First author publications

Galaxy and Quasar Fueling Caught in the Act from the Intragroup to the Interstellar Medium

Johnson, Sean D.; Chen, Hsiao-Wen; Straka, Lorrie A.; Schaye, Joop; Cantalupo, Sebastiano; Wendt, Martin; Muzahid, Sowgat; Bouché, Nicolas; Herenz, Edmund Christian; Kollatschny, Wolfram; Mulchaey, John S.; Marino, Rafaella A.; Maseda, Michael V.; Wisotzki, Lutz, ApJ Letters, in press

We report the discovery of six spatially extended (10-100 kpc) line-emitting nebulae in the z=0.57 galaxy group hosting PKS0405-123, one of the most luminous quasars at z<1. The discovery is enabled by the Multi Unit Spectroscopic Explorer (MUSE) and provides tantalizing evidence connecting large-scale gas streams with nuclear activity on scales of <10 proper kpc (pkpc). One of the nebulae exhibits a narrow, filamentary morphology extending over 50 pkpc toward the quasar with narrow internal velocity dispersion (50 km/s) and is not associated with any detected galaxies, consistent with a cool intragroup medium (IGrM) filament. Two of the nebulae are 10 pkpc North and South of the quasar with tidal arm like morphologies. These two nebulae, along with a continuum emitting arm extending 60 pkpc from the quasar are signatures of interactions which are expected to redistribute angular momentum in the host interstellar medium (ISM) to facilitate star formation and quasar fueling in the nucleus. The three remaining nebulae are among the largest and most luminous [O III] emitting `blobs' known (1400-2400 pkpc^2) and correspond both kinematically and morphologically with interacting galaxy pairs in the quasar host group, consistent with arising from stripped ISM rather than large-scale quasar outflows. The presence of these large- and small-scale nebulae in the vicinity of a luminous quasar bears significantly on the effect of large-scale environment on galaxy and black hole fueling, providing a natural explanation for the previously known correlation between quasar luminosity and cool circumgalactic medium (CGM).

https://www.dropbox.com/s/uyc4rynjlkn8kwk/NNMF.pdf?dl=0

https://www.dropbox.com/s/7wiey6h99bc7zwp/subtraction.pdf?dl=0

https://www.dropbox.com/s/r9jvtpe2kwqllqp/movie.avi?dl=0

The extent of chemically enriched gas around star-forming dwarf galaxies

Sean D. Johnson, Hsiao-Wen Chen, John S. Mulchaey, Joop Schaye, and Lorrie A. Straka, ApJ Letters, 2018, 850, 1, L10

Supernova driven winds are often invoked to remove chemically enriched gas from dwarf galaxies to match their low observed metallicities. In such shallow potential wells, outflows may produce massive amounts of enriched halo gas (circum-galactic medium or CGM) and pollute the intergalactic medium (IGM). Here, we present a survey of the CGM and IGM around 18 star-forming field dwarfs with stellar masses of 1e8-1e9 solar masses at z~0.2. Eight of these have CGM probed by quasar absorption spectra at projected distances, d, less than the host virial radius, Rh. Ten are probed in the surrounding IGM at d/Rh=1-3. The absorption measurements include neutral hydrogen, the dominant silicon ions for diffuse cool gas (T~1e4 K; Si II, Si III, and Si IV), moderately ionized carbon (C IV), and highly ionized oxygen (O VI). Metal absorption from the CGM of the dwarfs is less common and ~4x weaker compared to massive star-forming galaxies though O VI absorption is still common. None of the dwarfs probed at d/Rh =1-3 have definitive metal-line detections. Combining the available silicon ions, we estimate that the cool CGM of the dwarfs accounts for only 2-6% of the expected silicon budget from the yields of supernovae associated with past star-formation. The highly ionized O VI accounts for ~8% of the oxygen budget. As O VI traces an ion with expected equilibrium ion fractions of <~0.2, the highly ionized CGM may represent a significant metal reservoir even for dwarfs not expected to maintain gravitationally shock heated hot halos.

On the origin of excess cool gas in quasar host halos

Sean D. Johnson, Hsiao-Wen Chen, and John S. Mulchaey, Monthly Notices of the Royal Astronomical Society, Volume 452, Issue 3 p. 2553-2015, September 2015

(Abridged) Observations of quasar host halos at z≈2 have uncovered large quantities of cool gas that exceed what is found around inactive galaxies of both lower and higher masses. To better understand the source of this excess cool gas, we compiled an exhaustive sample of 195 quasars at z≈1 with constraints on MgII absorption in background quasar spectra from the SDSS. This quasar sample spans a luminosity range from Lbol=10^44.4 to 10^46.8 erg/s and allows an investigation of whether halo gas properties are connected with quasar properties. We find a strong correlation between luminosity and cool gas covering fraction. In particular, low-luminosity quasars exhibit a mean gas covering fraction comparable to inactive galaxies of similar masses, but more luminous quasars exhibit excess cool gas approaching what is reported previously at z≈2. Moreover, 30-40% of the MgII absorption occurs at radial velocities of |∆v|>300 km/s from the quasar, inconsistent with bound gas. The large velocity offsets and observed luminosity dependence of the cool gas near quasars can be explained if the gas arises from: (1) neighboring halos correlated through large-scale structure at Mpc scales, (2) feedback from luminous quasars, or (3) debris from the mergers thought to trigger luminous quasars.

