arXiv subjects

Rob J. Ivison

Publications and source records attributed to Rob J. Ivison.

At least 19 recordsLinked to original sources

arXiv2026

Tracing Radio AGN-Driven Quenching in Post-Starburst Galaxies at Cosmic Noon

We present a radio continuum study of photometrically selected cosmic noon (0.5 10^{11}$M$_\odot$. Massive PSBs have a comparable detection fraction to that of massive quiescent galaxies ($f_{det}=8\pm1\%$), and both classes have lower fractions than that of massive star-forming galaxies ($f_{det}=13\pm1\%$) in the same field. The radio luminosities of detected PSBs, ${\rm L}_{1.4}\sim 10^{22.8}-10^{24.9}$W/Hz, exceed those from star formation by a median factor of 37 indicative of a possible AGN origin. Their compact morphologies ($\lesssim15$ kpc at $z_{med}=1.5$) suggest low-luminosity AGN with less powerful jets. Stacking the undetected PSBs reveals a weak radio detection ($3.9\sigma$) in the highest mass bin (M$_*>10^{11}$M$_\odot$). In contrast, 1.4 GHz detected quiescent galaxies have radio luminosities reaching radio-loud levels, and a higher prevalence of extended morphologies indicative of large-scale jetted AGN. The AGN contribution is also detected in stacked measurements of quiescent galaxies. Overall, our results support a short radio AGN duty cycle for PSBs, characterized by weak radio jets, suggesting radio-driven maintenance mode feedback may become important at older ages.

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arXiv2025

ALMA Deep Field in SSA22: Reconstructed [CII] Luminosity Function at z = 6

The ADF22 line survey reported detections of two high-$z$ line-emitting source candidates above 6-$\sigma$, both of which were shown to be spurious after follow-up observations. We investigate the detectability of far-infrared emitters in ALMA deep fields using mock observations by injecting artificial line-emitting sources into the visibility planes. We also discuss our investigation, conducted together with the ALMA operations team, of a possible technical problem in the original observations. Finally, we devise a method to estimate the [CII] luminosity function (LF) at $z \sim 6$, including a full analysis of signal contamination and sample completeness. The comparison of pixel distributions between the real and mock datacubes does not show significant differences, confirming that the effect of non-Gaussian noise is negligible for the ADF22 datacube. Using 100 blank mock-mosaic datasets, we show 0.43 $\pm$ 0.67 false detections per datacube with the previous source-finding method. We argue that the underestimation of the contamination rate in the previous work is caused by the smaller number of datacubes, using only 4 real ADF22 datacubes. We compare the results of clump-finding between the time division mode and frequency division mode correlator datacubes and confirm that the velocity widths of the clumps in the TDM case are up to 3 times wider than in the FDM case. The LF estimation using our model shows that a correction for the number count is required, up to one order of magnitude, in the luminosity range of $\geq 5 \times 10^8 L_\odot$. Our reconstruction method for the line LF can be applied to future blind line surveys.

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arXiv2024

ALMACAL XII. Data characterisation and products

The ALMACAL survey is based on a database of reprocessed ALMA calibration scans suitable for scientific analysis, observed as part of regular PI observations. We present all the data accumulated from the start of ALMA operations until May 2022 for 1047 calibrator fields across the southern sky spanning ALMA Bands 3 to 10 (~ 84 - 950 GHz), so-called ALMACAL-22. Encompassing over 1000 square arcmin and accumulating over 2000 hours of integration time, ALMACAL is not only one of the largest ALMA surveys to date, but it continues to grow with each new scientific observation. We outline the methods for processing and imaging a subset of the highest-quality data ('pruned sample'). Using deconvolution techniques within the visibility data (uv plane), we created data cubes as the final product for further scientific analysis. We describe the properties and shortcomings of ALMACAL and compare its area and sensitivity with other sub-millimetre surveys. Notably, ALMACAL overcomes limitations of previous sub-millimetre surveys, such as small sky coverage and the effects of cosmic variance. Moreover, we discuss the improvements introduced by the latest version of this dataset that will enhance our understanding of dusty star-forming galaxies, extragalactic absorption lines, active galactic nucleus physics, and ultimately the evolution of molecular gas.

