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1. Rise of the Titans: Gas Excitation and Feedback in a Binary Hyperluminous Dusty Starburst Galaxy at z ∼ 6

   https://doi.org/10.3847/1538-4357/abcf2e  

   Riechers, Dominik A.; Nayyeri, Hooshang; Burgarella, Denis; Emonts, Bjorn H.; Clements, David L.; Cooray, Asantha; Ivison, Rob J.; Oliver, Seb; Pérez-Fournon, Ismael; Rigopoulou, Dimitra; et al (January 2021, The Astrophysical Journal)

   Abstract We report new observations toward the hyperluminous dusty starbursting major merger ADFS-27 ( z  = 5.655), using the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA). We detect CO ( J  = 2 → 1), CO ( J  = 8 → 7), CO ( J  = 9 → 8), CO ( J  = 10 → 9), and H 2 O (3 12  → 2 21 ) emission, and a P Cygni−shaped OH + (1 1  → 0 1 ) absorption/emission feature. We also tentatively detect H 2 O (3 21  → 3 12 ) and OH + (1 2 → 0 1 ) emission and CH + ( J  = 1 → 0) absorption. We find a total cold molecular mass of M gas  = (2.1 ± 0.2) × 10 11 ( α CO /1.0) M ⊙ . We also find that the excitation of the star-forming gas is overall moderate for a z > 5 dusty starburst, which is consistent with its moderate dust temperature. A high-density, high kinetic temperature gas component embedded in the gas reservoir is required to fully explain the CO line ladder. This component is likely associated with the “maximum starburst” nuclei in the two merging galaxies, which are separated by only 140 ± 13 km s −1 along the line of sight and 9.0 kpc in projection. The kinematic structure of both components is consistent with galaxy disks, but this interpretation remains limited by the spatial resolution of the current data. The OH + features are only detected toward the northern component, which is also the one that is more enshrouded in dust and thus remains undetected up to 1.6 μ m even in our sensitive new Hubble Space Telescope Wide Field Camera 3 imaging. The absorption component of the OH + line is blueshifted and peaks near the CO and continuum emission peak, while the emission is redshifted and peaks offset by 1.7 kpc from the CO and continuum emission peak, suggesting that the gas is associated with a massive molecular outflow from the intensely star-forming nucleus that supplies 125 M ⊙ yr −1 of enriched gas to its halo. 

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2. Close-up view of a luminous star-forming galaxy at z = 2.95

   https://doi.org/10.1051/0004-6361/202039743  

   Berta, S.; Young, A. J.; Cox, P.; Neri, R.; Jones, B. M.; Baker, A. J.; Omont, A.; Dunne, L.; Carnero Rosell, A.; Marchetti, L.; et al (February 2021, Astronomy & Astrophysics)

