arXiv subjects

Jeff Wagg

Publications and source records attributed to Jeff Wagg.

At least 37 records · Page 2Linked to original sources

arXiv2020

SCUBA2 High Redshift Bright Quasar Survey: Far-infrared Properties and Weak-line Features

We present a submillimetre continuum survey ('SCUBA2 High rEdshift bRight quasaR surveY', hereafter SHERRY) of 54 high redshift quasars at $5.6 3.5σ$). The new SHERRY detections indicate far-infrared (FIR) luminosities of $\rm 3.5\times10^{12}$ to $\rm 1.4\times10^{13}$ $L_{\odot}$, implying extreme star formation rates of 90 to 1060 $M_{\odot}$ yr$^{-1}$ in the quasar host galaxies. Compared with $z =$ 2$-$5 samples, the FIR luminous quasars ($L_{\rm FIR} > 10^{13}\,L_{\odot}$) are more rare at $z \sim 6$. The optical/near-infrared (NIR) spectra of these objects show 11% (6/54) of the sources have weak Ly$α$, emission line features, which may relate to different sub-phases of the central active galactic nuclei (AGNs). Our SCUBA2 survey confirms the trend reported in the literature that quasars with submillimeter detections tend to have weaker ultraviolet (UV) emission lines compared to quasars with nondetections. The connection between weak UV quasar line emission and bright dust continuum emission powered by massive star formation may suggest an early phase of AGN-galaxy evolution, in which the broad line region is starting to develop slowly or is shielded from the central ionization source, and has unusual properties such as weak line features or bright FIR emission.

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arXiv2020

Ionized and atomic interstellar medium in the z = 6.003 quasar SDSS J2310+1855

Observing the interstellar medium (ISM) in $z \gtrsim 6$ quasars host galaxies is essential for understanding the co-evolution between the supermassive black holes and their hosts. To probe the gas physical conditions and search for imprints of Active Galactic Nuclei (AGN) on the ISM, we report ALMA observations of the $\rm [N\ II]_{122 μm}$ and $\rm [O\ I]_{146 μm}$ lines and the underlying continuum from the $z=6.003$ quasar SDSS J231038.88+185519.7. Together with previous $\rm [C\ II]_{158 μm}$ and $\rm [O\ III]_{88 μm}$ observations, we use the ratios of these fine-structure lines to probe the ISM properties. Similar to other high-$z$ systems, this object exhibits a $\rm [C\ II]_{158 μm}$/$\rm [O\ I]_{146 μm}$ ratio comparable to the lowest values found in local (Ultra) luminous infrared galaxies, suggesting a "warmer" and "denser" gas component compared to typical local systems. The $\rm [O\ III]_{88 μm}$/$\rm [O\ I]_{146 μm}$ ratio is lower than that of other local and high-$z$ systems, indicating a smaller ionized gas fraction in this quasar. The $\rm [O\ III]_{88 μm}$/$\rm [N\ II]_{122 μm}$ ratio is comparable to that of local systems, and suggests a metallicity of $Z/Z_{\odot}$=1.5$-$2.1. Based on the $\rm [N\ II]_{122 μm}$ detection, we estimate that $17\%$ of the $\rm [C\ II]_{158 μm}$ emission is associated with ionized gas. The $\rm [N\ II]_{122 μm}$ line shows a "flux deficit" comparable to local systems. The $\rm [O\ I]_{146 μm}$ line, with a $\rm [O\ I]_{146 μm}$/FIR ratio $\ge 2\times$ than expected from the local relation, indicates no $\rm [O\ I]_{\rm 146 μm}$ deficit. The low $\rm [C\ II]_{158 μm}$/$\rm [O\ I]_{146 μm}$ ratio, together with the high $\rm [O\ I]_{146 μm}$/FIR ratio in J2310+1855, reveals that the warm and dense gas is likely a result of AGN heating to the ISM.

