Sample records for barred galaxy ngc

  1. Face on Barred and Ringed Spiral Galaxy NGC 3351

    NASA Technical Reports Server (NTRS)

    2005-01-01

    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.

  2. The Mass Inflow Rate in the Barred Galaxy NGC 1530

    E-print Network

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

    1997-04-01

    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.

  3. STAR FORMATION EFFICIENCY IN THE BARRED SPIRAL GALAXY NGC 4303

    SciTech Connect

    Momose, Rieko [Department of Astronomy, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Okumura, Sachiko K.; Sawada, Tsuyoshi [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Koda, Jin, E-mail: momo.s.rieko@nao.ac.j, E-mail: sokumura@nro.nao.ac.j, E-mail: tsawada@alma.c, E-mail: Jin.Koda@stonybrook.ed [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800 (United States)

    2010-09-20

    We present new {sup 12}CO (J = 1 - 0) observations of the barred galaxy NGC 4303 using the Nobeyama 45 m telescope (NRO45) and the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The H{alpha} images of barred spiral galaxies often show active star formation in spiral arms, but less so in bars. We quantify the difference by measuring star formation rate (SFR) and star formation efficiency (SFE) at a scale where local star formation is spatially resolved. Our CO map covers the central 2.'3 region of the galaxy; the combination of NRO45 and CARMA provides a high fidelity image, enabling accurate measurements of molecular gas surface density. We find that SFR and SFE are twice as high in the spiral arms as in the bar. We discuss this difference in the context of the Kennicutt-Schmidt (KS) law, which indicates a constant SFR at a given gas surface density. The KS law breaks down at our native resolution ({approx}250 pc), and substantial smoothing (to 500 pc) is necessary to reproduce the KS law, although with greater scatter.

  4. Multiband Images of the Barred Galaxy NGC 1097

    NASA Astrophysics Data System (ADS)

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

    1995-07-01

    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.

  5. The near-infrared structure of the barred galaxy NGC 253 from VISTA?

    NASA Astrophysics Data System (ADS)

    Iodice, E.; Arnaboldi, M.; Rejkuba, M.; Neeser, M. J.; Greggio, L.; Gonzalez, O. A.; Irwin, M.; Emerson, J. P.

    2014-07-01

    Context. The presence of a bar affects the distribution and dynamics of a stellar disk at all scales, from a fraction of a kpc in the inner central region to tens of kpc at the disk's edge. The quantitative study of the disk response to a bar can be hampered by the presence of dust, which is common in late type spirals. Aims: We want to quantify the structures in the stellar disk of the barred Sc galaxy NGC 253 located in the Sculptor group, at 3.47 Mpc distance. Methods: We use J and Ks band images acquired with the VISTA telescope as part of the Science Verification. The wide field of view and the high angular resolution of this survey facility allow the mapping of the large and small scale structure of the stellar disk in NGC 253. We use unsharp masking and two dimensional modelling of the smooth light distribution in the disk to identify and measure the sub-structures induced by the bar in the stellar disk of NGC 253. We build azimuthally-averaged profiles in the J and Ks bands to measure the radial surface brightness profile of the central bulge, bar and disk. Results: Moving outward from the galaxy center, we find a nuclear ring within the bright 1 kpc diameter nucleus, then a bar, a ring with 2.9 kpc radius, and spiral arms in the outer disk. From the Ks image we obtain a new measure of the de-projected length of the bar of 2.5 kpc. The bar's strength, as derived from the curvature of the dust lanes in the J-Ks image, is typical of weak bars with ?? = 25 degree/kpc. From the de-projected length of the bar, we establish the co-rotation radius (RCR = 3 kpc) and bar pattern speed (?b = 61.3 km s-1 kpc-1), which provides the connection between the high frequency structures in the disk and the orbital resonances induced by the bar. The nuclear ring is located at the Inner Lindblad resonance. The second ring (at 2.9 kpc) does not have a resonant origin, but it could be a merger remnant or a transient structure formed during an intermediate stage of the bar formation. The inferred bar pattern speed places the Outer Lindblad resonance within the optical disk at 4.9 kpc, in the same radial range as the peak in the HI surface density. The disk of NGC 253 has a down-bending profile with a break at R ~ 9.3 kpc, which corresponds to about 3 times the scale length of the inner disk. We discuss the evidence for a threshold in star formation efficiency as a possible explanation for the steep gradient in the surface brightness profile at large radii. Conclusions: The near-infrared photometry unveils the dynamical response of the NGC 253 stellar disk to its central bar. The formation of the bar may be related to the merger event that determined the truncation of stars and gas at large radii and the perturbation of the disk's outer edge. This work is based on observations taken at the ESO La Silla Paranal Observatory within the VISTA Science Verification Program ID 60.A-9285(A). The full set of OBs for the NGC 253 deep and shallow images are available on the ESO archive on the VISTA SV page, at the following link http://www.eso.org/sci/activities/vistasv/VISTA_SV.html

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

    NASA Technical Reports Server (NTRS)

    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

    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.

  7. The Disk and Dark Halo Mass of the Barred Galaxy NGC 4123. II. Fluid-Dynamical Models

    E-print Network

    Benjamin J. Weiner; J. A. Sellwood; T. B. Williams

    2000-08-14

    We report a dynamical determination of the separate contributions of disk and dark halo masses to the rotation curve of a spiral galaxy. We use fluid-dynamical models of gas flow in the barred galaxy NGC 4123 to constrain the dynamical properties of the galaxy: disk M/L, bar pattern speed, and the central density and scale radius of the dark halo. We derive a realistic barred potential directly from the light distribution. For each model we assume a value of the stellar M/L and a bar pattern speed Omega_p and add a dark halo to fit the rotation curve. We then compute the gas flow velocities with a 2-D gas dynamical code, and compare the model flow patterns to a 2-D velocity field derived from Fabry-Perot observations. The strong shocks and non-circular motions in the observed gas flow require a high stellar M/L and a fast-rotating bar. Models with I-band disk M/L of 2.0 -- 2.5 h_75, or 80 -- 100% of the maximum disk value, are highly favored. The corotation radius of the bar must be <= 1.5 times the bar semi-major axis. These results contradict some recent claimed ``universal'' galaxy disk/halo relations, since NGC 4123 is of modest size (rotation curve maximum 145 km/sec, and V_flat = 130 km/sec) yet is quite disk-dominated. The dark halo of NGC 4123 is less concentrated than favored by current models of dark halos based on cosmological simulations. Since some 30% of bright disk galaxies are strongly barred and have dust lanes indicating shock morphology similar to that of NGC 4123, it is likely that they also have high stellar M/L and low density halos. We suggest that luminous matter dominates inside the optical radius R_25 of high surface brightness disk galaxies.

  8. Stellar bar in NGC 1068

    SciTech Connect

    Scoville, N.Z.; Matthews, K.; Carico, D.P.; Sanders, D.B.

    1988-04-01

    High-resolution 2-micron mapping of the inner disk of NGC 1068 reveals a bar extending to + or - 16 arcsec from the nucleus at position angle 48 deg. The stellar mass distribution, presumably traced by the near-infrared light, is therefore strongly nonaxisymmetric with a contrast of approximately 3:1 between the major and minor axes of the bar. This large-scale galactic structure is probably responsible for the concentration of molecular clouds in a ring just outside the bar. The massive bar may also drive noncircular motions in the inner disk of the galaxy as possibly seen in the gaseous emission lines. 21 references.

  9. ASTE CO(3--2) Observations of the Southern Barred Spiral Galaxy NGC 986: a Large Gaseous Bar Filled with Dense Molecular Medium

    E-print Network

    Kohno, K; Miura, R; Muraoka, K; Sawada, T; Nakanishi, K; Kuno, N; Sakai, T; Sorai, K; Kamegai, K; Tanaka, K; Okuda, T; Endo, A; Hatsukade, B; Sameshima, M; Ezawa, H; Sakamoto, S; Kamazaki, T; Cortés, J; Tamura, Y; Fukuhara, M; Iono, D; Kawabe, R

    2008-01-01

    We present CO(3-2) emission observations toward the 3'x3' (or 20x20kpc at a distance of 23Mpc) region of the southern barred spiral galaxy NGC 986 using the Atacama Submillimeter Telescope Experiment (ASTE). This effort is a part of our on-going extragalactic CO(3-2) imaging project ADIoS (ASTE Dense gas Imaging of Spiral galaxies). Our CO(3-2) image revealed the presence of a large (the major axis is 14 kpc in total length) gaseous bar filled with dense molecular medium along the dark lanes observed in optical images. This is the largest ``dense-gas rich bar'' known to date. The dense gas bar discovered in NGC 986 could be a huge reservoir of possible ``fuel'' for future starbursts in the central region, and we suggest that the star formation in the central region of NGC 986 could still be in a growing phase. We found a good spatial coincidence between the overall distributions of dense molecular gas traced by CO(3-2) and the massive star formation depicted by H$\\alpha$. The global CO(3-2) luminosity $L'_{\\r...

  10. ASTE CO(3-2) Observations of the Southern Barred Spiral Galaxy NGC 986: a Large Gaseous Bar Filled with a Dense Molecular Medium

    NASA Astrophysics Data System (ADS)

    Kohno, Kotaro; Tosaki, Tomoka; Miura, Rie; Muraoka, Kazuyuki; Sawada, Tsuyoshi; Nakanishi, Kouichiro; Kuno, Nario; Sakai, Takeshi; Sorai, Kazuo; Kamegai, Kazuhisa; Tanaka, Kunihiko; Okuda, Takeshi; Endo, Akira; Hatsukade, Bunyo; Sameshima, Masahiro; Ezawa, Hajime; Sakamoto, Seiichi; Kamazaki, Takeshi; Yamaguchi, Nobuyuki; Cortés, Juan; Tamura, Yoichi; Fukuhara, Masayuki; Iono, Daisuke; Kawabe, Ryohei

    2008-06-01

    We present CO(3-2) emission observations toward the 3'×3' (or 20kpc×20kpc at a distance of 23Mpc) region of the southern barred spiral galaxy NGC 986 using the Atacama Submillimeter Telescope Experiment (ASTE). This effort is a part of our on-going extragalactic CO(3-2) imaging project, ADIoS (ASTE Dense gas Imaging of Spiral galaxies). Our CO(3-2) image revealed the presence of a large (the major axis is 14kpc in total length) gaseous bar filled with a dense molecular medium along the dark lanes observed in optical images. This is the largest “dense-gas rich bar” known to date. The dense gas bar, discovered in NGC 986, could be a huge reservoir of possible “fuel” for future starbursts in the central region, and we suggest that star formation in the central region of NGC 986 could still be in a growing phase. We found a good spatial coincidence between the overall distributions of dense molecular gas traced by CO(3-2) and massive star formation depicted by H?. The global CO(3-2) luminosity, LCO(3-2), of NGC 986 was determined to be (5.4±1.1)×108Kkms-1pc2. The CO(3-2)/CO(1-0) integrated intensity ratio was found to be 0.60±0.13 at a spatial resolution of 44'' or 5kpc, and the CO(3-2)/CO(2-1) ratio was 0.67±0.14 at a beam size of ˜25'' or ˜2.8kpc. These line ratios suggest moderate excitation conditions of CO lines (nH2˜103-4cm-3) in a few kiloparsec region of central NGC 986.

  11. ASTE CO(3--2) Observations of the Southern Barred Spiral Galaxy NGC 986: a Large Gaseous Bar Filled with Dense Molecular Medium

    E-print Network

    K. Kohno; T. Tosaki; R. Miura; K. Muraoka; T. Sawada; K. Nakanishi; N. Kuno; T. Sakai; K. Sorai; K. Kamegai; K. Tanaka; T. Okuda; A. Endo; B. Hatsukade; M. Sameshima; H. Ezawa; S. Sakamoto; T. Kamazaki; J. Cortes; Y. Tamura; M. Fukuhara; D. Iono; R. Kawabe

    2008-05-10

    We present CO(3-2) emission observations toward the 3'x3' (or 20x20kpc at a distance of 23Mpc) region of the southern barred spiral galaxy NGC 986 using the Atacama Submillimeter Telescope Experiment (ASTE). This effort is a part of our on-going extragalactic CO(3-2) imaging project ADIoS (ASTE Dense gas Imaging of Spiral galaxies). Our CO(3-2) image revealed the presence of a large (the major axis is 14 kpc in total length) gaseous bar filled with dense molecular medium along the dark lanes observed in optical images. This is the largest ``dense-gas rich bar'' known to date. The dense gas bar discovered in NGC 986 could be a huge reservoir of possible ``fuel'' for future starbursts in the central region, and we suggest that the star formation in the central region of NGC 986 could still be in a growing phase. We found a good spatial coincidence between the overall distributions of dense molecular gas traced by CO(3-2) and the massive star formation depicted by H$\\alpha$. The global CO(3-2) luminosity $L'_{\\rm CO(3-2)}$ of NGC 986 was determined to be $(5.4 \\pm 1.1) \\times 10^8$ K km s$^{-1}$ pc$^2$. The CO(3-2)/CO(1-0) integrated intensity ratio was found to be 0.60 +/- 0.13 at a spatial resolution of 44'' or 5 kpc, and a CO(3-2)/CO(2-1) ratio was 0.67 +/- 0.14 at a beam size of ~25'' or ~2.8 kpc. These line ratios suggest moderate excitation conditions of CO lines ($n_{\\rm H_2} \\sim 10^{3-4}$ cm$^{-3}$) in the central a few kpc region of NGC 986.

  12. Numerical Simulations of Major Barred Galaxies

    Microsoft Academic Search

    Chien-Chang Yen; L. Lin; C. Yuan

    2006-01-01

    Galaxies with major bars such as NGC1300 and NGC1097, are characterized by straight dust lanes, central starburst ring and outer spirals. Recent IR observations also show there are star formation patches and spur-like substructures. Through numerical simulations, we can reproduce the dust lanes, the central starburst ring, and the outer spirals by imposing a single strong bar potential on a

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

    SciTech Connect

    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

    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.

  14. Galaxy NGC 1512

    NASA Technical Reports Server (NTRS)

    1999-01-01

    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.

  15. Morphology of Cold Bars in Early and Late Type Galaxies

    E-print Network

    A. C. Quillen

    1996-09-05

    We compare stellar orbits in an early (NGC 4314) and a late-type barred galaxy (NGC 1073). We find that these bars are cold in the sense that the majority of stars can be described as being nearby to periodic orbits. We place limits of (65km/s)^2 and (50km/s)^2 on the components of the diagonalized velocity dispersion ellipsoid matrix for stars in the bars of NGC 4314 and NGC 1073 respectively. Both bars end near the inner 4:1 Lindblad (ultraharmonic) resonance. We conjecture that a large class of bars end near this resonance. The morphology of the bars depends on the strength of the 4:1 resonance, which is strong in the early-type barred galaxy and weak in the other. This results in a flat bar major axis surface brightness profile for the early-type bar and an exponential profile for the late-type bar.

  16. Kinematic and Photometric Evidence for a Bar in NGC 2683

    E-print Network

    de Naray, Rachel Kuzio; McGaugh, Stacy S

    2009-01-01

    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.

  17. KINEMATIC AND PHOTOMETRIC EVIDENCE FOR A BAR IN NGC 2683

    SciTech Connect

    Kuzio de Naray, Rachel [Center for Cosmology, Department of Physics and Astronomy, University of California, Irvine, CA 92697-4575 (United States); Zagursky, Matthew J.; McGaugh, Stacy S. [Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States)], E-mail: kuzio@uci.edu, E-mail: mzagursk@umd.edu, E-mail: ssm@astro.umd.edu

    2009-10-15

    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 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.

  18. Structure and kinematics of candidate double-barred galaxies

    E-print Network

    A. V. Moiseev; J. R. Valdes; V. H. Chavushyan

    2004-02-02

    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 6m telescope (BTA) of SAO RAS, with the MPFS spectrograph and the scanning Fabry-Perot Interferometer. NGC2681 was also observed with the long-slit spectrograph of the BTA. Optical and NIR images were obtained at the BTA and at the 2.1m telescope (OAN, M\\'exico). 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. NGC3368 and NGC3786 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 (NGC2681, NGC3368 and NGC5850) are considered. We found ionized-gas counter-rotation in the central kiloparsec of the lenticular galaxy NGC3945. Seven galaxies (NGC470, NGC2273, NGC2681, NGC3945, NGC5566, NGC5905, and NGC6951) 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.

  19. A two-arm gaseous spiral in the inner 200 pc of the early-type galaxy NGC 2974: signature of an inner bar

    NASA Astrophysics Data System (ADS)

    Emsellem, Eric; Goudfrooij, Paul; Ferruit, Pierre

    2003-11-01

    TIGER integral-field spectrography and Hubble Space Telescope Wide Field and Planetary Camera 2 (WFPC2) imaging of the E3 galaxy NGC 2974 are used to derive the kinematics of the stellar and ionized gas components in its central 500 pc. We derive a numerical two-integral distribution function from a multi-Gaussian expansion (MGE) mass model using the Hunter & Qian formalism. The TIGER and published long-slit stellar kinematics, including higher-order moments, are well fitted with this self-consistent model, requiring neither the addition of a significant mass contribution from a hidden disc structure nor the presence of a central dark mass (at that spatial resolution). The data reveal the presence of a striking, highly contrasted, two-arm gaseous spiral structure within a radius of ~200 pc, corresponding to a total mass of 6.8 × 104 solar masses of ionized gas. We use a deconvolved TIGER data cube to probe its kinematics at a resolution of about 0.35 arcsec FWHM. Strong departures from circular motions are observed, as well as high velocity dispersion values on the inner side of the arms. We interpret the observed gas morphology and kinematics as the signature of streaming gas flows driven by a ~540-pc diameter bar with ?p= 700 +/- 100 km s-1 kpc-1. This hypothesis is strongly supported by the predictions of a density wave model. This model predicts that the bar should lie at about 35° from the line of nodes, and implies gas inflow towards the central ~50 pc. The quadrupole perturbation due to this bar is estimated to represent less than 2 per cent of the underlying gravitational potential (a maximum torque of about 10 per cent), explaining the lack of a direct detection via broad-band photometry in the visible. Despite its weakness, the inner bar of NGC 2974 may be able to drive some gas within a 10-pc radius. We suggest that the presence of such inner bars might be more common among early-type disc galaxies than is generally thought, and that deep high-resolution emission-line imagery may be the best way to detect such structures.

  20. Gas flow in barred galaxies

    E-print Network

    E. Athanassoula

    2000-06-28

    I briefly review the properties of the gas flow in and around the region of the bar in a disc galaxy and discuss the corresponding inflow and the loci of star formation. I then review the flow of gas in barred galaxies which have an additional secondary bar. Finally I discuss the signatures of bars in edge-on galaxies.

  1. Galaxy NGC 1850

    NASA Technical Reports Server (NTRS)

    1999-01-01

    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.

  2. Are bars essential for starbursts in non-interacting galaxies

    NASA Technical Reports Server (NTRS)

    Pompea, Stephen M.; Rieke, G. H.

    1990-01-01

    Analyzed here are the 1.6 and 2.2 micron images of a sample of galaxies that are classified as unbarred by the Revised Shapley-Ames Catalog. These galaxies have characteristic properties of nuclear starbursts and are examined through near infrared imaging in a search for hidden bars. Researchers selected a sample of 36 galaxies from the Revised Shapley-Ames Catalog that have far infrared luminosities greater than 10(exp 10) solar luminosity and hot Infrared Astronomy Satellite (IRAS) colors between 60 and 100 microns, indicative of nuclear starbursts, but are not classified as Seyfert 1 or 2. Their determination of the presence of a bar relies primarily on an analysis of the 2 micron image using the Galaxy Surface Photometry (GASP) package (Cawson, 1983). The GASP analysis programs determine the galaxy surface brightness and ellipticity profiles as well as the position angle and the center coordinates of the ellipses. To test the way that GASP will characterize the surface brightness of barred galaxies, two galaxies with known bars, NGC 1068 and NGC 2523, were imaged with the 2 micron camera and analyzed with GASP. Fifteen of the sample that are not clearly barred from optical data and are isolated were imaged at 1.6 and 2.2 microns; 9 of these do not appear to have bars. Strong bars therefore do not appear to be an absolute requirement for high infrared luminosity in isolated galaxies.

  3. Molecular bar and star formation in the nucleus of NGC 6946

    SciTech Connect

    Ball, R.; Sargent, A.I.; Scoville, N.Z.; Lo, K.Y.; Scott, S.L.

    1985-11-15

    We have observed the bright, nearby galaxy NGC 6946 in the 2.6 mm line of CO with the Owens Valley Millimeter-Wave Interferometer, synthesizing a beam 7''.6 by 5''.4. The molecular gas in the central 1.5 kpc of the galaxy is confined to a bar of extent approx.2700 pc by 550 pc, which is centered on the nucleus and connects two dust lanes in the innermost spiral arms. The molecular bar is the likely source of the star formation activity suggested by optical and infrared studies in the nucleus of NGC 6946.

  4. Molecular bar and star formation in the nucleus of NGC 6946

    SciTech Connect

    Ball, R.; Sargent, A.I.; Scoville, N.Z.; Lo, K.Y.; Scott, S.L.

    1985-11-01

    The bright, nearby galaxy NGC 6946 in the 2.6 mm line of CO has been observed with the Owens Valley Millimeter-Wave Interferometer, synthesizing a beam 7.6 arc sec by 5.4 arc sec. The molecular gas in the central 1.5 kpc of the galaxy is confined to a bar of extent of approximately 2700 pc by 550 pc, which is centered on the nucleus and connects two dust lanes in the innermost spiral arms. The molecular bar is the likely source of the star formation activity suggested by optical and infrared studies in the nucleus of NGC 6946. 34 references.

  5. Photometric Decomposition of Barred Galaxies

    E-print Network

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

    2007-02-27

    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.

  6. On the bar pattern speed determination of NGC 3367

    E-print Network

    Gabbasov, R F; Rosado, M

    2009-01-01

    An important dynamic parameter of barred galaxies is the bar pattern speed. Among several methods that are used for the determination of the pattern speed the Tremaine-Weinberg method has the advantage of model independency and accuracy. In this work we apply the method to a simulated bar including gas dynamics and study the effect of 2D spectroscopy data quality on robustness of the method. We added a white noise and a Gaussian random field to the data and measured the corresponding errors in the pattern speed. We found that a signal to noise ratio in surface density ~5 introduces errors of ~20% for the Gaussian noise, while for the white noise the corresponding errors reach ~50%. At the same time the velocity field is less sensitive to contamination. On the basis of the performed study we applied the method to the NGC 3367 spiral galaxy using H{\\alpha} Fabry-Perot interferometry data. We found for the pattern speed 43 \\pm 6 km/s/kpc for this galaxy.

  7. The Superwind Galaxy NGC 4666

    NASA Astrophysics Data System (ADS)

    2010-09-01

    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 für 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".

  8. Dynamical Evolution of Barred Galaxies

    E-print Network

    E. Athanassoula

    2005-01-11

    Angular momentum redistribution within barred galaxies drives their dynamical evolution. Angular momentum is emitted mainly by near-resonant material in the bar region and absorbed by resonant material mainly in the outer disc and in the halo. This exchange determines the strength of the bar, the decrease of its pattern speed, as well as its morphology. If the galaxy has also a gaseous component and/or a companion or satellite, then these also take part in the angular momentum exchange. During the evolution a bar structure forms in the inner parts of the halo as well. This bar is shorter and fatter than the disc bar and stays so all through the simulation, although its length grows considerably with time. Viewed edge-on, the bar in the disc component acquires a boxy or peanut shape. I describe the families of periodic orbits that explain such structures and review the observations showing that boxy/peanut `bulges' are in fact just bars seen edge-on.

  9. MASSIVE BLACK HOLES IN GALAXIES NGC 3377, NGC 3379 AND NGC 4486B

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The three galaxies above are believed to contain central, supermassive black holes. The galaxy NGC 4486B (lower-left) shows a double nucleus (lower-right). The images of NGC 3377 and NGC 4486B are 2.7 arcseconds on a side, and for NGC 3379 the size is 5.4 arcseconds; the lower-right is a blow-up of the central 0.5 arcseconds of NGC 4486B. Credit: Karl Gebhardt (University of Michigan) and Tod Lauer (NOAO)

  10. Magnetohydrodynamic Simulations of Barred Galaxies

    NASA Astrophysics Data System (ADS)

    Kim, W.-T.

    2013-04-01

    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.

  11. Bar instabilities in Coma cluster galaxies

    SciTech Connect

    Thompson, L.A.

    1981-03-01

    The radial distribution of bar versus nonbar galaxies within the Coma cluster shows that a significantly larger fraction of bar galaxies are members of the cluster core. This result can be used either to estimate the time scale for the decay of bar instabilities or to argue that galaxies in the core of Coma are confined within the core.

  12. Constraining the formation of inner bars: photometry, kinematics and stellar populations in NGC 357

    NASA Astrophysics Data System (ADS)

    de Lorenzo-Cáceres, A.; Vazdekis, A.; Aguerri, J. A. L.; Corsini, E. M.; Debattista, Victor P.

    2012-02-01

    Double-barred galaxies are common in the local Universe, with approximately one-third of barred spirals hosting a smaller, inner bar. Nested bars have been proposed as a mechanism to transport gas to the very central regions of the galaxy, trigger star formation and contribute to the growth of the bulge. To test this idea, we perform for the first time a detailed analysis of the photometry, kinematics and stellar populations of a double-barred galaxy: NGC 357. We find that this galaxy is either hosting a pseudo-bulge or a classical bulge together with an inner disc. We compare the relative mean luminosity-weighted age, metallicity and ?-enhancement between the (pseudo-)bulge, inner bar and outer bar, finding that the three structures are nearly coeval and old. Moreover, the bulge and inner bar present the same metallicity and overabundance, whereas the outer bar tends to be less metal rich and more ?-enhanced. These results point out that, rather than the classical secular scenario in which gas and star formation play a major role, the redistribution of the existing stars is driving the formation of the inner structures. Based on observations carried out at the European Southern Observatory (ESO 70.B-0338).

  13. Galaxy Zoo: Observing Secular Evolution Through Bars

    NASA Astrophysics Data System (ADS)

    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

    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.

  14. Galaxy Zoo: Observing Secular Evolution Through Bars

    E-print Network

    Cheung, Edmond; 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

    2013-01-01

    Observations have shown that there is a connection between the presence of a bar and the properties of a galaxy. In a parallel effort, simulations have shown that this connection is consistent with the theory of bar-driven secular evolution. But observational evidence of bar-driven secular evolution has been sparse. In this paper, we use the Galaxy Zoo 2 dataset to look for evidence of this secular evolution. 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. We characterize bars by the bar likelihood, the likelihood a bar is present in a given galaxy, and the bar length. These two bar properties show interesting correlations with the specific star formation rate and the inner central structure of galaxies. Comparing these observations to state-of-the-art simulations of bar evolution, which include live halos and ...

  15. The Bar Pattern Speed of NGC 1433 Estimated Via Sticky-Particle Simulations

    E-print Network

    P. Treuthardt; H. Salo; P. Rautiainen; R. Buta

    2008-05-02

    We present detailed numerical simulations of NGC 1433, an intermediate-type barred spiral showing strong morphological features including a secondary bar, nuclear ring, inner ring, outer pseudoring, and two striking, detached spiral arcs known as ``plumes.'' This galaxy is an ideal candidate for recreating the observed morphology through dynamical models and determining the pattern speed. We derived a gravitational potential from an $H$-band image of the galaxy and simulated the behavior of a two-dimensional disk of 100,000 inelastically colliding gas particles. We find that the closest matching morphology between a $B$-band image and a simulation occurs with a pattern speed of 0.89 km s$^{-1}$ arcsec$^{-1}$ $\\pm$ 5-10%. We also determine that the ratio of corotation radius to the average published bar radius is 1.7 $\\pm$ 0.3, with the ambiguity in the bar radius being the largest contributor to the error.

  16. The Odd Offset between the Galactic Disk and Its Bar in NGC 3906

    E-print Network

    de Swardt, Bonita; Kim, Taehyun; Pardy, Stephen; D'Onghia, Elena; Wilcots, Eric; Hinz, Joannah; Munoz-Mateos, Juan-Carlos; Regan, Michael W; Athanassoula, E; Bosma, Albert; Buta, Ronald J; Cisternas, Mauricio; Comeron, S ebastien; Gadotti, Dimitri A; de Paz, Armando Gil; Jarrett, Thomas H; Elmegreen, Bruce G; Erroz-Ferrer, Santiago; Ho, Luis C; Knapen, Johan H; Laine, Jarkko; Laurikainen, Eija; Madore, Barry F; Meidt, Sharon; Menendez-Delmestre, Karin; Peng, Chien Y; Salo, Heikki; Schinnerer, Eva; Zaritsky, Dennis

    2015-01-01

    We use mid-infrared 3.6 and 4.5microns imaging of NGC 3906 from the Spitzer Survey of Stellar Structure in Galaxies (S4G) to understand the nature of an unusual offset between its stellar bar and the photometric center of an otherwise regular, circular outer stellar disk. We measure an offset of ~720 pc between the center of the stellar bar and photometric center of the stellar disk; the bar center coincides with the kinematic center of the disk determined from previous HI observations. Although the undisturbed shape of the disk suggests that NGC 3906 has not undergone a significant merger event in its recent history, the most plausible explanation for the observed offset is an interaction. Given the relatively isolated nature of NGC 3906 this interaction could be with dark matter sub structure in the galaxy's halo or from a recent interaction with a fast moving neighbor which remains to be identified. Simulations aimed at reproducing the observed offset between the stellar bar / kinematic center of the syste...

  17. Galaxy Zoo: Observing secular evolution through bars

    SciTech Connect

    Cheung, Edmond; Faber, S. M.; Koo, David C. [Department of Astronomy and Astrophysics, 1156 High Street, University of California, Santa Cruz, CA 95064 (United States); Athanassoula, E.; Bosma, A. [Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, F-13388, Marseille (France); Masters, Karen L.; Nichol, Robert C.; Melvin, Thomas [Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building, Portsmouth, PO1 3FX (United Kingdom); Bell, Eric F. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Lintott, Chris [Oxford Astrophysics, Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom); Schawinski, Kevin [Institute for Astronomy, Department of Physics, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich (Switzerland); Skibba, Ramin A. [Center for Astrophysics and Space Sciences, Department of Physics, 9500 Gilman Drive, University of California, San Diego, CA 92093 (United States); Willett, Kyle W., E-mail: ec2250@gmail.com [School of Physics and Astronomy, University of Minnesota, MN 55455 (United States)

    2013-12-20

    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).

  18. Galaxy Zoo: Observing Secular Evolution Through Bars

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    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 Sérsic 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).

  19. Galaxy Zoo: CANDELS Barred Disks and Bar Fractions

    E-print Network

    Simmons, B D; 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; Grutzbauch, Ruth; Guo, Yicheng; Haussler, Boris; Jek, Kian J; Kaviraj, Sugata; Lucas, Ray A; Peth, Michael; Salvato, Mara; Wiklind, Tommy; Wuyts, Stijn

    2014-01-01

    The formation of bars in disk galaxies is a tracer of the dynamical maturity of the population. Previous studies have found that the incidence of bars in disks decreases from the local Universe to z ~ 1, and by z > 1 simulations predict that bar features in dynamically mature disks should be extremely rare. Here we report the discovery of strong barred structures in massive disk galaxies at z ~ 1.5 in deep rest-frame optical images from CANDELS. From within a sample of 876 disk galaxies identified by visual classification in Galaxy Zoo, we identify 123 barred galaxies. Selecting a sub-sample 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% 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 disk galaxies have evolved over the last 11 bil...

  20. Galaxy Zoo: CANDELS barred discs and bar fractions

    NASA Astrophysics Data System (ADS)

    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.; Grützbauch, Ruth; Guo, Yicheng; Häußler, Boris; Jek, Kian J.; Kaviraj, Sugata; Lucas, Ray A.; Peth, Michael; Salvato, Mara; Wiklind, Tommy; Wuyts, Stijn

    2014-12-01

    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.

  1. Companions of Bright Barred Shapley-Ames Galaxies

    Microsoft Academic Search

    J. A. García-Barreto; Rene Carrillo; Nelson Vera-Villamizar

    2003-01-01

    Companion galaxy environment for a subset of 78 bright and nearby barred galaxies from the Shapley-Ames Catalog is presented. Among the spiral barred galaxies, there are Seyfert galaxies, galaxies with circumnuclear structures, galaxies not associated with any large-scale galaxy cloud structure, galaxies with peculiar disk morphology (crooked arms), and galaxies with normal disk morphology; the list includes all Hubble types.

  2. Modelling gaseous and stellar kinematics in the disc galaxies NGC 772, NGC 3898, and NGC 7782

    E-print Network

    E. Pignatelli; E. M. Corsini; J. C. Vega Beltran; C. Scarlata; A. Pizzella; J. G. Funes; S. J.; W. W. Zeilinger; J. E. Beckman; F. Bertola

    2000-11-19

    We present V-band surface photometry and major-axis kinematics of stars and ionized gas of three early-type spiral galaxies, namely NGC 772, NGC 3898 and NGC 7782. For each galaxy we present a self-consistent Jeans model for the stellar kinematics, adopting the light distribution of bulge and disc derived by means of a two-dimensional parametric photometric decomposition. This allowed us to investigate the presence of non-circular gas motions, and derive the mass distribution of luminous and dark matter in these objects. NGC 772 and NGC 7782 have apparently normal kinematics with the ionized gas tracing the gravitational equilibrium circular speed. This is not true in the innermost region (r < 8'') of NGC 3898 where the ionized gas is rotating more slowly than the circular velocity predicted by dynamical modelling. This phenomenon is common in the bulge-dominated galaxies for which dynamical modelling enables us to make the direct comparison between the gas velocity and the circular speed, and it poses questions about the reliability of galaxy mass distributions derived by the direct decomposition of the observed ionized-gas rotation curve into the contributions of luminous and dark matter.

  3. Hyperactive galaxy NGC 7673 [heic0205

    NASA Astrophysics Data System (ADS)

    2002-03-01

    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

  4. Radial migration in barred galaxies

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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).

  5. Dark Matter Halos of Barred Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Cervantes Sodi, Bernardo; Li, Cheng; Park, Changbom

    2015-07-01

    We use a large volume-limited sample of disk galaxies drawn from the Sloan Digital Sky Survey Data Release 7 to study the dependence of the bar fraction on the stellar-to-halo mass ratio, making use of a group catalog, and we identify central and satellite galaxies in our sample. For the central galaxies in the sample we estimate the stellar-to-halo mass ratio (M*/Mh) and find that the fraction of barred galaxies is a strong function of this ratio, especially for the case of strong bars. Bars are more common in galaxies with high {M}*/Mh values, as expected from early theoretical works that showed that systems with massive dark matter halos are more stable against bar instabilities. We find that the change of the bar fraction with Mh and {M}* is stronger if we consider a relation with the form {f}{bar}= {f}{bar}({M}*? /Mh) with ? = 1.5, and that the bar fraction is largely independent of other physical properties such as color and spin parameter when {M}*3/2/Mh is fixed. With our sample of galaxies segregated into centrals and satellites, we also compare the fraction of barred galaxies in each group, finding a slightly higher bar fraction for satellites when compared with centrals at fixed stellar mass, but at fixed color this difference becomes very weak. This result, in agreement with previous studies, confirms that the bar fraction does not directly depend on the group/cluster environment, but the dependence exists through its dependence on internal morphology.

  6. Three-dimensional decomposition of galaxies with bulge and long bar

    NASA Astrophysics Data System (ADS)

    Compère, P.; López-Corredoira, M.; Garzón, F.

    2014-11-01

    Context. Some observations indicate that the Milky Way has two inner components, a bulge and a long bar, which present a misalignment of ?? ? 20° that is against the predictions of some theoretical models that are based on numerical simulations. Aims: We wish to determine whether this misalignment between the bar and the bulge can be observed in barred galaxies other than the Milky Way. Methods: Each galaxy of our sample was decomposed based on its Ks-band 2MASS image by fitting and modelling in a three-dimensional (3D) space the following components: a disc, a bar, and a bulge. The ?2 goodness-of-fit estimation allowed retrieving the best-fit angle values for the bar and the bulge to detect any misalignment. Results: From the 3D decomposition of six barred galaxies, we have detected at least three galaxies (NGC 2217, NGC 3992, and NGC 4593) that present a significant misalignment between the bar and the bulge of ??> 20°.

  7. The local galaxy density and the bars of spiral galaxies

    Microsoft Academic Search

    Giuliano Giuricin; Fabio Mardirossian; Marino Mezzetti; Pierluigi Monaco

    1993-01-01

    Using a variety of parameters of local galaxy density, we have examined the effects of the environmental density on the presence of bar structures in spiral galaxies of various morphological types. For an extensive sample of nearby galaxies, listed in the Nearby Galaxies Catalog (Tully 1988), we have found that the spirals characterized by a high local density tend to

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

    NASA Astrophysics Data System (ADS)

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

    2011-05-01

    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.

  9. Modelling gaseous and stellar kinematics in the disc galaxies NGC 772, NGC 3898, and NGC 7782

    E-print Network

    Pignatelli, E; Vega-Beltrán, J C; Scarlata, C; Pizzella, A; Funes, J G; Zeilinger, W W; Beckman, J E; Bertola, F

    2000-01-01

    We present V-band surface photometry and major-axis kinematics of stars and ionized gas of three early-type spiral galaxies, namely NGC 772, NGC 3898 and NGC 7782. For each galaxy we present a self-consistent Jeans model for the stellar kinematics, adopting the light distribution of bulge and disc derived by means of a two-dimensional parametric photometric decomposition. This allowed us to investigate the presence of non-circular gas motions, and derive the mass distribution of luminous and dark matter in these objects. NGC 772 and NGC 7782 have apparently normal kinematics with the ionized gas tracing the gravitational equilibrium circular speed. This is not true in the innermost region (r < 8'') of NGC 3898 where the ionized gas is rotating more slowly than the circular velocity predicted by dynamical modelling. This phenomenon is common in the bulge-dominated galaxies for which dynamical modelling enables us to make the direct comparison between the gas velocity and the circular speed, and it poses que...

  10. A Multiwavelength Study of the Starburst Galaxy NGC 7771

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

    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.

  11. Galaxy Zoo: bar lengths in local disc galaxies

    Microsoft Academic Search

    Ben Hoyle; Karen. L. Masters; Robert C. Nichol; Edward M. Edmondson; Arfon M. Smith; Chris Lintott; Ryan Scranton; Steven Bamford; Kevin Schawinski; Daniel Thomas

    2011-01-01

    We present an analysis of bar length measurements of 3150 local galaxies in a volume-limited sample of low-redshift (z =3), and we find that observers were able to reproduce their own bar lengths to 3 per cent and each others' to better than 20 per cent. We find a colour bimodality in our disc galaxy population with bar length, i.e.

  12. TWO PSEUDOBULGES IN THE 'BOXY BULGE' GALAXY NGC 5746

    SciTech Connect

    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

    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.

  13. GASEOUS STRUCTURES IN BARRED GALAXIES: EFFECTS OF THE BAR STRENGTH

    SciTech Connect

    Kim, Woong-Tae; Seo, Woo-Young; Kim, Yonghwi, 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)

    2012-10-10

    Using hydrodynamic simulations, we investigate the physical properties of gaseous substructures in barred galaxies and their relationships with the bar strength. The gaseous medium is assumed to be isothermal and unmagnetized. The bar potential is modeled as a Ferrers prolate with index n. To explore situations with differing bar strength, we vary the bar mass f{sub bar} relative to the spheroidal component as well as its aspect ratio R. We derive expressions as functions of f{sub bar} and R for the bar strength Q{sub b} and the radius r(Q{sub b} ) where the maximum bar torque occurs. When applied to observations, these expressions suggest that bars in real galaxies are most likely to have f{sub bar} {approx} 0.25-0.50 and n {approx}< 1. Dust lanes approximately follow one of the x{sub 1}-orbits and tend to be straighter under a stronger and more elongated bar, but are insensitive to the presence of self-gravity. A nuclear ring of a conventional x{sub 2} type forms only when the bar is not so massive or elongated. The radius of an x{sub 2}-type ring is generally smaller than the inner Lindblad resonance, decreases systematically with increasing Q{sub b} , and is slightly larger when self-gravity is included. This is evidence that the ring position is not determined by the resonance, but instead by the amount of angular momentum loss at dust-lane shocks. Nuclear spirals exist only when the ring is of the x{sub 2} type and is sufficiently large in size. Unlike the other features, nuclear spirals are transient in that they start out being tightly wound and weak, and then, due to the nonlinear effect, unwind and become stronger until they turn into shocks, with an unwinding rate that is higher for larger Q{sub b} . The mass inflow rate to the galaxy center is found to be less than 0.01 M{sub Sun} yr{sup -1} for models with Q{sub b} {approx}< 0.2, while becoming larger than 0.1 M{sub Sun} yr{sup -1} when Q{sub b} {approx}> 0.2 and self-gravity is included.

  14. Gaseous Structures in Barred Galaxies: Effects of the Bar Strength

    NASA Astrophysics Data System (ADS)

    Kim, Woong-Tae; Seo, Woo-Young; Kim, Yonghwi

    2012-10-01

    Using hydrodynamic simulations, we investigate the physical properties of gaseous substructures in barred galaxies and their relationships with the bar strength. The gaseous medium is assumed to be isothermal and unmagnetized. The bar potential is modeled as a Ferrers prolate with index n. To explore situations with differing bar strength, we vary the bar mass f bar relative to the spheroidal component as well as its aspect ratio { R}. We derive expressions as functions of f bar and { R} for the bar strength Qb and the radius r(Qb ) where the maximum bar torque occurs. When applied to observations, these expressions suggest that bars in real galaxies are most likely to have f bar ~ 0.25-0.50 and n <~ 1. Dust lanes approximately follow one of the x 1-orbits and tend to be straighter under a stronger and more elongated bar, but are insensitive to the presence of self-gravity. A nuclear ring of a conventional x 2 type forms only when the bar is not so massive or elongated. The radius of an x 2-type ring is generally smaller than the inner Lindblad resonance, decreases systematically with increasing Qb , and is slightly larger when self-gravity is included. This is evidence that the ring position is not determined by the resonance, but instead by the amount of angular momentum loss at dust-lane shocks. Nuclear spirals exist only when the ring is of the x 2 type and is sufficiently large in size. Unlike the other features, nuclear spirals are transient in that they start out being tightly wound and weak, and then, due to the nonlinear effect, unwind and become stronger until they turn into shocks, with an unwinding rate that is higher for larger Qb . The mass inflow rate to the galaxy center is found to be less than 0.01 M ? yr-1 for models with Qb <~ 0.2, while becoming larger than 0.1 M ? yr-1 when Qb >~ 0.2 and self-gravity is included.

  15. Interferometric CO observations of the ultraluminous IRAS galaxies ARP 220, IC 694/NGC 3690, NGC 6420 and NGC 7469

    NASA Technical Reports Server (NTRS)

    Sargent, A. I.; Sanders, D. B.; Scoville, N. Z.; Soifer, B. T.

    1987-01-01

    High resolution CO observations of the IRAS galaxies Arp 220, IC 694/NGC 3690, NGC 6240 and NGC 7469 were made with the Millimeter Wave Interferometer of the Owen Valley Radio Observatory. These yield spatial information on scales of 1 to 5 kpc and allow the separation of compact condensations from the more extended emission in the galaxies. In the case of the obviously interacting system IC 694/NGC 3690 the contributions of each component can be discerned. For that galaxy, and also for Arp 220, the unusually high lumonisities may be produced by nonthermal processes rather than by intense bursts of star formation.

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

    SciTech Connect

    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

    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.

  17. Stellar archeology of the nearby LINER galaxies NGC 4579 and NGC 4736

    NASA Astrophysics Data System (ADS)

    Steiner, J. E.; Menezes, R. B.; Ricci, T. V.; de Oliveira, A. S.

    2010-04-01

    Stellar archeology of nearby LINER galaxies may reveal if there is a stellar young population that may be responsible for the LINER phenomenon. We show results for the classical LINER galaxies NGC 4579 and NGC 4736 and find no evidence of such populations.

  18. The Stellar Content of the Polar Rings in the Galaxies NGC 2685 and NGC 4650A

    Microsoft Academic Search

    G. M. Karataeva; I. O. Drozdovsky; V. A. Hagen-Thorn; V. A. Yakovleva; N. A. Tikhonov; O. A. Galazutdinova

    2004-01-01

    We present the results of stellar photometry of polar ring galaxies NGC 2685 and NGC 4650A, using the archival data obtained with the Hubble Space Telescope's Wide Field Planetary Camera 2. Polar rings of these galaxies were resolved into ~800 and ~430 stellar objects in the B, V, and IC bands, a considerable part of which are blue supergiants located

  19. GMRT radio continuum study of Wolf-Rayet galaxies - I. NGC 4214 and NGC 4449

    NASA Astrophysics Data System (ADS)

    Srivastava, S.; Kantharia, N. G.; Basu, Aritra; Srivastava, D. C.; Ananthakrishnan, S.

    2014-09-01

    We report low-frequency observations of Wolf-Rayet galaxies, NGC 4214 and NGC 4449 at 610, 325 and 150 MHz, using the Giant Meterwave Radio Telescope (GMRT). We detect diffuse extended emission from NGC 4214 at and NGC 4449. NGC 4449 is observed to be five times more radio luminous than NGC 4214, indicating vigorous star formation. We estimate synchrotron spectral index after separating the thermal free-free emission and obtain ?nt = -0.63 ± 0.04 (S? ? ^{? _nt}) for NGC 4214 and -0.49 ± 0.02 for NGC 4449. About 22 per cent of the total radio emission from NGC 4214 and ˜9 per cent from NGC 4449 at 610 MHz is thermal in origin. We also study the spectra of two compact star-forming regions in NGC 4214 from 325 MHz to 15 GHz and obtain ?nt = -0.32 ± 0.02 for NGC 4214-I and ?nt = -0.94 ± 0.12 for NGC 4214-II. The luminosities of these star-forming regions (˜1019 WHz-1) appear to be similar to those in circumnuclear rings in normal disc galaxies observed with similar linear resolution. We detect the supernova remnant SNR J1228+441 in NGC 4449 and estimate the spectral index of the emission between 325 and 610 MHz to be -1.8 in the epoch 2008-2009. The galaxies follow the radio-FIR correlation slopes suggesting that star formation in Wolf-Rayet galaxies, which are low-metallicity systems, are similar to that of normal disc galaxies.

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

    E-print Network

    J. Falcón-Barroso; R. F. Peletier; E. Emsellem; H. Kuntschner; K. Fathi; M. Bureau; R. Bacon; M. Cappellari; Y. Copin; R. L. Davies; T. de Zeeuw

    2004-02-10

    We present SAURON integral-field observations of the S0 galaxy NGC7332. Existing broad-band ground-based and HST photometry reveals a double disk structure and a boxy bulge interpreted as a bar viewed close to edge-on. The SAURON two-dimensional stellar kinematic maps confirm the existence of the bar and inner disk but also uncover the presence of a cold counter-rotating stellar component within the central 250 pc. The Hbeta and [OIII] emission line maps show that the ionised gas has a complex morphology and kinematics, including both a component counter-rotating with respect to the stars and a fainter co-rotating one. Analysis of the absorption line-strength maps show that NGC7332 is young everywhere. The presence of a large-scale bar can explain most of those properties, but the fact that we see a significant amount of unsettled gas, together with a few peculiar features in the maps, suggest that NGC7332 is still evolving. Interactions as well as bar-driven processes must thus have played an important role in the formation and evolution of NGC7332, and presumably of S0 galaxies in general.

  1. Longslit Spectra of the Galaxy NGC 1569

    NASA Technical Reports Server (NTRS)

    Duenas, Ely

    2000-01-01

    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.

  2. Longslit Spectra of the Galaxy NGC 1569

    NASA Astrophysics Data System (ADS)

    Duenas, Ely

    2000-11-01

    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.

  3. Stellar Populations of Barred Quiescent Galaxies

    NASA Astrophysics Data System (ADS)

    Cheung, Edmond; Conroy, Charlie; Athanassoula, E.; Bell, Eric F.; Bosma, A.; Cardamone, Carolin N.; Faber, S. M.; Koo, David C.; Lintott, Chris; Masters, Karen L.; Melvin, Thomas; Simmons, Brooke; Willett, Kyle W.

    2015-07-01

    Selecting centrally quiescent galaxies from the Sloan Digital Sky Survey (SDSS) to create high signal-to-noise ratio (? 100 Å?1) stacked spectra with minimal emission-line contamination, we accurately and precisely model the central stellar populations of barred and unbarred quiescent disk galaxies. By splitting our sample by redshift, we can use the fixed size of the SDSS fiber to model the stellar populations at different radii within galaxies. At 0.02\\lt z\\lt 0.04, the SDSS fiber radius corresponds to ?1 kpc, which is the typical half-light radii of both classical bulges and disky pseudobulges. Assuming that the SDSS fiber primarily covers the bulges at these redshifts, our analysis shows that there are no significant differences in the stellar populations, i.e., stellar age, [Fe/H], [Mg/Fe], and [N/Fe], of the bulges of barred versus unbarred quiescent disk galaxies. Modeling the stellar populations at different redshift intervals from z = 0.020 to z = 0.085 at fixed stellar masses produces an estimate of the stellar population gradients out to about half the typical effective radius of our sample, assuming null evolution over this ?1 Gyr epoch. We find that there are no noticeable differences in the slopes of the azimuthally averaged gradients of barred versus unbarred quiescent disk galaxies. These results suggest that bars are not a strong influence on the chemical evolution of quiescent disk galaxies.

  4. The PNLF distance to the Sculptor Group galaxy NGC 55

    E-print Network

    G. C. Van de Steene; G. H. Jacoby; C. Praet; R. Ciardullo; H. Dejonghe

    2004-08-03

    We identified 21 new Planetary Nebula (PN) candidates in the Sculptor Group galaxy NGC 55. We determined a most likely distance of 2.00 +/- 0.2 Mpc using the Planetary Nebulae Luminosity Function (PNLF) method. The distance to NGC 55 is larger than previously determined distances, which means that the Sculptor Group is a bit further away from the Local Group than previously thought. The distance to NGC 55 is again similar to the distance of NGC 300, adding support to the suggestion that these galaxies form a bound pair.

  5. A Technique for Separating the Gravitational Torques of Bars and Spirals in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Buta, R.; Block, D. L.; Knapen, J. H.

    2003-09-01

    We describe a Fourier-based method of separating bars from spirals in near-infrared images. The method takes advantage of the fact that a bar is typically a feature with a relatively fixed position angle and uses the simple assumption that the relative Fourier amplitudes due to the bar decline with radius past a maximum in the same or a similar manner as they rose to that maximum. With such an assumption, the bar can be extrapolated into the spiral region and removed from an image, leaving just the spiral and the axisymmetric background disk light. We refer to such a bar-subtracted image as the ``spiral plus disk'' image. The axisymmetric background (Fourier index m=0 image) can then be added back to the bar image to give the ``bar plus disk'' image. The procedure allows us to estimate the maximum gravitational torque per unit mass per unit square of the circular speed for the bar and spiral forcing separately, parameters that quantitatively define the bar strength Qb and the spiral strength Qs following the recent study of Buta & Block. For the first time, we are able to measure the torques generated by spiral arms alone, and we can now define spiral torque classes, in the same manner as bar torque classes are delineated. We outline the complete procedure here using a 2.1 ?m image of NGC 6951, a prototypical SAB(rs)bc spiral having an absolute blue magnitude of -21 and a maximum rotation velocity of 230 km s-1. Comparison between a rotation curve predicted from the m=0 near-infrared light distribution and an observed rotation curve suggests that NGC 6951 is maximum disk in its bar and main spiral region, implying that our assumption of a constant mass-to-light ratio in our analysis is probably reliable. We justify our assumption on how to make the bar extrapolation using an analysis of NGC 4394, a barred spiral with only weak near-infrared spiral structure, and we justify the number of needed Fourier terms using NGC 1530, one of the most strongly barred galaxies (bar class 7) known. We also evaluate the main uncertainties in the technique. Allowing for uncertainties in vertical scale height, bar extrapolation, sky subtraction, orientation parameters, and the asymmetry in the spiral arms themselves, we estimate Qb=0.28+/-0.04 and Qs=0.21+/-0.06 for NGC 6951.

  6. ON THE GALACTIC SPIN OF BARRED DISK GALAXIES

    SciTech Connect

    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

    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.

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

    E-print Network

    M. Bureau; A. Chung

    2005-12-06

    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.

  8. Multiband optical surface brightness profile decompositions of the Seyfert galaxies Mrk 79 and NGC 5548

    E-print Network

    Boyko Mihov; Lyuba Slavcheva-Mihova

    2010-02-01

    We present preliminary results of the Johnson-Cousins (U)BVRI surface brightness profile decompositions of the Seyfert galaxies Mrk 79 and NGC 5548. The profiles were modelled as a sum of a Gaussian law for the nucleus, a Sersic law for the bulge and an exponent law for the disk. A flat bar was added to the model profile of Mrk 79. The parameters and the total magnitudes of the structural components were derived.

  9. Absorption Line Gradients of an Elliptical Galaxy NGC 5322

    Microsoft Academic Search

    Young-Jong Sohn; Myung-Hyun Rhee; Suk-Jin Yoon

    1999-01-01

    Archival long-slit spectra, covering the wavelength range 4050Å - 5150Å, have been used to investigate the radial behavior of absorption line features (G4300, Fe4383, Ca4455, Fe44531, Fe4668, and Halpha) of an eliptical galaxy NGC 5322. The heliocentric recession velocity of NGC 5322 has been derived as 1888+\\/-51 km s-1. Metallic absorption lines of NGC 5322 show significant radial gradients through

  10. Dense gas and HII regions in the starburst galaxy NGC 253

    NASA Technical Reports Server (NTRS)

    Carlstrom, J. E.; Jackson, James M.; Ho, Paul T. P.; Turner, J. L.

    1990-01-01

    The energetic activity in the nuclear barred region of NGC 253 is attributable to a burst of star formation. NGC 253 is in many ways a twin of the prototypical starburst galaxy M82; the strong non-thermal radio continuum, high far-infrared luminosity, and bright molecular emission of the central 1 Kpc parallel the morphology of the M82 starburst. Furthermore, the filamentary low ionization optical emission and extended x ray emission along the minor axis in NGC 253 is similar to a scaled down version of the well developed galactic bipolar wind in M82. The infrared luminosity of NGC 253, 3(exp 10) solar luminosity, is comparable to M82 but is emitted from a smaller region (Telesco and Harper 1980). This suggests that the NGC 253 starburst may be more intense and at an earlier evolutionary stage than M82. However, the presence of a non-stellar AGN in NGC 253 may complicate the comparison (Turner and Ho, 1985). Researchers used the Hat Creek millimeter interferometer to map emission from the J = 1 to 0 transitions of HCN and HCO(+) as well as 3 mm continuum emission, toward the nuclear region of NGC 253. The HCO(+) and continuum observations are sensitive to spatial scales from 6 to 45 seconds. The 2 minute field of view comfortably includes the entire starburst region (about 40 seconds; 650 pc). Because the longer baseline HCN observations are not yet complete, they are only sensitive to spatial scales from 15 to 45 seconds.

  11. Warm molecular gas in galaxy-galaxy merger NGC6090

    NASA Astrophysics Data System (ADS)

    Wang, J.; SAO; ASIAA SMA Team

    2003-12-01

    This is the first results of both the CO 3-2 and CO 2-1 on merging galaxies at such high resolution of about 2".We observed the CO J=3-2 and J=2-1 lines toward the merging galaxy pair NGC6090 with the SMA. The maps show that the emission peaks of both CO lines are located at the overlap region of the two galaxies, where there is almost no near-IR emission. The CO 3-2/2-1 ratio shows that the gas associated with the face-on galaxy to the northwest is cold, while both the overlap region and the edge-on galaxy to the south are warmer. Channel maps of the CO J=2-1 line show similar structures as the CO J=1-0 line (Bryant and Scoville 1999 AJ 117, 2632). But the CO J=3-2 emission is more compact than the lower transitions, and comes mostly from the overlap region. These are the first results of both the CO J=3-2 and 2-1 lines from merging galaxies with an angular resolution as fine as 2". The SMA is a joint project of the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics.

  12. Optically Thick Giant H II Regions with Decreasing Density Gradients in three Barred Galaxies

    NASA Astrophysics Data System (ADS)

    de La Fuente, E.; García-Barreto, J. A.; Franco, J.

    2002-02-01

    Franco, García-Barreto, & de la Fuente (2000, hereinafter FGF00) have re-analyzed the radio continuum emission at 2, 6 and 20 cm from the circumnuclear regions of the barred galaxies NGC 1022, 1326 and 4314. The angular resolution of the observations is approximately 3.7 arcsec , roughly equiva-lent to 200 parsecs. Here we summarize the results discussed in FGF00

  13. Dissipative Cloud Collissions in Barred Galaxies

    NASA Astrophysics Data System (ADS)

    Palous, Jan

    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.

  14. Molecular Gas Kinematics in Barred Spiral Galaxies

    E-print Network

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

    1999-08-10

    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.

  15. The lives of double-barred galaxies: photometric properties

    NASA Astrophysics Data System (ADS)

    de Lorenzo-Cáceres, A.

    2015-05-01

    Double-barred galaxies are structurally complex objects, as the two bars show random orientations and independent pattern speeds. This fact has greatly hampered the study of these objects, even though inner bars are considered a main driver of gas inflow to the central regions of galaxies, where it may feed the AGN and/or promote the secular formation of bulges. Over the past years our group has faced the problem of the observational study of double bars from different standpoints. Thus, we have studied in detail the stellar and gas content of double bars, their particular properties with respect to single- and non-barred galaxies, and even how to identify new double-barred systems previously unknown. This proceeding summarizes the most relevant knowledge we have so far about double-barred galaxies, and presents preliminar results about the structural characterization of double bars.

  16. Deficiency of "Thin" Stellar Bars in Seyfert Host Galaxies.

    PubMed

    Shlosman; Peletier; Knapen

    2000-06-01

    Using all available major samples of Seyfert galaxies and their corresponding closely matched control samples of nonactive galaxies, we find that the bar ellipticities (or axial ratios) in Seyfert galaxies are systematically different from those in nonactive galaxies. Overall, there is a deficiency of bars with large ellipticities (i.e., "thin" or "strong" bars) in Seyfert galaxies compared to nonactive 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, 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 nonactive counterparts on scales of a few kiloparsecs. PMID:10835304

  17. Chandra Observations of the Collisional Ring Galaxy NGC 922

    NASA Astrophysics Data System (ADS)

    Prestwich, A. H.; Galache, J. L.; Linden, T.; Kalogera, V.; Zezas, A.; Roberts, T. P.; Kilgard, R.; Wolter, A.; Trinchieri, G.

    2012-03-01

    In this paper, we report on Chandra observations of the starburst galaxy NGC 922. NGC 922 is a drop-through ring galaxy with an expanding ring of star formation, similar in many respects to the Cartwheel galaxy. The Cartwheel galaxy is famous for hosting 12 ultraluminous X-ray sources (ULXs), most of which are in the star-forming ring. This is the largest number of ULXs seen in a single system and has led to speculation that the low metallicity of the Cartwheel (0.3 Z ?) may optimize the conditions for ULX formation. In contrast, NGC 922 has metallicity near solar. The Chandra observations reveal a population of bright X-ray sources, including seven ULXs. The number of ULXs in NGC 922 and the Cartwheel scales with the star formation rate: we do not find any evidence for an excess of sources in the Cartwheel. Simulations of the binary population in these galaxies suggest that the ULX population in both systems is dominated by systems with strong wind accretion from supergiant donors onto direct-collapse black holes. The simulations correctly predict the ratio of the number of sources in NGC 922 and the Cartwheel. Thus, it would appear that the metallicity of the Cartwheel is not low enough to see a difference in the ULX population compared to NGC 922.

