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1

A slow bar in the dwarf irregular galaxy NGC 3741  

NASA Astrophysics Data System (ADS)

Using the Tremaine-Weinberg method, we measure the speed of the H I bar seen in the disc of NGC 3741. NGC 3741 is an extremely gas-rich galaxy with an H I disc which extends to about 8.3 times its Holmberg radius. It is also highly dark matter dominated. Our calculated value of the pattern speed ?p is 17.1 ± 3.4 km s-1 kpc-1. We also find the ratio of the corotation radius to the bar semimajor axis to be ( 1.6 ± 0.3), indicating a slow bar. This is consistent with bar models in which dynamical friction results in a slow bar in dark-matter-dominated galaxies.

Banerjee, Arunima; Patra, Narendra Nath; Chengalur, Jayaram N.; Begum, Ayesha

2013-09-01

2

Cold dust in the giant barred galaxy NGC 1365  

NASA Astrophysics Data System (ADS)

Constraining the physcial properties of dust requires observations at submm wavelengths. This will provide important insight into the gas content of galaxies. We mapped NGC 1365 at 870 ?m with LABOCA, the Large APEX Bolometer Camera, allowing us to probe the central mass concentration as well as the rate at which the gas flows to the center. We obtained the dust physical properties both globally and locally for different locations in the galaxy. A 20 K modified black body represents about 98% of the total dust content of the galaxy, the rest can be represented by a warmer dust component of 40 K. The bar exhibits an east-west asymmetry in the dust distribution: The eastern bar is heavier than the western bar by more than a factor of 4. Integrating the dust spectral energy distribution, we derived a total infrared luminosity, LTIR, of 9.8 × 1010 L?, leading to a dust-enshrouded star formation rate of SFRTIR ? 16.7 M? yr-1 in NGC 1365. We derived the gas mass from the measurements of the dust emission, resulting in a CO-to-H2 conversion factor of XCO ? 1.2 × 1020 mol cm-2 (K km s-1)-1 in the central disk, including the bar. Taking into account the metallicity variation, the central gas mass concentration is only ?20% at R < 40? (3.6 kpc). On the other hand, the timescale on which the gas flows into the center, ?300 Myr, is relatively short. This indicates that the current central mass in NGC 1365 is evolving fast because of the strong bar.

Tabatabaei, F. S.; Weiß, A.; Combes, F.; Henkel, C.; Menten, K. M.; Beck, R.; Kovács, A.; Güsten, R.

2013-07-01

3

A Counterrotating Central Component in the Barred Galaxy NGC 5728  

NASA Astrophysics Data System (ADS)

We present a detailed study of the stellar kinematics in the barred galaxy NGC 5728 based on I-band photometry and long-slit spectroscopic observations in the region of the near-IR Ca II triplet. The analysis of the stellar line-of-sight velocity distribution (LOSVD) has revealed, in the central regions of the bar, the presence of a cold (v/sigma~2.5), prograde, S-shaped velocity component that coexists in the central 4 kpc, with a fainter and hotter (v/sigma~0.5) counterrotating component. Beyond 4 kpc from the nucleus, the LOSVD shows the stellar bar kinematics. The comparison of the radial surface brightness profile of the velocity components with that obtained from an I-band image shows that the counterrotating core follows a r^1/4 profile, while the S-shaped component does not follow the flat-bar surface brightness profile. Several possible scenarios accounting for such kinematic signatures found in the center of the bar in NGC 5728 are discussed. The data presented in this paper show for the first time the presence of extended retrograde motions in barred systems that, together with previous discoveries, seem to indicate that the stellar counterrotation is a phenomenon present all along the Hubble sequence.

Prada, F.; Gutiérrez, C. M.

1999-05-01

4

Hydrodynamical Simulations of the Barred Spiral Galaxy NGC 1097  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

5

STAR FORMATION EFFICIENCY IN THE BARRED SPIRAL GALAXY NGC 4303  

SciTech Connect

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.

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

6

Observations of the kinematics of barred spiral galaxies. I - NGC 1300  

NASA Astrophysics Data System (ADS)

The observed emission-line velocity field of the SBb galaxy NGC 1300 shows strong departures from the pattern expected for purely circular motions. A comparison of the observed data with the kinematics predicted by the Huntley barred galaxy model suggests that the underlying mass structure of the galaxy is in the form of an elongated bar whose major axis lies in the same position angle as the apparent optical bar; the deviations from circular motion are due to the response of the gaseous disk to the rotation of the stellar bar. The pattern of velocities further suggests that the actual mass distribution in the galaxy is more centrally condensed than that of the dynamically self-consistent models.

Peterson, C. J.; Huntley, J. M.

1980-12-01

7

Properties of the giant H II regions and bar in the nearby spiral galaxy NGC 5430  

NASA Astrophysics Data System (ADS)

In order to better understand the impact of the bar on the evolution of spiral galaxies, we measure the properties of giant H II regions and the bar in the SB(s)b galaxy NGC 5430. We use two complementary data sets, both obtained at the Observatoire du Mont-Mégantic: a hyperspectral data cube from the imaging Fourier transform spectrograph SpIOMM (Spectromètre-Imageur à transformée de Fourier de l-Observatoire du Mont-Mégantic) and high-resolution spectra across the bar from a long-slit spectrograph. We flux-calibrate SpIOMM spectra for the first time, and produce H? and [N II]?6584 Å intensity maps from which we identify 51 giant H II regions in the spiral arms and bar. We evaluate the type of activity, the oxygen abundance and the age of the young populations contained in these giant H II regions and in the bar. Thus, we confirm that NGC 5430 does not harbour a strong active galactic nucleus, and that its Wolf-Rayet knot shows a pure H II region nature. We find no variation in abundance or age between the bar and spiral arms, nor as a function of galactocentric radius. These results are consistent with the hypothesis that a chemical mixing mechanism is at work in the galaxy's disc to flatten the oxygen abundance gradient. Using the STARBURST99 model, we estimate the ages of the young populations, and again find no variations in age between the bar and the arms or as a function of radius. Instead, we find evidence for two galaxy-wide waves of star formation, about 7.1 and 10.5 Myr ago. While the bar in NGC 5430 is an obvious candidate to trigger these two episodes, it is not clear how the bar could induce widespread star formation on such a short time-scale.

Brière, É.; Cantin, S.; Spekkens, K.

2012-09-01

8

The Bulgeless Seyfert/LINER Galaxy NGC 3367: Disk, Bar, Lopsidedness, and Environment  

NASA Astrophysics Data System (ADS)

NGC 3367 is a nearby isolated active galaxy that shows a radio jet, a strong bar, and evidence of lopsidedness. We present a quantitative analysis of the stellar and gaseous structure of the galaxy disk and search for evidence of recent interaction. Our study is based on new UBVRI H? and JHK images and on archive H? Fabry-Perot and H I Very Large Array data. From a coupled one-dimensional/two-dimensional GALFIT bulge/bar/disk decomposition a (B/D ~ 0.07-0.1) exponential pseudobulge is inferred in all the observed bands. A near-infrared (NIR) estimate of the bar strength Q max T (R) = 0.44 places NGC 3367 bar among the strongest ones. The asymmetry properties were studied using (1) the optical and NIR concentration-asymmetry-clumpiness indices, (2) the stellar (NIR) and gaseous (H?, H I) A 1 Fourier mode amplitudes, and (3) the H I-integrated profile and H I mean intensity distribution. While the average stellar component shows asymmetry values close to the average found in the local universe for isolated galaxies, the young stellar component and gas values are largely decoupled showing significantly larger A 1 mode amplitudes suggesting that the gas has been recently perturbed and placing NGC 3367 in a global starburst phase. NGC 3367 is devoid of H I gas in the central regions where a significant amount of molecular CO gas exists instead. Our search for (1) faint stellar structures in the outer regions (up to ? R ~ 26 mag arcsec-2), (2) (H?) star-forming satellite galaxies, and (3) regions with different colors (stellar populations) along the disk all failed. Such an absence is interpreted by using results from recent numerical simulations to constrain either a possible tidal event with an LMC like galaxy to some dynamical times in the past or a very low mass but perhaps gas rich recent encounter. We conclude that a cold flow accretion mode (gas and small/dark galaxies) may be responsible for the nuclear activity and peculiar (young stars and gas) morphology regardless of the highly isolated environment. Black hole growth in bulgeless galaxies may be triggered by smooth mass accretion. Based on data obtained at the 0.84 m, 1.5 m, and 2.1 m telescopes of the Observatorio Astronómico Nacional, San Pedro Mártir operated by the Instituto de Astronomía, Universidad Nacional Autónoma de México.

Hernández-Toledo, H. M.; Cano-Díaz, M.; Valenzuela, O.; Puerari, I.; García-Barreto, J. A.; Moreno-Díaz, E.; Bravo-Alfaro, H.

2011-12-01

9

THE BULGELESS SEYFERT/LINER GALAXY NGC 3367: DISK, BAR, LOPSIDEDNESS, AND ENVIRONMENT  

SciTech Connect

NGC 3367 is a nearby isolated active galaxy that shows a radio jet, a strong bar, and evidence of lopsidedness. We present a quantitative analysis of the stellar and gaseous structure of the galaxy disk and search for evidence of recent interaction. Our study is based on new UBVRI H{alpha} and JHK images and on archive H{alpha} Fabry-Perot and H I Very Large Array data. From a coupled one-dimensional/two-dimensional GALFIT bulge/bar/disk decomposition a (B/D {approx} 0.07-0.1) exponential pseudobulge is inferred in all the observed bands. A near-infrared (NIR) estimate of the bar strength Q{sup max}{sub T}(R) = 0.44 places NGC 3367 bar among the strongest ones. The asymmetry properties were studied using (1) the optical and NIR concentration-asymmetry-clumpiness indices, (2) the stellar (NIR) and gaseous (H{alpha}, H I) A{sub 1} Fourier mode amplitudes, and (3) the H I-integrated profile and H I mean intensity distribution. While the average stellar component shows asymmetry values close to the average found in the local universe for isolated galaxies, the young stellar component and gas values are largely decoupled showing significantly larger A{sub 1} mode amplitudes suggesting that the gas has been recently perturbed and placing NGC 3367 in a global starburst phase. NGC 3367 is devoid of H I gas in the central regions where a significant amount of molecular CO gas exists instead. Our search for (1) faint stellar structures in the outer regions (up to {mu}{sub R} {approx} 26 mag arcsec{sup -2}), (2) (H{alpha}) star-forming satellite galaxies, and (3) regions with different colors (stellar populations) along the disk all failed. Such an absence is interpreted by using results from recent numerical simulations to constrain either a possible tidal event with an LMC like galaxy to some dynamical times in the past or a very low mass but perhaps gas rich recent encounter. We conclude that a cold flow accretion mode (gas and small/dark galaxies) may be responsible for the nuclear activity and peculiar (young stars and gas) morphology regardless of the highly isolated environment. Black hole growth in bulgeless galaxies may be triggered by smooth mass accretion.

Hernandez-Toledo, H. M.; Cano-Diaz, M.; Valenzuela, O.; Garcia-Barreto, J. A; Moreno-Diaz, E. [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-264, Mexico D. F., 04510 (Mexico); Puerari, I. [Instituto Nacional de Astrofisica, Optica y Electronica, Calle Luis Enrique Erro 1, 72840, Sta. Maria Tonantzintla, Puebla (Mexico); Bravo-Alfaro, H., E-mail: hector@astroscu.unam.mx [Departamento de Astronoma, Universidad de Guanajuato, Apdo. Postal 144, Guanajuato 36000 (Mexico)

2011-12-15

10

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

SciTech Connect

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

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

2011-06-10

11

High Resolution Neutral Hydrogen Observations of the Barred Spiral Galaxy NGC 1365  

NASA Astrophysics Data System (ADS)

We have observed the barred spiral galaxy NGC 1365 with the VLA in the BnA, CnB, and DnC configurations. We have refined the flux determination for partially cleaned images of very non-Gaussian VLA multiconfiguration naturally weighted beams as described in the Appendix. NGC 1365 is found to contain 15.2 x 1O^9^M_sun_ of HI. The velocity field is strongly affected by the bar in the inner parts, but it is relatively undisturbed in the outer parts. The H I morphology is similar to that in the optical, but the HI is more uniformly distributed and there is no trace of the bar. NGC 1365 is found to have four well developed arms and two rudimentary ones. The inclination of the inner disk is determined to be 40^deg^, substantially different from that obtained by optical means (55^deg^). There is a central H I hole which is filled with molecular gas. We find that NGC 1365 has the most strongly dropping rotation curve known to us, falling to 63% of its peak value. It starts to drop already at 2/3 of R_25_. In the outer 40% it is well modeled by a Keplerian. We deduce a total mass for NGC 1365 of 3.9 x 10^11^ M_sun_, resulting in a M/L_B_ of 4.8. Strongly noncircular motions (radial velocity residuals up to 100 km s^-1^) are seen in the bar region. The influence of the bar drops rapidly outside of it and the orbits become rather circular. The ratio between H I diameter and R_25_ is unusually small and NGC 1365 lacks a extended H I halo. A similar behavior is displayed by NGC 1300, data for which we have reduced anew, and we discuss whether this could be common among strongly barred galaxies. NGC 1365 has a warp which starts already at 2/3 of R_25_. The classical resonances may be identified with kinematical and morphological features of the spiral arms. The good agreement with gas dynamical models give strong support to this identification. We find a common corotation radius of arms and bar at 1.4 times the bar major axis. This corresponds to a pattern velocity of 21 +/- I km s^-`^ kpc^-1^. The -4/1 resonance is the most clearly seen feature. The corotation radius corresponds to the maximum deviation from circular motion in the arms. The bright parts of the arms end at the OLR. The spiral arms of NGC 1365 have a very circular symmetry when viewed face on, and are substantially more tightly wound than they appear in the sky plane. NGC 1365 shows a straight front on the W side, which may be a sign of interaction with the intergalactic medium. The H I is elongated in the direction of the Fornax cluster center.

Jorsater, Steven; van Moorsel, Gustaaf A.

1995-11-01

12

Structures and dynamics of NGC 3359: Observational and theoretical studies of a barred spiral galaxy  

NASA Astrophysics Data System (ADS)

This research is a synthesis of observational and theoretical studies of the barred spiral galaxy NGC 3359. Analysis of the observational data was combined with numerical simulations to gain a deeper understanding of the system. The galaxy is gas-rich, with the mass of H I making up about 6% of the total dynamical mass. The distribution of the material is globally symmetric about the center. Atomic hydrogen gas call be detected out as far as 24 kpc from the center (or approximately twice the length of the photometric disk-scale length). The galaxy has a grand design appearance with two spiral arms of similar pitch angles extending from the ends of the stellar bar. Along these structures reside most of the bright, giant H II regions of the galaxy. Two additional, purely H I gas arms also exist outside the optical disk. The nucleus of the galaxy is strongly covered in dust and contains little CO or Halpha emission. Although dust complexes are present within the bar region, they appear as dusty patches rather than the classical dust lanes. Radio continuum emission appears to be centrally concentrated and thermally induced, as it is detected predominantly around the brightest H II regions located within the bar. Analysis of the near-infrared and optical images of the galaxy have shown that, as the wavelength of observation increases, the disk scale length also increases; while the bar position angle decreases. Kinematical study of 21-cm and Halpha velocity fields show that the gases are circularly rotating. However, near the bar and spiral arms of the galaxy, strong; streaming motions as large as 50 km s-1 have been detected. Evidence also exists for out-of-plane motions near the brightest H II regions Such types of gas flow kelp to explain the curious double peak feature of the H I rotation curve. Numerical simulations of stellar orbits and gas flow within the disk of the galaxy have yielded the fascinating and rare result that the system has two pattern speeds. To reproduce the proper stellar orbits that build and support the observed bar structure, a pattern speed of 39.17 km s -1 kpc-1 is required. To match the pitch angles of the spiral arms with the SPH simulations, slower pattern speeds (between 10.00 and 15.52 kms-1 kpc-1) were used. The observed density distribution and kinematical results are also best reproduced by the lower-pattern-speed models.

Boonyasait, Veera

13

Star Formation Timescale in the Circumnuclear Starburst Ring of Barred Galaxy NGC 7552  

NASA Astrophysics Data System (ADS)

We present the multiple line observations carried out with interferometry. We observed the circumnuclear region of the barred galaxy NGC 7552 in molecular lines tracing diffuse molecular gas (12CO J = 2 - 1; observed by SMA) and relatively dense molecular gas (HCN J = 1 - 0; observed by ATCA). We also reprocessed a published HI image which covers the entire galaxy to gain an analytical image with higher resolution. The displacement between HCN (J = 1 - 0) and radio knots (3 cm continuum; ATCA archive data) is clearly seen in the circumnuclear starburst ring of NGC 7552. The propagation time derived from 12CO J = 2 - 1 and HI based rotation curve between the HCN (J = 1 - 0) and radio knots implies the timescale between the formation and death of massive stars. The timescale of NGC 7552 is about an order of magnitude shorter than 5 - 10 Myr timescale for OB stars to become supernovae. It is possible that star formation in the ring is top heavy, resulting in a shorter timescale.

Pan, Hsi-An; Lim, Jeremy; Matsushita, Satoki; Wong, Tony

2012-07-01

14

Molecular Gas in NUclei of GAlaxies (NUGA). XIV. The barred LINER/Seyfert 2 galaxy NGC 3627  

NASA Astrophysics Data System (ADS)

We present 12CO(1-0) and 12CO(2-1) maps of the interacting barred LINER/Seyfert 2 galaxy NGC 3627 obtained with the IRAM interferometer at resolutions of 2.1 arcsec × 1.3 arcsec and 0.9 arcsec × 0.6 arcsec, respectively. We also present single-dish IRAM 30 m 12CO(1-0) and 12CO(2-1) observations used to compute short spacings and complete interferometric measurements. These observations are complemented by IRAM 30 m measurements of HCN(1-0) emission detected in the center of NGC 3627. The molecular gas emission shows a nuclear peak, an elongated bar-like structure of ~18? (~900 pc) diameter in both 12CO maps and, in 12CO(1-0), a two-arm spiral feature from r ~ 9? (~450 pc) to r ~ 16? (~800 pc). The inner ~18? bar-like structure, with a north/south orientation (PA = 14°), forms two peaks at the extremes of this elongated emission region. The kinematics of the inner molecular gas shows signatures of non-circular motions associated both with the 18? bar-like structure and the spiral feature detected beyond it. The 1.6 ?m H-band 2MASS image of NGC 3627 shows a stellar bar with a PA = - 21°, different from the PA (= 14°) of the 12CO bar-like structure, indicating that the gas is leading the stellar bar. The far-infrared Spitzer-MIPS 70 and 160 ?m images of NGC 3627 show that the dust emission is intensified at the nucleus and at the ansae at the ends of the bar, coinciding with the 12CO peaks. The GALEX far-ultraviolet (FUV) morphology of NGC 3627 displays an inner elongated (north/south) ring delimiting a hole around the nucleus, and the 12CO bar-like structure is contained in the hole observed in the FUV. The torques computed with the HST-NICMOS F160W image and our PdBI maps are negative down to the resolution limit of our images, ~60 pc in 12CO(2-1). If the bar ends at ~3 kpc, coincident with corotation (CR), the torques are negative between the CR of the bar and the nucleus, down to the resolution limit of our observations. This scenario is compatible with a recently-formed rapidly rotating bar which has had insufficient time to slow down because of secular evolution, and thus has not yet formed an inner Lindblad resonance (ILR). The presence of molecular gas inside the CR of the primary bar, where we expect that the ILR will form, makes NGC 3627 a potential smoking gun of inner gas inflow. The gas is fueling the central region, and in a second step could fuel directly the active nucleus. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by the INSU/CNRS (France), MPG (Germany), and IGN (Spain).

Casasola, V.; Hunt, L. K.; Combes, F.; García-Burillo, S.; Neri, R.

2011-03-01

15

Dynamical Models Of Ngc 3124: A Galaxy With An Apparent Counter-winding Bar-spiral Hybrid  

NASA Astrophysics Data System (ADS)

The bar in the unusual SB(r)bc galaxy of NGC 3124 appears to be a very open spiral pattern winding in the opposite sense of the outer spiral arms. It is clearly observed in the high resolution B, V, R, I, and Ks-band images from the Carnegie-Irvine Galaxy Survey. We present preliminary results of our attempts to recreate the observed gaseous and stellar morphology through test particle simulations.

Treuthardt, Patrick M.; Seigar, M.; Salo, H.; Kennefick, D.; Kennefick, J.; Lacy, C. H. S.

2012-05-01

16

Stellar bar in NGC 1068  

SciTech Connect

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.

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

1988-04-01

17

EVIDENCE FOR A STRONG END-ON BAR IN THE RINGED {sigma}-DROP GALAXY NGC 6503  

SciTech Connect

We use WIYN High-resolution Infrared Camera H-band (1.6 {mu}m) imaging, archival Spitzer, Hubble Space Telescope, and Galaxy Evolution Explorer data simulations, and data from the literature to argue for the presence of a strong end-on bar in nearby spiral galaxy NGC 6503. The evidence consists of both photometric and kinematic signatures as well as resonant structures present in the galaxy which are most often associated with bars. These include a central peak followed by a plateau in the surface brightness profile, an extreme decrement in the central stellar velocity dispersion (a {sigma}-drop), and the presence of an inner ring as well as a circumnuclear disk with spiral structure. In this framework, the previously identified nuclear star-forming ring is instead a young inner ring spanned in diameter by the strong end-on bar.

Freeland, E.; Chomiuk, L.; Keenan, R.; Nelson, T. [Department of Astronomy, University of Wisconsin, Madison, WI 53706 (United States)], E-mail: freeland@astro.wisc.edu, E-mail: chomiuk@astro.wisc.edu, E-mail: keenan@astro.wisc.edu, E-mail: nelson@astro.wisc.edu

2010-03-15

18

The oxygen distribution in NGC 3359 or a disk galaxy in the early phase of bar formation  

NASA Astrophysics Data System (ADS)

Monochromatic imaging in the nebular lines H-alpha, H-beta, (O III) lambda 5007, and (N II) lambda 6584 has been performed on 77 H II regions from 0.13 Reff to 2.04 Reff in the barred spiral galaxy NGC 3359. The galaxy shows several bright H II regions along its bar; according to numerical simulations of barred galaxies, this morphology suggests that the barred structure was formed recently (within 1 Gyr). The O/H abundance gradient across the disk of NGC 3359 was derived from the abundance indicators (O III)/H-beta and (N II)/(O III) calibrated by Edmunds & Pagel (1984). A break in the slope of the O/H gradient is clearly seen near the corotation radius (approximately 4 kpc). The inner O/H gradient is steep (Delta log (O/H)/Delta R = -0.070 +/- 0.010 dex/kpc) and the O/H scatter is moderate (+/- 0.10 dex); outside the corotation, the gradient appears flat (Delta log (O/H)/ Delta R = 0.006 +/- 0.018 dex kpc) and the spread in O/H is significantly larger (+/- 0.2 dex) than in the inner parts. This result is in agreement with recent simulations of barred spiral galaxies: star formation inside the corotation radius is enhanced by large amounts of gas driven by radial flows induced by the bar and contributes to maintain the initial O/H gradient; in the outer parts, strong gas mixing induced by flows directed outward and along the spiral arms produces a flattened gradient (e.g., Friedli, Benz, & Kennicutt 1994). Based on previous H I kinematics data on NGC 3359 and results of numerical models of barred galaxies, we show that flows along the spiral arms have had enough time to wiped out the O/H gradient outside the corotation as far as at least 9.5 kpc. However, the presence of large azimuthal abundance fluctuations in the outer disk indicates that the age of the bar is approximately 4 x 108 yr. The steep inner O/H gradient is also discussed, and we suggest that the present star formation inside the corotation minimizes the dilution of the chemical composition by gas flows. Finally, a brief analysis of the global O/H gradients in disk galaxies with bars showing different star-forming activity is performed.

Martin, Pierre; Roy, Jean-Rene

1995-05-01

19

Molecular Gas in NUclei of GAlaxies (NUGA). IX. The decoupled bars and gas inflow in NGC 2782  

NASA Astrophysics Data System (ADS)

We present CO(1-0) and CO(2-1) maps of the starburst/Seyfert 1 galaxy NGC 2782 obtained with the IRAM interferometer, at 2.1 arcsec×1.5 arcsec and 0.7 arcsec×0.6 arcsec resolution respectively. The CO emission is aligned along the stellar nuclear bar of radius ~1 kpc, configured in an elongated structure with two spiral arms at high pitch angle ~90°. At the extremity of the nuclear bar, the CO changes direction to trace two more extended spiral features at a lower pitch angle. These are the beginning of two straight dust lanes, which are aligned parallel to an oval distortion, reminiscent of a primary bar, almost perpendicular to the nuclear one. The two embedded bars appear in Spitzer IRAC near-infrared images, and HST color images, although highly obscured by dust in the latter. We compute the torques exerted by the stellar bars on the gas, and find systematically negative average torques down to the resolution limit of the images, providing evidence of gas inflow tantalizingly close to the nucleus of NGC 2782. We propose a dynamical scenario based on numerical simulations to interpret coherently the radio, optical, and molecular gas features in the center of the galaxy. Star formation is occurring in a partial ring at ~1.3 kpc radius corresponding to the Inner Lindblad Resonance (ILR) of the primary bar; this ring-like structure encircles the nuclear bar, and is studded with H? emission. The gas traced by CO emission is driven inward by the gravity torques of the decoupled nuclear bar, since most of it is inside its corotation. N-body simulations, including gas dissipation, predict the secondary bar decoupling, the formation of the elongated ring at the ~1 kpc-radius ILR of the primary bar, and the gas inflow to the ILR of the nuclear bar at a radius of ~200-300 pc. The presence of molecular gas inside the ILR of the primary bar, transported by a second nuclear bar, is a potential “smoking gun”; the gas there is certainly fueling the central starburst, and in a second step could fuel directly the AGN. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by the INSU/CNRS (France), MPG (Germany), and IGN (Spain).

