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An important property of star-forming galaxies at z~1-2 is the high localstar-formation intensities they maintain over tens of kiloparsecs at levelsthat are only observed in the nearby Universe in the most powerful nuclearstarbursts. To investigate how these high star-formation intensities affect thewarm ionized medium, we present an analysis of the average spectra of about 50such galaxies at z~1.2-2.6 and of subsamples selected according to their localand global star-formation intensity. Stacking allows us to probe relativelyweak lines like [SII]\lambda \lambda 6716,6731 and [OI]\lambda 6300, which aretracers of the conditions of the ISM and are undetectable in most individualtargets. We find higher gas densities (hence pressures) in intenselystar-forming regions compared to fainter diffuse gas and, overall, values thatare comparable to starburst regions and the diffuse ISM in nearby galaxies. Bymodeling the H\alpha\ surface brightnesses and [SII]/H\alpha\ line ratios withthe Cloudy photoionization code, we find that our galaxies continue trendsobserved in local galaxies, where gas pressures scale with star-formationintensity. We discuss these results in the context of models of self-regulatedstar formation, where star formation determines the average thermal andturbulent pressure in the ISM, which in turn determines the rate at which starscan form, finding good agreement with our data. We also confirm the detectionof broad, faint lines underlying H\alpha\ and [NII], which have previously beenconsidered evidence of either outflows or active galactic nuclei. Finding thatthe broad component is only significantly detected in stacks with the highestaverage local and global star-formation intensities strongly supports theoutflow interpretation, and further emphasizes the importance of star-formationfeedback and self-regulation in the early Universe.

The Average Optical Spectra of Intense Starbursts at z~2: Outflows and the Pressurization of the ISM