¹Dept. of Physics, University of Durham, U.K. ²Institute of Astronomy, Cambridge, U.K.

Since the concept was proposed in the 1970s, galaxy cluster cooling flows have been a controversial topic in extragalactic astronomy. Until recently, the absence of an obvious sink for the cooled material was the reason for much of this hostility. New observational developments on two separate fronts have helped to bridge this particular impasse but have given rise to some new problems. Firstly, soft X-ray grating spectra show line emission from gas down to about one third of the cluster virial temperature, but not from cooler gas. At least half a dozen distinct mechanisms have been proposed to explain this fact, both with and without additional heat sources. Concurrent with this, the first widespread detections of cold gas in cooling flows have been made: assuming a standard CO:H2 conversion, some 1E9-1E11.5 M-sun of cool (~10-100 K) H2 have been found in 16 clusters. The solution to the soft X-ray cooling problem must account for this material.

In 2003 we started to use the UIST IFU to map the hot molecular hydrogen in the central galaxies of several cooling flows. Although small by mass (~1E5-1E6 M-sun), such ~2000K H2 forms an important link between the cool gas traced by CO and the ~10,000K gas seen in optical emission lines. As such, it gives insight into astrophysical processes relevant to the current cooling flow problem, such as the mixing of hot and cold gas, cloud evaporation and shocks. Here we report on our observations of NGC 1275, an FRI radio source at the centre of the Perseus cluster, one of the nearest and best-studied cluster cores.

FIGURE 1: The left-hand plot shows a contour map of H2 v=1-0 S(1) derived from a continuum-subtracted narrow-band cut through the datacube obtained with the HK grism. The image was smoothed with a 0.48 arcsec square top-hat filter prior to contouring; contour levels increase by sqrt(2) with the lowest set at 2 sigma of the background. North is to the left, east is down. To the right are shown the intensity and velocity profiles of H2 v=1-0 S(1) in the central IFU slit passing through the nucleus. On the former plot, the dashed lines show the contributions from two point sources of emission at offsets +-0.12 arcsec and the solid line their sum, which accounts for the bulk of the emission in the central 0.6 arcsec. The velocity is that of the stronger of two gaussians fitted to the line profile at each position, as shown in Figure 2.

During summit time in September 2003, we took advantage of 0.3-0.4 arcsec seeing to focus on the H2 emission in the nuclear region, acquiring data with both the HK grism (to include several H2 lines as well as Pa&alpha and [FeII]) and the short-K grism (for high resolution kinematic studies of the H2). The result is that, for the first time, the circumnuclear H2 in NGC 1275 has been resolved spatially and kinematically: the bulk of the emission is concentrated in a disk/torus structure 50 pc from the nucleus, orientated perpendicular to the radio-jet axis. Analysis of the H2 line ratios suggests that X-rays from the active nucleus are heating the gas, which could not survive in molecular form any closer to the nucleus. Thanks to the exquisite spatial resolution of the UIST IFU, we observed a 240 km/s shift in the H2 velocity across the nucleus, from which we made a simple dynamical estimate of the black hole mass of 3.4 x 10^8 M-sun - within 20 per cent of the value inferred from the M(BH)-sigma relation. Intriguingly, the H2 disk/torus appears to be an extension to much smaller scales of a coaxial 1.2 kpc-radius ring of CO emission (Inoue et al. 1996, AJ, 111, 1852), which is itself the terminus of a plume of emission extending some 10 kpc. We may be directly witnessing the delivery of fuel from the galactic scale to the AGN itself.

FIGURE 2: Short-K spectra of the H2 v=1-0 S(1) line along the peak IFU slit which passes east-west through the nucleus, starting from pixel (9,27) in the east to (9,32) in the west. Adjacent pixels are separated by 0.12 arcsec and the nucleus itself is assumed to lie mid-way between pixels (9,29) and (9,30) where the continuum peaks. Fits to the line with double gaussian profiles are also shown, and note the sharp shift in the velocity of the line peak across the nucleus.

These results illustrate the power of an image-slicing IFU for high spatial and spectral resolution observations of compact sources. Any loss of throughput compared with conventional longslit spectroscopy is minor compared with the effort which would be required to obtain a series of equivalently narrow long-slit spectra stepped across the target. Other clusters for which we have UIST IFU data, such as A2597, have a more extensive filamentary distribution of H2, which will illustrate the complementary advantages of IFU work for coarser spatial and kinematic mapping of very extended sources.

¹ The University of Nottingham, U.K.
² Joint Astronomy Center, Hilo, USA

The Red Rectangle is a remarkable object comprising a binary star, an oxygen-rich circumbinary disk and an extended carbon-rich nebula. It displays a very wide range of spectroscopic features including infrared (UIR/PAH and silicate) emission bands, unidentified optical emission bands that may originate in PAH-based molecules, and a broad 'extended red emission' (ERE) feature. It is a superb astronomical 'laboratory' which holds the potential for revealing the exact chemical nature of the carriers of 'unidentified' IR (UIR) emission bands, ERE and possibly the optical diffuse interstellar absorption bands, which can then provide new probes of astrophysical conditions and processes. These spectroscopic signatures are seen in many astrophysical sources, but detailed, widely-accepted assignments have proved elusive.

