J/ApJS/241/2 Ionization profiles of 8 Galactic H II regions (Luisi+, 2019)
Ionization profiles of Galactic H II regions.
Luisi M., Anderson L.D., Liu B., Roshi D.A., Churchwell Ed
<Astrophys. J. Suppl. Ser., 241, 2 (2019)>
=2019ApJS..241....2L 2019ApJS..241....2L
ADC_Keywords: H II regions; Interstellar medium; Radio lines
Keywords: H II regions; ISM: abundances; ISM: bubbles;
photon-dominated region (PDR); radio lines: ISM
Abstract:
Using Green Bank Telescope radio recombination line (RRL) data, we
analyze the role of leaking radiation from HII regions in maintaining
the ionization of the interstellar medium (ISM). We observed a sample
of eight Galactic HII regions of various sizes, morphologies, and
luminosities. For each region, the hydrogen RRL intensity decreases
roughly as a power-law with the distance from the center of the
region. This suggests that radiation leaking from the HII region is
responsible for the majority of surrounding ionized gas producing RRL
emission. Our results further indicate that the hydrogen RRL intensity
appears to be fundamentally related to the HII region sizes traced by
their photodissociation regions, such that physically smaller HII
regions show a steeper decrease in intensity with an increasing
distance from the region centers. As a result, giant HII regions may
have a much larger effect in maintaining the ionization of the ISM.
For six of the eight observed HII regions, we find a decrease in the
4He+/H+ abundance ratio with an increasing distance, indicating
that He-ionizing photons are being absorbed within the ionization
front of the HII region. There is enhanced carbon RRL emission toward
directions with strong continuum background, suggesting that the
carbon emission is amplified by stimulated emission.
Description:
We observed eight HII regions with the Green Bank Telescope (GBT) from
2017 February to 2017 May. The properties of the observed HII regions
are given in Table 1.
The individual pointings for each observed HII region lie along an
imaginary line on the plane of the sky intersecting the region center.
The angle of the line was chosen such that there is as little
confusion by other radio sources (e.g., nearby HII regions) as
possible. For each targeted HII region, between 7 and 17 positions
were observed. The locations of the observed positions for each source
are shown in Figure 1. The coordinates of all observed directions are
given in Table 3.
The GBT C-band instantaneous bandpass in combination with the
Versatile GBT Astronomical Spectrometer (VEGAS) backend includes 22
Hnα lines, 19 Hnβ lines, and 8 Hnγ lines between
4.054 and 7.793GHz.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 55 8 H II region properties
table3.dat 52 98 Observed positions
table4.dat 60 434 H, He, and C RRL parameters for the 98 sources
table5.dat 50 98 Radio continuum temperatures and source properties
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See also:
III/274 : Galactic O-Star Spectroscopic Survey (GOSSS) (Sota+, 2014)
J/ApJ/653/1226 : Physical properties of galactic HII regions (Quireza+, 2006)
J/ApJS/169/353 : Chandra sources in M17 (Broos+, 2007)
J/ApJ/738/27 : Galactic HII regions RRL and continuum data (Balser+, 2011)
J/MNRAS/411/705 : Spectrophotometric distances of HII regions (Moises+, 2011)
J/ApJ/755/40 : HII reg. in Magellanic clouds from MCELS (Pellegrini+, 2012)
J/ApJ/764/34 : HRDS IV. H, He & C radio recombination lines (Wenger+, 2013)
J/ApJS/212/1 : The WISE catalog of Galactic HII regions (Anderson+, 2014)
J/ApJ/810/42 : Hydrogen RRL parameters of H II regions (Anderson+, 2015)
J/ApJS/240/14 : SIGGMA: inner galaxy data release (Liu+, 2019)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Reg HII region identifier
7- 17 A11 --- OName Other name
19- 25 F7.3 deg GLON Galactic longitude
27- 33 F7.3 deg GLAT Galactic latitude
35- 38 F4.1 pc Rad [2.4/14.2] Radius of the HII region
(see Section 3)
40- 43 F4.1 kpc Rgal [4.5/11.6] Galactocentric radius
45- 47 F3.1 kpc Dist [0.4/8.4] Distance to the Sun
from Anderson+, 2014, J/ApJS/212/1
49- 53 A5 --- SpT Spectral type of the ionizing source(s)
55 I1 --- r_SpT [1/8] Reference (1)
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Note (1): Reference as follows:
1 = Broos et al. (2007, J/ApJS/169/353),
2 = Sota et al. (GOSSS; 2011, III/274),
3 = Watson et al. (2008ApJ...681.1341W 2008ApJ...681.1341W),
4 = Moises et al. (2011, J/MNRAS/411/705),
5 = Lahulla (1985A&AS...61..537L 1985A&AS...61..537L),
6 = Georgelin et al. (1973A&A....25..337G 1973A&A....25..337G),
7 = O'Dell et al. (2017ApJ...837..151O 2017ApJ...837..151O),
8 = Cesaroni et al. (1994A&A...288..903C 1994A&A...288..903C).
