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.

Photohadronic origin of $\boldsymbol {\gamma }$-ray BL Lac emission: implications for IceCube neutrinos

Abstract: The recent IceCube discovery of 0.1-1 PeV neutrinos of astrophysical origin opens up a new era for high-energy astrophysics. Although there are various astrophysical candidate sources, a firm association of the detected neutrinos with one (or more) of them is still lacking. A recent analysis of plausible astrophysical counterparts within the error circles of IceCube events showed that likely counterparts for nine of the IceCube neutrinos include mostly BL Lacs, among which Mrk 421. Motivated by this result and a previous independent analysis on the neutrino emission from Mrk 421, we test the BL Lac-neutrino connection in the context of a specific theoretical model for BL Lac emission. We model the spectral energy distribution (SED) of the BL Lacs selected as counterparts of the IceCube neutrinos using a one-zone leptohadronic model and mostly nearly simultaneous data. The neutrino flux for each BL Lac is self-consistently calculated, using photon and proton distributions specifically derived for every individual source. We find that the SEDs of the sample, although different in shape and flux, are all well fitted by the model using reasonable parameter values. Moreover, the model-predicted neutrino flux and energy for these sources are of the same order of magnitude as those of the IceCube neutrinos. In two cases, namely Mrk 421 and H 1914-194, we find a suggestively good agreement between the model prediction and the detected neutrino flux. Our predictions for all the BL Lacs of the sample are in the range to be confirmed or disputed by IceCube in the next few years of data sampling.

Molecular gas kinematics within the central 250 pc of the Milky Way

Abstract: Using spectral-line observations of HNCO, N2H+, and HNC, we investigate the kinematics of dense gas in the central ~250 pc of the Galaxy. We present SCOUSE (Semi-automated multi-COmponent Universal Spectral-line fitting Engine), a line fitting algorithm designed to analyse large volumes of spectral-line data efficiently and systematically. Unlike techniques which do not account for complex line profiles, SCOUSE accurately describes the {l, b, v_LSR} distribution of CMZ gas, which is asymmetric about Sgr A* in both position and velocity. Velocity dispersions range from 2.6 km/s 28. The gas is distributed throughout several "streams", with projected lengths ~100-250 pc. We link the streams to individual clouds and sub-regions, including Sgr C, the 20 and 50 km/s clouds, the dust ridge, and Sgr B2. Shell-like emission features can be explained by the projection of independent molecular clouds in Sgr C and the newly identified conical profile of Sgr B2 in {l ,b, v_LSR} space. These features have previously invoked supernova-driven shells and cloud-cloud collisions as explanations. We instead caution against structure identification in velocity-integrated emission maps. Three geometries describing the 3-D structure of the CMZ are investigated: i) two spiral arms; ii) a closed elliptical orbit; iii) an open stream. While two spiral arms and an open stream qualitatively reproduce the gas distribution, the most recent parameterisation of the closed elliptical orbit does not. Finally, we discuss how proper motion measurements of masers can distinguish between these geometries, and suggest that this effort should be focused on the 20 km/s and 50 km/s clouds and Sgr C.

The MiMeS survey of Magnetism in Massive Stars : magnetic analysis of the O-type stars

Abstract: We present the analysis performed on spectropolarimetric data of 97 O-type targets included in the framework of the Magnetism in Massive Stars (MiMeS) Survey Mean least-squares deconvolved Stokes I and V line profiles were extracted for each observation, from which we measured the radial velocity, rotational and non-rotational broadening velocities, and longitudinal magnetic field Bl The investigation of the Stokes I profiles led to the discovery of two new multiline spectroscopic systems (HD 46106, HD 204827) and confirmed the presence of a suspected companion in HD 37041 We present a modified strategy of the least-squares deconvolution technique aimed at optimizing the detection of magnetic signatures while minimizing the detection of spurious signatures in Stokes V Using this analysis, we confirm the detection of a magnetic field in six targets previously reported as magnetic by the MiMeS collaboration (HD 108, HD 47129A2, HD 57682, HD 148937, CPD-28 2561, and NGC 1624-2), as well as report the presence of signal in Stokes V in three new magnetic candidates (HD 36486, HD 162978, and HD 199579) Overall, we find a magnetic incidence rate of 7 ± 3 per cent, for 108 individual O stars (including all O-type components part of multiline systems), with a median uncertainty of the Bl measurements of about 50 G An inspection of the data reveals no obvious biases affecting the incidence rate or the preference for detecting magnetic signatures in the magnetic stars Similar to A- and B-type stars, we find no link between the stars’ physical properties (eg Teff, mass, and age) and the presence of a magnetic field However, the Of?p stars represent a distinct class of magnetic O-type stars

