#  Ionized gas metallicity of the strong [O iii]$\lambda$5007 emission-line
compact galaxies in the LAMOST survey

Siqi Liu CAS Key Laboratory of Optical Astronomy, National Astronomical
Observatories, Beijing 100101, China  School of Astronomy and Space Science,
University of Chinese Academy of Sciences, Beijing 100049, China  A-Li Luo∗
CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories,
Beijing 100101, China  School of Astronomy and Space Science, University of
Chinese Academy of Sciences, Beijing 100049, China  College of Computer and
Information Management & Institute for Astronomical Science, Dezhou
University, Dezhou 253023, China  Wei Zhang∗ CAS Key Laboratory of Optical
Astronomy, National Astronomical Observatories, Beijing 100101, China  Xiao
Kong CAS Key Laboratory of Optical Astronomy, National Astronomical
Observatories, Beijing 100101, China  Yan-Xia Zhang  CAS Key Laboratory of
Optical Astronomy, National Astronomical Observatories, Beijing 100101, China
School of Astronomy and Space Science, University of Chinese Academy of
Sciences, Beijing 100049, China  Shi-Yin Shen Key Laboratory for Research in
Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of
Sciences, 80 Nandan Road, Shanghai, 200030, China  Key Lab for Astrophysics,
Shanghai, 200034, China  Yong-Heng Zhao  CAS Key Laboratory of Optical
Astronomy, National Astronomical Observatories, Beijing 100101, China  School
of Astronomy and Space Science, University of Chinese Academy of Sciences,
Beijing 100049, China

###### Abstract

This article reports a sample of 1830 strong [O iii]$\lambda$5007 emission-
line compact galaxies discovered with the LAMOST spectroscopic survey and the
photometric catalog of SDSS. We newly identify 402 spectra of 346 strong [O
iii]$\lambda$5007 emission-line compact galaxies by finding compact isolated
point sources. Combined with the samples in our previous work (Liu et al.,
2022), this returns a sample of 1830 unique strong [O iii]$\lambda$5007
emission-line compact galaxies with 2033 spectra of $z\leq 0.53$. For the
sources with $2\sigma$ [O iii]$\lambda$4363 detections, we calculate the gas-
phase metallicity with the direct-$T_{e}$ method, and verify that the strong-
line metallicity diagnostics calibrated with the direct-$T_{e}$ method also
applies to this sample. The strong [O iii]$\lambda$5007 emission-line compact
galaxies fall below several $T_{e}$-calibrated mass-metallicity relations. The
N/O measurements of the strong [O iii]$\lambda$5007 emission-line compact
galaxies mainly locate at a plateau at low metallicity, indicating the product
of primary nucleosynthesis. The Ne3O2 and O32 relation follows a tight linear
relation with no redshift evolution. The Ne3O2 anti-correlates with the
stellar mass, and at fixed stellar mass the Ne3O2 increase with the redshift.
Eight sources with asymmetric [O iii]$\lambda 5007$ emission-line profiles
have been identified, however with no [O iii]$\lambda 4363$ detection, which
proves the rich metal content and complex ionized gas kinematics within the
galaxies. Higher-resolution spectroscopy will be necessary to identify the
ionized gas components in detail.

Chemical abundances (224), Compact galaxies (285), Metallicity (1031)

††facilities: LAMOST, SDSS, WISE, GALEX††software: astropy (Astropy
Collaboration et al., 2013, 2018), extinction (Barbary, 2016), LMFIT (Newville
et al., 2016), Matplotlib (Hunter, 2007), Numpy (Harris et al., 2020), pandas
(Wes McKinney, 2010; pandas development team, 2020), Scipy (Virtanen et al.,
2020), Source Extractor (Bertin & Arnouts, 1996), TOPCAT (Taylor, 2005).

##  1 Introduction

Strong [O iii]$\lambda$5007 emission-line compact galaxies are well-known for
their unique color, compactness, high star formation rate (SFR), low
metallicity, and being in isolated environments (Cardamone et al., 2009).
According to the redshifts and correspondingly the change of color, strong [O
iii]$\lambda$5007 emission-line compact galaxies are also called Blueberry
galaxies (at $z\leq 0.05$), Green Pea galaxies ($0.112\leq z<0.36$) and Purple
Grape galaxies ($0.05<z<0.112$ and $0.36\leq z\leq 0.53$).

In our previous work (Liu et al., 2022), we selected 1694 spectra with 1547
unique objects from the dedicated and non-dedicated survey in the LAMOST
spectra database (Wang et al., 1996; Su & Cui, 2004; Luo et al., 2012). We
further analyze the star formation rate (SFR), the mass-metallicity relation
(MZR), and the environment of these samples. In this work, in joint with newly
identified strong [O iii]$\lambda$5007 emission-line compact galaxies, we
compile a large sample of the strong [O iii]$\lambda 5007$ emission-line
compact galaxies and discuss the metallicity of the ionized gas. In the
following discussion, these samples are called strong [O iii]$\lambda$5007
emission-line compact galaxies, which consist of 2033 spectra of 1830 unique
galaxies.

The galaxies’ gas-phase metallicity and ionization parameter provides rich
information about their chemical evolution, among which gas-phase oxygen
abundances are the best approach to measure the current metallicity. Emission
lines in the spectra of the star-forming galaxies are acquired conveniently
across different redshift ranges and thus are potent indicators of chemical
compositions. The well-known scaling relation between the gas-phase
metallicity and the stellar mass, quoted as the mass-metallicity relation
(MZR, Lequeux et al. (1979)), has been studied extensively (Tremonti et al.,
2004; Lee et al., 2006; Mannucci et al., 2010; Lara-López et al., 2010;
Andrews & Martini, 2013; Maiolino & Mannucci, 2019; Yates et al., 2020; Curti
et al., 2020; Nakajima et al., 2022). The MZR brings crucial observational
information on understanding the build-up of the galaxies over time. Typically
there are two methods to measure the metallicity: the direct-$T_{e}$ method
and the strong-line method (Andrews & Martini, 2013). The direct-$T_{e}$
method employs the ionized gas’s electron temperature and thus the gas’s
metallicity, calculated from the flux ratio of the auroral line and the strong
lines. It is effective because metals are the ionized gas’s primary coolants.
The auroral and strong lines originate from the second and excited states
separately, where the electron temperature can be calculated from the relative
ratios of these two populations. The metallicity is strongly correlated with
the electron temperature, where the low electron temperature corresponds to
the high metallicity. It is suggested by Alloin et al. (1979); Pagel et al.
(1979) to use some emission lines to calibrate the oxygen abundances, usually
referred to as the “strong-line method”. The strong-line method does not
measure the metallicity directly. Due to their sensitivity to metallicities,
the strong lines are easier to measure when the auroral lines are too weak for
high-metal sources. However, there are systematic discrepancies (Kewley &
Ellison, 2008; López-Sánchez et al., 2012) comparing the metallicity
determined from the direct-$T_{e}$ method and the strong-line calibrations.
Systematical “strong-line" calibrations have been performed (Maiolino et al.,
2008; Jones et al., 2015; Curti et al., 2017; Patrício et al., 2018; Curti et
al., 2020), however, more tests at the low-metallicity regimes are needed.

