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1

Face on Barred and Ringed Spiral Galaxy NGC 3351  

NASA Technical Reports Server (NTRS)

Ultraviolet image (left) and visual image (right) of the face on barred and ringed spiral galaxy NGC 3351 (M95). The morphological appearance of a galaxy can change dramatically between visual and ultraviolet wavelengths. In the case of M95, the nucleus and bar dominate the visual image. In the ultraviolet, the bar is not even visible and the ring and spiral arms dominate.

2005-01-01

2

The Remarkable Central Structure of the Barred Galaxy NGC 1415  

E-print Network

A remarkable structure is observed in the innermost regions of the barred galaxy NGC 1415 : a small stellar bar, bright circumnuclear ionized gas seen in Halpha, two bright ionized gas sources, seen in Halpha, just beyond the ends of the small bar and a boxy distribution of optical continuum. We have developed a mass distribution model consisting in disk, a bulge, and a bar to approximate t he observed central morphology and its surface brightness. In order to reproduce the observed optical brightness distribution a two-component bar was used, with one component to model the elongated isophotes of the bar and the second component to model the boxy-shaped isophotes. We interpret the circumnuclear ionized gas as forming a circumnuclear ring and the two bright sources as a nuclear and/or circumnuclear outflow slightly out of the plane of the disk.

J. A. Garcia-Barreto; E. Moreno

1999-09-23

3

The Mass Inflow Rate in the Barred Galaxy NGC 1530  

E-print Network

Mass inflow in barred galaxies has been invoked to account for a wide variety of phenomena, but until now direct evidence for inflow has been lacking. We present Fabry-Perot H-alpha observations of the barred spiral galaxy NGC 1530 from which we determine velocities of the ionized gas for the entire region swept by the bar. We compare the velocity field to models of gas flow in barred spirals and show that it is well reproduced by ideal gas hydrodynamic models. Inspection of the models and observations reveals that gas entering the bar dust lanes streams directly down the dust lanes toward the 2 kpc radius nuclear ring. The models predict that approximately 20% of the gas flowing down the dust lane enters the nuclear ring; the remaining gas sprays around the ring to the other bar dust lane. The fraction of the gas entering the ring is relatively insensitive to the shape or size of the bar. Our observations of the velocity field and dust optical depth yield a mass inflow rate into the nuclear ring of 1 solar mass per year.

Michael W. Regan; Stuart N. Vogel; Peter J. Teuben

1997-04-01

4

Hydrodynamical Simulations of the Barred Spiral Galaxy NGC 6782  

E-print Network

NGC 6782 is an early-type barred spiral galaxy exhibiting a rich and complex morphology with multiple ring patterns. To provide a physical understanding of its structure and kinematical properties, two-dimensional hydrodynamical simulations have been carried out. Numerical calculations reveal that the striking features in NGC 6782 can be reproduced provided that the gas flow is governed by the gravitational potential associated with a slowly rotating strong bar. In particular, the response of the gaseous disk to the bar potential leads to the excitation of spiral density waves at the inner Lindblad resonance giving rise to the appearance of a nearly circular nuclear ring with a pair of dust lanes. For a sufficiently strong bar potential, the inner 4:1 spiral density waves are also excited. The interaction of the higher harmonic waves with the waves excited at the inner Lindblad resonance and confined by the outer Lindblad resonance results in the observed diamond-shaped (or pointy oval) inner ring structure. The overall gas morphology and kinematical features are both well reproduced by the model provided that the pattern speed of the bar is $\\sim 25$ km s$^{-1}$ kpc$^{-1}$.

Lien-Hsuan Lin; Chi Yuan; R. Buta

2008-05-23

5

HYDRODYNAMICAL SIMULATIONS OF THE BARRED SPIRAL GALAXY NGC 1097  

SciTech Connect

NGC 1097 is a nearby barred spiral galaxy believed to be interacting with the elliptical galaxy NGC 1097A located to its northwest. It hosts a Seyfert 1 nucleus surrounded by a circumnuclear starburst ring. Two straight dust lanes connected to the ring extend almost continuously out to the bar. The other ends of the dust lanes attach to two main spiral arms. To provide a physical understanding of its structural and kinematical properties, two-dimensional hydrodynamical simulations have been carried out. Numerical calculations reveal that many features of the gas morphology and kinematics can be reproduced provided that the gas flow is governed by a gravitational potential associated with a slowly rotating strong bar. By including the self-gravity of the gas disk in our calculation, we have found the starburst ring to be gravitationally unstable, which is consistent with the observation in Hsieh et al. Our simulations show that the gas inflow rate is 0.17 M{sub Sun} yr{sup -1} into the region within the starburst ring even after its formation, leading to the coexistence of both a nuclear ring and a circumnuclear disk.

Lin, Lien-Hsuan; Wang, Hsiang-Hsu; Hsieh, Pei-Ying; Taam, Ronald E. [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan (China); Yang, Chao-Chin [Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, Box 43, Lund SE-221 00 (Sweden); Yen, David C. C. [Department of Mathematics, Fu Jen Catholic University, Taipei 24205, Taiwan (China)

2013-07-01

6

Hydrodynamical simulations of the barred spiral galaxy NGC 1097  

NASA Astrophysics Data System (ADS)

NGC 1097 is a nearby barred spiral galaxy believed to be interacting with the elliptical galaxy NGC 1097A located to its northwest. It hosts a Seyfert 1 nucleus surrounded by a circumnuclear starburst ring. Two straight dust lanes connected to the ring extend almost continuously out to the bar. The other ends of the dust lanes attach to two main spiral arms. To provide a physical understanding of its structural and kinematical properties, two-dimensional hydrodynamical simulations have been carried out. Numerical calculations reveal that many features of the gas morphology and kinematics can be reproduced provided that the gas flow is governed by a gravitational potential associated with a slowly rotating strong bar. By including the self-gravity of the gas disk in our calculation, we have found the starburst ring to be gravitationally unstable which is consistent with the observation in Hsieh et al. (2011). Our simulations also show that gas can flow into the region within the starburst ring even after its formation, leading to the coexistence of both a nuclear ring and a circumnuclear disk.

Lin, Lien-Hsuan; Wang, Hsiang-Hsu; Hsieh, Pei-Ying; Taam, Ronald E.; Yang, Chao-Chin; Yen, David C. C.

2015-03-01

7

Multiband Images of the Barred Galaxy NGC 1097  

NASA Astrophysics Data System (ADS)

We present B, V, R, J, H, and K broadband images of the barred galaxy NGC 1097. The optical and infrared colors maps trace the location of the major dust features. The dust lanes are relatively free of star formation and have low opacity. The depth of the dust lanes decreases as a function of wavelength so that they are deepest at B and shallower at H and K where they are difficult to detect. We find that the dust lane on the Northwest side of the galaxy has colors consistent with those of a dust screen with opacity derived from the galactic extinction law. Thus, it must be located on the near side of the galaxy. The colors in the dust lane on the Southeast side of the galaxy, on the other hand, suggest that there are stars both in front of and behind the dust, consistent with this dust lane being located on the far side of the galaxy. From the K images, we estimate that the total stellar mass of the star forming spiral ring at a radius of - 1 kpc from the nucleus is of the same order as the molecular gas mass in the ring. The infrared images show a short bar inside the inner spiral ring. In the principal plane of the galaxy, the short bar is not perpendicular to the prominent outer bar. This suggests that there are torques between the inner bar and the spiral ring and that this inner bar may have a pattern speed different from the outer bar. Near the inner spiral ring (at ~17" = 1.4 kpc from the nucleus), the dust lane becomes double peaked with a peak to valley extinction ratio similar to that observed in radio continuum by Ondrechen & van der Hulst (1983). This suggests that if the cold diffuse component of the interstellar medium (traced by the dust) moves with the cosmic ray electron component then the magnetic field pressure is not a significant force in the shocks. Alternatively if the two phases do not move together a more detailed comparison may show differences in the shock shapes.

Quillen, A. C.; Frogel, Jay A.; Kuchinski, L. E.; Terndrup, D. M.

1995-07-01

8

The Abundance Gradient of NGC 1365: Evidence for a Recently Formed Bar in an Archetype Barred Spiral Galaxy?  

E-print Network

Emission-line optical spectrophotometry for 55 H II regions in the prominent southern barred spiral galaxy NGC 1365 is presented. Nebular diagnostic diagrams such as [N II]/[O II] and [S II]/[O II] versus [O II]/{O III] show that the H II regions of the barred galaxy have the same range of physical conditions as found in non-barred late-type galaxies. Extinction is moderately high across the disc and there is evidence for a slight trend of extinction with galactocentric distance; the logarithmic extinction at H-beta falls from about c = 1.2 in the centre to 0.6 -- 0.8 in the outer regions. The global O/H distribution has a moderate gradient of about -0.5 dex/rho0 (about -0.02 dex/kpc) consistent with the known trend between the slope of the abundance gradient and the strength of the bar. A break is seen in the O/H gradient just beyond the -4/1 resonance, the gradient being moderately steep at about -0.8 dex/rho0 (-0.05 dex/kpc) inside this resonance, and flat beyond rho/rho0 > 0.55. The abundance distribution is compared with another barred spiral galaxy, NGC 3359, and with that of two well-sampled normal spiral galaxies, NGC 2997 and M 101. The possibility that the bar formed recently in NGC 1365 is considered. The difficulties encountered in doing spectrophotometry with fibre optics are discussed and shown not to be insurmountable.

J. -R. Roy; J. R. Walsh

1997-05-06

9

Gas Dynamics in the Barred Seyfert Galaxy NGC4151 - II. High Resolution HI Study  

E-print Network

We present sensitive, high angular resolution (6" x 5") 21-cm observations of the neutral hydrogen in the nearby barred Seyfert galaxy, NGC4151. These HI observations, obtained using the VLA in B-configuration, are the highest resolution to date of this galaxy, and reveal hitherto unprecedented detail in the distribution and kinematics of the HI on sub-kiloparsec scales. A complete analysis and discussion of the HI data are presented and the global properties of the galaxy are related to the bar dynamics presented in Paper I.

C. G. Mundell; A. Pedlar; D. L. Shone; A. Robinson

1998-12-09

10

Investigating the Nuclear Activity of Barred Spiral Galaxies: The Case of NGC 1672  

NASA Technical Reports Server (NTRS)

We have performed an X-ray study of the nearby barred spiral galaxy NGC 1672, primarily to ascertain the effect of the bar on its nuclear activity. We use both Chandra and XMM-Newton observations to investigate its X-ray properties, together with supporting high-resolution optical imaging data from the Hubble Space Telescope (HST) infrared imaging from the Spitzer Space Telescope, and Australia Telescope Compact Array ground-based radio data. We detect 28 X-ray sources within the D25 area of the galaxy; many are spatially correlated with star formation in the bar and spiral arms, and two are identified as background galaxies in the HST images. Nine of the X-ray sources are ultraluminous X-ray sources, with the three brightest (LX 5 * 10(exp 39) erg s(exp -1)) located at the ends of the bar. With the spatial resolution of Chandra, we are able to show for the first time that NGC 1672 possesses a hard (1.5) nuclear X-ray source with a 2-10 keV luminosity of 4 * 10(exp 38) erg s(exp -1). This is surrounded by an X-ray-bright circumnuclear star-forming ring, comprised of point sources and hot gas, which dominates the 2-10 keV emission in the central region of the galaxy. The spatially resolved multiwavelength photometry indicates that the nuclear source is a low-luminosity active galactic nucleus (LLAGN), but with star formation activity close to the central black hole. A high-resolution multiwavelength survey is required to fully assess the impact of both large-scale bars and smaller-scale phenomena such as nuclear bars, rings, and nuclear spirals on the fueling of LLAGN.

Jenkins, L. P.; Brandt, W. N.; Colbert, E. J.; Koribalski, B.; Kuntz, K. D.; Levan, A. J.; Ojha, R.; Roberts, T. P.; Ward, M. J.; Zezas, A.

2011-01-01

11

INVESTIGATING THE NUCLEAR ACTIVITY OF BARRED SPIRAL GALAXIES: THE CASE OF NGC 1672  

SciTech Connect

We have performed an X-ray study of the nearby barred spiral galaxy NGC 1672, primarily to ascertain the effect of the bar on its nuclear activity. We use both Chandra and XMM-Newton observations to investigate its X-ray properties, together with supporting high-resolution optical imaging data from the Hubble Space Telescope (HST), infrared imaging from the Spitzer Space Telescope, and Australia Telescope Compact Array ground-based radio data. We detect 28 X-ray sources within the D{sub 25} area of the galaxy; many are spatially correlated with star formation in the bar and spiral arms, and two are identified as background galaxies in the HST images. Nine of the X-ray sources are ultraluminous X-ray sources, with the three brightest (L{sub X} > 5 x 10{sup 39} erg s{sup -1}) located at the ends of the bar. With the spatial resolution of Chandra, we are able to show for the first time that NGC 1672 possesses a hard ({Gamma} {approx} 1.5) nuclear X-ray source with a 2-10 keV luminosity of 4 x 10{sup 38} erg s{sup -1}. This is surrounded by an X-ray-bright circumnuclear star-forming ring, comprised of point sources and hot gas, which dominates the 2-10 keV emission in the central region of the galaxy. The spatially resolved multiwavelength photometry indicates that the nuclear source is a low-luminosity active galactic nucleus (LLAGN), but with star formation activity close to the central black hole. A high-resolution multiwavelength survey is required to fully assess the impact of both large-scale bars and smaller-scale phenomena such as nuclear bars, rings, and nuclear spirals on the fueling of LLAGN.

Jenkins, L. P. [Laboratory for X-ray Astrophysics, NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771 (United States); Brandt, W. N. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Colbert, E. J. M.; Kuntz, K. D. [Johns Hopkins University, Baltimore, MD 21218 (United States); Koribalski, B. [CSIRO, Australia Telescope National Facility (ATNF), Epping, NSW 1710 (Australia); Levan, A. J. [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Ojha, R. [NVI/United States Naval Observatory, Washington, DC 20392 (United States); Roberts, T. P.; Ward, M. J. [Department of Physics, Durham University, Durham DH1 3LE (United Kingdom); Zezas, A. [Department of Physics, University of Crete, GR-71003 Heraklion (Greece)

2011-06-10

12

Kinematics of Ionised Gas in the Barred Seyfert Galaxy NGC 4151  

E-print Network

We have determined the structure and kinematics of ionised gas in the weak oval bar of the archetypal Seyfert 1 galaxy, NGC 4151, using the TAURUS Fabry-Perot interferometer to simultaneously map the distribution and kinematics of Hbeta emission. We also present broad-band ultraviolet imaging of the host galaxy, obtained with XMM-Newton, that shows the detailed distribution of star formation in the bar and in the optically-faint outer spiral arms. We compare the distribution and kinematics of ionised gas with that previously determined in neutral hydrogen by Mundell & Shone; we suggest that the distribution of bright, patchy UV emission close to the HI shocks is consistent with ionisation by star clusters that have formed in compressed pre-shock gas. These clusters then travel ballistically through the gaseous shock to ionise gas downstream along the leading edge of the bar. In addition, we detect, for the first time, ionised gas within the shock itself which is streaming to smaller radii in the same manner as the neutral gas.

M. W. Asif; C. G. Mundell; A. Pedlar

2005-02-14

13

New Xray Constraints on Starburst and Seyfert Activity in the Barred Spiral Galaxy NGC 1672  

E-print Network

\\Gamma2 . Subject headings: galaxies: individual: NGC 1672 -- X­rays: galaxies -- galaxies: starburst in its direction is NH = (2 \\Sigma 1) \\Theta 10 20 cm \\Gamma2 (Heiles & Cleary 1979). X­ray emission a hard X­ray detection of a L 2\\Gamma10 keV ? 10 41 erg s \\Gamma1 Seyfert nucleus with the Ginga Large

Brandt, William Nielsen

14

U B V R I Photometry of Stellar Structures throughout the Disk of the Barred Galaxy NGC 3367  

E-print Network

We report new detailed surface U, B, V, R, and I photometry of 81 stellar structures in the disk of the barred galaxy NGC 3367. The images show many different structures indicating that star formation is going on in the most part of the disk. NGC 3367 is known to have a very high concentration of molecular gas distribution in the central regions of the galaxy and bipolar synchrotron emission from the nucleus with two lobes (at 6 kpc) forming a triple structure similar to a radio galaxy. We have determined the U, B, V, R, and I magnitudes and U - B, B - V, U - V, and V - I colors for the central region (nucleus), a region which includes supernovae 2003 AA, and 79 star associations throughout NGC 3367. Estimation of ages of star associations is very difficult due to several factors, among them: filling factor, metallicity, spatial distribution of each structure and the fact that we estimated the magnitudes with a circular aperture of 16 pixels in diameter, equivalent to $6''.8\\sim1.4$ kpc. However, if the colors derived for NGC 3367 were similar to the colors expected of star clusters with theoretical evolutionary star tracks developed for the LMC and had a similar metallicity, NGC 3367 show 51 percent of the observed structures with age type SWB I (few tens of Myrs), with seven sources outside the bright surface brightness visible disk of NGC 3367.

J. A. Garcia-Barreto; H. Hernandez-Toledo; E. Moreno-Diaz; T. Bernal-Marin; A. L. Villarreal-Castillo

2007-04-11

15

FORMATION OF DENSE MOLECULAR GAS AND STARS AT THE CIRCUMNUCLEAR STARBURST RING IN THE BARRED GALAXY NGC 7552  

SciTech Connect

We present millimeter molecular line complemented by optical observations, along with a reanalysis of archival centimeter H I and continuum data, to infer the global dynamics and determine where dense molecular gas and massive stars preferentially form in the circumnuclear starburst ring of the barred-spiral galaxy NGC 7552. We find diffuse molecular gas in a pair of dust lanes each running along the large-scale galactic bar, as well as in the circumnuclear starburst ring. We do not detect dense molecular gas in the dust lanes, but find such gas concentrated in two knots where the dust lanes make contact with the circumnuclear starburst ring. When convolved to the same angular resolution as the images in dense gas, the radio continuum emission of the circumnuclear starburst ring also exhibits two knots, each lying downstream of an adjacent knot in dense gas. The results agree qualitatively with the idea that massive stars form from dense gas at the contact points, where diffuse gas is channeled into the ring along the dust lanes, and later explode as supernovae downstream of the contact points. Based on the inferred rotation curve, however, the propagation time between the respective pairs of dense gas and centimeter continuum knots is about an order of magnitude shorter than the lifetimes of OB stars. We discuss possible reasons for this discrepancy, and conclude that either the initial mass function is top-heavy or massive stars in the ring do not form exclusively at the contact points where dense molecular gas is concentrated.

Pan, Hsi-An [Department of Astronomical Science, Graduate University for Advanced Studies, Shonan Village, Hayama, Kanagawa 240-0193 (Japan); Lim, Jeremy [Department of Physics, University of Hong Kong, Pokfulam (Hong Kong); Matsushita, Satoki [Academia Sinica, Institute of Astronomy and Astrophysics (ASIAA), P.O. Box 23-141, Taipei 10617, Taiwan (China); Wong, Tony [Department of Astronomy, University of Illinois, 1002 W. Green Street, Urbana, IL 61801 (United States); Ryder, Stuart, E-mail: pan.h.a@nao.ac.jp [Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW 1670 (Australia)

2013-05-01

16

Galaxy NGC 1512  

NASA Technical Reports Server (NTRS)

A rainbow of colors is captured in the center of a magnificent barred spiral galaxy, as witnessed by the three cameras of NASA's Hubble Space Telescope.

The color-composite image of the galaxy NGC 1512 was created from seven images taken with the JPL-designed and built Wide Field and Planetary Camera 2 (WFPC-2), along with the Faint Object Camera and the Near Infrared Camera and Multi-Object Spectrometer. Hubble's unique vantage point high above the atmosphere allows astronomers to see objects over a broad range of wavelengths from the ultraviolet to the infrared and to detect differences in the regions around newly born stars.

The new image is online at http://oposite.stsci.edu/pubinfo/pr/2001/16 and http://www.jpl.nasa.gov/images/wfpc .

The image reveals a stunning 2,400 light-year-wide circle of infant star clusters in the center of NGC 1512. Located 30 million light-years away in the southern constellation of Horologium, NGC 1512 is a neighbor of our Milky Way galaxy.

With the Hubble data, a team of Israeli and American astronomers performed one of the broadest, most detailed studies ever of such star-forming regions. Results will appear in the June issue of the Astronomical Journal. The team includes Dr. Dan Maoz, Tel-Aviv University, Israel and Columbia University, New York, N.Y.; Dr. Aaron J. Barth, Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.; Dr. Luis C. Ho, The Observatories of the Carnegie Institution of Washington; Dr. Amiel Sternberg, Tel-Aviv University, Israel; and Dr. Alexei V. Filippenko, University of California, Berkeley.

The Space Telescope Science Institute, Baltimore, Md., manages space operations for the Hubble Space Telescope for NASA's Office of Space Science, Washington, D.C. The Institute is operated by the Association of Universities for Research in Astronomy Inc., for NASA under contract with NASA's Goddard Space Flight Center, Greenbelt, Md. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. JPL is a division of the California Institute of Technology in Pasadena.

Additional information about the Hubble Space Telescope is online at http://www.stsci.edu . More information about the Wide Field and Planetary Camera 2 is at http://wfpc2.jpl.nasa.gov.

1999-01-01

17

Kinematic and Photometric Evidence for a Bar in NGC 2683  

E-print Network

We present optical long-slit and SparsePak Integral Field Unit emission line spectroscopy along with optical broadband and near IR images of the edge-on spiral galaxy NGC 2683. We find a multi-valued, figure-of-eight velocity structure in the inner 45 arcsec of the long-slit spectrum and twisted isovelocity contours in the velocity field. We also find, regardless of wavelength, that the galaxy isophotes are boxy. We argue that taken together, these kinematic and photometric features are evidence for the presence of a bar in NGC 2683. We use our data to constrain the orientation and strength of the bar.

de Naray, Rachel Kuzio; McGaugh, Stacy S

2009-01-01

18

Starburst Galaxy NGC 3310  

NASA Technical Reports Server (NTRS)

Scientists using NASA's Hubble Space Telescope are studying the colors of star clusters to determine the age and history of starburst galaxies, a technique somewhat similar to the process of learning the age of a tree by counting its rings.

This month's Hubble Heritage image showcases the galaxy NGC 3310. It is one of several starburst galaxies, which are hotbeds of star formation, being studied by Dr. Gerhardt Meurer and a team of scientists at Johns Hopkins University, Laurel, Md.

The picture, taken by Hubble's Wide Field and Planetary Camera 2, is online at http://heritage.stsci.edu and http://oposite.stsci.edu/pubinfo/pr/2001/26 and http://www.jpl.nasa.gov/images/wfpc . The camera was designed and built by NASA's Jet Propulsion Laboratory, Pasadena, Calif.

Most galaxies form new stars at a fairly slow rate, but starburst galaxies blaze with extremely active star formation. Measuring the clusters' colors yields information about stellar temperatures. Since young stars are blue and older stars redder, the colors relate to their ages.

NGC 3310 is forming clusters of new stars at a prodigious rate. The new image shows several hundred star clusters, visible as the bright blue, diffuse objects that trace the galaxy's spiral arms. Each of these star clusters represents the formation of up to about a million stars, a process that takes less than 100,000 years. In addition, hundreds of individual young, luminous stars can be seen throughout the galaxy.

The star clusters become redder with age as the most massive and bluest stars exhaust their fuel and burn out. Measurements in this image of the wide range of cluster colors show their ages range between about one million and more than one hundred million years. This suggests that the starburst 'turned on' more than 100 million years ago. It may have been triggered when NGC 3310 collided with a companion galaxy.

These observations may change astronomers' view of starbursts. Starbursts were once thought to be brief episodes, resulting from catastrophic events like a galactic collision. However, the wide range of cluster ages in NGC 3310 suggests that, once triggered, the starbursting can continue for a long time.

Located in the direction of the constellation Ursa Major, NGC 3310 is about 59 million light years from Earth. The image is based on observations made by the Wide Field and Planetary Camera 2 in March 1997 and September 2000. The Hubble Heritage Team created the color rendition of the combined images.

The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract with the Goddard Space Flight Center, Greenbelt, Md. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. JPL is a division of the California Institute of Technology in Pasadena.

Additional information about the Hubble Space Telescope is available at http://hubble.stsci.edu. More information about the Wide Field and Planetary Camera 2 is available at http://wfpc2.jpl.nasa.gov

1999-01-01

19

Galaxy NGC 1850  

NASA Technical Reports Server (NTRS)

By spying on a neighboring galaxy, NASA's Hubble Space Telescope has captured an image of a young, globular-like star cluster -- a type of object unknown in our Milky Way Galaxy.

The image, taken by Hubble's Wide Field and Planetary Camera 2, is online at http://oposite.stsci.edu/pubinfo/pr/2001/25 and http://www.jpl.nasa.gov/images/wfpc. The camera was designed and built by NASA's Jet Propulsion Laboratory, Pasadena, Calif.

The double cluster NGC 1850 lies in a neighboring satellite galaxy, the Large Magellanic Cloud. It has two relatively young components. The main, globular-like cluster is in the center. A smaller cluster is seen below and to the right, composed of extremely hot, blue stars and fainter red T-Tauri stars. The main cluster is about 50 million years old; the smaller one is 4 million years old.

A filigree pattern of diffuse gas surrounds NGC 1850. Scientists believe the pattern formed millions of years ago when massive stars in the main cluster exploded as supernovas.

Hubble can observe a range of star types in NGC 1850, including the faint, low-mass T-Tauri stars, which are difficult to distinguish with ground-based telescopes. Hubble's fine angular resolution can pick out these stars, even in other galaxies. Massive stars of the OB type emit large amounts of energetic ultraviolet radiation, which is absorbed by the Earth's atmosphere. From Hubble's position above the atmosphere, it can detect this ultraviolet light.

NGC 1850, the brightest star cluster in the Large Magellanic Cloud, is in the southern constellation of Dorado, called the Goldfish or the Swordfish. This image was created from five archival exposures taken by the Wide Field Planetary Camera 2 between April 3, 1994 and February 6, 1996. More information about the Hubble Space Telescope is online at http://www.stsci.edu. More information about the Wide Field and Planetary Camera 2 is at http://wfpc2.jpl.nasa.gov.

The Space Telescope Science Institute, Baltimore, Md., manages space operations for Hubble for NASA's Office of Space Science, Washington, D.C. The Institute is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract with the Goddard Space Flight Center, Greenbelt, Md. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. JPL is a division of the California Institute of Technology in Pasadena.

1999-01-01

20

Structure and kinematics of candidatedouble-barred galaxies  

NASA Astrophysics Data System (ADS)

Results of optical and NIR spectral and photometric observations of a sample of candidate double-barred galaxies are presented. Velocity fields and velocity dispersion maps of stars and ionized gas, continuum and emission-line images were constructed from integral-field spectroscopy observations carried out at the 6 m telescope (BTA) of SAO RAS, with the MPFS spectrograph and the scanning Fabry-Perot Interferometer. NGC 2681 was also observed with the long-slit spectrograph of the BTA. Optical and NIR images were obtained at the BTA and at the 2.1 m telescope (OAN, Mxico). High-resolution images were retrieved from the HST data archive. Morphological and kinematic features of all 13 sample objects are described in detail. Attention is focused on the interpretation of observed non-circular motions of gas and stars in circumnuclear (one kiloparsec-scale) regions. We have shown first of all that these motions are caused by the gravitational potential of a large-scale bar. NGC 3368 and NGC 3786 have nuclear bars only, their isophotal twist at larger radii being connected with the bright spiral arms. Three cases of inner polar disks in our sample (NGC 2681, NGC 3368 and NGC 5850) are considered. We found ionized-gas counter-rotation in the central kiloparsec of the lenticular galaxy NGC 3945. Seven galaxies (NGC 470, NGC 2273, NGC 2681, NGC 3945, NGC 5566, NGC 5905, and NGC 6951) have inner mini-disks nested in large-scale bars. Minispiral structures occur often in these nuclear disks. It is interesting that the majority of the observed, morphological and kinematical, features in the sample galaxies can be explained without the secondary bar hypothesis. Thus we suggest that a dynamically independent secondary bar is a rarer phenomenon than follows from isophotal analysis of the images only. Based on observations carried out at the 6 m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences, operated under the financial support of the Science Department of Russia (registration number 01-43), at the 2.1 m telescope of the Observatorio Astronnico Nacional, San Pedro Martir, Mxico, and from the data archive of the NASA/ESA Hubble Space Telescope at the Space Telescope Science Institute. STScI is operated by the association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. Tables 1 to 6 and Figures 2-13 and 15-18 are only available in electronic form at http://www.edpsciences.org

Moiseev, A. V.; Valds, J. R.; Chavushyan, V. H.

2004-07-01

21

New Portraits of Spiral Galaxies NGC 613, NGC 1792 and NGC 3627  

NASA Astrophysics Data System (ADS)

Not so long ago, the real nature of the "spiral nebulae", spiral-shaped objects observed in the sky through telescopes, was still unknown. This long-standing issue was finally settled in 1924 when the famous American astronomer Edwin Hubble provided conclusive evidence that they are located outside our own galaxy and are in fact "island universes" of their own. Nowadays, we know that the Milky Way is just one of billions of galaxies in the Universe. They come in vastly different shapes - spiral, elliptical, irregular - and many of them are simply beautiful, especially the spiral ones. Astronomers Mark Neeser from the Universitts-Sternwarte Mnchen (Germany) and Peter Barthel from the Kapteyn Institute in Groningen (The Netherlands) were clearly not insensitive to this when they obtained images of three beautiful spiral galaxies with ESO's Very Large Telescope (VLT). They did this in twilight during the early morning when they had to stop their normal observing programme, searching for very distant and faint quasars. The resulting colour images ( ESO PR Photos 33a-c/03 ) were produced by combining several CCD images in three different wavebands from the FORS multi-mode instruments. The three galaxies are known as NGC 613, NGC 1792 and NGC 3627 . They are characterized by strong far-infrared, as well as radio emission, indicative of substantial ongoing star-formation activity. Indeed, these images all display prominent dust as well as features related to young stars, clear signs of intensive star-formation. NGC 613 ESO PR Photo 33a/03 ESO PR Photo 33a/03 [Preview - JPEG: 470 x 400 pix - 25k] [Normal - JPEG: 939 x 800 pix - 416k] [Full Res - JPEG: 2702 x 2301 pix - 3.4M] PR Photo 33a/03 of the barred spiral galaxy NGC 613 was obtained with the FORS1 and FORS2 multi-mode instruments (at VLT MELIPAL and YEPUN, respectively) on December 16-18, 2001. It is a composite of three exposures in different wavebands, cf. the technical note below. The full-resolution version of this photo retains the original pixels. Note the many arms and the pronounced dust bands. North is up and East is left. NGC 613 is a beautiful barred spiral galaxy in the southern constellation Sculptor. This galaxy is inclined by 32 degrees and, contrary to most barred spirals, has many arms that give it a tentacular appearance. Prominent dust lanes are visible along the large-scale bar. Extensive star-formation occurs in this area, at the ends of the bar, and also in the nuclear regions of the galaxy. The gas at the centre, as well as the radio properties are indicative of the presence of a massive black hole in the centre of NGC 613. NGC 1792 ESO PR Photo 33b/03 ESO PR Photo 33b/03 [Preview - JPEG: 473 x 400 pix - 26k] [Normal - JPEG: 946 x 800 pix - 376k] [Full Res - JPEG: 2716 x 2297 pix - 3.2M] PR Photo 33b/03 shows the starburst spiral galaxy NGC 1792 . Note the numerous background galaxies in this sky field. North is up and East is to the left. NGC 1792 is located in the southern constellation Columba (The Dove) - almost on the border with the constellation Caelum (The Graving Tool) - and is a so-called starburst spiral galaxy. Its optical appearance is quite chaotic, due to the patchy distribution of dust throughout the disc of this galaxy. It is very rich in neutral hydrogen gas - fuel for the formation of new stars - and is indeed rapidly forming such stars. The galaxy is characterized by unusually luminous far-infrared radiation; this is due to dust heated by young stars. M 66 (NGC 3627) ESO PR Photo 33c/03 ESO PR Photo 33c/03 [Preview - JPEG: 469 x 400 pix - 24k] [Normal - JPEG: 938 x 800 pix - 383k] [Full Res - JPEG: 2698 x 2300 pix - 3.0M] PR Photo 33c/03 of the spiral galaxy M 66 (or NGC 3627). North towards upper left, West towards upper right. The third galaxy is NGC 3627 , also known as Messier 66, i.e. it is the 66th object in the famous catalogue of nebulae by French astronomer Charles Messier (1730 - 1817). It is located in the constellation Leo (The Lion). NGC 3627 is a beautiful spiral with a well-developed central

2003-12-01

22

A Kinematic Link Between Boxy Bulges, Stellar Bars, and Nuclear Activity in NGC 3079 and NGC 4388  

NASA Technical Reports Server (NTRS)

We present direct kinematic evidence for bar streaming in two active galaxies with boxy stellar bulges. The Hawaii Imaging Fabry-Perot Interferometer was used on the Canada-France-Hawaii 3.6-m telescope and the University of Hawaii 2.2-m telescope to derive the two-dimensional velocity field of the line-emitting gas in the disks of the Sc galaxy NGC 3079 and the Sb galaxy NGC 4388. In contrast to previous work based on long-slit data, the detection of the bar potential from the Fabry-Perot data does not rely on the existence of inner Lindblad resonances or strong bar-induced shocks. Simple kinematic models which approximate the intrinsic gas orbits as nonintersecting, inclined elliptical annuli that conserve angular momentum characterize the observed velocity fields. In NGC 3079, bar streaming motions with moderately eccentric orbits (e = b/a approx. 0.7) aligned along PA = 130 deg. intrinsic to the disk (PA = 97 deg. on the sky) are detected out to R(sub b) = 3.6 kpc. The orbits become increasingly circular beyond that radius (e = 1 at R(sub d) approx. = 6 kpc). The best model for NGC 4388 includes highly eccentric orbits (e approx. 0.3) for R(sub) less than or equal to 1.5 kpc which are aligned along PA = 135 deg. intrinsic to the disk (PA = 100 deg. on the sky). The observed "spiral arms" are produced by having the orbits become increasingly circular from the ends of the bar to the edge of the disk (R(sub d) approx. = 5 kpc), and the intrinsic bar PA shifting from 135 deg. to 90 deg.. Box-shaped bulges in both NGC 3079 and NGC 4388 are confirmed using new near-infrared images to reduce dust obscuration. Morphological analysis of starlight in these galaxies is combined with the gas kinematics derived from the Fabry-Perot spectra to test evolutionary models of stellar bars that involve transitory boxy bulges, and to quantify the importance of such bars in fueling active nuclei. Our data support the evolutionary bar models, but fail to prove convincingly that the stellar bars in NGC 3079 and NGC 4388 directly trigger or sustain the nuclear activity.

Veilleux, S.; Bland-Hawthrorn, J.; Cecil, Gerald

1999-01-01

23

Virgo High-Resolution CO Survey: IV. Spiral-Driven Gas Dynamics in the Non-Barred Seyfert Galaxy NGC 4501  

Microsoft Academic Search

We report on high-resolution interferometer observations of the 12CO(J = 1-0) emission in the central 5kpc region of the Seyfert 2 galaxy NGC 4501. The observations were made using the Nobeyama Millimeter Array during a long-term CO line survey of Virgo spirals. The major features are: (1) a nuclear concentration with a radius of r 5'' (390pc), which is

Sachiko Onodera; Jin Koda; Yoshiaki Sofue; Kotaro Kohno

2004-01-01

24

Photometric Decomposition of Barred Galaxies  

E-print Network

We present a non-parametric method for decomposition of the light of disk galaxies into disk, bulge and bar components. We have developed and tested the method on a sample of 68 disk galaxies for which we have acquired I-band photometry. The separation of disk and bar light relies on the single assumption that the bar is a straight feature with a different ellipticity and position angle from that of the projected disk. We here present the basic method, but recognise that it can be significantly refined. We identify bars in only 47% of the more nearly face-on galaxies in our sample. The fraction of light in the bar has a broad range from 1.3% to 40% of the total galaxy light. If low-luminosity galaxies have more dominant halos, and if halos contribute to bar stability, the luminosity functions of barred and unbarred galaxies should differ markedly; while our sample is small, we find only a slight difference of low significance.

A. S. Reese; T. B. Williams; J. A. Sellwood; Eric I. Barnes; Brian A. Powell

2007-02-27

25

BVRI photometric analysis for the galaxy group NGC 4410  

NASA Astrophysics Data System (ADS)

We present a BVRI CCD (Charge Coupled Device) surface photometry analysis of the galaxy group NGC 4410, which contains four galaxies in interaction. Along with our photometric study, we show residual images (after subtracting isophotal models) and unsharp masked images to uncover any hidden structures in this system of galaxies; we have also performed a two-dimensional bulge-disk decomposition for NGC 4410C and D, and a major axis sector profile for NGC 4410A. We have calculated BVRI surface brightnesses and colors within regions such as galaxy centers, bridges, tails and optical knots in the NGC 4410 system, generating B-V color maps and color profiles. The information obtained was used to discover the predominant stellar populations. The colors of the galaxies imply ages of ~2109 to ~21010 years for models using a range of metallicities. The bluer knots and H II regions have colors implying ages of a minimum of 5108 years, but possibly as high as 3109 years for stellar populations formed in the interaction. These results lead us to conclude that there is a moderate star formation rate and a tranquil evolving state of the system with a long timescale for interaction, much longer than the typical dynamical timescales of 108 years. Although we note that NGC 4410D has a blue nucleus (possible nuclear starburst?), bulge, bar, and short spiral arms, and may be interacting with a H I gas cloud. Some observed structures in NGC 4410A are coincident with previously studied H II regions, a tidal arm and optical/radio knots found in this galaxy. An optical knot E coincident with a radio knot may be an optical synchrotron emission or an H II region. The galaxy NGC 4410B appears to be a boxy giant elliptical with a possible dusty disk embedded (similar to Cen A?) and NGC 4410C is confirmed as a lenticular galaxy.

Prez Grana, J. A.; Kemp, S. N.; Katsiyannis, A. C.; Franco-Balderas, A.; de La Fuente, E.; Meaburn, J.; Khosroshahi, H. G.

2008-07-01

26

Bar Formation from Galaxy Flybys  

NASA Astrophysics Data System (ADS)

Recently, both simulations and observations have revealed that flybysfast, one-time interactions between two galaxy halosare surprisingly common, nearing/comparable to galaxy mergers. Since these are rapid, transient events with the closest approach well outside the galaxy disk, it is unclear if flybys can transform the galaxy in a lasting way. We conduct collisionless N-body simulations of three coplanar flyby interactions between pure-disk galaxies to take a first look at the effects flybys have on disk structure, with particular focus on stellar bar formation. We find that some flybys are capable of inciting a bar with bars forming in both galaxies during our 1:1 interaction and in the secondary during our 10:1 interaction. The bars formed have ellipticities >~ 0.5, sizes on the order of the host disk's scale length, and persist to the end of our simulations, ~5 Gyr after pericenter. The ability of flybys to incite bar formation implies that many processes associated with secular bar evolution may be more closely tied with interactions than previously thought.

Lang, Meagan; Holley-Bockelmann, Kelly; Sinha, Manodeep

2014-08-01

27

The Superwind Galaxy NGC 4666  

NASA Astrophysics Data System (ADS)

The galaxy NGC 4666 takes pride of place at the centre of this new image, made in visible light with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile. NGC 4666 is a remarkable galaxy with very vigorous star formation and an unusual "superwind" of out-flowing gas. It had previously been observed in X-rays by the ESA XMM-Newton space telescope, and the image presented here was taken to allow further study of other objects detected in the earlier X-ray observations. The prominent galaxy NGC 4666 in the centre of the picture is a starburst galaxy, about 80 million light-years from Earth, in which particularly intense star formation is taking place. The starburst is thought to be caused by gravitational interactions between NGC 4666 and its neighbouring galaxies, including NGC 4668, visible to the lower left. These interactions often spark vigorous star-formation in the galaxies involved. A combination of supernova explosions and strong winds from massive stars in the starburst region drives a vast flow of gas from the galaxy into space - a so-called "superwind". The superwind is huge in scale, coming from the bright central region of the galaxy and extending for tens of thousands of light-years. As the superwind gas is very hot it emits radiation mostly as X-rays and in the radio part of the spectrum and cannot be seen in visible light images such as the one presented here. This image was made as part of a follow-up to observations made with the ESA XMM-Newton space telescope in X-rays. NGC 4666 was the target of the original XMM-Newton observations, but thanks to the telescope's wide field-of-view many other X-ray sources were also seen in the background. One such serendipitous detection is a faint galaxy cluster seen close to the bottom edge of the image, right of centre. This cluster is much further away from us than NGC 4666, at a distance of about three billion light-years. In order to fully understand the nature of astronomical objects, researchers must study them at several wavelengths. This is because light of different wavelengths can tell us about different physical processes taking place. In this case the Wide Field Imager (WFI) [1] observations were made in visible light to further investigate these serendipitously detected X-ray objects - a good example of how astronomers using different telescopes work together to explore the Universe. Notes [1] The WFI is a joint project between the European Southern Observatory (ESO), the Max-Planck-Institut fr Astronomie (MPIA) in Heidelberg (Germany) and the Osservatorio Astronomico di Capodimonte (OAC) in Naples (Italy). More information ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world's most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and VISTA, the world's largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become "the world's biggest eye on the sky".

2010-09-01

28

Study of NGC 4442: A link between bars and boxy bulges  

NASA Astrophysics Data System (ADS)

We discuss the kinematics and the morphology of NGC 4442, a SB0 galaxy where the complex bar+lens appears in the images as a thick, boxy structure, but oblique with respect to the disc. This characteristic allows one to recognize the object as a barred galaxy and distinguish it from a boxy-bulged galaxy. The analysis of the morphology and kinematics of this galaxy shows that its properties are similar to those of the boxy and peanut bulges, supporting the hypothesis that these kind of structures are connected with edge-on bars. A comparison of our data (image, rotation curves and velocity dispersion profiles) with a model of thick bar presented in the literature shows a very good agreement.

Bettoni, Daniela; Galletta, Giuseppe

1994-01-01

29

Magnetohydrodynamic Simulations of Barred Galaxies  

NASA Astrophysics Data System (ADS)

Magnetic fields are pervasive in barred galaxies, especially in gaseous substructures such as dust lanes and nuclear rings. To explore the effects of magnetic fields on the formation of the substructures as well as on the mass inflow rates to the galaxy center, we run two-dimensional, ideal magnetohydrodynamic simulations. We use a modified version of the Athena code whose numerical magnetic diffusivity is shown to be of third order in space. In the bar regions, magnetic fields are compressed and abruptly bent around the dust-lane shocks. The associated magnetic stress not only reduces the peak density of the dust-lane shocks but also removes angular momentum further from the gas that is moving radially in. Nuclear rings that form at the location of centrifugal barrier rather than resonance with the bar are smaller and more radially distributed, and the mass flow rate to the galaxy center is correspondingly larger in models with stronger magnetic fields. Outside the bar regions, the bar potential and strong shear conspire to amplify the field strength near the corotation resonance. The amplified fields transport angular momentum outward, producing trailing magnetic arms with strong fields and low density. The base of the magnetic arms are found to be unstable to a tearing-mode instability of magnetic reconnection. This produces numerous magnetic islands that eventually make the outer regions highly chaotic.

Kim, W.-T.

2013-04-01

30

Galaxy Zoo: Observing Secular Evolution Through Bars  

NASA Astrophysics Data System (ADS)

Although often seen in galaxies, the role that bars play in galaxy evolution has been largely overlooked. Observations show that bars stellar linear-shaped structures have been present in galaxies since z 1, about 8 billion years ago, and that more and more galaxies are becoming barred with time. This trend has continued to the present, where about two-thirds of all disk galaxies are barred. Observations have also shown that there is a connection between the presence of a bar and the properties of a galaxy, including morphology, star formation, chemical abundance gradients, and nuclear activity. These trends are consistent with the predicted effects of bars on galaxy evolution, i.e., secular evolution. Thus, observations and simulations indicate that bars are important drivers of galaxy evolution. But despite these evidence, bars are still commonly omitted in the lore of galaxy evolution. This proceeding briefly highlights work by Cheung et al. (2013), which tries to change this common omission by presenting the best evidence of bar-driven secular evolution yet. This work implies that bars are not stagnant structures within galaxies, but are instead, critical drivers of galaxy evolution.

Cheung, E.; Athanassoula, E.; Masters, K. L.; Nichol, R. C.; Bosma, A.; Bell, E. F.; Faber, S. M.; Koo, D. C.; Lintott, C.; Melvin, T.; Schawinski, K.; Skibba, R. A.; Willett, K. W.

2014-03-01

31

TESTING THEORIES IN BARRED-SPIRAL GALAXIES  

SciTech Connect

According to one version of the recently proposed 'manifold' theory that explains the origin of spirals and rings in relation to chaotic orbits, galaxies with stronger bars should have a higher spiral arms pitch angle when compared to galaxies with weaker bars. A subsample of barred-spiral galaxies in the Ohio State University Bright Galaxy Survey was used to analyze the spiral arms pitch angle. These were compared with bar strengths taken from the literature. It was found that the galaxies in which the spiral arms maintain a logarithmic shape for more than 70 Degree-Sign seem to corroborate the predicted trend.

Martinez-Garcia, Eric E., E-mail: martinez@astroscu.unam.mx [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, AP 70-264, Distrito Federal 04510 (Mexico)

2012-01-10

32

Galaxy Zoo: Observing Secular Evolution through Bars  

NASA Astrophysics Data System (ADS)

In this paper, we use the Galaxy Zoo 2 data set to study the behavior of bars in disk galaxies as a function of specific star formation rate (SSFR) and bulge prominence. Our sample consists of 13,295 disk galaxies, with an overall (strong) bar fraction of 23.6% 0.4%, of which 1154 barred galaxies also have bar length (BL) measurements. These samples are the largest ever used to study the role of bars in galaxy evolution. We find that the likelihood of a galaxy hosting a bar is anticorrelated with SSFR, regardless of stellar mass or bulge prominence. We find that the trends of bar likelihood and BL with bulge prominence are bimodal with SSFR. We interpret these observations using state-of-the-art simulations of bar evolution that include live halos and the effects of gas and star formation. We suggest our observed trends of bar likelihood with SSFR are driven by the gas fraction of the disks, a factor demonstrated to significantly retard both bar formation and evolution in models. We interpret the bimodal relationship between bulge prominence and bar properties as being due to the complicated effects of classical bulges and central mass concentrations on bar evolution and also to the growth of disky pseudobulges by bar evolution. These results represent empirical evidence for secular evolution driven by bars in disk galaxies. This work suggests that bars are not stagnant structures within disk galaxies but are a critical evolutionary driver of their host galaxies in the local universe (z < 1). .

Cheung, Edmond; Athanassoula, E.; Masters, Karen L.; Nichol, Robert C.; Bosma, A.; Bell, Eric F.; Faber, S. M.; Koo, David C.; Lintott, Chris; Melvin, Thomas; Schawinski, Kevin; Skibba, Ramin A.; Willett, Kyle W.

2013-12-01

33

Galaxy Zoo: Observing Secular Evolution Through Bars  

NASA Astrophysics Data System (ADS)

In this talk, I use the Galaxy Zoo 2 dataset to study the behavior of bars in disk galaxies as a function of specific star formation rate (SSFR), and inner galactic structure, i.e., the prominence of the bulge as parameterized by Srsic index and central surface stellar mass density. Our sample consists of 13,295 disk galaxies, with an overall bar fraction of 23.6 0.4%, of which 1,154 barred galaxies also have bar length measurements. These samples are the largest ever used to study the role of bars in disk galaxy evolution. I find that the likelihood of a galaxy hosting a bar is anti-correlated with SSFR, regardless of stellar mass or bulge prominence. I find that the trends of bar likelihood with bulge prominence are bimodal with SSFR, i.e., in star-forming galaxies, bulges are more prominent in galaxies more likely to host bars, while in quiescent disk galaxies, bars are less frequent where there are prominent bulges. Our observations of bar length reveal a complex picture. In star-forming disks, longer bars are found where the bulges are more prominent, while in quiescent disks there is a maximum in the average bar length as a function of bulge prominence. I interpret these observations using state-of-the-art simulations of bar evolution which include live halos and the effects of gas and star formation. I suggest our observed trends of bar likelihood with SSFR are driven by the gas fraction of the disks; a factor demonstrated to significantly retard both bar formation and evolution in models. I interpret the bimodal relationship between bulge prominence and bar properties as due to the complicated effects of classical bulges and central mass concentrations on bar evolution, and also to the growth of disky pseudobulges by bar evolution. These results represent empirical evidence for secular evolution driven by bars in disk galaxies. This work suggests that bars are not stagnant structures within disk galaxies, but are a critical evolutionary driver of their host galaxies in the local universe (z < 1).

Cheung, Edmond; Athanassoula, L.; Masters, K.; Faber, S. M.; Koo, D. C.; Zoo, Galaxy

2014-01-01

34

Galaxy Zoo: CANDELS barred discs and bar fractions  

NASA Astrophysics Data System (ADS)

The formation of bars in disc galaxies is a tracer of the dynamical maturity of the population. Previous studies have found that the incidence of bars in discs decreases from the local Universe to z 1, and by z > 1 simulations predict that bar features in dynamically mature discs should be extremely rare. Here, we report the discovery of strong barred structures in massive disc galaxies at z 1.5 in deep rest-frame optical images from the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey. From within a sample of 876 disc galaxies identified by visual classification in Galaxy Zoo, we identify 123 barred galaxies. Selecting a subsample within the same region of the evolving galaxy luminosity function (brighter than L*), we find that the bar fraction across the redshift range 0.5 ? z ? 2 ( f_{bar} = 10.7^{+6.3}_{-3.5} per cent after correcting for incompleteness) does not significantly evolve. We discuss the implications of this discovery in the context of existing simulations and our current understanding of the way disc galaxies have evolved over the last 11 billion years.

Simmons, B. D.; Melvin, Thomas; Lintott, Chris; Masters, Karen L.; Willett, Kyle W.; Keel, William C.; Smethurst, R. J.; Cheung, Edmond; Nichol, Robert C.; Schawinski, Kevin; Rutkowski, Michael; Kartaltepe, Jeyhan S.; Bell, Eric F.; Casteels, Kevin R. V.; Conselice, Christopher J.; Almaini, Omar; Ferguson, Henry C.; Fortson, Lucy; Hartley, William; Kocevski, Dale; Koekemoer, Anton M.; McIntosh, Daniel H.; Mortlock, Alice; Newman, Jeffrey A.; Ownsworth, Jamie; Bamford, Steven; Dahlen, Tomas; Faber, Sandra M.; Finkelstein, Steven L.; Fontana, Adriano; Galametz, Audrey; Grogin, N. A.; Grtzbauch, Ruth; Guo, Yicheng; Huler, Boris; Jek, Kian J.; Kaviraj, Sugata; Lucas, Ray A.; Peth, Michael; Salvato, Mara; Wiklind, Tommy; Wuyts, Stijn

2014-12-01

35

The Star Clusters in the Irregular Galaxy NGC 4449  

E-print Network

We examine the star clusters in the irregular galaxy NGC 4449. We use a near-infrared spectrum and broad-band images taken with the HST to place a limit of 8--15 Myrs on the age of the bright central ojbect in NGC 4449. Its luminosity and size suggest that it is comparable to young super star clusters. However, there is a peculiar nucleated-bar structure at the center of this star cluster, and we suggest that this structure is debris from the interaction that has produced the counter-rotating gas systems and extended gas streamers in the galaxy. From the images we identify 60 other candidate compact star clusters in NGC 4449. Fourteen of these could be background elliptical galaxies or old globular star clusters. Of the star clusters, three, in addition to the central object, are potentially super star clusters, and many others are comparable to the populous clusters found in the LMC. The star clusters span a large range in ages with no obvious peak in cluster formation that might be attributed to the interaction that the galaxy has experienced.

Andrea E. Gelatt; Deidre A. Hunter; J. S. Gallagher

2000-10-25

36

Double-Barred Galaxies: I. A Catalog of Barred Galaxies with Stellar Secondary Bars and Inner Disks  

E-print Network

I present a catalog of 67 barred galaxies which contain distinct, elliptical stellar structures inside their bars. Fifty of these are double-barred galaxies: a small-scale, "inner" or "secondary" bar is embedded within a large-scale, "outer" or "primary" bar. I provide homogenized measurements of the sizes, ellipticities, and orientations of both inner and outer bars, along with with global parameters for the galaxies. The other 17 are classified as "inner-disk" galaxies, where a large-scale bar harbors an inner elliptical structure which is aligned with the galaxy's outer disk. Four of the double-barred galaxies also possess inner disks, located in between the inner and outer bars. While the inner-disk classification is ad-hoc -- and undoubtedly includes some inner bars with chance alignments (five such probable cases are identified) -- there is good evidence that inner disks form a statistically distinct population, and that at least some are indeed disks rather than bars. In addition, I list 36 galaxies which may be double-barred, but for which current observations are ambiguous or incomplete, and another 23 galaxies which have been previously suggested as potentially being double-barred, but which are probably *not*. False double-bar identifications are usually due to features such as nuclear rings and spirals being misclassified as bars; I provide some illustrated examples of how this can happen.

Peter Erwin

2003-12-14

37

A Galaxy Cluster Near NGC 720  

E-print Network

The galaxy cluster RXJ 0152.7-1357 is emitting X-rays at the high rate of 148 counts $ks^{-1}$. It would be one of the most luminous X-ray clusters known if it is at its redshift distance of z = .8325. It is conspicuously elongated, however, toward the bright, X-ray active galaxy NGC 720 about 14 arcmin away. At the same distance on the other side of NGC 720, and almost perfectly aligned, is an X-ray BSO of 5.8 cts/ks. It is reported here that the redshift of this quasar is z = .8312.

H. Arp

2005-10-06

38

Distribution and motions of atomic hydrogen in lenticular galaxies. IV - A ring of H I around NGC 4262  

Microsoft Academic Search

The distribution of H I in the normal, barred lenticular galaxy NGC 4262 in the Virgo Cluster has been mapped at a resolution of 13arcsec51arcsec. The gas is confined to a narrow ring, apparently in circular rotation about the galaxy center. The ring has a diameter about twice the optical diameter of the galaxy, and is inclined by at least

N. Krumm; W. van Driel; H. van Woerden

1985-01-01

39

The O/H Distribution in the Transition Magellanic Galaxy NGC 1313  

E-print Network

Multi-fibre emission-line spectrophotometry of 33 H II regions and 3 diffuse interstellar medium positions are presented for the barred Magellanic galaxy NGC 1313. The H II regions show a fairly narrow range of thermal conditions characteristic of high excitation nebular gas. Electron temperature was directly determined in four of the H II regions. The global O/H abundance distribution appears very flat across the disk at 12 + log O/H = 8.4 +/- 0.1, with possibly the bar regions having abundances higher by 0.2 dex than the outer disc. NGC 1313 is the highest mass barred galaxy known not to have any radial abundance gradient. The key role of the bar on the abundance distribution in disc galaxies is revisited.

J. R. Walsh; J. -R. Roy

1997-05-06

40

Radial migration in barred galaxies  

NASA Astrophysics Data System (ADS)

In this talk, I will present the result of high resolution numerical simulations of disk galaxies with various bulge/disk ratios evolving isolated, showing that: Most of migration takes place when the bar strength is high and decreases in the phases of low activity (in agreement with the results by Brunetti et el. 2011, Minchev et al. 2011). Most of the stars inside the corotation radius (CR) do not migrate in the outer regions, but stay confined in the inner disk, while stars outside CR can migrate either inwards or outwards, diffusing over the whole disk. Migration is accompanied by significative azimuthal variations in the metallicity distribution, of the order of 0.1 dex for an initial gradient of ~-0.07 dex/kpc. Boxy bulges are an example of stellar structures whose properties (stellar content, vertical metallicity, [?/Fe] and age gradients, ..) are affected by radial migration (see also Fig. 1).

Di Matteo, P.; Haywood, M.; Combes, F.; Semelin, B.; Babusiaux, C.; Gomez, A.

2015-03-01

41

Hyperactive galaxy NGC 7673 [heic0205  

NASA Astrophysics Data System (ADS)

Hyperactive galaxy NGC 7673 hi-res Size hi-res: 116 kb Credits: European Space Agency & Nicole Homeier (European Southern Observatory and University of Wisconsin-Madison) Hyperactive galaxy NGC 7673 The disturbed spiral galaxy NGC 7673 is ablaze with the light from millions of new stars. Each of its infant giant blue star clusters shines 100 times as brightly in the ultraviolet as similar immense star clusters in our own Galaxy. Scientists studying this object have two pressing questions: "What has triggered this enormous burst of star formation and how will this galaxy evolve in the future?" Telltale patches of blue light are signs of the formation of millions of new stars in the tangled spiral galaxy NGC 7673. Each of the bluish areas in this image consists of immense star clusters containing thousands of young stars. These clusters lie on the spiral arms of NGC 7673 and so emphasise its somewhat ragged look. This image, taken from Earth orbit by the ESA/NASA Hubble Space Telescope in 1996 and 1997, also shows two other galaxies seen in the background of the image, to the left and right of NGC 7673. These galaxies are further away and so appear redder, due to their higher redshift, an effect caused by the expansion of the Universe. The youngest blue stars in NGC 7673 are blazing with intense ultraviolet radiation. Each star cluster radiates 100 times more ultraviolet light than the famous Tarantula Nebula (30 Doradus), the largest star-forming region known in the local group of galaxies. Telltale patches of blue light are signs of the formation of millions of new stars in the tangled spiral galaxy NGC 7673. Each of the bluish areas in this image consists of immense star clusters containing thousands of young stars. These clusters lie on the spiral arms of NGC 7673 and so emphasise its somewhat ragged look. This image, taken from Earth orbit by the ESA/NASA Hubble Space Telescope in 1996 and 1997, also shows two other galaxies seen in the background of the image, to the left and right of NGC 7673. These galaxies are further away and so appear redder, due to their higher redshift, an effect caused by the expansion of the Universe. The youngest blue stars in NGC 7673 are blazing with intense ultraviolet radiation. Each star cluster radiates 100 times more ultraviolet light than the famous Tarantula Nebula (30 Doradus), the largest star-forming region known in the local group of galaxies. Although this image is another attractive example of 'space art' from Hubble, there is also a purpose behind the beauty. Extracting the secrets of NGC 7673 According to Nicole Homeier from the European Southern Observatory in Munich, Germany and the University of Wisconsin-Madison, USA, "NGC 7673 is a nearby example of the type of vigorous star formation that we think may have taken place in the early Universe. Our most pressing questions are: What has triggered this enormous burst of star formation and how will the galaxy evolve in the future?" There are two possible causes for this remarkable flurry of star formation: either a near miss or a collision between NGC 7673 and a nearby galaxy, or some unusual circumstances within the spiral galaxy itself - for example, there may have been an overabundance of gas in the galaxy's disc that became gravitationally unstable, forming huge gas clumps that then burst into stellar 'flame'. For Homeier and her collaborators in America and Europe, the Hubble image offers new opportunities. "For many years we have only been able to see the star-forming regions as fuzzy clumps from ground-based telescopes. Now, with Hubble we can study how these clumps may have originated and how this 'starburst galaxy' relates to the younger star-forming galaxies we see in the early Universe", she says. "We hope to find the answer to our questions in the next few years." NGC 7673 is located in the constellation of Pegasus at an approximate distance of 150 million light-years. This picture is composed of three images obtained with Hubble's Wide Field Planetary Camera 2 on 15 Oc

2002-03-01

42

2Cosmic Bar Graphs Galaxy Type  

E-print Network

2Cosmic Bar Graphs 0 20 40 60 80 100 S E SB I Galaxy Type Number 0 200 400 600 800 1000 FB SB Burst Classification Number Problem1 Astronomers have classified the 160 largest galaxies in the Virgo Cluster classed as E, 56 were classed as SB and 3 were classed as I. About what fraction of galaxies

43

Photometry of resolved galaxies. V - NGC 6822  

NASA Technical Reports Server (NTRS)

Three-color CCD frames of the local group irregular galaxy NGC 6822 have been reduced to GRI photometry for 3475 stars using RICHFLD point-spread function fitting techniques. The data are compared with earlier work on this galaxy, particularly with Kayser (1966) on a star-by-star basis. Color-magnitude diagrams are constructed from the data and compared with both theoretical stellar model tracks and the expected foreground star contamination. A luminosity function for the blue stars is derived; comparison of this luminosity function with those of 10 other irregular galaxies indicates that NGC 6822 has a typical young star population. The stellar birthrate and initial mass function are estimated for this galaxy. The slope at the bright end of the mass function looks similar to recent results for the Galaxy, the Magellanic Clouds, and the irregular galaxy Sextans A. NGC 6822 appears to be presently forming stars at a slower rate for its mass than Sextans A or the Magellanic Clouds.

Hoessel, J. G.; Anderson, N.

