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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 NTRS1984

The underlying galaxies of X-ray-selected quasars

Deep red images of 24 X-ray selected quasars were obtained using the SIT Area Photometer on the Palomar 1.5 meter telescope. About half were also imaged through green and violet filters. The images of all 15 of the quasars with redshifts up to 0.4 certainly are extended and the two at z = 0.45 probably are extended. The remainder of higher redshift are unresolved, presumably because they are too distant. The resolved structures are 10-30 in. across, symmetric, and centered on the point-like quasar nuclei. For most of the quasars the nuclear light and the extended emission can be roughly separated. Evidence that the extended emission is starlight from a surrounding galaxy is presented, permitting several properties of the host galaxy to be deduced. Its colors, surface brightness, linear extent, ellipticity, and frequent association with groups of galaxies indicate that it is usually a normal spiral galaxy.

Malkan, M. A.↗
NASA NTRS1993

Galaxy tracers in N-body simulations

Using the method of smoothed particle hydrodynamics, we have modeled the formation of a compact group of galaxies with sufficient resolution to trace galaxies. Radiative cooling allows the baryons to dissipate their thermal energy and collapse to overdensities characteristic of real galaxies. With their cross section greatly reduced, these galaxy tracers remain distinct during cluster formation while their dark matter halos merge. In addition, the number density, the mass distribution function, and even the morphology of these objects are similar to those of observed galaxies. A viable population of galaxy tracers can be unambiguously defined.

Summers, F. J.↗
NASA NTRS2010

Ultraviolet+Infrared Star Formation Rates: Hickson Compact Groups with Swift and SPitzer

We present Swift UVOT ultraviolet (UV; 1600-3000 A) data with complete three-band UV photometry for a sample of 41 galaxies in 11 nearby (<4500 km/s) Hickson Compact Groups (HCGs) of galaxies. We use UVOT uvw2-band (2000A) photometry to estimate the dust-unobscured component, SFR(sub uv), of the total star formation rate, SFR(sub TOTAL). We use Spitzer MIPS 24 micron photometry to estimate SFR(sub IR), the component of SFR(sub TOTAL) that suffers dust extinction in the UV and is re-emitted in the IR. By combining the two components, we obtain SFR(sub TOTAL) estimates for all HCG galaxies. We obtain total stellar mass, M(sub *) estimates by means of Two Micron All Sky Survey K(sub s)-band luminosities, and use them to calculate specific star formation rates, SSFR is identical with SFR(sub TOTAL)/ M (sub *). SSFR values show a clear and significant bimodality, with a gap between low (approximately <3.2 x 10(exp -11) / yr) and high-SSFR (approximately > 1.2 x lO)exp -10)/yr) systems. We compare this bimodality to the previously discovered bimodality in alpha-IRAC, the MIR activity index from a power-law fit to the Spitzer IRAC 4.5-8 micron data for these galaxies. We find that all galaxies with alpha-IRAC <= 0 (> 0) are in the high- (low-) SSFR locus, as expected if high levels of star-forming activity power MIR emission from polycyclic aromatic hydrocarbon molecules and a hot dust continuum. Consistent with this finding, all elliptical/SO galaxies are in the low-SSFR locus, while 22 out of 24 spirals / irregulars are in the high-SSFR locus, with two borderline cases. We further divide our sample into three subsamples (I, II, and III) according to decreasing H I richness of the parent galaxy group to which a galaxy belongs. Consistent with the SSFR and alpha-IRAC bimodality, 12 out of 15 type I (11 out of 12 type III) galaxies are in the high- (low-) SSFR locus, while type II galaxies span almost the full range of SSFR values. We use the Spitzer Infrared Nearby Galaxy Survey (SINGS) to construct a comparison subsample of galaxies that (1) match HCG galaxies in J-band total galaxy luminosity and (2) are not strongly interacting and largely isolated. This selection eliminates mostly low-luminosity dwarfs and galaxies with some degree of peculiarity, providing a substantially improved, quiescent control sample. Unlike HCG galaxies, galaxies in the comparison SINGS subsample are continuously distributed both in SSFR and alpha-IRAC, although they show ranges in SFR(sub TOTAL) values, morphologies and stellar masses similar to those for HCG systems. We test the SSFR bimodality against a number of uncertainties, and find that these can only lead to its further enhancement. Excluding galaxies belonging to HCGs with three giant galaxies (triplets) leaves both the SSFR and the alpha-IRAC bimodality completely unaffected. We interpret these results as further evidence that an environment characterized by high galaxy number densities and low galaxy velocity dispersions, such as the one found in compact groups, plays a key role in accelerating galaxy evolution by enhancing star formation processes in galaxies and favoring a fast transition to quiescence.

