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

Abstract

We present 3D spectroscopic observations of a sample of 10 nearby galaxies with the AAOmega-SPIRAL integral field spectrograph on the 3.9m AAT, the largest survey of its kind to date. The double-beam spectrograph provides spatial maps in a range of spectral diagnostics: [OIII] 5007, H-beta, Mg-b, NaD, [OI] 6300, H-alpha, [NII] 6583, [SII] 6717, 6731. 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 (AGN), although some objects appear to be a combination of these. The total ionizing photon budget available to both classes of galaxies is sufficient to ionise all of the wind-blown filamentation out to large radius. We find however that while AGN photoionisation always dominates in the wind filaments, this is not the case in starburst galaxies where shock ionisation 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 ``ionisation'' 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 ionisation timescale is arguably the strongest evidence yet that the starburst phenomenon is an impulsive event. A well-defined ionisation timescale is not expected in galaxies with a protracted history of circumnuclear star formation. Our 3D data provide important templates for comparisons with high redshift galaxies.[Abridged]