Rodger I. Thompson

NICMOS Imaging of Infrared-Luminous Galaxies

We present near-infrared images obtained with the Hubble Space Telescope NICMOS camera for a sample of nine luminous [LIGs: LIR(8?1000 ?m) ? 1011 L?] and 15 ultraluminous (ULIGS: LIR ? 1012 L?) infrared galaxies. The sample includes representative systems classified as warm (f25 ?m/f60 ?m > 0.2) and cold (f25 ?m/f60 ?m ? 0.2) based on the mid-infrared colors and systems with nuclear emission lines classified as H II (i.e., starburst), QSO, Seyfert, and LINER. The morphologies of the sample galaxies are diverse and provide further support for the idea that they are created by the collision or interactions of spiral galaxies. Although no new nuclei are seen in the NICMOS images, the NICMOS images do reveal new spiral structures, bridges, and circumnuclear star clusters. The colors and the luminosities of the observed clusters are consistent with them being young (107?108 yr), formed as a result of galactic interactions, and having masses much greater than those of Galactic globular clusters. In NGC 6090 and VV 114, they are preferentially situated along the area of overlap of the two galactic disks. With the exception of IR 17208-0018, all of the ULIGs have at least one compact (2.2??m FWHM ? 200 pc) nucleus. Analysis of the near-infrared colors (i.e., m1.1?1.6 vs. m1.6?2.2) derived from 11 diameter apertures suggests that the warm galaxies have near-infrared colors consistent with QSO+hot dust emission and the cold galaxies, as a group, have near-infrared colors consistent with reddened starlight. In addition, the cold ULIG UGC 5101 (and possibly three others) have near-infrared colors suggesting additional active galactic nucleus?like near-infrared components in their nuclei. In a 2 kpc diameter aperture measurement, the global colors of all of the cold galaxies except UGC 5101 are consistent with starlight with a few magnitudes of visual extinction. The general dichotomy of the near-infrared properties of the warm and the cold galaxies are further supported by the light distributions: seven of the eight warm galaxies have unresolved nuclear emission that contributes significantly (i.e., ?30%?40%) to the total near-infrared luminosity. The smooth, more extended light observed in all of the galaxies is most likely composed of giant and supergiant stars, but evidence at longer wavelengths suggests that these stars contribute little to the high 8?1000 ?m luminosity of these galaxies. Finally, light profiles of nine of the 24 systems were fitted well by an r1/4 law (and not so well by an exponential disk profile). Whether these star systems eventually become massive central bulges or giant elliptical galaxies will depend on how efficiently the present ISM is converted into stars.

Measuring Distances and Probing the Unresolved Stellar Populations of Galaxies Using Infrared Surface Brightness Fluctuations

To empirically calibrate the IR surface brightness fluctuation (SBF) distance scale and probe the properties of unresolved stellar populations, we measured fluctuations in 65 galaxies using NICMOS on the Hubble Space Telescope. The early-type galaxies in this sample include elliptical and S0 galaxies and spiral bulges in a variety of environments. Absolute fluctuation magnitudes in the F160W (1.6 ?m) filter (F160W) were derived for each galaxy using previously measured I-band SBF and Cepheid variable star distances. F160W SBFs can be used to measure distances to early-type galaxies with a relative accuracy of ~10%, provided that the galaxy color is known to ~0.035 mag or better. Near-IR fluctuations can also reveal the properties of the most luminous stellar populations in galaxies. Comparison of F160W fluctuation magnitudes and optical colors to stellar population model predictions suggests that bluer elliptical and S0 galaxies have significantly younger populations than redder ones and may also be more metal-rich. There are no galaxies in this sample with fluctuation magnitudes consistent with old, metal-poor (t > 5 Gyr, [Fe/H] < -0.7) stellar population models. Composite stellar population models imply that bright fluctuations in the bluer galaxies may be the result of an episode of recent star formation in a fraction of the total mass of a galaxy. Age estimates from the F160W fluctuation magnitudes are consistent with those measured using the H? Balmer-line index. The two types of measurements make use of completely different techniques and are sensitive to stars in different evolutionary phases. Both techniques reveal the presence of intermediate-age stars in the early-type galaxies of this sample.

