Role of feedback in AGN-host coevolution: A study from partially obscured active galactic nuclei

Abstract

Partially obscured AGNs within a redshift range z = 0.011 ∼ 0.256 are used to re-study the role of feedback in the AGN-host coevolution issue in terms of their [OIII]λ5007 emission line profile. The spectra of these objects enable us to determine the AGN's accretion properties directly from their broad Hα emission. This is essential for getting rid of the "circular reasoning" in our previous study of narrow emission-line galaxies, in which the [OIII] emission line was used not only as a proxy of AGN's bolometric luminosity, but also as a diagnostic of outflow. In addition, the measurement of D n (4000) index is improved by removing an underlying AGN's continuum according to the corresponding broad Hα emission. With these improvements, we confirm and reinforce the correlation between L/L Edd and stellar population age. More important is that this correlation is found to be related to both [OIII] line blue asymmetry and bulk blueshift velocity, which suggests a linkage between SMBH growth and host star formation through the feedback process. The current sample of partially obscured AGNs shows that the composite galaxies have younger host stellar population, higher Eddington ratio, less significant [OIII] blue wing and smaller bulk [OIII] line shift than do the Seyfert galaxies .

A Direct Linkage Between Agn Outflows in the Narrow-Line Regions and the X-Ray Emission From the Accretion Disks

“…The line strength from BLR is determined by the vertical structure of the accretion disk, governed by L/L Edd , in a way in which a large L/L Edd results in a large X-ray-heated volume that generates strong Fe II complex emission (e.g., BG92). In fact, a correlation between [O III] line profile asymmetry and L/L Edd has been frequently reported in previous studies (e.g., Wang et al 2011;Wang 2015;Zhang et al 2011;Boroson 2005;Bian et al 2005). A deficit of extended emission-line region in the AGNs with high L/L Edd is revealed by Matsuoka (2012).…”

“…On the other hand, by analyzing the optical spectra of narrow emission-line galaxies taken from SDSS survey, Wang et al (2011) proposed a trend in which AGNs with stronger blue asymmetries tend to be associated with younger stellar populations. This result is recently confirmed and reinforced in Wang (2015) by focusing on partially obscured AGNs. Combining these results implies that the SMBH growth through gas accretion and host galaxy building is potentially linked by the outflow launched from the accretion disk.…”

“…On the one hand, Wang et al (2013) identified a correlation between AGN's hard X-ray spectral index and host galaxy stellar population age in X-ray selected SDSS type-II AGNs: harder the X-ray spectrum, older the host stellar population will be. The important role of L/L Edd in the coevolution issue has been frequently revealed in previous studies by studying the relationship between L/L Edd and host stellar population (e.g., Goulding et al 2010;Kewley et al 2006;Wang et al 2006;Wang & Wei 2008, 2010Kauffmann et al 2007;Wild et al 2007;Wang 2015). On the other hand, by analyzing the optical spectra of narrow emission-line galaxies taken from SDSS survey, Wang et al (2011) proposed a trend in which AGNs with stronger blue asymmetries tend to be associated with younger stellar populations.…”

“…Both semianalytic models and numerical simulations indicate that this feedback process is useful not only for reproducing the observed M BH −σ * relation, luminosity functions of quasars and normal galaxies (e.g., Fabian 1999;Di Matteo et al 2005, 2007Hopkins et al 2007Hopkins et al , 2008Menci et al 2008;Silk & Rees 1998;Haehnelt et al 1998;Khalatyan et al 2008;Granato et al 2004;Somerville et al 2008;Kauffmann & Haehnelt 2000;Springel et al 2005;Croton et al 2006), but also for solving the "over cooling" problem in the Λ cold dark matter (ΛCDM) galaxy formation model in which the cooling predicted in galaxy groups and clusters are stronger than the observed one (e.g., Ciotti & Ostriker 2007;Somerville et al 2008;Hirschmann et al 2013). By using the SDSS spectroscopic survey, Wang et al (2011) and Wang (2015) recently suggest a co-evolution between the feedback and host galaxy based on a revealed fact that an AGN with stronger blue asymmetry of the [O III]λ5007 emission line tends to be associated with a younger stellar population.…”

“…Different results are, however, obtained by various authors. On the one hand, there is ample evidence that the [O III] line blue asymmetry and bulk velocity blueshift are strongly correlated with Eddington ratio (L/L Edd , where L Edd = 1.26× 10 38 (M BH /M ⊙ ) erg s −1 is the Eddington luminosity) of the central AGNs: higher the L/L Edd , stronger the blue asymmetry and larger the bulk velocity blueshift will be (e.g., Zhang et al 2011;Wang et al 2011;Wang 2015;Boroson 2005;Bian et al 2005). In addition, the extreme "blue outliers" usually defined as the objects with [O III] bulk blueshift larger than 250km s −1 (e.g., Zamanov et al 2002;Zhou et al 2006;Komossa et al 2008) are found to exclusively occur in the AGNs associated with high L/L Edd .…”