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All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

A comparison of compact, presumably young with extended, evolved radio active galactic nuclei

Context.The triggering and evolution of active galactic nuclei (AGNs) and the interaction of the AGN with its host galaxy is an important topic in extragalactic astrophysics. Radio sources with peaked spectra (peaked spectrum sources, PSS) and compact symmetric objects (CSO) are powerful, compact, and presumably young AGNs and therefore particularly suitable to study aspects of the AGN-host connection. Aims.We use a statistical approach to investigate properties of a PSS-CSO sample that are related to host galaxies and could potentially shed light on the link between host galaxies and AGNs. The main goal is to compare the PSS-CSO sample with a matching comparison sample of extended sources (ECS) to see if the two have significant differences. Methods.We analysed composite spectra, diagnostic line diagrams, multi-band spectral energy distributions (MBSEDs), star formation (SF) indicators, morphologies, and cluster environments for a sample of 121 PSSs and CSOs for which spectra are available from the Sloan Digital Sky Survey (SDSS). The statistical results were compared with those of the ECS sample, where we generally considered the two subsamples of quasi-stellar objects (QSOs) and radio galaxies separately. The analysis is based on a large set of archival data in the spectral range from the ultraviolet to mid-infrared. Results.We find significant differences between the PSS-CSO and the ECS sample. In particular, we find that the ECS sample has a higher proportion of passive galaxies with a lower star formation activity. This applies to both sub-samples (QSOs or radio galaxies) as well as to the entire sample. The star formation rates of the PSS-CSO host galaxies with available data are typically in the range ∼0 to 5 ℳ ⊙ yr −1 , and the stellar masses are in the range 3 × 10 11 to 10 12 ℳ ⊙ . Secondly, in agreement with previous results, we find a remarkably high proportion of PSS-CSO host galaxies with merger signatures. The merger fraction of the PSS-CSO sample is 0.61 ± 0.07, which is significantly higher than that of the comparison sample (0.15 ± 0.06). We suggest that this difference can be explained by assuming that the majority of the PSSs and CSOs cannot evolve to extended radio sources and are therefore not represented in our comparison sample.

Astronomy & Astrophysics↗
NASA NTRS2016

JPSS-1 VIIRS Version 2 At-Launch Relative Spectral Response Characterization and Performance

The relative spectral response (RSR) characterization of the JPSS-1 VIIRS spectral bands has achieved at launch status in the VIIRS Data Analysis Working Group February 2016 Version 2 RSR release. The Version 2 release improves upon the June 2015 Version 1 release by including December 2014 NIST TSIRCUS spectral measurements of VIIRS VisNIR bands in the analysis plus correcting CO2 influence on the band M13 RSR. The T-SIRCUS based characterization is merged with the summer 2014 SpMA based characterization of VisNIR bands (Version 1 release) to yield a fused RSR for these bands, combining the strengths of the T-SIRCUS and the SpMA measurement systems. The M13 RSR is updated by applying a model-based correction to mitigate CO2 attenuation of the SpMA source signal that occurred during M13 spectral measurements. The Version 2 release carries forward the Version 1 RSR for those bands that were not updated (M8-M12, M14-M16AB, I3-I5, DNBMGS). The Version 2 release includes band average (overall detectors and subsamples) RSR plus supporting RSR for each detector and subsample. The at-launch band average RSR have been used to populate Look-Up Tables supporting the sensor data record and environmental data record at-launch science products. Spectral performance metrics show that JPSS-1VIIRS RSR are compliant on specifications with a few minor exceptions. The Version 2 release, which replaces the Version 1 release, is currently available on the password-protected NASA JPSS-1 eRooms under EAR99 control.

