# Ionized Gas Outflows in Infrared-bright Dust-obscured Galaxies Selected with WISE and SDSS

Yoshiki Toba, Hyun-Jin Bae, Tohru Nagao, Jong-Hak Woo, Wei-Hao Wang,

Alexander Y. Wagner, Ai-Lei Sun, Yu-Yen Chang

► To cite this version:

Yoshiki Toba, Hyun-Jin Bae, Tohru Nagao, Jong-Hak Woo, Wei-Hao Wang, et al. Ionized Gas Outflows in Infrared-bright Dust-obscured Galaxies Selected with WISE and SDSS. The Astrophysical Journal, 2017, 850, 10.3847/1538-4357/aa918a. insu-03747423

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# Ionized Gas Outflows in Infrared-bright Dust-obscured Galaxies Selected with WISE and SDSS

Yoshiki Toba<fnref n="1" />,<fnref n="2" />, Hyun-Jin Bae<fnref n="3" />,<fnref n="4" />,<fnref n="5" />, Tohru Nagao<fnref n="2" />, Jong-Hak Woo<fnref n="3" />, Wei-Hao Wang<fnref n="1" />, Alexander Y. Wagner<fnref n="6" />,<fnref n="7" />, Ai-Lei Sun<fnref n="1" />,<fnref n="8" />, and Yu-Yen Chang<fnref n="1" />

Received 2017 June 11; revised 2017 September 21; accepted 2017 October 3; published 2017 November 27

## Abstract

We present the ionized gas properties of infrared (IR)-bright dust-obscured galaxies (DOGs) that show an extreme optical/IR color, $(i - [22])_{AB} > 7.0$, selected with the Sloan Digital Sky Survey (SDSS) and Wide-field Infrared Survey Explorer (WISE). For 36 IR-bright DOGs that show $[O III]\lambda5007$ emission in the SDSS spectra, we performed a detailed spectral analysis to investigate their ionized gas properties. In particular, we measured the velocity offset (the velocity with respect to the systemic velocity measured from the stellar absorption lines) and the velocity dispersion of the $[O III]$ line. We found that the derived velocity offset and dispersion of most IR-bright DOGs are larger than those of Seyfert 2 galaxies (Sy2s) at $z < 0.3$, meaning that the IR-bright DOGs show relatively strong outflows compared to Sy2s. This can be explained by the difference in IR luminosity contributed from active galactic nuclei, $L_{IR}$ (AGN), because we found that (i) $L_{IR}$ (AGN) correlates with the velocity offset and dispersion of $[O III]$ and (ii) our IR-bright DOG sample has larger $L_{IR}$ (AGN) than Sy2s. Nevertheless, the fact that about 75% IR-bright DOGs have a large $(>300 \text{ km s}^{-1})$ velocity dispersion, which is a larger fraction compared to other AGN populations, suggests that IR-bright DOGs are good laboratories to investigate AGN feedback. The velocity offset and dispersion of $[O III]$ and $[Ne III]\lambda3869$ are larger than those of $[O II]\lambda3727$, which indicates that the highly ionized gas tends to show stronger outflows.

**Key words:** catalogs – galaxies: active – galaxies: kinematics and dynamics – infrared: galaxies

**Supporting material:** machine-readable tables

## 1. Introduction

It is well-known that the mass of a supermassive black hole (SMBH) tightly correlates with the properties of its host galaxy such as spheroid component mass and stellar velocity dispersion, which suggests that SMBHs and galaxies coevolve (so-called “co-evolution”): e.g., Magorrian et al. 1998; Marconi & Hunt 2003; Kormendy & Ho 2013; McConnell & Ma 2013; Sun et al. 2013; Woo et al. 2013). Observations at various wavelengths have indicated that radiation, winds, and jets from an active galactic nucleus (AGN) can interact with the interstellar medium (ISM), and this can lead to the ejection or heating of gas. Therefore, AGN feedback has been increasingly considered as a key component for understanding galaxy formation and evolution (e.g., Fabian 2012, and references therein), which is also supported by hydro dynamical simulations (e.g., Wagner & Bicknell 2011; Faucher-Giguère & Quataert 2012; Wagner et al. 2013; Bieri et al. 2017). These powerful outflows resulting from feedback caused by the AGN regulate star formation (SF) and even AGN activity, and could control the co-evolution of galaxies and SMBHs (e.g., Di Matteo et al. 2005; Cano-Díaz et al. 2012; King & Pounds 2015). Measuring the kinematics of multi-phase gas is one of the useful ways to investigate gas outflows in AGNs. In particular, the velocity offset of the $[O III]\lambda5007 \AA$ narrow emission and its velocity dispersion are good tracers for probing AGN-driven outflows. Many works have reported strong $[O III]$ outflows in AGNs (e.g., Zamanov et al. 2002; Aoki et al. 2005; Bian et al. 2005; Boroson 2005; Komossa et al. 2008; Crenshaw

et al. 2010; Greene et al. 2011; Villar-Martín et al. 2011; Liu et al. 2013a, 2013b; Mullaney et al. 2013; Rodríguez Zaurín et al. 2013; Zakamska & Greene 2014; Sun et al. 2017) and investigated their statistical properties (e.g., Wang et al. 2011; Bae & Woo 2014; Woo et al. 2016, 2017). The advent of the integral-field unit (IFU) enables us to investigate AGN feedback, which provides spatial information on AGN outflows from the local universe (e.g., Barbosa et al. 2009; Harrison et al. 2014; McElroy et al. 2015; Karouzos et al. 2016a, 2016b; Bae et al. 2017) to the high-z universe (e.g., Alexander et al. 2010; Brusa et al. 2015; Carniani et al. 2016).

In this paper, we present the ionized gas properties of IR-bright dust-obscured galaxies (DOGs: Dey et al. 2008; Toba et al. 2015) that show an extreme optical and IR color, i.e., their flux densities in the mid-IR (MIR) regime are about 1000 times brighter than those in the optical regime, indicating that these objects are undergoing strong AGN and/or SF activity behind the large amount of dust. We have performed an IR-bright DOGs search and investigated their statistical and physical properties such as IR luminosity function (Toba et al. 2015), auto-correlation function (Toba et al. 2017a), and stellar mass and SF rate relation (Toba et al. 2017b). The IR luminosity of most of the IR-bright DOGs exceeds $10^{12} L_{\odot}$ or even $10^{13} L_{\odot}$, which are termed ultraluminous infrared galaxies (ULIRGs: Sanders & Mirabel 1996) and hyperluminous infrared galaxies (HyLIRGs: Rowan-Robinson 2000), respectively. In the context of a major merger scenario, the gas accreting onto the nucleus triggers the AGN activity due to the

<footnote n="1">¹Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan; toba@asiaa.sinica.edu.tw</footnote>

<footnote n="2">²Research Center for Space and Cosmic Evolution, Ehime University, Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan</footnote>

<footnote n="3">³Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 151-742, Korea</footnote>

<footnote n="4">⁴Department of Astronomy and Center for Galaxy Evolution Research, Yonsei University, Seoul 120-749, Korea</footnote>

<footnote n="5">⁵Biomedical engineering research center, Asan Medical Center, Seoul 05505, Korea</footnote>

<footnote n="6">⁶Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan</footnote>

<footnote n="7">⁷Institut d'Astrophysique de Paris 98 bis bd Arago, F-75014 Paris, France</footnote>

<footnote n="8">⁸Department of Physics and Astronomy, Bloomberg Center, Johns Hopkins University, Baltimore, MD 21218, USA</footnote>
<figure><img src="image_2.png" /><figcaption>Figure 1. IR luminosity as a function of redshift for our IR-bright DOG sample, as discovered by Toba & Nagao (2016). The red circles show objects that were used for the spectral analysis in this work.</figcaption></figure>

merger process, and enormous energy originating from the AGNs then significantly affects SF activity in the host galaxies (e.g., Hopkins et al. 2006, 2008). Since IR-bright DOGs may correspond to a maximum phase of AGN activity behind a large amount of dust (e.g., Narayanan et al. 2010), they are expected to be a good laboratory to investigate the AGN feedback phenomenon. Note that observations of molecular and atomic gas are quite useful to investigate the kinematics and energetics of outflowing gas (e.g., Cicone et al. 2014). However, these investigations often require follow-up observations with radio telescopes and the sample size is limited due to the low efficiency of these observations. In order to investigate the statistical aspects of outflowing gas in IR-bright DOGs, we focus on ionized gas.

