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The LISA Science Ground Segment

The mHz band of the gravitational wave (GW) spectrum contains an unprecedented abundance of galactic, extra-galactic, and cosmological sources. The Laser Interferometer Space Antenna (LISA) will survey the mHz GW band and provide unique observational constraints on the formation and evolution of compact binaries in the Milky Way, the origin and growth of massive black holes throughout cosmic history, the dynamics of dense stellar environments in galactic nuclei, the fundamental nature of gravity and black holes, and more. The richness of the LISA data comes at the price of a more complicated analysis framework than is required for currently operating GW observatories.

Tyson B. Littenberg↗

NASA NTRS1991

What COBE might see - The far-infrared cosmological background

The redshifted emission from infrared luminous galaxies should produce a diffuse background around 300 microns detectable by the Cosmic Background Explorer (COBE). The detection of such emission would provide evidence for evolution in the density or luminosity of galaxies in the infrared.

Beichman, C. A.↗

NASA NTRS2011

Using Dark Matter Haloes to Learn about Cosmic Acceleration: A New Proposal for a Universal Mass Function

Structure formation provides a strong test of any cosmic acceleration model because a successful dark energy model must not inhibit or overpredict the development of observed large-scale structures. Traditional approaches to studies of structure formation in the presence of dark energy or a modified gravity implement a modified Press-Schechter formalism, which relates the linear overdensities to the abundance of dark matter haloes at the same time. We critically examine the universality of the Press-Schechter formalism for different cosmologies, and show that the halo abundance is best correlated with spherical linear overdensity at 94% of collapse (or observation) time. We then extend this argument to ellipsoidal collapse (which decreases the fractional time of best correlation for small haloes), and show that our results agree with deviations from modified Press-Schechter formalism seen in simulated mass functions. This provides a novel universal prescription to measure linear density evolution, based on current and future observations of cluster (or dark matter) halo mass function. In particular, even observations of cluster abundance in a single epoch will constrain the entire history of linear growth of cosmological of perturbations.

Prescod-Weinstein, Chanda↗

NASA NTRS1992

Light-element abundances in Population II dwarfs

This paper reviews the abundances of the light elements lithium, beryllium, and boron in main-sequence and subgiant, Population II stars. Li is important to cosmology because it is synthesized in the Big Bang, but is also used to study stellar structure. Beryllium is useful for studying galactic chemical evolution because its formation in the interstellar medium involves different physics to stellar nucleosynthesis, and it thus provides independent data on the evolution of the halo. Some (though not all) inhomogeneous Big Bang nucleosynthesis codes predict a significant primordial component to this element, so its observed abundance may constrain such models. Boron, observations of which became feasible with the operation of the Hubble Space Telescope, provides complementary data to Be, helping check the element ratios predicted by calculations of spallation reactions in the interstellar medium, and will indicate whether the observed Be abundance has an excess over the expected spallation component, indicating a possible primordial component.

Ryan, Sean G.↗

NASA NTRS1992

A simple test of independence for truncated data with applications to redshift surveys

This paper presents an easily applied permutation test for H0, closely related to Lyden-Bell's (1971) estimate of the marginal distribution of truncated data. The test is applied to two redshift-magnitude surveys, one of galaxies and one of quasars. Assuming statistical independence, testing H0 amounts to testing validity of the cosmological model. Segal's (1986) chronomatic cosmological model is rejected under H0. On the other hand, for the quasar sample H0 is rejected strongly in a conventional cosmological model (and in a chronomatic model as well) indicating either incorrectness of the models or, as is more commonly assumed, indicating strong luminosity evolution.

Efron, Bradley↗

NASA NTRS1999

Theories of the Universe: A One Semester Course for Honors Undergraduates

For the last two years The University of Alabama in Huntsville (UAH) has delivered a one semester course entitled Theories of The Universe as a seminar for undergraduate honors students. The enrollment is limited to fifteen students to encourage a maximum amount of interaction and discussion. The course has been team-taught enlisting the support of four scientists from the NASA Marshall Space Flight Center as well as UAH faculty from the history, philosophy, biology and physics departments. The course mixes history, mythology, philosophy, religion, and, of course, science and astronomy. The course traces mankind's view of the universe and how that has changed from about 30,000 years BCE to the current observations and models. Starting with a brief history of mankind we trace the evolution of ideas including Prehistoric European, Babylonian, Egyptian, Asian, North, Central and South American, African, Chinese, Greek, Middle Ages, Copernican, Galileo, Kepler, the Renaissance and Enlightenment, Newton, Einstein, and Hawking etc. Namely, we try to touch on just about every different view to puzzles of quantum cosmology, missing mass and the cosmological constant. By the end of the course, students should have a good understanding of: (1) the human desire and need for understanding; (2) the interplay between observations, modeling and theory development, and the need for revisions based on further observations; (3) the role of developing technology in advancing knowledge; (4) the evolution of our views of the universe and our relation to it; and (5) where we are today in our quest. Students are required to write two term papers and present them to the class. The final exam is a open discussion on our views of what we have learned.

