Impact of Future Submillimeter and Millimeter Large Facilities on the Studies of Galaxy Formation and Evolution

Abstract

ABSTRACTWe investigate what we can learn about galaxy formation and evolution from the data which will be obtained by the forthcoming large submillimeter/millimeter facilities, mainly by the Atacama Submillimeter Telescope Experiment (ASTE) and the Atacama Large Millimeter Array/Large Millimeter and Submillimeter Array (ALMA/LMSA). We first calculate the source counts from 350 μm to 3 mm using the empirical infrared galaxy number count model of Takeuchi et al. Based on the number counts, we evaluate the source confusion and determine the confusion limit at various wave bands as a function of the characteristic beam size. At submillimeter wavelengths, source confusion with the 10–15 m class facilities becomes severe at the 0.1–1 mJy level, and astrometry and flux measurements will be difficult. However, we show that a very large area survey of submillimeter sources brighter than 10–50 mJy can provide a unique constraint on infrared galaxy evolution at z = 1–2, and such a survey is suitable for the ASTE. In addition, such a survey enables us to study the clustering properties of submillimeter sources, which are still highly unknown. We also find that the 5 σ confusion limit of LMSA is fainter than 1 μJy, which enables us to study the contribution of sources at extremely large redshift. When we discuss such a deep flux limit, the dynamic range of a detector should be taken into account, since extremely bright sources make it impossible to detect the faintest sources near the detection limit. We evaluate the probability that sources that are 103 times brighter than the 5 σ detection limit of LMSA and ALMA exist in the field of view. We find that the probability is ≲3 × 10-4, and therefore we do not have to worry about the dynamic range. The source counts at such faint flux levels give important information about the epoch of galaxy formation. We then show that multiband photometry from the infrared (by ASTRO‐F) to the millimeter can be used as a redshift estimator. We examined the performance of this method by Monte Carlo simulations and found that it works successfully if we have reasonable measurement accuracy. In addition, we compare the observed 1.4, 5, and 8 GHz source counts with our model counts to examine the contribution of star‐forming galaxies to faint radio galaxies. We find that the faintest radio number counts (∼1 μJy) are dominated by actively star‐forming galaxies which lie at intermediate redshift z∼1–2.