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1. The ALPINE-ALMA [C  ii ] survey: Investigation of 10 galaxies at z ∼ 4.5 with [O  ii ] and [C  ii ] line emission − ISM properties and [O  ii ]−SFR relation

   https://doi.org/10.1093/mnras/stac071  

   Vanderhoof, Brittany N; Faisst, A L; Shen, L; Lemaux, B C; Béthermin, M; Capak, P L; Cassata, P; Le Fèvre, O; Schaerer, D; Silverman, J; et al (February 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present 10 main-sequence ALPINE galaxies (log (M/M⊙) = 9.2−11.1 and $${\rm SFR}=23-190\, {\rm M_{\odot }\, yr^{-1}}$$) at z ∼ 4.5 with optical [O ii] measurements from Keck/MOSFIRE spectroscopy and Subaru/MOIRCS narrow-band imaging. This is the largest such multiwavelength sample at these redshifts, combining various measurements in the ultraviolet, optical, and far-infrared including [C ii]158 $$\mu$$m line emission and dust continuum from ALMA and H α emission from Spitzer photometry. For the first time, this unique sample allows us to analyse the relation between [O ii] and total star-formation rate (SFR) and the interstellar medium (ISM) properties via [O ii]/[C ii] and [O ii]/H α luminosity ratios at z ∼ 4.5. The [O ii]−SFR relation at z ∼ 4.5 cannot be described using standard local descriptions, but is consistent with a metal-dependent relation assuming metallicities around $$50{{\ \rm per\ cent}}$$ solar. To explain the measured dust-corrected luminosity ratios of $$\log (L_{\rm [OII]}/L_{\rm [CII]}) \sim 0.98^{+0.21}_{-0.22}$$ and $$\log (L_{\rm [OII]}/L_{\rm H\alpha }) \sim -0.22^{+0.13}_{-0.15}$$ for our sample, ionization parameters log (U) < −2 and electron densities $$\log (\rm n_e / {\rm [cm^{-3}]}) \sim 2.5-3$$ are required. The former is consistent with galaxies at z ∼ 2−3, however lower than at z > 6. The latter may be slightly higher than expected given the galaxies’ specific SFR. The analysis of this pilot sample suggests that typical log (M/M⊙) > 9 galaxies at z ∼ 4.5 to have broadly similar ISM properties as their descendants at z ∼ 2 and suggest a strong evolution of ISM properties since the epoch of reionization at z > 6. 

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2. The ALPINE−ALMA [C ii] Survey: on the nature of an extremely obscured serendipitous galaxy

   https://doi.org/10.1093/mnras/staa1546  

   Romano, M; Cassata, P; Morselli, L; Lemaux, B C; Béthermin, M; Capak, P; Faisst, A; Le Fèvre, O; Schaerer, D; Silverman, J; et al (July 2020, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We report the serendipitous discovery of a dust-obscured galaxy observed as part of the Atacama Large Millimeter Array (ALMA) Large Program to INvestigate [C ii] at Early times (ALPINE). While this galaxy is detected both in line and continuum emissions in ALMA Band 7, it is completely dark in the observed optical/near-infrared bands and only shows a significant detection in the UltraVISTA Ks band. We discuss the nature of the observed ALMA line, that is [C ii] at $$z$$ ∼ 4.6 or high-J CO transitions at $$z$$ ∼ 2.2. In the first case, we find a [C ii]/FIR luminosity ratio of $$\mathrm{log}{(L_{[\mathrm{ C}\, \rm {\small {II}}]}/L_{\mathrm{ FIR}})} \sim -2.5$$, consistent with the average value for local star-forming galaxies (SFGs). In the second case instead, the source would lie at larger CO luminosities than those expected for local SFGs and high-z submillimetre galaxies. At both redshifts, we derive the star formation rate (SFR) from the ALMA continuum and the physical parameters of the galaxy, such as the stellar mass (M*), by fitting its spectral energy distribution. Exploiting the results of this work, we believe that our source is a ‘main-sequence’, dusty SFG at $$z$$ = 4.6 (i.e. [C ii] emitter) with $$\mathrm{log(SFR/M_{\odot }\, yr^{-1})}\sim 1.4$$ and log(M*/M⊙) ∼ 9.9. As a support to this scenario our galaxy, if at this redshift, lies in a massive protocluster recently discovered at $$z$$ ∼ 4.57, at only ∼1 proper Mpc from its centre. This work underlines the crucial role of the ALPINE survey in making a census of this class of objects, in order to unveil their contribution to the global SFR density at the end of the Reionization epoch. 

