ESA Science & Technology - Publications Archive
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Publication archive
The May 2010 issue of Astronomy & Astrophysics is a special feature devoted to the new results obtained with the infrared satellite AKARI, a JAXA project with the participation of ESA. It includes 17 articles dealing with various subjects. Some papers are based on the AKARI all-sky survey, which has just been released. Others are dedicated to pointed observations of many astronomical targets from solar system bodies to distant galaxies.
Published: 02 April 2010
Aims. To separate stars and galaxies in the far infrared AKARI All-Sky Survey data, we have selected a sample with the complete color information available in the low extinction regions of the sky and constructed color-color plots for these data. We looked for the method of separating stars and galaxies using the color information.
Methods. We performed an extensive search for the counterparts of these selected All-Sky Survey objects in the NED and SIMBAD databases. Among 5176 selected objects, we found 4272 galaxies, 382 other extragalactic objects, 349 Milky Way stars, 50 other Galactic objects, and 101 sources detected before in various wavelengths but of an unknown origin. Twenty-two sources were left unidentified. Then, we checked the colors of stars and galaxies in the far-infrared flux-color and color-color plots.
Results. In the resulting diagrams, stars form two clearly separated clouds. One of them is easily distinguished from galaxies and allows for a simple method of excluding a large part of stars using the far-infrared data. The other smaller branch, overplotting galaxies, consists of stars known to have an infrared excess, like Vega and some fainter stars discovered by IRAS or 2MASS. The color properties of these objects in any case make them very difficult to distinguish from galaxies.
Conclusions. We conclude that the FIR color-color diagrams allow for a high-quality star-galaxy separation.With the proposed simple method we can select more that 95% of galaxies rejecting at least 80% of stars.
Methods. We performed an extensive search for the counterparts of these selected All-Sky Survey objects in the NED and SIMBAD databases. Among 5176 selected objects, we found 4272 galaxies, 382 other extragalactic objects, 349 Milky Way stars, 50 other Galactic objects, and 101 sources detected before in various wavelengths but of an unknown origin. Twenty-two sources were left unidentified. Then, we checked the colors of stars and galaxies in the far-infrared flux-color and color-color plots.
Results. In the resulting diagrams, stars form two clearly separated clouds. One of them is easily distinguished from galaxies and allows for a simple method of excluding a large part of stars using the far-infrared data. The other smaller branch, overplotting galaxies, consists of stars known to have an infrared excess, like Vega and some fainter stars discovered by IRAS or 2MASS. The color properties of these objects in any case make them very difficult to distinguish from galaxies.
Conclusions. We conclude that the FIR color-color diagrams allow for a high-quality star-galaxy separation.With the proposed simple method we can select more that 95% of galaxies rejecting at least 80% of stars.
Published: 24 March 2010
Aims. Dust-obscured star-formation increases with increasing intensity and increasing redshift. We aim to reveal the cosmic starformation history obscured by dust using deep infrared observation with AKARI.
Methods. We constructed restframe 8 micron, 12 micron, and total infrared (TIR) luminosity functions (LFs) at 0.15 < z < 2.2 using 4128 infrared sources in the AKARI NEP-Deep field. A continuous filter coverage in the mid-IR wavelength (2.4, 3.2, 4.1, 7, 9, 11, 15, 18, and 24 micron) by the AKARI satellite allowed us to estimate restframe 8 micron and 12 micron luminosities without using a large extrapolation based on an SED fit, which was the largest uncertainty in previous work.
Results. We find that all 8 micron (0.38 < z < 2.2), 12 micron (0.15 < z < 1.16), and TIR LFs (0.2 < z < 1.6) show continuous and strong evolution toward higher redshift. Our direct estimate of 8 micron LFs is useful since previous work often had to use a large extrapolation from the Spitzer 24 micron to 8 micron, where SED modeling is more difficult because of the PAH emissions. In terms of cosmic infrared luminosity density (OmegaIR), which was obtained by integrating analytic fits to the LFs, we find good agreement with previous work at z < 1.2. We find the OmegaIR evolves as proportinal to (1 + z)4.4±1.0. When we separate contributions to OmegaIR by LIRGs and ULIRGs, we found more IR luminous sources are increasingly more important at higher redshift. We find that the ULIRG (LIRG) contribution increases by a factor of 10 (1.8) from z=0.35 to z=1.4.
Methods. We constructed restframe 8 micron, 12 micron, and total infrared (TIR) luminosity functions (LFs) at 0.15 < z < 2.2 using 4128 infrared sources in the AKARI NEP-Deep field. A continuous filter coverage in the mid-IR wavelength (2.4, 3.2, 4.1, 7, 9, 11, 15, 18, and 24 micron) by the AKARI satellite allowed us to estimate restframe 8 micron and 12 micron luminosities without using a large extrapolation based on an SED fit, which was the largest uncertainty in previous work.
