Imaging Fabry-Perot Interferometer Research Articles

First results from SAM-FP: Fabry–Perot observations with ground-layer adaptive optics – the structure and kinematics of the core of 30 Doradus

The aim of this paper is to present the first data set obtained with SOAR Adaptive Module-Fabry-Parot (SAM-FP), a Fabry-Perot instrument mounted inside the SOAR telescope Adaptive-Optics Module. This is the only existing imaging Fabry-Perot interferometer using laser-assisted ground-layer adaptive optics. SAM-FP was used to observe the ionized gas, traced by Halpha, in the centre of the 30 Doradus starburst (the Tarantula Nebula) in the Large Magellanic Cloud, with high spatial (~0.6" or 0.15 pc) and spectral (R=11200) resolution. Radial velocity, velocity dispersion and monochromatic maps were derived. The region displays a mix of narrow, sigma ~ 20 km/s profiles and multiple broader profiles with sigma ~ 70-80 km/s, indicating the complex nature of the nebula kinematics. A comparison with previously obtained VLT/FLAMES spectroscopy demonstrates that the data agree well in the regions of overlap, but the Fabry-Perot data are superior in spatial coverage. A preliminary analysis of the observations finds a new expanding bubble south of R136, with a projected radius of r=5.6 pc and an expansion velocity of 29 +/- 4 km/s. In addition, the first-time detailed kinematic maps derived here for several complexes and filaments of 30 Doradus allow identification of kinematically independent structures. These data exemplify the power of the combination of a high-order Fabry-Perot with a wide-field imager (3' x 3' GLAO-corrected field of view) for high-resolution spatial and spectral studies. In particular, SAM-FP data cubes are highly advantageous over multifibre or long-slit data sets for nebula structure studies and to search for small-scale bubbles, given their greatly improved spatial coverage. For reference, this paper also presents two appendices with detailed descriptions of the usage of Fabry-Perot devices, including formulae and explanations for understanding Fabry-Perot observations.

New results on equatorial thermospheric winds and temperatures from Ethiopia, Africa

Abstract. Measurements of equatorial thermospheric winds, temperatures, and 630 nm relative intensities were obtained using an imaging Fabry–Perot interferometer (FPI), which was recently deployed at Bahir Dar University in Ethiopia (11.6° N, 37.4° E, 3.7° N magnetic). The results obtained in this study cover 6 months (53 nights of useable data) between November 2015 and April 2016. The monthly-averaged values, which include local winter and equinox seasons, show the magnitude of the maximum monthly-averaged zonal wind is typically within the range of 70 to 90 ms−1 and is eastward between 19:00 and 21:00 LT. Compared to prior studies of the equatorial thermospheric wind for this local time period, the magnitude is considerably weaker as compared to the maximum zonal wind speed observed in the Peruvian sector but comparable to Brazilian FPI results. During the early evening, the meridional wind speeds are 30 to 50 ms−1 poleward during the winter months and 10 to 25 ms−1 equatorward in the equinox months. The direction of the poleward wind during the winter months is believed to be mainly caused by the existence of the interhemispheric wind flow from the summer to winter hemispheres. An equatorial wind surge is observed later in the evening and is shifted to later local times during the winter months and to earlier local times during the equinox months. Significant night-to-night variations are also observed in the maximum speed of both zonal and meridional winds. The temperature observations show the midnight temperature maximum (MTM) to be generally present between 00:30 and 02:00 LT. The amplitude of the MTM was ∼ 110 K in January 2016 with values smaller than this in the other months. The local time difference between the appearance of the MTM and a pre-midnight equatorial wind was generally 60 to 180 min. A meridional wind reversal was also observed after the appearance of the MTM (after 02:00 LT). Climatological models, HWM14 and MSIS-00, were compared to the observations and the HWM14 model generally predicted the zonal wind observations well with the exception of higher model values by 25 ms−1 in the winter months. The HWM14 model meridional wind showed generally good agreement with the observations. Finally, the MSIS-00 model overestimated the temperature by 50 to 75 K during the early evening hours of local winter months. Otherwise, the agreement was generally good, although, in line with prior studies, the model failed to reproduce the MTM peak for any of the 6 months compared with the FPI data.