This paper is organized as follows. We describe the sample selection and spectral analysis in Section 2. The resultant outflow properties of [O III] are presented in Section 3. In Section 4, we discuss the dependence of the [O III] outflow properties on physical properties such as IR luminosity. We also discuss the energetics of AGN outflow in our sample and present the outflow properties of other emission lines. We summarize in Section 5. Throughout this paper, the adopted cosmology is a flat universe with $H_0 = 70 \text{ km s}^{-1} \text{ Mpc}^{-1}$, $\Omega_M = 0.3$, and $\Omega_\Lambda = 0.7$. Unless otherwise noted, all magnitudes refer to the AB system, and we adopt vacuum wavelengths for the analysis.

## 2. Data and Analysis

The DOG Sample for the spectral analysis was selected from an IR-bright DOG sample in Toba & Nagao (2016). They selected 67 IR-bright DOGs with $(i - [22])_{AB} > 7.0$ and flux density at $22 \ \mu\text{m} > 3.8 \ \text{mJy}$ from the Sloan Digital Sky Survey (SDSS) spectroscopic catalog (York et al. 2000; Alam et al. 2015) and Wide-field Infrared Survey Explorer (WISE) ALLWISE catalog (Wright et al. 2010; Cutri et al. 2014). Among them, we narrowed down to 36 objects with $0.05 < z < 1.02$ that clearly have [O III] in their SDSS spectra.<fnref n="9" /> Figure 1 shows IR luminosity, $L_{IR}$ (8–1000 $\mu$m), as a function of redshift for all IR-bright DOG samples and this subsample. The IR luminosities of the sample with 36 IR-bright DOGs are $\log L_{IR}$ [$L_{\odot}$] = 10.5–13.1, and

25/36 (~69%) objects are classified as ULIRGs/HyLIRGs (see Table 1). Recently, some authors have discovered many (obscured) ULIRGs/HyLIRGs based on the SDSS and WISE data and reported seeing powerful ionized outflows in their spectra (Ross et al. 2015; Zakamska et al. 2016; Bischetti et al. 2017; Hamann et al. 2017; Zhang et al. 2017), although they basically focus on high-$z$ ($z > 2$) objects.

The SDSS spectra for all 36 IR-bright DOGs are shown in Figures 13–16 (see the Appendix). The mean FWHM of their $H\beta$ line is about 503 km s$^{-1}$. When we adopt 1000 km s$^{-1}$ as a threshold to discriminate between type 1 and 2 AGNs (e.g., Yuan et al. 2016), 4/36 objects can be classified as a type 1 AGN, meaning that most objects in our DOG sample are type 2 AGNs (see Table 1). One prominent feature in these spectra is that they often show broad asymmetric profiles of [O III] lines, which could indicate some IR-bright DOGs are blowing out ionized gas. In order to characterize this [O III] outflow quantitatively, we need to perform a detailed spectral fitting for each spectrum. Since most objects in our sample are type 2 AGNs, the stellar continuum can be seen, which enables us to measure the systemic velocity determined by stellar fitting and to estimate the velocity offset with respect to the systemic velocity (see Section 3.1).

Therefore, we conducted the spectral analysis for 36 IR-bright DOGs to quantify the [O III] outflow, in the same manner as Bae & Woo (2014; see also references therein). First, we subtracted the stellar continuum using the templates of simple stellar population models (MILES; Sánchez-Blázquez et al. 2006), and we measured the velocity of the luminosity-weighted stellar component of the host galaxy (systemic velocity) based on the best-fit model. The fitting is based on the Penalized Pixel-Fitting method (pPXF; Cappellari & Emsellem 2004). The typical error of the measured systemic velocity is $52.6 \text{ km s}^{-1}$. For the starlight-subtracted spectra, we fitted the $H\beta$ and [O III] doublet ([O III]$\lambda$4959, 5007) with a single- and double-Gaussian function separately using MPFIT, an IDL $\chi^2$-minimization routine (Markwardt 2009). We assumed that the $H\beta$ and [O III] doublet have independent kinematics, while the [O III] lines (4959 and 5007 Å) have the same velocity and velocity dispersion as each other. If the peak amplitude of the broad component between the two Gaussian profiles is larger than the continuum noise (i.e., the amplitude-to-noise ratio is larger than 2), we adopted the fitting results with a double-Gaussian function. Otherwise, we adopted the result with a single Gaussian. Note that we visually checked whether the stellar continuum is reproduced well by the best-fit stellar fitting. We confirmed that 10/36 objects are well-fitted by the stellar template. For the remaining 26 objects, we alternatively utilized the narrow component of the $H\beta$ line as a proxy of the systemic velocity.

## 3. Results

### 3.1. Spectral Fitting

Using the best fit with single- or double-Gaussian components, we measured the velocity offset ($v_{line}$) and velocity dispersion ($\sigma_{line}$) in the same manner as Woo et al. (2016);

$$v_{\text{line}}(\lambda) = \frac{(\lambda_0 - \lambda_{\text{rest}})c}{\lambda_{\text{rest}}} - v_{\text{sys}}(\lambda), \quad (1)$$

$$\sigma_{\text{line}}(\lambda) = \sqrt{\frac{\int \lambda^2 f(\lambda) d\lambda}{\int f(\lambda) d\lambda} - \lambda_0^2}, \quad (2)$$

where $\lambda_{rest}$ is the rest-frame line center of a line ($\lambda_{rest} = 5008.24$ Å for [O III]), and c is the speed of light,

<footnote n="9">⁹ Within our sample, the spectra of SDSS1010+3725 (ID = 12), SDSS1248+4242 (ID = 21), SDSS1407+3601 (ID = 26), and SDSS1513+1451 (ID = 30) were also reported in Ross et al. (2015). They also mentioned that SDSS1010+3725 has unusually broad [O III] with non-Gaussian structure.</footnote>
<table><caption>**Table 1**

