There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Starburst99 is a comprehensive set of model predictions for spectrophotometric and related properties of galaxies with active star formation. The models are an improved and extended version of the data set previously published by Leitherer & Heckman. We have upgraded our code by implementing the latest set of stellar evolution models of the Geneva group and the model atmosphere grid compiled by Lejeune et al. Several predictions which were not included in the previous publication are shown here for the first time. The models are presented in a homogeneous way for five metallicities between Z = 0.040 and 0.001 and three choices of the initial mass function. The age coverage is 106—109 yr. We also show the spectral energy distributions which are used to compute colors and other quantities. The full data set is available for retrieval at a Web site, which allows users to run specific models with nonstandard parameters as well. We also make the source code available to the community.

https://iopscience.iop.org/article/10.1086/313233/pdf

Starburst99: Synthesis Models for Galaxies with Active Star Formation

Over the past two decades, an avalanche of data from multiwavelength imaging and spectroscopic surveys has revolutionized our view of galaxy formation and evolution. Here we review the range of complementary techniques and theoretical tools that allow astronomers to map the cosmic history of star formation, heavy element production, and reionization of the Universe from the cosmic "dark ages" to the present epoch. A consistent picture is emerging, whereby the star-formation rate density peaked approximately 3.5 Gyr after the Big Bang, at z~1.9, and declined exponentially at later times, with an e-folding timescale of 3.9 Gyr. Half of the stellar mass observed today was formed before a redshift z = 1.3. About 25% formed before the peak of the cosmic star-formation rate density, and another 25% formed after z = 0.7. Less than ~1% of today's stars formed during the epoch of reionization. Under the assumption of a universal initial mass function, the global stellar mass density inferred at any epoch matches reasonably well the time integral of all the preceding star-formation activity. The comoving rates of star formation and central black hole accretion follow a similar rise and fall, offering evidence for co-evolution of black holes and their host galaxies. The rise of the mean metallicity of the Universe to about 0.001 solar by z = 6, one Gyr after the Big Bang, appears to have been accompanied by the production of fewer than ten hydrogen Lyman-continuum photons per baryon, a rather tight budget for cosmological reionization.

/pdf/cosmic-star-formation-history-5ce1d74cmt.pdf

Cosmic Star-Formation History

(Abridged) We describe here the most ambitious survey currently planned in the optical, the Large Synoptic Survey Telescope (LSST). A vast array of science will be enabled by a single wide-deep-fast sky survey, and LSST will have unique survey capability in the faint time domain. The LSST design is driven by four main science themes: probing dark energy and dark matter, taking an inventory of the Solar System, exploring the transient optical sky, and mapping the Milky Way. LSST will be a wide-field ground-based system sited at Cerro Pachon in northern Chile. The telescope will have an 8.4 m (6.5 m effective) primary mirror, a 9.6 deg$^2$ field of view, and a 3.2 Gigapixel camera. The standard observing sequence will consist of pairs of 15-second exposures in a given field, with two such visits in each pointing in a given night. With these repeats, the LSST system is capable of imaging about 10,000 square degrees of sky in a single filter in three nights. The typical 5$\sigma$ point-source depth in a single visit in $r$ will be $\sim 24.5$ (AB). The project is in the construction phase and will begin regular survey operations by 2022. The survey area will be contained within 30,000 deg$^2$ with $\delta<+34.5^\circ$, and will be imaged multiple times in six bands, $ugrizy$, covering the wavelength range 320--1050 nm. About 90\% of the observing time will be devoted to a deep-wide-fast survey mode which will uniformly observe a 18,000 deg$^2$ region about 800 times (summed over all six bands) during the anticipated 10 years of operations, and yield a coadded map to $r\sim27.5$. The remaining 10\% of the observing time will be allocated to projects such as a Very Deep and Fast time domain survey. The goal is to make LSST data products, including a relational database of about 32 trillion observations of 40 billion objects, available to the public and scientists around the world.

/pdf/lsst-from-science-drivers-to-reference-design-and-5mqdgndbq1.pdf

LSST: from Science Drivers to Reference Design and Anticipated Data Products

We review progress over the past decade in observations of large-scale star formation, with a focus on the interface between extragalactic and Galactic studies. Methods of measuring gas contents and star-formation rates are discussed, and updated prescriptions for calculating star-formation rates are provided. We review relations between star formation and gas on scales ranging from entire galaxies to individual molecular clouds.

