Regulating Star Formation in Nearby Dusty Galaxies: Low Photoelectric Efficiencies in the Most Compact Systems

Abstract

Star formation in galaxies is regulated by the heating and cooling in the interstellar medium. In particular, the processing of molecular gas into stars will depend strongly on the ratio of gas heating to gas cooling in the neutral gas around sites of recent star-formation. In this work, we combine mid-infrared (mid-IR) observations of Polycyclic Aromatic Hydrocarbons (PAHs), the dominant heating mechanism of gas in the interstellar medium (ISM), with [C II], [O I], and [Si II] fine-structure emission, the strongest cooling channels in dense, neutral gas. The ratio of IR cooling line emission to PAH emission measures the photoelectric efficiency, a property of the ISM which dictates how much energy carried by ultraviolet photons gets transferred into the gas. We find that star-forming, IR luminous galaxies in the Great Observatories All-Sky LIRG Survey (GOALS) with high IR surface densities have low photoelectric efficiencies. These systems also have, on average, higher ratios of radiation field strength to gas densities, and larger average dust grain size distributions. The data support a scenario in which the most compact galaxies have more young star-forming regions per unit area, which exhibit less efficient gas heating. These conditions may be more common at high-z, and may help explain the higher star-formation rates at cosmic noon. We make predictions on how this can be investigated with JWST.

17 pages, 8 figures, 2 tables, accepted for publication in ApJ

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Cited by in corpus (6)

• Polycyclic Aromatic Hydrocarbons in Seyfert and star-forming galaxies
• High [OIII]/[CII] surface brightness ratios trace early starburst galaxies
• Contribution of polycyclic aromatic hydrocarbon ionization to neutral gas heating in galaxies: model versus observations
• The ALMA-CRISTAL survey: Dust temperature and physical conditions of the interstellar medium in a typical galaxy at z=5.66
• Polycyclic Aromatic Hydrocarbon Size Tracers
• The Calibration of Polycyclic Aromatic Hydrocarbon Dust Emission as a Star Formation Rate Indicator in the AKARI NEP Survey