Stephen Louis Tufte

The Wisconsin Hα Mapper Northern Sky Survey

The Wisconsin H-Alpha Mapper (WHAM) has completed a one-degree resolution, velocity-resolved northern sky survey of H-alpha emission from our Galaxy. The unprecedented sensitivity of the instrument and accurate spectral subtraction of atmospheric features allow us to detect Galactic features as faint as 0.1 Rayleighs (EM ~ 0.25 cm^{-6} pc). This survey allows a direct comparison of the ionized and neutral components of the ISM on a global scale for the first time. All-sky maps of H-alpha emission in select velocity bands highlight the rich kinematic structure of the Galaxys ionized gas. The full set of data from the WHAM survey is now available at this http URL (abridged)The Wisconsin Hα Mapper (WHAM) has surveyed the distribution and kinematics of ionized gas in the Galaxy above declination -30°. The WHAM Northern Sky Survey (WHAM-NSS) has an angular resolution of 1° and provides the first absolutely calibrated, kinematically resolved map of the Hα emission from the warm ionized medium (WIM) within ~±100 km s-1 of the local standard of rest. Leveraging WHAMs 12 km s-1 spectral resolution, we have modeled and removed atmospheric emission and zodiacal absorption features from each of the 37,565 spectra. The resulting Hα profiles reveal ionized gas detected in nearly every direction on the sky with a sensitivity of 0.15 R (3 σ). Complex distributions of ionized gas are revealed in the nearby spiral arms up to 1-2 kpc away from the Galactic plane. Toward the inner Galaxy, the WHAM-NSS provides information about the WIM out to the tangent point down to a few degrees from the plane. Ionized gas is also detected toward many intermediate velocity clouds at high latitudes. Several new H II regions are revealed around early B stars and evolved stellar cores (sdB/O). This work presents the details of the instrument, the survey, and the data reduction techniques. The WHAM-NSS is also presented and analyzed for its gross properties. Finally, some general conclusions are presented about the nature of the WIM as revealed by the WHAM-NSS.

A NEW SPIN ON GALACTIC DUST

We present a new puzzle involving Galactic microwave emission and attempt to resolve it. On one hand, a cross-correlation analysis of the Wisconsin Hα Mapper map with the Tenerife 10 and 15 GHz maps shows that the well-known DIRBE correlated microwave emission cannot be dominated by free-free emission. On the other hand, recent high-resolution observations in the 8-10 GHz range with the Green Bank 140 foot telescope by Finkbeiner et al. failed to find the corresponding 8 σ signal that would be expected in the simplest spinning-dust models. So what physical mechanism is causing this ubiquitous dust-correlated emission? We argue for a model predicting that spinning dust is the culprit after all, but that the corresponding small grains are well correlated with the larger grains seen at 100 μm only on large angular scales. In support of this grain-segregation model, we find that the best spinning-dust template involves higher frequency maps in the range 12-60 μm, in which emission from transiently heated small grains is important. Upcoming cosmic microwave background experiments such as ground-based interferometers, the Microwave Anisotropy Probe, and the Planck low-frequency interferometer with high resolution at low frequencies should allow a definitive test of this model.

Interstellar Hα Line Profiles toward HD 93521 and the Lockman Window

We have used the Wisconsin Hα Mapper (WHAM) facility to measure the interstellar Hα emission toward the high Galactic latitude O star HD 93521 (l = 1831, b = +622). Three emission components were detected along this line of sight. These components have radial velocities of -10, -51, and -90 km s-1 with respect to the local standard of rest (LSR) and have Hα intensities of 0.20, 0.15, and 0.023 R, respectively, corresponding to emission measures of 0.55, 0.42, and 0.06 cm-6 pc. We have also measured the Hα emission toward the direction l = 1485, b = +530, which lies in the region of exceptionally low H I column density known as the Lockman Window. An emission component is detected in this direction at -1 km s-1 (LSR), with an intensity of 0.20 R (0.55 cm-6 pc). In addition, we studied the direction l = 1635, b = +535. No Galactic emission was detected along this line of sight, and upper limits on the possible intensity of Galactic emission toward this direction are 0.11 R at the LSR and 0.06 R at -50 km s-1. As part of the process of separating the interstellar from the terrestrial emission, we also detected and characterized 12 faint (~0.03-0.15 R), unidentified atmospheric lines present in WHAM Hα spectra. Finally, we have used WHAM to obtain [O I] λ6300 spectra along the line of sight toward HD 93521. We do not conclusively detect interstellar [O I] emission toward the star, but place an upper limit of 0.060 R on the [O I] intensity of the intermediate-velocity (-51 km s-1) component. If the temperature of the gas is 10,000 K, this limit implies that, within the Hα-emitting region, the hydrogen ionization fraction n(H+)/n(H total) > 0.6.

WHAM Observations of Hα from High-Velocity Clouds: Are They Galactic or Extragalactic?

