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.

The SAURON project - XVI. On the sources of ionization for the gas in elliptical and lenticular galaxies

Abstract: Following our study on the incidence, morphology and kinematics of the ionised gas in early-type galaxies we now address the question of what is powering the observed nebular

Strong-lensing analysis of a1689 from deep advanced camera images

Abstract: We analyze deep multicolor Advanced Camera images of the largest known gravitational lens, A1689. Radial and tangential arcs delineate the critical curves in unprecedented detail, and many small counterimages are found near the center of mass. We construct a flexible light deflection field to predict the appearance and positions of counterimages. The model is refined as new counterimages are identified and incorporated to improve the model, yielding a total of 106 images of 30 multiply lensed background galaxies, spanning a wide redshift range, 1.0 < z < 5.5. The resulting mass map is more circular in projection than the clumpy distribution of cluster galaxies, and the light is more concentrated than the mass within r < 50 kpc h-1. The projected mass profile flattens steadily toward the center with a shallow mean slope of d log ?/d log r -0.55 ? 0.1, over the observed range r < 250 kpc h-1, matching well an NFW profile, but with a relatively high concentration, Cvir = 8.2. A softened isothermal profile (rcore = 20 ? 2'') is not conclusively excluded, illustrating that lensing constrains only projected quantities. Regarding cosmology, we clearly detect the purely geometric increase of bend angles with redshift. The dependence on the cosmological parameters is weak owing to the proximity of A1689, z = 0.18, constraining the locus, ?M + ?? ? 1.2. This consistency with standard cosmology provides independent support for our model, because the redshift information is not required to derive an accurate mass map. Similarly, the relative fluxes of the multiple images are reproduced well by our best-fitting lens model.

High‐precision wavelength calibration of astronomical spectrographs with laser frequency combs

Abstract: We describe a possible new technique for precise wavelength calibration of high-resolutionastronomical spectrographs using femtosecond-pulsed mode-locked lasers controlled by sta-ble oscillators such as atomic clocks. Such ‘frequency combs’ provide a series of narrowmodes which are uniformly spaced according to the laser’s pulse repetition rate and whoseabsolute frequencies are known a priori with relative precision better than 10 −12 . Simula-tions of frequency comb spectra show that the photon-limited wavelength calibration preci-sion achievable with existing echelle spectrographs should be ∼1cms −1 when integrated overa 4000A range. Moreover, comb spectra may be used to accurately characterise distortionsof the wavelength scale introduced by the spectrograph and detector system. The simulationsshow that frequency combs with pulse repetition rates of 5–30GHz are required, given thetypical resolving power of existing and possible future echelle spectrographs. Achieving suchhigh repetition rates, together with the desire to produce all comb modes with uniform inten-sity over the entire optical range, represent the only significant challenges in the design ofa practical system. Frequency comb systems may remove wavelength calibration uncertain-ties from all practical spectroscopic experiments, even those combining data from differenttelescopes over many decades.Key words: instrumentation: spectrographs – instrumentation: detectors – methods: labora-tory – techniques: spectroscopic

Dusty starburst galaxies in the early Universe as revealed by gravitational lensing

Abstract: In the past decade, our understanding of galaxy evolution has been revolutionized by the discovery that luminous, dusty starburst galaxies were 1,000 times more abundant in the early Universe than at present. It has, however, been difficult to measure the complete redshift distribution of these objects, especially at the highest redshifts (z > 4). Here we report a redshift survey at a wavelength of three millimetres, targeting carbon monoxide line emission from the star-forming molecular gas in the direction of extraordinarily bright millimetre-wave-selected sources. High-resolution imaging demonstrates that these sources are strongly gravitationally lensed by foreground galaxies. We detect spectral lines in 23 out of 26 sources and multiple lines in 12 of those 23 sources, from which we obtain robust, unambiguous redshifts. At least 10 of the sources are found to lie at z > 4, indicating that the fraction of dusty starburst galaxies at high redshifts is greater than previously thought. Models of lens geometries in the sample indicate that the background objects are ultra-luminous infrared galaxies, powered by extreme bursts of star formation.

Variations in the Galactic star formation rate and density thresholds for star formation

Abstract: The conversion of gas into stars is a fundamental process in astrophysics and cosmology. Stars are known to form from the gravitational collapse of dense clumps in interstellar molecular clouds, and it has been proposed that the resulting star formation rate is proportional to either the amount of mass above a threshold gas surface density, or the gas volume density. These star formation prescriptions appear to hold in nearby molecular clouds in our Milky Way Galaxy's disc as well as in distant galaxies where the star formation rates are often much larger. The inner 500 pc of our Galaxy, the Central Molecular Zone (CMZ), contains the largest concentration of dense, high-surface density molecular gas in the Milky Way, providing an environment where the validity of star formation prescriptions can be tested. Here, we show that by several measures, the current star formation rate in the CMZ is an order-of-magnitude lower than the rates predicted by the currently accepted prescriptions. In particular, the region 1 degrees several 10(3) cm(-3)) molecular gas - enough to form 1000 Orion-like clusters - but the present-day star formation rate within this gas is only equivalent to that in Orion. In addition to density, another property of molecular clouds must be included in the star formation prescription to predict the star formation rate in a given mass of molecular gas. We discuss which physical mechanisms might be responsible for suppressing star formation in the CMZ.