Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLyman-alpha absorption beyond the disk of simulated spiral galaxies
98
0
0.0
(
0
)
Authors
Bernhard Rottgers
Ask ChatGPT about the research
No Arabic abstract
We present an analysis of the origin and properties of the circum-galactic medium (CGM) in a suite of 11 cosmological zoom simulations resembling present day spiral galaxies. On average the galaxies retain about 50% of the cosmic fraction in baryons, almost equally divided into disc (interstellar medium) gas, cool CGM gas and warm-hot CGM gas. At radii smaller than 50 kpc the CGM is dominated by recycled warm-hot gas injected from the central galaxy, while at larger radii it is dominated by cool gas accreted onto the halo. The recycled gas typically accounts for one-third of the CGM mass. We introduce the novel publicly available analysis tool textsc{pygad} to compute ion abundances and mock absorption spectra. For Lyman-${alpha}$ absorption we find good agreement of the simulated equivalent width (EW) distribution and observations out to large radii. Disc galaxies with quiescent assembly histories show significantly more absorption along the disc major axis. By comparing the EW and HI column densities we find that CGM Lyman-${alpha}$ absorbers are best represented by an effective line-width $bapprox 50 - 70$ km s$^{-1}$ that increases mildly with halo mass, larger than typically assumed.
rate research
Read More
Using the Low Dispersion Survey Spectrograph 3 at the Magellan II Clay Telescope, we target {candidate absorption host galaxies} detected in deep optical imaging {(reaching limiting apparent magnitudes of 23.0-26.5 in $g, r, i,$ and $z$ filters) in the fields of three QSOs, each of which shows the presence of high metallicity, high $N_{rm HI}$ absorption systems in their spectra (Q0826-2230: $z_{abs}$=0.9110, Q1323-0021: $z_{abs}=0.7160$, Q1436-0051: $z_{abs}=0.7377, 0.9281$). We confirm three host galaxies {at redshifts 0.7387, 0.7401, and 0.9286} for two of the Lyman-$alpha$ absorption systems (one with two galaxies interacting). For these systems, we are able to determine the star formation rates (SFRs); impact parameters (from previous imaging detections); the velocity shift between the absorption and emission redshifts; and, for one system, also the emission metallicity.} Based on previous photometry, we find these galaxies have L$>$L$^{ast}$. The [O II] SFRs for these galaxies are in the range $11-25$ M$_{odot}$ yr$^{-1}$ {(uncorrected for dust)}, while the impact parameters lie in the range $35-54$ kpc. {Despite the fact that we have confirmed galaxies at 50 kpc from the QSO, no gradient in metallicity is indicated between the absorption metallicity along the QSO line of sight and the emission line metallicity in the galaxies.} We confirm the anti-correlation between impact parameter and $N_{rm HI}$ from the literature. We also report the emission redshift of five other galaxies: three at $z_{em}>z_{QSO}$, and two (L$<$L$^{ast}$) at $z_{em}<z_{QSO}$ not corresponding to any known absorption systems.
We perform Monte-Carlo radiative transfer calculations to model the Lyman alpha properties of galaxies in high-resolution, zoom-in cosmological simulations at z ~ 6.6. The simulations include both constrained and unconstrained runs, representing respectively a highly overdense region and an average field. Different galactic wind models are used in the simulations in order to investigate the effects of these winds on the apparent Ly alpha properties of galaxies. We find that, for models including galactic winds, the Ly alpha properties of massive galaxies residing in the overdense region match well recent observations of luminous Ly alpha emitters (LAEs) at z ~ 6-7, in terms of apparent Ly alpha luminosity, Ly alpha line width and Ly alpha equivalent width distributions. Without winds, the same galaxies appear less Ly alpha bright as a result of both differences in the line profile emerging from galaxies themselves, and, in the distributions of neutral gas in the circumgalactic (CGM) and intergalactic medium (IGM). We also study the relations between apparent Ly alpha luminosity and various galaxy properties: stellar mass, star formation rate (SFR) and host halo mass. At fixed halo mass, the apparent Ly alpha luminosity of galaxies appears to depend on the large-scale environment while this is no longer true for galaxies at a given stellar mass or SFR. We provide simple linear fits to these relations that can be used for quickly constructing mock LAE samples from N-body simulations. Our results suggest that the observed luminous LAEs at z ~ 6.6 are hosted by ~10^{12} h^{-1} Mo, dark matter haloes, residing in large, overdense ionized regions.