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arXiv2024

Fast SMBH growth in the SPT2349--56 protocluster at $z=4.3$

Protoclusters at $z>2$ are gas-rich regions characterized by high star-formation activity. The same physical properties that enhance star formation in protoclusters are also thought to boost the growth of SMBHs. We aim to test this scenario by probing the AGN content of SPT2349-56, a massive, gas-rich, and highly star-forming protocluster core at $z=4.3$ discovered as an overdensity of DSFGs, via Chandra (200 ks) observations, and comparing the results with the field environment. We detected two protocluster members, corresponding to an AGN fraction among DSFGs of $\approx10\%$. This value is consistent with other protoclusters at $z=2-4$, but higher than the AGN incidence among DSFGs in the field environment. Both AGN are heavily obscured sources and hosted in star-forming galaxies with $\approx3\times10^{10}\,\mathrm{M_\odot}$ stellar masses. We estimate that the ISM in the host galaxies can contribute significantly to the nuclear obscuration. One of the two AGN is highly luminous ($L_X=2\times10^{45}\,\mathrm{erg\,s^{-1}}$) and Compton-thick ($N_H=2\times10^{24}\,\mathrm{cm^{-2}}$), and likely powered by a $M_{BH}>6\times10^8\,\mathrm{M_\odot}$ SMBH. Its high accretion rate suggests that it is in the phase of efficient growth required to explain the presence of extremely massive SMBHs in the centers of local galaxy clusters. Considering SPT2349-56 and DRC, a similar protocuster at $z=4$, we find that gas-rich protocluster cores at $z\approx4$ enhance the triggering of luminous (log$\frac{L_X}{\mathrm{erg\,s^{-1}}}=45-46$) AGN by 3-5 orders of magnitude with respect to the field environment. Our results indicate that gas-rich protoclusters at high redshift boost the growth of SMBHs, which will likely impact the subsequent evolution of the structures, and thus represent key science targets to obtain a complete understanding of the relation between environment and galaxy evolution.

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arXiv2022

ALMACAL VIII: A pilot survey for untargeted extragalactic CO emission lines in deep ALMA calibration data

We present a pilot, untargeted extragalactic carbon monoxide (CO) emission-line survey using ALMACAL, a project utilizing ALMA calibration data for scientific purposes. In 33 deep (Texp > 40 min) ALMACAL fields we report six CO emission-line detections above S/N > 4, one-third confirmed by MUSE observations. With this pilot survey, we probe a cosmologically significant volume of ~10^5 cMpc^3, widely distributed over many pointings in the southern sky, making the survey largely insusceptible to the effects of cosmic variance. We derive the redshift probability of the CO detections using probability functions from the Shark semi-analytical model of galaxy formation. By assuming typical CO excitations for the detections, we put constraints on the cosmic molecular gas mass density evolution over the redshift range 0 < z < 1.5. The results of our pilot survey are consistent with the findings of other untargeted emission-line surveys and the theoretical model predictions and currently cannot rule out a non-evolving molecular gas mass density. Our study demonstrates the potential of using ALMA calibrator fields as a multi-sightline untargeted CO emission line survey. Applying this approach to the full ALMACAL database will provide an accurate, free of cosmic variance, measurement of the molecular luminosity function as a function of redshift.

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arXiv2020

Rise of the Titans: Gas Excitation and Feedback in a Binary Hyper-Luminous Dusty Starburst Galaxy at z~6

We report new observations toward the hyper-luminous dusty starbursting major merger ADFS-27 (z=5.655), using ATCA and ALMA. We detect CO 2-1, 8-7, 9-8, 10-9 and H2O(321-221) emission, and a P-Cygni-shaped OH+(11-01) absorption/emission feature. We also tentatively detect H2O(321-312) and OH+(12-01) emission and CH+(1-0) absorption. We find a total cold molecular mass of M_gas = (2.1+/-0.2) x 10^11 (alpha_CO/1.0) Msun. 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 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 towards the northern component, which is also the one that is more enshrouded in dust and thus remains undetected up to 1.6 um even in our sensitive new HST/WFC3 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 Msun/yr of enriched gas to its halo.

