# Publications

## Discovery of a nearby 1700 km/s star ejected from the Milky Way by Sgr A*

Monthly Notices of the Royal Astronomical Society Oxford University Press 491 (2019) 2465-2480

D Boubert, TS Li, D Erkal, GS Da Costa, DB Zucker, AP Ji, GF Lewis, K Kuehn, JD Simpson, D Mackey, N Shipp, V Belokurov, Z Wan, J Bland-Hawthorn, SL Martell, T Nordlander, D De Silva, M-Y Wang

<jats:title>Abstract</jats:title> <jats:p>We present the serendipitous discovery of the fastest Main Sequence hyper-velocity star (HVS) by the Southern Stellar Stream Spectroscopic Survey (S5). The star S5-HVS1 is a ∼2.35 M⊙ A-type star located at a distance of ∼9 kpc from the Sun and has a heliocentric radial velocity of 1017 ± 2.7  km s−1 without any signature of velocity variability. The current 3-D velocity of the star in the Galactic frame is 1755 ± 50  km s−1. When integrated backwards in time, the orbit of the star points unambiguously to the Galactic Centre, implying that S5-HVS1 was kicked away from Sgr A* with a velocity of ∼1800  km s−1 and travelled for 4.8 Myr to its current location. This is so far the only HVS confidently associated with the Galactic Centre. S5-HVS1 is also the first hyper-velocity star to provide constraints on the geometry and kinematics of the Galaxy, such as the Solar motion Vy, ⊙ = 246.1 ± 5.3  km s−1 or position R0 = 8.12 ± 0.23 kpc. The ejection trajectory and transit time of S5-HVS1 coincide with the orbital plane and age of the annular disk of young stars at the Galactic centre, and thus may be linked to its formation. With the S5-HVS1 ejection velocity being almost twice the velocity of other hyper-velocity stars previously associated with the Galactic Centre, we question whether they have been generated by the same mechanism or whether the ejection velocity distribution has been constant over time.</jats:p>

## KROSS-SAMI: a direct IFS comparison of the Tully-Fisher relation across 8 Gyr since z approximate to 1

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 482 (2019) 2166-2188

AL Tiley, M Bureau, L Cortese, CM Harrison, HL Johnson, JP Stott, AM Swinbank, I Smail, D Sobral, AJ Bunker, K Glazebrook, RG Bower, D Obreschkow, JJ Bryant, MJ Jarvis, J Bland-Hawthorn, G Magdis, AM Medling, SM Sweet, C Tonini, OJ Turner, RM Sharples, SM Croom, M Goodwin, IS Konstantopoulos, NPF Lorente, JS Lawrence, J Mould, MS Owers, SN Richards

## Action-based models for dwarf spheroidal galaxies and globular clusters

Monthly Notices of the Royal Astronomical Society Oxford University Press 488 (2019) 2423-2439

C Nipoti, J Binney, R Pascale, L Posti

A new family of self-consistent distribution function (DF)-based models of stellar systems is explored. The stellar component of the models is described by a DF depending on the action integrals, previously used to model the Fornax dwarf spheroidal galaxy (dSph). The stellar component may cohabit with either a dark halo, also described by a DF, or with a massive central black hole. In all cases we solve for the models self-consistent potential. Focussing on spherically symmetric models, we show how the stellar observables vary with the anisotropy prescribed by the DF, with the dominance and nature of the dark halo, and with the mass of the black hole. We show that precise fits to the observed surface brightness profiles of four globular clusters can be obtained for a wide range of prescribed velocity anisotropies. We also obtain precise fits to the observed projected densities of four dSphs. Finally, we present a three-component model of the Sculptor dSph with distinct DFs for the red and blue horizontal branch stars and the dark matter halo.