  18. CHANDRA OBSERVATIONS OF THE COLLISIONAL RING GALAXY NGC 922

    SciTech Connect

    Prestwich, A. H.; Galache, J. L.; Zezas, A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Linden, T. [University of Santa Cruz, Department of Physics 211 Interdisciplinary Sciences Building, 1156 High Street, Santa Cruz, CA 95064 (United States); Kalogera, V. [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States); Roberts, T. P. [Department of Physics, University of Durham, South Road, Durham DH1 3LE (United Kingdom); Kilgard, R. [Van Vleck Observatory, Wesleyan University, 96 Foss Hill Dr., Middletown, CT 06459 (United States); Wolter, A.; Trinchieri, G. [INAF, Osservatorio Astronomico di Brera, Via Brera 28, IT 20121 Milano (Italy)

    2012-03-10

    In this paper, we report on Chandra observations of the starburst galaxy NGC 922. NGC 922 is a drop-through ring galaxy with an expanding ring of star formation, similar in many respects to the Cartwheel galaxy. The Cartwheel galaxy is famous for hosting 12 ultraluminous X-ray sources (ULXs), most of which are in the star-forming ring. This is the largest number of ULXs seen in a single system and has led to speculation that the low metallicity of the Cartwheel (0.3 Z{sub Sun }) may optimize the conditions for ULX formation. In contrast, NGC 922 has metallicity near solar. The Chandra observations reveal a population of bright X-ray sources, including seven ULXs. The number of ULXs in NGC 922 and the Cartwheel scales with the star formation rate: we do not find any evidence for an excess of sources in the Cartwheel. Simulations of the binary population in these galaxies suggest that the ULX population in both systems is dominated by systems with strong wind accretion from supergiant donors onto direct-collapse black holes. The simulations correctly predict the ratio of the number of sources in NGC 922 and the Cartwheel. Thus, it would appear that the metallicity of the Cartwheel is not low enough to see a difference in the ULX population compared to NGC 922.

  19. CO abundances and star formation in the three irregular galaxies NGC 4449, NGC 4214, and NGC 3838

    NASA Astrophysics Data System (ADS)

    Tacconi, L. J.; Young, J. S.

    1985-03-01

    CO emission has been detected in the central 1.3 kpc of the three irregular galaxies NGC 4449, NGC 4214, and NGC 3738, and also in a gain H II complex in NGC 4449 using the 14 m telescope of teh Five College Radio Astronomy Observatory (HPBW = 50 arcsec). The CO distribution in NGC 4449 appears clumped, with stronger emission found in one H II complex than in the central region of the galaxy. Comparing the irregulars with the luminous Scd galaxy IC 342, all of which are roughly at the same distance, the central 50 arcsec of the irregulars have 2-5 times less blue luminosity than the central 50 arcsec in 1C 342 but have factors of 40-70 less CO. A power law relation is observed between the CO and blue fluxes in the irregular galaxies. This is significantly different from the roughly linear relationship found for the central 5kpc in late-type spirals (Young and Scoville, 1982). Thus, irregular galaxies with the same CO intensity as spirals are more optically luminous.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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).

  1. A tidally distorted dwarf galaxy near NGC 4449.

    PubMed

    Rich, R M; Collins, M L M; Black, C M; Longstaff, F A; Koch, A; Benson, A; Reitzel, D B

    2012-02-01

    NGC 4449 is a nearby Magellanic irregular starburst galaxy with a B-band absolute magnitude of -18 and a prominent, massive, intermediate-age nucleus at a distance from Earth of 3.8?megaparsecs (ref. 3). It is wreathed in an extraordinary neutral hydrogen (H?I) complex, which includes rings, shells and a counter-rotating core, spanning ?90?kiloparsecs (kpc; refs 1, 4). NGC 4449 is relatively isolated, although an interaction with its nearest known companion--the galaxy DDO 125, some 40?kpc to the south--has been proposed as being responsible for the complexity of its H?I structure. Here we report the presence of a dwarf galaxy companion to NGC 4449, namely NGC 4449B. This companion has a V-band absolute magnitude of -13.4 and a half-light radius of 2.7?kpc, with a full extent of around 8?kpc. It is in a transient stage of tidal disruption, similar to that of the Sagittarius dwarf near the Milky Way. NGC 4449B exhibits a striking S-shaped morphology that has been predicted for disrupting galaxies but has hitherto been seen only in a dissolving globular cluster. We also detect an additional arc or disk ripple embedded in a two-component stellar halo, including a component extending twice as far as previously known, to about 20?kpc from the galaxy's centre. PMID:22318602

  2. A tidally distorted dwarf galaxy near NGC 4449

    NASA Astrophysics Data System (ADS)

    Rich, R. M.; Collins, M. L. M.; Black, C. M.; Longstaff, F. A.; Koch, A.; Benson, A.; Reitzel, D. B.

    2012-02-01

    NGC 4449 is a nearby Magellanic irregular starburst galaxy with a B-band absolute magnitude of -18 and a prominent, massive, intermediate-age nucleus at a distance from Earth of 3.8 megaparsecs (ref. 3). It is wreathed in an extraordinary neutral hydrogen (H I) complex, which includes rings, shells and a counter-rotating core, spanning ~90 kiloparsecs (kpc; refs 1, 4). NGC 4449 is relatively isolated, although an interaction with its nearest known companion--the galaxy DDO 125, some 40 kpc to the south--has been proposed as being responsible for the complexity of its H I structure. Here we report the presence of a dwarf galaxy companion to NGC 4449, namely NGC 4449B. This companion has a V-band absolute magnitude of -13.4 and a half-light radius of 2.7 kpc, with a full extent of around 8 kpc. It is in a transient stage of tidal disruption, similar to that of the Sagittarius dwarf near the Milky Way. NGC 4449B exhibits a striking S-shaped morphology that has been predicted for disrupting galaxies but has hitherto been seen only in a dissolving globular cluster. We also detect an additional arc or disk ripple embedded in a two-component stellar halo, including a component extending twice as far as previously known, to about 20 kpc from the galaxy's centre.

  3. Near Infrared Observations of Merging Galaxy Systems NGC 1614 and NGC 520

    Microsoft Academic Search

    P. C. Turner; W. J. Forrest; J. L. Pipher

    1997-01-01

    High resolution near infrared array images of the nuclear regions of two merging galaxy systems, NGC 1614 and NGC 520, are presented. The broadband photometric images at 1.25, 1.65, and 2.23 micron wavelengths and the CO bandhead (2.3 microns) absorption index measurements are used to investigate the spatial distribution of starburst activity and extinction in the central regions of these

  4. Star formation in blue galaxies. I - Ultraviolet, optical, and infrared observations of NGC 4214 and NGC 4670

    Microsoft Academic Search

    J. P. Huchra; M. J. Geller; J. Gallagher; D. Hunter; L. Hartmann; G. Fabbiano; M. Aaronson

    1983-01-01

    NGC 4214 and NGC 4760 have been observed between 1150 A and 1950 A with the IUE satellite, and new infrared and optical broad-band photometry have been obtained. The spectra of both galaxies are dominated by O stars, and, in the spectrum of NGC 4214, the C IV 1550 A line exhibits a P Cygni profile indicative of hot stars

  5. Model-based pattern speed estimates for 38 barred galaxies

    NASA Astrophysics Data System (ADS)

    Rautiainen, P.; Salo, H.; Laurikainen, E.

    2008-08-01

    We have modelled 38 barred galaxies by using near-infrared and optical data from the Ohio State University Bright Spiral Galaxy Survey. We constructed the gravitational potentials of the galaxies from H-band photometry, assuming a constant mass-to-light ratio. The halo component we choose corresponds to the so-called universal rotation curve. In each case, we used the response of gaseous and stellar particle disc to rigidly rotating potential to determine the pattern speed. We find that the pattern speed of the bar depends roughly on the morphological type. The average value of corotation resonance radius to bar radius, , increases from 1.15 +/- 0.25 in types SB0/a-SBab to 1.44 +/- 0.29 in SBb and 1.82 +/- 0.63 in SBbc-SBc. Within the error estimates for the pattern speed and bar radius, all galaxies of type SBab or earlier have a fast bar , whereas the bars in later type galaxies include both fast and slow rotators. Of 16 later type galaxies with a nominal value of , there are five cases, where the fast-rotating bar is ruled out by the adopted error estimates. We also study the correlation between the parameter and other galactic properties. The clearest correlation is with the bar size: the slowest bars are also the shortest bars when compared to the galaxy size. A weaker correlation is seen with bar strength in a sense that slow bars tend to be weaker. These correlations leave room for a possibility that the determined pattern speed in many galaxies corresponds to actually that of the spiral, which rotates more slowly than the bar. No clear correlation is seen with either the galaxy luminosity or the colour.

  6. CCD imagery of the S0 galaxies NGC 3990 and NGC 3998

    SciTech Connect

    Welch, G.A.; Welch, D.M.K.; Dupuy, D.L. (Saint Mary's Univ., Halifax (Canada) Virginia Military Institute, Lexington (USA))

    1991-01-01

    The structure and colors of NGC 3990 and NGC 3998 are investigated using BR CCD imagery. Fits of bulge-disk models of the galaxies indicate that both disks are somewhat brighter and more compact than typical S0 galaxies in the Virgo and Fornax clusters. Although the two galaxies are separated by only about 3.5 arcmin, none of the obvious signs of gravitational interaction are seen. The colors of both galaxies are normal; the disk of NGC 3998 is somewhat bluer than its bulge. The search has failed to reveal the interstellar dust predicted from the neutral hydrogen observations of NGC 3998. The dust that is seen appears to be mixed with ionized gas which occupies the center of this galaxy and may be the same material seen at longer wavelengths by the IRAS experiment. Its low abundance relative to the neutral gas is consistent with the idea that the ISM was contributed by a gas-rich dwarf galaxy in a destructive merger. 31 refs.

  7. Thick disks and halos of spiral galaxies M 81, NGC 55 and NGC 300

    E-print Network

    N. A. Tikhonov; O. A. Galazutdinova; I. O. Drozdovsky

    2004-10-18

    By using images from the HST/WFPC2/ACS archive, we have analyzed the spatial distribution of the AGB and RGB stars along the galactocentric radius of nearby spiral galaxies M~81, NGC 300 and NGC 55. Using color-magnitude diagrams and stellar luminosity functions, we gauge the stellar contents of the surroundings of three galaxies. The red giant population (RGB) identified at large galactocentric radii yields a distance of $3.85\\pm0.08$ Mpc for M~81, $2.12\\pm0.10$ Mpc for NGC 55, and $2.00\\pm0.13$ Mpc for NGC 300, and a mean stellar metallicity of $-$0.65, $-$1.25, and $-$0.87. We find that there are two number density gradients of RGB stars along the radius, which correspond to the thick disk and halo components of the galaxies. We confirm the presence of metallicity gradient of evolved stars at these galaxies, based on the systematic changes of the color distribution of red giant stars. These results imply that thick disk might be a general feature of the spiral galaxies, and endorse a further investigation of the outer stellar edges of nearby spirals, which is critical in constraining the origin and evolution of galaxies.

  8. WIYN IMAGING OF THE GLOBULAR CLUSTER SYSTEMS OF THE SPIRAL GALAXIES NGC 891 AND NGC 4013

    SciTech Connect

    Rhode, Katherine L.; Windschitl, Jessica L.; Young, Michael D., E-mail: rhode@astro.indiana.ed [Department of Astronomy, Indiana University, Swain West 319, 727 East Third Street, Bloomington, IN 47405-7105 (United States)

    2010-08-15

    We present results from a WIYN 3.5 m telescope imaging study of the globular cluster (GC) systems of the edge-on spiral galaxies NGC 891 and NGC 4013. We used the 10' x 10' Minimosaic Imager to observe the galaxies in BVR filters to projected radii of {approx}20 kpc from the galaxy centers. We combined the WIYN data with archival and published data from the WFPC2 and AdvancedCameraforSurveys on the Hubble Space Telescope (HST) to assess the contamination level of the WIYN GC candidate sample and to follow the GC systems further in toward the galaxies' centers. We constructed radial distributions for the GC systems using both the WIYN and HST data. The GC systems of NGC 891 and NGC 4013 extend to 9 {+-} 3 kpc and 14 {+-} 5 kpc, respectively, before falling off to undetectable levels in our images. We use the radial distributions to calculate global values for the total number (N{sub GC}) and specific frequencies (S{sub N} and T) of GCs. NGC 4013 has N{sub GC} = 140 {+-} 20, S{sub N} = 1.0 {+-} 0.2, and T = 1.9 {+-} 0.5; our N{sub GC} value is {approx}40% smaller than a previous determination from the literature. The HST data were especially useful for NGC 891 because the GC system is concentrated toward the plane of the galaxy and was only weakly detected in our WIYN images. Although NGC 891 is thought to resemble the Milky Way in terms of its overall properties, it has only half as many GCs, with N{sub GC}= 70 {+-} 20, S{sub N} = 0.3 {+-} 0.1, and T = 0.6 {+-} 0.3. We also calculate the galaxy-mass-normalized number of blue (metal-poor) GCs in NGC 891 and NGC 4013 and find that they fall along a general trend of increasing specific frequency of blue GCs with increasing galaxy mass. Given currently available resources, the optimal method for studying the global properties of extragalactic GC systems is to combine HST data with wide-field, ground-based imaging with good resolution. The results here demonstrate the advantage gained by using both methods when possible.

  9. Revealing galactic scale bars with the help of Galaxy Zoo

    NASA Astrophysics Data System (ADS)

    Masters, Karen L.

    2015-03-01

    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.

  10. Millimeter interferometer observations of infrared luminous galaxies - NGC 828 and NGC 6240

    SciTech Connect

    Wang, Z.; Scoville, N.Z.; Sanders, D.B. (California Institute of Technology, Pasadena (USA) Hawaii Univ., Honolulu (USA))

    1991-02-01

    Millimeter interferometer observations of the infrared luminous galaxies NGC 828 and NGC 6240 at about 7 arcsec resolution are reported which reveal details of the spatial distribution and kinematics of molecular gas in these two high-luminosity IRAS galaxies. The centers of both galaxies have massive concentrations of molecular gas representing a large fraction of the total dynamical mass. These regions are likely to be extremely unstable to gravitational instability. The high infrared luminosity of these galaxies is probably triggered by the galactic interaction. However, the estimated available kinetic energy in the ISM indicates that the luminosity can be provided by the bulk kinetic energy release for no more than 10 to the 6th yr, far too short compared to the time scale for merging. In both galaxies, the CO data support the general picture that these are merger systems. 34 refs.

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

    SciTech Connect

    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

    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.

  12. 2D spectroscopy of double-barred galaxies

    E-print Network

    A. V. Moiseev; J. R. Valdes; V. H. Chavushyan

    2002-02-13

    The first results of the observational program of the study of 2D-kinematics in double-barred galaxies are presented. We show that, for the main part of the sample, the inner bars do not affect the circumnuclear stellar kinematics. Therefore, they are not dynamically decoupled structures. Various types of non-circular gas motion were found in many galaxies. The analysis of the ground-based and HST optical and NIR images reveals mini-spirals in about half of the investigated objects. We suggest that so called ``double-barred galaxies'' are, in fact, galaxies with very different circumnuclear structure.

  13. Physical Properties of Gaseous Features in Barred Galaxies: Effects of the Bar Strength

    NASA Astrophysics Data System (ADS)

    Kim, W.-T.; Seo, W.-Y.; Kim, Y.

    2014-09-01

    Barred galaxies commonly possess gaseous substructures such as a pair of dust lanes, a nuclear ring, and nuclear spirals at their centers. We use hydrodynamic simulations to study the physical properties of the substructures and their relationships with the bar strength. We vary the bar mass fbar relative to the spheroidal component as well as its aspect ratio, and increase the bar strength over 0.2Gyr. We find expressions for the bar strength Qb and the radius where the maximum bar torque occurs. When compared with observations, these suggest that bars in real galaxies are most likely to have fbar˜0.3. While dust lanes are aligned parallel to the bar and tend to be more straight under a stronger and more elongated bar, nuclear rings are aligned perpendicular to the bar. The radius of a nuclear ring, in general smaller than the inner Lindblad resonance radius, is a decreasing function of Qb, consistent with observations. This demonstrates that the ring size is determined primarily by the bar strength rather than the resonance. Nuclear spirals located inside nuclear rings are transient such that they unwind and become stronger with time until turning into shocks, with an unwinding rate higher for larger Qb, consistent with observations. All of these results suggest that it is the bar strength that determines the physical properties of gaseous substructures in barred galaxies.

  14. How can double-barred galaxies be long-lived?

    E-print Network

    Wozniak, Herve

    2015-01-01

    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...

  15. Evidence for an outflow from the Seyfert galaxy NGC 4051

    Microsoft Academic Search

    P. E. Christopoulou; A. J. Holloway; W. Steffen; C. G. Mundell; A. H. C. Thean; C. D. Goudis; J. Meaburn; A. Pedlar

    1996-01-01

    New observations using narrow band imaging, long-slit spectroscopy and MERLIN\\u000aobservations of the nuclear region of the Seyfert galaxy NGC~4051 have been\\u000amade. An edge brightened, triangular region of ionized gas extending 420 pc\\u000afrom the centre of the galaxy has been detected. Long-slit spectra of this\\u000aionised gas, taken at 1.5\\\\arcsec\\\\ from the core, show the \\\\oiii\\\\ emission line

  16. The Distribution of Bar Strengths in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Buta, R.; Laurikainen, E.; Salo, H.; Knapen, J. H.; Block, D. L.

    2007-05-01

    The distribution of bar strengths in disk galaxies is of fundamental importance in studies of galaxy evolution for two reasons. First, bars are the most important morphological features of galaxies that cross the spiral-S0 divide. They are a potentially fruitful way of comparing these two classes of disk galaxies and perhaps for better understanding the relation between them. Secondly, recent theoretical studies by Athanassoula show how a live halo can strongly impact the bar strength, while studies by Bournaud and Combes have shown that gas accretion can cause bar strength to be periodically variable over a Hubble time. The distribution of bar strengths should be a complex combination of halo-bar-disk angular momentum exchanges, external gas accretions, and possible effects of interactions, all over a Hubble time. The recent development of the gravitational torque method for quantifying bar strength, in conjunction with the availability of statistically well-defined image databases such as the Ohio State survey, has led to the first measures of the distribution of bar strengths in normal disk galaxies. After removal of the effects of spiral arm torques, the distribution of maximum relative bar torques in normal, massive spiral galaxies shows an approximately exponential decline with increasing bar strength. There are three issues that will be addressed in this presentation: (1) How do uncertainties in the assumed vertical scale heights, orientation parameters, and the dark matter affect this distribution? (2) Which of the above physical effects might have the greatest impact on the observed distribution? and (3) How do early-type galaxy bars compare with those seen in spirals, based on Fourier dissection studies and the same kind of bar strength analysis? This work has been supported by NSF grants AST020-5143 and AST050-7140, the Academy of Finland, the Magnus Ehrnrooth Foundation, the Leverhulme Trust, and the Anglo-American Chairman's Fund.

  17. Is NGC 3108 transforming itself from an early- to late-type galaxy - an astronomical hermaphrodite?

    NASA Astrophysics Data System (ADS)

    Hau, George K. T.; Bower, Richard G.; Kilborn, Virginia; Forbes, Duncan A.; Balogh, Michael L.; Oosterloo, Tom

    2008-04-01

    A common feature of hierarchical galaxy formation models is the process of `inverse' morphological transformation: a bulge dominated galaxy accretes a gas disc, dramatically reducing the system's bulge-to-disc mass ratio. During their formation, present-day galaxies may execute many such cycles across the Hubble diagram. A good candidate for such a `hermaphrodite' galaxy is NGC 3108: a dust-lane early-type galaxy which has a large amount of HI gas distributed in a large-scale disc. We present narrow-band H? and R-band imaging, and compare the results with the HI distribution from the literature. The emission is in two components: a nuclear bar and an extended disc component which coincides with the HI distribution. This suggests that a stellar disc is currently being formed out of the HI gas. The spatial distributions of the H? and HI emission and the HII regions are consistent with a barred spiral structure, extending some 20 kpc in radius. We measure an extinction-corrected star formation rate (SFR) of 0.42Msolaryr-1. The luminosity function of the HII regions is similar to other spiral galaxies, with a power-law index of -2.1, suggesting that the star formation mechanism is similar to other spiral galaxies. We measured the current disc mass and find that it is too massive to have been formed by the current SFR over the last few Gyr. It is likely that the SFR in NGC 3108 was higher in the past. With the current SFR, the disc in NGC 3108 will grow to be ~6.2 × 109Msolar in stellar mass within the next 5.5 Gyr. While this is substantial, the disc will be insignificant compared with the large bulge mass: the final stellar mass disc-to-bulge ratio will be ~0.02. NGC 3108 will fail to transform into anything resembling a spiral without a boost in the SFR and additional supply of gas.

  18. Galactic rings and secular evolution in barred galaxies

    NASA Astrophysics Data System (ADS)

    Knapen, Johan H.

    2015-03-01

    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 Falcón-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 Comerón 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, Comerón 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, Comerón 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 (Comerón 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.

  19. The velocity field of the Seyfert galaxy NGC 7469

    Microsoft Academic Search

    B. A. M. Westin

    1980-01-01

    Spectrographic observations of the type 1 Seyfert galaxy NGC 7469 have been made. Measurements have shown that the forbidden lines are blue-shifted, with respect to the permitted lines, thus confirming the results obtained by Barbieri et al. (1977). The tilt of the H-alpha line differs from that of the forbidden N II line, lambda 6584. Those two lines also extend

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

    NASA Astrophysics Data System (ADS)

    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

    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.

  1. Enormous disc of cool gas surrounding the nearby powerful radio galaxy NGC612 (PKS0131-36)

    NASA Astrophysics Data System (ADS)

    Emonts, B. H. C.; Morganti, R.; Oosterloo, T. A.; Holt, J.; Tadhunter, C. N.; van der Hulst, J. M.; Ojha, R.; Sadler, E. M.

    2008-06-01

    We present the detection of an enormous disc of cool neutral hydrogen (HI) gas surrounding the S0 galaxy NGC612, which hosts one of the nearest powerful radio sources (PKS0131-36). Using the Australia Telescope Compact Array, we detect MHI = 1.8 × 109Msolar of HI emission-line gas that is distributed in a 140-kpc wide disc-like structure along the optical disc and dust lane of NGC612. The bulk of the gas in the disc appears to be settled in regular rotation with a total velocity range of 850kms-1, although asymmetries in this disc indicate that perturbations are being exerted on part of the gas, possibly by a number of nearby companions. The HI disc in NGC612 suggests that the total mass enclosed by the system is Menc ~ 2.9 × 1012 sin-2 iMsolar, implying that this early-type galaxy contains a massive dark matter halo. We also discuss an earlier study by Holt et al. that revealed the presence of a prominent young stellar population at various locations throughout the disc of NGC612, indicating that this is a rare example of an extended radio source that is hosted by a galaxy with a large-scale star-forming disc. In addition, we map a faint HI bridge along a distance of 400kpc in between NGC612 and the gas-rich (MHI = 8.9 × 109Msolar) barred galaxy NGC619, indicating that likely an interaction between both systems occurred. From the unusual amounts of HI gas and young stars in this early-type galaxy, in combination with the detection of a faint optical shell and the system's high infrared luminosity, we argue that either ongoing or past galaxy interactions or a major merger event are a likely mechanism for the triggering of the radio source in NGC612. This paper is part of an ongoing study to map the large-scale neutral hydrogen properties of nearby radio galaxies and it presents the first example of large-scale HI detected around a powerful Fanaroff-Riley type II (FR-II) radio galaxy. The HI properties of the FR-II radio galaxy NGC612 are very similar to those found for low-power compact radio sources, but different from those of extended Fanaroff-Riley type I (FR-I) sources.

  2. ROSAT PSPC and HRI observations of the composite starburst/Seyfert 2 galaxy NGC 1672

    NASA Technical Reports Server (NTRS)

    Brandt, W. N.; Halpern, Jules P.; Iwasawa, K.

    1995-01-01

    The nearby barred spiral galaxy NGC 1672 has been observed with the Position Sensitive Proportional Counter (PSPC) and High Resolution Imager (HRI) instruments on board the ROSAT X-ray satellite. NGC 1672 is thought to have an obscured Seyfert nucleus, and it has strong starburst activity as well. Three bright X-ray sources with luminosities 1-2 x 10(exp 40) erg/s are clearly identified with NGC 1672. The strongest lies at the nucleus, and the other two lie at the ends of NGC 1672's prominent bar, locations that are also bright in H alpha and near-infrared images. The nuclear source is resolved by the HRI on about the scale of the recently identified nuclear ring, and one of the sources at the ends of the bar is also probably resolved. The X-ray spectrum of the nuclear source is quite soft, having a Raymond-Smith plasma temperature of approximately equals 0.7 keV and little evidence for intrinsic absorption. The ROSAT band X-ray flux of the nuclear source appears to be dominated not by X-ray binary emission but rather by diffuse gas emission. The absorption and emission properties of the sources, as well as their spatial extents, lead us to models of superbubbles driven by supernovae. However, the large density and emission measure of the nuclear X-ray source stretch the limits that can be comfortably accommodated by these models. We do not detect direct emission from the putative Seyfert nucleus, although an alternative model for the nuclear source is thermal emission from gas that is photoionized by a hidden Seyfert nucleus. The spectra of the other two X-ray sources are harder than that of the nuclear source, and have similar difficulties with regard to superbubble models.

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

    E-print Network

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

    2014-01-01

    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 $J = 1-0$ ...

  4. ROSAT HRI observations of the Local Group galaxies IC 10, NGC 147 and NGC 185

    E-print Network

    W. N. Brandt; M. J. Ward; A. C. Fabian; P. W. Hodge

    1997-08-22

    We report on pointed X-ray observations of IC 10, NGC 147 and NGC 185 made with the ROSAT High Resolution Imager (HRI). These are three Local Group galaxies that have never been previously studied in detail in the X-ray regime. IC 10 is the closest starburst galaxy to our own Galaxy, and NGC 147 and NGC 185 are companions to M31. We have discovered a variable X-ray source coincident with IC 10. The source is located near the centre of a large, non-thermal bubble of radio emission, and it is positionally coincident with an emission line star in IC 10 which has been classified as a WN type Wolf-Rayet star. We demonstrate that a confusing foreground or background source is improbable. The X-ray source is probably an X-ray binary in IC 10, and it may be a Wolf-Rayet + black hole binary. The source has mean and maximum 0.1--2.5 keV isotropic luminosities of about 2 and 4 times 10^{38} erg/s. We do not detect any sources in the central regions of NGC 147 or NGC 185. We place upper limits on their central X-ray emission, and we list all X-ray sources coincident with their outer extents. We also present the first X-ray detections of the well-studied Algol-type binary TV Cas and the W UMa-type binary BH Cas, which were both serendipitously observed during our IC 10 pointing.

  5. Resonance Rings in Early SB Galaxies: Estimating Bar Strength, Disk Star-Formation, Mass Density and M/L

    NASA Astrophysics Data System (ADS)

    Byrd, G.; Freeman, T.; Buta, R.

    2008-08-01

    We use our HST observations of the inner (r) and outer (R1) rings of the galaxy NGC 3081 [Buta, Byrd, & Freeman (2004: AJ, 127, 1982)] with n-body simulations to confirm a new analytical ring formulation [Byrd, Freeman, & Buta (2006: AJ, 131, 1377)]. The formulation takes into account the strong response for these rings which are just inside and outside co-rotation of the bar and orbital motion. We show how r and R1 sizes and shapes (plus the rotation curve) give the strength and pattern speed of the bar potential perturbation. The NGC 3081 HST observations show individual clusters in the inner ring, some of which appear to be as old as 400 Myr. We see evidence of aging in the cluster luminosity function and colors in orbital angle from the inner ring tips. Disk surface mass density (?) and mass-to-light ratio (M/L) is known with real certainty only at the solar orbital radius for the Milky Way galaxy (MW)---Flynn et al. (2006: MNRAS, 372, 1149). For other disk galaxies, there are mutually contradictory needs for accurate velocity-dispersion and thickness measurements normal to the disk. We derive how to use r and outer R1 rings to get disk ?'s. Using Fourier surface-brightness components, we obtained disk ?'s from the r through R1 ring radii for NGC 3081 and new results for NGC 6782. As with the MW, we also find the disk dynamics of both galaxies to be halo-dominated. Disk M/L's are also calculated. Contrary to common assumptions, we find that the disk M/L is not constant for either NGC 3081 or NGC 6782 but increases with radius. Having a variety of M/L's at different radii shows promise for studying secondary M/L indicators and disk star-formation history. We acknowledge grant support NASA/STScI GO 8707 and NSF AST-0206177.

  6. The H II regions of the irregular galaxy, NGC 3239

    NASA Astrophysics Data System (ADS)

    Krienke, Karl; Hodge, Paul

    1991-03-01

    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.

  7. The H II regions of the irregular galaxy, NGC 3239

    SciTech Connect

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

    1991-03-01

    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.

  8. Barred S0 Galaxies in the Coma Cluster

    E-print Network

    Lansbury, George B; Smith, Russell J

    2014-01-01

    This study uses r-band images from the Eighth Data Release of the Sloan Digital Sky Survey (SDSS DR8) to study bars in lenticular (S0) galaxies in one of the nearest rich cluster environments, the Coma cluster. We develop techniques for bar detection, and assess their success when applied to SDSS image data. To detect and characterise bars we perform 2D bulge+disk+bar light decompositions of galaxy images with GALFIT. Using a sample of artificial galaxy images we determine the faintest magnitude at which bars can be successfully measured at the depth and resolution of SDSS. We perform detailed decompositions of 83 S0 galaxies in Coma, 64 from a central sample, and 19 from a cluster outskirts sample. For the central sample, the S0 bar fraction is 72^{+5}_{-6}%. This value is significantly higher than that obtained using an ellipse fitting method for bar detection, 48^{+6}_{-6}%. At a fixed luminosity, barred S0s are redder in (g-r) colour than unbarred S0s by 0.02 mag. The frequency and strength of bars increa...

  9. NGC 4314. I - Visible and short-wavelength infrared surface photometry of the nucleus and bar

    NASA Technical Reports Server (NTRS)

    Benedict, G. F.; Higdon, J. L.; Tollestrup, E. V.; Hahn, J. M.; Harvey, P. M.

    1992-01-01

    BVI (TI CCD) and JHK (University of Texas IR Camera) surface photometry of NGC 4314, an SB (rs)ap anemic spiral with a nuclear ring containing recent star formation, is presented. The shortwave IR (SWIR) frames reveal a nuclear bar of length 2 arcsec at PA of 0 deg. The nuclear ring and associated dust were detected in all SWIR color indices. A nuclear spiral was detected in the visible and SWIR just exterior to the ring. Extremely low-amplitude spiral-shaped deficits were found in the stellar distribution in the SWIR in this same region. These are attributed to dust, since CO is detectable at or near these locations. Average minor-axis profiles show this galaxy to have a nuclear bulge obeying the de Vaucouleurs r exp 1/4 law for values in the range 2-7 arcsec. The extinction and scattering characteristics of dust near the sites of recent star formation in the nuclear ring are discussed.

  10. Soft X-ray emission from the spiral galaxy NGC 1313

    E-print Network

    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

    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 ...

  11. Intrinsic shapes of elliptical galaxy: NGC 1052 using modified prior

    NASA Astrophysics Data System (ADS)

    Kumar Singh, Arun; Chakraborty, D. K.

    Determination of intrinsic shapes of the individual elliptical galaxies using photometry is an important problem because the number of galaxies with good photometry is many more than those with good kinematics. We determine the intrinsic shapes of the light distribution of elliptical galaxies by combining the profiles of photometric data from the literature with triaxial models. We use ensembles of models so that the shape estimates are largely model independent. We follow the methodology as described in Statler (1994) which is modified to suit our requirements. We find that short to long axial ratios at very small radii and at very large radii, and the absolute value of the triaxiality difference are the best constrained shape parameters. Using a flat prior, the shapes of elliptical galaxies are reported by Chakraborty et al (2008) and Singh & Chakraborty (2009). The flat prior of 20 galaxies are superimposed over EAC-Ph other to obtain the distribution. This distribution is regarded as a prior (a modified prior) and shapes of 20 galaxies are again recalculated by using such modified prior. We determine the intrinsic shapes of the elliptical galaxy NGC 1052 using modified prior should be more reliable. These results are compared with the previous estimates which are determined by using flat prior. The plot shows the intrinsic shapes of the NGC 1052 as a function of (q0,q?) for two dimensional shapes and (q0,q?, |Td|) for three dimensional shapes, where q0 and q?(=q) are the short to long axial ratios at small and at large radii and |Td| is the absolute values of the triaxiality difference, defined as |Td|= |T? - T0|. The probability is shown in the dark gray region: darker is the region higher is the probability. We find that the galaxy NGC 1052 is flatter inside and flatter outside.

  12. NGC 5291: Implications for the Formation of Dwarf Galaxies

    NASA Technical Reports Server (NTRS)

    Malphrus, Benjamin K.; Simpson, Caroline E.; Gottesman, S. T.; Hawarden, Timothy G.

    1997-01-01

    The possible formation and evolution of dwarf irregular galaxies from material derived from perturbed evolved galaxies is addressed via an H I study of a likely example, the peculiar system NGC 5291. This system, located in the western outskirts of the cluster Abell 3574, contains the lenticular galaxy NGC 5291 which is in close proximity to a disturbed companion and is flanked by an extensive complex of numerous knots extending roughly 4 min north and 4 min south of the galaxy. In an initial optical and radio study, Longmore et al. (1979, MNRAS, 188, 285) showed that these knots have the spectra of vigorous star-forming regions, and suggested that some may in fact be young dwarf irregular galaxies. High resolution 21-cm line observations taken with the VLA are presented here and reveal that the H I distribution associated with this system encompasses not only the entire N-S complex of optical knots, but also forms an incomplete ring or tail that extends approximately 3 min to the west. The H I associated with NGC 5291 itself shows a high velocity range; the Seashell is not detected. The formation mechanism for this unusual system is unclear and two models - a large, low-luminosity ram-swept disk, and a ram-swept interaction-are discussed. The H I in the system contains numerous concentrations, mostly along the N-S arc of the star-forming complexes, which generally coincide with one or more optical knots; the larger H I features contain several x 10(exp 9) solar mass of gas. Each of the knots is compared to a set of criteria designed to determine if these objects are bound against their own internal kinetic energy and are tidally stable relative to the host galaxy. An analysis of the properties of the H I concentrations surrounding the optical star-forming complexes indicates that at least the largest of these is a bound system; it also possesses a stellar component. It is suggested that this object is a genuinely young dwarf irregular galaxy that has evolved from the material associated with the system and that this entire complex contains several proto- or young dwarf irregular galaxies in various stages of development. We are therefore witnessing the early evolution of a number of genuinely young galaxies. Given the evident importance of the NGC 5291 system as a 'nursery' for young galaxies, careful modeling is required if we are to understand this remarkable galaxy.

  13. Cosmic evolution of bars in simulations of galaxy formation

    NASA Astrophysics Data System (ADS)

    Okamoto, Takashi; Isoe, Mari; Habe, Asao

    2015-06-01

    We investigate the evolution of two bars formed in fully self-consistent hydrodynamic simulations of the formation of Milky Way-mass galaxies. One galaxy shows higher central mass concentration and has a longer and stronger bar than the other at z = 0. The stronger bar evolves by transferring its angular momentum mainly to the dark halo. Consequently the rotation speed of the bar decreases with time, while the amplitude of the bar increases with time. These features qualitatively agree with the results obtained by idealized simulations. The pattern speed of the stronger bar largely goes up and down within a half revolution in its early evolutionary stage. These oscillations occur when the bar is misaligned with the m = 4 Fourier component. These oscillations correlate with the oscillations in the triaxiality of the dark matter halo, but differently from the way identified by idealized simulations. The amplitude of the weaker bar does not increase despite the fact that its rotation slows down with time. This result contradicts what is expected from idealized simulations and is caused by the decline of the central density associated with the mass loss and feedback from the stellar populations. The amplitude of the weaker bar is further weakened by the angular momentum injection from interactions with stellar clumps in the disk. In the both galaxies, the bars are terminated around the 4:1 resonance.

  14. Gas Sloshing and Bubbles in the Galaxy Group NGC 5098

    E-print Network

    Randall, S W; Markevitch, M; Blanton, E L; Nulsen, P E J; Forman, W R

    2009-01-01

    We present results from Chandra observations of the galaxy pair and associated galaxy group NGC 5098, and find evidence for both gas sloshing and AGN heating. The X-ray brightness images show diffuse emission with a spiral structure, centered on NGC 5098a, and a sharp edge in the diffuse emission surrounding much of the galaxy at about 30 kpc. The spiral structure in the X-ray surface brightness and temperature maps, the offset between the peak of the cool gas and the central AGN, and the structure of the cold front edges all suggest gas sloshing in the core. The most likely perturber is the nearby galaxy NGC 5098b, which has been stripped of its gaseous atmosphere. Detailed images of the core reveal several X-ray cavities, two of which, just north and southeast of the central AGN, correlate with radio emission and have bright X-ray rims, similar to buoyant bubbles seen in the ICM of other systems. We estimate the pressures in the bubbles and rims and show that they are roughly equal, consistent with these be...

  15. Ultraviolet imaging of the AGN+starburst galaxy NGC 1068

    NASA Technical Reports Server (NTRS)

    Neff, Susan G.; Fanelli, Michael N.; Roberts, Laura J.; O'Connell, Robert W.; Bohlin, Ralph; Roberts, Morton S.; Smith, Andrew M.; Stecher, Theodore P.

    1994-01-01

    Images of the Seyfert 2 galaxy NGC 1068 were obtained at two ultraviolet wavelengths by the Ultraviolet Imaging Telescope (UIT). These data represent the first detailed UV imagery of a composite (active galactic nucleus + starburst) disk galaxy. NGC 1068 cotains multiple components at UV wavelengths: the central active galactic nucleus; a population of very luminous starburst knots; a bright oval inner disk; and a fainter, more circular halo. The most luminous knot, which is located approximately 750 pc from the nucleus at PA 315 deg, is approximately 80 times the luminosity of 30 Doradus and gives NGC 1068 a 'double nucleus' appearance in the UV. Significant extended emission is observed throughout the disk, unlike other disk galaxies so far observed in the UV. The radial brightness profile in both UV bandpasses generally follows an exponential decline to approximately 5 kpc. A faint halo extending to approximately 13 kpc is likely to be a galaxian-sized reflection nebula where ambient dust scatters the intense UV continuum from the inner galaxy. UV colors show a striking asymmetric morphology, which is correlated with the observed molecular CO emission.

  16. A survey of satellite galaxies around NGC 4258

    SciTech Connect

    Spencer, Meghin; Loebman, Sarah [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Yoachim, Peter, E-mail: meghins@umich.edu [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)

    2014-06-20

    We conduct a survey of satellite galaxies around the nearby spiral NGC 4258 by combining spectroscopic observations from the Apache Point Observatory 3.5 m telescope with Sloan Digital Sky Survey (SDSS) spectra. New spectroscopy is obtained for 15 galaxies. Of the 47 observed objects, we categorize 8 of them as probable satellites, 8 as possible satellites, and 17 as unlikely to be satellites. We do not speculate on the membership of the remaining 14 galaxies due to a lack of velocity and distance information. Radially integrating our best-fit NFW profile for NGC 4258 yields a total mass of 1.8 × 10{sup 12} M {sub ?} within 200 kpc. We find that the angular distribution of the satellites appears to be random, and not preferentially aligned with the disk of NGC 4258. In addition, many of the probable satellite galaxies have blue u–r colors and appear to be star-forming irregulars in SDSS images; this stands in contrast to the low number of blue satellites in the Milky Way and M31 systems at comparable distances.

  17. Black Hole Masses and the Merger of High Velocity Dispersion Galaxy NGC6861 with NGC6868 in the AS0851 Galaxy Group

    NASA Astrophysics Data System (ADS)

    Machacek, Marie

    2009-09-01

    We propose to probe the connection between the shape of the high mass end of the black hole scaling relations and galaxy interactions, AGN feedback, and black hole growth using ACIS-I X-ray observations of the merger of high velocity dispersion galaxy NGC6861 with NGC6868 in the AS0851 galaxy group. We will measure the temperature rise in the inner 300 pc of NGC6861 to investigate the mass of its central black hole and test the black hole mass - velocity dispersion correlation. We will measure temperatures and densities across cold fronts, shocks, tails and cavities to constrain the orbital parameters, dynamical forces and AGN feedback in the merger of NGC681 with NGC6868 to resolve the order of magnitude discrepancy between the black hole scaling relations for NGC6861.

  18. Constraining Galaxy Evolution With Bulge-Disk-Bar Decomposition

    E-print Network

    Tim Weinzirl; Shardha Jogee; Fabio D. Barazza

    2008-02-26

    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.

  19. XMM-NEWTON OBSERVATIONS OF LUMINOUS SOURCES IN NEARBY GALAXIES NGC 4395, NGC 4736, AND NGC 4258

    SciTech Connect

    Akyuz, A.; Avdan, H. [Department of Physics, University of Cukurova, 01330 Adana (Turkey); Kayaci, S. [Department of Astronomy, University of Erciyes, Kayseri (Turkey); Ozel, M. E. [Faculty of Arts and Sciences, Cag University, 33800 Yenice, Tarsus, Mersin (Turkey); Sonbas, E. [Department of Physics, University of Ad Latin-Small-Letter-Dotless-I yaman, 02040 Ad Latin-Small-Letter-Dotless-I yaman (Turkey); Balman, S., E-mail: aakyuz@cu.edu.tr [Department of Physics, Middle East Technical University, 06531 Ankara (Turkey)

    2013-03-15

    We present the results of a study of non-nuclear discrete sources in a sample of three nearby spiral galaxies (NGC 4395, NGC 4736, and NGC 4258) based on XMM-Newton archival data supplemented with Chandra data for spectral and timing analyses. A total of 75 X-ray sources have been detected within the D{sub 25} regions of the target galaxies. The large collecting area of XMM-Newton makes the statistics sufficient to obtain spectral fitting for 16 (about 20%) of these sources. Compiling the extensive archival exposures available, we were able to obtain the detailed spectral shapes of diverse classes of point sources. We have also studied temporal properties of these luminous sources. Eleven of them are found to show short-term (less than 80 ks) variation while eight of them show long-term variation within factors of {approx}2-5 during a time interval of {approx}2-12 years. Timing analysis provides strong evidence that most of these sources are accreting X-ray binary systems. One source that has properties different from others was suspected to be a supernova remnant, and our follow-up optical observation confirmed this. Our results indicate that sources within the three nearby galaxies are showing a variety of source populations, including several ultraluminous X-ray sources, X-ray binaries, transients together with a super soft source, and a background active galactic nucleus candidate.

  20. New ULX in the collisional ring galaxy NGC 922

    NASA Astrophysics Data System (ADS)

    Prestwich, Andrea; Galache, J.; Kalogera, V.; Linden, T.; Zezas, A.; Roberts, T.; Wolter, A.; Trinchieri, G.; Kilgard, R.

    2009-09-01

    We present a new Chandra observation of the nearby collisional ring galaxy NGC 922. NGC 922 is undergoing a violent burst of star formation as density waves are driven through the disk as a result of the collision. It is similar to the famous Cartwheel galaxy, except that the metallicity is somewhat higher and star formation rate lower. Our primary science goal is to determine whether a low metallicty environment is required to form the most luminous X-ray sources (L_x>10^{40} ergs s^{-1}). We find a total of 14 bright X-ray sources, 7 of which are ULX (L_x>10^{39} ergs s^{-1}). One source has L_x˜ 10^{40} ergs s^{-1}. The X-ray sources are associated with the H-alpha ring. However, they are NOT associated with the brightest H-alpha patches, suggesting that the ULX phase starts >1×10^{7} years after the starburst. Like the Cartwheel, the X-ray luminosity function of NGC 922 has a slope close to that of the ``cannonical'' HMXB slope of Gilfanov et al 2004. We conclude that NGC 922 is forming ULX as efficiently as the Cartwheel (after allowing for the difference in the star formation rate). We do not see a strong metallicity effect.

  1. Galaxy Zoo and ALFALFA: atomic gas and the regulation of star formation in barred disc galaxies

    NASA Astrophysics Data System (ADS)

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

    2012-08-01

    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' H I content from the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) blind H I 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 strangulation removing gas). All three explanations are consistent with the observed correlations. In addition our observations suggest bars may reduce or halt star formation in the outer parts of discs by holding back the infall of external gas beyond bar co-rotation, reddening the global colours of barred disc galaxies. This suggests that secular evolution driven by the exchange of angular momentum between stars in the bar, and gas in the disc, acts as a feedback mechanism to regulate star formation in intermediate-mass disc galaxies. This publication has been made possible by the participation of more than 200 000 volunteers in the Galaxy Zoo project. Their contributions are individually acknowledged at South East Physics Network, E-mail: karen.masters@port.ac.ukEinstein fellow.

  2. The Dynamical State of the Telescopium Galaxy Group - Deep Chandra Observations of NGC 6868 and NGC 6861

    NASA Astrophysics Data System (ADS)

    Ward-Duong, Kimberly; Randall, S. W.; Machacek, M. E.

    2011-01-01

    We present results from deep Chandra observations of NGC 6868 and NGC 6861, the two dominant elliptical galaxies in the Telescopium galaxy group (Abell S0851). We examine the diffuse gas in and around these galaxies to establish the possible interactions occurring within the group. Surface brightness images exhibit bright edges and tails, which indicate that the galaxy group is not dynamically relaxed. Spectral analysis reveals a spiral of cool gas with an associated cold front edge in NGC 6868, indicative of gas sloshing initiated by a passing galaxy or subgroup. NGC 6861 shows bright, swept back arms and a broad tail of emission, both to the northwest, suggesting that it is being ram pressure stripped due to interactions with a diffuse intracluster medium as it moves to the southeast. We find evidence that the arms are composed of cool gas originating from the galaxy core, and propose that, as seen in other systems, they may be filaments that have been buoyantly lifted by putative radio lobes inflated by the central AGN. Our results are consistent with previous suggestions that NGC 6868 and NGC 6861 are the central dominant members of two distinct subgroups, which are currently merging to form the Telescopium galaxy group. This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 0754568, by Chandra grant GO0-1009X issued under NASA contract NAS8-03060, and by the Smithsonian Institution.

  3. Image Decomposition of Barred Galaxies and AGN Hosts

    E-print Network

    Dimitri Alexei Gadotti

    2007-11-21

    I present the results of multi-component decomposition of V and R broadband images of a sample of 17 nearby galaxies, most of them hosting bars and active galactic nuclei. I use BUDDA v2.1 to produce the fits, allowing to include bars and AGN in the models. A comparison with previous results from the literature shows a fairly good agreement. It is found that the axial ratio of bars, as measured from ellipse fits, can be severely underestimated if the galaxy axisymmetric component is relatively luminous. Thus, reliable bar axial ratios can only be determined by taking into account the contributions of bulge and disc to the light distribution in the galaxy image. Through a number of tests, I show that neglecting bars when modelling barred galaxies can result in a overestimation of the bulge-to-total luminosity ratio of a factor of two. Similar effects result when bright, type 1 AGN are not considered in the models. By artificially redshifting the images, I show that the structural parameters of more distant galaxies can in general be reliably retrieved through image fitting, at least up to the point where the physical spatial resolution is ~ 1.5 Kpc. This exercise shows that disc parameters are particularly robust, but bulge parameters are prone to errors if its effective radius is small compared to the seeing radius, and might suffer from systematic effects. In this low resolution regime, the effects of ignoring bars are still present, but AGN light is smeared out. I briefly discuss the consequences of these results to studies of the structural properties of galaxies, in particular on the stellar mass budget in the local universe. With reasonable assumptions, it is possible to show that the stellar content in bars can be similar to that in classical bulges and elliptical galaxies. (Abridged)

  4. Black Hole Masses and the Merger of High Velocity Dispersion Galaxy NGC6861 with NGC6868 in the AS0851 Galaxy Group

    Microsoft Academic Search

    Marie Machacek

    2009-01-01

    We propose to probe the connection between the shape of the high mass end of the black hole scaling relations and galaxy interactions, AGN feedback, and black hole growth using ACIS-I X-ray observations of the merger of high velocity dispersion galaxy NGC6861 with NGC6868 in the AS0851 galaxy group. We will measure the temperature rise in the inner 300 pc

  5. NGC 4314 - a Galaxy Dynamicist's Playground

    Microsoft Academic Search

    G. F. Benedict; D. A. Howell; I. Jorgensen; B. J. Smith; J. D. P. Kenney

    2000-01-01

    Every morphological feature of NGC 4314 (see http:\\/\\/oposite.stsci.edu\\/pubinfo\\/pr\\/1998\\/21\\/ ) is a consequence of stellar or gas dynamics. Past studies have presented photometric evidence for a number of Lindblad Resonances (Benedict et al. 1992. AJ, 103, 757) and have established the dynamics of molecular gas associated with a 20 arcsec diameter nuclear ring (Benedict, Smith, & Kenney 1996, AJ, 112, 1318).

  6. X-raying a galaxy - PHL 6625 behind NGC 247

    Microsoft Academic Search

    Martin Elvis; Fabrizio Fiore; Paolo Giommi; Paolo Padovani

    1997-01-01

    PHL 6625, a z = 0.38, radio-quiet quasar, shows a clear excess of low-energy absorption in its ROSAT PSPC soft X-ray spectrum. This absorption is almost certainly produced by the ISM in NGC 247, a foreground spiral galaxy, which lies about 3.4 kpc (4.6 arcmin) away in projection. Comparison of the X-ray absorption and the 21-cm H I column density

  7. Chandra and Hubble Composite Image of Spiral Galaxy NGC 4631

    NASA Technical Reports Server (NTRS)

    2001-01-01

    This image shows the central region of the spiral galaxy NGC 4631 as seen edge-on from the Chandra X-Ray Observatory (CXO) and the Hubble Space Telescope (HST). The Chandra data, shown in blue and purple, provide the first unambiguous evidence for a halo of hot gas surrounding a galaxy that is very similar to our Milky Way. The structure across the middle of the image and the extended faint filaments, shown in orange, represent the observation from the HST that reveals giant bursting bubbles created by clusters of massive stars. Scientists have debated for more than 40 years whether the Milky Way has an extended corona, or halo, of hot gas. Observations of NGC 4631 and similar galaxies provide astronomers with an important tool in the understanding our own galactic environment. A team of astronomers, led by Daniel Wang of the University of Massachusetts at Amherst, observed NGC 4631 with CXO's Advanced Charge-Coupled Device (CCD) Imaging Spectrometer (ACIS). The observation took place on April 15, 2000, and its duration was approximately 60,000 seconds.

  8. The ISM in the Starburst Galaxy NGC 1569

    NASA Astrophysics Data System (ADS)

    Mühle, S.; Klein, U.; Hüttemeister, S.; Wilcots, E. M.

    2005-08-01

    The recent starburst in the nearby dwarf galaxy NGC 1569 has had a deep impact on the interstellar medium of the whole galaxy. In this paper, we discuss the consequences of this event for the distribution and kinematics of the neutral atomic hydrogen and demonstrate how strong star formation influences the properties of the surrounding molecular gas. The detection of a complex halo structure leads us to propose the accretion of an intergalactic cloud as the trigger and the gas reservoir of the remarkably strong starburst.

  9. Soft X-ray Emission from the Spiral Galaxy NGC 1313

    E-print Network

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

    1995-01-31

    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.

  10. The ratio of pattern speeds in double-barred galaxies

    E-print Network

    Font, Joan; Zaragoza-Cardiel, Javier; Fathi, Kambiz; Epinat, Benoît; Amram, Philippe

    2014-01-01

    We have obtained two-dimensional velocity fields in the ionized gas of a set of 8 double-barred galaxies, at high spatial and spectral resolution, using their H$\\alpha$ emission fields measured with a scanning Fabry-Perot spectrometer. Using the technique by which phase reversals in the non-circular motion indicate a radius of corotation, taking advantage of the high angular and velocity resolution we have obtained the corotation radii and the pattern speeds of both the major bar and the small central bar in each of the galaxies; there are few such measurements in the literature. Our results show that the inner bar rotates more rapidly than the outer bar by a factor between 3.3 and 3.6.

  11. Molecular and ionized gas in the peculiar galaxy NGC 2146

    SciTech Connect

    Young, J.S.; Claussen, M.J.; Kleinmann, S.G.; Rubin, V.C.; Scoville, N.

    1988-08-01

    New observations probing the molecular and ionized gas content of the ultrahigh surface brightness, peculiar spiral galaxy NGC 2146 are presented. The dynamical center of the galaxy lies toward a dense dust lane. The molecular mass of the galaxy in the central 15 kpc is 10 to the 10th solar. Strong emission from the central 5 kpc, as well as a string of H II regions extending along an arc 8 arcmin long are observed. Evidence is found for a high mass concentration within the central 100 pc, highly noncircular motions along the major axis, and a significant discrepancy between the velocities of the H II regions in the arc and those in the disk. The high-mass star formation efficiency is elevated by more than two orders of magnitude in the center of the galaxy relative to that in the outer disk. 25 references.

  12. Smooth dark spiral arms in the flocculent galaxy NGC2841

    NASA Astrophysics Data System (ADS)

    Block, David L.; Elmegreen, B. G.; Wainscoat, R. J.

    1996-06-01

    OPTICAL images of the arms of spiral galaxies invariably show massive blue stars forming in ridges of interstellar gas and dust1. These are particularly striking in 'grand-design' galaxies, in which the stellar positions are influenced by spiral density waves1. By contrast, many galaxies have a 'flocculent' appearance, with no obvious evidence of spiral structure at visible wavelengths. Here we report infrared observations of the prototype flocculent galaxy NGC2841, which reveal a remarkable system of long, dark spiral arms. These arms arise from concentrations of dust; they are hidden at optical wavelengths by light scattered from the dust. The mechanism that has organized the gas and dust into these dark arms is at present unclear; the arms might be highly sheared dense clouds, or they might correspond to density waves in the interstellar medium driven by an elongated central bulge, which would not affect the stable stellar disk.

  13. STAR FORMATION MODELS FOR THE DWARF GALAXIES NGC 2915 AND NGC 1705

    SciTech Connect

    Elson, E. C.; De Blok, W. J. G.; Kraan-Korteweg, R. C. [Astrophysics, Cosmology and Gravity Centre (ACGC), Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701 (South Africa)

    2012-01-15

    Crucial to a quantitative understanding of galaxy evolution are the properties of the interstellar medium that regulate galactic-scale star formation activity. We present here the results of a suite of star formation models applied to the nearby blue compact dwarf galaxies NGC 2915 and NGC 1705. Each of these galaxies has a stellar disk embedded in a much larger, essentially starless H I disk. These atypical stellar morphologies allow for rigorous tests of star formation models that examine the effects on star formation of the H I, stellar, and dark matter mass components, as well as the kinematics of the gaseous and stellar disks. We use far-ultraviolet and 24 {mu}m images from the Galaxy Evolution Explorer and the Spitzer Infrared Nearby Galaxies Survey, respectively, to map the spatial distribution of the total star formation rate surface density within each galaxy. New high-resolution H I line observations obtained with the Australia Telescope Compact Array are used to study the distribution and dynamics of each galaxy's neutral interstellar medium. The standard Toomre Q parameter is unable to distinguish between active and non-active star-forming regions, predicting the H I disks of the dwarfs to be sub-critical. Two-fluid instability models incorporating the stellar and dark matter components of each galaxy, in addition to the gaseous component, yield unstable portions of the inner disk. Finally, a formalization in which the H I kinematics are characterized by the rotational shear of the gas produces models that very accurately match the observations. This suggests the time available for perturbations to collapse in the presence of rotational shear to be an important factor governing galactic-scale star formation.

  14. The interstellar halo of spiral galaxies: NGC 891

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    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.

  15. H I Studies of the Sculptor Group Galaxies. IV - NGC 247

    NASA Astrophysics Data System (ADS)

    Carignan, C.; Puche, D.

    1995-07-01

    A VLA HI map was made of NGC 247. In this study, there is a continuum map (ngc0247.con), an HI data cube (ngc0247.cub), and moment maps (ngc0247.m0 = total HI, ngc0247.m1 = velocity field, and ngc0247.m2 = second moment). These maps have been used in an extensive dynamical and kinematical study of the Sculptor Group galaxies. The images and related TeX file come from the NRAO CDROM "Images From the Radio Universe" (c. 1992 National Radio Astronomy Observatory, used with permission).

  16. H I Studies of the Sculptor Group Galaxies. V - NGC 253

    NASA Astrophysics Data System (ADS)

    Puche, D.; Carignan, C.; van Gorkom, J. H.

    1995-07-01

    A VLA HI map was made of NGC 253. In this study, there is a continuum map (ngc0253.con), an HI data cube (ngc0253.cub), and moment maps (ngc0253.m0 = total HI, ngc0253.m1 = velocity field, and ngc0253.m2 = second moment). These maps have been used in an extensive dynamical and kinematical study of the Sculptor Group galaxies. The images and related TeX file come from the NRAO CDROM "Images From the Radio Universe" (c. 1992 National Radio Astronomy Observatory, used with permission).

  17. H I Studies of the Sculptor Group Galaxies. II - NGC 7793

    NASA Astrophysics Data System (ADS)

    Carignan, C.; Puche, D.

    1995-08-01

    A VLA HI map was made of NGC 7793. In this study, there is a continuum map (ngc7793.con), an HI data cube (ngc7793.cub), and moment maps (ngc7793.m0 = total HI, ngc7793.m1 = velocity field, and ngc7793.m2 = second moment). These maps have been used in an extensive dynamical and kinematical study of the Sculptor Group galaxies. The images and related TeX file come from the NRAO CDROM "Images From the Radio Universe" (c. 1992 National Radio Astronomy Observatory, used with permission).

  18. H I Studies of the Sculptor Group Galaxies. III - NGC 55

    NASA Astrophysics Data System (ADS)

    Puche, Daniel; Carignan, Claude; Wainscoat, Richard J.

    1995-07-01

    A VLA HI map was made of NGC 55. In this study, there is a continuum map (ngc0055.con), an HI data cube (ngc0055.cub), and moment maps (ngc0055.m0 = total HI, ngc0055.m1 = velocity field, and ngc0055.m2 = second moment). These maps have been used in an extensive dynamical and kinematical study of the Sculptor Group galaxies. The images and related TeX file come from the NRAO CDROM "Images From the Radio Universe" (c. 1992 National Radio Astronomy Observatory, used with permission).

  19. H I Studies of the Sculptor Group Galaxies. VI - NGC 300

    NASA Astrophysics Data System (ADS)

    Puche, D.; Carignan, C.; Bosma, A.

    1995-07-01

    A VLA HI map was made of NGC 300. In this study, there is a continuum map (ngc0300.con), an HI data cube (ngc0300.cub), and moment maps (ngc0300.m0 = total HI, ngc0300.m1 = velocity field, and ngc0300.m2 = second moment). These maps have been used in an extensive dynamical and kinematical study of the Sculptor Group galaxies. The images and related TeX file come from the NRAO CDROM "Images From the Radio Universe" (c. 1992 National Radio Astronomy Observatory, used with permission).

  20. Hard Gamma Ray Emission from the Starburst Galaxy NGC 253

    NASA Technical Reports Server (NTRS)

    Jackson, James M.; Marscher, Alan M.

    1996-01-01

    We have completed the study to search for hard gamma ray emission from the starburst galaxy NGC 253. Since supernovae are thought to provide the hard gamma ray emission from the Milky Way, starburst galaxies, with their extraordinarily high supernova rates, are prime targets to search for hard gamma ray emission. We conducted a careful search for hard gamma ray emission from NGC 253 using the archival data from the EGRET experiment aboard the CGRO. Because this starburst galaxy happens to lie near the South Galactic Pole, the Galactic gamma ray background is minimal. We found no significant hard gamma ray signal toward NGC 253, although a marginal signal of about 1.5 sigma was found. Because of the low Galactic background, we obtained a very sensitive upper limit to the emission of greater than 100 MeV gamma-rays of 8 x 10(exp -8) photons/sq cm s. Since we expected to detect hard gamma ray emission, we investigated the theory of gamma ray production in a dense molecular medium. We used a leaky-box model to simulate diffusive transport in a starburst region. Since starburst galaxies have high infrared radiation fields, we included the effects of self-Compton scattering, which are usually ignored. By modelling the expected gamma-ray and synchrotron spectra from NGC 253, we find that roughly 5 - 15% of the energy from supernovae is transferred to cosmic rays in the starburst. This result is consistent with supernova acceleration models, and is somewhat larger than the value derived for the Galaxy (3 - 10%). Our calculations match the EGRET and radio data very well with a supernova rate of 0.08/ yr, a magnetic field B approx. greater than 5 x 10(exp -5) G, a density n approx. less than 100/sq cm, a photon density U(sub ph) approx. 200 eV/sq cm, and an escape time scale tau(sub 0) approx. less than 10 Myr. The models also suggest that NGC 253 should be detectable with only a factor of 2 - 3 improvement in sensitivity. Our results are consistent with the standard picture of gamma-ray acceleration by supernovae.

  1. Halo properties and secular evolution in barred galaxies

    E-print Network

    E. Athanassoula

    2005-10-28

    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.

  2. LUMINOSITIES OF BARRED AND UNBARRED S0 GALAXIES

    SciTech Connect

    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

    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.