Results. We find that all 8 micron (0.38 < z < 2.2), 12 micron (0.15 < z < 1.16), and TIR LFs (0.2 < z < 1.6) show continuous and strong evolution toward higher redshift. Our direct estimate of 8 micron LFs is useful since previous work often had to use a large extrapolation from the Spitzer 24 micron to 8 micron, where SED modeling is more difficult because of the PAH emissions. In terms of cosmic infrared luminosity density (OmegaIR), which was obtained by integrating analytic fits to the LFs, we find good agreement with previous work at z < 1.2. We find the OmegaIR evolves as proportinal to (1 + z)4.4±1.0. When we separate contributions to OmegaIR by LIRGs and ULIRGs, we found more IR luminous sources are increasingly more important at higher redshift. We find that the ULIRG (LIRG) contribution increases by a factor of 10 (1.8) from z=0.35 to z=1.4.
Published: 05 February 2010
Aims. We explore spectral energy distributions (SEDs), star formation (SF), and dust extinction properties of galaxies in the Local Universe.
Methods. The AKARI All-Sky Survey provided the first bright point source catalog detected at 90 micron. Beginning with this catalog, we selected galaxies by matching the AKARI sources with those in the IRAS Point Source Catalog Redshift Survey. We measured the total GALEX FUV and NUV flux densities with a photometry software we specifically developed for this purpose. In a further step we matched this sample with the Sloan Digital Sky Survey (SDSS) and Two Micron All Sky Survey (2MASS) galaxies. With this procedure we obtained a basic sample which consists of 776 galaxies. After removing objects whose photometry was contaminated by foreground sources (mainly in the SDSS), we defined the "secure sample" which contains 607 galaxies.
Results. The sample galaxies have redshifts of <~ 0.15, and their 90-micron luminosities range from 106 to 1012 Lsun, with a peak at 1010 Lsun. The SEDs display a large variety, especially more than four orders of magnitude at the mid-far-infrared (M-FIR), but if we sort the sample with respect to 90 micron, the average SED shows a coherent trend: the more luminous an SED at 90 micron, the redder the global SED becomes. The Mr-NUV - r color-magnitude relation of our sample does not show bimodality, and the distribution is centered on the green valley.
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Methods. The AKARI All-Sky Survey provided the first bright point source catalog detected at 90 micron. Beginning with this catalog, we selected galaxies by matching the AKARI sources with those in the IRAS Point Source Catalog Redshift Survey. We measured the total GALEX FUV and NUV flux densities with a photometry software we specifically developed for this purpose. In a further step we matched this sample with the Sloan Digital Sky Survey (SDSS) and Two Micron All Sky Survey (2MASS) galaxies. With this procedure we obtained a basic sample which consists of 776 galaxies. After removing objects whose photometry was contaminated by foreground sources (mainly in the SDSS), we defined the "secure sample" which contains 607 galaxies.
Results. The sample galaxies have redshifts of <~ 0.15, and their 90-micron luminosities range from 106 to 1012 Lsun, with a peak at 1010 Lsun. The SEDs display a large variety, especially more than four orders of magnitude at the mid-far-infrared (M-FIR), but if we sort the sample with respect to 90 micron, the average SED shows a coherent trend: the more luminous an SED at 90 micron, the redder the global SED becomes. The Mr-NUV - r color-magnitude relation of our sample does not show bimodality, and the distribution is centered on the green valley.
- Remainder of abstract is truncated -
Published: 22 January 2010
We have made a deep and wide imaging survey with all nine AKARI/IRC bands from 2 to 24 micron within a half degree of the North Ecliptic Pole. The survey covered acircular area of 0.38deg2 centered at RA = 17h56m, Dec = 66°37' where a deep optical multi-band survey has been conducted by Subaru/Suprime-Cam. The 5-sigma sensitivity of the survey for point sources is 11.0, 48, 117, and 275 microJansky at wavelengths 3, 7, 15, and 24 micron, respectively. The survey is limited by sky noise at wavelengths from 7 to 24 micron, and limited by source confusion from 2 to 4 micron. We have also made a point source catalog at each band, consisting of more than 5000 sources with a 50% completeness limit of 93 microJansky at 15 micron. Our results are consistent with the pilot survey at faint fluxes and has better statistical significance at the bright fluxes. This is the first near- and mid-infrared sub-milliJansky extragalactic survey with contiguous wavelength coverage from 2 to 24 micron and a large band-merged catalogue. It will provide powerful and unique diagnostics of obscured star-formation and AGN activities in the galaxies up to z = 2.
Published: 25 December 2008