2022/10/11 2023/01/19 $\langle$publication date$\rangle$

ISM: H II regions — ISM: clouds — ISM: molecules — ISM: bubbles — stars:
formation — ISM: individual objects (N49, G028.83-0.25)

# Ammonia mapping observations of the Galactic infrared bubble N49: Three NH3
clumps along the molecular filament

Mikito Kohno11affiliation: Astronomy Section, Nagoya City Science Museum,
2-17-1 Sakae, Naka-ku, Nagoya, Aichi 460-0008, Japan 22affiliation: Department
of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-
ku, Nagoya, Aichi 464-8602, Japan ∗ James O. Chibueze33affiliation: Centre for
Space Research, Potchefstroom campus, North-West University, Potchefstroom
2531, South Africa 44affiliation: Department of Physics and Astronomy, Faculty
of Physical Sciences, University of Nigeria, Carver Building, 1 University
Road, Nsukka 410001, Nigeria Ross A. Burns55affiliation: National Astronomical
Observatory of Japan (NAOJ), National Institutes of Natural Sciences (NINS),
2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan Toshihiro Omodaka66affiliation:
Graduate School of Science and Engineering, Kagoshima University, 1-21-35
Korimoto, Kagoshima, Kagoshima 890-0065, Japan Toshihiro
Handa66affiliationmark:  77affiliation: Amanogawa Galaxy Astronomy Research
Center (AGARC), Kagoshima University, 1-21-35 Korimoto, Kagoshima, Kagoshima
890-0065, Japan Takeru Murase66affiliationmark:  Rin I.
Yamada22affiliationmark:  Takumi Nagayama88affiliation: Mizusawa VLBI
Observatory, National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka-
shi, Tokyo 181-8588, Japan Makoto Nakano99affiliation: Faculty of Science and
Technology, Oita University, 700 Dannoharu, Oita, Oita 870-1192, Japan
Kazuyoshi Sunada88affiliationmark:  Kengo Tachihara22affiliationmark:  Yasuo
Fukui22affiliationmark<EMAIL_ADDRESS><EMAIL_ADDRESS>
###### Abstract

We have carried out the NH3 $(J,K)=(1,1),(2,2),$ and $(3,3)$ mapping
observations toward the Galactic infrared bubble N49 (G28.83$-$0.25) using the
Nobeyama 45 m telescope. Three NH3 clumps (A, B, and C) were discovered along
the molecular filament with the radial velocities of $\sim$ 96, 87, and 89 km
s-1, respectively. The kinetic temperature derived from the NH3 (2,2)/NH3
(1,1) shows $T_{\rm kin}=27.0\pm 0.6$ K enhanced at Clump B in the eastern
edge of the bubble, where position coincides with massive young stellar
objects (MYSOs) associated with the 6.7 GHz class II methanol maser source.
This result shows the dense clump is locally heated by stellar feedback from
the embedded MYSOs. The NH3 Clump B also exists at the 88 km s-1and 95 km
s-1molecular filament intersection. We therefore suggest that the NH3 dense
gas formation in Clump B can be explained by a filament-filament interaction
scenario. On the other hand, NH3 Clump A and C at the northern and southern
side of the molecular filament might be the sites of spontaneous star
formation because these clumps are located $\sim$ 5$-$10 pc away from the edge
of the bubble.

##  1 Introduction

Ionized hydrogen (H II) regions are formed by the ultra-violet radiation from
OB-type stars. They are known to be sites of triggered star formation from
previous works of observations and theories (e.g., [Elmegreen (1998)]) and are
also identified as “interstellar bubbles” (e.g., [Castor et al. (1975), Weaver
et al. (1977)]). For example, the Galactic Legacy Infrared Mid-Plane Survey
Extraordinaire (GLIMPSE) by the Spitzer space telescope found $\sim 600$
infrared bubbles in the Galactic plane
($|l|\leq\timeform{65D},|b|\leq\timeform{1D}$: [Churchwell et al. (2006),
Churchwell et al. (2007)]). Most of them are H II regions excited by OB-type
stars inside the bubbles (Deharveng et al., 2010). Two star formation
scenarios regarding bubbles have recently been discussed as “collect-and-
collapse” (Deharveng et al. (2010)) and “cloud-cloud collisions” (Fukui et al.
(2021)) based on their morphology and distributions of parent clouds. The
former is shock compression by the expansion of H II regions which triggers
second generation star formation at the edge of the bubble (e.g., Elmegreen &
Lada (1977); Whitworth et al. (1994); Deharveng et al. (2005); Hosokawa &
Inutsuka (2006); Zavagno et al. (2006, 2007); Dale et al. (2007); Thompson et
al. (2012); Xu & Ju (2014); Palmeirim et al. (2017); Li et al. (2019); Luisi
et al. (2021)). The latter is the two clouds with different sizes colliding,
triggering the formation of exciting stars and forming arc-like morphology
(e.g., Habe & Ohta (1992); Hasegawa et al. (1994); Higuchi et al. (2014);
Torii et al. (2015); Baug et al. (2016); Fukui et al. (2018); Ohama et al.
(2018); Koide et al. (2019); Fujita et al. (2019); Kohno et al. (2021b);
Yamada et al. (2021); Enokiya & Fukui (2022)). These scenarios are possibly
related to infrared bubbles, however, the dominant mechanism remains unclear.

Figure 1: (a) Spitzer three color composite image of the infrared bubble N49.
Blue, green, and red show $3.6\ \mu$m, $8.0\ \mu$m, and $24\ \mu$m,
respectively. Yellow enclosed area indicates the NH3 mapping region of our
project. (b) The close-up image of (a). White contours show the VLA 1.4 GHz
continuum image (Helfand et al., 2006). The lowest contour level and interval
are 2 and 1 mJy/beam, respectively. The ultra-compact H II region, YSO #1, and
YSO #3 are labeled (see Figure 18 in Deharveng et al. (2010) and Watson et al.
(2008)). (c) The peak intensity ($T_{\rm MB}$) map of 13CO $J=$1-0 obtained by
the FUGIN project (Umemoto et al., 2017; Torii et al., 2019). The black lowest
contour level and interval are 3.5 and 1.0 K, respectively. White contours
show the VLA 1.4 GHz continuum image. The white contour levels are 2.0, 3.0,
4.0, 5.0, and 6.0 mJy/beam. The white cross indicates the position of the 6.7
GHz class II methanol maser source (Cyganowski et al., 2008, 2009).

