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Submillimetre galaxies (SMGs) are some of the most extreme star-forming systems in the Universe, whose place in the framework of galaxy evolution is as yet uncertain. It has been hypothesized that SMGs are progenitors of local early-type galaxies, requiring that SMGs generally reside in galaxy cluster progenitors at high redshift. We test this hypothesis and explore SMG environments using a narrow-band VLT/HAWK-I+GRAAL study of H  |$\alpha$| and [O  iii ] emitters around an unbiased sample of three ALMA-identified and spectroscopically confirmed SMGs at |$z \sim 2.3$| and |$\sim 3.3$|⁠ , where these SMGs were selected solely on spectroscopic redshift. Comparing with blank-field observations at similar epochs, we find that one of the three SMGs lies in an overdensity of emission-line sources on the |$\sim 4$| Mpc scale of the HAWK-I field of view, with overdensity parameter |$\delta _{g} = 2.6^{+1.4}_{-1.2}$|⁠. A second SMG is significantly overdense only on |$\lesssim 1.6$| Mpc scales and the final SMG is consistent with residing in a blank field environment. The total masses of the two overdensities are estimated to be |$\log (M_{h}/{\rm M}_{\odot }) =$| 12.1–14.4, leading to present-day masses of |$\log (M_{h,z=0}/{\rm M}_{\odot }) =$| 12.9–15.9. These results imply that SMGs occupy a range of environments, from overdense protoclusters or protogroups to the blank field, suggesting that while some SMGs are strong candidates for the progenitors of massive elliptical galaxies in clusters, this may not be their only possible evolutionary pathway. [ABSTRACT FROM AUTHOR]

We present specific star formation rates (sSFRs) for 40 ultraviolet (UV)-bright galaxies at z ∼ 7–8 observed as part of the Reionization Era Bright Emission Line Survey (REBELS) Atacama Large Millimeter/submillimeter Array (ALMA) large programme. The sSFRs are derived using improved star formation rate (SFR) calibrations and spectral energy distribution (SED)-based stellar masses, made possible by measurements of far-infrared (FIR) continuum emission and [C  ii ]-based spectroscopic redshifts. The median sSFR of the sample is |$18_{-5}^{+7}$|  Gyr−1, significantly larger than literature measurements lacking constraints in the FIR, reflecting the larger obscured SFRs derived from the dust continuum relative to that implied by the UV+optical SED. We suggest that such differences may reflect spatial variations in dust across these luminous galaxies, with the component dominating the FIR distinct from that dominating the UV. We demonstrate that the inferred stellar masses (and hence sSFRs) are strongly dependent on the assumed star formation history in reionization-era galaxies. When large sSFR galaxies (a population that is common at z > 6) are modelled with non-parametric star formation histories, the derived stellar masses can increase by an order of magnitude relative to constant star formation models, owing to the presence of a significant old stellar population that is outshined by the recent burst. The [C  ii ] line widths in the largest sSFR systems are often very broad, suggesting dynamical masses capable of accommodating an old stellar population suggested by non-parametric models. Regardless of these systematic uncertainties among derived parameters, we find that sSFRs increase rapidly toward higher redshifts for massive galaxies (9.6 < log (M */M⊙) < 9.8), evolving as (1 + z)1.7 ± 0.3, broadly consistent with expectations from the evolving baryon accretion rates. [ABSTRACT FROM AUTHOR]

We report the detection of a massive neutral gas outflow in the z = 2.09 gravitationally lensed dusty star-forming galaxy HATLAS J085358.9+015537 (G09v1.40), seen in absorption with the OH+(11−10) transition using spatially resolved (0.″5 × 0.″4) Atacama Large Millimeter/submillimeter Array (ALMA) observations. The blueshifted OH+ line is observed simultaneously with the CO(9−8) emission line and underlying dust continuum. These data are complemented by high-angular-resolution (0.″17 × 0.″13) ALMA observations of CH+(1−0) and underlying dust continuum, and Keck 2.2 μm imaging tracing the stellar emission. The neutral outflow, dust, dense molecular gas, and stars all show spatial offsets from each other. The total atomic gas mass of the observed outflow is 6.7 × 109M⊙, >25% as massive as the gas mass of the galaxy. We find that a conical outflow geometry best describes the OH+ kinematics and morphology and derive deprojected outflow properties as functions of possible inclination (0.°38–64°). The neutral gas mass outflow rate is between 83 and 25,400 M⊙ yr−1, exceeding the star formation rate (788 ± 300 M⊙ yr−1) if the inclination is >3.°6 (mass-loading factor = 0.3–4.7). Kinetic energy and momentum fluxes span (4.4–290) × 109L⊙ and (0.1–3.7) × 1037 dyne, respectively (energy-loading factor = 0.013–16), indicating that the feedback mechanisms required to drive the outflow depend on the inclination assumed. We derive a gas depletion time between 29 and 1 Myr, but find that the neutral outflow is likely to remain bound to the galaxy unless the inclination is small and may be reaccreted if additional feedback processes do not occur. [ABSTRACT FROM AUTHOR]

