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Register a new userALMACAL III: A combined ALMA and MUSE Survey for Neutral, Molecular, and Ionised Gas in an HI-Absorption-Selected System
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A. Klitsch
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Studying the flow of baryons into and out of galaxies is an important part of understanding the evolution of galaxies over time. We present a detailed case study of the environment around an intervening Ly $alpha$ absorption line system at $z_{rm abs} = 0.633$, seen towards the quasar J0423$-$0130 ($z_{rm QSO} = 0.915$). We detect with ALMA the $^{12}$CO(2--1), $^{12}$CO(3--2) and $1.2$~mm continuum emission from a galaxy at the redshift of the Ly $alpha$ absorber at a projected distance of $135$ kpc. From the ALMA detections, we infer ISM conditions similar to those in low redshift Luminous Infrared Galaxies. DDT MUSE integral field unit observations reveal the optical counterpart of the $^{12}$CO emission line source and three additional emission line galaxies at the absorber redshift, which together form a galaxy group. The $^{12}$CO emission line detections originate from the most massive galaxy in this group. While we cannot exclude that we miss a fainter host, we reach a dust-uncorrected star-formation rate (SFR) limit of > $0.3 text{M}_{odot} text{ yr}^{-1}$ within $100$ kpc from the sightline to the background quasar. We measure the dust-corrected SFR (ranging from $3$ to $50$ M$_{odot}$ yr$^{-1}$), the morpho-kinematics and the metallicities of the four group galaxies to understand the relation between the group and the neutral gas probed in absorption. We find that the Ly $alpha$ absorber traces either an outflow from the most massive galaxy or intra-group gas. This case study illustrates the power of combining ALMA and MUSE to obtain a census of the cool baryons in a bounded structure at intermediate redshift.
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We present results of MUSE-ALMA Halos, an ongoing study of the Circumgalactic Medium (CGM) of galaxies ($z leq$ 1.4). Using multi-phase observations we probe the neutral, ionised and molecular gas in a sub-sample containing six absorbers and nine associated galaxies in the redshift range $z sim 0.3-0.75$. Here, we give an in-depth analysis of the newly CO-detected galaxy Q2131-G1 ($z=0.42974$), while providing stringent mass and depletion time limits for the non-detected galaxies. Q2131-G1 is associated with an absorber with column densities of $textrm{log}(N_textrm{HI}/textrm{cm}^{-2}) sim 19.5$ and $textrm{log}(N_{textrm{H}_2}/textrm{cm}^{-2}) sim 16.5$, has a star formation rate of $textrm{SFR} = 2.00 pm 0.20 ; textrm{M}_{odot} textrm{yr}^{-1}$, a dark matter fraction of $f_textrm{DM}(r_{1/2}) = 0.24 - 0.54$ and a molecular gas mass of $M_textrm{mol} = 3.52 ^{+3.95}_{-0.31} times 10^9 ; textrm{M}_{odot}$ resulting in a depletion time of $tau_textrm{dep} < 4.15 ; textrm{Gyr}$. Kinematic modelling of both the CO (3--2) and [OIII] $lambda 5008$ emission lines of Q2131-G1 shows that the molecular and ionised gas phases are well aligned directionally and that the maximum rotation velocities closely match. These two gas phases within the disk are strongly coupled. The metallicity, kinematics and orientation of the atomic and molecular gas traced by a two-component absorption feature is consistent with being part of the extended rotating disk with a well-separated additional component associated with infalling gas. Compared to emission-selected samples, we find that HI-selected galaxies have high molecular gas masses given their low star formation rate. We consequently derive high depletion times for these objects.
We aim at analysing systematically the distribution and physical properties of neutral and mildly ionised gas in the Milky Way halo, based on a large absorption-selected data set. Multi-wavelength studies were performed combining optical absorption line data of CaII and NaI with follow-up HI 21-cm emission line observations along 408 sight lines towards low- and high-redshift QSOs. We made use of archival optical spectra obtained with UVES/VLT. HI data were extracted from the Effelsberg-Bonn HI survey and the Galactic All-Sky survey. For selected sight lines we obtained deeper follow-up observations using the Effelsberg 100-m telescope. CaII (NaI) halo absorbers at intermediate and high radial velocities are present in 40-55% (20-35%) of the sightlines, depending on the column density threshold chosen. Many halo absorbers show multi-component absorption lines, indicating the presence of sub-structure. In 65% of the cases, absorption is associated with HI 21-cm emission. The CaII (NaI) column density distribution function follows a power-law with a slope of -2.2 (-1.4). Our absorption-selected survey confirms our previous results that the Milky Way halo is filled with a large number of neutral gas structures whose high column density tail represents the population of common HI high- and intermediate-velocity clouds seen in 21-cm observations. We find that CaII/NaI column density ratios in the halo absorbers are typically smaller than those in the Milky Way disc, in the gas in the Magellanic Clouds, and in damped Lyman-alpha systems. The small ratios (prominent in particular in high-velocity components) indicate a lower level of Ca depletion onto dust grains in Milky Way halo absorbers compared to gas in discs and inner regions of galaxies.