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arXiv2020

Chandra reveals a luminous Compton-thick QSO powering a $Lyα$ blob in a $z=4$ starbursting protocluster

Galaxy clusters in the local universe descend from high-redshift overdense regions known as protoclusters. The large gas reservoirs and high rate of galaxy interaction in protoclusters are expected to trigger star-formation activity and luminous SMBH accretion in the host galaxies. We investigated the AGN content of a gas-rich and starbursting protocluster at $z=4$, known as the Distant Red Core (DRC). We observed with Chandra (139 ks) the 13 identified members of the structure, and searched for luminous and possibly obscured AGN among them. We also tested whether a hidden AGN can power the $Lyα$ blob (LAB) detected with VLT/MUSE in the DRC. We detected obscured X-ray emission from the two most gas-rich members of the DRC, named DRC-1 and DRC-2. Both of them are resolved into multiple interacting clumps in high-resolution ALMA and HST observations. In particular, DRC-2 is found to host a luminous ($L_{2-10\,\mathrm{keV}}\approx3\times10^{45}\,\mathrm{erg\,s^{-1}}$) Compton-thick ($N_H\gtrsim10^{24}\,\mathrm{cm^{-2}}$) QSO, comparable to the most luminous QSOs known at all cosmic times. The AGN fraction among DRC members is consistent with results found for lower redshift protoclusters. However, X-ray stacking analysis reveals that SMBH accretion is likely also taking place in other DRC galaxies that are not detected individually by Chandra. Our results point toward the presence of a strong link between large gas reservoirs, galaxy interactions, and luminous and obscured nuclear activity in protocluster members. The powerful and obscured QSO detected in DRC-2 is likely powering the nearby LAB detected with VLT/MUSE, possibly through photoionization; however, we propose that the diffuse $Lyα$ emission may be due to gas shocked by a massive outflow launched by DRC-2 over a $\approx10$ kpc scale.

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arXiv2020

VLA-ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (VLASPECS): Total Cold Gas Masses and CO Line Ratios for z=2-3 "Main Sequence" Galaxies

Using the NSF's Karl G. Jansky Very Large Array (VLA), we report six detections of CO(J=1-0) emission and one upper limit in z=2-3 galaxies originally detected in higher-J CO emission in the Atacama Large submillimeter/Millimeter Array (ALMA) Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS). From the CO(J=1-0) line strengths, we measure total cold molecular gas masses of M_gas = 2.4-11.6 x 10^10 (alpha_CO/3.6) Msun. We also measure a median CO(J=3-2) to CO(J=1-0) line brightness temperature ratio of r_31 = 0.84 +/- 0.26, and a CO(J=7-6) to CO(J=1-0) ratio range of r_71 <0.05 to 0.17. These results suggest that CO(J=3-2) selected galaxies may have a higher CO line excitation on average than CO(J=1-0) selected galaxies, based on the limited, currently available samples from the ASPECS and VLA CO Luminosity Density at High Redshift (COLDz) surveys. This implies that previous estimates of the cosmic density of cold gas in galaxies based on CO(J=3-2) measurements should be revised down by a factor of ~=2 on average based on assumptions regarding CO excitation alone. This correction further improves the agreement between the best currently existing constraints on the cold gas density evolution across cosmic history from line scan surveys, and the implied characteristic gas depletion times.

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arXiv2020

COLDz: A High Space Density of Massive Dusty Starburst Galaxies ~1 Billion Years after the Big Bang

We report the detection of CO($J$=2$\to$1) emission from three massive dusty starburst galaxies at $z$$>$5 through molecular line scans in the NSF's Karl G. Jansky Very Large Array (VLA) CO Luminosity Density at High Redshift (COLDz) survey. Redshifts for two of the sources, HDF 850.1 ($z$=5.183) and AzTEC-3 ($z$=5.298), were previously known. We revise a previous redshift estimate for the third source GN10 ($z$=5.303), which we have independently confirmed through detections of CO $J$=1$\to$0, 5$\to$4, 6$\to$5, and [CII] 158 $μ$m emission with the VLA and the NOrthern Extended Milllimeter Array (NOEMA). We find that two currently independently confirmed CO sources in COLDz are "optically dark", and that three of them are dust-obscured galaxies at $z$$>$5. Given our survey area of $\sim$60 arcmin$^2$, our results appear to imply a $\sim$6-55 times higher space density of such distant dusty systems within the first billion years after the Big Bang than previously thought. At least two of these $z$$>$5 galaxies show star-formation rate surface densities consistent with so-called "maximum" starbursts, but we find significant differences in CO excitation between them. This result may suggest that different fractions of the massive gas reservoirs are located in the dense, star-forming nuclear regions - consistent with the more extended sizes of the [CII] emission compared to the dust continuum and higher [CII]-to-far-infrared luminosity ratios in those galaxies with lower gas excitation. We thus find substantial variations in the conditions for star formation between $z$$>$5 dusty starbursts, which typically have dust temperatures $\sim$57%$\pm$25% warmer than starbursts at $z$=2-3 due to their enhanced star formation activity.

