J/AJ/170/74 N2H+ & CCS abundances in HII star forming regions (Chen+, 2025)
The chemical clock of high-mass star-forming regions: N2H+/CCS.
Chen J.L., Zhang J.S., Ge J.X., Wang Y.X., Yu H.Z., Zou Y.P., Yan Y.T.,
Wang X.Y., Wei D.Y.
<Astron. J., 170, 74 (2025)>
=2025AJ....170...74C 2025AJ....170...74C
ADC_Keywords: H II regions; Abundances; Molecular data; Radio lines;
Star Forming Region
Keywords: Astrochemistry ; Chemical abundances ; Massive stars ;
Abundance ratios
Abstract:
Using the Institut de Radioastronomie Millmetrique 30m telescope, we
presented observations of N2H+J=1-0, CCS JN=87-76 and
77-66 lines toward a large sample of ultracompact H II regions
(UC H IIs). Among our 88 UC H IIs, 87 and 33 sources were detected in
the N2H+J=1-0 and CCS JN=87-76 lines, respectively. For the
CCS 77-66 transition, we detected emission in 10 out of 82
targeted sources, all of which also exhibited emission in the
CCS JN=87-76 line. Physical parameters are derived for our
detections, including the optical depth and excitation temperature of
N2H+, the rotational temperature of CCS and the column density.
Combining our results and previous observation results in different
stages of high-mass star-forming regions (HMSFRs), we found that the
column density ratio N(N2H+)/N(CCS) increases from high-mass
starless cores through high-mass protostellar cores to UC H IIs. This
implies that N(N2H+)/N(CCS) can trace the evolution process of
HMSFRs. It was supported by our gas-grain chemical model, which shows
that N(N2H+)/N(CCS) increases with the evolution age of HMSFRs.
The temperature, density and chemical age were also constrained from
our best-fit model at each stage. Thus, we propose N(N2H+)/N(CCS)
as a reliable chemical clock of HMSFRs.
Description:
The observations of the N2H+J=1-0 and CCS JN=87-76 lines
were observed simultaneously toward 10 UC H IIs (including 4 sources
being observed in CCS 77-66 line) in 2016 June within project
013-16, with the IRAM 30m single-dish telescope, at the Pico Veleta
Observatory (Granada, Spain). In 2020 August, we performed
observations toward the other 78 sources within project 022-20 with
IRAM 30m telescope. During this observations, the N2H+J=1-0, CCS
JN=87-76 and CCS 77-66 lines were observed simultaneously.
In summary, 88 UC H IIs were observed in N2H+J=1-0 and CCS
JN=87-76 lines, while 82 sources were observed in CCS 77-66
lines. The rest frequencies of N2H+J=1-0, CCS JN=87-76 and
77-66 lines are 93173.700, 93870.107 and 90686.381MHz,
respectively, with a corresponding beam size of ∼27". The on-source
integration time depended on the line intensity, with an integration
time ranging from 4 to 120min, and the spectral resolution was
∼0.6km/s around 93GHz.
