Fishing Power Functions in Aggregate Bioeconomic Models

A method for estimating fishing power in the Beverton-Holt tradition in the absence of firm-level data is developed. This enables the construction of a standardized measure of fishing effort that can facilitate the analysis and implementation of various management alternatives. The methodology is applied to the Gulf of Mexico Reef Fish Fishery.Environmental Economics and Policy, Research Methods/ Statistical Methods, Resource /Energy Economics and Policy, Risk and Uncertainty,

Abundances in Damped Ly-alpha Galaxies

Damped Ly_alpha galaxies provide a sample of young galaxies where chemical abundances can be derived throughout the whole universe with an accuracy comparable to that for the local universe. Despite a large spread in redshift, HI column density and metallicity, DLA galaxies show a remarkable uniformity in the elemental ratios rather suggestive of similar chemical evolution if not of an unique population. These galaxies are characterized by a moderate, if any, enhancement of alpha-elements over Fe-peak elemental abundance with [S/Zn] about 0 and [O/Zn] about 0.2, rather similarly to the dwarfs galaxies in the Local Group. Nitrogen shows a peculiar behaviour with a bimodal distribution and possibly two plateaux. In particular, the plateau at low N abundances ([N/H] < -3), is not observed in other atrophysical sites and might be evidence for primary N production by massive stars.Comment: To appear in the Proceedings of the ESO/Arcetri Workshop on "Chemical Abundances and Mixing in Stars in the Milky Way and its Satellites", eds., L. Pasquini and S. Randich (Springer-Verlag Series, "ESO Astrophysics Symposia"

The color excess of quasars with intervening DLA systems- Analysis of the SDSS data release five

We analyzed the spectroscopic and photometric database of the 5th data release of the Sloan Digital Sky Survey (SDSS) to search for evidence of the quasar reddening produced by dust embedded in intervening damped Ly alpha (DLA) systems. From a list of 5164 quasars in the interval of emission redshift 2.25 /= 4, we built up an "absorption sample" of 248 QSOs with a single DLA system in the interval of absorption redshift 2.2 < z_a </= 3.5 and a "pool" of 1959 control QSOs without DLA systems or strong metal systems. For each QSO of the absorption sample we extracted from the pool a subset of control QSOs that are closest in redshift and magnitude. The mean color of this subset was used as a zero point to measure the "deviation from the mean color" of individual DLA-QSOs, Delta_i. The colors were measured using "BEST" ugriz SDSS imaging data. The mean color excess of the absorption sample, , was estimated by averaging the individual color deviations Delta_i. We find = 27 +/- 9 x 10**(-3) mag and = 54 +/- 12 x 10**(-3) mag. These values are representative of the reddening of DLA systems at z_a ~ 2.7 in SDSS QSOs with limiting magnitude r =/~ 20.2. The detection of the mean reddening is confirmed by several statistical tests. Analysis of the results suggests an origin of the reddening in dust embedded in the DLA systems, with an SMC-type extinction curve. By converting the reddening into rest-frame extinction, we derive a mean dust-to-gas ratio ~ 2 to 4 x 10**(-23) mag cm^2. This value is ~ -1.25 dex lower than the mean dust-to-gas ratio of the Milky Way, in line with the lower level of metallicity in the present DLA sample.Comment: Accepted for publication on Astronomy & Astrophysics, 17 pages, 10 figure

The SDSS Damped Lya Survey: Data Release 1

We present the results from an automated search for damped Lya (DLA) systems in the quasar spectra of Data Release 1 from the Sloan Digital Sky Survey (SDSS-DR1). At z~2.5, this homogeneous dataset has greater statistical significance than the previous two decades of research. We derive a statistical sample of 71 damped Lya systems (>50 previously unpublished) at z>2.1 and measure HI column densities directly from the SDSS spectra. The number of DLA systems per unit redshift is consistent with previous measurements and we expect our survey has >95% completeness. We examine the cosmological baryonic mass density of neutral gas Omega_g inferred from the damped Lya systems from the SDSS-DR1 survey and a combined sample drawn from the literature. Contrary to previous results, the Omega_g values do not require a significant correction from Lyman limit systems at any redshift. We also find that the Omega_g values for the SDSS-DR1 sample do not decline at high redshift and the combined sample shows a (statistically insignificant) decrease only at z>4. Future data releases from SDSS will provide the definitive survey of DLA systems at z~2.5 and will significantly reduce the uncertainty in Omega_g at higher redshift.Comment: 12 pages, includes color figures. Accepted to PASP, April 20 200