N49 (also known as G28.83$-$0.25) is an infrared bubble at
$(l,b)\sim(\timeform{28.83D},\timeform{-0.23D})$ in the Galactic plane
(Zavagno et al., 2010), which is identified as a “closed bubble” based on
AKARI 9 $\mu$m infrared morphology (Hattori et al., 2016; Hanaoka et al.,
2019, 2020). It has been studied as a representative “wind-blown bubble”
(Everett & Churchwell, 2010). The distance to N49 from the solar system is
5.07 kpc associated with the Scutum Arm (Dirienzo et al., 2012; Dewangan et
al., 2017). Figure 1(a) shows the three-color composite image of the Spitzer
space telescope (Werner et al., 2004). Blue, green, and red present the 3.6
$\mu$m, 8.0 $\mu$m, and 24 $\mu$m images, respectively. These bands trace the
thermal emission from the stars, polycyclic aromatic hydrocarbons (PAH)
emission in the photo-dissociation region (e.g., Draine & Li (2007); Draine
(2003)), and hot dust heated by OB-type stars (e.g., Carey et al. (2009)),
respectively. Figure 1(b) presents the close-up image of the N49 bubble. White
contours indicate the Very Large Array (VLA) 1.4 GHz continuum image, which
traces distributions of the ionized gas. The distribution of the ionized gas
coincide the hot dust emission traced by Spitzer 24 $\mu$m image. YSO $\\#$1,
YSO $\\#$3, and the ultra-compact H II region (UCH II ) exist at the bubble’s
eastern edge (see Figure 18 in Deharveng et al. (2010)). Previous studies
reported that YSO $\\#$3 is associated with the 6.7 GHz class II methanol
maser embedded in the massive YSOs and referred to as extended green objects
(EGOs: Cyganowski et al. (2008, 2009), and see also data base of astrophysical
masers Ladeyschikov et al. (2019)
111https://maserdb.net/object.pl?object=G28.833-0.252). Figure 1(c) shows the
13CO $J=$1-0 peak intensity map obtained by the Nobeyama 45 m telescope
(Umemoto et al., 2017; Torii et al., 2019). The optically thinner 13CO $J=$1-0
can trace a molecular hydrogen density of $n(\rm{H_{2}})\sim 10^{3}$ cm-3
(e.g., Solomon et al. (1979); Nagahama et al. (1998); Kawamura et al. (1998);
Jackson et al. (2006); Torii et al. (2019)). Thus, it is appropriate to study
the large-scale structure in the surrounding of the dense gas. 13CO has the
filamentary structure and arc-like morphology around the ionized gas at the
eastern side of the N49 bubble (see also Figure 12 in Yan et al. (2016)).

Previous studies of the N49 bubble suggested triggering of star formation by
expanding H II region (Watson et al., 2008; Dirienzo et al., 2012). Xu et al.
(2019) performed CO observations toward the molecular filament and bubble. The
authors argue that feedback from the H II region affects star formation and
helps to drive the turbulence in the filament. On the other hand, Dewangan et
al. (2017) found two different radial velocity filaments associated with the
bubble. They argued that the filament-filament collision scenario could
explain the massive star formation at the edge of the bubble.

Star formation scenarios are discussed in previous works, while the dense gas
formation mechanism related to star formation of the N49 bubble and the
molecular filament is not yet clear. The NH3 emission can trace dense gas
($n(\rm{H_{2}})\gtrsim 10^{4}$ cm-3) and derive the kinetic temperature of
molecular gas because of the excitation of the NH3 inversion transitions in
the lowest metastable rotational energy states at low temperatures. It also
allows us to derive the optical depth and column density, using the splitting
of the inversion transitions into different hyperfine structure components
around 23GHz (e.g., Cheung et al. (1968, 1969); Morris et al. (1973); Walmsley
& Ungerechts (1983); Ho & Townes (1983)). Previous studies of NH3 observations
toward the N49 bubble focused only on the dust clumps identified by the APEX
Telescope Large Area Survey of the Galaxy (ATLASGAL: e.g.,Wienen et al.
(2012)). In order to trace the large-scale structure of the environment around
the dust clumps, we performed mapping observations (of about 30 pc) of the NH3
inversion transition of $(J,K)=(1,1),(2,2),$ and $(3,3)$ using the Nobeyama 45
m telescope (see the yellow enclosed area in Figure 1a and c). $J$ and $K$ are
the quantum number of the total angular momentum and their projection along
the molecular axis (Ho & Townes, 1983). In this paper, we adopted the energy
levels of each NH3 transition from the Jet Propulsion Laboratory (JPL)
spectral line catalog222https://spec.jpl.nasa.gov (Pickett et al., 1998). This
paper is structured as follows: section 2 introduces observations and the
archive data; section 3 presents the NH3 results; in section 4, we discuss
dense gas and star formation scenarios in three NH3 clumps along the molecular
filament, and in section 5, we show a summary of this paper.

##  2 Observations

Properties of our observations.  Telescope Molecule Transition $E_{u}/k_{\rm
B}$ $\nu_{0}$ Receiver Grid HPBW Velocity RMS noise [K] [GHz] spacing
Resolution level (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) Nobeyama 45 m NH3
$(J,K)=(1,1)$ 23.3 23.694 H22 37.5” 75” 0.39 km s-1 $\sim 0.03$ K NH3
$(J,K)=(2,2)$ 64.4 23.723 H22 37.5” 75” 0.39 km s-1 $\sim 0.03$ K NH3
$(J,K)=(3,3)$ 123.5 23.870 H22 37.5” 75” 0.39 km s-1 $\sim 0.03$ K Columns:
(1) Telescope name (2) Molecules (3) Transitions. $J$ and $K$ are the quantum
number of total angular momentum and their projection along the molecular
axis, respectively. (4) Upper energy levels ($E_{u}$) of inversion transitions
above the ground state divided by the Boltzmann constant ($k_{\rm B}$). (5)
Rest frequency ($\nu_{0}$) (6) Receiver name (7) Grid spacing of the multi-ON-
OFF switching observations (8) Half-power beam width (9) Velocity resolution
(10) r.m.s noise level of the $T_{\rm MB}$ scale.