Quantifying Resolving Power in Astronomical Spectra

AbstractThe spectral resolving power R = λ/δλ is a key property of any spectrograph, but its definition is vague because the ‘smallest resolvable wavelength difference’ δλ does not have a consistent definition. Often, the FWHM is used, but this is not consistent when comparing the resolution of instruments with different forms of spectral line-spread function. Here, two methods for calculating resolving power on a consistent scale are given. The first method is based on the principle that two spectral lines are just resolved when the mutual disturbance in fitting the fluxes of the lines reaches a threshold (here equal to that of sinc2 profiles at the Rayleigh criterion). The second criterion assumes that two spectrographs have equal resolving powers if the wavelength error in fitting a narrow spectral line is the same in each case (given equal signal flux and noise power). The two criteria give similar results and give rise to scaling factors that can be applied to bring resolving power calculated using the FWHM on to a consistent scale. The differences among commonly encountered line-spread functions are substantial, with a Lorentzian profile (as produced by an imaging Fabry–Perot interferometer) being a factor of two worse than the boxy profile from a projected circle (as produced by integration across the spatial dimension of a multi-mode fibre) when both have the same FWHM. The projected circle has a larger FWHM than its true resolution, so using FWHM to characterise the resolution of a spectrograph which is fed by multi-mode fibres significantly underestimates its true resolving power if it has small aberrations and a well-sampled profile.

Simulations of imaging Fabry–Perot interferometers for measuring upper-atmospheric temperatures and winds

We apply an onion-peeling inversion to simulated imaging Fabry-Perot interferometer (FPI) observations for retrieving altitude profiles of neutral temperatures and winds in the thermosphere in order to investigate the effects of realistic gradients in thermospheric parameters on the retrieved parameters. A forward model is developed that simulates the interference spectrum observed by an FPI using the redline (630.0 nm) and greenline (557.7 nm) emissions simulated based on climatological models. This forward model is applicable to both ground- and satellite-based simulations and generates a two-dimensional interference ring pattern. We simulate both a single-band ground-based FPI and a dual-band satellite-based FPI in order to study the effects of realistic vertical and horizontal gradients on the retrieved parameters.

A 205 μm [N II] MAP OF THE CARINA NEBULA

We present the results of a � 250 arcmin 2 mapping of the 205 �m [NII] fine-structure emission over the northern Carina Nebula, including the Car I and Car II HII regions. Spectra were obtained using the South Pole Imaging Fabry-Perot Interferometer (SPIFI) at the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) at South Pole. We supplement the 205 �m data with new reductions of far-IR fine-structure spectra from the Infrared Space Observatory (ISO) Long Wavelength Spectrometer (LWS) in 63 �m [OI], 122 �m [NII], 146 �m [OI], and 158 �m [CII]; the 146 �m [OI] data include 90 raster positions which have not been previously published. Morphological comparisons are made with optical, radio continuum and CO maps. The 122/205 line ratio is used to probe the density of the low-ionization gas, and the 158/205 line ratio is used to probe the fraction of C + arising from photodissociation regions (PDRs). The [OI] and [CII] lines are used to construct a PDR model of Carina. When the PDR properties are compared with other sources, Carina is found to be more akin to 30 Doradus than galactic star-forming regions such as Orion, M17, or W49; this is consistent with the view of Carina as a more evolved region, where much of the parent molecular cloud has been ionized or swept away. These data constitute the first ground-based detection of the 205 �m [NII] line, and the third detection overall since those of the COBE FIRAS and the KAO in the early 1990s. Subject headings: HII regions — infrared: ISM — ISM: individual (Carina nebula) — ISM: lines and bands — photon-dominated region (PDR) — submillimeter: ISM

Simulation and analysis of a multi-order imaging Fabry–Perot interferometer for the study of thermospheric winds and temperatures

