Star Formation Rates in [Ne V] 3426 Å Selected Active Galactic Nuclei: Evidence for a Decrease along the Main Sequence?

Abstract

Studying the behavior along the galaxy main sequence is key in furthering our understanding of the possible connection between active galactic nucleus (AGN) activity and star formation. We select a sample of 1215 AGN from the catalog of Sloan Digital Sky Survey galaxy properties from the Portsmouth group by detection of the high-ionization [Ne v ] 3426 Å emission line. Our sample extends from 10 40 to 10 42.5 erg s −1 in [Ne v ] luminosity in a redshift range z = 0.17 to 0.57. We compare the specific star formation rates (sSFRs; SFR scaled by galaxy mass) obtained from the corrected [O ii ] and H α luminosities, and the spectral energy distribution (SED)–determined values from Portsmouth. We find that the emission-line-based sSFR values are unreliable for the [Ne v ] sample due to the AGN contribution, and proceed with the SED sSFRs for our study of the main sequence. We find evidence for a decrease in sSFR along the main sequence in the [Ne v ] sample, which is consistent with results from the hard X-ray Burst Alert Telescope AGN sample, which extends to lower redshifts than our [Ne v ] sample. Although we do not find evidence that the concurrent AGN activity is suppressing star formation, our results are consistent with a lower gas fraction in the host galaxies of the AGN as compared to that of the star-forming galaxies. If the evacuation of gas, and therefore suppression of star formation, is due to AGN activity, it must have occurred in a previous epoch.