R. D. Joseph

Spectroscopy of luminous infrared galaxies at 2 microns: 1. The ultraluminous galaxies (L(sub IR) approximately greater than 10 (exp 12) solar luminosity)

We present high-quality spectra covering the K window at a resolving power of 340 for a sample of 13 ultraluminous (L(sub IR) approximately greater than 10(exp 12) solar luminosity) infrared-selected galaxies, and line fluxes for a comparison sample of 24 lower luminosity galaxies. The 2 micrometers spectra of 10 of the ultraluminous galaxies are characterized by emission and absorption features commonly associated with stars and star formation; two others have the red power-law spectra and Br gamma line widths of Seyfert 1 galaxies; the final galaxy has strong emission from hot dust. We have found no broad-line active nuclei not already known from optical observations, despite the fact that the extinction at 2 micrometers is 1/10 that at optical wavelengths; any putative Seyfert 1 nuclei must be deeply buried. Powerful continua and emission lines from H2 and Br gamma are detected in all the ultraluminous galaxies. Comparing the H2 1-0 S(1), Br gamma, and 2 micrometers and far-infrared luminosities to those of the lower luminosity galaxies yields several major results. First, the dereddened Br gamma emission, relative to the far-infrared luminosity is significantly depressed in the ultraluminous sample, when compared to the lower luminosity galaxies. Five of the ultraluminous galaxies have L(sub Br gamma)L(sub IR) ratios lower than for any of the comparison objects. Second, the H2 1-0 S(1) luminosity is also responsible, directly or indirectly, for producing the excited H2, and that the H2 apparently comes from optically thin regions in both classes of objects. Third, eight of the 13 ultraluminous systems have lower 2 micrometers/far-infrared luminosity ratios than any of the lower luminosity galaxies, and five of these are the galaxies also deficient in Br gamma. These three findings may be understood if the the H2, Br gamma, and 2 mircometers continua in the ultraluminous galaxies arise from spatially distinct regions, with the continuum and Br gamma largely coming from volumes optically thick even at 2 micrometers, and obscured in such a fashion that the extinctions measured using optical spectroscopy do not properly measure the true optical depths. If this is the case, then even near-infrared spectroscopy may be unable to exclude the presence of undetected powerful active galactive nuclei in the ultraluminous galaxies.

Two extremely red galaxies

Abstract : This report concerns one of the major observational studies in the ISO Central Programme, the ISO Normal Galaxy Survey. This is a survey of an unbiased sample of spiral and lenticular galaxies selected from the Revised Shapley-Ames Catalog. It is therefore optically-selected, with a brightness limit of blue magnitude = 12, and otherwise randomly chosen. The original sample included 150 galaxies, but this was reduced to 74 when the allocated observing time was expended because the ISO overheads encountered in flight were much larger than predicted.

Spectroscopy of Luminous Infrared Galaxies at 2 Microns. III. Analysis for Galaxies with log (LIR/L?) 11.2

We have obtained spectra across the K window for the first large sample of luminous galaxies selected from the IRAS survey. This paper contains the principal analysis of the 43 systems in our sample with luminosities of 11.2 log (LIR/L?) 11.9. The spectra themselves were presented in a companion paper by Goldader et al. (Paper II). The Br? luminosities are proportional to LIR, at levels similar to those of star-forming regions. This strongly suggests that star formation accounts for the bulk of the energy production in these objects, in general agreement with previous studies. Good agreement is found for the continuous star formation models of Leitherer & Heckman with upper mass cutoffs well below 100 -->?. The models accommodate a range in starburst ages of ~107 to 109 yr. Instantaneous starburst models fit the data but imply an unrealistically short range of ages for the entire sample. It is difficult to avoid concluding that the initial mass functions are deficient in stars of less than ~1 -->?. Strong emission lines from molecular hydrogen are detected. The H2 v = 1-0 S(1) line luminosities are proportional to LIR; the correlation extends through the ultraluminous infrared galaxies. The H2 emission in the galaxies tends to be more spatially extended than the Br? emission. Measured values and upper limits for the ratios of the various H2 lines visible in our spectra indicate that the H2 seen in emission at 2 ?m is consistent with being shock excited. However, other mechanisms, operating at sufficiently high densities that the H2 energy levels are thermalized by collisions, cannot be excluded. Based on energy considerations, we suggest that the shocks are due to supernova remnants expanding into the interstellar medium. The frequency of Type II supernovae necessary to account for the H2 line emission agrees with frequencies deduced from the starburst models and the radio/far-infrared correlation. However, there remain a number of galaxies that cannot be made to fit this model. A decade after its discovery, a universal explanation of the strong H2 emission in luminous infrared galaxies continues to elude us. No previously unrecognized broad-line active nuclei were discovered in our survey; either they are weak or absent or the true optical depths at 2 ?m are much higher than indicated by conventional extinction measures. However, there are clear differences between the K-band properties of galaxies that contain broad-line active nuclei and those that do not. The differences seem to be due to the presence of strong nonstellar continuum emission coming from the active nuclei themselves. With the addition of the 13 ultraluminous galaxies with log (LIR/L?) 12 from Goldader et al. (Paper I), the number of systems observed in this program totals 56. We have incorporated these ultraluminous galaxies in some parts of the analysis to examine properties across the entire luminosity range of our sample.

