[en] One of the most interesting questions concerns the nature of the weakly active nucleus of the Galaxy. Gamma spectroscopy contributes an important share to clarify the problem. Beside the measurement of the 0.511 MeV line arising from positron annihilation from the galactic center, a 1.81 MeV line was found, stemming from the decay of Al²⁶ and subsequent formation of Mg²⁶. A scenario for the processes going on in the galactic center is outlined. (UPO)

[en] Some examples of an optical study of faint IRAS-selected galaxies are presented. Deep, direct CCD images have been obtained for 100 fields. In many cases one or several galaxies with extremely peculiar structure are found at the IRAS positions. Long-slit CCD spectra show emission lines typical for HII and starburst galaxies. Obvious interactions are very common among these objects. Redshifts between 0.01 and 0.24 have been measured in 40 fields. Broad band CCD B and R photometry results in absolute B magnitude M_B of quite normal galaxies between -19 mag and -21 mag. All objects are very powerful in the far infrared, luminosities between 40 μm and 120 μm ranging from 10¹⁰ up to 1.5^.10¹² L. Thus the ratio L_FIR/L_B extends from 1 to extreme values of about 100. Very red regions in the B-R colour maps are supposed to indicate the sites of the far infrared radiation sources

[en] We present Herschel far-infrared (FIR) photometry of 11 quasars at redshift z > 5 that have previously been detected at 1.2 mm. We perform full spectral energy distribution (SED) fits over the wavelength range λ_rest ∼ 0.1-400 μm for those objects with good Herschel detections. These fits reveal the need for an additional FIR component besides the emission from a dusty active galactic nucleus (AGN)-powered torus. This additional FIR component has temperatures of T_FIR ∼ 40-60 K with luminosities of L_8-1000μm ∼ 10¹³ L_☉ (accounting for 25%-60% of the bolometric FIR luminosity). If the FIR dust emission is due to star formation it would suggest star formation rates in excess of 1000 solar masses per year. We show that at long wavelengths (λ_rest ∼> 50 μm) the contribution of the AGN-powered torus emission is negligible. This explains how previous FIR studies of high-redshift quasars that relied on single-component fits to (ground-based) observations at λ_obs ∼> 350 μm reached T_FIR and L_FIR values similar to our complete SED fits. Stacking the Herschel data of four individually undetected sources reveals a significant average signal in the PACS bands but not in SPIRE. The average SED of sources with individual Herschel detections shows a striking surplus in near- and mid-infrared (MIR) emission when compared to common AGN templates. The comparison between two average SEDs (sources with and without individual Herschel detections) matched in the UV/optical indicates that for these objects the strength of the MIR emission may correlate with the strength of the FIR emission

[en] We present spectral energy distributions (SEDs) of 69 QSOs at z > 5, covering a rest frame wavelength range of 0.1 μm to ∼80 μm, and centered on new Spitzer and Herschel observations. The detection rate of the QSOs with Spitzer is very high (97% at λ_rest ≲ 4 μm), but drops toward the Herschel bands with 30% detected in PACS (rest frame mid-infrared) and 15% additionally in the SPIRE (rest frame far-infrared; FIR). We perform multi-component SED fits for Herschel-detected objects and confirm that to match the observed SEDs, a clumpy torus model needs to be complemented by a hot (∼1300 K) component and, in cases with prominent FIR emission, also by a cold (∼50 K) component. In the FIR-detected cases the luminosity of the cold component is of the order of 10¹³ L _☉ which is likely heated by star formation. From the SED fits we also determine that the active galactic nucleus (AGN) dust-to-accretion disk luminosity ratio declines with UV/optical luminosity. Emission from hot (∼1300 K) dust is common in our sample, showing that nuclear dust is ubiquitous in luminous QSOs out to redshift 6. However, about 15% of the objects appear under-luminous in the near infrared compared to their optical emission and seem to be deficient in (but not devoid of) hot dust. Within our full sample, the QSOs detected with Herschel are found at the high luminosity end in L _UV/opt and L _NIR and show low equivalent widths (EWs) in Hα and in Lyα. In the distribution of Hα EWs, as determined from the Spitzer photometry, the high-redshift QSOs show little difference to low-redshift AGN.