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The PAH model predicts many weak emission features in the 1-5 $mu$m region that can resolve significant questions that it has faced since its inception in the mid-80s. These features contain fundamental information about the PAH population that is inaccessible via the much stronger PAH bands in the 5-20 $mu$m region. Apart from the 3.3 $mu$m band and plateau, PAH spectroscopy across most of the 1-5 $mu$m region has been unexplored due to its low intrinsic intensity. ISO and Akari covered some of this wavelength range, but lacked the combined sensitivity and resolution to measure the predicted bands with sufficient fidelity. The spectroscopic capabilities of the NIRSpec instrument on board JWST will make it possible to measure and fully characterize many of the PAH features expected in this region. These include the fundamental, overtone and combination C-D and C$equiv$N stretching bands of deuterated PAHs, cyano-PAHs (PAH-C$equiv$ N), and the overtones and combinations of the strong PAH bands that dominate the 5-20 $mu$m region. These bands will reveal the amount of D tied up in PAHs, the PAH D/H ratio, the D distribution between PAH aliphatic and aromatic subcomponents, and delineate key stages in PAH formation and evolution on an object-by-object basis and within extended objects. If cyano-PAHs are present, these bands will also reveal the amount of cyano groups tied up in PAHs, determine the N/C ratio within that PAH subset, and distinguish between the bands near 4.5 $mu$m that arise from CD versus C$equiv$N.
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We present Gran Telescopio CANARIAS CanariCam 8.7$mu$m imaging and 7.5-13$mu$m spectroscopy of six local systems known to host an active galactic nucleus (AGN) and have nuclear star formation. Our main goal is to investigate whether the molecules responsible for the 11.3$mu$m polyclyclic aromatic hydrocarbon (PAH) feature are destroyed in the close vicinity of an AGN. We detect 11.3$mu$m PAH feature emission in the nuclear regions of the galaxies as well as extended PAH emission over a few hundred parsecs. The equivalent width (EW) of the feature shows a minimum at the nucleus but increases with increasing radial distances, reaching typical star-forming values a few hundred parsecs away from the nucleus. The reduced nuclear EW are interpreted as due to increased dilution from the AGN continuum rather than destruction of the PAH molecules. We conclude that at least those molecules responsible for the 11.3$mu$m PAH feature survive in the nuclear environments as close as 10pc from the AGN and for Seyfert-like AGN luminosities. We propose that material in the dusty tori, nuclear gas disks, and/or host galaxies of AGN is likely to provide the column densities necessary to protect the PAH molecules from the AGN radiation field.
We present spectro-photometry spanning 1-5 $mu$m of 51 Eridani b, a 2-10 M$_text{Jup}$ planet discovered by the Gemini Planet Imager Exoplanet Survey. In this study, we present new $K1$ (1.90-2.19 $mu$m) and $K2$ (2.10-2.40 $mu$m) spectra taken with the Gemini Planet Imager as well as an updated $L_P$ (3.76 $mu$m) and new $M_S$ (4.67 $mu$m) photometry from the NIRC2 Narrow camera. The new data were combined with $J$ (1.13-1.35 $mu$m) and $H$ (1.50-1.80 $mu$m) spectra from the discovery epoch with the goal of better characterizing the planet properties. 51 Eri b photometry is redder than field brown dwarfs as well as known young T-dwarfs with similar spectral type (between T4-T8) and we propose that 51 Eri b might be in the process of undergoing the transition from L-type to T-type. We used two complementary atmosphere model grids including either deep iron/silicate clouds or sulfide/salt clouds in the photosphere, spanning a range of cloud properties, including fully cloudy, cloud free and patchy/intermediate opacity clouds. Model fits suggest that 51 Eri b has an effective temperature ranging between 605-737 K, a solar metallicity, a surface gravity of $log$(g) = 3.5-4.0 dex, and the atmosphere requires a patchy cloud atmosphere to model the SED. From the model atmospheres, we infer a luminosity for the planet of -5.83 to -5.93 ($log L/L_{odot}$), leaving 51 Eri b in the unique position as being one of the only directly imaged planet consistent with having formed via cold-start scenario. Comparisons of the planet SED against warm-start models indicates that the planet luminosity is best reproduced by a planet formed via core accretion with a core mass between 15 and 127 M$_{oplus}$.
