arXiv subjects

Fabian Walter

Publications and source records attributed to Fabian Walter.

At least 199 records · Page 11Linked to original sources

arXiv2020

No Redshift Evolution in the Broad Line Region Metallicity up to z=7.54: Deep NIR Spectroscopy of ULAS J1342+0928

We present deep (9 hours) Gemini-N/GNIRS near-infrared spectroscopic observations of ULAS J1342+0928, a luminous quasar at z=7.54. Various broad emission lines were detected, as well as the underlying continuum and iron forests over the rest-frame wavelength 970-2930A. There is a clear trend that higher-ionization emission lines show larger blueshifts with CIV1549 exhibiting 5510^{+240}_{-110} km s-1 blueshift with respect to the systematic redshift from the far-infrared [CII] 158um emission line. Those high ionization lines have wide profiles with FWHM more than 10000 km s-1. A modest blueshift of 340^{+110}_{-80} km s-1 is also seen in MgII, the lowest ionization line identified in the spectrum. The updated MgII-based black hole mass of M_BH=9.1_{-1.3}^{+1.4} x 10^8 M_sun and the Eddington ratio of L_bol/L_Edd=1.1_{-0.2}^{+0.2} confirm that ULAS J1342+0928 is powered by a massive and actively accreting black hole. There is no significant difference in the emission line ratios such as SiIV/CIV and AlIII/CIV when compared to lower-redshift quasars in a similar luminosity range, which suggests early metal pollution of the broad-line-region clouds. This trend also holds for the FeII/MgII line ratio, known as a cosmic clock that traces the iron enrichment in the early universe. Different iron templates and continuum fitting ranges were used to explore how the FeII/MgII measurement changes as a function of spectral modeling. Quasars at even higher redshift or at fainter luminosity range (L_bol<10^46 erg s-1) are needed to probe the sites of early metal enrichment and a corresponding change in the FeII/MgII ratio.

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arXiv2020

Pōniuā'ena: A Luminous $z=7.5$ Quasar Hosting a 1.5 Billion Solar Mass Black Hole

We report the discovery of a luminous quasar, J1007+2115 at $z=7.515$ ("Pōniuā'ena"), from our wide-field reionization-era quasar survey. J1007+2115 is the second quasar now known at $z>7.5$, deep into the reionization epoch. The quasar is powered by a $(1.5\pm0.2)\times10^9$ $M_{\odot}$ supermassive black hole (SMBH), based on its broad MgII emission-line profile from Gemini and Keck near-IR spectroscopy. The SMBH in J1007+2115 is twice as massive as that in quasar J1342+0928 at $z=7.54$, the current quasar redshift record holder. The existence of such a massive SMBH just 700 million years after the Big Bang significantly challenges models of the earliest SMBH growth. Model assumptions of Eddington-limited accretion and a radiative efficiency of 0.1 require a seed black hole of $\gtrsim 10^{4}$ $M_{\odot}$ at $z=30$. This requirement suggests either a massive black hole seed as a result of direct collapse or earlier periods of rapid black hole growth with hyper-Eddington accretion and/or a low radiative efficiency. We measure the damping wing signature imprinted by neutral hydrogen absorption in the intergalactic medium (IGM) on J1007+2115's Ly$α$ line profile, and find that it is weaker than that of J1342+0928 and two other $z\gtrsim7$ quasars. We estimate an IGM volume-averaged neutral fraction $\langle x\rm_{HI}\rangle=0.39^{+0.22}_{-0.13}$. This range of values suggests a patchy reionization history toward different IGM sightlines. We detect the 158 $μ$m [C II] emission line in J1007+2115 with ALMA; this line centroid yields a systemic redshift of $z=7.5149\pm0.0004$ and indicates a star formation rate of $\sim210$ $M_{\odot}$ yr$^{-1}$ in its host galaxy.

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arXiv2020

The Molecular ISM in the Super Star Clusters of the Starburst NGC 253

We present submillimeter spectra of the (proto-)super star cluster (SSC) candidates in the starbursting center of the nearby galaxy NGC 253 identified by Leroy et al. (2018). The 2.5pc resolution of our ALMA cycle 3 observations approach the size of the SSCs and allows the study of physical and chemical properties of the molecular gas in these sources. In the 14 SSC sources and in the frequency ranges 342.0-345.8 GHz and 353.9-357.7 GHz we detect 55 lines belonging to 19 different chemical species. The SSCs differ significantly in chemical complexity, with the richest clusters showing 19 species and the least complex showing 4 species. We detect HCN isotopologues and isomers (H$^{13}$CN, HC$^{15}$N, H$^{15}$NC), abundant HC$_3$N, SO and S$^{18}$O, SO$_2$, and H$_2$CS. The gas ratios CO/HCN, CO/HCO$^+$ are low, ~1-10, implying high dense gas fractions in the SSCs. Line ratio analyses suggests chemistry consistent with photon-dominated regions and mechanical heating. None of the SSCs near the galaxy center show line ratios that imply an X-ray dominated region, suggesting that heating by any (still unknown) AGN does not play a major role. The gas temperatures are high in most sources, with an average rotational temperature of ~130 K in SO$_2$. The widespread existence of vibrationally excited HCN and HC$_3$N transitions implies strong IR radiation fields, potentially trapped by a greenhouse effect due to high continuum opacities.