An alternative chemical abundance diagnostic is nitrogen, probed by N/O, which
compared with oxygen produced from Helium fusion, the formation is more
complex. N/O is sensitive to the chemical evolution history of a galaxy
because nitrogen is the product of a primary nucleosynthetic product
(independent of metallicity) and a secondary nucleosynthetic product
(dependent on the metallicity of the gas cloud) (Hayden-Pawson et al., 2022).
Studies have shown at low metallicities, the N/O ratios stay at a plateau and
do not vary with O/H; while towards higher metallicity as the galaxies evolve,
the N/O begins to increase with O/H (Shi et al., 2005; Pilyugin et al., 2012;
Andrews & Martini, 2013; Hayden-Pawson et al., 2022). The samples in this work
will provide valuable information about the N/O vs O/H relation at the low
metallicity regime.

The [Ne iii]$\lambda$3869 lines serve as an additional crucial probe of the
ionized gas. Ne3O2 ([Ne iii]$\lambda 3869$/[O ii]$\lambda\lambda 3727,3729$)
was first initiated as the metallicity diagnostic (Nagao et al., 2006; Shi et
al., 2007). However, Pérez-Montero et al. (2007); Levesque & Richardson (2014)
addressed the reason why Ne3O2 anti-correlates with the metallicity is the
change of the ionization parameter. Compared with the commonly used O32 ([O
iii]$\lambda 5007$/[O ii]$\lambda\lambda 3727,3729$), Ne3O2 is less prone to
dust extinction due to the proximity of the wavelength coverage and can be
applied to sources of higher redshifts. The strong emission-line samples in
this work provide ample samples to re-examine the correlation of these two
ionization parameters.

We also look into the kinematics of the ionized gas which reflects the star
formation history. There are detailed optical (Amorín et al., 2010, 2012a,
2012b; Bosch et al., 2019; Hogarth et al., 2020) and UV (Jaskot & Oey, 2014;
Henry et al., 2015; Yang et al., 2016; Izotov et al., 2018) spectroscopic
studies of Green Pea galaxies, where the authors have identified double-peak
or asymmetric profiles of the emission lines. Amorín et al. (2012b) has
identified the spatially offset H$\alpha$ emission line profiles in their 2D
spectra. Bosch et al. (2019) analyzed the kinematics of a single Green Pea
galaxy with the Gemini Multi-Object Spectrograph and confirmed the existence
of three components: a rotating disk, a turbulent mixing layer, and gas
outflow. Hogarth et al. (2020) concluded the triple component might come from
two starbursts by fitting three components from all the optical emissions
lines from deep high-resolution spectra. This has revealed the presence of
complex ionized gas structures within these galaxies.

The structure of the paper is summarized below. In Section 2, we introduce the
newly spectroscopically-confirmed strong [O iii]$\lambda$5007 emission-line
compact galaxies from LAMOST. In Section 3, we explain how to measure the
stellar mass from multi-wavelength photometry, obtain the emission line flux
and the corresponding error, and measure the velocity dispersion from the [O
iii]$\lambda$5007 emission line. In Section 4, we demonstrate the result of
the metallicity from the direct-$T_{e}$ method and compare it with the strong-
line calibrations. In Section 5, we discuss the mass-metallicity relation, the
N/O vs O/H relation, the Ne3O2 vs O32 relation, the Ne3O2 vs stellar mass
relation, and the asymmetric [O iii]$\lambda$5007 profiles of eight sources.
Finally, we present a summary of the measurements, results, and discussions in
Section 6.

In this work, we use Wilkinson Microwave Anisotropy Probe (WMAP) 9 cosmology
(Hinshaw et al., 2013)($\rm H_{0}=69.3\leavevmode\nobreak\
km\leavevmode\nobreak\ s^{-1}Mpc^{-1}$, $\rm\Omega_{m}=0.287$ and flat
Universe), AB magnitudes (Oke & Gunn, 1983), a Chabrier initial mass function
(IMF; Chabrier (2003)), and Bruzual & Charlot (2003) stellar population
synthesis (SPS) models.

##  2 Sample and Data

###  2.1 LAMOST spectra

####  2.1.1 Sample selection

Instead of the traditional color selection criteria as in Cardamone et al.
(2009), we select the strong [O iii]$\lambda 5007$ emission line galaxies,
which are compact and isolated. The reasons for removing the strict color
selection are two-fold: to include the emission line galaxies with a broader
redshift range and to select the galaxies with less severe emission lines.

We select the sources from SDSS CasJob with the following criteria, where “?"
represents each of the $ugriz$ SDSS bands:

  * •

petroRad_r<3, -- compact object

  * •

specObjID=0, --no spectrum has been taken in SDSS

  * •

clean=1, -- reliable photometry

  * •

mode<3 , --primary or secondary object

  * •

parentID=0, -- no parent (if the object is deblended) or bright detection (if
the object has one parent),

  * •

petroRadErr_?>0, -- morphology is certain in these five bands,

  * •

petroR50Err_?>0

  * •

petroR90Err_?>0

  * •

cModelMagErr_g<0.2, cModelMagErr_r<0.2, cModelMagErr_i<0.2,

  * •

17<cModelMag_r<22.

This returns 594863 sources.

Using the massive amount of spectra available in the LAMOST database (Wang et
al., 1996; Su & Cui, 2004; Luo et al., 2012), we cross-match the photometry
sources with LAMOST DR10111http://www.lamost.org/dr10/ with a searching radius
of 3” and have obtained 2847 spectra that match these positions. The goal of
this work is to investigate the metallicity of the ionized gas in these
low-$z$ galaxies, the AGN components will bias the predictions from the
photoionization models. Therefore, we remove the sources that show broad
Balmer emission lines and display the [Mg ii]$\lambda$2800 line if located
within the wavelength coverage to eliminate AGNs from our sample. Furthermore,
based on the emission line ratios, we calculate the BPT diagram as in Figure 1
and keep the sources classified as ‘SF’ or ‘comp’ for further analysis in this
work. We select the ones that have significant [O iii]$\lambda$5007 emission
lines with $\geq 2\sigma$ detection. Thus, we have obtained 402 new spectra
with 346 new sources in this work.

Figure 1: BPT diagram for the selected sources. Only ’SF’ and ‘comp’ sources
are kept for further analysis.

####  2.1.2 Flux calibration

Following the procedures in Wang et al. (2018); Liu et al. (2022), we re-
calibrate the LAMOST spectra according to the SDSS $gri$ photometry. LAMOST
spectra are convolved with the SDSS $gri$ filters (Fukugita et al., 1996) in
the observed frame to obtain the synthetic magnitudes for these three bands
and we calculate the difference of the synthetic magnitudes with the observed
SDSS photometric magnitudes. A zeroth-order or first-order polynomial is used
to fit the magnitude difference array and apply this correction to the LAMOST
spectra.

