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This report provides detailed findings on the critical laboratory astrophysics data needs that are required to maximize the scientific return for NASA's current and near-term planned astrophysics missions. It also provides prioritized rankings on said laboratory astrophysics data, generally by waveband. The Report is based on community input gathered at the 2018 NASA Laboratory Astrophysics Workshop (LAW) from presentations, from discussions during workshop breakout sessions, and from other solicited input deemed appropriate by the Scientific Organizing Committee (SOC) obtained prior to and after the meeting. Hence, the Report is a direct reflection of the spirit and participant make-up of LAW 2018. The Report also outlines specific opportunities and threats facing NASA's Laboratory Astrophysics Program, and articulates concrete actions by which the Agency can capitalize on the opportunities and mitigate the challenges. The Report was prepared by the SOC, with help from some invited speakers, and input and review from community members.

We report Ultra-High-Frequency (UHF, 800MHz-1GHz) Radio Frequency Identification (RFID) transponders consisting of printed dipole antennas combined with RFID microchips. These are fabricated on Kapton via screen printing and on paper via spray coating, using inks obtained via microfluidization of graphite. We introduce a hybrid antenna structure, where an Al loop (small compared to the overall size of the antenna) is connected to a microchip with the double function of matching the impedances of antenna and microchip and avoiding bonding between exfoliated graphite and chip. The transponders have reading distance~11m at UHF RFID frequencies, larger than previously reported for graphene-based RFID and comparable with commercial transponders based on metallic antennas.

We report the exfoliation of graphite in aqueous solutions under high shear rate [$\sim10^8s^{-1}$] turbulent flow conditions, with a 100\% exfoliation yield. The material is stabilized without centrifugation at concentrations up to 100 g/L using carboxymethylcellulose sodium salt to formulate conductive printable inks. The sheet resistance of blade coated films is below$\sim2\Omega/\square$. This is a simple and scalable production route for graphene-based conductive inks for large area printing in flexible electronics.

The Frontier Fields are a director's discretionary time campaign with HST and the Spitzer Space Telescope to see deeper into the universe than ever before. The Frontier Fields combine the power of HST and Spitzer with the natural gravitational telescopes of massive high-magnification clusters of galaxies to produce the deepest observations of clusters and their lensed galaxies ever obtained. Six clusters - Abell 2744, MACSJ0416.1-2403, MACSJ0717.5+3745, MACSJ1149.5+2223, Abell S1063, and Abell 370 - were selected based on their lensing strength, sky darkness, Galactic extinction, parallel field suitability, accessibility to ground-based facilities, HST, Spitzer and JWST observability, and pre-existing ancillary data. These clusters have been targeted by the HST ACS/WFC and WFC3/IR with coordinated parallels of adjacent blank fields for over 840 HST orbits. The Spitzer Space Telescope has dedicated > 1000 hours of director's discretionary time to obtain IRAC 3.6 and 4.5 micron imaging to ~26.5, 26.0 ABmag 5-sigma point-source depths in the six cluster and six parallel Frontier Fields. The Frontier Field parallel fields are the second-deepest observations thus far by HST with ~29th ABmag 5-sigma point source depths in seven optical - near-infrared bandpasses. Galaxies behind the Frontier Field cluster lenses experience typical magnification factors of a few, with small regions near the critical curves magnified by factors 10-100. Therefore, the Frontier Field cluster HST images achieve intrinsic depths of ~30-33 magnitudes over very small volumes. Early studies of the Frontier Fields have probed galaxies fainter than any seen before during the epoch of reionization 6 < z < 10, mapped out the cluster dark matter to unprecedented resolution, and followed lensed transient events., Comment: submitted to ApJ; 18 pages; see http://www.stsci.edu/hst/campaigns/frontier-fields/ and http://ssc.spitzer.caltech.edu/warmmission/scheduling/approvedprograms/ddt/frontier/ for data and more information

We present the results of a program of optical and near-infrared spectroscopic follow-up of candidate Active Galactic Nuclei (AGN) selected in the mid-infrared. This survey selects both normal and obscured AGN closely matched in luminosity across a wide range, from Seyfert galaxies with bolometric luminosities L_bol~10^10L_sun, to highly luminous quasars (L_bol~10^14L_sun), and with redshifts from 0-4.3. Samples of candidate AGN were selected through mid-infrared color cuts at several different 24 micron flux density limits to ensure a range of luminosities at a given redshift. The survey consists of 786 candidate AGN and quasars, of which 672 have spectroscopic redshifts and classifications. Of these, 137 (20%) are type-1 AGN with blue continua, 294 (44%) are type-2 objects with extinctions A_V>~5 towards their AGN, 96 (14%) are AGN with lower extinctions (A_V~1) and 145 (22%) have redshifts, but no clear signs of AGN activity in their spectra. 50% of the survey objects have L_bol >10^12L_sun, in the quasar regime. We present composite spectra for type-2 quasars and for objects with no signs of AGN activity in their spectra. We also discuss the mid-infrared - emission-line luminosity correlation and present the results of cross-correlations with serendipitous X-ray and radio sources. The results show that: (1) obscured objects dominate the overall AGN population, (2) there exist mid-infrared selected AGN candidates which lack AGN signatures in their optical spectra, but have AGN-like X-ray or radio counterparts, and (3) X-ray and optical classifications of obscured and unobscured AGN often differ., Comment: ApJS, in press

We present Hubble Space Telescope images, and spectral energy distributions from optical to infrared wavelengths for a sample of six 0.3

