Phase decorrelation, streamwise vortices and acoustic radiation in mixing layers

Several direct numerical simulations were performed and analyzed to study various aspects of the early development of mixing layers. Included are the phase jitter of the large-scale eddies, which was studied using a 2-D spatially-evolving mixing layer simulation; the response of a time developing mixing layer to various spanwise disturbances; and the sound radiation from a 2-D compressible time developing mixing layer

The Relationship Between Luminosity and Broad-Line Region Size in Active Galactic Nuclei

We reinvestigate the relationship between the characteristic broad-line region size (R_blr) and the Balmer emission-line, X-ray, UV, and optical continuum luminosities. Our study makes use of the best available determinations of R_blr for a large number of active galactic nuclei (AGNs) from Peterson et al. Using their determinations of R_blr for a large sample of AGNs and two different regression methods, we investigate the robustness of our correlation results as a function of data sub-sample and regression technique. Though small systematic differences were found depending on the method of analysis, our results are generally consistent. Assuming a power-law relation R_blr \propto L^\alpha, we find the mean best-fitting \alpha is about 0.67+/-0.05 for the optical continuum and the broad H\beta luminosity, about 0.56+/-0.05 for the UV continuum luminosity, and about 0.70+/-0.14 for the X-ray luminosity. We also find an intrinsic scatter of about 40% in these relations. The disagreement of our results with the theoretical expected slope of 0.5 indicates that the simple assumption of all AGNs having on average same ionization parameter, BLR density, column density, and ionizing spectral energy distribution, is not valid and there is likely some evolution of a few of these characteristics along the luminosity scale.Comment: 11 pages, 2 figures, emulateapj, accepted for publication in The Astrophysical Journa

A Search for the Damped Ly-alpha Absorber at z=1.86 toward QSO 1244+3443 with NICMOS

We have carried out a high-resolution imaging search for the galaxy associated with the damped Lyman-alpha (DLA) absorber at z=1.859 toward the z_{em}=2.48 quasar QSO 1244+3443, using the HST and the NICMOS. Images were obtained in the broad filter F160W and the narrow filter F187N with camera 2 on NICMOS with the goal of detecting the rest-frame optical continuum and the H-alpha line emission from the DLA. After PSF subtraction, two weak features are seen at projected separations of 0.16-0.24" from the quasar. Parts of these features may be associated with the DLA absorber, although we cannot completely rule out that they could be artifacts of the point spread function (PSF). If associated with the DLA, the objects would be ~1-2 h_{70}^{-1} kpc in size with integrated flux densities of 2.5 and 3.3 mu Jy in the F160W filter, implying luminosities at lambda_{central}=5600 A in the DLA rest frame of 4.4-5.9 x 10^{9} h_{70}^{-2} L_{solar} at z=1.86, for q0=0.5. However, no significant H-alpha line emission is seen from these objects, suggesting low star formation rates (SFRs). Our 3 sigma upper limit on the SFR in the DLA is 1.3 h_{70}^{-2} M_{solar}/yr for q0 = 0.5 (2.4 h_{70}^{-2} M_{solar} yr^{-1} for q0 = 0.1). This together with our earlier result for LBQS 1210+1731 mark a significant improvement over previous constraints on the star formation rates of DLAs. A combination of low SFR and some dust extinction is likely to be responsible for the lack of H-alpha emission. Alternatively, the objects, may be associated with the quasar host galaxy. In any case, our observations suggest that the DLA is not a large bright proto-disk, but a compact object or a low-surface brightness galaxy. If the two features are PSF artifacts then the constraints on DLA properties are even more severe.Comment: 28 pages, 9 figures. Accepted for publication in The Astrophysical Journal. Figures are given at a slightly lower resolution here, to decrease file sizes. The higher resolution versions can be found in the Ap