Chris Moeller↗
DOE OSTI2014

Faraday rotation from magnesium II absorbers toward polarized background radio sources

Strong singly ionized magnesium (Mg II) absorption lines in quasar spectra typically serve as a proxy for intervening galaxies along the line of sight. Previous studies have found a correlation between the number of these Mg II absorbers and the Faraday rotation measure (RM) at ≈5 GHz. We cross-match a sample of 35,752 optically identified non-intrinsic Mg II absorption systems with 25,649 polarized background radio sources for which we have measurements of both the spectral index and RM at 1.4 GHz. We use the spectral index to split the resulting sample of 599 sources into flat-spectrum and steep-spectrum subsamples. We find that our flat-spectrum sample shows significant (∼3.5σ) evidence for a correlation between Mg II absorption and RM at 1.4 GHz, while our steep-spectrum sample shows no such correlation. We argue that such an effect cannot be explained by either luminosity or other observational effects, by evolution in another confounding variable, by wavelength-dependent polarization structure in an active galactic nucleus, by the Galactic foreground, by cosmological expansion, or by partial coverage models. We conclude that our data are most consistent with intervenors directly contributing to the Faraday rotation along the line of sight, and that the intervening systems must therefore have coherent magnetic fields of substantial strength ( B-bar =1.8±0.4 μG). Nevertheless, the weak nature of the correlation will require future high-resolution and broadband radio observations in order to place it on a much firmer statistical footing.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

PERIODOGRAMS FOR MULTIBAND ASTRONOMICAL TIME SERIES

This paper introduces the multiband periodogram, a general extension of the well-known Lomb–Scargle approach for detecting periodic signals in time-domain data. In addition to advantages of the Lomb–Scargle method such as treatment of non-uniform sampling and heteroscedastic errors, the multiband periodogram significantly improves period finding for randomly sampled multiband light curves (e.g., Pan-STARRS, DES, and LSST). The light curves in each band are modeled as arbitrary truncated Fourier series, with the period and phase shared across all bands. The key aspect is the use of Tikhonov regularization which drives most of the variability into the so-called base model common to all bands, while fits for individual bands describe residuals relative to the base model and typically require lower-order Fourier series. This decrease in the effective model complexity is the main reason for improved performance. After a pedagogical development of the formalism of least-squares spectral analysis, which motivates the essential features of the multiband model, we use simulated light curves and randomly subsampled SDSS Stripe 82 data to demonstrate the superiority of this method compared to other methods from the literature and find that this method will be able to efficiently determine the correct period in the majority of LSST’s bright RR Lyrae stars with as little as six months of LSST data, a vast improvement over the years of data reported to be required by previous studies. A Python implementation of this method, along with code to fully reproduce the results reported here, is available on GitHub.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2019

JPSS-2 VIIRS version 2 at-launch relative spectral response characterization

The JPSS-2 VIIRS sensor has completed its pre-launch test program and is now awaiting launch in the 2022 timeframe. The VIIRS spectral characterization, in the form of band averaged and supporting detector level relative spectral response (RSR) for each VIIRS band, was completed in 2019 and is based upon independent SpMA dual monochromator (all bands) and GSFC GLAMR laser system (reflectance bands only) spectral measurements, including first time measurements of the VIIRS SWIR bands by a laser system. The measurements and subsequent analysis effort by subject matter experts of the VIIRS DAWG has led to the July 2019 VIIRS Version 2 RSR release, the official at-launch RSR characterization for the JPSS-2 VIIRS mission. Version 2 replaces and improves upon the August 2018 Version 1 release by incorporating the GLAMR measurements into the analysis to produce an updated “fused” RSR for reflective solar bands (M1- M10, I1-I3, DNBLGS, DNBMGS) and by applying a CO2 absorption correction to the SpMA measurements for thermal band M13. For all other bands (M11, M12, M14-M16, I4, I5), the Version 1 characterization, based entirely upon the SpMA measurements, is carried forward into the Version 2 release. An assessment on compliance with spectral performance metrics finds that VIIRS is compliant on nearly all metrics, with a few minor exceptions. The version 2 RSR release includes band average (over all detectors and subsamples) RSR plus supporting RSR for each detector and subsample, and is available under EAR99 restrictions to the science community at a restricted access NASA eRoom site.

