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 Swift GRB Host Galaxy Legacy Survey. II. Rest-frame Near-IR Luminosity Distribution and Evidence for a Near-solar Metallicity Threshold

Abstract: We present rest-frame near-IR (NIR) luminosities and stellar masses for a large and uniformly selected population of gamma-ray burst (GRB) host galaxies using deep Spitzer Space Telescope imaging of 119 targets from the Swift GRB Host Galaxy Legacy Survey spanning 0.03 < z < 6.3, and we determine the effects of galaxy evolution and chemical enrichment on the mass distribution of the GRB host population across cosmic history. We find a rapid increase in the characteristic NIR host luminosity between z ~ 0.5 and z ~ 1.5, but little variation between z ~ 1.5 and z ~ 5. Dust-obscured GRBs dominate the massive host population but are only rarely seen associated with low-mass hosts, indicating that massive star-forming galaxies are universally and (to some extent) homogeneously dusty at high redshift while low-mass star-forming galaxies retain little dust in their interstellar medium. Comparing our luminosity distributions with field surveys and measurements of the high-z mass–metallicity relation, our results have good consistency with a model in which the GRB rate per unit star formation is constant in galaxies with gas-phase metallicity below approximately the solar value but heavily suppressed in more metal-rich environments. This model also naturally explains the previously reported "excess" in the GRB rate beyond z gsim 2; metals stifle GRB production in most galaxies at z < 1.5 but have only minor impact at higher redshifts. The metallicity threshold we infer is much higher than predicted by single-star models and favors a binary progenitor. Our observations also constrain the fraction of cosmic star formation in low-mass galaxies undetectable to Spitzer to be small at z < 4.

HiZELS:a high-redshift survey of Hα emitters - II. the nature of star-forming galaxies at z = 0.84

Abstract: New results from a large survey of Hα emission-line galaxies at z = 0.84 using the Wide Field Camera on the United Kingdom Infrared Telescope and a custom narrow-band filter in the J band are presented as part of the High-z Emission Line Survey (HiZELS). The deep narrow-band images reach an effective flux limit of F Hα ∼ 10 -16 erg s -1 cm -2 in a comoving volume of 1.8 × 10 5 Mpc 3, resulting in the largest and deepest survey of its kind ever done at z ∼ 1. There are 1517 potential line emitters detected across ∼1.4 deg 2, of which 743 are selected as Hα emitters, based on their photometric and spectroscopic redshifts. These are then used to calculate the Hα luminosity function, which is well fitted by a Schechter function with L* = 10 42.26±0.05 erg s -1, φ* = 10 -1.92±0.10 Mpc -3 and α = -1.65 ± 0.15, and are used to estimate the volume average star formation rate (SFR) at z = 0.845, ρ SFR: 0.15 ± 0.01 M ⊙ yr -1 Mpc -3 (corrected for 15 per cent active galactic nucleus contamination and integrated down to 2.5 M ⊙ yr -1). These results robustly confirm a strong evolution of ρ SFR from the present day out to z ∼ 1 and then flattening to z ∼ 2 using a single star formation indicator: Hα luminosity. Out to z ∼ 1, both the characteristic luminosity and space density of the Hα emitters increase significantly; at higher redshifts, L* continues to increase, but φ* decreases. The z = 0.84 Hα emitters are mostly disc galaxies (82 ± 3 per cent), while 28 ± 4 per cent of the sample shows signs of merger activity; mergers account for ∼20 per cent of the total integrated ρ SFR at this redshift. Irregulars and mergers dominate the Hα luminosity function above L*, while discs are dominant at fainter luminosities. These results demonstrate that it is the evolution of 'normal' disc galaxies that drives the strong increase in the SFR density from the current epoch to z ∼ 1, although the continued strong evolution of L* beyond z = 1 suggests an increasing importance of merger activity at higher redshifts. © 2009 RAS.

An Overdensity of Galaxies at z = 5.9 ? 0.2 in the Hubble Ultra Deep Field Confirmed Using the ACS Grism

Abstract: We present grism spectra taken with the Advanced Camera for Surveys (ACS) to identify 29 red sources with (i775 - z850) ? 0.9 in the Hubble Ultra Deep Field (HUDF). Of these, 23 are found to be galaxies at redshifts between z = 5.4 and 6.7, identified by the break at 1216 ? due to intergalactic medium (IGM) absorption; two are late-type dwarf stars with red colors; and four are galaxies with colors and spectral shapes similar to dust-reddened or old galaxies at redshifts z ? 1-2. This constitutes the largest uniform, flux-limited sample of spectroscopically confirmed galaxies at such faint fluxes (z850 ? 27.5). Many are also among the most distant spectroscopically confirmed galaxies (at redshifts up to z = 6.7). We find a significant overdensity of galaxies at redshifts z = 5.9 ? 0.2. Nearly two-thirds of the galaxies in our sample (15/23) belong to this peak. Taking into account the selection function and the redshift sensitivity of the survey, we get a conservative overdensity of at least a factor of 2 along the line of sight. The galaxies found in this redshift peak are also localized in the plane of the sky in a nonrandom manner, occupying about half of the ACS chip. Thus the volume overdensity is a factor of 4. The star formation rate derived from detected sources in this overdense region is sufficient to reionize the local IGM.

