Using the radiative transfer code Torus, we produce spectral-line cubes of
the predicted HI profile from global SPH simulations of spiral galaxies. Torus
grids the SPH galaxy using Adaptive Mesh Refinement, then applies a ray-tracing
method to infer the HI profile along the line(s) of sight. The gridded galaxy
can be observed from any direction, which enables us to model the observed HI
profile for galaxies of any orientation. We can also place the observer inside
the galaxy, to simulate HI observations taken from the Earth's position in the
Milky Way.Comment: 4 pages, 2 figures, conference proceedings for "Panoramic Radio
  Astronomy: 1-2 Ghz Research on Galaxy Evolution" June 2-5, 2009 Groninge

Chris Brunt

Clare Dobbs

David Acreman

Kevin A. Douglas

English

arXiv

Using the radiative transfer code Torus, we produce spectral-line cubes of the predicted HI profile from global SPH simulations of spiral galaxies. Torus grids the SPH galaxy using Adaptive Mesh Refinement, then applies a ray-tracing method to infer the HI profile along the line(s) of sight. The gridded galaxy can be observed from any direction, which enables us to model the observed HI profile for galaxies of any orientation. We can also place the observer inside the galaxy, to simulate HI observations taken from the Earth's position in the Milky Way.

Dobbs, Clare,

Acreman, David,

Douglas, Kevin A.,

Brunt, Chris,

University of Groningen Digital Archive

Synthetic Observations of the HI Line in SPH-Simulated Spiral Galaxies

Using the radiative transfer code Torus, we produce spectral-line cubes of the predicted HI profile from global SPH simulations of spiral galaxies. Torus grids the SPH galaxy using Adaptive Mesh Refinement, then applies a ray-tracing method to infer the HI profile along the line(s) of sight. The gridded galaxy can be observed from any direction, which enables us to model the observed HI profile for galaxies of any orientation. We can also place the observer inside the galaxy, to simulate HI observations taken from the Earth's position in the Milky Way

Douglas, Kevin A.

