The role of antibiosis in the antagonism of different bacteria towards Helminthosporium solani, the causal agent of potato silver scurf

Bacterial antagonists of Helminthosporium solani were submitted to different tests in order to determine the role of antibiosis in their antagonistic interaction. Among the bacterial strains tested, seven (Alcaligenes piechaudii, Aquaspirillum autotrophicum, Cellulomonas fimi, Pseudomonas chlororaphis, Pseudomonas putida (strains 94-19 and E-30) and Streptomyces griseus) were shown to produce agar diffusible metabolites inhibiting H. solani mycelial growth and/or conidial germination. Differential activity was revealed when diffusible metabolites were extracted from either pure cultures of these antagonists or dual culture in the presence of H. solani. The results presented indicate that the methodology employed could be a decisive factor in whether or not antibiosis can be identified as a mode of action of biocontrol agents.Des antagonistes bactériens envers Helminthosporium solani ont été soumis à différents essais en vue de déterminer le rôle de l'antibiose dans l'antagonisme observé. Parmi les souches bactériennes évaluées, sept (Alcaligenes piechaudii, Aquaspirillum autotrophicum, Cellulomonas fimi, Pseudomonas chlororaphis, Pseudomonas putida (souches 94-19 et E-30) et Streptomyces griseus) ont produit dans le milieu gélosé des métabolites inhibant la croissance mycélienne et/ou la germination des conidies de H. solani. Les métabolites produits en culture pure et en culture mixte ont présenté une activité différente sur la croissance mycélienne de H. solani. Les résultats présentés indiquent que la méthodologie employée peut être un facteur déterminant dans l'identification de l'antibiose comme mode d'action d'un agent antagoniste

The infrared imaging spectrograph (IRIS) for TMT: the science case

The InfraRed Imaging Spectrograph (IRIS) is a first-light instrument being designed for the Thirty Meter Telescope (TMT). IRIS is a combination of an imager that will cover a 16.4" field of view at the diffraction limit of TMT (4 mas sampling), and an integral field unit spectrograph that will sample objects at 4-50 mas scales. IRIS will open up new areas of observational parameter space, allowing major progress in diverse fields of astronomy. We present the science case and resulting requirements for the performance of IRIS. Ultimately, the spectrograph will enable very well-resolved and sensitive studies of the kinematics and internal chemical abundances of high-redshift galaxies, shedding light on many scenarios for the evolution of galaxies at early times. With unprecedented imaging and spectroscopy of exoplanets, IRIS will allow detailed exploration of a range of planetary systems that are inaccessible with current technology. By revealing details about resolved stellar populations in nearby galaxies, it will directly probe the formation of systems like our own Milky Way. Because it will be possible to directly characterize the stellar initial mass function in many environments and in galaxies outside of the the Milky Way, IRIS will enable a greater understanding of whether stars form differently in diverse conditions. IRIS will reveal detailed kinematics in the centers of low-mass galaxies, allowing a test of black hole formation scenarios. Finally, it will revolutionize the characterization of reionization and the first galaxies to form in the universe.Comment: to appear in Proc. SPIE 773

The InfraRed Imaging Spectrograph (IRIS) for TMT: latest science cases and simulations

The Thirty Meter Telescope (TMT) first light instrument IRIS (Infrared Imaging Spectrograph) will complete its preliminary design phase in 2016. The IRIS instrument design includes a near-infrared (0.85 - 2.4 micron) integral field spectrograph (IFS) and imager that are able to conduct simultaneous diffraction-limited observations behind the advanced adaptive optics system NFIRAOS. The IRIS science cases have continued to be developed and new science studies have been investigated to aid in technical performance and design requirements. In this development phase, the IRIS science team has paid particular attention to the selection of filters, gratings, sensitivities of the entire system, and science cases that will benefit from the parallel mode of the IFS and imaging camera. We present new science cases for IRIS using the latest end-to-end data simulator on the following topics: Solar System bodies, the Galactic center, active galactic nuclei (AGN), and distant gravitationally-lensed galaxies. We then briefly discuss the necessity of an advanced data management system and data reduction pipeline.Comment: 15 pages, 7 figures, SPIE (2016) 9909-0

What turns galaxies off? The different morphologies of star-forming and quiescent galaxies since z~2 from CANDELS

We use HST/WFC3 imaging from the CANDELS Multicycle Treasury Survey, in conjunction with the Sloan Digital Sky Survey, to explore the evolution of galactic structure for galaxies with stellar masses >3e10M_sun from z=2.2 to the present epoch, a time span of 10Gyr. We explore the relationship between rest-frame optical color, stellar mass, star formation activity and galaxy structure. We confirm the dramatic increase from z=2.2 to the present day in the number density of non-star-forming galaxies above 3e10M_sun reported by others. We further find that the vast majority of these quiescent systems have concentrated light profiles, as parametrized by the Sersic index, and the population of concentrated galaxies grows similarly rapidly. We examine the joint distribution of star formation activity, Sersic index, stellar mass, inferred velocity dispersion, and stellar surface density. Quiescence correlates poorly with stellar mass at all z<2.2. Quiescence correlates well with Sersic index at all redshifts. Quiescence correlates well with `velocity dispersion' and stellar surface density at z>1.3, and somewhat less well at lower redshifts. Yet, there is significant scatter between quiescence and galaxy structure: while the vast majority of quiescent galaxies have prominent bulges, many of them have significant disks, and a number of bulge-dominated galaxies have significant star formation. Noting the rarity of quiescent galaxies without prominent bulges, we argue that a prominent bulge (and perhaps, by association, a supermassive black hole) is an important condition for quenching star formation on galactic scales over the last 10Gyr, in qualitative agreement with the AGN feedback paradigm.Comment: The Astrophysical Journal, in press; 20 pages with 13 figure