   Exploiting the sensitivity of the IRAM NOrthern Extended Millimeter Array (NOEMA) and its ability to process large instantaneous bandwidths, we have studied the morphology and other properties of the molecular gas and dust in the star forming galaxy, H-ATLAS J131611.5+281219 (HerBS-89a), at z = 2.95. High angular resolution (0 . ″3) images reveal a partial 1 . ″0 diameter Einstein ring in the dust continuum emission and the molecular emission lines of 12 CO(9−8) and H 2 O(2 02  − 1 11 ). Together with lower angular resolution (0 . ″6) images, we report the detection of a series of molecular lines including the three fundamental transitions of the molecular ion OH + , namely (1 1  − 0 1 ), (1 2  − 0 1 ), and (1 0  − 0 1 ), seen in absorption; the molecular ion CH + (1 − 0) seen in absorption, and tentatively in emission; two transitions of amidogen (NH 2 ), namely (2 02  − 1 11 ) and (2 20  − 2 11 ) seen in emission; and HCN(11 − 10) and/or NH(1 2  − 0 1 ) seen in absorption. The NOEMA data are complemented with Very Large Array data tracing the 12 CO(1 − 0) emission line, which provides a measurement of the total mass of molecular gas and an anchor for a CO excitation analysis. In addition, we present Hubble Space Telescope imaging that reveals the foreground lensing galaxy in the near-infrared (1.15  μ m). Together with photometric data from the Gran Telescopio Canarias, we derive a photometric redshift of z phot = 0.9 −0.5 +0.3 for the foreground lensing galaxy. Modeling the lensing of HerBS-89a, we reconstruct the dust continuum (magnified by a factor μ  ≃ 5.0) and molecular emission lines (magnified by μ  ∼ 4 − 5) in the source plane, which probe scales of ∼0 . ″1 (or 800 pc). The 12 CO(9 − 8) and H 2 O(2 02  − 1 11 ) emission lines have comparable spatial and kinematic distributions; the source-plane reconstructions do not clearly distinguish between a one-component and a two-component scenario, but the latter, which reveals two compact rotating components with sizes of ≈1 kpc that are likely merging, more naturally accounts for the broad line widths observed in HerBS-89a. In the core of HerBS-89a, very dense gas with n H 2  ∼ 10 7 − 9 cm −3 is revealed by the NH 2 emission lines and the possible HCN(11 − 10) absorption line. HerBS-89a is a powerful star forming galaxy with a molecular gas mass of M mol  = (2.1 ± 0.4) × 10 11   M ⊙ , an infrared luminosity of L IR  = (4.6 ± 0.4) × 10 12   L ⊙ , and a dust mass of M dust  = (2.6 ± 0.2) × 10 9   M ⊙ , yielding a dust-to-gas ratio δ GDR  ≈ 80. We derive a star formation rate SFR = 614 ± 59  M ⊙ yr −1 and a depletion timescale τ depl  = (3.4 ± 1.0) × 10 8 years. The OH + and CH + absorption lines, which trace low (∼100 cm −3 ) density molecular gas, all have their main velocity component red-shifted by Δ V  ∼ 100 km s −1 relative to the global CO reservoir. We argue that these absorption lines trace a rare example of gas inflow toward the center of a galaxy, indicating that HerBS-89a is accreting gas from its surroundings. 

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3. Cold gas disks in main-sequence galaxies at cosmic noon: Low turbulence, flat rotation curves, and disk-halo degeneracy

   https://doi.org/10.1051/0004-6361/202245105  

   Lelli, Federico; Zhang, Zhi-Yu; Bisbas, Thomas G.; Lin, Lingrui; Papadopoulos, Padelis; Schombert, James M.; Di Teodoro, Enrico; Marasco, Antonino; McGaugh, Stacy S. (April 2023, Astronomy & Astrophysics)

   We study the dynamics of cold molecular gas in two main-sequence galaxies at cosmic noon (zC-488879 at z  ≃ 1.47 and zC-400569 at z  ≃ 2.24) using new high-resolution ALMA observations of multiple 12 CO transitions. For zC-400569 we also reanalyze high-quality H α data from the SINS/zC-SINF survey. We find that (1) both galaxies have regularly rotating CO disks and their rotation curves are flat out to ∼8 kpc contrary to previous results pointing to outer declines in the rotation speed V rot ; (2) the intrinsic velocity dispersions are low ( σ CO  ≲ 15 km s −1 for CO and σ Hα  ≲ 37 km s −1 for H α ) and imply V rot / σ CO  ≳ 17 − 22 yielding no significant pressure support; (3) mass models using HST images display a severe disk-halo degeneracy, that is models with inner baryon dominance and models with “cuspy” dark matter halos can fit the rotation curves equally well due to the uncertainties on stellar and gas masses; and (4) Milgromian dynamics (MOND) can successfully fit the rotation curves with the same acceleration scale a 0 measured at z  ≃ 0. The question of the amount and distribution of dark matter in high- z galaxies remains unsettled due to the limited spatial extent of the available kinematic data; we discuss the suitability of various emission lines to trace extended rotation curves at high z . Nevertheless, the properties of these two high- z galaxies (high V rot / σ V ratios, inner rotation curve shapes, bulge-to-total mass ratios) are remarkably similar to those of massive spirals at z  ≃ 0, suggesting weak dynamical evolution over more than 10 Gyr of the Universe’s lifetime. 

