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.

Isocam-Cvf 5-12 Micron Spectroscopy of Ultraluminous Infrared Galaxies

Abstract: We present low-resolution mid-infrared (MIR) spectra of 16 ultraluminous infrared galaxies (ULIRGs) obtained with the circular variable filter (CVF) spectroscopy mode of ISOCAM on board the Infrared Space Observatory (ISO). Our sample completes previous ISO spectroscopy of ultra- and hyperluminous infrared galaxies toward higher luminosities. The combined samples cover an infrared luminosity range of ~1012-1013.1 L☉. To discriminate active galactic nucleus (AGN) and starburst activity, we use the AGN-related MIR continuum and the starburst-related 6.2, 7.7, 8.6, and 11.3 μm MIR emission bands attributed to aromatic carbonaceous material. For about half of the high-luminosity ULIRGs studied here, strong aromatic emission bands suggest starburst dominance. Other spectra are dominated by a strong AGN-related continuum with weak superposed emission features of uncertain nature. Our sample contains one unusual example, IRAS F00183-7111, of an AGN that is highly obscured even in the MIR. An improved method to characterize quantitatively the relative contribution of star formation and AGN activity to the MIR emission of ULIRGs is presented. The ULIRG spectra are fitted by a superposition of a starburst and an AGN spectrum, both of which may be obscured at different levels. Models in which starburst and AGN obscuration differ are significantly more successful than models with a single extinction. Previous results based on a simpler line-to-continuum measure of aromatic emission strength are confirmed, further supporting the robustness of the aromatic emission feature as a diagnostic of ULIRG power sources. As dominant sources of the bolometric luminosity, starbursts prevail at the lower end and AGNs at the higher end of this range. The transition between mostly starburst and mostly AGN powered occurs at ~1012.4-1012.5 L☉, and individual luminous starbursts are found up to ~1012.65 L☉.

The dust scaling relations of the Herschel Reference Survey

Abstract: We combine new Herschel/SPIRE sub-millimeter observations with existing multiwavelength data to investigate the dust scaling relations of the Herschel Reference Survey, a magnitude-, volume-limited sample of similar to 300 nearby galaxies in different environments. We show that the dust-to-stellar mass ratio anti-correlates with stellar mass, stellar mass surface density and NUV - r colour across the whole range of parameters covered by our sample. Moreover, the dust-to-stellar mass ratio decreases significantly when moving from late-to early-type galaxies. These scaling relations are similar to those observed for the Hi gas-fraction, supporting the idea that the cold dust is tightly coupled to the cold atomic gas component in the interstellar medium. We also find a weak increase of the dust-to-Hi mass ratio with stellar mass and colour but no trend is seen with stellar mass surface density. By comparing galaxies in different environments we show that, although these scaling relations are followed by both cluster and field galaxies, Hi-deficient systems have, at fixed stellar mass, stellar mass surface density and morphological type systematically lower dust-to-stellar mass and higher dust-to-Hi mass ratios than Hi-normal/field galaxies. This provides clear evidence that dust is removed from the star-forming disk of cluster galaxies but the effect of the environment is less strong than what is observed in the case of the Hi disk. Such effects naturally arise if the dust disk is less extended than the Hi and follows more closely the distribution of the molecular gas phase, i.e., if the dust-to-atomic gas ratio monotonically decreases with distance from the galactic center.

A spectroscopic survey of Herbig Ae/Be stars with X-shooter – I. Stellar parameters and accretion rates

Abstract: Herbig Ae/Be stars (HAeBes) span a key mass range that links low- and high-mass stars, and thus provide an ideal window from which to explore their formation. This paper presents Very Large Telescope/X-shooter spectra of 91 HAeBes, the largest spectroscopic study of HAeBe accretion to date. A homogeneous approach to determining stellar parameters is undertaken for the majority of the sample. Measurements of the ultraviolet are modelled within the context of magnetospheric accretion, allowing a direct determination of mass accretion rates. Multiple correlations are observed across the sample between accretion and stellar properties: the youngest and often most massive stars are the strongest accretors, and there is an almost 1:1 relationship between the accretion luminosity and stellar luminosity. Despite these overall trends of increased accretion rates in HAeBes when compared to classical T Tauri stars, we also find noticeable differences in correlations when considering the Herbig Ae and Herbig Be subsets. This, combined with the difficulty in applying a magnetospheric accretion model to some of the Herbig Be stars, could suggest that another form of accretion may be occurring within Herbig Be mass range.