###  2.1 The KAGONMA project: NH3 mapping observations using the Nobeyama 45 m
telescope

We carried out the NH3 $(J,K)=(1,1),(2,2),$ and $(3,3)$ mapping observations
using the Nobeyama 45 m telescope led by Kagoshima University. Our NH3 survey
project is also called “KAGONMA”333See also conference proceedings by Handa et
al. (2006); Murase et al. (2020); Takeba et al. (2022). (Kagoshima galactic
object survey with the Nobeyama 45-metre telescope by mapping in ammonia
lines) and making use of this survey papers on the Galactic Center and massive
star forming regions were published (Nagayama et al. (2007, 2009); Toujima et
al. (2011); Chibueze et al. (2013); Nakano et al. (2017); Burns et al. (2019);
Murase et al. (2022); Kohno et al. (2022); Hirata et al. (2022)). We utilized
the dual-polarization and the multi-ON-OFF switching (three ON points per one
OFF point) mode. The observational period was from December 2014 to June 2015
(PI T. Omodaka:
BU145001444https://www.nro.nao.ac.jp/~nro45mrt/html/prop/accept/accept2014.html).
The half-power beam width (HPBW) and grid spacing was 75” at 23 GHz and 37.5”,
respectively. We used the High Electron Mobility Transistor (HEMT) receiver
named H22 at 22 GHz as the front-end. The pointing accuracy was checked within
5” observing the H2O maser source OH43.8-0.1 $(\alpha_{\rm J2000},\delta_{\rm
J2000})=(\timeform{19h11m54s},\timeform{+09d35^{\prime}55"})$ before starting
observations. The FX-type digital spectrometer was used as the back-end
system. It is named Spectral Analysis Machine of the 45 m telescope (SAM 45
:Kuno et al. (2011); Kamazaki et al. (2012)). The system noise temperature
($T_{\rm sys}$) including the atmosphere was 150-250 K during observations. We
used 8 intermediate frequencies (IFs) to observe the NH3 $(J,K)=(1,1),(2,2)$,
$(3,3)$, and H2O maser with the dual-polarization simultaneously. Each IF’s
frequency bandwidth and resolution were 125 MHz and 30.52 kHz corresponding to
the velocity coverage of 1600 km s-1and spacing of 0.39 km s-1at 23 GHz,
respectively. The chopper wheel method was adopted to calibrate to the
intensity of the antenna temperature ($T_{a}^{*}$: Ulich, & Haas (1976);
Kutner, & Ulich (1981)). We used the NEWSTAR software package (Ikeda et al.,
2001)555https://www.nro.nao.ac.jp/~nro45mrt/html/obs/newstar/index.html to
make the cube file from the raw data. We subtract baselines with a first-order
polynomial function from the spectra. The baseline ranges were set up
emission-free channels of each spectrum. Then, we applied the hanning
smoothing (width=5) in the velocity domain to improve the signal-to-noise
ratio. The antenna temperature was converted to the main-beam temperature
($T_{\rm MB}$) using the relation of $T_{\rm MB}=T_{a}^{*}/\eta_{\rm MB}$. The
main-beam efficiency ($\eta_{\rm MB}$) is 0.835, the average value of two
channels of the H22 receiver in the Nobeyama 45 m telescope. The kinetic
temperature and physical parameters are not dependent on the main-beam
efficiency because we can derive them from intensity ratios of different
transitions around 23 GHz obtained by the same instrument of a radio
telescope. The root-mean-square noise level for the final data was $\sim 0.03$
K at the $T_{\rm MB}$ scale (corresponding to $\sim 0.025$ K at the
$T_{a}^{*}$ scale). The parameters of our NH3 data are summarized in Table 2.

###  2.2 Archival data

We utilized the 13CO $J=$1-0 data comparing with NH3 spatial and velocity
distributions. It was obtained by the FOREST Unbiased Galactic plane Imaging
survey with the Nobeyama 45-m telescope (FUGIN666https://nro-fugin.github.io:
Umemoto et al. (2017); Kohno et al. (2018); Nishimura et al. 2018,2021; Torii
et al. (2019); Sofue et al. (2019); Nakanishi et al. (2020); Sato et al.
(2021); Fujita et al. (2021); Kohno et al. (2021a)). The FUGIN CO survey
adopted the On-the-fly (OTF) mapping mode (Sawada et al., 2008) and used the
FOur-beam REceiver System on the 45m Telescope (FOREST) with the four beams,
dual-polarization, side-band separating receiver (Minamidani et al., 2016;
Nakajima et al., 2019). The HPBW and effective resolution convolved by the
Gaussian kernel function is $\timeform{15"}$ and $\timeform{21"}$ at 110 GHz,
respectively. The effective velocity resolution is 1.3 km s-1. Smoothing the
data cube by a Gaussian kernel function resulted in a resolution of
$\sim\timeform{40"}$. The r.m.s noise level is $\sim 0.3$ K at the main beam
temperature scale. We used the 1.4 GHz ($=$ 20 cm) radio continuum image with
the angular resolution of $\sim$ 6” taken from the Multi-Array Galactic Plane
Imaging Survey (MAGPIS) with VLA (White et al., 2005; Helfand et al., 2006).
The 1.4 GHz radio continuum image is useful to investigate the free-free
emission corresponding to the ionized gas from H II regions. We also obtained
the archive data of the Spitzer Space telescope with the wavelength of $3.6\
\mu$m, $8\ \mu$m (Benjamin et al., 2003; Churchwell et al., 2009), and $24\
\mu$m (Carey et al., 2009). The 870 $\mu$m dust continuum image is also taken
from ATLASGAL777http://www3.mpifr-bonn.mpg.de/div/atlasgal/ (Schuller et al.,
2009). These fits cubes were taken from the MAGPIS web
page888https://third.ucllnl.org/gps/.