The Atacama Large Millimeter/submillimeter Array (ALMA) Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS) Band 6 scan (212–272 GHz) covers potential [C ii ] emission in galaxies at 6 ≤ z ≤ 8 throughout a 2.9 arcmin2 area. By selecting on known Lyα emitters (LAEs) and photometric dropout galaxies in the field, we perform targeted searches down to a 5σ [C ii ] luminosity depth L[C II ] ∼ 2.0 × 108L⊙, corresponding roughly to star formation rates (SFRs) of 10–20 M⊙ yr−1 when applying a locally calibrated conversion for star-forming galaxies, yielding zero detections. While the majority of galaxies in this sample are characterized by lower SFRs, the resulting upper limits on [C ii ] luminosity in these sources are consistent with the current literature sample of targeted ALMA observations of z = 6–7 LAEs and Lyman-break galaxies (LBGs), as well as the locally calibrated relations between L[C ii ] and SFR—with the exception of a single [C ii ]-deficient, UV-luminous LBG. We also perform a blind search for [C ii ]-bright galaxies that may have been missed by optical selections, resulting in an upper limit on the cumulative number density of [C ii ] sources with L[C II ] > 2.0 × 108L⊙ (5σ) to be less than 1.8 × 10−4 Mpc−3 (90% confidence level). At this luminosity depth and volume coverage, we present an observed evolution of the [C ii ] luminosity function from z = 6–8 to z ∼ 0 by comparing the ASPECS measurement to literature results at lower redshift. [ABSTRACT FROM AUTHOR]

We present an ALMA 1.3 mm (Band 6) continuum survey of lensed submillimeter galaxies (SMGs) at z = 1.0 to ∼3.2 with an angular resolution of ∼0.″2. These galaxies were uncovered by the Herschel Lensing Survey and feature exceptionally bright far-infrared continuum emission (Speak ≳ 90 mJy) owing to their lensing magnification. We detect 29 sources in 20 fields of massive galaxy clusters with ALMA. Using both the Spitzer/IRAC (3.6/4.5 μm) and ALMA data, we have successfully modeled the surface brightness profiles of 26 sources in the rest-frame near- and far-infrared. Similar to previous studies, we find the median dust-to-stellar continuum size ratio to be small (Re,dust/Re,star = 0.38 ± 0.14) for the observed SMGs, indicating that star formation is centrally concentrated. This is, however, not the case for two spatially extended main-sequence SMGs with a low surface brightness at 1.3 mm (≲0.1 mJy arcsec−2), in which the star formation is distributed over the entire galaxy (Re,dust/Re,star > 1). As a whole, our SMG sample shows a tight anticorrelation between (Re,dust/Re,star) and far-infrared surface brightness (ΣIR) over a factor of ≃1000 in ΣIR. This indicates that SMGs with less vigorous star formation (i.e., lower ΣIR) lack central starburst and are likely to retain a broader spatial distribution of star formation over the whole galaxies (i.e., larger Re,dust/Re,star). The same trend can be reproduced with cosmological simulations as a result of central starburst and potentially subsequent "inside-out" quenching, which likely accounts for the emergence of compact quiescent galaxies at z ∼ 2. [ABSTRACT FROM AUTHOR]

