J/A+A/579/A71 Infrared emission of young HII regions (Cesaroni+, 2015)
Infrared emission of young HII regions: a Herschel/Hi-GAL study.
Cesaroni R., Pestalozzi M., Beltran M.T., Hoare M.G., Molinari S., Olmi L.,
Smith M.D., Stringfellow G.S., Testi L., Thompson M.A.
<Astron. Astrophys., 579, A71-71 (2015)>
=2015A&A...579A..71C 2015A&A...579A..71C (SIMBAD/NED BibCode)
ADC_Keywords: H II regions ; Stars, early-type ; Photometry, infrared
Keywords: stars: early-type - stars: formation - HII regions
Abstract:
Investigating the relationship between radio and infrared emission of
HII regions may help shed light on the nature of the ionizing stars
and the formation mechanism of early-type stars in general. We have
taken advantage of recent unbiased surveys of the Galactic plane such
as Herschel/Hi-GAL and VLA/CORNISH to study a bona fide sample of
young HII regions located in the Galactic longitude range
10°-65° by comparing the mid- and far-IR continuum emission to
the radio free-free emission at 5GHz. We have identified the Hi-GAL
counterparts of 230 CORNISH HII regions and reconstructed the spectral
energy distributions of 204 of these by complementing the Hi-GAL
fluxes with ancillary data at longer and shorter wavelengths. Using
literature data, we obtained a kinematical distance estimate for 200
HII regions with Hi-GAL counterparts and determined their luminosities
by integrating the emission of the corresponding spectral energy
distributions. We have also estimated the mass of the associated
molecular clumps from the (sub)millimeter flux densities. Our main
finding is that for ∼1/3 of the HII regions the Lyman continuum
luminosity appears to be greater than the value expected for a
zero-age main-sequence star with the same bolometric luminosity. This
result indicates that a considerable fraction of young, embedded
early-type stars presents a "Lyman excess" possibly due to UV
photons emitted from shocked material infalling onto the star itself
and/or a circumstellar disk. Finally, by comparing the bolometric and
Lyman continuum luminosities with the mass of the associated clump, we
derive a star formation efficiency of 5%. The results obtained suggest
that accretion may still be present during the early stages of the
evolution of HII regions, with important effects on the production of
ionizing photons and thus on the circumstellar environment. More
reliable numerical models describing the accretion process onto
massive stars are required to shed light on the origin of the observed
Lyman excess.
Description:
Since the main scope of our study is to investigate the IR and radio
properties of young massive stars, we have selected the sources
classified as "ultracompact" and "compact" HII regions in the
CORNISH catalogue. This a classification was obtained after visual
inspection also using the Spitzer IRAC and MIPSGAL images (more
details on the method are given in Purcell et al. 2013ApJS..205....1P 2013ApJS..205....1P,
Cat. J/ApJS/205/1)
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 137 204 Flux density densities of the HII regions
classified as "ultracompact" and "compact" in
the CORNISH catalogue
tablea2.dat 25 200 Distances, Lyman continuum photon rates,
bolometric luminosities, and clump masses of
the 200 HII regions of our sample for which a
distance estimate was possible
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See also:
J/ApJS/205/1 : CORNISH project. II. Source catalog (Purcell+, 2013)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq Sequential number
5- 21 A17 --- Name CORNISH name, GLLL.llll+BB.bbbb
23- 30 F8.4 deg RAdeg CORNISH right ascension (J2000)
32- 39 F8.4 deg DEdeg CORNISH declination (J2000)
41- 46 F6.1 mJy S5GHz Flux density at 5GHz
49- 56 F8.4 deg RAHdeg ? Hi-GAL right ascension (J2000)
57 A1 --- n_RAHdeg [a] Note when no position (1)
60- 67 F8.4 deg DEHdeg ? Hi-GAL declination (J2000)
68 A1 --- n_DEHdeg [a] Note when no position (1)
70- 76 F7.2 Jy S21um ?=- Flux density at 21um (2)
78- 84 F7.2 Jy S22um ?=- Flux density at 22um (2)
86- 93 F8.2 Jy S70um ?=- Flux density at 70um (2)
95-101 F7.2 Jy S160um ?=- Flux density at 160um (2)
103-109 F7.2 Jy S250um ?=- Flux density at 250um (2)
111-116 F6.2 Jy S350um ?=- Flux density at 350um (2)
118-123 F6.2 Jy S500um ?=- Flux density at 500um (2)
125-130 F6.2 Jy S870um ?=- Flux density at 870um (2)
132-137 F6.2 Jy S1100um ?=- Flux density at 1100um (2)
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Note (1): a: The peak coordinates could not be determined because some of the
Hi-GAL images are saturated.
Note (2): The flux densities were obtained from the Hi-GAL images and
ancillary data (see Sect. 3.1).
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq Sequential number
5- 8 F4.1 kpc d Distance
9 A1 --- n_d [a] Note on d (1)
11- 15 F5.2 [s-1] log10NLy Lyman continuum photon rate
17- 20 F4.2 [Lsun] log10L Bolometric luminosity
22- 25 F4.2 [Msun] log10Mgas Clump mass
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Note (1): a: KDA not solved: far kinematic distance adopted (see Sect. 3.2).
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 30-Sep-2015