Showing papers by "Fabian Walter published in 2019"

Exploring Reionization-era Quasars. III. Discovery of 16 Quasars at 6.4 ≲ z ≲ 6.9 with DESI Legacy Imaging Surveys and the UKIRT Hemisphere Survey and Quasar Luminosity Function at z ∼ 6.7

Abstract: National Key RD National Science Foundation of ChinaNational Natural Science Foundation of China [11533001, 11721303]; US NSF grantNational Science Foundation (NSF) [AST-1515115]; NASA ADAP grant [NNX17AF28G]; National Science Foundation through REU grant [AST-1560461]; NOAO program [GN-2018A-C-1]; ESO Programme [179.A-2010, 179.A-2004]; National Aeronautics and Space AdministrationNational Aeronautics & Space Administration (NASA); National Astronomical Observatories, Chinese Academy of SciencesChinese Academy of Sciences; Special Fund for Astronomy from the Ministry of Finance in China

COLDz: Shape of the CO Luminosity Function at High Redshift and the Cold Gas History of the Universe

Abstract: We report the first detailed measurement of the shape of the CO luminosity function at high redshift, based on >320 hr of the NSF's Karl G. Jansky Very Large Array (VLA) observations over an area of ~60 arcmin^2 taken as part of the CO Luminosity Density at High Redshift (COLDz) survey. COLDz "blindly" selects galaxies based on their cold gas content through CO(J = 1 → 0) emission at z ~ 2–3 and CO(J = 2 → 1) at z ~ 5–7 down to a CO luminosity limit of log(L’_(CO)/K km s^(−1) pc^2) ≃ 9.5. We find that the characteristic luminosity and bright end of the CO luminosity function are substantially higher than predicted by semi-analytical models, but consistent with empirical estimates based on the infrared luminosity function at z ~ 2. We also present the currently most reliable measurement of the cosmic density of cold gas in galaxies at early epochs, i.e., the cold gas history of the universe, as determined over a large cosmic volume of ~375,000 Mpc3. Our measurements are in agreement with an increase of the cold gas density from z ~ 0 to z ~ 2–3, followed by a possible decline toward z ~ 5–7. These findings are consistent with recent surveys based on higher-J CO line measurements, upon which COLDz improves in terms of statistical uncertainties by probing ~50–100 times larger areas and in the reliability of total gas mass estimates by probing the low-J CO lines accessible to the VLA. Our results thus appear to suggest that the cosmic star formation rate density follows an increased cold molecular gas content in galaxies toward its peak about 10 billion years ago, and that its decline toward the earliest epochs is likely related to a lower overall amount of cold molecular gas (as traced by CO) bound in galaxies toward the first billion years after the Big Bang.

The ALMA Spectroscopic Survey in the HUDF : co luminosity functions and the molecular gas content of galaxies through cosmic history.

Abstract: We use the results from the ALMA large program ASPECS, the spectroscopic survey in the Hubble Ultra Deep Field (HUDF), to constrain CO luminosity functions of galaxies and the resulting redshift evolution of ρ(H2). The broad frequency range covered enables us to identify CO emission lines of different rotational transitions in the HUDF at z > 1. We find strong evidence that the CO luminosity function evolves with redshift, with the knee of the CO luminosity function decreasing in luminosity by an order of magnitude from ~2 to the local universe. Based on Schechter fits, we estimate that our observations recover the majority (up to ~90%, depending on the assumptions on the faint end) of the total cosmic CO luminosity at z = 1.0–3.1. After correcting for CO excitation, and adopting a Galactic CO-to-H2 conversion factor, we constrain the evolution of the cosmic molecular gas density ρ(H2): this cosmic gas density peaks at z ~ 1.5 and drops by a factor of ${6.5}_{-1.4}^{+1.8}$ to the value measured locally. The observed evolution in ρ(H2), therefore, closely matches the evolution of the cosmic star formation rate density ρ SFR. We verify the robustness of our result with respect to assumptions on source inclusion and/or CO excitation. As the cosmic star formation history can be expressed as the product of the star formation efficiency and the cosmic density of molecular gas, the similar evolution of ρ(H2) and ρ SFR leaves only little room for a significant evolution of the average star formation efficiency in galaxies since z ~ 3 (85% of cosmic history).

Gemini GNIRS Near-infrared Spectroscopy of 50 Quasars at z ≳ 5.7

Abstract: National Key RD National Science Foundation of China [11473002, 11533001, 11721303]; Alfred P. Sloan Research Fellowship; National Science Foundation [AST-1614213, AST-1715579]; Independent Research Fund Denmark [DFF 4002-00275, 8021-00130]

The Discovery of a Gravitationally Lensed Quasar at z=6.51

Abstract: US NSF [AST-1716585, AST-1515115]; NASA ADAP [NNX17AF28G]; Space Telescope Science Institute [HST-GO-13644]; NSF [AST-1211874]; NASA Chandra award [AR8-19021A]; Yale Keck program [Y144]; ERC grant "Cosmic Dawn"; NSFC [11533001]; ERC grant "Cosmic Gas"