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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- 5 A5 --- Reg HII region identifier
6 A1 --- --- [_]
7- 11 A5 --- Source Source name within HII region (1)
13- 14 I2 h RAh Hour of right ascension (J2000)
16- 17 I2 min RAm Minute of right ascension (J2000)
19- 22 F4.1 s RAs Second of right ascension (J2000)
24 A1 --- DE- Sign of declination (J2000)
25- 26 I2 deg DEd Degree of declination (J2000)
28- 29 I2 arcmin DEm Arcminute of declination (J2000)
31- 32 I2 arcsec DEs Arcsecond of declination (J2000)
34- 40 F7.3 deg GLON [14.7/210] Galactic longitude
42- 48 F7.3 deg GLAT [-20.2/1.6] Galactic latitude
50- 52 A3 --- PDR Photodissociation region (PDR) boundary (2)
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Note (1): The locations of the observed positions for each source are shown
in Figure 1. The locations are labeled according to their predominant
direction from the region center in Galactic coordinates (N ... north,
S ... south, E ... east, W ... west) and their distance from the
center of the regions in multiples of 2 x HPBW.
Note (2): Location of the observed direction with respect to the PDR
boundary (see Section 3) as follows:
out = outside the PDR;
in = inside the PDR;
on = on the PDR
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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- 5 A5 --- Reg HII region identifier
6 A1 --- --- [_]
7- 11 A5 --- Source Source name within HII region
13- 17 A5 --- Trans Line transition; alpha, beta, or gamma
19- 20 A2 --- El Element; H, He, or C
22- 28 F7.1 mK TL [1.2/14831]? Line intensity
30- 33 F4.1 mK e_TL [0.1/22]? Mean 1σ error on TL
35- 38 F4.1 km/s FWHM [2.7/58.1]? FWHM line width
40- 42 F3.1 km/s e_FWHM [0/4]? Mean 1σ error on FWHM
44- 48 F5.1 km/s VLSR [-30/123.5]? LSR velocity
50- 52 F3.1 km/s e_VLSR [0.1/2]? Mean 1σ error on VLSR
54- 57 F4.1 mK rms [0.5/25.6]? rms noise
59- 60 I2 min tintg [3/36] Total on-source integration time
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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- 5 A5 --- Reg HII region identifier
6 A1 --- --- [_]
7- 11 A5 --- Source Source name within HII region
13- 18 F6.2 K Tc [0.01/215]? Continuum antenna temperature TC
20- 24 F5.2 K e_Tc [0.01/34]? 1σ uncertainty in Tc
26- 30 I5 K Te [1240/10780]? Local thermodynamic equilibrium
(LTE) electron temperature
32- 35 I4 K e_Te [680/2140]? 1σ uncertainty in Te
37- 43 I7 pc/cm6 EM [270/2418330]? Emission measure
45- 50 I6 pc/cm6 e_EM [360/492550]? 1σ uncertainty in EM
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 27-May-2019