Recent Publications
Please see below for a list of recent publications that members of our laboratory have produced or contributed to. Only publications from 2014 onwards are included, if you want anything earlier follow the paper trail on ADS or look to the individual researcher’s website.
* note: conference proceedings etc. are omitted.
2016 |
Sofue, Y; Habe, A; Kataoka, J; Totani, T; Inoue, Y; Nakashima, S; Matsui, H; Akita, M Galactic Centre hypershell model for the North Polar Spurs Journal Article Monthly Notices of the RAS, 459 (1), pp. 108-120, 2016. @article{2016MNRAS.459..108S, title = {Galactic Centre hypershell model for the North Polar Spurs}, author = {Y {Sofue} and A {Habe} and J {Kataoka} and T {Totani} and Y {Inoue} and S {Nakashima} and H {Matsui} and M {Akita}}, url = {https://ui.adsabs.harvard.edu/abs/2016MNRAS.459..108S/abstract}, doi = {10.1093/mnras/stw623}, year = {2016}, date = {2016-01-01}, journal = {Monthly Notices of the RAS}, volume = {459}, number = {1}, pages = {108-120}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Inoue, Akio K; Tamura, Yoichi ; Matsuo, Hiroshi ; Mawatari, Ken ; Shimizu, Ikkoh ; Shibuya, Takatoshi ; Ota, Kazuaki ; Yoshida, Naoki ; Zackrisson, Erik ; Kashikawa, Nobunari ; Kohno, Kotaro ; Umehata, Hideki ; Hatsukade, Bunyo ; Iye, Masanori ; Matsuda, Yuichi ; Okamoto, Takashi ; Yamaguchi, Yuki Detection of an oxygen emission line from a high-redshift galaxy in the reionization epoch Journal Article Science, 352 (6293), pp. 1559-1562, 2016. @article{2016Sci...352.1559Ib, title = {Detection of an oxygen emission line from a high-redshift galaxy in the reionization epoch}, author = {Akio K {Inoue} and Yoichi {Tamura} and Hiroshi {Matsuo} and Ken {Mawatari} and Ikkoh {Shimizu} and Takatoshi {Shibuya} and Kazuaki {Ota} and Naoki {Yoshida} and Erik {Zackrisson} and Nobunari {Kashikawa} and Kotaro {Kohno} and Hideki {Umehata} and Bunyo {Hatsukade} and Masanori {Iye} and Yuichi {Matsuda} and Takashi {Okamoto} and Yuki {Yamaguchi}}, url = {https://ui.adsabs.harvard.edu/abs/2016Sci...352.1559I/abstract}, doi = {10.1126/science.aaf0714}, year = {2016}, date = {2016-01-01}, journal = {Science}, volume = {352}, number = {6293}, pages = {1559-1562}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Shimizu, Ikkoh ; Inoue, Akio K; Okamoto, Takashi ; Yoshida, Naoki Nebular line emission from z > 7 galaxies in a cosmological simulation: rest-frame UV to optical lines Journal Article Monthly Notices of the RAS, 461 (4), pp. 3563-3575, 2016. @article{2016MNRAS.461.3563S, title = {Nebular line emission from z > 7 galaxies in a cosmological simulation: rest-frame UV to optical lines}, author = {Ikkoh {Shimizu} and Akio K {Inoue} and Takashi {Okamoto} and Naoki {Yoshida}}, url = {https://ui.adsabs.harvard.edu/abs/2016MNRAS.461.3563S/abstract}, doi = {10.1093/mnras/stw1423}, year = {2016}, date = {2016-01-01}, journal = {Monthly Notices of the RAS}, volume = {461}, number = {4}, pages = {3563-3575}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2015 |
Haworth, Thomas; Shima, Kazuhiro; Tasker, Elizabeth; Fukui, Yasuo; Torii, Kazufumi; Dale, Jim; Takahira, Ken; Habe, Asao Isolating signatures of major cloud-cloud collisions - II. The lifetimes of broad bridge features Journal Article MNRAS, 454 , 2015. @article{Haworth2015b, title = {Isolating signatures of major cloud-cloud collisions - II. The lifetimes of broad bridge features}, author = {Thomas Haworth and Kazuhiro Shima and Elizabeth Tasker and Yasuo Fukui and Kazufumi Torii and Jim Dale and Ken Takahira and Asao Habe}, url = {http://adsabs.harvard.edu/abs/2015MNRAS.454.1634H}, doi = {10.1093/mnras/stv2068}, year = {2015}, date = {2015-12-01}, journal = {MNRAS}, volume = {454}, abstract = {We investigate the longevity of broad bridge features in position-velocity diagrams that appear as a result of cloud-cloud collisions. Broad bridges will have a finite lifetime due to the action of feedback, conversion of gas into stars and the time-scale of the collision. We make a series of analytic arguments with which to estimate these lifetimes. Our simple analytic arguments suggest that for collisions between clouds larger than R ˜ 10 pc the lifetime of the broad bridge is more likely to be determined by the lifetime of the collision rather than the radiative or wind feedback disruption time-scale. However, for smaller clouds feedback becomes much more effective. This is because the radiative feedback time-scale scales with the ionizing flux Nly as R^{7/4}N_{ly}^{-1/4} so a reduction in cloud size requires a relatively large decrease in ionizing photons to maintain a given time-scale. We find that our analytic arguments are consistent with new synthetic observations of numerical simulations of cloud-cloud collisions (including star formation and radiative feedback). We also argue that if the number of observable broad bridges remains ˜ constant, then the disruption time-scale must be roughly equivalent to the collision rate. If this is the case, our analytic arguments also provide collision rate estimates, which we find are readily consistent with previous theoretical models at the scales they consider (clouds larger than about 10 pc) but are much higher for smaller clouds.