1986-01-01

44

A gas-rich nuclear bar fuelling a powerful central starburst in NGC 2782  

E-print Network

We present evidence that the peculiar interacting starburst galaxy NGC 2782 (Arp 215) harbors a gas-rich nuclear stellar bar feeding an M82-class powerful central starburst, from a study based on OVRO CO (J=1->0) data, WIYN BVR & Halpha observations, along with available NIR images, a 5 GHz RC map and HST images. NGC 2782 harbors a clumpy, bar-like CO feature of radius ~ 7.5'' (1.3 kpc) which leads a nuclear stellar bar of similar size. The nuclear CO bar is massive: it contains ~2.5x10**9 M_sun of molecular gas, which makes up ~ 8 % of the dynamical'mass present within a 1.3 kpc radius. Within the CO bar, emission peaks in two extended clumpy lobes which lie on opposite sides of the nucleus, separated by ~ 6'' (1 kpc). Between the CO lobes, in the inner 200 pc radius, resides a powerful central starburst which is forming stars at a rate of 3 to 6 M_sun yr-1. While circular motions dominate the CO velocity field, the CO lobes show weak bar-like streaming motions on the leading side of the nuclear stellar bar, suggestive of gas inflow. We estimate semi-analytically the gravitational torque from the nuclear stellar bar on the gas, and suggest large gas inflow rates from the CO lobes into the central starburst. These observations, which are amongst the first ones showing a nuclear stellar bar fuelling molecular gas into an intense central starburst, are consistent with simulations and theory which suggest that nuclear bars provide an efficient way of transporting gas closer to the galactic center to fuel central activity. Furthermore, several massive clumps are present at low radii, and dynamical friction might produce further gas inflow. We suggest that the nuclear molecular gas bas and central activity will be very short-lived, likely disappearing within 5x10**8 years.

Shardha Jogee; Jeffrey D. P. Kenney; Beverly J. Smith

1999-07-07

45

Kinematic and Photometric Evidence for a Bar in NGC 2683  

Microsoft Academic Search

We present optical long-slit and SparsePak Integral Field Unit emission line spectroscopy along with optical broadband and near-IR images of the edge-on spiral galaxy NGC 2683. We find a multi-valued, figure-of-eight velocity structure in the inner 45'' of the long-slit spectrum and twisted isovelocity contours in the velocity field. We also find, regardless of wavelength, that the galaxy isophotes are

Rachel Kuzio de Naray; Matthew J. Zagursky; Stacy S. McGaugh

2009-01-01

46

KINEMATIC AND PHOTOMETRIC EVIDENCE FOR A BAR IN NGC 2683  

Microsoft Academic Search

We present optical long-slit and SparsePak Integral Field Unit emission line spectroscopy along with optical broadband and near-IR images of the edge-on spiral galaxy NGC 2683. We find a multi-valued, figure-of-eight velocity structure in the inner 45'' of the long-slit spectrum and twisted isovelocity contours in the velocity field. We also find, regardless of wavelength, that the galaxy isophotes are

Rachel Kuzio de Naray; Matthew J. Zagursky; Stacy S. McGaugh

2009-01-01

47

Kinematic and Photometric Evidence for a Bar in NGC 2683  

Microsoft Academic Search

We present optical long-slit and SparsePak Integral Field Unit emission line spectroscopy along with optical broadband and near IR images of the edge-on spiral galaxy NGC 2683. We find a multi-valued, figure-of-eight velocity structure in the inner 45\\

Rachel Kuzio de Naray; M. J. Zagursky; S. S. McGaugh

2009-01-01

48

Enigmatic Masks of Cosmic Dust: 8.0?m Morphology of Nearby Barred Spiral Galaxies  

NASA Astrophysics Data System (ADS)

Early observations of barred galaxies, such as NGC1300, NGC1530, NGC3351 and NGC5921 by Curtis, revealed the prevalence of characteristic dark bands or streaks across the disk of the galaxy. These dark bands were interpreted to be lanes of "occulting material obscuring luminous objects behind them. While being nothing more than a nuisance to observers at the turn of the twentieth century, it is these lanes of dust to which we now turn, seen glowing in emission at 8.0?m. Comparing Spitzer IRAC images of a sample of nearby barred galaxies, we find a separation of 3.6?m images into two distinct classes or form families. The first class comprises galaxies whose 8.0?m morphology tightly traces the underlying barred stellar backbone at 3.6?m, while the second class does not reveal a bar at all at 8.0?m. Spectacular lanes of dust are however evident in this second class and are understood to be signatures of shock loci at the outer edges of the bar. These two distinct form families are discussed in greater detail.

Groess, Robert; Block, D. L.; Fazio, G. G.

2011-05-01

49

Modeling Interacting Galaxies: NGC 4449 revisited  

NASA Astrophysics Data System (ADS)

Observing nearby interacting galaxies is a key to understanding galactic physics provided that we know the spatial and temporal perturbations acting on these galaxies. Thus, we have to know the orbits and the gross internal properties of the galaxies. In order to cope with the related extended parameter space, we developed the code MINGA which combines a genetic algorithm with a fast N-body method. As an example for this method, we present a re-analysis of the prototypical system NGC 4449 which is now based on both, the full HI data cube of the NGC 4449 system and on improved determinations of the galactic orbits within a restricted N-body calculation.

Theis, C.; Jungwirth, G.; Petsch, H.; Walter, F.

2011-01-01

50

Quasars around the Seyfert Galaxy NGC3516  

E-print Network

We report redshift measurements of 5 X-ray emitting blue stellar objects (BSO's) located less than 12 arc min from the X-ray Seyfert galaxy, NGC 3516. We find these quasars to be distributed along the minor axis of the galaxy and to show a very good correlation between their redshift and their angular distance from NGC 3516. Moreover the redshifts of these 5 quasars are: 0.33, 0.69, 0.93, 1.40 and 2.10 which are very near the peaks of the redshift periodicity distribution (i.e. z=0.3, 0.6, 0.96, 1.41 and 1.96). All these observed properties strikingly confirm, around this single example of a Seyfert, the composite picture derived from previous physical associations of quasars with low redshift, active galaxies.

Y. Chu; J. Wei; J. Hu; X. Zhu; H. Arp

1997-12-02

51

Imaging of the Shell Galaxies NGC 474 and NGC 7600, and Implications for their Formation  

E-print Network

We present photometric observations of two shell galaxies, NGC 474 and NGC 7600. We examine the photometric colours and surface brightnesses of the shells and their host galaxies, and the isophotal parameters of each galaxy. In the case of NGC 474, we find that the shell formation is consistent with a merger origin although it is possible that the close companion NGC 470 is contributing to the shell system via mass transfer. NGC 7600 exhibits shell geometry and colours which also favour a merger origin.

A. J. Turnbull; T. J. Bridges; D. Carter

1999-05-05

52

MERGING COLD FRONTS IN THE GALAXY PAIR NGC 7619 AND NGC 7626  

Microsoft Academic Search

We present results from Chandra observations of the galaxy pair NGC 7619 and NGC 7626, the two dominant members of the Pegasus group. The X-ray images show a brightness edge associated with each galaxy, which we identify as merger cold fronts. The edges are sharp, and the axes of symmetry of the edges are roughly antiparallel, suggesting that these galaxies

S. W. Randall; C. Jones; R. Kraft; W. R. Forman; E. OSullivan

2009-01-01

53

Merging Cold Fronts in the Galaxy Pair NGC 7619 and NGC 7626  

Microsoft Academic Search

We present results from Chandra observations of the galaxy pair NGC 7619 and NGC 7626, the two dominant members of the Pegasus group. The X-ray images show a brightness edge associated with each galaxy, which we identify as merger cold fronts. The edges are sharp, and the axes of symmetry of the edges are roughly antiparallel, suggesting that these galaxies

S. W. Randall; C. Jones; R. Kraft; W. R. Forman; E. O'Sullivan

2009-01-01

54

A Multiwavelength Study of the Starburst Galaxy NGC 7771  

NASA Technical Reports Server (NTRS)

We present a multiwavelength study of the interacting starburst galaxy NGC 7771, including new optical and ultra-violet spectra and a previously unpublished soft X-ray ROSAT image and spectrum. The far-infrared, radio, and X-ray fluxes suggest that a massive burst of star-formation is currently in progress but the small equivalent width of the Balmer emission lines (equivalent width H(alpha approximately equals 100 A), the weak UV flux, the low abundance of ionised oxygen, and the shape of the optical spectrum lead us to conclude that there are few 0 stars. This might normally suggest that star-formation has ceased but the galaxy's barred gravitational potential and large gas reserves imply that this should not be so, and we therefore consider other explanations. We argue that the observations cannot be due to effects of geometry, density bounded nebulae, or dust within the nebulae, and conclude that a truncated IMF is required. The dwarf galaxy NGC 7770 appears to be in the initial stages of a merger with NGC 7771, and the resulting tidal perturbations may have induced the apparent two-armed spiral pattern, and driven a substantial fraction of the disk gas inwards. The presence of a bulge in NGC 7771 may be moderating the starburst so that, while still occuring on a large scale with a supernova rate of 0.8-1/yr, it is less violent and the IMF has a relatively low upper mass limit. We find that there is a cluster of stars obscuring part of the starburst region, and we offer an explanation of its origin.

Davies, Richard I.; Alonso-Herrero, Almudena; Ward, Martin J.

1997-01-01

55

BVRI photometric analysis for the galaxy group NGC 4410  

Microsoft Academic Search

We present a BVRI CCD (Charge Coupled Device) surface photometry analysis of the galaxy group NGC 4410, which contains four galaxies in interaction. Along with our photometric study, we show residual images (after subtracting isophotal models) and unsharp masked images to uncover any hidden structures in this system of galaxies; we have also performed a two-dimensional bulge-disk decomposition for NGC

J. A. Prez Grana; S. N. Kemp; A. C. Katsiyannis; A. Franco-Balderas; E. de La Fuente; J. Meaburn; H. G. Khosroshahi

2008-01-01

56

Magnetic Fields and Mass Inflow in Central Regions of Barred Galaxies  

NASA Astrophysics Data System (ADS)

Radio continuum emission is an excellent tracer of star formation in central regions of galaxies. We observed a sample of 20 galaxies with massive bars. The regular magnetic fields around the bar, as traced by the polarized emission, do not always follow the gas flow predicted from numerical simulations and show little compression by the shock. The galaxies with the longest bars show the strongest deviations of the magnetic field pattern from axial symmetry, and most of them host nuclear rings. The total magnetic fields in these nuclear rings of up to ~= 100 ?G are among the strongest fields known in spiral galaxies. The regular field in the nuclear ring of NGC 1097 is of spiral shape. Magnetic stress in the ring can drive mass inflow of about one solar mass per year which is sufficient to feed the active nucleus. This process may also work in non-barred galaxies.

Beck, Rainer; Ehle, Matthias; Fletcher, Andrew; Harnett, Julienne; Shoutenkov, Vladimir; Shukurov, Anvar; Sokoloff, Dmitry

2005-08-01

57

TWO PSEUDOBULGES IN THE 'BOXY BULGE' GALAXY NGC 5746  

SciTech Connect

Galaxy formation and growth under the {Lambda}CDM paradigm is expected to proceed in a hierarchical, bottom-up fashion by which small galaxies grow into large galaxies; this mechanism leaves behind large 'classical bulges' kinematically distinct from 'pseudobulges' grown by internal, secular processes. We use archival data (Spitzer Space Telescope 3.6 {mu}m wavelength, Hubble Space Telescope H-band, Two Micron All Sky Survey K{sub s} -band, and Sloan Digital Sky Survey gri-band) to measure composite minor- and major-axis surface brightness profiles of the almost-edge-on spiral galaxy NGC 5746. These light profiles span a large range of radii and surface brightnesses to reveal an inner, high surface brightness stellar component that is distinct from the well-known boxy bulge. It is well fitted by Sersic functions with indices n = 0.99 {+-} 0.08 and 1.17 {+-} 0.24 along the minor and major axes, respectively. Since n < 2, we conclude that this innermost component is a secularly evolved pseudobulge that is distinct from the boxy pseudobulge. This inner pseudobulge makes up 0.136 {+-} 0.019 of the total light of the galaxy. It is therefore considerably less luminous than the boxy structure, which is now understood to be a bar seen nearly end-on. The infrared imagery shows further evidence for secular evolution in the form of a bright inner ring of inner radius 9.1 kpc and width 1.6 kpc. NGC 5746 is therefore a giant, pure-disk SB(r)bc galaxy with no sign of a merger-built bulge. We do not understand how such galaxies form in a {Lambda}CDM universe.

Barentine, John C.; Kormendy, John [Department of Astronomy, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712-0259 (United States)

2012-08-01

58

Recycling of ghost galaxies: The origin of giant HI ring around NGC 1533  

E-print Network

We propose that the giant HI ring recently discovered by HIPASS for S0 galaxy NGC 1533 is formed by unequal-mass merging between gas-rich LSB (low surface brightness: ``ghost'') galaxies and HSB disks. The NGC 1533 progenitor HSB spiral is transformed into a barred S0 during merging and the outer HI gas disk of the LSB is transformed into the giant HI ring. We also discuss two different possibilities for the origin of isolated star-forming regions (``ELdot'' objects) in the giant gas ring.

Kenji Bekki; Warrick J. Couch; Emma Ryan-Weber; Rachel Webster

2003-10-14

59

Observations of CO in the Magellanic irregular galaxy NGC 55  

NASA Technical Reports Server (NTRS)

The content of molecular gas in galaxies, mainly H2, is one of the key observations necessary for the understanding of star formation processes and history. As the CO molecule is the most widely distributed molecule after H2 and has easily observable mm lines, it is used as a tracer for the molecular gas. CO was detected towards the direction where the H alpha and 6 cm radio continuum emission is strongest (Hummel et al. 1986). Here, researchers present the Gaussian line parameters in tabular form. The distribution of CO corresponds well with the intense HI cloud near the bar of NGC 55. The extent of the CO cloud is about 975 pc perpendicular to the major axis. As the radio continuum and the H alpha emission also peaks in this region, it is most probably associated with the star forming region in NGC 55. Assuming that the molecular gas is in virial equilibrium, researchers derive a mass of about 8 times 10(exp 7) solar magnitude. The molecular mass found indicates that the conversion factor for the molecular mass in Irr galaxies as inferred from CO line emission is indeed higher by up to a factor of 20 compared to the canonical value for the Galaxy.

Heithausen, Andreas; Dettmar, Ralf-Juergen

1990-01-01

60

Atomic and molecular gas in the merger galaxy NGC 1316 (Fornax A) and its environment  

NASA Astrophysics Data System (ADS)

We present and interpret observations of atomic and molecular gas toward the southern elliptical galaxy NGC 1316 (Fornax A), a strong double-lobe radio source with a disturbed optical morphology that includes numerous shells and loops. The 12CO(1-0), 12CO(2-1), and Hi observations were made with SEST and the VLA. CO emission corresponding to a total molecular hydrogen mass of ~ 5 x 108 Msun was detected towards the central position as well as northwest and southeast of the nucleus in the regions of the dust patches. The origin of that gas is likely external and due to accretion of one or several small gas-rich galaxies. Hi was not detected in the central region of NGC 1316, but ~ 2 x 107 Msun of atomic gas was found towards the giant Hii region discovered by Schweizer (1980) located 6{farcm }7 (or 36.2 kpc) from the nucleus. Hi was also found at three other locations in the outer part of NGC 1316. The Hi distributions and kinematics of the two nearby spiral companions of NGC 1316, NGC 1317 (a barred galaxy to the north) and NGC 1310 (to the west) could be studied. Both galaxies have unusually small Hi disks that may have been affected by ram-pressure stripping.

Horellou, C.; Black, J. H.; van Gorkom, J. H.; Combes, F.; van der Hulst, J. M.; Charmandaris, V.

2001-09-01

61

GLOBULAR CLUSTER SYSTEMS OF SPIRAL AND S0 GALAXIES: RESULTS FROM WIYN IMAGING OF NGC 1023, NGC 1055, NGC 7332, AND NGC 7339  

SciTech Connect

We present results from a study of the globular cluster (GC) systems of four spiral and S0 galaxies imaged as part of an ongoing wide-field survey of the GC systems of giant galaxies. The target galaxies-the SB0 galaxy NGC 1023, the SBb galaxy NGC 1055, and an isolated pair comprised of the Sbc galaxy NGC 7339 and the S0 galaxy NGC 7332-were observed in BVR filters with the WIYN 3.5 m telescope and Minimosaic camera. For two of the galaxies, we combined the WIYN imaging with previously published data from the Hubble Space Telescope and the Keck Observatory to help characterize the GC distribution in the central few kiloparsecs. We determine the radial distribution (surface density of GCs versus projected radius) of each galaxy's GC system and use it to calculate the total number of GCs (N{sub GC}). We find N{sub GC} = 490 {+-} 30, 210 {+-} 40, 175 {+-} 15, and 75 {+-} 10 for NGC 1023, NGC 1055, NGC 7332, and NGC 7339, respectively. We also calculate the GC specific frequency (N{sub GC} normalized by host galaxy luminosity or mass) and find values typical of those of the other spiral and E/S0 galaxies in the survey. The two lenticular galaxies have sufficient numbers of GC candidates for us to perform statistical tests for bimodality in the GC color distributions. We find evidence at a high confidence level (>95%) for two populations in the B - R distribution of the GC system of NGC 1023. We find weaker evidence for bimodality (>81% confidence) in the GC color distribution of NGC 7332. Finally, we identify eight GC candidates that may be associated with the Magellanic dwarf galaxy NGC 1023A, which is a satellite of NGC 1023.

Young, Michael D.; Dowell, Jessica L.; Rhode, Katherine L., E-mail: youngmd@indiana.edu, E-mail: jlwind@astro.indiana.edu, E-mail: rhode@astro.indiana.edu [Department of Astronomy, Indiana University, 727 East Third Street, Bloomington, IN 47405-7105 (United States)

2012-10-01

62

Longslit Spectra of the Galaxy NGC 1569  

NASA Technical Reports Server (NTRS)

Longslit spectra of the starburst galaxy NGC 1569 are displayed. This ground-based data was acquired at the 90-inch telescope of the Steward Observatory (Kitt Peak, Arizona) in September 1998. Results for the red region of the spectrum are presented. The variation of ionization and gas density as a function of position in the galaxy are shown. The background stellar component of the galaxy is separated from the nebular emission spectrum. These ground-based results will be used with space-based data to be acquired by astronomers at South Carolina State University, the University of Maryland and Rice University as part of an approved Cycle 8 Hubble Space Telescope program.

Duenas, Ely

2000-01-01

63

Complex statistics in Hamiltonian barred galaxy models  

E-print Network

We use probability density functions (pdfs) of sums of orbit coordinates, over time intervals of the order of one Hubble time, to distinguish weakly from strongly chaotic orbits in a barred galaxy model. We find that, in the weakly chaotic case, quasi-stationary states arise, whose pdfs are well approximated by $q$-Gaussian functions (with $1galaxy models has been investigated thoroughly in recent years due of their ability to support galaxy structures for relatively long time scales. In this paper, we demonstrate, on specific orbits of 2 and 3 degree of freedom barred galaxy models, that the proposed statistical approach can distinguish weakly from strongly chaotic motion accurately and efficiently, especially in cases where Lyapunov exponents and other local dynamic indicators appear to be inconclusive.

Tassos Bountis; Thanos Manos; Chris Antonopoulos

2011-11-17

64

Surface Photometry of Star Clusters in the Dwarf Elliptical Galaxies NGC 185 and NGC 205  

E-print Network

We present the surface photometry of star clusters in the nearby dwarf elliptical galaxies NGC 185 and NGC 205, obtained from deep HST WFPC2 F555W (V) and F814W (I) images. We have obtained surface brightness and color profiles of six star clusters in NGC 185, seven star clusters in NGC 205, and one recently discovered non-stellar object in NGC 205. The surface brightness profiles of ten star clusters are fitted well by the King model, and those of four star clusters are fitted well by the power-law. Three out of ten star clusters fitted well with King model show signs of tidal tails.

Sang Chul Kim; Myung Gyoon Lee; Doug Geisler; Ata Sarajedini; Taft E. Armandroff; Gary S. Da Costa

2001-09-14

65

Atomic and Molecular Gas in the Merger Galaxy NGC 1316 (Fornax A) and its Environment  

NASA Astrophysics Data System (ADS)

We present and interpret observations of atomic and molecular gas toward the southern elliptical galaxy NGC 1316 (Fornax A), a strong double-lobe radio source with a disturbed optical morphology that includes numerous shells and loops. The 12CO(1--0), 12CO(2--1), and Hi observations were made with SEST and the VLA. CO emission corresponding to a total molecular hydrogen mass of ~4x108 Msun was detected toward the central position as well as northwest and southeast of the nucleus in the regions of the dust patches. The origin of that gas is likely external and due to accretion of one or several small gas-rich galaxies. No Hi was detected toward NGC 1316 itself but ~2x107 Msun of atomic gas was found toward the giant Hii region discovered by Schweizer (1980) located 6.7 m (or 36.2 kpc) from the nucleus. The Hi distributions and kinematics of the two nearby spiral companions of NGC 1316, NGC 1317 (a barred galaxy to the north) and NGC 1310 (to the west) could be studied. Both galaxies have unusually small Hi disks that may have been affected by ram-pressure stripping.

van Gorkom, J. H.; Horellou, C.; Black, J. H.; Combes, F.; van der Hulst, J. M.; Charmandaris, V.

2001-11-01

66

ON THE GALACTIC SPIN OF BARRED DISK GALAXIES  

SciTech Connect

We present a study of the connection between the galactic spin parameter (?{sub d}) and the bar fraction in a volume-limited sample of 10,674 disk galaxies drawn from the Sloan Digital Sky Survey Data Release 7. The galaxies in our sample are visually classified into one of three groups: non-barred galaxies and galaxies hosting long or short bars, respectively. We find that the spin distributions of these three classes are statistically different, with galaxies hosting long bars having the lowest ?{sub d} values, followed by non-barred galaxies, while galaxies with short bars present typically high spin parameters. The bar fraction presents its maximum at low to intermediate ?{sub d} values for the case of long bars, while the maximum for short bars is at high ?{sub d}. This bimodality is in good agreement with previous studies finding longer bars hosted by luminous, massive, red galaxies with a low content of cold gas, while short bars were found in low luminosity, low mass, blue galaxies that were typically gas rich. In addition, the rise and fall of the bar fraction as a function of ?{sub d}, within the long-bar sample shown in our results, can be explained as a result of two competing factors: the self-gravity of the disk that enhances bar instabilities and the support by random motions, instead of ordered rotational motion, that prevents the formation/growth of bars.

Cervantes-Sodi, Bernardo; Li, Cheng; Wang, Lixin [Partner Group of the Max Planck Institute for Astrophysics and Key Laboratory for Research in Galaxies and Cosmology of Chinese Academy of Sciences, Shanghai Astronomical Observatory, Nandan Road 80, Shanghai 200030 (China); Park, Changbom, E-mail: bernardo@shao.ac.cn [Korea Institute for Advanced Study, Dongdaemun-gu, Seoul 130-722 (Korea, Republic of)

2013-09-20

67

Discovery of Counter-Rotating Gas in the Galaxies NGC1596 and NGC3203 and the Incidence of Gas Counter-Rotation in S0 Galaxies  

E-print Network

We have identified two new galaxies with gas counter-rotation (NGC1596 and NGC3203) and have confirmed similar behaviour in another one (NGC128), this using results from separate studies of the ionized-gas and stellar kinematics of a well-defined sample of 30 edge-on disc galaxies. Gas counter-rotators thus represent 10+/-5% of our sample, but the fraction climbs to 21+/-11% when only lenticular (S0) galaxies are considered and to 27+/-13% for S0s with detected ionized-gas only. Those fractions are consistent with but slightly higher than previous studies. A compilation from well-defined studies of S0s in the literature yields fractions of 15+/-4% and 23+/-5%, respectively. Although mainly based on circumstantial evidence, we argue that the counter-rotating gas originates primarily from minor mergers and tidally-induced transfer of material from nearby objects. Assuming isotropic accretion, twice those fractions of objects must have undergone similar processes, underlining the importance of (minor) accretion for galaxy evolution. Applications of gas counter-rotators to barred galaxy dynamics are also discussed.

M. Bureau; A. Chung

2005-12-06

68

Surface Photometry and Mass Distribution in the Spiral Galaxies NGC1087 and NGC1090  

NASA Astrophysics Data System (ADS)

Photographic surface photometry and rotation curves based on long-slit spectra have been obtained for NGC 1087 and NGC 1090. Both galaxies were originally considered to be members of the Cetus I group, but NGC 1090 has a velocity 5? higher than that of the group so is probably a background object. Total masses and luminosities for the galaxies are 2.7 0.2 1010 Msun, 1.4 1010 Lsun for NGC l087 and l.l 0.2 1011 Msun, 2.7 1010 Lsun for NGC l090, where H0 = 100 h km s-1 Mpc-1. NGC l094/ANON, apparently in the same group, are a background binary pair with combined masses > 9.4 1010 h-1 Msun and luminosities of 5.4 1010 Lsun.

Blackman, C. P.

1980-02-01

69

AN IONIZATION CONE IN THE DWARF STARBURST GALAXY NGC 5253  

E-print Network

There are few observational constraints on how the escape of ionizing photons from starburst galaxies depends on galactic parameters. Here we report on the first major detection of an ionization cone in NGC 5253, a nearby ...

Zastrow, Jordan

70

Dissipative Cloud Collissions in Barred Galaxies  

NASA Astrophysics Data System (ADS)

The evolution of a system of dissipative giant molecular clouds (GMC) moving in a galaxy is investigated using an N-body code. The GMC may collide when close enough and dissipate certain amount of their kinetic energy. The observed large scale structures are compared with simulations. In particular, we attack the problem of molecular rings in barred galaxies. The simulations showing multiple rings connected to different resonances are discussed. The inelastic collisions play the key role, thus we are able to investigate the importance of viscosity.

Palous, Jan

71

Observational study of the candidate polar-ring galaxies NGC 304 and NGC 7625  

NASA Astrophysics Data System (ADS)

We present the results of our photometric ( BV R) and spectroscopic CCD observations of NGC 304 and NGC 7625, candidate polar-ring galaxies, performed with the 6-m Special Astrophysical Observatory telescope. For NGC 304, such a study has been carried out for the first time. We have obtained basic integrated characteristics of the galaxies and determined their morphological types (S0 for NGC 304 and Sa for NGC 7625). The absolute magnitudes of the galaxies, M B = -20m.81 for NGC 304 and M B = -19m.34 for NGC7625, are indicative of their fairly high luminosities. The disk and bulge parameters have been determined forNGC 304 (0 = 20m.60, h = 3.86 kpc, e = 21m.59, r e = 1.26 kpc in the B band); these correspond to the parameters of S0-type objects. The rotation velocity for NGC 304 (200 km s-1) reaches its maximum at a galactocentric distance of 3.1 kpc, which yields a mass estimate for the galaxy of 2.8 1010 mathcal{M}_ odot . The observed photometric features at the center of NGC 304 indicate that it may have an inner ring structure, although we have failed to confirm the existence of two kinematic systems based on our spectroscopic observations. In NGC 7625, the disk makes a dominant contribution to the total brightness. The derived integrated color indices ( B-V = 0m.81 and V-R = 0m.61) agree with previous determinations of other authors. We have estimated the ?????????? in the inner galactic regions. In the outer regions, we have detected structures with bluer colors ( B-V = 0m.60), which may be indicative of a polar ring with a minor stellar component.

Karataeva, G. M.; Kuznetsov, A. N.

2008-09-01

72

The SLUGGS Survey: new evidence for a tidal interaction between the early-type galaxies NGC 4365 and NGC 4342  

NASA Astrophysics Data System (ADS)

We present new imaging and spectral data for globular clusters (GCs) around NGC 4365 and NGC 4342. NGC 4342 is a compact, X-ray luminous S0 galaxy with an unusually massive central black hole. NGC 4365 is another atypical galaxy that dominates the W' group of which NGC 4342 is a member. Using imaging from the MegaCam instrument on the Canada-France-Hawaii Telescope we identify a stream of GCs between the two galaxies and extending beyond NGC 4342. The stream of GCs is spatially coincident with a stream/plume of stars previously identified. We find that the photometric colours of the stream GCs match those associated with NGC 4342, and that the recession velocity of the combined GCs from the stream and NGC 4342 matches the recession velocity for NGC 4342 itself. These results suggest that NGC 4342 is being stripped of GCs (and stars) as it undergoes a tidal interaction with the nearby elliptical galaxy NGC 4365. We compare NGC 4342 to two well-known, tidally stripped galaxies (M32 and NGC 4486B) and find various similarities. We also discuss previous claims by Bogdn et al. that NGC 4342 cannot be undergoing significant tidal stripping because it hosts a large dark matter halo.

Blom, Christina; Forbes, Duncan A.; Foster, Caroline; Romanowsky, A. J.; Brodie, Jean P.

2014-04-01

73

Molecular Gas Kinematics in Barred Spiral Galaxies  

E-print Network

To quantify the effect that bar driven mass inflow can have on the evolution of a galaxy requires an understanding of the dynamics of the inflowing gas. In this paper we study the kinematics of the dense molecular gas in a set of seven barred spiral galaxies to determine which dynamical effects dominate. The kinematics are derived from observations of the CO J=(1-0) line made with the Berkeley-Illinois-Maryland Association (BIMA) millimeter array. We compare the observed kinematics to those predicted by ideal gas hydrodynamic and ballistic cloud-based models of gas flow in a barred potential. The hydrodynamic model is in good qualitative agreement with both the current observations of the dense gas and previous observations of the kinematics of the ionized gas. The observed kinematics indicate that the gas abruptly changes direction upon entering the dust lanes to flow directly down the dust lanes along the leading edge of the bar until the dust lanes approach the nuclear ring. Near the location where the dust lanes intersect the nuclear ring, we see two velocity components: a low velocity component, corresponding to gas on circular orbits, and a higher velocity component, which can be attributed to the fraction of gas flowing down the bar dust lane which sprays past the contact point toward the other half of the bar. The ballistic cloud-based model of the ISM is not consistent with the observed kinematics. The kinematics in the dust lanes require large velocity gradients which cannot be reproduced by an ISM composed of ballistic clouds with long mean-free-paths. Therefore, even the dense ISM responds to hydrodynamic forces.

Michael W. Regan; Kartik Sheth; Stuart N. Vogel

1999-08-10

74

AGN spiral galaxies in groups: effects of bars  

NASA Astrophysics Data System (ADS)

Aims: We explore properties of barred active spiral galaxies in groups and clusters selected from the Sloan Digital Sky Survey data release 7 (SDSS-DR7), with the aim of assessing the effects of bars on active galactic nuclei (AGN) and the role of the high density environment. Methods: We identified barred active galaxies that reside in groups and clusters by cross-correlating the total barred AGN sample with the SDSS-DR7 group catalog. With the goal of providing a suitable quantification of the effects of bars, a reliable control sample of unbarred active galaxies in high density environments with similar redshift, magnitude, morphology, and bulge size distributions was also constructed. Results: We found that the fraction of barred AGN galaxies in groups and clusters (?38%) is higher than those in the total barred AGN sample (?28%), indicating that AGN spiral galaxies in groups are more likely to be barred than those in the field. We also found that barred AGN galaxies are more concentrated towards the group centers than the other unbarred AGN group members. In addition, barred AGN host galaxies show an excess of population dominated by red colors, with respect to the control sample, suggesting that bars produce an important effect on galaxy colors of AGN hosts. The groups of AGN galaxies with and without bars show similar virial masses; however, the host groups of the barred AGN exhibit a larger fraction of red colors than the host groups of the corresponding unbarred active galaxies in the control sample. Color-magnitude relations of both host groups of AGN differ significantly: the host group colors of barred active galaxies display distributions spreading toward red populations, at the same (Mr)Group, with respect to the host groups of the unbarred AGN objects. This trend is more significant in less massive groups than in groups with MVirial> 1013.5M?. Barred active galaxies show an excess of nuclear activity compared to galaxies without bars in the control sample. We found that barred active galaxies located farther from the group-center have stronger Lum[OIII], while the nuclear activity in AGN galaxies without bars remain approximately constant with the group-centric distance. In addition, for both AGN samples, nuclear activity increases in bluer host groups however, barred active objects systematically show higher Lum[OIII] values, irrespective of the global group colors. Our findings suggest that the efficiency of bars to transport material towards the more central regions of the AGN galaxies in high density environments reveals an important dependence on the localization of objects within the group/cluster and on the host group colors.

Alonso, Sol; Coldwell, Georgina; Lambas, Diego G.

2014-12-01

75

Formation and evolution of S0 galaxies: a SAURON case study of NGC7332  

Microsoft Academic Search

We present SAURON integral-field observations of the S0 galaxy NGC7332.\\u000aExisting broad-band ground-based and HST photometry reveals a double disk\\u000astructure and a boxy bulge interpreted as a bar viewed close to edge-on. The\\u000aSAURON two-dimensional stellar kinematic maps confirm the existence of the bar\\u000aand inner disk but also uncover the presence of a cold counter-rotating stellar\\u000acomponent within

Reynier F. Peletier; Eric Emsellem; Harald Kuntschner; Kambiz Fathi; Martin Bureau; Roland Bacon; Michele Cappellari; Yannick Copin; Roger L. Davies; Tim de Zeeuw

2004-01-01

76

Stellar diffusion in barred spiral galaxies  

NASA Astrophysics Data System (ADS)

We characterize empirically the radial diffusion of stars in the plane of a typical barred disk galaxy by calculating the local spatial diffusion coefficient and diffusion time-scale for bulge-disk-halo N-body self-consistent systems which initially differ in the Safronov-Toomre-QT parameter. We find different diffusion scenarios that depend on the bar strength and on the degree of instability of the disk. Marginally stable disks, with QT ~ 1, have two families of bar orbits with different values of angular momentum and energy, which determine a large diffusion in the corotation region. In hot disks, QT > 1, stellar diffusion is reduced with respect to the case of marginally stable disks. In cold models, we find that spatial diffusion is not constant in time and strongly depends on the activity of the bar, which can move stars all over the disk recurrently. We conclude that to realistically study the impact of radial migration on the chemical evolution modeling of the Milky Way the role of the bar has to be taken into account.

Brunetti, M.; Chiappini, C.; Pfenniger, D.

2011-10-01

77

Surface Photometry of the Dwarf Elliptical Galaxies NGC 185 and NGC 205  

E-print Network

We present BVRI CCD surface photometry for the central (6'.35 X 6'.35) regions of the dwarf elliptical galaxies NGC 185 and NGC 205 in the Local Group. Surface brightness profiles of NGC 185 (R = 25". The colors of NGC 205 get bluer inward at 1" photometry, supplemented by the photometry based on the far-ultraviolet and visual images of the HST archive data, shows that there is an inversion of color at the very nucleus region (at about 1"). The implications of the redder color of the core part of the nucleus compared with neighboring regions are discussed. The amount of the excess components in the central regions of these galaxies is estimated to be ~10^5 solar luminosity. Distributions of dust clouds in the central regions of the two galaxies are also investigated.

Sang Chul Kim; Myung Gyoon Lee

1998-06-02

78

Velocity mapping and models of the elliptical galaxies NGC 720, NGC 1052, and NGC 4697  

NASA Technical Reports Server (NTRS)

CCD surface photometry and extensive long-slit spectroscopy are used to construct detailed models of the flattened ellipticals NGC 720, 1052, and 4697. The models are combined with the Jeans equations to yield predicted fields of line-of-sight velocity dispersion and streaming velocity. By comparing these fields with observed velocities, it is concluded that none of these systems can have isotropic velocity dispersion tensors, and diminishing the assumed inclination of any given galaxy tends to decrease the line-of-sight velocity dispersion and, counterintuitively, to increase the line-of-sight rotation speeds. The ratio of the line-of-sight velocity dispersion along the minor axis to that along the major axis is found to be a sensitive diagnostic of the importance of a third integral for the galaxy's structure.

Binney, J. J.; Davies, Roger L.; Illingworth, Garth D.

1990-01-01

79

The SLUGGS Survey: New evidence for a tidal interaction between the early type galaxies NGC 4365 and NGC 4342  

E-print Network

We present new imaging and spectral data for globular clusters (GCs) around NGC 4365 and NGC 4342. NGC 4342 is a compact, X-ray luminous S0 galaxy with an unusually massive central black hole. NGC 4365 is another atypical galaxy that dominates the W' group of which NGC 4342 is a member. Using imaging from the MegaCam instrument on the Canada-France-Hawaii Telescope (CFHT) we identify a stream of GCs between the two galaxies and extending beyond NGC 4342. The stream of GCs is spatially coincident with a stream/plume of stars previously identified. We find that the photometric colours of the stream GCs match those associated with NGC 4342, and that the recession velocity of the combined GCs from the stream and NGC 4342 match the recession velocity for NGC 4342 itself. These results suggest that NGC 4342 is being stripped of GCs (and stars) as it undergoes a tidal interaction with the nearby elliptical galaxy NGC 4365. We compare NGC 4342 to two well-known, tidally stripped galaxies (M32 and NGC 4486B) and find ...

Blom, Christina; Foster, Caroline; Romanowsky, Aaron J; Brodie, Jean P

2014-01-01

80

The effect of supernova rate on the magnetic field evolution in barred galaxies  

NASA Astrophysics Data System (ADS)

Context. For the first time, our magnetohydrodynamical numerical calculations provide results for a three-dimensional model of barred galaxies involving a cosmic-ray driven dynamo process that depends on star formation rates. Furthermore, we argue that the cosmic-ray driven dynamo can account for a number of magnetic features in barred galaxies, such as magnetic arms observed along the gaseous arms, magnetic arms in the inter-arm regions, polarized emission that is at the strongest in the central part of the galaxy, where the bar is situated, polarized emission that forms ridges coinciding with the dust lanes along the leading edges of the bar, as well as their very strong total radio intensity. Aims: Our numerical model probes what kind of physical processes could be responsible for the magnetic field topology observed in barred galaxies (modes, etc.). We compare our modelled results directly with observations, constructing models of high-frequency (Faraday rotation-free) polarized radio emission maps out of the simulated magnetic field and cosmic ray pattern in our modeled galaxy. We also take the effects of projection into account as well as the limited resolution. Methods: We applied global 3D numerical calculations of a cosmic-ray driven dynamo in barred galaxies with different physical input parameters such as the supernova (SN) rate. Results: Our simulation results lead to the modelled magnetic field structure similar to the one observed on the radio maps of barred galaxies. Moreover, they cast new light on a number of properties in barred and spiral galaxies, such as fast exponential growth of the total magnetic energy to the present values. The quadrupole modes of magnetic field are often identified in barred galaxies, but the dipole modes (e.g., in NGC 4631) are found very seldom. In our simulations the quadrupole configuration dominates and the dipole configuration only appears once in the case of model S100, apparently as a consequence of the choice of the random number seed. Synthetic radio maps of our models display X-type structure similar to what is observed in real galaxies. Conclusions: We conclude that a cosmic-ray driven dynamo process in barred galaxies can amplify magnetic fields efficiently. The fastest rate of magnetic field increase is 195 yr for a SN frequency of 1/50 yr-1.The obtained strength of magnetic field corresponds to the observational values (a few in spiral arms). The polarization and rotation measure maps also agree with observations. We found the effect of shifting magnetic arms in 4 models (out of the sample of 5).

Kulpa-Dybe?, K.; Nowak, N.; Otmianowska-Mazur, K.; Hanasz, M.; Siejkowski, H.; Kulesza-?ydzik, B.

2015-03-01

81

Starlight morphology of the interacting galaxy NGC 5195  

Microsoft Academic Search

We present near-infrared, red, and optical observations of NGC 5195, the interacting companion of NGC 5194 (M51). Three intrinsic components are suggested by the near-infrared data: a bright nuclear maximum, a low-contrast bar centered symmetrically on the nucleus, and a nearly face-on exponential disk. This organized near-infrared morphology contrasts strongly with the irregular appearance of optical images. Neither dust nor

J. Smith; R. D. Gehrz; G. L. Grasdalen; John A. Hackwell; R. D. Dietz; Scott D. Friedman

1990-01-01

82

NGC 6212 - An X-ray-selected active elliptical galaxy  

NASA Technical Reports Server (NTRS)

Optical and X-ray data on the elliptical galaxy NGC 6212 are reported. The X-ray flux varies by a factor of four on a time scale of months. The optical spectrum shows broad Balmer emission lines and narrow forbidden lines which are typical of low-luminosity X-ray selected Seyfert galaxies. The continuum is predominantly stellar, with no evidence for a nonthermal contribution. Narrow emission lines extend at least 11 kpc from the nucleus and are used to derive a rotation curve. The X-ray variability and relatively weak radio emission of NGC 6212 are not unusual for Seyfert galaxies.

Halpern, J. P.; Filippenko, A. V.

1986-01-01

83

HST/ACS Direct Ages of the Dwarf Elliptical Galaxies NGC 147 and NGC 185  

E-print Network

We present the deepest optical photometry for any dwarf elliptical (dE) galaxy based on Hubble Space Telescope ACS observations of the Local Group dE galaxies NGC 147 and NGC 185. The resulting F606W and F814W color-magnitude diagrams are the first to reach below the main sequence turnoff in a dE galaxy, allowing us to determine full star formation histories in these systems. The ACS fields are located ~1.5 effective radii from the galaxy center to avoid photometric crowding. While our ACS pointings in both dEs show unambiguous evidence for old and intermediate age stars, the mean age in NGC 147 is ~ 4 Gyr younger as compared to NGC 185. In NGC 147, only 40% of stars were in place 12.5 Gyrs ago (z~5), with the bulk of the remaining stellar population forming between 5 to 7 Gyr. In contrast, 70% of stars were formed in NGC 185 field more than12.5 Gyr ago with the majority of the remaining population forming between 8 to 10 Gyr. Star formation ceased in both ACS fields at least 3 Gyr ago. Previous observations ...

Geha, M; Grocholski, A; Dolphin, A; van der Marel, R P; Guhathakurta, P

2015-01-01

84

Stellar populations and Star Formation Rates in NGC 6872, the Condor galaxy  

NASA Astrophysics Data System (ADS)

We present a detailed analysis of the Spectral Energy Distributions (SEDs) of 10 kpc regions across the giant spiral galaxy NGC 6872, the Condor galaxy. We made use of archival data from the FUV (GALEX) to 22 ?m (WISE). In order to find any signature of the recent interaction 130 Myr) with its companion, the S0 galaxy IC 4970, we inspected the SED of Condor's bar. One possibility is that is would have been formed by passage of the companion. We find that it is a particularly long bar (9 kpc semi-major axis), with a size almost twice as large as the average found in other barred galaxies (4.5 kpc median in the local universe, Gadotti 2011). A bulge/bar/disk 2D decomposition using the Spitzer 3.6 ?m image and the budda package (de Souza et al. 2004; Gadotti 2008) reveals that the ratio of the bar semi-major axis to the disk scale-length is 1.4, which is a value typically found in other barred galaxies (see Fig. 1 in Gadotti 2011). The disk scale-length is ~ 7 kpc, which is extremely large (2.8 kpc median in local galaxies, Gadotti 2009). Our analysis also shows that there are no signs of recent star formation along the bar. We find no signs of a box-peanut structure near the central regions, which is also another signature of an evolved bar. Taken altogether, the evidence points to a bar formed at least a few billion years ago and the stars in the bar seem to be a fossil record of the stellar population in the galaxy before the interaction with its companion. Then, we modeled the SFH of each 10 kpc region as constant Star Formation Rate (SFR) for the past 100 Myr superposed on an exponentially decaying, longstanding SFR. We find a single exponential SFH to account for all the recent SFR of the galaxy, with no need for an additional SFR due to the interaction. Av is low all across the galaxy 0.25), but increases near 0.7) the point of collision. The SFH of the arms are asymmetric. The northeastern arm having older ages 5 Gyr) and SFH closer to constant, while the southwestern one has much younger age 1.5 Gyr) and SFR closer to a single burst. The derived total stellar mass of each region correlates linearly with the Spitzer 4.5 ?m fluxes and non-linearly with the derived bolometric luminosity.

Eufrasio, Rafael T.; De Mello, D. F.; Dwek, E.; Arendt, R. G.; Gadotti, D. A.

2014-01-01

85

Near-infrared mapping of spiral barred galaxies  

NASA Technical Reports Server (NTRS)

In external galaxies, near-infrared emission originates from stellar populations, hot dust, free-free emission from H+ regions, gaseous emission, non-thermal nucleus if any. Because of the low extinction compared to the visible, infrared wavelengths are useful to probe regions obscured by dust such as central parts where starburst phenomena can occur because of the large quantity of matter. The results presented were obtained with a 32 x 32 InSb charge injection device (CID) array cooled at 4K, at the f/36 cassegrain focus of the 3m60 Canada-France-Hawaii telescope with a spatial resolution of 0.5 inches per pixel. The objects presented are spiral barred galaxies mapped at J(1.25 microns), H(1.65 microns) and K(2.2 microns). The non-axisymetric potential due to the presence of a bar induces dynamical processes leading to the confinement of matter and peculiar morphologies. Infrared imaging is used to study the link between various components. Correlations with other wavelengths ranges and 2-colors diagrams ((J-H), (H-K)) lead to the identification of star forming regions, nucleus. Maps show structures connected to the central core. The question is, are they flowing away or toward the nucleus. Observations of M83 lead to several conclusions. The star forming region, detected in the visible and the infrared cannot be very compact and must extend to the edge of the matter concentration. The general shape of the near-infrared emission and the location of radio and 10 micron peaks suggest the confinement of matter between the inner Linblad resonances localized from CO measurements about 100 and 400 pc. The distribution of color indices in the arc from southern part to the star forming region suggests an increasing amount of gas and a time evolution eventually triggered by supernova explosions. Close to the direction of the bar, a bridge-like structure connects the arc to the nucleus with peculiar color indices. Perhaps, this structure can be linked to a height velocity component seen in UV and we can attribute it to a jet and/or a matter flow along the bar toward the nucleus, fuelling it. NGC 1068 is the nearest Seyfert 2 galaxy. It has been a subject of many studies at all wavelengths. This object was mapped at J, H, K, L and M, and in polaro-imagery. Results are given.

Gallais, P.; Rouan, D.; Lacombe, F.

1990-01-01

86

Central regions of the early-type galaxies in the NGC 3169 group  

Microsoft Academic Search

We have investigated the central regions of the galaxies in the NGC 3169\\/NGC 3166\\/NGC 3156 group with the multipupil fiber spectrograph of the 6-m telescope; the first (central) galaxy in the group is a spiral (Sa) one and the other two galaxies are lenticular ones. The group is known to have an extended HI cloud with a size of more

O. K. Sil'chenko; V. L. Afanasiev

2006-01-01

87

Line Ratio Diagnostics Along the Disc of Two Edge-on Lenticular Galaxies, NGC 4710 and NGC 5866  

NASA Astrophysics Data System (ADS)

We present interferometric observations of a multitude of CO lines and dense gas tracers in two nearby edge-on lenticular galaxies, NGC~4710 and NGC~5866. 12CO(1-0), 12CO(2-1), 13CO(1-0), 13CO(2-1), HCN(1-0), HCO+(1-0), HNC(1-0) ad HNCO(4-3) were detected in both galaxies. The detections of HNC(1-0) and HNCO(4-3) are presenting here for the first time in these early-types. Our observations reveal that the CO gas is much more extended compared with the dense gas tracers which are generally centrally concentrated except HCN(1-0) which was also detected in the outskirts of NGC~5866. The unique X-shape (two-component velocity distributions indicating nuclear disc and inner ring) position-velocity diagram (PVD) of these barred edge-on galaxies allows us to study integrated line intensity ratios as a function projected radius along the velocity components. We study the gas physical conditions of two-component molecular ISM, i.e. one traced by CO and one traced by HCN, HCO+, HNC and HNCO, in each velocity component separately seen on the PVD by performing line ratio diagnostics in three complementary ways. In the nuclear disc, the CO gas is gravitationally unstable, optically thinner, hotter and dense gas fraction is higher, while in the inner ring the gas is more settled, optically thick, colder and the dense gas fraction is lower. We also compare the line ratios to that obtained in the nucleus of other lenticular, spiral, seyfert, starburst and peculiar galaxies as well as that obtained in the GMCs of some other spirals/starbursts. We found that the gas in the nuclear discs of NGC~4710 and NGC~5866 has line ratios similar to that in the center of starburst galaxies while the gas in the inner rings show some differences. We finally perform non-LTE radiative transfer code to the two-component ISM using a multitude of tracers. The model results, which are agree with the empirical results, indicate that there is a factor of 2 difference in the density of the gas traced by CO and the one traced by high density tracers in the nuclear disc but average kinetic temperature is similar, while the gas in the inner ring is relatively colder and less dense compared with the gas in the nuclear disc.

Topal, Selcuk; Bureau, Martin; Davis, Timothy A.; Young, Lisa; Krips, Melanie

2015-01-01

88

Gaseous Vortices in Barred Spiral Galaxies  

NASA Technical Reports Server (NTRS)

During the course of examining many two-dimensional, as well as a smaller sample of three-dimensional, models of gas flows in barred spiral galaxies, we have been impressed by the ubiquitous presence fo vortex pairs, oriented roughly perpendicular to their bars, with one vortex on each side. The vortices are obvious only when viewed in the bar frame, and the centers of their velocity fields usually are near Lagrangian points L(sub 4,5). In all models that we have studied, the vortices form on essentially the same time scale as that for the development of gaseous spiral arms, typically two bar rotations. Usually the corotation radius, r(sub c), lies slightly beyond the end of the bar. Depending upon the mass distributions of the various components, gas spirals either into, or out of, the vortices: In the former case, the vortices become regions of high density, whereas the opposite is true if the gas spirals out of a vortex. The models described in this paper have low-density vortices, as do most of the models we have studied. Moreover, usually the vortex centers lie approximately within +/- 15 deg of L(sub 4,5). In the stellar dynamic limit, when pressure and viscous forces are absent, short-period orbits exist, centered on L(sub 4,5). These orbits need not cross and therefore their morphology is that of gas streamlines, that is, vortices. We believe that the gas vortices in our models are hydrodynamic analogues of closed, short-period, libration orbits centered on L(sub 4,5).

England, Martin N.; Hunter, James H., Jr.

1995-01-01

89

Diffuse and Gravitationally Stable Molecular Gas in the Post-Starburst Galaxy NGC 5195  

NASA Astrophysics Data System (ADS)

The Nobeyama Millimeter Array (NMA) has been used to make aperture synthesis CO(1 - 0) observations of the post-starburst galaxy NGC 5195. CO(1 - 0) and HCN(1 - 0) observations of NGC 5195 using the Nobeyama 45 m telescope are also presented. High-resolution (1".9 1".8 or 86 pc 81 pc or D = 9.3 Mpc) NMA maps show a strong concentration of CO emission toward the central a few 100 pc region of NGC 5195, despite the fact that the current massive star formation is suppressed there. The face-on gas surface density, ?gas, within the r < 2'' or 90pc region reaches 3.7 103 pc-2 if a Galactic NH2/ICO conversion factor is applied. The extent of the central CO peak is about 5'', or 230pc, and is elongated along the E-W direction with two-armed spiral-like structures, which are typical for barred disk galaxies. The HCN-to-CO integrated intensity rat io on the brightness temperature scale, RHCN/CO, is about 0.02 within the central r < 400 pc region. This RHCN/CO is smaller than those in starburst regions by a factor of 5 - 15. These molecular-gas properties would explain why NGC 5195 is in a post-starburst phase; most of the dense molecular cores (i.e., the very sites of massive star formation) have been consumed away by a past starburst event, and therefore a burst of massive star formation can no longer last, although a large amount of low density gas still exists. We find a steep rise of the rotation velocity toward the center of NGC 5195. As a consequence, the critical gas surface density for a local gravitational instability of the gas disk becomes very high ?crit 6.9 103 Modot pc-2), suggesting that the molecular gas in the central region of NGC 5195 is gravitationally stable! ! , in contrast to that of starburst galaxies. We propose that dense molecular gas can not be formed from remaining diffuse molecular gas because the molecular gas in the center of NGC 5195 is too stable to form dense cores via gravitational instabilities of diffuse molecular gas. The deduced very high threshold density seems to be due to a high mass concentration in NGC 5195. The known trends on the occurrence and luminosity of nuclear star formation in early-type galaxies can be understood naturally if the high threshold density is characteristic for early-type galaxies.

Kohno, Kotaro; Tosaki, Tomoka; Matsushita, Satoki; Vila-Vila, Baltasar; Shibatsuka, Toshihito; Kawabe, Ryohei

2002-08-01

90

HALOGAS: H I OBSERVATIONS AND MODELING OF THE NEARBY EDGE-ON SPIRAL GALAXY NGC 4565  

SciTech Connect

We present 21 cm observations and models of the neutral hydrogen in NGC 4565, a nearby, edge-on spiral galaxy, as part of the Westerbork Hydrogen Accretion in LOcal GAlaxieS survey. These models provide insight concerning both the morphology and kinematics of H I above, as well as within, the disk. NGC 4565 exhibits a distinctly warped and asymmetric disk with a flaring layer. Our modeling provides no evidence for a massive, extended H I halo. We see evidence for a bar and associated radial motions. Additionally, there are indications of radial motions within the disk, possibly associated with a ring of higher density. We see a substantial decrease in rotational velocity with height above the plane of the disk (a lag) of -40{sup +5} {sub -20} km s{sup -1} kpc{sup -1} and -30{sup +5} {sub -30} km s{sup -1} kpc{sup -1} in the approaching and receding halves, respectively. This lag is only seen within the inner {approx}4.'75 (14.9 kpc) on the approaching half and {approx}4.'25 (13.4 kpc) on the receding half, making this a radially shallowing lag, which is now seen in the H I layers of several galaxies. When comparing results for NGC 4565 and those for other galaxies, there are tentative indications of high star formation rate per unit area being associated with the presence of a halo. Finally, H I is found in two companion galaxies, one of which is clearly interacting with NGC 4565.

Zschaechner, Laura K.; Rand, Richard J. [Department of Physics and Astronomy, University of New Mexico, 1919 Lomas Boulevard NE, Albuquerque, NM 87131-1156 (United States); Heald, George H.; Jozsa, Gyula [Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, NL-7990 AA Dwingeloo (Netherlands); Gentile, Gianfranco, E-mail: zschaech@unm.edu, E-mail: rjr@phys.unm.edu, E-mail: heald@astron.nl, E-mail: jozsa@astron.nl, E-mail: gianfranco.gentile@ugent.be [Sterrenkundig Observatorium, Ghent University, Krijgslaan 281 S9, B-9000 Ghent (Belgium)

2012-11-20

91

Revealing galactic scale bars with the help of Galaxy Zoo  

NASA Astrophysics Data System (ADS)

We use visual classifications of the brightest 250,000 galaxies in the Sloan Digital Sky Survey Main Galaxy Sample provided by citizen scientists via the Galaxy Zoo project (www.galaxyzoo.org, Lintott et al. 2008) to identify a sample of local disc galaxies with reliable bar identifications. These data, combined with information on the atomic gas content from the ALFALFA survey (Haynes et al. 2011) show that disc galaxies with higher gas content have lower bar fractions. We use a gas deficiency parameter to show that disc galaxies with more/less gas than expected for their stellar mass are less/more likely to host bars. Furthermore, we see that at a fixed gas content there is no residual correlation between bar fraction and stellar mass. We argue that this suggests previously observed correlations between galaxy colour/stellar mass and (strong) bar fraction (e.g. from the sample in Masters et al. 2011, and also see Nair & Abraham 2010) could be driven by the interaction between bars and the gas content of the disc, since more massive, optically redder disc galaxies are observed to have lower gas contents. Furthermore we see evidence that at a fixed gas content the global colours of barred galaxies are redder than those of unbarred galaxies. We suggest that this could be due to the exchange of angular momentum beyond co-rotation which might stop a replenishment of gas from external sources, and act as a source of feedback to temporarily halt or reduce the star formation in the outer parts of barred discs. These results (published as Masters et al. 2012) combined with those of Skibba et al. (2012), who use the same sample to show a clear (but subtle and complicated) environmental dependence of the bar fraction in disc galaxies, suggest that bars are intimately linked to the evolution of disc galaxies.

Masters, Karen L.

2015-03-01

92

Bar pattern speeds in CALIFA galaxies. I. Fast bars across the Hubble sequence  

NASA Astrophysics Data System (ADS)

Context. The bar pattern speed (?b) is defined as the rotational frequency of the bar, and it determines the bar dynamics. Several methods have been proposed for measuring ?b. The non-parametric method proposed by Tremaine & Weinberg (1984, ApJ, 282, L5; TW) and based on stellar kinematics is the most accurate. This method has been applied so far to 17 galaxies, most of them SB0 and SBa types. Aims: We have applied the TW method to a new sample of 15 strong and bright barred galaxies, spanning a wide range of morphological types from SB0 to SBbc. Combining our analysis with previous studies, we investigate 32 barred galaxies with their pattern speed measured by the TW method. The resulting total sample of barred galaxies allows us to study the dependence of ?b on galaxy properties, such as the Hubble type. Methods: We measured ?b using the TW method on the stellar velocity maps provided by the integral-field spectroscopy data from the CALIFA survey. Integral-field data solve the problems that long-slit data present when applying the TW method, resulting in the determination of more accurate ?b. In addition, we have also derived the ratio ? of the corotation radius to the bar length of the galaxies. According to this parameter, bars can be classified as fast (? < 1.4) and slow (? > 1.4). Results: For all the galaxies, ? is compatible within the errors with fast bars. We cannot rule out (at 95% level) the fast bar solution for any galaxy. We have not observed any significant trend between ? and the galaxy morphological type. Conclusions: Our results indicate that independent of the Hubble type, bars have been formed and then evolve as fast rotators. This observational result will constrain the scenarios of formation and evolution of bars proposed by numerical simulations.

Aguerri, J. A. L.; Mndez-Abreu, J.; Falcn-Barroso, J.; Amorin, A.; Barrera-Ballesteros, J.; Cid Fernandes, R.; Garca-Benito, R.; Garca-Lorenzo, B.; Gonzlez Delgado, R. M.; Husemann, B.; Kalinova, V.; Lyubenova, M.; Marino, R. A.; Mrquez, I.; Mast, D.; Prez, E.; Snchez, S. F.; van de Ven, G.; Walcher, C. J.; Backsmann, N.; Cortijo-Ferrero, C.; Bland-Hawthorn, J.; del Olmo, A.; Iglesias-Pramo, J.; Prez, I.; Snchez-Blzquez, P.; Wisotzki, L.; Ziegler, B.

2015-04-01

93

Dwarf galaxies in the Dynamically Evolved NGC 1407 Group  

E-print Network

The NGC 1407 Group stands out among nearby structures by its properties that suggest it is massive and evolved. It shares properties with entities that have been called fossil groups: the 1.4 magnitude differential between the dominant elliptical galaxy and the second brightest galaxy comes close to satisfying the definition that has been used to define the fossil class. There are few intermediate luminosity galaxies, but a large number of dwarfs in the group. We estimate there are 250 group members to the depth of our survey. The slope of the faint end of the luminosity function (reaching M_R = -12) is alpha = -1.35. Velocities for 35 galaxies demonstrate that this group with one dominant galaxy has a mass of 7 X 10^13 M_sun and M/L_R = 340. Two galaxies in close proximity to NGC 1407 have very large blueshifts. The most notable is the second brightest galaxy, NGC 1400, with a velocity of -1072 km/s with respect to the group mean. We report the detection of X-ray emission from this galaxy and from the group.

Neil Trentham; R. Brent Tully; Andisheh Mahdavi

2006-05-10

94

ORBITAL SUPPORT OF FAST AND SLOW INNER BARS IN DOUBLE-BARRED GALAXIES  

SciTech Connect

We analyze how the orbital support of the inner bar in a double-barred galaxy (nested bars) depends on the angular velocity (i.e., pattern speed) of this bar. We study orbits in seven models of double bars using the method of invariant loops. The range of pattern speed is covered exhaustively. We find that not all pattern speeds are allowed when the inner bar rotates in the same direction as the outer bar. Below a certain minimum pattern speed orbital support for the inner bar abruptly disappears, while at high values of this speed the orbits indicate an increasingly round bar that looks more like a twist in the nuclear isophotes than a dynamically independent component. For values between these two extremes, orbits supporting the inner bar extend further out as the bar's pattern speed decreases, their corresponding loops become more eccentric, pulsate more, and their rotation becomes increasingly non-uniform, as they speed up and slow down in their motion. Lower pattern speeds also lead to a less coherent bar, as the pulsation and acceleration increasingly varies among the loops supporting the inner bar. The morphologies of fast and slow inner bars expected from the orbital structure studied here have been recently recovered observationally by decomposition of double-barred galaxies. Our findings allow us to link the observed morphology to the dynamics of the inner bar.

Maciejewski, Witold; Small, Emma E., E-mail: wxm@astro.livjm.ac.u [Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead, CH41 1LD (United Kingdom)

2010-08-10

95

The Bar-Halo Interaction in SB Galaxies  

E-print Network

We describe fully self-consistent N-body experiments of barred galaxies with massive halos. A rotating bar is braked through dynamical friction with the halo, which occurs on a short time scale when the central density of the halo is high. On the other hand, friction is weak in a model with a central halo density low enough that the disk dominates the rotation curve in the inner parts; this model supports a fast bar for a Hubble time. We conclude that real barred galaxies in which the bar rotates rapidly, which is believed to be the rule, must have close to maximum disks.

