Description

NGC 7552 is an infrared-luminous, nearly face-on, barred spiral galaxy at a redshift of z = 0.0054 (D ~ 20.4 Mpc) with a possibe active nucleus surrounded by a powerful circum-nuclear starburst ring (diameter~ 5arcsec ~ 0.5 kpc; [forbes_nuclear_1994, forbes_ngc_1994]; see [pan_formation_2013, brandl_high_2012] for recent detailed studies). The nucleus has been optically classified as a LINER [durret_imaging_1987] or H II [yuan_role_2010]. The presence of an AGN is supported by the detection of a compact nuclear source in hard X-rays [grier_discovery_2011, brightman_xmm-newton_2011]. However, we conservatively treat NGC 7552 as an uncertain AGN. Initial MIR observations of NGC 7552 are reported in [kleinmann_10-micron_1974], followed by many ground-based observations [frogel_8-13_1982, phillips_8-13_1984, roche_atlas_1991, schinnerer_circumnuclear_1997, siebenmorgen_mid-infrared_2004]. The latter two works present the first subarcsecond-resolution MIR images, which resolve the starburst ring as a clumpy structure. NGC 7552 was also observed with the space-based ISO [rigopoulou_large_1999, roussel_atlas_2001, verma_mid-infrared_2003] and Spitzer/IRAC, IRS and MIPS. The corresponding IRAC and MIPS images do not completely resolve the starburst ring, which appears as a dominating central source embedded within the spiral-like host galaxy emission (see also [brandl_high_2012]). We measure the nuclear flux component in the non-saturated IRAC 5.8 μm and MIPS 24 μm post-BCD images, which conclusively results in significantly lower values than in the literature (e.g. [dale_infrared_2005, munoz-mateos_radial_2009]). The IRS LR mapping-mode spectrum shows strong PAH emission and possibly weak silicate 10 μm absorption with a red spectral slope in νF_ν-space (see also [smith_mid-infrared_2007, marble_aromatic_2010]). As expected, the arcsecond-scale MIR SED appears to be star-formation dominated. The nuclear region of NGC 7552 was imaged with VISIR in eleven N-band and one Q-band filters in 2005 (partly published in [brandl_high_2012]). At least the brightest knots of the starburst ring are detected in all images, while the nucleus remains undetected (see [brandl_high_2012] for the analysis of the ring). A compact source is faintly visible at the nuclear position (< 2σ) only in the longest-wavelength N-band filters. Therefore, we determine flux upper limits on the nuclear emission, which are on average ~ 94% lower than the Spitzer spectrophotometry. We conclude that a very weak AGN might be present in NGC 7552 but star formation is dominating its MIR emission completely.

