529 research outputs found
The Great Chicago Fire- October 8-10, 1871
Essay on the Great Chicago Fire of 1871.unpublishednot peer reviewe
Attenuation modified by DIG and dust as seen in M31
The spatial distribution of dust in galaxies affects the global attenuation,
and hence inferred properties, of galaxies. We trace the spatial distribution
of dust in five fields (at 0.6-0.9 kpc scale) of M31 by comparing optical
attenuation with the total dust mass distribution. We measure the attenuation
from the Balmer decrement using Integral Field Spectroscopy and the dust mass
from Herschel far-IR observations. Our results show that M31's dust attenuation
closely follows a foreground screen model, contrary to what was previously
found in other nearby galaxies. By smoothing the M31 data we find that spatial
resolution is not the cause for this difference. Based on the emission line
ratios and two simple models, we conclude that previous models of dust/gas
geometry need to include a weakly or non-attenuated diffuse ionized gas (DIG)
component. Due to the variation of dust and DIG scale heights with galactic
radius, we conclude that different locations in galaxies will have different
vertical distributions of gas and dust and therefore different measured
attenuation. The difference between our result in M31 with that found in other
nearby galaxies can be explained by our fields in M31 lying at larger galactic
radii than the previous studies that focused on the centres of galaxies.Comment: 20 pages, 13 figures, ApJ accepted and in pres
A physically-based model of the ionizing radiation from active galaxies for photoionization modeling
We present a simplified model of Active Galactic Nucleus (AGN) continuum
emission designed for photoionization modeling. The new model {\sc oxaf}
reproduces the diversity of spectral shapes that arise in physically-based
models. We identify and explain degeneracies in the effects of AGN parameters
on model spectral shapes, with a focus on the complete degeneracy between the
black hole mass and AGN luminosity. Our re-parametrized model {\sc oxaf}
removes these degeneracies and accepts three parameters which directly describe
the output spectral shape: the energy of the peak of the accretion disk
emission , the photon power-law index of the non-thermal
emission , and the proportion of the total flux which is emitted in the
non-thermal component . The parameter is
presented as a function of the black hole mass, AGN luminosity, and `coronal
radius' of the {\sc optxagnf} model upon which {\sc oxaf} is based. We show
that the soft X-ray excess does not significantly affect photoionization
modeling predictions of strong emission lines in Seyfert narrow-line regions.
Despite its simplicity, {\sc oxaf} accounts for opacity effects where the
accretion disk is ionized because it inherits the `color correction' of {\sc
optxagnf}. We use a grid of {\sc mappings} photoionization models with {\sc
oxaf} ionizing spectra to demonstrate how predicted emission-line ratios on
standard optical diagnostic diagrams are sensitive to each of the three {\sc
oxaf} parameters. The {\sc oxaf} code is publicly available in the Astrophysics
Source Code Library.Comment: 14 pages, 9 figures, 1 table. Accepted for publication in Ap
The mass-metallicity relation of local active galaxies
We systematically measure the gas-phase metallicities and the
mass-metallicity relation of a large sample of local active galaxies for the
first time. Observed emission-line fluxes from the Sloan Digital Sky Survey
(SDSS) are compared to a four-dimensional grid of photoionization models using
the Bayesian parameter estimation code NebulaBayes. For the first time we take
into account arbitrary mixing between HII region and narrow-line region (NLR)
emission, and the models are also varied with metallicity, ionization parameter
in the NLR, and the gas pressure. The active galactic nucleus (AGN) oxygen
abundance is found to increase by dex as a function
of host galaxy stellar mass over the range .