Victor P. Debattista; J. A. Sellwood

1996-10-01

96

Globular cluster system of the NGC7626\\/NGC7619 pair of giant elliptical galaxies in the Pegasus I group  

Microsoft Academic Search

NGC 7619 and NGC 7626 are the two dominant elliptical galaxies in the Pegasus I group (~50 Mpc). This group includes about 13 members and firm evidence that it hosts an ongoing merger. This kind of event is one of the most powerful ways of modifying the galaxies and group structure, morphologies and contents. The globular clusters (GCs) are known

Favio Raul Faifer; Carlos G. Escudero; Analia Smtih Castelli; Juan C. Forte Forte; Lilia P. Bassino

2011-01-01

97

Merging Cold Fronts in the Galaxy Pair NGC 7619 and NGC 7626  

E-print Network

We present results from {\\it Chandra} observations of the galaxy pair NGC 7619 and NGC 7626, the two dominant members of the Pegasus group. The X-ray images show a brightness edge associated with each galaxy, which we identify as merger cold fronts. The edges are sharp, and the axes of symmetry of the edges are roughly anti-parallel, suggesting that these galaxies are falling towards one another in the plane of the sky. The detection of merger cold fronts implies a merging subgroup scenario, since the alternative is that the galaxies are falling into a pre-existing $\\sim1$ keV halo without a dominant galaxy of its own, and such objects are not observed. We estimate the 3D velocities from the cold fronts and show that the velocity vectors are indeed most likely close to the plane of the sky, with a relative velocity of $\\sim1190\\kms$. The relative velocity is consistent with what is expected from the infall of two roughly equal mass subgroups whose total viral mass equals that of the Pegasus group. We conclude that the Pegasus cluster is currently forming from a major merger of two subgroups, dominated by NGC 7619 and NGC 7626. NGC 7626 contains a strong radio source, a core with two symmetric jets and radio lobes. Although we find no associated structure in the X-ray surface brightness map, the temperature map reveals a clump of cool gas just outside the southern lobe, presumably entrained by the lobe, and an extension of cooler gas into the lobe itself. The jet axis is parallel with the projected direction of motion of NGC 7626 (inferred from the symmetry axis of the merger cold front), and the southern leading jet is foreshortened as compared to the northern trailing one, possibly due to the additional ram pressure the forward jet encounters.

S. W. Randall; C. Jones; R. Kraft; W. R. Forman; E. O'Sullivan

2009-01-22

98

How can double-barred galaxies be long-lived?  

E-print Network

Double-barred galaxies account for almost one third of all barred galaxies, suggesting that secondary stellar bars, which are embedded in large-scale primary bars, are long-lived structures. However, up to now it has been hard to self-consistently simulate a disc galaxy that sustains two nested stellar bars for longer than a few rotation periods. N-body/hydrodynamical simulations including star formation recipes have been performed. Their properties have been compared with the most recent observational data in order to prove that they are representative of double-barred galaxies, even SB0. Overlaps in dynamical resonances and bar modes have been looked for using Fourier spectrograms. Double-barred galaxies have been successfully simulated with lifetimes as long as 7 Gyr. The stellar population of the secondary bar is younger on average than for the primary large-scale bar. An important feature of these simulations is the absence of any resonance overlap for several Gyr. In particular, there is no overlap betw...

Wozniak, Herve

2015-01-01

99

How can double-barred galaxies be long-lived?  

NASA Astrophysics Data System (ADS)

Context. Double-barred galaxies account for almost one third of all barred galaxies, suggesting that secondary stellar bars, which are embedded in large-scale primary bars, are long-lived structures. However, up to now it has been hard to self-consistently simulate a disc galaxy that sustains two nested stellar bars for longer than a few rotation periods. Aims: The dynamical and physical requirements for long-lived triaxiality in the central region of galaxies still need to be clarified. Methods: N-body/hydrodynamical simulations including star formation recipes have been performed. Their properties (bar lengths, pattern speeds, age of stellar population, and gas content) have been compared with the most recent observational data in order to prove that they are representative of double-barred galaxies, even SB0. Overlaps in dynamical resonances and bar modes have been looked for using Fourier spectrograms. Results: Double-barred galaxies have been successfully simulated with lifetimes as long as 7 Gyr. The stellar and gaseous distributions in the central regions are time dependent and display many observed morphological features (circumnuclear rings, pseudo-bulges, triaxial bulges, ovals, etc.) typical of barred galaxies, even early-type. The stellar population of the secondary bar is younger on average than for the primary large-scale bar. An important feature of these simulations is the absence of any resonance overlap for several Gyr. In particular, there is no overlap between the primary bar inner Lindblad resonance and the secondary bar corotation. Therefore, mode coupling cannot sustain the secondary bar mode. Star formation is identified here as possibly being responsible for bringing energy to the nuclear mode. Star formation is also responsible for limiting the amount of gas in the central region which prevents the orbits sustaining the secondary bar from being destroyed. Therefore, the secondary bar can dissolve but reappear after ?1 Gyr as the associated wave is persistent as long as central star formation is active. When star formation is switched off the dynamical perturbation associated with the secondary bar needs several Gyr to fully vanish, although the central morphological signature is almost undetectable after 2 Gyr. Conclusions: Double-bars can be long-lived in numerical simulations with a gaseous component, even in the absence of overlap of resonances or mode coupling, provided that star formation remains active, even moderately, in the central region where the nuclear bar lies.

Wozniak, Herv

2015-03-01

100

MASSIVE CLUSTERS IN THE INNER REGIONS OF NGC 1365: CLUSTER FORMATION AND GAS DYNAMICS IN GALACTIC BARS  

SciTech Connect

Cluster formation and gas dynamics in the central regions of barred galaxies are not well understood. This paper reviews the environment of three 10{sup 7} M {sub sun} clusters near the inner Lindblad resonance (ILR) of the barred spiral NGC 1365. The morphology, mass, and flow of H I and CO gas in the spiral and barred regions are examined for evidence of the location and mechanism of cluster formation. The accretion rate is compared with the star formation rate to infer the lifetime of the starburst. The gas appears to move from inside corotation in the spiral region to looping filaments in the interbar region at a rate of approx6 M {sub sun} yr{sup -1} before impacting the bar dustlane somewhere along its length. The gas in this dustlane moves inward, growing in flux as a result of the accretion to approx40 M {sub sun} yr{sup -1} near the ILR. This inner rate exceeds the current nuclear star formation rate by a factor of 4, suggesting continued buildup of nuclear mass for another approx0.5 Gyr. The bar may be only 1-2 Gyr old. Extrapolating the bar flow back in time, we infer that the clusters formed in the bar dustlane outside the central dust ring at a position where an interbar filament currently impacts the lane. The ram pressure from this impact is comparable to the pressure in the bar dustlane, and both are comparable to the pressure in the massive clusters. Impact triggering is suggested. The isothermal assumption in numerical simulations seems inappropriate for the rarefaction parts of spiral and bar gas flows. The clusters have enough lower-mass counterparts to suggest they are part of a normal power-law mass distribution. Gas trapping in the most massive clusters could explain their [Ne II] emission, which is not evident from the lower-mass clusters nearby.

Elmegreen, Bruce G. [IBM Research Division, T.J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598 (United States); Galliano, Emmanuel [Observatorio Nacional, Rua General Jose Cristino, 77, 20921-400 Sao Cristovao, Rio de Janeiro (Brazil); Alloin, Danielle, E-mail: bge@watson.ibm.co, E-mail: egallian@on.b, E-mail: danielle.alloin@cea.f [Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, IRFU/Service d'Astrophysique, Bat. 709, CEA/Saclay, F-91191 Gif-sur-Yvette Cedex (France)

2009-10-01

101

Galactic rings and secular evolution in barred galaxies  

NASA Astrophysics Data System (ADS)

Rings are common in galaxies. Several kinds of rings are known: collisional, polar, and resonance rings, of which the latter is by far most common. Resonance rings are prime tracers of the underlying dynamical structure of disk galaxies, in particular of orbital resonances and of manifolds. Rings are also indicators of angular momentum transport, and this is a key factor in secular evolution (see the various reviews in Falcn-Barroso & Knapen 2012). Resonance rings come in three flavours, primarily defined by their size, namely nuclear, inner, and outer rings. From studies like those of Buta (1995), Knapen (2005) and Comern et al. (2010, 2013) we know that the radii of nuclear rings range from a few tens of parsec to some 3.5 kpc, while inner rings and outer rings have typical radii of 1.2 and 2.5-3 times the length of the bar. Many host galaxies of rings are barred, but so are most galaxies in general. Some 20% of all rings occur in non-barred galaxies, which implies that rings do not, or hardly, occur preferentially in barred galaxies (Knapen 2005, Comern et al. 2010, 2013). In most non-barred ringed galaxies an oval, a past interaction, or even a prominent spiral pattern lies at the dynamical origin of the ring, but this needs additional scrutiny. From an inventory of all known nuclear rings, Comern et al. (2010) reach the following conclusions. Star-forming nuclear rings occur in 20 +/- 2% of disk galaxies with -3 < T < 7; 18/96 occur in disk galaxies without a bar (19%); they are found in S0 to Sd galaxies, peaking in types Sab Sb; when nuclear rings occur in barred galaxies, the ring radius is limited to one quarter of the bar radius; and stronger bars host smaller rings (cf. Knapen 2005). We are now using the Spitzer Survey of Spiral Structure in Galaxies (S4G; Sheth et al. 2010) to expand our survey to inner and outer rings (Comern et al. 2013). We aim to study the relations between ring and host properties - as we did before for nuclear rings. We will use the S4G sample size and image depth to reach further insight into the secular evolution of galaxies by measuring structural properties of rings, as well as those of components like bars and disks. We will then be able to tackle outstanding questions such as the origin of rings in non-barred galaxies, and how exactly ring properties are determined by the bar.

Knapen, Johan H.

2015-03-01

102

Black Holes in Bulgeless Galaxies: An XMM-Newton Investigation of NGC 3367 AND NGC 4536  

NASA Technical Reports Server (NTRS)

The vast majority of optically identified active galactic nuclei (AGNs) in the local Universe reside in host galaxies with prominent bulges, supporting the hypothesis that black hole formation and growth is fundamentally connected to the build-up of galaxy bulges. However, recent mid-infrared spectroscopic studies with Spitzer of a sample of optically "normal" late-type galaxies reveal remarkably the presence of high-ionization [NeV] lines in several sources, providing strong evidence for AGNs in these galaxies. We present follow-up X-ray observations recently obtained with XMM-Newton of two such sources, the late-type optically normal galaxies NGC 3367 and NGC 4536. Both sources are detected in our observations. Detailed spectral analysis reveals that for both galaxies, the 2-10 keV emission is dominated by a power law with an X-ray luminosity in the L(sub 2- 10 keV) approximates 10(exp 39) - 10(exp 40) ergs/s range, consistent with low luminosity AGNs. While there is a possibility that X-ray binaries account for some fraction of the observed X-ray luminosity, we argue that this fraction is negligible. These observations therefore add to the growing evidence that the fraction of late-type galaxies hosting AGNs is significantly underestimated using optical observations alone. A comparison of the midinfrared [NeV] luminosity and the X-ray luminosities suggests the presence of an additional highly absorbed X-ray source in both galaxies, and that the black hole masses are in the range of 10(exp 5) - 10(exp 7) solar M for NGC 3367 and 10(exp 4) - (exp 10) solar M for NGC 4536

McAlpine, W.; Satyapal, S.; Gliozzi, M.; Cheung, C. C.; Sambruna, R. M.; Eracleous, Michael

2012-01-01

103

RXTE observations of the Seyfert 2 galaxy NGC4507:  

NASA Astrophysics Data System (ADS)

Preliminary results of the RXTE observation of the Seyfert 2 Galaxy NGC4507 are presented. The observed broadband [4-100 keV] spectrum is intrinsically hard (Gamma = 1.2); an iron line is detected with a relatively high equivalent width (EW = 400 eV). The remaining calibration uncertanties are briefly discussed, as well as the scientific implications of our results.

Guainazzi, M.; Matt, G.; Piro, L.; Robba, N. R.

104

NGC 5523: An Isolated Product of a Soft Galaxy Merger  

NASA Astrophysics Data System (ADS)

Isolated galaxies are sometimes considered to be systems that have evolved with minimal influence from galaxy-galaxy interactions. The late-type isolated spiral galaxy NGC 5523 offers a counter example to this assumption. Our analysis of multi-band imaging of this system shows a number of unusual features consistent with NGC 5523 (D=20 Mpc) having experienced a significant merger: (1) Near infrared imaging from WHIRC on the WIYN 3.5-m telescope and the Spitzer Space Telescope reveal a nucleated bulge-like structure that is offset from the center of the outer disk by approximately 1 kpc. (2) A feature with characteristics of a tidal stream extends from the bulge structure along the disk. (3) The outermost disk is somewhat asymmetric and appears to have a low density of older stars. We interpret these properties as the results of a past non-disruptive merger between NGC 5523 and a former companion galaxy, which raises the possibility that some galaxies are isolated because they have merged with former companions.

Fulmer, Leah; Gallagher, John S.; Xia, Zishan

2015-01-01

105

Bar strength and star formation activity in late-type barred galaxies.  

NASA Astrophysics Data System (ADS)

With the prime aim of better probing and understanding the intimate link between star formation activity and the presence of bars, a representative sample of 32 non-interacting late-type galaxies with well-determined bar properties has been selected. We show that all the galaxies displaying the highest current star forming activity have both strong and long bars. Conversely not all strong and long bars are intensively creating stars. Except for two cases, strong bars are in fact long as well. Numerical simulations allow to understand these observational facts as well as the connection between bar axis ratio, star formation activity, and chemical abundance gradient: Very young strong bars are first characterized by a raging episode of star formation and two different radial gaseous abundance gradients, one steep in the bar and one shallow in the disc. Then, principally due to gas consumption, galaxies progressively fall back in a more quiescent state with a nearly flat abundance gradient across the whole galaxy. On the contrary, weak bars are unable to trigger significant star formation or to generate flat abundance gradients. The selected galaxies have tentatively been classified in four classes corresponding to main stages of secular evolution scenario.

Martinet, L.; Friedli, D.

1997-07-01

106

The Cuspy Liner Nucleus of the S0/a Galaxy NGC 2681  

NASA Astrophysics Data System (ADS)

The nucleus of the bulge-dominated, multiply barred S0/a galaxy NGC 2681 is studied in detail using the high-resolution Hubble Space Telescope Faint Object Camera (FOC), Near-Infrared Camera and Multiobject Spectrometer (NICMOS) imaging, and the Faint Object Spectrograph (FOS). The ionized gas central velocity dispersion is found to increase by a factor ~2 when narrowing the aperture from R~1.5" (ground) to R~0.1" (FOS). Dynamical modeling of these velocity dispersions suggests that NGC 2681 does host a supermassive black hole (BH) for which one can estimate a firm mass upper limit MBH<~6107 Msolar. This upper limit is consistent with the relation between the central BH mass and velocity dispersion MBH-? known for other galaxies. The emission-line ratios place the nucleus of NGC 2681 among LINERs. It is likely that the emission-line region comes from a rather mild, but steady, feeding of gas to the central BH in this galaxy. The inner stellar population lacks any measurable color gradient (to a radius of 0.6 kpc) from the infrared to the ultraviolet, consistently with FOC, FOS, and IUE data, all indicating that this system underwent a starburst ~1 Gyr ago that encompassed its whole interior, down to its very center. The most likely source of such a widely distributed starburst is the dumping of tidally extruded gas from a galaxy neighbor. If so, then NGC 2681 can be considered as the older brother of M82, seen face-on as opposed to the edge-on view we have for M82. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

Cappellari, Michele; Bertola, Francesco; Burstein, David; Buson, Lucio M.; Greggio, Laura; Renzini, Alvio

2001-04-01

107

An extremely optically dim tidal feature in the gas-rich interacting galaxy group NGC 871/NGC 876/NGC 877  

NASA Astrophysics Data System (ADS)

We present Giant Metrewave Radio Telescope H I observations and deep Canada-France-Hawaii Telescope (CFHT) MegaCam optical images of the gas-rich interacting galaxy group NGC 871/NGC 876/NGC 877 (hereafter NGC 871/6/7). Our high-resolution data sets provide a census of the H I and stellar properties of the detected gas-rich group members. In addition to a handful of spiral, irregular and dwarf galaxies, this group harbours an intriguing H I feature, AGC 749170, that has a gas mass of 109.3 M?, a dynamical-to-gas mass ratio of 1 (assuming that the cloud is rotating and in dynamical equilibrium) and no optical counterpart in previous imaging. Our observations have revealed a faint feature in the CFHT g' and r' bands; if it is physically associated with AGC 749170, the latter has M/L_g >1000 M_{{?}}/L_{{?}} as well as a higher metallicity (estimated using photometric colours) and a significantly younger stellar population than the other low-mass gas-rich group members. These properties, as well as its spectral and spatial location with respect to its suspected parent galaxies, strongly indicate a tidal origin for AGC 749170. Overall, the H I properties of AGC 749170 resemble those of other optically dark/dim clouds that have been found in groups. These clouds could represent a class of relatively long-lived H I-rich tidal remnants that survive in intermediate-density environments.

Lee-Waddell, K.; Spekkens, K.; Cuillandre, J.-C.; Cannon, J.; Haynes, M. P.; Sick, J.; Chandra, P.; Patra, N.; Stierwalt, S.; Giovanelli, R.

2014-10-01

108

Numerical Simulations of Interacting Gas-Rich Barred Galaxies  

E-print Network

Using an N-body+SPH code we have performed numerical simulations to investigate the dynamical effects of an interaction between an initially barred galaxy and a small spherical companion. In the models described here the small companion passes through the disk of the larger galaxy perpendicular to its plane. The impact positions and times are varied with respect to the evolutionary phase of the bar and disc. The interactions produce expanding ring structures, offset bars, spokes, and other asymmetries in the stars and gas. They also affect the strength and pattern speed of the bar.

I. Berentzen; C. H. Heller; E. Athanassoula; K. J. Fricke

1999-04-12

109

The Nuclear Spectrum of the Radio Galaxy NGC 5128 (Centaurus A)  

NASA Technical Reports Server (NTRS)

We present near-infrared spectra of the nucleus of the nearby radio galaxy NGC 5128 (Centaurus A). The observed emission line strengths suggest that NGC 5128 should be classified as a LINER, and appear to be powered by shocks.

Simpson, C.; Meadows, V.

1998-01-01

110

Central regions of the early-type galaxies in the NGC 3169 group  

NASA Astrophysics Data System (ADS)

We have investigated the central regions of the galaxies in the NGC 3169/NGC 3166/NGC 3156 group with the multipupil fiber spectrograph of the 6-m telescope; the first (central) galaxy in the group is a spiral (Sa) one and the other two galaxies are lenticular ones. The group is known to have an extended HI cloud with a size of more than 100 kpc that is associated in its position, orientation, and rotation with the central galaxy NGC 3169. The mean age of the stellar populations in the centers of all three galaxies has been found to be approximately the same, 1 Gyr. Since the galaxies are early-type ones and since NGC 3166 and NGC 3156 show no global star formation, we are dealing here with a synchronous star formation burst in the centers of all three galaxies.

Sil'chenko, O. K.; Afanasiev, V. L.

2006-08-01

111

Bars and secular evolution in disk galaxies: Theoretical input  

NASA Astrophysics Data System (ADS)

Bars play a major role in driving the evolution of disk galaxies and in shaping their present properties. They cause angular momentum to be redistributed within the galaxy, emitted mainly from (near-)resonant material at the inner Lindblad resonance of the bar, and absorbed mainly by (near-)resonant material in the spheroid (i.e., the halo and, whenever relevant, the bulge) and in the outer disk. Spheroids delay and slow down the initial growth of the bar they host, but, at the later stages of the evolution, they strengthen the bar by absorbing angular momentum. Increased velocity dispersion in the (near-)resonant regions delays bar formation and leads to less strong bars. When bars form they are vertically thin, but soon their inner parts puff up and form what is commonly known as the boxy/peanut bulge. This gives a complex and interesting shape to the bar which explains a number of observations and also argues that the COBE/DIRBE bar and the Long bar in our Galaxy are, respectively, the thin and the thick part of a single bar. The value of the bar pattern speed may be set by optimising the balance between emitters and absorbers, so that a maximum amount of angular momentum is redistributed. As they evolve, bars grow stronger and rotate slower. Bars also redistribute matter within the galaxy, create a disky bulge (pseudo-bulge), increase the disk scale-length and extent and drive substructures such as spirals and rings. They also affect the shape of the inner part of the spheroid, which can evolve from spherical to triaxial.

Athanassoula, E.

2013-10-01

112

Hydrogen Fluoride toward Luminous Nearby Galaxies: NGC 253 and NGC 4945  

E-print Network

We present the detection of hydrogen fluoride, HF, in two luminous nearby galaxies NGC 253 and NGC 4945 using the Heterodyne Instrument for the Far-Infrared (HIFI) on board the Herschel Space Observatory. The HF line toward NGC 253 has a P-Cygni profile, while an asymmetric absorption profile is seen toward NGC 4945. The P-Cygni profile in NGC 253 suggests an outflow of molecular gas with a mass of M(H$_2$)$_{out}$ $\\sim$ 1 $\\times$ 10$^7$ M$_\\odot$ and an outflow rate as large as \\.{M} $\\sim$ 6.4 M$_\\odot$ yr$^{-1}$. In the case of NGC 4945, the axisymmetric velocity components in the HF line profile is compatible with the interpretation of a fast-rotating nuclear ring surrounding the nucleus and the presence of inflowing gas. The gas falls into the nucleus with an inflow rate of $\\le$ 1.2 M$_\\odot$ yr$^{-1}$, inside a inner radius of $\\le$ 200 pc. The gas accretion rate to the central AGN is much smaller, suggesting that the inflow can be triggering a nuclear starburst. From these results, the HF $J = 1-0$ ...

Monje, R R; Falgarone, E; Lis, D C; Neufeld, D A; Phillips, T G; Gsten, R

2014-01-01

113

Radio Recombination Lines from Starbursts: NGC 3256, NGC 4945 and the Circinus Galaxy  

E-print Network

A renewed attempt to detect radio recombination lines from external galaxies has resulted in the measurement of lines from several bright starburst galaxies. The lines are produced by hydrogen ionized by young, high-mass stars and are diagnostic of the conditions and gas dynamics in the starburst regions without problems of dust obscuration. We present here detections of the lines H91alpha and H92alpha near 8.6 GHz from the starburst nuclei in NGC 3256, NGC 4945, and the Circinus galaxy using the ATCA and VLA. Modelling the line emitting region as a collection of H II regions, we derive the required number of H II regions, their temperature, density, and distribution.

A. L. Roy; W. M. Goss; Niruj R. Mohan; T. Oosterloo; K. R. Anantharamaiah

2004-11-04

114

Neutral hydrogen in the starburst galaxy NGC3690/IC694  

NASA Technical Reports Server (NTRS)

Researchers made observations of the neutral hydrogen (HI) emission structure surrounding the very deep absorption peak (observed earlier by Dickey (1986)) in the galaxy pair NGC3690/IC694. This galaxy pair is highly luminous in the far infrared, and known to exhibit extensive star formation as well as nuclear activity. Knowledge of the spatial distribution and velocity structure of the HI emission is of great importance to the understanding of the dynamics of the interaction and the resulting environmental effects on the galaxies.

Tolstoy, E.; Dickey, John M.; Israel, F. P.

1990-01-01

115

The BeppoSAX long looks at the Seyfert 1 galaxies NGC 5548 and NGC 3783  

NASA Astrophysics Data System (ADS)

BeppoSAX has observed two Seyfert 1 galaxies, namely NGC 5548 and NGC 3783, for ~8 days and ~5 days, respectively. The long exposures have provided very high quality spectra. We were able to detect the high energy cut-off in these two sources for the first time. In addition, we observed an emission feature at 0.57 keV, probably due to the OVII K? transition. Flux and spectral variations on time scales of hours and days were observed. A time resolved spectral analysis indicates that this spectral variability is due to a change of the intrinsic power law slope. .

de Rosa, A.; Piro, L.; Nicastro, F.; Grandi, P.; Dadina, M.; Fiore, F.; Haardt, F.; Kaastra, J.; Maraschi, L.; Matt, G.; Mineo, T.; Perola, G. C.; Petrucci, P. O.; Treves, A.

2001-12-01

116

The H II regions of the irregular galaxy, NGC 3239  

SciTech Connect

The luminosities of the 88 H II regions of NGC 3239, very likely a merging galaxy system, were measured by digital analysis of a photographic plate (20 A bandwidth filter). Despite evidence for earlier starburst activity, the present H II luminosity function is very similar to that for the LMC, including a supergiant H II region of 0.76 the luminosity of 30 Dor. The measured H II regions of NGC 3239 have an H-alpha total luminosity of 1.3 x 10 to the 40th erg/s. 13 refs.

Krienke, K.; Hodge, P. (Seattle Pacific University, WA (USA) Washington, University, Seattle (USA))

1991-03-01

117

Characterizing Barred Galaxies in the Abell 901/902 Supercluster  

E-print Network

In dense clusters, higher densities at early epochs as well as physical processes, such as ram pressure stripping and tidal interactions become important, and can have direct consequences for the evolution of bars and their host disks. To study bars and disks as a function of environment, we are using the STAGES ACS HST survey of the Abell 901/902 supercluster (z~0.165), along with earlier field studies based the SDSS and the Ohio State University Bright Spiral Galaxy Survey (OSUBSGS). We explore the limitations of traditional methods for characterizing the bar fraction, and in particular highlight uncertainties in disk galaxy selection in cluster environments. We present an alternative approach for exploring the proportion of bars, and investigate the properties of bars as a function of host galaxy color, Sersic index, stellar mass, star formation rate (SFR), specific SFR, and morphology.

I. Marinova; S. Jogee; D. Bacon; M. Balogh; M. Barden; F. D. Barazza; E. F. Bell; A. Bohm; J. A. R. Caldwell; M. E. Gray; B. Haussler; C. Heymans; K. Jahnke; E. van Kampen; S. Koposov; K. Lane; D. H. McIntosh; K. Meisenheimer; C. Y. Peng; H. -W. Rix; S. F. Sanchez; A. Taylor; L. Wisotzki; C. Wolf; X. Zheng

2008-02-26

118

Testing MOND gravity in the shell galaxy NGC 3923  

NASA Astrophysics Data System (ADS)

Context. The elliptical galaxy NGC 3923 is surrounded by numerous stellar shells that are concentric arcs centered on the Galactic core. They are very likely a result of a minor merger and they consist of stars in nearly radial orbits. For a given potential, the shell radii at a given time after the merger can be calculated and compared to observations. The MOdified Newtonian Dynamics (MOND) is a theory that aims to solve the missing mass problem by modifying the laws of classical dynamics in the limit of small accelerations. Hernquist & Quinn (1987, ApJ, 312, 1) claimed that the shell distribution of NGC 3923 contradicted MOND, but Milgrom (1988, ApJ, 332, 86) found several substantial insufficiencies in their work. Aims: We test whether the observed shell distribution in NGC 3923 is consistent with MOND using the current observational knowledge of the shell number and positions and of the host galaxy surface brightness profile, which supersede the data available in the 1980s when the last (and negative) tests of MOND viability were performed on NGC 3923. Methods: Using the 3.6 ?m bandpass image of NGC 3923 from the Spitzer space telescope we construct the mass profile of the galaxy. The evolution of shell radii in MOND is then computed using analytical formulae. We use 27 currently observed shells and allow for their multi-generation formation, unlike the Hernquist & Quinn one-generation model that used the 18 shells known at the time. Results: Our model reproduces the observed shell radii with a maximum deviation of ~5% for 25 out of 27 known shells while keeping a reasonable formation scenario. A multi-generation nature of the shell system, resulting from successive passages of the surviving core of the tidally disrupted dwarf galaxy, is one of key ingredients of our scenario supported by the extreme shell radial range. The 25 reproduced shells are interpreted as belonging to three generations.

Blek, M.; Jungwiert, B.; Jlkov, L.; Ebrov, I.; Bartokov, K.; K?ek, M.

2013-11-01

119

Soft X-ray emission from the spiral galaxy NGC 1313  

E-print Network

The nearby barred spiral galaxy NGC 1313 has been observed with the PSPC instr- ument on board the ROSAT X-ray satellite. Ten individual sources are found. Three sources (X-1, X-2 and X-3 [SN~1978K]) are very bright (~10^40 erg/s) and are unusual in that analogous objects do not exist in our Galaxy. We present an X-ray image of NGC~1313 and \\xray spectra for the three bright sources. The emission from the nuclear region (R ~~ 10^3 Msun. Additional emission (L_X ~ 10^39 erg/s) in the nuclear region extends out to ~2.6 kpc and roughly follows the spiral arms. This emission is from 4 sources with luminosity of several x 10^38 erg/s, two of which are consistent with emission from population I sources (e.g., supernova remnants, and hot interstellar gas which has been heated by supernova remnants). The other two sources could be emission from population II sources (e.g., low-mass \\xray binaries). The bright sources X-2 and SN~1978K are positioned in the southern disk of NGC~1313. X-2 is variable and has no optical ...

Colbert, E J M; Schlegel, E M; Ryder, S D; Colbert, Edward J M; Petre, R; Schlegel, E M; Ryder, S D

1995-01-01

120

Deficiency of ''Thin'' Stellar Bars in Seyfert Host Galaxies  

NASA Technical Reports Server (NTRS)

Using all available major samples of Seyfert galaxies and their corresponding control samples of closely matched non-active galaxies, we find that the bar ellipticities (or axial ratios) in Seyfert galaxies are systematically different from those in non-active galaxies. Overall, there is a deficiency of bars with large ellipticities (i.e., 'fat' or 'weak' bars) in Seyferts, compared to non-active galaxies. Accompanied with a large dispersion due to small number statistics, this effect is strictly speaking at the 2 sigma level. To obtain this result, the active galaxy samples of near-infrared surface photometry were matched to those of normal galaxies in type, host galaxy ellipticity, absolute magnitude, and, to some extent, in redshift. We discuss possible theoretical explanations of this phenomenon within the framework of galactic evolution, and, in particular, of radial gas redistribution in barred galaxies. Our conclusions provide further evidence that Seyfert hosts differ systematically from their non-active counterparts on scales of a few kpc.

Shlosman, Isaac; Peletier, Reynier F.; Knapen, Johan

1999-01-01

121

Constraining Galaxy Evolution With Bulge-Disk-Bar Decomposition  

E-print Network

Structural decomposition of galaxies into bulge, disk, and bar components is important to address a number of scientific problems. Measuring bulge, disk, and bar structural parameters will set constraints on the violent and secular processes of galaxy assembly and recurrent bar formation and dissolution models. It can also help to quantify the fraction and properties of bulgeless galaxies (those systems having no bulge or only a relatively insignificant disky-pseudobulges), which defy galaxy formation paradigms requiring almost every disk galaxy to have a classical bulge at its core. We demonstrate a proof of concept and show early results of our ongoing three-component bulge-disk-bar decomposition of NIR images for a sample of three complementary samples spanning different epochs and different environments (field and cluster). In contrast to most early studies, which only attempt two-component bulge-disk decomposition, we fit three components using GALFIT: a bulge, a disk, and a bar. We show that it is important to include the bar component, as this can significantly lower the bulge-to-total luminosity ratio (B/T), in many cases by a factor of two or more, thus effectively changing the Hubble type of a galaxy from early to late.

Tim Weinzirl; Shardha Jogee; Fabio D. Barazza

2008-02-26

122

Kinematics in the Interacting, Star-Forming Galaxies NGC 3395/3396 and NGC 3991/3994/3995  

NASA Technical Reports Server (NTRS)

It has been suggested that induced star formation is more sensitive to galaxy dynamics than to local phenomena and that enhanced star formation is found in galaxies with disturbed velocity structures. We are studying the stellar populations of several UV-bright, interacting galaxies to try to understand the detailed star formation process in these systems. We present preliminary results of an investigation of the kinematics of star-forming regions in the interacting systems NGC 3395/3396 and NGC 3991/3994/3995. Regions of powerful star formation are observed throughout these galaxies. The observatation will be used to investigate rotation curves in the galaxies and motion in the tidal tails.

Weistrop, Donna; Nelson, Charles H.

1999-01-01

123

Central regions of the early-type galaxies in the NGC 3169 group  

Microsoft Academic Search

We have investigated the central regions of the galaxies in the NGC 3169\\/NGC 3166\\/NGC 3156 group with the multipupil fiber\\u000a spectrograph of the 6-m telescope; the first (central) galaxy in the group is a spiral (Sa) one and the other two galaxies\\u000a are lenticular ones. The group is known to have an extended HI cloud with a size of more

O. K. Silchenko; V. L. Afanasiev

2006-01-01

124

GIANT GALAXIES, DWARFS, AND DEBRIS SURVEY. I. DWARF GALAXIES AND TIDAL FEATURES AROUND NGC 7331  

SciTech Connect

The Giant GAlaxies, Dwarfs, and Debris Survey (GGADDS) concentrates on the nearby universe to study how galaxies have interacted in groups of different morphology, density, and richness. In these groups, we select the dominant spiral galaxy and search its surroundings for dwarf galaxies and tidal interactions. This paper presents the first results from deep wide-field imaging of NGC 7331, where we detect only four low-luminosity candidate dwarf companions and a stellar stream that may be evidence of a past tidal interaction. The dwarf galaxy candidates have surface brightnesses of {mu}{sub r} Almost-Equal-To 23-25 mag arcsec{sup -2} with (g - r){sub 0} colors of 0.57-0.75 mag in the Sloan Digital Sky Survey filter system, consistent with their being dwarf spheroidal (dSph) galaxies. A faint stellar stream structure on the western edge of NGC 7331 has {mu}{sub g} Almost-Equal-To 27 mag arcsec{sup -2} and a relatively blue color of (g - r){sub 0} = 0.15 mag. If it is tidal debris, then this stream could have formed from a rare type of interaction between NGC 7331 and a dwarf irregular or transition-type dwarf galaxy. We compare the structure and local environments of NGC 7331 to those of other nearby giant spirals in small galaxy groups. NGC 7331 has a much lower ({approx}2%) stellar mass in the form of early-type satellites than found for M31 and lacks the presence of nearby companions like luminous dwarf elliptical galaxies or the Magellanic Clouds. However, our detection of a few dSph candidates suggests that it is not deficient in low-luminosity satellites.

Ludwig, Johannes; Pasquali, Anna; Grebel, Eva K. [Astronomisches Rechen-Institut, Zentrum fuer Astronomie der Universitaet Heidelberg, Moenchhofstr. 12-14, D-69120 Heidelberg (Germany); Gallagher, John S. III, E-mail: ludwig@ari.uni-heidelberg.de [Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706-1582 (United States)

2012-12-01

125

ALMA-backed NIR high resolution integral field spectroscopy of the NUGA galaxy NGC 1433  

NASA Astrophysics Data System (ADS)

Aims: We present the results of near-infrared (NIR) H- and K-band European Southern Observatory SINFONI integral field spectroscopy (IFS) of the Seyfert 2 galaxy NGC 1433. We investigate the central 500 pc of this nearby galaxy, concentrating on excitation conditions, morphology, and stellar content. NGC 1433 was selected from our extended NUGA(-south) sample, which was additionally observed with the Atacama Large Millimeter/submillimeter Array (ALMA). NGC 1433 is a ringed, spiral galaxy with a main stellar bar in roughly east-west direction (PA 94) and a secondary bar in the nuclear region (PA 31). Several dusty filaments are detected in the nuclear region with the Hubble Space Telescope. ALMA detects molecular CO emission coinciding with these filaments. The active galactic nucleus is not strong and the galaxy is also classified as a low-ionization emission-line region (LINER). Methods: The NIR is less affected by dust extinction than optical light and is sensitive to the mass-dominating stellar populations. SINFONI integral field spectroscopy combines NIR imaging and spectroscopy, allowing us to analyse several emission and absorption lines to investigate the stellar populations and ionization mechanisms over the 10? 10? field of view (FOV). Results: We present emission and absorption line measurements in the central kpc of NGC 1433. We detect a narrow Balmer line and several H2 lines. We find that the stellar continuum peaks in the optical and NIR in the same position, indicating that there is no covering of the center by a nuclear dust lane. A strong velocity gradient is detected in all emission lines at that position. The position angle of this gradient is at 155 whereas the galactic rotation is at a position angle of 201. Our measures of the molecular hydrogen lines, hydrogen recombination lines, and [Fe ii] indicate that the excitation at the nucleus is caused by thermal excitation, i.e., shocks that can be associated with active galactic nuclei emission, supernovae, or outflows. The line ratios [Fe ii]/Pa? and H2/Br? show a Seyfert to LINER identification of the nucleus. We do not detect high star formation rates in our FOV. The stellar continuum is dominated by spectral signatures of red-giant M stars. The stellar line-of-sight velocity follows the galactic field whereas the light continuum follows the nuclear bar. Conclusions: The dynamical center of NGC 1433 coincides with the optical and NIR center of the galaxy and the black hole position. Within the central arcsecond, the molecular hydrogen and the 12CO(3-2) emissions - observed in the NIR and in the submillimeter with SINFONI and ALMA, respectively - are indicative for a nuclear outflow originating from the galaxy's SMBH. A small circum-nuclear disk cannot be fully excluded. Derived gravitational torques show that the nuclear bar is able to drive gas inward to scales where viscosity torques and dynamical friction become important. The black hole mass, derived using stellar velocity dispersion, is ~107M?. Based on the ESO-VLT proposal ID: 090.B-0657(A) and on observations carried out with ALMA in cycle 0.Appendix A is available in electronic form at http://www.aanda.org

Smaji?, Semir; Moser, Lydia; Eckart, Andreas; Valencia-S., Mnica; Combes, Franoise; Horrobin, Matthew; Garca-Burillo, Santiago; Garca-Marn, Macarena; Fischer, Sebastian; Zuther, Jens

2014-07-01

126

The Vertical Stellar Kinematics in Face-On Barred Galaxies: Estimating the Ages of Bars  

E-print Network

In order to perform a detailed study of the stellar kinematics in the vertical axis of bars, we obtained high signal-to-noise spectra along the major and minor axes of the bars in a sample of 14 face-on galaxies, and used them to determine the line of sight stellar velocity distribution, parameterized as Gauss-Hermite series. With these data, we developed a diagnostic tool that allows one to distinguish between recently formed and evolved bars, as well as estimate their ages, assuming that bars form in vertically thin disks, recognizable by low values for the vertical velocity dispersion sigma_z. Through N-body realizations of bar unstable disk galaxies we could also check the time scales involved in the processes which give bars an important vertical structure. We show that sigma_z in evolved bars is roughly around 100 Km/s, which translates to a height scale of about 1.4 Kpc, giving support to scenarios in which bulges form through disk material. Furthermore, the bars in our numerical simulations have values for sigma_z generally smaller than 50 Km/s even after evolving for 2 Gyr, suggesting that a slow process is responsible for making bars as vertically thick as we observe. We verify theoretically that the Spitzer-Schwarzschild mechanism is quantitatively able to explain these observations if we assume that giant molecular clouds are twice as much concentrated along the bar as in the remaining of the disk.

Dimitri A. Gadotti; Ronaldo E. de Souza

2005-04-28

127

IUE observations of NGC 4649, an elliptical galaxy with a strong ultraviolet flux  

NASA Technical Reports Server (NTRS)

As in the previously studied elliptical galaxies, the flux f(lambda) in NGC 4649 has a minimum at 2500 A followed by a rapid increase towards shorter wavelengths. In NGC 4649, the flux level of this rising branch is the highest so far observed and seems not to be correlated with the luminosity or activity in the galaxy. The excess shortward of 4000 A, observed in M87, another high level rising branch galaxy, is not present in NGC 4649. The UV spectrum of NGC 4649 down to 2500 A matches closely those of NGC 3379 and NGC 4472. The implications of the UV properties of elliptical galaxies on the stellar content as well as on magnitudes and colors of distant galaxies are discussed

Bertola, F.; Capaccioli, M.; Oke, J. B.

1982-01-01

128

MODELING DUST AND STARLIGHT IN GALAXIES OBSERVED BY SPITZER AND HERSCHEL: NGC 628 AND NGC 6946  

SciTech Connect

We characterize the dust in NGC 628 and NGC 6946, two nearby spiral galaxies in the KINGFISH sample. With data from 3.6 {mu}m to 500 {mu}m, dust models are strongly constrained. Using the Draine and Li dust model (amorphous silicate and carbonaceous grains), for each pixel in each galaxy we estimate (1) dust mass surface density, (2) dust mass fraction contributed by polycyclic aromatic hydrocarbons, (3) distribution of starlight intensities heating the dust, (4) total infrared (IR) luminosity emitted by the dust, and (5) IR luminosity originating in regions with high starlight intensity. We obtain maps for the dust properties, which trace the spiral structure of the galaxies. The dust models successfully reproduce the observed global and resolved spectral energy distributions (SEDs). The overall dust/H mass ratio is estimated to be 0.0082 {+-} 0.0017 for NGC 628, and 0.0063 {+-} 0.0009 for NGC 6946, consistent with what is expected for galaxies of near-solar metallicity. Our derived dust masses are larger (by up to a factor of three) than estimates based on single-temperature modified blackbody fits. We show that the SED fits are significantly improved if the starlight intensity distribution includes a (single intensity) 'delta function' component. We find no evidence for significant masses of cold dust (T {approx}< 12 K). Discrepancies between PACS and MIPS photometry in both low and high surface brightness areas result in large uncertainties when the modeling is done at PACS resolutions, in which case SPIRE, MIPS70, and MIPS160 data cannot be used. We recommend against attempting to model dust at the angular resolution of PACS.

Aniano, G.; Draine, B. T. [Princeton University Observatory, Peyton Hall, Princeton, NJ 08544-1001 (United States); Calzetti, D.; Crocker, A. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Dale, D. A. [Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States); Engelbracht, C. W. [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Gordon, K. D. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Hunt, L. K. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze (Italy); Kennicutt, R. C.; Galametz, M. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA (United Kingdom); Krause, O.; Rix, H.-W.; Sandstrom, K.; Walter, F. [Max-Planck-Institut fur Astronomie, Konigstuhl 17, D-69117 Heidelberg (Germany); Leroy, A. K. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Roussel, H. [Institut d'Astrophysique de Paris, UMR7095 CNRS, Universite Pierre and Marie Curie, 98 bis Boulevard Arago, 75014 Paris (France); Sauvage, M. [CEA/DSM/DAPNIA/Service d'Astrophysique, UMR AIM, CE Saclay, 91191 Gif sur Yvette Cedex (France); Armus, L. [Spitzer Science Center, California Institute of Technology, MC 314-6, Pasadena, CA 91125 (United States); Bolatto, A. D. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Donovan Meyer, J., E-mail: ganiano@astro.princeton.edu, E-mail: draine@astro.princeton.edu [Department of Physics and Astronomy, SUNY Stony Brook, Stony Brook, NY 11794-3800 (United States); and others

2012-09-10

129

Bar pattern speeds in CALIFA galaxies: I. Fast bars across the Hubble sequence  

E-print Network

The bar pattern speed ($\\Omega_{\\rm b}$) is defined as the rotational frequency of the bar, and it determines the bar dynamics. Several methods have been proposed for measuring $\\Omega_{\\rm b}$. The non-parametric method proposed by Tremaine \\& Weinberg (1984; TW) and based on stellar kinematics is the most accurate. This method has been applied so far to 17 galaxies, most of them SB0 and SBa types. We have applied the TW method to a new sample of 15 strong and bright barred galaxies, spanning a wide range of morphological types from SB0 to SBbc. Combining our analysis with previous studies, we investigate 32 barred galaxies with their pattern speed measured by the TW method. The resulting total sample of barred galaxies allows us to study the dependence of $\\Omega_{\\rm b}$ on galaxy properties, such as the Hubble type. We measured $\\Omega_{\\rm b}$ using the TW method on the stellar velocity maps provided by the integral-field spectroscopy data from the CALIFA survey. Integral-field data solve the problem...

Aguerri, J A L; Falcn-Barroso, J; Amorin, A; Barrera-Ballesteros, J; Fernandes, R Cid; Garca-Benito, R; Garca-Lorenzo, B; Delgado, R M Gonzlez; Husemann, B; Kalinova, V; Lyubenova, M; Marino, R A; Mrquez, I; Mast, D; Prez, E; Snchez, S F; van de Ven, G; Walcher, C J; Backsmann, N; Cortijo-Ferrero, C; Bland-Hawthorn, J; del Olmo, A; Iglesias-Pramo, J; Prez, I; Snchez-Blzquez, P; Wisotzki, L; Ziegler, B

2015-01-01

130

Dynamics of the Polar Disk Galaxy NGC 4650A  

NASA Astrophysics Data System (ADS)

We present the dark matter distribution around the polar disk galaxy NGC 4650A. We use extended H I data along the polar disk and long slit kinematics along the spheroid and constrain the dark matter halo scales along the two directions under equilibrium assumptions and a Navarro-Frank-White profile. The different scale lengths along the two axes show that the the dark halo has an axis ratio c/a?0.5 in agreement with expectations from cosmological simulations.

Napolitano, N. R.; Iodice, E.; Arnaboldi, M.

2014-05-01

131

The Araucaria Project: Distance to the Local Group Galaxy NGC 3109 from Near-Infrared Photometry of Cepheids  

E-print Network

We present near-infrared J- and K-band photometry of 77 Cepheid variables in the Local Group galaxy NGC 3109. Combining our data with the previously published optical V- and I-band photometry of Cepheids in this galaxy we derive an accurate distance and interstellar reddening to NGC 3109. Adopting a distance modulus of 18.5 mag for the Large Magellanic Cloud, we obtain a true distance modulus to NGC 3109 of (m-M)_0 = 25.571 +- 0.024 mag (random error), corresponding to a distance of 1.30 +- 0.02 Mpc. The systematic uncertainty on this value (apart from the adopted LMC distance) is of the order of +-3%, the main contributors to this value being the uncertainty on the photometric zero points, and the effect of blending with unresolved companion stars. The total reddening determined from our multiwavelength solution is E(B-V)=0.087 +- 0.012 mag. About half of the reddening is produced internal to NGC 3109. Our distance result is consistent with previous determinations of the distance to NGC 3109, but has significantly reduced error bars.

I. Soszynski; W. Gieren; G. Pietrzynski; F. Bresolin; R. -P. Kudritzki; J. Storm

2006-05-10

132

The Araucaria Project: Distance to the Local Group Galaxy NGC 3109 from Near-Infrared Photometry of Cepheids  

NASA Astrophysics Data System (ADS)

We present near-infrared J- and K-band photometry of 77 Cepheid variables in the Local Group galaxy NGC 3109. Combining our data with the previously published optical V- and I-band photometry of Cepheids in this galaxy, we derive an accurate distance and interstellar reddening toward NGC 3109. Adopting a distance modulus of 18.5 mag for the Large Magellanic Cloud, we obtain a true distance modulus to NGC 3109 of (m-M)0=25.571+/-0.024 mag (random error), corresponding to a distance of 1.30+/-0.02 Mpc. The systematic uncertainty of this value (apart from the adopted LMC distance) is of the order of +/-3%, the main contributors to this value being the uncertainty of the photometric zero points and the effect of blending with unresolved companion stars. The total reddening determined from our multiwavelength solution is E(B-V)=0.087+/-0.012 mag. About half of the reddening is produced internal to NGC 3109. Our distance result is consistent with previous determinations of the distance to NGC 3109 but has significantly reduced error bars. Based on observations obtained with the ESO VLT for Large Program 171.D-0004.

Soszy?ski, I.; Gieren, W.; Pietrzy?ski, G.; Bresolin, F.; Kudritzki, R.-P.; Storm, J.

2006-09-01

133

ISM Parameters in the Normal Galaxy NGC 5713  

NASA Technical Reports Server (NTRS)

We report ISO Long Wavelength Spectrometer (LWS) observations fo the Sbc(s) pec galaxy NGC 5713. We have obtained strong detections of the fine-structure forbidden transitions [C(sub ii)] 158(micro)m, [O(sub i)]63(micro)m, and [O(sub iii)] 88(micro)m, and significant upper limits for[N(sub ii)]122(micro)m, [O(sub iii)] 52(micro)m, and [N(sub iii)] 57(micro)m. We also detect the galaxy's dust continuum emission between 43 and 197 microns.

Lord, S. D.; Malhotra, S.; Lim, T.; Helou, G.; Beichman, C. A.; Dinerstein, H.; Hollenbach, D. J.; Hunter, D. A.; Lo, K. Y.; Lu, N. Y.; Rubin, R. H.; Stacey, G. J.; Thronson, H. A., Jr.; Werner, M. W.

1996-01-01

134

Merging Cold Fronts in the Galaxy Pair NGC 7619 and NGC 7626  

E-print Network

We present results from {\\it Chandra} observations of the galaxy pair NGC 7619 and NGC 7626, the two dominant members of the Pegasus group. The X-ray images show a brightness edge associated with each galaxy, which we identify as merger cold fronts. The edges are sharp, and the axes of symmetry of the edges are roughly anti-parallel, suggesting that these galaxies are falling towards one another in the plane of the sky. The detection of merger cold fronts implies a merging subgroup scenario, since the alternative is that the galaxies are falling into a pre-existing $\\sim1$ keV halo without a dominant galaxy of its own, and such objects are not observed. We estimate the 3D velocities from the cold fronts and show that the velocity vectors are indeed most likely close to the plane of the sky, with a relative velocity of $\\sim1190\\kms$. The relative velocity is consistent with what is expected from the infall of two roughly equal mass subgroups whose total viral mass equals that of the Pegasus group. We conclude...

Randall, S W; Kraft, R; Forman, W R; O'Sullivan, E

2008-01-01

135

Optical and x-ray variability of seyfert galaxies NGC 5548, NGC 7469, NGC 3227, NGC 4051, NGC 4151, Mrk 509, Mrk 79, Akn 564  

Microsoft Academic Search

We present the results of a study of the optical and X-ray variability properties of sample of AGNs: NGC 5548, NGC 7469, NGC 3227, NGC 4051, NGC 4151, Mrk 509, Mrk 79, Akn 564. Tte results of simultaneous BVRI observations were carried out at the Crimean Astrophysical Observatory with the 70-cm telescope and RXTE observations. We used the structure function

Nadya Chesnok; Sergey Sergeev; Irina Vavilova

2008-01-01

136

XMM-Newton observation of the interacting galaxies NGC 1512 and NGC 1510  

NASA Astrophysics Data System (ADS)

Context. The galaxy NGC 1512 is interacting with the smaller galaxy NGC 1510 and shows a peculiar morphology, characterised by two extended arms immersed in an HI disc whose size is about four times larger than the optical diameter of NGC 1512. Aims: For the first time we performed a deep X-ray observation of the galaxies NGC 1512 and NGC 1510 with XMM-Newton to gain information on the population of X-ray sources and diffuse emission in a system of interacting galaxies. Methods: We identified and classified the sources detected in the XMM-Newton field of view by means of spectral analysis, hardness-ratios calculated with a Bayesian method, X-ray variability, and cross-correlations with catalogues in optical, infrared, and radio wavelengths. We also made use of archival Swift (X-ray) and Australia Telescope Compact Array (radio) data to better constrain the nature of the sources detected with XMM-Newton. Results: We detected 106 sources in the energy range of 0.2-12 keV, out of which 15 are located within the D25 regions of NGC 1512 and NGC 1510 and at least six sources coincide with the extended arms. We identified and classified six background objects and six foreground stars. We discussed the nature of a source within the D25 ellipse of NGC 1512, whose properties indicate a quasi-stellar object or an intermediate ultra-luminous X-ray source. Taking into account the contribution of low-mass X-ray binaries and active galactic nuclei, the number of high-mass X-ray binaries detected within the D25 region of NGC 1512 is consistent with the star formation rate obtained in previous works based on radio, infrared optical, and UV wavelengths. We detected diffuse X-ray emission from the interior region of NGC 1512 with a plasma temperature of kT = 0.68 (0.31-0.87) keV and a 0.3-10 keV X-ray luminosity of 1.3 1038 erg s-1, after correcting for unresolved discrete sources. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. The radio observations were obtained with the Australia Telescope Compact Array, which is part of the Australia Telescope National Facility funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO.Tables B.1 and B.2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/566/A115

Ducci, L.; Kavanagh, P. J.; Sasaki, M.; Koribalski, B. S.

2014-06-01

137

Soft X-ray Emission from the Spiral Galaxy NGC 1313  

E-print Network

The nearby barred spiral galaxy NGC 1313 has been observed with the PSPC instr- ument on board the ROSAT X-ray satellite. Ten individual sources are found. Three sources (X-1, X-2 and X-3 [SN~1978K]) are very bright (~10^40 erg/s) and are unusual in that analogous objects do not exist in our Galaxy. We present an X-ray image of NGC~1313 and \\xray spectra for the three bright sources. The emission from the nuclear region (R ~images do not indicate the presence of an active galactic nucleus at that position; however, the compact nature of the \\xray source (X-1) suggests that it is an accretion-powered object with central mass M >~ 10^3 Msun. Additional emission (L_X ~ 10^39 erg/s) in the nuclear region extends out to ~2.6 kpc and roughly follows the spiral arms. This emission is from 4 sources with luminosity of several x 10^38 erg/s, two of which are consistent with emission from population I sources (e.g., supernova remnants, and hot interstellar gas which has been heated by supernova remnants). The other two sources could be emission from population II sources (e.g., low-mass \\xray binaries). The bright sources X-2 and SN~1978K are positioned in the southern disk of NGC~1313. X-2 is variable and has no optical counterpart brighter than 20.8 mag (V-band). It is likely that it is an accretion-powered object in NGC~1313. The type-II supernova SN~1978K (Ryder \\etal 1993) has become extra- ordinarily luminous in X-rays $\\sim$13 years after optical maximum.

E. J. M. Colbert; R. Petre; E. M. Schlegel; S. D. Ryder

1995-01-31

138

Kinematics and stellar population of the lenticular galaxy NGC 4124  

NASA Astrophysics Data System (ADS)

Results of spectroscopic and photometric studies for the locally isolated lenticular galaxy NGC 4124 are presented. A model of the mass distribution consistent with photometric data has been constructed on the basis of a kinematic analysis. In this model, the halo mass within the optical radius is almost half the diskmass. The disk is shown to be in a dynamical state close to amarginally stable one. This rules out dynamical disk heating for the galaxy through a strong external action or a merger with a massive system. However, the presence of a gaseous disk inclined to the main plane of the galaxy in the central kiloparsec region suggests probable cannibalization of a small satellite that also produced a late starburst in the central region. This is confirmed by the younger mean age (2 Gyr) of the stellar population in the galaxy's central region than the disk age (5-7 Gyr).

Zasov, A. V.; Sil'chenko, O. K.; Katkov, I. Yu.; Dodonov, S. N.

2013-01-01

139

NGC 4438: Ram pressure sweeping of a tidally disrupted galaxy  

NASA Technical Reports Server (NTRS)

NGC 4438 is the highly HI deficient peculiar spiral in the center of the Virgo cluster. Observations are given of the neutral hydrogen emission obtained with the Very Large Array (VLA) in the D-array configuration. These observations map out the total HI as determined from single dish measurements, and show the hydrogen to be confined to a region about one third the size of the optical disk and displaced to the side of the galaxy opposite M87. The hydrogen content of the galaxy is over an order of magnitude less than that expected for a galaxy of its type. The data suggest that the HI deficiency is a result of ram pressure stripping of the gas in the outer regions of the galaxy by the hot intracluster medium after being tidally perturbed.

Hibbard, J. E.; Vangorkom, Jacqueline H.

1990-01-01

140

Halo properties and secular evolution in barred galaxies  

E-print Network

The halo plays a crucial role in the evolution of barred galaxies. Its near-resonant material absorbs angular momentum emitted from some of the disc particles and helps the bar become stronger. As a result, a bar (oval) forms in the inner parts of the halo of strongly barred disc galaxies. It is thinner in the inner parts (but still considerably fatter than the disc bar) and tends to spherical at larger radii. Its length increases with time, while always staying shorter than the disc bar. It is roughly aligned with the disc bar, which it trails only slightly, and it turns with roughly the same pattern speed. The bi-symmetric component of the halo density continues well outside the halo bar, where it clearly trails behind the disc bar. The length and strength of the disc and halo bars correlate; the former being always much stronger than the latter. If the halo is composed of weakly interacting massive particles, then the formation of the halo bar, by redistributing the matter in the halo and changing its shape, could influence the expected annihilation signal. This is indeed found to be the case if the halo has a core, but not if it has a steep cusp. The formation and evolution of the bar strongly affect the halo orbits. A fraction of them becomes near-resonant, similar to the disc near-resonant orbits at the same resonance, while another fraction becomes chaotic. Finally, a massive and responsive halo makes it harder for a central mass concentration to destroy the disc bar.

E. Athanassoula

2005-10-28

141

LUMINOSITIES OF BARRED AND UNBARRED S0 GALAXIES  

SciTech Connect

Lenticular galaxies with M{sub B} < -21.5 are almost exclusively unbarred, whereas both barred and unbarred objects occur at fainter luminosity levels. This effect is observed both for objects classified in blue light, and for those that were classified in the infrared. This result suggests that the most luminous (massive) S0 galaxies find it difficult to form bars. As a result, the mean luminosity of unbarred lenticular galaxies in both B and IR light is observed to be {approx}0.4 mag brighter than that of barred lenticulars. A small contribution to the observed luminosity difference that is found between SA0 and SB0 galaxies may also be due to the fact that there is an asymmetry between the effects of small classification errors on SA0 and SB0 galaxies. An elliptical (E) galaxy might be misclassified as a lenticular (S0) or an S0 as an E. However, an E will never be misclassified as an SB0, nor will an SB0 ever be called an E. This asymmetry is important because E galaxies are typically twice as luminous as S0 galaxies. The present results suggest that the evolution of luminous lenticular galaxies may be closely linked to that of elliptical galaxies, whereas fainter lenticulars might be more closely associated with ram-pressure stripped spiral galaxies. Finally, it is pointed out that fine details of the galaxy formation process might account for some of the differences between the classifications of the same galaxy by individual competent morphologists.

Van den Bergh, Sidney, E-mail: sidney.vandenbergh@nrc.gc.ca [Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)

2012-07-20

142

The interstellar halo of spiral galaxies: NGC 891  

NASA Technical Reports Server (NTRS)

Researchers have detected the Warm Ionized Medium (WIM) phase in the galaxy NGC 891. They found that the radial distribution of the WIM follows the molecular or young star distribution - an expected dependence. The amount of the WIM in this galaxy exceeds that in our Galaxy. The major surprize is the large thickness of the WIM phase - about 9 kpc instead 3 kpc as in our Galaxy. Clearly, this is the most significant result of the observations. The presence of low ionization gas at high z as well as at large galactocentric radii (where young stars are rare) is an important clue to the origin of the halo and observations such as the one reported here provide important data on this crucial question. In particular, the ionization of gas at high absolute z implies that either the UV photons manage to escape from the disk of the galaxy or that the extragalactic UV background plays an important role. The bulk of the WIM in spiral galaxies is a result of star-formation activity and thus these results can be understood by invoking a high star formation rate in NGC 891. Only the concerted action of supernovae can get the gas to the large z-heights as is observed in this galaxy. Support for this view comes from our detection of many worms i.e., bits and pieces of supershells in the form of kilo-parsec long vertical filaments. Researchers also saw a 600-pc size supershell located nearly one kpc above the plane of the galaxy.

Kulkarni, Shrinivas R.; Rand, R. J.; Hester, J. Jeff

1990-01-01

143

Galaxy Zoo and ALFALFA: Atomic Gas and the Regulation of Star Formation in Barred Disc Galaxies  

E-print Network

We study the observed correlation between atomic gas content and the likelihood of hosting a large scale bar in a sample of 2090 disc galaxies. Such a test has never been done before on this scale. We use data on morphologies from the Galaxy Zoo project and information on the galaxies' HI content from the ALFALFA blind HI survey. Our main result is that the bar fraction is significantly lower among gas rich disc galaxies than gas poor ones. This is not explained by known trends for more massive (stellar) and redder disc galaxies to host more bars and have lower gas fractions: we still see at fixed stellar mass a residual correlation between gas content and bar fraction. We discuss three possible causal explanations: (1) bars in disc galaxies cause atomic gas to be used up more quickly, (2) increasing the atomic gas content in a disc galaxy inhibits bar formation, and (3) bar fraction and gas content are both driven by correlation with environmental effects (e.g. tidal triggering of bars, combined with strangu...