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arXiv2019

The evolution of CNO isotopes: the impact of massive stellar rotators

Chemical abundances and abundance ratios measured in galaxies provide precious information about the mechanisms, modes and time scales of the assembly of cosmic structures. Yet, the nucleogenesis and chemical evolution of elements heavier than helium are dictated mostly by the physics of the stars and the shape of the stellar mass spectrum. In particular, estimates of CNO isotopic abundances in the hot, dusty media of high-redshift starburst galaxies offer a unique glimpse into the shape of the stellar initial mass function (IMF) in extreme environments that can not be accessed with direct observations (star counts). Underlying uncertainties in stellar evolution and nucleosynthesis theory, however, may hurt our chances of getting a firm grasp of the IMF in these galaxies. In this work, we adopt new yields for massive stars, covering different initial rotational velocities. First, we implement the new yield set in a well-tested chemical evolution model for the Milky Way. The calibrated model is then adapted to the specific case of a prototype submillimeter galaxy (SMG). We show that, if the formation of fast-rotating stars is favoured in the turbulent medium of violently star-forming galaxies irrespective of metallicity, the IMF needs to be skewed towards high-mass stars in order to explain the CNO isotope ratios observed in SMGs. If, instead, stellar rotation becomes negligible beyond a given metallicity threshold, as is the case for our own Galaxy, there is no need to invoke a top-heavy IMF in starbursts.

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arXiv2019

ADF22: Blind detections of [CII] line emitters shown to be spurious

We report Atacama Large Millimetre/submillimeter Array (ALMA) Cycle-5 follow-up observations of two candidate [CII] emitters at z ~ 6 in the ALMA deep field in SSA22 (ADF22). The candidates were detected blindly in a Cycle-2 ALMA survey covering ~ 5 square arcmins, with a single tuning, along with two CO lines associated with galaxies at lower redshifts. Various tests suggested at least one of the two > 6-sigma [CII] candidates should be robust (Hayatsu et al. 2017). Nevertheless, our new, deeper observations recover neither candidate, demonstrating a higher contamination rate than expected. The cause of the spurious detections is under investigation but at present it remains unclarified.

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arXiv2019

The case for a 'sub-millimeter SDSS': a 3D map of galaxy evolution to z~10

The Sloan Digital Sky Survey (SDSS) was revolutionary because of the extraordinary breadth and ambition of its optical imaging and spectroscopy. We argue that a 'sub-millimeter SDSS' - a sensitive large-area imaging+spectroscopic survey in the sub-mm window - will revolutionize our understanding of galaxy evolution in the early Universe. By detecting the thermal dust continuum emission and atomic and molecular line emission of galaxies out to z~10 it will be possible to measure the redshifts, star formation rates, dust and gas content of hundreds of thousands of high-z galaxies down to ~L*. Many of these galaxies will have counterparts visible in the deep optical imaging of the Large Synoptic Survey Telescope. This 3D map of galaxy evolution will span the peak epoch of galaxy formation all the way back to cosmic dawn, measuring the co-evolution of the star formation rate density and molecular gas content of galaxies, tracking the production of metals and charting the growth of large-scale structure.

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arXiv2019

ALMA twenty-six arcmin$^2$ survey of GOODS-S at one-millimeter (ASAGAO): Near-infrared-dark faint ALMA sources

We report detections of two 1.2 mm continuum sources ($S_\mathrm{1.2mm}$ ~ 0.6 mJy) without any counterparts in the deep $H$- and/or $K$-band image (i.e., $K$-band magnitude $\gtrsim$ 26 mag). These near-infrared-dark faint millimeter sources are uncovered by ASAGAO, a deep and wide-field ($\simeq$ 26 arcmin$^2$) Atacama Large Millimeter/submillimeter Array (ALMA) 1.2 mm survey. One has a red IRAC (3.6 and 4.5 $μ$m) counterpart, and the other has been independently detected at 850 and 870 $μ$m using SCUBA2 and ALMA Band 7, respectively. Their optical to radio spectral energy distributions indicate that they can lie at $z \gtrsim$ 3-5 and can be in the early phase of massive galaxy formation. Their contribution to the cosmic star formation rate density is estimated to be ~ 1 $\times$ 10$^{-3}$ $M_\odot$ yr$^{-1}$ Mpc$^{-3}$ if they lie somewhere in the redshift range of $z$ ~ 3-5. This value can be consistent with, or greater than that of bright submillimeter galaxies ($S_\mathrm{870μm}>$ 4.2 mJy) at $z$ ~ 3-5. We also uncover 3 more candidates near-infrared-dark faint ALMA sources without any counterparts ($S_\mathrm{1.2mm}$ ~ 0.45-0.86 mJy). These results show that an unbiased ALMA survey can reveal the dust-obscured star formation activities, which were missed in previous deep optical/near-infrared surveys.

