Near-infrared Coronal Line Observations of Dwarf Galaxies Hosting AGN-driven Outflows

Our sample of nine dwarf galaxies is from the AGN sample of MK19. Briefly, Reines et al. (2013), Moran et al. (2014), and Sartori et al. (2015) have identified hundreds of dwarf galaxies with optical and IR signatures indicative of AGN activity. MK19 created a subsample of candidate AGNs whose optical line ratios place them above the star-forming region of the BPT and Veilleux & Osterbrock (1987, hereafter VO87) line ratio diagrams or that have He ii λ4686 emission (see Shirazi & Brinchmann 2012). They obtained Keck Low Resolution Imaging Spectrometer (LRIS; e.g., Oke et al. 1995; Rockosi et al. 2010) spectroscopy of 29 of these galaxies, nine of which showed blue asymmetries in their [O iii] λ5007 profile. This blue wing is often regarded as an indicator of outflowing gas, where the asymmetry arises due to the redshifted gas being blocked from our line of sight. These nine dwarf galaxies with spatially extended outflows form our sample for this article. Their stellar masses range from 8.77 < log(M_*/M_⊙) < 9.97 (median of 9.34), and all have a redshift of z < 0.05.

NIR spectroscopy was obtained on three separate dates: on 2017 October 29 using Keck II NIRSPEC (McLean et al. 1998) and on 2018 October 25 and 2019 January 25 with Keck II Near-Infrared Echellette Spectrometer (NIRES; Wilson et al. 2004). NIRSPEC is a NIR echelle spectrograph with a wavelength coverage ranging from 0.9–5.5 μm. The NIRSPEC-7 filter was used in low-resolution mode with a cross-dispersion angle of 35.31°. This resulted in a wavelength coverage of ∼1.97–2.39 μm. The 42'' × 0.76'' slit was used, and a spectral resolution of 196 km s⁻¹ (R ≈ 1500) at 2.20 μm was measured with a seeing of ∼0.50''. Observations throughout the night were done under mostly clear conditions. Note that these observations were done before the NIRSPEC upgrade. NIRES is an NIR echelette spectrograph with the slit being 18'' × 0.55'', and the wavelength coverage set from 0.94–2.45 μm across 5 orders. There is a small gap in coverage between 1.85 and 1.88 μm, but this is a region of low atmospheric transmission. The average spectral resolution of the 5 orders range between 84 and 89 km s⁻¹ (R ≈ 3400), and these differ less than 5% for each galaxy. Observations on 2018 October 25 were taken under variable and heavy cloud cover, however, the majority of our sample was observed on 2019 January 25, where cloud cover was light. Individual exposures for all sets of observations were 4 minutes each and were done using the standard ABBA nodding. A telluric standard star, typically of A0 spectral class with measured magnitudes in J, H, and K bands, was observed either directly before or after the target galaxy to correct for the atmospheric absorption features. Typical airmass differences with the target were below 0.10. A summary of the NIR observations is shown in Table 1.

In addition to the Keck NIRES and LRIS observations, follow-up optical integral field unit (IFU) observations with Keck Cosmic Web Imager (KCWI; Morrissey et al. 2018) and Gemini Multi-Object Spectrographs (GMOS; Allington-Smith et al. 2002; Gimeno et al. 2016) were done to obtain high spatial resolution of the outflows. The details of this analysis are discussed in L20.

Four of our targets (J0811+2328, J0906+5610, J0954+4717, and J1005+1257) were observed with the Chandra X-ray Observatory. Baldassare et al. (2017) report hard X-ray emission that is likely originating from the AGNs in J0906+5610 and J0954+4717. Additionally, Wang et al. (2016) provide fluxes, corrected for galactic absorption, for J0811+2328 and J1005+1257, from which we calculated a luminosity using the cosmology listed above. We discuss these results in Section 4.1.

The data were reduced using two modified pipelines. The first provided flat fielding and a robust background subtraction by using the techniques described in Kelson (2003) and Becker et al. (2009). In short, this routine maps the 2D science frame and models the sky background before rectification thus reducing the possibility of artifacts appearing due to the binning of sharp features. The sky subtraction attained with this procedure is excellent despite the strong OH lines present in the NIR; the procedure is also quite insensitive to cosmic rays and hot pixels and is reliable regardless of skyline intensity.

Rectification, telluric correction, wavelength calibration, and extraction were all done with a slightly modified version of REDSPEC. ⁴ Telluric correction was done by dividing by the spectrum of the telluric standard star and multiplying by a blackbody curve of the same temperature. Strong OH skylines were used for wavelength calibration, and the 1D spectra were then median combined. Flux calibration of individual exposures was done using the telluric star and the Spitzer Science Center unit converter ⁵ to convert the magnitude of the star to the associated flux in that band. A small corrective factor (<5%) was introduced due to the differences between the center NIR bands and that of the wavelength coverage.

3.1.1. NIR Fitting

3.1.2. Sloan Digital Sky Survey Fitting

We note that L20 reports extinction values calculated from the Hγ/Hβ Balmer decrement. However, for J0100-0110 and J0811+2328, they used Hα/Hβ measurements from SDSS due to weak Hγ emission in their spectra. In addition, they did not observe J1442+2054. We thus opted to use the Hα/Hβ Balmer decrement measured from SDSS for our entire sample.

To quantify the extinction, we used the intrinsic line ratio of Hα/Hβ = 3.1, typically used for AGNs (e.g., VO87 ; Osterbrock et al. 1992), and a Cardelli reddening law (Cardelli et al. 1989) with an extinction factor of R_V = 3.1. We used the narrow-line flux measurements from the SDSS data (see Section 3.1.2), where we have decomposed the Hα and Hβ emission into narrow and broad (outflow) components. For the two galaxies, J0840+1818 and J1442+2054, where no outflow component was detected, we used the full emission line to obtain a flux. These values of the Balmer decrement and E(B − V) for each galaxy are listed in Table 2, and all flux values in the Appendix reflect extinction-corrected fluxes. Note that three galaxies, J0840+1818, J0842+0319, and J0906+5610, have Balmer decrements slightly below the intrinsic ratio so we did not apply any extinction correction to them.