We present an analysis of the effects of luminosity on the shape of the mid-infrared spectral energy distributions (SEDs) of 234 radio-quiet quasars originally presented by Richards et al. In quasars without evident dust extinction, the spectrally integrated optical and infrared luminosities are linearly correlated over nearly three decades in luminosity. We find a significant (>99.99% confidence) correlation between the 1.8-8.0 micron spectral index and infrared luminosity that indicates an enhancement of the mid-infrared continuum with increasing luminosity. Coupled with strong evidence for spectral curvature in more luminous quasars, we conclude this trend is likely a manifestation of the `near-infrared (3-5 micron) bump' noticed in earlier quasar SED surveys. The strength of this feature is indicative of the contribution of emission from the hottest (>1000 K) dust to the mid-infrared spectrum; higher luminosity quasars tend to show more hot dust emission. Finally, the comparable distribution of bolometric corrections from the monochromatic 3 micron luminosity as well as its lack of sensitivity to dust extinction as compared to the standard bolometric correction from nu*L_{5100A} suggest that the former may be a more robust indicator of bolometric quasar luminosity. The close link between the power in the mid-infrared and optical and the effect of luminosity on the shape of the mid-infrared continuum indicate that considering mid-infrared emission independent of the properties of the quasar itself is inadequate for understanding the parsec-scale quasar environment., Comment: Comments: 13 pages, 11 figures (3 color), uses emulateapj. Accepted for publication in ApJ

We present optical spectroscopy of a sample of 77 luminous AGN and quasars selected on the basis of their mid-infrared colors. Our objects are selected from the Spitzer Extragalactic First Look Survey and SWIRE XMM-LSS fields, with a typical 24mu flux density of 5mJy. The median redshift is 0.6, with a range of ~0.05-4. Only 33% (25/77) of these objects are normal type-1 quasars, with no obscuration. 44% (34/77) are type-2 objects, with high-ionization, narrow emission lines, 14% (11/77) are dust-reddened type-1 quasars, showing broad lines but a dust-reddened or unusually weak quasar continuum. 9% (7/77) show no sign of an AGN in the optical spectrum, having either starburst spectra or spectra which could be of either starburst or LINER types. These latter objects are analogous to the X-ray detected population of AGN with weak or non-existent optical AGN emission (the ``XBONGs''). 21 of our objects from the SWIRE field fall within moderately-deep XMM exposures. All the unobscured quasars, and about half the obscured quasars are detected in these exposures. This sample, when taken together with other samples of Spitzer selected AGN and quasars, and results from X-ray studies, confirms that obscured AGN dominate the AGN and quasar number counts of all rapidly-accreting supermassive black hole systems, at least for z~<4. This implies a high radiative efficiency for the black hole accretion process., Comment: 30 pages, 10 figures (some color), accepted by AJ

We present a preliminary investigation of the spectral energy distributions (SEDs), and star-formation properties of a sample of Mid-IR selected Quasars. The mid-infrared SEDs of our objects are consistent with that expected from clumpy torus models. At longer wavelengths, the radio to infrared ratios of several objects are consistent with those of star-forming galaxies., Comment: Comments: 4 pages, 4 figures. To appear in the proceedings for the Spitzer Science Center 2005 Conference: Infrared Diagnostics of Galaxy Evolution, Ed. R. Chary. November, 2005, Pasadena

A multi-wavelength set of photometric data including UV (GALEX), optical, near-IR, infrared (Spitzer) and radio (VLA 20cm) images and spectroscopic observations are used to map the dust-obscured and unobscured star formation in the galaxy pair ARP 32. The system consists of an actively star-forming galaxy and another one with depressed star formation. The most active galaxy has disrupted morphology and different sites of star formation. Spectroscopic data show hints of nuclear activity in its core, intense star formation in limited regions of the galaxy as well as an underlying population of stars witnessing a past episode of star formation. Current star formation rates are estimated from UV and bolometric IR luminosities., Comment: 4 pages, 3 figures, to be published in the Proceedings of the Spitzer Science Center 2005 Conference: Infrared Diagnostics of Galaxy Evolution (14-16 November 2005, Pasadena, CA)

We present the reduction of the 24 micron data obtained during the first cosmological survey performed by the Spitzer Space Telescope (First Look Survey, FLS). The survey consists of a shallow observation of 2.5x2 sq deg centered at 17h18m +59d30m (main survey) and a deeper observation of 1x0.5 sq deg centered at 17h17m +59d45m(verification survey). Issues with the reduction of the 24 micron MIPS data are discussed and solutions to attenuate instrumental effects are proposed and applied to the data. Approximately 17000 sources are extracted with a SNR greater than five. The photometry of the point sources is evaluated through PSF fitting using an empirical PSF derived from the data. Aperture corrections and the absolute calibration have been checked using stars in the field. Astrometric and photometric errors depend on the SNR of the source varying between 0.35-1 arcsec and 5-15%, respectively, for sources detected at 20-5 sigma. The flux of the 123 extended sources have been estimated through aperture photometry. The extended sources cover less than 0.3% of the total area of the survey. Based on simulations, the main and verification surveys are 50% complete at 0.3 and 0.15 mJy, respectively. Counterparts have been searched for in optical and radio catalogs. More than 80% of the 24 micron sources have a reliable optical counterpart down to R=25.5. 16% of the sources have a 20 cm counterpart down to 0.1 mJy and ~ 80% of the radio-infrared associations have a reliable optical counterpart. A residual map is obtained by subtracting point sources detected at the 3-sigma level and interpolating the regions occupied by extended sources. Several galactic clouds with low and intermediate velocities are identified by comparison with neutral Hydrogen data from this field., Comment: 25 pages, 27 figures. 7 figures are given as png to reduce their size. Paper accepted for publication by AJ (June 2006, vol. 131). Full-resolution version of the paper and machine-readable catalogs are available at http://spider.ipac.caltech.edu/staff/fadda/inpress.html