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We investigate the longevity of broad bridge features in position-velocity diagrams that appear as a result of cloud-cloud collisions. Broad bridges will have a finite lifetime due to the action of feedback, conversion of gas into stars and the time-scale of the collision. We make a series of analytic arguments with which to estimate these lifetimes. Our simple analytic arguments suggest that for collisions between clouds larger than R ˜ 10 pc the lifetime of the broad bridge is more likely to be determined by the lifetime of the collision rather than the radiative or wind feedback disruption time-scale. However, for smaller clouds feedback becomes much more effective. This is because the radiative feedback time-scale scales with the ionizing flux Nly as R^{7/4}N_{ly}^{-1/4} so a reduction in cloud size requires a relatively large decrease in ionizing photons to maintain a given time-scale. We find that our analytic arguments are consistent with new synthetic observations of numerical simulations of cloud-cloud collisions (including star formation and radiative feedback). We also argue that if the number of observable broad bridges remains ˜ constant, then the disruption time-scale must be roughly equivalent to the collision rate. If this is the case, our analytic arguments also provide collision rate estimates, which we find are readily consistent with previous theoretical models at the scales they consider (clouds larger than about 10 pc) but are much higher for smaller clouds. |
Pan, Hsi-An; Fujimoto, Yusuke; Tasker, Elizabeth; Rosolowsky, Erik; Colombo, Dario; Benincasa, Samantha; Wadsley, James What is a GMC? Are observers and simulators discussing the same star-forming clouds? Journal Article MNRAS , 453 , 2015. @article{Pan2015, title = {What is a GMC? Are observers and simulators discussing the same star-forming clouds?}, author = {Hsi-An Pan and Yusuke Fujimoto and Elizabeth Tasker and Erik Rosolowsky and Dario Colombo and Samantha Benincasa and James Wadsley}, url = {http://adsabs.harvard.edu/abs/2015MNRAS.453.3082P}, doi = {10.1093/mnras/stv1843}, year = {2015}, date = {2015-11-01}, journal = {MNRAS }, volume = {453}, abstract = {As both simulations and observations reach the resolution of the star-forming molecular clouds, it becomes important to clarify if these two techniques are discussing the same objects in galaxies. We compare clouds formed in a high-resolution galaxy simulation identified as continuous structures within a contour, in the simulator's position-position-position (PPP) coordinate space and the observer's position-position-velocity space (PPV). Results indicate that the properties of the cloud populations are similar in both methods and up to 70 per cent of clouds have a single counterpart in the opposite data structure. Comparing individual clouds in a one-to-one match reveals a scatter in properties mostly within a factor of 2. However, the small variations in mass, radius and velocity dispersion produce significant differences in derived quantities such as the virial parameter. This makes it difficult to determine if a structure is truly gravitationally bound. The three cloud types originally found in the simulation in Fujimoto et al. are identified in both data sets, with around 80 per cent of the clouds retaining their type between identification methods. We also compared our results when using a peak decomposition method to identify clouds in both PPP and PPV space. The number of clouds increased with this technique, but the overall cloud properties remained similar. However, the more crowded environment lowered the ability to match clouds between techniques to 40 per cent. The three cloud types also became harder to separate, especially in the PPV data set. The method used for cloud identification therefore plays a critical role in determining cloud properties, but both PPP and PPV can potentially identify the same structures.}, keywords = {}, pubstate = {published}, tppubtype = {article} } As both simulations and observations reach the resolution of the star-forming molecular clouds, it becomes important to clarify if these two techniques are discussing the same objects in galaxies. We compare clouds formed in a high-resolution galaxy simulation identified as continuous structures within a contour, in the simulator's position-position-position (PPP) coordinate space and the observer's position-position-velocity space (PPV). Results indicate that the properties of the cloud populations are similar in both methods and up to 70 per cent of clouds have a single counterpart in the opposite data structure. Comparing individual clouds in a one-to-one match reveals a scatter in properties mostly within a factor of 2. However, the small variations in mass, radius and velocity dispersion produce significant differences in derived quantities such as the virial parameter. This makes it difficult to determine if a structure is truly gravitationally bound. The three cloud types originally found in the simulation in Fujimoto et al. are identified in both data sets, with around 80 per cent of the clouds retaining their type between identification methods. We also compared our results when using a peak decomposition method to identify clouds in both PPP and PPV space. The number of clouds increased with this technique, but the overall cloud properties remained similar. However, the more crowded environment lowered the ability to match clouds between techniques to 40 per cent. The three cloud types also became harder to separate, especially in the PPV data set. The method used for cloud identification therefore plays a critical role in determining cloud properties, but both PPP and PPV can potentially identify the same structures. |