It has been suggested that high-velocity clouds may be distributed throughout the Local Group and are therefore not in general associated with the Milky Way. With the aim of testing this hypothesis, we have made observations in the Hα line of high-velocity clouds selected as the most likely candidates for being at larger than average distances. We have found Hα emission from four out of five of the observed clouds, suggesting that the clouds under study are being illuminated by a Lyman continuum flux greater than that of the metagalactic ionizing radiation. Therefore, it appears likely that these clouds are in the Galactic halo and not distributed throughout the Local Group.

A Map of the Ionized Component of the Intermediate-Velocity Cloud Complex K

The Wisconsin H-Alpha Mapper (WHAM) Northern Sky Survey is revealing that many intermediate-velocity (|vLSR| ≤ 100 km s-1) neutral clouds and complexes have an associated ionized component. We present the first map of the Hα emission from an intermediate- or high-velocity structure: Complex K. This large, high-latitude feature stretches from l ≈ 10° to 70°, b ≈ +30° to +70° and peaks in velocity over vLSR ≈ -60 to -80 km s-1. The neutral and ionized gas generally trace each other quite well in the complex, but the detailed structure is not identical. In particular, the Hα emission peaks in brightness at slightly higher Galactic longitudes than corresponding 21 cm features. The ionized gas has a peak Hα intensity of 0.5 R, corresponding to an emission measure of 1.1 cm-6 pc. Structures in the complex are traced by WHAM down to about 0.1 R (0.2 cm-6 pc). Typical line widths of the Hα emission are ~30 km s-1, limiting temperatures in the ionized gas to less than 20,000 K. If radiation is the primary ionizing mechanism, the Lyman continuum flux required to sustain the most strongly emitting ionized regions is 1.2 × 106 photons cm-2 s-1. There appears to be no local, stellar source capable of maintaining the ionization of the gas; however, the required ionizing flux is consistent with current models of the escape of Lyman continuum radiation from OB stars in the disk and of ionizing radiation produced by cooling supernova remnants.

Galactic Contamination in the QMAP Experiment

We quantify the level of foreground contamination in the QMAP cosmic microwave background data with two objectives: (1) to measure the level to which the QMAP power spectrum measurements need to be corrected for foregrounds and (2) to use this data set to further refine current foreground models. We cross-correlate the QMAP data with a variety of foreground templates. The 30 GHz Ka-band data are found to be significantly correlated with the Haslam 408 MHz and Reich & Reich 1420 MHz synchrotron maps but not with the Diffuse Infrared Background Experiment 240, 140, and 100 μm maps or the Wisconsin H-Alpha Mapper survey. The 40 GHz Q band has no significant template correlations. We discuss the constraints that this places on synchrotron, free-free, and dust emission. We also reanalyze the foreground-cleaned Ka-band data and find that the two band power measurements are lowered by 2.3% and 1.3%, respectively.

Observations of the Extended Distribution of Ionized Hydrogen in the Plane of M31

We have used the Wisconsin H-Alpha Mapper to observe the spatially extended distribution of ionized hydrogen in M31 beyond the stellar disk. We obtained five sets of observations, centered near the photometric major axis of M31, that extend from the center of the galaxy to just off the edge of the southwestern H I disk. Beyond the bright stellar disk, but within the H I disk, weak Hα is detected with an intensity IHα = 0.05 R. Since M31 is inclined 77° with respect to the line of sight, this implies that the ambient intergalactic ionizing flux on each side of M31 is Φ0 ≤ 1.6 × 104 photons cm-2 s-1. Just beyond the outer boundary of the H I disk, we find no significant detection of Hα and place an upper limit IHα ≤ 0.019 R.

The Extragalactic Background and Its Fluctuations in the Far-Infrared Wavelengths

A Cosmic Far-InfraRed Background (CFIRB) has long been predicted that would traces the intial phases of galaxy formation. It has been first detected by Puget et al.(1996) using COBE data and has been later confirmed by several recent studies (Fixsen et al. 1998, Hauser et al. 1998, Lagache et al. 1999). We will present a new determination of the CFIRB that uses for the first time, in addition to COBE data, two independent gas tracers: the HI survey of Leiden/Dwingeloo (hartmann, 1998) and the WHAM H

Ionized Gas Associated with HVCs

_{\alpha}

A Comparison of Diffuse Ionized and Neutral Hydrogen Away from the Galactic Plane: H alpha -emitting H i Clouds

survey (Reynolds et al 1998). We will see that the CFIRB above 100 micron is now very well constrained. The next step is to see if we can detect its fluctuations. To search for the CFIRB fluctuations, we have used the FIRBACK observations. FIRBACK is a deep cosmological survey conducted at 170 micron with ISOPHOT (Dole et al., 2000). We show that the emission of unresolved extra-galactic sources clearly dominates, at arcminute scales, the background fluctuations in the lowest galactic emission regions. This is the first detection of the CFIRB fluctuations.