NICMOS imaging of the HR 4796A circumstellar disk

We report the first near-infrared (NIR) imaging of a circumstellar annular disk around the young (~8 Myr), Vega-like star HR 4796A. NICMOS coronagraph observations at 1.1 and 1.6 μm reveal a ringlike symmetrical structure that peaks in reflected intensity 105±002 (~70 AU) from the central A0 V star. The ring geometry, with an inclination of 731±12 and a major axis position angle of 268±06, is in good agreement with recent 12.5 and 20.8 μm observations of a truncated disk. The ring is resolved with a characteristic width of less than 026 (17 AU) and appears abruptly truncated at both the inner and outer edges. The region of the disk-plane inward of ~60 AU appears to be relatively free of scattering material. The integrated flux density of the part of the disk that is visible (greater than 065 from the star) is found to be 7.6±0.5 and 7.4±1.2 mJy at 1.1 and 1.6 μm, respectively. Correcting for the unseen area of the ring yields total flux densities of 12.8±1.0 and 12.5±2.0 mJy, respectively (Vega magnitudes equal to 12.92±0.08 and 12.35±0.18). The NIR luminosity ratio is evaluated from these results and ground-based photometry of the star. At these wavelengths, L(λ)/L(λ) is equal to 1.4±0.2×10 and 2.4±0.5×10, giving reasonable agreement between the stellar flux scattered in the NIR and that which is absorbed in the visible and reradiated in the thermal infrared. The somewhat red reflectance of the disk at these wavelengths implies a mean particle size in excess of several microns, which is larger than typical interstellar grains. The confinement of material to a relatively narrow annular zone implies dynamical constraints on the disk particles by one or more as yet unseen bodies.

INITIAL ON-ORBIT PERFORMANCE OF NICMOS

On 1997 February 13, Space Shuttle astronauts placed the Near-Infrared Camera and Multiobject Spectrometer (NICMOS) into the Hubble Space Telescope. Following installation, the servicing mission orbital verification program (SMOV) performed extensive testing of the instrument to verify that it can be operated and calibrated effectively. This program is essentially completed, and routine science observations have begun in most of the NICMOS modes of operation. This Letter describes the performance levels of NICMOS at this time.

Near-Infrared Camera and Multi-Object Spectrometer Observations of the Hubble Deep Field: Observations, Data Reduction, and Galaxy Photometry

This paper presents data obtained during the NICMOS Guaranteed Time Observations of a portion of the Hubble Deep Field. The data are in a catalog format similar to the publication of the original WFPC2 Hubble Deep Field program (Williams et al.). The catalog contains 342 objects in a 49farcs1 × 48farcs4 subfield of the total observed field, 235 of which are considered coincident with objects in the WFPC2 catalog. The 3 σ signal-to-noise ratio level is at an aperture AB magnitude of approximately 28.8 at 1.6 μm. The catalog sources, listed in order of right ascension, are selected to satisfy a limiting signal-to-noise ratio criterion of greater than or equal to 2.5. This introduces a few false detections into the catalog, and users should take careful note of the completeness and reliability levels for the catalog discussed in §§ 9 and 10. The catalog also contains a test parameter indicating the results of half-catalog tests and the degree of coincidence with the original WFPC2 catalog.

Star formation at z ∼ 6: The hubble ultra deep parallel fields

We report on the i-dropouts detected in two exceptionally deep Advanced Camera for Surveys fields (B435, V606, i775, and z850 with 10 σ limits of 28.8, 29.0, 28.5, and 27.8, respectively) taken in parallel with the Ultra Deep Field Near-Infrared Camera and Multi-Object Spectrometer observations. Using an i-z > 1.4 cut, we find 30 i-dropouts over 21 arcmin2 down to z850, AB = 28.1, or 1.4 i-dropouts arcmin-2, with significant field-to-field variation (as expected from cosmic variance). This extends i-dropout searches some ~0.9 mag further down the luminosity function than was possible in the Great Observatories Origins Deep Survey (GOODS) fields, yielding a ~7 times increase in surface density. An estimate of the size evolution for UV-bright objects is obtained by comparing the composite radial flux profile of the bright i-dropouts (z850, AB < 27.2) with scaled versions of the Hubble Deep Field-North and -South U-dropouts. The best fit is found with a (1 + z) scaling in size (for fixed luminosity), extending lower redshift (1 < z < 5) trends to z ~ 6. Adopting this scaling and the brighter i-dropouts from both GOODS fields, we make incompleteness estimates and construct a z ~ 6 luminosity function (LF) in the rest-frame continuum UV (~1350 A) over a 3.5 mag baseline, finding a shape consistent with that found at lower redshift. To evaluate the evolution in the LF from z ~ 3.8, we make comparisons against different scalings of a lower redshift B-dropout sample. Although a strong degeneracy is found between luminosity and density evolution, our best-fit model scales as (1 + z)-2.8 in number and (1 + z)0.1 in luminosity, suggesting a rest-frame continuum UV luminosity density at z ~ 6 that is just 0.38 times that at z ~ 3.8. Our inclusion of the size evolution makes the present estimate lower than previous z ~ 6 estimates.We report on the i-dropouts detected in two exceptionally deep ACS fields (B435, V606, i775, and z850 with 10σ limits of 28.8, 29.0, 28.5, and 27.8, respectively) taken in parallel with the UDF NICMOS observations. Using an i − z > 1.4 cut, we find 30 i-dropouts over 21 arcmin down to z850,AB = 28.1, or 1.4 i-dropouts arcmin, with significant field-to-field variation (as expected from cosmic variance). This extends i-dropout searches some ∼0.9 further down the luminosity function than was possible in the GOODS field, netting a ∼7× increase in surface density. An estimate of the size evolution for UV bright objects is obtained by comparing the composite radial flux profile of the bright i-dropouts (z850,AB < 27.2) with scaled versions of the HDF-N + HDF-S U -dropouts. The best-fit is found with a (1+z) +0.50 −0.53 scaling in size (for fixed luminosity), extending lower redshift (1 < z < 5) trends to z ∼ 6. Adopting this scaling and the brighter i-dropouts from both GOODS fields, we make incompleteness estimates and construct a z ∼ 6 LF in the rest-frame continuum UV (∼ 1350Å) over a 3.5 magnitude baseline, finding a shape consistent with that found at lower redshift. To evaluate the evolution in the LF from z ∼ 3.8, we make comparisons against different scalings of a lower redshift B-dropout sample. Though a strong degeneracy is found between luminosity and density evolution, our best-fit model scales as (1 + z) in number and (1 + z) in luminosity, suggesting a rest-frame continuum UV luminosity density at z ∼ 6 which is just 0.38 −0.07× that at z ∼ 3.8. Our inclusion of size evolution makes the present estimate lower than previous z ∼ 6 estimates. Subject headings: galaxies: evolution — galaxies: high-redshift — galaxies: luminosity function, mass