Hunt, L. K.; Combes, F.; García-Burillo, S.; Schinnerer, E.; Krips, M.; Baker, A. J.; Boone, F.; Eckart, A.; Léon, S.; Neri, R.; Tacconi, L. J.

2008-04-01

20

NGC 4340: Double Bar + Fossil Nuclear Ring  

NASA Astrophysics Data System (ADS)

NGC 4340 is a double-barred SB0 galaxy in the Virgo cluster (Wozniak et al. 1995). Here, we present evidence that this galaxy also posseses a luminous stellar nuclear ring of relatively old stars with little or no gas. The ring lies just outside the inner bar, at the probable inner inner Lindblad resonance (IILR) of the outer bar. Careful inspection of the isophotes and unsharp masks shows that the two bars are slightly misaligned, which suggests they may be independently rotating.

Erwin, Peter; Vega Beltrán, Juan Carlos; Beckman, John

21

Kinematics in irregular galaxies: NGC 4449.  

NASA Astrophysics Data System (ADS)

A kinematical analysis of the irregular galaxy NGC 4449 is presented based on the Fabry-Perot interferometer PUMA observations. In NGC 4449 we analyse its global velocity field, HII regions population as well as the SNR population identified on radioastronomy studies. Our first results for NGC 4449 show that the optical velocity field, presents a decreasing gradient in velocity along the optical bar and an anticorrelation with respect to the velocity field of the HI halo.

Valdez, M.; Rosado, M.

1998-11-01

22

Formation of Dense Molecular Gas and Stars at the Circumnuclear Starburst Ring in the Barred Galaxy NGC 7552  

NASA Astrophysics Data System (ADS)

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

Pan, Hsi-An; Lim, Jeremy; Matsushita, Satoki; Wong, Tony; Ryder, Stuart

2013-05-01

23

Molecular gas in NUclei of GAlaxies (NUGA). VII. NGC 4569, a large scale bar funnelling gas into the nuclear region  

Microsoft Academic Search

This work is part of the NUGA survey of CO emission in nearby active galaxies. We present observations of NGC 4569, a member of the Virgo Cluster. We analyse the molecular gas distribution and kinematics in the central region and we investigate a possible link to the strong starburst present at the nucleus. 70% of the [ 1.1±0.2] ×109 M&sun;

F. Boone; A. J. Baker; E. Schinnerer; F. Combes; S. García-Burillo; R. Neri; L. K. Hunt; S. Léon; M. Krips; L. J. Tacconi; A. Eckart

2007-01-01

24

Spitzer commissioning observations of the interacting spiral galaxy NGC2442  

Microsoft Academic Search

The southern peculiar barred spiral galaxy NGC2442 was observed as a commissioning target during the science verification phase of the Spitzer mission by both the IRAC and MIPS instruments. NGC2442 has a disturbed morphology apparently resulting from the interaction with a dwarf galaxy in the same group. Star-forming regions are spread throughout the arms, but are concentrated in the Northern

M. Lacy; A. Noriega-Crespo; P. N. Appleton; B. Bhattacharya; S. J. Carey; S. Laine; P. J. Lowrance; F. R. Marleau; B. O. Nelson; W. R. Reach; A. Sajina; J. Surace; G. Wilson

2004-01-01

25

Morphology of the Barred Spiral Galaxy 2903  

NASA Astrophysics Data System (ADS)

In this study I present the morphology of the barred spiral galaxy NGC 2903. CCD images were obtained in the BVR optical and JH near infrared (NIR) bands at Mount Laguna Observatory. NGC 2903 is classified as a SAB(rs)bc galaxy. The bar in NGC 2903 is evident in all the optical and NIR images, but is most evident in the NIR. Its profiles suggest that it has a flat bar morphology consistent with other early type galaxies. NGC 2903 is also classified as a hot spot galaxy. This morphology is explained by both the accelerated star formation rate in the nucleus and the presence of a lot of gas and dust. Extinction is responsible for the splotchy appearance of the galaxy. The structure of the nuclear region does smooth out as it is observed at longer wavelengths, indicating that there is less extinction due to gas and dust. I studied the ring classification of NGC 2903 and theoretical fits to the resonance rings. Not all resonances are present, but I was able to detect the Outer Lindblad Resonance, Corotation, and the inner 4:1 resonance. I was also able to detect an inner bar by measuring the change in the position angle of isophotal ellipses of the nuclear region.

Dosaj, Anil

1998-05-01

26

NGC 3627: a galaxy-dwarf collision?  

NASA Astrophysics Data System (ADS)

Context. Group galaxies very often show distinct signs of interaction with both companion galaxies and the intragroup medium. X-ray observations are particularly helpful because they provide information on the temperatures and the densities of the hot gas in galaxies and intergalactic space. This can put important constraints on the nature and timescales of these interactions. Aims: We use the XMM-Newton X-ray observations of NGC 3627 in the Leo Triplet galaxy group to explain peculiar features visible in the polarized radio maps. Methods: We analyzed soft X-ray (0.2-1 keV) emission from NGC 3627 to study the distribution of the hot gas and its temperature in different areas of the galaxy. Any change throughout the disk can reflect distortions visible in the radio polarized emission. We also studied two bright point sources that are probably tightly linked to the evolution of the galaxy. Results: We find an increase in the temperature of the hot gas in the area of the polarized radio ridge in the western arm of the galaxy. In the eastern part of the disk we find two ultra-luminous X-ray sources. We note a large hot gas temperature difference (by a factor of 2) between the two bar ends. Conclusions: The polarized radio ridge in the western arm of NGC 3627 is most likely formed by ram-pressure effects caused by the movement of the galaxy through the intragroup medium. To explain the distortions visible in the eastern part of the disk in polarized radio maps, the asymmetry of the bar, and the distortion of the eastern arm, we propose a recent collision of NGC 3627 with a dwarf companion galaxy. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.

We?gowiec, M.; Soida, M.; Bomans, D. J.

2012-08-01

27

Molecular gas in NUclei of GAlaxies (NUGA). XI. A complete gravity torque map of NGC 4579: new clues to bar evolution  

NASA Astrophysics Data System (ADS)

In this paper we create a complete gravity torque map of the disk of the LINER/Seyfert 1.9 galaxy NGC 4579. We quantify the efficiency of angular momentum transport and search for signatures of secular evolution in the fueling process from r ~ 15 kpc down to the inner r ~ 50 pc around the active galactic nucleus (AGN). We use both the 1-0 and 2-1 line maps of 12CO obtained with the Plateau de Bure Interferometer (PdBI) as part of the NUclei of Galaxies-(NUGA)-project. The CO(1-0) and CO(2-1) PdBI maps at 2.0 arcsec × 1.3 arcsec and 1.0 arcsec × 0.6 arcsec resolution, respectively, include the short spacing correction provided by IRAM-30 m data. We derive the stellar potential from an NIR (K band) wide field image of the galaxy. The K-band image, which reveals a large-scale stellar bar and a weak nuclear oval, together with a high-resolution Hi map of NGC 4579 obtained with the Very Large Array (VLA), allow us to extend the gravity torque analysis to the outer r ? 2 kpc disk. The bulk of the gas response traced by the new CO PdBI+30 m maps of NGC 4579 presented here follows the expected gas flow pattern induced by the bar potential in the presence of two inner Lindblad resonances (ILR) at r ~ 500 pc and r ~ 1.3 kpc. The morphology of the outer disk traced by Hi suggests that the neutral gas is currently piling up in a pseudo-ring formed by two winding spiral arms that are morphologically decoupled from the bar structure. The pseudo-ring is located inside the bar corotation (r_CR ~ 6 kpc) and close to the predicted position of the ultra harmonic resonance (UHR) (r_UHR ~ 3.8 kpc). The derived gravity torque budget in NGC 4579 shows that inward gas flow is occurring on different spatial scales in the disk. In the outer disk, the decoupling of the spiral allows the gas to efficiently populate the UHR region, and thus produce net gas inflow on intermediate scales. The corotation barrier seems to be overcome by secular evolution processes. The gas in the inner disk (r ? 2 kpc) is efficiently funneled by gravity torques down to r ~ 300 pc. Closer to the AGN (r < 200 pc), gas feels negative torques due to the combined action of the large-scale bar and the inner oval. The two m=2 modes act in concert to produce net gas inflow down to r ~ 50 pc, providing clear smoking gun evidence of inward gas transport on short dynamical timescales (~1-3 rotation periods). Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

García-Burillo, S.; Fernández-García, S.; Combes, F.; Hunt, L. K.; Haan, S.; Schinnerer, E.; Boone, F.; Krips, M.; Márquez, I.

2009-03-01

28

Fossil Nuclear Rings in Barred Galaxies  

NASA Astrophysics Data System (ADS)

We present observations and analysis of three barred S0 galaxies which contain smooth, luminous, stellar nuclear rings within their bars. These rings, which have little or no dust and are approximately the same color as surrounding bar and bulge, are probably the old remnants of bar-driven circumnuclear starburst episodes similar to those seen in many barred galaxies today. Using kinematic data from long-slit spectroscopy, we construct rotation and resonance curves and relate the relative sizes of the rings to possible bar resonances. Two of the galaxies are actually double-barred, with misaligned secondary bars inside the nuclear rings. In at least one of these (NGC 4340), the resonance curves indicate that the nuclear ring lies near or at one of the outer bar's inner Lindblad resonances; this is a plausible location for the secondary bar's corotation radius. We also discuss the difficulties inherent in detecting and identifying such rings, and show some of the surprising ways in which stellar rings can distort galaxy isophotes and ellipse fits.

Erwin, P.; Vega Beltran, J. C.; Beckman, J.

2000-12-01

29

The Isolated Interacting Galaxy Pair NGC 5426/27 (Arp 271)  

NASA Astrophysics Data System (ADS)

The isolated interacting galaxy pair NGC 5426/27 (Arp 271) was observed using the scanning Fabry-Perot interferometer PUMA. The velocity field, various kinematical parameters and rotation curve for each galaxy were derived. We found a small bar-like structure in NGC 5426 and a severely distorted velocity field for NGC 5427. A range of possible masses was computed for each galaxy.

Fuentes-Carrera, I.; Rosado, M.; Amram, P.; Dultzin-Hacyan, D.; Bernal, A.; Salo, H.; Laurikainen, E.; Cruz-González, I.; Le Coarer, E.

2001-03-01

30

Pseudobulges in the Disk Galaxies NGC 7690 and NGC 4593  

Microsoft Academic Search

We present Ks-band surface photometry of NGC 7690 (Hubble type Sab) and NGC 4593 (SBb). We find that, in both galaxies, a major part of the ``bulge'' is as flat as the disk and has approximately the same color as the inner disk. In other words, the ``bulges'' of these galaxies have disklike properties. We conclude that these are examples

John Kormendy; Mark E. Cornell; David L. Block; Johan H. Knapen; Emma L. Allard

2006-01-01

31

Stellar Kinematics of Late-Type Barred Spiral Galaxies  

NASA Astrophysics Data System (ADS)

We present the results of a study of the stellar kinematics of a small sample of late-type barred spiral galaxies, including NGC 4123 and the Magellanic spiral, NGC 2537. Our data is obtained using Sparsepak, an integral field unit on the WIYN 3.5m telescope. The spectra obtained were analyzed for the Mg I absorption triplet and the OIII emission line. Gaussian curves are fit to the absorption lines to best estimate the stellar velocity dispersion, rotation curve, and the dynamical mass of each galaxy. We derive values for the stellar velocity dispersion to be between 60 and 80 km/s. We compare results with previous studies of Magellanic spirals, NGC 4618 and NGC 4625, to explore the kinematics of stellar bars in late-type galaxies. This work was supported by the National Science Foundation's REU program through NSF Award AST-1004881.

Klawiter, Steffi; Wilcots, E. M.

2013-01-01

32

Stellar Nuclear Rings in Barred Galaxies: Fossils of Past Circumnuclear Starbursts?  

NASA Astrophysics Data System (ADS)

We have found four barred S0 galaxies---NGC 936, NGC 3945, NGC 4340, and NGC 4371---which contain smooth, luminous, purely stellar nuclear rings within their bars. These rings have little or no dust, no evidence for recent star formation, and are approximately the same color as the surrounding bar and bulge. Thus, they are probably the aged remnants of bar-driven circumnuclear starburst episodes similar to those seen in barred galaxies today. Using kinematic data from long-slit spectroscopy, we construct rotation and resonance curves for two of the galaxies. In both cases, the nuclear rings appear to be located near or at the inner inner Lindblad resonances of the large-scale bars. We also discuss the difficulties inherent in detecting and identifying such rings, and show some of the surprising ways in which stellar rings can distort galaxy isophotes and ellipse fits.

Erwin, Peter; Vega Beltrán, Juan Carlos; Beckman, John E.

33

Properties of barred spiral galaxies  

NASA Astrophysics Data System (ADS)

Blue and near-infrared surface photometry of 15 barred spiral galaxies, combined with results from photometric and kinematic studies of barred galaxies, reveals that: (1) early Hubble types have flat bars with uniform intensities along their lengths and stellar spiral arms with amplitudes that decrease with radius, and (2) late Hubble types have bars with exponential-like intensity profiles and spiral arm amplitudes that increase or remain constant with radius. Relative bar luminosities are derived using Fourier decompositions of the bar azimuthal profiles. It is concluded that bars in early-type galaxies probably contain highly elongated stellar orbits out to the corotation vicinity and also stimulate stellar spiral structure either by continuously growing, in the case of a non-self-gravitating stellar disk, or by exciting a wave mode at a resonance, in the case of a strongly self-gravitating stellar disk. It is shown that bars in some late-type galaxies may extend out only to the inner Lindbald resonances and that they appear to be too short or too weak to drive prominent stellar spirals because the spirals in these galaxies are often irregular.

Elmegreen, B. G.; Elmegreen, D. M.

1985-01-01

34

Molecular bar and star formation in the nucleus of NGC 6946  

SciTech Connect

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.

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

1985-11-15

35

Molecular bar and star formation in the nucleus of NGC 6946  

SciTech Connect

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.

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

1985-11-01

36

The ultraluminous interacting galaxy NGC6240  

NASA Astrophysics Data System (ADS)

A peak in IR emissions located by the IRAS spacecraft has been identified with the galaxy NGC 6420. The galaxy has an IR luminosity 60 times that of a normal starburst galaxy. However, the radiation centers around 100 microns, indicating massive star formation and thermalization of dust. The strong radio emissions of NGC 6420 suggest that there are supernova remnants within the starburst region. A model of interaction between two gas-rich galaxies is suggested, with the interaction occurring with sufficiently small kinetic energy to allow the galaxies to merge.

Wright, G. S.; Joseph, R. D.; Meikle, W. P. S.

1984-05-01

37

Structures out of Chaos in Barred-Spiral Galaxies  

NASA Astrophysics Data System (ADS)

We review the dynamical mechanisms we have found to support the morphological features in barred-spiral galaxies based on chaotic motions of stars in their gravitational fields. These morphological features are the spiral arms, that emerge out of the ends of the bar, but also shape the bar itself. The potentials used have been estimated directly from near-infrared images of barred-spiral galaxies. In this paper, we present the results from the study of the dynamics of the potentials of the galaxies NGC 4314, NGC 1300 and NGC 3359. The main unknown parameter in our models is the pattern speed of the system Ωp. By varying Ωp, we have investigated several cases trying to match the results of our modeling with available photometrical and kinematical data. We found realistic models with stars on spirals in chaotic motion, while their bars are built by stars usually on regular orbits. However, we also encountered cases, where a major part of trajectories of the stars even in the bar is chaotic as well. Finally, we examined the gas dynamics of barred-spiral systems, and found that the presence of gas reinforces the intensity of the "chaotic" spiral arms.

Patsis, P. A.

2012-09-01

38

Barred Galaxies: Intrinsic or Extrinsic?  

NASA Astrophysics Data System (ADS)

A unified picture is presented of the formation of bar structures in disk galaxies of various morphological types. In order to discuss bar formation in the context of galactic disk formation, a simple analytic model is constructed of the growth of galactic disks by infall of primordial gas from halos and subsequent star formation in the disks. It is monitored during the course of disk growth whether or not the condition for spontaneous bar formation (i.e., bar instability) is fulfilled for the stellar disk component. It is found that the infall timescale is a key parameter that controls the dynamical property of the resulting stellar disk. Disks that grow fast by rapid infall experience gas-rich phases, in which massive gas clumps arising from gravitational instability in the gas disk heat the stellar disk component dynamically. When the disk has fully grown and becomes mostly stellar, it has already acquired enough random motions to suppress bar instability. On the other hand, when the gas infall from the halo region proceeds slowly, star formation (though less intense than in rapid infall cases) keeps gas mass in the disk low, leading to a dynamically cold stellar component due to lack of strong heating by massive gas clumps. Therefore, the stellar disk becomes unstable and forms a bar once its mass fraction relative to the total galaxy mass reaches a critical value. Based on this result, we propose that late-type barred galaxies, the disks of which are considered to have formed by slow accretion of the halo gas, have intrinsic origin, whereas the bars in early-type galaxies, whose disks are likely to have grown quickly, have been formed in tidal interactions with other galaxies. Numerical simulations have been carried out which show that the bars created by tidal perturbations tend to have a relatively flat density profile along the bar major axis with "shoulders" (abrupt steepening of the gradient) at the bar ends, whereas spontaneous bars have a steeper profile. The formation scenario described above, combined with this numerical result, can explain the observed dichotomy that early-type galaxies generally have a flat bar, while late-type galaxies have a bar of exponential type.

Noguchi, Masafumi

1996-10-01

39

Searching for non-axisymmetries in NGC 6503: a weak end-on bar  

NASA Astrophysics Data System (ADS)

The isolation, simple apparent structure and low luminosity of the nearby spiral galaxy NGC 6503 make it an ideal candidate for an in-depth kinematic and photometric study. We introduce a new publicly available code, DISKFIT, that implements procedures for fitting non-axisymmetries in either kinematic or photometric data. We use DISKFIT to analyse new H? and CO velocity field data as well as H I kinematics from Greisen et al. to search for non-circular motions in the disc of NGC 6503. We find NGC 6503 to have remarkably regular gas kinematics that are well described by rotation only. We also use DISKFIT and a new Ks-band image of NGC 6503 to constrain photometric models of the disc, bar and bulge. We find the galaxy to be photometrically dominated by the disc. We find NGC 6503 to contain a faint bar and an exponential bulge which together contribute only ˜5 per cent of the total galaxy light. The combination of our kinematic and photometric DISKFIT models suggests that NGC 6503 contains a weak, end-on bar that may have produced its Type II surface brightness profile but is unlikely to be responsible for its strong ?-drop.

Kuzio de Naray, Rachel; Arsenault, Cameron A.; Spekkens, Kristine; Sellwood, J. A.; McDonald, Michael; Simon, Joshua D.; Teuben, Peter

2012-12-01

40

NGC 3934: a shell galaxy in a compact galaxy environment  

NASA Astrophysics Data System (ADS)

Context. Mergers/accretions are considered the main drivers of the evolution of galaxies in groups. We investigate the NGC 3933 poor galaxy association that contains NGC 3934, which is classified as a polar-ring galaxy. Aims: The multi-band photometric analysis of NGC 3934 allows us to investigate the nature of this galaxy and to re-define the NGC 3933 group members with the aim to characterize the group's dynamical properties and its evolutionary phase. Methods: We imaged the group in the far (FUV, ?eff = 1539 Å) and near (NUV, ?eff = 2316 Å) ultraviolet (UV) bands of the Galaxy Evolution Explorer (GALEX). From the deep optical imaging we determined the fine structure of NGC 3934. We measured the recession velocity of PGC 213894 which shows that it belongs to the NGC 3933 group. We derived the spectral energy distribution (SED) from FUV to far-IR emission of the two brightest members of the group. We compared a grid of smooth particle hydrodynamical (SPH) chemo-photometric simulations with the SED and the integrated properties of NGC 3934 and NGC 3933 to devise their possible formation/evolutionary scenarios. Results: The NGC 3933 group has six bright members: a core composed of five galaxies, which have Hickson's compact group characteristics, and a more distant member, PGC 37112. The group velocity dispersion is relatively low (157 ± 44 km s-1). The projected mass, from the NUV photometry, is ~7 × 1012 M? with a crossing time of 0.04 Hubble times, suggesting that at least in the center the group is virialized. We do not find evidence that NGC 3934 is a polar-ring galaxy, as suggested by the literature, but find that it is a disk galaxy with a prominent dust-lane structure and a wide type-II shell structure. Conclusions: NGC 3934 is a quite rare example of a shell galaxy in a likely dense galaxy region. The comparison between physically motivated SPH simulations with multi-band integrated photometry suggests that NGC 3934 is the product of a major merger.

Bettoni, D.; Galletta, G.; Rampazzo, R.; Marino, A.; Mazzei, P.; Buson, L. M.

2011-10-01

41

Mapping the HI Neighborhood Around Starburst Dwarf Galaxies NGC 1569, NGC 4214 and NGC 4163  

NASA Astrophysics Data System (ADS)

Dwarf galaxies are believed to be the building blocks of larger galaxies. However, there are some studies that indicate the dwarf galaxies observed in the nearby universe may have formed later, after the most massive galaxies coalesced. Dwarf galaxy formation and evolution is important for our understanding of cosmology. If dwarf galaxies mimic their more massive counterparts, then starburst dwarfs may be present day merger remnants and provide information on the building block hypothesis. The origins of starburst dwarf irregular galaxies of the Magellanic type (dIm) are not well known. The role of interactions and mergers as mechanisms to create these systems has been hypothesized, but not well studied. We present deep HI maps around three starburst dwarf galaxies NGC 1569, NGC 4214 and NGC 4163. The purpose of these maps is to determine if there are tenuous HI structures around these objects that would indicate a recent interaction or merger. We detect HI filamentary structures that may be connected with NGC 1569 thereby indicating a recent interaction with nearby dwarf irregular UGCA 92. However, our map of NGC 4163 and NGC 4214 does not show any tenuous HI at our 5? sensitivity limit of 1 x 10^18 for a 25 km/s line width.

Johnson, Megan C.; LITTLE THINGS Team

2013-01-01

42

Towards the Secondary Bar: Gas Morphology and Dynamics in NGC 4303  

Microsoft Academic Search

The bulk of the molecular line emission in the double barred galaxy NGC4303\\u000aas observed in its CO(1-0) line with the OVRO mm-interferometer comes from two\\u000astraight gas lanes which run north-south along the leading sides of the\\u000alarge-scale primary bar. Inside a radius of ~ 400 pc the molecular gas forms a\\u000aspiral pattern which, for the northern arm,

E. Schinnerer; W. Maciejewski; N. Z. Scoville; L. A. Moustakas

2002-01-01

43

The Apparent Counter-Winding Bar-Spiral Hybrid of NGC 3124  

NASA Astrophysics Data System (ADS)

The bar in the unusual SB(r)bc galaxy of NGC 3124 appears to be a very open spiral pattern winding in the opposite sense of the outer spiral arms. We show preliminary results of our photometric analysis of high resolution B, V, R, and I-band images from the Carnegie-Irvine Galaxy Survey. We also show preliminary results of our attempts to recreate the observed morphology with inelastically colliding test particle simulations.

Treuthardt, Patrick M.; Seigar, M.

2012-01-01

44

A new optical and H I study of the nearby galaxy NGC 1313  

Microsoft Academic Search

We describe the results of a lambda 21 cm study of the morphology and dynamics of the nearby, southern, barred spiral galaxy NGC 1313 made with the Australian Telescope Compact Array (ATCA). The galaxy has a high H I surface density (the azimuthal average peaking at approximately solar mass\\/sq pc) and a very extensive (24 kpc) disk, containing outer H

Stuart D. Ryder; Lister Staveley-Smith; David Malin; Wilfred Walsh

1995-01-01

45

Magnetohydrodynamic Simulations of Barred Galaxies  

NASA Astrophysics Data System (ADS)

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

Kim, W.-T.