[O III] Properties of WISE-SDSS Spec DOGs</caption><thead><tr><th>ID</th><th>Obj. name</th><th>R.A.<sup>a</sup><br>hms</th><th>Decl.<sup>a</sup><br>dms</th><th>Plate</th><th>FiberID</th><th>MJD</th><th>Redshift</th><th>Type<sup>b</sup></th><th>i - [22]<br>AB mag</th><th>log L<sub>IR</sub><sup>c</sup><br>L<sub>☉</sub></th><th>log L<sub>bol</sub><sup>d</sup><br>erg s<sup>-1</sup></th><th>w<sub>[O III]</sub><sup>e</sup></th><th>v<sub>[O III]</sub><sup>f</sup><br>km s<sup>-1</sup></th><th>σ<sub>[O III]</sub><sup>f</sup><br>km s<sup>-1</sup></th></tr></thead><tbody><tr><td>1</td><td>SDSS J0045+1339</td><td>00:45:29.1</td><td>+13:39:08.6</td><td>419</td><td>137</td><td>51879</td><td>0.295</td><td>type 2</td><td>7.11</td><td>10.70</td><td>44.58</td><td>1</td><td>16.8 ± 20.8</td><td>99.3 ± 3.5</td></tr><tr><td>2</td><td>SDSS J0048-0046</td><td>00:48:46.4</td><td>-00:46:11.9</td><td>3590</td><td>256</td><td>55201</td><td>0.939</td><td>type 2</td><td>7.55</td><td>12.45</td><td>46.26</td><td>1</td><td>-1427.8 ± 191.5</td><td>1125.4 ± 80.2</td></tr><tr><td>3</td><td>SDSS J0749+3353</td><td>07:49:34.6</td><td>+33:53:08.6</td><td>3751</td><td>813</td><td>55234</td><td>0.620</td><td>type 2</td><td>7.14</td><td>12.39</td><td>46.07</td><td>1</td><td>-151.3 ± 107.3</td><td>316.7 ± 136.9</td></tr><tr><td>4</td><td>SDSS J0751+2958</td><td>07:51:20.5</td><td>+29:58:47.1</td><td>3752</td><td>435</td><td>55236</td><td>0.437</td><td>type 2</td><td>7.14</td><td>12.14</td><td>45.94</td><td>1</td><td>43.8 ± 27.6</td><td>230.6 ± 6.7</td></tr><tr><td>5</td><td>SDSS J0756+4432</td><td>07:56:09.9</td><td>+44:32:22.8</td><td>6376</td><td>806</td><td>56269</td><td>0.510</td><td>type 2</td><td>7.18</td><td>12.39</td><td>46.22</td><td>1</td><td>-555.0 ± 88.9</td><td>978.6 ± 63.4</td></tr><tr><td>6</td><td>SDSS J0819+4417</td><td>08:19:47.3</td><td>+44:17:22.8</td><td>6379</td><td>933</td><td>56340</td><td>0.578</td><td>type 2</td><td>7.28</td><td>12.38</td><td>46.22</td><td>1</td><td>-717.2 ± 130.8</td><td>777.2 ± 70.9</td></tr><tr><td>7</td><td>SDSS J0832+4606</td><td>08:32:48.2</td><td>+46:06:02.6</td><td>5160</td><td>330</td><td>55895</td><td>0.721</td><td>type 2</td><td>7.10</td><td>11.90</td><td>45.73</td><td>0</td><td>-229.3 ± 500.1</td><td>801.5 ± 45.0</td></tr><tr><td>8</td><td>SDSS J0833+4508</td><td>08:33:38.5</td><td>+45:08:33.5</td><td>7326</td><td>452</td><td>56710</td><td>0.925</td><td>type 2</td><td>7.05</td><td>12.15</td><td>46.04</td><td>1</td><td>-252.6 ± 38.0</td><td>360.9 ± 81.9</td></tr><tr><td>9</td><td>SDSS J0847+4740</td><td>08:47:15.0</td><td>+47:40:14.0</td><td>7320</td><td>160</td><td>56722</td><td>0.713</td><td>type 2</td><td>7.39</td><td>12.10</td><td>45.88</td><td>1</td><td>-56.9 ± 36.3</td><td>290.5 ± 62.2</td></tr><tr><td>10</td><td>SDSS J0919+5914</td><td>09:19:45.0</td><td>+59:14:30.9</td><td>5712</td><td>229</td><td>56602</td><td>0.829</td><td>type 2</td><td>7.22</td><td>12.68</td><td>46.34</td><td>1</td><td>-184.0 ± 199.2</td><td>536.3 ± 43.0</td></tr><tr><td>11</td><td>SDSS J1009+4935</td><td>10:09:41.3</td><td>+49:35:26.5</td><td>7381</td><td>548</td><td>56717</td><td>0.308</td><td>type 2</td><td>7.19</td><td>11.23</td><td>44.90</td><td>0</td><td>5.6 ± 24.2</td><td>76.7 ± 0.6</td></tr><tr><td>12</td><td>SDSS J1010+3725</td><td>10:10:34.2</td><td>+37:25:14.7</td><td>1426</td><td>110</td><td>52993</td><td>0.282</td><td>type 1</td><td>7.23</td><td>12.07</td><td>45.89</td><td>1</td><td>-613.6 ± 29.5</td><td>971.1 ± 6.7</td></tr><tr><td>13</td><td>SDSS J1028+5011</td><td>10:28:01.5</td><td>+50:11:02.5</td><td>6694</td><td>430</td><td>56386</td><td>0.776</td><td>type 1</td><td>7.20</td><td>11.97</td><td>45.84</td><td>1</td><td>-11.9 ± 259.3</td><td>476.0 ± 45.4</td></tr><tr><td>14</td><td>SDSS J1029+0501</td><td>10:29:05.9</td><td>+05:01:32.4</td><td>4772</td><td>617</td><td>55654</td><td>0.493</td><td>type 2</td><td>7.11</td><td>12.16</td><td>45.96</td><td>0</td><td>-1485.0 ± 207.7</td><td>986.9 ± 146.6</td></tr><tr><td>15</td><td>SDSS J1042+2451</td><td>10:42:41.1</td><td>+24:51:07.0</td><td>6417</td><td>509</td><td>56308</td><td>1.026</td><td>type 2</td><td>7.02</td><td>12.40</td><td>46.29</td><td>1</td><td>-414.8 ± 311.8</td><td>489.2 ± 147.6</td></tr><tr><td>16</td><td>SDSS J1057+3609</td><td>10:57:14.5</td><td>+36:09:03.3</td><td>4626</td><td>442</td><td>55647</td><td>0.885</td><td>type 2</td><td>7.06</td><td>12.28</td><td>46.06</td><td>0</td><td>761.0 ± 570.1</td><td>371.1 ± 271.4</td></tr><tr><td>17</td><td>SDSS J1159+1100</td><td>11:59:15.3</td><td>+11:00:42.8</td><td>5388</td><td>398</td><td>55983</td><td>0.351</td><td>type 2</td><td>7.01</td><td>11.90</td><td>45.57</td><td>0</td><td>-255.5 ± 57.4</td><td>578.0 ± 46.0</td></tr><tr><td>18</td><td>SDSS J1210+6105</td><td>12:10:56.9</td><td>+61:05:51.5</td><td>6972</td><td>272</td><td>56426</td><td>0.926</td><td>type 2</td><td>7.63</td><td>12.54</td><td>46.34</td><td>1</td><td>195.1 ± 133.3</td><td>583.4 ± 10.2</td></tr><tr><td>19</td><td>SDSS J1212+1916</td><td>12:12:36.5</td><td>+19:16:23.7</td><td>5848</td><td>737</td><td>56029</td><td>0.620</td><td>type 2</td><td>7.37</td><td>12.37</td><td>46.19</td><td>1</td><td>-1.0 ± 48.8</td><td>695.9 ± 19.5</td></tr><tr><td>20</td><td>SDSS J1235+4827</td><td>12:35:44.9</td><td>+48:27:15.4</td><td>6670</td><td>254</td><td>56389</td><td>1.023</td><td>type 2</td><td>7.50</td><td>13.06</td><td>46.70</td><td>1</td><td>-26.1 ± 150.3</td><td>834.7 ± 37.6</td></tr><tr><td>21</td><td>SDSS J1248+4242</td><td>12:48:36.1</td><td>+42:42:59.3</td><td>4703</td><td>632</td><td>55617</td><td>0.682</td><td>type 2</td><td>7.11</td><td>11.85</td><td>45.66</td><td>1</td><td>-12.8 ± 130.5</td><td>632.1 ± 45.4</td></tr><tr><td>22</td><td>SDSS J1309+2157</td><td>13:09:56.3</td><td>+21:57:00.8</td><td>2650</td><td>23</td><td>54505</td><td>0.609</td><td>type 1</td><td>7.49</td><td>12.06</td><td>45.88</td><td>0</td><td>-518.0 ± 348.2</td><td>485.5 ± 104.2</td></tr><tr><td>23</td><td>SDSS J1315+2618</td><td>13:15:14.0</td><td>+26:18:41.3</td><td>2243</td><td>171</td><td>53794</td><td>0.305</td><td>type 2</td><td>8.03</td><td>10.93</td><td>44.77</td><td>1</td><td>12.4 ± 20.9</td><td>82.1 ± 2.6</td></tr><tr><td>24</td><td>SDSS J1324+4501</td><td>13:24:40.1</td><td>+45:01:33.8</td><td>6625</td><td>124</td><td>56386</td><td>0.774</td><td>type 2</td><td>7.78</td><td>12.38</td><td>46.20</td><td>1</td><td>-118.1 ± 234.9</td><td>1009.2 ± 103.6</td></tr><tr><td>25</td><td>SDSS J1353+4134</td><td>13:53:34.6</td><td>+41:34:39.0</td><td>6631</td><td>212</td><td>56364</td><td>0.686</td><td>type 2</td><td>7.43</td><td>12.29</td><td>45.93</td><td>1</td><td>67.2 ± 93.3</td><td>214.1 ± 44.9</td></tr><tr><td>26</td><td>SDSS J1407+3601</td><td>14:07:44.0</td><td>+36:01:09.5</td><td>3854</td><td>24</td><td>55247</td><td>0.783</td><td>type 1</td><td>7.17</td><td>12.58</td><td>46.36</td><td>0</td><td>-257.5 ± 56.4</td><td>754.9 ± 43.4</td></tr><tr><td>27</td><td>SDSS J1431+2557</td><td>14:31:36.4</td><td>+25:57:06.8</td><td>2135</td><td>482</td><td>53827</td><td>0.481</td><td>type 2</td><td>7.26</td><td>11.92</td><td>45.72</td><td>1</td><td>-63.2 ± 22.5</td><td>340.1 ± 4.3</td></tr><tr><td>28</td><td>SDSS J1435+2807</td><td>14:35:40.3</td><td>+28:07:25.5</td><td>6018</td><td>975</td><td>56067</td><td>0.346</td><td>type 2</td><td>7.28</td><td>11.76</td><td>45.56</td><td>1</td><td>-208.7 ± 102.0</td><td>854.6 ± 92.2</td></tr><tr><td>29</td><td>SDSS J1513+0402</td><td>15:13:33.8</td><td>+04:02:22.8</td><td>4776</td><td>25</td><td>55652</td><td>0.597</td><td>type 2</td><td>7.23</td><td>12.54</td><td>46.38</td><td>1</td><td>-121.1 ± 24.7</td><td>481.8 ± 6.2</td></tr><tr><td>30</td><td>SDSS J1513+1451</td><td>15:13:54.4</td><td>+14:51:25.2</td><td>5486</td><td>200</td><td>56030</td><td>0.882</td><td>type 2</td><td>7.33</td><td>12.49</td><td>46.30</td><td>1</td><td>-539.3 ± 186.3</td><td>902.4 ± 141.3</td></tr><tr><td>31</td><td>SDSS J1525+1234</td><td>15:25:04.7</td><td>+12:34:01.7</td><td>5492</td><td>818</td><td>56010</td><td>0.851</td><td>type 2</td><td>7.19</td><td>12.18</td><td>46.01</td><td>1</td><td>10.5 ± 45.9</td><td>562.5 ± 19.9</td></tr><tr><td>32</td><td>SDSS J1531+4533</td><td>15:31:05.1</td><td>+45:33:03.4</td><td>6735</td><td>246</td><td>56397</td><td>0.871</td><td>type 2</td><td>7.47</td><td>12.20</td><td>46.05</td><td>1</td><td>-1009.2 ± 387.8</td><td>855.6 ± 152.5</td></tr><tr><td>33</td><td>SDSS J1635+3040</td><td>16:35:59.3</td><td>+30:40:32.8</td><td>5202</td><td>322</td><td>55824</td><td>0.578</td><td>type 2</td><td>7.09</td><td>12.37</td><td>46.02</td><td>1</td><td>-515.7 ± 224.2</td><td>932.1 ± 100.7</td></tr><tr><td>34</td><td>SDSS J1711+3509</td><td>17:11:45.7</td><td>+35:09:27.7</td><td>4994</td><td>525</td><td>55739</td><td>0.316</td><td>type 2</td><td>7.33</td><td>11.74</td><td>45.58</td><td>1</td><td>-5.2 ± 22.0</td><td>258.8 ± 5.2</td></tr><tr><td>35</td><td>SDSS J2303+2028</td><td>23:03:01.6</td><td>+20:28:20.5</td><td>6121</td><td>70</td><td>56187</td><td>0.788</td><td>type 2</td><td>7.32</td><td>12.40</td><td>46.26</td><td>1</td><td>890.7 ± 467.9</td><td>857.3 ± 170.9</td></tr><tr><td>36</td><td>SDSS J2351+1248</td><td>23:51:20.1</td><td>+12:48:19.9</td><td>6145</td><td>163</td><td>56266</td><td>0.052</td><td>type 2</td><td>7.11</td><td>10.52</td><td>44.21</td><td>1</td><td>-100.9 ± 20.5</td><td>99.6 ± 0.5</td></tr></tbody></table>