Tzanavaris, P.↗
NASA NTRS1992

The X-ray spectra of galaxies. II - Average spectral properties and emission mechanisms

The Imaging Proportional Counter data in the Einstein database is used to study the X-ray spectra of normal galaxies. The X-ray emission temperature of spirals is found to be higher on the average than that of ellipticals. This supports the idea that accreting binaries are a major source of X-rays in spirals, while a hot interstellar medium (ISM) is present in ellipticals. The X-ray spectra of Sa galaxies are intermediate between those of ellipticals and spirals, suggesting that these galaxies contain hot gaseous emission as well as emission from accreting binaries. In E and SO galaxies the emission temperature becomes higher with a decreasing X-ray to optical luminosity ratio, which suggests that the emission of X-ray faint early-type galaxies consists of a large evolved stellar component, while the gaseous emission becomes dominant in X-ray brighter galaxies. The group with the lowest X-ray to optical ratio does not follow this trend; in these galaxies a very soft X-ray component, amounting to about half the total X-ray emission, is found in addition to the hard X-ray component. Possible explanations are integrated emission of M stars and a relatively cool ISM. A very soft component is also found in several spiral galaxies. This may indicate that some spirals contain hot gaseous components similar to those seen in NGC 253 and M82.

Kim, D.-W.↗
NASA NTRS2004

XMM Cluster Abundances

I will present a review of the recent data on the chemical abundances in clusters of galaxies and groups based on X-ray spectroscopy. I will talk about class properties, correlations and the implications for galaxy evolution. In particular I will compare and contrast recent XMM results and those from previous observatories.

Mushotzky, Richard↗
NASA NTRS1981

Constraints on neutrinos and axions from cosmology

A review is made of the astrophysical arguments with regard to neutrino properties. It is shown that the best fit to the present baryon density and He-4 abundance is obtained with three neutrino species. It is also shown that astrophysical constraints on neutrino and axion lifetime-mass combinations rule out weakly interacting particles with lifetimes between 1/1000 to 10 to the 23rd sec for M up to 10 MeV. There is an allowed astrophysical window for neutrinos with M up to 10 MeV and tau less than 1000 sec. The possible role of massive neutrinos in the dark mass of galaxies is discussed. It is shown that the baryon density in the universe is comparable to the density obtained from the dynamics of binary galaxies. Therefore, massive neutrinos are only required if the cosmological mass density is greater than that implied by binaries and small groups of galaxies. The only objects which might imply such high densities are large clusters. For neutrinos to cluster with these large clusters requires a neutrino mass of at least 3 eV.

Schramm, D. N.↗
NASA NTRS1992

New Cepheid distances to nearby galaxies based on BVRI CCD photometry. III - NGC 300

A true distance modulus of (m - M) sub 0 = 26.66 +/- 0.10 mag (corresponding to 2.1 +/- 0.1 Mpc) has been determined for the Sculptor Group spiral galaxy NGC 300. New CCD data have been obtained for a sample of known Cepheids in this galaxy from which apparent distance moduli at B, V, R, and I wavelengths are determined. Combining the data available at different wavelenghts, and assuming a true distance modulus to the LMC of 18.5 mag, a true distance modulus is obtained for NGC 300, corrected for the effects of interstellar reddening. The availability of a new distance to NGC 300 brings to five the total number of galaxies with new CCD photometry of Cepheids, useful for calibration of the Hubble constant.