2013-04-01

46

Turbulence in the harassed galaxy NGC4254  

NASA Astrophysics Data System (ADS)

Galaxy harassment is an important mechanism for the morphological evolution of galaxies in clusters. The spiral galaxy NGC4254 in the Virgo cluster is believed to be a harassed galaxy. We have analysed the power spectrum of HI emission fluctuations from NGC4254 to investigate whether it carries any imprint of galaxy harassment. The power spectrum, as determined using the 16 central channels which contain most of the HI emission, is found to be well fitted by a power law P(U) = AU? with ? = -1.7 +/- 0.2 at length-scales 1.7 to 8.4kpc. This is similar to other normal spiral galaxies which have a slope of ~ -1.5 and is interpreted as arising from two-dimensional turbulence at length-scales larger than the galaxy's scaleheight. NGC4254 is hence yet another example of a spiral galaxy that exhibits scale-invariant density fluctuations out to length-scales comparable to the diameter of the HI disc. While a large variety of possible energy sources like protostellar winds, supernovae, shocks, etc. have been proposed to produce turbulence, it is still to be seen whether these are effective on length-scales comparable to that of the entire HI disc. On separately analysing the HI power spectrum in different parts of NGC4254, we find that the outer parts have a different slope (? = -2.0 +/- 0.3) compared to the central part of the galaxy (? = -1.5 +/- 0.2). Such a change in slope is not seen in other, undisturbed galaxies. We suggest that, in addition to changing the overall morphology, galaxy harassment also affects the fine scale structure of the interstellar medium, causing the power spectrum to have a steeper slope in the outer parts.

Dutta, Prasun; Begum, Ayesha; Bharadwaj, Somnath; Chengalur, Jayaram N.

2010-06-01

47

Structural analysis of disk galaxies of the NGC 524 group  

NASA Astrophysics Data System (ADS)

Members of the NGC 524 group of galaxies are studied using data obtained on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences, with the SCORPIO reducer in an imaging mode. Surface photometry has been carried out and parameters of the large-scale structural components—disks and bulges—have been determined for the six largest galaxies of the group. A lowered percentage of bars and enhanced percentage of ring structures were found. The integrated B- V colors of a hundred of dwarf galaxies in the vicinity (within 30 kpc) of the six largest galaxies of the group have been measured. A considerable number of blue irregular galaxies with ongoing star formation is present among nearby dwarf satellites of lenticular galaxies of the group. The luminosity function for dwarf members of the group suggests that the total mass of the group is not very high, and that the X-ray emitting gas observed in the direction of NGC 524 does not belong to the group halo.

Il'ina, M. A.; Sil'chenko, O. K.

2012-08-01

48

The Collisional Ring Galaxy NGC922  

NASA Astrophysics Data System (ADS)

We request WFPC2 images of the newly recognized collisional ring galaxy NGC922 which will become the nearest such system observed by HST. These will be used to get a clear understanding of the geometry of the interaction and the induced star formation in this system. Quantitive modeling of the colors of the star clusters and stellar populations will be used to constrain the star formation history of the system. They will also be used to test the "infant mortality" scenario for star cluster evolution. The derived population ages will test predictions of how star formation evolves in the various components ring, core, spokes of collisional rings, and will improve our own simulations of this system. These will be used to determine the final fate of the stars formed in the present burst - some will end up in a central bar or bulge while others will become part of a thickened disk. By analogy this will tell us how similar collisions enrich stellar populations in the early universe. This is especially relevant since the number density of collisional rings increases rapidly with redshift.;

Meurer, Gerhardt

2007-07-01

49

Modeling the Bar Component in Dusty Spiral Galaxies  

NASA Astrophysics Data System (ADS)

We make use of a 3D radiative transfer model of spiral galaxies in order to investigate the effects of a stellar bar component in the morphology of a spiral galaxy. The model galaxy is described by three axisymmetric components (i.e., a stellar disk, a dusty disk and a stellar bulge) and one non-axisymmetric (a stellar bar). The basic characteristics of the stellar bar that are observed in spiral galaxies (e.g. the X-shape central feature and the boxy/peanut shape of the bulge) are well described with our model. Our model is applied on four spiral galaxies (namely, NGC 4013, IC 2531, UGC2048, and the Milky Way) and the geometrical characteristics of the stellar bar (semi-major axis, height and position angle) are determined very accurately. Finally, we also conduct diagnostic studies of how the morphology of the galaxy changes with various geometrical parameters like the inclination angle and the position angle of the galaxy.

Akras, S.; Xilouris, E.; Patsis, P.; Boumis, P.

2010-07-01

50

Kinematic Evidence of Minor Mergers in Normal SA Galaxies: NGC 3626, NGC 3900, NGC 4772, and NGC 5854  

NASA Astrophysics Data System (ADS)

BVRI and H? imaging and long-slit optical spectroscopic data are presented for four morphologically normal and relatively isolated Sa galaxies, NGC 3626, NGC 3900, NGC 4772, and NGC 5854. VLA H I synthesis imaging is presented for the first three objects. In all four galaxies, evidence of kinematic decoupling of ionized gas components is found in the long-slit spectroscopic data; the degree and circumstances of the distinct kinematics vary from complete counterrotation of all of the gas from all of the stars (NGC 3626) to nuclear gas disks decoupled from the stars (NGC 5854) to anomalous velocity central gas components (NGC 3900 and NGC 4772). In the three objects mapped in H I, the neutral gas extends far beyond the optical radius, RH I/R25>=2. In general, the H I surface density is very low, and the outer H I is patchy and asymmetric (NGC 3900) or found in a distinct ring, exterior to the optical edge (NGC 3626 and NGC 4772). While the overall H I velocity fields are dominated by circular motions, strong warps are suggested in the outer regions by bending of the minor axis isovelocity contours (NGC 3900) and/or systematic shifts in position angle between inner and outer rings (NGC 3626 and NGC 4772). In the interior, coincidence is found between the H? and H I in rings, sometimes partial and crisscrossed by dust lanes. Optical imaging is also presented for NGC 4138 previously reported by Jore et al. to show counterrotating stellar components. The multiwavelength evidence is interpreted in terms of the kinematic ``memory'' of past minor mergers in objects that otherwise exhibit no morphological signs of interaction.

Haynes, Martha P.; Jore, Katherine P.; Barrett, Elizabeth A.; Broeils, Adrick H.; Murray, Brian M.

2000-08-01

51

Hyperactive galaxy NGC 7673 [heic0205  

NASA Astrophysics Data System (ADS)

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

2002-03-01

52

TESTING THEORIES IN BARRED-SPIRAL GALAXIES  

SciTech Connect

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

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

2012-01-10

53

An HI and Optical Study of Interacting Galaxies NGC 672 and IC 1727  

NASA Astrophysics Data System (ADS)

We present VLA HI radio data and WIYN broadband optical observations of NGC 672 and IC 1727, two nearby, late-type, spiral galaxies. In the optical NGC 672 appears as a symmetric barred spiral with defined spiral arms and a scale length of 1.2 kpc. IC 1727 is asymmetric, lacks a true bar, and has a scale length of 2. 4 kpc. In the HI, we see tidal bridge, indicating interaction between the two galaxies. We map the distribution and kinematics of the neutral hydrogen gas in order to understand the nature of the true distribution of mass in these systems and present the resulting mass models.

Stanchfield, Sara; Wilcots, E.; Prescott, M.

2012-05-01

54

Patching the Odd Galaxy, NGC 4622  

Microsoft Academic Search

Morphological studies of galaxies often require that an image be cleaned of all field star. We have used the star cleaning program, PATCH, which we describe here, to clean a variety of images. This patch program works best on smooth and slowly varying backgrounds. We illustrate our success on NGC 4622 which is of particular interest as it is a

D. A. Crocker

1992-01-01

55

NGC 4365: A Truly Triaxial Galaxy  

NASA Astrophysics Data System (ADS)

NGC 4365 is a photometrically ordinary, but kinematically intriguing, E2-3 galaxy. The map of the stellar mean velocity field obtained by the SAURON integral field spectrograph on the William Herschel Telescope shows that the apparent rotation axis, or zero-velocity contour (ZVC), is unaligned with the photometric axes, and that the velocity field (VF) is not symmetric about the ZVC. These traits are both expected hallmarks of non-axisymmetry. Moreover, the galaxy has a pronounced counterrotating core. We have modeled the VF and surface photometry of NGC 4365 using an approach in which the equation of continuity is solved in ellipsoidal coordinates and the resulting projected models are compared with the data by Bayesian methods to constrain the shape profile and orientation of the galaxy. We find that NGC 4365 is indeed highly triaxial, with mean axis ratios of roughly 1 : 0.8 : 0.6. Axisymmetric shapes are strongly ruled out. There is no indication of a significant change of intrinsic shape anywhere in the galaxy, including the counterrotating core. Since absorption line index measurements and the lack of photometric fine structure both indicate that NGC 4365 is at least 10 Gyr old, the dynamical results demonstrate that triaxiality in stellar systems can be long lived, and is not necessarily destroyed by orbital chaos.

Statler, T. S.; SAURON Team

2003-08-01

56

Study of the structure and kinematics of the NGC 7465/64/63 triplet galaxies  

NASA Astrophysics Data System (ADS)

We analyze new observational data obtained at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences with the multimode SCORPIO instrument and the Multi-Pupil Fiber Spectrograph for the group of galaxies NGC 7465/64/63. For one of the group members (NGC 7465), the presence of a polar ring has been suspected. We have constructed the large-scale brightness distributions, the ionized-gas velocity and velocity dispersion fields for all three galaxies as well as the line-of-sight velocity curves based on emission and absorption lines and the stellar velocity field in the central region for NGC 7465. As a result of our analysis of the data obtained, we have discovered an inner stellar disk ( r ? 0.5 kpc) and a warped gaseous disk in NGC 7465, in addition to the main stellar disk. Based on a joint study of our photometric and spectroscopic data, we have established that NGC 7464 is an irregular IrrI-type galaxy whose structural and kinematic peculiarities most likely resulted from its gravitational interaction with NGC 7465. The velocity field of the ionized gas in NGC 7463 turns out to be typical of barred spiral galaxies, and the warp of the outer parts of its disk could arise from a close encounter with one of the galaxies of the environment.

Merkulova, O. A.; Karataeva, G. M.; Yakovleva, V. A.; Burenkov, A. N.

2012-05-01

57

Toward the Secondary Bar: Gas Morphology and Dynamics in NGC 4303  

Microsoft Academic Search

We report on the molecular gas properties in the central kiloparsec of the almost face-on double-barred galaxy NGC 4303 (M61), using the 12CO 1-0 line emission observed with the Owens Valley Radio Observatory (OVRO) millimeter interferometer. The bulk of the molecular line emission comes from two straight gas lanes that run north-south along the leading sides of the large-scale primary

Eva Schinnerer; Witold Maciejewski; Nick Scoville; Leonidas A. Moustakas

2002-01-01

58

How large are the bars in barred galaxies?  

NASA Astrophysics Data System (ADS)

I present a study of the sizes (semimajor axes) of bars in disc galaxies, combining a detailed R-band study of 65 S0-Sb galaxies with the B-band measurements of 70 Sb-Sd galaxies from Martin (1995). As has been noted before with smaller samples, bars in early-type (S0-Sb) galaxies are clearly larger than bars in late-type (Sc-Sd) galaxies; this is true both for relative sizes (bar length as fraction of isophotal radius R25 or exponential disc scalelength h) and absolute sizes (kpc). S0-Sab bars extend to ~1-10 kpc (mean ~ 3.3 kpc), ~0.2-0.8R25 (mean ~ 0.38R25) and ~0.5-2.5h (mean ~ 1.4h). Late-type bars extend to only ~0.5-3.5 kpc, ~0.05-0.35R25 and 0.2-1.5h their mean sizes are ~1.5 kpc, ~ 0.14R25 and ~0.6h. Sb galaxies resemble earlier-type galaxies in terms of bar size relative to h; their smaller R25-relative sizes may be a side effect of higher star formation, which increases R25 but not h. Sbc galaxies form a transition between the early- and late-type regimes. For S0-Sbc galaxies, bar size correlates well with disc size (both R25 and h); these correlations are stronger than the known correlation with MB. All correlations appear to be weaker or absent for late-type galaxies; in particular, there seems to be no correlation between bar size and either h or MB for Sc-Sd galaxies. Because bar size scales with disc size and galaxy magnitude for most Hubble types, studies of bar evolution with redshift should select samples with similar distributions of disc size or magnitude (extrapolated to present-day values); otherwise, bar frequencies and sizes could be mis-estimated. Because early-type galaxies tend to have larger bars, resolution-limited studies will preferentially find bars in early-type galaxies (assuming no significant differential evolution in bar sizes). I show that the bars detected in Hubble Space Telescope (HST) near-infrared(IR) images at z~ 1 by Sheth et al. have absolute sizes consistent with those in bright, nearby S0-Sb galaxies. I also compare the sizes of real bars with those produced in simulations and discuss some possible implications for scenarios of secular evolution along the Hubble sequence. Simulations often produce bars as large as (or larger than) those seen in S0-Sb galaxies, but rarely any as small as those in Sc-Sd galaxies.

Erwin, Peter

2005-11-01

59

TWO PSEUDOBULGES IN THE 'BOXY BULGE' GALAXY NGC 5746  

SciTech Connect

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

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

2012-08-01

60

Two Pseudobulges in the "Boxy Bulge" Galaxy NGC 5746  

NASA Astrophysics Data System (ADS)

Galaxy formation and growth under the ?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 ?m wavelength, Hubble Space Telescope H-band, Two Micron All Sky Survey Ks -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 Sérsic 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 ?CDM universe.

Barentine, John C.; Kormendy, John

2012-08-01

61

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

NASA Astrophysics Data System (ADS)

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.

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

1987-05-01

62

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

SciTech Connect

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

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

2012-10-01

63

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

NASA Astrophysics Data System (ADS)

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.

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

2010-04-01

64

Longslit Spectra of the Galaxy NGC 1569  

NASA Astrophysics Data System (ADS)

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

Duenas, Ely

2000-11-01

65

The isolated interacting galaxy pair NGC 5426/27 (Arp 271)  

NASA Astrophysics Data System (ADS)

We present H? observations of the isolated interacting galaxy pair NGC 5426/27 using the scanning Fabry-Perot interferometer PUMA. The velocity field, various kinematical parameters and rotation curve for each galaxy were derived. The FWHM map and the residual velocities map were also computed to study the role of non-circular motions of the gas. Most of these motions can be associated with the presence of spiral arms and structure such as central bars. We found a small bar-like structure in NGC 5426, a distorted velocity field for NGC 5427 and a bridge-like feature between both galaxies which seems to be associated with NGC 5426. Using the observed rotation curves, a range of possible masses was computed for each galaxy. These were compared with the orbital mass of the pair derived from the relative motion of the participants. The rotation curve of each galaxy was also used to fit different mass distribution models considering the most common theoretical dark halo models. An analysis of the interaction process is presented and a possible 3D scenario for this encounter is also suggested. Table 1 is only available in electronic form at http://www.edpsciences.org

Fuentes-Carrera, I.; Rosado, M.; Amram, P.; Dultzin-Hacyan, D.; Cruz-González, I.; Salo, H.; Laurikainen, E.; Bernal, A.; Ambrocio-Cruz, P.; Le Coarer, E.

2004-02-01

66

HI Study of Barred Magellanic Type Galaxies  

NASA Astrophysics Data System (ADS)

We present the preliminary results of an HI survey of a small sample of Barred Magellanic type galaxies. The data were obtained using the D configuration of the VLA and our observations show: (1) bar morphology seen in the optical data is manifested in the HI distribution and kinematics, (2) SBm/IBm galaxies are commonly found with gaseous companions, and (3) there is strong evidence of significant gravitational interaction between the SBm/IBm galaxy and its companion. These data complement other study in suggesting that gravitational interactions play a strong role in determining the physical properties of SBm/IBm galaxies.

Wilcots, E.; Lehman, C.; Miller, B.

1994-12-01

67

An estimate of the gas inflow rate along the bar in NGC 7479  

NASA Astrophysics Data System (ADS)

We present images of the barred galaxy NGC 7479 in the optical and near-infrared broad bands B, V, R, J, H, K, and images in H-alpha + (N II) and CO (J = 1-0) emission. The H-alpha and CO emission in the bar are coincident and confined to narrow linear features that are offset from the center of the bar as observed in the near-infrared. We estimate the gravitational potential from the K image, which provides an estimate of the torque on the gas at the position of the CO emission in the bar. We find that the implied gas inflow velocity derived from the torque is 10-20 km/s. Our inflow velocity is independent of the large streaming motions which can be observed in CO and H I.

Quillen, A. C.; Frogel, Jay A.; Kenney, Jeffrey D. P.; Pogge, R. W.; Depoy, D. L.

1995-03-01

68

Warm molecular gas in galaxy-galaxy merger NGC6090  

NASA Astrophysics Data System (ADS)

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.

Wang, J.; SAO; ASIAA SMA Team

2003-12-01

69

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

NASA Astrophysics Data System (ADS)

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

Blackman, C. P.

1980-02-01

70

FISICA observations of the starburst galaxy, NGC 1569  

NASA Astrophysics Data System (ADS)

Using the Florida Image Slicer for Infrared Cosmology and Astrophysics (FISICA) we obtained observations of the dwarf starburst galaxy NGC 1569. We present our JH band spectra, particularly noting the existence of extended emission in Paschen ? and He I.

Clark, D. M.; Eikenberry, S. S.; Raines, S. N.; Gruel, N.; Elston, R.; Guzman, R.; Julian, J.; Boreman, G.; Glenn, P. E.; Hull-Allen, C. G.; Hoffman, J.; Rodgers, M.; Thompson, K.; Flint, S.; Comstock, L.; Myrick, B.

2006-06-01

71

K-Band observations of barred spiral galaxies.  

NASA Astrophysics Data System (ADS)

Observations in K band are used to investigate the bar and arm structures in the central regions of ten nearby barred southern spiral galaxies. Bar-interbar contrasts increase with radius for all galaxies. Arm-interarm contrasts reach a peak in mid-disk, where the m=2 Fourier components also peak. Isophotal twists are observed in half of the flat-barred galaxies, but in none of the exponential-barred galaxies. In all galaxies, the ellipticities reach a maximum at bar's end. Flat bars have a constant width with radius and a constant luminosity per unit length.

Regan, Michael W.; Elmegreen, Debra Meloy

1997-09-01

72

Gas dynamics and star formation in the galaxy pair NGC1512/1510  

NASA Astrophysics Data System (ADS)

Here we present HI line and 20-cm radio continuum data of the nearby galaxy pair NGC1512/1510 as obtained with the Australia Telescope Compact Array (ATCA). These are complemented by GALEX (Galaxy Evolution Explorer) ultraviolet (UV)-, SINGG H?- and Spitzer mid-infrared images, allowing us to compare the distribution and kinematics of the neutral atomic gas with the locations and ages of the stellar clusters within the system. For the barred, double-ring galaxy NGC1512 we find a very large HI disc, ~four times its optical diameter, with two pronounced spiral/tidal arms. Both its gas distribution and the distribution of the star-forming regions are affected by gravitational interaction with the neighbouring blue compact dwarf galaxy NGC1510. While the inner disc of NGC1512 shows quite regular rotation, deviations are visible along the outer arms and at the position of NGC1510. From the HI rotation curve of NGC1512 we estimate a dynamical mass of Mdyn >~ 3 × 1011Msolar, compared to an HI mass of MHI = 5.7 × 109Msolar (~2 per cent Mdyn). The two most distant HI clumps, at radii of ~80kpc, show signs of star formation (SF) and are likely tidal dwarf galaxies (TDGs). Both lie along an extrapolation of the eastern-most HI arm, with the most compact HI cloud located at the tip of the arm. The 20-cm radio continuum map indicates extended SF activity not only in the central regions of both galaxies but also in between them. SF in the outer disc of NGC1512 is revealed by deep optical- and two-colour UV images. Using the latter we determine the properties of >~200 stellar clusters and explore their correlation with dense HI clumps in the even larger 2X-HI disc. Outside the inner star-forming ring of NGC1512, which must contain a large reservoir of molecular gas, HI turns out to be an excellent tracer of SF activity. The multiwavelength analysis of the NGC1512/1510 system, which is probably in the first stages of a minor merger having started ~400Myr ago, links stellar and gaseous galaxy properties on scales from 1 to 100kpc. The observations were obtained with the Australia Telescope which is funded by the Commonwealth of Australia for operations as a National Facility managed by CSIRO. E-mail: Baerbel.koribalski@csiro.au

Koribalski, Bärbel S.; López-Sánchez, Ángel R.

2009-12-01

73

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

NASA Astrophysics Data System (ADS)

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 Sérsic 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.

Mihov, Boyko; Slavcheva-Mihova, Lyuba

74

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

Microsoft Academic Search

We analyze the gas kinematics and star formation properties of the nearby\\u000aRSab galaxy NGC 4736 using interferometric and single-dish CO(1-0) data and\\u000apreviously published Halpha and HI data. The CO morphology is dominated by a\\u000acentral molecular bar and tightly wound spiral arms associated with a bright\\u000aring of star formation. Strong HI emission is also found in the

Tony Wong; Leo Blitz

1999-01-01

75

Dense gas and HII regions in the starburst galaxy NGC 253  

NASA Astrophysics Data System (ADS)

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, 310 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.

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

1990-07-01

76

Gas flows in Galaxies: Mergers Versus Bars  

NASA Astrophysics Data System (ADS)

In this contribution, I will review the latest results of our ongoing work to study the central gas flows in merging galaxies, focusing on triggered star formation, presence of an AGN and changes in the gas-phase metallicity. Results from a sample of close galaxy pairs are compared with bar driven gas inflows in order to quantify the relative importance of hierarchical versus secular processes.

Ellison, S. L.; Patton, D. R.; Nair, P.; Mendel, J. T.; Scudder, J. M.; Simard, L.

2013-10-01

77

ROSAT PSPC Observations of Two Dynamically Young Elliptical Galaxies: NGC 4125 and NGC 3610  

NASA Astrophysics Data System (ADS)

We present the results of ROSAT PSPC X-ray observations of NGC 4125 and NGC 3610. These two galaxies are among the best representatives of a newly recognized class of elliptical galaxies that may be the product of recent mergers. NGC 4125 shows two plumes or disks crossing at right angles; NGC 3610 has the richest fine structure of all elliptical galaxies cataloged by Schweizer and Seitzer. Our X-ray observations show that these galaxies do not retain large gaseous halos, contrary to the suggested link between merging and X-ray brightness. Their X-ray luminosities (0.1-2 keV) are in the range 1040-41 ergs s-1, low compared with those of hot gas-rich elliptical galaxies. The X-ray to optical ratio of NGC 3610 is in the range of those of X-ray faint elliptical galaxies, consistent with the value found for the bulge of M31, where the X-ray emission is dominated by low-mass binaries; its X-ray spectrum is also comparable with those of X-ray faint elliptical galaxies, presenting significant very soft excess emission. The X-ray to optical ratio of NGC 4125 is larger and might suggest the presence of some hot interstellar medium. This suggestion is supported by the spectrum of NGC 4125, which shows evidence of Fe L emission. This spectrum can be fitted with either a low-abundance single-temperature Raymond model or with a two-temperature model with solar abundances. Further work is needed to firmly resolve the question of gaseous versus stellar X-ray emission in NGC 4125.

Fabbiano, G.; Schweizer, Francois

1995-07-01

78

CHANDRA OBSERVATIONS OF THE COLLISIONAL RING GALAXY NGC 922  

SciTech Connect

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.

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

79

Chandra Observations of the Collisional Ring Galaxy NGC 922  

NASA Astrophysics Data System (ADS)

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.

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

2012-03-01

80

Corrugated velocity patterns in the spiral galaxies: NGC 278, NGC 1058, NGC 2500 & UGC 3574 .  

NASA Astrophysics Data System (ADS)

In this work we address the study of the detection in Halpha of a radial corrugation in the vertical velocity field in a sample of four nearly face-on, spiral galaxies. The geometry of the problem is a main criterion in the selection of the sample as well as of the azimuthal angle of the slits. These spatial corrugations must be equally associated with wavy vertical motions in the galactic plane with a strong large-scale consistency. Evidence of these kinematic waves were first detected in the analysis of the rotation curves of spiral galaxies (eg Vaucoleurs & de Vaucaleurs 1963, Pismis 1965), but it was not until 2001 that Alfaro et al. analyzed in more detail the velocity corrugations in NGC 5427 and a possible physical mechanism for their origin. The aim of this study is to analyze the corrugated velocity pattern in terms of the star formation processes. We describe the geometry of the problem and establish its fundamental relationships.

Sánchez Gil, M. C.; Alfaro, E. J.; Pérez, E.

81

The galactic habitable zone in barred galaxies  

Microsoft Academic Search

One of the criteria for the concept of a galactic habitable zone (GHZ) is that the pattern speed of the stars in the GHZ should be close to the pattern speed of the spiral arms. Another criteria is that the stars in it should have a high enough metallicity. In a barred galaxy, the GHZ will be more complicated to

M. Sundin

2006-01-01

82

Molecular Gas Dynamics in NGC 6946: A Bar-driven Nuclear Starburst ``Caught in the Act''  

NASA Astrophysics Data System (ADS)

We present high angular resolution (~1" and 0.6") millimeter interferometric observations of the 12CO(1-0) and 12CO(2-1) line emission in the central 300 pc of the late-type spiral galaxy NGC 6946. The data, obtained with the IRAM Plateau de Bure Interferometer (PdBI), allow the first detection of a molecular gas spiral in the inner ~10" (270 pc) with a large concentration of molecular gas (MH2~1.6×107 Msolar) within the inner 60 pc. This nuclear clump shows evidence for a ringlike geometry with a radius of ~10 pc as inferred from the position-velocity diagrams. Both the distribution of the molecular gas and its kinematics can be well explained by the influence of an inner stellar bar of about 400 pc length. A qualitative model of the expected gas flow shows that streaming motions along the leading sides of this bar are a plausible explanation for the high nuclear gas density. Thus, NGC 6946 is a prime example of molecular gas kinematics being driven by a small-scale, secondary stellar bar. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

Schinnerer, Eva; Böker, Torsten; Emsellem, Eric; Lisenfeld, Ute

2006-09-01

83

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

NASA Astrophysics Data System (ADS)

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.