The Clustering of Extragalactic Extremely Red Objects

We have measured the angular and spatial clustering of 671 K5 Extremely Red Objects (EROs) from a 0.98 square degree sub-region of the NOAO Deep Wide-Field Survey (NDWFS). Our study covers nearly 5 times the area and has twice the sample size of any previous ERO clustering study. The wide field of view and BwRIK passbands of the NDWFS allow us to place improved constraints on the clustering of z=1 EROs. We find the angular clustering of EROs is slightly weaker than in previous measurements, and w(1')=0.25+/-0.05 for K<18.40 EROs. We find no significant correlation of ERO spatial clustering with redshift, apparent color or absolute magnitude, although given the uncertainties, such correlations remain plausible. We find the spatial clustering of K5 EROs is well approximated by a power-law, with r_0=9.7+/-1.1 Mpc/h in comoving coordinates. This is comparable to the clustering of 4L* early-type galaxies at z<1, and is consistent with the brightest EROs being the progenitors of the most massive ellipticals. There is evidence of the angular clustering of EROs decreasing with increasing apparent magnitude, when NDWFS measurements of ERO clustering are combined with those from the literature. Unless the redshift distribution of K>20 EROs is very broad, the spatial clustering of EROs decreases from r_0=9.7+/-1.1 Mpc/h for K20 EROs.Comment: Accepted for publication in the ApJ. 29 pages with 10 figures. The NOAO Deep Wide-Field Survey Bootes data release is available online at http://www.noao.edu/noao/noaodeep

Gravitational instability of Einstein-Gauss-Bonnet black holes under tensor mode perturbations

We analyze the tensor mode perturbations of static, spherically symmetric solutions of the Einstein equations with a quadratic Gauss-Bonnet term in dimension $D > 4$. We show that the evolution equations for this type of perturbations can be cast in a Regge-Wheeler-Zerilli form, and obtain the exact potential for the corresponding Schr\"odinger-like stability equation. As an immediate application we prove that for $D \neq 6$ and $\alpha >0$, the sign choice for the Gauss-Bonnet coefficient suggested by string theory, all positive mass black holes of this type are stable. In the exceptional case $D =6$, we find a range of parameters where positive mass asymptotically flat black holes, with regular horizon, are unstable. This feature is found also in general for $\alpha < 0$.Comment: 7 pages, 1 figure, minor corrections, references adde

Red Galaxy Growth and the Halo Occupation Distribution

We have traced the past 7 Gyr of red galaxy stellar mass growth within dark matter halos. We have determined the halo occupation distribution, which describes how galaxies reside within dark matter halos, using the observed luminosity function and clustering of 40,696 0.2<z<1.0 red galaxies in Bootes. Half of 10^{11.9} Msun/h halos host a red central galaxy, and this fraction increases with increasing halo mass. We do not observe any evolution of the relationship between red galaxy stellar mass and host halo mass, although we expect both galaxy stellar masses and halo masses to evolve over cosmic time. We find that the stellar mass contained within the red population has doubled since z=1, with the stellar mass within red satellite galaxies tripling over this redshift range. In cluster mass halos most of the stellar mass resides within satellite galaxies and the intra-cluster light, with a minority of the stellar mass residing within central galaxies. The stellar masses of the most luminous red central galaxies are proportional to halo mass to the power of a third. We thus conclude that halo mergers do not always lead to rapid growth of central galaxies. While very massive halos often double in mass over the past 7 Gyr, the stellar masses of their central galaxies typically grow by only 30%.Comment: Accepted for publication in the ApJ. 34 pages, 22 Figures, 5 Table

NICMOS Imaging of a Damped Lyman-alpha Absorber at z=1.89 toward LBQS 1210+1731 : Constraints on Size and Star Formation Rate

We report results of a high-resolution imaging search (in rest frame H-$\alpha$ and optical continuum) for the galaxy associated with the damped Lyman-$\alpha$ (DLA) absorber at $z=1.892$ toward the $z_{em}=2.543$ quasar LBQS 1210+1731, using HST/NICMOS. After PSF subtraction, a feature is seen in both the broad-band and narrow-band images, at a projected separation of 0.25\arcsec from the quasar. If associated with the DLA, the object would be $\approx 2-3$ $h_{70}^{-1}$ kpc in size with a flux of $9.8 \pm 2.4$ $\mu$Jy in the F160W filter, implying a luminosity at $\lambda_{central}=5500$ {\AA} in the rest frame of $1.5 \times 10^{10}$ $h_{70}^{-2}$ L$_{\odot}$ at $z=1.89$, for $q_{0}=0.5$. However, no significant H-$\alpha$ emission is seen, suggesting a low star formation rate (SFR) (3 $\sigma$ upper limit of 4.0 $h_{70}^{-2}$ M$_{\odot}$ yr$^{-1}$), or very high dust obscuration. Alternatively, the object may be associated with the host galaxy of the quasar. H-band images obtained with the NICMOS camera 2 coronagraph show a much fainter structure $\approx 4-5$ $h_{70}^{-1}$ kpc in size and containing four knots of continuum emission, located 0.7\arcsec away from the quasar. We have probed regions far closer to the quasar sight-line than in most previous studies of high-redshift intervening DLAs. The two objects we report mark the closest detected high-redshift DLA candidates yet to any quasar sight line. If the features in our images are associated with the DLA, they suggest faint, compact, somewhat clumpy objects rather than large, well-formed proto-galactic disks or spheroids.Comment: 52 pages of text, 19 figures, To be published in Astrophysical Journal (accepted Dec. 8, 1999