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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

A Significantly Neutral Intergalactic Medium Around the Luminous z=7 Quasar J0252-0503

Luminous $z\ge7$ quasars provide direct probes of the evolution of supermassive black holes (SMBHs) and the intergalactic medium (IGM) during the epoch of reionization (EoR). The Ly$α$ damping wing absorption imprinted by neutral hydrogen in the IGM can be detected in a single EoR quasar spectrum, allowing the measurement of the IGM neutral fraction towards that line of sight. However, damping wing features have only been detected in two $z>7$ quasars in previous studies. In this paper, we present new high quality optical and near-infrared spectroscopy of the $z=7.00$ quasar DES J025216.64--050331.8 obtained with Keck/NIRES and Gemini/GMOS. By using the MgII single-epoch virial method, we find that it hosts a $\rm (1.39\pm0.16) \times10^{9} ~M_\odot$ SMBH accreting at an Eddington ratio of $λ_{\rm Edd}=0.7\pm0.1$, consistent with the values seen in other luminous $z\sim 7$ quasars. Furthermore, the Ly$α$ region of the spectrum exhibits a strong damping wing absorption feature. The lack of associated metal absorption in the quasar spectrum indicates that this absorption is imprinted by a neutral IGM. Using a state-of-the-art model developed by Davies et al., we measure a volume-averaged neutral hydrogen fraction at $z=7$ of $\langle x_{\rm HI} \rangle = 0.70^{+0.20}_{-0.23} (^{+0.28}_{-0.48})$ within 68% (95%) confidence intervals when marginalizing over quasar lifetimes of $10^3\le t_{\rm Q}\le10^8$ yr. This is the highest IGM neutral fraction yet measured using reionization-era quasar spectra.

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arXiv2020

Plateau de Bure High-z Blue-Sequence Survey 2 (PHIBSS2): Search for Secondary Sources, CO Luminosity Functions in the Field, and the Evolution of Molecular Gas Density through Cosmic Time

We report on the results of a search for serendipitous sources in CO emission in 110 cubes targeting CO(2-1), CO(3-2), and CO(6-5) at z ~ 1-2 from the second Plateau de Bure High-z Blue-Sequence Survey (PHIBSS2). The PHIBSS2 observations were part of a 4-year legacy program at the IRAM Plateau de Bure Interferometer aimed at studying early galaxy evolution from the perspective of molecular gas reservoirs. We present a catalog of 67 candidate secondary sources from this search, with 45 out of the 110 data cubes showing sources in addition to the primary target that appear to be field detections, unrelated to the central sources. This catalog includes the redshifts, line widths, fluxes, as well as an estimation of their reliability based on their false positive probability. We perform a search in the 3D-HST/CANDELS catalogs for the secondary CO detections and tentatively find that ~64% of these have optical counterparts, which we use to constrain their redshifts. Finally, we use our catalog of candidate CO detections to derive the CO(2-1), CO(3-2), CO(4-3), CO(5-4), and CO(6-5) luminosity functions over a range of redshifts, as well as the molecular gas mass density evolution. Despite the different methodology, these results are in very good agreement with previous observational constraints derived from blind searches in deep fields. They provide an example of the type of "deep field" science that can be carried out with targeted observations.

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arXiv2020

A metal-poor damped Ly-alpha system at redshift 6.4

We identify a strong Ly-alpha damping wing profile in the spectrum of the quasar P183+05 at z=6.4386. Given the detection of several narrow metal absorption lines at z=6.40392, the most likely explanation for the absorption profile is that it is due to a damped Ly-alpha system. However, in order to match the data a contribution of an intergalactic medium 5-38% neutral or additional weaker absorbers near the quasar is also required. The absorption system presented here is the most distant damped Ly-alpha system currently known. We estimate an HI column density ($10^{20.68\pm0.25}\,$cm$^{-2}$), metallicity ([O/H]$=-2.92\pm 0.32$), and relative chemical abundances of a system consistent with a low-mass galaxy during the first Gyr of the universe. This object is among the most metal-poor damped Ly-alpha systems known and, even though it is observed only ~850 Myr after the big bang, its relative abundances do not show signatures of chemical enrichment by Population III stars.