On the possible environmental effect in distributing heavy elements beyond individual gaseous haloes

Johnson, Sean D., Chen, Hsiao-Wen, and Mulchaey, John S., Monthly Notices of the Royal Astronomical Society, Volume 449, Issue 3, p.3263-3273, May 2015

(Abridged): We present a study of extended galaxy halo gas through HI and OVI absorption over two decades in projected distance at z ≈ 0.2 based on a sample of 95 galaxies from a highly complete (>80%) survey of faint galaxies (L>0.1L*) with archival quasar absorption spectra. The high completeness of the galaxy survey enables an investigation of environmental dependence of extended gas properties. Galaxies with nearby neighbors exhibit a modest increase in OVI covering fraction at d>Rh compared to isolated galaxies but no excess HI absorption. These findings suggest that environmental effects play a role in distributing heavy elements beyond the enriched gaseous haloes of individual galaxies.

Discovery of a transparent sightline at ρ ≲ 20 kpc from an interacting pair of galaxies

Johnson, Sean D., et al. Monthly Notices of the Royal Astronomical Society, Volume 438, Issue 4, p.3039-3048, March 2014

(Abridged): We report the discovery of a transparent sightline at projected distances of ρ ≲ 20 kpc to an interacting pair of mature galaxies at z = 0.12. Deep optical images reveal tidal features indicative of close interactions. Despite the small projected distances, the quasar sightline shows little absorption associated with the galaxy pair with a total HI column density at least two orders of magnitude less than what is expected from non-interacting galaxies. The probability of seeing such little absorption in a sightline passing at a small projected distance from two non-interacting galaxies is 0.2%. The absence of strong absorbers near the galaxy pair suggests that the cool gas reservoirs of the galaxies have been significantly depleted by the galaxy interaction.

Probing the IGM-galaxy connection at z < 0.5 - II. New insights into the galaxy environments of OVI absorbers in PKS 0405-123

Johnson, Sean D., Chen, Hsiao-Wen, and Mulchaey, John S., Monthly Notices of the Royal Astronomical Society, Volume 434, Issue 2, p.1765-1778, Sept. 2013

(Abridged): We present new absorption-line analysis and galaxy survey data obtained for the field around PKS 0405-123 at z = 0.57. Combining previously known OVI absorbers with new identifications in the higher S/N UV spectra obtained with the Cosmic Origins Spectrograph, we have established a sample of 7 OVI absorbers and 12 individual components at z = 0.0918-0.495 along the sightline. We complement the available UV absorption spectra with galaxy survey data that reach high completeness for faint galaxies near the sightline. The high level of completeness achieved by our survey reveals that OVI absorbers are closely associated with gas-rich environments containing at least one low-mass, emission-line galaxy. An intriguing exception is a strong OVI system at z ≈ 0.183 that does not have a galaxy found at ρ<4 Mpc.

 

Feasibility of U.S. renewable portfolio standards under cost caps and case study for Illinois

Johnson, Sean D. and Moyer, Elisabeth J., Energy Policy, Volume 49, Pages 499–514, Oct. 2012

(Abridged): Recently enacted state renewable portfolio standards (RPSs) collectively require that U.S. electricity generation by non-hydro renewables more than double by 2025. These goals are not certain to be met, however, because many RPSs apply cost caps that alter requirements if costs exceed targets. We analyze here the 2008 Illinois RPS, which is fairly typical, and find that at current electricity prices, complete implementation will require significant decreases in renewables costs. Full implementation is possible but not assured. The statutory design raises additional concerns about unintended potential consequences. The fact that windpower and solar carveouts fall under a single cost cap means that in failure mode, a less cost-effective technology can curtail deployment of a more cost-effective one.