**Notes.**

a The coordinates in the SDSS DR12.

b 1: type 1 AGN. 2: type 2 AGN (see Section 2).

c The infrared luminosity at 8–1000 µm derived in Toba & Nagao (2016).

d The bolometric luminosity calculated by integrating the best-fit SED template at wavelengths longward of Lyα (see Section 4.1).

e 0: there is no broad wing of the [O III] line. 1: there is a broad wing of the [O III] line (see Section 3.1).

(This table is available in its entirety in machine-readable form.)
<figure><img src="image_3.png" /><figcaption>Figure 2. Example of the SDSS gri-composite images of our IR-bright DOG sample.</figcaption></figure>

while $v_{sys}$ ($\lambda$) is the systemic velocity measured by the fitting with a stellar component or a narrow component of H$\beta$ (see Section 2). $f(\lambda)$ is the flux density at each wavelength and $\lambda_0$ is the first moment of the line profile (flux-weighted center),

$$ \lambda_0 = \frac{\int \lambda f(\lambda) d\lambda}{\int f(\lambda) d\lambda}. \qquad (3) $$

The measured velocity dispersions were corrected for the wavelength-dependent instrumental resolution of the SDSS. The measurement errors were estimated from a Monte Carlo realization; we adopted the $1\sigma$ dispersion of each value by measuring them 100 times for spectra while randomly adding the noise (see Woo et al. 2016, in detail).

The resultant velocity offset ($v_{[O III]}$) and dispersion ($\sigma_{[O III]}$) for the [O III] line of our DOG sample are tabulated in Table 1. We found that 29/36 objects show a broad wing of [O III] (we labeled them as $w_{[O III]} = 1$; see Table 1), thus we fit them with a double Gaussian. For the seven remaining objects ($w_{[O III]} = 0$), we fit them with a single Gaussian. Figure 2 shows some examples of the SDSS composite images made by g, r, and i images. Some DOGs show a green or red color, since strong [O III] lines fall in the r- or i-band, depending on the redshift.

Hereafter, we compare the outflow properties of our IR-bright DOG sample with those of local Seyfert 2 galaxies (Sy2s). In order to ensure a fair comparison, we only focus on 36–4 = 32 IR-bright DOGs that are classified as type 2 AGNs, unless otherwise noted. Note that among 32 DOGs, 12 objects have very large uncertainties of velocity offset ($\delta_{v_{[O III]}}$), i.e., $\delta_{v_{[O III]}} > v_{[O III]}$, although all objects have $\delta_{\sigma_{[O III]}} < \sigma_{[O III]}$. We exclude them and focus on 32–12 = 20 DOGs when arguing about the velocity offset. We found that 24/32 (~75%) IR-bright DOGs have a large (>300 km s$^{-1}$) velocity dispersion, which is larger than that of local Sy2s at $z < 0.3$ as found by Woo et al. (2016), who reported that only 3.58% of the Sy2 sample showed $\sigma_{[O III]} > 300$ km s$^{-1}$. Also, 19/20 (~95%) DOGs have $|v_{[O III]}| > 50$ km s$^{-1}$, which is larger than those (~50%) of local (narrow-line) Seyfert 1 and 2 galaxies (e.g., Komossa et al. 2008; Zhang et al. 2011; Bae & Woo 2014). Since the velocity offset and (particularly) velocity dispersion

are expected to be due to the ionized gas outflow, this large outflow fraction could indicate that IR-bright DOGs are likely to be a good laboratory to investigate the AGN feedback phenomenon (see also Section 3.3).

## 3.2. Relation between [O III] Luminosity and IR Luminosity

Here, we estimate the extinction-corrected [O III] luminosity using the following formula (see Calzetti et al. 1994; Domínguez et al. 2013):

$$ L_{[O III]}^{\text{cor}} = L_{[O III]}^{\text{obs}} 10^{0.4k_{[O III]} E(B-V)}, \qquad (4) $$

where $L_{[O III]}^{\text{obs}}$ is the observed [O III] luminosity, $k_{[O III]}$ is the extinction value at $\lambda = 5008.24 \AA$ provided by Calzetti et al. (2000), and $E(B-V)$ is the color excess. We note that $E(B-V)$ was estimated based on the spectral energy distribution (SED) fitting with a code: SED Analysis using BAYesian Statistics (SEABASS: Rovilos et al. 2014). This fitting code provides up to three-component fitting (AGN, SF, and stellar component) based on the maximum likelihood method (see Rovilos et al. 2014; Toba & Nagao 2016, in detail). Among the three-component fitting, $E(B-V)$ was determined by the stellar component fitting with a library of synthetic stellar templates from Bruzual & Charlot (2003) stellar population models reddened using a Calzetti et al. (2000) dust extinction law. We used photometric data from 9 sources (u, g, r, i, and z, and 3.4, 4.6, 12, and 22 $\mu$m, obtained from the SDSS and WISE, respectively) for the SED fitting. We note that all DOGs in our sample were detected in all nine bands. The typical value of $E(B-V)$ is 0.68. We also calculated the 22 $\mu$m luminosity at the observed frame, $\nu L_{\nu}^{\text{obs}}$ (22 $\mu$m), from the observed flux multiplied by $4\pi d_L^2$ for each DOG, where $d_L$ is the luminosity distance. IR-bright DOGs tend to have flat SED at the MIR regime (see Toba & Nagao 2016; Toba et al. 2017b) and we found that $\nu L_{\nu}^{\text{obs}}$ (22 $\mu$m) is perfectly correlated with IR luminosity (Toba et al. 2017b). In addition, some authors claimed that the IR luminosities of AGNs are correlated with [O III] luminosity (e.g., Goto
<figure><img src="image_4.png" /><figcaption>**Figure 3.** (Left) Examples of the SED fitting for the IR-bright DOG sample. The cyan and yellow circles represent the data from the SDSS and WISE, respectively. The contributions from the stellar and AGN components to the total SEDs are shown as blue and red lines, respectively. The black solid line represents the resultant (the combination of the stellar and AGN) SEDs. (Right) Comparison of a composite spectrum of IR-bright DOGs (red line with a shaded region) with other SED templates of local ULIRGs/AGNs presented by Polletta et al. (2007). Each SED is normalized by the flux density at 1 µm.</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>**Figure 4.** 22 µm luminosity at the observed frame as a function of the [O III] luminosity of the broad component (left), the [O III] luminosity of the narrow component (middle), and the [O III] luminosity (right). The red line shows the best-fit linear function. The Spearman rank correlation coefficients ($r_s$) with null hypothesis probabilities ($P$) for each relation are noted at the bottom right of each panel.</figcaption></figure>

et al. 2011), suggesting that at 22 µm luminosity, the observed frame correlates with [O III] luminosity.

