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Register a new userIonized and molecular gas kinematics in a z=1.4 star-forming galaxy
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We present deep observations of a $z=1.4$ massive, star-forming galaxy in molecular and ionized gas at comparable spatial resolution (CO 3-2, NOEMA; H$alpha$, LBT). The kinematic tracers agree well, indicating that both gas phases are subject to the same gravitational potential and physical processes affecting the gas dynamics. We combine the one-dimensional velocity and velocity dispersion profiles in CO and H$alpha$ to forward-model the galaxy in a Bayesian framework, combining a thick exponential disk, a bulge, and a dark matter halo. We determine the dynamical support due to baryons and dark matter, and find a dark matter fraction within one effective radius of $f_{rm DM}(leq$$R_{e})=0.18^{+0.06}_{-0.04}$. Our result strengthens the evidence for strong baryon-dominance on galactic scales of massive $zsim1-3$ star-forming galaxies recently found based on ionized gas kinematics alone.
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We constrain the rate of gas inflow into and outflow from a main-sequence star-forming galaxy at z~1.4 by fitting a simple analytic model for the chemical evolution in a galaxy to the observational data of the stellar mass, metallicity, and molecular gas mass fraction. The molecular gas mass is derived from CO observations with a metallicity-dependent CO-to-H2 conversion factor, and the gas metallicity is derived from the H{alpha} and [NII]{lambda} 6584 emission line ratio. Using a stacking analysis of CO integrated intensity maps and the emission lines of H{alpha} and [NII], the relation between stellar mass, metallicity, and gas mass fraction is derived. We constrain the inflow and outflow rates with least-chi-square fitting of a simple analytic chemical evolution model to the observational data. The best-fit inflow and outflow rates are ~1.7 and ~0.4 in units of star-formation rate, respectively. The inflow rate is roughly comparable to the sum of the star-formation rate and outflow rate, which supports the equilibrium model for galaxy evolution; i.e., all inflow gas is consumed by star formation and outflow.
We report on the galaxy MACSJ0032-arc at z=3.6314 discovered during the Herschel Lensing snapshot Survey of massive galaxy clusters, and strongly lensed by the cluster MACSJ0032.1+1808. The successful detections of its rest-frame UV, optical, FIR, millimeter, and radio continua, and of its CO emission enable us to characterize, for the first time at such a high redshift, the stellar, dust, and molecular gas properties of a compact star-forming galaxy with a size smaller than 2.5 kpc, a fairly low stellar mass of 4.8x10^9 Msun, and a moderate IR luminosity of 4.8x10^11 Lsun. We find that the bulk of the molecular gas mass and star formation seems to be spatially decoupled from the rest-frame UV emission. About 90% of the total star formation rate is undetected at rest-frame UV wavelengths because of severe obscuration by dust, but is seen through the thermal FIR dust emission and the radio synchrotron radiation. The observed CO(4-3) and CO(6-5) lines demonstrate that high-J transitions, at least up to J=6, remain excited in this galaxy, whose CO spectral line energy distribution resembles that of high-redshift submm galaxies, even though the IR luminosity of MACSJ0032-arc is ten times lower. This high CO excitation is possibly due to the compactness of the galaxy. We find evidence that this high CO excitation has to be considered in the balance when estimating the CO-to-H2 conversion factor. The inferred depletion time of the molecular gas in MACSJ0032-arc supports the decrease in the gas depletion timescale of galaxies with redshift, although to a lesser degree than predicted by galaxy evolution models. Instead, the measured molecular gas fraction as high as 60-79% in MACSJ0032-arc favors the continued increase in the gas fraction of galaxies with redshift as expected, despite the plateau observed between z~1.5 and z~2.5.