We investigate the instantaneous star formation rates (SFR) and extinction properties for a large (N=274), near-infrared (2.2 micron) + mid-infrared (24 micron) selected sample of normal to ultra-luminous infrared galaxies (ULIRGs) [10^9~0.8 in the Spitzer Extragalactic First Look Survey. We combine Spitzer MIPS 24-micron observations with high-resolution, optical Keck Deimos spectroscopy to derive optical emission-line and infrared star formation rates (SFR_{opt} & SFR_{IR}, respectively). Direct comparison of these SFR diagnostics reveals that our sample exhibits a wide range of extinction (1.01, which make up a large fraction of our sample, have SFR~100 M_{sun}/yr and ~2.5 mag. This translates to a 97% mean attenuation of the [OII] forbidden line doublet, with the most extreme sources having as much as 99.7% of their [OII] line flux extinguished by dust. Based on a SFR_{IR}/SFR_{opt} diagnostic, we derive an IR-luminosity-dependent Av^{IR} function [Av^{IR}=0.75*log(L_{IR}/L_{sun})-6.35 mag] that we use to extinction correct our emission line luminosities. Application of this correction results in a correlation between SFR_{IR} and SFR_{opt} that has a dispersion of 0.2 dex. Investigation of the Av dependence on redshift reveals that for a fixed L_{IR}, there is no significant Av evolution. The mean attenuation of our sample is intermediate between that of local optical/UV- and radio-selected samples and has a marginally stronger L_{IR} dependence., Comment: accepted by the Astrophysical Journal; 19 pages, including 14 figures

We present Spitzer 70um and 160um observations of the Spitzer extragalactic First Look Survey (xFLS). The data reduction techniques and the methods for producing co-added mosaics and source catalogs are discussed. Currently, 26% of the 70um sample and 49% of the 160um-selected sources have redshifts. The majority of sources with redshifts are star-forming galaxies at z<0.5, while about 5% have infrared colors consistent with AGN. The observed infrared colors agree with the spectral energy distribution (SEDs) of local galaxies previously determined from IRAS and ISO data. The average 160um/70um color temperature for the dust is Td~= 30+/-5 K, and the average 70um/24um spectral index is alpha~= 2.4+/-0.4. The observed infrared to radio correlation varies with redshift as expected out to z~1 based on the SEDs of local galaxies. The xFLS number counts at 70um and 160um are consistent within uncertainties with the models of galaxy evolution, but there are indications that the current models may require slight modifications. Deeper 70um observations are needed to constrain the models, and redshifts for the faint sources are required to measure the evolution of the infrared luminosity function., Comment: 16 pages including 11 figures. Accepted AJ

We present Infrared Array Camera (IRAC) data and source catalogs from the Spitzer Space Telescope Extragalactic First Look Survey. The data were taken in four broad bands centered at nominal wavelengths of 3.6, 4.5, 5.8 and 8.0 microns. A set of mosaics and catalogs have been produced which are ~80% complete and ~99% reliable to their chosen flux density limits. The main field survey covers 3.8 deg^2, and has flux density limits of 20muJy, 25muJy, 100muJy and 100muJy at wavelengths of 3.6, 4.5, 5.8 and 8.0 microns,respectively. The deeper ``verification'' survey covers 0.25 deg^2 with limits of 10muJy, 10muJy, 30muJy and 30muJy, respectively. We also include deep data in the ELAIS-N1 field which covers 0.041deg^2 with limits of 4muJy, 3muJy, 10muJy and 10muJy, respectively, but with only two wavelength coverage at a given sky position. The final bandmerged catalogs contain 103193 objects in the main field, 12224 in the verification field and 5239 in ELAIS-N1. Flux densities of high signal-to-noise objects are accurate to about 10%, and the residual systematic error in the absolute flux density scale is ~2-3%. We have successfully extracted sources at source densities as high as 100000 deg^-2 in our deepest 3.6 and 4.5 micron data. The mosaics and source catalogs will be made available through the Spitzer Science Center archive and the Infrared Science Archive., Comment: 12 pages, 6 figures, ApJS, in press. FITS images and ascii catalogs are available online at http://data.spitzer.caltech.edu/popular/fls/extragalactic_FLS/Enhanced_IRAC/

We present early results from the spectroscopic follow-up of a sample of candidate obscured AGN selected in the mid-infrared from the Spitzer First Look Survey. Our selection allows a direct comparison of the numbers of obscured and unobscured AGN at a given luminosity for the first time, and shows that the ratio of obscured to unobscured AGN at infrared luminosities corresponding to low luminosity quasars is ~1:1 at z~0.5. Most of our optically-faint candidate obscured AGN have the high-ionization, narrow-line spectra expected from type-2 AGN. A composite spectrum shows evidence for Balmer absorption lines, indicating recent star-formation activity in the host galaxies. There is tentative evidence for a decrease in the obscured AGN fraction with increasing AGN luminosity., Comment: To appear in the proceedings of the workshop "Multiband approach to AGN" Bonn October 2004 in Memorie della Societa Astronomica Italiana

