ترغب بنشر مسار تعليمي؟ اضغط هنا

The Local Lyman-alpha Forest. II: Distribution of HI Absorbers, Doppler Widths, and Baryon Content

148   0   0.0 ( 0 )
 نشر من قبل Steven V. Penton
 تاريخ النشر 1999
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

In Paper I of this series (astro-ph/9911117) we described observations of 15 extragalactic targets taken with the Hubble Space Telescope GHRS/G160M grating for studies of the low-z Lya forest. We reported the detection of 110 Lya absorbers at significance level >3 sigma in the redshift range z=0.002-0.069, over a total pathlength of 116,000 km/s. In this second paper, we evaluate the physical properties of these Lya absorbers and compare them to their high-z counterparts. The distribution of Doppler parameters is similar to that at high redshift, with mean b = 35.0 +- 16.6 km/s. The true Doppler parameter may be somewhat lower, owing to component blends and non-thermal velocities. The distribution of equivalent widths exhibits a significant break at W~133mA, with an increasing number of weak absorbers (10mA-100mA). Adopting a curve of growth with b = 25 +- 5km/s and applying a sensitivity correction as a function of equivalent width and wavelength, we derive the distribution in column density, Nh^{-1.72+-0.06} for Nh<10^14 cm^-2. We find no redshift evolution in the sample at z<0.07, but we do see a significant decline in dN/dz compared to values at z>1.6. A 3 sigma signal in the two-point correlation function of Lya absorbers for velocity separations Delta v <150 km/s is consistent with results at high-z. Applying a photoionization correction, we find that the low-z Lya forest may contain ~20% of the total number of baryons, with closure parameter Omega_lya = (0.008+-0.001), for a standard absorber size and ionizing radiation field. Some of these clouds appear to be primordial matter, owing to the lack of detected metals in a composite spectrum. Our data suggest that a fraction of the absorbers are associated with gas in galaxy associations (filaments), while a second population is distributed more uniformly.