Freedman, Wendy L.↗
NASA NTRS1992

Discovery of intermediate redshift galaxy clusters in the ROSAT NEP field

We report preliminary results from a program to identify optical counterparts of ROSAT sources in the North Ecliptic Pole (NEP) region. The most striking X-ray feature reported by Hasinger et al. (1991) is an extended low surface brightness region of X-ray emission. Within the two X-ray contours of highest count rate we find a cluster of galaxies at a redshift of 0.09 and an early-type galaxy at a redshift of 0.03. X-ray emission from these objects may provide an explanation for the observed X-ray morphology. We also find evidence that other X-ray sources in this region are coincident with clusters or groups of galaxies at redshifts between 0.08 and 0.09. The presence of at least five X-ray detected clusters or groups in this narrow redshift band within a 1.5 deg radius field seems to indicate the existence of a moderate redshift supercluster. The existence of these clusters will have major implications for the study of large-scale structure through X-ray surveys such as ROSAT.

Burg, R.↗
NASA NTRS1993

The mass function of clusters of galaxies

The mass function of clusters of galaxies is derived separately from optical and X-ray observations of their respective properties. The mass function was extended to the faint end, to lower masses than the rich clusters, using small groups of galaxies. The derived mass function is within the mass range from approximately 10 exp 12 to not less than 10 exp 15/h solar masses. The deduced density range n is approximately 10 exp -2 to 10 exp -8 cubic h/cubic Mpc. The observed shape of the mass function exhibits a shallow power-law decrease with mass at the faint end, and a steep exponential decrease with mass at the massive end. A summary of some constraints placed by the observed mass function on current cosmological models is presented.

Bahcall, Neta A.↗
NASA NTRS2004

Observations of Distant Clusters

The is the proceedings and papers supported by the LTSA grant: Homer, D. J.\& Donahue, M. 2003, in "The Emergence of Cosmic Structure": 13'h Astrophysics Conference Proceedings, Vol. 666,3 1 1-3 14, (AIP). Baumgartner, W. H., Loewenstein, M., Horner, D. J., Mushotzky, R. F. 2003, HEAD- AAS, 35.3503. Homer, D. J. , Donahue, M., Voit G. M. 2003, HEAD-AAS, 35.1309. Nowak, M. A., Smith, B., Donahue, M., Stocke, J. 2003, HEAD-AAS, 35.1316. Scott, D., Borys, C., Chapman, S. C., Donahue, M., Fahlman, G. G., Halpem, M. Newbury, P. 2002, AAS, 128.01. Jones, L. R. et al. 2002, A new era in cosmology, ASP Conference Proceedings, Vol. 283, p. 223 Donahue, M., Daly, R. A., Homer, D. J. 2003, ApJ, 584, 643, Constraints on the Cluster Environments and Hotspot magnetic field strengths for radio sources 3~280 and 3~254. Donahue, M., et al. 2003, ApJ, 598, 190. The mass, baryonic fraction, and x-ray temperature of the luminous, high-redshift cluster of galaxies MS045 1.6-0305 Perlman, E. S. et al. 2002, ApJS, 140, 256. Smith, B. J., Nowak, M., Donahue, M., Stocke, J. 2003, AJ, 126, 1763. Chandra Observations of the Interacting NGC44 10 Group of Galaxies. Postman, M., Lauer, T. R., Oegerle, W., Donahue, M. 2002, ApJ, 579, 93. The KPNO/deep-range cluster survey I. The catalog and space density of intermediate-redshift clusters. Molnar, S. M., Hughes, J. P., Donahue, M., Joy, M. 2002, ApJ, 573, L91, Chandra Observations of Unresolved X-Ray Sources around Two Clusters of Galaxies. Donahue, M., Mack, J., 2002 NewAR, 46, 155, HST NIcmos and WFPC2 observations of molecular hydrogen and dust around cooling flows. Koekemoer, A. M. et al. 2002 NewAR, 46, 149, Interactions between the A2597 central radio source and dense gas host galaxy. Donahue, M. et al. 2002 ApJ, 569,689, Distant cluster hunting II.

