Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Kinematics and Dark Matter Fractions of TNG50 Galaxies at z=2 from an Observational Perspective
74
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We contrast the gas kinematics and dark matter contents of $z=2$ star-forming galaxies (SFGs) from state-of-the-art cosmological simulations within the $Lambda$CDM framework to observations. To this end, we create realistic mock observations of massive SFGs ($M_*>4times10^{10} M_{odot}$, SFR $>50~M_{odot}$ yr$^{-1}$) from the TNG50 simulation of the IllustrisTNG suite, resembling near-infrared, adaptive-optics assisted integral-field observations from the ground. Using observational line fitting and modeling techniques, we analyse in detail the kinematics of seven TNG50 galaxies from five different projections per galaxy, and compare them to observations of twelve massive SFGs by Genzel et al. (2020). The simulated galaxies show clear signs of disc rotation but mostly exhibit more asymmetric rotation curves, partly due to large intrinsic radial and vertical velocity components. At identical inclination angle, their one-dimensional velocity profiles can vary along different lines of sight by up to $Delta v=200$ km s$^{-1}$. From dynamical modelling we infer rotation speeds and velocity dispersions that are broadly consistent with observational results. We find low central dark matter fractions compatible with observations ($f_{rm DM}^v(<R_e)=v_{rm DM}^2(R_e)/v_{rm circ}^2(R_e)sim0.32pm0.10$), however for disc effective radii $R_e$ that are mostly too small: at fixed $R_e$ the TNG50 dark matter fractions are too high by a factor of $sim2$. We speculate that the differences in gas kinematics and dark matter content compared to the observations may be due to physical processes that are not resolved in sufficient detail with the numerical resolution available in current cosmological simulations.
rate research
Read More
We study the dynamical properties of massive quiescent galaxies at $1.4 < z < 2.1$ using deep Hubble Space Telescope WFC3/F160W imaging and a combination of literature stellar velocity dispersion measurements and new near-infrared spectra obtained using KMOS on the ESO VLT. We use these data to show that the typical dynamical-to-stellar mass ratio has increased by $sim$0.2 dex from $z = 2$ to the present day, and investigate this evolution in the context of possible changes in the stellar initial mass function (IMF) and/or fraction of dark matter contained within the galaxy effective radius, $f_mathrm{DM}$. Comparing our high-redshift sample to their likely descendants at low-redshift, we find that $f_mathrm{DM}$ has increased by a factor of more than 4 since $z approx 1.8$, from $f_mathrm{DM}$ = $6.6pm1.0$% to $sim$24%. The observed increase appears robust to changes in the methods used to estimate dynamical masses or match progenitors and descendants. We quantify possible variation of the stellar IMF through the offset parameter $alpha$, defined as the ratio of dynamical mass in stars to the stellar mass estimated using a Chabrier IMF. We demonstrate that the correlation between stellar velocity dispersion and $alpha$ reported among quiescent galaxies at low-redshift is already in place at $z = 2$, and argue that subsequent evolution through (mostly minor) merging should act to preserve this relation while contributing significantly to galaxies overall growth in size and stellar mass.
How stellar mass assembles within galaxies is still an open question. We present measurements of the stellar mass distribution on kpc-scale for $sim5500$ galaxies with stellar masses above $log(M_{ast}/M_{odot})geqslant9.8$ up to the redshift $2.0$. We create stellar mass maps from Hubble Space Telescope observations by means of the pixel-by-pixel SED fitting method. These maps are used to derive radii encompassing $20%$, $50%$, and $80%$ ($r_{20}$, $r_{50}$ and $r_{80}$) of the total stellar mass from the best-fit Sersic models. The reliability and limitations of the structural parameter measurements are checked extensively using a large sample ($sim3000$) of simulated galaxies. The size-mass relations and redshift evolution of $r_{20}$, $r_{50}$ and $r_{80}$ are explored for star-forming and quiescent galaxies. At fixed mass, the star-forming galaxies do not show significant changes in their $r_{20}$, $r_{50}$ and $r_{80}$ sizes, indicating self-similar growth. Only above the pivot stellar mass of $log(M_{ast}/M_{odot})simeq10.5$, $r_{80}$ evolves as $r_{80}propto(1+z)^{-0.85pm0.20}$, indicating that mass builds up in the outskirts of these systems (inside-out growth). The Sersic values also increase for the massive star-forming galaxies towards late cosmic time. Massive quiescent galaxies show stronger size evolution at all radii, in particular the $r_{20}$ sizes. For these massive galaxies, Sersic values remain almost constant since at least $zsim1.3$, indicating that the strong size evolution is related to the changes in the outer parts of these galaxies. We make all the structural parameters publicly available.
