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1. Central concentration of warm and dense molecular gas in a strongly lensed submillimeter galaxy at z = 6

   https://doi.org/10.1093/pasj/psac082  

   Tsujita, Akiyoshi ; Tadaki, Ken-ichi ; Kohno, Kotaro ; Hatsukade, Bunyo ; Egusa, Fumi ; Tamura, Yoichi ; Nishimura, Yuri ; Zavala, Jorge ; Saito, Toshiki ; Umehata, Hideki ; et al ( October 2022 , Publications of the Astronomical Society of Japan)

   We report the detection of the CO(12–11) line emission toward G09-83808 (or H-ATLAS J090045.4+004125), a strongly-lensed submillimeter galaxy at z = 6.02, with Atacama Large Millimeter/submillimeter Array observations. Combining previously detected [O iii] 88 μm, [N ii] 205 μm, and dust continuum at 0.6 mm and 1.5 mm, we investigate the physical properties of the multi-phase interstellar medium in G09-83808. A source-plane reconstruction reveals that the region of the CO(12–11) emission is compact ($R_\mathrm{{e, CO}}=0.49^{+0.29}_{-0.19}\:\mbox{kpc}$) and roughly coincides with that of the dust continuum. Non-local thermodynamic equilibrium radiative transfer modeling of CO spectral-line energy distribution reveals that most of the CO(12–11) emission comes from a warm (kinetic temperature of Tkin = 320 ± 170 K) and dense [log (nH2/cm−3) = 5.4 ± 0.6] gas, indicating that the warm and dense molecular gas is concentrated in the central 0.5 kpc region. The luminosity ratio in G09-83808 is estimated to be LCO(12-11)/LCO(6-5) = 1.1 ± 0.2. The high ratio is consistent with those in local active galactic nuclei (AGNs) and 6 < z < 7 quasars, the fact of which implies that G09-83808 would be a good target to explore dust-obscured AGNs in the epoch of reionization. In the reconstructed [O iii] 88 μm and [N ii] 205 μm cubes, we also find that a monotonic velocity gradientmore »is extending over the central starburst region by a factor of 2 and that star-forming sub-components exist. High-resolution observations of bright [C ii] 158 μm line emissions will enable us to characterize the kinematics of a possible rotating disk and the nature of the sub-components.

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2. Millimeter methanol emission in the high-mass young stellar object G24.33+0.14

   https://doi.org/10.1093/pasj/psac067  

   Hirota, Tomoya ; Wolak, Pawel ; Hunter, Todd R. ; Brogan, Crystal L. ; Bartkiewicz, Anna ; Durjasz, Michal ; Kobak, Agnieszka ; Olech, Mateusz ; Szymczak, Marian ; Burns, Ross A. ; et al ( September 2022 , Publications of the Astronomical Society of Japan)

   In 2019 September, a sudden flare of the 6.7 GHz methanol maser was observed toward the high-mass young stellar object (HMYSO) G24.33+0.14. This may represent the fourth detection of a transient mass accretion event in an HMYSO after S255IR NIRS3, NGC 6334I-MM1, and G358.93−0.03-MM1. G24.33+0.14 is unique among these sources as it clearly shows a repeating flare with an 8 yr interval. Using the Atacama Large Millimeter/submillimeter Array (ALMA), we observed the millimeter continuum and molecular lines toward G24.33+0.14 in the pre-flare phase in 2016 August (ALMA Cycle 3) and the mid-flare phase in 2019 September (ALMA Cycle 6). We identified three continuum sources in G24.33+0.14, and the brightest source, C1, which is closely associated with the 6.7 GHz maser emission, shows only a marginal increase in flux density with a flux ratio (Cycle 6$/$Cycle 3) of 1.16 ± 0.01, considering an additional absolute flux calibration uncertainty of $10\%$. We identified 26 transitions from 13 molecular species other than methanol, and they exhibit similar levels of flux differences with an average flux ratio of 1.12 ± 0.15. In contrast, eight methanol lines observed in Cycle 6 are brighter than those in Cycle 3 with an average flux ratio of 1.23 ± 0.13, and the higher excitation lines tend to showmore »a larger flux increase. If this systematic increasing trend is real, it would suggest radiative heating close to the central HMYSO due to an accretion event which could expand the size of the emission region and/or change the excitation conditions. Given the low brightness temperatures and small flux changes, most of the methanol emission is likely to be predominantly thermal, except for the 229.759 GHz (8−1–70 E) line known as a class I methanol maser. The flux change in the millimeter continuum of G24.33+0.14 is smaller than in S255IR NIRS3 and NGC 6334I-MM1 but is comparable with that in G358.93−0.03-MM1, suggesting different amounts of accreted mass in these events.

