177 research outputs found
Interview with James R. Hopkins
James Hopkins talks about the Kokosing river valley.https://digital.kenyon.edu/lak_interviews/1009/thumbnail.jp
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
The Formation of High Redshift Submillimeter Galaxies
We describe a model for the formation of \zsim 2 Submillimeter Galaxies
(SMGs) which simultaneously accounts for both average and bright SMGs while
providing a reasonable match to their mean observed spectral energy
distributions (SEDs). By coupling hydrodynamic simulations of galaxy mergers
with the high resolution 3D polychromatic radiative transfer code Sunrise, we
find that a mass sequence of merger models which use observational constraints
as physical input naturally yield objects which exhibit black hole, bulge, and
H2 gas masses similar to those observed in SMGs. The dominant drivers behind
the 850 micron flux are the masses of the merging galaxies and the stellar
birthcloud covering fraction. The most luminous (S850 ~ 15 mJy) sources are
recovered by ~10^13 Msun 1:1 major mergers with a birthcloud covering fraction
close to unity, whereas more average SMGs ~5-7 mJy) may be formed in lower mass
halos ~5x10^12 Msun. These models demonstrate the need for high spatial
resolution hydrodynamic and radiative transfer simulations in matching both the
most luminous sources as well as the full SEDs of SMGs. While these models
suggest a natural formation mechanism for SMGs, they do not attempt to match
cosmological statistics of galaxy populations; future efforts along this line
will help ascertain the robustness of these models.Comment: MNRAS Accepted; Revised version includes expanded discussion of
simulated radio properties of SMG
Benefits to Adolescents Who Perform Community Service: A Perspective from Adolescent Health Researchers
In the arenas of health, social scientists have learned over the past two decades that engagement in community service among adolescents often result in valuable outcomes. In other words, the persons being served are not the only ones benefiting from the experience, the providers of the service benefit as well. The purpose of this paper is to share with the legal community some of what we as social science researchers have learned from our research and also learned from the research of others in both health and education regarding benefits of community service among adolescents. We also will share with the readers what we have learned about structuring a successful community service and/or service learning program or process
Decades of Research Shows Adolescents Do Better With Community Service Rather than Incarceration
The purpose of this article is to share with the legal community some of what we as social science researchers have learned from our research and the research of others, regarding the health and education benefits of community service among adolescents. In other words, we will attempt to answer the question of whether there are benefits of performing community service to the individuals performing the service, and to describe what these benefits are
Imagining sustainable energy and mobility transitions: valence, temporality, and radicalism in 38 visions of a low-carbon future
Based on an extensive synthesis of semi-structured interviews, media content analysis, and reviews, this article conducts a qualitative meta-analysis of more than 560 sources of evidence to identify 38 visions associated with seven different low-carbon innovations – automated mobility, electric vehicles, smart meters, nuclear power, shale gas, hydrogen, and the fossil fuel divestment movement – playing a key role in current deliberations about mobility or low-carbon energy supply and use. From this material, it analyzes such visions based on rhetorical features such as common problems and functions, storylines, discursive struggles, and rhetorical effectiveness. It also analyzes visions based on typologies or degrees of valence (utopian vs. dystopian), temporality (proximal vs. distant), and radicalism (incremental vs. transformative). The article is motivated by the premise that tackling climate change via low-carbon energy systems (and practices) is one of the most significant challenges of the twenty-first century, and that effective decarbonization will require not only new energy technologies, but also new ways of understanding language, visions, and discursive politics surrounding emerging innovations and transitions
A Physical Model for z~2 Dust Obscured Galaxies
We present a physical model for the origin of z~2 Dust-Obscured Galaxies
(DOGs), a class of high-redshift ULIRGs selected at 24 micron which are
particularly optically faint (24/R>1000). By combining N-body/SPH simulations
of high redshift galaxy evolution with 3D polychromatic dust radiative transfer
models, we find that luminous DOGs (with F24 > 0.3 mJy at z~2 are well-modeled
as extreme gas-rich mergers in massive (~5x10^12-10^13 Msun) halos, with
elevated star formation rates (~500-1000 Msun/yr) and/or significant AGN growth
(Mdot > 0.5 Msun/yr), whereas less luminous DOGs are more diverse in nature. At
final coalescence, merger-driven DOGs transition from being starburst dominated
to AGN dominated, evolving from a "bump" to a power-law shaped mid-IR (IRAC)
spectral energy distribution (SED). After the DOG phase, the galaxy settles
back to exhibiting a "bump" SED with bluer colors and lower star formation
rates. While canonically power-law galaxies are associated with being
AGN-dominated, we find that the power-law mid-IR SED can owe both to direct AGN
contribution, as well as to a heavily dust obscured stellar bump at times that
the galaxy is starburst dominated. Thus power-law galaxies can be either
starburst or AGN dominated. Less luminous DOGs can be well-represented either
by mergers, or by massive ($M_{\rm baryon} ~5x10^11 Msun) secularly evolving
gas-rich disc galaxies (with SFR > 50 Msun/yr). By utilising similar models as
those employed in the SMG formation study of Narayanan et al. (2010), we
investigate the connection between DOGs and SMGs. We find that the most heavily
star-forming merger driven DOGs can be selected as Submillimetre Galaxies
(SMGs), while both merger-driven and secularly evolving DOGs typically satisfy
the BzK selection criteria.Comment: Accepted by MNRAS; major changes include better description of
dependency on ISM specification and updated models allowing dust to evolve
with metallicity
Mixing between Seyfert and HII-region excitation in local active galaxies
We fit theoretical models to the emission-line spectra of 2766 Seyfert
galaxies from the Sloan Digital Sky Survey (SDSS). The model line fluxes are
derived by `mixing' photoionization model predictions of active galactic
nucleus (AGN) narrow line region (NLR) emission and HII region emission. The
observed line fluxes in each spectrum were directly compared to the grid of
mixed models using the Bayesian parameter estimation code NebulaBayes, thereby
measuring the degree of mixing in each spectrum for the first time. We find
that the majority of the Balmer line emission in the majority of
Seyfert-classified SDSS spectra arises from contaminating HII regions within
the fixed-size aperture. Even for spectra with log [OIII]/Hb , a
median of ~30% of the Balmer flux arises in HII regions. We show that the
results are qualitatively insensitive to the assumed Seyfert ionizing
continuum, and that ionizing spectra with a peak energy of E_peak ~ 40-50 eV
produce the most plausible distributions of mixing fractions. The analysis
cleanly quantifies how the starburst - AGN `mixing fraction' increases on the
BPT diagram for SDSS galaxies. Apart from the mixing fraction, the models also
vary with the ionization parameter in the NLR, the gas pressure, and the
metallicity. Measurements for the metallicity in particular will be presented
in a companion paper.Comment: 9 pages, 3 figures, and 1 table; accepted for ApJ
Tourism, Sustainability and Recovery : Asia Pacific Expert Outlook : Wakayama-CTR Webinar Series 2020
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