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Published August 1, 2015 | Published + Submitted
Journal Article Open

Correlation between star formation activity and electron density of ionized gas at z = 2.5


In the redshift interval of 2 < z < 3, the physical conditions of the interstellar medium (ISM) in star-forming galaxies are likely to be different from those in the local Universe because of lower gaseous metallicities, higher gas fractions, and higher star formation activities. In fact, observations suggest that higher electron densities, higher ionization parameters, and harder UV radiation fields are common. In this paper, based on the spectra of H α-selected star-forming galaxies at z = 2.5 taken with Multi-Object Spectrometer for InfraRed Exploration on Keck-1 telescope, we measure electron densities (n_e) using the oxygen line ratio ([O II] λλ3726,3729), and investigate the relationships between the electron density of ionized gas and other physical properties. As a result, we find that the specific star formation rate (sSFR) and the surface density of SFR (Σ_(SFR)) are correlated with the electron density at z = 2.5 for the first time. The Σ_(SFR)–n_e relation is likely to be linked to the star formation law in H II regions (where star formation activity is regulated by interstellar pressure). Moreover, we discuss the mode of star formation in those galaxies. The correlation between sSFR and Σ_(SFR) suggests that highly star-forming galaxies (with high sSFR) tend to be characterized by higher surface densities of star formation (Σ_(SFR)) and thus higher n_e values as well.

Additional Information

© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 April 22. Received 2015 March 25. In original form 2014 November 5. First published online June 5, 2015. We are grateful to the anonymous referee for useful comments. The data presented in this paper were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Data analyses were in part carried out on common use data analysis computer system at the Astronomy Data Center, ADC, of the National Astronomical Observatory of Japan.

Attached Files

Submitted - 1411.1408v3.pdf

Published - MNRAS-2015-Shimakawa-1284-9.pdf


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August 22, 2023
August 22, 2023