JPSS-2↗
NASA NTRS2018

Subsample Difference Correction for Terra MODIS SWIR Bands 5-7 Using Lunar Observations

The Moderate Resolution Imaging Spectroradiometer (MODIS) is one of the key instruments on board the Terra (EOS (Earth Observing Satellite) AM-1) spacecraft. MODIS has 36 spectral bands ranging in wavelength between 0.4 and 14.2 microns, at three spatial resolutions of 250 meters (bands 1-2), 500 meters (bands 3-7), and 1 kilometer (bands 8-36). For each 1-km sample, the 250-m and 500-m bands use 4 and 2 detectors with each acquiring 4 and 2 subsamples respectively in order to maintain consistent along-scan and along-track resolutions at nadir. The SWIR (Short-Wave Infrared) bands, 57 and 26, share the same focal-plane array as the 1-km thermal emissive bands, 20-25. During one of the two 500-m subsamples for bands 57, sampling of the 1-km bands introduces increased electronic crosstalk contamination, resulting in a subsample difference for both Earth-view and on-board calibrator observations. For this work, we use data from lunar and on-board blackbody observations, which occur at different signal levels for bands 20-25, to derive a correction to the contamination. This correction can be applied to reduce the subsample differences in the MODIS Earth-view data over a wide range of scenes. The impact of this correction on the sensor calibration and Earth-view data will be assessed.

SWIR↗
NASA NTRS1994

X-ray spectra of a complete sample of extragalactic core-dominated radio sources

We present ROSAT soft X-ray spectra for the members of a complete sample of 13 core-dominated, flat radio spectrum sources. The sample comprises all radio sources from a flux-limited radio catalog (S(sub 5GHz) greater than 1 Jy; Kuehr et al. 1981) which are north of delta = 70 deg, at galactic latitudes b greater than 10 deg, and have a flat radio spectrum between 1.4 and 5 GHz (alpha(sub r) less than 0.5; f approximately nu(sup -alpha)). The sources have already undergone much study at radio and optical wavelengths and are classified in broad terms as quasars (8 sources) and BL Lac objects (5 sources). We find mean X-ray power-law energy indices of alpha(sub x) = 0.59 +/- 0.19 for the quasars and 1.36 +/- 0.27 for the BL Lac objects (68% confidence range for two parameters of interest as determined by a maximum likelihood method), supporting earlier Einstein Observatory results for heterogeneous samples of sources (Worrall & Wilkes 1990). A non-zero dispersion on alpha(sub x) is found for both the quasars and the BL Lac objects. When we incorporate published radio, mm, and optical measurements and compare the X-ray and broad-band spectral indices alpha(sub x), alpha(sub rx), alpha(sub mm,x), and alpha(sub ox), the most obvious difference between the quasar and BL Lac subsamples lies within the X-ray band. We have fitted the multi-wavelength data to inhomogeneous synchotron-self-Compton models and find that, for the BL Lac objects with steep X-ray spectra, synchotron emission can account for the radio to soft X-ray measurements, whereas the BL Lac objects with hard X-ray spectra and the quasars require significant Compton emission to model the spectral flattening indicated by alpha(sub x) less than alpha(sub ox).

Brunner, H.↗
NASA NTRS2002

Unveiling the Engines In QSOS: A Multi-Wavelength Study

In the past year, the project has passed three major milestones: 1. Completed the spectroscopic emission line measurements for the full Hubble preCOSTAR FOS sample, resulting in the publication of "Emission Line Properties of AGN from a pre-COSTAR FOS HST Spectral Atlas" in the ApJ. 2. By compiling narrow absorption line (NAL) and broad emission line (BEL) measurements for the subsample of FOS AGN showing both NV and CIV absorption, we have given the first conclusive evidence that the NAL clouds and BEL clouds have similar metallicity. The resulting paper, just resubmitted to ApJL after a largely congratulatory referee report, is entitled "Evidence for a Strong Abundance Correlation Between Emission and Absorption Lines in AGN". 3) Collaboration with Dr. Crenshaw at GSU has also yielded a complete merged atlas of FOS spectra from the postCOSTAR epoch. These will be analyzed and published in the next year, along with investigations of correlations to high energy (X-ray) emission.