The Atacama Large Millimeter/submillimeter Array Spectroscopic Survey in the Hubble Ultra Deep Field: CO Emission Lines and 3 mm Continuum Sources

Abstract: The Atacama Large Millimeter/submillimeter Array (ALMA) SPECtroscopic Survey in the Hubble Ultra Deep Field (HUDF) is an ALMA large program that obtained a frequency scan in the 3 mm band to detect emission lines from the molecular gas in distant galaxies. Here we present our search strategy for emission lines and continuum sources in the HUDF. We compare several line search algorithms used in the literature, and critically account for the line widths of the emission line candidates when assessing significance. We identify 16 emission lines at high fidelity in our search. Comparing these sources to multiwavelength data we find that all sources have optical/ infrared counterparts. Our search also recovers candidates of lower significance that can be used statistically to derive, e.g., the CO luminosity function. We apply the same detection algorithm to obtain a sample of six 3 mm continuum sources. All of these are also detected in the 1.2 mm continuum with optical/near-infrared counterparts. We use the continuum sources to compute 3 mm number counts in the sub-millijansky regime, and find them to be higher by an order of magnitude than expected for synchrotron-dominated sources. However, the number counts are consistent with those derived at shorter wavelengths (0.85–1.3 mm) once extrapolating to 3 mm with a dust emissivity index of β = 1.5, dust temperature of 35 K, and an average redshift of z = 2.5. These results represent the best constraints to date on the faint end of the 3 mm number counts.

EMPIRE: The IRAM 30 m dense gas survey of nearby galaxies

Abstract: We present EMPIRE, an IRAM 30-m large program that mapped $\lambda = 3{-}4$ mm dense gas tracers at $\sim 1{-}2\,$kpc resolution across the whole star-forming disk of nine nearby, massive, spiral galaxies. We describe the EMPIRE observing and reduction strategies and show new whole-galaxy maps of HCN(1-0), HCO$^+$(1-0), HNC(1-0) and CO(1-0). We explore how the HCN-to-CO and IR-to-HCN ratios, observational proxies for the dense gas fraction and dense gas star formation efficiency, depend on host galaxy and local environment. We find that the fraction of dense gas correlates with stellar surface density, gas surface density, molecular-to-atomic gas ratio, and dynamical equilibrium pressure. In EMPIRE, the star formation rate per unit dense gas anti-correlates with these same environmental parameters. Thus, although dense gas appears abundant the central regions of many spiral galaxies, this gas appears relatively inefficient at forming stars. These results qualitatively agree with previous work on nearby galaxies and the Milky Way's Central Molecular Zone. To first order, EMPIRE demonstrates that the conditions in a galaxy disk set the gas density distribution and that the dense gas traced by HCN shows an environment-dependent relation to star formation. However, our results also show significant ($\pm 0.2$ dex) galaxy-to-galaxy variations. We suggest that gas structure below the scale of our observations and dynamical effects likely also play an important role.

ALMA Reveals Potential Evidence for Spiral Arms, Bars, and Rings in High-redshift Submillimeter Galaxies

Abstract: We present subkiloparsec-scale mapping of the 870 μm ALMA continuum emission in six luminous (L IR ~ 5 × 1012 L ⊙) submillimeter galaxies (SMGs) from the ALESS survey of the Extended Chandra Deep Field South. Our high-fidelity 0farcs07-resolution imaging (~500 pc) reveals robust evidence for structures with deconvolved sizes of lesssim0.5–1 kpc embedded within (dominant) exponential dust disks. The large-scale morphologies of the structures within some of the galaxies show clear curvature and/or clump-like structures bracketing elongated nuclear emission, suggestive of bars, star-forming rings, and spiral arms. In this interpretation, the ratio of the "ring" and "bar" radii (1.9 ± 0.3) agrees with that measured for such features in local galaxies. These potential spiral/ring/bar structures would be consistent with the idea of tidal disturbances, with their detailed properties implying flat inner rotation curves and Toomre-unstable disks (Q < 1). The inferred one-dimensional velocity dispersions (σ r lesssim 70–160 km s−1) are marginally consistent with the limits implied if the sizes of the largest structures are comparable to the Jeans length. We create maps of the star formation rate density (ΣSFR) on ~500 pc scales and show that the SMGs are able to sustain a given (galaxy-averaged) ΣSFR over much larger physical scales than local (ultra)luminous infrared galaxies. However, on 500 pc scales, they do not exceed the Eddington limit set by radiation pressure on dust. If confirmed by kinematics, the potential presence of nonaxisymmetric structures would provide a means for net angular momentum loss and efficient star formation, helping to explain the very high star formation rates measured in SMGs.

