J/ApJ/882/5 ALMA data for 5 luminous & ultraluminous IR gal. (Wilson+, 2019)
The Kennicutt-Schmidt law and gas scale height in luminous and ultraluminous
infrared galaxies.
Wilson C.D., Elmegreen B.G., Bemis A., Brunetti N.
<Astrophys. J., 882, 5 (2019)>
=2019ApJ...882....5W 2019ApJ...882....5W
ADC_Keywords: Galaxies, IR; Interstellar medium; Carbon monoxide;
Velocity dispersion; Molecular data
Keywords: Infrared galaxies ; Interstellar medium ; Star formation ;
Starburst galaxies
Abstract:
A new analysis of high-resolution data from the Atacama Large
Millimeter/submillimeter Array for five luminous or ultraluminous
infrared galaxies gives a slope for the Kennicutt-Schmidt (KS)
relation equal to 1.74-0.07+0.09 for gas surface densities
Σmol>103M☉/pc2 and an assumed constant CO-to-H2
conversion factor. The velocity dispersion of the CO line, σv,
scales approximately as the inverse square root of Σmol,
making the empirical gas scale height determined from
H∼0.5σ2/(πGΣmol) nearly constant, 150-190pc, over
1.5 orders of magnitude in Σmol. This constancy of H implies
that the average midplane density, which is presumably dominated by
CO-emitting gas for these extreme star-forming galaxies, scales
linearly with the gas surface density, which in turn implies that the
gas dynamical rate (the inverse of the freefall time) varies with
Σmol1/2, thereby explaining most of the super-linear slope
in the KS relation. Consistent with these relations, we also find that
the mean efficiency of star formation per freefall time is roughly
constant, 5%-7%, and the gas depletion time decreases at high
Σmol, reaching only ∼16Myr at Σmol∼104M☉/pc2.
The variation of σv with Σmol and the constancy of H
are in tension with some feedback-driven models, which predict
σv to be more constant and H to be more variable. However,
these results are consistent with simulations in which large-scale
gravity drives turbulence through a feedback process that maintains an
approximately constant Toomre Q instability parameter.
Description:
To study the Kennicutt-Schmidt (KS) relation at high star formation
rates, we searched the Atacama Large Millimeter/submillimeter Array
(ALMA) archive for ultraluminous infrared galaxies (ULIRGs) for which
suitable observations of the CO J=1-0 line were available (Table 1).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 59 5 (Ultra-)Luminous IR Galaxies observed with ALMA
table2.dat 148 53 *Binned data used in this paper
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Note on table2.dat: In this table, each row reports our measurements for
one large pixel in one galaxy (see Appendix).
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See also:
J/AJ/136/2782 : Star formation efficiency in nearby galaxies (Leroy+, 2008)
J/MNRAS/433/2240 : SALT2 parameters & distances for SNe (Ganeshalingam+, 2013)
J/ApJ/799/10 : Arp 220 6 and 33GHz images (Barcos-Munoz+, 2015)
J/ApJ/860/172 : Cloud-scale molecular gas data in 15 galaxies (Sun+, 2018)
J/ApJ/872/16 : Integrated star formation law rev. I. (de los Reyes+, 2019)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Name Galaxy name
17- 19 I3 Mpc Dist [44/182] Distance (1)
21- 23 F3.1 kpc2 Area [1.1/5.2] Map area (2)
25- 33 A9 arcsec Beam Beam FWHM
35- 39 F5.3 mJy/beam sig [0.015/0.1] σcont
41- 45 F5.3 mJy/beam*km/s sigCO [0.043/0.18] σCO(1-0)
47- 49 I3 pc Pix [345/650] Binned pixel size
51- 59 A9 --- Gal Abbreviated galaxy name as in Table 2
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Note (1): From redshift (corrected to the 3K CMB reference frame) and assuming
Ho=70.5km/s/Mpc.
For NGC 7469, SN Type Ia distance from Ganeshalingam+ (2013, J/MNRAS/433/2240).
Note (2): The area of high signal-to-noise emission used in this analysis;
the ALMA maps detect emission over a larger area, especially in CO.
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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- 9 A9 --- Gal Galaxy identifier
10 A1 --- --- [_]
11- 12 I2 --- Seq Pixel identifier within Gal
14- 22 F9.5 deg RAdeg [156.9/346] Right Ascension (J2000) (1)
24- 32 F9.5 deg DEdeg [-55.2/23.6] Declination (J2000) (1)
34- 42 F9.5 km/s sigv [29/156.2] Observed CO J=1-0
velocity dispersion
44- 51 F8.5 km/s e_sigv [0.7/25.5] Uncertainty on sigv
53- 59 F7.5 [Msun/pc2] log-MMol [2.4/4] Log of molecular mass
surface density
61- 67 F7.5 [Msun/pc2] e_log-MMol [0.02/0.03] Uncertainty on log-MMol
69- 75 F7.5 [Msun/yr/kpc2] log-SFR [0.1/2.8] Log of star formation
rate surface density
77- 83 F7.5 [Msun/yr/kpc2] e_log-SFR [0.01/0.2] Uncertainty on log-SFR
85- 91 F7.5 [yr] log-tdep [7.2/8.7] Log of depletion time
93- 99 F7.5 [yr] e_log-tdep [0.03/0.2] Uncertainty on log-tdep
101-107 F7.5 [yr] log-tff [6/7.2] Log of free-fall timescale
109-115 F7.5 [yr] e_log-tff [0.02/0.2] Uncertainty on log-tff
117-124 F8.5 [-] log-eff [-2.2/-0.9] Log of efficiency per tff
126-132 F7.5 [-] e_log-eff [0.04/0.2] Uncertainty on log-eff
134-140 F7.5 [pc] log-H [1.7/2.7] Log of molecular gas
scale height
142-148 F7.5 [pc] e_log-H [0.02/0.3] Uncertainty on log-H
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Note (1): Central coordinates of the pixel.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 29-Jan-2021