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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1986

IUE study of the very local interstellar medium

The IUE and Copernicus results for the very local interstellar medium are compared. Despite its lower resolution, IUE produces results of comparable quality, giving important confirmation of Copernicus results on the density, temperature, turbulence, and deuterium-to-hydrogen ratio in the region within 10 pc of the Sun. The stars observed are in a very low-density quarter of the galaxy: multicomponent structure seen in other directions may not be present in the direction of most of the observed stars. The exceedingly low densities observed in certain directions encourages the idea that EUV studies of certain normal stars may be possible.

Henry, R. C.↗
NASA NTRS1993

Decaying neutrinos in galaxy clusters

The DM profile in clusters of galaxies was studied and simulated using the Harrison-Zel'dovich spectrum of density fluctuations, and an amplitude previously derived from numerical simulations and in agreement with microwave background fluctuations. Neutrino DM densities, with this amplitude normalization cluster, are comparable to observed cluster DM values. It was concluded that given this normalization, the cluster DM should be al least largely composed of neutrinos. The constraint of Davidson et al., who argued that the failure to detect uv photons from the dark matter (DM) in cluster A665 excludes the decaying neutrino hypothesis, could be somewhat weakened by the presence of baryonic DM; but it cannot be eliminated given our assumptions.

Melott, Adrian L.↗
DOE OSTI2024

GAINN: The Galaxy Assembly and Interaction Neural Networks for High-redshift JWST Observations

We present the Galaxy Assembly and Interaction Neural Networks (Gainn), a series of artificial neural networks for predicting the redshift, stellar mass, halo mass, and mass-weighted age of simulated galaxies based on James Webb Space Telescope (JWST) photometry. Our goal is to determine the best neural network for predicting these variables at 11 < z < 15. The parameters of the optimal neural network can then be used to estimate these variables for real, observed galaxies. The inputs of the neural networks are JWST filter magnitudes of a subset of five broadband filters (F150W, F200W, F277W, F356W, and F444W) and two medium-band filters (F162M and F182M). We compare the performance of the neural networks using different combinations of these filters, as well as different activation functions and numbers of layers. The best neural network predicted redshift with a normalized rms error of $0.010^{+0.003}_{-0.001}$, stellar mass with rms = $0.089^{+0.044}_{-0.022}$, halo mass with a mean-squared error of $0.022^{+0.014}_{-0.008}$, and mass-weighted age with rms = $12.466^{+5.065}_{-2.408}$. We also test the performance of Gainn on real data from MACS0647JD, an object observed by JWST. Predictions from Gainn for the first projection of the object (JD1) have normalized bias $\langle$Δz$\rangle$ < 0.00228, which is significantly smaller than found with template-fitting methods. We find that the optimal filter combination is F277W, F356W, F162M, and F200W when considering both theoretical accuracy and observational resources from JWST.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

The Rest-frame Submillimeter Spectrum of High-redshift, Dusty, Star-forming Galaxies from the SPT-SZ Survey

We present the average rest-frame spectrum of the final catalog of dusty star-forming galaxies (DSFGs) selected from the South Pole Telescope's SPT-SZ survey and measured with Band 3 of the Atacama Large Millimeter/submillimeter Array. This work builds on the previous average rest-frame spectrum, given in Spilker et al. (2014) for the first 22 sources, and is comprised of a total of 78 sources, normalized by their respective apparent dust masses. The spectrum spans 1.9 < z < 6.9 and covers rest-frame frequencies of 240–800 GHz. Combining this data with low-J CO observations from the Australia Telescope Compact Array, we detect multiple bright line features from 12 CO, [Ci], and H 2 O, as well as fainter molecular transitions from 13 CO, HCN, HCO + , HNC, CN, H 2 O + , and CH. We use these detections, along with limits from other molecules, to characterize the typical properties of the interstellar medium (ISM) for these high-redshift DSFGs. We are able to divide the large sample into subsets in order to explore how the average spectrum changes with various galaxy properties, such as effective dust temperature. We find that systems with hotter dust temperatures exhibit differences in the bright 12 CO emission lines, and contain either warmer and more excited dense gas tracers or larger dense gas reservoirs. These observations will serve as a reference point to studies of the ISM in distant luminous DSFGs (L IR > 10 12 L ⊙ ), and will inform studies of chemical evolution before the peak epoch of star formation at z = 2–3.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Type Ia supernova magnitude step from the local dark matter environment

