| 1. |
- Blasco-Herrera, J., et al.
(författare)
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H alpha kinematics of 11 starburst galaxies selected from the Sloan Digital Sky Survey
- 2013
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 435:3, s. 1958-1983
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Tidskriftsartikel (refereegranskat)abstract
- We present analysis of Fabry-Perot interferometric observations for a sample of 11 starburst galaxies with redshift z less than or similar to 0.03 selected from the Sloan Digital Sky Survey. We have targeted the H alpha lambda 6562.78 emission line at spatial sampling of 0.2arcsec-0.4 arcsec and at spectral resolution of R similar to 16 000. Studying two-dimensional maps for the velocity, velocity dispersion, line emission and continuum deliver new insights into the nature of starburst and postburst galaxies. The velocity fields are fitted to an exponential disc model, providing scalelengths and masses, to be compared with the photometric scalelength and the mass estimated from the velocity dispersions. From the line emission, the star formation rates are also calculated and compared with values in the literature. We have found that between 55 and 64 per cent of our sample show large-scale dominating rotation, while 27 per cent show local rotation typically restricted to the central part of each system. The morphology and line profiles in the centre of eight objects are consistent with a recent merger, while another two seem to be involved in a accretion process which, for the moment, has not disrupted their kinematics.
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| 2. |
- Fathi, Kambiz, et al.
(författare)
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ALMA FOLLOWS STREAMING OF DENSE GAS DOWN TO 40 PC FROM THE SUPERMASSIVE BLACKHOLE IN NGC 1097
- 2013
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Ingår i: Astrophysical Journal Letters. - 2041-8205. ; 770:2, s. L27-
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Tidskriftsartikel (refereegranskat)abstract
- We present a kinematic analysis of the dense gas in the central 200 parsecs of thenearby galaxy NGC1097, based on Cycle 0 observations with the Atacama LargeMillimeter/sub-millimeter Array (ALMA). We use the HCN(4-3) line to trace the densest interstellar molecular gas (nH2 ~ 10^8 cm-3), and quantify its kinematics by means of Fourier decomposition. We find a striking similarity between the ALMA kinematic data and the analytic spiral in ow model that we have previously constructed based onionized gas velocity fields on larger scales. We are able to follow dense gas streamingdown to 40 pc distance from the supermassive black hole in this Seyfert 1 galaxy. In order to fulll marginal stability, we deduce that the dense gas is conned to a very thin disc, with 6.0+2.2-2.7 10^6 Msun dynamical mass inside a radius of 40 pc. Finally, we derive a dense gas in ow rate of 0.09Msun yr-1 at 40 pc radius. Combined with previous valuesfrom the H and CO gas, we calculate a combined molecular and ionized gas in ow rateof 0.2Msun yr-1 at 40 pc distance from the central supermassive black hole of NGC1097.
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| 3. |
- Izumi, Takuma, et al.
(författare)
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Submillimeter ALMA Observations of the Dense Gas in the Low-Luminosity Type-1 Active Nucleus of NGC 1097
- 2013
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Ingår i: Publications of the Astronomical society of Japan. - : Oxford University Press (OUP). - 0004-6264 .- 2053-051X. ; 65:5
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Tidskriftsartikel (refereegranskat)abstract
- We present the first 100 pc scale view of the dense molecular gas in the central similar to 1.3 kpc of the type-1 Seyfert NGC 1097, traced by HCN (J = 4-3) and HCO+ (J = 4-3) lines afforded with ALMA band 7. This galaxy shows significant HCN enhancement with respect to HCO+ and CO in the low-J transitions, which seems to be a common characteristic in AGN environments. Using the ALMA data, we consider the characteristics of the dense gas around this AGN, and search for the mechanism of HCN enhancement. We find a high HCN (J = 4-3) to HCO+ (J = 4-3) line ratio in the nucleus. The upper limit of the brightness temperature ratio of HCN (nu(2) = 1(1f), J = 4-3) to HCN (J = 4-3) is 0.08, which indicates that IR pumping does not significantly affect the pure rotational population in this nucleus. We also find a higher HCN (J = 4-3) to CS (J = 7-6) line ratio in NGC 1097 than in starburst galaxies, which is more than 12.7 on the brightness temperature scale. Combined with similar observations from other galaxies, we tentatively suggest that this ratio appears to be higher in AGN-host galaxies than in pure starburst ones, similar to the widely used HCN to HCO+ ratio. LTE and non-LTE modeling of the observed HCN and HCO+ lines using J = 4-3 and 1-0 data from ALMA, and J = 3-2 data from SMA, reveals a high HCN to HCO+ abundance ratio (5 <= [HCN]/[HCO+] <= 20: non-LTE analysis) in the nucleus, and that the high-J lines (J = 4-3 and 3-2) are emitted from dense (10(4.5) cm(-3) <= n(H2) <= 10(6) cm(-3)), hot (70 K <= T-kin <= 550 K) regions. Finally we propose that high-temperature chemistry is more plausible to explain the observed enhanced HCN emission in NGC 1097 than pure gas-phase PDR/XDR chemistry.