Our results are slightly different but generally agree with those calculated by L20. The discrepancies are likely caused by the different line ratios (Hγ/Hβ versus Hα/Hβ) and line profiles used, where we only used the narrow profile while L20 used the full (narrow + broad) profile. When comparing the effect of these two methods, the difference in flux measurements amounts to <5% for the majority of our sample. For the rest of this article, we use these extinction-corrected flux values unless otherwise specified.

55% (5/9) of our sample have NIR CL emission within the spectral window of 0.94–2.45 μm (see Table 1). For a similar spectral window and galaxy type, Sy1 and Sy2, this rate is consistent with others found in the literature: 66% (36 out of 54, Rodríguez-Ardila et al. 2011), 25% (5 out of 20, Mason et al. 2015), and 43% (44 out of 102, Lamperti et al. 2017). Our detections predominately come from sulfur and silicon species: [S viii] 0.9913 μm, [S ix] 1.2523 μm, [Si x] 1.4305 μm, and [Si vi] 1.9630 μm. We also detect [Ca viii] 2.3214 μm but it falls within the CO(3-1) absorption band at 2.3226 μm, making their measurements more uncertain. All of the detected NIR CLs are shown in Figure 1, where we include our MCMC fits to the emission line profiles. We do not detect other common NIR CLs such as [Fe xiii] 1.0747 μm, [S xi] 1.9196 μm, and [Al ix] 2.0450 μm. The most prominent CL is [Si vi] and is detected in four of the five galaxies with CL detections. This is not surprising since it has a lower ionization potential (IP) level than other CLs and is not near any absorption features. In three of these four galaxies, we find broad [Si vi] emission and thus use a two-component fit to the profile in accordance with the F-test mentioned in Section 3.1.1. Details of the multicomponent fits to [Si vi] and plots of the entire spectra are presented in the Appendix.

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No NIR CL emission is detected in the other four galaxies. To investigate this, we plotted total [Si vi] flux versus Wide-field Infrared Survey Explorer (WISE) W2 (4.6 μm) flux in Figure 2. Note that one galaxy, J0842+0319, has a CL detection, [Ca viii], but does not show any [Si vi] emission. Upper limit fluxes to the non-[Si vi] detections were calculated by integrating over a Gaussian with a width equaling the resolution element and amplitude equaling the 1σ noise level where [Si vi] should appear. This value was multiplied by three to obtain the 3σ upper limit that is plotted in Figure 2. We also plot the AGN sample (black dots) from Müller-Sánchez et al. (2018) from which we derive the plotted line of best fit. This relation (J. Cann 2021, private communication) provides an expected value for [Si vi] based on W2 flux. Our non-detections lie below most of our [Si vi] measurements, suggesting that deeper observations may be required to detect any CL emission. Further discussion of our non-detections is covered in Section 4.1.

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The optical data also reveal a number of CLs, particularly in those with NIR CL detections. 55% (5/9) of our sample have strong optical CL emission. The most common detections in our sample include [Ne v] λ3426, [Fe vii] λ6087, and [Fe x] λ6374. Less common lines include [Ne v] λ3346 and [Fe vii] λ5721. Most galaxies that have NIR CL emission also have optical CL emission, and the only exceptions are J0840+1818 and J0842+0319, where the latter only shows NIR CL emission. For J0840+1818, MK19 reported the detection of [Ne v] λ3426 but we do not find any NIR CLs. No other significant detections are seen in the rest of the sample. Additional details for each galaxy are covered in the Appendix. For the remainder of this article, we label galaxies as either having NIR CL emission or not.

Although there is evidence for AGN activity in our dwarf galaxy sample, including optical BPT/VO87 AGN line ratios, the addition of NIR lines allows us to run additional AGN diagnostics. With the inclusion of [S iii] λ9531, we can test our sample with the AGN diagnostics presented in Osterbrock et al. (1992). Specifically, we use the [S iii] λ λ 9069+9531/Hα versus [S ii] λ λ 6718+6732/Hα, [S iii] λ λ 9069+9531/Hα versus [O ii] λ λ 7320+7330/Hα, and [S ii] λ λ 6718+6732/Hα versus [O ii] λ λ 7320+7330/Hα (their Figures 4, 5, and 7). All three of these relations are plotted in Figure 3, where we include the AGNs and star-forming samples from Osterbrock et al. (1992). We overplot narrow-line fluxes of our sample as stars and exclude the galaxies with no measurable [O ii] λ λ 7320, 7330. J0100-0110 is also omitted since its [S iii] λ9531 is outside the wavelength coverage of NIRSPEC. Since [S iii] λ9069 is outside the wavelength coverage of NIRES, we use the intrinsic flux ratio of [S iii] λ9531/λ9069 = 2.6 to obtain flux values for [S iii] λ9069.

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In all three relations, our dwarf sample falls within the scatter of the AGN sample in Osterbrock et al. (1992). As discussed in Section 3.3, not every galaxy in our sample show CLs. To check if this has any effect, we separate our sample into two groups: those with CL emission and those without. We find that they all lie in similar regions and we see no clear distinction between them in all three relations. While no single line ratio can confidently separate AGN activity from star formation, our dwarf sample shows optical and NIR line ratios that, when considered collectively, strongly suggest the presence of AGNs.

