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 VLT-UVES survey for molecular hydrogen in high-redshift damped Lyman-alpha systems

Abstract: We have searched for molecular hydrogen in damped Lyman-alpha (DLA) and sub-DLA systems at z>1.8 using UVES at the VLT. Out of the 33 systems in our sample, 8 have firm and 2 have tentative detections of associated H2 absorption lines. Considering that 3 detections were already known from past searches, H2 is detected in 13 to 20 percent of the newly-surveyed systems. We report new detections of molecular hydrogen at z=2.087 and 2.595 toward, respectively, Q 1444+014 and Q 0405-443, and also reanalyse the system at z=3.025 toward Q 0347-383. We find that there is a correlation between metallicity and depletion factor in both our sample and also the global population of DLA systems (60 systems in total). The DLA and sub-DLA systems where H2 is detected are usually amongst those having the highest metallicities and the largest depletion factors. Moreover, the individual components where H2 is detected have depletion factors systematically larger than other components in the profiles. In two different systems, one of the H2-detected components even has [Zn/Fe]>=1.4. These are the largest depletion factors ever seen in DLA systems. All this clearly demonstrates the presence of dust in a large fraction of the DLA systems. The mean H2 molecular fraction is generally small in DLA systems and similar to what is observed in the Magellanic Clouds. From 58 to 75 percent of the DLA systems have log f 1000 K) and/or the ionizing flux is enhanced relative to what is observed in our Galaxy.

Suppression of star formation in the galaxy NGC 253 by a starburst-driven molecular wind

Abstract: Observations of the galaxy NGC 253 show that the cool molecular wind from the central starburst region limits star-formation activity and the final stellar content. New interferometric observations from the ALMA radio telescope reveal the central two kiloparsec region of the nearby starburst galaxy NGC 253 in unprecedented detail. Using the new data it is now possible to measure the mass-outflow rate of the starburst system for the first time. By ejecting around nine solar masses per year (three times the mass converted to stars in the same period), the starburst-driven 'superwind' limits the star-formation rate and the number of stars produced in this galaxy. The under-abundance of very massive galaxies1,2 in the Universe is frequently attributed to the effect of galactic winds3,4,5,6. Although ionized galactic winds are readily observable, most of the expelled mass (that is, the total mass flowing out from the nuclear region) is likely to be in atomic7,8 and molecular phases9,10,11 that are cooler than the ionized phases. Expanding molecular shells observed in starburst systems such as NGC 253 (ref. 12) and M 82 (refs 13, 14) may facilitate the entrainment of molecular gas in the wind. Although shell properties are well constrained12, determining the amount of outflowing gas emerging from such shells and the connection between this gas and the ionized wind requires spatial resolution better than 100 parsecs coupled with sensitivity to a wide range of spatial scales, a combination hitherto not available. Here we report observations of NGC 253, a nearby15 starburst galaxy (distance ∼ 3.4 megaparsecs) known to possess a wind16,17,18,19,20, that trace the cool molecular wind at 50-parsec resolution. At this resolution, the extraplanar molecular gas closely tracks the Hα filaments, and it appears to be connected to expanding molecular shells located in the starburst region. These observations allow us to determine that the molecular outflow rate is greater than 3 solar masses per year and probably about 9 solar masses per year. This implies a ratio of mass-outflow rate to star-formation rate of at least 1, and probably ∼3, indicating that the starburst-driven wind limits the star-formation activity and the final stellar content.

The Millennium Galaxy Catalogue : morphological classification and bimodality in the colour-concentration plane