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arXiv2019

Discovery of a Lya emitting dark-cloud within z ~ 2.8 SMMJ02399-0136 system

We present Keck/KCWI integral field spectrograph observations of the complex system surrounding SMM J02399$-$0136 (a lensed $z=2.8$ sub-mm galaxy), including an associated Ly$\rm α$ nebula, a dust-obscured, broad-absorption-line quasar, and neighboring galaxies. At a 3$σ$ surface brightness contour of 1.6$\times$ 10$^{-17}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$, the Ly$\rm α$ nebula extends over 17 arcsec ($\gtrsim 140$ physical kpc) and has a total Ly$\rm α$ luminosity of $2.5 \times 10^{44} \, \rm erg \, s^{-1}$ (uncorrected for lensing). The nebula exhibits a kinematic shear of $\sim$ 1000 km s$^{-1}$ over 100 pkpc with lowest velocities east of SMM J02399$-$0136 and increasing to the southwest. We also discover a bright, Ly$\rm α$ emitter, separated spatially and kinematically from the nebula, at a projected separation of $\approx$60 kpc from the quasar. This source has no clear central counterpart in deep $Hubble \, Space \, Telescope$ imaging, giving an intrinsic Ly$\rm α$ rest-frame equivalent width greater than 312 $ \rm \mathring{A}$ (5-$σ$). We argue that this 'dark cloud' is illuminated by the quasar with a UV flux that is orders of magnitude brighter than the emission along our sightline. This result confirms statistical inferences that luminous quasars at $z>2$ emit UV radiation anisotropically. Future KCWI observations of other lines, e.g. Ly$\rm β$, He$\rm _{II}$, C$\rm _{IV}$, etc, and with polarimetry will further reveal the origin of the Ly$\rm α$ nebula and nature of the dark cloud.

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arXiv2019

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

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 $\sim$60 arcmin$^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$\to$0) emission at $z$$\sim$2-3 and CO($J$=2$\to$1) at $z$$\sim$5-7 down to a CO luminosity limit of log($L'_{\rm CO}$/K km s$^{-1}$ pc$^2$)$\simeq$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$$\sim$2. We also present the currently most reliable measurement of the cosmic density of cold gas in galaxies at early epochs, i.e., the cold gas history of the universe, as determined over a large cosmic volume of $\sim$375,000 Mpc$^3$. Our measurements are in agreement with an increase of the cold gas density from $z$$\sim$0 to $z$$\sim$2-3, followed by a possible decline towards $z$$\sim$5-7. These findings are consistent with recent surveys based on higher-$J$ CO line measurements, upon which COLDz improves in terms of statistical uncertainties by probing $\sim$50-100 times larger areas and in the reliability of total gas mass estimates by probing the low-$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 towards its peak about 10 billion years ago, and that its decline towards the earliest epochs is likely related to a lower overall amount of cold molecular gas (as traced by CO) bound in galaxies towards the first billion years after the Big Bang.

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arXiv2018

Alma Twenty-six Arcmin^2 Survey Of Goods-s At One-millimeter (asagao): Source Catalog And Number Counts

We present the survey design, data reduction, construction of images, and source catalog of the Atacama Large Millimeter/submillimeter Array (ALMA) twenty-six arcmin^2 survey of GOODS-S at one-millimeter (ASAGAO). ASAGAO is a deep (1sigma ~ 61 uJy/beam for a 250 klambda-tapered map with a synthesized beam size of 0.51" x 0.45") and wide area (26 arcmin^2) survey on a contiguous field at 1.2 mm. By combining with ALMA archival data in the GOODS-South field, we obtained a deeper map in the same region (1sigma ~ 30 uJy/beam for a deep region with a 250 klambda-taper, and a synthesized beam size of 0.59" x 0.53"), providing the largest sample of sources (25 sources at >=5.0sigma, 45 sources at >=4.5sigma) among ALMA blank-field surveys to date. The number counts shows that 52(+11 -8)% of the extragalactic background light at 1.2 mm is resolved into discrete sources at S1.2m > 135 uJy. We create infrared (IR) luminosity functions (LFs) in the redshift range of z = 1-3 from the ASAGAO sources with KS-band counterparts, and constrain the faintest luminosity of the LF at 2.0 < z < 3.0. The LFs are consistent with previous results based on other ALMA and SCUBA-2 observations, which suggest a positive luminosity evolution and negative density evolution with increasing redshift. We find that obscured star-formation of sources with IR luminosities of log(L(IR)/Lsun)} ~> 11.8 account for ~~60%-90% of the z ~ 2 cosmic star-formation rate density.