We collected observation data of N2H+ and CCS in other evolution
stages (HMSC and HMPO), to make comparison on results between them and
our UC H II sample. The HMSC data were collected from
Fontani+ (2011A&A...529L...7F 2011A&A...529L...7F, 2023A&A...680A..58F 2023A&A...680A..58F) by the Institute
for Radio Astronomy in the Millimetre Range (IRAM) 30m telescope in
Spain (with a beam size of 26") and Chen+2025 (in preparation) by the
Arizona Radio Observatory (ARO)in the USA 12m telescope (a beam size
of 66"). The HMPO data were taken from Nobeyama 45m observation (a
beam size of 17", K. Taniguchi+, 2019ApJ...872..154T 2019ApJ...872..154T) and the ARO 12m
observation (a beam size of 66"; Chen+2025, in preparation).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 51 88 Detailed information of our Ultracompact (UC) HII
sample
table3.dat 95 426 Our UC HII observational parameters of N2H+(J=1-0)
and CCS obtained from Gaussian fits
table4.dat 86 88 Derived parameters of CCS and N2H+ in our UC HII
sample
table5.dat 125 33 Derived Parameters of CCS and N2H+ in HMSCs and
HMPOs
table9.dat 52 15 Basic information of High-Mass Starless Cores
(HMSC) and High-Mass Protostellar Cores (HMPO)
sample from Chen+2025 (in preparation)
--------------------------------------------------------------------------------
See also:
J/A+AS/133/29 : Molecular line survey towards UC HII (Hatchell+ 1998)
J/ApJ/566/945 : Massive star forming regions at 1.2mm (Beuther+, 2002)
J/A+A/417/615 : Maser and outflows in UC HII region (Codella+, 2004)
J/AJ/129/348 : Radio compact HII regions in the Milky Way (Giveon+, 2005)
J/AJ/130/156 : Galactic radio compact HII regions at 1.4GHz (Giveon+, 2005)
J/ApJ/641/389 : Millimetric observations of IRDC cores (Rathborne+, 2006)
J/A+A/453/1003 : SCUBA ultracompact HII regions (Thompson+, 2006)
J/A+A/461/11 : Radio observations of MYSO candidates (Urquhart+, 2007)
J/A+A/498/147 : High mass protostellar objects physical param. (Grave+, 2009)
J/A+A/501/539 : RMS survey. 6cm observations of YSOs (Urquhart+, 2009)
J/ApJ/741/110 : The BGPS. VII. Massive star-forming regions (Dunham+, 2011)
J/MNRAS/418/1689 : Red MSX water maser and ammonia emissions (Urquhart+, 2011)
J/A+A/527/A88 : Chemistry in infrared dark clouds (Vasyunina+, 2011)
J/ApJ/756/60 : A 3mm line survey in 37 IR dark clouds (Sanhueza+, 2012)
J/ApJ/777/157 : 90GHz obs. of high-mass star-forming regions (Hoq+, 2013)
J/ApJS/205/1 : CORNISH project. II. Source catalog (Purcell+, 2013)
J/MNRAS/435/400 : ATLASGAL. Properties of compact HII regions (Urquhart+, 2013)
J/A+A/565/A75 : ATLASGAL: dust condensations in Gal. plane (Csengeri+, 2014)
J/A+A/567/L5 : W3(OH) high angular resolution 7mm images (Dzib+, 2014)
J/A+A/563/A97 : IRAM 30m reduced spectra of 59 sources (Gerner+, 2014)
J/ApJ/783/130 : Parallaxes of high mass star forming regions (Reid+, 2014)
J/A+A/579/A71 : Infrared emission of young HII regions (Cesaroni+, 2015)
J/A+A/579/A80 : Star-forming regions deuteration (Gerner+, 2015)
J/ApJS/219/28 : C18O/C17O ratios in the Galactic center (Zhang+, 2015)
J/ApJ/833/18 : Ultra-compact HII regions & methanol masers. I. (Hu+, 2016)
J/ApJ/822/59 : BGPS. XIV. Molecular cloud clumps GBT obs. (Svoboda+, 2016)