• [brandl_high_2012] B. R. Brandl, N. L. Martín-Hernández, D. Schaerer, M. Rosenberg, and P. P. van der Werf. High resolution IR observations of the starburst ring in NGC 7552. one ring to rule them all? . A&A , 543 pp. 61, July 2012.
• [brightman_xmm-newton_2011] Murray Brightman and Kirpal Nandra. An XMM-Newton spectral survey of 12 μm selected galaxies - II. implications for AGN selection and unification . MNRAS , 414 pp. 3084–3104, July 2011.
• [dale_infrared_2005] D. A. Dale, G. J. Bendo, C. W. Engelbracht, K. D. Gordon, M. W. Regan, L. Armus, J. M. Cannon, D. Calzetti, B. T. Draine, G. Helou, R. D. Joseph, R. C. Kennicutt, A. Li, E. J. Murphy, H. Roussel, F. Walter, H. M. Hanson, D. J. Hollenbach, T. H. Jarrett, L. J. Kewley, C. A. Lamanna, C. Leitherer, M. J. Meyer, G. H. Rieke, M. J. Rieke, K. Sheth, J. D. T. Smith, and M. D. Thornley. Infrared spectral energy distributions of nearby galaxies . ApJ , 633 pp. 857–870, November 2005.
• [durret_imaging_1987] F. Durret and J. Bergeron. Imaging of the ionized gas and stars in emission line galaxies . A&A , 173 pp. 219–228, February 1987.
• [forbes_ngc_1994] Duncan A. Forbes, Jari K. Kotilainen, and A. F. M. Moorwood. NGC 7552: A galaxy with a dormant active nucleus? . ApJL , 433 pp. L13–L16, September 1994.
• [forbes_nuclear_1994] Duncan A. Forbes, R. P. Norris, Gerard M. Williger, and R. Chris Smith. A nuclear starburst ring in the spiral galaxy NGC 7552 . AJ , 107 pp. 984–991, March 1994.
• [frogel_8-13_1982] J. F. Frogel, J. H. Elias, and M. M. Phillips. 8-13 micron observations of nine emission-line galaxies . ApJ , 260 pp. 70–74, September 1982.
• [grier_discovery_2011] C. J. Grier, S. Mathur, H. Ghosh, and L. Ferrarese. Discovery of nuclear x-ray sources in sings galaxies . ApJ , 731 pp. 60, April 2011.
• [kleinmann_10-micron_1974] D. E. Kleinmann and E. L. Wright. 10-MICRON observations of southern-hemisphere galaxies . ApJL , 191 pp. L19, July 1974.
• [marble_aromatic_2010] A. R. Marble, C. W. Engelbracht, L. van Zee, D. A. Dale, J. D. T. Smith, K. D. Gordon, Y. Wu, J. C. Lee, R. C. Kennicutt, E. D. Skillman, L. C. Johnson, M. Block, D. Calzetti, S. A. Cohen, H. Lee, and M. D. Schuster. An aromatic inventory of the local volume . ApJ , 715 pp. 506–540, May 2010.
• [munoz-mateos_radial_2009] J. C. Muñoz-Mateos, A. Gil de Paz, J. Zamorano, S. Boissier, D. A. Dale, P. G. Pérez-González, J. Gallego, B. F. Madore, G. Bendo, A. Boselli, V. Buat, D. Calzetti, J. Moustakas, and R. C. Kennicutt. Radial distribution of stars, gas, and dust in SINGS galaxies. i. surface photometry and morphology . ApJ , 703 pp. 1569–1596, October 2009.
• [pan_formation_2013] Hsi-An Pan, Jeremy Lim, Satoki Matsushita, Tony Wong, and Stuart Ryder. Formation of dense molecular gas and stars at the circumnuclear starburst ring in the barred galaxy NGC 7552 . ApJ , 768 pp. 57, May 2013.
• [phillips_8-13_1984] M. M. Phillips, D. K. Aitken, and P. F. Roche. 8-13 micron spectrophotometry of galaxies. i - galaxies with giant h II region nuclei . MNRAS , 207 pp. 25–33, March 1984.
• [rigopoulou_large_1999] D. Rigopoulou, H. W. W. Spoon, R. Genzel, D. Lutz, A. F. M. Moorwood, and Q. D. Tran. A large mid-infrared spectroscopic and near-infrared imaging survey of ultraluminous infrared galaxies: Their nature and evolution . AJ , 118 pp. 2625–2645, December 1999.
• [roche_atlas_1991] Patrick F. Roche, David K. Aitken, Craig H. Smith, and Martin J. Ward. An atlas of mid-infrared spectra of galaxy nuclei . MNRAS , 248 pp. 606–629, February 1991.
• [roussel_atlas_2001] H. Roussel, L. Vigroux, A. Bosma, M. Sauvage, C. Bonoli, P. Gallais, T. Hawarden, J. Lequeux, S. Madden, and P. Mazzei. An atlas of mid-infrared dust emission in spiral galaxies . A&A , 369 pp. 473–509, April 2001.
• [schinnerer_circumnuclear_1997] E. Schinnerer, A. Eckart, A. Quirrenbach, T. Boker, L. E. Tacconi-Garman, A. Krabbe, and A. Sternberg. The circumnuclear starburst in NGC 7552: First results from near-infrared spectral synthesis . ApJ , 488 pp. 174, October 1997.
• [siebenmorgen_mid-infrared_2004] R. Siebenmorgen, E. Krügel, and H. W. W. Spoon. Mid-infrared emission of galactic nuclei. TIMMI2 versus ISO observations and models . A&A , 414 pp. 123–139, January 2004.
• [smith_mid-infrared_2007] J. D. T. Smith, B. T. Draine, D. A. Dale, J. Moustakas, R. C. Kennicutt, G. Helou, L. Armus, H. Roussel, K. Sheth, G. J. Bendo, B. A. Buckalew, D. Calzetti, C. W. Engelbracht, K. D. Gordon, D. J. Hollenbach, A. Li, S. Malhotra, E. J. Murphy, and F. Walter. The mid-infrared spectrum of star-forming galaxies: Global properties of polycyclic aromatic hydrocarbon emission . ApJ , 656 pp. 770–791, February 2007.
• [verma_mid-infrared_2003] A. Verma, D. Lutz, E. Sturm, A. Sternberg, R. Genzel, and W. Vacca. A mid-infrared spectroscopic survey of starburst galaxies: Excitation and abundances . A&A , 403 pp. 829–846, June 2003.
• [yuan_role_2010] T.-T. Yuan, L. J. Kewley, and D. B. Sanders. The role of starburst-active galactic nucleus composites in luminous infrared galaxy mergers: Insights from the new optical classification scheme . ApJ , 709 pp. 884–911, February 2010.

Images

SEDs

MIR SED. The description of the symbols in all the SED plots (where present) is the following: Grey crosses and solid lines mark the Spitzer/IRAC, MIPS and IRS data. The colour coding of the other symbols is as follows: green for COMICS, magenta for Michelle, blue for T-ReCS and red for VISIR data. Darker-coloured solid lines mark spectra of the corresponding instrument. The black filled circles mark the nuclear 12 and 18 micron continuum emission estimate from the data (where present). The ticks on the top axis mark positions of common MIR emission lines, while the light grey horizontal bars mark wavelength ranges affected by the silicate 10 and 18 micron features.