Figure 3 shows examples of the SED fitting in which the data are well-fitted by SEABASS (see also Toba & Nagao 2016). Their composite spectrum normalized by the flux density at 1 µm is also shown in this figure. Some SED templates of local ULIRGs and AGNs presented by Polletta et al. (2007) are also plotted. Compared with these templates, our IR-bright DOG sample shows a steep SED in the near-IR

(NIR) and MIR regions that could have originated from hot dust heated by strong AGN radiations.

Figure 4 shows the relation between [O III] luminosity and 22 µm luminosity at the observed frame. As many authors have reported that [O III] luminosities are well correlated with MIR luminosity (e.g., Toba et al. 2014; Yuan et al. 2016; Sun et al. 2017) for SDSS galaxies/AGNs, we confirmed that [O III] luminosity correlates with 22 µm (but at the observed frame) luminosity for our DOG sample, which is useful to infer the
<figure><img src="image_6.png" /><figcaption>Figure 5. [O III] velocity offset-velocity dispersion (VVD) diagram for IR-bright DOGs (red circle) and SDSS Seyfert 2 galaxies (blue circle) derived by Woo et al. (2016).</figcaption></figure>

expected [O III] luminosity for IR-bright DOGs from 22 µm flux density without considering the k-correction. The relations between the [O III] luminosity for each of the broad and narrow components and $νL_ν^{obs}$ (22 µm) are also shown in Figure 4. Note that if an object does not have a broad [O III] wing (see Section 2), we derive the extinction-corrected [O III] luminosity based on results with a single Gaussian fitting, and use them as $L_{[O III]}^{cor}$ (broad+narrow). In other words, the [O III] luminosities of the broad and narrow components in the left and middle panels of Figure 4 are derived only from objects with broad wings. We fitted each relation with linear regression lines using a IDL routine, MPFITEXY, that takes into account errors in both variables. The Spearman rank correlation coefficients ($r_s$) for $L_{[O III]}^{cor}$ (broad)-$νL_ν^{obs}$ (22 µm), $L_{[O III]}^{cor}$ (narrow)-$νL_ν^{obs}$ (22 µm), and $L_{[O III]}^{cor}$ (broad+narrow)-$νL_ν^{obs}$ (22 µm) relations are ~0.80, 0.46, and 0.75, with null hypothesis probabilities $P \sim 5.21 \times 10^{-7}$, $2.12 \times 10^{-2}$, and $9.56 \times 10^{-7}$, respectively. This means that $νL_ν^{obs}$ (22 µm) is well correlated with the broad component of [O III] luminosity. Note that the SEDs of our IR-bright DOG sample at around 22 µm appear flat, as shown in Figure 3 (see also Toba et al. 2017b). Given the somewhat narrow redshift range of our sample ($0.05 < z < 1.02$), the luminosity in the MIR regime is roughly constant, which would result in a correlation even when using the observed-frame 22 µm luminosity. Since 22 µm luminosity could trace AGN activity and the broad component is likely to be more strongly affected by AGN outflows compared to the narrow component, the broad component of [O III] outflow tends to have better correlation with 22 µm luminosity. However, we should keep in mind that, at the same time, the above correlation may be applicable only for IR-bright DOGs, because whether or not other population follows this relation is still unknown.

### 3.3. VVD Diagram

Here, we show the [O III] velocity offset with respect to the systemic velocity and velocity dispersion diagram (hereafter VVD diagram) for our IR-bright DOG sample and the SDSS Seyfert 2 galaxy sample taken from Woo et al. (2016), who investigated outflow properties using a large sample of ~40,000 Sy2s at $z < 0.3$. Figure 5 shows the resultant VVD diagram of IR-bright DOGs and SDSS Sy2s where only objects

with $δ_{V_{[O III]}} < V_{[O III]}$ and $δ_{σ_{[O III]}} < σ_{[O III]}$ are plotted. We found that 16/20 (80%) DOGs show blueshifted [O III], which supports the biconical outflow model combined with dust extinction suggested by Crenshaw et al. (2010; see also Barrows et al. 2013); the redshifted component of outflow (receding cone) tends to be easily hidden by foreground dust. However, this fraction (0.80) is larger than that of SDSS Sy2s (0.56), with $v_{[O III]}$ measurements better than $1σ$ probably because the receding component of outflowing gas in DOGs is more preferentially hidden by large amounts of dust. Although the dust geometry between DOGs and Sy2s could be different, it is easier for DOGs to hide the receding outflow than to approach the outflows to the line of sight. We also found that the majority of the IR-bright DOGs lie above the SDSS Sy2 on the VVD diagram. These results could indicate that the IR-bright DOGs are associated with stronger ionized gas outflow (but see Section 4.1).

## 4. Discussions

### 4.1. VVD Diagram as a Function of IR Luminosity

In Section 3.3, we found the IR-bright DOG sample has a larger velocity offset and dispersion than those of the SDSS Sy2 sample on the VVD diagram. However, one caution is that more luminous AGNs could drive stronger outflow, i.e., we have to compare outflow properties with fixed AGN luminosity. Since Toba & Nagao (2016) derived the IR luminosity contributed from AGNs, $L_{IR}$ (AGN), using the SED fitting for the IR-bright DOG sample, we also estimated the $L_{IR}$ (AGN) for the SDSS Sy2 sample. In order to derive precise the IR luminosity contributed from AGNs, we compiled far-IR (FIR) data using the AKARI (Murakami et al. 2007) Far-Infrared Surveyor (FIS: Kawada et al. 2007) bright source catalog (BSC) version 2.0 (I. Yamamura et al. 2017, in preparation). We selected about 400 objects with 65, 90, 140, and 160 µm data from the SDSS Sy2 sample in Woo et al. (2016), and conducted the SED fitting with SEABASSs in the same manner as Toba et al. (2017b). Note that we confirmed that the resultant IR luminosity based on this method is consistent with those in local SDSS galaxies selected from Salim et al. (2016; see Toba et al. 2017b, in detail).

Figure 6 shows the absolute value of the velocity offset and velocity dispersion as a function of IR luminosity contributed from AGNs for IR-bright DOGs and SDSS Sy2s. We found that they are continuously distributed on those planes, and $L_{IR}$ (AGN) is well correlated both with velocity offset and dispersion. We obtained the following correlation formulae:

$$ \log|v_{[O III]}| = (0.377 \pm 0.002)\log L_{IR} (AGN) - (1.887 \pm 0.024), \quad (5) $$

$$ \log \sigma_{[O III]} = (0.163 \pm 0.001)\log L_{IR} (AGN) + (0.660 \pm 0.012). \quad (6) $$

Also, our IR-bright DOG sample is basically brighter than Sy2 galaxies, which means that the offset of the IR-bright DOG sample compared to the SDSS Sy2 sample on the VVD diagram shown in Figure 5 is likely due to the difference in IR luminosity originating from AGN activity.

