| 1. |
- Beckman, John, et al.
(författare)
-
The Tremaine-Weinberg method for pattern speeds using H-alpha emission from ionized gas
- 2008
-
Ingår i: Formation and Evolution of Galaxy Disks. - : Astronomical Society of the Pacific. - 9781583816622 ; , s. 353-
-
Konferensbidrag (populärvet., debatt m.m.)abstract
- The Fabry-Perot interferometer FaNTOmM was used at the 3.6m Canada France Hawaii Telescope and the 1.6m Mont Megantic Telescope to obtain data cubes in H-alpha of 9 nearby spiral galaxies from which maps in integrated intensity, velocity, and velocity dispersion were derived. We then applied the Tremaine-Weinberg method, in which the pattern speed can be deduced from its velocity field, by finding the integrated value of the mean velocity along a slit parallel to the major axis weighted by the intensity and divided by the weighted mean distance of the velocity points from the tangent point measured along the slit. The measured variables can be used either to make separate calculations of the pattern speed and derive a mean, or in a plot of one against the other for all the points on all slits, from which a best fit value can be derived. Linear fits were found for all the galaxies in the sample. For two galaxies a clearly separate inner pattern speed with a higher value, was also identified and measured.
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| 2. |
- Blasco-Herrera, Javier, et al.
(författare)
-
An improved method for statistical studies of the internal kinematics of H ii regions : the case of M83
- 2010
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 407:4, s. 2519-2529
-
Tidskriftsartikel (refereegranskat)abstract
- We present the integrated H alpha emission line profile for 157 H ii regions in the central 3.4 x 3.4 arcmin2 of the galaxy M83 (NGC 5236). Using the Fabry-Perot interferometer GH alpha FaS, on the 4.2-m William Herschel Telescope on La Palma, we show the importance of a good characterization of the instrumental response function for the study of line profile shapes. The luminosity-velocity dispersion relation is also studied, and in the log(L)-log(Sigma) plane we do not find a linear relation, but an upper envelope with equation log(L-H alpha) = 0.9 log(Sigma) + 38.1. For the adopted distance of 4.5 Mpc, the upper envelope appears at the luminosity L = 1038.5 erg s-1, in full agreement with previous studies of other galaxies, reinforcing the idea of using H ii regions as standard candles.
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| 3. |
- Blasco-Herrera, J., et al.
(författare)
-
H alpha kinematics of 11 starburst galaxies selected from the Sloan Digital Sky Survey
- 2013
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 435:3, s. 1958-1983
-
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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| 4. |
- Blasco-Herrera, Javier, 1981-, et al.
(författare)
-
Halpha kinematics of 11 starburst galaxies selected from the Sloan Digital Sky Survey
- 2012
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present analysis of Fabry-Perot interferometric observations for a sample of 11starburst galaxies with redshift z . 0.03 selected from the Sloan Digital Sky Survey.We have targeted the H 6562.78 emission line at spatial sampling of 0.002−0.004 andat spectral resolution of R 16000, and studying two-dimensional velocity, velocitydispersion, line emission and continuum maps deliver new insights into the nature ofstarburst and postburst galaxies. The velocity fields are fitted to an exponential discmodel, providing scale lengths and masses, to be compared with the photometric scalelength and the mass estimated from the velocity dispersions. From the line emissionthe star formation rates are also calculated and compared with values in the literature.We have found that between 55% and 64% of our sample show large scale dominatingrotation, while 27% show local rotation typically restricted to the central part of eachsystem. The morphology and line profiles in the centre of eight objects are consistentwith a recent merger, while another two seem to be involved in a accretion processwhich has not disrupted their kin
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| 5. |
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| 6. |
- Blasco-Herrera, Javier, 1981-, et al.
(författare)
-
Structural parameters of starburst and postburst galaxies
- 2012
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present two samples of 1173 starbursts and 145 postburst in the redshift range0.01 < z < 0.083, selected from Sloan Digital Sky Survey Data Release 7. We charac-terize both samples using 2D Sersic profiles and measure their asymmetry. The Sersicindex, n, and the effective radii show that starburst galaxies are more concentratedthan the postburst sample, with median n 1.85 for starbursts and 2.85 for post-bursts. There is a large fraction of disky (n < 2) postbursts, a fraction larger thanreported by previous studies. Part of the excess comes from low luminosity (Mr > −19)objects, vastly dominated by discs. We estimate the mass from the velocity dispersionof the H emission line, both for the starbursts and those postbursts with residualemission, finding that Lr / Mb, with b = 1.35 for starbursts and b = 1.5 for post-bursts. The typical values of the mass-to-light ratio range between 0 and 10. This,now, is surprising for starburst galaxies, for which mass-to-light ratios 1 have beenpreviously found.