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

1985-03-01

84

DETECTION OF INFALLING HYDROGEN IN TRANSFER BETWEEN THE INTERACTING GALAXIES NGC 5426 AND NGC 5427  

SciTech Connect

Using velocity tagging we have detected hydrogen from NGC 5426 falling onto its interacting partner NGC 5427. Our observations, with the GHaFaS Fabry-Perot spectrometer, produced maps of the two galaxies in H{alpha} surface brightness and radial velocity. We found emission with the range of velocities associated with NGC 5426 along lines of sight apparently emanating from NGC 5427, superposed on the velocity map of the latter. After excluding instrumental effects we assign the anomalous emission to gas pulled from NGC 5426 during its passage close to NGC 5427. Its distribution, more intense between the arms and just outside the disk of NGC 5427, and weak, or absent, in the arms, suggests that the infalling gas is behind the disk, ionized by Lyman continuum photons escaping from NGC 5427. Modeling this, we estimate the distances of these gas clouds behind the plane: a few hundred parsecs to a few kiloparsecs. We also estimate the mass of the infalling (ionized plus neutral) gas, finding an infall rate of 10 M{sub sun} per year, consistent with the high measured star formation rate across the disk of NGC 5427 and with the detected circumnuclear galactic wind.

Font, Joan; Beckman, John E.; Fathi, Kambiz; Gutierrez, Leonel, E-mail: jfont@iac.es, E-mail: jeb@iac.es, E-mail: kambiz@astro.su.se, E-mail: leonel@astrosen.unam.mx [Instituto de Astrofisica de Canarias, c/Via Lactea, s/n, E38205, La Laguna, Tenerife (Spain)

2011-10-10

85

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

Microsoft Academic Search

NGC 4826 (M64) is a nearby Sab galaxy with an outstanding, absorbing dust lane (called the Evil Eye) asymmetrically placed across its prominent bulge. In addition, its central region is associated with several regions of ongoing star formation activity. We obtained accurate low-resolution (4.3 Å pixel-1) long-slit spectroscopy (KPNO 4 m) of NGC 4826 in the 5300-9100 Å spectral range,

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

2002-01-01

86

UBVRI observations of variability of nuclei of the Seyfert galaxies NGC 1275 and NGC 4151. Rapid flares on light curves of the galaxy NGC 1275  

NASA Astrophysics Data System (ADS)

Simultaneous UBVRI observations of the Seyfert galaxies NGC 1275 and NGC 4151 were obtained since 1989 till 1994. The unusual brightening of the NGC 4151 nucleus was accompanied by reddening of the blue region of its spectrum. Variations in brightness and colour indices of the NGC 1275 nucleus are complicated and unsynchronous. There are fast flares of two types on light curves within one night. Type I flares are characterized by maximal changes in U filter. During the flare of type II maximum flux increase in I band is accompanied by the constant flux in U band. Amplitudes of observed flares were 5-20%, their durations were 15-30 minutes.

Merkulova, N.; Metik, L.

87

The population of barred galaxies in the local universe. I. Detection and characterisation of bars  

NASA Astrophysics Data System (ADS)

Context: Bars are very common in the centre of the disc galaxies, and they drive the evolution of their structure. The state-of-the-art imaging and redshift surveys of galaxies allow us to study the relationships between the properties of the bars and those of their hosts in statistically significant samples. Aims: A volume-limited sample of 2106 disc galaxies was studied to derive the bar fraction, length, and strength as a function of the morphology, size, local galaxy density, light concentration, and colour of the host galaxy. The sample galaxies were selected to not be strongly disturbed/interacting. Methods: The bar and galaxy properties were obtained by analysing the r-band images of the sample galaxies available in the Sloan Digital Sky Survey Data Release 5. Results: The bars were detected using the ellipse fitting method and Fourier analysis method. They were tested and calibrated with extensive simulations on artificial images. The ellipse fitting method was found to be more efficient in detecting bars in spiral galaxies. The fraction of barred galaxies turned out to be 45%. A bar was found in 29% of the lenticular galaxies, in 55% and 54% of the early- and late-type spirals, respectively. The bar length (normalised by the galaxy size) of late-type spirals is shorter than in early-type or lenticular ones. A correlation between the bar length and galaxy size was found with longer bars hosted by larger galaxies. The bars of the lenticular galaxies are weaker than those in spirals. Moreover, the unimodal distribution of the bar strength found for all the galaxy types argues against a quick transition between the barred and unbarred statues. There is no difference between the local galaxy density of barred and unbarred galaxies. Besides, neither the length nor strength of the bars are correlated with the local density of the galaxy neighbourhoods. In contrast, a statistical significant difference between the central light concentration and colour of barred and unbarred galaxies was found. Bars are mostly located in less concentrated and bluer galaxies. Conclusions: These results indicate that the properties of bars are strongly related to those of their host galaxies, but do not depend on the local environment.

Aguerri, J. A. L.; Méndez-Abreu, J.; Corsini, E. M.

2009-02-01

88

Molecular Study of CO in near galaxies: NGC 253 and NGC 4945 case  

NASA Astrophysics Data System (ADS)

In this work we present molecular analysis of CO and isotopes ^{13}CO, ^{17}CO,^{18}CO, ^{13}C^{17}O and ^{13}C^{18}O derived from the obtained spectra for near galaxies NGC 253 and NGC 4945 observed with APEX Telescope (Atacama Pathfinder Experiment telescope) with 5100 m elevation on Chajnator plateu at Atacama Chile. APEX is a 12 m telescope working in millimetric and submillimetric wavelength.

Villicaña Pedraza, I.; Martin-Pintado, J.

2013-05-01

89

Dynamical simulations of the interacting galaxies in the NGC 520\\/UGC 957 system  

Microsoft Academic Search

Numerical simulations of the interacting galaxies in the NGC 520\\/UGC 957 system are presented. Two sets of models were produced to investigate the postulated three-galaxy system of two colliding disk galaxies within NGC 520 and the dwarf galaxy UGC 957. The first set of models simulated a dwarf perturbing one-disk galaxy, which tested the possibility that NGC 520 contains only

S. A. Stanford; Marc Balcells

1991-01-01

90

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

SciTech Connect

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

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

2012-11-20

91

Lenticular Galaxies at the Outskirts of the Leo II Group: NGC 3599 and NGC 3626  

NASA Astrophysics Data System (ADS)

We have studied unbarred S0 galaxies, NGC 3599 and NGC 3626, the members of the X-ray bright group Leo II, by means of three-dimensional spectroscopy, long-slit spectroscopy, and imaging, with the aim of identifying the epoch and mechanisms of their transformation from spirals. Both galaxies have appeared to bear complex features obviously resulting from minor merging: decoupled gas kinematics, nuclear star-forming rings, and multi-tiered oval large-scale stellar disks. The weak emission line nucleus of NGC 3599 bears all signs of Seyfert activity, according to the line-ratio diagnostics of the gas excitation mechanism. We conclude that the transformation of these lenticular galaxies took place about 1-2 Gyr ago, through gravitational mechanisms unrelated to the hot intragroup medium of Leo II.

Sil'chenko, O. K.; Moiseev, A. V.; Shulga, A. P.

2010-11-01

92

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

SciTech Connect

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.

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

1991-02-01

93

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

SciTech Connect

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.

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

94

The STIS GTO Galaxy Nuclear Dynamics Project: Preliminary Results for Galaxy NGC 4742  

Microsoft Academic Search

We present STIS high spatial resolution long-slit spectroscopy of the nuclear region of NGC 4742 as part of the STIS GTO program dedicated to understanding the demographics of supermassive central black holes in galaxies. NGC 4742 is a relavely nearby (13 Mpc), early-type galaxy. It was chosen as a low luminosity (MV = -19.32) candidate in the WFPC-I program to

M. E. Kaiser; G. A. Bower; R. F. Green

1999-01-01

95

Interstellar Gas in the NGC 4410 Galaxy Group  

NASA Astrophysics Data System (ADS)

We present new radio continuum, 21 cm H I, 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-lobed structure, with a high surface brightness lobe extending 3.6? (~100 kpc) to the southeast and a 6.2? (~180 kpc) low surface brightness feature in the northwest. Molecular gas is abundant in NGC 4410A, with MH2~4×109 Msolar (using the standard Galactic conversion factor) but is undetected in NGC 4410B. H I is less abundant, with MHI~109 Msolar for the pair. Our H I map shows a 3×108 Msolar H I tail extending 1.7? (50 kpc) to the southeast of the pair, coincident with a faint optical tail and partially overlapping with the southeastern radio lobe. The H I tail is anticoincident 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, we infer (3-8)×108 Msolar of hot gas in this feature. This may be either intracluster gas or shocked gas associated with the bridge. Our detection of abundant interstellar gas in this pair, including an H I-rich tidal tail near the southeastern radio lobe, suggests that the observed distortions in this lobe may have been caused by the interstellar medium in this system. The gravitational 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 and distort 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. Using our VLA data, we also searched for H I counterparts to the other 10 known members of the NGC 4410 group and CO from three other galaxies in the inner group. In our velocity range of 6690-7850 km s-1, we detected six other galaxies above our H I sensitivity limits of 2×108 Msolar for the inner group and 4×108 Msolar for the outer group. The total H I in the group is 1.4×1010 Msolar, 80% of which arises from four galaxies in the outer group. Three of these galaxies (VCC 822, VCC 831, and VCC 847) are spirals with MHI/LB ratios typical of field galaxies, while FGC 170A appears to be a gas-rich dwarf galaxy (MB~-18, MHI~3×109 Msolar). In the inner group, the SBa galaxy NGC 4410D (VCC 934) was detected in H I and CO (MHI~5×108 Msolar and MH2~8×108 Msolar) and has a 1' (28 kpc) long H I tail that points toward the nearby disk galaxy NGC 4410F. NGC 4410F was also detected in H I (MHI~4×108 Msolar). The galaxies in the inner group appear to be somewhat deficient in H I compared to their blue luminosities, suggesting phase changes driven by galaxy-galaxy or galaxy-intracluster medium encounters.

Smith, Beverly J.

2000-10-01

96

Interferometric CO Observations of the Ultraluminous IRAS (Infrared Astronomy satellite) Galaxies Arp 220, IC 694/NGC 3690, NGC 6420 and NGC 7469.  

National Technical Information Service (NTIS)

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 ...

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

1987-01-01

97

Molecular gas in NUclei of GAlaxies (NUGA). X. The Seyfert 2 galaxy NGC 3147  

NASA Astrophysics Data System (ADS)

We present 12CO(1-0) and 12CO(2-1) observations of the SA(rs)bc Seyfert 2 galaxy NGC 3147, obtained with the IRAM interferometer at 1.9 arcsec × 1.6 arcsec and 1.6 arcsec × 1.4 arcsec resolutions, respectively. We have also observed the central region of NGC 3147 with the IRAM 30 m telescope (at resolutions of 22´´ and 12´´ for 12CO(1-0) and 12CO(2-1), respectively), in order to obtain complete sampling at low spatial frequencies. These observations have been made in the context of the NUclei of GAlaxies (NUGA) project, aimed at the study of the different mechanisms for gas fueling of active galactic nuclei (AGN). A central peak seen mainly in 12CO(2-1) and a ring-like structure at r ? 10´´~ 2 kpc dominate the 12CO maps. In 12CO(1-0) an outer spiral at r ? 20 arcsec˜4 kpc is also detected, not visible in 12CO(2-1) emission because it falls outside the field-of-view of the primary beam. The average I21/I10 line ratio is ~0.7 in temperature units over the region mapped in both lines, consistent with the optically thick emission expected in the nuclei of spiral galaxies. The kinematics of the molecular structures are quite regular, although there is evidence for local non-circular or streaming motions. We show that the molecular gas distribution is similar but not exactly identical to those of star formation tracers, i.e., infrared (Spitzer) and ultraviolet (GALEX) emission. This agreement is consistent with a scenario of steady, ongoing formation of stars from the molecular clouds at a rate of ~1 M_? yr-1 within the innermost 4 kpc in radius. Using a near-infrared (NIR) image obtained with adaptive optics at the Canada-France-Hawaii Telescope (CFHT), we identify a weak bar in NGC 3147, which is classified as non-barred galaxy in the optical. We then compute the gravity torques exerted by this stellar bar on the gas. The torque is obtained first at each point in the map, and then azimuthally averaged with a weighting determined by the gas surface density traced by the CO emission. We find that the gas inside the inner CO ring is subject to a net negative torque and loses angular momentum. This is expected for gas at the ultra-harmonic resonance (UHR), just inside the corotation resonance of the stellar bar. In contrast, the gas outside corotation, in the spiral arms comprising the outer spiral structure, suffers positive torques and is driven outwards. We conclude that some molecular gas is presently flowing into the central region, since we find negative torques down to the resolution limit of our images.

Casasola, V.; Combes, F.; García-Burillo, S.; Hunt, L. K.; Léon, S.; Baker, A. J.

2008-10-01

98

ISO LWS Observations of the Two Nearby Spiral Galaxies NGC 6946 and NGC 1313  

NASA Astrophysics Data System (ADS)

We present the analysis of Infrared Space Observatory long-wavelength spectrometer (LWS) observations of the two nearby late-type galaxies NGC 1313 and NGC 6946. Both galaxies have been fully mapped in the [C II] far-infrared fine-structure line at 158 ?m, and some regions have been observed also in the [O I] 63 ?m and [N II] 122 ?m lines. We use these observations to derive the physical properties of the atomic interstellar medium, to establish how they relate to other interstellar medium components (gas and dust), and to establish how they vary with different galaxy components such as nucleus, spiral arms, and disk. The [C II] line is the main cooling line of the atomic medium. In NGC 6946 and NGC 1313, its emission represents 0.8% of the infrared emission. Moreover, the [C II] emission can be spatially associated with three components: the nucleus, the star-forming regions in spiral arms, and the diffuse galaxy disk. This last component contributes <~40% in NGC 6946 and ~30% in NGC 1313 to the total emission. We apply the photodissociation region (PDR) model by Kaufman et al. to derive PDR physical parameters responsible for the neutral atomic gas emission (G0, n, and Ts). The results do not significantly differ from what Malhotra et al. recently found by modeling the integrated emission of a sample of 60 normal galaxies. This suggests that the emission in each region under the LWS beam in NGC 6946 and NGC 1313 (corresponding to a linear size of ~1.5 kpc) is likely to arise from a mixture of components similar to the mixture producing the integrated emission of normal galaxies. However, some regions in NGC 6946 have a G0/n ratio ~2-3 times smaller than the mean value found for the normal galaxy sample (1.3), suggesting that the beam-averaged contribution of a less active component in these regions is higher than its contribution in the integrated emission of normal galaxies or, conversely, that the bulk of the integrated emission of the normal galaxies is dominated by a few active regions probably located in their nuclei. CO(1-0) and [C II] in NGC 6946 are well correlated, and the mean [C II]/CO ratio agrees with the mean integrated ratios of the normal galaxies sample. This value (~500) is a factor of ~2 less than the mean ratio found for a sample of normal galaxies observed with the Kupier Airborne Observatory (KAO) by Stacey et al. This difference is probably due to the fact that the KAO beam (55") is smaller than the LWS beam (75"), such that the Stacey et al. KAO observations are likely to be more biased toward the nucleus of the galaxies and therefore toward more active regions. In NGC 1313 only four LWS regions have been observed in CO(1-0), and three of them were detected. The [C II]/CO(1-0) seems to systematically increase from the northeast to the south, along the S-shaped spiral arm, indicating that the interstellar medium conditions in NGC 1313 are much more inhomogeneous than the conditions in NGC 6946. H I and [C II] in NGC 6946 are completely uncorrelated, probably because they arise from different gas components: [C II] arises principally in dense and warm PDR and H I from diffuse (n<~3×103 cm-3) gas. On the other hand, in NGC 1313 we successfully detect two distinct gas components: a cirrus-like component, for which H I and [C II] are weakly correlated as observed in our Galaxy, and a component associated with dense PDRs completely uncorrelated from H I as observed in NGC 6946. Finally, we find that the H I residing in dense gas surrounding the star-forming regions and presumably recently photodissociated constitutes a few percent of the total H I. In turn, this dense gas component produces most of the [C II] emission emitted by the atomic neutral medium, even if its contribution is lower in NGC 1313 than in NGC 6946. On the other hand, the [C II] emission arising from ionized gas is higher in NGC 1313 than in NGC 6946.

Contursi, Alessandra; Kaufman, Michael J.; Helou, George; Hollenbach, David J.; Brauher, James; Stacey, Gordon J.; Dale, Daniel A.; Malhotra, Sangeeta; Rubio, Monica; Rubin, Robert H.; Lord, Steven D.

2002-08-01

99

HST Observations of the Dynamically Young Elliptical Galaxy NGC 3610  

NASA Astrophysics Data System (ADS)

High-resolution images of the candidate dynamically young elliptical galaxy NGC 3610 have been obtained with the WFPC2 of the Hubble Space Telescope. Our observations show that NGC 3610 contains a remarkably twisted stellar disk within 2.7'' (0.4 kpc) of the center, but no apparent dust features. The smooth, symmetric appearance of this disk and the lack of correlation with the color image suggest that it is a relaxed stellar component, possibly a disk twisted by differential precession. A search for intermediate-age globular clusters formed during merger or accretion events reveals a population of roughly 70 candidates in NGC 3610 which are 0.2 mag redder in V-I and 1.0 mag brighter in V than a typical old, metal-poor population. Both the color and magnitude differences are consistent with an age of 3 +/- 1 Gyr for these clusters, assuming solar metallicity, a Salpeter IMF, the same mass function as the old clusters, and Bruzual-Charlot stellar evolution models. Combining these results with HST observations of five other merger remnants shows generally good agreement between previous age estimates based on photometric, spectroscopic, and kinematic observations of the remnants, and age estimates based on the colors and luminosities of young and intermediate-age star clusters. Hence, the star clusters can be used to help establish a link between ongoing mergers (e.g., NGC 4038/4039), recent merger remnants (e.g., NGC 3921, NGC 7252), intermediate-age merger remnants classified as ellipticals (e.g., NGC 3610), and even old ellipticals (NGC 4486 = M87). A comparison of the candidate young/intermediate-age globular clusters with the old globular clusters in NGC 7252, NGC 3610, and M87 suggests that the typical increase in the number of clusters during a merger event is 70 %.

Whitmore, B.; Miller, B.; Schweizer, F.; Fall, S. M.

1996-12-01

100

THE ARECIBO GALAXY ENVIRONMENT SURVEY. III. OBSERVATIONS TOWARD THE GALAXY PAIR NGC 7332/7339 AND THE ISOLATED GALAXY NGC 1156  

SciTech Connect

Two 5 deg{sup 2} regions around the NGC 7332/9 galaxy pair and the isolated galaxy NGC 1156 have been mapped in the 21 cm line of neutral hydrogen (H I) with the Arecibo L-band Feed Array out to a redshift of {approx}0.065 ({approx}20,000 km s{sup -1}) as part of the Arecibo Galaxy Environment Survey. One of the aims of this survey is to investigate the environment of galaxies by identifying dwarf companions and interaction remnants; both of these areas provide the potential for such discoveries. The neutral hydrogen observations were complemented by optical and radio follow-up observations with a number of telescopes. A total of 87 galaxies were found, of which 39 (45%) were previously cataloged and 15 (17%) have prior redshifts. Two dwarf galaxies have been discovered in the NGC 7332 group and a single dwarf galaxy in the vicinity of NGC 1156. A parallel optical search of the area revealed one further possible dwarf galaxy near NGC 7332.

Minchin, R. F. [Arecibo Observatory, HC03 Box 53995, Arecibo, PR 00612 (United States); Momjian, E. [NRAO, Dominici Science Operations Center, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801 (United States); Auld, R.; Davies, J. I.; Smith, M. W. L.; Taylor, R. [School of Physics and Astronomy, Cardiff University, Cardiff, CF24 3YB (United Kingdom); Valls-Gabaud, D.; Van Driel, W. [GEPI, CNRS UMR 8111, Observatoire de Paris, 5 Place Jules Janssen, 92195 Meudon Cedex (France); Karachentsev, I. D. [Special Astrophysical Observatory, Russian Academy of Sciences, Nizhnii Arkhyz, Zelencukskaya, Karachai-Cherkessia 369167 (Russian Federation); Henning, P. A. [Department of Physics and Astronomy, University of New Mexico, 800 Yale Boulevard Northeast, Albuquerque, NM 87131 (United States); O'Neil, K. L. [NRAO Green Bank, P.O. Box 2, Route 28/92, Green Bank, WV 24944 (United States); Schneider, S.; Stage, M. D. [Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States)

2010-10-15

101

H? kinematics of S4G spiral galaxies - I. NGC 864  

NASA Astrophysics Data System (ADS)

We present a study of the kinematics of the isolated spiral galaxy NGC 864, using H? Fabry-Perot data obtained with the Galaxy H? Fabry-Perot System (GH?FaS) instrument at the William Herschel Telescope in La Palma, complemented with images at 3.6 ?m, in the R band and in H? filter, and integral-field spectroscopic data. The resulting data cubes and velocity maps allow the study of the kinematics of the galaxy, including in-depth investigations of the rotation curve, velocity moment maps, velocity residual maps, gradient maps and position-velocity diagrams. We find asymmetries in the velocity field in the bar zone, caused by non-circular motions, probably in response to the potential of the bar. We also find a flat-profile bar, in agreement with the strong bar, with the grand design spiral pattern, and with the gap between the ends of the bar and the start of the spiral arms. We quantify the rate of massive star formation, which is concentrated in the two spiral arms.

Erroz-Ferrer, Santiago; Knapen, Johan H.; Font, Joan; Beckman, John E.; Falcón-Barroso, Jesús; Sánchez-Gallego, José Ramón; Athanassoula, E.; Bosma, Albert; Gadotti, Dimitri A.; Muñoz-Mateos, Juan Carlos; Sheth, Kartik; Buta, Ronald J.; Comerón, Sébastien; Gil de Paz, Armando; Hinz, Joannah L.; Ho, Luis C.; Kim, Taehyun; Laine, Jarkko; Laurikainen, Eija; Madore, Barry F.; Menéndez-Delmestre, Karín; Mizusawa, Trisha; Regan, Michael W.; Salo, Heikki; Seibert, Mark

2012-12-01

102

Understanding the Structure of NGC 1569 and Dwarf Irregular Galaxies  

NASA Astrophysics Data System (ADS)

NGC 1569 is a post-starburst dwarf irregular (dIm) galaxy located in the IC 342 galaxy group. It has 3 supermassive star clusters (SSCs) and is a well studied object in the literature. We present an in depth study of the kinematics of the stellar and gas disks of NGC 1569 and analyze the three dimensional shape of this dIm galaxy. There are three forms of data we use to determine the shape of this system. First, we obtained long-slit, high resolution spectroscopy of the stars in NGC 1569 using the KPNO 4-meter + Echelle spectrograph. For these stellar spectra, we used a filter that targets the Mg Ib absorption features. During one of our 4-meter+Echelle observing runs, we changed the filter to target the [OIII]?5007Å emission line. Using this filter, we observed radial velocities of the ionized gas in NGC 1569, the second form of data in our study. Thirdly, we used high spatial and high spectral resolution, 21 cm, VLA HI line data obtained by THINGS. These data were mapped using a multi-scale cleaning algorithm implemented in AIPS by the LITTLE THINGS team. The kinematics of the gas were obtained using a double Gaussian decomposition method to separate a bulk motion velocity field from random, non-circular motions. In addition to the kinematic study, we also present our results of a large, 9° x 2° HI emission map made using the Robert C. Byrd Green Bank Telescope. We detect large-scale HI structure around NGC 1569 indicative of possible interactions with IC 342 galaxy group members. We conclude the dissertation talk by highlighting two more dwarf irregular galaxies for which both stellar and gas kinematics have been obtained and analyzed. This research has been funded by the NSF LITTLE THINGS grant AST-0707563 and by the NRAO Student Observing Support award GSSP10-0001.

Jackson, Megan C.; Hunter, D.; Oh, S.; LITTLE THINGS Team

2011-01-01

103

The optical morphology of the kinematically peculiar galaxy NGC 4826  

NASA Astrophysics Data System (ADS)

We present charge coupled device (CCD) BVI photometry of the galaxy NGC 4826, the Evil- or Black-Eye galaxy, which was recently found to have two counter-rotating gas disks. We study the extinction in the inner gas disk, which gives NGC 4826 its nickname, and find that this disk can be coplanar or close to coplanar with the stellar disk and still cause the strong absorption that is seen on one side of the galaxy. We try to constrain the orientation of the outer gas disk by looking for a small overall asymmetry in the light distribution which would be present if there is dust in this disk, and if it is significantly tilted with respect to the main body of the galaxy. The test shows that the light distribution does not preclude the outer gas disk from being coplanar with the stellar disk as well. NGC 4826 has a small bulge, with a bulge to total light ratio of 0.17 in B. We confirm that this galaxy is indeed a spiral, with a perfect exponential disk down to 27 mag/sq arcsec in B. The close to coplanar orientation of the gas disks is one aspect which is in good agreement with what is expected on the basis of a merger model for the counter-rotating gas. The rotation direction of the inner gas disk with respect to the stars, however, is not. In addition, the existence of a well defined exponential disk probably implies that if a merger did occur it must have been between a gas-rich dwarf and a spiral, not between two equal mass spirals. The stellar spiral arms of NGC 4826 are trailing over part of the disk and leading in the outer disk. Recent numerical calculations by Byrd et al. for NGC 4622 suggest that long lasting leading arms could be formed by a close retrograde passage of a small companion. In this scenario, the outer counter-rotating gas disk in NGC 4826 might be the tidally stripped gas from the dwarf. However, in NGC 4826 the outer arms are leading, while it appears that in NGC 4622 the inner arms are leading. A realistic N-body/hydro simulation of a dwarf-spiral encounter is clearly needed. It may also be possible that the counter-rotating outer gas disk is due to gradual infall of gas from the halo, rather than from a discrete merger event.

