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Ground-Based Mid Infra-Red Observations of Nearby Starburst and AGN Galaxies
Bo jan Nikoliґ Paul Alexander, Garret Cotter, c, Malcolm Longair AP group, Cavendish Laboratory, Cambridge, U.K. Marcel Clemens Universita degli Studi di Padova, Italy

1

Intro duction

4

Results

We present the first results from recent observations with the United Kingdom Infra-Red Telescope (UKIRT) using the MICHELLE instrument. MICHELLE is a new generation Mid-IR imager and spectrograph built at the ATC, Edinburgh, and is to be shared between UKIRT and Gemini North telescopes. The combination of new technology detectors and world class telescopes means that it will probably produce the best ground based Mid-IR measurements carried out so far. The diffraction limited beam width of UKIRT at 10µm is 0.7 arcseconds. We have started a programme of observations of nearby starburst and AGN galaxies with MICHELLE, with the aim of investigating the spatial extent of "Unidentified Infrared Bands (UIB)" emission in these galaxies, and in particular relating these to multi-frequency matched resolution radio maps. UIB are very commonly seen in galactic and extragalactic ob jects, with the ma jor bands centred at rest wavelengths of: 6.2µm, 7.7µm 8.6µm, 11.3µm and 12.7µm.

· The spectra we have presented show that MICHELLE is a capable instrument, offering high spatial resolution and sufficient sensitivity for extragalactic work. · The spatially integrated MICHELLE spectrum of NGC 7469 in the 8 - 11.5µm range shows an equivalent width of 11.3µm UIB feature which is much smaller then measured by ISO. · It is possible to explain this discrepancy by using the common hypothesis that emission from the nucleus is relatively featureless (due to high-energy photons from the AGN destroying carriers of UIB) while UIB themselves originate mostly from the circum-nuclear starburst ring. Figure 3: Digital Sky Survey Image of NGC7469 and its interacting companion IC 5283 (which is about 80 arcsecs north NGC7469) · Tentative evidence that this is the case for NGC 7469 has been published before (e.g., [?]). We believe our data show the first clear spatially resolved measurement of the equivalent width of the 11.3µm UIB and adds significant weight to the body of evidence that UIB in the spectrum of NGC 7469 originate in an circum-nuclear ring rather the nucleus.

Acknowledgements
This poster is based on data obtained on he United Kingdom Infrared Telescope which is operated by the Joint Astronomy Centre on behalf of the U.K. Particle Physics and Astronomy Research Council. Based on observations with ISO, an ESA pro ject with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555 BN would like to acknowledge the support of the U.K. Particle Physics and Astronomy Research Council (PPARC).

Figure 1: Michelle Mid-IR spectrum of Makarian 231 The specific questions we aim to answer are: · Do the UIB originate from the same parts of the galaxy as the underlying continuum? · Is the intensity of UIB reduced near strong shocks (traced by radio emission), and can we therefore associate these with large molecules (PAHs, [?]) which are liable to be destroyed in harsh environments. · What is the relationship between UIB and intense star-formation (again, traced by radio emission) We characterise the radio emission by producing matched resolution radio continuum maps at L band (1.4GHz), C band(4.8GHz), X band (8.4GHz) and U band (14.9GHz). These will be obtained mostly from a new observational programme which is now underway with the Very Large Array (VLA), as well as VLA archive and possibly other telescopes. These four spectral points will enable to fit an aged synchrotron + thermal spectrum and relate these to the intensities of UIB.

References
[1] A. Leger and J. L. Puget. Identification of the 'unidentified' IR emission features of interstellar dust? Astronomy and Astrophysics, 137:L5­L8, August 1984. Figure 4: HST image of NGC7469 at 1.1µm (top) and 2.2µm (bottom). The position of the slit is shown in the top image. Intensity scale: bar to the right indicates log10 of Counts/second [2] C. K. Seyfert. Nuclear Emission in Spiral Nebulae. Astrophysical Journal, 97:28+, January 1943. [3] J. W. Miles, J. R. Houck, and T. L. Hayward. High-resolution midinfrared observations of NGC 7469. Astrophysical Journal Letters, 425:L37­L40, April 1994. [4] R. Genzel, L. Weitzel, L. E. Tacconi-Garman, M. Blietz, M. Cameron, A. Krabbe, D. Lutz, and A. Sternberg. Infrared imaging and spectroscopy of NGC 7469. Astrophysical Journal, 444:129­145, May 1995.

2

Sample selection

We selected targets according to following criteria: · Specific 12µm luminosity > 1023Hz-1 as selected from the extended 12µm galaxy sample (Rush at al. 1993). · Good quality ISO data · Angular size < 90arcsecs

3

NGC 7469

The spiral galaxy NGC 7469 (z = 0.016) appeared in Seyferts original list of active galactic nuclei (AGN)[?]. It is an Ultra Luminous Infra Red Galaxy (ULIRG) with L8µm--1000µm = 1011.56L . ISO spectroscopic observations of this galaxy show a pronounced 11.3µm PAH feature, which is surprising considering the evidence for an AGN including an X-ray flux of 3.4 в 10-11ergs-1cm-2. Ground based MidIR imaging by Miles, Houck and Hayward[?], show evidence of an IR bright circumnuclear ring which is probably powered by a starburst. Comprehensive Near IR imaging and spectroscopy (see below, and [?]) also support this hypothesis.

Figure 5: Comparison of ISO(black) and integrated Michelle spectra(red)

Figure 2: United Kingdom InfraRed Telescope

Figure 6: Comparison of broad band flux density (black) and flux density of UIB emission (red) as function of distance from peak of emission.

Figure 7: Equivalent width of the 11.3 UIB as function of distance from the peak of continuum emission