The ALMA Spectroscopic Survey in the HUDF: the Molecular Gas Content of Galaxies and Tensions with IllustrisTNG and the Santa Cruz SAM

Abstract: The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS) provides new constraints for galaxy formation models on the molecular gas properties of galaxies. We compare results from ASPECS to predictions from two cosmological galaxy formation models: the IllustrisTNG hydrodynamical simulations and the Santa Cruz semianalytic model (SC SAM). We explore several recipes to model the H2 content of galaxies, finding them to be consistent with one another, and take into account the sensitivity limits and survey area of ASPECS. For a canonical CO-to-H2 conversion factor of αCO = 3.6 Me/(K km s−1 pc2 ) the results of our work include: (1) the H2 mass of z > 1 galaxies predicted by the models as a function of their stellar mass is a factor of 2–3 lower than observed; (2) the models do not reproduce the number of H2-rich (M M H2 > ´3 1010 ) galaxies observed by ASPECS; (3) the H2 cosmic density evolution predicted by IllustrisTNG (the SC SAM) is in tension (in tension but with less disagreement than IllustrisTNG) with the observed cosmic density, even after accounting for the ASPECS selection function and field-to-field variance effects. The tension between models and observations at z > 1 can be alleviated by adopting a CO-to-H2 conversion factor in the range αCO = 2.0–0.8 Me/(K km s−1 pc2 ). Additional work on constraining the CO-to-H2 conversion factor and CO excitation conditions of galaxies through observations and theory will be necessary to more robustly test the success of galaxy formation models.

PHIBSS2: survey design and z = 0.5 – 0.8 results Molecular gas reservoirs during the winding-down of star formation

Abstract: Following the success of the Plateau de Bure high-z Blue Sequence Survey (PHIBSS), we present the PHIBSS2 legacy program, a survey of the molecular gas properties of star-forming galaxies on and around the star-formation main sequence (MS) at different redshifts using IRAM's NOrthern Extended Millimeter Array (NOEMA). This survey significantly extends the existing sample of star-forming galaxies with CO molecular gas measurements, probing the peak epoch of star formation (z = 1 − 1.6) as well as its building-up (z = 2 − 3) and winding-down (z = 0.5 − 0.8) phases. The targets are drawn from the well-studied GOODS, COSMOS, and AEGIS cosmological deep fields and uniformly sample the MS in the stellar mass (M)-star formation rate (SFR) plane with log(M /M) = 10 − 11.8 and SFR = 3.5 − 500 M yr −1 without morphological selection, thus providing a statistically meaningful census of star-forming galaxies at different epochs. We describe the survey strategy and sample selection before focusing on the results obtained at redshift z = 0.5 − 0.8, where we report 60 CO(2-1) detections out of 61 targets. We determine molecular gas masses between 2 × 10 9 and 5 × 10 10 M and separately obtain disc sizes and bulge-to-total (B/T) luminosity ratios from HST I-band images. The median molecular gas-to-stellar mass ratio µ gas = 0.28 ± 0.04, gas fraction f gas = 0.22 ± 0.02, and depletion time t depl = 0.84 ± 0.07 Gyr as well as their dependence with stellar mass and offset from the MS follow published scaling relations for a much larger sample of galaxies spanning a significantly wider range of redshifts, the cosmic evolution of the SFR being mainly driven by that of the molecular gas fraction. The galaxy-averaged molecular Kennicutt-Schmidt (KS) relation between molecular gas and SFR surface densities is strikingly linear, pointing towards similar star formation timescales within galaxies at any given epoch. In terms of morphology, the molecular gas content, the SFR, the disc stellar mass, and the disc molecular gas fraction do not seem to correlate with B/T and the stellar surface density, which suggests an ongoing supply of fresh molecular gas to compensate for the build-up of the bulge. Our measurements do not yield any significant variation of the depletion time with B/T and hence no strong evidence for morphological quenching within the scatter of the MS.

The ALMA Spectroscopic Survey in the HUDF: CO emission lines and 3 mm continuum sources

Abstract: The ALMA SPECtroscopic Survey in the {\it Hubble} Ultra Deep Field is an ALMA large program that obtained a frequency scan in the 3\,mm band to detect emission lines from the molecular gas in distant galaxies. We here present our search strategy for emission lines and continuum sources in the HUDF. We compare several line search algorithms used in the literature, and critically account for the line-widths of the emission line candidates when assessing significance. We identify sixteen emission lines at high fidelity in our search. Comparing these sources to multi-wavelength data we find that all sources have optical/infrared counterparts. Our search also recovers candidates that have lower significance that can be used statistically to derive, e.g. the CO luminosity function. We apply the same detection algorithm to obtain a sample of six 3 mm continuum sources. All of these are also detected in the 1.2 mm continuum with optical/near-infrared counterparts. We use the continuum sources to compute 3 mm number counts in the sub-mJy regime, and find them to be higher by an order of magnitude than expected for synchrotron-dominated sources. However, the number counts are consistent with those derived at shorter wavelengths (0.85--1.3\,mm) once extrapolating to 3\,mm with a dust emissivity index of $\beta=1.5$, dust temperature of 35\,K and an average redshift of $z=2.5$. These results represent the best constraints to date on the faint end of the 3 mm number counts.