It should be noted that the velocity offset or velocity dispersion itself is not always a good indicator of the strength of AGN outflows because they are affected by dust extinction
<figure><img src="image_7.png" /><figcaption>**Figure 6.** Absolute value of the velocity offset (top) and dispersion (bottom) as a function of IR luminosity contributed from AGNs for the IR-bright DOG sample (red) and SDSS Sy2 sample (blue). The yellow lines represent the best-fit linear function for both data.</figcaption></figure>

(Bae & Woo 2016). However, the influence of dust extinction can be minimized if we use the following quantity (Bae & Woo 2016; Bae et al. 2017);

$$ \sigma_0 = \sqrt{v_{[O III]}^2 + \sigma_{[O III]}^2}. \qquad (7) $$

Figure 7 shows the relation between $\sigma_0$ and AGN luminosity. They are well correlated with each other and we obtained the following correlation formula:

$$ \log \sigma_0 = (0.241 \pm 0.001) \log L_{\text{IR}} (\text{AGN}) - (0.152 \pm 0.011). \qquad (8) $$

The Spearman rank correlation coefficients ($r_s$) for $L_{IR}$ (AGN)–$v_{[O III]}$, $L_{IR}$ (AGN)–$\sigma_{[O III]}$, and $L_{IR}$ (AGN)–$\sigma_0$ are ~0.51, 0.51, and 0.54, with null hypothesis probabilities $P \sim 7.04 \times 10^{-10}$, $4.88 \times 10^{-10}$, and $6.10 \times 10^{-11}$, respectively. We confirmed that the correlation between $\sigma_0$ and $L_{IR}$ (AGN) is slightly stronger than that of others. Note that Woo et al. (2016) reported that the $\sigma_0$ of SDSS Sy2s correlates with [O III] luminosity, where they used [O III] luminosity as an indicator of AGN luminosity. We conclude that more luminous AGNs traced by $L_{IR}$ (AGN) or $L_{[O III]}$ drive strong outflows. Wagner & Bicknell (2011) conducted hydrodynamical

<figure><img src="image_8.png" /><figcaption>**Figure 7.** $\sigma_0$ as a function of IR luminosity contributed from AGNs for the IR-bright DOG sample (red) and SDSS Sy2 sample (blue). The yellow lines represent the best-fit linear function for both data.</figcaption></figure>

simulations of AGN feedback in gas-rich galaxies and concluded that outflow velocities and dispersions of energy-driven outflows are determined by the power of the AGN, and all the scatter is determined by the properties of the ISM properties, in particular the column density of clumpy gas (see also Wagner et al. 2013). Bieri et al. (2017) showed with radiation hydrodynamic simulations of AGN outflows that, for radiation-driven winds, the infrared photons provide most of the mechanical advantage of driving outflows to high velocities, and that the properties of the outflows evolved according to the optical depth of infrared photons. Our observational results support the above conclusions.

## 4.2. $\sigma_0$ as a Function of other Properties

In Section 4.1, we found that $\sigma_0$, an indicator of the strength of an AGN outflow, depends on $L_{IR}$ (AGN). Here, we investigate the dependence of $\sigma_0$ on other physical quantities: the black hole mass ($M_{BH}$), Eddington luminosity ($L_{Edd}$), bolometric luminosity ($L_{bol}$), and Eddington ratio ($\lambda_{Edd} \equiv L_{bol}/L_{Edd}$). The black hole mass is estimated from the stellar mass ($M_*$) using an empirical relation reported in Reines & Volonteri (2015): $\log(M_{BH}/M_\odot) = 1.05 \log(M_*/10^{11} M_\odot) + 7.45$ with a scatter of 0.24 dex. The stellar mass is estimated using SEABASSs by employing synthetic stellar templates from Bruzual & Charlot (2003) stellar population models assuming a Chabrier (2003) initial mass function, and reddening using a Calzetti et al. (2000) dust extinction law (see also Toba et al. 2017b). The Eddington luminosity in units of erg s⁻¹ is estimated using $L_{Edd} = 1.3 \times 10^{46} (M_{BH}/10^8 M_\odot)$ (Ferrarese & Ford 2005). The bolometric luminosity is estimated by integrating the best-fit SED template output by SEABASSs over wavelengths longward of Ly$\alpha$ in the same manner as Assef et al. (2010). Note that the mean of $L_{bol}/L_{IR}$ for IR-bright DOGs is $1.61 \pm 0.27$, which is consistent with that reported in Fan et al. (2016).

Figure 8 shows $\sigma_0$ as functions of black hole mass, Eddington luminosity, bolometric luminosity, and Eddington ratio. For any of these quantities, the values of $\sigma_0$ of IR-bright DOGs tend to be larger than those of Sy2. However, the
<figure><img src="image_9.png" /><figcaption>**Figure 8.** $\sigma_0$ as functions of (a) black hole mass, (b) Eddington luminosity, (c) bolometric luminosity, and (d) Eddington ratio. The symbols are the same as those in Figure 7.</figcaption></figure>

correlations of these quantities with $\sigma_0$ are not strong compared to the correlation of $L_{IR}$ (AGN) with $\sigma_0$. Their Spearman rank correlation coefficients are less than 0.4, which could indicate that $M_{BH}$, $L_{Edd}$, $L_{bol}$, and $\lambda_{Edd}$ are unlikely to be a primal parameters, while $L_{IR}$ (AGN) is a primal parameter tracing the outflow strength.

### 4.3. Energetics of AGN Outflows

We discuss the energetics of AGN-driven outflows in terms of the mass outflow rate, energy injection rate, and momentum flux of our IR-bright DOG sample. However, an accurate estimate of these quantities is challenging because such estimates require detailed kinematic modeling for each object. We thus adopt a simple outflow model for the entire sample to provide first-order constraints on the energetics of IR-bright DOGs.

If we assume a spherical volume of outflowing ionized gas (e.g., Harrison et al. 2014; Bae et al. 2017), the mass outflow rate ($\dot{M}_{out}$), energy injection rate ($\dot{E}_{out}$), and momentum flux ($\dot{P}_{out}$) are given by

$$ \dot{M}_{out} = \frac{3M_{gas}v_{out}}{R_{out}}, \qquad (9) $$

$$ \dot{E}_{out} = \frac{1}{2} \dot{M}_{out} v_{out}^2, \qquad (10) $$

$$ \dot{P}_{out} = \dot{M}_{out} v_{out}, \qquad (11) $$

where $M_{gas}$ is the ionized gas mass, $R_{out}$ is the outflow radius, and $v_{out}$ is the flux-weighted intrinsic outflow velocity or bulk velocity of the outflows. Assuming case-B recombination, the mass of Hβ-emitting gas can be estimated as follows (Nesvadba et al. 2011):

$$ M_{gas} = 2.82 \times 10^9 \left( \frac{L_{H\beta}}{10^{43} \text{ erg s}^{-1}} \right) \left( \frac{n_e}{100 \text{ cm}^{-3}} \right)^{-1}, \qquad (12) $$

where $L_{H\beta}$ is Hβ luminosity in units of erg s⁻¹ and $n_e$ is the electron density in units of cm⁻³. In this work, we adopt $n_e=100$ cm⁻³ as routinely assumed in similar works (e.g., Liu et al. 2013b; Brusa et al. 2015) and this value is roughly consistent with that derived from the [S II] doublet in a luminous obscured quasar at z ~ 1.5 (Perna et al. 2015). For $R_{out}$, we first estimate the size of the narrow-line region ($R_{NLR}$) using an empirical relation between $R_{NLR}$ and extinction-uncorrected

[O III] luminosity reported by Bae et al. (2017),

$$ \log R_{NLR} = (0.41 \pm 0.02) \log L_{[O III]} - (14.00 \pm 0.77). \qquad (13) $$

We then simply choose $R_{out} = 2R_{NLR}$ (Bae et al. 2017). For $v_{out}$, we also use an empirical relation between $v_{out}$ and $\sigma_0$ reported by Bae et al. (2017),

$$ v_{out} = (2.0 \pm 0.5)\sigma_0. \qquad (14) $$

We caution that the electron density depends on the object and $v_{out}$ depends on the dust extinction and inclination of each object (see Greene et al. 2011; Harrison et al. 2014; Bae et al. 2017, and references therein), which means that the derived quantities under our simple assumptions could induce large uncertainties. The resultant values estimated using Equations (9)–(14) are summarized in Table 2.

Figure 9 shows the energetics ($\dot{M}_{out}$, $\dot{E}_{out}$, and $\dot{P}_{out}$) as a function of $L_{IR}$ (AGN) for IR-bright DOGs and type 2 AGNs reported by Bae et al. (2017). Bae et al. (2017) observed type 2 AGNs at z < 0.1 with integral-field spectroscopy and investigated their energetics. We estimate their $L_{IR}$ (AGN) based on the SED fitting in the same manner as those we described in Section 4.1 and four AGNs are plotted in Figure 9. We found that our IR-bright DOG sample has systematically larger values than those of local type 2 AGNs. Since these values are clearly connected to AGN activity as shown in Figure 9 (see also Bae et al. 2017), this result can be explained by the difference in AGN luminosity as discussed in Section 4.1.

