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 $\Delta {\rm O/H} \sim 0.1$ dex as a function of host galaxy stellar mass over the range $10.1 < \log M_* / M_\odot < 11.3$. 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 $\gtrsim 0.9$, 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