2019ApJ...872..146J

We explore the relation between the star formation rate surface density (ΣSFR) and the interstellar gas pressure for nearby compact starburst galaxies. The sample consists of 17 green peas and 19 Lyman break analogs (LBAs). Green peas are nearby analogs of Lyα emitters at high redshift and LBAs are nearby analogs of Lyman break galaxies at high redshift. We measure the sizes of green peas using Hubble Space Telescope Cosmic Origins Spectrograph near-UV images with a spatial resolution of ∼0.''05. We estimate the gas thermal pressure in H II regions by P = N_totalTk_B ≃ 2n_eTk_B. The electron density is derived using the [S II] doublet at 6716,6731 Å and the temperature is calculated from the [O III] lines. The correlation is characterized by ΣSFR = 2.40×10^–3M_☉yr^–1kpc^–2(P/k_B{10⁴cm^–3K})^1.33. Green peas and LBAs have high ΣSFR up to 1.2 M_☉ yr^–1 kpc^–2 and high thermal pressure in the H II region up to P/k_B ∼ 10^7.2 K cm^–3. These values are at the highest end of the range seen in nearby starburst galaxies. The high gas pressure and the correlation are in agreement with those found in star-forming galaxies at z ∼ 2.5. These extreme pressures are shown to be responsible for driving galactic winds in nearby starbursts. These outflows may be crucial in enabling Lyα and Lyman-continuum to escape.