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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

The ALMA Spectroscopic Survey in the HUDF: A model to explain observed 1.1 and 0.85 millimeter dust continuum number counts

We present a new semi-empirical model for the dust continuum number counts of galaxies at 1.1 millimeter and 850 \micron. Our approach couples an observationally motivated model for the stellar mass and SFR distribution of galaxies with empirical scaling relations to predict the dust continuum flux density of these galaxies. Without a need to tweak the IMF, the model reproduces the currently available observations of the 1.1 millimeter and 850 \micron number counts, including the observed flattening in the 1.1 millimeter number counts below 0.3 mJy \citep{Gonzalez2019numbercounts} and the number counts in discrete bins of different galaxy properties. Predictions of our work include : (1) the galaxies that dominate the number counts at flux densities below 1 mJy (3 mJy) at 1.1 millimeter (850 $μ$m) have redshifts between $z=1$ and $z=2$, stellar masses of $\sim 5\times10^{10}~\rm{M}_\odot$, and dust masses of $\sim 10^{8}~\rm{M}_\odot$; (2) the flattening in the observed 1.1 millimeter number counts corresponds to the knee of the 1.1 millimeter luminosity function. A similar flattening is predicted for the number counts at 850 $μ$m; (3) the model reproduces the redshift distribution of current 1.1 millimeter detections; (4) to efficiently detect large numbers of galaxies through their dust continuum, future surveys should scan large areas once reaching a 1.1 millimeter flux density of 0.1 mJy rather than integrating to fainter fluxes. Our modeling framework also suggests that the amount of information on galaxy physics that can be extracted from the 1.1 millimeter and 850 $μ$m number counts is almost exhausted.

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arXiv2020

Deceptively cold dust in the massive starburst galaxy GN20 at $z\sim4$

We present new observations, carried out with IRAM NOEMA, of the atomic neutral carbon transitions [CI](1-0) at 492 GHz and [CI](2-1) at 809 GHz of GN20, a well-studied star-bursting galaxy at $z=4.05$. The high luminosity line ratio [CI](2-1)/[CI](1-0) implies an excitation temperature of $48^{+14}_{-9}$ K, which is significantly higher than the apparent dust temperature of $T_{\rm d}=33\pm2$ K ($β=1.9$) derived under the common assumption of an optically thin far-infrared dust emission, but fully consistent with $T_{\rm d}=52\pm5$ K of a general opacity model where the optical depth ($τ$) reaches unity at a wavelength of $λ_0=170\pm23$ $μ$m. Moreover, the general opacity solution returns a factor of $\sim 2\times$ lower dust mass and, hence, a lower molecular gas mass for a fixed gas-to-dust ratio, than with the optically thin dust model. The derived properties of GN20 thus provide an appealing solution to the puzzling discovery of starbursts appearing colder than main-sequence galaxies above $z>2.5$, in addition to a lower dust-to-stellar mass ratio that approaches the physical value predicted for starburst galaxies.

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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

X-ray Observations of a $z\sim6.2$ Quasar/Galaxy Merger

Quasars at early redshifts ($z > 6$) with companion galaxies offer unique insights into the growth and evolution of the first supermassive black holes. Here, we report on a 150 ks Chandra observation of PSO J308.0416$-$21.2339, a $z=6.23$ quasar with a merging companion galaxy identified in [C II] and rest-frame UV emission. With $72.3^{+9.6}_{-8.6}$ net counts, we find that PSO J308.0416$-$21.2339 is powerful ($L_X = 2.31^{+1.14}_{-0.76} \times 10^{45}\ \textrm{erg}\,\textrm{s}^{-1}\,\textrm{cm}^{-2}$ in rest-frame $2.0-10.0$ keV) yet soft (spectral power-law index $Γ=2.39^{+0.37}_{-0.36}$ and optical-to-X-ray slope $α_{\rm OX} = -1.41 \pm 0.11$). In addition, we detect three hard-energy photons $2.''0$ to the west of the main quasar, cospatial with the brightest UV emission of the merging companion. As no soft-energy photons are detected in the same area, this is potentially indicative of a highly-obscured source. With conservative assumptions, and accounting for both background fluctuations and the extended wings of the quasar's emission, these photons only have a probability $P=0.021$ of happening by chance. If confirmed by deeper observations, this system is the first high redshift quasar and companion individually detected in X-rays and is likely a dual AGN.

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arXiv2019

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

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.

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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 z=7.54 Quasar ULAS J1342+0928 Is Hosted by a Galaxy Merger

We present ALMA 0.28"x0.20" (1.4kpc x 1.0kpc) resolution observations of the [CII] 158um line and underlying dust continuum in the host galaxy of the most distant quasar currently known, ULAS J1342+0928 at z=7.5413. Both the [CII] and continuum are detected and spatially resolved. The [CII] line is ~1.5 times more extended than the continuum emission, showing an elongated and complex structure of approximately 3.2kpc x 6.4kpc. Two separate peaks are clearly seen (>6sigma each) in three 100 km/s width [CII] channel maps. The velocity field of the [CII] gas does not show evidence of a coherent rotation field but rather chaotic motion, reminiscent of an on-going merger.

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