ABSTRACT
Galaxy haloes appear to be missing a large fraction of their baryons, most probably hiding in the circumgalactic medium (CGM), a diffuse component within the dark matter halo that extends ...far from the inner regions of the galaxies. A powerful tool to study the CGM gas is offered by absorption lines in the spectra of background quasars. Here, we present optical (MUSE) and mm (ALMA) observations of the field of the quasar Q1130−1449 which includes a log N(H i)/cm−2 = 21.71 ± 0.07 absorber at z = 0.313. Ground-based VLT/MUSE 3D spectroscopy shows 11 galaxies at the redshift of the absorber down to a limiting SFR > 0.01 M⊙ yr−1 (covering emission lines of O ii, Hβ, O iii, N ii, and H α), 7 of which are new discoveries. In particular, we report a new emitter with a smaller impact parameter to the quasar line of sight (b = 10.6 kpc) than the galaxies detected so far. Three of the objects are also detected in CO(1–0) in our ALMA observations indicating long depletion time-scales for the molecular gas and kinematics consistent with the ionized gas. We infer from dedicated numerical cosmological ramses zoom-in simulations that the physical properties of these objects qualitatively resemble a small group environment, possibly part of a filamentary structure. Based on metallicity and velocity arguments, we conclude that the neutral gas traced in absorption is only partly related to these emitting galaxies while a larger fraction is likely the signature of gas with surface brightness almost four orders of magnitude fainter that current detection limits. Together, these findings challenge a picture where strong-$N(\rm H\,{\small I})$ quasar absorbers are associated with a single bright galaxy and favour a scenario where the H i gas probed in absorption is related to far more complex galaxy structures.
We present an unprecedented view of the morphology and kinematics of the extended narrow-line region (ENLR) and molecular gas around the prototypical hyperluminous quasar 3C 273 (Lbol ∼ 1047 erg s−1 ...at z = 0.158) based on VLT-MUSE optical 3D spectroscopy and ALMA observations. We find the following: (1) the ENLR size of 12.1 0.2 kpc implies a smooth continuation of the size-luminosity relation out to large radii or a much larger break radius as previously proposed. (2) The kinematically disturbed ionized gas with line splits reaching 1000 km s−1 out to 6.1 1.5 kpc is aligned along the jet axis. (3) The extreme line broadening on kiloparsec scales is caused by the spatial and spectral blending of many distinct gas clouds separated on subarcsecond scales by different line-of-sight (LOS) velocities. The ENLR velocity field combined with the known jet orientation rules out a simple scenario of a radiatively driven radial expansion of the outflow. Instead, we propose that a pressurized expanding hot gas cocoon created by the radio jet is impacting on an inclined gas disk, leading to transverse and/or backflow motion with respect to our LOS. The molecular gas morphology may be explained by either a density wave at the front of the outflow expanding along the jet direction as predicted by the positive feedback scenario or the cold gas may be trapped in a stellar overdensity caused by a recent merger event. Using 3C 273 as a template for observations of high-redshift hyperluminous quasars reveals that large-scale ENLRs and kiloparsec-scale outflows may often be missed, due to the brightness of the nuclei and the limited sensitivity of current near-IR instrumentation.
The under-abundance of very massive galaxies in the Universe is frequently attributed to the effect of galactic winds. Although ionized galactic winds are readily observable, most of the expelled ...mass (that is, the total mass flowing out from the nuclear region) is likely to be in atomic and molecular phases that are cooler than the ionized phases. Expanding molecular shells observed in starburst systems such as NGC 253 (ref. 12) and M 82 (refs 13, 14) may facilitate the entrainment of molecular gas in the wind. Although shell properties are well constrained, determining the amount of outflowing gas emerging from such shells and the connection between this gas and the ionized wind requires spatial resolution better than 100 parsecs coupled with sensitivity to a wide range of spatial scales, a combination hitherto not available. Here we report observations of NGC 253, a nearby starburst galaxy (distance ∼ 3.4 megaparsecs) known to possess a wind, that trace the cool molecular wind at 50-parsec resolution. At this resolution, the extraplanar molecular gas closely tracks the Hα filaments, and it appears to be connected to expanding molecular shells located in the starburst region. These observations allow us to determine that the molecular outflow rate is greater than 3 solar masses per year and probably about 9 solar masses per year. This implies a ratio of mass-outflow rate to star-formation rate of at least 1, and probably ∼3, indicating that the starburst-driven wind limits the star-formation activity and the final stellar content.
