Dense-gas tracers and carbon isotopes in five 2.5 < z < 4 lensed dusty star-forming galaxies from the SPT SMG sample

M. Béthermin, T. R. Greve, C. De Breuck, J. D. Vieira, M. Aravena, S. C. Chapman, Chian Chou Chen, C. Dong, C. C. Hayward, Y. Hezaveh, Daniel P Marrone, D. Narayanan, K. A. Phadke, C. A. Reuter, J. S. Spilker, A. A. Stark, M. L. Strandet, A. Weiß

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Abstract

The origin of the high star formation rates (SFR) observed in high-redshift dusty star-forming galaxies is still unknown. Large fractions of dense molecular gas might provide part of the explanation, but there are few observational constraints on the amount of dense gas in high-redshift systems dominated by star formation. In this paper, we present the results of our Atacama large millimeter array (ALMA) program targeting dense-gas tracers (HCN(5-4), HCO+(5-4), and HNC(5-4)) in five strongly lensed galaxies from the South Pole Telescope (SPT) submillimeter galaxy sample. We detected two of these lines (S/N > 5) in SPT-125-47 at z = 2.51 and tentatively detected all three (S/N ∼ 3) in SPT0551-50 at z = 3.16. Since a significant fraction of our target lines is not detected, we developed a statistical method to derive unbiased mean properties of our sample taking into account both detections and non-detections. On average, the HCN(5-4) and HCO+(5-4) luminosities of our sources are a factor of ∼1.7 fainter than expected, based on the local L′HCN(5-4) - LIR relation, but this offset corresponds to only ∼2σ if we consider sample variance. We find that both the HCO+/HCN and HNC/HCN flux ratios are compatible with unity. The first ratio is expected for photo-dominated regions (PDRs) while the second is consistent with PDRs or X-ray dominated regions (XDRs) and/or mid-infrared (IR) pumping of HNC. Our sources are at the high end of the local relation between the star formation efficiency, determined using the LIR/[CI] and LIR/CO ratios, and the dense-gas fraction, estimated using the HCN/[CI] and HCN/CO ratios. Finally, in SPT0125-47, which has the highest signal-to-noise ratio, we found that the velocity profiles of the lines tracing dense (HCN, HCO+) and lower-density (CO, [CI]) molecular gas are similar. In addition to these lines, we obtained one robust and one tentative detection of 13CO(4-3) and found an average I12CO(4-3)I 13CO(4-3) flux ratio of 26.1-3.5 +4.5, indicating a young but not pristine interstellar medium. We argue that the combination of large and slightly enriched gas reservoirs and high dense-gas fractions could explain the prodigious star formation in these systems.

Original languageEnglish (US)
Article numberA115
JournalAstronomy and Astrophysics
Volume620
DOIs
StatePublished - Dec 1 2018

Fingerprint

carbon isotopes
tracers
carbon isotope
poles
isotopes
tracer
telescopes
galaxies
stars
star formation
gases
gas
molecular gases
star formation rate
tracing
unity
velocity profile
pumping
signal to noise ratios
signal-to-noise ratio

Keywords

  • Galaxies: High-redshift
  • Galaxies: ISM
  • Galaxies: Star formation
  • Galaxies: Starburst
  • Submillimeter: Galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Béthermin, M., Greve, T. R., De Breuck, C., Vieira, J. D., Aravena, M., Chapman, S. C., ... Weiß, A. (2018). Dense-gas tracers and carbon isotopes in five 2.5 < z < 4 lensed dusty star-forming galaxies from the SPT SMG sample. Astronomy and Astrophysics, 620, [A115]. https://doi.org/10.1051/0004-6361/201833081

Dense-gas tracers and carbon isotopes in five 2.5 < z < 4 lensed dusty star-forming galaxies from the SPT SMG sample. / Béthermin, M.; Greve, T. R.; De Breuck, C.; Vieira, J. D.; Aravena, M.; Chapman, S. C.; Chen, Chian Chou; Dong, C.; Hayward, C. C.; Hezaveh, Y.; Marrone, Daniel P; Narayanan, D.; Phadke, K. A.; Reuter, C. A.; Spilker, J. S.; Stark, A. A.; Strandet, M. L.; Weiß, A.

In: Astronomy and Astrophysics, Vol. 620, A115, 01.12.2018.

Research output: Contribution to journalArticle

Béthermin, M, Greve, TR, De Breuck, C, Vieira, JD, Aravena, M, Chapman, SC, Chen, CC, Dong, C, Hayward, CC, Hezaveh, Y, Marrone, DP, Narayanan, D, Phadke, KA, Reuter, CA, Spilker, JS, Stark, AA, Strandet, ML & Weiß, A 2018, 'Dense-gas tracers and carbon isotopes in five 2.5 < z < 4 lensed dusty star-forming galaxies from the SPT SMG sample', Astronomy and Astrophysics, vol. 620, A115. https://doi.org/10.1051/0004-6361/201833081
Béthermin, M. ; Greve, T. R. ; De Breuck, C. ; Vieira, J. D. ; Aravena, M. ; Chapman, S. C. ; Chen, Chian Chou ; Dong, C. ; Hayward, C. C. ; Hezaveh, Y. ; Marrone, Daniel P ; Narayanan, D. ; Phadke, K. A. ; Reuter, C. A. ; Spilker, J. S. ; Stark, A. A. ; Strandet, M. L. ; Weiß, A. / Dense-gas tracers and carbon isotopes in five 2.5 < z < 4 lensed dusty star-forming galaxies from the SPT SMG sample. In: Astronomy and Astrophysics. 2018 ; Vol. 620.
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TY - JOUR

T1 - Dense-gas tracers and carbon isotopes in five 2.5 < z < 4 lensed dusty star-forming galaxies from the SPT SMG sample

AU - Béthermin, M.

