We investigate the molecular gas content of z ∼ 6 quasar host galaxies using the Institut de Radioastronomie Millimétrique Northern Extended Millimeter Array. We targeted the 3 mm dust continuum, and the line emission from CO(6–5), CO(7–6), and [C I ] 2−1 in ten infrared–luminous quasars that have been previously studied in their 1 mm dust continuum and [C II ] line emission. We detected CO(7–6) at various degrees of significance in all the targeted sources, thus doubling the number of such detections in z ∼ 6 quasars. The 3 mm to 1 mm flux density ratios are consistent with a modified black body spectrum with a dust temperature T dust ∼ 47 K and an optical depth τ ν = 0.2 at the [C II ] frequency. Our study provides us with four independent ways to estimate the molecular gas mass, M H2 , in the targeted quasars. This allows us to set constraints on various parameters used in the derivation of molecular gas mass estimates, such as the mass per luminosity ratios α CO and α [CII] , the gas-to-dust mass ratio δ g/d , and the carbon abundance [C]/H 2 . Leveraging either on the dust, CO, [C I ], or [C II ] emission yields mass estimates of the entire sample in the range M H2 ∼ 10 10 –10 11 M ⊙ . We compared the observed luminosities of dust, [C II ], [C I ], and CO(7–6) with predictions from photo-dissociation and X-ray dominated regions. We find that the former provide better model fits to our data, assuming that the bulk of the emission arises from dense ( n H > 10 4 cm −3 ) clouds with a column density N H ∼ 10 23 cm −2 , exposed to a radiation field with an intensity of G 0 ∼ 10 3 (in Habing units). Our analysis reiterates the presence of massive reservoirs of molecular gas fueling star formation and nuclear accretion in z ∼ 6 quasar host galaxies. It also highlights the power of combined 3 mm and 1 mm observations for quantitative studies of the dense gas content in massive galaxies at cosmic dawn.
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Discovery of a Highly Collimated Flow from the High-mass Protostar ISOSS J23053+5953 SMM2
Abstract We present Very Large Array C- , X- , and Q -band continuum observations, as well as 1.3 mm continuum and CO(2-1) observations with the Submillimeter Array toward the high-mass protostellar candidate ISOSS J23053+5953 SMM2. Compact centimeter continuum emission was detected near the center of the SMM2 core with a spectral index of 0.24(± 0.15) between 6 and 3.6 cm, and a radio luminosity of 1.3(±0.4) mJy kpc 2 . The 1.3 mm thermal dust emission indicates a mass of the SMM2 core of 45.8 (±13.4) M ⊙ , and a density of 7.1 (±1.2)× 10 6 cm −3 . The CO(2-1) observations reveal a large, massive molecular outflow centered on the SMM2 core. This fast outflow (>50 km s −1 from the cloud systemic velocity) is highly collimated, with a broader, lower-velocity component. The large values for outflow mass (45.2 ± 12.6 M ⊙ ) and momentum rate (6 ± 2 × 10 −3 M ⊙ km s −1 yr −1 ) derived from the CO emission are consistent with those of flows driven by high-mass YSOs. The dynamical timescale of the flow is between 1.5 and 7.2 × 10 4 yr. We also found from the C 18 O to thermal dust emission ratio that CO is depleted by a factor of about 20, possibly due to freeze-out of CO molecules on dust grains. Our data are consistent with previous findings that ISOSS J23053 + 5953 SMM2 is an emerging high-mass protostar in an early phase of evolution, with an ionized jet and a fast, highly collimated, and massive outflow.
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- NSF-PAR ID:
- 10335534
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 922
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 66
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/1538-4357/ac2366
