Hubble Deep Field Galaxies Research Articles

Galaxy Number Counts in the Hubble Deep Field as a Strong Constraint on a Hierarchical Galaxy Formation Model

Number counts of galaxies are reanalyzed using a semianalytic model (SAM) of galaxy formation based on the hierarchical clustering scenario. We have determined the astrophysical parameters in the SAM that reproduce observations of nearby galaxies and used them to predict the number counts and redshifts of faint galaxies for three cosmological models: (1) the standard cold dark matter (CDM) universe, (2) a low-density flat universe with nonzero cosmological constant, and (3) a low-density open universe with zero cosmological constant. The novelty of our SAM analysis is the inclusion of selection effects arising from the cosmological dimming of the surface brightness of high-redshift galaxies and also from the absorption of visible light by internal dust and intergalactic H I clouds. Contrary to previous SAM analyses that do not take into account such selection effects, we find from comparison with observed counts and redshifts of faint galaxies in the Hubble Deep Field (HDF) that the standard CDM universe is not preferred, and a low-density universe either with or without a cosmological constant is favorable, as suggested by other recent studies. Moreover, we find that a simple prescription for the timescale of star formation (SF), being proportional to the dynamical timescale of the formation of the galactic disk, is unable to reproduce the observed number-redshift relation for HDF galaxies, and that the SF timescale should be nearly independent of redshift, as suggested by other SAM analyses for the formation of quasars and the evolution of damped Lyα systems.

Topology of the Galaxy Distribution in the Hubble Deep Fields

We have studied topology of the distribution of the high redshift galaxies identified in the Hubble Deep Field (HDF) North and South. The two-dimensional genus is measured from the projected distributions of the HDF galaxies at angular scales from $3.8''$ to $ 6.1''$. We have also divided the samples into three redshift slices with roughly equal number of galaxies using photometric redshifts to see possible evolutionary effects on the topology. The genus curve of the HDF North clearly indicates clustering of galaxies over the Poisson distribution while the clustering is somewhat weaker in the HDF South. This clustering is mainly due to the nearer galaxies in the samples. We have also found that the genus curve of galaxies in the HDF is consistent with the Gaussian random phase distribution with no significant redshift dependence.

Galaxy Structural Parameters: Star Formation Rate and Evolution with Redshift

The evolution of the structure of galaxies as a function of redshift is investigated using two parameters: the metric radius of the galaxy (Rη) and the power at high spatial frequencies in the disk of the galaxy (χ). A direct comparison is made between nearby (z~0) and distant (0.2 z 1) galaxies by following a fixed range in rest frame wavelengths. The data of the nearby galaxies comprise 136 broadband images at ~4500 A observed with the 0.9 m telescope at Kitt Peak National Observatory (23 galaxies) and selected from the catalog of digital images of Frei et al. (113 galaxies). The high-redshift sample comprises 94 galaxies selected from the Hubble Deep Field (HDF) observations with the Hubble Space Telescope using the Wide Field Planetary Camera 2 in four broad bands that range between ~3000 and ~9000 A (Williams et al.). The radius is measured from the intensity profile of the galaxy using the formulation of Petrosian, and it is argued to be a metric radius that should not depend very strongly on the angular resolution and limiting surface brightness level of the imaging data. It is found that the metric radii of nearby and distant galaxies are comparable to each other. The median value of the radius of the local sample is Rη ~ 5±1 kpc, and the median radius of the HDF sample is Rη ~ 6±2 kpc for q0 = 0.5, H0 = 65 km s-1 Mpc-1; however, for q0 = 0.1, Rη ~ 7 kpc and for q0 = 1, Rη ~ 5 kpc. In the HDF, galaxies with redshifts larger than z > 0.6 have flatter Rη distributions than galaxies with redshifts smaller than z ≤ 0.6. However, the median Rη values of high- and low-redshift galaxies are consistent with each other. This result is consistent with the simulations of galaxy images at redshifts z = 0.35, z = 0.5, and z = 0.9, which show that the metric sizes can be recovered within ±2 kpc. The flocculency or power at high spatial frequencies is quantified using a simple method that is based on surface photometry in one band and that depends on the size of the star-forming regions and on the intensity profile of the galaxy. In nearby galaxies, the flocculency is found to trace the star formation rate as χ is correlated with optical colors (B-V) and the strength of the hydrogen recombination lines (Hα). In the HDF, galaxies at redshifts smaller than z~1 and with fluxes brighter than B = 25 have values of χ similar to what is measured in nearby galaxies and to what is expected from simulations of distant galaxy images. Among the HDF galaxies, I find that at most 4% can be identified as dwarf galaxies with rates of star formation similar to NGC 4449 and NGC 1569. Most HDF galaxies are giants with star formation rates similar to those in nearby giant galaxies. In summary, in this study I have introduced a method to measure the metric sizes and flocculency of the two-dimensional light distribution of galaxies. As a result, I find that the high spatial frequency power is related to the star formation rate. Further, I find that the sizes and power at high spatial frequencies of HDF galaxies remain largely unchanged between the present epoch and redshifts lower than z~1.