Context. Spatially resolved observations of the ionized and molecular gas are critical for understanding the physical processes that govern the interstellar medium (ISM) in galaxies. The observation of starburst systems is also important as they present extreme gas conditions that may help to test different ISM models. However, matched resolution imaging at ∼kpc scales for both ISM gas phases are usually scarce, and the ISM properties of starbursts still remain poorly understood. Aims. We aim to study the morpho-kinematic properties of the ionized and molecular gas in three dusty starburst galaxies at z = 0.12−0.17 to explore the relation between molecular ISM gas phase dynamics and the star-formation activity. Methods. We employ two-dimensional dynamical modelling to analyse Atacama Large Millimeter/submillimiter Array CO(1–0) and seeing-limited Spectrograph for INtegral Field Observations in the Near Infrared Paschen-α (Paα) observations, tracing the molecular and ionized gas morpho-kinematics at ∼kpc-scales. We use a dynamical mass model, which accounts for beam-smearing effects, to constrain the CO-to-H2 conversion factor and estimate the molecular gas mass content. Results. One starburst galaxy shows irregular morphology, which may indicate a major merger, while the other two systems show disc-like morpho-kinematics. The two disc-like starbursts show molecular gas velocity dispersion values comparable with those seen in local luminous and ultra luminous infrared galaxies but in an ISM with molecular gas fraction and surface density values in the range of the estimates reported for local star-forming galaxies. We find that these molecular gas velocity dispersion values can be explained by assuming vertical pressure equilibrium. We also find that the star-formation activity, traced by the Paα emission line, is well correlated with the molecular gas content, suggesting an enhanced star-formation efficiency and depletion times of the order of ∼0.1−1 Gyr. We find that the star-formation rate surface density (ΣSFR) correlates with the ISM pressure set by self-gravity (Pgrav) following a power law with an exponent close to 0.8. Conclusions. In dusty disc-like starburst galaxies, our data support the scenario in which the molecular gas velocity dispersion values are driven by the ISM pressure set by self-gravity and are responsible for maintaining the vertical pressure balance. The correlation between ΣSFR and Pgrav suggests that, in these dusty starbursts galaxies, the star-formation activity arises as a consequence of the ISM pressure balance. [ABSTRACT FROM AUTHOR]

We present an Atacama Large Millimeter/submillimeter Array observation of the Submillimeter galaxy ID 141 at z = 4.24 in the [N ii ] 205 μm line (hereafter [N ii ]) and the underlying continuum at (rest-frame) 197.6 μm. Benefiting from lensing magnification by a galaxy pair at z = 0.595, ID 141 is one of the brightest SMGs. At the angular resolutions of –1.″5 (1″ ∼6.9 kpc), our observation clearly separates and moderately resolves the two lensed images in both continuum and line emission at a signal-to-noise ratio >5. Our continuum-based lensing model implies an averaged amplification factor of ∼5.8 and reveals that the delensed continuum image has a Sérsic index and Sérsic radius of ∼0.″18 (∼1.24 kpc). Furthermore, the reconstructed [N ii ] velocity field in the source plane is dominated by a rotation component with a maximum velocity of ∼300 km s−1 at large radii, indicating a dark matter halo mass of ∼10. This, together with the reconstructed velocity dispersion field being smooth and modest in value (<100 km s−1) over much of the outer parts of the galaxy, favors the interpretation of ID 141 being a disk galaxy dynamically supported by rotation. The observed [N ii ] /CO (7−6) and [N ii ] /[C ii ] 158 μm line-luminosity ratios, which are consistent with the corresponding line ratio versus far-infrared color correlation from local luminous infrared galaxies, imply a delensed star formation rate of (1.8 yr−1 and provide an independent estimate of the size of the star-forming region kpc in radius. [ABSTRACT FROM AUTHOR]

Follow-up observations of (sub-)mm-selected gravitationally lensed systems have allowed a more detailed study of the dust-enshrouded phase of star formation up to very early cosmic times. Here, the case of the gravitationally lensed merger in HATLAS J142935.3–002836 (also known as H1429−0028; z lens = 0.218, z bkg = 1.027) is revisited following recent developments in the literature and new Atacama Pathfinder EXperiment (APEX) observations targeting two carbon monoxide (CO) rotational transitions Jup = 3 and 6. We show that the line profiles comprise three distinct velocity components, where the fainter high velocity one is less magnified and more compact. The modelling of the observed spectral line energy distribution of CO Jup = 2–6 and [C  i ] 3 P 1−3 P 0 assumes a large velocity gradient scenario, where the analysis is based on four statistical approaches. Since the detected gas and dust emission comes exclusively from only one of the two merging components (the one oriented north–south, NS), we are only able to determine upper limits for the companion. The molecular gas in the NS component in H1429−0028 is found to have a temperature of ∼70 K, a volume density of log (n [cm−3]) ∼ 3.7, to be expanding at ∼10 km s−1 pc−1, and amounts to |${M_{\rm H_2} = 4_{-2}^{+3} \times 10^9\,{\rm M}_\odot }$|⁠. The CO to H2 conversion factor is estimated to be |$\alpha _{\rm CO} = 0.4_{-0.2}^{+0.3}\,$|  M⊙/(K km s−1 pc2). The NS galaxy is expected to have a factor of ≳10× more gas than its companion (⁠|${M_{\rm H_2}}\lesssim 3\times 10^8$|  M⊙). Nevertheless, the total amount of molecular gas in the system comprises only up to 15 per cent (1σ upper limit) of the total (dynamical) mass. [ABSTRACT FROM AUTHOR]