Acreman, David

Dobbs, Clare

Brunt, Chris

ARTS repository - University of Groningen

   University of GroningenSynthetic Observations of the HI Line in SPH-Simulated Spiral GalaxiesDouglas, Kevin A.; Acreman, David; Dobbs, Clare; Brunt, ChrisPublished in:Panoramic Radio Astronomy: 1-2 Ghz Research on Galaxy EvolutionIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2009Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Douglas, K. A., Acreman, D., Dobbs, C., & Brunt, C. (2009). Synthetic Observations of the HI Line in SPH-Simulated Spiral Galaxies. In Panoramic Radio Astronomy: 1-2 Ghz Research on Galaxy EvolutionUniversity of Groningen.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 13-02-2023arXiv:0909.0187v1  [astro-ph.GA]  1 Sep 2009Synthetic Observations of the H I Line inSPH-Simulated Spiral GalaxiesKevin A. Douglas∗University of ExeterE-mail: douglas@astro.ex.ac.ukDavid Acreman, Clare Dobbs, Chris BruntUniversity of ExeterUsing the radiative transfer code Torus, we produce spectral-line cubes of the predicted H I profilefrom global SPH simulations of spiral galaxies. Torus gridsthe SPH galaxy using Adaptive MeshRefinement, then applies a ray-tracing method to infer the H Iprofile along the line(s) of sight.The gridded galaxy can be observed from any direction, whichenables us to model the observedH I profile for galaxies of any orientation. We can also place th observer inside the galaxy, tosimulate H I observations taken from the Earth’s position inthe Milky Way.Panoramic Radio Astronomy: Wide-field 1-2 GHz research on galaxy evolutionJune 2-5 2009Groningen, the Netherlands∗Speaker.c© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licen. http://pos.sissa.it/Synthetic H I Observations of SPH Galaxies Kevin A. Douglas1. IntroductionA significant difference between observations and numerical simulations of the interstellarmedium is that while observers detect emission through spectral line or continuum processes, of-ten using frequency/wavelength information to convert to radial velocity scales, numerical modelsdirectly trace the total density of interstellar matter, with no reliance on kinematics to assign dis-tances to features seen in the simulations. We seek to bridgethat gap, using the Torus code [1]which can apply radiative transfer to a gridded simulation (n our case an entire galaxy) and predictthe emission from selected tracer species.2. Torus and the 21-cm lineAs one of the best tracers of interstellar and galactic structu e, the 21-cm neutral hydrogen(H I) spectral line is the first species we have implemented into our analysis. The simplicity of thedetailed balance governing this two-level hyperfine transition enables the easy calculation of impor-tant parameters such as the emissivity and opacity of the line, a d its profile function. The relevantphysical variables needed to perform these calculations are the density (of H I), temperature andvelocity of the gas.In our work, Torus grids an SPH-simualted spiral galaxy ontoan Adaptive Mesh Refinement(AMR) grid, essentially transforming the particle view of the galaxy into a gridded view. Thegalaxy model we have used comes from a simulation investigating molecular cloud formation inspiral galaxies by [2], based on the Milky Way and containinga full thermodynamical model ofthe ISM, and a consistent treatment of the formation of molecular hydrogen. Once the galaxy isgridded, the Torus code can manipulate the grid spatially, and perform radiative transfer and raytracing calculations to infer a synthetic line profile from an rbitrary observer position. Tracingmultiple lines of sight can generate an image, or a three-dimensional cube of the selected tracerspecies in the case of spectral lines, which is directly comparable to real observations.To simulate extragalactic H I observations of (nearby) spiral galaxies, we can orient the SPHgalaxy to arbitrary position and inclination angles, and assign to it some systemic recessional orapproach velocity, so that the simulated datacube may be compared directly to typical radioastro-nomical observational data.3. M33 as a test caseAs a demonstration of our ability to produce synthetic spectral datacubes that successfullyimitate the observed H I profile, we