We investigate the absorption features associated with a gas-rich dwarf galaxy using cosmological hydrodynamics simulations. Our goal is to explore whether the progenitors of the lowest mass dwarf galaxies known to harbor neutral hydrogen today (M_star~10^6 solar mass, M_halo=4x10^9 solar mass) could possibly be detected as Damped Lyman-alpha Absorbers (DLAs) over cosmic time. We trace the evolution of a single dwarf galaxy, pre-selected to contain DLAs, from the era of the first metal-free, so-called Population~III (Pop~III), stars, down to z=0, thus allowing us to study the metal enrichment history of DLAs associated with the simulated galaxy. We find that the progenitors of the simulated dwarf are expected to be seen for most of their evolution as DLAs that are contaminated by normal, Population~II, stars. The time period during which DLAs are only metal-enriched by Pop~III stars, on the other hand, is likely very brief, confined to high redshifts, z~6. The susceptibility of the dwarfs to the external UV radiation background allows them to preserve neutral gas only at the centre (a few ~100 pc). This results in a small probability that the simulated dwarf would be observed as a DLA. This study suggests that DLAs are unlikely to be hosted in the lowest mass dwarfs that can harbor neutral gas (M_halo~ 4x10^9 solar mass), below which neutral gas is unlikely to exist. However, this study does illustrate that, when detected, absorption lines provide a powerful method for probing ISM conditions inside the smallest dwarf galaxies at intermediate to high redshifts.
We examine the dust geometry and Ly{alpha} scattering in the galaxies of the Lyman Alpha Reference Sample (LARS), a set of 14 nearby (0.02 < $z$ < 0.2) Ly{alpha} emitting and starbursting systems with Hubble Space Telescope Ly{alpha}, H{alpha}, and H{beta} imaging. We find that the global dust properties determined by line ratios are consistent with other studies, with some of the LARS galaxies exhibiting clumpy dust media while others of them show significantly lower Ly{alpha} emission compared to their Balmer decrement. With the LARS imaging, we present Ly{alpha}/H{alpha} and H{alpha}/H{beta} maps with spatial resolutions as low as $sim$ 40 pc, and use these data to show that in most galaxies, the dust geometry is best modeled by three distinct regions: a central core where dust acts as a screen, an annulus where dust is distributed in clumps, and an outer envelope where Ly{alpha} photons only scatter. We show that the dust that affects the escape of Ly{alpha} is more restricted to the galaxies central regions, while the larger Ly{alpha} halos are generated by scattering at large radii. We present an empirical modeling technique to quantify how much Ly{alpha} scatters in the halo, and find that this characteristic scattering distance correlates with the measured size of the Ly{alpha} halo. We note that there exists a slight anti-correlation between the scattering distance of Ly{alpha} and global dust properties.
With the Multi Unit Spectroscopic Explorer (MUSE), it is now possible to detect spatially extended Lyman alpha emission from individual faint (M_UV ~ -18) galaxies at redshifts, 3 < z < 6, tracing gas out to circum-galactic scales comparable to the dark matter halo virial radius. To explore the implications of such observations, we present a cosmological radiation hydrodynamics simulation of a single galaxy, chosen to be typical of the Lyman alpha-emitting galaxies detected by MUSE in deep fields. We use this simulation to study the origin and dynamics of the high-redshift circum-galactic medium (CGM). We find that the majority of the mass in the diffuse CGM is comprised of material infalling for the first time towards the halo center, but with the inner CGM also containing a comparable amount of mass that has moved past first-pericentric passage, and is in the process of settling into a rotationally supported configuration. Making the connection to Lyman alpha emission, we find that the observed extended surface brightness profile is due to a combination of three components: scattering of galactic Lyman alpha emission in the CGM, in-situ emission of CGM gas (mostly infalling), and Lyman alpha emission from small satellite galaxies. The weight of these contributions vary with distance from the galaxy such that (1) scattering dominates the inner regions (r < 7 kpc), at surface brightness larger than a few 10^-19 cgs, (2) all components contribute equally around r ~ 10 kpc (or SB ~10^-19), and (3) the contribution of small satellite galaxies takes over at large distances (or SB ~10^-20). Our simulation fails to reproduce the characteristic observed Lyman alpha spectral morphology that is red-shifted with respect to the systemic velocity, with the implication that the simulation is missing an important component of neutral outflowing gas.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