Identifying gaps in flaring Herbig Ae/Be disks using spatially resolved mid-infrared imaging - Are all group I disks transitional?

Abstract: Context. The evolution of young massive protoplanetary disks toward planetary systems is expected to correspond to structural changes in observational appearance, which includes the formation of gaps and the depletion of dust and gas. Aims. A special group of disks around Herbig Ae/Be stars do not show prominent silicate emission features, although they still bear signs of flaring disks, the presence of gas, and small grains. We focus our attention on four key Herbig Ae/Be stars to understand the structural properties responsible for the absence of silicate feature emission. Methods. We investigate Q- and N-band images taken with Subaru/COMICS, Gemini South/T-ReCS and VLT/VISIR. We perform radiative transfer modeling to examine the radial distribution of dust and PAHs. Our solutions require a separation of inner- and outerdisks by a large gap. From this we characterize the radial density structure of dust and PAHs in the disk. Results. The inner edge of the outer disk has a high surface brightness and a typical temperature between 100‐150 K and therefore dominates the emission in the Q-band. All four disks are characterized by large gaps. We derive radii of the inner edge of the outer disk of 34 +4 , 23 +3 , 30 +5 and 63 +4 AU for HD 97048, HD 169142, HD 135344 B and Oph IRS 48 respectively. For HD 97048 this is the first detection of a disk gap. The large gaps deplete the entire population of silicate particles with temperatures suitable for prominent midinfrared feature emission, while small carbonaceous grains and PAHs can still show prominent emission at mid-infrared wavelengths. The continuum emission in the N-band is not due to emission in the wings of PAHs. This continuum emission can be due to VSGs or to thermal emission from the inner disk. We find that PAH emission is not always dominated by PAHs on the surface of the outer disk. Conclusions. The absence of silicate emission features is due to the presence of large gaps in the critical temperature regime. Many, if not all Herbig disks with Spectral Energy Distribution (SED) classification ‘group I’ are disks with large gaps and can be characterized as (pre-) transitional. An evolutionary path from the observed group I to the observed group II sources seems no longer likely. Instead, both might derive from a common ancestor.

ALMA reveals the molecular medium fueling the nearest nuclear starburst

Abstract: We use ALMA observations to derive mass, length, and time scales associated with NGC?253's nuclear starburst. This region forms ~2 M ??yr?1 of stars and resembles other starbursts in ratios of gas, dense gas, and star formation tracers, with star formation consuming the gas reservoir at a normalized rate 10 times higher than in normal galaxy disks. We present new ~35?pc resolution observations of bulk gas tracers (CO), high critical density transitions (HCN, HCO+, and CS), and their isotopologues. The starburst is fueled by a highly inclined distribution of dense gas with vertical extent <100?pc and radius ~250?pc. Within this region, we identify 10 starburst giant molecular clouds (GMCs) that appear as both peaks in the dense gas tracer cubes and the HCN-to-CO ratio map. These are massive (~107 M ?) structures with sizes (~30?pc) similar to GMCs in other systems, but compared to GMCs in normal galaxy disks, they have high line widths (? ~ 20-40?km?s?1, Mach number ) and high surface and volume densities (?mol ~ 6000 M ? pc?2, n H2 ~ 2000?cm?3). The self gravity from such high densities can explain the high line widths and the short free fall time ?ff ~ 0.7?Myr in the clouds helps explain the more efficient star formation in NGC?253. Though the high inclination obscures the geometry somewhat, we show that simple models suggest a compact, clumpy region of high gas density embedded in a more extended, non-axisymmetric, bar-like distribution. Over the starburst, the surface density still exceeds that of a typical disk galaxy GMC and, as in the clouds, timescales in the disk as a whole are short compared to those in normal galaxy disks. The orbital time (~10?Myr), disk free fall time ( 3?Myr), and disk crossing time ( 3?Myr) are each an order of magnitude shorter than in a normal galaxy disk. Finally, the CO-to-H2 conversion factor implied by our cloud calculations is approximately Galactic, contrasting with results showing a low value for the whole starburst region. The contrast provides resolved support for the idea of mixed molecular ISM phases in starburst galaxies.