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)Comment: 44 pages, 12 figures, to appear in ApJ v591, July 10, 200

Deep H-band Galaxy Counts and Half-light Radii from HST/NICMOS Parallel Observations

We present deep galaxy counts and half-light radii from F160W ($\lambda_c=1.6\mu$) images obtained with NICMOS on HST. Nearly 9 arcmin$^2$ have been imaged with camera 3, with $3\sigma$ depths ranging from H = 24.3 to 25.5 in a 0.6$''$ diameter aperture. The slope of the counts fainter than H~$= 20$ is 0.31, and the integrated surface density to H$\leq 24.75$ is $4 \times 10^5$ galaxies per square degree. The half-light radii of the galaxies declines steeply with apparent magnitude. At H~$=24$ we are limited by both the delivered FWHM and the detection threshold of the images.Comment: 8 pages. Accepted for publication in ApJ Letter

NICMOS observations of the HDF

This paper presents initial results and performance levels from the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) observations of the Hubble Deep Field (HDF). These observations represent the deepest view of individual objects yet obtained with photometric colors of some objects indicating redshift values greater than 6. These observations add significant value to the previous optical observations of the HDF with the Wide Field and Planetary Camera II (WFPC II)

The HDF, The Arizona View

We present an initial analysis of the star formation rates in the deep NICMOS field of the Hubble Deep Field. The analysis utilizes template photometric redshift and extinction techniques on the combination of six optical and near infrared fluxes available for this region from observations with both NICMOS and WFPC2. Our results are consistent with a constant star formation rate for a redshift range of 1 to 6

Photometric Redshifts Applied to WFPC2 and NICMOS HDF Data

A photometric redshift analysis of optical and infrared images of the Northern Hubble Deep Field indicate a constant star formation rate for redshifts between 1 and 6. The small size of the field and small number of high redshift objects limits this finding to just the area of the NICMOS image. The photometric redshift technique is a modified version of chi square fits to observed and calculated galaxy spectral energy distribution templates

Star Formation History in the NICMOS Northern Hubble Deep Field

We present the results of an extensive analysis of the star formation rates determined from the NICMOS deep images of the northern Hubble Deep Field. We use SED template fitting photometric techniques to determine both the redshift and the extinction for each galaxy in our field. Measurement of the individual extinctions provides a correction for star formation hidden by dust obscuration. We determine star formation rates for each galaxy based on the 1500 Å UV flux and add the rates in redshift bins of width 1.0 centered on integer redshift values. We find a rise in the star formation rate from a redshift of 1 to 2 then a falloff from a redshift of 2 to 3. However, within the formal limits of the error bars this could also be interpreted as a constant star formation rate from a redshift of 1 to 3. The star formation rate from a redshift of 3 to 5 is roughly constant followed by a possible drop in the rate at a redshift of 6. The measured star formation rate at a redshift of 6 is approximately equal to the present day star formation rate determined in other work. The high star formation rate measured at a redshift of 2 is due to the presence of two possible ULIRGs in the field. If real, this represents a much higher density of ULIRGs than measured locally. We also develop a new method to correct for faint galaxies or faint parts of galaxies missed by our sensitivity limit, based on the assumption that the star formation intensity distribution function is independent of redshift. We measure the 1.6 μm surface brightness due to discrete sources and predict the 850 μm brightness of all of our galaxies based on the determined extinction. We find that the far-infrared fluxes predicted in this manner are consistent with the lack of detections of 850 μm sources in the deep NICMOS HDF, the measured 850 μm sky brightness due to discrete sources and the ratio of optical-UV sky brightness to far-infrared sky brightness. From this we infer that we are observing a population of sources that contributes significantly to the total star formation rate and these sources are not overwhelmed by the contribution from sources such as the extremely superluminous galaxies represented by the SCUBA detections. We have estimated the errors in the star formation rate due to a variety of sources including photometric errors, the near-degeneracy between reddening and intrinsic spectral energy distribution as well as the effects of sampling errors and large-scale structure. We have tried throughout to give as realistic and conservative an estimate of the errors in our analysis as possible

The Nature of the Small Galaxies in the Hubble Deep Field

We present results from a study of very small galaxies (isophotal area ≤ 0.2°”) with photometric redshifts 1 ≤ z ≤ 4.5 detected in the region of the northern Hubble Deep Field covered by NICMOS observations at 1.6 and 1.1 microns. We estimate that ~50 percent of these sources are star-forming galaxies at redshifts 2 < z < 3.5 and ~45 percent at are 3.5 < z < 4.5, with the remaining 5% at 1 < z < 2. We have examined averaged images of these faint (V_(606) ~ 27-29), compact objects to search for extended, surrounding flux from older, fainter populations of stars. We find no evidence that the small objects in the Hubble Deep Field are embedded in fainter, more extended galaxies. The majority are indeed isolated and compact. We estimate the 5σ depth of the averaged images to be H_(160) ≈29.8 AB magnitudes per square arcsecond

Deep H-Band Galaxy Counts and Half-Light Radii from Hubble Space Telescope/NICMOS Parallel Observations

We present deep galaxy counts and half-light radii from F160W (λ_c=1.6 μm) images obtained with the Near-Infrared Camera and Multiobject Spectrograph on the Hubble Space Telescope. Nearly 9 arcmin^2 have been imaged with camera 3, with 3 σ depths ranging from H=24.3 to 25.5 in a 0."6 diameter aperture. The slope of the counts fainter than H = 20 is 0.31, and the integrated surface density to H ≤ 24.75 is 4×10^5 galaxies deg^(-2). The half-light radii of the galaxies decline steeply with apparent magnitude. At H = 24, we are limited by both the delivered FWHM and the detection threshold of the images

The Host Galaxy of the Broad Absorption Line QSO PG 1700+518 and Its Ring Galaxy Companion: NICMOS 1.6 Micron Imaging

The 1.6 μm Near Infrared Camera and Multiobject Spectrometer image of the broad absorption line QSO PG 1700+518 clearly resolves the QSO host galaxy and a ringlike companion. The companion is most likely a ring galaxy produced in a collision with the QSO galaxy ~5×10^7 yr ago. The morphology of the PG 1700+518 system is very similar to IRAS 04505-2958 (Boyce et al. 1996). Both objects were identified in a sample of eight QSOs selected by "warm" far-IR colors and extreme IR luminosities (Low et al. 1988). All eight QSOs show signs of strong interaction, and the presence of two head-on colliding systems in this sample may suggest that small impact parameters favor the energizing of IR-luminous QSOs