Mapping the molecular gas content of the universe is key to our understanding of the build-up of galaxies over cosmic time. Spectral line scans in deep fields, such as the Hubble Ultra Deep Field (HUDF), provide a unique view on the cold gas content out to high redshift. By conducting `spectroscopy-of-everything, these flux-limited observations are sensitive to the molecular gas in galaxies without preselection, revealing the cold gas content of galaxies that would not be selected in traditional studies. In order to capitalize on the molecular gas observations, knowledge about the physical conditions of the galaxies detected in molecular gas, such as their interstellar medium conditions, is key. Fortunately, deep surveys with integral-field spectrographs are providing an unprecedented view of the galaxy population, providing redshifts and measurements of restframe UV/optical lines for thousands of galaxies. We present the results from the synergy between the ALMA Spectroscopic Survey of the HUDF (ASPECS), with deep integral field spectroscopy from the MUSE HUDF survey and multi-wavelength data. We discuss the nature of the galaxies detected in molecular gas without preselection and their physical properties, such as star formation rate and metallicity. We show how the combination of ALMA and MUSE integral field spectroscopy can constrain the physical properties in galaxies located around the main sequence during the peak of galaxy formation.
We are just starting to understand the physical processes driving the dramatic change in cosmic star-formation rate between $zsim 2$ and the present day. A quantity directly linked to star formation is the molecular gas density, which should be measured through independent methods to explore variations due to cosmic variance and systematic uncertainties. We use intervening CO absorption lines in the spectra of mm-bright background sources to provide a census of the molecular gas mass density of the Universe. The data used in this work are taken from ALMACAL, a wide and deep survey utilizing the ALMA calibrator archive. While we report multiple Galactic absorption lines and one intrinsic absorber, no extragalactic intervening molecular absorbers are detected. However, thanks to the large redshift path surveyed ($Delta z=182$), we provide constraints on the molecular column density distribution function beyond $zsim 0$. In addition, we probe column densities of N(H$_2$) > 10$^{16}$ atoms~cm$^{-2}$, five orders of magnitude lower than in previous studies. We use the cosmological hydrodynamical simulation IllustrisTNG to show that our upper limits of $rho ({rm H}_2)lesssim 10^{8.3} text{M}_{odot} text{Mpc}^{-3}$ at $0 < z leq 1.7$ already provide new constraints on current theoretical predictions of the cold molecular phase of the gas. These results are in agreement with recent CO emission-line surveys and are complementary to those studies. The combined constraints indicate that the present decrease of the cosmic star-formation rate history is consistent with an increasing depletion of molecular gas in galaxies compared to $zsim 2$.
We have used the Atacama Large Millimeter/submillimeter Array (ALMA) to carry out a search for CO (3$-$2) or (4$-$3) emission from the fields of 12 high-metallicity ([M/H]~$geq -0.72$,dex) damped Lyman-$alpha$ absorbers (DLAs) at $z approx 1.7-2.6$. We detected CO emission from galaxies in the fields of five DLAs (two of which have been reported earlier), obtaining high molecular gas masses, $rm M_{mol} approx (1.3 - 20.7) times (alpha_{rm CO}/4.36) times 10^{10} ; M_odot$. The impact parameters of the CO emitters to the QSO sightline lie in the range $b approx 5.6-100$~kpc, with the three new CO detections having $b lesssim 15$~kpc. The highest CO line luminosities and inferred molecular gas masses are associated with the highest-metallicity DLAs, with [M/H]~$gtrsim -0.3$,dex. The high inferred molecular gas masses may be explained by a combination of a stellar mass-metallicity relation and a high molecular gas-to-stars mass ratio in high-redshift galaxies; the DLA galaxies identified by our CO searches have properties consistent with those of emission-selected samples. None of the DLA galaxies detected in CO emission were identified in earlier optical or near-IR searches and vice-versa; DLA galaxies earlier identified in optical/near-IR searches were not detected in CO emission. The high ALMA CO and C[{sc ii}]~158$mu$m detection rate in high-$z$, high-metallicity DLA galaxies has revolutionized the field, allowing the identification of dusty, massive galaxies associated with high-$z$ DLAs. The H{sc i}-absorption criterion identifying DLAs selects the entire high-$z$ galaxy population, including dusty and UV-bright galaxies, in a wide range of environments.
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