The Peculiar Type II Supernova 1997D: A Case for a Very Low 56Ni Mass

Abstract: SN 1997D in NGC 1536 is possibly the least luminous and energetic Type II supernova discovered to date. The entire light curve is subluminous, never reaching MV=-14.65. The radioactive tail follows the 56Co decay slope. In the case of a nearly complete trapping of the γ-rays, the 56Ni mass derived from the tail brightness is extremely small, ~0.002 M☉. At discovery, the spectra showed a red continuum and line velocities on the order of 1000 km s−1. The luminosity and the photospheric expansion velocity suggest that the explosion occurred about 50 days before discovery and that a plateau probably followed. Model light curves and spectra of the explosion of a 26 M☉ star successfully fitted the observations. Low-mass models are inconsistent with the observations. The radius of the progenitor, constrained by the prediscovery upper limits, is R0 300 R☉. A low explosion energy of ~4 × 1050 ergs is then required in the modeling. The strong Ba II lines in the photospheric spectra are reproduced with a solar abundance and low Teff. A scenario in which the low 56Ni mass observed in SN 1997D is due to fallback of material onto the collapsed remnant of the explosion of a 25-40 M☉ star appears to be favored over the case of the explosion of an 8-10 M☉ star with low 56Ni production.

A Wide Area Survey for High-Redshift Massive Galaxies. I. Number Counts and Clustering of BzKs and EROs

Abstract: We present the results of a deep, wide area, optical and near-IR survey of massive high-redshift galaxies. The Suprime-Cam on the Subaru telescope was used to obtain BRIz' imaging over 2 × 940 arcmin2 fields, while JKs imaging was provided by the SOFI camera at the New Technology Telescope (NTT) for a subset of the area, partly from the EIS. In this paper, we report on the properties of K-band-selected galaxies, identified from a total area of ~920 arcmin2 to KVega = 19, of which 320 arcmin2 are complete to KVega = 20. The BzK selection technique was used to assemble complete samples of about 500 candidate massive star-forming galaxies (sBzKs) and about 160 candidate massive passively evolving galaxies (pBzKs) at 1.4 z 2.5; and the (R - K)Vega > 5 color criterion was used to assemble a sample of about 850 extremely red objects (EROs). We accurately measure surface densities of 1.20 ± 0.05 and 0.38 ± 0.03 arcmin-2 for the sBzKs and the pBzKs, respectively. Both sBzKs and pBzKs are strongly clustered, at a level at least comparable to that of EROs, with pBzKs appearing more clustered than sBzKs. We estimate the reddening, star formation rates (SFRs), and stellar masses (M*) for the ensemble of sBzKs, confirming that to KVega ~ 20 typical (median) values are M* ~ 1011 M☉, SFR ~ 190 M☉ yr-1, and E(B - V) ~ 0.44. A correlation is detected such that the most massive galaxies at z ~ 2 are also the most actively star-forming, an effect that can be seen as a manifestation of downsizing at early epochs. The space density of massive pBzKs at z ~ 1.4-2 that we derive is 20% ± 7% that of similarly massive early-type galaxies at z ~ 0. Adding this space density to that of our massive star-forming class, sBzKs, in the same redshift range produces a closer comparison with the local early-type galaxy population, naturally implying that we are detecting star formation in a sizable fraction of massive galaxies at z > 1.4, which has been quenched by the present day. Follow-up optical and near-infrared spectroscopy is in progress at the ESO Very Large Telescope (VLT) and at the Subaru telescope in order to elucidate more thoroughly the formation and evolution of massive galaxies.