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arXiv2020

Observations by GMRT at 323 MHz of radio-loud quasars at $z>5$

We present Giant Metrewave Radio Telescope (GMRT) 323 MHz radio continuum observations toward 13 radio-loud quasars at $z>5$, sampling the low-frequency synchrotron emission from these objects. Among the 12 targets successfully observed, we detected 10 above $4σ$ significance, while 2 remain undetected. All of the detected sources appear as point sources. Combined with previous radio continuum detections from the literature, 9 quasars have power-law spectral energy distributions throughout the radio range; for some the flux density drops with increasing frequency while it increases for others. Two of these sources appear to have spectral turnover. For the power-law-like sources, the power-law indices have a positive range between 0.18 and 0.67 and a negative values between $-0.90$ and $-0.27$. For the turnover sources, the radio peaks around $\sim1$ and $\sim10$ GHz in the rest frame, the optically thin indices are $-0.58$ and $-0.90$, and the optically thick indices are 0.50 and 1.20. A magnetic field and spectral age analysis of SDSS J114657.59+403708.6 at $z=5.01$ may indicate that the turnover is not caused by synchrotron self-absorption, but rather by free-free absorption by the high-density medium in the nuclear region. Alternatively, the apparent turnover may be an artifact of source variability. Finally, we calculated the radio loudness $R_{2500\rm\, Å}$ for our sample, which spans a very wide range from 12$^{+13}_{-13}$ to 4982$^{+279}_{-254}$.

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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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arXiv2020

SKA LFAA Station Design Report

This report was submitted as part of the SKA Low Frequency Aperture Array Critical Design Review describing the design of the SKA1-LOW station that took place between 2013 and 2018. The SKA1 LOW field station is inscribed in a circular area having an effective station diameter (centre to centre) of 38 meters and has 256 SKALA4 elements. This document describes the electromagnetic design of the field station. In particular it describes the layout design and the electromagnetic modelling and characteristics of the station. This document describes the effects associated with the layout and array such as mutual coupling effects, side lobe pattern and beam shape (eg. smoothness, calibration models) and presents the state of the art of our ability to measure the array performance and validate the simulation work. The current LFAA field node requirements, derived from the SKA L1 requirements, have evolved over the last years since the LFAA PDR and the System Baseline Design. The SKA1 LOW field station has been designed to meet those requirements and has therefore tracked their evolution (eg. sensitivity requirements, array diameter, etc.). The aforementioned requirements represent a very tight space with a desire for very high sensitivity over a large frequency range (7 to 1) and wide field of view (90 degrees cone around zenith) while keeping the station diameter to a minimum, so as the filling factor but at the same time allowing for sufficient space between antennas to allow for easy maintenances, amongst many others. This results in a complex design.

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arXiv2020

The ALMA Spectroscopic Survey in the HUDF: The Cosmic Dust and Gas Mass Densities in Galaxies up to $z\sim3$

Using the deepest 1.2 mm continuum map to date in the Hubble Ultra Deep Field obtained as part of the ALMA Spectroscopic Survey (ASPECS) large program, we measure the cosmic density of dust and implied gas (H$_{2}+$H I) mass in galaxies as a function of look-back time. We do so by stacking the contribution from all $H$-band selected galaxies above a given stellar mass in distinct redshift bins, $ρ_{\rm dust}(M_\ast>M,z)$ and $ρ_{\rm gas}(M_\ast>M,z)$. At all redshifts, $ρ_{\rm dust}(M_\ast>M,z)$ and $ρ_{\rm gas}(M_\ast>M,z)$ grow rapidly as $M$ decreases down to $10^{10}\,M_\odot$, but this growth slows down towards lower stellar masses. This flattening implies that at our stellar mass-completeness limits ($10^8\,M_\odot$ and $10^{8.9}\,M_\odot$ at $z\sim0.4$ and $z\sim3$), both quantities converge towards the total cosmic dust and gas mass densities in galaxies. The cosmic dust and gas mass densities increase at early cosmic time, peak around $z\sim2$, and decrease by a factor $\sim4$ and 7, compared to the density of dust and molecular gas in the local universe, respectively. The contribution of quiescent galaxies -- i.e., with little on-going star-formation -- to the cosmic dust and gas mass densities is minor ($\lesssim10\%$). The redshift evolution of the cosmic gas mass density resembles that of the star-formation rate density, as previously found by CO-based measurements. This confirms that galaxies have relatively constant star-formation efficiencies (within a factor $\sim2$) across cosmic time. Our results also imply that by $z\sim0$, a large fraction ($\sim90\%$) of dust formed in galaxies across cosmic time has been destroyed or ejected to the intergalactic medium.

