J/ApJ/798/58 HELGA VI. Giant molecular cloud associations in M31 (Kirk+, 2015)
The Herschel Exploitation of Local Galaxy Andromeda (HELGA).
VI. The distribution and properties of molecular cloud associations in M31.
Kirk J.M., Gear W.K., Fritz J., Smith M.W.L., Ford G., Baes M., Bendo G.J.,
De Looze I., Eales S.A., Gentile G., Gomez H.L., Gordon K., O'Halloran B.,
Madden S.C., Roman-Duval J., Verstappen J., Viaene S., Boselli A.,
Cooray A., Lebouteiller V., Spinoglio L.
<Astrophys. J., 798, 58 (2015)>
=2015ApJ...798...58K 2015ApJ...798...58K
ADC_Keywords: Galaxies, nearby ; Molecular clouds ; Photometry, infrared
Keywords: galaxies: individual: M31; galaxies: ISM; galaxies: structure;
ISM: clouds
Abstract:
In this paper we present a catalog of giant molecular clouds (GMCs) in
the Andromeda (M31) galaxy extracted from the Herschel Exploitation of
Local Galaxy Andromeda (HELGA) data set. GMCs are identified from the
Herschel maps using a hierarchical source extraction algorithm. We
present the results of this new catalog and characterize the spatial
distribution and spectral energy properties of its clouds based on the
radial dust/gas properties found by Smith et al. (Paper II,
2012ApJ...756...40S 2012ApJ...756...40S). A total of 326 GMCs in the mass range
104-107M☉ are identified; their cumulative mass distribution
is found to be proportional to M-2.34, in agreement with earlier
studies. The GMCs appear to follow the same correlation of cloud mass
to LCO observed in the Milky Way. However, comparison between this
catalog and interferometry studies also shows that the GMCs are
substructured below the Herschel resolution limit, suggesting that we
are observing associations of GMCs. Following Gordon et al.
(2006ApJ...638L..87G 2006ApJ...638L..87G), we study the spatial structure of M31 by
splitting the observed structure into a set of spiral arms and offset
rings. We fit radii of 10.3 and 15.5kpc to the two most prominent
rings. We then fit a logarithmic spiral with a pitch angle of 8.9°
to the GMCs not associated with either ring. Last, we comment on the
effects of deprojection on our results and investigate the effect
different models for M31's inclination will have on the projection of
an unperturbed spiral arm system.
Description:
M31 was observed on 2010 December 18-20 and 2011 January 23
(Observation Days 584-586 and 620) using the parallel mode of the
SPIRE and PACS cameras aboard the Herschel Space Observatory. These
data used PACS filters centered at wavelengths of 100um and 160um,
with angular resolutions of 12.5" and 13.3", respectively, and SPIRE
filters centered at wavelengths of 250um, 350um, and 500um, with
angular resolutions of 18.2", 24.5", and 36.0", respectively. The
observation strategy and data reduction methods are described in
detail in Paper I (Fritz+, 2012A&A...546A..34F 2012A&A...546A..34F).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 99 326 Measured leaf-node parameters
table2.dat 28 326 SED parameters
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See also:
VI/139 : Herschel Observation Log (Herschel Science Centre, 2013)
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
VII/7 : Lynds' Catalogue of Dark Nebulae (LDN) (Lynds 1962)
J/ApJ/752/146 : Star forming complexes in Galactic WMAP sources (Lee+, 2012)
J/A+A/542/A108 : Giant molecular clouds in M33 (Gratier+, 2012)
J/MNRAS/422/1071 : Cores in IR Dark Clouds for 300≤l≤330 (Wilcock+, 2012)
J/AJ/142/139 : A new catalog of HII regions in M31 (Azimlu+, 2011)
J/ApJ/723/492 : Properties of GRS molecular clouds (Roman-Duval+, 2010)
J/ApJ/680/349 : Galactic distribution of IRDCs (Jackson+, 2008)
J/ApJ/661/830 : Giant molecular clouds of M33 (Rosolowsky+, 2007)
J/ApJ/654/240 : Giant molecular clouds in M31 (Rosolowsky+, 2007)
J/AJ/87/1165 : Reddening Maps derived from HI & Galaxy Counts (Burstein+ 1982)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [1/326] Running sequence number
5- 6 I2 h RAh [0] Hour of Right Ascension (J2000) (1)
8- 9 I2 min RAm [38/47] Minute of Right Ascension (J2000) (1)
11- 14 F4.1 s RAs Second of Right Ascension (J2000) (1)
16 A1 --- DE- [+] Sign of Declination (J2000) (1)
17- 18 I2 deg DEd [40/42] Degree of Declination (J2000) (1)
20- 21 I2 arcmin DEm Arcminute of Declination (J2000) (1)
23- 24 I2 arcsec DEs Arcsecond of Declination (J2000) (1)
26- 30 F5.1 kpc X X offset (2)
32- 36 F5.1 kpc Y Y offset (2)
38- 41 F4.1 kpc R [0.2/21] Galactocentric distance (3)
43- 45 I3 pc FWHM [78/890] Geometric mean of deconvolved FWHM
47 A1 --- l_S350 Limit flag on S350
49- 53 F5.3 Jy S350 [0.025/4.7] Herschel/SPIRE 350 micron filter
flux density
55- 59 F5.3 Jy e_S350 [0.004/0.1]? Uncertainty in S350
61- 65 F5.3 Jy S250 [0.07/9.6] Herschel/SPIRE 250 micron filter
flux density
67- 71 F5.3 Jy e_S250 [0.004/0.2] Uncertainty in S250
73 A1 --- l_S160 Limit flag on S160
74- 79 F6.3 Jy S160 [0.05/13] Herschel/PACS 160 micron filter
flux density
81- 85 F5.3 Jy e_S160 [0.01/1]? Uncertainty in S160
87 A1 --- l_S100 Limit flag on S100
89- 93 F5.3 Jy S100 [0.03/7] Herschel/PACS 100 micron filter
flux density
95- 99 F5.3 Jy e_S100 [0.008/0.5]? Uncertainty in S100
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Note (1): Of the centroid of the half-power contour in the 250 micron filter.
Note (2): In the rotated, deprojected frame (θ=38°, i=77°).
Note (3): The positional accuracy is on the order of the the pixel size as
the map is Nyquist sampled. Using the 350um pixel grid this is
8arcsec which equates to 30pc along the un-deprojected x-axis
and ∼140pc along the deprojected y-axis.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/326] Running sequence number
5- 11 F7.3 10+5Msun Mass [0.08/140]? Total cloud mass
13- 14 I2 K Temp [14/33]? Temperature
16- 20 F5.2 10+5Lsun LFIR [0.3/55]? Far-IR (10-1000µm) luminosity;
22- 22 A1 --- l_LCO Limit on LCO
24- 28 F5.2 10+4K.km/s/pc2 LCO [0.2/56]? Integrated CO luminosity
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History:
From electronic version of the journal
References:
Fritz et al. Paper I. 2012A&A...546A..34F 2012A&A...546A..34F
Smith et al. Paper II. 2012ApJ...756...40S 2012ApJ...756...40S
Ford et al. Paper III. 2013ApJ...769...55F 2013ApJ...769...55F
Viaene et al. Paper IV. 2014A&A...567A..71V 2014A&A...567A..71V Cat. J/A+A/567/71
Mattson et al. Paper V. 2014MNRAS.444..797M 2014MNRAS.444..797M
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 18-May-2015