## The energetics of starburst-driven outflows at z ∼ 1 from KMOS

Monthly Notices of the Royal Astronomical Society Oxford University Press 487 (2019) 381–393-

AM Swinbank, CM Harrison, AL Tiley, HL Johnson, I Smail, JP Stott, PN Best, M Bureau, RG Bower, A Bunker, M Cirasuolo, GE Magdis, M Jarvis, RM Sharples, D Sobral

We present an analysis of the gas outflow energetics from KMOS observations of ∼ 529 main-sequence star-forming galaxies at z ∼ 1 using broad, underlying H α and forbidden lines of [N II] and [S II]. Based on the stacked spectra for a sample with median star-formation rates and stellar masses of SFR = 7 M⊙   yr−1 and M⋆ = (1.0 ± 0.1) × 1010 M⊙, respectively, we derive a typical mass outflow rate of M˙wind = 1–4 M⊙ yr−1 and a mass loading of M˙wind / SFR = 0.2–0.4. By comparing the kinetic energy in the wind with the energy released by supernovae, we estimate a coupling efficiency between the star formation and wind energetics of ϵ ∼  0.03. The mass loading of the wind does not show a strong trend with star-formation rate over the range ∼ 2–20 M⊙ yr−1, although we identify a trend with stellar mass such that dM / dt / SFR ∝ M0.26±0.07⋆⁠. Finally, the line width of the broad H α increases with disc circular velocity with a sub-linear scaling relation FWHMbroad ∝ v0.21 ± 0.05. As a result of this behaviour, in the lowest mass galaxies (M⋆ ≲ 1010 M⊙), a significant fraction of the outflowing gas should have sufficient velocity to escape the gravitational potential of the halo whilst in the highest mass galaxies (M⋆ ≳ 1010 M⊙) most of the gas will be retained, flowing back on to the galaxy disc at later times.

## The fifteenth data release of the Sloan Digital Sky Surveys: First release of MaNGA-derived quantities, data visualization tools, and Stellar Library

Astrophysical Journal Supplement Institute of Physics 240 (2019)

DS Aguado, R Ahumada, A Almeida, M Cappellari, R Davies, C Lintott

Twenty years have passed since first light for the Sloan Digital Sky Survey (SDSS). Here, we release data taken by the fourth phase of SDSS (SDSS-IV) across its first three years of operation (2014 July–2017 July). This is the third data release for SDSS-IV, and the 15th from SDSS (Data Release Fifteen; DR15). New data come from MaNGA—we release 4824 data cubes, as well as the first stellar spectra in the MaNGA Stellar Library (MaStar), the first set of survey-supported analysis products (e.g., stellar and gas kinematics, emission-line and other maps) from the MaNGA Data Analysis Pipeline, and a new data visualization and access tool we call "Marvin." The next data release, DR16, will include new data from both APOGEE-2 and eBOSS; those surveys release no new data here, but we document updates and corrections to their data processing pipelines. The release is cumulative; it also includes the most recent reductions and calibrations of all data taken by SDSS since first light. In this paper, we describe the location and format of the data and tools and cite technical references describing how it was obtained and processed. The SDSS website (www.sdss.org) has also been updated, providing links to data downloads, tutorials, and examples of data use. Although SDSS-IV will continue to collect astronomical data until 2020, and will be followed by SDSS-V (2020–2025), we end this paper by describing plans to ensure the sustainability of the SDSS data archive for many years beyond the collection of data.

## JINGLE, a JCMT legacy survey of dust and gas for galaxy evolution studies: II. SCUBA-2 850 μm data reduction and dust flux density catalogues

Monthly Notices of the Royal Astronomical Society Oxford University Press 486 (2019) 4166–4185-

MWL Smith, CJR Clark, I De Looze, I Lamperti, A Saintonge, CD Wilson, G Accurso, E Brinks, M Bureau, EJ Chung, PJ Cigan, DL Clements, T Dharmawardena, L Fanciullo, Y Gao, Y Gao, WK Gear, HL Gomez, J Greenslade, HS Hwang, F Kemper, JC Lee, C Li, L Lin, L Liu