###  2.3 Software packages

In this paper, we used the following software packages to create the maps,
extract the spectra, and calculate physical parameters (Astropy: Astropy
Collaboration et al. (2013, 2018), NumPy: van der Walt et al. (2011),
Matplotlib: Hunter (2007), IPython: Perez, & Granger (2007), Miriad: Sault et
al. (1995), and APLpy: Robitaille & Bressert (2012)).

##  3 Results

###  3.1 NH3 spatial distributions

Figure 2 shows the peak temperature map of the main line in (a) NH3
$(J,K)=(1,1)$, (b) NH3 (2,2), and (c) NH3 (3,3). The white contours present
the ionized gas distribution traced by the VLA 1.4 GHz radio continuum image.
We identified three clumps in the NH3 (1,1) line as revealed by the intensity
peaks along the molecular filament (Figure 2a). Hereafter, we called these
clumps “Clump A”, “Clump B”, and “Clump C”. The NH3 (1,1) peak in Clump B
exists on the eastern side of the N49 bubble offset from the ionized gas. We
detected the NH3 (2,2) in Clump A, B, and C (Figure 2b). The NH3 (3,3)
emission is enhanced in Clump B at the eastern edge of the bubble (Figure 2c).

Figure 2: Peak intensity ($T_{\rm MB}$) map of (a) NH3 $(J,K)=(1,1)$, (b) NH3
(2,2), and (c) NH3 (3,3). The lowest cyan contour level and intervals of NH3
are 0.12 K ($\sim 4\sigma$) and 0.12 K ($\sim 4\sigma$), respectively. Three
NH3 clumps are labeled in panel (a). A, B, and C show the positions of the
spectra in Figure 3. The white contour levels of the VLA 1.4 GHz continuum
image are 2.0, 3.0, 4.0, 5.0, and 6.0 mJy/beam. Red cross indicates the
position of the 6.7 GHz class II methanol maser source (Cyganowski et al.,
2008, 2009).

Figure 3: NH3 spectra at A $(l,b)=(\timeform{28.921D},\timeform{-0.237D})$, B
$(l,b)=(\timeform{28.827D},\timeform{-0.268D})$, and C
$(l,b)=(\timeform{28.712D},\timeform{-0.299D})$. These positions are also
presented in Figure 2(a). Red lines show the results from a Gaussian function
fitted to the emission at the main component. NH3 (1,1) emissions include four
satellite components of $F_{1}=1\rightarrow 0$, $F_{1}=1\rightarrow
2$,$F_{1}=2\rightarrow 1$, and $F_{1}=0\rightarrow 1$ (from left to right on
the velocity axis).

Figure 3 shows the NH3 peak spectrum at Clump A, B, and C. The locations of
each spectrum are labeled in Figure 2(a). In the NH3 (1,1) emission, the main
line exists as the center velocity of each spectrum. We also detected the
hyper-fine structures of the inner ($F_{1}=1\rightarrow 2,2\rightarrow 1$) and
outer satellite lines ($F_{1}=1\rightarrow 0$, $0\rightarrow 1$), where
$F_{1}$ is the quantum number of the angular momentum, contributing to the
nitrogen nuclear-spin. The intensity peak of NH3 (1,1) exists at Clump C,
while NH3 (3,3) has a peak intensity at Clump B. We derived the peak
temperature, peak velocity, and full-width half maximum (FWHM: hereafter, we
call it the line width) obtained by a Gaussian fitting toward the main line of
each profile. The profile parameters are summarized in Table 3.1. The errors
are the standard deviations of each fitting parameter.

NH3 spectra parameters of the main line in each NH3 clump  Name $l$ $b$
Transition ${T_{\rm MB}}$ $v_{\rm LSR}$ $\Delta v$ [degree] [degree] $(J,K)$
[K] [km s-1] [km s-1] (1) (2) (3) (4) (5) (6) (7) A $28.921$ $-0.237$ (1,1)
${0.61\pm 0.02}$ $96.4\pm 0.04$ $2.3\pm 0.10$ (2,2) ${0.22\pm 0.01}$ $96.4\pm
0.05$ $1.9\pm 0.11$ (3,3) ${0.10\pm 0.01}$ $95.6\pm 0.12$ $2.6\pm 0.29$ B
$28.827$ $-0.268$ (1,1) ${1.09\pm 0.04}$ $86.9\pm 0.02$ $2.5\pm 0.10$ (2,2)
${0.56\pm 0.007}$ $86.9\pm 0.02$ $2.8\pm 0.04$ (3,3) ${0.39\pm 0.007}$
$86.8\pm 0.03$ $3.3\pm 0.06$ C $28.712$ $-0.299$ (1,1) ${1.26\pm 0.05}$
$88.7\pm 0.04$ $1.9\pm 0.10$ (2,2) ${0.47\pm 0.01}$ $88.5\pm 0.03$ $1.8\pm
0.06$ (3,3) ${0.11\pm 0.008}$ $88.4\pm 0.19$ $4.9\pm 0.44$ Columns: (1) Name
of each spectra (2) Galactic Longitude (3) Galactic Latitude (4) Rotational
transition (5) Peak temperature ($T_{\rm MB}$) (6) Peak velocity by a single
Gaussian fitting (7) The line width ($2\sigma\sqrt{2\ln 2}$) of spectra by a
Gaussian fitting, where $\sigma$ is the standard deviation of the line
profile. The errors are the standard deviations of each fitting parameter.

###  3.2 Three NH3 clumps with the different radial velocity

Figure 4, 5, and 6 show the NH3 (1,1), NH3 (2,2) ,and NH3 (3,3) velocity
channel map, respectively. Clump A, B, and C has an intensity peak of all
transitions at 96-97 km s-1(panel i in Figure 4-6), 85-88 km s-1(panel b and c
in Figure 4-6), and 88-90 km s-1(panel d in Figure 4-6), respectively. Clump A
and B connect with the diffuse NH3 (1,1) emission of 94-97 km s-1(Figure 4h
and 4i). To investigate the velocity field of each clump in more detail, we
made the peak velocity and line width map of the NH3 (1,1) main line obtained
by a Gaussian fitting toward a profile at each pixel.