The Spitzer Space Telescope was used to study the mid-infrared to far-infrared properties of NGC 300, and to compare dust emission to Halpha to elucidate the heating of the ISM and the star formation cycle at scales < 100 pc. The new data allow us to discern clear differences in the spatial distribution of 8 micron dust emission with respect to 24 micron dust and to HII regions traced by the Halpha light. The 8 micron emission highlights the rims of HII regions, and the 24 micron emission is more strongly peaked in star forming regions than at 8 microns. We confirm the existence and approximate amplitude of interstellar dust emission at 4.5 microns, detected statistically in Infrared Space Observatory (ISO) data, and conclude it arises in star forming regions. When averaging over regions larger than ~ 1 kpc, the ratio of Halpha to Aromatic Feature emission in NGC 300 is consistent with the values observed in disks of spiral galaxies. The mid-to-far-infrared spectral energy distribution of dust emission is generally consistent with pre-Spitzer models., Comment: to appear in the ApJS Spitzer special issue (September 2004)

We present the first results of the angular auto-correlation function of the galaxies detected by the Infrared Array Camera (IRAC) instrument in the First Look Survey (FLS) of the Spitzer Space Telescope. We detect significant signals of galaxy clustering within the survey area. The angular auto-correlation function of the galaxies detected in each of the four IRAC instrument channels is consistent with a power-law form $w(\theta)=A\theta^{1-\gamma}$ out to $\theta = 0.2\arcdeg$, with the slope ranging from $\gamma = 1.5$ to 1.8. We estimate the correlation amplitudes $A$ to be $2.95 \times 10^{-3}$, $2.03 \times 10^{-3}$, $4.53 \times 10^{-3}$, and $2.34 \times 10^{-3}$ at $\theta=1\arcdeg$ for galaxies detected in the IRAC 3.6$\mu$m, 4.5$\mu$m, 5.8$\mu$m, and 8.0$\mu$m instrument channels, respectively. We compare our measurements at 3.6$\mu$m with the previous K-band measurements, and discuss the implications of these results., Comment: Accepted for publication in the ApJ Supplements Spitzer Special Issue; 12 pages including 3 figures and 1 table

We report on submillimeter and infrared observations of 28 radio-selected galaxies in the Spitzer First Look Survey Verification field (FLSV). All of the radio-selected galaxies that show evidence for emission at 850um with SCUBA have Spitzer counterparts at 24um, while only half of the radio-selected galaxies without 850um emission have detectable counterparts at 24um. The data show a wide range of infrared colors (S70/S24 < 5--30, S8/S3.6 < 0.3--4), indicative of a mixture of infrared-warm AGN and cooler starburst dominated sources. The galaxies showing 850um emission have Spitzer flux densities and flux density ratios consistent with the range of values expected for high-redshift (z=1--4) ultraluminous infrared galaxies., Comment: Accepted for Spitzer ApJS Special Edition, 12 pages including 4 figures and 1 table

We present Multiband Imaging Photometer for Spitzer (MIPS) observations of M81 at 24, 70, and 160 micron. The grand design nature of M81 is clearly seen, showing two well resolved spiral arms containing numerous bright star forming regions. The MIPS images reveal a significant amount of cold dust associated with the spiral arms. We investigate the variation of the ultraviolet (UV), H-alpha, and infrared (IR) luminosities and star formation rate (SFR) indicators across the face of M81 using the MIPS images and archival UV and H-alpha images. For regions in M81, we find that UV and H-alpha SFRs (uncorrected for dust attenuation) are always lower than the IR SFR. The cause of this behavior is dust attenuation and/or using SFR calibrations appropriate for entire galaxies, not regions in galaxies. The characteristics of the dust attenuation for the regions indicate the dust grains and/or geometry are different from those in starburst galaxies. The behavior of the infrared-radio correlation in M81 is seen to vary from the global average, with variations correlated with the morphology of M81., Comment: 7 pages, 6 embedded figures, paper with full resolution figures available at http://dirty.as.arizona.edu/~kgordon/papers/PS_files/m81_mips.pdf

We carried out the direct measurement of the fraction of dusty sources in a sample of extremely red galaxies with (R - Ks) > 5.3mag and Ks < 20.2mag, using 24um data from the Spitzer Space Telescope. Combining deep 24um, Ks- and R-band data over an area of 64sq.arcmin in ELAIS N1, we find that 50%+-6% of our ERO sample have measurable 24um flux above the 3sigma flux limit of 40uJy. This flux limit corresponds to a SFR of 12Msun/yr at z~1. The 24um-detected EROs have 24-to-2.2 and 24-to-0.7um flux ratios consistent with infrared luminous, dusty sources at z>1, and an order of magnitude too red to be explained by an infrared quiescent spiral or a pure old stellar population at any redshift. Keck optical spectroscopy of a sample of similarly selected EROs in the FLS field suggests that most of the EROs in ELAIS N1 are probably at z~1. The mean 24um flux (167uJy) of the 24um-detected ERO sample roughly corresponds to the total infrared luminosity of (3-10)x10^(11)Lsun at z=1-1.5, which is similar to that of local LIRGs and ULIGs. The corresponding SFR is ~(50-170)Msun/yr. If the time scale of this starbursting phase is on the order of 10^8yr as inferred for the local LIRGs and ULIGs, the lower limit on the masses of these 24um-detected EROs is (5-20)x10^9Msun. It is plausible that some of the starburst EROs are in the midst of violent transformation to become massive early type galaxies at the epoch of z ~ 1-2., Comment: Accepted for publication in ApJ (Spitzer Special Issue)

