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The results of an investigation into whether or not eclipse shadow bands have an atmospheric origin are presented. Using high altitude balloon and ground-based photodiode arrays during the 21 August 2017 total solar eclipse, data revealing the light patterns before and after totality were collected. These data were then analyzed using spectrograms. Both at the altitude of the balloon and on the ground, a sustained ~ 4.5 Hz signal was detected a few minutes before and after totality. This signal was coherent over a scale greater than 10 cm and detected in four separate balloon photodiodes and 16 ground photodiodes. At higher frequencies, up to at least 30 Hz, brief chaotic signals that were disorganized as a function of time were detected on the ground, but not at the altitude of the balloon and appeared mostly uncorrelated over a length scale of 10 cm. Some of our ground arrays utilized red and blue filters, but neither the sustained 4.5 Hz signal nor the higher frequency signals showed a strong dependence on filter color. On the ground we made a video of the shadow bands on a scaled white screen. We judged that the bands were roughly parallel to the orientation of the bright thin crescent Sun before and after totality and inferred that their propagation velocity was about v ~ 59 cm /s. Shadow band signals other than the sustained signal at ~ 4.5 Hz are consistent with atmospheric scintillation theory. These results are surprising. Based on accounts in the literature we expected to confirm the atmospheric scintillation theory of eclipse shadow bands, but instead we detected a sustained ~ 4.5 Hz signal at both high altitude and on the ground. This signal cannot be due to atmospheric scintillation and we ran a check to make sure this signal is not an artifact of our electronics. We recommend that additional searches for eclipse shadow bands be made at high altitude in the future., Comment: 11 pages, 8 figures. Accepted for publication, JASTP

We present ten metallicity measurements for quasar absorbers near $z=1.2$ that were selected for having unusually significant ZnII absorption in their SDSS spectra. Follow-up UV space spectroscopy of the Ly$\alpha$ region shows that all ten have damped Ly$\alpha$ (DLA) absorption, corresponding to neutral hydrogen column densities in the range $2.4\times 10^{20}$ $\le$ N(HI) $\le$ $2.5\times 10^{21}$ atoms cm$^{-2}$, and indicating that the gas is very optically thick and essentially neutral. The sample is a very small subset of systems compiled by searching the University of Pittsburgh catalog of $\approx 30,000$ intervening MgII absorption line systems in SDSS quasar spectra up to DR7. We started by isolating $\approx 3,000$ that had strong MgII absorption in the redshift interval $1.0 < z < 1.5$ in brighter background quasars. Of these, 36 exhibited significant absorption near ZnII. Space UV spectroscopy was then obtained for nine of these (25% of the total), and a tenth system in a fainter quasar was found in the HST archives. The result is a representative sample of the highest Zn$^+$ columns of gas within the DLA population. These ZnII-selected systems define the upper envelope of DLA metallicities near $z=1.2$. They show a tight anti-correlation between N(HI) and [Zn/H], with the higher metallicity systems clearly exhibiting more depletion based on [Cr/Zn] values. The various metal-line measurements (Zn, Cr, Si, Fe, Mn) indicate evolved neutral gas with $-0.9 \le$ [Zn/H] $\le +0.4$., Comment: Accepted for publication in MNRAS

We derive the statistical properties of neutral gas at redshifts 0.11

We present the study of a sample of nine QSO fields, with damped-Ly-alpha (DLA) or sub-DLA systems at z~0.6, observed with the X-Shooter spectrograph at the Very Large Telescope. By suitably positioning the X-Shooter slit based on high spatial resolution images of HST/ACS we are able to detect absorbing galaxies in 7 out of 9 fields (~ 78\% success rate) at impact parameters from 10 to 30 kpc. In 5 out of 7 fields the absorbing galaxies are confirmed via detection of multiple emission lines at the redshift of DLAs where only 1 out of 5 also emits a faint continuum. In 2 out of these 5 fields we detect a second galaxy at the DLA redshift. Extinction corrected star formation rates (SFR) of these DLA-galaxies, estimated using their H-alpha fluxes, are in the range 0.3-6.7 M_sun yr^-1. The emission metallicities of these five DLA-galaxies are estimated to be from 0.2 to 0.9 Z_sun. Based on the Voigt profile fits to absorption lines we find the metallicity of the absorbing neutral gas to be in a range of 0.05--0.6 Z_sun. The two remaining DLA-galaxies are quiescent galaxies with SFR < 0.4 M_sun yr^-1 (3-sigma) presenting continuum emission but weak or no emission lines. Using X-Shooter spectrum we estimate i-band absolute magnitude of -19.5+/-0.2 for both these DLA-galaxies that indicates they are sub-L* galaxies. Comparing our results with that of other surveys in the literature we find a possible redshift evolution of the SFR of DLA-galaxies., Comment: MNRAS accepted