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| 4. |
- Karlsson, Roland, et al.
(författare)
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Hydroxyl, water, ammonia, carbon monoxide, and neutral carbon towards the Sagittarius A complex VLA, Odin, and SEST observations
- 2013
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 554
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Tidskriftsartikel (refereegranskat)abstract
- Aims. The Sagittarius A complex in the Galactic centre comprises an ensemble of molecular clouds of different species with a variety of geometrical and kinematic properties. This work aims to study molecular abundances, morphology, and kinematics by comparing hydroxyl, water, carbon monoxide, ammonia, and atomic carbon and some of their isotopologues, in the +50 km s(-1) cloud, the circumnuclear disk (CND), the +20 km s(-1) cloud, the expanding molecular ring and the line-of-sight spiral arm features, including the Local/Sgr arm, the -30 km s(-1) arm, and the 3-kpc arm. Methods. We observed the +50 km s(-1) cloud, the CND and the +20 km s(-1) cloud, and other selected positions at the Galactic centre with the VLA, and the Odin satellite. The VLA was used to map the 1665 and 1667 MHz OH lambda doublet main lines of the (H-2(3/2)) state, and the Odin satellite was used to map the 557 GHz H2O (1(10)-1(01)) line as well as to observe the 548 GHz (H2O)-O-18 (1(10)-1(01)) line, the 572 GHz NH3 (1(0)-0(0)) line, the 576 GHz CO J = 5-4 line and the 492 GHz C-I (P-3(1)-P-3(0)) line. Furthermore, the SEST was used to map a 4'.5 x 6' region of the SgrAcomplex in the 220 GHz (CO)-O-18 J = 2-1 line. Results. Strong OH absorption, H2O emission and absorption lines were seen at all observed positions, and the (H2O)-O-18 line was detected in absorption towards the +50 km s(-1) cloud, the CND, the +20 km s(-1)cloud, the expanding molecular ring, and the 3-kpc arm. Strong CO J = 5-4, (CO)-O-18 J = 2-1, and neutral carbon C-I emissions were seen towards the +50 and +20 km s(-1) clouds. NH3 was only detected in weak absorption originating in the line-of-sight spiral arm features. The abundances of OH and H2O in the +50 and +20 km s(-1) clouds reflect the different physical environments in the clouds, where shocks and star formation prevail in the +50 km s(-1) cloud and giving rise to a higher rate of H2O production there than in the +20 km s(-1) cloud. In the CND, cloud collisions and shocks are frequent, and the CND is also subject to intense UV-radiation emanating from the supermassive black hole and the central star cluster. The CND is rich in (HO)-O-2 and OH, and these abundances are considerably higher than in the +50 and +20 km s(-1) clouds. We compare our estimated abundances of OH, H2O, and NH3 with similar and differing results for some other sources available in the literature. As compared to the quiescent cloud values of a few x 10(-9), or lower, the H2O abundance is markedly enhanced in the front sides of the Sgr A molecular cloud cores, (2-7) x 10(-8), as observed in absorption, and highest in the CND. A similar abundance enhancement is seen in OH. The likely explanation is PDR chemistry including grain surface reactions, and perhaps also the influence of shocks. In the redward high-velocity line wings of the +50 and +20 km s(-1) clouds and the CND, the H2O abundances are estimated to be (1-6) x 10(-6) or higher, i.e., similar to the water abundances in outflows of the Orion KL and DR21 molecular clouds, which are said to be caused by the combined action of shock desorption from icy grain mantles and high-temperature, gas-phase shock chemistry.