We present the Spitzer MIPS 24 micron source counts in the Extragalactic First Look Survey main, verification and ELAIS-N1 fields. Spitzer's increased sensitivity and efficiency in large areal coverage over previous infrared telescopes, coupled with the enhanced sensitivity of the 24 micron band to sources at intermediate redshift, dramatically improve the quality and statistics of number counts in the mid-infrared. The First Look Survey observations cover areas of, respectively, 4.4, 0.26 and 0.015 sq.deg. and reach 3-sigma depths of 0.11, 0.08 and 0.03 mJy. The extragalactic counts derived for each survey agree remarkably well. The counts can be fitted by a super-Euclidean power law of index alpha=-2.9 from 0.2 to 0.9 mJy, with a flattening of the counts at fluxes fainter than 0.2 mJy. Comparison with infrared galaxy evolution models reveals a peak's displacement in the 24 micron counts. This is probably due to the detection of a new population of galaxies with redshift between 1 and 2, previously unseen in the 15 micron deep counts., Comment: Accepted for publication in special Spitzer ApJS issue, 4 pages

IRAC images of M81 show three distinct morphological constituents: a smooth distribution of evolved stars with bulge, disk, and spiral arm components; a clumpy distribution of dust emission tracing the spiral arms; and a pointlike nuclear source. The bulge stellar colors are consistent with M-type giants, and the disk colors are consistent with a slightly younger population. The dust emission generally follows the blue and ultraviolet emission, but there are large areas that have dust emission without ultraviolet and smaller areas with ultraviolet but little dust emission. The former are presumably caused by extinction, and the latter may be due to cavities in the gas and dust created by supernova explosions. The nucleus appears fainter at 8 um than expected from ground-based 10 um observations made four years ago., Comment: ApJS in press (Spitzer special issue); 15 pages, 3 figures. Changes: unused references removed, numbers and labels in Table 1 changed

In this Letter, we present the initial characterization of extragalactic 24um sources in the Spitzer First Look Survey (FLS) by examining their counterparts at 8um and R-band. The color-color diagram of 24-to-8 vs. 24-to-0.7um is populated with 18,734 sources brighter than the 3sigma flux limit of 110uJy, over an area of 3.7sq.degrees. The 24-to-0.7um colors of these sources span almost 4 orders of magnitudes, while the 24-to-8um colors distribute at least over 2 orders of magnitudes. In addition to identifying ~30% of the total sample with infrared quiescent, mostly low redshift galaxies, we also found that: (1) 23% of the 24um sources (~1200/sq.degrees) have very red 24-to-8 and 24-to-0.7 colors and are probably infrared luminous starbursts with L(IR)>3x10^(11)Lsun at z>1. In particular, 13% of the sample (660/sq.degrees) are 24um detected only, with no detectable emission in either 8um or R-band. These sources are the candidates for being ULIRGs at z>2. (2) 2% of the sample (85/sq.degrees) have colors similar to dust reddened AGNs, like Mrk231 at z~0.6-3. (3) We anticipate that some of these sources with extremely red colors may be new types of sources, since they can not be modelled with any familiar type of spectral energy distribution. We find that 17% of the 24um sources have no detectable optical counterparts brighter than R limit of 25.5mag. Optical spectroscopy of these optical extremely faint 24um sources would be very difficult, and mid-infrared spectroscopy from the Spitzer would be critical for understanding their physical nature (Abridged)., Comment: Accepted for publication in ApJ (Spitzer Special Issue)

Selection of active galactic nuclei (AGN) in the infrared allows the discovery of AGN whose optical emission is extinguished by dust. In this paper, we use the Spitzer Space Telescope First Look Survey (FLS) to assess what fraction of AGN with mid-infrared luminosities comparable to quasars are missed in optical quasar surveys due to dust obscuration. We begin by using the Sloan Digital Sky Survey (SDSS) database to identify 54 quasars within the 4 deg^2 extragalactic FLS. These quasars occupy a distinct region in mid-infrared color space by virtue of their strong, red, continua. This has allowed us to define a mid-infrared color criterion for selecting AGN candidates. About 2000 FLS objects have colors consistent with them being AGN, but most are much fainter in the mid-infrared than the SDSS quasars, which typically have 8 micron flux densities, S(8.0), ~1 mJy. We have investigated the properties of the 43 objects with S(8.0) >= 1 mJy satisfying our AGN color selection. This sample should contain both unobscured quasars, and AGN which are absent from the SDSS survey due to extinction in the optical. After removing 16 known quasars, three probable normal quasars, and eight spurious or confused objects from the initial sample of 43, we are left with 16 objects which are likely to be obscured quasars or luminous Seyfert-2 galaxies. This suggests the numbers of obscured and unobscured AGN are similar in samples selected in the mid-infrared at S(8.0)~1 mJy., Comment: To appear in the ApJS Spitzer Special Issue