We describe the algorithm used to select the Luminous Red Galaxy (LRG) sample for the extended Baryon Oscillation Spectroscopic Survey (eBOSS) of the Sloan Digital Sky Survey IV (SDSS-IV) using photometric data from both the SDSS and the Wide-Field Infrared Survey Explorer (WISE). LRG targets are required to meet a set of color selection criteria and have z-band and i-band MODEL magnitudes z < 19.95 and 19.9 < i < 21.8, respectively. Our algorithm selects roughly 50 LRG targets per square degree, the great majority of which lie in the redshift range 0.6 < z < 1.0 (median redshift 0.71). We demonstrate that our methods are highly effective at eliminating stellar contamination and lower-redshift galaxies. We perform a number of tests using spectroscopic data from SDSS-III/BOSS to determine the redshift reliability of our target selection and its ability to meet the science requirements of eBOSS. The SDSS spectra are of high enough signal-to-noise ratio that at least 89% of the target sample yields secure redshift measurements. We also present tests of the uniformity and homogeneity of the sample, demonstrating that it should be clean enough for studies of the large-scale structure of the universe at higher redshifts than SDSS-III/BOSS LRGs reached., Comment: Submitted in ApJS, 15 pages, 10 figures

We describe a new method of combining optical and infrared photometry to select Luminous Red Galaxies (LRGs) at redshifts $z > 0.6$. We explore this technique using a combination of optical photometry from CFHTLS and HST, infrared photometry from the WISE satellite, and spectroscopic or photometric redshifts from the DEEP2 Galaxy Redshift Survey or COSMOS. We present a variety of methods for testing the success of our selection, and present methods for optimization given a set of rest-frame color and redshift requirements. We have tested this selection in two different regions of the sky, the COSMOS and Extended Groth Strip (EGS) fields, to reduce the effect of cosmic/sample variance. We have used these methods to assemble large samples of LRGs for two different ancillary programs as a part of the SDSS-III/ BOSS spectroscopic survey. This technique is now being used to select $\sim$600,000 LRG targets for SDSS-IV/eBOSS, which began observations in Fall 2014, and will be adapted for the proposed DESI survey. We have found these methods can select high-redshift LRGs efficiently with minimal stellar contamination; this is extremely difficult to achieve with selections that rely on optical photometry alone., Comment: 10 pages, 13 figures, Published in the Astrophysical Journal

We present measurements of element abundance ratios and dust in CaII~absorbers identified in SDSS DR7+DR9. In an earlier paper we formed a statistical sample of 435 CaII absorbers and postulated that their statistical properties might be representative of at least two populations of absorbers. Here we show that if the absorbers are roughly divided into two subsamples with CaII rest equivalent widths larger and smaller than $W_0^{\lambda 3934} = 0.7$ \AA, they are then representative of two physically different populations. Comparisons of abundance ratios between the two CaII absorber populations indicate that the weaker $W_0^{\lambda 3934}$ absorbers have properties consistent with halo-type gas, while the stronger absorbers have properties intermediate between halo- and disk-type gas. We also show that, on average, the dust extinction properties of the overall sample is consistent with a LMC or SMC dust law, and the stronger absorbers are nearly 6 times more reddened than their weaker counterparts. The absorbed-to-unabsorbed composite flux ratio at $\lambda_{rest} = 2200$ \AA\ is $\mathcal{R} \approx 0.73$ and $E(B-V) \approx 0.046$ for the stronger CaII absorbers ($W_0^{\lambda 3934} \ge 0.7$ \AA), and $\mathcal{R} \approx 0.95$ and $E(B-V) \approx 0.011$ for the weaker CaII absorbers ($W_0^{\lambda 3934} < 0.7$ \AA)., Comment: Submitted to MNRAS. 19 pages, 12 figures

Quasar damped Ly-alpha (DLA) absorption line systems with redshifts z<1.65 are used to trace neutral gas over approximately 70 per cent of the most recent history of the Universe. However, such systems fall in the UV and are rarely found in blind UV spectroscopic surveys. Therefore, it has been difficult to compile a moderate-sized sample of UV DLAs in any narrow cosmic time interval. However, DLAs are easy to identify in low-resolution spectra because they have large absorption rest equivalent widths. We have performed an efficient strong-MgII-selected survey for UV DLAs at redshifts z=[0.42,0.70] using HST's low-resolution ACS-HRC-PR200L prism. This redshift interval covers ~1.8 Gyr in cosmic time, i.e., t~[7.2,9.0] Gyrs after the Big Bang. A total of 96 strong MgII absorption-line systems identified in SDSS spectra were successfully observed with the prism at the predicted UV wavelengths of Ly-alpha absorption. We found that 35 of the 96 systems had a significant probability of being DLAs. One additional observed system could be a very high N(HI) DLA (N(HI)~2x10^22 atoms cm^-2 or possibly higher), but since very high N(HI) systems are extremely rare, it would be unusual for this system to be a DLA given the size of our sample. Here we present information on our prism sample, including our best estimates of N(HI) and errors for the 36 systems fitted with damped Ly-alpha profiles. This list is valuable for future follow-up studies of low-redshift DLAs in a small redshift interval, although such work would clearly benefit from improved UV spectroscopy to more accurately determine their neutral hydrogen column densities., Comment: Accepted for publication in MNRAS

