Previous: Tracing AGN in MaNGA
Under the supervision of Dr. Julie Comerford and Dr. Francisco Müller Sánchez , Jimmy analyzed Active Galactic Nuclei (AGN) utilizing the Sloan Digital Sky Survey (SDSS), a major multi-spectral imaging and spectroscopic redshift survey compiled using a dedicated 2.5-meter wide-angle optical telescope at Apache Point Observatory in New Mexico.
Specifically, he analyzed galactic spectra in the SDSS's Mapping Nearby Galaxies at APO (MaNGA) catalog, which consists of 10,000 galaxies observed with Integral Field Unit (IFU) spectroscopy. Within the MaNGA catalog, he identified high ionization and broad line emission signatures, which are characteristic features of AGN, to determine the number of AGN within the sample.
Publication: “A Catalog of 71 Coronal Line Galaxies in MaNGA: [Ne V] Is an Effective AGN Tracer”, James Negus, Julia M. Comerford, et al. 2023, ApJ, 945, 127.
Resolved Spectroscopy”, Julia M. Comerford, James Negus, et al. 2022, ApJ, 927, 1.
Publication: “The Physics of the Coronal Line Region for Galaxies in MaNGA”, James Negus,
Julia M. Comerford, et al. 2021, ApJ, 920, 62.
Publication: “A Catalog of 406 AGNs in MaNGA: A Connection between Radio-mode AGNs and Star Formation Quenching”, Julia M. Comerford, James Negus, et al. 2020, ApJ, 901, 159.
A face-on spiral galaxy imaged by MaNGA – the purple hexagon shows the coverage of the IFU
instrument (left), the circles are individual IFU fibers used to measure spectra (right).
Previous: Studying AGN Activation in Galaxy Mergers
An image of two spiral galaxies merging.
At the core of each galaxy, there exists a supermassive black hole, a dense cosmic region
with a mass equivalence of up to a billion solar masses. When two galaxies merge, the black holes residing at their centers will ultimately merge as well.
Supermassive black holes that accrete gas during a galaxy merger are visible as Active
Galactic Nuclei (AGN). The merger creates < 10 kpc separation supermassive black hole
pairs, and when one of the black holes in the merger is an AGN, it is considered an offset
AGN. If both supermassive black holes are AGN, they are classified as dual AGN.
Simulations predict that galaxy mergers drive central gas inflows that result in a higher AGN
fraction, the ratio of AGN to non-accreting supermassive black holes, at black hole
pair separations 1 kpc (Blecha et al. 2013). Observations have also shown that the AGN
fraction increases as the separation between two merging galaxies decrease from 100 kpc to
10 kpc (Koss et al. 2012); however, the trend has not yet been measured in the pivotal sub
10 kpc regime, where activity may drastically increase.
To test whether the AGN fraction indeed peaks at separations 1 kpc, we need a uniform
sample of dual and offset AGN, and an understanding of the timescales spent by black
hole pairs at various separations during a galaxy merger. For example, if there are the same
numbers of dual and offset AGN with separations of 5 kpc and 1 kpc, we might intuitively
assume that the AGN fraction remains the same from 5 kpc to 1 kpc separations. However,
if black hole pairs, in fact, spend 10 times longer at separations of 5 kpc than 1 kpc, then the
AGN fraction would actually be 10 times higher at 1 kpc separations than 5 kpc separations.
Pairing AGN observational data with hydrodynamic N-body merger simulations will determine where during a galaxy merger AGN are fueled.
Previous: Atmospheric Physics
1. “A New Narrowbeam, Multi-Frequency Scanning Radiometer and Its Application to In-Flight Icing Detection”, D. Serke, J. Negus, R. Ware, K. Reed, L. Blanchette, and P. Kennedy, Atmospheric Research, 2016:
An image of a dual-polarization radiometer.
A one-degree beamwidth, multi-frequency (20 to 30 and 89 GHz), dual-polarization radiometer with full azimuth and elevation scanning capabilities was built with the purpose of improving the detection of in-flight icing hazards to aircraft in the near airport environment. This goal was achieved by collocating the radiometer with Colorado State University’s CHILL polarized Doppler radar and leveraging the similar beam-width and volume scan regiments of the two instruments. The collocated instruments allowed for the liquid water path and water vapor measurements derived from the radiometer to be merged with the radar moment fields to determine microphysical and water phase characteristics aloft. The radiometer was field tested at Colorado State University’s CHILL radar site near Greeley, Colorado during the summer of 2009. Instrument design, calibration, and initial field testing results are discussed in this paper.
2. “Icing Characterization Based on In-Situ Aircraft and Remote Sensing Platform Observations”, R. Ware, D. Berchoff, E. Campos, R. Carpenter, N. Cimini, J. Fisher, M. Freer, I. Gultepe, J. Henrie, P. Holbrook, M. Klein, G. Kok, S. McLaughlin, M. Murakami, J. Negus, S. Nesbitt, M. Nelson, S. Parkinson, K. Reed, L. Sankey, D. Serke, M. Sharkey, S. Tessendorf, R. Stone, and B. Williams, AMS, 2017:
An aircraft has been outfitted with microwave radiometer, cloud particle spectral, and liquid water content sensors for icing condition detection and avoidance research. Complementary ground-based microwave radiometer, cross polarization lidar and weather radar observations are planned, along with high-resolution weather model analysis. We present initial findings from this unique cloud microphysics investigation focused on icing environments.
3. “Integrated Wind and Thermodynamic Profiling for High-Impact Nowcasting”, R. Baxter, J. Bhate, L. Blanchette, D. Berchoff, C. B. Clements, B. Demoz, P. Drewniak, M. D. Eilts, J. M. Freedman, D. M. Holland, K. R. Knupp, E. Lau, S. A. McLaughlin, J. Negus, M. Nelson, G. Pandithurai, R. Parmentier, M. Rajeevan, K. Reed, P. Roller, N. Sette, L. Thobois, S. Vanderburg, P. Wiker, and T. Wilfong, AMS, 2017:
Continuous boundary layer wind and thermodynamic profiles from regional networks are widely acknowledged as essential for accurate high-impact weather modeling and forecasting. Single-site integrated profiles became available more than a decade ago and networks are now proliferating. Integrated profiles can be ingested in radiosonde analysis and display software, providing continuously updated Forecast Indices and Tools. The profiles can also be assimilated in numerical weather models. We present integrated thermodynamic (radiometer) and wind (radar, lidar, sodar) profiles combined with numerical weather models via variational analysis, and discuss resulting high impact Nowcasting case studies.
4. “Boundary Layer Thermodynamic and Wind Observations for Improved Fog and Marine Layer Modeling and Forecasting”, R. Ware, L. Blanchette, D. Berchoff, W. Callahan, C. Clements, P. Croft, M. Eilts, P. Flatau, I. Gultepe, R. Hipschman, D. Holland, J. Kleissl, B. Koch, S. McLaughlin, M. Nelson, J. Negus, E. Osler, R. Parmentier, K. Reed, P. Roller, N. Sette, L. Thobois, S. Vandenburg, Y. Xie, and J. Zack, AMS, 2016:
We present continuous boundary layer thermodynamic and liquid profiles derived from microwave radiometer observations at San Francisco and other locations. A close correlation is found between these data and fog and marine layer formation and dissipation. Boundary layer winds also play an important role in fog and marine layer processes. The current status of boundary layer thermodynamic and wind observation and use to improve fog and marine layer modeling and forecasting will be discussed.