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Kenneth M. Lanzetta

Publications and source records attributed to Kenneth M. Lanzetta.

At least 37 records · Page 2Linked to original sources
arXiv2001

The Gaseous Extent of Galaxies and the Origin of Lya Absorption Systems. V. Optical and Near-Infrared Photometry of Lya-absorbing Galaxies at z < 1

(Abridged) We present results of a program to obtain and analyze HST WFPC2 images and ground-based images of galaxies identified in an imaging and spectroscopic survey of faint galaxies in fields of HST spectroscopic target QSOs. We confirm and improve the results presented by Lanzetta et al. (1995) and Chen et al. (1998) that (1) extended gaseous envelopes are a common and generic feature of galaxies of a wide range of luminosity and morphological type, (2) the extent of tenuous gas (N(H I) > 10^{14} cm^{-2} around galaxies scales with galaxy B-band luminosity as r\propto L_B^{0.39+/-0.09}, and (3) galaxy interactions do not play an important role in distributing tenuous gas around galaxies in most cases. We further demonstrate that (4) the gaseous extent of galaxies scales with galaxy K-band luminosity as r\propto L_K^{0.28+/-0.08}, and (5) tenuous gas around typical L_* galaxies is likely to be distributed in spherical halos of radius ~ 180 h^{-1} kpc of covering factor of nearly unity. Because galaxies of all morphological types possess extended gaseous halos and because the extent of tenuous gas around galaxies scales with galaxy K-band luminosity, we argue that galaxy mass---rather than recent star-formation activity---is likely to be the dominant factor that determines the extent of tenuous gas around galaxies. Nevertheless, applying the scaling relationship between the extent of Lya absorbing gas around galaxies and galaxy B-band luminosity, the results of our analysis also suggest that the number density evolution of Lya absorption systems may serve to constrain the evolution of the comoving galaxy B-band luminosity density (at least for the redshift interval between z~0 and z~1 that has been studied in our survey).

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arXiv2001

The Origin of C IV Absorption Systems at Redshifts z<1---Discovery of Extended C IV Envelopes Around Galaxies

(Abridged) We report the discovery of extended CIV gaseous envelopes around galaxies of a wide range of luminosity and morphological type. First, we show that CIV absorption systems are strongly clustered around galaxies on velocity scales of v < 250 km/s and impact parameter scales of rho < 100 h^{-1} kpc but not on larger velocity or impact parameter scales. Next, adopting measurements of galaxy properties presented in previous papers, we examine how properties of the CIV absorption systems depend on properties of the galaxies. On the basis of 14 galaxy and absorber pairs and 36 galaxies that do not produce corresponding CIV absorption lines to within sensitive upper limits, we find that: (1) Galaxies of a range of morphological type and luminosity appear to possess extended CIV gaseous envelopes of radius R ~ 100 h^{-1} kpc, with abrupt boundaries between the CIV absorbing and non-absorbing regions. (2) The extent of CIV-absorbing gas around galaxies scales with galaxy B-band luminosity as R \propto L_B^{0.5 +/- 0.1} but does not depend strongly on galaxy surface brightness, redshift, or morphological type. And (3) the covering factor of CIV clouds within ~ 100 h^{-1} kpc of galaxies is nearly unity, but there is a large scatter in the mean number of clouds encountered along the line of sight. The most significant implication of the study is that galaxies of a wide range of luminosity and morphological type are surrounded by chemically enriched gas that extends for at least ~ 100 h^{-1} kpc. We consider various scenarios that may have produced metals at large galactic distance and conclude that accreting satellites are most likely to be responsible for chemically enriched gas at large galactic distances to regular looking galaxies.

