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NASA NTRS2019

Energetic Particles of Cosmic Accelerators II: Active Galactic Nuclei and Gamma-ray Bursts

The high-energy universe has revealed that energetic particles are ubiquitous in the cosmos and play a vital role in the cultivation of cosmic environments on all scales. Our pursuit of more than a century to uncover the origins and fate of these cosmic energetic particles has given rise to some of the most interesting and challenging questions in astrophysics. Within our own galaxy, we have seen that energetic particles engage in a complex interplay with the galactic environment and even drive many of its key characteristics (for more information, see the first white paper in this series). On cosmological scales, the energetic particles supplied by the jets of active galactic nuclei (AGN) are an important source of energy for the intracluster and intergalactic media, providing a mechanism for regulating star formation and black hole growth and cultivating galaxy evolution (AGN feedback). Gamma-ray burst (GRB) afterglows encode information about their circumburst environment, which has implications for massive stellar winds during previous epochs over the stellar lifecycle. As such, GRB afterglows provide a means for studying very high-redshift galaxies since GRBs can be detected even if their host galaxy cannot. It has even been suggest that GRB could be used to measure cosmological distance scales if they could be shown to be standard candles. Though they play a key role in cultivating the cosmological environment and/or enabling our studies of it, there is still much we do not know about AGNs and GRBs, particularly the avenue in which and through which they supply radiation and energetic particles, namely their jets. Despite the enormous progress in particle-in-cell and magnetohydrodynamic simulations, we have yet to pinpoint the processes involved in jet formation and collimation and the conditions under which they can occur. For that matter, we have yet to identify the mechanism(s) through which the jet accelerates energetic particles – is it the commonly invoked diffusive shock acceleration process or is another mechanism, such as magnetic reconnection, required? Do AGNs and GRBs accelerate hadrons, and if so, do they accelerate them to ultra-high energies and are there high-energy neutrinos associated with them? MeV gamma-ray astronomy, enabled by technological advances that will be realized in the coming decade, will provide a unique and indispensable perspective on the persistent mysteries of the energetic universe. This White Paper is the second of a two-part series highlighting the most well-known high-energy cosmic accelerators and contributions that MeV gamma-ray astronomy will bring to understanding their energetic particle phenomena. Specifically, MeV astronomy will: 1. Determine whether AGNs accelerate CRs to ultra-high energies; 2. Provide the missing pieces for the physics of the GRB prompt emission; 3. Measure magnetization in cosmic accelerators and search for acceleration via reconnection.

Venters, Tonia M.↗
NASA NTRS2009

Finding the First Galaxies

Astronomers study distant galaxies by taking long exposures in deep survey fields. They choose fields that are empty of known sources, so that they are statistically representative of the Universe as a whole. Astronomers can compare the distribution of the detected galaxies in brightness, color, morphology and redshift to theoretical models, in order to puzzle out the processes of galaxy evolution. In 2004, the Hubble Space Telescope was pointed at a small, deep-survey field in the southern constellation Fornax for more than 500 hours of exposure time. The resulting Hubble Ultra-Deep Field could see the faintest and most distant galaxies that the telescope is capable of viewing. These galaxies emitted their light less than 1 billion years after the Big Bang. From the Ultra Deep Field and other galaxy surveys, astronomers have built up a history of star formation in the universe. the peak occurred about7 billion years ago, about half of the age of the current universe, then the number of stars that were forming was about 15 time the rate today. Going backward in time to when the very first starts and galaxies formed, the average star-formation rate should drop to zero. but when looking at the most distant galaxies in the Ultra Deep field, the star formation rate is still higher than it is today. The faintest galaxies seen by Hubble are not the first galaxies that formed in the early universe. To detect these galaxies NASA is planning the James Webb Space Telescope for launch in 2013. Webb will have a 6.5-meter diameter primary mirror, much bigger than Hubble's 2.4-meter primary, and will be optimized for infrared observations to see the highly redshifted galaxies.

