Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCharacterizing the Circumgalactic Medium of Nearby Galaxies with HST/COS and HST/STIS Absorption-Line Spectroscopy: II. Methods and Models
242
0
0.0
(
0
)
Authors
Brian A. Keeney
Ask ChatGPT about the research
No Arabic abstract
We present basic data and modeling for a survey of the cool, photo-ionized Circum-Galactic Medium (CGM) of low-redshift galaxies using far-UV QSO absorption line probes. This survey consists of targeted and serendipitous CGM subsamples, originally described in Stocke et al. (2013, Paper 1). The targeted subsample probes low-luminosity, late-type galaxies at $z<0.02$ with small impact parameters ($langlerhorangle = 71$ kpc), and the serendipitous subsample probes higher luminosity galaxies at $zlesssim0.2$ with larger impact parameters ($langlerhorangle = 222$ kpc). HST and FUSE UV spectroscopy of the absorbers and basic data for the associated galaxies, derived from ground-based imaging and spectroscopy, are presented. We find broad agreement with the COS-Halos results, but our sample shows no evidence for changing ionization parameter or hydrogen density with distance from the CGM host galaxy, probably because the COS-Halos survey probes the CGM at smaller impact parameters. We find at least two passive galaxies with H I and metal-line absorption, confirming the intriguing COS-Halos result that galaxies sometimes have cool gas halos despite no on-going star formation. Using a new methodology for fitting H I absorption complexes, we confirm the CGM cool gas mass of Paper 1, but this value is significantly smaller than found by the COS-Halos survey. We trace much of this difference to the specific values of the low-$z$ meta-galactic ionization rate assumed. After accounting for this difference, a best-value for the CGM cool gas mass is found by combining the results of both surveys to obtain $log{(M/M_{odot})}=10.5pm0.3$, or ~30% of the total baryon reservoir of an $L geq L^*$, star-forming galaxy.
rate research
Read More
The Circumgalactic Medium (CGM) of late-type galaxies is characterized using UV spectroscopy of 11 targeted QSO/galaxy pairs at z < 0.02 with the Hubble Space Telescope Cosmic Origins Spectrograph and ~60 serendipitous absorber/galaxy pairs at z < 0.2 with the Space Telescope Imaging Spectrograph. CGM warm cloud properties are derived, including volume filling factors of 3-5%, cloud sizes of 0.1-30 kpc, masses of 10-1e8 solar masses and metallicities of 0.1-1 times solar. Almost all warm CGM clouds within 0.5 virial radii are metal-bearing and many have velocities consistent with being bound, galactic fountain clouds. For galaxies with L > 0.1 L*, the total mass in these warm CGM clouds approaches 1e10 solar masses, ~10-15% of the total baryons in massive spirals and comparable to the baryons in their parent galaxy disks. This leaves >50% of massive spiral-galaxy baryons missing. Dwarfs (<0.1 L*) have smaller area covering factors and warm CGM masses (<5% baryon fraction), suggesting that many of their warm clouds escape. Constant warm cloud internal pressures as a function of impact parameter ($P/k ~ 10 cm^{-3} K) support the inference that previous COS detections of broad, shallow O VI and Ly-alpha absorptions are of an extensive (~400-600 kpc), hot (T ~ 1e6 K) intra-cloud gas which is very massive (>1e11 solar masses). While the warm CGM clouds cannot account for all the missing baryons in spirals, the hot intra-group gas can, and could account for ~20% of the cosmic baryon census at z ~ 0 if this hot gas is ubiquitous among spiral groups.
To characterize the absorption properties of this circumgalactic medium (CGM) and its relation to the LG we present the so-far largest survey of metal absorption in Galactic high-velocity clouds (HVCs) using archival ultraviolet (UV) spectra of extragalactic background sources. The UV data are obtained with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST) and are supplemented by 21 cm radio observations of neutral hydrogen. Along 270 sightlines we measure metal absorption in the lines of SiII, SiIII, CII, and CIV and associated HI 21 cm emission in HVCs in the velocity range |v_LSR|=100-500 km s^-1. With this unprecedented large HVC sample we were able to improve the statistics on HVC covering fractions, ionization conditions, small-scale structure, CGM mass, and inflow rate. For the first time, we determine robustly the angular two point correlation function of the high-velocity absorbers, systematically analyze antipodal sightlines on the celestial sphere, and compare the absorption characteristics with that of Damped Lyman alpha absorbers (DLAs) and constrained cosmological simulations of the LG. Our study demonstrates that the Milky Way CGM contains sufficient gaseous material to maintain the Galactic star-formation rate at its current level. We show that the CGM is composed of discrete gaseous structures that exhibit a large-scale kinematics together with small-scale variations in physical conditions. The Magellanic Stream clearly dominates both the cross section and mass flow of high-velocity gas in the Milky Ways CGM. The possible presence of high-velocity LG gas underlines the important role of the local cosmological environment in the large-scale gas-circulation processes in and around the Milky Way (abridged).