Although CLs are excellent tracers of AGN activity, they do not always appear in AGN spectra and a number of reasons have been proposed to explain this. In general, CL detections decrease with increasing IP and our results agree with this; we do not detect any of the high-IP CLs, [Fe xiii] 1.0747 μm (330.8 eV) and [S xi] 1.9196 μm (447.1 eV). Stellar absorption features can also affect detection rates by attenuating the CL emission profile. Such is the case with [Ca viii], which falls within the CO (3-1) absorption feature. In addition, Ca and Al species can be affected by metallicity and depletion onto dust. Moreover, telluric absorption from the atmosphere always has to be contended within ground-based observations.

In nearby low-luminosity AGNs, circumnuclear stellar populations can dominate the NIR continuum and thus drown out any CL emission. Bright AGNs, particularly at high redshift, can also hamper CL emission due to their strong continuum. These effects can be seen in the results of Rodríguez-Ardila et al. (2011) who found that many galaxies with stars contributing ∼90% of the continuum do not show CL emission. They also found their CL detection rate decreased by 17% when selecting galaxies with a redshift >0.05.

Our coverage of J, H, and K bands allows us to estimate the contribution of circumnuclear stellar populations. The CO(6-3) absorption at 1.62 μm can provide an estimate to the flux contribution of red giants to the H-band continuum (Martins et al. 2010), where the continuum level arises due to stellar and AGN contribution. For a population of GKM giants, the typical observed depth of the absorption is ∼20% of the continuum (Schinnerer et al. 1998). Our sample ranges from 7%–14% (median of 11%), suggesting a large contribution to the H-band continuum from red giants, up to 70%. The weighted average of the depth of galaxies with no CL detections is 28% deeper than those with CL emission. One possibility is that a larger population of red giants near the center could be the cause of the deeper absorption and are thus directly increasing the continuum level. Alternatively, a shallower CO absorption may be indicative of a stronger AGN contribution to the continuum, which would likely lead to stronger CL emission that is more easily detectable.

Baldassare et al. (2017) reported 0.5–7 keV X-ray luminosities for J0906+5610 and J0954+4717, from which we convert to L_{2–10 keV} using the Portable, Interactive Multi-Mission Simulator. ⁸ This results in a L_{2–10 keV} of 2.89 × 10⁴⁰ erg s⁻¹ and 6.12 × 10³⁹ erg s⁻¹ for J0906+5610 and J0954+4717, respectively. Additionally, using 0.3–8 keV fluxes from Wang et al. (2016), we calculated 2–10 keV luminosities for J0811+2328 (1.33 × 10³⁹ erg s⁻¹) and J1005+1257 (5.20 × 10³⁹ erg s⁻¹). Although J0811+2328 does have the lowest X-ray luminosity, we find no clear distinctions between galaxies with CL detections and those without. We do note, however, that these X-ray luminosities are about 2 orders of magnitude lower than the L_{2–10 keV}–L_W2 relation discussed in Secrest et al. (2015). Indeed, all four targets have L_{2–10 keV}/L_W2 < −2.1. Similar low L_X have been reported in low-mass galaxies (Dong et al. 2012; Simmonds et al. 2016; Cann et al. 2020), suggesting obscuration of the X-ray source emission or that AGNs in dwarf galaxies are X-ray weak compared to their mid-IR emission.

Photoionization is widely considered as the main excitation mechanism behind CL emission, although Rodríguez-Ardila et al. (2006) found that their models more precisely matched emission line ratios from their data when shocks were included. If, however, photoionization is the principle excitation mechanism behind CLs, then we expect a correlation between the FWHM and IP. Emission from a high-IP line would suggest that the emitting gas is located closer to the central ionizing source and thus be deeper in the gravitational well, causing a broadening of its emission line profile. Because of their high range of IPs (∼100–500 eV), CLs are ideal in investigating the gas kinematics near the AGNs. Indeed, positive correlations between line width and IP have been found in past studies (e.g., De Robertis & Osterbrock 1984; De Robertis & Shaw 1990; Veilleux 1991a) for optical high ionization lines. A positive trend has also been found between line width and critical density in these studies. Similar trends between line width and IP for NIR lines have been seen in some galaxies (Rodríguez-Ardila et al. 2002), but larger samples are starting to show more varied CL widths (e.g., Rodríguez-Ardila et al. 2011; Villar Martín et al. 2015; Cerqueira-Campos et al. 2021), and in many cases no trends are found at all. Rodríguez-Ardila et al. (2011) found a positive slope up to ∼300 eV, after which the slope turned negative (i.e., higher IP, lower FWHM). They attribute this to the increase in electron density when approaching the central AGNs. Due to densities exceeding the critical densities of the high-IP CL ions, these lines may be suppressed. Specifically, collisional de-excitation could reduce emission associated with the broader, high velocity components, thus causing us to only see the narrow emission and explaining the decrease in the FWHM at high IPs.

We run a similar analysis by plotting a narrow-component FWHM versus IP and critical density for the CLs detected in our sample in Figure 4. We have also included optical (open circles) and NIR low-ionization lines to draw comparisons (see Table 3). In two galaxies, J0906+5610 and J1005+1257, the widths peak around 250–300 eV and subsequently decrease, consistent with collisional de-excitation of the broader components of high-IP ions. The CL emission in the other three galaxies have a lower S/N so it is difficult to evaluate any trends. Aside from these low S/N measurements (as indicated by their error bars), these CLs have widths consistent with the lower IP lines. However, some uncertainty may arise from overestimating/underestimating the broad/narrow component of the line profile. For instance, the relatively small width of [Si vi] (166.8 eV) in J0954+4717, where we have added a secondary broad component, could be due to overestimating the broad component. Regardless, our results are consistent with the recent reports finding no clear trends between the FWHM and IP.