  3. Surface Brighteness Distribrtion of NGC 7755

    NASA Astrophysics Data System (ADS)

    Chun, Mun-Suk; Sohn, Seong-Min

    1992-06-01

    Isophote map and luminosity profile of the barred spiral galaxy NGC 7755 are obtained from PDS scanning of PAL 0-471 plate. From the isophote map, NGC 7755 can be classified SBbc(r) with asymmetric bar ring. We get several physical parameters (MTo, U(R)CD, D/B, Cij, M/L) of NGC 7755 from the analysis of the luminosity distribution.

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

    E-print Network

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

    2012-01-01

    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...

  5. Globular Clusters in the Sombrero Galaxy (NGC 4594)

    E-print Network

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

    1997-01-20

    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.

  6. CHANDRA OBSERVATION DIFFUSE GAS AND LOWMASS XRAY BINARIES THE ELLIPTICAL GALAXY NGC 4649 (M60)

    E-print Network

    Sarazin, Craig

    CHANDRA OBSERVATION DIFFUSE GAS AND LOW­MASS X­RAY BINARIES THE ELLIPTICAL GALAXY NGC 4649 (M60 a Chandra X­ray observation X­ray bright elliptical galaxy NGC 4649. addition bright diffuse emission, resolve 165 discrete sources, most which presumably low­mass X­ray binaries. found previous studies

  7. XMMNEWTON OBSERVATION DIFFUSE GAS AND LOWMASS XRAY BINARIES THE ELLIPTICAL GALAXY NGC 4649 (M60)

    E-print Network

    Sarazin, Craig

    XMM­NEWTON OBSERVATION DIFFUSE GAS AND LOW­MASS X­RAY BINARIES THE ELLIPTICAL GALAXY NGC 4649 (M60­Newton X­ray observation X­ray--bright elliptical galaxy NGC 4649. In addition bright diffuse emission sources power law, while diffuse spectrum requires a hard and a soft component, presumably relatively

  8. Dark matter deprivation in the field elliptical galaxy NGC 7507

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    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), Ministério da Ciência e Tecnologia (Brazil) and SECYT (Argentina).

  9. Gas Flows and Star Formation in the Ringed Galaxy NGC 4736

    NASA Astrophysics Data System (ADS)

    Wong, Tony; Blitz, Leo

    2001-03-01

    We present high-resolution (~5'') BIMA CO observations of the ringed galaxy NGC 4736, along with previously published VLA HI data (Braun, 1995). Strong CO emission is detected from the star-forming ring at r=45'' and in the central region, where a molecular bar is apparent. The azimuthally averaged gas surface density is still much less than the Toomre critical density within r=60'', despite the starburst conditions in the ring (gas depletion time <~1 Gyr). Both CO and HI velocity fields show strong departures from a circular rotating disc model. The velocity residuals are consistent with inflowing gas near the ends of the central bar, outflowing gas between the bar and the ring, and inflowing gas outside the ring. We propose that the high star formation efficiency in the ring results from gas being driven out towards the OLR of the bar and in towards the ILR of the larger oval distortion. However, the strong signature of inflow outside the ring is probably due in part to gas motion in elliptical orbits.

  10. GAS SLOSHING AND BUBBLES IN THE GALAXY GROUP NGC 5098

    SciTech Connect

    Randall, S. W.; Jones, C.; Markevitch, M.; Nulsen, P. E. J.; Forman, W. R. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Blanton, E. L. [Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States)], E-mail: srandall@cfa.harvard.edu, E-mail: cjf@cfa.harvard.edu, E-mail: mmarkevitch@cfa.harvard.edu, E-mail: wrf@cfa.harvard.edu, E-mail: eblanton@bu.edu

    2009-08-01

    We present results from Chandra observations of the galaxy pair and associated galaxy group NGC 5098, and find evidence for both gas sloshing and active galactic nucleus (AGN) heating. The X-ray brightness images show diffuse emission with a spiral structure, centered on NGC 5098a, and a sharp edge in the diffuse emission surrounding much of the galaxy at about 30 kpc. The spiral structure in the X-ray surface brightness and temperature maps, the offset between the peak of the cool gas and the central AGN, and the structure of the cold front edges all suggest gas sloshing in the core. The most likely perturber is the nearby galaxy NGC 5098b, which has been stripped of its gaseous atmosphere. Detailed images of the core reveal several X-ray cavities, two of which, just north and southeast of the central AGN, correlate with radio emission and have bright X-ray rims, similar to buoyant bubbles seen in the intracluster medium of other systems. We estimate the pressures in the bubbles and rims and show that they are roughly equal, consistent with these being young features, as suggested by their close proximity to the central AGN. We assume that the other X-ray cavities in the core, which show no correlation with existing radio observations, are ghost cavities from previous AGN outbursts. An estimate of the mechanical energy required to inflate the cavities indicates that it is sufficient to offset radiative cooling of the gas for 15 Myr. Therefore, for a typical cycle time of 10{sup 7} yr, the central AGN energy output is enough to balance cooling over long timescales.

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

    SciTech Connect

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

    1988-07-01

    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.

  12. Cepheid Variables in the Maser-host Galaxy NGC 4258

    NASA Astrophysics Data System (ADS)

    Hoffmann, Samantha L.; Macri, Lucas M.

    2015-06-01

    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 very long baseline interferometry observations of water masers. We imaged two fields within this galaxy using the Gemini North telescope and the Gemini Multi-Object Spectrograph, obtaining 16 epochs of data in the Sloan Digital Sky Survey gri bands over 4 yr. We carried out point-spread function 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 should enable Cepheid searches out to at least 10 Mpc.

  13. Cepheid Variables in the Maser-Host Galaxy NGC 4258

    E-print Network

    Hoffmann, Samantha L

    2015-01-01

    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.

  14. Two-micron spectrophotometry of the galaxy NGC 253

    NASA Technical Reports Server (NTRS)

    Wynn-Williams, C. G.; Becklin, E. E.; Matthews, K.; Neugebauer, G.

    1979-01-01

    A very strong Brackett-gamma hydrogen emission line, and the 2.3 micron CO stellar absorption feature were measured in NGC 253. The presence and strength of the CO feature indicates that late type giant stars produce most of the 2.2 micron continuum emission, while the rate of ionization implied by strength of the Brackett-gamma line indicates that much, perhaps all, of the luminosity detected at far infrared wavelengths originates from a large number of OB stars. As compared to the corresponding region of the Galaxy, the number of massive young stars in the central 200 pc of NGC 253 is thirty times greater, but the total mass of stars is roughly the same.

  15. Stellar populations in the dwarf elliptical galaxy NGC 185

    NASA Technical Reports Server (NTRS)

    Lee, Myung G.; Freedman, Wendy L.; Madore, Barry F.

    1993-01-01

    The study presents BVRI CCD photometry of about 5300 stars in the central area of the dwarf elliptical galaxy NGC 185 in the Local Group. The color-magnitude diagram shows three distinct stellar populations: a dominant RGB population, AGB stars located above the tip of the RGB stars, and a small number of young stars having blue to yellow colors. The foreground reddening is estimated to be 0.19 +/- 0.03 mag using the (B - V) - (V - I) diagram for the bright foreground stars with good photometry. Surface photometry of the central area of NGC 185 is presented; it shows that the colors become rapidly bluer inside R of about 10 arcsec. Structural parameters indicate that the mass-to-luminosity ratio ranges from 3 to 5.

  16. X-raying a galaxy - PHL 6625 behind NGC 247

    NASA Astrophysics Data System (ADS)

    Elvis, Martin; Fiore, Fabrizio; Giommi, Paolo; Padovani, Paolo

    1997-11-01

    PHL 6625, a z = 0.38, radio-quiet quasar, shows a clear excess of low-energy absorption in its ROSAT PSPC soft X-ray spectrum. This absorption is almost certainly produced by the ISM in NGC 247, a foreground spiral galaxy, which lies about 3.4 kpc (4.6 arcmin) away in projection. Comparison of the X-ray absorption and the 21-cm H I column density through NGC 247 suggests a larger than expected effect in X-rays. Several possibilities are considered to explain this apparent discrepancy. Additional high-velocity H I components of the ISM are currently the most plausible cause. PHL 6625 also clearly decreased in its soft X-ray flux by a factor of two in six months.

  17. Seeing Galaxies though Thick and Thin. IV. The Superimposed Spiral Galaxies of NGC 3314

    E-print Network

    William C. Keel; Raymond E. White III

    2001-06-04

    The superimposed pair of spiral galaxies NGC 3314 offers a unique opportunity to trace the dust properties in a spiral galaxy. We analyze multicolor HST imaging, supported by ground-based near-IR imaging and fiber-array spectroscopy to measure dust extinction in the foreground Sc galaxy NGC 3314A, which is backlit by the Sb system NGC 3314B. We can measure extinctions over a wide range of galactocentric radii in the foreground galaxy, from 0.4-4.5 kpc. In the outer disk, the extinction is strongly localized in discrete dust lanes. These dust features show an extinction curve with a slope close to the Galactic mean (R = 3.5+/-0.3) from 1.6 to 3.8 kpc, with no radial trend. Using the I-K color of the background nucleus, we derive an extinction A(I) = 3.3 through the disk at a projected distance 400 pc from the nucleus of NGC 3314A. The extinction in even the inner disk of NGC 3314A is quite patchy, since background H-alpha emission is detected from all parts of the system. Local anticorrelations between foreground and background line emission demonstrate that the dust is concentrated to star-forming regions, as has been found for the blue light in several systems. Colors of dust lanes in NGC 3314A which are projected only partially against the background disk indicate that the dust scale height in the foreground disk is substantially smaller than that of the stars.

  18. Why Buckling Stellar Bars Weaken in Disk Galaxies

    E-print Network

    Inma Martinez-Valpuesta; Isaac Shlosman

    2004-08-13

    Young stellar bars in disk galaxies experience a vertical buckling instability which terminates their growth and thickens them, resulting in a characteristic peanut/boxy shape when viewed edge on. Using N-body simulations of galactic disks embedded in live halos, we have analyzed the bar structure throughout this instability and found that the outer third of the bar dissolves completely while the inner part (within the vertical inner Lindblad resonance) becomes less oval. The bar acquires the frequently observed peanut/boxy-shaped isophotes. We also find that the bar buckling is responsible for a mass injection above the plane, which is subsequently trapped by specific 3-D families of periodic orbits of particular shapes explaining the observed isophotes, in line with previous work. Using a 3-D orbit analysis and surfaces of sections, we infer that the outer part of the bar is dissolved by a rapidly widening stochastic region around its corotation radius -- a process related to the bar growth. This leads to a dramatic decrease in the bar size, decrease in the overall bar strength and a mild increase in its pattern speed, but is not expected to lead to a complete bar dissolution. The buckling instability appears primarily responsible for shortening the secular diffusion timescale to a dynamical one when building the boxy isophotes. The sufficiently long timescale of described evolution, ~1 Gyr, can affect the observed bar fraction in local universe and at higher redshifts, both through reduced bar strength and the absence of dust offset lanes in the bar.

  19. Interstellar Gas in the NGC 4410 Galaxy Group

    E-print Network

    Beverly J. Smith

    2000-05-04

    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.

  20. THE HOT INTERSTELLAR MEDIUM OF THE INTERACTING GALAXY NGC 4490

    SciTech Connect

    Richings, A. J.; Fabbiano, G.; Wang Junfeng [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Roberts, T. P. [Department of Physics, University of Durham, South Road, Durham, DH1 3LE (United Kingdom)

    2010-11-10

    We present an analysis of the hot interstellar medium (ISM) in the spiral galaxy NGC 4490, which is interacting with the irregular galaxy NGC 4485, using {approx}100 ks of Chandra ACIS-S observations. The high angular resolution of Chandra enables us to remove discrete sources and perform spatially resolved spectroscopy for the star-forming regions and associated outflows, allowing us to look at how the physical properties of the hot ISM such as temperature, hydrogen column density, and metal abundances vary throughout these galaxies. We find temperatures of >0.41 keV and 0.85{sup +0.59}{sub -0.12} keV, electron densities of >1.87{eta}{sup -1/2} x 10{sup -3} cm{sup -3} and 0.21{sup +0.03}{sub -0.04{eta}}{sup -1/2} x 10{sup -3} cm{sup -3}, and hot gas masses of >1.1{eta}{sup 1/2} x 10{sup 7} M{sub sun} and {approx}3.7{eta}{sup 1/2} x 10{sup 7} M{sub sun} in the plane and halo of NGC 4490, respectively, where {eta} is the filling factor of the hot gas. The abundance ratios of Ne, Mg, and Si with respect to Fe are found to be consistent with those predicted by theoretical models of type II supernovae (SNe). The thermal energy in the hot ISM is {approx}5% of the total mechanical energy input from SNe, so it is likely that the hot ISM has been enriched and heated by type II SNe. The X-ray emission is anticorrelated with the H{alpha} and mid-infrared emission, suggesting that the hot gas is bounded by filaments of cooler ionized hydrogen mixed with warm dust.

  1. The Warm Absorber of the Seyfert Galaxy NGC 5548

    NASA Astrophysics Data System (ADS)

    Andrade, M.; Krongold, Y.; Elvis, M.; Nicastro, F.; Binette, L.; Brickhouse, N.

    2008-04-01

    We present a spectral analysis of the X-ray Chandraof the Seyfert 1 Galaxy NGC 5548. The warm absorber present in this object was modeled with the code PHASE. We detected two different outflow velocity systems in this source. One of the absorbing systems has outflow velocity of -1091+/-63 km s(-1) and the other of -568+/-49 km s(-1) . Each system required two absorption components with different ionization level to fit the observed features. Each velocity system may consist of a multi-phase medium.

  2. The Bar Instability Many disk galaxies contain a bar : a linear structure crossing the disk. Bars can be analyzed

    E-print Network

    Barnes, Joshua Edward

    , they may act as `engines' of evolutionary change in their host galaxies (Kormendy 1982). Bars to\\Omega 2 b in (19.2) represents the outward­directed centrifugal pseudoforce present in a rotating and L5 lie along the y axis; these are the places where the centrifugal pseudoforce balances gravity. L3

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

    SciTech Connect

    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

    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.

  4. GMOS Spectroscopy of the S0 galaxy NGC 3115

    E-print Network

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

    2006-01-10

    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.

  5. Extra-planar HI in the starburst galaxy NGC 253

    E-print Network

    Rense Boomsma; Tom Oosterloo; Filippo Fraternali; Thijs van der Hulst; Renzo Sancisi

    2004-10-03

    Observations of the nearby starburst galaxy NGC 253 in the 21-cm line reveal the presence of neutral hydrogen in the halo, up to 12 kpc from the galactic plane. This extra-planar HI is found only in one half of the galaxy and is concentrated in a half-ring structure and plumes which are lagging in rotation with respect to the disk. The HI plumes are seen bordering the bright Halpha and X-ray halo emission. It is likely that, as proposed earlier for the Halpha and the X-rays, also the origin of the extra-planar HI is related to the central starburst and to the active star formation in the disk. A minor merger and gas accretion are also discussed as possible explanations. The HI disk is less extended than the stellar disk. This may be the result of ionization of its outer parts or, alternatively, of tidal or ram pressure stripping.

  6. Wind and Reflections From Black Hole in Galaxy NGC 1068

    NASA Technical Reports Server (NTRS)

    2000-01-01

    Chandra X-Ray Observatory provided this composite X-ray (blue and green) and optical (red) image of the active galaxy NGC 1068 showing gas blowing away in a high-speed wind from the vicinity of a central supermassive black hole. Regions of intense star formation in the irner spiral arms of the galaxy are highlighted by both optical and x-ray emissions. A doughnut shaped cloud of cool gas and dust surrounding the black hole, known as the torus, appears as the elongated white spot . It has has a mass of about 5 million suns and is estimated to extend from within a few light years of the black hole out to about 300 light years.

  7. Resolving Molecular Clouds in the Nearby Galaxy NGC 300

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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.

  8. A violent interaction between the dwarf galaxy UGC 7636 and the giant elliptical galaxy NGC 4472

    NASA Technical Reports Server (NTRS)

    Mcnamara, Brian R.; Sancisi, Renzo; Henning, Patricia A.; Junor, William

    1994-01-01

    We present new U, B, R, and H I imagery of the Virgo Cluster giant elliptical galaxy NGC 4472 and its interacting dwarf companion galaxy UGC 7636. Using a composite image reconstruction technique, we show that a trail of debris approx. 5 arcmin in length and approx. 1 arcmin in width (30x6 kpc for a Virgo cluster distance of 20 Mpc) is projected northward from the dwarf galaxy. A cloud of H I is projected along the northwest edge of the debris between the dwarf and gE. The dwarf's nuclear morphology is irregular and bow-shaped on what appears to be its leading edge. Apart from a number of isolated blue regions, most of of the trailing debris is similar in color to the dwarf's nucleus. Only a modest enhancement of star formation appears to have been induced by the interaction. Although separated by 15 kpc, the H I and stellar morphologies are remarkably similar. The stars and H I appear to have been tidally distorted in situ, prior to the cloud's removal by ram pressure. If the H I has maintained its shape by magnetic support, a magnetic field strength an order of magnitude larger than the galaxy's is required. Ram pressure deceleration due to the cloud's motion through NGC 4472's x-ray-emitting interstellar medium shold be sufficient for the cloud to become gravitationally bound to NGC 4472. The H I cloud is not self-gravitating and may fragment and be destroyed in the interaction. UGC 7636 will probably be disrupted by NGC 4472's strong tidal forces; the stellar debris will disperse into the Virgo cluster or become bound to NGC 4472's halo on eccentric orbits. The debris captured in the collision will have a negligible impact on NGC 4472's stellar and gaseous content. On the other hand, if similar interactions are common in giant elliptical galaxies, they could alter or deplete surrounding dwarf galaxy populations, fuel bursts of nuclear activity, and perhaps provide a source of magnetic energy to their interstellar media.

  9. Applying Schwarzschild's orbit superposition method to barred or non-barred disc galaxies

    E-print Network

    Vasiliev, Eugene

    2015-01-01

    We present an implementation of the Schwarzschild orbit superposition method which can be used for constructing self-consistent equilibrium models of barred or non-barred disc galaxies, or of elliptical galaxies with figure rotation. This is a further development of the publicly available code SMILE; its main improvements include a new efficient representation of an arbitrary gravitational potential using two-dimensional spline interpolation of Fourier coefficients in the meridional plane, as well as the ability to deal with rotation of the density profile and with multicomponent mass models. We compare several published methods for constructing composite axisymmetric disc--bulge--halo models and demonstrate that our code produces the models that are closest to equilibrium. We also apply it to create models of triaxial elliptical galaxies with cuspy density profiles and figure rotation, and find that such models can be found and are stable over many dynamical times in a wide range of pattern speeds and angula...

  10. Deep H I Survey of the Spiral Galaxy NGC 2403

    E-print Network

    Filippo Fraternali; Gustaaf van Moorsel; Renzo Sancisi; Tom Oosterloo

    2002-03-22

    High sensitivity H I observations of the nearby spiral galaxy NGC 2403 obtained with the VLA are presented and discussed. The properties of the extended, differentially rotating H I layer with its H I holes, spiral structure and outer warp are described. In addition, these new data reveal the presence of a faint, extended and kinematically anomalous component. This shows up in the H I line profiles as extended wings of emission towards the systemic velocity. In the central regions these wings are very broad (up to 150 km/s) and indicate large deviations from circular motion. We have separated the anomalous gas component from the cold disk and have obtained for it a separate velocity field and a separate rotation curve. The mass of the anomalous component is 1/10 of the total H I mass. The rotation velocity of the anomalous gas is 25-50 km/s lower than that of the disk. Its velocity field has non-orthogonal major and minor axes that we interpret as due to an overall inflow motion of 10-20 km/s towards the centre of the galaxy. The picture emerging from these observations is that of a cold H I disk surrounded by a thick and clumpy H I layer characterized by slower rotation and inflow motion towards the center. The origin of this anomalous gas layer is unclear. It is likely, however, that it is related to the high rate of star formation in the disk of NGC 2403 and that its kinematics is the result of a galactic fountain type of mechanism. We suggest that these anomalous H I complexes may be analogous to a part of the High Velocity Clouds of our Galaxy.

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

    SciTech Connect

    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

    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.

  12. Hydrodynamical Simulations of Nuclear Rings in Barred Galaxies

    NASA Astrophysics Data System (ADS)

    Li, Zhi; Shen, Juntai; Kim, Woong-Tae

    2015-06-01

    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 rings are allowed only in the radial range of {x}2 orbits. A round nuclear ring forms exactly at the radius where the residual angular momentum of infalling gas balances the centrifugal force, which can be described by a parameter {f}{ring} measured from the rotation curve. The gravitational torque on gas in high pattern speed models is larger, leading to a smaller ring size than in the low pattern speed models. Our result may have important implications for using nuclear rings to measure the parameters of real barred galaxies with 2D gas kinematics.

  13. Applying Schwarzschild's orbit superposition method to barred or non-barred disc galaxies

    NASA Astrophysics Data System (ADS)

    Vasiliev, Eugene; Athanassoula, E.

    2015-07-01

    We present an implementation of the Schwarzschild orbit superposition method, which can be used for constructing self-consistent equilibrium models of barred or non-barred disc galaxies, or of elliptical galaxies with figure rotation. This is a further development of the publicly available code SMILE; its main improvements include a new efficient representation of an arbitrary gravitational potential using two-dimensional spline interpolation of Fourier coefficients in the meridional plane, as well as the ability to deal with rotation of the density profile and with multicomponent mass models. We compare several published methods for constructing composite axisymmetric disc-bulge-halo models and demonstrate that our code produces the models that are closest to equilibrium. We also apply it to create models of triaxial elliptical galaxies with cuspy density profiles and figure rotation, and find that such models can be found and are stable over many dynamical times in a wide range of pattern speeds and angular momenta, covering both slow- and fast-rotator classes. We then attempt to create models of strongly barred disc galaxies, using an analytic three-component potential, and find that it is not possible to make a stable dynamically self-consistent model for this density profile. Finally, we take snapshots of two N-body simulations of barred disc galaxies embedded in nearly-spherical haloes, and construct equilibrium models using only information on the density profile of the snapshots. We demonstrate that such reconstructed models are in near-stationary state, in contrast with the original N-body simulations, one of which displayed significant secular evolution.

  14. Ring structure and warp of NGC5907 -- Interaction with dwarf galaxies

    E-print Network

    Zhaohui Shang; Zhongyuan Zheng; Elias Brinks; Jiansheng Chen; David Burstein; Hongjun Su; Yong-IK Byun; Licai Deng; Zugan Deng; Xiaohui Fan; Zhaoji Jiang; Yong Li; Weipeng Lin; Feng Ma; Wei-hsin Sun; Beverley Wills; Rogier A. Windhorst; Hong Wu; Xiaoyang Xia; Wen Xu; Suijian Xue; Haojing Yan; Xu Zhou; Jin Zhu; Zhenlong Zou

    1998-06-30

    The edge-on, nearby spiral galaxy NGC5907 has long been used as the prototype of a ``non-interacting'' warped galaxy. We report here the discovery of two interactions with companion dwarf galaxies that substantially change this picture. First, a faint ring structure is discovered around this galaxy that is likely due to the tidal disruption of a companion dwarf spheroidal galaxy. The ring is elliptical in shape with the center of NGC5907 close to one of the ring's foci. This suggests the ring material is in orbit around NGC5907. No gaseous component to the ring has been detected either with deep H$\\alpha$ images or in Very Large Array (VLA) HI 21-cm line maps. The visible material in the ring has an integrated luminosity dwarf spheroidal galaxy. Second, we find that NGC5907 has a dwarf companion galaxy, PGC54419, projected to be only 36.9 kpc from the center of NGC5907, close in radial velocity (\\Delta V = 45 km s^{-1}) to the giant spiral galaxy. This dwarf is seen at the tip of the HI warp and in the direction of the warp. Hence, NGC5907 can no longer be considered ``non-interacting,'' but is obviously interacting with its dwarf companions much as the Milky Way interacts with its dwarf galaxies. These results, coupled with the finding by others that dwarf galaxies tend to be found around giant galaxies, suggest that tidal interaction with companions, even if containing a mere 1% of the mass of the parent galaxy, might be sufficient to excite the warps found in the disks of many large spiral galaxies.

  15. Star formation properties in barred galaxies. III. Statistical study of bar-driven secular evolution using a sample of nearby barred spirals

    SciTech Connect

    Zhou, Zhi-Min; Wu, Hong [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Cao, Chen, E-mail: zmzhou@bao.ac.cn, E-mail: hwu@bao.ac.cn, E-mail: caochen@sdu.edu.cn [School of Space Science and Physics, Shandong University at Weihai, Weihai, Shandong 264209 (China)

    2015-01-01

    Stellar bars are important internal drivers of secular evolution in disk galaxies. Using a sample of nearby spiral galaxies with weak and strong bars, we explore the relationships between the star formation feature and stellar bars in galaxies. We find that galaxies with weak bars tend coincide with low concentrical star formation activity, while those with strong bars show a large scatter in the distribution of star formation activity. We find enhanced star formation activity in bulges toward stronger bars, although not predominantly, consistent with previous studies. Our results suggest that different stages of the secular process and many other factors may contribute to the complexity of the secular evolution. In addition, barred galaxies with intense star formation in bars tend to have active star formation in their bulges and disks, and bulges have higher star formation densities than bars and disks, indicating the evolutionary effects of bars. We then derived a possible criterion to quantify the different stages of the bar-driven physical process, while future work is needed because of the uncertainties.

  16. PNe in the dwarf galaxy NGC 6822: Detection of new candidates

    E-print Network

    P. Leisy; R. L. M. Corradi; L. Magrini; R. Greimel; A. Mampaso; M. Dennefeld

    2005-03-15

    We have discovered 13 new candidate Planetary Nebulae (PNe) in the dwarf irregular galaxy NGC 6822, increasing its total number to 17 objects. Our sample of candidate PNe is complete down to 3.5 mag below the brightest PN.

  17. Cover: An image of the galaxy NGC6643, taken by BU undergrads Ian Cohen, Anthony

    E-print Network

    Goldberg, Bennett

    faculty and research associates authored or co-authored a total of 9 refereed, scholarly papers #12;Cover: An image of the galaxy NGC6643, taken by BU undergrads Ian Cohen, Anthony Lollo, Mary.................................................................................... Research

  18. HI Observations of Interacting Galaxy Pair NGC 4038/9

    E-print Network

    S. Gordon; B. Koribalski; K. Jones

    2001-04-25

    We present the results of new radio interferometer HI line observations for the merging galaxy pair NGC 4038/9 (`The Antennae'), obtained using the Australia Telescope Compact Array. The results improve substantially on those of van der Hulst (1979) and show in detail the two merging galactic disks and the two tidal tails produced by their interaction. The small edge-on spiral dwarf galaxy ESO 572-G045 is also seen near the tip of the southern tail, but distinct from it. It shows no signs of tidal interaction. The northern tidal tail of the Antennae shows no HI connection to the disks and has an extension towards the west. The southern tidal tail is continuous, with a prominent HI concentration at its tip, roughly at the location of the tidal dwarf galaxy observed optically by Mirabel, Dottori & Lutz (1992). Clear velocity structure is seen along the tidal tails and in the galactic disks. Radio continuum images at 20-cm and 13-cm are also presented, showing the disks in detail.

  19. Diffuse Ionized Gas inside the Dwarf Irregular Galaxy NGC 6822

    NASA Astrophysics Data System (ADS)

    Hidalgo-Gámez, A. M.; Peimbert, A.

    2007-05-01

    We have studied the differences between the diffuse ionized gas (DIG) and the H II regions along a slit position in the local dwarf irregular galaxy NGC 6822. The slit position passes through the two most prominent H II regions: Hubble V and Hubble X. Important differences have been found in the excitation, ionization, and [N II] ?6584/H? and [S II] ?6717/H? line ratios between the DIG and the H II locations. Moreover, the values of all the line ratios are not similar to those in the DIG locations of spiral galaxies but are very similar to the values in other irregular galaxies, such as IC 10. We also determined the rate of recombination using the He I ?5875 line. Finally, we obtained a picture of the ionization sources of the DIG. We consider that the leakage of photons from the H II regions might explain most of the line ratios, except [N II]/H?, which might be explained by turbulence. Based on observations collected at the European Southern Observatory, Chile, proposal 69.C-0203(A).

  20. DUST DISK AROUND A BLACK HOLE IN GALAXY NGC 4261

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This is a Hubble Space Telescope image of an 800-light-year-wide spiral-shaped disk of dust fueling a massive black hole in the center of galaxy, NGC 4261, located 100 million light-years away in the direction of the constellation Virgo. By measuring the speed of gas swirling around the black hole, astronomers calculate that the object at the center of the disk is 1.2 billion times the mass of our Sun, yet concentrated into a region of space not much larger than our solar system. The strikingly geometric disk -- which contains enough mass to make 100,000 stars like our Sun -- was first identified in Hubble observations made in 1992. These new Hubble images reveal for the first time structure in the disk, which may be produced by waves or instabilities in the disk. Hubble also reveals that the disk and black hole are offset from the center of NGC 4261, implying some sort of dynamical interaction is taking place, that has yet to be fully explained. Credit: L. Ferrarese (Johns Hopkins University) and NASA Image files in GIF and JPEG format, captions, and press release text may be accessed on Internet via anonymous ftp from oposite.stsci.edu in /pubinfo:

  1. Non-circular Gas Kinematics and Star Formation in the Ringed Galaxy NGC 4736

    E-print Network

    Tony Wong; Leo Blitz

    2000-04-27

    We analyze the gas kinematics and star formation properties of the nearby RSab galaxy NGC 4736 using interferometric and single-dish CO(1-0) data and previously published Halpha and HI data. The CO morphology is dominated by a central molecular bar and tightly wound spiral arms associated with a bright ring of star formation. Strong HI emission is also found in the ring, but HI is absent from the central regions. Comparison of the HI and Halpha distributions suggests that HI in the ring is primarily dissociated H$_2$. Modeling of the CO kinematics reveals gas motion in elliptical orbits around the central bar, and we argue that the ring represents both the OLR of the bar and the ILR of a larger oval distortion. The HI kinematics show evidence for axisymmetric inflow towards the ring and are inconsistent with streaming in aligned elliptical orbits, but the highly supersonic (~40 km/s) inflow velocities required, corresponding to mass inflow rates of ~2 Msol/yr, suggest that more sophisticated models (e.g., gas orbiting in precessed elliptical orbits) should be considered. The radial CO and Halpha profiles are poorly correlated in the vicinity of the nuclear bar, but show a better correlation (in rough agreement with the Schmidt law) at the ring. Even along the ring, however, the azimuthal correspondence between CO and Halpha is poor, suggesting that massive stars form more efficiently at some (perhaps resonant) locations than at others. These results indicate that the star formation rate per unit gas mass exhibits strong spatial variations and is not solely a function of the available gas supply. The localization of star formation to the ring is broadly consistent with gravitational instability theory, although the instability parameter $Q \\sim 3$ on average in the ring, only falling below 1 in localized regions.

  2. Line asymmetry in the Seyfert Galaxy NGC 3783

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

    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.

  3. Stellar Clusters Forming in the Blue Dwarf Galaxy NGC 5253

    NASA Astrophysics Data System (ADS)

    2004-11-01

    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

  4. STAR FORMATION IN NUCLEAR RINGS OF BARRED GALAXIES

    SciTech Connect

    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

    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.

  5. ALMA observations of feeding and feedback in nearby Seyfert galaxies: an AGN-driven outflow in NGC 1433

    NASA Astrophysics Data System (ADS)

    Combes, F.; García-Burillo, S.; Casasola, V.; Hunt, L.; Krips, M.; Baker, A. J.; Boone, F.; Eckart, A.; Marquez, I.; Neri, R.; Schinnerer, E.; Tacconi, L. J.

    2013-10-01

    We report ALMA observations of CO(3-2) emission in the Seyfert 2 galaxy NGC 1433 at the unprecedented spatial resolution of 0.''5 = 24 pc. Our aim is to probe active galactic nucleus (AGN) feeding and feedback phenomena through the morphology and dynamics of the gas inside the central kpc. The galaxy NGC 1433 is a strongly barred spiral with three resonant rings: one at the ultra-harmonic resonance near corotation, and the others at the outer and inner Lindblad resonances (OLR and ILR). A nuclear bar of 400 pc radius is embedded in the large-scale primary bar. The CO map, which covers the whole nuclear region (nuclear bar and ring), reveals a nuclear gaseous spiral structure, inside the nuclear ring encircling the nuclear stellar bar. This gaseous spiral is well correlated with the dusty spiral seen in Hubble Space Telescope (HST) images. The nuclear spiral winds up in a pseudo-ring at ~200 pc radius, which might correspond to the inner ILR. Continuum emission is detected at 0.87 mm only at the very centre, and its origin is more likely thermal dust emission than non-thermal emission from the AGN. It might correspond to the molecular torus expected to exist in this Seyfert 2 galaxy. The HCN(4-3) and HCO+(4-3) lines were observed simultaneously, but only upper limits are derived, with a ratio to the CO(3-2) line lower than 1/60 at 3?, indicating a relatively low abundance of very dense gas. The kinematics of the gas over the nuclear disk reveal rather regular rotation only slightly perturbed by streaming motions due to the spiral; the primary and secondary bars are too closely aligned with the galaxy major or minor axis to leave a signature in the projected velocities. Near the nucleus, there is an intense high-velocity CO emission feature redshifted to 200 km s-1 (if located in the plane), with a blue-shifted counterpart, at 2'' (100 pc) from the centre. While the CO spectra are quite narrow in the centre, this wide component is interpreted as an outflow involving a molecular mass of 3.6 × 106 M? and a flow rate ~7 M?/yr. The flow could be in part driven by the central star formation, but is mainly boosted by the AGN through its radio jets. Based on observations carried out with ALMA in Cycle 0.

  6. Non-axisymmetric structure in the satellite dwarf galaxy NGC 2976: Implications for its dark/bright mass distribution and evolution

    SciTech Connect

    Valenzuela, Octavio; Hernandez-Toledo, Hector; Cano, Mariana; Pichardo, Bárbara [Instituto de Astronomía, Universidad Nacional Autonóma de Mexico, A.P. 70-264, 04510 México, D.F. (Mexico); Puerari, Ivanio [Instituto Nacional de Astrofísica Optica y Electrónica, Calle Luis Enrique Erro 1, 72840 Sta. Maria Tonantzintla, Puebla (Mexico); Buta, Ronald [Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL 35487 (United States); Groess, Robert, E-mail: octavio@astro.unam.mx [School of Computational and Applied Mathematics, University of Witwatersrand, Private Bag 3, WITS 2050 (South Africa)

    2014-02-01

    We present the result of an extensive search for non-axisymmetric structures in the dwarf satellite galaxy of M81, NGC 2976, using multiwavelength archival observations. The galaxy is known to present kinematic evidence for a bisymmetric distortion; however, the stellar bar presence is controversial. This controversy motivated the possible interpretation of NGC 2976 as presenting an elliptical disk triggered by a prolate dark matter halo. We applied diagnostics used in spiral galaxies in order to detect stellar bars or spiral arms. The m = 2 Fourier phase has a jump around 60 arcsec, consistent with a central bar and bisymmetric arms. The CO, 3.6 ?m surface brightness, and the dust lanes are consistent with a gas-rich central bar and possibly with gaseous spiral arms. The bar-like feature is offset close to 20° from the disk position angle, in agreement with kinematic estimations. The kinematic jumps related to the dust lanes suggest that the bar perturbation in the disk kinematics is non-negligible and the reported non-circular motions, the central gas excess, and the nuclear X-ray source (active galactic nucleus/starburst) might be produced by the central bar. Smoothed particle hydrodynamics simulations of disks inside triaxial dark halos suggest that the two symmetric spots at 130 arcsec and the narrow arms may be produced by gas at turning points in an elliptical disk, or, alternatively, the potential ellipticity can be produced by a tidally induced strong stellar bar/arms; in both cases the rotation curve interpretation is, importantly, biased. The M81 group is a natural candidate to trigger the bisymmetric distortion and the related evolution as suggested by the H I tidal bridge detected by Chynoweth et al. We conclude that both mechanisms, the gas-rich bar and spiral arms triggered by the environment (tidal stirring) and primordial halo triaxiality, can explain most of the NGC 2976 non-circular motions, mass redistribution, and nuclear activity. Distinguishing between them requires detailed modeling of environmental effects. A similar analysis to ours may reveal such structures in other nearby dwarf satellite galaxies; if this is confirmed, the same evolutionary scenario will be applicable to them. This implies biases in constraining their dark matter distribution and also in making comparisons against theoretical predictions for isolated galaxies.

  7. Multimolecule ALMA observations toward the Seyfert 1 galaxy NGC 1097

    NASA Astrophysics Data System (ADS)

    Martín, 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

    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.

  8. Detection of CO (J=1-0) in the dwarf elliptical galaxy NGC 185

    NASA Technical Reports Server (NTRS)

    Wiklind, Tommy; Rydbeck, Gustaf

    1987-01-01

    The detection of CO (J = 1-0) emission in the dwarf elliptical galaxy NGC 185 is reported. The presence of massive molecular clouds in this early-type galaxy supports the idea of recent or ongoing stellar formation indicated by the population of blue stars in the center. The CO was detected in two positions in the galaxy, the center, and a prominent dustcloud. The emission profile has two peaks, roughly centered around the systemic velocity. It is found that NGC 185 is overluminous in blue light for its CO luminosity compared with Sc galaxies. This might indicate a higher star-formation efficiency for NGC 185 than for the late-type galaxies.

  9. Bar-Halo Friction in Galaxies. III. Halo Density Changes

    NASA Astrophysics Data System (ADS)

    Sellwood, J. A.

    2008-05-01

    The predicted central densities of dark matter halos in ?CDM models exceed those observed in some galaxies. Weinberg & Katz argue that angular momentum transfer from a rotating bar in the baryonic disk can lower the halo density, but they also contend that N-body simulations of this process will not reveal the true continuum result unless many more than the usual numbers of particles are employed. Adopting their simplified model of a rotating rigid bar in a live halo, I have been unable to find any evidence to support their contention. I find that both the angular momentum transferred and the halo density change are independent of the number of particles over the range usually employed, up to that advocated by these authors. I show that my results do not depend on any numerical parameters and that field methods perform equally with grid methods. I also identify the reasons that the required particle number suggested by Weinberg & Katz is excessive. I further show that when countervailing compression by baryonic settling is ignored, moderate bars can reduce the mean density of the inner halo by 20%-30%. Long, massive, skinny bars can reduce the mean inner density by a factor ~10. The largest density reductions are achieved at the expense of removing most of the angular momentum likely to reside in the baryonic component. Compression of the halo by baryonic settling must reduce, and may even overwhelm, the density reduction achievable by bar friction.

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

    E-print Network

    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

    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 GMOS spectra of the NGC 4649 GCs.

  11. The M bh-? Diagram and the Offset Nature of Barred Active Galaxies

    NASA Astrophysics Data System (ADS)

    Graham, Alister W.; Li, I.-hui

    2009-06-01

    From a sample of 50 predominantly inactive galaxies with direct supermassive black hole mass measurements, it has recently been established that barred galaxies tend to reside rightward of the M bh-? relation defined by nonbarred galaxies. Either black holes in barred galaxies tend to be anemic or the central velocity dispersions in these galaxies have a tendency to be elevated by the presence of the bar. The latter option is in accord with studies connecting larger velocity dispersions in galaxies with old bars, while the former scenario is at odds with the observation that barred galaxies do not deviate from the M bh-luminosity relation. Using a sample of 88 galaxies with active galactic nuclei, whose supermassive black hole masses have been estimated from their associated emission lines, we reveal for the first time that they also display this same general behavior in the M bh-? diagram depending on the presence of a bar or not. A new symmetrical and nonsymmetrical "barless" M bh-? relation is derived using 82 nonbarred galaxies. The barred galaxies are shown to reside on or up to ~1 dex below this relation. This may explain why narrow-line Seyfert 1 galaxies appear offset from the "barless" M bh-? relation, and has far-reaching implications given that over half of the disk galaxy population are barred.

  12. Spectroscopic observations of southern nearby galaxies. I. NGC 2442

    NASA Astrophysics Data System (ADS)

    Bajaja, E.; Agüero, E.; Paolantonio, S.

    1999-04-01

    The galaxy NGC 2442 was observed with a REOSC spectrograph, installed in the 2.15 m CASLEO telescope, in order to derive galactic parameters from the observed optical lines and to compare them with the results of radioastronomical observations made in the continuum, at 843 MHz, with the MOST and in the CO lines with the SEST telescope. Recent publications allowed us to extend the comparison to results from interferometric observations of H? and H I 21 cm lines and of the continuum at 1415 MHz. The long slit observations were made placing the 5farcm 8 slit at six different positions on the optical image of the galaxy. The emission line intensity ratios at the nuclear region indicate that NGC 2442 is a LINER. The electron temperature and volume density are Te ~ 14 000 K and Ne ~ 530 cm(-3) , respectively. In contrast, a spectrum of a region 87arcsec to the NE shows the typical characteristics of a H Ii region. In this case Te ~ 6,500 K and Ne ~ 10 cm(-3) . Good correlations between the distributions of intensities, velocity fields and rotation curves have been found for the optical and radio lines. It is shown that the three intensity peaks along the line at PA = 40degr were not resolved by the observations at radio frequencies. The steep central rotation curve seen in CO has been confirmed and improved showing the existence of a disc or a ring, with a radius of 12.5 arcsec, rotating at 216/sin(i) km s(-1). Two velocity components in three optical spectra obtained in the nuclear region, have been related to two small H? regions close to the nucleus and to the central ring. Asymmetries in the distributions of the emitting sources and irregularities in their velocity fields indicate the need of modelling the galaxy before any dynamical study is attempted. Based on observations made in the Complejo Astronomico El Leoncito, operated under agreement between the Consejo Nacional de Investigaciones Cientificas y Tecnicas de la Republica Argentina and the National Universities of La Plata, Cordoba and San Juan.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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.

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

    E-print Network

    Sidney van den Bergh

    2006-11-20

    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.

  15. Ionized gas outflow in the isolated S0 galaxy NGC 4460

    NASA Astrophysics Data System (ADS)

    Moiseev, Alexei; Karachentsev, Igor; Kaisin, Serafim

    2010-04-01

    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

  16. Detection, Photometry, and Slitless Radial Velocities of 197 PNe in the Elliptical Galaxy NGC 1344

    Microsoft Academic Search

    A. M. Teodorescu; R. H. Méndez; R. P. Saglia; A. Riffeser; R. P. Kudritzki; O. E. Gerhard; J. Kleyna

    2005-01-01

    We present photometric and kinematic results obtained by measuring 197 PNe discovered in the flattened Fornax elliptical galaxy NGC 1344. We build the PN luminosity function (PNLF), which gives a distance modulus m - M = 31.4+\\/-0.2. From the radial velocities we obtain the line-of-sight velocity dispersion, which indicates the presence of a dark matter halo around this galaxy.

  17. Detection, Photometry, and Slitless Radial Velocities of 197 PNe in the Elliptical Galaxy NGC 1344

    Microsoft Academic Search

    A. M. Teodorescu; R. H. Me´ndez; R. P. Saglia; A. Riffeser; R. P. Kudritzki; O. E. Gerhard; J. Kleyna

    2005-01-01

    We present photometric and kinematic results obtained by measuring 197 PNe discovered in the flattened Fornax elliptical galaxy NGC 1344. We build the PN luminosity function (PNLF), which gives a distance modulus m ? M = 31.4±0.2. From the radial velocities we obtain the line-of-sight velocity dispersion, which indicates the presence of a dark matter halo around this galaxy.

  18. Model of outgrowths in the spiral galaxies NGC 4921 and NGC 7049 and the origin of spiral arms

    NASA Astrophysics Data System (ADS)

    Carlqvist, Per

    2013-02-01

    NGC 4921 and 7049 are two spiral galaxies presenting narrow, distinct dust features. A detailed study of the morphology of those features has been carried out using Hubble Space Telescope archival images. NGC 4921 shows a few but well-defined dust arms midway to its centre while NGC 7049 displays many more dusty features, mainly collected within a ring-shaped formation. Numerous dark and filamentary structures, called outgrowths, are found to protrude from the dusty arms in both galaxies. The outgrowths point both outwards and inwards in the galaxies. Mostly they are found to be V-shaped or Y-shaped with the branches connected to dark arm filaments. Often the stem of the Y appears to consist of intertwined filaments. Remarkably, the outgrowths show considerable similarities to elephant trunks in H ii regions. A model of the outgrowths, based on magnetized filaments, is proposed. The model provides explanations of both the shapes and orientations of the outgrowths. Most important, it can also give an account for their intertwined structures. It is found that the longest outgrowths are confusingly similar to dusty spiral arms. This suggests that some of the outgrowths can develop into such arms. The time-scale of the development is estimated to be on the order of the rotation period of the arms or shorter. Similar processes may also take place in other spiral galaxies. If so, the model of the outgrowths can offer a new approach to the old winding problem of spiral arms.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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.

  20. The Opacity of Nearby Galaxies from Colors and Counts of Background Galaxies; 1, The Synthetic Field Method and its Application to NGC 4536 and NGC 3664

    E-print Network

    González, R A; Dirsch, B; Ferguson, H C; Calzetti, D; Panagia, N; Gonzalez, Rosa A.; Dirsch, Boris; Ferguson, Harry C.; Calzetti, Daniela; Panagia, Nino

    1998-01-01

    We describe a new, direct method for determining the opacity of foreground galaxies which does not require any a priori assumptions about the spatial distribution or the reddening law of the obscuring material. The method is to measure the colors and counts of background galaxies which can be identified through the foreground system. The method is calibrated, and the effects of confusion and obscuration are decoupled by adding various versions of a suitable deep reference frame containing only field galaxies with known properties into the image of the foreground galaxy, and analyzing these ``synthetic field'' images in the same way as the real images. We test the method on HST WFPC2 archived images of two galaxies which are quite different: NGC 4536 is a large Sc spiral, and NGC 3664 is a small Magellanic irregular. The reference frames are taken from the Hubble Deep Field. From the background galaxy counts, NGC 4536 shows an extinction A_I ~ 1 mag in the northwestern arm region, and lower than 0.5 mag in the...

  1. Bar slowdown and the distribution of dark matter in barred galaxies

    NASA Astrophysics Data System (ADS)

    Athanassoula, E.

    2014-02-01

    `Conspiracy' between the dark and the baryonic matter prohibits an unambiguous decomposition of disc galaxy rotation curves into the corresponding components. Several methods have been proposed to counter this difficulty, but their results are widely discrepant. In this paper, I revisit one of these methods, which relies on the relation between the halo density and the decrease of the bar pattern speed. The latter is routinely characterized by the ratio R of the corotation radius RCR to the bar length Lb, R = R_CR/L_b. I use a set of N-body+SPH simulations, including subgrid physics, whose initial conditions cover a range of gas fractions and halo shapes. The models, by construction, have roughly the same azimuthally averaged circular velocity curve and halo density and they are all submaximal, i.e. according to previous works, they are expected to have all roughly the same R value, well outside the fast bar range (1.2 ± 0.2). Contrary to these expectations, however, these simulations end up having widely different R values, either within the fast bar range or well outside it. This shows that the R value cannot constrain the halo density, nor determine whether galactic discs are maximal or submaximal. I argue that this is true even for early-type discs (S0s and Sas).

  2. Direct Evidence from Spitzer for a Low-Luminosity AGN at the Center of the Elliptical Galaxy NGC 315

    E-print Network

    Gu, Q.-S.; Huang, J.-S.; Wilson, Graham Wallace; Fazio, G. G.

    2007-12-20

    We present Spitzer Space Telescope InfraRed Array Camera (IRAC) and Multiband Imaging Photometer (MIPS) observations of the elliptical galaxy NGC 315. After removal of the host galaxy's stellar emission, we detected for the first time an infrared...

  3. Multicolor CCD photometry of six lenticular and spiral galaxies. Structure of the galaxies

    NASA Astrophysics Data System (ADS)

    Gusev, A. S.

    2006-03-01

    The results of multicolor surface photometry of the S0 galaxies NGC 524, NGC 1138, and NGC 7280 and the spiral galaxies NGC 532, NGC 783, and NGC 1589 are reported. U BV RI observations were acquired with the 1.5-m telescope of the Maidanak Observatory (Uzbekistan), while JHK data were taken from the 2MASS catalog. The overall structure of the galaxies is analyzed and the galaxy images decomposed into bulge and disk components. The parameters of the galaxy components—rings, bars, spiral arms, and dust lanes—are determined. The bulge/disk decompositions based on averaged one-dimensional photometric profiles yield incorrect parameters for the bulges of the S0-Sa galaxies with bars and/or rings, whose inner regions are dominated by the radiation of the bulge.

  4. ALMA observations of feeding and feedback in nearby Seyfert galaxies: an AGN-driven outflow in NGC 1433

    E-print Network

    Combes, F; Casasola, V; Hunt, L; Krips, M; Baker, A J; Boone, F; Eckart, A; Marquez, I; Neri, R; Schinnerer, E; Tacconi, L J

    2013-01-01

    We report ALMA observations of CO(3-2) emission in the Seyfert 2 double-barred galaxy NGC1433, at the unprecedented spatial resolution of 0.5"=24 pc. Our aim is to probe AGN feeding and feedback phenomena through the morphology and dynamics of the gas inside the central kpc. The CO map, which covers the whole nuclear region (nuclear bar and ring), reveals a nuclear gaseous spiral structure, inside the nuclear ring encircling the nuclear stellar bar. This gaseous spiral is well correlated with the dusty spiral seen in Hubble Space Telescope images. The nuclear spiral winds up in a pseudo-ring at 200 pc radius, which might correspond to the inner ILR. Continuum emission is detected at 0.87 mm only at the very centre, and its origin is more likely thermal dust emission than non-thermal emission from the AGN. It might correspond to the molecular torus expected to exist in this Seyfert 2 galaxy. The HCN(4-3) and HCO+(4-3) lines were observed simultaneously, but only upper limits are derived, with a ratio to the CO...

  5. The Environment of Barred Galaxies in the Low-redshift Universe

    NASA Astrophysics Data System (ADS)

    Lin, Ye; Cervantes Sodi, Bernardo; Li, Cheng; Wang, Lixin; Wang, Enci

    2014-12-01

    We present a study of the environment of barred galaxies using a volume-limited sample of over 30,000 galaxies drawn from the Sloan Digital Sky Survey. We use four different statistics to quantify the environment: the projected two-point cross-correlation function, the background-subtracted number count of neighbor galaxies, the overdensity of the local environment, and the membership of our galaxies to galaxy groups to segregate central and satellite systems. For barred galaxies as a whole, we find a very weak difference in all the quantities compared to unbarred galaxies of the control sample. When we split our sample into early- and late-type galaxies, we see a weak but significant trend for early-type galaxies with a bar to be more strongly clustered on scales from a few 100 kpc to 1 Mpc when compared to unbarred early-type galaxies. This indicates that the presence of a bar in early-type galaxies depends on the location within their host dark matter halos. This is confirmed by the group catalog in the sense that for early-types, the fraction of central galaxies is smaller if they have a bar. For late-type galaxies, we find fewer neighbors within ~50 kpc around the barred galaxies when compared to unbarred galaxies from the control sample, suggesting that tidal forces from close companions suppress the formation/growth of bars. Finally, we find no obvious correlation between overdensity and the bars in our sample, showing that galactic bars are not obviously linked to the large-scale structure of the universe.

  6. The Opacity of Nearby Galaxies from Colors and Counts of Background Galaxies: I. The Synthetic Field Method and its Application to NGC 4536 and NGC 3664

    E-print Network

    Rosa A. Gonzalez; R. J. Allen; Boris Dirsch; Harry C. Ferguson; Daniela Calzetti; Nino Panagia

    1998-05-30

    We describe a new, direct method for determining the opacity of foreground galaxies which does not require any a priori assumptions about the spatial distribution or the reddening law of the obscuring material. The method is to measure the colors and counts of background galaxies which can be identified through the foreground system. The method is calibrated, and the effects of confusion and obscuration are decoupled by adding various versions of a suitable deep reference frame containing only field galaxies with known properties into the image of the foreground galaxy, and analyzing these ``synthetic field'' images in the same way as the real images. We test the method on HST WFPC2 archived images of two galaxies which are quite different: NGC 4536 is a large Sc spiral, and NGC 3664 is a small Magellanic irregular. The reference frames are taken from the Hubble Deep Field. From the background galaxy counts, NGC 4536 shows an extinction A_I ~ 1 mag in the northwestern arm region, and lower than 0.5 mag in the corresponding interarm region (no correction for inclination has been attempted). However, from the galaxy colors, the same reddening of E(V - I) ~ 0.2 is observed in both the arm and the interarm regions. In the interarm region, the combination of extinction and reddening can be explained by a diffuse component with a Galactic reddening law (R_V ~ 3). In the spiral arm, however, the same diffuse, low opacity component seems to coexist with regions of much higher opacity. Since the exposures are shorter the results for NGC 3664 are less clear, but also appear to be consistent with a two component distribution.

  7. Gas-driven evolution of stellar orbits in barred galaxies

    E-print Network

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

    1998-06-10

    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.

  8. A GIANT STAR FACTORY IN NEIGHBORING GALAXY NGC 6822

    NASA Technical Reports Server (NTRS)

    2002-01-01

    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.

  9. Triggered star formation in a merging, gas-rich dwarf galaxy around NGC 7241

    NASA Astrophysics Data System (ADS)

    Leaman, Ryan; Erroz-Ferrer, Santiago; Cisternas, Mauricio; Knapen, Johan H.

    2015-07-01

    Using multiwavelength kinematic and photometric data we have analysed the gaseous and stellar properties of a previously uncharacterized low-mass star-forming companion and newly discovered stellar stream seen projected against the edge-on spiral galaxy NGC 7241. The companion object was identified serendipitously as an offset velocity component in H ? Fabry-Perot observations along the line of sight to NGC 7241, and is most prominent visually in UV and blue wavelengths. Its occulting position with respect to NGC 7241 allows measurement of its dust extinction properties which are then combined with photometric spectral energy distribution fitting and long-slit spectroscopy to study star formation (SF) in this gas-rich accreting dwarf galaxy. The dynamical properties of the stream and companion suggest that they may likely be remnants of the same low-mass progenitor dwarf galaxy which is being disrupted during its accretion on to NGC 7241 - with the companion's recent SF triggered during its passage with the disc of NGC 7241. This is supported by the companion's metallicity and SF rates, the asymmetric SF in the disc of NGC 7241, as well as the coincident velocity of the extraplanar H I filament and the star-forming companion. In contrast, mass estimates from dynamical modelling of NGC 7241 rule out an interaction between NGC 7241 and UGC 11964 (the other large spiral galaxy in the group) within the last ˜3 Gyr - making such an interaction a poor candidate for inducing the recent SF in the system. Together, the data for this system offer a window into how SF proceeds in low-mass mergers.

  10. A Study of the X-ray Source Population in the Dwarf Galaxy NGC 6822

    NASA Technical Reports Server (NTRS)

    Tennant, Allyn F.; Swartz, Douglas A.; Ghosh, Kajal K.; Wu, Kinwah

    2003-01-01

    The dlrr galaxy NGC 6822 is a distant member of the Local Group. It is a site of recent star formation, rich in HII regions and OB associations, as well as containing an older globular cluster population. We present results of a deep Chandra observation of NGC 6822. The brightest source is extended and most likely a SNR. In addition to spectral analysis of the brightest sources, we extend the luminosity function down to the 10(sup)35 erg/s range.

  11. Hierarchical Star Formation across the ring galaxy NGC 6503

    E-print Network

    Gouliermis, Dimitrios A; Elmegreen, Bruce G; Elmegreen, Debra M; Calzetti, Daniela; Lee, Janice C; Adamo, Angela; Aloisi, Alessandra; Cignoni, Michele; Cook, David O; Dale, Daniel; Gallagher, John S; Grasha, Kathryn; Grebel, Eva K; Davo, Artemio Herrero; Hunter, Deidre A; Johnson, Kelsey E; Kim, Hwihyun; Nair, Preethi; Nota, Antonella; Pellerin, Anne; Ryon, Jenna; Sabbi, Elena; Sacchi, Elena; Smith, Linda J; Tosi, Monica; Ubeda, Leonardo; Whitmore, Brad

    2015-01-01

    We present a detailed clustering analysis of the young stellar population across the star-forming ring galaxy NGC 6503, based on the deep HST photometry obtained with the Legacy ExtraGalactic UV Survey (LEGUS). We apply a contour-based map analysis technique and identify in the stellar surface density map 244 distinct star-forming structures at various levels of significance. These stellar complexes are found to be organized in a hierarchical fashion with 95% being members of three dominant super-structures located along the star-forming ring. The size distribution of the identified structures and the correlation between their radii and numbers of stellar members show power-law behaviors, as expected from scale-free processes. The self-similar distribution of young stars is further quantified from their autocorrelation function, with a fractal dimension of ~1.7 for length-scales between ~20 pc and 2.5 kpc. The young stellar radial distribution sets the extent of the star-forming ring at radial distances betwe...

  12. The circumnuclear environment of the peculiar galaxy NGC 3310

    E-print Network

    Hagele, Guillermo F; Cardaci, Monica V; Terlevich, Elena; Terlevich, Roberto

    2009-01-01

    Gas and star velocity dispersions have been derived for eight circumnuclear star-forming regions (CNSFRs) and the nucleus of the spiral galaxy NGC3310 using high resolution spectroscopy in the blue and far red. Stellar velocity dispersions have been obtained from the CaII triplet in the near-IR, using cross-correlation techniques, while gas velocity dispersions have been measured by Gaussian fits to the Hb 4861A and [OIII]5007A emission lines. The CNSFRs stellar velocity dispersions range from 31 to 73 km/s. These values, together with the sizes measured on archival HST images, yield upper limits to the dynamical masses for the individual star clusters between 1.8 and 7.1 x 10$^6$ M$_\\odot$, for the whole CNSFR between 2 x 10$^7$ and 1.4 x 10$^8$ M$_\\odot$, and 5.3 x 10$^7$ M$_\\odot$ for the nucleus inside the inner 14.2 pc. The masses of the ionizing stellar population responsible for the HII region gaseous emission have been derived from their published Ha luminosities and are found to be between 8.7 x 10$^...

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

    PubMed

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

    2012-11-29

    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

  14. The 0.3-30 keV Spectra of Powerful Starburst Galaxies: NuSTAR and Chandra Observations of NGC 3256 and NGC 3310

    NASA Astrophysics Data System (ADS)

    Lehmer, B. D.; Tyler, J. B.; Hornschemeier, A. E.; Wik, D. R.; Yukita, M.; Antoniou, V.; Boggs, S.; Christensen, F. E.; Craig, W. W.; Hailey, C. J.; Harrison, F. A.; Maccarone, T. J.; Ptak, A.; Stern, D.; Zezas, A.; Zhang, W. W.

    2015-06-01

    We present nearly simultaneous Chandra and NuSTAR observations of two actively star-forming galaxies within 50 Mpc: NGC 3256 and NGC 3310. Both galaxies are significantly detected by both Chandra and NuSTAR, which together provide the first-ever spectra of these two galaxies spanning 0.3–30 keV. The X-ray emission from both galaxies is spatially resolved by Chandra; we find that hot gas dominates the E < 1–3 keV emission while ultraluminous X-ray sources (ULXs) provide majority contributions to the emission at E > 1–3 keV. The NuSTAR galaxy-wide spectra of both galaxies follow steep power-law distributions with ? ? 2.6 at E > 5–7 keV. Using new and archival Chandra data, we search for signatures of heavily obscured or low luminosity active galactic nuclei (AGNs). We find that both NGC 3256 and NGC 3310 have X-ray detected sources coincident with nuclear regions; however, the steep NuSTAR spectra of both galaxies restricts these sources to be either low luminosity AGNs (L2?10 keV/LEdd ? 10?5) or non-AGNs in nature (e.g., ULXs or crowded X-ray sources that reach L2?10 keV ? 1040 erg s?1 cannot be ruled out). Combining our constraints on the 0.3–30 keV spectra of NGC 3256 and NGC 3310 with equivalent measurements for nearby star-forming galaxies M83 and NGC 253, we analyze the star formation rate (SFR) normalized spectra of these starburst galaxies. The spectra of all four galaxies show sharply declining power-law slopes at energies above 3–6 keV primarily due to ULX populations. Our observations therefore constrain the average spectral shape of galaxy-wide populations of luminous accreting binaries (i.e., ULXs). Interestingly, despite a completely different galaxy sample selection, emphasizing here a range of SFRs and stellar masses, these properties are similar to those of super-Eddington accreting ULXs that have been studied individually in a targeted NuSTAR ULX program. We also find that NGC 3310 exhibits a factor of ?3–10 elevation of X-ray emission over the other star-forming galaxies due to a corresponding overabundance of ULXs. We argue that the excess of ULXs in NGC 3310 is most likely explained by the relatively low metallicity of the young stellar population in this galaxy, a property that is expected to produce an excess of luminous X-ray binaries for a given SFR.