We perform a kinematic analysis of galaxies at $zsim2$ in the COSMOS legacy field using near-infrared (NIR) spectroscopy from Keck/MOSFIRE as part of the ZFIRE survey. Our sample consists of 75 Ks-band selected star-forming galaxies from the ZFOURGE survey with stellar masses ranging from log(M$_{star}$/M$_{odot}$)$=9.0-11.0$, 28 of which are members of a known overdensity at $z=2.095$. We measure H$alpha$ emission-line integrated velocity dispersions ($sigma_{rm int}$) from 50$-$230 km s$^{-1}$, consistent with other emission-line studies of $zsim2$ field galaxies. From these data we estimate virial, stellar, and gas masses and derive correlations between these properties for cluster and field galaxies at $zsim2$. We find evidence that baryons dominate within the central effective radius. However, we find no statistically significant differences between the cluster and the field, and conclude that the kinematics of star-forming galaxies at $zsim2$ are not significantly different between the cluster and field environments.
Due to the fact that HI mass measurements are not available for large galaxy samples at high redshifts, we apply a photometric estimator of the HI-to-stellar mass ratio (M_HI/M_*) calibrated using a local Universe sample of galaxies to a sample of galaxies at z ~ 1 in the DEEP2 survey. We use these HI mass estimates to calculate HI mass functions (HIMFs) and cosmic HI mass densities (Omega_HI), and to examine the correlation between star formation rate and HI gas content, for galaxies at z ~ 1. We have estimated HI gas masses for ~ 7,000 galaxies in the DEEP2 survey with redshifts in the range 0.75 < z < 1.4 and stellar masses M_* > 10^{10} M_solar, using a combination of the rest-frame ultraviolet-optical colour (NUV - r) and stellar mass density (mu_*) as a way to estimate M_HI/M_*. It is found that the high mass end of high-z HI mass function (HIMF) is quite similar to that of the local HIMF. The lower limit of Omega_HI,limit = 2.1 * 10^{-4} h_70^{-1}, obtained by directly integrating the HI mass of galaxies with M_* > 10^{10} M_solar, confirms that massive star-forming galaxies do not dominate the neutral gas at z ~ 1. We study the evolution of the HI mass to stellar mass ratio from z ~ 1 to today and find a steeper relation between HI gas mass fraction and stellar mass at higher redshifts. Specifically, galaxies with M_* = 10^{11} M_solar at z ~ 1 are found to have 3 - 4 times higher neutral gas fractions than local galaxies, while the increase is as high as 4 - 12 times at M_* = 10^{10} M_solar. The quantity M_HI/SFR exhibits very large scatter, and the scatter increases from a factor of 5 - 7 at z = 0 to factors close to a hundred at z = 1. This implies that there is no relation between HI gas and star formation in high redshift galaxies. The HI gas must be linked to cosmological gas accretion processes at high redshifts.
We compare the kinetic energy and momentum injection rates from intense star formation, bolometric AGN radiation, and radio jets with the kinetic energy and momentum observed in the warm ionized gas in 24 powerful radio galaxies at z~2. These galaxies are amongst our best candidates for being massive galaxies near the end of their active formation period, when intense star formation, quasar activity, and powerful radio jets all co-exist. All galaxies have VLT/SINFONI imaging spectroscopy of the rest-frame optical line emission, showing emission-line regions with large velocity offsets (up to 1500 km/s) and line widths (typically 800-1000 km/s) consistent with very turbulent, often outflowing gas. As part of the HeRGE sample, they also have FIR estimates of the star formation and quasar activity obtained with Herschel/PACS and SPIRE, which enables us to measure the relative energy and momentum release from each of the three main sources of feedback in massive, star-forming AGN host galaxies during their most rapid formation phase. We find that star formation falls short by factors 10-1000 of providing the energy and momentum necessary to power the observed gas kinematics. The obscured quasars in the nuclei of these galaxies provide enough energy and momentum in about half of the sample, however, only if these are transfered to the gas relatively efficiently. We compare with theoretical and observational constraints on the efficiency of the energy and momentum transfer from jet and AGN radiation, which advocates that the radio jet is the main driver of the gas kinematics.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
