J/ApJ/820/83 ALMA galaxy properties in the COSMOS survey field (Scoville+, 2016)
ISM masses and the star formation law at z=1 to 6: ALMA observations of dust
continuum in 145 galaxies in the COSMOS survey field.
Scoville N., Sheth K., Aussel H., Vanden Bout P., Capak P., Bongiorno A.,
Casey C.M., Murchikova L., Koda J., Alvarez-Marquez J., Lee N., Laigle C.,
McCracken H.J., Ilbert O., Pope A., Sanders D., Chu J., Toft S.,
Ivison R.J., Manohar S.
<Astrophys. J., 820, 83 (2016)>
=2016ApJ...820...83S 2016ApJ...820...83S (SIMBAD/NED BibCode)
ADC_Keywords: Galaxy catalogs ; Interstellar medium ; Star Forming Region ;
Redshifts ; Millimetric/submm sources
Keywords: cosmology: observations - galaxies: evolution - galaxies: ISM
Abstract:
ALMA Cycle 2 observations of long-wavelength dust emission in 145
star-forming galaxies are used to probe the evolution of the
star-forming interstellar medium (ISM). We also develop a physical
basis and empirical calibration (with 72 low-z and z∼2 galaxies) for
using the dust continuum as a quantitative probe of ISM masses. The
galaxies with the highest star formation rates (SFRs) at =2.2 and 4.4
have gas masses up to 100 times that of the Milky Way and gas mass
fractions reaching 50%-80%, i.e., gas masses 1-4x their stellar masses.
We find a single high-z star formation law:
SFR=35 Mmol0.89x(1+z)z=20.95x(sSFR)MS0.23 M☉/yr
- an approximately linear dependence on the ISM mass and an increased
star formation efficiency per unit gas mass at higher redshift.
Galaxies above the main sequence (MS) have larger gas masses but are
converting their ISM into stars on a timescale only slightly shorter
than those on the MS; thus, these "starbursts" are largely the
result of having greatly increased gas masses rather than an increased
efficiency of converting gas to stars. At z>1, the entire population
of star-forming galaxies has ∼2-5 times shorter gas depletion times
than low-z galaxies. These shorter depletion times indicate a different
mode of star formation in the early universe - most likely dynamically
driven by compressive, high-dispersion gas motions - a natural
consequence of the high gas accretion rates.
Description:
Our sample of 145 galaxies is taken from the COSMOS 2 deg2 survey
(Scoville et al. 2007ApJS..172....1S 2007ApJS..172....1S). This survey field has excellent
photometric redshifts (Ilbert et al. 2013, J/A+A/556/A55; Laigle 2016,
A&A submitted) derived from deep 34-band (UV-Mid IR) photometry. The
galaxies were selected to sample stellar masses Mstellar in the range
0.2-4x1011M☉ and the range of SFRs at each stellar mass.
The ALMA Cycle 2 observations (#2013.1.00034.S) were obtained in
2014-2015. The z=1.15 and 2.2 samples were observed in Band 7 (345 GHz)
and the z=4.4 sample in Band 6 (240 GHz). On-source integration times
were ∼2 minutes per galaxy and average rms sensitivities were 0.152
(Band 7) and 0.065 mJy/beam (Band 6). Synthesized beam sizes were ∼0.6"-1".
Data were calibrated and imaged with natural weighting using CASA.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table6.dat 83 58 Low-z Galaxy Sample in Band 7 (345 GHz)
table7.dat 83 64 Mid-z Galaxy Sample in Band 7 (345 GHz)
table8.dat 83 23 High-z Galaxy Sample in Band 6 (240 GHz)
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See also:
J/A+A/556/A55 : Multi-color photometry of star-forming galaxies
(Ilbert+, 2013)
J/A+A/592/A122 : Starburst galaxies in the COSMOS field (Hinojosa-Goni+, 2016)
J/ApJ/839/58 : ALMA submm galaxies multi-wavelength data (Simpson+, 2017)
Byte-by-byte Description of file: table6.dat table7.dat table8.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- Num [6496/985857] Observation number
8- 15 F8.4 deg RAdeg Right Ascension in decimal degrees (J2000)
17- 22 F6.4 deg DEdeg Declination in decimal degrees (J2000)
24- 27 F4.2 --- zphot Photometric redshift (1)
29- 33 F5.2 mJy STot Total flux density at 345GHz (Band 7,
tables 6,7) and at 240GHz (Band 6, table 8)
35- 38 F4.2 mJy e_STot Uncertainty in STot
40- 43 F4.2 mJy Speak Peak flux density at 345GHz (Band 7,
tables 6,7) and at 240GHz (Band 6, table 8)
45- 48 F4.2 mJy e_Speak Uncertainty in Speak
50- 55 F6.2 --- S/N Signal-to-noise ratio (2)
57- 60 F4.2 10+11Msun M* Stellar mass (1)
62- 65 F4.2 [Msun/yr] logSFR Star formation rate (1)
67- 71 F5.2 --- sSFR Specific star formation rate (SFR/M*)
(in sSFRMS units)
73 A1 --- l_Mmol [<] Limit flag on Mmol
74- 78 F5.2 10+10Msun Mmol Molecular gas mass
80- 83 F4.2 10+10Msun e_Mmol ? Uncertainty in Mmol
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Note (1): The photometric redshifts and stellar masses of the galaxies are from
Ilbert et al. (2013, J/A+A/556/A55) and the accuracy of those
quantities is discussed in detail there.
The SFRs are derived from the rest-frame UV continuum and the infrared
using Herschel PACS and SPIRE data as detailed in Scoville et al.
(2013ApJS..206....3S 2013ApJS..206....3S).
All of the galaxies have greater than 10σ photometry
measurements, and so the uncertainties in M* and SFR associated with
their measurements are always less than 10%. As discussed in
Ilbert et al. (2013, J/A+A/556/A55), the uncertainties in models used
to derive the M* and SFR from the photometry are larger but generally
less than a factor of 2.
Note (2): S/Ntot and S/Npeak are calculated separately and the column S/N
lists the larger in absolute magnitude of those two S/Ns. Note that
we let the S/N be negative in cases where the flux estimate is
negative so that several sigma negative flux values do not end up with
a positive S/N above the detection thresholds.
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 06-Feb-2018