19 research outputs found
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The Coevolution of AGN and Their Host Galaxies in Late Stage Mergers
As galaxies grow and evolve, the supermassive black holes (SMBHs) thought to exist at the center of most galaxies coevolve with them. During periods of growth, these SMBHs can become observable as active galactic nuclei (AGN). My work is focused on studying and understanding the environmental factors that precipitate AGN – galaxy coevolution, and the precise manner in which this coevolution takes place. The first work I present focuses on understanding how a general population of AGN coevolve with their host galaxies; specifically, how AGN luminosity, as a proxy for SMBH growth, relates to host galaxy parameters, such as star formation, in a general AGN population. I then shift my focus to how AGN coevolve with their host galaxies during galaxy merger events. The second work presented is centered around identifying a large sample of AGN host galaxies currently in late-stage mergers — a task that has presented considerable difficulties in the past — and then using this sample to study how AGN coevolve with their host galaxies as a function of their merger environment. The last work I present builds on the previous work by further classifying these AGN host merger systems as either offset AGN or dual AGN systems. This allows me to add nuance to previous findings and further probe key aspects of AGN activation and galaxy coevolution during late stage mergers. Finally, I discuss exciting avenues of future research that can build upon my past work, and expand our knowledge of SMBH – galaxy coevolution. This thesis reflects the entirety of my graduate work, focused on studying the coevolution of AGN and their host galaxies through the rigorous identification and analysis of AGN and the mergers of their host galaxies.</p
The Origin of Double-peaked Narrow Lines in Active Galactic Nuclei. IV. Association with Galaxy Mergers
Double-peaked narrow emission lines in active galactic nucleus (AGN) spectra
can be produced by AGN outflows, rotation, or dual AGNs, which are AGN pairs in
ongoing galaxy mergers. Consequently, double-peaked narrow AGN emission lines
are useful tracers of the coevolution of galaxies and their supermassive black
holes, as driven by AGN feedback and AGN fueling. We investigate this concept
further with follow-up optical longslit observations of a sample of 95 Sloan
Digital Sky Survey (SDSS) galaxies that have double-peaked narrow AGN emission
lines. Based on a kinematic analysis of the longslit spectra, we confirm
previous work that finds that the majority of double-peaked narrow AGN emission
lines are associated with outflows. We also find that eight of the galaxies
have companion galaxies with line-of-sight velocity separations < 500 km/s and
physical separations <30 kpc. Since we find evidence of AGNs in both galaxies,
all eight of these systems are compelling dual AGN candidates. Galaxies with
double-peaked narrow AGN emission lines occur in such galaxy mergers at least
twice as often as typical active galaxies. Finally, we conclude that at least
3% of SDSS galaxies with double-peaked narrow AGN emission lines are found in
galaxy mergers where both galaxies are resolved in SDSS imaging.Comment: 14 pages, 2 figures, ApJ in pres
Discovery and Characterization of Galactic-scale Dual Supermassive Black Holes Across Cosmic Time
The hierarchical structure formation paradigm predicts the formation of pairs
of supermassive black holes in merging galaxies. When both (or one) members of
the SMBH pair are unobscured AGNs, the system can be identified as a dual (or
offset) AGN. Quantifying the abundance of these AGN pairs as functions of
separation, redshift and host properties is crucial to understanding SMBH
formation and AGN fueling in the broad context of galaxy formation. The High
Latitude Wide Area Survey with Roman, with its unprecedented combination of
sensitivity, spatial resolution, area and NIR wavelength coverage, will
revolutionize the study of galactic-scale environments of SMBH pairs. This
white paper summarizes the science opportunities and technical requirements on
the discovery and characterization of SMBH pairs down to galactic scales (i.e.,
less than tens of kpc) over broad ranges of redshift (1<z<7) and luminosity
(Lbol>1E42 erg/s).Comment: Roman Core Community Survey White Paper, focusing on the High
Latitude Wide Area Surve
Massive Black Hole Binaries as LISA Precursors in the Roman High Latitude Time Domain Survey
With its capacity to observe faint active galactic nuclei
(AGN) out to redshift , Roman is poised to reveal a population of
black holes during an epoch of vigorous galaxy
assembly. By measuring the light curves of a subset of these AGN and looking
for periodicity, Roman can identify several hundred massive black hole binaries
(MBHBs) with 5-12 day orbital periods, which emit copious gravitational
radiation and will inevitably merge on timescales of years. During
the last few months of their merger, such binaries are observable with the
Laser Interferometer Space Antenna (LISA), a joint ESA/NASA gravitational wave
mission set to launch in the mid-2030s. Roman can thus find LISA precursors,
provide uniquely robust constraints on the LISA source population, help
identify the host galaxies of LISA mergers, and unlock the potential of
multi-messenger astrophysics with massive black hole binaries.Comment: White Paper for the Nancy Grace Roman Space Telescope's Core
Community Surveys (https://roman.gsfc.nasa.gov/science/ccs_white_papers.html
Searching for the Highest-z Dual AGN in the Deepest Chandra Surveys
International audienceWe present an analysis searching for dual AGN among 62 high-redshift () X-ray sources selected from publicly available deep Chandra fields. We aim to quantify the frequency of dual AGN in the high-redshift Universe, which holds implications for black hole merger timescales and low-frequency gravitational wave detection rates. We analyze each X-ray source using BAYMAX, an analysis tool that calculates the Bayes factor for whether a given archival Chandra AGN is more likely a single or dual point source. We find no strong evidence for dual AGN in any individual source in our sample. We then increase our sensitivity to search for dual AGN across the sample by comparing our measured distribution of Bayes factors to that expected from a sample composed entirely of single point sources, and again find no evidence for dual AGN in the observed sample distribution. Although our analysis utilizes one of the largest Chandra catalogs of high- X-ray point sources available to study, the findings remain limited by the modest number of sources observed at the highest spatial resolution with Chandra and the typical count rates of the detected sources. Our non-detection allows us to place an upper-limit on the X-ray dual AGN fraction between of 4.8%. Expanding substantially on these results at X-ray wavelengths will require future surveys spanning larger sky areas and extending to fainter fluxes than has been possible with Chandra. We illustrate the potential of the AXIS mission concept in this regard