We also estimate the “momentum boost,” i.e., the ratio of the momentum flux ($\dot{P}$) and the AGN radiative momentum output ($L_{IR}$ (AGN)/c) (see Table 2). We found that the estimated initial velocity ($v_{in}$) from the nucleus for most objects, assuming that the observed outflows are energy-conserving (see Faucher-Giguère & Quataert 2012; Cicone et al. 2014), is $v_{in} = (0.01–0.2)c$. This result suggests that some IR-bright DOGs show an ultrafast outflow (UFO) with $v_{in} = (0.05–0.3)c$ (e.g., Tombesi et al. 2011; Gofford et al. 2013).

### 4.4. VVD Diagram for other Lines

We discuss the outflow properties of other emission lines. Figure 10 shows examples of the spectra fitting for [O II]λ3727 and [Ne III]λ3869 lines. Both lines are well-fitted by single or double Gaussians. Figure 11 shows the VVD diagram for [Ne III], [O II], and [O III] for our IR-bright DOG sample. We found that [Ne III] have similar velocity offsets and dispersions as [O III], while [O II] have smaller values than [O III]. It should
<table><caption>**Table 2**
Energetics of WISE-SDSS spec DOGs</caption><thead><tr><th>ID</th><th>log L<sub>Hβ</sub><br>erg s<sup>-1</sup></th><th>log M<sub>gas</sub><br>M<sub>☉</sub></th><th>log v<sub>out</sub><br>km s<sup>-1</sup></th><th>log R<sub>out</sub><br>pc</th><th>log M&#775;<sub>out</sub><br>M<sub>☉</sub> yr<sup>-1</sup></th><th>log E&#775;<sub>out</sub><br>erg s<sup>-1</sup></th><th>log P&#775;<sub>out</sub><br>dyne</th><th>ρ<sub>out</sub><br>L<sub>IR</sub> (AGN) / c</th></tr></thead><tbody><tr><td>1</td><td>41.7</td><td>8.2</td><td>2.3</td><td>3.8</td><td>1.2</td><td>41.3</td><td>34.3</td><td>3.0</td></tr><tr><td>2</td><td>41.3</td><td>7.8</td><td>3.6</td><td>4.1</td><td>1.8</td><td>44.4</td><td>36.1</td><td>3.7</td></tr><tr><td>3</td><td>41.4</td><td>7.9</td><td>2.8</td><td>3.5</td><td>1.7</td><td>42.9</td><td>35.3</td><td>0.7</td></tr><tr><td>4</td><td>41.2</td><td>7.7</td><td>2.7</td><td>3.6</td><td>1.2</td><td>42.1</td><td>34.7</td><td>0.3</td></tr><tr><td>5</td><td>41.7</td><td>8.1</td><td>3.4</td><td>3.9</td><td>2.0</td><td>44.2</td><td>36.2</td><td>5.0</td></tr><tr><td>6</td><td>41.3</td><td>7.8</td><td>3.3</td><td>3.7</td><td>1.9</td><td>44.1</td><td>36.1</td><td>3.8</td></tr><tr><td>7</td><td>41.7</td><td>8.2</td><td>3.2</td><td>3.7</td><td>2.2</td><td>44.1</td><td>36.2</td><td>16.1</td></tr><tr><td>8</td><td>42.9</td><td>9.4</td><td>2.9</td><td>4.1</td><td>2.7</td><td>44.1</td><td>36.4</td><td>14.9</td></tr><tr><td>9</td><td>42.2</td><td>8.7</td><td>2.8</td><td>3.9</td><td>2.0</td><td>43.0</td><td>35.5</td><td>2.1</td></tr><tr><td>10</td><td>42.0</td><td>8.5</td><td>3.1</td><td>4.0</td><td>2.0</td><td>43.6</td><td>35.9</td><td>1.2</td></tr><tr><td>11</td><td>41.5</td><td>7.9</td><td>2.2</td><td>3.6</td><td>1.0</td><td>40.9</td><td>34.0</td><td>0.4</td></tr><tr><td>14</td><td>41.1</td><td>7.6</td><td>3.6</td><td>3.7</td><td>1.8</td><td>44.4</td><td>36.2</td><td>8.6</td></tr><tr><td>15</td><td>42.4</td><td>8.8</td><td>3.1</td><td>3.9</td><td>2.5</td><td>44.2</td><td>36.4</td><td>8.1</td></tr><tr><td>16</td><td>40.5</td><td>6.9</td><td>3.2</td><td>3.6</td><td>1.1</td><td>43.0</td><td>35.1</td><td>0.5</td></tr><tr><td>17</td><td>40.6</td><td>7.1</td><td>3.1</td><td>3.3</td><td>1.4</td><td>43.1</td><td>35.3</td><td>1.9</td></tr><tr><td>18</td><td>42.6</td><td>9.1</td><td>3.1</td><td>4.2</td><td>2.5</td><td>44.2</td><td>36.4</td><td>5.3</td></tr><tr><td>19</td><td>42.3</td><td>8.8</td><td>3.1</td><td>4.1</td><td>2.3</td><td>44.1</td><td>36.3</td><td>6.3</td></tr><tr><td>20</td><td>42.4</td><td>8.9</td><td>3.2</td><td>4.3</td><td>2.3</td><td>44.3</td><td>36.3</td><td>1.5</td></tr><tr><td>21</td><td>41.6</td><td>8.0</td><td>3.1</td><td>3.9</td><td>1.7</td><td>43.4</td><td>35.6</td><td>4.9</td></tr><tr><td>23</td><td>41.8</td><td>8.2</td><td>2.2</td><td>3.7</td><td>1.2</td><td>41.1</td><td>34.2</td><td>1.4</td></tr><tr><td>24</td><td>42.1</td><td>8.5</td><td>3.3</td><td>4.0</td><td>2.3</td><td>44.4</td><td>36.4</td><td>8.0</td></tr><tr><td>25</td><td>41.6</td><td>8.0</td><td>2.7</td><td>3.5</td><td>1.7</td><td>42.5</td><td>35.2</td><td>0.6</td></tr><tr><td>27</td><td>42.2</td><td>8.6</td><td>2.8</td><td>4.0</td><td>2.0</td><td>43.1</td><td>35.6</td><td>3.8</td></tr><tr><td>28</td><td>41.0</td><td>7.5</td><td>3.2</td><td>3.4</td><td>1.8</td><td>43.8</td><td>35.8</td><td>9.1</td></tr><tr><td>29</td><td>42.4</td><td>8.9</td><td>3.0</td><td>4.1</td><td>2.2</td><td>43.7</td><td>36.0</td><td>2.4</td></tr><tr><td>30</td><td>42.2</td><td>8.7</td><td>3.3</td><td>4.1</td><td>2.4</td><td>44.6</td><td>36.5</td><td>8.6</td></tr><tr><td>31</td><td>42.4</td><td>8.8</td><td>3.1</td><td>4.2</td><td>2.2</td><td>43.8</td><td>36.0</td><td>5.5</td></tr><tr><td>32</td><td>41.3</td><td>7.7</td><td>3.4</td><td>3.8</td><td>1.8</td><td>44.2</td><td>36.0</td><td>5.4</td></tr><tr><td>33</td><td>42.0</td><td>8.5</td><td>3.3</td><td>3.7</td><td>2.5</td><td>44.7</td><td>36.7</td><td>15.3</td></tr><tr><td>34</td><td>42.0</td><td>8.4</td><td>2.7</td><td>3.9</td><td>1.8</td><td>42.7</td><td>35.3</td><td>2.7</td></tr><tr><td>35</td><td>40.8</td><td>7.3</td><td>3.4</td><td>3.6</td><td>1.6</td><td>43.8</td><td>35.8</td><td>1.7</td></tr><tr><td>36</td><td>40.6</td><td>7.0</td><td>2.5</td><td>3.2</td><td>0.8</td><td>41.2</td><td>34.0</td><td>2.5</td></tr></tbody></table>

(This table is available in its entirety in machine-readable form.)

be noted that [O II] is not well-fitted with double-Gaussian components in many cases due to the blending of the λ3726, 3729 Å doublet. If we use only a single Gaussian, alternatively, it yields a much larger velocity dispersion ($\sigma_{[O II]}$). We should keep in mind the above uncertainties before interpreting the discrepancy between [Ne III] and [O III], and [O II] in Figure 11.

