Hubble Deep Field Research Articles

The Origin of Lyα Absorption Systems at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $z> 1$ \end{document} : 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 $W\apg0.32$ \AA can 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.

3 Micron Imaging of the Hubble Deep Field

Images of the Hubble Deep Field (HDF) at 3.2 μm, taken with the 10 m Keck Telescope, are presented. The images cover a total area of ~2.5 arcmin^2. To a 5 σ limit of [3.2]_(tot) ≈ 17.5 mag (Vega relative), 11 sources are detected, nine of which are extragalactic. The integrated galaxy number counts are therefore ~1.3 × 10^4 deg^(-2) to this depth. The galaxies detected at 3.2 μm have a median redshift of z = 0.56. All 3.2 μm sources have 1.6 μm, 1.1 μm, and visual counterparts, all of fairly regular morphology; several also have 6.7 μm, 15 μm, 850 μm, 8.5 GHz, or 1.4 GHz counterparts. No sources are found that are either anomalously red or anomalously blue in their H-[3.2] color, and there are significant detections of most of the known near-infrared HDF sources for which detection in these 3.2 μm data seemed likely.

Protogalactic Starbursts at High Redshift

We have computed the evolving ultraviolet-millimeter spectral energy distribution (SED) produced by protogalactic starbursts at high redshift, incorporating the chemical evolution of the interstellar medium in a consistent manner. Dust extinction is calculated in a novel way that is not based on empirical calibrations of extinction curves, but rather on the lifetime of molecular clouds which delays the emergence of each successive generation of stars at ultraviolet wavelengths by typically 15 Myr. The predicted rest-frame far-infrared-to-millimeter-wave emission includes the calculation of molecular emission-line luminosities (12CO and O2 among other molecules) consistent with the evolving chemical abundances. Here we present details of this new model along with the results of comparing its predictions with several high-redshift observables, namely, the ultraviolet SEDs of Lyman limit galaxies, the high-redshift radio galaxies 4C 41.17 and 8C 1435, the SCUBA submillimeter survey of the Hubble Deep Field (HDF), and the SEDs of intermediate-redshift elliptical galaxies. With our new reddening method, we are able to fit the spectrum of the Lyman limit galaxy 1512-cB58, and we find an extinction of about 1.9 mag at 1600 A. This extinction applies to starbursts with spectral slope α in the range 0 α 1.5. The model also predicts that most Lyman limit galaxies should have a value of α inside that range, as is observed. The 850 μm flux density of a typical Lyman limit galaxy is expected to be only 0.5 mJy, and therefore the optical counterparts of the most luminous submillimeter sources in the HDF (or any other currently feasible submillimeter survey) are unlikely to be Lyman break galaxies. The passive evolution of our starburst model is also compared with Keck observations of the reddest known elliptical galaxy at z ~ 1.5 and with the SED of a typical nearby elliptical galaxy. The SED of the high-redshift elliptical is nicely matched by the starburst model with an age of 4 Gyr and the SED of the nearby elliptical galaxy with an age of 13 Gyr.

Hubble Space TelescopeWeak‐Lensing Study of thez=0.83 Cluster MS 1054−03

We have measured the weak gravitational lensing of faint, distant background galaxies by MS 1054-03, a rich and X-ray luminous cluster of galaxies at a redshift of z = 0.83, using a two-color mosaic of deep WFPC2 images. The small corrections for the size of the point-spread function and the high number density of background galaxies obtained in these observations result in an accurate and well-calibrated measurement of the lensing induced distortion. The strength of the lensing signal depends on the redshift distribution of the background galaxies. We used photometric redshift distributions from the northern and southern Hubble Deep Fields to relate the lensing signal to the mass. The predicted variations of the signal as a function of apparent source magnitude and color agrees well with the observed lensing signal The uncertainty in the redshift distribution results in a 10% systematic uncertainty in the mass measurement. We determine a mass of (1.2 +/- 0.2) x 10(15) h(50)(-1) M. within an aperture of radius 1 h(50)(-1) Mpc. Under the assumption of an isothermal mass distribution, the corresponding velocity dispersion is 1311(-89)(+83) km s(-1). For the mass-to-light ratio we find 269 +/- 37 h(50) M./L-B. after correcting for passband and luminosity evolution. The errors in the mass and mass-to-light ratio include the contribution from the random intrinsic ellipticities of the source galaxies, but not the (systematic) error due to the uncertainty in the redshift distribution. However, the estimates for the mass and mass-to-light ratio of MS 1054-03 agree well with other estimators, suggesting that the mass calibration works well. The reconstruction of the projected mass surface density shows a complex mass distribution, consistent with the light distribution. The results indicate that MS 1054-03 is a young system. The timescale for relaxation is estimated to be at least 1 Gyr. Ne have also studied the masses of the cluster galaxies, by averaging the tangential sheer around the cluster galaxies. Using the Faber-Jackson scaling relation, we find the velocity dispersion of an L* galaxy (L-B = 8 x 10(10) h(50)(-2) L-B. for MS 1054-03) is 203 +/- 33 km s(-1).

