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Register a new userA deep 6.7um survey in the SSA13 field with ISO
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Y. Sato
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We present results of a deep mid-infrared survey in the SSA13 field with the Infrared Space Observatory (ISO). In order to probe the near-infrared light at high redshifts, we surveyed the field with the broad band LW2 (5-8.5um) filter of the mid-infrared camera ISOCAM. Adopting a highly redundant imaging strategy for the 23 hour observation and carefully treating gradual changes in the detector responsivity caused by a very high rate of cosmic ray impacts, we succeeded in reaching an 80% completeness limit of 16uJy in the central 7 arcmin2 region. Utilizing the signal-to-noise ratio map, we detected 65 sources down to 6uJy in the 16 arcmin2 field. Integral galaxy number counts at 6.7um are then derived, reaching 1.3e4/deg2 at the faint limit with a slope of -1.6 between 13uJy and 130uJy. Integrating individual sources in this flux range, the resolved fraction of the extragalactic background light at 6.7um is estimated to be 0.56nW/m2/sr. These results, which reach a flux limit three times fainter than those in the Hubble Deep Fields, are in fairly good agreement with a model prediction by Franceschini et al. (1997). Finally, we discuss the relation of distant massive E/S0 galaxies to the faint 6.7um galaxy population.
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Studying the formation and evolution of galaxies at the earliest cosmic times, and their role in reionization, requires the deepest imaging possible. Ultra-deep surveys like the HUDF and HFF have pushed to mag mAB$,sim,$30, revealing galaxies at the faint end of the LF to $z$$,sim,$9$,-,$11 and constraining their role in reionization. However, a key limitation of these fields is their size, only a few arcminutes (less than a Mpc at these redshifts), too small to probe large-scale environments or clustering properties of these galaxies, crucial for advancing our understanding of reionization. Achieving HUDF-quality depth over areas $sim$100 times larger becomes possible with a mission like the Wide Field Infrared Survey Telescope (WFIRST), a 2.4-m telescope with similar optical properties to HST, with a field of view of $sim$1000 arcmin$^2$, $sim$100$times$ the area of the HST/ACS HUDF. This whitepaper motivates an Ultra-Deep Field survey with WFIRST, covering $sim$100$,-,$300$times$ the area of the HUDF, or up to $sim$1 deg$^2$, to mAB$,sim,$30, potentially revealing thousands of galaxies and AGN at the faint end of the LF, at or beyond $z$,$sim$,9$,-,$10 in the epoch of reionization, and tracing their LSS environments, dramatically increasing the discovery potential at these redshifts. (Note: This paper is a somewhat expanded version of one that was submitted as input to the Astro2020 Decadal Survey, with this version including an Appendix (which exceeded the Astro2020 page limits), describing how the science drivers for a WFIRST Ultra Deep Field might map into a notional observing program, including the filters used and exposure times needed to achieve these depths.)
The ISOGAL project is an infrared survey of specific regions sampling the Galactic Plane selected to provide information on Galactic structure,stellar populations,stellar mass-loss and the recent star formation history of the inner disk and Bulge of the Galaxy. ISOGAL combines 7 and 15 micron ISOCAM observations - with a resolution of 6 at worst - with DENIS IJKs data to determine the nature of the sources and theinterstellar extinction. We have observed about 16 square degrees with a sensitivity approaching 10-20mJy, detecting ~10^5 sources,mostly AGB stars,red giants and young stars. The main features of the ISOGAL survey and the observations are summarized in this paper,together with a brief discussion of data processing and quality. The primary ISOGAL products are described briefly (a full description is given in Schuller et al. 2003, astro-ph/0304309): viz. the images and theISOGAL-DENIS five-wavelength point source catalogue. The main scientific results already derived or in progress are summarized. These include astrometrically calibrated 7 and 15um images,determining structures of resolved sources; identification and properties of interstellar dark clouds; quantification of the infrared extinction law and source dereddening; analysis of red giant and (especially) AGB stellar populations in the central Bulge,determining luminosity,presence of circumstellar dust and mass--loss rate,and source classification,supplemented in some cases by ISO/CVF spectroscopy; detection of young stellar objects of diverse types,especially in the inner Bulge with information about the present and recent star formation rate; identification of foreground sources with mid-IR excess. These results are the subject of about 25 refereed papers published or in preparation.
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