J/ApJ/846/71 M51 ISM structures from the CO maps of PAWS (Leroy+, 2017)
Cloud-scale ISM structure and star formation in M51.
Leroy A.K., Schinnerer E., Hughes A., Kruijssen J.M.D., Meidt S.,
Schruba A., Sun J., Bigiel F., Aniano G., Blanc G.A., Bolatto A.,
Chevance M., Colombo D., Gallagher M., Garcia-Burillo S., Kramer C.,
Querejeta M., Pety J., Thompson T.A., Usero A.
<Astrophys. J., 846, 71 (2017)>
=2017ApJ...846...71L 2017ApJ...846...71L
ADC_Keywords: Galaxies, nearby ; Carbon monoxide ; Interstellar medium ;
Molecular data
Keywords: galaxies: individual (M51) ; galaxies: ISM ; galaxies: spiral ;
galaxies: star formation ; ISM: general ; ISM: structure
Abstract:
We compare the structure of molecular gas at 40pc resolution to the
ability of gas to form stars across the disk of the spiral galaxy M51.
We break the PdBI Arcsecond Whirlpool Survey (PAWS; Schinnerer+
2013ApJ...779...42S 2013ApJ...779...42S) into 370pc and 1.1kpc resolution elements, and
within each we estimate the molecular gas depletion time
(τDepmol), the star-formation efficiency per free-fall time
(εff), and the mass-weighted cloud-scale (40pc) properties
of the molecular gas: surface density, Σ, line width, σ,
and b=Σ/σ2∝αvir-1, a parameter that
traces the boundedness of the gas. We show that the cloud-scale
surface density appears to be a reasonable proxy for mean volume
density. Applying this, we find a typical star-formation efficiency
per free-fall time, εff(<Σ40pc>)∼0.3%-0.36%, lower
than adopted in many models and found for local clouds. Furthermore,
the efficiency per free-fall time anti-correlates with both Σ
and σ, in some tension with turbulent star-formation models. The
best predictor of the rate of star formation per unit gas mass in our
analysis is b=Σ/σ2, tracing the strength of
self-gravity, with τDepmol∝b-0.9. The sense of the
correlation is that gas with stronger self-gravity (higher b) forms
stars at a higher rate (low τDepmol). The different regions of
the galaxy mostly overlap in τDepmol as a function of b, so
that low b explains the surprisingly high τDepmol found toward
the inner spiral arms found by Meidt et al. (2013ApJ...779...45M 2013ApJ...779...45M).
Description:
Schinnerer+ (2013ApJ...779...42S 2013ApJ...779...42S) and Pety+ (2013ApJ...779...43P 2013ApJ...779...43P)
present the PdBI Arcsecond Whirlpool Survey (PAWS), which mapped
CO(1-0) emission from the central region of M51 at
1.16"x0.97"∼1.06"∼40pc resolution with ∼5km/s velocity resolution.
PAWS includes short and zero-spacing information.
We also use broad-band maps of IR emission from Herschel and Spitzer.
These were obtained as part of the Spitzer Infrared Nearby Galaxy
Survey (SINGS; Kennicutt+ 2003PASP..115..928K 2003PASP..115..928K) and the Herschel Very
Nearby Galaxies Survey (Mentuch Cooper+ 2012ApJ...755..165M 2012ApJ...755..165M).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 69 2059 Cloud-scale structure, IR, and CO in M51
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See also:
J/A+A/291/943 : Protostellar cores (Ossenkopf+, 1994)
J/ApJ/479/231 : PNe in M51, M96 & M101 (Feldmeier+ 1997)
J/ApJ/577/31 : PNe in six galaxies (Ciardullo+, 2002)
J/ApJ/633/871 : Positions and photometry of HII knots in M51 (Calzetti+, 2005)
J/ApJ/671/333 : Aperture photometry in NGC 5194 (Kennicutt+, 2007)
J/ApJ/686/948 : CO in extragalactic giant molecular clouds (Bolatto+, 2008)
J/AJ/136/2782 : Star formation efficiency in nearby galaxies (Leroy+, 2008)
J/AJ/136/2563 : HI Nearby Galaxy Survey, THINGS (Walter+, 2008)
J/ApJ/704/842 : VIRUS-P spectroscopy of NGC 5194 (Blanc+, 2009)