High-resolution near-infrared images and models of the circumstellar disk in hh 30

We present Hubble Space Telescope near-infrared camera and multiobject spectrometer observations of the reflection nebulosity associated with the T Tauri star HH 30. The images show the scattered-light pattern characteristic of a highly inclined, optically thick disk with a prominent dust lane whose width decreases with increasing wavelength. The reflected nebulosity exhibits a lateral asymmetry in the upper lobe on the opposite side to that reported in previously published Wide Field Planetary Camera 2 images. The radiation transfer model that most closely reproduces the data has a flared accretion disk with dust grains larger than standard interstellar medium grains by a factor of approximately 2.1. A single hot spot on the stellar surface provides the necessary asymmetry to fit the images and is consistent with previous modeling of the light curve and images. Photometric analysis results in an estimated extinction of AV 80; however, since the photometry measures only scattered light rather than direct stellar flux, this a lower limit. The radiative transfer models require an extinction of AV = 7900.

The Near-Infrared Camera and Multi-Object Spectrometer Ultra Deep Field: Observations, data reduction, and galaxy photometry

This paper describes the observations and data reduction techniques for the version 2.0 images and catalog of the NICMOS Ultra Deep Field Treasury program. All sources discussed in this paper are based on detections in the combined NICMOS F110W and F160W bands only. The NICMOS images are drizzled to 0.09 arc second pixels and aligned to the ACS UDF F850LP image which was rebinned to the same pixel scale. These form the NICMOS version 2.0 UDF images. The catalog sources are chosen with a conservative detection limit to avoid the inclusion of numerous spurious sources. The catalog contains 1293 objects in the 144 x 144 arc sececonds NICMOS subfield of the UDF. The 5 sigma signal to noise level is an average 0.6 arc second diameter aperture AB magnitude of ~27.7 at 1.1 and 1.6 microns. The catalog sources, listed in order of right ascension, satisfy a minimum signal to noise criterion of 1.4 sigma in at least 7 contiguous pixels of the combined F110W and F160W image

11. Fourier Spectrometers

Publisher Summary This chapter examines the theory and applications of Fourier transform spectroscopy. A Michelson interferometer is ideally suited for work in high-resolution infrared spectroscopy of astronomical objects. In this application the available signal-to-noise ratio limits the number of observable objects and, therefore, any gain in signal-to-noise is of tremendous importance. The Michelson interferometer is a device for interfering two beams of light. Light entering the interferometer is divided into two separate beams by a beam splitter and is recombined after a controllable phase delay has been applied to one of the beams The use of digital computers in performing the Fourier transform of the interferogram, implies that the data be supplied in digital form. The effect of the slow-beat frequency is to make the contributions from spectral elements near the calculated element essentially positive rather than averaging to zero. The dispersive properties of the beam splitter can cause wave number-dependent phase shifts. The data recording and processing systems are as important as the optical and mechanical systems of the interferometer.

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 A 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.