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Register a new userThe VLT LBG Redshift Survey - IV. Gas and galaxies at z ~ 3 in observations and simulations
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Pimpunyawat Tummuangpak
Publication date
2013
fields
Physics
and research's language is
English
Authors
P. Tummuangpak
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We use observations and simulation to study the relationship between star-forming galaxies and the intergalactic medium at z~3. The observed galaxy sample is based on spectroscopic redshift data from a combination of the VLT LBG Redshift Survey and Keck observations in fields centred on bright z>3 QSOs, whilst the simulation data is taken from GIMIC. In the simulation, we find that the dominant peculiar velocities are in the form of large-scale coherent motions of gas and galaxies. Gravitational infall of galaxies towards one another is also seen. At smaller scales, the peculiar velocities in the simulation over-predict the difference between the simulated real- and z-space galaxy correlation functions. Peculiar velocity pairs separated by <1Mpc/h have a smaller dispersion and explain the z-space correlation function better. The Ly{alpha} auto- and cross-correlation functions in the GIMIC simulation show infall smaller than implied by previous work. This reduced infall may be due to the galaxy wide outflows implemented in the simulation. The main challenge in comparing these simulated results with the observed correlation functions comes from the presence of velocity errors for the observed LBGs which dominate at ~1Mpc/h scales. When these are taken into account, the observed LBG correlation function is well matched by a simulated $M_*>10^9M_odot$ galaxy sample. The simulated cross-correlation shows similar neutral gas densities around galaxies as are seen in the observations. The simulated and observed Ly{alpha} z-space autocorrelation functions agree well with each other. Our overall conclusion is that gas and galaxy peculiar velocities are towards the low end of expectation. Finally, little direct evidence is seen in either simulation or observations for high transmission near galaxies due to feedback. (Abridged)
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We have measured redshifts for 243 z ~3 quasars in nine VLT VIMOS LBG redshift survey areas, each of which is centred on a known bright quasar. Using spectra of these quasars, we measure the cross-correlation between neutral hydrogen gas causing the Lya forest and 1020 Lyman-break galaxies at z ~3. We find an increase in neutral hydrogen absorption within 5 h^-1 Mpc of a galaxy in agreement with the results of Adelberger et al. (2003, 2005). The Lya-LBG cross-correlation can be described by a power-law on scales larger than 3 h^-1 Mpc. When galaxy velocity dispersions are taken into account our results at smaller scales (<2 h^-1 Mpc) are also in good agreement with the results of Adelberger et al. (2005). There is little immediate indication of a region with a transmission spike above the mean IGM value which might indicate the presence of star-formation feedback. To measure the galaxy velocity dispersions, which include both intrinsic LBG velocity dispersion and redshift errors, we have used the LBG-LBG redshift space distortion measurements of Bielby et al. (2010). We find that the redshift-space transmission spike implied in the results of Adelberger et al. (2003) is too narrow to be physical in the presence of the likely LBG velocity dispersion and is likely to be a statistical fluke. Nevertheless, neither our nor previous data can rule out the presence of a narrow, real-space transmission spike, given the evidence of the increased Lya absorption surrounding LBGs which can mask the spikes presence when convolved with a realistic LBG velocity dispersion. Finally, we identify 176 CIV systems in the quasar spectra and find an LBG-CIV correlation strength on scales of 10 h^-1 Mpc consistent with the relation measured at ~Mpc scales.
We present a catalogue of 2135 galaxy redshifts from the VLT LBG Redshift Survey (VLRS), a spectroscopic survey of z ~ 3 galaxies in wide fields centred on background quasi-stellar objects. We have used deep optical imaging to select galaxies via the Lyman-break technique. Spectroscopy of the Lyman-break galaxies (LBGs) was then made using the Visible Multi-Object Spectrograph (VIMOS), giving a mean redshift of z=2.79. We analyse the clustering properties of the VLRS sample and also of the VLRS sample combined with the smaller area Keck-based survey of Steidel et al. From the semiprojected correlation function, wp({sigma}) we find that the results are well fit with a single power-law model, with clustering scale lengths of r0=3.46+-0.41 and 3.83+-0.24 Mpc/h, respectively. We note that the corresponding combined {xi}(r) slope is flatter than for local galaxies at {gamma} = 1.5-1.6 rather than {gamma}=1.8. This flat slope is confirmed by the z-space correlation function, {xi}(s), and in the range 10<s<100 Mpc/h the VLRS shows ~2.5{sigma} excess over the {Lambda} cold dark matter. This excess may be consistent with recent evidence for non-Gaussianity in clustering results at z~1. We then analyse the LBG z-space distortions using the 2D correlation function, {xi}({sigma}, {pi}), finding for the combined sample a large-scale infall parameter of $beta$ = 0.38+-0.19 and a velocity dispersion of 420km/s. Based on our measured {beta}, we are able to determine the gravitational growth rate, finding a value of f(z = 3)=0.99+-0.50 (or f{sigma}8 = 0.26+-0.13), which is the highest redshift measurement of the growth rate via galaxy clustering and is consistent with {Lambda}CDM. Finally, we constrain the mean halo mass for the LBG population, finding that the VLRS and combined sample suggest mean halo masses of log(MDM/Msun) = 11.57+-0.15 and 11.73+-0.07, respectively.