Donahue, Megan↗
NASA NTRS1994

Surface Brightness Profiles and Energetics of Intracluster Gas in Cool Galaxy Clusters and ROSAT Observations of Bright, Early-Type Galaxies

Preliminary results on the elliptical galaxy NGC 1407 were published in the proceedings of the first ROSAT symposium. NGC 1407 is embedded in diffuse X-ray-emitting gas which is extensive enough that it is likely to be related to the surrounding group of galaxies, rather than just NGC 1407. Spectral data for NGC 1407 (AO2) and IC 1459 (AO3) are also included in a complete sample of elliptical galaxies I compiled in collaboration with David Davis. This allowed us to construct the first complete X-ray sample of optically-selected elliptical galaxies. The complete sample allows us to apply Malmquist bias corrections to the observed correlation between X-ray and optical luminosities. I continue to work on the implications of this first complete X-ray sample of elliptical galaxies. Paul Eskridge Dave Davis and I also analyzed three long ROSAT PSPC observations of the small (but not dwarf) elliptical galaxy M32. We found the X-ray spectra and variability to be consistent with either a Low Mass X-Ray Binary (LMXRB) or a putative 'micro"-AGN.

White, Raymond E., III↗
NASA NTRS1986

New X-ray and optical observations of the X-ray discovered QSO-galaxy pair 1E 0104.2 + 3153

New X-ray and optical observations are presented of the QSO-galaxy pair 1E 0104.2 + 3153, originally discovered as a serendipitous source in the Einstein Observatory Medium Sensitivity Survey (Gioia et al., 1984). Results from an extremely deep Exosat observation are used to suggest that the QSO rather than the compact group of galaxies is the optical counterpart of the IPC source. High-resolution (1-A) spectroscopy of the broad-absorption-line QSO, which fails to confirm the Ca II H and K absorption features reported by Stocke et al., (1984), is presented and discussed. The presence of broad absorption lines in the QSO spectrum may indicate that intrinsic absorption is the cause of the nondetection of this source in the soft Exosat energy band. Optical monitoring of the QSO over a 2-yr period indicates variability. Possible interpretations of this phenomenon are intrinsic luminosity variation or a cessation of a gravitational lensing effect acting at the time of the Einstein observation.

Gioia, I. M.↗
NASA NTRS1981

Galaxy formation in an intergalactic medium dominated by explosions

The evolution of galaxies in an intergalactic medium dominated by explosions of star systems is considered analogously to star formation by nonlinearly interacting processes in the interstellar medium. Conditions for the existence of a hydrodynamic instability by which galaxy formation leads to more galaxy formation due to the propagation of the energy released at the death of massive stars are examined, and it is shown that such an explosive amplification is possible at redshifts less than about 5 and stellar system masses between 10 to the 8th and 10 to the 12th solar masses. Explosions before a redshift of about 5 are found to lead primarily to the formation of massive stars rather than galaxies, while those at a redshift close to 5 will result in objects of normal galactic scale. The model also predicts a dusty interstellar medium preventing the detection of objects of redshift greater than 3, numbers and luminosities of protogalaxies comparable to present observations, unvirialized groups of galaxies lying on two-dimensional surfaces, and a significant number of black holes in the mass range 1000-10,000 solar masses.

Ostriker, J. P.↗
NASA NTRS1990

Intergalactic HI in the NGC5018 group

The cold interstellar and intergalactic medium is in the small group of galaxies whose brightest member is the elliptical galaxy NGC5018. Researchers' attention was first drawn to this galaxy as possibly containing cold interstellar gas by the detection by the Infrared Astronomy Satellite (IRAS) of emission at lambda 60 microns and lambda 100 microns at an intensity of about 1 Jy (Knapp et al. 1989), which is relatively strong for an elliptical (Jura et al. 1987). These data showed that the temperature of the infrared emission is less than 30K and that its likely source is therefore interstellar dust. A preliminary search for neutral hydrogen (HI) emission from this galaxy using the Very Large Array (VLA) showed that there appears to be HI flowing between NGC5018 and the nearby Sc galaxy NGC5022 (Kim et al. 1988). Since NGC5018 has a well-developed system of optical shells (cf. Malin and Carter 1983; Schweizer 1987) this observation suggests that NGC5018 may be in the process of forming its shell system by the merger of a cold stellar system with the elliptical, as suggested by Quinn (1984). Researchers describe follow-up HI observations of improved sensitivity and spatial resolution, and confirm that HI is flowing between NCG5022 and NGC5018, and around NGC5018. The data show, however, that the HI bridge actually connects NGC5022 and another spiral in the group, MCG03-34-013, both spatially and in radial velocity, and that in doing so it flows through and around NGC5018, which lies between the spiral galaxies. This is shown by the total HI map, with the optical positions of the above three galaxies labelled.

