Browsing by Author "Kewley, Lisa J."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    The slow flow model of dust eflux in local star-forming galaxies
    (Oxford University Press, 2013) Zahid, H.; Torrey, Paul; Dave, Romeel; Geller, Margaret; Kudritzki, Rolf; Kewley, Lisa J.
    We develop a dust efflux model of radiation pressure acting on dust grains which successfully reproduces the relation between stellar mass, dust opacity and star forma- tion rate observed in local star-forming galaxies. The dust content of local star-forming galaxies is set by the competition between the physical processes of dust production and dust loss in our model. The dust loss rate is proportional to the dust opacity and star formation rate. Observations of the relation between stellar mass and star formation rate at several epochs imply that the majority of local star-forming galax- ies are best characterized as having continuous star formation histories. Dust loss is a consequence of sustained interaction of dust with the radiation field generated by continuous star formation. Dust efflux driven by radiation pressure rather than dust destruction offers a more consistent physical interpretation of the dust loss mechanism. By comparing our model results with the observed relation between stellar mass, dust extinction and star formation rate in local star-forming galaxies we are able to con- strain the timescale and magnitude of dust loss. The timescale of dust loss is long and therefore dust is effluxed in a “Slow Flow". Dust loss is modest in low mass galaxies but massive galaxies may lose up to 70 80% of their dust over their lifetime. Our Slow Flow model shows that mass loss driven by dust opacity and star formation may be an important physical process for understanding normal star-forming galaxy evolution.
  • Thumbnail Image
    Item
    Theoretical evolution of optical strong lines across cosmic time
    (The American Astronomical Society, 2013) Kewley, Lisa J.; Dopita, Michael A.; Dave, Romeel; Leitherer, Claus; Yuan, Tiantian; Allen, Mark; Groves, Brent; Sutherland, Ralph
    We use the chemical evolution predictions of cosmological hydrodynamic simulations with our latest theoretical stellar population synthesis, photoionization, and shock models to predict the strong line evolution of ensembles of galaxies from z = 3 to the present day. In this paper, we focus on the brightest optical emission-line ratios, [N ii]/Hα and [O iii]/Hβ. We use the optical diagnostic Baldwin–Phillips–Terlevich (BPT) diagram as a tool for investigating the spectral properties of ensembles of active galaxies. We use four redshift windows chosen to exploit new near-infrared multi-object spectrographs. We predict how the BPT diagram will appear in these four redshift windows given different sets of assumptions. We show that the position of star-forming galaxies on the BPT diagram traces the interstellar medium conditions and radiation field in galaxies at a given redshift. Galaxies containing active galactic nucleus (AGN) form a mixing sequence with purely star-forming galaxies. This mixing sequence may change dramatically with cosmic time, due to the metallicity sensitivity of the optical emission-lines. Furthermore, the position of the mixing sequence may probe metallicity gradients in galaxies as a function of redshift, depending on the size of the AGN narrow-line region. We apply our latest slow shock models for gas shocked by galactic-scale winds. We show that at high redshift, galactic wind shocks are clearly separated from AGN in line ratio space. Instead, shocks from galactic winds mimic high metallicity starburst galaxies. We discuss our models in the context of future large near-infrared spectroscopic surveys.