Browsing by Author "Yoon, Ilsang"

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    A Potential Recoiling Supermassive Black Hole, CXO J101527.2+625911
    (2017) Kim, D. -C.; Yoon, Ilsang; Privon, G. C.; Evans, A. S.; Harvey, D.; Stierwalt, S.; Kim, Ji Hoon
    We have carried out a systematic search for recoiling supermassive black holes (rSMBH) using the Chandra Source and SDSS Cross-Match Catalog. From the survey, we have detected a potential rSMBH, CXO J101527.2 +625911, at z = 0.3504. The source CXO J101527.2+625911 has a spatially offset (1.26 +/- 0.05 kpc) active SMBH and kinematically offset broad emission lines (175 +/- 25 km s(-1) relative to the systemic velocity). The observed spatial and velocity offsets suggest that this galaxy could be an rSMBH, but we have also considered the possibility of a dual SMBH scenario. The column density toward the galaxy center was found to be Compton thin, but no X-ray source was detected. The non-detection of the X-ray source in the nucleus suggests that either there is no obscured actively accreting SMBH or that there exists an SMBH, but it has a low accretion rate (i.e., a low luminosity AGN (LLAGN)). The possibility of the LLAGN was investigated and found to be unlikely based on the Ha luminosity, radio power, and kinematic arguments. This, along with the null detection of an X-ray source in the nucleus, supports our hypothesis that CXO J101527.2+625911 is an rSMBH. Our GALFIT analysis shows the host galaxy to be a bulge-dominated elliptical. The weak morphological disturbance and small spatial and velocity offsets suggest that CXO J101527.2+625911 could be in the final stage of a merging process and about to turn into a normal elliptical galaxy.
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    Searching for Compact Obscured Nuclei in Compton-thick Active Galactic Nuclei
    (Institute of Physics, 2025) Johnstone, Makoto A.; Privon, George C.; Barcos-Muñoz, Loreto; Evans, A. S.; Aalto, S.; Armus, Lee; Bauer, Franz Erik; Blecha L.; Gallagher, J. S.; König, S.; Ricci, Claudio; Treister, Ezequiel; Eibensteiner, Cosima; Emig, Kimberly L.; Green, Kara N.; Kunneriath, Devaky; Nagarajan-Swenson, Jaya; Saravia, Alejandro; Yoon, Ilsang
    Compact obscured nuclei (CONs) are heavily obscured infrared cores that have been found in local (ultra-)luminous infrared galaxies. They show bright emission from vibrationally excited rotational transitions of HCN, known as HCN-vib, and are thought to harbor Compton-thick (CT, NH ≥ 1024 cm−2) active galactic nuclei (AGNs) or extreme compact starbursts. We explore the potential evolutionary link between CONs and CT-AGNs by searching for CONs in hard-X-ray-confirmed CT-AGNs from the Great Observatories All-sky LIRG Survey (GOALS). Here, we present new Atacama Large Millimeter/submillimeter Array Band 6 observations that targeted HCN-vib emission in four hard-X-ray-confirmed CT-AGNs. We analyze these objects together with literature HCN-vib measurements of five additional hard-X-ray-confirmed CT-AGNs from the GOALS sample. We do not detect any CONs in this combined sample of nine CT-AGNs. We then explore a proposed evolutionary sequence in which CONs evolve into X-ray-detectable CT-AGNs once outflows and feedback reduce the column densities of the enshrouding gas. We find, however, no evidence of well-developed dense molecular outflows in the observed CT-AGNs. While this could suggest that CT-AGNs are not universally linked to CONs, it could also be explained by a short duty cycle for molecular outflows.
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    The Arp 240 Galaxy Merger: A Detailed Look at the Molecular Kennicutt-Schmidt Star Formation Law on Subkiloparsec Scales
    (IOP Publishing Ltd, 2025) Saravia, Alejandro; Rodas Quito, Eduardo; Barcos Muñoz, Loreto; Evans, Aaron; Kunneriath, Devaky; Privon, George; Song, Yiqing; Yoon, Ilsang; Emig, Kimberly L.; Sánchez Garcia, María; Linden, Sean; Green, Kara Noelle; Johnstone, Makoto; Nagarajan Swenson, Jaya; Meza, Gabriela A.; Momjian, Emmanuel; Armus, Lee; Charmandaris, Vassilis; Díaz Santos, Tanio; Treister, Ezequiel
    The molecular Kennicutt-Schmidt Law has been key for understanding star formation (SF) in galaxies across allredshifts. However, recent subkiloparsec observations of nearby galaxies reveal deviations from the nearly unityslop e(N) obtained with disk-averaged measurements. We study SF and molecular gas (MG) distribution in theearly-stage luminous infrared galaxy merger Arp 240(NGC 5257-8). Using Very Large Array radio continuum (RC) and Atacama Large Millimeter/submillimeter Array CO(2-1)observations at 500 pc scale, with a uniformgrid analysis, we estimate SF rates and MG surface densities (Sigma(SFR) and H-2, respectively). In Arp 240,Nissublinear at 0.52 +/- 0.17. For NGC 5257 and NGC 5258,Nis 0.52 +/- 0.16 and 0.75 +/- 0.15, respectively. Weidentify two SF regimes: high surface brightness (HSB) regions in RC with N similar to 1, and low surface brightness (LSB) regions with shallow N (ranging 0.15 +/- 0.09-0.48 +/- 0.04). Median CO(2-1) linewidth and MG turbulent pressure (P-turb) are 25 km s(-1) and 9 x 10(5) K cm(-3). No significant correlation was found between Sigma(SFR) and CO(2-1) linewidth. However, Sigma(SFR) correlates with P-turb, particularly in HSB regions (rho>0.60). In contrast, SF efficiency moderately anticorrelates with P-turb in LSB regions but shows no correlation in HSB regions. Additionally, we identify regions where peaks in SF and MG are decoupled, yielding a shallow N (<= 0.28 +/- 0.18). Overall, the range of N reflects distinct physical properties and distribution of both the SF and MG, which can be masked by disk-averaged measurements.