A DEEP K-BAND PHOTOMETRIC SURVEY OF MERGER REMNANTS

We present K-band photometry for 51 candidate merger remnants to assess the viability of whether spiral-spiral mergers can produce bona fide elliptical galaxies. Using both the de Vaucouleurs r1/4 and Sersic r1/n fitting laws, it is found that the stellar component in a majority of the galaxies in the sample has undergone violent relaxation. However, the sample shows evidence for incomplete phase mixing. The analysis also indicates the presence of excess light in the surface brightness profiles of nearly one-third of the merger remnants. Circumstantial evidence suggests that this is due to the effects of a starburst induced by the dissipative collapse of the gas. The integrated light of the galaxies also shows that mergers can make L* elliptical galaxies, in contrast to earlier infrared studies. The isophotal shapes and related structural parameters are also discussed, including the fact that 70% of the sample show evidence for disky isophotes. The data and results presented are part of a larger photometric and spectroscopic campaign to thoroughly investigate a large sample of mergers in the local universe.

The role of H3+in planetary atmospheres

Spectroscopic studies of the upper atmospheres of the giant planets using infrared wavelengths sensitive to the H3+ molecular ion show that this species plays a critical role in determining the physical conditions there. For Jupiter, we propose that the recently detected H3+ electrojet holds the key to the mechanism by which the equatorial plasma sheet is kept in (partial) co–rotation with the planet, and that this mechanism also provides a previously unconsidered source of energy that helps explain why the jovian thermosphere is considerably hotter than expected. For Saturn, we show that the H3+ auroral emission is ca. 1% of that of Jupiter because of the lower ionospheric/thermospheric temperature and the lower flux of ionizing particles precipitated there; it is probably unnecessary to invoke additional chemistry in the auroral/polar regions. For Uranus, we report further evidence that its emission intensity is controlled by the cycle of solar activity. And we propose that H3+ emission may just be detectable using current technology from some of the giant extra–solar planets that have been detected orbiting nearby stars, such as Tau Bootes.

Infrared emissions of H3(+) in the atmosphere of Jupiter in the 2. 1 and 4. 0 micron region

Infrared spectra of the Jovian atmosphere around 2.1 and 4.0 microns, measured using the NASA Infrared Telescope Facility at Mauna Kea, Hawaii, are presented. The observations were made between February 6 and 8, 1990. In both spectral regions, features attributable to H3(+) were visible. The intensity ratio of lines in the 2 and 4 microns regions measured from the northern auroral hot spot during the same night leads to a rovibrational temperature of 1100 + or - 100 K for this molecular ion, close to a previous measurement of the rotational temperature of 1099 + or - 100 K. This indicates that the upper energy levels are being populated by purely thermal processes, rather than by resonant energy exchange. The para-H3(+) fractional abundance of 0.58 determined by previous workers is found to be consistent with this study. The time dependency of the H3(+) emission phenomena is confirmed. 9 refs.