We describe an analysis procedure for estimating the thermospheric winds and temperatures from the multi-order two-dimensional (2D) interferograms produced by an imaging Fabry-Perot interferometer (FPI) as imaged by a CCD detector. We also present a forward model describing the 2D interferograms. To investigate the robustness and accuracy of the analysis, we perform several Monte Carlo simulations using this forward model for an FPI that has recently been developed and deployed to northeastern Brazil. The first simulation shows that a slight cross-contamination at high temperatures exists between neighboring orders in the interferogram, introducing a bias in the estimated temperatures and increasing errors in both the estimated temperatures and winds when each order is analyzed in full. The second simulation investigates how using less than an entire order in the analysis reduces the cross contamination observed in the first set of simulations, improving the accuracy of the estimated temperatures. The last simulation investigates the effect of the signal-to-noise ratio on the errors in the estimated parameters. It is shown that, for the specific FPI simulated in this study, a signal-to-noise ratio of 1.5 is required to obtain thermospheric wind errors of 5 m/s and temperature errors of 20 K.

New results on equatorial thermospheric winds and the midnight temperature maximum

Abstract. Optical observations of thermospheric winds and temperatures determined with high resolution measurements of Doppler shifts and Doppler widths of the OI 630-nm equatorial nightglow emission have been made with improved accuracy at Arequipa, Peru (16.4° S, 71.4° W) with an imaging Fabry-Perot interferometer. An observing procedure previously used at Arecibo Observatory was applied to achieve increased spatial and temporal sampling of the thermospheric wind and temperature with the selection of eight azimuthal directions, equally spaced from 0 to 360°, at a zenith angle of 60°. By assuming the equivalence of longitude and local time, the data obtained using this technique is analyzed to determine the mean neutral wind speeds and mean horizontal gradients of the wind field in the zonal and meridional directions. The new temperature measurements obtained with the improved instrumental accuracy clearly show the midnight temperature maximum (MTM) peak with amplitudes of 25 to 200 K in all directions observed for most nights. The horizontal wind field maps calculated from the mean winds and gradients show the MTM peak is always preceded by an equatorward wind surge lasting 1–2 h. The results also show for winter events a meridional wind abatement seen after the MTM peak. On one occasion, near the September equinox, a reversal was observed during the poleward transit of the MTM over Arequipa. Analysis inferring vertical winds from the observed convergence yielded inconsistent results, calling into question the validity of this calculation for the MTM structure at equatorial latitudes during solar minimum. Comparison of the observations with the predictions of the NCAR general circulation model indicates that the model fails to reproduce the observed amplitude by a factor of 5 or more. This is attributed in part to the lack of adequate spatial resolution in the model as the MTM phenomenon takes place within a scale of 300–500 km and ~45 min in local time. The model shortcoming is also attributed in part to the need for the model to include a hydrodynamical mechanism to describe the merging of the zonal wind with the meridional tidal winds that converge onto the geographical equator. Finally, a conclusion of this work is that the MTM compressional heating takes place along the perimeter of the pressure bulge rather than within the bulge, an issue previously not appreciated.

Detection of the 205 μm [N ii ] Line from the Carina Nebula

We report the first detection of the 205 μm 3P1 P0 [N II] line from a ground-based observatory using a direct detection spectrometer. The line was detected from the Carina star formation region using the South Pole Imaging Fabry-Perot Interferometer (SPIFI) on the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) at the South Pole. The [N II] 205 μm line strength indicates a low-density (n ~ 32 cm-3) ionized medium, similar to the low-density ionized halo previously reported in its [O III] 52 and 88 μm line emission. When compared with the Infrared Space Observatory [C II] observations of this region, we find that 27% of the [C II] line emission arises from this low-density ionized gas, but the large majority (~73%) of the observed [C II] line emission arises from the neutral interstellar medium. This result supports and underpins prior conclusions that most of the observed [C II] 158 μm line emission from Galactic and extragalactic sources arises from the warm, dense photodissociated surfaces of molecular clouds. The detection of the [N II] line demonstrates the utility of Antarctic sites for THz spectroscopy.

