We present new infrared observations of the emission/reflection nebula IC 405 obtained with the Spitzer Space Telescope. Infrared images in the four IRAC bands (3.6,4.5, 5.8, and 8.0 km) and two MIPS ...bands (24 and 70 km) are complemented by IRS spectroscopy (5-30 km) of two nebular filaments. The IRAC (8.0 km) and MIPS imaging shows evidence of a bow shock associated with the runaway 09.5 V star, HD 34078, created by the interaction between the star and nebular material. The ratio of emission at 24 to 70 km is higher in the immediate vicinity of HD 34078 than in the outer filaments, providing evidence for elevated dust temperatures (T sub(d) 90 K) in the shock region. The nebular imaging reveals that the morphology is band dependent, with varying contributions from aromatic emission features, H sub(2), and dust emission. Nebular spectroscopy is used to quantify these contributions, showing several aromatic emission bands between 6-14 km, the S(5), S(3), S(2), and S(1) pure rotational emission lines of H sub(2), and atomic fine-structure lines of Ne, S, and Ar. The low-dispersion spectra provide constraints on the ionization state of the large molecules responsible for the aromatic infrared features. H sub(2) rotational temperatures of the two bright nebular filaments are determined from the observed line strengths. An average T(H sub(2)) 6 400 K is inferred, with evidence for additional nonuniform excitation by UV photons in the intense radiation field of HD 34078. The photoexcitation hypothesis is supported by direct measurement of the far-UV H sub(2) fluorescence spectrum, obtained with FUSE.
The diffuse ultraviolet background radiation has been mapped over most of the sky with 2′ resolution using data from the Galaxy Evolution Explorer survey. We utilize this map to study the correlation ...between the UV background and clusters of galaxies discovered via the Sunyaev-Zeldovich effect in the Planck survey. We use only high Galactic latitude ( ) galaxy clusters to avoid contamination by Galactic foregrounds, and we only analyze clusters with a measured redshift. This leaves us with a sample of 142 clusters over the redshift range of 0.02 ≤ z ≤ 0.72, which we further subdivide into four redshift bins. In analyzing our stacked samples binned by redshift, we find evidence for a central excess of UV background light compared to local backgrounds for clusters with z < 0.3. We then stacked these z < 0.3 clusters to find a statistically significant excess of 12 2.3 photon cm−2 s−1 sr−1 −1 over the median of ∼380 photon cm−2 s−1 sr−1 −1 measured around random blank fields. We measure the stacked radial profile of these clusters, and find that the excess UV radiation decays to the level of the background at a radius of ∼1 Mpc, roughly consistent with the maximum radial extent of the clusters. Analysis of possible physical processes contributing to the excess UV brightness indicates that non-thermal emission from relativistic electrons in the intracluster medium and faint, unresolved UV emission from cluster member galaxies and intracluster light are likely the dominant contributors.
Partial frequency redistribution (PRD), describing the formation of the line profile, has negligible observational effects for optical depths smaller than ~103, at the resolving power of most current ...instruments. However, when the spectral resolution is sufficiently high, PRD modeling becomes essential in interpreting the line shapes and determining the total line fluxes. We demonstrate the effects of PRD on the H2 line profiles observed at high spectral resolution by the Far-Ultraviolet Spectroscopic Explorer (FUSE) in the atmospheres of Jupiter and Saturn. In these spectra, the asymmetric shapes of the lines in the Lyman (v''-6) progression pumped by the solar Ly Delta *b are explained by coherent scattering of the photons in the line wings. We introduce a simple computational approximation to mitigate the numerical difficulties of radiative transfer with PRD and show that it reproduces the exact radiative transfer solution to better than 10%. The lines predicted by our radiative transfer model with PRD, including the H2 density and temperature distribution as a function of height in the atmosphere, are in agreement with the line profiles observed by FUSE. We discuss the observational consequences of PRD and show that this computational method also allows us to include PRD in modeling the continuum pumped H2 fluorescence treating about 4000 lines simultaneously.
Galaxy Evolution Explorer (GALEX) observations of comet 9P/Tempel 1 using the near-ultraviolet (NUV) objective grism were made before, during and after the Deep Impact event that occurred on 2005 ...July 4 at 05:52:03 UT when a 370 kg NASA spacecraft was maneuvered into the path of the comet. The NUV channel provides usable spectral information in a bandpass covering 2000-3400 A with a point source spectral resolving power of R {approx} 100. The primary spectral features in this range include solar continuum scattered from cometary dust and emissions from OH and CS molecular bands centered near 3085 and 2575 A, respectively. In particular, we report the only cometary CS emission detected during this event. The observations allow the evolution of these spectral features to be tracked over the period of the encounter. In general, the NUV emissions observed from Tempel 1 are much fainter than those that have been observed by GALEX from other comets. However, it is possible to derive production rates for the parent molecules of the species detected by GALEX in Tempel 1 and to determine the number of these molecules liberated by the impact. The derived quiescent production rates are Q(H{sub 2}O) = 6.4 x 10{sup 27} molecules s{sup -1} and Q(CS{sub 2}) = 6.7 x 10{sup 24} molecules s{sup -1}, while the impact produced an additional 1.6 x 10{sup 32} H{sub 2}O molecules and 1.3 x 10{sup 29} CS{sub 2} molecules, a similar ratio as in quiescent outgassing.