Pettitt, Alex; Dobbs, Clare; Acreman, David; Bate, Matthew The morphology of the Milky Way - II. Reconstructing CO maps from disc galaxies with live stellar distributions Journal Article MNRAS, 449 (4), pp. 3911-3926, 2015. @article{Pettitt2015, title = {The morphology of the Milky Way - II. Reconstructing CO maps from disc galaxies with live stellar distributions}, author = {Alex Pettitt and Clare Dobbs and David Acreman and Matthew Bate}, url = {http://adsabs.harvard.edu/abs/2015MNRAS.449.3911P https://www.youtube.com/watch?v=THVeoZf5FpA}, year = {2015}, date = {2015-06-01}, journal = {MNRAS}, volume = { 449}, number = {4}, pages = {3911-3926}, abstract = {The arm structure of the Milky Way remains somewhat of an unknown, with observational studies hindered by our location within the Galactic disc. In the work presented here, we use smoothed particle hydrodynamics and radiative transfer to create synthetic longitude-velocity observations. Our aim is to reverse engineer a top-down map of the Galaxy by comparing synthetic longitude-velocity maps to those observed. We set up a system of N-body particles to represent the disc and bulge, allowing for dynamic creation of spiral features. Interstellar gas, and the molecular content, is evolved alongside the stellar system. A 3D-radiative transfer code is then used to compare the models to observational data. The resulting models display arm features that are a good reproduction of many of the observed emission structures of the Milky Way. These arms however are dynamic and transient, allowing for a wide range of morphologies not possible with standard density wave theory. The best-fitting models are a much better match than previous work using fixed potentials. They favour a four-armed model with a pitch angle of approximately 20°, though with a pattern speed that decreases with increasing Galactic radius. Inner bars are lacking, however, which appear required to fully reproduce the central molecular zone.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The arm structure of the Milky Way remains somewhat of an unknown, with observational studies hindered by our location within the Galactic disc. In the work presented here, we use smoothed particle hydrodynamics and radiative transfer to create synthetic longitude-velocity observations. Our aim is to reverse engineer a top-down map of the Galaxy by comparing synthetic longitude-velocity maps to those observed. We set up a system of N-body particles to represent the disc and bulge, allowing for dynamic creation of spiral features. Interstellar gas, and the molecular content, is evolved alongside the stellar system. A 3D-radiative transfer code is then used to compare the models to observational data. The resulting models display arm features that are a good reproduction of many of the observed emission structures of the Milky Way. These arms however are dynamic and transient, allowing for a wide range of morphologies not possible with standard density wave theory. The best-fitting models are a much better match than previous work using fixed potentials. They favour a four-armed model with a pitch angle of approximately 20°, though with a pattern speed that decreases with increasing Galactic radius. Inner bars are lacking, however, which appear required to fully reproduce the central molecular zone. |
Haworth, Thomas; Tasker, Elizabeth; Fukui, Yasuo; Torii, Kazufumi; Dale, Jim; Shima, Kazuhiro; Takahira, Ken; Habe, Asao; Hasegawa, Kenji Isolating signatures of major cloud-cloud collisions using position-velocity diagrams Journal Article MNRAS, 450 , pp. 10-20, 2015. @article{Haworth2015, title = {Isolating signatures of major cloud-cloud collisions using position-velocity diagrams}, author = {Thomas Haworth and Elizabeth Tasker and Yasuo Fukui and Kazufumi Torii and Jim Dale and Kazuhiro Shima and Ken Takahira and Asao Habe and Kenji Hasegawa}, url = {http://adsabs.harvard.edu/abs/2015MNRAS.450...10H}, doi = {10.1093/mnras/stv639}, year = {2015}, date = {2015-06-01}, journal = {MNRAS}, volume = {450}, pages = {10-20}, abstract = {Collisions between giant molecular clouds are a potential mechanism for triggering the formation of massive stars, or even super star clusters. The trouble is identifying this process observationally and distinguishing it from other mechanisms. We produce synthetic position-velocity diagrams from models of cloud-cloud collisions, non-interacting clouds along the line of sight, clouds with internal radiative feedback and a more complex cloud evolving in a galactic disc, to try and identify unique signatures of collision. We find that a broad bridge feature connecting two intensity peaks, spatially correlated but separated in velocity, is a signature of a high-velocity cloud-cloud collision. We show that the broad bridge feature is resilient to the effects of radiative feedback, at least to around 2.5 Myr after the formation of the first massive (ionizing) star. However for a head-on 10 km s-1 collision, we find that this will only be observable from 20 to 30 per cent of viewing angles. Such broad-bridge features have been identified towards M20, a very young region of massive star formation that was concluded to be a site of cloud-cloud collision by Torii et al., and also towards star formation in the outer Milky Way by Izumi et al.