The Distribution of Warm Ionized Medium in Galaxies

Ionized nebulae have been targets of interest since the introduction of the telescope centuries ago. These isolated, "classical" H II regions gave us some of the earliest insight into the copious feedback energy that stars inject into the interstellar medium. Their unique spectra contain information about the quality and quantity of the ionizing field as well as the temperature, density, and metallicity of these discrete locations in the Galaxy. With increasing sensitivity across many spectral domains, we now know that ionized gas is not localized to massive star regions in many star-forming galaxies. In particular, recent observational studies allow a thorough comparison of the physical conditions and distribution of the well-studied classical H II regions to the more widespread warm, diffuse gas. By more realistically evolving a dynamic interstellar medium, models are beginning to reproduce the observed emission measure variations and provide a natural solution to the propagation of ionizing flux from a predominantly neutral galactic disk to the distant halo.Comment: 11 pages, 3 figures. To appear in "The Dynamic ISM: A celebration of the Canadian Galactic Plane Survey," ASP Conference Serie

The Ionization Structure of Sharpless 2-264: Multiwavelength Observations of the {\lambda} Ori H II Region

We present velocity-resolved maps taken with the Wisconsin H-Alpha Mapper (WHAM) in H{\alpha}, [S II] {\lambda}6716, and [N II] {\lambda}6583 around the well-known O8 III star {\lambda} Ori A (HD 36861) (l = 185{\deg} to 205{\deg}, b = -24{\deg} to -1{\deg}). The integrated intensity (v(LSR) = -80 to +80 km/s), I(H{\alpha}), within WHAM's one-degree beams varies from ~ 190 R near the center to ~ 10 R on the periphery of the nebula where it becomes comparable to foreground and/or background emission in this complex region. Intensity ratios for [N II]/H{\alpha} and [S II]/H{\alpha} average 0.28 and 0.35, respectively. In both ratios, higher values are found preferentially at larger radii from {\lambda} Ori, although the behavior of [N II]/H{\alpha} is complicated near the edges of the nebula. The [S II]/[N II] intensity ratio ranges from ~ 0.5 to ~ 1.0, with the value increasing toward larger radii (and lower H{\alpha} intensities). Variations of [S II]/H{\alpha}, [N II]/H{\alpha}, and [S II]/[N II] line ratios in this diffuse region show some similar trends to those seen in the warm ionized medium (WIM) but with generally lower metal-line ratios. As with the WIM, the trends are driven by changes in the underlying physical parameters, most notably the ionization states and gas temperature. We use these extremely high signal-to-noise observations to construct a map of temperature and non-thermal velocity throughout the nebula. Using the line widths of H{\alpha} and [S II], we separate thermal and non-thermal components and find spatial trends of these parameters within the nebula.Comment: 16 pages, 9 figures, Accepted by Astronomical Journa

Probing Interstellar Turbulence in the Warm Ionized Medium using Emission Lines

The nature of turbulence in the warm ionized component of the interstellar medium (WIM) can be investigated using Fabry-Perot spectroscopy of optical emission lines. The H-alpha intensity provides the emission measure (EM) along a line of sight, which is used in conjunction with the scattering measure, rotation measure, and dispersion measure to study interstellar turbulence. Observations at high spectral resolution (10 km/s) allow measurements of the bulk radial velocity structure of the emitting gas and investigations of thermal and non-thermal (turbulent) broadening mechanisms through the line widths. By measuring the widths of the H-alpha line and an emission line from a heavier atom (e.g. the [S II] 6716 line), one can separate the thermal and non-thermal contributions to the line width. Preliminary studies using this method have shown that the broad range of H-alpha line widths (typically 15 - 50 km/s) is mostly due to differences in the non-thermal component of the width and that along many lines of sight this component dominates. The Wisconsin H-Alpha Mapper (WHAM) is in the process of producing a very sensitive kinematic map of the northern sky in H-alpha at one degree angular resolution and 12 km/s spectral resolution. WHAM is also mapping emission lines from heavier atoms such as sulfur and nitrogen for selected regions of the sky. This data set will provide unique new information concerning turbulence in the WIM.Comment: Latex, 7 pages, 4 figures. To be published in the Proceedings of the 2nd Guillermo Haro Conference on Interstellar Turbulence held in Puebla, M