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arXiv2001

On the compared accuracy and reliability of spectroscopic and photometric redshift measurements

We present a comparison between the spectroscopic catalog of the HDF recently published by Cohen et al and the redshifts measured by our group for those objects using photometric techniques. We perform this comparison in order to characterize the errors associated to the photometric redshift technique. The spectroscopic sample includes over 140 objects in the HDF proper, representing the deepest, cleanest, most complete spectroscopic catalog ever compiled. We study each object for which our redshift and the one measured by Cohen et al disagree. In most cases the photometric evidence is strong enough to call for a careful review of the spectroscopic values, as they seem to be in error. It is possible to characterize the systematic errors associated to our technique, which when combined with the photometric errors allow us to obtain complete information on the redshift of each galaxy and its associated confidence interval, regardless of apparent magnitude. One of the main conclusions of this study is that, to date, all the redshifts from our published catalog that have been checked have been shown to be correct (within the stated confidence limits). This implies that our galaxy template set is a fair representation of the galaxy population at all redshifts (0<z<6) and magnitudes (R<24) explored to date. On the other hand, spectroscopy of faint sources is subject to unknown and uncharacterized systematic errors, that will in turn be transmitted to any photometric redshift technique which uses spectroscopic samples as calibration. Our analysis proves that photometric redshift techniques can and must be used to extend the range of applicability of the spectroscopic redshift measurements. (Abridged)

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arXiv2000

The Unusual Spectral Energy Distribution of a Galaxy Previously Reported to be at Redshift 6.68

Observations of distant galaxies are important both for understanding how galaxies form and for probing the physical conditions of the universe at the earliest epochs. It is, however, extremely difficult to identify galaxies at redshift z>5, because these galaxies are faint and exhibit few spectral features. In a previous work, we presented observations that supported the identification of a galaxy at redshift z = 6.68 in a deep STIS field. Here we present new ground-based photometry of the galaxy. We find that the galaxy exhibits moderate detections of flux in the optical B and V images that are inconsistent with the expected absence of flux at wavelength shortward of the redshifted Lyman-alpha emission line of a galaxy at redshift z>5. In addition, the new broad-band imaging data not only show flux measurements of this galaxy that are incompatible with the previous STIS measurement, but also suggest a peculiar spectral energy distribution that cannot be fit with any galaxy spectral template at any redshift. We therefore conclude that the redshift identification of this galaxy remains undetermined.

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arXiv2000

On the Small-Scale Clustering of Ly-alpha Forest Clouds

Recent measurements of the autocorrelation function of the Ly-alpha clouds are analyzed from the point of view of a simple model with strong clustering on the small scales. It is shown that this toy model reproduces fairly well the important linear relation between amplitude of the absorber autocorrelation function and neutral hydrogen column density. In addition, it predicts a correct evolutionary trend of correlation amplitudes. Some possible ramifications of these results are discussed.

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arXiv2000

Photometry and Photometric Redshifts of Faint Galaxies in the Hubble Deep Field South NICMOS Field

We present a catalog of photometry and photometric redshifts of 335 faint objects in the HDF-S NICMOS field. The analysis is based on (1) infrared images obtained with the Hubble Space Telescope (HST) using the Near Infrared Camera and Multi-Object Spectrograph (NICMOS) with the F110W, F160W, and F222M filters, (2) an optical image obtained with HST using the Space Telescope Imaging Spectrograph (STIS) with no filter, and (3) optical images obtained with the European Southern Observatory (ESO) Very Large Telescope (VLT) with U, B, V, R, and I filters. The primary utility of the catalog of photometric redshifts is as a survey of faint galaxies detected in the NICMOS F160W and F222M images. The sensitivity of the survey varies significantly with position, reaching a limiting depth of AB(16,000) ~ 28.7 and covering 1.01 arcmin^2 to AB(16,000) = 27 and 1.05 arcmin^2 to AB(16,000) = 26.5. The catalog of photometric redshifts identifies 21 galaxies (or 6% of the total) of redshift z > 5, 8 galaxies (or 2% of the total) of redshift z > 10, and 11 galaxies (or 3% of the total) of best-fit spectral type E/S0, of which 5 galaxies (or 1% of the total) are of redshift z > 1.

