J/AJ/146/150 Velocity dispersions of 12 nearby galaxies (Caldu-Primo+, 2013)
A high-dispersion molecular gas component in nearby galaxies.
Caldu-Primo A., Schruba A., Walter F., Leroy A., Sandstrom K.,
de Blok W.J.G., Ianjamasimanana R., Mogotsi K.M.
<Astron. J., 146, 150 (2013)>
=2013AJ....146..150C 2013AJ....146..150C
ADC_Keywords: Galaxies, nearby ; Velocity dispersion
Keywords: galaxies: ISM - ISM: molecules - radio lines: galaxies
Abstract:
We present a comprehensive study of the velocity dispersion of the
atomic (HI) and molecular (H2) gas components in the disks
(R≲R25) of a sample of 12 nearby spiral galaxies with moderate
inclinations. Our analysis is based on sensitive high-resolution data
from the THINGS (atomic gas) and HERACLES (molecular gas) surveys. To
obtain reliable measurements of the velocity dispersion, we stack
regions several kiloparsecs in size, after accounting for intrinsic
velocity shifts due to galactic rotation and large-scale motions. We
stack using various parameters: the galactocentric distance, star
formation rate surface density, HI surface density, H2 surface
density, and total gas surface density. We fit single Gaussian
components to the stacked spectra and measure median velocity
dispersions for HI of 11.9±3.1km/s and for CO of 12.0±3.9km/s. The
CO velocity dispersions are thus, surprisingly, very similar to the
corresponding ones of HI, with an average ratio of
σHI/σCO=1.0±0.2 irrespective of the stacking
parameter. The measured CO velocity dispersions are significantly
higher (factor of ∼2) than the traditional picture of a cold molecular
gas disk associated with star formation. The high dispersion implies
an additional thick molecular gas disk (possibly as thick as the HI
disk). Our finding is in agreement with recent sensitive measurements
in individual edge-on and face-on galaxies and points toward the
general existence of a thick disk of molecular gas, in addition to the
well-known thin disk in nearby spiral galaxies.
Description:
We present resolved measurements of HI and CO velocity dispersions in
12 nearby galaxies taken from the THINGS (Walter et al., 2008, cat.
J/AJ/136/2563) and HERACLES (2009AJ....137.4670L 2009AJ....137.4670L) surveys. The HI data
come from the THINGS survey. We obtain the CO(2-1) line emission
from the cubes of the HERACLES survey.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 30 12 Properties of the galaxies used in this study
table5.dat 27 158 Velocity dispersions measured in radial bins
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See also:
J/AJ/136/2563 : HI Nearby Galaxy Survey, THINGS (Walter+, 2008)
J/ApJS/173/185 : GALEX ultraviolet atlas of nearby galaxies (Gil de Paz+, 2007)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- --- [NGC]
5- 8 I4 --- NGC Galaxy NGC number
10- 13 F4.1 Mpc Dist Distance
15- 16 I2 deg i [0/90] Inclination
18- 20 I3 deg PA [0/360] Position angle
22- 25 F4.1 kpc Rad Optical radius R25
27- 30 F4.2 kpc Res [0.2/0.7] Resolution
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- --- [NGC]
5- 8 I4 --- NGC Galaxy NGC number
10- 13 F4.2 --- Rgc Relative galactocentric distance (R/R25)
15- 18 F4.1 km/s sigHI [7.5/21] The HI velocity dispersion σ(HI)
20- 23 F4.1 km/s sigCO [6.7/24] The CO velocity dispersion σ(CO)
25- 27 F3.1 --- Ratio [0.7/1.5] The σ(HI) to σ(CO) ratio
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 23-Jul-2014