15205380
NICMOS imaging of molecular hydrogen emission in seyfert galaxies
We present near-infrared (NICMOS) imaging of broadband and molecular hydrogen emission in Seyfert galaxies. In six of 10 Seyfert galaxies we detect resolved or extended emission in the 1-0 S(1) 2.121 μm or 1-0 S(3) 1.9570 μm molecular hydrogen lines. We did not detect emission in the most distant galaxy or in two Seyfert 1 galaxies because of the luminosity of the nuclear point sources. In NGC 5643, NGC 2110, and Mrk 1066, molecular hydrogen emission is detected in the extended narrow-line region on scales of a few hundred parsecs from the nucleus. Emission is coincident with [O III] and Hα + [N II] line emission. This emission is also near dust lanes observed in the visible to near-infrared color maps, suggesting that a multiphase medium exists near the ionization cones and that the morphology of the line emission is dependent on the density of the ambient media. The high 1-0 S(1) or S(3) H2 to Hα flux ratio suggests that shock excitation of molecular hydrogen (rather than UV fluorescence) is the dominant excitation process in these extended features. In NGC 2992 and NGC 3227 the molecular hydrogen emission is from 800 and 100 pc diameter "disks" (respectively) that are not directly associated with [O III] emission and are near high levels of extinction (AV 10). The molecular hydrogen emission in NGC 4945 appears to be from the edge of a 100 pc superbubble. The molecular gas in these three galaxies could be excited by processes associated with local star formation. We confirm previous spectroscopic studies finding that no single mechanism is likely to be responsible for the molecular hydrogen excitation in Seyfert galaxies.
120151930
New constraints on the unified model of Seyfert galaxies
2943456
A near‐infrared polarized bipolar cone in the Circinus galaxy
We present near–infrared broad–band polarization images of the nuclear regions of the Circinus galaxy in the J, H and K bands. For the first time the south–eastern reflection cone is detected in polarized light, which is obscured at optical wavelengths behind the galactic disk. This biconical structure is clearly observed in J and H band polarized flux whilst in the K band a more compact structure is detected. Total flux J–K and H–K colour maps reveal a complex colour gradient toward the south–east direction (where the Circinus galactic disk is nearer to us). We find enhanced extinction in an arc shaped structure, at about 200pc from the nucleus, probably part of the starformation ring. We model the polarized flux images with the scattering and torus model of Young et al. , with the same basic input parameters as used by Alexander et al. in the spectropolarimetry modelling of Circinus. The best fit to the polarized flux is achieved with a torus radius of �16pc, and a visual extinction AV , through the torus, to the near–infrared emission regions of >66 mags.
18339380
Nuclear properties of a sample of nearby spirals from STIS imaging
We present surface photometry for the central regions of a sample of 48 spiral galaxies (mostly unbarred and barred of types Sbc or Sc) observed with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. Surface brightness profiles were derived and modeled with a Nuker law. We also analyzed archival Wide Field Planetary Camera 2 images with a larger field of view, available for 18 galaxies in our sample. We modeled the extracted bulge surface brightness profiles with an exponential, an r1/4, or an rn profile. In agreement with previous studies, we find that bulges of Sbc galaxies fall into two categories: bulges well described by an exponential profile and those well described by an r1/4 profile. Only one galaxy requires the use of a more general Sersic profile to properly describe the bulge. Nuclear photometrically distinct components are found in ∼ 55% of the galaxies. For those that we classify as star clusters based on their resolved extent we find absolute magnitudes that are brighter on average than those previously identified in spiral galaxies. This might be due to a bias in our sample toward star forming galaxies, combined with a trend for star forming galaxies to host brighter central clusters. Department of Astronomy, Univeristà degli Studi di Padova, Padova, Italy Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 Department of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield, Hertfordshire, AL10 9AB, UK Department of Physics, RIT, 84 Lomb Memorial Dr., Rochester, NY 14623-5603 Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 Oxford University, Theoretical Physics, Keble Road, Oxford, OX1 3NP, UK INAF-Osservatorio Astronomico di Torino, I-10025 Pino Torinese, Italy Physics Department, ETH, Hoenggerberg HPF G4.3, CH–8092 Zurich, Switzerland INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy School of Physics and Astronomy, University of Nottingham, NG7 2RD, UK Center for Astrophysical Sciences, Johns Hopkins University, 239 Bloomberg Center for Physics & Astronomy, 3400 North Charles Street, Baltimore, MD 21218
9424089
Constraints on the nuclear emission of the Circinus galaxy: the torus
In the context of the unified model of Seyfert galaxies, we use observations from the literature and a radiative transfer model to investigate the near–IR to mm emission produced by the presumed torus in the Circinus galaxy, from 2µm to 1.3mm. From the infrared SED modelling, we find that the total luminosity (LIR) in this wavelength range, consists of similar contributions from the torus and starburst with a ratio of nuclear luminosity to starburst luminosity (LNUC/LSB) � 0.8. By using a similar torus model to that of NGC1068, but without the conical dust, we find an upper limit to the outer torus radius of �12pc with a best fit of �2pc. The upper limit torus size estimated from the radiative transfer modelling is consistent with the 16pc torus radius estimated from near–IR imaging polarimetry of Circinus.
