Different dependence of narrow H$α$ line luminosity on optical continuum luminosity between starforming galaxies and Type-2 AGN: globally negative AGN feedback in local Type-2 AGN?

XueGuang Zhang

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arXiv · 2402.05365

Different dependence of narrow H$α$ line luminosity on optical continuum luminosity between starforming galaxies and Type-2 AGN: globally negative AGN feedback in local Type-2 AGN?

XueGuang Zhang

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Abstract

In this manuscript, clues are provided to support globally negative AGN feedback on star formation in the host galaxies of the local low-redshift SDSS Type-2 AGN, based on the different dependence of narrow H$α$ line luminosity $L_{Hα}$ on optical continuum luminosity $λL_{cont}$ between the starforming galaxies and the Type-2 AGN. Through the measured $L_{Hα}$ and $λL_{cont}$ in SDSS starforming galaxies, there is a strong linear correlation between $λL_{cont}$ and $L_{Hα}$, accepted as a standard correlation without effects of AGN activity. Meanwhile, considering apparent contributions of AGN activity to narrow H$α$ line emissions in the Type-2 AGN, the correlation between $λL_{cont}$ and $L_{Hα}$ in the SDSS Type-2 AGN leads to statistically lower $L_{Hα}$ in the Type-2 AGN than in the starforming galaxies, with significance level higher than 5$σ$, even after considering necessary effects (including effects of host galaxy properties), leading to accepted conclusion on the globally negative AGN feedback in the local Type-2 AGN. Meanwhile, properties of Dn(4000) and H$δ_A$ can provide indirect clues to support the globally negative AGN feedback in the local Type-2 AGN, due to older stellar ages in the Type-2 AGN. Moreover, it is interesting to expect more than 50\% narrow H$α$ emissions globally suppressed in the host galaxies of the Type-2 AGN relative to the starforming galaxies. The results not only support globally negative AGN feedback in the local Type-2 AGN, but also show further clues on the quantification of suppressions of star formation by the globally negative AGN feedback.

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XueGuang Zhang. 2024-02-08. Different dependence of narrow H$α$ line luminosity on optical continuum luminosity between starforming galaxies and Type-2 AGN: globally negative AGN feedback in local Type-2 AGN?. https://arxiv.org/abs/2402.05365

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