Star Formation in the Milky Way and Nearby Galaxies

The optical constants of thin films of CsI, KI, and KBr and the quantum efficiency (QE) of planar photocathodes made with these alkali halides in the 53.6-174.4-nm spectral range are presented. The optical constants were obtained from measurements of the reflectance as a function of incidence angle. The effect of film heating and exposure to UV irradiation on the optical properties and on the QE of the three alkali halides was investigated. KBr was found to be the most stable material for both heating and UV irradiation. KI appeared to be close to temperature stable, whereas UV exposure affected its optical constants. CsI optical constants changed after 420 K heating and after UV exposure. The changes in the optical constants were related to the QE changes, and a certain correlation between both variations was determined. However, it was also demonstrated that the QE changes cannot be explained solely by the changes in optical constants.

/pdf/optical-properties-and-quantum-efficiency-of-thin-film-1dm7e70r3a.pdf

Optical properties and quantum efficiency of thin-film alkali halides in the far ultraviolet

The Far Ultraviolet (FUV) detector for the Cosmic Origins Spectrograph (COS), scheduled to be installed in the Hubble Space Telescope in June 2003, is currently being built by the Experimental Astrophysics Group at The University of California, Berkeley. The COS FUV detector system is based on the detectors flown on the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite with changes to take advantage of technological improvements since the development of those detectors. The COS FUV detector is a dual segmented, cylindrical input face, MCP detector with cross delay line (XDL) readouts. Each segment is a Z-stack of MCPs with an active area 85 mm by 10 mm. The segments are abutted end to end to form a total active area approximately 180 mm by 10 mm (with a gap in the middle). Detector spatial resolution in the long (spectral) dimension is better than 25 microns and in the short dimension (cross-dispersion) is better than 50 microns. The MCPs are coated with a CsI photocathode to achieve the optimal quantum detection efficiency (QDE) in the 1150 - 1750 angstrom bandpass. Improvements in the understanding of the processing required to produce higher QDE MCPs has lead to significant improvements in the FUV QDE relative to previous missions. This paper presents the basic design parameters and performance characteristics of the COS FUV detector.

Cosmic Origins Spectograph FUV detector

We have studied the UV sensitivity degradation of CsI and KBr thin films under UV illumination and the stability of their visible light rejection for CsI and KBr opaque photocathodes evaporated on microchannel plates. For both materials the greatest degradation of the relative quantum detection efficiency was observed near the photocathode sensitivity cut off, while there was almost no change in their EUV response. The aging of the photocathodes is likely to be independent of the angle of radiation incidence. Of the two materials the CsI films appeared to be more solar blind and less subject to visible sensitivity activation by UV exposure.

Stability of quantum efficiency and visible light rejection of alkali halide photocathodes

EUV, X-Ray, and Gamma-Ray Instrumentation for Astronomy X

Micromachined silica microchannel plates (MCPs) under development have a number of advantages over standard glass MCPs and open completely new possibilities in detector technologies. In this article we present the results of our studies on the thermal properties of silica microchannel plates (sMCPs). Similar to standard glass microchanel plates the resistance of silica MCPs was measured to change exponentially with temperature with a negative thermal coefficient of -0.036 per degreesC, somewhat larger than that of standard glass MCPs. The resistance also decreases linearly with the applied voltage, with the voltage coefficient of -3.1x10(-4) V-1. With the knowledge of these two coefficients, our thermal model allows the calculation of the maximum voltage, which can be applied to a given MCP without inducing a thermal runaway. A typical 25 mm diam, 240 mum thick sMCP with 6 mum pores has to have the resistance larger than similar to30 MOmega to operate safely at voltages up to 800 V. With this model we can also calculate the time required for a given silica MCP to reach the point of thermal equilibrium after a voltage increase. We hope that the ongoing efforts on a proper modification of the sMCP semiconducting layer will lead to the production of new MCPs with a small negative or even a positive thermal coefficient, reducing the possibility of thermal runaways of low-resistance MCPs required for high count rate applications. (C) 2004 American Institute of Physics.

/pdf/thermal-dependence-of-electrical-characteristics-of-f085l15a8d.pdf

Oswald H. W. Siegmund

Papers

Optical properties and quantum efficiency of thin-film alkali halides in the far ultraviolet

Cosmic Origins Spectograph FUV detector

Stability of quantum efficiency and visible light rejection of alkali halide photocathodes

EUV, X-Ray, and Gamma-Ray Instrumentation for Astronomy X

Thermal dependence of electrical characteristics of micromachined silica microchannel plates