Guhathakurta, P.↗
NASA NTRS2016

The e-astrogam Gamma-Ray Space Mission

e-ASTROGAM is a gamma-ray space mission to be proposed as the M5 Medium-size mission of the European Space Agency. It is dedicated to the observation of the Universe with unprecedented sensitivity in the energy range 0.2-100 MeV, extending up to GeV energies, together with a groundbreaking polarization capability. It is designed to substantially improve the COMPTEL and Fermi sensitivities in the MeV-GeV energy range and to open new windows of opportunity for astrophysical and fundamental physics space research. e-ASTROGAM will operate as an open astronomical observatory, with a core science focused on (1) the activity from extreme particle accelerators, including gamma-ray bursts and active galactic nuclei and the link of jet astrophysics to the new astronomy of gravitational waves, neutrinos, ultra-high energy cosmic rays, (2) the high-energy mysteries of the Galactic center and inner Galaxy, including the activity of the supermassive black hole, the Fermi Bubbles, the origin of the Galactic positrons, and the search for dark matter signatures in a new energy window; (3) nucleosynthesis and chemical evolution, including the life cycle of elements produced by supernovae in the Milky Way and the Local Group of galaxies. e-ASTROGAM will be ideal for the study of high-energy sources in general, including pulsars and pulsar wind nebulae, accreting neutron stars and black holes, novae, supernova remnants, and magnetars. And it will also provide important contributions to solar and terrestrial physics. The e-ASTROGAM telescope is optimized for the simultaneous detection of Compton and pair-producing gamma-ray events over a large spectral band. It is based on a very high technology readiness level for all subsystems and includes many innovative features for the detectors and associated electronics.

Compton and pair creation telescope↗
NASA NTRS1982

BL Lac objects and their associated galaxies

CCD photometry of five BL Lac objects indicates that at least three, and possibly four, are located at the centers of giant elliptical galaxies. The redshift for one of these objects, 1218+304, is estimated. A lower limit is placed on the redshift of 1219+28, for which no associated galaxy has been detected. Separation of the galaxy emission from the total observed flux makes possible comparison of the optical - far red flux from the point source alone with radio and X-ray data. This comparison suggests the emission from 1727+50 and 1218+304 can be interpreted as due to direct synchrotron emission. Observations of a small group of galaxies associated with the BL Lac object 1400+162 are also discussed.

Weistrop, D.↗
NASA NTRS1996

The Non-Axisymmetric Milky Way

The Dwek et al. model represents the current state-of-the-art model for the stellar structure of our Galaxy. The improvements we have made to this model take a number of forms: (1) the construction of a more detailed dust model so that we can extend our modeling to the galactic plane; (2) simultaneous fits to the bulge and the disk; (3) the construction of the first self-consistent model for a galactic bar; and (4) the development and application of algorithms for constructing nonparametric bar models. The improved Galaxy model has enabled a number of exciting science projects. In Zhao et al., we show that the number and duration of microlensing events seen by the OGLE and MACHO collaborations towards the bulge were consistent with the predictions of our bar model. In Malhotra et al., we constructed an infrared Tully-Fisher (TF) relation for the local group. We found the tightest TF relation ever seen in any band and in any group of galaxies. The tightness of the correlation places strong constraints on galaxy formation models and provides a independent check of the Cepheid distance scale.

Spergel, David N.↗
NASA NTRS1981

Quasar number density evolution

A simple model of quasar number density evolution is presented based on the occurrence of quasar-like radio galaxies (i.e., strong optical emission lines and type 2 radio morphology) exclusively in regions of low galaxy and intergalactic medium (IGM) density. This suggests a limit for the IGM density of 10 to the -4th (+ or - 1) per cu cm below which quasars are allowed to form and above which they are not allowed. In the recent past (z not greater than 1), the inferred quasar environments are the outskirts of clusters and near the centers of groups of galaxies. However, models of rich cluster evolution consistent with current X-ray observations predict gas densities of less than 10 to the -4th per cu cm in cluster cores in the more distant past (z between 1 and 5). This suggests that quasars were allowed to form in the cores of rich clusters at those epochs, which explains both the rich absorption spectra of high-redshift quasars and the absence of clusters surrounding quasars at lower redshift.

Stocke, J. T.↗