Narrow-line region gas kinematics of 24 264 optically selected AGN: the radio connection

• Published in: Monthly notices of the Royal Astronomical Society Vol. 433; no. 1; pp. 622 - 638
• Main Authors: Mullaney, J. R., Alexander, D. M., Fine, S., Goulding, A. D., Harrison, C. M., Hickox, R. C
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 21-07-2013
• Subjects: Astrophysics; Kinematics; Luminosity; Star & galaxy formation; quasars: emission lines; catalogues; galaxies: active; ISM: kinematics and dynamics; radio continuum: galaxies
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stt751

Using a sample of 24 264 optically selected active galactic nuclei (AGNs) from the SDSS DR7 data base, we characterize how the profile of the [O iii] λ5007 emission line relates to bolometric luminosity (L
AGN), Eddington ratio, radio loudness, radio luminosity (L
1.4 GHz) and optical class (i.e. broad/narrow-line Seyfert 1, type 2) to determine what drives the kinematics of this kpc-scale line emitting gas. First, we use spectral stacking to characterize how the average [O iii] λ5007 profile changes as a function of these five variables. After accounting for the known correlation between L
AGN and L
1.4 GHz, we report that L
1.4 GHz has the strongest influence on the [O iii] λ5007 profile, with AGNs of moderate radio luminosity (L
1.4 GHz = 1023-1025 W Hz−1) having the broadest [O iii] λ5007 profiles. Conversely, we find only a modest change in the [O iii] λ5007 profile with increasing radio loudness and find no significant difference between the [O iii] λ5007 profiles of broad- and narrow-line Seyfert 1s. When binned according to Eddington ratio, only the AGNs in our highest bin (i.e. >0.3) show any signs of having broadened [O iii] λ5007 profiles, although the small numbers of such extreme AGNs in our sample mean we cannot rule out that other processes (e.g. radio jets) are responsible for this broadening. The [O iii] λ5007 profiles of type 1 and type 2 AGNs show the same trends in terms of line width, but type 1 AGNs display a much stronger 'blue wing', which we interpret as evidence of outflowing ionized gas. We perform multicomponent fitting to the Hβ, [O iii] λλ4959, 5007, [N ii] λλ6548, 6584 and Hα lines for all the AGNs in our sample to calculate the proportions of AGNs with broad [O iii] λ5007 profiles. The individual fits confirm the results from our stacked spectra; AGNs with L
1.4 GHz > 1023 W Hz−1 are roughly five times more likely to have extremely broad [O iii] λ5007 lines (full width at half-maximum, FWHMAvg > 1000 km s−1) compared to lower L
1.4 GHz AGNs, and the width of the [O iii] λ5007 line peaks in moderate-radio-luminosity AGNs (L
1.4 GHz ∼ 1024 W Hz−1). Our results are consistent with the most disturbed gas kinematics being induced by compact radio cores (rather than powerful radio jets), although broadened [O iii] λ5007 lines are also present, but much rarer, in low-L
1.4 GHz systems. Our catalogue of multicomponent fits is freely available as an online resource for statistical studies of the kinematics and luminosities of the narrow- and broad-line AGN regions and the identification of potential targets for follow-up observations at http://sites.google.com/site/sdssalpaka.