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| 7. |
- Carignan, Claude, et al.
(författare)
-
GHaFaS: Galaxy H alpha Fabry-Perot Spectrometer for the WHT
- 2008
-
Ingår i: Pathways Through an Eclectic Universe. - 9781583816509 ; , s. 168-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A new scanning Fabry-Perot system will soon be available at the Nasmyth focus of the 4.2 m William Herschel Telescope. It has been designed by the Laboratoire d'Astrophysique Expérimentale in Montréal and is being built in collaboration with astronomers at the Instituto de Astrofísica de Canarias. The instrument will see first light at the beginning of July 2007.
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| 8. |
- Carignan, Claude, et al.
(författare)
-
GHαFaS: galaxy Hα Fabry-Perot system for the WHT
- 2008
-
Ingår i: SPIE--The International Society for Optical Engineering. - : SPIE. ; 7014:188
-
Forskningsöversikt (populärvet., debatt m.m.)abstract
- GHαFaS is a new Fabry-Perot system available at the William Herschel Telescope. It was mounted, for the first time, at the Nasmyth focus of the 4.2 m WHT in La Palma in 2007 July. With a spectral resolution of the order R~15000 and a seeing limited spatial resolution, GHαFaS provides a new look at the Hα-emitting gas over a 4 arcminutes circular field in the nearby universe. Many types of objects can be observed with a scanning Fabry-Perot system on a 4.2 m class telescope such as galaxies, HII regions, planetary nebulae, supernova remnants outflows from stars and the diffuse interstellar medium. Astronomers from the Laboratoire d'Astrophysique Experimentale (LAE) in Montreal, the Laboratoire d'Astrophysique de Marseille (LAM), and the Instituto de Astrofisica de Canarias (IAC), have inaugurated GHαFaS by studying in detail the dynamics of nearby spiral galaxies. A robust set of tools for reducing and analyzing the data cubes obtained with GHαFaS has also been developed.
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| 9. |
- Cumming, Robert, et al.
(författare)
-
Stellar dynamics of blue compact galaxies. II. Further indications of a merger in ESO 338-IG04
- 2007
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Luminous blue compact galaxies, common at z~1 but now relatively rare, show disturbed kinematics in emission lines. As part of a programme to understand their formation and evolution, we have investigated the stellar dynamics of a number of nearby objects in this class. We obtained long-slit spectra with VLT/FORS2 in the spectral region covering the near-infrared calcium triplet. In this paper we focus on the well-known luminous blue compact galaxy ESO 338-IG04 (Tololo 1924-416). A previous investigation, using Fabry-Perot interferometry, showed that this galaxy has a chaotic H-alpha velocity field, indicating that either the galaxy is not in dynamical equilibrium or that H-alpha does not trace the gravitational potential due to feedback from star formation. Along the apparent major axis, the stellar and ionised gas velocities for the most part follow each other. The chaotic velocity field must therefore be a sign that the young stellar population in ESO 338-IG04 is not in dynamical equilibrium. The most likely explanation, which is also supported by its morphology, is that the galaxy has experienced a merger and that this has triggered the current starburst. Summarising the results of our programme so far, we note that emission-line velocity fields are not always reliable tracers of stellar motions, and go on to assess the implications for kinematic studies of similar galaxies at intermediate redshift.
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| 10. |
- Cumming, Robert, 1967, et al.
(författare)
-
Stellar dynamics of blue compact galaxies - II. Further indications of a merger in ESO 338-IG04
- 2008
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 479:3, s. 725-733
-
Tidskriftsartikel (refereegranskat)abstract
- Context. Luminous blue compact galaxies, common at z similar to 1 but now relatively rare, show disturbed kinematics in emission lines. Aims. As part of a programme to understand their formation and evolution, we have investigated the stellar dynamics of a number of nearby objects in this class. Methods. We obtained long-slit spectra with VLT/FORS2 in the spectral region covering the near-infrared calcium triplet. In this paper we focus on the well-known luminous blue compact galaxy ESO338-IG04 (Tololo 1924 - 416). A previous investigation, using Fabry-Perot interferometry, showed that this galaxy has a chaotic Ha velocity field, indicating that either the galaxy is not in dynamical equilibrium or that Ha does not trace the gravitational potential due to feedback from star formation. Results. Along the apparent major axis, the stellar and ionised gas velocities for the most part follow each other. The chaotic velocity field must therefore be a sign that the young stellar population in ESO338-IG04 is not in dynamical equilibrium. The most likely explanation, which is also supported by its morphology, is that the galaxy has experienced a merger and that this has triggered the current starburst. Summarising the results of our programme so far, we note that emission-line velocity fields are not always reliable tracers of stellar motions, and go on to assess the implications for kinematic studies of similar galaxies at intermediate redshift.