An ALMA Multiline Survey of the Interstellar Medium of the Redshift 7.5 Quasar Host Galaxy J1342+0928

Abstract: We use ALMA observations of the host galaxy of the quasar ULAS-J1342+0928 at z=7.54 to study the dust continuum and far infrared lines emitted from its interstellar medium. The Rayleigh-Jeans tail of the dust continuum is well sampled with eight different spectral setups, and from a modified black body fit we obtain an emissivity coefficient of beta=1.85+-0.3. Assuming a standard dust temperature of 47 K we derive a dust mass of Mdust=0.35x10^8 Msol and a star formation rate of 150+-30 Msol/yr. We have >4sigma detections of the [CII]_158, [OIII]_88 and [NII]_122 atomic fine structure lines and limits on the [CI]_369, [OI]_146 and [NII]_205 emission. We also report multiple limits of CO rotational lines with Jup >= 7, as well as a tentative 3.3sigma detection of the stack of four CO lines (Jup=11, 10, 8, 7). We find line deficits that are in agreement with local ultra luminous infrared galaxies. Comparison of the [NII]_122 and [CII]_158 lines indicates that the [CII]_158 emission arises predominantly from the neutral medium, and we estimate that the photo-disassociation regions in J1342+0928 have densities 180 cm^-3. Our observations favor a low gas-to-dust ratio of <100 and a metallicity of the interstellar medium comparable to the Solar value. All the measurements presented here suggest that the host galaxy of J1342+0928 is highly enriched in metal and dust, despite being observed just 680 Myr after the Big Bang.

The REQUIEM Survey. I. A Search for Extended Lyα Nebular Emission around 31 z > 5.7 Quasars

Abstract: The discovery of quasars few hundred megayears after the Big Bang represents a major challenge to our understanding of black holes and galaxy formation and evolution. Their luminosity is produced by extreme gas accretion onto black holes, which already reached masses of MBH > 10 M by z ∼ 6. Simultaneously, their host galaxies form hundreds of stars per year, using up gas in the process. To understand which environments are able to sustain the rapid formation of these extreme sources we started a VLT/MUSE effort aimed at characterizing the surroundings of a sample of 5.7 < z < 6.6 quasars dubbed: the Reionization Epoch QUasar InvEstigation with MUSE (REQUIEM) survey. We here present results of our searches for extended Lyα halos around the first 31 targets observed as part of this program. Reaching 5–σ surface brightness limits of 0.1−1.1×10−17erg s−1 cm−2 arcsec−2 over a 1 arcsec aperture, we were able to unveil the presence of 12 Lyα nebulae, 8 of which are newly discovered. The detected nebulae show a variety of emission properties and morphologies with luminosities ranging from 8× 10 to 2× 10 erg s−1, FWHMs between 300 and 1700 km s−1, sizes< 30 pkpc, and redshifts consistent with those of the quasar host galaxies. As the first statistical and homogeneous investigation of the circum–galactic medium of massive galaxies at the end of the reionization epoch, the REQUIEM survey enables the study of the evolution of the cool gas surrounding quasars in the first 3 Gyr of the Universe. A comparison with the extended Lyα emission observed around bright (M1450 . −25 mag) quasars at intermediate redshift indicates little variations on the properties of the cool gas from z ∼ 6 to z ∼ 3 followed by a decline in the average surface brightness down to z ∼ 2.

Strong Far-ultraviolet Fields Drive the [C II]/Far-infrared Deficit in z ∼ 3 Dusty, Star-forming Galaxies

Abstract: We present 0farcs15 (1 kpc) resolution ALMA observations of the [C ii] 157.74 μm line and rest-frame 160 μm continuum emission in two z ~ 3 dusty, star-forming galaxies—ALESS 49.1 and ALESS 57.1, combined with resolved CO (3–2) observations. In both sources, the [C ii] surface brightness distribution is dominated by a compact core ≤1 kpc in radius, a factor of 2–3 smaller than the extent of the CO (3–2) emission. In ALESS 49.1, we find an additional extended (8 kpc radius), low surface brightness [C ii] component. Based on an analysis of mock ALMA observations, the [C ii] and 160 μm continuum surface brightness distributions are inconsistent with a single-Gaussian surface brightness distribution with the same size as the CO (3–2) emission. The [C ii] rotation curves flatten at sime2 kpc radius, suggesting that the kinematics of the central regions are dominated by a baryonic disk. Both galaxies exhibit a strong [C ii]/far-IR (FIR) deficit on 1 kpc scales, with FIR surface brightness to [C ii]/FIR slope steeper than in local star-forming galaxies. A comparison of the [C ii]/CO (3–2) observations with photodissociation region models suggests a strong far-UV (FUV) radiation field (G 0 ~ 104) and high gas density (n(H) ~ 104–105 cm−3) in the central regions of ALESS 49.1 and ALESS 57.1. The most direct interpretation of the pronounced [C ii]/FIR deficit is a thermal saturation of the C+ fine-structure levels at temperatures ≥500 K, driven by the strong FUV field.