Figure 4: Velocity channel map of NH3 $(J,K)=(1,1)$. The lowest cyan contour
level and intervals are 0.05 K km s-1 ($\sim 3\sigma$) and 0.13 K km s-1
($\sim 8\sigma$), respectively. The red cross and white contours are the same
as in Figure 2a. The white contour levels of the VLA 1.4 GHz continuum image
are 2.0, 3.0, 4.0, 5.0, and 6.0 mJy/beam. Figure 5: Same as Figure 4, but for
NH3 $(J,K)=(2,2)$. Figure 6: Same as Figure 4, but for NH3 $(J,K)=(3,3)$.

Figure 7(a) and (b) shows the peak velocity and line width map of the NH3
(1,1) main line, respectively. Clump A, B, and C have different radial
velocities at $\sim 96$, $\sim 87$, and $\sim 89$ km s-1(Figure 7a). We also
find the 100 km s-1velocity component at
$(l,b)\sim(\timeform{28.72D},\timeform{-0.24D})$ around the northwestern side
of Clump C. The line width of Clump A is $\sim 2.3$ km s-1. Clump B has a
large line width of $\sim 3.0$ km s-1around the methanol maser source shown in
the cross mark. Finally, we point out that Clump C has a uniform line width of
$\sim 2.0$ km s-1.

Figure 7: (a) Peak velocity and (b) velocity width maps of the NH3
$(J,K)=(1,1)$ line resulting from a Gaussian function fitted to the emission
within pixels above 0.12 K ($>4\sigma)$. The black contours show the NH3
$(J,K)=(1,1)$ peak intensity. The lowest black contour level and intervals are
0.12 K ($\sim 4\sigma$). The red cross and white contours are the same as in
Figure 2a. The white contour levels of the VLA 1.4 GHz continuum image are
2.0, 3.0, 4.0, 5.0, and 6.0 mJy/beam.

###  3.3 Physical properties of NH3 clumps

Following procedures, we estimated the physical parameters of three NH3 clumps
from our NH3 data (Ho & Townes, 1983; Ungerechts et al., 1986; Mangum et al.,
1992; Mangum & Shirley, 2015). First of all, we defined the clump radius ($r$)
by

$\displaystyle r$ $\displaystyle=\sqrt{S\over\pi},$ (1)

where $S$ is the clump area detected above $3\sigma$, assuming spherical
shapes of the NH3 (1,1) and NH3 (2,2) emission. The radius of Clump A, B, and
C is $\sim 2$ pc, $\sim 3$ pc, and $\sim 3$ pc, respectively.

Then, we estimated the optical depth ($\tau$), rotational temperature ($T_{\rm
rot}$), and total column density ($N_{\rm TOT}$). The optical depth
[$\tau(1,1,m)$] of the NH3 (1,1) main line was derived from the intensity
ratio of the main and satellite line above $2\sigma$ using the following
equation.

$\displaystyle{{T_{\rm MB}}({\rm main})\over{T_{\rm MB}}({\rm
sate})}={1-e^{-\tau({\rm 1,1,m})}\over 1-e^{-a\tau({\rm 1,1,m})}},$ (2)

where $T_{\rm MB}$ is the main-beam temperature, $a$ is the theoretical
intensity ratio, the main to the inner and outer-satellite lines are $a=0.278$
and $a=0.222$, respectively (McGary & Ho, 2002). In this paper, we adopted the
median value of four optical depths derived from the ratios of the main to
four satellite lines. The mean optical depth in Clump A, B, and C are $1.4\pm
0.6,1.6\pm 0.7,$ and $1.7\pm 0.9$, respectively. The error shows the standard
deviations of the mean value.

We estimated the rotational temperature from the NH3 (2,2)/(1,1) intensity
ratio of the main line detected above $3\sigma$. If we assume that the same
line widths of NH3 (1,1) and NH3 (2,2) (e.g., Urquhart et al. (2011); Wienen
et al. (2018)), the rotational temperature is given by

$\displaystyle T_{\rm rot}(2,2:1,1)$
$\displaystyle=-41.1\bigg{/}\ln\left[\left({-0.282\over\tau(1,1,m)}\right)\times\ln\left\\{1-{{T_{\rm
MB}}(2,2,m)\over{T_{\rm
MB}}(1,1,m)}\times(1-e^{-\tau(1,1,m)})\right\\}\right]\ [{\rm K}].$

We converted the rotational temperature to kinetic temperature ($T_{\rm kin}$)
by adopting the Monte Carlo method (Appendix B of Tafalla et al. (2004)). The
error of the kinetic temperature and rotational temperature was calculated by
the error of the Gaussian fitting toward the peak intensity of NH3 (1, 1), NH3
(2, 2), and satellite lines.

$\displaystyle T_{\rm kin}$ $\displaystyle=T_{\rm
rot}\bigg{/}\left\\{1-{T_{\rm rot}\over 41.1}\ln\left[1+1.1\exp\left(-{16\over
T_{\rm rot}}\right)\right]\right\\}\ [{\rm K}]$ (4)

Figure 8 presents the kinetic temperature distribution. The center of Clump A
has $T_{\rm kin}=17.7\pm 0.1$ K, and the northern part at
$(l,b)\sim(\timeform{28.96D},\timeform{-0.206D})$ has a high temperature of
$T_{\rm kin}=26.4\pm 0.3$ K. Clump B around the methanol maser source is
enhanced of $T_{\rm kin}=27.0\pm 0.6$ K. This peak value is consistent with
$T_{\rm dust}\sim 27$ K obtained by the Herschel continuum image (see Figure
8a in Dewangan et al. (2017)). Clump C has uniform temperature distribution of
$T_{\rm kin}\sim 14$-$18$ K.

Figure 8: The kinetic temperature map obtained by the (2,2)/(1,1) integrated
intensity ratio above the $3\sigma$ noise level. The black contours show the
NH3 $(J,K)=(1,1)$ peak intensity. The lowest black contour level and intervals
are 0.12 K ($\sim 4\sigma$). The black cross and white contours are the same
as in Figure 2a. The white contour levels of the VLA 1.4 GHz continuum image
are 2.0, 3.0, 4.0, 5.0, and 6.0 mJy/beam.

