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We present an analysis of the long-term optical variability for $\sim50,000$nearby (z<0.055) galaxies from the NASA-Sloan Atlas, $35,000$ of which arelow-mass ($M_{\ast}<10^{10}~M_{\odot}$). We use difference imaging of PalomarTransient Factory (PTF) R-band observations to construct light curves withtypical baselines of several years. We then search for subtle variations in thenuclear light output. We determine whether detected variability is AGN-like byassessing the fit quality to a damped random walk model. We identify 424variability-selected AGN, including 244 with stellar masses between $10^{7}$and $10^{10}~M_{\odot}$. 75% of low-mass galaxies with AGN-like variabilityhave narrow emission lines dominated by star formation. After controlling fornucleus magnitude, the fraction of variable AGN is constant down to$M_{\ast}=10^{9}~M_{\odot}$, suggesting no drastic decline in the BH occupationfraction down to this stellar mass regime. Combining our NASA-Sloan Atlassample with samples of nearby galaxies with broad H$\alpha$ emission, we findno dependence of variability properties with black hole mass. However, wecaution that the variable AGN fraction is strongly dependent on baseline. Forbaselines less than two years, the variable fraction for the full sample is0.25%, compared to 1.0% for baselines longer than two years. Finally, comparingStripe 82 light curves (Baldassare et al. 2018) to PTF light curves, we findpopulations of changing-look AGN: 8 galaxies that are variable in Stripe 82,but quiescent in PTF, and 15 galaxies where the reverse is true. Our PTF workdemonstrates the promise of long-term optical variability searches in low-massgalaxies for finding AGNs missed by other selection techniques.

A search for optical AGN variability in 35,000 low-mass galaxies with the Palomar Transient Factory