Multi-Pupil Fiber Spectrograph Research Articles

Spectroscopic study of the peculiar galaxy IC 883

We analyze new optical spectroscopic observations obtained at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences with the SCORPIO focal reducer (in the modes of a Fabry–Perot interferometer (FPI) and long-slit spectroscopy) and the Multi-Pupil Fiber Spectrograph for the galaxy IC 883. We have confirmed that the main body of the galaxy rotates around its minor axis. The positions of the dynamical axes of the stellar and gaseous components have been found to differ by ~10°. The velocities in the SE tail do not correspond to the circular rotation around the galaxy’s minor axis. This structure is probably a fragment of an unwound curved spiral arm. Regions with high velocity dispersions and peculiarities in the velocity fields have been found along the minor axis. Our study of the age and metallicity of the galaxy’s stellar population has shown that the mean values of these parameters in the stellar disk, except for the central region (r ≤ 5ʺ), are ≈1 Gyr and ≈−0.4 dex, respectively. Both young (2−5 × 108 yr) and old (5−10 × 109 yr) stellar populations are present in the circumnuclear region. Our analysis of the spectroscopic data for the bright feature 8ʺ south of the nucleus coincident in position with a compact X-ray source has shown that this is apparently a dwarf galaxy or a remnant of a companion galaxy. Our FPI observations in the Hα emission line and direct images have revealed a region of ionized gas that together with the already known structures along the minor axis forms a clumpy tidal structure of ionized gas pulled from the companion galaxy. The results of our study confirm the previously proposed hypothesis that the observed peculiar structures were formed by the merger of two galaxies. However, it can be said that IC 883 does not belong to the class of polar-ring galaxies.

Study of the structure and kinematics of the NGC 7465/64/63 triplet galaxies

This paper is devoted to the analysis of new observational data for the group of galaxies NGC 7465/64/63, which were obtained at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) with the multimode instrument SCORPIO and the Multi Pupil Fiber Spectrograph. For one of group members (NGC 7465) the presence of a polar ring was suspected. Large-scale brightness distributions, velocity and velocity dispersion fields of the ionized gas for all three galaxies as well as line-of-sight velocity curves on the basis of emission and absorption lines and a stellar velocity field in the central region for NGC 7465 were constructed. As a result of the analysis of the obtained information, we revealed an inner stellar disk (r ~ 0.5 kpc) and a warped gaseous disk in addition to the main stellar disk, in NGC 7465. On the basis of the joint study of photometric and spectral data it was ascertained that NGC 7464 is the irregular galaxy of the IrrI type, whose structural and kinematic peculiarities resulted most likely from the gravitational interaction with NGC 7465. The velocity field of the ionized gas of NGC 7463 turned out typical for spiral galaxies with a bar, and the bending of outer parts of its disk could arise owing to the close encounter with one of galaxies of the environment.

Ionized gas in the Irr galaxy IC 10: The emission spectrum and ionization sources

We present the results of observations of the Irr galaxy IC 10 at the 6-m SAO telescope with the panoramic Multi-Pupil Fiber Spectrograph (MPFS). Based on the results of these observations and our long-slit spectroscopy performed previously, we have investigated the ionized-gas emission spectrum in the region of intense star formation and refined the gas metallicity estimates. We show that the "diagnostic diagrams" constructed from our observations agree best with the new improved ionization models by Martin-Manjon et al. Using these models, we have determined the electron density and gas ionization parameter and ionizing-cluster characteristics, the age and mass, from the spectra of the investigated HII regions. The cluster age and mass are shown to be within the ranges 2.5 - 5 Myr and (0.2 - 1)*10^5 M(sun), respectively.

Origin of the Gas in the Extended Narrow-Line Region of Nearby Seyfert Galaxies: The Case of Mrk 6

AbstractIonization cones are one of the most important pieces of evidence supporting the AGN unified model (Antonucci & Miller 1985; Urry & Padovani 1995). Until now, the physical processes at work in the cones are not completely understood. A still open question concerns the origin of the gas. To study the origin of the ionized gas, we first selected a sample of nearby (z<0.03) Seyfert galaxies showing extended [O iii] λ5007 emission. We then observed these galaxies with the MultiPupil Fiber Spectrograph (MPFS) at the 6-m telescope of the Special Astrophysical Observatory (Russia). Here we present very preliminary results on the properties of the narrow-line region (NLR) of the intermediate Seyfert galaxy Mrk 6.

