Abstract
(abridged) We investigate the properties of feedback-driven shocks in 8
nearby starburst galaxies using narrow-band imaging data from the Hubble Space
Telescope (HST). We identify the shock--ionized component via the line
diagnostic diagram øiii/vs. (or \nii)/\ha, applied to resolved
regions 3--15 pc in size. We divide our sample into three sub-samples:
sub-solar (Holmberg II, NGC 1569, NGC 4214, NGC 4449, and NGC 5253), solar (He
2-10, NGC 3077) and super-solar (NGC 5236) for consistent shock measurements.
For the sub-solar sub-sample, we derive three scaling relations: (1) $L_shock
SFR^~0.62$, (2) $L_shock \Sigma_SFR,HL^~0.92$, and
(3) $L_shock/L_tot (L_H/L_ødot,H)^-0.65$, where $L_shock$
is the luminosity from shock--ionized gas, $\Sigma_SFR,HL$ the SFR per
unit half-light area, $L_tot$ the total luminosity, and $L_H/L_ødot,H$
the absolute H-band luminosity from 2MASS normalized to solar luminosity. The
other two sub--samples do not have enough number statistics, but appear to
follow the first scaling relation. The energy recovered indicates that the
shocks from stellar feedback in our sample galaxies are fully radiative. If the
scaling relations are applicable in general to stellar feedback, our results
are similar to those by Hopkins et al. (2012) for galactic super winds. This
similarity should, however, be taken with caution at this point, as the
underlying physics that enables the transition from radiative shocks to gas
outflows in galaxies is still poorly understood.
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