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

Abstract

The dynamical mass (M_dyn) is a key property of any galaxy, yet a determination of M_dyn is not straight-forward if spatially resolved measurements are not available. This situation occurs in single-dish HI 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 the CO linewidth can in most cases 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 significantly affects the shape of the global profiles. In particular, in the case of high (~50 kms-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. 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: HI 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.

Accepted for Astronomical Journal

References in corpus (5)

• High-Resolution Rotation Curves and Galaxy Mass Models from THINGS
• What is Driving the HI Velocity Dispersion?
• A Survey of Galaxy Kinematics to z ~ 1 in the TKRS/GOODS-N Field. I. Rotation and Dispersion Properties
• Kinematic modelling of disk galaxies I. A new method to fit tilted rings to data cubes
• WSRT Ultra-Deep Neutral Hydrogen Imaging of Galaxy Clusters at z=0.2, a Pilot Survey of Abell 963 and Abell 2192

Cited by in corpus (28)

• An ALMA [CII] survey of 27 quasars at z>5.94
• Resolving the ISM at the peak of cosmic star formation with ALMA - The distribution of CO and dust continuum in z~2.5 sub-millimetre galaxies
• ALMA resolves turbulent, rotating [CII] emission in a young starburst galaxy at z=4.8
• The Kinematics of z ~ 6 Quasar Host Galaxies
• A Study in Blue: The Baryon Content of Isolated Low Mass Galaxies
• Dust and gas in luminous proto-cluster galaxies at z=4.05: the case for different cosmic dust evolution in normal and starburst galaxies
• ALMA suggests outflows in z~5.5 galaxies
• The WISSH QSOs project IX. Cold gas content and environment of luminous QSOs at z~2.4-4.7
• Resolved [CII] Emission from z>6 Quasar Host -- Companion Galaxy Pairs
• Formation of S0 galaxies through mergers. Evolution in the Tully-Fisher relation since $z\sim 1$
• ALMA hints at the presence of turbulent disk galaxies at z > 5
• An ALMA Spectroscopic Survey of the Brightest Submillimeter Galaxies in the SCUBA-2-COSMOS field (AS2COSPEC): Survey Description and First Results
• The host galaxy of the short GRB111117A at $z=2.211$: impact on the short GRB redshift distribution and progenitor channels
• A Comparison of the Stellar, CO and Dust-Continuum Emission from Three, Star-Forming HUDF Galaxies at $z\sim 2$
• The Impact of Molecular Gas on Mass Models of Nearby Galaxies
• First Connection between Cold Gas in Emission and Absorption: CO Emission from a Galaxy-Quasar Pair
• Comparing [CII], HI, and CO dynamics of nearby galaxies
• The interstellar medium distribution, gas kinematics, and system dynamics of the far-infrared luminous quasar SDSS J2310+1855 at $z=6.0$
• A model of spectral line broadening in signal forecasts for line-intensity mapping experiments
• BUDHIES IV: Deep 21-cm neutral Hydrogen, optical and UV imaging data of Abell 963 and Abell 2192 at z $\simeq$ 0.2
• A Multiwavelength Study of ELAN Environments (AMUSE${}^2$): Detection of a dusty star-forming galaxy within the enormous Lyman $\alpha$ nebula at $z=2.3$ sheds light on its origin
• Tully-Fisher Distances and Dynamical Mass Constraints for 24 Host Galaxies of Reverberation-Mapped AGN
• HI Galaxy Signatures in the SARAO MeerKAT Galactic Plane Survey -- II. The Local Void and its substructure
• BUDHIES V: The baryonic Tully-Fisher relation at z=0.2 based on direct HI detections
• Infrared fine-structure lines at high redshift
• MIGHTEE-HI: Discovery of an HI-rich galaxy group at z = 0.044 with MeerKAT
• Parametrized Asymmetric Neutral hydrogen Disk Integrated Spectrum Characterization (PANDISC) I: Introduction to A Physically Motivated H I Model
• ALMA survey of a massive node of the Cosmic Web at $z\sim 3$. II. A dynamically cold and massive disk galaxy in the proximity of a hyperluminous quasar