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 Gemini NICI Planet-Finding Campaign: The Frequency of Giant Planets around Young B and A Stars

Abstract: We have carried out high contrast imaging of 70 young, nearby B and A stars to search for brown dwarf and planetary companions as part of the Gemini NICI Planet-Finding Campaign. Our survey represents the largest, deepest survey for planets around high-mass stars (1.5-2.5 M ☉) conducted to date and includes the planet hosts β Pic and Fomalhaut. We obtained follow-up astrometry of all candidate companions within 400 AU projected separation for stars in uncrowded fields and identified new low-mass companions to HD 1160 and HIP 79797. We have found that the previously known young brown dwarf companion to HIP 79797 is itself a tight (3 AU) binary, composed of brown dwarfs with masses 58 M Jup and 55 M Jup, making this system one of the rare substellar binaries in orbit around a star. Considering the contrast limits of our NICI data and the fact that we did not detect any planets, we use high-fidelity Monte Carlo simulations to show that fewer than 20% of 2 M ☉ stars can have giant planets greater than 4 M Jup between 59 and 460 AU at 95% confidence, and fewer than 10% of these stars can have a planet more massive than 10 M Jup between 38 and 650 AU. Overall, we find that large-separation giant planets are not common around B and A stars: fewer than 10% of B and A stars can have an analog to the HR 8799 b (7 M Jup, 68 AU) planet at 95% confidence. We also describe a new Bayesian technique for determining the ages of field B and A stars from photometry and theoretical isochrones. Our method produces more plausible ages for high-mass stars than previous age-dating techniques, which tend to underestimate stellar ages and their uncertainties.

Cluster versus Field Elliptical Galaxies and Clues on Their Formation

Abstract: Using new observations for a sample of 931 early-type galaxies, we investigate whether the Mg2-σ0 relation shows any dependence on the local environment. The galaxies have been assigned to three different environments depending on the local overdensity (clusters, groups, and field); we used our complete redshift database to guide the assignment of galaxies. It is found that cluster, group, and field early-type galaxies follow almost identical Mg2-σ0 relations, with the largest Mg2 zero-point difference (clusters minus field) being only 0.007±0.002 mag. No correlation of the residuals is found with the morphological type or the bulge-to-disk ratio. Using stellar population models in a differential fashion, this small zero-point difference implies a luminosity-weighted age difference of only ~1 Gyr between the corresponding stellar populations, with field galaxies being younger. The mass-weighted age difference could be significantly smaller if minor events of late star formation took place preferentially in field galaxies. We combine these results with the existing evidence for the bulk of stars in cluster early-type galaxies having formed at very high redshift and conclude that the bulk of stars in galactic spheroids had to form at high redshifts (z3), no matter whether such spheroids now reside in low- or high-density regions. The cosmological implications of these findings are briefly discussed.

Star formation relations and co spectral line energy distributions across the J-ladder and redshift

Abstract: We present FIR [50-300 mu m]-CO luminosity relations (i.e., log L-FIR = alpha log L'(CO) + beta) for the full CO rotational ladder from J = 1-0 up to J = 13-12 for a sample of 62 local (z 10(11) L-circle dot) using data from Herschel SPIRE-FTS and ground-based telescopes. We extend our sample to high redshifts (z > 1) by including 35 submillimeter selected dusty star forming galaxies from the literature with robust CO observations, and sufficiently well-sampled FIR/submillimeter spectral energy distributions (SEDs), so that accurate FIR luminosities can be determined. The addition of luminous starbursts at high redshifts enlarge the range of the FIR-CO luminosity relations toward the high-IR-luminosity end, while also significantly increasing the small amount of mid-J/high-J CO line data (J = 5-4 and higher) that was available prior to Herschel. This new data set (both in terms of IR luminosity and J-ladder) reveals linear FIR-CO luminosity relations (i.e., a similar or equal to 1) for J = 1-0 up to J = 5-4, with a nearly constant normalization (beta similar to 2). In the simplest physical scenario, this is expected from the (also) linear FIR-(molecular line) relations recently found for the dense gas tracer lines (HCN and CS), as long as the dense gas mass fraction does not vary strongly within our (merger/starburst)-dominated sample. However, from J = 6-5 and up to the J = 13-12 transition, we find an increasingly sublinear slope and higher normalization constant with increasing J. We argue that these are caused by a warm (similar to 100 K) and dense (>10(4) cm(-3)) gas component whose thermal state is unlikely to be maintained by star-formation-powered far-UV radiation fields (and thus is no longer directly tied to the star formation rate). We suggest that mechanical heating (e.g., supernova-driven turbulence and shocks), and not cosmic rays, is the more likely source of energy for this component. The global CO spectral line energy distributions, which remain highly excited from J = 6-5 up to J = 13-12, are found to be a generic feature of the (U)LIRGs in our sample, and further support the presence of this gas component.