ABSTRACT Residuals in the Hubble diagram at optical wavelengths and host galaxy stellar mass are observed to correlate in type Ia supernovae (SNe Ia) (‘magnitude step’). Among possible progenitor channels for the associated explosions, those based on dark matter (DM) have attracted significant attention, including our recent proposal that ‘normal’ SNe Ia from bare detonations in sub-Chandrasekhar white dwarf stars are triggered by the passage of asteroid-mass primordial black holes (PBHs): the magnitude step could then originate from a brightness dependence on stellar properties, on DM properties, or both. Here, we present a method to estimate the local DM density and velocity dispersion of the environment of SN Ia progenitors. We find a luminosity step of $0.52\pm 0.11\,$ mag corresponding to bins of high versus low DM density in a sample of 222 low-redshift events from The Open Supernova Catalog. We investigate whether the magnitude step can be attributed to local DM properties alone, assuming asteroid-mass PBHs. Given the inverse correlation between SN Ia brightness and PBH mass, an intriguing explanation is a spatially inhomogeneous PBH mass function. If so, a strong mass segregation in the DM density-dependent PBH mass scale is needed to explain the magnitude step. While mass segregation is observed in dense clusters, it is unlikely to be realized on galactic scales. Therefore, if DM consists of asteroid-mass PBHs, the magnitude step is more likely to exist, and dominantly to be attributed to local stellar properties.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1975

Observation of soft X-rays from cosmic sources

A binary X-ray source, an extended extragalactic X-ray source and several nearby stars were surveyed for X-ray emission. The energy spectrum and time structure of X-ray flux from the binary source, Her X-l, was investigated in the range from 0.15 to 6 KeV. This source was observed at a binary phase of 0.18 with the system near elongation normal to the line of sight. Intense pulsations were observed in optical emission lines near this binary phase. The spectrum and angular distribution of X-ray emission from the X-ray source in the Virgo Cluster of Galaxies, near M 87, was also observed. In addition, the stars Alpha Leo, Zeta Her, and Epsilon Vir were investigated. Epsilon Aur and Alpha Aur were also scanned. These stars were studied since there is increasing evidence that such objects may be transient sources of soft X-rays.

Catura, R. C.↗
NASA NTRS2011

SN 2010ay is a Luminous and Broad-lined Type Ic Supernova within a Low-metallicity Host Galaxy

We report on our serendipitous pre-discovery detection and detailed follow-up of the broad-lined Type Ic supernova SN2010ay at z approx 0.067 imaged by the Pan-STARRS1 3pi survey just approx 4 days after explosion. Combining our photometric observations with those available in the literature, we estimate the explosion date and the peak luminosity of the SN, M(sub R) approximately equals 20.2 mag, significantly brighter than known GRB-SNe and one of the most luminous SNe Ibc ever discovered. We measure the photospheric expansion velocity of the explosion from our spectroscopic follow-up observations, v(sub ph) approximately equals 19.2 X 10 (exp 3) km/s at approx 40 days after explosion. In comparison with other broad-lined SNe, the characteristic velocity of SN2010ay is 2 - 5 X higher and similar to the measurements for GRB-SNe at comparable epochs. Moreover the velocity declines two times slower than other SNe Ic-BL and GRB-SNe. Assuming that the optical emission is powered by radioactive decay, the peak magnitude implies the synthesis of an unusually large mass of Ni-56, M(sub Ni) = 0.9(+0.1/-0.1) solar mass. Our modeling of the light-curve points to a total ejecta mass, M(sub ej) approx 4.7 Solar Mass, and total kinetic energy, E(sub K,51) approximately equals 11. Thus the ratio of M(sub Ni) to M(sub ej) is at least twice as large for SN2010ay than in GRB-SNe and may indicate an additional energy reservoir. We also measure the metallicity (log(O/H) + 12 = 8.19) of the explosion site within the host galaxy using a high S/N optical spectrum. Our abundance measurement places this SN in the low-metallicity regime populated by GRB-SNe, and approx 0.2(0.5) dex lower than that typically measured for the host environments of normal (broad-lined) Ic supernovae. Despite striking similarities to the recent GRB-SN100316D/2010bh, we show that gamma-ray observations rule out an associated GRB with E(sub gamma) approx < 6 X 10(exp 48) erg (25-150 keV). Similarly, our deep radio follow-up observations with the Expanded Very Large Array rule out relativistic ejecta with energy, E approx > 10(exp 48) erg. These observations challenge the importance of progenitor metallicity for the production of a GRB, and suggest that other parameters also play a key role.