We have used the Submillimeter Array (SMA) at 860  $\mu$ m to observe the brightest sources in the Submillimeter Common User Bolometer Array-2 (SCUBA-2) Cosmology Legacy Survey (S2CLS). The goal of this survey is to exploit the large field of the S2CLS along with the resolution and sensitivity of the SMA to construct a large sample of these rare sources and to study their statistical properties. We have targeted 70 of the brightest single-dish SCUBA-2 850  $\mu$ m sources down to S850 ≈  8 mJy, achieving an average synthesized beam of 2.4 arcsec and an average rms of σ860 =  1.5 mJy beam−1 in our primary beam-corrected maps. We searched our SMA maps for 4σ peaks, corresponding to S860 ≳  6 mJy sources, and detected 62, galaxies, including three pairs. We include in our study 35 archival observations, bringing our sample size to 105 bright single-dish submillimetre sources with interferometric follow-up. We compute the cumulative and differential number counts, finding them to overlap with previous single-dish survey number counts within the uncertainties, although our cumulative number count is systematically lower than the parent S2CLS cumulative number count by 14 ±  6 per cent between 11 and 15 mJy. We estimate the probability that a ≳10 mJy single-dish submillimetre source resolves into two or more galaxies with similar flux densities to be less than 15 per cent. Assuming the remaining 85 per cent of the targets are ultraluminous starburst galaxies between z =  2 and 3, we find a likely volume density of ≳400 M⊙ yr−1 sources to be ${\sim }\,3^{+0.7}_{-0.6}\,{\times }\,10^{-7}$  Mpc−3. We show that the descendants of these galaxies could be ≳4 ×  1011 M⊙ local quiescent galaxies, and that about 10 per cent of their total stellar mass would have formed during these short bursts of star formation. [ABSTRACT FROM AUTHOR]

Gas-rich minor mergers contribute significantly to the gas reservoir of early-type galaxies (ETGs) at low redshift, yet the star formation efficiency (SFE; the star formation rate divided by the molecular gas mass) appears to be strongly suppressed following some of these events, in contrast to the more well-known merger-driven starbursts. We present observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of six ETGs, which have each recently undergone a gas-rich minor merger, as evidenced by their disturbed stellar morphologies. These galaxies were selected because they exhibit extremely low SFEs. We use the resolving power of ALMA to study the morphology and kinematics of the molecular gas. The majority of our galaxies exhibit spatial and kinematical irregularities, such as detached gas clouds, warps, and other asymmetries. These asymmetries support the interpretation that the suppression of the SFE is caused by dynamical effects stabilizing the gas against gravitational collapse. Through kinematic modelling we derive high velocity dispersions and Toomre Q stability parameters for the gas, but caution that such measurements in edge-on galaxies suffer from degeneracies. We estimate merger ages to be about 100 Myr based on the observed disturbances in the gas distribution. Furthermore, we determine that these galaxies lie, on average, two orders of magnitude below the Kennicutt-Schmidt relation for star-forming galaxies as well as below the relation for relaxed ETGs. We discuss potential dynamical processes responsible for this strong suppression of star formation surface density at fixed molecular gas surface density. [ABSTRACT FROM AUTHOR]

The Herschel Space Observatory has revealed a very different galaxyscape from that shown by optical surveys which presents a challenge for galaxy-evolution models. The Herschel surveys reveal (1) that there was rapid galaxy evolution in the very recent past and (2) that galaxies lie on a single Galaxy Sequence (GS) rather than a star-forming 'main sequence' and a separate region of 'passive' or 'red-and-dead' galaxies. The form of the GS is now clearer because far-infrared surveys such as the Herschel ATLAS pick up a population of optically red starforming galaxies that would have been classified as passive using most optical criteria. The space-density of this population is at least as high as the traditional star-forming population. By stacking spectra of H-ATLAS galaxies over the redshift range 0.001 < z < 0.4, we show that the galaxies responsible for the rapid low-redshift evolution have high stellar masses, high star-formation rates but, even several billion years in the past, old stellar populations - they are thus likely to be relatively recent ancestors of early-type galaxies in the Universe today. The form of the GS is inconsistent with rapid quenching models and neither the analytic bathtub model nor the hydrodynamical EAGLE simulation can reproduce the rapid cosmic evolution. We propose a new gentler model of galaxy evolution that can explain the new Herschel results and other key properties of the galaxy population. [ABSTRACT FROM AUTHOR]