The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Evolution of the Molecular Gas in CO-selected Galaxies

Abstract: We analyze the interstellar medium properties of a sample of 16 bright CO line emitting galaxies identified in the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS) Large Program. This CO−selected galaxy sample is complemented by two additional CO line emitters in the UDF that are identified based on their MultiUnit Spectroscopic Explorer (MUSE) optical spectroscopic redshifts. The ASPECS CO−selected galaxies cover a larger range of star formation rates (SFRs) and stellar masses compared to literature CO emitting galaxies at z > 1 for which scaling relations have been established previously. Most of ASPECS CO-selected galaxies follow these established relations in terms of gas depletion timescales and gas fractions as a function of redshift, as well as the SFR–stellar mass relation (“galaxy main sequence”). However, we find that ∼30% of the galaxies (5 out of 16) are offset from the galaxy main sequence at their respective redshift, with ∼12% (2 out of 16) falling below this relationship. Some CO-rich galaxies exhibit low SFRs, and yet show substantial molecular gas reservoirs, yielding long gas depletion timescales. Capitalizing on the well-defined cosmic volume probed by our observations, we measure the contribution of galaxies above, below, and on the galaxy main sequence to the total cosmic molecular gas density at different lookback times. We conclude that main-sequence galaxies are the largest contributors to the molecular gas density at any redshift probed by our observations (z ∼ 1−3). The respective contribution by starburst galaxies above the main sequence decreases from z ∼ 2.5 to z ∼ 1, whereas we find tentative evidence for an increased contribution to the cosmic molecular gas density from the passive galaxies below the main sequence

The ALMA Spectroscopic Survey in the HUDF : nature and physical properties of gas-mass selected galaxies using MUSE spectroscopy.

Abstract: We discuss the nature and physical properties of gas-mass selected galaxies in the ALMA spectroscopic survey (ASPECS) of the Hubble Ultra Deep Field (HUDF). We capitalize on the deep optical integral-field spectroscopy from the Multi Unit Spectroscopic Explorer (MUSE) HUDF Survey and multiwavelength data to uniquely associate all 16 line emitters, detected in the ALMA data without preselection, with rotational transitions of carbon monoxide (CO). We identify 10 as CO(2–1) at 1 < z < 2, 5 as CO(3–2) at 2 < z < 3, and 1 as CO(4–3) at z = 3.6. Using the MUSE data as a prior, we identify two additional CO(2–1) emitters, increasing the total sample size to 18. We infer metallicities consistent with (super-)solar for the CO-detected galaxies at z „ 1.5, motivating our choice of a Galactic conversion factor between CO luminosity and molecular gas mass for these galaxies. Using deep Chandra imaging of the HUDF, we determine an X-ray AGN fraction of 20% and 60% among the CO emitters at z ∼ 1.4 and z ∼ 2.6, respectively. Being a CO-flux-limited survey, ASPECS-LP detects molecular gas in galaxies on, above, and below the main sequence (MS) at z ∼ 1.4. For stellar masses …1010 (1010.5) M, we detect about 40% (50%) of all galaxies in the HUDF at 1 < z < 2 (2 < z < 3). The combination of ALMA and MUSE integral-field spectroscopy thus enables an unprecedented view of MS galaxies during the peak of galaxy formation.

The REQUIEM Survey I: A Search for Extended Ly-Alpha Nebular Emission Around 31 z>5.7 Quasars.

Abstract: The discovery of quasars few hundred megayears after the Big Bang represents a major challenge to our understanding of black holes and galaxy formation and evolution. Their luminosity is produced by extreme gas accretion onto black holes, which already reached masses of 10$^9$ M$_\odot$ by z ~ 6. Simultaneously, their host galaxies form hundreds of stars per year, using up gas in the process. To understand which environments are able to sustain the rapid formation of these extreme sources we started a VLT/MUSE effort aimed at characterizing the surroundings of a sample of 5.7 < z < 6.6 quasars dubbed: the Reionization Epoch QUasar InvEstigation with MUSE (REQUIEM) survey. We here present results of our searches for extended Ly-Alpha halos around the first 31 targets observed as part of this program. Reaching 5-sigma surface brightness limits of 0.1-1.1 x 10$^{-17}$ erg/s/cm$^2$/arcsec$^2$ over a 1 arcsec$^2$ aperture, we were able to unveil the presence of 12 Ly-Alpha nebulae, 8 of which are newly discovered. The detected nebulae show a variety of emission properties and morphologies with luminosities ranging from 8 x 10$^{42}$ to 2 x 10$^{44}$ erg/s, FWHMs between 300 and 1700 km/s, sizes < 30 pkpc, and redshifts consistent with those of the quasar host galaxies. As the first statistical and homogeneous investigation of the circum-galactic medium of massive galaxies at the end of the reionization epoch, the REQUIEM survey enables the study of the evolution of the cool gas surrounding quasars in the first 3 Gyr of the Universe. A comparison with the extended Ly-Alpha emission observed around bright (M$_{1450}$ < -25 mag) quasars at intermediate redshift indicates little variations on the properties of the cool gas from z ~ 6 to z ~ 3 followed by a decline in the average surface brightness down to z ~ 2.