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Critical density, defined as the density when the collision rate matches the radiative de-excitation rate, is plotted against the FWHM in the bottom panels of Figure 4. Consistent with past works (De Robertis & Osterbrock 1986; Veilleux 1991b; Ferguson et al. 1997), we find linear correlation in some galaxies with varying degrees of slope. Regardless, we find a stronger correlation of the FWHM increasing with critical density, consistent with past studies.

Table 4 lists the kinematic properties of the narrow and broad (outflow) components of [O iii] and [Si vi], where the [O iii] values come from L20. The higher spectral resolution of the IFU data of L20 allowed for the decomposition of the emission line profile into two or three components. Generally, the C1 component traces the gas in the narrow-line region, while C2 and C3 represent the broader and bluer components to the multicomponent fit and thus likely trace the outflow. For J0811+2328, only one component (C1) was fit but it is blueshifted relative to the stellar velocity and broader than the stellar velocity dispersion, and thus L20 suggested that it is likely part of the outflow. For v₅₀, the median velocity offset of the profile relative to systemic velocity, we take the minimum values (i.e., maximum blue offset) for [O iii].

The velocity of an outflow is often calculated through the use of W₈₀, the width containing 80% of the flux of an emission line (Harrison et al. 2014). For a single Gaussian profile, W₈₀ = 1.09 × FWHM. To measure W₈₀ for [Si vi] , we use the full profile due to the relatively large uncertainties in the broad component. We can define the outflow velocity as

$$\begin{eqnarray}&&{v}_{\mathrm{out}}=-{v}_{50}+\displaystyle \frac{{W}_{80}}{2}.\end{eqnarray} \tag{ 1 }$$

Although C1 likely traces the narrow-line gas, L20 and Manzano-King & Canalizo (2020, hereafter MC20) found cases where outflowing gas can be represented as a single-component profile. For this reason, we include v_out calculations for all [O iii] components. In addition, for [Si vi] v_out, we use v₅₀ of the full profile if a multicomponent fit was used. This is because of the large uncertainties associated with the broad component fits.

Our data show the outflow velocities seen in [Si vi], measured through either W₈₀ or v_out, are generally faster than those seen in [O iii]. The main exception to this are the velocities seen in the C3 components. This is likely due to combining the narrow and broad components of [Si vi] when calculating W₈₀ and v₅₀. Using only the broad component, we find velocities to be consistent or higher than those of C3, albeit with much higher uncertainty. This overall trend of higher velocities seen in [Si vi] than in [O iii] implies a decelerating outflow, one where a high velocity wind originates near the AGNs and slows down as it approaches the outer, lower ionization gas.

We also note that the objects with the fastest outflows and broadest profiles seen in [O iii], J0906+5610, J0954+4717, and J1005+1257, have the broadest [Si vi] emission. This is perhaps unsurprising since we are observing the same outflow, just at different locations.

We also list the bolometric AGN luminosities (L_AGN) in Table 4. These values were derived from the observed [O iii] λ5007 flux in L20. Empirical bolometric correlation factors from Lamastra et al. (2009) were used: L_AGN = 87 L_{[O III]} for 38 < log(L_{[O III]}) < 40 and L_AGN = 142 L_{[O III]} for 40 < log(L_{[O III]}) < 42. To correct for extinction, we applied the extinction values listed in Table 2. We find no strong correlation between AGN luminosity and outflow speeds, but there is a trend for the more luminous AGNs to have a higher number and more luminous CL detections. If we assume a simple biconical outflow starting close to the AGNs (for a detailed analysis, see Müller-Sánchez et al. 2011), highly ionized gas (i.e., CLs) could more easily be sent out to farther, possibly less obscured regions due to a fast outflow. Although it is difficult to make any firm conclusions due to the CL region being unresolved in our data, it appears that faster outflows may result in stronger and broader CL emission.

In this section, we investigate whether AGNs or stellar processes (or both) are the primary source of ionization and the driving mechanism for the outflows.

4.3.1. AGNs or Stellar Ionization?

The analysis of line ratios by L20 indicates that AGNs are the primary source of ionization in our sample. However, they note that ionization from shocks, possibly originating from starburst driven winds (Sharp & Bland-Hawthorn 2010), cannot be ruled out. To investigate this further, we compare line ratios in our sample to ionization models found in the literature. Riffel et al. (2013) and Colina et al. (2015) plot [Fe ii] 1.64 μm/Brγ versus H₂ 2.12 μm/Brγ to separate AGNs from star-forming samples. However, the five galaxies with obtainable line ratios fall within the overlap between the AGN and SNe-dominated distributions (see Figure 5 from Colina et al. 2015). We instead use the flux ratios of [Si vi]/Brγ and [Fe ii] 1.64 μm/Brγ, where [Fe ii] is a sensitive indicator of shocks (U et al. 2013) and Brγ serves as an indicator of stellar activity and the ionizing radiation field. We compare these ratios to the AGN ionization models from Groves et al. (2004a, 2004b) and shock models from Allen et al. (2008). We extracted these models from the IDL Tool for Emission-line Ratio Analysis library (Groves & Allen 2010) and plotted them in Figure 5. The shock model (Figure 5, left) takes into account both the shocked gas and precursor gas, which lies ahead of the shock front. Quick inspection of shock-only model (not plotted) shows a shift toward higher [Fe ii]/Brγ ratios, farther away from our measured line ratios. We thus focus our analysis on the shock + precursor model (hereafter simply shock model) since the individual regions cannot be resolved in our data. Free parameters for the shock model include the shock velocity v_shock (10–1000 km s⁻¹) and the magnetic field parameter B/n^1/2 (10⁻⁴–10 μG cm^3/2), where B is the transverse magnetic field. The AGN model free parameters include the power-law index α and the ionization parameter U, where U ≡ n_ion/n_e, n_ion is the density of the ionizing photons, and n_e is the electron density. The model uses a simple power law, F_ν ∝ ν^α , where 5 eV < ν < 1000 eV (see Groves et al. 2004a, 2004b, for further details).