Masters, Karen L; Haynes, Martha P; Keel, William C; Lintott, Chris; Simmons, Brooke; Skibba, Ramin; Bamford, Steven; Giovanelli, Riccardo; Schawinski, Kevin

2012-01-01

144

WARM MOLECULAR HYDROGEN EMISSION IN NORMAL EDGE-ON GALAXIES NGC 4565 AND NGC 5907  

SciTech Connect

We have observed warm molecular hydrogen in two nearby edge-on disk galaxies, NGC 4565 and NGC 5907, using the Spitzer high-resolution infrared spectrograph. The 0-0 S(0) 28.2 {mu}m and 0-0 S(1) 17.0 {mu}m pure rotational lines were detected out to 10 kpc from the center of each galaxy on both sides of the major axis, and in NGC 4565 the S(0) line was detected at r = 15 kpc on one side. This location is beyond the transition zone where diffuse neutral atomic hydrogen starts to dominate over cold molecular gas and marks a transition from a disk dominated by high surface-brightness far-infrared (far-IR) emission to that of a more quiescent disk. It also lies beyond a steep drop in the radio continuum emission from cosmic rays (CRs) in the disk. Despite indications that star formation activity decreases with radius, the H{sub 2} excitation temperature and the ratio of the H{sub 2} line and the far-IR luminosity surface densities, {Sigma}(L{sub H{sub 2}})/{Sigma}(L{sub TIR}), change very little as a function of radius, even into the diffuse outer region of the disk of NGC 4565. This suggests that the source of excitation of the H{sub 2} operates over a large range of radii and is broadly independent of the strength and relative location of UV emission from young stars. Although excitation in photodissociation regions is the most common explanation for the widespread H{sub 2} emission, CR heating or shocks cannot be ruled out. At r = 15 kpc in NGC 4565, outside the main UV- and radio-continuum-dominated disk, we derived a higher than normal H{sub 2} to 7.7 {mu}m polycyclic aromatic hydrocarbon (PAH) emission ratio, but this is likely due to a transition from mainly ionized PAH molecules in the inner disk to mainly neutral PAH molecules in the outer disk. The inferred mass surface densities of warm molecular hydrogen in both edge-on galaxies differ substantially, being 4(-60) M{sub sun} pc{sup -2} and 3(-50) M{sub sun} pc{sup -2} at r = 10 kpc for NGC 4565 and NGC 5907, respectively. The higher values represent very unlikely point-source upper limits. The point-source case is not supported by the observed emission distribution in the spectral slits. These mass surface densities cannot support the observed rotation velocities in excess of 200 km s{sup -1}. Therefore, warm molecular hydrogen cannot account for dark matter in these disk galaxies, contrary to what was implied by a previous Infrared Space Observatory study of the nearby edge-on galaxy NGC 891.

Laine, Seppo [Spitzer Science Center, Caltech, MS 220-6, Pasadena, CA 91125 (United States); Appleton, Philip N. [NASA Herschel Science Center, California Institute of Technology, Pasadena, CA 91125 (United States); Gottesman, Stephen T. [Department of Astronomy, University of Florida, Gainesville, FL 32611-2055 (United States); Ashby, Matthew L. N. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Garland, Catherine A., E-mail: seppo@ipac.caltech.ed, E-mail: apple@ipac.caltech.ed, E-mail: gott@astro.ufl.ed, E-mail: mashby@cfa.harvard.ed, E-mail: catherine.garland@castleton.ed [Natural Sciences Department, Castleton State College, Castleton, VT 05735 (United States)

2010-09-15

145

Stellar and Ionized Gas Kinematics in the Circumnuclear Region of the Galaxy NGC 7331  

NASA Astrophysics Data System (ADS)

We present simultaneous two-dimensional spectroscopy of the circumnuclear region (12" 9") of the galaxy NGC 7331, obtained with an optical fiber system coupled to the ISIS double spectrograph of the 4.2 m William Herschel Telescope. The system allows simultaneous observation of 125 regions of this galaxy in two spectral ranges: 4590-5400 at high resolution (1.5 ) and 6400-9620 at low resolution (5 ). These spectra are mainly used to study the stellar and gas kinematics in the innermost region of this galaxy. The stellar velocity fields inferred from the Mg I b and Ca II absorption lines are in good agreement. They show a solid-body rotational pattern with the line of nodes along the position angle of the apparent major axis of the galaxy. The relatively large local stellar velocity dispersion suggests that we are observing the bulge rather than the disk kinematics. The two-dimensional kinematic data agree with previous one-dimensional studies that found no evidence for a massive black hole in NGC 7331. The [O III] emission lines are split into three components. One is distributed around the systemic velocity, another is systematically blueshifted, and the last is systematically redshifted. We propose that these arise from two distinct gaseous systems: a warped disk of irregular rotational pattern with the kinematic axes shifted by about 30 with respect to those of the stars, and a shell of gas flowing radially. Although alternative interpretations in terms of inflow driven by a central bar or outflow produced by a galactic wind are possible, the latter seems preferable. In NGC 7331 the ionized gas and stars are kinematically decoupled, the velocity dispersion of the ionized gas being substantially lower than that of the stars. This last result differs from what is generally found in Seyfert galaxies. However, NGC 7331 and M31 show a large degree of similarity, and the type of LINERs that they harbor are probably produced by the same type of phenomenon.

Mediavilla, E.; Arribas, S.; Garca-Lorenzo, B.; del Burgo, C.

1997-10-01

146

Globular Clusters in the Sombrero Galaxy (NGC 4594)  

E-print Network

The Sombrero galaxy, NGC 4594, contains the most numerous globular cluster system of any nearby spiral. It is an ideal candidate in which to study the globular clusters and contrast them with those in Local Group spirals. Here we present B and I imaging from the CTIO Schmidt telescope which gives a field-of-view of 31' x 31'. Using DAOPHOT we have detected over 400 globular clusters and derived their magnitudes, B--I colors and photometric metallicities. We have attempted to separate our sample into disk and bulge/halo globular cluster populations, based on location in the galaxy. There is some evidence that the disk population is more metal--rich than the bulge/halo globular clusters, however contamination, dust reddening and small number statistics makes this result very tentative. We find that the median metallicity of the bulge/halo globular clusters is [Fe/H] = -0.8. This metallicity is consistent with previous estimates based on smaller samples. It is also similar to the metallicity predicted by the globular cluster metallicity -- galaxy luminosity relation. As with our Galaxy, there is no radial metallicity gradient in the halo globular clusters. This suggests that the spheriodal component of NGC 4594 did not form by a dissipational process.

Duncan A. Forbes; Carl J. Grillmair; R. Chris Smith

1997-01-20

147

Dark matter deprivation in the field elliptical galaxy NGC 7507  

NASA Astrophysics Data System (ADS)

Context. Previous studies have shown that the kinematics of the field elliptical galaxy NGC 7507 do not necessarily require dark matter. This is troubling because, in the context of ?CDM cosmologies, all galaxies should have a large dark matter component. Aims: Our aims are to determine the rotation and velocity dispersion profile out to larger radii than do previous studies, and, therefore, more accurately estimate of the dark matter content of the galaxy. Methods: We use penalised pixel-fitting software to extract velocities and velocity dispersions from GMOS slit mask spectra. Using Jeans and MONDian modelling, we then produce models with the goal of fitting the velocity dispersion data. Results: NGC 7507 has a two-component stellar halo, with the outer halo counter rotating with respect to the inner halo, with a kinematic boundary at a radius of ~110'' (~12.4 kpc). The velocity dispersion profile exhibits an increase at ~70'' (~7.9 kpc), reminiscent of several other elliptical galaxies. Our best fit models are those under mild anisotropy, which include ~100 times less dark matter than predicted by ?CDM, although mildly anisotropic models that are completely dark matter free fit the measured dynamics almost equally well. Our MONDian models, both isotropic and anisotropic, systematically fail to reproduce the measured velocity dispersions at almost all radii. Conclusions: The counter-rotating outer halo implies a merger remnant, as does the increase in velocity dispersion at ~70''. From simulations it seems plausible that the merger that caused the increase in velocity dispersion was a spiral-spiral merger. Our Jeans models are completely consistent with a no dark matter scenario, however, some dark matter can be accommodated, although at much lower concentrations than predicted by ?CDM simulations. This indicates that NGC 7507 may be a dark matter free elliptical galaxy. Regardless of whether NGC 7507 is completely dark matter free or very dark matter poor, it is at odds with predictions from current ?CDM cosmological simulations. It may be possible that the observed velocity dispersions could be reproduced if the galaxy is significantly flattened along the line of sight (e.g. due to rotation); however, invoking this flattening is problematic. Based on observations taken at the Gemini Observatory, operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministrio da Cincia e Tecnologia (Brazil) and SECYT (Argentina).

Lane, Richard R.; Salinas, Ricardo; Richtler, Tom

2015-02-01

148

Peanuts at an angle: detecting and measuring the three-dimensional structure of bars in moderately inclined galaxies  

NASA Astrophysics Data System (ADS)

We show that direct detection and measurement of the vertically thickened parts of bars (so-called `boxy' or `peanut-shaped' bulges) are possible not only for edge-on galaxies but also for galaxies with moderate inclinations (i < 70), and that examples are relatively common in the nearby Universe. The analysis of a sample of 78 nearby, moderately inclined (i ? 65) early-type (S0-Sb) barred galaxies shows that the isophotal signature of the box/peanut can usually be detected for inclinations as low as i 40 - and in exceptional cases down to i 30. In agreement with the predictions from N-body simulations, the signature is most easily detectable when the bar's position angle is within 50 of the galaxy major axis; in particular, galaxies where the bar lies very close to the minor axis do not show the signature clearly or at all. For galaxies with i = 40-65 and relative angles <45, we find evidence for the signature ?2/3 of the time; the true frequency of box/peanut structures in bars may be higher. Comparison with N-body models also allows us to link observed photometric morphology with 3D physical structures, and thus estimate the relative sizes of box/peanut structures and bars. For our local sample, we find that box/peanut structures range in radial size (measured along the bar major axis) from 0.4 to 3.8 kpc (mean =1.5 0.9 kpc) and span 0.26-0.58 of the bar length (mean of 0.38 0.08). This is a clear observational confirmation that when bars thicken, it is not the entire bar which does so, but only the inner part. This technique can also be used to identify galaxies with bars which have not vertically thickened. We suggest that NGC 3049 and IC 676 may be particularly good examples, and that the fraction of S0-Sb bars which lack box/peanut structures is at least 13 per cent.

Erwin, Peter; Debattista, Victor P.

2013-06-01

149

Slow Jets in Seyfert Galaxies: NGC 1068  

E-print Network

We have used the Very Long Baseline Array at 5 GHz to image the nucleus of NGC 1068 at two epochs separated by 2.92 yr. No relative motion was detected between the high brightness-temperature knots within components NE and C relative to the nuclear component S1, placing an upper limit of 0.075 c on the relative component speeds at distances of 21 pc and 43 pc from the AGN. The low speed is consistent with the low bulk flow speed previously inferred from indirect arguments based on ram pressure at the bow shock and on line emission from the jet-cloud collision at cloud C. The components are probably shocks in the jet, and the bulk flow speed could conceivably be higher than the limit reported here.

A. L. Roy; A. S. Wilson; J. S. Ulvestad; E. J. M. Colbert

2000-09-26

150

Interacting binary galaxies. III. Observations of NGC 1587/1588 and NGC 7236/7237  

SciTech Connect

The catalog of isolated galaxy pairs prepared by Karachentsev has been culled for its E-E constituents, and the results are reported. Radial variations of rotation velocity and velocity dispersion are extracted from the spectroscopic data for each of the two galaxies of a given pair. Such observations are described for two Karachentsev pairs, Nos. 99 and 564. The observed disturbances in rotation velocity and luminosity distribution are discussed in terms of the gravitational interaction hypothesis. It is argued that observational evidence of tidal friction in action is evidenced by these findings. One of the highest rotation rates known for an E2 galaxy of average luminosity is found in NGC 1587, the brighter component of K99. Because this rotation is in the same sense as the binary orbital motion, the net angular momentum in this isolated binary system is large, challenging simple tidal torque theories to identify the source of the momentum. 62 references.

Borne, K.D.; Hoessel, J.G.

1988-07-01

151

Cepheid Variables in the Maser-Host Galaxy NGC 4258  

E-print Network

We present results of a ground-based survey for Cepheid variables in NGC 4258. This galaxy plays a key role in the Extragalactic Distance Scale due to its very precise and accurate distance determination via VLBI observations of water masers. We imaged two fields within this galaxy using the Gemini North telescope and GMOS, obtaining 16 epochs of data in the SDSS gri bands over 4 years. We carried out PSF photometry and detected 94 Cepheids with periods between 7 and 127 days, as well as an additional 215 variables which may be Cepheids or Population II pulsators. We used the Cepheid sample to test the absolute calibration of theoretical gri Period-Luminosity relations and found good agreement with the maser distance to this galaxy. The expected data products from the Large Synoptic Survey Telescope (LSST) should enable Cepheid searches out to at least 10 Mpc.

Hoffmann, Samantha L

2015-01-01

152

Reverberation Mapping of the Seyfert 1 Galaxy NGC 7469  

NASA Astrophysics Data System (ADS)

A large reverberation-mapping study of the Seyfert 1 galaxy NGC 7469 has yielded emission-line lags for H? ?4861 and He II ?4686 and a central black hole mass measurement M BH ? 1 107 M ?, consistent with previous measurements. A very low level of variability during the monitoring campaign precluded meeting our original goal of recovering velocity-delay maps from the data, but with the new H? measurement, NGC 7469 is no longer an outlier in the relationship between the size of the H?-emitting broad-line region and the luminosity of the active galactic nucleus. It was necessary to detrend the continuum and H? and He II ?4686 line light curves and those from archival UV data for different time-series analysis methods to yield consistent results.

Peterson, B. M.; Grier, C. J.; Horne, Keith; Pogge, R. W.; Bentz, M. C.; De Rosa, G.; Denney, K. D.; Martini, Paul; Sergeev, S. G.; Kaspi, S.; Minezaki, T.; Zu, Y.; Kochanek, C. S.; Siverd, R. J.; Shappee, B.; Araya Salvo, C.; Beatty, T. G.; Bird, J. C.; Bord, D. J.; Borman, G. A.; Che, X.; Chen, C.-T.; Cohen, S. A.; Dietrich, M.; Doroshenko, V. T.; Drake, T.; Efimov, Yu. S.; Free, N.; Ginsburg, I.; Henderson, C. B.; King, A. L.; Koshida, S.; Mogren, K.; Molina, M.; Mosquera, A. M.; Motohara, K.; Nazarov, S. V.; Okhmat, D. N.; Pejcha, O.; Rafter, S.; Shields, J. C.; Skowron, D. M.; Skowron, J.; Valluri, M.; van Saders, J. L.; Yoshii, Y.

2014-11-01

153

Detecting chaotic and ordered motion in barred galaxies  

NASA Astrophysics Data System (ADS)

A very important issue in the area of galactic dynamics is the detection of chaotic and ordered motion inside galaxies. In order to achieve this target, we use the Smaller ALignment Index (SALI) method, which is a very suitable tool for this kind of problem. Here, we apply this index to 3D barred galaxy potentials and we present some results on the chaotic behavior of the model when its main parameters vary.

Manos, T.; Athanassoula, E.

2005-12-01

154

Interstellar Gas in the NGC 4410 Galaxy Group  

E-print Network

We present new radio continuum, 21 cm HI, and 2.6 mm CO data for the peculiar radio galaxy NGC 4410A and its companion NGC 4410B, and compare with available optical and X-ray maps. Our radio continuum maps show an asymmetric double-lobedstructure, with a high surface brightness lobe extending 3.6 arcmin (~100 kpc) to the southeast and a 6.2 arcmin (~180 kpc) low surface brightness feature in the northwest. Molecular gas is abundant in NGC 4410A, with M(H2) ~ 4 X 10^9 M(sun) (using the standard Galactic conversion factor), but is undetected in NGC 4410B. HI is less abundant, with M(HI) ~ 10^9 M(sun) for the pair. Our HI map shows a 3 X 10^8 M(sun) HI tail extending 1.7 arcmin (50 kpc) to the southeast of the pair, coincident with a faint optical tail and partially overlapping with the southeastern radio lobe. The HI tail is anti-coincident with a 2' (56 kpc) long X-ray structure aligned with a stellar bridge that connects the pair to a third galaxy. If this X-ray emission is associated with the group, there is 3 - 8 X 10^8 M(sun) of hot gas in this feature: either intracluster gas or shocked gas associated with the bridge. Our detection of abundant interstellar gas in this pair suggests that the distortions in this lobe map have been caused by the interstellar medium in this system. The interaction of the two galaxies and the subsequent motion of the interstellar medium in the system relative to the jet may have produced sufficient ram pressure to bend the radio jet. An alternative hypothesis is that the jet was distorted by ram pressure due to an intracluster medium, although the small radial velocity of NGC 4410A relative to the group and the lack of diffuse X-ray emission in the group makes this less likely unless the group is not virialized or is in the process of merging with another group.

Beverly J. Smith

2000-05-04

155

Secular- and merger-built bulges in barred galaxies  

NASA Astrophysics Data System (ADS)

Context. Historically, galaxy bulges were thought to be single-component objects at the center of galaxies. However, this picture is now questioned since different bulge types with different formation paths, namely classical and pseudobulges, have been found coexisting within the same galaxy. Aims: We study the incidence and nature of composite bulges in a sample of 10 face-on barred galaxies to constrain the formation and evolutionary processes of the central regions of disk galaxies. Methods: We analyze the morphological, photometric, and kinematic properties of each bulge. Then, by using a case-by-case analysis we identify composite bulges and classify every component into a classical or pseudobulge. In addition, bar-related boxy/peanut (B/P) structures were also identified and characterized. Results: We find only three galaxies hosting a single-component bulge (two pseudobulges and one classical bulge). Thus, we demonstrate the high incidence of composite bulges (70%) in barred galaxies. We find evidence of composite bulges coming in two main types based on their formation: secular-built and merger- and secular-built. We denote as secular-built those composite bulges that are made up of structures associated with secular processes, such as pseudobulges, central disks, or B/P bulges. We find four composite bulges of this kind in our sample. On the other hand, merger- and secular-built bulges are those where structures with different formation paths coexist within the same galaxy, i.e., a classical bulge coexisting with a secular-built structure (pseudobulge, central disk, or B/P). Three bulges of this kind were found in the sample. We notice the importance of detecting kinematic structures such as ?-drops to identify composite bulges. A high percentage (~80%) of galaxies were found to host ?-drops or ?-plateaus in our sample, revealing their high incidence in barred galaxies. Conclusions: The high frequency of composite bulges in barred galaxies points toward a complex formation and evolutionary scenario. Moreover, the evidence of coexisting merger- and secular-built bulges reinforce this idea. We discuss how the presence of different bulge types with different formation histories and timescales can constrain current models of bulge formation.

Mndez-Abreu, J.; Debattista, V. P.; Corsini, E. M.; Aguerri, J. A. L.

2014-12-01

156

The circumnuclear environment of the Seyfert 1 galaxy NGC 3516  

SciTech Connect

Results of an emission-line imaging and spectrophotometric study of the ionized gas in the circumnuclear regions of the Seyfert 1 galaxy NGC 3516 are reported. The morphology and ionization of the gas are consistent with excitation by the power law continuum from the active nucleus. The optical emission-line gas is well aligned with the extended 6 cm radio-continuum emission. The ionization, structure, and published kinematical data are strongly suggestive of an outflow origin for the circumnuclear gas, although important details are missing to firmly establish outflow as the origin of all of the ionized gas. 31 refs.

Pogge, R.W. (Lick Observatory, Santa Cruz, CA (USA); McDonald Observatory, Austin, TX (USA))

1989-07-01

157

Peculiarities in the optical variability of the galaxy NGC 4151  

SciTech Connect

Photographic and photoelectric observations of the optical variability of the nucleus of the Seyfert galaxy NGC 4151 are analyzed. The presence of a quasiperiodic 126/sup d/ component is confirmed. The 126/sup d/ period varies in cycles of roughly-equal20 yr. If these fluctuations represent orbital motion about a central body (such as a supermassive black hole), its mass would be roughly-equal10/sup 8/ M/sub sun/ and the orbital velocity would be roughly-equal10/sup 4/ km/sec.

Lyutyi, V.M.; Oknyanskii, V.L.

1981-11-01

158

TIDAL DWARF GALAXIES AROUND A POST-MERGER GALAXY, NGC 4922  

SciTech Connect

One possible channel for the formation of dwarf galaxies involves birth in the tidal tails of interacting galaxies. We report the detection of a bright UV tidal tail and several young tidal dwarf galaxy (TDG) candidates in the post-merger galaxy NGC 4922 in the Coma cluster. Based on a two-component population model (combining young and old stellar populations), we find that the light of tidal tail predominantly comes from young stars (a few Myr old). The Galaxy Evolution Explorer ultraviolet data played a critical role in the parameter (age and mass) estimation. Our stellar mass estimates of the TDG candidates are {approx}10{sup 6-7} M {sub sun}, typical for dwarf galaxies.

Sheen, Yun-Kyeong; Jeong, Hyunjin; Lee, Young-Wook [Department of Astronomy, Yonsei University, Seoul 120-749 (Korea, Republic of); Ferreras, Ignacio [Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey, RH5 6NT (United Kingdom); Lotz, Jennifer M.; Olsen, Knut A. G.; Dickinson, Mark [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Barnes, Sydney [Lowell Observatory, Flagstaff, AZ 86001 (United States); Park, Jang-Hyun; Ree, Chang H. [Korea Astronomy and Space Science Institute, Hwaam 61-1, Yuseong, Daejeon 305-348 (Korea, Republic of); Madore, Barry F. [Observatories of the Carnegie Institution of Washington, 813 Santa Barbara St., Pasadena, CA 91101 (United States); Barlow, Tom A.; Conrow, Tim; Foster, Karl; Friendman, Peter G.; Martin, D. Christopher; Morrissey, Patrick [California Institute of Technology, MC 405-47, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Neff, Susan G. [Laboratory for Astronomy and Solar Physics, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Schiminovich, David [Department of Astronomy, Columbia University, New York, NY 10027 (United States); Yi, Sukyoung K., E-mail: yi@yonsei.ac.kr (and others)

2009-12-15

159

A Compton thick AGN in the barred spiral NGC 4785  

E-print Network

We present X-ray observations of the active galactic nucleus (AGN) in NGC 4785. The source is a local Seyfert 2 which has not been studied so far in much detail. It was recently detected with high significance in the 15-60 keV band in the 66 month Swift/BAT all sky survey, but there have been no prior pointed X-ray observations of this object. With Suzaku, we clearly detect the source below 10 keV, and find it to have a flat continuum and prominent neutral iron fluorescence line with equivalent width >~1 keV. Fitting the broadband spectra with physical reflection models shows the source to be a bona fide Compton thick AGN with Nh of at least 2x10^{24} cm^{-2} and absorption-corrected 2-10 keV X-ray power L(2-10) ~ few times 10^{42} erg s^{-1}. Realistic uncertainties on L(2-10) computed from the joint confidence interval on the intrinsic power law continuum photon index and normalization are at least a factor of 10. The local bona fide Compton thick AGN population is highly heterogeneous in terms of WISE mid-...

Gandhi, P; Ricci, C; Asmus, D; Mushotzky, R F; Ueda, Y; Terashima, Y; La Parola, V

2014-01-01

160

Rotation of classical bulges during secular evolution of barred galaxies  

NASA Astrophysics Data System (ADS)

Bar driven secular evolution plays a key role in changing the morphology and kinematics of disk galaxies, leading to the formation of rapidly rotating boxy/peanut bulges. If these disk galaxies also hosted a preexisting classical bulge, how would the secular evolution influence the classical bulge, and also the observational properties. We first study the co-evolution of a bar and a preexisting non-rotating low-mass classical bulge such as might be present in galaxies like the Milky Way. It is shown with N-body simulations that during the secular evolution, such a bulge can gain significant angular momentum emitted by the bar through resonant and stochastic orbits. Thereby it transforms into a cylindrically rotating, anisotropic and triaxial object, embedded in the fast rotating boxy bulge that forms via disk instability (Saha et al. 2012). The composite boxy/peanut bulge also rotates cylindrically. We then show that the growth of the bar depends only slightly on the rotation properties of the preexisting classical bulge. For the initially rotating small classical bulge, cylindrical rotation in the resulting composite boxy/peanut bulge extends to lower heights (Saha & Gerhard 2013). More massive classical bulges also gain angular momentum emitted by the bar, inducing surprisingly large rotational support within about 4 Gyrs (Saha et al. in prep).

Saha, Kanak; Gerhard, Ortwin

2015-03-01

161

The Central Region of the Nearby Seyfert 2 Galaxy NGC 4945: A Pair of Spirals  

NASA Astrophysics Data System (ADS)

NGC 4945 is a Seyfert 2 galaxy at a distance of 3.82 Mpc. Its relative proximity has permitted a detailed Submillimeter Array study of the circumnuclear molecular gas in a galaxy exhibiting an active galactic nucleus (AGN). Based on an analysis of the high-resolution velocity field of the central region (20'' 20'', 1'' = 19 pc), we demonstrate that the S-shaped structure of the isovelocity contours is well reproduced by the numerical results of a two-dimensional hydrodynamical simulation. In particular, the velocity structure is represented by the bending produced by a shock along the spiral density waves, which are excited at the outer-inner Lindblad resonance (OILR) by a fast rotating bar. The simulated density map reveals a pair of tightly wound spirals in the center which pass through most of the ring-like (claimed to be a circumnuclear starburst ring by other authors) high-intensity region in the observations as well as intersect several Pa? emission line knots located outside the ring-like region. The calculated mass inflow rate at a scale of 50 pc is about three times the inferred mass accretion rate of the AGNs of NGC 4945. We find that self-gravity of the gas is important and should be included in our model for NGC 4945. The model is compared with the gas orbit model discussed in Lim et al., and it is shown that the hydrodynamic model provides a better match to the observed position-velocity diagram and, hence, provides a more reliable prediction of the OILR position.

Lin, Lien-Hsuan; Taam, Ronald E.; Yen, David C. C.; Muller, S.; Lim, J.

2011-04-01

162

Spiral Galaxy NGC 3982 Lithograph and In Search of...Spiral Galaxies  

NSDL National Science Digital Library

This lithograph features an image from the Hubble Space Telescope, showcasing the well-known features of NGC 3982, a face-on spiral galaxy. The accompanying activity, In Search Of...Spiral Galaxies, is a curriculum support tool designed for use as an introductory inquiry activity. In this activity, students will use the lithograph image and text to generate questions about spiral galaxies, and then research the answers to those questions. Students will then create a presentation to demonstrate their understanding of the material.

2014-01-17

163

RR Lyrae stars in local group galaxies. II - NGC 147  

NASA Technical Reports Server (NTRS)

Deep CCD images of NGC 147 taken with the '4-shooter' on the Hale 5 m telescope have been processed to find and photometrically measure RR Lyrae stars. 36 variable stars have been found, of which 32 are surmised to be RR Lyrae stars. Finding charts, periods, and light curves are presented. The mean magnitude of the RR Lyraes is determined to be 25.25 mag. A distance modulus 23.92 is derived, based on the best currently available values of foreground extinction and mean absolute magnitudes of RR Lyrae stars. A wide range of periods is seen for the RR Lyrae stars, indicating a correspondingly wide range of metallicities for the stars in NGC 147. The distance modulus derived here places NGC 147 at a distance of 154 kpc from the center of M31, and in conjunction with the line sight velocities of these two galaxies, this implies a lower limit of 7.2 x 10 to the 11th solar masses for the mass of M31.

Saha, A.; Hoessel, John G.; Mossman, Amy E.

1990-01-01

164

GMOS Spectroscopy of the S0 galaxy NGC 3115  

E-print Network

We present Gemini GMOS longslit spectroscopy of the isolated S0 galaxy NGC 3115. We have determined kinematical data and Lick/IDS absorption line-strength indices for the major axis out to around 9 kpc and for the minor axis out to around 5 kpc (around 2Re). Using stellar population models which include the effects of variable [alpha/Fe] ratios we derive metallicities, abundance ratios and ages for the stellar population of NGC 3115. We find that [alpha/Fe] remains fairly constant with increasing radius at around [alpha/Fe] = 0.17 for the major axis but increases rapidly for the minor axis to around [alpha/Fe] = 0.3. We also find that to first order this behaviour can be explained by a simple spheroid + disc model, where the spheroid has [alpha/Fe] = 0.3 and the disc shows close to solar abundance ratios. The disc also appears considerably younger than the spheroid, having an age of around 6 Gyr compared to 12 Gyr for the spheroid. We compare these results to those previously presented for the globular cluster system of NGC 3115.

Mark A. Norris; Ray M. Sharples; Harald Kuntschner

2006-01-10

165

RR Lyrae stars in local group galaxies. II. NGC 147  

SciTech Connect

Deep CCD images of NGC 147 taken with the 4-shooter on the Hale 5 m telescope have been processed to find and photometrically measure RR Lyrae stars. 36 variable stars have been found, of which 32 are surmised to be RR Lyrae stars. Finding charts, periods, and light curves are presented. The mean magnitude of the RR Lyraes is determined to be 25.25 mag. A distance modulus 23.92 is derived, based on the best currently available values of foreground extinction and mean absolute magnitudes of RR Lyrae stars. A wide range of periods is seen for the RR Lyrae stars, indicating a correspondingly wide range of metallicities for the stars in NGC 147. The distance modulus derived here places NGC 147 at a distance of 154 kpc from the center of M31, and in conjunction with the line sight velocities of these two galaxies, this implies a lower limit of 7.2 x 10 to the 11th solar masses for the mass of M31. 23 refs.

Saha, A.; Hoessel, J.G.; Mossman, A.E. (Mount Wilson and Las Campanas Observatories, Pasadena, CA (USA) Space Telescope Science Institute, Baltimore, MD (USA) Washburn Observatory, Madison, WI (USA))

1990-07-01

166

Vibrationally Excited HCN in the Luminous Infrared Galaxy NGC 4418  

NASA Astrophysics Data System (ADS)

Infrared pumping and its effect on the excitation of HCN molecules can be important when using rotational lines of HCN to probe dense molecular gas in galaxy nuclei. We report the first extragalactic detection of (sub)millimeter rotational lines of vibrationally excited HCN, in the dust-enshrouded nucleus of the luminous infrared galaxy NGC 4418. We estimate the excitation temperature of Tvib ? 230 K between the vibrational ground and excited (v 2 = 1) states. This excitation is most likely due to infrared radiation. At this high vibrational temperature the path through the v 2 = 1 state must have a strong impact on the rotational excitation in the vibrational ground level, although it may not be dominant for all rotational levels. Our observations also revealed nearly confusion-limited lines of CO, HCN, HCO+, H13CN, HC15N, CS, N2H+, and HC3N at ? ~ 1 mm. Their relative intensities may also be affected by the infrared pumping.

Sakamoto, Kazushi; Aalto, Susanne; Evans, Aaron S.; Wiedner, Martina C.; Wilner, David J.

2010-12-01

167

Infrared observations of the spiral galaxy NGC 891  

NASA Astrophysics Data System (ADS)

This thesis is a detailed, multi-waveband study of the inner 14 kpc of the famous spiral galaxy, NCG 891. The primary data have come from the Infrared Space Observatory's Camera. These data are images of the galaxy in 9 different mid-infrared wavebands. We have supported these data with archived data from the Spitzer Infrared Array Camera in 4 similar wavebands. Surface brightness contour maps of the galaxy were created and examined to determine where the mid-infrared emitters are located with respect to the galactic plane. We have determined that the main mid-infrared emission, due to warm dust and PAHs, lies in a thin disk of width 700 - 800 pc, but has faint emission that reaches up to about 2.3 kpc into the halo. The infrared spectral energy distribution (SED) for four environments in NGC 891 were created from the above mentioned wavebands as well as measurements from Spitzer's Multiband Imaging Photometer (3 Far-Infrared wavebands), the Two Micron All Sky Survey J, H, and K near-infrared wavebands, and the Sub- millimeter Common User Bolometer Array 450 and 850 mm bands. These spectra were fit with a SED model created by Frederic Galliano, and the physical properties of these environments were computed. The maps and SED show that while there is a relatively large amount of dust in NGC 891's halo, there is a depletion of PAHs beyond 2.3 kpc from the mid-plane. This is only the fourth galaxy to date that has PAH emission discovered in the halo, and it is the first in which the SED has been modeled for the halo.

Whaley, Cynthia

2007-08-01

168

Barred Galaxies: Studying the Chaotic and Ordered Nature of Orbits  

NASA Astrophysics Data System (ADS)

The chaotic or ordered character of orbits in galactic models is an important issue, since it can influence dynamical evolution. This distinction can be achieved with the help of the Smaller ALingment Index. - (SALI). We describe here briefly this method and its advantages. Then we apply it to that case of 2D and 3D barred galaxy potentials. In particular, we find the fraction of chaotic and ordered orbits in such potentials and present how this fraction changes when the main parameters of the model are varied. For this, we consider models with different bar mass, bar thickness or pattern speed. Varying only one parameter at a time, we find that bars that are more massive, or thinner, or faster, have a larger fraction of chaotic orbits.

Manos, T.; Athanassoula, E.

2006-08-01

169

Young star clusters in interacting galaxies - NGC 1487 and NGC 4038/4039  

E-print Network

We estimate the dynamical masses of several young (~10 Myr) massive star clusters in two interacting galaxies, NGC 4038/4039 ("The Antennae") and NGC 1487, under the assumption of virial equilibrium. These are compared with photometric mass estimates from K-band photometry and assuming a standard Kroupa IMF. The clusters were selected to have near-infrared colors dominated by red supergiants, and hence to be old enough to have survived the earliest phases of cluster evolution when the interstellar medium is rapidly swept out from the cluster, supported by the fact that there is no obvious Halpha emission associated with the clusters. All but one of the Antennae clusters have dynamical and photometric mass estimates which are within a factor ~2 of one another, implying both that standard IMFs provide a good approximation to the IMF of these clusters, and that there is no significant extra-virial motion, as would be expected if they were rapidly dispersing. These results suggest that almost all of the Antennae clusters in our sample have survived the gas removal phase as bound or marginally bound objects. Two of the three NGC 1487 clusters studied here have M_dyn estimates which are significantly larger than the photometric mass estimates. At least one of these two clusters, and one in the Antennae, may be actively in the process of dissolving. The process of dissolution contributes a component of non-virial motion to the integrated velocity measurements, resulting in an estimated M_dyn which is too high relative to the amount of measured stellar light. The dissolution candidates in both galaxies are amongst the clusters with the lowest pressures/densities measured in our sample.

Sabine Mengel; Matthew D. Lehnert; Niranjan A. Thatte; William D. Vacca; Brad Whitmore; Rupali Chandar

2008-05-16

170

Resolving Molecular Clouds in the Nearby Galaxy NGC 300  

NASA Astrophysics Data System (ADS)

We present results from our ongoing Submillimeter Array (SMA) survey in which we resolve Giant Molecular Clouds (GMCs) for the first time in the nearby (D = 1.9 Mpc) spiral galaxy NGC 300. We have conducted CO(2-1) and 1.3 mm dust continuum observations of several massive star-forming regions in NGC 300, following up on the Atacama Pathfinder Experiment (APEX) survey of Faesi et al. (2014). We find that the unresolved CO sources detected with APEX at ~250 pc resolution typically resolve into one dominant GMC in our SMA observations, which have a resolution of ~3.5' (30 pc). The majority of sources are significantly detected in CO, but only one exhibits dust continuum emission. Comparing with archival H-alpha, GALEX far-ultraviolet, and Spitzer 24 micron images, we note physical offsets between the young star clusters, warm dust, and ionized and molecular gas components in these regions. We recover a widely varying fraction -- between 30% and almost 100% -- of the full APEX single dish flux with our interferometric observations. This implies that the fraction of CO-emitting molecular gas that is in a diffuse state (i.e. with characteristic spatial scales > 100 pc) differs greatly amongst star forming regions in NGC 300. We investigate potential trends in the implied diffuse molecular gas fraction with GMC properties and star formation activity. We compute virial masses and analyze the velocity structure of these resolved extragalactic GMCs and compare to results from surveys of the Milky Way and other nearby galaxies.

Faesi, Christopher; Lada, Charles J.; Forbrich, Jan

2015-01-01

171

A Giant Outflow from the Virgo Cluster Galaxy NGC 4569  

NASA Astrophysics Data System (ADS)

The Virgo Clustere spiral galaxy NGC 4569 has been observed in X-rays and in the optical (R, B, H?). The X-ray contours show a diffuse extended halo that seems to be fed by a central bipolar outflow. Although the resulting physical properties of this X-ray halo are comparable to those derived from others in edge-on galaxies, like e. g. NGC 253, the halo is asymmetric: its western component is more extended, while the eastern counterpart is compressed and elongated along the disk toward the south. From the absorption of the softest X-radiation the inclination of the disk can be derived and agrees with results from extinction as well as rotation analyses: one is looking to below the disk from the east, so that the western X-ray halo lies behind the disk. In connection with the westwards extended X-ray halo we discovered a giant spur of diffuse H? emission. Since this stands perpendicularly to the major axis of the visible ellipsoid, it seems plausible that it sticks out also perpendicularly from the disk. Then it reaches to almost 10 kpc above the plane. In addition, information about the H? kinematics clearly shows that this filament is decoupled from the NGC 4569 disk. Most impressively the velocities prove the H? filament to be a huge outflow. We derive the physical parameters of the H? spur, discuss its possible origin and the cause for the halo asymmetry. Bomans D., Tschke D., Hensler G., Boselli A., 2001, A&A, submitted Tschke D., Hensler G., Bomans D., Junkes N., 2001, A&A, submitted

Hensler, G.; Bomans, D.; Tschke, D.; Boselli, A.

172

Bar-Halo Friction in Galaxies II: Metastability  

E-print Network

It is well-established that strong bars rotating in dense halos generally slow down as they lose angular momentum to the halo through dynamical friction. Angular momentum exchanges between the bar and halo particles take place at resonances. While some particles gain and others lose, friction arises when there is an excess of gainers over losers. This imbalance results from the generally decreasing numbers of particles with increasing angular momentum, and friction can therefore be avoided if there is no gradient in the density of particles across the major resonances. Here we show that anomalously weak friction can occur for this reason if the pattern speed of the bar fluctuates upwards. After such an event, the density of resonant halo particles has a local inflexion created by the earlier exchanges, and bar slowdown can be delayed for a long period; we describe this as a metastable state. We show that this behavior in purely collisionless N-body simulations is far more likely to occur in methods with adaptive resolution. We also show that the phenomenon could arise in nature, since bar-driven gas inflow could easily raise the bar pattern speed enough to reach the metastable state. Finally, we demonstrate that mild external, or internal, perturbations quickly restore the usual frictional drag, and it is unlikely therefore that a strong bar in a galaxy having a dense halo could rotate for a long period without friction.

J. A. Sellwood; Victor P. Debattista

2005-11-05

173

Nested and Single Bars in Seyfert and Non-Seyfert Galaxies  

E-print Network

We analyze the observed properties of nested and single stellar bar systems in disk galaxies. The 112 galaxies in our sample comprise the largest matched Seyfert vs. non-Seyfert sample of nearby galaxies with complete near-infrared or optical imaging sensitive to lengthscales ranging from tens of pc to tens of kpc. We find that a significant fraction of the sample galaxies, 17% +/- 4%, has more than one bar, and that 28% +/- 5% of barred galaxies have nested bars. The bar fractions appear to be stable according to reasonable changes in our adopted bar criteria. For these nested bars, we detect a clear division in length between the large-scale (primary) bars and small-scale (secondary) bars, both in absolute and normalized (to the size of the galaxy) length. We argue that this bimodal distribution can be understood within the framework of the inner Lindblad resonances (ILRs), which are located where the gravitational potential of the innermost galaxy switches effectively from 3D to 2D. While primary bars are found to correlate with the host galaxy sizes, no such correlation is observed for the secondary bars. Moreover, we find that secondary bars differ morphologically from single bars. Overall, our matched Seyfert and non-Seyfert samples show a statistically significant excess of bars among the Seyfert galaxies at practically all lengthscales. We confirm our previous result that Seyfert galaxies always show a preponderance of "thick" bars compared to the bars in non-Seyfert galaxies. Finally, no correlation is observed between the presence of a bar and that of companion galaxies, even relatively bright ones.

Seppo Laine; Isaac Shlosman; Johan H. Knapen; Reynier F. Peletier

2001-10-25

174

Hydrodynamical Simulations of Nuclear Rings in Barred Galaxies  

E-print Network

Dust lanes, nuclear rings, and nuclear spirals are typical gas structures in the inner region of barred galaxies Their shapes and properties are linked to the physical parameters of the host galaxy. We use high-resolution hydrodynamical simulations to study 2D gas flows in simple barred galaxy models. The nuclear rings formed in our simulations can be divided into two groups: one group is nearly round and the other is highly elongated. We find that roundish rings may not form when the bar pattern speed is too high or the bulge central density is too low. We also study the periodic orbits in our galaxy models, and find that the concept of inner Lindblad resonance (ILR) may be generalized by the extent of $x_2$ orbits. All roundish nuclear rings in our simulations settle in the range of $x_2$ orbits (or ILRs). However, knowing the resonances is insufficient to pin down the exact location of these nuclear rings. We suggest that the backbone of round nuclear rings is the $x_2$ orbital family, i.e. round nuclear r...

Li, Zhi; Kim, Woong-Tae

2015-01-01

175

The properties and origins of molecular gas in the lenticular galaxies NGC 404, 4710 and 5195  

Microsoft Academic Search

Properties of the molecular interstellar medium in three SO galaxies (NGC 404, NGC 4710, and NGC 5195) were examined. The (C-12)O J = 2-1 (230 GHz) and (C-13)O J = 1-2 spectra were obtained during December 1988 observations with the NRAO 12-m telescope at Kitt Peak, and were compared to (C-12)O J = 1-0 spectra. The resultant line ratios were

L. J. Sage

1990-01-01

176

The complex nature of the Seyfert galaxy NGC 7592  

NASA Technical Reports Server (NTRS)

Long slit spectra of NGC 7592 were taken on Sep. 26 to 30, 1989 at the 1.52 cm European Southern Observatory (ESO) telescope, equipped with a Boller and Chivens spectrograph and an RCA High Resolution charge coupled device (CCD) camera. The problem of the nature of Region C is addressed at first. C shows an heliocentric radial velocity very similar to that of Regions A and B. Moreover, the arm departing from C is most probably a tidal tail, because its extension is large and its orientation is peculiar. The high H alpha luminosity of C is typical of a starburst nucleus. These facts argue in favor of C being the nucleus of a third galactic component (southern component S) physically interacting with the SE component of NGC 7592. The directions of the velocity vectors in various regions of NGC 7592 are marked. It is noteworthy that the SE component rotates clockwise, if the radial velocity difference delta v sub r from its nucleus B is due to rotation. Under the same assumption for the delta v sub r = v sub r-v sub r, A, the NW component seems to rotate counterclockwise. Thus, the gas in the regions where the two galactic bodies are in contact moves in the same way, suggesting that a prograde encounter is occurring. It is known (e.g., Toomre and Toomre, 1972) that prograde encounters have the most disruptive effects on the interacting galaxies, leading to the formation of tidal tails. The interpretation of the wing of the NW component in terms of a tidal tail thus appears very likely. A similar situation holds for the interaction between SE and S too, where S rotates counterclockwise. The interpretation of the arm departing from C as a tidal tail is supported also in this case. The difference in radial velocity between A and B (delta v sub r approx. equal - 40 km s(exp-1)) and the morphology of NGC 7592 suggests that the NW component is beyond the SE one and is approaching it. The most heavily reddened regions (E(B - V) approx. equals 0.7, derived from the H alpha/H beta ratio) are B2 and B4, namely the regions between A and B. Moreover, the small difference in radial velocity between A,B,C suggests that the three galaxies form a bound system, and their kinematics hints that they are most probably in the early stage of a merging phenomenon.

Rafanelli, Piero; Marziani, Paolo

1990-01-01

177

Star formation in isolated AMIGA galaxies: dynamical influence of bars  

NASA Astrophysics Data System (ADS)

Context: Star formation depends strongly on both the local environment of galaxies and the internal dynamics of the interstellar medium. To disentangle the two effects, we obtained, in the framework of the AMIGA project, H? and Gunn r photometric data for more than 200 spiral galaxies lying in very low-density regions of the local Universe. Aims: We characterise the H? emission, tracing current star formation, of the 45 largest and least inclined galaxies observed for which we estimate the torques between the gas and the bulk of the optical matter. We subsequently study the H? morphological aspect of these isolated spiral galaxies. Methods: Using Fourier analysis, we focus on the modes of the spiral arms and also on the strength of the bars, computing the torques between the gas and newly formed stars (H?), and the bulk of the optical matter (Gunn r). Results: We interpret the various bar/spiral morphologies observed in terms of the secular evolution experienced by galaxies in isolation. We also classify the different spatial distributions of star forming regions in barred galaxies. The observed frequency of particular patterns brings constraints on the lifetime of the various evolution phases. We propose an evolutive sequence accounting for the transitions between the different phases we observed. Conclusions: Isolated galaxies do not appear to be preferentially barred or unbarred. Fitting the H? distributions using numerical simulations yields constraints on the star formation law, which is likely to differ from a genuine Schmidt law. In particular, it is probable that the relative velocity of the gas in the bar also needs to be taken into account. Partially based on observations collected at the Centro Astronmico Hispano Alemn (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut fr Astronomie and the Instituto de Astrofsica de Andaluca (CSIC), as well as at the Observatorio de Sierra Nevada (OSN), operated by the IAA/CSIC. Table [see full text] and Figs. [see full text]-[see full text] are only available in electronic form at http://www.aanda.org

Verley, S.; Combes, F.; Verdes-Montenegro, L.; Bergond, G.; Leon, S.

2007-10-01

178

HUBBLE SPACE TELESCOPE PIXEL ANALYSIS OF THE INTERACTING S0 GALAXY NGC 5195 (M51B)  

SciTech Connect

We report the properties of the interacting S0 galaxy NGC 5195 (M51B), revealed in a pixel analysis using the Hubble Space Telescope/Advanced Camera for Surveys images in the F435W, F555W, and F814W (BVI) bands. We analyze the pixel color-magnitude diagram (pCMD) of NGC 5195, focusing on the properties of its red and blue pixel sequences and the difference from the pCMD of NGC 5194 (M51A; the spiral galaxy interacting with NGC 5195). The red pixel sequence of NGC 5195 is redder than that of NGC 5194, which corresponds to the difference in the dust optical depth of 2 < {Delta}{tau}{sub V} < 4 at fixed age and metallicity. The blue pixel sequence of NGC 5195 is very weak and spatially corresponds to the tidal bridge between the two interacting galaxies. This implies that the blue pixel sequence is not an ordinary feature in the pCMD of an early-type galaxy, but that it is a transient feature of star formation caused by the galaxy-galaxy interaction. We also find a difference in the shapes of the red pixel sequences on the pixel color-color diagrams (pCCDs) of NGC 5194 and NGC 5195. We investigate the spatial distributions of the pCCD-based pixel stellar populations. The young population fraction in the tidal bridge area is larger than that in other areas by a factor >15. Along the tidal bridge, young populations seem to be clumped particularly at the middle point of the bridge. On the other hand, the dusty population shows a relatively wide distribution between the tidal bridge and the center of NGC 5195.

Lee, Joon Hyeop; Kim, Sang Chul; Ree, Chang Hee; Kim, Minjin; Jeong, Hyunjin; Lee, Jong Chul; Kyeong, Jaemann, E-mail: jhl@kasi.re.kr, E-mail: sckim@kasi.re.kr, E-mail: chr@kasi.re.kr, E-mail: mkim@kasi.re.kr, E-mail: hyunjin@kasi.re.kr, E-mail: jclee@kasi.re.kr, E-mail: jman@kasi.re.kr [Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of)

2012-08-01

179

Kinematics and ionization of extended ionized gas in active galaxies. I - The X-ray luminous galaxies NGC 2110, NGC 5506, and MCG -5-23-16  

NASA Technical Reports Server (NTRS)

Direct CCD imaging and long-slit Vidicon spectroscopy have been used to map the emission-line ratios, profiles, and velocity fields over the extended narrow-line regions in three nearby Seyfert galaxies, NGC 2110, NGC 5506, and MCG -5-23-16. The gas in the letter is spatially unresolved. Similarities between the other two nebulae include the excitation mechanism (photoionization by a central nonthermal source) and the overall profiles of the very broad emission lines close to the nucleus. The nebulae are, however, quite different in their global kinematic behavior. In NGC 2110, the gas appears to lie in a disk or flattened spheroid and to be in ordered rotation, with a classical rotation curve, about an axis parallel to the minor axis of the stellar isophotes. The velocity field of NGC 5506 is quite irregular, but a component of rotation in the plane of the galaxy seems to exist.

Wilson, A. S.; Baldwin, J. A.; Ulvestad, J. S.

1985-01-01

180

A search for ultra-compact dwarf galaxies in the NGC 1023 group of galaxies  

E-print Network

We present a photometric search for UCD candidates in the nearby galaxy group NGC 1023 (d=11 Mpc) -- the poorest environment searched for UCDs yet --, based on wide field imaging with CFHT. After photometric and morphological selection, we obtain a sample of 21 UCD candidates with -12group, the mass spectrum of analogs to Fornax/Virgo UCD is restricted to about 1/4 of the maximum Fornax/Virgo UCD mass. More spectroscopy is needed to further constrain the mass range of UCDs in this galaxy group.

S. Mieske; M. J. West; C. Mendes de Oliveira

2006-03-20

181

AN INITIAL MASS FUNCTION STUDY OF THE DWARF STARBURST GALAXY NGC 4214  

E-print Network

The production rate of ionizing photons in young (?8 Myr), unresolved stellar clusters in the nearby irregular galaxy NGC 4214 is probed using multi-wavelength Hubble Space Telescope WFC3 data. We normalize the ionizing ...

Andrews, J. E.

182

Toward an Understanding of the Globular Cluster Overabundance around the Central Giant Elliptical Galaxy NGC 1399  

NASA Astrophysics Data System (ADS)

We investigate the kinematics of a combined sample of 74 globular clusters around NGC 1399. Their high velocity dispersion, increasing with radius, indicates their association with the gravitational potential of the galaxy cluster rather than with that of NGC 1399 itself. We find no evidence for rotation in the full sample, although there is some indication of rotation in the outer regions. The data do not allow us to detect differences between the kinematics of the blue and red subpopulations of globular clusters. A comparison of the globular cluster systems of NGC 1399 and those of NGC 1404 and NGC 1380 indicates that the globular clusters in all three galaxies are likely to have formed via similar mechanisms and at similar epochs. The only property that distinguishes the NGC 1399 globular cluster system from these others is that it is 10 times more abundant. We summarize the evidence for associating these excess globular clusters with the galaxy cluster rather than with NGC 1399 itself and suggest that the overabundance can be explained by tidal stripping, at an early epoch, of neighboring galaxies and subsequent accumulation of globular clusters in the gravitational potential of the galaxy cluster.

Kissler-Patig, Markus; Grillmair, Carl J.; Meylan, Georges; Brodie, Jean P.; Minniti, Dante; Goudfrooij, Paul

1999-03-01

183

Cold dust emission from the spiral galaxy NGC 3627  

NASA Astrophysics Data System (ADS)

We present a high resolution dust continuum map of the nearby spiral galaxy NGC 3627. Using the MPIfR 7-channel bolometer on the IRAM 30-m telescope, it was possible to trace the emission from cold (T approximately 20 K) dust along the spiral arms of this galaxy. The total flux density at lambda 1.28 mm = 570 +/- 90 mJy. Using reasonable assumptions about the column densities and the source angles of H2 for different temperatures, we fit a three component modified Planck function to the dust emission spectrum between 1.3 mm and 12 micrometers resulting in a dominant 19.5 K component for the large scale dust emission at mm wavelengths. The total flux density and dust temperature is used to estimate the total gas mass of this galaxy. Using Galactic values for the gas-to-dust ratio and for the absorption coefficient, the total gas mass is in excellent agreement with that obtained by CO measurements.

Sievers, A. W.; Reuter, H.-P.; Haslam, C. G. T.; Kreysa, E.; Lemke, R.

1994-01-01

184

Bar-halo Friction in Galaxies I: Scaling Laws  

E-print Network

It has been known for some time that rotating bars in galaxies slow due to dynamical friction against the halo. However, recent attempts to use this process to place constraints on the dark matter density in galaxies and possibly also to drive dark matter out of the center have been challenged. This paper uses simplified numerical experiments to clarify several aspects of the friction mechanism. I explicitly demonstrate the Chandrasekhar scaling of the friction force with bar mass, halo density, and halo velocity dispersion. I present direct evidence that exchanges between the bar and halo orbits at major resonances are responsible for friction and study both individual orbits and the net changes at these resonances. I also show that friction alters the phase space density of particles in the vicinity of a major resonance, which is the reason the magnitude of the friction force depends on the prior evolution. I demonstrate that bar slow down can be captured correctly in simulations having modest spatial resolution and practicable numbers of particles. Subsequent papers in this series delineate the dark matter density that can be tolerated in halos of different density profiles.

J. A. Sellwood

2005-09-28

185

STAR FORMATION IN NUCLEAR RINGS OF BARRED GALAXIES  

SciTech Connect

Nuclear rings in barred galaxies are sites of active star formation. We use hydrodynamic simulations to study the temporal and spatial behavior of star formation occurring in nuclear rings of barred galaxies where radial gas inflows are triggered solely by a bar potential. The star formation recipes include a density threshold, an efficiency, conversion of gas to star particles, and delayed momentum feedback via supernova explosions. We find that the star formation rate (SFR) in a nuclear ring is roughly equal to the mass inflow rate to the ring, while it has a weak dependence on the total gas mass in the ring. The SFR typically exhibits a strong primary burst followed by weak secondary bursts before declining to very small values. The primary burst is associated with the rapid gas infall to the ring due to the bar growth, while the secondary bursts are caused by re-infall of the ejected gas from the primary burst. While star formation in observed rings persists episodically over a few Gyr, the duration of active star formation in our models lasts for only about half of the bar growth time, suggesting that the bar potential alone is unlikely to be responsible for gas supply to the rings. When the SFR is low, most star formation occurs at the contact points between the ring and the dust lanes, leading to an azimuthal age gradient of young star clusters. When the SFR is large, on the other hand, star formation is randomly distributed over the whole circumference of the ring, resulting in no apparent azimuthal age gradient. Since the ring shrinks in size with time, star clusters also exhibit a radial age gradient, with younger clusters found closer to the ring. The cluster mass function is well described by a power law, with a slope depending on the SFR. Giant gas clouds in the rings have supersonic internal velocity dispersions and are gravitationally bound.

Seo, Woo-Young; Kim, Woong-Tae, E-mail: seowy@astro.snu.ac.kr, E-mail: wkim@astro.snu.ac.kr [Center for the Exploration of the Origin of the Universe (CEOU), Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 151-742 (Korea, Republic of)

2013-06-01

186

Monitoring the long term variable Seyfert 2 galaxy NGC 2992  

NASA Astrophysics Data System (ADS)

We propose to observe with XMM-Newton in AO5 the highly variable Seyfert 2 galaxy NGC 2992. The source has been observed to vary in flux by more than one order of magnitude in a few years. The time behaviour of the iron line is very interesting, suggesting the presence of two components, one narrow and constant on time scale of years, the other broad and probably originating in the accretion disc. We propose to observe the source twice, once per visibility window (i.e. about six months apart), 25 ks per pointing, not only to confirm the presence of the relativistic line (if the source will still be in high state, in at least one of the two observations) but also to study continuum and iron line variations on time scale of months and, when compared to previous observations, of years.

Matt, Giorgio

2005-10-01

187

RR Lyrae stars in local group galaxies. I - NGC 185  

NASA Technical Reports Server (NTRS)

Deep CCD images of NGC 185 taken with the '4-shooter' on the Hale 5-m telescope have been processed to find and photometrically measure RR Lyrae stars. 176 variable stars have been found, of which 151 are surmised to be RR Lyrae stars. Finding charts, periods, and light curves are presented. The RR Lyrae stars in this galaxy have a very wide distribution of periods indicating a wide range of metallicity. The mean magnitudes of the RR Lyraes is determined to be 25.20 mag. A distance modulus of 23.79 is derived, based on the best currently available values of foreground extinction and mean absolute magnitudes of RR Lyrae stars.

Saha, A.; Hoessel, John G.

1990-01-01

188

RR Lyrae stars in local group galaxies. I. NGC 185  

SciTech Connect

Deep CCD images of NGC 185 taken with the 4-shooter on the Hale 5-m telescope have been processed to find and photometrically measure RR Lyrae stars. 176 variable stars have been found, of which 151 are surmised to be RR Lyrae stars. Finding charts, periods, and light curves are presented. The RR Lyrae stars in this galaxy have a very wide distribution of periods indicating a wide range of metallicity. The mean magnitudes of the RR Lyraes is determined to be 25.20 mag. A distance modulus of 23.79 is derived, based on the best currently available values of foreground extinction and mean absolute magnitudes of RR Lyrae stars. 33 refs.

Saha, A.; Hoessel, J.G. (Mount Wilson and Las Campanas Observatories, Pasadena, CA (USA) Space Telescope Science Institute, Baltimore, MD (USA) Washburn Observatory, Madison, WI (USA))

1990-01-01

189

Line asymmetry in the Seyfert Galaxy NGC 3783  

NASA Technical Reports Server (NTRS)

We have reanalyzed the 900 ks Chandra X-ray spectrum of NGC 3783, finding evidence on the asymmetry of the spectral absorption lines. The lines are fitted with a parametric expression that results from an analytical treatment of radiatively driven winds. The line asymmetry distribution derived from the spectrum is consistent with a non-spherical outflow with a finite optical depth. Within this scenario, our model explains the observed correlations between the line velocity shifts and the ionization parameter and between the line velocity shift and the line asymmetry. The present results may provide a framework for detailed testing of models for the dynamic and physical properties of warm absorber in Seyfert galaxies.

Ramirez, J. M.; Bautista, Manuel; Kallman, Timothy

2005-01-01

190

A Dynamical Model for the cD Galaxy NGC 6086  

NASA Astrophysics Data System (ADS)

We present a dynamical model for the cD galaxy NGC6086 in the Abell 2162 cluster. Deep long-slit major axis spectra of NGC6086, NGC6166 and NGC6173 were obtained on the INT in La Palma by D. Carter, T. Bridges and G. Hau in order to probe the halo dynamics and metallicity gradients out to at least 1.5 Re. The dynamical model was fitted directly to the spectra using a modeling technique developed at the University of Gent. This approach makes parameterization of the LOSVDs unnecessary and allows the use of a mix of several template stars to avoid template mismatch.

De Rijcke, S.; Dejonghe, H.; Carter, D.; Bridges, T. J.; Hau, G. K. T.

191

Stellar Clusters Forming in the Blue Dwarf Galaxy NGC 5253  

NASA Astrophysics Data System (ADS)

Star formation is one of the most basic phenomena in the Universe. Inside stars, primordial material from the Big Bang is processed into heavier elements that we observe today. In the extended atmospheres of certain types of stars, these elements combine into more complex systems like molecules and dust grains, the building blocks for new planets, stars and galaxies and, ultimately, for life. Violent star-forming processes let otherwise dull galaxies shine in the darkness of deep space and make them visible to us over large distances. Star formation begins with the collapse of the densest parts of interstellar clouds, regions that are characterized by comparatively high concentration of molecular gas and dust like the Orion complex (ESO PR Photo 20/04) and the Galactic Centre region (ESO Press Release 26/03). Since this gas and dust are products of earlier star formation, there must have been an early epoch when they did not yet exist. But how did the first stars then form? Indeed, to describe and explain "primordial star formation" - without molecular gas and dust - is a major challenge in modern Astrophysics. A particular class of relatively small galaxies, known as "Blue Dwarf Galaxies", possibly provide nearby and contemporary examples of what may have occurred in the early Universe during the formation of the first stars. These galaxies are poor in dust and heavier elements. They contain interstellar clouds which, in some cases, appear to be quite similar to those primordial clouds from which the first stars were formed. And yet, despite the relative lack of the dust and molecular gas that form the basic ingredients for star formation as we know it from the Milky Way, those Blue Dwarf Galaxies sometimes harbour very active star-forming regions. Thus, by studying those areas, we may hope to better understand the star-forming processes in the early Universe. Very active star formation in NGC 5253 NGC 5253 is one of the nearest of the known Blue Dwarf Galaxies; it is located at a distance of about 11 million light-years in the direction of the southern constellation Centaurus. Some time ago a group of European astronomers [1] decided to take a closer look at this object and to study star-forming processes in the primordial-like environment of this galaxy. True, NGC 5253 does contains some dust and heavier elements, but significantly less than our own Milky Way galaxy. However, it is quite extreme as a site of intense star formation, a profuse "starburst galaxy" in astronomical terminology, and a prime object for detailed studies of large-scale star formation. ESO PR Photo 31a/04 provides an impressive view of NGC 5253. This composite image is based on a near-infrared exposure obtained with the multi-mode ISAAC instrument mounted on the 8.2-m VLT Antu telescope at the ESO Paranal Observatory (Chile), as well as two images in the optical waveband obtained from the Hubble Space Telescope data archive (located at ESO Garching). The VLT image (in the K-band at wavelength 2.16 ?m) is coded red, the HST images are blue (V-band at 0.55 ?m) and green (I-band at 0.79 ?m), respectively. The enormous light-gathering capability and the fine optical quality of the VLT made it possible to obtain the very detailed near-infrared image (cf. PR Photo 31b/04) during an exposure lasting only 5 min. The excellent atmospheric conditions of Paranal at the time of the observation (seeing 0.4 arcsec) allow the combination of space- and ground-based data into a colour photo of this interesting object. A major dust lane is visible at the western (right) side of the galaxy, but patches of dust are visible all over, together with a large number of colourful stars and stellar clusters. The different colour shades are indicative of the ages of the objects and the degree of obscuration by interstellar dust. The near-infrared VLT image penetrates the dust clouds much better than the optical HST images, and some deeply embedded objects that are not detected in the optical therefore appear as red in the combined image. Me

2004-11-01

192

Chandra Observations of the Luminous IR Galaxy NGC3256  

E-print Network

We present a detailed analysis of high-resolution Chandra observations of the merger system NGC3256, the most IR luminous galaxy in the nearby universe. The X-ray data show that several discrete sources embedded in complex diffuse emission contribute ~>20 of the total emission (L_x^tot ~8E41 ergs/s in the 0.5-10 keV energy range). The compact sources are hard and extremely bright and their emission is probably dominated by accretion driven processes. Both galaxy nuclei are detected with L_x ~3-10E40 ergs/s. No evidence is found for the presence of an active nucleus in the southern nucleus, contrary to previous speculation. Once the discrete sources are removed, the diffuse component has a soft spectrum which can be modelled by the superposition of 3 thermal plasma components with temperatures kT = 0.6, 0.9 and 3.9 keV. Alternatively, the latter component can be described as a power-law with index Gamma ~3. Some evidence is found for a radial gradient of the amount of absorption and temperature of the diffuse component. We compare the X-ray emission with optical, Halpha and NICMOS images of NGC3256 and find a good correlation between the inferred optical/near-IR and X-ray extinctions. Although Inverse Compton scattering could be important in explaining the hard X-rays seen in the compact sources associated with the nuclei, the observed diffuse emission is probably of thermal origin. The observed X-ray characteristics support a scenario in which the powerful X-ray emission is driven solely by the current episode of star formation.

