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Articles 1 - 4 of 4
Full-Text Articles in Physical Sciences and Mathematics
Deep Silicate Absorption Features In Compton-Thick Active Galactic Nuclei Predominantly Arise Due To Dust In The Host Galaxy, A. D. Goulding, D. M. Alexander, F. E. Bauer, W. R. Forman, R. C. Hickox
Deep Silicate Absorption Features In Compton-Thick Active Galactic Nuclei Predominantly Arise Due To Dust In The Host Galaxy, A. D. Goulding, D. M. Alexander, F. E. Bauer, W. R. Forman, R. C. Hickox
Dartmouth Scholarship
We explore the origin of mid-infrared (mid-IR) dust extinction in all 20 nearby (z < 0.05) bona fide Compton-thick (N H > 1.5 × 1024 cm–2) active galactic nuclei (AGNs) with hard energy (E > 10 keV) X-ray spectral measurements. We accurately measure the silicate absorption features at λ ~ 9.7 μm in archival low-resolution (R ~ 57-127) Spitzer Infrared Spectrograph spectroscopy, and show that only a minority (≈45%) of nearby Compton-thick AGNs have strong Si-absorption features (S 9.7 = ln (f int/f obs) 0.5) which would indicate significant dust attenuation. The majority (≈60%) are star …
The Hidden “Agn Main Sequence”: Evidence For A Universal Black Hole Accretion To Star Formation Rate Ratio Since Z ∼ 2 Producing An M Bh - M * Relation, J. R. Mullaney, E. Daddi, M. Béthermin, D. Elbaz, S. Juneau, M. Pannella, M. T. Sargent, D. M. Alexander, R. C. Hickox
The Hidden “Agn Main Sequence”: Evidence For A Universal Black Hole Accretion To Star Formation Rate Ratio Since Z ∼ 2 Producing An M Bh - M * Relation, J. R. Mullaney, E. Daddi, M. Béthermin, D. Elbaz, S. Juneau, M. Pannella, M. T. Sargent, D. M. Alexander, R. C. Hickox
Dartmouth Scholarship
Using X-ray stacking analyses we estimate the average amounts of supermassive black hole (SMBH) growth taking place in star-forming galaxies at z ~ 1 and z ~ 2 as a function of galaxy stellar mass (M *). We find that the average SMBH growth rate follows remarkably similar trends with M * and redshift as the average star formation rates (SFRs) of their host galaxies (i.e., \dot{M}_BH vprop M * 0.86 ± 0.39 for the z ~ 1 sample and \dot{M}_BH vprop M * 1.05 ± 0.36 for the z ~ 2 sample). It follows that the ratio of …
11-12 Gyr Old White Dwarfs 30 Pc Away, Mukremin Kilic, John R. Thorstensen, P. M. Kowalski, J. Andrews
11-12 Gyr Old White Dwarfs 30 Pc Away, Mukremin Kilic, John R. Thorstensen, P. M. Kowalski, J. Andrews
Dartmouth Scholarship
We present a detailed model atmosphere analysis of two of the oldest stars known in the solar neighbourhood, the high proper motion white dwarfs SDSS J110217.48+411315.4 (hereafter J1102) and WD 0346+246 (hereafter WD0346). We present trigonometric parallax observations of J1102, which places it at a distance of only 33.7 ± 2.0 pc. Based on the state-of-the-art model atmospheres, optical, near-infrared, mid-infrared photometry and distances, we constrain the temperatures, atmospheric compositions, masses and ages for both stars. J1102 is an 11-Gyr-old (white dwarf plus main-sequence age), 0.62 M⊙ white dwarf with a pure H atmosphere and Teff= 3830 …
Ionized Reflection Spectra From Accretion Disks Illuminated By X-Ray Pulsars, D. R. Ballantyne, J. D. Purvis, R. G. Strausbaugh, R. C. Hickox
Ionized Reflection Spectra From Accretion Disks Illuminated By X-Ray Pulsars, D. R. Ballantyne, J. D. Purvis, R. G. Strausbaugh, R. C. Hickox
Dartmouth Scholarship
X-ray reflection signatures are observed around multiple classes of accreting compact objects. Modelling these features yield important constraints on the physics of accretion disks, motivating the development of X-ray reflection models appropriate for a variety of systems and illumination conditions. Here, constant density ionized X-ray reflection models are presented for a disk irradiated with a very hard power-law X-ray spectrum (\Gamma < 1) and a variable high-energy cutoff. These models are then applied to the Suzaku data of the accreting X-ray pulsar LMC X-4, where very good fits are obtained with a highly ionized reflector responsible for both the broad Fe K line and the soft excess. The ionized reflector shows strong evidence for significant Doppler broadening and is redshifted by ~10^4 km/s. These features indicate that the reflecting material is associated with the complex dynamics occurring at the inner region of the magnetically-truncated accretion disk. Thus, reflection studies of X-ray pulsar spectra may give important insights into the accretion physics at the magnetospheric radius.