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| 11. |
- Cumming, Robert, et al.
(författare)
-
Stellar kinematics in blue compact galaxies
- 2009
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In a programme of observations of local luminous blue compact galaxies (BCGs), we are investigating kinematics by using tracers of both stars and ionized gas. Here we summarise our program and present new data on the local Lyman break galaxy analogue Haro 11. From spatially-resolved spectroscopy around the near-infrared Ca II triplet, we find that its stars and ionized gas have similar velocity fields. Our programme so far indicates however that emission line velocities can differ locally by a few tens of km/s from the Ca II values. Comparing our data to simple stellar population models, we assess which stellar population the Ca II triplet traces and its potential beyond the local universe.
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| 12. |
- Dicaire, Isabel, et al.
(författare)
-
Hα kinematics of the Spitzer Infrared Nearby Galaxies Survey
- 2008
-
Ingår i: Monthley Notices of Royal Astronomical Society (MNRAS). - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 385, s. 52-
-
Tidskriftsartikel (refereegranskat)abstract
- This is the second part of an Hα kinematics follow-up survey of the Spitzer Infrared Nearby Galaxies Survey (SINGS) sample. The aim of this paper is to shed new light on the role of baryons and their kinematics and on the dark/luminous matter relation in the star-forming regions of galaxies, in relation with studies at other wavelengths. The data for 37 galaxies are presented. The observations were made using Fabry-Perot interferometry with the photon-counting camera FaNTOmM on four different telescopes, namely the Canada-France-Hawaii 3.6-m, the ESO La Silla 3.6-m, the William Herschel 4.2-m and the Observatoire du mont Mégantic 1.6-m telescopes. The velocity fields are computed using custom IDL routines designed for an optimal use of the data. The kinematical parameters and rotation curves are derived using the GIPSY software. It is shown that non-circular motions associated with galactic bars affect the kinematical parameters fitting and the velocity gradient of the rotation curves. This leads to incorrect determinations of the baryonic and dark matter distributions in the mass models derived from those rotation curves.
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| 13. |
- Dicaire, I, et al.
(författare)
-
Hα kinematics of the Spitzer Infrared Nearby Galaxies Survey - II
- 2008
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 385:2, s. 553-605
-
Tidskriftsartikel (refereegranskat)abstract
- This is the second part of an Hα kinematics follow-up survey of the Spitzer Infrared Nearby Galaxies Survey (SINGS) sample. The aim of this paper is to shed new light on the role of baryons and their kinematics and on the dark/luminous matter relation in the star-forming regions of galaxies, in relation with studies at other wavelengths. The data for 37 galaxies are presented. The observations were made using Fabry-Perot interferometry with the photon-counting camera FaNTOmM on four different telescopes, namely the Canada-France-Hawaii 3.6-m, the ESO La Silla 3.6-m, the William Herschel 4.2-m and the Observatoire du mont Mégantic 1.6-m telescopes. The velocity fields are computed using custom IDL routines designed for an optimal use of the data. The kinematical parameters and rotation curves are derived using the GIPSY software. It is shown that non-circular motions associated with galactic bars affect the kinematical parameters fitting and the velocity gradient of the rotation curves. This leads to incorrect determinations of the baryonic and dark matter distributions in the mass models derived from those rotation curves.
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| 14. |
- Falcón-Barroso, Jesús, et al.
(författare)
-
A Sauron Study of Stars and Gas in SA Bulges
- 2007
-
Ingår i: Island Universes.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present results from our ongoing effort to understand the morphological and kinematical properties of early-type galaxies using the integral-field spectrograph SAURON. We discuss the relation between the stellar and gas morphology and kinematics in our sub-sample of 24 representative Sa spiral bulges. We focus on the frequency of kinematically decoupled components and on the presence of star formation in circumnuclear rings.
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| 15. |
- Fathi, Kambiz, et al.