###  2.2 Comparison sample

To check whether there is redshift evolution of the relations discussed in
Section 5, there are also measurements at different redshift ranges included
in this work for comparison. At $z\sim 0$, we use the measurements from the
composite spectra of SDSS emission line galaxies in Andrews & Martini (2013).

At higher redshifts, we make use of two stacked measurements. Zeimann et al.
(2015) used stacked low-resolution near-IR grism spectra from the Hubble Space
Telescope (HST) and obtained composite measurements of $z\sim 2$ low-mass
(median $\rm 10^{9}\leavevmode\nobreak\ M_{\odot}$) galaxies. We include the
measurements of five stellar mass bins in the composite spectra. Jeong et al.
(2020) measure the doubly ionized Neon ([Ne iii]$\lambda 3869$) for $z\sim 2$
galaxies in the MOSFIRE DEEP Evolution Field (MOSDEF) survey (Kriek et al.,
2015). We use the measurements from the stacked spectra in four stellar mass
bins, which have no requirements of the [Ne iii]$\lambda 3869$ detection.

The revolutionary James Webb Space Telescope (JWST) and its near-IR
spectrograph NIRSpec (Ferruit et al., 2022; Jakobsen et al., 2022) has opened
the new possibility of investigating the chemical abundances at higher-$z$.
Among the 35 objects detected in the field of the lensed galaxies of cluster
SMACS J0723.3-7327 (Ebeling et al., 2001, 2007, 2010; Mann & Ebeling, 2012)
from the Early Release Observations (ERO) of JWST, there are three sources at
$z\sim 7.7-8.5$. These three sources show similar rest-frame optical spectra
as the strong [O iii]$\lambda$5007 emission-line compact galaxies in this
sample, which is worth to be compared with. We use the measurements in Curti
et al. (2023) in this work.

##  3 Physical Parameters

###  3.1 Multi-wavelength spectral energy distribution fitting

We cross-match the sources with the Galaxy Evolution Explorer (GALEX) (Bianchi
et al., 2017) to obtain the NUV photometry and cross-match the sources with
the AllWISE Multiepoch Photometry Table (Wright et al., 2010; Wright, Edward
L. and Eisenhardt, Peter R. M. and Mainzer, Amy K. et al., 2019) to obtain the
$W_{1}$ to $W_{4}$ photometry. For the stellar mass measurement, we fit the
sources with multiwavelength photometry with CIGALE (Burgarella et al., 2005;
Boquien et al., 2019) combining the GALEX NUV, SDSS $ugriz$, and AllWISE
$W_{1}$ to $W_{4}$ photometry. For the configuration of the fitting, we use
the delayed$-\tau$ star formation history, BC03 stellar population models
(Bruzual & Charlot, 2003), Chabrier IMF (Chabrier, 2003), nebular emission
lines, the dust attenuated modified starburst model, the dust emission model
from Casey (2012), and the Fritz et al. (2006) AGN model.

###  3.2 Emission line flux, equivalent width, and velocity dispersion

We fit the emission lines with LMFIT (Newville et al., 2016). For emission
line error estimation, we use the Monte Carlo method. For each instance, we
perturb the flux at each wavelength sampling point 200 times by running a
Gaussian distribution centered on the flux measurement with a width set by the
flux error. The mean value of the resulting emission line flux is the
resulting flux measurement, and the standard deviation marks the flux error.
An example demonstrating the measurement of [O iii]$\lambda$4363 line is in
Figure 2.

(a)  (b)

Figure 2:  The H$\gamma$ and [O iii]$\lambda$4363 emission lines fitted with
the Gaussian profiles (left panel) and histogram of the measurement of each
realization (right panel). In the left panel, the flux of each realization is
marked with a black line, and the fitted Gaussian profile is marked with an
orange curve. In the right panel, the mean value of the distribution is marked
with the black solid line, and the 1$\sigma$ region is marked with the dashed
lines.

We measure the color excess of the galaxies from the flux ratio of the
H$\alpha$ to H$\beta$ assuming the case B recombination with the intrinsic
line ratio of 2.86. The color excess from the flux ratio is calculated with

$\displaystyle\rm
E(B-V)_{gas}=\frac{\log_{10}[(f_{H\alpha}/f_{H\beta})/2.86]}{0.4\times[k(H\beta)-k(H\alpha)]},$
(1)

where $k(\rm H\alpha)=3.33$ and $k(\rm H\beta)=4.6$ as in Jiang et al. (2019).
If the flux ratio is less than 2.86, the color excess is considered to be set
to 0. The distribution of the flux ratios and E(B-V) are displayed in Figure
3.

Figure 3:  The distribution of the flux ratio of $\rm H\alpha/H\beta$ (left
panel) and the E(B-V) (right panel).

All of the emission line flux measurements are corrected with the extinction
correction using the Calzetti et al. (2000) extinction law, with the color
excess measured from the Balmer decrement.

We demonstrate an example of the spectrum with the emission lines marked in
Figure 4.

Figure 4: An example spectrum of the strong [O iii]$\lambda$5007 emission-line
compact galaxy. The emission lines used for following metallicity and
kinematics measurements and discussions are marked at different wavelengths.
The grey-shaded regions mark the flux error.

Specifically, we also calculate the velocity dispersion of the [O iii]$\lambda
5007$ emission line. To calculate the intrinsic velocity dispersion of the
sources, we subtract the instrumental and thermal broadening of the sources as
in Bosch et al. (2019); Hogarth et al. (2020). Assuming an electron
temperature $\rm T_{e}=1.2\times 10^{4}\rm K$ (Amorín et al., 2010, 2012b),
the typical thermal broadening for these galaxies are $\rm\sigma_{\rm
ther}=\frac{c\lambda_{\rm em}}{\lambda_{\rm
obs}}\sqrt{\frac{k_{B}T_{e}}{m_{\rm ion}c^{2}}}$. The thermal broadening of a
galaxy at $z=0.26$ is about 2.50 km s-1. We refer to the values given in Shi
et al. (2014) for the instrumental FWHM as an average value of 3.5 Å for
LAMOST spectrographs.

The rest-frame equivalent widths (EWs) of the [O iii]$\lambda 5007$ emission
lines are measured to be compared with other work. Figure 5 demonstrates the
distribution for the measured EWs.222Due to the faint continuum, some of the
EWs are extremely large, thus the measured result for EW$>10^{5}$Å is not
completely reliable.

Figure 5:  The distribution of the rest-frame EWs of the [O iii]$\lambda 5007$
emission lines.

All the above measurements are compiled into a catalog https://nadc.china-
vo.org/res/r101238, and the descriptions of the catalog are listed in Table 1.