H-alpha from High Velocity Clouds

Optical emission lines provide an important new window on the HVCs. Recent studies of the H-alpha line reveal that ionized gas is pervasively associated with the neutral hydrogen in HVCs. The Wisconsin H-Alpha Mapper (WHAM) instrument has so far detected H-alpha from high-velocity clouds in the M, A, and C complexes. We find a close spatial correspondence between the neutral and ionized portions of the HVCs with some evidence that the ionized gas envelopes the neutral part of the clouds. The velocities of the H-alpha and 21-cm detections are well correlated, but the intensities are not. If the clouds are photoionized, the H-alpha intensity is a direct measure of the Lyman continuum flux in the Galactic halo. Forthcoming observations of the H-alpha line in combination with other emission lines will give new insights into the high-velocity cloud phenomena and will also probe the physical conditions of their environment.Comment: 12 pages, 10 figures. To be published in the Proceedings of the Stromlo Workshop on High Velocity Clouds, eds. B. K. Gibson and M. E. Putnam (ASP Conf. Series

The Wisconsin H-Alpha Mapper Northern Sky Survey

The Wisconsin H-Alpha Mapper (WHAM) has completed a survey in Balmer Alpha of the entire Northern sky above declination -30 deg. This survey provides the first calibrated, velocity-resolved map of the H-Alpha emission from the Galaxy. With one-degree spatial resolution, 12 km s^{-1} velocity resolution, and sensitivity to features as faint as 0.1 R (EM ~ 0.2 cm^{-6} pc), this survey provides the deepest maps of the ionized content of the Galaxy to date. In addition to probing the detailed kinematic structure of the Warm Ionized Medium and the vertical structure of the ionized content in spiral arms, initial results include the discovery of several faint, extended (d > 1\deg) H II regions and the first map of the ionized component of an intermediate velocity cloud.Comment: 8 pages, 3 figures; preseneted at the Fourth Tetons Conference: Galactic Structure, Stars, and the Interstellar Medium, to be published in ASP Conf. Series; for more information and slightly higher quality figures see http://www.astro.wisc.edu/wham

The Ionized Component of Intermediate-Velocity Cloud Complex L

We present the first full map of the H-alpha emission from the intermediate-velocity cloud Complex L. Kinematically resolved emission components from the ionized gas reveal a close spatial and velocity correspondence to that of the neutral gas as mapped by 21 cm line observations. Using a simple Gaussian component fitting technique, we compare the details of the emission from the two phases of Complex L. The mean velocity of the H-alpha and 21 cm emission are strongly correlated, but we find that the some of the ionized gas is systematically offset ~ -4 km/s relative to the neutral gas. Line widths are qualitatively comparable, but both emission components are too low signal-to-noise to study any differences between the phases. Finally, as with our previous study toward Complex K, we find I(H-alpha) is not strongly correlated to N(H I) along the same lines of sight through Complex L.Comment: 8 pages, 9 figures, to appear in ASP Conf. Proc.: "Extra-planar Gas", ed. R. Braun. Original quality paper & figures available at http://www.astro.wisc.edu/wham/papers-dir/haffner_dwingeloo.ps.g