The Unusual Infrared Object HDF‐N J123656.3+621322

We describe an object in the Hubble Deep Field North with very unusual near-infrared properties. It is readily visible in Hubble Space Telescope NICMOS images at 1.6 ?m and from the ground at 2.2 ?m, but it is undetected (with S/N 2) in very deep WFPC2 and NICMOS data from 0.3 to 1.1 ?m. The f? flux density drops by a factor 8.3 (97.7% confidence) from 1.6 to 1.1 ?m. The object is compact but may be slightly resolved in the NICMOS 1.6 ?m image. In a low-resolution, near-infrared spectrogram, we find a possible emission line at 1.643 ?m, but a reobservation at higher spectral resolution failed to confirm the line, leaving its reality in doubt. We consider various hypotheses for the nature of this object. Its colors are unlike those of known Galactic stars, except perhaps the most extreme carbon stars or Mira variables with thick circumstellar dust shells. It does not appear to be possible to explain its spectral energy distribution as that of a normal galaxy at any redshift without additional opacity from either dust or intergalactic neutral hydrogen. The colors can be matched by those of a dusty galaxy at z 2, by a maximally old elliptical galaxy at z 3 (perhaps with some additional reddening), or by an object at z 10 whose optical and 1.1 ?m light have been suppressed by the intergalactic medium. Under the latter hypothesis, if the luminosity results from stars and not an AGN, the object would resemble a classical, unobscured protogalaxy, with a star formation rate 100 M? yr-1. Such UV-bright objects are evidently rare at 2 < z < 12.5, however, with a space density several hundred times lower than that of present-day L* galaxies.

Tests of Statistical Methods for Estimating Galaxy Luminosity Function and Applications to the Hubble Deep Field

We study statistical methods for the estimation of the luminosity function (LF) of galaxies. We focus on four nonparametric estimators: the 1/Vmax estimator, the stepwise maximum-likelihood estimator, Chołoniewski's estimator, and the improved Lynden-Bell estimator. The performance of the 1/Vmax estimator has recently been questioned, especially for the faint-end estimation of the LF. We improve these estimators for studies of the distant universe, and examine their performances for various classes of functional forms by Monte Carlo simulations. We also apply these estimation methods to the mock Two-Degree Field (2dF) redshift survey catalog prepared by Cole et al. We find that the 1/Vmax estimator yields a completely unbiased result if there is no inhomogeneity, but is not robust against clusters or voids. This is consistent with the well-known results, and we do not confirm the bias trend of 1/Vmax claimed by Willmer in the case of a homogeneous sample. We also find that the other three maximum-likelihood type estimators are quite robust and give consistent results with each other. In practice, we recommend Chołoniewski's estimator for two reasons: (1) it simultaneously provides the shape and normalization of the LF; and (2) it is the fastest among these four estimators, because of its algorithmic simplicity. We then analyze the photometric redshift data of the Hubble Deep Field prepared by Fernández-Soto et al. using the above four methods. We also derive the luminosity density, ρL, at the B and I bands. Our B-band estimation is roughly consistent with that of Sawicki, Lin, & Yee, but it is a few times lower at 2.0 < z < 3.0. The evolution of ρL(I) is found to be less prominent.

Caltech Faint Galaxy Redshift Survey. IX. Source Detection and Photometry in the Hubble Deep Field Region

Detection and photometry of sources in the U_n, G, ℛ, and K_s bands in a 9 × 9 arcmin^2 region of the sky, centered on the Hubble Deep Field, are described. The data permit construction of complete photometric catalogs to roughly U_n = 25, G = 26, ℛ = 25.5, K_s = 20 mag and significant photometric measurements somewhat fainter. The galaxy number density is 1.3 × 10^5 deg^(-2) to ℛ = 25.0 mag. Galaxy number counts have slopes d log N/dm = 0.42, 0.33, 0.27, and 0.31 in the U_n, G, ℛ, and K_s bands, consistent with previous studies and the trend that fainter galaxies are, on average, bluer. Galaxy catalogs selected in the ℛ and K_s bands are presented, containing 3607 and 488 sources in field areas of 74.8 and 59.4 arcmin^2, to ℛ = 25.5 and K_s = 20 mag.