Walterbos, R. A. M.; Braun, R.; Kennicutt, R. C., Jr.

1994-01-01

104

Dynamics of the interstellar matter in galaxies : isolated barred spiral galaxies : cloud formation processes  

NASA Astrophysics Data System (ADS)

The dynamical components of six isolated barred spiral (SB) galaxies are investigated. No evidence is found supporting the hypothesis of a low amount of dark matter being characteristic of SB galaxies. The presence of companion galaxies is found to correlate with an increased statistical spread in the neutral hydrogen (HI) extent. It is concluded that the selection of galaxies with large HI extent may introduce a bias towards tidally interacting systems. The circumnuclear region of the SB galaxy NGC 1365 is studied with the Hubble Space Telescope (HST). Numerous bright "super star clusters" (SSCs) are detected, surrounding the active nucleus. The bright compact radio source NGC 1365:A is found to coincide spatially with one of the SSCs. We conclude that the source is a "radio supernova". In the [OIII] l 5007 line, the HST resolves individual clouds within the conical outflow from the nucleus, some of which gather in larger agglomerations. An in-depth study of the dynamics of the SB galaxy NGC 1300 is presented. Multi-wavelength data yield an estimate of the velocity field and gravitational potential. Subsequent hydrodynamical simulations are able to reproduce the morphology and kinematics in the bar region using a pure bar perturbing potential. To reproduce the spiral structure a weak spiral component has to be added, indicative of stellar spiral response to the bar and/or self-gravitating gas in the arms. Two separate models, differing mainly with respect to pattern speed and associated resonance structure, are found to reproduce the observations. We study numerically the linear polarization and extinction of light from background stars passing through molecular clouds, illuminating the intricacies of the derivation of the magnetic-field-line pattern in a cloud from the observed polarization pattern: Due to a higher gas-grain collision frequency within the cloud, the polarization caused by the cloud may well be dominated by background/foreground polarization. Furthermore, variations in field-orientation along the line-of-sight may cause notable differences between the observed polarization vectors and the true magnetic-field-line pattern. Small-scale, helical, interstellar filaments are discussed on the basis of optical observations of an "elephant trunk" structure in the Rosette nebula. The observed sinusoidal filaments are suggested to be helices lined up by magnetic fields. We propose that the Rosette elephant trunks form an interconnected system of rope-like structures which are relics from filamentary skeletons of magnetic fields in the primordial cloud. Stochastic mass fractionation of a molecular cloud is simulated numerically. It is found that geometry alone may constrain the resulting mass spectrum of molecular cloud clumps. We demonstrate that further fragmentation of the cloud clumps, under the assumption of a lower limit of the self-similar regime, produces a mass spectrum that has qualitative and quantitative similarities with the empirically determined stellar initial mass function.

Helmuth, Kristen

1998-12-01

105

Molecular gas in NUclei of GAlaxies (NUGA). VIII. The Seyfert 2 NGC 6574  

NASA Astrophysics Data System (ADS)

Within the frame of the NUclei of GAlaxies (NUGA) project, we have determined the distribution and kinematics of the molecular gas within the central kpc with high spatial resolution (100-150 pc), for a sample of active galaxies. The goal is to study the gas-fueling mechanisms in AGN. We present interferometric observations of 12CO(1-0) and 12CO(2-1) line emission from the Seyfert 2 galaxy NGC 6574, obtained with the IRAM Plateau de Bure Interferometer (PdBI). These data have been combined with 30 m mapping data in these lines to correct for the flux resolved by the interferometer. At an angular resolution of 0.7 arcsec (?110 pc), the 12CO(2-1) emission is resolved into an inner disk with a radius of 300 pc. The molecular gas in NGC 6574 is primarily distributed in four components: nucleus, bar, spiral arms - winding up into a pseudo-ring - and an extended underlying disk component. For the overall galaxy host, we find a 12CO(2-1) to 12CO(1-0) line ratio of ~0.3 indicative of cold or sub-thermally excited gas. For the nucleus, this ratio is close to unity, indicating emission from dense and warm molecular gas. Modeling the gas kinematics with elliptical orbits shows that the molecular gas in the differentially rotating disk of NGC 6574 is strongly influenced by the presence of a stellar bar. The nuclear component shows an extension toward the southeast that may be an indication of the lopsidedness of the nuclear gas distribution. We computed the gravity torques exerted from the stellar bar on the gas, deriving the gravitational potential from near-infrared images, and weighting the torques by the CO distribution. We find negative torques for the gas inside the ring, since the gas aligned with the bar has a slight advance phase shift, leading the bar. This means that gas is flowing in towards the center, at least down to 400 pc in radius, which can explain the observed high nuclear gas concentration. This concentration corresponds to a possible inner Lindblad resonance of the bar, according to the measured rotation curve. The gas has been piling up in this location quite recently, since no startburst has been observed yet.

Lindt-Krieg, E.; Eckart, A.; Neri, R.; Krips, M.; Pott, J.-U.; García-Burillo, S.; Combes, F.

2008-02-01

106

Galaxy Zoo: The Environmental Dependence of Bars and Bulges in Disc Galaxies  

NASA Astrophysics Data System (ADS)

We present an analysis of the environmental dependence of bars and bulges in disc galaxies, using a volume-limited catalogue of 16397 galaxies at z<0.06 from the Sloan Digital Sky Survey that have visual morphologies from the Galaxy Zoo 2 project. We confirm that the likelihood of having a bar or bulge in disc galaxies increases when the galaxies have redder optical colours and larger stellar masses, and observe a transition in the bar and bulge likelihoods, such that massive disc galaxies with high stellar mass surface densities, old stellar populations, and low star formation rates and gas masses are more likely to host bulges and bars. However, we find that bar and bulge likelihood are not monotonically correlated with each other. In addition, while most bulge-dominated disc galaxies are massive and on the 'red sequence' of the colour-magnitude diagram, a wider variety of optical colours is seen in galaxies that host bars. We use two-point galaxy clustering methods to demonstrate statistically significant environmental correlations of both barred and bulged galaxies, from projected separations of 150 kpc/h to 3 Mpc/h. We demonstrate that a large fraction (30-90%) of the bar-environment correlation is explained by more massive dark matter haloes hosting redder disc galaxies which in turn are more likely to have bars. This is shown with two independent tests: (1) by shuffling the bar likelihood at a given colour; and (2) using an SDSS-like mock galaxy catalogue in which bar likelihoods are assigned based on the model galaxy colour. In contrast, the environmental dependence of stellar mass explains less of the bar-environment correlation. Finally, by analyzing the clustering measurements with halo occupation models, we argue that unbarred galaxies are dominated by central galaxies in low-mass haloes, while the satellite disc galaxies in more massive haloes are more likely to form bars.

Skibba, Ramin A.; Masters, K. L.; Nichol, R. C.; Zehavi, I.; Hoyle, B.; Edmondson, E. M.; Zoo, Galaxy

2012-01-01

107

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

SciTech Connect

We present results from Chandra observations of the galaxy pair NGC 7619 and NGC 7626, the two dominant members of the Pegasus group. The X-ray images show a brightness edge associated with each galaxy, which we identify as merger cold fronts. The edges are sharp, and the axes of symmetry of the edges are roughly antiparallel, suggesting that these galaxies are falling toward one another in the plane of the sky. The detection of merger cold fronts in each of the two dominant member galaxies implies a merging subgroup scenario, since the alternative is that the galaxies are falling into a preexisting {approx}1 keV halo without a dominant galaxy of its own, and such objects are not observed. We estimate the three-dimensional velocities from the cold fronts and, using the observed radial velocities of the galaxies, show that the velocity vectors are indeed most likely close to the plane of the sky, with a relative velocity of {approx}1190 km s{sup -1}. The relative velocity is consistent with what is expected from the infall of two roughly equal mass subgroups whose total viral mass equals that of the Pegasus group. We conclude that the Pegasus cluster is most likely currently forming from a major merger of two subgroups, dominated by NGC 7619 and NGC 7626. NGC 7626 contains a strong radio source, consisting of a core with two symmetric jets, and radio lobes. Although we find no associated structure in the X-ray surface brightness map, the temperature map reveals a clump of cool gas just outside the southern lobe, presumably entrained by the lobe, and possibly an extension of cooler gas into the lobe itself. The jet axis is parallel with the projected direction of motion of NGC 7626 (inferred from the symmetry axis of the merger cold front), and the southern leading jet is foreshortened as compared to the northern trailing one, possibly due to the additional ram pressure encountered by the forward jet.

Randall, S. W.; Jones, C.; Kraft, R.; Forman, W. R.; O'Sullivan, E. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)

2009-05-10

108

Atomic hydrogen in the NGC 4631 group of galaxies  

NASA Astrophysics Data System (ADS)

We present WSRT observations of 21-cm line emission from the disturbed, edge-on galaxy NGC 4631. Maps at resolutions 12"x22", 35", and 45"x89" are presented, and these are used in conjunction with position-velocity cuts through the various data cubes in order to understand the structure of the disk and the many tidal spurs which protrude from this interacting galaxy. We also study the two companions NGC 4656 and NGC 4627, and three dwarfs in the system with H I detections. We first attempt to get a rough idea of the structure of the disk of NGC 4631. The data can be well modelled by a differentially rotating disk with a steep fall-off beyond 4 kpc, and an outer disk restricted to the radius range 7-15 kpc. The latter component could simply be a set of spiral arms. Radial motions are probably present in the central few arcminutes. The inner disk bends upwards with increasing distance from the center on both the east and west sides. Strong tides may be responsible. The H I layer at high resolution shows many disturbances, a large extent parallel to the minor axis, and a ragged appearance along its edges. The velocity structure of the gas far from the major axis of NGC 4631 suggests that most of this emission is due to the galaxy being not quite edge-on, a rather large (500-1000 pc) scale-height in the outer galaxy, and the connection of one of the spurs with the disk. A few high latitude features with a probable inner disk origin are found, and these are more likely to be due to gas raised out of the plane by stellar winds and supernovae. However, outer galaxy star formation may contribute to the large H I scale-height there. No gas can be unambiguously associated with the dwarf elliptical companion, NGC 4627. It is difficult to identify any of the spurs as gas that once belonged to this galaxy (despite recent signs of star formation), as in the model of Combes. Modelling of the tidal encounters should now be redone, since more tidal debris has been discovered and an optical velocity of NGC 4627 has been determined. Position-velocity diagrams parallel to the major axis of the edge-on companion, NGC 4656, reveal a ring-like structure in the inner 15 kpc. Furthermore, the high and low-velocity sides of the ring arise from opposite sides of the midplane. Two possible explanations are given for this structure. First, NGC 4656 may consist primarily of two loosely wrapped tidal arms, viewed not quite edge-on. Second, NGC 4656 may be a ring galaxy similar to the Cartwheel. The south-west side of the disk shows many "worms" (or vertical filaments) with velocities consistent with an outer disk origin. The most prominent worm, however, is on the north-east side, above the center of the major axis. Its mass is ~3 x 10^7^ Msun_. At very marginal signal-to-noise ratios, the worm bends around to form a complete loop.

Rand, R. J.

1994-05-01

109

The Arecibo Galaxy Environment Survey-Data of NGC7448  

NASA Astrophysics Data System (ADS)

The Arecibo Galaxy Environment Survey (AGES) is a neutral hydrogen galaxy survey. It is searching for galaxies by 21cm emission from neutral hydrogen gas in their interstellar media. I studied the area within NGC 7448; with a 7.5 square degrees field detected with the Mock spectrometer and covering a redshift range of z ~0.03 - 0.15. A catalogue of 88 sources was obtained. I analyzed and compared the data with the SDSS for optical counterparts. The catalogue includes measured parameters such as HI mass, velocity width, and mass-to-light ratios for the sources. The results include a ring galaxy, galaxies with high redshifts, high HI masses and high mass-to-light ratios.

Vázquez Colón, Clarissa; Taylor, R.; Minchin, R. F.

2013-01-01

110

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

SciTech Connect

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

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

2012-12-01

111

New ULX in the collisional ring galaxy NGC 922  

NASA Astrophysics Data System (ADS)

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.

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

2009-09-01

112

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

NASA Astrophysics Data System (ADS)

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.

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

2011-01-01

113

The relation between bar formation, galaxy luminosity, and environment.  

NASA Astrophysics Data System (ADS)

We derive the bar fraction in three different environments ranging from the field to Virgo and Coma clusters, covering an unprecedentedly large range of galaxy luminosities (or, equivalently, stellar masses). We confirm that the fraction of barred galaxies strongly depends on galaxy luminosity. We also show that the difference between the bar fraction distributions as a function of galaxy luminosity (and mass) in the field and Coma cluster are statistically significant, with Virgo being an intermediate case. We interpret this result as a variation of the effect of environment on bar formation depending on galaxy luminosity. We speculate that brighter disk galaxies are stable enough against interactions to keep their cold structure, thus, the interactions are able to trigger bar formation. For fainter galaxies the interactions become strong enough to heat up the disks inhibiting bar formation and even destroying the disks. Finally, we point out that the controversy regarding whether the bar fraction depends on environment could be resolved by taking into account the different luminosity ranges of the galaxy samples studied so far.

Corsini, E. M.; Méndez-Abreu, J.; Sánchez-Janssen, R.; Aguerri, J. A. L.; Zarattini, S.

114

The three rings of the isolated galaxy NGC 7217.  

NASA Astrophysics Data System (ADS)

We present WSRT H I line observations, together with CCD-BVRI photometry, of NGC 7217, which is known to be an isolated galaxy with an inner ring, an inner pseudoring and an outer ring, but for which no clear bi-symmetric distortion is immediately apparent. Assuming, as is known to be the case for barred galaxies, that the outer ring corresponds to the outer Lindblad resonance, we have derived the expected locations for the other resonances using a combined optical/H I rotation curve. Our result is that the observed inner ring coincides with the inner Lindblad resonance and the inner pseudoring with the ultraharmonic (4:1) resonance. The associated pattern speed is 86.0km/s/kpc. However, it is less clear which feature is actually setting up this pattern. The outer ring, which has a size of =~6.3x5.9kpc, contains roughly two-thirds of the total H I mass, and has bluer colours and more intense H? emission than the main disk. A Fourier analysis of the B-I colour along this ring suggests that it is composed of 9 blobs, indicating the existence of a bead instability. This is in agreement with a simple calculation showing that the number of Jeans lengths along the ring is also 9, and that self-gravity is probably important here. Clumps also exist in the inner pseudoring, but they are less well defined, and there is no H I concentration along it. This ring has redder colours than the outer ring. The blue inner ring is incomplete, coincides with a complete and intense H? ring, and is surrounded by a redder ring. A spiral-like structure extends from the inner ring out to the inner pseudoring, with the same winding direction as the outer flocculent arms. We have constructed a mass model, from which we obtain a mass-to-I-band luminosity ratio of 5.1 for the bulge, and 1.8 for the disk. The core radius of the halo is 11.0kpc, and its central density 0.062Msun_pc^-3^. The ratio of halo core radius to optical radius is thus of order unity.

Verdes-Montenegro, L.; Bosma, A.; Athanassoula, E.

1995-08-01

115

Photometric Properties of the Bright Lenticular Galaxy NGC 5102  

NASA Astrophysics Data System (ADS)

Using the photographic imagery of the SO galaxy NGC 5102, the equivalent luminosity profile and the fractional integrated luminosity curve have been derived. Several photometric parameters of the galaxy, such as a total magnitude (B_T), equivalent radius (r^star_e), effective surface brightness (mu^star_e), and concentration indices (C_21, C_32) were derived from the luminosity profiles. According to the decomposition method from nonlinear least squares fitting, photometric parameters of the bulge (mu_e, r_e) and the exponential disk (mu(0), alpha^-1), and the bulge to total luminosity ratio (B/T) were obtained. The derived central disk surface brightness (mu(0) = 22.06 +- 0.18 mag/*+/- and the evaluated B/T ratio (= 0.52) of the NGC 5102 are close to the mean values (mu(0) = 21.65 +- 0.3 mag/*+/-", B/T = 0.63) of the SO galaxies. Analysis showed that a lens-like hump is embedded in the equivalent luminosity profile of the NGC 5102.

Sohn, Young-Jong; Chun, Mun-Suk; Byun, Yong-Ik

1991-12-01

116

Modeling Dust and Starlight in Galaxies Observed by Spitzer and Herschel: NGC 628 and NGC 6946  

NASA Astrophysics Data System (ADS)

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

Aniano, G.; Draine, B. T.; Calzetti, D.; Dale, D. A.; Engelbracht, C. W.; Gordon, K. D.; Hunt, L. K.; Kennicutt, R. C.; Krause, O.; Leroy, A. K.; Rix, H.-W.; Roussel, H.; Sandstrom, K.; Sauvage, M.; Walter, F.; Armus, L.; Bolatto, A. D.; Crocker, A.; Donovan Meyer, J.; Galametz, M.; Helou, G.; Hinz, J.; Johnson, B. D.; Koda, J.; Montiel, E.; Murphy, E. J.; Skibba, R.; Smith, J.-D. T.; Wolfire, M. G.

2012-09-01

117

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

SciTech Connect

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

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

2012-09-10

118

Molecular and ionized gas in the peculiar galaxy NGC 2146  

SciTech Connect

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.

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

1988-08-01

119

Kinematics and stellar population of the lenticular galaxy NGC 4124  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

120

The Distribution of Bar Strengths in Disk Galaxies  

NASA Astrophysics Data System (ADS)

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.

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

2007-05-01

121

The Stellar Content of NGC 6789, A Blue Compact Dwarf Galaxy in the Local Void  

Microsoft Academic Search

We find that NGC 6789 is the most nearby example of a blue compact dwarf galaxy known to date. With the help of the Wide Field Planetary Camera 2 aboard the Hubble Space Telescope, we resolve NGC 6789 into over 15,000 point sources in the V and I bands. The young stars of NGC 6789 are found exclusively near the

Igor O. Drozdovsky; Regina E. Schulte-Ladbeck; Ulrich Hopp; Mary M. Crone; Laura Greggio

2001-01-01

122

A barred spiral at the centre of the giant elliptical radio galaxy Centaurus A  

NASA Astrophysics Data System (ADS)

We report observations at mid-infrared and sub-millimeter wavelengths of Centaurus A (Cen A, NGC 5128), the giant elliptical galaxy that harbors the closest radio loud Active Galactic Nucleus (AGN) to Earth. The dust emission from the deep interior of Cen A reveals a bisymmetric structure with a diameter of 5(') (5 kpc), centred at the AGN. This structure is remarkably similar to that of a barred spiral galaxy, with the bar lying in a plane that is tilted ~ 18(deg) from the line of sight. The true nature of the distribution of dust in the inner regions of Cen A is noticeably displaced from the more chaotic and widespread optical obscuration. The barred spiral is a quasi-stable structure formed at the center of the giant elliptical from the tidal debris of a gas-rich object(s) accreted in the past 10(9) years. The total size and mass of interstellar gas in the barred spiral at the center of Cen A is comparable to the small Local Group spiral galaxy Messier 33. The observation of this remarkable structure opens the more general question on whether the dusty hosts of giant radio galaxies like Cen A, are ``symbiotic" galaxies composed of a barred spiral inside an elliptical, where the bar serves to funnel gas toward the AGN. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with participation of ISAS and NASA.

Mirabel, I. F.; Laurent, O.; Sanders, D. B.; Sauvage, M.; Tagger, M.; Charmandaris, V.; Vigroux, L.; Gallais, P.; Cesarsky, C.; Block, D. L.

1999-01-01

123

Dynamical simulations of the interacting galaxies in the NGC 520/UGC 957 system  

NASA Astrophysics Data System (ADS)

Numerical simulations of the interacting galaxies in the NGC 520/UGC 957 system are presented. Two sets of models were produced to investigate the postulated three-galaxy system of two colliding disk galaxies within NGC 520 and the dwarf galaxy UGC 957. The first set of models simulated a dwarf perturbing one-disk galaxy, which tested the possibility that NGC 520 contains only one galaxy disturbed by the passage of UGC 957. The resulting morphology of the perturbed single disk in the simulation fails to reproduce the observed tidal tails and northwest mass condensation of NGC 520. A second set of models simulated two colliding disks, which tested the hypothesis that NGC 520 itself contains two galaxies in a strong collision and UGC 957 is unimportant to the interaction. These disk-disk models produced a good match to the morphology of the present NGC 520. It is concluded that (1) NGC 520 contains two colliding disk galaxies which have produced the brighter southern half of the long tidal tail and (2) UGC 957, which may originally have been a satellite of one of the disk galaxies, formed the diffuse northern tail as it orbited NGC 520.

Stanford, S. A.; Balcells, Marc

1991-03-01

124

Star Formation Models for the Dwarf Galaxies NGC 2915 and NGC 1705  

NASA Astrophysics Data System (ADS)

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 ?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.

Elson, E. C.; de Blok, W. J. G.; Kraan-Korteweg, R. C.

2012-01-01

125

A Counterrotating Bulge in the S(b) Galaxy NGC 7331  

NASA Astrophysics Data System (ADS)

We have found that the bulge of the large, nearby Sb galaxy NGC 7331 rotates retrograde to its disk. Analysis of spectra in the region of the near-IR Ca II triplet along the major axis shows that, in the radial range between 5" and ~20", the line-of-sight velocity distribution of the absorption lines has two distinct peaks and can be decomposed into a fast-rotating component with {v} / sigma > 3, and a slower rotating, retrograde component with {v} / sigma ~ 1--1.5. The radial surface brightness profile of the counterrotating component follows that of the bulge, obtained from a two-dimensional bulge-disk decomposition of a near-infrared K-band image, while the fast-rotating component follows the disk. At the radius at which the disk starts to dominate, the isophotes change from being considerably boxy to being very disky. Although a number of spiral galaxies have been found that contain cold, counterrotating disks, this is the first galaxy known to have a boxy, probably triaxial, fairly warm, counterrotating component, which is dominating in the central regions. If it is a bar seen end-on, this bar has to be thicker than the disk. We find that NGC 7331, even though it is a fairly early-type spiral, does not have a conventional, corotating bulge. The fact that the inner component is retrograde makes us believe that it was formed from infalling material in either stellar or gaseous form (see, e.g. Balcells & Quinn). Another possibility, however, is that the structure has been there since the formation of the galaxy. In this case, it will be a challenge to explain the large change in orientation of the angular momentum when going outward radially.

Prada, F.; Gutierrez, C. M.; Peletier, R. F.; McKeith, C. D.

1996-05-01

126

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

SciTech Connect

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

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

2010-08-10

127

LOCAL GROUP DWARF ELLIPTICAL GALAXIES. II. STELLAR KINEMATICS TO LARGE RADII IN NGC 147 AND NGC 185  

SciTech Connect

We present kinematic and metallicity profiles for the M 31 dwarf elliptical (dE) satellite galaxies NGC 147 and NGC 185. The profiles represent the most extensive spectroscopic radial coverage for any dE galaxy, extending to a projected distance of 8 half-light radii (8r{sub eff} {approx} 14'). We achieve this coverage via Keck/DEIMOS multislit spectroscopic observations of 520 and 442 member red giant branch stars in NGC 147 and NGC 185, respectively. In contrast to previous studies, we find that both dEs have significant internal rotation. We measure a maximum rotational velocity of 17 +- 2 km s{sup -1} for NGC 147 and 15 +- 5 km s{sup -1} for NGC 185. While both rotation profiles suggest a flattening in the outer regions, there is no indication that we have reached the radius of maximum rotation velocity. The velocity dispersions decrease gently with radius with average dispersions of 16 +- 1 km s{sup -1} and 24 +- 1 km s{sup -1} for NGC 147 and NGC 185, respectively. The average metallicities for NGC 147 and NGC 185 are [Fe/H] = -1.1 +- 0.1 and [Fe/H] = -1.3 +- 0.1, respectively; both dEs have internal metallicity dispersions of 0.5 dex, but show no evidence for a radial metallicity gradient. We construct two-{integral} axisymmetric dynamical models and find that the observed kinematical profiles cannot be explained without modest amounts of non-baryonic dark matter. We measure central mass-to-light ratios of M/L{sub V} = 4.2 +- 0.6 and M/L{sub V} = 4.6 +- 0.6 for NGC 147 and NGC 185, respectively. Both dE galaxies are consistent with being primarily flattened by their rotational motions, although some anisotropic velocity dispersion is needed to fully explain their observed shapes. The velocity profiles of all three Local Group dEs (NGC 147, NGC 185, and NGC 205) suggest that rotation is more prevalent in the dE galaxy class than previously assumed, but often manifests only at several times the effective radius. Since all dEs outside the Local Group have been probed to only inside the effective radius, this opens the door for formation mechanisms in which dEs are transformed or stripped versions of gas-rich rotating progenitor galaxies.