  15. On the link between central black holes, bar dynamics and dark matter haloes in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Treuthardt, Patrick; Seigar, Marc S.; Sierra, Amber D.; Al-Baidhany, Ismaeel; Salo, Heikki; Kennefick, Daniel; Kennefick, Julia; Lacy, Claud H. S.

    2012-07-01

    The discovery of a relationship between supermassive black hole (SMBH) mass and spiral arm pitch angle (P) is evidence that SMBHs are tied to the overall secular evolution of a galaxy. The discovery of SMBHs in late-type galaxies with little or no bulge suggests that an underlying correlation between the dark matter halo concentration and SMBH mass (MBH) exists, rather than between the bulge mass and MBH. In this paper we measure P using a two-dimensional fast Fourier transform and estimate the bar pattern speeds of 40 barred spiral galaxies from the Carnegie-Irvine Galaxy Survey. The pattern speeds were derived by estimating the gravitational potentials of our galaxies from Ks-band images and using them to produce dynamical simulation models. The pattern speeds allow us to identify those galaxies with low central dark halo densities, or fast rotating bars, while P provides an estimate of MBH. We find that a wide range of MBH exists in galaxies with low central dark matter halo densities, which appears to support other theoretical results. We also find that galaxies with low central dark halo densities appear to follow more predictable trends in P versus de Vaucouleurs morphological type (T) and bar strength versus T than barred galaxies in general. The empirical relationship between MBH and total gravitational mass of a galaxy (Mtot) allows us to predict the minimum Mtot that will be observationally measured of our fast bar galaxies. These predictions will be investigated in a subsequent paper.

  16. Effect of bars in AGN host galaxies and black hole activity

    NASA Astrophysics Data System (ADS)

    Alonso, M. S.; Coldwell, G.; Lambas, D. G.

    2013-01-01

    Aims: With the aim of assessing the effects of bars on active galactic nuclei (AGN), we present an analysis of host characteristics and nuclear activity of active galaxies with and without bars. Methods: We selected AGN host galaxies from the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7), using the available emission-line fluxes. By visual inspection of SDSS images we classified the face-on spiral hosts of AGNs brighter than g-mag < 16.5 into barred or unbarred. With the purpose of providing an appropriate quantification of the effects of bars, we also constructed a suitable control sample of unbarred active galaxies with similar redshift, magnitude, morphology, bulge sizes, and local environment distributions. Results: We find that the bar fraction, with respect to the full sample of spiral face-on AGN host galaxies, is 28.5%, in good agreement with previous works. barred AGN host galaxies show an excess of young stellar populations (as derived with the Dn(4000) spectral index), dominated by red u - r and g - r colors, with respect to the control sample, suggesting that bars produce an important effect on galaxy properties of AGN hosts. Regarding the nuclear activity distribution, we find that barred active galaxies show a shift toward higher Lum [OIII] values with respect to AGN without bars. In addition, we also find that this trend is more significant in less massive, younger stellar population and bluer AGN host galaxies. We found that the fraction of powerful AGN increases toward more massive hosts with bluer colors and younger stellar populations residing in denser environments. However, barred host AGN systematically show a higher fraction of powerful active nuclei galaxies with respect to the control sample. We also explored the accretion rate onto the central black holes, finding that barred AGN host show an excess of objects with high accretion rate values with respect to unbarred active galaxies.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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.

  18. THE GLOBULAR CLUSTER POPULATION OF NGC 7457: CLUES TO THE EVOLUTION OF FIELD S0 GALAXIES

    SciTech Connect

    Hargis, Jonathan R.; Rhode, Katherine L. [Department of Astronomy, Indiana University, 727 East 3rd Street, Swain West 319, Bloomington, IN 47405 (United States); Strader, Jay [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Brodie, Jean P., E-mail: jhargis@astro.indiana.edu [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States)

    2011-09-01

    In this paper, we present the results of a wide-field imaging study of the globular cluster (GC) system of the field S0 galaxy NGC 7457. To derive the global properties of the GC system, we obtained deep BVR images with the WIYN 3.5 m telescope and Minimosaic Imager and studied the GC population of NGC 7457 to a projected radius of {approx}30 kpc. Our ground-based data were combined with archival and published Hubble Space Telescope data to probe the properties of the GC system close to the galaxy center and reduce contamination in the GC candidate sample from foreground stars and background galaxies. We performed surface photometry of NGC 7457 and compared the galaxy's surface brightness profile with the surface density profile of the GC system. The profiles have similar shapes in the inner 1' (3.9 kpc), but the GC system profile appears to flatten relative to the galaxy light at larger radii. The GC system of NGC 7457 is noticeably elliptical in our images; we measure {epsilon} = 0.66 {+-} 0.14 for the GC distribution, which is consistent with our measured ellipticity of the galaxy light. We integrated the radial surface density profile of the GC system to derive a total number of GCs, N{sub GC} = 210 {+-} 30. The GC specific frequencies normalized by the galaxy luminosity and mass are S{sub N} = 3.1 {+-} 0.7 and T = 4.8 {+-} 1.1, respectively. Comparing the derived GC system properties and other empirical data for NGC 7457 to S0 formation scenarios suggests that this field S0 galaxy may have formed in an unequal-mass merger.

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

    E-print Network

    A. V. Moiseev

    2001-11-12

    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.

  20. The extra-planar neutral gas in the edge-on spiral galaxy NGC 891

    E-print Network

    Filippo Fraternali; Tom Oosterloo; Renzo Sancisi; Rob Swaters

    2004-10-15

    We present neutral hydrogen observations of the nearby edge-on spiral galaxy NGC891 which show extended extra-planar emission up to distances of 15 kpc from the plane. 3D modeling of the galaxy shows that this emission comes from halo gas rotating more slowly than the gas in the disk.We derive the rotation curves of the gas above the plane and find a gradient in rotation velocity of -15 km/s/kpc. We also present preliminary results of a galactic fountain model applied to NGC891.

  1. INTEGRAL FIELD SPECTROSCOPY AND MULTI-WAVELENGTH IMAGING OF THE NEARBY SPIRAL GALAXY NGC 5668 : AN UNUSUAL FLATTENING IN METALLICITY GRADIENT

    SciTech Connect

    Marino, R. A.; Gil de Paz, A.; Castillo-Morales, A.; Perez-Gonzalez, P. G.; Gallego, J.; Zamorano, J. [CEI Campus Moncloa, UCM-UPM, Departamento de Astrofisica y CC. de la Atmosfera, Facultad de CC. Fisicas, Universidad Complutense de Madrid, Avda. Complutense s/n, 28040 Madrid (Spain); Munoz-Mateos, J. C. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475 (United States); Sanchez, S. F. [Centro Astronomico Hispano Aleman, Calar Alto (CSIC-MPG), C/Jesus Durban Remon 2-2, E-04004 Almeria (Spain); Alonso-Herrero, A. [Instituto de Fisica de Cantabria, CSIC-UC, Avenida de los Castros s/n, 39005 Santander (Spain); Boissier, S., E-mail: ramarino@fis.ucm.es [Laboratoire dAstrophysique de Marseille, OAMP, Universite Aix-Marseille and CNRS UMR 6110, 38 rue Frederic Joliot-Curie, 13388 Marseille cedex 13 (France)

    2012-07-20

    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 {approx}36'' {approx} 4.4 kpc {approx} 0.36 (D{sub 25}/2) the derived O/H ratio follows the radial gradient typical of spiral galaxies, the abundance gradient beyond r {approx} 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 {lambda} = 0.053 and v{sub c} = 167 km s{sup -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 {approx}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.

  2. HII regions in the spiral galaxy NGC 3389

    E-print Network

    Abdel-Hamid, H; Notni, P; Lee, Sang-Gak

    2003-01-01

    CCD observations in V, I and H$_\\alpha$ for NGC 3389 are used to present photometry of 61 HII regions. Their $\\alpha$ and $\\delta$ positions, diameters and their absolute luminosities have been determined. The luminosity and size distribution functions of the HII regions in NGC 3389 are discussed.

  3. HII regions in the spiral galaxy NGC 3389

    E-print Network

    Hamed Abdel-Hamid; Sang-Gak Lee; Peter Notni

    2003-06-20

    CCD observations in V, I and H$_\\alpha$ for NGC 3389 are used to present photometry of 61 HII regions. Their $\\alpha$ and $\\delta$ positions, diameters and their absolute luminosities have been determined. The luminosity and size distribution functions of the HII regions in NGC 3389 are discussed.

  4. The dynamically hot stellar halo around NGC 3311: a small cluster-dominated central galaxy

    E-print Network

    Ventimiglia, G; Arnaboldi, M; Coccato, L

    2010-01-01

    An important open question is the relation between intracluster light and the halos of central galaxies in galaxy clusters. Here we report results from an on going project with the aim to characterize the dynamical state in the core of the Hydra I (Abell 1060) cluster around NGC 3311. Methods: We analyze deep long-slit absorption line spectra reaching out to ~25 kpc in the halo of NGC 3311. Results: We find a very steep increase in the velocity dispersion profile from a central sigma_0=150 km/s to sigma_out ~450 km/s at R ~ 12 kpc. Farther out, to ~25 kpc, sigma appears to be constant at this value, which is ~60% of the velocity dispersion of the Hydra I galaxies. With its dynamically hot halo kinematics, NGC 3311 is unlike other normal early-type galaxies. Conclusions: These results and the large amount of dark matter inferred from X-rays around NGC 3311 suggest that the stellar halo of this galaxy is dominated by the central intracluster stars of the cluster, and that the transition from predominantly galax...

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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

  6. Nuclear Stellar Disks in Spiral Galaxies

    E-print Network

    Pizzella, A; Morelli, L; Sarzi, M; Scarlata, C; Stiavelli, M; Bertola, F

    2002-01-01

    We report evidence for nuclear stellar disks in 3 early-type spirals, namely NGC 1425, NGC 3898 and NGC 4698, revealed by WFPC2/F606W images out of a sample of 38 spiral galaxies, selected from the Hubble Space Telescope Data Archive. Adopting the photometric method introduced by Scorza & Bender we derived their central surface brightness and scalelength by assuming them to be infinitesimally thin exponential disks. No nuclear disk was found in barred galaxies or galaxies of Hubble type later than Sb. The external origin of the disk in NGC 4698 is strongly suggested by its orthogonal geometrical decoupling with respect to the host galaxy.

  7. Nuclear Stellar Disks in Spiral Galaxies

    E-print Network

    A. Pizzella; E. M. Corsini; L. Morelli; M. Sarzi; C. Scarlata; M. Stiavelli; F. Bertola

    2002-03-04

    We report evidence for nuclear stellar disks in 3 early-type spirals, namely NGC 1425, NGC 3898 and NGC 4698, revealed by WFPC2/F606W images out of a sample of 38 spiral galaxies, selected from the Hubble Space Telescope Data Archive. Adopting the photometric method introduced by Scorza & Bender we derived their central surface brightness and scalelength by assuming them to be infinitesimally thin exponential disks. No nuclear disk was found in barred galaxies or galaxies of Hubble type later than Sb. The external origin of the disk in NGC 4698 is strongly suggested by its orthogonal geometrical decoupling with respect to the host galaxy.

  8. AN INVESTIGATION OF THE DUST CONTENT IN THE GALAXY PAIR NGC 1512/1510 FROM NEAR-INFRARED TO MILLIMETER WAVELENGTHS

    E-print Network

    Draine, Bruce T.

    masses. The two galaxies form a pair consisting of a large, high-metallicity spiral (NGC 1512) and a low/MH i ratio of the NGC 1512/NGC 1510 pair is not associated with the star-forming disks and the sub-regions of NGC 1512, in order to derive and compare the dust masses associated with warm and cool

  9. A bar in the inner halo of barred galaxies I. Structure and kinematics of a representative model

    E-print Network

    E. Athanassoula

    2007-03-08

    N-body simulations argue that the inner haloes of barred galaxies should not be spherical, nor even axisymmetric, but triaxial. The departure from sphericity is strongest near the centre and decreases outwards; typical axial ratios for the innermost parts are of the order of 0.8. The halo shape is prolate-like in the inner parts up to a certain radius and then turns to oblate-like. I call this inner halo structure the `halo bar' and analyse here in depth its structure and kinematics in a representative model. It is always considerably shorter than the disc bar. It lags the disc bar by only a few degrees at all radii and the difference between the two bar phases increases with distance from the centre. The two bars turn with roughly the same pattern speed. This means that the halo bar is a slow bar, since its corotation radius is much larger than its length. The bisymmetric component in the halo continues well outside the halo bar in the form of an open spiral, trailing behind the disc bar. The inner parts of the halo display some mean rotation in the same sense as the disc rotation. This is more important for particles nearer to the equatorial plane and decreases with increasing distance from it, but is always much smaller than the disc rotation.

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

    NASA Technical Reports Server (NTRS)

    Smith, Beverly J.; Wallin, John F.

    1992-01-01

    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.

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

    SciTech Connect

    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

    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.

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

    SciTech Connect

    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

    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.

  13. Modelling gaseous and stellar kinematics in the disc galaxies NGC 772, 3898 and 7782

    Microsoft Academic Search

    E. Pignatelli; E. M. Corsini; J. C. Vega Beltrán; C. Scarlata; A. Pizzella; J. G. Funes; W. W. Zeilinger; J. E. Beckman; F. Bertola

    2001-01-01

    We present V-band surface photometry and major-axis kinematics of stars and ionized gas of three early-type spiral galaxies, namely NGC 772, 3898 and 7782. For each galaxy we present a self-consistent Jeans model for the stellar kinematics, adopting the light distribution of bulge and disc derived by means of a two-dimensional parametric photometric decomposition. This allows us to investigate the

  14. Polarimetric imaging of the polar ring galaxy NGC 660 - evidence for dust outside the stellar disk

    Microsoft Academic Search

    P. B. Alton; D. P. Stockdale; S. M. Scarrott; R. D. Wolstencroft

    2000-01-01

    Optical imaging polarimetry has been carried out for the polar ring, starburst galaxy NGC 660. This galaxy has a highly inclined, severely tidally-disturbed disk which is sur- rounded by a gas-rich, polar ring. We detect scattered light from a large part of the halo and this is attributable to dust grains re- siding up to ' 2:5 kpc from the

  15. Polarimetric imaging of the polar ring galaxy NGC 660 - evidence for dust outside the stellar disk

    Microsoft Academic Search

    P. B. Alton; D. P. Stockdale; S. M. Scarrott; R. D. Wolstencroft

    2000-01-01

    Optical imaging polarimetry has been carried out for the polar ring, starburst galaxy NGC 660. This galaxy has a highly inclined, severely tidally-disturbed disk which is surrounded by a gas-rich, polar ring. We detect scattered light from a large part of the halo and this is attributable to dust grains residing up to =~ 2.5 kpc from the stellar disk.

  16. Kinematics and morphology of the narrow-line region in the Seyfert galaxy NGC 1386

    Microsoft Academic Search

    J. Rossa; M. Dietrich; S. J. Wagner

    2000-01-01

    We present a high spatial and spectral resolution 2-D echelle spectrogram of the Narrow-Line Region in the Seyfert 2 galaxy NGC 1386. This Seyfert galaxy was observed with CASPEC in the wavelength range 5270-7725 Å which covers the Halpha and the [N Ii] lines. With the use of spatially high resolved images taken with the WFPC2 aboard the Hubble Space

  17. Very Extended Emission-Line Region around the Seyfert 2 Galaxy NGC 4388

    Microsoft Academic Search

    M. Yoshida; M. Yagi; S. Okamura; K. Aoki; Y. Ohyama; Y. Komiyama; N. Yasuda; M. Iye; N. Kashiawa; M. Doi; H. Furusawa; M. Hamabe; M. Kimura; M. Miyazaki; S. Miyazaki; F. Nakata; M. Ouchi; M. Sekiguchi; K. Shimasaku; H. Ohtani

    2003-01-01

    We found a very large, about 35 kpc, emission-line region (VEELR) around the Seyfert type 2 galaxy NGC 4388, using deep narrow-band imaging with the Suprime-Cam of the Subaru telescope. This region consists of many faint gas clouds or filaments, and extends northeastwards from the galaxy. The total ionized gas mass calculated from the L_Halpha is about 4 x 10^6

  18. A Multiwavelength Study of a Young, Z-shaped, FR I Radio Galaxy NGC~3801

    Microsoft Academic Search

    Ananda Hota; Jeremy Lim; Youichi Ohyama; D. J. Saikia; Dihn-v-Trung; J. H. Croston

    2009-01-01

    We present preliminary results from a multi-wavelength study of a merger candidate, NGC~3801, hosting a young FR I radio galaxy, with a Z-shaped structure. We find two H I emission blobs on either side of the host galaxy, suggesting a 30 kpc sized rotating gas disk aligned with stellar rotation, but rotating significantly faster than the stars. Broad, faint, blue-shifted

  19. The luminous infrared composite Seyfert 2 galaxy NGC 7679 through the [O III] 5007 emission line

    E-print Network

    I. M. Yankulova; V. K. Golev; K. Jockers

    2007-04-05

    NGC 7679 is a nearby luminous infrared Sy2 galaxy in which starburst and AGN activities co-exist. The ionization structure is maintained by both the AGN power-law continuum and starburst. The galaxy is a bright X-ray source possessing a low X-ray column density N_H 10^41 erg s^{-1} possesses a hidden AGN source (abridged).

  20. Far-Ultraviolet Imagery of the Edge-on Spiral Galaxy NGC 4631

    Microsoft Academic Search

    Andrew M. Smith; Nicholas R. Collins; William H. Waller; Morton S. Roberts; Denise A. Smith; Ralph C. Bohlin; K.-P. Cheng; Michael N. Fanelli; Susan G. Neff; Robert W. O'Connell; Ronald A. Parise; Eric P. Smith; Theodore P. Stecher

    2001-01-01

    Far-ultraviolet (FUV) imagery of the edge-on, Sc\\/SBd galaxy NGC 4631 reveals very strong FUV emission, resulting from active star formation, uniformly distributed along the galactic midplane. Multiband imagery, H I and H II position-velocity curves, and extinction considerations all imply that the emission is from the outer edges of the visible galaxy. The overall FUV morphology of this edge-on disk

  1. WHICH GALAXIES HOST BARS AND DISKS? A STUDY OF THE COMA CLUSTER

    SciTech Connect

    Mendez-Abreu, J.; Aguerri, J. A. L. [Instituto de Astrofisica de Canarias, Calle VIa Lactea s/n, E-38200 La Laguna, Tenerife (Spain); Sanchez-Janssen, R. [European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago (Chile)], E-mail: jairo@iac.es, E-mail: jalfonso@iac.es, E-mail: rsanchez@eso.org

    2010-03-10

    We present a study of the bar fraction in the Coma Cluster galaxies based on a sample of {approx}190 galaxies selected from the Sloan Digital Sky Survey Data Release 6 and observed with the Hubble Space Telescope (HST) Advanced Camera for Survey (ACS). The unprecedented resolution of the HST-ACS images allows us to explore the presence of bars, detected by visual classification, throughout a luminosity range of 9 mag (-23 {approx}< M{sub r} {approx}< -14), permitting us to study the poor known region of dwarf galaxies. We find that bars are hosted by galaxies in a tight range of both luminosities (-22 {approx}< M{sub r} {approx}< -17) and masses (10{sup 9}{approx}galaxies. In addition, we find that the bar fraction does not vary significantly when going from the center to the cluster outskirts, implying that cluster environment plays a second-order role in bar formation/evolution. The shape of the bar fraction distribution with respect to both luminosity and mass is well matched by the luminosity distribution of disk galaxies in Coma, indicating that bars are good tracers of cold stellar disks. We discuss the implications of our results for the formation and evolution scenarios of bars and disks.

  2. Stellar kinematics in the nucleus of NGC 6240: A massive galaxy revealed

    NASA Astrophysics Data System (ADS)

    Lester, Dan F.; Gaffney, Niall I.

    1994-08-01

    We have used the 2.3 micron bandhead of CO to measure the kinematics of the red stellar population in the nucleus of the luminous galaxy NGC 6240, the near-infrared spectrum of which is dominated by lines of shocked gas. With this manifest evidence for dissipative effects in the gas, it is such stellar velocity dispersion that is most unambiguously indicative of gravitational potential. We find a nuclear velocity dispersion sigma = 350 km/sec which is considerably larger than that seen in any gaseous component of this galaxy. At least one partner in this merger must therefore have been very massive, with MB approximately -23. In view of conventional wisdom that the high luminosity of NGC 6240 derives from star formation, it is suprising that we find M/L to be of order unity. While there seems to be little question that star formation is taking place in this interacting system, this high M/L calls into question the importance of star formation in the luminosity budget of the galaxy. In particular, it seems likely that the red starlight in NGC 6240 is produced by giants rather than a population of young red supergiants. This brings into question the (now reflexive) association of relatively deep CO bands in galaxies (which are conspicuously strong in NGC 6240) with recent star formation.

  3. On the offset of barred galaxies from the black hole M {sub BH}-? relationship

    SciTech Connect

    Brown, Jonathan S.; Valluri, Monica [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Shen, Juntai [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030 (China); Debattista, Victor P., E-mail: brojonat@umich.edu, E-mail: mvalluri@umich.edu [Jeremiah Horrocks Institute, University of Central Lancashire, Preston, PR1 2HE (United Kingdom)

    2013-12-01

    We use collisionless N-body simulations to determine how the growth of a supermassive black hole (SMBH) influences the nuclear kinematics in both barred and unbarred galaxies. In the presence of a bar, the increase in the velocity dispersion ? (within the effective radius) due to the growth of an SMBH is on average ? 10%, whereas the increase is only ? 4% in an unbarred galaxy. In a barred galaxy, the increase results from a combination of three separate factors: (1) orientation and inclination effects; (2) angular momentum transport by the bar that results in an increase in the central mass density; and (3) an increase in the vertical and radial velocity anisotropy of stars in the vicinity of the SMBH. In contrast, the growth of the SMBH in an unbarred galaxy causes the velocity distribution in the inner part of the nucleus to become less radially anisotropic. The increase in ? following the growth of the SMBH is insensitive to a variation of a factor of 10 in the final mass of the SMBH, showing that it is the growth process rather than the actual SMBH mass that alters bar evolution in a way that increases ?. We argue that using an axisymmetric stellar dynamical modeling code to measure SMBH masses in barred galaxies could result in a slight overestimate of the derived M {sub BH}, especially if a constant M/L ratio is assumed. We conclude that the growth of a black hole in the presence of a bar could result in an increase in ? that is roughly 4%-8% larger than the increase that occurs in an axisymmetric system. While the increase in ? due to SMBH growth in a barred galaxy might partially account for the claimed offset of barred galaxies and pseudo bulges from the M {sub BH}-? relation obtained for elliptical galaxies and classical bulges in unbarred galaxies, it is inadequate to account for all of the offset.

  4. ROSAT PSPC observations of two X-ray-faint early-type galaxies: NGC 4365 and NGC 4382

    NASA Technical Reports Server (NTRS)

    Fabbiano, G.; Kim, D.-W.; Trinchieri, G.

    1994-01-01

    We present the results of ROSAT Positive Sensitive Proportional Counter (PSPC) observations of the two early-type galaxies NGC 4365 and NGC 4382. These galaxies are among those observed with Einstein to have the lowest X-ray to optical flux ratios of early-type galaxies. The PSCP data show that for radii r greater than 50 arcsec the radial distributions of the X-ray surface brightness are consistent with the optical distributions of King (1978). We also find that these galaxies have X-ray spectra significantly different from those observed in X-ray-bright ellipticals, with a relative excess of counts detected in the softest spectral channels. This confirms earlier Einstein results. The characteristics of the ROSAT PSPC do not allow us to discriminate between possible spectral models. If we adopt a two-component thermal model on the grounds of physical plausibility, we find that the spectral data can be fitted with a very soft optically thin component, with kT approximately 0.2 keV, and a hard component with kT greater than (1.0-1.5) keV. The hard component has a luminosity consistent with that expected from the integrated emission of a population of low mass-X-ray binaries in these galaxies; the nature of the very soft component is more speculative. Candidates include the coronal emission of late-type stars, supersoft X-ray sources, RS CVn, and perhaps a hot Interstellar Medium (ISM). Alternatively, the spectal data may be fitted with a 0.6-1 keV bremsstrahlung spectrum (expontential plus Gaunt), and may suggest the presence of a totally new population of X-ray sources.

  5. GALEX UV observations of the interacting galaxy NGC 4438 in the Virgo cluster

    E-print Network

    A. Boselli; S. Boissier; L. Cortese; A. Gil de Paz; V. Buat; J. Iglesias-Paramo; B. F. Madore; T. Barlow; L. Bianchi; Y. -I. Byun; J. Donas; K. Forster; P. G. Friedman; T. M. Heckman; P. Jelinsky; Y. -W. Lee; R. Malina; D. C. Martin; B. Milliard; P. Morrissey; S. Neff; R. M. Rich; D. Schiminovich; M. Seibert; O. Siegmund; T. Small; A. S. Szalay; B. Welsh; T. K. Wyder

    2005-02-02

    We present GALEX NUV (2310 A) and FUV (1530 A) images of the interacting galaxy NGC 4438 (Arp 120) in the center of the Virgo cluster. These images show an extended (20 kpc) tidal tail at the north-west edge of the galaxy previously undetected at other wavelengths, at 15-25 kpc from its nucleus. Except in the nucleus, the UV morphology of NGC 4438 is totally different from the Halpha+[NII] one, more similar to the X-ray emission, confirming its gas cooling origin. We study the star formation history of NGC 4438 combining spectro-photometric data in the UV-visible-near-IR wavelength range with population synthesis and galaxy evolution models. The data are consistent with a recent (~ 10 Myr), instantaneous burst of star formation in the newly discovered UV north-western tail which is significantly younger than the age of the tidal interaction with NGC 4435, dated by dynamical models at ~ 100 Myr ago. Recent star formation events are also present at the edge of the northern arm and in the southern tail, while totally lacking in the other regions, which are dominated by the old stellar population perturbed during the dynamical interaction with NGC 4435. The contribution of this recent starburst to the total galaxy stellar mass is lower than 0.1%, an extremely low value for such a violent interaction. High-velocity, off-center tidal encounters such as that observed in Arp 120 are thus not sufficient to significantly increase the star formation activity of cluster galaxies.

  6. Formation of a Tidal Dwarf Galaxy in the Interacting System Arp 245 (NGC 2992/93)

    NASA Astrophysics Data System (ADS)

    Duc, P.-A.; Brinks, E.; Springel, V.; Pichardo, B.; Weilbacher, P.; Mirabel, I. F.

    2000-09-01

    Among the various phenomena observed in interacting galaxies is the ejection due to tidal forces of stellar and gaseous material into the intergalactic medium and its subsequent rearranging which can lead to the formation of self-gravitating tidal dwarf galaxies (TDGs). We investigate this process with a detailed multiwavelength study of the interacting system Arp 245 and a numerical model of the collision computed with a Tree-SPH code. Our observations consist of optical/near-infrared broadband imaging, H? imaging, optical spectroscopy, H I VLA cartography and CO line mapping. The system, composed of the two spiral galaxies NGC 2992 and NGC 2993, is observed at an early stage of the interaction, about 100 Myr after perigalacticon, though at a time when tidal tails have already developed. The VLA observations disclose a third partner to the interaction: an edge-on, flat galaxy, FGC 0938, which looks strikingly undisturbed and might just be falling toward the NGC 2992/93 system. Our H I map shows prominent counterparts to the optical tails. Whereas the stellar and gaseous components of the plume that originates from NGC 2992 match, the stellar and H I tails emanating from NGC 2993 have a different morphology. In particular, the H I forms a ring, a feature that has been successfully reproduced by our numerical simulations. The H I emission in the system as a whole peaks at the tip of the NGC 2992 tail where a gas reservoir of about 109 Msolar, about 60% of the H I toward NGC 2992, coincides with a star-forming optical condensation, A245N. The latter tidal object exhibits properties ranging between those of dwarf irregular galaxies (structural parameters, gas content, star formation rate) and those of spiral disks (metallicity, star formation efficiency, stellar population). Although it is likely, based on our analysis of the H I and model data cube, that A245N might become an independent dwarf galaxy, the dynamical evidence is still open to debate. Prompted by the questions raised for this particular object, we discuss some issues related to the definition and identification of TDGs and highlight some specific conditions which seem required to form them. Finally, we outline what is needed in terms of future numerical simulations in order to further our understanding of these objects.

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

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

    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.

  8. Extended soft X-ray emission in Seyfert galaxies: ROSAT HRI observations of NGC 3516, NGC 4151, and Markarian 3

    NASA Technical Reports Server (NTRS)

    Morse, Jon A.; Wilson, Andrew S.; Elvis, Martin; Weaver, Kimberly A.

    1995-01-01

    We have used the ROSAT High Resolution Imager (HRI) to examine the distribution of soft X-rays in three nearby Seyfert galaxies with approximately 4 to 5 arcsecs FWHM spatial resolution. A feature of our analysis is an attempt to remove errors in the aspect solution using a method developed by one of us (J.M.). NGC 4151 shows resolved X-ray emission that is spatially correlated with the optical extended narrow-line region (ENLR), confirming the results obtained with the Einstein HRI by Elvis, Briel, & Henry. NGC 3516 is elongated along a position angle of approximately 40 to 220 deg, similar to the direction of the Z-shaped narrow-line region. MRK 3 is very faint in our HRI image and is probably spatially unresolved. We detect the faint X-ray source approximately 2 arcmins west of the MRK 3 nucleus previously found by Turner, Urry, & Mushotzky. We also detected the BL Lac object BL 1207 + 39 approximately 5 arcmins north-northwest of NGC 4151. This object appears spatially unresolved, but some excess X-ray emission may be observed in the azimuthally averaged radial brightness profile of BL 1207 + 39 between radii of 10 arcsecs and 30 arcsecs when compared to a calibration source. A much deeper image is necessary to confirm this result.

  9. High-energy monitoring of Seyfert galaxies: the case of NGC 5548 and NGC 4593

    NASA Astrophysics Data System (ADS)

    Ursini, F.

    2015-07-01

    We discuss results of broad-band monitoring programs on the active galactic nuclei (AGNs) NGC 5548 and NGC 4593, focusing on the high-energy view with XMM, NuSTAR and INTEGRAL. NGC 5548 was the object of a successful multi-satellite campaign conducted from May 2013 to February 2014, during which the source appeared unusually obscured by a clumpy stream of ionized gas, causing strong absorption in the X-ray band and simultaneous deep, broad UV absorption troughs (Kaastra et al. 2014). A talk giving an overview of the campaign on NGC 5548 is also proposed at this conference (Cappi et al.). Concerning NGC 4593, it was the object of a monitoring program of 5 × 20 ks joint XMM/NuSTAR observations in January 2015, spaced by two days. In both cases, the availability of multiple, broad-band observations with a high signal-to-noise ratio allows us to disentangle the different spectral components present in the high-energy spectrum and properly study their variability. The use of realistic Comptonization models provides good constraints on the physical parameters of the hot corona responsible for the hard X-ray emission.

  10. The Inner Resonance Ring of NGC 3081. II. Star Formation, Bar Strength, Disk Surface Mass Density, and Mass-to-Light Ratio

    NASA Astrophysics Data System (ADS)

    Byrd, Gene G.; Freeman, Tarsh; Buta, Ronald J.

    2006-03-01

    We complement our Hubble Space Telescope (HST) observations of the inner ring of the galaxy NGC 3081 using an analytical approach and n-body simulations. We find that a gas cloud inner (r) ring forms under a rotating bar perturbation with very strong azimuthal cloud crowding where the ring crosses the bar major axis. Thus, star formation results near to and ``downstream'' of the major axis. From the dust distribution and radial velocities, the disk rotates counterclockwise (CCW) on the sky like the bar pattern speed. We explain the observed CCW color asymmetry crossing the major axis as due to the increasing age of stellar associations inside the r ring major axis. These move faster than the pattern speed. The exterior point of the r ring at the bar major axis has an orbital rate equal to the pattern speed. We show how the perturbation strength can be estimated from the ring shapes and relative spacing over the inner through outer ring regions. The bar strength (maximum tangential/radial force) appears to be constant from 6 to 15 kpc. We derive how the perturbation, the fractional long wavelength m=2 intensity, and the rotation curve can be used to calculate the disk surface mass density versus radius. The disk surface density at 7 kpc is 13 Msolar pc-2 rising to 19 at 13 kpc. The latter is insufficient by a factor of seven to generate the observed rotation curve, implying halo domination. The surface density may have been reduced at 7 kpc due to inner ring gas cloud scattering. The surface density plus the observed surface brightness gives a disk mass-to-light (M/L) ratio which increases from 7 kpc through 13 kpc, contradicting the usual assumption in bar strength calculations. The simulation ring lifetime of several billion years is consistent with our ~400 Myr HST estimates. With a sufficiently high gas cloud surface mass density, our simulations form gas cloud ``associations'' near the ends of the bar as observed. Too high a density destroys the ring.

  11. Tracing of the chemical evolution of the massive elliptical galaxy NGC 3377 using a merger scenario

    NASA Astrophysics Data System (ADS)

    Nykytyuk, T.

    2015-05-01

    Mergers are thought to play a significant role in the formation of galaxies in clusters. The chemical evolution of the halo of the massive elliptical galaxy NGC 3377, a member of the Leo cluster, is considered in the framework of such a merger scenario. An open chemical evolution model is set up to calculate the metallicity distributions of pre-merging fragments. The model assumes that pristine gas was accreted onto the fragments during their whole evolution before their merger. The metallicity distribution resulting from the overlay of a variable number of fragments is then compared to observational data for NGC 3377. It was found that the observed metallicity distribution function of this elliptical galaxy is reproduced by merging at least five fragments from two different groups, namely low-and high-metallicity fragments.

  12. Diffuse X-ray emission from the spiral galaxy NGC 2403 discovered with Chandra

    E-print Network

    Filippo Fraternali; Massimo Cappi; Renzo Sancisi; Tom Oosterloo

    2002-06-18

    We have detected diffuse soft X-ray emission (0.4-1 keV) from the disk of the spiral galaxy NGC 2403 with Chandra. This diffuse emission (with a total luminosity of 2.1 x 10^38 erg/s and a gas temperature of 2-8 x 10^6 K) is well separated from the numerous bright point sources. NGC 2403 is a luminous spiral galaxy with a high rate of star formation. Recent HI observations have revealed an extended HI halo with anomalous velocities and a general inflow towards the central regions of the galaxy. This result and the present detection of a diffuse, hot X-ray emitting gas point at a very active disk-halo connection and galactic fountain types of phenomena.

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

    NASA Astrophysics Data System (ADS)

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

    2008-05-01

    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.

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

    SciTech Connect

    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

    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.

  15. Optical Datacubes of Infrared Luminous Galaxies NGC7130 and VV114

    NASA Astrophysics Data System (ADS)

    Knop, R.; Chynoweth, K.; Gibbons, R.; Mahmud, N.; Stricker, J.

    2006-06-01

    We have constructed large-scale optical emission-line datacubes of two nearby Bright Galaxy Sample members--- interacting starburst galaxy VV 114 and Seyvert 2 galaxy NGC 7130. Data were obtained using the RC Spectrograph on the SMARTS 1.5m telescope at CTIO. Spectral resolution is ˜ 2000, and spatial resolution is ˜ 2.6". In both galaxies, vigorous star formation activity is observed widely distributed across the galaxy, and the strongest sites of star formaton are not always coincident with the optical or infrared nuceli. The [NII]/H? and [OIII]/H? flux ratios are observed to vary strongly with position. In addition, there are differences the details of the kinematics (line center distribution, line widths) between the lines, and those differences themselves vary with position on the galaxy.

  16. A Stellar Dynamical Black Hole Mass for the Reverberation-Mapped Active Galaxy NGC6814

    NASA Astrophysics Data System (ADS)

    Bentz, Misty; Manne-Nicholas, Emily; Onken, Christopher; Valluri, Monica

    2013-08-01

    We propose to obtain spatially-resolved spectroscopy of the nucleus of the nearby (z=0.005) AGN NGC 6814 with Gemini NIFS+ALTAIR to model the gravitational influence of the central supermassive black hole on the stellar dynamics of the inner galaxy. A recent reverberation-based black hole mass of 2.0 x 10^7 M_sun for NGC 6814 places the black hole sphere of influence within the spatial resolution range of current ground-based AO systems. Because of the differing technical limitations of dynamical mass modeling and reverberation mapping, NGC 6814 is only the third galaxy where it is currently possible to directly compare a reverberation and a dynamical mass. Such a direct comparison provides an independent constraint on the geometric scaling factor that is currently the largest uncertainty in reverberation-based masses. All AGN black hole masses from spectroscopic surveys fundamentally rely on the reverberation sample, and thus our current understanding of the growth and evolution of black holes and galaxies across cosmic time relies on the accuracy of reverberation-based black hole masses. A stellar dynamical mass for NGC 6814 will increase by 50% the small sample of black holes that provide an independent check on the stability of the entire AGN black hole mass scale. We are also currently targeting additional AGNs for reverberation-mapping campaigns with the intent of further increasing this sample in the future.

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

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

    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.

  18. The Mg II line profile in the Seyfert galaxy NGC 4151: A new outflowing component

    NASA Technical Reports Server (NTRS)

    Leech, Kieron J.; Penston, M. V.; Snijders, M. A. J.; Gull, T.

    1986-01-01

    The Mg II 2795, 2802A doublet in the Seyfert galaxy NGC 4151 was examined to search for velocity systems in absorption and emission. Evidence for a narrow, outflowing absorption system in Mg II having a velocity of +825 km/sec relative to the Sun, -165 km/sec relative to the systemic velocity of NGC 4151 is presented. This feature is not present in Ly alpha or C IV and possible explanations for this are considered. For the Mg II and C IV lines a model decomposition of the line profile is shown.

  19. The Mg II line profile in the Seyfert galaxy NGC 4151 - A new outflowing component

    NASA Technical Reports Server (NTRS)

    Leech, Kieron J.; Penston, M. V.; Snijders, M. A. J.; Gull, T. R.

    1987-01-01

    This paper examines the Mg II 2795-2802 A doublet in the Seyfert galaxy NGC 4151 at a higher resolution than has previously been used, searching for velocity systems in absorption and emission. Evidence is presented for a new, narrow, outflowing absorption system in Mg II having a velocity of 825 km/s relative to the sun, and -165 km/s relative to the systemic velocity of NGC 4151. This feature is not present in Ly-alpha or C IV and possible explanations for this are considered. For the Mg II and C IV lines, a model decomposition of the line profile is presented.

  20. Kinematic modeling of disk galaxies. III. The warped ``Spindle'' NGC 2685

    NASA Astrophysics Data System (ADS)

    Józsa, G. I. G.; Oosterloo, T. A.; Morganti, R.; Klein, U.; Erben, T.

    2009-02-01

    This is the third of a series of papers in which the structure and kinematics of disk galaxies is studied. By employing direct tilted-ring fits to the data cube as introduced in Paper I, we analyzed the “Spindle” galaxy NGC 2685, previously regarded as a two-ringed polar ring galaxy. Deep H I and optical (i'-band) observations are presented. The H I observations strongly suggest that the gaseous structure of NGC 2685 does not consist of two separate mutually inclined regions, but forms a coherent, extremely warped disk, the appearance of two rings being due to projection effects. By comparing the H I total-intensity maps with the optical image, we demonstrate that at large radii a faint stellar disk is well aligned with the outer H I disk. The shape of the dust lanes obscuring the NE part of the inner stellar body indicates that, also at smaller radii, NGC 2685 possesses a disk containing gas, dust, and stars in which the various constituents are aligned. At smaller radii, this disk is kinematically decoupled from the central stellar body; hence, in the region of the bright, central stellar body, NGC 2685 appears to consist of two disks that share a common center, but have different orientation: a bright stellar lenticular body apparently devoid of dust and gas, and a heavily warped low-surface brightness disk containing stars, gas, and dust. The low-surface-brightness disk changes its orientation gradually and at large radii assumes the orientation of the central stellar S0 disk. Since, according to our analysis, the intrinsic orientation of the low-surface-brightness disk changes through 70°, the gaseous disk is coherent, and is at no radius oriented perpendicularly with respect to the central stellar body, NGC 2685 is not likely to be a classical polar-ring galaxy.

  1. Interferometric 12CO J = 2-1 Image of the Nuclear Region of Seyfert 1 Galaxy NGC 1097

    NASA Astrophysics Data System (ADS)

    Hsieh, Pei-Ying; Matsushita, Satoki; Lim, Jeremy; Kohno, Kotaro; Sawada-Satoh, Satoko

    2008-08-01

    We have mapped the central region of the Seyfert 1 galaxy NGC 1097 in 12CO J=2-1 with the Submillieter Array (SMA). The 12CO J=2-1 map shows a central concentration and a surrounding ring coinciding, respectively, with the Seyfert nucleus and a starburst ring. The line intensity peaks at the nucleus, whereas in a previously published 12 CO J=1-0 map the intensity peaks at the starburst ring. The azimuthally averaged 12 CO J=1-0 intensity ratio R21 of the ring is about unity, which is similar to those in nearby active star-forming galaxies, suggesting that most of the molecular gas in the ring is involved in fueling the starburst. The ratio of molecular gas to dynamical mass in the starburst ring shows a somewhat lower value than that found in nearby star-forming galaxies, suggesting that the high R21 of unity may be caused by additional effects, such as shocks induced by gas infall along the bar. The molecular gas can last for about 1.2×108 yr without further replenishment, assuming a constant star formation rate. The central gas is rotating with the molecular ring in the same direction, while its velocity gradient is steeper than that of the ring, and similar to what usually observed in Seyfert 2 galaxies. To view the Seyfert nucleus without obscuration, the central gas can be a low-inclined disk or torus but not too low to be less massive than the mass of the host galaxy, or be a highly inclined thin disk or clumpy and thick torus, inner part of the galactic disk is also possible. The R21 of ~1.9 of the central gas is significantly higher than that of the ring, indicates that the activity of the Seyfert nucleus may significant influence the central gas.

  2. The Nature of the X-Ray Point Source in the Bar of NGC 6822

    E-print Network

    Paul B. Eskridge; Raymond E. White, III

    1997-06-17

    We have analysed archival ROSAT PSPC and Einstein HRI data for the x-ray point source in the bar of NGC 6822. The source decreased in x-ray flux by at least half an order of magnitude in the 13 years between the HRI and PSPC observations. It has a PSPC flux of f_X = 8 x 10E-14 erg/cm^2/s, giving L_X = 2.4 x 10E36 erg/s for a distance of 500 kpc. The source appears to be related to the optical emission-line object Ho 12. It is unclear if Ho 12 is an HII region or a supernova remnant, although the latter interpretation is better supported by the available optical data. The x-rays are unlikely to be direct emission from a supernova remnant, due to the observed strong x-ray variability. The x-ray spectrum of the source is very soft. Acceptable fits are found for either a Raymond-Smith thermal model with kT = 0.56 keV, or a blackbody model with kT = 0.06 keV. The latter model would place the source amongst the class of Super-Soft x-ray sources first found in the Magellanic Clouds. If the thermal model is correct, the source appears similar to Galactic and Magellanic Cloud stellar-mass black hole binary candidates. We have identified a list of potential optical counterparts from published photometry. However, for either model discussed above, we expect the apparent magnitude of the optical counterpart to be in the range 21.5 < V < 24.0. Thus the optical counterpart may be below the limit of published photometry.

  3. Counterrotating stars in the disk of the Sab galaxy NGC 7217

    NASA Technical Reports Server (NTRS)

    Merrifield, Michael R.; Kuijken, Konrad

    1994-01-01

    We have analyzed high signal-to-noise spectra of the disk galaxy NGC 7217 in order to extract the full line-of-sight velocity distribution along both its major and minor axes. The data reveal that 20%-30% of the stars in this galaxy are in a distinct component on retrograde orbits. This counterrotating population cannot be explained away as a systematic error, and it does not seem to be caused by the bulge's contribution to the velocity distribution. We have developed a new technique for fitting dynamical disk models directly to the galaxy spectra, and application of this method confirms the presence of the distinct counterrotating disk population. NGC 7217 is only the second disk galaxy known to contain counterrotating stars, but we argue that similar components in other regular disk systems would not have been detected by traditional techniques, and so there could exist many such systems. The existence of disk stars on retrograde orbits provides a new clue as to the manner in which the galaxy formed: it favors a scenario in which matter continues to accrete onto the galaxy over a long period of time, with rapid, substantial changes occurring in the angular momentum of the infalling material. The observable consequences of this evolutionary history include a large bulge-to-disk ratio and the absence of strong spiral structure, and so the presence or absnece of a counterrotating component may go some way toward explaining the Hubble sequence for disk galaxies.

  4. Deep imaging of the shell elliptical galaxy NGC3923 with MegaCam

    E-print Network

    Bílek, Michal; Gwyn, Stephen; Ebrová, Ivana; Bartošková, Kate?ina; Jungwiert, Bruno; Jílková, Lucie

    2015-01-01

    Context. The elliptical galaxy NGC 3923 is known to be surrounded by a number of stellar shells, a probable remnant of an accreted galaxy. Despite its uniqueness, the deepest images of its outskirts come from the 80s. B\\'{i}lek et al. (2014) predicted a new shell to lie in this region on the basis of the MOND theory of modified dynamics. Aims. To obtain the deepest image ever of the galaxy and to map the tidal features in it. Methods. The image of the galaxy was taken by the MegaCam camera at the Canada-France-Hawaii Telescope in the $g'$ band. It reached the surface-brightness limit of 29 mag arcsec$^{-2}$. Moreover, we reanalyze an archival HST image of the galaxy. Results. We detected up to 42 shells in NGC 3923. This is by far most of all galaxies. We present the description of the shells and other tidal features in the galaxy. A probable progenitor of some of these features was discovered. The shell system likely originates from two or more progenitors. The predicted shell was not detected, but we found ...

  5. A kinematic study of the irregular dwarf galaxy NGC 2366 using HI and Halpha observations

    E-print Network

    van Eymeren, J; Koribalski, B; Dettmar, R -J; Bomans, D J; Gach, J L; Balard, P

    2008-01-01

    Abridged. Context. The metal content of dwarf galaxies and the metal enrichment of the intergalactic medium both suggest that mass loss from galaxies is a significant factor for the chemical evolution history of galaxies, in particular of dwarf galaxies. However, no clear evidence of a blow-away in local dwarf galaxies has been found so far. Aims. We therefore performed a detailed kinematic analysis of the neutral and ionised gas in the nearby star-forming irregular dwarf galaxy NGC 2366 in order to make predictions about the fate of the gas and to get a more complete picture of this galaxy. Methods. A deep Halpha image and Fabry-Perot interferometric data of NGC 2366 were obtained. They were complemented by HI synthesis data from the THINGS survey. We searched for line-splitting both in Halpha and HI by performing a Gaussian decomposition. To get an idea whether the expansion velocities are high enough for a gas blow-away, we used the pseudo-isothermal halo model, which gives us realistic values for the esca...

  6. The stellar populations in the low-luminosity, early-type galaxy NGC 59

    NASA Astrophysics Data System (ADS)

    Sansom, A. E.; Thirlwall, J. J.; Deakin, M. A.; Väisänen, P.; Kniazev, A. Y.; van Loon, J. Th.

    2015-06-01

    Low-luminosity galaxies may be the building blocks of more luminous systems. Southern African Large Telescope observations of the low-luminosity, early-type galaxy NGC 59 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 [?/Fe] ratio is subsolar, which indicates an extended star formation history in NGC 59. 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.

  7. XMM-Newton Observation of an X-ray Trail Between the Spiral Galaxy NGC6872 and the Central Elliptical NGC6876 in the Pavo Group

    E-print Network

    M. Machacek; P. Nulsen; L. Stirbat; C. Jones; W. Forman

    2004-12-09

    We present XMM-Newton observations of a trail of enhanced X-rayemission extending along the 8'.7 X 4' region between the spiral NGC6872 and the dominant elliptical NGC6876 in the Pavo Group,the first known X-ray trail associated with a spiral galaxy in a poor galaxy group and, with projected length of 90 kpc, one of the longest X-ray trails observed in any system. The X-ray surface brightness in the trail region is roughly constant beyond ~20 kpc of NGC6876 in the direction of NGC6872. The trail is hotter (~ 1 keV) than the undisturbed Pavo IGM (~0.5 keV) and has low metal abundances (0.2 Zsolar). The 0.5-2 keV luminosity of the trail, measured using a 67 X 90 kpc rectangular region, is 6.6 X 10^{40} erg/s. We compare the properties of gas in the trail to the spectral properties of gas in the spiral NGC6872 and in the elliptical NGC6876 to constrain its origin. We suggest that the X-ray trail is either IGM gas gravitationally focused into a Bondi-Hoyle wake, a thermal mixture of ~64% Pavo IGM gas with ~36% galaxy gas that has been removed from the spiral NGC6872 by turbulent viscous stripping, or both, due to the spiral's supersonic motion at angle xi ~ 40 degrees with respect to the plane of the sky, past the Pavo group center (NGC6876) through the densest region of the Pavo IGM. Assuming xi = 40 degrees and a filling factor eta in a cylindrical volume with radius 33 kpc and projected length 90 kpc, the mean electron density and total hot gas mass in the trail is 9.5 X 10^{-4}*eta^{-1/2} cm^{-3} and 1.1 X 10^{10}*eta^{1/2} Msolar, respectively.

  8. Discovery of Remote Star Clusters in the Halo of the Irregular Galaxy NGC 6822

    E-print Network

    Hwang, N; Lee, J C; Park, W K; Park, H S; Park, J H; Sohn, S T; Lee, S G; Lee, H M; Chun, M S; Lee, Y W; Sohn, Y J; Yuk, I S; Kim, S C; Kim, H I; Han, W; Hwang, Narae; Lee, Myung Gyoon; Lee, Jong Chul; Park, Won-Kee; Park, Hong Soo; Park, Jang-Hyun; Sohn, Sangmo Tony; Lee, Sang-Gak; Lee, Hyung Mok; Chun, Mun-Suk; Lee, Young-Wook; Sohn, Young-Jong; Yuk, In-Soo; Kim, Sang Chul; Kim, Ho-Il; Han, Wonyong

    2005-01-01

    We report the discovery of three new star clusters in the halo of the Local Group dwarf irregular galaxy NGC 6822. These clusters were found in the deep images taken with the MegaPrime at the CFHT, covering a total field of 2 deg x 2 deg. The most remote cluster is found to be located as far as 79 arcmin away from the center of NGC 6822. This distance is several times larger than the size of the region in NGC 6822 where star clusters were previously found. Morphological structures of the clusters and color-magnitude diagrams of the resolved stars in the clusters show that at least two of these clusters are proabably old globular clusters.

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Rubin, Vera C.

    1994-01-01

    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.

  11. The supermassive black hole in the Seyfert 2 galaxy NGC 5252

    E-print Network

    Alessandro Capetti; Alessandro Marconi; Duccio Macchetto; David Axon

    2004-11-03

    We present results from HST/STIS long-slit spectroscopy of the gas motions in the nuclear region of the Seyfert 2 galaxy NGC 5252. The observed velocity field is consistent with gas in regular rotation with superposed localized patches of disturbed gas. The dynamics of the circumnuclear gas can be accurately reproduced by adding to the stellar mass component a compact dark mass of MBH = 0.95 (-0.45;+1.45) 10E9 M(sun), very likely a supermassive black hole. Contrarily to results obtained in similar studies rotational broadening is sufficient to reproduce also the behaviour of line widths. The MBH estimated for NGC 5252 is in good agreement with the correlation between MBH and bulge mass. The comparison with the MBH vs sigma relationship is less stringent (mostly due to the relatively large error in sigma); NGC 5252 is located above the best fit line by between 0.3 and 1.2 dex, i.e. 1 - 4 times the dispersion of the correlation. Both the galaxy's and MBH of NGC 5252 are substantially larger than those usually estimated for Seyfert galaxies but, on the other hand, they are typical of radio-quiet quasars. Combining the determined MBH with the hard X-ray luminosity, we estimate that NGC 5252 is emitting at a fraction ~ 0.005 of L(Edd). In this sense, this active nucleus appears to be a quasar relic, now probably accreting at a low rate, rather than a low black hole mass counterpart of a QSO.

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

    NASA Astrophysics Data System (ADS)

    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

    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.

  13. Ultra-Luminous X-ray Sources in the Collisional Ring Galaxy NGC 922

    NASA Astrophysics Data System (ADS)

    Prestwich, Andrea H.; Galache, J.; Kalogara, V.; Linden, T.; Kilgard, R.; Zezas, A.; Wolter, A.; Trinchieri, G.

    2010-01-01

    We present a new Chandra observation of the nearby collisional ring galaxy NGC 922. NGC 922 is undergoing a violent burst of star formation as density waves are driven through the disk as a result of the collision. It is similar to the famous Cartwheel galaxy, except that the metallicity is somewhat higher and star formation rate lower. Our primary science goal is to determine whether a low metallicty environment is required to form the most luminous X-ray sources (Lx>1E40 ergs s-1). We find a total of 14 bright X-ray sources, 7 of which are ULX ((Lx>1E39 ergs s-1). One source has Lx 1E40 ergs/s. The X-ray sources are associated with the H-alpha ring. However, they are NOT associated with the brightest H-alpha patches, suggesting that the ULX phase starts >1 x 1E7 years after the starburst. Like the Cartwheel, the X-ray luminosity function of NGC 922 has a slope close to that of the “cannonical” HMXB slope of Gilfanov et al 2004. We conclude that NGC 922 is forming ULX as efficiently as the Cartwheel (after allowing for the difference in the star formation rate). We do not see a strong metallicity effect.

  14. The Tip of the Red Giant Branch Distances to Type Ia Supernova Host Galaxies. III. NGC 4038/39 and NGC 5584

    E-print Network

    Jang, In Sung

    2015-01-01

    We present the tip of the red giant branch (TRGB) distances to Type Ia supernova (SNe Ia) host galaxies NGC 4038/39 and NGC 5584. Based on the deep images constructed using archival Hubble Space Telescope data, we detect red giant branch stars in each galaxy. VI photometry of the resolved stars and corresponding I-band luminosity functions show the TRGB to be at I_{TRGB} = 27.67 \\pm 0.05 for NGC 4038/39 and I_{TRGB} = 27.77 \\pm 0.04 for NGC 5584. From these estimates, we determine the distance modulus to NGC 4038/39 to be (m-M)_0 = 31.67 \\pm 0.05 (random) \\pm 0.12 (systematic) (corresponding to a linear distance of 21.58 \\pm 0.50 \\pm 1.19 Mpc) and the distance modulus to NGC 5584 to be (m-M)_0 = 31.76 \\pm 0.04 (random) \\pm 0.12 (systematic) (corresponding to a linear distance of 22.49 \\pm 0.41 \\pm 1.24 Mpc). We derive a mean absolute maximum magnitude of SNe Ia of M_V = -19.29 \\pm 0.08 from the distance estimates of five SNe Ia (including two SNe in this study and three SNe Ia from our previous studies), and ...

  15. High-resolution Observations of Molecular Gas in the Early-type Dwarf Galaxy NGC 404

    NASA Astrophysics Data System (ADS)

    Taylor, Christopher L.; Petitpas, Glen R.; del Rio, M. S.

    2015-06-01

    We present Berkeley–Illinois–Maryland Association CO (1–0) observations of the nearby dwarf elliptical galaxy NGC 404. The detected CO emission is concentrated in a small feature, slightly larger than the beam size, at the center of the optical galaxy. For an assumed CO-to-H2 conversion factor of 2.3 × {{10}20} (K km s?1)?1, the molecular gas mass is 9.0 × {{10}6} M?. The velocity field suggests rotation, with a position angle ?90° different from previous single-dish observations. Both position angles are different from that of the extended H i distribution detected by del Rió et al. The lack of agreement between the postion angle of the CO velocity field and other position angles suggests an external origin for the central molecular gas clump in NGC 404.

  16. Rapid Compton-thick\\/Compton-thin Transitions in the Seyfert 2 Galaxy NGC 1365

    Microsoft Academic Search

    G. Risaliti; M. Elvis; G. Fabbiano; A. Baldi; A. Zezas

    2005-01-01

    We present multiple Chandra and XMM-Newton observations of the type 1.8 Seyfert galaxy NGC 1365, which shows the most dramatic X-ray spectral changes observed so far in an active galactic nucleus: the source switched from reflection-dominated to transmission-dominated and back in just 6 weeks. During this time the soft thermal component, arising from an ~1 kpc region around the center,

  17. Multiwavelength studies of the Seyfert 1 galaxy NGC7469. I - Far UV observations with FUSE

    Microsoft Academic Search

    G. A. Kriss; A. Blustin; G. Branduardi-Raymont; R. F. Green; J. Hutchings; M. E. Kaiser

    2003-01-01

    We obtained far-ultraviolet spectra of the Seyfert 1 galaxy NGC 7469 using\\u000athe FUSE on 1999 December 6. Our spectra cover the wavelength range 990-1187 A\\u000awith a resolution of 0.05 A. We see broad emission lines of CIII, NIII, OVI,\\u000aand HeII as well as intrinsic absorption lines in the OVI 1032,1038 resonance\\u000adoublet. The absorption arises in two

  18. Water-Vapor Maser Disk at the Nucleus of the Seyfert 2 Galaxy NGC 3079

    Microsoft Academic Search

    Aya Yamauchi; Naomasa Nakai; Naoko Sato; Philip Diamond

    2004-01-01

    We observed a Seyfert 2\\/LINER galaxy NGC 3079 using the NRO 45-m telescope from 1992 to 2002, and the Very Long Baseline Array (VLBA) in 2001 December, at 22GHz. The 45-m telescope detected weak red-shifted and systemic features as well as strong blue-shifted features. High spatial resolution observations with the VLBA indicated that the H2O maser spots are distributed along

  19. 6.7 GHz methanol absorption toward the Seyfert 2 galaxy NGC 3079

    Microsoft Academic Search

    C. M. V. Impellizzeri; C. Henkel; A. L. Roy; K. M. Menten

    2008-01-01

    The detection of the 6.7 GHz line of methanol (CH3OH) is reported for the first time toward an object beyond the Magellanic Clouds. Using the Effelsberg 100 m telescope, two absorption features were identified toward the Seyfert 2 galaxy NGC 3079. Both components probably originated on lines-of-sight toward the central region, presumably absorbing the radio continuum of the nuclear sources

  20. Resolving the Intrinsic C IV Absorption in the Seyfert 1 Galaxy NGC 3516

    Microsoft Academic Search

    D. Michael Crenshaw; Stephen P. Maran; Richard F. Mushotzky

    1997-01-01

    We observed the Seyfert 1 galaxy NGC 3516 with the Goddard High Resolution\\u000aSpectrograph on the Hubble Space Telescope, and obtained UV spectra at a\\u000aresolution of about 20,000 in the redshifted C IV 1549 region. The intrinsic C\\u000aIV absorption in the core of the broad emission line is resolved for the first\\u000atime into four distinct kinematic components,

  1. Shaken, Not Stirred: The Disrupted Disk of the Starburst Galaxy NGC 253

    Microsoft Academic Search

    T. J. Davidge

    2010-01-01

    Near-infrared images obtained with WIRCam on the Canada-France-Hawaii Telescope are used to investigate the recent history of the nearby Sculptor Group spiral NGC 253, which is one of the nearest starburst galaxies. Bright asymptotic giant branch (AGB) stars are traced out to projected distances of ~22-26 kpc (~13-15 disk scale lengths) along the major axis. The distribution of stars in

  2. NGC 1365

    NASA Astrophysics Data System (ADS)

    Lindblad, Per Olof

    The aim of the present review is to give a global picture of the supergiant barred galaxy NGC 1365. This galaxy with its strong bar and prominent spiral structure displays a variety of nuclear activity and ongoing star formation. The kinematics of the galaxy has been mapped in detail by optical long slit and Fabry-Perot observations as well as radio observations of Hi and CO interstellar lines. From these observations a combined velocity field has been derived, describing the circulation of interstellar gas in the symmetry plane of the galaxy. With a gravitational potential based on near infrared photometry of the bar and the shape of the apparent rotation curve, computer simulations of the dynamics of the interstellar gas have been made with the aim to reproduce both the morphology of the interstellar matter as well as the observed velocity field. The simulations demonstrate the role of the bar and the importance of resonances between the bar rotation and the rotation of the galaxy for the formation of the spiral structure. Polarization of radio radiation reveals magnetic fields concentrated to the dust lanes along and across the bar, where they are aligned with the flow pattern of the gas, and along the spiral arms. The kinematics of the outer region of the galaxy with a fairly unique decline of the rotation curve leads to the conclusion that NGC 1365 lacks a very massive dark matter halo, which may permit the formation of a very strong bar. The galaxy contains an active nucleus with both broad and narrow components of the permitted spectral emission lines. The nucleus is surrounded by a molecular torus, numerous star forming regions and continuum radio sources. The star forming regions are, as seen with the Hubble Space Telescope (HST), resolved into a large number of super star clusters suggested to be young globular clusters. A very compact radio source, seen at high spatial resolution with the Very Large Array (VLA), has been claimed to coincide with one of the super star clusters. This compact source has a radio brightness of the order of 100 times that of the bright galactic supernova remnant Cas A and is suggested to be a so called `radio supernova'. Two other such compact radio sources, positioned in the prominent dark dust lane penetrating the nuclear region, are identified as strong infrared sources by observations with the Very Large Telescope (VLT). The cause of this infrared radiation may be dust heated by the objects that drive the radio sources. The X-ray radiation from the nucleus is interpreted to consist of hard continuum radiation from the active nucleus itself, Fe-K line emission from a rotating disk, and thermal emission from the surrounding star burst activity. A secondary, highly variable source has been discovered close to the nuclear region. It seems to be one of the most luminous and most highly variable off-nuclear X-ray sources known. The higher excitation optical emission lines in the nuclear region, primarily from [Oiii], reveal a velocity field quite different from that described by the galactic rotation. The deviating [Oiii] morphology and velocity field in the nuclear region is interpreted in terms of a high excitation outflow double-cone with its apex at the nucleus and symmetry axis perpendicular to the symmetry plane of the galaxy. One of the circumnuclear radio sources seems to be a one-sided jet emerging from the nucleus aligned with the cone axis. According to the model, the outward flow within the cone is accelerated and the flow velocity highest at the cone axis.