We present the first high-resolution (6.2 to 7.7 km/s FWHM) spectra of the APM BR J0307-4945 quasar at z_em = 4.73 obtained with UVES on the 8.2m VLT Kueyen telescope. We focus our analysis on a damped Ly-alpha (DLA) system at z_abs = 4.466 with a neutral hydrogen column density N(HI) = (4.68 +/- 0.97) 10^{20} cm^{-2}. It is the most distant DLA system known to the present date, observed when the age of the universe was only 1.3 Gyr. It shows complex low- and high-ionization line profiles spanning ~240 and 300 km/s in velocity space respectively. We derive accurate abundances for N, O, Al, Si and Fe, and place a lower limit on C and an upper limit on Ni: [N/H] = -3.07 +/- 0.15, [O/H] = -1.63 +/- 0.19, [Al/H] = -1.79 +/- 0.11, [Si/H] = -1.54 +/- 0.11, [Fe/H] = -1.97 +/- 0.19, [C/H] > -1.63 and [Ni/H] < -2.35. The derived high metallicity, 1/90 solar, shows that this very young absorber (< 1.3 Gyr) has already experienced a significant metal enrichment. The [O/Si] ratio is nearly solar suggesting a limited amount of dust, the relative [Si,O/Fe] abundance ratios show a similar enhancement as observed in the Milky Way stars with comparable metallicities, and the [N/O] ratio is very low. All these results point to an enrichment pattern dominated by Type II supernovae which suggests a Milky Way type evolutionary model., Comment: 11 pages, 5 figures, Accepted for publication in A&A

We present a catalog of extremely red objects discovered using the NICMOS/HST parallel imaging database and ground-based optical follow-up observations. Within an area of 16 square arc-minutes, we detect 15 objects with $\rm R - F160W > 5$ and $\rm F160W < 21.5$. We have also obtained K-band photometry for a subset of the 15 EROs. All of the $\rm R - F160W$ selected EROs imaged at K-band have $\rm R - K > 6$. Our objects have $\rm F110W - F160W$ colors in the range of 1.3 - 2.1, redder than the cluster ellipticals at $z \sim 0.8$ and nearly 1 magnitude redder than the average population selected from the F160W images at the same depth. In addition, among only 22 NICMOS pointings, we detected two groups or clusters in two fields, each contains 3 or more EROs, suggesting that extremely red galaxies may be strongly clustered. At bright magnitudes with $\rm F160W < 19.5$, the ERO surface density is similar to what has been measured by other surveys. At the limit of our sample, F160W = 21.5, our measured surface density is 0.94$\pm 0.24$ arcmin^{-2}. Excluding the two possible groups/clusters and the one apparently stellar object, reduces the surface density to 0.38$\pm 0.15$ arcmin^{-2}., Comment: To appear in the AJ August issue. Replaced with the published version

We present the first results of a survey of random fields with the slitless G141 ($\lambda_c = 1.5\mu, \Delta\lambda=0.8\mu$) grism on NICMOS. Approximately 64 square arcminutes have been observed at intermediate and high galactic latitudes. The 3$\sigma$ limiting line and continuum fluxes in each field vary from $7.5 \times 10^{-17}$ to $1 \times 10^{-17} erg/cm^2/sec$ and from H = 20 to 22, respectively. Our median and area weighted $3\sigma $ limiting line fluxes within a 4 pixel aperture are nearly identical at $4.1 \times 10^{-17} erg/cm^2/sec$ and are 60% deeper than the deepest narrow-band imaging surveys from the ground. We have identified 33 emission-line objects and derive their observed wavelengths, fluxes and equivalent widths. We argue that the most likely line identification is H$\alpha$ and that the redshift range probed is from 0.75 to 1.9. The 2$\sigma$ rest-frame equivalent width limits range from 9\AA to 130\AA with an average of 40\AA. The survey probes an effective co-moving volume of $10^5 h_{50}^{-3} Mpc^3$ for $q_0=0.5$. Our derived co-moving number density of emission line galaxies in the range $0.7 < z < 1.9$ is $3.3\times10^{-4} h_{50}^{3} Mpc^{-3}$, very similar to that of the bright Lyman break objects at $z \sim 3$. The objects with detected emission-lines have a median F160W magnitude of 20.4 (Vega scale) and a median H$\alpha$ luminosity of $2.7 \times 10^{42} erg/sec$. The implied star formation rates range from 1 to 324 M_{\odot}/yr, with an average [NII]6583,6548 corrected rate of 21 M_{\odot}/yr for H_0=50 km/s/Mpc and $q_0=0.5$ (34 M_{\odot}/yr for $q_0=0.1$)., Comment: 32 pages, including 6 figures and 4 tables. Accepted for publication in the Astrophysical Journal

We have detected the host galaxies of 16 nearby, radio-quiet quasars using images obtained with the Near-Infrared Camera and Multi-Object Spectrometer (NICMOS). We confirm that these luminous quasars tend to live in luminous, early-type host galaxies, and we use the host-galaxy magnitudes to refine the luminosity/host-mass limit inferred from ground-based studies. If quasars obey the relation $M_{black hole}/M_{spheroid}\sim0.006$ found for massive dark objects in nonactive galaxies, then our analysis implies that they radiate at up to $\sim20%$ of the Eddington rate. An analogous analysis for ultraluminous infrared galaxies shows them to accrete at up to similar Eddington fractions, consistent with the hypothesis that some of them are powered by embedded quasars., Comment: 9 pages, includes 2 eps figs, accepted to ApJLett