Gardner, Jonathan P.↗
NASA NTRS2017

Multiwavelength Characterization of an ACT-Selected, Lensed Dusty Star-Forming Galaxy at zeta 2.64

We present C I(21) and multi-transition C-12 O observations of a dusty star-forming galaxy, ACT J2029+0120,which we spectroscopically confirm to lie at zeta = 2.64. We detect CO(3-2), CO(5-4), CO(7-6), CO(8-7), and C I(2-1) at high significance, tentatively detect HCO+(4-3), and place strong upper limits on the integrated strength of dense gas tracers (HCN(4-3) and CS(7-6)). Multi-transition CO observations and dense gas tracers can provide valuable constraints on the molecular gas content and excitation conditions in high-redshift galaxies. We therefore use this unique data set to construct a CO spectral line energy distribution (SLED) of the source, which is most consistent with that of a ULIRG Seyfert or QSO host object in the taxonomy of the Herschel Comprehensive ULIRG Emission Survey. We employ RADEX models to fit the peak of the CO SLED, inferring a temperature of T approximately 117 K and n(sub H2) approximately 10(exp5) cm(exp -3), most consistent with a ULIRGQSO object and the presence of high-density tracers. We also find that the velocity width of the C I line is potentially larger than seen in all CO transitions forth is object, and that the L'(sub Ci(2-1))/L'(sub CO(3-2))ratio is also larger than seen in other lensed and unlensed submillimeter galaxies and QSO hosts; if confirmed, this anomaly could be an effect of differential lensing of a shocked molecular outflow.

Roberts-Borsani, G. W.↗
NASA NTRS2003

An Array of Frequency Selective Bolometers (FSB) for the Spectral Energy Distribution (SPEED) Camera

The SPEED camera is being developed to study the spectral energy distributions of high redshift galaxies using the Heinrich Hertz Telescope (HHT) in Arizona. SPEED requires a small cryogenic detector array of 2x2 pixels with each pixel having four frequency bands in the 150-350 GHz range. Here we describe the development of the detector array of these high efficiency FSBs. The FSB design provides the multi-pixel multi-spectral band capability required for SPEED in a compact stackable array. The SPEED bolometers will use proximity effect superconducting transition edge sensors as their temperature-sensing element allowing for higher levels of multiplexing in future applications.

Silverberg, R. F.↗
NASA NTRS2004

Background-Limited Infrared-Submillimeter Spectroscopy (BLISS)

The bulk of the cosmic far-infrared background light will soon be resolved into its individual sources with Spitzer, Astro-F, Herschel, and submm/mm ground-based cameras. The sources will be dusty galaxies at z approximately equal to 1-4. Their physical conditions and processes in these galaxies are directly probed with moderate-resolution spectroscopy from 20 micrometers to 1 mm. Currently large cold telescopes are being combined with sensitive direct detectors, offering the potential for mid-far-IR spectroscopy at the background limit (BLISS). The capability will allow routine observations of even modest high-redshift galaxies in a variety of lines. The BLISS instrument's capabilities are described in this presentation.

spectrometers↗
NASA NTRS1983

Large Deployable Reflector Science and Technology Workshop. Volume 2: Scientific Rationale and Technology Requirements

The scientific rationale for the large deployable reflector (LDR) and the overall technological requirements are discussed. The main scientific objectives include studies of the origins of planets, stars and galaxies, and of the ultimate fate of the universe. The envisioned studies require a telescope with a diameter of at least 20 m, diffraction-limited to wavelengths as short as 30-50 micron. In addition, light-bucket operation with 1 arcsec spatial resolution in the 2-4 microns wavelength region would be useful in studies of high-redshifted galaxies. Such a telescope would provide a large increase in spectroscopic sensitivity and spatial resolving power compared with existing or planned infrared telescopes.

