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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 NTRS2021

The Heraklion Extragalactic Catalogue (HECATE): A Value-added Galaxy Catalogue for Multimessenger Astrophysics

We present the Heraklion Extragalactic Catalogue, or HECATE, an all-sky value-added galaxy catalogue, aiming to facilitate present and future multiwavelength and multi messenger studies in the local Universe. It contains 204 733 galaxies up to a red shift of 0.047 (D200 Mpc), and it is>50 per cent complete in terms of the B-band luminosity density at distances in the0–170 Mpc range. By incorporating and homogenizing data from astronomical data bases and multiwavelength surveys, the catalogue offers positions, sizes, distances, morphological classifications, star formation rates, stellar masses, metallicities, and nuclear activity classifications. This wealth of information can enable a wide range of applications, such as (i) demographic studies of extragalactic sources, (ii) initial characterization of transient events, and (iii) searches for electromagnetic counterparts of gravitational-wave events. The catalogue is publicly available to the community at a dedicated portal, which will also host future extensions in terms of the covered volume and data products.

K Kovlakas↗
NASA NTRS2022

GJ 229B: Solving the Puzzle of the First Known T Dwarf with the APOLLO Retrieval Code

GJ 229B was the first T dwarf to be discovered in 1995, and its spectrum has been more thoroughly observed than that of most other brown dwarfs. Yet a full spectroscopic analysis of its atmosphere has not been done with modern techniques. This spectrum has several peculiar features, and recent dynamical estimates of GJ 229B’s mass and orbit have disagreed widely, both of which warrant closer investigation. With a separation of tens of astronomical units from its host star, GJ 229B falls near the border of the planet and stellar population formation regimes, so its atmosphere could provide clues to formation processes for intermediate objects of this type. In an effort to resolve these questions, we performed retrievals on published spectra of GJ 229B over a wide range of wavelengths (0.5–5.1 μm) using the open-source APOLLO code. Based on these retrievals, we present a more precise mass estimate of 41.6 ± 3.3MJ and an effective temperature estimate of 869 +5 −7 K, which are more consistent with evolutionary models for brown dwarfs and suggest an older age for the system of >1.0 Gyr. We also present retrieved molecular abundances for the atmosphere, including replicating the previously observed high CO abundance, and discuss their implications for the formation and evolution of this object. This retrieval effort will give us insight into how to study other brown dwarfs and directly imaged planets, including those observed with JWST and other next-generation telescopes.

Alex R Howe↗
NASA NTRS2015

Submillimeter Observations of CLASH 2882 and the Evolution of Dust in this Galaxy

Two millimeter observations of the MACS J1149.6+2223 cluster have detected a source that was consistent with the location of the lensed MACS 1149-JD galaxy at z = 9.6. A positive identification would have rendered this galaxy as the youngest dust forming galaxy in the universe. Follow up observation with the AzTEC 1.1 mm camera and the IRAM NOrthern Extended Millimeter Array (NOEMA) at 1.3 mm have not confirmed this association. In this paper we show that the NOEMA observations associate the 2 mm source with [PCB2012] 2882,12 source number 2882 in the Cluster Lensing And Supernova survey with Hubble (CLASH) catalog of MACS J1149.6 +2223. This source, hereafter referred to as CLASH 2882, is a gravitationally lensed spiral galaxy at z = 0.99. We combine the Goddard IRAM Superconducting 2-Millimeter Observer (GISMO) 2 mm and NOEMA 1.3 mm fluxes with other (rest frame) UV to far-IR observations to construct the full spectral energy distribution of this galaxy, and derive its star formation history, and stellar and interstellar dust content. The current star formation rate of the galaxy is 54/mu/Solar Mass/yr, and its dust mass is about 5 × 10(exp 7)/mu Solar Mass, where mu is the lensing magnification factor for this source, which has a mean value of 2.7. The inferred dust mass is higher than the maximum dust mass that can be produced by core collapse supernovae and evolved AGB stars. As with many other star forming galaxies, most of the dust mass in CLASH 2882 must have been accreted in the dense phases of the interstellar medium.