  3. Diffuse Gamma-Ray Emission from the Starburst Galaxy NGC 253

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    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.

  4. NGC 2110 - An X-ray/radio galaxy with elliptical morphology

    NASA Technical Reports Server (NTRS)

    Bradt, H. V.; Burke, B. F.; Canizares, C. R.; Greenfield, P. E.; Kelley, R. L.; Mcclintock, J. E.; Koski, A. T.; Van Paradijs, J.

    1978-01-01

    The detection of X-ray emission from NGC 2110, a narrow-emission-line galaxy of apparently elliptical morphology, is reported. A relatively hard 2-11-keV energy spectrum with an index of 0.1 + or - 0.3 is obtained, and the X-ray luminosity in this energy band is shown to be 1.2 x 10 to the 43rd erg/s for the redshift distance of 43 Mpc. Optical and radio observations are discussed which indicate a galactocentric redshift of approximately 0.0071, a resolved nonstellar optical nucleus about 4 arcsec in extent, Seyfert type 2 emission lines from the nucleus, and a nonthermal radio source located 3.0 arcsec from the position of the optical nucleus. No evidence is found for X-ray source variability in NGC 2110. It is suggested that the four to seven known X-ray-emitting high-excitation narrow-emission-line galaxies appear to be nearby examples of the Seyfert type 2 phenomenon and that the elliptical morphology of NGC 2110, if confirmed, may be unique among known Seyfert galaxies.

  5. The ionization cone, obscured nucleus, and gaseous outflow in NGC 3281 - A prototypical Seyfert 2 galaxy?

    NASA Technical Reports Server (NTRS)

    Storchi-Bergmann, Thaisa; Wilson, Andrew S.; Baldwin, Jack A.

    1992-01-01

    Narrow-band images and long-slit spectroscopy of the central region of the highly inclined Seyfert galaxy NGC 3281 are presented. The image of the continuum-subtracted forbidden 4959 emission line shows a very clear conical morphology for the high-excitation gas. A possible similar structure can also be seen on the other side of the nucleus, but is dimmed by patchy obscuration in the dusk. The continuum images and long-slit spectroscopy are used to derive and map the extinction in the inner regions of NGC 3281; heavy obscuration is found along the present line of sight to the apex of the cone, suggesting that the true nucleus is located at the apex and is obscured. Low-resolution long-slit spectra are used to study the stellar population, which is found to be old, uniform within 2.5 kpc of the nucleus, and typical of the bulges of early-type galaxies. It is suggested that NGC3281 may be another example of a 'hidden' Seyfert 1, even though there is no direct evidence for a broad-line region in this particular galaxy.

  6. The Complex Gas Kinematics in the Nucleus of the Seyfert 2 Galaxy NGC 1386: Rotation, Outflows, and Inflows

    NASA Astrophysics Data System (ADS)

    Lena, D.; Robinson, A.; Storchi-Bergman, T.; Schnorr-Müller, A.; Seelig, T.; Riffel, R. A.; Nagar, N. M.; Couto, G. S.; Shadler, L.

    2015-06-01

    We present optical integral field spectroscopy of the circum-nuclear gas of the Seyfert 2 galaxy NGC 1386. The data cover the central 7? × 9? (530 × 680 pc) at a spatial resolution of 0.? 9 (68 pc), and the spectral range 5700–7000 Å at a resolution of 66 km s?1. The line emission is dominated by a bright central component, with two lobes extending ?3? north and south of the nucleus. We identify three main kinematic components. The first has low velocity dispersion (\\bar{? } ? 90 km s?1), extends over the whole field of view, and has a velocity field consistent with gas rotating in the galaxy disk. We interpret the lobes as resulting from photoionization of disk gas in regions where the active galactic nucleus radiation cones intercept the disk. The second has higher velocity dispersion (\\bar{? } ? 200 km s?1) and is observed in the inner 150 pc around the continuum peak. This component is double peaked, with redshifted and blueshifted components separated by ?500 km s?1. Together with previous Hubble Space Telescope imaging, these features suggest the presence of a bipolar outflow for which we estimate a mass outflow rate of \\dot{M} ? 0.1 {{M}? } yr?1. The third component is revealed by velocity residuals associated with enhanced velocity dispersion and suggests that outflow and/or rotation is occurring approximately in the equatorial plane of the torus. A second system of velocity residuals may indicate the presence of streaming motions along dusty spirals in the disk.

  7. Stellar and Gas Kinematics in the Tully-Fisher Deviant Virgo Cluster Galaxy NGC 4424

    NASA Astrophysics Data System (ADS)

    Cortes, J. R.; Kenney, J. D. P.

    2000-05-01

    NGC 4424 is a peculiar, gas-deficient, Virgo Cluster Sa galaxy which is probably the result of a merger. This galaxy seems to deviate from the Tully-Fisher relationship, as shown by Kenney et al (1996) and Rubin et al (1999). We present stellar and gas kinematics of NGC 4424 measured with Integral Field Spectroscopy using the Densepak fiber array on the WIYN telescope. Using a cross-correlation technique, we derive velocities and velocity dispersions of the stars thoughout the central region of the galaxy. We find that the mean line-of-sight velocities for both gas and stars are approximately a factor of 2 smaller than would be expected for the rotational motions of a galaxy of its luminosity and apparent inclination. Preliminary estimates of the stellar velocity dispersion are also lower than would be expected for the Faber-Jackson relationship. We discuss possible explanations for this behaviour, including the possibility that this disturbed galaxy is rotating in a plane different than the plane of the apparent disk, and is a tumbling object.

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

    E-print Network

    Beverly J. Smith

    1998-01-11

    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.

  9. The Interacting Dwarf Galaxy NGC 3077 The Interplay of Atomic and Molecular Gas with Violent Star Formation

    E-print Network

    Walter, F; Martin, C; Scoville, N Z

    2002-01-01

    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 ...

  10. DETECTION OF A HOT GASEOUS HALO AROUND THE GIANT SPIRAL GALAXY NGC 1961

    SciTech Connect

    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

    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.

  11. Determination of resonance locations in barred spiral galaxies using multiband photometry

    NASA Astrophysics Data System (ADS)

    Sierra, Amber D.; Seigar, Marc S.; Treuthardt, Patrick; Puerari, Ivânio

    2015-06-01

    In this paper, we apply a method identified by Puerari & Dottori to find the corotation radii (CR) in spiral galaxies. We apply our method to 57 galaxies, 17 of which have already have their CR locations determined using other methods. The method we adopted entails taking Fourier transforms along radial cuts in the u, g, r, i, and z wavebands and comparing the phase angles as a function of radius between them. The radius at which the phase angles cross indicates the location of the corotation radius. We then calculated the relative bar pattern speed, {R}, and classified the bar as `fast', where {R} < 1.4, slow, where {R} ? 1.4, or intermediate, where the errors on {R} are consistent with the bar being `slow' or `fast'. For the 17 galaxies that had their CR locations previously measured, we found that our results were consistent with the values of {R} obtained by the computer simulations of Rautiainen, Salo & Laurikainen. For the larger sample, our results indicate that 34 out of 57 galaxies (?60 per cent) have fast bars. We discuss these results in the context of its implications for dark matter concentrations in disc galaxies. We also discuss these results in the context of different models for spiral structure in disc galaxies.

  12. Serendipitous discovery of a dying Giant Radio Galaxy associated with NGC 1534, using the Murchison Widefield Array

    E-print Network

    Hurley-Walker, Natasha; 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, Andre; 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

    2014-01-01

    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 $\\sim$700\\,kpc. We present details of the radio emission along with a detailed comparison with other radio galaxies with disks. NGC1534 is the lowest surface brightness radio galaxy known with an estimated scaled 1.4-GHz surface brightness of just 0.2\\,mJy\\,arcmin$^{-2}$. The radio lobes have one of the steepest spectral indices yet observed: $\\alpha=-2.1\\pm0.1$, and the core to lobe luminosity ratio is $<0.1$\\%. We estimate the space density of this low brightness (dying) phase of radio galaxy evolution as $7\\times10^{-7}$\\,Mpc$^{-3}$ and argue that normal AGN cannot spend more than 6\\% of...

  13. Formation and evolution of bars in disc galaxies

    E-print Network

    E. Athanassoula

    2002-09-22

    I follow a bar from its formation, via its evolution, to its destruction and, perhaps, regeneration. I discuss the main features at each stage and particularly the role of the halo. Bars can form even in sub-maximum discs. In fact, such bars can be stronger than bars which have grown in maximum discs. This is due to the response of the halo and, in particular, to the exchange of energy and angular momentum between the disc particles constituting the bar and the halo particles at resonance with it. The bar slowdown depends on the initial central concentration of the halo and the initial value of the disc Q. Contrary to the halo mass distribution, the disc changes its radial density profile considerably during the evolution. Applying the Sackett criterion, I thus find that discs become maximum in many simulations in which they have started off as sub-maximum. I briefly discuss the evolution if a gaseous component is present, as well as the destruction and regeneration of bars.

  14. A new, kinematically anomalous HI component in the spiral galaxy NGC 2403

    E-print Network

    Filippo Fraternali; Tom Oosterloo; Renzo Sancisi; Gustaaf van Moorsel

    2001-10-16

    We discuss new, high sensitivity HI observations of the spiral galaxy NGC2403 which show extended emission at anomalous velocities with respect to the `cold' disk. This `anomalous' gas component (~1/10 of the total HI mass) is probably located in the region of the halo and rotates more slowly (~20-50 km/s) than the gas in the disk. Moreover, it shows a distortion in the velocity field that we interpret as a large-scale radial motion (10-20 km/s inflow) towards the centre of the galaxy. The most likely explanation for its origin and kinematics seems to be that of a galactic fountain. There is, however, a significant part of the anomalous gas which seems to be moving contrary to rotation and is difficult to understand in such a picture. These anomalous gas complexes discovered in NGC 2403 may be analogous to the High Velocity Clouds of our Galaxy. They may be rather common in spiral galaxies and not have been detected yet for lack of sensitivity.

  15. Is the EGRET Source 3EG J1621+8203 the Radio Galaxy NGC 6251?

    NASA Astrophysics Data System (ADS)

    Mukherjee, R.; Halpern, J.; Mirabal, N.; Gotthelf, E. V.

    2002-08-01

    We discuss the nature of the unidentified EGRET source 3EG J1621+8203. In an effort to identify the gamma-ray source, we have examined X-ray images of the field from ROSAT PSPC, ROSAT HRI, and ASCA GIS. Of the several faint X-ray point sources in the error circle of 3EG J1621+8203, most are stars or faint radio sources, unlikely to be counterparts to the EGRET source. The most notable object in the gamma-ray error box is the bright FR I radio galaxy NGC 6251. If 3EG J1621+8203 corresponds to NGC 6251, then it would be the second radio galaxy to be detected in high-energy gamma rays after Cen A, which provided the first clear evidence of the detection above 100 MeV of an active galactic nucleus (AGN) with a large-inclination jet. If the detection of more radio galaxies by EGRET has been limited by its threshold sensitivity, there exists the exciting possibility that new high-energy gamma-ray instruments, with much higher sensitivity, will detect a larger number of radio galaxies in the future.

  16. Is the EGRET source 3EG J1621+8203 the radio galaxy NGC 6251?

    E-print Network

    R. Mukherjee; J. Halpern; N. Mirabal; E. V. Gotthelf

    2002-04-29

    We discuss the nature of the unidentified EGRET source 3EG J1621+8203. In an effort to identify the gamma-ray source, we have examined X-ray images of the field from ROSAT PSPC, ROSAT HRI, and ASCA GIS. Of the several faint X-ray point sources in the error circle of 3EG J1621+8203, most are stars or faint radio sources, unlikely to be counterparts to the EGRET source. The most notable object in the gamma-ray error box is the bright FR I radio galaxy NGC 6251. If 3EG J1621+8203 corresponds to NGC 6251, then it would be the second radio galaxy to be detected in high energy gamma rays, after Cen A, which provided the first clear evidence of the detection above 100 MeV of an AGN with a large-inclination jet. If the detection of more radio galaxies by EGRET has been limited by its threshold sensitivity, there exists the exciting possibility that new high energy gamma-ray instruments, with much higher sensitivity, will detect a larger number of radio galaxies in the future.

  17. Multi-Band Bar/Bulge/Disk Image Decomposition of a Thousand Galaxies

    E-print Network

    Dimitri Gadotti; Guinevere Kauffmann

    2007-02-02

    The structural parameters of bulges, disks and bars of a sample of nearly 1000 nearby galaxies are being determined through sophisticated image decomposition in the g, r and i bands. The sample is carefully drawn from the Sloan Digital Sky Survey Data Release 2 (SDSS DR2), contains 963 galaxies, of which 407 host AGN, and we show that it is representative of the galaxy and AGN populations in the local universe. A large number of other physical properties have also been determined for these galaxies within the SDSS collaboration. With these data, we reinforce several recent studies and find a number of results leading to new insights into how the different galaxy components relate to each other and the extent to which the hosts galaxies of AGN differ from quiescent galaxies.

  18. 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)

    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.; Mühle, S.; Sánchez-Gallego, J. R.; Tilanus, R. P. J.; Usero, A.; van der Werf, P.; Zhu, M.

    2013-11-01

    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.

  19. Ballistic Models for Radio Jets in Colliding Galaxies: 3C 278 (NGC 4782/4783)

    NASA Technical Reports Server (NTRS)

    Borne, Kirk D.; Colina, Luis

    1993-01-01

    We present here a general numerical simulation algorithm for ballistic radio jets. The evolution of the jets is determined by their response to mechanical forces (i.e., gravity and ram pressure). Using a previously derived collision model for the interacting pair of elliptical galaxies NGC 4782/4783, we have used this algorithm to simulate the specific two-sided jet morphology seen in the radio source associated with NGC 4782 (3C 278). This is the first time such simulations have been attempted for a galaxy pair whose relative orbit was determined independently from the jet modeling. The general morphological features of the jets in 3C 278 (e.g., position angles, lengths, curvature, and deflection angles) are well matched by the simulations, indicating that our model of the mechanical forces acting on the jets can indeed reproduce most of the basic details of the jet morphology and thereby provide an opportunity to model a combination of detailed optical, radio, and X-ray data for a wide variety of interacting radio-jet galaxies. Our models constrain the initial jet parameters (i.e., the ejection speed, direction, and starting time), the properties of the gaseous medium into which the jets are ejected, and the relative importance of gravitational deflection versus ram pressure bending in influencing the jet morphology. For 3C 278, we find that the effects of ram pressure dominate the structural evolution of the jets. In our best-fit simulation the jet ejection speed is of order 10(exp 4) km/s, to within 50%, suggesting that similar low-luminosity radio jets are also significantly subluminal. We also find that the jets are ejected within approximately 5 deg of the line of sight, the ISM in the nonjet galaxy has a much larger effect on the jet deflection than does the host galaxy, and the jet activity began just over 70 million years ago, roughly 50 million years before the pericenter passage of the two galaxies. Therefore, the onset of nuclear activity appears in 3C 278 to be related to the kinematically observed tidal shock that has been induced in the core of NGC 4782 as a result of its deeply penetrating collision with NGC 4783.

  20. A Method to Resolve the Nuclear Activity in Galaxies, as Applied to NGC 1358

    NASA Astrophysics Data System (ADS)

    Lindblad, Per-Olof; Fathi, Kambiz

    2011-12-01

    Nuclear regions of galaxies generally host a mixture of components with different exitation, composition, and kinematics. Derivation of emission line ratios and kinematics could then be misleading, if due correction is not made for the limited spatial and spectral resolutions of the observations. The aim of this paper is to demonstrate, with application to a long slit spectrum of the Seyfert 2 galaxy NGC 1358, how line intensities and velocities, together with modelling and knowledge of the point spread function, may be used to resolve the differing structures. In the situation outlined, the observed kinematics differs for different spectral lines. From the observed intensity and velocity distributions of a number of spectral lines and with some reasonable assumptions to diminish the number of free parameters, the true line ratios and velocity structures may be deduced. A preliminary solution for the nuclear structure of NGC 1358 is obtained, involving a nuclear point source and an emerging outflow of high excitation with a post shock cloud, as well as a nuclear emission line disk rotating in the potential of a stellar bulge and expressing a radial exitation gradient. The method results in a likely scenario for the nuclear structure of NGC 1358. For definitive results an extrapolation of the method to two dimensions combined with the use of integral field spectroscopy will generally be necessary.

  1. A HST study of the stellar populations in the cometary dwarf irregular galaxy NGC 2366

    E-print Network

    Thuan, T X

    2005-01-01

    We present V and I photometry of the resolved stars in the cometary dwarf irregular galaxy NGC 2366, using Wide Field Planetary Camera 2 images obtained with the Hubble Space Telescope. The resulting color-magnitude diagram reaches down to I~26.0 mag. It reveals not only a young population of blue main-sequence stars (age 100 Myr) and red giant branch (RGB) stars (age >1 Gyr). The measured magnitude I=23.65+/-0.10 mag of the RGB tip results in a distance modulus m-M=27.67+/-0.10, which corresponds to a distance of 3.42+/-0.15 Mpc, in agreement with previous distance determinations. The youngest stars are associated with the bright complex of HII regions NGC 2363=Mrk 71 in the southwest extremity of the galaxy. As a consequence of the diffusion and relaxation processes of stellar ensembles, the older the stellar population is, the smoother and more extended is its spatial distribution. An underlying population of older stars is found throughout the body of NGC 2366. The most notable feature of this older popul...

  2. The SLUGGS Survey: Globular cluster kinematics in a "double sigma" galaxy - NGC 4473

    E-print Network

    Alabi, Adebusola B; Forbes, Duncan A; Romanowsky, Aaron J; Pastorello, Nicola; Brodie, Jean P; Spitler, Lee R; Strader, Jay; Usher, Christopher

    2015-01-01

    NGC 4473 is a so--called double sigma (2$\\sigma$) galaxy, i.e. a galaxy with rare, double peaks in its 2D stellar velocity dispersion. Here, we present the globular cluster (GC) kinematics in NGC 4473 out to $\\sim10\\,R_e$ (effective radii) using data from combined HST/ACS and Subaru/Suprime--Cam imaging and Keck/DEIMOS spectroscopy. We find that the 2$\\sigma$ nature of NGC 4473 persists up to 3 $R_e$, though it becomes misaligned to the photometric major axis. We also observe a significant offset between the stellar and GC rotation amplitudes. This offset can be understood as a co--addition of counter--rotating stars producing little net stellar rotation. We identify a sharp radial transition in the GC kinematics at $\\sim4\\,R_e$ suggesting a well defined kinematically distinct halo. In the inner region ($4\\,R_e$), the red GCs rotate in an opposite direction compared to the inner region red GCs, along the photometric major axis, while the blue GCs rotate along an axis intermediate between the major and minor p...

  3. PLANETARY NEBULAE IN THE ELLIPTICAL GALAXY NGC 821: KINEMATICS AND DISTANCE DETERMINATION

    SciTech Connect

    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

    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.

  4. A Stellar Dynamical Measurement of the Black Hole Mass in the Maser Galaxy NGC 4258

    NASA Astrophysics Data System (ADS)

    Siopis, Christos; Gebhardt, Karl; Lauer, Tod R.; Kormendy, John; Pinkney, Jason; Richstone, Douglas; Faber, S. M.; Tremaine, Scott; Aller, M. C.; Bender, Ralf; Bower, Gary; Dressler, Alan; Filippenko, Alexei V.; Green, Richard; Ho, Luis C.; Magorrian, John

    2009-03-01

    We determine the mass of the black hole at the center of the spiral galaxy NGC 4258 by constructing axisymmetric dynamical models of the galaxy. These models are constrained by high spatial resolution imaging and long-slit spectroscopy of the nuclear region obtained with the Hubble Space Telescope, complemented by ground-based observations extending to larger radii. Our best mass estimate is M • = (3.3 ± 0.2) × 107 M sun for a distance of 7.28 Mpc (statistical errors only). This is within 15% of (3.82 ± 0.01) × 107 M sun, the mass determined from the kinematics of water masers (rescaled to the same distance), assuming they are in Keplerian rotation in a warped disk. The construction of accurate dynamical models of NGC 4258 is somewhat compromised by an unresolved active nucleus and color gradients; the latter caused by variations in the stellar population and/or obscuring dust. Depending on how these effects are treated, as well as on assumptions about the ellipticity and inclination of the galaxy, we obtain black hole masses ranging from 2.4 × 107 M sun to 3.6 × 107 M sun. This spread is mainly due to uncertainties in the stellar mass profile inside the central 2'' (~70 pc). Obscuration of high-velocity stars by circumnuclear dust (possibly associated with the masing disk) could lead to an underestimate of the black hole mass, which is hard to correct. These problems are not present in the ~30 other black hole mass determinations from stellar dynamics that have been published by us and other groups; thus, the relatively close agreement between the stellar-dynamical mass and the maser mass in NGC 4258 enhances our confidence in the black hole masses determined in other galaxies from stellar dynamics using similar methods and data of comparable quality.

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

    Microsoft Academic Search

    Victor P. Debattista; J. A. Sellwood

    2000-01-01

    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

  6. An Optical Datacube of Seyfert/Starburst Composite Galaxy NGC1365

    NASA Astrophysics Data System (ADS)

    Chynoweth, Katie M.; Knop, R. A., Jr.; Gibbons, R. A.

    2006-12-01

    As part of a larger survey of nearby infrared luminous galaxies (LIR>1011,L?), we have obtained an R=2000 spectroscopic datacube of infrared-luminous starburst/Seyfert composite galaxy NGC 1365, using the SMARTS 1.5m telescope at CTIO. The spectra have 2.6'' spatial resolution, and emission lines are mapped out to 24'' away from the nucleus, using the SMARTS 1.5m telescope at CTIO. We present maps of line fluxes, line ratios, and velocities of the ionized gas as measured from the emission lines. These measurements allow us to determine the spatial extent of the starburst in the galaxy, and to measure kinematic signatures both of the AGN activity in the nucleus and any outflows or winds associated with the starburst.

  7. Possible Evidence for a Truncated Thin Disk in Seyfert 1 Galaxy NGC4593

    E-print Network

    Youjun Lu; Tinggui Wang

    2000-06-01

    We compile the multi-band spectral energy distribution (SED) of Seyfert 1 galaxy NGC4593, and investigate its optical-to-ultraviolet (OUV) continuum and iron K\\alpha line profile. No strong ``big blue bump'' is found in OUV band. The iron K\\alpha line profile is not as broad as expected from a disk which extends down to the last stable orbit. Both of them can be modeled by a truncated thin disk, and support the existence of a truncated thin disk in the system. It is of much interest that NGC4593 may be a typical object with an accretion rate \\dot{m}=\\dot{M}/M_{Edd} \\sim 0.01-0.1 and harbors a two component accretion flow: an outer thin disk and an inner hot flow--possibly ADAF, analogous to the low and intermediate state of low mass X-ray binaries (LMXB).

  8. Hierarchical Stellar Structures in the Local Group Dwarf Galaxy NGC 6822

    NASA Astrophysics Data System (ADS)

    Gouliermis, Dimitrios A.; Schmeja, Stefan; Klessen, Ralf S.; de Blok, W. J. G.; Walter, Fabian

    2010-12-01

    We present a comprehensive study of the star cluster population and the hierarchical structure in the clustering of blue stars with ages lsim500 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? above the average stellar density. The size distribution of the detected clusters can be very well approximated by a Gaussian with a peak at ~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 103-104 M sun. Their number distribution is fitted very well by a power law with index ? ~ 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?, 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? density thresholds are hierarchically constructed with a fractal dimension of D ? 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.

  9. HIERARCHICAL STELLAR STRUCTURES IN THE LOCAL GROUP DWARF GALAXY NGC 6822

    SciTech Connect

    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

    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.

  10. The radio core structure of the luminous infrared galaxy NGC 4418. A young clustered starburst revealed?

    NASA Astrophysics Data System (ADS)

    Varenius, E.; Conway, J. E.; Martí-Vidal, I.; Aalto, S.; Beswick, R.; Costagliola, F.; Klöckner, H.-R.

    2014-06-01

    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.

  11. Radio continuum emission and HI gas accretion in the NGC 5903/5898 compact group of galaxies

    NASA Astrophysics Data System (ADS)

    Wiita, Paul; Gopal-Krishna; Mhaskey, Mukul

    2012-03-01

    We investigate the nature of the multi-component radio continuum and HI emission associated with the nearby galaxy group comprised of two dominant ellipticals, NGC 5898 and NGC 5903 and a dwarf lenticular ESO514-G003. Striking new details of radio emission come from the ongoing TIFR.GMRT.SKY.SURVEY (TGSS) which provides images with a resolution of ˜24^'' x18^'' and rms noise of 5 mJy at 150 MHz. Previous observations of this compact triplet include images at higher frequencies of the radio continuum as well as huge HI trails originating from the vicinity of NGC 5903. The TGSS 150 MHz image has revealed a large asymmetric radio halo around NGC 5903 and also established that the dwarf SO galaxy ESO514-G003 is the host to a previously known bright double radio source. The radio emission from NGC 5903 is found to have a very steep radio spectrum (?˜-1.5) and to envelope a network of radio continuum filaments bearing a spatial relationship to the HI trails. Both its radio loud members are also the only galaxies that are seen to be connected to an HI filament. This correlation is consistent with the premise that cold gas accretion is of prime importance for triggering powerful jet activity in the nuclei of early-type galaxies.

  12. The STIS GTO Galaxy Nuclear Dynamics Project: The Stellar Dynamics in the Center of the Galaxy NGC 1023

    NASA Astrophysics Data System (ADS)

    Bower, G. A.; Green, R. F.; Gebhardt, K.; Bender, R.; STIS Team

    1999-12-01

    The STIS Investigation Definition Team is conducting a long-term program to confirm the presence of dark compact objects (presumably supermassive black holes, hereafter BHs) in the nuclei of several galaxies based on preliminary evidence from earlier studies, and to search for evidence of BHs in a sample of galaxies where the ground-based dynamical evidence for a BH is non-existent or weak. Through this program, we will contribute to the effort toward understanding the demographics of BHs, which are interesting for two reasons. Firstly, present data indicate a possible relationship between the mass of a BH and the mass of the galaxy spheroid within which it is embedded, thus suggesting that BH formation may be closely linked to the formation of galaxy bulges. Secondly, the demographics of local BHs provide a constraint on the accretion properties of quasars at earlier cosmological epochs. In this talk and others by our team in this session, we present preliminary results from our STIS spectroscopy of a selection of galaxies from our program. The primary observational diagnostic of a dark compact mass is measuring and interpreting the nuclear stellar dynamics in the sphere of influence of the candidate BH. The observations involve long-slit spectroscopy of a galaxy nucleus with the wavelength coverage including the strong Ca II triplet absorption lines near 8600 Angstroms. After calibrating the spectrum, we measure the stellar dynamics using the Fourier Correlation Quotient method. These measurements map the nuclear gravitational potential. Using the observed stellar dynamics and surface brightness distribution as input, we fit galaxy dynamical models to these observations to determine if there is evidence for a dark compact object. This talk presents this methodology applied to NGC 1023, which was the first galaxy observed in our program. Support for this work was provided to the STIS IDT by NASA.

  13. THE GLOBULAR CLUSTER SYSTEM OF NGC 4636 AND FORMATION OF GLOBULAR CLUSTERS IN GIANT ELLIPTICAL GALAXIES

    SciTech Connect

    Park, Hong Soo; Lee, Myung Gyoon [Astronomy Program, Department of Physics and Astronomy, Seoul National University (Korea, Republic of); Hwang, Ho Seong [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Kim, Sang Chul [Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of); Arimoto, Nobuo; Yamada, Yoshihiko [National Astronomical Observatory of Japan, Tokyo (Japan); Tamura, Naoyuki [Kavli Institute for Physics and Mathematics of the Universe, University of Tokyo, Kashiwa City 277-8583 (Japan); Onodera, Masato, E-mail: hspark@astro.snu.ac.kr, E-mail: mglee@astro.snu.ac.kr, E-mail: hhwang@cfa.harvard.edu, E-mail: sckim@kasi.re.kr, E-mail: arimoto.n@nao.ac.jp, E-mail: yoshihiko.yamada@nao.ac.jp, E-mail: naoyuki.tamura@ipmu.jp, E-mail: monodera@phys.ethz.ch [Institute for Astronomy, ETH Zuerich, Wolfgang-Pauli-strasse 27, 8093 Zuerich (Switzerland)

    2012-11-10

    We present a spectroscopic analysis of the metallicities, ages, and alpha-elements of the globular clusters (GCs) in the giant elliptical galaxy (gE) NGC 4636 in the Virgo Cluster. Line indices of the GCs are measured from the integrated spectra obtained with Faint Object Camera and Spectrograph on the Subaru 8.2 m Telescope. We derive [Fe/H] values of 59 GCs based on the Brodie and Huchra method, and [Z/H], age, and [{alpha}/Fe] values of 33 GCs from the comparison of the Lick line indices with single stellar population models. The metallicity distribution of NGC 4636 GCs shows a hint of a bimodality with two peaks at [Fe/H] = -1.23({sigma} = 0.32) and -0.35({sigma} = 0.19). The age spread is large from 2 Gyr to 15 Gyr and the fraction of young GCs with age <5 Gyr is about 27%. The [{alpha}/Fe] of the GCs shows a broad distribution with a mean value [{alpha}/Fe] Almost-Equal-To 0.14 dex. The dependence of these chemical properties on the galactocentric radius is weak. We also derive the metallicities, ages, and [{alpha}/Fe] values for the GCs in other nearby gEs (M87, M49, M60, NGC 5128, NGC 1399, and NGC 1407) from the line index data in the literature using the same methods as used for NGC 4636 GCs. The metallicity distribution of GCs in the combined sample of seven gEs including NGC 4636 is found to be bimodal, supported by the KMM test with a significance level of >99.9%. All these gEs harbor some young GCs with ages less than 5 Gyr. The mean age of the metal-rich GCs ([Fe/H] >-0.9) is about 3 Gyr younger than that of the metal-poor GCs. The mean value of [{alpha}/Fe] of the gE GCs is smaller than that of the Milky Way GCs. We discuss these results in the context of GC formation in gEs.

  14. Structure and Formation of cD Galaxies: NGC 6166 in ABELL 2199

    NASA Astrophysics Data System (ADS)

    Bender, Ralf; Kormendy, John; Cornell, Mark E.; Fisher, David B.

    2015-07-01

    ?Hobby–Eberly Telescope (HET) spectroscopy is used to measure the velocity dispersion profile of the nearest prototypical cD galaxy, NGC 6166 in the cluster Abell 2199. We also present composite surface photometry from many telescopes. We confirm the defining feature of a cD galaxy; i.e., (we suggest), a halo of stars that fills the cluster center and that is controlled dynamically by cluster gravity, not by the central galaxy. Our HET spectroscopy shows that the velocity dispersion of NGC 6166 rises from ? ? 300 km s?1 in the inner r? 10\\prime\\prime to ? =865+/- 58 km s?1 at r ? 100? in the cD halo. This extends published observations of an outward ? increase and shows for the first time that ? rises all the way to the cluster velocity dispersion of 819 ± 32 km s?1. We also observe that the main body of NGC 6166 moves at +206 ± 39 km s?1 with respect to the cluster mean velocity, but the velocity of the inner cD halo is ?70 km s?1 closer to the cluster velocity. These results support our picture that cD halos consist of stars that were stripped from individual cluster galaxies by fast tidal encounters. ?However, our photometry does not confirm the widespread view that cD halos are identifiable as an extra, low-surface-brightness component that is photometrically distinct from the inner, steep-Sérsic-function main body of an otherwise-normal giant elliptical galaxy. Instead, all of the brightness profile of NGC 6166 outside its core is described to ±0.037 V mag arcsec?2 by a single Sérsic function with index n? 8.3. The cD halo is not recognizable from photometry alone. This blurs the distinction between cluster-dominated cD halos and the similarly-large-Sérsic-index halos of giant, core-boxy-nonrotating ellipticals. These halos are believed to be accreted onto compact, high-redshift progenitors (“red nuggets”) by large numbers of minor mergers. They belong dynamically to their central galaxies. Still, cDs and core-boxy-nonrotating Es may be more similar than we think: both may have outer halos made largely via minor mergers and the accumulation of tidal debris. ?We construct a main-body+cD-halo decomposition that fits both the brightness and dispersion profiles. To fit ? (r), we need to force the component Sérsic indices to be smaller than a minimum-{? }2 photometric decomposition would suggest. The main body has {M}V? -22.8? 30% of the total galaxy light. The cD halo has {M}V? -23.7, ?1/2 mag brighter than the brightest galaxy in the Virgo cluster. A mass model based on published cluster dynamics and X-ray observations fits our observations if the tangential dispersion is larger than the radial dispersion at r? 20\\prime\\prime –60\\prime\\prime . The cD halo is as enhanced in ? element abundances as the main body of NGC 6166. Quenching of star formation in ?1 Gyr suggests that the center of Abell 2199 has been special for a long time during which dynamical evolution has liberated a large mass of now-intracluster stars. Based on observations obtained with the Hobby–Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.

  15. Analysis of Off-Nuclear X-Ray Sources in Galaxy NGC 4945

    SciTech Connect

    Harrison, Sarah M.; /MIT /SLAC

    2006-09-11

    Recently, X-ray astronomy has been used to investigate objects such as galaxies, clusters of galaxies, Active Galactic Nuclei (AGN), quasars, starburst superbubbles of hot gas, X-ray binary systems, stars, supernova remnants, and interstellar and intergalactic material. By studying the x-ray emission patterns of these objects, we can gain a greater understanding of their structure and evolution. We analyze X-ray emission from the galaxy NGC 4945 using data taken by the Chandra X-ray Observatory. The Chandra Interactive Analysis of Observations (CIAO) software package was used to extract and fit energy spectra and to extract light curves for the brightest off-nuclear sources in two different observations of NGC 4945 (January, 2000 and May, 2004). A majority of sources were closely fit by both absorbed power law and absorbed bremsstrahlung models, with a significantly poorer {chi}{sup 2}/dof for the absorbed blackbody model, and most sources had little variability. This indicates that the sources are accreting binary systems with either a neutron star or black hole as the compact object. The calculated luminosities were about 10{sup 38} erg/s, which implies that the mass of the accreting object is close to 10 solar masses and must be a black hole.

  16. Polycyclic Aromatic Hydrocarbon in the Central Region of the Seyfert 2 Galaxy NGC1808

    E-print Network

    Sales, Dinalva A; Riffel, R; Winge, Claudia

    2012-01-01

    We present mid infrared (MIR) spectra of the Seyfert 2 (Sy 2) galaxy NGC 1808, obtained with the Gemini's Thermal-Region Camera Spectrograph (T-ReCS) at a spatial resolution of 26 pc. The high spatial resolution allowed us to detect bright polycyclic aromatic hydrocarbons (PAHs) emissions at 8.6micron and 11.3micron in the galaxy centre (26 pc) up to a radius of 70 pc from the nucleus. The spectra also present [Ne ii]12.8micron ionic lines, and H2 S(2)12.27micron molecular gas line. We found that the PAHs profiles are similar to Peeters's A class, with the line peak shifted towards the blue. The differences in the PAH line profiles also suggests that the molecules in the region located 26 pc NE of the nucleus are more in the neutral than in the neutral state, while at 26 pc SW of the nucleus, the molecules are mainly in ionised state. After removal of the underlying galaxy contribution, the nuclear spectrum can be represented by a Nenkova's clumpy torus model, indicating that the nucleus of NGC 1808 hosts a d...

  17. Star formation in the outer regions of the early type galaxy NGC 4203

    E-print Network

    Y?ld?z, Mustafa K; Oosterloo, Tom A; Peletier, Reynier F; Morganti, Raffaella; Duc, Pierre-Alain; Cuillandre, Jean-Charles; Karabal, Emin

    2015-01-01

    NGC 4203 is a nearby early-type galaxy surrounded by a very large, low-column-density HI disc. In this paper we study the star formation efficiency in the gas disc of NGC 4203 by using the UV, deep optical imaging and infrared data. We confirm that the HI disc consists of two distinct components: an inner star forming ring with radius from $\\sim$ 1 to $\\sim$ 3 R$_{eff}$, and an outer disc. The outer HI disc is 9 times more massive than the inner HI ring. At the location of the inner HI ring we detect spiral-like structure both in the deep $g'-r'$ image and in the 8 $\\mu$m $Spitzer$-IRAC image, extending in radius up to $\\sim$ 3 R$_{eff}$. These two gas components have a different star formation efficiency likely due to the different metallicity and dust content. The inner component has a star formation efficiency very similar to the inner regions of late-type galaxies. Although the outer component has a very low star formation efficiency, it is similar to that of the outer regions of spiral galaxies and dwarf...

  18. A Multi-wavelength Analysis of NGC 4178: A Bulgeless Galaxy with an Active Galactic Nucleus

    NASA Astrophysics Data System (ADS)

    Secrest, N. J.; Satyapal, S.; Moran, S. M.; Cheung, C. C.; Giroletti, M.; Gliozzi, M.; Bergmann, M. P.; Seth, A. C.

    2013-11-01

    We present Gemini longslit optical spectroscopy and Very Large Array radio observations of the nuclear region of NGC 4178, a late-type bulgeless disk galaxy recently confirmed to host an active galactic nucleus (AGN) through infrared and X-ray observations. Our observations reveal that the dynamical center of the galaxy is coincident with the location of the Chandra X-ray point source discovered in a previous work, providing further support for the presence of an AGN. While the X-ray and IR observations provide robust evidence for an AGN, the optical spectrum shows no evidence for the AGN, underscoring the need for the penetrative power of mid-IR and X-ray observations in finding buried or weak AGNs in this class of galaxy. Finally, the upper limit to the radio flux, together with our previous X-ray and IR results, is consistent with the scenario in which NGC 4178 harbors a deeply buried AGN accreting at a high rate.

  19. The fluorescence-dominated X-ray spectrum of the spiral galaxy NGC 6552

    NASA Technical Reports Server (NTRS)

    Fukazawa, Yasushi; Makishima, Kazuo; Ebisawa, Ken; Fabian, Andrew C.; Gendreau, Keith C.; Ikebe, Yasushi; Iwasawa, Kazushi; Kii, Tsuneo; Mushotzky, Richard F.; Ohashi, Takaya

    1994-01-01

    A hard X-ray source with a 2-10 keV flux of approximately 6 x 10(exp -13) ergs/sec/sq cm was detected with ASCA in the north ecliptic pole region. It is identified with the spiral galaxy NGC 6552 at a redshift of z = 0.026, which is optically classified as a Seyfert 2 galaxy. The X-ray spectrum consists of a series of atomic K-emission lines from (nearly-) neutral species of at least seven abundant elements, and a heavily absorbed (N(sub H) approx. = 6 x 10(exp 23)/sq cm) hard continuum. The iron line has an equivalent width as large as approximately 0.9 keV. Our results show that NGC 6552 is an extreme type 2 Seyfert galaxy, in which the fluorescent lines are produced when hard X-rays from a hidden active nucleus are reflected off thick cool matter into our line of sight. The intrinsic 2-10 keV luminosity of the nucleus is estimated to be at least 6 x 10(exp 42) ergs/s.

  20. Multi-component models for disk galaxies. A test case on NGC 5866

    E-print Network

    E. Pignatelli

    1999-06-24

    We present an application of a new set of detailed, self-consistent, dynamical models for disc galaxies. We start from the hypothesis that each galaxy can be decomposed in a bulge, following the r^{1/4} law, and a disc with an exponential projected density profile; and that the isodensity surfaces of each component can be represented by similar concentric spheroids. After taking into account both the asymmetric drift effects and the integration along the line of sight, we produce the rotational velocity and velocity dispersion profile,_and_ the approximate shape of the line of sight velocity distributions for the stars as parameterized by the h3 and h4 coefficients of the Gauss-Hermite expansion of the line profile. Photometric and kinematical data have been taken from the literature for the test case of the S0 galaxy NGC 5866, for which detailed stellar kinematical data are available at different positions across the galaxy. Apart from the very inner, dust-obscured regions of the galaxy, where observational effects are likely to be dominant, the model successfully reproduce the whole set of dynamical data available as well as giving a good fit to the photometry. The galaxy is shown to have an isotropic velocity dispersion tensor, thus giving a hint on a dissipational formation process.

  1. THE MASSIVE ELLIPTICAL GALAXY NGC 4649 FROM THE PERSPECTIVE OF EXTENDED GRAVITY

    SciTech Connect

    Jimenez, M. A.; Garcia, G.; Hernandez, X. [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-264 C.P. 04510 Mexico D.F. (Mexico); Nasser, L., E-mail: mjimenez@astro.unam.mx [Department of Science and Mathematics, Columbia College, Chicago, 1L 60605 (United States)

    2013-05-10

    Elliptical galaxies are systems where dark matter is usually less necessary to explain observed dynamics than in the case of spiral galaxies; however, there are some instances where Newtonian gravity and the observable mass are insufficient to explain their observed structure and kinematics. Such is the case of NGC 4649, a massive elliptical galaxy in the Virgo cluster for which recent studies report a high fraction of dark matter, 0.78 at 4 R{sub e} . However, this galaxy has been studied within the MOdified Newtonian Dynamics (MOND) hypothesis, where a good agreement with the observed values of velocity dispersion is found. Using a MONDian gravity force law, here we model this galaxy as a self-consistent gravitational equilibrium dynamical system. This force law reproduces the MOND phenomenology in the a < a{sub 0} regime, and reduces to the Newtonian case when a > a{sub 0}. Within the MONDian a < a{sub 0} scales, centrifugal equilibrium or dispersion velocities become independent of radius, and show a direct proportionality to the fourth root of the total baryonic mass, V {sup 4}{proportional_to}(MGa{sub 0}). We find that the recent detailed observations of the surface brightness profile and the velocity dispersion profile for this galaxy are consistent with the phenomenology expected in MONDian theories of modified gravity, without the need to invoke the presence of any hypothetical dark matter.

  2. A Close Nuclear Black Hole Pair in the Spiral Galaxy NGC 3393

    E-print Network

    Fabbiano, G; Elvis, M; Risaliti, G

    2011-01-01

    The current picture of galaxy evolution advocates co-evolution of galaxies and their nuclear massive black holes (MBHs), through accretion and merging. Quasar pairs (6,000-300,000 light-years separation) exemplify the first stages of this gravitational interaction. The final stages, through binary MBHs and final collapse with gravitational wave emission, are consistent with the sub-light-year separation MBHs inferred from optical spectra and light-variability of two quasars. The double active nuclei of few nearby galaxies with disrupted morphology and intense star formation (e.g., NGC 6240 and Mkn 463; ~2,400 and ~12,000 light-years separation respectively) demonstrate the importance of major mergers of equal mass spirals in this evolution, leading to an elliptical galaxy, as in the case of the double radio nucleus (~15 light-years separation) elliptical 0402+379. Minor mergers of galaxies with a smaller companion should be a more common occurrence, evolving into spiral galaxies with active MBH pairs, but hav...

  3. A CHANDRA VIEW OF NGC 3621: A BULGELESS GALAXY HOSTING AN AGN IN ITS EARLY PHASE?

    SciTech Connect

    Gliozzi, Mario; Satyapal, Shobita; Titarchuk, Lev [George Mason University, 4400 University Drive, Fairfax, VA 22030 (United States); Eracleous, Michael [Department of Astronomy and Astrophysics and Center for Gravitational Wave Physics, The Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States); Cheung, Chi C. [Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

    2009-08-01

    We report the detection of a weak X-ray point-source coincident with the nucleus of the bulgeless disk galaxy NGC 3621, recently discovered by Spitzer to display high-ionization mid-infrared lines typically associated with active galactic nucleus (AGN). These Chandra observations provide confirmation for the presence of an AGN in this galaxy, adding to the growing evidence that black holes do form and grow in isolated bulgeless disk galaxies. Although the low signal-to-noise ratio of the X-ray spectrum prevents us from carrying out a detailed spectral analysis of the nuclear source, the X-ray results, combined with the IR and optical spectroscopic results, suggests that NGC 3621 harbors a heavily absorbed AGN, with a supermassive black hole of relatively small mass accreting at a high rate. Chandra also reveals the presence of two bright sources straddling the nucleus located almost symmetrically at 20'' from the center. Both sources have 0.5-8 keV spectra that are well fitted by an absorbed power-law model. Assuming they are at the distance of NGC 3621, these two sources have luminosities of the order of 10{sup 39} erg s{sup -1}, which make them ultraluminous X-ray sources and suggest that they are black hole systems. Estimates of the black hole mass based on the X-ray spectral analysis and scaling laws of black hole systems suggest that the two bright sources might be intermediate mass black holes with M{sub BH} of the order of a few thousand solar masses. However, higher quality X-ray data combined with multiwavelength observations are necessary to confirm these conclusions.

  4. Warm Dust and Spatially Variable PAH Emission in the Dwarf Starburst Galaxy NGC 1705

    E-print Network

    John M. Cannon; John-David T. Smith; Fabian Walter; George J. Bendo; Daniela Calzetti; Daniel A. Dale; Bruce T. Draine; Charles W. Engelbracht; Karl D. Gordon; George Helou; Robert C. Kennicutt, Jr.; Claus Leitherer; Lee Armus; Brent A. Buckalew; David J. Hollenbach; Thomas H. Jarrett; Aigen Li; Martin J. Meyer; Eric J. Murphy; Michael W. Regan; George H. Rieke; Marcia J. Rieke; Helene Roussel; Kartik Sheth; Michele D. Thornley

    2006-04-28

    We present Spitzer observations of the dwarf starburst galaxy NGC 1705 obtained as part of SINGS. The galaxy morphology is very different shortward and longward of ~5 microns: short-wavelength imaging shows an underlying red stellar population, with the central super star cluster (SSC) dominating the luminosity; longer-wavelength data reveals warm dust emission arising from two off-nuclear regions offset by ~250 pc from the SSC. These regions show little extinction at optical wavelengths. The galaxy has a relatively low global dust mass (~2E5 solar masses, implying a global dust-to-gas mass ratio ~2--4 times lower than the Milky Way average). The off-nuclear dust emission appears to be powered by photons from the same stellar population responsible for the excitation of the observed H Alpha emission; these photons are unassociated with the SSC (though a contribution from embedded sources to the IR luminosity of the off-nuclear regions cannot be ruled out). Low-resolution IRS spectroscopy shows moderate-strength PAH emission in the 11.3 micron band in the eastern peak; no PAH emission is detected in the SSC or the western dust emission complex. There is significant diffuse 8 micron emission after scaling and subtracting shorter wavelength data; the spatially variable PAH emission strengths revealed by the IRS data suggest caution in the interpretation of diffuse 8 micron emission as arising from PAH carriers alone. The metallicity of NGC 1705 falls at the transition level of 35% solar found by Engelbracht and collaborators; the fact that a system at this metallicity shows spatially variable PAH emission demonstrates the complexity of interpreting diffuse 8 micron emission. A radio continuum non-detection, NGC 1705 deviates significantly from the canonical far-IR vs. radio correlation. (Abridged)

  5. VLBA Identification of the Milliarcsecond Active Nucleus in the Seyfert Galaxy NGC 4151

    E-print Network

    James S. Ulvestad; Diane S. Wong; Gregory B. Taylor; Jack F. Gallimore; Carole G. Mundell

    2005-05-07

    The Seyfert galaxy NGC 4151 has been imaged at resolution better than 0.1 pc using a VLBI array consisting of the VLBA and three 100m-class telescopes. A flat-spectrum 3-mJy source with a monochromatic radio power of ~10^{37} ergs/s has been detected, apparently at the location of the active galactic nucleus (AGN) and its central black hole. The radio source has a minimum brightness temperature of 2.1 x 10^8 K and a size upper limit of 0.035 pc, about 10 times the diameter of the broad-line region and 15,000 times the diameter of the black hole's event horizon. An additional flat-spectrum component located within a parsec of the apparent nucleus is likely to be a knot in the inner radio jet. The presence of some steep-spectrum radio emission within 0.1 pc of the galaxy nucleus limits the emission measure of a possible ionized torus to a maximum value of 10^8 cm^{-6}pc. If the hard X-ray source in NGC 4151 is associated with the radio AGN, its radio to X-ray ratio is less than 10^{-5}, putting NGC 4151 securely in the radio-quiet class of AGNs. The radio image reveals a 0.2 pc two-sided base to the well-known arcsecond radio jet. Apparent speeds of jet components relative to the radio AGN are <0.050c and <0.028c at respective nuclear distances of 0.16 pc and 6.8 pc. These are the lowest speed limits yet found for a Seyfert galaxy, and indicate non-relativistic jet motions, possibly due to thermal plasma, on a scale only an order of magnitude larger than the broad-line region.

  6. Polycyclic aromatic hydrocarbon in the central region of the Seyfert 2 galaxy NGC 1808

    NASA Astrophysics Data System (ADS)

    Sales, Dinalva A.; Pastoriza, M. G.; Riffel, R.; Winge, Cláudia

    2013-03-01

    We present mid-infrared spectra of the Seyfert 2 galaxy NGC 1808, obtained with the Gemini's Thermal-Region Camera Spectrograph at a spatial resolution of ˜26 pc. The high spatial resolution allowed us to detect bright polycyclic aromatic hydrocarbons (PAHs) emissions at 8.6 and 11.3 ?m in the galaxy centre (˜26 pc) up to a radius of 70 pc from the nucleus. The spectra also present [Ne II]12.8 ?m ionic lines, and H2 S(2) 12.27 ?m molecular gas line. We found that the PAHs profiles are similar to Peeters's A class, with the line peak shifted towards the blue. The differences in the PAH line profiles also suggest that the molecules in the region located 26 pc north-east of the nucleus are more in the neutral than in the ionized state, while at 26 pc south-west of the nucleus, the molecules are mainly in ionized state. After removal of the underlying galaxy contribution, the nuclear spectrum can be represented by a Nenkova's CLUMPY torus model, indicating that the nucleus of NGC 1808 hosts a dusty toroidal structure with an angular cloud distribution of ? = 70°, observer's view angle i = 90° and an outer radius of R0 ˜ 0.55 pc. The derived column density along the line of sight is NH = 1.5 × 1024 cm2, which is sufficient to block the hard radiation from the active nucleus, and would explain the presence of PAH molecules near to the NGC 1808's active nucleus.

  7. Star formation in the outer regions of the early-type galaxy NGC 4203

    NASA Astrophysics Data System (ADS)

    Y?ld?z, Mustafa K.; Serra, Paolo; Oosterloo, Tom A.; Peletier, Reynier F.; Morganti, Raffaella; Duc, Pierre-Alain; Cuillandre, Jean-Charles; Karabal, Emin

    2015-07-01

    NGC 4203 is a nearby early-type galaxy surrounded by a very large, low-column-density H I disc. In this paper, we study the star formation efficiency in the gas disc of NGC 4203 by using the UV, deep optical imaging and infrared data. We confirm that the H I disc consists of two distinct components: an inner star-forming ring with radius from ˜1 to ˜3 Reff and an outer disc. The outer H I disc is nine times more massive than the inner H I ring. At the location of the inner H I ring, we detect spiral-like structure both in the deep g' - r' image and in the 8 ?m Spitzer-Infrared Array Camera image, extending in radius up to ˜ 3 Reff. These two gas components have a different star formation efficiency likely due to the different metallicity and dust content. The inner component has a star formation efficiency very similar to the inner regions of late-type galaxies. Although the outer component has a very low star formation efficiency, it is similar to that of the outer regions of spiral galaxies and dwarfs. We suggest that these differences can be explained with different gas origins for the two components such as stellar mass loss for the inner H I ring and accretion from the inter galactic medium for the outer H I disc. The low-level star formation efficiency in the outer H I disc is not enough to change the morphology of NGC 4203, making the depletion time of the H I gas much too long.

  8. The Fate of Spiral Galaxies in Clusters: The Star Formation History of the Anemic Virgo Cluster Galaxy NGC 4569

    NASA Astrophysics Data System (ADS)

    Boselli, A.; Boissier, S.; Cortese, L.; Gil de Paz, A.; Seibert, M.; Madore, B. F.; Buat, V.; Martin, D. C.

    2006-11-01

    We present a new method for studying the star formation history of late-type cluster galaxies undergoing gas starvation or a ram pressure stripping event by combining bidimensional multifrequency observations with multizone models of galactic chemical and spectrophotometric evolution. This method is applied to the Virgo Cluster anemic galaxy NGC 4569. We extract radial profiles from recently obtained UV GALEX images at 1530 and 2310 Å, from visible and near-IR narrow (H?) and broadband images at different wavelengths (u, B, g, V, r, i, z, J, H, and K), from Spitzer IRAC and MIPS images, and from atomic and molecular gas maps. The model in the absence of interaction (characterized by its rotation velocity and spin parameter) is constrained by the unperturbed H-band light profile and by the H? rotation curve. We can reconstruct the observed total gas radial density profile and the light surface brightness profiles at all wavelengths in a ram pressure stripping scenario by making simple assumptions about the gas removal process and the orbit of NGC 4569 inside the cluster. The observed profiles cannot be reproduced by simply stopping gas infall, thus mimicking starvation. Gas removal is required, which is more efficient in the outer disk, inducing radial quenching in the star formation activity, as observed and reproduced by the model. This observational result, consistent with theoretical predictions that a galaxy cluster-IGM interaction is able to modify structural disk parameters without gravitational perturbations, is discussed in the framework of the origin of lenticular galaxies in clusters.

  9. Kinematics of the Ionised Gas in the Spiral Galaxy NGC 2403

    E-print Network

    Filippo Fraternali; Tom Oosterloo; Renzo Sancisi

    2004-05-31

    We present a study of the kinematics of the ionised gas in the nearby spiral galaxy NGC 2403 using deep long-slit spectra obtained with the 4.2-m William Herschel Telescope. The data show the presence of a halo component of ionised gas that is rotating more slowly than the gas in the disk. The kinematics of this ionised halo gas is similar to that of the neutral halo gas. On small scales, broad line profiles (up to 300 km/s wide) indicate regions of fast outflows of ionised gas. We discuss these new results in the context of galactic fountain models.

  10. CCD surface photometry of the edge-on galaxy NGC 6835

    SciTech Connect

    Schroder, M.F.S.; Pastoriza, M.G.; Kepler, S.O. (Rio Grande do Sul Univ. Federal, Porto Alegre (Brazil))

    1990-06-01

    CCD frames in the B, V, R, and I passbands were obtained for the nearly edge-on spiral galaxy NGC 6835. The frames were analyzed to derive standard geometric and photometric parameters as well as luminosity and color distributions. The analysis of the luminosity profiles shows the existence of a flattened bulge and an exponential disk. The face-on parameters of the disk were obtained from a fit of an exponential disk seen edge-on to the observed data. The distribution of color indices along the major axis shows a pronounced blue gradient toward the nucleus, which is interpreted as a region of recent stellar formation. 23 refs.

  11. OT1_jglenn_1: NGC 1266: Probing an extraordinary phase of galaxy evolution with Herschel

    NASA Astrophysics Data System (ADS)

    Glenn, J.

    2010-07-01

    Two important, coupled questions in galaxy evolution are: how did gas-rich galaxies deplete their interstellar media to become gas poor and how do feedback mechanisms from star formation and active galactic nuclei (AGN) regulate star formation and supermassive black hole growth? Thus, observing galaxies with substantial gas content, nuclear activity, and outflows can make a significant impact on our understanding of galaxy evolution. Recently, observations of an early-type galaxy, NGC 1266, an S0 LINER, revealed a powerful molecular outflow associated with a compact (300-pc radius) and massive reservoir (of order 10^9 solar masses) of molecular gas. The outflow velocity exceeds the galaxy escape velocity, with an estimated flow of 40 solar masses per year. At this rate, the galaxy will deplete its molecular gas within 30 Myrs. There is evidence for an AGN, but the star-formation activity is weak given the gas surface density and no companion galaxy is visible. These unusual characteristics make NGC 1266 an excellent candidate for detailed study of the molecular gas with Herschel to help characterize gas depletion and feedback mechanisms in galaxies. With HIFI and the SPIRE FTS, the CO spectral lines will be measured, from J = 5 4 to J = 13 - 12, which, combined with detailed models of the line emission, will yield precisely the temperature, density, optical depth, and mass of the molecular gas in the core and outflow. High signal-to-noise line detections and good velocity resolution, provided by HIFI, will enable the core line emission to be robustly separated from the outflow line emission, and to study the dynamics of the outflow. With the SPIRE-FTS, a full low resolution spectral view from 4501500 GHz will be obtained to detect tracers of dense gas, such as HCN, HCO+, and HNC. The dense fraction of the gas can be assessed and the dust continuum emission can be used to infer an independent measure of molecular gas mass. Herschel is the only facility capable of making these observations.

  12. Chemical abundances of giant stars in NGC 5053 and NGC 5634, two globular clusters associated with the Sagittarius dwarf spheroidal galaxy?

    NASA Astrophysics Data System (ADS)

    Sbordone, L.; Monaco, L.; Moni Bidin, C.; Bonifacio, P.; Villanova, S.; Bellazzini, M.; Ibata, R.; Chiba, M.; Geisler, D.; Caffau, E.; Duffau, S.