Geha, M. [Astronomy Department, Yale University, New Haven, CT 06520 (United States); Van der Marel, R. P.; Kalirai, J. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Guhathakurta, P. [UCO/Lick Observatory, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Gilbert, K. M. [Department of Astronomy, University of Washington, Seattle, WA 98195-1580 (United States); Kirby, E. N., E-mail: marla.geha@yale.ed [California Institute of Technology, Department of Astronomy, 1200 E California Blvd, Pasadena, CA 91125 (United States)

2010-03-01

128

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

NASA Astrophysics Data System (ADS)

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.

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

2008-08-01

129

The variable X\\/-ray spectrum of the Seyfert 2 galaxy NGC7172  

Microsoft Academic Search

A broad band X-, gamma-ray spectral study of the Seyfert 2 galaxy NGC 7172 is presented. We use our ASCA ob- servations from May 1995 and combine these with the CGRO OSSE data from March 1995. The only Seyfert 2 galaxy previ- ously to have been modelled over such a broad spectral range is NGC 4945. The ASCA GIS data

F. Ryde; J. Poutanen; R. Svensson; S. Larsson; S. Ueno

130

The variable X\\/gamma -ray spectrum of the Seyfert 2 galaxy NGC 7172  

Microsoft Academic Search

A broad band X-, gamma-ray spectral study of the Seyfert 2 galaxy NGC 7172 is presented. We use our ASCA observations from May 1995 and combine these with the CGRO OSSE data from March 1995. The only Seyfert 2 galaxy previously to have been modelled over such a broad spectral range is NGC 4945. The ASCA GIS data alone, can

Felix Ryde; Juri Poutanen; Roland Svensson; Stefan Larsson; Shiro Ueno

1997-01-01

131

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

SciTech Connect

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

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

2010-09-15

132

Circumnuclear Structures in the Interacting Seyfert Galaxy NGC 1241: Kinematics and Optical/Infrared Morphology  

NASA Astrophysics Data System (ADS)

We studied the spiral pattern in the inner 6.5" (1''=257 pc) central regions of the interacting active nucleus galaxy NGC 1241 using Gemini North Telescope high-resolution Ks- and J-band images and Hubble Space Telescope (HST) Pa? and H- and (V+R)-band images with high resolution in the range from ~0.1" to ~0.3" along with intermediate to large-scale spectroscopy using the Multifunction Spectrograph at the Córdoba Observatory in Argentina. Our analysis of Pa? emission images revealed a faint two-armed leading spiral pattern ending in the 5.6"×3.4" clumpy ring discovered by Böker and coworkers, harboring a 1.6" long barlike structure almost perpendicular to the large-scale bar of NGC 1241. When we applied two-dimensional Fourier analysis at circumnuclear scales, we found that a two-arm trailing mode was dominant in Ks- and J-band images while the (V+R)-band images showed more complex structural features with a strong one-armed trailing mode. One-dimensional Fourier analysis showed a corotation (CR) located outward from the edge of the Pa? bar. Our kinematics data gave an angular speed ?CN of 350+/-50 km s-1 kpc-1 for the trailing mode pattern. The rotation curve showed that the circumnuclear ring is located just inside the large-scale pattern inner Lindblad resonance (ILR), which has a radius of about r~1 kpc. We also found, within the uncertainties present in such measurements, that the outer Lindblad resonance (OLR) of the circumnuclear pattern is coincident with the large-scale pattern ILR, indicating a possible connection between circumnuclear and global dynamics. Nevertheless, the estimated high molecular gas fraction (>=13%) and the inner pattern high angular speed at the central region of NGC 1241 point to a nuclear bar formation via self-gravitational instability.

Díaz, Rubén J.; Dottori, Horacio; Vera-Villamizar, Nelson; Carranza, Gustavo

2003-11-01

133

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

SciTech Connect

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

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

2009-12-15

134

THE MAGNETIC FIELD OF THE IRREGULAR GALAXY NGC 4214  

SciTech Connect

We examine the magnetic field in NGC 4214, a nearby irregular galaxy, using multi-wavelength radio continuum polarization data from the Very Large Array. We find that the global radio continuum spectrum shows signs that free-free absorption and/or synchrotron losses may be important. The 3 cm radio continuum morphology is similar to that of the H{alpha} while the 20 cm emission is more diffuse. We estimate that 50% of the radio continuum emission in the center of the galaxy is thermal. Our estimate of the magnetic field strength is 30 {+-} 9.5 {mu}G in the center and 10 {+-} 3 {mu}G at the edges. We find that the hot gas, magnetic, and the gravitational pressures are all the same order of magnitude. Inside the central star-forming regions, we find that the thermal and turbulent pressures of the H II regions dominate the pressure balance. We do not detect any significant polarization on size scales greater than 200 pc. We place an upper limit of 8 {mu}G on the uniform field strength in this galaxy. We suggest that the diffuse synchrotron region, seen to the north of the main body of emission at 20 cm, is elongated due to a uniform magnetic field with a maximum field strength of 7.6 {mu}G. We find that, while the shear in NGC 4214 is comparable to that of the Milky Way, the supernova rate is half that of the Milky Way and suggest that the star formation episode in NGC 4214 needs additional time to build up enough turbulence to drive an {alpha}-{omega} dynamo.

Kepley, Amanda A.; Zweibel, Ellen G.; Wilcots, Eric M. [Washburn Observatory, University of Wisconsin, 475 North Charter Street, Madison, WI 53706 (United States); Johnson, Kelsey E. [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904 (United States); Robishaw, Timothy, E-mail: kepley@astro.wisc.edu, E-mail: zweibel@astro.wisc.edu, E-mail: ewilcots@astro.wisc.edu, E-mail: kej7a@virginia.edu, E-mail: tim.robishaw@sydney.edu.au [Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006 (Australia)

2011-08-01

135

THE HOT INTERSTELLAR MEDIUM OF THE INTERACTING GALAXY NGC 4490  

SciTech Connect

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.

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

136

Distribution and motions of atomic hydrogen in lenticular galaxies. VIII - The S0/a galaxies NGC 3619, 3626, and 3900  

NASA Astrophysics Data System (ADS)

The NGC 3619, 3626, and 3900 galaxies were mapped in the 21-cm H-I line with a spatial resolution of about 30 arcsec and a velocity resolution of 40 km/s. An encounter with the nearby spiral NGC 3625, or a merge with a dwarf galaxy, some 0.5 to 10 to the 9th years ago may explain the optical and H-I properties of NGC 3619. The H-I distribution of S0/a galaxies is shown to resemble that of Sa, rather than S0, galaxies, suggesting an internal origin for the H-I gas in S0/a galaxies. The Tully-Fisher relation and total M/L ratios of S0/a galaxies are found to be similar to those of other types of galaxies.

van Driel, W.; Balkowski, C.; van Woerden, H.

1989-07-01

137

Disk-halo interactions in the starburst galaxy NGC 6810  

NASA Astrophysics Data System (ADS)

NGC 6810, a highly inclined southern starburst galaxy, exhibits extraplanar soft X-ray and Halpha emission. For a multi-wavelength study of the halo and its dependence on the star formation properties of the underlying disk high-resolution radio data are required due to the small source extent (150"x30"). We propose to fill the gap in the uv-plane of archival 375+750+1.5 km array ATCA data reduced by us with one full synthesis in a 6-km configuration for a detailed study in both HI and radio continuum.

Dahlem, Michael; Strickland, David

2007-04-01

138

PHOTODISSOCIATION CHEMISTRY FOOTPRINTS IN THE STARBURST GALAXY NGC 253  

SciTech Connect

UV radiation from massive stars is thought to be the dominant heating mechanism of the nuclear interstellar medium (ISM) in the late stages of evolution of starburst galaxies, creating large photodissociation regions (PDRs) and driving a very specific chemistry. We report the first detection of PDR molecular tracers, namely HOC{sup +} and CO{sup +}, and also confirm the detection of the PDR tracer HCO toward the starburst galaxy NGC 253, claimed to be mainly dominated by shock heating and in an earlier stage of evolution than M 82, the prototypical extragalactic PDR. Our CO{sup +} detection suffers from significant blending to a group of transitions of {sup 13}CH{sub 3}OH, tentatively detected for the first time in the extragalactic ISM. These species are efficiently formed in the highly UV-irradiated outer layers of molecular clouds, as observed in the late stage nuclear starburst in M 82. The molecular abundance ratios we derive for these molecules are very similar to those found in M 82. This strongly supports the idea that these molecules are tracing the PDR component associated with the starburst in the nuclear region of NGC 253. The presence of large abundances of PDR molecules in the ISM of NGC 253, which is dominated by shock chemistry, clearly illustrates the potential of chemical complexity studies to establish the evolutionary state of starbursts in galaxies. A comparison with the predictions of chemical models for PDRs shows that the observed molecular ratios are tracing the outer layers of UV-illuminated clouds up to two magnitudes of visual extinction. We combine the column densities of PDR tracers reported in this paper with those of easily photodissociated species, such as HNCO, to derive the fraction of material in the well-shielded core relative to the UV-pervaded envelopes. Chemical models, which include grain formation and photodissociation of HNCO, support the scenario of a photo-dominated chemistry as an explanation to the abundances of the observed species. From this comparison, we conclude that the molecular clouds in NGC 253 are more massive and with larger column densities than those in M 82, as expected from the evolutionary stage of the starbursts in both galaxies.

MartIn, Sergio [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., 02138, Cambridge, MA (United States); MartIn-Pintado, J. [Centro de AstrobiologIa (CSIC-INTA), Ctra de Torrejon a Ajalvir, km 4, 28850 Torrejon de Ardoz, Madrid (Spain); Viti, S., E-mail: smartin@cfa.harvard.ed [Physics and Astronomy Department, University College London, Gower Street, London, WC1E 6BT (United Kingdom)

2009-12-01

139

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

SciTech Connect

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

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

1990-07-01

140

LUMINOSITIES OF BARRED AND UNBARRED S0 GALAXIES  

SciTech Connect

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

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

2012-07-20

141

First Interferometric Observations of Molecular Gas in a Polar Ring: The Helix Galaxy NGC 2685  

NASA Astrophysics Data System (ADS)

We have detected four giant molecular cloud associations (sizes <=6.6"~430 pc) in the western and eastern regions of the polar ring in NGC 2685 (the Helix galaxy) using the Owens Valley Radio Observatory millimeter interferometer. Emission from molecular gas is found close to the brightest H? and H I peaks in the polar ring and is confirmed by new IRAM 30 m single-dish observations. The CO and H I line velocities are very similar, providing additional kinematic confirmation that the CO emission emerges from the polar ring. For the first time, the total molecular mass within a polar ring is determined [MH2~(8-11)×106 Msolar, using the standard Galactic conversion factor]. We detect about MH2~4.4×106 Msolar in the nuclear region with the single dish. Our upper limit derived from the interferometric data is lower (MH2<=0.7×106 Msolar), suggesting that the molecular gas is distributed in an extended (>=1.3 kpc) diffuse disk. These new values are an order of magnitude lower than in previous reports. The total amount of molecular gas and the atomic gas content of the polar ring are consistent with formation due to accretion of a small gas-rich object, such as a dwarf irregular. The properties of the NGC 2685 system suggest that the polar ring and the host galaxy have been in a stable configuration for a considerable time (a few gigayears). The second (outer) H I ring within the disk of NGC 2685 is very likely at the outer Lindblad resonance of the ~11 kpc long stellar bar.

Schinnerer, Eva; Scoville, Nick

2002-10-01

142

THE CENTRAL REGION OF THE NEARBY SEYFERT 2 GALAXY NGC 4945: A PAIR OF SPIRALS  

SciTech Connect

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

Lin, Lien-Hsuan; Taam, Ronald E.; Lim, J. [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan (China); Yen, David C. C. [Department of Mathematics, Fu Jen Catholic University, Taipei 24205, Taiwan (China); Muller, S. [Onsala Space Observatory, SE-43992 Onsala (Sweden)

2011-04-10

143

RING STAR FORMATION RATES IN BARRED AND NONBARRED GALAXIES  

SciTech Connect

Nonbarred ringed galaxies are relatively normal galaxies showing bright rings of star formation in spite of lacking a strong bar. This morphology is interesting because it is generally accepted that a typical galactic disk ring forms when material collects near a resonance, set up by the pattern speed of a bar or bar-like perturbation. Our goal in this paper is to examine whether the star formation properties of rings are related to the strength of a bar or, in the absence of a bar, to the non-axisymmetric gravity potential in general. For this purpose, we obtained H{alpha} emission line images and calculated the line fluxes and star formation rates (SFRs) for 16 nonbarred SA galaxies and four weakly barred SAB galaxies with rings. For comparison, we combine our new observations with a re-analysis of previously published data on five SA, seven SAB, and 15 SB galaxies with rings, three of which are duplicates from our sample. With these data, we examine what role a bar may play in the star formation process in rings. Compared to barred ringed galaxies, we find that the inner ring SFRs and H{alpha}+[N II] equivalent widths in nonbarred ringed galaxies show a similar range and trend with absolute blue magnitude, revised Hubble type, and other parameters. On the whole, the star formation properties of inner rings, excluding the distribution of H II regions, are independent of the ring shapes and the bar strength in our small samples. We confirm that the deprojected axis ratios of inner rings correlate with maximum relative gravitational force Q{sub g} ; however, if we consider all rings, a better correlation is found when a local bar forcing at the radius of the ring, Q{sub r} , is used. Individual cases are described and other correlations are discussed. By studying the physical properties of these galaxies, we hope to gain a better understanding of their placement in the scheme of the Hubble sequence and how they formed rings without the driving force of a bar.

Grouchy, R. D.; Buta, R. J. [Cerro-Tololo Inter-American Observatory, La Serena (Chile); Salo, H.; Laurikainen, E. [Department of Physical Sciences, Astronomy Division, University of Oulu, FI-90014 Oulu (Finland)

2010-06-15

144

Dense cloud formation and star formation in a barred galaxy  

NASA Astrophysics Data System (ADS)

We investigate the properties of massive, dense clouds formed in a barred galaxy and their possible relation to star formation, performing a two-dimensional hydrodynamical simulation with the gravitational potential obtained from the 2MASS data from the barred spiral galaxy, M83. Since the environment for cloud formation and evolution in the bar region is expected to be different from that in the spiral arm region, barred galaxies are a good target to study the environmental effects on cloud formation and the subsequent star formation. Our simulation uses for an initial 80 Myr isothermal flow of non-self gravitating gas in the barred potential, then including radiative cooling, heating and self-gravitation of the gas for the next 40 Myr, during which dense clumps are formed. We identify many cold, dense gas clumps for which the mass is more than 104 M? (a value corresponding to the molecular clouds) and study the physical properties of these clumps. The relation of the velocity dispersion of the identified clump's internal motion with the clump size is similar to that observed in the molecular clouds of our Galaxy. We find that the virial parameters for clumps in the bar region are larger than that in the spiral arm region. From our numerical results, we estimate star formation in the bar and spiral arm regions by applying the simple model of Krumholz & McKee (2005). The mean relation between star formation rate and gas surface density agrees well with the observed Kennicutt-Schmidt relation. The star formation efficiency in the bar region is ˜60 per cent of the spiral arm region. This trend is consistent with observations of barred galaxies.

Nimori, M.; Habe, A.; Sorai, K.; Watanabe, Y.; Hirota, A.; Namekata, D.

2013-03-01

145

Intrinsic shapes and orientations of the elliptical galaxies, NGC 3379 and NGC 7619 using photometric data  

NASA Astrophysics Data System (ADS)

Determination of the intrinsic shape and the orientation of individual elliptical galaxies is an important problem. The statistical method to determine the shape and orientation was developed by Statler and his coworkers. These authors use the photometric, as well as, the kinematical data of the galaxies. As the numbers of galaxies with good photometry are many more as compared to those with good kinematics, we attempt the shape estimates using photometric data alone. We determine the intrinsic shapes and orientations of the light distribution of galaxies by combining the pro?les of photometric data from the literature with triaxial models. The intrinsic shapes and orientations are given by a Bayesian probability distribution. The likelihood of obtaining the data from a model is a function of the parameters describing intrinsic shape and orientation. We apply the method to infer the shape and orientation of a galaxy, using the ellipticities and the difference in the position angles at two suitably chosen points from the pro?les of the photometric data. The expectation values (< q_0 >, < q_? >, < |T_d | >) and most probable values (< q_{0P} >, < q_{? P} >, < |T_{dP} | >) constitute a summary of the shape of NGC 3379, we ?nd < q_{0P} >= 0.93, < q_{? P} >= 0.78, < |T_{dP} | >= 0.03, = 0.88, q_? = 0.72 and < |T_d | >= 0.29. These can be compared with the values < cL >= 0.75, |T_{dP}| = 0.03, cLP = 0.87, TmP = 0.0, reported in Statler (1994, ApJ, 425, 500; hereafter S 94). The expected as well as the most probable values of the short to long axial ratios of our calculation agree extremely well with the values in S94. This agreement establishes our methodology, quite ?rmly. We also ?nd that the orientation of NGC 3379 is not well constrained. This is again in agreement with the results obtained by Statler (1994, Astr.J., 108, 111) We ?nd that the position angle difference plays the crucial role in orientation estimates. Orientation of the elliptical galaxies with position angle difference ? 40.0 are well constrained. The results of shapes and orientations of other galaxies can also be compared with the values reported by other workers.

Diwakar, Arun Kumar

146

An Ionization Cone in the Dwarf Starburst Galaxy NGC 5253  

NASA Astrophysics Data System (ADS)

There are few observational constraints on how the escape of ionizing photons from starburst galaxies depends on galactic parameters. Here we report on the first major detection of an ionization cone in NGC 5253, a nearby starburst galaxy. This high-excitation feature is identified by mapping the emission-line ratios in the galaxy using [S III] ?9069, [S II] ?6716, and H? narrowband images from the Maryland-Magellan Tunable Filter at Las Campanas Observatory. The ionization cone appears optically thin, which suggests the escape of ionizing photons. The cone morphology is narrow with an estimated solid angle covering just 3% of 4? steradians, and the young, massive clusters of the nuclear starburst can easily generate the radiation required to ionize the cone. Although less likely, we cannot rule out the possibility of an obscured active galactic nucleus source. An echelle spectrum along the minor axis shows complex kinematics that are consistent with outflow activity. The narrow morphology of the ionization cone supports the scenario that an orientation bias contributes to the difficulty in detecting Lyman continuum emission from starbursts and Lyman break galaxies. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Zastrow, Jordan; Oey, M. S.; Veilleux, Sylvain; McDonald, Michael; Martin, Crystal L.

2011-11-01

147

AN IONIZATION CONE IN THE DWARF STARBURST GALAXY NGC 5253  

SciTech Connect

There are few observational constraints on how the escape of ionizing photons from starburst galaxies depends on galactic parameters. Here we report on the first major detection of an ionization cone in NGC 5253, a nearby starburst galaxy. This high-excitation feature is identified by mapping the emission-line ratios in the galaxy using [S III] {lambda}9069, [S II] {lambda}6716, and H{alpha} narrowband images from the Maryland-Magellan Tunable Filter at Las Campanas Observatory. The ionization cone appears optically thin, which suggests the escape of ionizing photons. The cone morphology is narrow with an estimated solid angle covering just 3% of 4{pi} steradians, and the young, massive clusters of the nuclear starburst can easily generate the radiation required to ionize the cone. Although less likely, we cannot rule out the possibility of an obscured active galactic nucleus source. An echelle spectrum along the minor axis shows complex kinematics that are consistent with outflow activity. The narrow morphology of the ionization cone supports the scenario that an orientation bias contributes to the difficulty in detecting Lyman continuum emission from starbursts and Lyman break galaxies.

Zastrow, Jordan; Oey, M. S. [Department of Astronomy, University of Michigan, 830 Dennison Building, Ann Arbor, MI 48109-1042 (United States); Veilleux, Sylvain [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); McDonald, Michael [Kavli Institute for Astrophysics and Space Research, MIT, Cambridge, MA 02139 (United States); Martin, Crystal L., E-mail: jazast@umich.edu [Department of Physics, University of California, Santa Barbara, CA 93106 (United States)

2011-11-01

148

Kinematics and Morphology of NGC 520: One, Two, or Three Galaxies.  

National Technical Information Service (NTIS)

The peculiar galaxy NGC 520 (Arp 157) is often interpreted as an interacting pair of galaxies. The identification of the two bulges and overall morphology of the two galaxies has long been a puzzle which the authors attempt to solve here. New longslit opt...

S. A. Stanford M. Balcells

1990-01-01

149

The Galaxy Component and Nuclear Flux Measurements of NGC 5548 from Direct Imaging  

Microsoft Academic Search

We present the results of analysis of direct imaging data of the galaxy NGC 5548. This galaxy hosts a time-variable active nucleus which has been the focus of intensive spectroscopic monitoring. We focus here on data obtainable from direct imaging of the object. First, we use an image modeling program to derive an image of the galaxy component alone, with

W. Romanishin; T. J. Balonek; R. Ciardullo; H. R. Miller; B. M. Peterson; A. C. Sadun; G. M. Stirpe; K. Takagishi; B. W. Taylor; V. Zitelli

1995-01-01

150

DYNAMIC S0 GALAXIES: A CASE STUDY OF NGC 5866  

SciTech Connect

S0 galaxies are often thought to be passively evolved from spirals after star formation is quenched. To explore what is actually occurring in such galaxies, we present a multi-wavelength case study of NGC 5866-a nearby edge-on S0 galaxy in a relatively isolated environment. This study shows strong evidence for dynamic activities in the interstellar medium, which are most likely driven by supernova explosions in the galactic disk and bulge. Understanding these activities can have strong implications for studying the evolution of such galaxies. We utilize Chandra, Hubble Space Telescope, and Spitzer data as well as ground-based observations to characterize the content, structure, and physical state of the medium and its interplay with the stellar component in NGC 5866. A cold gas disk is detected with an exponential scale height of approx10{sup 2} pc. Numerous distinct off-disk dusty spurs are also clearly present: prominent ones can extend as far as approx3 x 10{sup 2} pc from the galactic plane and are probably produced by individual SNe, whereas faint filaments can have approxkpc scale and are likely produced by SNe collectively in the disk/bulge. We also detect substantial amounts of diffuse Halpha- and Palpha-emitting gas with a comparable scale height as the cold gas. We find that the heating of the dust and warm ionized gas cannot be explained by the radiation from evolved stars alone, strongly indicating the presence of young stars in the galactic disk, though at a slow formation rate of approx0.05 M{sub sun} yr{sup -1}. We further reveal the presence of diffuse X-ray-emitting hot gas, which extends as far as 3.5 kpc away from the galactic plane and can be heated easily by Type Ia SNe in the bulge. However, the mean temperature of this gas is approx0.2 keV, substantially lower than what might be expected from the mass loss of evolved stars and Type Ia SNe heating alone in the galaxy, indicating that the mass loading from the cool gas is important. The total masses of the cold, warm ionized, and hot gases are approx5 x 10{sup 8} M{sub sun}, 4 x 10{sup 4} M{sub sun}, and 3 x 10{sup 7} M{sub sun}, respectively. The relative richness of the gases, apparently undergoing circulations between the disk and halo of the galaxy, is perhaps a result of its relative isolation.

Li Jiangtao; Chen Yang [Department of Astronomy, Nanjing University, 22 Hankou Road, Nanjing 210093 (China); Wang, Q. Daniel; Li Zhiyuan [Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States)

2009-11-20

151

Galaxy Zoo: are we observing an epoch of bar formation in massive disk galaxies?.  

NASA Astrophysics Data System (ADS)

We combine photometric and spectroscopic data from from Cosmic Evolution Survey (COSMOS) with visual galaxy classifications from Galaxy Zoo: Hubble (GZH) to produce a volume (0.4galaxies, with 330 of these identified as hosting a barred structure. We find that the fraction of bars found in disk galaxies decreases towards higher redshifts, confirming the redshift evolution trend seen by \\cite{2008ApJ...675.1141S}. We extend this trend to higher redshifts than previously seen (from z?0.84 to z=1.0) for such a sample size, finding that the bar fraction decreases across the timescales we explore; from fbar ?0.22 at tlookback ? 4.2Gyrs (z?0.4) to fbar ? 0.06 at tlookback ?7.8Gyrs (z?1.0). To explore whether this evolution depends on stellar mass, we split our disk sample into three stellar mass bins (9.7bar fraction is driven by the more massive galaxies, while the bar fraction of low mass galaxies remains constant across the whole epoch explored. We extend our results to include a low redshift sample of disk galaxies \\citep{2012MNRAS.424.2180M}, which shows that the higher bar fraction in the local universe is also due to the more massive galaxies, while the low mass galaxies exhibit a similar bar fraction as seen in our high redshift sample of galaxies. We suggest that the more massive galaxies become disk dominated and dynamically cool sooner than lower mass galaxies, thus allowing them to form and sustain a barred structure. We also suggest that disk galaxies are reaching a point where they are less dominated by violent galaxy-galaxy interactions, and that secular processes begin to dominate their evolution, and so this produces and epoch of bar formation in the most massive galaxies at z=0.8- 1.