CO measurements of z~1-4 galaxies have found that their baryonic gas fractions are significantly higher than galaxies at z=0, with values ranging from 20-80 %. Here, we suggest that the gas fractions inferred from observations of star-forming galaxies at high-z are overestimated, owing to the adoption of locally-calibrated CO-H2 conversion factors (Xco). Evidence from both observations and numerical models suggest that Xco varies smoothly with the physical properties of galaxies, and that Xco can be parameterised simply as a function of both gas phase metallicity and observed CO surface brightness. When applying this functional form, we find fgas ~10-40 % in galaxies with M*=10^10-10^12 Msun at high-z. Moreover, the scatter in the observed fgas-M* relation is lowered by a factor of two. The lower inferred gas fractions arise physically because the interstellar media of high-z galaxies have higher velocity dispersions and gas temperatures than their local counterparts, which results in an Xco that is lower than the z=0 value for both quiescent discs and starbursts. We further compare these gas fractions to those predicted by cosmological galaxy formation models. We show that while the canonically inferred gas fractions from observations are a factor of 2-3 larger at a given stellar mass than predicted by models, our rederived Xco values for z=1-4 galaxies results in revised gas fractions that agree significantly better with the simulations.
We obtained ESI/Keck rotation curves of 10 MgII absorption selected galaxies (0.3 < z < 1.0) for which we have WFPC-2/HST images and high resolution HIRES/Keck and UVES/VLT quasar spectra of the MgII absorption profiles. We perform a kinematic comparison of these galaxies and their associated halo MgII absorption. For all 10 galaxies, the majority of the absorption velocities lie in the range of the observed galaxy rotation velocities. In 7/10 cases, the absorption velocities reside fully to one side of the galaxy systemic velocity and usually align with one arm of the rotation curve. In all cases, a constant rotating thick-disk model poorly reproduces the full spread of observed MgII absorption velocities when reasonably realistic parameters are employed. In 2/10 cases, the galaxy kinematics, star formation surface densities, and absorption kinematics have a resemblance to those of high redshift galaxies showing strong outflows. We find that MgII absorption velocity spread and optical depth distribution may be dependent on galaxy inclination. To further aid in the spatial-kinematic relationships of the data, we apply quasar absorption line techniques to a galaxy (v_c=180 km/s) embedded in LCDM simulations. In the simulations, MgII absorption selects metal enriched halo gas out to roughly 100 kpc from the galaxy, tidal streams, filaments, and small satellite galaxies. Within the limitations inherent in the simulations, the majority of the simulated MgII absorption arises in the filaments and tidal streams and is infalling towards the galaxy with velocities between -200 < v_r < -180 km/s. The MgII absorption velocity offset distribution (relative to the simulated galaxy) spans ~200 km/s with the lowest frequency of detecting MgII at the galaxy systematic velocity.
We present a comparison between the observed color distribution, number and mass density of massive galaxies at 1.5 < z < 3 and a model by Hopkins et al. that relates the quasar and galaxy population on the basis of gas-rich mergers. In order to test the hypothesis that quiescent red galaxies are formed after a gas-rich merger involving quasar activity, we confront photometry of massive (M > 4x10^10 Msun) galaxies extracted from the FIRES, GOODS-South, and MUSYC surveys, together spanning an area of 496 arcmin^2, with synthetic photometry from hydrodynamical merger simulations. As in the Hopkins et al. (2006b) model, we use the observed quasar luminosity function to estimate the merger rate. We find that the synthetic U-V and V-J colors of galaxies that had a quasar phase in their past match the colors of observed galaxies that are best characterized by a quiescent stellar population. At z ~ 2.6, the observed number and mass density of quiescent red galaxies with M > 4x10^10 Msun is consistent with the model in which every quiescent massive galaxy underwent a quasar phase in the past. At z ~ 1.9, 2.8 times less quiescent galaxies are observed than predicted by the model as descendants of higher redshift quasars. The merger model also predicts a large number of galaxies undergoing merger-driven star formation. We find that the predicted number and mass density accounts for 30-50% of the observed massive star-forming galaxies. However, their colors do not match those of observed star-forming galaxies. In particular, the colors of dusty red galaxies are not reproduced by the simulations. Several possible origins of this discrepancy are discussed. The observational constraints on the validity of the model are currently limited by cosmic variance and uncertainties in stellar population synthesis and radiative transfer.
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