Open Access. Powered by Scholars. Published by Universities.®
- Discipline
-
- Stars, Interstellar Medium and the Galaxy (177)
- External Galaxies (116)
- Cosmology, Relativity, and Gravity (78)
- Physics (35)
- Physical Processes (30)
-
- The Sun and the Solar System (15)
- Quantum Physics (7)
- Instrumentation (6)
- Other Astrophysics and Astronomy (6)
- Atmospheric Sciences (3)
- Elementary Particles and Fields and String Theory (3)
- Oceanography and Atmospheric Sciences and Meteorology (3)
- Plasma and Beam Physics (3)
- Condensed Matter Physics (2)
- Other Physics (2)
- Applied Statistics (1)
- Computer Sciences (1)
- Earth Sciences (1)
- Engineering Physics (1)
- Medicine and Health Sciences (1)
- Numerical Analysis and Scientific Computing (1)
- Statistical, Nonlinear, and Soft Matter Physics (1)
- Statistics and Probability (1)
- Keyword
-
- Astrophysics (171)
- Cosmology and astronomy (78)
- Galaxies (62)
- Stars (52)
- Supernova remnants (31)
-
- Supernovae (29)
- Cosmology (25)
- Astronomy (23)
- Quasars (22)
- Mass (20)
- Star evolution (20)
- Novae (18)
- Photometry (18)
- Red shift (18)
- Emission (17)
- Galaxy evolution (17)
- Luminosity (17)
- General relativity and quantum cosmology (16)
- Clusters (15)
- Cosmology and nongalactic astrophysics (15)
- High energy physics (15)
- Telescopes (15)
- Binaries (14)
- Evolution (14)
- Galaxy nuclei (14)
- X radiation (14)
- X-rays (14)
- Active galaxies (13)
- Cataclysmic variables (13)
- Cd (13)
- Publication Year
- Publication
- Publication Type
- File Type
Articles 91 - 120 of 447
Full-Text Articles in Astrophysics and Astronomy
Effects Of Ionospheric Damping On Mhd Wave Mode Structure, D. -H. Lee, K. -H. Kim, R. E. Denton, K. Takahashi
Effects Of Ionospheric Damping On Mhd Wave Mode Structure, D. -H. Lee, K. -H. Kim, R. E. Denton, K. Takahashi
Dartmouth Scholarship
We calculate the mode structure of magnetospheric MHD waves on a meridional plane. We have added the effect of ionospheric dissipation to the three-dimensional dipole field MHD model of Lee and Lysak (1999); this model allows a realistic Alfven speed profile for the plasmasphere and realistic boundary conditions at the outer boundaries that vary with respect to local time. Using power spectra and plots of spatial mode structure, we show that the two-dimensional transverse modes on the dipolar meridian are strongly affected by ionospheric damping, but the compressional modes are not. The location of field line resonances spreads wide as …
Superdiffusion Revisited In View Of Collisionless Reconnection, R. A. Treumann, W. Baumjohann
Superdiffusion Revisited In View Of Collisionless Reconnection, R. A. Treumann, W. Baumjohann
Dartmouth Scholarship
The concept of diffusion in collisionless space plasmas like those near the magnetopause and in the geomagnetic tail during reconnection is reexamined making use of the division of particle orbits into waiting orbits and break-outs into ballistic motion lying at the bottom, for instance, of Lévy flights. The rms average displacement in this case increases with time, describing superdiffusion, though faster than classical, is still a weak process, being however strong enough to support fast reconnection. Referring to two kinds of numerical particle-in-cell simulations we determine the anomalous diffusion coefficient, the anomalous collision frequency on which the diffusion process is …
Magnetic Inhibition Of Convection And The Fundamental Properties Of Low-Mass Stars. Ii. Fully Convective Main-Sequence Stars, Gregory A. Feiden, Brian Chaboyer
Magnetic Inhibition Of Convection And The Fundamental Properties Of Low-Mass Stars. Ii. Fully Convective Main-Sequence Stars, Gregory A. Feiden, Brian Chaboyer
Dartmouth Scholarship
We examine the hypothesis that magnetic fields are inflating the radii of fully convective main-sequence stars in detached eclipsing binaries (DEBs). The magnetic Dartmouth stellar evolution code is used to analyze two systems in particular: Kepler-16 and CM Draconis. Magneto-convection is treated assuming stabilization of convection and also by assuming reductions in convective efficiency due to a turbulent dynamo. We find that magnetic stellar models are unable to reproduce the properties of inflated fully convective main-sequence stars, unless strong interior magnetic fields in excess of 10 MG are present. Validation of the magnetic field hypothesis given the current generation of …
Obscuration By Gas And Dust In Luminous Quasars, S. M. Usman, S. S. Murray, R. C. Hickox, M. Brodwin
Obscuration By Gas And Dust In Luminous Quasars, S. M. Usman, S. S. Murray, R. C. Hickox, M. Brodwin
Dartmouth Scholarship
We explore the connection between absorption by neutral gas and extinction by dust in mid-infrared (IR) selected luminous quasars. We use a sample of 33 quasars at redshifts 0.7 < z < 3 in the 9 deg^2 Bo\"otes multiwavelength survey field that are selected using Spitzer Space Telescope Infrared Array Camera colors and are well-detected as luminous X-ray sources (with >150 counts) in Chandra observations. We divide the quasars into dust-obscured and unobscured samples based on their optical to mid-IR color, and measure the neutral hydrogen column density N_H through fitting of the X-ray spectra. We find that all subsets of quasars have consistent power law photon indices equal to 1.9 that are uncorrelated with N_H. We classify the quasars as gas-absorbed or gas-unabsorbed if N_H > 10^22 cm^-2 or N_H < 10^22 cm^-2, respectively. Of 24 dust-unobscured quasars in the sample, only one shows clear evidence for significant intrinsic N_H, while 22 have column densities consistent with N_H < 10^22 cm^-2. In contrast, of the nine dust-obscured quasars, six show evidence for intrinsic gas absorption, and three are consistent with N_H < 10^22 cm^-2. We conclude that dust extinction in IR-selected quasars is strongly correlated with significant gas absorption as determined through X-ray spectral fitting. These results suggest that obscuring gas and dust in quasars are generally co-spatial, and confirm the reliability of simple mid-IR and optical photometric techniques for separating quasars based on obscuration.
The Angular Clustering Of Infrared-Selected Obscured And Unobscured Quasars, M. A. Dipompeo, A. D. Myers, R. C. Hickox, J. E. Geach, K. N. Hainline
The Angular Clustering Of Infrared-Selected Obscured And Unobscured Quasars, M. A. Dipompeo, A. D. Myers, R. C. Hickox, J. E. Geach, K. N. Hainline
Dartmouth Scholarship
Recent studies of luminous infrared-selected active galactic nuclei (AGN) suggest that the reddest, most obscured objects display a higher angular clustering amplitude, and thus reside in higher-mass dark matter halos. This is a direct contradiction to the prediction of the simplest unification-by-orientation models of AGN and quasars. However, clustering measurements depend strongly on the "mask" that removes low-quality data and describes the sky and selection function. We find that applying a robust, conservative mask to WISE-selected quasars yields a weaker but still significant difference in the bias between obscured and unobscured quasars. These findings are consistent with results from previous …
Gemini Long-Slit Observations Of Luminous Obscured Quasars: Further Evidence For An Upper Limit On The Size Of The Narrow-Line Region, Kevin N. Hainline, Ryan C. Hickox, Jenny E. Greene, Adam D. Myers
Gemini Long-Slit Observations Of Luminous Obscured Quasars: Further Evidence For An Upper Limit On The Size Of The Narrow-Line Region, Kevin N. Hainline, Ryan C. Hickox, Jenny E. Greene, Adam D. Myers
Dartmouth Scholarship
We examine the spatial extent of the narrow-line regions (NLRs) of a sample of 30 luminous obscured quasars at 0.4 < z < 0.7 observed with spatially resolved Gemini-N GMOS long-slit spectroscopy. Using the [O III] λ5007 emission feature, we estimate the size of the NLR using a cosmology-independent measurement: the radius where the surface brightness falls to 10–15 erg s–1 cm–2 arcsec–2. We then explore the effects of atmospheric seeing on NLR size measurements and conclude that direct measurements of the NLR size from observed profiles are too large by 0.1-0.2 dex on average, as compared to measurements made to best-fit Sérsic or Voigt profiles convolved with the seeing. These data, which span a full order of magnitude in IR luminosity (log (L 8 μm/erg s–1) = 44.4-45.4), …
Galaxy Pairs In The Sloan Digital Sky Survey - Ix. Merger-Induced Agn Qctivity As Traced By The Wide-Field Infrared Survey Explorer, Shobita Satyapal, Sara L. Ellison, William Mcalpine, Ryan C. Hickox
Galaxy Pairs In The Sloan Digital Sky Survey - Ix. Merger-Induced Agn Qctivity As Traced By The Wide-Field Infrared Survey Explorer, Shobita Satyapal, Sara L. Ellison, William Mcalpine, Ryan C. Hickox