Abstract: Using 10095 galaxies (B < 20 mag) from the Millennium Galaxy Catalogue, we derive B-band luminosity distributions and selected bivariate brightness distributions for the galaxy population subdivided by eyeball morphology; Sersic index (n); two-degree Field Galaxy Redshift Survey (2dFGRS) η parameter; rest-(u - r) colour (global and core); MGC continuum shape; half-light radius; (extrapolated) central surface brightness; and inferred stellar mass-to-light ratio. All subdivisions extract highly correlated subsets of the galaxy population which consistently point towards two overlapping distributions: an old, red, inert, predominantly luminous, high central-surface brightness subset; and a young, blue, star forming, intermediate surface brightness subset. A clear bimodality in the observed distribution is seen in both the rest-(u - r) colour and log (n) distributions. Whilst the former bimodality was well established from Sloan Digital Sky Survey data, we show here that the rest-(u - r) colour bimodality becomes more pronounced when using the core colour as opposed to global colour. The two populations are extremely well separated in the colour-log(n) plane. Using our sample of 3314 (B < 19 mag) eyeball classified galaxies, we show that the bulge-dominated, early-type galaxies populate one peak and the bulge-less, late-type galaxies occupy the second. The early- and mid-type spirals sprawl across and between the peaks. This constitutes extremely strong evidence that the fundamental way to divide the luminous galaxy population (M BMGC -5 log h < -16 mag, i.e. dwarfs not included) is into bulges (old red, inert, high concentration) and discs (young, blue, star forming, low concentration) and that the galaxy bimodality reflects the two-component nature of galaxies and not two distinct galaxy classes. We argue that these two components require two independent formation mechanisms/processes and advocate early bulge formation through initial collapse and ongoing disc formation through splashback, infall and merging/accretion. We calculate the B-band luminosity densities and stellar mass densities within each subdivision and estimate that the z ≈ 0 stellar mass content in spheroids, bulges and discs is 35 ± 2, 18 ± 7 and 47 ± 7 per cent, respectively.

The Nature of the Dense Core Population in the Pipe Nebula: Thermal Cores Under Pressure

Abstract: In this paper we present the results of a systematic investigation of an entire population of predominately starless dust cores within a single molecular cloud, the Pipe Nebula. Analysis of extinction data shows the cores to be dense objects characterized by a narrow range of density with a median value of -->n(H2) = 7 ? 103. The nonthermal velocity dispersions measured in molecular emission lines are found to be subsonic for the large majority of the cores and show no correlation with core mass (or size). Thermal pressure is found to be the dominate source of internal gas pressure and support for most of the core population. The total internal pressures of the cores are found to be roughly independent of core mass over the entire (0.2-20 M?) range of the core mass function (CMF) indicating that the cores are in pressure equilibrium with an external source of pressure. This external pressure is most likely provided by the weight of the surrounding molecular cloud. Most of the cores appear to be pressure confined, gravitationally unbound entities whose fundamental physical properties are determined by only a few factors, which include self-gravity, gas temperature, and the simple requirement of pressure equilibrium with the surrounding environment. The entire core population is found to be characterized by a single critical Bonnor-Ebert mass of approximately 2 M?. This mass coincides with the characteristic mass of the Pipe CMF suggesting that the CMF (and ultimately the stellar IMF) has its origin in the physical process of thermal fragmentation in a pressurized medium.

Galaxy And Mass Assembly (GAMA): Structural Investigation of Galaxies via Model Analysis

Abstract: We present single-Sersic two-dimensional (2D) model fits to 167 600 galaxies modelled independently in the ugrizYJHK bandpasses using reprocessed Sloan Digital Sky Survey Data Release Seven (SDSS DR7) and UKIRT Infrared Deep Sky Survey Large Area Survey imaging data available from the Galaxy And Mass Assembly (GAMA) data base. In order to facilitate this study we developed Structural Investigation of Galaxies via Model Analysis (sigma), an r wrapper around several contemporary astronomy software packages including source extractor, psf extractor and galfit 3. sigma produces realistic 2D model fits to galaxies, employing automatic adaptive background subtraction and empirical point spread function measurements on the fly for each galaxy in GAMA. Using these results, we define a common coverage area across the three GAMA regions containing 138 269 galaxies. We provide Sersic magnitudes truncated at 10re which show good agreement with SDSS Petrosian and GAMA photometry for low Sersic index systems (n 4), recovering as much as Δm= 0.5 mag in the r band. We employ a K-band Sersic index/u−r colour relation to delineate the massive (n > ∼2) early-type galaxies (ETGs) from the late-type galaxies (LTGs). The mean Sersic index of these ETGs shows a smooth variation with wavelength, increasing by 30 per cent from g through K. LTGs exhibit a more extreme change in Sersic index, increasing by 52 per cent across the same range. In addition, ETGs and LTGs exhibit a 38 and 25 per cent decrease, respectively, in half-light radius from g through K. These trends are shown to arise due to the effects of dust attenuation and stellar population/metallicity gradients within galaxy populations.