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Register a new userNear-infrared spectroscopy of Seyfert galaxies
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J.K. Kotilainen ESO
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Results from near-infrared 1.5 - 2.5 micron long-slit spectroscopy of 14 nearby Seyfert galaxies are presented.
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(Abridged) We present new K-band spectroscopy for a sample of 48 starburst galaxies, obtained using UKIRT in Hawaii. This constitutes a fair sample of the most common types of starburst galaxies found in the nearby Universe. The variety of near infrared spectral features shown by these galaxies implies different bursts characteristics, which suggests that we survey galaxies with different star formation histories or at different stages of their burst evolution. Using synthetic starburst models, we conclude that the best ensemble of parameters which describe starburst galaxies in the nearby universe are a constant rate of star formation, a Salpeter IMF with an upper mass cutoff equal to 30 solar mass and bursts ages between 10 Myr and 1 Gyr. The model is fully consistent with the differences observed in the optical and FIR between the different types of starbursts. It suggests that HII galaxies have younger bursts and lower metallicities than SBNGs, while LIRGs have younger bursts but higher metallicities. Our observations suggest that the starburst phenomenon must be a sustained or self--sustained phenomenon: either star formation is continuous in time or multiple bursts happen in sequence over a relatively long period of time. The generality of our observations implies that this is a characteristic of starburst galaxies in the nearby Universe.
This is the first of two papers in which a study is made of a sample of 12 southern radio-luminous Seyfert galaxies. Our aim is to investigate possible correlations between radio morphology and nuclear/circumnuclear emission-line properties. In this paper we present radio images at 13, 6, and 3 cm taken with the Australia Telescope Compact Array (ATCA), global far-infrared (FIR) properties for the whole sample, and optical and near-infrared (NIR) spectroscopy of an interesting subset. We find a mixture of radio morphologies, including linear, diffuse and compact sources. When the FIR colors of the galaxies are considered there is an indication that the compact radio sources have warmer FIR colors than the diffuse sources, whereas the linear sources span a wide range of FIR colors. There is a wide variation in radio spectral-indices, suggesting that free-free absorption is significant in some systems, particularly IRAS 11249-2859, NGC 4507, and NGC 7213. Detailed emission-line studies are presented of 4 galaxies IC 3639, NGC 5135, NGC 3393 & IRAS 11249-2859. In IC 3639 we present evidence of vigorous, compact star formation enclosed by very extended [OI]6300 emission, suggestive of the boundary between a diffuse outflow and the surrounding ISM. In another galaxy, IC 5063, we see evidence for the possible interaction of a highly collimated outflow and the surrounding rotating inner disk. Of the 5 galaxies which show compact radio emission, 4 have radio/FIR flux ratios consistent with an energetically dominant AGN, whereas IC 4995 exhibits evidence for a very compact starburst.
We present the results of deep near-infrared spectroscopy of seven submillimetre-selected galaxies from the SCUBA 8-mJy and CUDSS surveys. These galaxies were selected because they are too faint to be accessible to optical spectrographs on large telescopes. We obtain a spectroscopic redshift for one object, and likely redshifts for two more, based on a combination of marginal emission line detections and the shape of the continuum. All three redshifts broadly agree with estimates from their radio/submm spectral energy distributions. From the emission line strengths of these objects, we infer star formation rates of 10-25 Msun/yr, while the lack of detections in the other objects imply even lower rates. By comparing our results with those of other authors, we conclude it is likely that the vast majority (more than 90 per cent) of the star formation in these objects is completely extinguished at rest-frame optical wavelengths, and the emission lines originate in a relatively unobscured region. Finally, we look at future prospects for making spectroscopic redshift determinations of submm galaxies.
We present low resolution near-infrared spectroscopy of an unbiased sample of 24 ultraluminous infrared galaxies (ULIRGs), selected from samples previously observed spectroscopically in the mid-infrared with the Infrared Space Observatory (ISO). Qualitatively, the near-infrared spectra resemble those of starbursts. Only in one ULIRG, IRAS 04114-5117E, do we find spectroscopic evidence for AGN activity. The spectroscopic classification in the near-infrared is in very good agreement with the mid-infrared one. For a subset of our sample for which extinction corrections can be derived from Pa-alpha and Br-gamma, we find rather high Pa-alpha luminosities, in accordance with the powering source of these galaxies being star formation.[Fe] emission is strong in ULIRGs and may be linked to starburst and superwind activity. Additionally, our sample includes two unusual objects. The first, IRAS F00183-7111, exhibits extreme [Fe] emission and the second, IRAS F23578-5307, is according to our knowledge one of the most luminous infrared galaxies in H2 rotation-vibration emission.
Results from an analysis of low resolution (R~250) near-IR long-slit spectra covering simultaneously the I, J, H, and K bands, for a sample of 15 Seyfert galaxies and the N5253 starburst nucleus, are presented. The Seyfert galaxies were selected as presenting `linear or cone-like high excitation emission line in the optical, most probably due to the collimation of the central sources radiation by a dusty molecular torus. Our goal was to look for signatures of this torus, and to investigate the gaseous distribution, excitation and reddening. The IR emission lines are spatially extended in most cases, and we have used the [FeII]/Pa(beta) ratio as a measure of the gaseous excitation in Mrk573, N1386, and N7582. Values for this ratio between 1.5 and 6 are found, suggesting excitation of [FeII] by X-rays or shock waves in some regions. Nuclear Pa(beta) in N1365, and possibly nuclear Br(gama) in Mrk573, are broad. From analysis of the spatial distribution of the continuum (J-H) and (H-K) colours derived from our spectra, we find redder colours for the nucleus than the nearby bulge in most of the Seyfert 2s observed. Comparison with models including emission from dust and stars shows that hot (T~1000 K) dust emission dominates the nuclear continuum in N1365, N2110, N3281, N7582, and ESO362-G18. In N1386, N5643, and N5728 the main contributor is the underlying stellar population, combined with some foreground reddening and/or cool dust emission. In a few cases, the (J-H) colours on opposite sides of the nucleus differ by 0.3-0.8 mag, an effect that we interpret as partly due to differences in the local stellar population, and possibly extinction gradients.
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