Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEffect of lithium hydride on the cooling of primordial gas
63
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We complete the formulation of the standard model of first star formation by exploring the possible impact of $mathrm{LiH}$ cooling, which has been neglected in previous simulations of non-linear collapse. Specifically, we find that at redshift $zgtrsim 5$, the cooling by $mathrm{LiH}$ has no effect on the thermal evolution of shocked primordial gas, and of collapsing primordial gas into minihaloes or relic HII regions, even if the primordial lithium abundance were enhanced by one order of magnitude. Adding the most important lithium species to a minimum network of primordial chemistry, we demonstrate that insufficient $mathrm{LiH}$ is produced in all cases considered, about $[mathrm{LiH/Li}]sim 10^{-9}$ for $Tlesssim 100$ K. Indeed, $mathrm{LiH}$ cooling would only be marginally significant in shocked primordial gas for the highly unlikely case that the $mathrm{LiH}$ abundance were increased by nine orders of magnitude, implying that $all$ lithium would have to be converted into $mathrm{LiH}$. In this study, photo-destruction processes are not considered, and the collisional disassociation rate of $mathrm{LiH}$ is possibly underestimated, rendering our results an extreme upper limit. Therefore, the cooling by $mathrm{LiH}$ can safely be neglected for the thermal evolution of Population~III star-forming gas.
rate research
Read More
We have conducted Combined Array for Research in Millimeter-wave Astronomy (CARMA) observations of LiH, in absorption, toward three quasars. These quasars, B0218+357, PKS1830-211, and PKS0201+113, have redshifts of z = 0.685 - 3.387$, and shift the LiH J=1-0 transition to the 1 mm and 3mm wavelength bands, where atmospheric absorption is sharply reduced from that predominating near the rest frequency of 443 GHz. We report a 3$sigma$ detection of LiH toward B0218+357 with a column density of 1.4x10^{12} cm^{-2} and place an upper limit on the ^6Li/^7Li ratio of <0.16. LiH was not detected toward any other source.
Deuterium and lithium are light elements of high cosmological and astrophysical importance. In this work we report the first detection of deuterated molecules and a search for lithium hydride, 7LiH, at redshift z=0.89 in the spiral galaxy intercepting the line of sight to the quasar PKS1830-211. We used ALMA to observe several submillimeter lines of ND, NH2D, and HDO, and their related isotopomers NH2, NH3, and H2^18O, in absorption against the southwest image of the quasar, allowing us to derive XD/XH abundance ratios. The absorption spectra mainly consist of two distinct narrow velocity components for which we find remarkable differences. One velocity component shows XD/XH abundances that is about 10 times larger than the primordial elemental D/H ratio, and no variability of the absorption profile during the time span of our observations. [...] The second component has XD/XH abundances that are 100 times larger than the primordial D/H ratio, a deepening of the absorption by a factor of two within a few months, and a rich chemical composition, with relative enhancements of N2H+, CH3OH, SO2, and complex organic molecules. We therefore speculate that this component is associated with the analog of a Galactic dark cloud, while the first component is likely more diffuse. Our search for the 7LiH (1--0) line was unsuccessful and we derive an upper limit 7LiH/H2 = 4 x 10^-13 (3sigma) in the z=0.89 absorber toward PKS1830-211. Besides, with ALMA archival data, we could not confirm the previous tentative detections of this line in the z=0.68 absorber toward B0218+357; we derive an upper limit 7LiH/H2 = 5 x 10^-11 (3sigma), although this is less constraining than our limit toward PKS1830-211. We conclude that, as in the Milky Way, only a tiny fraction of lithium nuclei are possibly bound in LiH in these absorbers at intermediate redshift.
We analyze the effect of dissipation on the shapes of dark matter (DM) halos using high-resolution cosmological gasdynamics simulations of clusters and galaxies in the LCDM cosmology. We find that halos formed in simulations with gas cooling are significantly more spherical than corresponding halos formed in adiabatic simulations. Gas cooling results in an average increase of the principle axis ratios of halos by ~ 0.2-0.4 in the inner regions. The systematic difference decreases slowly with radius but persists almost to the virial radius. We argue that the differences in simulations with and without cooling arise both during periods of quiescent evolution, when gas cools and condenses toward the center, and during major mergers. We perform a series of high-resolution N-body simulations to study the shapes of remnants in major mergers of DM halos and halos with embedded stellar disks. In the DM halo-only mergers, the shape of the remnants depends only on the orbital angular momentum of the encounter and not on the internal structure of the halos. However, significant shape changes in the DM distribution may result if stellar disks are included. In this case the shape of the DM halos is correlated with the morphology of the stellar remnants.
The first generation of stars is quite unique. The absence of metals likely affects their formation, with current models suggesting a much more top-heavy initial mass fraction than what we observe today, and some of their other properties, such as rotation rates and binarity, are largely unknown or constrained by direct observations. But even non-rotation single stars of a given mass will evolve quite differently due to the absence of the metals: the stars will mostly remain much more compact until their death, with the hydrogen-rich later reaching down ten teems deeper in radius then in modern stars. When they explode as supernovae, the exposure to the supernova neutrino flux is much enhanced, allowing for copious production of lithium. This production will not be constant for all stars but largely vary across the mass range. Such production even more challenges the presence of the Spite Plateau.
We study the effect of the gas accretion rate ($dot M_{rm accr}$) on the radial gas metallicity profile (RMP) of galaxies using the EAGLE cosmological hydrodynamic simulations, focusing on central galaxies of stellar mass $M_star gtrsim 10^9 , {rm M_odot}$ at $z le 1$. We find clear relations between $dot M_{rm accr}$ and the slope of the RMP (measured within an effective radius), where higher $dot M_{rm accr}$ are associated with more negative slopes. The slope of the RMPs depends more strongly on $dot M_{rm accr}$ than on stellar mass, star formation rate or gas fraction, suggesting $dot M_{rm accr}$ to be a more fundamental driver of the RMP slope of galaxies. We find that eliminating the dependence on stellar mass is essential for pinning down the properties that shape the slope of the RMP. Although $dot M_{rm accr}$ is the main property modulating the slope of the RMP, we find that it causes other correlations that are more easily testable observationally: at fixed stellar mass, galaxies with more negative RMP slopes tend to have higher gas fractions and SFRs, while galaxies with lower gas fractions and SFRs tend to have flatter metallicity profiles within an effective radius.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
