J/A+A/550/A41 CO line survey in 0.2<z<1 of galaxies (Combes+, 2013)
Gas fraction and star formation efficiency at z < 1.0.
Combes F., Garcia-Burillo S., Braine J., Schinnerer E., Walter F., Colina L.
<Astron. Astrophys. 550, A41 (2013)>
=2013A&A...550A..41C 2013A&A...550A..41C
ADC_Keywords: Galaxies, peculiar ; Galaxies, radio ; Galaxies, spectra
Keywords: galaxies: high redshift - galaxies: ISM - galaxies: starburst -
radio lines: galaxies
Abstract:
After new observations of 39 galaxies at z=0.6-1.0 obtained at the
IRAM 30m telescope, we present our full CO line survey covering the
redshift range 0.2<z<1. Our aim is to determine the driving factors
accounting for the steep decline in the star formation rate during
this epoch. We study both the gas fraction, defined as
Mgas/(Mgas+Mstar), and the star formation efficiency (SFE) defined by
the ratio between far-infrared luminosity and molecular gas mass
(LFIR/M(H2), i.e. a measure for the inverse of the gas depletion
time. The sources are selected to be ultra-luminous infrared galaxies
(ULIRGs), with LFIR greater than 1012L☉, and experiencing
starbursts. When we adopt a standard ULIRG CO-to-H2 conversion
factor, their molecular gas depletion time is less than 100Myr. Our
full survey has now filled the gap of CO observations in the 0.2<z<1
range covering almost half of cosmic history. The detection rate in
the 0.6<z<1 interval is 38% (15 galaxies out of 39), compared to 60%
for the 0.2<z<0.6 interval. The average CO luminosity is
L'CO=1.8x1010K.km/s.pc2, corresponding to an average H2 mass
of 1.45x1010M☉. From observation of 7 galaxies in both CO(2-1)
and CO(4-3), a high gas excitation has been derived; together with the
dust mass estimation, this supports the choice of our low ULIRG
conversion factor between CO luminosity and H2 for our sample
sources. We find that both the gas fraction and the SFE significantly
increase with redshift, by factors of 3±1 from z=0 to 1, and
therefore both quantities play an important role and complement each
other in cosmic star formation evolution.
Description:
21 reduced spectra obtained at IRAM-30m at Pico Veleta, Spain, in two
periods, January and June 2011, with a few remaining sources observed
in the pool between November 2011 and February 2012.
They are presented in Figure 2, 3, 4 of the paper.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 73 39 Source sample, with list of spectra
table2.dat 86 46 Observed line parameters
sp/* . 21 Individual 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- 3 A3 --- Gal Source name
5- 28 A24 --- Name Galaxy name
31- 32 I2 h RAh Right Ascension J2000 (hours)
33 A1 --- --- [:]
34- 35 I2 min RAm Right Ascension J2000 (minutes)
36 A1 --- --- [:]
37- 40 F4.1 s RAs Right Ascension J2000 (seconds)
42 A1 --- DE- Declination J2000 (sign)
43- 44 I2 deg DEd Declination J2000 (degrees)
45 A1 --- --- [:]
46- 47 I2 arcmin DEm Declination J2000 (minutes)
48 A1 --- --- [:]
49- 50 I2 arcsec DEs Declination J2000 (seconds)
53- 57 F5.3 --- z Redshift
59- 60 I2 --- Sp1 [1/21]? First spectrum number (1)
61- 65 A5 --- CO1 CO line transition (2-1), (3-2) or (4-3)
67- 68 I2 --- Sp2 [1/21]? Second spectrum number (1)
69- 73 A5 --- CO2 CO line transition (4-3)
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Note (1): number corresponding to name of file in "sp" subdirectory,
e.g. "1" corresponds to the file sp/spec12.dat
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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 A3 --- Gal Source name
5- 11 A7 --- Line Observed line: CO(2-1), (3-2) or (4-3)
13- 19 F7.3 GHz nu Onserved frequency
21 A1 --- l_S(CO) Limit flag on S(CO)nu
22- 25 F4.1 Jy.km/s S(CO) CO flux density (1)
27- 29 F3.1 Jy.km/s e_S(CO) ? rms uncertainty on S(CO) (2)
31- 34 I4 km/s V ? Velocity is relative to the optical
redshift given in Table 1
36- 37 I2 km/s e_V ? rms uncertainty on V (2)
39- 42 I4 km/s DVFWHM ?=- VFWHM difference
44- 46 I3 km/s e_DVFWHM ? rms uncertainty on DVFWHM (2)
48 A1 --- l_L'CO Limit flag on L'CO
49- 52 F4.2 10+10K.km/s/pc2 L'CO CO luminosity
54- 57 F4.2 Jy S60 ? 60um flux density (3)
58 A1 --- n_S60 [e] Spitzer 70um flux (6)
60 A1 --- l_S100 Limit flag on S100
61- 64 F4.2 Jy S100 ? 100um flux density (3)
65 A1 --- n_S100 [e] Spitzer 160um flux (6)
67- 71 F5.2 [Lsun] logFIR ? FIR luminosity (4)
73- 78 F6.1 mJy F1.4GHz ?=- 1.4GHz flux (5)
80- 84 F5.2 [Msun] logM* ? Stellar mass
85- 86 A2 --- n_logM* [gh] Note on derivation of logM* (6)
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Note (1): The upper limits are at 3σ with an assumed DV=300km/s,
except for S16, where DV is known.
Note (2): Quoted errors are statistical errors from Gaussian fits.
The systematic calibration uncertainty is 10%.
Note (3): 60 and 100um fluxes are from NED (http://nedwww.ipac.caltech.edu/)
or Stanford et al. (2000, Cat. J/ApJS/131/185)
Note (4): The derivation of LFIR is described in Sec. 2, and
logSFR(M☉/yr)=logLFIR(L☉)-9.76 (cf Sec.4.2).
Note (5): From the FIRST catalog (http://sundog.stsci.edu/, or Cat. VIII/90).
Errors are typically 0.14mJy.
Note (6): Notes as follows:
e = For these objects, the Spitzer 70 and 160um fluxes replace the
IRAS 60 and 100um ones
f = Stellar masses were obtained through SED fitting (see Sec. 4.6),
with SDSS fluxes for all galaxies
g = with Spitzer-IRAC data for galaxies in addition of note f
h = with 2MASS for galaxies in addition of note f
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Byte-by-byte Description of file: sp/*
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Bytes Format Units Label Explanations
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1- 9 F9.2 km/s Vel Velocity with respect to redshift in table1.dat
10- 20 F11.6 mK Tmb Main beam temperature
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Acknowledgements:
Francoise Combes, francoise.combes(at)obspm.fr
History:
* 13-Dec-2012: Original version
* 22-Jun-2013: Added table1
(End) Francoise Combes [LERMA, France], Patricia Vannier [CDS] 13-Dec-2012