chose the nearby spiral galaxy M33, primarily because ofthe availability of high-quality observational data [3] with which our results could be compared.Quantitative differences are to be expected, given the circula rotation of M33 is approximately 100km/s [4] while the SPH galaxy, modelled to be more akin to the Milky Way, hasvrot ≈ 220 km/s.Moreover, the interaction of M33 with its surroundings (espcially M31) gives rise to extended H Iemission well beyond its main disk, and we would therefore not expect even a qualitative match tothe SPH galaxy in this component.In Figure 1 we show a total column density image of the SPH galaxy, oriented to match thedisk of M33. Numerically, we can resolve the structure in theSPH galaxy better than the angular2Synthetic H I Observations of SPH Galaxies Kevin A. DouglasFigure 1: Column Density image of the SPH galaxy, oriented to match M33’s position and inclinationangles. Note that the SPH calculation does not trace gas within 5 kpc of the galaxy’s center. The axes reflectthe datacube pixel values.resolution of the M33 data, so we convolve our synthetic datacube with a Gaussian beam to simulatethe observations being done by a single-dish telescope.The qualitative agreement we seek is the basic, expected obsrvation of the galaxy’s main diskbeing traced by a series of isovelocity curves as we step throug the cube in radial velocity. Weshow four such curves as contour plots for the M33 cube in the left panel of figure 2. Our results inthe right panel of figure 2 show a good qualitative match to thegeneral rotational structure of M33.The structure contained in the simulated cube at the native resolution of the simulations hintsat the effects of spiral shocks and other noncircular motions contained within the rotating galaxydisk. Very high resolution observations with interferometric radio telescopes, and eventually theSKA, will make such investigations of fine structure in the spiral arms of galaxies routine.4. Conclusion and Future DirectionsWe have described a model to transform output from numericalsimulations into synthetic3Synthetic H I Observations of SPH Galaxies Kevin A. DouglasFigure 2: Isovelocity contour plots of M33 (left) and the SPH galaxy (right). The four contours are fromdifferent channel maps of the H I data cube, with the top contour showing the most blueshifted H I andprogressing to the most redshifted H I in the bottom contours. Axes reflect the datacube pixel scales.H I datacubes, which could be measured by an ‘observer’ inside, or outside a galaxy. For externalobservers, the case most relevant to this conference, we canproduce maps of higher resolution thanavailable with current instruments. Within a galaxy, this process has the advantage that distancesto features are known precisely, rather than being subject to large kinematic uncertainties.As with all situations, this method is only as good as the model. We have begun with anSPH simulation of a spiral galaxy which emulates many of the aspects of the Milky Way. However,important physical processes such as stellar feedback havenot y t been implemented, and so certainquantitative matches have not yet been achieved. Neverthelss this line of work may prove valuableto the study of spiral structure in galaxies, especially as instruments leading to the Square KilometreArray continue to push the limits of angular resolution.AcknowledgmentsThe research leading to these results has received funding from the Seventh Framework Pro-gramme under grant agreement no PIIF-GA-2008-221289. KAD wishes to thank the PRA confer-ence organisers for a thoroughly enjoyable and forward-looking experience in Groningen.References[1] T. J. Harries,Synthetic line profiles of rotationally distorted hot-starwinds, MNRAS315 (2000) 722[2] C. L. Dobbs, S. C. O. Glover, P. C. Clark, & R. S. Klessen,The ISM in spiral galaxies: can cooling inspiral shocks produce molecular clouds? MNRAS389 (2008) 1097[3] M. E. Putman, J. E. G. Peek, A. Muratov, O. Y. Gnedin, W. Hsu, K. A. Douglas, C. Heiles,S. Stanimirovic, E. J. Korpela, S. J. GibsonThe Disruption and Fuelling of M33, ApJ, (2009),accepted[4] E. Corbelli & P. SalucciThe extended rotation curve and the dark matter halo of M33 MNRAS311(2000) 4414

