Sasmirala Individual Information for NGC 6810

Description

NGC 6810 is an edge-on spiral galaxy at a distance of D = 28.6 ± 5.2 Mpc (NED redshift-independent median) with a poorly studied active nucleus. Initially, it was classified optically as a Sy 2 [kirhakos_x-ray_1990], while it turned out later to be either an H II or H II/AGN transition or composite nucleus [strickland_new_2007, brightman_nature_2008, brightman_xmm-newton_2011-1, yuan_role_2010]. In particular, [strickland_new_2007] find no evidence for an AGN in X-rays and based on other diagnostics. No compact radio source was detected in the nucleus either [kewley_compact_2000]. Kiloparsec-scale Hα outflow filaments along the minor galaxy axis have been detected [hameed_h_1999]. We conservatively treat NGC 6810 as an uncertain AGN. After being detected in the MIR with IRAS for the first time, NGC 6810 was followed up with Spitzer/IRAC, IRS and MIPS. The corresponding IRAC images show a nucleus elongated in north-south direction and embedded within complex host emission. The nucleus remains mostly unresolved in the MIPS 24 μm images. Particularly bright knots of star-formation are seen ~ 10arcsec ~ 1.4 kpc to the south-east and ~ 11.5arcsec ~ 1.6 kpc to the north-west. The nucleus and both knots are aligned roughly along PA~ 146^∘ = 326^∘. Our nuclear IRAC 5.8 and 8.0 μm photometry is significantly lower than the values by [gallimore_infrared_2010] but consistent with the IRS mapping-mode post-BCD spectrum. The latter exhibits strong PAH emission, possibly silicate 10 μm absorption and a steep red spectral slope in νF_ν-space (see also [buchanan_spitzer_2006, wu_spitzer/irs_2009, tommasin_spitzer-irs_2010, gallimore_infrared_2010]). Thus, the arcsecond-scale MIR SED appears to be completely star-formation dominated. Note that no AGN-indicative [Ne V] emission was detected in the IRS spectrum (e.g. [tommasin_spitzer-irs_2010]). The nuclear region of NGC 6810 was imaged with T-ReCS in the broad N filter in 2004 [videla_nuclear_2013], and a nucleus extended in north-south direction was detected (FWHM(major axis)~ 0.77arcsec ~ 107 pc; PA~ 164^∘). The slightly S-shaped extended emission has a total diameter of at least ~ 4arcsec ~ 0.6 kpc along the major axis, and the south-eastern star-formation knots are faintly visible as well. We fit only the unresolved nuclear component with manual PSF-scaling so that the residual emission becomes smooth. The resulting flux is ~ 92% lower than the Spitzer spectrophotometry and also ~ 30% lower than the value published by [videla_nuclear_2013]. Note, however, that the flux measurement method is very uncertain, and applying slightly different parameters results in flux uncertainties of ~30%. The nuclear flux might still be affected or dominated by star-formation. Therefore, there is no evidence for an AGN in NGC 6810 from the MIR point of view.

• [brightman_nature_2008] Murray Brightman and Kirpal Nandra. On the nature of unabsorbed seyfert 2 galaxies . MNRAS , 390 pp. 1241–1249, November 2008.
• [brightman_xmm-newton_2011-1] Murray Brightman and Kirpal Nandra. An XMM-Newton spectral survey of 12 μm selected galaxies - i. x-ray data . MNRAS , 413 pp. 1206–1235, May 2011.
• [buchanan_spitzer_2006] Catherine L. Buchanan, Jack F. Gallimore, Christopher P. O'Dea, Stefi A. Baum, David J. Axon, Andrew Robinson, Moshe Elitzur, and Martin Elvis. Spitzer IRS spectra of a large sample of seyfert galaxies: A variety of infrared spectral energy distributions in the local active galactic nucleus population . AJ , 132 pp. 401–419, July 2006.
• [gallimore_infrared_2010] J. F. Gallimore, A. Yzaguirre, J. Jakoboski, M. J. Stevenosky, D. J. Axon, S. A. Baum, C. L. Buchanan, M. Elitzur, M. Elvis, C. P. O'Dea, and A. Robinson. Infrared spectral energy distributions of seyfert galaxies: Spitzer space telescope observations of the 12 μm sample of active galaxies . ApJS , 187 pp. 172–211, March 2010.
• [hameed_h_1999] Salman Hameed and Nick Devereux. Hα imaging of early-type (SA-SAB) spiral galaxies. i. . AJ , 118 pp. 730–751, August 1999.
• [kewley_compact_2000] L. J. Kewley, C. A. Heisler, M. A. Dopita, R. Sutherland, R. P. Norris, J. Reynolds, and S. Lumsden. Compact radio emission from warm infrared galaxies . ApJ , 530 pp. 704–718, February 2000.
• [kirhakos_x-ray_1990] S. D. Kirhakos and J. E. Steiner. X-ray and infrared selected AGN. II - optical spectroscopy . AJ , 99 pp. 1722–1739, June 1990.
• [strickland_new_2007] David K. Strickland. A new superwind galaxy: XMM-Newton observations of NGC 6810 . MNRAS , 376 pp. 523–533, April 2007.
• [tommasin_spitzer-irs_2010] Silvia Tommasin, Luigi Spinoglio, Matthew A. Malkan, and Giovanni Fazio. Spitzer-IRS high-resolution spectroscopy of the 12 μm seyfert galaxies. II. results for the complete data set . ApJ , 709 pp. 1257–1283, February 2010.
• [videla_nuclear_2013] Liza Videla, Paulina Lira, Heather Andrews, Almudena Alonso-Herrero, David M. Alexander, and Martin Ward. Nuclear infrared spectral energy distribution of type II active galactic nuclei . ApJS , 204 pp. 23, February 2013.
• [wu_spitzer/irs_2009] Yanling Wu, Vassilis Charmandaris, Jiasheng Huang, Luigi Spinoglio, and Silvia Tommasin. Spitzer/IRS 5-35 μm low-resolution spectroscopy of the 12 μm seyfert sample . ApJ , 701 pp. 658–676, August 2009.
• [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.