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To estimate the CL gas density, Landt et al. (2015a, 2015b) used line ratios of the [Fe vii] λ λ λ3759, 5159, 6087 optical CLs. Although we do not detect all these lines in our optical data, some targets do have two [Fe vii] emission lines that are measurable. For these targets, we calculated an upper limit flux to the third [Fe vii] line and obtained a rough estimate of the gas density. These values are consistent with a density of 1000 cm⁻³. In addition, L20 used the S ii λ6716/S ii λ6731 line ratio (e.g., Sanders et al. 2016) and obtained values of ∼500 cm⁻³ for most of their sample. They thus use a density of 1000 cm⁻³ in their models. Therefore, in both of our models, we use a gas density of 1000 cm⁻³. Lastly, metallicity was set to solar.

We use the total flux for each emission line and plot the ratios over the shock model (Figure 5, left) and AGN model (Figure 5, right). It is clear that the line ratios are well within the AGN model parameters (−2.0 ≲ α ≲ −1.2 and −3.3 ≲ log(U) ≲ −2.0). As for the shock models, the line ratios are offset by more than 0.5 dex and all have systematically larger [Fe ii]/Brγ ratios. In order to match the measured data, it appears a relatively large magnetic parameter (>10³) is required. Thus, it is likely that AGNs are the dominant ionizing source in our sample, though a small contribution from shocks cannot be formally ruled out.

4.3.2. AGNs or Stellar Driven Winds?

J0100-0110 is one of only two galaxies in the composite region of the BPT diagram. Based on optical emission line measurements, MC20 reported disturbed gas that is offset from the stellar rotation curve derived from a Navarro–Frenk–White dark matter density profile (Navarro et al. 1996). Indeed, L20 reported strong, blueshifted [O iii] emission in the southern portion of J0100-0110, seen predominately in the C2 component. They suggested that this could be emission from the near side of a biconical outflow.

The NIR spectrum of J0100-0110 is shown in Figure 6 and line measurements are listed in Table 5. It is the only galaxy in our sample observed with NIRSPEC (wavelength coverage from ∼1.97–2.39 μm). Because of this, we cannot make estimates to the stellar age as we have done with the rest of the sample. The spectrum shows strong Paα and Brγ; it shows no CL emission in the K band. No significant optical CL emission is detected in this galaxy.

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Moran et al. (2014) reported a lower limit to the BH mass of log(M_BH/M_⊙) > 4.4 based on Eddington luminosity arguments. Wang et al. (2016) reported Chandra 0.3–8 keV flux, from which we calculate a 2–10 keV luminosity of 1.33 × 10³⁹ erg s⁻¹. MC20 reported both disturbed and stratified gas in J0811+2328. Here, the gas is both offset from the stellar rotation curve, and the Balmer and forbidden lines are kinematically distinct from one another. In L20, only a single component was needed to fit the [O iii] profile, but the larger line widths (relative to the velocity dispersion of the stellar components) and velocity offsets (up to −60 km s⁻¹) indicate that the outflow could be traced by this single profile.

The NIR spectrum of J0811+2328 is shown in Figure 7 and line measurements are listed in Table 6. We detect no NIR CL emission at the 2σ level, though deeper observations could reveal faint [S viii], [Fe xiii], [S ix], and [Ca viii]. These lines either fall on skylines or their S/N is consistent with the noise level so we do not include them in our analysis. The rest of the spectrum is relatively featureless aside from a handful of typically strong NIR lines, such as [S iii] 0.9531 μm and He i 1.0830 μm. Unfortunately, the CN absorption at 1.1 μm falls within heavy telluric absorption so we cannot make an estimate on the contribution of a younger stellar population.

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Table 6. J0811 NIR Emission Line Parameters

Emission	FWHM	Flux	Notes
	(km s−1)	(10−17 erg cm−2 s−1)
[S III] 0.9531 μm	173 ± 9	153 ± 26	Low transmission
He I 1.0830 μm total	137 ± 16	98 ± 17	...
[Fe II] 1.2486 μm	${19}_{-19}^{+42}$	21 ± 6	On skyline
[Fe II] 1.2567 μm	265 ± 44	61 ± 13	On skyline
Paβ 1.2822 μm	51 ± 48	19 ± 6	On skyline
[Fe II] 1.6435 μm	110 ± 19	39 ± 6	On skyline
H2 2.1218 μm	${66}_{-57}^{+32}$	11 ± 2	...
CO(6-3) 1.62 μm	386 ± 81	⋯	Absorption feature

Note. Same as Table 5. The CO(6-3) absorption feature at 1.62 μm is added at the bottom, along with the FWHM. The depth of the absorption feature measures about 13% of the continuum, suggesting roughly 65% of the H-band continuum comes from GMK red giants.

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Like J0811+2328, Moran et al. (2014) also reported a lower limit to the black hole (BH) mass for J0840+1818, log(M_BH/M_⊙) > 4.3. MC20 reported evidence of disturbed gas and MK19 detect an outflow through a multicomponent fit to [O iii]. Data from L20, however, show velocity offsets ranging from −30 km s⁻¹ to +20 km s⁻¹ and only a single Gaussian was used in the fit. In addition, the line widths are smaller than the velocity dispersions of the stellar component. This all suggests that the gas is rotating in the same direction as the stars and they found no clear evidence of outflows in their data.

The NIR spectrum of J0840+1818 is shown in Figure 8 and line measurements are listed in Table 7. We find no CLs at the 2σ detection level, though faint [Ca viii] may be present. Similar to J0811+2328, we only detect a handful of emission lines and the 1.1 μm CN absorption falls within significant telluric absorption. MK19 do report the optical CL [Ne v] λ3426 emission.