We calculated the NH3 column density from the NH3 (1,1) and NH3 (2,2) data
points above $3\sigma$. The NH3 (1,1) column density assuming Local Thermal
Equilibrium (LTE) is given by

$\displaystyle N(1,1)$ $\displaystyle=2.78\times
10^{13}\tau(1,1,m)\left({T_{\rm rot}\over[\rm K]}\right)\left({\Delta
v\over[\rm km\ s^{-1}]}\right)[{\rm cm^{-2}}],$ (5)

where $\Delta v$ is the line width of the main line. Furthermore, the NH3
column density (Turner, 1991; Wilson et al., 2013) summing up the total energy
levels is given by

$\displaystyle N_{\rm TOT}(\rm NH_{3})$ $\displaystyle=$
$\displaystyle{N(J,K)\over g_{J}\cdot g_{I}\cdot g_{K}}Q_{\rm
rot}\exp\left({E_{u}(J,K)\over kT_{\rm rot}}\right)$ (6) $\displaystyle\sim$
$\displaystyle N(1,1)\Biggr{[}{1\over 3}\exp\left({23.3\over T_{\rm
rot}}\right)+1+{5\over 3}\exp\left({-41.1\over T_{\rm rot}}\right)+{14\over
3}\exp\left({-100.2\over T_{\rm rot}}\right)\Biggr{]},$ (7)

where $Q_{\rm rot}$ is the partition function expressed as follows.

$\displaystyle Q_{\rm rot}={\displaystyle\sum_{J}\sum_{K}}g_{J}\cdot
g_{I}\cdot g_{K}\exp\left(-{E_{u}(J,K)\over kT_{\rm rot}}\right),$ (8)

where $g_{J}$ is rotational degeneracy, $g_{I}$ is nuclear spin degeneracy,
$g_{K}$ is K-degeneracy, $k$ is Boltzmann constant, and $E_{u}(J,K)$ is the
upper energy level of inversion transition from the grand state, respectively.
The uncertainties of total column densities were estimated by taking into
account errors in the rotational temperature.

Figure 9 shows the NH3 total column density map. Clump B has a high column
density of $(9.1\pm 0.4)\times 10^{15}$ cm-2 at
$(l,b)=(\timeform{28.837D},\timeform{-0.247D})$, which coincides with the UCH
II region. In contrast, Clump A and C have a low of
$(1.8^{+0.09}_{-0.08})\times 10^{15}$ cm-2 and $\sim(3.7\pm 0.3)\times
10^{15}$ cm-2, respectively. These values correspond to $\sim 3.6\times
10^{23}$ cm-2, $\sim 7.2\times 10^{22}$ cm-2, and $\sim 1.5\times 10^{23}$
cm-2 of the H2 column density, respectively. We used the $N({\rm NH_{3}})$ to
$N({\rm H_{2}}$) conversion factor of $X({\rm NH_{3}})=2.5\times 10^{-8}$
derived from the massive star-forming regions in the Galactic plane (Urquhart
et al., 2015). The peak H2 column density around the methanol maser source is
factor 4 larger than $\sim 9\times 10^{22}$ cm-2 obtained by the Herschel dust
continuum image (Dewangan et al., 2017).

Figure 9: The NH3 total column density map above the $3\sigma$ noise level.
The contours show the NH3 $(J,K)=(1,1)$ peak intensity. The lowest black
contour level and intervals are 0.12 K ($\sim 4\sigma$). The black cross and
white contours are the same as in Figure 2a. The white contour levels of the
VLA 1.4 GHz continuum image are 2.0, 3.0, 4.0, 5.0, and 6.0 mJy/beam.

Physical parameters in each NH3 clump  Name Radius ${\tau(1,1,m)}$ ${T_{\rm
rot}}$ ${T_{\rm kin}}$ ${N_{\rm tot}}$(NH3) ${N({\rm H_{2}})}$ $M_{\rm LTE}$
[pc] [K] [K] [cm-2] [cm-2] [$M_{\odot}$] (1) (2) (3) (4) (5) (6) (7) (8) Clump
A 1.6 $1.4\pm 0.6$ $16.5\pm 2.0$ $19.2\pm 3.0$ ($2.9\pm 1.0)\times 10^{15}$
$(1.2\pm 0.4)\times 10^{23}$ $2.0\times 10^{4}$ Clump B 2.8 $1.6\pm 0.7$
$15.4\pm 3.9$ $17.9\pm 5.2$ $(4.3\pm 2.2)\times 10^{15}$ $(1.7\pm 0.9)\times
10^{23}$ $9.5\times 10^{4}$ Clump C 2.8 $1.5\pm 0.6$ $14.6\pm 1.5$ $16.5\pm
2.1$ $\left(3.2\pm 1.2\right)\times 10^{15}$ $\left(1.3\pm 0.5\right)\times
10^{23}$ $7.1\times 10^{4}$ Columns: (1) Clump name (2) The clump radius
defined above $3\sigma$ of the NH3 (1,1) and NH3 (2,2) emission. (3) The mean
value of optical depth. (4) The mean value of rotational temperature. (5) The
mean value of the kinetic temperature. (6) The mean value of the total NH3
column density. (7) The mean value of H2 column density. (8) The total LTE
mass of a clump. The errors are derived by the standard deviation of the mean
value in each clump.