We present the results of a survey for CaII 3934,3969 absorption-line systems culled from ~ 95,000 Sloan Digital Sky Survey (SDSS) Data Release 7 and Data Release 9 quasar spectra. With 435 doublets identified in the catalog, this list is the largest CaII catalog compiled to date, spanning redshifts z < 1.34, which corresponds to the most recent ~ 8.9 Gyrs of the history of the Universe. We derive statistics on the CaII rest equivalent width distribution (REW) and incidence (number density per unit redshift). We find that the lambda3934 REW distribution cannot be described by a single exponential function. A double exponential function is required to produce a satisfactory description. The function can be written as a sum of weak and strong components: dn/dW = (N_wk*/W_wk*) exp(-W/W_wk*) + (N_str*/W_str*) exp(-W/W_str*). A maximum likelihood fit to the unbinned data indicates: N_wk*=0.140 +/- 0.029, W_wk*=0.165 +/- 0.020 A, N_str*=0.024 +/- 0.020, and W_str*=0.427 +/- 0.101 A. This suggests that the CaII absorbers are composed of at least two distinct populations. The incidence (product of integrated absorber cross section and their co-moving number density) of the overall CaII absorber population does not show evidence for evolution in the standard cosmology. The normalization of the no-evolution curve, i.e., the value of the CaII incidence extrapolated to redshift z=0, for lambda 3934 >= 0.3 A, is n_0=0.017 +/- 0.001. In comparison to MgII surveys, we found that only 3% of MgII systems in the SDSS have CaII, confirming that it is rare to identify CaII in quasar absorption-line surveys. We also report on some preliminary investigations of the nature of the two populations of CaII absorbers, and show that they can likely be distinguished using their MgII properties., Comment: Submitted to MNRAS

We present results from a search for galaxies that give rise to damped Lyman alpha (DLA), subDLA, and Lyman limit system (LLS) absorption at redshifts 0.1 ~< z ~< 1 in the spectra of background quasars. The sample was formed from a larger sample of strong MgII absorbers (W_0^(2796) >= 0.3 A) whose HI column densities were determined by measuring the Ly-alpha line in HST UV spectra. Photometric redshifts, galaxy colors, and proximity to the quasar sightline, in decreasing order of importance, were used to identify galaxies responsible for the absorption. Our sample includes 80 absorption systems for which the absorbing galaxies have been identified, of which 54 are presented here for the first time. The main results of this study are: (i) the surface density of galaxies falls off exponentially with increasing impact parameter, b, from the quasar sightline relative to a constant background of galaxies, with an e-folding length of ~46 kpc. Galaxies with b >~ 100 kpc calculated at the absorption redshift are statistically consistent with being unrelated to the absorption system. (ii) log N(HI) is inversely correlated with b at the 3.0 sigma level of significance. DLA galaxies are found systematically closer to the quasar sightline, by a factor of two, than are galaxies which give rise to subDLAs or LLSs. The median impact parameter is 17.4 kpc for the DLA galaxy sample, 33.3 kpc for the subDLA sample, and 36.4 kpc for the LLS sample. (iii) Absorber galaxy luminosity relative to L*, L/L*, is not significantly correlated with W_0^(2796), log N(HI), or b. (iv) DLA, subDLA, and LLS galaxies comprise a mix of spectral types, but are inferred to be predominantly late type galaxies based on their spectral energy distributions. The implications of these results are discussed. (Abridged), Comment: Accepted for publication in MNRAS

We present a catalog of intervening MgII quasar absorption-line systems in the redshift interval 0.36 <= z <= 2.28. The catalog was built from Sloan Digital Sky Survey Data Release Four (SDSS DR4) quasar spectra. Currently, the catalog contains > 17,000 measured MgII doublets. We also present data on the ~44,600 quasar spectra which were searched to construct the catalog, including redshift and magnitude information, continuum-normalized spectra, and corresponding arrays of redshift-dependent minimum rest equivalent widths detectable at our confidence threshold. The catalog is available on the web. A careful second search of 500 random spectra indicated that, for every 100 spectra searched, approximately one significant MgII system was accidentally rejected. Current plans to expand the catalog beyond DR4 quasars are discussed. Many MgII absorbers are known to be associated with galaxies. Therefore, the combination of large size and well understood statistics makes this catalog ideal for precision studies of the low-ionization and neutral gas regions associated with galaxies at low to moderate redshift. An analysis of the statistics of MgII absorbers using this catalog will be presented in a subsequent paper., Comment: AJ, in press