Browsing by Author "Heckman, Timothy M."

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    Do galaxy global relationships emerge from local ones? The SDSS IV MaNGA surface mass density-metallicity relation
    (OXFORD UNIV PRESS, 2016) Barrera Ballesteros, Jorge K.; Heckman, Timothy M.; Zhu, Guangtun B.; Zakamska, Nadia L.; Sanchez, Sebastian F.; Law, David; Wake, David; Green, Jenny E.; Bizyaev, Dmitry; Oravetz, Daniel; Simmons, Audrey; Malanushenko, Elena; Pan, Kaike; Roman Lopes, Alexandre; Lane, Richard R.
    We present the stellar surface mass density versus gas metallicity (Sigma(*)-Z) relation for more than 500 000 spatially resolved star-forming resolution elements (spaxels) from a sample of 653 disc galaxies included in the SDSS IV MaNGA survey. We find a tight relation between these local properties, with higher metallicities as the surface density increases. This relation extends over three orders of magnitude in the surface mass density and a factor of 4 in metallicity. We show that this local relationship can simultaneously reproduce two well-known properties of disc galaxies: their global mass-metallicity relationship and their radial metallicity gradients. We also find that the Sigma(*)-Z relation is largely independent of the galaxy's total stellar mass and specific star formation rate (sSFR), except at low stellar mass and high sSFR. These results suggest that in the present-day universe local properties play a key role in determining the gas-phase metallicity in typical disc galaxies.
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    Tracing the Ionization Structure of the Shocked Filaments of NGC 6240
    (2021) Medling, Anne M.; Kewley, Lisa J.; Calzetti, Daniela; Privon, George C.; Larson, Kirsten; Rich, Jeffrey A.; Armus, Lee; Allen, Mark G.; Bicknell, Geoffrey V.; Díaz-Santos, Tanio; Heckman, Timothy M.; Leitherer, Claus; Max, Claire E.; Rupke, David S. N.; Treister, Ezequiel; Messias, Hugo; Wagner, Alexander Y.
    We study the ionization and excitation structure of the interstellar medium in the late-stage gas-rich galaxy merger NGC 6240 using a suite of emission-line maps at similar to 25 pc resolution from the Hubble Space Telescope, Keck/NIRC2 with Adaptive Optics, and the Atacama Large Millimeter/submillimeter Array (ALMA). NGC 6240 hosts a superwind driven by intense star formation and/or one or both of two active nuclei; the outflows produce bubbles and filaments seen in shock tracers from warm molecular gas (H-2 2.12 mu m) to optical ionized gas ([O iii], [N ii], [S ii], and [O i]) and hot plasma (Fe XXV). In the most distinct bubble, we see a clear shock front traced by high [O iii]/H beta and [O iii]/[O i]. Cool molecular gas (CO(2-1)) is only present near the base of the bubble, toward the nuclei launching the outflow. We interpret the lack of molecular gas outside the bubble to mean that the shock front is not responsible for dissociating molecular gas, and conclude that the molecular clouds are partly shielded and either entrained briefly in the outflow, or left undisturbed while the hot wind flows around them. Elsewhere in the galaxy, shock-excited H-2 extends at least similar to 4 kpc from the nuclei, tracing molecular gas even warmer than that between the nuclei, where the two galaxies' interstellar media are colliding. A ridgeline of high [O iii]/H beta emission along the eastern arm aligns with the southern nucleus' stellar disk minor axis; optical integral field spectroscopy from WiFeS suggests this highly ionized gas is centered at systemic velocity and likely photoionized by direct line of sight to the southern active galactic nucleus.