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Table 7. J0840 Emission Line Parameters

Emission	FWHM	Flux	Notes
	(km s−1)	(10−17 erg cm−2 s−1)
[S III] 0.9531 μm	82 ± 2	410 ± 4	Low transmission
He I 1.0830 μm	89 ± 4	109 ± 2	...
Paγ 1.0941 μm	${10}_{-10}^{+19}$	32 ± 2	Within telluric absorption
[Fe II] 1.2567 μm	43 ± 31	28 ± 4	On skyline
Paβ 1.2822 μm	${3}_{-3}^{+34}$	57 ± 4	On skyline
Brγ 2.1661 μm	152 ± 140	11 ± 5	...
CO(6-3) 1.62 μm	518 ± 126	⋯	Absorption feature, on skyline

Note. Same as Table 6. The depth of the absorption feature measures about 14% of the continuum, suggesting roughly 70% of the H-band continuum comes from GMK red giants.

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MK19 reported broad Hα J0842+0319, from which they calculated a BH mass of log(M_BH/M_⊙) = 5.84. MC20 reported both disturbed and stratified gas, which is consistent with the findings of L20 where they found blueshifted gas up to −160 km s⁻¹.

The NIR spectrum of J0842+0319 is shown in Figure 9 and line measurements are listed in Table 8. We detect [Ca viii] as the only NIR CL in this object. To provide a more accurate measurement of the flux and width, we include simultaneous fits to the CO band absorption. Of the objects that show NIR CL emission, J0842+0319 has the lowest L_AGN and deepest CO(6-3) band absorption feature. Deeper observations may reveal other, more faint CLs. The rest of the spectrum shows a number of hydrogen recombination, H₂, and He i lines, and significant CN absorption is seen, suggesting an older stellar population.

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Table 8. J0842 Emission Line Parameters

Emission	FWHM	Flux	Notes
	(km s−1)	(10−17 erg cm−2 s−1)
[S III] 0.9531 μm total	⋯	950 ± 14	Order 7, F > 2
Narrow	62 ± 3	341 ± 8	Order 7
Broad	415 ± 8	609 ± 11	Order 7
[S III] 0.9531 μm total	⋯	986 ± 19	Order 6, low transmission, F = 2
Narrow	62 ± 6	310 ± 12	Order 6
Broad	350 ± 6	677 ± 15	Order 6
Pa 0.9549 μm	155 ± 16	76 ± 5	Order 7, blend with [S III]λ 9531
Pa 0.9549 μm	171 ± 15	103 ± 6	Order 6, blend with [S III]λ 9531
Paδ 1.0052 μm	48 ± 34	24 ± 3	Order 7
Paδ 1.0052 μm	77 ± 60	24 ± 4	Order 6
[S II] 1.0323 μm	299 ± 40	71 ± 7	...
[S II] 1.0339 μm	71 ± 40	20 ± 4	...
He I 1.0830 μm	200 ± 6	618 ± 13	...
[Fe II] 1.2567 μm	280 ± 46	159 ± 16	...
Paβ 1.2822 μm	127 ± 12	152 ± 28	Blue asymmetric tail
[Fe II] 1.6435 μm	269 ± 27	152 ± 12	On skyline
Paα 1.8756 μm	192 ± 3	661 ± 7	Within telluric absorption
H2 1.9576 μm	165 ± 21	84 ± 7	...
H2 2.0338 μm	129 ± 74	17 ± 5	On skyline
He I 2.0587 μm	64 ± 34	25 ± 4	On skyline
H2 2.1218 μm	82 ± 13	53 ± 3	...
Brγ 2.1661 μm	136 ± 29	30 ± 4	...
H2 2.2235 μm	50 ± 35	14 ± 5	...
[Ca VIII] 2.3214 μm	90 ± 53	29 ± 13	...
CO(6-3) 1.62 μm	723 ± 136	⋯	Absorption feature

Note. Same as Table 6. The depth of the absorption feature measures about 13% of the continuum, suggesting roughly 65% of the H-band continuum comes from GMK red giants.

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Reines & Volonteri (2015) reported a BH mass of log(M_BH/M_⊙) = 5.40, based on virial mass estimates. Marleau et al. (2017) also reported a BH mass using bolometric luminosities from WISE IR data, from which they calculate log(M_BH/M_⊙) = 6.93. Baldassare et al. (2017) reported bright X-ray emission, L_{0.5–7 keV} = 4.47 × 10⁴⁰ erg s⁻¹, in Chandra data that is higher than what is expected from high-mass X-ray binaries. They concluded that AGN activity is the likely source of this X-ray emission. MC20 reported disturbed gas and three components were used in the fits done by L20. Maximum widths of the third component reach up 1250 km s⁻¹, the largest seen in the sample and is indicative of a fast outflow.

We also note that the C2 component of [O iii] measured in L20 is redshifted 60 km s⁻¹ relative to the systemic velocity. One explanation for this is that they are observing the far side of the outflow. Interestingly, this redshifted component is also seen in [Si vi], where it is offset by ∼90 km s⁻¹. Since the two values are consistent with each other, we are both likely observing the far side of the outflow.

The NIR spectrum of J0906+5610 is shown in Figure 10 and line measurements are listed in Table 9. The spectrum has an abundant number of emission lines, including strong hydrogen recombination, H₂, and He i lines. The CL emission is also strong, with significant emission from [Si vi], [S ix], and [Si x]. We also detect weaker emission from [S viii] and [Ca viii]. [Si vi] is best fit with two Gaussian components (see Figure 11), while only one Gaussian was necessary to fit the other CLs properly. It is noteworthy that [Si vi] falls within a region of telluric absorption and skylines. However, on closer inspection of the telluric standard star used, the degree of absorption is comparable to that seen redward at 1.98 μm. Thus, we expect the noise level around [Si vi] to be at similar levels. The skylines are also similar to those blueward and the effects can be seen in the residuals of the fit. Lastly, we do not detect CN absorption in the J band.