AU - Greve, T. R.

AU - De Breuck, C.

AU - Vieira, J. D.

AU - Aravena, M.

AU - Chapman, S. C.

AU - Chen, Chian Chou

AU - Dong, C.

AU - Hayward, C. C.

AU - Hezaveh, Y.

AU - Marrone, Daniel P

AU - Narayanan, D.

AU - Phadke, K. A.

AU - Reuter, C. A.

AU - Spilker, J. S.

AU - Stark, A. A.

AU - Strandet, M. L.

AU - Weiß, A.

PY - 2018/12/1

Y1 - 2018/12/1

N2 - The origin of the high star formation rates (SFR) observed in high-redshift dusty star-forming galaxies is still unknown. Large fractions of dense molecular gas might provide part of the explanation, but there are few observational constraints on the amount of dense gas in high-redshift systems dominated by star formation. In this paper, we present the results of our Atacama large millimeter array (ALMA) program targeting dense-gas tracers (HCN(5-4), HCO+(5-4), and HNC(5-4)) in five strongly lensed galaxies from the South Pole Telescope (SPT) submillimeter galaxy sample. We detected two of these lines (S/N > 5) in SPT-125-47 at z = 2.51 and tentatively detected all three (S/N ∼ 3) in SPT0551-50 at z = 3.16. Since a significant fraction of our target lines is not detected, we developed a statistical method to derive unbiased mean properties of our sample taking into account both detections and non-detections. On average, the HCN(5-4) and HCO+(5-4) luminosities of our sources are a factor of ∼1.7 fainter than expected, based on the local L′HCN(5-4) - LIR relation, but this offset corresponds to only ∼2σ if we consider sample variance. We find that both the HCO+/HCN and HNC/HCN flux ratios are compatible with unity. The first ratio is expected for photo-dominated regions (PDRs) while the second is consistent with PDRs or X-ray dominated regions (XDRs) and/or mid-infrared (IR) pumping of HNC. Our sources are at the high end of the local relation between the star formation efficiency, determined using the LIR/[CI] and LIR/CO ratios, and the dense-gas fraction, estimated using the HCN/[CI] and HCN/CO ratios. Finally, in SPT0125-47, which has the highest signal-to-noise ratio, we found that the velocity profiles of the lines tracing dense (HCN, HCO+) and lower-density (CO, [CI]) molecular gas are similar. In addition to these lines, we obtained one robust and one tentative detection of 13CO(4-3) and found an average I12CO(4-3)I 13CO(4-3) flux ratio of 26.1-3.5 +4.5, indicating a young but not pristine interstellar medium. We argue that the combination of large and slightly enriched gas reservoirs and high dense-gas fractions could explain the prodigious star formation in these systems.

AB - The origin of the high star formation rates (SFR) observed in high-redshift dusty star-forming galaxies is still unknown. Large fractions of dense molecular gas might provide part of the explanation, but there are few observational constraints on the amount of dense gas in high-redshift systems dominated by star formation. In this paper, we present the results of our Atacama large millimeter array (ALMA) program targeting dense-gas tracers (HCN(5-4), HCO+(5-4), and HNC(5-4)) in five strongly lensed galaxies from the South Pole Telescope (SPT) submillimeter galaxy sample. We detected two of these lines (S/N > 5) in SPT-125-47 at z = 2.51 and tentatively detected all three (S/N ∼ 3) in SPT0551-50 at z = 3.16. Since a significant fraction of our target lines is not detected, we developed a statistical method to derive unbiased mean properties of our sample taking into account both detections and non-detections. On average, the HCN(5-4) and HCO+(5-4) luminosities of our sources are a factor of ∼1.7 fainter than expected, based on the local L′HCN(5-4) - LIR relation, but this offset corresponds to only ∼2σ if we consider sample variance. We find that both the HCO+/HCN and HNC/HCN flux ratios are compatible with unity. The first ratio is expected for photo-dominated regions (PDRs) while the second is consistent with PDRs or X-ray dominated regions (XDRs) and/or mid-infrared (IR) pumping of HNC. Our sources are at the high end of the local relation between the star formation efficiency, determined using the LIR/[CI] and LIR/CO ratios, and the dense-gas fraction, estimated using the HCN/[CI] and HCN/CO ratios. Finally, in SPT0125-47, which has the highest signal-to-noise ratio, we found that the velocity profiles of the lines tracing dense (HCN, HCO+) and lower-density (CO, [CI]) molecular gas are similar. In addition to these lines, we obtained one robust and one tentative detection of 13CO(4-3) and found an average I12CO(4-3)I 13CO(4-3) flux ratio of 26.1-3.5 +4.5, indicating a young but not pristine interstellar medium. We argue that the combination of large and slightly enriched gas reservoirs and high dense-gas fractions could explain the prodigious star formation in these systems.

KW - Galaxies: High-redshift

KW - Galaxies: ISM

KW - Galaxies: Star formation

KW - Galaxies: Starburst

KW - Submillimeter: Galaxies

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