Nuclear star formation activity and black hole accretion in nearby Seyfert galaxies

Recent theoretical and observational works indicate the presence of a correlation between the star-formation rate (SFR) and active galactic nucleus (AGN) luminosity (and, therefore, the black hole accretion rate, ) of Seyfert galaxies. This suggests a physical connection between the gas-forming stars on kpc scales and the gas on sub-pc scales that is feeding the black hole. We compiled the largest sample of Seyfert galaxies to date with high angular resolution (~0.''4-0.''8) mid-infrared (8-13 μm) spectroscopy. The sample includes 29 Seyfert galaxies drawn from the AGN Revised Shapley-Ames catalog. At a median distance of 33 Mpc, our data allow us to probe nuclear regions on scales of ~65 pc (median value). We found no general evidence of suppression of the 11.3 μm polycyclic aromatic hydrocarbon (PAH) emission in the vicinity of these AGN, and we used this feature as a proxy for the SFR. We detected the 11.3 μm PAH feature in the nuclear spectra of 45% of our sample. The derived nuclear SFRs are, on average, five times lower than those measured in circumnuclear regions of 600 pc in size (median value). However, the projected nuclear SFR densities (median value of 22 M☉ yr–1 kpc–2) are a factor of 20 higher than those measured on circumnuclear scales. This indicates that the SF activity per unit area in the central ~65 pc region of Seyfert galaxies is much higher than at larger distances from their nuclei. We studied the connection between the nuclear SFR and and showed that numerical simulations reproduce our observed relation fairly well.

Note:

16 pages, 8 figures. Accepted for publication in ApJ

galaxies: nuclei
galaxies: Seyfert
infrared: galaxies

References(1)

Figures(37)

[1]

(2006), (2) González-Martín et al (2013), (3) Hönig et al (2008), (4) Hönig et al (2010), (5) Young et al (2007), (6) Mason et al (2006), (7) Alonso Herrero et al (2012), (8) Sales et al (2013), (9) Mason et al (2009), (10) Colling (2011), (11) Sales et al (2011), (12) Alonso Herrero et al (2011), (13) Díaz Santos et al (2010), (14) Roche et al (2007). performed by Michelle Glasse et al 1997) on the 8.1 m Gemini-North telescope, which has a higher spectral resolution by a factor of two (R ∼ 200), were obtained with slit widths of ∼ 0.4′′. Finally, observations with the VLT spectrometer and imager for the mid-infrared (VISIR, Lagage et al 2004) instrument mounted on the 8.2 m VLT UT3 telescope at the ESO/Paranal observatory were obtained with the low spectral resolution mode (R ∼ 300) and a slit width of 0′′.75 or 1′′ (and 0.4′′ for NGC 1068). For the typical distances of our sample the ground-based slit widths probe typical physical scales of ∼ 65 pc. These range from ∼ 7-255pc for all objects except for Mrk 509 (545 pc), which is by far the most distant galaxy in the sample. Sixteen sources were observed with Gemini/T-ReCS

Roche