Atomic carbon as a powerful tracer of molecular gas in the high-redshift Universe: perspectives for ALMA

The bright 3P1–3P0 ([CI] 1–0) and 3P2–3P1 ([CI] 2–1) lines of atomic carbon are becoming more and more widely employed as tracers of the cold neutral gas in high-redshift galaxies. Here we present observations of these lines in the 11 galaxies of the set of Planck’s Dusty GEMS, the brightest gravitationally lensed galaxies on the extragalactic submillimeter sky probed by the Planck satellite. We have [CI] 1–0 and [CI] 2–1 measurements for seven and eight of these galaxies, respectively, including four galaxies where both lines have been measured. We use our observations to constrain the gas excitation mechanism, excitation temperatures, optical depths, atomic carbon and molecular gas masses, and carbon abundances. Ratios of LCI/LFIR are similar to those found in the local universe, and suggest that the total cooling budget through atomic carbon has not significantly changed in the last 12 Gyr. Both lines are optically thin and trace 1 − 6 × 107 M⊙ of atomic carbon. Carbon abundances, XCI, are between 2.5 and 4 × 10−5, for an ultra-luminous infrared galaxy (ULIRG) CO-to-H2 conversion factor of αCO = 0.8 M⊙ / [K km s−1 pc2]. Ratios of molecular gas masses derived from [CI] 1–0 and CO agree within the measurement uncertainties for five galaxies, and agree to better than a factor of two for another two with [CI] 1–0 measurements, after carefully taking CO excitation into account. This does not support the idea that intense, high-redshift starburst galaxies host large quantities of “CO-dark” gas. These results support the common assumptions underlying most molecular gas mass estimates made for massive, dusty, high-redshift starburst galaxies, although the good agreement between the masses obtained with both tracers cannot be taken as independent confirmation of either αCO or XCI.

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Extreme conditions in the molecular gas of lensed star-forming galaxies at z ~3

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732560 ◽

2018 ◽

Vol 615 ◽

pp. A142 ◽

Cited By ~ 7

Author(s):

Paola Andreani ◽

Edwin Retana-Montenegro ◽

Zhi-Yu Zhang ◽

Padelis Papadopoulos ◽

Chentao Yang ◽

...

Keyword(s):

Carbon Monoxide ◽

Gas Phase ◽

High Redshift ◽

Molecular Gas ◽

Extreme Conditions ◽

Atomic Carbon ◽

Power Sources ◽

High Redshift Galaxies ◽

Star Forming ◽

Nearby Galaxies

Context. Atomic carbon can be an efficient tracer of the molecular gas mass, and when combined to the detection of high-J and low-J CO lines it yields also a sensitive probe of the power sources in the molecular gas of high-redshift galaxies. Aims. The recently installed SEPIA 5 receiver at the focus of the APEX telescope has opened up a new window at frequencies 159–211 GHz allowing the exploration of the atomic carbon in high-z galaxies, at previously inaccessible frequencies from the ground. We have targeted three gravitationally lensed galaxies at redshift of about 3 and conducted a comparative study of the observed high-J CO/CI ratios with well-studied nearby galaxies. Methods. Atomic carbon (CI(2–1)) was detected in one of the three targets and marginally in a second, while in all three targets the J = 7→6 CO line is detected. Results. The CO(7–6)/CI(2–1), CO(7–6)/CO(1–0) line ratios and the CO(7–6)/(far-IR continuum) luminosity ratio are compared to those of nearby objects. A large excitation status in the ISM of these high-z objects is seen, unless differential lensing unevenly boosts the CO line fluxes from the warm and dense gas more than the CO(1–0), CI(2–1), tracing a more widely distributed cold gas phase. We provide estimates of total molecular gas masses derived from the atomic carbon and the carbon monoxide CO(1–0), which within the uncertainties turn out to be equal.

