- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
The VLT LBG redshift survey – VI. Mapping H?i in the proximity of z?～?3 LBGs with X-Shooter
摘要： We present an analysis of the spatial distribution and dynamics of neutral hydrogen gas around galaxies using new X-Shooter observations of z ～ 2.5–4 quasars. Adding the X-Shooter data to our existing data set of high-resolution quasar spectroscopy, we use a total sample of 29 quasars alongside ～1700 Lyman Break Galaxies (LBGs) in the redshift range 2 (cid:2) z (cid:2) 3.5. We measure the Lyα forest auto-correlation function, finding a clustering length of s0 = 0.081 ± 0.006 h?1 Mpc, and the cross-correlation function with LBGs, finding a cross-clustering length of s0 = 0.27 ± 0.14 h?1 Mpc and power-law slope γ = 1.1 ± 0.2. Our results highlight the weakly clustered nature of neutral hydrogen systems in the Lyα forest. Building on this, we make a first analysis of the dependence of the clustering on absorber strength, finding a clear preference for stronger Lyα forest absorption features to be more strongly clustered around the galaxy population, suggesting that they trace on average higher mass haloes. Using the projected and 2-D cross-correlation functions, we constrain the dynamics of Lyα forest clouds around z ～ 3 galaxies. We find a significant detection of large-scale infall of neutral hydrogen, with a constraint on the Lyα forest infall parameter of βF = 1.02 ± 0.22.
关键词： cosmology: observations,large-scale structure of Universe,intergalactic medium,galaxies: kinematics and dynamics
更新于2025-09-23 15:22:29
-
MCMC determination of the cosmic UV background at <i>z</i> ? 0 from Hα fluorescence.
摘要： In a recent paper (Fumagalli et al. 2017) we reported on the detection of a di?use Hα glow in the outskirts of the nearby, edge-on disc galaxy UGC 7321 observed with the Multi Unit Spectroscopic Explorer (MUSE) at the ESO Very Large Telescope. By interpreting the Hα emission as ?uorescence arising from hydrogen ionised by an external (i.e., extragalactic) radiation ?eld, we estimated the UV background (UVB) intensity in terms of H I ionisation rate (per ion) at z (cid:39) 0 to be in the range ΓHI ～ 6 ? 8 × 10?14 s?1. In the present work, by performing radiative transfer calculations over a large set of models of the gaseous disc of UGC 7321, we re?ne our estimate and through an MCMC analysis derive a value for the photoionisaton rate of ΓHI = 7.27+2.93 ?2.90 × 10?14 s?1. In particular, our analysis demonstrates that this value is robust against large variations in the galaxy model and that the uncertainties are mainly driven by the errors associated with the observed Hα surface brightness. Our measurement is consistent with several recent determinations of the same quantity by a completely independent technique (i.e., ?ux decrement analysis of the Lyα-forest), and support the notion that the low redshift UVB is largely dominated by active galactic nuclei (AGNs), possibly with no need of further contribution from star forming galaxies.
关键词： radiative transfer,methods: numerical,cosmology: theory,intergalactic medium
更新于2025-09-23 15:21:21
-
Hunting for metals using XQ-100 Legacy Survey composite spectra
摘要： We investigate the N V absorption signal along the line of sight of background quasars, in order to test the robustness of the use of this ion as the criterion to select intrinsic (i.e. physically related to the quasar host galaxy) narrow absorption lines (NALs). We build composite spectra from a sample of ～ 1000 CIV absorbers, covering the redshift range 2.55 < z < 4.73, identified in 100 individual sight lines from the XQ-100 Legacy Survey. We detect a statistically significant NV absorption signal only within 5000 km s?1 of the systemic redshift, zem. This absorption trough is ～ 15σ when only C IV systems with N(CIV) > 1014 cm?2 are included in the composite spectrum. This result confirms that N V offers an excellent statistical tool to identify intrinsic systems. We exploit stacks of 11 different ions to show that the gas in proximity to a quasar exhibits a considerably different ionization state with respect to gas in the transverse direction and intervening gas at large velocity separations from the continuum source. Indeed, we find a dearth of cool gas, as traced by low-ionization species and in particular by Mg II, in the proximity of the quasar. We compare our findings with the predictions given by a range of CLOUDY ionization models and find that they can be naturally explained by ionization effects of the quasar.