Dust Filaments and Star Formation in OMC-2 and OMC-3

Abstract: We have mapped the 1300 μm dust emission of a 6' × 16' field in the OMC-2 and -3 region and detected an extended filamentary structure with at least 11 embedded condensations in OMC-2 and 10 in OMC-3. Six have been observed previously at 1300 μm, and two were also detected by IRAS. We observed eight of the new sources at six wave bands from 350 to 2000 μm and derived upper limits for their far-infrared (FIR) emission from the IRAS raw data. The millimeter/submillimeter emission originates from cold dust (Td ~ 20 K), and the individual components have gas masses of 5 M☉ < Mgas < 36 M☉. The ratio Lbol/Lsmm is below 70 for six sources associated with OMC-3, indicating that they are class 0-type objects. Condensations in the OMC-2 region have Lbol/Lsmm ≤ 360, suggesting an evolutionary effect from north to south. We report the discovery of a highly collimated bipolar CO outflow, most likely driven by the source OMC-3 MMS 8. The flow is over 5' (0.7 pc) long and less than 1' (0.15 pc) wide and is oriented nearly east-west. Less prominent outflows are associated with OMC-2 FIR 2/3 and OMC-3 MMS 6. The 1300 μm continuum emission is confined to a ridge less than 1' wide while the emission in J = 2-113CO, C18O, and CS is between 5' and 10' wide. The continuum emission is displaced toward the eastern side of the molecular ridge that contains it. Most 1300 μm sources lie in or close to line emission peaks. However, not all line emission peaks contain prominent 1300 μm continuum sources. The curved filamentary structure of the large-scale dust and molecular emission is likely the result of compression by the superbubble centered ~25-70 pc further north, plus the impact of energy from the younger 1c subgroup of the Orion OB association, which lies 10-50 pc in front of our mapped region, and by the very recent expansion of the NGC 1977 and M42 H II regions.

A census of star-forming galaxies in the z ∼ 9-10 universe based on hst+spitzer observations over 19 clash clusters: three candidate z ∼ 9-10 galaxies and improved constraints on the star formation rate density at z ∼ 9.2*

Abstract: We utilise a two-color Lyman-Break selection criterion to search for z � 9-10 galaxies over the first 19 clusters in the CLASH program. Key to this search are deep observations over our clusters in five near-IR passbands to 1.6µm, allowing us good constraints on the position of the Lyman break to z � 10. A systematic search yields three z � 9-10 candidates in total above a 6� detection limit. While we have already reported the most robust of these candidates, MACS1149-JD, in a previous publication, two additional z � 9 candidates are also revealed in our expanded search. The new candidates have H160-band AB magnitudes of �26.2-26.9 and are located behind MACSJ1115.9+0129 and MACSJ1720.3+3536. The observed H160 Spitzer/IRAC colors for the sources are sufficiently blue to strongly favor redshifts of z � 9 for these sources. A careful assessment of various sources of contamination suggests .1 contaminants for our z � 9-10 selection. To determine the implications of these search results for the LF and SFR density at z � 9, we introduce a new differential approach to deriving these quantities in lensing fields. Our procedure is to derive the evolution by comparing the number of z � 9-10 galaxy candidates found in CLASH with the number of galaxies in a slightly lower redshift sample (after correcting for the differences in selection volumes), here taken to be z � 8. This procedure takes advantage of the fact that the relative selection volumes available for the z � 8 and z � 9-10 selections behind lensing clusters are not greatly dependent on the details of the gravitational lensing models. We find that the normalization of the UV LF at z � 9 is just 0.22 +0.30 −0.15 × that at z � 8, �2 +31× lower than what we would infer extrapolating z � 4-8 LF results. These results therefore suggest a more rapid evolution in the UV LF at z > 8 than seen at lower redshifts (although the current evidence here is weak). Compared to similar evolutionary findings from the HUDF, our result is much more insensitive to large-scale structure uncertainties, given our many independent sightlines on the high-redshift universe. Subject headings: galaxies: evolution — galaxies: high-redshift