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Collisions between giant molecular clouds are a potential mechanism for triggering the formation of massive stars, or even super star clusters. The trouble is identifying this process observationally and distinguishing it from other mechanisms. We produce synthetic position-velocity diagrams from models of cloud-cloud collisions, non-interacting clouds along the line of sight, clouds with internal radiative feedback and a more complex cloud evolving in a galactic disc, to try and identify unique signatures of collision. We find that a broad bridge feature connecting two intensity peaks, spatially correlated but separated in velocity, is a signature of a high-velocity cloud-cloud collision. We show that the broad bridge feature is resilient to the effects of radiative feedback, at least to around 2.5 Myr after the formation of the first massive (ionizing) star. However for a head-on 10 km s-1 collision, we find that this will only be observable from 20 to 30 per cent of viewing angles. Such broad-bridge features have been identified towards M20, a very young region of massive star formation that was concluded to be a site of cloud-cloud collision by Torii et al., and also towards star formation in the outer Milky Way by Izumi et al. |
Tasker, Elizabeth; Wadsley, James; Pudritz, Ralph Star Formation in Disk Galaxies. III. Does Stellar Feedback Result in Cloud Death? Journal Article The Astrophysical Journal, 801 (1), pp. 14, 2015. @article{Tasker2015, title = {Star Formation in Disk Galaxies. III. Does Stellar Feedback Result in Cloud Death?}, author = {Elizabeth Tasker and James Wadsley and Ralph Pudritz}, url = {http://adsabs.harvard.edu/abs/2015ApJ...801...33T}, doi = {10.1088/0004-637X/801/1/33}, year = {2015}, date = {2015-03-00}, journal = {The Astrophysical Journal}, volume = {801}, number = {1}, pages = {14}, abstract = {Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatly suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatly suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear. |
Okamoto, Takashi ; Isoe, Mari ; Habe, Asao Cosmic evolution of bars in simulations of galaxy formation Journal Article Publications of the ASJ, 67 (4), pp. 63, 2015. @article{2015PASJ...67...63O, title = {Cosmic evolution of bars in simulations of galaxy formation}, author = {Takashi {Okamoto} and Mari {Isoe} and Asao {Habe}}, url = {https://ui.adsabs.harvard.edu/abs/2015PASJ...67...63O/abstract}, doi = {10.1093/pasj/psv037}, year = {2015}, date = {2015-01-01}, journal = {Publications of the ASJ}, volume = {67}, number = {4}, pages = {63}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Shirakata, H; Okamoto, T; Enoki, M; Nagashima, M; Kobayashi, M ~A ~R; Ishiyama, T; Makiya, R The impact of dust in host galaxies on quasar luminosity functions. Journal Article Monthly Notices of the RAS, 450 , pp. L6-L10, 2015. @article{2015MNRAS.450L...6S, title = {The impact of dust in host galaxies on quasar luminosity functions.}, author = {H {Shirakata} and T {Okamoto} and M {Enoki} and M {Nagashima} and M ~A ~R {Kobayashi} and T {Ishiyama} and R {Makiya}}, url = {https://ui.adsabs.harvard.edu/abs/2015MNRAS.450L...6S/abstract}, doi = {10.1093/mnrasl/slv035}, year = {2015}, date = {2015-01-01}, journal = {Monthly Notices of the RAS}, volume = {450}, pages = {L6-L10}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Tanaka, Satoshi ; Yoshikawa, Kohji ; Okamoto, Takashi ; Hasegawa, Kenji A new ray-tracing scheme for 3D diffuse radiation transfer on highly parallel architectures Journal Article Publications of the ASJ, 67 (4), pp. 62, 2015. @article{2015PASJ...67...62T, title = {A new ray-tracing scheme for 3D diffuse radiation transfer on highly parallel architectures}, author = {Satoshi {Tanaka} and Kohji {Yoshikawa} and Takashi {Okamoto} and Kenji {Hasegawa}}, url = {https://ui.adsabs.harvard.edu/abs/2015PASJ...67...62T/abstract}, doi = {10.1093/pasj/psv027}, year = {2015}, date = {2015-01-01}, journal = {Publications of the ASJ}, volume = {67}, number = {4}, pages = {62}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2014 |
Inayoshi, Kohei; Omukai, Kazuyuki; Tasker, Elizabeth Formation of an embryonic supermassive star in the first galaxy Journal Article Monthly Notices of the Royal Astronomical Society: Letters, 445 , pp. L109-L113, 2014. @article{2014MNRAS.445L.109I, title = {Formation of an embryonic supermassive star in the first galaxy}, author = {Kohei Inayoshi and Kazuyuki Omukai and Elizabeth Tasker}, url = {http://adsabs.harvard.edu/abs/2014MNRAS.445L.109I}, doi = {10.1093/mnrasl/slu151}, year = {2014}, date = {2014-11-00}, journal = {Monthly Notices of the Royal Astronomical Society: Letters}, volume = {445}, pages = {L109-L113}, abstract = {We studied the gravitational collapse of a warm (˜8000 K) primordial-gas cloud as a candidate progenitor for a supermassive star (SMS; ≳ 105 M⊙) using a three-dimensional hydrodynamical simulation including all the relevant cooling processes of both H2 