| 1. |
- Fathi, Kambiz, et al.
(författare)
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AN H alpha NUCLEAR SPIRAL STRUCTURE IN THE E0 ACTIVE GALAXY Arp 102B
- 2011
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 736:2, s. 77-
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of a two-armed mini-spiral structure within the inner kiloparsec of the E0 LINER/Seyfert 1 galaxy Arp 102B. The arms are observed in H alpha emission and located east and west of the nucleus, extending up to approximate to 1 kpc from it. We use narrow-band imaging from the Hubble Space Telescope Advanced Camera for Surveys, in combination with archival Very Large Array radio images at 3.6 and 6 cm to investigate the origin of the nuclear spiral. From the H alpha luminosity of the spiral, we obtain an ionized gas mass of the order of 10(6) solar masses. One possibility is that the nuclear spiral represents a gas inflow triggered by a recent accretion event which has replenished the accretion disk, giving rise to the double-peaked emission-line profiles characteristic of Arp 102B. However, the radio images show a one-sided curved jet which correlates with the eastern spiral arm observed in the H alpha image. A published milliarcsecond radio image also shows a one-sided structure at position angle approximate to 40 degrees, approximately aligned with the inner part of the eastern spiral arm. The absence of a radio counterpart to the western spiral arm is tentatively interpreted as indicating that the jet is relativistic, with an estimated speed of 0.45c. Estimates of the jet kinetic energy and the ionizing luminosity of the active nucleus indicate that both are capable of ionizing the gas along the spiral arms. We conclude that, although the gas in the nuclear region may have originated in an accretion event, the mini spiral is most likely the result of a jet-cloud interaction rather than an inflowing stream.
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| 2. |
- Font, Joan, et al.
(författare)
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DETECTION OF INFALLING HYDROGEN IN TRANSFER BETWEEN THE INTERACTING GALAXIES NGC 5426 AND NGC 5427
- 2011
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Ingår i: The Astrophysical Journal. Letters. - 2041-8205. ; 740:1, s. L1-
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Tidskriftsartikel (refereegranskat)abstract
- Using velocity tagging we have detected hydrogen from NGC 5426 falling onto its interacting partner NGC 5427. Our observations, with the GHaFaS Fabry-Perot spectrometer, produced maps of the two galaxies in H alpha surface brightness and radial velocity. We found emission with the range of velocities associated with NGC 5426 along lines of sight apparently emanating from NGC 5427, superposed on the velocity map of the latter. After excluding instrumental effects we assign the anomalous emission to gas pulled from NGC 5426 during its passage close to NGC 5427. Its distribution, more intense between the arms and just outside the disk of NGC 5427, and weak, or absent, in the arms, suggests that the infalling gas is behind the disk, ionized by Lyman continuum photons escaping from NGC 5427. Modeling this, we estimate the distances of these gas clouds behind the plane: a few hundred parsecs to a few kiloparsecs. We also estimate the mass of the infalling (ionized plus neutral) gas, finding an infall rate of 10 M(circle dot) per year, consistent with the high measured star formation rate across the disk of NGC 5427 and with the detected circumnuclear galactic wind.
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| 3. |
- Font, Joan, et al.
(författare)
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RESONANT STRUCTURE IN THE DISKS OF SPIRAL GALAXIES, USING PHASE REVERSALS IN STREAMING MOTIONS FROM TWO-DIMENSIONAL H alpha FABRY-PEROT SPECTROSCOPY
- 2011
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Ingår i: The Astrophysical Journal Letters. - 2041-8205. ; 741:1, s. L14-
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Tidskriftsartikel (refereegranskat)abstract
- In this Letter, we introduce a technique for finding resonance radii in a disk galaxy. We use a two-dimensional velocity field in H alpha emission obtained with Fabry-Perot interferometry, derive the classical rotation curve, and subtract it off, leaving a residual velocity map. As the streaming motions should reverse sign at corotation, we detect these reversals and plot them in a histogram against galactocentric radius, excluding points where the amplitude of the reversal is smaller than the measurement uncertainty. The histograms show well-defined peaks which we assume to occur at resonance radii, identifying corotations as the most prominent peaks corresponding to the relevant morphological features of the galaxy (notably bars and spiral arm systems). We compare our results with published measurements on the same galaxies using other methods and different types of data.
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| 4. |
- Pinol-Ferrer, Nuria, et al.
(författare)
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Physical condition of the molecular gas at the centre of NGC 1097
- 2011
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 414:1, s. 529-537
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Tidskriftsartikel (refereegranskat)abstract
- We have used the X(CO) conversion factor, local thermodynamic equilibrium and large velocity gradient approximation to parametrize the cold and warm phases of the interstellar medium from five different low transitions of the CO molecule in the central 21 arcsec (kpc) region of NGC 1097. We have applied a one-component model and derived a typical kinetic temperature of about 33 K, a molecular hydrogen density of 4.9 x 10(3) M(circle dot) pc(-3) and a CO column density of 1.2 x 10(-2) M(circle dot) pc(-2). A two-component model results in 85 per cent cold-to-total gas fraction in the presence of a 90 K warm counterpart. Furthermore, we 'resolve' the spatially unresolved single-dish observations by selecting velocity channels that in an interferometric velocity map correspond to specific regions. We have selected five such regions and found that the physical properties in these regions are comparable to those derived from the full line profile. This implies that the central kpc of NGC 1097 is rather homogeneous in nature and, although the regions are not uniquely located within the ring, the star formation along the ring is homogeneously distributed (in agreement with recent Herschel observations). We have further revised the mass-inflow rate on to the supermassive black hole in this prototype low-ionization nuclear emission-line region/Seyfert 1 galaxy and found that accounting for the total interstellar medium and applying a careful contribution of the disc thickness and corresponding stability criterion increases the previous estimations by a factor of 10. Finally, we have calculated the X(CO) conversion factor for the centre of NGC 1097 using an independent estimation of the surface density to the CO emission and obtained X(CO) = (2.8 +/- 0.5) x 10(20) cm(-2) (K km s(-1))(-1) at a radius 10.5 arcsec and X(CO) = (5.0 +/- 0.5) x 10(20) cm(-2) (K km s(-1))(-1) at a radius 7.5 arcsec. With the approach and analysis described in this paper, we have demonstrated that important physical properties can be derived to a resolution beyond the single-dish resolution element; however, caution is necessary while interpreting the results.
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