Submillimeter↗
NASA NTRS1982

Einstein observations of cool stars

Observations of cool stars with the Einstein Observatory (HEAO-2) have brought about a fundamental change in our knowledge and understanding of stellar coronae. The existence of X-ray emission from stars throughout the H-R diagram, the wide range of X-ray luminosity within a given spectral and luminosity class, and the strong correlation of X-ray luminosity with stellar age and rotation are among the more significant Einstein results. These results are strong evidence for the influence of stellar dynamo action on the formation and heating of stellar coronae. A discussion of relevant consortium and guest observations is given. The Hyades cluster, in particular, serves as an example to demonstrate the usefulness of X-ray observations in the study of stellar activity and coronal evolution.

Stern, R. A.↗
NASA NTRS1985

The star-formation history of very young clusters

The popular idea that star formation has proceeded sequentially from lowest to highest mass members in open clusters is examined critically. For extremely young clusters, such as NGC 2264 and NGC 6530, this sequential hypothesis is a consequence of the assignment of pre-main-sequence contraction ages to all member stars. However, such ages yield a formation history which is implausible from a physical point of view, since the critical time for the onset of formation at any stellar mass is equal to the pre-main-sequence contraction time for that mass. Moreover, these ages are in conflict with the strong observational evidence that a substantial fraction of cluster members have already reached the main sequence. After reconsideration of the probable main-sequence members, the stellar ages in NGC 2264 and NGC 6530 are consistent with a variety of formation histories, and, in particular, with the view that all stellar masses form in approximately the same interval of time within a given cluster, i.e., that there is no mass-age correlation. A notion closely related to the sequential hypothesis, that the total star-formation rate increases exponentially with time, is subject to the same criticism.

Stahler, S. W.↗
NASA NTRS2015

Metal-Poor, Strongly Star-Forming Galaxies in the DEEP2 Survey: The Relationship Between Stellar Mass, Temperature-Based Metallicity, and Star Formation Rate

We report on the discovery of 28 redshift (z) approximately equal to 0.8 metal-poor galaxies in DEEP2. These galaxies were selected for their detection of the weak [O (sub III)] lambda 4363 emission line, which provides a "direct" measure of the gas-phase metallicity. A primary goal for identifying these rare galaxies is to examine whether the fundamental metallicity relation (FMR) between stellar mass, gas metallicity, and star formation rate (SFR) holds for low stellar mass and high SFR galaxies. The FMR suggests that higher SFR galaxies have lower metallicity (at fixed stellar mass). To test this trend, we combine spectroscopic measurements of metallicity and dust-corrected SFR with stellar mass estimates from modeling the optical photometry. We find that these galaxies are 1.05 plus or minus 0.61 dex above the redshift (z) approximately 1 stellar mass-SFR relation and 0.23 plus or minus 0.23 dex below the local mass-metallicity relation. Relative to the FMR, the latter offset is reduced to 0.01 dex, but significant dispersion remains dex with 0.16 dex due to measurement uncertainties). This dispersion suggests that gas accretion, star formation, and chemical enrichment have not reached equilibrium in these galaxies. This is evident by their short stellar mass doubling timescale of approximately equal to 100 (sup plus 310) (sub minus 75) million years which suggests stochastic star formation. Combining our sample with other redshift (z) of approximately 1 metal-poor galaxies, we find a weak positive SFR-metallicity dependence (at fixed stellar mass) that is significant at 94.4 percent confidence. We interpret this positive correlation as recent star formation that has enriched the gas but has not had time to drive the metal-enriched gas out with feedback mechanisms.