Sanders, N. E.↗
DOE OSTI2024

Improving Photometric Redshift Estimates with Training Sample Augmentation

Abstract Large imaging surveys will rely on photometric redshifts (photo- z 's), which are typically estimated through machine-learning methods. Currently planned spectroscopic surveys will not be deep enough to produce a representative training sample for Legacy Survey of Space and Time (LSST), so we seek methods to improve the photo- z estimates that arise from nonrepresentative training samples. Spectroscopic training samples for photo- z 's are biased toward redder, brighter galaxies, which also tend to be at lower redshift than the typical galaxy observed by LSST, leading to poor photo- z estimates with outlier fractions nearly 4 times larger than for a representative training sample. In this Letter, we apply the concept of training sample augmentation, where we augment simulated nonrepresentative training samples with simulated galaxies possessing otherwise unrepresented features. When we select simulated galaxies with ( g - z ) color, i -band magnitude, and redshift outside the range of the original training sample, we are able to reduce the outlier fraction of the photo- z estimates for simulated LSST data by nearly 50% and the normalized median absolute deviation (NMAD) by 56%. When compared to a fully representative training sample, augmentation can recover nearly 70% of the degradation in the outlier fraction and 80% of the degradation in NMAD. Training sample augmentation is a simple and effective way to improve training samples for photo- z 's without requiring additional spectroscopic samples.

Moskowitz, Irene (ORCID:0000000222068589)↗
NASA NTRS1992

Diffuse 0.511 MeV line emission and the distribution of positron annihilation in the galaxy

We model the distribution in the Galaxy of 0.511 MeV line emission and the implied positron annihilation using plausible distributions based on observations at other photon energies. We use 0.511 MeV line observations from the Galactic center and from directions away from the Galactic center to normalize the two-dimensional 0.511 MeV sky maps. We find that in order to understand all of the available data it is necessary to invoke the presence of a time-variable component of 0.511 MeV line emission in addition to an underlying diffuse component. The large 0.511 MeV fluxes observed with broad field of view detectors, such as the SMM gamma-ray spectrometer, can be reconciled with the small fluxes seen with narrow field-of-view instruments (GRIS and OSSE) from directions away from the Galactic center if the diffuse emission follows the distribution of Galactic novae for which the recently detected 0.511 MeV line emission from the Galactic center with OSSE is predominantly of diffuse origin. For future GRIS and HEXAGONE observations from the direction of the Galactic center we predict a minimum 0.511 MeV line flux of (6.0 +/- 0.9) x 10 exp -4 photons/sq cm/s.

Skibo, J. G.↗
DOE OSTI2021

The Distribution and Evolution of Quasar Proximity Zone Sizes

In this paper, we study the sizes of quasar proximity zones with synthetic quasar absorption spectra obtained by postprocessing a Cosmic Reionization On Computers (CROC) simulation. CROC simulations have both relatively large box sizes and high spatial resolution, allowing us to resolve Lyman limit systems (LLSs), which are crucial for modeling the quasar absorption spectra. We find that before reionization, most quasar proximity zone sizes grow steadily for ~10 Myr, while after reionization, they grow rapidly but only for ~0.1 Myr. We also find a slow growth of R obs with decreasing turn-on redshift. In addition, we find that ~1%–2% of old quasars (30 Myr old) display extremely small proximity zone sizes (<1 proper Mpc), the vast majority of which are due to the occurrence of a damped Lyα absorber (DLA) or an LLS along the line of sight. These DLAs and LLSs are contaminated with metal, which offers a way to distinguish them from the normal proximity zones of young quasars.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1986