Metallicity Evolution in the Early Universe

Observations of the damped Lya systems provide direct measurements on the chemical enrichment history of neutral gas in the early universe. In this Letter, we present new measurements for four damped Lya systems at high redshift. Combining these data with [Fe/H] values culled from the literature, we investigate the metallicity evolution of the universe from z~1.5-4.5. Contrary to our expectations and the predictions of essentially every chemical evolution model, the N(HI)-weighted mean [Fe/H] metallicity exhibits minimal evolution over this epoch. For the individual systems, we report tentative evidence for an evolution in the unweighted [Fe/H] mean and the scatter in [Fe/H] with the higher redshift systems showing lower scatter and lower typical [Fe/H] values. We also note that no damped Lya system has [Fe/H] < -2.7 dex. Finally, we discuss the potential impact of small number statistics and dust on our conclusions and consider the implications of these results on chemical evolution in the early universe.Comment: 6 pages, 2 encapsulated figures, Latex2e, uses emulateapj.sty and onecolfloat.sty. Accepted for publication in ApJ Letters: Feb 28, 200

Survey for Galaxies Associated with z~3 Damped Lyman alpha Systems I: Spectroscopic Calibration of u'BVRI Photometric Selection

We present a survey for z~3 Lyman break galaxies (LBGs) associated with damped Lyman alpha systems (DLAs) with the primary purpose of determining the DLA-LBG cross-correlation. This paper describes the acquisition and analysis of imaging and spectroscopic data of 9 quasar fields having 11 known z~3 DLAs covering an area of 465 arcmin^2. Using deep u'BVRI images, 796 LBG candidates to an apparent R_AB magnitude of 25.5 were photometrically selected from 17,343 sources detected in the field. Spectroscopic observations of 529 LBG candidates using Keck LRIS yielded 339 redshifts. We have conservatively identified 211 z>2 objects with =3.02+/-0.32. We discuss our method of z~3 LBG identification and present a model of the u'BVRI photometric selection function. We use the 339 spectra to evaluate our u'BVRI z~3 Lyman break photometric selection technique.Comment: 26 pages, 6 tables, 11 figures, accepted for publication in Ap

On the Nature of Velocity Fields in High z Galaxies

We analyze the gas kinematics of damped Lya systems (DLAs) hosting high z gamma-ray bursts (GRBs) and those toward quasars (QSO-DLAs) focusing on threestatistics: (1) dv, the velocity interval encompassing 90% of the totaloptical depth, (2,3) Wsi and Wciv, the rest equivalent widths of the SiII1526 and CIV1548 transitions. The dv distributions of the GRB-DLAs and QSO-DLAs are similar, each has median dv~80km/s and a significant tail to several hundred km/s. This suggests comparable galaxy masses for the parent populations of GRB-DLAs and QSO-DLAs and we infer the average dark matter halo mass of GRB galaxies is <~10^{12} Msol. The unique configuration of GRB-DLA sightlines and the presence (and absence) of fine-structure absorption together give special insight into the nature of high z, protogalactic velocity fields. The data support a scenario where the dv statistic reflects dynamics in the interstellar medium (ISM) and Wsi traces motions outside the ISM (e.g. halo gas, galactic-scale winds). The Wsi statistic and gas metallicity [M/H] are tightly correlated, especially for the QSO-DLAs: [M/H]=a + b log(Wsi/1A) with a=-0.92+/-0.05 and b=-1.41+/-0.10. We argue that the Wsi statistic primarily tracks dynamical motions in the halos of high z galaxies and interpret this correlation as a mass-metallicity relation with very similar slope to the trend observed in local, low-metallicity galaxies. Finally, the GRB-DLAs exhibit systematically larger Wsi values (>0.5A) than the QSO-DLAs (~ 0.5A) which may suggest galactic-scale outflows contribute to the largest observed velocity fields.Comment: 14 pages, 9 figures. Submitted to Ap

CII* Absorption in Damped Lyman Alpha Systems: (II) A New Window on the Star Formation History of the Universe

Starting from the SFR per unit physical area, determined for DLAs using the C II* method, we obtain the SFR per unit comoving volume at $z$ $\approx$ 3, and find that it agrees with that for the Lyman Break Galaxies (LBGs). Though the mass of produced stars indicated by the SFRs is consistent with the current densities of known stellar populations, the mass of metals produced by $z$=2.5 is 30 times larger than detected in absorption in DLAs. The most likely solutions to this ``missing metals'' problem is that star formation occurs in compact bulge regions. We search for evidence of feedback and find no correlations between the SFR per unit area and N(H I), but possible correlations between SFR per unit area and low-ion velocity width and SFR per unit area and metal abundance. We show that (a) the correlation between cooling rate and dust-to-gas ratio is positive evidence for grain photoelectric heating, (b) the CMB does not significantly populate the C II excited fine-structure states, and (c) the ratio of CII* to resonance-line optical depths is a sensitive probe of the multi-phase structure of the DLA gas. We address recent arguments that DLAs are comprised only of WNM gas, and show them to be inconclusive. Despite the rough agreement between SFR per unit comoving volume for DLAs and LBGs, current evidence indicates these are distinct populations