Metal-Poor↗
NASA NTRS2019

The CANDELS/SHARDS Multi-Wavelength Catalog in GOODS-N: Photometry, Photometric Redshifts, Stellar Masses, Emission Line Fluxes and Star Formation Rates

We present a WFC3 F160W (H-band) selected catalog in the CANDELS/GOODS-N field containing photometry from the ultraviolet (UV) to the far-infrared (IR), photometric redshifts and stellar pa-rameters derived from the analysis of the multi-wavelength data. The catalog contains 35,445 sourcesover the 171 arcmin2of the CANDELS F160W mosaic. The 5σdetection limits (within an aperture ofradius 0.′′17) of the mosaic range betweenH= 27.8, 28.2 and 28.7 in the wide, intermediate and deepregions, that span approximately 50%, 15% and 35% of the total area. The multi-wavelength photom-etry includes broad-band data from UV (U band from KPNO and LBC), optical (HST/ACS F435W,F606W, F775W, F814W, and F850LP), near-to-mid IR (HST/WFC3 F105W, F125W, F140W andF160W, Subaru/MOIRCS Ks, CFHT/Megacam K, andSpitzer/IRAC 3.6, 4.5, 5.8, 8.0μm) and far IR(Spitzer/MIPS 24μm, HERSCHEL/PACS 100 and 160μm, SPIRE 250, 350 and 500μm) observations.In addition, the catalog also includes, optical medium-band data (R∼50) in 25 consecutive bands,λ= 500 to 950 nm, from the SHARDS survey and WFC3 IR spectroscopic observations with theG102 and G141 grisms (R∼210 and 130). The use of higher spectral resolution data to estimate pho-tometric redshifts provides very high, and nearly uniform, precision fromz= 0−2.5. The comparisonto 1,485 good quality spectroscopic redshifts up toz∼3 yields ∆z/(1+zspec)=0.0032 and an outlierfraction ofη=4.3%. In addition to the multi-band photometry, we release added-value catalogs withemission line fluxes, stellar masses, dust attenuations, UV- and IR-based star formation rates andrest-frame colors.

Guillermo Barro↗
NASA NTRS2017

Evidence for Reduced Species Star Formation Rates in the Centers of Massive Galaxies at zeta = 4

We perform the first spatially-resolved stellar population study of galaxies in the early universe z equals 3.5 -6.5, utilizing the Hubble Space Telescope Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) imaging dataset over the GOODS-S field. We select a sample of 418 bright and extended galaxies at z less than or approximately equal to 3.5-6.5 from a parent sample of approximately 8000 photometric-redshift selected galaxies from Finkelstein et al. We first examine galaxies at 3.5 less than or equal to z less than or approximately equal to 4.0 using additional deep K-band survey data from the HAWK-I UDS and GOODS Survey (HUGS) which covers the 4000 Angstrom break at these redshifts. We measure the stellar mass, star formation rate, and dust extinction for galaxy inner and outer regions via spatially-resolved spectral energy distribution fitting based on a Markov Chain Monte Carlo algorithm. By comparing specific star formation rates (sSFRs) between inner and outer parts of the galaxies we find that the majority of galaxies with the high central mass densities show evidence for a preferentially lower sSFR in their centers than in their outer regions, indicative of reduced sSFRs in their central regions. We also study galaxies at z approximately equal to 5 and 6 (here limited to high spatial resolution in the rest-frame ultraviolet only), finding that they show sSFRs which are generally independent of radial distance from the center of the galaxies. This indicates that stars are formed uniformly at all radii in massive galaxies at z approximately equal to 5-6, contrary tomassive galaxies at z. less than approximately equal to 4.

early universe – galaxies: bulges – galaxies: ↗
NASA NTRS2016

Evolution of Intrinsic Scatter in the SFR-Stellar Mass Correlation at 0.5 less than z Less Than 3

We present estimates of intrinsic scatter in the star formation rate (SFR)--stellar mass (M*) correlation in the redshift range 0.5 less than z less than 3.0 and in the mass range 10(exp 7) less than M* less than 10(exp 11) solar mass. We utilize photometry in the Hubble Ultradeep Field (HUDF12) and Ultraviolet Ultra Deep Field (UVUDF) campaigns and CANDELS/GOODS-S and estimate SFR, M* from broadband spectral energy distributions and the best-available redshifts. The maximum depth of the UDF photometry (F160W 29.9 AB, 5 sigma depth) probes the SFR--M* correlation down to M* approximately 10(exp 7) solar mass, a factor of 10-100 x lower in M* than previous studies, and comparable to dwarf galaxies in the local universe. We find the slope of the SFR-M* relationship to be near unity at all redshifts and the normalization to decrease with cosmic time. We find a moderate increase in intrinsic scatter with cosmic time from 0.2 to 0.4 dex across the epoch of peak cosmic star formation. None of our redshift bins show a statistically significant increase in intrinsic scatter approximately 100 Myr. Our results are consistent with a picture of gradual and self-similar assembly of galaxies across more than three orders of magnitude in stellar mass from as low as 10(exp 7) solar mass.