The high energy transmission grating spectrometer for AXAF

Attention is given to a high energy transmission grating spectrometer that operates over the range 0.4-8 keV, giving resolving powers of 100-1000 and effective areas of 10-200 sq cm. The instrument, which is part of the MIT high resolution X-ray spectroscopy investigation, consists of a single array of grating facets of two types: medium energy gratings of 0.6-micron period, 0.5-micron thick silver mounted behind the outer three AXAF mirrors, and high energy gratings of 0.2-micron period, 1.0-micron thick gold mounted behind the inner three mirrors. The gratings are oriented so as to correct for coma and so that the medium and high energy spectra form a shallow 'X' at the AXAF focal plane. Likely targets include normal stars, binary X-ray sources, active galactic nuclei and quasars. The HETGS can also be used to give moderate resolution spectra of slightly extended sources and monochromatic images of sources with strong lines, such as supernova remnants in nearby galaxies.

Canizares, C. R.↗
DOE OSTI2024

Hawai‘i Supernova Flows: a peculiar velocity survey using over a Thousand Supernovae in the near-infrared

ABSTRACT We introduce the Hawai‘i Supernova Flows project and present summary statistics of the first 1217 astronomical transients observed, 668 of which are spectroscopically classified Type Ia Supernovae (SNe Ia). Our project is designed to obtain systematics-limited distances to SNe Ia while consuming minimal dedicated observational resources. To date, we have performed almost 5000 near-infrared (NIR) observations of astronomical transients and have obtained spectra for over 200 host galaxies lacking published spectroscopic redshifts. In this survey paper, we describe the methodology used to select targets, collect/reduce data, calculate distances, and perform quality cuts. We compare our methods to those used in similar studies, finding general agreement or mild improvement. Our summary statistics include various parametrizations of dispersion in the Hubble diagrams produced using fits to several commonly used SN Ia models. We find the lowest dispersions using the SNooPy package’s EBV_model2, with a root mean square deviation of 0.165 mag and a normalized median absolute deviation of 0.123 mag. The full utility of the Hawai‘i Supernova Flows data set far exceeds the analyses presented in this paper. Our photometry will provide a valuable test bed for models of SN Ia incorporating NIR data. Differential cosmological studies comparing optical samples and combined optical and NIR samples will have increased leverage for constraining chromatic effects like dust extinction. We invite the community to explore our data by making the light curves, fits, and host galaxy redshifts publicly accessible.

Do, Aaron (ORCID:0000000334297845)↗
DOE OSTI2025

Constraints on dark photon dark matter from Lyman- α forest simulations and an ultrahigh signal-to-noise quasar spectrum

The ultralight dark photon is a well-motivated, hypothetical dark matter candidate. In a dilute plasma, they can resonantly convert into photons, and heat up the intergalactic medium between galaxies. In this work, we explore the dark photon dark matter parameter space by comparing synthetic Lyman- α forest data from cosmological hydrodynamical simulations to observational data from VLT/UVES of the quasar HE0940-1050 ( z em = 3.09 ). We use a novel flux normalization technique that targets underdense gas, reshaping the flux probability distribution. Not only do we place robust constraints on the kinetic mixing parameter of dark photon dark matter, but notably our findings suggest that this model can still reconcile simulated and observed Doppler parameter distributions of z ∼ 0 Lyman- α lines, as seen by HST/COS. This work opens new pathways for the use of the Lyman- α forest to explore new physics, and can be extended to other scenarios such as primordial black hole evaporation, dark matter decay, and annihilation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Where do $AMS-02$ anti-helium events come from?

We discuss the origin of the anti-helium-3 and -4 events possibly detected by AMS-02. Using up-to-date semi-analytical tools, we show that spallation from primary hydrogen and helium nuclei onto the ISM predicts a anti-helium-3 flux typically one to two orders of magnitude below the sensitivity of AMS-02 after 5 years, and a anti-helium-4 flux roughly 5 orders of magnitude below the AMS-02 sensitivity. We argue that dark matter annihilations face similar difficulties in explaining this event. We then entertain the possibility that these events originate from anti-matter-dominated regions in the form of anti-clouds or anti-stars. In the case of anti-clouds, we show how the isotopic ratio of anti-helium nuclei might suggest that BBN has happened in an inhomogeneous manner, resulting in anti-regions with a anti-baryon-to-photon ratio of one in a thousand of the baryon-to-photon ratio. We discuss properties of these regions, as well as relevant constraints on the presence of anti-clouds in our Galaxy. We present constraints from the survival of anti-clouds in the Milky-Way and in the early Universe, as well as from gamma-ray observations. In particular, these require the anti-clouds to be almost free of normal matter. We also discuss an alternative where anti-domains are dominated by surviving anti-stars. We suggest that part of the unindentified sources in the 3FGL catalog can originate from anti-clouds or anti-stars. AMS-02 and GAPS data could further probe this scenario.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2013