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arXiv2020

The ALMA Spectroscopic Survey in the HUDF: Deep 1.2 mm continuum number counts

We present the results from the 1.2 mm continuum image obtained as part of the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS). The 1.2 mm continuum image has a size of 2.9 (4.2) arcmin$^2$ within a primary beam response of 50% (10%) and a rms value of $9.3\thinspace{\rmμJy\thinspace beam^{-1}}$. We detect 35 sources at high significance (Fidelity $\geq0.5$), 32 of these have well characterized near-infrared HST counterparts. We estimate the 1.2 mm number counts to flux levels of $<30\thinspace{\rmμJy}$ in two different ways: we first use the detected sources to constrain the number counts and find a significant flattening of the counts below $S_ν\sim 0.1$ mJy. In a second approach, we constrain the number counts by using a probability of deflection statistics (P(D)) analysis. For this latter approach, we describe new methods to accurately measure the noise in interferometric imaging (employing jack-knifing in the cube and in the visibility plane). This independent measurement confirms the flattening of the number counts. Our analysis of the differential number counts shows that we are detecting $\sim$93% ($\sim$100% if we include the lower fidelity detections) of the total continuum dust emission associated to galaxies in the HUDF. The ancillary data allows us to study the dependence of the 1.2 mm number counts on redshift ($z=0-4$), galaxy dust mass (${\rm M}_{\rm dust}=10^{7}-10^{9}{\rm M}_{\odot}$), stellar mass (${\rm M}_{*}=10^{9}-10^{12}{\rm M}_{\odot}$), and star-formation rate (${\rm SFR}=1-1000\thinspace{\rm M}_{\odot}\thinspace{\rm yr^{-1}}$). In an accompanying paper we show that the number counts are crucial to constrain galaxy evolution models and the understanding of star-forming galaxies at high redshift.

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arXiv2020

Investigating overdensities around z>6 galaxies through ALMA observations of [CII]

We present a search for companion [CII] emitters to known luminous sources at $6<$ z $<6.5$ in deep, archival ALMA observations. The observations are deep enough to detect sources with L$_{\rm [CII]} \sim 10^8$ at z $\sim6$. We identify four robust line detections from a blind search of five deep fields centered on ultra-luminous infrared galaxies and QSOs, over an order of magnitude more than expected based on current observations and predictions, suggesting that these objects may be highly biased tracers of mass in the early Universe. We find these companion lines to have comparable properties to other known galaxies at the same epoch. All companions lie less than 650 km s$^{-1}$ and between 20 -- 70 kpc (projected) from their central source, providing a constraint on their halo masses of the central galaxies ranging from 2.5$\times$10$^{12}$ M$_\odot$ to 4$\times$10$^{13}$ M$_\odot$. To place these discoveries in context, we employ a mock galaxy catalog to estimate the luminosity function for [CII] during reionization and compare to our observations. The simulations support this result by showing a similar level of elevated counts found around such luminous sources.

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arXiv2019

Probing the full CO spectral line energy distribution (SLED) in the nuclear region of a quasar-starburst system at $z=6.003$

We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO $(8-7)$, $(9-8)$, $\rm H_{2}O (2_{0,2}-1_{1,1})$ and $\rm OH^{+} (1_{1}-0_{1})$ and NOrthern Extended Millimeter Array (NOEMA) observations of CO $(5-4)$, $(6-5)$, $(12-11)$ and $(13-12)$ towards the $z = 6.003$ quasar SDSS J231038.88+185519.7, aiming to probe the physical conditions of the molecular gas content of this source. We present the best sampled CO spectral line energy distribution (SLED) at $z = 6.003$, and analyzed it with the radiative transfer code MOLPOP-CEP. Fitting the CO SLED to a one-component model indicates a kinetic temperature $T_{\rm kin} = 228 \ \rm K$, molecular gas density $log (n(\rm H_{2})/\rm cm^{-3}$ )=4.75, and CO column density $log(N(\rm CO)/\rm cm^{-2}) =17.5$, although a two-component model better fits the data. In either case, the CO SLED is dominated by a "warm" and "dense" component. Compared to samples of local (Ultra) Luminous Infrared Galaxies ((U)LIRGs), starburst galaxies and high redshift Submillimeter Galaxies (SMGs), J2310+1855 exhibits higher CO excitation at ($J \geq 8$), like other high redshift quasars. The high CO excitation, together with the enhanced $L_{\rm H_{2}O}/ L_{IR} $, $L_{\rm H_{2}O}/ L_{CO} $ and $L_{OH^{+}}/L_{\rm H_{2}O} $ ratios, suggests that besides the UV radiation from young massive stars, other mechanisms such as shocks, cosmic rays and X-rays might also be responsible for the heating and ionization of the molecular gas. In the nuclear region probed by the molecular emissions lines, any of these mechanisms might be present due to the powerful quasar and the starburst activity.

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arXiv2019

Anticipated Performance of the Square Kilometre Array -- Phase 1 (SKA1)

The Square Kilometre Array (SKA), currently under design, will be a transformational facility for studying the Universe at centimetre and metre wavelengths in the next decade and beyond. This paper provides the current best estimate of the anticipated performance of SKA Phase 1 (SKA1), using detailed design work, before actual on-sky measurements have been made. It will be updated as new information becomes available. The information contained in this paper takes precedent over any previous documents.

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arXiv2019

The ALMA Spectroscopic Survey in the HUDF: Constraining cumulative CO emission at $1 \lesssim z \lesssim 4$ with power spectrum analysis of ASPECS LP data from 84 to 115 GHz

We present a power spectrum analysis of the ALMA Spectroscopic Survey Large Program (ASPECS LP) data from 84 to 115 GHz. These data predominantly probe small-scale fluctuations ($k=10$-$100$ h Mpc$^{-1}$) in the aggregate CO emission in galaxies at $1 \lesssim z \lesssim 4$. We place an integral constraint on CO luminosity functions (LFs) in this redshift range via a direct measurement of their second moments in the three-dimensional (3D) auto-power spectrum, finding a total CO shot noise power $P_{\textrm{CO,CO}}(k_{\textrm{CO(2-1)}}) \leq 1.9\times10^2$ $μ$K$^2$ (Mpc h$^{-1}$)$^3$. This upper limit ($3σ$) is consistent with the observed ASPECS CO LFs in Decarli et al. 2019, but rules out a large space in the range of $P_{\textrm{CO,CO}}(k_{\textrm{CO(2-1)}})$ inferred from these LFs, which we attribute primarily to large uncertainties in the normalization $Φ_*$ and knee $L_*$ of the Schechter-form CO LFs at $z > 2$. Also, through power spectrum analyses of ASPECS LP data with 415 positions from galaxies with available optical spectroscopic redshifts, we find that contributions to the observed mean CO intensity and shot noise power of MUSE galaxies are largely accounted for by ASPECS blind detections, though there are $\sim20$% contributions to the CO(2-1) mean intensity due to sources previously undetected in the blind line search. Finally, we sum the fluxes from individual blind CO detections to yield a lower limit on the mean CO surface brightness at 99 GHz of $\langle T_{\textrm{CO}} \rangle = 0.55\pm0.02$ $μ$K, which we estimate represents $68$-$80$% of the total CO surface brightness at this frequency.

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arXiv2019

Resolving the interstellar medium in the nuclear region of two z=5.78 quasar host galaxies with ALMA

We present ALMA observations of the [CII] 158 $μ$m fine structure line and dust continuum emission from two quasars, SDSS J104433.04-012502.2 and SDSS J012958.51-003539.7, at z=5.78. The ALMA observations at 0.2'' resolution map the dust and gas on kpc scales. The spatially resolved emission shows a similar trend of decreasing [CII]-FIR ratios with increasing FIR surface brightnesses as was found in the infrared luminous galaxies with intense star formation. We confirm the velocity gradients of [CII] emission found previously in SDSS J0129-0035. No clear evidence of order motion is detected in SDSS J1044-0125. The velocity maps and PV-diagrams also suggest turbulent gas clumps in both objects. We tentatively detect a [CII] peak offset 4.9 kpc to the East of SDSS J1044-0125. This may be associated with an infalling companion, or node of gas outflow. All these results suggest significant dynamical evolution of the ISM in the nuclear region of these young quasar-starburst systems. We fit the velocity map of the [CII] emission from SDSS J0129-0035 with a rotating disk model. The result suggests a face-on system with an inclination angle of 16 +/- 20 degree and constrains the lower limit of the host galaxy dynamical mass to be 2.6x10^10 Msun within the [CII] emitting region. It is likely that SDSS J0129-0035, as well as other young quasars with super massive black hole masses on order of 10^7 to 10^8 Msun, falls close to the black hole and host galaxy mass relation defined by local galaxies.

