Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userFollowing the Metals in the Intergalactic and Circumgalactic Medium over Cosmic Time
83
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The circumgalactic medium (CGM) of galaxies serves as a record of the influences of outflows and accretion that drive the evolution of galaxies. Feedback from star formation drives outflows that carry mass and metals away from galaxies to the CGM, while infall from the intergalactic medium (IGM) is thought to bring in fresh gas to fuel star formation. Such exchanges of matter between IGM-CGM-galaxies have proven critical to producing galaxy scaling relations in cosmological simulations that match observations. However, the nature of these processes, of the physics that drives outflows and accretion, and their evolution with cosmic time are not fully characterized. One approach to constraining these processes is to characterize the metal enrichment of gas around and beyond galaxies. Measurements of the metallicity distribution functions of CGM/IGM gas over cosmic time provide independent tests of cosmological simulations. We have made great progress over the last decade as direct result of a very sensitive, high-resolution space-based UV spectrograph and the rise of ground-based spectroscopic archives. We argue the next transformative leap to track CGM/IGM metals during the epoch of galaxy formation and transformation into quiescent galaxies will require 1) a larger space telescope with an even more sensitive high-resolution spectrograph covering both the far- and near-UV (1,000-3,000 AA); and 2) ground-based archives housing science-ready data.
rate research
Read More
We investigate the association between galaxies and metal-enriched and metal-deficient absorbers in the local universe ($z < 0.16$) using a large compilation of FUV spectra of bright AGN targets observed with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope. In this homogeneous sample of 18 O VI detections at $N_{rm O,{VI}}geq13.5~mathrm{cm}^{-2}$ and 18 non-detections at $N_{rm O,{VI}}<13.5~mathrm{cm}^{-2}$ using Lya absorbers with ${N_{rm H,{I}}geq} 10^{14}~mathrm{cm}^{-2}$, the maximum distance O VI extends from galaxies of various luminosities is $sim0.6$ Mpc, or $sim5$ virial radii, confirming and refining earlier results. This is an important value that must be matched by numerical simulations, which input the strength of galactic winds at the sub-grid level. We present evidence that the primary contributors to the spread of metals into the circum- and intergalactic media are sub-$L^*$ galaxies ($0.25L^*<L<L^*$). The maximum distances that metals are transported from these galaxies is comparable to, or less than, the size of a group of galaxies. These results suggest that, where groups are present, the metals produced by the group galaxies do not leave the group. Since many O VI non-detections in our sample occur at comparably close impact parameters as the metal-bearing absorbers, some more pristine intergalactic material appears to be accreting onto groups where it can mix with metal-bearing clouds.
We study the $zapprox3.5$ intergalactic medium (IGM) by comparing new, high-quality absorption spectra of eight QSOs with $langle z_{rm QSO} rangle=3.75$, to virtual observations of the EAGLE cosmological hydrodynamical simulations. We employ the pixel optical depth method and uncover strong correlations between various combinations of HI, CIII, CIV, SiIII, SiIV, and OVI. We find good agreement between many of the simulated and observed correlations, including OVI(HI). However, the observed median optical depths for the CIV(HI) and SiIV(HI) relations are higher than those measured from the mock spectra. The discrepancy increases from up to $approx0.1$ dex at $tau_{rm HI}=1$ to $approx1$ dex at $tau_{rm HI}=10^2$, where we are likely probing dense regions at small galactocentric distances. As possible solutions, we invoke (a) models of ionizing radiation softened above 4 Ryd to account for delayed completion of HeII reionization; (b) simulations run at a higher resolution; (c) the inclusion of additional line broadening due to unresolved turbulence; and (d) increased elemental abundancess; however, none of these factors can fully explain the observed differences. Enhanced photoionization of HI by local sources, which was not modelled, could offer a solution. However, the much better agreement with the observed OVI(HI) relation, which we find probes a hot and likely collisionally-ionized gas phase, indicates that the simulations are not in tension with the hot phase of the IGM, and suggests that the simulated outflows may entrain insufficient cool gas.
