J/ApJ/707/283 VLA observation of molecular clumps (Johnston+, 2009)
Ionized gas toward molecular clumps: physical properties of massive
star-forming regions.
Johnston K.G., Shepherd D.S., Aguirre J.E., Dunham M.K., Rosolowsky E.,
Wood K.
<Astrophys. J., 707, 283-309 (2009)>
=2009ApJ...707..283J 2009ApJ...707..283J
ADC_Keywords: H II regions ; Radio continuum ; Galactic plane ;
Millimetric/submm sources
Keywords: circumstellar matter - H II regions - radio continuum: stars -
stars: formation - stars: winds, outflows
Abstract:
We have conducted a search for ionized gas at 3.6cm, using the Very
Large Array, toward 31 Galactic intermediate- and high-mass clumps
detected in previous millimeter continuum observations. In the 10
observed fields, 35 HII regions are identified, of which 20 are newly
discovered. Many of the HII regions are multiply peaked indicating
the presence of a cluster of massive stars. We find that the ionized
gas tends to be associated toward the millimeter clumps; of the 31
millimeter clumps observed, nine of these appear to be physically
related to ionized gas, and a further six have ionized gas emission
within 1'. For clumps with associated ionized gas, the combined mass
of the ionizing massive stars is compared to the clump masses to
provide an estimate of the instantaneous star formation efficiency.
These values range from a few percent to 25%, and have an average of
7%±8%. We also find a correlation between the clump mass and the
mass of the ionizing massive stars within it, which is consistent with
a power law. This result is comparable to the prediction of star
formation by competitive accretion that a power-law relationship
exists between the mass of the most massive star in a cluster and the
total mass of the remaining stars.
Description:
The selected millimeter sources were observed on two occasions with
the D configuration of the National Radio Astronomy Observatory VLA,
in 3.6cm (8.4GHz) continuum mode on 2007 April 6 and on 2007 May 1,
under the program AS895.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 149 31 Observed millimeter clumps
table3.dat 179 71 Observed parameters of VLA 3.6cm sources
table5.dat 102 71 Derived physical properties for VLA 3.6cm sources
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See also:
J/ApJS/195/14 : The Bolocam Galactic Plane Survey (BGPS). V. (Schlingman+,
2011)
J/ApJS/188/123 : The Bolocam Galactic Plane Survey. II. (Rosolowsky+, 2010)
J/ApJS/182/131 : Molecular clouds and clumps in the GRS (Rathborne+, 2009)
J/ApJ/699/1153 : Kinematic distances to GRS molecular clouds (Roman-Duval+,
2009)
J/A+A/447/221 : Dust continuum emission from IRAS sources (Beltran+, 2006)
J/A+A/366/481 : ATCA/VLA OH 1612 MHz survey. III. (Sevenster+, 2001)
J/A+AS/115/81 : A CS(2-1) survey of UC HII regions (Bronfman+, 1996)
J/ApJS/107/239 : 327MHz survey of the galactic plane (Taylor+ 1996)
J/ApJS/91/347 : A 5-GHz VLA Survey of the Galactic Plane (Becker+ 1994)
J/ApJS/74/181 : Small-diameter radiosources catalogue (Zoonematkermani+, 1990)
J/AJ/96/1655 : Galactic plane VLA survey (Garwood+ 1988)
http://www.bu.edu/galacticring/ : Galactic Ring Survey (GRS) home page
http://irsa.ipac.caltech.edu/data/BOLOCAM_GPS/ : BOLOCAM GPS archive
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- Name Millimeter clump name
25- 26 I2 h RAh Hour of right ascension (J2000)
28- 29 I2 min RAm Minute of right ascension (J2000)
31- 34 F4.1 s RAs Second of right ascension (J2000)
36 A1 --- DE- Sign of declination (J2000)
37- 38 I2 deg DEd Degree of declination (J2000)
40- 41 I2 arcmin DEm Arcminute of declination (J2000)
43- 44 I2 arcsec DEs Arcsecond of declination (J2000)
46- 52 F7.4 deg GLON Galactic longitude of millimeter clump
54- 60 F7.4 deg GLAT Galactic latitude of millimeter clump
62- 65 F4.1 km/s Vel ? Mean velocity of associated 13CO Galactic
Ring Survey (Jackson et al. 2006ApJS..163..145J 2006ApJS..163..145J)
67- 69 F3.1 km/s e_Vel ? Vel uncertainty
71- 73 F3.1 kpc Dnear Near distance to millimeter clump
75- 77 F3.1 kpc E_Dnear ? Positive error on Dnear
79- 81 F3.1 kpc e_Dnear ? Negative error on Dnear
82 A1 --- f_Dnear [a] Flag on Dnear (1)
84- 87 F4.1 kpc Dfar ? Far distance to millimeter clump
89- 91 F3.1 kpc E_Dfar ? Positive error on Dfar
93- 95 F3.1 kpc e_Dfar ? Negative error on Dfar
96 A1 --- f_Dfar [a] Flag on Dfar (1)
98-109 A12 --- Dist Assumed distance ("Near" or "Far"), Method (2)
111-120 A10 [10+3Lsun] LIRAS Luminosity of associated IRAS source
121 A1 --- f_LIRAS [b] Questionable IRAS association (3)
123-126 F4.2 Jy Smm The millimeter flux (at 1.1mm (BGPS) or 1.2mm
(B06)) (4)
128-131 F4.2 Jy e_Smm ? Smm uncertainty
133-136 I4 Msun Mass Calculated dust mass of the millimeter clump
138-141 A4 --- Ref Reference (BGPS or B06) (4)
143-149 A7 --- Type Selection source type (4)
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Note (1):
a = The velocity of this source is too high to be explained by the galactic
rotation curve at this galactic longitude, therefore the highest possible
velocity at this longitude was instead assumed. These sources were
originally thought to be at a different velocity, placing them at
dnear∼1kpc.