Table 1: Catalog: Table Description Name | Description
---|---
combined_obsid | unique object id in LAMOST database
combined_lmjd | Local Modified Julian Day (LMJD )of the spectroscopic observation
combined_planid | spectroscopic plan identifications
combined_spid | spectrograph identification
combined_fiberid | fiber number of the spectrum
combined_objtype | object type from input catalog
combined_class | class of object
combined_z | spectroscopic redshift
combined_tfrom | Target catalog
combined_ra | R.A in decimal degrees (J2000)
combined_dec | declination in decimal degrees (J2000)
objID | unique SDSS identifier
type | type classification of the object (0=UNKNOWN, 3=galaxy, 6=star)
clean | clean photometry flag (1=clean, 0=unclean).
cModelMag_? | DeV+Exp magnitude, “?" represents each of the $ugriz$ SDSS bands
cModelMagErr_? | DeV+Exp magnitude error, “?" represents each of the $ugriz$ SDSS bands
petroRad_r | Petrosian radius in the $r-$band
petroR50_r | Radius containing 50% of Petrosian flux in the $r-$band
petroR90_r | Radius containing 90% of Petrosian flux in the $r-$band
OII_flux(_err) | [O ii]$\lambda\lambda$3727,3729 line flux and flux error in units of $\rm 10^{-17}erg\leavevmode\nobreak\ s^{-1}cm^{-2}$
NeIII3869_flux(_err) | [Ne iii]$\lambda$3869 line flux and flux error in units of $\rm 10^{-17}erg\leavevmode\nobreak\ s^{-1}cm^{-2}$
OIII4363_flux(_err) | [O iii]$\lambda$4363 line flux and flux error in units of $\rm 10^{-17}erg\leavevmode\nobreak\ s^{-1}cm^{-2}$
Hb_flux(_err) | H$\beta$ line flux and flux error in units of $\rm 10^{-17}erg\leavevmode\nobreak\ s^{-1}cm^{-2}$
OIII4959_flux(_err) | [O iii]$\lambda$4959 line flux and flux error in units of $\rm 10^{-17}erg\leavevmode\nobreak\ s^{-1}cm^{-2}$
OIII5007_flux(_err) | [O iii]$\lambda$5007 flux and flux error in units of $\rm 10^{-17}erg\leavevmode\nobreak\ s^{-1}cm^{-2}$
NII6548_flux(_err) | [N ii]$\lambda$6548 flux and flux error in units of $\rm 10^{-17}erg\leavevmode\nobreak\ s^{-1}cm^{-2}$
Ha_flux(_err) | H$\alpha$ line flux and flux error in units of $\rm 10^{-17}erg\leavevmode\nobreak\ s^{-1}cm^{-2}$
NII6584_flux(_err) | [N ii]$\lambda$6584 flux and flux error in units of $\rm 10^{-17}erg\leavevmode\nobreak\ s^{-1}cm^{-2}$
SII6716_flux(_err) | [S ii]$\lambda$6716 flux and flux error in units of $\rm 10^{-17}erg\leavevmode\nobreak\ s^{-1}cm^{-2}$
SII6731_flux(_err) | [S ii]$\lambda$6731 flux and flux error in units of $\rm 10^{-17}erg\leavevmode\nobreak\ s^{-1}cm^{-2}$
EW_OIII5007 | Equivalent width of the [O iii]$\lambda$5007 emission line in units of Å
ne | electron number density in units of $\rm cm^{-3}$
cigale_mass | stellar mass in units of $\rm M_{\odot}$
sigma_5007 | velocity dispersion of the [O iii]$\lambda 5007$ emission line, in units of Å

##  4 Results

###  4.1 Direct-$T_{e}$ method gas-phase metallicity

With the auroral [O iii]$\lambda 4363$ line, the gas-phase metallicity could
be estimated in a direct-$T_{e}$ method (Aller, 1984; Izotov et al., 2006).
This approach assumes the electron temperatures for $\rm O^{+}$ and $\rm
O^{++}$ in a two-zone photoionization model: the high-ionization zone traced
by the $\rm O^{++}$ and the low-ionization one traced by the $\rm O^{+}$. We
calculate the $\rm O^{++}$ electron temperature with the following equation
(as in Izotov et al. (2006) Eqs (1) and (2)):

$\displaystyle\rm t=\frac{1.432}{\log[(\lambda 4959+\lambda 5007)/\lambda
4363]-\log C_{T}},$ (2)

where $\rm t=10^{-4}T_{e}([\rm O\leavevmode\nobreak\ \textsc{iii}])$, and

$\displaystyle\rm
C_{T}=(8.44-1.09t+0.5t^{2}-0.08t^{3})\frac{1+0.0004x}{1+0.044x},$ (3)

where $\rm x=10^{-4}n_{e}t^{-0.5}$. As addressed in Andrews & Martini (2013);
Curti et al. (2017), at low-metallicity environments, the $\rm O^{++}$
abundance is dominant over that of $\rm O^{+}$. Besides, there is no direct
temperature diagnostic for the low-ionization zone, the electron temperature
of [O ii] for the low-metallicity situation is estimated with Izotov et al.
(2006) as:

$\displaystyle\rm T_{e}([{\rm O\leavevmode\nobreak\ \textsc{ii}}])$
$\displaystyle=$ $\displaystyle\rm-0.577+T_{e}([{\rm O\leavevmode\nobreak\
\textsc{iii}}])\times$ (4) $\displaystyle\rm(2.065-0.498T_{e}([{\rm
O\leavevmode\nobreak\ \textsc{iii}}])).$

This is also the method that Jiang et al. (2019) use for calculation, and they
state that their measurement of the oxygen abundance depends little on the
relation between $\rm t_{2}$ and $\rm t_{3}$. Similarly, we use the term $\rm
t_{2}=10^{-4}T_{e}([{\rm O\leavevmode\nobreak\ \textsc{ii}}])$ and $\rm
t_{3}=10^{-4}T_{e}([{\rm O\leavevmode\nobreak\ \textsc{iii}}])$ for clarity.

We follow the treatment as in Jiang et al. (2019) using the [S
ii]$\lambda,\lambda$6716,6731 lines to estimate the electron density $\rm
n_{e}$. For 1052 sources with both $2\sigma$ detections for the [S
ii]$\lambda$6716 and [S ii]$\lambda$6731 emission lines, the flux ratio is
defined as $\rm R(n_{e})=\frac{\lambda 6716}{\lambda 6731}$, and the electron
density is estimated333For $\rm R(n_{e})>1.43$, quoting the low-density limits
below the flux ratio is unrealistic, thus it is merged with the situation with
$\rm 0.51\leq R(n_{e})\leq 1.43$.:

$\rm n_{e}(R)=\begin{cases}\rm\frac{ab-Rc}{R-a},&\rm R\geq 0.51\\\ 100,&\rm
otherwise\\\ \end{cases}$ (5)

in units of $\rm cm^{-3}$, where $a=0.4441,b=2514,c=779.3$. The derived
distribution of $\rm n_{e}$ is in Figure 6.

