Dissecting galaxies: Separating star formation, shock excitation and AGN activity in the central region of NGC 613

Rebecca L. Davies, Brent Groves, Lisa J. Kewley, Anne M. Medling, Prajval Shastri, Jaya Maithil, Preeti Kharb, Julie Banfield, Fergus Longbottom, Michael A. Dopita, Elise J. Hampton, Julia Scharwächter, Ralph Sutherland, Chichuan Jin, Ingyin Zaw, Bethan James, Stéphanie Juneau

Research output: Contribution to journalArticlepeer-review


The most rapidly evolving regions of galaxies often display complex optical spectra with emission lines excited by massive stars, shocks and accretion on to supermassive black holes. Standard calibrations (such as for the star formation rate) cannot be applied to such mixed spectra. In this paper, we isolate the contributions of star formation, shock excitation and active galactic nucleus (AGN) activity to the emission line luminosities of individual spatially resolved regions across the central 3 × 3 kpc2 region of the active barred spiral galaxy NGC 613. The star formation rate and AGN luminosity calculated from the decomposed emission line maps are in close agreement with independent estimates from data at other wavelengths. The star formation component traces the B-band stellar continuum emission, and the AGN component forms an ionization cone which is aligned with the nuclear radio jet. The optical line emission associated with shock excitation is cospatial with strong H2 and [Fe II] emission and with regions of high ionized gas velocity dispersion (σ ≳ 100 km s-1). The shock component also traces the outer boundary of the AGN ionization cone and may therefore be produced by outflowing material interacting with the surrounding interstellar medium. Our decomposition method makes it possible to determine the properties of star formation, shock excitation and AGN activity from optical spectra, without contamination from other ionization mechanisms.

Original languageEnglish (US)
Pages (from-to)4974-4988
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Oct 2017


  • Galaxies: ISM
  • Galaxies: Seyfert
  • Galaxies: evolution

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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