400 pc Imaging of a Massive Quasar Host Galaxy at a Redshift of 6.6

Abstract: We report high spatial resolution (~0farcs076, 410 pc) Atacama Large Millimeter/submillimeter Array imaging of the dust continuum and the ionized carbon line [C ii] in a luminous quasar host galaxy at z = 6.6, 800 million years after the big bang. Based on previous studies, this galaxy hosts a ~1 × 10^9 M_⊙ black hole and has a star formation rate of ~1500 M_⊙ yr^(−1). The unprecedented high resolution of the observations reveals a complex morphology of gas within 3 kpc of the accreting central black hole. The gas has a high velocity dispersion with little ordered motion along the line of sight, as would be expected from gas accretion that has yet to settle in a disk. In addition, we find the presence of [C ii] cavities in the gas distribution (with diameters of ~0.5 kpc), offset from the central black hole. This unique distribution and kinematics cannot be explained by a simple model. Plausible scenarios are that the gas is located in a truncated or warped disk, or the holes are created by interactions with nearby galaxies or due to energy injection into the gas. In the latter case, the energy required to form the cavities must originate from the central active galactic nucleus, as the required energy far exceeds the energy output expected from supernovae. This energy input into the gas, however, does not inhibit the high rate of star formation. Both star formation and black hole activity could have been triggered by interactions with satellite galaxies; our data reveal three additional companions detected in [C ii] emission around the quasar.

The Molecular Gas Reservoirs of $z\sim 2$ Galaxies: A comparison of CO(1-0) and dust-based molecular gas masses

Abstract: We test the use of long-wavelength dust continuum emission as a molecular gas tracer at high redshift, via a unique sample of 12, z~2 galaxies with observations of both the dust continuum and CO(1-0) line emission (obtained with the Atacama Large Millimeter Array and Karl G. Jansky Very Large Array, respectively). Our work is motivated by recent, high redshift studies that measure molecular gas masses (\ensuremath{\rm{M}_{\rm{mol}}}) via a calibration of the rest-frame $850\mu$m luminosity ($L_\mathrm{850\mu m,rest}$) against the CO(1-0)-derived \ensuremath{\rm{M}_{\rm{mol}}}\ of star-forming galaxies. We hereby test whether this method is valid for the types of high-redshift, star-forming galaxies to which it has been applied. We recover a clear correlation between the rest-frame $850\mu$m luminosity, inferred from the single-band, long-wavelength flux, and the CO(1-0) line luminosity, consistent with the samples used to perform the $850\mu$m calibration. The molecular gas masses, derived from $L_\mathrm{850\mu m,rest}$, agree to within a factor of two with those derived from CO(1-0). We show that this factor of two uncertainty can arise from the values of the dust emissivity index and temperature that need to be assumed in order to extrapolate from the observed frequency to the rest-frame at 850$\mathrm{\mu m}$. The extrapolation to 850$\mathrm{\mu m}$ therefore has a smaller effect on the accuracy of \Mmol\ derived via single-band dust-continuum observations than the assumed CO(1-0)-to-\ensuremath{\rm{M}_{\rm{mol}}}\ conversion factor. We therefore conclude that single-band observations of long-wavelength dust emission can be used to reliably constrain the molecular gas masses of massive, star-forming galaxies at $z\gtrsim2$.

Resolved [CII] Emission from z>6 Quasar Host -- Companion Galaxy Pairs

Abstract: We report on ~0.35"(~2 kpc) resolution observations of the [CII] and dust continuum emission from five z>6 quasar host-companion galaxy pairs obtained with the Atacama Large Millimeter/submillimeter Array. The [CII] emission is resolved in all galaxies, with physical extents of 3.2-5.4 kpc. The dust continuum is on-average 40% more compact, which results in larger [CII] deficits in the center of the galaxies. However, the measured [CII] deficits are fully consistent with those found at lower redshifts. Four of the galaxies show [CII] velocity fields that are consistent with ordered rotation, while the remaining six galaxies show no clear velocity gradient. All galaxies have high (~80-200 km/s) velocity dispersions, consistent with the interpretation that the interstellar medium (ISM) of these high redshift galaxies is turbulent. By fitting the galaxies with kinematic models, we estimate the dynamical mass of these systems, which range between (0.3 -> 5.4) x 1E10 Msun. For the three closest separation galaxy pairs, we observe dust and [CII] emission from gas in between and surrounding the galaxies, which is an indication that tidal interactions are disturbing the gas in these systems. Although gas exchange in these tidal interactions could power luminous quasars, the existence of quasars in host galaxies without nearby companions suggests that tidal interactions are not the only viable method for fueling their active centers. These observations corroborate the assertion that accreting supermassive black holes do not substantially contribute to the [CII] and dust continuum emission of the quasar host galaxies, and showcase the diverse ISM properties of galaxies when the universe was less than one billion years old.