Dartmouth Scholarship
Interactions between galaxies are predicted to cause gas inflows that can potentially trigger nuclear activity. Since the inflowing material can obscure the central regions of interacting galaxies, a potential limitation of previous optical studies is that obscured Active Galactic Nuclei (AGNs) can be missed at various stages along the merger sequence. We present the first large mid-infrared study of AGNs in mergers and galaxy pairs, in order to quantify the incidence of obscured AGNs triggered by interactions. The sample consists of galaxy pairs and post-mergers drawn from the Sloan Digital Sky Survey that are matched to detections by the Wide …
Massive Compact Galaxies With High-Velocity Outflows: Morphological Analysis And Constraints On Agn Activity, P. H. Sell, C. A. Tremonti, R. C. Hickox, A. M. Diamond-Stanic
Massive Compact Galaxies With High-Velocity Outflows: Morphological Analysis And Constraints On Agn Activity, P. H. Sell, C. A. Tremonti, R. C. Hickox, A. M. Diamond-Stanic
Dartmouth Scholarship
We investigate the process of rapid star formation quenching in a sample of 12 massive galaxies at intermediate redshift (z~0.6) that host high-velocity ionized gas outflows (v>1000 km/s). We conclude that these fast outflows are most likely driven by feedback from star formation rather than active galactic nuclei (AGN). We use multiwavelength survey and targeted observations of the galaxies to assess their star formation, AGN activity, and morphology. Common attributes include diffuse tidal features indicative of recent mergers accompanied by bright, unresolved cores with effective radii less than a few hundred parsecs. The galaxies are extraordinarily compact for their …
Transition To Order After Hilltop Inflation, Marcelo Gleiser, Noah Graham
Transition To Order After Hilltop Inflation, Marcelo Gleiser, Noah Graham
Dartmouth Scholarship
We investigate the rich nonlinear dynamics during the end of hilltop inflation by numerically solving the coupled Klein-Gordon-Friedmann equations in an expanding universe. In particular, we search for coherent, nonperturbative configurations that may emerge due to the combination of nontrivial couplings between the fields and resonant effects from the cosmological expansion. We couple a massless field to the inflaton to investigate its effect on the existence and stability of coherent configurations and the effective equation of state at reheating. For parameters consistent with data from the Planck and WMAP satellites, and for a wide range of couplings between the inflaton …
A Comparison Of X-Ray And Optical Emission In Cassiopeia A, Daniel J. Patnaude, Robert A. Fesen
A Comparison Of X-Ray And Optical Emission In Cassiopeia A, Daniel J. Patnaude, Robert A. Fesen
Dartmouth Scholarship
Broadband optical and narrowband Si XIII X-ray images of the young Galactic supernova remnant Cassiopeia A (Cas A) obtained over several decades are used to investigate spatial and temporal emission correlations on both large and small angular scales. The data examined consist of optical and near infrared ground-based and Hubble Space Telescope images taken between 1951 and 2011, and X-ray images from Einstein, ROSAT, and Chandra taken between 1979 and 2013. We find weak spatial correlations between the remnant’s X-ray and optical emission features on large scales, but several cases of good optical/X-ray correlations on small scales for features which …
Weighing Obscured And Unobscured Quasar Hosts With The Cosmic Microwave Background, M. A. Dipompeo, A. D. Myers, R. C. Hickox, J. E. Geach, G. Holder, K. N. Hainline, S. W. Hall
Weighing Obscured And Unobscured Quasar Hosts With The Cosmic Microwave Background, M. A. Dipompeo, A. D. Myers, R. C. Hickox, J. E. Geach, G. Holder, K. N. Hainline, S. W. Hall
Dartmouth Scholarship
We cross-correlate a cosmic microwave background (CMB) lensing map with the projected space densities of quasars to measure the bias and halo masses of a quasar sample split into obscured and unobscured populations, the first application of this method to distinct quasar subclasses. Several recent studies of the angular clustering of obscured quasars have shown that these objects likely reside in higher-mass halos compared to their unobscured counterparts. This has important implications for models of the structure and geometry of quasars, their role in growing supermassive black holes, and mutual quasar/host galaxy evolution. However, the magnitude and significance of this …
The Acs Survey Of Globular Clusters. Xiii. Photometric Calibration In Comparison With Stetson Standards, Maren Hempel, Ata Sarajedini, Jay Anderson, Antonio Aparicio, Luigi R. Bedin, Brian Chaboyer
The Acs Survey Of Globular Clusters. Xiii. Photometric Calibration In Comparison With Stetson Standards, Maren Hempel, Ata Sarajedini, Jay Anderson, Antonio Aparicio, Luigi R. Bedin, Brian Chaboyer
Dartmouth Scholarship
In this study we compare the photometric data of 34 Milky Way globular clusters, observed within the Advanced Camera for Surveys (ACS) Treasury Program (PI: A. Sarajedini) with the corresponding ground-based data, provided by the Photometric Standard Field Catalogs of Stetson. We focus on the transformation between the Hubble Space Telescope/ACS F606W to V-band and F814W to I-band only. The goal is to assess the validity of the filter transformation equations by Sirianni et al. with respect to their dependence on metallicity, horizontal branch morphology, mass, and integrated (V – I) color of the various …
Star Formation And Substructure In Galaxy Clusters, Seth A. Cohen, Ryan C. Hickox, Gary A. Wegner, Maret Einasto, Jaan Vennik
Star Formation And Substructure In Galaxy Clusters, Seth A. Cohen, Ryan C. Hickox, Gary A. Wegner, Maret Einasto, Jaan Vennik
Dartmouth Scholarship
We investigate the relationship between star formation (SF) and substructure in a sample of 107 nearby galaxy clusters using data from the Sloan Digital Sky Survey (SDSS). Several past studies of individual galaxy clusters have suggested that cluster mergers enhance cluster SF, while others find no such relationship. The SF fraction in multi-component clusters (0.228 +/- 0.007) is higher than that in single-component clusters (0.175 +/- 0.016) for galaxies with M^0.1_r < -20.5. In both single- and multi-component clusters, the fraction of star-forming galaxies increases with clustercentric distance and decreases with local galaxy number density, and multi-component clusters show a higher SF fraction than single-component clusters at almost all clustercentric distances and local densities. Comparing the SF fraction in individual clusters to several statistical measures of substructure, we find weak, but in most cases significant at greater than 2 sigma, correlations between substructure and SF fraction. These results could indicate that cluster mergers may cause weak but significant SF enhancement in clusters, or unrelaxed clusters exhibit slightly stronger SF due to their less evolved states relative to relaxed clusters.
Tracing The Evolution Of Active Galactic Nuclei Host Galaxies Over The Last 9 Gyr Of Cosmic Time, A. D. Goulding, W. R. Forman, R. C. Hickox, C. Jones
Tracing The Evolution Of Active Galactic Nuclei Host Galaxies Over The Last 9 Gyr Of Cosmic Time, A. D. Goulding, W. R. Forman, R. C. Hickox, C. Jones
Dartmouth Scholarship
We present the results of a combined galaxy population analysis for the host galaxies of active galactic nuclei (AGN) identified at 0 < z < 1.4 within the Sloan Digital Sky Survey, Boötes, and DEEP2 surveys. We identified AGN in a uniform and unbiased manner at X-ray, infrared, and radio wavelengths. Supermassive black holes undergoing radiatively efficient accretion (detected as X-ray and/or infrared AGN) appear to be hosted in a separate and distinct galaxy population than AGN undergoing powerful mechanically dominated accretion (radio AGN). Consistent with some previous studies, radiatively efficient AGN appear to be preferentially hosted in modest star-forming galaxies, with little dependence on AGN or galaxy luminosity. AGN exhibiting radio-emitting jets due to mechanically dominated accretion are almost exclusively observed in massive, passive galaxies. Crucially, we now provide strong evidence that the observed host-galaxy trends are independent of redshift. In particular, these different accretion-mode AGN have remained as separate galaxy populations throughout the last 9 Gyr. Furthermore, it appears that galaxies hosting AGN have evolved along the same path as galaxies that are not hosting AGN with little evidence for distinctly separate evolution.
Interaction Between The Broad-Lined Type Ic Supernova 2012ap And Carriers Of Diffuse Interstellar Bands, Dan Milisavljevic, Raffaella Margutti, Kyle N. Crabtree, Jonathan B. Foster, Alicia M. Soderberg, Robert A. Fesen, Jerod T. Parrent
Interaction Between The Broad-Lined Type Ic Supernova 2012ap And Carriers Of Diffuse Interstellar Bands, Dan Milisavljevic, Raffaella Margutti, Kyle N. Crabtree, Jonathan B. Foster, Alicia M. Soderberg, Robert A. Fesen, Jerod T. Parrent
Dartmouth Scholarship
Diffuse interstellar bands (DIBs) are absorption features observed in optical and near-infrared spectra that are thought to be associated with carbon-rich polyatomic molecules in interstellar gas. However, because the central wavelengths of these bands do not correspond to electronic transitions of any known atomic or molecular species, their nature has remained uncertain since their discovery almost a century ago. Here we report on unusually strong DIBs in optical spectra of the broad-lined Type Ic supernova SN 2012ap that exhibit changes in equivalent width over short ( 30 days) timescales. The 4428 Å and 6283 Å DIB features get weaker with …
Evidence For A Weak Wind From The Young Sun, Brian E. Wood, Hans-Reinhard Müller, Seth Redfield, Eric Edelman
Evidence For A Weak Wind From The Young Sun, Brian E. Wood, Hans-Reinhard Müller, Seth Redfield, Eric Edelman
Dartmouth Scholarship
The early history of the solar wind has remained largely a mystery due to the difficulty of detecting winds around young stars that can serve as analogs for the young Sun. Here we report on the detection of a wind from the 500 Myr old solar analog π1 UMa (G1.5 V), using spectroscopic observations from the Hubble Space Telescope. We detect H I Lyα absorption from the interaction region between the stellar wind and interstellar medium, i.e., the stellar astrosphere. With the assistance of hydrodynamic models of the π1 UMa astrosphere, we infer a wind only half as strong as …
Black Hole Variability And The Star Formation-Active Galactic Nucleus Connection: Do All Star-Forming Galaxies Host An Active Galactic Nucleus?, Ryan C. Hickox, James R. Mullaney, David M. Alexander, Chien-Ting J. Chen, Francesca M. Civano, Andy D. Goulding, Kevin N. Hainline
Black Hole Variability And The Star Formation-Active Galactic Nucleus Connection: Do All Star-Forming Galaxies Host An Active Galactic Nucleus?, Ryan C. Hickox, James R. Mullaney, David M. Alexander, Chien-Ting J. Chen, Francesca M. Civano, Andy D. Goulding, Kevin N. Hainline
Dartmouth Scholarship
We investigate the effect of active galactic nucleus (AGN) variability on the observed connection between star formation and black hole accretion in extragalactic surveys. Recent studies have reported relatively weak correlations between observed AGN luminosities and the properties of AGN hosts, which has been interpreted to imply that there is no direct connection between AGN activity and star formation. However, AGNs may be expected to vary significantly on a wide range of timescales (from hours to Myr) that are far shorter than the typical timescale for star formation (100 Myr). This variability can have important consequences for observed correlations. We …
The Halo Occupation Distribution Of X-Ray-Bright Active Galactic Nuclei: A Comparison With Luminous Quasars, Jonathan Richardson, Suchetana Chatterjee, Zheng Zheng, Adam D. Myers, Ryan Hickox
The Halo Occupation Distribution Of X-Ray-Bright Active Galactic Nuclei: A Comparison With Luminous Quasars, Jonathan Richardson, Suchetana Chatterjee, Zheng Zheng, Adam D. Myers, Ryan Hickox
Dartmouth Scholarship
We perform halo occupation distribution (HOD) modeling of the projected two-point correlation function (2PCF) of high-redshift (z~1.2) X-ray-bright active galactic nuclei (AGN) in the XMM-COSMOS field measured by Allevato et al. The HOD parameterization is based on low-luminosity AGN in cosmological simulations. At the median redshift of z~1.2, we derive a median mass of (1.02+0.21/-0.23)x10^{13} Msun/h for halos hosting central AGN and an upper limit of ~10% on the AGN satellite fraction. Our modeling results indicate (at the 2.5-sigma level) that X-ray AGN reside in more massive halos compared to more bolometrically luminous, optically-selected quasars at similar redshift. The modeling …