The metallicity-luminosity relation at medium redshift based on faint CADIS emission line galaxies

The emission line survey within the Calar Alto Deep Imaging Survey (CADIS) detects galaxies with very low continuum brightness by using an imaging Fabry-Perot interferometer. With spectroscopic follow-up observations of MB>~-19 CADIS galaxies using FORS2 at the VLT and DOLORES at TNG we obtained oxygen abundances of 5 galaxies at z~0.4 and 10 galaxies at z~0.64. Combining these measurements with published oxygen abundances of galaxies with MB<~-19 we find evidence that a metallicity-luminosity relation exists at medium redshift, but it is displaced to lower abundances and higher luminosities compared to the metallicity-luminosity relation in the local universe. Comparing the observed metallicities and luminosities of galaxies at z<3 with Pegase2 chemical evolution models we have found a favoured scenario in which the metallicity of galaxies increases by a factor of ~2 between z~0.7 and today, and their luminosity decreases by ~0.5-0.9mag.

Star forming rates between z = 0.25 and z = 1.2 from the CADIS emission line survey

The emission line survey within the Calar Alto Deep Imaging Survey (CADIS) detects emission line galaxies by a scan with an imaging Fabry-Perot interferometer. It covers 5 fields of each in three wavelengths windows centered on , 820, and 920 nm, and reaches to a typical limiting line flux of W m-2. This is the deepest emission line survey covering a field of several 100 . Galaxies between and are detected by prominent emission lines (from Hα to [O ii]372.7) falling into the FP scans. Additional observations with a dozen medium band filters allow to establish the line identification and thus the redshift of the galaxies to better than . On the basis of a total of more than 400 emission line galaxies detected in Hα (92 galaxies), [O iii]500.7 (124 galaxies), or [O ii]372.7 (222 galaxies) we measure the instantaneous star formation rate (SFR) in the range . With this purely emission line selected sample we are able to reach much fainter emission line galaxies than previous, continuum-selected samples. Thus completeness corrections are much less important. Although the relative [O iii] emission line strength depends on excitation and metallicity and shows strong variation, the mean line ratios yield SFR[O iii] values consistent with the SFR evolution. Our results substantiates the indications from previous studies (based on small galaxy samples) that the SFR decreases by a factor of ~20 between and today. In fact, for a cosmology, we find an exponential decline Gyr). This decrease of the SFR with time follows an exponential law which is compatible with the decreasing galaxy merger rate as expected from model calculations. The inferred SF density is in perfect agreement with that deduced from the FIR emission of optically selected galaxies which is explained by a large overlap between both populations. We show that self-consistent extinction corrections of both our emission lines and the UV continua lead to consistent results for the SF density.

Constraints to the evolution of Ly-αbright galaxies betweenz= 3 andz= 6

Galaxies at high redshift with a strong Ly-α emission line trace massive star formation in the absence of dust, and can therefore be regarded as a prime signature of the first major starburst in galaxies. We report results of the Ly-α search within the Calar Alto Deep Imaging Survey (CADIS). With the imaging Fabry-Perot interferometer, CADIS can detect emission lines in three waveband windows free of night-sky emission lines at 700 nm, 820 nm, and 920 nm. The typical flux detection limit for Ly-α emission redshifted into these windows, Flim > 3 × 10 −20 Wm −2 , corresponds to (unobscured) star formation rates of >10 M� /yr at z = 6. Candidate Ly-α-emitting galaxies are selected from the total emission line sample, which contains more than 97% of objects at z 5 than the assumption of a non-evolving population would predict. Therefore we conclude that the Ly-α bright phase of primeval star formation episodes reached its peak at redshifts 3 < z < 6.

Tridimensional Spectroscopic Observation of the Interacting System NGC 7592

Abstract We performed a tridimensional spectroscopic study of NGC 7592, an infrared-luminous interacting system of three galaxies, one of which contains a Seyfert 2 nucleus. Narrow-band images of $\mathrm{H}\alpha$ and [O iii] were obtained using an imaging Fabry–Perot interferometer with a tunable filter. An area-spectroscopic observation was also made by a slit scan in a direction perpendicular to the slit. The Seyfert nucleus was found to be surrounded by a knotty star-forming region of disk- or ring-shape. Along the axis of the disk or ring, a highly-ionized bipolar gaseous region was identified. From kinematical analyses, it has been suggested that this system is composed of two galaxies; one apparent nucleus is considered to be a giant H ii region belonging to one galaxy. This result is supported by the morphological properties in near-infrared. Further, it has been suggested that one galaxy is an early-type spiral, whereas the other is a late-type one, and the two galaxies show a marked difference in the distribution of the star-forming regions within each. The cause of the difference was argued in relation with the dynamical perturbation between the two galaxies.

