Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCircumgalactic Pressure Profiles Indicate Precipitation-Limited Atmospheres for $M_* sim 10^9$$-$$10^{11.5},M_odot$
51
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Cosmic gas cycles in and out of galaxies, but outside of galaxies it is difficult to observe except for the absorption lines that circumgalactic clouds leave in the spectra of background quasars. Using photoionization modeling of those lines to determine cloud pressures, we find that galaxies are surrounded by extended atmospheres that confine the clouds and have a radial pressure profile that depends on galaxy mass. Motivated by observations of the universes most massive galaxies, we compare those pressure measurements with models predicting the critical pressure at which cooler clouds start to precipitate out of the hot atmosphere and rain toward the center. We find excellent agreement, implying that the precipitation limit applies to galaxies over a wide mass range.
rate research
Read More
A wavelike solution for the non-relativistic universal dark matter (wave-DM) is rapidly gaining interest, following distinctive predictions of pioneering simulations of cosmic structure as an interference pattern of coherently oscillating bosons. A prominent solitonic standing wave is predicted at the center of every galaxy, representing the ground state, that has been identified with the wide, kpc scale dark cores of common dwarf-spheroidal galaxies, providing a boson mass of, $simeq 10^{-22}$ eV. A denser soliton is predicted for Milky Way sized galaxies where momentum is higher, so the de Broglie scale of the soliton is smaller, $simeq 100$ pc, of mass $simeq 10^9 M_odot$. Here we show the central motion of bulge stars in the Milky Way implies the presence of such a dark core, where the velocity dispersion rises inversely with radius to a maximum of $simeq 130$ km/s, corresponding to an excess central mass of $simeq 1.5times 10^9 M_odot$ within $simeq 100$ pc, favouring a boson mass of $simeq 10^{-22}$ eV. This quantitative agreement with such a unique and distinctive prediction is therefore strong evidence for a light bosonic solution to the long standing Dark Matter puzzle, such as the axions generic in String Theory.
We calculate the neutrino signal from Population III supermassive star collapse using a neutrino transfer code originally developed for core collapse supernovae and massive star collapse. Using this code, we are able to investigate the supermassive star mass range thought to undergo neutrino trapping ($sim 10^4$ M$_odot$), a mass range which has been neglected by previous works because of the difficulty of neutrino transfer. For models in this mass range, we observe a neutrino-sphere with a large radius and low density compared to typical massive star neutrino-spheres. We calculate the neutrino light-curve emitted from this neutrino-sphere. The resulting neutrino luminosity is significantly lower than the results of a previous analytical model. We briefly discuss the possibility of detecting a neutrino burst from a supermassive star or the neutrino background from many supermassive stars and conclude that the former is unlikely with current technology, unless the SMS collapse is located as close as 1 Mpc, while the latter is also unlikely even under very generous assumptions. However, the supermassive star neutrino background is still of interest as it may serve as a source of noise in proposed dark matter direct detection experiments.
We introduce a novel abundance matching technique that produces a more accurate estimate of the pre-infall halo mass, $M_{200}$, for satellite galaxies. To achieve this, we abundance match with the mean star formation rate, averaged over the time when a galaxy was forming stars, $langle {rm SFR}rangle$, instead of the stellar mass, $M_*$. Using data from the Sloan Digital Sky Survey, the GAMA survey and the Bolshoi simulation, we obtain a statistical $langle {rm SFR}rangle-{rm M}_{200}$ relation in $Lambda{rm CDM}$. We then compare the pre-infall halo mass, $M^{rm abund}_{200}$, derived from this relation with the pre-infall dynamical mass, $M^{rm dyn}_{200}$, for 21 nearby dSph and dIrr galaxies, finding a good agreement between the two. As a first application, we use our new $langle {rm SFR}rangle-{rm M}_{200}$ relation to empirically measure the cumulative mass function of a volume-complete sample of bright Milky Way satellites within 280 kpc of the Galactic centre. Comparing this with a suite of cosmological zoom simulations of Milky Way-mass halos that account for subhalo depletion by the Milky Way disc, we find no missing satellites problem above $M_{200} sim 10^9,{rm M}_odot$ in the Milky Way. We discuss how this empirical method can be applied to a larger sample of nearby spiral galaxies.
We investigate the possibility of a supernova in supermassive ($5 times 10^4 ;M_odot$) population III stars induced by a general relativistic instability occurring in the helium burning phase. This explosion could occur via rapid helium burning during an early contraction of the isentropic core. Such an explosion would be visible to future telescopes and could disrupt the proposed direct collapse formation channel for early universe supermassive black holes. We simulate first the stellar evolution from hydrogen burning using a 1D stellar evolution code with a post Newtonian approximation; at the point of dynamical collapse, we switch to a 1D (general relativistic) hydrodynamics code with the Misner-Sharpe metric. In opposition to a previous study, we do not find an explosion in the non rotating case, although our model is close to exploding for a similar mass to the explosion in the previous study. When we include slow rotation, we find one exploding model, and we conclude that there likely exist additional exploding models, though they may be rare.
During the last decade, numerous and varied observations, along with increasingly sophisticated numerical simulations, have awakened astronomers to the central role the circumgalactic medium (CGM) plays in regulating galaxy evolution. It contains the majority of the baryonic matter associated with a galaxy, along with most of the metals, and must continually replenish the star forming gas in galaxies that continue to sustain star formation. And while the CGM is complex, containing gas ranging over orders of magnitude in temperature and density, a simple emergent property may be governing its structure and role. Observations increasingly suggest that the ambient CGM pressure cannot exceed the limit at which cold clouds start to condense out and precipitate toward the center of the potential well. If feedback fueled by those clouds then heats the CGM and causes it to expand, the pressure will drop and the rain will diminish. Such a feedback loop tends to suspend the CGM at the threshold pressure for precipitation. The coming decade will offer many opportunities to test this potentially fundamental principle of galaxy evolution.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