    2015-07-01

    Context. The tidal disruption of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) is producing the most prominent substructure in the Milky Way (MW) halo, the Sagittarius Stream. Aside from field stars, it is suspected that the Sgr dSph has lost a number of globular clusters (GC). Many Galactic GC are thought to have originated in the Sgr dSph. While for some candidates an origin in the Sgr dSph has been confirmed owing to chemical similarities, others exist whose chemical composition has never been investigated. Aims: NGC 5053 and NGC 5634 are two of these scarcely studied Sgr dSph candidate-member clusters. To characterize their composition we analyzed one giant star in NGC 5053, and two in NGC 5634. Methods: We analyze high-resolution and signal-to-noise spectra by means of the MyGIsFOS code, determining atmospheric parameters and abundances for up to 21 species between O and Eu. The abundances are compared with those of MW halo field stars, of unassociated MW halo globulars, and of the metal-poor Sgr dSph main body population. Results: We derive a metallicity of [Fe ii/H] = -2.26 ± 0.10 for NGC 5053, and of [Fe i/H] = -1.99 ± 0.075 and -1.97 ± 0.076 for the two stars in NGC 5634. This makes NGC 5053 one of the most metal-poor globular clusters in the MW. Both clusters display an ? enhancement similar to the one of the halo at comparable metallicity. The two stars in NGC 5634 clearly display the Na-O anticorrelation widespread among MW globulars. Most other abundances are in good agreement with standard MW halo trends. Conclusions: The chemistry of the Sgr dSph main body populations is similar to that of the halo at low metallicity. It is thus difficult to discriminate between an origin of NGC 5053 and NGC 5634 in the Sgr dSph, and one in the MW. However, the abundances of these clusters do appear closer to that of Sgr dSph than of the halo, favoring an origin in the Sgr dSph system. Appendix A is available in electronic form at http://www.aanda.orgAtomic data 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/vol/A104

  13. Multiple bars and secular evolution

    NASA Astrophysics Data System (ADS)

    Shen, Juntai

    2015-03-01

    Bars are the most important driver of secular evolution. A significant fraction of barred galaxies also harbor small secondary bars. Secondary bars are visible even in near-infrared images, so they are not just dusty and blue, but stellar features (Erwin & Sparke 2002). Since they are quite common, secondary bars are probably long-lived stellar features. The random relative orientation of the two bars indicates that they are dynamically decoupled with different pattern speeds (Buta & Crocker 1993). Corsini et al. (2003) presented conclusive direct kinematic evidence for a decoupled secondary bar in NGC 2950. Dynamically decoupled secondary bars have long been hypothesized to be a mechanism to drive gas past the ILR of primary bars to feed active galactic nuclei (Shlosman et al. 1989). However, the dynamics of secondary bars are still not well understood, and it is still unclear what role secondary bars play in the AGN fueling process. Numerical simulations offer the best approach to understanding double-barred systems. Decoupled secondary bar in the earlier gaseous simulations only last a short time (< 1 Gyr, e.g. Friedli & Martinet 1993). Orbital studies of double-barred systems discovered a family of loop orbits that may be building blocks of long-lived nuclear stellar bars (Maciejewski & Sparke 1997, 2000). To complement orbital studies, which are not fully self-consistent, N-body simulations are preferred to further our understanding of double-barred systems. Debattista & Shen (2007) and Shen & Debattista (2009) managed to form long-lived double-barred systems with purely collisionless simulations, where a pre-existing rotating pseudo-bulge is introduced initially. The shape and size of secondary bars in the models are comparable to observed ones. They found that the rotation of the two bars is not rigid. The amplitude and pattern speed of the secondary bars oscillate as they rotate through their primary counterparts. Although the secondary bar rotates faster than the primary bar in this model, the stellar velocity field in the central region only shows a weakly twisted kinematic minor axis. Recently more simulations of double-barred galaxies with simpler initial conditions are explored (Du, Shen & Debattista 2014). We expect that the new models can be used to cross-check with the kinematic properties of double-barred galaxies from IFU observations such as SAURON and Atlas3D.

  14. Rotation and outflow in the central kiloparsec of the water megamaser galaxies IC 2560, NGC 1386, NGC 1052, and Mrk 1210

    E-print Network

    H. Schulz; C. Henkel

    2002-12-20

    Optical emission-line profiles were evaluated in order to explore the structure of galactic nuclei containing H2O megamaser sources. Galactic rotation and outflow of narrow-line gas are common features of this sample of water megamaser galaxies. All decomposed line-systems exhibit AGN typical line ratios. Recent detections of H2O megamasers in starburst galaxies and the apparent asssociation of one megamaser with a Seyfert 1 AGN suggest that megamasers can possibly be triggered by optically detectable outflows. The frequently encountered edge-on geometry favoring large molecular column densities appears to be verified for NGC 1386 and IC 2560. For NGC 1052 and Mrk 1210, maser emission triggered by the optically detected outflow components cannot be ruled out.

  15. The BaLROG project - I. Quantifying the influence of bars on the kinematics of nearby galaxies

    NASA Astrophysics Data System (ADS)

    Seidel, M. K.; Falcón-Barroso, J.; Martínez-Valpuesta, I.; Díaz-García, S.; Laurikainen, E.; Salo, H.; Knapen, J. H.

    2015-07-01

    We present the BaLROG (Bars in Low Redshift Optical Galaxies) sample of 16 morphologically distinct barred spirals to characterize observationally the influence of bars on nearby galaxies. Each galaxy is a mosaic of several pointings observed with the integral-field unit (IFU) SAURON leading to a tenfold sharper spatial resolution (˜100 pc) compared to ongoing IFU surveys. In this paper we focus on the kinematic properties. We calculate the bar strength Q__b from classical torque analysis using 3.6-?m Spitzer (S4G) images, but also develop a new method based solely on the kinematics. A correlation between the two measurements is found and backed up by N-body simulations, verifying the measurement of Q__b. We find that bar strengths from ionized gas kinematics are ˜2.5 larger than those measured from stellar kinematics and that stronger bars have enhanced influence on inner kinematic features. We detect that stellar angular momentum `dips' at 0.2 ± 0.1 bar lengths and half of our sample exhibits an anticorrelation of h3-stellar velocity (v/?) in these central parts. An increased flattening of the stellar ? gradient with increasing bar strength supports the notion of bar-induced orbit mixing. These measurements set important constraints on the spatial scales, namely an increasing influence in the central regions (0.1-0.5 bar lengths), revealed by kinematic signatures due to bar-driven secular evolution in present-day galaxies.

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

    E-print Network

    Walter, F; Hüttemeister, S; Scoville, N Z; McIntyre, V

    2000-01-01

    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...

  17. A MILLIMETER-WAVE INTERFEROMETRIC SEARCH FOR A MOLECULAR TORUS IN THE RADIO GALAXY NGC 4261

    SciTech Connect

    Okuda, Takeshi [Department of Physics and Astrophysics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602 (Japan); Iguchi, Satoru [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Kohno, Kotaro, E-mail: okuda@a.phys.nagoya-u.ac.jp [Institute of Astronomy, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan)

    2013-05-01

    NGC 4261 is an elliptical galaxy with a pair of symmetric kiloparsec-scale jets. We observed a nucleus of NGC 4261 at 2.6 mm and 1.3 mm with the NRO RAINBOW interferometer, the Nobeyama Millimeter Array, and the IRAM Plateau de Bure Interferometer to determine the excitation state of molecular gas. In this observation, neither CO(J = 2-1) nor CO(J = 1-0) absorption lines were detected even at higher sensitivity than the previous work. The 3{sigma} upper limits on the optical depths of CO lines were 0.098 for J = 2-1 and 0.042 for J = 1-0, respectively. These upper limits are much smaller than the optical depth obtained from the previous claimed detection of CO(J = 2-1) absorption (0.7), indicating that the claimed CO(J = 2-1) absorption profile could be a false feature. Our results suggest that there is a possibility that CO molecules are highly excited by the active galactic nucleus, since the optical depths of low-J CO molecules in NGC 4261 are significantly low.

  18. MRK 1216 & NGC 1277 - An orbit-based dynamical analysis of compact, high velocity dispersion galaxies

    E-print Network

    Y?ld?r?m, Ak?n; van de Ven, Glenn; Husemann, Bernd; Lyubenova, Mariya; Walsh, Jonelle L; Gebhardt, Karl; Gültekin, Kayhan

    2015-01-01

    We present a dynamical analysis to infer the structural parameters and properties of the two nearby, compact, high velocity dispersion galaxies MRK1216 & NGC1277. Combining deep HST imaging, wide-field IFU stellar kinematics, and complementary long-slit spectroscopic data out to 3 R_e, we construct orbit-based models to constrain their black hole masses, dark matter content and stellar mass-to-light ratios. We obtain a black hole mass of log(Mbh/Msun) = 10.1(+0.1/-0.2) for NGC1277 and an upper limit of log(Mbh/Msun) = 10.0 for MRK1216, within 99.7 per cent confidence. The stellar mass-to-light ratios span a range of Upsilon_V = 6.5(+1.5/-1.5) in NGC1277 and Upsilon_H = 1.8(+0.5/-0.8) in MRK1216 and are in good agreement with SSP models of a single power-law Salpeter IMF. Even though our models do not place strong constraints on the dark halo parameters, they suggest that dark matter is a necessary ingredient in MRK1216, with a dark matter contribution of 22(+30/-20) per cent to the total mass budget withi...

  19. Orbit-based Dynamical Models of the Sombrero Galaxy (NGC 4594)

    NASA Astrophysics Data System (ADS)

    Jardel, John R.; Gebhardt, Karl; Shen, Juntai; Fisher, David B.; Kormendy, John; Kinzler, Jeffry; Lauer, Tod R.; Richstone, Douglas; Gültekin, K.

    2011-09-01

    We present axisymmetric, orbit-based models to study the central black hole (BH), stellar mass-to-light ratio (M/L), and dark matter (DM) halo of NGC 4594 (M104, the Sombrero Galaxy). For stellar kinematics, we use published high-resolution kinematics of the central region taken with the Hubble Space Telescope, newly obtained Gemini long-slit spectra of the major axis, and integral field kinematics from the Spectroscopic Areal Unit for Research on Optical Nebulae instrument. At large radii, we use globular cluster kinematics to trace the mass profile and apply extra leverage to recovering the DM halo parameters. We find a BH of mass M • = (6.6 ± 0.4) × 108 M sun and determine the stellar M/LI = 3.4 ± 0.05 (uncertainties are the 68% confidence band marginalized over the other parameters). Our best-fit DM halo is a cored logarithmic model with asymptotic circular speed Vc = 376 ± 12 km s-1 and core radius rc = 4.7 ± 0.6 kpc. The fraction of dark to total mass contained within the half-light radius is 0.52. Taking the bulge and disk components into account in our calculation of ? e puts NGC 4594 squarely on the M-? relation. We also determine that NGC 4594 lies directly on the M-L relation.

  20. The NGC 1614 interacting galaxy. Molecular gas feeding a "ring of fire"

    NASA Astrophysics Data System (ADS)

    König, S.; Aalto, S.; Muller, S.; Beswick, R. J.; Gallagher, J. S.

    2013-05-01

    Minor mergers frequently occur between giant and gas-rich low-mass galaxies and can provide significant amounts of interstellar matter to refuel star formation and power active galactic nuclei (AGN) in the giant systems. Major starbursts and/or AGN result when fresh gas is transported and compressed in the central regions of the giant galaxy. This is the situation in the starburst minor merger NGC 1614, whose molecular medium we explore at half-arcsecond angular resolution through our observations of 12CO (2-1) emission using the Submillimeter Array (SMA). We compare our 12CO (2-1) maps with optical and Pa?, Hubble Space Telescope and high angular resolution radio continuum images to study the relationships between dense molecular gas and the NGC 1614 starburst region. The most intense 12CO emission occurs in a partial ring with ~230 pc radius around the center of NGC 1614, with an extension to the northwest into the dust lane that contains diffuse molecular gas. We resolve ten giant molecular associations (GMAs) in the ring, which has an integrated molecular mass of ~8 × 108 M?. Our interferometric observations filter out a large part of the 12CO (1-0) emission mapped at shorter spacings, indicating that most of the molecular gas is diffuse and that GMAs only exist near and within the circumnuclear ring. The molecular ring is uneven with most of the mass on the western side, which also contains GMAs extending into a pronounced tidal dust lane. The spatial and kinematic patterns in our data suggest that the northwest extension of the ring is a cosmic umbilical cord that is feeding molecular gas associated with the dust lane and tidal debris into the nuclear ring, which contains the bulk of the starburst activity. The astrophysical process for producing a ring structure for the final resting place of accreted gas in NGC 1614 is not fully understood, but the presence of numerous GMAs suggests an orbit-crowding or resonance phenomenon. There is some evidence that star formation is progressing radially outward within the ring, indicating that a self-triggering mechanism may also affect star formation processes. The net result of this merger therefore very likely increases the central concentration of stellar mass in the NGC 1614 remnant giant system.

  1. SHAKEN, NOT STIRRED: THE DISRUPTED DISK OF THE STARBURST GALAXY NGC 253

    SciTech Connect

    Davidge, T. J., E-mail: tim.davidge@nrc.c [Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)

    2010-12-10

    Near-infrared images obtained with WIRCam on the Canada-France-Hawaii Telescope are used to investigate the recent history of the nearby Sculptor Group spiral NGC 253, which is one of the nearest starburst galaxies. Bright asymptotic giant branch (AGB) stars are traced out to projected distances of {approx}22-26 kpc ({approx}13-15 disk scale lengths) along the major axis. The distribution of stars in the disk is lopsided, in the sense that the projected density of AGB stars in the northeast portion of the disk between 10 and 20 kpc from the galaxy center is {approx}0.5 dex higher than on the opposite side of the galaxy. A large population of red supergiants is also found in the northeast portion of the disk and, with the exception of the central 2 kpc, this area appears to have been the site of the highest levels of star-forming activity in the galaxy during the past {approx}0.1 Gyr. It is argued that such high levels of localized star formation may have produced a fountain that ejected material from the disk, and the extraplanar H I detected by Boomsma et al. may be one manifestation of such activity. Diffuse stellar structures are found in the periphery of the disk, and the most prominent of these is to the south and east of the galaxy. Bright AGB stars, including cool C stars that are identified based on their J - K colors, are detected out to 15 kpc above the disk plane, and these are part of a diffusely distributed, flattened extraplanar component. Comparisons between observed and model luminosity functions suggest that the extraplanar regions contain stars that formed throughout much of the age of the universe. Additional evidence of a diffuse, extraplanar stellar component that contains moderately young stars comes from archival Galaxy Evolution Explorer images. It is suggested that the disk of NGC 253 was disrupted by a tidal encounter with a now defunct companion. This encounter introduced asymmetries that remain to this day, and the projected distribution of stars in and around NGC 253 suggests that the companion had an orbit that was prograde and moderately inclined to the NGC 253 disk. The star-forming history of the extraplanar stars suggests that they either originated in the NGC 253 disk, or in a gas-rich companion. In the latter case, the companion must have had an initial M{sub B} < -15 in order to produce the more-or-less continuous star-forming history that is suggested by the stellar content. The ages of the youngest extraplanar stars suggest that the event that produced the extraplanar population, and presumably induced the starburst, occurred within the past {approx}0.2 Gyr.

  2. The Fate of the X-ray Emitting Gas in the Early-Type Galaxy NGC 5044

    NASA Astrophysics Data System (ADS)

    David, Laurence

    2014-08-01

    The early-type galaxy NGC 5044 resides at the center of the X-ray brightest group in the sky. Chandra observations show that the central region of NGC 5044 has been repeated perturbed by AGN outbursts. Low frequency radio observations have detected several distinct AGN outbursts and an ALMA observation shows that the AGN is bright at 230 GHz, probably due a recent accretion event. While the hot gas in NGC 5044 is likely subject to AGN feedback, the presence of Ha filaments, [CII] line emission and numerous molecular structures indicate that some gas is able to condense out of the X-ray emitting phase. By combining the wealth of multi-frequency data for NGC 5044 we can discuss the history of gas in a cooling flow from the hot phase through to molecular cloud formation.

  3. The Hubble Space Telescope Extragalactic Distance Scale Key Project. VII. The Discovery of Cepheids in the Leo I Group Galaxy NGC 3351

    NASA Astrophysics Data System (ADS)

    Graham, John A.; Phelps, Randy L.; Freedman, Wendy L.; Saha, Abhijit; Ferrarese, Laura; Stetson, Peter B.; Madore, Barry F.; Silbermann, N. A.; Sakai, Shoko; Kennicutt, Robert C.; Harding, Paul; Bresolin, Fabio; Turner, Anne; Mould, Jeremy R.; Rawson, Daya M.; Ford, Holland C.; Hoessel, John G.; Han, Mingsheng; Huchra, John P.; Macri, Lucas M.; Hughes, Shaun M.; Illingworth, Garth D.; Kelson, Daniel D.

    1997-03-01

    We report of the discovery and properties of Cepheid variable stars in the barred spiral galaxy NGC 3351 which is a member of the Leo I group of galaxies. NGC 3351 is one of 18 galaxies being observed as part of the Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale which aims to determine the Hubble constant to 10% accuracy. Our analysis is based on observations made with the Wide Field Planetary Camera 2 during 1994 and early 1995. The Leo I group contains several bright galaxies of diverse types and is very suitable for linking together a number of secondary calibrators which can be employed at much greater distances than the Cepheid variables. We identify 49 probable Cepheids within NGC 3351 in the period range 10-43 days which have been observed at 12 epochs with the F555W filter and 4 epochs using the F814W filter. The HST F555W and F814W data have been transformed to the Johnson V and Cousins I magnitude systems, respectively. Photometry has principally been carried out using the DAOPHOT/ALLFRAME package. Reference is made to parallel measurements being made with the DoPHOT package. Apparent period-luminosity functions for V and I have been constructed assuming values of ?0 = 18.50 +/- 0.10 mag and E(B - V) = 0.10 mag for the distance modulus and reddening of the Large Magellanic Cloud. A true distance modulus of 30.01 +/- 0.19 mag is derived corresponding to a distance of 10.05 +/- 0.88 Mpc with a reddening E(V - I) = 0.15 mag. A comparison is made with distances estimated for other galaxies in the Leo I group using various distance indicators. There is good agreement with the surface brightness fluctuation and planetary nebula luminosity function methods as calibrated by the Cepheids in M31. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, operated by AURA, Inc. under NASA contract No. NAS5-26555.

  4. Spectroscopic Study of Extended Star Clusters in Dwarf Galaxy NGC 6822

    NASA Astrophysics Data System (ADS)

    Hwang, Narae; Park, Hong Soo; Lee, Myung Gyoon; Lim, Sungsoon; Hodge, Paul W.; Kim, Sang Chul; Miller, Bryan; Weisz, Daniel

    2014-03-01

    We present a spectroscopic study of the four extended star clusters (ESCs) in NGC 6822 based on the data obtained with the Gemini Multi-Object Spectrograph on the Gemini-South 8.1 m telescope. The radial velocities derived from the spectra range from -61.2 ± 20.4 km s-1 (for C1) to -115.34 ± 57.9 km s-1 (for C4) and, unlike the intermediate-age carbon stars, they do not display any sign of systematic rotation around NGC 6822. The ages and metallicities derived using the Lick indices show that the ESCs are old (>=8 Gyr) and metal poor ([Fe/H] <~ -1.5). NGC 6822 is found to have both metal poor ([Fe/H] ?-2.0) and metal rich ([Fe/H] ?-0.9) star clusters within 15' (2 kpc) from the center, whereas only metal poor clusters are observed in the outer halo with r >= 20'(2.6 kpc). The kinematics, old ages, and low metallicities of ESCs suggest that ESCs may have accreted into the halo of NGC 6822. Based on the velocity distribution of ESCs, we have determined the total mass and the mass-to-light ratio of NGC 6822: M_{N6822} = 7.5^{+4.5}_{-0.1} \\times 10^{9}\\ M_{\\odot } and (M/L)_{N6822} = 75^{+45}_{-1} (M/L)_{\\odot }. It shows that NGC 6822 is one of the most dark matter dominated dwarf galaxies in the Local Group. Based on observations obtained at the Gemini Observatory, which is 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), Ministério da Ciência, Tecnologia e Inovação (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).

  5. The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey IX: $^{12}$CO $J=3\\to2$ Observations of NGC 2976 and NGC 3351

    E-print Network

    Tan, Boon-Kok; 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; Mühle,; Sánchez-Gallego, J R; Tilanus, R P J; Usero, A; van der Werf, P; Zhu, M

    2013-01-01

    We present $^{12}$CO \\textit{J=3$\\rightarrow$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 $^{12}$CO \\textit{J=1$\\rightarrow$0} data and find that the computed $^{12}$CO \\textit{J=3$\\rightarrow$2} to $^{12}$CO \\textit{J=1$\\rightarrow$0} line ratio ($R_{31}$) agrees with values measured in other NGLS field galaxies. We compute the M$_{\\rm{H_2}}$ value and find that it is robust against the value of $R_{31}$ used. Using \\textsc{Hi} data from the The \\textsc{Hi} Nearby Galaxy Survey (THINGS) survey, we find a tight correlation between surface density of H$_2$ and star formation rate density for NGC 3351 when $^{12}$CO \\textit{J=3$\\rightarrow$2} data are used. Finally, we compare the $^{12}$CO \\textit{J=3$\\rightarrow$2} intensity with the PAH 8 $\\mu$m surface brightness and find a good correlation in the high surface brightness regions. We extend this study to incl...

  6. Hard X-ray emission from a type 2 Seyfert galaxy (NGC 1068)

    NASA Technical Reports Server (NTRS)

    Elvis, Martin; Lawrence, A.

    1988-01-01

    Exosat observations of the type 2 Seyfert galaxy NGC 1068 have detected a source in the 2-10 KeV range with a flux density at 2 keV of 0.6 micron-Jy. It has a flat power-law spectrum similar to type 1 Seyferts. Combined with Low Energy Exosat filter data and Einstein IPC observations, these data show that spectral curvature is necessary, flattening the X-ray spectrum to high energies. The spectrum can be decomposed into two components: a steep low-energy part and a flat high-energy part. Any intrinsic absorption is small. There is no evidence for variability within or between any of the observations, which sample time scales from 30 minutes to 4 yr. These data support the 'obscuration' model of type 2 Seyfert galaxies in which the nucleus is seen only in flux scattered from above a 'wall' of material that completely blocks the direct view.

  7. A Radio Continuum and Spectral Line Outburst in the Nearby Galaxy NGC 660

    NASA Astrophysics Data System (ADS)

    Minchin, Robert F.; Ghosh, T.; Momjian, E.; Salter, C. J.

    2013-01-01

    We have detected a radio continuum and spectral-line outburst in the nearby peculiar galaxy, NGC 660, using the Arecibo 305-m telescope. A new continuum component appeared between 2008.0 and 2012.0 having a GHz-Peaked Spectrum (GPS) and a peak flux density of about 0.5 Jy at 5 GHz. This continuum outburst has been paralleled by the development of OH maser emission/absortption in the 6-cm wavelength transitions of OH. H2CO absorption is also detected against the new continuum component. Such rapid change in the molecular medium of an external galaxy is very unusual, but could have been initiated by supernova shocks or the interaction of nuclear radio jets with interstellar GMCs. We have also obtained observations at 8.5 and 11.5 GHz with the VLA, and VLBI C- and X-band High Sensitivity Array (HSA) data that will provide continuum and spectral-line imaging.

  8. Compact molecular gas structure in the interacting galaxy pair Arp 299 (IC 694-NGC 3690)

    NASA Technical Reports Server (NTRS)

    Sargent, A. I.; Sanders, D. B.; Scoville, N. Z.; Soifer, B. T.

    1987-01-01

    High-resolution (about 5-arcsec) CO observations of the interacting galaxy pair Arp 299 (IC 694-NGC 3690) show that about 40 percent of the total molecular gas content is concentrated in two compact regions each of mass 1.4 x 10 to the 9th solar mass. One component lies at the nucleus of IC 694, while the other spans the region of overlap between the two galaxies. The properties of the latter component are consistent with its being a region of greatly enhanced star formation. However, the unusually high L(FIR)/M(H2) ration for IC 694, together with the presence of a flat-spectrum radio source, suggest that its remarkable luminosity may be largely produced by nonthermal processes.

  9. Red Supergiants as Cosmic Abundance Probes: The Sculptor Galaxy NGC 300

    NASA Astrophysics Data System (ADS)

    Gazak, J. Zachary; Kudritzki, Rolf; Evans, Chris; Patrick, Lee; Davies, Ben; Bergemann, Maria; Plez, Bertrand; Bresolin, Fabio; Bender, Ralf; Wegner, Michael; Bonanos, Alceste Z.; Williams, Stephen J.

    2015-06-01

    We present a quantitative spectroscopic study of 27 red supergiants (RSGs) in the Sculptor Galaxy NGC 300. J-band spectra were obtained using KMOS on the Very Large Telescope and studied with state of the art synthetic spectra including NLTE corrections for the strongest diagnostic lines. We report a central metallicity of [Z] = ?0.03 ± 0.05 with a gradient of ?0.083 ± 0.014 [dex/kpc], in agreement with previous studies of blue supergiants and H ii-region auroral line measurements. This result marks the first application of the J-band spectroscopic method to a population of individual RSG stars beyond the Local Group of galaxies and reveals the great potential of this technique. Data collected under ESO Program ID 092.B-0088.

  10. An H I study of NGC 3521 - a galaxy with a slow-rotating halo

    NASA Astrophysics Data System (ADS)

    Elson, E. C.

    2014-02-01

    A study is presented of H I line observations of the nearby spiral galaxy NGC 3521 observed with the Very Large Array as part of The H I Nearby Galaxy Survey. Clearly evident in the H I data cube is the presence of an anomalous H I component that is both diffuse and slow rotating. The data cube is dynamically decomposed into regular and anomalous H I components. A mass of M_{H {I}}=1.5× 10^9 M? is estimated for the anomalous H I - 20 per cent of the total H I mass. Standard H I data products and rotation curves are produced for each dynamical component. In terms of circular rotation speed, the anomalous H I is found to lag the regular H I by ˜25-125 km s-1. Three-dimensional models are generated and used to determine the possible location of the anomalous H I. The results strongly suggest it to be distributed in a thick disc with a scale-height of a few kpc (˜3.5 kpc). It is concluded that the anomalous H I in NGC 3521 constitutes a slow-rotating halo gas component, consistent with similar findings for other nearby galaxies. A study of the radial distribution of the anomalous H I shows it to be spatially coincident with the inner regions of the stellar disc where the star formation rate is highest. It is most likely a galactic fountain that has deposited gas from the disc of the galaxy into the halo.

  11. Mapping the frosty exotic ISM around the deeply buried AGN in the nearby starburst galaxy NGC4945

    NASA Astrophysics Data System (ADS)

    Spoon, Henrick; Bernard-Salas, Jeronimo; Charmandaris, Vassilis; Devost, Daniel; Farrah, Duncan; Roussel, Helene; Smith, John-David

    2007-05-01

    The nearly edge-on galaxy NGC4945 is one of the closest galaxies where an AGN and starburst coexist. Hard X-ray observations have shown the central black hole in this galaxy to be obscured by a Compton-thick hydrogen column of N_H=5 x 10^24 cm^-2. Despite this huge column, the AGN in NGC4945 is one of the brightest extragalactic sources in the sky at 100keV. In contrast, at optical and infrared wavelengths the AGN has remained undetected until very recently. Instead, at these wavelengths the central region is dominated by a starburst responsible for a spectacular starburst wind-blown, conical shaped cavity aligned with the galaxy's minor axis. Near and mid-infrared spectroscopy of the nucleus have shown the central region to be dominated by very strong obscuration, rivaled only in strength by some of the most deeply obscured UltraLuminous Infrared Galaxies (ULIRGs). This obscuring medium is littered with cold molecular clouds, as evidenced by the presence of strong absorption bands of water ice and volatile ice species such as CO2, CO and `XCN' in the 3-5 micron range, as well as by a very deep 10 micron silicate absorption feature. Other similarly inclined nearby starburst galaxies such as M82 and NGC253 do not show similar spectral properties on these scales. This makes NGC4945 a unique laboratory to study an environment otherwise only found in distant ULIRGs and, likely, their higher redshift counterparts. We therefore propose to map the bright central region of NGC4945 in SL, LL and SH to obtain the spatial distribution of ISM emission and absorption features, which will allow a characterization of the physical conditions in the frosty exotic ISM exposed to the hostile radiation from the circumnuclear starburst which coexists with a deeply buried AGN.

  12. Stellar population gradients in galaxy discs from the CALIFA survey. The influence of bars

    NASA Astrophysics Data System (ADS)

    Sánchez-Blázquez, P.; Rosales-Ortega, F. F.; Méndez-Abreu, J.; Pérez, I.; Sánchez, S. F.; Zibetti, S.; Aguerri, J. A. L.; Bland-Hawthorn, J.; Catalán-Torrecilla, C.; Cid Fernandes, R.; de Amorim, A.; de Lorenzo-Caceres, A.; Falcón-Barroso, J.; Galazzi, A.; García Benito, R.; Gil de Paz, A.; González Delgado, R.; Husemann, B.; Iglesias-Páramo, Jorge; Jungwiert, B.; Marino, R. A.; Márquez, I.; Mast, D.; Mendoza, M. A.; Mollá, M.; Papaderos, P.; Ruiz-Lara, T.; van de Ven, G.; Walcher, C. J.; Wisotzki, L.

    2014-10-01

    While studies of gas-phase metallicity gradients in disc galaxies are common, very little has been done towards the acquisition of stellar abundance gradients in the same regions. We present here a comparative study of the stellar metallicity and age distributions in a sample of 62 nearly face-on, spiral galaxies with and without bars, using data from the CALIFA survey. We measure the slopes of the gradients and study their relation with other properties of the galaxies. We find that the mean stellar age and metallicity gradients in the disc are shallow and negative. Furthermore, when normalized to the effective radius of the disc, the slope of the stellar population gradients does not correlate with the mass or with the morphological type of the galaxies. In contrast to this, the values of both age and metallicity at ~2.5 scale lengths correlate with the central velocity dispersion in a similar manner to the central values of the bulges, although bulges show, on average, older ages and higher metallicities than the discs. One of the goals of the present paper is to test the theoretical prediction that non-linear coupling between the bar and the spiral arms is an efficient mechanism for producing radial migrations across significant distances within discs. The process of radial migration should flatten the stellar metallicity gradient with time and, therefore, we would expect flatter stellar metallicity gradients in barred galaxies. However, we do not find any difference in the metallicity or age gradients between galaxies with and without bars. We discuss possible scenarios that can lead to this lack of difference. Tables 1-3 and Appendices are available in electronic form at http://www.aanda.org

  13. GALAXIES M32 AND NGC 5102 CONFIRM A NEAR-INFRARED SPECTROSCOPIC CHRONOMETER

    SciTech Connect

    Jesse Miner; Cecil, Gerald [Infrared Telescope Facility, which is operated by the University of Hawaii under Cooperative Agreement no. NNX-08AE38A with the National Aeronautics and Space Administration, Science Mission Directorate, Planetary Astronomy Program. (United States); Rose, James A. [Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27516 (United States)

    2011-01-20

    We present near-infrared (NIR) IRTF/SpeX spectra of the intermediate-age galaxy M32 and the post-starburst galaxy NGC 5102. We show that features from thermally pulsing asymptotic giant branch (TP-AGB) and main-sequence turnoff (MSTO) stars yield similar ages to those derived from optical spectra. The TP-AGB can dominate the NIR flux of a coeval stellar population between {approx}0.1 and {approx}2 Gyr, and the strong features of (especially C-rich) TP-AGB stars are useful chronometers in integrated light studies. Likewise, the Paschen series in MSTO stars is strongly dependent on age and is an indicator of a young stellar component in integrated spectra. We define four NIR spectroscopic indices to measure the strength of absorption features from both C-rich TP-AGB stars and hydrogen features in main-sequence stars, in a preliminary effort to construct a robust chronometer that probes the contributions from stars in different evolutionary phases. By comparing the values of the indices measured in M32 and NGC 5102 to those in the Maraston stellar population synthesis models for various ages and metallicities, we show that model predictions for the ages of the nuclei of M32 and NGC 5102 agree with previous results obtained from integrated optical spectroscopy and color-magnitude diagram analysis of the giant branches. The indices discriminate between an intermediate-age population of {approx}3-4 Gyr, a younger population of {approx}<1 Gyr, and can also detect the signatures of very young {approx}<100 Myr populations.

  14. RXTE View of the Starburst Galaxies M82 and NGC 253

    E-print Network

    Yoel Rephaeli; Duane Gruber

    2002-04-25

    The two nearby starburst galaxies M82 and NGC 253 were observed for 100 ksec over a 10-month period in 1997. An increase of the M82 flux by a factor ~2 was measured during the period July-November, when compared with the flux measured earlier in 1997. The flux measured in the field centered on M82 includes ~38 of the emission from the Seyfert 1 galaxy M81. The best-fitting model for the earlier emission from M82 is thermal with kT = 6.7 +/- 0.1 keV. In the high flux state, the emission additionally includes either an absorbed second thermal component or absorbed power-law component, with the former providing a much better fit. A likely origin for the temporal variability is a single source in M82. The flux of NGC 253, which did not vary significantly during the period of observations, can be well fit by either a thermal spectrum with kT ~ 3.8 +/- 0.3 keV, or by a power law with photon index of 2.7 +/- 0.10. We have also attempted fitting the measurements to more realistic composite models with thermal and power-law components, such as would be expected from a dominant contribution from binary systems, or Compton scattering of (far) IR radiation by radio emitting electrons. However, the addition of any amount of a power-law component, even with cutoff at 20 keV, only increases chi-square. The 90% confidence upper limit for power law emission with (photon) index 1.5 is only 2.4% of the 2 -- 10 keV flux of M82; the corresponding limit for NGC 253, with index 2.0, is 48%.

  15. An Unusual Outburst from the Nucleus of the Quiescent Galaxy NGC 1589

    NASA Astrophysics Data System (ADS)

    Filippenko, Alex

    2010-09-01

    As part of the Lick Observatory Supernova Search {LOSS}, we have recently identified a highly unusual optical outburst from the nucleus {within 0.05", or 10 pc in projection} of the nearby {d 50 Mpc} spiral {S0/a} galaxy NGC 1589. Over a decade of photometric monitoring with LOSS, together with archival spectroscopy from the CfA Redshift Survey, suggest that the galaxy does not harbor an active nucleus. Likewise, the transient, bright observed X-ray emission and broad H-alpha emission-line profile do not appear to closely resemble those of any known Type II supernova. We therefore consider this transient source {dubbed NGC1589-OT} to be the most viable candidate for a tidal disruption flare {TDF} ever discovered in real time. Here we request UV {STIS} spectroscopy with HST to search for "smoking gun" evidence in favor of the TDF interpretation: photoionized stellar debris ejected by the disruption process. DD time is necessary because the outburst will almost certainly not be visible by the time Cycle 19 observations commence. We did not propose for analogous observations during the normal course of a previous GO cycle due to the extraordinarily small number of good, real-time TDF candidates detected in the past.

  16. An Unusual Outburst from the Nucleus of the Quiescent Galaxy NGC 1589

    NASA Astrophysics Data System (ADS)

    Filippenko, Alexei

    2010-09-01

    As part of the Lick Observatory Supernova Search (LOSS), we have recently identified an unusual optical outburst from the nucleus (within 0.05";, or 10 pc in projection) of the nearby (d ~ 50 Mpc) spiral (S0/a) galaxy NGC 1589. Over a decade of photometric monitoring with LOSS, together with archival spectroscopy from the CfA Redshift Survey, suggest the galaxy does not harbor an active galactic nucleus. Likewise, the bright observed X-ray emission and complex H-alpha emission profile do not appear to resemble any known Type II supernova. We therefore believe this transient source (dubbed NGC1589-OT) represents the most viable candidate for a tidal disruption flare (TDF) ever discovered in real time. Here we request a 10 ks Chandra/ACIS DD observation to accurately constrain the X-ray spectral properties (power-law vs. thermal) and environment (n_H) of this unique, fascinating source. In a separate proposal, we are also requesting HST time to get a UV spectrum of it.

  17. 6.7 GHz methanol absorption toward the Seyfert 2 galaxy NGC 3079

    E-print Network

    Impellizzeri, C M V; Roy, A L; Menten, K M

    2008-01-01

    The detection of the 6.7 GHz line of methanol (CH3OH) is reported for the first time toward an object beyond the Magellanic Clouds. Using the Effelsberg 100 m telescope, two absorption features were identified toward the Seyfert 2 galaxy NGC 3079. Both components probably originated on lines-of-sight toward the central region, presumably absorbing the radio continuum of the nuclear sources A, B, and E of NGC 3079. One absorption feature, at the systemic velocity, is narrow and may arise from gas not related to the nuclear environment of the galaxy. The weaker blue-shifted component is wider and may trace outflowing gas. Total A-type CH3OH column densities are estimated to be between a few times 10^13 and a few times 10^15 cm^-2. Because of a highly frequency-dependent continuum background, the overall similarity of HI, OH, and CH3OH absorption profiles hints at molecular clouds that cover the entire area occupied by the nuclear radio continuum sources ~ 4 pc.

  18. SAMI Galaxy Survey: Disk and Bar Kinematics, Mass Decompositions with Dark Matter

    NASA Astrophysics Data System (ADS)

    Cecil, Gerald N.; Bland-Hawthorn, Jonathan; Fogarty, Lisa; SAMI Galaxy Survey Team, GAMA Survey Team

    2015-01-01

    The SAMI Galaxy Survey (SGS, P.I. Scott Croom, U. of Sydney) uses a custom multiple-integral-field feed to the Australian Astronomical Telescope (AAT) AAOmega dual-spectrograph to map the inner 15 arcsec diameter of 3400 galaxies a dozen at a time. The SGS spans environmental densities up to clusters, out to z = 0.1. (See http://sami-survey.org/edr for ~100 galaxies in the public Early Release Data.) We discuss circular speed curves (CSCs) of gas and stars derived from non-parametric fits to a flat disk in ~130 late-type barred and unbarred galaxies across the full mass range of the SGS, and at radii up to 4 r_e. Gas and stellar rotational fields agree well, but can differ substantially in line of nodes. At least 2/3 of the fitted CSCs are compatible with the ``universal rotation curve''. Velocity model residuals are compared to residuals from single-Sersic profile fits to SDSS photometry that highlight light asymmetries. For galaxies where photometry minus model residuals delineate stellar bars, the VIKING Z-band image is fit with a dual-Sersic form, one component addressing the bulge/bar, then gas kinematics are refit to include a bisymmetric (m=2) velocity distortion in the disk. This distortion often aligns with photometric residuals, and has amplitude at most 80 km/s but usually <20 km/s in the disk plane. Thus we debias the CSC from, and map the effects of, gas streaming due to a bar/oval. Because of generally low in-plane velocity distortions, only 2 of 18 barred galaxies have shock-indicating, emission-line flux ratios that correlate with m=2 spatio-kinematical variations and concentrate near the bar ends. Each dual- or single-Sersic fit is mapped into mass using one M/L constant with radius and the non-axisymmetric or axisymmetric CSC to decompose the mass distribution into luminous bulge and disk, and dark halo components. Some fits require a maximal luminous disk, others require a non-negligible or even dominant dark halo within the SAMI aperture. We discuss interesting individual systems and statistics of our sample from the first 600 galaxies surveyed. GC was a visiting professor supported by U. of Sydney. The SAMI and GAMA surveys are supported by grants from the Australian Research Council.

  19. A COMPREHENSIVE X-RAY AND MULTIWAVELENGTH STUDY OF THE COLLIDING GALAXY PAIR NGC 2207/IC 2163

    E-print Network

    Mineo, S.

    We present a comprehensive study of the total X-ray emission from the colliding galaxy pair NGC 2207/IC 2163, based on Chandra, Spitzer, and GALEX data. We detect 28 ultraluminous X-ray sources (ULXs), 7 of which were not ...

  20. An ISOPHOT Study of the Disk of Galaxy NGC6946: 60(micro)m Infrared and Radio Continuum Correlation

    NASA Technical Reports Server (NTRS)

    Lu, N. Y.; Helou, G.; Tuffs, R.; Xu, C.; Malhotra, S.; Werner, M. W.; Thronson, H.

    1996-01-01

    We combine the ISOPHOT 60(micro)m image of Tuffs, et al. (1996) and VLA radio continuum images at 6 and 20cm from the literature to study the 60(micro)m light distribution and its correlation with radio continuum within the disk of nearby spiral galaxy NGC6946, at an effective resolution of + - 52.

  1. XMM-NEWTON OBSERVATIONS OF THE SEYFERT 2 GALAXY NGC 7590: THE NATURE OF X-RAY ABSORPTION

    SciTech Connect

    Shu, X. W.; Liu, T.; Wang, J. X., E-mail: xwshu@mail.ustc.edu.c [CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2010-10-10

    We present the analysis of three XMM-Newton observations of the Seyfert 2 galaxy NGC 7590. The source was found to have no X-ray absorption in the low spatial resolution ASCA data. The XMM-Newton observations provide a factor of {approx}10 better spatial resolution than previous ASCA data. We find that the X-ray emission of NGC 7590 is dominated by an off-nuclear ultra-luminous X-ray source and an extended emission from the host galaxy. The nuclear X-ray emission is rather weak compared with the host galaxy. Based on its very low X-ray luminosity as well as the small ratio between the 2-10 keV and the [O III] fluxes, we interpret NGC 7590 as Compton-thick rather than being an 'unobscured' Seyfert 2 galaxy. Future higher resolution observations such as Chandra are crucial to shed light on the nature of the NGC 7590 nucleus.

  2. Galaxy Zoo: Are Bars Responsible for the Feeding of Active Galactic Nuclei at 0.2 < z < 1.0?

    NASA Astrophysics Data System (ADS)

    Cheung, Edmond; Trump, Jonathan; Athanassoula, Lia; Bamford, Steven; Bell, Eric F.; Bosma, Albert; Cardamone, Carolin N.; Casteels, Kevin; Faber, Sandra M.; Fang, Jerome J.; Fortson, Lucy; Kocevski, Dale; Koo, David C.; Laine, Seppo J.; Lintott, Chris; Masters, Karen; Melvin, Tom; Nichol, Robert; Schawinski, Kevin; Simmons, Brooke D.; Smethurst, Rebecca; Willett, Kyle; Galaxy Zoo, Aegis, Cosmos, Goods

    2015-01-01

    We present a new study investigating whether active galactic nuclei (AGN) beyond the local universe are preferentially fed via large-scale bars. Our investigation combines data from Chandra and Galaxy Zoo: Hubble (GZH) in the AEGIS, COSMOS, and GOODS-S surveys to create samples of face-on, disk galaxies at 0.2 < z < 1.0. We use a novel method to robustly compare a sample of 120 AGN host galaxies, defined to have 1042 erg s-1 < LX < 1044erg s-1, with inactive control galaxies matched in stellar mass, rest-frame color, size, Sérsic index, and redshift. Using the GZH bar classifications of each sample, we demonstrate that AGN hosts show no statistically significant enhancement in bar fraction or average bar likelihood compared to closely-matched inactive galaxies. In detail, we find that the AGN bar fraction cannot be enhanced above the bar fraction in the control sample by more than a factor of two, at 99.7% confidence. We similarly find no significant difference in the AGN fraction among barred and non-barred galaxies. Thus we find no compelling evidence that large-scale bars directly fuel AGN at 0.2 < z < 1.0. This result, coupled with previous results at z = 0, implies that moderate-luminosity AGN have not been preferentially fed by large-scale bars since z = 1. Furthermore, given the low bar fractions at z > 1, our findings suggest that large-scale bars have likely never directly been a dominant fueling mechanism for supermassive black hole growth.

  3. Galaxy Zoo: Are bars responsible for the feeding of active galactic nuclei at 0.2 < z < 1.0?

    NASA Astrophysics Data System (ADS)

    Cheung, Edmond; Trump, Jonathan R.; Athanassoula, E.; Bamford, Steven P.; Bell, Eric F.; Bosma, A.; Cardamone, Carolin N.; Casteels, Kevin R. V.; Faber, S. M.; Fang, Jerome J.; Fortson, Lucy F.; Kocevski, Dale D.; Koo, David C.; Laine, Seppo; Lintott, Chris; Masters, Karen L.; Melvin, Thomas; Nichol, Robert C.; Schawinski, Kevin; Simmons, Brooke; Smethurst, Rebecca; Willett, Kyle W.

    2015-02-01

    We present a new study investigating whether active galactic nuclei (AGN) beyond the local universe are preferentially fed via large-scale bars. Our investigation combines data from Chandra and Galaxy Zoo: Hubble (GZH) in the AEGIS (All-wavelength Extended Groth strip International Survey), COSMOS (Cosmological Evolution Survey), and (Great Observatories Origins Deep Survey-South) GOODS-S surveys to create samples of face-on, disc galaxies at 0.2 < z < 1.0. We use a novel method to robustly compare a sample of 120 AGN host galaxies, defined to have 1042 erg s-1 < LX < 1044 erg s-1, with inactive control galaxies matched in stellar mass, rest-frame colour, size, Sérsic index, and redshift. Using the GZH bar classifications of each sample, we demonstrate that AGN hosts show no statistically significant enhancement in bar fraction or average bar likelihood compared to closely-matched inactive galaxies. In detail, we find that the AGN bar fraction cannot be enhanced above the control bar fraction by more than a factor of 2, at 99.7 per cent confidence. We similarly find no significant difference in the AGN fraction among barred and non-barred galaxies. Thus we find no compelling evidence that large-scale bars directly fuel AGN at 0.2 < z < 1.0. This result, coupled with previous results at z = 0, implies that moderate-luminosity AGN have not been preferentially fed by large-scale bars since z = 1. Furthermore, given the low bar fractions at z > 1, our findings suggest that large-scale bars have likely never directly been a dominant fuelling mechanism for supermassive black hole growth.

  4. The Star-forming Histories of the Nucleus, Bulge, and Inner Disk of NGC 5102: Clues to the Evolution of a Nearby Lenticular Galaxy

    NASA Astrophysics Data System (ADS)

    Davidge, T. J.

    2015-01-01

    Long slit spectra recorded with the Gemini Multi-Object Spectrograph on Gemini South are used to examine the star-forming history (SFH) of the lenticular galaxy NGC 5102. Structural and supplemental photometric information are obtained from archival Spitzer [3.6] images. Absorption features at blue and visible wavelengths are traced out along the minor axis to galactocentric radii ~60 arcsec (~0.9 kpc), sampling the nucleus, bulge, and disk components. Comparisons with model spectra point to luminosity-weighted metallicities that are consistent with the colors of resolved red giant branch stars in the disk. The nucleus has a luminosity-weighted age at visible wavelengths of {˜ } 1+0.2-0.1 Gyr, and the integrated light is dominated by stars that formed over a time period of only a few hundred Myr. For comparison, the luminosity-weighted ages of the bulge and disk are {˜ } 2+0.5-0.2 Gyr and 10+2-2 Gyr, respectively. The g' - [3.6] colors of the nucleus and bulge are consistent with the spectroscopically based ages. In contrast to the nucleus, models that assume star-forming activity spanning many Gyr provide a better match to the spectra of the bulge and disk than simple stellar population models. Isophotes in the bulge have a disky shape, hinting that the bulge was assembled from material with significant rotational support. The SFHs of the bulge and disk are consistent with the bulge forming from the collapse of a long-lived bar, rather than from the collapse of a transient structure that formed as the result of a tidal interaction. It is thus suggested that the progenitor of NGC 5102 was a barred disk galaxy that morphed into a lenticular galaxy through the buckling of its bar. This research has made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

  5. The far-infrared distribution in the Dusty Hand Galaxy NGC 2146

    NASA Technical Reports Server (NTRS)

    Smith, Beverly J.; Harvey, Paul M.; Lester, Dan F.

    1995-01-01

    Our high spatial resolution 50 and 100 micro m observations of the peculiar galaxy NGC 2146 show that the FIR emission arises in a 21 arc-sec x is less than 16 arc-sec (1.5 kpc x is less than 1.1 kpc) region (FWHM) elongated along the major axis. This size limit is similar to that of the radio continuum, the (12)CO (1 - 0), and the H alpha. From an investigation of the energetics in this galaxy, we conclude that young massive stars are largely responsible for powering the FIR luminosity of this galaxy. The FIR and CO (1 - 0) distributions differ from the extinction morphology as seen in optical images and in the Br gamma/H alpha ratio. The starlight and the ionized gas are most highly reddened at the prominent dust lane 15 arc-sec to the west of the nucleus, while the CO and FIR emission peak near the nucleus. This result can be explained by either a high proportion of cold dust and gas at the dust lane, or a geometry in which the dust lane lies in front of the main body of the galaxy.

  6. The Magellanic irregular galaxy NGC 4214 - Star formation and the interstellar medium

    NASA Technical Reports Server (NTRS)

    Thronson, Harley A., Jr.; Greenhouse, Matthew; Hunter, Deidre A.; Telesco, C. M.; Harper, D. A.

    1988-01-01

    Near- and far-IR data and mm-wave CO observations are used to study the star-forming properties of the Magellanic irregular galaxy NGC 4214 and its interstellar medium. The galaxy is forming stars at present at about 0.5-1 solar mass/yr in its central few arcmin, if the new stars follow the Salpeter initial mass function from 0.1 to 100 solar masses. This has been maintained for around a Hubble time, although some regions of the galaxy may undergo periods of enhanced and depressed star formation. Based on the mass of dust in emission at 160 microns, a plausible star formation efficiency of about 1.5 percent is estimated, if the H I gas does not take part in forming stars. Molecular masses derived using the H + 1 - 0 line and a conversion to M(H2) appropriate to spiral galaxies produces a mass estimate that is too low by a factor of five to ten.

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

    E-print Network

    Walsh, Jonelle L; Gebhardt, Karl; Y?ld?r?m, Ak?n; Gültekin, Kayhan; Husemann, Bernd; Richstone, Douglas O

    2015-01-01

    Located in the Perseus cluster, NGC 1271 is an early-type galaxy with a small effective radius of 2.2 kpc and a large stellar velocity dispersion of 276 km/s for its K-band luminosity of 8.9x10^{10} L_sun. We present a mass measurement for the black hole in this compact, high-dispersion galaxy using observations from the integral field spectrograph NIFS on the Gemini North telescope assisted by laser guide star adaptive optics, large-scale integral field unit observations with PPAK at the Calar Alto Observatory, and Hubble Space Telescope WFC3 imaging observations. We are able to map out the stellar kinematics on small spatial scales, within the black hole sphere of influence, and on large scales that extend out to four times the galaxy's effective radius. We find that the galaxy is rapidly rotating and exhibits a sharp rise in the velocity dispersion. Through the use of orbit-based stellar dynamical models, we determine that the black hole has a mass of (3.0^{+1.0}_{-1.1}) x 10^9 M_sun and the H-band stellar...

  8. A Multiwavelength Study of a Young, Z-shaped, FR I Radio Galaxy NGC 3801

    E-print Network

    Hota, Ananda; Ohyama, Youichi; Saikia, D J; Dinh-V-Trung,; Croston, J H

    2009-01-01

    We present preliminary results from a multi-wavelength study of a merger candidate, NGC3801, hosting a young FR I radio galaxy, with a Z-shaped structure. Analysing archival data from the VLA, we find two HI emission blobs on either side of the host galaxy, suggesting a 30 kpc sized rotating gas disk aligned with stellar rotation, but rotating significantly faster than the stars. Broad, faint, blue-shifted absorption wing and an HI absorption clump associated with the shocked shell around the eastern lobe are also seen, possibly due to an jet-driven outflow. While 8.0 um dust and PAH emission, from Spitzer and near and far UV emission from GALEX is seen on a large scale in an S-shape, partially coinciding with the HI emission blobs, it reveals a ~2 kpc radius ring-like, dusty, starforming structure in the nuclear region, orthogonal to the radio jet axis. Its similarities with Kinematically Decoupled Core galaxies and other evidences have been argued for a merger origin of this young, bent jet radio galaxy.

  9. Survey of Water and Ammonia in Nearby galaxies (SWAN): Physical Conditions in NGC 253

    NASA Astrophysics Data System (ADS)

    Gorski, Mark; Ott, Jüergen; Rand, Richard J.; Meier, David S.; Momjian, Emmanuel; Walter, Fabian

    2015-01-01

    Nearby galaxies provide the vital link between local Galactic findings and integrated, galaxy-wide properties of star formation. We have observed four nearby star forming galaxies with the VLA in K and Ka bands, yielding a resolution on order of a few tens of parsecs. The sample spans a range of star formation rates and galactic environments. We present the first results from the nearby, prototypical starburst galaxy NGC 253. The K band observations cover ammonia inversion transitions from (1,1) to (5,5) in addition to the 22.3GHz water maser line with a resolution of ?63pc. Ammonia is a known temperature probe and traces gas densities greater than 102 cm-3. We observe relatively warm and uniform temperature distribution in the inner 0.5 kpc. The (3,3) line appears to be masing in the innermost 200 pc. Furthermore, we see indications of extended H20 maser components in the direction of the galactic outflow.

  10. ON THE MASS-LOSS RATE OF MASSIVE STARS IN THE LOW-METALLICITY GALAXIES IC 1613, WLM, AND NGC 3109

    SciTech Connect

    Tramper, F.; Sana, H.; De Koter, A.; Kaper, L., E-mail: F.Tramper@uva.nl [Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands)

    2011-11-01

    We present a spectroscopic analysis of Very Large Telescope/X-Shooter observations of six O-type stars in the low-metallicity (Z {approx} 1/7 Z {sub sun}) galaxies IC 1613, WLM, and NGC 3109. The stellar and wind parameters of these sources allow us, for the first time, to probe the mass loss versus metallicity dependence of stellar winds at metallicities below that of the Small Magellanic Cloud (at Z {approx} 1/5 Z {sub sun}) by means of a modified wind momentum versus luminosity diagram. The wind strengths that we obtain for the objects in WLM and NGC 3109 are unexpectedly high and do not agree with theoretical predictions. The objects in IC 1613 tend toward a higher than expected mass-loss rate, but remain consistent with predictions within their error bars. We discuss potential systematic uncertainties in the mass-loss determinations to explain our results. However, if further scrutinization of these findings point towards an intrinsic cause for this unexpected sub-SMC mass-loss behavior, implications would include a higher than anticipated number of Wolf-Rayet stars and Ib/Ic supernovae in low-metallicity environments, but a reduced number of long-duration gamma-ray bursts produced through a single-star evolutionary channel.

  11. Hubble space telescope observations of young star clusters in NGC-4038/4039, 'the antennae' galaxies

    NASA Technical Reports Server (NTRS)

    Whitmore, Bradley C.; Schweizer, Francois

    1995-01-01

    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 images reveal a population of over 700 blue pointlike objects within the disks. The mean absolute magnitude of these objects is M(sub V) = -11 mag, with the brightest objects reaching M(sub V) approximately -15. Their mean apparent color indices ar U - V = -0.7 mag and V - 1 = 0.8 mag on the Johnson UVI passband system, while their mean indices corrected for internal reddening are (u - v)(sub 0) = -1.0 mag and (V - I(sub 0) = 0.5. Their mean effective radius, determined from slightly resolved images, is 18 pc (for H(sub 0) = 50 km/s /Mpc). Based on their luminosities and resolution, most of these objects cannot be individual stars, but are likely young compact star clusters. The brighter ones are similar to the objects found in NGC 1275 and NGC 7252, which appear to be young globular clusters formed during recent galazy mergers. Based on their U - V and V - I colors, the brightest, bluest clusters of NGC 4038/4039 appear to be less than 10 Myr old. Most of these bright clusters are relatively tightly clustered themselves, with typically a dozen individual clusters belonging to a complex identified as a giant H II region from ground-based observations. The cluster luminosity function (LF) is approximately a power law, phi(L)dL proportional to L(exp -1.78+/-0.05)dL, with no hint of a turnover at fainter magnitudes. This power-law shape agrees with the LF of Magellanic Cloud clusters and Galactic open clusters, but differs from the LF of old globular cluster systems that is typically Gaussian with a Full Width at Half Maximum (FWHM) of approximately 3 mag. Besides the blue clusters, we also find about a dozen extremely red objects with V - I greater than 3.0. The highest number density of these red objects is found in the SE quadrant, where star formation appears to be most recent. We propose that these objects may be very young star clusters still embedded in their placental dust cocoons.

  12. FIREWORKS NEAR A BLACK HOLE IN THE CORE OF SEYFERT GALAXY NGC 4151

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The Space Telescope Imaging Spectrograph (STIS) simultaneously records, in unprecedented detail, the velocities of hundreds of gas knots streaming at hundreds of thousands of miles per hour from the nucleus of NGC 4151, thought to house a supermassive black hole. This is the first time the velocity structure in the heart of this object, or similar objects, has been mapped so vividly this close to its central black hole. The twin cones of gas emission are powered by the energy released from the supermassive black hole believed to reside at the heart of this Seyfert galaxy. The STIS data clearly show that the gas knots illuminated by one of these cones is rapidly moving towards us, while the gas knots illuminated by the other cone are rapidly receding. The images have been rotated to show the same orientation of NGC 4151. The figures show: WFPC2 (upper left) -- A Hubble Wide Field Planetary Camera 2 image of the oxygen emission (5007 Angstroms) from the gas at the heart of NGC 4151. Though the twin cone structure can be seen, the image does not provide any information about the motion of the oxygen gas. STIS OPTICAL (upper right) -- In this STIS spectral image of the oxygen gas, the velocities of the knots are determined by comparing the knots of gas in the stationary WFPC2 image to the horizontal location of the knots in the STIS image. STIS OPTICAL (lower right) -- In this false color image the two emission lines of oxygen gas (the weaker one at 4959 Angstroms and the stronger one at 5007 Angstroms) are clearly visible. The horizontal line passing through the image is from the light generated by the powerful black hole at the center of NGC 4151. STIS ULTRAVIOLET (lower left) -- This STIS spectral image shows the velocity distribution of the carbon emission from the gas in the core of NGC 4151. It requires more energy to make the carbon gas glow (CIV at 1549 Angstroms) than it does to ionize the oxygen gas seen in the other images. This means we expect that the carbon emitting gas is closer to the heart of the energy source. Credit: John Hutchings (Dominion Astrophysical Observatory), Bruce Woodgate (GSFC/NASA), Mary Beth Kaiser (Johns Hopkins University), Steven Kraemer (Catholic University of America), and the STIS Team. Image files in GIF and JPEG format and captions may be accessed on the Internet via anonymous ftp from ftp.stsci.edu in /pubinfo.

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

    E-print Network

    Pietrzynski, G; Soszynski, I; Udalski, A; Bresolin, F; Kudritzki, R P; Mennickent, R; Walker, A; García, A; Szewczyk, O; Szymanski, M; Kubiak, M; Wyrzykowski, L

    2006-01-01

    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 ...

  14. The Cepheid distance to the maser-host galaxy NGC 4258: studying systematics with the Large Binocular Telescope

    NASA Astrophysics Data System (ADS)

    Fausnaugh, M. M.; Kochanek, C. S.; Gerke, J. R.; Macri, L. M.; Riess, A. G.; Stanek, K. Z.

    2015-07-01

    We identify and phase a sample of 81 Cepheids in the maser-host galaxy NGC 4258 using the Large Binocular Telescope, and obtain calibrated mean magnitudes in up to four filters for a subset of 43 Cepheids using archival Hubble Space Telescope data. We employ three models to study the systematic effects of extinction, the assumed extinction law, and metallicity on the Cepheid distance to NGC 4258. We find a correction to the Cepheid colours consistent with a greyer extinction law in NGC 4258 compared to the Milky Way (RV = 4.9_{-0.7}^{+0.9}), although we believe this is indicative of other systematic effects. If we combine our Cepheid sample with previously known Cepheids, we find a significant metallicity adjustment to the distance modulus of ?1 = -0.61 ± 0.21 mag dex-1 for the Zaritsky et al. metallicity scale, as well as a weak trend of Cepheid colours with metallicity. Conclusions about the absolute effect of metallicity on Cepheid mean magnitudes are limited by the available data on the metallicity gradient in NGC 4258, but our Cepheid data require at least some metallicity adjustment to make the Cepheid distance consistent with independent distances to the Large Magellanic Cloud (LMC) and NGC 4258. From our ensemble of models and the geometric maser distance of NGC 4258 (?N4258 = 29.40 ± 0.06 mag), we estimate ?LMC = 18.57 ± 0.14 mag (51.82 ± 3.23 kpc), including the uncertainties due to metallicity.

  15. Multiwavelength Study of the Starburst Galaxy NGC 7714. II: The Balance between Young, Intermediate Age and Old Stars

    E-print Network

    Ariane Lancon; Jeff D. Goldader; Claus Leitherer; Rosa M. Gonzalez Delgado

    2001-01-18

    We combine existing multiwavelength data (incl. an HST/GHRS UV spectrum, an optical spectrum, far-IR, Xray and radio fluxes) with new HST/WFPC2 images, near-IR photometry and K band spectroscopy. We use these data to constrain the young, the intermediate age and the old stellar populations in the central 330 pc of the starburst galaxy NGC 7714. [...] We find that the young burst responsible for the UV light is only a small part of an extended episode of enhanced star formation (SF) [...]. The mass of young and intermediate age stars thus formed equals at least 10% of the mass locked in pre-existing stars of the underlying galaxy nucleus [...]. The spectrophotometric SF timescale is long compared to the ~110 Myr elapsed since closest contact with NGC 7715. The trigger of the starburst remains elusive. NGC 7714 owes its brightness in the UV to a few low extinction lines of sight towards young stars. [...] The different extinction estimates obtained from different indicators result naturally from the coexistence of populations with various ages and obscurations. The near-IR continuum image looks smoothest, as a consequence of lower sensitivity to extinction and of a larger contribution of old stars. We compare the nuclear properties of NGC 7714 with results from studies in larger apertures. We emphasize that the global properties of starburst galaxies are the result of the averaging over many lines of sight with diverse properties in terms of obscuration and stellar ages.