قيم البحث

اقرأ أيضاً

We present HST STIS/G140M spectra of 15 extragalactic targets, which we combine with GHRS/G160M data to examine the statistical properties of the low-z Ly-alpha forest. We evaluate the physical properties of these Ly-alpha absorbers and compare them to their high-z counterparts. We determine that the warm, photoionized IGM contains 29+/-4% of the total baryon inventory at z = 0. We derive the distribution in column density, N_HI^(1.65+/-0.07) for 12.5 < log [N_HI] < 14.5, breaking to a flatter slope above log [N_HI] > 14.5. The slowing of the number density evolution of high-W Ly-alpha clouds is not as great as previously measured, and the break to slower evolution may occur later than previously suggested (z~1.0 rather than 1.6). We find a 7.2sigma excess in the two-point correlation function (TPCF) of Ly-alpha absorbers for velocity separations less than 260 km/s, which is exclusively due to the higher column density clouds. From our previous result that higher column density Ly-alpha clouds cluster more strongly with galaxies, this TPCF suggests a physical difference between the higher and lower column density clouds in our sample.
We present the analysis of a sample of the Ly-$alpha$ forest spectra of 152 quasars taken with the HST FOS. The Ly-$alpha$ lines show little evolution at $0<z<1.7$. We see a difference between the evolution indices for weak and strong lines.
117 - John T. Stocke 2001
We describe recent discoveries of low column density [N(HI) < 10^14.5 cm^-2] H I Ly-alpha absorbers made with the Hubble Space Telescope (HST), which have allowed us a first look at gas in local intergalactic space between us and the Great Wall. Desp ite the mere 2.4m aperture of HST, these new observations allow us to detect absorbers with column densities, N(HI) approx 10^12.5 cm^-2, as low as those found using Keck/HIRES at high-z. Owing to the proximity of these absorbers to the Earth, the 197 absorbers in our combined GHRS + STIS sample (Penton, Stocke, & Shull 2001) provide our best view of the relationship between these absorbers and galaxies, voids, and supercluster filaments. Unlike previous results based on galaxy surveys near higher-N(HI) absorbers, we find no evidence that these lower-N(HI) absorbers are extended galaxy halos. Rather, the majority (78%) are associated with large-scale filamentary structures of galaxies, while 22% are found in galaxy voids. Since these Ly-alpha absorbers are currently the only baryons detected in the voids, we use their properties to estimate that the voids contain 4.5 (+/-1.5)% of the Universal baryon density.
124 - Juna A. Kollmeier 2002
We use hydrodynamic simulations to predict correlations between Lya forest absorption and galaxies at redshift z~3. The probability distribution function (PDF) of Lya flux decrements shifts systematically towards higher values in the vicinity of gala xies, reflecting the overdense environments in which these galaxies reside. The predicted signal remains strong in spectra smoothed over 50-200 km/s, allowing tests with moderate resolution quasar spectra. The strong bias of high redshift galaxies towards high density regions imprints a clear signature on the flux PDF, but the predictions are not sensitive to galaxy baryon mass or star formation rate, and they are similar for galaxies and for dark matter halos. The dependence of the flux PDF on galaxy proximity is sensitive to redshift determination errors, with rms errors of 150-300 km/s substantially weakening the predicted trends. On larger scales, the mean galaxy overdensity in a cube of 5 or 10 Mpc/h (comoving) is strongly correlated with the mean Lya flux decrement on a line of sight through the cube center. The slope of the correlation is ~3 times steeper for galaxies than for dark matter as a result of galaxy bias. The predicted large scale correlation is in qualitative agreement with recently reported observational results. However, observations also show a drop in absorption in the immediate vicinity of galaxies, which our models do not predict even if we allow the galaxies or AGNs within them to be ionizing sources. This decreased absorption could be a signature of galaxy feedback on the surrounding IGM, perhaps via galactic winds. Peculiar velocities often allow gas at comoving distances ~1.5 Mpc/h to produce saturated absorption at the galaxy redshift, so any feedback mechanism must suppress neutral hydrogen out to these radii to match the data. (Abridged)
200 - Celine Peroux 2001
We present a study of the evolution of the column density distribution, f(N,z), and total neutral hydrogen mass in high-column density quasar absorbers using candidates from a recent high-redshift survey for damped Lyman-alpha (DLA) and Lyman limit s ystem (LLS) absorbers. The observed number of LLS (N(HI)> 1.6 * 10^{17} atom/cm^2) is used to constrain f(N,z) below the classical DLA Wolfe et al. (1986) definition of 2 * 10^{20} atom/cm^2. The joint LLS-DLA analysis shows unambiguously that f(N,z) deviates significantly from a single power law and that a Gamma-law distribution of the form f(N,z)=(f_*/N_*)(N/N_*)^{-Beta} exp(-N/N_*) provides a better description of the observations. These results are used to determine the amount of neutral gas contained in DLAs and in systems with lower column density. Whilst in the redshift range 2 to 3.5, ~90% of the neutral HI mass is in DLAs, we find that at z>3.5 this fraction drops to only 55% and that the remaining missing mass fraction of the neutral gas lies in sub-DLAs with N(HI) 10^{19} - 2 * 10^{20} atom/cm^2. The characteristic column density, N_*, changes from 1.6 * 10^{21} atom/cm^2 at z<3.5 to 2.9 * 10^{20} atom/cm^2 at z>3.5, supporting a picture where at z>3.5, we are directly observing the formation of high column density neutral hydrogen DLA systems from lower column density units. Moreover since current metallicity studies of DLA systems focus on the higher column density systems they may be giving a biased or incomplete view of global galactic chemical evolution at z>3. After correcting the observed mass in HI for the ``missing neutral gas the comoving mass density now shows no evidence for a decrease above z=2. (abridged)
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا