Proceedings of The National Conference
On Undergraduate Research (NCUR) 2012
Webster State University Ogden, Utah
March 29 - March 31, 2012
The Kinematics of the Ionized Hydrogen in NGC 3372 (Carina Nebula)
2
Clarissa D. Vázquez Colón, 2Milennys Velázquez Flores, 2Milzaida Merced Sanabria
, and 1Grace M. Fontánez Santana
1
Petra Mercado Bougart High School
Humacao P.R. 00791
2
Department of Physics and Electronics
University of Puerto Rico at Humacao,
Humacao, P.R. 00791
Faculty Advisor: Juan C. Cersosimo and Rafael Muller
Abstract
A typical characteristic of the Carina Nebula is its complex kinematical structure which is observed in optical and
radio lines. Due to the existence of many young and massive stars, there are considerable amounts of ionized gas.
By using observations of the atomic transition H166α radio recombination line (RRL) the behavior of the
kinematics of the ionized gas in the region was studied. In this work a grid of about 600 profiles, obtained with the
Parkes Radio-telescope, has been analyzed. Each profile was processed in order to fit a base line and after that a
Gaussian fit was made for each position. The radial velocity resolution of the profiles is about 4 km s-1. Finally, the
region was mapped for different radial velocity at interval of 10 km s-1. A set of maps shows the kinematics of the
gas which suggests a shell like structure of ionized gas. It is apparent that the structure is spatially correlated with
the young open clusters Trumpler (Tr) 14 and 16. As a result it is suggesting that the ionized gas is being blown
out by the stellar wind of the young stars of the cluster.
Keywords: Interstellar matter, Carina Nebula
1. Introduction
Radio recombination lines (RRLs) provide relevant information about the physical conditions of an HII region: the
gas distribution, the kinematic, and the physical conditions where the line is detected. In the southern sky the NGC
3372 has been observed at various radio recombination lines, and the main discussion about its distribution is if the
ionized gas arises from two separated structures or if there exists, an expansion showing profiles with concentrations
at two radial velocities. (It is not clear what that sentence is trying to say.) As was shown in early observations the
typical characteristic of the Carina Nebula is its complex kinematical structure. In Figure 1 are shown the location of
the NGC3372 and the stellar clusters catalogued in the area1. The open clusters Tr 14 and 16 are located at the
distance of the Carina Nebula.
The large-scale dynamics measured across the nebula are extremely complex. Some interpretations involve
merging spiral arms2, rotating neutral clouds3 and the low density extended HII regions4. Systematic HII studies in
Carina Nebula were also undertaken5. In this paper we report on a detailed study of ionized hydrogen in the region
of the open clusters Tr 14 and 16, located in Carina nebula’s region. It is suggested that only the clusters Tr 14 and
16 are associated with the ionized gas, at a distance of about 2400 pc6,7.
Figure 1: Map1 of the region studied. It shows the relative spatial distribution of the optical emission (bright areas)
and infrared (dark areas). The boxes indicate the stellar clusters. Tr 14 and 16 are located in the area of NGC 3372.
The remaining clusters are at different distances.
2. Observations
The region l = 287o < l < 288o.4 and b = −1o.3 < b < 0o.1 was mapped at the H166α line frequency (1424.734 MHz).
The receiver used was the Parkes multibeam, a 13-beam receiver package mounted at the prime focus of the Parkes
Radio-telescope. The inner 7 beams are packed in a hexagonal configuration with a beam separation on the sky of
29’.1. On-the-fly mapping was performed by scanning the telescope at a rate of 1◦ minute−1 in R.A., recording
spectra every 5 s. The data were recorded in 512 channels across a 4 MHz bandwidth, giving a channel width of 7.8
kHz (∆v = 1.6 km).
The frequency switching mode was used to allow for robust band-pass correction. We switched every 5 s between
center frequencies of 1423.5 and 1425.0 MHz. Band-pass calibration was performed using the Live data package
that also performed the Doppler correction to shift the spectra to the kinematic local standard of rest (LSR).
Absolute brightness temperature calibration was checked nightly against α = 19h:34m, δ = −6o 38’ (J2000) and
Hydra A. The calibrated spectra were gridded into a data cube using the Gridzilla package of the Australia
Telescope National Facility (ATNF). The effective resolution of the gridded data is 16’. The per-channel rms in the
resulting cube is 28 mK. The data have not been corrected for stray radiation.
3. Results
The results are summarized in Fig. 2. In it a series of seven line-power of the emission line contour maps are shown
on l, b diagrams. The radial velocity of each map is indicated in the upper left corner and contour levels are given in
K km s-1. By inspecting such maps, besides the strong emission features present at, one gets the impression to be
looking at cross cuts through an expanding shell. The map displays a typical ionized hydrogen distribution of an HII
region, representative of structures on a galactic scale, and emission line contour lines more or less parallel to the
galactic plane. In the velocity range from –60 to –50, –50 to –40, –40 to –30, –30 to –20, and –20 to –10 to 0.0, and
0 to 10 km s-1 at extreme velocities range the weak emission of the ionized gas is occupying the region around l =
287.7o, b = –0.7o. The power of the line was calculated by = , where is the line temperature and is
the velocity range, and are the extremes of the velocity range. Figure 2 shows velocity cuts of the line-power
at longitude-latitude maps for the region studied. Such distribution show a gap of electron density between velocities
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-30 to -10 km s-1 around l = 287.7o, b = –0.7o with respect to the East and West position. The emission for extreme
velocities, which range from –10 to 0 and 0 to +10 km s-1 , are suggesting a ring-like structure, characteristic
signature of an expanding shell that is partially recognized. At extreme radial velocities, -60.0 to -50.0 km s-1 and 0
to +10 km s-1 respectively, regions tentatively associated with approaching and receding caps are envisaged. In
order to justify our hypothesis about the mechanical interaction between the ionized hydrogen and the stars, we
show in Fig. 3 cross-cuts of the line distribution across such shell. The cuts were obtained for different galactic
latitude and using the integrated power of the line. Over the cuts are shown the position of the shell and the gap of
the gas. It is apparent that the gap is well correlated with the position of the open clusters Tr 14 and 16. The shell
center has been derived as the centroid of the total shell emission distribution. Linear dimensions of the shell were
derived from measurements carried out at different position angles from the shell center. The diameter of the shell at
the peak is about 18 pc. The position is around l = 287.5o, b = −0.7o, and the Shell thickness, 7.7 pc. A typical error
of such parameters amount is about 10-15 % of the quoted values in Table 1.
Figure 2: Latitude-Longitude map of brightness line contour maps for the velocity range -60 to -50, -50 to
-40, -40 to -30, -30 to -20, -20 to -10, -10, to 0, 0 to +10 km s-1 . The scale of the contour is shown to the
bottom-right corner. The contour levels are in K km s-1.
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Table 1: Parameter of the HII expanding structure:
Properties
Shell centre
HII systemic velocity
Shell radio at the peak
Expansion velocity
Shell thickness
l = 287.5o, b = −0.7o
−20 km s-1
18 pc
30 km s-1
7.7 pc
Figure 3: Full velocity integrated line-power emission between -60 and +10 km s-1 as a function of the
galactic longitude at four galactic latitudes. The arrow marks the shell’s wall position, and the gap of the
ionized hydrogen is indicated.
4. Conclusions
Observational evidence of a large and expanding H II (region of ionized hydrogen) structure located in a region of
NGC 3372 has been presented. The distance of the ionized gas agrees well with the photometric distance of the
clusters5,6. The following chain of events may explain the observations: 1) after the birth of Tr 14 and 16, 7 and 6
million of years ago, respectively, its most massive stars by the action of strong stellar winds, together with UV
radiation, gave rise to an ionized interstellar bubble, 2) such bubble, while expanding, swept up interstellar material
and slowed down, forming the wall, probably stopped by molecular clouds7.
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5. Acknowledgements
We thank to professors Idalia Ramos and Gilda Jiménez for encourage and support the present research. This work
was partially supported by NSF-DMR-0934195 (PREM).
6. References
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Structure of the Carina Nebula” The Astrophysical Journal 532 (2000): L145-L148.
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Monthly Notices of the Royal Astronomical Society 249 (1991): 716-721.
3. J. Meaburn, J. A. Lopez, and D. Keir, “Insect-eye, Fabry-Perot observations of the largescale motions within
the Carina nebula (NGC 3372, RCWS3)” Monthly Notices of the Royal Astronomical Society 211 (1984): 267-276.
4. I. N. Azcárate, J. C. Cersosimo, and F. R. Cólomb, “The H166α Recombination Line in the Carina Nebula”
Revista Mexicana de Astronomia y Astrofísica 6 (1981): 267-272.
5. K. J. Brooks, J. W. V. Storey, and J. B. Whiteoak, “HllOa recombination-line emission and 4.8-GHz
Continuum emission in the Carina nebula” Monthly Notices of the Royal Astronomical Society 327 (2001): 46-54.
6. K. J. Brooks, (2000), PhD “An investigation of the Carina Nebula” thesis Univ. New South Wales. (2000)
7. Kris Davidson, and Roberta M. Humphreys, “Eta Carina and Its Environment” Annual Review of Astronomy
and Astrophysics 35 (1997): 1-32.
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