arXiv subjects

Ray J. Weymann

Publications and source records attributed to Ray J. Weymann.

11 recordsLinked to original sources

arXiv2003

High Redshift Candidates and the Nature of Small Galaxies in the Hubble Deep Field

We present results on two related topics: 1. A discussion of high redshift candidates (z>4.5), and 2. A study of very small galaxies at intermediate redshifts, both sets being detected in the region of the northern Hubble Deep Field covered by deep NICMOS observations at 1.6 and 1.1 microns. The high redshift candidates are just those with redshift z>4.5 as given in the recent catalog of Thompson, Weymann and Storrie-Lombardi, while the ``small galaxy'' sample is defined to be those objects with isophotal area <= 0.2 squ. arcsec and with photometric redshifts 1<z<4.5. Of the 19 possible high redshift candidates listed in the Thompson et al. catalog, 11 have (nominal) photometric redshifts less than 5.0. Of these, however, only 4 are ``robust'' in the sense of yielding high redshifts when the fluxes are randomly perturbed with errors comparable to the estimated measuring error in each wave band. For the 8 other objects with nominal photometric redshifts greater than 5.0, one (WFPC2 4--473) has a published spectroscopic redshift. Of the remaining 7, 4 are robust in the sense indicated above. Two of these form a close pair (NIC 586 and NIC 107). The redshift of the object having formally the highest redshift, at 6.56 (NIC118 = WFPC2 4--601), is problematic, since F606W and F814W flux are clearly present, and the nature of this object poses a dilemma. (abridged)

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arXiv2000

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.

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arXiv2000

Star Formation History in the Nicmos Northern Hubble Deep Field

This paper presents the star formation history in the NICMOS Northern Deep HDF. It uses the techniques of photometric redshifts and extinctions to correct for extinction of the ultra-violet flux. It presents a new method for correcting for surface brightness diming. It also predicts the 850 micron fluxes of the objects for comparison with SCUBA measurements

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arXiv2000

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-$α$ and optical continuum) for the galaxy associated with the damped Lyman-$α$ (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 $9.8 \pm 2.4$ $μ$Jy in the F160W filter, implying a luminosity at $λ_{central}=5500$ Å 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-$α$ emission is seen, suggesting a low star formation rate (SFR) (3 $σ$ 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.

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arXiv1999

The H$α$ Luminosity Function and Global Star Formation Rate From Redshifts of One to Two

We present a luminosity function for H$α$ emission from galaxies at redshifts between 0.7 and 1.9 based on slitless spectroscopy with NICMOS on HST. The luminosity function is well fit by a Schechter function over the range $6 \times 10^{41} < L(Hα) < 2 \times 10^{43} erg/sec$ with $L^* = 7 \times 10^{42} erg/sec$ and $ϕ^* = 1.7 \times 10^{-3} Mpc^{-3}$ for $H_0=50 km/s Mpc^{-1}$ and $q_0=0.5$. We derive a volume averaged star formation rate at $z = 1.3 \pm 0.5$ of 0.13 M_{\odot} yr^{-1} Mpc^{-3} without correction for extinction. The SFR that we derive at $\sim 6500 Åis a factor of 3 higher than that deduced from 2800 Åcontinua. If this difference is due entirely to reddening, the extinction correction at 2800 Åis quite significant. The precise magnitude of the total extinction correction at rest-frame UV wavelengths (e.g. 2800 Åand 1500 Å) is sensitive to the relative spatial distribution of the stars, gas and dust, as well as on the extinction law. In the extreme case of a homogeneous foreground dust screen and a MW or LMC extinction law, we derive a total extinction at 2800 Åof 2.1 magnitudes, or a factor of 7 correction to the UV luminosity density. If we use the Calzetti reddening curve, which was derived for the model where stars, gas and dust are well mixed and nebular gas suffers more extinction than stars, our estimate of A$_{2800}$ is increased by more than one magnitude.

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arXiv1998

NICMOS Observations of the Hubble Deep Field: Observations, Data Reduction, and Galaxy Photometry

This paper contains a catlog of sources observed in a portion of the Hubble Deep Field by the NICMOS instrument. Methods of observation and data analysis are discussed. The catalog has two parts. The first is a listing of all sources with signal to noise ratios greater than or equal to 2.5. The second part contains sources with signal to noise ratios less than 2.5. The second part is intended for researchers who wish to know the limits to which sources may appear at a location.

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arXiv1998

Studying the Evolution of Field Galaxies Using NICMOS/HST Parallel Imaging and Grism Data

We present results from our analysis of F160W NICMOS Parallel images. These data cover $\sim$~9~sq. arcminutes and reach 3$σ$ depths of H$=$ 24.3 $-$ 25.5 in a $0.6''$ diameter aperture with integration times of 2,000 to 13,000 seconds. We derive the first deep H band galaxy counts. The slope of the counts for H$<$ 20 is 0.31, consistent with various K-band measurements from the Keck telescopes. The measured number counts vs. magnitude relation is reasonably well fitted with no-evolution models with a low $Ω$ value. The half-light radii of the galaxies declines steeply with apparent magnitude and reaches the NIC3 resoltion limit at H$=$23.5. Deep ground-based VRI imaging of one NICMOS field has revealed an extremely red galaxy with R$-$H $=$ 6 and H of 18.8. Our analyses of the grism data show that we can reach 3$σ$ flux limits of of $1\times 10^{-16}$ to $2\times10^{-17}$ ergs/sec/cm$^2$ for integration times of 2,000 to 21,000~seconds. We have detected a total of 33 emission line galaxies. The comoving number density is $\rm \sim 2\times 10^{-4} Mpc^{-3}$. The detected emission lines are probably H$_α$~6563Å. Thus, the derived star formation rates, without extinction correction, are $10 - 163 M\odot$ per year for galaxies at redshifts between 0.7 and 1.9.