and H, which can potentially induce cloud fragmentation. This is the first simulation of this kind to resolve protostar formation. We find that from a weakly turbulent initial condition, the cloud undergoes runaway collapse without a major episode of fragmentation. Although the H2 fraction jumps by a large factor via the three-body reaction at ˜10-13 g cm-3, its cooling remains inefficient due to the optical thickness, and the temperature remains ≳ 3000 K. When the central core of the cloud becomes opaque to continuum radiation at ˜10-8 g cm-3, a hydrostatic protostar with ≃0.2 M⊙ is formed. The protostar grows to the mass ≃1 M⊙ and the radius ≃2 au within ˜1 yr via rapid accretion of dense filamentary flows. With high accretion rate, ˜2 M⊙ yr-1, the protostar is expected to turn into an SMS within its lifetime, eventually collapsing to a seed for the supermassive black hole observed in the early Universe at z ˜ 7.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We studied the gravitational collapse of a warm (˜8000 K) primordial-gas cloud as a candidate progenitor for a supermassive star (SMS; ≳ 105 M⊙) using a three-dimensional hydrodynamical simulation including all the relevant cooling processes of both H2 and H, which can potentially induce cloud fragmentation. This is the first simulation of this kind to resolve protostar formation. We find that from a weakly turbulent initial condition, the cloud undergoes runaway collapse without a major episode of fragmentation. Although the H2 fraction jumps by a large factor via the three-body reaction at ˜10-13 g cm-3, its cooling remains inefficient due to the optical thickness, and the temperature remains ≳ 3000 K. When the central core of the cloud becomes opaque to continuum radiation at ˜10-8 g cm-3, a hydrostatic protostar with ≃0.2 M⊙ is formed. The protostar grows to the mass ≃1 M⊙ and the radius ≃2 au within ˜1 yr via rapid accretion of dense filamentary flows. With high accretion rate, ˜2 M⊙ yr-1, the protostar is expected to turn into an SMS within its lifetime, eventually collapsing to a seed for the supermassive black hole observed in the early Universe at z ˜ 7. |
Fujimoto, Yusuke; Tasker, Elizabeth; Habe, Asao Environmental dependence of star formation induced by cloud collisions in a barred galaxy Journal Article Monthly Notices of the Royal Astronomical Society: Letters, 445 (1), pp. 65-69, 2014. @article{Fujimoto2014b, title = {Environmental dependence of star formation induced by cloud collisions in a barred galaxy}, author = {Yusuke Fujimoto and Elizabeth Tasker and Asao Habe}, url = {http://adsabs.harvard.edu/abs/2014MNRAS.445L..65F}, doi = {10.1093/mnrasl/slu138}, year = {2014}, date = {2014-11-00}, journal = {Monthly Notices of the Royal Astronomical Society: Letters}, volume = {445}, number = {1}, pages = {65-69}, abstract = {Cloud collision has been proposed as a way to link the small-scale star formation process with the observed global relation between the surface star formation rate and gas surface density. We suggest that this model can be improved further by allowing the productivity of such collisions to depend on the relative velocity of the two clouds. Our adjustment implements a simple step function that results in the most successful collisions being at the observed velocities for triggered star formation. By applying this to a high-resolution simulation of a barred galaxy, we successfully reproduce the observational result that the star formation efficiency (SFE) in the bar is lower than that in the spiral arms. This is not possible when we use an efficiency dependent on the internal turbulence properties of the clouds. Our results suggest that high-velocity collisions driven by the gravitational pull of the clouds are responsible for the low bar SFE.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Cloud collision has been proposed as a way to link the small-scale star formation process with the observed global relation between the surface star formation rate and gas surface density. We suggest that this model can be improved further by allowing the productivity of such collisions to depend on the relative velocity of the two clouds. Our adjustment implements a simple step function that results in the most successful collisions being at the observed velocities for triggered star formation. By applying this to a high-resolution simulation of a barred galaxy, we successfully reproduce the observational result that the star formation efficiency (SFE) in the bar is lower than that in the spiral arms. This is not possible when we use an efficiency dependent on the internal turbulence properties of the clouds. Our results suggest that high-velocity collisions driven by the gravitational pull of the clouds are responsible for the low bar SFE. |