THREE-DIMENSIONAL SPECTROSCOPIC STUDY OF THE LINE-EMITTING REGIONS OF Mrk 493

We report the results of three-dimensional spectroscopic observations of Mrk 493 (narrow-line Seyfert 1 galaxy) with the integral-field spectrograph MultiPupil Fiber Spectrograph of the Special Astrophysical Observatory of the Russian Academy of Sciences 6 m telescope. The difference in the slope of the optical continuum emission intensity across the nucleus part and an extensive continuum emission region is detected. The emission in lines (Hα, Hβ, [O III], etc.) coincides with a composite nuclear region: an active galactic nucleus plus a circumnuclear star-forming ring observed in the Hubble Space Telescope UV/optical images. The [S II] emission region tends to be up to 1 kpc around the center. The Hα and Hβ could be decomposed into three components (broad ~2000 km s–1, intermediate ~700 km s–1, and narrow ~250 km s–1). We found that the width (~750 km s–1) of the Fe II lines corresponds to the intermediate component that may indicate a non-broad-line region (non-BLR) origin of the Fe II lines, or that a large fraction of the Fe II emission arises in the outer parts of the BLR. The weak broad component detected in the Hα, Hβ, and Heλ4686 may come from the unresolved central BLR, but also could be partly produced by violent starburst in the circumnuclear ring. Moreover, diagnostic diagrams clearly show the presence of the H II regions (not an Sy 1 nucleus) in the narrow-line region of Mrk 493.

The gas kinematics in the Mrk 533 nucleus and circumnuclear region: a gaseous outflow

We present an analysis of 3D spectra of Mrk 533, observed with the integral-field spectrograph MultiPupil Fiber Spectrograph (MPFS) and using the Fabry-Perot Interferometer (FPI) of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) 6-m telescope. We found emissions of gas from the active type 2 Seyfert nucleus in the centre and also from the H ii regions in a spiral structure and a circumnuclear region. The gas kinematics shows regular non-circular motions in the wide range of galactocentric distances from 500 pc up to 15 kpc. The maps of inward and outward radial motions of the ionized gas were constructed. We found that the narrow-line region (NLR) is composed of at least two (probably three) kinematically separated regions. We detect a stratification in the NLR of Mrk 533 with the outflow velocity ranging from 20–50 km s−1 to 600–700 km s−1, respectively, on the radial distances of ∼2.5 and ∼1.5 kpc. The maximal outflow velocity comes from the nucleus and corresponds to the position of the observed radio structure, which is assumed to be created in an approaching jet. We suggest that these ionized gas outflows are triggered by the radio jet intrusion in an ambient medium.

Central regions of the early-type galaxies in the NGC 3169 group

We have investigated the central regions of the galaxies in the NGC 3169/NGC 3166/NGC 3156 group with the multipupil fiber spectrograph of the 6-m telescope; the first (central) galaxy in the group is a spiral (Sa) one and the other two galaxies are lenticular ones. The group is known to have an extended HI cloud with a size of more than 100 kpc that is associated in its position, orientation, and rotation with the central galaxy NGC 3169. The mean age of the stellar populations in the centers of all three galaxies has been found to be approximately the same, ∼1 Gyr. Since the galaxies are early-type ones and since NGC 3166 and NGC 3156 show no global star formation, we are dealing here with a synchronous star formation burst in the centers of all three galaxies.

Chemically decoupled nuclei in five lenticular galaxies from SAURON data

We analyze data from the SAURON integral-field spectrograph of the William Herschel 4-m telescope for five lenticular galaxies in which we previously found chemically decoupled nuclei from observations with the Multipupil Fiber Spectrograph of the 6-m Special Astrophysical Observatory telescope. In a larger field of view, we confirmed the presence of peaks of the equivalent width of the Mg Ib λ5175 absorption line in the nuclei of all five galaxies. However, the structure of the chemically decoupled regions turned out to be highly varied even in such a small sample: from compact unresolved knots to disks with an extent of several hundred parsecs and, in one case, a triaxial compact minibar-type structure. We confirmed the presence of an inner gaseous polar ring in NGC 7280 and found it in NGC 7332. In their outer parts, the planes of these polar rings are warped toward the plane of stellar rotation in such a way that the gas counterrotates with respect to the stars. This behavior of the gas in a triaxial potential was predicted by several theoretical models.

NGC 7468: A galaxy with an inner polar disk

We present our spectroscopic observations of the galaxy NGC 7468 performed at the 6-m Special Astrophysical Observatory telescope using the UAGS long-slit spectrograph, the MPFS multi-pupil fiber spectrograph, and the IFP scanning Fabry-Perot interferometer. We found no significant deviations from the circular rotation of the galactic disk in the velocity field in the regions of brightness excess along the major axis of the galaxy (the putative polar ring). Thus, these features are either tidal structures or weakly developed spiral arms. However, we detected a gaseous disk at the center of the galaxy whose rotation plane is almost perpendicular to the plane of the galactic disk. The central collision of NGC 7468 with a gas-rich dwarf galaxy and their subsequent merging seem to be responsible for the formation of this disk.