Figure 6: The distribution of the derived $\rm n_{e}$.

As addressed in Jiang et al. (2019), under $\rm n_{e}=10,100$ or $\rm
10^{3}\leavevmode\nobreak\ cm^{-3}$, the results do not vary much.

With Eqs. (3) and (5) in Izotov et al. (2006), we calculate the ionic
abundances as follows:

$\displaystyle\rm 12+\log\frac{O^{+}}{H^{+}}$ $\displaystyle=$
$\displaystyle\rm\log\frac{\lambda
3727}{H\beta}+5.961+\frac{1.676}{t_{2}}-0.40\log t_{2}$ (6)
$\displaystyle\rm-0.034t_{2}+\log(1+1.35x),$

and

$\displaystyle\rm 12+\log\frac{O^{++}}{H^{+}}$ $\displaystyle=$
$\displaystyle\rm\log\frac{\lambda 4959+\lambda
5007}{H\beta}+6.200+\frac{1.251}{t_{3}}$ (7) $\displaystyle\rm-0.55\log
t_{3}-0.014t_{3},$

Since the majority of the ions of oxygen are $\rm O^{+}$ and $\rm O^{++}$, we
use $\rm\frac{O}{H}=\frac{O^{+}}{H}+\frac{O^{++}}{H}$ to determine the oxygen
abundance, neglecting the contribution from higher ionization states.

Among the total sample of the strong [O iii]$\lambda$5007 emission-line
compact galaxies, there are 450 sources with 2$\sigma$ [O iii]$\lambda 4363$
detection. Only the sources where the $\rm t_{3}$ range from 5 000 to 20 000
K, as noted in Izotov et al. (2006), are selected for metallicity discussion,
which counts to 372. For this sub-sample, we estimate the gas-phase
metallicity and use them for the following metallicity measurements and
discussions.

###  4.2 Strong-line calibration

We use different strong-line calibrations and verify whether these strong [O
iii]$\lambda$5007 emission-line compact galaxies follow the derived scaling
relations of the strong-line calibrations. The definitions of the strong-line
calibration are listed in Table 2. Comparing with the strong-line calibrated
polynomial forms from Maiolino et al. (2008); Jones et al. (2015); Curti et
al. (2020)444The Ne3O2 calibration is from Maiolino et al. (2008), and the
Ne3O3 calibration is from Jones et al. (2015). as in Figure 7, we find that
the strong [O iii]$\lambda$5007 emission-line compact galaxies agree with
these strong-line diagnostics. This set of calibration is valid in $\rm
7.6\leq 12+\log(O/H)\leq 8.9$.

For the low-metallicity regime, we also include the strong-line calibration
from Nakajima et al. (2022).555We adopt Ne3O2 relation for large EW samples in
Nakajima et al. (2022). The optical-line gas metallicity diagnostics are
established by the combination of local SDSS galaxies (Curti et al., 2017) and
the largest compilation of extremely metal-poor galaxies (EMPGs) identified by
the Subaru EMPRESS survey (Kojima et al., 2020). This set of calibrations
reaches the lower metallicity roughly down to $\rm 12+\log(O/H)\sim 6.9$.

Table 2: Strong-line calibration Notation | Line Ratio
---|---
$\rm R_{2}$ | [O ii]$\lambda\lambda 3727,3729$/H$\beta$
$\rm R_{3}$ | [O iii]$\lambda 5007$/H$\beta$
$\rm R_{23}$ | ([O ii]$\lambda,\lambda 3727,3729$ \+ [O iii]$\lambda\lambda 4959,5007$)/H$\alpha$
$\rm O_{32}$ | [O iii]$\lambda 5007$/[O ii]$\lambda\lambda 3727,3729$
$\rm N_{2}$ | [N ii]$\lambda 6584$/H$\alpha$
$\rm O_{3}N_{2}$ | ([O iii]$\lambda 5007$/H$\beta$)/([N ii]$\lambda 6584$/H$\alpha$)
$\rm S_{2}$ | [S ii]$\lambda\lambda 6717,6731$/H$\alpha$
$\rm RS_{23}$ | [O iii]$\lambda 5007$/H$\beta$ \+ [S ii]$\lambda\lambda 6717,6731$/H$\alpha$
$\rm O_{3}S_{2}$ | ([O iii]$\lambda 5007$/H$\beta$)/([S ii]$\lambda\lambda 6717,6731$/H$\alpha$)
$\rm Ne_{3}O_{2}$ | [Ne iii]$\lambda 3869$/[O ii]$\lambda\lambda 3727,3729$
$\rm Ne_{3}O_{3}$ | [Ne iii]$\lambda 3869$/[O iii]$\lambda 5007$
Figure 7: The set of strong-line calibrations from Maiolino et al. (2008);
Jones et al. (2015); Curti et al. (2020) (black curve) and Nakajima et al.
(2022) (sienna curve). The x-axis marks the metallicity obtained from the
direct-$T_{e}$ method. The distribution of the strong [O iii]$\lambda$5007
emission-line compact galaxies is displayed with blue scatter points. The
crimson stars mark the three galaxies from JWST at $z\sim 7.7-8.5$ with the
measurements from Curti et al. (2023).

##  5 Discussions

###  5.1 Mass-metallicity relation

With the gas-phase metallicity determined from the direct-$T_{e}$ method, we
demonstrate in Figure 8 that the metallicity increases with the stellar mass
and falls below several $T_{e}$-calibrated MZRs.

Tremonti et al. (2004) and later works (Mannucci et al., 2010) adopt the
calibration from different grids of photoionization models. The MZR from Yates
et al. (2020) is based on the samples with auroral detections from the revised
version of the classical $T_{e}$-based method. Furthermore, Curti et al.
(2020) provide the MZR by fully anchoring the metallicity determinations for
SDSS galaxies on the $T_{e}$ abundance employing the strong-line metallicity
calibrations, which better captures the turnover mass. The mass range is from
$7.95<\log(\rm M/M_{\odot})<11.85$, which can be extrapolated to the low-mass
regime. The MZR of Yates et al. (2020) is characterized by a lower
normalization, which might be caused by the requirement of the [O iii]$\lambda
4363$ detection in the mass range of $5.67<\log(\rm M/M_{\odot})<9.87$. As
shown in Fig.4 in Curti et al. (2020), the galaxies in SDSS-DR7 with auroral
detections locate below the MZR at low stellar masses. The majority of these
strong [O iii]$\lambda 4363$ emission-line compact galaxies (the strong [O
iii]$\lambda$5007 emission-line compact galaxies) in this work are below the
direct-$T_{e}$ method calibrated Tremonti et al. (2004); Curti et al. (2020)
mass-metallicity relation, and overlap the Yates et al. (2020) relation. This
is reasonable because at fixed stellar mass, requiring the [O iii]$\lambda
4363$ detection preferentially selects the metal-poor galaxies.