Airships: A New Horizon for Science

The "Airships: A New Horizon for Science" study at the Keck Institute for Space Studies investigated the potential of a variety of airships currently operable or under development to serve as observatories and science instrumentation platforms for a range of space, atmospheric, and Earth science. The participants represent a diverse cross-section of the aerospace sector, NASA, and academia. Over the last two decades, there has been wide interest in developing a high altitude, stratospheric lighter-than-air (LTA) airship that could maneuver and remain in a desired geographic position (i.e., "station-keeping") for weeks, months or even years. Our study found considerable scientific value in both low altitude (< 40 kft) and high altitude (> 60 kft) airships across a wide spectrum of space, atmospheric, and Earth science programs. Over the course of the study period, we identified stratospheric tethered aerostats as a viable alternative to airships where station-keeping was valued over maneuverability. By opening up the sky and Earth's stratospheric horizon in affordable ways with long-term flexibility, airships allow us to push technology and science forward in a project-rich environment that complements existing space observatories as well as aircraft and high-altitude balloon missions.Comment: This low resolution version of the report is 8.6 MB. For the high resolution version see: http://kiss.caltech.edu/study/airship

Morphological Properties of z~0.5 Absorption-Selected Galaxies: The Role of Galaxy Inclination

We have used GIM2D to quantify the morphological properties of 40 intermediate redshift MgII absorption-selected galaxies (0.03<Wr(2796)<2.9 Ang), imaged with WFPC-2/HST, and compared them to the halo gas properties measured form HIRES/Keck and UVES/VLT quasar spectra. We find that as the quasar-galaxy separation, D, increases the MgII equivalent decreases with large scatter, implying that D is not the only physical parameter affecting the distribution and quantity of halo gas. Our main result shows that inclination correlates with MgII absorption properties after normalizing out the relationship (and scatter) between the absorption properties and D. We find a 4.3 sigma correlation between Wr(2796) and galaxy inclination, normalized by impact parameter, i/D. Other measures of absorption optical depth also correlate with i/D at greater than 3.2 sigma significance. Overall, this result suggests that MgII gas has a co-planer geometry, not necessarily disk-like, that is coupled to the galaxy inclination. It is plausible that the absorbing gas arises from tidal streams, satellites, filaments, etc., which tend to have somewhat co-planer distributions. This result does not support a picture in which MgII absorbers with Wr(2796)<1A are predominantly produced by star-formation driven winds. We further find that; (1) MgII host galaxies have quantitatively similar bulge and disk scale length distribution to field galaxies at similar redshifts and have a mean disk and bulge scale length of 3.8kpc and 2.5kpc, respectively; (2) Galaxy color and luminosity do not correlate strongly with absorption properties, implying a lack of a connection between host galaxy star formation rates and absorption strength; (3) Parameters such as scale lengths and bulge-to-total ratios do not significantly correlate with the absorption parameters, suggesting that the absorption is independent of galaxy size or mass.Comment: 21 pages, 7 figures, 7 tables. Accepted for publication in MNRAS. Revised v3 updates Table 5 columns 8 and 11. ArXiv copy includes full version of Fig. 1 (additional 6 pages

CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey - The Hubble Space Telescope Observations, Imaging Data Products and Mosaics

This paper describes the Hubble Space Telescope imaging data products and data reduction procedures for the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). This survey is designed to document the evolution of galaxies and black holes at $z\sim1.5-8$, and to study Type Ia SNe beyond $z>1.5$. Five premier multi-wavelength sky regions are selected, each with extensive multiwavelength observations. The primary CANDELS data consist of imaging obtained in the Wide Field Camera 3 / infrared channel (WFC3/IR) and UVIS channel, along with the Advanced Camera for Surveys (ACS). The CANDELS/Deep survey covers \sim125 square arcminutes within GOODS-N and GOODS-S, while the remainder consists of the CANDELS/Wide survey, achieving a total of \sim800 square arcminutes across GOODS and three additional fields (EGS, COSMOS, and UDS). We summarize the observational aspects of the survey as motivated by the scientific goals and present a detailed description of the data reduction procedures and products from the survey. Our data reduction methods utilize the most up to date calibration files and image combination procedures. We have paid special attention to correcting a range of instrumental effects, including CTE degradation for ACS, removal of electronic bias-striping present in ACS data after SM4, and persistence effects and other artifacts in WFC3/IR. For each field, we release mosaics for individual epochs and eventual mosaics containing data from all epochs combined, to facilitate photometric variability studies and the deepest possible photometry. A more detailed overview of the science goals and observational design of the survey are presented in a companion paper.Comment: 39 pages, 25 figure