An ALMA multi-line survey of the interstellar medium of the redshift 7.5 quasar host galaxy J1342+0928

Abstract: We use ALMA observations of the host galaxy of the quasar ULAS-J1342+0928 at z=7.54 to study the dust continuum and far infrared lines emitted from its interstellar medium. The Rayleigh-Jeans tail of the dust continuum is well sampled with eight different spectral setups, and from a modified black body fit we obtain an emissivity coefficient of beta=1.85+-0.3. Assuming a standard dust temperature of 47 K we derive a dust mass of Mdust=0.35x10^8 Msol and a star formation rate of 150+-30 Msol/yr. We have >4sigma detections of the [CII]_158, [OIII]_88 and [NII]_122 atomic fine structure lines and limits on the [CI]_369, [OI]_146 and [NII]_205 emission. We also report multiple limits of CO rotational lines with Jup >= 7, as well as a tentative 3.3sigma detection of the stack of four CO lines (Jup=11, 10, 8, 7). We find line deficits that are in agreement with local ultra luminous infrared galaxies. Comparison of the [NII]_122 and [CII]_158 lines indicates that the [CII]_158 emission arises predominantly from the neutral medium, and we estimate that the photo-disassociation regions in J1342+0928 have densities 180 cm^-3. Our observations favor a low gas-to-dust ratio of <100 and a metallicity of the interstellar medium comparable to the Solar value. All the measurements presented here suggest that the host galaxy of J1342+0928 is highly enriched in metal and dust, despite being observed just 680 Myr after the Big Bang.

EMPIRE: The IRAM 30-m Dense Gas Survey of Nearby Galaxies

Abstract: We present EMPIRE, an IRAM 30-m large program that mapped $\lambda = 3{-}4$ mm dense gas tracers at $\sim 1{-}2\,$kpc resolution across the whole star-forming disk of nine nearby, massive, spiral galaxies. We describe the EMPIRE observing and reduction strategies and show new whole-galaxy maps of HCN(1-0), HCO$^+$(1-0), HNC(1-0) and CO(1-0). We explore how the HCN-to-CO and IR-to-HCN ratios, observational proxies for the dense gas fraction and dense gas star formation efficiency, depend on host galaxy and local environment. We find that the fraction of dense gas correlates with stellar surface density, gas surface density, molecular-to-atomic gas ratio, and dynamical equilibrium pressure. In EMPIRE, the star formation rate per unit dense gas anti-correlates with these same environmental parameters. Thus, although dense gas appears abundant the central regions of many spiral galaxies, this gas appears relatively inefficient at forming stars. These results qualitatively agree with previous work on nearby galaxies and the Milky Way's Central Molecular Zone. To first order, EMPIRE demonstrates that the conditions in a galaxy disk set the gas density distribution and that the dense gas traced by HCN shows an environment-dependent relation to star formation. However, our results also show significant ($\pm 0.2$ dex) galaxy-to-galaxy variations. We suggest that gas structure below the scale of our observations and dynamical effects likely also play an important role.

Far-infrared Properties of the Bright, Gravitationally Lensed Quasar J0439+1634 at z = 6.5

Abstract: US NSF [AST-1716585, AST 15-15115]; NASA ADAP [NNX17AF28G]; ERC grant "Cosmic Gas"; National Key RD National Science Foundation of China [11533001, 11721303]; INSU/CNRS (France); MPG (Germany); IGN (Spain);[S18DO];[W18EI]

The DSA-2000 -- A Radio Survey Camera

Abstract: We present the DSA-2000: a world-leading radio survey telescope and multi-messenger discovery engine for the next decade. The array will be the first true radio camera, outputting science-ready image data over the 0.7 - 2 GHz frequency range with a spatial resolution of 3.5 arcsec. With 2000 x 5 m dishes, the DSA-2000 will have an equivalent point-source sensitivity to SKA1-mid, but with ten times the survey speed. The DSA-2000 is envisaged as an all-sky survey instrument complementary to the ngVLA, and as a counterpart to the LSST (optical), SPHEREx (near-infrared) and SRG/eROSITA (X-ray) all-sky surveys. Over a five-year prime phase, the DSA-2000 will image the entire sky above declination -30 degrees every four months, detecting > 1 unique billion radio sources in a combined full-Stokes sky map with 500 nJy/beam rms noise. This all-sky survey will be complemented by intermediate and deep surveys, as well as spectral and polarization image cubes. The array will be a cornerstone for multi-messenger science, serving as the principal instrument for the US pulsar timing array community, and by searching for radio afterglows of compact object mergers detected by LIGO and Virgo. The array will simultaneously detect and localize ~10,000 fast radio bursts each year, realizing their ultimate use as a cosmological tool. The DSA-2000 will be proposed to the NSF Mid-Scale Research Infrastructure-2 program with a view to first light in 2026

The ALMA Spectroscopic Survey in the HUDF: CO luminosity functions and the molecular gas content of galaxies through cosmic history