P. Lira; M. Ward; A. Zezas; A. Alonso-Herrero; S. Ueno

2001-10-05

193

Chandra observations of the luminous infrared galaxy NGC 3256  

NASA Astrophysics Data System (ADS)

We present a detailed analysis of high-resolution Chandra observations of the merger system NGC 3256, the most infrared-luminous galaxy in the nearby universe. The X-ray data show that several discrete sources embedded in complex diffuse emission contribute >~20 per cent of the total emission (LtotX\\sim 8\\times 1041\\,erg\\,s-1 in the 0.5-10keV energy range). The compact sources are hard and extremely bright and their emission is probably dominated by accretion-driven processes. Both galaxy nuclei are detected with LX~3-101040ergs-1. No evidence is found for the presence of an active nucleus in the southern nucleus, contrary to previous speculation. Once the discrete sources are removed, the diffuse component has a soft spectrum that can be modelled by the superposition of three thermal plasma components with temperatures kT=0.6, 0.9 and 3.9keV. Alternatively, the latter component can be described as a power law with index ?~3. Some evidence is found for a radial gradient of the amount of absorption and temperature of the diffuse component. We compare the X-ray emission with optical, H? and NICMOS images of NGC 3256 and find a good correlation between the inferred optical/near-infrared and X-ray extinctions. Although inverse Compton scattering could be important in explaining the hard X-rays seen in the compact sources associated with the nuclei, the observed diffuse emission is probably of thermal origin. The observed X-ray characteristics support a scenario in which the powerful X-ray emission is driven solely by the current episode of star formation.

Lira, P.; Ward, M.; Zezas, A.; Alonso-Herrero, A.; Ueno, S.

2002-02-01

194

Multimolecule ALMA observations toward the Seyfert 1 galaxy NGC 1097  

NASA Astrophysics Data System (ADS)

Context. The nearby Sy 1 galaxy NGC 1097 represents an ideal laboratory for exploring the molecular chemistry in the surroundings of an active galactic nucleus (AGN). Aims: Exploring the distribution of different molecular species allows us to understand the physical processes affecting the interstellar medium both in the AGN vicinity and in the outer star forming molecular ring. Methods: We carried out 3 mm ALMA observations that include seven different molecular species, namely HCN, HCO+, CCH, CS, HNCO, SiO, HC3N, and SO, as well as the 13C isotopologues of the first two. Spectra were extracted from selected positions and all species were imaged over the central 2 kpc (~30'') of the galaxy at a resolution of ~2.2'' 1.5'' (150 pc 100 pc). Results: HCO+ and CS appear to be slightly enhanced in the star forming ring. CCH shows the largest variations across NGC 1097 and is suggested to be a good tracer of both obscured and early stage star formation. HNCO, SiO, and HC3N are significantly enhanced in the inner circumnuclear disk surrounding the AGN. Conclusions: Differences in the molecular abundances are observed between the star forming ring and the inner circumnuclear disk. We conclude that the HCN/HCO+ and HCN/CS differences observed between AGN-dominated and starburst (SB) galaxies are not due to a HCN enhancement due to X-rays, but rather this enhancement is produced by shocked material at distances of 200 pc from the AGN. Additionally, we claim that lower HCN/CS is a combination of a small underabundance of CS in AGNs, together with excitation effects, where a high density gas component (~106 cm-3) may be more prominent in SB galaxies. However, the most promising are the differences found among the dense gas tracers that, at our modest spatial resolution, seem to outline the physical structure of the molecular disk around the AGN. In this picture, HNCO probes the well-shielded gas in the disk, surrounding the dense material moderately exposed to the X-ray radiation traced by HC3N. Finally SiO might be the innermost molecule in the disk structure.

Martn, S.; Kohno, K.; Izumi, T.; Krips, M.; Meier, D. S.; Aladro, R.; Matsushita, S.; Takano, S.; Turner, J. L.; Espada, D.; Nakajima, T.; Terashima, Y.; Fathi, K.; Hsieh, P.-Y.; Imanishi, M.; Lundgren, A.; Nakai, N.; Schinnerer, E.; Sheth, K.; Wiklind, T.

2015-01-01

195

THE FORMATION OF SHELL GALAXIES SIMILAR TO NGC 7600 IN THE COLD DARK MATTER COSMOGONY  

SciTech Connect

We present new deep observations of 'shell' structures in the halo of the nearby elliptical galaxy NGC 7600, alongside a movie of galaxy formation in a cold dark matter (CDM) universe. The movie, based on an ab initio cosmological simulation, shows how continuous accretion of clumps of dark matter and stars creates a swath of diffuse circumgalactic structures. The disruption of a massive clump on a near-radial orbit creates a complex system of transient concentric shells which bare a striking resemblance to those of NGC 7600. With the aid of the simulation we interpret NGC 7600 in the context of the CDM model.

Cooper, Andrew P. [Max Planck Institut fuer Astrophysik, Karl-Schwarzschild-Str. 1, D-85741 Garching (Germany); Martinez-Delgado, David [Max Planck Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Helly, John; Frenk, Carlos; Cole, Shaun [Institute for Computational Cosmology, Department of Physics, University of Durham, South Road, DH1 3LE Durham (United Kingdom); Crawford, Ken [Rancho del Sol Observatory, Camino, CA 95709 (United States); Zibetti, Stefano [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark); Carballo-Bello, Julio A. [Instituto de Astrofisica de Canarias, Via Lactea s/n, E-38205 La Laguna, Tenerife (Spain); Jay GaBany, R., E-mail: acooper@mpa-garching.mpg.de, E-mail: delgado@mpia-hd.mpg.de [Black Bird Observatory II, 5660 Brionne Drive, San Jose, CA 95118 (United States)

2011-12-10

196

Nested and Single Bars in Seyfert and Non-Seyfert Galaxies  

NASA Astrophysics Data System (ADS)

We analyze the observed properties of nested and single stellar bar systems in disk galaxies. The 112 galaxies in our sample comprise the largest matched Seyfert versus non-Seyfert galaxy sample of nearby galaxies with complete near-infrared or optical imaging sensitive to length scales ranging from tens of parsecs to tens of kiloparsecs. The presence of bars is deduced by fitting ellipses to isophotes in Hubble Space Telescope (HST) H-band images up to 10" radius and in ground-based near-infrared and optical images outside the H-band images. This is a conservative approach that is likely to result in an underestimate of the true bar fraction. We find that a significant fraction of the sample galaxies, 17%+/-4%, have more than one bar, and that 28%+/-5% of barred galaxies have nested bars. The bar fractions appear to be stable according to reasonable changes in our adopted bar criteria. For the nested bars, we detect a clear division in length between the large-scale (primary) bars and small-scale (secondary) bars, in both absolute and normalized (to the size of the galaxy) length. We argue that this bimodal distribution can be understood within the framework of disk resonances, specifically the inner Lindblad resonances (ILRs), which are located where the gravitational potential of the innermost galaxy switches effectively from three-dimensional to two-dimensional. This conclusion is further strengthened by the observed distribution of the sizes of nuclear rings which are dynamically associated with the ILRs. While primary bar sizes are found to correlate with the host galaxy sizes, no such correlation is observed for the secondary bars. Moreover, we find that secondary bars differ morphologically from single bars. Our matched Seyfert and non-Seyfert samples show a statistically significant excess of bars among the Seyfert galaxies at practically all length scales. We confirm our previous results that bars are more abundant in Seyfert hosts than in non-Seyfert galaxies and that Seyfert galaxies always show a preponderance of ``thick'' bars compared to the bars in non-Seyfert galaxies. Finally, no correlation is observed between the presence of a bar and that of companion galaxies, even relatively bright ones. Overall, since star formation and dust extinction can be significant even in the H band, the stellar dynamics of the central kiloparsec cannot always be revealed reliably by the use of near-infrared surface photometry alone.

Laine, Seppo; Shlosman, Isaac; Knapen, Johan H.; Peletier, Reynier F.

2002-03-01

197

Comparison between 2-D and 3-D codes in dynamical simulations of gas flow in barred galaxies  

E-print Network

Context: One of the ways to determine the contribution of the dark halo to the gravitational potential of a galaxy is the study of non-circular (streaming) motions and the associated gas shocks in the bar region. These motions, determined by the potential in the inner parts, can break the disk-halo degeneracy. Here, two main fluid dynamical approaches have been chosen to model the non-circular motions in the bar region; a 2-D Eulerian grid code for an isothermal gas (FS2) and a 3-D smoothed particle hydrodynamic code (N-body/SPH). Aims: The aim of this paper is to compare and quantify the differences of the gas flows in rotating barred potential obtained using two different fluid dynamical approaches. We analyse the effect of using 2-D and a 3-D codes in the calculation of gas flow in barred galaxies and to which extend the results are affected by the code. To do this, we derive the velocity field and density maps for the mass model of NGC 4123 using a 3-D N-body/SPH code and compare the results to the previous 2-D Eulerian grid code results. Methods: Numerical modelling, 3-D N-body/SPH simulations Results: The global velocity field and the gas distribution is very similar in both models. The study shows that the position and strength of the shocks developed in the SPH simulations do not vary significantly compared to the results derived from the 2-D FS2 code. The largest velocity difference across the shock is 20\\kms between the 2-D and 3-D fluid dynamical models. Conclusions: The results obtained in the studies deriving the dark matter content of barred galaxies using the bar streaming motions and strength and position of shocks are robust to the fluid dynamical model used. The effect of 2-D and 3-D modelling can be neglected in this type of studies.

I. Perez

2007-10-15

198

STARS AND IONIZED GAS IN THE S0 GALAXY NGC 7743: AN INCLINED LARGE-SCALE GASEOUS DISK  

SciTech Connect

We used deep, long-slit spectra and integral-field spectral data to study the stars, ionized gas kinematics, and stellar population properties in the lenticular barred galaxy NGC 7743. We show that ionized gas at distances larger than 1.5 kpc from the nucleus settles in the disk, which is significantly inclined toward the stellar disk of the galaxy. Making different assumptions about the geometry of the disks and including different sets of emission lines in the fitting, under the assumption of thin, flat-disk circular rotation, we obtain the full possible range of angles between the disks to be 34{sup 0} {+-} 9{sup 0} or 77{sup 0} {+-} 9{sup 0}. The most probable origin of the inclined disk is the external gas accretion from a satellite orbiting the host galaxy, with a corresponding angular momentum direction. The published data on the H I distribution around NGC 7743 suggest that the galaxy has a gas-rich environment. The emission-line ratio diagrams imply the domination of shock waves in the ionization state of the gaseous disk, whereas the contribution of photoionization from recent star formation seems to be negligible. In some parts of the disk, a difference between the velocities of the gas emitting from the forbidden lines and Balmer lines is detected. This may be caused by the mainly shock-excited inclined disk, whereas some fraction of the Balmer-line emission is produced by a small amount of gas excited by young stars in the main stellar disk of NGC 7743. In the circumnuclear region (R < 200 pc), some evidence of the active galactic nucleus jet's interaction with an ambient interstellar medium was found.

Katkov, Ivan Yu.; Sil'chenko, Olga K. [Sternberg Astronomical Institute, Moscow 119992 (Russian Federation); Moiseev, Alexei V., E-mail: katkov.ivan@gmail.com, E-mail: moisav@gmail.com, E-mail: olga@sai.msu.su [Special Astrophysical Observatory, Russian Academy of Sciences, Nizhnii Arkhyz, Karachaevo-Cherkesskaya Republic 369167 (Russian Federation)

2011-10-20

199

Integral field spectroscopy and multi-wavelength imaging of the nearby spiral galaxy NGC 5668: a case for MEGARA  

NASA Astrophysics Data System (ADS)

In order to improve our understanding of the mechanisms that drive the evolution of disk galaxies we analyze the full bi-dimensional spectral cube of the nearby spiral galaxy NGC 5668, which was obtained as a mosaic of 6 pointings, covering a total area of 2 3 arcmin^{2}, obtained with the PPAK Integral Field Unit at the Calar Alto (CAHA) observatory 3.5 m telescope. From these data we obtain the bidimensional spatial distribution maps of the attenuation of the ionized gas, and chemical abundances of oxygen. We find a mean ionized-gas attenuation of A_V1 mag, with the gas attenuation appearing larger than the continuum attenuation by a factor of 3. With respect to the oxygen abundance, we find that, while inwards of r 36'' 4.4kpc 0.36 ({D_{25}}/{2}) the derived O/H ratio follows the radial gradient typical of the disks of spiral galaxies, the abundance gradient beyond r36'' flattens out. The multi-wavelength surface brightness profiles of NGC 5668 are compared with those predicted by chemo-spectrophotometric evolutionary models of galaxy disks in the context of the inside-out scenario of disk formation. Both the deviations of the color profiles and the shape of the metallicity radial distribution indicate that a secondary mechanism, possibly gas transfer induced by the presence of a young bar, must have played a role in shaping the recent chemical and star formation histories of NGC5668 beyond what is predicted by the inside-out scenario. This study demonstrates the strength of the combination of IFU and multi-wavelength imaging data. With MEGARA, the future optical IFU & MOS for 10.4-m GTC we will fill the gap currently existing in astronomical instrumentation with high spectral resolution and large area coverage simultaneously addressing such fundamental issues in galactic structure and evolution.

Marino, R. A.; Gil de Paz, A.; Castillo-Morales, A.; Muoz-Mateos, J. C.; Snchez, S. F.; Prez-Gonzlez, P. G.; Gallego, J.; Zamorano, J.; Alonso-Herrero, A.; Boissier, S.

2013-05-01

200

Chandra Observations of the Luminous IR Galaxy NGC3256  

E-print Network

We present a detailed analysis of high-resolution Chandra observations of the merger system NGC3256, the most IR luminous galaxy in the nearby universe. The X-ray data show that several discrete sources embedded in complex diffuse emission contribute ~>20 of the total emission (L_x^tot ~8E41 ergs/s in the 0.5-10 keV energy range). The compact sources are hard and extremely bright and their emission is probably dominated by accretion driven processes. Both galaxy nuclei are detected with L_x ~3-10E40 ergs/s. No evidence is found for the presence of an active nucleus in the southern nucleus, contrary to previous speculation. Once the discrete sources are removed, the diffuse component has a soft spectrum which can be modelled by the superposition of 3 thermal plasma components with temperatures kT = 0.6, 0.9 and 3.9 keV. Alternatively, the latter component can be described as a power-law with index Gamma ~3. Some evidence is found for a radial gradient of the amount of absorption and temperature of the diffuse ...

Lira, P; Ueno, S; Ward, M; Zezas, A L

2002-01-01

201

The difference in age of the two counter-rotating stellar disks of the spiral galaxy NGC 4138  

NASA Astrophysics Data System (ADS)

Context. Galaxies accrete material from the environment through acquisitions and mergers. These processes contribute to the galaxy assembly and leave their fingerprints on the galactic morphology, internal kinematics of gas and stars, and stellar populations. Aims: The Sa spiral NGC 4138 is known to host two counter-rotating stellar disks, with the ionized gas co-rotating with one of them. We measured the kinematics and properties of the two counter-rotating stellar populations to constrain their formation scenario. Methods: A spectroscopic decomposition of the observed major-axis spectrum was performed to disentangle the relative contribution of the two counter-rotating stellar and one ionized-gas components. The line-strength indices of the two counter-rotating stellar components were measured and modeled with single stellar population models that account for the ?/Fe overabundance. Results: The counter-rotating stellar population is younger, marginally more metal poor, and more ?-enhanced than the main stellar component. The younger stellar component is also associated with a star-forming ring. Conclusions: The different properties of the counter-rotating stellar components of NGC 4138 rule out the idea that they formed because of bar dissolution. Our findings support the results of numerical simulations in which the counter-rotating component assembled from gas accreted on retrograde orbits from the environment or from the retrograde merging with a gas-rich dwarf galaxy. Based on observation carried out at the Galileo 1.22 m telescope at Padua University.

Pizzella, A.; Morelli, L.; Corsini, E. M.; Dalla Bont, E.; Coccato, L.; Sanjana, G.

2014-10-01

202

Ionized gas outflow in the isolated S0 galaxy NGC 4460  

NASA Astrophysics Data System (ADS)

We used integral-field and long-slit spectroscopy to study a bright extended nebulosity recently discovered in the isolated lenticular galaxy NGC 4460 during an H? survey of nearby galaxies. An analysis of archival Sloan Digital Sky Survey, GALEX and Hubble Space Telescope images indicates that current star formation is entirely concentrated in the central kiloparsec of the galaxy disc. The observed ionized gas parameters (morphology, kinematics and ionization state) can be explained by a gas outflow above the plane of the galaxy, caused by star formation in the circumnuclear region. Galactic wind parameters in NGC 4460 (outflow velocity, total kinetic energy) are several times smaller, compared with the known galactic wind in NGC 253, which is explained by the substantially lower total star formation rate. We discuss the cause of the star formation processes in NGC 4460 and in two other known isolated lenticular (S0) and elliptical (E) galaxies of the Local Volume: NGC 404 and 855. We provide evidence suggesting that the feeding of isolated galaxies by intergalactic gas on a cosmological time-scale is a steady process without significant variations. Based on observations collected with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences, which is operated under the financial support of the Science Department of Russia (registration number 01-43). E-mail: moisav@gmail.com

Moiseev, Alexei; Karachentsev, Igor; Kaisin, Serafim

2010-04-01

203

A Comparison Between the Globular Clusters in NGC 5128 and the Galaxy  

E-print Network

Some of the properties of the globular clusters in NGC 5128 are compared to those of Galactic globular clusters. Assuming the color- metallicity relations that hold for Galactic globular clusters then the metal-poor clusters in NGC 5128 that have [Fe/H] globulars in that galaxy. No such metallicity dependent luminosity difference is observed among the globular clusters associated with the Milky Way. Furthermore the NGC 5128 cluster sample contains two objects that, on the basis of their observed colors, appear to be super metal-poor. It is speculated that many of these apparently faint and metal-poor clusters in NGC 5128 are actually objects resembling intermediate-age Galactic open clusters. It is also found that large clusters with FWHM > 10 pc are typically less luminous in NGC 5128 than are their more more compact counterparts. In this respect the NGC 5128 cluster system is similar to the Galactic globular cluster system. Finally, the present data may hint at the possibility that the NGC 5128 cluster system differs from that surrounding the Milky Way, in that the NGC 5128 objects do not seem to exhibit a clear cut gap between the regions of the FWHM vs M_v plane that are occupied by globular clusters and dwarf spheroidal galaxies.

Sidney van den Bergh

2006-11-20

204

CO Observations of the Interacting Galaxy Pair NGC 5394/95  

E-print Network

BIMA CO 1-0 observations are presented of the spiral galaxies NGC 5394 and NGC 5395 that have undergone a recent, grazing encounter. In NGC 5394, 80% of the CO emission detected by BIMA is concentrated in the central 800 pc (FWHM) starburst region.In an encounter simulation that reproduces some of the main features of this galaxy pair, a considerable amount of gas in NGC 5394 falls into the central region early in the collision. The observed total gas distribution in the disk of NGC 5394 is lopsided, with more HI, CO, and H-alpha emission coming from the western or southwestern side. The innermost western arm of NGC 5394 is seen in CO and H-alpha emission, but the eastern inner-disk arm, which is very bright in the optical continuum, is not detected in CO or H-alpha emission. From a comparison of the radio continuum, H-alpha, 60 micron, and CO luminosities, we estimate that the average visual extinction of the starburst is 3 - 4 mag and the conversion factor N(H2)/I(CO) in the starburst is a factor of 3 - 4 below the standard value. Comparison of NGC 5394 with two other systems previously studied suggests that in prograde grazing encounters a central starburst may not develop until near the end of the ocular phase. Very little of the CO emission from NGC 5395 found in previous single-dish observations is detected by BIMA.

Michele Kaufman; Kartik Sheth; Curtis Struck; Bruce G. Elmegreen; Magnus Thomasson; Debra Meloy Elmegreen; Elias Brinks

2001-11-13

205

Molecular Gas in the Perseus Cooling Flow Galaxy, NGC 1275  

E-print Network

The central arcminute of the Perseus cooling flow galaxy, NGC 1275, has been mapped with the JCMT in 12CO(2-1) at 21 arcsec resolution, with detections out to at least 36 arcsec (12 kpc). Within the limits of the resolution and coverage, the distribution of gas appears to be roughly E-W, consistent with previous observations of CO, X-ray, H alpha, and dust emission. The total detected molecular hydrogen mass is ~ 1.6 x 10^10 solar masses, using a Galactic conversion factor. The inner central rotating disk is apparent in the data, but the overall distribution is not one of rotation. Rather, the line profiles are bluewards asymmetric, consistent with previous observations in HI and [OIII]. We suggest that the blueshift may be due to an acquired mean velocity of ~ 150 km/sec imparted by the radio jet in the advancing direction. Within the uncertainties of the analysis, the available radio energy appears to be sufficient, and the interpretation is consistent with that of Bohringer et al. (1993) for displaced X-ray emission. We have also made the first observations of 13CO(2-1) and 12CO(3-2) emission from the central 21 arcsec region of NGC 1275 and combined these data with IRAM data supplied by Reuter et al. (1993) to form line ratios over equivalent, well-sampled regions. An LVG radiative transfer analysis indicates that the line ratios are not well reproduced by a single value of kinetic temperature, molecular hydrogen density, and abundance per unit velocity gradient. At least two temperatures are suggested by a simple two-component LVG model, possibly reflecting a temperature gradient in this region.

Terry Bridges; Judith Irwin

1998-07-16

206

The Circumnuclear Molecular Gas in the Seyfert Galaxy NGC4945  

E-print Network

We have mapped the central region of NGC 4945 in the $J=2\\to1$ transition of $^{12}$CO, $^{13}$CO, and C$^{18}$O, as well as the continuum at 1.3 mm, at an angular resolution of $5\\farc \\times 3\\farc$ with the Submillimeter Array. The relative proximity of NGC 4945 (distance of only 3.8 Mpc) permits a detailed study of the circumnuclear molecular gas and dust in a galaxy exhibiting both an AGN (classified as a Seyfert 2) and a circumnuclear starburst in an inclined ring with radius $\\sim$2\\farcs5 ($\\sim$50 pc). We find that all three molecular lines trace an inclined rotating disk with major axis aligned with that of the starburst ring and large-scale galactic disk, and which exhibits solid-body rotation within a radius of $\\sim$5\\farc ($\\sim$95 pc). We infer an inclination for the nuclear disk of $62^{\\circ} \\pm 2^{\\circ}$, somewhat smaller than the inclination of the large-scale galactic disk of $\\sim$$78^{\\circ}$. The continuum emission at 1.3 mm also extends beyond the starburst ring, and is dominated by thermal emission from dust. If it traces the same dust emitting in the far-infrared, then the bulk of this dust must be heated by star-formation activity rather than the AGN. We discover a kinematically-decoupled component at the center of the disk with a radius smaller than $1\\farcs4$ (27 pc), but which spans approximately the same range of velocities as the surrounding disk. This component has a higher density than its surroundings, and is a promising candidate for the circumnuclear molecular torus invoked by AGN unification models.

Richard C. Y. Chou; A. B. Peck; J. Lim; S. Matsushita; S. Muller; S. Sawada-Satoh; Dinh-V-Trung; F. Boone; C. Henkel

2007-09-25

207

Triple Scoop from Galaxy Hunter  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site] [figure removed for brevity, see original site] [figure removed for brevity, see original site] Figure 1Figure 2Figure 3

Silver Dollar Galaxy: NGC 253 (figure 1) Located 10 million light-years away in the southern constellation Sculptor, the Silver Dollar galaxy, or NGC 253, is one of the brightest spiral galaxies in the night sky. In this edge-on view from NASA's Galaxy Evolution Explorer, the wisps of blue represent relatively dustless areas of the galaxy that are actively forming stars. Areas of the galaxy with a soft golden glow indicate regions where the far-ultraviolet is heavily obscured by dust particles.

Gravitational Dance: NGC 1512 and NGC 1510 (figure 2) In this image, the wide ultraviolet eyes of NASA's Galaxy Evolution Explorer show spiral galaxy NGC 1512 sitting slightly northwest of elliptical galaxy NGC 1510. The two galaxies are currently separated by a mere 68,000 light-years, leading many astronomers to suspect that a close encounter is currently in progress.

The overlapping of two tightly wound spiral arm segments makes up the light blue inner ring of NGC 1512. Meanwhile, the galaxy's outer spiral arm is being distorted by strong gravitational interactions with NGC 1510.

Galaxy Trio: NGC 5566, NGC 5560, and NGC 5569 (figure 3) NASA's Galaxy Evolution Explorer shows a triplet of galaxies in the Virgo cluster: NGC 5560 (top galaxy), NGC 5566 (middle galaxy), and NGC 5569 (bottom galaxy).

The inner ring in NGC 5566 is formed by two nearly overlapping bright arms, which themselves spring from the ends of a central bar. The bar is not visible in ultraviolet because it consists of older stars or low mass stars that do not emit energy at ultraviolet wavelengths. The outer disk of NGC 5566 appears warped, and the disk of NGC 5560 is clearly disturbed. Unlike its galactic neighbors, the disk of NGC 5569 does not appear to have been distorted by any passing galaxies.

2006-01-01

208

Young tidal dwarf galaxies around the gas-rich disturbed lenticular NGC 5291  

Microsoft Academic Search

NGC 5291 is an early type galaxy at the edge of the cluster Abell 3574 which drew the attention because of the unusual high amount of atomic gas ( ~ 5 x 10(10) {M_{\\\\odot}}) found associated to it. The HI is distributed along a huge and fragmented ring, possibly formed after a tidal interaction with a companion galaxy. We present

P.-A. Duc; I. F. Mirabel

1998-01-01

209

"Active Galaxies" An example of 2 "active" galaxies (NGC 2207 and IC 2163). This image was taken with the Wide-Field Camera on the  

E-print Network

"Active Galaxies" An example of 2 "active" galaxies (NGC 2207 and IC 2163). This image was taken with the Wide-Field Camera on the Hubble Space Telescope. These two, nearly face-on spiral galaxies are in the process of merging into a single galaxy that will most likely become a large Elliptical galaxy. During

Sanders, David B.

210

NGC 2276: a remarkable galaxy with a large number of ultraluminous X-ray sources  

NASA Astrophysics Data System (ADS)

The starbusting, nearby (D = 32.9 Mpc) spiral (Sc) galaxy NGC 2276 belongs to the sparse group dominated by the elliptical galaxy NGC 2300. NGC 2276 is a remarkable galaxy, as it displays a disturbed morphology at many wavelengths. This is possibly due to gravitational interaction with the central elliptical galaxy of the group. Previous ROSAT and XMM-Newton observations resulted in the detection of extended hot gas emission and of a single very bright (1041 erg s-1) ultraluminous X-ray source (ULX) candidate. Here, we report on a study of the X-ray sources of NGC 2276 based on Chandra data taken in 2004. Chandra was able to resolve 16 sources, 8 of which are ULXs, and to reveal that the previous ULX candidate is actually composed of a few distinct objects. We construct the luminosity function of NGC 2276, which can be interpreted as dominated by high-mass X-ray binaries, and estimate the star formation rate (SFR) to be 5-15 M? yr-1, consistent with the values derived from optical and infrared observations. By means of numerical simulations, we show that both ram pressure and viscous transfer effects are necessary to produce the distorted morphology and the high SFR observed in NGC 2276, while tidal interaction have a marginal effect.

Wolter, Anna; Esposito, Paolo; Mapelli, Michela; Pizzolato, Fabio; Ripamonti, Emanuele

2015-03-01

211

Gas-driven evolution of stellar orbits in barred galaxies  

E-print Network

We carry out a detailed orbit analysis of gravitational potentials selected at different times from an evolving self-consistent model galaxy consisting of a two-component disk (stars+gas) and a live halo. The results are compared with a pure stellar model, subject to nearly identical initial conditions, which are chosen as to make the models develop a large scale stellar bar. The bars are also subject to hose-pipe (buckling) instability which modifies the vertical structure of the disk. The diverging morphological evolution of both models is explained in terms of gas radial inflow, the resulting change in the gravitational potential at smaller radii, and the subsequent modification of the main families of orbits, both in and out of the disk plane. We find that dynamical instabilities become milder in the presence of the gas component, and that the stability of planar and 3D stellar orbits is strongly affected by the related changes in the potential -- both are destabilized with the gas accumulation at the center. This is reflected in the overall lower amplitude of the bar mode and in the substantial weakening of the bar, which appears to be a gradual process. The vertical buckling of the bar is much less pronounced and the characteristic peanut shape of the galactic bulge almost disappears when there is a substantial gas inflow towards the center. Milder instability results in a smaller bulge whose basic parameters are in agreement with observations. We also find that the overall evolution in the model with a gas component is accelerated due to the larger central mass concentration and resulting decrease in the characteristic dynamical time.

I. Berentzen; C. H. Heller; I. Shlosman; K. J. Fricke

1998-06-10

212

The Isolated Elliptical NGC 1132 Evidence For a Merged Group of Galaxies?  

E-print Network

Numerical simulations predict that some poor groups of galaxies have merged by the present epoch into giant ellipticals (cf. Barnes 1989). To identify the possible remnants of such mergers, we have compiled a sample of nearby, isolated ellipticals (Colbert, Mulchaey, & Zabludoff 1998). ASCA observations of the first galaxy studied, NGC 1132 reveal an X-ray halo that extends out to at least 250 kpc. The temperature, metallicity and luminosity of NGC 1132's X-ray halo are comparable to those of poor group halos. The total mass inferred from the X-ray emission is also like that of an X-ray detected group. Optical imaging uncovers a dwarf galaxy population clustered about NGC 1132 that is consistent in number density and in projected radial distribution with that of an X-ray group. The similarities of NGC 1132 to poor groups in both the X-ray band and at the faint end of the galaxy luminosity function, combined with the deficit of luminous galaxies in the NGC 1132 field, are compatible with the merged group p...

Mulchaey, J S; Mulchaey, John S.; Zabludoff, Ann I.

1999-01-01

213

NGC 6340: an old S0 galaxy with a young polar disc. Clues from morphology, internal kinematics, and stellar populations  

Microsoft Academic Search

Context: Lenticular galaxies are believed to form by a combination of environmental effects and secular evolution. Aims: We study the nearby disc-dominated S0 galaxy NGC 6340 photometrically and spectroscopically to understand the mechanisms of S0 formation and evolution in groups. Methods: We use SDSS images to build colour maps and the light profile of NGC 6340, which we decompose using

I. V. Chilingarian; A. P. Novikova; V. Cayatte; F. Combes; P. Di Matteo; A. V. Zasov

2009-01-01

214

A GIANT STAR FACTORY IN NEIGHBORING GALAXY NGC 6822  

NASA Technical Reports Server (NTRS)

Resembling curling flames from a campfire, this magnificent nebula in a neighboring galaxy is giving astronomers new insight into the fierce birth of stars as it may have more commonly happened in the early universe. The glowing gas cloud, called Hubble-V, has a diameter of about 200 light-years. A faint tail of nebulosity trailing off the top of the image sits opposite a dense cluster of bright stars at the bottom of the irregularly shaped nebula. NASA's Hubble Space Telescope's resolution and ultraviolet sensitivity reveals a dense knot of dozens of ultra-hot stars nestled in the nebula, each glowing 100,000 times brighter than our Sun. These youthful 4-million-year-old stars are too distant and crowded together to be resolved from ground-based telescopes. The small, irregular host galaxy, called NGC 6822, is one of the Milky Way's closest neighbors and is considered prototypical of the earliest fragmentary galaxies that inhabited the young universe. The galaxy is 1.6 million light-years away in the constellation Sagittarius. The Hubble-V image data was taken with Hubble's Wide Field Planetary Camera 2 (WFPC2) by two science teams: C. Robert O'Dell of Vanderbilt University and collaborators, and Luciana Bianchi of Johns Hopkins University and Osservatorio Astronomico, Torinese, Italy, and collaborators. This color image was produced by The Hubble Heritage Team (STScI). A Hubble image of Hubble-X, another intense star-forming region in NGC 6822, was released by The Heritage Team in January 2001. Credits: NASA, ESA and The Hubble Heritage Team (STScI/AURA) Acknowledgment: C. R. O'Dell (Vanderbilt University) and L. Bianchi (Johns Hopkins University and Osservatorio Astronomico, Torinese, Italy) NOTE TO EDITORS: For additional information, please contact C. R. O'Dell, Vanderbilt University, Physics and Astronomy Dept., Box 1807 Station B, Nashville, TN 37235, (phone) 615-343-1779, (fax) 615-343-7263, (e-mail) cr.odell@vanderbilt.edu or Luciana Bianchi, Johns Hopkins University, Physics and Astronomy Dept., Baltimore, MD 21218, (phone) 410-516-4009, (fax) 410-516-7239, (e-mail) bianchi@pha.jhu.edu or Keith Noll, Space Telescope Science Institute, Baltimore, MD 21218, (phone) 410-338-1828, (fax) 410-338-4579, (e-mail) noll@stsci.edu. Electronic images and additional information are available at: http://heritage.stsci.edu http://oposite.stsci.edu/pubinfo/pr/2001/39 and via links in http://oposite.stsci.edu/pubinfo/latest.html http://oposite.stsci.edu/pubinfo/pictures.html http://hubble.stsci.edu/go/news To receive STScI press releases electronically, send an Internet electronic mail message to public-request@stsci.edu. Leave the subject line blank, and type the word subscribe in the body of the message. The system will respond with a confirmation of the subscription, and you will receive new press releases as they are issued. Please subscribe using the email account with which you would like to receive list messages. To unsubscribe, send mail to public-request@stsci.edu. Leave the subject line blank, and type the word unsubscribe in the body of the message. Please unsubscribe using the email account that you used to subscribe to the list.

2002-01-01

215

Revealing Galactic scale bars with the help of Galaxy Zoo and ALFALFA .  

NASA Astrophysics Data System (ADS)

We use visual classifications of the brightest 250,000 galaxies in the Sloan Digital Sky Survey Main Galaxy Sample provided by citizen scientists via the Galaxy Zoo project (www.galaxyzoo.org, Lintott et al. 2008) to identify a sample of local disc galaxies with reliable bar identifications. These data, combined with information on the atomic gas content from the ALFALFA survey (Haynes et al. 2011) show that disc galaxies with higher gas content have lower bar fractions. We use a gas deficiency parameter to show that disc galaxies with more/less gas than expected for their stellar mass are less/more likely to host bars. Furthermore, we see that at a fixed gas content there is no residual correlation between bar fraction and stellar mass. We argue that this suggests previously observed correlations between galaxy colour/stellar mass and (strong) bar fraction (e.g. from the sample in Masters et al. 2011, and also see Nair & Abraham 2010) could be driven by the interaction between bars and the gas content of the disc, since more massive, optically redder disc galaxies are observed to have lower gas contents. Furthermore we see evidence that at a fixed gas content the global colours of barred galaxies are redder than those of unbarred galaxies. We suggest that this could be due to the exchange of angular momentum beyond co-rotation which might stop a replenishment of gas from external sources, and act as a source of feedback to temporarily halt or reduce the star formation in the outer parts of barred discs. These results (published as Masters et al. 2012) combined with those of Skibba et al. (2012), who use the same sample to show a clear (but subtle and complicated) environmental dependence of the bar fraction in disc galaxies, suggest that bars are intimately linked to the evolution of disc galaxies.

Masters, K. L.; the Galaxy Zoo Team

216

Hubble space telescope observations of young star clusters in NGC4038\\/4039, 'the antennae' galaxies  

Microsoft Academic Search

New, high-resolution images of the disks of NGC 4038\\/4039 obtained with the Wide Field Camera of the Hubble Space Telescope (HST) are presented. NGC 4038\\/4039, nicknamed The Antennae, is a prototypical example of a pair of colliding galaxies believed to be at an early stage of a merger. Down to the limiting magnitude of V approximately 23 mag, the HST

Bradley C. Whitmore; Francois Schweizer

1995-01-01

217

DETERMINING THE NATURE OF THE EXTENDED H I STRUCTURE AROUND LITTLE THINGS DWARF GALAXY NGC 1569  

SciTech Connect

This work presents an extended, neutral hydrogen emission map around Magellanic-type dwarf irregular galaxy (dIm) NGC 1569. In the spring of 2010, the Robert C. Byrd Green Bank Telescope was used to map a 9 Degree-Sign Multiplication-Sign 2 Degree-Sign region in H I line emission that includes NGC 1569 and IC 342 as well as two other dwarf galaxies. The primary objective for these observations was to search for structures potentially connecting NGC 1569 with IC 342 group members in order to trace previous interactions and thus, provide an explanation for the starburst and peculiar kinematics prevalent in NGC 1569. A large, half-degree diameter H I cloud was detected that shares the same position and velocity as NGC 1569. Also, two long structures were discovered that are reminiscent of intergalactic filaments extending out in a V-shaped manner from NGC 1569 toward UGCA 92, a nearby dwarf galaxy. These filamentary structures extend for about 1. Degree-Sign 5, which is 77 kpc at NGC 1569. There is a continuous velocity succession with the 0. Degree-Sign 5 H I cloud, filaments, and main body of the galaxy. The 0. Degree-Sign 5 H I cloud and filamentary structures may be foreground Milky Way, but are suggestive as possible remnants of an interaction between NGC 1569 and UGCA 92. The data also show two tidal tails extending from UGCA 86 and IC 342, respectively. These structures may be part of a continuous H I bridge but more data are needed to determine if this is the case.

Johnson, Megan, E-mail: mjohnson@nrao.edu [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); National Radio Astronomy Observatory, P.O. Box 2, Green Bank, WV 24915 (United States)

2013-06-15

218

Stellar velocity dispersion in ARP 220 and NGC 6240: Elliptical galaxies in formation  

Microsoft Academic Search

We present high-resolution (R is approximately 7000) spectra of the 2.3 micron CO absorption bandhead of two luminous merging galaxies, NGC 6240 and Arp 220, obtained with CGS4 on the United Kingdom Infrared Telescope. We have also secured subarcsecond images of NGC 6240 at 2.2 micron using the Montreal Infrared Camera (MONICA) on the Canada-France-Hawaii Telescope (CFHT). The velocity dispersion

Rene Doyon; M. Wells; G. S. Wright; R. D. Joseph; D. Nadeau; P. A. James

1994-01-01

219

THE ACS NEARBY GALAXY SURVEY TREASURY. XI. THE REMARKABLY UNDISTURBED NGC 2403 DISK  

SciTech Connect

We present detailed analysis of color-magnitude diagrams of NGC 2403, obtained from a deep (m {approx}< 28) Hubble Space Telescope (HST) Wide Field Planetary Camera 2 observation of the outer disk of NGC 2403, supplemented by several shallow (m {approx}< 26) HST Advanced Camera for Surveys fields. We derive the spatially resolved star formation history of NGC 2403 out to 11 disk scale lengths. In the inner portions of the galaxy, we compare the recent star formation rates (SFRs) we derive from the resolved stars with those measured using GALEX FUV + Spitzer 24{mu} fluxes, finding excellent agreement between the methods. Our measurements also show that the radial gradient in recent SFR mirrors the disk exponential profile to 11 scale lengths with no break, extending to SFR densities a factor of {approx}100 lower than those that can be measured with GALEX and Spitzer ({approx}2 Multiplication-Sign 10{sup -6} M{sub Sun} yr{sup -1} kpc{sup -2}). Furthermore, we find that the cumulative stellar mass of the disk was formed at similar times at all radii. We compare these characteristics of NGC 2403 to those of its ''morphological twins'', NGC 300 and M 33, showing that the structure and age distributions of the NGC 2403 disk are more similar to those of the relatively isolated system NGC 300 than to those of the Local Group analog M 33. We also discuss the environments and HI morphologies of these three nearby galaxies, comparing them to integrated light studies of larger samples of more distant galaxy disks. Taken together, the physical properties and evolutionary history of NGC 2403 suggest that the galaxy has had no close encounters with other M 81 group members and may be falling into the group for the first time.

Williams, Benjamin F.; Dalcanton, Julianne J.; Stilp, Adrienne; Radburn-Smith, David [Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195 (United States); Dolphin, Andrew [Raytheon, 1151 E. Hermans Road, Tucson, AZ 85706 (United States); Skillman, Evan D., E-mail: ben@astro.washington.edu, E-mail: jd@astro.washington.edu, E-mail: adrienne@astro.washington.edu, E-mail: dolphin@raytheon.com, E-mail: skillman@astro.umn.edu [Department of Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455 (United States)

2013-03-10

220

An over-massive black hole in the compact lenticular galaxy NGC?1277.  

PubMed

Most massive galaxies have supermassive black holes at their centres, and the masses of the black holes are believed to correlate with properties of the host-galaxy bulge component. Several explanations have been proposed for the existence of these locally established empirical relationships, including the non-causal, statistical process of galaxy-galaxy merging, direct feedback between the black hole and its host galaxy, and galaxy-galaxy merging and the subsequent violent relaxation and dissipation. The empirical scaling relations are therefore important for distinguishing between various theoretical models of galaxy evolution, and they furthermore form the basis for all black-hole mass measurements at large distances. Observations have shown that the mass of the black hole is typically 0.1 per cent of the mass of the stellar bulge of the galaxy. Until now, the galaxy with the largest known fraction of its mass in its central black hole (11 per cent) was the small galaxy NGC?4486B. Here we report observations of the stellar kinematics of NGC?1277, which is a compact, lenticular galaxy with a mass of 1.2??10(11) solar masses. From the data, we determine that the mass of the central black hole is 1.7??10(10) solar masses, or 59 per cent of its bulge mass. We also show observations of five other compact galaxies that have properties similar to NGC?1277 and therefore may also contain over-massive black holes. It is not yet known if these galaxies represent a tail of a distribution, or if disk-dominated galaxies fail to follow the usual black-hole mass scaling relations. PMID:23192149

van den Bosch, Remco C E; Gebhardt, Karl; Gltekin, Kayhan; van de Ven, Glenn; van der Wel, Arjen; Walsh, Jonelle L

2012-11-29

221

Extended Red Emission in the Evil Eye Galaxy (NGC 4826)  

NASA Astrophysics Data System (ADS)

NGC 4826 (M64) is a nearby Sab galaxy with an outstanding, absorbing dust lane (called the Evil Eye) asymmetrically placed across its prominent bulge. In addition, its central region is associated with several regions of ongoing star formation activity. We obtained accurate low-resolution (4.3 pixel-1) long-slit spectroscopy (KPNO 4 m) of NGC 4826 in the 5300-9100 spectral range, with a slit of 4.4? length, encompassing the galaxy's bulge size, positioned across its nucleus. The wavelength-dependent effects of absorption and scattering by the dust in the Evil Eye are evident when comparing the observed stellar spectral energy distributions (SEDs) of pairs of positions symmetrically located with respect to the nucleus, one on the dust lane side and one on the symmetrically opposite side of the bulge, under the assumption that the intrinsic (i.e., unobscured) radiation field is to first-order axisymmetric. We analyzed the SED ratios for a given number of pairs of positions through the multiple-scattering radiative transfer model of Witt & Gordon. As a main result, we discovered strong residual extended red emission (ERE) from a region of the Evil Eye within a projected distance of about 13" from the nucleus, adjacent to a broad, bright H II region, intercepted by the spectrograph slit. ERE is an established phenomenon well-covered in the literature and interpreted as originating from photoluminescence by nanometer-sized clusters, illuminated by UV/optical photons of the local radiation field. In the innermost part of the Evil Eye, the ERE band extends from about 5700 to 9100 , with an estimated peak intensity of ~3.710-6 ergs s -1 -1 cm-2 sr-1 near 8300 and with an ERE to scattered light band integrated intensity ratio, I(ERE)/I(sca), of about 0.7. At farther distances, approaching the broad, bright H II region, the ERE band and peak intensity shift toward longer wavelengths, while the ERE band-integrated intensity, I(ERE), diminishes and, eventually, vanishes at the inner edge of this H II region. The radial variation of I(ERE) and I(ERE)/I(sca) does not match that of the optical depth of the model derived for the dust lane. By contrast, the radial variation of I(ERE), I(ERE)/I(sca) and of the ERE spectral domain seems to depend strongly on the strength and hardness of the illuminating radiation field. In fact, I(ERE) and I(ERE)/I(sca) diminish and the ERE band shifts toward longer wavelengths when both the total integrated Lyman continuum photon rate, Q(H0)TOT, and the characteristic effective temperature, Teff, of the illuminating OB stars increase. Q(H0)TOT and Teff are estimated from the extinction-corrected H? (?=6563 ) line intensity and line intensity ratios [N II] (?6583)/H? and [S II](??6716+6731)/H?, respectively, and are consistent with model and observed values typical of OB associations. Unfortunately, we do not have data shortward of 5300 , so that the census of the UV/optical flux is incomplete. The complex radial variation of the ERE peak intensity and peak wavelength of I(ERE) and I(ERE)/I(sca) with optical depth and strength of the UV/optical radiation field is reproduced in a consistent way through the theoretical interpretation of the photophysics of the ERE carrier by Smith & Witt, which attributes a key role to the experimentally established recognition that photoionization quenches the luminescence of nanoparticles. When examined within the context of ERE observations in the diffuse interstellar medium (ISM) of our Galaxy and in a variety of other dusty environments, such as reflection nebulae, planetary nebulae, and the Orion Nebula, we conclude that the ERE photon conversion efficiency in NGC 4826 is as high as found elsewhere but that the size of the actively luminescing nanoparticles in NGC 4826 is about twice as large as those thought to exist in the diffuse ISM of our Galaxy.

Pierini, D.; Majeed, A.; Boroson, T. A.; Witt, A. N.

2002-04-01

222

The Evolution of Interacting Spiral Galaxy NGC 5194  

E-print Network

NGC 5194 (M51a) is a grand-design spiral galaxy and undergoing interactions with its companion. Here we focus on investigating main properties of its star-formation history (SFH) by constructing a simple evolution model, which assumes that the disc builds up gradually by cold gas infall and the gas infall rate can be parameterizedly described by a Gaussian form. By comparing model predictions with the observed data, we discuss the probable range for free parameter in the model and then know more about the main properties of the evolution and SFH of M51a. We find that the model predictions are very sensitive to the free parameter and the model adopting a constant infall-peak time $t_{\\rm p}\\,=\\,7.0{\\rm Gyr}$ can reproduce most of the observed constraints of M51a. Although our model does not assume the gas infall time-scale of the inner disc is shorter than that of the outer disc, our model predictions still show that the disc of M51a forms inside-out. We find that the mean stellar age of M51a is younger than t...

Kang, Xiaoyu; Zhang, Fenghui; Cheng, Liantao; Wang, Lang

2015-01-01

223

Discovery of New Dwarf Galaxy Near the Isolated Spiral Galaxy NGC 6503  

NASA Astrophysics Data System (ADS)

We report the discovery of a new dwarf galaxy (NGC 6503-d1) during the Subaru extended ultraviolet disk survey. It is a likely companion of the spiral galaxy NGC 6503. The resolved images, in the B, V, R, i, and H? bands, show an irregular appearance due to bright stars with underlying, smooth and unresolved stellar emission. It is classified as the transition type (dwarf irregular (dIrr)/dwarf spheroidal (dSph)) between the dIrr and dSph types. Its structural properties are similar to those of the dwarfs in the Local Group, with an absolute magnitude {{M}V}? -10.5, half-light radius {{r}e}? 400 pc, and central surface brightness {{? }0,V}? 25.2. Despite the low stellar surface brightness environment, one H ii region was detected, though its H? luminosity is low, indicating an absence of any appreciable O-stars at the current epoch. The presence of multiple stellar populations is indicated by the colormagnitude diagram of ?300 bright resolved stars and the total colors of the dwarf, with the majority of its total stellar mass ? 4 {{10}6} {{M}? } in an old stellar population.

Koda, Jin; Yagi, Masafumi; Komiyama, Yutaka; Boissier, Samuel; Boselli, Alessandro; Bouquin, Alexandre Y. K.; Donovan Meyer, Jennifer; Gil de Paz, Armando; Imanishi, Masatoshi; Madore, Barry F.; Thilker, David A.

2015-04-01

224

Suzaku X-Ray Monitoring of Gamma-Ray-Emitting Radio Galaxy, NGC 1275  

E-print Network

NGC 1275 is a gamma-ray-emitting radio galaxy at the center of the Perseus cluster. Its multi-wavelength spectrum is similar to that of blazers, and thus a jet-origin of gamma-ray emissions is believed. In the optical and X-ray region, NGC 1275 also shows a bright core, but their origin has not been understood, since a disk emission is not ruled out. In fact, NGC 1275 exhibits optical broad emission lines and a X-ray Fe-K line, which are typical for Seyfert galaxies. In our precious studies of NGC 1275 with Suzaku/XIS, no X-ray time variability was found from 2006 to 2011, regardless of moderate gamma-ray variability observed by {it Fermi}-LAT~\\cite{Yamazaki}. We have continued monitoring observations of NGC 1275 with Suzaku/XIS. In 2013-2014, MeV/GeV gams-ray flux of NGC 1275 gradually increased and reached the maximum at the beginning of 2014. Correlated with this recent gamma-ray activity, we found that X-ray flux also increased, and this is the first evidence of X-ray variability of NGC 1275. Following th...

Edahiro, Ikumi; Kawaguchi, Kenji; Tanaka, Yasuyuki; Itoh, Ryosuke; Kanda, Yuka; Shiki, Kensei

2015-01-01

225

Galaxy Zoo: AGN may be fueled by stellar bars in the local Universe  

NASA Astrophysics Data System (ADS)

Bars are a mechanism that have been proposed to explain how gas in the outer regions of a galaxy can be channeled inward and fuel AGN. Multiple observational studies have reported a significantly higher bar fraction in AGN than non-AGN. To accurately probe whether an excess of bars in AGN host galaxies exists because the galaxies host a bar, it is necessary to compare bar and AGN fractions at fixed mass and color, because the presence of bars strongly correlates with both. Thus, a sufficiently large sample is necessary to maintain adequate numbers in subsets of fixed mass and color. We have created a large, volume-limited sample of 19,765 disc galaxies using data from the Sloan Digital Sky Survey. By using morphological classifications from the Galaxy Zoo 2 project, we identify stellar bars in 51.8% of AGN hosts and 37.1% of star-forming disk galaxies. Once mass and color are fixed, there remains a statistically significant increase in the fraction of barred AGN over their unbarred counterparts. Using the L[O III]/MBH ratio as a measure of accretion efficiency, we also show that barred AGN do not exhibit stronger accretion than unbarred AGN at fixed mass or color. The data are consistent with a model in which bar-driven fueling does contribute to the probability of an actively growing black hole, but in which other dynamical mechanisms must contribute to AGN fueling via smaller, non-axisymmetric perturbations.

Galloway, Melanie; Willett, Kyle; Fortson, Lucy; Galaxy Zoo Science Team

2015-01-01

226

Velocity dispersion of stars and gas motion in double-barred galaxies  

E-print Network

The current state of the problem of double-barred galaxies investigation is reviewed. The necessity for application of the panoramic spectroscopy methods to a detailed study of kinematics of these objects is being proved. The first results of observing double-barred galaxies at the 6m telescope using the multipupil spectrograph MPFS and the scanning interferometer Fabry-Perot are described.

A. V. Moiseev

2001-11-12

227

Modeling the radial abundance distribution of the transition galaxy ngc 1313  

E-print Network

NGC 1313 is the most massive disk galaxy showing a flat radial abundance distribution in its interstellar gas, a behavior generally observed in magellanic and irregular galaxies. We have attempted to reproduce this flat abundance distribution using a multiphase chemical evolution model, which has been previously used sucessfully to depict other spiral galaxies along the Hubble morphological sequence. We found that it is not possible to reproduce the flat radial abundance distribution in NGC 1313, and at the same time, be consistent with observed radial distributions of other key parameters such the surface gas density and star formation profiles. We conclude that a more complicated galactic evolution model including radial flows, and possibly mass loss due to supernova explosions and winds, is necessary to explain the apparent chemical uniformity of the disk of NGC 1313

Mercedes Molla; Jean-Rene Roy

1999-03-09

228

Absorption Line Gradients in the Spectrum of an Elliptical Galaxy NGC 5846A  

NASA Astrophysics Data System (ADS)

The archival long-slit spectra, covering the wavelength range 4050-5150 , have been used to investigate the radial behavior of absorption line features (G4300, Fe4383, Ca4455, Fe4531, and H? ) of an elliptical galaxy NGC5846A. The heliocentric recession velocity of NGC 5846A has been derived as 1949+/-87kms-1. Fe absorption lines of NGC 5846A show significant radial gradients with the mean slope of /(r) =-0.863+/-0.202. There is also a significant radial gradient of G band with a slope of -1.109 +/- 0.098. On the other hand, no radial gradients has been detected on the Ca4455 and H? absorptions of NGC 5846A. A metallicity gradient, which is derived from the Fe line gradients, is similar to the abundance gradient predicted by Larson's (1975) dissipative models for the formation of elliptical galaxies. We also note that a galaxy-galaxy interaction could a ect the line gradients of NGC 5846A.

Sohn, Young-Jong; Yoon, Suk-Jin; Oh, Jungmin

1999-06-01

229

The richness of the globular cluster system of NGC 3923: Clues to elliptical galaxy formation  

NASA Technical Reports Server (NTRS)

We present new data on the globular cluster system of the elliptical galaxy NGC 3923 which show that it has the most globular clusters per unit luminosity of any noncluster elliptical yet observed, with S(sub N) = 6.4 +/- 1.4. NGC 3923 is also among the brightest ellipticals outside of a galaxy cluster for which the number of globular clusters has been determined. Our observation of a large number of clusters per unit luminosity (high S(sub N)-value) for a bright elliptical in a sparse environment is consistent with the suggestion of Djorgovski and Santiago that the number of globular clusters is a power-law function of the luminosity with an exponent greater than 1. We relate this higher specific frequency of globular clusters in more luminous galaxies to other observations which indicate that the physical conditions within elliptical galaxies at the time of their formation were dependent on galaxy mass.

Zepf, Stephen E.; Geisler, Doug; Ashman, Keith M.

1994-01-01

230

Radio Galaxy NGC 1265 Unveils the Accretion Shock Onto the Perseus Galaxy Cluster  

NASA Astrophysics Data System (ADS)

We present a consistent three-dimensional model for the head-tail radio galaxy NGC 1265 that explains the complex radio morphology and spectrum by a past passage of the galaxy and radio bubble through a shock wave. Using analytical solutions to the full Riemann problem and hydrodynamical simulations, we study how this passage transformed the plasma bubble into a toroidal vortex ring. Adiabatic compression of the aged electron population causes it to be energized and to emit low surface brightness and steep-spectrum radio emission. The large infall velocity of NGC 1265which is barely gravitationally bound to the Perseus cluster at its current positionand the low Faraday rotation measure values and variance of the jet strongly argue that this transformation was due to the accretion shock onto Perseus situated roughly at R 200. Estimating the volume change of the radio bubble enables inferring a shock Mach number of M? 4.2_{-1.2}^{+0.8}, a density jump of 3.4+0.2 -0.4, a temperature jump of 6.3+2.5 -2.7, and a pressure jump of 21.5 10.5 while allowing for uncertainties in the equation of state of the radio plasma and volume of the torus. Extrapolating X-ray profiles, we obtain upper limits on the gas temperature and density in the infalling warm-hot intergalactic medium of kT <~ 0.4 keV and n <~ 5 10-5 cm-3. The orientation of the ellipsoidally shaped radio torus in combination with the direction of the galaxy's head and tail in the plane of the sky is impossible to reconcile with projection effects. Instead, this argues for post-shock shear flows that have been caused by curvature in the shock surface with a characteristic radius of 850 kpc. The energy density of the shear flow corresponds to a turbulent-to-thermal energy density of 14%consistent with cosmological simulations. The shock-injected vorticity might be important in generating and amplifying magnetic fields in galaxy clusters. We suggest that future polarized radio observations by, e.g., LOFAR of head-tail galaxies can be complementary probes of accretion shocks onto galaxy clusters and are unique in determining their detailed flow properties.

Pfrommer, C.; Jones, T. W.

2011-03-01

231

Molecular Gas in Candidate Double Barred Galaxies III. A Lack of Molecular Gas?  

E-print Network

Most models of double-barred galaxies suggest that a molecular gas component is crucial for maintaining long-lived nuclear bars. We have undertaken a CO survey in an attempt to determine the gas content of these systems and to locate double barred galaxies with strong CO emission that could be candidates for high resolution mapping. We observed 10 galaxies in CO J=2-1 and J=3-2 and did not detect any galaxies that had not already been detected in previous CO surveys. We preferentially detect emission from galaxies containing some form of nuclear activity. Simulations of these galaxies require that they contain 2% to 10% gas by mass in order to maintain long-lived nuclear bars. The fluxes for the galaxies for which we have detections suggest that the gas mass fraction is in agreement with these models requirements. The lack of emission in the other galaxies suggests that they contain as little as 7 x 10^6 solar masses of molecular material which corresponds to gas by mass. This result combined with the wide variety of CO distributions observed in double barred galaxies suggests the need for models of double-barred galaxies that do not require a large, well ordered molecular gas component.

Glen Petitpas; Christine Wilson

2004-01-20

232

Bar effects on ionized gas properties and dust content in galaxy centers  

NASA Astrophysics Data System (ADS)

Observations and simulations indicate that bars are important agents to transfer material towards galaxy centers. However, observational studies devoted to investigate the effects of bars in galaxy centers are not yet conclusive. We have used a sample (Coelho & Gadotti 2011) of nearby face-on galaxies with available spectra (SDSS database) to investigate the footprints of bars in galaxy centers by analysing the central ionized gas properties of barred and unbarred galaxies separately. We find statistically significant differences in the H? Balmer extinction, star formation rate per unit area, in the [S ii]?6717/[S ii]?6731 line ratio, and notably in the N2 parameter (N2 = log([N ii]?6583/H?)). A deeper analysis reflects that these differences are only relevant for the less massive bulges (<~1010M?). These results have important consequences for studies on bulge formation and galaxy evolution.

Zurita, A.; Florido, E.; Prez, I.; Coelho, P.; Gadotti, D. A.

2015-02-01

233

Integral Field Spectroscopy and Multi-wavelength Imaging of the nearby Spiral Galaxy NGC 5668: An Unusual Flattening in Metallicity Gradient  

NASA Astrophysics Data System (ADS)

We present an analysis of the full bidimensional optical spectral cube of the nearby spiral galaxy NGC 5668, observed with the Pmas fiber PAcK Integral Field Unit (IFU) at the Calar Alto observatory 3.5 m telescope. We make use of broadband imaging to provide further constraints on the evolutionary history of the galaxy. This data set will allow us to improve our understanding of the mechanisms that drive the evolution of disks. We investigated the properties of 62 H II regions and concentric rings in NGC 5668 and derived maps in ionized-gas attenuation and chemical (oxygen) abundances. We find that while inward of r ~36'' ~ 4.4 kpc ~ 0.36 (D 25/2) the derived O/H ratio follows the radial gradient typical of spiral galaxies, the abundance gradient beyond r ~ 36'' flattens out. The analysis of the multi-wavelength surface brightness profiles of NGC 5668 is performed by fitting these profiles with those predicted by chemo-spectrophotometric evolutionary models of galaxy disks. From this, we infer a spin and circular velocity of ? = 0.053 and vc = 167 km s-1, respectively. The metallicity gradient and rotation curve predicted by this best-fitting galaxy model nicely match the values derived from the IFU observations, especially within r ~36''. The same is true for the colors despite some small offsets and a reddening in the bluest colors beyond that radius. On the other hand, deviations of some of these properties in the outer disk indicate that a secondary mechanism, possibly gas transfer induced by the presence of a young bar, must have played a role in shaping the recent chemical and star formation histories of NGC 5668. Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck-Institut fr Astronomie Heidelberg and the Instituto de Astrofsica de Andaluca (CSIC).