We present the SCUBA-2 850μm component of JINGLE, the new JCMT large survey for dust and gas in nearby galaxies, which with 193 galaxies is the largest targeted survey of nearby galaxies at 850 μm. We provide details of our SCUBA-2 data reduction pipeline, optimized for slightly extended sources, and including a calibration model adjusted to match conventions used in other far-infrared (FIR) data. We measure total integrated fluxes for the entire JINGLE sample in 10 infrared/submillimetre bands, including all WISE, Herschel-PACS, Herschel-SPIRE, and SCUBA-2 850 μm maps, statistically accounting for the contamination by CO(J = 3–2) in the 850 μm band. Of our initial sample of 193 galaxies, 191 are detected at 250 μm with a ≥5σ significance. In the SCUBA-2 850 μm band we detect 126 galaxies with ≥3σ significance. The distribution of the JINGLE galaxies in FIR/sub-millimetre colour–colour plots reveals that the sample is not well fit by single modified-blackbody models that assume a single dust-emissivity index (β). Instead, our new 850 μm data suggest either that a large fraction of our objects require β &lt; 1.5, or that a model allowing for an excess of sub-mm emission (e.g. a broken dust emissivity law, or a very cold dust component ≲10 K) is required. We provide relations to convert FIR colours to dust temperature and β for JINGLE-like galaxies. For JINGLE the FIR colours correlate more strongly with star-formation rate surface-density rather than the stellar surface-density, suggesting heating of dust is greater due to younger rather than older stellar-populations, consistent with the low proportion of early-type galaxies in the sample.

## The GALAH survey and Gaia DR2: dissecting the stellar disc's phase space by age, action, chemistry, and location

Monthly Notices of the Royal Astronomical Society Oxford University Press 486 (2019) 1167-1191

J Bland-Hawthorn, S Sharma, T Tepper-Garcia, J Binney, KC Freeman, J Kos, D De Silva, S Ellis, GF Lewis, M Asplund, S Buder, AR Casey, V D'Orazi, L Duong, S Khanna, J Lin, K Lind, SL Martell, MK Ness, JD Simpson, DB Zucker, T Zwitter, PR Kafle, AC Quillen

We use the second data releases of the European Space AgencyGaia astrometric survey and the high-resolution Galactic Archaeology with HERMES (GALAH) spectroscopic survey to analyse the structure of our Galaxy’s disc components. With GALAH, we separate the α-rich and α-poor discs (with respect to Fe), which are superposed in both position and velocity space, and examine their distributions in action space. We study the distribution of stars in the zVz phase plane, for both Vϕ and VR, and recover the remarkable ‘phase spiral’ discovered by Gaia. We identify the anticipated quadrupole signature in zVz of a tilted velocity ellipsoid for stars above and below the Galactic plane. By connecting our work with earlier studies, we show that the phase spiral is likely to extend well beyond the narrow solar neighbourhood cylinder in which it was found. The phase spiral is a signature of corrugated waves that propagate through the disc, and the associated non-equilibrium phase mixing. The radially asymmetric distribution of stars involved in the phase spiral reveals that the corrugation, which is mostly confined to the α-poor disc, grows in z-amplitude with increasing radius. We present new simulations of tidal disturbance of the Galactic disc by the Sagittarius (Sgr) dwarf. The effect on the zVz phase plane lasts ≳2Gyr⁠, but a subsequent disc crossing wipes out the coherent structure. We find that the phase spiral was excited ≲0.5Gyr ago by an object like Sgr with total mass ∼3 × 1010 M⊙ (stripped down from ∼5 × 1010 M⊙ when it first entered the halo) passing through the plane.