The UV Properties of the Narrow Line Quasar I Zwicky 1

I Zw 1 is the prototype narrow line quasar. We report here the results of our study of the UV emission of I Zw 1 using a high S/N (50-120) spectrum obtained with the HST FOS. The following main new results are obtained: 1. The Mg II and Al III doublets are partially/fully resolved. The measured doublet ratios verify theoretical predictions that the lines are thermalized in the BLR. 2. A weak associated UV absorption system is detected in N~V, and possibly also in C IV and Lya, suggesting an outflow with a velocity of 1870 km/s and velocity dispersion <300 km/s. 3. Lines from ions of increasing ionization level show increasing excess blue wing flux, and an increasing line peak velocity shift, reaching a maximum blueshift of about 2000 km/s for He II 1640. This may indicate an out-flowing component in the BLR, where the ionization level increases with velocity, and which is visible only in the approaching direction. The highest velocity part of this outflow may produce the associated UV absorption system. 4. The small C III] 1909 EW, and the small C III] 1909/Lya and C III] 1909/Si III] 1892 flux ratios indicate a typical BLR density of 10^11, i.e. about an order of magnitude larger than implied by C III] 1909 in most quasars. A BLR component of a higher density is implied by the EW and doublet ratio of the Al III 1857 doublet. 5. Prominent Fe II UV 191 emission is seen, together with weaker line emission at 1294 and 1871 A. These three features have been proposed as evidence for significant Lya pumping of the 8-10 eV levels of Fe II. 6. Significant Fe III emission is present. The Fe III UV 34 and UV 48 multiplets are clearly resolved, and Fe III UV 1, UV 47, UV 50, and UV 68 may also be present. (Shortened version)Comment: 28 pages, 1 table and 7 figures included. Uses aas2pp4.sty. Scheduled for the Astrophysical Journal November 10, 1997 issue, Vol. 48

Presentation and Outcomes After Medical and Surgical Treatment Versus Medical Treatment Alone of Spontaneous Infectious Spondylodiscitis: A Systematic Literature Review and Meta-Analysis.

Study Design: Systematic literature review. Objectives: The aims of this study were to (1) describe the clinical features, disabilities, and incidence of neurologic deficits of pyogenic spondylodiscitis prior to treatment and (2) compare the functional outcomes between patients who underwent medical treatment alone or in combination with surgery for pyogenic spondylodiscitis. Methods: A systematic literature review was performed using PubMed according to PRISMA guidelines. No year restriction was put in place. Statistical analysis of pooled data, when documented in the original report (ie, number of patients with desired variable and number of patients evaluated), was conducted to determine the most common presenting symptoms, incidence of pre- and postoperative neurologic deficits, associated comorbidities, infectious pathogens, approach for surgery when performed, and duration of hospitalization. Outcomes data, including return to work status, resolution of back pain, and functional recovery were also pooled among all studies and surgery-specific studies alone. Meta-analysis of studies with subgroup analysis of pain-free outcome in surgical and medical patients was performed. Results: Fifty of 1286 studies were included, comprising 4173 patients undergoing either medical treatment alone or in combination with surgery. Back pain was the most common presenting symptom, reported in 91% of patients. Neurologic deficit was noted in 31% of patients. Conclusion: Medical management remains first-line treatment of infectious pyogenic spondylodiscitis. Surgery may be indicated for progressive pain, persistent infection on imaging, deformity or neurologic deficits. If surgery is required, reported literature shows potential for significant pain reduction, improved neurologic function and a high number of patients returning to a normal functional/work status