J/ApJ/784/3 The PAWS catalogs of GMCs and islands in M51 (Colombo+, 2014)
The PdBI Arcsecond Whirlpool Survey (PAWS): environmental dependence of giant
molecular cloud properties in M51.
Colombo D., Hughes A., Schinnerer E., Meidt S.E., Leroy A.K., Pety J.,
Dobbs C.L., Garcia-Burillo S., Dumas G., Thompson T.A., Schuster K.F.,
Kramer C.
<Astrophys. J., 784, 3 (2014)>
=2014ApJ...784....3C 2014ApJ...784....3C (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Molecular clouds ; Radial velocities ;
Velocity dispersion ; Interstellar medium ; Carbon monoxide
Keywords: evolution - galaxies: individual (M51, NGC 5194) - galaxies: spiral -
galaxies: star formation - ISM: clouds - ISM: structure
Abstract:
Using data from the PdBI Arcsecond Whirlpool Survey (PAWS), we have
generated the largest extragalactic giant molecular cloud (GMC)
catalog to date, containing 1507 individual objects. GMCs in the inner
M51 disk account for only 54% of the total 12CO(1-0) luminosity of
the survey, but on average they exhibit physical properties similar to
Galactic GMCs. We do not find a strong correlation between the GMC
size and velocity dispersion, and a simple virial analysis suggests
that ∼30% of GMCs in M51 are unbound. We have analyzed the GMC
properties within seven dynamically motivated galactic environments,
finding that GMCs in the spiral arms and in the central region are
brighter and have higher velocity dispersions than inter-arm clouds.
Globally, the GMC mass distribution does not follow a simple power-law
shape. Instead, we find that the shape of the mass distribution varies
with galactic environment: the distribution is steeper in inter-arm
region than in the spiral arms, and exhibits a sharp truncation at
high masses for the nuclear bar region. We propose that the observed
environmental variations in the GMC properties and mass distributions
are a consequence of the combined action of large-scale dynamical
processes and feedback from high-mass star formation. We describe some
challenges of using existing GMC identification techniques for
decomposing the 12CO(1-0) emission in molecule-rich environments,
such as M51's inner disk.
Description:
The Plateau de Bure Interferometer (PdBI) Arcsecond Whirlpool Survey
(PAWS; Schinnerer et al., 2013ApJ...779...42S 2013ApJ...779...42S) is a large IRAM program
involving 210hr of observations with the Plateau de Bure
Interferometer (PdBI) and IRAM 30m telescope to conduct a sensitive,
high angular resolution (1.16''*0.97''), 12CO(1-0) survey of the
inner disk of M51a (field-of-view, FoV ∼270''*170''). The spatial
resolution at our assumed distance to M51 of 7.6Mpc (Ciardullo et al.
2002, cat. J/ApJ/577/31) is ∼40pc. The inclusion of the 30m single
dish data during joint deconvolution ensures that flux information on
all spatial scales is conserved. The rms of the noise fluctuations in
the cube is ∼0.4K per 5km/s channel. This sensitivity is sufficient to
detect an object with a gas mass of 1.2*105M☉ at the
5σrms level. The PAWS data cube covers the LSR velocity range
between 173 and 769km/s. A detailed description of the observing
strategy, calibration and data reduction is presented by Pety et al.
(2013ApJ...779...43P 2013ApJ...779...43P).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 110 1507 PdBI Arcsecond Whirlpool Survey (PAWS) Giant
Molecular Cloud (GMC) catalog
table7.dat 110 309 PdBI Arcsecond Whirlpool Survey (PAWS) island
catalog
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See also:
J/ApJ/772/107 : GMCs in nearby galaxies (Donovan Meyer+, 2013)
J/A+A/542/A108 : Giant molecular clouds in M33 (Gratier+, 2012)
J/ApJS/197/16 : CO observations of LMC molecular clouds (MAGMA). (Wong+, 2011)
J/ApJ/699/1092 : Giant molecular clouds (SRBY) (Heyer+, 2009)
J/ApJS/178/56 : CO observations of LMC Giant Molecular clouds (Fukui+, 2008)
J/ApJ/686/948 : CO in extragalactic giant molecular clouds (Bolatto+, 2008)
J/ApJ/654/240 : Giant molecular clouds in M31 (Rosolowsky+, 2007)
J/ApJS/149/343 : Giant molecular clouds in M33 (Engargiola+, 2003)
J/ApJ/577/31 : PNe in six galaxies (Ciardullo+, 2002)
J/ApJ/551/852 : FCRAO CO survey of the outer Galaxy (Heyer+, 2001)
J/PASJ/53/971 : CO catalog of LMC molecular clouds (Mizuno+, 2001)
Byte-by-byte Description of file: table[17].dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Seq [1/1507] Object identification number (1)
6- 7 I2 h RAh Hour of Right Ascension (J2000)
9- 10 I2 min RAm Minute of Right Ascension (J2000)
12- 16 F5.2 s RAs Second of Right Ascension (J2000)
18- 19 I2 deg DEd Degree of Declination (J2000)
21- 22 I2 arcmin DEm Arcminute of Declination (J2000)
