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We present the AKARI InfraRed Camera (IRC) imaging observation of early-type galaxies in A2218 at z ≃ 0.175. Mid-infrared (MIR) emission from early-type galaxies traces circumstellar dust emission from AGB stars or/and residual star formation. Including the unique imaging capability at 11 and 15 µm, our AKARI data provide an effective way to investigate MIR properties of early-type galaxies in the cluster environment. Among our flux-limited sample of 22 red sequence early-type galaxies with precise dynamical and line strength measurements (< 18 mag at 3 µm), we find that at least 41% have MIR-excess emission. The N 3 − S11 versus N 3 (3 and 11 µm) colormagnitude relation shows the expected blue sequence, but the MIR-excess galaxies add a red wing to the relation especially at the fainter end. A SED analysis reveals that the dust emission from AGB stars is the most likely cause for the MIR-excess, with low level of star formation being the next possible explanation. The MIR-excess galaxies show a wide spread of N 3 − S11 colors, implying a significant spread (2-11 Gyr) in the estimated mean ages of stellar populations. We study the environmental dependence of MIR-excess early-type galaxies over an area out to a half virial radius (∼1 Mpc). We find that the MIR-excess early-type galaxies are preferentially located in the -2outer region. From these evidences, we suggest that the fainter, MIR-excess early-type galaxies have just joined the red sequence, possibly due to the infall and subsequent morphological/spectral transformation induced by the cluster environment.

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We present an 850-μm mosaic map and extracted catalogue of submillimetre sources in the extended North Ecliptic Pole (NEP) region over about 2 deg2. The 850-μm map is constructed using newly obtained observations by SCUBA-2 at the East Asian Observatory’s James Clerk Maxwell Telescope, carried out using the observatory’s large programme opportunities. The recent 850-μm survey has extended the submillimetre data coverage by almost a factor of 4 compared to previous surveys, with a depth of σrms  =  1.0–2.3 mJy beam−1. The catalogue contains 549 sources selected above a significance level of 4σ, where the false-detection rate is 10 per cent; a higher threshold of 4.5σ is required in order to achieve a false-detection rate below 3 per cent, which results in 342 sources being selected. Despite the large spatial variation of the noise, the deboosted flux density of sources is comparable to results from the SCUBA-2 Cosmology Legacy Survey (S2CLS), which covered the central 0.6 deg2 of our survey area with better sensitivity. We construct the source counts at 850 μm, finding results in agreement with other 850-μm surveys in cosmological blank fields over S850 = 4–15 mJy. We find a slight excess of bright galaxies (S850  &gt;  15 mJy), which can be considered to be at zphot  =  2–4. The 850-μm data adds valuable long-wavelength information to mid-infrared-selected sources from the AKARI NEP-deep and NEP-wide surveys, which will be helpful in preparing for future near-infrared to millimetre wavelength observations in the NEP region. Our 850-μm mosaic map and source catalogue will be made publicly available.

We report a search for fluctuations of the sky brightness toward the North Ecliptic Pole with AKARI, at 2.4, 3.2, and 4.1 µm. The stacked images with a diameter of 10 arcminutes of the AKARI-Monitor Field show a spatial structure on the scale of a few hundred arcseconds. A power spectrum analysis shows that there is a significant excess fluctuation at angular scales larger than 100 arcseconds that cannot be explained by zodiacal light, diffuse Galactic light, shot noise of faint galaxies, or clustering of low-redshift galaxies. These findings indicate that the detected fluctuation could be attributed to the first stars of the universe, i.e., Population III stars.