SUBARU AND GEMINI HIGH SPATIAL RESOLUTION INFRARED 18 μm IMAGING OBSERVATIONS OF NEARBY LUMINOUS INFRARED GALAXIES

Abstract

We present the results of a ground-based, high spatial resolution infrared 18 µm imaging study of nearby luminous infrared galaxies (LIRGs), using the Subaru 8.2-m and Gemini South 8.1-m telescopes. The diffraction-limited images routinely achieved with these telescopes in the Q-band (17-23 µm) allow us to investigate the detailed spatial distribution of infrared emission in these LIRGs. We then investigate whether the emission surface brightnesses are modest, as observed in starbursts, or are so high that luminous active galactic nuclei (AGNs; high emission surface brightness energy sources) are indicated. The sample consists of 18 luminous buried AGN candidates and starburst-classified LIRGs identified in earlier infrared spectroscopy. We find that the infrared 18 µm emission from the buried AGN candidates is generally compact, and the estimated emission surface brightnesses are high, sometimes exceeding the maximum value observed in and theoretically predicted for a starburst phenomenon. The starburst-classified LIRGs usually display spatially extended 18 µm emission and the estimated emission surface brightnesses are modest, within the range sustained by a starburst phenomenon. The general agreement between infrared spectroscopic and imaging energy diagnostic methods suggests that both are useful tools for understanding the hidden energy sources of the dusty LIRG population.

The Circumnuclear Environment of IRAS 20551-4250: A Case Study of AGN/Starburst Connection forJWST

“…Ground-based imaging at 18 μm reveals a compact unresolved source (<120 pc) with high surface brightness and large Si optical depth (τ 18 = 0.7), in agreement with a buried AGN interpretation [20]. It is also worth noting that τ 9.7 can be combined with the EW of the 6.2 μm PAH feature in a diagnostic diagram that provides not only a direct classification but also possible indications on the evolutionary path of a source, by probing the age of the SB and the geometrical structure of the dust [21].…”

The nuclear and extended mid-infrared emission of Seyfert galaxies

“…Only six Sy2 galaxies present extended MIR emission at large-scales (>400 pc, which is the sample average value) in the high angular resolution MIR data. These galaxies were previously studied in the MIR: a) NGC 4945 (Imanishi et al 2011 Here we make a comparison between this large-scale MIR emission as detected in the arcsecond and subarcsecond resolution data. In Fig.…”

“…Díaz-Santos et al 2010, Díaz-Santos et al 2011, Imanishi et al 2011). Díaz-Santos et al (2010 found that, on average, the MIR continuum becomes more compact than the PAH emission as the MIR is increasingly dominated by the AGN.…”

“…Díaz-Santos et al (2010 found that, on average, the MIR continuum becomes more compact than the PAH emission as the MIR is increasingly dominated by the AGN. In Imanishi et al (2011), the authors studied a sample of 18 ULIGRs and found that SFdominated galaxies have more extended emission, with low surface brightnesses, than AGN-dominated galaxies, which show more compact MIR morphologies. Soifer et al (2001) found different sizes (ranging from 100 pc to 1.5 kpc) for the MIR emission using ground-based data of a sample of starburst galaxies.…”

Signs of active galactic nucleus quenching in a merger remnant with radio jets

“…This suggests that AGN activity in Arp 187 might be already weaken and/or obscured. Infrared (IR) observations give us another secure way to find AGN since the AGN dust torus emission is dominated in mid-IR (Imanishi et al 2011;Ichikawa et al 2012Ichikawa et al , 2014Ichikawa et al , 2015. Utilizing the Spitzer mid-IR imaging data, Ohyama et al (2015) found AGN signs in the southern nucleus of NGC 3256 hosting molecule outflows (Sakamoto et al 2014).…”