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Inspection of the available optical data from SDSS, LRIS, GMOS, and KCWI yields a number of CLs. These include [Ne v] λ3426, [Fe vii] λ λ λ5721, 5159, 6087, and [Fe x] λ6374.

Both Reines & Volonteri (2015) and Marleau et al. (2017) reported a BH mass for J0954+4717. Using the methods described in Section A.5, they reported log(M_BH/M_⊙) equal to 5.00 and 6.46, respectively. Similar to J0906+5610, Baldassare et al. (2017) also reported strong X-ray emission, L_{0.5–7 keV} = 9.77 × 10³⁹ erg s⁻¹ that is likely coming from AGN activity. MC20 reported disturbed gas, and as shown in L20, three components were needed to properly describe the profile. Both of these indicate the presence of outflows.

The NIR spectrum of J0954+4717 is shown in Figure 12 and line measurements are listed in Table 10. Strong emission is seen in various hydrogen recombination, H₂, and He i lines. A large number of these emission lines require a multicomponent fit to properly match their profile, possibly due to the outflow. [Si vi], plotted in Figure 13, is the only strong CL. Inspecting the skyline immediately on top of [Si vi], we find it to be of similar strength to those redward. As shown in the bottom panel, the residuals at the locations of the skylines are comparable, leading us to believe our fit is representative of the emission. Evaluating the emission profile of [Si vi], we obtain an F-test value of ∼1.5 when adding a broad component. Although this is suggestive of the presence of broad emission, we cannot say for certain whether adding a broad component is justifiable. As such, we treat this as an upper limit to the broad flux and width.

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Table 10. J0954 Emission Line Parameters

Emission	FWHM	Flux	Notes
	(km s−1)	(10−17 erg cm−2 s−1)
[S III] 0.9531 μm total	⋯	1719 ± 75	Order 7, F > 2
Narrow	87 ± 2	1251 ± 56	Order 7
Broad	530 ± 36	468 ± 46	Order 7
[S III] 0.9531 μm total	⋯	1736 ± 74	Order 6, F > 2
Narrow	73 ± 2	1147 ± 60	Order 6
Broad	401 ± 21	590 ± 43	Order 6
Pa 0.9549 μm	75 ± 24	52 ± 10	Order 7, blend with [S III]λ 9531
Pa 0.9549 μm	129 ± 42	64 ± 13	Order 6
[C I] 0.9853 μm	75 ± 45	24 ± 8	Order 7, on skyline
[S VIII] 0.9913 μm	109 ± 30	30 ± 5	Order 6
Paδ 1.0052 μm	119 ± 10	108 ± 8	Order 7, on skyline
Paδ 1.0052 μm	102 ± 12	89 ± 8	Order 6, on skyline
He II 1.0126 μm	194 ± 23	56 ± 6	...
[S II] 1.0289 μm	128 ± 44	28 ± 7	...
[S II] 1.0323 μm	80 ± 28	38 ± 7	...
[S II] 1.0339 μm	128 ± 29	37 ± 7	...
He I 1.0830 μm total	⋯	1391 ± 44	Red asymmetric tail, F > 2
Narrow	152 ± 5	1065 ± 35	...
Broad	805 ± 61	325 ± 26	...
Paγ 1.0941 μm	96 ± 7	162 ± 10	On skyline
[S IX] 1.2523 μm	387 ± 116	24 ± 9	On skyline
Fe II 1.2567 μm total	⋯	197 ± 57	On skyline, F = 2
Narrow	125 ± 19	102 ± 39	...
Broad	400 ± 124	95 ± 42	...
Paβ 1.2822 μm total	⋯	342 ± 53	On skyline, F > 2
Narrow	59 ± 18	186 ± 40	...
Broad	252 ± 64	157 ± 35	...
Fe II 1.6435 μm total	⋯	150 ± 21	On skyline, F > 2
Narrow	114 ± 16	90 ± 15	...
Broad	440 ± 115	61 ± 15	...
Paα 1.8756 μm total	⋯	952 ± 36	Within telluric absorption, F > 2
Narrow	63 ± 5	655 ± 27	...
Broad	309 ± 30	298 ± 24	...
Brδ 1.9451 μm	83 ± 11	33 ± 2	Within telluric absorption
H2 1.9576 μm	64 ± 28	25 ± 3	...
[Si VI] 1.9630 μm total	⋯	53 ± 11	On skyline, F ∼ 1.5
Narrow	142 ± 54	19 ± 7	...
Broad	687 ± 164	35 ± 8	...
H2 2.0338 μm	117 ± 29	11 ± 2	...
He I 2.0587 μm	111 ± 8	35 ± 2	...
H2 2.0735 μm	105 ± 60	4 ± 2	...
H2 2.1218 μm	71 ± 12	28 ± 2	...
Brγ 2.1661 μm total	⋯	79 ± 10	F > 2
Narrow	60 ± 19	45 ± 7	...
Broad	374 ± 94	35 ± 7	...
H2 2.2235 μm	160 ± 39	12 ± 2	...
CO(6-3) 1.62 μm	553 ± 63	⋯	Absorption feature

Note. Same as Table 6. The depth of the absorption feature measures about 11% of the continuum, suggesting roughly 55% of the H-band continuum comes from GMK red giants.

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In addition to [Si vi], we also detect two sulfur lines, [S viii] and [S ix]. Similar to the other galaxies in our sample, we do not detect any CN absorption in the J band.

