Stella Offner added missing citations  over 8 years ago

Commit id: 0319af075dc135fb9528a4949a369836348aad1a

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One fundamental puzzle in star formation is why the efficiency at which dense gas forms stars is only a few percent per free fall time \citep[][]{krumholz14review}. Early three-dimensional hydrodynamic simulations discovered that supersonic turbulence decays rapidly and predicted that without additional energy input turbulence should decay significantly within a dynamical time \citep{stone98,maclow99}. This implies that gravity should be able to efficiently form stars after a dynamical time. However, turbulence observed within molecular clouds does not appear to weaken and star formation efficiencies are small after several dynamical times \citep{KandT07} One explanation for the longevity of observed turbulence is that motions are driven internally via feedback from forming or evolved stars \citep[][and references therein]{krumholz14ppvi}. In principle this should introduce a characteristic energy input scale \citep{carroll09,hansen12,Offner_2015}, which should impact turbulent statistics. However, from an observational prospective, stellar feedback is {\it messy} and identifying clear feedback signatures is complex for the reasons mentioned above. %Analysis is typically restricted by the assumption that the velocities and extent along perpendicular directions are s  Disentangling feedback signatures from the turbulent background and assessing their role is challenging since any low-velocity motions excited by feedback are lost in the general cloud turbulence \citep{swift08,arce10,arce11}.   Few prior numerical or observational studies have examined the response of a turbulent statistic to feedback. The most commonly computed turbulent statistic, velocity power spectra, may reflect the characteristic scale of energy input from feedback. Turbulence with both isolated and clusters of outflow exhibit a steepened velocity power spectrum \citet{nakamura07,cunningham09, carroll09}. \citet{nakamura07,cunningham09,carroll09}.  While \citet{swift08} identified a break in the power spectrum of the $^{13}$CO intensity moment map, which they attribute to a characteristic scale associated with the embedded protostellar outflows (the break is absent in the $^{12}$CO data). Numerical simulation with point-source (supernovae) driving, also find changes in the power spectrum slope \citep{joung06}. \citet{burkhart??}, in an observational analysis of HI, noted the possible signature of supernovae on the bispectrum.   %Jung & Mac Low 2006 -pdf, velocity and ke power spectrum, 2-pt correlation function  %hansen 2-point correlation function - outflows+compare to rho Oph, little dependence on feedback