Journal Article

Sub-millimetre brightness of early star-forming galaxies

Hidenobu Yajima, Masayuki Umemura and Masao Mori

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 420, issue 4, pages 3381-3388
Published in print March 2012 | ISSN: 0035-8711
Published online March 2012 | e-ISSN: 1365-2966 | DOI:
Sub-millimetre brightness of early star-forming galaxies

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Based on a three-dimensional model of an early star-forming galaxy, we explore the evolution of the sub-millimetre brightness. The model galaxy is employed from an ultra-high-resolution chemodynamic simulation of a primordial galaxy by Mori & Umemura, where the star formation rate (SFR) is ∼10 M yr−1 at tage≲ 0.3 Gyr and several M yr−1 at tage >0.3 Gyr. The former phase well reproduces the observed properties of Lyman alpha emitters (LAEs) and the latter does Lyman break galaxies (LBGs). We solve the three-dimensional radiative transfer in the clumpy interstellar media in this model galaxy, taking the size distributions of dust grains into account, and calculate the dust temperature as a function of galactic evolutionary time. We find that the clumpiness of interstellar media plays an important role for the sub-millimetre brightness. In the LAE phase, dust grains are concentrated on clumpy star-forming regions that are distributed all over the galaxy, and the grains can effectively absorb ultraviolet (UV) radiation from stars. As a result, the dust is heated up to Tdust≳35 K. In the LBG phase, the continuous supernovae drive dust grains far away from star-forming regions. Then, the grains cannot absorb much radiation from stars, and become a cold state close to the cosmic microwave background (CMB) temperature. Consequently, the dust temperature decreases with the evolutionary time, where the mass-weighted mean temperature is Tdust= 26 K at tage= 0.1 Gyr and Tdust= 21 K at tage= 1.0 Gyr. By this analysis, it turns out that the sub-millimetre brightness is higher in the LAE phase than that in the LBG phase, although the dust-to-gas ratio increases monotonically as a function of time. We derive the spectral energy distributions by placing the model galaxy at a given redshift. The peak flux at 850 μ m is found to be S850∼ 0.2–0.9 mJy if the model galaxy is placed at 6 ≥z≥ 2. This means that Atacama Large Millimetre/sub-millimetre Array (ALMA) can detect an early star-forming galaxy with SFR of ∼10 M yr−1 by less than one hour integration with 16 antennas.

Keywords: radiative transfer; methods: numerical; dust, extinction; galaxies: evolution; galaxies: formation; galaxies: high-redshift

Journal Article.  4851 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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