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3. Molecular gas in AzTEC/C159: a star-forming disk galaxy 1.3Gyr after the Big Bang

   Jiménez-Andrade, E. F.; Magnelli, B.; Karim, A.; Jones, G. C.; Carilli, C. L.; Romano-Díaz, E.; Gómez-Guijarro, C.; Toft, S.; Bertoldi, F.; Riechers, D. A.; et al (January 2018, Astronomy & astrophysics)

   We studied the molecular gas properties of AzTEC/C159, a star-forming disk galaxy at $z=4.567$. We secured $$^{12}$$CO molecular line detections for the $$J=2\to1$$ and $$J=5\to4$$ transitions using the Karl G. Jansky VLA and the NOEMA interferometer. The broad (FWHM$$\sim750\,{\rm km\,s}^{-1}$$) and tentative double-peaked profiles of both $$^{12}$$CO lines are consistent with an extended molecular gas reservoir, which is distributed in a rotating disk as previously revealed from [CII] 158$$\mu$$m line observations. Based on the $$^{12}$$CO(2$$\to$$1) emission line we derived $$L'_{\rm{CO}}=(3.4\pm0.6)\times10^{10}{\rm \,K\,km\,s}^{-1}{\rm \,pc}^{2}$$, that yields a molecular gas mass of $$M_{\rm H_2 }(\alpha_{\rm CO}/4.3)=(1.5\pm0.3)\times 10^{11}{\rm M}_\odot$$ and unveils a gas-rich system with $$\mu_{\rm gas}(\alpha_{\rm CO}/4.3)\equiv M_{\rm H_2}/M_\star=3.3\pm0.7$$. The extreme star formation efficiency (SFE) of AzTEC/C159, parametrized by the ratio $$L_{\rm{IR}}/L'_{\rm{CO}}=(216\pm80)\, {\rm L}_{\odot}{\rm \,(K\,km\,s}^{-1}{\rm \,pc}^{2})^{-1}$$, is comparable to merger-driven starbursts such as local ultra-luminous infrared galaxies (ULIRGs) and SMGs. Likewise, the $$^{12}$$CO(5$$\to$$4)/CO(2$$\to$$1) line brightness temperature ratio of $$r_{52}= 0.55\pm 0.15$$ is consistent with high excitation conditions, similar to that observed in SMGs. We constrained the value for the $$L'_{\text{CO}}-{\rm H}_2$$ mass conversion factor in AzTEC/C159, i.e. $$\alpha_{\text{CO}}=3.9^{+2.7}_{-1.3}{\rm \,M}_{\odot}{\rm \,K}^{-1}{\rm \,km}^{-1}{\rm \,s\,pc}^{-2}$$, that is consistent with a self-gravitating molecular gas distribution as observed in local star-forming disk galaxies. Cold gas streams from cosmological filaments might be fueling a gravitationally unstable gas-rich disk in AzTEC/C159, which breaks into giant clumps forming stars as efficiently as in merger-driven systems and generate high gas excitation. 