关键词： galaxies: high-redshift,(galaxies:) quasars: absorption lines,(galaxies:) intergalactic medium
更新于2025-09-23 15:21:01
-
Enhanced characteristics of fused silica fibers using laser polishing
摘要： We present a measurement of the mean density pro?le of Ca ii gas around galaxies out to ～200 kpc, traced by Fraunhofer’s H & K absorption lines. The measurement is based on cross-correlating the positions of about one million foreground galaxies at z ～ 0.1 and the ?ux decrements induced in the spectra of about 105 background quasars from the Sloan Digital Sky Survey. This technique allows us to trace the total amount of Ca ii absorption induced by the circumgalactic medium, including absorbers too weak to be detected in individual spectra. We can statistically measure Ca ii rest equivalent widths down to several m?, corresponding to column densities of about 5 × 1010 cm?2. We ?nd that the Ca ii column density distribution follows NCa ii ～ r ?1.4 and the mean Ca ii mass in the halo within 200 kpc is ～5 × 103 M(cid:4), averaged over the foreground galaxy sample with median mass ～1010.3 M(cid:4). This is about an order-of-magnitude larger than the Ca ii mass in the interstellar medium of the Milky Way, suggesting that more than 90% of Ca ii in the universe is in the circum- and inter-galactic environments. Our measurements indicate that the amount of Ca ii in halos is larger for galaxies with higher stellar mass and higher star formation rate. For edge-on galaxies we ?nd Ca ii to be more concentrated along the minor axis, i.e., in the polar direction. This suggests that bipolar out?ows induced by star formation must have played a signi?cant role in producing Ca ii in galaxy halos.
关键词： quasars: absorption lines,galaxies: halos,galaxies: evolution,intergalactic medium
更新于2025-09-11 14:15:04
-
The <i>Swift</i> X-ray Telescope Cluster Survey
摘要： Aims. We present a spectral analysis of a new, ?ux-limited sample of 72 X-ray selected clusters of galaxies identi?ed with the X-ray Telescope (XRT) on board the Swift satellite down to a ?ux limit of ～10?14 erg s?1 cm?2 (SWXCS). We carry out a detailed X-ray spectral analysis with the twofold aim of measuring redshifts and characterizing the properties of the intracluster medium (ICM) for the majority of the SWXCS sources. Methods. Optical counterparts and spectroscopic or photometric redshifts for some of the sources are obtained with a cross-correlation with the NASA/IPAC Extragalactic Database. Additional photometric redshifts are computed with a dedicated follow-up program with the Telescopio Nazionale Galileo and a cross-correlation with the SDSS. In addition, we also blindly search for the Hydrogen-like and He-like iron Kα emission line complex in the X-ray spectrum. We detect the iron emission lines in 35% of the sample, and hence obtain a robust measure of the X-ray redshift zX with typical rms error 1–5%. We use zX whenever the optical redshift is not available. Finally, for all the sources with measured redshift, background-subtracted spectra are ?tted with a single-temperature mekal model to measure global temperature, X-ray luminosity and iron abundance of the ICM. We perform extensive spectral simulations to accounts for ?tting bias, and to assess the robustness of our results. We derive a criterion to select reliable best-?t models and an empirical formula to account for ?tting bias. The bias-corrected values are then used to investigate the scaling properties of the X-ray observables. Results. Overall, we are able to characterize the ICM of 46 sources with redshifts (64% of the sample). The sample is mostly constituted by clusters with temperatures between 3 and 10 keV, plus 14 low-mass clusters and groups with temperatures below 3 keV. The redshift distribution peaks around z ～ 0.25 and extends up to z ～ 1, with 60% of the sample at 0.1 < z < 0.4. We derive the luminosity?temperature relation for these 46 sources, ?nding good agreement with previous studies. Conclusions. Thanks to the good X-ray spectral quality and the low background of Swift/XRT, we are able to measure ICM temperatures and X-ray luminosities for the 46 sources with redshifts. Once redshifts are available for the remaining 26 sources, this sample will constitute a well-characterized, ?ux-limited catalog of clusters distributed over a broad redshift range (0.1 ≤ z ≤ 1.0) providing a statistically complete view of the cluster population with a selection function that allows a proper treatment of any measurement bias. The quality of the SWXCS sample is comparable to other samples available in the literature and obtained with much larger X-ray telescopes. Our results have interesting implications for the design of future X-ray survey telescopes, characterized by good-quality PSF over the entire ?eld of view and low background.
关键词： intergalactic medium,galaxies: high-redshift,X-rays: galaxies: clusters,galaxies: clusters: general,cosmology: observations
更新于2025-09-09 09:28:46