24- 28 F5.2 arcsec DEs Arcsecond of Declination (J2000)
30- 35 F6.1 km/s Vlsr [-125.1/132.6] Local standard of rest
radial velocity (ΔVLSR) (2)
37- 40 F4.1 K Tmax [1.1/16.5] Peak brightness temperature
(Tmax) (3)
42- 45 F4.1 --- S/N [3.5/41.6] Peak Signal-to-Noise ratio
47- 50 I4 pc Reff [5/2346] Effective radius (4)
52- 54 I3 pc e_Reff [0/133] Uncertainty in Reff
56- 59 F4.1 km/s sigma [0.7/50.7] Velocity dispersion (σv) (6)
61- 64 F4.1 km/s e_sigma [0/23.7] Uncertainty in sigma
66- 71 F6.1 --- LCO [0.1/6446.7] The CO luminosity LCO
(in 105K.km/s.pc2 units) (7)
73- 76 F4.1 --- e_LCO [0.1/56.5] Uncertainty in LCO
(in 105K.km/s.pc2 units)
78- 84 F7.1 10+5Msun Mvir [0.2/62661.8] Mass inferred from virial theorem
(Mvir) (8)
86- 91 F6.1 10+5Msun e_Mvir [0/1090.1] Uncertainty in Mvir
93- 97 F5.2 --- alpha [0.01/48.5] Virial parameter α (9)
99-101 I3 deg PA [0/179] Position angle of object major
axis (10)
103-105 F3.1 --- b/a [0.1/5.6] Minor-to-major axis ratio (11)
107-108 A2 --- Reg Region of M51 where a given object has been
identified (CR, SA, or IA) (12)
110 I1 --- f_Reff [0/1] Radius measurement flag (1=upper limit,
0=actual measurement) (5)
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Note (1): Islands are connected emission structures inside the working area
spanning at least one telescope beam area and one velocity channel. Because
of the high sensitivity of the Plateau de Bure Interferometer (PdBI)
Arcsecond Whirlpool Survey (PAWS) cube, the island catalog is dominated by
the presence of a huge central object that contains more than 50% of the
total flux present in the data cube and more than 70% of the total emission
contoured by the CPROPS algorithm (Rosolowsky & Leroy, 2006PASP..118..590R 2006PASP..118..590R)
island identification. It embodies almost the whole central region and a
significant portion of the spiral arms. Excluding this entity, the
remaining islands are evenly distributed between the spiral arm and
inter-arm regions, with only a few objects located in the central region.
Approximately, 70% of the islands are associated with a single Giant
Molecular Cloud (GMC), the majority of which are located in the inter-arm
region.
Note (2): With respect to the systematic velocity of M51 (VLSR=472 km/s;
Shetty et al., 2007ApJ...665.1138S 2007ApJ...665.1138S).
Note (3): The peak brightness temperature of a GMC is the CO brightness at the
local maximum within the cloud. It is measured directly from the data,
i.e., without extrapolation or deconvolution.
Note (4): Deconvolved, extrapolated effective radius. The effective radius of
the cloud is defined as the radius of a circle that encompasses an area
equivalent to the projected area of the cloud. See additional details in
Section 3.2.1.
Note (5): See Section 3.2 for details.
Note (6): Deconvolved, extrapolated velocity dispersion.
Note (7): Integrated and extrapolated CO luminosity.
Note (8): The virial mass depends on the density profile of the cloud. For a
cloud with a density profile of p∝r-1 the virial mass is:
Mvir[M☉]=1040σv2Rad, (Eq. (8)),
where Rad is the cloud radius in parsec, and σv is the velocity
dispersion in km/s.
Note (9):
The dimensionless virial parameter α has a value of order unity and
characterizes deviations from the virial theorem applied to a
non-magnetized cloud with no external pressure and constant density (see
Bertoldi & McKee, 1992ApJ...395..140B 1992ApJ...395..140B). This parameter quantifies the ratio
of the cloud's kinetic to gravitational energy, i.e.,
α=5σv2Reff/GMlum=1161σv2Reff/Mlum (12),
* α∼1 = Cloud considered as gravitationally bound and stabilized by
internal thermal and turbulent pressure against collapse;
* α≫1 = Cloud either externally bound or transient features of the
interstellar medium (ISM);
* α=2 = Regarded as the threshold between gravitationally bound and
unbound object;
* α≪1 = If long-lived, cloud must be supported against collapse by
something more than its internal turbulent motions, such
as the magnetic field.
Note (10): Measured clockwise, i.e., from north through west, with north set to
PA=0°. See more details in Section 3.2.1.
Note (11): The ratio between the major and minor axis is obtained directly from
the spatial moments σb(0K) and σa(0K) without conversion
into their physical quantities. The axis ratio, b/a, parameterizes the
shape of the cloud:
b/a=1 = Round cloud;
b/a<1 = Elongated cloud.
Note (12): The three regions are defined as below:
CR = Center;
SA = Spiral arms;
IA = Inter-arm.
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History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 08-Aug-2016