Marino, R. A.; Gil de Paz, A.; Castillo-Morales, A.; Muoz-Mateos, J. C.; Snchez, S. F.; Prez-Gonzlez, P. G.; Gallego, J.; Zamorano, J.; Alonso-Herrero, A.; Boissier, S.

2012-07-01

234

A Possible High Nova Rate for Two Local Group Dwarf Galaxies: M32 and NGC 205  

E-print Network

We report the results of a preliminary nova survey of Local Group dwarf ellipticals. We used the Tenagra Observatory to observe M32, NGC 205, NGC 147, and NGC 185 in their entirety every clear night over a 4.5 month interval and discovered one nova in M32 and a candidate nova in NGC 205. The nova in M32 was verified spectroscopically. The nova candidate in NGC 205 had an unusually low peak luminosity (M_V = -5.1), and we were unable to obtain spectroscopic verification. We report a high bulk nova rate for M32 of 2(+2.4,-1.0) yr^-1 and, assuming the candidate nova is correctly identified, for NGC 205 of 2(+2.2,-1.0) yr^-1. If the NGC 205 variable is not a nova, we calculate an upper limit on the bulk nova rate for NGC 205 of 1.5 yr^-1. We report upper limits on the bulk nova rates in NGC 147 of 2 yr^-1 and NGC 185 of 1.8 yr^-1 and a combined bulk nova rate for the four galaxies of 4(+4.2,-1.4) yr^-1 (2{+3.9,-1.4} yr^-1 without the NGC 205 nova candidate). From the bulk rates, integrated and extinction corrected V-band photometry, and (V-K)_0 colors we derive a luminosity specific nova rate for M32 of 12.0(+14.4,-6.0) yr^-1 [10^10 L_Sun,K]^-1 and for NGC 205 of 29.3(+32.3,-14.7) yr^-1 [10^10 L_Sun,K]^-1 and for the combined 4 galaxies of 14.1(+14.8,-4.9) yr^-1 [10^10 L_Sun,K]^-1 (7.0{+13.7,-4.9} yr^-1[10^10 L_Sun,K]^-1 without the NGC 205 nova candidate). If the higher rate is confirmed by surveys in subsequent seasons, it would imply that either dwarf ellipticals have a higher interacting binary fraction than their higher mass counter parts, or that the completeness is higher for these less complex systems and the nova rates for larger, more distant systems are systematically underestimated.

James D. Neill; Michael M. Shara

2005-01-03

235

Globular Cluster Systems in Dwarf Elliptical Galaxies. I. The dE, N Galaxy NGC 3115 DW1  

NASA Astrophysics Data System (ADS)

We present new BV photometry of the globular cluster system (GCS) around the dE1,N dwarf companion galaxy to NGC 3115. Its GCS has a total population of 59 +/- 23 clusters and a mean metallicity <[Fe/H]> ~ -1.2 +/- 0.13, which is about 0.5 dex more metal poor (in the mean) than that of the dE halo light. Neither the GCS nor the galaxy halo exhibits a radial color gradient. We derive a distance modulus (m - M)_V_ = 30.3_- 0.5_^+0.8^ (d ~ 11_-2.3_^+5^ Mpc) by using the turnover of the globular cluster luminosity function (GCLF); this result is consistent with the dwarf being a physical satellite of NGC 3115. The specific frequency of NGC 3115 DW 1 is S_N_ = 4.9 +/- 1.9 considerably larger than that of NGC 3115 itself, but similar to those of dE's in the Local Group, as well as many large ellipticals. Finally, we find that the GCS mass spectrum follows a power law dN/dm ~ m^1.8^ above the turnover of the GCLF. This slope is similar to those found in many larger elliptical and spiral galaxies and suggests that the mechanisms of globular cluster formation are similar in galaxies of a large range in mass.

Durrell, Patrick R.; McLaughlin, Dean E.; Harris, Willliam E.; Hanes, David A.

1996-06-01

236

CO (J = 3 ? 2) observations of the starburst galaxy NGC 1808 with ASTE  

NASA Astrophysics Data System (ADS)

We present the first map of 12CO (J = 3 ? 2) and the first detection of 13CO (J = 3 ? 2) in the nearby starburst galaxy with a superwind, NGC 1808. The molecular gas is concentrated in the inner 2 kpc region of the galaxy with extended structure along the galactic bar and along the minor galactic axis. The minor-axis structure can be explained as molecular gas entrained in a galactic wind observed as a dust outflow at optical wavelengths. We have carried out a radiative transfer analysis of the excitation conditions of molecular gas in the starburst region (radius 550 pc) by using the ratios of J = 1 ? 0, J = 2 ? 1, and J = 3 ? 2 emission lines of 12CO and 13CO, and the large velocity gradient approximation. The beam-averaged density and kinetic temperature of molecular gas can be fitted at n H2 ? 103.5 cm-3 and Tk ? 35 K, indicating the presence of warm molecular gas, close to the estimated dust temperature of Td ? 34-37 K. The abundance ratio of the CO isotopologues is found to be [12CO]/[13CO] ? 34. The calculations show that, for the derived physical parameters, J = 2 ? 1 and J = 3 ? 2 transitions of 12CO are optically thick, 12CO J = 1 ? 0 is moderately optically thick, and all transitions of 13CO are optically thin. We have estimated an average CO-H2 conversion factor of XCO ? 0.8 1020 cm-2 (K km s-1)-1 in the central 550 pc by using a simple theoretical model assuming homogeneous, gravitationally bound gas clouds with turbulent velocities. In the same region the molecular gas mass is 3.0 108 M? available to fuel the nuclear starburst.

Salak, Dragan; Nakai, Naomasa; Kitamoto, Shoko

2014-10-01

237

A state-of-the-art analysis of the dwarf irregular galaxy NGC 6822  

NASA Astrophysics Data System (ADS)

We present a detailed photometric study of the dwarf irregular galaxy NGC 6822 aimed at investigating the properties of its stellar populations and, in particular, the presence of stellar radial gradients. Our goal is to analyse the stellar populations in six fields, which cover the whole bar of this dwarf galaxy. We derived the quantitative star formation history (SFH) of the six fields using the IAC method, involving IAC-pop/MinnIAC codes. The solutions we derived show an enhanced star formation rate (SFR) in Fields 1 and 3 during the past 500 Myr. The SFRs of the other fields are almost extinguished at very recent epochs and. We study the radial gradients of the SFR and consider the total mass converted into stars in two time intervals (between 0 and 0.5 Gyr ago and between 0.5 and 13.5 Gyr ago). We find that the scale lengths of the young and intermediate-to-old populations are perfectly compatible, with the exception of the young populations in Fields 1 and 3. The recent SF in these two fields is greater than in the other ones. This might be an indication that in these two fields we are sampling incipient spiral arms. Further evidence and new observations are required to prove this hypothesis. In addition, we derived the age-metallicity relations. As expected, the metallicity increases with time for all of the fields. We do not observe any radial gradient in the metallicity. Based on observations collected with the ACS on board the NASA/ESA HST.The photometric catalogue is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/572/A26

Fusco, F.; Buonanno, R.; Hidalgo, S. L.; Aparicio, A.; Pietrinferni, A.; Bono, G.; Monelli, M.; Cassisi, S.

2014-12-01

238

High-energy emission from the starburst galaxy NGC 253  

NASA Astrophysics Data System (ADS)

Measurement sensitivity in the energetic ?-ray region has improved considerably and is about to increase further in the near future, motivating a detailed calculation of high-energy (HE; >=100MeV) and very high-energy (VHE; >=100GeV) ?-ray emission from the nearby starburst galaxy NGC 253. Adopting the convection-diffusion model for energetic electron and proton propagation, and accounting for all the relevant hadronic and leptonic processes, we determine the steady-state energy distributions of these particles by a detailed numerical treatment. The electron distribution is directly normalized by the measured synchrotron radio emission from the central starburst region; a commonly expected theoretical relation is then used to normalize the proton spectrum in this region. Doing so fully specifies the electron spectrum throughout the galactic disc and, with an assumed spatial profile of the magnetic field, the predicted radio emission from the full disc matches well the observed spectrum, confirming the validity of our treatment. The resulting radiative yields of both particles are calculated; the integrated HE and VHE fluxes from the entire disc are predicted to be f(>=100MeV) ~= (1.8+1.5-0.8) 10-8cm-2s-1 and f(>=100GeV) ~= (3.6+3.4-1.7) 10-12cm-2s-1, with a central magnetic field value B0 ~= 190 +/- 10?G. We discuss the feasibility of measuring emission at these levels with the space-borne Fermi and ground-based Cherenkov telescopes.

Rephaeli, Yoel; Arieli, Yinon; Persic, Massimo

2010-01-01

239

The Star Clusters in the Starburst Irregular Galaxy NGC 1569  

E-print Network

We examine star clusters in the irregular, starburst galaxy NGC 1569 from HST images. In addition to the two known super star clusters, we identify 45 other clusters that are compact but resolved. Integrated UVI colors of the clusters span a large range, and suggest that ages range from 3 Myrs to 1 Gyr. However, most of the clusters were formed at the tail end of the recent starburst. Numerous clusters in addition to the know super star clusters are similar in luminosity to a small globular cluster. We examined the radial surface brightness of four of the clusters. Their half-light radii and core radii are in the range observed in present-day globular clusters. Therefore, conditions that produced the recent starburst have also been those necessary for producing compact, bright star clusters. We examine resolved stars in the outer parts of the two super star clusters. Cluster A is dominated by bright blue stars with a small population of red supergiants. Sub-components A1 and A2 have similar colors and a two-dimensional color map does not offer evidence that one component is dominated by red supergiants and the other not. The contradiction of the presence of red super- giants with Wolf-Rayet stars may instead not be a contradiction at all since there coexistence in a coeval population is not inconsistent with the evolution of massive stars. Cluster B is dominated by red supergiants, and this is confirmed by the presence of the stellar CO absorption feature in an integrated spectrum. The various age indicators are consistent with a picture in which cluster B is of order 10--20 Myrs old, and cluster A is >4-5 Myrs old.

D. A. Hunter; R. W. O'Connell; J. S. Gallagher; T. A. Smecker-Hane

2000-09-18

240

Molecular gas in the type 1 Seyfert galaxy NGC 7469 Implications for nuclear activity  

SciTech Connect

The results of a search for 2.12-micron H2 1-0 S(1) line emission from the nuclear (not greater than 1 kpc) region in 11 active galaxies are reported. The galaxies observed included type 1 and type 2 Seyferts, LINERs, and starburst nucleus galaxies. H2 emission was detected in one galaxy, the classical type 1 Seyfert NGC 7469. Also reported is the detection of very luminous C-12O 2.6-mm emission from NGC 7469, and optical narrow-band images and long-slit spectroscopy data concerning the ionized gas in this galaxy are presented. These data imply that NGC 7469 not only contains a highly active compact nucleus but also is undergoing a luminous circumnuclear (few-kpc scale) starburst. Most of the other galaxies with known H2 emission also seem to be composite monster/starburst systems and/or interacting galaxies. This result may arise because the molecular gas is associated with the starburst, while the primary form of the mechanical energy necessary to shock-excite the H2 is either outflow (possibly a wind) driven by the compact active nucleus or noncircular motions of gravitational origin. In either case, high-velocity (greater than 300 km/s) collisions between dense molecular clouds and a more ubiquitous, less dense gas phase can drive slow (10-30 km/s) shocks into the molecular clouds, exciting the observed H2 emission. 68 references.

Heckman, T.M.; Beckwith, S.; Skrutskie, M.; Blitz, L.; Wilson, A.S.

1986-06-01

241

Midlife Crises in Dwarf Galaxies in the NGC 5353/4 Group  

E-print Network

This third paper in a series about the dwarf galaxy populations in groups within the Local Supercluster concerns the intermediate mass (2.1 x 10^13 solar) NGC 5353/4 Group with a core dominated by S0 systems and a periphery of mostly spiral systems. Dwarf galaxies are strongly concentrated toward the core. The mass to light ratio M/L_R=105 in solar units is a factor 3 lower than for the two groups studied earlier in the series. The properties of the group suggest it is much less dynamically evolved than those two groups of early type galaxies. By comparison, the NGC 5353/4 Group lacks superluminous systems but has a large fraction of intermediate luminosity galaxies; or equivalently, a luminosity function with a flatter faint end slope. The luminosity function for the NGC 5353/4 Group should steepen as the intermediate luminosity galaxies merge. Evidence for the ongoing collapse of the group is provided by the unusually large incidence of star formation activity in small galaxies with early morphological types. The pattern in the distribution of galaxies with activity suggests a succession of infall events. Residual gas in dwarfs that enter the group is used up in sputtering events. The resolution of midlife crises is exhaustion.

R. Brent Tully; Neil Trentham

2008-02-12

242

Chandra Observation of the Starburst Galaxy NGC 2146  

E-print Network

We present six monitoring observations of the starburst galaxy NGC 2146 using the Chandra X-ray Observatory. We have detected 67 point sources in the 8'.7 x 8'.7 field of view of the ACIS-S detector. Six of these sources were Ultra-Luminous X-ray Sources, the brightest of which has a luminosity of 5 x 10^{39} ergs s^{-1}. One of the source, with a luminosity of ~1 x 10^{39} ergs s^{-1}, is coincident with the dynamical center location, as derived from the ^{12}CO rotation curve. We suggest that this source may be a low-luminosity active galactic nucleus. We have produced a table where the positions and main characteristics of the Chandra-detected sources are reported. The comparison between the positions of the X-ray sources and those of compact sources detected in NIR or radio does not indicate any definite counterpart. Taking profit of the relatively large number of sources detected, we have derived a logN-logS relation and a luminosity function. The former shows a break at \\~10^{-15} ergs cm^{-2} s^{-1}, that we interpret as due to a detection limit. The latter has a slope above the break of 0.71, which is similar to those found in the other starburst galaxies. In addition, a diffuse X-ray emission has been detected in both, soft (0.5--2.0keV) and hard (2.0--10.0keV), energy bands. The spectra of the diffuse component has been fitted with a two (hard and soft) components. The hard power-law component, with a luminosity of ~4 x 10^{39} ergs s^{-1}, is likely originated by unresolved point sources, while the soft component is better described by a thermal plasma model with a temperature of 0.5keV and high abundances for Mg and Si.

Tatsuya Inui; Hironori Matsumoto; Takeshi Go Tsuru; Katsuji Koyama; Satoki Matsushita; Alison B. Peck; Andrea Tarchi

2004-12-10

243

Suppression of star formation in the galaxy NGC 253 by a starburst-driven molecular wind  

NASA Astrophysics Data System (ADS)

We present Atacama Large (Sub)Millimeter Array (ALMA) CO (J=1-0) observations of the nearby, nuclear starburst galaxy NGC 253. NGC 253 is host to a "superwind" emanating from the central ~200 pc. Galaxy superwinds are thought to help shape the galactic mass function, play a critical role in galaxy evolution, and pollute the intergalactic medium with heavy metals. Detailed studies of nearby systems frequently focus on the warm or hot phases of the wind, visible in X-ray or Halpha emission. However, most of the mass in the outflowing material is thought to be in the form of neutral atomic and molecular gas. We use the observed CO luminosities and velocities to estimate the mass, mass loss rate, and energetics of the molecular wind. We compute an outflow mass of M_mo 6.6x10^6 Msun. The observed projected velocities of the CO filaments range from ~30-60 km s^-1 resulting in a mass loss rate of ~9 Msun yr^-1. The nuclear region of NGC 253 has a star formation rate of ~3 Msun yr^-1 resulting in a mass loading parameter 1-3. It is not immediately clear if the outflowing gas will escape the halo or eventually rain back onto the disk. What is clear is that NGC 253 will exhaust its nuclear star forming gas in ~60-120 Myr at its current mass loss rate, cementing the superwind as an important contributor in the evolution of NGC 253.

Warren, Steven R.; Bolatto, A. D.; Leroy, A. K.; Walter, F.; Veilleux, S.; Ostriker, E. C.; Ott, J.; Zwaan, M.; Fisher, D. B.; Weiss, A.; Rosolowsky, E.; Hodge, J.

2014-01-01

244

The Araucaria Project. An Accurate Distance to the Local Group Galaxy NGC 6822 from Near-Infrared Photometry of Cepheid Variables  

E-print Network

We have measured near-infrared magnitudes in the J and K bands for 56 Cepheid variables in the Local Group galaxy NGC 6822 with well-determined periods and optical light curves in the V and I bands. Using the template light curve approach of Soszynski, Gieren and Pietrzynski, accurate mean magnitudes were obtained from these data which allowed us to determine with unprecedented accuracy the distance to NGC 6822 from a multi-wavelength period-luminosity solution in the VIJK bands. From our data, we obtain a distance to NGC 6822 of (m-M)_{0} = 23.312 +- 0.021 (random error) mag, with an additional systematic uncertainty of about 3 %. This distance value is tied to an assumed LMC distance modulus of 18.50. From our multiwavelength approach, we find for the total (average) reddening to the NGC 6822 Cepheids E(B-V) = 0.356 +- 0.013 mag, which is in excellent agreement with a previous determination of McGonegal et al. from near-infrared photometry and implies significant internal reddening of the Cepheids in NGC 6822. Our present, definitive distance determination of NGC 6822 from Cepheids agrees within 2 % with the previous distance we had derived from optical photometry alone, but has significantly reduced error bars. Our Cepheid distance to NGC 6822 is in excellent agreement with the recent independent determination of Cioni and Habing from the I-band magnitude of the tip of the red giant branch. It also agrees well, within the errors, with the early determination of McGonegal et al. (1983) from random-phase H-band photometry of nine Cepheids.

W. Gieren; G. Pietrzynski; K. Nalewajko; I. Soszynski; F. Bresolin; R. P. Kudritzki; D. Minniti; A. Romanowsky

2006-05-09

245

The Araucaria Project: An Accurate Distance to the Local Group Galaxy NGC 6822 from Near-Infrared Photometry of Cepheid Variables  

NASA Astrophysics Data System (ADS)

We have measured near-infrared magnitudes in the J and K bands for 56 Cepheid variables in the Local Group galaxy NGC 6822 with well-determined periods and optical light curves in the V and I bands. Using the template light-curve approach of Soszy?ski and coworkers, accurate mean magnitudes were obtained from these data, which allowed us to determine with unprecedented accuracy the distance to NGC 6822 from a multiwavelength period-luminosity solution in the VIJK bands. From our data, we obtain a distance to NGC 6822 of (m-M)0=23.312+/-0.021 (random error) mag, with an additional systematic uncertainty of ~3%. This distance value is tied to an assumed LMC distance modulus of 18.50. From our multiwavelength approach, we find for the total (average) reddening to the NGC 6822 Cepheids E(B-V)=0.356+/-0.013 mag, which is in excellent agreement with a previous determination by McGonegal and coworkers from near-infrared photometry and implies significant internal reddening of the Cepheids in NGC 6822. Our present, definitive distance determination of NGC 6822 from Cepheids agrees within 2% with the previous distance we had derived from optical photometry alone, but has significantly reduced error bars. Our Cepheid distance to NGC 6822 is in excellent agreement with the recent independent determination of Cioni & Habing from the I-band magnitude of the tip of the red giant branch. It also agrees well, within the errors, with the early determination of McGonegal et al. (1983) from random-phase H-band photometry of nine Cepheids. Based on observations obtained with the European Southern Observatory (ESO) New Technology Telescope (NTT) for Large Program 171.D-0004, and with the Magellan Telescope of Las Campanas Observatory.

Gieren, Wolfgang; Pietrzy?ski, Grzegorz; Nalewajko, Krzysztof; Soszy?ski, Igor; Bresolin, Fabio; Kudritzki, Rolf-Peter; Minniti, Dante; Romanowsky, Aaron

2006-08-01

246

The circumnuclear X-ray reflectors in NGC 1068 and the Circinus galaxy  

NASA Astrophysics Data System (ADS)

The ASCA and BeppoSAX spectra of the Circinus galaxy and NGC 1068 are analysed and compared with photoionization models based on cloudy. In the case of Circinus, a single, mildly ionized reflector can account for the line spectrum, while in NGC 1068 at least three different reflectors (with different ionization states) are needed. We suggest that the reflector in Circinus and the low ionized one in NGC 1068 are the inner and visible part of the material responsible for the X-ray absorption. With this assumption, we estimate for the inner radius of the absorber a value of 0.2pc for Circinus and of a few parsecs for NGC 1068.

Bianchi, Stefano; Matt, Giorgio; Iwasawa, Kazushi

2001-04-01

247

The evolutionary history of the interacting Galaxy system NGC 7714/7715 (Arp 284)  

NASA Technical Reports Server (NTRS)

The distribution and kinematics of atomic hydrogen in an interacting galaxy pair are studied to develop a model of its formation and assess its implications. H I gas peaks, bridges, and tails for NGC 7714/7715 (Arp 284) are identified with the VLA observations, and the velocity field appears to indicate that of an inclined rotating disk. A parabolic off-center collision is modeled for two disk galaxies with different masses, and formation scenario leads to results consistent with the observations. The point of closest approach occurred 1.1 x 10 exp 8 years ago, and the inclination angle for NGC 7714 is given at around 30 deg. This ring galaxy's lack of star formation is attributed to the large impact parameter associated with the parabolic off-center collision considered for Arp 284. Star formation and the initial mass function of the interacting galaxy pair are studied to assess the age and composition of the objects.

Smith, Beverly J.; Wallin, John F.

1992-01-01

248

Galaxy Zoo: the effect of bar-driven fueling on the presence of an active galactic nucleus in disc galaxies  

E-print Network

We study the influence of the presence of a strong bar in disc galaxies which host an active galactic nucleus (AGN). Using data from the Sloan Digital Sky Survey and morphological classifications from the Galaxy Zoo 2 project, we create a volume-limited sample of 19,756 disc galaxies at $0.01bar. Within this sample, AGN host galaxies have a higher overall percentage of bars (51.8%) than inactive galaxies exhibiting central star formation (37.1%). This difference is primarily due to known effects; that the presence of both AGN and galactic bars is strongly correlated with both the stellar mass and integrated colour of the host galaxy. We control for this effect by examining the difference in AGN fraction between barred and unbarred galaxies in fixed bins of mass and colour. Once this effect is accounted for, there remains a small but statistically significant increase that represents 16% of the average barred AGN fraction. Using the $L_{\\rm...

Galloway, Melanie A; Fortson, Lucy F; Cardamone, Carolin N; Schawinski, Kevin; Cheung, Edmond; Lintott, Chris J; Masters, Karen L; Melvin, Thomas; Simmons, Brooke D

2015-01-01

249

arXiv:1402.6619v1[astro-ph.GA]26Feb2014 Hydrogen Fluoride toward Luminous Nearby Galaxies: NGC 253  

E-print Network

arXiv:1402.6619v1[astro-ph.GA]26Feb2014 Hydrogen Fluoride toward Luminous Nearby Galaxies: NGC 253 ­ ABSTRACT We present the detection of hydrogen fluoride, HF, in two luminous nearby galaxies NGC 253 and NGC of the fundamental J = 1 - 0 rotational transition of hydrogen fluoride (HF) at 1.232 THz (243 µm) and the discovery

Low, Steven H.

250

STAR FORMATION RATES IN RESOLVED GALAXIES: CALIBRATIONS WITH NEAR- AND FAR-INFRARED DATA FOR NGC 5055 AND NGC 6946  

SciTech Connect

We use the near-infrared Br{gamma} hydrogen recombination line as a reference star formation rate (SFR) indicator to test the validity and establish the calibration of the Herschel/PACS 70 {mu}m emission as a SFR tracer for sub-galactic regions in external galaxies. Br{gamma} offers the double advantage of directly tracing ionizing photons and of being relatively insensitive to the effects of dust attenuation. For our first experiment, we use archival Canada-France-Hawaii Telescope Br{gamma} and Ks images of two nearby galaxies: NGC 5055 and NGC 6946, which are also part of the Herschel program KINGFISH (Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel). We use the extinction corrected Br{gamma} emission to derive the SFR(70) calibration for H II regions in these two galaxies. A comparison of the SFR(70) calibrations at different spatial scales, from 200 pc to the size of the whole galaxy, reveals that about 50% of the total 70 {mu}m emission is due to dust heated by stellar populations that are unrelated to the current star formation. We use a simple model to qualitatively relate the increase of the SFR(70) calibration coefficient with decreasing region size to the star formation timescale. We provide a calibration for an unbiased SFR indicator that combines the observed H{alpha} with the 70 {mu}m emission, also for use in H II regions. We briefly analyze the PACS 100 and 160 {mu}m maps and find that longer wavelengths are not as good SFR indicators as 70 {mu}m, in agreement with previous results. We find that the calibrations show about 50% difference between the two galaxies, possibly due to effects of inclination.

Li Yiming; Crocker, Alison F.; Calzetti, Daniela [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Wilson, Christine D. [Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1 (Canada); Kennicutt, Robert C.; Galametz, M. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Murphy, Eric J. [Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Brandl, Bernhard R.; Groves, B. [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Draine, B. T. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Johnson, B. D. [Institut d'Astrophysique de Paris, UMR7095 CNRS, Universite Pierre and Marie Curie, 98 bis Boulevard Arago, F-75014 Paris (France); Armus, L. [Spitzer Science Center, California Institute of Technology, MC 314-6, Pasadena, CA 91125 (United States); Gordon, K. D. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Croxall, K. [Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606 (United States); Dale, D. A. [Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States); Engelbracht, C. W.; Hinz, J. [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Hao, C.-N. [Tianjin Astrophysics Center, Tianjin Normal University, Tianjin 300387 (China); Helou, G. [NASA Herschel Science Center, IPAC, California Institute of Technology, Pasadena, CA 91125 (United States); Hunt, L. K., E-mail: yimingl@astro.umass.edu [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy); and others

2013-05-10

251

The 0.3-30 keV spectra of Powerful Starburst Galaxies: NuSTAR and Chandra observations ofNGC 3256 and NGC 3310  

NASA Astrophysics Data System (ADS)

We present nearly simultaneous Chandra and NuSTAR observations of two actively star-forming galaxies: NGC 3256 and NGC 3310. The NuSTAR galaxy-wide spectra of both galaxies follow steep power law distributions, similar to the spectra of bright individual ultra-luminous X-ray sources (ULXs) that have been studied by NuSTAR. The X-ray emission from both galaxies is spatially resolved by Chandra, which indicates that hot gas dominates the E < 1 - 3 keV emission, while ULXs make up a majority of the emission at E > 1-3 keV. Using new and archival Chandra data we found that both galaxies have candidate AGNs coincident with nuclear regions. However, the steep NuSTAR spectra of both galaxies restricts these candidates to be low luminosity AGN, and a non-AGN nature cannot be ruled out. We find the average 0.3 -30 keV SFR-normalized spectra of NGC 3256 and NGC 3310, combined with equivalent measurements for M83 and NGC 253, show sharpening power-law slopes at energies above 3 - 6 keV due to ULX populations. Our observations therefore constrain the average spectral shape of an unbiased population of ULXs to be similar to the super-Eddington accreting ULXs that have been studied by NuSTAR. We also find that for NGC 3310, there is a factor of 5 times excess X-ray emission, due to an overabundance of ULXs in the galaxy compared to typical galaxies. We argue that the excess is due to the relatively low metallicity of the young stellar population in the galaxy.

Tyler, Joshua; Lehmer, Bret; Hornschemeier, Ann E.; Yukita, Mihoko; Wik, Daniel R.; Ptak, Andrew; Stern, Daniel; Harrison, Fiona; Maccarone, Tom; Zezas, Andreas; Antoniou, Vallia; NuSTAR Starburst Team

2015-01-01

252

EXTENDED STAR CLUSTERS IN THE REMOTE HALO OF THE INTRIGUING DWARF GALAXY NGC 6822  

SciTech Connect

We present a study on four new star clusters discovered in the halo of the intriguing dwarf irregular galaxy NGC 6822 from a wide-field survey covering 3{sup 0} x 3{sup 0} area carried out with MegaCam at the Canada-France-Hawaii Telescope. The star clusters have extended structures with half-light radii R{sub h} {approx} 7.5-14.0 pc, larger than typical Galactic globular clusters and other known globular clusters in NGC 6822. The integrated colors and color-magnitude diagrams of resolved stars suggest that the new star clusters are 2-10 Gyr old and relatively metal poor with Z = 0.0001-0.004 based on the comparison with theoretical models. The projected distance of each star cluster from the galaxy center ranges from 10.'7 ({approx}1.5 kpc) to 77' ({approx}11 kpc), far beyond the optical body of the galaxy. Interestingly, the new star clusters are aligned along the elongated old stellar halo of NGC 6822, which is almost perpendicular to the H I gas distribution where young stellar populations exist. We also find that the colors and half-light radii of the new clusters are correlated with the galactocentric distance: clusters farther from the galaxy center are larger and bluer than those closer to the galaxy center. We discuss the stellar structure and evolution of NGC 6822 implied by these new extended star clusters in the halo. We also discuss the current status of observational and theoretical understandings regarding the origin of extended star clusters in NGC 6822 and other galaxies.

Hwang, Narae [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Lee, Myung Gyoon; Lee, Jong Chul; Park, Hong Soo [Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of); Park, Won-Kee [CEOU, Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of); Kim, Sang Chul; Park, Jang-Hyun, E-mail: narae.hwang@nao.ac.jp [Korea Astronomy and Space Science Institute, 61-1 Hwaam-Dong, Yuseong-Gu, Daejeon 305-348 (Korea, Republic of)

2011-09-01

253

A 2 mm spectral line survey of the starburst galaxy NGC 253  

E-print Network

We present the first unbiased molecular line survey towards an extragalactic source, namely the nuclear region of the starburst galaxy NGC 253. The scan covers the frequency band from 129.1 to 175.2 GHz, i.e. most of the 2mm atmospheric window. We identify 111 spectral features as transitions from 25 different molecular species. Eight of which (three tentatively) are detected for the first time in the extragalactic interstellar medium. Among these newly detected species, we detected the rare isotopomers 34SO and HC18O+. Tentative detections of two deuterated species, DNC and N2D+, are reported for the first time from a target beyond the Magellanic Clouds. Additionally, three hydrogen recombination lines are identified, while no organic molecules larger than methanol are detected. Column densities and rotation temperatures are calculated for all the species, including an upper limit to the ethanol abundance. A comparison of the chemical composition of the nuclear environment of NGC 253 with those of selected nearby galaxies demonstrates the chemical resemblance of IC 342 and NGC 4945 to that of NGC 253. On the other hand, the chemistries characterizing NGC 253 and M 82 are clearly different. We also present a comparison of the chemical composition of NGC 253 with those observed in Galactic prototypical sources. The chemistry of NGC 253 shows a striking similarity with the chemistry observed toward the Galactic center molecular clouds, which are thought to be dominated by low-velocity shocks. This resemblance strongly suggests that the heating in the nuclear environment of NGC 253 is dominated by the same mechanism as that in the central region of the Milky Way.

S. Martn; R. Mauersberger; J. Martn-Pintado; C. Henkel; S. Garca-Burillo

2006-02-16

254

VERITAS UPPER LIMIT ON THE VERY HIGH ENERGY EMISSION FROM THE RADIO GALAXY NGC 1275  

SciTech Connect

The recent detection by the Fermi gamma-ray space telescope of high-energy gamma-rays from the radio galaxy NGC 1275 makes the observation of the very high energy (VHE: E>100 GeV) part of its broadband spectrum particularly interesting, especially for the understanding of active galactic nuclei with misaligned multi-structured jets. The radio galaxy NGC 1275 was recently observed by VERITAS at energies above 100 GeV for about 8 hr. No VHE gamma-ray emission was detected by VERITAS from NGC 1275. A 99% confidence level upper limit of 2.1% of the Crab Nebula flux level is obtained at the decorrelation energy of approximately 340 GeV, corresponding to 19% of the power-law extrapolation of the Fermi Large Area Telescope result.

Acciari, V. A.; Benbow, W. [Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645 (United States); Aliu, E.; Boltuch, D. [Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716 (United States); Arlen, T.; Celik, O. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Aune, T. [Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064 (United States); Bautista, M.; Cogan, P. [Physics Department, McGill University, Montreal, QC H3A 2T8 (Canada); Beilicke, M.; Buckley, J. H.; Bugaev, V.; Dickherber, R. [Department of Physics, Washington University, St. Louis, MO 63130 (United States); Bradbury, S. M. [School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT (United Kingdom); Byrum, K. [Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439 (United States); Cannon, A. [School of Physics, University College Dublin, Belfield, Dublin 4, Republic of Ireland (Ireland); Cesarini, A. [School of Physics, National University of Ireland, Galway, Republic of Ireland (Ireland); Ciupik, L. [Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605 (United States); Cui, W. [Department of Physics, Purdue University, West Lafayette, IN 47907 (United States); Duke, C., E-mail: ngalante@cfa.harvard.ed [Department of Physics, Grinnell College, Grinnell, IA 50112-1690 (United States)

2009-12-01

255

The total mass of the early-type galaxy NGC 4649 (M60)  

E-print Network

In this paper we analyze the problem of the total mass and the total mass-to-light ratio of the early-type galaxy NGC 4649 (M60). We have used two independent techniques: the X-ray methodology which is based on the temperature of the X-ray halo of NGC 4649 and the tracer mass estimator (TME) which uses globular clusters (GCs) observed in this galaxy. We calculated the mass in Newtonian and MOdified Newtonian Dynamics (MOND) approaches and found that interior to 3 effective radii (Re) there is no need for large amounts of dark matter. Beyond 3Re dark matter starts to play important dynamical role. We also discuss possible reasons for the discrepancy between the estimates of the total mass based on X-rays and TME in the outer regions of NGC 4649.

S. Samurovic; M. M. Cirkovic

2008-11-05

256

The circumnuclear X-ray reflectors in NGC 1068 and the Circinus Galaxy  

NASA Astrophysics Data System (ADS)

We present the results of the comparison of photoionization models with the X-ray emission line spectra of two Seyfert 2 galaxies. The spectrum of the Circinus Galaxy is well reproduced by the reflection of the nuclear continuum from a partially ionized material at a distance of 0.4 pc from the nucleus (the torus) and metal abundance AZ = 3. Three different reflectors with AZ = 3.3 are instead needed to account for the rather complex spectrum of NGC 1068.

Bianchi, Stefano; Matt, Giorgio

257

Giant Molecular Clouds in the Early-Type Galaxy NGC4526  

E-print Network

We present a high spatial resolution ($\\approx 20$ pc) of $^{12}$CO($2-1$) observations of the lenticular galaxy NGC4526. We identify 103 resolved Giant Molecular Clouds (GMCs) and measure their properties: size $R$, velocity dispersion $\\sigma_v$, and luminosity $L$. This is the first GMC catalog of an early-type galaxy. We find that the GMC population in NGC4526 is gravitationally bound, with a virial parameter $\\alpha \\sim 1$. The mass distribution, $dN/dM \\propto M^{-2.39 \\pm 0.03}$, is steeper than that for GMCs in the inner Milky Way, but comparable to that found in some late-type galaxies. We find no size-linewidth correlation for the NGC4526 clouds, in contradiction to the expectation from Larson's relation. In general, the GMCs in NGC4526 are more luminous, denser, and have a higher velocity dispersion than equal size GMCs in the Milky Way and other galaxies in the Local Group. These may be due to higher interstellar radiation field than in the Milky Way disk and weaker external pressure than in the ...

Utomo, Dyas; Davis, Timothy; Rosolowsky, Erik; Bureau, Martin; Cappellari, Michele; Sarzi, Marc

2015-01-01

258

X-Ray Source Population in the Elliptical Galaxy NGC 720 with Chandra  

E-print Network

With a Chandra ACIS-S3 observation, we detect 42 X-ray point sources in the elliptical galaxy NGC 720, including a possible central source. Most of these sources will be low-mass X-ray binaries, and 12 are located within ...

Canizares, Claude R.

259

A WIYN Study of the Globular Cluster Population of the Virgo Elliptical Galaxy NGC 4473  

NASA Astrophysics Data System (ADS)

We present results from an analysis of the globular cluster system of NGC 4473, a moderate-luminosity elliptical galaxy in the Virgo Cluster. The properties of globular clusters - in particular, their ages, luminosities, and spatial distributions - make them especially useful probes of the star formation and assembly histories of their host galaxies. We used the 10' x 10' Minimosaic camera on the WIYN 3.5-meter telescope to image the globular cluster system of NGC 4473 over its full radial extent. Globular cluster candidates were identified as point sources and selected by their magnitudes and colors in three filters (B, V, R) in order to minimize contamination from foreground and background sources. Our deep images, which have 0.5' - 0.7' seeing and 50% completeness levels for point-source detection at B = 25.7, V = 25.5, and R = 25.2, allow us to cover 75 percent of the intrinsic globular cluster luminosity function (GCLF) for NGC 4473. The surface density of globular clusters in our final corrected radial profile drops to zero within the errors at ~7', or ~33 kpc from the galaxy center. These results will be presented along with our findings regarding the total number (NGC = 480 50), specific frequency (SN = 2.2 0.4), and color (metallicity) distribution of the globular clusters in this galaxy.

Panetta, Margaret; Rhode, Katherine L.; West, Michael, , Dr.

2015-01-01

260

The Araucaria Project: Near-Infrared Photometry of Cepheid Variables in the Sculptor Galaxy NGC 300  

Microsoft Academic Search

We have obtained deep near-infrared images in J and K filters of three fields in the Sculptor galaxy NGC 300 with the ESO VLT and ISAAC Camera. For 16 Cepheid variables in these fields, we have determined J and K magnitudes at two different epochs and have derived their mean magnitudes in these bands. The slopes of the resulting period-luminosity

Wolfgang Gieren; Grzegorz Pietrzynski; Igor Soszynski; Fabio Bresolin; Rolf-Peter Kudritzki; Dante Minniti; Jesper Storm

2005-01-01

261

Radio continuum observations of the quasar-galaxy pair 3C 232-NGC 3067  

NASA Technical Reports Server (NTRS)

The quasar-galaxy pair 3C 232-NGC 3067 is well known to show absorption by gas associated with the foreground galaxy against the background quasar (see Stocke et al. this volume). Observations by Carilli, van Gorkom, and Stocke (Nature 338, 134, 1989) found that the absorbing gas is located in a long tail of gas which extends from the galaxy toward the quasar and beyond (in projection). Though the HI observations of NGC 3067 indicate that the galaxy has been severely disturbed, there is no obvious candidate in the field which could cause such a disturbance, leading to the conclusion that the system has undergone a recent merger. The radio continuum observations of this system were designed to study the nature of this highly disturbed galaxy. New continuum observations confirm the notion that NGC 3067 is a highly disturbed system, and, in particular, the notion that the western half of the galaxy extends only 1/2 as far in radius as the eastern half. This disturbance must have occurred recently, since the galactic rotation would smooth out the observed asymmetry in about 10(exp 8) years. Researchers are left with the problem that there are no obvious candidates which could have caused such a disturbance.

Haxthausen, Eric; Carilli, Chris; Vangorkom, Jacqueline H.

1990-01-01

262

The Black Hole in the Compact, High-dispersion Galaxy NGC 1271  

NASA Astrophysics Data System (ADS)

Correlations linking the mass of the black hole in the centers of galaxies to bulge properties have been clearly established over the past decade; however there still remain major open questions, particularly concerning the sparsely populated upper end of the black hole mass distribution. Through a large survey with the Hobby Eberly Telescope at McDonald Observatory, we have identified a sample of ideal galaxies for studying the upper end of the black hole mass scaling relations. These galaxies are compact, rapidly rotating, and have low luminosities for their very large stellar velocity dispersions, in sharp contrast to the objects typically found at the high end of the black holes mass - bulge relationships. In this talk, we focus on one galaxy in the sample: the nearby S0 galaxy NGC 1271. We present laser guide star adaptive optics observations of NGC 1271 with the integral field spectrograph NIFS on the Gemini North telescope. By combining the high spatial resolution stellar kinematics measured from the NIFS observations with imaging and large-scale stellar kinematics, we construct orbit-based stellar dynamical models. We will present results of the dynamical modeling, emphasizing the constraints on the black hole mass, and place NGC 1271 on the black hole mass - host galaxy relationships.

Walsh, Jonelle; van den Bosch, R.; Gebhardt, K.; Yildirim, A.; Gultekin, K.; Richstone, D. O.

2014-01-01

263

Kinematic evidence for different Planetary Nebulae Populations in the elliptical galaxy NGC 4697  

E-print Network

We have analysed the magnitudes, kinematics and positions of a complete sample of 320 PNs in the elliptical galaxy NGC 4697. We show (i) that the PNs in NGC 4697 do not constitute a single population that is a fair tracer of the distribution of all stars. The radial velocity distributions, mean velocities, and dispersions of bright and faint subsamples differ with high statistical confidence. (ii) Using the combined data for PNs brighter than 26.2, we have identified a subpopulation of PNs which is azimuthally unmixed and kinematically peculiar, and which thus neither traces the distribution of all stars nor can it be in dynamical equilibrium with the galaxy potential. (iii) The planetary nebula luminosity functions (PNLF) of two kinematic subsamples in NGC 4697 differ with 99.7% confidence, ruling out a universal PNLF. We estimate that the inferred secondary PN population introduces an uncertainty in the bright cutoff magnitude of ~ 0.15 mag for this galaxy. -- We argue that this secondary PN distribution may be associated with a younger, >~ 1 Gyr old stellar population, perhaps formed in tidal structures that have now fallen back onto the galaxy, as has previously been suggested for the X-ray point sources in this galaxy, or coming from a more recent merger/accretion with a red galaxy. The use of PNs for extragalactic distance determinations is not necessarily compromised, but their use as dynamical tracers of dark halos will require deep observations and careful analysis of large PN samples.

Niranjan Sambhus; Ortwin Gerhard; Roberto H. Mendez

2005-10-17

264

Relics of dissipational merging and past violent starbursts in elliptical galaxies - the gE galaxy NGC 4365.  

NASA Astrophysics Data System (ADS)

The Virgo elliptical galaxy NGC 4365 harbours a kinematically decoupled, counter-rotating core region. Its line-of-sight integrated velocity distributions are studied along 3 spectroscopic axes using Gauss-Hermite moments and double-gaussian line models. Stellar populations are investigated through high-resolution (B-R) colour photometry and spectroscopic absorbtion line indices Mg_2_ , H? and , which are compared to population models of Worthey (1992). We find consistent evidences for a distinct core population C of stars with disk or bar-like structure, high rotation velocity and low kinematic temperature (v/?=1.3), flattened density distribution (?_C_=0.39+/-0.07 versus ?_spheroid_=0.21 ...0.245) and a mass content of at least (8.1+/-2.5) .10 9Msun_. The metallicity of this core population shows an excessively flattened distribution (relative to the isophotes) and reaches values of at least 2.3Zsun_ at a population age of about <=(7 +/-1.5)Gyr. We favour a formation scenario with gas included in early hierarchical or late major mergers, where the gas is subject to strong dissipation effects and chemical enrichment and produces a violent starburst of order 10 2Msun_/yr. Our line indices show the well-known enhanced [Mg/Fe] of massive Es, but furthermore excessive enhancement of magnesium relative to iron in the innermost core region. This is interpreted as confirming evidence for a violent gaseous merger which probably over-produced SNii versus SNia due to a top-heavy IMF or because of its burst-like star formation history.

Surma, P.; Bender, R.

1995-06-01

265

Gemini/GMOS Imaging of Globular Clusters in the Virgo Galaxy NGC 4649 (M60)  

E-print Network

We present Sloan g and i imaging from the GMOS instrument on the Gemini North telescope for the globular cluster (GC) system around the Virgo galaxy NGC 4649 (M60). Our three pointings, taken in good seeing conditions, cover an area of about 90 sq. arcmins. We detect 2,151 unresolved sources. Applying colour and magnitude selection criteria to this source list gives 995 candidate GCs that is greater than 90% complete to a magnitude of i = 23.6, with little contamination from background galaxies. We find fewer than half a dozen potential Ultra Compact Dwarf galaxies around NGC 4649. Foreground extinction from the nearby spiral NGC 4647 is limited to be A_V < 0.1. We confirm the bimodality in the GC colour distribution found by earlier work using HST/WFPC2 imaging. As is commonly seen in other galaxies, the red GCs are concentrated towards the centre of the galaxy, having a steeper number density profile than the blue GC subpopulation. The varying ratio of red-to-blue GCs with radius can largely explain the overall GC system colour gradient. The underlying galaxy starlight has a similar density profile slope and colour to the red GCs. This suggests a direct connection between the galaxy field stars and the red GC subpopulation. We estimate a total GC population of 3700 +/- 900, with the uncertainty dominated by the extrapolation to larger radii than observed. This total number corresponds to a specific frequency S_N = 4.1 +/- 1.0. Future work will present properties derived from GMOS spectra of the NGC 4649 GCs.

Duncan A. Forbes; Favio Raul Faifer; Juan Carlos Forte; Terry Bridges; Michael A. Beasley; Karl Gebhardt; David A. Hanes; Ray Sharples; Stephen E. Zepf

2004-08-23

266

Red giants in the outer halo of the elliptical galaxy NGC 5128/Centaurus A  

NASA Astrophysics Data System (ADS)

We used VIMOS on VLT to perform V and I band imaging of the outermost halo of NGC 5128/Centaurus A ((m - M)0 = 27.910.08), 65 kpc from the galaxy's center and along the major axis. The stellar population has been resolved to I0 ? 27 with a 50% completeness limit of I0 = 24.7, well below the tip of the red-giant branch (TRGB), which is seen at I0 ? 23.9. The surface density of NGC 5128 halo stars in our fields was sufficiently low that dim, unresolved background galaxies were a major contaminant in the source counts. We isolated a clean sample of red-giant-branch (RGB) stars extending to ?0.8 mag below the TRGB through conservative magnitude and color cuts, to remove the (predominantly blue) unresolved background galaxies. We derived stellar metallicities from colors of the stars via isochrones and measured the density falloff of the halo as a function of metallicity by combining our observations with HST imaging taken of NGC 5128 halo fields closer to the galaxy center. We found both metal-rich and metal-poor stellar populations and found that the falloff of the two follows the same de Vaucouleurs' law profiles from ?8 kpc out to ?70 kpc. The metallicity distribution function (MDF) and the density falloff agree with the results of two recent studies of similar outermost halo fields in NGC 5128. We found no evidence of a "transition" in the radial profile of the halo, in which the metal-rich halo density would drop rapidly, leaving the underlying metal-poor halo to dominate by default out to greater radial extent, as has been seen in the outer halo of two other large galaxies. If NGC 5128 has such a transition, it must lie at larger galactocentric distances.

Bird, Sarah A.; Flynn, Chris; Harris, William E.; Valtonen, Mauri

2015-03-01

267

Quantifying the Bias in the Masses of Supermassive Black Holes in Barred Galaxies  

NASA Astrophysics Data System (ADS)

Recent studies of simulations of barred galaxies with supermassive black holes {BH} show that a bar can cause an increase in the central line-of-sight velocity dispersion {sigma} of about 7-12% - an increase that is consistent with the average offset observed for barred galaxies relative to unbarred ones. A more serious consequence of the presence of a bar is that its unique orbital structure {the combination of the radially biased bar orbits and the high bar pattern speed}, results in a high central velocity dispersion but negative 4th Gauss-Hermite parameters, even in the vicinity of the BH. This unique combination of kinematical parameters can result in a systematic over-estimate of the BH mass - if the bar is modelled as axisymmetric. Although nearly 60% of spiral/SO galaxies with existing stellar dynamically BH masses are in barred galaxies, their masses have been derived using axisymmetric models! An overestimate of BH mass in barred disks would erase morphological differences between the BH scaling relations of disks and ellipticals, which could be crucial to understanding the co-evolution of BHs and their host galaxies. In this theory proposal we will use N-body simulations to generate mock kinematic datasets {STIS, FOS and ground based IFU} for barred disk galaxies, model them with an axisymmetric orbit superposition code, and thereby quantify the magnitude of the bias in existing BH mass measurements. This analysis will provide crucial input for developing new and accurate methods for determining BH masses in galaxies of different morphological types, thereby revealing the true extent of intrinsic differences in the supermassive BH scaling relationships.

Valluri, Monica

2014-10-01

268

Bar-driven evolution of fast rotators: the role and fate of bars in early and late-type galaxies  

NASA Astrophysics Data System (ADS)

We have performed state-of-the-art high resolution simulations of early-type galaxies with bars, including (multi-phase) gas, star formation and feedback. The aim of this programme is to better understand the observed morphology, kinematical structures, (2D) metallicity distribution, observed in fast rotators with bars. Our simulations were designed via a newly developed code allowing us to build a library of initial conditions closely mimicking barred galaxies in the Atlas3D sample. We will present the role and importance of bars on the gas fueling, redistribution of angular momentum, and overall secular evolution of fast rotators. These results are compared with actual observations (IFU, CO maps, stellar population distributions) obtained in the course of the Atlas3D project. The results from these ``early-type`` simulations will also be compared in the context of recently conducted simulations of later-type barred galaxies, including one of a Milky-Way type object with a resolution down to 0.05 parsec.

Emsellem, Eric; Florent, Renaud

2015-03-01

269

A Study of Bar Strengths in Early-Type Disk Galaxies  

NASA Astrophysics Data System (ADS)

Angular momentum exchange between a bar and a massive halo is thought to be responsible for producing strong bars in disk galaxies (Athanassoula, 2003), while gas transport to the center is believed to weaken or even dissolve bars (Bournaud and Combes 2002). We are carrying out a systematic survey of early-type disk galaxies with the main emphasis to derive the distribution of their bar strengths and to examine their Fourier amplitude properties. We propose to use FLAMINGOS with the KPNO 2.1m to obtain 2.2(micron) K_s-band observations of 16 galaxies for the ``Near-Infrared S0 Survey", a project already in progress to measure the bulge, disk, and bar properties of a statistically well-defined sample of 184 galaxies in the type range S0^- to Sa, including some possibly mis-classified elliptical galaxies. The principal goals of the survey, which was started 5 years ago and is now 90% completed, are to allow us to (1) compare relative Fourier near- IR intensity profiles of observed early-type galaxy bars with equivalent Fourier mass profiles of various Athanassoula models; (2) derive the distribution of bar strengths for the early-type sample and compare it with the known distribution for spirals; and (3) examine the properties of bulges and disks in early-type galaxies in order to better understand the origin of bulges (classical verus pseudo) in such galaxies. Our study is the first attempt to quantify bar strength in S0 galaxies. We are asking for enough KPNO 2.1m time to help complete our survey.

Buta, Ronald J.; Laurikainen, Eija; Salo, Heikki; Knapen, Johan H.

2009-02-01

270

Velocity dispersions in galaxies. I - The E7 galaxy NGC 7332.  

NASA Technical Reports Server (NTRS)

A coude spectrum of the E7 galaxy NGC 7332 with 0.9 A-resolution from 4186 to 4364 A was obtained with the Princeton SEC vidicon television camera and the Hale telescope. Comparisons with spectra of G and K giant stars, numerically broadened for various Maxwellian velocity distributions, give a dispersion velocity in the line of sight of 160 (plus or minus 20) km/sec with the best fit at G8 III. The dispersion appears to be constant within plus or minus 35 km/sec out to 1.4 kpc. After correction for projection, the rotation curve has a slope of 0.18 km/sec per pc at the center and a velocity of 130 km/sec at 1.4 kpc where it is still increasing. For an estimated effective radius of 3.5 kpc enclosing half the light, the virial theorem gives a mass of 140 billion solar masses if the mass-to-light ratio is constant throughout the galaxy.

Morton, D. C.; Chevalier, R. A.

1972-01-01

271

Galaxy Zoo: the effect of bar-driven fuelling on the presence of an active galactic nucleus in disc galaxies  

NASA Astrophysics Data System (ADS)

We study the influence of the presence of a strong bar in disc galaxies which host an active galactic nucleus (AGN). Using data from the Sloan Digital Sky Survey and morphological classifications from the Galaxy Zoo 2 project, we create a volume-limited sample of 19 756 disc galaxies at 0.01 < z < 0.05 which have been visually examined for the presence of a bar. Within this sample, AGN host galaxies have a higher overall percentage of bars (51.8 per cent) than inactive galaxies exhibiting central star formation (37.1 per cent). This difference is primarily due to known effects: that the presence of both AGN and galactic bars is strongly correlated with both the stellar mass and integrated colour of the host galaxy. We control for this effect by examining the difference in AGN fraction between barred and unbarred galaxies in fixed bins of mass and colour. Once this effect is accounted for, there remains a small but statistically significant increase that represents 16 per cent of the average barred AGN fraction. Using the L_{[O III]}/MBH ratio as a measure of AGN strength, we show that barred AGNs do not exhibit stronger accretion than unbarred AGNs at a fixed mass and colour. The data are consistent with a model in which bar-driven fuelling does contribute to the probability of an actively growing black hole, but in which other dynamical mechanisms must contribute to the direct AGN fuelling via smaller, non-axisymmetric perturbations.

Galloway, Melanie A.; Willett, Kyle W.; Fortson, Lucy F.; Cardamone, Carolin N.; Schawinski, Kevin; Cheung, Edmond; Lintott, Chris J.; Masters, Karen L.; Melvin, Thomas; Simmons, Brooke D.

2015-04-01

272

COLD DUST BUT WARM GAS IN THE UNUSUAL ELLIPTICAL GALAXY NGC 4125  

SciTech Connect

Data from the Herschel Space Observatory have revealed an unusual elliptical galaxy, NGC 4125, which has strong and extended submillimeter emission from cold dust but only very strict upper limits to its CO and H I emission. Depending on the dust emissivity, the total dust mass is 2-5 10{sup 6} M {sub ?}. While the neutral gas-to-dust mass ratio is extremely low (<12-30), including the ionized gas traced by [C II] emission raises this limit to <39-100. The dust emission follows a similar r {sup 1/4} profile to the stellar light and the dust to stellar mass ratio is toward the high end of what is found in nearby elliptical galaxies. We suggest that NGC 4125 is currently in an unusual phase where evolved stars produced in a merger-triggered burst of star formation are pumping large amounts of gas and dust into the interstellar medium. In this scenario, the low neutral gas-to-dust mass ratio is explained by the gas being heated to temperatures ?10{sup 4} K faster than the dust is evaporated. If galaxies like NGC 4125, where the far-infrared emission does not trace neutral gas in the usual manner, are common at higher redshift, this could have significant implications for our understanding of high redshift galaxies and galaxy evolution.

Wilson, C. D.; Cridland, A.; Foyle, K.; Parkin, T. J.; Cooper, E. Mentuch [Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1 (Canada)] [Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1 (Canada); Roussel, H. [Institut d'Astrophysique de Paris, Universit Pierre et Marie Curie, CNRS UMR 7095, F-75014 Paris (France)] [Institut d'Astrophysique de Paris, Universit Pierre et Marie Curie, CNRS UMR 7095, F-75014 Paris (France); Sauvage, M.; Lebouteiller, V.; Madden, S. [Laboratoire AIM, CEA/DSM-CNRS-Universit Paris Diderot DAPNIA/Service d'Astrophysique, Bt. 709, CEA-Saclay, F-91191 Gif-sur-Yvette Cedex (France)] [Laboratoire AIM, CEA/DSM-CNRS-Universit Paris Diderot DAPNIA/Service d'Astrophysique, Bt. 709, CEA-Saclay, F-91191 Gif-sur-Yvette Cedex (France); Smith, M. W. L.; Gear, W. [School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA (United Kingdom)] [School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA (United Kingdom); Baes, M.; De Looze, I. [Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, B-9000 Gent (Belgium)] [Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, B-9000 Gent (Belgium); Bendo, G. [UK ALMA Regional Centre Node, Jodrell Bank Center for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom)] [UK ALMA Regional Centre Node, Jodrell Bank Center for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom); Boquien, M.; Boselli, A.; Ciesla, L. [Aix-Marseille Universit, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, F-13388 Marseille (France)] [Aix-Marseille Universit, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, F-13388 Marseille (France); Clements, D. L. [Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ (United Kingdom)] [Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ (United Kingdom); Cooray, A. [Department of Physics and Astronomy, University of California, Irvine, CA 92697 (United States)] [Department of Physics and Astronomy, University of California, Irvine, CA 92697 (United States); Galametz, M. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)] [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); and others

2013-10-20

273

OLD MASSIVE GLOBULAR CLUSTERS AND THE STELLAR HALO OF THE DWARF STARBURST GALAXY NGC 4449  

SciTech Connect

We use Hubble Space Telescope imaging to show that the nearby dwarf starburst galaxy NGC 4449 has an unusual abundance of luminous red star clusters. Joint constraints from integrated photometry, low-resolution spectroscopy, dynamical mass-to-light ratios, and resolved color-magnitude diagrams provide evidence that some of these clusters are old globular clusters (GCs). Spectroscopic data for two massive clusters suggest intermediate metallicities ([Fe/H] {approx}-1) and subsolar Mg enhancement ([Mg/Fe] {approx}-0.1 to -0.2). One of these clusters may be the nucleus of a tidally disrupting dwarf galaxy; the other is very massive ({approx}3 Multiplication-Sign 10{sup 6} M{sub Sun} ). We have also identified a population of remote halo GCs. NGC 4449 is consistent with an emerging picture of the ubiquity of stellar halos among dwarf galaxies, and study of its GCs may help distinguish between accretion and in situ scenarios for such halos.

Strader, Jay; Seth, Anil C.; Caldwell, Nelson, E-mail: jstrader@cfa.harvard.edu [Department of Physics and Astronomy, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

2012-02-15

274

The Environment of X-Ray Binaries in the Dwarf Starburst Galaxy NGC 1569  

NASA Astrophysics Data System (ADS)

We use deep, J and Ks observations of NGC 1569 acquired with FLAMINGOS on the KPNO 4-m to search for star cluster counterparts to X-ray binaries identified in archived Chandra images of this dwarf starburst galaxy. Performing near-IR photometry on the star cluster counterparts, we determine their colors, luminosities and masses. Comparing these results to the properties for all clusters in this galaxy, we search for trends in clusters associated with X-ray sources. Combining this study with FISICA, near-IR spectral observations, we further characterize the surroundings to X-ray binaries in NGC 1569. Contrasting this work with findings from a similar study performed on the Antennae galaxies, a large, merging system, we investigate the differences in X-ray binary environments.

Clark, David M.; Eikenberry, Stephen S.; Raines, Steven N.

2008-05-01

275

Optical rotation velocities and images of the spiral galaxy NGC 3198  

NASA Technical Reports Server (NTRS)

H-alpha rotation velocities obtained from an echelle spectrogram to a radius of 2 arcmin for the spiral galaxy NGC 3198 agree well with the 21 cm rotation velocities of van Albada et al. (1985). The rotation curve is typical of Sc type galaxies in spite of NGC 3198's extended H I disk. From optical R and H-alpha-emission images, used to search for star-forming regions in the outer parts of this galaxy, several H-alpha knots are identified as far out as the Holmberg radius. With increasing radial distance out to 2 arcmin, the R-band surface brightness falls, the H-alpha is approximately constant, and the H I surface brightness rises.

Hunter, D. A.; Rubin, V. C.; Gallagher, J. S., III

1986-01-01

276

The Araucaria Project. Near-Infrared Photometry of Cepheid Variables in the Sculptor Galaxy NGC 55  

E-print Network

We have obtained deep images in the near-infrared J and K filters of four fields in the Sculptor Group spiral galaxy NGC 55 with the ESO VLT and ISAAC camera. For 40 long-period Cepheid variables in these fields which were recently discovered by Pietrzy{\\'n}ski et al., we have determined mean J and K magnitudes from observations at two epochs, and derived distance moduli from the observed PL relations in these bands. Using these values together with the previously measured distance moduli in the optical V and I bands, we have determined a total mean reddening of the NGC 55 Cepheids of E(B-V)=0.127 $\\pm$ 0.019 mag, which is mostly produced inside NGC 55 itself. For the true distance modulus of the galaxy, our multiwavelength analysis yields a value of 26.434 $\\pm$ 0.037 mag (random error), corresponding to a distance of 1.94 $\\pm$ 0.03 Mpc. This value is tied to an adopted true LMC distance modulus of 18.50 mag. The systematic uncertainty of our derived Cepheid distance to NGC 55 (apart from the uncertainty on the adopted LMC distance) is $\\pm$4%, with the main contribution likely to come from the effect of blending of some of the Cepheids with unresolved companion stars. The distance of NGC 55 derived from our multiwavelength Cepheid analysis agrees within the errors with the distance of NGC 300, strengthening the case for a physical association of these two Sculptor Group galaxies.