## Spectroscopy of the Young Stellar Association Price-Whelan 1: Origin in the Magellanic Leading Arm and Constraints on the Milky Way Hot Halo

ASTROPHYSICAL JOURNAL 887 (2019) ARTN 115

AM Price-Whelan, DL Nidever, D Boubert, RL Beaton, TT Hansen, Y Choi, R Ezzeddine, NW Evans, D Aguado, S Oh

## The quick and the dead: finding the surviving binary companions of galactic supernovae with Gaia

Astrophysical Journal American Astronomical Society 871 (2019) 92-

M Fraser, D Boubert

We use Gaia Data Release 2 to search for possible surviving binary companions to three of the best-studied historical Milky Way core-collapse supernovae. Consistent with previous work, we find there to be no plausible binary companion to either the Crab or Cas A supernovae. For the first time, we present a systematic search for a former companion to the Vela supernova, and rule out essentially any surviving luminous (&gt;L ⊙) companion. Based on parallax and proper motion, we identify a faint source (Star A; Gaia Source ID 5521955992667891584) that is kinematically consistent with being a former binary companion to the Vela SN progenitor. However, the inferred absolute magnitude of this source is extremely faint, raising the possibility that it may in fact be a background interloper. In addition, we derive a new distance (${3.37}_{-0.97}^{+4.04}$ kpc) to the Crab SN based on the Gaia parallax measurements, which is significantly further than the 2 kpc distance typically adopted. Finally, we demonstrate that Gaia can be used to measure the secular decline in the luminosity of the Crab pulsar, and provide a new test of pulsar models.

## Lessons from the curious case of the ‘fastest’ star in Gaia DR2

Monthly Notices of the Royal Astronomical Society Oxford University Press 486 (2019) 2618–2630-

D Boubert, J Strader, D Aguado, G Seabroke, Koposov, JL Sanders, L Chomiuk, S Swihart, NW Evans

Gaia DR2 5932173855446728064 was recently proposed to be unbound from the Milky Way based on the −614.3 ± 2.5 km s−1 median radial velocity given in Gaia DR2. We obtained eight epochs of spectroscopic follow-up and find a very different median radial velocity of −56.5 ± 5.3 km s−1. If this difference were to be explained by binarity, then the unseen companion would be an intermediate-mass black hole; we therefore argue that the Gaia DR2 radial velocity must be in error. We find it likely that the spectra obtained by Gaia were dominated by the light from a star 4.3 arcsec away, and that, due to the slitless, time delay integration nature of Gaia spectroscopy, this angular offset corresponded to a spurious 620 km s−1 shift in the calcium triplet of the second star. We argue that such unanticipated alignments between stars may account for 105 of the 202 stars with radial velocities faster than 500 km s−1 in Gaia DR2 and propose a quality cut to exclude stars that are susceptible. We propose further cuts to remove stars where the colour photometry is suspect and stars where the radial velocity measurement is based on fewer than four transits, and thus produce an unprecedentedly clean selection of Gaia radial velocities for use in studies of Galactic dynamics.

## Dust properties in the cold and hot gas phases of the ATLAS(3D) early-type galaxies as revealed by AKARI

ASTRONOMY & ASTROPHYSICS 622 (2019) ARTN A87

T Kokusho, H Kaneda, M Bureau, T Suzuki, K Murata, A Kondo, M Yamagishi, T Tsuchikawa, T Furuta

## The AGN fuelling/feedback cycle in nearby radio galaxies I. ALMA observations and early results

Monthly Notices of the Royal Astronomical Society Oxford University Press 484 (2019) 4239–4259-

I Ruffa, I Prandoni, R Laing, R Paladino, P Parma, H de Ruiter, A Mignano, TA Davis, M Bureau, J Warren

