J/ApJ/803/16 Giant molecular clouds in NGC4526 based on 12CO (Utomo+, 2015)
Giant molecular clouds in the early-type galaxy NGC 4526.
Utomo D., Blitz L., Davis T., Rosolowsky E., Bureau M., Cappellari M.,
Sarzi M.
<Astrophys. J., 803, 16 (2015)>
=2015ApJ...803...16U 2015ApJ...803...16U
ADC_Keywords: Galaxies, nearby ; Molecular clouds ; Velocity dispersion ;
Radio lines
Keywords: galaxies: elliptical and lenticular, cD;
galaxies: individual: NGC 4526;
galaxies: ISM; ISM: clouds; radio lines: ISM
Abstract:
We present a high spatial resolution (∼20pc) of 12CO(2-1)
observations of the lenticular galaxy NGC 4526. We identify 103
resolved giant molecular clouds (GMCs) and measure their properties:
size R, velocity dispersion σv, and luminosity L. This is the
first GMC catalog of an early-type galaxy. We find that the GMC
population in NGC 4526 is gravitationally bound, with a virial
parameter α∼1. The mass distribution,
dN/dM∝M-2.39±0.03, is steeper than that for GMCs in the
inner Milky Way, but comparable to that found in some late-type
galaxies. We find no size-line width correlation for the NGC 4526
clouds, in contradiction to the expectation from Larson's relation. In
general, the GMCs in NGC 4526 are more luminous, denser, and have a
higher velocity dispersion than equal-size GMCs in the Milky Way and
other galaxies in the Local Group. These may be due to higher
interstellar radiation field than in the Milky Way disk and weaker
external pressure than in the Galactic center. In addition, a
kinematic measurement of cloud rotation shows that the rotation is
driven by the galactic shear. For the vast majority of the clouds, the
rotational energy is less than the turbulent and gravitational energy,
while the four innermost clouds are unbound and will likely be torn
apart by the strong shear at the galactic center. We combine our data
with the archival data of other galaxies to show that the surface
density Σ of GMCs is not approximately constant, as previously
believed, but varies by ∼3 orders of magnitude. We also show that the
size and velocity dispersion of the GMC population across galaxies are
related to the surface density, as expected from the gravitational and
pressure equilibrium, i.e., σvR-1/2∝Σ1/2.
Description:
NGC 4526 was observed in the 12CO(2-1) line (230GHz or 1.3mm) using
the Combined Array for Research in Millimeter-wave Astronomy (CARMA).
The data were taken as part of the mm-Wave Interferometric Survey of
Dark Object Masses project. Results for the innermost CO were reported
by Davis et al. (2013Natur.494..328D 2013Natur.494..328D). The beamwidth of the
observations is 0.278x0.173arcsec2, and the spectral resolution
(after Hanning smoothing) is 10km/s.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 95 241 NGC4526 cloud properties from 12CO(2-1) line
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See also:
J/A+A/565/A128 : Dust SED in HRS nearby galaxies (Ciesla+, 2014)
J/A+A/542/A108 : Giant molecular clouds in M33 (Gratier+, 2012)
J/ApJS/197/16 : CO obs. of LMC molecular clouds (MAGMA). (Wong+, 2011)
J/MNRAS/413/813 : ATLAS3D project. I. (Cappellari+, 2011)
J/ApJ/699/1092 : Giant molecular clouds (SRBY) (Heyer+, 2009)
J/ApJ/686/948 : CO in extragalactic giant molecular clouds (Bolatto+, 2008)
J/ApJS/178/56 : CO observations of LMC Giant Molecular clouds (Fukui+, 2008)
J/ApJ/661/830 : Giant molecular clouds of M33 (Rosolowsky+, 2007)
J/ApJ/654/240 : Giant molecular clouds in M31 (Rosolowsky+, 2007)
J/ApJS/149/343 : Giant molecular clouds in M33 (Engargiola+, 2003)
J/ApJ/551/852 : FCRAO CO survey of the outer Galaxy (Heyer+, 2001)
J/A+AS/134/241 : Rotation in molecular clouds (Phillips 1999)
J/ApJ/428/693 : Rosette Nebula & Maddalena Cloud structures (Williams+ 1994)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/241] Running sequence number
5- 6 I2 h RAh [12] Hour of the Right Ascension (J2000)
8- 9 I2 min RAm [34] Min of the Right Ascension (J2000)
11- 13 F3.1 s RAs [2/4] Second of RA (J2000)
15 A1 --- DE- [+] Sign of Declination (J2000)
16 I1 deg DEd [7] Degree of Declination (J2000)
18- 19 I2 arcmin DEm [41/42] Arcminute of Declination (J2000)
21- 24 F4.1 arcsec DEs Arcsecond of Declination (J2000)
26- 30 F5.1 km/s VLSR [276/959] Local Standard of Rest velocity
32- 36 F5.2 pc R [3/41]? Cloud size (1)
38- 42 F5.2 pc e_R [2/15]? Uncertainty in R (1)
44- 48 F5.2 km/s sigv [3.7/27.5] Velocity dispersion σ
50- 54 F5.2 km/s e_sigv i[0.3/158] Uncertainty in sigv
56- 60 F5.2 10+5K.km/s.pc2 Lum [0.1/12] Luminosity in 12CO(2-1) (1.3mm)
62- 65 F4.2 10+5K.km/s.pc2 e_Lum [0.09/2.14] Uncertainty in Lum
67- 70 F4.2 10+6Msun Mass [0.09/6] Cloud mass
72- 75 F4.2 10+6Msun e_Mass [0.05/1.1] Uncertainty in Mass
77- 79 F3.1 --- S/N [3/7.5] Signal-to-noise ratio
81- 84 F4.1 K Tbmax [3.7/10.4] Maximum brightness temperature
86- 90 F5.2 km/s/pc Omega [0.4/66.1]? Angular velocity Ωshear
due to the galactic shear
92- 95 I4 pc Dist [10/874]? Distance from NGC4526 center (2)
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Note (1): The size of unresolved clouds are less than the linear size of the
beam and are blank in this table.
Note (2): Assuming clouds are in the plane of the galaxy with axis ratio
of 0.216 and position angle of 20.2 degrees.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 29-Jul-2015