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arXiv1999

The Origin of \lya Absorption Systems at $z>1$---Implications from the Hubble Deep Field

The Hubble Deep Field images have provided us with a unique chance to relate statistical properties of high-redshift galaxies to statistical properties of \lya absorption systems. Combining an {\em empirical} measure of the galaxy surface density versus redshift with an {\em empirical} measure of the gaseous extent of galaxies, we predict the number density of \lya absorption systems that originate in extended gaseous envelopes of galaxies versus redshift. We show that at least 50% and as much as 100% of observed \lya absorption systems of $W\apg0.32$ Åcan be explained by extended gaseous envelops of galaxies. Therefore, we conclude that known galaxies of known gaseous extent must produce a significant fraction and perhaps all of \lya absorption systems over a large redshift range.

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arXiv1999

Galaxies of Redshift z > 5: The View from Stony Brook

We report on some aspects of our efforts to establish properties of the extremely faint galaxy population by applying our photometric redshift technique to the HDF and HDF-S WFPC2 and NICMOS fields. We find that cosmological surface brightness dimming effects play a dominant role in setting what is observed at redshifts z > 2, that the comoving number density of high intrinsic surface brightness regions increases monotonically with increasing redshift, and that previous estimates neglect a significant or dominant fraction of the ultraviolet luminosity density of the universe due to surface brightness effects. The ultraviolet luminosity density of the universe plausibly increases monotonically with increasing redshift to redshifts beyond z = 5.

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arXiv1999

Photometric/Spectroscopic Redshift Identification of Faint Galaxies in STIS Slitless Spectroscopy Observations

We present a new spectrum extraction technique which employs optimal weights for the spectral extraction, deblends the overlapping spectra, determines the precise sky background, and takes into account correlations between errors correctly for STIS slitless observations. We obtained roughly 250 optimally extracted spectra in a deep STIS field as well as self-confirming redshift measurements for these objects, including a galaxy at $z=6.68$. In addition, we identified five isolated emission-line objects in the dispersed image that were not accounted for by objects detected in the direct image. Assuming that these are \lya\ emission line galaxies at high redshifts and adopting a simple $δ$-function galaxy luminosity function for these objects, we find, based on a likelihood analysis, that \lya\ emission line galaxies at $\langle z\rangle\approx 4.69$ may contribute at most 15\% of the star formation rate density measured in Lyman break galaxies at $z\approx 4$.

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arXiv1999

A Spectroscopically Identified Galaxy of Probable Redshift z = 6.68

The detection and identification of distant galaxies is a prominent goal of observational cosmology because distant galaxies are seen as they were in the distant past and hence probe early galaxy formation, due to the cosmologically significant light travel time. We have sought to identify distant galaxies in very deep spectroscopy by combining a new spectrum extraction technique with photometric and spectroscopic analysis techniques. Here we report the identification of a galaxy of redshift z = 6.68, which is the most distant object ever identified. The spectrum of the galaxy is characterized by an abrupt discontinuity at wavelength $λ\approx 9300$ Å, which we interpret as the \lya decrement (produced by intervening Hydrogen absorption), and by an emission line at wavelength $λ\approx 9334$, which we interpret as \lya. The galaxy is relatively bright, and the ultraviolet luminosity density contributed by the galaxy alone is almost ten times the value measured at $z \approx 3$.

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arXiv1998

Photometry and Photometric Redshifts of Galaxies in the Hubble Deep Field South Nicmos Field

We present an electronic catalog of infrared and optical photometry and photometric redshifts of 323 galaxies in the Hubble Deep Field South NICMOS field at http://www.ess.sunysb.edu/astro/hdfs/home.html. The analysis is based on infrared images obtained with the Hubble Space Telescope using the Near Infrared Camera and Multi-Object Spectrograph and the Space Telescope Imaging Spectrograph together with optical images obtained with the Very Large Telescope. The infrared and optical photometry is measured by means of a new quasi-optimal photometric technique that fits model spatial profiles of the galaxies determined by Pixon image reconstruction techniques to the images. In comparison with conventional methods, the new technique provides higher signal-to-noise-ratio measurements and accounts for uncertainty correlations between nearby, overlapping neighbors. The photometric redshifts are measured by means of our redshift likelihood technique, incorporating six spectrophotometric templates which, by comparison with spectroscopic redshifts of galaxies identified in the Hubble Deep Field North, are known to provide redshift measurements accurate to within an RMS relative uncertainty of (Delta z)/(1 + z) < 0.1 at all redshifts z < 6. The analysis reaches a peak H-band sensitivity threshold of AB(16000) = 28.3 and covers 1.02 acrmin^2 to AB(16000) = 27, 1.27 arcmin^2 to AB(16000) = 26, and 1.44 arcmin^2 to AB(16000) = 25. The analysis identifies galaxies at redshifts ranging from z near 0 through z greater than 10, including 17 galaxies of redshift 5 < z < 10 and five candidate galaxies of redshift z > 10.