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Other publications

Zahedy, F. S., Chen, H.-W., Johnson, S. D.; Pierce, R. M., Rauch, M., Huang, Y.-H., Weiner, B. D., Gauthier, J.-R., 2018, Characterizing Circumgalactic Gas around Massive Ellipticals at z ≈ 0.4 - II. Physical Properties and Elemental Abundances, MNRAS in review (arxiv: 1809.05115)

Schmidt, S. J., Shappee, B.-J., van Saders, J. L.; Stanek, K. Z., Brown, J. S.; Kochanek, C. S.; Dong, S.; Drout, M. R.; Frank, S; Holoien, T. W.-S.; Johnson, S. D.; Madore, B. F..; Prieto, J. L.; Seibert, M.; Seidel, M. K.; Simonian, G. V. A., The largest M dwarfs flares from ASAS-SN, ApJ, submitted

Chen H.-W., Zahedy F. S., Johnson S. D., Pierce R. M., Huang Y.-H., Weiner B. J., Gauthier J.-R., 2018, Characterizing Circumgalactic Gas Around Massive Ellipticals at z ≈ 0.4 - I. Initial results MNRAS, 479, 2547C

Sun, A.-L., Greene, J. E., Zakamska, N. L., Goulding, A., Strauss, M. A., Huang, S., Johnson, S.D., Kawaguchi, T., Matsuoka, Y., Marsteller, A. A., Nagao, T., Tobo, Y., et al. 2018, MNRAS, 480, 2302S

Stern, J., Faucher-Gig ́ere, C.-A., Hennawi, J. F., Hafen, Z., Johnson, S. D., Fielding, D., 2018, Does circumgalactic O VI trace low-pressure gas beyond the accretion shock? clues from H I ab- sorption, dust extinction, and line kinematics, ApJ, 865, 91S

Lan T.-W., Menard B., Baron D., Johnson S. D., Poznanski D., Prochaska J. X., O’Meara J. M., 2018, MNRAS, 477, 3520L

Goulding, A. D., Greene, J. E., Bezanson, R., Greco, J., Johnson, S. D., Leauthaud, A, Masuoka, Y., Medezinski, E., Price-Whelan, A.M., 2017, Galaxy Interactions Trigger Rapid Black Hole Growth: an unprecedented view from the Hyper Suprime-Cam Survey, PASJ, 70S, 37G

Chen, H.-W., Johnson, S. D., Zahedy, F. S., Rauch, M., & Mulchaey, J. S. 2017, Gauging Metallicity of Diffuse Gas under an Uncertain Ionizing Radiation Field, ApJ letters, 842L, 19C

Straka, L., Johnson, S. D., York, D. G., Bowen, D. V., Florian, M., Kulkarni, V. P., Lundgren, B., Celine, P. 2016, Magellan LDSS3 emission confirmation of galaxies hosting metal-rich Lyman-alpha absorption systems, MNRAS, 458, 3760S

Huang, Y.-H., Chen, H.-W., Johnson, S. D., Weiner, B. J. 2016, Characterizing the Chemically-Enriched Circumgalactic Medium of ~38000 Luminous Red Galaxies in SDSS DR12, MNRAS, 455, 1713H

Chen, H.-W., Gauthier, J.-R., Sharon, K., Johnson, S. D., Nair, P., & Liang, C. J. 2014, Spatially resolved velocity maps of halo gas around two intermediate-redshift galaxies, MNRAS, 438, 1435

Oka, T., Welty, D. E., Johnson, S. D., York, D. G., Dahlstrom, J., & Hobbs, L. M., 2013, Anomalous Diffuse Interstellar Bands in the Spectrum of Herschel 36. II. Analysis of Radiatively Excited CH+, CH, and Diffuse Interstellar Bands, ApJ, 773, 42

Dahlstrom, J., York, D. G., Welty, D. E., Oka, T., Hobbs, L. M., Johnson, S. D., Friedman, S. D., Jiang, Z., Rachford, B. L., Sherman, R., Snow, T. P., Sonnentrucker, P., 2013, Anomalous Diffuse Interstellar Bands in the Spectrum of Herschel 36. I. Observations of Rotationally Excited CH and CH+ Absorption and Strong, Extended Redward Wings on Several DIBs, ApJ, 773, 41

Moyer, E. J., Johnson, S. D., Goldberger, L., & Zhu, J., 2012, Feasibility and Implications of the Michigan 2012 Proposal 3 for a 25% State Renewable Portfolio Standard, RDCEP Policy Analysis Paper Series

York, D. G., Straka, L. A., Bishof, M., Kuttruff, S., Bowen, D., Kulkarni, V. P., Subbarau, M., Richards, G., Vanden Berk, D., Hall, P. B., Heckman, T., Khare, P., Quashnock, J., Ghering, L., & Johnson, S. D., Galaxies with background QSOs - I. A search for strong galactic Hα lines 2012, MNRAS, 423, 3692

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Department of Astrophysical Sciences

Princeton University

sdj "at" astro.princeton.edu