Hollenbach, D.↗
NASA NTRS1992

Hubble Space Telescope imaging of distant galaxies - 4C 41.17 at z = 3.8

The Hubble Space Telescope has been used to image the continuum emission from 4C 41.17 at z = 3.8, the most distant galaxy known. The galaxy was detected with good signal-to-noise ratio and was spatially resolved at the 0.1 arcsec (440 pc) HST resolution. About 35 percent of this emission is in the form of a high brightness clumpy region extending by about 0.5 arcsec (1.7 kpc), whose morphology is remarkably similar to that of the radio components. A fainter more diffuse region of optical emission extends westward from the center of the nuclear complex for about 1.2 arcsec (5.3 kpc) out along the radio axis. The clumpiness of the optical emission and its close correspondence with the radio structure on the subkiloparsec scale is discussed in the light of current models for high-redshift galaxies. Our observations imply that the material in the center of this galaxy is clumpy on the subkiloparsec scale.

Miley, G. K.↗
NASA NTRS1997

Spectral Energy Distribution of Star-Forming Galaxies

Our analysis allowed us to address the following points: 1) the nature of the featureless ultraviolet continuum in Seyfert 2's, in particular the amount of stellar population that contributes to this waveband; 2) the difference between Seyfert l's and Seyfert 2's in the ratio of ultraviolet (lambda)1400A to soft X-rays continuum, which is larger in Seyfert 2's and apparently contradicts the Unified Model, but may be resolved if we consider the stellar population; 3) search for anisotropic radiation escaping from the nucleus of Seyfert 2's, by comparing the number of ionizing photons, estimated from the ultraviolet continuum photons, to the number of recombination photons, calculated using the H(beta) line flux. In addition, the research from this grant produced template spectra that have been used in a wide variety of applications, including the identification of high redshift galaxies in the Slone survey.

Kinney, A. L.↗
NASA NTRS1994

Dust extinction of the stellar continua in starburst galaxies: The ultraviolet and optical extinction law

We analyze the International Ultraviolet Explorer (IUE) UV and the optical spectra of 39 starburst and blue compact galaxies in order to study the average properties of dust extinction in extended regions of galaxies. The optical spectra have been obtained using an aperture which matches that of IUE, so comparable regions within each galaxy are sampled. The data from the 39 galaxies are compared with five models for the geometrical distribution of dust, adopting as extinction laws both the Milky Way and the Large Magellanic Cloud laws. The commonly used uniform dust screen is included among the models. We find that none of the five models is in satisfactory agreement with the data. In order to understand the discrepancy between the data and the models, we have derived an extinction law directly from the data in the UV and optical wavelength range. The resulting curve is characterized by an overall slope which is more gray than the Milky Way extinction law's slope, and by the absence of the 2175 A dust feature. Remarkably, the difference in optical depth between the Balmer emission lines H(sub alpha) and H(sub beta) is about a factor of 2 larger than the difference in the optical depth between the continuum underlying the two Balmer lines. We interpret this discrepancy as a consequence of the fact that the hot ionizing stars are associated with dustier regions than the cold stellar population is. The absence of the 2175 A dust feature can be due either to the effects of the scattering and clumpiness of the dust or to a chemical composition different from that of the Milky Way dust grains. Disentangling the two interpretations is not easy because of the complexity of the spatial distribution of the emitting regions. The extinction law of the UV and optical spectral continua of extended regions can be applied to the spectra of medium- and high-redshift galaxies, where extended regions of a galaxy are, by necessity, sampled.

Calzetti, Daniela↗
NASA NTRS1987

The Large Deployable Reflector (LDR) - Plans and progress

The program history, scientific aims, design, and projected performance of the LDR, a 20-m-primary two-stage four-mirror orbiting sub-mm/FIR astronomical observatory under NASA development, are reviewed. It is shown that the LDR would provide capabilities complementary to those of IRAS, the Kuiper Airborne Observatory, the IRTF, the Hubble Space Telescope, and the planned Space IR Telescope Facility for observations of small-scale background anisotropies, high-redshift galaxies, and objects at temperatures of a few times 10 K or lower. The current design concept is illustrated with extensive drawings, diagrams, and tables of instrument parameters. Particular attention is given to the graphite-epoxy facing and Al-honeycomb core of the primary structure, the focal-plane instruments, and outstanding technological problems.