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DYNAMO Survey: An Upclose View of Clumpy Galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314009454 ◽

2014 ◽

Vol 10 (S309) ◽

pp. 129-132 ◽

Cited By ~ 1

Author(s):

David Fisher ◽

Keyword(s):

Star Formation ◽

Velocity Dispersion ◽

High Redshift ◽

Molecular Gas ◽

Gas Velocity ◽

Star Forming ◽

Turbulent Dynamo ◽

Hα Emission ◽

High Redshift Universe ◽

Gas Fractions

AbstractWe highlight recent results on the DYNAMO survey of turbulent, clumpy disks galaxies found at z=0.1. Bright star forming DYNAMO galaxies are found to be very similar in properties to star forming galaxies in the high redshift Universe. Typical star formation rates of turbulent DYNAMO galaxies range 10-80 M⊙ yr−1. Roughly 2/3 of DYNAMO galaxies have Hα kinematics that are consistent with rotation. The typical gas velocity dispersion of DYNAMO galaxies is σHα ~ 20 - 60 km s−1. We show that, when convolved to the same resolution, maps of Hα emission in DYNAMO galaxies have essentially identical morphology as that of z ~ 1 - 3 galaxies. Finally, DYNAMO galaxies have high molecular gas fractions fmol ~ 20 - 35%. We note that DYNAMO galaxies are not dwarfs, typical masses are Mstar ~ 0.8 - 8 × 1010 M⊙. These data are all consistent with a scenario in which despite being at relatively low redshift the DYNAMO galaxies are forming stars similarly to that observed in the high-redshift Universe, that is to say star formation is occurring in very massive (Mclump ~ 109 M⊙), very large (rclump ~ 300 pc) clumps of gas.

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Cold gas studies of a z = 2.5 protocluster

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320004226 ◽

2020 ◽

Vol 15 (S359) ◽

pp. 136-140

Author(s):

Minju M. Lee ◽

Ichi Tanaka ◽

Rohei Kawabe

Keyword(s):

Galaxy Evolution ◽

High Redshift ◽

Kinematic Model ◽

Molecular Gas ◽

General View ◽

Massive Galaxies ◽

Star Forming ◽

Gas Kinematics ◽

Narrow Band Filter ◽

Stellar Masses

AbstractWe present studies of a protocluster at z =2.5, an overdense region found close to a radio galaxy, 4C 23.56, using ALMA. We observed 1.1 mm continuum, two CO lines (CO (4–3) and CO (3–2)) and the lower atomic carbon line transition ([CI](3P1-3P0)) at a few kpc (0″.3-0″.9) resolution. The primary targets are 25 star-forming galaxies selected as Hα emitters (HAEs) that are identified with a narrow band filter. These are massive galaxies with stellar masses of > 1010Mʘ that are mostly on the galaxy main sequence at z =2.5. We measure the molecular gas mass from the independent gas tracers of 1.1 mm, CO (3–2) and [CI], and investigate the gas kinematics of galaxies from CO (4–3). Molecular gas masses from the different measurements are consistent with each other for detection, with a gas fraction (fgas = Mgas/(Mgas+ Mstar)) of ≃ 0.5 on average but with a caveat. On the other hand, the CO line widths of the protocluster galaxies are typically broader by ˜50% compared to field galaxies, which can be attributed to more frequent, unresolved gas-rich mergers and/or smaller sizes than field galaxies, supported by our high-resolution images and a kinematic model fit of one of the galaxies. We discuss the expected scenario of galaxy evolution in protoclusters at high redshift but future large surveys are needed to get a more general view.

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The global star formation law: from dense cores to extreme starbursts

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307001688 ◽

2006 ◽

Vol 2 (S237) ◽

pp. 331-335

Author(s):

Yu Gao

Keyword(s):

Star Formation ◽

Linear Correlation ◽

Molecular Clouds ◽

High Redshift ◽

Gas Content ◽

Molecular Gas ◽

Giant Molecular Clouds ◽

Active Star ◽

Dense Cores ◽

The Galaxy

AbstractActive star formation (SF) is tightly related to the dense molecular gas in the giant molecular clouds' dense cores. Our HCN (measure of the dense molecular gas) survey in 65 galaxies (including 10 ultraluminous galaxies) reveals a tight linear correlation between HCN and IR (SF rate) luminosities, whereas the correlation between IR and CO (measure of the total molecular gas) luminosities is nonlinear. This suggests that the global SF rate depends more intimately upon the amount of dense molecular gas than the total molecular gas content. This linear relationship extends to both the dense cores in the Galaxy and the hyperluminous extreme starbursts at high-redshift. Therefore, the global SF law in dense gas appears to be linear all the way from dense cores to extreme starbursts, spanning over nine orders of magnitude in IR luminosity.

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Exploration of the high-redshift universe enabled by THESEUS

Experimental Astronomy ◽

10.1007/s10686-021-09778-w ◽

2021 ◽

Author(s):

N. R. Tanvir ◽

E. Le Floc’h ◽

L. Christensen ◽

J. Caruana ◽

R. Salvaterra ◽

...

