C. del Burgo

INTEGRAL: a matrix optical fiber system for WYFFOS

INTEGRAL is an optical fiber unit for performing 2D spectroscopy of extended objects at the 4.2 m. William Herschel Telescope (WHT). It is mounted at the GHRIL Nasmyth focus together with newly built acquisition, guiding, and calibration units. It makes use of the specially designed fiber spectrograph WYFFOS. This system allows up to six bundles to be mounted simultaneously. It currently contains three science oriented fiber bundles, any one of which can be easily and quickly placed in the telescope beam. Their spatial resolution elements (fiber core diameters) are 0.45, 0.9, and 2.7, respectively. Hence, depending on the prevailing seeing conditions the instrument can be easily optimized for the scientific program. INTEGRAL was successfully commissioned at the WHT during a six night period in July 1997. Here we will discuss its main characteristics.

Stellar and Ionized-Gas Kinematics of the Seyfert 1 Galaxy NGC 3516

We present bidimensional spectroscopy of the central region (94 × 122) of the Seyfert galaxy NGC 3516 in the two spectral ranges 4186-5839 A and 6110-7890 A. The data (95 × 2 spectra) were simultaneously obtained with an optical fibre system (2D-FIS). The two-dimensional velocity map of the stellar component was obtained from the Mg I b absorption lines. The kinematic axes of this stellar velocity field agree very well with the geometrical axes determined from the outer isophotes. In consequence, despite the existence of an outer ring and a bar, the stars in the circumnuclear region rotate regularly. New accurate value for the systemic velocity (2593 ± 15 km s-1), the orientation of the line of nodes (53° ± 5°), and the amplitude of the velocity field (~80 km s-1) are presented. The center of rotation has also been determined and could be spatially displaced with respect to the active nucleus. We have performed an emission-line profile decomposition and identified several components. In addition to the component responsible for the Z-shaped morphology of the line-emission region, gaseous systems showing large widths (FWHM ~ 10-20 A) and extreme blueshift (-900 km s-1) have been found. The comparison between the stellar and ionized-gas velocity maps favors the precessing twin-jet model over the bent-outflow hypothesis to explain the Z-shaped morphology and two-dimensional kinematics of the line-emission region.

Two-dimensional line-strength maps in three well-studied early-type galaxies

Integral field spectroscopy has been obtained for the nuclear regions of three large, well-studied, early-type galaxies. From these spectra we have obtained line-strength maps for about 20 absorption lines, mostly belonging to the Lick system. An extensive comparison with multilenslet spectroscopy shows that accurate kinematic maps can be obtained, and also reproducible line-strength maps. Comparison with long-slit spectroscopy also produces good agreement. n n n nWe show that Mg is enhanced with respect to Fe in the inner disc of one of the three galaxies studied, the Sombrero. [Mg/Fe] there is larger than in the rest of the bulge. The large values of Mg/Fe in the central disc are consistent with the centres of other early-type galaxies, and not with large discs, like the disc of our Galaxy, where [Mg/Fe] ∼0. We confirm with this observation a recent result of Worthey: that Mg/Fe is determined only by the central kinetic energy, or escape velocity, of the stars, and not by the formation time-scale of the stars. n n n nA stellar population analysis using the models of Vazdekis et al. shows that our observed Hγ agrees well with what is predicted based on the other lines. Given the fact that Hβ is often contaminated by emission lines, we confirm the statement of Worthey & Ottaviani, Kuntschner & Davies and others that if one tries to measure ages of galaxies, Hγ is a much better index to use than Hβ. Using the line strength of the Caxa0ii IR triplet as an indicator of the abundance of Ca, we find that Ca follows Fe, and not Mg, in these galaxies. This is peculiar, given the fact that Ca is an α element. Finally, by combining the results of this paper with those of Vazdekis et al., we find that the line-strength gradients in the three galaxies are primarily caused by variations in metallicity.

Two-dimensional Spectroscopy Reveals an Arc of Extended Emission in the Gravitational Lens System Q2237+0305

We present two-dimensional spectroscopy of the gravitational lens system Q2237+0305 (Einstein Cross) obtained with the INTEGRAL fiber system in subarcsecond seeing conditions. The four components of the system appear clearly separated in the continuum intensity maps. However, the intensity map of the C III] ?1909 line exhibits an arc of extended emission connecting the A, D, and B components. This result can be explained if, as is usually assumed, the continuum arises from a compact source 0.05 pc in extent in the nucleus of the object while the line emission comes from a much larger region. A lens model fitted to the positions of the four compact images also accounts for the arc morphology. In the framework of this model, the region generating the C III] ?1909 emission would have dimensions of about 400 h-1 pc across. We interpret the observed arc as a gravitational lens image of the extended narrow line region of the source.

Evidence of Two Kinematically Different Stellar Systems in NGC 1068

We have obtained simultaneous two-dimensional spectroscopy of the Ca II triplet lines in the central 24 × 20 of NGC 1068, using an optical fiber system. The stellar velocity field derived from these data shows a kinematic off-centering between the inner (r 5) regions, indicative of a nonsymmetric gravitational potential. Both regions exhibit kinematic minor axes aligned with PA ~ 0° and could have similar systemic velocities. However, their kinematic centers are displaced by ~25. We propose that two kinematically different stellar systems rotating around parallel but shifted axes are present in NGC 1068. The origin of this peculiarity is discussed in relation to the gravitational potential of the galaxy and the hypothesis of a minor merger event.