The circumgalactic medium (CGM), which harbors > 50% of all the baryons in a galaxy, is both the reservoir of gas for subsequent star formation and the depository of chemically processed gas, energy, and angular momentum from feedback. As such, the CGM obviously plays a critical role in galaxy evolution. We discuss the opportunity to image this component using recombination line emission, beginning with the early results coming from recent statistical detection of this emission to the final goal of realizing spectral-line images of the CGM in individual nearby galaxies. Such work will happen in the next decade and provide new insights on the galactic baryon cycle.
We use the EAGLE (Evolution and Assembly of GaLaxies and their Environments) cosmological simulation to study the distribution of baryons, and far-ultraviolet (O VI), extreme-ultraviolet (Ne VIII) and X-ray (O VII, O VIII, Ne IX, and Fe XVII) line absorbers, around galaxies and haloes of mass $mathrm{M}_{200c}=10^{11}$-$10^{14.5},mathrm{M}_{odot}$ at redshift 0.1. EAGLE predicts that the circumgalactic medium (CGM) contains more metals than the interstellar medium across halo masses. The ions we study here trace the warm-hot, volume-filling phase of the CGM, but are biased towards temperatures corresponding to the collisional ionization peak for each ion, and towards high metallicities. Gas well within the virial radius is mostly collisionally ionized, but around and beyond this radius, and for O VI, photoionization becomes significant. When presenting observables we work with column densities, but quantify their relation with equivalent widths by analysing virtual spectra. Virial-temperature collisional ionization equilibrium ion fractions are good predictors of column density trends with halo mass, but underestimate the diversity of ions in haloes. Halo gas dominates the highest column density absorption for X-ray lines, but lower density gas contributes to strong UV absorption lines from O VI and Ne VIII. Of the O VII (O VIII) absorbers detectable in an Athena X-IFU blind survey, we find that 41 (56) per cent arise from haloes with $mathrm{M}_{200c}=10^{12.0}$-$10^{13.5},mathrm{M}_{odot}$. We predict that the X-IFU will detect O VII (O VIII) in 77 (46) per cent of the sightlines passing $mathrm{M}_{star}=10^{10.5}$-$10^{11.0},mathrm{M}_{odot}$ galaxies within 100 pkpc (59 (82) per cent for $mathrm{M}_{star}>10^{11.0},mathrm{M}_{odot}$). Hence, the X-IFU will probe covering fractions comparable to those detected with the Cosmic Origins Spectrograph for O VI.
In order to study the circumgalactic medium (CGM) of galaxies we develop an automated pipeline to estimate the optical continuum of quasars and detect intervening metal absorption line systems with a matched kernel convolution technique and adaptive S/N criteria. We process $sim$ one million quasars in the latest Data Release 16 (DR16) of the Sloan Digital Sky Survey (SDSS) and compile a large sample of $sim$ 160,000 MgII absorbers, together with $sim$ 70,000 FeII systems, in the redshift range $0.35<z_{abs}<2.3$. Combining these with the SDSS DR16 spectroscopy of $sim1.1$ million luminous red galaxies (LRGs) and $sim 200,000$ emission line galaxies (ELGs), we investigate the nature of cold gas absorption at $0.5<z<1$. These large samples allow us to characterize the scale dependence of MgII with greater accuracy than in previous work. We find that there is a strong enhancement of MgII absorption within $sim 50$ kpc of ELGs, and the covering fraction within $0.5r_{rm vir}$ of ELGs is 2-5 times higher than for LRGs. Beyond 50 kpc, there is a sharp decline in MgII for both kinds of galaxies, indicating a transition to the regime where the CGM is tightly linked with the dark matter halo. The MgII covering fraction correlates strongly with stellar mass for LRGs, but weakly for ELGs, where covering fractions increase with star formation rate. Our analysis implies that cool circumgalactic gas has a different physical origin for star forming versus quiescent galaxies.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