Keyword(s):

Star Formation ◽

Gamma Ray ◽

High Redshift ◽

Formation Rate ◽

Star Forming ◽

Chemical Enrichment ◽

Long Duration ◽

Absorption Studies ◽

Population Iii Stars ◽

High Redshift Universe

AbstractAt peak, long-duration gamma-ray bursts are the most luminous sources of electromagnetic radiation known. Since their progenitors are massive stars, they provide a tracer of star formation and star-forming galaxies over the whole of cosmic history. Their bright power-law afterglows provide ideal backlights for absorption studies of the interstellar and intergalactic medium back to the reionization era. The proposed THESEUS mission is designed to detect large samples of GRBs at z > 6 in the 2030s, at a time when supporting observations with major next generation facilities will be possible, thus enabling a range of transformative science. THESEUS will allow us to explore the faint end of the luminosity function of galaxies and the star formation rate density to high redshifts; constrain the progress of re-ionisation beyond $z\gtrsim 6$ z ≳ 6 ; study in detail early chemical enrichment from stellar explosions, including signatures of Population III stars; and potentially characterize the dark energy equation of state at the highest redshifts.

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Molecular gas in the Herschel-selected strongly lensed submillimeter galaxies at z ~ 2–4 as probed by multi-J CO lines

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731391 ◽

2017 ◽

Vol 608 ◽

pp. A144 ◽

Cited By ~ 41

Author(s):

C. Yang ◽

A. Omont ◽

A. Beelen ◽

Y. Gao ◽

P. van der Werf ◽

...

Keyword(s):

Star Formation ◽

High Redshift ◽

Line Emission ◽

Far Infrared ◽

Molecular Gas ◽

Kinetic Temperature ◽

Large Area ◽

Line Energy ◽

Submillimeter Galaxies ◽

Dust Mass

We present the IRAM-30 m observations of multiple-J CO (Jup mostly from 3 up to 8) and [C I](3P2 → 3P1) ([C I](2–1) hereafter) line emission in a sample of redshift ~2–4 submillimeter galaxies (SMGs). These SMGs are selected among the brightest-lensed galaxies discovered in the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS). Forty-seven CO lines and 7 [C I](2–1) lines have been detected in 15 lensed SMGs. A non-negligible effect of differential lensing is found for the CO emission lines, which could have caused significant underestimations of the linewidths, and hence of the dynamical masses. The CO spectral line energy distributions (SLEDs), peaking around Jup ~ 5–7, are found to be similar to those of the local starburst-dominated ultra-luminous infrared galaxies and of the previously studied SMGs. After correcting for lensing amplification, we derived the global properties of the bulk of molecular gas in the SMGs using non-LTE radiative transfer modelling, such as the molecular gas density nH2 ~ 102.5–104.1 cm-3 and the kinetic temperature Tk ~ 20–750 K. The gas thermal pressure Pth ranging from~105 K cm-3 to 106 K cm-3 is found to be correlated with star formation efficiency. Further decomposing the CO SLEDs into two excitation components, we find a low-excitation component with nH2 ~ 102.8–104.6 cm-3 and Tk ~ 20–30 K, which is less correlated with star formation, and a high-excitation one (nH2 ~ 102.7–104.2 cm-3, Tk ~ 60–400 K) which is tightly related to the on-going star-forming activity. Additionally, tight linear correlations between the far-infrared and CO line luminosities have been confirmed for the Jup ≥ 5 CO lines of these SMGs, implying that these CO lines are good tracers of star formation. The [C I](2–1) lines follow the tight linear correlation between the luminosities of the [C I](2–1) and the CO(1–0) line found in local starbursts, indicating that [C I] lines could serve as good total molecular gas mass tracers for high-redshift SMGs as well. The total mass of the molecular gas reservoir, (1–30) × 1010M⊙, derived based on the CO(3–2) fluxes and αCO(1–0) = 0.8 M⊙ ( K km s-1 pc2)-1, suggests a typical molecular gas depletion time tdep ~ 20–100 Myr and a gas to dust mass ratio δGDR ~ 30–100 with ~20%–60% uncertainty for the SMGs. The ratio between CO line luminosity and the dust mass L′CO/Mdust appears to be slowly increasing with redshift for high-redshift SMGs, which need to be further confirmed by a more complete SMG sample at various redshifts. Finally, through comparing the linewidth of CO and H2O lines, we find that they agree well in almost all our SMGs, confirming that the emitting regions of the CO and H2O lines are co-spatially located.

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