We have conducted a search for ionized gas at 3.6 cm, using the Very Large Array, towards 31 Galactic intermediate- and high-mass clumps detected in previous millimeter continuum observations. In the 10 observed fields, 35 HII regions are identified, of which 20 are newly discovered. Many of the HII regions are multiply peaked indicating the presence of a cluster of massive stars. We find that the ionized gas tends to be associated towards the millimeter clumps; of the 31 millimeter clumps observed, 9 of these appear to be physically related to ionized gas, and a further 6 have ionized gas emission within 1. For clumps with associated ionized gas, the combined mass of the ionizing massive stars is compared to the clump masses to provide an estimate of the instantaneous star formation efficiency. These values range from a few percent to 25%, and have an average of 7 +/- 8%. We also find a correlation between the clump mass and the mass of the ionizing massive stars within it, which is consistent with a power law. This result is comparable to the prediction of star formation by competitive accretion that a power law relationship exists between the mass of the most massive star in a cluster and the total mass of the remaining stars.
We present a comparative study of molecular and ionized gas kinematics in nearby galaxies. These results are based on observations from the EDGE survey, which measured spatially resolved $^{12}$CO(J=1-0) in 126 nearby galaxies. Every galaxy in EDGE has corresponding resolved ionized gas measurements from CALIFA. Using a sub-sample of 17 rotation dominated, star-forming galaxies where precise molecular gas rotation curves could be extracted, we derive CO and H$alpha$ rotation curves using the same geometric parameters out to $gtrsim$1 $R_e$. We find that $sim$75% of our sample galaxies have smaller ionized gas rotation velocities than the molecular gas in the outer part of the rotation curve. In no case is the molecular gas rotation velocity measurably lower than that of the ionized gas. We suggest that the lower ionized gas rotation velocity can be attributed to a significant contribution from extraplanar diffuse ionized gas in a thick, turbulence supported disk. Using observations of the H$gamma$ transition also available from CALIFA, we measure ionized gas velocity dispersions and find that these galaxies have sufficiently large velocity dispersions to support a thick ionized gas disk. Kinematic simulations show that a thick disk with a vertical rotation velocity gradient can reproduce the observed differences between the CO and H$alpha$ rotation velocities. Observed line ratios tracing diffuse ionized gas are elevated compared to typical values in the midplane of the Milky Way. In galaxies affected by this phenomenon, dynamical masses measured using ionized gas rotation curves will be systematically underestimated.
BOSS-EUVLG1 is the most ultraviolet (UV) and Ly$alpha$ luminous galaxy detected so far in the Universe, going through a very active starburst phase, and forming stars at a rate (SFR) of 955 $pm$ 118 M$_{odot}$ yr$^{-1}$. We report the detection of a broad H$alpha$ component carrying 25% of the total H$alpha$ flux. The broad H$alpha$ line traces a fast and massive ionized gas outflow characterized by a total mass, $log(M_{out}[M_{odot}]),$ of 7.94 $pm$ 0.15, an outflowing velocity (V$_{out}$) of 573 $pm$ 151 km s$^{-1}$, and an outflowing mass rate ($dot{M}_{out}$) of 44 $pm$ 20 M$_{odot}$ yr$^{-1}$. The presence of the outflow in BOSS-EUVLG1 is also supported by the identification of blueshifted UV absorption lines in low and high ionization states. The energy involved in the H$alpha$ outflow can be explained by the ongoing star formation without the need for an Active Galactic Nucleus. The derived low mass loading factor ($eta$= 0.05 $pm$ 0.03) indicates that although massive, this phase of the outflow can not be relevant for the quenching of the star formation. In addition, only a small fraction ($leq$ 15%) of the ionized outflowing material with velocities above 372 km s$^{-1}$ could escape the gravitational potential, and enrich the surrounding circum-galactic medium at distances above tens of kpc. The ionized phase of the outflow does not carry the mass and energy to play a relevant role neither in the evolution of the host galaxy nor in the enrichment of the intergalactic medium. Other phases of the outflow could be carrying most of the outflow energy and mass in the form of hot X-ray emitting gas as predicted by some recent simulations. The expected emission of the extended X-ray emitting halo associated with the outflow in BOSS-EUVLG1 and similar galaxies could be detected with the future X-ray observatory, {it ATHENA} but could not be resolved spatially.
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