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4. Wide-field CO isotopologue emission and the CO-to-H ₂ factor across the nearby spiral galaxy M101

   https://doi.org/10.1051/0004-6361/202245718  

   den Brok, Jakob S.; Bigiel, Frank; Chastenet, Jérémy; Sandstrom, Karin; Leroy, Adam; Usero, Antonio; Schinnerer, Eva; Rosolowsky, Erik W.; Koch, Eric W.; Chiang, I-Da; et al (August 2023, Astronomy & Astrophysics)

   Carbon monoxide (CO) emission constitutes the most widely used tracer of the bulk molecular gas in the interstellar medium (ISM) in extragalactic studies. The CO-to-H 2 conversion factor, α 12 CO(1−0) , links the observed CO emission to the total molecular gas mass. However, no single prescription perfectly describes the variation of α 12 CO(1−0) across all environments within and across galaxies as a function of metallicity, molecular gas opacity, line excitation, and other factors. Using spectral line observations of CO and its isotopologues mapped across a nearby galaxy, we can constrain the molecular gas conditions and link them to a variation in α 12 CO(1−0) . Here, we present new, wide-field (10 × 10 arcmin 2 ) IRAM 30-m telescope 1 mm and 3 mm line observations of 12 CO, 13 CO, and C 18 O across the nearby, grand-design, spiral galaxy M101. From the CO isotopologue line ratio analysis alone, we find that selective nucleosynthesis and changes in the opacity are the main drivers of the variation in the line emission across the galaxy. In a further analysis step, we estimated α 12 CO(1−0) using different approaches, including (i) via the dust mass surface density derived from far-IR emission as an independent tracer of the total gas surface density and (ii) local thermal equilibrium (LTE) based measurements using the optically thin 13 CO(1–0) intensity. We find an average value of ⟨ α 12 CO(1 − 0) ⟩ = 4.4  ±  0.9  M ⊙  pc −2  (K km s −1 ) −1 across the disk of the galaxy, with a decrease by a factor of 10 toward the 2 kpc central region. In contrast, we find LTE-based α 12 CO(1−0) values are lower by a factor of 2–3 across the disk relative to the dust-based result. Accounting for α 12 CO(1−0) variations, we found significantly reduced molecular gas depletion time by a factor 10 in the galaxy’s center. In conclusion, our result suggests implications for commonly derived scaling relations, such as an underestimation of the slope of the Kennicutt Schmidt law, if α 12 CO(1−0) variations are not accounted for. 

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5. The Dragonfly Galaxy. III. Jet Brightening of a High-redshift Radio Source Caught in a Violent Merger of Disk Galaxies

   https://doi.org/10.3847/1538-4357/acd3ed  

   Lebowitz, Sophie; Emonts, Bjorn; Terndrup, Donald M.; Burchett, Joseph N.; Prochaska, J. Xavier; Drouart, Guillaume; Villar-Martín, Montserrat; Lehnert, Matthew; De Breuck, Carlos; Vernet, Joël; et al (July 2023, The Astrophysical Journal)

   Abstract The Dragonfly galaxy (MRC 0152-209), the most infrared-luminous radio galaxy at redshiftz∼ 2, is a merger system containing a powerful radio source and large displacements of gas. We present kiloparsec-resolution data from the Atacama Large Millimeter/submillimeter Array and the Very Large Array of carbon monoxide (6−5), dust, and synchrotron continuum, combined with Keck integral field spectroscopy. We find that the Dragonfly consists of two galaxies with rotating disks that are in the early phase of merging. The radio jet originates from the northern galaxy and brightens when it hits the disk of the southern galaxy. The Dragonfly galaxy therefore likely appears as a powerful radio galaxy because its flux is boosted into the regime of high-zradio galaxies by the jet–disk interaction. We also find a molecular outflow of (1100 ± 550)M_⊙yr⁻¹associated with the radio host galaxy, but not with the radio hot spot or southern galaxy, which is the galaxy that hosts the bulk of the star formation. Gravitational effects of the merger drive a slower and longer-lived mass displacement at a rate of (170 ± 40)M_⊙yr⁻¹, but this tidal debris contains at least as much molecular gas mass as the much faster outflow, namelyM_H2= (3 ± 1) × 10⁹(α_CO/0.8)M_⊙. This suggests that both the active-galactic-nucleus-driven outflow and mass transfer due to tidal effects are important in the evolution of the Dragonfly system. The Keck data show Lyαemission spread across 100 kpc, and Civand Heiiemission across 35 kpc, confirming the presence of a metal-rich and extended circumgalactic medium previously detected in CO(1–0). 

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