Ralph C. Bohlin

Template Ultraviolet to Near-Infrared Spectra of Star-forming Galaxies and Their Application to K-Corrections

Template UV-optical spectra of quiescent and starburst galaxies are presented and used to derive Kcorrections as a function of morphological type and redshift. IUE observations and archival data are used for the UV template spectra. The optical spectra are from ground-based observations obtained in apertures that match closely the 200 arcsec 2 IUE aperture. The templates of quiescent galaxies are built according to morphological type, elliptical, bulge, SO, Sa, Sb, and So, and the templates of starburst galaxies according to color excess. The unprecedented characteristics of these templates is that UV and optical spectra have been obtained in matched apertures to produce consistent spectral information from 1200 to 10,000 A. Despite the relatively small IUE aperture, the galaxy stellar populations are well represented in the elliptical, SO, Sa, and Sc, and in the starburst templates. The spectra are available digitally. The UV-optical templates can be applied to the classification of high-redshift galaxies and to the identification of the host galaxies of quasars. The templates predict that observed magnitudes from traditional ground-based photometric surveys can be uniquely interpreted. For example, U, B, and I magnitudes uniquely determine both the redshift and the morphological type of a galaxy. The template spectra are also used to calculate K-corrections for galaxies as a function of morphological type and redshift, up to z = 2. These improved K-corrections are not sufficient to explain the excess counts in faint blue galaxies. A subset of our galaxy templates are linked with published data from the radio to the X-ray for galaxies and quasars. A comparison between the quiescent galaxies and the quasars suggests that, in the optical band, the host galaxy is a factor of 10-100 fainter in flux than the quasar. Subject headings: galaxies: distances and redshifts --galaxies: photometry -galaxies: starburst -galaxies: stellar content -quasars: general

HST FOS spectroscopy of M87: Evidence for a disk of ionized gas around a massive black hole

Using the Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST) to observe the central region of M87, we have obtained spectra covering approximately 4600-6800 A at a spectral dispersion approximately 4.4 A per resolution element through the .26 sec diameter entrance aperture. One spectrum was obtained centered on the nucleus of M87 and two centered 0.25 sec off the nucleus at position angles of 21 deg and 201 deg, thus sampling the anticipated major axis of the disklike structure (described in a companion Letter) expected to lie approximately perpendicular to the axis of the M87 jet. Pointing errors for these observations are estimated to be less than 0.02 sec. Radial velocities of the ionized gas in the two positions 0.25 sec on either side of the nucleus are measured to be approx. equals +/- 500 km/s relative to the M87 systemic velocity. These observations plus emission-line spectra obtained at two additional locations near the nucleus show the ionized gas to be in Keplerian rotation about a mass M = (2.4 +/- 0.7) x 10(exp 9) solar mass within the inner 0.25 sec of M87. Our results provide strong evidence for the presence of a supermassive nuclear black hole in M87.

The 0.12-2.5 micron Absolute Flux Distribution of the Sun for Comparison With Solar Analog Stars

An absolute ux calibrated reference spectrum of the Sun covering the 0.12 to 2.5 m wavelength range is presented. The ultraviolet and optical spectrum is based on absolute ux measurements from satellites and from the ground. The near-infrared spectrum is based on measurements using the NASA CV-990 aircraft and on a model spectrum. The synthetic optical and near-infrared magnitudes of the absolute calibrated solar reference spectrum agree with published values to 0.01 0.03 magnitudes, i.e. within the uncertainties of the measurements. The absolute ux of the reference spectrum over the optical and near-infrared 0.4 to 2.5 m range is known with an uncertainty of 5%, or better. In the blue and ultraviolet, especially for wavelengths in the 0.12 to 0.2 m interval, the uncertainty increases up to about 20% due to the variability of the solar energy output at these wavelengths. The absolute ux spectrum of the Sun presented here will help to establish the absolute calibration of NICMOS, the HST near-infrared camera and Multi-object Spectrograph.

An atlas of ultraviolet spectra of star-forming galaxies

A systematic study is presented of the UV spectra of star-forming galaxies of different morphological type and activity class using a sample drawn from a uniformly reduced IUE data set. The spectra for a wide variety of galaxies, including normal spiral, LINER, starburst, blue compact, blue compact dwarf, and Seyfert 2 galaxies, are presented in the form of spectral energy distributions to demonstrate the overall characteristics according to morphology and activity class and in the form of absolute flux distributions to better show the absorption and emission features of individual objects. The data support the picture based on UV spectra of the Orbiting Astronomical Observatory and of the Astronautical Netherlands Satellite that spiral galaxies of later Hubble class have more flux at the shortest UV wavelengths than do spiral galaxies of earlier Hubble class.