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4. The ‘Red Radio Ring’: ionized and molecular gas in a starburst/active galactic nucleus at z ∼ 2.55

   https://doi.org/10.1093/mnras/stz1740  

   Harrington, Kevin C; Vishwas, A; Weiß, A; Magnelli, B; Grassitelli, L; Zajaček, M; Jiménez-Andrade, E F; Leung, T K; Bertoldi, F; Romano-Díaz, E; et al (July 2019, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We report the detection of the far-infrared (FIR) fine-structure line of singly ionized nitrogen, [N ii] 205 $$\mu$$m , within the peak epoch of galaxy assembly, from a strongly lensed galaxy, hereafter ‘The Red Radio Ring’; the RRR, at z = 2.55. We combine new observations of the ground-state and mid-J transitions of CO (Jup = 1, 5, 8), and the FIR spectral energy distribution (SED), to explore the multiphase interstellar medium (ISM) properties of the RRR. All line profiles suggest that the H ii regions, traced by [N ii] 205 $$\mu$$m , and the (diffuse and dense) molecular gas, traced by CO, are cospatial when averaged over kpc-sized regions. Using its mid-IR-to-millimetre (mm) SED, we derive a non-negligible dust attenuation of the [N ii] 205 $$\mu$$m line emission. Assuming a uniform dust screen approximation results a mean molecular gas column density >1024 cm−2, with a molecular gas-to-dust mass ratio of 100. It is clear that dust attenuation corrections should be accounted for when studying FIR fine-structure lines in such systems. The attenuation corrected ratio of $$L_{\rm N\,{\small II}205} / L_{\rm IR(8\!-\!1000\, \mu m)} = 2.7 \times 10^{-4}$$ is consistent with the dispersion of local and z > 4 SFGs. We find that the lower limit, [N ii] 205 $$\mu$$m -based star formation rate (SFR) is less than the IR-derived SFR by a factor of 4. Finally, the dust SED, CO line SED, and $$L_{\rm N\,{\small II}205}$$ line-to-IR luminosity ratio of the RRR is consistent with a starburst-powered ISM. 

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5. The dual role of starburst and active galactic nuclei in driving extreme molecular outflows

   Gowardhan, Avani; Spoon, Henrik; Riechers, Dominik A.; González-Alfonso, Eduardo; Farrah, Duncan; Fischer, Jacqueline; Darling, Jeremy; Fergulio, Chiara; Afonso, Jose; Bizzocchi, Luca (January 2018, The Astrophysical journal)

   We report molecular gas observations of IRAS 20100-4156 and IRAS 03158+4227, two local ultraluminous infrared galaxies (ULIRGs) hosting some of the fastest and most massive molecular outflows known. Using ALMA and PdBI observations, we spatially resolve the CO(1-0) emission from the outflowing molecular gas in both and find maximum outflow velocities of $$ v_{\rm max} \sim 1600$$ and $$\sim 1700$$ km/s for IRAS 20100-4156 and IRAS 03158+4227, respectively. We find total gas mass outflow rates of $$\dot M_{\rm OF} \sim 670$$ and $$\sim 350$$ Msun/yr, respectively, corresponding to molecular gas depletion timescales $$\tau^{\rm dep}_{\rm OF} \sim 11$$ and $$\sim 16$$ Myr. This is nearly 3 times shorter than the depletion timescales implied by star formation, $$\tau^{\rm dep}_{\rm SFR} \sim 33$$ and $$\sim 46$$ Myr, respectively. To determine the outflow driving mechanism, we compare the starburst ($$L_{*}$$) and AGN ($$L_{\rm AGN}$$) luminosities to the outflowing energy and momentum fluxes, using mid-infrared spectral decomposition to discern $$L_{\rm AGN}$$. Comparison to other molecular outflows in ULIRGs reveals that outflow properties correlate similarly with $$L_{*}$$ and $$L_{\rm IR}$$ as with $$L_{\rm AGN}$$, indicating that AGN luminosity alone may not be a good tracer of feedback strength and that a combination of AGN and starburst activity may be driving the most powerful molecular outflows. We also detect the OH 1.667 GHz maser line from both sources and demonstrate its utility in detecting molecular outflows. 

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