SPIFI: a direct-detection imaging spectrometer for submillimeter wavelengths.

The South Pole Imaging Fabry-Perot Interferometer (SPIFI) is the first instrument of its kind-a direct-detection imaging spectrometer for astronomy in the submillimeter band. SPIFI's focal plane is a square array of 25 silicon bolometers cooled to 60 mK; the spectrometer consists of two cryogenic scanning Fabry-Perot interferometers in series with a 60-mK bandpass filter. The instrument operates in the short submillimeter windows (350 and 450 microm) available from the ground, with spectral resolving power selectable between 500 and 10,000. At present, SPIFI's sensitivity is within a factor of 1.5-3 of the photon background limit, comparable with the best heterodyne spectrometers. The instrument's large bandwidth and mapping capability provide substantial advantages for specific astrophysical projects, including deep extragalactic observations. We present the motivation for and design of SPIFI and its operational characteristics on the telescope.

Star Formation in M51 Triggered by Galaxy Interaction

We have mapped the inner 360'' regions of M51 in the 158micron [CII] line at 55'' spatial resolution using the Far-infrared Imaging Fabry-Perot Interferometer (FIFI) on the Kuiper Airborne Observatory (KAO). The emission is peaked at the nucleus, but is detectable over the entire region mapped, which covers much of the optical disk of the galaxy. There are also two strong secondary peaks at ~43% to 70% of the nuclear value located roughly 120'' to the north-east, and south-west of the nucleus. These secondary peaks are at the same distance from the nucleus as the corotation radius of the density wave pattern. The density wave also terminates at this location, and the outlying spiral structure is attributed to material clumping due to the interaction between M51 and NGC5195. This orbit crowding results in cloud-cloud collisions, stimulating star formation, that we see as enhanced [CII] line emission. The [CII] emission at the peaks originates mainly from photodissociation regions (PDRs) formed on the surfaces of molecular clouds that are exposed to OB starlight, so that these [CII] peaks trace star formation peaks in M51. The total mass of [CII] emitting photodissociated gas is ~2.6x10^{8} M_{sun}, or about 2% of the molecular gas as estimated from its CO(1-0) line emission. At the peak [CII] positions, the PDR gas mass to total gas mass fraction is somewhat higher, 3-17%, and at the secondary peaks the mass fraction of the [CII] emitting photodissociated gas can be as high as 72% of the molecular mass.... (continued)

Three-channel imaging Fabry–Perot interferometer for measurement of mid-latitude airglow

We have developed a three-channel imaging Fabry-Perot interferometer with which to measure atmospheric wind and temperature in the mesosphere and thermosphere through nocturnal airglow emissions. The interferometer measures two-dimensional wind and temperature for wavelengths of 630.0 nm (OI, altitude, 200-300 km), 557.7 nm (OI, 96 km), and 839.9 nm (OH, 86 km) simultaneously with a time resolution of 20 min, using three cooled CCD detectors with liquid-N(2) Dewars. Because we found that the CCD sensor moves as a result of changes in the level of liquid N(2) in the Dewars, the cooling system has been replaced by thermoelectric coolers. The fringe drift that is due to changes in temperature of the etalon is monitored with a frequency-stabilized He-Ne laser. We also describe a data-reduction scheme for calculating wind and temperature from the observed fringes. The system is fully automated and has been in operation since June 1999 at the Shigaraki Observatory (34.8N, 136.1E), Shiga, Japan.

