A Survey of Weak MgII Absorbers at 0.4 < z < 2.4

We present results from a survey of weak MgII absorbers in the VLT/UVES spectra of 81 QSOs obtained from the ESO archive. In this survey, we identified 112 weak MgII systems within the redshift interval 0.4 < z < 2.4 with 86% completeness down to a rest-frame equivalent width of W_r(2796) = 0.02A, covering a cumulative redshift path length of deltaZ=77.3. From this sample, we estimate that the number of weak absorbers per unit redshift dN/dz increases from 1.06 +/- 0.04 at =1.9 to 1.76 +/- 0.08 at =1.2 and thereafter decreases to 1.51 +/- 0.09 at =0.9 and 1.06 +/- 0.10 at =0.6. Thus we find evidence for an evolution in the population of weak MgII absorbers, with their number density peaking at z=1.2. We also determine the equivalent width distribution of weak systems at =0.9 and =1.9. At 0.4 < z < 1.4, there is evidence for a turnover from a powerlaw of the form n(W_r) \propto W_r^{-1.04} at W_r(2796) < 0.1A. This turnover is more extreme at 1.4 < z < 2.4, where the equivalent width distribution is close to an extrapolation of the exponential distribution function found for strong MgII absorbers. Based on these results, we discuss the possibility that some fraction of weak MgII absorbers, particularly single cloud systems, are related to satellite clouds surrounding strong MgII systems. These structures could also be analogs to Milky Way high velocity clouds. In this context, the paucity of high redshift weak MgII absorbers is caused by a lack of isolated accreting clouds on to galaxies during that epoch.Comment: 14 pages, 11 figures, ApJ accepte

The Chemical and Ionization Conditions in Weak Mg II Absorbers

We present an analysis of the chemical and ionization conditions in a sample of 100 weak Mg II absorbers identified in the VLT/UVES archive of quasar spectra. Using a host of low ionization lines associated with each absorber in this sample, and on the basis of ionization models, we infer that the metallicity in a significant fraction of weak Mg II clouds is constrained to values of solar or higher, if they are sub-Lyman limit systems. Based on the observed constraints, we present a physical picture in which weak Mg II absorbers are predominantly tracing two different astrophysical processes/structures. A significant population of weak Mg II clouds, those in which N(Fe II) is much less than N(Mg II), identified at both low (z ~ 1) and high (z ~ 2) redshift, are potentially tracing gas in the extended halos of galaxies, analogous to the Galactic high velocity clouds. These absorbers might correspond to alpha-enhanced interstellar gas expelled from star-forming galaxies, in correlated supernova events. On the other hand, N(FeII) approximately equal to N(Mg II) clouds, which are prevalent only at lower redshifts (z < 1.5), must be tracing Type Ia enriched gas in small, high metallicity pockets in dwarf galaxies, tidal debris, or other intergalactic structures.Comment: 35 pages (including tables & figures). Accepted for publication in ApJ. A high resolution version of the paper is available at "http://www.astro.wisc.edu/~anand/weakMgII.pdf

The Kinematic Evolution of Strong MgII Absorbers

We consider the evolution of strong (W_r(2796) > 0.3A) MgII absorbers, most of which are closely related to luminous galaxies. Using 20 high resolution quasar spectra from the VLT/UVES public archive, we examine 33 strong MgII absorbers in the redshift range 0.3 < z < 2.5. We compare and supplement this sample with 23 strong MgII absorbers at 0.4 < z < 1.4 observed previously with HIRES/Keck. We find that neither equivalent width nor kinematic spread (the optical depth weighted second moment of velocity) of MgII2796 evolve. However, the kinematic spread is sensitive to the highest velocity component, and therefore not as sensitive to additional weak components at intermediate velocities relative to the profile center. The fraction of absorbing pixels within the full velocity range of the system does show a trend of decreasing with decreasing redshift. Most high redshift systems (14/20) exhibit absorption over the entire system velocity range, which differs from the result for low redshift systems (18/36) at the 95% level. This leads to a smaller number of separate subsystems for high redshift systems because weak absorping components tend to connect the stronger regions of absorption. We hypothesize that low redshift MgII profiles are more likely to represent well formed galaxies, many of which have kinematics consistent with a disk/halo structure. High redshift MgII profiles are more likely to show evidence of complex protogalactic structures, with multiple accretion or outflow events. Although these results are derived from measurements of gas kinematics, they are consistent with hierarchical galaxy formation evidenced by deep galaxy surveys.Comment: Accepted to the Astrophysical Journa

Author Correction: Clustering and climate associations of Kawasaki Disease in San Diego County suggest environmental triggers.

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Quantum entanglement and Bell violation of two coupled cavity fields in dissipative environment

We study the quantum entanglement between two coupled cavities, in which one is initially prepared in a mesoscopic superposition state and the other is in the vacuum in dissipative environment and show how the entanglement between two cavities can arise in the dissipative environment. The dynamic behavior of the nonlocality for the system is also investigated.Comment: 12 pages, 5 figure

A survey of weak MgII absorbers at redshift <z>=1.78

The exact nature of weak MgII absorbers (those with W_r(2796) < 0.3 A) is a matter of debate, but most are likely related to areas of local star formation or supernovae activity outside of giant galaxies. Using 18 QSO spectra obtained with the Ultra-Violet Echelle Spectrograph (UVES) on the Very Large Telescope (VLT), we have conducted a survey for weak MgII absorbers at 1.4 < z < 2.4. We searched a redshift path length of 8.51, eliminating regions badly contaminated by atmospheric absorption so that the survey is close to 100% complete to W_r(2796) = 0.02 A. We found a total of 9 weak absorbers, yielding a number density of absorbers of dN/dz = 1.06 +/- 0.12 for 0.02 <= W_r(2796) < 0.3 A. Narayanan et al. (2005) found dN/dz = 1.00 +/- 0.20 at 0 < z < 0.3 and Churchill et al. (1999) found dN/dz = 1.74 +/- 0.10 at 0.4 < z < 1.4. Therefore, the population of weak MgII absorbers appears to peak at z~1. We explore the expected evolution of the absorber population subject to a changing extragalactic background radiation (EBR) from z = 0.9 to z = 1.78 (the median redshift of our survey), and find that the result is higher than the observed value. We point out that the peak epoch for weak MgII absorption at z~1 may coincide with the peak epoch of global star formation in the dwarf galaxy environment.Comment: 25 pages, 14 figures, to be published in ApJ 01 March 2006, v639,