Green, P.↗
DOE OSTI2013

ULTRALUMINOUS INFRARED GALAXIES IN THE WISE AND SDSS SURVEYS

In this paper, we present a large catalog of 419 Ultraluminous infrared galaxies (ULIRGs), carefully selected from the Wide-field Infrared Survey Explorer mid-infrared data and the Sloan Digital Sky Survey eighth data release, and classify them into three subsamples, based on their emission line properties: H II-like ULIRGs, Seyfert 2 ULIRGs, and composite ULIRGs. We apply our new efficient spectral synthesis technique, which is based on mean field approach to Bayesian independent component analysis (MF-ICA) method, to the galaxy integrated spectra. We also analyze the stellar population properties, including percentage contribution, stellar age, and stellar mass, for these three types of ULIRGs, and explore the evolution among them. We find no significant difference between the properties of stellar populations in ULIRGs with or without active galactic nucleus components. Our results suggest that there is no evolutionary link among these three type ULIRGs.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

Observations on the long-period variability of the Gulf Stream downstream of Cape Hatteras

To examine the long-period variability of the Gulf Stream, sea level residuals relative to a 2-year mean sea level in the Gulf Stream downstream of Cape Hatteras (between 75 deg W and 60 deg W longitude) are used. Residuals, as derived from Geosat altimetry between November 1986 and December 1988, were gridded in space and time at a temporal resolution of 10 days and spatial resolution of 1/4 deg. Complex empirical orthogonal function (CEOF) analysis was applied to the data set to extract the spatially correlated signal with the original data subsampled to 1/2 deg. In addition to determining the space-time scales and propagation characterisitics of the different modes, wavenumber-frequency spectral techniques were used to separate the variability into propagating and stationary components. The CEOF technique applied to the data set indicated that the first four CEOF modes accounted for 60% of the variability and were found to be above the noise leve 99% of the time. CEOF 1 was associated with westward propagation at 5 km/d at a wavelength of 2000 km and eastward propagation at 1-2 km/d centered at a 500-km wavelength. This first CEOF is in good agreement with thin-jet equivalent barotropic models which predict westward propagation for wavelengths greater than 1130 km. A deflection of the wavelike pattern at 65 deg W also indicates a possible topographic effect. A simple scaling of the effect of topography indicates that for length scales longer than the internal Rossby radius of deformation, the topographic term is at least of the same order of magnitude as the beta effect. The second CEOF was more broadbanded in wavenumber space, with eastward propagation occurring in a wavenumber-frequency band between 300 and 1400 km and 0.5 and 2.0 cycles/yr. The third CEOF is similar in structure to the first, but with less energy. CEOF 4 was clearly identifiable with higher frequencies than the first three with westward propagation at 4 km/d. The spatial location of this mode along with the westward propagation indicates possible influences from eddy-stream interactions. Thus topography, Rossby wave dynamics and eddy-stream interactions all appear to have a significant role in determining the space-time scales and propagation properties of the long-period response of sea level in the Gulf Stream.

Vazquez, Jorge↗
DOE OSTI2015

FUNDAMENTAL PARAMETERS AND SPECTRAL ENERGY DISTRIBUTIONS OF YOUNG AND FIELD AGE OBJECTS WITH MASSES SPANNING THE STELLAR TO PLANETARY REGIME

We combine optical, near-infrared, and mid-infrared spectra and photometry to construct expanded spectral energy distributions for 145 field age (>500 Myr) and 53 young (lower age estimate <500 Myr) ultracool dwarfs (M6-T9). This range of spectral types includes very low mass stars, brown dwarfs, and planetary mass objects, providing fundamental parameters across both the hydrogen and deuterium burning minimum masses for the largest sample assembled to date. A subsample of 29 objects have well constrained ages as probable members of a nearby young moving group. We use 182 parallaxes and 16 kinematic distances to determine precise bolometric luminosities (L{sub bol}) and radius estimates from evolutionary models give semi-empirical effective temperatures (T{sub eff}) for the full range of young and field age late-M, L, and T dwarfs. We construct age-sensitive relationships of luminosity, temperature, and absolute magnitude as functions of spectral type and absolute magnitude to disentangle the effects of degenerate physical parameters such as T{sub eff}, surface gravity, and clouds on spectral morphology. We report bolometric corrections in J for both field age and young objects and find differences of up to a magnitude for late-L dwarfs. Our correction in Ks shows a larger dispersion but not necessarily a different relationship for young and field age sequences. We also characterize the NIR–MIR reddening of low gravity L dwarfs and identify a systematically cooler T{sub eff} of up to 300 K from field age objects of the same spectral type and 400 K cooler from field age objects of the same M{sub H} magnitude.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

Young low mass stars in the vicinity of Sigma Scorpii

The region near Sigma Scorpii, a member of the Sco-Cen OB association, is examined for signs of recent star formation. Thirteen candidate young stellar objects are identified over an 80 x 80 arcmin region centered on Sigma Sco using the Point source Catalog and a recent survey for H-alpha emission-line stars. Near-infrared photometry, improved IRAS fluxes, and optical spectra are used to determine the nature of these objects. Four definite young stars are revealed, as well as one additional such object that fell just outside of the present target region. These stars, all of spectral type K or M, are argued to have formed in the vicinity of the B1 giant star Sigma Scorpii and to represent a subsample of the low-mass members of the association.

Meyer, Michael R.↗
NASA NTRS2016

Evidence for the Thermal Sunyaev Zeldovich Effect Associated with Quasar Feedback

Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar catalogue, spanning redshifts 0.5-3.5, we derive the mean millimetre and far-infrared quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We constrain the form of the far-infrared emission and find 3 sigma-4 sigma evidence for the thermal Sunyaev-Zel'dovich (SZ) effect, characteristic of a hot ionized gas component with thermal energy (6.2 plus or minus 1.7) × 10 (exp 60) erg. This amount of thermal energy is greater than expected assuming only hot gas in virial equilibrium with the dark matter haloes of (1-5) × 10(exp 12) h(exp −1) solar mass that these systems are expected to occupy, though the highest quasar mass estimates found in the literature could explain a large fraction of this energy. Our measurements are consistent with quasars depositing up to (14.5 +/- 3.3)tau (sub 8)(exp -1) per cent of their radiative energy into their circumgalactic environment if their typical period of quasar activity is tau(sub 8) x 108 yr. For high quasar host masses, approximately 10(exp 13) h(exp −1) solar mass, this percentage will be reduced. Furthermore, the uncertainty on this percentage is only statistical and additional systematic uncertainties enter at the 40 per cent level. The SEDs are dust dominated in all bands and we consider various models for dust emission. While sufficiently complex dust models can obviate the SZ effect, the SZ interpretation remains favoured at the 3 sigma-4 sigma level for most models.

Sunyaev-Zeldovich (SZ)↗
NASA NTRS2010

Herschel-ATLAS: Dust Temperature and Redshift Distribution of SPIRE and PACS Detected Sources Using Submillimetre Colours

We present colour-colour diagrams of detected sources in the Herschel-ATLAS Science Demonstration Field from 100 to 500/microns using both PACS and SPIRE. We fit isothermal modified-blackbody spectral energy distribution (SED) models in order to extract the dust temperature of sources with counterparts in GAMA or SDSS with either a spectroscopic or a photometric redshift. For a subsample of 331 sources detected in at least three FIR bands with significance greater than 30 sigma, we find an average dust temperature of (28 plus or minus 8)K. For sources with no known redshifts, we populate the colour-colour diagram with a large number of SEDs generated with a broad range of dust temperatures and emissivity parameters and compare to colours of observed sources to establish the redshift distribution of those samples. For another subsample of 1686 sources with fluxes above 35 mJy at 350 microns and detected at 250 and 500 microns with a significance greater than 3sigma, we find an average redshift of 2.2 plus or minus 0.6.

Amblard, A.↗
DOE OSTI2021

Host Star Metallicity of Directly Imaged Wide-orbit Planets: Implications for Planet Formation

Directly imaged planets (DIPs) are self-luminous companions of pre-main-sequence and young main-sequence stars. They reside in wider orbits (∼tens to thousands of astronomical units) and generally are more massive compared to the close-in (≲10 au) planets. Determining the host star properties of these outstretched planetary systems is important to understand and discern various planet formation and evolution scenarios. We present the stellar parameters and metallicity ([Fe/H]) for a subsample of 18 stars known to host planets discovered by the direct imaging technique. We retrieved the high-resolution spectra for these stars from public archives and used the synthetic spectral fitting technique and Bayesian analysis to determine the stellar properties in a uniform and consistent way. For eight sources, the metallicities are reported for the first time, while the results are consistent with the previous estimates for the other sources. Our analysis shows that metallicities of stars hosting DIPs are close to solar with a mean [Fe/H] = −0.04 ± 0.27 dex. The large scatter in metallicity suggests that a metal-rich environment may not be necessary to form massive planets at large orbital distances. We also find that the planet mass–host star metallicity relation for the directly imaged massive planets in wide orbits is very similar to that found for the well-studied population of short-period (≲1 yr) super-Jupiters and brown dwarfs around main-sequence stars.

36 MATERIALS SCIENCE↗
NASA NTRS1993

The consistency of standard cosmology and the BATSE number versus brightness relation

The integrated number-peak-flux relation measured by the Burst and Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory is compared with several standard cosmological distributions for gamma-ray bursts (GRBs). Friedmann-Robertson-Walker models were used along with the assumption that the bursts are standard candles and have no number or luminosity evolution. For a given Omega spectral shape, we used a free parameter, essentially the comoving number density of bursts, to generate a best fit between the cosmology and the measured relation. Our results are shown for a subsample of the first 260 GRBs recorded by BATSE. We find acceptable fits between simple cosmological models and the brightness distribution data, as determined by the Kolmogorov-Smirnov one-distribution statistical test. One cannot distinguish a single best cosmological model from the goodness of the fits. The best fit implies that BATSE GRBs are complete out to a redshift of about unity. However, significantly higher and lower redshifts, by as much as a factor of 2, are possible for other marginally acceptable fits.

Wickramasinghe, W. A. D. T.↗
DOE OSTI2017

Far-infrared Properties of Infrared-bright Dust-obscured Galaxies Selected with IRAS and AKARI Far-infrared All-sky Survey

We investigate the star-forming activity of a sample of infrared (IR)-bright dust-obscured galaxies (DOGs) that show an extreme red color in the optical and IR regime, (i−[22]){sub AB}>7.0. Combining an IR-bright DOG sample with the flux at 22 μm > 3.8 mJy discovered by Toba and Nagao with the IRAS faint source catalog version 2 and AKARI far-IR (FIR) all-sky survey bright source catalog version 2, we selected 109 DOGs with FIR data. For a subsample of seven IR-bright DOGs with spectroscopic redshifts (0.07<z<1.0) that were obtained from the literature, we estimated their IR luminosity, star formation rate (SFR), and stellar mass based on the spectral energy distribution fitting. We found that (1) the WISE 22 μm luminosity at the observed frame is a good indicator of IR luminosity for IR-bright DOGs and (2) the contribution of the active galactic nucleus to IR luminosity increases with IR luminosity. By comparing the stellar mass and SFR relation for our DOG sample and the literature, we found that most of the IR-bright DOGs lie significantly above the main sequence of star-forming galaxies at similar redshift, indicating that the majority of IRAS- or AKARI-detected IR-bright DOGs are starburst galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2007

Gamma-Ray Burst Afterglows as Probes of Environment and Blastwave Physics II: The Distribution of p and Structure of the Circumburst Medium

We constrain blastwave parameters and the circumburst media of a subsample of BeppoSAX Gamma-Ray Bursts. For this sample we derive the values of the injected electron energy distribution index, p, and the density structure index of the circumburst medium, k, from simultaneous spectral fits to their X-ray, optical and nIR afterglow data. The spectral fits have been done in count space and include the effects of metallicity, and are compared with the previously reported optical and X-ray temporal behaviour. Assuming the fireball model, we can find a mean value of p for the sample as a whole of 2.035. A statistical analysis Of the distribution demonstrates that the p values in this sample are inconsistent with a single universal value for p at the 3sigma level or greater. This approach provides us with a measured distribution of circumburst density structures rather than considering only the cases of k = 0 (homogeneous) and k = 2 (wind-like). We find five GRBs for which k can be well constrained, and in four of these cases the circumburst medium is clearly wind-like. The fifth source has a value of 0 less than or equal to k less than or equal to 1, consistent with a homogeneous circumburst medium.

Starling, R. L. C.↗