Evidence for dust emission in the Warm Ionised Medium using WHAM data

We have used the WHAM H_alpha survey and Leiden/Dwingeloo HI data to decompose the Far-infrared emission (from 100 to 1000 micron) at high Galactic latitude into components associated with the Warm Ionised Medium (WIM) and the Warm Neutral Medium (WNM). This decomposition is possible for the first time thanks to preliminary WHAM data that cover a significant fraction of the sky (about 10%). We confirm the first detection of dust emission from the WIM (Lagache et al. 1999) and show that the WIM dust temperature and emissivity are very similar to those in the WNM. The analysis suggests moreover that about 25% of the far-IR dust emission at high galactic latitude is uncorrelated with the HI gas. The decomposition again reveals a Cosmic Far-Infrared Background (CFIRB) which is determined for the first time from 100 to 1000 micron using two independant gas tracers.Comment: Astronomy and Astrophysics, in pres

The Wisconsin H-Alpha Mapper Northern Sky Survey of Galactic Ionized Hydrogen

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 Galaxy's ionized gas. The full set of data from the WHAM survey is now available at http://www.astro.wisc.edu/wham/. (abridged)Comment: 4 pages, 1 figure, to appear in: "Seeing Through the Dust: The Detection of HI and the Exploration of the ISM in Galaxies", eds. R. Taylor, T. Landecker, & T. Willis (ASP: San Francisco), 200

Warm Ionized Gas Revealed in the Magellanic Bridge Tidal Remnant: Constraining the Baryon Content and the Escaping Ionizing Photons around Dwarf Galaxies

The Magellanic System includes some of the nearest examples of galaxies disturbed by galaxy interactions. These interactions have redistributed much of their gas into the halos of the Milky Way and the Magellanic Clouds. We present Wisconsin H-alpha Mapper kinematically resolved observations of the warm ionized gas in the Magellanic Bridge over the velocity range of +100 to +300 km/s in the local standard-of-rest reference frame. These observations include the first full H-alpha intensity map and the corresponding intensity-weighted mean velocity map of the Magellanic Bridge across (l, b) = (281.5, -30.0) to (302.5, -46.7). Using the H-alpha emission from the SMC-Tail and the Bridge we estimate that the mass of the ionized material is between (0.7-1.7)x10^8 times the mass of the Sun, compared to 3.3x10^8 times the mass of the Sun for the neutral mass over the same region. The diffuse Bridge is significantly more ionized than the SMC-Tail, with an ionization fraction of 36-52% compared to 5-24% for the Tail. The H-alpha emission has a complex multiple-component structure with a velocity distribution that could trace the sources of ionization or distinct ionized structures. We find that incident radiation from the extragalactic background and the Milky Way alone are insufficient to produced the observed ionization in the Magellanic Bridge and present a model for the escape fraction of the ionizing photons from both the Small and Large Magellanic Clouds. With this model, we place an upper limit of 4.0% for the average escape fraction of ionizing photons from the LMC and an upper limit of 5.5% for the SMC. These results, combined with the findings of a half a dozen results for dwarf galaxies in different environments, provide compelling evidence that only a small percentage of the ionizing photons escape from dwarf galaxies in the present epoch to influence their surroundings.Comment: Accepted to ApJ May 20, 2013, updated to correct a typ

Three-Dimensional Studies of the Warm Ionized Medium in the Milky Way using WHAM

The Wisconsin H-Alpha Mapper (WHAM) is a high throughput Fabry-Perot facility developed specifically to detect and explore the warm, ionized component of the interstellar medium at high spectral resolution. It began operating at Kitt Peak, Arizona in 1997 and has recently completed the WHAM Northern Sky Survey (WHAM-NSS), providing the first global view of the distribution and kinematics of the warm, diffuse H II in the Milky Way. This H-alpha survey reveals a complex spatial and kinematic structure in the warm ionized medium and provides a foundation for studies of the temperature and ionization state of the gas, the spectrum and strength of the ionizing radiation, and its relationship to other components of the interstellar medium and sources of ionization and heating within the Galactic disk and halo. More information about WHAM and the Survey can be found at http://www.astro.wisc.edu/wham/.Comment: 12 pages, 4 figures, Invited talk to appear in "Galaxies: The Third Dimension", eds. M. Rosada, L. Binette, & L. Arias (ASP: San Francisco), 200