J/ApJS/231/11 : High-mass starless clump candidates from ATLASGAL (Yuan+, 2017)
J/A+A/615/A103 : CORNISH project. III. UCHII region catalogue (Kalcheva+, 2018)
J/A+A/611/A6 : ATLASGAL massive clumps H2CO data (Tang+, 2018)
J/MNRAS/487/1057 : Massive SFR beyond the solar circle (Djordjevic+, 2019)
J/ApJS/244/35 : VLA observations of the Central Molecular Zone (Lu+, 2019)
J/ApJ/885/131 : ∼200 high-mass SFR plx & proper motion with VLBI (Reid+, 2019)
J/ApJ/877/154 : H2CO TMRT obs. of Galactic molecular clouds (Yan+, 2019)
J/ApJ/899/145 : Sulfur isotopes in SFR with 12m ARO and 30m IRAM (Yu+, 2020)
J/ApJS/249/6 : Galactic interstellar ratio 18O/17O. I. (Zhang+, 2020)
J/ApJS/257/39 : NH3 isotope ratios of Galactic disk sources (Chen+, 2021)
J/ApJS/258/19 : 12.2GHz methanol maser surv. toward 6.7GHz masers (Song+, 2022)
J/MNRAS/510/3389 : High-mass star formation evol. trends (Urquhart+, 2022)
J/MNRAS/520/1073 : CORNISH-South Survey and Catalogue (Irabor+, 2023)
J/ApJS/264/48 : HC3N & N2H+ obs. toward 61 ultracomp. HII reg. (Wang+, 2023)
J/ApJS/266/29 : IRAM 3mm, 2mm & 1.3mm obs. of star-forming reg. (Zhao+, 2023)
J/ApJS/268/56 : Obs. of Gal. interstellar ratio 18O/17O. II. (Zou+, 2023)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- Name UC HII object name
15- 16 I2 h RAh Hour of Right Ascension (J2000)
18- 19 I2 min RAm Minute of Right Ascension (J2000)
21- 25 F5.2 s RAs Second of Right Ascension (J2000)
27- 27 A1 --- DE- Sign of the Declination (J2000)
28- 29 I2 deg DEd Degree of Declination (J2000)
31- 32 I2 arcmin DEm Arcminute of Declination (J2000)
34- 37 F4.1 arcsec DEs Arcsecond of Declination (J2000)
39- 43 F5.2 kpc Dist [0.7/20.41] Heliocentric Distance
45- 49 F5.2 kpc e_Dist [0.04/10.29] Uncertainty in Dist
51- 51 I1 --- r_Dist [1/9] References (1)
--------------------------------------------------------------------------------
Note (1): References as follows:
1 = Dzib+2014 (J/A+A/567/L5)
2 = Hu+2016 (J/ApJ/833/18)
3 = Lu+2019 (J/ApJS/244/35)
4 = Giveon+2005a (J/AJ/129/348)
5 = Codella+2004 (J/A+A/417/615)
6 = Khan+2022 (2022A&A...664A.140K 2022A&A...664A.140K)
7 = Urquhart+2009 (J/A+A/501/539)
8 = Vastel+2001 (2001A&A...376.1064V 2001A&A...376.1064V)
9 = Song+2022 (J/ApJS/258/19)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- Name UC HII object name
15- 43 A29 --- Trans Molecule and transition lines (1)
45- 50 F6.2 min ExpTime [3.8/119.8]? Total integration time
52- 56 F5.3 K RMS [6e-3/0.12]? RMS Noise
58- 62 F5.2 K.km/s Tmbdv [0.07/81.14]? Integrated line intensity for
Trans (1)
64- 67 F4.2 K.km/s e_Tmbdv [0.01/1.64]? Uncertainty Tmbdv
69- 74 F6.2 km/s VLSR [-80.0/126.13]? Radial velocity relative to
local standard of rest (1)
76- 79 F4.2 km/s e_VLSR [0.01/0.63]? Uncertainty in VLSR
81- 84 F4.2 km/s DV [0.63/7.84]? Line width, Δ V (1)
86- 89 F4.2 km/s e_DV [0.01/1.44]? Uncertainty in DV
91- 95 F5.2 K Tmb [0.04/12.35]? Main beam brightness
temperature (1)
--------------------------------------------------------------------------------
Note (1): For six sources without observation in CCS (JN=77-66) line
(G133.94+01.06, G009.62+00.19, G012.81-00.19, G34.3+0.2, G033,
and G035.14), the line data is left blank.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- Name UC HII object name
15- 18 F4.2 --- tau-N2H+ [0.03/5.24]? Optical depth, τ, N2H+
20- 23 F4.2 --- e_tau-N2H+ [0.04/0.41]? Uncertainty in tau-N2H+
25- 29 F5.2 K Tex-N2H+ [2.99/19.02]? Excitation temperature,
N2H+
31- 34 F4.2 K e_Tex-N2H+ [0.07/7.53]? Uncertainty in Tex-N2H
36- 40 F5.2 10+13cm-2 N-N2H+ [0.2/24.08]? Column density, N2H+
42- 45 F4.2 10+13cm-2 e_N-N2H+ [0.1/2.84]? Uncertainty in N-N2H+
47- 51 F5.2 K Trot-CCS [4.88/24.65]? Rotational temperature, CCS
53- 57 F5.2 K e_Trot-CCS [0.59/17.7]? Uncertainty in Trot-CCS
59 A1 --- f_Trot-CCS Flag on Trot-CCS (1)
61- 65 F5.2 10+11cm-2 N-CCS [0.85/16.6]? Column density, CCS
67- 71 F5.2 10+11cm-2 e_N-CCS [0.21/2.41]? Uncertainty in N-CCS
73 A1 --- f_N-CCS Flag on N-CCS (1)
75- 80 F6.2 --- NRatio [13.39/375.03]? Column density Ratio,
N(N2H+)/N(CCS)
82- 86 F5.2 --- e_NRatio [2.78/97.66]? Uncertainty in NRatio
--------------------------------------------------------------------------------
Note (1): Flag as follows:
* = Average value of Trot-CCS and the corresponding column density
of N-CCS.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Stage Evolutionary State (1)
6- 18 A13 --- Name Object name
20- 23 F4.2 --- tau-N2H+ [0.1/5.0]? Optical depth, τ, N2H+
25- 28 F4.2 --- e_tau-N2H+ [0.01/2.0]? Uncertainty in tau-N2H+
30- 34 F5.2 K Tex-N2H+ [3.0/44.1]? Excitation temperature, N2H+
36- 39 F4.2 K e_Tex-N2H+ [0.05/4.0]? Uncertainty in Tex-N2H
41- 44 F4.2 10+13cm-2 N-N2H+ [0.24/3.61]? Column density, N2H+
46- 49 F4.2 10+13cm-2 e_N-N2H+ [0.05/2.27]? Uncertainty in N-N2H+
51- 55 F5.2 10+11cm-2 N-CCS [0.51/18.83]? Column density, CCS
57- 60 F4.2 10+11cm-2 e_N-CCS [0.25/4.96]? Uncertainty in N-CCS
62- 67 F6.2 --- NRatio [3.35/242.98]? Column density Ratio,
N(N2H+)/N(CCS)
69- 74 F6.2 --- e_NRatio [1.41/161.78]? Uncertainty in NRatio
76- 125 A50 --- Ref References for measurements
--------------------------------------------------------------------------------
Note (1): Evolutionary state as follows:
HMSC = High-Mass Starless Cores (14 occurrences)
HMPO = High-Mass Protostellar Cores (19 occurrences)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table9.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- Name HMSC and HMPO Sample name
15- 16 I2 h RAh Hour of Right Ascension (J2000)
18- 19 I2 min RAm Minute of Right Ascension (J2000)
21- 24 F4.1 s RAs Second of Right Ascension (J2000)
26- 26 A1 --- DE- Sign of the Declination (J2000)
27- 28 I2 deg DEd Degree of Declination (J2000)
30- 31 I2 arcmin DEm Arcminute of Declination (J2000)
33- 34 I2 arcsec DEs Arcsecond of Declination (J2000)
36- 40 F5.2 kpc Dist [3.04/10.8] Heliocentric Distance
42- 45 F4.2 kpc e_Dist [0.46/1.61] Uncertainty in Dist
47- 50 A4 --- Stage Evolutionary State (1)
52- 52 I1 --- Ref [1/2] References (2)
--------------------------------------------------------------------------------
Note (1): Evolutionary state as follows:
HMSC = High-Mass Starless Cores (8 occurrences)
HMPO = High-Mass Protostellar Cores (7 occurrences)
Note (2): References as follows:
1 = Sridharan+2005 (2005ApJ...634L..57S 2005ApJ...634L..57S)
2 = Sridharan+2002 (2002ApJ...566..931S 2002ApJ...566..931S)
--------------------------------------------------------------------------------
History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Robin Leichtnam [CDS] 21-May-2026