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arXiv2019

The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Evolution of the molecular gas in CO-selected galaxies

We analyze the interstellar medium properties of a sample of sixteen 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 a couple of additional CO line emitters in the UDF that are identified based on their MUSE optical spectroscopic redshifts. The ASPECS CO$-$selected galaxies cover a larger range of star-formation rates 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 star-formation rate-stellar mass relation (`galaxy main sequence'). However, we find that $\sim30\%$ of the galaxies (5 out of 16) are offset from the galaxy main sequence at their respective redshift, with $\sim12\%$ (2 out of 16) falling below this relationship. Some CO-rich galaxies exhibit low star-formation rates, 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 contributor to the molecular gas density at any redshift probed by our observations (z$\sim$1$-$3). The respective contribution by starburst galaxies above the main sequence decreases from z$\sim$2.5 to z$\sim$1, whereas we find tentative evidence for an increased contribution to the cosmic molecular gas density from the passive galaxies below the main sequence.

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arXiv2019

Neutral carbon and highly excited CO in a massive star-forming main sequence galaxy at z=2.2

We used the Plateau De Bure Interferometer to observe multiple CO and neutral carbon transitions in a z=2.2 main sequence disk galaxy, BX610. Our observation of CO(7-6), CO(4-3), and both far-infrared(FIR) [CI] lines complements previous observations of H$α$ and low-J CO, and reveals a galaxy that is vigorously forming stars with UV fields (Log($G$ G$_0^{-1}) \lesssim3.25);$ although less vigorously than local ultra-luminous infrared galaxies or most starbursting submillimeter galaxies in the early universe. Our observations allow new independent estimates of the cold gas mass which indicate $M_\textrm{gas}\sim2\times10^{11}$M$_\odot$, and suggest a modestly larger $α_{\textrm{CO}}$ value of $\sim$8.2. The corresponding gas depletion timescale is $\sim$1.5 Gyr. In addition to gas of modest density (Log($n$ cm$^3)\lesssim3$ ) heated by star formation, BX610 shows evidence for a significant second gas component responsible for the strong high-J CO emission. This second component might either be a high-density molecular gas component heated by star formation in a typical photodissociation region, or could be molecular gas excited by low-velocity C shocks. The CO(7-6)-to-FIR luminosity ratio we observe is significantly higher than typical star-forming galaxies and suggests that CO(7-6) is not a reliable star-formation tracer in this galaxy.

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arXiv2019

The ALMA Spectroscopic Survey in the HUDF: the molecular gas content of galaxies and tensions with IllustrisTNG and the Santa Cruz SAM

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 semi-analytic model (SC SAM). We explore several recipes to model the H$_2$ 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-H$_2$ conversion factor of $α_{\rm CO} = 3.6\,\rm{M}_\odot/(\rm{K}\,\rm{km/s}\,\rm{pc}^{2})$ the results of our work include: (1) the H$_2$ 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 H$_2$-rich ($M_{\rm H2} > 3\times 10^{10}\,\rm{M}_\odot$) galaxies observed by ASPECS; (3) the H$_2$ cosmic density evolution predicted by IllustrisTNG (the SC SAM) is in tension (only just agrees) 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-H$_2$ conversion factor in the range $α_{\rm CO} = 2.0 - 0.8\,\rm{M}_\odot/(\rm{K}\,\rm{km/s}\,\rm{pc}^{2})$. Additional work on constraining the CO-to-H$_2$ 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.

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arXiv2019

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

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 $ρ$(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 $ρ$(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 $ρ$(H$_2$) therefore closely matches the evolution of the cosmic star formation rate density $ρ_{\rm SFR}$. 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 $ρ$(H$_2$) and $ρ_{\rm SFR}$ leaves only little room for a significant evolution of the average star formation efficiency in galaxies since $z\sim 3$ (85% of cosmic history).

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arXiv2019

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

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 MUSE HUDF Survey and multi-wavelength data to uniquely associate all 16 line-emitters, detected in the ALMA data without preselection, with rotational transitions of carbon monoxide (CO). We identify ten as CO(2-1) at $1 < z < 2$, five as CO(3-2) at $2 < z < 3$ and one 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 $z \le 1.5$, 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 $z \sim 1.4$ and $z \sim 2.6$, respectively. Being a CO-flux limited survey, ASPECS-LP detects molecular gas in galaxies on, above and below the main sequence (MS) at $z \sim 1.4$. For stellar masses $\ge 10^{10} (10^{10.5})$ M$_{\odot}$, 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 on MS galaxies during the peak of galaxy formation.

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