Ecliptic pole

Abstract: The Infrared Array Camera (IRAC) on the Spitzer Space Telescope is absolutely calibrated by comparing photometry of a set of A stars near the north ecliptic pole to predictions based on ground‐based observations and a stellar atmosphere model The brightness of point sources is calibrated to an accuracy of 3%, relative to models for A‐star stellar atmospheres, for observations performed and analyzed in the same manner as for the calibration stars This includes corrections for the location of the star in the array and the location of the centroid within the peak pixel Long‐term stability of the IRAC photometry was measured by monitoring the brightness of A dwarfs and K giants (near the north ecliptic pole) observed several times per month; the photometry is stable to 15% (rms) over a year Intermediate‐timescale stability of the IRAC photometry was measured by monitoring at least one secondary calibrator (near the ecliptic plane) every 12 hr while IRAC was in nominal operations; the intermediat

Abstract: AKARI (formerly ASTRO-F) is an infrared space telescope designed for an all-sky survey at 10-180 (mu)m, and deep pointed surveys of selected areas at 2-180 (mu)m. The deep pointed surveys with AKARI will significantly advance our understanding of galaxy evolution, the structure formation of the Universe, the nature of the buried AGNs, and the cosmic infrared background. Here we describe the important characteristics of the AKARI mission: the orbit, and the attitude control system, and investigate the optimum survey area based on the updated pre-flight sensitivities of AKARI, taking into account the cirrus confusion noise as well as the surface density of bright stars. The North Ecliptic Pole (NEP) is concluded to be the best area for 2-26 (mu)m deep surveys, while the low-cirrus noise regions around the South Ecliptic Pole (SEP) are worth considering for 50-180 (mu)m pointed surveys to high sensitivities limited by the galaxy confusion noise. Current observational plans of these pointed surveys are described in detail. Comparing these surveys with the deep surveys with the Spitzer Space Telescope, the AKARI deep surveys are particularly unique in respect of their continuous wavelength coverage over the 2-26 (mu)m range in broad-band deep imaging, and their slitless spectroscopy mode over the same wavelength range.

Abstract: We report a search for fluctuations of the sky brightness toward the north ecliptic pole with the Japanese infrared astronomical satellite AKARI, at 2.4, 3.2, and 4.1 {mu}m. We obtained circular maps with 10' diameter fields of view, which clearly 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'' that cannot be explained by zodiacal light, diffuse Galactic light, shot noise of faint galaxies, or clustering of low-redshift galaxies. These results are consistent with observations at 3.6 and 4.5 {mu}m by NASA's Spitzer Space Telescope. The fluctuating component observed at large angular scales has a blue stellar spectrum which is similar to that of the spectrum of the excess isotropic emission observed with the Infrared Telescope in Space. A significant spatial correlation between wavelength bands was found, and the slopes of the linear correlations are consistent with the spectrum of the excess fluctuation. These findings indicate that the detected fluctuation could be attributed to the first stars of the universe, i.e., Population III stars. The observed fluctuation provides an important constraint on the era of the first stars.

Abstract: Clusters of galaxies at redshifts nearing 1 are of special importance since they may be caught at the epoch of formation. At these high redshifts there are very few known clusters. We present follow-up ASCA, ROSAT High Resolution Imager, and Keck LRIS observations of the cluster RX J1716.6+6708, which was discovered during the optical identification of X-ray sources in the north ecliptic pole region of the ROSAT All-Sky Survey. At z = 0.809, RX J1716.6+6708 is the second most distant X-ray–selected cluster so far published and the only one with a large number of spectroscopically determined cluster member velocities. The optical morphology of RX J1716.6+6708 resembles an inverted S-shape filament with the X-rays coming from the midpoint of the filament. The X-ray contours have an elongated shape that roughly coincides with the weak lensing contours. The cluster has a low temperature, kT = 5.66 keV, and a very high velocity dispersion σlos = 1522 km s-1. While the temperature is commensurate with its X-ray luminosity of (8.19 ± 0.43) × 1044 h ergs s-1 (2–10 keV rest frame), its velocity dispersion is much higher than expected from the σ-TX relationship of present-day clusters with comparable X-ray luminosity. RX J1716.6+6708 could be an example of a protocluster, where matter is flowing along filaments and the X-ray flux is maximum at the impact point of the colliding streams of matter.