Galaxy Structural Parameters: Star Formation Rate and Evolution with Redshift

The evolution of the structure of galaxies as a function of redshift is investigated using two parameters: the metric radius of the galaxy (Rη) and the power at high spatial frequencies in the disk of the galaxy (χ). A direct comparison is made between nearby (z~0) and distant (0.2 z 1) galaxies by following a fixed range in rest frame wavelengths. The data of the nearby galaxies comprise 136 broadband images at ~4500 A observed with the 0.9 m telescope at Kitt Peak National Observatory (23 galaxies) and selected from the catalog of digital images of Frei et al. (113 galaxies). The high-redshift sample comprises 94 galaxies selected from the Hubble Deep Field (HDF) observations with the Hubble Space Telescope using the Wide Field Planetary Camera 2 in four broad bands that range between ~3000 and ~9000 A (Williams et al.). The radius is measured from the intensity profile of the galaxy using the formulation of Petrosian, and it is argued to be a metric radius that should not depend very strongly on the angular resolution and limiting surface brightness level of the imaging data. It is found that the metric radii of nearby and distant galaxies are comparable to each other. The median value of the radius of the local sample is Rη ~ 5±1 kpc, and the median radius of the HDF sample is Rη ~ 6±2 kpc for q0 = 0.5, H0 = 65 km s-1 Mpc-1; however, for q0 = 0.1, Rη ~ 7 kpc and for q0 = 1, Rη ~ 5 kpc. In the HDF, galaxies with redshifts larger than z > 0.6 have flatter Rη distributions than galaxies with redshifts smaller than z ≤ 0.6. However, the median Rη values of high- and low-redshift galaxies are consistent with each other. This result is consistent with the simulations of galaxy images at redshifts z = 0.35, z = 0.5, and z = 0.9, which show that the metric sizes can be recovered within ±2 kpc. The flocculency or power at high spatial frequencies is quantified using a simple method that is based on surface photometry in one band and that depends on the size of the star-forming regions and on the intensity profile of the galaxy. In nearby galaxies, the flocculency is found to trace the star formation rate as χ is correlated with optical colors (B-V) and the strength of the hydrogen recombination lines (Hα). In the HDF, galaxies at redshifts smaller than z~1 and with fluxes brighter than B = 25 have values of χ similar to what is measured in nearby galaxies and to what is expected from simulations of distant galaxy images. Among the HDF galaxies, I find that at most 4% can be identified as dwarf galaxies with rates of star formation similar to NGC 4449 and NGC 1569. Most HDF galaxies are giants with star formation rates similar to those in nearby giant galaxies. In summary, in this study I have introduced a method to measure the metric sizes and flocculency of the two-dimensional light distribution of galaxies. As a result, I find that the high spatial frequency power is related to the star formation rate. Further, I find that the sizes and power at high spatial frequencies of HDF galaxies remain largely unchanged between the present epoch and redshifts lower than z~1.

Quantitative Morphology of Galaxies in the Hubble Deep Field

We measure quantitative structural parameters of galaxies in the Hubble Deep Field (HDF) on the drizzled F814W images. Our structural parameters are based on a two-component surface brightness made up of a S\'ersic profile and an exponential profile. We compare our results to the visual classification of van den Bergh et al. (1996) and the $C-A$ classification of Abraham et al. (1996a). Our morphological analysis of the galaxies in the HDF indicates that the spheroidal galaxies, defined here as galaxies with a dominant bulge profile, make up for only a small fraction, namely 8% of the galaxy population down to m$_{F814W}(AB)$ = 26.0. We show that the larger fraction of early-type systems in the van den Bergh sample is primarily due to the difference in classification of 40% of small round galaxies with half-light radii 2$) from this sample are disk-dominated. Our analysis reveals a subset of HDF galaxies which have profiles flatter than a pure exponential profile.