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arXiv1998

Constraints on the Unseen Galaxy Population from the Lyman-alpha Forest

Here we describe results of our attempt to determine what types of galaxies are responsible for the Lyman-alpha forest absorption systems, based on our ongoing imaging and spectroscopic survey of faint galaxies in fields of HST spectroscopic target QSOs. Our primary conclusions are that the bulk of the Lyman-alpha forest arises in more or less normal galaxies (that span the normal range of luminosity and morphology) and that any ``unseen'' low surface brightness galaxies are unlikely to contribute significantly to the luminosity density of the universe.

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arXiv1998

Galaxies at Redshifts z > 5

Here we describe our attempts to establish statistically complete samples of very high redshift galaxies by obtaining photometric redshifts of galaxies in Medium Deep Survey (MDS) fields and photometric and spectroscopic redshifts of galaxies in very deep STIS slitless spectroscopy fields. On the basis of this analysis, we have identified galaxies of redshift z = 4.92 in an MDS field and of redshift z = 6.68 in a very deep STIS field.

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arXiv1998

Environmental Dependence of the Nature of Gaseous Envelopes of Galaxies at z < 1

We present new statistical study on the origin of Lyman-alpha absorption systems that are detected in QSO fields. The primary objective is to investigate environmental dependence of the relationship between galaxies and Lyman-alpha absorption systems. We find that galaxies exhibit no environmental dependence in giving rise to Lyman-alpha absorbers in their halos. Conversely, Lyman-alpha absorbers do not exhibit preference as to the environment where they reside.

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arXiv1998

An Empirical Limit on Extremely High Redshift Galaxies

We apply the Lyman absorption signature to search for galaxies at redshifts z \~ 6 - 17 using optical and infrared images of the Hubble Deep Field. The infrared images are sensitive to a point source 5 sigma detection threshold of AB(22,000) = 23.8, which adopting plausible assumptions to relate rest-frame ultraviolet flux densities to unobscured star formation rates is easily sufficient to detect the star formation rates expected for massive elliptical galaxy formation to quite high redshifts. For q_0 = 0.5, the infrared images are sensitive to an unobscured star formation rate of 100 h^-2 solar masses per year to redshifts as large as z = 17, and for q_0 = 0, the infrared images are sensitive to an unobscured star formation rate of 300 h^-2 solar masses per year to redshifts as large as z = 14. The primary result of the analysis is that only one extremely high redshift galaxy candidate is identified at the 5 sigma level of significance (and four at the 4 sigma level). This implies a strict upper limit to the surface density of extremely high redshift galaxies of < 1.5 arcmin^-2 to a limiting magnitude threshold AB(22,000) = 23.8. This also implies a strict upper limit to the volume density of extremely high redshift galaxies if (and only if) such galaxies are not highly obscured by dust.

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arXiv1998

A blind test of photometric redshift prediction

Results of a blind test of photometric redshift predictions against spectroscopic galaxy redshifts obtained in the Hubble Deep Field with the Keck Telescope are presented. The best photometric redshift schemes predict spectroscopic redshifts with a redshift accuracy of |Delta-z|<0.1 for more than 68 percent of sources and with |Delta-z|<0.3 for 100 percent, when single-feature spectroscopic redshifts are removed from consideration. This test shows that photometric redshift schemes work well at least when the photometric data are of high quality and when the sources are at moderate redshifts.

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