Stellar and Ionized Gas Kinematics in the Circumnuclear Region of the Galaxy NGC 7331

We present simultaneous two-dimensional spectroscopy of the circumnuclear region (12 × 9) of the galaxy NGC 7331, obtained with an optical fiber system coupled to the ISIS double spectrograph of the 4.2 m William Herschel Telescope. The system allows simultaneous observation of 125 regions of this galaxy in two spectral ranges: 4590-5400 A at high resolution (1.5 A) and 6400-9620 A at low resolution (5 A). These spectra are mainly used to study the stellar and gas kinematics in the innermost region of this galaxy. The stellar velocity fields inferred from the Mg I b and Ca II absorption lines are in good agreement. They show a solid-body rotational pattern with the line of nodes along the position angle of the apparent major axis of the galaxy. The relatively large local stellar velocity dispersion suggests that we are observing the bulge rather than the disk kinematics. The two-dimensional kinematic data agree with previous one-dimensional studies that found no evidence for a massive black hole in NGC 7331. The [O III] emission lines are split into three components. One is distributed around the systemic velocity, another is systematically blueshifted, and the last is systematically redshifted. We propose that these arise from two distinct gaseous systems: a warped disk of irregular rotational pattern with the kinematic axes shifted by about 30° with respect to those of the stars, and a shell of gas flowing radially. Although alternative interpretations in terms of inflow driven by a central bar or outflow produced by a galactic wind are possible, the latter seems preferable. In NGC 7331 the ionized gas and stars are kinematically decoupled, the velocity dispersion of the ionized gas being substantially lower than that of the stars. This last result differs from what is generally found in Seyfert galaxies. However, NGC 7331 and M31 show a large degree of similarity, and the type of LINERs that they harbor are probably produced by the same type of phenomenon.

Two-dimensional Spectroscopy in the Circumnuclear Region of the Seyfert 1 Ring Galaxy NGC 985

We present two-dimensional optical spectroscopy of the central region (94×122) of the Seyfert 1 ring galaxy NGC 985 obtained with an optical fiber system (two-dimensional Fiber ISIS System). The 95 spectra presented here include the Hβ-[O III] λλ4959, 5007 emission lines and the Mg I b absorption lines, which permit the study of the distribution and kinematics of the ionized gas and the stars in two dimensions. In agreement with the results of other authors, the continuum maps show the presence of two maxima: the bright Seyfert 1 nucleus and a second nucleus located about 37 to the northwest. These observations confirm that this second nucleus is an extragalactic object at the same redshift as that of NGC 985. These observations indicate an anisotropic distribution of the ionized gas around the Seyfert nucleus. Despite this, the velocity field of the ionized gas shows a rather regular pattern, its general kinematic properties being similar to those found in other unperturbed spiral Seyfert galaxies. Many of the spectra in the region between the Seyfert and the secondary nucleus have asymmetric and relatively broad [O III] emission-line profiles. The kinematic center of the stellar velocity field is located in the neighborhood of the Seyfert nucleus, suggesting that this nucleus is related to the main stellar component. Therefore, these observations support the hypothesis that NGC 985 is the result of a two-galaxy collision in which the intruder (elliptical or spheroidal) galaxy would be what is now the secondary nucleus, while the Seyfert activity is associated with the nucleus of the primary disk galaxy. In spite of the strong disruption that defines the large-scale morphology of NGC 985, the stellar and ionized gas kinematics do not appear significantly perturbed in the circumnuclear region.

Extended Broad Balmer Emission in the Seyfert 1 Galaxy Markarian 509

We present two-dimensional spectroscopic observations of the circumnuclear region of Mrk 509. The spectra show extended (off-nuclear) broad Balmer emission (FWZI>15,000 km s-1) in a region of about 8 in diameter (8 kpc if H -->0=50 km s-1 Mpc-1). These features are interpreted as reflected radiation coming from the unresolved active nucleus. The nearly isotropic appearance of the scattering region can be explained within the framework of the unified picture for active galactic nuclei, if the scatterers lie outside the galaxys disk; otherwise, the present observations would not support simple anisotropic models for the Seyfert nucleus in Mrk 509.

Stellar Velocity Field in the Central Region of NGC 1068

We present the velocity field of the stars in the central 25″ × 22″ of NGC 1068 derived from 2-D spectroscopy of the Ca II triplet. A preliminary analysis provides evidence for two distinct stellar systems in the centre of NGC 1068. In the outer regions (say r > 10″), the mean stellar velocity field seems coupled to those of the ionized and molecular gas, indicating aproximately regular rotation with the kinematic minor axis at PA ~ 0°. However, in the inner region, the stars are rotating, whereas the ionized gas is outflowing in the NE-SW direction probably due to the effects of the nuclear activity, and the molecular gas is responding to the bar potential.

Ionized Gas Velocity Field in Central Region of NGC 1068 Inferred from the [O III] λλ 4959,5007 and [S III] λ 9069 Lines

From 2-D spectroscopy of the [O III] λλ 4959,5007 and [S III] λ 9069 lines we have studied the ionized gas-velocity field in the central regions of NGC 1068. The existence of a strong bipolar outflow of ionized gas is confirmed. The origin of this outflow, which is probably related to the active nucleus, is about 1.4″ NE of the optical nucleus; therefore, this region is a candidate to host the hidden nucleus of NGC 1068.