Energy Feedback from X-ray Binaries in the Early Universe

X-ray photons, because of their long mean-free paths, can easily escape the galactic environments where they are produced, and interact at long distances with the intergalactic medium, potentially having a significant contribution to the heating and reionization of the early universe. The two most important sources of X-ray photons in the universe are active galactic nuclei (AGNs) and X-ray binaries (XRBs). In this Letter we use results from detailed, large scale population synthesis simulations to study the energy feedback of XRBs, from the first galaxies (z (redshift) approximately equal to 20) until today.We estimate that X-ray emission from XRBs dominates over AGN at z (redshift) greater than or approximately equal to 6-8. The shape of the spectral energy distribution of the emission from XRBs shows little change with redshift, in contrast to its normalization which evolves by approximately 4 orders of magnitude, primarily due to the evolution of the cosmic star-formation rate. However, the metallicity and the mean stellar age of a given XRB population affect significantly its X-ray output. Specifically, the X-ray luminosity from high-mass XRBs per unit of star-formation rate varies an order of magnitude going from solar metallicity to less than 10% solar, and the X-ray luminosity from low-mass XRBs per unit of stellar mass peaks at an age of approximately 300 Myr (million years) and then decreases gradually at later times, showing little variation for mean stellar ages 3 Gyr (Giga years, or billion years). Finally, we provide analytical and tabulated prescriptions for the energy output of XRBs, that can be directly incorporated in cosmological simulations.

galaxies↗
NASA NTRS1986

General constraints on the age and chemical evolution of the Galaxy

The formalism of Schramm and Wasserburg (1970) for determining the mean age of the elements is extended to develop as model-independent a range for the Galaxy's age as possible that takes all nuclear and meteoritic data uncertainties into account. A model-independent upper limit to that age is derived from an expansion of the equation giving the mean age of the elements in moments of the normalized effective nucleosynthesis rate. This limit depends only on the ratio of the mean time of formation of the elements to the total duration of nucleosynthesis, and on model-independent data. It is shown tht the Th-232/U-238. U-235/U-238, and Pu-244/U-238 chronometric pairs can give constraints on the relative rate of nucleosynthesis over the history of the synthesis of the solar system material.

Meyer, Bradley S.↗
NASA NTRS1992

Cosmic string with a light massive neutrino

We have estimated the power spectra of density fluctuations produced by cosmic strings with neutrino hot dark matter (HDM). Normalizing at 8/h Mpc, we find that the spectrum has more power on small scales than HDM + inflation, less than cold dark matter (CDM) + inflation, and significantly less the CDM + strings. With HDM, large wakes give significant contribution to the power on the galaxy scale and may give rise to large sheets of galaxies.

Albrecht, Andreas↗
NASA NTRS1994

Decaying neutrinos in galaxy clusters

Davidsen et al. (1991) have argued that the failure to detect UV photons from the dark matter (DM) in cluster A665 excludes the decaying neutrino hypothesis. Sciama et al. (1993) argued that because of high central concentration the DM in that cluster must be baryonic. We study the DM profile in clusters of galaxies simulated using the Harrison-Zel'dovich spectrum of density fluctuations, and an amplitude previously derived from numerical simulations (Melott 1984b; Anninos et al. 1991) and in agreement with microwave background fluctuations (Smoot et al. 1992). We find that with this amplitude normalization cluster neutrino DM densities are comparable to observed cluster DM values. We conclude that given this normalization, the cluster DM should be at least largely composed of neutrinos. The constraint of Davidsen et al. can be somewhat weakened by the presence of baryonic DM; but it cannot be eliminated given our assumptions.

Melott, Adrian L.↗