Browsing by Author "Farrah, Duncan"
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- Consistent Analysis of the AGN LF in X-Ray and MIR in the XMM-LSS FieldRunburg, Jack; Farrah, Duncan; Sajina, Anna; Lacy, Mark; Lidua, Jenna; Hatziminaoglou, Evanthia; Brandt, W. N.; Chen, Chien-Ting J.; Nyland, Kristina; Shirley, Raphael; Clements, D. L.; Pitchford, Lura K. (IOP, 2022-01-01)The luminosity function of active galactic nuclei (AGN) probes the history of supermassive black hole assembly and growth across cosmic time. To mitigate selection biases, we present a consistent analysis of the AGN luminosity functions (LFs) derived for both X-ray and mid-infrared (MIR) selected AGN in the XMM-Large Scale Structure field. There are 4268 AGN used to construct the MIR luminosity function (IRLF) and 3427 AGN used to construct the X-ray luminosity function (XLF), providing the largest census of the AGN population out to z = 4 in both bands with significant reduction in uncertainties. We are able for the first time to see the knee of the IRLF at z > 2 and observe a flattening of the faint-end slope as redshift increases. The bolometric luminosity density, a proxy for the cosmic black hole accretion history, computed from our LFs, shows a peak at z approximate to 2.25, consistent with recent estimates of the peak in the star formation rate density (SFRD). However, at earlier epochs, the AGN luminosity density is flatter than the SFRD. If confirmed, this result suggests that the build up of black hole mass outpaces the growth of stellar mass in high-mass systems at z greater than or similar to 2.5. This is consistent with observations of redshift z similar to 6 quasars that lie above the local M - sigma relationship. The luminosity density derived from the IRLF is higher than that from the XLF at all redshifts. This is consistent with the dominant role of obscured AGN activity in the cosmic growth of supermassive black holes.
- Modified Dark Matter: Relating Dark Energy, Dark Matter and Baryonic MatterEdmonds, Douglas; Farrah, Duncan; Minic, Djordje; Ng, Y. J.; Takeuchi, Tatsu (2017-09-13)Modi ed dark matter (MDM) is a phenomenological model of dark matter, inspired by gravitational thermodynamics. For an accelerating Universe with positive cosmological constant ( ), such phenomenological considerations lead to the emergence of a critical acceleration parameter related to . Such a critical acceleration is an effective phenomenological manifestation of MDM, and it is found in correlations between dark matter and baryonic matter in galaxy rotation curves. The resulting MDM mass profiles, which are sensitive to , are consistent with observational data at both the galactic and cluster scales. In particular, the same critical acceleration appears both in the galactic and cluster data fits based on MDM. Furthermore, using some robust qualitative arguments, MDM appears to work well on cosmological scales, even though quantitative studies are still lacking. Finally, we comment on certain non-local aspects of the quanta of modified dark matter, which may lead to novel non-particle phenomenology and which may explain why, so far, dark matter detection experiments have failed to detect dark matter particles.
- Quasar Outflows: Their Scale, Behavior and Influence in the Host GalaxyChamberlain, Carter W. (Virginia Tech, 2016-05-04)Quasar outflows are a major candidate for Active Galactic Nuclei (AGN) feedback, and their capacity to influence the evolution of their host galaxy depends on the mass-flow rate (M) and kinetic luminosity (E) of the outflowing material. Both quantities require measurement of the distance (R) to the outflow from the central source as well as physical conditions of the outflow, which can be determined using spectral observations of the quasar. This thesis presents spectral analyses leading to measurements of R, M and E for three different quasar outflows. Analysis of LBQS J1206+1052 revealed multiple diagnostic spectral features that could each be used to independently determine R. These diagnostics yielded measurements that were in close agreement, resulting in a robust outflow distance of 840 pc from the central source. This measurement is much larger than predicted from radiative acceleration models (~0.01-0.1 pc), suggesting that outflows appear much farther from the central source than is generally assumed. The outflow in SDSS J0831+0354 was found to carry a kinetic luminosity of 1045.7 erg/s, which corresponds to 5.2 per cent of the Eddington luminosity of the quasar. This outflow is one of the most energetic outflows to date and satisfies the criteria required to produce AGN feedback effects. A variability study of NGC 5548 revealed an obscuring cloud of gas that shielded the outflow components, dramatically lowering their ionization state. This resulted in the appearance of absorption from the rare element Phosphorus, as well as from sparsely-populated energy levels of CIII and SiIII. These spectral features allowed for an accurate determination of R and for constraints on the ionization phase to be obtained. The latter constraints were used to develop a self-consistent model that explained the variability of all six outflow components during five observing epochs spanning 16 years.
