J/A+A/627/A107 CO observations of major merger pairs at z=0 (Lisenfeld+, 2019)
CO observations of major merger pairs at z=0:
molecular gas mass and star formation.
Lisenfeld U., Xu C.K., Gao Y., Domingue D.L., Cao C., Yun M.S., Zuo P.
<Astron. Astrophys. 627, A107 (2019)>
=2019A&A...627A.107L 2019A&A...627A.107L (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, IR ; Interstellar medium ; Carbon monoxide
Keywords: galaxies: evolution - galaxies: general - galaxies: interactions -
galaxies: starburst - ISM: molecular
Abstract:
We present CO observations of 78 spiral galaxies in local merger
pairs. These galaxies represent a subsample of a Ks-band-selected
sample consisting of 88 close major-merger pairs (HKPAIRs), 44
spiral-spiral (S+S) pairs, and 44 spiral-elliptical (S+E) pairs, with
separation <20h-1kpc and mass ratio <2.5. For all objects, the star
formation rate (SFR) and dust mass were derived from Herschel PACS and
SPIRE data, and the atomic gas mass, MHI, from the Green Bank
Telescope HI observations. The complete data set allows us to study
the relation between gas (atomic and molecular) mass, dust mass, and
SFR in merger galaxies. We derive the molecular gas fraction
(MH2/M*), molecular-to-atomic gas mass ratio (MH2/MHI),
gas-to-dust mass ratio and SFE (=SFR/MH2) and study their
dependences on pair type (S+S compared to S+E), stellar mass, and the
presence of morphological interaction signs. We find an overall
moderate enhancement (∼2x) in both molecular gas fraction (MH2/M*)
and molecular-to-atomic gas ratio (MH2/MHI) for star-forming
galaxies in major-merger pairs compared to non-interacting comparison
samples, whereas no enhancement was found for the SFE nor for the
total gas mass fraction ((MHI+MH2)/M^Cstar). When divided into S+S and
S+E, low mass and high mass, and with and without interaction signs,
there is a small difference in SFE, a moderate difference in MH2/M*,
and a strong difference in MH2/MHI between subsamples. For the
molecular-to-atomic gas ratio MH2/MHI, the difference between S+S
and S+E subsamples is 0.55±0.18dex and between pairs with and
without interaction signs is 0.65±0.16dex. Together, our results
suggest that (1) star formation enhancement in close major-merger
pairs occurs mainly in S+S pairs after the first close encounter
(indicated by interaction signs)^Mbecause the HI gas is compressed
into star-forming molecular gas by the tidal torque; and (2) this
effect is much weakened in the S+E pairs.
Description:
Observations were carried out between July 2015 and May 2018 with the
Institut de Radioastronomie Milimetrique (IRAM) 30m telescope on Pico
Veleta. We observed the redshifted 12CO(1-0) and 12CO(2-1) lines
in parallel in the central position of each galaxy.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 75 78 Results of CO(1-0) and CO(2-1) observations
table2.dat 35 78 Molecular gas mass
listco10.dat 112 78 List of CO(1-0) spectra
spco10.fits 2880 64 CO(1-0) spectra
listco21.dat 112 63 List of CO(2-1) spectra
spco21.fits 2880 30 CO(2-1) spectra
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- Galaxy Name of the galaxy (JHHMMSSss+DDMMSSs)
19- 28 A10 --- Group Name of the pair (JHHMM+DDMM)
30- 33 F4.2 mK rmsCO10 Root-mean-square noise of the
CO(1-0) spectrum
35 A1 --- l_ICO10 Upper limit flag on ICO10
36- 40 F5.2 K.km/s ICO10 Velocity integrated intensity of the
CO(1-0) spectrum
42- 45 F4.2 K.km/s e_ICO10 ?=- Error of the velocity integrated
intensity of the CO(1-0) spectrum
46 A1 --- n_ICO10 [*] Note on ICO10 (1)
48- 51 I4 km/s dVCO10 ?=- Zero-level line width of the
CO(1-0) spectrum
53- 57 F5.2 mK rmsCO21 ?=- Root-mean-square noise of the
CO(2-1) spectrum
59 A1 --- l_ICO21 Upper limit flag on ICO(2-1)
60- 64 F5.2 K.km/s ICO21 ?=- Velocity integrated intensity of the
CO(2-1) spectrum
66- 69 F4.2 K.km/s e_ICO21 ?=- Error of the velocity integrated
intensity of the CO(2-1) spectrum
70 A1 --- n_ICO21 [*] Note on ICO21 (1)
72- 75 I4 km/s dVCO21 ?=- Zero-level line width of the
CO(2-1) spectrum
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Note (1): * means tentative detection.
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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- 17 A17 --- Galaxy Name of the galaxy (JHHMMSSss+DDMMSSs)
19- 23 F5.1 Mpc Dist Distance
25 A1 --- l_logMmol0 Upper limit flag on logMmol0
26- 30 F5.2 [Msun] logMmol0 Decimal logarithm of the molecular gas mass
extrapolated to the entire disk
32- 35 F4.2 --- faper Aperture correction factor (ratio between the
molecular gas mass in the central pointing
and the extrapolated value)
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Byte-by-byte Description of file: listco10.dat listco21.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- Line Observed line
14- 23 A10 --- Name Galaxy pair name (JHHMM+DDMM)
24 A1 ---- n_Name [AB] Multiplicity index on Name
25 A1 --- f_Name [*] Flag on Name
27- 34 F8.4 deg RAdeg Right ascension (J2000)
36- 45 F10.6 deg DEdeg Declination (J2000)
47- 58 E12.6 Hz RestFreq Rest frequency
60- 71 E12.6 Hz ImgFreq Image frequency
72- 83 E12.6 m/s Vel Velocity
85- 92 A8 --- n_Vel Velocity reference (RADI-HEL or RADI-LSR)
94-101 F8.1 m/s DVel Velocity resolution
103-112 A10 "date" Obs.Date Observation date
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Acknowledgements:
Ute Lisenfeld, ute(at)ugr.es
(End) Ute Lisenfeld [Universidad Granada], Patricia Vannier [CDS] 18-Jun-2019