As part of a major programme of study of the Red Rectangle UIR bands and other emission features we used Michelle on UKIRT to obtain high-quality long-slit spectra in the 7-13 &mu range. The data were obtained employing the LowN (R=200) and MedN1 (R = 1000) gratings, giving wide spectral coverage and high-resolution data on individual band profiles, respectively. A key target was to record the evolution of the spectral intensities and band profiles as a function of offset from the central star. This was achieved by aligning the slit along the north-west (NW)/south-east (SE) 'whisker' or 'bicone wall' of the nebula. The principal UIR bands falling in the 7-13 &mu region lie near 7.7 &mu, 8.6 &mu, 11.2 &mu and 12.7 &mu . They are generally attributed to the C-H and C-C (7.7 &mu) vibrational motions in polycyclic aromatic hydrocarbon (PAH) molecules or dust grains.

Figure 1 - LowN (R=200) spectra of the Red Rectangle in the 7-13 &mu range recorded along the SE bicone interface.

Our mid-IR Michelle results build on a high-resolution study of the 3.3 &mu (C-H stretch) feature recorded as a function of offset using CGS4 on UKIRT (Song et al. 2003). We deduced that the most likely interpretation for the major part of the evolution of the band profile was the increase in relative intensity of a previously unrecognized emission band centred near 3.28 &mu . In the current programme the attractive combination of continuous spectral coverage at moderate resolution and detailed band profile information (when working with the MedN1 grating), both taken in conjunction with information on the spatial dependence of the band shapes, provides a powerful approach to solving the UIR band assignment problems.

Using the LowN grating, spectra across the 7-13 &mu range were taken along the NW/SE 'whisker' and including the central star (HD 44179). In Figure 1 the panels show spectra for the inner 4'' offset (SE) together with the results of simultaneous fitting of Lorentzian profiles to the emission features. The 11.2 &mu on-star feature likely comprises contributions from both silicate and PAH emission (Miyata et al. 2004). Of interest is the emergence of the 12.7 &mu feature away from the central star, and the 7.7 &mu emission feature appears to split. Band shifts to shorter wavelength are found for the 7.7 &mu and 8.6 &mu features, but the 12.7 &mu feature appears to shift to slightly longer wavelength as a function of offset.

Figure 2 - MedN1 (R = 1000) spectra of the 11.2 (m emission band along the SE interface.

Use of the MedN1 grating has allowed a more detailed recording of the 7.7 &mu, 8.6 &mu and 11.2 &mu individual features. In Figure 2 we show the high-resolution profile of the 11.2 &mu feature at 1.9" and 3.8" offset. The asymmetry of the band has been recognized elsewhere (Hony et al. 2001; van Diedenhoven et al. 2004) but these new data indicate that, in addition to the weak feature near 11.0 &mu, the long-wavelength tail may be interpreted in terms of the emergence of a new feature centred at ~ 11.4 &mu . If confirmed, this would represent a similar evolution to that seen for the 3.3 &mu Red Rectangle feature as a function of offset (Song et al. 2003). We are now undertaking detailed modelling of the high-resolution UIR bands in the 7-13 &mu range to elucidate the origin of the shifts and components in band structure, including the effects of temperature, isotopic composition and chemical structure.

References
Hony S., Van Kerckhoven C., Peeters E., et al. 2001, A&A 370, 1030
Miyata T., Kataza H., Okamoto Y.K., et al. 2004, A&A, 415, 179
Song I.-O., Kerr T.H., McCombie J., Sarre P.J., 2003, MNRAS, 346, L1
van Diedenhoven B., Peeters E., Van Kerckhoven C., et al. 2004, ApJ, 611, 928

¹UK-ATC, Edinburgh, U.K.
²University of Oxford, U.K.

In its last month at UKIRT, Michelle made a new observation of the magnetic field directions in the central parsec of our galaxy. The first results of this project are shown in Figure 1 below. Though not yet fully analysed or calibrated, they show an intriguing connection between the magnetic field and the fainter filamentary structure in this region.

The gray scale image in Figure 1 shows the thermal emission from dust grains at a wavelength of 12.5 &mu . The blue contours show the flux density increasing in factors of two from the lowest at 150 mJy/arcsec2. The coordinate origin is close to the position of Sgr A*.

FIGURE 1: 12.5 &mu imaging polarimetry of the Galactic Centre with Michelle at UKIRT

The radiation from the warm dust grains is polarised in a direction normal to the magnetic field. The red vectors in Figure 1 then show the magnetic field direction as inferred from the linear polarisation measured by Michelle. The vector lengths are proportional to the polarisation fraction in the plane of the sky, averaged over a box 0.85" on a side.

The general validity of the picture is confirmed by comparison with previous observations of the polarisation in the bright (> 700 mJy/sq. arcsec) region of the Northern Arm (Aitken et al. 1998, MNRAS, 299,743).

The impression from the new image is that, in the region of filamentary structure to the west of the Northern Arm, the large scale field direction is predominantly to the north and north east. In the filaments themselves the polarisation fraction appears to be small, and tends to follow the filament direction (for example in the filament at Dec = +14", which runs from RA = -5" to -25"). A fuller explanation of these observations requires further analysis of the images.