W. Gieren; G. Pietrzynski; I. Soszynski; F. Bresolin; R. P. Kudritzki; J. Storm; D. Minniti

2007-09-15

277

The Araucaria Project: Near-Infrared Photometry of Cepheid Variables in the Sculptor Galaxy NGC 55  

NASA Astrophysics Data System (ADS)

We have obtained deep images in the near-infrared J and K filters of four fields in the Sculptor group spiral galaxy NGC 55 with the ESO VLT and ISAAC camera. For 40 long-period Cepheid variables in these fields, which were recently discovered by Pietrzy?ski et al., we have determined mean J and K magnitudes from observations at two epochs, and derived distance moduli from the observed period-luminosity (PL) relations in these bands. Using these values together with the previously measured distance moduli in the optical V and I bands, we have determined a total mean reddening of the NGC 55 Cepheids of E(B-V)=0.127+/-0.019 mag, which is mostly produced inside NGC 55 itself. For the true distance modulus of the galaxy, our multiwavelength analysis yields a value of 26.434+/-0.037 mag (random error), corresponding to a distance of 1.94+/-0.03 Mpc. This value is tied to an adopted true Large Magellanic Cloud (LMC) distance modulus of 18.50 mag. The systematic uncertainty of our derived Cepheid distance to NGC 55 (apart from the uncertainty on the adopted LMC distance) is +/-4%, with the main contribution likely to come from the effect of blending of some of the Cepheids with unresolved companion stars. The distance of NGC 55 derived from our multiwavelength Cepheid analysis agrees within the errors with the distance of NGC 300, strengthening the case for a physical association of these two Sculptor group galaxies. Based on observations obtained with the ESO VLT for Large Program 171.D-0004.

Gieren, Wolfgang; Pietrzy?ski, Grzegorz; Soszy?ski, Igor; Bresolin, Fabio; Kudritzki, Rolf-Peter; Storm, Jesper; Minniti, Dante

2008-01-01

278

Constraints from Dynamical Friction on the Dark Matter Content of Barred Galaxies  

E-print Network

We show that bars in galaxy models having halos of moderate density and a variety of velocity distributions all experience a strong drag from dynamical friction unless the halo has large angular momentum in the same sense as the disk. The frictional drag decreases the bar pattern speed, driving the corotation point out to distances well in excess of those estimated in barred galaxies. The halo angular momentum required to avoid strong braking is unrealistically large, even when rotation is confined to the inner halo only. We conclude, therefore, that bars are able to maintain their observed high pattern speeds only if the halo has a central density low enough for the disk to provide most of the central attraction in the inner galaxy. We present evidence that this conclusion holds for all bright galaxies.

Victor P. Debattista; J. A. Sellwood

2000-06-20

279

Gas Flow and Star Formation in the `Antennae' Galaxies NGC 4038/9  

E-print Network

The prominent interacting galaxy pair NGC 4038/9 contains many active star-forming regions and is continuously forming new star clusters. We present a self-consistent n-body model for this system which includes an SPH gas component. The model qualitatively explains the apparent concentration of gas in the so-called overlap region between the two nuclei as a bridge of gas connecting the two galaxies. Projected on the sky, the bridge appears as a dense spot of gas. We discuss some implications for the evolution of Ultra-luminous infrared galaxies.

P. Englmaier; D. Rigopoulou; S. Mengel

2000-08-23

280

A variable ultra-luminous X-ray source in the colliding galaxy NGC 7714  

E-print Network

We studied the colliding galaxy NGC 7714 with two XMM-Newton observations, six months apart. The galaxy contains two bright X-ray sources: we show that they have different physical nature. The off-nuclear source is an accreting compact object, one of the brightest ultraluminous X-ray sources (ULXs) found to date. It showed spectral and luminosity changes between the two observations, from a low/soft to a high/hard state; in the high state, it reached L_x ~ 6 x 10^{40} erg/s. Its lightcurve in the high state suggests variability on a ~ 2-hr timescale. Its peculiar location, where the tidal bridge between NGC 7714 and NGC 7715 joins the outer stellar ring of NGC 7714, makes it an interesting example of the connection between gas flows in colliding galaxies and ULX formation. The nuclear source (L_x ~ 10^{41} erg/s) coincides with a starburst region, and is the combination of thin thermal plasma emission and a point-source contribution (with a power-law spectrum). Variability in the power-law component between the two observations hints at the presence of a single, bright point source (L_x >~ 3 x 10^{40} erg/s): either a hidden AGN or another ULX.

Roberto Soria; Christian Motch

2004-02-13

281

Multiwavelength Study of the Bright X-ray Source Population in the Interacting Galaxies NGC 5774/NGC 5775  

NASA Technical Reports Server (NTRS)

The X-ray source population in the field of the interacting pair of galaxies NGC 5774/5775 is reported. A total of 49 discrete sources are detected, including 12 ultraluminous X-ray source candidates with lum inosities above 10(exp 39)erg/s in the 0.5 - 8.0 keV X-ray band. Several of these latter are transient X-ray sources that fall below detect ion levels in one of two X-ray observations spaced 15 months apart. X-ray source positions are mapped onto optical and radio images to sear ch for potential counterparts. Eleven sources have optically-bright c ounterparts. Optical colors are used to differentiate these sources, which are mostly located outside the optical extent of the interacting galaxies, as potential globular clusters (3 sources) and quasars (5) . Follow-up optical spectroscopy confirms two of the latter are background quasars.

Ghosh, Kajal K.; Swartz, Douglas A.; Tennant, Allyn F.; Saripalli, Lakshmi; Gandhi, Poshak; Foellmi, Cedric; Gutierrez, Carlos M.; Lopez-Corredoira, Martin

2006-01-01

282

Giant Molecular Clouds in the Early-type Galaxy NGC 4526  

NASA Astrophysics Data System (ADS)

We present a high spatial resolution (?20 pc) of 12CO(2 ?1) observations of the lenticular galaxy NGC 4526. We identify 103 resolved giant molecular clouds (GMCs) and measure their properties: size R, velocity dispersion ?v, and luminosity L. This is the first GMC catalog of an early-type galaxy. We find that the GMC population in NGC 4526 is gravitationally bound, with a virial parameter ? ? 1. The mass distribution, dN/dM ? M?2.39 0.03, is steeper than that for GMCs in the inner Milky Way, but comparable to that found in some late-type galaxies. We find no sizeline width correlation for the NGC 4526 clouds, in contradiction to the expectation from Larsons relation. In general, the GMCs in NGC 4526 are more luminous, denser, and have a higher velocity dispersion than equal-size GMCs in the Milky Way and other galaxies in the Local Group. These may be due to higher interstellar radiation field than in the Milky Way disk and weaker external pressure than in the Galactic center. In addition, a kinematic measurement of cloud rotation shows that the rotation is driven by the galactic shear. For the vast majority of the clouds, the rotational energy is less than the turbulent and gravitational energy, while the four innermost clouds are unbound and will likely be torn apart by the strong shear at the galactic center. We combine our data with the archival data of other galaxies to show that the surface density ? of GMCs is not approximately constant, as previously believed, but varies by ?3 orders of magnitude. We also show that the size and velocity dispersion of the GMC population across galaxies are related to the surface density, as expected from the gravitational and pressure equilibrium, i.e., ?v R?1/2 ? ?1/2.

Utomo, Dyas; Blitz, Leo; Davis, Timothy; Rosolowsky, Erik; Bureau, Martin; Cappellari, Michele; Sarzi, Marc

2015-04-01

283

The Role of Bars in AGN Fueling in Disk Galaxies Over the Last Seven Billion Years  

NASA Astrophysics Data System (ADS)

We present empirical constraints on the influence of stellar bars on the fueling of active galactic nuclei (AGNs) out to z = 0.84 using a sample of X-ray-selected AGNs hosted in luminous non-interacting face-on and moderately inclined disk galaxies from the Chandra COSMOS survey. Using high-resolution Hubble Space Telescope imaging to identify bars, we find that the fraction of barred active galaxies displays a similar behavior as that of inactive spirals, declining with redshift from 71% at z? 0.3, to 35% at z? 0.8. With active galaxies being typically massive, we compare them against a mass-matched sample of inactive spirals and show that, while at face value the AGN bar fraction is slightly higher at all redshifts, we cannot rule out that the bar fractions of active and inactive galaxies are the same. The presence of a bar has no influence on the AGN strength, with barred and unbarred active galaxies showing equivalent X-ray luminosity distributions. From our results, we conclude that the occurrence and the efficiency of the fueling process is independent of the large scale structure of a galaxy. The role of bars, if any, may be restricted to providing the suitable conditions for black hole fueling to occur, i.e., bring a fresh supply of gas to the central 100 pc. At the high-redshift end, we find that roughly 60% of active disk galaxies are unbarred. We speculate this to be related with the known dynamical state of disks at higher redshiftsmore gas-rich and prone to instabilities than local spiralswhich could also lead to gas inflows without the need of bars.

Cisternas, Mauricio; Sheth, Kartik; Salvato, Mara; Knapen, Johan H.; Civano, Francesca; Santini, Paola

2015-04-01

284

Peanut-shaped bulges in face-on disk galaxies  

E-print Network

We present high resolution absorption-line spectroscopy of 3 face-on galaxies, NGC 98, NGC 600, and NGC 1703 with the aim of searching for box/peanut (B/P)-shaped bulges. These observations test and confirm the prediction of Debattista et al. (2005) that face-on B/P-shaped bulges can be recognized by a double minimum in the profile of the fourth-order Gauss-Hermite moment h_4. In NGC 1703, which is an unbarred control galaxy, we found no evidence of a B/P bulge. In NGC 98, a clear double minimum in h_4 is present along the major axis of the bar and before the end of the bar, as predicted. In contrast, in NGC 600, which is also a barred galaxy but lacks a substantial bulge, we do not find a significant B/P shape.

Mendez-Abreu, J; Debattista, V P; De Rijcke, S; Aguerri, J A L; Pizzella, A

2010-01-01

285

NGC 6340: an old S0 galaxy with a young polar disc. Clues from morphology, internal kinematics and stellar populations  

Microsoft Academic Search

Lenticular galaxies are believed to form by a combination of environmental\\u000aeffects and secular evolution. We study the nearby disc-dominated S0 galaxy NGC\\u000a6340 photometrically and spectroscopically to understand the mechanisms of S0\\u000aformation and evolution in groups. We use SDSS images to build colour maps and\\u000alight profile of NGC 6340 which we decompose using a three-component model\\u000aincluding

Igor Chilingarian; Alexandra Novikova; Veronique Cayatte; Francoise Combes; Paola Di Matteo; Anatoly Zasov

2009-01-01

286

Spectral decomposition of the stellar kinematics in the polar disk galaxy NGC 4650A  

NASA Astrophysics Data System (ADS)

Context. The prototype of polar ring galaxies NGC 4650A contains two main structural components, a central spheroid, which is the host galaxy, and an extended polar disk. Both photometric and kinematic studies revealed that these two components co-exist on two different planes within the central regions of the galaxy. Aims: The aim of this work is to study the spectroscopic and kinematic properties of the host galaxy and the polar disk in the central regions of NGC 4650A by disentangling their contributions to the observed galaxy spectrum. Methods: We applied the spectral decomposition technique introduced in previous works to long-slit spectroscopic observations in the CaII triplet region. We focused the analysis along the PA = 152 that corresponds to the photometric minor axis of the host galaxy, where the superimposition of the two components is more relevant and the spectral decomposition is necessary. We aim to disentangle the stars that move in the equatorial plane of the host galaxy from those that move in the meridan plane, which is along the polar disk. Results: We successfully disentangled the spectra of the two structural components of NGC 4650A and measured their line-of-sight velocity and velocity dispersion profiles, and the stellar content along PA = 152. The host galaxy shows significant rotation along its photometric minor axis, indicating that the gravitational potential is not axisymmetric. The polar disk shows a kinematic decoupling: the inner regions counter-rotating with respect the outer-regions and the host spheroid. This suggests a complex formation history for the polar disk, characterised by mass accretion with decoupled angular momenta.

Coccato, L.; Iodice, E.; Arnaboldi, M.

2014-09-01

287

Behavior of Neutral Hydrogen in the NGC 877/6 Galaxy Group  

NASA Astrophysics Data System (ADS)

We observed a 5 square degree area centered on -02:17:31, 14:32:00 at 21-cm as part of the Arecibo Galaxy Environment Survey (AGES) with the NGC 877/6 galaxy group at a velocity of 4000 km/s as the primary target. Our observations covered the redshift range -5,000 < cz < 20,000 km/s allowing for a large volume in front and behind the complex to be analyzed. The NGC 877/6 group contains 8 galaxies inside a common HI envelope with a total neutral hydrogen mass of LogMHI = 10.73. HI is detected outside of the optically-identified galaxies and there are a number of tidal features within the complex. These include AGC 749170, a possible tidal remnant identified by ALFALFA and whose detection we confirm here. Another, smaller group associated with UGC 1742 (LogMHI = 9.95; cz = 6900 km/s) was identified as showing signs of galaxy interaction as well as the possibility of a tidal formation not catalogued in NED as a galaxy. Of the 44 HI sources identified in the data cube, 12 (27%) were not previously recorded in the NED database as galaxies. We will continue our analysis with data from the Mock spectrometers which will extend the redshift range to 45000 km/s.

Manning Hall, Porter; Minchin, Robert F.; Taylor, Rhys

2015-01-01

288

The Rings Survey. I. H? and H I Velocity Maps of Galaxy NGC 2280  

NASA Astrophysics Data System (ADS)

Precise measurements of gas kinematics in the disk of a spiral galaxy can be used to estimate its mass distribution. The Southern African Large Telescope has a large collecting area and field of view, and is equipped with a FabryProt (FP) interferometer that can measure gas kinematics in a galaxy from the H? line. To take advantage of this capability, we have constructed a sample of 19 nearby spiral galaxies, the RSS Imaging and Spectroscopy Nearby Galaxy Survey, as targets for detailed study of their mass distributions and have collected much of the needed data. In this paper, we present velocity maps produced from H? FP interferometry and H i aperture synthesis for one of these galaxies, NGC 2280, and show that the two velocity measurements are generally in excellent agreement. Minor differences can mostly be attributed to the different spatial distributions of the excited and neutral gas in this galaxy, but we do detect some anomalous velocities in our H? velocity map of the kind that have previously been detected in other galaxies. Models produced from our two velocity maps agree well with each other and our estimates of the systemic velocity and projection angles confirm previous measurements of these quantities for NGC 2280. Based in part on observations obtained with the Southern African Large Telescope (SALT) program 20113-RU-003.

Mitchell, Carl J.; Williams, T. B.; Spekkens, Kristine; Lee-Waddell, K.; Kuzio de Naray, Rachel; Sellwood, J. A.

2015-03-01

289

Cosmic-ray induced gamma-ray emission from the starburst galaxy NGC 253  

SciTech Connect

Cosmic rays in galaxies interact with the interstellar medium and give us a direct view of nuclear and particle interactions in the cosmos. For example, cosmic-ray proton interactions with interstellar hydrogen produce gamma rays via PcrPism??{sup 0}???. For a 'normal' star-forming galaxy like the Milky Way, most cosmic rays escape the Galaxy before such collisions, but in starburst galaxies with dense gas and huge star formation rate, most cosmic rays do suffer these interactions [1,2]. We construct a 'thick-target' model for starburst galaxies, in which cosmic rays are accelerated by supernovae, and escape is neglected. This model gives an upper limit to the gamma-ray emission. Only two free parameters are involved in the model: cosmic-ray proton acceleration energy rate from supernova and the proton injection spectral index. The pionic gamma-radiation is calculated from 10 MeV to 10 TeV for the starburst galaxy NGC 253, and compared to Fermi and HESS data. Our model fits NGC 253 well, suggesting that cosmic rays in this starburst are in the thick target limit, and that this galaxy is a gamma-ray calorimeter.

Wang, Xilu; Fields, Brian D. [Department of Astronomy, MC-221, 1002 W. Green Street, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States)

2014-05-09

290

The stellar populations in the low luminosity, early-type galaxy NGC59  

E-print Network

Low luminosity galaxies may be the building blocks of more luminous systems. Southern African Large Telescope (SALT) observations of the low luminosity, early-type galaxy NGC59 are obtained and analysed. These data are used to measure the stellar population parameters in the centre and off-centre regions of this galaxy, in order to uncover its likely star formation history. We find evidence of older stars, in addition to young stars in the emission line regions. The metallicity of the stellar population is constrained to be [Z/H] ~ -1.1 to -1.6, which is extremely low, even for this low luminosity galaxy, since it is not classed as a dwarf spheroidal galaxy. The measured [alpha/Fe] ratio is sub-solar, which indicates an extended star formation history in NGC59. If such objects formed the building blocks of more massive, early-type galaxies, then they must have been gaseous mergers, rather than dry mergers, in order to increase the metals to observed levels in luminous, early-type galaxies.

Sansom, A E; Deakin, M A; Visnen, P; Kniazev, A Y; van Loon, J Th

2015-01-01

291

Numerical simulations of interacting gas-rich barred galaxies. Vertical impact of small companions  

E-print Network

We investigate the dynamical effects of an interaction between an initially barred galaxy and a small spherical companion using an N-body/SPH algorithm. In the models described here the small companion passes through the disc of the larger galaxy near-perpendicular to its plane. The impact positions and times are varied with respect to the phase of the bar and the dynamical evolution of the disc. The interactions produce expanding ring structures, offset bars, spokes,and other asymmetries in the stars and gas. These characteristic signatures of the interaction are present in the disc for about 1 Gyr. We find that in some cases it is possible to destroy the bar while keeping the disc structure. In general the central impacts cause larger damage to the bar and the disc than the peripheral ones. The interaction tends to accelerate the transition from a strongly barred galaxy to a weakly or non-barred galaxy. The final disc morphology is determined more by the impact position relative to the bar rather than the impact time.

I. Berentzen; E. Athanassoula; C. H. Heller; K. J. Fricke

2003-01-15

292

Mon. Not. R. Astron. Soc. 348, 12551274 (2004) doi:10.1111/j.1365-2966.2004.07444.x Neutral hydrogen gas in interacting galaxies: the NGC 6221/6215  

E-print Network

hydrogen gas in interacting galaxies: the NGC 6221/6215 galaxy group B¨arbel Koribalski1 and John M. Dickey hydrogen observations of the spiral galaxies NGC 6221 and 6215 with the Australia Telescope Compact Array group (1 arcsec = 87 pc) results in a projected distance between the two main galaxies of 100 kpc. NGC

Koribalski, Bärbel

293

ATCA ? Hi Observations of the NGC 6845 Galaxy Group  

E-print Network

The Hi properties, tidal features and star formation rates in interacting galaxies are important to study because they reveal how various components of the ISM evolve under the forces of gravity. Compact groups of galaxies are particularly

Scott Gordon; Brbel Koribalski; Keith Jones

2003-01-01

294

Dynamics of early-type galaxies. III - The rotation curve of the S0 galaxy NGC 4762  

Microsoft Academic Search

The rotation curve of the flat S0 galaxy NGC 4762 is derived from measurements of the Ca II H and K absorption lines out to a distance of 1.1 arcmin (5 kpc) from the nucleus. This curve shows a moderate central gradient and a steady increase up to a value of 165 km\\/s, with no definite indication that the turnover

F. Bertola; M. Capaccioli

1978-01-01

295

Kinematics of NGC 4826: A sleeping beauty galaxy, not an evil eye  

NASA Technical Reports Server (NTRS)

A recent high resolution H I study of the Sab galaxy NGC 4826 (1992) reveals that the sense of rotation of the neutral gas reverses from the inner to the outer disk. The present paper reports on optical spectra at high velocity resolution in four position angles in NGC 4826, which cover the region of the gas reversal and which reveal a high degree of complexity. In the inner disk, which includes the prominent dusty lane, the stars and gas rotate in concert, and the spiral arms trail (for the adopted geometry). Arcs of ionized gas are observed partially encircling the nucleus; expansion velocities reach 400 km/s. At distances just beyond the prominent dust lane, the ionized gas exhibits a rapid, orderly velocity fall and within 500 parsecs it has reversed from 180 km/s prograde to 200 km/s retrograde; it also has a component radial toward the nucleus of over 100 km/s. The stars, however, continue their prograde rotation. Beyond this transition zone, the neutral gas continues its retrograde rotation, stellar velocities are prograde, but the sense of the almost circular arms is not established. Because of its kinematical complexity as well as its proximity, NGC 4826 is an excellent early-type galaxy in which to observe the long term effects of gas acquistion or a galaxy merger on a disk galaxy.

Rubin, Vera C.

1994-01-01

296

Red giants in the outer halo of the elliptical galaxy NGC 5128 / Centaurus A  

E-print Network

We used VIMOS on VLT to perform $V$ and $I$ band imaging of the outermost halo of NGC 5128 / Centaurus A ($(m-M)_0=27.91\\pm0.08$), 65 kpc from the galaxy's center and along the major axis. The stellar population has been resolved to $I_0 \\approx 27$ with a $50\\%$ completeness limit of $I_0 = 24.7$, well below the tip of the red-giant branch (TRGB), which is seen at $I_0 \\approx 23.9$. The surface density of NGC 5128 halo stars in our fields was sufficiently low that dim, unresolved background galaxies were a major contaminant in the source counts. We isolated a clean sample of red-giant-branch (RGB) stars extending to $\\approx 0.8$ mag below the TRGB through conservative magnitude and color cuts, to remove the (predominantly blue) unresolved background galaxies. We derived stellar metallicities from colors of the stars via isochrones and measured the density falloff of the halo as a function of metallicity by combining our observations with HST imaging taken of NGC 5128 halo fields closer to the galaxy center...

Bird, Sarah A; Harris, William E; Valtonen, Mauri

2014-01-01

297

The distribution of far-infrared light in the 'Dusty Hand' galaxy NGC 2146  

NASA Technical Reports Server (NTRS)

The Kuiper Airborne Observatory (KAO) has been used to obtain high spatial resolution 50 and 100 micrometers observations of the peculiar galaxy NGC 2146. We find that the far-infrared luminosity of NGC 2146 arises in a 21 arcsecs x less than or = 16 arcsecs (1.5 kpc x less than or equal 1.1 kpc) region (FWHM) elongated along the major axis. This limit is consistent with the size of the central radio continuum and (12)CO (1-0) sources. The far-infrared distribution is slightly more compact than that of the H-alpha; this difference is consistent with observed pattern of extinction in this galaxy. From a study of the energetics in this galaxy, we conclude that young massive stars are largely responsible for powering the far-infrared luminosity of NGC 2146. The far-infrared and CO (1-0) distributions differ from the reddening morphology as seen in optical images and in the Br-gamma/H-alpha ratio. The starlight and the ionized gas appear most highly reddened at the prominent dust lane 15 arcsecs to the west of the nucleus, while the CO and far-infrared emission peak near the nucleus. This result dust lane lies in front of the main body of the galaxy.

Smith, Beverly J.; Harvey, P. M.; Lester, D. F.

1995-01-01

298

Discovery of a New Faint Dwarf Galaxy Associated with NGC 253  

NASA Astrophysics Data System (ADS)

We report the discovery of a new faint dwarf galaxy, which we dub Scl-MM-Dw1, at a projected distance of ~65 kpc from the spiral galaxy NGC 253. The discovery results from the Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS), a program with the Magellan/Megacam imager to study faint substructure in resolved stellar light around massive galaxies outside of the Local Group. We measure a tip of the red giant branch distance to Scl-MM-Dw1 of D = 3.9 0.5 Mpc, consistent with that of NGC 253, making their association likely. The new dwarf's stellar population is complex, with an old, metal-poor red giant branch (gsim10 Gyr, [Fe/H] ~ -2), and an asymptotic giant branch with an age of ~500 Myr. Scl-MM-Dw1 has a half-light radius of rh = 340 50 pc and an absolute magnitude of MV = -10.3 0.6 mag, comparable to the Milky Way's satellites at the same luminosity. Once complete, our imaging survey of NGC 253 and other nearby massive galaxies will provide a census of faint substructure in halos beyond the Local Group, both to put our own environment into context and to confront models of hierarchical structure formation. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Sand, D. J.; Crnojevi?, D.; Strader, J.; Toloba, E.; Simon, J. D.; Caldwell, N.; Guhathakurta, P.; McLeod, B.; Seth, A. C.

2014-09-01

299

Radiation processes in the Seyfert galaxy NGC 4151  

NASA Astrophysics Data System (ADS)

Aims: The main aim of this work was to investigate if the radiative process photoexcitation by accidental resonance (PAR) is producing Fe II lines in the UV region of NGC 4151. At the same time I searched for collisionally excited Fe II emission. While doing so, the broad line region (BLR), intermediate line region (ILR) and narrow line region (NLR) contributions to the Mg II resonance doublet were also investigated. Methods: The focus was on the 2000 to 3000 wavelength region, in which decay from both the collisionally and PAR excited Fe II levels would form emission lines. I examined three archived Space Telescope Imaging Spectrograph (STIS) spectra of NGC 4151. Theoretical spectra based on calculated ranges for possible fluxes of the collisionally excited lines and pumping rates through the Fe II channels were then fitted to the observed spectra Results: I show that the UV region is influenced by PAR and that the Fe II fluorescence lines are clearly needed to explain the spectrum between 2000 to 3000 . The best fit of the theoretical spectra to the STIS spectra was obtained by assuming a similar radiation power of Fe+ ions and Mg+ ions. Conclusions: The PAR is active in the BLR of NGC 4151 and the total power of the Fe II fluorescence is a significant fraction of the total emission in the 2000 to 3000 wavelength region. Therefore it is important to incorporate this in models of NGC 4151 and possibly also in models of other active galactic nuclei. There are also many collisionally excited Fe II lines that are blended by each other and are therefore not individually observable in the NGC 4151 spectra.

Eriksson, M.

2012-11-01

300

The Araucaria Project. Near-Infrared Photometry of Cepheid Variables in the Sculptor Galaxy NGC 300  

E-print Network

We have obtained deep near-infrared images in J and K filters of three fields in the Sculptor galaxy NGC 300 with the ESO VLT and ISAAC camera. For 16 Cepheid variables in these fields, we have determined J and K magnitudes at two different epochs, and have derived their mean magnitudes in these bands. The slopes of the resulting period-luminosity relations are in very good agreement with the slopes of these relations measured in the LMC by Persson et al. Fitting the LMC slopes to our data, we have derived distance moduli in J and K. Using these values together with the values derived in the optical V and I bands in our previous work, we have determined an improved total reddening for NGC 300 of E(B-V)=0.096 +/- 0.006 mag, which yields extremely consistent values for the absorption-corrected distance modulus of the galaxy from VIJK bands. Our distance result for NGC 300 from this combined optical/near infrared Cepheid study is (m-M)_0 = 26.37 +/- 0.04 (random) +/- 0.03 (systematic) mag and is tied to an adopted true LMC distance modulus of 18.50 mag. Both random and systematic uncertainties are dominated by photometric errors, while errors due to reddening, metallicity effects and crowding are less important. Our distance determination is consistent with the earlier result from near-infrared (H-band) photometry of two Cepheids in NGC 300 by Madore et al., but far more accurate. Our distance value also agrees with the HST Key Project result of Freedman et al., and with the recent distance estimate for NGC 300 from Butler et al. from the TRGB I-band magnitude when our improved reddening is used to calculate the absorption corrections. Our distance results from the different optical and near-infrared bands indicate that the reddening law in NGC 300 must be very similar to the Galactic one.

W. Gieren; G. Pietrzynski; I. Soszynski; F. Bresolin; R. P. Kudritzki; D. Minniti; J. Storm

2005-03-29

301

NGC 770: A Counter-Rotating Core in a Low-Luminosity Elliptical Galaxy  

E-print Network

We present evidence for a counter-rotating core in the low-luminosity (M_B = -18.2) elliptical galaxy NGC 770 based on internal stellar kinematic data. This counter-rotating core is unusual as NGC 770 is not the primary galaxy in the region and it lies in an environment with evidence of on-going tidal interactions. We discovered the counter-rotating core via single-slit Keck/ESI echelle spectroscopy; subsequent integral field spectroscopy was obtained with the Gemini/GMOS IFU. The counter-rotating region has a peak rotation velocity of 21 km/s as compared to the main galaxy's rotation speed of greater than 45 km/s in the opposite direction. The counter-rotating region extends to a radius of 4'' (0.6 kpc), slightly smaller than the half-light radius of the galaxy which is 5.3'' (0.8 kpc) and is confined to a disk whose scale height is less than 0.8'' (0.1 kpc). We compute an age and metallicity of the inner counter-rotating region of 3 +/- 0.5 Gyr and [Fe/H] = 0.2 +/- 0.2 dex, based on Lick absorption-line indices. The lack of other large galaxies in this region limits possible scenarios for the formation of the counter-rotating core. We discuss several scenarios and favor one in which NGC 770 accreted a small gas-rich dwarf galaxy during a very minor merging event. If this scenario is correct, it represents one of the few known examples of merging between two dwarf-sized galaxies.

M. Geha; P. Guhathakurta; R. van der Marel

2005-03-16

302

Optical observations of NGC 2915: A nearby blue compact dwarf galaxy  

NASA Technical Reports Server (NTRS)

This paper presents B and R band Charge Coupled Device (CCD) images and medium resolution spectroscopy of NGC 2915, a relatively isolated BCD (blue compact dwarf) galaxy at a distance of approximately 5 Mpc. NGC 2915 contains two stellar populations: a high surface brightness blue core population and a red diffuse population. The core population contains all of the H II, and numerous embedded objects. It is the locus of current high mass star formation. The brightest embedded objects are likely to be young ionizing clusters, while many of the fainter objects are likely to be individual supergiant stars with masses up to approximately 25 solar mass, or blends of a few such stars. Curious aligned structures on the SE side of the galaxy are seen and their nature discussed. The spectrum of the core is dominated by bright narrow emission lines like that of a high excitation and low metallicity (less than half solar) H II region. The continuum is flat, with Balmer and Ca II features seen in absorption. The velocity of the Ca II features suggest contamination by galactic interstellar absorption. There is a significant velocity gradient in the spectra, probably indicative of rotation. Outside of its core, NGC 2915 resembles a dE (dwarf elliptical) galaxy, in that it has an exponential surface brightness profile, is red ((B-R)(sub 0) = 1.65), and has a low extrapolated central surface brightness (B(0)(sub c) = 22.44). NGC 2915's properties are compared with other BCDs, concentrating on two morphologically similar BCDs that are near enough to resolve into stars: NGC 1705 and NGC 5253. It is noted that the presence of winds in BCDs invalidates closed box chemical evolution models and the remaining constraints on star formation duration are relatively weak. Some BCDs, including NGC 2915, may be able to maintain their present star formation rate for Gyr time scales. This suggests that the overall evolution of these BCDs may be much slower than the approximately 10 Myr burst time scales commonly quoted. However, shortly after the formation of a massive (10(exp 6) solar mass) cluster a BCD will have all the properties of strong starburst galaxy).

Meurer, G. R.; Mackie, G.; Carignan, C.

1994-01-01

303

The Araucaria Project: Near-Infrared Photometry of Cepheid Variables in the Sculptor Galaxy NGC 300  

NASA Astrophysics Data System (ADS)

We have obtained deep near-infrared images in J and K filters of three fields in the Sculptor galaxy NGC 300 with the ESO VLT and ISAAC Camera. For 16 Cepheid variables in these fields, we have determined J and K magnitudes at two different epochs and have derived their mean magnitudes in these bands. The slopes of the resulting period-luminosity relations are in very good agreement with the slopes of these relations measured in the Large Magellanic Cloud (LMC) by Persson et al. Fitting the LMC slopes to our data, we have derived distance moduli in J and K. Using these values together with the values derived in the optical V and I bands in our previous work, we have determined an improved total reddening for NGC 300 of E(B-V)=0.096+/-0.006 mag, which yields extremely consistent values for the absorption-corrected distance modulus of the galaxy from VIJK bands. Our distance result for NGC 300 from this combined optical/near-infrared Cepheid study is (m-M)0=26.37+/-0.05 (random) +/- 0.03 (systematic) mag and is tied to an adopted true LMC distance modulus of 18.50 mag. Both random and systematic uncertainties are dominated by photometric errors, while errors due to reddening, metallicity effects, and crowding are less important. Our distance determination is consistent with the earlier result from near-infrared (H-band) photometry of two Cepheids in NGC 300 by Madore et al., but far more accurate. Our distance value also agrees with the HST Key Project result of Freedman et al. and with the recent distance estimate for NGC 300 from Butler et al. from the tip of the red giant branch (TRGB) I-band magnitude when our improved reddening is used to calculate the absorption corrections. Our distance results from the different optical and near-infrared bands indicate that the reddening law in NGC 300 must be very similar to the Galactic one. With the results of this work, the distance of NGC 300 relative to the LMC now seems determined with an accuracy of approximately +/-3%. The distance to this nearby Sculptor galaxy is therefore now known with higher accuracy than that of most (nearer) Local Group galaxies. Based on observations obtained with the ESO VLT for Large Programme 171.D-0004.

Gieren, Wolfgang; Pietrzy?ski, Grzegorz; Soszy?ski, Igor; Bresolin, Fabio; Kudritzki, Rolf-Peter; Minniti, Dante; Storm, Jesper

2005-08-01

304

Star Formation Rates in Resolved Galaxies: Calibrations with Near- and Far-infrared Data for NGC 5055 and NGC 6946  

NASA Astrophysics Data System (ADS)

We use the near-infrared Br? hydrogen recombination line as a reference star formation rate (SFR) indicator to test the validity and establish the calibration of the Herschel/PACS 70 ?m emission as a SFR tracer for sub-galactic regions in external galaxies. Br? offers the double advantage of directly tracing ionizing photons and of being relatively insensitive to the effects of dust attenuation. For our first experiment, we use archival Canada-France-Hawaii Telescope Br? and Ks images of two nearby galaxies: NGC 5055 and NGC 6946, which are also part of the Herschel program KINGFISH (Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel). We use the extinction corrected Br? emission to derive the SFR(70) calibration for H II regions in these two galaxies. A comparison of the SFR(70) calibrations at different spatial scales, from 200 pc to the size of the whole galaxy, reveals that about 50% of the total 70 ?m emission is due to dust heated by stellar populations that are unrelated to the current star formation. We use a simple model to qualitatively relate the increase of the SFR(70) calibration coefficient with decreasing region size to the star formation timescale. We provide a calibration for an unbiased SFR indicator that combines the observed H? with the 70 ?m emission, also for use in H II regions. We briefly analyze the PACS 100 and 160 ?m maps and find that longer wavelengths are not as good SFR indicators as 70 ?m, in agreement with previous results. We find that the calibrations show about 50% difference between the two galaxies, possibly due to effects of inclination. Based on observations obtained with WIRCam, a joint project of CFHT, Taiwan, Korea, Canada, France, and the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institute National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

Li, Yiming; Crocker, Alison F.; Calzetti, Daniela; Wilson, Christine D.; Kennicutt, Robert C.; Murphy, Eric J.; Brandl, Bernhard R.; Draine, B. T.; Galametz, M.; Johnson, B. D.; Armus, L.; Gordon, K. D.; Croxall, K.; Dale, D. A.; Engelbracht, C. W.; Groves, B.; Hao, C.-N.; Helou, G.; Hinz, J.; Hunt, L. K.; Krause, O.; Roussel, H.; Sauvage, M.; Smith, J. D. T.

2013-05-01

305

Distribution and motions of atomic hydrogen in lenticular galaxies. X - The blue S0 galaxy NGC 5102  

NASA Technical Reports Server (NTRS)

Results of the mapping of the blue gas-rich S0 galaxy NGC 5102 in the 21-cm H I line with a spatial resolution of 34 x 37 arcsec (delta(alpha) x Delta(delta)) and a velocity resolution of 12 km/s are presented. The H I distribution has a pronounced central depression of 1.9 kpc radius, and most of the H I is concentrated in a 3.6 kpc wide ring with an average radius of 3.7 kpc, assuming a distance of 4 Mpc for NGC 5102. The maximum azimuthally averaged H I surface density in the ring is 1.4 solar mass/sq pc, comparable to that found in other S0 galaxies. The HI velocity field is quite regular, showing no evidence for large-scale deviations from circular rotation, and the H I is found to rotate in the plane of the stellar disk. Both the H I mass/blue luminosity ratio and the radial H I distribution are similar to those in early-type spirals. The H I may be an old disk or it may have been acquired through capture of a gas-rich smaller galaxy. The recent starburst in the nuclear region, which gave the galaxy its blue color, may have been caused by partial radial collapse of the gas disk, or by infall of a gas-rich dwarf galaxy.

Van Woerden, H.; Van Driel, W.; Braun, R.; Rots, A. H.

1993-01-01

306

The Interaction between the ISM and Star Formation in the Dwarf Starburst Galaxy NGC 4214  

E-print Network

We present the first interferometric study of the molecular gas in the metal-poor dwarf starburst galaxy NGC 4214. Our map of the 12CO(1-0) emission, obtained at the OVRO millimeter array, reveals an unexpected structural wealth. We detected three regions of molecular emission in the north-west (NW), south-east (SE) and centre of NGC 4214 which are in very different and distinct evolutionary stages (total molecular mass: 5.1 x 10^6 M_sun). These differences are apparent most dramatically when the CO morphologies are compared to optical ground based and HST imaging: massive star formation has not started yet in the NW region; the well-known starburst in the centre is the most evolved and star formation in the SE complex started more recently. We derive a star formation efficiency of 8% for the SE complex. Using high--resolution VLA observations of neutral hydrogen HI and our CO data we generated a total gas column density map for NGC 4214 (HI + H_2). No clear correlation is seen between the peaks of HI, CO and the sites of ongoing star formation. This emphasizes the irregular nature of dwarf galaxies. The HI and CO velocities agree well, so do the H-alpha velocities. In total, we cataloged 14 molecular clumps in NGC 4214. Our results from a virial mass analysis are compatible with a Galactic CO-to-H_2 conversion factor for NGC 4214 (lower than what is usually found in metal-poor dwarf galaxies).

F. Walter; C. Taylor; S. Huettemeister; N. Scoville; V. McIntyre

2000-11-04

307

Nuclear Gas Dynamics of NGC2110: A Black Hole Offset from the Host Galaxy Mass Center?  

NASA Technical Reports Server (NTRS)

It has been suggested that the central regions of many galaxies are unlikely to be in a static steady state, with instabilities caused by sinking satellites, the influence of a supermassive black hole or residuals of galaxy formation, resulting in the nuclear black hole orbiting the galaxy center. The observational signature of such an orbiting black hole is an offset of the active nucleus (AGN) from the kinematic center defined by the galaxy rotation curve. This orbital motion may provide fuel for the AGN, as the hole 'grazes' on the ISM, and bent radio jets, due to the motion of their source. The early type (E/SO) Seyfert galaxy, NGC2210, with its striking twin, 'S'-shaped radio jets, is a unique and valuable test case for the offset-nucleus phenomenon since, despite its remarkably normal rotation curve, its kinematically-measured mass center is displaced both spatially (260 pc) and kinematically (170 km/s) from the active nucleus located in optical and radio studies. However, the central kinematics, where the rotation curve rises most steeply, have been inaccessible with ground-based resolutions. We present new, high resolution WFPC2 imaging and long-slit STIS spectroscopy of the central 300 pc of NGC2110. We discuss the structure and kinematics of gas moving in the galactic potential on subarcsecond scales and the reality of the offset between the black hole and the galaxy mass center.

Mundell, C. G.; Ferruit, P.; Nagar, N.; Wilson, A. S.

2004-01-01

308

The X-ray Emission from the Nucleus of the Dwarf Elliptical Galaxy NGC 3226  

E-print Network

We present the first high resolution X-ray image of the dwarf elliptical galaxy NGC 3226. The data were obtained during an observation of the nearby Seyfert Galaxy NGC 3227 using the Chandra X-ray Observatory. We detect a point X-ray source spatially consistent with the optical nucleus of NGC 3226 and a recently-detected, compact, flat-spectrum, radio source. The X-ray spectrum can be measured up to ~10 keV and is consistent with a power law with a photon index 1.7 band ~10^{40} h_{75}^{-1} erg/s. We find marginal evidence that the nucleus varies within the observation. These characteristics support evidence from other wavebands that NGC 3226 harbors a low-luminosity, active nucleus. We also comment on two previously-unknown, fainter X-ray sources x 10^{38} -- few x 10^{39} erg/s) consistent with black-hole binary systems.

I. M. George; R. F. Mushotzky; T. Yaqoob; T. J. Turner; S. Kraemer; A. F. Ptak; K. Nandra; D. M. Crenshaw; H. Netzer

2001-05-04

309

The Araucaria Project. Near-Infrared Photometry of Cepheid Variables in the Sculptor Galaxy NGC 55  

E-print Network

We have obtained deep images in the near-infrared J and K filters of four fields in the Sculptor Group spiral galaxy NGC 55 with the ESO VLT and ISAAC camera. For 40 long-period Cepheid variables in these fields which were recently discovered by Pietrzy{\\'n}ski et al., we have determined mean J and K magnitudes from observations at two epochs, and derived distance moduli from the observed PL relations in these bands. Using these values together with the previously measured distance moduli in the optical V and I bands, we have determined a total mean reddening of the NGC 55 Cepheids of E(B-V)=0.127 $\\pm$ 0.019 mag, which is mostly produced inside NGC 55 itself. For the true distance modulus of the galaxy, our multiwavelength analysis yields a value of 26.434 $\\pm$ 0.037 mag (random error), corresponding to a distance of 1.94 $\\pm$ 0.03 Mpc. This value is tied to an adopted true LMC distance modulus of 18.50 mag. The systematic uncertainty of our derived Cepheid distance to NGC 55 (apart from the uncertainty on...

Gieren, W; Soszynski, I; Bresolin, F; Kudritzki, R P; Storm, J; Minniti, D

2007-01-01

310

The Mass of the Central Black Hole in the Nearby Seyfert Galaxy NGC 5273  

NASA Astrophysics Data System (ADS)

We present the results of a reverberation-mapping program targeting NGC 5273, a nearby early-type galaxy with a broad-lined active galactic nucleus (AGN). Over the course of the monitoring program, NGC 5273 showed strong variability that allowed us to measure time delays in the responses of the broad optical recombination lines to changes in the continuum flux. A weighted average of these measurements results in a black hole mass determination of M BH = (4.7 1.6) 106 M ?. An estimate of the size of the black hole sphere of influence in NGC 5273 puts it just at the limit of the resolution achievable with current ground-based large aperture telescopes. NGC 5273 is therefore an important future target for a black hole mass determination from stellar dynamical modeling, especially because it is the only nearby early-type galaxy hosting an AGN with a reverberation-based mass, allowing the best comparison for the masses determined from these two techniques.

Bentz, Misty C.; Horenstein, Daniel; Bazhaw, Craig; Manne-Nicholas, Emily R.; Ou-Yang, Benjamin J.; Anderson, Matthew; Jones, Jeremy; Norris, Ryan P.; Parks, J. Robert; Saylor, Dicy; Teems, Katherine G.; Turner, Clay

2014-11-01

311

Jet-cloud collisions in the jet of the Seyfert galaxy NGC3079  

E-print Network

We report the results from a six-year, multi-epoch very long baseline interferomertry monitoring of the Seyfert galaxy NGC3079. We have observed NGC3079 during eight epochs between 1999 and 2005 predominantly at 5GHz, but covering the frequency range of 1.7GHz to 22GHz. Using our data and observations going back to 1985, we find that the separation of two of the three visible nuclear radio components underwent two decelerations. At the time of these decelerations, the flux density of one of the components increased by factors of five and two, respectively. We interpret these events as a radio jet component undergoing compression, possibly as a result of a collision with ISM material. This interpretation strongly supports the existence of jets surrounded by a clumpy medium of dense clouds within the first few parsecs from the central engine in NGC3079. Moreover, based on recently published simulations of jet interactions with clumpy media, this scenario is able to explain the nature of two additional regions of ageing synchrotron material detected at the lower frequencies as by-products of such interactions, and also the origin of the kpc-scale super bubble observed in NGC3079 as the result of the spread of the momentum of the jets impeded from propagating freely. The generalization of this scenario provides an explanation why jets in Seyfert galaxies are not able to propagate to scales of kpc as do jets in radio-loud AGN.

Enno Middelberg; Ivan Agudo; Alan L. Roy; Thomas P. Krichbaum

2007-02-19

312

Dissipation in barred galaxies - The growth of bulges and central mass concentrations  

NASA Astrophysics Data System (ADS)

Basic dynamical mechanisms that produce an amplification of the accretion rate of gas clouds into the central regions of barred galaxies, and their subsequent effects on the evolution of barred galaxies, are discussed. Weakly dissipative orbits, representing gas clouds, are computed in a barred galaxy model with a central mass concentration such as a black hole, or a secondary small inner bar. Amplified accretion across resonances that is especially rapid inside the inner Lindblad resonance, large excursions outside the galactic plane, and the existence of nontrivial attractors like strange (chaotic) attractors or limit cycles are found. The underlying physical mechanisms are, in general, due to the presence of broad horizontal and vertical resonances through which weakly dissipative particles can rapidly traverse. The principal physical implications of these findings are discussed.

Pfenniger, Daniel; Norman, Colin

1990-11-01

313

The Araucaria Project. The Distance to the Sculptor Group Galaxy NGC 55 from a Newly Discovered Abundant Cepheid Population  

E-print Network

We have detected, for the first time, Cepheid variables in the Sculptor Group SB(s)m galaxy NGC 55. From wide-field images obtained in the optical V and I bands during 77 nights in 2002-2003, we have found 143 Cepheids with periods ranging from 5.6 to 175.9 days. 133 of these objects have periods longer than 10 days, making NGC 55 to-date the galaxy with the largest known number of long-period Cepheids in the Sculptor Group. We construct period-luminosity relations from our data and obtain distance moduli corrected for the small foreground reddening to NGC 55 of 26.79 $\\pm$ 0.04 mag (internal error) in V, 26.66 $\\pm$ 0.03 mag in I and 26.40 $\\pm$ 0.05 mag in the reddening-independent V-I Wesenheit index. The trend of increasing distance moduli with shorter wavelength hints at the existence of significant reddening intrinsic to NGC 55 which affects the measured Cepheid magnitudes. From our data, we determine the intrinsic mean reddening of the Cepheids in NGC 55 as E(B-V) = 0.102 mag which brings the distance determinations from the different bands into excellent agreement. Our best distance estimate for NGC 55 from the present optical Cepheid photometry is 26.40 mag $\\pm$ 0.05 mag (internal error) $\\pm$ 0.09 mag (systematic error). This value is tied to an assumed LMC distance of 18.50 mag. Our quoted systematic error of the present NGC 55 Cepheid distance does not take into account the current uncertainty on the distance of the fiducial LMC galaxy itself. Within the small respective uncertainties, the Sculptor Group galaxies NGC 55 and NGC 300 are at the same distance of 1.9 Mpc, strengthening the case for a physical association of these galaxies

G. Pietrzynski; W. Gieren; I. Soszynski; A. Udalski; F. Bresolin; R. -P. Kudritzki; R. Mennickent; A. Walker; A. Garcia; O. Szewczyk; M. Szymanski; M. Kubiak; L. Wyrzykowski

2006-10-19

314

The Araucaria Project: The Distance to the Sculptor Group Galaxy NGC 55 from a Newly Discovered Abundant Cepheid Population  

NASA Astrophysics Data System (ADS)

We have detected, for the first time, Cepheid variables in the Sculptor Group SB(s)m galaxy NGC 55. From wide-field images obtained in the optical V and I bands during 77 nights in 2002-2003, we have found 143 Cepheids with periods ranging from 5.6 to 175.9 days; 133 of these objects have periods longer than 10 days, making NGC 55 to date the galaxy with the largest known number of long-period Cepheids in the Sculptor Group. We construct period-luminosity relations from our data and obtain distance moduli corrected for the small foreground reddening to NGC 55 of 26.79+/-0.04 mag (internal error) in V, 26.66+/-0.03 mag in I, and 26.40+/-0.05 mag in the reddening-independent V-I Wesenheit index. The trend of increasing distance moduli with shorter wavelength hints at the existence of significant reddening intrinsic to NGC 55, which affects the measured Cepheid magnitudes. From our data we determine the intrinsic mean reddening of the Cepheids in NGC 55 as E(B-V)=0.102 mag, which brings the distance determinations from the different bands into excellent agreement. Our best distance estimate for NGC 55 from the present optical Cepheid photometry is 26.40+/-0.05 (internal error) +/-0.09 mag (systematic error). This value is tied to an assumed LMC distance of 18.50 mag. Our quoted systematic error of the present NGC 55 Cepheid distance does not take into account the current uncertainty in the distance of the fiducial LMC galaxy itself. Within the small respective uncertainties, the Sculptor Group galaxies NGC 55 and NGC 300 are at the same distance of 1.9 Mpc, strengthening the case for a physical association of these galaxies. Based on observations obtained with the 1.3 m Warsaw telescope at Las Campanas Observatory, Chile.

Pietrzy?ski, Grzegorz; Gieren, Wolfgang; Soszy?ski, Igor; Udalski, Andrzej; Bresolin, Fabio; Kudritzki, Rolf-Peter; Mennickent, Ronald; Walker, Alistair; Garcia, Alejandro; Szewczyk, Olaf; Szyma?ski, Micha?; Kubiak, Marcin; Wyrzykowski, ?ukasz

2006-12-01

315

Bar properties as seen in the Spitzer Survey of Stellar Structure in Galaxies  

NASA Astrophysics Data System (ADS)

Bars serve a crucial signpost in galaxy evolution because they form quickly once a disk is sufficiently massive and dynamically cold. Although the bar fraction in the local Universe is well-established since the mid-60s, a variety of studies have concluded varying bar fractions due to different definitions of bars, use of low quality data or different sample selection. The Spitzer Survey of Stellar Structure in Galaxies (S4G) offers us the ideal data set for resolving this outstanding issue once and for all. S4G consists of over 2000 nearby galaxies chosen based on optical brightness, distance, galactic latitude and size in a 40 Mpc volume. With a 4 minute integration time per pixel over >1.5 D25 diameter for each galaxy, the data provide the deepest, homogenous, mid-infrared (3.6 and 4.5 microns) data on the nearby Universe. The data are so deep that we are tracing stellar surface densities << 1 solar mass per square parsec. With these data we can confidently constrain the bar fraction and thus shed important light on the evolutionary state of galaxies as a function of mass, environment and other galaxy host properties.

Sheth, Kartik

2015-03-01

316

Rapid X-ray variability from the Seyfert 1 galaxy NGC 4051  

NASA Astrophysics Data System (ADS)

Strong variable X-ray emission from the nearby low luminosity Seyfert 1 galaxy NGC 4051 was discovered during observations with the imaging proportional counter of the Einstein Observatory. During one 2304 second observation, the X-ray flux more than doubled in an approximately linear fashion, and a 70 percent increase for 150 seconds was seen during another 968 second observation. Evidence is presented which demonstrates that the X-ray spectrum of NGC 4051 is unusually soft compared to Seyfert 1 galaxies or QSOs. The emission mechanism is probably not synchrotron or synchrotron self-Compton, but the emission can be plausibly explained by various black hole accretion models. Previously announced in STAR as N83-23265

Marshall, F. E.; Holt, S. S.; Mushotzky, R. F.; Becker, R. H.

1983-06-01

317

NGC 1614 - An IR-luminous merger but not (yet?) an active galaxy  

NASA Technical Reports Server (NTRS)

New observations of the merging galaxy NGC 1614 are described. The system has a nuclear region of QSO-like luminosity, but shows no direct evidence for an active nucleus. It is heavily and unevenly reddened across its nucleus, while infrared imaging also shows a 'ridge' of dust. The inner spiral structure of the galaxy has normal rotation for an inclined disk, as indicated by the H-alpha emission. A linear 'tail' to the S and extended arms to the E have more positive velocities, and probably are the remains of an interacting companion and the tidal plume(s) caused by the collision. The only H I seen in emission appears to coincide with bright knots of H-alpha and forbidden O III emission of the base of the tail. The lack of direct evidence for an active nucleus indicates that if NGC 1614 is a precursor to a Seyfert-like system the AGN has not yet turned on.

Neff, S. G.; Hutchings, J. B.; Standord, S. A.; Unger, S. W.

1990-01-01

318

SPECTRAL: A new evolutionary synthesis code. Application to the irregular Galaxy NGC 1560  

NASA Astrophysics Data System (ADS)

We have developed a new evolutionary synthesis code, which incorporates the output from chemical evolution models. We compare results of this new code with other published codes, and we apply it to the irregular galaxy NGC 1560 using sophisticated chemical evolution models. The code makes important contributions in two areas: a) the generation of synthetic populations with time-dependent star formation rates and stellar populations of different metallicities; b) the extension of the set of stellar tracks from the Geneva group by adding the AGB phases for mi/Msun >= 0.8, as well as the low mass stars. Our code predicts spectra, broad band colors, and Lick indices by using a spectral library, covering a more complete grid of stellar parameters than previous models. The application of the code to the galaxy NGC 1560 constrains the star formation age of its stellar population at around 10.0 Gyr.

Vzquez, G. A.; Carigi, L.; Gonzlez, J. J.

2003-03-01

319

NGC 3147: a `true' type 2 Seyfert galaxy without the broad-line region  

NASA Astrophysics Data System (ADS)

We report on simultaneous optical and X-ray observations of the Seyfert galaxy, NGC 3147. The XMM-Newton spectrum shows that the source is unabsorbed in the X-rays (NH < 5 1020 cm-2). On the other hand, no broad lines are present in the optical spectrum. The origin of this optical/X-rays misclassification (with respect to the Unification Model) cannot be attributed to variability, since the observations in the two bands are simultaneous. Moreover, a Compton-thick nature of the object can be rejected on the basis of the low-equivalent width of the iron K? line (~=130 eV) and the large ratio between the 2-10 keV and the [OIII] fluxes. It seems therefore inescapable to conclude that NGC 3147 intrinsically lacks the Broad-Line Region, making it the first `true' type 2 Seyfert galaxy.

Bianchi, S.; Corral, A.; Panessa, F.; Barcons, X.; Matt, G.; Bassani, L.; Carrera, F. J.; Jimnez-Bailn, E.

2008-03-01

320

Detection of the H92alpha recombination line from the starbursts in the Circinus galaxy and NGC 1808  

E-print Network

Context. Gas ionized by starburst activity radiates radio recombination lines (RRLs), from which one can derive the plasma conditions and the number of massive stars formed in the burst, free of dust obscuration effects. Aims. We aimed to find RRL emission from additional starburst systems and to use the line properties to estimate the properties of the ionized gas. Methods. We conducted a search for RRLs in the nearby extragalactic starburst or Seyfert galaxies NGC 1808, the Circinus galaxy, NGC 4038/9, II Zw 40, NGC 6221, NGC 7552, IRAS 18325-5926, IC 5063, and VV 114. We used the VLA and the ATCA to search for the RRLs H91alpha and H92alpha with rest frequencies of 8.6 GHz and 8.3 GHz. Results. We detected for the first time RRLs from the starburst nuclei in the Circinus galaxy and NGC 1808. The Circinus galaxy was detected with a line strength integrated over the source of 3.2 mJy, making it the fourth-strongest extragalactic RRL emitter known at this frequency (after NGC 4945, M 82, and NGC 253). The line and continuum emission can be matched by a model consisting of a collection of 50 to 10 000 H II regions with 300 to 9000 O5 stars required to maintain the ionization, inferring a star formation rate of 0.2 Msun/yr to 6 Msun/yr. NGC 1808 was detected in RRL emission at 3.9 sigma with a line strength of 0.47 mJy at the expected velocity. Conclusion. We have detected RRLs from two galaxies, adding to the small but growing number of known extragalactic RRL emitters. The Circinus galaxy is strong and especially suited to high-quality follow-up spectroscopic study. We derived conditions and star formation rates in the starbursting regions. Uncertainties can be reduced by future multi-transition studies.

A. L. Roy; W. M. Goss; K. R. Anantharamaiah

2008-02-21

321

Multi-phase Absorption in Lenticular Galaxies: On the Outskirts of NGC 4203  

Microsoft Academic Search

We present UV and optical spectroscopy of the quasar Ton 1480, which is projected behind the outer HI ring of the lenticular galaxy NGC 4203. The spectra from HST, FUSE, and the VLT\\/UVES show absorption from a variety of low- and high-ionization species, including HI, NI, OI, NaI, CII, MgII, SiII, CaII, FeII, SiIII, CIV (marginal), and OVI. This absorber

E. D. Miller; S. L. Ellison; M. T. Murphy; J. N. Bregman

2004-01-01

322

The dynamics and structure of the S0 galaxy NGC 7332  

NASA Technical Reports Server (NTRS)

Spectroscopic and photometric observations of the edge-on S0 galaxy NGC 7332 are presented. The spectra show the galaxy to possess a rapidly counter-rotating extended gas disk as detected from both (O III) 5007 A and H alpha emission. Multiple slit orientations at a variety of position angles clearly show the decoupling of the angular momenta between the stellar and gaseous components. The gas is distributed asymmetrically and displays noncircular motions indicating that it has not reached equilibrium. These observations are strong evidence in support of an accretion process having occurred in NGC 7332. Broad R and B band CCD images show the boxy isophotes that NGC 7332 has long been known to possess while offset spectra taken parallel to the major and minor axes display the cylindrical rotation common to galaxies with box-shaped bulges. The bulge of NGC 7332 is well described by an r(exp 1/4)-law on both the major and minor axes while the outer disk is exponential. The B-R color of the disk is uniform; the only indication of a trend to blue colors is a Delta(B-R(sub c))/Delta log r= -0.04 +/- 0.01 gradient seen perpendicular to the bulge and disk. There exists a 10 sec long region of nearly constant surface brightness along the major axis between the bulge and disk components. Not likely due to absorbing material, the relation of this feature to the already complicated structure of the galaxy is considered.

Fisher, David; Illingworth, Garth; Franx, Marijn

1994-01-01

323

Measuring the Black Hole Mass in the Brightest Cluster Galaxy NGC 1275  

NASA Astrophysics Data System (ADS)

NGC 1275 is the brightest and most massive galaxy in the Perseus Cluster, and is an excellent laboratory in which to examine the processes of black hole fueling and feedback in a cluster core environment. Our goal is to carry out a direct measurement of the black hole mass in NGC 1275 using ionized gas dynamics, by resolving the H-alpha and [N II] kinematics within the black hole's dynamical sphere of influence. We request five orbits to carry out STIS G750M spectroscopy at five parallel positions of the 0.1 arcsec-wide slit, in order to map the ionized gas kinematics and measure the central mass using the same methods successfully used for other giant ellipticals such as M84 and M87. We will compare the ionized gas kinematics with our observations of the H_2 molecular kinematics recently measured at 0.02-arcsecond sampling with Keck adaptive optics data in order to better understand the interplay between the different components of the ISM in this complex environment. We also request one orbit for WFC3/IR imaging of NGC 1275 in order to measure its near-IR surface brightness profile with unprecedented depth and resolution and model the galaxy's stellar mass profile. The results of this work will provide the first accurate measurement of the black hole mass in this highly unusual brightest cluster galaxy. Together with new and planned Keck AO observations, these HST observations will provide a critical new test of black hole mass measurement techniques by direct comparison of ionized gas dynamics, molecular gas dynamics, and stellar dynamics, and NGC 1275 is a nearly unique example of a galaxy in which all three methods are feasible.

Barth, Aaron

2014-10-01

324

The extended Halpha-emitting filaments surrounding NGC 4696, the central galaxy of the Centaurus cluster  

Microsoft Academic Search

We present images of NGC 4696, the central galaxy in the Centaurus cluster, showing the large extent of cool filaments which are bright in H ? line emission. These filaments share the detailed structure of both the central dust lane and the inne r regions of the arc-like plumes seen in soft X-ray emission. The X-ray gas is at its

C. S. Crawford; N. A. Hatch; A. C. Fabian; J. S. Sanders

2005-01-01

325

The extended Halpha-emitting filaments surrounding NGC 4696, the central galaxy of the Centaurus cluster  

Microsoft Academic Search

We present images of NGC 4696, the central galaxy in the Centaurus cluster, showing the large extent of cool filaments that are bright in Halpha line emission. These filaments share the detailed structure of both the central dust lane and the inner regions of the arc-like plumes seen in soft X-ray emission. The X-ray gas is at its coolest and

C. S. Crawford; N. A. Hatch; A. C. Fabian; J. S. Sanders

2005-01-01

326

X-Ray Variability Characteristics of the Seyfert 1 Galaxy NGC 3783  

Microsoft Academic Search

We have characterized the energy-dependent X-ray variability properties of the Seyfert 1 galaxy NGC 3783 using archival XMM-Newton and Rossi X-Ray Timing Explorer data. The high-frequency fluctuation power spectral density function (PSD) slope is consistent with flattening toward higher energies. Light-curve cross-correlation functions yield no significant lags, but peak coefficients generally decrease as energy separation of the bands increases on

A. Markowitz

2005-01-01

327

The ROSAT PSPC spectrum of the Seyfert 2 galaxy NGC 4388.  