  16. Multi-frequency study of extragalactic supernova remnants and H II regions. Sculptor group Sd galaxy NGC 300

    NASA Astrophysics Data System (ADS)

    Payne, J. L.; Filipovi?, M. D.; Pannuti, T. G.; Jones, P. A.; Duric, N.; White, G. L.; Carpano, S.

    2004-10-01

    We present a multi-frequency study of supernova remnants (SNRs) and H I I regions in the nearby Sculptor Group Sd galaxy NGC 300, based on new ATCA observations at the wavelengths of 13 and 20 cm, XMM-Newton observations, newly-processed ROSAT (PSPC/HRI; \\citealt{read}) and VLA (20/6 cm) images of this galaxy. We have investigated the physical properties at the X-ray and radio wavelengths of the 28 optical SNRs found by \\citet{blair} and have expanded on the multi-wavelength work by \\citet{pannuti} on this same galaxy. From a total of 54 radio sources and 11 X-ray sources, we report 18 SNRs and three (3) SNR candidates (classified by spectral index alone) in NGC 300. Five of these 18 SNRs are associated with reported optical SNRs and three have X-ray counterparts. An additional 12 radio SNRs are seen in the \\citet{blair} [S II] images. We also investigate the luminosity function of our SNRs. Three background radio sources are confirmed and 12 other sources could represent additional background objects. Twenty two radio correlations with OB associations within NGC 300 correspond to either H I I regions or SNRs making them a good tracer of SNRs near star-forming regions. Additionally, two radio sources coincide with potential globular clusters of NGC 300 reported by \\citet{kim}. Figures 8 and 9 are only available in electronic form at\\ http://www.edpsciences.org

  17. The 'sleeping beauty' galaxy NGC 4826: an almost textbook example of the Abelian Higgs vorto-source (-sink)

    NASA Astrophysics Data System (ADS)

    Saniga, Metod

    1995-03-01

    It is demonstrated that the kinematic 'peculiarity' of the early Sab galaxy NGC 4826 can easily be understood in terms of the Abelian Higgs (AH) model of spiral galaxies. A cylindrically symmetric AH vorto-source (-sink) with a disk-to-bulge ratio Omega greater than 1 is discussed and the distributions of the diagonal components of the corresponding stress-energy tensor Tmu,nu are presented. It is argued that the sign-changing component Tphiphi could account for the existence of two counter-rotating gas disks while negative values of Trr imply inward gas motions as observed in the outer and transition regions of the galaxy.

  18. The Star Formation History of the Virgo early-type galaxy NGC4435: the Spitzer Mid Infrared view

    E-print Network

    P. Panuzzo; O. Vega; A. Bressan; L. Buson; M. Clemens; R. Rampazzo; L. Silva; J. R. Valdes; G. L. Granato; L. Danese

    2006-10-11

    We present a population synthesis study of NGC4435, an early-type Virgo galaxy interacting with NGC4438. We combine new spectroscopic observations obtained with the Spitzer Space Telescope IRS instrument with IRAC archival data and broad band data from the literature. The IRS spectrum shows prominent PAH features, low ionization emission lines and H_2 rotational lines arising from the dusty circumnuclear disk characterizing this galaxy. The central SED, from X-ray to radio, is well fitted by a model of an exponential burst superimposed on an old simple stellar population. From the lack of high excitation nebular lines, the [NeIII]15.5/[NeII]12.8 ratio, the temperature of molecular hydrogen, and the fit to the full X-ray to radio SED we argue that the present activity of the galaxy is driven by star formation alone. The AGN contribution to the ionizing flux is constrained to be less than 2%. The age of the burst is found to be around 190 Myr and it is fully consistent with the notion that the star formation process has been triggered by the interaction with NGC4438. The mass involved in the rejuvenation episode turns out to be less than 1.5% of the stellar galaxy mass sampled in a 5" central aperture. This is enough to render NGC4435 closely similar to a typical interacting early-type galaxy with inverted CaII[H+K] lines that will later turn into a typical cluster E+A galaxy and enforces the notion that these objects are the result of a recent rejuvenation episode rather than a genuine delayed formation.

  19. STAR FORMATION AND DUST OBSCURATION IN THE TIDALLY DISTORTED GALAXY NGC 2442

    SciTech Connect

    Pancoast, Anna; Sajina, Anna [Haverford College, Haverford, PA 19041 (United States); Lacy, Mark [North American ALMA Science Center, National Radio Astronomy Observatory, Charlottesville, VA 22903 (United States); Noriega-Crespo, Alberto [Spitzer Science Center, Caltech, Pasadena, CA 91125 (United States); Rho, Jeonghee [NASA Ames Research Center, SOFIA, M/C 211-3, Moffett Field, CA 94035 (United States)

    2010-11-01

    We present a detailed investigation of the morphological distribution and level of star formation and dust obscuration in the nearby tidally distorted galaxy NGC 2442. Spitzer images in the IR at 3.6, 4.5, 5.8, 8.0, and 24 {mu}m and GALEX images at 1500 A and 2300 A allow us to resolve the galaxy on scales between {approx}240 and 600 pc. We supplement these with archival data in the B, J, H, and K bands. We use the 8 {mu}m, 24 {mu}m, and FUV (1500 A) emission to study the star formation rate (SFR). We find that, globally, these tracers of star formation give a range of results of {approx}6-11 M{sub sun} yr{sup -1}, with the dust-corrected FUV giving the highest value of SFR. We can reconcile the UV- and IR-based estimates by adopting a steeper UV extinction curve that lies in between the starburst (Calzetti) and Small Magellanic Cloud extinction curves. However, the regions of the highest SFR intensity along the spiral arms are consistent with a starburst-like extinction. Overall, the level of star formation we find is higher than previously published for this galaxy, by about a factor of 2, which, contrary to previous conclusions, implies that the interaction that caused the distorted morphology of NGC 2442 likely also triggered increased levels of star formation activity. We also find marked asymmetry in that the north spiral arm has a noticeably higher SFR than the southern arm. The tip of the southern spiral arm shows a likely tidally distorted peculiar morphology. It is UV bright and shows unusual IRAC colors, consistent with other published tidal features IRAC data. Outside of the spiral arms, we discover what appears to be a superbubble, {approx}1.7 kpc across, which is seen most clearly in the IRAC images. Significant H{alpha}, UV, and IR emission in the area also suggest vigorous ongoing star formation. A known, recent supernova (SN 1999ga) is located at the edge of this superbubble. Although speculative at this stage, this area suggests a large star-forming region with a morphology shaped by generations of supernovae. Lastly, we discover an 8 {mu}m (polycyclic aromatic hydrocarbon) circumnuclear ring with an {approx}0.8 kpc radius. The H{alpha} emission is largely concentrated inside that ring and shows a vague spiral structure in the rest of the galaxy. The nuclear region shows the highest obscuration levels in the galaxy (A{sub 1600} {approx} 3-4) most likely due to the circumnuclear dust ring.

  20. The origin of the soft X-ray excess in the Seyfert 2 galaxy NGC 2110

    NASA Technical Reports Server (NTRS)

    Weaver, K. A.; Mushotzky, R. F.; Serlemitsos, P. J.; Wilson, A. S.; Elvis, M.; Briel, U.

    1995-01-01

    We present and discuss an X-ray image and a medium-resolution X-ray spectrum of the Seyfert 2 galaxy NGC 2110 obtained with the high-resolution imager (HRI) on ROSAT (0.1-2.4 keV) and Goddard's Broad Band X-ray Telescope (BBXRT; 0.3-11 keV), respectively. Spatially resolved soft X-ray emission, which peaks 4 arcsecs to the north of the nucleus and near the position of the highest excitation optical emission line gas is seen in the HRI observation. The extent has a flux of approximately 3 x 10(exp -13) ergs/sq cm/s and accounts for 11% +/- 3% of the total 0.1-2.4 keV flux. To model the BBXRT spectrum, a soft excess component is required which has a flux of approximately 3.5 x 10(exp -13) ergs/sq cm/s and accounts for approximately 14% +/- 6% of the total 0.1-2.4 keV flux. In addition, BBXRT confirms the presence of an approximately 175 eV equivalent width Fe K alpha flourescence line in NGC 2110. Because of the good agreement between their fluxes, we propose that the soft excess in NGC 2110 is due to leakage of the X-ray continuum through a patchy absorber. The temperature of the gas responsible for the soft excess is too high to be accounted for by local shock heating. In order to explain the soft excess and extent as either scattered continuum X-rays or flourescence from gas photoionized by the nuclear source, the hard X-rays must be emitted anisotropically. However, the soft excess and extent can be well modeled as thermal emission from a hot, outflowing wind, which may also be responsible for confirming at least some portion of the optical narrow line-emitting clouds.

  1. Physical Conditions in the Inner Narrow-Line Region of the Seyfert 2 Galaxy NGC 1068

    E-print Network

    Steven B. Kraemer; Jose R. Ruiz; D. Michael Crenshaw

    1998-06-25

    The physical conditions in the inner narrow line region (NLR) of the Seyfert 2 galaxy, NGC 1068, are examined using ultraviolet and optical spectra and photoionization models. The spectra are Hubble Space Telescope (HST) Harchive data obtained with the Faint Object Spectrograph (FOS). We selected spectra of four regions, taken through the 0.3" FOS aperture, covering the full FOS 1200A to 6800A waveband. Each region is approximately 20 pc in extent, and all are within 100 pc of the apparent nucleus of NGC 1068. The spectra show similar emission-line ratios from wide range of ionization states for the most abundant elements. After extensive photoionization modeling, we interpret this result as an indication that each region includes a range of gas densities, which we included in the models as separate components. Supersolar abundances were required for several elements to fit the observed emission line ratios. Dust was included in the models but apparently dust to gas fraction varies within these regions. The low ionization lines in these spectra can be best explained as arising in gas that is partially shielded from the ionizing continuum. Although the predicted line ratios from the photoionization models provide a good fit to the observed ratios, it is apparent that the model predictions of electron temperatures in the ionized gas are too low. We interpret this as an indication of additional collisional heating due to shocks and/or energetic particles associated with the radio jet that traverses the NLR of NGC 1068. The density structure within each region may also be the result of compression by the jet.

  2. Interstellar absorption lines in the spectrum of the starburst galaxy NGC 1705

    E-print Network

    M. S. Sahu

    1998-06-01

    I present a GHRS archival study of the interstellar absorption lines in the line-of-sight to the HI-rich starburst dwarf galaxy NGC 1705, in the 1170 to 1740A range at ~ 120 km/s resolution. The absorption features arising due to photospheric lines are distinctly different from the interstellar lines. The interstellar lines consist of three relatively narrow components at LSR velocities of -20, 260 and 540 km/s and include absorption by neutral atoms, singly ionized atoms and atoms in higher ionization states. The analysis presented in this paper consists of (1) a list of all interstellar absorption features with > 3 sigma significance and their measured equivalent widths and (2) plots of the lines in the various atomic species together with the results of non-linear least square fit profiles to the observed data and (3) unpublished 21-cm maps from the Wakker & van Woerden survey showing the large-scale HI distribution in the region near the NGC 1705 sightline and high velocity cloud HVC 487. Further, I report weak N I 1200A triplet absorption for the supershell component, which in the absence of dust depletion and ionization corrections implies a low N abundance. A low N abundance for the supershell is consistent with an interpretation of nucleosynthetic enrichment by time-delayed "primary" nitrogen production, the age estimate of 10 - 20 x 10^6 years for the central superstar cluster NGC 1705-1 (Heckman and Leitherer, 1997) and the underabundance of Fe reported by Sahu and Blades (1997).

  3. The nuclear and extended infrared emission of the Seyfert galaxy NGC 2992 and the interacting system Arp 245

    NASA Astrophysics Data System (ADS)

    García-Bernete, I.; Ramos Almeida, C.; Acosta-Pulido, J. A.

    2015-05-01

    We present subarcsecond resolution infrared (IR) imaging and mid-IR (MIR) spectroscopic observations of the Seyfert 1.9 galaxy NGC 2992. The data were obtained using the Gemini North telescope and the Gran Telescopio CANARIAS (GTC). In the N-band, the galaxy was observed with a spatial resolution of 0.32'' (55 pc) and the imaging data reveal faint extended emission out to ˜ 3 kpc. By comparing the MIR spectra of the nuclear and extended emission of the galaxy, we conclude that the origin of the extended emission is likely dust in the inner galaxy disk, with some contribution from star formation. We also report arcsecond resolution MIR and far-IR (FIR) imaging of the interacting system Arp 245 (NGC 2992,NGC 2993 and Arp 245 North), taken with the Spitzer Space Telescope and the Herschel Space Observatory. For NGC 2992, we obtained Spitzer MIR and Herschel FIR nuclear fluxes using different methods and compared them with the subarcsecond resolution data. Using imaging data, we find that we can only recover the nuclear fluxes obtained from high angular resolution data at 20--25 ?m, where emission from the AGN dominates. We fitted the nuclear IR spectral energy distribution (SED) of NGC 2992, including the 7.5--13 ?m GTC/CanariCam (CC) nuclear spectrum, with clumpy torus models. We then used the best-fitting torus model to decompose the 5--30 ?m Spitzer/IRS spectrum (˜ 630 pc) in AGN and starburst (SB) components, using different SB templates. We find that, whereas at shorter wavelengths the SB component dominates the MIR emission, with 64 % contribution at 6 ?m, the AGN component reaches 90 % at 20 ?m. Finally, we reproduced the dust emission in the Arp 245 system using a set of modified blackbodies, from which we derived dust temperatures, star-formation rates (SFRs) and dust masses.

  4. Environmental dependence of star formation induced by cloud collisions in a barred galaxy

    NASA Astrophysics Data System (ADS)

    Fujimoto, Yusuke; Tasker, Elizabeth J.; Habe, Asao

    2014-11-01

    Cloud collision has been proposed as a way to link the small-scale star formation process with the observed global relation between the surface star formation rate and gas surface density. We suggest that this model can be improved further by allowing the productivity of such collisions to depend on the relative velocity of the two clouds. Our adjustment implements a simple step function that results in the most successful collisions being at the observed velocities for triggered star formation. By applying this to a high-resolution simulation of a barred galaxy, we successfully reproduce the observational result that the star formation efficiency (SFE) in the bar is lower than that in the spiral arms. This is not possible when we use an efficiency dependent on the internal turbulence properties of the clouds. Our results suggest that high-velocity collisions driven by the gravitational pull of the clouds are responsible for the low bar SFE.

  5. Galaxy Zoo: Are Bars Responsible for the Feeding of Active Galactic Nuclei at 0.2 < z < 1.0?

    E-print Network

    Cheung, Edmond; Athanassoula, E; Bamford, Steven P; Bell, Eric F; Bosma, A; Cardamone, Carolin N; Casteels, Kevin R V; Faber, S M; Fang, Jerome J; Fortson, Lucy F; Kocevski, Dale D; Koo, David C; Laine, Seppo; Lintott, Chris; Masters, Karen L; Melvin, Thomas; Nichol, Robert C; Schawinski, Kevin; Simmons, Brooke; Smethurst, Rebecca; Willett, Kyle W

    2014-01-01

    We present a new study investigating whether active galactic nuclei (AGN) beyond the local universe are preferentially fed via large-scale bars. Our investigation combines data from Chandra and Galaxy Zoo: Hubble (GZH) in the AEGIS, COSMOS, and GOODS-S surveys to create samples of face-on, disc galaxies at 0.2 1, our findings suggest that large-scale bars have likely never directly been a dominant fueling mechanism for supermassive black hole growth.

  6. 2-D stationary gas dynamics in a barred galaxy

    NASA Astrophysics Data System (ADS)

    Mulder, W. A.

    2015-06-01

    A code for solving the 2-D isothermal Euler equations of gas dynamics in a rotating disc is presented. The gravitational potential represents a weak bar and controls the flow. A damped Newton method solves the second-order upwind discretisation of the equations for a steady-state solution, using a consistent linearisation and a direct solver. Successive grid refinement, starting from a finite-volume grid with 8 by 8 cells, is applied to find solutions on subsequently finer meshes. On coarser meshes, a first-order spatial discretisation is used. The method obtains quadratic convergence once the solution approaches the steady state. The initial search is quick with the first-order scheme and slower with the second-order discretisation, up to 256 by 256 cells. Beyond, with 512 by 512 cells, the number of iterations becomes too large to be of practical use. Potential causes are discussed. The code can be applied as a tool for generating flow models if used on not too fine meshes.

  7. Warm Dust and Spatially Variable PAH Emission in the Dwarf Starburst Galaxy NGC 1705

    E-print Network

    Cannon, J M; Bendo, G J; Buckalew, B A; Calzetti, D; Dale, D A; Draine, B T; Engelbracht, C W; Gordon, K D; Helou, G; Hollenbach, D J; Jarrett, T H; Kennicutt, R C; Leitherer, C; Li, A; Meyer, M J; Murphy, E J; Regan, M W; Rieke, G H; Rieke, M J; Roussel, H; Sheth, K; Smith, J D T; Thornley, M D; Walter, F; Armus, Lee; Bendo, George J.; Buckalew, Brent A.; Calzetti, Daniela; Cannon, John M.; Dale, Daniel A.; Draine, Bruce T.; Engelbracht, Charles W.; Gordon, Karl D.; Helou, George; Hollenbach, David J.; Jarrett, Thomas H.; Kennicutt, Robert C.; Leitherer, Claus; Li, Aigen; Meyer, Martin J.; Murphy, Eric J.; Regan, Michael W.; Rieke, George H.; Rieke, Marcia J.; Roussel, Helene; Sheth, Kartik; Smith, John-David T.; Thornley, Michele D.; Walter, Fabian

    2006-01-01

    We present Spitzer observations of the dwarf starburst galaxy NGC 1705 obtained as part of SINGS. The galaxy morphology is very different shortward and longward of ~5 microns: short-wavelength imaging shows an underlying red stellar population, with the central super star cluster (SSC) dominating the luminosity; longer-wavelength data reveals warm dust emission arising from two off-nuclear regions offset by ~250 pc from the SSC. These regions show little extinction at optical wavelengths. The galaxy has a relatively low global dust mass (~2E5 solar masses, implying a global dust-to-gas mass ratio ~2--4 times lower than the Milky Way average). The off-nuclear dust emission appears to be powered by photons from the same stellar population responsible for the excitation of the observed H Alpha emission; these photons are unassociated with the SSC (though a contribution from embedded sources to the IR luminosity of the off-nuclear regions cannot be ruled out). Low-resolution IRS spectroscopy shows moderate-streng...

  8. A distance to the galaxy NGC4258 from observations of Cepheid variable stars.

    PubMed

    Maoz, E; Newman, J A; Ferrarese, L; Stetson, P B; Zepf, S E; Davis, M; Freedman, W L; Madore, B F

    1999-09-23

    Cepheid variable stars pulsate in a way that is correlated with their intrinsic luminosity, making them useful as 'standard candles' for determining distances to galaxies; the potential systematic uncertainties in the resulting distances have been estimated to be only 8-10%. They have played a crucial role in establishing the extragalactic distance scale and hence the value of the Hubble constant. Here we report observations of Cepheids in the nearby galaxy NGC4258; the distance calculated from the Cepheids is 8.1 +/- 0.4 Mpc, where the uncertainty does not include possible systematic errors. There is an independently determined geometric distance to this galaxy of 7.2 +/- 0.5 Mpc, based on the observed proper motions of water masers orbiting the central black hole; the distances differ by 1.3sigma. If the maser-based distance is adopted and the Cepheid distance scale revised accordingly, the derived value of the Hubble constant would increase by 12 +/- 9%, while the expansion age of the Universe would decrease by the same amount. PMID:16862105

  9. The extremely populated globular cluster system of the lenticular galaxy NGC 6861

    E-print Network

    Escudero, Carlos G; Bassino, Lilia P; Calderon, Juan Pablo; Caso, Juan Pablo

    2015-01-01

    We present a photometric study of the globular cluster (GC) system associated to the lenticular galaxy (S0) NGC 6861, which is located in a relatively low density environment. It is based on GEMINI/GMOS images in the filters g', r', i' of three fields, obtained under good seeing conditions. Analyzing the colour-magnitude and colour-colour diagrams, we find a large number of GC candidates, which extends out to 100 kpc, and we estimate a total population of 3000+/-300 GCs. Besides the well known blue and red subpopulations, the colour distribution shows signs of the possible existence of a third subpopulation with intermediate colours. This could be interpreted as evidence of a past interaction or fusion event. Other signs of interactions presented by the galaxy, are the non-concentric isophotes and the asymmetric spatial distribution of GC candidates with colours (g'-i')_0>1.16. As observed in other galaxies, the red GCs show a steeper radial distribution than the blue GCs. In addition, the spatial distributio...

  10. Spectroscopy of globular clusters in the low-luminosity spiral galaxy NGC 45

    E-print Network

    Marcelo D. Mora; Soeren S. Larsen; Markus Kissler-Patig

    2008-08-06

    CONTEXT: Extragalactic globular clusters have been studied in elliptical galaxies and in a few luminous spiral galaxies, but little is known about globular clusters in low-luminosity spirals. AIMS: Past observations with the ACS have shown that NGC 45 hosts a large population of globular clusters (19), as well as several young star clusters. In this work we aim to confirm the bona fide globular cluster status for 8 of 19 globular cluster candidates and to derive metallicities, ages, and velocities. METHODS: VLT/FORS2 multislit spectroscopy in combination with the Lick/IDS system was used to derive velocities and to constrain metallicities and [alpha/Fe] element ratio of the globular clusters. RESULTS: We confirm the 8 globular clusters as bona fide globular clusters. Their velocities indicate halo or bulge-like kinematics, with little or no overall rotation. From absorption indices such as H_beta, H_gamma, and H_delta and the combined [MgFe]' index, we found that the globular clusters are metal-poor [Z/H]globular clusters formed during the assembling of the galaxy.

  11. HALOGAS: H I OBSERVATIONS AND MODELING OF THE NEARBY EDGE-ON SPIRAL GALAXY NGC 4244

    SciTech Connect

    Zschaechner, Laura K.; Rand, Richard J. [Department of Physics and Astronomy, University of New Mexico, 1919 Lomas Blvd NE, Albuquerque, NM 87131-1156 (United States); Heald, George H. [Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo (Netherlands); Gentile, Gianfranco [Department of Physics and Astronomy, Universiteit Gent, Krijgslaan 281, B-9000 Gent (Belgium); Kamphuis, Peter, E-mail: zschaech@unm.edu, E-mail: rjr@phys.unm.edu, E-mail: heald@astron.nl, E-mail: Gianfranco.Gentile@ugent.be, E-mail: peter.kamphuis@astro.rub.de [Astronomisches Institut der Ruhr-Universitaet Bochum, Universitaetsstr. 150, 44780 Bochum (Germany)

    2011-10-10

    We present 21 cm observations and models of the H I kinematics and distribution of NGC 4244, a nearby edge-on Scd galaxy observed as part of the Westerbork HALOGAS (Hydrogen Accretion in LOcal GAlaxieS) survey. Our models give insight into the H I kinematics and distribution with an emphasis on the potential existence of extraplanar gas as well as a negative gradient in rotational velocity with height above the plane of the disk (a lag). Our models yield strong evidence against a significantly extended halo and instead favor a warp component along the line of sight as an explanation for most of the observed thickening of the disk. Based on these models, we detect a lag of -9{sup +3}{sub -2} km s{sup -1} kpc{sup -1} in the approaching half and -9 {+-} 2 km s{sup -1} kpc{sup -1} in the receding half. This lag decreases in magnitude to -5 {+-} 2 km s{sup -1} kpc{sup -1} and -4 {+-} 2 km s{sup -1} kpc{sup -1} near a radius of 10 kpc in the approaching and receding halves, respectively. Additionally, we detect several distinct morphological and kinematic features including a shell that is probably driven by star formation within the disk.

  12. The incidence of bar-like kinematic flows in CALIFA galaxies

    E-print Network

    Holmes, L; Sánchez, S F; Walcher, C J; García-Benito, R; Mast, D; Cortijo-Ferrero, C; Kalinova, V; Marino, R A; Mendez-Abreu, J; Barrera-Ballesteros, J K

    2015-01-01

    We carry out a direct search for bar-like non-circular flows in intermediate-inclination, gas-rich disk galaxies with a range of morphological types and photometric bar classifications from the first data release (DR1) of the CALIFA survey. We use the DiskFit algorithm to apply rotation only and bisymmetric flow models to H$\\alpha$ velocity fields for 49/100 CALIFA DR1 systems that meet our selection criteria. We find satisfactory fits for a final sample of 37 systems. DiskFit is sensitive to the radial or tangential components of a bar-like flow with amplitudes greater than $15\\,$km$\\,$s$^{-1}$ across at least two independent radial bins in the fit, or ~2.25 kpc at the characteristic final sample distance of ~75 Mpc. The velocity fields of 25/37 $(67.6^{+6.6}_{-8.5}\\%)$ galaxies are best characterized by pure rotation, although only 17/25 $(68.0^{+7.7}_{-10.4}\\%)$ of them have sufficient H$\\alpha$ emission near the galaxy centre to afford a search for non-circular flows. We detect non-circular flows in the r...

  13. Dynamics of the NGC 4636 Globular Cluster System - An extremely dark matter dominated galaxy?

    E-print Network

    Y. Schuberth; T. Richtler; B. Dirsch; M. Hilker; S. S. Larsen; M. Kissler-Patig; U. Mebold

    2006-04-13

    We present the first dynamical study of the globular cluster system of NGC 4636. This giant elliptical galaxy is claimed to be extremely dark matter dominated, according to X-ray observations. Using the VLT with FORS2/MXU, we obtained velocities for 174 globular clusters. The clusters have projected galactocentric distances in the range 4 to 70 kpc, the overwhelming majority lie within 30 kpc. We find some indication for a rotation of the red (metal-rich) clusters about the minor axis. Out to a radius of 30 kpc, we find a roughly constant projected velocity dispersion for the blue clusters of ~200 km/s. The red clusters exhibit a distinctly different behavior: at a radius of about 13 kpc, the velocity dispersion drops by ~50 km/s to about 170 km/s which then remains constant out to a radius of 30 kpc. Using only the blue clusters as dynamical tracers, we perform Jeans-analyses for different assumptions of the orbital anisotropy. Depending on the anisotropy and the adopted M/L-values, we find that the dark matter fraction within one effective radius can vary between 20% and 50% with most a probable range between 20% and 30%. A main source of uncertainty is the ambiguity of the velocity dispersion in the outermost bin. Although the dark halo mass still cannot be strongly constrained, NGC 4636 does not seem to be extremely dark matter dominated. The derived circular velocities are also consistent with Modified Newtonian Dynamics.

  14. Cold dust and its relation to molecular gas in the dwarf irregular galaxy NGC 4449

    E-print Network

    C. Boettner; U. Klein; A. Heithausen

    2003-06-30

    We present observations of the dwarf irregular galaxy NGC 4449 at 850 $\\mu$m and 450 $\\mu$m obtained with SCUBA at the JCMT. The distribution of the cold dust agrees well with that of the CO and H$\\alpha$ emission. To explain the integrated mm- through far-infrared continuum spectrum three dust components are required, with temperatures of 16 K, 39 K and 168 K, respectively. The dust mass is dominated by the cold dust component; we derive a total dust mass of \\~3.8 x10^6 Msun, and with the local gas-to-dust ratio of ~130 a total gas mass of M(HI+H_2}~4.9 x 10^8 Msun. Comparison with the HI mass leads to a total molecular gas mass of ~3.4 x 10^8 Msun. We derive a conversion factor of the CO line intensity to molecular hydrogen column density XCO = N(H_2)/I(CO) which is at least 11 times larger than the Galactic value. These values are in accord with the lower metallicity of NGC 4449.

  15. The Tip of the Red Giant Branch Distances to Type Ia Supernova Host Galaxies. III. NGC 4038/39 and NGC 5584

    NASA Astrophysics Data System (ADS)

    Jang, In Sung; Lee, Myung Gyoon

    2015-07-01

    We present the tip of the red giant branch (TRGB) distances to Type Ia supernova (SNe Ia) host galaxies NGC 4038/39 and NGC 5584. Based on the deep images constructed using archival Hubble Space Telescope data, we detect red giant branch stars in each galaxy. VI photometry of the resolved stars and corresponding I-band luminosity functions show the TRGB to be at {I}{TRGB}=27.67+/- 0.05 for NGC 4038/39 and {I}{TRGB}=27.77+/- 0.04 for NGC 5584. From these estimates, we determine the distance modulus to NGC 4038/39 to be {(m-M)}0=31.67+/- 0.05 (random) ± 0.12 (systematic) (corresponding to a linear distance of 21.58+/- 0.50+/- 1.19 Mpc) and the distance modulus to NGC 5584 to be {(m-M)}0=31.76+/- 0.04 (random) ± 0.12 (systematic) (corresponding to a linear distance of 22.49+/- 0.41+/- 1.24 Mpc). We derive a mean absolute maximum magnitude of SNe Ia of {M}V=-19.27+/- 0.08 from the distance estimates of five SNe Ia (including two SNe in this study and three SNe Ia from our previous studies), and we derive a value of {M}V=-19.19+/- 0.10 using three low-reddened SNe Ia among the five SNe Ia. With these estimates, we derive a value of the Hubble constant, {H}0=69.8+/- 2.6 (random) ± 3.9 (systematic) km s?1 Mpc?1 and 72.2 ± 3.3 (random) ± 4.0(systematic) km s?1 Mpc?1, respectively. The value from the five SNe is similar to those from the cosmic microwave background analysis, and not much different within errors, from those of recent Cepheid calibrations of SNe Ia. The value from the three SNe is between the values from the two methods.

  16. Search for Obscured Nucleus in a Luminous IRAS Galaxy NGC 6240

    NASA Technical Reports Server (NTRS)

    Leighly, Karen

    1999-01-01

    IRAS discovered very luminous objects which emit the vast majority of their radiation in the infrared wavelength. The energy source of such a tremendous amount of emission is not understood. Starburst and active galactic nuclei (AGN) are thought to be the origin of their power. X-ray observations are expected to be able to reveal the characteristics of the AGN component. However, some are very X-ray quiet, because the AGN is thought to be obscured by a large column density. In order to determine the primary luminosity of the nucleus, we need an X-ray observation with a wide energy band at least up to several tens of keV. We propose to observe NGC 6240, one of the luminous IRAS galaxies, to investigate the characteristics of its AGN, which must be obscured by large column density.

  17. The dust SED in the dwarf galaxy NGC 1569: Indications for an altered dust composition?

    NASA Astrophysics Data System (ADS)

    Lisenfeld, U.; Israel, F. P.; Stil, J. M.; Sievers, A.; Haas, M.

    2005-04-01

    We discuss the interpretation of the dust SED from the mid-infrared to the millimeter range of NGC 1569. The model developed by Désert et al. including three dust components (Polyaromatic Hydrocarbons, Very Small Grams and big grains) can explain the data using a realistic interstellar radiation field and adopting an enhanced abundance of VSGs. A simple three-temperature model is also able to reproduce the data but requires a very low dust temperature which is considered to be unlikely in this low-metallicity starburst galaxy. The high abundance of Very Small Grains might be due to large grain destruction in supernova shocks. This possibility is supported by ISO data showing that the emission at 14.3 ?m, tracing VSGs, is enhanced with respect to the emission at 6.7 ?m and 850 ?m in regions of high star formation.

  18. X-ray Halo Around the Spiral Galaxy NGC 4631 Observed with Suzaku

    E-print Network

    Yamasaki, Noriko Y; Mitsuishi, Ikuyuki; Ohashi, Takaya

    2008-01-01

    Suzaku observation of the edge-on spiral galaxy NGC 4631 confirmed its X-ray halo extending out to about 10 kpc from the galactic disk. The XIS spectra yielded the temperature and metal abundance for the disk and the halo regions. The observed abundance pattern for O, Ne, Mg, Si and Fe is consistent with the metal yield from type II supernovae, with an O mass of about 1E6 Msun contained in the halo. These features imply that metal-rich gas produced by type II supernova is brought into the halo region very effectively, most likely through a galactic wind. Temperature and metal abundance may be affected by charge exchange and dust. An upper limit for the hard X-ray flux was obtained, corresponding to a magnetic field higher than 0.5 uG.

  19. X-ray Halo Around the Spiral Galaxy NGC 4631 Observed with Suzaku

    E-print Network

    Noriko Y. Yamasaki; Kosuke Sato; Ikuyuki Mitsuishi; Takaya Ohashi

    2008-08-31

    Suzaku observation of the edge-on spiral galaxy NGC 4631 confirmed its X-ray halo extending out to about 10 kpc from the galactic disk. The XIS spectra yielded the temperature and metal abundance for the disk and the halo regions. The observed abundance pattern for O, Ne, Mg, Si and Fe is consistent with the metal yield from type II supernovae, with an O mass of about 1E6 Msun contained in the halo. These features imply that metal-rich gas produced by type II supernova is brought into the halo region very effectively, most likely through a galactic wind. Temperature and metal abundance may be affected by charge exchange and dust. An upper limit for the hard X-ray flux was obtained, corresponding to a magnetic field higher than 0.5 uG.

  20. X-Ray Halo around the Spiral Galaxy NGC 4631 Observed with Suzaku

    NASA Astrophysics Data System (ADS)

    Yamasaki, Noriko Y.; Sato, Kosuke; Mitsuishi, Ikuyuki; Ohashi, Takaya

    2009-01-01

    A Suzaku observation of the edge-on spiral galaxy NGC 4631 confirmed its X-ray halo extending out to about 10kpc from the galactic disk. The XIS spectra yielded the temperature and metal abundance for the disk and the halo regions. The observed abundance pattern for O, Ne, Mg, Si, and Fe is consistent with the metal yield from type II supernovae, with an O mass of about 106Modot contained in the halo. These features imply that metal-rich gas produced by type II supernova is brought into the halo region very effectively, most likely through a galactic wind. The temperature and metal abundance may be affected by charge exchange and dust. An upper limit for the hard X-ray flux was obtained, corresponding to a magnetic field higher than 0.5?G.

  1. A NOVEL APPROACH TO CONSTRAIN THE MASS RATIO OF MINOR MERGERS IN ELLIPTICAL GALAXIES: APPLICATION TO NGC 4889, THE BRIGHTEST CLUSTER GALAXY IN COMA

    SciTech Connect

    Gu Meng; Huang Song [School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China); Ho, Luis C. [Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Peng, Chien Y. [Giant Magellan Telescope Organization, 251 South Lake Avenue, Suite 300, Pasadena, CA 91101 (United States)

    2013-08-10

    Minor mergers are thought to be important for the buildup and structural evolution of massive elliptical galaxies. In this work, we report the discovery of a system of four shell features in NGC 4889, one of the brightest members of the Coma cluster, using optical images taken with the Hubble Space Telescope and the Sloan Digital Sky Survey. The shells are well aligned with the major axis of the host and are likely to have been formed by the accretion of a small satellite galaxy. We have performed a detailed two-dimensional photometric decomposition of NGC 4889 and of the many overlapping nearby galaxies in its vicinity. This comprehensive model allows us not only to firmly detect the low-surface brightness shells, but, crucially, also to accurately measure their luminosities and colors. The shells are bluer than the underlying stars at the same radius in the main galaxy. We make use of the colors of the shells and the color-magnitude relation of the Coma cluster to infer the luminosity (or mass) of the progenitor galaxy. The shells in NGC 4889 appear to have been produced by the minor merger of a moderate-luminosity (M{sub I} Almost-Equal-To -18.7 mag) disk (S0 or spiral) galaxy with a luminosity (mass) ratio of {approx}90:1 with respect to the primary galaxy. The novel methodology presented in this work can be exploited to decode the fossil record imprinted in the photometric substructure of other nearby early-type galaxies.

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

    PubMed

    Bolatto, Alberto D; Warren, Steven R; Leroy, Adam K; Walter, Fabian; Veilleux, Sylvain; Ostriker, Eve C; Ott, Jürgen; Zwaan, Martin; Fisher, David B; Weiss, Axel; Rosolowsky, Erik; Hodge, Jacqueline

    2013-07-25

    The under-abundance of very massive galaxies in the Universe is frequently attributed to the effect of galactic winds. Although ionized galactic winds are readily observable, most of the expelled mass (that is, the total mass flowing out from the nuclear region) is likely to be in atomic and molecular phases that are cooler than the ionized phases. Expanding molecular shells observed in starburst systems such as NGC 253 (ref. 12) and M 82 (refs 13, 14) may facilitate the entrainment of molecular gas in the wind. Although shell properties are well constrained, determining the amount of outflowing gas emerging from such shells and the connection between this gas and the ionized wind requires spatial resolution better than 100?parsecs coupled with sensitivity to a wide range of spatial scales, a combination hitherto not available. Here we report observations of NGC 253, a nearby starburst galaxy (distance ??3.4 megaparsecs) known to possess a wind, that trace the cool molecular wind at 50-parsec resolution. At this resolution, the extraplanar molecular gas closely tracks the H? filaments, and it appears to be connected to expanding molecular shells located in the starburst region. These observations allow us to determine that the molecular outflow rate is greater than 3 solar masses per year and probably about 9 solar masses per year. This implies a ratio of mass-outflow rate to star-formation rate of at least 1, and probably ?3, indicating that the starburst-driven wind limits the star-formation activity and the final stellar content. PMID:23887428

  3. Properties of Hot Stars in the Wolf-Rayet galaxy NGC5253 from ISO Spectroscopy

    E-print Network

    Paul A. Crowther; S. C. Beck; Allan J. Willis; Peter S. Conti; Pat W. Morris; Ralph S. Sutherland

    1998-12-03

    ISO-SWS spectroscopy of the WR galaxy NGC5253 is presented, and analysed to provide estimates of its hot young star population. Our approach differs from previous investigations in that we are able to distinguish between the regions in which different infrared fine-structure lines form, using complementary ground-based observations. The high excitation nebular [SIV] emission is formed in a very compact region, which we attribute to the central super-star-nucleus, and lower excitation [NeII] nebular emission originates in the galactic core. We use photo-ionization modelling coupled with the latest theoretical O-star flux distributions to derive effective stellar temperatures and ionization parameters of Teff>38kK, logQ=8.25 for the compact nucleus, with Teff=35kK, logQsynthesis models. We assess the contribution that Wolf-Rayet stars may make to highly ionized nebular lines (e.g. [OIV]). From our Br(alpha) flux, the 2" nucleus contains the equivalent of approximately 1000 O7V star equivalents and the starburst there is 2-3Myr old; the 20" core contains about 2500 O7V star equivalents, with a representative age of 5Myr. The Lyman ionizing flux of the nucleus is equivalent to the 30 Doradus region. These quantities are in good agreement with the observed mid-IR dust luminosity of 7.8x10^8 L(sun) Since this structure of hot clusters embedded in cooler emission may be common in dwarf starbursts, observing a galaxy solely with a large aperture may result in confusion. Neglecting the spatial distribution of nebular emission in NGC5253, implies `global' stellar temperatures (or ages) of 36kK (4.8Myr) and 39kK (2.9 or 4.4Myr) from the observed [NeIII/II] and [SIV/III] line ratios, assuming logQ=8.

  4. Near-infrared polarimetry of the edge-on galaxy NGC 891

    SciTech Connect

    Montgomery, J. D.; Clemens, D. P., E-mail: montgojo@bu.edu, E-mail: clemens@bu.edu [Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States)

    2014-05-01

    The edge-on galaxy NGC 891 was probed using near-infrared (NIR) imaging polarimetry in the H band (1.6 ?m) with the Mimir instrument on the 1.8 m Perkins Telescope. Polarization was detected with a signal-to-noise ratio greater than three out to a surface brightness of 18.8 mag arcsec{sup –2}. The unweighted average and dispersion in polarization percentage (P) across the full disk were 0.7% and 0.3%, respectively, and the same quantities for polarization position angle (P.A.) were 12° and 19°, respectively. At least one polarization null point, where P falls nearly to zero, was detected in the northeast disk but not the southwest disk. Several other asymmetries in P between the northern and southern disk were found and may be related to spiral structure. Profiles of P and P.A. along the minor axis of NGC 891 suggest a transition from magnetic (B) field tracing dichroic polarization near the disk mid-plane to scattering dominated polarization off the disk mid-plane. A comparison between NIR P.A. and radio (3.6 cm) synchrotron polarization P.A. values revealed similar B-field orientations in the central-northeast region, which suggests that the hot plasma and cold, star-forming interstellar medium may share a common B-field. Disk-perpendicular polarizations previously seen at optical wavelengths are likely caused by scattered light from the bright galaxy center and are unlikely to be tracing poloidal B-fields in the outer disk.

  5. Comparing X-ray and Dynamical Mass Profiles in the Early-type Galaxy NGC 4636

    NASA Astrophysics Data System (ADS)

    Johnson, Ria; Chakrabarty, Dalia; O'Sullivan, Ewan; Raychaudhury, Somak

    2009-12-01

    We present the results of an X-ray mass analysis of the early-type galaxy NGC 4636, using Chandra data. We have compared the X-ray mass density profile with that derived from a dynamical analysis of the system's globular clusters (GCs). Given the observed interaction between the central active galactic nucleus and the X-ray emitting gas in NGC 4636, we would expect to see a discrepancy in the masses recovered by the two methods. Such a discrepancy exists within the central ~10 kpc, which we interpret as the result of non-thermal pressure support or a local inflow. However, over the radial range ~10-30 kpc, the mass profiles agree within the 1? errors, indicating that even in this highly disturbed system, agreement can be sought at an acceptable level of significance over intermediate radii, with both methods also indicating the need for a dark matter halo. However, at radii larger than 30 kpc, the X-ray mass exceeds the dynamical mass, by a factor of 4-5 at the largest disagreement. A Fully Bayesian Significance Test finds no statistical reason to reject our assumption of velocity isotropy, and an analysis of X-ray mass profiles in different directions from the galaxy center suggests that local disturbances at large radius are not the cause of the discrepancy. We instead attribute the discrepancy to the paucity of GC kinematics at large radius, coupled with not knowing the overall state of the gas at the radius where we are reaching the group regime (>30 kpc), or a combination of the two.

  6. A Chandra Observation of the Nearby Lenticular Galaxy NGC 5102: Where are the X-ray Binaries?

    E-print Network

    R. P. Kraft; L. A. Nolan; T. J. Ponman; C. Jones; S. Raychaudhury

    2005-05-19

    We present results from a 34 ks Chandra/ACIS-S observation of the nearby (d=3.1 Mpc) lenticular galaxy NGC 5102, previously shown to have an unusually low X-ray luminosity. We detect eleven X-ray point sources within the the $D_{25}$ optical boundary of the galaxy (93% of the light), one third to one half of which are likely to be background AGN. One source is coincident with the optical nucleus and may be a low-luminosity AGN. Only two sources with an X-ray luminosity greater than 10$^{37}$ ergs s$^{-1}$ in the 0.5-5.0 keV band were detected, one of which is statistically likely to be a background AGN. We expected to detect 6 such luminous sources if the XRB population scales linearly with optical magnitude of the host galaxy. NGC 5102 has an unusually low number of XRBs. NGC 5102 is unusually blue for its morphological type, and has undergone at least two recent bursts of star formation. We present the results of optical/UV spectral synthesis analysis and demonstrate that a significant fraction ($>$50%) of the stars in this galaxy are comparatively young ($<3\\times10^9$ years old). If the lack of X-ray binaries is related to the relative youth of most of the stars, this would support models of LMXB formation and evolution that require wide binaries to shed angular momentum on a timescale of Gyrs. We find that NGC 5102 has an unusually low specific frequency of globular clusters ($S_N\\sim$0.4), which could also explain the lack of LMXBs. We also detect diffuse X-ray emission in the central $\\sim$1 kpc of the galaxy. This hot gas is most likely a superbubble created by multiple supernovae of massive stars born during the most recent star burst, and is driving the shock into the ISM which was inferred from optical observations.

  7. Molecular distribution and kinematics in nearby galaxies. II. Sub-mm observations of NGC4945.

    NASA Astrophysics Data System (ADS)

    Mauersberger, R.; Henkel, C.; Whiteoak, J. B.; Chin, Y.-N.; Tieftrunk, A. R.

    1996-05-01

    The central 80"x80" of the nearby edge-on starburst galaxy NGC4945 has been mapped in the J=3-2 line of ^12^CO with a resolution of 15". Spectra of the J=3-2 transition of ^13^CO and tentative detections of the J=4-3 line of HCN and the J_K_a_K_c__=3_12_-2_11_ line of H_2_CO are also presented. The CO J=3-2 emission is concentrated toward the kinematical center of the galaxy with a deconvolved full width at half power (FWHP) size of (11.5+/-3)" corresponding to (200+/-50)pc at a distance D=3.7Mpc. This is less than the extent of the nuclear molecular complex as derived from the distributions of the lower rotational CO transitions. Position-velocity maps reveal three condensations located at the center and at offsets of 5" toward either side of the nucleus. The dynamical mass in the inner R<=600pc is ~3x10^9^Msun_. Applying a "standard" N(H_2_)/I(CO) conversion factor of 2x10^20^cm^-2^/(K.km/s), the central molecular gas mass is ~9x10^8^Msun_. Like in the case of the central regions of the Milky Way and NGC253, integrated ^12^CO line intensities combined with a standard conversion factor yield a gas mass which is 6 to 14 times higher than that obtained from multi-transition CO models and from the dust continuum emission. If the latter results are correct, we find a conversion factor of only 0.15-0.35x10^20^cm^-2^/(K.km/s) for the central region of NGC4945. An embedded active nucleus may contribute to the very high "star forming efficiency" L_IR_/M_gas_~140Lsun_/Msun_. The contribution of the CO lines to the "continuum" flux density in a 50GHz 1.3mm band is comparable to that of the dust. From the strength of the CO J=3-2 emission and our tentative detection of high density tracing molecules, the bulk of the CO emitting gas should have a high density (n(H_2_)=10^3.5^-10^4^cm^-3^) and is clumped with a beam filling factor of roughly 20%.

  8. Constraints on the formation history of the elliptical galaxy NGC 3923 from the colors of its globular clusters

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    We present a study of the colors of globular clusters associated with the elliptical galaxy NGC 3923. Our final sample consists of Wasington system C and T(sub 1) photometry for 143 globular cluster candidates with an expected contamination of no more than 10%. We find that the color distribution of the NGC 3923 globular cluster system (GCS) is broad and appears to have at least two peaks. A mixture modeling analysis of the color distribution indicates that a two-component model is favored over a single-component one at a high level of confidence (greater than 99%). This evidence for more than one population in the GCS of NGC 3923 is similar to that previously noted for the four other elliptical galaxies for which similar data have been published. Furthermore, we find that the NGC 3923 GCS is redder than the GCSs of previously studed elliptical galaxies of similar luminosity. The median metallicity inferred from our (C-(T(sub 1)))(sub 0) colors is (Fe/H)(sub med) = -0.56, with an uncertainty of 0.14 dex arising from all sources of uncertainty in the mean color. This is more metal rich than the median metallicity found for the GCS of M87 using the same method, (Fe/H)(sub med) = -0.94. Since M87 is more luminous than NGC 3923, this result points to significant scatter about any trend of higher GCS metallicity with increasing galaxy luminosity. We also show that there is a color gradient in the NGC 3923 GCS corresponding to about -0.5 dex in Delta(Fe/H)/Delta(log r). We conclude that the shape of the color distribution of individual GCSs and the variation in mean color among the GCSs of ellipticals are difficult to understand if elliptical galaxies are formed in a single protogalactic collapse. Models in which ellipticals and their globular clusters are formed in more than one event, such as a merger scenario, are more successful in accounting for these observations.

  9. THE SUZAKU VIEW OF THE DISK-JET CONNECTION IN THE LOW-EXCITATION RADIO GALAXY NGC 6251

    SciTech Connect

    Evans, D. A.; Kraft, R. P.; Lee, J. C. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Summers, A. C. [Department of Physics, Elon University, 100 Campus Drive, Elon, NC 27244 (United States); Hardcastle, M. J. [School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB (United Kingdom); Gandhi, P. [Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara 252-5210 (Japan); Croston, J. H. [School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ (United Kingdom)

    2011-11-01

    We present results from an 87 ks Suzaku observation of the canonical low-excitation radio galaxy (LERG) NGC 6251. We have previously suggested that LERGs violate conventional active galactic nucleus unification schemes: they may lack an obscuring torus and are likely to accrete in a radiatively inefficient manner, with almost all of the energy released by the accretion process being channeled into powerful jets. We model the 0.5-20 keV Suzaku spectrum with a single power law of photon index {Gamma} = 1.82{sup +0.04} {sub -0.05}, together with two collisionally ionized plasma models whose parameters are consistent with the known galaxy- and group-scale thermal emission. Our observations confirm that there are no signatures of obscured, accretion-related X-ray emission in NGC 6251, and we show that the luminosity of any such component must be substantially sub-Eddington in nature.

  10. A detailed X-ray variability study of the Seyfert galaxy NGC 4051

    NASA Astrophysics Data System (ADS)

    Papadakis, I. E.; Lawrence, A.

    1995-01-01

    We present a detailed and rigorous examination of the X-ray variability characteristics of the Seyfert galaxy NGC 4051, using the 1985 EXOSAT observation and our improved power spectrum modelling techniques. The Medium Energy (ME) power spectrum is adequately fitted by a power-law model, but the Low Energy (LE) spectrum is not. We find an excellent fit by adding a broad quasi-periodic oscillation (QPO) feature on a time-scale of ~1h, which contains 1/4 of the overall variance. A similar, but much weaker, feature may exist in the ME power spectrum as well. The LE power spectrum is also clearly steeper than the ME spectrum. There is no significant lag between the ME and LE data (at most 60 s), but the cross-correlation function is noticeably asymmetric. We confirm earlier claims of a correlation between softness and flux, and show that this is essentially caused by the presence of high peaks present in the LE but not in the ME light curve. We discuss various generic models for X-ray variability. In particular, several features (especially the softness effect and the cross-correlation asymmetry) are suggestive of thermal Comptonization models. We examined one of these models in detail, with parameters suggested by recent fits to the OSSE energy spectra of Seyfert galaxies. However, this model predicts that the ME spectrum should be much steeper, in contradiction with the observed facts.

  11. X-ray Variability Characteristics of the Seyfert 1 Galaxy NGC 3783

    E-print Network

    A. Markowitz

    2005-11-22

    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 towards higher energies. Light curve cross correlation functions yield no significant lags, but peak coefficients generally decrease as energy separation of the bands increases on both short and long timescales. We have measured the coherence between various X-ray bands over the temporal frequency range of 6e-8 to 1e-4 Hz; this range includes the temporal frequency of the low-frequency power spectral density function (PSD) break tentatively detected by Markowitz et al. and includes the lowest temporal frequency over which coherence has been measured in any AGN to date. Coherence is generally near unity at these temporal frequencies, though it decreases slightly as energy separation of the bands increases. Temporal frequency-dependent phase lags are detected on short time scales; phase lags are consistent with increasing as energy separation increases or as temporal frequency decreases. All of these results are similar to those obtained previously for several Seyfert galaxies and stellar-mass black hole systems. Qualitatively, these results are consistent with the variability models of Kotov et al. and Lyubarskii, wherein the X-ray variability is due to inwardly propagating variations in the local mass accretion rate.

  12. Modeling the physical properties in the ISM of the low-metallicity galaxy NGC4214

    E-print Network

    Dimaratos, A; Bigiel, F; Madden, S C

    2015-01-01

    We present a model for the interstellar medium of NGC4214 with the objective to probe the physical conditions in the two main star-forming regions and their connection with the star formation activity of the galaxy. We used the spectral synthesis code Cloudy to model an HII region and the associated photodissociation region (PDR) to reproduce the emission of mid- and far-infrared fine-structure cooling lines from the Spitzer and Herschel space telescopes for these two regions. Input parameters of the model, such as elemental abundances and star formation history, are guided by earlier studies of the galaxy, and we investigated the effect of the mode in which star formation takes place (bursty or continuous) on the line emission. Furthermore, we tested the effect of adding pressure support with magnetic fields and turbulence on the line predictions. We find that this model can satisfactorily predict (within a factor of ~2) all observed lines that originate from the ionized medium ([SIV] 10.5um, [NeIII] 15.6um,...

  13. The NGC 1614 Interacting Galaxy: Molecular Gas Feeding a "Ring of Fire"

    E-print Network

    König, S; Muller, S; Beswick, R J; Gallagher, J S

    2013-01-01

    Minor mergers frequently occur between giant and gas-rich low mass galaxies and can provide significant amounts of interstellar matter to refuel star formation and power AGN in the giant systems. Major starbursts and/or AGN result when fresh gas is transported and compressed in the central regions of the giant galaxy. This is the situation in NGC1614, whose molecular medium we explore at half arcsecond angular resolution through our observations of 12CO(2-1) emission using the SMA. We compare our maps with optical and Pa alpha, HST and high angular resolution radio continuum images to study the relationships between dense molecular gas and the starburst region. The most intense CO emission occurs in a partial ring with ~230pc radius around the center, with an extension to the north-west into the dust lane that contains diffuse molecular gas. We resolve 10 GMAs in the ring which has an integrated molecular mass of ~8x10^8M_sun. Our observations filter out a large part of the CO(1-0) emission mapped at shorter ...

  14. Evidence for a Physically Compact Narrow-Line Region in the Seyfert 1 Galaxy NGC 5548

    E-print Network

    Krämer, S B; Filippenko, A V; Peterson, B M; Kraemer, Steven B.; Filippenko, Alexei V.; Peterson, Bradley M.

    1997-01-01

    We have combined HST/FOS and ground-based spectra of the Seyfert 1 galaxy NGC 5548 to study the narrow emission lines over the 1200 -- 10,000 angstrom region. All of the spectra were obtained when the broad emission line and continuum fluxes were at an historic low level, allowing us to accurately determine the contribution of the narrow-line region (NLR) to the emission lines. We have generated multicomponent photoionization models to investigate the relative strength of the high ionization lines compared to those in Seyfert 2 galaxies, and the weakness of the narrow Mg II 2800 line. We present evidence for a high ionization component of NLR gas that is very close to the nucleus (~1 pc). This component must be optically thin to ionizing radiation at the Lyman edge (tau = 2.5) to avoid producing [O I] and Mg II in a partially ionized zone. The very high ionization lines (N V, [Ne V], [Fe VII], [Fe X]) are stronger than the predictions of our standard model, and we show that this may be due to supersolar abund...

  15. STAR CLUSTERS IN THE NEARBY LATE-TYPE GALAXY NGC 1311

    SciTech Connect

    Eskridge, Paul B. [Department of Physics and Astronomy, Minnesota State University, Mankato, MN 56001 (United States); Grijs, Richard de [Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH (United Kingdom); Anders, Peter [Sterrenkundig Instituut, Universiteit Utrecht, NL-3508 TA Utrecht (Netherlands); Windhorst, Rogier A.; Jansen, Rolf A. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States); Mager, Violet A., E-mail: paul.eskridge@mnsu.edu [Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287 (United States)

    2008-01-15

    Ultraviolet, optical and near-infrared images of the nearby (D {approx} 5.5 Mpc) SBm galaxy NGC 1311, obtained with the Hubble Space Telescope, reveal a small population of 13 candidate star clusters. We identify candidate star clusters based on a combination of their luminosity, extent, and spectral energy distribution. The masses of the cluster candidates range from {approx}10{sup 3} M{sub sun} up to {approx}10{sup 5} M{sub sun}, and show a strong positive trend of larger mass with increasing with cluster age. Such a trend follows from the fading and dissolution of old, low-mass clusters, and the lack of any young super-star clusters of the sort often formed in strong starbursts. The cluster age distribution is consistent with a bursting mode of cluster formation, with active episodes of age {approx}10 Myr, {approx}100 Myr, and {approx}>Gyr. The ranges of age and mass we probe are consistent with those of the star clusters found in quiescent Local Group dwarf galaxies.

  16. Kinetics and ionization of extended gas in active galaxies. II - A circumnuclear starburst in the type 1 Seyfert NGC 7469

    Microsoft Academic Search

    A. S. Wilson; J. A. Baldwin; Sze-Dung Sun; A. E. Wright

    1986-01-01

    Long-slit, high-dispersion mapping of the emission lines H-beta, forbidden O III 4959 A, 5007 A, H-alpha, and forbidden N II 6548 A, 6584 A in the circumnuclear regions of the type I Seyfert galaxy NGC 7469 is reported. The spatially extended, emission line gas is found to be made up of two components. One is highly excited, shows velocities preferentially

  17. Kinetics and ionization of extended gas in active galaxies. II. A circumnuclear starburst in the type 1 Seyfert NGC 7469

    Microsoft Academic Search

    A. S. Wilson; J. A. Baldwin; Sze-Dung Sun; A. E. Wright

    1986-01-01

    Long-slit, high-dispersion mapping of the emission lines H-beta, forbidden O III 4959 A, 5007 A, H-alpha, and forbidden N II 6548 A, 6584 A in the circumnuclear regions of the type I Seyfert galaxy NGC 7469 is reported. The spatially extended, emission line gas is found to be made up of two components. One is highly excited, shows velocities preferentially

  18. A Search for X-ray Counterparts to Candidate Radio Supernova Remnants in the Galaxy NGC 4258

    NASA Astrophysics Data System (ADS)

    Grimes, Caleb; Pannuti, T.; Laine, S.

    2012-01-01

    We present a search for X-ray counterparts to known candidate radio supernova remnants (SNRs) in the nearby spiral galaxy NGC 4258. This galaxy features an enhanced rate of star formation compared to normal spirals: numerous discrete radio sources - including the candidate radio SNRs - were identified by a survey conducted by Hyman et al. (2001) at 6cm and 20cm: the radio luminosities of several of these sources as calculated by Hyman et al. 2001 exceed the radio luminosity of the Galactic SNR Cassiopeia A. To conduct our search, we have downloaded archival X-ray observations made of this galaxy using the Chandra X-ray Observatory: the superior angular resolution attained by Chandra (approximately one arcsecond) is essential for identifying X-ray counterparts to the candidate radio SNRs with significant positional confidence. Results from our analysis have identified two possible X-ray binary sources associated (within 2.5 arcseconds) with highly luminous candidate radio SNRs identified by Hyman et al. 2001. We have analyzed the properties of analogous extragalactic X-ray binary systems with candidate radio SNR counterparts -- namely MF16 and X-7 in NGC 6946 and M81 respectively -- as well as the Galactic X-ray binary/radio SNR system SS433/W50 to provide a context for these systems found in NGC 4258. We have also searched for other candidate X-ray SNRs based on their soft X-ray spectra sources coincident with regions of H-alpha emission in the galaxy NGC 4258. Results will be presented and discussed.

  19. Interferometric 12CO J = 2-1 Image of the Nuclear Region of Seyfert 1 Galaxy NGC 1097

    Microsoft Academic Search

    Pei-Ying Hsieh; Satoki Matsushita; Jeremy Lim; Kotaro Kohno; Satoko Sawada-Satoh

    2008-01-01

    We have mapped the central region of the Seyfert 1 galaxy NGC 1097 in 12CO J=2-1 with the Submillieter Array (SMA). The 12CO J=2-1 map shows a central concentration and a surrounding ring coinciding, respectively, with the Seyfert nucleus and a starburst ring. The line intensity peaks at the nucleus, whereas in a previously published 12 CO J=1-0 map the

  20. ROSAT detection of diffuse hot gas in the edge-on galaxy NGC 4631

    NASA Technical Reports Server (NTRS)

    Wang, Q. David; Walterbos, Rene A. M.; Steakley, Michael F.; Norman, Colin A.; Braun, Robert

    1994-01-01

    ROSAT observation is presented of the edge-on spiral galaxy NGC 4631, a nearby Sc/SBd galaxy best known for its extended radio halo. Because of the low foreground Galactic X-ray-absorbing gas column density, N(sub H) approximately 1.4 x 10(exp 20)cm(exp -2), this observation is sensitive to gas of temperature greater than or equal to a few times 10(exp 5) K. A soft (approximately 0.25 keV) X-ray radiation out to more than 8 kpc above the midplane of the galaxy was detected. The strongest X-ray emission in the halo is above the central disk, a region of about 3 kpc radius which shows high star formation activity. The X-ray emission in the halo is bordered by two extended filaments of radio continuum emission. Diffuse X-ray emission from hot gas in the galaxy's disk was found. The spectrum of the radiation can be characterized by a thermal plasma with a temperature of 3 x 10(exp 6) K and a radiative cooling rate of approximately 8 x 10(exp 39) ergs s(exp -1). This rate is only a few percent of the estimated supernova energy release in the interstellar medium of the galaxy. Analysis of the X-ray spectrum shows evidence for the presence of a cooler (several times 10(exp 5) K) halo gas component that could consume a much larger fraction of the supernova energy. Strong evidence was found for disk/halo interaction. Hot gas apparently blows out from supershells in the galaxy's disk at a rate of approximately 1 solar mass yr(exp -1). This outflow of hot gas drags magnetic field lines up in the halo and forms a magnetized gaseous halo. If the magnetic field lines are still anchored to the disk gas at large disk radii, the outflowing gas may be confined high above the disk by magnetic pressure. A strong X-ray source which coincides spatially with an H I supershell has been identified. However, the source is likely an extremely luminous X-ray binary with L(sub chi)(0.1 - 2 keV) approximately 5 x 10(exp 39) ergs s(exp -1), which makes it a stellar mass black hole candidate.