Resonant array bandpass filters for the far infrared

An array of square apertures in a conducting film behaves as a high-pass filter element. By contrast, an array of cross-shaped apertures exhibits bandpass behavior. We have investigated experimentally how variations in the pattern periodicity, the crossarm width, and the separation between the crosses alter the spectral behavior. We find that these bandpass filters can have excellent peak transmission and good shortwave rejection. The wavelength of peak transmission is determined by the length of the crossarm (and not by the array period itself), while the bandwidth is determined chiefly by coupling between the crosses. These results are qualitatively consistent with a coupled-dipole model. This model appears to have more utility for practical filter design than the commonly used transmission-line model.

Supersonic winds in Jupiter's aurorae

Jupiter has a giant magnetosphere that is coupled to the planets upper atmosphere; as the planet rotates, its magnetic field drags a dense ionized equatorial sheet of plasma, which must interact with the upper atmosphere. Jupiters aurorae are much more powerful, than the Earths, and cause significant local heating of the upper atmosphere. Auroral electrojets—ion winds that race around Jupiters auroral ovals—play a key role in theoretical models of how Jupiters rotational energy is transferred to the plasma sheet, and how winds may transport energy from auroral heating to lower latitudes. But there has hitherto been no direct observational evidence for the existence of such electrojets. Here we report observations of electrojets that have winds approaching or in excess of the local speed of sound. The energy produced by these electrojets could heat the whole upper atmosphere, if the auroral regions couple efficiently with the rest of the planet.

A SURVEY OF MERGER REMNANTS. II. THE EMERGING KINEMATIC AND PHOTOMETRIC CORRELATIONS

This paper is the second in a series exploring the properties of 51 optically selected, single-nuclei merger remnants. Spectroscopic data have been obtained for a subsample of 38 mergers and combined with previously obtained infrared photometry to test whether mergers exhibit the same correlations as elliptical galaxies among parameters such as stellar luminosity and distribution, central stellar velocity dispersion (σ0), and metallicity. Paramount to the study is to test whether mergers lie on the fundamental plane. Measurements of σ0 have been made using the Ca triplet absorption line at 8500 A for all 38 mergers in the subsample. Additional measurements of σ0 were made for two of the mergers in the subsample using the CO absorption line at 2.29 μm. The results indicate that mergers show a strong correlation among the parameters of the fundamental plane but fail to show a strong correlation between σ0 and metallicity (Mg2). In contrast to earlier studies, the σ0 values of the mergers are consistent with objects that lie somewhere between intermediate-mass and luminous giant elliptical galaxies. However, the discrepancies with earlier studies appear to correlate with whether the Ca triplet or CO absorption lines are used to derive σ0, with the latter almost always producing smaller values. Finally, the photometric and kinematic data are used to demonstrate for the first time that the central phase-space densities of mergers are equivalent to those in elliptical galaxies. This resolves a long-standing criticism of the merger hypothesis.

Spitzer and JCMT Observations of the Active Galactic Nucleus in the Sombrero Galaxy (NGC 4594)

We present Spitzer 3.6–160 μm images, Spitzer mid-infrared spectra, and JCMT SCUBA 850 μm images of the Sombrero Galaxy (NGC 4594), an Sa galaxy with a 10^9 Mo ; low-luminosity active galactic nucleus (AGN). The brightest infrared sources in the galaxy are the nucleus and the dust ring. The spectral energy distribution of the AGN demonstrates that, while the environment around the AGN is a prominent source of mid-infrared emission, it is a relatively weak source of far-infrared emission, as had been inferred for AGNs in previous research. The weak nuclear 160 μm emission and the negligible polycyclic aromatic hydrocarbon emission from the nucleus also implies that the nucleus is a site of only weak star formation activity and the nucleus contains relatively little cool interstellar gas needed to fuel such activity. We propose that this galaxy may be representative of a subset of low-ionization nuclear emission region galaxies that are in a quiescent AGN phase because of the lack of gas needed to fuel circumnuclear star formation and Seyfert-like AGN activity. Surprisingly, the AGN is the predominant source of 850 μm emission. We examine the possible emission mechanisms that could give rise to the 850 μm emission and find that neither thermal dust emission, CO line emission, bremsstrahlung emission, nor the synchrotron emission observed at radio wavelengths can adequately explain the measured 850 μm flux density by themselves. The remaining possibilities for the source of the 850 μm emission include a combination of known emission mechanisms, synchrotron emission that is self-absorbed at wavelengths longer than 850 μm, or unidentified spectral lines in the 850 μm band.