Properties of the Photodissociated Gas in NGC 6334

To investigate the properties of photodissociated gas in strong radiation fields, the massive star formation region NGC 6334 has been mapped with the Far-Infrared Imaging Fabry-Perot Interferometer (FIFI) instrument in the far-infrared fine-structure transitions [C II] 158 μm, [O I] 146 μm, and [O I] 63 μm. Bright [C II] 158 μm emission is found throughout the cloud, whereas the [O I] 146 μm emission is associated only with the star-forming ridge. Comparison of the relative intensities of the lines with single-component photodissociation region models suggests densities of nH ~ 104 cm-3. The models imply unphysically large radiation fields for three sources, particularly for NGC 6334A, which is probably caused by self-absorption in the [O I] 63 μm line. An alternative method for estimating physical conditions, based on the correlation between [C II] 158 μm and CO line intensities, is explored. This method implies hydrogen column densities of NH 1022-23 cm-2, which agree well with those from molecular excitation models. The relative distribution of the [C II] 158 μm and [O I] 146 μm emission supports clumpy photodissociation region models that suggest the [C II] 158 μm emission arises from interclump gas and thus should be more extended than the [O I] 146 μm emission that arises from the denser clumps. The spatial coincidence of [C II] 158 μm emission peaks with minima in the molecular gas emission indicates that at least some of the molecular holes contain photodissociated gas. The relative pressures of the ionized, photodissociated, and molecular gas are compared: the photodissociated and molecular gas are in approximate pressure equilibrium, but the ionized gas is overpressurized by at least an order of magnitude at the continuum sources.

The Biconical Outflow in the Seyfert Galaxy NGC 2992

We report on a detailed kinematic study of the galactic-scale outflow in the Seyfert galaxy NGC 2992. The TAURUS-2 imaging Fabry-Perot interferometer was used on the 3.9 m Anglo-Australian Telescope to derive the two-dimensional velocity field of the Hα-emitting gas over the central arcminute of NGC 2992. The complete two-dimensional coverage of the data combined with simple kinematic models of rotating axisymmetric disks allow us to differentiate the outflowing material from the line-emitting material associated with the galactic disk. The kinematics of the disk component out to R = 3.0 kpc are well modeled by pure circular rotation in a plane inclined at i = 68° ± 3° from the plane of the sky and with kinematic major axis along P.A. = 32° ± 3°. The outflow component is distributed into two wide cones with opening angle ≈125°–135° and extending ~2.8 kpc (18'') on both sides of the nucleus at nearly right angles ( ≈ 116° ± 5°) to the disk kinematic major axis. The outflow on the southeastern side of the nucleus is made of two distinct kinematic components interpreted as the front and back walls of a cone. The azimuthal velocity gradient in the back-wall component reflects residual rotational motion, which indicates either that the outflowing material was lifted from the disk or that the underlying galactic disk is contributing slightly to this component. A single outflow component is detected in the northwestern cone. A biconical outflow model with velocities ranging from 50 to 200 km s-1 and oriented nearly perpendicular to the galactic disk can explain the data. The broad-line profiles and asymmetries in the velocity fields suggest that some of the entrained line-emitting material may lie inside the biconical structure rather than only on the surface of the bicone. The mass involved in this outflow is of order ~1 × 107 n M⊙, and the bulk and turbulent kinematic energies are ~6 × 1053 n ergs and ~3 × 1054 n ergs, respectively. The most likely energy source is a hot, bipolar, thermal wind powered on a subkiloparsec scale by the active galactic nucleus and diverted along the galaxy's minor axis by the pressure gradient of the ISM in the host galaxy. The data are not consistent with a starburst-driven wind or a collimated outflow powered by radio jets.

Tridimensional Spectrophotometric Study of the Extended Emission-Line Regions of the Infrared-Luminous Merger Markarian 266

An extensive tridimensional spectrophotometric study of the extended emission-line regions of Mrk 266, a merging system of a Seyfert galaxy and a LINER, was performed. We obtained its narrow-band images of Hα, [OIII] λ5007, and [SII] λλ 6716, 6731 using an imaging Fabry-Perot interferometer with a tunable filter and area spectroscopic data by means of a slit-scan. From these data were found high-excitation regions characterized by large [OIII]/Hβ (∼ 10) and large HeII λ 4686/Hβ (≥ 0.2). These regions can be considered as being photoionized by a power-law continuum from the Seyfert nucleus. If the continuum is radiated isotropically, an ionizing luminosity of 1055–56 photons s−1 is required. This implies that the Seyfert nucleus is one of the most luminous Seyfert nuclei, and can dominate the heating of dust, emitting the enormous amount of infrared emission of Mrk 266 (∼ 3 × 1011L⊙). The line ratios and emission-line luminosities of the LINER nucleus can be interpreted as an indication of a central starburst with a bolometric luminosity of about 2–6 × 1010L⊙ and a large-scale outflow (“superwind”). Finally, we remark on the evolutionary nature of activities of Mrk 266.

