We measure the optical variability in ∼16 500 low-redshift (z ∼ 0.1) galaxies to map the relations between active galactic nucleus (AGN) activity and galaxy stellar mass, specific star formation rate, half-light radius, and bulge-to-total ratio. To do this, we use a reduced χ2 variability measure on >10 epoch light curves from the Zwicky Transient Facility and combine with spectroscopic data and derive galaxy parameters from the Sloan Digital Sky Survey. We find that below the stellar mass of 1011 M⊙, galaxies classed as star-forming via the Baldwin–Phillips–Terlevich diagram have higher mean variabilities than AGN or composite galaxies. Revealingly, the highest mean variabilities occur in star-forming galaxies in a narrow range of specific star formation rate: −11 < log(sSFR/yr−1) < −10. In very actively star-forming galaxies [log(sSFR/yr−1) > −10], the reduced variability implies a lack of instantaneous correlation with star formation rate. Our results may indicate that a high level of variability, and thus black hole growth, acts as a precursor for reduced star formation, bulge growth, and revealed AGN-like emission lines. These results add to the mounting evidence that optical variability can act as a viable tracer for low-mass AGNs and that such AGNs can strongly affect their host galaxy.
Local galaxies from the Sloan Digital Sky Survey (SDSS) are used to provide additional support for an evolutionary pathway in which active galactic nucleus activity is associated with star formation quenching. Composite, Seyfert 2, and LINER galaxies account for ∼60 per cent of all star formation in massive galaxies (M⋆ > 1010.5 M⊙). Inclusion of these galaxies results in a ‘turnover’ in the star formation rate and stellar mass (SFR−M⋆) relation for massive galaxies. Our analysis shows that bulge growth has already occurred in the most massive galaxies (M⋆ > 1010.5 M⊙), and bulges continue to grow as galaxies quench and redden, (g − r) = 0.5 → 0.75. Significant bulge growth is also occurring in low mass starburst galaxies (M⋆ < 1010.5 M⊙) at 0.5 dex above the ‘main sequence’ (MS), where we find an increase in B/T from 0.1 → 0.3 and bluer colours, (g − r) < 0.25 compared to low-mass galaxies on the MS.
more » « less- NSF-PAR ID:
- 10485818
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society: Letters
- Volume:
- 482
- Issue:
- 1
- ISSN:
- 1745-3925
- Format(s):
- Medium: X Size: p. L129-L133
- Size(s):
- ["p. L129-L133"]
- Sponsoring Org:
- National Science Foundation
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