  1. Interplay between chaotic and regular motion in a time-dependent barred galaxy model

    NASA Astrophysics Data System (ADS)

    Manos, T.; Bountis, T.; Skokos, Ch

    2013-06-01

    We study the distinction and quantification of chaotic and regular motion in a time-dependent Hamiltonian barred galaxy model. Recently, a strong correlation was found between the strength of the bar and the presence of chaotic motion in this system, as models with relatively strong bars were shown to exhibit stronger chaotic behavior compared to those having a weaker bar component. Here, we attempt to further explore this connection by studying the interplay between chaotic and regular behavior of star orbits when the parameters of the model evolve in time. This happens for example when one introduces linear time dependence in the mass parameters of the model to mimic, in some general sense, the effect of self-consistent interactions of the actual N-body problem. We thus observe, in this simple time-dependent model also, that the increase of the bar’s mass leads to an increase of the system’s chaoticity. We propose a new way of using the generalized alignment index (GALI) method as a reliable criterion to estimate the relative fraction of chaotic versus regular orbits in such time-dependent potentials, which proves to be much more efficient than the computation of Lyapunov exponents. In particular, GALI is able to capture subtle changes in the nature of an orbit (or ensemble of orbits) even for relatively small time intervals, which makes it ideal for detecting dynamical transitions in time-dependent systems. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Lyapunov analysis: from dynamical systems theory to applications’.

  2. Spatial Distributions of Dust and Polycyclic Aromatic Hydrocarbons in the Nearby Elliptical Galaxy NGC 4589 Observed with AKARI

    NASA Astrophysics Data System (ADS)

    Kaneda, Hidehiro; Suzuki, Toyoaki; Onaka, Takashi; Okada, Yoko; Sakon, Itsuki

    2008-12-01

    We report on near- to far-infrared (IR) observations of the nearby elliptical galaxy NGC 4589 by AKARI. NGC 4589 has acomplex stellar rotation field with aposition angle difference of 45° between the kinematic and morphological axes, although its morphology shows asmooth optical profile that closely follows the de Vaucouleurs law. The galaxy has aminor-axis dust lane, which is twisted toward the main stellar rotation. These properties strongly support that the galaxy is arelatively old merger remnant. We have obtained the spatial distributions of dust from far-IR emission and near-IR absorption, separately. We have also estimated the distribution of polycyclic aromatic hydrocarbons (PAHs) from the difference between images in the mid-IR bands. The spatial distributions of the dust and PAHs resemble each other, both showing significant deviations from the smooth stellar distribution. They extend to the main stellar rotation and the direction of the twisted inner dust lane, thus following the relics of the merger. Therefore, alarge fraction of the dust and PAHs in NGC 4589 are likely to originate from apast merger event.

  3. Hubble space telescope absolute proper motions of NGC 6681 (M70) and the sagittarius dwarf spheroidal galaxy

    SciTech Connect

    Massari, D.; Ferraro, F. R.; Dalessandro, E.; Lanzoni, B. [Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, v.le Berti Pichat 6/2, I-40127 Bologna (Italy); Bellini, A.; Van der Marel, R. P.; Anderson, J. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2013-12-10

    We have measured absolute proper motions for the three populations intercepted in the direction of the Galactic globular cluster NGC 6681: the cluster itself, the Sagittarius dwarf spheroidal galaxy, and the field. For this, we used Hubble Space Telescope ACS/WFC and WFC3/UVIS optical imaging data separated by a temporal baseline of 5.464 yr. Five background galaxies were used to determine the zero point of the absolute-motion reference frame. The resulting absolute proper motion of NGC 6681 is (?{sub ?}cos ?, ?{sub ?}) = (1.58 ± 0.18, –4.57 ± 0.16) mas yr{sup –1}. This is the first estimate ever made for this cluster. For the Sgr dSph we obtain (?{sub ?}cos ?, ?{sub ?}) = –2.54 ± 0.18, –1.19 ± 0.16) mas yr{sup –1}, consistent with previous measurements and with the values predicted by theoretical models. The absolute proper motion of the Galaxy population in our field of view is (?{sub ?}cos ?, ?{sub ?}) = (– 1.21 ± 0.27, –4.39 ± 0.26) mas yr{sup –1}. In this study we also use background Sagittarius Dwarf Spheroidal stars to determine the rotation of the globular cluster in the plane of the sky and find that NGC 6681 is not rotating significantly: v {sub rot} = 0.82 ± 1.02 km s{sup –1} at a distance of 1' from the cluster center.

  4. Long-Lived Triaxiality in the Dynamically Old Elliptical Galaxy NGC 4365: A Limit on Chaos and Black Hole Mass

    E-print Network

    Thomas S. Statler; Eric Emsellem; Reynier F. Peletier; Roland Bacon

    2004-06-03

    Supermassive black holes in the centres of giant elliptical galaxies are thought to induce chaos and eliminate triaxiality in their hosts. We address whether this process operates in real systems, by modeling the stellar kinematics of the old elliptical NGC 4365. This galaxy has a mean stellar population age > 12 Gyr and is known for its kinematically decoupled core and skew rotation at larger radii. We fit the two-dimensional mean velocity field obtained by the SAURON integral-field spectrograph, and the isophotal ellipticity and position-angle profiles, using the velocity field fitting approach. We find NGC 4365 to be strongly triaxial (triaxiality parameter T approximately 0.45) and somewhat flatter than it appears. Axisymmetry or near axisymmetry (T 95% confidence. In the most probable orientation the long axis points roughly toward the observer, extending to the southwest in projection. Strong triaxiality has persisted for hundreds of dynamical times, ruling out black holes above 3 x 10^9 solar masses. The M-sigma relation predicts 4 x 10^8 solar masses, which would not preclude long-lived triaxiality and is consistent with the observations. NGC 4365 lends support to a picture in which supermassive black holes, while omnipresent in luminous giant elliptical galaxies, are not massive enough to alter their global structure through chaos.

  5. THE TWO-PHASE FORMATION HISTORY OF SPIRAL GALAXIES TRACED BY THE COSMIC EVOLUTION OF THE BAR FRACTION

    SciTech Connect

    Kraljic, Katarina; Bournaud, Frederic [Laboratoire AIM Paris-Saclay, CEA/IRFU/SAp, CNRS/INSU, Universite Paris Diderot, 91191 Gif-sur-Yvette Cedex (France); Martig, Marie [Centre for Astrophysics and Supercomputing, Swinburne University of Technology, P.O. Box 218, Hawthorn, VIC 3122 (Australia)

    2012-09-20

    We study the evolution of galactic bars and the link with disk and spheroid formation in a sample of zoom-in cosmological simulations. Our simulation sample focuses on galaxies with present-day stellar masses in the 10{sup 10}-10{sup 11} M{sub Sun} range, in field and loose group environments, with a broad variety of mass growth histories. In our models, bars are almost absent from the progenitors of present-day spirals at z > 1.5, and they remain rare and generally too weak to be observable down to z Almost-Equal-To 1. After this characteristic epoch, the fractions of observable and strong bars rise rapidly, bars being present in 80% of spiral galaxies and easily observable in two thirds of these at z {<=} 0.5. This is quantitatively consistent with the redshift evolution of the observed bar fraction, although the latter is presently known up to z Almost-Equal-To 0.8 because of band-shifting and resolution effects. Our models hence predict that the decrease in the bar fraction with increasing redshift should continue with a fraction of observable bars not larger than 10%-15% in disk galaxies at z > 1. Our models also predict later bar formation in lower-mass galaxies, in agreement with existing data. We find that the characteristic epoch of bar formation, namely redshift z Almost-Equal-To 0.8-1 in the studied mass range, corresponds to the epoch at which today's spirals acquire their disk-dominated morphology. At higher redshift, disks tend to be rapidly destroyed by mergers and gravitational instabilities and rarely develop significant bars. We hence suggest that the bar formation epoch corresponds to the transition between an early 'violent' phase of spiral galaxy formation at z {>=} 1 and a late 'secular' phase at z {<=} 0.8. In the secular phase, the presence of bars substantially contributes to the growth of the (pseudo-)bulge, but the bulge mass budget remains statistically dominated by the contribution of mergers, interactions, and disk instabilities at high redshift. Early bars at z > 1 are often short-lived, while most of the bars formed at z {<=} 1 persist down to z = 0, late cosmological gas infall being necessary to maintain some of them.

  6. AN INVESTIGATION OF THE DUST CONTENT IN THE GALAXY PAIR NGC 1512/1510 FROM NEAR-INFRARED TO MILLIMETER WAVELENGTHS

    SciTech Connect

    Liu Guilin; Calzetti, Daniela; Yun, Min S. [Astronomy Department, University of Massachusetts, Amherst, MA 01003 (United States)], E-mail: gliu@astro.umass.edu, E-mail: calzetti@astro.umass.edu, E-mail: myun@astro.umass.edu (and others)

    2010-03-15

    We combine new ASTE/AzTEC 1.1 mm maps of the galaxy pair NGC 1512/1510 with archival Spitzer IRAC and MIPS images covering the wavelength range 3.6-160 {mu}m from the SINGS project. The availability of the 1.1 mm map enables us to measure the long-wavelength tail of the dust emission in each galaxy, and in sub-galactic regions in NGC 1512, and to derive accurate dust masses. The two galaxies form a pair consisting of a large, high-metallicity spiral (NGC 1512) and a low-metallicity, blue compact dwarf (NGC 1510), which we use to compare similarities and contrast differences. Using the models of Draine and Li, the derived total dust masses are (2.4 {+-} 0.6) x 10{sup 7} M {sub sun} and (1.7 {+-} 3.6) x 10{sup 5} M {sub sun} for NGC 1512 and NGC 1510, respectively. The derived ratio of dust mass to H I gas mass for the galaxy pair, M{sub d}/M{sub H{sub 1}}{approx}0.0034, is much lower (by at least a factor of 3) than expected, as previously found by Draine et al. In contrast, regions within NGC 1512, specifically the central region and the arms, do not show such unusually low M{sub d}/M{sub H{sub 1}} ratios; furthermore, the dust-to-gas ratio is within expectations for NGC 1510. These results suggest that a fraction of the H I included in the determination of the M{sub d}/M{sub H{sub 1}} ratio of the NGC 1512/NGC 1510 pair is not associated with the star-forming disks/regions of either galaxy. Using the dust masses derived from the models of Draine and Li as references, we perform simple two-temperature modified blackbody fits to the far-infrared/millimeter data of the two galaxies and the sub-regions of NGC 1512, in order to derive and compare the dust masses associated with warm and cool dust temperature components. As generally expected, the warm dust temperature of the low-metallicity, low-mass NGC 1510 (T{sub w} {approx} 36 K) is substantially higher than the corresponding warm temperature of the high-metallicity spiral NGC 1512 (T{sub w} {approx} 24 K). In both galaxies (albeit with a large uncertainty for NGC 1510), our fits indicate that a substantial fraction (>93%) of the total dust mass is in a cool dust component, with temperatures {approx}14-16 K for NGC 1512 and {approx}15-24 K for NGC 1510. This result is similar to what is determined for a few other nearby galaxies. In contrast, the warm dust component in the sub-galactic regions of NGC 1512 represents a much larger fraction of the total dust content, in agreement with the fact that all three regions have higher specific star formation rates than the average in the galaxy; in the center, the warm dust represents about 40% of the total, while in the arms the fractions are close to {approx}20%.

  7. Chandra Observations of Diffuse Gas and Luminous X-Ray Sources around the X-Ray-bright Elliptical Galaxy NGC 1600

    NASA Astrophysics Data System (ADS)

    Sivakoff, Gregory R.; Sarazin, Craig L.; Carlin, Jeffrey L.

    2004-12-01

    We observed the X-ray-bright E3 galaxy NGC 1600 and nearby members of the NGC 1600 group with the Chandra X-Ray Observatory ACIS-S3 to study their X-ray properties. Unresolved emission dominates the observation; however, we resolved some of the emission into 71 sources, most of which are low-mass X-ray binaries associated with NGC 1600. Twenty-one of the sources have LX>2×1039 ergs s-1 (0.3-10.0 keV; assuming they are at the distance of NGC 1600), marking them as ultraluminous X-ray point source (ULX) candidates; we expect that only 11+/-2 are unrelated foreground/background sources. NGC 1600 may have the largest number of ULX candidates in an early-type galaxy to date; however, cosmic variance in the number of background active galactic nuclei cannot be ruled out. The spectrum and luminosity function (LF) of the resolved sources are more consistent with sources found in other early-type galaxies than with sources found in star-forming regions of galaxies. The source LF and the spectrum of the unresolved emission both indicate that there are a large number of unresolved point sources. We propose that these sources are associated with globular clusters (GCs) and that NGC 1600 has a large GC specific frequency. Observations of the GC population in NGC 1600 would be very useful for testing this prediction. Approximately 50%-75% of the unresolved flux comes from diffuse gaseous emission. The spectral fits, hardness ratios, and X-ray surface brightness profile all point to two gas components. We interpret the soft inner component (a<~25'', kT~0.85 keV) as the interstellar medium of NGC 1600 and the hotter outer component (a>~25'', kT~1.5 keV) as the intragroup medium of the NGC 1600 group. The X-ray image shows several interesting structures. First, there is a central region of excess emission that is roughly cospatial with H? and dust filaments immediately west of the center of NGC 1600. There appear to be holes in the X-ray emission to the north and south of the galaxy center that are roughly coincident with the lobes of the NGC 1600 radio source. On larger scales, there is excess emission to the northeast, which we suggest may indicate the center of the group potential. The group galaxy NGC 1603 shows a tail of X-ray emission to its west that is probably due to ram pressure stripping.

  8. Spiral and bar driven peculiar velocities in Milky Way sized galaxy simulations

    E-print Network

    Grand, Robert J J; Kawata, Daisuke; Hunt, Jason A S; Famaey, Benoit; Siebert, Arnaud; Monari, Giacomo; Cropper, Mark

    2015-01-01

    We investigate the kinematic signatures induced by spiral and bar structure in a set of simulations of Milky Way-sized spiral disc galaxies. The set includes test particle simulations that follow a quasi-stationary density wave-like scenario with rigidly rotating spiral arms, and $N$-body simulations that host a bar and transient, co-rotating spiral arms. From a location similar to that of the Sun, we calculate the radial, tangential and line-of-sight peculiar velocity fields of a patch of the disc and quantify the fluctuations by computing the power spectrum from a two-dimensional Fourier transform. We find that the peculiar velocity power spectrum of the simulation with a bar and transient, co-rotating spiral arms fits very well to that of APOGEE red clump star data, while the quasi-stationary density wave spiral model without a bar does not. We determine that the power spectrum is sensitive to the number of spiral arms, spiral arm pitch angle and position with respect to the spiral arm. However, it is nece...

  9. Tracing PAHs and Warm Dust Emission in the Seyfert Galaxy NGC 1068

    E-print Network

    Justin H. Howell; Joseph M. Mazzarella; Ben H. P. Chan; Steven Lord; Jason A. Surace; David T. Frayer; P. N. Appleton; Lee Armus; Aaron S. Evans; Greg Bothun; Catherine M. Ishida; Dong-Chan Kim; Joseph B. Jensen; Barry F. Madore; David B. Sanders; Bernhard Schulz; Tatjana Vavilkin; Sylvain Veilleux; Kevin Xu

    2007-07-23

    We present a study of the nearby Seyfert galaxy NGC 1068 using mid- and far- infrared data acquired with the IRAC, IRS, and MIPS instruments aboard the Spitzer Space Telescope. The images show extensive 8 um and 24 um emission coinciding with star formation in the inner spiral approximately 15" (1 kpc) from the nucleus, and a bright complex of star formation 47" (3 kpc) SW of the nucleus. The brightest 8 um PAH emission regions coincide remarkably well with knots observed in an Halpha image. Strong PAH features at 6.2, 7.7, 8.6, and 11.3 um are detected in IRS spectra measured at numerous locations inside, within, and outside the inner spiral. The IRAC colors and IRS spectra of these regions rule out dust heated by the AGN as the primary emission source; the SEDs are dominated by starlight and PAH emission. The equivalent widths and flux ratios of the PAH features in the inner spiral are generally consistent with conditions in a typical spiral galaxy ISM. Interior to the inner spiral, the influence of the AGN on the ISM is evident via PAH flux ratios indicative of a higher ionization parameter and a significantly smaller mean equivalent width than observed in the inner spiral. The brightest 8 and 24 um emission peaks in the disk of the galaxy, even at distances beyond the inner spiral, are located within the ionization cones traced by [O III]/Hbeta, and they are also remarkably well aligned with the axis of the radio jets. Although it is possible that radiation from the AGN may directly enhance PAH excitation or trigger the formation of OB stars that subsequently excite PAH emission at these locations in the inner spiral, the orientation of collimated radiation from the AGN and star formation knots in the inner spiral could be coincidental. (abridged)

  10. H I observations of the nearest starburst galaxy NGC 253 with the SKA precursor KAT-7

    NASA Astrophysics Data System (ADS)

    Lucero, D. M.; Carignan, C.; Elson, E. C.; Randriamampandry, T. H.; Jarrett, T. H.; Oosterloo, T. A.; Heald, G. H.

    2015-07-01

    We present H I observations of the Sculptor group starburst spiral galaxy NGC 253, obtained with the Karoo Array Telescope (KAT-7). KAT-7 is a pathfinder for the Square Kilometre Array precursor MeerKAT, under construction. The short baselines and low system temperature of the telescope make it very sensitive to large-scale, low-surface-brightness emission. The KAT-7 observations detected 33 per cent more flux than previous Very Large Array observations, mainly in the outer parts and in the halo for a total H I mass of 2.1 ± 0.1 × 109 M?. H I can be found at large distances perpendicular to the plane out to projected distances of ˜9-10 kpc away from the nucleus and ˜13-14 kpc at the edge of the disc. A novel technique, based on interactive profile fitting, was used to separate the main disc gas from the anomalous (halo) gas. The rotation curve (RC) derived for the H I disc confirms that it is declining in the outer parts, as seen in previous optical Fabry-Perot measurements. As for the anomalous component, its RC has a very shallow gradient in the inner parts and turns over at the same radius as the disc, kinematically lagging by 100 km s-1. The kinematics of the observed extra-planar gas is compatible with an outflow due to the central starburst and galactic fountains in the outer parts. However, the gas kinematics shows no evidence for inflow. Analysis of the near-IR WISE data, shows clearly that the star formation rate is compatible with the starburst nature of NGC 253.

  11. THE HST/ACS COMA CLUSTER SURVEY. VIII. BARRED DISK GALAXIES IN THE CORE OF THE COMA CLUSTER

    SciTech Connect

    Marinova, Irina; Jogee, Shardha; Weinzirl, Tim [Department of Astronomy, University of Texas at Austin, Austin, TX (United States); Erwin, Peter [Max-Planck-Insitut fuer extraterrestrische Physik, Giessenbachstrasse, 85748 Garching (Germany); Trentham, Neil [Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA (United Kingdom); Ferguson, Henry C.; Goudfrooij, Paul [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Hammer, Derek [Department of Physics and Astronomy, Johns Hopkins, Baltimore, MD 21218 (United States); Den Brok, Mark; Peletier, Reynier F.; Kleijn, Gijs V. [Kapteyn Astronomical Institute, University of Groningen, Groningen (Netherlands); Graham, Alister W. [Centre for Astrophysics and Supercomputing, Swinburne University, Hawthorn (Australia); Carter, David; Mouhcine, Mustapha [Astrophysics Research Institute, Liverpool John Moores University, Birkenhead (United Kingdom); Balcells, Marc [Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife (Spain); Guzman, Rafael; Hoyos, Carlos [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Mobasher, Bahram [Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States); Peng, Eric W., E-mail: marinova@astro.as.utexas.edu, E-mail: sj@astro.as.utexas.edu [Department of Astronomy, Peking University, Beijing 100871 (China)

    2012-02-20

    We use high-resolution ({approx}0.''1) F814W Advanced Camera for Surveys (ACS) images from the Hubble Space Telescope ACS Treasury survey of the Coma cluster at z {approx} 0.02 to study bars in massive disk galaxies (S0s), as well as low-mass dwarf galaxies in the core of the Coma cluster, the densest environment in the nearby universe. Our study helps to constrain the evolution of bars and disks in dense environments and provides a comparison point for studies in lower density environments and at higher redshifts. Our results are: (1) we characterize the fraction and properties of bars in a sample of 32 bright (M{sub V} {approx}< -18, M{sub *} > 10{sup 9.5} M{sub Sun }) S0 galaxies, which dominate the population of massive disk galaxies in the Coma core. We find that the measurement of a bar fraction among S0 galaxies must be handled with special care due to the difficulty in separating unbarred S0s from ellipticals, and the potential dilution of the bar signature by light from a relatively large, bright bulge. The results depend sensitively on the method used: the bar fraction for bright S0s in the Coma core is 50% {+-} 11%, 65% {+-} 11%, and 60% {+-} 11% based on three methods of bar detection, namely, strict ellipse fit criteria, relaxed ellipse fit criteria, and visual classification. (2) We compare the S0 bar fraction across different environments (the Coma core, A901/902, and Virgo) adopting the critical step of using matched samples and matched methods in order to ensure robust comparisons. We find that the bar fraction among bright S0 galaxies does not show a statistically significant variation (within the error bars of {+-}11%) across environments which span two orders of magnitude in galaxy number density (n {approx} 300-10,000 galaxies Mpc{sup -3}) and include rich and poor clusters, such as the core of Coma, the A901/902 cluster, and Virgo. We speculate that the bar fraction among S0s is not significantly enhanced in rich clusters compared to low-density environments for two reasons. First, S0s in rich clusters are less prone to bar instabilities as they are dynamically heated by harassment and are gas poor as a result of ram pressure stripping and accelerated star formation. Second, high-speed encounters in rich clusters may be less effective than slow, strong encounters in inducing bars. (3) We also take advantage of the high resolution of the ACS ({approx}50 pc) to analyze a sample of 333 faint (M{sub V} > -18) dwarf galaxies in the Coma core. Using visual inspection of unsharp-masked images, we find only 13 galaxies with bar and/or spiral structure. An additional eight galaxies show evidence for an inclined disk. The paucity of disk structures in Coma dwarfs suggests that either disks are not common in these galaxies or that any disks present are too hot to develop instabilities.

  12. The stellar population study of the polar rings in the galaxies NGC 2685 and NGC 4650A

    Microsoft Academic Search

    G. M. Karataeva; I. O. Drozdovsky; N. A. Tikhonov; O. A. Galazutdinova; V. A. Yakovleva

    2003-01-01

    Polar ring galaxies (PRGs) are dynamically peculiar systems with a ring or annulus of gas, stars and dust orbiting in a plane nearly perpendicular to the equatorial plane of the host galaxy (Withmore 1990). According to the most popular point of view, PRGs are the result of galaxy interaction, which ranges from simple gas accretion to a complete merger. Alternatively,

  13. Ionized Gas and Intrinsic Magnetic Fields in the Spiral Galaxy NGC6946

    NASA Astrophysics Data System (ADS)

    Ehle, M.; Beck, R.

    1993-06-01

    The spiral galaxy NGC 6946 was observed in radio continuum at ?2.8 cm with the Effelsberg 100-m telescope both in total intensity and linear polarization at 68" (~2.5 kpc) angular resolution. The distribution of polarized intensity at ?2.8 cm is rather symmetric with respect to the nucleus, in contrast to observations at decimeter wavelengths which are strongly affected by asymmetric Faraday depolarization effects. A consistent model for Faraday rotation, depolarization and thermal radio emission is presented in which most of the ionized gas resides in small clouds within a thin disk of ~100 pc full thickness. Each cloud has a mean electron density of 5.4 +/- 2.7 cm^-3^, decreasing with galactocentric radius proportional to the star-formation rate, and a mean size of ~1 pc. Their averages of = 0.27+/-0.05cm^-3^ and = 1.5 +/- 0.7 cm^-6^ are higher than the values for classical HII regions and for the diffuse ionized gas in our Galaxy. The average filling factor in NGC 6946 of f = 0.05 +/- 0.03 is ~ 3x higher than for the suspected similar population of small H II regions in our Galaxy. The uniform component of the intrinsic magnetic field almost precisely follows the spiral arms. The strongest polarized intensities and degrees of polarization (up to 19%) occur in interarm regions. The pitch angles in interarm regions are smaller than those in the spiral arms which indicates an influence of the density-wave gas flow on the field lines. A large fraction of the magnetic field is ordered on scalelengths below 2.5 kpc, not yet resolved by the present observations. The observed large-scale structure of the uniform magnetic field and the general distribution of polarized intensities are fairly well simulated by a dynamo model (axisymmetric spiral mode S0). The model parameters indicate that the dynamo does not only operate in the disk, but also in the halo. Faraday rotation between ?2.8 cm and ?6.3 cm shows a singly-periodical variation with azimuthal angle in the plane of NGC 6946 giving further support to an axisymmetric S0 field. The Faraday rotation measures (RM) are explained by the thin disk of small HII regions containing a uniform field of 12 +/- 2 microG. At ?20.5 cm the thickness effective for RM is reduced to ~15 pc because the disk is no longer transparent to polarized radio waves due to Faraday depolarization. A close correspondence between RM and HI velocity dispersion is interpreted in terms of vertical field lines due to Parker instabilities or outflow of gas.

  14. The Nature of Infrared Emission in the Local Group Dwarf Galaxy NGC 6822 As Revealed by Spitzer

    E-print Network

    John M. Cannon; Fabian Walter; Lee Armus; George J. Bendo; Daniela Calzetti; Bruce T. Draine; Charles W. Engelbracht; George Helou; Robert C. Kennicutt Jr.; Claus Leitherer; Helene Roussel; Caroline Bot; Brent Buckalew; Daniel A. Dale; W. J. G. de Blok; Karl D. Gordon; David J. Hollenbach; Thomas H. Jarrett; Martin J. Meyer; Eric J. Murphy; Kartik Sheth; Michele D. Thornley

    2006-08-11

    We present Spitzer imaging of the metal-deficient (Z ~30% Z_sun) Local Group dwarf galaxy NGC 6822. On spatial scales of ~130 pc, we study the nature of IR, H alpha, HI, and radio continuum emission. Nebular emission strength correlates with IR surface brightness; however, roughly half of the IR emission is associated with diffuse regions not luminous at H alpha (as found in previous studies). The global ratio of dust to HI gas in the ISM, while uncertain at the factor of ~2 level, is ~25 times lower than the global values derived for spiral galaxies using similar modeling techniques; localized ratios of dust to HI gas are about a factor of five higher than the global value in NGC 6822. There are strong variations (factors of ~10) in the relative ratios of H alpha and IR flux throughout the central disk; the low dust content of NGC 6822 is likely responsible for the different H alpha/IR ratios compared to those found in more metal-rich environments. The H alpha and IR emission is associated with high-column density (> ~1E21 cm^-2) neutral gas. Increases in IR surface brightness appear to be affected by both increased radiation field strength and increased local gas density. Individual regions and the galaxy as a whole fall within the observed scatter of recent high-resolution studies of the radio-far IR correlation in nearby spiral galaxies; this is likely the result of depleted radio and far-IR emission strengths in the ISM of this dwarf galaxy.

  15. The SLUGGS survey: multipopulation dynamical modelling of the elliptical galaxy NGC 1407 from stars and globular clusters

    NASA Astrophysics Data System (ADS)

    Pota, Vincenzo; Romanowsky, Aaron J.; Brodie, Jean P.; Peñarrubia, Jorge; Forbes, Duncan A.; Napolitano, Nicola R.; Foster, Caroline; Walker, Matthew G.; Strader, Jay; Roediger, Joel C.

    2015-07-01

    We perform in-depth dynamical modelling of the luminous and dark matter (DM) content of the elliptical galaxy NGC 1407. Our strategy consists of solving the spherical Jeans equations for three independent dynamical tracers: stars, blue globular clusters (GCs) and red GCs in a self-consistent manner. We adopt a maximum-likelihood Markov Chain Monte Carlo fitting technique in the attempt to constrain the inner slope of the DM density profile (the cusp/core problem), and the stellar initial mass function (IMF) of the galaxy. We find the inner logarithmic slope of the DM density profiles to be ? = 0.6 ± 0.4, which is consistent with either a DM cusp (? = 1) or with a DM core (? = 0). Our findings are consistent with a Salpeter IMF, and marginally consistent with a Kroupa IMF. We infer tangential orbits for the blue GCs, and radial anisotropy for red GCs and stars. The modelling results are consistent with the virial mass-concentration relation predicted by ? cold dark matter (CDM) simulations. The virial mass of NGC 1407 is log Mvir = 13.3 ± 0.2M?, whereas the stellar mass is log M* = 11.8 ± 0.1 M?. The overall uncertainties on the mass of NGC 1407 are only 5 per cent at the projected stellar effective radius. We attribute the disagreement between our results and previous X-ray results to the gas not being in hydrostatic equilibrium in the central regions of the galaxy. The halo of NGC 1407 is found be DM-dominated, with a dynamical mass-to-light ratio of M/L=260_{-100} ^{+174} M_{?}/L_{?, B}. However, this value can be larger up to a factor of 3 depending on the assumed prior on the DM scale radius.

  16. A multi-wavelength view of the central kiloparsec region in the luminous infrared galaxy NGC 1614

    SciTech Connect

    Herrero-Illana, Rubén; Pérez-Torres, Miguel Á.; Alberdi, Antxon; Hernández-García, Lorena [Instituto de Astrofísica de Andalucía-CSIC, P.O. Box 3004, E-18008 Granada (Spain); Alonso-Herrero, Almudena [Instituto de Física de Cantabria, CSIC-Universidad de Cantabria, E-39005 Santander (Spain); Colina, Luis [Centro de Astrobiología (INTA-CSIC), Ctra. de Torrejón a Ajalvir, km 4, E-28850 Torrejón de Ardoz, Madrid (Spain); Efstathiou, Andreas [School of Sciencies, European University Cyprus, Diogenes Street, Engomi, 1516 Nicosia (Cyprus); Miralles-Caballero, Daniel [Instituto de Física Teórica, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Väisänen, Petri [South African Astronomical Observatory, P.O. Box 9, Observatory 7935 Cape Town (South Africa); Packham, Christopher C. [Department of Physics and Astronomy, University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249 (United States); Rajpaul, Vinesh [Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom); Zijlstra, Albert A. [Jodrell Bank Centre for Astrophysics, University of Manchester, Manchester M13 9PL (United Kingdom)

    2014-05-10

    The Luminous Infrared Galaxy NGC 1614 hosts a prominent circumnuclear ring of star formation. However, the nature of the dominant emitting mechanism in its central ?100 pc is still under debate. We present sub-arcsecond angular resolution radio, mid-infrared, Pa?, optical, and X-ray observations of NGC 1614, aimed at studying in detail both the circumnuclear ring and the nuclear region. The 8.4 GHz continuum emission traced by the Very Large Array and the Gemini/T-ReCS 8.7 ?m emission, as well as the Pa? line emission, show remarkable morphological similarities within the star-forming ring, suggesting that the underlying emission mechanisms are tightly related. We used a Hubble Space Telescope/NICMOS Pa? map of similar resolution to our radio maps to disentangle the thermal free-free and non-thermal synchrotron radio emission, from which we obtained the intrinsic synchrotron power law for each individual region within the central kiloparsec of NGC 1614. The radio ring surrounds a relatively faint, steep-spectrum source at the very center of the galaxy, suggesting that the central source is not powered by an active galactic nucleus (AGN), but rather by a compact (r ? 90 pc) starburst (SB). Chandra X-ray data also show that the central kiloparsec region is dominated by SB activity, without requiring the existence of an AGN. We also used publicly available infrared data to model-fit the spectral energy distribution of both the SB ring and a putative AGN in NGC 1614. In summary, we conclude that there is no need to invoke an AGN to explain the observed bolometric properties of the galaxy.

  17. Positional Coincidence of H2O Maser and a Plasma Obscuring Torus in Radio Galaxy NGC 1052

    E-print Network

    Satoko Sawada-Satoh; Seiji Kameno; Kayoko Nakamura; Daichi Namikawa; Katsunori M. Shibata; Makoto Inoue

    2008-02-28

    We present multi-frequency simultaneous VLBA observations at 15, 22 and 43 GHz towards the nucleus of the nearby radio galaxy NGC 1052. These three continuum images reveal a double-sided jet structure, whose relative intensity ratios imply that the jet axis is oriented close to the sky plane. The steeply rising spectra at 15-43 GHz at the inner edges of the jets strongly suggest that synchrotron emission is absorbed by foreground thermal plasma. We detected H2O maser emission in the velocity range of 1550-1850 km/s, which is redshifted by 50-350 km/s with respect to the systemic velocity of NGC 1052. The redshifted maser gas appears projected against both sides of the jet, in the same manner as the HI seen in absorption. The H2O maser gas are located where the free-free absorption opacity is large. This probably imply that the masers in NGC 1052 are associated with a circumnuclear torus or disk as in the nucleus of NGC 4258. Such circumnuclear structure can be the sence of accreting onto the central engine.

  18. The Cepheid distance to the maser-host galaxy NGC 4258: Studying systematics with the Large Binocular Telescope

    E-print Network

    Fausnaugh, M M; Gerke, J R; Macri, L M; Riess, A G; Stanek, K Z

    2014-01-01

    We identify and phase a sample of 81 Cepheids in the maser-host galaxy NGC 4258 using the Large Binocular Telescope (LBT), and obtain calibrated mean magnitudes in up to 4 filters for a subset of 43 Cepheids using archival HST data. We employ 3 models to study the systematic effects of extinction, the assumed extinction law, and metallicity on the Cepheid distance to NGC 4258. We find a correction to the Cepheid colors consistent with a grayer extinction law in NGC 4258 compared to the Milky Way ($R_V =4.9$), although we believe this is indicative of other systematic effects. If we combine our Cepheid sample with previously known Cepheids, we find a significant metallicity adjustment to the distance modulus of $\\gamma_1 = -0.60 \\pm 0.21$ mag/dex, for the Zaritsky et al. (1994) metallicity scale, as well as a weak trend of Cepheid colors with metallicity. Conclusions about the absolute effect of metallicity on Cepheid mean magnitudes appear to be limited by the available data on the metallicity gradient in NGC...

  19. Co Observations of Edge-on Galaxies. IV, NGC 4565: Radial Variation of the H2-to-Hi Ratio

    E-print Network

    Y. Sofue; N. Nakai

    1993-08-31

    The edge-on galaxy NGC 4565 has been observed in the 12CO(J=1-0)-line emission using the Nobeyama 45-m telescope with an angular resolution of 15". We obtained a scan along the major axis for +/-5' (+/- 15 kpc) about the galactic center, and some scans perpendicular to the galactic plane. The radial density distribution shows a dense molecular gas ring of 5 kpc radius, which is associated with an HI ring. The molecular disk comprises two components: an unresolved thin and dense disk, and a thick disk (or a halo) extending to a height greater than 1.4 kpc. The position-velocity diagram shows that the general rotation of the entire galaxy is circular with a flat rotation curve. However, the radial distribution of molecular gas is asymmetric with respect to the galaxy center in the sense that the molecular gas is much richer in the NW side. We derived a radial variation of \\htwo-to-(HI+ \\htwo) density ratio, and found that int erstellar gas in the central 4 kpc region is almost entirely H2, while HI is dominant beyond 10 kpc. A similar HI-vs-\\htwo\\ behavior was found in the edge-on galaxy NGC 891.

  20. Multiwavelength Study of the Starburst Galaxy NGC 7714. II The Balance between Young, Intermediate Age and Old Stars

    E-print Network

    Lançon, A; Leitherer, C; González-Delgado, R M; Lancon, Ariane; Goldader, Jeff D.; Leitherer, Claus; Delgado, Rosa M. Gonzalez

    2001-01-01

    We combine existing multiwavelength data (incl. an HST/GHRS UV spectrum, an optical spectrum, far-IR, Xray and radio fluxes) with new HST/WFPC2 images, near-IR photometry and K band spectroscopy. We use these data to constrain the young, the intermediate age and the old stellar populations in the central 330 pc of the starburst galaxy NGC 7714. [...] We find that the young burst responsible for the UV light is only a small part of an extended episode of enhanced star formation (SF) [...]. The mass of young and intermediate age stars thus formed equals at least 10% of the mass locked in pre-existing stars of the underlying galaxy nucleus [...]. The spectrophotometric SF timescale is long compared to the ~110 Myr elapsed since closest contact with NGC 7715. The trigger of the starburst remains elusive. NGC 7714 owes its brightness in the UV to a few low extinction lines of sight towards young stars. [...] The different extinction estimates obtained from different indicators result naturally from the coexistence...

  1. Witness of gas infall and outflow in the young starburst dwarf galaxy NGC 5253

    NASA Astrophysics Data System (ADS)

    Miura, Rie E.; Espada, Daniel; Sugai, Hajime; Nakanishi, Kouichiro; Hirota, Akihiko

    2014-12-01

    We present 12CO(2-1) observations towards the dwarf galaxy NGC 5253 using the Submillimeter Array. The data shows that a large amount of molecular gas is located in the central ˜ 200 pc starburst region, physically associated with two young super stellar clusters (SSCs). The molecular gas traced by 12CO(2-1) is elongated along the minor axis (dust lane) of the galaxy and its kinematics suggest that there is an inflow of molecular gas to the direction of the central SSCs, as is also observed in H I gas at a larger scale. Due to their correlation in spatial and velocity domains, the central SSCs were likely formed from molecular gas in the nucleus. We compare the 12CO(2-1) with available H2 1-0 S(1) data, and show that while the relatively cold gas traced by 12CO(2-1) is distributed around the central starburst region but also along the dust lane, the warm gas traced by H2 1-0 S(1) is associated with the central H II region and other star-forming regions. Interestingly, a cavity in the H2 1-0 S(1) emission is found to be spatially correlated with a H? shell. This H? shell may trace a bipolar outflow from the central SSCs and the H2 1-0 S(1) gas, the gas shocked by the outflow encountering the surrounding quiescent gas. We calculate a molecular gas inflow rate of ˜ 2 M? yr-1, a star formation rate of 0.3-0.5 M? yr-1, and an ionized gas outflow being emitted from the SSCs with a rate of (5-25)× 10-3 f M? yr-1, where f is a volume filling factor.

  2. NGC 1266: Characterization of the Nuclear Molecular Gas in an Unusual SB0 Galaxy

    NASA Astrophysics Data System (ADS)

    Glenn, J.; Rangwala, N.; Maloney, P. R.; Kamenetzky, J. R.

    2015-02-01

    With a substantial nuclear molecular gas reservoir and broad, high-velocity CO molecular line wings previously interpreted as an outflow, NGC 1266 is a rare SB0 galaxy. Previous analyses of interferometry, spectrally resolved low-J CO emission lines, and unresolved high-J emission lines have established basic properties of the molecular gas and the likely presence of an active galactic nucleus. Here, new spectrally resolved CO J = 5-4 to J = 8-7 lines from Herschel Space Observatory HIFI observations are combined with ground-based observations and high-J Herschel SPIRE observations to decompose the nuclear and putative outflow velocity components and to model the molecular gas to quantify its properties. Details of the modeling and results are described, with comparisons to previous results and exploration of the implications for the gas excitation mechanisms. Among the findings, like for other galaxies, the nuclear and putative outflow molecular gas are well represented by components that are cool (T_nuclear {=} 6+10-2 K and T outflow ~ 30 K), comprising bulk of the mass (log M_nuclear/M? {=} 8.3+0.5-0.4 and log M_outflow/M? {=} 7.6+0.3-0.3), and the minority of the luminosity (log L_nuclear/L? {=} 5.44+0.22-0.18 and log L outflow/L ? ~ 6.5) and warm (T_nuclear {=} 74+130-26 K and T outflow > 100 K), comprising a minority of the mass (log M_nuclear/M? {=} 7.3+0.5-0.5 and log M outflow/M ? ~ 6.3) but the majority of the luminosity (log L_nuclear/L? {=} 6.90+0.16-0.16 and log L outflow/L ? ~ 7.2). The outflow has an anomalously high L CO/L FIR of 1.7 × 10-3 and is almost certainly shock excited.

  3. Rapid Compton-thick/Compton-thin Transitions in the Seyfert 2 Galaxy NGC 1365

    NASA Technical Reports Server (NTRS)

    Risaliti, G.; Elvis, M.; Fabbiano, G.; Baldi, A.; Zezas, A.

    2006-01-01

    We present multiple Chandra and XMM-Newton observations of the type 1.8 Seyfert galaxy NGC 1365, which shows the most dramatic X-ray spectral changes observed so far in an active galactic nucleus: the source switched from reflection-dominated to transmission-dominated and back in just 6 weeks. During this time the soft thermal component, arising from a approx. 1 kpc region around the center, remained constant. The reflection component is constant at all timescales, and its high flux relative to the primary component implies the presence of thick gas covering a large fraction of the solid angle. The presence of this gas, and the fast variability timescale, suggest that the Compton-thick to Compton-thin change is due to variation in the line-of-sight absorber rather than to extreme intrinsic emission variability. We discuss a structure of the circumuclear absorber/reflector that can explain the observed X-ray spectral and temporal properties.

  4. Dynamics of the NGC 4636 Globular Cluster System - An extremely dark matter dominated galaxy?

    E-print Network

    Schuberth, Y; Hilker, M; Kissler-Patig, M; Larsen, S S; Mebold, U; Richtler, T

    2006-01-01

    We present the first dynamical study of the globular cluster system of NGC 4636. This giant elliptical galaxy is claimed to be extremely dark matter dominated, according to X-ray observations. Using the VLT with FORS2/MXU, we obtained velocities for 174 globular clusters. The clusters have projected galactocentric distances in the range 4 to 70 kpc, the overwhelming majority lie within 30 kpc. We find some indication for a rotation of the red (metal-rich) clusters about the minor axis. Out to a radius of 30 kpc, we find a roughly constant projected velocity dispersion for the blue clusters of ~200 km/s. The red clusters exhibit a distinctly different behavior: at a radius of about 13 kpc, the velocity dispersion drops by ~50 km/s to about 170 km/s which then remains constant out to a radius of 30 kpc. Using only the blue clusters as dynamical tracers, we perform Jeans-analyses for different assumptions of the orbital anisotropy. Depending on the anisotropy and the adopted M/L-values, we find that the dark mat...

  5. Unveiling the Ongoing Star Formation in the Starburst Galaxy NGC 253

    NASA Astrophysics Data System (ADS)

    Minh, Y. C.; Muller, S.; Liu, S.-Y.; Yoon, T. S.

    2007-06-01

    The H2S 22, 0-21, 1 and SO 55-44 transitions were observed simultaneously toward the starburst galaxy NGC 253 using the Submillimeter Array. Two H2S emission peaks are found at positions ~2" northeast (30 pc) and ~5" southwest (80 pc) from the galactic center, associated with the circumnuclear disk and coinciding with the inner ring structure seen on the SiO map by García-Burillo and coworkers. SO emission is detected, weakly, only toward the northeast. By combining data in the literature, we estimate H2S rotational temperatures of 130 K toward the northeast H2S peak and 46 K toward the southwest peak and derive H2S column densities of ~3 and ~1×1015 cm-2 and SO column densities of ~4 and <=3×1014 cm-2 toward the northeast and southwest peaks, respectively. The fractional abundances, relative to molecular hydrogen, are f~(1-3)×10-8 and 4×10-9 for H2S and SO, comparable with the values observed in Galactic massive star forming cores. The H2S emission is supposed to trace the ongoing star formation through hot core activity, and a rough comparison with the massive star forming region Orion KL indicates that several thousands of Orion KL-like cores may exist toward each of the H2S peaks.

  6. Disk mass and disk heating in the spiral galaxy NGC 3223

    E-print Network

    Gentile, G; Baes, M; De Geyter, G; Koleva, M; Angus, G W; de Blok, W J G; Saftly, W; Viaene, S

    2015-01-01

    We present the stellar and gaseous kinematics of an Sb galaxy, NGC 3223, with the aim of determining the vertical and radial stellar velocity dispersion as a function of radius, which can help to constrain disk heating theories. Together with the observed NIR photometry, the vertical velocity dispersion is also used to determine the stellar mass-to-light (M/L) ratio, typically one of the largest uncertainties when deriving the dark matter distribution from the observed rotation curve. We find a vertical-to-radial velocity dispersion ratio of sigma_z/sigma_R=1.21+-0.14, significantly higher than expectations from known correlations, and a weakly-constrained Ks-band stellar M/L ratio in the range 0.5-1.7, at the high end of (but consistent with) the predictions of stellar population synthesis models. Such a weak constraint on the stellar M/L ratio, however, does not allow us to securely determine the dark matter density distribution. To achieve this, either a statistical approach or additional data (e.g. integr...

  7. THE NEAR VICINITY OF THE BLACK HOLE AT THE CORE OF GALAXY NGC 4261 - ARTIST CONCEPT

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This is an illustration of how the night sky might look to a dweller in the core of galaxy NGC 4261, which harbors an 800-light-year-wide disk of dust and 1.2 billion-solar-mass black hole. This imaginary view is from a hypothetical planet inside the dust dusk, looking toward the black hole. The black hole's white-hot glow from super-heated gas is reddened by intervening dust. A 'lighthouse beam' from the hot accretion disk around the black hole, along with invisible radio jets, radiates above and below the hole at right angles to the dark dust disk encircling the hole. This dark, dusty disk bisects the sky, blocking out light from the star behind it, and reddening starlight traveling near it by optical scattering - much in the same way the sunlight turns red at sunset by scatter from dust in our atmosphere. The imaginary planet, and surrounding stars, are destined to be swallowed by the black hole, and material in the disk spirals into its gravitational abyss. Illustration by J. Gitlin (Space Telescope Science Institute)

  8. Disk mass and disk heating in the spiral galaxy NGC 3223

    NASA Astrophysics Data System (ADS)

    Gentile, G.; Tydtgat, C.; Baes, M.; De Geyter, G.; Koleva, M.; Angus, G. W.; de Blok, W. J. G.; Saftly, W.; Viaene, S.

    2015-04-01

    We present the stellar and gaseous kinematics of an Sb galaxy, NGC 3223, with the aim of determining the vertical and radial stellar velocity dispersion as a function of radius, which can help to constrain disk heating theories. Together with the observed NIR photometry, the vertical velocity dispersion is also used to determine the stellar mass-to-light (M/L) ratio, typically one of the largest uncertainties when deriving the dark matter distribution from the observed rotation curve. We find a vertical-to-radial velocity dispersion ratio of ?z/?R = 1.21 ± 0.14, significantly higher than expectations from known correlations, and a weakly-constrained Ks-band stellar M/L ratio in the range 0.5-1.7, which is at the high end of (but consistent with) the predictions of stellar population synthesis models. Such a weak constraint on the stellar M/L ratio, however, does not allow us to securely determine the dark matter density distribution. To achieve this, either a statistical approach or additional data (e.g. integral-field unit) are needed. Based on observations collected at the European Southern Observatory, Chile, under proposal 68.B-0588.

  9. Stellar metallicity of the extended disk and distance of the spiral galaxy NGC 3621

    SciTech Connect

    Kudritzki, Rolf-Peter; Bresolin, Fabio; Hosek, Matthew W. Jr. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Urbaneja, Miguel A.; Przybilla, Norbert, E-mail: kud@ifa.hawaii.edu, E-mail: bresolin@ifa.hawaii.edu, E-mail: mwhosek@ifa.hawaii.edu, E-mail: Miguel.Urbaneja-Perez@uibk.ac.at, E-mail: Norbert.Przybilla@uibk.ac.at [Institute for Astro- and Particle Physics, University of Innsbruck, Technikerstr. 25/8, A-6020 Innsbruck (Austria)

    2014-06-10

    Low resolution (?4.5 Å) ESO VLT/FORS spectra of blue supergiant stars are analyzed to determine stellar metallicities (based on elements such as iron, titanium, and magnesium) in the extended disk of the spiral galaxy, NGC 3621. Mildly subsolar metallicity (–0.30 dex) is found for the outer objects beyond 7 kpc, independent of galactocentric radius and compatible with the absence of a metallicity gradient, confirming the results of a recent investigation of interstellar medium H II region gas oxygen abundances. The stellar metallicities are slightly higher than those from the H II regions when based on measurements of the weak forbidden auroral oxygen line at 4363 Å but lower than the ones obtained with the R {sub 23} strong line method. It is shown that the present level of metallicity in the extended disk cannot be the result of chemical evolution over the age of the disk with the present rate of in situ star formation. Additional mechanisms must be involved. In addition to metallicity, stellar effective temperatures, gravities, interstellar reddening, and bolometric magnitudes are determined. After the application of individual reddening corrections for each target, the flux-weighted gravity-luminosity relationship of blue supergiant stars is used to obtain a distance modulus of 29.07 ± 0.09 mag (distance D = 6.52 ± 0.28 Mpc). This new distance is discussed in relation to Cepheid and the tip of the red giant branch distances.

  10. Evidence for a supermassive black hole in the nucleus of the Seyfert galaxy NGC 5548

    NASA Technical Reports Server (NTRS)

    Crenshaw, D. Michael; Blackwell, James H., Jr.

    1990-01-01

    The international campaign to monitor the variable Seyfert 1 galaxy NGC 5548 with the IUE has provided an extensive and well-sampled set of spectroscopic observations. These observations are used to study the response of the C IV 1550 A emission-line profile to changes in the photoionizing continuum. Near the end of the IUE campaign, the continuum flux at 1440 A and the total C IV flux dopped by factors of 2.9 and 1.8, respectively, in 16 days. The red wing of the C IV profile responded more rapidly to the sharp continuum drop than the blue wing, indicating that clouds in the inner broad-line region (BLR) are undergoing gravitational infall. These results provide direct evidence that the central engine is a supermassive object, presumably a black hole, with a mass on the order of 10 to the 7th solar masses. Analysis of the profile variations also demonstrates that excess emission in the blue wing of C IV is from a component that is physically distinct from the bulk of the BLR.

  11. A non-thermal study of the brightest cluster galaxy NGC 1275 - the Gamma-Radio connection over four decades

    NASA Astrophysics Data System (ADS)

    Dutson, K. L.; Edge, A. C.; Hinton, J. A.; Hogan, M. T.; Gurwell, M. A.; Alston, W. N.

    2014-08-01

    Emission from the active nucleus in the core of the brightest cluster galaxy of the Perseus cluster, NGC 1275, has varied dramatically over the past four decades. Prompted by the Fermi detection of flaring in the ?-ray band, we present the recent increased activity of this source in the context of its past radio and ?-ray output. The broad correspondence between the high-frequency radio data and the high-energy (HE) emission is striking. However, on short time-scales this correlation breaks down and the 1.3 mm Submillimeter Array flux is apparently unaffected during Fermi -detected flaring activity. The fact that NGC 1275 is also detected at TeV energies during the periods of HE ?-ray flaring suggests that the short-time-scale variation might be primarily related to changes in the inverse Compton scattering of photons by the electron population in the jet. The longer-time-scale changes suggest a 30-40 year variation in the fuelling of the black hole that affects the power of the inner jet. NCG 1275 is a laboratory for the class of brightest cluster galaxies, and its variability on these time-scales has implications for our understanding of massive galaxies in cooling-core clusters. The case of NGC 1275 highlights the need for wide coverage across the radio band to correctly account for the contribution to emission from a synchrotron self-absorbed core (for example when considering contamination of Sunyaev-Zel'dovich effect observations), and the danger of variability biases in radio surveys of galaxies.

  12. THE ADVANCED CAMERA FOR SURVEYS NEARBY GALAXY SURVEY TREASURY. IV. THE STAR FORMATION HISTORY OF NGC 2976

    SciTech Connect

    Williams, Benjamin F.; Dalcanton, Julianne J.; Stilp, Adrienne; Gilbert, Karoline M.; Roskar, Rok; Gogarten, Stephanie M. [Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195 (United States); Seth, Anil C. [CfA Fellow, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Weisz, Daniel; Skillman, Evan [Department of Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455 (United States); Dolphin, Andrew [Raytheon, 1151 E. Hermans Road, Tucson, AZ 85706 (United States); Holtzman, Jon, E-mail: ben@astro.washington.ed, E-mail: jd@astro.washington.ed, E-mail: roskar@astro.washington.ed, E-mail: stephanie@astro.washington.ed, E-mail: aseth@cfa.harvard.ed, E-mail: dweisz@astro.umn.ed, E-mail: skillman@astro.umn.ed, E-mail: dolphin@raytheon.co, E-mail: holtz@nmsu.ed [Department of Astronomy, New Mexico State University, Box 30001, 1320 Frenger St., Las Cruces, NM 88003 (United States)

    2010-01-20

    We present resolved stellar photometry of NGC 2976 obtained with the Advanced Camera for Surveys (ACS) as part of the ACS Nearby Galaxy Survey Treasury (ANGST) program. The data cover the radial extent of the major axis of the disk out to 6 kpc, or approx6 scale lengths. The outer disk was imaged to a depth of M{sub F606W} approx 1, and an inner field was imaged to the crowding limit at a depth of M{sub F606W} approx -1. Through detailed analysis and modeling of the resulting color-magnitude diagrams, we have reconstructed the star formation history (SFH) of the stellar populations currently residing in these portions of the galaxy, finding similar ancient populations at all radii but significantly different young populations at increasing radii. In particular, outside of the well-measured break in the disk surface brightness profile, the age of the youngest population increases with distance from the galaxy center, suggesting that star formation is shutting down from the outside-in. We use our measured SFH, along with H I surface density measurements, to reconstruct the surface density profile of the disk during previous epochs. Comparisons between the recovered star formation rates and reconstructed gas densities at previous epochs are consistent with star formation following the Schmidt law during the past 0.5 Gyr, but with a drop in star formation efficiency at low gas densities, as seen in local galaxies at the present day. The current rate and gas density suggest that rapid star formation in NGC 2976 is currently in the process of ceasing from the outside-in due to gas depletion. This process of outer disk gas depletion and inner disk star formation was likely triggered by an interaction with the core of the M81 group approx>1 Gyr ago that stripped the gas from the galaxy halo and/or triggered gas inflow from the outer disk toward the galaxy center.

  13. Elliptical galaxies with rapidly decreasing velocity dispersion profiles: NMAGIC models and dark halo parameter estimates for NGC 4494

    NASA Astrophysics Data System (ADS)

    Morganti, Lucia; Gerhard, Ortwin; Coccato, Lodovico; Martinez-Valpuesta, Inma; Arnaboldi, Magda

    2013-06-01

    NGC 4494 is one of several intermediate-luminosity elliptical galaxies inferred to have an unusually diffuse dark matter halo. We use the ?2-made-to-measure particle code NMAGIC to construct axisymmetric models of NGC 4494 from photometric and various kinematic data. The extended kinematics include light spectra in multiple slitlets out to 3.5Re, and hundreds of planetary nebula velocities out to ?7Re, thus allowing us to probe the dark matter content and orbital structure in the halo. We use Monte Carlo simulations to estimate confidence boundaries for the halo parameters, given our data and modelling set-up. We find that the true potential of the dark matter halo is recovered within ?G (merit function) ? 26 (??2 ? 59) at the 70 per cent confidence level (CL), and within ?G ? 32 (??2 ? 70) at the 90 per cent CL. These numbers are much larger than the usually assumed ??2 = 2.3 (4.6) for the 70 per cent (90 per cent) CL for two free parameters, perhaps case dependent, but calling into question the general validity of the standard assumptions used for halo and black hole mass determinations. The best-fitting models for NGC 4494 have a dark matter fraction of about 0.6 ± 0.1 at 5Re (70 per cent CL) and are embedded in a dark matter halo with circular velocity ˜200 km s-1. The total circular velocity curve (CVC) is approximately flat at vc = 220 km s-1 outside ˜0.5Re. The orbital anisotropy of the stars is moderately radial. These results are independent of the assumed inclination of the galaxy, and edge-on models are preferred. Comparing with the haloes of NGC 3379 and NGC 4697, whose velocity dispersion profiles also decrease rapidly from the centre outwards, the outer CVCs and dark matter haloes are quite similar. NGC 4494 shows a particularly high dark matter fraction inside ˜ 3Re, and a strong concentration of baryons in the centre.

  14. The Recent Cluster Formation Histories of NGC 5253 and NGC 3077: Environmental Impact on Star Formation

    E-print Network

    J. Harris; D. Calzetti; J. S. Gallagher III; D. A. Smith; C. J. Conselice

    2003-11-20

    We present multicolor photometry of bright star cluster candidates in the nearby starburst galaxies NGC 3077 and NGC 5253, observed with the Hubble Space Telescope Wide Field and Planetary Camera 2 in both broadband (F300W, F547M and F814W) and narrowband (F487N and F656N) filters. By comparing the photometry with theoretical population synthesis models, we estimate the age and mass of each star cluster, which provides constraints on the recent star formation histories of the host galaxies. We compare the star cluster populations in these dwarf starburst galaxies to those of the nuclear starburst in the barred spiral M 83, and discuss implications for our understanding of the nature and evolution of starburst events.

  15. GLOBAL SIMULATIONS OF THE MAGNETIC FIELD EVOLUTION IN BARRED GALAXIES UNDER THE INFLUENCE OF THE COSMIC-RAY-DRIVEN DYNAMO

    SciTech Connect

    Kulpa-Dybel, K.; Otmianowska-Mazur, K.; Kulesza-Zydzik, B.; Kowal, G. [Astronomical Observatory, Jagiellonian University, ul Orla 171, 30-244 Krakow (Poland); Hanasz, M.; Woltanski, D.; Kowalik, K. [Torun Centre for Astronomy, Nicolaus Copernicus University, 87-148 Torun/Piwnice (Poland)

    2011-06-01

    We present three-dimensional global numerical simulations of the cosmic-ray (CR) driven dynamo in barred galaxies. We study the evolution of the interstellar medium of the barred galaxy in the presence of non-axisymmetric component of the potential, i.e., the bar. The magnetohydrodynamical dynamo is driven by CRs, which are continuously supplied to the disk by supernova (SN) remnants. No magnetic field is present at the beginning of simulations but one-tenth of SN explosions is a source of a small-scale randomly oriented dipolar magnetic field. In all models we assume that 10% of 10{sup 51} erg SN kinetic energy output is converted into CR energy. To compare our results directly with the observed properties of galaxies, we construct realistic maps of polarized radio emission. The main result is that the CR-driven dynamo can amplify weak magnetic fields up to a few {mu}G within a few Gyr in barred galaxies. The obtained e-folding time is equal to 300 Myr and the magnetic field reaches equipartition at time t {approx} 4.0 Gyr. Initially, the completely random magnetic field evolves into large-scale structures. An even (quadrupole-type) configuration of the magnetic field with respect to the galactic plane can be observed. Additionally, the modeled magnetic field configuration resembles maps of the polarized intensity observed in barred galaxies. Polarization vectors are distributed along the bar and between spiral arms. Moreover, the drift of magnetic arms with respect to the spiral pattern in the gas density distribution is observed during the entire simulation time.

  16. The globular cluster systems of NGC 3258 and NGC 3268 in the Antlia cluster

    Microsoft Academic Search

    B. Dirsch; T. Richtler; L. P. Bassino

    2003-01-01

    The Antlia galaxy cluster is the third nearest galaxy cluster after Virgo and Fornax. We used the wide-field MOSAIC camera of the 4-m CTIO telescope to search in the brightest cluster galaxies for globular cluster systems, which were detected in the two larger ellipticals - NGC 3258 and NGC 3268. These galaxies each contain several thousand clusters; NGC 3258 more

  17. Color-magnitude Diagrams of the Star-forming Galaxies Ho IX, Cam B, NGC 2976, and UGC 1281

    NASA Astrophysics Data System (ADS)

    Georgiev, T. B.; Bomans, D. J.

    We report results on a study of nearby late type galaxies performed with the 2m RC telescope of the Rozhen NAO with with 1×1 K CCD camera. The scale and the frame size are 0.32''/pix and 5.4'×5.4', respectively. At typical seeing of 1'' the data reach routinely a limiting magnitude of ˜4 mag. With these parameters many nearby galaxies, including the members of the IC 342 and M81 groups can be resolved into star-like and diffuse objects. This allows the determination of several fundamental properties of the galaxies, based on surface photometry and study of the brightest resolved objects. The most crucial parameter is the distance to the galaxy. It can be estimated to a standard error of 20 % usi