Takahira, Ken; Tasker, Elizabeth; Habe, Asao Do Cloud-Cloud Collisions Trigger High-mass Star Formation? I. Small Cloud Collisions Journal Article ApJ, 792 , 2014. @article{Takahira2014, title = {Do Cloud-Cloud Collisions Trigger High-mass Star Formation? I. Small Cloud Collisions}, author = {Ken Takahira and Elizabeth Tasker and Asao Habe}, url = {http://adsabs.harvard.edu/abs/2014ApJ...792...63T}, doi = {10.1088/0004-637X/792/1/63}, year = {2014}, date = {2014-09-01}, journal = {ApJ}, volume = {792}, abstract = {We performed sub-parsec (~0.06 pc) scale simulations of two idealized molecular clouds with different masses undergoing a collision. Gas clumps with densities greater than 10–20 g cm–3 (0.3 × 104 cm–3) were identified as pre-stellar cores and tracked throughout the simulation. The colliding system showed a partial gas arc morphology with core formation in the oblique shock front at the collision interface. These characteristics support NANTEN observations of objects suspected to be colliding giant molecular clouds (GMCs). We investigated the effect of turbulence and collision speed on the resulting core population and compared the cumulative mass distribution to cores in observed GMCs. Our results suggest that a faster relative velocity increases the number of cores formed but that cores grow via accretion predominately while in the shock front, leading to a slower shock being more important for core growth. The core masses obey a power-law relation with index γ = –1.6, in good agreement with observations. This suggests that core production through collisions should follow a similar mass distribution as quiescent formation, albeit at a higher mass range. If cores can be supported against collapse during their growth, then the estimated ram pressure from gas infall is of the right order to counter the radiation pressure and form a star of 100 M ☉.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We performed sub-parsec (~0.06 pc) scale simulations of two idealized molecular clouds with different masses undergoing a collision. Gas clumps with densities greater than 10–20 g cm–3 (0.3 × 104 cm–3) were identified as pre-stellar cores and tracked throughout the simulation. The colliding system showed a partial gas arc morphology with core formation in the oblique shock front at the collision interface. These characteristics support NANTEN observations of objects suspected to be colliding giant molecular clouds (GMCs). We investigated the effect of turbulence and collision speed on the resulting core population and compared the cumulative mass distribution to cores in observed GMCs. Our results suggest that a faster relative velocity increases the number of cores formed but that cores grow via accretion predominately while in the shock front, leading to a slower shock being more important for core growth. The core masses obey a power-law relation with index γ = –1.6, in good agreement with observations. This suggests that core production through collisions should follow a similar mass distribution as quiescent formation, albeit at a higher mass range. If cores can be supported against collapse during their growth, then the estimated ram pressure from gas infall is of the right order to counter the radiation pressure and form a star of 100 M ☉. |
Shirakata, Hikari; Okamoto, Takashi; Enoki, Motohiro; Nagashima, Masahiro; Kobayashi, Masakazu; Ishiyama, Tomoaki; Makiya, Ryu The impact of dust in host galaxies on quasar luminosity functions Journal Article Monthly Notices of the Royal Astronomical Society: Letters, 450 (1), pp. 6-10, 2014. @article{Shirakata2014, title = {The impact of dust in host galaxies on quasar luminosity functions}, author = {Hikari Shirakata and Takashi Okamoto and Motohiro Enoki and Masahiro Nagashima and Masakazu Kobayashi and Tomoaki Ishiyama and Ryu Makiya}, url = {http://adsabs.harvard.edu/abs/2015MNRAS.450L...6S}, doi = {10.1093/mnrasl/slv035}, year = {2014}, date = {2014-06-00}, journal = {Monthly Notices of the Royal Astronomical Society: Letters}, volume = {450}, number = {1}, pages = {6-10}, abstract = {We have investigated effects of dust attenuation on quasar luminosity functions at z ˜ 2 using a semi-analytic galaxy formation model combined with a large cosmological N-body simulation. We estimate the dust attenuation of quasars self-consistently with that of galaxies by considering the dust in their host bulges. We find that the luminosity of the bright quasars is strongly dimmed by the dust attenuation, ˜2 mag in the B-band. Assuming the empirical bolometric corrections for active galactic nuclei (AGNs) by Marconi et al., we find that this dust attenuation is too strong to explain the B-band and X-ray quasar luminosity functions simultaneously. We consider two possible mechanisms that weaken the dust attenuation. As such a mechanism, we introduce a time delay for AGN activity, that is, gas fuelling to a central black hole starts sometime after the beginning of the starburst induced by a major merger. The other is the anisotropy in the dust distribution. We find that in order to make the dust attenuation of the quasars negligible, either the gas accretion into the black holes has to be delayed at least three times the dynamical time-scale of their host bulges or the dust covering factor is as small as ˜0.1.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We have investigated effects of dust attenuation on quasar luminosity functions at z ˜ 2 using a semi-analytic galaxy formation model combined with a large cosmological N-body simulation. We estimate the dust attenuation of quasars self-consistently with that of galaxies by considering the dust in their host bulges. We find that the luminosity of the bright quasars is strongly dimmed by the dust attenuation, ˜2 mag in the B-band. Assuming the empirical bolometric corrections for active galactic nuclei (AGNs) by Marconi et al., we find that this dust attenuation is too strong to explain the B-band and X-ray quasar luminosity functions simultaneously. We consider two possible mechanisms that weaken the dust attenuation. As such a mechanism, we introduce a time delay for AGN activity, that is, gas fuelling to a central black hole starts sometime after the beginning of the starburst induced by a major merger. The other is the anisotropy in the dust distribution. We find that in order to make the dust attenuation of the quasars negligible, either the gas accretion into the black holes has to be delayed at least three times the dynamical time-scale of their host bulges or the dust covering factor is as small as ˜0.1. |