Infrared emission is an invaluable tool for quantifying star formation in galaxies. Because the 8 μm polycyclic aromatic hydrocarbon (PAH) emission has been found to correlate with other well-known star formation tracers, it has widely been used as a star formation rate (SFR) tracer. There are, however, studies that challenge the accuracy and reliability of the 8 μm emission as a SFR tracer. Our study, part of the Herschel (Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA) M33 Extended Survey (HERM33ES) open time key program, aims at addressing this issue by analyzing the infrared emission from the nearby spiral galaxy M33 at the high spatial scale of ∼75 pc. Combining data from the Herschel Space Observatory and the Spitzer Space Telescope, we find that the 8 μm emission is better correlated with the 250 μm emission, which traces cold interstellar gas, than with the 24 μm emission. Furthermore, the L(8)/L(250) ratio is more tightly correlated with the 3.6 μm emission, a tracer of evolved stellar populations and stellar mass, than with a combination of Hα and 24 μm emission, a tracer of SFR. The L(8)/L(24) ratio is highly depressed in 24 μm luminous regions, which correlate with known H II regions. We also compare our results with the dust emission models by Draine & Li. We confirm that the depression of 8 μm PAH emission near star-forming regions is higher than what is predicted by models; this is possibly an effect of increased stellar radiation from young stars destroying the dust grains responsible for the 8 μm emission as already suggested by other authors. We find that the majority of the 8 μm emission is fully consistent with heating by the diffuse interstellar medium, similar to what recently determined for the dust emission in M31 by Draine et al. We also find that the fraction of 8 μm emission associated with the diffuse interstellar radiation field ranges between ∼60% and 80% and is 40% larger than the diffuse fraction at 24 μm. [ABSTRACT FROM AUTHOR]

We determine star formation rates (SFRs) in a sample of color-selected, star-forming (sBzK) galaxies (KAB < 21.8 in the Extended Chandra Deep Field-South. To identify and avoid active galactic nuclei, we use X-ray, IRAC color and IR/radio flux ratio selection methods. Photometric redshift-binned, average flux densities are measured wit stacking analyses in Spitzer-MIPS IR, BLAST and APEX/LABOCA submillimeter, VLA and GMRT radio, and Chandra X-ray data. We include averages of aperture fluxes in MUSYC UBVRIz JHK images to determin UV-through-radio spectral energy distributions. We determine the total IR luminosities and compare SFR calibrations from FIR, 24µm, UV, radio, and X-ray wavebands. We find consistency with our best estimator SFRIR+UV, to within errors for the preferred radio SFR calibration. Our results imply that 24 µm only and X-ray SFR estimates should be applied to high-redshift galaxies with caution. Average IR luminosities are consistent with luminous infrared galaxies. We find SFRIR+UV for our stacked sBzKs at median redshifts 1.4, 1.8, and 2.2 to b 55 ± 6 (random error), 74 ± 8, and 154 ± 17Mʘ yr-1, respectively, with additional systematic uncertainty of factor of ~2. [ABSTRACT FROM AUTHOR]

We present a joint analysis of the overlapping Balloon-borne Large Aperture Submillimetre Telescope (BLAST) 250, 350, 500 m, and LABOCA 870 m observations [from the LABOCA ECDFS Submm Survey (LESS) survey] of the Extended Chandra Deep Field-South. Out to , the BLAST filters sample near the peak wavelength of thermal far-infrared (FIR) emission from galaxies (rest-frame wavelengths 60-200 m), primarily produced by dust heated through absorption in star-forming clouds. However, identifying counterparts to individual BLAST peaks is very challenging, given the large beams [full-width at half-maximum (FWHM) 36-60 arcsec]. In contrast, the ground-based 870 m observations have a significantly smaller 19 arcsec FWHM beam, and are sensitive to higher redshifts (-5, and potentially beyond) due to the more favourable negative -correction. We use the LESS data, as well as deep Spitzer and VLA imaging, to identify 118 individual sources that produce significant emission in the BLAST bands. We characterize the temperatures and FIR luminosities for a subset of 69 sources which have well-measured submillimetre (submm) spectral energy distributions (SEDs) and redshift measurements out to . For flux-limited sub-samples in each BLAST band, and a dust emissivity index , we find a median temperature K (all bands) as well as median redshifts: (interquartile range 0.2-1.9) for mJy; (interquartile range 0.6-2.1) for mJy; and (interquartile range 1.3-2.3) for mJy. Taking into account the selection effects for our survey (a bias towards detecting lower-temperature galaxies), we find no evidence for evolution in the local FIR-temperature correlation out to . Comparing with star-forming galaxy SED templates, about 8 per cent of our sample appears to exhibit significant excesses in the radio and/or mid-IR, consistent with those sources harbouring active galactic nuclei (AGN). Since our statistical approach differs from most previous studies of submm galaxies, we describe the following techniques in two appendices: our 'matched filter' for identifying sources in the presence of point-source confusion; and our approach for identifying counterparts using likelihood ratios. This study is a direct precursor to future joint FIR/submm surveys, for which we outline a potential identification and SED measurement strategy. [ABSTRACT FROM AUTHOR]