- Star formation in unobscured quasarsPitchford, Lura Katherine (Virginia Tech, 2021-08-30)It is now well established that a substantial fraction of all galaxy assembly occurs in intense bursts of star formation and black hole accretion, but the role of these two modes and how much they affect one another remains unclear. We thus investigate this in three complementary studies. In the first, we assemble a sample of 513 quasars identified by the Sloan Digital Sky Survey with detections by Herschel. These objects span a redshift range of 0 < z < 4, and their SEDs give a mean SFR of ~1000M☉/year. When comparing these SFRs to the intrinsic properties of the quasars, we find no clear connections between the quasars and the ongoing star formation events in their hosts. We then look for evidence of AGN feedback in broad absorption line (BAL) quasars, as such features are indicative of outflowing material. We find that high-ionization BAL quasars have indistinguishable properties to those of classical quasars. In our second study, which describes an iron low-ionization BAL quasar, SDSS J121441.42-000137.8, our results are again consistent with no feedback. Thus, it seems unlikely that feedback plays a dominant role in quenching star formation at the extreme SFRs seen in our BAL objects. We lastly study the host of an optically-bright quasar, SDSS J160705.16+355358.6, with evidence of an ongoing merger. We create the Point Spread Function (PSF) using a star that is in the same part of the field as our object, a method which is relatively unexplored. By subtracting the PSF, we are able to extract some of the host properties. We compare two PSF creation methods and find the empirical approach to be superior. Fits to the SEDs of the two galaxies are consistent with both falling on or above the main sequence of star formation. It is additionally plausible that these two galaxies could coalesce into a single massive quiescent galaxy by z ~ 2, and thus serve as progenitors to this class of galaxy that has proven challenging to our understanding of galaxy assembly.
- UV-bright nearby early-type galaxies observed in the mid-infrared: evidence for a multi-stage formation history by way of WISE and GALEX imagingPetty, S. M.; Neill, J. D.; Jarrett, T. H.; Blain, A. W.; Farrah, Duncan; Rich, R. M.; Tsai, C. W.; Benford, D. J.; Bridge, C. R.; Lake, S. E.; Masci, F. J.; Wright, E. L. (IOP Publishing Ltd., 2013-10)In the local universe, 10% of massive elliptical galaxies are observed to exhibit a peculiar property: a substantial excess of ultraviolet emission than what is expected from their old, red stellar populations. Several origins for this ultraviolet excess (UVX) have been proposed including a population of hot young stars and a population of old, blue horizontal branch or extended horizontal branch (BHB or EHB) stars that have undergone substantial mass loss from their outer atmospheres. We explore the radial distribution of UVX in a selection of 49 nearby E/S0-type galaxies by measuring their extended photometry in the UV through mid-infrared (mid-IR) with the Galaxy Evolution Explorer (GALEX), the Sloan Digital Sky Survey, and the Wide-field Infrared Survey Explorer (WISE). We compare UV/optical and UV/mid-IR colors with the Flexible Stellar Population Synthesis models, which allow for the inclusion of EHB stars. We find that combined WISE mid-IR and GALEX UV colors are more effective in distinguishing models than optical colors, and that the UV/mid-IR combination is sensitive to the EHB fraction. There are strong color gradients, with the outer radii bluer than the inner half-light radii by similar to 1 mag. This color difference is easily accounted for with an increase in the BHB fraction of 0.25 with radius. We estimated that the average ages for the inner and outer radii are 7.0 +/- 0.3 Gyr, and 6.2 +/- 0.2 Gyr, respectively, with the implication that the outer regions are likely to have formed similar to 1 Gyr after the inner regions. Additionally, we find that metallicity gradients are likely not a significant factor in the color difference. The separation of color between the inner and outer regions, which agrees with a specific stellar population difference (e. g., higher EHB populations), and the similar to 0.5-2 Gyr age difference suggests multi-stage formation. Our results are best explained by inside-out formation: rapid star formation within the core at early epochs (>4 Gyr ago) and at least one later stage starburst event coinciding with z similar to 1.
- Visualize This: Lessons from the Front-lines of High Performance VisualizationMohammed, Ayat; Polys, Nicholas F.; Farrah, Duncan (Department of Computer Science, Virginia Polytechnic Institute & State University, 2020-04-02)This paper presents a comprehensive workflow to address two major factors in multivariate multidimensional (MVMD) scientific visualization: the scalability of rendering and the scalability of representation (for perception). Our workflow integrates the metrics of scientific computing and visualization across di fferent STEM domains to deliver perceivable visualizations that meet scientists’ expectations. Our approach attempts to balance the performance of MVMD visualizations using techniques such as sub-sampling, domain decomposition, and parallel rendering. When mapping data to visual form we considered: the nature of the data (dimensionality, type, and distribution), the computing power (serial or parallel), and the rendering power (rendering mechanism, format, and display spectrum). We used HPC clusters to perform remote parallel processing and visualization of large-scale data sets such as 3D point clouds, galaxy catalogs, and airflow simulations. Our workflow brings these considerations into a structured form to guide the decisions of visualization designers who deal with large heterogeneous data sets.