A Catalog of Color-based Redshift Estimates for [ITAL][CLC]z[/CLC][/ITAL] ≲ 4 Galaxies in the Hubble Deep Field

We derive simple empirical color-redshift relations for $z\la 4$ galaxies in the Hubble Deep Field (HDF) using a linear function of three photometric colors ($U-B$, $B-V$, $V-I$). The dispersion between the estimated redshifts and the spectroscopically observed ones is small for relations derived in several separate color regimes; the dispersions range from $\sigma_z\simeq 0.03$ to 0.1 for $z\la 2$ galaxies, and from $\sigma_z\simeq 0.14$ to 0.25 for $z\ga 2 $ galaxies. We apply the color-redshift relations to the HDF photometric catalog and obtain estimated redshifts that are consistent with those derived from spectral template fitting methods. The advantage of these color-redshift relations is that they are simple and easy to use and do not depend on the assumption of any particular spectral templates; they provide model independent redshift estimates for $z\la 4$ galaxies using only multi-band photometry, and they apply to about 90% of all galaxies. We provide a color-based estimated redshift catalog of HDF galaxies to $z\la 4$. We use the estimated redshifts to investigate the redshift distribution of galaxies in the HDF; we find peaks in the redshift distribution that suggest large-scale clustering of galaxies to at least $z\sim 1$ and that are consistent with those identified in spectroscopic probes of the HDF.

Cloning Hubble Deep Fields. I. A Model‐independent Measurement of Galaxy Evolution

We present a model-independent method of quantifying galaxy evolution in high- resolution images, which we apply to the Hubble Deep Field (HDF). Our procedure is to k-correct the pixels belonging to the images of a complete set of bright galaxies and then to replicate each galaxy image to higher redshift by the product of its space density, 1/V_{max}, and the cosmological volume. The set of bright galaxies is itself selected from the HDF because presently the HDF provides the highest quality UV images of a redshift-complete sample of galaxies (31 galaxies with I<21.9, \bar{z}=0.5, and for which V/V_{max} is spread fairly). These galaxies are bright enough to permit accurate pixel-by-pixel k-corrections into the restframe UV (\sim 2000 A). We match the shot noise, spatial sampling and PSF smoothing of the HDF, resulting in entirely empirical and parameter free ``no-evolution'' deep fields of galaxies for direct comparison with the HDF. We obtain the following results. Faint HDF galaxies (I>24) are much smaller, more numerous, and less regular than our ``no-evolution'' extrapolation, for any relevant geometry. A higher proportion of HDF galaxies ``dropout'' in both U and B, indicating that some galaxies were brighter at higher redshifts than our ``cloned'' z\sim0.5 population. By simple image transformations we demonstrate that bolometric luminosity evolution generates galaxies which are too large and the contribution of any evolving dwarf population is uninterestingly small. A plausible fit is provided by `mass-conserving' density-evolution, consistent with hierarchical growth of small-scale structure. Finally, we show the potential for improvement using the Advanced Camera, with its superior UV and optical performance.

The Evolution of the Global Star Formation History as Measured from the Hubble Deep Field

The Hubble Deep Field (HDF) is the deepest set of multicolor optical photometric observations ever undertaken, and it offers a valuable data set with which to study galaxy evolution. Combining the optical WFPC2 data with ground-based near-infrared photometry, we derive photometrically estimated redshifts for HDF galaxies with J 2, and they bridge the redshift gap between those two samples. The overall star formation or metal enrichment rate history is consistent with the theoretical models of White and Frenk and the predictions of Pei and Fall based on the evolving H I content of Lyα QSO absorption line systems.

Observations of the Hubble Deep Field with the Infrared Space Observatory - IV. Association of sources with Hubble Deep Field galaxies

We discuss the identification of sources detected by ISO at 6.7 and 15 micron in the Hubble Deep Field (HDF) region. We conservatively associate ISO sources with objects in existing optical and near-infrared HDF catalogues using the likelihood ratio method, confirming these results (and, in one case, clarifying them) with independent visual searches. We find fifteen ISO sources to be reliably associated with bright [I(AB) < 23] galaxies in the HDF, and one with an I(AB)=19.9 star, while a further eleven are associated with objects in the Hubble Flanking Fields (ten galaxies and one star). Amongst optically bright HDF galaxies, ISO tends to detect luminous, star-forming galaxies at fairly high redshift and with disturbed morphologies, in preference to nearby ellipticals.