We explore the relationships between the 3.3 {mu}m polycyclic aromatic hydrocarbon (PAH) feature and active galactic nucleus (AGN) properties of a sample of 54 hard X-ray selected bright AGNs, including both Seyfert 1 and Seyfert 2 type objects, using the InfraRed Camera (IRC) on board the infrared astronomical satellite AKARI. The sample is selected from the 9-month Swift/BAT survey in the 14-195 keV band and all of them have measured X-ray spectra at $E lesssim 10$ keV. These X-ray spectra provide measurements of the neutral hydrogen column density ($N_{rm H}$) towards the AGNs. We use the 3.3 {mu}m PAH luminosity ($L_{rm 3.3{mu}m}$) as a proxy for star formation activity and hard X-ray luminosity ($L_{rm 14-195keV}$) as an indicator of the AGN activity. We search for possible difference of star-formation activity between type 1 (un-absorbed) and type 2 (absorbed) AGNs. We have made several statistical analyses taking the upper-limits of the PAH lines into account utilizing survival analysis methods. The results of our $log(L_{rm 14-195keV})$ versus $log(L_{rm 3.3{mu}m})$ regression shows a positive correlation and the slope for the type 1/unobscured AGNs is steeper than that of type 2/obscured AGNs at a $3sigma$ level. Also our analysis show that the circum-nuclear star-formation is more enhanced in type 2/absorbed AGNs than type 1/un-absorbed AGNs for low X-ray luminosity/low Eddington ratio AGNs, while there is no significant dependence of star-formation activities on the AGN type in the high X-ray luminosities/Eddington ratios.
Aims. The aim of this work is to further investigate the nature of PAH excitation and emission especially in the context of tracing star formation in a variety of extragalactic environments. Here we turn our attention to the energetic environment of the closest AGN in our sample, Centaurus A. Methods. Using ISAAC on the ESO VLT UT1 (Antu) we have made high spatial resolution 3.3 {mu}m imaging observations of the central kiloparsec of CenA. These observations have been compared with star formation tracers in the near- and mid-infrared, as well as with mid-infrared tracers of nuclear activity. Results. The nucleus is not devoid of PAH emission, implying that the PAH particles are not destroyed in the nucleus as might be expected for such a harsh environment. However, we see the feature to continuum ratio decrease towards the AGN. As well, the 3.3 {mu}m PAH feature emission generally traces the sites of star formation in Cen A, but in detail there are spatial offsets, consistent with an earlier study of the starburst galaxies NGC 253 and NGC 1808. However, the feature-to-continuum ratio does not drop at the positions of star formation as was previously seen in that earlier study. The cause for this difference remains uncertain. Finally, our data reveal possible evidence for a nearly face-on, circular or spiral, dust structure surrounding the nucleus.
Evolutionary properties of infrared (IR) luminous galaxies are important keys to understand dust-obscured star formation history and galaxy evolution. Based on the near- to mid-IR imaging with 9 continuous filters of AKARI space telescope, we present the characteristics of dusty star-forming (SF) galalxies showing polycyclic aromatic hydrocarbon (PAH) features observed by the North Ecliptic Pole (NEP) wide field survey of AKARI and Herschel. All the sample galaxies from the AKARI/NEP-Wide data are selected based both on the Herschel/SPIRE 250 {mu}m detection and optical spectroscopic redshift data. The physical modelling of spectral energy distribution (SED) using all available data points from u to sub-mm 500 {mu}m band, including WISE and PACS data where available, takes unique advantages of the continuous near to mid-IR coverage, reliable constraint on far-IR peak, spectroscopically determined accurate redshifts, as well as energy balance principle by MAGPHYS. This enables us to derive physically meaningful and accurate total infrared luminosity and 8 {mu}m (or PAH) luminosity consistently. Our sample galaxies are in the redshift range z <1, and majority of them appear to be normal SF/spiral populations showing PAH features near the 8 {mu}m. These SF galaxies showing PAHs in the mid-IR include various types from quiescent to starbursts. Some of our sample show shortage of 8 {mu}m luminosity compared to the total IR luminosity and this PAH deficit gets severe in more luminous IR galaxies, suggesting PAH molecules in these galaxies destroyed by strong radiation field from SF region or a large amount of cold dust in ISM. The specific SFR of our sample shows mass dependent time evolution which is consistent with downsizing evolutionary pattern.
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