Spectroscopic study of the broad component of [O III]λ5007 profile in type 1 AGNs

Abstract

The spectra of type 1 active galactic nuclei (AGNs) often exhibit broad component in [O III]$λ$5007, which are typically blue-shifted and associated with strong outflows. We systematically analyze the [O III] emission-line properties of type 1 AGNs with broad components to investigate how these kinematic features relate to the physical properties of the central engine. From a parent sample of 11,557 QSOs at $z<0.3$ in Data Release 16 of the Sloan Digital Sky Survey, we select 2,290 type 1 AGNs exhibiting broad components in [O III]. Previous studies have reported a strong correlation between the blue emission, defined as the full extent of the broad component on the blue side, and black hole mass when the latter is estimated from the $M_{\rm BH}$--$σ_{\ast}$ relation using the line width $σ$ of the [O III] core component as a surrogate for $σ_{\ast}$. By the same way, the black hole mass also shows a strong correlation with the blue emission parameter in our sample. However, this correlation becomes negligible when virial black hole masses are adopted. Besides, the velocity shifts between the broad and core components of [O III] show a weak correlation with the Eddington ratio. This is consistent with the expectation that higher accretion rates enhance radiative pressure, thereby driving faster or more prominent outflows. In future work, we will compare [O III] broad component properties between typical type 1 AGNs and those with double-peaked [O III] to probe differences in narrow-line region kinematics and the impact of outflows or dual AGNs.

Figures (12)

• Figure 1: Two examples of spectra and corresponding best fitting results in our sample. In each panel, the information of Plate-Mjd-Fiberid is shown in the title, the solid red line ($f_{best}$) shows the best fitting results with $\chi^2/\rm dof$ (if present) shown in the title. In the left panels, the solid black lines show observed spectra. In the top-left panel, the solid blue line shows starlight, the dashed green line represents the AGN continuum emission, and the solid dark green line represents the line spectrum calculated by the SDSS spectrum minus the best fitting results. In the top of middle and right panels, the solid black lines ($f_{obs}$) show the line spectra after subtracting starlight (if present), the dashed red lines represent continuum emissions, the solid green lines represent broad H$\beta$ and H$\alpha$ emission lines, the dashed green lines represent narrow H$\beta$ and H$\alpha$ emission lines, the dashed purple lines represent core components of [O iii], [O i], [N ii] and [S ii] doublets, the solid blue lines represent the broad component of [O iii]. In the bottom of middle and right panels, the solid blue lines represent the normalized residuals calculated by $(f_{obs}-f_{best})/err$, where $err$ is the uncertainty of SDSS spectrum, the horizontal solid and dashed green lines show residuals=0, ±1, respectively.
• Figure 2: An example of type 1 AGN with [O iii] broad component determined by F-test. In the top panels, the solid black lines show the line spectra after subtracting starlight with Plate-Mjd-Fiberid shown in the title, the solid red lines represent the best fitting results with $\chi_A^2/dof_A$ ($\chi_B^2/dof_B$) for [O iii] doublet with (without) broad component in the title, the dashed purple lines show the core component of [O iii] doublet, and the solid blue lines show the broad component, the dashed red lines represent continuum emission. In the bottom panels, the solid blue lines represent the normalized residuals, the horizontal solid and dashed green lines show residuals=0, ±1, respectively.
• Figure 3: The redshift distribution (left panel) and BPT diagram (right panel) for the 2,290 objects in our sample. In the right panel, the star-forming, composite, and AGN regions are labeled. The solid purple line represents the dividing line defined by Ka03, below which objects are classified as star-forming galaxies. The solid green line shows the dividing line from Ke01; objects above this line are classified as AGNs, while those between the two lines are considered composite galaxies.
• Figure 4: The line width $\sigma$ distributions of [O iii] broad (left panel) and [O iii] core (middle panel), and the line flux ratio distribution (right panel).
• Figure 5: The distribution of black hole mass log($\rm M_{\rm BH}$/$\rm M_{\odot}$) for the 2,290 type 1 AGNs in our sample (left panel), and the relation of black hole mass log($\rm M_{\rm BH}$/$\rm M_{\odot}$) for 367 objects estimated in our sample and collected from the SDSS DR7 QSO catalog presented by Sh11 (right panel). The dashed black line indicates the 1:1 relation. The pink shadow shows 5$\sigma$ confidence bands derived from F-test.