Photometric Redshifts and Morphologies of Galaxies in the NICMOS Parallel Fields

We present positions, magnitudes, sizes and morphological classifications for 111 galaxies discovered in the Hubble Space Telescope NICMOS Camera 1 and Camera 2 parallel fields. We combine the magnitudes measured in the JHK-analog filters with those from deep ground-based images in V and/or R to measure photometric redshifts for 71 objects using Bruzual-Charlot population synthesis models. We find that these objects fall in the range z ~ 0.0 - 2.7, with a mean redshift of 0.8 and a mean luminosity of 1.6 L*. The NICMOS images reveal many of the objects to be ordered spirals and ellipticals similar to those in the local universe. However, we find a higher fraction (~ 14%) of morphologically peculiar and/or interacting galaxies than is observed among local galaxies (~ 3% - 4%). This is consistent with the results from other deep HST images including the Hubble Deep Field and Hubble Medium Deep Survey Field that the fraction of peculiar and interacting galaxies increases with redshift. As the NICMOS images of the sample galaxies cover their rest-frame near infrared and optical emission, this result increases confidence that such changes in morphology are genuine, as opposed to an effect produced by viewing galaxies in the rest-frame ultraviolet. We also find that at least 26 of the sample galaxies appear to be members of (non-interacting) pairs or groups, based on their proximity to one another and photometric redshifts. This is consistent with the results of recent ground-based optical surveys covering larger areas, and with the detection of galaxy groups and filaments at redshifts higher than those covered by our sample.

Deep galaxy counts, extragalactic background light and the stellar baryon budget

We assess the constraints imposed by the observed extragalactic background light (EBL) on the cosmic history of star formation and the stellar-mass density today. The logarithmic slope of the galaxy number–magnitude relation from the Southern Hubble Deep Field imaging survey is flatter than 0.4 in all seven UBVIJHK optical bandpasses, i.e. the light from resolved galaxies has converged from the UV to the near-IR. We find a lower limit to the surface brightness of the optical extragalactic sky of about 15 nW m−2 sr−1, comparable to the intensity of the far-IR background from COBE data. Assuming a Salpeter initial mass function with a lower cut-off consistent with observations of M subdwarf disc stars, we set a lower limit of Ωg+sh2>0.0013 I50 to the visible (processed gas + stars) mass density required to generate an EBL at a level of 50 I50 nW m−2 sr−1; our ‘best-guess’ value is Ωg+sh2≈0.0031 I50. Motivated by the recent microlensing results of the MACHO collaboration, we consider the possibility that massive dark haloes around spiral galaxies are composed of faint white dwarfs, and show that only a small fraction (≲5 per cent) of the nucleosynthetic baryons can be locked in the remnants of intermediate-mass stars forming at zF≲5, as the bright early phases of such haloes would otherwise overproduce the observed EBL.

Comparing the Evolution of the Galaxy Disk Sizes with Cold Dark Matter Models: The Hubble Deep Field.

The intrinsic sizes of the field galaxies with I</=26 in the Hubble and ESO New Technology Telescope (NTT) Deep Fields are shown as a function of their redshifts and absolute magnitudes using photometric redshifts derived from the multicolor catalogs and are compared with the cold dark matter (CDM) predictions. Extending to the lower luminosities and to the higher z that our previous analysis performed on the NTT field alone, we find the distribution of the galaxy disk sizes at different cosmic epochs is within the range predicted by typical CDM models. However, the observed size distribution of faint (MB>-19) galaxies is skewed with respect to the CDM predictions, and an excess of small-size disks (Rd<2 kpc) is already present at z approximately 0.5. The excess persists up to z approximately 3 and involves brighter galaxies. Such an excess may be reduced if luminosity-dependent effects, like starburst activity in interacting galaxies, are included in the physical mechanisms governing the star formation history in CDM models.

Young Red Spheroidal Galaxies in the Hubble Deep Fields: Evidence for a Truncated Initial Mass Function at approximately 2 M middle dot in circle and a Constant Space Density to z approximately 2.