NASA Astrophysics Data System (ADS)

The ROSAT PSPC spectrum of the Seyfert 2 galaxy NGC 4388 is analyzed, with the aim to better understand the nature of the extended (a few kpc) soft X-ray emission discovered by the ROSAT HRI. Fitting the spectrum with an optically thin thermal model we find evidence for a metal abundance significantly lower than solar. We therefore argue that the emission is due at least in part to another component, maybe unresolved emission from compact sources.

Antonelli, L. A.; Matt, G.; Piro, L.

1997-02-01

328

Sulfur chemistry and isotopic ratios in the starburst galaxy NGC 253  

Microsoft Academic Search

Based on observations of the most abundant sulfur-bearing molecules (H2S, CS, NS, SO, H2CS, OCS, and SO2) carried out with the IRAM 30m telescope 1 and SEST 2, we present the first analysis of the sulfur chemistry of an extragalac- tic source, the nuclear region of the starburst galaxy NGC253. This is the first time that H2S and, tentatively, H2CS

S. Mart n; J. Mart n-Pintado; R. Mauersberger; C. Henkel

329

Evidence for a triaxial bulge in the spiral galaxy NGC 4845  

SciTech Connect

Spectroscopic observations for the Sa galaxy NGC 4845 in five position angles reveal a regular but nonaxisymmetric velocity field for the gas at r of 1.5 kpc or less. Photometry indicates a possible slight twisting between the disk and bulge isophotes. These phenomena are interpreted as a manifestation of a triaxial bulge, and estimates of the ranges of b/a and c/a are obtained. 20 refs.

Bertola, F.; Zeilinger, W.W.; Rubin, V.C. (Padova Universita, Padua (Italy) Carnegie Institution of Washington, Washington, DC (USA))

1989-10-01

330

Diffuse Gamma-Ray Emission from the Starburst Galaxy NGC 253  

NASA Technical Reports Server (NTRS)

The starburst galaxy NGC 253 was observed with the Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory (CGRO) satellite. We obtain a 2 sigma upper limit to the gamma-ray emission above 100 MeV of 8 x 10(exp -8) photons/sq cm/s. Because of their large gas column densities and supernova rates, nearby starburst galaxies were predicted to have gamma-ray fluxes detectable by EGRET. Our nondetection of gamma-rays from NGC 253 motivates us to reexamine in detail the premise of supernova acceleration of cosmic rays and the effect of enhanced cloud densities, photon densities, and magnetic fields on the high-energy spectra of galaxies. By modeling the expected gamma-ray and synchrotron spectra from NGC 253, we find that up to 20% of the energy from supernovae is transferred to cosmic rays in the starburst, which is consistent with supernova acceleration models. Our calculations match the EGRET and radio data well with a supernova rate of 0.08/yr, a magnetic field B greater than or approximately equal to 5 x 10(exp -5) G, a density n approximately 300/cu cm, a photon density U(sub ph) approximately 200 eV/cu cm, and an escape timescale tau(sub o) less than or approximately equal to 10 Myr.

Bertsch, David L.; Paglione, Timothy A. D.; Marscher, Alan P.; Jackson, James M.

1995-01-01

331

Quantifying the role of bars in the build-up of central mass concentrations in disc galaxies  

NASA Astrophysics Data System (ADS)

We analyse the role of bars in the build-up of central mass concentrations in massive, disc galaxies. Our parent sample consists of 3757 face-on disc galaxies with redshifts between 0.01 and 0.05, selected from the seventh Data Release of the Sloan Digital Sky Survey. 1555 galaxies with bars are identified using the position angle and ellipticity profiles of the i-band light. We compare the ratio of the specific star formation rate measured in the 1-3 kpc central region of the galaxy to that measured for the whole galaxy. Galaxies with strong bars have centrally enhanced star formation; the degree of enhancement depends primarily on the ellipticity of the bar and not on the size of the bar or on the mass or structure of the host galaxy. The fraction of galaxies with strong bars is highest at stellar masses greater than 3 1010 M?, stellar surface densities less than 3 108 M? and concentration indices less than 2.5. In this region of parameter space, galaxies with strong bars either have enhanced central star formation rates, or star formation that is suppressed compared to the mean. This suggests that bars may play a role in the eventual quenching of star formation in galaxies. Only 50 per cent of galaxies with strongly concentrated star formation have strong bars, indicating that other processes such as galaxy interactions also induce central starbursts. We also find that the ratio of the size of the bar to that of the disc depends mainly on the colour of the galaxy, suggesting that the growth and destruction of bars are regulated by gas accretion, as suggested by simulations.

Wang, Jing; Kauffmann, Guinevere; Overzier, Roderik; Tacconi, Linda J.; Kong, Xu; Saintonge, Amelie; Catinella, Barbara; Schiminovich, David; Moran, Sean M.; Johnson, Benjamin

2012-07-01

332

Using Bars in S4G and COSMOS to Identify the Fastest Evolving Galaxy Disks at All Epochs  

NASA Astrophysics Data System (ADS)

The steeply declining bar fraction from 65% in the local Universe to <20% 7 Gyr ago allowed us to constrain the detailed mass assembly of disk galaxies from the COSMOS survey. We showed that the most massive galaxies formed their bars first and by z1, >50% of massive disks already had bars. The low mass galaxies evolved to acquire their bars only very recently. Now using the Spitzer Survey of Stellar Structure in Galaxies (S4G) we show that this mass-dependent trend is extremely clear in the 2300+ galaxy sample. Galaxies with masses log M > 9.5 have bar fractions of 65% whereas galaxies masses log M < 9 have almost no bars -- in direct contrast to other studies that have claimed an increase in bars at the low mass end. We show that elongations due to poor quality imaging and blurring of nearby star forming regions likely lead to a mis-classification of bars in late type, low mass galaxies. At log M 9.2 there is a increase in the bar fraction indicating that the bar formation is occurring at the fastest rate in these systems - that is now the epoch of mature disk building.

Sheth, Kartik; S4G Team

2014-01-01

333

ISOCAM Mid-Infrared Imaging of the Quiescent Spiral Galaxy NGC 7331  

E-print Network

Using the mid-infrared camera (ISOCAM) on the Infrared Space Observatory (ISO), the Sb LINER galaxy NGC 7331 has been imaged in two broadband and four narrowband filters between 6.75 and 15 microns. These maps show a prominent circumnuclear ring of radius 0.25 arcminutes X 0.75 arcminutes (1.1 X 3.3 kpc) encircling an extended central source. The 7.7 and 11.3 micron dust emission features are strong in this galaxy, contributing approximately 1/3 of the total IRAS 12 micron broadband flux from this galaxy. In contrast to starburst galaxies, the 15 micron continuum is weak in NGC 7331. The mid-infrared spectrum does not vary dramatically with position in this quiescent galaxy, showing neither large-scale destruction of the carriers of the emission bands or a large increase in the 15 micron continuum in the star forming ring. In the bulge, there is some enhancement of the 6.75 micron flux, probably because of contributions from photospheric light, however, the 11.3 micron dust feature is also seen, showing additional emission from interstellar or circumstellar dust.

Beverly J. Smith

1998-01-11

334

HUBBLE PROBES THE VIOLENT BIRTH OF STARS IN GALAXY NGC 253 [Left  

NASA Technical Reports Server (NTRS)

An image of the spiral galaxy NGC 253, taken with a ground-based telescope. The galaxy is located about 8 million light-years away in the constellation Sculptor. Credit: Jay Gallagher (University of Wisconsin-Madison), Alan Watson (Lowell Observatory, Flagstaff, AZ), and NASA [Right] This NASA Hubble Space Telescope image of the core of the nearest starburst spiral galaxy, NGC 253, reveals violent star formation within a region 1,000 light-years across. A starburst galaxy has an exceptionally high rate of star birth, first identified by its excess of infrared radiation from warm dust. Hubble's high resolution allows astronomers to quantify complex structures in the starburst core of the galaxy for the first time, including luminous star clusters, dust lanes which trace regions of dense gas and filaments of glowing gas. Hubble identifies several regions of intense star formation, which include a bright, super-compact star cluster. These observations confirm that stars are often born in dense clusters within starbursts, and that dense gas coexists with and obscures the starburst core. This image was taken with Hubble's Wide Field Planetary Camera 2 (in PC mode). Credit: Carnegie Institution of Washington

2002-01-01

335

Stellar populations in edge-on galaxies from deep CCD surface photometry, 1: NGC 5907  

NASA Technical Reports Server (NTRS)

We present extremely deep charge coupled device (CCD) surface photometry of the edge-on Sc galaxy NGC 5907. Our data reach reliably to a surface brightness of R=27 mag/sq arcsec, some two magnitudes fainter than any previous work. We obtained this improvement using a 2048X2048 CCD with a wide (approximately 24 min) field, which made it possible to sky subtract directly from the galaxy frame, and by taking many dark sky flatfields. Our analysis of these data, using a full 2D model fitting procedure with a detailed error model, confirm the thin disk parameters of van der Kruit & Searle (1981). In particular, we confirm that the galaxy's disk has a radial cutoff and a constant scale height with radius. We find evidence for a stellar warp in this system, which has the same orientation as the H I warp. Our deep data also confirm that NGC 5907 has no thick disk. This suggests that theories of thick disk formation from star formation in the early stages of disk collapse, or by secular heating mechanisms, are unlikely to be correct, because they would predict that every galaxy would have a thick disk. Thick disk formation from the accretion of satellite galaxies is more likely.

Morrison, Heather L.; Boroson, Todd A.; Harding, Paul

1994-01-01

336

Molecular gas in the elliptical galaxy NGC759. Interferometric CO observations  

E-print Network

Interferometric observations of the CO(1-0) line in the elliptical galaxy NGC759 shows that it contains 2 10^9 Mo of molecular gas, confined to a circumnuclear ring with an average radius of only 650pc. The maximum gas surface density is 750 Mo/pc^2, which is comparable to the critical gas surface density for large scale gravitational instabilities. The low CO(2-1)/CO(1-0) ratio of 0.4 is consistent with a two-component molecular gas, consisting of a cold and dense phase, containing most of the mass, and a warm and diffuse component dominating the CO emission. We use a mass model for the underlying galaxy which is applicable to spherical galaxies with an r^1/4 luminosity profile. This leads to more modest estimates of the molecular gas fraction and gas surface density then would have been derived using simpler models, suggesting that many of the spectacular molecular gas properties of ultraluminous FIR galaxies, which could be described by similar mass models, may have to be revised. We discuss the possibility that NGC759 is in a late stage of a merging between two gas-rich disk galaxies.

Tommy Wiklind; Francoise Combes; Christian Henkel; Friedrich Wyrowski

1997-02-10

337

X-ray study of NGC 1399 in the Fornax cluster of galaxies  

NASA Technical Reports Server (NTRS)

Observations of the cD galaxy NGC 1399 in the Fornax cluster of galaxies with Ginga have detected extended X-ray emission out to a radius of more than about 360 kpc. The energy spectrum of this emission is well fitted with an optically thin thermal spectrum with kT = 1.46 +0.05/-0.21 keV with a strong iron emission line corresponding to an iron abundance of 1.1 +1.3/-0.5 times solar. The mass of the hot gas responsible for X-ray emission is nearly the same as the total stellar mass of the cluster. Therefore the presence of iron at near-solar abundance suggests that the mass of the hot gas ejected from galaxies is comparable to the total stellar mass. This result indicates that most of the hot gas in a very poor cluster is created through ejections from galaxies, rather than being primordial.

Ikebe, Y.; Ohashi, T.; Makishima, K.; Tsuru, T.; Fabbiano, G.; Kim, D.-W.; Trinchieri, G.; Hatsukade, I.; Yamashita, K.; Kondo, H.

1992-01-01

338

Where galaxies collide. II - NGC 5195, the M51 system and the luminosity function of H II regions  

Microsoft Academic Search

The characteristics of the interstellar medium and massive star formation in the lenticular galaxy NTGC 5195 and adjacent overlying parts of the Whirlpool spiral are investigated via broadband red and H-alpha imaging. Although NGC 5195 has a moderate amount of interstellar gas, no visual line emission that is unambiguously associated with star formation in this galaxy is found. R and

Harley A. Thronson Jr.; Helen Rubin; Amy Ksir

1991-01-01

339

DETECTION OF A HOT GASEOUS HALO AROUND THE GIANT SPIRAL GALAXY NGC 1961  

SciTech Connect

Hot gaseous halos are predicted around all large galaxies and are critically important for our understanding of galaxy formation, but they have never been detected at distances beyond a few kpc around a spiral galaxy. We used the ACIS-I instrument on board Chandra to search for diffuse X-ray emission around an ideal candidate galaxy: the isolated giant spiral NGC 1961. We observed four quadrants around the galaxy for 30 ks each, carefully subtracting background and point-source emission, and found diffuse emission that appears to extend to 40-50 kpc. We fit {beta}-models to the emission and estimate a hot halo mass within 50 kpc of 5 x 10{sup 9} M{sub sun}. When this profile is extrapolated to 500 kpc (the approximate virial radius), the implied hot halo mass is 1-3 x 10{sup 11} M{sub sun}. These mass estimates assume a gas metallicity of Z = 0.5 Z{sub sun}. This galaxy's hot halo is a large reservoir of gas, but falls significantly below observational upper limits set by pervious searches, and suggests that NGC 1961 is missing 75% of its baryons relative to the cosmic mean, which would tentatively place it below an extrapolation of the baryon Tully-Fisher relationship of less massive galaxies. The cooling rate of the gas is no more than 0.4 M{sub sun} yr{sup -1}, more than an order of magnitude below the gas consumption rate through star formation. We discuss the implications of this halo for galaxy formation models.

Anderson, Michael E.; Bregman, Joel N., E-mail: michevan@umich.edu, E-mail: jbregman@umich.edu [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States)

2011-08-10

340

MOND prediction of a new giant shell in the elliptical galaxy NGC 3923  

NASA Astrophysics Data System (ADS)

Context. Stellar shells, which form axially symmetric systems of arcs in some elliptical galaxies, are most likely remnants of radial minor mergers. They are observed up a radius of ~100 kpc. The stars in them oscillate in radial orbits. The radius of a shell depends on the free-fall time at the position of the shell and on the time since the merger. We previously verified the consistency of shell radii in the elliptical galaxy NGC 3923 with its most probable MOND potential. Our results implied that an as yet undiscovered shell exists at the outskirts of the galaxy. Aims: We here extend our study by assuming more general models for the gravitational potential to verify the prediction of the new shell and to estimate its position. Methods: We tested the consistency of the shell radial distribution observed in NGC 3923 with a wide variety of MOND potentials of the galaxy. The potentials differed in the mass-to-light ratio and in distance to the galaxy. We considered different MOND interpolation functions, values of the acceleration constant a0, and density profiles of the galaxy. We verified the functionality of our code on a Newtonian self-consistent simulation of the formation of a shell galaxy. Results: Our method reliably predicts that exactly one new outermost shell exists at a galactocentric radius of about 1900'' (~210 kpc) on the southwestern side of the galaxy. Its estimated surface brightness is about 28 mag arcsec-2 in B - a value accessible by current instruments. This prediction enables a rare test of MOND in an elliptical down to an acceleration of a0/ 10. The predictive power of our method is verified by reconstructing the position of the largest known shell from the distribution of the remaining shells.

Blek, M.; Bartokov, K.; Ebrov, I.; Jungwiert, B.

2014-06-01

341

The Interacting Dwarf Galaxy NGC 3077: The Interplay of Atomic and Molecular Gas with Violent Star Formation  

E-print Network

We present a comprehensive multi-wavelength study of the nearby interacting dwarf galaxy NGC3077 (member of the M81 triplet). High resolution VLA HI observations show that most of the atomic gas (~90%) around NGC3077 is situated in a prominent tidal arm with a complex velocity structure. Little HI (~5 x 10^7 M_sun) is associated with NGC3077 itself. High resolution OVRO observations of the molecular component (CO) reveal the presence of 16 molecular complexes near the center of NGC3077 (total mass: ~1.6 x 10^6 M_sun). A virial mass analysis of the individual complexes yields a lower CO-to-H_2 conversion factor in NGC3077 than the Galactic value - a surprising result for a dwarf galaxy. The total (atomic and molecular) gas content in the centre of NGC3077 is displaced from the stellar component of NGC3077 -- this implies that not only the gas at large galactocentric radii is affected by the interaction within the triplet but also the center. We speculate that the starburst activity of NGC3077 was triggered by this redistribution of gas in the center. Some of these supershells are surrounded by neutral hydrogen. In a few cases, the rims of the ionized supershells are associated with dust absorption. The most prominent star forming region in NGC3077 as probed by Pa-alpha observations is hidden behind a dust cloud which is traced by the molecular complexes. Correcting for extinction we derive a star forming rate of 0.05 M_sun year^-1, i.e. given the reservoir in atomic and molecular gas in NGC3077, star formation may proceed at a similar rate for a few 10^8 years. The efficiency to form stars out of molecular gas in NGC3077 is similar to that in M82.

F. Walter; A. Weiss; C. Martin; N. Scoville

2001-10-27

342

The Interplay between Bulge-Disk-Bar Photometric Measures in the Most Isolated Spiral Galaxies  

NASA Astrophysics Data System (ADS)

We perform bulge-disk-bar decomposition using the BUDDA code (de Souza, Gadotti, dos Anjos 2004) on i-band SDSS images for a sample isolated galaxies from the AMIGA sample (Verdes-Montenegro et al. 2004). We studied 100 of the isolated galaxies classified Sb-Sc that were also included in SDSS. This appears to be the dominant population of isolated galaxies representing 2/3 of the reasonably complete AMIGA sample. We report a series of correlations and scaling relations between the photometrically derived parameters describing the three main structural components i.e. bulges, disks and bars. We illustrate how various measures that quantify the structure of galaxies evolve along the Sb-Sbc-Sc morphological sequence. Comparison with other studies seems to suggest that both the frecquency of barred galaxies and the bar sizes are sensitive to environment. Additionally our results suggest that most galaxies in our sample host pseudobulges rather than classical bulges, consistent with the idea that classical bulges are environmentally formed and fostered.

Durbala, Adriana; Sulentic, J. W.; Verdes-Montenegro, L.

2008-05-01

343

Kinematics of Superbubbles and Supershells in the Irregular Galaxy, NGC1569  

NASA Astrophysics Data System (ADS)

We present observations in the optical lines of H? and [S II] (??6717, 6731 ) and in X-rays of the irregular galaxy, NGC 1569. The observations in H? and [S II] were made with the UNAM scanning Fabry-Perot interferometer (PUMA) and the X-ray data were obtained from the Chandra data archive. We detected several superbubbles, filaments, and supershells in NGC 1569 for which we determined size as well as their kinematic properties. We present a catalog of expansion velocities of 12 superbubbles, listing their positions, diameters, and physical parameters. Likewise, we present a catalog of 15 filaments and 4 supershells. In order to identify possible X-ray emission from the superbubbles in this galaxy, we analyzed the X-ray emission of NGC 1569 in two energy bands: 0.2-2.0 keV (soft X-rays) and 2.0-8.0 keV (hard X-rays). Based on X-ray images, we detected X-ray emission that could possibly be related to some of the superbubbles. The spectrum of the X-ray superbubbles can be described by an optically thin thermal plasma model. In order to identify the possible coexistence of galactic super winds and superbubbles we have performed adiabatic three-dimensional N-body/smoothed particle hydrodynamics simulations to follow the evolution of the most important stellar clusters in this galaxy, SSC A and SSC B, using the GADGET-2 code. Those simulations demonstrate that depending on the specific initial conditions, the formation of superbubbles or a galactic superwind can result in NGC 1569.

Snchez-Cruces, M.; Rosado, M.; Rodrguez-Gonzlez, A.; Reyes-Iturbide, J.

2015-02-01

344

Serendipitous discovery of a dying Giant Radio Galaxy associated with NGC 1534, using the Murchison Widefield Array  

NASA Astrophysics Data System (ADS)

Recent observations with the Murchison Widefield Array at 185 MHz have serendipitously unveiled a heretofore unknown giant and relatively nearby (z = 0.0178) radio galaxy associated with NGC 1534. The diffuse emission presented here is the first indication that NGC 1534 is one of a rare class of objects (along with NGC 5128 and NGC 612) in which a galaxy with a prominent dust lane hosts radio emission on scales of 700 kpc. We present details of the radio emission along with a detailed comparison with other radio galaxies with discs. NGC 1534 is the lowest surface brightness radio galaxy known with an estimated scaled 1.4-GHz surface brightness of just 0.2 mJy arcmin-2. The radio lobes have one of the steepest spectral indices yet observed: ? = -2.1 0.1, and the core to lobe luminosity ratio is <0.1 per cent. We estimate the space density of this low brightness (dying) phase of radio galaxy evolution as 7 10-7 Mpc-3 and argue that normal AGN cannot spend more than 6 per cent of their lifetime in this phase if they all go through the same cycle.

Hurley-Walker, Natasha; Johnston-Hollitt, Melanie; Ekers, Ron; Hunstead, Richard; Sadler, Elaine M.; Hindson, Luke; Hancock, Paul; Bernardi, Gianni; Bowman, Judd D.; Briggs, Frank; Cappallo, Roger; Corey, Brian; Deshpande, Avinash A.; Emrich, David; Gaensler, Bryan M.; Goeke, Robert; Greenhill, Lincoln; Hazelton, Bryna J.; Hewitt, Jacqueline; Kaplan, David L.; Kasper, Justin; Kratzenberg, Eric; Lonsdale, Colin; Lynch, Mervyn; Mitchell, Daniel; McWhirter, Russell; Morales, Miguel; Morgan, Edward; Oberoi, Divya; Offringa, Andr; Ord, Stephen; Prabu, Thiagaraj; Rogers, Alan; Roshi, Anish; Shankar, Udaya; Srivani, K.; Subrahmanyan, Ravi; Tingay, Steven; Waterson, Mark; Wayth, Randall B.; Webster, Rachel; Whitney, Alan; Williams, Andrew; Williams, Chris

2015-03-01

345

Testing the nature of S0 galaxies using planetary nebula kinematics in NGC 1023  

NASA Astrophysics Data System (ADS)

We investigate the manner in which lenticular galaxies are formed by studying their stellar kinematics: an S0 formed from a fading spiral galaxy should display similar cold outer disc kinematics to its progenitor, while an S0 formed in a minor merger should be more dominated by random motions. In a pilot study, an attempt to distinguish between these scenarios, we have measured the planetary nebula (PN) kinematics of the nearby S0 system NGC 1023. Using the Planetary Nebula Spectrograph, we have detected and measured the line-of-sight velocities of 204 candidate planetary nebulae (PNe) in the field of this galaxy. Out to intermediate radii, the system displays the kinematics of a normal rotationally supported disc system. After correction of its rotational velocities for asymmetric drift, the galaxy lies just below the spiral galaxy Tully-Fisher relation, as one would expect for a fading system. However, at larger radii the kinematics undergo a gradual but major transition to random motion with little rotation. This transition does not seem to reflect a change in the viewing geometry or the presence of a distinct halo component, since the number counts of PNe follow the same simple exponential decline as the stellar continuum with the same projected disc ellipticity out to large radii. The galaxy's small companion, NGC 1023A, does not seem to be large enough to have caused the observed modification either. This combination of properties would seem to indicate a complex evolutionary history in either the transition to form an S0 or in the past life of the spiral galaxy from which the S0 formed. More data sets of this type from both spirals and S0s are needed in order to definitively determine the relationship between these types of system.

Noordermeer, E.; Merrifield, M. R.; Coccato, L.; Arnaboldi, M.; Capaccioli, M.; Douglas, N. G.; Freeman, K. C.; Gerhard, O.; Kuijken, K.; de Lorenzi, F.; Napolitano, N. R.; Romanowsky, A. J.

2008-03-01

346

NGC 5128 - a nearby laboratory for planetary nebulae in a giant early-type galaxy  

NASA Astrophysics Data System (ADS)

NGC 5128 at 3.8 Mpc is the nearest large elliptical galaxy and is ideally suited to a detailed study of its planetary nebula population. Two spectroscopic programmes are summarised. More than 1200 PNe candidates are known from imaging campaigns in NGC 5128 and accurate radial velocities of 1070 have been measured with the VLT FLAMES/Giraffe spectrometer. From these data a variety of studies of the galaxy kinematics are enabled, such as search for PN sub-groups, representing the relics of accretion of small galaxies. Emission line spectra were observed with VLT FORS and the light element abundances determined for 40 PNe through photoionization modelling. A spread in O abundance of about 0.9 dex is found but no obvious radial gradient out to 19 kpc. Comparison of the O abundance from these PN with the metallicity for the stellar population in the neighbourhood of the PN will probe the star formation and enrichment history of the galaxy. Full results from this analysis will be presented in a forthcoming paper.

Walsh, Jeremy R.; Jacoby, George H.; Kuntschner, Harald; Peletier, Reynier F.; Rejkuba, Marina; Walton, Nicholas A.; Woodley, Kristin A.

2012-08-01

347

Atomic and Molecular Gas near NGC3077: The Making of a New Dwarf Galaxy?  

E-print Network

Using the IRAM 30m radio telescope we have mapped the tidal arm feature south-east of NGC 3077 where we recently detected molecular gas in the CO (1-0) and (2-1) transitions. We find that the molecular gas is much more extended than previously thought (several kpc). The CO emission can be separated into at least 3 distinct complexes with equivalent radii between 250pc and 700pc - the newly detected complexes therefore range among the largest molecular complexes in the local universe. Mass estimates based on virialization and employing an X_CO factor yield a total mass for the complexes of order 4 x 10^7 M_sun, i.e. more than the estimated molecular mass within NGC 3077 itself. This implies that interactions between galaxies can efficiently remove heavy elements and molecules from a galaxy and enrich the intergalactic medium. A comparison of the distribution of HI and CO shows no clear correlation. However, CO is only found in regions where the HI column density exceeds 1.1 x 10^21 cm^-2. HI masses for the molecular complexes mapped are of the same order as the corresponding molecular masses. Since the complexes have all the ingredients to form stars in the future, we are thus presumably witnessing the birth of a dwarf galaxy. This process may have dominated the creation of dwarf galaxies at larger look-back times.

Fabian Walter; Andreas Heithausen

2000-08-22

348

A close nuclear black-hole pair in the spiral galaxy NGC 3393.  

PubMed

The current picture of galaxy evolution advocates co-evolution of galaxies and their nuclear massive black holes, through accretion and galactic merging. Pairs of quasars, each with a massive black hole at the centre of its galaxy, have separations of 6,000 to 300,000 light years (refs 2 and 3; 1 parsec = 3.26 light years) and exemplify the first stages of this gravitational interaction. The final stages of the black-hole merging process, through binary black holes and final collapse into a single black hole with gravitational wave emission, are consistent with the sub-light-year separation inferred from the optical spectra and light-variability of two such quasars. The double active nuclei of a few nearby galaxies with disrupted morphology and intense star formation (such as NGC 6240 with a separation of about 2,600 light years and Mrk 463 with a separation of about 13,000 light years between the nuclei) demonstrate the importance of major mergers of equal-mass spiral galaxies in this evolution; such mergers lead to an elliptical galaxy, as in the case of the double-radio-nucleus elliptical galaxy 0402+379 (with a separation of about 24 light years between the nuclei). Minor mergers of a spiral galaxy with a smaller companion should be a more common occurrence, evolving into spiral galaxies with active massive black-hole pairs, but have hitherto not been seen. Here we report the presence of two active massive black holes, separated by about 490 light years, in the Seyfert galaxy NGC 3393 (50 Mpc, about 160 million light years). The regular spiral morphology and predominantly old circum-nuclear stellar population of this galaxy, and the closeness of the black holes embedded in the bulge, provide a hitherto missing observational point to the study of galaxy/black hole evolution. Comparison of our observations with current theoretical models of mergers suggests that they are the result of minor merger evolution. PMID:21881560

Fabbiano, G; Wang, Junfeng; Elvis, M; Risaliti, G

2011-09-22

349

Gas Kinematics and the Black Hole Mass at the Center of the Radio Galaxy NGC 4335  

NASA Astrophysics Data System (ADS)

We investigate the kinematics of the central gas disk of the radio-loud elliptical galaxy NGC 4335, derived from Hubble Space Telescope (HST) long-slit spectroscopic observations of H?+[N II] along three parallel slit positions. The observed mean velocities are consistent with a rotating thin disk. We model the gas disk in the customary way, taking into account the combined potential of the galaxy and a putative black hole with mass M, as well as the influence on the observed kinematics of the point-spread function and finite slit width. This sets a 3 ? upper limit of 108 Msolar on M. The velocity dispersion at r<~0.5" is in excess of that predicted by the thin rotating disk model. This does not invalidate the model if the excess dispersion is caused by localized turbulent motion in addition to bulk circular rotation. However, if instead the dispersion is caused by the black hole (BH) potential then the thin disk model provides an underestimate of M. A BH mass M~6108 Msolar is inferred by modeling the central gas dispersion as due to an isotropic spherical distribution of collisionless gas cloudlets. The stellar kinematics for NGC 4335 are derived from a ground-based (William Herschel Telescope/ISIS) long-slit observation along the galaxy major axis. A two-integral model of the stellar dynamics yields M>~3109 Msolar. However, there is reason to believe that this model overestimates M. Reported correlations between black hole mass and inner stellar velocity dispersion ? predict M to be >=5.4108 Msolar in NGC 4335. If our standard thin disk modeling of the gas kinematics is valid, then NGC 4335 has an unusually low M for its velocity dispersion. If, on the other hand, this approach is flawed and provides an underestimate of M, then black hole masses for other galaxies derived from HST gas kinematics with the same assumptions should be treated with caution. In general, a precise determination of the M-? relation and its scatter will benefit from (1) joint measurements of M from gas and stellar kinematics in the same galaxies and (2) a better understanding of the physical origin of the excess velocity dispersion commonly observed in nuclear gas disks of elliptical galaxies. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Verdoes Kleijn, Gijs A.; van der Marel, Roeland P.; de Zeeuw, P. Tim; Noel-Storr, Jacob; Baum, Stefi A.

2002-11-01

350

The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey - IX. 12CO J = 3?2 observations of NGC 2976 and NGC 3351  

NASA Astrophysics Data System (ADS)

We present 12CO J = 3?2 maps of NGC 2976 and NGC 3351 obtained with the James Clerk Maxwell Telescope (JCMT), both early targets of the JCMT Nearby Galaxy Legacy Survey (NGLS). We combine the present observations with 12CO J = 1?0 data and find that the computed 12CO J = 3?2 to 12CO J = 1?0 line ratio (R31) agrees with values measured in other NGLS field galaxies. We compute the MH2 value and find that it is robust against the value of R31 used. Using H I data from The H I Nearby Galaxy Survey, we find a tight correlation between the surface density of H2 and star formation rate density for NGC 3351 when 12CO J = 3?2 data are used. Finally, we compare the 12CO J = 3?2 intensity with the polycyclic aromatic hydrocarbon (PAH) 8 ?m surface brightness and find a good correlation in the high surface brightness regions. We extend this study to include all 25 Spitzer Infrared Nearby Galaxies Survey galaxies within the NGLS sample and find a tight correlation at large spatial scales. We suggest that both PAH 8 ?m and 12CO J = 3?2 are likely to originate in regions of active star formation.

Tan, Boon-Kok; Leech, J.; Rigopoulou, D.; Warren, B. E.; Wilson, C. D.; Attewell, D.; Azimlu, M.; Bendo, G. J.; Butner, H. M.; Brinks, E.; Chanial, P.; Clements, D. L.; Heesen, V.; Israel, F.; Knapen, J. H.; Matthews, H. E.; Mortier, A. M. J.; Mhle, S.; Snchez-Gallego, J. R.; Tilanus, R. P. J.; Usero, A.; van der Werf, P.; Zhu, M.

2013-11-01

351

Constraints from Dynamical Friction on the Dark Matter Content of Barred Galaxies  

Microsoft Academic Search

We show that bars in galaxy models having halos of moderate density and a\\u000avariety of velocity distributions all experience a strong drag from dynamical\\u000afriction unless the halo has large angular momentum in the same sense as the\\u000adisk. The frictional drag decreases the bar pattern speed, driving the\\u000acorotation point out to distances well in excess of those

Victor P. Debattista; J. A. Sellwood

2000-01-01

352

The Properties of Local Barred Disks in the Field and Dense Environments: Implications for Galaxy Evolution  

NASA Astrophysics Data System (ADS)

Stellar bars are the most efficient internal drivers of disk evolution because they redistribute material and angular momentum within the galaxy and dark matter halo. Mounting evidence suggests that processes other than major mergers, such as minor mergers, secular processes driven by bars, and clump coalescence, as well as smooth accretion, play an important role in galaxy evolution since z = 2. As a key step toward characterizing this evolution and constraining theoretical models, we determine the frequency and properties of bars in the local Universe in both field and cluster environment, based on three of our studies: Marinova & Jogee (2007), Barazza, Jogee, & Marinova (2008) and Marinova et al. (2009). Among field spirals of intermediate Hubble types in the OSU survey, we find using ellipse fitting that the bar fraction is 44% in the optical and 60% in the NIR, giving an extinction correction factor of approximately 1.4 at z 0. Using data from the Abell 901/902 cluster system at z 0.165 from the HST ACS survey STAGES, we find that the optical bar fraction is a strong trend of both absolute magnitude and host bulge-to-total ratio, increasing for galaxies that are brighter and/or more disk-dominated. The latter trend is also found in the field from SDSS. For bright early types and faint late types the optical bar fraction in the cluster is similar to that in the field. We find that between the core region and the virial radii of the clusters the optical bar fraction is not a strong function of local environment density. We discuss the implications of our results in the context of theoretical models of the impact of bars on galaxy evolution.

Marinova, I.; Jogee, S.; Barazza, F. D.; Heiderman, A.; Gray, M. E.; Barden, M.; Wolf, C.; Peng, C. Y.; Bacon, D.; Balogh, M.; Bell, E. F.; Bhm, A.; Caldwell, J. A. R.; Huler, B.; Heymans, C.; Jahnke, K.; van Kampen, E.; Lane, K.; McIntosh, D. H.; Meisenheimer, K.; Snchez, S. F.; Sommerville, R. S.; Taylor, A.; Wisotzki, L.; Zheng, X.

2009-12-01

353

The structure and dynamics of ringed galaxies. III - Surface photometry and kinematics of the ringed nonbarred spiral NGC 7531  

Microsoft Academic Search

The photometric and kinematic properties of the southern galaxy NGC 7531, a large example of a nonbarred spiral possessing a very bright inner ring, are explored via UVBRI surface photometry and emission-line spectroscopy. The galaxy is a global, two-armed spiral galaxy possessing a bright inner ring with a radius of 2.3 kpc. The ring has an average surface brightness in

R. Buta

1987-01-01

354

IRAC and MIPS Observations of the Interacting Galaxies IC 2163 and NGC 2207: Clumpy Emission  

E-print Network

IC 2163 and NGC 2207 are interacting galaxies that have been well studied at optical and radio wavelengths and simulated in numerical models to reproduce the observed kinematics and morphological features. Spitzer IRAC and MIPS observations reported here show over 200 bright clumps from young star complexes. The brightest IR clump is a morphologically peculiar region of star formation in the western arm of NGC 2207. This clump, which dominates the Halpha and radio continuum emission from both galaxies, accounts for ~12% of the total 24mu m flux. Nearly half of the clumps are regularly spaced along some filamentary structure, whether in the starburst oval of IC 2163 or in the thin spiral arms of NGC 2207. This regularity appears to influence the clump luminosity function, making it peaked at a value nearly a factor of 10 above the completeness limit, particularly in the starburst oval. This is unlike the optical clusters inside the clumps, which have a luminosity function consistent with the usual power law form. The giant IR clumps presumably formed by gravitational instabilities in the compressed gas of the oval and the spiral arms, whereas the individual clusters formed by more chaotic processes, such as turbulence compression, inside these larger-scale structures.

Debra Meloy Elmegreen; Bruce G. Elmegreen; Michele Kaufman; Kartik Sheth; Curtis Struck; Magnus Thomasson; Elias Brinks

2006-05-20

355

The Araucaria Project. Near-Infrared Photometry of Cepheid Variables in the Sculptor Galaxy NGC 300  

E-print Network

We have obtained deep near-infrared images in J and K filters of three fields in the Sculptor galaxy NGC 300 with the ESO VLT and ISAAC camera. For 16 Cepheid variables in these fields, we have determined J and K magnitudes at two different epochs, and have derived their mean magnitudes in these bands. The slopes of the resulting period-luminosity relations are in very good agreement with the slopes of these relations measured in the LMC by Persson et al. Fitting the LMC slopes to our data, we have derived distance moduli in J and K. Using these values together with the values derived in the optical V and I bands in our previous work, we have determined an improved total reddening for NGC 300 of E(B-V)=0.096 +/- 0.006 mag, which yields extremely consistent values for the absorption-corrected distance modulus of the galaxy from VIJK bands. Our distance result for NGC 300 from this combined optical/near infrared Cepheid study is (m-M)_0 = 26.37 +/- 0.04 (random) +/- 0.03 (systematic) mag and is tied to an adopt...

Gieren, W; Soszynski, I; Bresolin, F; Kudritzki, R P; Minniti, D; Storm, J

2005-01-01

356

ROSAT PSPC observation of the X-ray faint early-type galaxy NGC5866  

E-print Network

We present the results of the analysis of the ROSAT PSPC pointed observation of the S0 galaxy NGC5866. Previous Einstein observations had revealed that this galaxy has a low X-ray to optical ratio Lx/Lb. Theoretical models of the X-ra emission of early-type galaxies had suggested that in objects of this kind the emission is not dominated by the presence of a hot diffuse gas, but should originate in stellar sources. We discuss the evidence in favor of this hypothesis following from the results of the analysis of the ROSAT PSPC data. The X-ray spectrum shows properties similar to those of the other two low Lx/Lb early-type galaxies observed by ROSAT so far, including the presence of very soft emission. So, these galaxies can be recognized as a group with homogeneous properties, and a more exhaustive picture of the nature of the X-ray emission across the Lx/Lb plane of early-type galaxies can be outlined. We also discuss the importance of rotation in the X-ray emission of S0 galaxies, and suggest that it could explain why on average S0s are less X-ray luminous than ellipticals.

S. Pellegrini

1994-07-03

357

PLANETARY NEBULAE IN THE ELLIPTICAL GALAXY NGC 821: KINEMATICS AND DISTANCE DETERMINATION  

SciTech Connect

Using a slitless spectroscopy method with the 8.2 m Subaru telescope and its FOCAS Cassegrain spectrograph, we have increased the number of planetary nebula (PN) detections and PN velocity measurements in the flattened elliptical galaxy NGC 821. A comparison with the detections reported previously by the Planetary Nebulae Spectrograph group indicates that we have confirmed most of their detections. The velocities measured by the two groups, using different telescopes, spectrographs, and slitless techniques, are in good agreement. We have built a combined sample of 167 PNs and have confirmed the Keplerian decline of the line-of-sight velocity dispersion reported previously. We also confirm misaligned rotation from the combined sample. A dark matter halo may exist around this galaxy, but it is not needed to keep the PN velocities below the local escape velocity as calculated from the visible mass. We have measured the m(5007) magnitudes of 145 PNs and produced a statistically complete sample of 40 PNs in NGC 821. The resulting PN luminosity function (PNLF) was used to estimate a distance modulus of 31.4 mag, equivalent to 19 Mpc. We also estimated the PN formation rate. NGC 821 becomes the most distant galaxy with a PNLF distance determination. The PNLF distance modulus is smaller than the surface brightness fluctuation (SBF) distance modulus by 0.4 mag. Our kinematic information permits to rule out the idea that a shorter PNLF distance could be produced by the contamination of the PNLF by background galaxies with emission lines redshifted into the on-band filter transmission curve.

Teodorescu, A. M.; Mendez, R. H.; Kudritzki, R. P. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Bernardi, F. [Universita di Pisa, Largo B. Pontecorvo 5, 56127, Pisa (Italy); Riffeser, A., E-mail: ana@ifa.hawaii.ed, E-mail: mendez@ifa.hawaii.ed [Universitaets-Sternwarte Muenchen, Scheinerstr. 1, D-81679 Muenchen (Germany)

2010-09-20

358

Mapping the galaxy NGC 4486 (M87) through its globular cluster system  

NASA Astrophysics Data System (ADS)

As shown in previous works, globular clusters (GCs) can be used to trace the overall structure of the diffuse stellar populations in early-type galaxies if the number of clusters per unit stellar mass depends on metallicity. In this paper we further test this assumption in the galaxy NGC 4486 (M87) by combining several data sources. The results show that GCs allow the mapping of the galaxy in terms of the surface brightness profile, integrated colour gradient, chemical abundance and mass-to-luminosity ratios up to 1000 arcsec (or 80.4 kpc) from its centre (i.e. some 10 effective radii). The analysis indicates the presence of a dominant high-metallicity bulge associated with the red globulars, whose ellipticity increases outwards, and of a more flattened low-metallicity halo connected with the blue globulars. The chemical abundance gradient of the composite stellar population is remarkably similar to that inferred from X-ray observations of hot gas. The mass-metallicity spectrum of the stellar population can, in principle, be understood in terms of inhomogeneous enrichment models. In turn, the distribution of the bluest GCs, and lowest metallicity halo stars, has an intriguing similarity with that of dark matter, a feature shared with NGC 1399. Also, in these two galaxies, the number of blue GCs per dark mass unit is identical within the errors, ?1.0(0.3) 10-9. The total stellar mass derived for NGC 4486 is 6.8(1.1) 1011 M? with a baryonic mass fraction fb= 0.08(0.01).

Forte, Juan C.; Vega, E. Irene; Faifer, Favio

2012-03-01

359

Hubble Space Telescope images of the Seyfert galaxies NGC 5929 and MCG 8-11-11  

NASA Technical Reports Server (NTRS)

We present the initial results of a program to obtain high resolution images of Seyfert galaxies with the Planetary Camera aboard the Hubble Space Telescope (HST). In this paper we discuss the images of the type 2 Seyfert NGC 5929 and the type 1.5 Seyfert MCG 8-11-11 (= UGC 3374). The images were obtained in the emission lines of (O III) lambda lambda 4959 and 5007 A and H alpha + (N II) lambda lambda 6548 and 6583 A and their adjacent continua. The high-excitation gas in the narrow line region (NLR) of NGC 5929 is resolved into individual clouds in the central 1 sec .5. Although the (O III) emission is clearly not spherically symmetric with respect to the nucleus, it does not define a distinct 'bicone' morphology, as observed by the HST in a few other Seyfert galaxies. We find no direct evidence for the reddening and/or obscuration effects characteristic of a dusty torus, which, in the context of 'unified models', is expected to obscure the active galactic nucleus (AGN) in type 2 Seyfert galaxies. The correspondence between the emission line gas and the radio morphology suggests that the structure of the NLR in NGC 5929 is governed by matter ejected from the AGN. A comparison of the recombination rate of hydrogen in the brightest emission line cloud with an upper limit on the ionizing luminosity emitted toward Earth provides no evidence that the central ionizing source radiates anisotropically. The images of MCG 8-11-11 show only an unresolved nuclear source. No emission line gas associated with the extended radio source is detected. We estimate upper limits on the intensity of extended line emission in this galaxy and examine their significance.

Bower, Gary A.; Wilson, Andrew S.; Mulchaey, John S.; Miley, George K.; Heckman, Timothy M.; Krolik, Julian H.

1994-01-01

360

X-RAY NUCLEAR ACTIVITY IN S{sup 4}G BARRED GALAXIES: NO LINK BETWEEN BAR STRENGTH AND CO-OCCURRENT SUPERMASSIVE BLACK HOLE FUELING  

SciTech Connect

Stellar bars can lead to gas inflow toward the center of a galaxy and stimulate nuclear star formation. However, there is no compelling evidence on whether they also feed a central supermassive black hole: by measuring the fractions of barred active and inactive galaxies, previous studies have yielded conflicting results. In this paper, we aim to understand the lack of observational evidence for bar-driven active galactic nucleus (AGN) activity by studying a sample of 41 nearby (d < 35 Mpc) barred galaxies from the Spitzer Survey for Stellar Structure in Galaxies. We use Chandra observations to measure nuclear 2-10 keV X-ray luminosities and estimate Eddington ratios, together with Spitzer 3.6 ?m imaging to quantify the strength of the stellar bar in two independent ways: (1) from its structure, as traced by its ellipticity and boxiness, and (2) from its gravitational torque Q{sub b} , taken as the maximum ratio of the tangential force to the mean background radial force. In this way, rather than discretizing the presence of both stellar bars and nuclear activity, we are able to account for the continuum of bar strengths and degrees of AGN activity. We find nuclear X-ray sources in 31 out of 41 galaxies with median X-ray luminosity and Eddington ratio of L{sub X} = 4.3 10{sup 38} erg s{sup 1} and L{sub bol}/L{sub Edd} = 6.9 10{sup 6}, respectively, consistent with low-luminosity AGN activity. Including upper limits for those galaxies without nuclear detections, we find no significant correlation between any of the bar strength indicators and the degree of nuclear activity, irrespective of galaxy luminosity, stellar mass, Hubble type, or bulge size. Strong bars do not favor brighter or more efficient nuclear activity, implying that at least for the low-luminosity regime, supermassive black hole fueling is not closely connected to large-scale features.

Cisternas, Mauricio; Knapen, Johan H.; Gonzlez-Martn, Omaira; Erroz-Ferrer, Santiago [Instituto de Astrofsica de Canarias, E-38205 La Laguna, Tenerife (Spain); Gadotti, Dimitri A.; Kim, Taehyun [European Southern Observatory, Casilla 19001, Santiago 19 (Chile); Daz-Garca, Simn; Laurikainen, Eija; Salo, Heikki; Comern, Sbastien; Laine, Jarkko [Division of Astronomy, Department of Physical Sciences, University of Oulu, Oulu FI-90014 (Finland); Ho, Luis C. [The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Elmegreen, Bruce G. [IBM T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598 (United States); Zaritsky, Dennis; Hinz, Joannah L. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Sheth, Kartik [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Athanassoula, E.; Bosma, Albert [Aix Marseille Universit, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, F-13388 Marseille (France); Gil de Paz, Armando [Departamento de Astrofsica, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Holwerda, Benne W., E-mail: mauricio@iac.es [European Space Agency, ESTEC, Keplerlaan 1, 2200 AG Noordwijk (Netherlands); and others

2013-10-10

361

The X-ray nature of the low luminosity Seyfert 2 galaxy NGC 7590  

NASA Astrophysics Data System (ADS)

Observations have detected a class of X-ray unabsorbed Seyfert 2 galaxies (NH<10^22 cm^-2). Interesting results have been obtained recently towards whether these sources may genuinely lack a broad-line region, in contrast to the standard unification model. However, only few objects have yet been securely identified. Seyfert 2 galaxy NGC 7590 was previously identified as X-ray unobscured based on ASCA data. New XMM images have shown its X-ray emission is dominated by extended component from the host galaxy and an off-nuclear ULX. The nature of the nuclear X-ray emission remains unclear due to strong contamination. With its superb spatial resolution, Chandra exposure would enable us the first time to detect the nuclear X-ray emission, and to measure the nuclear obscuration if existed.

Shu, Xinwen

2010-09-01

362

Tilted-ring models of the prolate spiral galaxies NGC 5033 and 5055  

NASA Technical Reports Server (NTRS)

Observations of the kinematics of H I in the disks of spiral galaxies have shown that isovelocity contours often exhibit a twisted pattern. The shape of a galaxy's gravitational potential well (whether due to luminous matter or dark matter) can be determined from the direction of the twist. If this twist is a manifestation of the precession of a nonsteady-state disk, it is shown that the twists of NGC 5033 and 5055 imply an overall prolate shape, with the major axis of the potential well aligned along the rotation axis of the disk. Therefore, the luminous disks of these galaxies must be embedded in dark halos that are prolate spheroids or prolatelike triaxial figures.

Christodoulou, Dimitris M.; Tohline, Joel E.; Steiman-Cameron, Thomas Y.

1988-01-01

363

The Mass of the Central Black Hole in the Seyfert Galaxy NGC 3783  

NASA Technical Reports Server (NTRS)

Improved analysis of ultraviolet and optical monitoring data on the Seyfert 1 galaxy NGC 3783 provides evidence for the existence of a supermassive, (8.7 +/- 1.1) x 10(exp 6) solar mass, black hole in this galaxy. By using recalibrated spectra from the International Ultraviolet Explorer satellite and ground-based optical data, as well as refined techniques of reverberation mapping analysis, we have reduced the statistical uncertainties in the response of the emission lines to variations in the ionizing continuum. The different time lags in the emission-line responses indicate a stratification in the ionization structure of the broad-line region and are consistent with the virial relationship suggested by the analysis of similar active galaxies.

Onken, Christopher A.; Peterson, Bradley M.

2004-01-01

364

Ram pressure stripping of the multiphase ISM in the Virgo cluster spiral galaxy NGC 4438  

E-print Network

Ram pressure stripping of the multiphase ISM is studied in the perturbed Virgo cluster spiral galaxy NGC 4438. This galaxy underwent a tidal interaction ~100 Myr ago and is now strongly affected by ram pressure stripping. Deep VLA radio continuum observations at 6 and 20 cm are presented. We detect prominent extraplanar emission to the west of the galactic center, which extends twice as far as the other tracers of extraplanar material. The spectral index of the extraplanar emission does not steepen with increasing distance from the galaxy. This implies in situ re-acceleration of relativistic electrons. The comparison with multiwavelength observations shows that the magnetic field and the warm ionized interstellar medium traced by Halpha emission are closely linked. The kinematics of the northern extraplanar Halpha emission, which is ascribed to star formation, follow those of the extraplanar CO emission. In the western and southern extraplanar regions, the Halpha measured velocities are greater than those of ...

Vollmer, B; Chung, A; Chemin, L; Braine, J; Boselli, A; Beck, R

2009-01-01

365

The radio source and bipolar nebulosity in the Seyfert galaxy NGC 3516  

NASA Technical Reports Server (NTRS)

Results of radio continuum and optical emission-line observations of the type 1 Seyfert galaxy NGC 3516 are presented. The radio maps reveal an elongated one-sided curved structure, which comprises a series of small-scale 'blobs' and extends up to 4 kpc from the nucleus. This radio structure is aligned and cospatial with one side of the double-sided and highly symmetric Z-shaped emission-line structure. It is argued that these morphological features are associated with a bipolar gaseous outflow from the nucleus of NGC 3516. The radio 'blobs' are elongated roughly perpendicular to the apparent local direction of the outflow, a result which is interpreted in terms of synchrotron emission from outflow-driven shock waves.

Miyaji, Takamitsu; Wilson, Andrew S.; Perez-Fournon, Ismael

1992-01-01

366

NGC 3147: a 'true' type 2 Seyfert galaxy without the broad-line region  

NASA Astrophysics Data System (ADS)

We report on simultaneous optical and X-ray observations of the Seyfert galaxy, NGC3147. The XMM-Newton spectrum shows that the source is unabsorbed in the X-rays ( N_H < 5 10^20 cm ^-2 ). On the other hand, no broad lines are present in the optical spectrum. The origin of this optical/X-rays misclassification (with respect to the Unification Model) cannot be attributed to variability, since the observations in the two bands are simultaneous. Moreover, a Compton-thick nature of the object can be rejected on the basis of the low equivalent width of the iron K alpha line ( ~eq 130 eV) and the large ratio between the 2-10 keV and the [OIII] fluxes. It seems therefore inescapable to conclude that NGC3147 intrinsically lacks the Broad Line Region (BLR), making it the first 'true' Seyfert 2.

Bianchi, S.; Corral, A.; Panessa, F.; Barcons, X.; Matt, G.; Bassani, L.; Carrera, F. J.; Jimnez-Bailn, E.

2008-10-01

367

The X-ray spectrum and variability of the Seyfert 2 galaxy NGC 7172  

NASA Astrophysics Data System (ADS)

We present evidence of flux variability, on both short (hours) and long (months) time-scales, of the Seyfert 2 galaxy NGC 7172. These results are based on the ASCA observation of NGC 7172 performed in 1996 May. The source was detected at a rather low flux level, about 3 times fainter than its usual state (including 1 yr before, when it was also observed by ASCA). The source also varied by about 30 per cent during the observation, confirming the presence of a type 1 nucleus in its centre. However, its spectrum appears to be flatter than the typical Seyfert 1 spectrum (in agreement with findings on other Seyfert 2s), posing problems for the unification model unless complex absorption is invoked.

Guainazzi, M.; Matt, G.; Antonelli, L. A.; Fiore, F.; Piro, L.; Ueno, S.

1998-08-01

368

HIERARCHICAL STELLAR STRUCTURES IN THE LOCAL GROUP DWARF GALAXY NGC 6822  

SciTech Connect

We present a comprehensive study of the star cluster population and the hierarchical structure in the clustering of blue stars with ages {approx}<500 Myr in the Local Group dwarf irregular galaxy NGC 6822. Our observational material comprises the most complete optical stellar catalog of the galaxy from imaging with the Suprime-Cam at the 8.2 m Subaru Telescope. We identify 47 distinct star clusters with the application of the nearest-neighbor density method to this catalog for a detection threshold of 3{sigma} above the average stellar density. The size distribution of the detected clusters can be very well approximated by a Gaussian with a peak at {approx}68 pc. The total stellar masses of the clusters are estimated by extrapolating the cumulative observed stellar mass function of all clusters to be in the range 10{sup 3}-10{sup 4} M{sub sun}. Their number distribution is fitted very well by a power law with index {alpha} {approx} 1.5 {+-} 0.7, which is consistent with the cluster mass functions of other Local Group galaxies and the cluster initial mass function. In addition to the detected star clusters of the galaxy, the application of the nearest-neighbor density method for various density thresholds, other than 3{sigma}, enabled the identification of stellar concentrations in various lengthscales. The stellar density maps constructed with this technique provide a direct proof of hierarchically structured stellar concentrations in NGC 6822, in the sense that smaller dense stellar concentrations are located inside larger and looser ones. We illustrate this hierarchy by the so-called dendrogram, or structure tree of the detected stellar structures, which demonstrates that most of the detected structures split up into several substructures over at least three levels. We quantify the hierarchy of these structures with the use of the minimum spanning tree method. We find that structures detected at 1, 2, and 3{sigma} density thresholds are hierarchically constructed with a fractal dimension of D {approx} 1.8. Some of the larger stellar concentrations, particularly in the northern part of the central star-forming portion of the galaxy, coincide with IR-bright complexes previously identified with Spitzer and associated with high column density neutral gas, indicating structures that currently form stars. The morphological hierarchy in stellar clustering, which we observe in NGC 6822, resembles that of the turbulent interstellar matter, suggesting that turbulence on pc and kpc scales has been probably the major agent that regulated clustered star formation in NGC 6822.

Gouliermis, Dimitrios A.; Walter, Fabian [Max Planck Institute for Astronomy, Koenigstuhl 17, 69117 Heidelberg (Germany); Schmeja, Stefan; Klessen, Ralf S. [Zentrum fuer Astronomie der Universitaet Heidelberg, Institut fuer Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg (Germany); De Blok, W. J. G., E-mail: dgoulier@mpia-hd.mpg.d, E-mail: walter@mpia-hd.mpg.d, E-mail: sschmeja@ita.uni-heidelberg.d, E-mail: rklessen@ita.uni-heidelberg.d, E-mail: edeblok@ast.uct.ac.z [University of Cape Town, Private Bag X3, Rondebosch 7701 (South Africa)

2010-12-20

369

The radio core structure of the luminous infrared galaxy NGC 4418. A young clustered starburst revealed?  

NASA Astrophysics Data System (ADS)

Context. The galaxy NGC 4418 contains one of the most compact obscured nuclei within a luminous infrared galaxy (LIRG) in the nearby Universe. This nucleus contains a rich molecular gas environment and an unusually high ratio of infrared-to-radio luminosity (q-factor). The compact nucleus is powered by either a compact starburst or an active galactic nucleus (AGN). Aims: The aim of this study is to constrain the nature of the nuclear region (starburst or AGN) within NGC 4418 via very-high-resolution radio imaging. Methods: Archival data from radio observations using the European Very Long Baseline Interferometry Network (EVN) and Multi-Element Radio Linked Interferometer Network (MERLIN) interferometers are imaged. Sizes and flux densities are obtained by fitting Gaussian intensity distributions to the image. The average spectral index of the compact radio emission is estimated from measurements at 1.4 GHz and 5.0 GHz. Results: The nuclear structure of NGC 4418 visible with EVN and MERLIN consists of eight compact (<49 mas i.e. <8 pc) features spread within a region of 250 mas, i.e. 41 pc. We derive an inverted spectral index ? ? 0.7 (S? ? ??) for the compact radio emission. Conclusions: Brightness temperatures >104.8 K indicate that these compact features cannot be HII-regions. The complex morphology and inverted spectrum of the eight detected compact features is evidence against the hypothesis that an AGN alone is powering the nucleus of NGC 4418. The compact features could be super star clusters with intense star formation, and their associated free-free absorption could then naturally explain both their inverted radio spectrum and the low radio-to-IR ratio of the nucleus. The required star formation area density is extreme, however, and close to the limit of what can be observed in a well-mixed thermal/non-thermal plasma produced by star formation, and is also close to the limit of what can be physically sustained.

Varenius, E.; Conway, J. E.; Mart-Vidal, I.; Aalto, S.; Beswick, R.; Costagliola, F.; Klckner, H.-R.

2014-06-01

370

DEEP CHANDRA OBSERVATIONS OF EDGES AND BUBBLES IN THE NGC 5846 GALAXY GROUP  

SciTech Connect

We use a combined 120 ks Chandra exposure to analyze X-ray edges produced by non-hydrostatic gas motions (sloshing) from galaxy collisions, and cavities formed by active galactic nucleus (AGN) activity. Evidence for gas sloshing is seen in the spiral morphology and multiple cold front edges in NGC 5846's X-ray surface brightness distribution, while the lack of spiral structure in the temperature map suggests that the perturbing interaction was not in the plane of the sky. Density and spectral modeling across the edges indicate that the relative motion of gas in the cold fronts is at most transonic. Evidence for AGN activity is seen in two inner bubbles at 0.6 kpc, filled with 5 GHz and 1.5 GHz radio plasma and coincident with H{alpha} emission, and in a ghost bubble at 5.2 kpc west of NGC 5846's nucleus. The outburst energy and ages for the inner (ghost) bubbles are {approx}10{sup 55} erg and {approx}2 Myr ({approx}5 Multiplication-Sign 10{sup 55} erg and 12 Myr), respectively, implying an AGN duty cycle of 10 Myr. The inner bubble rims are threaded with nine knots, whose total 0.5-2 keV X-ray luminosity is 0.3 Multiplication-Sign 10{sup 40} erg s{sup -1}, a factor {approx}2-3 less than that of the surrounding rims, and 0.7 keV mean temperature is indistinguishable from that of the rims. We suggest that the knots may be transient clouds heated by the recent passage of a shock from the last AGN outburst. We also observe gas stripping from a cE galaxy, NGC 5846A, in a 0.5 kpc long ({approx}10{sup 5} M{sub Sun }) hot gas tail, as it falls toward NGC 5846.

Machacek, Marie E.; Jerius, Diab; Kraft, Ralph; Forman, William R.; Jones, Christine; Randall, Scott [Harvard-Smithsonian Center for Astrophysics 60 Garden Street, Cambridge, MA 02138 (United States); Giacintucci, Simona [Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States); Sun Ming, E-mail: mmachacek@cfa.harvard.edu [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22901 (United States)

2011-12-10

371

THE YOUNG STELLAR POPULATION OF THE NEARBY LATE-TYPE GALAXY NGC 1311  

SciTech Connect

We have extracted point-spread-function-fitted stellar photometry from near-ultraviolet, optical, and near-infrared images, obtained with the Hubble Space Telescope, of the nearby (D {approx} 5.5 Mpc) SBm galaxy NGC 1311. The ultraviolet and optical data reveal a population of hot main-sequence (MS) stars with ages of 2-10 Myr. We also find populations of blue supergiants with ages between 10 and 40 Myr and red supergiants with ages between 10 and 100 Myr. Our near-infrared data show evidence of star formation going back {approx}1 Gyr, in agreement with previous work. Fits to isochrones indicate a metallicity of Z {approx} 0.004. The ratio of blue to red supergiants is consistent with this metallicity. This indicates that NGC 1311 follows the well-known luminosity-metallicity relation for late-type dwarf galaxies. About half of the hot MS stars and blue supergiants are found in two regions in the inner part of NGC 1311. These two regions are each about 200 pc across, and thus have crossing times roughly equal to the 10 Myr age we find for the dominant young population. The luminosity functions of the supergiants indicate a slowly rising star formation rate ({approx}10{sup -3} M{sub sun} yr{sup -1}) from {approx}100 Myr ago until {approx}15 Myr ago, followed by a strong enhancement ({approx}10{sup -2} M{sub sun} yr{sup -1}) at {approx}10 Myr ago. We see no compelling evidence for gaps in the star-forming history of NGC 1311 over the last 100 Myr, and, with lower significance, none over the last Gyr. This argues against a bursting mode, and in favor of a gasping or breathing mode for the rece