We present results from a deep mid-infrared survey of the Hubble Deep Field South (HDF-S) region performed at 6.7 and 15 µm with the ISOCAM instrument on board the Infrared Space Observatory (ISO). We find reliable optical/near-infrared associations for 32 of the 35 sources detected in this field by Oliver et al. (Paper I): eight of them are identified as stars, one is definitely an active galactic nucleus (AGN), a second seems likely to be an AGN too, while the remaining 22 appear to be normal spiral or starburst galaxies. Using model spectral energy distributions (SEDs) of similar galaxies, we compare methods for estimating the star formation rates (SFRs) in these objects, finding that an estimator based on integrated (3-1000 µm) infrared luminosity reproduces the model SFRs best. Applying this estimator to model fits to the SEDs of our 22 spiral and starburst galaxies, we find that they are forming stars at rates of ∼ 1-100M...yr[sup -l], with a median value of ∼40M...yr[sup -1], assuming an Einstein-de Sitter universe with a Hubble constant of 50 km s[sup -1] Mpc[sup -1], and star formation taking place according to a Salpeter initial mass function (IMF) across the mass range 0.1-100M.... We split the redshift range 0.0 ≤ z ≤ 0.6 into two equal-volume bins to compute raw estimates of the star formation rate density, ...[sub *], contributed by these sources, assuming the same cosmology and IMF as above and computing errors based on estimated uncertainties in the SFRs of individual galaxies. We compare these results with other estimates of ...[sub *] made with the same assumptions, showing them to be consistent with the results of Flores et al. from their ISO survey of the CFRS 1415+52 field. However, the relatively small volume of our survey means that our ...[sub *] estimates suffer from a large sampling variance, implying that our results, by themselves, do not place tight constraints on the global mean star formation rate density. [ABSTRACT FROM AUTHOR]

We used the SPIRE/FTS instrument aboard the Herschel Space Observatory to obtain the Spectral Line Energy Distributions (SLEDs) of CO from J = 4-3 to J = 13-12 of Arp 193 and NGC 6240, two classical merger/starbursts selected from our molecular line survey of local Luminous Infrared Galaxies (LIR ⩾ 1011L☼). The high-J CO SLEDs are then combined with ground-based low-J CO, 13CO, HCN, HCO+, CS line data and used to probe the thermal and dynamical states of their large molecular gas reservoirs. We find the two CO SLEDs strongly diverging from J = 4-3 onward, with NGC 6240 having a much higher CO line excitation than Arp 193, despite their similar low-J CO SLEDs and LFIR/LCO, 1 – 0, LHCN/LCO (J = 1-0) ratios (proxies of star formation efficiency and dense gas mass fraction). In Arp 193, one of the three most extreme starbursts in the local universe, the molecular SLEDs indicate a small amount (∼5%-15%) of dense gas (n ⩾ 104 cm–3) unlike NGC 6240 where most of the molecular gas (∼60%-70%) is dense (n ∼ (104-105) cm–3). Strong star-formation feedback can drive this disparity in their dense gas mass fractions, and also induce extreme thermal and dynamical states for the molecular gas. In NGC 6240, and to a lesser degree in Arp 193, we find large molecular gas masses whose thermal states cannot be maintained by FUV photons from Photon-Dominated Regions. We argue that this may happen often in metal-rich merger/starbursts, strongly altering the initial conditions of star formation. ALMA can now directly probe these conditions across cosmic epoch, and even probe their deeply dust-enshrouded outcome, the stellar initial mass function averaged over galactic evolution. [ABSTRACT FROM AUTHOR]