Melvin, T.; Masters, K.; the Galaxy Zoo Team

152

The ionized gas in the CALIFA early-type galaxies. I. Mapping two representative cases: NGC 6762 and NGC 5966  

NASA Astrophysics Data System (ADS)

As part of the ongoing CALIFA survey, we have conducted a thorough bidimensional analysis of the ionized gas in two E/S0 galaxies, NGC 6762 and NGC 5966, aiming to shed light on the nature of their warm ionized ISM. Specifically, we present optical (3745-7300 Å) integral field spectroscopy obtained with the PMAS/PPAK integral field spectrophotometer. Its wide field-of-view (1' × 1') covers the entire optical extent of each galaxy down to faint continuum surface brightnesses. To recover the nebular lines, we modeled and subtracted the underlying stellar continuum from the observed spectra using the STARLIGHT spectral synthesis code. The pure emission-line spectra were used to investigate the gas properties and determine the possible sources of ionization. We show the advantages of IFU data in interpreting the complex nature of the ionized gas in NGC 6762 and NGC 5966. In NGC 6762, the ionized gas and stellar emission display similar morphologies, while the emission line morphology is elongated in NGC 5966, spanning ~6 kpc, and is oriented roughly orthogonal to the major axis of the stellar continuum ellipsoid. Whereas gas and stars are kinematically aligned in NGC 6762, the gas is kinematically decoupled from the stars in NGC 5966. A decoupled rotating disk or an "ionization cone" are two possible interpretations of the elongated ionized gas structure in NGC 5966. The latter would be the first "ionization cone" of such a dimension detected within a weak emission-line galaxy. Both galaxies have weak emission-lines relative to the continuum[EW(H?) ? 3 Å] and have very low excitation, log([Oiii]?5007/H?) ? 0.5. Based on optical diagnostic ratios ([Oiii]?5007/H?, [Nii]?6584/H?, [Sii]?6717, 6731/H?, [Oi]?6300/H?), both objects contain a LINER nucleus and an extended LINER-like gas emission. The emission line ratios do not vary significantly with radius or aperture, which indicates that the nebular properties are spatially homogeneous. The gas emission in NGC 6762 can be best explained by photoionization by pAGB stars without the need of invoking any other excitation mechanism. In the case of NGC 5966, the presence of a nuclear ionizing source seems to be required to shape the elongated gas emission feature in the "ionization cone" scenario, although ionization by pAGB stars cannot be ruled out. Further study of this object is needed to clarify the nature of its elongated gas structure. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck-Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).

Kehrig, C.; Monreal-Ibero, A.; Papaderos, P.; Vílchez, J. M.; Gomes, J. M.; Masegosa, J.; Sánchez, S. F.; Lehnert, M. D.; Cid Fernandes, R.; Bland-Hawthorn, J.; Bomans, D. J.; Marquez, I.; Mast, D.; Aguerri, J. A. L.; López-Sánchez, Á. R.; Marino, R. A.; Pasquali, A.; Perez, I.; Roth, M. M.; Sánchez-Blázquez, P.; Ziegler, B.

2012-04-01

153

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

SciTech Connect

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

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

2012-08-01

154

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

NASA Astrophysics Data System (ADS)

The nearby barred spiral galaxy NGC 1672 is thought to have a weak Seyfert nucleus in addition to its strong starburst activity. Observations with the Position Sensitive Proportional Counter (PSPC) and High Resolution Imager (HRI) instruments on board the ROSAT X-ray satellite show that three X-ray sources with luminosities (1-2)×1040 erg s-1 are clearly identified with NGC 1672. The strongest X-ray source lies at the nucleus, and the other two lie near the ends of the prominent bar, locations that are also bright in H? and near-infrared images. The nuclear source is resolved by the HRI on about the scale of the 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 ?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. While the properties of the nuclear source are generally supportive of a superbubble interpretation, its large density and emission measure stretch the limits that can be comfortably accommodated by such models. The authors 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 superbubble models for them have the same strengths and weaknesses.

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

1996-07-01

155

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

Microsoft Academic Search

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

Vera C. Rubin

1994-01-01

156

IRAC Imaging of the Unique, Face-on Spiral Galaxy NGC 309  

Microsoft Academic Search

The late type galaxy NGC 309 is one of the largest and most luminous spiral galaxies known. At a redshift distance of 83 Mpc (H=70 km\\/s\\/Mpc; Spergel et al. 2003), the absolute blue magnitude is -22.52 and the diameter is ~ 70 kpc (1 arcsec = 0.40 kpc). NGC 309 belongs to the multiple arm class 9 of Elmegreen &

Giovanni Fazio; Matthew Ashby; David Block; Debra Elmegreen; Bruce Elmegreen; Ken Freeman; Steven Willner

2007-01-01

157

Stellar Clusters Forming in the Blue Dwarf Galaxy NGC 5253  

NASA Astrophysics Data System (ADS)

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

2004-11-01

158

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

SciTech Connect

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

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

1990-01-01

159

Chandra observations of the luminous infrared galaxy NGC 3256  

NASA Astrophysics Data System (ADS)

We present a detailed analysis of high-resolution Chandra observations of the merger system NGC 3256, the most infrared-luminous galaxy in the nearby universe. The X-ray data show that several discrete sources embedded in complex diffuse emission contribute >~20 per cent of the total emission (LtotX\\sim 8\\times 1041\\,erg\\,s-1 in the 0.5-10keV energy range). The compact sources are hard and extremely bright and their emission is probably dominated by accretion-driven processes. Both galaxy nuclei are detected with LX~3-10×1040ergs-1. No evidence is found for the presence of an active nucleus in the southern nucleus, contrary to previous speculation. Once the discrete sources are removed, the diffuse component has a soft spectrum that can be modelled by the superposition of three thermal plasma components with temperatures kT=0.6, 0.9 and 3.9keV. Alternatively, the latter component can be described as a power law with index ?~3. Some evidence is found for a radial gradient of the amount of absorption and temperature of the diffuse component. We compare the X-ray emission with optical, H? and NICMOS images of NGC 3256 and find a good correlation between the inferred optical/near-infrared and X-ray extinctions. Although inverse Compton scattering could be important in explaining the hard X-rays seen in the compact sources associated with the nuclei, the observed diffuse emission is probably of thermal origin. The observed X-ray characteristics support a scenario in which the powerful X-ray emission is driven solely by the current episode of star formation.

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

2002-02-01

160

A Dynamical Model for the cD Galaxy NGC 6086  

NASA Astrophysics Data System (ADS)

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

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

161

Structural Properties of Barred Galaxies in the Spitzer Survey of Stellar Structure in Galaxies (S4G)  

NASA Astrophysics Data System (ADS)

We have performed two-dimensional decompositions on 3.6 micron images for 145 barred galaxies, covering Hubble types from SB0 to SBd, drawn from the Spitzer Survey of Stellar Structure in Galaxies (S4G). We decompose galaxies into bulge (if any), bar and disk (allowing for disk breaks), and investigate their structural properties. Previous studies have shown that early Hubble type galaxies (earlier than SBb) have bars with flat surface brightness radial profiles, whereas late type galaxies (later than SBc) have bars showing steeply decreasing profiles. We quantify how flat or steep bar profiles are by measuring their Sersic indices, and study how this varies with bulge prominence, using the bulge-to-total fraction (B/T). We find that bars in higher B/T galaxies are flatter than bars in smaller B/T and bulgeless galaxies. In particular, we find that the presence of a bulge almost always guarantees that the bar is flat. Conversely, bulgeless galaxies mostly have bars with steep profiles. We show that the normalized bar length is correlated with B/T, which is consistent with bars growing longer with time. For galaxies with disk breaks, we also find that the ratio of the break radius to the length of the bar (R_br/L_bar) is linked to B/T.

Kim, Taehyun; Gadotti, D.; Sheth, K.; Lee, M.; S4G Team

2013-01-01

162

Separating C Stars from Dust in the Central Region of the Seyfert 2 Galaxy NGC 1241  

NASA Astrophysics Data System (ADS)

The Seyfert 2 galaxy NGC 1241 presents a 1.5 kpc large circumnuclear ring (CNR) of star formation embracing a small bar plus leading arms. Those structures are Pa? emitters but barely seen in H?. It also presents stellar trailing arms inside the CNR. Gemini and HST imagery allow the construction of high-resolution (V-H) and (J-Ks) color maps, as well as a (J-Ks) versus K color-magnitude diagram of this complex region. The CNR is heavily obscured in V, but a fairly transparent window appears in the direction of the nucleus. Nonetheless, the nucleus presents a (J-Ks) color that is redder than the CNR. The CNR is composed of extremely young H II regions still enshrouded in their dust cocoons. However, the nuclear (J-Ks) color cannot be explained in this manner. Therefore, we propose the contribution of C stars as the most feasible mechanism for explaining the colors. If the nuclear stellar population is comparable to that of the Large Magellanic Cloud bar, 500 C stars and 25,000 asymptotic giant branch O-rich stars inside 50 pc may reproduce the observed colors. C stars release enriched material to the nuclear environment, probably fueling the central engine of this Seyfert 2 galaxy during the lifetime of stars with masses in the range 2 Msolargalaxies and is consistent with the significant contribution of intermediate age stars to the optical continuum of low-luminosity active galactic nuclei.

Dottori, Horacio; Díaz, Rubén J.; Carranza, Gustavo; Lípari, Sebastián; Santos, João, Jr.

2005-08-01

163

Molecular gas in NUclei of GAlaxies (NUGA). XV. Molecular gas kinematics in the inner 3 kpc of NGC 6951  

NASA Astrophysics Data System (ADS)

Within the NUclei of GAlaxies (NUGA) project we have obtained IRAM PdBI and 30 m 12CO(1-0) and 12CO(2-1) observations of the spiral galaxy NGC 6951. Previous work shows that there is indirect evidence of gas inflow from 3 kpc down to small radii: a large-scale stellar bar, a prominent starburst ring (r ? 580 pc) and a LINER/Seyfert 2 nucleus. In this paper we study the gas kinematics as traced by the CO line emission in detail. We quantify the influence of the large-scale stellar bar by constructing an analytical model of the evolution of gas particles in a barred potential. From this model gravitational torques and mass accumulation rates are computed. We compare our model-based gravitational torque results with previous observationally-based ones. The model also shows that the large-scale stellar bar is indeed the dominant force for driving the gas inward, to the starburst ring. Inside the ring itself a nuclear stellar oval might play an important role. Detailed analysis of the CO gas kinematics there shows that emission arises from two co-spatial, but kinematically distinct components at several locations. The main emission component can always be related to the overall bar-driven gas kinematics. The second component exhibits velocities that are larger than expected for gas on stable orbits, has a molecular gas mass of 1.8 × 106 M?, is very likely connected to the nuclear stellar oval, and is consistent with inflowing motion towards the very center. This may form the last link in the chain of gas inflow towards the active galactic nucleus in NGC 6951. Based on observations carried out with the IRAM Plateau de Bure Interferometer and 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

van der Laan, T. P. R.; Schinnerer, E.; Boone, F.; García-Burillo, S.; Combes, F.; Haan, S.; Leon, S.; Hunt, L.; Baker, A. J.

2011-05-01

164

NGC 4449: The Dr. Jekyll/Mr. Hyde of Magellanic Irregular Galaxies  

NASA Astrophysics Data System (ADS)

NGC 4449 is a nearby galaxy that has long been considered to be representative of normal giant Magellanic irregulars with an unusually large, quiescent disk. We present a VLA mosaic of the extended HI disk around NGC 4449 that shatters this preconception. Our data show NGC 4449 to contain a bright central condensation of gas associated with the optical galaxy. A long stream of gas emanates from the southern end of this condensation and curves 3/4 of the way around the galaxy. We estimate the total length of this arc to be ~ 80 kpc. Additionally, a second streamer emanates from the northern end of the central condensation. While the morphology of the gas suggests that it has been disturbed by an external perturbation, it is dynamically cold and in regular rotation about the center of NGC 4449.

Wilcots, E. M.; Hunter, D.; Gallagher, J. S.; van Woerden, H.

1996-09-01

165

NGC 4656UV: A UV-selected Tidal Dwarf Galaxy Candidate  

NASA Astrophysics Data System (ADS)

We report the discovery of a UV-bright tidal dwarf galaxy (TDG) candidate in the NGC 4631/4656 galaxy group, which we designate NGC 4656UV. Using survey and archival data spanning from 1.4 GHz to the ultraviolet, we investigate the gas kinematics and stellar properties of this system. The H I morphologies of NGC 4656UV and its parent galaxy NGC 4656 are extremely disturbed, with significant amounts of counterrotating and extraplanar gas. From UV-FIR photometry, computed using a new method to correct for surface gradients on faint objects, we find that NGC 4656UV has no significant dust opacity and a blue spectral energy distribution. We compute a star formation rate of 0.027 M ? yr-1 from the far-ultraviolet flux and measure a total H I mass of 3.8 × 108 M ? for the object. Evolutionary synthesis modeling indicates that NGC 4656UV is a low-metallicity system whose only major burst of star formation occurred within the last ~260-290 Myr. The age of the stellar population is consistent with a rough timescale for a recent tidal interaction between NGC 4656 and NGC 4631, although we discuss the true nature of the object—whether it is tidal or pre-existing in origin—in the context of its metallicity being a factor of 10 lower than its parent galaxy. We estimate that NGC 4656UV is either marginally bound or unbound. If bound, it contains relatively low amounts of dark matter. The abundance of archival data allows for a deeper investigation into this dynamic system than is currently possible for most TDG candidates. Based in part on observations made with the NASA Galaxy Evolution Explorer. GALEX is operated for NASA by the California Institute of Technology under NASA contract NAS5-98034.

Schechtman-Rook, Andrew; Hess, Kelley M.

2012-05-01

166

Undergraduate ALFALFA Team: Star Formation in the NGC 5846 Group of Galaxies  

NASA Astrophysics Data System (ADS)

We examine gas and star formation properties of galaxies in the NGC 5846 group. Narrowband Halpha and broadband R images for a sample of galaxies were obtained at the KPNO WIYN 0.9m with MOSAIC and the SMARTS 0.9m telescope at CTIO. Neutral hydrogen data from the Arecibo Legacy Fast ALFA (ALFALFA) survey trace the cold neutral gas content. The amounts and extents of star formation in a subsample of galaxies are compared as a function of cold gas content and position in the group. The typical star formation rates and extents of NGC 5846 galaxies are less than those of isolated galaxies and similar to those of galaxies located in the Virgo Cluster and other group environments. This work is part of the Undergraduate ALFALFA (Arecibo Legacy Fast ALFA) Team Groups Project, a collaborative undertaking of faculty and undergraduates at 11 institutions, aimed at investigating properties of galaxy groups surveyed by the ALFALFA blind HI survey.

Viani, Lucas; Koopmann, R. A.; Darling, H.; ALFALFA Team

2013-01-01

167

3D chaotic diffusion in barred spiral galaxies  

NASA Astrophysics Data System (ADS)

We study the diffusion of 3D orbits in an N-body model simulating a barred spiral galaxy. 3D chaotic orbits with initial conditions close to stable or unstable periodic orbits, inside corotation, stay trapped close to rotational tori or along unstable asymptotic manifolds, in the 4D phase space, and support the shape of the bar for very long times compared to the age of the Universe, before getting diffused outwards through `Arnold diffusion' and finally escape from the system. During their initial time of diffusion, these orbits support the inner parts of the spiral structure of the galaxy. On the other hand 3D chaotic orbits with initial conditions outside corotation can stay close and along unstable asymptotic manifolds (in cases when no rotational tori exist at all), supporting the outer parts of the spiral structure of the galaxy for approximately 1/3 of the Hubble time.

Contopoulos, G.; Harsoula, M.

2013-09-01

168

VIBRATIONALLY EXCITED HCN IN THE LUMINOUS INFRARED GALAXY NGC 4418  

SciTech Connect

Infrared pumping and its effect on the excitation of HCN molecules can be important when using rotational lines of HCN to probe dense molecular gas in galaxy nuclei. We report the first extragalactic detection of (sub)millimeter rotational lines of vibrationally excited HCN, in the dust-enshrouded nucleus of the luminous infrared galaxy NGC 4418. We estimate the excitation temperature of T{sub vib} {approx} 230 K between the vibrational ground and excited (v{sub 2} = 1) states. This excitation is most likely due to infrared radiation. At this high vibrational temperature the path through the v{sub 2} = 1 state must have a strong impact on the rotational excitation in the vibrational ground level, although it may not be dominant for all rotational levels. Our observations also revealed nearly confusion-limited lines of CO, HCN, HCO{sup +}, H{sup 13}CN, HC{sup 15}N, CS, N{sub 2}H{sup +}, and HC{sub 3}N at {lambda} {approx} 1 mm. Their relative intensities may also be affected by the infrared pumping.

Sakamoto, Kazushi [Academia Sinica, Institute of Astronomy and Astrophysics, Taipei, Taiwan (China); Aalto, Susanne [Onsala Space Observatory, Onsala (Sweden); Evans, Aaron S. [Department of Astronomy, University of Virginia, Charlottesville, VA (United States); Wiedner, Martina C. [Observatoire de Paris, Paris (France); Wilner, David J., E-mail: ksakamoto@asiaa.sinica.edu.t [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)

2010-12-20

169

GALEX UV properties of the polar ring galaxy MCG-05-07-001 and the shell galaxies NGC 1210 and NGC 5329  

NASA Astrophysics Data System (ADS)

Context: Systems of shells and polar rings in early-type galaxies are considered “bona fide” tracers of mass accretion and/or mergers. Their high frequency in low density environments suggests that these processes could drive the evolution of at least a fraction of the early-type galaxy population. Aims: We investigate the star formation histories of this type of galaxies. Their UV emission is important for testing whether these galaxies host ongoing or recent star formation and how this formation varies across the galaxy. Methods: We used far- and near- ultraviolet, optical, near-infrared images, neutral hydrogen HI maps, and line-strength indices to investigate the nuclear and outer regions of these galaxies as well as the regions where fine structures are present. Results: The GALEX near UV (NUV) and far UV (FUV) images of MCG-05-07-001 and NGC 1210 show complex tidal tails and debris structures. The far UV morphology of both galaxies appears so different from the optical morphology that the early-type classification may not apply. In both GALEX bands, the polar ring of MCG-05-07-001 is the dominant feature, whereas an extended tidal tail dominates the FUV bands of NGC 1210. In MCG-05-07-001 and NGC 1210, there is a strong correlation between structures detected in the FUV and NUV bands and in HI. In contrast, NGC 5329 does not show evidence of shells in the GALEX bands. We try to constrain the age of the accretion episode or merger that produced the shells and polar rings with the aid of composite stellar populations that take the presence of dust into account. The presence of HI in both MCG-05-07-001 and NGC 1210 argues in favour of wet mergers. Models suggest the presence of very young stellar populations in MCG-05-07-001: the observations could be explained in the framework of a conspicuous burst of star formation that occurred ?1 Gyr ago and involved a large fraction of the galaxy mass. Our models suggest that also the nuclei of NGC 1210 and NGC 5329 could have been rejuvenated by an accretion episode about 2-4 Gyr ago. Based on GALEX observations: GI1-059 PI D. Bettoni

Marino, A.; Iodice, E.; Tantalo, R.; Piovan, L.; Bettoni, D.; Buson, L. M.; Chiosi, C.; Galletta, G.; Rampazzo, R.; Rich, R. M.

2009-12-01

170

Ionized gas outflow in the isolated S0 galaxy NGC 4460  

NASA Astrophysics Data System (ADS)

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

Moiseev, Alexei; Karachentsev, Igor; Kaisin, Serafim

2010-04-01

171

Counter-rotating gaseous disks in the 'Evil Eye' galaxy NGC4826  

Microsoft Academic Search

The discovery of two counterrotating gaseous disks in the otherwise normal early-type spiral NGC4826 is reported. This is the most disklike galaxy in which any kinematic substructure has yet been found. This discovery raises the possibility that even spiral galaxies may have undergone a significant degree of structural evolution due to mergers.

Robert Braun; Rene A. M. Walterbos; Robert C. Kennicutt Jr.

1992-01-01

172

Counter-rotating gaseous disks in the 'Evil Eye' galaxy NGC4826  

NASA Astrophysics Data System (ADS)

The discovery of two counterrotating gaseous disks in the otherwise normal early-type spiral NGC4826 is reported. This is the most disklike galaxy in which any kinematic substructure has yet been found. This discovery raises the possibility that even spiral galaxies may have undergone a significant degree of structural evolution due to mergers.

Braun, Robert; Walterbos, Rene A. M.; Kennicutt, Robert C., Jr.

1992-12-01

173

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

SciTech Connect

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

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

2011-10-20

174

Stars and Ionized Gas in the S0 Galaxy NGC 7743: An Inclined Large-scale Gaseous Disk  

NASA Astrophysics Data System (ADS)

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

Katkov, Ivan Yu.; Moiseev, Alexei V.; Sil'chenko, Olga K.

2011-10-01

175

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

NASA Astrophysics Data System (ADS)

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.

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

176

Double-barred galaxies at intermediate redshifts: a feasibility study  

NASA Astrophysics Data System (ADS)

Despite the increasing number of studies of barred galaxies at intermediate and high redshifts, double-barred (S2B) systems have only been identified in the nearby (z <= 0.04) universe thus far. In this feasibility study, we demonstrate that the detection and analysis of S2Bs is possible at intermediate redshifts (0.1 <~ z <~ 0.5) with the exquisite resolution of the Hubble Space Telescope Advanced Camera for Surveys (HST/ACS). We identify barred galaxies in the HST/ACS data of the Great Observatories Origins Deep Survey (GOODS) using a novel method. The radial profile of the Gini coefficient - a model-independent structure parameter - is able to detect bars in early-type galaxies that are large enough that they might host an inner bar of sufficient angular size. Using this method and subsequent examination with unsharp masks and ellipse fits, we identified the two most distant S2Bs currently known (at redshifts z = 0.103 and 0.148). We investigate the underlying stellar populations of these two galaxies through a detailed colour analysis, in order to demonstrate the analysis that could be performed on a future sample of intermediate-redshift S2Bs. We also identify two S2Bs and five S2B candidates in the HST/ACS data of the Cosmic Evolution Survey (COSMOS). Our detections of distant S2Bs show that deep surveys like GOODS and COSMOS have the potential to push the limit for S2B detection and analysis out by a factor of 10 in redshift and look-back time (z ~ 0.5, ?t ~ 5Gyr) compared to the previously known S2Bs. This in turn would provide new insight into the formation of these objects.

Lisker, Thorsten; Debattista, Victor P.; Ferreras, Ignacio; Erwin, Peter

2006-07-01

177

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

NASA Astrophysics Data System (ADS)

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.

Carlqvist, Per

2013-02-01

178

Measuring the Fraction of Bars and Offset Bars Using the Spitzer Survey of Stellar Structure in Galaxies  

NASA Astrophysics Data System (ADS)

Using the Spitzer Survey of Stellar Structure in Galaxies at 3.6 and 4.5?m, I have measured a preliminary bar fraction and offset bar fraction in the local universe by visually identifying bar structure within a sample of 2,140 local galaxies. A sample this large has not been used since 1963, when Gerard de Vaucouleurs found the bar fraction to be roughly fbar ? 0.6 in the Third Reference Catalog of Bright Galaxies. Since then, there has been much debate over the true value of the bar fraction. The purpose of finding a bar fraction using S4G is to provide a final say in this debate. I have found that the bar fraction in the local universe is fbar = 0.69 when including both definite bars (SB) and candidate bars (SAB). I have also measured a preliminary value for the fraction of offset bars using the same sample. Offset bars are a very rare phenomenon. Of the sample used, 91 galaxies are found to be definite offset bars while an additional 39 are found to be candidate offset bars. When including both definite offset bars and candidate offset bars, the offset bar fraction in the local universe becomes fob = 0.12. I also measure the fraction of offset bars as a function of Hubble type and stellar mass. We find that 54% of offset bars are found in disks having a stellar mass of M ? 108 M?. Late-type disks possess significantly more offset bars than early-type with 60% of offset bars being found in disks having a Hubble type t ? 6.

Ross, Alexa

2012-01-01

179

Photographic photometry of galaxies using the INMP. II - NGC 3557 - A fast rotating elliptical galaxy?  

NASA Astrophysics Data System (ADS)

A study of the photometric and geometric properties of the elliptical NGC 3557, a galaxy which has been reported to have a high rotational velocity, rather exceptional for its class and reminiscent of those of S0 bulges, is presented. The morphological classification is quantitatively confirmed by showing that the luminosity profile follows closely the r to the 1/4 power law from 5 arcsec to the last observed point at mu = 27.05 B-mass. It is also found that the galaxy has a nuclear component in excess over the best fitting r to the 1/4 power law. Finally, the somewhat conflicting evidence (oblateness versus triaxiality) resulting from the analysis of the kinematical and geometrical parameters is pointed out.

Capaccioli, M.; Held, E. V.; Rampazzo, R.

