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Register a new user3-5 micron spectroscopy of obscured AGNs in ULIRGs
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Authors
E. Sani
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We present the results of infrared L-band (3-4 micron) and M-band (4-5 micron) VLT-ISAAC spectroscopy of five bright Ultraluminous InfraRed Galaxies (ULIRGs) hosting an AGN. From our analysis we distinguish two types of sources: ULIRGs where the AGN is unobscured (with a flat continuum and no absorption features at 3.4 micron and 4.6 micron), and those with highly obscured AGNs (with a steep, reddened continuum and absorption features due to hydrocarbons and CO). Starburst activity is also present in all of the sources as inferred from the 3.3 micron PAH emission line. A strong correlation is found between continuum slope and CO optical depth, which suggests that deep carbon monoxide absorption is a common feature of highly obscured ULIRG AGN. Finally we show that the AGN dominates the 3-4 micron emission, even if its contribution to the bolometric luminosity is small.
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We present 3-5 micron spectroscopy of the interacting system NGC 6240, showing the presence of two active galactic nuclei. The brightest (southern) nucleus shows up with a starburst-like emission, with a prominent 3.3 micron emission feature. However, the presence of an AGN is revealed by the detection of a broad Br alpha emission line, with a width of ~1,800 km/s. The spectrum of the faintest (northern) nucleus shows typical AGN features, such as a steep continuum and broad absorption features in the M-band. We discuss the physical properties of the dusty absorbers/emitters, and show that in both nuclei the AGN is dominant in the 3-5 micron band, but its contribution to the total luminosity is small (a few percent of the starburst emission).
We performed a spectroscopic survey toward five intermediate-mass class I YSOs located in the Southern Vela molecular cloud in the L and M bands at resolving powers 600-800 up to 10,000, using the Infrared Spectrometer and Array Camera mounted on the VLT-ANTU. Lower mass companion objects were observed simultaneously in both bands. Solid H2O at 3 micron is detected in all sources, including the companion objects. CO ice at 4.67 micron is detected in a few main targets and one companion object. One object (LLN 19) shows little CO ice but strong gas-phase CO ro-vibrational lines in absorption. The CO ice profiles are different from source to source. The amount of water ice and CO ice trapped in a water-rich mantle may correlate with the flux ratio at 12 and 25 micron. The abundance of H2O-rich CO likely correlates with that of water ice. A weak feature at 3.54 mu attributed to solid CH3OH and a broad feature near 4.62 mu are observed toward LLN17, but not toward the other sources. The derived abundances of solid CH3OH and OCN- are ~10% and ~1% of the H2O ice abundance respectively. The H2O optical depths do not show an increase with envelope mass, nor do they show lower values for the companion objects compared with the main protostar. The line-of-sight CO ice abundance does not correlate with the source bolometric luminosity. Comparison of the solid CO profile toward LLN17, which shows an extremely broad CO ice feature, and that of its lower mass companion at a few thousand AU, which exhibits a narrow profile, together with the detection of OCN- toward LLN17 provide direct evidences for local thermal processing of the ice.
Clio is an adaptive-optics camera mounted on the 6.5 meter MMT optimized for diffraction-limited L and M-band imaging over a ~15 field. The instrument was designed from the ground up with a large well-depth, fast readout thermal infrared (~3-5 micron) 320 by 256 pixel InSb detector, cooled optics, and associated focal plane and pupil masks (with the option for a coronograph) to minimize the thermal background and maximize throughput. When coupled with the MMTs adaptive secondary AO (two warm reflections) systems low thermal background, this instrument is in a unique position to image nearby warm planets, which are the brightest in the L and M-band atmospheric windows. We present the current status of this recently commissioned instrument that performed exceptionally during first light. Our instrument sensitivities are impressive and are sky background limited: for an hour of integration, we obtain an L-band 5 sigma detection limit of of 17.0 magnitudes (Strehl ~80%) and an M-band limit of 14.5 (Strehl ~90%). Our M-band sensitivity is lower due to the increase in thermal sky background. These sensitivities translate to finding relatively young planets five times Jupiter mass at 10 pc within a few AU of a star. Presently, a large Clio survey of nearby stellar systems is underway including a search for planets around solar-type stars, M dwarfs, and white dwarfs. Even with a null result, we can place strong constraints on planet distribution models.
Images obtained with NIRI on the Gemini North telescope are used to investigate the photometric properties of the central regions of M31 in the 3 - 5 micron wavelength range. The light distribution in the central arcsecond differs from what is seen in the near-infrared in the sense that the difference in peak brigh tness between P1 and P2 is larger in M than in K; no obvious signature of P3 is dete cted in M. These results can be explained if there is a source of emission that contributes ~ 20% of the peak M light of P1 and has an effective temperature of no more than a few hundred K that is located between P1 and P2. Based on the red K-M color of this source, it is suggested that the emission originates in a circumstellar dust shell surrounding a single bright AGB star. A similar bright source that is ~ 8 arcsec from the center of the galaxy is also detected in M. Finally, the (L, K-L) color-magnitude diagram of unblended stars shows a domin ant AGB population with photometric characteristics that are similar to those of the most luminous M giants in the Galactic bulge.
A sample of 196 AGNs and ULIRGs observed by the Infrared Spectrograph (IRS) on Spitzer is analyzed to study the distribution of the strength of the 9.7 micron silicate feature. Average spectra are derived for quasars, Seyfert 1 and Seyfert 2 AGNs, and ULIRGs. We find that quasars are characterized by silicate features in emission and Seyfert 1s equally by emission or weak absorption. Seyfert 2s are dominated by weak silicate absorption, and ULIRGs are characterized by strong silicate absorption (mean apparent optical depth about 1.5). Luminosity distributions show that luminosities at rest frame 5.5 micron are similar for the most luminous quasars and ULIRGs and are almost 10^5 times more luminous than the least luminous AGN in the sample. The distributions of spectral characteristics and luminosities are compared to those of optically faint infrared sources at z~2 being discovered by the IRS, which are also characterized by strong silicate absorption. It is found that local ULIRGs are a similar population, although they have lower luminosities and somewhat stronger absorption compared to the high redshift sources.
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