Figure 8: The mass metallicity relation of the strong [O iii]$\lambda$5007
emission-line compact galaxies. Different mass-metallicity relations from
Tremonti et al. (2004); Yates et al. (2020); Curti et al. (2020) are marked
with curves with the corresponding colors as noted in the legend. The crimson
stars mark the three galaxies from JWST at $z\sim 7.7-8.5$ with the
measurements from Curti et al. (2023).

###  5.2 N/O vs O/H relation

The total N/O ratio is not easy to measure since the [N iii] lines are not
readily observable, therefore, $\rm N^{+}/O^{+}$ are often used as a proxy of
N/O abundance. We determine the ratios following Pagel et al. (1992); Shi et
al. (2005) as :

$\displaystyle\rm\log\frac{N}{O}$ $\displaystyle=$
$\displaystyle\rm\log\frac{N^{+}}{O^{+}}$ (8) $\displaystyle=$
$\displaystyle\rm\log\frac{I([N\leavevmode\nobreak\ \textsc{ii}]\lambda\lambda
6548,6584)}{I([O\leavevmode\nobreak\ \textsc{ii}]\lambda\lambda
3727,3729)}+0.31-\frac{0.726}{T_{e}([N\leavevmode\nobreak\ \textsc{ii}])}$
$\displaystyle\rm-0.02\log T_{e}([N\leavevmode\nobreak\
\textsc{ii}])-\log\frac{1+1.35x}{1+0.12x},$

where the $\rm T_{e}([N\leavevmode\nobreak\
\textsc{ii}])=T_{e}([O\leavevmode\nobreak\ \textsc{ii}])$, and the definition
of $\rm x$ is the same as in Equation 3.

The relation of the N/O vs O/H is displayed in Figure 9. Most of the samples
are located in the horizontal range of the distribution with an approximately
constant value, where the majority of the nitrogen is produced from the
primary nucleosynthesis process. The colors of the scatter mark the flux ratio
of $\rm H\alpha$ to $\rm H\beta$.

Figure 9: The N/O vs O/H relation of the strong [O iii]$\lambda$5007 emission-
line compact galaxies. The colors of the scatter points mark the flux ratio of
$\rm H\alpha$ to $\rm H\beta$. The measurements of the stacked spectra in bins
of stellar mass and SFR from Andrews & Martini (2013) at $z\sim 0$ are marked
with gray stars. The blue curve is the predictions from Andrews & Martini
(2013). The green curve is the fitting result from the KLEVER survey at $z\sim
2$ (Hayden-Pawson et al., 2022).

It is well-known that there is a plateau in the N/O ratio at low metallicity
(Pagel, 1997; Vincenzo et al., 2016; Hayden-Pawson et al., 2022). At $\rm
12+\log O/H=8.5$ there is a transition that N/O increases with the
metallicity, which is strongly influenced by the star formation efficiency
(Mollá et al., 2006). With the evolution of the galaxies, low- to
intermediate-mass stars produce secondary and primary nitrogen that increases
the N/O ratio with the increase of metallicity at the same time. These strong
[O iii]$\lambda$5007 emission-line compact galaxies are mainly young galaxies
with low metallicity. The N/O values of the strong [O iii]$\lambda$5007
emission-line compact galaxies almost have a constant value, indicated by the
horizontal lines (Andrews & Martini, 2013; Hayden-Pawson et al., 2022) in
Figure 9.

As demonstrated in Figure 9, a considerable number of samples show N/O value
above the plateau at low metallicity. However, the reason for this offset is
not clear. No systematic trend of the flux ratio of $\rm H\alpha$ to $\rm
H\beta$, as shown with the color of the scatter points, with this offset is
observed. Amorín et al. (2010) claim similar trends of the Green Pea samples
compared with the SDSS star-forming galaxies. The inflow of gas might explain
this offset as well as the high SFR, compactness, and disturbed morphology.
Amorín et al. (2010) also add another explanation that this process is coupled
with the selective metal-rich gas loss, driven by supernova winds. However,
based on IFU observations, Komarova et al. (2021) argue that the broad wings
from local Green Pea analogs do not originate from stellar winds or
supernovae, but are more likely driven by radiation. It would be worth further
investigation regarding the origin of this N/O offset at the low metallicity
regime.

Vincenzo et al. (2016) have modeled that the impact of changing IMF mainly is
to shift the chemical evolution tracks along the metallicity axis, and the
data from SDSS is best-fit with the Kroupa IMF (Kroupa, 2001). As demonstrated
in Fig.8 in Vincenzo et al. (2016), if assuming the model with the Geneva
stellar yields by taking the mass loss and rotation into consideration, the
chemical evolution model predicted a dip in the N/O ratios. Based on the
observations of the metal-poor stars in Spite et al. (2005), Fig.2 in
Chiappini et al. (2005) demonstrates the N/O vs O/H plane, where there is also
a significant scatter at low metallicity. In Figure 9, the scatter in N/O of
the strong [O iii]$\lambda$5007 emission-line compact galaxies in this work is
comparable to that of the Andrews & Martini (2013) samples.

###  5.3 Ne3O2 vs O32 relation and Ne3O2 vs mass relation

Ne3O2 and O32 are both metallicity indicators (Pérez-Montero et al., 2007; Shi
et al., 2007) as well as ionization parameter indicators (Levesque &
Richardson, 2014). The tight correlation between these two ratios is verified
by different star-forming galaxies, which indicate similar evolution. This is
also checked for different metallicity as demonstrated in the Ne3O3 vs
metallicity relation in Figure 7, where Ne3O3 is almost flat for different
metallicity ranges. The strong [O iii]$\lambda$5007 emission-line compact
galaxies provide rich sources to verify the relations of the two ratios in the
local Universe, especially at the high ionization regime.

In Figure 10, we demonstrate the relation of these two line ratios of the
strong [O iii]$\lambda$5007 emission-line compact galaxies in this work, the
SDSS local star-forming galaxies from Andrews & Martini (2013), the
measurements of the stacked spectra in Jeong et al. (2020), and three $z\sim
7.7-8.5$ sources from JWST. The two ratios follow tight linear relations,
although the scatter is significant at the low ratio regime as predicted by
the photoionization models (Levesque & Richardson, 2014). There is no
significant redshift evolution of the linear relationship between these two
parameters as seen from the measurements in Jeong et al. (2020); Curti et al.
(2023). At the low ionization regime, there are offsets between the Jeong et
al. (2020) measurement and the local measurements from Andrews & Martini
(2013). Due to the compactness of the strong [O iii]$\lambda$5007 emission-
line compact galaxies, they are less prone to the effects of the diffuse
ionized gas (DIG) at the low ionization regime as seen in Jeong et al. (2020).
The strong [O iii]$\lambda$5007 emission-line compact galaxies in addition to
the local H ii regions are more appropriate local comparison samples for
high-$z$ star-forming galaxies on investigating the ionization parameters
(Sanders et al., 2017). The offset might be explained by harder ionizing
sources at higher redshifts (Strom et al., 2017; Shapley et al., 2019) or the
evolution of the fundamental metallicity relation (Sanders et al., 2016).

