The impact of the gas distribution on the determination of dynamical masses of galaxies using unresolved observations

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dc.contributor.authorde Blok, W J G
dc.contributor.authorWalter, Fabian
dc.date.accessioned2021-10-08T07:20:34Z
dc.date.available2021-10-08T07:20:34Z
dc.date.issued2014
dc.description.abstractDynamical mass (M dyn) is a key property of any galaxy, yet a determination of M dyn is not straightforward if spatially resolved measurements are not available. This situation occurs in single-dish H I observations of the local universe, but also frequently in high-redshift observations. M dyn measurements in high-redshift galaxies are commonly obtained through observations of the CO line, the most abundant tracer of the molecular medium. Even though in most cases the CO line width can be determined with reasonable accuracy, a measurement of the size of the emitting region is typically challenging given current facilities. We show how the integrated spectra ("global profiles") of a variety of galaxy models depend on the spatial distribution of the tracer gas as well as its velocity dispersion. We demonstrate that the choice of tracer emission line (e.g., H I tracing extended, "flat," emission versus CO tracing more compact, "exponential," emission) significantly affects the shape of the global profiles. In particular, in the case of high (~50 km s–1) velocity dispersions, compact tracers (such as CO) result in Gaussian-like (non-double-horned) profiles, as is indeed frequently seen in high-redshift observations. This leads to significantly different determinations of M dyn if different distributions of the tracer material ("flat" versus "exponential") are considered. We determine at which radii the rotation curve reaches the rotation velocity corresponding to the velocity width, and find that for each tracer this happens at a well-defined radius: H I velocity widths typically originate at ~5 optical scale lengths, while CO velocity widths trace the rotation velocity at ~2 scale lengths. We additionally explore other distributions to take into account that CO distributions at high redshift likely differ from those at low redshift. Our models, while not trying to reproduce individual galaxies, define characteristic radii that can be used in conjunction with the measured velocity widths in order to define dynamical masses consistent with the assumed gas distribution.
dc.identifier.apacitationde Blok, W. J. G., & Walter, F. (2014). The impact of the gas distribution on the determination of dynamical masses of galaxies using unresolved observations. <i>The Astronomical Journal</i>, 147(5), 96 - 177. http://hdl.handle.net/11427/34955en_ZA
dc.identifier.chicagocitationde Blok, W J G, and Fabian Walter "The impact of the gas distribution on the determination of dynamical masses of galaxies using unresolved observations." <i>The Astronomical Journal</i> 147, 5. (2014): 96 - 177. http://hdl.handle.net/11427/34955en_ZA
dc.identifier.citationde Blok, W.J.G. & Walter, F. 2014. The impact of the gas distribution on the determination of dynamical masses of galaxies using unresolved observations. <i>The Astronomical Journal.</i> 147(5):96 - 177. http://hdl.handle.net/11427/34955en_ZA
dc.identifier.issn0004-6256
dc.identifier.issn1538-3881
dc.identifier.ris TY - Journal Article AU - de Blok, W J G AU - Walter, Fabian AB - Dynamical mass (M dyn) is a key property of any galaxy, yet a determination of M dyn is not straightforward if spatially resolved measurements are not available. This situation occurs in single-dish H I observations of the local universe, but also frequently in high-redshift observations. M dyn measurements in high-redshift galaxies are commonly obtained through observations of the CO line, the most abundant tracer of the molecular medium. Even though in most cases the CO line width can be determined with reasonable accuracy, a measurement of the size of the emitting region is typically challenging given current facilities. We show how the integrated spectra ("global profiles") of a variety of galaxy models depend on the spatial distribution of the tracer gas as well as its velocity dispersion. We demonstrate that the choice of tracer emission line (e.g., H I tracing extended, "flat," emission versus CO tracing more compact, "exponential," emission) significantly affects the shape of the global profiles. In particular, in the case of high (~50 km s–1) velocity dispersions, compact tracers (such as CO) result in Gaussian-like (non-double-horned) profiles, as is indeed frequently seen in high-redshift observations. This leads to significantly different determinations of M dyn if different distributions of the tracer material ("flat" versus "exponential") are considered. We determine at which radii the rotation curve reaches the rotation velocity corresponding to the velocity width, and find that for each tracer this happens at a well-defined radius: H I velocity widths typically originate at ~5 optical scale lengths, while CO velocity widths trace the rotation velocity at ~2 scale lengths. We additionally explore other distributions to take into account that CO distributions at high redshift likely differ from those at low redshift. Our models, while not trying to reproduce individual galaxies, define characteristic radii that can be used in conjunction with the measured velocity widths in order to define dynamical masses consistent with the assumed gas distribution. DA - 2014 DB - OpenUCT DP - University of Cape Town IS - 5 J1 - The Astronomical Journal LK - https://open.uct.ac.za PY - 2014 SM - 0004-6256 SM - 1538-3881 T1 - The impact of the gas distribution on the determination of dynamical masses of galaxies using unresolved observations TI - The impact of the gas distribution on the determination of dynamical masses of galaxies using unresolved observations UR - http://hdl.handle.net/11427/34955 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/34955
dc.identifier.vancouvercitationde Blok WJG, Walter F. The impact of the gas distribution on the determination of dynamical masses of galaxies using unresolved observations. The Astronomical Journal. 2014;147(5):96 - 177. http://hdl.handle.net/11427/34955.en_ZA
dc.language.isoeng
dc.publisher.departmentDepartment of Astronomy
dc.publisher.facultyFaculty of Science
dc.sourceThe Astronomical Journal
dc.source.journalissue5
dc.source.journalvolume147
dc.source.pagination96 - 177
dc.source.urihttps://dx.doi.org/10.1088/0004-6256/147/5/96
dc.subject.otherastrophysics
dc.subject.othercosmology and astronomy
dc.subject.otheraccuracy
dc.subject.othercarbon monoxide
dc.subject.otherdispersions
dc.subject.otheremission
dc.subject.othergalaxies
dc.subject.othergases
dc.subject.otherline widths
dc.subject.othermass
dc.subject.otherred shift
dc.subject.otherrotation
dc.subject.otherspatial distribution
dc.subject.otherspectra
dc.subject.otheruniverse
dc.subject.othervelocity
dc.titleThe impact of the gas distribution on the determination of dynamical masses of galaxies using unresolved observations
dc.typeJournal Article
uct.type.publicationResearch
uct.type.resourceJournal Article
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