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  1. Home
  2. Browse by Author

Browsing by Author "Armus, Lee"

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    A Hard X-Ray Test of HCN Enhancements As a Tracer of Embedded Black Hole Growth
    (2020) Privon, George C.; Ricci, Claudio; Aalto, S.; Viti, Serena; Armus, Lee; Diaz-Santos, Tanio; González-Alfonso, E.; Treister, Ezequiel; Bauer, Franz Erik; Garg, P.
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    A Herschel Space Observatory Spectral Line Survey of Local Luminous Infrared Galaxies from 194 to 671 Microns
    (IOP PUBLISHING LTD, 2017) Lu, Nanyao; Zhao, Yinghe; Diaz Santos, Tanio; Kevin Xu, C.; Gao, Yu; Armus, Lee; Isaak, Kate G.; Mazzarella, Joseph M.; van der Werf, Paul P.; Appleton, Philip N.; Charmandaris, Vassilis; Evans, Aaron S.; Howell, Justin; Iwasawa, Kazushi; Leech, Jamie; Lord, Steven; Petric, Andreea O.; Privon, George C.; Sanders, David B.; Schulz, Bernhard; Surace, Jason A.
    We describe a Herschel Space Observatory 194-671 mu m spectroscopic survey of a sample of 121 local luminous infrared galaxies and report the fluxes of the CO J to J-1 rotational transitions for 4 <= J <= 13, the [N II] 205 mu m line, the [C I] lines at 609 and 370 mu m, as well as additional and usually fainter lines. The CO spectral line energy distributions (SLEDs) presented here are consistent with our earlier work, which was based on a smaller sample, that calls for two distinct molecular gas components in general: (i) a cold component, which emits CO lines primarily at J less than or similar to 4 and likely represents the same gas phase traced by CO (1-0), and (ii) a warm component, which dominates over the mid-J regime (4 < J less than or similar to 10) and is intimately related to current star formation. We present evidence that the CO line emission associated with an active galactic nucleus is significant only at J > 10. The flux ratios of the two [C I] lines imply modest excitation temperatures of 15-30 K; the [C I] 370 mu m line scales more linearly in flux with CO (4-3) than with CO (7-6). These findings suggest that the [C I] emission is predominantly associated with the gas component defined in (i) above. Our analysis of the stacked spectra in different far-infrared (FIR) color bins reveals an evolution of the SLED of the rotational transitions of H2O vapor as a function of the FIR color in a direction consistent with infrared photon pumping.
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    Characterizing the Molecular Gas in Infrared Bright Galaxies with CARMA
    (2024) Alatalo, Katherine; Petric, Andreea O.; Lanz, Lauranne; Rowlands, Kate; Vivian, U.; Larson, Kirsten L.; Armus, Lee; Barcos-Munoz, Loreto; Evans, Aaron S.; Koda, Jin; Luo, Yuanze; Medling, Anne M.; Nyland, Kristina E.; Otter, Justin A.; Patil, Pallavi; Penaloza, Fernando; Salim, Diane; Sanders, David B.; Sazonova, Elizaveta; Skarbinski, Maya; Song, Yiqing; Treister, Ezequiel; Urry, C. Meg
    We present the CO(1-0) maps of 28 infrared-bright galaxies from the Great Observatories All-Sky Luminous Infrared Galaxy Survey (GOALS) taken with the Combined Array for Research in Millimeter Astronomy (CARMA). We detect 100 GHz continuum in 16 of the 28 CARMA GOALS galaxies, which trace both active galactic nuclei (AGNs) and compact star-forming cores. The GOALS galaxies show a variety of molecular gas morphologies, though in the majority of cases the average velocity fields show a gradient consistent with rotation. We fit the full continuum spectral energy distributions (SEDs) of each of the sources using either magphys or SED3FIT (if there are signs of an AGN) to derive the total stellar mass, dust mass, and SFRs of each object. We adopt a value determined from luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) of alpha CO = 1.5-0.8+1.3 M circle dot (K km s-1 pc2)-1, which leads to more physical values for f mol and the gas-to-dust ratio. Mergers tend to have the highest gas-to-dust ratios. We assume the cospatiality of the molecular gas and star formation and plot the CARMA GOALS sample on the Schmidt-Kennicutt relation, where we find that they preferentially lie above the line set by normal star-forming galaxies. This hyper-efficiency is likely due to the increased turbulence in these systems, which decreases the freefall time compared to star-forming galaxies, leading to "enhanced" star formation efficiency. Line wings are present in a non-negligible subsample (11/28) of the CARMA GOALS sources and are likely due to outflows driven by AGNs or star formation, gas inflows, or additional decoupled gas components.
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    Excitation Mechanisms for HCN (1-0) and HCO+ (1-0) in Galaxies from the Great Observatories All-sky LIRG Survey.
    (2015) Privon, G. C.; Treister, Ezequiel; Herrero-Illana, R.; Evans, Aaron S.; Iwasawa, K.; Perez-Torres, M. A.; Armus, Lee; Díaz-Santos, T.; Murphy, E. J.; Stierwalt, S.; Aalto, S.
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    Growing supermassive black holes in the late stages of galaxy mergers are heavily obscured.