Kurczynski, Peter↗
NASA NTRS2015

A Photometric Machine-Learning Method to Infer Stellar Metallicity

Following its formation, a star's metal content is one of the few factors that can significantly alter its evolution. Measurements of stellar metallicity ([Fe/H]) typically require a spectrum, but spectroscopic surveys are limited to a few x 10(exp 6) targets; photometric surveys, on the other hand, have detected > 10(exp 9) stars. I present a new machine-learning method to predict [Fe/H] from photometric colors measured by the Sloan Digital Sky Survey (SDSS). The training set consists of approx. 120,000 stars with SDSS photometry and reliable [Fe/H] measurements from the SEGUE Stellar Parameters Pipeline (SSPP). For bright stars (g' < or = 18 mag), with 4500 K < or = Teff < or = 7000 K, corresponding to those with the most reliable SSPP estimates, I find that the model predicts [Fe/H] values with a root-mean-squared-error (RMSE) of approx.0.27 dex. The RMSE from this machine-learning method is similar to the scatter in [Fe/H] measurements from low-resolution spectra..

machine learning↗
NASA NTRS1997

Scenarios for galaxy formation

The gravitational instability theory and its application to the origin of large scale structure are reviewed. The modeling of galaxy formation is described, from forwards and backwards perspectives. The emphasis is on the interactions between stellar and galactic formation.

Silk, Joseph↗
NASA NTRS1985

Star formation - An overview

Methods for studying star formation are reviewed. Stellar clusters and associations, as well as field stars, provide a fossil record of the star formation process. Regions of current star formation provide a series of snapshots of different epochs of star formation. A simplified picture of individual star formation as it was envisioned in the late 1970s is contrasted with the results of recent observations, in particular the outflow phenomenon.

Evans, N. J., II↗
NASA NTRS2014

A Magnified View of the Kinematics and Morphology of RCSGA 032727-132609: Zooming in on a Merger at z = 1.7

We present a detailed analysis of multi-wavelength Hubble Space Telescope/Wide Field Camera 3 (WFC3) imaging and Keck/OSIRIS near-infrared adaptive optics-assisted integral field spectroscopy for a highly magnified lensed galaxy at z = 1.70. This young starburst is representative of ultraviolet-selected star-forming galaxies (SFGs) at z approx. 2 and contains multiple individual star-forming regions. Due to the lensing magnification, we can resolve spatial scales down to 100 pc in the source plane of the galaxy. The velocity field shows disturbed kinematics suggestive of an ongoing interaction and there is a clear signature of a tidal tail. We constrain the age, reddening, star formation rate, and stellar mass of the star-forming clumps from spectral energy distribution (SED) modeling of the WFC3 photometry and measure their H(alpha) luminosity, metallicity, and outflow properties from the OSIRIS data.With strong star-formation-driven outflows in four clumps, RCSGA0327 is the first high-redshift SFG at stellar mass <10(exp 10) Stellar Mass with spatially resolved stellar winds. We compare the H(alpha) luminosities, sizes, and dispersions of the star-forming regions with other high-z clumps as well as local giant H(II) regions and find no evidence for increased clump star formation surface densities in interacting systems, unlike in the local universe. Spatially resolved SED modeling unveils an established stellar population at the location of the largest clump and a second mass concentration near the edge of the system that is not detected in H(alpha) emission. This suggests a picture of an equal-mass mixed major merger, which has not triggered a new burst of star formation or caused a tidal tail in the gas-poor component.

Magnified↗
NASA NTRS1992

Some astronomical challenges for the twenty-first century

This paper addresses some of the scientific puzzles that astronomers may face in the next century. Four areas in astronomy are discussed in detail. These include cosmology and galaxy formation, active galaxies and quasars, supernovae and stellar remnants, and the formation of stars and planets. A variety of observatories on the Moon are proposed to attack these astronomical challenges.