The LTE mass is estimated by

$\displaystyle M_{\rm LTE}$ $\displaystyle=\mu_{\rm H_{2}}m_{\rm
H}D^{2}\sum_{i}\Omega\ N_{i}(\rm{H_{2}}),$ (9)

where $\mu_{\rm H_{2}}\sim 2.8$ is the mean molecular weight per hydrogen
molecule (Appendix A.1 in Kauffmann et al. (2008)), $m_{\rm H}=1.67\times
10^{-24}$g is the proton mass, $D=5.07$ kpc is the distance to N49,
$N_{i}(\rm{H_{2}})$ is the $\rm{H_{2}}$ column density at the $i$th pixel, and
$\Omega$ is the solid angle of each grid. The LTE mass of Clump A, Clump B,
and Clump C is $2.0\times 10^{4}\ M_{\odot},9.5\times 10^{4}\ M_{\odot}$, and
$7.1\times 10^{4}\ M_{\odot}$, respectively. Dewangan et al. (2017) identified
the dust clumps using the Herschel far-infrared continuum data (see Figure 9
and Table 1 in Dewangan et al. (2017)). Our identified three NH3 clumps of A,
B, and C correspond to their dust clumps of #15 ($M_{\rm clump}=5.5\times
10^{3}\ M_{\odot}$), #12-#13 ($M_{\rm clump}=2.0\times 10^{4}\ M_{\odot}$),
and #7-#8-#9 ($M_{\rm clump}=1.5\times 10^{4}\ M_{\odot}$), respectively. We
point out that the mass of clump #12-#13 and clump #7-#8-#9 is the sum of the
individual Herschel clumps in Dewangan et al. (2017). The LTE mass calculated
from NH3 data is factor 4-5 larger than the dust clump mass estimated by
Dewangan et al. (2017). Table 3.3 presents the physical parameters of each NH3
clump. The errors were estimated by the standard deviation of the mean value
in each clump.

##  4 Discussion

###  4.1 Distributions of cold dust condensations and star formation in NH3
clumps

Figure 10 shows the NH3 distributions presented by pink contours superposed on
the 870 $\mu$m dust continuum image. We point out Clump A, B, and C
corresponding to the dust condensations of
AGAL028.922-00.227999https://atlasgal.mpifr-bonn.mpg.de/cgi-
bin/ATLASGAL_SEARCH_RESULTS.cgi?text_field_1=AGAL028.922-00.227,
AGAL028.831-00.252101010https://atlasgal.mpifr-bonn.mpg.de/cgi-
bin/ATLASGAL_SEARCH_RESULTS.cgi?text_field_1=AGAL028.831-00.252, and
AGAL028.707-00.294111111https://atlasgal.mpifr-bonn.mpg.de/cgi-
bin/ATLASGAL_SEARCH_RESULTS.cgi?text_field_1=AGAL028.707-00.294, respectively.
These dust clumps were identified by the ATLASGAL survey (Csengeri et al.
(2014); Urquhart et al. (2014)). The dust peak also exists at
$(l,b)\sim(\timeform{28.96D},\timeform{-0.20D})$, which is the northern side
of Clump A. The NH3 peaks of Clump B coincide with three dust condensations of
#1, #3, and #4 along with the edge of the N49 bubble (see also Figure 18 in
Deharveng et al. (2010)).

Figure 10: The NH3 $(J,K)=(1,1)$ peak intensity shown as pink contours
superposed on the APEX 870 $\mu$m continuum image. The lowest pink contour
level and intervals are 0.12 K ($\sim 4\sigma$). The red cross is the same as
in Figure 2a. The orange contour levels of the VLA 1.4 GHz continuum image are
2.0, 3.0, 4.0, 5.0, and 6.0 mJy/beam. #1, #3, and #4 indicate the dust
condensations identified by Deharveng et al. (2010).

Figure 11 presents the distributions of YSOs identified by Dirienzo et al.
(2012). The image and pink contours show the Spitzer 8 $\mu$m and peak
intensity of NH3 (1,1), respectively. Dirienzo et al. (2012) classified YSOs
to “Stage I, Stage II, and Stage III” with their evolutional stage defined by
Robitaille et al. (2006). Clump A and C have Stage I YSOs shown in blue
circles. Clump B has Stage I YSOs at the edge and inside the bubble. Stage II
YSOs exist on the eastern side of Clump B. We suggest that the low mass star
formation proceeds at each NH3 clump in the molecular filament because YSOs
exist at each dense clump. Clump A and C exists at $\sim 5$ pc and $\sim 10$
pc away from the edge of the bubble traced by the 1.4 GHz radio continuum
image. Therefore, we propose that these clumps might not be affected by the
external shock compression or ionization from the N49 bubble, but the sites of
spontaneous star formation. Clump C has low kinetic temperatures of 14-18 K
(Figure 8) and the uniform line width of $\sim 2.0$ km s-1(Figure 7b), while
it includes NH3 dense gas, cold dust condensation, and Stage I YSOs (Figure
10). We suppose that they show signatures of the early stage of star formation
in Clump C. Clump A and C are not detected in the radio continuum emission
even though dust condensations and YSOs. Therefore, these clumps might be the
more initial stage or small scale of star formation than Clump B.

Figure 11: YSO distributions superposed on the Spitzer 8 $\mu$m continuum
image. Pink contours indicate the NH3 $(J,K)=(1,1)$ peak intensity. The lowest
pink contour level and intervals are 0.12 K ($\sim 4\sigma$). Blue, green, red
circles show the Stage I, Stage II, and Stage III YSOs identified by Dirienzo
et al. (2012) based on the classification model of Robitaille et al. (2006).

###  4.2 Impact of the N49 bubble to the NH3 clump

The NH3 (1,1) main line has a large line width of $3.8\pm 0.3$ km s-1at
$(l,b)=(\timeform{28.837D},\timeform{-0.226D})$, which corresponds to the
northern interface of Clump B and ionized gas (Figure 7b). This result
suggests that the turbulent motion is enhanced locally by the interaction of
gas within the bubble and the NH3 dense clump. The distributions of kinetic
temperature have a local high $T_{\rm kin}=27.0\pm 0.6$ K at the 6.7 GHz
methanol maser source associated with MYSOs (Cyganowski et al., 2009), while
it has a low $T_{\rm kin}<18$ K at the northern and western edge of the bubble
(Figure 8). We propose that this shows the feedback from the young ($<10^{5}$
yr) embedded MYSOs are heating the dense clump locally. Our previous studies
support this result (e.g., Monkey Head nebula: Chibueze et al. (2013),
AFGL-333: Nakano et al. (2017), W33: Murase et al. (2022), and Sh 2-255: Kohno
et al. (2022)). These papers concluded that embedded cluster and the compact H
II region with their age of $<10^{5}$ yr can affect the local heating of the
dense NH3 clump.