    (2017) Ricci, Claudio; Bauer, Franz Erik; Treister, Ezequiel; Privon, G. C.; Schawinski, K.; Blecha, L.; Arevalo, P.; Armus, Lee; Harrison, F.; Ho, L. C.; Iwasawa, K.; Sanders, David B.; Stern, Daniel
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    How to fuel an AGN: mapping circumnuclear gas in NGC 6240 with ALMA
    (2019) Medling, Anne M.; Privon, George C.; Barcos Muñoz, Loreto; Treister, Ezequiel; Cicone, Claudia; Messias, Hugo; Sanders, David B.; Scoville, Nick Z.; U, Vivian; Bauer, Franz Erik; Armus, Lee; Chang, Chin-Shin; Comerford, Julia M.; Evans, Aaron S.; Max, Claire E.; Müller-Sánchez, Francisco; Nagar, Neil; Sheth, Kartik
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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.
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    The Dense Molecular Gas and Nuclear Activity in the ULIRG IRAS 13120-5453
    (2017) Privon, G. C.; Aalto, S.; Falstad, N.; Muller, S.; González, Alfonso E.; Sliwa, K.; Treister, Ezequiel; Costagliola, F.; Armus, Lee; Evans, Aaron S.; Garcia, S.; Izumi, T.; Sakamoto, K.; Van Der Werf, P.; Chu, J.
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    Tracing the Ionization Structure of the Shocked Filaments of NGC 6240
    (2021) Medling, Anne M.; Kewley, Lisa J.; Calzetti, Daniela; Privon, George C.; Larson, Kirsten; Rich, Jeffrey A.; Armus, Lee; Allen, Mark G.; Bicknell, Geoffrey V.; Díaz-Santos, Tanio; Heckman, Timothy M.; Leitherer, Claus; Max, Claire E.; Rupke, David S. N.; Treister, Ezequiel; Messias, Hugo; Wagner, Alexander Y.
    We study the ionization and excitation structure of the interstellar medium in the late-stage gas-rich galaxy merger NGC 6240 using a suite of emission-line maps at similar to 25 pc resolution from the Hubble Space Telescope, Keck/NIRC2 with Adaptive Optics, and the Atacama Large Millimeter/submillimeter Array (ALMA). NGC 6240 hosts a superwind driven by intense star formation and/or one or both of two active nuclei; the outflows produce bubbles and filaments seen in shock tracers from warm molecular gas (H-2 2.12 mu m) to optical ionized gas ([O iii], [N ii], [S ii], and [O i]) and hot plasma (Fe XXV). In the most distinct bubble, we see a clear shock front traced by high [O iii]/H beta and [O iii]/[O i]. Cool molecular gas (CO(2-1)) is only present near the base of the bubble, toward the nuclei launching the outflow. We interpret the lack of molecular gas outside the bubble to mean that the shock front is not responsible for dissociating molecular gas, and conclude that the molecular clouds are partly shielded and either entrained briefly in the outflow, or left undisturbed while the hot wind flows around them. Elsewhere in the galaxy, shock-excited H-2 extends at least similar to 4 kpc from the nuclei, tracing molecular gas even warmer than that between the nuclei, where the two galaxies' interstellar media are colliding. A ridgeline of high [O iii]/H beta emission along the eastern arm aligns with the southern nucleus' stellar disk minor axis; optical integral field spectroscopy from WiFeS suggests this highly ionized gas is centered at systemic velocity and likely photoionized by direct line of sight to the southern active galactic nucleus.
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    Warm Molecular Hydrogen in Nearby, Luminous Infrared Galaxies
    (2018) Petric, Andreea O.; Armus, Lee; Flagey, Nicolas; Guillard, Pierre; Howell, Justin; Inami, Hanae; Charmandaris, Vassillis; Evanss, Aaron; Stierwalt, Sabrina; Diaz-Santos, Tanio; Lu, Nanyao; Spoon, Henrik; Mazzarella, Joe; Appleton, Phil; Chan, Ben; Chu, Jason; Hand, Derek; Privon, George; Sanders, David; Surace, Jason; Xu, Kevin; Zhao, Yinghe
    Mid-infrared molecular hydrogen (H-2) emission is a powerful cooling agent in galaxy mergers and in radio galaxies; it is a potential key tracer of gas evolution and energy dissipation associated with mergers, star formation, and accretion onto supermassive black holes. We detect mid-IR H-2 line emission in at least one rotational transition in 91% of the 214 Luminous Infrared Galaxies (LIRGs) observed with Spitzer as part of the Great Observatories All-sky LIRG Survey. We use H-2 excitation diagrams to estimate the range of masses and temperatures of warm molecular gas in these galaxies. We find that LIRGs in which the IR emission originates mostly from the Active Galactic Nuclei (AGN) have about 100 K higher H-2 mass-averaged excitation temperatures than LIRGs in which the IR emission originates mostly from star formation. Between 10% and 15% of LIRGs have H-2 emission lines that are sufficiently broad to be resolved or partially resolved by the high-resolution modules of Spitzer's Infrared Spectrograph (IRS). Those sources tend to be mergers and contain AGN. This suggests that a significant fraction of the H-2 line emission is powered by AGN activity through X-rays, cosmic rays, and turbulence. We find a statistically significant correlation between the kinetic energy in the H-2 gas and the H-2 to IR luminosity ratio. The sources with the largest warm gas kinetic energies are mergers. We speculate that mergers increase the production of bulk inflows leading to observable broad H-2 profiles and possibly denser gas.

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