Swanson, Paul N.↗
NASA NTRS1993

Evidence for a multiphase, inhomogeneous interstellar medium in damped Ly alpha systems

The large optical depth in absorption of the Ly-alpha line in damped Ly-alpha systems implies that the emission line produced by H2 regions is very broad, since the number of diffusions is very large. The emission lines observed in DLy-alpha systems are narrow, a fact that can only be explained if the emission comes from the outer layers alone, or if the interstellar medium (ISM) is clumpy and multiphase. It is shown how discrete, cold H1 clouds embedded in a hot, fully ionized phase, produce narrow lines. This might provide evidence for a supernova remnant SNR-dominated ISM at high redshift, in agreement with the observed metallicity and chemical evolution models. Other high redshift galaxies also offer evidence for such a multiphase, in homogeneous ISM.

Valls-Gabaud, David↗
NASA NTRS1993

Ionization states of metallic absorption-line systems in continua of quasars

Ionization states of metallic absorption-line systems in continua of quasars (QSO's) are studied, assuming that the metallic lines arise in gaseous halos of high-redshift galaxies in photoionization equilibrium under the background UV radiation, and constraints on the intensity and spectral shape of the UV radiation are obtained. Then a structure of absorbers suitable for all of the metallic absorption line systems are discussed.

Denda, Kiyomi↗
NASA NTRS1995

The Caltech airborne submillimeter SIS receiver

We have constructed a sensitive submillimeter receiver for the NASA Kuiper Airborne Observatory (KAO) which at present operates in the 500-750 GHz band. The DSB receiver noise temperature is about 5 h nu/k(sub B) over the 500-700 GHz range. This receiver has been used to detect H2O(18)O, HCl, and CH in interstellar molecular clouds, and also to search for C(+) emission from the highly redshifted galaxy (z = 2.3) IRAS 10214.

Zmuidzinas, Jonas↗
NASA NTRS1997

The Decay of Optical Emission from the gamma-Ray Burst GRB970228

The origin of gamma-ray bursts has been one of the great unsolved mysteries in high-energy astrophysics for almost 30 years. The recent discovery of fading sources at X-ray and optical wavelengths coincident with the location of the gamma-ray burst GRB970228 therefore provides an unprecedented opportunity to probe the nature of these high-energy events. The optical counterpart appears to be a transient point source embedded in a region of extended nebulosity, the latter having been tentatively identified as a high-redshift galaxy. This would seem to favour models that place gamma-ray bursts at cosmological distances, although a range of mechanisms for producing the bursts is still allowed. A crucial piece of information for distinguishing between such models is how the brightness of the optical counterpart evolves with time. Here we re-evaluate the existing photometry of the optical counterpart of GRB970228 to construct an optical light curve for the transient event. We find that between 21 hours and six days after the burst, the R-band brightness decreased by a factor of approximately 40, with any subsequent decrease in brightness occurring at a much slower rate. As the point source faded, it also became redder. The initial behaviour of the source appears to be consistent with the 'fireball' model, but the subsequent decrease in the rate of fading may prove harder to explain.