We present Keck LRIS spectroscopy along with NICMOS F110W (~J) and F160W (~H) images of the galaxy HDF4-473.0 (hereafter 4-473) in the Hubble Deep Field, with a detection of an emission line consistent with Ly-alpha at a redshift of z=5.60. Attention to this object as a high redshift galaxy was first drawn by Lanzetta, Yahil and Fernandez-Soto and appeared in their initial list of galaxies with redshifts estimated from the WFPC2 HDF photometry. It was selected by us for spectroscopic observation, along with others in the Hubble Deep Field, on the basis of the NICMOS F110W and F160W and WFPC2 photometry. For H_0 = 65 and q_0 = 0.125, use of simple evolutionary models along with the F814W (~I), F110W, and F160W magnitudes allow us to estimate the star formation rate (~13 M(solar)/yr). The colors suggest a reddening of E(B-V) ~ 0.06. The measured flux in the Ly-alpha line is approximately 1.0*10^(-17) ergs/cm/s and the restframe equivalent width, correcting for the absorption caused by intervening HI, is approximately 90AA. The galaxy is compact and regular, but resolved, with an observed FWHM of ~0.44". Simple evolutionary models can accurately reproduce the colors and these models predict the Ly-alpha flux to within a factor of 2. Using this object as a template shifted to higher redshifts, we calculate the magnitudes through the F814W and two NICMOS passbands for galaxies at redshifts 6 < z < 10., Comment: accepted version--ApJ Letters, predicted high-z colors refined, improved references to earlier photometric redshift estimates, title changed

Eleven candidate damped Lya absorption systems were identified in 27 spectra of the quasars from the APM z>4 survey covering the redshift range 2.83.5). High resolution echelle spectra (0.8A FWHM) have been obtained for three quasars, including 2 of the highest redshift objects in the survey. Two damped systems have confirmed HI column densities of N(HI) >= 10^20.3 atoms cm^-2, with a third falling just below this threshold. We have discovered the highest redshift damped Lya absorber known at z=4.383 in QSO BR1202-0725. The APM QSOs provide a substantial increase in the redshift path available for damped surveys for z>3. We combine this high redshift sample with other quasar samples covering the redshift range 0.008 < z < 4.7 to study the redshift evolution and the column density distribution function for absorbers with log N(HI)>=17.2. In the HI column density distribution f(N)=kN^-beta we find evidence for breaks in the power law, flattening for 17.2< log N(HI)<21 and steepening for log N(HI)>21.2. The column density distribution function for the data with log N(HI)>=20.3 is better fit with the form f(N)=(f*/N*)(N/N*)^-beta exp(-N/N*). Significant redshift evolution in the number density per unit redshift is evident in the higher column density systems with an apparent decline in N(z) for z>3.5., Comment: To appear in MNRAS. Latex file (10 pages of text) plus 14 separate postscript figure files. Requires mn.sty. Postscript version with figures embedded is available at http://www.ociw.edu/~lisa/publications.html

Though observationally rare, damped Lya absorption systems dominate the mass density of neutral gas in the Universe. Eleven high redshift damped Lya systems covering 2.84 QSO Survey, extending these absorption system surveys to the highest redshifts currently possible. Combining our new data set with previous surveys we find that the cosmological mass density in neutral gas, omega_g, does not rise as steeply prior to z~2 as indicated by previous studies. There is evidence in the observed omega_g for a flattening at z~2 and a possible turnover at z~3. When combined with the decline at z>3.5 in number density per unit redshift of damped systems with column densities log N(HI)>21 atoms cm^-2, these results point to an epoch at z>3 prior to which the highest column density damped systems are still forming. We find that over the redshift range 2

The APM multicolor survey for bright z > 4 objects, covering 2500 deg^2 of sky to m(R)~19, resulted in the discovery of thirty-one quasars with z > 4. High signal-to-noise optical spectrophotometry at 5A resolution has been obtained for the twenty-eight quasars easily accessible from the northern hemisphere. These spectra have been surveyed to create new samples of high redshift Lyman-limit systems, damped Lyman-alpha absorbers, and metal absorption systems (e.g. CIV and MgII). In this paper we present the spectra, together with line lists of the detected absorption systems. The QSOs display a wide variety of emission and absorption line characteristics, with 5 exhibiting broad absorption lines and one with extremely strong emission lines (BR2248-1242). Eleven candidate damped Ly-alpha absorption systems have been identified covering the redshift range 2.83.5). An analysis of the measured redshifts of the high ionization emission lines with the low ionization lines shows them to be blueshifted by 430+/-60 km/s. In a previous paper (Storrie-Lombardi et. al. 1994) we discussed the redshift evolution of the Lyman limit systems catalogued here. In subsequent papers we will discuss the properties of the Ly-alpha forest absorbers and the redshift and column density evolution of the damped Ly-alpha absorbers., Comment: To appear in 1 September 1996, ApJS, 10 pages text, 22 pages of figures, 11 pages of tables

We have obtained high signal:to:noise optical spectroscopy at 5\AA\ resolution of 27 quasars from the APM z$>$4 quasar survey. The spectra have been analyzed to create new samples of high redshift Lyman-limit and damped Lyman-$\alpha$ absorbers. These data have been combined with published data sets in a study of the redshift evolution and the column density distribution function for absorbers with $\log$N(HI)$\ge17.5$, over the redshift range 0.01 $<$ z $<$ 5. The main results are: \begin{itemize} \item Lyman limit systems: The data are well fit by a power law $N(z) = N_0(1 + z)^{\gamma}$ for the number density per unit redshift. For the first time intrinsic evolution is detected in the product of the absorption cross-section and comoving spatial number density for an $\Omega = 1$ Universe. We find $\gamma = 1.55$ ($\gamma = 0.5$ for no evolution) and $N_0 = 0.27$ with $>$99.7\% confidence limits for $\gamma$ of 0.82 \& 2.37. \item Damped \lya systems: The APM QSOs provide a substantial increase in the redshift path available for damped surveys for $z>3$. Eleven candidate and three confirmed damped Ly$\alpha$ absorption systems, have been identified in the APM QSO spectra covering the redshift range $2.8\le z \le 4.4$ (11 with $z>3.5$). Combining the APM survey confirmed and candidate damped \lya absorbers with previous surveys, we find evidence for a turnover at z$\sim$3 or a flattening at z$\sim$2 in the cosmological mass density of neutral gas, $\Omega_g$. \end{itemize} The Lyman limit survey results are published in Storrie-Lombardi, et~al., 1994, ApJ, 427, L13. Here we describe the results for the DLA population of absorbers., Comment: latex, 5 pages + 4 postscript figures