The difference in $v_{line}$ and $\sigma_{line}$ for each line gives us a hint toward understanding the physicochemical properties of outflowing gas. The ionization potentials of [O II]λ3727, [O III] λ5007, and [Ne III]λ3869 are 13.61, 35.15, and 41.07 eV, respectively. The critical electron densities for collisional de-excitation of [O II]λ3727, [O III]λ5007, and [Ne III]λ3869 are $3.4 \times 10^3$, $6.8 \times 10^5$, and $9.5 \times 10^6$ cm$^{-3}$, respectively. The fraction of objects with $|v_{line}| > 50$ km s$^{-1}$ and $\sigma_{line} > 500$ km s$^{-1}$ for [O II], [O III], and [Ne III] are 0.15, 0.55, and 0.55, respectively. This means that more dense and ionized gas tends to show larger velocity offsets and dispersions. Since it is naturally expected that electron densities will increase toward the nuclear region and gas located there is highly ionized by AGN radiation, [O III] and [Ne III] are ejected with high velocity, while [O II] are less affected by AGN radiation, a picture that is consistent with those suggested by Barrows et al. (2013; see also Komossa et al. 2008).

### 4.5. MEx Diagram

Finally, we discuss the Mass-Excitation (MEx) diagram (Juneau et al. 2011, 2014) that enables us to perform AGN diagnostics for objects with even $z > 0.4$. Since SEBASS outputs stellar mass ($M_*$) and we measured [O III] and Hβ line flux, we here investigate where IR-bright DOGs lie in the MEx diagram. Note the our estimate based on this method have an uncertainty because we did not take into account the influence from the scattered light by AGNs (see also Hamann et al. 2017; Toba et al. 2017b). We also note that we excluded DOGs classified as type 1 AGN (see Section 2) in this analysis because MEx diagram is optimized for galaxies/AGNs with narrow-line emission.

Figure 12 shows the MEx diagnostic diagram for the IR-bright DOGs, suggesting that IR-bright DOGs can be classified as AGNs, which is consistent with our inspection based on the SED and IR flux dependence of the AGN fraction for DOGs (see Toba et al. 2015; Toba & Nagao 2016). At the same time, there are no significant dependences of $\sigma_0$ on the MEx diagram. This could indicate that [O III]/Hβ is unlikely to be a good tracer of outflow strength partly because [O III]/Hβ also depends on other quantities such as metallicity. On the other hand, after removing data with large error, i.e., when focusing
<figure><img src="image_10.png" /><figcaption>**Figure 9.** Mass outflow rate $\dot{M}_{\text{out}}$ (top), the energy injection rate $\dot{E}_{\text{out}}$ (middle), and momentum flux $\dot{P}_{\text{out}}$ (bottom) as a function of the IR luminosity contributed from the AGNs ($L_{\text{IR}}$ (AGN)) of IR-bright DOGs (red circle) and type 2 AGNs at $z < 0.1$ (blue circle) presented by Bae et al. (2017).</figcaption></figure>

only on data with $SN > 3$ both for [O III]/H$\beta$ and stellar mass, stellar mass is likely to be correlated with $\sigma_0$. Since stellar mass correlates with stellar dispersion that also correlates with $\sigma_0$ (Woo et al. 2016), this tendency is naturally expected.

**5. Summary**

In this work, we investigated the outflowing ionized gas properties of IR-bright DOGs by performing detailed spectral analyses for their SDSS spectra. Among 67 IR-bright DOGs selected with the WISE and SDSS spectroscopic catalogs, 36

<figure><img src="image_11.png" /><figcaption>**Figure 10.** Example of spectral fitting for [O II] and [Ne III] lines. The gray line shows the starlight-subtracted spectra. The red line shows the best fitting with a single or double Gaussian for each emission line. The green and orange lines show narrow and broad emission line components, respectively. The vertical blue dashed lines correspond to the rest-frame wavelength for the [O II] and [Ne III] lines.</figcaption></figure>

objects show a [O III]λ5007 line and we estimated its velocity offset with respect to the systemic velocity and velocity dispersion. In particular, we conducted spectral fitting with single- or double-Gaussian components depending on whether or not they have broad wings. The main results are as follows.

1. Among a sample of 32 IR-bright DOGs that are classified as type 2 AGNs, 24 (~75%) objects have large [O III] velocity dispersion with 300 km s$^{-1}$. This fraction is larger than that of other AGN populations, indicating that IR-bright DOGs show stronger ionized gas outflow.

2. The [O III] luminosity is correlated with the observed-frame luminosity at 22 µm. In particular, the 22 µm luminosity at the observed frame may be a good indicator
<figure><img src="image_12.png" /><figcaption>**Figure 11.** VVD diagram for [O II] (green), [Ne III] (blue), [O III] (red) lines.</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>**Figure 12.** MEx diagnostic diagram for the IR-bright DOGs. The color scheme indicates $\sigma_0 = \sqrt{v_{[O III]}^2 + \sigma_{[O III]}^2}$. The two solid lines curves are empirically determined to distinguish AGN, SF, and composite types of galaxies. The data with red squares have $\text{SN} > 3$ both for [O III]/H$\beta$ and stellar mass.</figcaption></figure>

of the luminosity of the broad component of the [O III] line for IR-bright DOGs.

3. The infrared luminosity contributed from AGNs for the IR-bright DOG + SDSS Seyfert 2 sample is well correlated with velocity offset ($v_{[O III]}$), dispersion ($\sigma_{[O III]}$), and particularly $\sigma_0 = \sqrt{v_{[O III]}^2 + \sigma_{[O III]}^2}$. This indicates that objects with higher AGN luminosities tend to launch stronger outflowing gas.

4. The data of the IR-bright DOG sample have larger velocity offsets and dispersions than those of the SDSS Seyfert 2 sample, which can be interpreted as the difference in their AGN luminosities.

5. The energetics ($\dot{M}_{\text{out}}$, $\dot{E}_{\text{out}}$, and $\dot{P}_{\text{out}}$) of IR-bright DOGs correlate with AGN luminosity. Some IR-bright DOGs

have initial outflow velocities ($v_{\text{in}}$) > 0.1c, which means that some IR-bright DOGs show an ultrafast outflow.

6. The velocity offsets and dispersions of [O III] and [Ne III]$\lambda$3869 are larger than those of [O II]$\lambda$3727, suggesting that denser and more ionized gases are effectively affected by AGN radiation.

The authors gratefully acknowledge the anonymous referee for a careful reading of the manuscript and very helpful comments. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. The SDSS-III web site is http://www.sdss3.org/. SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofísica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This research is based on observations with AKARI, a JAXA project with the participation of ESA. This research has made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Y. Toba and W.H. Wang acknowledge the support from the Ministry of Science and Technology of Taiwan (MOST 105-2112-M-001-029-MY3). T. Nagao is financially supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (16H01101 and 16H03958). J.H. Woo acknowledges the support by the National Research Foundation of Korea grant funded by the Korea government (No. 2016R1A2B3011457).

# Appendix

## The SDSS Spectra of IR-bright DOGs with a Powerful [O III] Outflow

Here, we present the SDSS spectra for all 36 IR-bright DOGs (Figures 13–16).
<figure><img src="image_14.png" /><figcaption>**Figure 13.** SDSS spectra for the IR-bright DOG sample with ID = 1–10. The yellow lines show our best fits to the continuum. The right panel for each object shows the starlight-subtracted spectra with a gray solid line. The red line shows the best-fitting with single or double Gaussians for each emission line. The green and orange lines show narrow and broad emission line components for each double Gaussian, respectively. The vertical blue dashed lines correspond to the rest-frame wavelengths for [O II], [Ne III], Hβ, and [O III] lines.</figcaption></figure>
<figure><img src="image_15.png" /><figcaption>Figure 14. Same as Figure 13, but for DOGs with ID = 11–20.</figcaption></figure>
<figure><img src="image_16.png" /><figcaption>Figure 15. Same as Figure 13, but for DOGs with ID = 21–30.</figcaption></figure>
<figure><img src="image_17.png" /><figcaption>Figure 16. Same as Figure 13, but for DOGs with ID = 31–36.</figcaption></figure>

ORCID iDs

Yoshiki Toba https://orcid.org/0000-0002-3531-7863

Hyun-Jin Bae https://orcid.org/0000-0001-5134-5517

Jong-Hak Woo https://orcid.org/0000-0002-8055-5465

Wei-Hao Wang https://orcid.org/0000-0003-2588-1265

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