II. (Walsh+, 1998)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- Region Nearest HII region in this sample (G1)
14- 16 A3 --- OName HII region identifier in Churchwell et al.
(2006, cat. J/ApJ/649/759)
18- 19 I2 h RAh Hour of Right Ascension (J2000)
21- 22 I2 min RAm Minute of Right Ascension (J2000)
24- 27 F4.1 s RAs Second of Right Ascension (J2000)
29 A1 --- DE- Sign of the Declination (J2000)
30- 31 I2 deg DEd Degree of Declination (J2000)
33- 34 I2 arcmin DEm Arcminute of Declination (J2000)
36- 37 I2 arcsec DEs Arcsecond of Declination (J2000)
39- 46 A8 --- Type Principle morphology (bubble or cometary)
48- 51 F4.1 km/s RV Radial velocity
53 A1 --- r_RV Source of RV (1)
55- 58 F4.2 kpc Dist1 Near kinematic distance (2)
60- 64 F5.2 kpc Dist2 Far kinematic distance (2)
66- 71 A6 --- HII Nearest HII region short name (added at CDS) (G1)
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Note (1): Source of RV as follows:
c = Radio recombination line velocity from Lockman (1989, cat. VIII/58);
d = Radio recombination line velocity from Lockman et al. (1996ApJ...472..173L 1996ApJ...472..173L)
e = CMT CO (3-2) velocity from Beaumont & Williams (2010ApJ...709..791B 2010ApJ...709..791B).
Note (2): Using the galactic rotation curve of Reid et al. (2009ApJ...700..137R 2009ApJ...700..137R)
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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- 6 A6 --- HII Nearest HII region in this sample (G1)
8 A1 --- r_YSO [GM] Origin of the YSO (G=GLIMPSE) (1)
9- 24 A16 --- YSO YSO name (LLL.llll+BB.bbbb)
26- 28 A3 --- St Evolutionary stage (I, II or III) (2)
30- 33 F4.2 --- chi2 Best-fit parameter (χ2best/ndata)
35 A1 --- f24 Presence of a 24µm point source? (Y or N)
37- 40 F4.1 Msun Mass Mass of central source (3)
42- 44 F3.1 Msun e_Mass Uncertainty in Mass (3)
46- 48 F3.1 [Lsun] logL Log of total luminosity
51- 53 F3.1 [Lsun] e_logL ? Log of uncertainty in logL (4)
55- 59 F5.1 [Msun/yr] logMe ? Log of envelope accretion rate (5)
61- 64 F4.1 [Msun/yr] e_logMe [-9.5/-3.3]? Log of uncertainty in logMe (5)
66- 69 F4.1 [Msun] logMd Log of accretion disk mass
71- 74 F4.1 [Msun] e_logMd [-4.1/-0.8]? Log of uncertainty in logMd (4)
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Note (1): Flag on Name as follows:
G = Source from the GPSC (GLIMPSE Point Source Catalog; Benjamin et al.,
2003PASP..115..953B 2003PASP..115..953B, Cat. II/293)
M = Manually identified source. In addition to the sources from the GPSC, we
identified point sources that were seen in IRAC 8µm and/or MIPS 24µm
images but were missing from the catalog. The GPSC was finely tuned to have
very high reliability in regions of complex diffuse emission, at the cost
of the inevitable loss of some completeness. To improve the completeness of
our final YSO list, we included these manually identified sources.
Note (2): We adopt the YSO "Stage" classification scheme of Robitaille et al.
(2006ApJS..167..256R 2006ApJS..167..256R) (see Section 2.2.1 for more details) as follows:
I = Object that have Mdotenv/M*>10-6/yr, where Mdotenv is the
envelope accretion rate and M* is the mass of the central source;
II = Object with Mdotenv/M*<10-6/yr and Mdisk/Mstar>10-6, where
Mdisk is the disk mass;
III = Object with Mdotenv/Mstar<10-6/yr and Mdisk/M*<10-6.
Note (3): Values for all quantities are determined by the parameters of
model SEDs that fit the source such that (χ2-χ2b)/N_<6
(the index b represents the best-fit, N is the number of photometric
measurements). Averages and uncertainties are the mean and standard
deviation values of the fit parameters weighted by the probability of
the corresponding model, exp(-χ2/2) (see Section 2.2). A blank
uncertainty indicates no spread in the models that fit the data.
Note (4): Blank indicates a linear uncertainty of ±0.0.
Note (5): The data are sometimes fit by disk-only models with no accreting
envelope, and thus the values and errors are both left blank.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- HII Nearest HII region in this sample (G1)
7 A1 --- m_HII Multiplicity flag on HII (1)
9- 14 F6.3 deg GLON Galactic longitude of peak (lpeak)
16- 20 F5.2 deg GLAT Galactic latitude of peak (bpeak)
22- 26 F5.2 km/s RV Radial velocity of peak (vpeak)
28- 30 F3.1 pc Rad Clump effective radius (Rcl)
32- 34 F3.1 km/s sigma Clump velocity dispersion (σcl)
36- 38 F3.1 pc Sep Clump nearest neighbor (peak-to-peak)
separation in the plane of the sky (dcl)
40- 43 F4.1 10+21cm-2 NH2 Peak column density of the molecular gas for
the clump (Ncl(H2)) (see Equation (4) in
Section 2.4)
45- 47 I3 cm-3 <nH2> Average number density of the gas for the
clump (ncl(H2))
49- 52 I4 Msun Mcl Total mass in molecular gas for the clump
(Mcl(H2)) (see Eq. (5) in Section 2.4)
54- 57 F4.1 --- alpha Virial parameter (αvir) (2)
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Note (1): Multiplicity flag on HII as follows:
a = The HII region is G028.83-0.25 (83.8-90.0km/s);
b = The HII region is G028.83-0.25 (91.9-98.8km/s).
Note (2): αvir=Mvir/Mcl=5σcl2Rcl/G.Mcl (Equation (6)
in Section 2.4).
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Global notes:
Note (G1): Nearest HII region in this sample as belows:
G28.83 = G028.83-0.25;
G28.83a = G028.83-0.25 (83.8-90.0km/s);
G28.83b = G028.83-0.25 (91.9-98.8km/s);
G41.10 = G041.10-0.15;
G41.91 = G041.91-0.12;
G41.92 = G041.92+0.04;
G41.9X = G041.91-0.12 and G041.92+0.04;
G44.28 = G044.28+0.11;
G44.34 = G044.34-0.82.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 08-Jan-2014