European Southern Observatory

About: European Southern Observatory is a facility organization based out in Garching bei München, Germany. It is known for research contribution in the topics: Galaxy & Stars. The organization has 3594 authors who have published 16157 publications receiving 823095 citations. The organization is also known as: The European Southern Observatory，ESO & ESO.

Timescale stretch parameterization of Type Ia supernova B-band light curves

Abstract: R-band intensity measurements along the light curve of Type Ia supernovae discovered by the Cosmology Project (SCP) are fitted in brightness to templates allowing a free parameter the time-axis width factor w identically equal to s times (1+z). The data points are then individually aligned in the time-axis, normalized and K-corrected back to the rest frame, after which the nearly 1300 normalized intensity measurements are found to lie on a well-determined common rest-frame B-band curve which we call the composite curve. The same procedure is applied to 18 low-redshift Calan/Tololo SNe with Z < 0.11; these nearly 300 B-band photometry points are found to lie on the composite curve equally well. The SCP search technique produces several measurements before maximum light for each supernova. We demonstrate that the linear stretch factor, s, which parameterizes the light-curve timescale appears independent of z, and applies equally well to the declining and rising parts of the light curve. In fact, the B band template that best fits this composite curve fits the individual supernova photometry data when stretched by a factor s with chi 2/DoF ~;~; 1, thus as well as any parameterization can, given the current data sets. The measurement of the data of explosion, however, is model dependent and not tightly constrained by the current data. We also demonstrate the 1 + z light-cure time-axis broadening expected from cosmological expansion. This argues strongly against alternative explanations, such as tired light, for the redshift of distant objects.

The Space Density of Compton-Thick Active Galactic Nucleus and the X-Ray Background

Abstract: We constrain the number density and evolution of Compton-thick (CT) active galactic nuclei (AGNs). In the local universe, we use the wide-area surveys from the Swift and INTEGRAL satellites, while for high redshifts we explore candidate selections based on a combination of X-ray and mid-infrared (mid-IR) parameters. We find a significantly lower space density of CT AGNs in the local universe than expected from published AGN population synthesis models to explain the X-ray background (XRB). This can be explained by the numerous degeneracies in the parameters of those models; we use the high-energy surveys described here to remove those degeneracies. We show that only direct observations of CT AGNs can currently constrain the number of heavily obscured supermassive black holes. At high redshift, the inclusion of IR-selected CT AGN candidates leads to a much higher space density, implying (1) a different (steeper) evolution for these sources compared to less-obscured AGNs, (2) that the IR selection includes a large number of interlopers, and/or (3) that there is a large number of reflection-dominated AGNs missed in the INTEGRAL and Swift observations. The contribution of CT AGN to the XRB is small, ~9%, with a comparable contribution to the total cosmic accretion, unless reflection-dominated CT AGNs significantly outnumber transmission-dominated CT AGNs, in which case their contribution can be much higher. Using estimates derived here for the accretion luminosity over cosmic time, we estimate the local mass density in supermassive black holes and find a good agreement with available constraints for an accretion efficiency of ~10%. Transmission-dominated CT AGNs contribute only ~8% to total black hole growth.

Cluster-formation in the Rosette molecular cloud at the junctions of filaments

Abstract: For many years feedback processes generated by OB-stars in molecular clouds, including expanding ionization fronts, stellar winds, or UV-radiation, have been proposed to trigger subsequent star formation. However, hydrodynamic models including radiation and gravity show that UV-illumination has little or no impact on the global dynamical evolution of the cloud. The Rosette molecular cloud, irradiated by the NGC2244 cluster, is a template region for triggered star-formation, and we investigated its spatial and density structure by applying a curvelet analysis, a filament-tracing algorithm (DisPerSE), and probability density functions (PDFs) on Herschel column density maps, obtained within the HOBYS key program. The analysis reveals not only the filamentary structure of the cloud but also that all known infrared clusters except one lie at junctions of filaments, as predicted by turbulence simulations. The PDFs of sub-regions in the cloud show systematic differences. The two UV-exposed regions have a double-peaked PDF we interprete as caused by shock compression. The deviations of the PDF from the log-normal shape typically associated with low- and high-mass star-forming regions at Av~3-4m and 8-10m, respectively, are found here within the very same cloud. This shows that there is no fundamental difference in the density structure of low- and high-mass star-forming regions. We conclude that star-formation in Rosette - and probably in high-mass star-forming clouds in general - is not globally triggered by the impact of UV-radiation. Moreover, star formation takes place in filaments that arose from the primordial turbulent structure built up during the formation of the cloud. Clusters form at filament mergers, but star formation can be locally induced in the direct interaction zone between an expanding HII--region and the molecular cloud.