Narrowband HST images of M87: Evidence for a disk of ionized gas around a massive black hole

We present Hubble Space Telescope Wide Field/Planetary Camera-2 (HST WFPC2) narrowband H-alpha + (N II) images of M87 which show a small disk of ionized gas with apparent spiral structure surrounding the nucleus of M87. The jet projects approximately 19.5 deg from the minor axis of the disk, which suggests that the jet is approximately normal to the disk. In a companion Letter, Harms et al. measure the radial velocities at r = +/- 0.25 sec along a line perpendicular to the jet, showing that one side of the disk is approaching at 500 +/- 50 km/s and the other side of the disk is receding at 500 +/- 50 km/s. Absorption associated with the disk and the sense of rotation imply that the apparent spiral arms trail the rotation. The observed radial velocites corrected for a 42 deg inclination of the disk imply rotation at +/- 750 km/s. Analysis of velocity measurements at four positions near the nucleus gives a total mass of approximately 2.4 +/- 0.7 x 10(exp 9) solar mass within 18 pc of the nucleus, and a mass-to-light ratio (M/L)(sub I) = 170. We conclude that there is a disk of ionized gas feeding a massive black hole in the center of M87.

The On-Orbit Performance of the Space Telescope Imaging Spectrograph

The Space Telescope Imaging Spectrograph (STIS) was successfully installed into the Hubble Space Telescope (HST) in 1997 February, during the second HST servicing mission, STS-82. STIS is a versatile spectrograph, covering the 115-1000 nm wavelength range in a variety of spectroscopic and imaging modes that take advantage of the angular resolution, unobstructed wavelength coverage, and dark sky offered by the HST. In the months since launch, a number of performance tests and calibrations have been carried out and are continuing. These tests demonstrate that the instrument is performing very well. We present here a synopsis of the results to date.

HUBBLE SPACE TELESCOPE ABSOLUTE SPECTROPHOTOMETRY OF VEGA FROM THE FAR-ULTRAVIOLET TO THE INFRARED

The Space Telescope Imaging Spectrograph (STIS) has measured the absolute flux for Vega from 0.17–1.01 μm on the Hubble Space Telescope white dwarf (WD) flux scale. These data are saturated by up to a factor of 80 overexposure but retain linearity to a precision of 0.2% because the charge bleeds along the columns and is recovered during readout of the CCD. The signal-to-noise ratio per pixel exceeds 1000, and the resolution R is about 500. A V magnitude of 0.026 ± 0.008 is established for Vega, and the absolute flux level is 3.46 × 10-9 ergs cm-2 s-1 at 5556 A. In the regions of Balmer and Paschen lines, the STIS equivalent widths differ from the pioneering work of Hayes in 1985 but do agree with predictions of a Kurucz model atmosphere, so that the STIS flux distribution is preferred to that of Hayes. Over the full wavelength range, the model atmosphere calculation shows excellent agreement with the STIS flux distribution and is used to extrapolate predicted fluxes into the IR region. However, the IR fluxes are 2% lower than the standard Vega model of Cohen. IUE data provide the extension of the measured STIS flux distribution from 0.17 down to 0.12 μm. The STIS relative flux calibration is based on model atmosphere calculations of pure hydrogen WDs, while the Hayes flux calibration is based on the physics of laboratory lamps and blackbody ovens. The agreement to 1% of these two independent methods for determining the relative stellar flux distributions suggests that both methods may be correct from 0.5–0.8 μm and adds confidence to claims that the fluxes relative to 5500 A are determined to better than 4% by the pure hydrogen WD models from 0.12 to 3 μm.

Spectrophotometric Standards From the Far-UV to the Near-IR on the White Dwarf Flux Scale

The second generation instruments to be installed in 1997 on the Hubble Space Telescope (HST) require spectrophotometric standard stars for ux calibrations to 1.1 m for the imaging spectrograph (STIS) and to 2.5 m for the infrared camera (NICMOS). Calculated model atmosphere ux distributions from 0.1 to 3 m for four pure hydrogen white dwarfs provide the fundamental basis for a new set of spectrophotometric standard stars. Precise visual photometry sets the absolute level of the model uxes, while FOS spectrophotometry validates the relative V magnitudes to 1% and the relative uxes at other wavelengths to 2%. Extensive FOS observations of four more stars from 1140{8500 A expand the set of primary standards to eight stars. These eight ux distributions are compared with IUE uxes in the UV and with Oke spectrophotometry in the visual to de ne corrections as a function of wavelength. These corrections plus a wavelength independent correction to the Oke uxes are accurate to 3% and provide 18 additional standards on the WD scale from 1150{9200 A. One more standard Lyr consists of IUE data plus the ground based spectrum of Hayes.

The White Dwarf Distance to the Globular Cluster NGC 6752 (and Its Age) with the HUBBLE SPACE TELESCOPE

Deep Hubble Space Telescope (HST) observations with WFPC2 of the nearby globular cluster NGC 6752 have allowed us to obtain accurate photometry for the cluster white dwarfs (WD). A sample of local WDs of known trigonometric parallax and mass close to that of the cluster WDs have also been observed with WFPC2. Matching the cluster and the local WD sequences provides a direct measure of the distance to the cluster:

Spectrophotometric Standards from the Far-Ultraviolet to the Near-Infrared: STIS and NICMOS Fluxes

(m-M)_\circ=13.05