(författare)
-
ALMA FOLLOWS STREAMING OF DENSE GAS DOWN TO 40 PC FROM THE SUPERMASSIVE BLACKHOLE IN NGC 1097
- 2013
-
Ingår i: Astrophysical Journal Letters. - 2041-8205. ; 770:2, s. L27-
-
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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| 16. |
- Fathi, Kambiz, et al.
(författare)
-
AN H alpha NUCLEAR SPIRAL STRUCTURE IN THE E0 ACTIVE GALAXY Arp 102B
- 2011
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 736:2, s. 77-
-
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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| 17. |
- Fathi, Kambiz, et al.
(författare)
-
Disc scalelengths out to redshift 5.8
- 2012
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925. ; 423:1, s. l112-L116
-
Tidskriftsartikel (refereegranskat)abstract
- We compute the exponential disc scalelength for 686 disc galaxies with spectroscopic redshifts out to redshift 5.8 based on Hubble Space Telescope archival data. We compare the results with our previous measurements based on 30 000 nearby galaxies from the Sloan Digital Sky Survey. Our results confirm the presence of a dominating exponential component in galaxies out to this redshift. At the highest redshifts, the disc scalelength for the brightest galaxies with absolute magnitude between -24 and -22 is up to a factor of 8 smaller compared to that in the local Universe. This observed scalelength decrease is significantly greater than the value predicted by a cosmological picture in which baryonic disc scalelength scales with the virial radius of the dark matter halo.
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| 18. |
- Fathi, Kambiz, et al.
(författare)
-
Evolution of structure in late-type spiral galaxies. I : Ionized gas kinematics in NGC 628
- 2007
-
Ingår i: Astronomy and Astrophysics. ; 466:905
-
Tidskriftsartikel (refereegranskat)abstract
- Aims.We study two dimensional Fabry-Perot interferometric observations of the nearby face-on late-type spiral galaxy, NGC 628, in order to analyse the ionized gas component of the interstellar medium. Covering the galaxy out to a radius larger than 12 kpc, and with a spatial sampling of 1.6'', we aim to investigate the large-scale dynamics as well as feedback from individual H ii regions into their surrounding medium. Methods: The observed Hα emission distribution and kinematics are compared with auxiliary data from molecular and atomic gas observations, which display many similarities. We decompose the observed line-of-sight velocities into rotational and higher-order harmonic components, and study the role of gravitational perturbations along with that of external triggers which can disturb the kinematics and morphology of NGC 628. We calculate radial profiles of the emission-line velocity dispersion which we use to study the role of feedback from individual H ii regions. Results: We verify the presence of an inner rapidly rotating disc-like component in NGC 628, which we interpret as caused by slow secular evolution of the large-scale spiral arms and oval structure. In combination with auxiliary data, we find indication for that gas is falling in from the outer parts towards the central regions, where a nuclear ring has formed at the location of the inner Lindblad resonance radius of an an m=2 perturbation. Complementary continuum subtracted narrow band images in Hα have been used to identify 376 H ii regions with calibrated luminosities. The mean velocity dispersion for the ionized gas (even when excluding pixels belonging to H ii regions) is almost constant out to 12 kpc, although it varies from 14 to 20 km s-1, with a steady decline in the outer parts. Conclusions: We have found kinematic signatures of radial motions caused by an m=2 perturbation. Such a perturbation may well be responsible for the inflow of material forming the nuclear ring and the inner rapidly rotating disc-like structure. The latter, in turn, could help build a pseudo-bulge in NGC 628. The current paper demonstrates a number of tools that we have developed for building a solid frame work for studying the evolution of structure in spiral galaxies using two dimensional kinematic observations.
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| 19. |
- Fathi, Kambiz, et al.
(författare)
-
Fabry-Perot Interferometry and Spiral Galaxy Dynamics
- 2008
-
Ingår i: Pathways Through an Eclectic Universe. - 9781583816509 ; , s. 182-
-
Konferensbidrag (populärvet., debatt m.m.)abstract
- We present two-dimensional Fabry-Perot observations of the emission-line distribution and kinematics in nearby spiral galaxies. We have developed and demonstrated the utility of a number of analysis tools which have general applicability, but which we have, so far, applied to only one galaxy (M74, Fathi et al. 2007). In this galaxy, we have found kinematic signatures of radial motions caused by an m=2 perturbation. Such a perturbation may well be responsible for the inflow of material forming the nuclear ring and the inner rapidly rotating disk-like structure. The latter, in turn, could help build a pseudo-bulge. In the second paper in this series, we will apply the kinematic analysis tools to a sample of nine late-type spiral galaxies observed with the FaNTOmM Fabry-Perot spectrometer at the Canada-France-Hawaii Telescope.