Protoclusters associated with z > 2 radio galaxies - I. Characteristics of high redshift protoclusters

Abstract: We present the results of a large program conducted with the Very Large Telescope and augmented by observations with the Keck telescope to search for forming clusters of galaxies near powerful radio galaxies at $2.0 α emitting galaxies in ~$3\times3$ Mpc 2 areas near the radio galaxies. A total of 300 candidate emitters were found with a rest-frame Ly α equivalent width of EW $_0 > 15$ A and significance $\Sigma \equiv {\it EW}_0/\Delta {\it EW}_0 > 3$. Follow-up spectroscopy was performed on 152 candidates in seven of the radio galaxy fields. Of these, 139 were confirmed to be Ly α emitters, four were low redshift interlopers and nine were non-detections. With the adopted criteria the success rate is $139/152 = 91$%. In addition, 14 objects with EW $_0 α emitters. Combined with the 15 Ly α emitters near MRC 1138-262, we have determined Ly α redshifts for 168 objects near eight radio galaxies. At least six of our eight fields are overdense in Ly α emitters by a factor 3-5 as compared to the field density of Ly α emitters at similar redshifts, although the statistics in our highest redshift field ($z = 5.2$) are poor. Also, the emitters show significant clustering in velocity space. In the overdense fields, the width of the velocity distributions of the emitters is a factor 2-5 smaller than the width of the narrow-band filters. Taken together, we conclude that we have discovered six forming clusters of galaxies (protoclusters). We estimate that roughly 75% of powerful ($L_\mathrm{2.7\,GHz} > 10^{33}$ erg s -1 Hz -1 sr -1 ) high redshift radio galaxies reside in a protocluster. The protoclusters have sizes of at least 1.75 Mpc, which is consistent with the structure sizes found by other groups. By using the volume occupied by the overdensities and assuming a bias parameter of $b=3{-}6$, we estimate that the protoclusters have masses in the range $2{-}9 \times 10^{14}$ $M_{\odot}$. These protoclusters are likely to be progenitors of present-day (massive) clusters of galaxies. For the first time, we have been able to estimate the velocity dispersion of cluster progenitors from $z\sim5$ to ~2. The velocity dispersion of the emitters increases with cosmic time, in agreement with the dark matter velocity dispersion in numerical simulations of forming massive clusters.

Active galactic nuclei: what’s in a name?

Abstract: Active galactic nuclei (AGN) are energetic astrophysical sources powered by accretion onto supermassive black holes in galaxies, and present unique observational signatures that cover the full electromagnetic spectrum over more than twenty orders of magnitude in frequency. The rich phenomenology of AGN has resulted in a large number of different “flavours” in the literature that now comprise a complex and confusing AGN “zoo”. It is increasingly clear that these classifications are only partially related to intrinsic differences between AGN and primarily reflect variations in a relatively small number of astrophysical parameters as well the method by which each class of AGN is selected. Taken together, observations in different electromagnetic bands as well as variations over time provide complementary windows on the physics of different sub-structures in the AGN. In this review, we present an overview of AGN multi-wavelength properties with the aim of painting their “big picture” through observations in each electromagnetic band from radio to $$\gamma $$ -rays as well as AGN variability. We address what we can learn from each observational method, the impact of selection effects, the physics behind the emission at each wavelength, and the potential for future studies. To conclude, we use these observations to piece together the basic architecture of AGN, discuss our current understanding of unification models, and highlight some open questions that present opportunities for future observational and theoretical progress.