J/ApJ/864/120 ALMA obs. toward NGC 5253. I. Molecular clouds (Miura+, 2018)
ALMA observations toward the starburst dwarf galaxy NGC 5253.
I. Molecular cloud properties and scaling relations.
Miura R.E., Espada D., Hirota A., Nakanishi K., Bendo G.J., Sugai H.
<Astrophys. J., 864, 120-120 (2018)>
=2018ApJ...864..120M 2018ApJ...864..120M (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby; Molecular clouds; Carbon monoxide;
Velocity dispersion; Millimetric/submm sources
Keywords: galaxies: dwarf; galaxies: starburst;
galaxies: star clusters: individual: NGC 5253
Abstract:
We present high-spatial-resolution (∼0.2", or ∼3pc) CO(2-1)
observations of the nearest young starburst dwarf galaxy, NGC 5253,
taken with the Atacama Large Millimeter/submillimeter Array. We have
identified 118 molecular clouds with average values of 4.3 pc in
radius and 2.2km/s in velocity dispersion, which comprise the
molecular cloud complexes observed previously with ∼100pc resolution.
We derive for the first time in this galaxy the I(CO)-N(H2)
conversion factor, X=4.1-2.4+5.9x1020cm-2(K.km/s)-1, based
on the virial method. The line width and mass-to-size relations of the
resolved molecular clouds present an offset on average toward higher
line widths and masses with respect to quiescent regions in other
nearby spiral galaxies and our Galaxy. The offset in the scaling
relation reaches its maximum in regions close to the central
starburst, where velocity dispersions are ∼0.5dex higher and gas mass
surface densities are as high as ΣH2=103M_☉/pc2. These
central clouds are gravitationally bound despite the high internal
pressure. A spatial comparison with star clusters found in the
literature enables us to identify six clouds that are associated with
young star clusters. Furthermore, the star formation efficiencies
(SFEs) of some of these clouds exceed those found in
star-cluster-forming clouds within our Galaxy. We conclude that once a
super star cluster is formed, the parent molecular clouds are rapidly
dispersed by the destructive stellar feedback, which results in such a
high SFE in the central starburst of NGC 5253.
Description:
The ALMA data were obtained during 2014 June and 2015 July using Band 6
(project code 2013.1.00210.S; PI: R. E. Miura). The data consisted of
12 executions: two ACA 7m array data sets, three 12m array data sets,
and seven Total Power (TP) array data sets.
We simultaneously observed 12CO(2-1) (νrest=230.538GHz) and
H30α (νrest=231.900GHz) emissions toward two overlapping
pointings covering the dust lane and the center of NGC5253 (Figure 1).
The field of view (half-power beam width, HPBW) is 25" and 43" (at
230GHz) for the 12m and 7m antennas, respectively.
Finally, the mosaicked 12CO(2-1) interferometric 12 and 7m data cube
was combined with the TP image. The spatial resolution of the final
images is 0.2" (corresponding to 3.1pc at a distance of 3.15Mpc).
The results on the H30α and CS(5-4) (νrest=244.936GHz) in
the upper side band continuum data will be reported in separate papers
(Miura+ 2018, in preparation; see also Bendo+ 2017MNRAS.472.1239B 2017MNRAS.472.1239B).
See Section 2 for further details.
Objects:
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RA (ICRS) DE Designation(s)
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13 39 55.99 -31 38 24.1 NGC 5253 = ESO 445-4
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 72 118 Properties of molecular clouds in NGC 5253
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See also:
J/ApJ/551/852 : FCRAO CO survey of the outer Galaxy (Heyer+, 2001)
J/ApJ/603/503 : HST photometry in NGC 5253 and NGC 3077 (Harris+, 2004)
J/AJ/128/2170 : Hα imaging of irregular galaxies (Hunter+, 2004)
J/ApJ/656/168 : Spectrophotometry in NGC 5253 (Lopez-Sanchez+, 2007)
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/699/1092 : Giant molecular clouds (SRBY) (Heyer+, 2009)
J/ApJS/184/1 : Molecular clouds in the LMC by NANTEN. II. (Kawamura+, 2009)
J/AJ/140/1194 : FUV/HI relations in nearby galaxies (Bigiel+, 2010)
J/ApJS/197/16 : CO observations of LMC molecular clouds (MAGMA). (Wong+, 2011)
J/ApJ/761/37 : CO observations in giant molecular clouds of M33 (Miura+, 2012)
J/A+A/550/A88 : Data cubes of NGC 5253 (476-682nm) (Westmoquette+, 2013)
J/MNRAS/431/2917 : NGC5253 star clusters age and mass (de Grijs+, 2013)
J/ApJ/772/107 : Giant molecular clouds in nearby gal. (Donovan Meyer+, 2013)
J/ApJ/784/3 : The PAWS catalogs of GMCs and islands in M51 (Colombo+, 2014)
J/A+A/566/A71 : HI study of 18 nearby dwarf galaxies (Lelli+, 2014)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/118] Running sequence number
5- 9 F5.1 arcsec RAoff [-11.3/20] Intensity-weighted peak position
relative to the galaxy center,
Δα (1)
11- 15 F5.1 arcsec DEoff [-10.6/12.4] Intensity-weighted peak position
relative to the galaxy center,
Δδ (1)
17- 19 I3 km/s Vlsr [356/448] Local Standard of Rest velocity
21- 23 F3.1 km/s sigV [0.5/8.1] Velocity dispersion, σV
25- 27 F3.1 km/s e_sigV [0.1/5.3] sigV uncertainty
29- 32 F4.1 pc maj [1.5/17.1] Major axis of the cloud without
beam deconvolution, σmaj
34 A1 --- --- [x]
36- 38 F3.1 pc min [1/8] Minor axis of the cloud without
beam deconvolution, σmin
40- 42 I3 deg PA [-89/89] Position angle (measured
counterclockwise from north to east)
44- 47 F4.1 pc Rad [0.9/21]? Radius (2)(3)
49- 51 F3.1 pc e_Rad [0.4/10]? Rad uncertainty
53- 56 F4.2 Jy.km/s SCO [0.06/9] CO(2-1) flux density, SCO(2-1)
58- 61 F4.2 Jy.km/s e_SCO [0.04/0.7] SCO uncertainty
63- 67 F5.1 10+4Msun Mvir [0.1/107]? Virial mass (2)
69- 72 F4.1 10+4Msun e_Mvir [0.1/42.1]? Mvir uncertainty
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Note (1): Intensity-weighted peak position relative to the center at the
optically defined galaxy center, RAJ2000=13:39:56.041,DEJ2000=-31:38:30.03.
Note (2): Radius and virial masses are not shown for the cloud whose minor axis
is too small to calculate a deconvolved minor axis.
Note (3): The radius is defined as
R=1.91([σmajor2-σbeam2]1/2
[σminor2-σbeam2]1/2)0.5,
where σmajor and σminor are the (extrapolated) rms
sizes of the major and minor axes of the cloud, σbeam is the
synthesized beam size, and the coefficient 1.91 converts the rms sizes
to the effective spherical radius of the cloud using the factor
3.4/π1/2, following Solomon+ (1987ApJ...319..730S 1987ApJ...319..730S).
See Section 3.2.
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 06-Oct-2023