Magnetic Inhibition Of Convection And The Fundamental Properties Of Low-Mass Stars. I. Stars With A Radiative Core, Gregory A. Feiden, Brian Chaboyer
Magnetic Inhibition Of Convection And The Fundamental Properties Of Low-Mass Stars. I. Stars With A Radiative Core, Gregory A. Feiden, Brian Chaboyer
Dartmouth Scholarship
Magnetic fields are hypothesized to inflate the radii of low-mass stars—defined as less massive than 0.8 M ☉—in detached eclipsing binaries (DEBs). We investigate this hypothesis using the recently introduced magnetic Dartmouth stellar evolution code. In particular, we focus on stars thought to have a radiative core and convective outer envelope by studying in detail three individual DEBs: UV Psc, YY Gem, and CU Cnc. Our results suggest that the stabilization of thermal convection by a magnetic field is a plausible explanation for the observed model-radius discrepancies. However, surface magnetic field strengths required by the models are significantly stronger …
Information-Entropic Stability Bound For Compact Objects: Application To Q-Balls And The Chandrasekhar Limit Of Polytropes, Marcelo Gleiser, Damian Sowinski
Information-Entropic Stability Bound For Compact Objects: Application To Q-Balls And The Chandrasekhar Limit Of Polytropes, Marcelo Gleiser, Damian Sowinski
Dartmouth Scholarship
Spatially-bound objects across diverse length and energy scales are characterized by a binding energy. We propose that their spatial structure is mathematically encoded as information in their momentum modes and described by a measure known as configurational entropy (CE). Investigating solitonic Q-balls and stars with a polytropic equation of state P=Kργ, we show that objects with large binding energy have low CE, whereas those at the brink of instability (zero binding energy) have near maximal CE. In particular, we use the CE to find the critical charge allowing for classically stable Q-balls and the Chandrasekhar limit for white dwarfs (γ=4/3) …
Spectral Energy Distributions Of Type 1 Agn In Xmm-Cosmos – Ii. Shape Evolution, Heng Hao, Martin Elvis, Francesca Civano, Gianni Zamorani
Spectral Energy Distributions Of Type 1 Agn In Xmm-Cosmos – Ii. Shape Evolution, Heng Hao, Martin Elvis, Francesca Civano, Gianni Zamorani
Dartmouth Scholarship
The mid-infrared to ultraviolet (0.1 -- 10 μm) spectral energy distribution (SED) shapes of 407 X-ray-selected radio-quiet type 1 AGN in the wide-field ``Cosmic Evolution Survey" (COSMOS) have been studied for signs of evolution. For a sub-sample of 200 radio-quiet quasars with black hole mass estimates and host galaxy corrections, we studied their mean SEDs as a function of a broad range of redshift, bolometric luminosity, black hole mass and Eddington ratio, and compared them with the Elvis et al. (1994, E94) type 1 AGN mean SED. We found that the mean SEDs in each bin are closely similar to …
Freezing Out Early Dark Energy, Jannis Bielefeld, W. L. Kimmy Wu, Robert R. Caldwell, Olivier Doré
Freezing Out Early Dark Energy, Jannis Bielefeld, W. L. Kimmy Wu, Robert R. Caldwell, Olivier Doré
Dartmouth Scholarship
A phenomenological model of dark energy that tracks the baryonic and cold dark matter at early times but resembles a cosmological constant at late times is explored. In the transition between these two regimes, the dark energy density drops rapidly as if it were a relic species that freezes out, during which time the equation of state peaks at +1. Such an adjustment in the dark energy density, as it shifts from scaling to potential domination, could be the signature of a trigger mechanism that helps explain the late-time cosmic acceleration. We show that the non-negligible dark energy density at …
The Xmm-Newton Spectrum Of A Candidate Recoiling Supermassive Black Hole: An Elusive Inverted P-Cygni Profile, G. Lanzuisi, F. Civano, S. Marchesi, A. Comastri
The Xmm-Newton Spectrum Of A Candidate Recoiling Supermassive Black Hole: An Elusive Inverted P-Cygni Profile, G. Lanzuisi, F. Civano, S. Marchesi, A. Comastri
Dartmouth Scholarship