Note (2): Assumed distance used to calculate the IRAS luminosity and clump mass.
The method used to determine whether the source is at the near or far
distance is also given as follows:
H I SA = HI self-absorption,
CA = 21cm continuum absorption
B06 = taken from Beltran et al. (2006, Cat. Cat. J/A+A/447/221),
KB94 = Kuchar & Bania (1994ApJ...436..117K 1994ApJ...436..117K).
See section 2.1 for further details.
Note (3):
b = It is not certain which of the clumps listed by B06 is associated with
IRAS 18424-0329, however the general 1.2mm emission in this field is
coincident with the IRAS source.
Note (4): Ten sources were selected ("Select.") from preliminary images
from the Bolocam Galactic Plane Survey (BGPS; J. E. Aguirre et al.
2009, in preparation), and five were selected from Beltran et al.
(B06; 2006, Cat. J/A+A/447/221). The remaining 16 sources were
observed serendipitously ("Serend."), as their positions lay within
the observed VLA 3.6cm fields.
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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- 19 A19 --- Field Observed field(s)
21- 28 A8 --- Name VLA source name (1)
30- 37 F8.3 mJy Flux ? Integrated flux density at 3.6cm
39- 44 F6.3 mJy e_Flux ? Flux uncertainty (2)
45 A1 --- f_Flux [b] multiply peaked source (2)
47- 48 I2 h RAh ? Peak hour of right ascension (J2000) (3)
50- 51 I2 min RAm ? Peak minute of right ascension (J2000)
53- 56 F4.1 s RAs ? Peak second of right ascension (J2000)
58 A1 --- DE- Peak sign of declination (J2000) (3)
59- 60 I2 deg DEd ? Peak degree of declination (J2000)
62- 63 I2 arcmin DEm ? Peak arcminute of declination (J2000)
65- 66 I2 arcsec DEs ? Peak arcsecond of declination (J2000)
68- 74 F7.3 mJy Pk ? Peak flux density in mJy/beam
76- 80 F5.3 mJy e_Pk ? Pk uncertainty
82 A1 --- l_amaj Limit flag on amaj
83- 87 F5.1 arcsec amaj ? Angular size for the major axis
89 A1 --- l_bmin Limit flag on bmin
90- 94 F5.1 arcsec bmin ? Angular size for the minor axis
96- 98 I3 deg PA [-80,178]? Position angle
99 A1 --- f_PA [u] u: unresolved
101-105 F5.2 10-8sr SA ? Solid angle in units of steradiansx10-8
unit (4)
107-179 A73 --- OName Alernative identifier(s) for VLA source or "New"
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Note (1): Sub-sources are denoted by "A, B, C...," and components of
sources which are fully or nearly unresolved (e.g., point-like), are
denoted by "-P". See also the "Nomenclature notes" section below.
Note (2):
b = An additional error of ∼10%-20% of the measured flux should be added to
the flux errors of the components of multiply peaked sources. This is to
account for the uncertainty in where the aperture is placed to divide the
components of the source.
Note (3): The reported peak positions are measured from the peak pixel of
the source, except for fully or nearly unresolved sources, whose peak
positions are determined from the peak in the fitted Gaussian.