Like J0906+5610, inspection of the available optical data from SDSS, LRIS, GMOS, and KCWI yields a number of CLs. These include [Ne v] λ λ 3346, 3426, [Fe v] λ3839, and [Fe vii] λ λ 5159, 6087.

Marleau et al. (2017) reported a BH mass of log(M_BH/M_⊙) = 6.47 and MC20 found disturbed gas in their optical data. Like J0811+2328, Wang et al. (2016) reported a L_{0.3–8 keV} flux for J1005+1257, from which we obtain a L_{2–10 keV} of 5.20 × 10³⁹ erg s⁻¹. L20 fit three components to the [O iii] emission line profile, and the broadest component, C3, have widths up to 1200 km s⁻¹. This is the second broadest they see in the sample and suggests the presence of a fast outflow.

The NIR spectrum of J1005+1257 is shown in Figure 14 and line measurements are listed in Table 11. Like the other galaxies with CL emission, its spectrum shows a wealth of strong emission lines. Of particular note is [Si vi], which shows a strong broad component (see Figure 15, right). Unfortunately, the emission falls in a number of small telluric absorption features, but they do not drastically alter the fit. The region that was most affected was the large telluric feature redward of the [Si vi] line. In order to not overestimate the [Si vi] emission, particularly the broad component, we masked out the entire telluric feature (as represented as the large yellow block) from the fit.

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We also detect strong emission of [Si x] and [S ix], and weaker emission of [S viii] and [Ca viii]. We detect [Si x] in two NIRES orders and list both measurements. We select the values from order 5 since the S/N is higher and the measurements are less uncertain. Also, we do not detect any CN absorption in the J band.

Optical data reveal [Fe x] λ6374 emission and possible [Fe vii] λ5721 emission. The relative abundance of NIR CL emission and lack of optical CL emission is not surprising since J1005+1257 exhibits the highest extinction of our sample (see Table 2).

Moran et al. (2014) provided an upper limit to the BH mass through Eddington luminosity arguments, log(M_BH/M_⊙) > 5.1. In addition, MC20 reported disturbed gas and a two-component fit was needed to properly fit the IFU data in L20. Due to the kinematic differences and velocity offsets between the C1 and C2 components, they suggested that the C2 component could represent a tilted, biconcial outflow, similar to that of J0100-0110.

The NIR spectrum of J1009+2656 is shown in Figure 16 and line measurements are listed in Table 12. Only one component is needed to properly fit [Si vi] (see Figure 17), this being the only case in our sample. Although there appears to be a red broad component, closer inspection of the standard star reveals telluric absorption in that region, which leads us to believe that it is due to a poorly corrected telluric feature. We also detect weak emission in [S viii], [S ix], and [Ca viii]. Lastly, we detect no CN absorption.

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Table 12. J1009 Emission Line Parameters

Emission	FWHM	Flux	Notes
	(km s−1)	(10−17 erg cm−2 s−1)
[S III] 0.9531 μm	83 ± 1	507 ± 20	Order 7
[S III] 0.9531 μm	128 ± 2	552 ± 26	Order 6, low transmission
Pa 0.9549 μm	125 ± 7	47 ± 4	Order 7
[S VIII] 0.9913 μm	145 ± 40	17 ± 4	Order 7
Paδ 1.0052 μm	44 ± 17	14 ± 2	Order 7
Paδ 1.0052 μm	26 ± 21	23 ± 3	Order 6
He II 1.0126 μm	67 ± 22	39 ± 6	Order 7
He II 1.0126 μm	114 ± 13	44 ± 4	Order 6
[S II] 1.0339 μm	92 ± 37	9 ± 3	...
He I 1.0830 μm	116 ± 3	189 ± 8	Red asymmetric tail, F < 2
Paγ 1.0941 μm	71 ± 30	35 ± 7	...
He I 1.1629 μm	106 ± 45	22 ± 3	...
[S IX] 1.2523 μm	269 ± 90	11 ± 3	On skyline
[Fe II] 1.2567 μm	71 ± 16	22 ± 2	On skyline
Paβ 1.2822 μm	83 ± 6	68 ± 2	...
[Fe II] 1.6435 μm	83 ± 22	18 ± 2	...
Paα 1.8756 μm	86 ± 2	197 ± 7	Within telluric absorption
Brδ 1.9451 μm	INDEF	6 ± 1	Within telluric absorption, width < telescope spectral resolution
H2 1.9576 μm	76 ± 34	5 ± 1	On skyline
[Si VI] 1.9630 μm	99 ± 15	17 ± 1	Adjacent to skyline
H2 2.0338 μm	${48}_{-48}^{+26}$	5 ± 1	...
He I 2.0587 μm	117 ± 70	4 ± 1	...
H2 2.1218 μm	128 ± 26	8 ± 1	On skyline
Brγ 2.1661 μm	63 ± 22	12 ± 1	...
[Ca VIII] 2.3214 μm	323 ± 79	12 ± 6	...
CO(6-3) 1.62 μm	237 ± 39	⋯	Absorption feature

Note. Same as Table 6. The depth of the absorption feature measures about 11% of the continuum, suggesting roughly 55% of the H-band continuum comes from GMK red giants.

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We also detect the optical CL [Ne v] λ3426, with other possible detections including [Fe vii] λ λ 5721, 6087. Deeper observations will be needed to confirm these detections.

J1442+2054 is one of two galaxies in our sample that falls in the composite region of the BPT diagram (see MK19). MC20 found both disturbed and stratified gas in their optical data. This object was not observed in L20 and no BH mass has been reported to date.

The NIR spectrum of J1442+2054 is shown in Figure 18 and line measurements are listed in Table 13. The NIR is relatively featureless, with only a handful of typically strong emission lines appearing. We detect no CL emission (optical nor NIR) in this galaxy. We also do not detect any CN absorption.

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