This is the first paper of a series exploring the multi-frequency properties of a sample of eleven nearby low excitation radio galaxies (LERGs) in the southern sky. We are conducting an extensive study of different galaxy components (stars, warm and cold gas, radio jets) with the aim of improving our understanding of the AGN fuelling/feedback cycle in LERGs. We present ALMA Band 6 12CO(2-1) and continuum observations of nine sources. Continuum emission from the radio cores was detected in all objects. Six sources also show mm emission from jets on kpc/sub-kpc scales. The jet structures are very similar at mm and cm wavelengths. We conclude that synchrotron emission associated with the radio jets dominates the continuum spectra up to 230 GHz. The 12CO(2-1) line was detected in emission in six out of nine objects, with molecular gas masses ranging from 2 × 107 to 2 × 1010 M⊙. The CO detections show disc-like structures on scales from ≈0.2 to ≈10 kpc. In one case (NGC 3100) the CO disc presents some asymmetries and is disrupted in the direction of the northern radio jet, indicating a possible jet/disc interaction. In IC 4296, CO is detected in absorption against the radio core as well as in emission. In four of the six galaxies with CO detections, the gas rotation axes are roughly parallel to the radio jets in projection; the remaining two cases show large misalignments. In those objects where optical imaging is available, dust and CO appear to be co-spatial.

## WISDOM project – IV. A molecular gas dynamical measurement of the supermassive black hole mass in NGC 524

Monthly Notices of the Royal Astronomical Society Oxford University Press 485 (2019) 4359–4374-

MD Smith, M Bureau, TA Davis, M Cappellari, L Liu, EV North, K Onishi, S Iguchi, M Sarzi

We present high angular resolution (0.3 arcsec or 37 pc) Atacama Large Millimeter/submillimeter Array observations of the CO(2–1) line emission from a central disc in the early-type galaxy NGC 524. This disc is shown to be dynamically relaxed, exhibiting ordered rotation about a compact 1.3 mm continuum source, which we identify as emission from an active supermassive black hole (SMBH). There is a hole at the centre of the disc slightly larger than the SMBH sphere of influence. An azimuthal distortion of the observed velocity field is found to be due to either a position angle warp or radial gas flow over the inner 2. 5. By forward-modelling the observations, we obtain an estimate of the SMBH mass of 4.0+3.5 −2.0 × 108 M, where the uncertainties are at the 3σ level. The uncertainties are dominated by the poorly constrained inclination and the stellar mass-to-light ratio of this galaxy, and our measurement is consistent with the established correlation between SMBH mass and stellar velocity dispersion. Our result is roughly half that of the previous stellar dynamical measurement, but is consistent within the uncertainties of both. We also present and apply a new tool for modelling complex molecular gas distributions.

## The shapes of the rotation curves of star-forming galaxies over the last approximate to 10 Gyr

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 485 (2019) 934-960

AL Tiley, AM Swinbank, CM Harrison, I Smail, OJ Turner, M Schaller, JP Stott, D Sobral, T Theuns, RM Sharples, S Gillman, RG Bower, AJ Bunker, P Best, J Richard, R Bacon, M Bureau, M Cirasuolo, G Magdis

## SIGNALS: I. Survey description

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 489 (2019) 5530-5546

L Rousseau-Nepton, RP Martin, C Robert, L Drissen, P Amram, S Prunet, T Martin, I Moumen, A Adamo, A Alarie, P Barmby, A Boselli, F Bresolin, M Bureau, L Chemin, RC Fernandes, F Combes, C Crowder, L Della Bruna, S Duarte Puertas, F Egusa, B Epinat, VF Ksoll, M Girard, V Gómez Llanos, D Gouliermis, K Grasha, C Higgs, J Hlavacek-Larrondo, I-T Ho, J Iglesias-Páramo, G Joncas, ZS Kam, P Karera, RC Kennicutt, RS Klessen, S Lianou, L Liu, Q Liu, AL de Amorim, JD Lyman, H Martel, B Mazzilli-Ciraulo, AF McLeod, A-L Melchior, I Millan, M Mollá, R Momose, C Morisset, H-A Pan, AK Pati, A Pellerin, E Pellegrini, I Pérez, A Petric, H Plana, D Rahner, T Ruiz Lara, L Sánchez-Menguiano, K Spekkens, G Stasińska, M Takamiya, N Vale Asari, JM Vílchez