Figure 10:  Ne3O2 vs O32 relation. The pea samples strong [O iii]$\lambda$5007
emission-line compact galaxies are demonstrated with sienna error bars. The
samples at $z\sim 0$ from Andrews & Martini (2013) are marked with gray stars.
The stacked samples with the dust corrected from Jeong et al. (2020) are
marked with dark cyan diamonds. The crimson stars mark the three galaxies from
JWST.

In Figure 11, we demonstrate the anti-correlation of the Ne3O2 with the
stellar mass at the mass range $\rm\log M/M_{\odot}<9.5$. This anti-
correlation is also consistent with the mass-metallicity relation, based on
the anti-correlation between the ionization parameter and metallicity. This
trend is also demonstrated in Pharo et al. (2023) for SDSS galaxies at $z\sim
0$(Andrews & Martini, 2013), and HALO7D galaxies at $z\sim 0.8$(Cunningham et
al., 2019a, b). At fixed stellar mass, with the increase of redshift, the
Ne3O2 is higher for the strong [O iii]$\lambda$5007 emission-line compact
galaxies in this work as demonstrated by the color of the scatter points. The
Ne3O2 offset is also obvious with measurements from the stacked spectra at
$z\sim 2$ (Zeimann et al., 2015; Jeong et al., 2020). The small offset between
Zeimann et al. (2015) and Jeong et al. (2020) is due to the blended He i and H
$\zeta$ lines in the low-resolution HST grism spectra.

Figure 11: The relation of the Ne3O2 vs stellar mass of the strong [O
iii]$\lambda$5007 emission-line compact galaxies, where the colors of the
scatter points mark the redshift of the source. The samples at $z\sim 0$ from
Andrews & Martini (2013) are marked with gray stars, the stacked measurement
results with the dust corrected from Jeong et al. (2020) are marked with dark
cyan diamonds, the stacked measurement results from the Jeong et al. (2020)
are marked with dark orchid squares (Zeimann et al., 2015). The crimson stars
mark the three galaxies from JWST.

###  5.4 Ionized gas kinematics from the asymmetric [O iii]$\lambda$5007
profile

Visually inspecting the [O iii]$\lambda 5007$ emission-line lines, we notice
that some sources show significant asymmetric profiles. By comparing the
fitting result of the double-Gaussian model with the single-Gaussian model, we
select the model where the $\chi^{2}_{\nu}$ is closer to 1. The degree of
freedom is the number of spectral points within the wavelength range of
4985–5029 Å minus 6 for a double-Gaussian model, or minus 3 for a single-
Gaussian model. We have identified eight sources that show asymmetric [O
iii]$\lambda 5007$ emission-line profiles as demonstrated in Figure 12, where
the $\rm\chi^{2}_{\nu,double}$ is less than 90% of the
$\rm\chi^{2}_{\nu,single}$. The properties for these sources are listed in
Table 3.

To ensure the validness of the asymmetric emission line profiles, we visually
check the positions of the bad pixels to avoid contaminating the spectra. In
the original LAMOST spectra, the primary data arrays store the andmask and the
ormask666http://www.lamost.org/dr9/v1.0/doc/lr-data-production-description.
The andmask is a decimal integer. If one of the six situations (bad pixel on
CCD, bad profile in extraction, no sky information at this wavelength, sky
level too high, fiber trace out of the CCD, or no good data) always appears in
each exposure, the andmask will be set to 1. Similarly, the ormask is set to 1
if one of the above six situations happens in any of the exposures. We have
checked carefully for the masks in these sources, and none of the H$\beta$, [O
iii]$\lambda 5007$ and [O iii]$\lambda 5007$ spectral regions is marked with 1
with either allmask or ormask.

We also check the single-exposure spectra to validate the accuracy of the
asymmetry profiles. The measured velocity dispersion, the number of exposures,
the number of exposures used, and the measurement error are in Table 4.
Specifically for source 811511143, we demonstrate double-Gaussian fitting
result for both the [O iii]$\lambda 4959$ and [O iii]$\lambda 5007$ emission
lines for each of the selected single exposures in Figure 13.

Amorín et al. (2012a, b); Bosch et al. (2019); Hogarth et al. (2020); Lin et
al. (2023) have discussed the phenomenon of the double-peak or asymmetric
profile in their spectra of the Green Pea galaxies. Amorín et al. (2012b) have
identified multiple components with spatially-resolved offsets in their two-
dimensional spectra. By analyzing the chemical abundances of each component,
Hogarth et al. (2020) conclude that the outflows and turbulence are the
driving force for the escape of ionizing photons and chemical enrichment.
These studies show that the multiple gas component is not unique in Green Pea
galaxies but also exists in $z\sim 1-2$ extreme emission-line galaxies (Maseda
et al., 2014; Masters et al., 2014; Terlevich et al., 2015) with high-velocity
dispersions up to about 240 km s-1, as well as detected in the integral field
spectroscopy of other compact star-forming galaxies (Law et al., 2009; Yang et
al., 2017; Turner et al., 2017) and giant H ii regions (Castaneda et al.,
1990).

Due to the limits of the instrumentation resolution ($R\approx 1800$), it is
impossible for us to identify narrower components. It is worthwhile to conduct
follow-up high-resolution spectroscopy with a longer exposure time to confirm
the existence of the multi-components.

##  6 Conclusions

Our work aims to learn about the chemical composition and kinematics of the
strong [O iii]$\lambda$5007 emission-line compact galaxies in the LAMOST
survey. With the photometric catalog of SDSS and spectra database from LAMOST,
we newly identify 402 spectra and 346 new strong [O iii]$\lambda$5007
emission-line compact galaxies by finding compact isolated point sources, and
confirm by LAMOST spectra. Combined with the Blueberry, Green Pea, and Purple
Grape samples in our previous work (Liu et al., 2022), this returns a sample
of strong [O iii]$\lambda$5007 emission-line compact galaxies with 1830 unique
strong [O iii]$\lambda$5007 emission-line compact galaxies with 2033 spectra
up to redshift of 0.53. Using the emission lines, we check the metallicity of
these sources.

Our conclusions are as follows:

  * •

The strong-line metallicity diagnostics calibrated from the direct-$T_{e}$
method also apply to the strong [O iii]$\lambda$5007 emission-line compact
galaxies.

  * •

The strong [O iii]$\lambda$5007 emission-line compact galaxies fall below
several $T_{e}$-calibrated mass-metallicity relations, especially Yates et al.
(2020); Curti et al. (2020).

  * •

The N/O vs O/H relation of the strong [O iii]$\lambda$5007 emission-line
compact galaxies mainly follows the relation at low metallicity when the
nitrogen is primarily produced from primary nucleosynthesis.