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| 20. |
- Fathi, Kambiz, et al.
(författare)
-
LOCAL INSTABILITY SIGNATURES IN ALMA OBSERVATIONS OF DENSE GAS IN NGC 7469
- 2015
-
Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213 .- 1538-4357 .- 0004-637X. ; 806:2
-
Tidskriftsartikel (refereegranskat)abstract
- We present an unprecedented measurement of the disk stability and local instability scales in the luminous infrared Seyfert 1 host, NGC 7469, based on ALMA observations of dense gas tracers and with a synthesized beam of 165 x 132 pc. While we confirm that non-circular motions are not significant in redistributing the dense interstellar gas in this galaxy, we find compelling evidence that the dense gas is a suitable tracer for studying the origin of its intensely high-mass star-forming ringlike structure. Our derived disk stability parameter Q accounts for a thick disk structure, and its value falls below unity at the radii in which intense star formation is found. Furthermore, we derive the characteristic instability scale lambda(c) and find a striking agreement between our measured scale of similar to 180 pc and the typical sizes of individual complexes of young and massive star clusters seen in high-resolution images.
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| 21. |
- Fathi, Kambiz, et al.
(författare)
-
Pattern Speeds of Bars and Spiral Arms from Hα Velocity Fields
- 2009
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 704, s. 1657-1675
-
Tidskriftsartikel (refereegranskat)abstract
- We have applied the Tremaine-Weinberg method to 10 late-type barred spiral galaxies using data cubes, in Hα emission, from the FaNTOmM and GHAFAS Fabry-Perot spectrometers. We have combined the derived bar (and/or spiral) pattern speeds with angular frequency plots to measure the corotation radii for the bars in these galaxies. We base our results on a combination of this method with a morphological analysis designed to estimate the corotation radius to bar-length ratio using two independent techniques on archival near-infrared images, and although we are aware of the limitation of the application of the Tremaine-Weinberg method using Hα observations, we find consistently excellent agreement between bar and spiral arm parameters derived using different methods. In general, the corotation radius, measured using the Tremaine-Weinberg method, is closely related to the bar length, measured independently from photometry and consistent with previous studies. Our corotation/bar-length ratios and pattern speed values are in good agreement with general results from numerical simulations of bars. In systems with identified secondary bars, we measure higher Hα velocity dispersion in the circumnuclear regions, whereas in all the other galaxies, we detect flat velocity dispersion profiles. In the galaxies where the bar is almost purely stellar, Hα measurements are missing, and the Tremaine-Weinberg method yields the pattern speeds of the spiral arms. The excellent agreement between the Tremaine-Weinberg method results and the morphological analysis and bar parameters in numerical simulations suggests that although the Hα emitting gas does not obey the continuity equation, it can be used to derive the bar pattern speed. In addition, we have analyzed the Hα velocity dispersion maps to investigate signatures of secular evolution of the bars in these galaxies. The increased central velocity dispersion in the galaxies with secondary bars suggests that the formation of inner bars or disks may be a necessary step in the formation of bulges in late-type spiral galaxies.
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| 22. |
- Fathi, Kambiz, et al.
(författare)
-
Quantifying Resonant Structure in NGC 6946 from Two-dimensional Kinematics
- 2007
-
Ingår i: Astrophysical Journal Letters. ; 667:137
-
Tidskriftsartikel (refereegranskat)abstract
- We study the two-dimensional kinematics of the Hα-emitting gas in the nearby barred Scd galaxy NGC 6946, in order to determine the pattern speed of the primary m=2 perturbation mode. The pattern speed is a crucial parameter for constraining the internal dynamics, estimating the impact velocities of the gravitational perturbation at the resonance radii, and setting up an evolutionary scenario for NGC 6946. Our data allow us to derive the best-fitting kinematic position angle and the geometry of the underlying gaseous disk, which we use to derive the pattern speed using the Tremaine-Weinberg method. We find a main pattern speed ΩPp=22+4-1 km s-1 kpc-1, but our data clearly reveal the presence of an additional pattern speed ΩSp=47+3-2 km s-1 kpc-1 in a zone within 1.25 kpc of the nucleus. Using the epicyclic approximation, we deduce the location of the resonance radii and confirm that inside the outer inner Lindblad resonance radius of the main oval, a primary bar has formed rotating at more than twice the outer pattern speed. We further confirm that a nuclear bar has formed inside the inner Lindblad resonance radius of the primary bar, coinciding with the inner inner Lindblad resonance radius of the large-scale m=2 mode oval.