The optical-IR images of the northern and southern Hubble Deep Fields are used to measure the spectral and density evolution of early-type galaxies. The mean spectral energy distribution is found to evolve passively toward a mid-F star-dominated spectrum by z approximately 2, becoming more sharply peaked around the 4000 Å break. We demonstrate with realistic simulations that hotter elliptical galaxies would be readily visible if evolution progressed blueward and brightward at z>2, following a standard initial mass function (IMF). The color distributions are best fitted by a "red" IMF, deficient above approximately 2 M middle dot in circle and with a spread of formation in the range 1.5<zf<2.5. Traditional age dating is spurious in this context; a distant elliptical can be young but appear red, with an apparent age greater than 3 Gyr independent of its formation redshift. Regarding density evolution, we demonstrate that the sharp decline in numbers claimed at z>1 results from a selection bias against distant red galaxies in the optical, where the flux is too weak for morphological classification, but is remedied with relatively modest IR exposures that reveal a roughly constant space density to z approximately 2, with 32 and 16 elliptical galaxies detected above and below z=1, respectively. We point out that the lack of high-mass star formation inferred here and the requirement of metals implicates cooling flows of preenriched gas in the creation of the stellar content of spheroidal galaxies. Deep-field X-ray images will be very helpful in examining this possibility.

Near-Infrared Emission-Line Galaxies in the Hubble Deep Field North

We present the 2.12 μm narrow-band image of the Hubble Deep Field North taken with the near-infrared camera (CISCO) on the Subaru telescope. Among five targets whose Hα or [OIII] emission lines are redshifted into our narrow-band range expected from their spectroscopic redshift, four of them have strong emission lines, especially for the two [OIII] emission-line objects. The remaining one target shows no Hα emission in spite of its bright rest-UV luminosity, indicating that this object is already under the post-starburst phase. The volume-averaged SFR derived from the detected two Hα emission is roughly consistent with that evaluated from the rest-UV continuum.

The Hubble Deep Field South: STIS Imaging

We present the imaging observations made with the Space Telescope Imaging Spectrograph (STIS) of the Hubble Deep Field South. The field was imaged in four bandpasses: a clear CCD bandpass for 156 ks, a long-pass filter for 22–25 ks pixel-1 typical exposure, a near-UV bandpass for 23 ks, and a far-UV bandpass for 52 ks. The clear, visible image is the deepest observation ever made in the UV-optical wavelength region, reaching a 10 σ AB magnitude of 29.4 for an object of area 0.2 arcsec2. The field contains QSO J2233-606, the target of the STIS spectroscopy, and extends 50'' × 50'' for the visible images, and 25'' × 25'' for the ultraviolet images. We present the images, catalog of objects, and galaxy counts obtained in the field.

Mapping the Evolution of High-Redshift Dusty Galaxies with Submillimeter Observations of a Radio-selected Sample

Direct submillimeter imaging has recently revealed the 850 μm background to be mostly composed of a population of distant ultraluminous infrared galaxies, but identifying the optical/near-infrared (NIR) counterparts to these sources has proved difficult because of the poor submillimeter spatial resolution. However, the proportionality of both centimeter and submillimeter data to the star formation rate suggests that high-resolution radio continuum maps with subarcsecond positional accuracy can be exploited to locate submillimeter sources. In this paper we present results from a targeted SCUBA survey of microjansky radio sources in the flanking fields of the Hubble Deep Field. The sources were selected from the uniform (8 μJy at 1 σ) 1.4 GHz VLA image of Richards. Even with relatively shallow SCUBA observations (a 3 σ detection limit of 6 mJy at 850 μm), we were successful at making submillimeter detections of optical/NIR-faint (I 24 and K 21–22) radio sources, and our counts closely match the bright counts from submillimeter surveys. An important corollary is that a large fraction of the bright (>6 mJy) submillimeter sources in untargeted submillimeter surveys have extremely faint optical/NIR counterparts and hence are inaccessible to optical imaging and spectroscopy. However, redshift estimates can be made from the ratio of the submillimeter flux to the radio flux across the 100 GHz break in the spectral energy distribution. This procedure, which we refer to as millimetric redshift estimation, places the bright submillimeter population at z = 1–3, where it forms the high-redshift tail of the faint radio population. The star formation rate density (SFRD) due to ultraluminous infrared galaxies increases by more than 2 orders of magnitude from z ~ 0 to z ~ 1–3. The SFRD at high-redshift inferred from our >6 mJy submillimeter observations is comparable with that observed in the ultraviolet/optical.

Reconstructing Galaxy Spectral Energy Distributions from Broadband Photometry

We present a novel approach to photometric redshifts, one that merges the advantages of both the template-fitting and empirical-fitting algorithms without any of their disadvantages. This technique derives a set of templates describing the spectral energy distributions of galaxies from a catalog with both multicolor photometry and spectroscopic redshifts. The algorithm is essentially using the shapes of the templates as the fitting parameters. From simulated multicolor data we show that for a small training set of galaxies we can reconstruct robustly the underlying spectral energy distributions even in the presence of substantial errors in the photometric observations. We apply these techniques to the multicolor and spectroscopic observations of the Hubble Deep Field, building a set of template spectra that reproduced the observed galaxy colors to better than 10%. Finally, we demonstrate that these improved spectral energy distributions lead to a photometric redshift relation for the Hubble Deep Field that is more accurate than standard template-based approaches.