122151847
New infrared observations of seyfert 2 galaxies and unification theories
14792267
The chemical composition of the galactic H II regions M8 and M17. A revision based on deep vlt echelle spectrophotometry
We present new echelle spectrophotometry of the Galactic H II regions M8 and M17. The data have been taken with the VLT UVES echelle spectrograph in the 3100 to 10400 A range. We have measured the intensities of 375 and 260 emission lines in M8 and M17 respectively, increasing signicativ ely the number of emission lines measured in previous spectrophotometric studies of these nebulae. Most of the detected lines are permitted lines. Electron temperatures and densities have been determined using dieren t diagnostics. We have derived He + , C ++ , O + and O ++ ionic abundances from pure recombination lines. We have also derived abundances from collisionally excited lines for a large number of ions of dieren t elements. Highly consistent estimations of t 2 have been obtained by using dieren t independent indicators; the values are moderate and very similar to those obtained in other Galactic H II regions. We report the detection of deuterium Balmer emission lines, up to D , in M8 and show that their intensities are consistent with continuum uorescence as their main excitation mechanism.
13941541
The Chemical Composition of the Small Magellanic Cloud H II Region NGC 346 and the Primordial Helium Abundance
Spectrophotometry in the λλ3400-7400 range is presented for 13 areas of the brightest H II region in the SMC: NGC 346. The observations were obtained at CTIO with the 4 m telescope. Based on these observations, its chemical composition is derived. The helium and oxygen abundances by mass are given by Y(SMC) = 0.2405 ± 0.0018 and O(SMC) = 0.00171 ± 0.00025. From models and observations of irregular and blue compact galaxies it is found that ΔY/ΔO = 3.5 ± 0.9 and, consequently, that the primordial helium abundance by mass is given by Yp = 0.2345 ± 0.0026 (1 σ). This result is compared with values derived from big bang nucleosynthesis and with other determinations of Yp.
14952037
THE CALIBRATION OF THE O/H ABUNDANCE INDICATORS FOR EXTRAGALACTIC H II REGIONS BASED ON O II RECOMBINATION LINES
Based on O II recombination lines we present a new calibration (called O IIRL) of Pagel’s O23 indicator to determine the O/H abundance ratio in extragalactic H II regions and emission line galaxies. The O IIRL calibration produces O/H abundances about a factor of two higher than those derived from the T (4363) method with t 2 = 0.00. The O IIRL calibration has implications for the study of dieren t properties of emission line galaxies such as their metallicity, star formation rate, and initial mass function. The O IIRL calibration also aects the abundance determinations based on other O/H indicators, that include collisionally excited lines, like those known as O3N2, N2, S23, Ar3O3, and S3O3. We argue that the controversy between the T (4363) method and the photoionization models method to derive O/H values is mainly due to temperature variations inside the observed H II regions.
9196866
Evidence for a precessing accretion disk in the nucleus of NGC 1097
We present new spectroscopic observations of the LINER (and now Seyfert 1) nucleus of NGC 1097, and discuss the evolution of its broad, double-peaked Balmer lines. When originally discovered in 1991, the red peak of the double-peaked Hα line was stronger than the blue, while by 1994 the Hα profile had become almost symmetric and the integrated line flux had decreased to half its original value. Our new spectrum, taken in 1996, shows that the broad, double-peaked lines have returned to almost their original strengths, the profiles of Hβ and Hα are identical to within errors, and the broad-line emitting region is unreddened. However, the profile of the Balmer lines is now such that the blue peak is stronger than the red, opposite to the asymmetry observed in 1991. Various models are considered for the observed behavior, all assuming that the emission lines originate in an accretion disk. We present a refined version of the precessing, planar, elliptical accretion-ring model proposed by Storchi-Bergmann et al. and Eracleous et al. This model provides an acceptable fit to the line profiles. We also consider the possibility that the line-profile evolution results from a precessing warp in the disk, induced by irradiation from the center, and show that the range of radii and precession timescales expected in this model are consistent with the observations. The sudden appearance of the "disklike" broad-line profiles in NGC 1097 could have resulted from the formation of a new accretion disk due, for example, to the tidal disruption of a star or the illumination of a preexisting disk by a transient ionizing source at the center of the disk.
118395096
Milli-magnitude IR Planetary Transit Detection: OGLE-TR-113