Galama, T.↗
NASA NTRS1997

The Decay of Optical Emission Form the Gamma-Ray Burst GRB 970228

The origin of gamma-ray bursts has been one of the great unsolved mysteries in high-energy astrophysics for almost 30 years. The recent discovery of fading sources at X-ray and optical wave-lengths coincident with the location of the gamma-ray burst GRB970228 therefore provides an unprecedented opportunity to probe the nature of these high-energy events. The optical counterpart appears to be a transient point source embedded in a region of extended nebulosity, the latter having been tentatively identified as a high-redshift galaxy. This would seem to favour models that place gamma-ray bursts at cosmological distances, although a range of mechanisms for producing the bursts is still allowed. A crucial piece of information for distinguishing between such models is how the brightness of the optical counterpart evolves with time. Here we re-evaluate the existing photometry of the optical counterpart of GRB970228 to construct an optical light curve for the transient event. We find that between 21 hours and six days after the burst, the R-band brightness decreased by a factor of approx. 50, with any subsequent decrease in brightness occurring at a much slower rate. As the point source faded, it also became redder. The initial behaviour of the source appears to be consistent with the 'fireball' model, in which the burst results from the merger of two neutron stars, but the subsequent decrease in the rate of fading may prove harder to explain. The gamma-ray burst of 28 February 1997, detected with the Gamma-Ray Burst Monitor on board the BeppoSAX satellite, and located with an approx. 3 feet radius position with the Wide Field Camera on the same satellite, was the first for which a fading X-ray and optical counterpart were discovered. The optical Counterpart was discovered from a comparison of V- and I-band images taken with the William Herschel Telescope (WHT) on February 28.99 UT, and the Isaac Newton Telescope (INT; V band) and the WHT (I band) on March 8.8 uT.

Galama, T.↗
NASA NTRS2004

Putting Priors in Mixture Density Mercer Kernels

This paper presents a new methodology for automatic knowledge driven data mining based on the theory of Mercer Kernels, which are highly nonlinear symmetric positive definite mappings from the original image space to a very high, possibly infinite dimensional feature space. We describe a new method called Mixture Density Mercer Kernels to learn kernel function directly from data, rather than using predefined kernels. These data adaptive kernels can en- code prior knowledge in the kernel using a Bayesian formulation, thus allowing for physical information to be encoded in the model. We compare the results with existing algorithms on data from the Sloan Digital Sky Survey (SDSS). The code for these experiments has been generated with the AUTOBAYES tool, which automatically generates efficient and documented C/C++ code from abstract statistical model specifications. The core of the system is a schema library which contains template for learning and knowledge discovery algorithms like different versions of EM, or numeric optimization methods like conjugate gradient methods. The template instantiation is supported by symbolic- algebraic computations, which allows AUTOBAYES to find closed-form solutions and, where possible, to integrate them into the code. The results show that the Mixture Density Mercer-Kernel described here outperforms tree-based classification in distinguishing high-redshift galaxies from low- redshift galaxies by approximately 16% on test data, bagged trees by approximately 7%, and bagged trees built on a much larger sample of data by approximately 2%.

Srivastava, Ashok N.↗
NASA NTRS2005

The Space Infrared Interferometric Telescope (SPIRIT)

SPIRIT, a candidate NASA "Origins Probe," is a spatial and spectral interferometer with an operating wavelength range 25 - 400 microns. SPIRIT will provide sub-arcsecond resolution images and spectra with resolution R = 3000 in a 1 arcmin field of view to accomplish three primary scientific objectives: (1) Learn how planetary systems form from protostellar disks, and how they acquire their chemical organization; (2) Characterize the family of extrasolar planetary systems by imaging the structure in debris disks to understand how and where planets form, and why some planets are ice giants and others are rocky; and (3) Learn how high-redshift galaxies formed and merged to form the present-day population of galaxies. Observations with the space-based SPIRIT will be complementary to those of ground-based submillimeter and millimeter arrays and to JWST. We report results of a recently-completed pre-Phase A mission study.

Leisawitz, David↗
NASA NTRS2006

The Origin and Evolution of Interstellar Dust

In this lecture I will discuss the many different manifestation of interstellar dust, and current dust models that satisfy interstellar extinction, diffuse infrared emission, and interstellar abundances constraints. Dust is made predominantly in AGB stars and Type I1 supernovae, and I will present observational evidence for the presence of dust in these sources. I will then present chemical evolution models that follow the abundance of dust which is determined by the combined processes of formation, destruction by interstellar shock waves, and accretion in molecular clouds. The model will be applied to the evolution of PAHs and the evolution of dust in the high-redshift galaxy (z=6.42) JD11.

Dwek, Eli↗