A homogeneous sample of sub-damped Lyman α systems — III. Total gas mass ΩH i+He ii at z > 2⋆

Abstract: Absorbers seen in the spectrum of background quasars are a unique tool with which to select H I-rich galaxies at all redshifts. In turns, these galaxies allow us to determine the cosmologi- cal evolution of the H I gasH I+He II, which is a possible indicator of gas consumption as star formation proceeds. The damped Lyman α (Lyα) systems (DLAs with N H I 10 20.3 cm −2 ), in particular, are believed to contain a large fraction of the H I gas but there are also indica- tions that lower column-density systems, called 'sub-damped Lyα' systems, play a role at high redshift. Here we present the discovery of high-redshift sub-DLAs based on 17 z > 4 quasar spectra observed with the Ultraviolet-Visual Echelle Spectrograph (UVES) on the Very Large Telescope (VLT). This sample is composed of 21 new sub-DLAs which, together with another 10 systems from previous European Southern Observatory archive studies, make up a homo- geneous sample. The redshift evolution of the number density of several classes of absorbers is derived and shows that all systems seem to be evolving in the redshift range from z = 5 to z ∼ 3. These results are further used to estimate the redshift evolution of the characteristic radius of these classes of absorbers, assuming a Holmberg relation and one unique underlying parent population. DLAs are found to have R ∗ ∼ 20 h −1 kpc, while sub-DLAs have R ∗ ∼ 40 h −1 kpc. The redshift evolution of the column density distribution, f(N,z), down to N H I = 10 19 cm −2 is also presented. A departure from a power law due to a flattening of f(N,z) in the sub-DLA regime is present in the data. f(N,z) is further used to determine the H I gas mass contained in sub-DLAs at z > 2. The complete sample shows that sub-DLAs are important at all redshifts from z = 5t oz = 2. Finally, the possibility that sub-DLAs are less affected by the effects of dust obscuration than classical DLAs is discussed. Ke yw ords: galaxies: abundances - galaxies: high-redshift - quasars: absorption lines - quasars: general.

Galaxies in X-Ray Groups. I. Robust Membership Assignment and the Impact of Group Environments on Quenching

Abstract: Understanding the mechanisms that lead dense environments to host galaxies with redder colors, more spheroidal morphologies, and lower star formation rates than field populations remains an important problem. As most candidate processes ultimately depend on host halo mass, accurate characterizations of the local environment, ideally tied to halo mass estimates and spanning a range in halo mass and redshift, are needed. In this work, we present and test a rigorous, probabilistic method for assigning galaxies to groups based on precise photometric redshifts and X-ray-selected groups drawn from the COSMOS field. The groups have masses in the range 10^(13) ≾ M_(200c)/M_☉ ≾ 10^(14) and span redshifts 0 < z < 1. We characterize our selection algorithm via tests on spectroscopic subsamples, including new data obtained at the Very Large Telescope, and by applying our method to detailed mock catalogs. We find that our group member galaxy sample has a purity of 84% and completeness of 92% within 0.5R_(200c). We measure the impact of uncertainties in redshifts and group centering on the quality of the member selection with simulations based on current data as well as future imaging and spectroscopic surveys. As a first application of our new group member catalog which will be made publicly available, we show that member galaxies exhibit a higher quenched fraction compared to the field at fixed stellar mass out to z ~ 1, indicating a significant relationship between star formation and environment at group scales. We also address the suggestion that dusty star-forming galaxies in such groups may impact the high-l power spectrum of the cosmic microwave background and find that such a population cannot explain the low power seen in recent Sunyaev-Zel'dovich measurements.