<jats:title>ABSTRACT</jats:title> <jats:p>SIGNALS, the Star formation, Ionized Gas, and Nebular Abundances Legacy Survey, is a large observing programme designed to investigate massive star formation and H ii regions in a sample of local extended galaxies. The programme will use the imaging Fourier transform spectrograph SITELLE at the Canada–France–Hawaii Telescope. Over 355 h (54.7 nights) have been allocated beginning in fall 2018 for eight consecutive semesters. Once completed, SIGNALS will provide a statistically reliable laboratory to investigate massive star formation, including over 50 000 resolved H ii regions: the largest, most complete, and homogeneous data base of spectroscopically and spatially resolved extragalactic H ii regions ever assembled. For each field observed, three datacubes covering the spectral bands of the filters SN1 (363–386 nm), SN2 (482–513 nm), and SN3 (647–685 nm) are gathered. The spectral resolution selected for each spectral band is 1000, 1000, and 5000, respectively. As defined, the project sample will facilitate the study of small-scale nebular physics and many other phenomena linked to star formation at a mean spatial resolution of ∼20 pc. This survey also has considerable legacy value for additional topics, including planetary nebulae, diffuse ionized gas, and supernova remnants. The purpose of this paper is to present a general outlook of the survey, notably the observing strategy, galaxy sample, and science requirements.</jats:p>

## Orbit-superposition models of discrete, incomplete stellar kinematics: application to the Galactic centre

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2019)

J Magorrian

We present a method for fitting orbit-superposition models to the kinematics of discrete stellar systems when the available stellar sample has been filtered by a known selection function. The fitting method can be applied to any model in which the distribution function is represented as a linear superposition of basis elements with unknown weights. As an example, we apply it to Fritz et al.'s kinematics of the innermost regions of the Milky Way's nuclear stellar cluster. Assuming spherical symmetry, our models fit a black hole of mass $M_\bullet=(3.76\pm0.22)\times10^6\,M_\odot$, surrounded by an extended mass $M_\star=(6.57\pm0.54)\times10^6\,M_\odot$ within $4\,\pc$. Within $1\,\pc$ the best-fitting mass models have an approximate power-law density cusp $\rho\propto r^{-\gamma}$ with $\gamma=1.3\pm0.3$. We carry out an extensive investigation of how our modelling assumptions might bias these estimates: $M_\bullet$ is the most robust parameter and $\gamma$ the least. Internally the best-fitting models have broadly isotropic orbit distributions, apart from a bias towards circular orbits between 0.1 and 0.3 parsec.

## WISDOM project – V. Resolving molecular gas in Keplerian rotation around the supermassive black hole in NGC 0383

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 490 (2019) 319-330

EV North, TA Davis, M Bureau, M Cappellari, S Iguchi, L Liu, K Onishi, M Sarzi, MD Smith, TG Williams

<jats:title>ABSTRACT</jats:title> <jats:p>As part of the mm-Wave Interferometric Survey of Dark Object Masses (WISDOM), we present a measurement of the mass of the supermassive black hole (SMBH) in the nearby early-type galaxy NGC 0383 (radio source 3C 031). This measurement is based on Atacama Large Millimeter/sub-millimeter Array (ALMA) cycle 4 and 5 observations of the 12CO(2–1) emission line with a spatial resolution of 58 × 32 pc2 (0.18 arcsec × 0.1 arcsec). This resolution, combined with a channel width of 10 km s−1, allows us to well resolve the radius of the black hole sphere of influence (measured as RSOI = 316 pc  =  0.98 arcsec), where we detect a clear Keplerian increase of the rotation velocities. NGC 0383 has a kinematically relaxed, smooth nuclear molecular gas disc with weak ring/spiral features. We forward model the ALMA data cube with the Kinematic Molecular Simulation (KinMS) tool and a Bayesian Markov Chain Monte Carlo method to measure an SMBH mass of (4.2 ± 0.7) × 109 M⊙, a F160W-band stellar mass-to-light ratio that varies from 2.8 ± 0.6 M⊙/L$_{\odot ,\, \mathrm{F160W}}$ in the centre to 2.4 ± 0.3 M⊙$/\rm L_{\odot ,\, \mathrm{F160W}}$ at the outer edge of the disc and a molecular gas velocity dispersion of 8.3 ± 2.1 km s−1(all 3σ uncertainties). We also detect unresolved continuum emission across the full bandwidth, consistent with synchrotron emission from an active galactic nucleus. This work demonstrates that low-J CO emission can resolve gas very close to the SMBH ($\approx 140\, 000$ Schwarzschild radii) and hence that the molecular gas method is highly complimentary to megamaser observations, as it can probe the same emitting material.</jats:p>