  * •

The ionization parameter mapped from Ne3O2 and O32 follows a tight linear
relation. No significant redshift evolution is observed.

  * •

The Ne3O2 anti-correlates with the stellar mass for these strong [O
iii]$\lambda$5007 emission-line compact galaxies at
$\rm\log(M_{\star}/M_{\odot})<9.5$. At fixed stellar mass, the Ne3O2 is higher
at higher redshifts.

  * •

Three sources from JWST follow a similar relation with the strong [O
iii]$\lambda$5007 emission-line compact galaxies in this work in MZR, N/O vs
O/H relation, and the Ne3O2 vs O32 relation.

  * •

Eight sources with asymmetric [O iii]$\lambda 5007$ emission-line profiles
have been identified however with no [O iii]$\lambda 4363$ detection, which
proves the rich metal content and complex ionized gas kinematics within the
galaxies (Amorín et al., 2012a, b; Bosch et al., 2019; Hogarth et al., 2020).
However, due to limited spectral resolution, we cannot identify the components
with velocity dispersion less than 70 km s-1.

## Acknowledgements

This work is supported by the National Science Foundation of China (No.
12273075) and the National Key R&D Program of China (No. 2019YFA0405502).
Guoshoujing Telescope (the Large Sky Area Multi-Object Fiber Spectroscopic
Telescope, LAMOST) is a National Major Scientific Project built by the Chinese
Academy of Sciences. Funding for the project has been provided by the National
Development and Reform Commission. LAMOST is operated and managed by the
National Astronomical Observatories, the Chinese Academy of Sciences. W. Zhang
acknowledges support from the National Science Foundation of China (No.
12090041), the National Key R&D Program of China (No. 2021YFA1600401,
2021YFA1600400), and the Guangxi Natural Science Foundation (No.
2019GXNSFFA245008). S.L. thanks for the useful discussion with Jun-Qiang Ge,
Qing Liu, Xiang-Lei Chen, and Yun-Jin Zhang.

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##  Appendix A Asymmetric [O iii]$\lambda 5007$ emission-line profiles

(a)  (b)

Figure 12: Asymmetric [O iii]$\lambda 5007$ emission-line profiles of the
first four sources. The black step plot is the re-calibrated LAMOST spectra
with the continuum subtracted. The error region from the inverse variance is
marked with the gray-shaded regions. The central wavelengths from the spectral
fit and the velocity dispersions of the profiles are marked above the emission
lines. The velocity separation of the [O iii]$\lambda 5007$ emission line is
marked on the right part of the plot.

Table 3: Asymmetric [O iii]$\lambda 5007$ emission-line sources

obsid | SDSS objID |  $\rm\log[M_{\star}/M_{\odot}$] | $\rm\log[\rm Age/year]$ | z | H$\beta$ | [O iii]$\lambda 4959$ | [O iii]$\lambda 5007$ | H$\alpha$ | [N ii]$\lambda 6585$ | BPT
---|---|---|---|---|---|---|---|---|---|---
|  |  |  |  | flux1 | [flux | flux | flux | flux |
173508168 | 12376787790009073330 | 10.46 | 7.22 | 0.3596 | 219.68 | 126.64 | 527.68 | 1336.49 | 325.93 | comp
219710125 | 1237658492798304476 | 10.07 | 7.41 | 0.3627 | 237.18 | 98.29 | 457.23 | 860.11 | 337.10 | comp
285715023 | 1237664339319324770 | 9.33 | 8.96 | 0.1001 | 160.66 | 240.00 | 693.60 | 518.8 | 54.4 | –
369415227 | 1237678847182701297 | 12.84 | 7.00 | 0.3928 | 66.54 | 373.16 | 1206.71 | – | – | –
545310067 | 1237662620260761989 | 8.88 | 8.00 | 0.2719 | 122.26 | 189.29 | 518.23 | 181.32 | 9.73 | SF
559407231 | 1237658492798304476 | 10.07 | 7.41 | 0.3557 | 237.18 | 98.29 | 457.23 | 443.63 | 40.16 | comp
730308233 | 1237668350281777525 | 8.69 | 6.01 | 0.3520 | 47.50 | 105.87 | 352.50 | – | – | –
811511143 | 1237659132207104211 | 8.34 | 6.40 | 0.2707 | 81.22 | 218.78 | 634.63 | 395.44 | 197.77 | SF

11footnotetext: The unit is $10^{-17}$ erg s-1 cm-2.

Table 4: Single exposure measurement of the asymmetric [O iii]$\lambda 5007$
emission-line profiles

obsid | # of exposures | # of exposures used2 |  $\bm\sigma[\lambda 5007]$(km s-1) |  $\bm\sigma[\lambda 5007]$(wide)(km s-1) |  $\bm\Delta_{\rm peak}[\rm\lambda 5007]$(km s-1)
---|---|---|---|---|---
$173508168$ | $5$ | $3$ | $163.11\pm 3.12$ | $787.95\pm 27.12$ | $310.12\pm 150.43$
$219710125$ | $6$ | $3$ | $152.00\pm 11.04$ | $510.73\pm 141.61$ | $254.65\pm 61.80$
$285715023$ | $3$ | $3$ | $48.95\pm--^{3}$ | $442.77\pm 67.31$ | $104.43\pm 178.64$
$369415227$ | $3$ | $3$ | $186.40\pm 8.14$ | $492.28\pm 44.38$ | $114.56\pm 62.17$
$545310067$ | $2$ | $2$ | $88.40\pm 0.39$ | $453.93\pm 35.33$ | $488.63\pm 69.43$
$559407231$ | $3$ | $3$ | $212.53\pm 2.22$ | $483.04\pm 5.45$ | $77.17\pm 3.69$
$730308233$ | $6$ | $5$ | $202.88\pm 49.79$ | $413.18\pm 58.50$ | $94.05\pm 30.71$
$811511143$ | $4$ | $3$ | $184.00\pm 6.09$ | $517.37\pm 9.51$ | $24.56\pm 21.61$

11footnotetext: The velocity dispersions in this table have been corrected
from instrumental and thermal broadening.

22footnotetext: We only use selected single exposures to calculate the
velocity dispersion of the asymmetric [O iii]$\lambda 5007$ emission line, for
the rest of the single exposures, the emission line is not detected.

33footnotetext: Only one measurement is valid for the $\sigma[\lambda
5007]$(km s-1) measurement after subtracting the thermal broadening.

Figure 13: Asymmetric [O iii]$\lambda 4959$ and [O iii]$\lambda 5007$
emission-line profiles for each single exposure of 811511143. The black step
plot is the original 1D spectra with the sky emission subtracted. The error
region from the inverse variance is marked with the gray-shaded regions. The
central wavelengths from the spectral fit and the velocity dispersions of the
profiles are marked above the emission lines. The velocity separations of the
[O iii]$\lambda 4959$ and [O iii]$\lambda 5007$ emission lines are marked on
the right part of the plot.