A Kinematic Link Between Boxy Bulges, Stellar Bars, and Nuclear Activity in NGC 3079 and NGC 4388

We present direct kinematic evidence for bar streaming in two active galaxies with boxy stellar bulges. The Hawaii Imaging Fabry-Perot Interferometer was used on the Canada-France-Hawaii 3.6-m telescope and the University of Hawaii 2.2-m telescope to derive the two-dimensional velocity field of the line-emitting gas in the disks of the Sc galaxy NGC 3079 and the Sb galaxy NGC 4388. In contrast to previous work based on long-slit data, the detection of the bar potential from the Fabry-Perot data does not rely on the existence of inner Lindblad resonances or strong bar-induced shocks. Simple kinematic models which approximate the intrinsic gas orbits as nonintersecting, inclined elliptical annuli that conserve angular momentum characterize the observed velocity fields. In NGC 3079, bar streaming motions with moderately eccentric orbits (e = b/a approx. 0.7) aligned along PA = 130 deg. intrinsic to the disk (PA = 97 deg. on the sky) are detected out to R(sub b) = 3.6 kpc. The orbits become increasingly circular beyond that radius (e = 1 at R(sub d) approx. = 6 kpc). The best model for NGC 4388 includes highly eccentric orbits (e approx. 0.3) for R(sub) less than or equal to 1.5 kpc which are aligned along PA = 135 deg. intrinsic to the disk (PA = 100 deg. on the sky). The observed spiral arms are produced by having the orbits become increasingly circular from the ends of the bar to the edge of the disk (R(sub d) approx. = 5 kpc), and the intrinsic bar PA shifting from 135 deg. to 90 deg.. Box-shaped bulges in both NGC 3079 and NGC 4388 are confirmed using new near-infrared images to reduce dust obscuration. Morphological analysis of starlight in these galaxies is combined with the gas kinematics derived from the Fabry-Perot spectra to test evolutionary models of stellar bars that involve transitory boxy bulges, and to quantify the importance of such bars in fueling active nuclei. Our data support the evolutionary bar models, but fail to prove convincingly that the stellar bars in NGC 3079 and NGC 4388 directly trigger or sustain the nuclear activity.

Galactic‐Scale Outflow and Supersonic Ram‐Pressure Stripping in the Virgo Cluster Galaxy NGC 4388

The Hawaii Imaging Fabry-Perot Interferometer (HIFI) on the University of Hawaii 2.2 m telescope was used to map the Hα and [O III] λ5007 emission-line profiles across the entire disk of the edge-on Sb galaxy NGC 4388. We confirm a rich complex of highly ionized gas that extends ~4 kpc above the disk of this galaxy. Low-ionization gas associated with star formation is also present in the disk. Evidence for bar streaming is detected in the disk component and is discussed in a companion paper. Nonrotational blueshifted velocities of 50-250 km s-1 are measured in the extraplanar gas northeast of the nucleus. The brighter features in this complex tend to have more blueshifted velocities. A redshifted cloud is also detected 2 kpc southwest of the nucleus. The velocity field of the extraplanar gas of NGC 4388 appears to be unaffected by the inferred supersonic (Mach number M ≈ 3) motion of this galaxy through the ICM of the Virgo cluster. We argue that this is because the galaxy and the high-|z| gas lie behind a Mach cone with opening angle ~80°. The shocked ICM that flows near the galaxy has a velocity of ~500 km s-1 and exerts insufficient ram pressure on the extraplanar gas to perturb its kinematics. We consider several explanations of the velocity field of the extraplanar gas. Velocities, especially blueshifted velocities on the north of the galaxy, are best explained as a bipolar outflow that is tilted by >12° from the normal to the disk. The observed offset between the extraplanar gas and the radio structure may be due to buoyancy or refractive bending by density gradients in the halo gas. Velocity substructure in the outflowing gas also suggests an interaction with ambient halo gas.