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.

SIMBA survey of southern high-mass star forming regions. I. Physical parameters of the 1.2-mm/IRAS sources

Abstract: We report the results of a 1.2 mm continuum emission survey toward 146 IRAS sources thought to harbour high- mass star forming regions. The sources have FIR colors typical of UCHII regions and were detected in the CS(2 → 1) line survey of Bronfman et al. (1996). Regions of 15 � × 10 � , centered on each IRAS source, were mapped with an angular resolution of ∼24 �� , using the SIMBA array on the SEST telescope. 1.2 mm emission was detected toward all IRAS sources. We find that the dust cores associated with these sources have typical sizes of 0.4 pc and masses of 5 × 10 3 M� . Dust temperatures and luminosities, derived from the SED, are typically 32 K and 2.3 × 10 5 L� .

Explosive Nucleosynthesis in Aspherical Hypernova Explosions and Late-Time Spectra of SN 1998bw

Abstract: Aspherical explosion models for the hypernova (hyperenergetic supernova) SN 1998bw are presented. Nucleosynthesis in aspherical explosions is examined with a two-dimensional hydrodynamical code and a detailed nuclear reaction network. Aspherical explosions lead to a strong α-rich freezeout, thus enhancing the abundance ratios [44Ca, 48Ti, 64Zn/Fe] in the ejecta. The nebular line profiles of the Fe-dominated blend near 5200 A and of [O I] 6300, 6363 A are calculated and compared with the observed late-time spectra of SN 1998bw. Compared with the spherical model, the unusual features of the observed nebular spectra can be better explained if SN 1998bw is a strongly aspherical explosion with a kinetic energy of ~1052 ergs viewed from near the jet direction.

2MASS wide field extinction maps. I. The Pipe nebula

Abstract: Aims We present a 8° x 6°, high resolution extinction map of the Pipe nebula using 45 million stars from the Two Micron All Sky Survey (2MASS) point source catalog Methods The use of NICER (Lombardi & Alves 2001, A&A, 377, 1023), a robust and optimal technique to map the dust column density, allows us to detect a Av = 05 mag extinction at a 3-σ level with a 1 arcmin resolution Results (i) We find for the Pipe nebula a normal reddening law, E(J - H) = (185 ± 015)E(H - K) (ii) We measure the cloud distance using Hipparchos and Tycho parallaxes, and obtain 130 +24 -58 pc This, together with the total estimated mass, 10 4 M ⊙ , makes the Pipe the closest massive cloud complex to Earth (iii) We compare the NICER extinction map to the NANTEN 12 CO observations and derive with unprecedented accuracy the relationship between the near-infrared extinction and the 12 CO column density and hence (indirectly) the 12 CO X-factor, that we estimate to be 291 x 10 20 cm -2 K -1 km -1 s in the range Av ∈ [09, 54] mag (iv) We identify approximately 1500 OH/IR stars located within the Galactic bulge in the direction of the Pipe field This represents a significant increase of the known numbers of such stars in the Galaxy Conclusions Our analysis confirms the power and simplicity of the color excess technique to study molecular clouds The comparison with the NANTEN 12 CO data corroborates the insensitivity of CO observations to low column densities (up to approximately 2 mag in Av), and shows also an irreducible uncertainty in the dust-CO correlation of about 1 mag of visual extinction

Chasing highly obscured QSOs in the COSMOS field

Abstract: A large population of heavily obscured, Compton-thick active galactic nuclei (AGNs) is predicted by AGN synthesis models for the cosmic X-ray background and by the "relic" supermassive black hole mass function measured from local bulges. However, even the deepest X-ray surveys are inefficient to search for these elusive AGNs. Alternative selection criteria, combining mid-infrared with near-infrared, and optical photometry, have instead been successful in pinpointing a large population of Compton-thick AGNs. We take advantage of the deep Chandra and Spitzer coverage of a large area (more than 10 times the area covered by the Chandra deep fields, CDFs) in the Cosmic Evolution Survey (COSMOS) field to extend the search of highly obscured, Compton-thick active nuclei to higher luminosity. These sources have low surface density, and therefore large samples can be provided only through large area surveys, like the COSMOS survey. We analyze the X-ray properties of COSMOS MIPS sources with 24 μm fluxes higher than 550 μJy. For the MIPS sources not directly detected in the Chandra images, we produce stacked images in soft and hard X-rays bands. To estimate the fraction of Compton-thick AGN in the MIPS source population, we compare the observed stacked count rates and hardness ratios to those predicted by detailed Monte Carlo simulations, including both obscured AGN and star-forming galaxies. The volume density of Compton-thick QSOs (log L(2-10 keV) = 44-45 erg s^(–1), or logλL_λ(5.8 μm) = 44.79-46.18 erg s^(–1) for a typical infrared to X-ray luminosity ratio) evaluated in this way is (4.8 ± 1.1) × 10^(–6) Mpc^(–3) in the redshift bin 1.2-2.2. This density is ~44% of all X-ray-selected QSOs in the same redshift and luminosity bin, and it is consistent with the expectation of the most up-to-date AGN synthesis models for the cosmic X-ray background (Gilli et al. 2007). The density of lower luminosity Compton-thick AGNs (log L(2-10 keV) = 43.5-44) at z = 0.7-1.2 is (3.7 ± 1.1) × 10^(–5) Mpc^(–3), corresponding to ~67% of X-ray-selected AGNs. The comparison between the fraction of infrared-selected, Compton-thick AGNs to the X-ray selected, unobscured, and moderately obscured AGNs at high and low luminosity suggests that Compton-thick AGNs follow a luminosity dependence similar to that discovered for Compton-thin AGNs, becoming relatively rarer at high luminosities. We estimate that the fraction of AGNs (unobscured, moderately obscured, and Compton thick) to the total MIPS source population is 49 ± 10%, a value significantly higher than that previously estimated at similar 24 μm fluxes. We discuss how our findings can constrain AGN feedback models.

The 3D structure of the Virgo cluster from H-band Fundamental Plane and Tully—Fisher distance determinations

Abstract: We undertook a surface photometry survey of 200 galaxies in the Virgo cluster (complete to B<14.0 mag) carried out in the near-infrared (NIR) H band. Combining velocity dispersion measurements from the literature with new spectroscopic data for 11 galaxies, we derive distances of 59 early-type galaxies using the Fundamental Plane (FP) method. The distances of another 75 late-type galaxies are determined using the Tully--Fisher (TF) method. For this purpose we use the maximum rotational velocity, as derived from H I spectra from the literature, complemented with new Hα rotation curves of eight highly H I-deficient galaxies. The zero-points of the FP and TF template relations are calibrated assuming the distance modulus of Virgo μ0=31.0, as determined with the Cepheids method. Using these 134 distance determinations (with individual uncertainties of 0.35 mag (TF) and 0.45 mag (FP)) we find that the distance of cluster A, associated with M87, is μ0=30.84 ± 0.06. Cluster B, offset to the south, is found at μ0=31.84 ± 0.10. This subcluster is falling on to A at about 750 km s-1. Clouds W and M are at twice the distance of A. Galaxies on the north-west and south-east of the main cluster A belong to two clouds composed almost exclusively of spiral galaxies with distances consistent with A, but with significantly different velocity distributions, suggesting that they are falling on to cluster A at approximately 770 km s-1 from the far side and at 200 km s-1 from the near side respectively. The mass of Virgo inferred from the peculiar motions induced on its vicinity is consistent with the virial expectation.