Note (4): The solid angle is given for irregular/extended sources only,
found from the number of pixels above 1xΔS within the photometry
aperture.
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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- 19 A19 --- Field Observed field(s)
21- 28 A8 --- Name VLA source name
30 A1 --- P [I/U] I: Irregular or U: Unresolved (5)
32- 35 F4.1 kpc Dist ? Assumed distance (6)
37 A1 --- l_theta [<] Limit flag on theta
38- 42 F5.1 arcsec theta ? Effective angular diameter of the source (7)
44 A1 --- l_s [<] Limit flag on s
45- 48 F4.2 pc s ? Physical size (Δs) (8)
50 A1 --- l_Tb [>] Limit flag on Tb
51- 56 F6.2 K Tb ? Brightness temperature (7)
58 A1 --- l_tau [>] Limit flag on tau
59- 64 F6.3 10-3 tau ? Optical depth (7)
66 A1 --- l_EM [>] Limit flag on EM
67- 72 F6.3 10+6pc/cm6 EM ? Emission measure (5)(9)
74- 78 F5.2 mm-3 ne ? Number density of electrons (ne)
(in 103/cm3) (7)
80- 84 F5.2 pc/cm2 U ? Excitation parameter U (rne2/3) (7)
86- 90 F5.2 [s-1] logNLy ? Ionization rate (7)
92- 95 A4 --- SpT MK Spectral type (5)(10)
97-102 F6.2 10+3Lsun Lcm ? Luminosity (5)(10)
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Note (5): Properties of unresolved and partially resolved sources were
derived assuming they are spherically symmetric, optically thin,
homogeneous, and ionization-bounded HII regions. In the case of
irregularly shaped sources, we assume they are optically thin,
homogeneous, and ionization-bounded HII regions, and that the observed
area in the plane of the sky is projected along a depth Δs,
estimated from the geometrical mean of the size of the source on the
sky. We do not take the effect of dust into our calculations, which
means our calculated spectral types and luminosities are in fact lower
limits.
Note (6): The assumed distance for each 3.6cm source was taken to be the
distance of the millimeter source closest in projection on the sky
within the observed fields.
Note (7): Uncertainties were calculated using a Monte Carlo error
propagation code, assuming Gaussian errors for the 3.6cm integrated
flux density, the 3.6cm source size, the assumed distance for each
3.6cm source, and the electron temperature Te. The approximate
uncertainties in the calculated HII region properties are: uncertainty
in theta∼9%, uncertainty in s∼20%, uncertainty in Tb∼15%, uncertainty
in τ∼45%, uncertainty in EM∼20%, uncertainty in ne and U∼15%, and
uncertainty in log10NLy∼15%. Therefore, the quoted spectral types are
at least correct to within a spectral type, which is also the case for
the corresponding luminosities.
Note (8): The error in the source size was estimated to be 5" in the case
of extended sources, and in the case of unresolved sources the errors
given by IMFIT were assumed, which was usually ≲5%. However the
sources G50.271 and G50.283 VLA 4-P; IRAS 18256-0742 VLA 3-P; IRAS
18256-0742 VLA 5-P; and IRAS 18424-0329: VLA 1-P have uncertainties in
their sizes ranging from 10% to 40%, and the size of IRAS 18256-0742:
VLA 1-P has a 110% uncertainty.
Note (9): The emission measure, EM, is given by (equation 3):
EM=τ/(8.235x10-2α(ν,Te)Te-1.35ν-2.1)(cm-6pc)
where Te=8200K and ν is in GHz. The correction factor
{alph}(ν,Te), which is of order unity, rectifies the small
discrepancy between the approximation shown in Equation (3), given by
Altenhoff et al. (1960, Veroff. Sternwarte Bonn No., 59, 48), and the
original derivation by Oster (1961RvMP...33..525O 1961RvMP...33..525O). We take
α(ν,Te)=0.9828 from Table 6 in Mezger & Henderson
(1967ApJ...147..471M 1967ApJ...147..471M), for Te=8000K and ν=8GHz.
Note (10): Assuming the observed HII regions are created by single OB
stars, the corresponding spectral type and luminosity, Lcm, of the
exciting star required to sustain each observed HII region are listed.
These were found using the results of Panagia (1973AJ.....78..929P 1973AJ.....78..929P).
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Nomenclature notes:
In tables 3 and 5, objects are <[JSA2009] GLL.lll VLA NA-P> or
<[JSA2009] IRAS HHMMm+DDMM VLA NA-P> in Simbad. If the observed field
has two parts, eg. "G50.271 and G50.283", only the first part is kept
in the format.
History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 29-Dec-2011