Active Galactic Nuclei and STaR fOrmation in Nearby Galaxies AGNSTRONG. III. A Study on Ionized and Warm Molecular Gas Outflows of 6 Type-2 AGNs

TL;DR

This paper addresses how AGN-driven feedback manifests in multiple gas phases by comparing ionized and warm molecular outflows in six nearby type-2 AGNs, using spatially resolved NIR (H$_2$ 1-0 S(1)) and optical ([O III], Pa$\alpha$) spectroscopy. The authors refine host redshifts, decompose emission lines into multiple components with Bayesian and Gaussian fits, and derive outflow properties under a biconical framework, finding a significant warm-molecular outflow only in ID 2 while ionized outflows are present in several objects. A positive correlation between AGN strength and outflow kinematics emerges for the ionized gas, and NLR sizes are generally consistent with luminosity when compared to literature, though warm molecular detections are sparse due to observational limits. The study highlights that deeper, multi-phase observations, including cold molecular gas tracers, are essential to obtain a complete picture of AGN feedback and its impact on host galaxies. The results provide constraints on the energetics and spatial scales of feedback, informing models of SMBH-galaxy co-evolution. $L_{ m bol} = 3500\times L_{\rm [O III]}$ is used for bolometric estimates and $V' = 2\sqrt{V^2+\sigma^2}$ for outflow speeds.

Abstract

Active galactic nucleus (AGN)-driven gas outflows are one of the best tracers of AGN feedback in action, as these powerful outflows expel/heat or compress the surrounding interstellar medium (ISM), thus quenching or enhancing star-forming activity in their hosts. Studying the kinematics of outflows in different gas phases is crucial for comprehending how AGNs impact the ISM within their host galaxies. However, the differences in the physical natures of ionized and warm molecular gas outflows remain largely unexplored. To obtain a complete picture of AGN outflows and their feedback effects, we present a study of both ionized and warm molecular gas outflows in six type-2 AGNs ($z<0.1$) that exhibit strong ionized outflows in previous optical observations. Utilizing the Triple Spectrograph and Double Spectrograph instruments on the Palomar 200-inch Hale Telescope, we conduct spatially resolved measurements in the slit direction of strong emission lines from both ionized and warm molecular gas, such as $\rm [O\ III]$, $\rm Paα$, $\rm H_{2}$ 1-0 S(1), etc., allowing for a direct comparison of their outflow properties. One out of six AGNs shows significant ionized and warm molecular outflows in near-infrared bands, exhibiting the most powerful kinematics and highest luminosity. A positive correlation between the kinematics and AGN luminosity is shown, suggesting that more luminous AGNs, which reflect higher levels of AGN activity, tend to have a greater impact on the gases, probably driving the outflows.

Figures (14)

• Figure 1: [O III] diagram of the luminosity-limited sample of AGNs with dust-corrected [O III] luminosity $L_{\rm [O\ III];cor} > 10^{42}\rm\ erg\ s^{-1}$ and $z <0.1$ from woo_prevalence_2016. We highlight our sample of six type-2 AGNs using the green squares, while the solid box serves as a reference for high velocity ($|V|>250 \rm \ km\ s^{-1}$) or large velocity dispersion ($\sigma>400 \rm \ km\ s^{-1}$). Figure adapted from karouzos_unraveling_2016.
• Figure 2: SDSS gri composite images of the targets. The blue solid lines show the direction of the slits of TPSP. The scale bar is displayed at the upper left corner of each panel, representing the scale of $\rm 15\hbox{$^{\prime\prime}$}$, and the corresponding spatial size is marked in brackets.
• Figure 3: Examples of 2D spectral images and integrated emission line profiles for the TPSP observations. The images of 2D spectra close to the emission lines are shown in zscale following the IRAF zscale algorithm (top). The x-axis is the wavelength, and the y-axis is the spatial pixels on the slit. The observed integrated emission lines (black) are fitted with Gaussian profiles (middle). The red curve shows the best-fit model, while the blue, cyan, and yellow curves represent the individual Gaussian components in the double- and triple-Gaussian fits. The black dashed line represents the reference wavelength of each line, while the red dashed line represents the centroid wavelength of the total line profile. The residuals are shown at the bottom. The wavelength ranges used to estimate the outflow size are shaded.
• Figure 4: Examples of 2D spectral images and integrated emission line profiles of optical [O III] emission lines in the DBSP observations. On the top are the images of 2D spectra. The observed integrated emission lines (black) are fitted with Gaussian profiles. The red curve shows the best-fit model, while the blue and brown curves represent the individual Gaussian components.
• Figure 5: Distributions of flux (yellow dots), velocity (blue), and velocity dispersion (red) of emission lines along the slits. The NIR data are binned with a size of 3 pixels, and the kinematics of optical $\rm [O\ III]$ lines is shown in light blue and magenta without binning.