We examine the effects of SMBH feedback on the CGM using a cosmological hydrodynamic simulation citep[{sc Romulus25};][]{Tremmel2017} and a set of four zoom-in `genetically modified Milky Way-mass galaxies sampling different evolutionary paths. By tracing the distribution of metals in the circumgalactic medium (CGM), we show that ion{O}{6} is a sensitive indicator of supermassive black hole (SMBH) feedback. First, we calculate the column densities of ion{O}{6} in simulated Milky Way-mass galaxies and compare them with observations from the COS-Halos Survey. Our simulations show column densities of ion{O}{6} in the CGM consistent with those of COS-Halos star forming and quenched galaxies. These results contrast with those from previous simulation studies which typically underproduce CGM column densities of ion{O}{6}. We determine that a galaxys star formation history and assembly record have little effect on the amount of ion{O}{6} in its CGM. Instead, column densities of ion{O}{6} are closely tied to galaxy halo mass and BH growth history. The set of zoom-in, genetically modified Milky Way-mass galaxies indicates that the SMBH drives highly metal-enriched material out into its host galaxys halo which in turn elevates the column densities of ion{O}{6} in the CGM.
We describe a new approach to studying the intergalactic and circumgalactic medium in the local Universe: direct detection through narrow-band imaging of ultra-low surface brightness visible-wavelength line emission. We use the hydrodynamical cosmological simulation EAGLE to investigate the expected brightness of this emission at low redshift ($z$ $lesssim$ 0.2). H$alpha$ emission in extended halos (analogous to the extended Ly$alpha$ halos/blobs detected around galaxies at high redshifts) has a surface brightness of $gtrsim700$ photons cm$^{-2}$ sr$^{-1}$ s$^{-1}$ out to $sim$100 kpc. Mock observations show that the Dragonfly Telephoto Array, equipped with state-of-the-art narrow-band filters, could directly image these structures in exposure times of $sim$10 hours. H$alpha$ fluorescence emission from this gas can be used to place strong constraints on the local ultra-violet background, and on gas flows around galaxies. Detecting H$alpha$ emission from the diffuse intergalactic medium (the cosmic web) is beyond current capabilities, but would be possible with a hypothetical 1000-lens Dragonfly array.
Using the Cosmic Origins Spectrograph aboard the Hubble Space Telescope, we measured the abundances of six ions (C III, C IV, Si III, Si IV, N V, O VI) in the low-redshift (z < 0.4) intergalactic medium and explored C and Si ionization corrections from adjacent ion stages. Both C IV and Si IV have increased in abundance by a factor of ~10 from z = 5.5 to the present. We derive ion mass densities, (rho_ion) = (Omega_ion)(rho_cr) with Omega_ion expressed relative to closure density. Our models of the mass-abundance ratios, (Si III / Si IV) = 0.67(+0.35,-0.19), (C III / C IV) = 0.70(+0.43,-0.20), and (Omega_CIII + Omega_CIV) / (Omega_SiIII + Omega_SiIV) = 4.9(+2.2,-1.1), are consistent with a hydrogen photoionization rate Gamma_H = (8 +/- 2) x 10^{-14} s^{-1} at z < 0.4 and specific intensity I_0 = (3 +/- 1) x 10^{-23} erg/(cm^2 s Hz sr) at the Lyman limit. We find mean photoionization parameter log U = -1.5 +/- 0.4, baryon overdensity Delta_b = 200 +/- 50, and Si/C enhanced to three times its solar ratio (enhancement of alpha-process elements). We compare these metal abundances to the expected IGM enrichment and abundances in higher photoionized states of carbon (C V) and silicon (Si V, Si VI, Si VII). Our ionization modeling infers IGM metal densities of (5.4 +/- 0.5) x 10^5 M_sun / Mpc^3 in the photoionized Lya forest traced by the C and Si ions and (9.1 +/- 0.6) x 10^5 M_sun / Mpc^3 in hotter gas traced by O VI. Combining both phases, the heavy elements in the IGM have mass density rho_Z = (1.5 +/- 0.8) x 10^6 M_sun / Mpc^3 or Omega_Z = 10^{-5}. This represents 10 +/- 5 percent of the metals produced by (6 +/- 2) x 10^8 M_sun / Mpc^3 of integrated star formation with yield y_m = 0.025 +/- 0.010. The missing metals at low redshift may reside within galaxies and in undetected ionized gas in galaxy halos and circumgalactic medium.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