Abstract: We use the results from the ALMA large program ASPECS, the spectroscopic survey in the Hubble Ultra Deep Field (HUDF), to constrain CO luminosity functions of galaxies and the resulting redshift evolution of $\rho$(H$_2$). The broad frequency range covered enables us to identify CO emission lines of different rotational transitions in the HUDF at $z>1$. We find strong evidence that the CO luminosity function evolves with redshift, with the knee of the CO luminosity function decreasing in luminosity by an order of magnitude from $\sim$2 to the local universe. Based on Schechter fits, we estimate that our observations recover the majority (up to $\sim$90%, depending on the assumptions on the faint end) of the total cosmic CO luminosity at $z$=1.0-3.1. After correcting for CO excitation, and adopting a Galactic CO-to-H$_2$ conversion factor, we constrain the evolution of the cosmic molecular gas density $\rho$(H$_2$): this cosmic gas density peaks at $z\sim1.5$ and drops by factor of $6.5_{-1.4}^{+1.8}$ to the value measured locally. The observed evolution in $\rho$(H$_2$) therefore closely matches the evolution of the cosmic star formation rate density $\rho_{\rm SFR}$. We verify the robustness of our result with respect to assumptions on source inclusion and/or CO excitation. As the cosmic star formation history can be expressed as the product of the star formation efficiency and the cosmic density of molecular gas, the similar evolution of $\rho$(H$_2$) and $\rho_{\rm SFR}$ leaves only little room for a significant evolution of the average star formation efficiency in galaxies since $z\sim 3$ (85% of cosmic history).

The molecular outflow in NGC253 at a resolution of two parsecs

Abstract: We present 0.15'' (~2.5pc) resolution ALMA CO(3-2) observations of the starbursting center in NGC253. Together with archival ALMA CO(1-0) and CO(2-1) data we decompose the emission into a disk and non-disk component. We find ~7-16% of the CO luminosity to be associated with the non-disk component ($1.2-4.2 \times 10^7$ K km s$^{-1}$ pc$^2$). The total molecular gas mass in the center of NGC253 is $\sim 3.6 \times 10^8$ M$_\odot$ with $\sim 0.5 \times 10^8$ M$_\odot$ (~15%) in the non-disk component. These measurements are consistent across independent mass estimates through three CO transitions. The high-resolution CO(3-2) observations allow us to identify the molecular outflow within the non-disk gas. Using a starburst conversion factor, we estimate the deprojected molecular mass outflow rate, kinetic energy and momentum in the starburst of NGC253. The deprojected molecular mass outflow rate is in the range ~14-39 M$_\odot$ yr$^{-1}$ with an uncertainty of 0.4dex. The large spread arises due to different interpretations of the kinematics of the observed gas while the errors are due to unknown geometry. The majority of this outflow rate is contributed by distinct outflows perpendicular to the disk, with a significant contribution by diffuse molecular gas. This results in a mass loading factor $\eta = \dot{M}_\mathrm{out} / \dot{M}_\mathrm{SFR}$ in the range $\eta \sim 8-20$ for gas ejected out to ~300pc. We find the kinetic energy of the outflow to be $\sim 2.5-4.5 \times 10^{54}$ erg and ~0.8dex typical error which is ~0.1% of the total or ~8% of the kinetic energy supplied by the starburst. The outflow momentum is $4.8-8.7 \times 10^8$ M$_\odot$ km s$^{-1}$ (~0.5dex error) or ~2.5-4% of the kinetic momentum released into the ISM by feedback. The unknown outflow geometry and launching sites are the primary source of uncertainty in this study.

Strong FUV fields drive the [CII]/FIR deficit in z~3 dusty, star-forming galaxies

Abstract: We present 0.15-arcsec (1 kpc) resolution ALMA observations of the [CII] 157.74 um line and rest-frame 160-um continuum emission in two z~3 dusty, star-forming galaxies - ALESS 49.1 and ALESS 57.1, combined with resolved CO(3-2) observations. In both sources, the [CII] surface brightness distribution is dominated by a compact core $\leq$1 kpc in radius, a factor of 2-3 smaller than the extent of the CO(3-2) emission. In ALESS 49.1, we find an additional extended (8-kpc radius), low surface-brightness [CII] component. Based on an analysis of mock ALMA observations, the [CII] and 160-um continuum surface brightness distributions are inconsistent with a single-Gaussian surface brightness distribution with the same size as the CO(3-2) emission. The [CII] rotation curves flatten at $\simeq$2 kpc radius, suggesting the kinematics of the central regions are dominated by a baryonic disc. Both galaxies exhibit a strong [CII]/FIR deficit on 1-kpc scales, with FIR-surface-brightness to [CII]/FIR slope steeper than in local star-forming galaxies. A comparison of the [CII]/CO(3-2) observations with PDR models suggests a strong FUV radiation field ($G_0\sim10^4$) and high gas density ($n\mathrm{(H)}\sim10^4-10^5$ cm$^{-3}$) in the central regions of ALESS 49.1 and 57.1. The most direct interpretation of the pronounced [CII]/FIR deficit is a thermal saturation of the C+ fine-structure levels at temperatures $\geq$500 K, driven by the strong FUV field.