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Register a new userGas around galaxy haloes - II: hydrogen absorption signatures from the environments of galaxies at redshifts 2 < z < 3
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A. Meiksin
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We compare predictions of large-scale cosmological hydrodynamical simulations for neutral hydrogen absorption signatures in the vicinity of 1e11 - 1e12.5 MSun haloes with observational measurements. Two different hydrodynamical techniques and a variety of prescriptions for gas removal in high density regions are examined. Star formation and wind feedback play only secondary roles in the HI absorption signatures outside the virial radius, but play important roles within. Accordingly, we identify three distinct gaseous regions around a halo: the virialized region, the mesogalactic medium outside the virial radius arising from the extended haloes of galaxies out to about two turnaround radii, and the intergalactic medium beyond. Predictions for the amount of absorption from the mesogalactic and intergalactic media are robust across different methodologies, and the predictions agree with the amount of absorption observed around star-forming galaxies and QSO host galaxies. Recovering the measured amount of absorption within the virialized region, however, requires either a higher dynamic range in the simulations, additional physics, or both.
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Modern theories of galaxy formation predict that galaxies impact on their gaseous surroundings, playing the fundamental role of regulating the amount of gas converted into stars. While star-forming galaxies are believed to provide feedback through galactic winds, Quasi-Stellar Objects (QSOs) are believed instead to provide feedback through the heat generated by accretion onto a central supermassive black hole. A quantitative difference in the impact of feedback on the gaseous environments of star-forming galaxies and QSOs has not been established through direct observations. Using the Sherwood cosmological simulations, we demonstrate that measurements of neutral hydrogen in the vicinity of star-forming galaxies and QSOs during the era of peak galaxy formation show excess LyA absorption extending up to comoving radii of about 150 kpc for star-forming galaxies and 300 - 700 kpc for QSOs. Simulations including supernovae-driven winds with the wind velocity scaling like the escape velocity of the halo account for the absorption around star-forming galaxies but not QSOs.
We have carried out deep and wide field imaging observations with narrow bands targeting 11 quasar fields to systematically study the possible photoevaporation effect of quasar radiation on surrounding low mass galaxies at $zsim2-3$. We focused on Lyman alpha emitters (LAEs) at the same redshifts as the quasars that lie within the quasar proximity zones, where the ultra-violet radiation from the quasars is higher than the average background at that epoch. We found that LAEs with high rest-frame equivalent width of Ly$alpha$ emission ($EW_0$) of $gtrsim 150$AA$~$ with low stellar mass ($lesssim 10^8 M_{odot}$), are predominantly scarce in the quasar proximity zones, suggesting that quasar photoevaporation effects may be taking place. The halo mass of LAEs with $EW_0>150$AA$~$ is estimated to be $3.6^{+12.7}_{-2.3}times10^9 M_{odot}$ either from the Spectral Energy Distribution (SED) fitting or the main sequence. Based on a hydrodynamical simulation, the predicted delay in star formation under a local UV background intensity with $J ( u_L)gtrsim10^{-21}$ erg s$^{-1}$ cm$^{-2}$ Hz$^{-1}$ sr$^{-1}$ for galaxies having less than this halo mass is about $>20$ Myr, which is longer than the expected age of LAEs with $EW_0>150$AA. On the other hand, the photoevaporation seems to be less effective around very luminous quasars, which is consistent with the idea that these quasars are still in an early stage of quasar activity.
