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Register a new userThe Evolution and Origin of Ionized Gas Velocity Dispersion from $zsim2.6$ to $zsim0.6$ with KMOS$^{rm 3D}$
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We present the $0.6<z<2.6$ evolution of the ionized gas velocity dispersion in 175 star-forming disk galaxies based on data from the full KMOS$^{rm 3D}$ integral field spectroscopic survey. In a forward-modelling Bayesian framework including instrumental effects and beam-smearing, we fit simultaneously the observed galaxy velocity and velocity dispersion along the kinematic major axis to derive the intrinsic velocity dispersion $sigma_0$. We find a reduction of the average intrinsic velocity dispersion of disk galaxies as a function of cosmic time, from $sigma_0sim45$ km s$^{-1}$ at $zsim2.3$ to $sigma_0sim30$ km s$^{-1}$ at $zsim0.9$. There is substantial intrinsic scatter ($sigma_{sigma_0, {rm int}}approx10$ km s$^{-1}$) around the best-fit $sigma_0-z$-relation beyond what can be accounted for from the typical measurement uncertainties ($deltasigma_0approx12$ km s$^{-1}$), independent of other identifiable galaxy parameters. This potentially suggests a dynamic mechanism such as minor mergers or variation in accretion being responsible for the scatter. Putting our data into the broader literature context, we find that ionized and atomic+molecular velocity dispersions evolve similarly with redshift, with the ionized gas dispersion being $sim10-15$ km s$^{-1}$ higher on average. We investigate the physical driver of the on average elevated velocity dispersions at higher redshift, and find that our galaxies are at most marginally Toomre-stable, suggesting that their turbulent velocities are powered by gravitational instabilities, while stellar feedback as a driver alone is insufficient. This picture is supported through comparison with a state-of-the-art analytical model of galaxy evolution.
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In order to study the state of gas in galaxies, diagrams of the relation of optical emission line fluxes are used allowing one to separate main ionization sources: young stars in the H II regions, active galactic nuclei, and shock waves. In the intermediate cases, when the contributions of radiation from OB stars and from shock waves mix, identification becomes uncertain, and the issue remains unresolved on what determines the observed state of the diffuse ionized gas (DIG) including the one on large distances from the galactic plane. Adding of an extra parameter - the gas line-of-sight velocity dispersion - to classical diagnostic diagrams helps to find a solution. In the present paper, we analyze the observed data for several nearby galaxies: for UGC 10043 with the galactic wind, for the star forming dwarf galaxies VII Zw 403 and Mrk 35, for the galaxy Arp 212 with a polar ring. The data on the velocity dispersion are obtained at the 6-m SAO RAS telescope with the Fabry-Perot scanning interferometer, the information on the relation of main emission-line fluxes - from the published results of the integral-field spectroscopy (the CALIFA survey and the MPFS spectrograph). A positive correlation between the radial velocity dispersion and the contribution of shock excitation to gas ionization are observed. In particular, in studying Arp 212, BPT-sigma relation allowed us to confirm the assumption on a direct collision of gaseous clouds on the inclined orbits with the main disk of the galaxy.
We revisit the possibility of redshift evolution in the $M_{rm{BH}}-sigma_*$ relation with a sample of 22 Seyfert 1 galaxies with black holes (BHs) in the mass range $10^{6.3}-10^{8.3}~M_odot$ and redshift range $0.03<z<0.57$ with spectra obtained from spatially resolved Keck/Low-Resolution Imaging Spectrometer observations. Stellar velocity dispersions were measured directly from the Mg Ib region, taking into consideration the effect of Fe II contamination, active galactic nucleus (AGN) dilution, and host-galaxy morphology on our measurements. BH masses are estimated using the H$beta$ line width, and the luminosity at 5100 $overset{lower.5emcirc}{mathrm{A}}$ is estimated from surface brightness decomposition of the AGN from the host galaxy using high-resolution imaging from the Hubble Space Telescope. Additionally, we investigate the use of the [O III]$lambda5007$ emission line width as a surrogate for stellar velocity dispersion, finding better correlation once corrected for Fe II contamination and any possible blueshifted wing components. Our selection criteria allowed us to probe lower-luminosity AGNs and lower-mass BHs in the non-local universe than those measured in previous single-epoch studies. We find that any offset in the $M_{rm{BH}}-sigma_*$ relation up to $zsim0.6$ is consistent with the scatter of local BH masses, and address the sources of biases and uncertainties that contribute to this scatter.