Inner Polar Rings in Regular Lenticular Galaxies

We have investigated a sample of S0 galaxies, mostly with circumnuclear dust lanes orthogonal to their major axes, chosen from Hubble Space Telescope Wide Field Planetary Camera 2 images. Two-dimensional spectroscopy undertaken with the Multipupil Fiber Spectrograph of the 6 m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences has revealed that indeed the ionized gas in the centers of these eight lenticular galaxies rotate in the planes nearly orthogonal to the rotation (and symmetry) planes of their central stellar components. Although almost all the galaxies are located in dense environments, an external origin of this rotation plane tilt is not obvious because all the galaxies but one are known to have extended H I disks, and in two cases where the angular resolution of H I observations allows, we find orthogonality of the external H I and inner ionized gas disks. We discuss a possible relation of the inner gas polar rings to a triaxiality of galactic potential. The stellar populations in the nuclei of all but two galaxies are very old, which excludes recent star formation bursts and proves that the polar orbits of the circumnuclear gas are rather stable. In the nuclei of NGC 2655 and NGC 4111, we have found signatures of star formation bursts some 1.5–2 Gyr ago. This finding can be related to very central gas in NGC 2655, which is coplanar to the circumnuclear stellar disk and to radial gas inflow in NGC 4111; just these gas reservoirs and not the polar rings may be responsible for fueling nuclear star formation.

Complex Formation History of the Lenticular Galaxies with Stellar Counterrotation: NGC 4138 and NGC 4550

Two lenticular galaxies with counterrotating stellar components in their disks have been studied with the Multi-Pupil Fiber Spectrograph of the 6 m telescope (at the Special Astrophysical Observatory). In NGC 4138 the nucleus is certainly chemically distinct, with the central concentration of magnesium enhancement marginally exceeding that of iron. The ionized gas within R =4 00 of the nucleus rotates circularly in an inclined ring, perhaps a kind of a circumnuclear polar ring surrounding a compact stellar minibar. NGC 4550 exhibits complex extended structures in its center that can be identified by enhanced levels of magnesium and iron indices; the stellar population of the unresolved nucleus is younger than that of the circumnuclear region. We conclude that although NGC 4550 does not possess a chemically distinct nucleus in the ordinary sense of the term, there are nevertheless clear signatures of a secondary star formation burst confined perhaps to the counterrotating stellar gaseous disk. We argue that the inclination of the counterrotating disk differs from that of the main stellar disk, implying that the two disks are not coplanar. Both galaxies seem to have possessed bars, either actually present or already dissolved.

Interstellar medium surrounding the WO star in the galaxy IC 1613: New optical and radio observations

Observations of the nebula S3 associated with the WO star in the galaxy IC 1613 and of an extended region surrounding S3 are reported. The star and bright core of the nebula were observed with a multipupil fiber spectrograph mounted on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. Images in the principle spectral lines and integrated spectra of the star and three compact clumps were obtained, and the radial-velocity field constructed. An extended region of the galaxy was observed with the Very Large Array at 21 cm. A giant ring or H I shell enclosing a large fraction of the stellar population in IC 1613 was discovered. The WO star and associated bipolar nebula, which we discovered earlier, lie at the inner edge of the H I ring. A local H I deficiency and two arclike H I ridges were also detected for the first time and probably represent the neutral component of the bipolar shell surrounding the WO star. The two arclike ridges may also have been produced by the collective stellar wind (and supernova explosions?) in OB association No. 9 from the list of Hodge. A scenario for the formation of the extended bipolar feature is discussed, based on the new data.

Young Stellar Nuclei in the Lenticular Galaxies. II. NGC 7280

We have undertaken bidimensional spectroscopy of the central part of the nearby lenticular galaxy NGC 7280 with the Multi-Pupil Fiber Spectrograph of the 6 m telescope of the Special Astrophysical Observatory. We find a rather young stellar nucleus, with a mean population age of 1.5 ± 0.5 Gyr, which is more metal-rich than the bulge at R ≈ 1 kpc by an order of magnitude. The chemically and age-decoupled nucleus seems to be spatially resolved: the circumnuclear absorption index isolines represent ellipses elongated in P.A. ≈ 100°–110°. The same orientation, P.A. = 103°, is found for the elongated circumnuclear stellar structure, revealed from the morphological analysis of the Hubble Space Telescope (HST) WFPC2 and NICMOS images of NGC 7280 and seen best of all at R = 1''. Taking into account the stellar kinematics inside R ≈ 2'', we conclude that this structure is a circumnuclear stellar disk inclined with respect to the global plane of the galaxy. Meanwhile, both photometric and kinematical data in the radius range 2''–8'' imply the existence of an intermediate-scale bar elongated in P.A. ≈ 60°. The circumnuclear ionized gas is distributed and rotates in the plane orthogonal to the plane of the circumnuclear stellar disk.