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| 23. |
- Fathi, Kambiz
(författare)
-
REVISITING THE SCALE LENGTH-mu(0) PLANE AND THE FREEMAN LAW IN THE LOCAL UNIVERSE
- 2010
-
Ingår i: Astrophysical Journal letters. - 2041-8205. ; 722:1, s. L120-L125
-
Tidskriftsartikel (refereegranskat)abstract
- We have used Virtual Observatory technology to analyze the disk scale length r(d) and central surface brightness mu(0) for a sample of 29,955 bright disk galaxies from the Sloan Digital Sky Survey. We use the results in the r band and revisit the relation between these parameters and the galaxy morphology, and find the average value = 20.2 +/- 0.7 mag arcsec(-2). We confirm that late-type spirals populate the lower left corner of the r(d)-mu(0) plane and that the early and intermediate spirals are mixed in this diagram, with disky ellipticals at the top left corner. We further investigate the Freeman Law and confirm that it indeed defines an upper limit for mu(0) in bright disk galaxies with r(mag) < 17.0, and that disks in late-type spirals ( T >= 6) have fainter central surface brightness. Our results are based on a volume-corrected sample of galaxies in the local universe (z < 0.3) that is two orders of magnitudes larger than any sample previously studied and deliver statistically significant implications that provide a comprehensive test bed for future theoretical studies and numerical simulations of galaxy formation and evolution.
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| 24. |
- Fathi, Kambiz, et al.
(författare)
-
Scale Length of Disk Galaxies
- 2009
-
Konferensbidrag (populärvet., debatt m.m.)abstract
- As a part of a Euro-VO research initiative, we have undertaken a programme aimed at studying the scale length of 54909 Sa-Sd spiral galaxies from the SDSS DR6 catalogue. We have retrieved u, g, r, i, z-band images for all galaxies in order to derive the light profiles. We also calculate asymmetry parameters to select non-disturbed disks for which we will derive exponential disk scale lengths. As images in different bands probe different optical depths and stellar populations, it is likely that a derived scale length value should depend on waveband, and our goal is to use the scale length variations with band pass, inclination, galaxy type, redshift, and surface brightness, in order to better understand the nature of spiral galaxies.
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| 25. |
- Fathi, Kambiz, et al.
(författare)
-
Scalelength of disc galaxies
- 2010
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 406:3, s. 1595-1608
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Tidskriftsartikel (refereegranskat)abstract
- We have derived disc scalelengths for 30 374 non-interacting disc galaxies in all five Sloan Digital Sky Survey (SDSS) bands. Virtual Observatory methods and tools were used to define, retrieve and analyse the images for this unprecedentedly large sample classified as disc/spiral galaxies in the LEDA catalogue. Cross-correlation of the SDSS sample with the LEDA catalogue allowed us to investigate the variation of the scalelengths for different types of disc/spiral galaxies. We further investigate asymmetry, concentration and central velocity dispersion as indicators of morphological type, and are able to assess how the scalelength varies with respect to galaxy type. We note, however, that the concentration and asymmetry parameters have to be used with caution when investigating type dependence of structural parameters in galaxies. Here, we present the scalelength derivation method and numerous tests that we have carried out to investigate the reliability of our results. The average r-band disc scalelength is 3.79 kpc, with an rms dispersion of 2.05 kpc, and this is a typical value irrespective of passband and galaxy morphology, concentration and asymmetry. The derived scalelengths presented here are representative for a typical galaxy mass of 1010.8 +/- 0.54 M-circle dot, and the rms dispersion is larger for more massive galaxies. Separating the derived scalelengths for different galaxy masses, the r-band scalelength is 1.52 +/- 0.65 kpc for galaxies with total stellar mass 109-1010 M-circle dot and 5.73 +/- 1.94 kpc for galaxies with total stellar mass between 1011 and 1012 M-circle dot. Distributions and typical trends of scalelengths have also been derived in all the other SDSS bands with linear relations that indicate the relation that connect scalelengths in one passband to another. Such transformations could be used to test the results of forthcoming cosmological simulations of galaxy formation and evolution of the Hubble sequence.
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