Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userTracing the simulated high-redshift circum-galactic medium with Lyman alpha emission
121
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
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.
rate research
Read More
Gas flows in and out of galaxies through their circumgalactic medium (CGM) are poorly constrained and direct observations of this faint, diffuse medium remain challenging. We use a sample of five $z$ $sim$ 1-2 galaxy counterparts to Damped Lyman-$alpha$ Absorbers (DLAs) to combine data on cold gas, metals and stellar content of the same galaxies. We present new HST/WFC3 imaging of these fields in 3-5 broadband filters and characterise the stellar properties of the host galaxies. By fitting the spectral energy distribution, we measure their stellar masses to be in the range of log($M_*$/$text{M}_{odot}$) $sim$ 9.1$-$10.7. Combining these with IFU observations, we find a large spread of baryon fractions inside the host galaxies, between 7 and 100 percent. Similarly, we find gas fractions between 3 and 56 percent. Given their star formation rates, these objects lie on the expected main sequence of galaxies. Emission line metallicities indicate they are consistent with the mass-metallicity relation for DLAs. We also report an apparent anti-correlation between the stellar masses and $N$(HI), which could be due to a dust bias effect or lower column density systems tracing more massive galaxies. We present new ALMA observations of one of the targets leading to a molecular gas mass of log($M_{rm mol}$/$text{M}_{odot}$) < 9.89. We also investigate the morphology of the DLA counterparts and find that most of the galaxies show a clumpy structure and suggest ongoing tidal interaction. Thanks to our high spatial resolution HST data, we gain new insights in the structural complexity of the CGM.
We present simulations of isolated disc galaxies in a realistic environment performed with the Tree-SPMHD-Code Gadget-3. Our simulations include a spherical circum-galactic medium (CGM) surrounding the galactic disc, motivated by observations and the results of cosmological simulations. We present three galactic models with different halo masses between 10e10 Msol and 10e12 Msol, and for each we use two different approaches to seed the magnetic field, as well as a control simulation without a magnetic field. We find that the amplification of the magnetic field in the centre of the disc leads to a biconical magnetic outflow of gas that magnetizes the CGM. This biconical magnetic outflow reduces the star formation rate (SFR) of the galaxy by roughly 40 percent compared to the simulations without magnetic fields. As the key aspect of our simulations, we find that small scale turbulent motion of the gas in the disc leads to the amplification of the magnetic field up to tens of 10e-6 G, as long as the magnetic field strength is low. For stronger magnetic fields turbulent motion does not lead to significant amplification but is replaced by an alpha-omega dynamo. The occurance of a small scale turbulent dynamo becomes apparent through the magnetic power spectrum and analysis of the field lines curvature. In accordance with recent observations we find an anti-correlation between the spiral structure in the gas density and in the magnetic field due to a diffusion term added to the induction equation.
In the context of the FLASHLIGHT survey, we obtained deep narrow band images of 15 $zsim2$ quasars with GMOS on Gemini-South in an effort to measure Ly$alpha$ emission from circum- and inter-galactic gas on scales of hundreds of kpc from the central quasar. We do not detect bright giant Ly$alpha$ nebulae (SB~10$^{-17}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ at distances >50 kpc) around any of our sources, although we routinely ($simeq47$%) detect smaller scale <50 kpc Ly$alpha$ emission at this SB level emerging from either the extended narrow emission line regions powered by the quasars or by star-formation in their host galaxies. We stack our 15 deep images to study the average extended Ly$alpha$ surface brightness profile around $zsim2$ quasars, carefully PSF-subtracting the unresolved emission component and paying close attention to sources of systematic error. Our analysis, which achieves an unprecedented depth, reveals a surface brightness of SB$_{rm Lyalpha}sim10^{-19}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ at $sim200$ kpc, with a $2.3sigma$ detection of Ly$alpha$ emission at SB$_{rm Lyalpha}=(5.5pm3.1)times10^{-20}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ within an annulus spanning 50 kpc <R< 500 kpc from the quasars. Assuming this Ly$alpha$ emission is powered by fluorescence from highly ionized gas illuminated by the bright central quasar, we deduce an average volume density of $n_{rm H}=0.6times10^{-2}$ cm$^{-3}$ on these large scales. Our results are in broad agreement with the densities suggested by cosmological hydrodynamical simulations of massive ($Msimeq10^{12.5}M_odot$) quasar hosts, however they indicate that the typical quasars at these redshifts are surrounded by gas that is a factor of ~100 times less dense than the (~1 cm$^{-3}$) gas responsible for the giant bright Ly$alpha$ nebulae around quasars recently discovered by our group.
We use cosmological simulations from the Feedback In Realistic Environments (FIRE) project, which implement a comprehensive set of stellar feedback processes, to study ultra-violet (UV) metal line emission from the circum-galactic medium of high-redshift (z=2-4) galaxies. Our simulations cover the halo mass range Mh ~ 2x10^11 - 8.5x10^12 Msun at z=2, representative of Lyman break galaxies. Of the transitions we analyze, the low-ionization C III (977 A) and Si III (1207 A) emission lines are the most luminous, with C IV (1548 A) and Si IV (1394 A) also showing interesting spatially-extended structures. The more massive halos are on average more UV-luminous. The UV metal line emission from galactic halos in our simulations arises primarily from collisionally ionized gas and is strongly time variable, with peak-to-trough variations of up to ~2 dex. The peaks of UV metal line luminosity correspond closely to massive and energetic mass outflow events, which follow bursts of star formation and inject sufficient energy into galactic halos to power the metal line emission. The strong time variability implies that even some relatively low-mass halos may be detectable. Conversely, flux-limited samples will be biased toward halos whose central galaxy has recently experienced a strong burst of star formation. Spatially-extended UV metal line emission around high-redshift galaxies should be detectable by current and upcoming integral field spectrographs such as the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope and Keck Cosmic Web Imager (KCWI).
We calculate the void probability function (VPF) in simulations of Lyman-$alpha$ emitters (LAEs) across a wide redshift range ($z=3.1, 4.5, 5.7, 6.6$). The VPF measures the zero-point correlation function (i.e. places devoid of galaxies) and naturally connects to higher order correlation functions while being computationally simple to calculate. We explore the Poissonian and systematic errors on the VPF, specify its accuracy as a function of average source density and the volume probed, and provide the appropriate size scales to measure the VPF. At small radii the accuracy of the VPF is limited by galaxy density, while at large radii the VPF is limited by the number of independent volumes probed. We also offer guidelines for understanding and quantifying the error in the VPF. We approximate the error in the VPF by using independent sub-volumes of the catalogs, after finding that jackknife statistics underestimate the uncertainty. We use the VPF to probe the strength of higher order correlation functions by measuring and examining the hierarchical scaling between the correlation functions using count-in-cells. The negative binomial model (NBM) has been shown to best describe the scaling between the two point correlation function and VPF for low-redshift galaxy observations. We further test the fit of the NBM by directly deriving the volume averaged two-point correlation function from the VPF and vice versa. We find the NBM best describes the $z=3.1, 4.5, 5.7$ simulated LAEs, with a 1$sigma$ deviation from the model in the $z=6.6$ catalog. This suggests that LAEs show higher order clustering terms similar to those of normal low redshift galaxies.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
