1,899 research outputs found
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
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
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
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
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