16 research outputs found
Recommended from our members
Parameter justification report for DRSPALL.
A new conceptual model has been developed for drilling intrusion into the Waste Isolation Pilot Plant. The model is implemented in a new code, DRSPALL, which captures the physics of the spallings release phenomena. The new conceptual model and code required parallel development of a family of parameters that adequately describe the properties of the system. This report introduces the various parameters implemented in the new spallings model, and provides justification for values and ranges of new parameters not currently in the performance assessment database
The Messy Nature of Fiber Spectra: Star-Quasar Pairs Masquerading as Dual Type 1 AGNs
Theoretical studies predict that the most significant growth of supermassive
black holes occurs in late-stage mergers, coinciding with the manifestation of
dual active galactic nuclei (AGNs), and both major and minor mergers are
expected to be important for dual AGN growth. In fact, dual AGNs in minor
mergers should be signposts for efficient minor merger-induced SMBH growth for
both the more and less massive progenitor. We identified two candidate dual
AGNs residing in apparent minor mergers with mass ratios of 1:7 and
1:30. SDSS fiber spectra show broad and narrow emission lines in the
primary nuclei of each merger while only a narrow [O III] emission line and a
broad and prominent H/[N II] complex is observed in the secondary
nuclei. The FWHMs of the broad H lines in the primary and secondary
nuclei are inconsistent in each merger, suggesting that each nucleus in each
merger hosts a Type 1 AGN. However, spatially-resolved LBT optical spectroscopy
reveal rest-frame stellar absorption features, indicating the secondary sources
are foreground stars and that the previously detected broad lines are likely
the result of fiber spillover effects induced by the atmospheric seeing at the
time of the SDSS observations. This study demonstrates for the first time that
optical spectroscopic searches for Type 1/Type 1 pairs similarly suffer from
fiber spillover effects as has been observed previously for Seyfert 2 dual AGN
candidates. The presence of foreground stars may not have been clear if an
instrument with more limited wavelength range or limited sensitivity had been
used.Comment: 15 pages including appendix and references, 6 figures, 1 table.
Accepted for publication in Ap
Multi-wavelength observations of SDSS J105621.45+313822.1, a broad-line, low-metallicity AGN
In contrast to massive galaxies with Solar or super-Solar gas phase
metallicities, very few Active Galactic Nuclei (AGN) are found in
low-metallicity dwarf galaxies. Such a population could provide insight into
the origins of supermassive black holes. Here we report near-infrared
spectroscopic and X-ray observations of SDSS J105621.45+313822.1, a low-mass,
low-metallicity galaxy with optical narrow line ratios consistent with star
forming galaxies but a broad H line and mid-infrared colors consistent
with an AGN. We detect the [Si VI] 1.96m coronal line and a broad
Pa line with a FWHM of ~km~s. Together with the
optical broad lines and coronal lines seen in the SDSS spectrum, we confirm the
presence of a highly accreting black hole with mass ~M, with a bolometric luminosity of
~erg~s based on the coronal line luminosity, implying a
highly accreting AGN. Chandra observations reveal a weak nuclear point source
with ~erg~s,
orders of magnitude lower than that predicted by the mid-infrared
luminosity, suggesting that the AGN is highly obscured despite showing broad
lines in the optical spectrum. The low X-ray luminosity and optical narrow line
ratios of J1056+3138 highlight the limitations of commonly employed diagnostics
in the hunt for AGNs in the low metallicity low mass regime.Comment: 13 pages, 6 figures, accepted to Ap
NuSTAR Observes Two Bulgeless Galaxies: No Hard X-Ray AGN Detected in NGC 4178 or J0851+3926
The discovery over the last several decades of low- and moderate-luminosity active galactic nuclei (AGNs) in disk-dominated galaxies—which show no “classical” bulges—suggests that secular mechanisms represent an important growth pathway for supermassive black holes in these systems. We present new follow-up NuSTAR observations of the optically elusive AGNs in two bulgeless galaxies, NGC 4178 and J0851+3926. Galaxy NGC 4178 was originally reported as hosting an AGN based on the detection of [Ne v ] mid-infrared emission detected by Spitzer, and based on Chandra X-ray imaging, it has since been argued to host either a heavily obscured AGN or a supernova remnant. Galaxy J0851+3926 was originally identified as an AGN based on its Wide-Field Infrared Survey Explorer mid-IR colors, and follow-up near-infrared spectroscopy previously revealed a hidden broad-line region, offering compelling evidence for an optically elusive AGN. Neither AGN is detected within the new NuSTAR imaging, and we derive upper limits on the hard X-ray 10–24 keV fluxes of 24.2 and 24.1, respectively. The nature of the nuclear activity in NGC 4178 remains inconclusive; it is plausible that the [Ne v ] traces a period of higher activity in the past, but that the AGN is relatively quiescent now. The nondetection in J0851+3926 and multiwavelength properties are consistent with the AGN being heavily obscured