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Paper: A Mass-dependent Star Formation History of Field Galaxies in the Extended Groth Strip Survey
Volume: 381, The Second Annual Spitzer Science Center Conference: Infrared Diagnostics of Galaxy Evolution
Page: 485
Authors: Noeske, K.G.; the AEGIS Collaboration
Abstract: The All Wavelength Extended Groth Strip International Survey (AEGIS) combines panchromatic space- and ground based photometry, HST images, and high resolution spectroscopy. We use this dataset to study the history of star formation and stellar mass buildup in field galaxies out to z = 1.4, from a combination of UV-/optical and Spitzer MIPS IR-derived star formation rates, and stellar masses. We find that the specific star formation rates of field galaxies as a function of stellar mass and z can be well described by exponential star formation histories with mass-dependent e-folding times τ , and possibly mass-dependent switch-on redshifts (“stagedτ models), throughout the stellar mass range we can observe (∼ 1010M at z < 1). This model allows a first quantification of the mass dependency of star formation timescales in field galaxies from direct observations of masses and star formation rates up to z > 1.

Our results suggest that gradual gas exhaustion, including loss or heating of cold gas, may be a dominant process in the evolution of star formation in field galaxies over a wide range in mass and redshift, consistent with the regular morphologies of strongly star-forming, IR-luminous galaxies at intermediate z. An increasing fraction of younger galaxies towards lower masses may explain the observed high specific star formation rates without requiring a high fraction of starbursts. The inferred mass-dependent parametrization of star formation timescales and ages qualitatively reproduces the observed color-magnitude bimodality, and suggests that this bimodality can be a natural consequence of different evolutionary timescales of galaxies.

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