We measure the neutral atomic hydrogen (H i) gas content of field galaxies at intermediate redshifts of z ∼ 0.1 and ∼0.2 using hydrogen 21-cm emission lines observed with the Westerbork Synthesis ...Radio Telescope. In order to make high signal-to-noise ratio detections, an H i signal stacking technique is applied: H i emission spectra from multiple galaxies, optically selected by the second Canadian Network for Observational Cosmology redshift survey project, are co-added to measure the average H i mass of galaxies in the two redshift bins. We calculate the cosmic H i gas densities (ΩHi
) at the two redshift regimes and compare those with measurements at other redshifts to investigate the global evolution of the H i gas density over cosmic time. From a total of 59 galaxies at z ∼ 0.1 we find ΩHi
= (0.33 ± 0.05) × 10−3, and at z ∼ 0.2 we find ΩHi
= (0.34 ± 0.09) × 10−3, based on 96 galaxies. These measurements help bridge the gap between high-z damped Lyman α observations and blind 21-cm surveys at z = 0. We find that our measurements of ΩHi
at z ∼ 0.1 and ∼0.2 are consistent with the H i gas density at z ∼ 0 and that all measurements of ΩHi
from 21-cm emission observations at z 0.2 are in agreement with no evolution of the H i gas content in galaxies during the last 2.4 Gyr.
Abstract
Young massive clusters play an important role in the evolution of their host galaxies, and feedback from the high-mass stars in these clusters can have profound effects on the surrounding ...interstellar medium. The nuclear starburst in the nearby galaxy NGC 253 at a distance of 3.5 Mpc is a key laboratory in which to study star formation in an extreme environment. Previous high-resolution (1.9 pc) dust continuum observations from the Atacama Large Millimeter/submillimeter Array (ALMA) discovered 14 compact, massive super star clusters (SSCs) still in formation. We present here ALMA data at 350 GHz with 28 mas (0.5 pc) resolution. We detect blueshifted absorption and redshifted emission (P-Cygni profiles) toward three of these SSCs in multiple lines, including CS 7−6 and H
13
CN 4−3, which represent direct evidence for previously unobserved outflows. The mass contained in these outflows is a significant fraction of the cluster gas masses, which suggests we are witnessing a short but important phase. Further evidence of this is the finding of a molecular shell around the only SSC visible at near-IR wavelengths. We model the P-Cygni line profiles to constrain the outflow geometry, finding that the outflows must be nearly spherical. Through a comparison of the outflow properties with predictions from simulations, we find that none of the available mechanisms completely explains the observations, although dust-reprocessed radiation pressure and O star stellar winds are the most likely candidates. The observed outflows will have a very substantial effect on the clusters’ evolution and star formation efficiency.
ABSTRACT
We are just starting to understand the physical processes driving the dramatic change in cosmic star formation rate between z ∼ 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, due to the large redshift path surveyed (Δz = 182), we provide constraints on the molecular column density distribution function beyond z ∼ 0. In addition, we probe column densities of N(H2) > 1016 atoms cm−2, 5 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 ≤ 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 z ∼ 2.
We study the origin of the wide distribution of angles between the angular momenta of the stellar and gas components, αG, S, in early-type galaxies (ETGs). We use the GALFORM model of galaxy ...formation, set in the Λ cold dark matter framework, and coupled it with a Monte Carlo simulation to follow the angular momenta flips driven by matter accretion on to haloes and galaxies. We consider a gas disc to be misaligned with respect to the stellar body if αG,S > 30 deg. By assuming that the only sources of misalignments in galaxies are galaxy mergers, we place a lower limit of 2–5 per cent on the fraction of ETGs with misaligned gas/stellar components. These low fractions are inconsistent with the observed value of ≈42 ± 6 per cent in ATLAS3D. In the more general case, in which smooth gas accretion in addition to galaxy mergers can drive misalignments, our calculation predicts that ≈46 per cent of ETGs have αG, S > 30 deg. In this calculation, we find correlations between αG, S and stellar mass, cold gas fraction and star formation rate, such that ETGs with high masses, low cold gas fractions and low star formation rates are more likely to display aligned cold gas and stellar components. We confirm these trends observationally for the first time using ATLAS3D data. We argue that the high fraction of misaligned gas discs observed in ETGs is mostly due to smooth gas accretion (e.g. cooling from the hot halo of galaxies) which takes place after most of the stellar mass of the galaxy is in place and comes misaligned with respect to the stellar component. Galaxies that have accreted most of their cold gas content prior to the time where most of the stellar mass was in place show aligned components.