A search for nearby counterparts to the moving objects in the Hubble Deep Field

Ibata et al. have recently discovered very faint, moving objects in the Hubble Deep Field (HDF). The number, apparent magnitudes and proper motions of these objects are consistent with old white dwarfs making up part of the Galactic dark halo. We review a number of ground-based proper motion surveys in which nearby dark-halo white dwarfs might be present, if they have the colours and absolute magnitudes proposed. No such objects have been found, whereas we argue here that several times more would be expected than in the HDF. We conclude that it is unlikely that hydrogen-atmosphere white dwarfs make up a significant fraction of the Galactic dark matter. No limits can be placed as yet on helium-atmosphere dwarfs from optical searches.

NICMOS Imaging of the Dusty Microjansky Radio Source VLA J123642+621331 at z = 4.424.

We present the discovery of a radio galaxy at a likely redshift of z=4.424 in one of the flanking fields of the Hubble Deep Field (HDF). Radio observations with the Very Large Array and MERLIN centered on the HDF yielded a complete sample of microjansky radio sources, of which about 20% have no optical counterpart to I</=25 mag. In this Letter, we address the possible nature of one of these sources through deep Hubble Space Telescope near-infrared camera and multiobject spectrometer (NICMOS) images in the F110W (J110) and F160W (H160) filters. VLA J123642+621331 has a single emission line at 6595 Å, which we identify with Lyalpha at z=4.424. We argue that this faint (H160=23.9 mag), compact (re approximately 0&farcs;2), red (I814-K=2.0) object is most likely a dusty, star-forming galaxy with an embedded active nucleus.

The Contribution of Normal, Dim, and Dwarf Galaxies to the Local Luminosity Density.

From the Hubble Deep Field catalog recently presented by Driver et al., we derive the local (0.3<z<0.5) bivariate brightness distribution of field galaxies within a 326 Mpc3 volume-limited sample. The sample contains 47 galaxies which uniformly sample the underlying galaxy population within the specified redshift, magnitude, and surface brightness limits (0.3<z<0.5, -21.3<MB<-13.7 mag, 18.0<µB<24.55 mag arcsec-2). We conclude that (1) a luminosity-surface brightness relation exists for both the field and cluster galaxy populations, MB approximately &sqbl0;&parl0;1.5+/-0.2&parr0;µe-&parl0;50+/-2&parr0;&sqbr0;, (2) luminous low surface brightness galaxies account for less than 10% of the L* population, and (3) low-luminosity low surface brightness galaxies outnumber Hubble types by a factor of approximately 1.4; however, their space density is not sufficient to explain the faint blue excess either by themselves or as faded remnants. In terms of the local luminosity density and galaxy dynamical mass budget, normal galaxies (i.e., the Hubble tuning fork) contribute 88% and 72%, respectively. This compares to 7% and 12% for dim galaxies and 5% and 16% for dwarf galaxies (within the above specified limits).

Optically Faint Microjansky Radio Sources.

We report on the identifications of radio sources from our survey of the Hubble Deep Field (HDF) and the Small Selected Area 13 fields, both of which comprise the deepest radio surveys to date at 1.4 and 8.5 GHz, respectively. About 80% of the microjansky radio sources are associated with moderate-redshift starburst galaxies or active galactic nuclei within the I-magnitude range of 17-24 with a median of I=22 mag. Thirty-one (20%) of the radio sources are (1) fainter than I>25 mag, with two objects in the HDF IAB>28.5, (2) often identified with very red objects I-K>4, and (3) not significantly different in radio properties than the brighter objects. We suggest that most of these objects are associated with heavily obscured starburst galaxies with redshifts between 1 and 3. However, other mechanisms are discussed and cannot be ruled out with the present observations.

Quasars as Absorption Probes of the Hubble Deep Field

We present a catalog of 30 QSOs and their spectra, in the square degree of sky centered on the northern Hubble Deep Field. These QSOs were selected by multicolor photometry and subsequently confirmed with spectroscopy. They range in magnitude from 17.6 < B < 21.0 and in redshift from 0.44 < z < 2.98. We also include in the catalog an AGN with redshift z=0.135. Together, these objects comprise a new grid of absorption probes which can be used to study the correlation between luminous galaxies, non-luminous halos and Lyman-alpha absorbers along the line of sight toward the Hubble Deep Field.