## JINGLE, a JCMT legacy survey of dust and gas for galaxy evolution studies - I. Survey overview and first results

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 481 (2018) 3497-3519

A Saintonge, CD Wilson, T Xiao, L Lin, HS Hwang, T Tosaki, M Bureau, PJ Cigan, CJR Clark, DL Clements, I De Looze, T Dharmawardena, Y Gao, WK Gear, J Greenslade, I Lamperti, JC Lee, C Li, MJ Michalowski, A Mok, H-A Pan, AE Sansom, M Sargent, MWL Smith, T Williams, C Yang, M Zhu, G Accurso, P Barmby, E Brinks, N Bourne, T Brown, A Chung, EJ Chung, A Cibinel, K Coppin, J Davies, TA Davis, S Eales, L Fanciullo, T Fang, Y Gao, DHW Glass, HL Gomez, T Greve, J He, LC Ho, F Huang, H Jeong, X Jiang, Q Jiao, F Kemper, JH Kim, M Kim, T Kim, J Ko, X Kong, K Lacaille, CG Lacey, B Lee, JH Lee, W-K Lee, K Masters, S-H Oh, P Papadopoulos, C Park, S-J Park, H Parsons, K Rowlands, P Scicluna, JM Scudder, R Sethuram, S Serjeant, Y Shao, Y-K Sheen, Y Shi, H Shim, CMA Smith, K Spekkens, A-L Tsai, A Verma, S Urquhart, G Violino, S Viti, D Wake, J Wang, J Wouterloot, Y Yang, K Yim, F Yuan, Z Zheng

## The origin of the Gaia phase-plane spiral

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 481 (2018) 1501-1506

J Binney, R Schonrich

## The effects of galaxy interactions on molecular gas properties

Astrophysical Journal American Astronomical Society 868 (2018) 132

H-A Pan, L Lin, B-C Hsieh, M Bureau

Galaxy interactions are often accompanied by an enhanced star formation rate (SFR). Since molecular gas is essential for star formation, it is vital to establish whether and by how much galaxy interactions affect the molecular gas properties. We investigate the effect of interactions on global molecular gas properties by studying a sample of 58 galaxies in pairs and 154 control galaxies. Molecular gas properties are determined from observations with the JCMT, PMO, and CSO telescopes and supplemented with data from the xCOLD GASS and JINGLE surveys at 12CO(1–0) and 12CO(2–1). The SFR, gas mass (${M}_{{{\rm{H}}}_{2}}$), and gas fraction (f gas) are all enhanced in galaxies in pairs by ~2.5 times compared to the controls matched in redshift, mass, and effective radius, while the enhancement of star formation efficiency (SFE ≡SFR/${M}_{{{\rm{H}}}_{2}}$) is less than a factor of 2. We also find that the enhancements in SFR, ${M}_{{{\rm{H}}}_{2}}$ and f gas, increase with decreasing pair separation and are larger in systems with smaller stellar mass ratio. Conversely, the SFE is only enhanced in close pairs (separation &lt;20 kpc) and equal-mass systems; therefore, most galaxies in pairs lie in the same parameter space on the SFR–${M}_{{{\rm{H}}}_{2}}$ plane as controls. This is the first time that the dependence of molecular gas properties on merger configurations is probed statistically with a relatively large sample and a carefully selected control sample for individual galaxies. We conclude that galaxy interactions do modify the molecular gas properties, although the strength of the effect is dependent on merger configuration.