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arXiv2018

The CO Luminosity Density at High-z (COLDz) Survey: A Sensitive, Large Area Blind Search for Low-J CO Emission from Cold Gas in the Early Universe with the Karl G. Jansky Very Large Array

We describe the CO Luminosity Density at High-z (COLDz) survey, the first spectral line deep field targeting CO(1-0) emission from galaxies at $z=1.95-2.85$ and CO(2-1) at $z=4.91-6.70$. The main goal of COLDz is to constrain the cosmic density of molecular gas at the peak epoch of cosmic star formation. By targeting both a wide ($\sim$51 arcmin$^2$) and a deep area ($\sim$9 arcmin$^2$), the survey is designed to robustly constrain the bright end and the characteristic luminosity of the CO(1-0) luminosity function. An extensive analysis of the reliability of our line candidates, and new techniques provide detailed completeness and statistical corrections as necessary to determine the best constraints to date on the CO luminosity function. Our blind search for CO(1-0) uniformly selects starbursts and massive Main Sequence galaxies based on their cold molecular gas masses. Our search also detects CO(2-1) line emission from optically dark, dusty star-forming galaxies at $z>5$. We find a range of spatial sizes for the CO-traced gas reservoirs up to $\sim40$ kpc, suggesting that spatially extended cold molecular gas reservoirs may be common in massive, gas-rich galaxies at $z\sim2$. Through CO line stacking, we constrain the gas mass fraction in previously known typical star-forming galaxies at $z=2$-3. The stacked CO detection suggests lower molecular gas mass fractions than expected for massive Main Sequence galaxies by a factor of $\sim3-6$. We find total CO line brightness at $\sim34\,$GHz of $0.45\pm0.2\,μ$K, which constrains future line intensity mapping and CMB experiments.

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arXiv2018

A resolved warm/dense gas Schmidt-Kennicutt relationship in a binary HyLIRG at $z=2.41$

Hyperluminous infrared galaxies (HyLIRGs) provide crucial "long lever arm" constraints on galaxy evolution. H-ATLAS $J084933.4+021443$, a $z=2.41$ binary HyLIRG with at least two additional luminous companion galaxies, is thus an optimal test-ground for studies of star formation and galaxy evolution during "cosmic noon". We have used ALMA to obtain resolved imaging and kinematics of atomic and molecular emission lines, and rest-frame $340$ to $1160$GHz continuum emission, for the known luminous component galaxies in H-ATLAS $J084933.4+021443$: W, T, M, C. All four component galaxies are spatially ($\sim 0 .\!\!^{''} 3$ or $2.5$kpc) resolved in CO J:7-6, [C$_\mathrm{I}$] 2-1, H$_2$O and the millimetre (mm) to sub-mm continuum. Rotation-dominated gas kinematics is confirmed in W and T. The significant extension to component T, in gas and continuum, along its kinematic minor axis, is attributable to its lensing magnification. Spatially resolved sub-mm spectral energy distributions reveal that component W is well fit with greybody emission from dust at a single temperature over the full extent of the galaxy, despite it containing a powerful AGN, while component T requires an additional component of hotter nuclear dust and additional sources of emission in the mm. We confirm that [C$_\mathrm{I}$] 2-1 can be used as a rough tracer of warm/dense molecular gas in extreme systems, though the [C$_\mathrm{I}$] 2-1/CO luminosity ratio increases sub-linearly. We obtain an exquisite and unprecedented resolved ($2.5$-kpc-scale) "warm/dense molecular gas" Schmidt-Kennicutt (SK) relationship for components W and T. Gas exhaustion times for all apertures in W (T) are $1-4$Gyr ($0.5-2$Gyr). Both W and T follow a resolved "warm/dense gas" SK relationship with power law $n\sim1.7$, significantly steeper than the $n\sim1$ found previously via "cold" molecular gas in nearby "normal" star-forming galaxies.

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