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| 5. |
- Piñol Ferrer, Núria, 1984-
(författare)
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Rearrangement of gas in disc galaxies
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Active galactic nuclei and bursts of star formation are two distinct phenomena that amply change their host environments. They are present in a significant number of galaxies at all redshifts. In this thesis, we aim toward a better understanding of the physical processes that allow for the formation and maintenance of these two phenomena. We focus on the study of the physical conditions of the interstellar gas in the central kiloparsec region of the barred active galaxy NGC 1097 (Paper I). In Paper I we present different CO transitions and the consequent analysis realized in order to derive the molecular gas content together with the molecular mass inflow toward the centre of the galactic gravitational potential well. To completely understand the physical processes that drive such gas rearrangement, a coherent picture for a dynamical system has to be considered. We have developed a code, Paper II, in order to model the dynamics of a predominantly rotating system with an arbitrary mass distribution. The formalism we have used is based on analytical solutions of the first order approximation of the equations of motion of a smooth medium that may be subject to dissipation. The most important free parameter to constrain the boundary conditions of the model is the angular frequency of the perturbing pattern, which may be assumed virtually invariant over significant ranges of galactocentric radii. We constrain the pattern velocity using the Tremaine-Weinberg method (Paper III). Hence, we have prepared all procedures needed to comprehend the physical processes that sustain the nuclear activity and bursts of star formation: the amount of gas in the region and the dynamics of the system. In Paper IV, we model the neutral and ionized gas kinematics in NGC 1097 and apply a combination of the methods described in Paper II and Paper III to comprehend the rearrangement of gas in the galaxy. In order to observationally discern the gas inflow in the nuclear region at a higher resolution, we apply the methods developed and used in this thesis to Cycle-0 ALMA observations of our target galaxy, and we confirm that we are able to follow the streaming of gas from 20 kiloparsec distances down to 40 parsecs from its central central supermassive black hole (Paper V).
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| 6. |
- Sandberg, Andreas, et al.
(författare)
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Neutral gas in Lyman-alpha emitting galaxies Haro 11 and ESO 338-IG04 measured through sodium absorption
- 2013
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 552
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Tidskriftsartikel (refereegranskat)abstract
- Context. The Lyman alpha emission line of neutral hydrogen is an important tool for finding galaxies at high redshift, thus for probing the structure of the early universe. However, the resonance nature of the line and its sensitivity to dust and neutral gas is still not fully understood. Aims. We present measurements of the velocity, covering fraction and optical depth of neutral gas in front of two well-known, local blue compact galaxies that show Lyman alpha in emission: ESO 338-IG 04 and Haro 11. We thus observationally test the hypothesis that Lyman alpha can escape through neutral gas by being Doppler shifted out of resonance. Methods. We present integral field spectroscopy, obtained with the GIRAFFE/Argus spectrograph at VLT/FLAMES in Paranal, Chile. The excellent wavelength resolution allowed us to accurately measure the velocity of the ionized and neutral gas through the Ha emission and Na D absorption, which trace the ionized medium and cold interstellar gas, respectively. We also present independent measurements from the VLT/X-shooter spectrograph that confirm our results. Results. For ESO 338-IG 04 we measure no significant shift of neutral gas: the best fit velocity offset is -15 +/- 16 km s(-1). For Haro 11, we see an outflow from knot B at 44 +/- 13 km s(-1), and infalling gas towards knot C with 32 +/- 12 km s(-1). Based on the relative strength of the Na D absorption lines, we estimate low covering fractions of neutral gas (down to 10%) in all three cases. Conclusions. The Na D absorption most likely occurs in dense clumps with higher column densities than the medium in which the bulk of the Ly alpha scattering takes place. Still, we find no strong correlation between outflowing neutral gas and strong Ly alpha emission. The Ly alpha photons from these two galaxies are therefore likely to be escaping due to a low column density and/or covering fraction.
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