We present a detailed spectral analysis of new XMM-Newton data of the source CXOC J100043.1+020637, also known as CID-42, detected in the COSMOS survey at z = 0.359. Previous works suggested that CID-42 is a candidate recoiling supermassive black hole (SMBH) showing also an inverted P-Cygni profile in the X-ray spectra at ~6 keV (rest) with an iron emission line plus a redshifted absorption line (detected at 3σ in previous XMM-Newton and Chandra observations). Detailed analysis of the absorption line suggested the presence of ionized material flowing into the black hole at high velocity. In the …
Spectral Distortion In A Radially Inhomogeneous Cosmology, R. R. Caldwell, N. A. Maksimova
Spectral Distortion In A Radially Inhomogeneous Cosmology, R. R. Caldwell, N. A. Maksimova
Dartmouth Scholarship
The spectral distortion of the cosmic microwave background blackbody spectrum in a radially inhomogeneous space-time, designed to exactly reproduce a ΛCDM expansion history along the past light cone, is shown to exceed the upper bound established by COBE-FIRAS by a factor of approximately 3700. This simple observational test helps uncover a slew of pathological features that lie hidden inside the past light cone, including a radially contracting phase at decoupling and, if followed to its logical extreme, a naked singularity at the radially inhomogeneous big bang.
Finding Rare Agn: Xmm-Newton And Chandra Observations Of Sdss Stripe 82, Stephanie M. Lamassa, C. Megan Urry, Nico Cappelluti, Francesca Civano
Finding Rare Agn: Xmm-Newton And Chandra Observations Of Sdss Stripe 82, Stephanie M. Lamassa, C. Megan Urry, Nico Cappelluti, Francesca Civano
Dartmouth Scholarship
We have analysed the XMM–Newton and Chandra data overlapping ∼16.5 deg2 of Sloan Digital Sky Survey Stripe 82, including ∼4.6 deg2 of proprietary XMM–Newton data that we present here. In total, 3362 unique X-ray sources are detected at high significance. We derive the XMM–Newton number counts and compare them with our previously reported Chandra logN–logS relations and other X-ray surveys. The Stripe 82 X-ray source lists have been matched to multiwavelength catalogues using a maximum likelihood estimator algorithm. We discovered the highest redshift (z = 5.86) quasar yet identified in an X-ray survey. We …
Optical And X-Ray Studies Of 10 X-Ray-Selected Cataclysmic Binaries, John R. Thorstensen, Jules Halpern
Optical And X-Ray Studies Of 10 X-Ray-Selected Cataclysmic Binaries, John R. Thorstensen, Jules Halpern
Dartmouth Scholarship
We report on ground-based optical observations of 10 cataclysmic binaries that were discovered through their X-ray emission. Time-resolved radial velocity spectroscopy yields unambiguous orbital periods for eight objects and ambiguous results for the remaining two. The orbital periods range from 87 minutes to 9.38 hr. We also obtained time-series optical photometry for six targets, four of which have coherent pulsations. These periods are 1218 s for 1RXS J045707.4+452751, 628 s for AX J1740.2–2903, 477 s for AX J1853.3–0128, and 935 s for IGR J19267+1325. A total of seven of the sources have coherent oscillations in X-rays or optical, indicating that …
A Bayesian Approach To Deriving Ages Of Individual Field White Dwarfs, Erin M. O'Malley, Ted Von Hippel, David A. Van Dyk
A Bayesian Approach To Deriving Ages Of Individual Field White Dwarfs, Erin M. O'Malley, Ted Von Hippel, David A. Van Dyk
Dartmouth Scholarship
We apply a self-consistent and robust Bayesian statistical approach to determine the ages, distances, and zero-age main sequence (ZAMS) masses of 28 field DA white dwarfs (WDs) with ages of approximately 4-8 Gyr. Our technique requires only quality optical and near-infrared photometry to derive ages with <15% uncertainties, generally with little sensitivity to our choice of modern initial-final mass relation. We find that age, distance, and ZAMS mass are correlated in a manner that is too complex to be captured by traditional error propagation techniques. We further find that the posterior distributions of age are often asymmetric, indicating that the standard approach to deriving WD ages can yield misleading results.