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3. Thermal formaldehyde emission in NGC 7538 IRS 1

   https://doi.org/10.1093/mnras/stab933  

   Shuvo, Onic I ; Araya, E D ; Tan, W S ; Hofner, P ; Kurtz, S ; Pihlström, Y M ; Hoffman, I M ( April 2021 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Spectral lines from formaldehyde (H2CO) molecules at cm wavelengths are typically detected in absorption and trace a broad range of environments, from diffuse gas to giant molecular clouds. In contrast, thermal emission of formaldehyde lines at cm wavelengths is rare. In previous observations with the 100 m Robert C. Byrd Green Bank Telescope (GBT), we detected 2 cm formaldehyde emission towards NGC 7538 IRS1 – a high-mass protostellar object in a prominent star-forming region of our Galaxy. We present further GBT observations of the 2 and 1 cm H2CO lines to investigate the nature of the 2 cm H2CO emission. We conducted observations to constrain the angular size of the 2 cm emission region based on a East–West and North–South cross-scan map. Gaussian fits of the spatial distribution in the East–West direction show a deconvolved size (at half maximum) of the 2 cm emission of 50 arcsec ± 8 arcsec. The 1 cm H2CO observations revealed emission superimposed on a weak absorption feature. A non-LTE radiative transfer analysis shows that the H2CO emission is consistent with quasi-thermal radiation from dense gas (${\sim}10^5$–$10^6$ cm−3). We also report detection of four transitions of CH3OH (12.2, 26.8, 28.3, 28.9 GHz), the (8,8) transition of NH3 (26.5 GHz), and a cross-scan map of the 13 GHzmore »SO line that shows extended emission (>50 arcsec).« less
4. ALMA multiline survey of the ISM in two quasar host–companion galaxy pairs at z > 6

   https://doi.org/10.1051/0004-6361/202039696  

   Pensabene, A. ; Decarli, R. ; Bañados, E. ; Venemans, B. ; Walter, F. ; Bertoldi, F. ; Fan, X. ; Farina, E. P. ; Li, J. ; Mazzucchelli, C. ; et al ( August 2021 , Astronomy & Astrophysics)

   We present a multiline survey of the interstellar medium (ISM) in two z  > 6 quasar host galaxies, PJ231−20 ( z  = 6.59) and PJ308−21 ( z  = 6.23), and their two companion galaxies. Observations were carried out using the Atacama Large (sub-)Millimeter Array (ALMA). We targeted 11 transitions including atomic fine-structure lines (FSLs) and molecular lines: [NII] 205 μm , [CI] 369 μm , CO ( J up  = 7, 10, 15, 16), H 2 O 3 12  − 2 21 , 3 21  − 3 12 , 3 03  − 2 12 , and the OH 163 μm doublet. The underlying far-infrared (FIR) continuum samples the Rayleigh-Jeans tail of the respective dust emission. By combining this information with our earlier ALMA [CII] 158 μm observations, we explored the effects of star formation and black hole feedback on the ISM of the galaxies using the CLOUDY radiative transfer models. We estimated dust masses, spectral indexes, IR luminosities, and star-formation rates from the FIR continuum. The analysis of the FSLs indicates that the [CII] 158 μm and [CI] 369 μm emission arises predominantly from the neutral medium in photodissociation regions (PDRs). We find that line deficits agree with those of local luminous IR galaxies. The CO spectral line energy distributions (SLEDs) reveal significant high- J COmore »excitation in both quasar hosts. Our CO SLED modeling of the quasar PJ231−20 shows that PDRs dominate the molecular mass and CO luminosities for J up  ≤ 7, while the J up  ≥ 10 CO emission is likely driven by X-ray dissociation regions produced by the active galactic nucleus (AGN) at the very center of the quasar host. The J up  > 10 lines are undetected in the other galaxies in our study. The H 2 O 3 21  − 3 12 line detection in the same quasar places this object on the L H 2 O  −  L TIR relation found for low- z sources, thus suggesting that this water vapor transition is predominantly excited by IR pumping. Models of the H 2 O SLED and of the H 2 O-to-OH 163 μm ratio point to PDR contributions with high volume and column density ( n H  ∼ 0.8 × 10 5 cm −3 , N H  = 10 24 cm −2 ) in an intense radiation field. Our analysis suggests a less highly excited medium in the companion galaxies. However, the current data do not allow us to definitively rule out an AGN in these sources, as suggested by previous studies of the same objects. This work demonstrates the power of multiline studies of FIR diagnostics in order to dissect the physical conditions in the first massive galaxies emerging from cosmic dawn.« less
5. Discovery of 22 GHz Water Masers in the Serpens South Region

   https://doi.org/10.3847/1538-3881/ac052c  

   Ortiz-León, Gisela N. ; Plunkett, Adele L. ; Loinard, Laurent ; Dzib, Sergio A. ; Rodríguez-Garza, Carolina B. ; Pillai, Thushara ; Gong, Yan ; Brunthaler, Andreas ( July 2021 , The Astronomical Journal)

   Abstract Using the Karl G. Jansky Very Large Array (VLA), we have conducted a survey for 22 GHz, 6 1,6 –5 2,3 H 2 O masers toward the Serpens South region. The masers were also observed with the Very Long Baseline Array following the VLA detections. We detect for the first time H 2 O masers in the Serpens South region that are found to be associated to three Class 0–Class I objects, including the two brightest protostars in the Serpens South cluster, known as CARMA-6 and CARMA-7. We also detect H 2 O masers associated to a source with no outflow or jet features. We suggest that this source is most probably a background asymptotic giant branch star projected in the direction of Serpens South. The spatial distribution of the emission spots suggest that the masers in the three Class 0–Class I objects emerge very close to the protostars and are likely excited in shocks driven by the interaction between a protostellar jet and the circumstellar material. Based on the comparison of the distributions of bolometric luminosity of sources hosting 22 GHz H 2 O masers and 162 young stellar objects covered by our observations, we identify a limitmore »of L Bol ≈ 10 L ⊙ for a source to host water masers. However, the maser emission shows strong variability in both intensity and velocity spread, and therefore masers associated to lower-luminosity sources may have been missed by our observations. We also report 11 new sources with radio continuum emission at 22 GHz.« less