We also measure the metallicity and ionization parameter of 231000 star-forming
galaxies for comparison with the sample of 7670 Seyfert 2 galaxies. A
systematic offset in oxygen abundance of 0.09 dex is observed between the
mass-metallicity relations of the star-forming and active galaxies. We
investigate potential causes of the offset, including sample selection and the
treatment in the models of diffuse ionized gas, pressure, and ionization
parameter. We cannot identify the major cause(s), but suspect contributions due
to deficiencies in modeling the ionizing spectra and the treatment of dust
physics. Optical diagnostic diagrams are presented with the star-forming and
Seyfert data colored by the inferred oxygen abundance, ionization parameter and
gas pressure, clearly illustrating the trends in these quantities.Comment: 12 pages, 4 figures and 1 table; accepted for publication in Ap
Interrogating Seyferts with NebulaBayes: Spatially probing the narrow-line region radiation fields and chemical abundances
NebulaBayes is a new Bayesian code that implements a general method of
comparing observed emission-line fluxes to photoionization model grids. The
code enables us to extract robust, spatially resolved measurements of
abundances in the extended narrow line regions (ENLRs) produced by Active
Galactic Nuclei (AGN). We observe near-constant ionization parameters but
steeply radially-declining pressures, which together imply that radiation
pressure regulates the ENLR density structure on large scales. Our sample
includes four `pure Seyfert' galaxies from the S7 survey that have extensive
ENLRs. NGC2992 shows steep metallicity gradients from the nucleus into the
ionization cones. An {\it inverse} metallicity gradient is observed in
ESO138-G01, which we attribute to a recent gas inflow or minor merger. A
uniformly high metallicity and hard ionizing continuum are inferred across the
ENLR of Mrk573. Our analysis of IC5063 is likely affected by contamination from
shock excitation, which appears to soften the inferred ionizing spectrum. The
peak of the ionizing continuum E_peak is determined by the nuclear spectrum and
the absorbing column between the nucleus and the ionized nebula. We cannot
separate variation in this intrinsic E_peak from the effects of shock or HII
region contamination, but E_peak measurements nevertheless give insights into
ENLR excitation. We demonstrate the general applicability of NebulaBayes by
analyzing a nuclear spectrum from the non-active galaxy NGC4691 using a HII
region grid. The NLR and HII region model grids are provided with NebulaBayes
for use by the astronomical community.Comment: Accepted for publication in ApJ; 29 pages with 10 figures and 3
table
A new diagnostic to separate line emission from star formation, shocks, and AGNs simultaneously in IFU data
In the optical spectra of galaxies, methods for the separation of line emission arising from star formation and an additional hard component, such as shocks or active galactic nuclei (AGNs), is well-understood and possible with current diagnostics. However, such diagnostics fail when attempting to separate and define line emission which arises from shocked gas, and that arising from AGNs. We present a new three-dimensional diagnostic diagram for integral field unit data which can simultaneously separate the line emission amongst star formation, shocks, and AGNs within a galaxy. We show that regions we define as AGN-dominated correlate well with the hard X-ray distribution in our test case NGC 1068, as well as with known regions of AGN activity in NGC 1068. Similarly, spaxels defined as shock-dominated correlate strongly with regions of high-velocity dispersion within the galaxy.Parts of this research were conducted by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3Dimensions (ASTRO 3D), through project number CE170100013
Revision of Madagascar's Dwarf Lemurs (Cheirogaleidae:Cheirogaleus): Designation of Species, Candidate Species Status and Geographic Boundaries Based on Molecular and Morphological Data
The genus Cheirogaleus, the dwarf lemurs, is a radiation of strepsirrhine primates endemic to the island of Madagascar.
The dwarf lemurs are taxonomically grouped in the family Cheirogaleidae (Infraorder: Lemuriformes) along with the genera
Microcebus, Mirza, Allocebus, and Phaner. The taxonomic history of the genus Cheirogaleus has been controversial since its
inception due to a paucity of evidence in support of some proposed species. In this study, we addressed this issue by expanding the
geographic breadth of samples by 91 individuals and built upon existing mitochondrial (cytb and COII) and nuclear (FIBA and
vWF) DNA datasets to better resolve the phylogeny of Cheirogaleus. The mitochondrial gene fragments D-loop and PAST as well
as the CFTR-PAIRB nuclear loci were also sequenced. In agreement with previous genetic studies, numerous deep divergences
were resolved in the C. major, C. minor and C. medius lineages. Four of these lineages were segregated as new species, seven
were identified as confirmed candidate species, and four were designated as unconfirmed candidate species based on comparative
mitochondrial DNA sequence data gleaned from the literature or this study. Additionally, C. thomasi was resurrected. Given the
widespread distribution of the genus Cheirogaleus throughout Madagascar, the methodology employed in this study combined
all available lines of evidence to standardize investigative procedures in a genus with limited access to type material and a lack of
comprehensive sampling across its total distribution. Our results highlighted lineages that likely represent new species and identified
localities that may harbor an as-yet undescribed cryptic species diversity pending further field and laboratory work.We
are most grateful to the Ahmanson Foundation, the Theodore
F. and Claire M. Hubbard Family Foundation, the Primate
Action Fund / Conservation International, the Margot
Marsh Biodiversity Foundation, and the National Geographic
Society, for financial assistance
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