Max Planck Institute for Astronomy - Annual Report 2005

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44 II. Highlights log IR luminosity density / [h L � /Mpc –3 ] 9 8.5 8 Detected + Stacked + Extrapolated LF fits with fixed z = 0 LF shape Detected + Stacked Detected 0 0.2 0.4 0.6 0.8 1 Redshift z Fig. II.7.3: IR luminosity density as a function of redshift (solid line), reflecting the decay of the global star-formation rate for z � 1 to the present. The red dot in the lower left indicates the value for the present-day universe. The red dashed line represents the results of another, independent study. Fig. II.7.4: Evolution of the IR energy density, total (green) and for different galaxy types. Blue: low-luminosity galaxies (L IR , 10 11 L � ), orange : lirgs, red: ulirgs. The solid line shows a decrease with a power-law dependence on redshift and an exponent of 3.9. � IR [L � / Mpc 3 ] 10 9 10 8 10 7 0.0 0.2 0.4 0.6 0.8 Redshift z to resemble that of local galaxies, at least for z�0.8 (Fig. II.7.2). The question now was how to convert the measured fluxes at 24 µm (corresponding to a rest wavelength of 15 µm), which is a measure for the thermal IR, as well as the 380-nm-flux, which is a measure for the UV, into a star formation rate. These two quantities should be crucial: in the UV we are directly observing the emission of the young, hot stars while in the IR we are seeing the light from these same stars that has been absorbed by dust and subsequently re-radiated. The overall UV flux from 1216 to 3000 Angström has to be calculated from the CoMbo-17 magnitudes measured at 2800 Angström with the help of an empirical relationship. The star formation rate then follows from a formula containing the sum of the UV and IR luminosities. The essential result of this study is that all galaxies clearly follow the trend seen in local galaxies, according to which the luminosity ratio L IR /L UV increases with the star formation rate. This is true at least to a redshift of 0.8, the redshift limit of this study. Finally, astronomers were able to calculate the cosmic star formation rate from the IR luminosity. Compared to previous work, this was particularly significant because the new data account for the contribution from faint galaxies that were missing from previous samples. The result shows the overall IR luminosity (within a unit volume that is co-moving with the expansion of the Universe) as a function of redshift (Fig. II.7.3). We see that the thermal IR luminosity has decreased by a factor of nine over the last eight billion years. These results demonstrate that the star formation rate has strongly decreased in the second half of the life of the Universe. The crucial question now is which galaxy types are primarily responsible for the dramatic decline of the cosmic star formation. 1 0.1 0.01 SFR [M � a –1 Mpc –3 ] 0.001
The Disappearance of Luminous and Ultra-luminous Infrared Galaxies To investigate this question, astronomers studied a subset of about 2600 relatively bright galaxies on the MipS image with IR fluxes larger than 80 µJy. This sample is dominated by luminous (lirg) and ultra luminous infrared galaxies (ulirg). In the wavelength range from 8 to 1000 µm these galaxies have luminosities between 10 11 and 10 12 solar luminosities or more. The newly analyzed data clearly shows that these two galaxy types were significantly more frequent in the past, and that they provided the major part of the total luminosity density in the infrared range (Fig. II.7.4). At a redshift of z � 1 lirgs (pictured in orange in the figure) contribute about 70 percent of the infrared radiation, while Ulirgs (red) contribute about ten percent. Subsequently, the number of lirgs and ulirgs has strongly decreased, and about five billion years ago (z � 0.5), low-luminosity galaxies (blue) started to dominate the IR luminosity density – these are actually close to »normal« spirals galaxies. On the whole, the density of galaxies with IR luminosities higher than 10 11 solar luminosities has decreased by more than a factor of 100 over the last eight billion years, with a particularly strong decline of ulirgs. This suggests that these galaxies extremely rich in dust with high star formation rates were much more frequent in an earlier era of the Universe (z � 1) than at z � 1. II.7 Observations of Distant Galaxies with Spitzer 45 They may be responsible for the peak of the cosmic star formation rate at redshifts between 2 and 3. Further evidence that the fraction of dust-rich galaxies was much larger in the past is also indicated by the fact that IR luminosity density decreases with the redshift raised to almost the fourth power. Over the same period of time, the UV density (the direct stellar radiation not absorbed by dust) has decreased with the redshift raised to only the second power. Thus the new IR images obtained with the Spitzer telescope allowed astronomers to study the evolution of cosmic star formation over the last eight billion years in detail. The accuracy of the results crucially depends on the calculation of the overall luminosities from a few observed spectral data points. Therefore observations in the mid- and far-infrared range (e.g. with herSChel) as well as in the submillimeter and millimeter range (with alMa) will yield more accurate results in the future. (Eric F. Bell, Xianzhong Zheng, Hans-Walter Rix. Participating institutes: Steward Observatory, Tucson; Observatoire de Paris-Meudon; Institut d�Astrophysique Spatiale, Paris; Instituto de Estructura de la Materia, Madrid; Space Science Institute, Boulder; National Optical Astronomy Observatory, Tucson)
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Page 5: Contents Preface ..................
Page 8 and 9: 6 I. General I.1 Scientific Goals U
Page 10 and 11: 8 I. General massive protostars and
Page 12 and 13: 10 I. General achieve higher angula
Page 14 and 15: 12 I. General The institute is co-l
Page 16 and 17: 14 I. General Point Source sensitiv
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Page 20 and 21: 18 II. Highlights II.1 Light Echoes
Page 22 and 23: 20 II. Highlights 10 arcsec Fig. II
Page 24 and 25: 22 II. Highlights AB Dor C AB Dor A
Page 26 and 27: 24 II. Highlights II.3 The First He
Page 28 and 29: 26 II. Highlights II.4 Planetesimal
Page 30 and 31: 28 II. Highlights azimuthal directi
Page 32 and 33: 30 II. Highlights ticles fall faste
Page 34 and 35: 32 II. Highlights ANTU Seyfert 2 ga
Page 36 and 37: 34 II. Highlights cretion disk, one
Page 38 and 39: 36 II. Highlights 8.5 �m 2.3 ly 0
Page 40 and 41: 38 II. Highlights II.6 Massive Star
Page 42 and 43: 40 II. Highlights log M� /pc2 �
Page 44 and 45: 42 II. Highlights II.7 Observations
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Page 52 and 53: 50 III. Selected Research Areas III
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144 Staff Directors: Henning (Actin
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148 Cooperation with industrial Fir
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150 Conferences Conferences and Mee
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152 Conferences D. Lemke: JWST-miri
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156 Publications Szalay, I. Szapudi
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160 Publications Brinkmann, D. G. Y
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162 Publications Zheng, X. Z., F. H
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The Max Planck Society The Max Plan
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Max Planck Institute for Astronomy - Annual Report 2005

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