We carried out the direct measurement of the fraction of dusty sources in a sample of extremely red galaxies with (R-K(sub s)) greater than or equal to 5.3 mag and K(sub s) less than 20.2 mag, using from the Spitzer Space Telescope. Combining deep 24 micrometers, K(sub s)- and R-band data over an area of approximately 64 sq.arcmin in the ELAIS N1 field of the Spitzer First Look Survey (FLS), we find that 50 +/- 60% of our ERO sample have measurable 24 micrometer flux above the 3(sigma) flux limit of 40 microns Jy. This flux limit corresponds to a SFR of 12 solar mass/yr at z approximately 1, much mo previous long wavelength measurement. The 24fJ,m-detected EROs have 24-to2.2 and 24-to-0.7micrometr flux ratios consistent with infrared luminous, dusty sources at z approx. 1, and an order of magnitude too red to be explained by an infrared quiescent spiral or a pure old stellar population at any redshift. Some of these 24 micrometer-detected EROs could be AGN, however, the fraction among the whole ERO sample is probably small, 10-20%, as suggested by deep X-ray observations as well as optical spectroscopy. Keck optical spectroscopy of a sample of similarly selected EROs in the FLS field suggests that most of the EROs in ELAIS Nl are probably at z approx. 1.

We carried out direct measurement of the fraction of dusty sources in a sample of extremely red galaxies with (R - Ks) >= 5.3 mag and Ks < 20:2 mag, using 24 micron data from the Spitzer Space Telescope. Combining deep 24 micron Ks- and R-band data over an area of ~64 arcmin(sup 2) in ELAIS N1 of the Spitzer First Look Survey (FLS), we find that 50% +/- 6% of our extremely red object (ERO) sample have measurable 24 micron flux above the 3 (sigma) flux limit of 40 (micro)Jy. This flux limit corresponds to a star formation rate (SFR) of 12 solar masses per year ~1, much more sensitive than any previous long-wavelength measurement. The 24 micron-detected EROs have 24 micron/2.2 micron and 24 micron/0.7 micron flux ratios consistent with infrared luminous, dusty sources at z >= 1, and are an order of magnitude too red to be explained by an infrared quiescent spiral or a pure old stellar population at any redshift. Some of these 24 micron-detected EROs could be active galactic nuclei; however, the fraction among the whole ERO sample is probably small, 10%-20%, as suggested by deep X-ray observations as well as optical spectroscopy. Keck optical spectroscopy of a sample of similarly selected EROs in the FLS field suggests that most of the EROs in ELAIS N1 are probably at z ~1. The mean 24 micron flux (167 (micro)Jy) of the 24 micron-detected ERO sample roughly corresponds to the rest-frame 12 micron luminosity, (nu)L(nu)(12 micron, of 3x10(exp 10)(deg) solar luminosities at z ~1. Using the c IRAS (nu)L(nu)(12 (micron) and infrared luminosity LIR(8-1000 (micron), we infer that the (LIR) of the 24 micron- detected EROs is 3 x 10(exp 11) and 1 x 10(exp 12) solar luminosities at z = 1.0 and similar to that of local luminous infrared galaxies (LIRGs) and ultraluminous infrared galaxies (ULIRGs). The corresponding SFR would be roughly 50-170 solar masses per year. If the timescale of this starbursting phase is on the order of 108 yr as inferred for the local LIRGs and ULIRGs, the lower limit on the masses of these 24 micron-detected EROs is 5 x 10(exp 9) to 2 x 10(exp 10) solar masses. It is plausible that some of the starburst EROs are in the midst of a violent transformation to become massive early type galaxies at the epoch of z ~1-2.

We present R-band images covering more than 11 square degrees of sky that were obtained in preparation for the Spitzer Space Telescope First-Look Survey (FLS).

Studies of damped Lya systems provide us with a good measure of the evolution of the HI column density distribution function and the contribution to the comoving mass density in neutral gas out to redshifts of z = 5 . The column density distribution function at high redshift steepens for the highest column density HI absorbers, though the contribution to the comoving mass density of neutral gas remains fiat from 2 < z < 5 . Results from studies at z < 2 are finding substantial numbers of damped absorbers identified from MgII absorption, compared to previous blind surveys. These results indicate that the contribution to the comoving mass density in neutral gas may be constant from z ~ 0 to z ~ 5. Details of recent work in the redshift range z < 2 work is covered elsewhere in this volume (see D. Nestor). We review here recent results for the redshift range 2 < z < 5.

We have completed spectroscopic observations using LRIS on the Keck 1 telescope of 30 very high redshift quasars, 11 selected for the presence of damped Ly alpha absorption systems and 19 with redshifts z>3.5 not previously surveyed for absorption systems.