Galaxy clusters magnify background objects through strong gravitational lensing. Typical magnifications for lensed galaxies are factors of a few but can also be as high as tens or hundreds, ...stretching galaxies into giant arcs
. Individual stars can attain even higher magnifications given fortuitous alignment with the lensing cluster. Recently, several individual stars at redshifts between approximately 1 and 1.5 have been discovered, magnified by factors of thousands, temporarily boosted by microlensing
. Here we report observations of a more distant and persistent magnified star at a redshift of 6.2 ± 0.1, 900 million years after the Big Bang. This star is magnified by a factor of thousands by the foreground galaxy cluster lens WHL0137-08 (redshift 0.566), as estimated by four independent lens models. Unlike previous lensed stars, the magnification and observed brightness (AB magnitude, 27.2) have remained roughly constant over 3.5 years of imaging and follow-up. The delensed absolute UV magnitude, -10 ± 2, is consistent with a star of mass greater than 50 times the mass of the Sun. Confirmation and spectral classification are forthcoming from approved observations with the James Webb Space Telescope.
Flux estimates for ionizing radiation escaping from star-forming galaxies with characteristic UV luminosities (\({L}_{1500* (1+z)}^{* }\)), derived from GALEX and the VIMOS-VLT Deep Survey, are ...presented as a function of redshift and assumed escape fraction. These estimates offer guidance to the design of instrumentation and observing strategies, be they spectroscopic or photometric, for attempting to detect LyC escaping star-forming galaxies for redshifts \(z\lt 3\). Examples are given that relate the integrated escape fraction (f e LyC) of ionizing photons, obtained by integrating over the entire extreme UV (EUV) bandpass, to the relative escape fraction (f e 900) observed just shortward of the ionization edge at 911.8 Å as a function of H i, He i, and He ii column densities. We find that for \(\mathrm{log}{N}_{{\rm{H}}{\rm{I}}}({\mathrm{cm}}^{-2})\gtrsim 17.0\), f e LyC is significantly greater than f e 900. Detection of LyC “drop-ins” in the rest-frame EUV will provide enhanced fidelity to determinations of the integrated fraction of ionizing photons f e LyC that escape star-forming galaxies and contribute to the metagalactic ionizing background (MIB).
One of the goals of the Hubble Space Telescope program to observe periodic comet 9P/Tempel 1 in conjunction with NASA's Deep Impact mission was to study the generation and evolution of the gaseous ...coma resulting from the impact. For this purpose, the Solar Blind Channel of the Advanced Camera for Surveys was used with the F140LP filter, which is sensitive primarily to the ultraviolet emission (.1400 AA) from the CO fourth positive system. Following the impact we detected an increase in brightness, which if all due to CO corresponds to 1.5 x 10 super(31) molecules, or a mass of 6.6 x 10 super(5) kg, an amount that would normally be produced by 7-10 hours of quiescent outgassing from the comet. This number is ,10% of the number of water molecules excavated and suggests that the volatile content of the material excavated by the impact did not differ significantly from the surface or near-subsurface material responsible for the quiescent outgassing of the comet.
Abstract
The origins of Lyman continuum (LyC) photons responsible for the reionization of the universe are as of yet unknown and highly contested. Detecting LyC photons from the Epoch of Reionization ...is not possible due to absorption by the intergalactic medium, which has prompted the development of several indirect diagnostics to infer the rate at which galaxies contribute LyC photons to reionize the universe by studying lower-redshift analogs. We present the Low-redshift Lyman Continuum Survey (LzLCS) comprising measurements made with the Hubble Space Telescope Cosmic Origins Spectrograph for a
z
= 0.2–0.4 sample of 66 galaxies. After careful processing of the far-UV spectra, we obtain a total of 35 Lyman continuum emitters (LCEs) detected with 97.725% confidence, nearly tripling the number of known local LCEs. We estimate escape fractions from the detected LyC flux and upper limits on the undetected LyC flux, finding a range of LyC escape fractions up to 50%. Of the 35 LzLCS LCEs, 12 have LyC escape fractions greater than 5%, more than doubling the number of known local LCEs with cosmologically relevant LyC escape.
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