Gnedin, Nickolay; Tasker, Elizabeth; Fujimoto, Yusuke Emergence of the Kennicutt-Schmidt Relation from the Small-scale SFR-Density Relation Journal Article ApJL, 787 , 2014. @article{Gnedin2014, title = {Emergence of the Kennicutt-Schmidt Relation from the Small-scale SFR-Density Relation}, author = {Nickolay Gnedin and Elizabeth Tasker and Yusuke Fujimoto}, url = {http://adsabs.harvard.edu/abs/2014ApJ...787L...7G}, doi = {10.1088/2041-8205/787/1/L7}, year = {2014}, date = {2014-05-01}, journal = {ApJL}, volume = {787}, abstract = {We use simulations of isolated galaxies with a few parsec resolution to explore the connection between the small-scale star formation rate (SFR)-gas density relation and the induced large-scale correlation between the SFR surface density and the surface density of the molecular gas (the Kennicutt-Schmidt relation). We find that, in the simulations, a power-law small-scale "star formation law" directly translates into an identical power-law Kennicutt-Schmidt relation. If this conclusion holds in the reality as well, it implies that the observed approximately linear Kennicutt-Schmidt relation must reflect the approximately linear small-scale "star formation law."}, keywords = {}, pubstate = {published}, tppubtype = {article} } We use simulations of isolated galaxies with a few parsec resolution to explore the connection between the small-scale star formation rate (SFR)-gas density relation and the induced large-scale correlation between the SFR surface density and the surface density of the molecular gas (the Kennicutt-Schmidt relation). We find that, in the simulations, a power-law small-scale "star formation law" directly translates into an identical power-law Kennicutt-Schmidt relation. If this conclusion holds in the reality as well, it implies that the observed approximately linear Kennicutt-Schmidt relation must reflect the approximately linear small-scale "star formation law." |
Fujimoto, Yusuke; Tasker, Elizabeth; Wakayama, Mariko; Habe, Asao Do giant molecular clouds care about the galactic structure? Journal Article MNRAS, 439 (1), pp. 936-953, 2014. @article{Fujimoto2014, title = {Do giant molecular clouds care about the galactic structure?}, author = {Yusuke Fujimoto and Elizabeth Tasker and Mariko Wakayama and Asao Habe}, url = {http://adsabs.harvard.edu/abs/2014MNRAS.439..936F}, year = {2014}, date = {2014-03-01}, journal = {MNRAS}, volume = {439}, number = {1}, pages = {936-953}, abstract = {We investigate the impact of galactic environment on the properties of simulated giant molecular clouds (GMCs) formed in an M83-type barred spiral galaxy. Our simulation uses a rotating stellar potential to create the grand design features and resolves down to 1.5 pc. From the comparison of clouds found in the bar, spiral and disc regions, we find that the typical GMC is environment independent, with a mass of 5 × 105 M⊙ and radius 11 pc. However, the fraction of clouds in the property distribution tails varies between regions, with larger, more massive clouds with a higher velocity dispersion being found in greatest proportions in the bar, spiral and then disc. The bar clouds also show a bimodality that is not reflected in the spiral and disc clouds except in the surface density, where all three regions show two distinct peaks. We identify these features as being due to the relative proportion of three cloud types, classified via the mass-radius scaling relation, which we label A, B and C. Type A clouds have the typical values listed above and form the largest fraction in each region. Type B clouds are massive giant molecular associations (GMAs) while type C clouds are unbound, transient clouds that form in dense filaments and tidal tails. The fraction of each clouds type depends on the cloud-cloud interactions, which cause mergers to build up the GMA type Bs and tidal features in which the type C clouds are formed. The number of cloud interactions is greatest in the bar, followed by the spiral, causing a higher fraction of both cloud types compared to the disc. While the cloud types also exist in lower resolution simulations, their identification becomes more challenging as they are not well-separated populations on the mass-radius relation or distribution plots. Finally, we compare the results for three star formation models to estimate the star formation rate and efficiency in each galactic region.