From Interstellar Clouds to Star-Forming Galaxies: Universal Processes?, E15, 1 of 2 Proceedings IAU Symposium No. 315, 2016 P. Jablonka, Ph. Andr´ e, & F. van der Tak, eds. c  International Astronomical Union 2016 doi:10.1017/S1743921316007766 Detecting H II Regions in “Pure” Starburst Galaxies with SDSS Data Anthony Crider 1,2 , Chris Richardson 1 , and Ben Kaiser 1 1 Department of Physics, Elon University, 2625 Campus Box, Elon NC 27244 2 Email: acrider@elon.edu Abstract. The relationship between active galactic nuclei (AGN) and starburst galaxies is poorly understood, partially due to galaxies exhibiting both AGN and starburst activity. To better understand the connection, we analyze a sample of “pure” AGN or starburst at redshift z =0.1 selected using mean field independent component analysis (MFICA). Simulations of starburst galaxy emission suggests that the locally optimally-emitting cloud (LOC) model can fit observations and improve our ability to distinguish the impact of differences in metallicity, ionization parameter, and ionizing flux. To test for the existence of such clouds in our galaxy sample, we examine the Sloan Digital Sky Survey (SDSS) images of our pure galaxies. At this distance, even large star-forming H II regions (e.g. 30 Doradus) only fill part of an SDSS pixel. However, we compare the morphology of the distant galaxies to more nearby ones (i.e. NGC 4713, NGC 4038/4039) to estimate the number of larger H II regions. While the clumpiness parameter of a galaxy in theory might indicate the existence of these regions, a straightforward calculation of the clumpiness parameter is ineffective for galaxies at z =0.1. Typically, one subtracts a smoothed version of a galaxy image from the same image. We instead test a different approach to establish a smooth image and thus better identify the clumps. We subtract the smoother infrared z-band from the sharper ultraviolet u-band. We test this procedure using NGC 4713, a nearby starburst galaxy, artificially degraded to match images of our “pure” starburst galaxies. Keywords. galaxies: starburst, techniques: image processing, H II regions 1. H II Regions and Clumpiness of “Pure” Starburst Galaxies The Baldwin, Phillips, & Terlevich (BPT; 1981) diagram has been used for decades to de- lineate emission-line galaxies into those dominated by active galactic nuclei (AGN) versus star- bursts. Using mean field independent component analysis (MFICA), Allen et al.(2013) extracted “pure” AGN and “pure” starburst galaxies. Richardson et al.(2015) has shown that the emission lines from pure starburst galaxies are best explained by variations in the ionizing flux, assuming an locally-optimally emitting cloud (LOC) model, rather than with changes in the metallicity (Levesque, Kewley, & Larson 2010). We have tested wheter the “clumpiness” of the z =0.1 galaxies could be used to estimate the contributions of H II regions to the overall flux. Several metrics are used to quantify the morphologies of galaxies, including concentration C, asymmetry A, and smoothness/clumpiness S. The average concentration C for our pure star-forming galaxies is ∼ 2.6. The smoothness S has a median value of 0.02 (using the Lotz, Primack, Madau definition) or 0.2 (using the Conselice definition). The asymmetries show some dependence on the ionization. However, none of these parameters shows a strong correlation with the clearly different morphologies evident in the Sloan Digital Sky Survey (SDSS) images. The clumpiness, which might indicate the presence of H II regions, shows no strong relationship with the ionization. By degrading the resolution and signal-to-noise of an SDSS image of a nearby sprial galaxy, NGC 4713 (d = 14 Mpc) to progressively further distances, we found that the calculated clumpiness S is greatly affected by distance. The “background clumpiness” quickly dominates the “signal clumpiness.” We next explored if multiple bands might provide a more reliable clumpiness (S ). Given that u-band images of NGC 4713 show much sharper features than the z-band images, we can https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921316007766 Downloaded from https://www.cambridge.org/core. IP address: 34.228.24.229, on 16 Jun 2020 at 18:55:01, subject to the Cambridge Core terms of use, available at