J/ApJ/699/1092 : Giant molecular clouds (SRBY) (Heyer+, 2009)
J/ApJ/700/1299 : Gas-phase element depletions in the ISM (Jenkins, 2009)
J/ApJS/184/1 : Molecular clouds in the LMC by NANTEN. II. (Kawamura+, 2009)
J/ApJ/723/1019 : Galactic SFR and gas surface densities (Heiderman+, 2010)
J/ApJ/784/3 : The PAWS catalogs of GMCs and islands in M51 (Colombo+, 2014)
J/ApJ/789/81 : Multiwavelength survey of HII regions in NGC300 (Faesi+, 2014)
J/ApJ/808/42 : CHemical Abundances of Spirals II. M51 (Croxall+, 2015)
J/ApJ/833/229 : Star forming cloud-giant MC complexes (Lee+, 2016)
J/A+A/593/A118 : HCN(1-0) cube for the nucleus of M51 (Querejeta+, 2016)
J/ApJ/834/57 : MW molecular clouds from 12CO (Miville-Deschenes+, 2017)
J/ApJ/835/278 : Molecular clouds in the dwarf galaxy NGC6822 (Schruba+, 2017)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg [202.4/202.6] Right Ascension (J2000)
11- 18 F8.5 deg DEdeg [47.1/47.3] Declination (J2000)
20- 21 I2 arcsec Beam [10/30] Beam size
23- 25 F3.1 kpc Rgal [0/5] Galactocentric radius (1)
27- 31 F5.1 Msun/pc2 SigCO [5/518] CO molecular gas surface
density (Σmol) (2)
33- 38 F6.4 Msun/yr/kpc2 SigSFR [0.004/0.4] Star formation rate
surface density (ΣSFR) (3)
40- 44 F5.1 Msun/pc2 SigCO40pc [46.6/841.7] Cloud-scale CO
molecular gas surface density
(<Σ40pc>) (2)
46- 49 F4.1 km/s rmsCO40pc [2.5/20.2] Cloud-scale RMS line
width of CO (<σ40pc>)
51- 54 F4.2 Msun/pc2/km2/s2 b40pc [1/7.7] Boundedness parameter
(b=Σ/σ2
∝αvir-1) (2)
56- 59 F4.2 --- farm [0/1] Beam fraction, CO flux, arm (4)
61- 64 F4.2 --- fia [0/1] Beam fraction, CO flux,
interarm (4)
66- 69 F4.2 --- fctr [0/1] Beam fraction, CO flux,
central region (4)
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Note (1): Galactocentric radius for a thin disk and the orientation
parameters quoted in Section 2.3.
Uncertainty in the distance, ∼10%, linearly affects rgal.
Note (2): Molecular mass linearly translated from CO surface brightness
using αCO=4.35M☉/pc2 (K/km/s)-1
For Σmol a ∼10% gain uncertainty applies to both resolutions,
the statistical noise is on average 2.25M☉/pc2 at
10" resolution and 0.5M☉/pc2 at 30" resolution,
Note (3): The SFR is a linear transformation of the TIR emission.
See Section 2.3
Calibration uncertainties are of the order of 5%-10%, multiband TIR
estimates from Galametz+ (2013MNRAS.431.1956G 2013MNRAS.431.1956G) are uncertain by
∼0.08dex, translation from 70um to TIR scatters by an additional
∼0.05dex, and statistical noise is ∼2.5x106L☉/kpc2
(∼4x10-4M☉/yr/kpc2) at 30" and ∼9.4x106L☉/kpc2
at 10" resolution (∼1.3x10-4M☉/yr/kpc2),
Note (4): Fraction of the CO flux in the beam that arises from arm (f-arm),
interarm (f-interarm), or central (f-ctr) regions as defined following
Colombo+ (2014, J/ApJ/784/3).
From our Monte Carlo calculation, typical statistical uncertainties
in <Σ40pc>, <σ40pc>, and <b40pc> are 1.5%, 2%, and
3% at 30" resolution and 4%, 5%, and 6% at 10" resolution. Covariance
in uncertainty at both resolutions is about 0.7 between
<Σ40pc> and <σ40pc>, -0.4 between <Σ40pc> and
<b40pc>, and -0.9 between <σ40pc> and <b_40pc>. The ∼10%
gain uncertainty also applies to <Σ40pc> and <b40pc>. These
uncertainties do not account for translation to physical quantities.
Selection criteria: at 30", we include all lines of sight where at
least 50% of the beam lies in the PAWS field. At 10", we include all
lines of sight where 95% of the beam lies in the PAWS field,
Σmol>5M☉/pc2, and
ΣSFR>7.5x10-3M☉/yr/kpc2.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 19-Apr-2018