Salt Long-Slit Spectroscopy Of Luminous Obscured Quasars: An Upper Limit On The Size Of The Narrow-Line Region?, Kevin N. Hainline, Ryan Hickox, Jenny E. Greene, Adam D. Myers, Nadia L. Zakamska
Salt Long-Slit Spectroscopy Of Luminous Obscured Quasars: An Upper Limit On The Size Of The Narrow-Line Region?, Kevin N. Hainline, Ryan Hickox, Jenny E. Greene, Adam D. Myers, Nadia L. Zakamska
Dartmouth Scholarship
We present spatially resolved long-slit spectroscopy from the Southern African Large Telescope (SALT) to examine the spatial extent of the narrow-line regions (NLRs) of a sample of 8 luminous obscured quasars at 0.10 < z < 0.43. Our results are consistent with an observed shallow slope in the relationship between NLR size and L_[OIII], which has been interpreted to indicate that NLR size is limited by the density and ionization state of the NLR gas rather than the availability of ionizing photons. We also explore how the NLR size scales with a more direct measure of instantaneous AGN power using mid-IR photometry from WISE, which probes warm to hot dust near the central black hole and so, unlike [OIII], does not depend on the properties of the NLR. Using our results as well as samples from the literature, we obtain a power-law relationship between NLR size and L_8micron that is significantly steeper than that observed for NLR size and L_[OIII]. We find that the size of the NLR goes approximately as L^(1/2)_8micron, as expected from the simple scenario of constant-density clouds illuminated by a central ionizing source. We further see tentative evidence for a flattening of the relationship between NLR size and L_8micron at the high luminosity end, and propose that we are seeing a limiting NLR size of 10 - 20 kpc, beyond which the availability of gas to ionize becomes too low. We find that L_[OIII] ~ L_8micron^(1.4), consistent with a picture in which the L_[OIII] is dependent on the volume of the NLR. These results indicate that high-luminosity quasars have a strong effect in ionizing the available gas in a galaxy.
The Fast And Furious Decay Of The Peculiar Type Ic Supernova 2005ek, M. R. Drout, A. M. Soderberg, P. A. Mazzali, J. T. Parrent
The Fast And Furious Decay Of The Peculiar Type Ic Supernova 2005ek, M. R. Drout, A. M. Soderberg, P. A. Mazzali, J. T. Parrent
Dartmouth Scholarship
We present extensive multi-wavelength observations of the extremely rapidly declining Type Ic supernova (SN Ic), SN 2005ek. Reaching a peak magnitude of MR = –17.3 and decaying by ~3 mag in the first 15 days post-maximum, SN 2005ek is among the fastest Type I supernovae observed to date. The spectra of SN 2005ek closely resemble those of normal SN Ic, but with an accelerated evolution. There is evidence for the onset of nebular features at only nine days post-maximum. Spectroscopic modeling reveals an ejecta mass of ~0.3 M ☉ that is dominated by oxygen (~80%), while the pseudo-bolometric light …
A Detailed Kinematic Map Of Cassiopeia A'S Optical Main Shell And Outer High-Velocity Ejecta, Dan Milisavljevic, Robert A. Fesen
A Detailed Kinematic Map Of Cassiopeia A'S Optical Main Shell And Outer High-Velocity Ejecta, Dan Milisavljevic, Robert A. Fesen
Dartmouth Scholarship
We present three-dimensional (3D) kinematic reconstructions of optically emitting material in the young Galactic supernova remnant Cassiopeia A (Cas A). These Doppler maps have the highest spectral and spatial resolutions of any previous survey of Cas A and represent the most complete catalog of its optically emitting material to date. We confirm that the bulk of Cas A’s optically bright ejecta populate a torus-like geometry tilted approximately 30◦ with respect to the plane of the sky with a − 4000 to +6000 km s−1 radial velocity asymmetry. Near-tangent viewing angle effects and an inhomogeneous surrounding circumstellar material/ interstellar medium environment …