We present a study of the metal-enriched cool halo gas traced by MgII absorption around 228 galaxies at z~0.8-1.5 within 28 quasar fields from the MUSE Analysis of Gas around Galaxies (MAGG) survey. We observe no significant evolution in the MgII equivalent width versus impact parameter relation and in the MgII covering fraction compared to surveys at z<~0.5. The stellar mass, along with distance from galaxy centre, appears to be the dominant factor influencing the MgII absorption around galaxies. With a sample that is 90% complete down to a star formation rate of ~0.1 Msun/yr and up to impact parameters ~250-350 kpc from quasars, we find that the majority (67^{+12}_{-15}% or 14/21) of the MgII absorption systems are associated with more than one galaxy. The complex distribution of metals in these richer environments adds substantial scatter to previously-reported correlations. Multiple galaxy associations show on average five times stronger absorption and three times higher covering fraction within twice the virial radius than isolated galaxies. The dependence of MgII absorption on galaxy properties disfavours the scenario in which a widespread intra-group medium dominates the observed absorption. This leaves instead gravitational interactions among group members or hydrodynamic interactions of the galaxy haloes with the intra-group medium as favoured mechanisms to explain the observed enhancement in the MgII absorption strength and cross section in rich environments.
We present a study of the environment of 27 z=3-4.5 bright quasars from the MUSE Analysis of Gas around Galaxies (MAGG) survey. With medium-depth MUSE observations (4 hours on target per field), we characterise the effects of quasars on their surroundings by studying simultaneously the properties of extended gas nebulae and Lyalpha emitters (LAEs) in the quasar host haloes. We detect extended (up to ~ 100 kpc) Lyalpha emission around all MAGG quasars, finding a very weak redshift evolution between z=3 and z=6. By stacking the MUSE datacubes, we confidently detect extended emission of CIV and only marginally detect extended HeII up to ~40 kpc, implying that the gas is metal enriched. Moreover, our observations show a significant overdensity of LAEs within 300 km/s from the quasar systemic redshifts estimated from the nebular emission. The luminosity functions and equivalent width distributions of these LAEs show similar shapes with respect to LAEs away from quasars suggesting that the Lyalpha emission of the majority of these sources is not significantly boosted by the quasar radiation or other processes related to the quasar environment. Within this framework, the observed LAE overdensities and our kinematic measurements imply that bright quasars at z=3-4.5 are hosted by haloes in the mass range ~ 10^{12.0}-10^{12.5} Msun.
Lyman- and Werner-band absorption of molecular hydrogen (H$_2$) is detected in $sim$50% of low redshift ($z<1$) DLAs/sub-DLAs with $N$(H$_2$) > 10$^{14.4}$ cm$^{-2}$. However the true origin(s) of the H$_2$ bearing gas remain elusive. Here we report a new detection of an H$_{2}$ absorber at $z=$ 0.4298 in the HST/COS spectra of quasar PKS 2128-123. The total $N$(HI) of 10$^{19.50pm0.15}$ cm$^{-2}$ classifies the absorber as a sub-DLA. H$_{2}$ absorption is detected up to the $J=3$ rotational level with a total $log N$(H$_{2}$) = 16.36$pm$0.08 corresponding to a molecular fraction of log $f$(H$_{2}$) = $-$2.84$pm$0.17. The excitation temperature of $T_{ex}$ = 206$pm$6K indicates the presence of cold gas. Using detailed ionization modelling we obtain a near-solar metallicity (i.e., [O/H]= $-$0.26$pm$0.19) and a dust-to-gas ratio of $log kappa sim -0.45$ for the H$_{2}$ absorbing gas. The host-galaxy of the sub-DLA is detected at an impact parameter of $rho sim$ 48 kpc with an inclination angle of $i sim$ 48 degree and an azimuthal angle of $Phi sim$ 15 degree with respect to the QSO sightline. We show that co-rotating gas in an extended disk cannot explain the observed kinematics of Mg II absorption. Moreover, the inferred high metallicity is not consistent with the scenario of gas accretion. An outflow from the central region of the host-galaxy, on the other hand, would require a large opening angle (i.e., 2$theta>$150 degree), much larger than the observed outflow opening angles in Seyfert galaxies, in order to intercept the QSO sightline. We thus favor a scenario in which the H$_2$ bearing gas is stemming from a dwarf-satellite galaxy, presumably via tidal and/or ram-pressure stripping. Detection of a dwarf galaxy candidate in the HST/WFPC2 image at an impact parameter of $sim$12 kpc reinforces such an idea.
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