Dimmock, John O.↗

NASA NTRS1990

Causal compensated perturbations in cosmology

A theoretical framework is developed to calculate linear perturbations in the gravitational and matter fields which arise causally in response to the presence of stiff matter sources in a FRW cosmology. It is shown that, in order to satisfy energy and momentum conservation, the gravitational fields of the source must be compensated by perturbations in the matter and gravitational fields, and the role of such compensation in containing the initial inhomogeneities in their subsequent evolution is discussed. A complete formal solution is derived in terms of Green functions for the perturbations produced by an arbitrary source in a flat universe containing cold dark matter. Approximate Green function solutions are derived for the late-time density perturbations and late-time gravitational waves in a universe containing a radiation fluid. A cosmological energy-momentum pseudotensor is defined to clarify the nature of energy and momentum conservation in the expanding universe.

Veeraraghavan, Shoba↗

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 NTRS1979

Galaxies and gamma-ray astronomy

The nature of the high-energy spectra of several types of active galaxies and their contribution to the measured diffuse gamma-ray emission between 1 and 150 MeV are considered, using X-ray spectra of active galaxies and SAS 2 data regarding the intensity upper limits to the gamma-ray emission above 35 MeV. It is found that a substantial increase in slope of the photon energy spectrum must occur in the low energy gamma-ray region for Seyfert galaxies, BL Lac objects, and emission line galaxies; the power-law spectra observed in the X-ray range must steepen substantially between 50 keV and 50 MeV. In addition, a cosmological integration shows that Seyfert galaxies, BL Lac objects, and quasars may account for most of the 1-150 MeV diffuse background, even without significant evolution.

Bignami, G. F.↗

NASA NTRS1986

The advanced X-ray Astrophysics Facility

The basic characteristics and capabilities of the Advanced X-ray Astrophysics Facility (AXAF) are described. The use of the AXAF to perform mass determinations in galaxies and in cluster of galaxies is discussed. The study of galaxy evolution, the interactions of galaxies with their environment, and the properties of galactic halos with the AXAF is proposed. The application of the facility to cosmological measurements, the estimation of the age of the universe, and the analysis of stars, galaxy clusters, and protogalaxies is examined.

Tananbaum, H.↗

NASA NTRS1996

X-ray spectra of clusters and groups

The high quality spectra obtained with X-ray imaging spectroscopy enables the abundance of the alpha burning elements and abundance gradients for low redshift clusters to be determined. The X-ray spectra of relaxed systems are discussed with emphasis on the recent determination of the abundances of alpha burning elements for clusters and groups, the evolution of temperature and abundance, and the mass distributions of rich clusters. Typical X-ray results from the Rosat and the Advance Satellite for Cosmology and Astrophysics (ASCA) are presented and discussed.

Mushotzky, Richard↗

NASA NTRS1990

Ultraviolet spectroscopy of planetary nebulae: Cosmological implications

Optical spectrophotometry of PW Vulpeculae (Nova Vul 1984 no. 1) is combined with ultraviolet data to estimate electron temperatures, densities, and abundances in the ejecta of this slow classical nova. The reddening, distance, and evolution of the ultraviolet spectrum are also discussed. Abundances are nearly solar, with the exception of Nitrogen, which is substantially higher. Although Neon has been reported to be enhanced in several novae, it does not seem to be the case for PW Vul. Photoionization model calculations are presented of the ejecta that give a reasonable match of the observed emission spectrum. A strong featureless continuum shows that very hot, presumably shock heated, gas plays a major role in determining the energetics of this nova. Emission from this hot gas is responsible for the ionization of the nebular gas. A calculation of the masses of both the hot coronal gas and the cooler nebular gas shows that the former may account for most of the mass of the ejecta.

Ferland, Gary J.↗

NASA NTRS2021

Probing Galaxy Evolution in Massive Clusters Using ACT and DES: Splashback as a Cosmic Clock

We measure the projected number density profiles of galaxies and the splashback feature in clusters selected by the Sunyaev–Zel'dovich effect from the Advanced Atacama Cosmology Telescope (AdvACT) survey using galaxies observed by the Dark Energy Survey (DES). The splashback radius is consistent with CDM-only simulations and is located at-+-h2.4 Mpc0.40.31. We split the galaxies on color and find significant differences in their profile shapes. Red and green-valley galaxies show a splashback-like minimum in their slope profile consistent with theory, while the bluest galaxies show a weak feature at a smaller radius. We develop a mapping of galaxies to subhalos in simulations and assign colors based on infall time onto their hosts. We find that the shift in location of the steepest slope and different profile shapes can be mapped to the average time of infall of galaxies of different colors. The steepest slope traces a discontinuity in the phase space of dark matter halos. By relating spatial profiles to infall time, we can use splashback as a clock to understand galaxy quenching. We find that red galaxies have on average been in clusters over 3.2 Gyr, green galaxies about 2.2 Gyr, while blue galaxies have been accreted most recently and have not reached apocenter. Using the full radial profiles, we fit a simple quenching model and find that the onset of galaxy quenching occurs after a delay of about a gigayear and that galaxies quench rapidly thereafter with an exponential timescale of 0.6 Gyr.