Burns, Jack O.↗
NASA NTRS2013

The Spatial Extent and Distribution of Star Formation in 3D-HST Mergers at z is approximately 1.5

We present an analysis of the spatial distribution of star formation in a sample of 60 visually identified galaxy merger candidates at z greater than 1. Our sample, drawn from the 3D-HST survey, is flux-limited and was selected to have high star formation rates based on fits of their broad-band, low spatial resolution spectral energy distributions. It includes plausible pre-merger (close pairs) and post-merger (single objects with tidal features) systems,with total stellar masses and star formation rates derived from multi-wavelength photometry. Here we use near-infrared slitless spectra from 3D-HST which produce H or [OIII] emission line maps as proxies for star-formation maps. This provides a first comprehensive high-resolution, empirical picture of where star formation occurred in galaxy mergers at the epoch of peak cosmic star formation rate. We find that detectable star formation can occur in one or both galaxy centres, or in tidal tails. The most common case (58%) is that star formation is largely concentrated in a single, compact region, coincident with the centre of (one of) the merger components. No correlations between star formation morphology and redshift, total stellar mass, or star formation rate are found. A restricted set of hydrodynamical merger simulationsbetween similarly massive and gas-rich objects implies that star formation should be detectable in both merger components, when the gas fractions of the individual components are the same. This suggests that z is approximately 1.5 mergers typically occur between galaxies whose gas fractions, masses, andor star formation rates are distinctly different from one another.

Spatial↗
NASA NTRS2017

Search for Primitive Matter in the Solar System

Recent astronomical observations and theoretical modeling led to a consensus regarding the global scenario of the formation of young stellar objects (YSO) from a cold molecular cloud of interstellar dust (organics and minerals) and gas that, in some cases, leads to the formation of a planetary system. In the case of our Solar System, which has already evolved for approximately 4567 Ma, the quest is to access, through the investigation of planets, moons, cometary and asteroidal bodies, meteorites, micrometeorites, and interplanetary dust particles, the primitive material that contains the key information about the early Solar System processes and its evolution. However, laboratory analyses of extraterrestrial samples, astronomical observations and dynamical models of the Solar System evolution have not brought yet any conclusive evidence on the nature and location of primitive matter in the Solar System, preventing a clear understanding of its early stages.

Libourel, G.↗
NASA NTRS1985

Contribution functions for Zeeman-split lines, and line formation in photospheric faculae

The transfer of polarized light in an inhomogeneous stellar atmosphere, and the formation of magnetically sensitive spectral lines, are discussed. A new method for the solution of the transfer equations is proposed. The method gives a natural definition of the contribution functions for Stokes' parameters, i.e., functions describing the contributions from different parts along the line-of-sight (LOS). The formalism includes all magneto-optical effects, and allows for an arbitrary variation of magnetic field, velocity field, temperature, density, etc., along the LOS. The formation of FeI lambda 5250.2 in photospheric faculae is described. A potential-field model of a facular element is presented, and spectra profiles and contribution functions are computed for the Stokes parameters I, Q, and V.

Vanballegooijen, A. A.↗
NASA NTRS1993

Infrared and optical imaging of IRAS sources with CO outflow - A snapshot of early star formation

We present multiband imaging of three IRAS sources associated with CO molecular outflows. We find stellar density enhancements around all three IRAS sources. Optical and near-IR photometry indicates that at least 60 percent of the near-IR sources in the vicinity of the IRAS sources are pre-main-sequence stars. Using the photometric data at nbL and M, we are able to identify candidates for the near-IR counterparts of the IRAS sources. We also find that (1) the spectral energy distribution of the deeply embedded sources could be complicated by source confusion and scattered light from the young stellar objects; (2) star formation in the vicinity of the IRAS sources is a continuous process with an age span of 0.5-3 Myr; and (3) stellar density enhancement is probably a phenomenon found at the earliest stage of star formation.

Chen, H.↗