NARCIS 

   University of GroningenSynthetic Observations of the HI Line in SPH-Simulated Spiral GalaxiesDouglas, Kevin A.; Acreman, David; Dobbs, Clare; Brunt, ChrisPublished in:Panoramic Radio Astronomy: 1-2 Ghz Research on Galaxy EvolutionIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2009Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Douglas, K. A., Acreman, D., Dobbs, C., & Brunt, C. (2009). Synthetic Observations of the HI Line in SPH-Simulated Spiral Galaxies. In Panoramic Radio Astronomy: 1-2 Ghz Research on Galaxy EvolutionUniversity of Groningen.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 31-10-2023arXiv:0909.0187v1  [astro-ph.GA]  1 Sep 2009Synthetic Observations of the H I Line inSPH-Simulated Spiral GalaxiesKevin A. Douglas∗University of ExeterE-mail: douglas@astro.ex.ac.ukDavid Acreman, Clare Dobbs, Chris BruntUniversity of ExeterUsing the radiative transfer code Torus, we produce spectral-line cubes of the predicted H I profilefrom global SPH simulations of spiral galaxies. Torus gridsthe SPH galaxy using Adaptive MeshRefinement, then applies a ray-tracing method to infer the H Iprofile along the line(s) of sight.The gridded galaxy can be observed from any direction, whichenables us to model the observedH I profile for galaxies of any orientation. We can also place th observer inside the galaxy, tosimulate H I observations taken from the Earth’s position inthe Milky Way.Panoramic Radio Astronomy: Wide-field 1-2 GHz research on galaxy evolutionJune 2-5 2009Groningen, the Netherlands∗Speaker.c© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licen. http://pos.sissa.it/Synthetic H I Observations of SPH Galaxies Kevin A. Douglas1. IntroductionA significant difference between observations and numerical simulations of the interstellarmedium is that while observers detect emission through spectral line or continuum processes, of-ten using frequency/wavelength information to convert to radial velocity scales, numerical modelsdirectly trace the total density of interstellar matter, with no reliance on kinematics to assign dis-tances to features seen in the simulations. We seek to bridgethat gap, using the Torus code [1]which can apply radiative transfer to a gridded simulation (n our case an entire galaxy) and predictthe emission from selected tracer species.2. Torus and the 21-cm lineAs one of the best tracers of interstellar and galactic structu e, the 21-cm neutral hydrogen(H I) spectral line is the first species we have implemented into our analysis. The simplicity of thedetailed balance governing this two-level hyperfine transition enables the easy calculation of impor-tant parameters such as the emissivity and opacity of the line, a d its profile function. The relevantphysical variables needed to perform these calculations are the density (of H I), temperature andvelocity of the gas.In our work, Torus grids an SPH-simualted spiral galaxy ontoan Adaptive Mesh Refinement(AMR) grid, essentially transforming the particle view of the galaxy into a gridded view. Thegalaxy model we have used comes from a simulation investigating molecular cloud formation inspiral galaxies by [2], based on the Milky Way and containinga full thermodynamical model ofthe ISM, and a consistent treatment of the formation of molecular hydrogen. Once the galaxy isgridded, the Torus code can manipulate the grid spatially, and perform radiative transfer and raytracing calculations to infer a synthetic line profile from an rbitrary observer position. Tracingmultiple lines of sight can generate an image, or a three-dimensional cube of the selected tracerspecies in the case of spectral lines, which is directly comparable to real observations.To simulate extragalactic H I observations of (nearby) spiral galaxies, we can orient the SPHgalaxy to arbitrary position and inclination angles, and assign to it some systemic recessional orapproach velocity, so that the simulated datacube may be compared directly to typical radioastro-nomical observational data.3. M33 as a test caseAs a demonstration of our ability to produce synthetic spectral datacubes that successfullyimitate the observed H I profile, we chose the nearby spiral galaxy