THREE-DIMENSIONAL INTEGRAL FIELD OBSERVATIONS OF 10 GALACTIC WINDS. I. EXTENDED PHASE (≳10 Myr) OF MASS/ENERGY INJECTION BEFORE THE WIND BLOWS

Abstract

In recent years, we have come to recognize the widespread importance of large-scale winds in the life cycle of galaxies. The onset and evolution of a galactic wind is a highly complex process which must be understood if we are to understand how energy and metals are recycled throughout the galaxy and beyond. Here we present three-dimensional spectroscopic observations of a sample of 10 nearby galaxies with the AAOmega-SPIRAL integral-field spectrograph on the 3.9 m Anglo-Australian Telescope, the largest survey of its kind to date. The double-beam spectrograph provides spatial maps in a range of spectral diagnostics:, 6731. We demonstrate that these flows can often separate into highly ordered structures through the use of ionization diagnostics and kinematics. All of the objects in our survey show extensive wind-driven filamentation along the minor axis, in addition to large-scale disk rotation. Our sample can be divided into either starburst galaxies or active galactic nuclei (AGNs), although some objects appear to be a combination of these. The total ionizing photon budget available to both classes of galaxies is sufficient to ionize all of the windblown filamentation out to large radius. We find, however, that while AGN photoionization always dominates in the wind filaments, this is not the case in starburst galaxies where shock ionization dominates. This clearly indicates that after the onset of star formation, there is a substantial delay ( 10 Myr) before a starburst wind develops. We show why this behavior is expected by deriving "ionization" and dynamical timescales for both AGNs and starbursts. We establish a sequence of events that lead to the onset of a galactic wind. The clear signature provided by the ionization timescale is arguably the strongest evidence yet that the starburst phenomenon is an impulsive event. A well-defined ionization timescale is not expected in galaxies with a protracted history of circumnuclear star formation. Our three-dimensional data provide important templates for comparisons with high-redshift galaxies.

Physical drivers of galaxies’ cold-gas content: exploring environmental and evolutionary effects with Dark Sage

“…This feedback manifests in the form of energetic winds that eject and/or heat gas reserves, as evidenced and detailed by a variety of observations (e.g. Sharp & Bland-Hawthorn 2010;Feruglio et al 2010;Anderson et al 2015;Cicone et al 2015;Nielsen et al 2016) and simulations (e.g. Springel & Hernquist 2003;Brook et al 2011;Costa, Sijacki & Haehnelt 2015;Taylor & Kobayashi 2015;Bower et al 2017).…”

Shocked gas in IRAS F17207-0014: ISM collisions and outflows

“…Mixing between AGN and star formation can also exist (Davies et al 2014b), but such mixing increases the [O III]/Hβ ratio more strongly, shifting points towards the Seyfert region of the diagnostic diagrams. By comparing these ionization line ratios in spatially-resolved spectroscopy to photoionization and shock models, it is thus possible to map out the shocked regions and identify the relative contribution to the luminosity from shocks, star formation, and AGN (Monreal-Ibero et al 2006, 2010Sharp & Bland-Hawthorn 2010;Rich et al 2010Rich et al , 2011Westmoquette et al 2011;Freeland et al 2011;Davis et al 2012;Fogarty et al 2012;Yuan et al 2012;Vogt et al 2013;Ho et al 2014).…”

“…Comparisons of these line ratios and [O III]/Hβ, used as diagnostics of the energy source (as in the BPT/VO87 diagrams; Baldwin, Phillips & Terlevich 1981;Veilleux & Osterbrock 1987), would misidentify a starburst galaxy with shocks as a LINER or composite galaxy (e.g. Armus et al 1989;Veilleux et al 1995;Martin 1997;Dopita et al 1997;Kim et al 1998;Allen et al 1999;Veilleux et al 1999;Sharp & Bland-Hawthorn 2010;Rich et al 2010Rich et al , 2011Rich et al , 2014. Measurements that rely on emission line fluxes or ratios, such as star formation rate and metallicity, can also be affected unless shocks are identified and removed from the calculation.…”

Evolution of multiple supernova remnants

“…It is interesting to note that recent observations of 10 starburst galaxies show that there is a time lag of ∼ 10 Myr between the onset of star formation and the excitation of galactic winds (Sharp & Bland-Hawthorn 2010). Our simulations and the important result of percolation of hot gas when the overall filling factor crosses a threshold of ∼ 0.3, therefore, allow us to interpret this time lag as required for heating efficiency to become sufficiently large for an outflow to be launched.…”