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We investigate the impact of galactic environment on the properties of simulated giant molecular clouds (GMCs) formed in an M83-type barred spiral galaxy. Our simulation uses a rotating stellar potential to create the grand design features and resolves down to 1.5 pc. From the comparison of clouds found in the bar, spiral and disc regions, we find that the typical GMC is environment independent, with a mass of 5 × 105 M⊙ and radius 11 pc. However, the fraction of clouds in the property distribution tails varies between regions, with larger, more massive clouds with a higher velocity dispersion being found in greatest proportions in the bar, spiral and then disc. The bar clouds also show a bimodality that is not reflected in the spiral and disc clouds except in the surface density, where all three regions show two distinct peaks. We identify these features as being due to the relative proportion of three cloud types, classified via the mass-radius scaling relation, which we label A, B and C. Type A clouds have the typical values listed above and form the largest fraction in each region. Type B clouds are massive giant molecular associations (GMAs) while type C clouds are unbound, transient clouds that form in dense filaments and tidal tails. The fraction of each clouds type depends on the cloud-cloud interactions, which cause mergers to build up the GMA type Bs and tidal features in which the type C clouds are formed. The number of cloud interactions is greatest in the bar, followed by the spiral, causing a higher fraction of both cloud types compared to the disc. While the cloud types also exist in lower resolution simulations, their identification becomes more challenging as they are not well-separated populations on the mass-radius relation or distribution plots. Finally, we compare the results for three star formation models to estimate the star formation rate and efficiency in each galactic region. |
Hirota, Akihiko ; Kuno, Nario ; Baba, Junichi ; Egusa, Fumi ; Habe, Asao ; Muraoka, Kazuyuki ; Tanaka, Ayako ; Nakanishi, Hiroyuki ; Kawabe, Ryohei Publications of the ASJ, 66 (2), pp. 46, 2014. @article{2014PASJ...66...46H, title = {Wide-field $^12$CO (J = 1-0) imaging of the nearby barred galaxy M 83 with NMA and Nobeyema 45 m telescope: Mole cular gas kinematics and star formation along the bar}, author = {Akihiko {Hirota} and Nario {Kuno} and Junichi {Baba} and Fumi {Egusa} and Asao {Habe} and Kazuyuki {Muraoka} and Ayako {Tanaka} and Hiroyuki {Nakanishi} and Ryohei {Kawabe}}, url = {https://ui.adsabs.harvard.edu/abs/2014PASJ...66...46H/abstract}, doi = {10.1093/pasj/psu006}, year = {2014}, date = {2014-01-01}, journal = {Publications of the ASJ}, volume = {66}, number = {2}, pages = {46}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Higuchi, Aya E; Chibueze, James O; Habe, Asao ; Takahira, Ken ; Takano, Shuro ALMA View of G0.253+0.016: Can Cloud-Cloud Collision form the Cloud? Journal Article Astronomical Journal, 147 (6), pp. 141, 2014. @article{2014AJ....147..141H, title = {ALMA View of G0.253+0.016: Can Cloud-Cloud Collision form the Cloud?}, author = {Aya E {Higuchi} and James O {Chibueze} and Asao {Habe} and Ken {Takahira} and Shuro {Takano}}, url = {https://ui.adsabs.harvard.edu/abs/2014AJ....147..141H/abstract}, doi = {10.1088/0004-6256/147/6/141}, year = {2014}, date = {2014-01-01}, journal = {Astronomical Journal}, volume = {147}, number = {6}, pages = {141}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Inoue, A ~K; Shimizu, I; Tamura, Y; Matsuo, H; Okamoto, T; Yoshida, N ALMA Will Determine the Spectroscopic Redshift z > 8 with FIR [O III] Emission Lines Journal Article Astrophysical Journal, Letters, 780 (2), pp. L18, 2014. @article{2014ApJ...780L..18I, title = {ALMA Will Determine the Spectroscopic Redshift z > 8 with FIR [O III] Emission Lines}, author = {A ~K {Inoue} and I {Shimizu} and Y {Tamura} and H {Matsuo} and T {Okamoto} and N {Yoshida}}, url = {https://ui.adsabs.harvard.edu/abs/2014ApJ...780L..18I/abstract}, doi = {10.1088/2041-8205/780/2/L18}, year = {2014}, date = {2014-01-01}, journal = {Astrophysical Journal, Letters}, volume = {780}, number = {2}, pages = {L18}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Shimizu, Ikkoh ; Inoue, Akio K; Okamoto, Takashi ; Yoshida, Naoki Physical properties of UDF12 galaxies in cosmological simulations Journal Article Monthly Notices of the RAS, 440 (1), pp. 731-745, 2014. @article{2014MNRAS.440..731S, title = {Physical properties of UDF12 galaxies in cosmological simulations}, author = {Ikkoh {Shimizu} and Akio K {Inoue} and Takashi {Okamoto} and Naoki {Yoshida}}, url = {https://ui.adsabs.harvard.edu/abs/2014MNRAS.440..731S/abstract}, doi = {10.1093/mnras/stu265}, year = {2014}, date = {2014-01-01}, journal = {Monthly Notices of the RAS}, volume = {440}, number = {1}, pages = {731-745}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Okamoto, Takashi ; Shimizu, Ikkoh ; Yoshida, Naoki Reproducing cosmic evolution of galaxy population from z = 4 to 0 Journal Article Publications of the ASJ, 66 (4), pp. 70, 2014. @article{2014PASJ...66...70O, title = {Reproducing cosmic evolution of galaxy population from z = 4 to 0}, author = {Takashi {Okamoto} and Ikkoh {Shimizu} and Naoki {Yoshida}}, url = {https://ui.adsabs.harvard.edu/abs/2014PASJ...66...70O/abstract}, doi = {10.1093/pasj/psu046}, year = {2014}, date = {2014-01-01}, journal = {Publications of the ASJ}, volume = {66}, number = {4}, pages = {70}, keywords = {}, pubstate = {published}, tppubtype = {article} } |