M33, primarily because ofthe availability of high-quality observational data [3] with which our results could be compared.Quantitative differences are to be expected, given the circula rotation of M33 is approximately 100km/s [4] while the SPH galaxy, modelled to be more akin to the Milky Way, hasvrot ≈ 220 km/s.Moreover, the interaction of M33 with its surroundings (espcially M31) gives rise to extended H Iemission well beyond its main disk, and we would therefore not expect even a qualitative match tothe SPH galaxy in this component.In Figure 1 we show a total column density image of the SPH galaxy, oriented to match thedisk of M33. Numerically, we can resolve the structure in theSPH galaxy better than the angular2Synthetic H I Observations of SPH Galaxies Kevin A. DouglasFigure 1: Column Density image of the SPH galaxy, oriented to match M33’s position and inclinationangles. Note that the SPH calculation does not trace gas within 5 kpc of the galaxy’s center. The axes reflectthe datacube pixel values.resolution of the M33 data, so we convolve our synthetic datacube with a Gaussian beam to simulatethe observations being done by a single-dish telescope.The qualitative agreement we seek is the basic, expected obsrvation of the galaxy’s main diskbeing traced by a series of isovelocity curves as we step throug the cube in radial velocity. Weshow four such curves as contour plots for the M33 cube in the left panel of figure 2. Our results inthe right panel of figure 2 show a good qualitative match to thegeneral rotational structure of M33.The structure contained in the simulated cube at the native resolution of the simulations hintsat the effects of spiral shocks and other noncircular motions contained within the rotating galaxydisk. Very high resolution observations with interferometric radio telescopes, and eventually theSKA, will make such investigations of fine structure in the spiral arms of galaxies routine.4. Conclusion and Future DirectionsWe have described a model to transform output from numericalsimulations into synthetic3Synthetic H I Observations of SPH Galaxies Kevin A. DouglasFigure 2: Isovelocity contour plots of M33 (left) and the SPH galaxy (right). The four contours are fromdifferent channel maps of the H I data cube, with the top contour showing the most blueshifted H I andprogressing to the most redshifted H I in the bottom contours. Axes reflect the datacube pixel scales.H I datacubes, which could be measured by an ‘observer’ inside, or outside a galaxy. For externalobservers, the case most relevant to this conference, we canproduce maps of higher resolution thanavailable with current instruments. Within a galaxy, this process has the advantage that distancesto features are known precisely, rather than being subject to large kinematic uncertainties.As with all situations, this method is only as good as the model. We have begun with anSPH simulation of a spiral galaxy which emulates many of the aspects of the Milky Way. However,important physical processes such as stellar feedback havenot y t been implemented, and so certainquantitative matches have not yet been achieved. Neverthelss this line of work may prove valuableto the study of spiral structure in galaxies, especially as instruments leading to the Square KilometreArray continue to push the limits of angular resolution.AcknowledgmentsThe research leading to these results has received funding from the Seventh Framework Pro-gramme under grant agreement no PIIF-GA-2008-221289. KAD wishes to thank the PRA confer-ence organisers for a thoroughly enjoyable and forward-looking experience in Groningen.References[1] T. J. Harries,Synthetic line profiles of rotationally distorted hot-starwinds, MNRAS315 (2000) 722[2] C. L. Dobbs, S. C. O. Glover, P. C. Clark, & R. S. Klessen,The ISM in spiral galaxies: can cooling inspiral shocks produce molecular clouds? MNRAS389 (2008) 1097[3] M. E. Putman, J. E. G. Peek, A. Muratov, O. Y. Gnedin, W. Hsu, K. A. Douglas, C. Heiles,S. Stanimirovic, E. J. Korpela, S. J. GibsonThe Disruption and Fuelling of M33, ApJ, (2009),accepted[4] E. Corbelli & P. SalucciThe extended rotation curve and the dark matter halo of M33 MNRAS311(2000) 4414

