We study the molecular environment, the onset of starbursts, and secular evolution in the circumnuclear (inner 1–2 kpc) region of barred galaxies using a carefully selected sample of barred non-starbursts and starbursts, along with a panchromatic dataset made of high resolution CO (J=1–0) observations, optical, NIR, Hα, radio continuum, Brγ, and archival HST data. (1) We find that the molecular environment which has built up in the inner kpc of barred galaxies departs markedly from that present in the outer disk of galaxies. It involves molecular gas masses of 3 × 10 8 to 2 × 10 9 M ⊙, molecular gas surface densities of 500-3500 M ⊙ pc −2, gas mass fractions of 10 to 30 %, and epicyclic frequencies of several 100 to several 1000 km s −1 kpc −1. In this environment, gravitational instabilities can set in only at very high gas densities (few 100-1000 M ⊙ pc −2), but once triggered, they grow on a short timescale of a few Myrs. This high density short timescale ‘burst ’ mode may explain why the most intense starbursts tend to be in the central parts of galaxies. The molecular environment in the inner kpc of the ultra luminous infrared galaxy Arp 220 is a scaled up version of the one shown by barred starbursts, suggesting that interactions build up even more extreme conditions. (2) The barred starbursts and non-starbursts have circumnuclear SFRs of 3–11 and 0.1–2 M ⊙ yr −1, respectively, although they host comparable amount
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