We use ALMA observations to derive mass, length, and time scales associated with NGC 253's nuclear starburst. This region forms ∼2 M {sub ☉} yr{sup –1} of stars and resembles other starbursts in ...ratios of gas, dense gas, and star formation tracers, with star formation consuming the gas reservoir at a normalized rate 10 times higher than in normal galaxy disks. We present new ∼35 pc resolution observations of bulk gas tracers (CO), high critical density transitions (HCN, HCO{sup +}, and CS), and their isotopologues. The starburst is fueled by a highly inclined distribution of dense gas with vertical extent <100 pc and radius ∼250 pc. Within this region, we identify 10 starburst giant molecular clouds (GMCs) that appear as both peaks in the dense gas tracer cubes and the HCN-to-CO ratio map. These are massive (∼10{sup 7} M {sub ☉}) structures with sizes (∼30 pc) similar to GMCs in other systems, but compared to GMCs in normal galaxy disks, they have high line widths (σ ∼ 20-40 km s{sup –1}, Mach number M∼90) and high surface and volume densities (Σ{sub mol} ∼ 6000 M {sub ☉} pc{sup –2}, n {sub H2} ∼ 2000 cm{sup –3}). The self gravity from such high densities can explain the high line widths and the short free fall time τ{sub ff} ∼ 0.7 Myr in the clouds helps explain the more efficient star formation in NGC 253. Though the high inclination obscures the geometry somewhat, we show that simple models suggest a compact, clumpy region of high gas density embedded in a more extended, non-axisymmetric, bar-like distribution. Over the starburst, the surface density still exceeds that of a typical disk galaxy GMC and, as in the clouds, timescales in the disk as a whole are short compared to those in normal galaxy disks. The orbital time (∼10 Myr), disk free fall time (≲ 3 Myr), and disk crossing time (≲ 3 Myr) are each an order of magnitude shorter than in a normal galaxy disk. Finally, the CO-to-H{sub 2} conversion factor implied by our cloud calculations is approximately Galactic, contrasting with results showing a low value for the whole starburst region. The contrast provides resolved support for the idea of mixed molecular ISM phases in starburst galaxies.
We present spatially resolved Atacama Large Millimeter/submillimeter Array (ALMA) Cii observations of the z = 4.7555 submillimetre galaxy, ALESS 73.1. Our 0.̋5 FWHM map resolves the Cii emitting gas ...which is centred close to the active galactic nucleus (AGN). The gas kinematics are dominated by rotation but with high turbulence, vrot/σint ~ 3.1, and a Toomre Q parameter <1 throughout the disk. By fitting three independent thin rotating disk models to our data, we derive a total dynamical mass of 3 ± 2 × 1010 M⊙. This is close to the molecular gas mass derived from previous CO(2-1) observations, and implies a CO to H2 conversion factor αCO < 2.3 M⊙ (K km s-1 pc2)-1. The mass budget also constrains the stellar mass to <3.1 × 1010 M⊙, and entails a gas fraction of fgas ≳ 0.4. The diameter of the dust continuum emission is <2 kpc, while the star-formation rate is as high as 1000 M⊙ yr-1. Combined with our stellar mass constraint, this implies an extreme specific star formation rate >80 Gyr-1, especially since there are no clear indications of recent merger activity. Finally, our high signal-to-noise Cii measurement revises the observed Nii/Cii ratio, which suggests a close to solar metallicity, unless the Cii flux contains significant contributions from Hii regions. Our observations suggest that ALESS73.1 is a nascent galaxy undergoing its first major burst of star formation, embedded within an unstable but metal-rich gas disk.
We present a 3° × 3°, 105-pointing, high-resolution neutral hydrogen (H i) mosaic of the M81 galaxy triplet, (including the main galaxies M81, M82, and NGC 3077, as well as dwarf galaxy NGC 2976) ...obtained with the Very Large Array C and D arrays. This H i synthesis mosaic uniformly covers the entire area and velocity range of the triplet. The observations have a resolution of ∼20″ or ∼420 pc. The data reveal many small-scale anomalous velocity features highlighting the complexity of the interacting M81 triplet. We compare our data with Green Bank Telescope observations of the same area. This comparison provides evidence for the presence of a substantial reservoir of low-column density gas in the northern part of the triplet, probably associated with M82. Such a reservoir is not found in the southern part. We report a number of newly discovered kpc-sized low-mass H i clouds with H i masses of a few times 106 M . A detailed analysis of their velocity widths show that their dynamical masses are much larger than their baryonic masses, which could indicate the presence of dark matter if the clouds are rotationally supported. However, due to their spatial and kinematical association with H i tidal features, it is more likely that the velocity widths indicate tidal effects or streaming motions. We do not find any clouds that are not associated with tidal features down to an H i mass limit of a few times 104 M . We compare the H i column densities with resolved stellar density maps and find a star formation threshold around 3-6 × 1020 cm−2. We investigate the widths of the H i velocity profiles in the triplet and find that extreme velocity dispersions can be explained by a superposition of multiple components along the line of sight near M81 as well as winds or outflows around M82. The velocity dispersions found are high enough that these processes could explain the linewidths of damped-Ly absorbers observed at high redshift.
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