University of Groningen

   University of GroningenSynthetic Observations of the HI Line in SPH-Simulated Spiral GalaxiesDouglas, Kevin A.; Acreman, David; Dobbs, Clare; Brunt, ChrisPublished in:Panoramic Radio Astronomy: 1-2 Ghz Research on Galaxy EvolutionIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2009Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Douglas, K. A., Acreman, D., Dobbs, C., & Brunt, C. (2009). Synthetic Observations of the HI Line in SPH-Simulated Spiral Galaxies. In Panoramic Radio Astronomy: 1-2 Ghz Research on Galaxy EvolutionUniversity of Groningen.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 12-11-2019arXiv:0909.0187v1  [astro-ph.GA]  1 Sep 2009Synthetic Observations of the H I Line inSPH-Simulated Spiral GalaxiesKevin A. Douglas∗University of ExeterE-mail: douglas@astro.ex.ac.ukDavid Acreman, Clare Dobbs, Chris BruntUniversity of ExeterUsing the radiative transfer code Torus, we produce spectral-line cubes of the predicted H I profilefrom global SPH simulations of spiral galaxies. Torus grids the SPH galaxy using Adaptive MeshRefinement, then applies a ray-tracing method to infer the H I profile along the line(s) of sight.The gridded galaxy can be observed from any direction, which enables us to model the observedH I profile for galaxies of any orientation. We can also place the observer inside the galaxy, tosimulate H I observations taken from the Earth’s position in the Milky Way.Panoramic Radio Astronomy: Wide-field 1-2 GHz research on galaxy evolutionJune 2-5 2009Groningen, the Netherlands∗Speaker.c© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/Synthetic H I Observations of SPH Galaxies Kevin A. Douglas1. IntroductionA significant difference between observations and numerical simulations of the interstellarmedium is that while observers detect emission through spectral line or continuum processes, of-ten using frequency/wavelength information to convert to radial velocity scales, numerical modelsdirectly trace the total density of interstellar matter, with no reliance on kinematics to assign dis-tances to features seen in the simulations. We seek to bridge that gap, using the Torus code [1]which can apply radiative transfer to a gridded simulation (in our case an entire galaxy) and predictthe emission from selected tracer species.2. Torus and the 21-cm lineAs one of the best tracers of interstellar and galactic structure, the 21-cm neutral hydrogen(H I) spectral line is the first species we have implemented into our analysis. The simplicity of thedetailed balance governing this two-level hyperfine transition enables the easy calculation of impor-tant parameters such as the emissivity and opacity of the line, and its profile function. The relevantphysical variables needed to perform these calculations are the density (of H I), temperature andvelocity of the gas.In our work, Torus grids an SPH-simualted spiral galaxy onto an Adaptive Mesh Refinement(AMR) grid, essentially transforming the particle view of the galaxy into a gridded view. Thegalaxy model we have used comes from a simulation investigating molecular cloud formation inspiral galaxies by [2], based on the Milky Way and containing a full thermodynamical model ofthe ISM, and a consistent treatment of the formation of molecular hydrogen. Once the galaxy isgridded, the Torus code can manipulate the grid spatially, and perform radiative transfer and raytracing calculations to infer a synthetic line profile from an arbitrary observer position. Tracingmultiple lines of sight can generate an image, or a three-dimensional cube of the selected tracerspecies in the case of spectral lines, which is directly comparable to real observations.To simulate extragalactic H I observations of (nearby) spiral galaxies, we can orient the SPHgalaxy to arbitrary position and inclination angles, and assign to it some systemic recessional orapproach velocity, so that the simulated datacube may be compared directly to typical radioastro-nomical observational data.3. M33 as a test caseAs a demonstration of our ability to produce synthetic spectral datacubes that successfullyimitate the observed H I profile, we chose the nearby spiral galaxy M33, primarily because ofthe availability of high-quality observational data [3] with which our results could be compared.Quantitative differences are to be expected, given the circular rotation of M33 is approximately 100km/s [4] while the SPH galaxy, modelled to be more akin to the Milky Way, has vrot ≈ 220 km/s.Moreover, the interaction of M33 with its surroundings (especially M31) gives rise to extended H Iemission well beyond its main disk, and we would therefore not expect even a qualitative match tothe SPH galaxy in this component.In Figure 1 we show a total column density image of the SPH galaxy, oriented to match thedisk of M33. Numerically, we can resolve the structure in the SPH galaxy better than the angular2Synthetic H I Observations of SPH Galaxies Kevin A. DouglasFigure 1: Column Density image of the SPH galaxy, oriented to match M33’s position and inclinationangles. Note that the SPH calculation does not trace gas within 5 kpc of the galaxy’s center. The axes reflectthe datacube pixel values.resolution of the M33 data, so we convolve our synthetic datacube with a Gaussian beam to simulatethe observations being done by a single-dish telescope.The qualitative agreement we seek is the basic, expected observation of the galaxy’s main diskbeing traced by a series of isovelocity curves as we step through the cube in radial velocity. Weshow four such curves as contour plots for the M33 cube in the left panel of figure 2. Our results inthe right panel of figure 2 show a good qualitative match to the general rotational structure of M33.The structure contained in the simulated cube at the native resolution of the simulations hintsat the effects of spiral shocks and other noncircular motions contained within the rotating galaxydisk. Very high resolution observations with interferometric radio telescopes, and eventually theSKA, will make such investigations of fine structure in the spiral arms of galaxies routine.4. Conclusion and Future DirectionsWe have described a model to transform output from numerical simulations into synthetic3Synthetic H I Observations of SPH Galaxies Kevin A. DouglasFigure 2: Isovelocity contour plots of M33 (left) and the SPH galaxy (right). The four contours are fromdifferent channel maps of the H I data cube, with the top contour showing the most blueshifted H I andprogressing to the most redshifted H I in the bottom contours. Axes reflect the datacube pixel scales.H I datacubes, which could be measured by an ‘observer’ inside, or outside a galaxy. For externalobservers, the case most relevant to this conference, we can produce maps of higher resolution thanavailable with current instruments. Within a galaxy, this process has the advantage that distancesto features are known precisely, rather than being subject to large kinematic uncertainties.As with all situations, this method is only as good as the model. We have begun with anSPH simulation of a spiral galaxy which emulates many of the aspects of the Milky Way. However,important physical processes such as stellar feedback have not yet been implemented, and so certainquantitative matches have not yet been achieved. Nevertheless this line of work may prove valuableto the study of spiral structure in galaxies, especially as instruments leading to the Square KilometreArray continue to push the limits of angular resolution.AcknowledgmentsThe research leading to these results has received funding from the Seventh Framework Pro-gramme under grant agreement no PIIF-GA-2008-221289. KAD wishes to thank the PRA confer-ence organisers for a thoroughly enjoyable and forward-looking experience in Groningen.References[1] T. J. Harries, Synthetic line profiles of rotationally distorted hot-star winds, MNRAS 315 (2000) 722[2] C. L. Dobbs, S. C. O. Glover, P. C. Clark, & R. S. Klessen, The ISM in spiral galaxies: can cooling inspiral shocks produce molecular clouds? MNRAS 389 (2008) 1097[3] M. E. Putman, J. E. G. Peek, A. Muratov, O. Y. Gnedin, W. Hsu, K. A. Douglas, C. Heiles,S. Stanimirovic, E. J. Korpela, S. J. Gibson The Disruption and Fuelling of M33, ApJ, (2009),accepted[4] E. Corbelli & P. Salucci The extended rotation curve and the dark matter halo of M33 MNRAS 311(2000) 4414

Synthetic Observations of the HI Line in SPH-Simulated Spiral Galaxies

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