Galaxy clusters↗

NASA NTRS1973

Distortion of the microwave blackbody background radiation implied by the baryon-symmetric cosmology of omnes and the galaxy formation theory of Stecker and Puget

Theories on the distortion of microwave black body spectrum are presented. Data suggest that continuous annihilation of matter-antimatter, during all stages of universe evolution cause distortion by thermal energy distribution at red shifts less than 10,000. Data also show distortions in the Rayleigh-Jeans spectrum are caused by energy depositions at red shifts between 10,000 and 1,000 while those in the Wien spectrum are due to energy deposition at lower red shifts after the cosmic gas cools to its atomic state and thermalization does not take place properly.

Stecker, F. W.↗

NASA NTRS2011

X-Ray Binary Populations in a Cosmological Context, Including NuSTAR Predictions

The new ultradeep 4 Ms Chandra Deep Field South has afforded the deepest view ever of X-ray binary populations. We report on the latest results on both LMXB and HMXB evolution out to redshifts of approximately four, including comparison with the latest theoretical models, using this deepest-ever view of the X-ray universe with Chandra. The upcoming NuSTAR mission will open up X-ray binary populations in the hard X-ray band, similar to the pioneering work of Fabbiano et al. in the Einstein era. We report on plans to study both Local Group and starburst galaxies as well as the implications those observations may have for X-ray binary populations in galaxies contributing to the Cosmic X-ray Background.

Cardiff, Ann Hornschemeier↗

NASA NTRS1979

A look at the universe in gamma rays

The scientific background and objectives, proposed instruments, spacecraft constraints, operations plans and present status and schedule of the Gamma Ray Observatory (GRO), a shuttle-launched free-flyer satellite currently planned by NASA, are reviewed. Objectives for the satellite study of the highest energy electromagnetic radiation in the cosmos discussed include the investigation of the evolution of compact objects, nucleosynthesis, gamma-ray objects whose nature is not yet known, the gamma-ray properties of the Galaxy and other galaxies, cosmological effects and intense gamma-ray bursts. The five instruments considered in the definition study which span six decades in energy are presented and proposed experiments are outlined. Although a spacecraft has not yet been selected, several feasible alternatives have been identified, and a launch in the mid-1980s is planned.

Kniffen, D. A.↗

NASA NTRS2012

Joint Analysis of X-Ray and Sunyaev-Zel'Dovich Observations of Galaxy Clusters Using an Analytic Model of the Intracluster Medium

We perform a joint analysis of X-ray and Sunyaev-Zel'dovich effect data using an analytic model that describes the gas properties of galaxy clusters. The joint analysis allows the measurement of the cluster gas mass fraction profile and Hubble constant independent of cosmological parameters. Weak cosmological priors are used to calculate the overdensity radius within which the gas mass fractions are reported. Such an analysis can provide direct constraints on the evolution of the cluster gas mass fraction with redshift. We validate the model and the joint analysis on high signal-to-noise data from the Chandra X-ray Observatory and the Sunyaev-Zel'dovich Array for two clusters, A2631 and A2204.

Galaxies↗

NASA NTRS2003

Project Status Update and SIM Science Breadth Discussion for the Origins Subcommittee (OS)

This viewgraph presentation is composed of two sections The first reviews the features and the science goals of the Space Interferometry Mission (SIM). The goals are: (1) Perform a search for other planetary systems by surveying 2000 nearby stars for astrometric signatures of planetary companion, (2) Survey a sample of 200 nearby stars for orbiting planets down to terrestrial-type masses (3) Improve best current catalog of star positions by >lOOx and extend to fainter stars to allow extension of stellar knowledge to include our entire galaxy (4) Study dynamics and evolution of stars and star clusters in our galaxy to understand how our galaxy was formed and how it will evolve. (5) Calibrate luminosities of important stars and cosmological distance indicators to improve our understanding of stellar processes and to measure precise distance in the distant universe. The presentation also reviews the accomplishments since 2002, the plans for the subsequent 6 months. The second entitled "The Breadth of SIM Science," reviews SIM science goals in a larger context. SIM will serve to complement and pave the way for the Terrestrial Planet Finder (TPF). SIM observations of the motions of stars will tell us about the distribution of all gravitating mass (light plus dark matter) in the Galaxy. SIM observations of the motions of dwarf galaxies around our own will determine the mass distribution (light plus dark matter in the Halo. SIM will greatly extend these observations to test the theories of accretion disks around super massive black holes. SIM has advantages for studying AGN and other very compact objects.

Michelson stellar interferometers↗