We analyze the intrinsic velocity dispersion properties of 648 star-forming galaxies observed by the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, to explore the relation of intrinsic gas velocity dispersions with star formation rates (SFRs), SFR surface densities ($rm{Sigma_{SFR}}$), stellar masses and stellar mass surface densities ($rm{Sigma_{*}}$). By combining with high z galaxies, we found that there is a good correlation between the velocity dispersion and the SFR as well as $rm{Sigma_{SFR}}$. But the correlation between the velocity dispersion and the stellar mass as well as $rm{Sigma_{*}}$ is moderate. By comparing our results with predictions of theoretical models, we found that the energy feedback from star formation processes alone and the gravitational instability alone can not fully explain simultaneously the observed velocity-dispersion/SFR and velocity-dispersion/$rm{Sigma_{SFR}}$ relationships.
We compare the molecular and ionized gas velocity dispersion of 9 nearby turbulent disks, analogues to high-redshift galaxies, from the DYNAMO sample using new ALMA and GMOS/Gemini observations. We combine our sample with 12 galaxies at $zsim $0.5-2.5 from the literature. We find that the resolved velocity dispersion is systematically lower by a factor $2.45pm0.38$ for the molecular gas compared to the ionized gas, after correcting for thermal broadening. This offset is constant within the galaxy disks and indicates the co-existence of a thin molecular and thick ionized gas disks. This result has a direct impact on the Toomre $Q$ and pressure derived in galaxies. We obtain pressures $sim0.22$ dex lower on average when using the molecular gas velocity dispersion, $sigma_{0,mol}$. We find that $sigma_{0,mol}$ increases with gas fraction and star formation rate. We also obtain an increase with redshift and show that the EAGLE and FIRE simulations overall overestimate $sigma_{0,mol}$ at high redshift. Our results suggest that efforts to compare the kinematics of gas using ionized gas as a proxy for the total gas may overestimate the velocity dispersion by a significant amount in galaxies at the peak of cosmic star formation. When using the molecular gas as a tracer, our sample is not consistent with predictions from constant efficiency star formation models, even when including transport as a source of turbulence. Feedback models with variable star formation efficiency, $epsilon_{ff}$, and/or feedback efficiency, $p_*/m_*$, better predict our observations.
We investigate what drives the redshift evolution of the typical electron density ($n_e$) in star-forming galaxies, using a sample of 140 galaxies drawn primarily from KMOS$^{rm 3D}$ ($0.6lesssim{z}lesssim{2.6}$) and 471 galaxies from SAMI ($z<0.113$). We select galaxies that do not show evidence of AGN activity or outflows, to constrain the average conditions within H II regions. Measurements of the [SII]$lambda$6716/[SII]$lambda$6731 ratio in four redshift bins indicate that the local $n_e$ in the line-emitting material decreases from 187$^{+140}_{-132}$ cm$^{-3}$ at $zsim$ 2.2 to 32$^{+4}_{-9}$ cm$^{-3}$ at $zsim$ 0; consistent with previous results. We use the H$alpha$ luminosity to estimate the root-mean-square (rms) $n_e$ averaged over the volumes of star-forming disks at each redshift. The local and volume-averaged $n_e$ evolve at similar rates, hinting that the volume filling factor of the line-emitting gas may be approximately constant across $0lesssim{z}lesssim{2.6}$. The KMOS$^{rm 3D}$ and SAMI galaxies follow a roughly monotonic trend between $n_e$ and star formation rate, but the KMOS$^{rm 3D}$ galaxies have systematically higher $n_e$ than the SAMI galaxies at fixed offset from the star-forming main sequence, suggesting a link between the $n_e$ evolution and the evolving main sequence normalization. We quantitatively test potential drivers of the density evolution and find that $n_e$(rms) $simeq{n_{H_2}}$, suggesting that the elevated $n_e$ in high-$z$ H II regions could plausibly be the direct result of higher densities in the parent molecular clouds. There is also tentative evidence that $n_e$ could be influenced by the balance between stellar feedback, which drives the expansion of H II regions, and the ambient pressure, which resists their expansion.
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