###  4.3 Two molecular filaments and triggered star formation

Figure 12: The FUGIN 13CO spectra at
$(l,b)=(\timeform{28.836D},\timeform{-0.244D})$. Blue and pink area show the
integrated velocity range of the two molecular filaments in Figure 13(a) and
13(b), respectively.  Figure 13: The FUGIN 13CO integrated intensity map of
two molecular filaments identified by Dewangan et al. (2017). The integrated
velocity range of (a) 83.0-90.8 km s-1and (b) 92.1-99.9 km s-1, respectively.
White contours indicate the NH3 $(J,K)=(1,1)$ peak intensity. The lowest white
contour level and intervals are 0.12 K ($\sim 4\sigma$). (c) The integrated
intensities of the 88 km s-1component (orange contours) and 95 km
s-1components (background image). White contours indicate the NH3
$(J,K)=(2,2)$ peak intensity. The black cross is the same as in Figure 2a. (d)
The longitude-velocity diagram of 13CO $J=$1-0 shown as white contours. The
lowest white contour level and intervals are 0.1 K degree. The black contours
present the NH3 (2,2) intensity of the same integrated latitude range. The
lowest black contour level and intervals are 0.0036 K degree and 0.002 K
degree, respectively.

Figure 12 shows the FUGIN 13CO $J=$1-0 spectra at the edge of the bubble. We
can find the two velocity components of $\sim 88$ km s-1and $\sim 95$ km s-1.
Dewangan et al. (2017) reported the molecular filaments composed of these two
velocity components from the 13CO $J=$1-0 Galactic Ring Survey data (Jackson
et al., 2006). Figure 13(a) and (b) present NH3 peak intensity distributions
superposed on the molecular filaments of $\sim 88$ km s-1and $\sim 95$ km
s-1components, respectively. The NH3 peak of Clump B and C corresponds to the
CO peak of the $\sim 88$ km s-1component. Clump A coincides with the CO peak
of the $\sim 95$ km s-1component. Figure 13(c) demonstrates NH3 (2,2) peak
intensity overlaid on the two velocity components shown in the image of 95 km
s-1and orange contours of 88 km s-1. Clump B exists at the overlapped region
of the two velocity components. This result supports the filament-filament
collision-induced dense gas and massive star formation at the edge of the
bubble proposed by Dewangan et al. (2017). Figure 13 (d) shows the longitude-
velocity diagram. Black contours indicate the NH3 (2,2) distribution. The 88
km s-1and 95 km s-1component connect with the bridge feature on the velocity
space reported by Dewangan et al. (2017). This is evidence of the collisional
interaction of two clouds from the numerical simulation by Haworth et al.
(2015) based on the model of Takahira et al. (2014). The NH3 (2,2) peaks
coincide with the 13CO dense points of the 88 km s-1and 95 km s-1component.
The NH3 (2,2) intensity is more enhanced at 88 km s-1 than the 95 km
s-1component. We suggest that the dense gas produced by the shocked
compression of filament collision is likely to exist at the 88 km s-1
component. Indeed, the numerical simulation showed that the shock compression
by cloud-cloud collision induces dense gas formation traced by NH3 (Priestley
& Whitworth, 2021). Therefore, our NH3 results support that the current
massive star and dense gas formation at the edge of the bubble was triggered
by the collision event suggested by Dewangan et al. (2017).

##  5 Summary

The conclusions of our paper are summarized as follows:

  1. 1.

We have performed the NH3 $(J,K)=(1,1),(2,2),$ and $(3,3)$ survey toward the
Galactic infrared bubble N49 (G28.83-0.25) as a part of the KAGONMA project
led by the Kagoshima University.

  2. 2.

We found three NH3 clumps (A, B, and C) along the molecular filament with the
radial velocities of $\sim$ 96, 87, and 89 km s-1, respectively.

  3. 3.

The kinetic temperature derived from the NH3 (2,2)/NH3 (1,1) shows $T_{\rm
kin}=27.0\pm 0.6$ K enhanced at Clump B in the eastern edge of the bubble,
where position coincides with MYSOs associated with the 6.7 GHz methanol maser
source. This result shows the dense clump is locally heated by the stellar
feedback from the embedded MYSOs.

  4. 4.

The NH3 Clump B also exists at the 88 km s-1and 95 km s-1molecular filament
intersection. Therefore, we suggest that the filament-filament interaction
scenario argued by Dewangan et al. (2017) can explain the NH3 dense gas
formation in Clump B.

  5. 5.

The NH3 Clump A and C at the northern and southern sides of the molecular
filament exist $\sim 5$ \- $10$ pc apart from the edge of the bubble traced by
the 1.4 GHz radio continuum image. This result suggests that these clumps are
likely to occur in spontaneous star formation, not to be affected by the
ionization feedback from the N49 bubble.

## Acknowledgements

We are grateful to the anonymous referee for carefully reading our manuscript
and giving us thoughtful suggestions, which greatly improved of the paper. The
Nobeyama 45-m radio telescope is operated by Nobeyama Radio Observatory, a
branch of the National Astronomical Observatory of Japan. The authors wish to
thank all staff of the Nobeyama radio observatory for their assistance in our
backup observations. The NH3 backup observations are promoted on a lot of
contributions of Kagoshima university, so the authors would like to thank all
them, Dr. Tatsuya Kamezaki, Dr. Gabor Orosz, Dr. Mitsuhiro Matsuo, Mr. Hideo
Hamabata, Mr. Tatsuya Baba, Mr. Ikko Hoshihara, Mr. Kohei Mizukubo, Mr.
Tatsuya Sera, and Mr. Masahiro Uesugi. I appreciated the curator members of
the Astronomy section of Nagoya city science museum supporting my research
works. The data of the FUGIN project was retrieved from the JVO portal
(http://jvo.nao.ac.jp/portal/) operated by ADC/NAOJ. The data analysis was
carried out at the Astronomy Data Center of the National Astronomical
Observatory of Japan. The ATLASGAL project is a collaboration between the Max-
Planck-Gesellschaft, the European Southern Observatory (ESO) and the
Universidad de Chile. It includes projects E-181.C-0885, E-078.F-9040(A),
M-079.C-9501(A), M-081.C-9501(A) plus Chilean data. This work is based in part
on observations made with the Spitzer Space Telescope, which was operated by
the Jet Propulsion Laboratory, California Institute of Technology under a
contract with NASA.

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