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arXiv1998

The Hubble Space Telescope Quasar Absorption Line Key Project XIII. A Census of Absorption Line Systems at Low Redshift

We present a catalogue of absorption lines obtained from the analysis of the ultra-violet spectra of 66 quasars. The data were acquired with the Faint Object Spectrograph of the HST as part of the Quasar Absorption Line Survey, a Key Project for the first four cycles of HST observations. This is the third of a series of catalogues of absorption lines produced from the survey and increases the number of quasars whose higher resolution (R=1300) spectra we have published from 17 to 83. The general properties and execution of the survey are reviewed, including descriptions of the final sample of observed objects and the algorithmic processes used to construct the catalogue. The detection of a single damped Ly-a system in a path length of Delta_z=49 yields an observed number of damped systems per unit redshift of (dN/dz)_{damp}(z=0.58)=0.020 with 95% confidence boundaries of 0.001 to 0.096 systems per unit redshift. We include notes on our analysis of each of the observed quasars and the absorption systems detected in each spectrum. Some especially interesting systems include low redshift Ly-a absorbers suitable for extensive follow-up observations (in the spectra of TON28 and PG1216+069), possibly physically associated pairs of extensive metal line absorption systems (e.g., in the spectrum of PG0117+213), and systems known to be associated with galaxies (e.g., in the spectrum of 3C232).

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arXiv1998

The HST Quasar Absorption Line Key Project. XIV. The Evolution of Ly-alpha Absorption Lines in the Redshift Interval 0 to 1.5

We present an analysis of the evolution of the Ly alpha absorption lines in the redshift interval 0.0 to \sim 1.5 based upon a sample of 987 lines identified in the spectra of 63 QSOs obtained with the Faint Object Spectrograph on the Hubble Space Telescope. Fits to the number of absorbers per unit redshift dN/dz = A \times (1+z)^γyield values of γin the range 0.1 to 0.3, decidedly flatter than results from groundbased data pertaining to the redshift range z > 1.7. The combination of the space and groundbased data suggest a marked transition in the rate of evolution of the Ly alpha lines at a redshift of about 1.7. The distribution in redshift is well represented by a power law and the distribution of equivalent widths above a rest equivalent width of 0.1 Åis fit well by an exponential. The sample of Ly alpha systems which has ions from heavy elements has a much larger value of γthan a sample of lines of comparable strength without heavy elements. We argue that this is not likely due to either line misidentification or incomplete spectral coverage and suggest that it is due to rapid evolution of the very highest column density systems, rather than differences in metallicity. We also find evidence that the rate of evolution increases with increasing equivalent width. We compare our results for the variation of line density with redshift to recent numerical simulations of Ly alpha absorbers, and find fairly good agreement. Our results for the stronger Ly alpha lines in our sample are compatible with the recent analysis of the absorber--galaxy correlation by Chen et al. 1998 but for the weaker lines our results suggest that the association between absorbers and galaxies is different from that for the stronger lines.

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arXiv1996

GHRS Monitoring of the Outflowing Material in NGC 4151

We present the results of a GHRS program to monitor the absorption lines in the spectrum of the Seyfert 1 galaxy NGC 4151 caused by outflowing gas from the nucleus. Although we see subtle changes over the four year period in the GHRS spectra of the broader of the absorption features, the wavelength constancy of all the features is remarkable. The limits on the secular acceleration suggest that either (1) The absorbing clouds are well beyond the broad emission line region, or (2) The clouds are experiencing significant drag from an intercloud medium. The exception to this constancy occurred during one of the epochs of our monitoring when a broad shallow C IV trough appeared at an outflow velocity of 3750 km/s and then subsequently disappeared.

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arXiv1995

The HST Quasar Absorption Line Key Project VII. Absorption Systems at $z_{\rm abs} \leq 1.3$

We present evidence that clumps of \lya lines are physically associated with about half of the extensive metal-line systems (absorption systems with four or more observed metal-line species) found in this paper, demonstrate that all four \lylimit systems discussed here correspond to extensive metal-line absorption systems, and present an extraordinary pair of extensive metal-line absorption systems within 2000~km/s of each other at $z~=~0.95$ that are probably an early manifestation of large scale structure. These results are obtained using ultraviolet spectra, taken with the higher-resolution gratings of the Faint Object Spectrograph of the Hubble Space Telescope, for four quasars with emission-line redshifts between 1.0 and 1.3. We also determine the evolution of \lya absorption lines at redshifts less than 1.3 by combining the results for 13 smaller redshift quasars discussed in Paper I of this series with the 4 moderate redshift quasars analyzed in the present paper. For $z_{\rm abs}~\leq~1.3$, the density of \lya lines with equivalent widths greater than 0.24~Å is adequately fit by $\left(dN/dz\right) =\left(dN/dz\right)_0 \cdot(1 + z)^γ$ with $(dN/dz)_0 = 24.3 \pm 6.6$ \lya lines per unit redshift, and $γ= 0.58 \pm 0.50$ (1-$σ$ uncertainties). This rate of evolution at low redshifts is less than the evolutionary rate inferred from several different ground-based data samples that pertain to high redshifts. The observed gaseous structures at redshifts of $0.5$ to $1.0$ with velocity dispersions of $6 \times 10^2$ \kms to $1.4 \times 10^3$ \kms (or velocity spans of $1.2 \times 10^3$ \kms to $3 \times 10^3$ \kms) constitute a constraint on cosmological models of structure formation.

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