1984-06-01

180

Self-gravitation gas flow in barred spiral galaxies  

SciTech Connect

A series of two-dimensional numerical experiments is performed in order to test the response of an isothermal, self-gravitating gas disk to a uniformly rotating, barlike gravitational potential. The barlike potential is an equilibrium stellar model from the n-body calculations of Miller and Smith. In the bar-dominated, central regions of the disk, as gas bar whose phase depends primarily on the location of principal resonances in the disk is formed. This response can be understood in terms of orbit-crowding effects. In the gas-dominated outer regions of the disk, two-armed trailing spiral waves are formed. The local pitch angle of these waves increases with increasing fractional gas mass. These self-gravitating gas waves are not self-sustaining. They are driven from the ends of equilibrium stellar bars, and their phase does not depend on the location of resonances in the disk. The relevance of these self-gravitating waves to observations and models of barred spiral galaxies is duscussed. It is concluded that these waves and their associated ringlike structures may be consistent with the morphological distribution of gas features in barred spiral galaxies.

Huntley, J.M.

1980-06-01

181

Appearance of Barred Galaxies at Early and Late Stages of Their Evolution  

NASA Astrophysics Data System (ADS)

Barred galaxies represent more than 2/3 among disk galaxies. The evolution of barred galaxies is deeply influenced by the dynamics of the bar. Moreover, the evolution of the bar itself determines the morphology of the rest of the galaxy. In this work, and by means of numerical simulations, we will show the evolution of isolated barred galaxies from two points of view, face-on and edge-on. In the face-on view we will show how the shape of the bar changes from a typical bar at early stages to ansae at later times of evolution. In the edge-on view we will show how the morphology of the bar changes with time to form a peanut/boxy shaped bulge and how these bulges are related to the bar itself.

Martinez-Valpuesta, I.

2010-10-01

182

An over-massive black hole in the compact lenticular galaxy NGC1277  

NASA Astrophysics Data System (ADS)

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 NGC4486B. Here we report observations of the stellar kinematics of NGC1277, which is a compact, lenticular galaxy with a mass of 1.2×1011 solar masses. From the data, we determine that the mass of the central black hole is 1.7×1010 solar masses, or 59 per cent of its bulge mass. We also show observations of five other compact galaxies that have properties similar to NGC1277 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.

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

2012-11-01

183

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

PubMed

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

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

2012-11-29

184

Dynamics of barred galaxies: effects of disc height  

NASA Astrophysics Data System (ADS)

We study dynamics of bars in models of disc galaxies embedded in realistic dark matter haloes. We find that disc thickness plays an important, if not dominant, role in the evolution and structure of the bars. We also make extensive numerical tests of different N-body codes used to study bar dynamics. Models with thick discs typically used in this type of modelling (height-to-length ratio hz/Rd = 0.2) produce slowly rotating, and very long, bars. In contrast, more realistic thin discs with the same parameters as in our Galaxy (hz/Rd ~ 0.1) produce bars with normal length Rbar ~ Rd, which rotate quickly with the ratio of the corotation radius to the bar radius compatible with observations. Bars in these models do not show a tendency to slow down, and may lose as little as 2-3 per cent of their angular momentum due to dynamical friction with the dark matter over cosmological time. We attribute the differences between the models to a combined effect of high phase-space density and smaller Jeans mass in the thin-disc models, which result in the formation of a dense central bulge. Special attention is paid to numerical effects, such as the accuracy of orbital integration, force and mass resolution. Using three N-body codes - GADGET, adaptive refinement tree (ART) and PKDGRAV - we find that numerical effects are very important and, if not carefully treated, may produce incorrect and misleading results. Once the simulations are performed with sufficiently small time-steps and with adequate force and mass resolution, all the codes produce nearly the same results: we do not find any systematic deviations between the results obtained with TREE codes (GADGET and PKDGRAV) and with the adaptive mesh refinement (ART) code.

Klypin, Anatoly; Valenzuela, Octavio; Colín, Pedro; Quinn, Thomas

2009-09-01

185

Deep Fabry-Perot H? observations of two Sculptor group galaxies, NGC 247 and 300  

NASA Astrophysics Data System (ADS)

It has been suggested that diffuse ionized gas can extend all the way to the end of the H I disc, and even beyond, such as in the case of the warped galaxyNGC 253 (Bland-Hawthorn et al.). Detecting ionized gas at these radii could carry significant implications as to the distribution of dark matter in galaxies. With the aim of detecting this gas, we carried out a deep H? kinematical analysis of two Sculptor group galaxies, NGC 247 and 300. The Fabry-Perot data were taken at the 36-cm Marseille Telescope in La Silla, Chile, offering a large field of view. With almost 20 hours of observations for each galaxy, very faint diffuse emission is detected. Typical emission measures of 0.1 cm-6 pc are reached. For NGC 247, emission extending up to a radius comparable with that of the H I disc (r˜ 13 arcmin) is found, but no emission is seen beyond the H I disc. For NGC 300, we detect ionized gas on the entirety of our field of view (rmax˜ 14 arcmin), and find that the bright H II regions are embedded in a diffuse background. Using the deep data, extended optical rotation curves are obtained, as well as mass models. These are the most extended optical rotation curves thus far for these galaxies. We find no evidence suggesting that NGC 247 has a warped disc, and to account for our non-detection of H? emission beyond its H I disc, as opposed to the warped galaxy NGC 253, our results favour the model in which, only through a warp, ionization by hot young stars in the central region of a galaxy can let photons escape and ionize the interstellar medium in the outer parts.

Hlavacek-Larrondo, J.; Marcelin, M.; Epinat, B.; Carignan, C.; de Denus-Baillargeon, M.-M.; Daigle, O.; Hernandez, O.

2011-09-01

186

Gas Distribution and Starburst Activity in the Widely Separated Interacting Galaxy Pair NGC 6670  

NASA Astrophysics Data System (ADS)

We present high-resolution H I 21 cm line, 20 cm radio continuum, and CO (1-0) line observations of the luminous infrared galaxy pair NGC 6670. NGC 6670 consists of two edge-on disk galaxies (NGC 6670E and NGC 6670W) with a projected nuclear separation of ~16 kpc. While there are no optically identified tidal features and the molecular disks are not distorted much, we have detected a 90 kpc long H I tail, which suggests that the galaxies are interacting and have already experienced at least one close encounter. The galaxies appear to be gravitationally bound and in a prograde-prograde orbit, which is the most efficient for producing tidal tails. Our observations suggest that the H I at larger galactic radii has been ejected to form the tails and the remnant H I disks have been perturbed by the interaction. In particular, we find that the H I disk of NGC 6670E appears to have been nearly destroyed. We conclude that the previous encounter between the galaxies had a large impact parameter and that the system is still in an early stage of interaction. Even though NGC 6670 is in an early stage of interaction, we find that there is evidence for nuclear starbursts already present. The CO (1-0) observations show large molecular gas reservoirs in the central regions, and the 20 cm radio continuum observations reveal enhanced star formation activity in the nuclear regions of both galaxies. The spatial extent of the 20 cm emission and the far-infrared-radio correlation further rule out active galactic nuclei as the source of the IR luminosity from NGC 6670. We estimate the ratio LIR/MH2, which is often used as an indicator of star formation efficiency, in the nuclear regions of NGC 6670E and NGC 6670W to be 18 and 11 Lsolar/Msolar, respectively. The nuclear star formation efficiency of these two galaxies has been elevated to the level observed in other nearby starburst galaxies (LIR/MH2>10 Lsolar/Msolar). Other indicators of starburst activity, such as CO brightness temperature and infrared surface brightness, are also observed.

Wang, Wei-Hao; Lo, K. Y.; Gao, Yu; Gruendl, Robert A.

2001-07-01

187

Solving the Problem of the Core Structures and Spectra of Nearby Radio Galaxies NGC 6251 and NGC 4261  

NASA Astrophysics Data System (ADS)

ROSAT PSPC and HRI observations of the low-power radio galaxies NGC~6251 (z=0.0234) and NGC~4261 (z=0.0089) have shown complicated X-ray structures and spectra. In both objects we find an extended atmosphere and a small-scale bright component associated with the active nucleus. However, the interpretation of this nuclear X-ray emission is complicated by the presence of multiple spectral components, and has remained ambiguous in the absence of X-ray data with good spatial and spectral resolution. Here we propose ACIS observations of these galaxies to determine the fraction of their core X-radiation which originates in non-thermal processes, and to study the gas components of the cores and envelopes. X-ray emission from the jets will also be detectable.

Birkinshaw, Mark

1999-09-01

188

The ACS Nearby Galaxy Survey Treasury. XI. The Remarkably Undisturbed NGC 2403 Disk  

NASA Astrophysics Data System (ADS)

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

Williams, Benjamin F.; Dalcanton, Julianne J.; Stilp, Adrienne; Dolphin, Andrew; Skillman, Evan D.; Radburn-Smith, David

2013-03-01

189

A Multi-Year X-ray Study of the Seyfert Galaxy NGC 4151  

Microsoft Academic Search

The nearby bright Seyfert 1.5 galaxy NGC 4151 has been well studied over many wavelengths. Observation data from the recently-launched Chandra and XMM-Newton X-ray observatories have facilitated a view of NGC 4151 heretofore unavailable, presenting a clearer picture of the physical state and evolution of this AGN. Using numerous observations from 2000-2007, I will detail the physical state and changes

Bryan Armentrout; S. Kraemer; J. Turner

2007-01-01

190

Determining the Nature of the Extended H I Structure around LITTLE THINGS Dwarf Galaxy NGC 1569  

NASA Astrophysics Data System (ADS)

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

Johnson, Megan

2013-06-01

191

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

NASA Astrophysics Data System (ADS)

NGC 4826 (M64) is a nearby Sab galaxy with an outstanding, absorbing dust lane (called the Evil Eye) asymmetrically placed across its prominent bulge. In addition, its central region is associated with several regions of ongoing star formation activity. We obtained accurate low-resolution (4.3 Å pixel-1) long-slit spectroscopy (KPNO 4 m) of NGC 4826 in the 5300-9100 Å spectral range, with a slit of 4.4? length, encompassing the galaxy's bulge size, positioned across its nucleus. The wavelength-dependent effects of absorption and scattering by the dust in the Evil Eye are evident when comparing the observed stellar spectral energy distributions (SEDs) of pairs of positions symmetrically located with respect to the nucleus, one on the dust lane side and one on the symmetrically opposite side of the bulge, under the assumption that the intrinsic (i.e., unobscured) radiation field is to first-order axisymmetric. We analyzed the SED ratios for a given number of pairs of positions through the multiple-scattering radiative transfer model of Witt & Gordon. As a main result, we discovered strong residual extended red emission (ERE) from a region of the Evil Eye within a projected distance of about 13" from the nucleus, adjacent to a broad, bright H II region, intercepted by the spectrograph slit. ERE is an established phenomenon well-covered in the literature and interpreted as originating from photoluminescence by nanometer-sized clusters, illuminated by UV/optical photons of the local radiation field. In the innermost part of the Evil Eye, the ERE band extends from about 5700 to 9100 Å, with an estimated peak intensity of ~3.7×10-6 ergs s -1 Å-1 cm-2 sr-1 near 8300 Å and with an ERE to scattered light band integrated intensity ratio, I(ERE)/I(sca), of about 0.7. At farther distances, approaching the broad, bright H II region, the ERE band and peak intensity shift toward longer wavelengths, while the ERE band-integrated intensity, I(ERE), diminishes and, eventually, vanishes at the inner edge of this H II region. The radial variation of I(ERE) and I(ERE)/I(sca) does not match that of the optical depth of the model derived for the dust lane. By contrast, the radial variation of I(ERE), I(ERE)/I(sca) and of the ERE spectral domain seems to depend strongly on the strength and hardness of the illuminating radiation field. In fact, I(ERE) and I(ERE)/I(sca) diminish and the ERE band shifts toward longer wavelengths when both the total integrated Lyman continuum photon rate, Q(H0)TOT, and the characteristic effective temperature, Teff, of the illuminating OB stars increase. Q(H0)TOT and Teff are estimated from the extinction-corrected H? (?=6563 Å) line intensity and line intensity ratios [N II] (?6583)/H? and [S II](??6716+6731)/H?, respectively, and are consistent with model and observed values typical of OB associations. Unfortunately, we do not have data shortward of 5300 Å, so that the census of the UV/optical flux is incomplete. The complex radial variation of the ERE peak intensity and peak wavelength of I(ERE) and I(ERE)/I(sca) with optical depth and strength of the UV/optical radiation field is reproduced in a consistent way through the theoretical interpretation of the photophysics of the ERE carrier by Smith & Witt, which attributes a key role to the experimentally established recognition that photoionization quenches the luminescence of nanoparticles. When examined within the context of ERE observations in the diffuse interstellar medium (ISM) of our Galaxy and in a variety of other dusty environments, such as reflection nebulae, planetary nebulae, and the Orion Nebula, we conclude that the ERE photon conversion efficiency in NGC 4826 is as high as found elsewhere but that the size of the actively luminescing nanoparticles in NGC 4826 is about twice as large as those thought to exist in the diffuse ISM of our Galaxy.

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

2002-04-01

192

Noncircular Gas Kinematics and Star Formation in the Ringed Galaxy NGC 4736  

NASA Astrophysics Data System (ADS)

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 H? and H I 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 H I emission is also found in the ring, but H I is absent from the central regions. Comparison of the H I and H? distributions suggests that H I in the ring is primarily dissociated H2. Modeling of the CO kinematics reveals gas motion in elliptical orbits around the central bar, and we argue that the ring represents both the outer Lindblad resonance of the bar and the inner Lindblad resonance of a larger oval distortion. The H I kinematics show evidence for axisymmetric inflow toward the ring and are inconsistent with streaming in aligned elliptical orbits, but the highly supersonic (~40 km s-1) inflow velocities required, corresponding to mass inflow rates of ~2 Msolar yr-1, suggest that more sophisticated models (e.g., gas orbiting in precessed elliptical orbits) should be considered. The radial CO and H? 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 H? 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~3 on average in the ring, only falling below 1 in localized regions. Large-scale dynamical effects, by concentrating gas at resonances and influencing the star formation rate, appear to play a key role in this galaxy's evolution.

Wong, Tony; Blitz, Leo

2000-09-01

193

Global disc models for galaxies NGC 1365, 6946, 7793 and UGC 6446  

NASA Astrophysics Data System (ADS)

Spiral galaxies are studied using a simple global disc model as a means for approximate determination of mass profiles. Based on rotation curves and the amount of gas (HI+He), we find global surface mass densities consistent with measurements and compare them with B-band surface brightness profiles. As a result we obtain mass-to-light ratio profiles. We give some arguments for why our approach is reliable and sometimes better than those assuming ad hoc the presence of a massive non-baryonic dark matter halo. Using this model, we study galaxies NGC 7793, 1365, 6946 and UGC 6446. Based on a rotation curve from The HI Nearby Galaxy Survey (THINGS) we also study galaxy NGC 4536 and compare the results with those we published elsewhere for the same galaxy.

Ja?ocha, Joanna; Bratek, ?ukasz; Kutschera, Marek; Skindzier, Piotr

2010-08-01

194

A new superwind galaxy: XMM-Newton observations of NGC 6810  

NASA Astrophysics Data System (ADS)

We present the first imaging X-ray observation of the highly inclined (i = 78°) Sab Seyfert 2 galaxy NGC 6810 using XMM-Newton, which reveals soft X-ray emission that extends out to a projected height of ~7 kpc away from the plane of the galaxy. The soft X-ray emission beyond the optical disc of the galaxy is most plausibly extraplanar, although it could instead come from large galactic radius. This extended X-ray emission is spatially associated with diffuse H? emission, in particular with a prominent 5-kpc-long H? filament on the north-west of the disc. A fraction <~35 per cent of the total soft X-ray emission of the galaxy arises from projected heights |z| >= 2 kpc. Within the optical disc of the galaxy the soft X-ray emission is associated with the star-forming regions visible in ground-based H? and XMM-Newton optical monitor near-UV imaging. The temperature, supersolar ?-element-to-iron abundance ratio, soft X-ray/H? correlation, and X-ray to far-infrared (FIR) flux ratio of NGC 6810 are all consistent with local starbursts with winds, although the large base radius of the outflow would make NGC 6810 one of the few `disc-wide' superwinds currently known. Hard X-ray emission from NGC 6810 is weak, and the total E = 2-10 keV luminosity and spectral shape are consistent with the expected level of X-ray binary emission from the old and young stellar populations. The X-ray observations provide no evidence of any active galactic nucleus activity. We find that the optical, IR and radio properties of NGC 6810 are all consistent with a starburst galaxy, and that the old classification of this galaxy as a Seyfert 2 galaxy is probably incorrect.

Strickland, David K.

2007-04-01

195

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

SciTech Connect

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.

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

196

Modeling and Analysis of the Nearby Colliding Galaxy Pair NGC 6621/22  

NASA Astrophysics Data System (ADS)

We present an analysis of the nearby interacting galaxies NGC 6621/22 (Arp 81), comparing the results of a combined N-body/SPH simulation of the collision between two suitable disk galaxy models with multi-wavelength observations. Arp 81 is undergoing a strong collision that has triggered periods of intense star formation in the pair. We use archived IRAC and HST images to identify regions of extensive star formation that took place in the system at previous times. From the simulation we obtain information on the physical conditions that likely existed in these regions, and that drove the star formation. By scaling the models, using best estimates of the mass and radius of each galaxy, we find the timescale for various star formation events. We deduce that there has been mass transfer from the more massive NGC 6621 to the less massive NGC 6622, and that this has led to nuclear star formation in NGC 6622. There has also been extensive star formation in two extended `arms' in NGC 6621, one of which formed a bridge between the two galaxies. (This work was supported in part by the National Science Foundation, under grant PHY-0243675, and by the Department of Energy under contract DOE LLNL B506657. The numerical simulations were performed on the Turing Computer Cluster in the College of Engineering at UIUC.)

Schwenk, D. R.; Lamb, S. A.; Van Schelt, J. A.; Hearn, N. C.

2005-12-01

197

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

NASA Astrophysics Data System (ADS)

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.

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

2009-06-01

198

Spontaneous formation of double bars in dark-matter-dominated galaxies  

NASA Astrophysics Data System (ADS)

Although nearly one-third of barred galaxies host an inner, secondary bar, the formation and evolution of double barred galaxies remain unclear. We show here an example model of a galaxy, dominated by a live dark matter halo, in which double bars form naturally, without requiring gas, and we follow its evolution for a Hubble time. The inner bar in our model galaxy rotates almost as slowly as the outer bar, and it can reach up to half of its length. The route to the formation of a double bar may be different from that of a single strong bar. Massive dark matter halo or dynamically hot stellar disc may play an important role in the formation of double bars and their subsequent evolution.

Saha, Kanak; Maciejewski, Witold

2013-06-01

199

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

NASA Astrophysics Data System (ADS)

This third paper in a series about the dwarf galaxy populations in groups within the Local Supercluster concerns the intermediate mass (2.1 × 1013 M sun) NGC 5353/4 Group with a core dominated by S0 systems and a periphery of mostly spiral systems. Dwarf galaxies are strongly concentrated toward the core. The mass-to-light ratio M/LR = 105 M sun/L sun is a factor of 3 lower than for the two groups studied earlier in the series. The properties of the group suggest it is much less dynamically evolved than those two groups of early-type galaxies. By comparison, the NGC 5353/4 Group lacks superluminous systems but has a large fraction of intermediate-luminosity galaxies; or equivalently, a luminosity function with a flatter faint-end slope. The luminosity function for the NGC 5353/4 Group should steepen as the intermediate-luminosity galaxies merge. Evidence for the ongoing collapse of the group is provided by the unusually large incidence of star-formation activity in small galaxies with early morphological types. The pattern in the distribution of galaxies with activity suggests a succession of infall events. Residual gas in dwarfs that enter the group is used up in sputtering events. The resolution of midlife crises is exhaustion.

Tully, R. Brent; Trentham, Neil

2008-04-01

200

Two-dimensional Magnetohydrodynamic Simulations of Barred Galaxies  

NASA Astrophysics Data System (ADS)

Barred galaxies are known to possess magnetic fields that may affect the properties of bar substructures such as dust lanes and nuclear rings. We use two-dimensional high-resolution magnetohydrodynamic (MHD) simulations to investigate the effects of magnetic fields on the formation and evolution of such substructures, as well as on the mass inflow rates to the galaxy center. The gaseous medium is assumed to be infinitesimally thin, isothermal, non-self-gravitating, and threaded by initially uniform, azimuthal magnetic fields. We find that there exists an outermost x 1-orbit relative to which gaseous responses to an imposed stellar bar potential are completely different between inside and outside. Inside this orbit, gas is shocked into dust lanes and infalls to form a nuclear ring. Magnetic fields are compressed in dust lanes, reducing their peak density. Magnetic stress removes further angular momentum of the gas at the shocks, temporarily causing the dust lanes to bend into an "L" shape and eventually leading to a smaller and more centrally distributed ring than in unmagnetized models. The mass inflow rates in magnetized models correspondingly become larger, by more than two orders of magnitude when the initial fields have an equipartition value with thermal energy, than in the unmagnetized counterparts. Outside the outermost x 1-orbit, on the other hand, an MHD dynamo due to the combined action of the bar potential and background shear operates near the corotation and bar-end regions, efficiently amplifying magnetic fields. The amplified fields shape into trailing magnetic arms with strong fields and low density. The base of the magnetic arms has a thin layer in which magnetic fields with opposite polarity reconnect via a tearing-mode instability. This produces numerous magnetic islands with large density that propagate along the arms to turn the outer disk into a highly chaotic state.

Kim, Woong-Tae; Stone, James M.

2012-06-01

201

The triaxial bulge of the Sa galaxy NGC 4845  

Microsoft Academic Search

Consideration is given to the use of kinematic and photometric data to determine the axial ratios of a triaxial bulge. The method is applied to the (Sa) spiral NGC 4845, where recent observations suggest that the emission-line velocity field in the bulge region is very regular but not axisymmetric. It is shown that NGC 4845's velocity field is very well

Ortwin E. Gerhard; Mario Vietri; Stephen M. Kent

1989-01-01

202

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

SciTech Connect

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.

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

203

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

NASA Astrophysics Data System (ADS)

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

Marino, R. A.; Gil de Paz, A.; Castillo-Morales, A.; Muñoz-Mateos, J. C.; Sánchez, S. F.; Pérez-González, P. G.; Gallego, J.; Zamorano, J.; Alonso-Herrero, A.; Boissier, S.

2012-07-01

204

The X-ray properties of the dwarf Magellanic-type galaxy NGC 55  

Microsoft Academic Search

We present an analysis of the X-ray properties of the Magellanic-type galaxy NGC 55 based on two contiguous XMM-Newton observations. We detect a total of 137 X-ray sources in the field of view, down to a flux of ~5 × 10-15ergcm-2s-1 (0.3-6 keV), 42 of which are located within the optical confines of the galaxy. On the basis of X-ray

A.-M. Stobbart; T. P. Roberts; R. S. Warwick

2006-01-01

205

The Nature of the Extended H i Gas around NGC 4449: The Dr. Jekyll/Mr. Hyde of Irregular Galaxies  

NASA Astrophysics Data System (ADS)

We present interferometric H I 21 cm line observations of the extended gas around the irregular galaxy NGC 4449 covering 67' on the sky at a resolution of ~1'. The main star-forming body of NGC 4449 is relatively normal for a Magellanic irregular galaxy, but the galaxy is unusual in that it has two counterrotating gas systems and H I that extends to 6 times the Holmberg radius. Our new, detailed H I maps of this extended gas show that most of the extended H I is located in large, highly structured, extended clouds and very long streamers. We compare NGC 4449 with other systems in the context of possible models for the origin of these structures, the most likely of which involves an interaction with another galaxy. Thus, NGC 4449 no longer fits the standard picture of an irregular galaxy quietly evolving in isolation.

Hunter, Deidre A.; Wilcots, Eric M.; van Woerden, Hugo; Gallagher, J. S.; Kohle, Sven

1998-03-01

206

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

SciTech Connect

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

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

2009-12-01

207

The Total Mass of the Early-Type Galaxy NGC 4649 (M60)  

NASA Astrophysics Data System (ADS)

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

Samurovic, S.; Cirkovic, M. M.

2008-12-01

208

A 2 Millimeter Spectral Line Survey of the Starburst Galaxy NGC 253  

NASA Astrophysics Data System (ADS)

We present the first unbiased molecular line survey toward an extragalactic source, namely the nuclear region of the starburst galaxy NGC 253. The scan covers the frequency band from 129.1 to 175.2 GHz, i.e., most of the 2 mm atmospheric window. We identify 111 spectral features as transitions from 25 different molecular species. Eight of which (three tentatively) are detected for the first time in the extragalactic interstellar medium. Among these newly detected species, we detected the rare isotopomers 34SO and HC18O+. Tentative detections of two deuterated species, DNC and N2D+, are reported for the first time from a target beyond the Magellanic Clouds. In addition, three hydrogen recombination lines are identified, while no organic molecules larger than methanol are detected. Column densities and rotation temperatures are calculated for all the species, including an upper limit to the ethanol abundance. A comparison of the chemical composition of the nuclear environment of NGC 253 with those of selected nearby galaxies demonstrates the chemical resemblance of IC 342 and NGC 4945 to that of NGC 253. On the other hand, the chemistries characterizing NGC 253 and M82 are clearly different. We also present a comparison of the chemical composition of NGC 253 with those observed in Galactic prototypical sources. The chemistry of NGC 253 shows a striking similarity with the chemistry observed toward the Galactic center molecular clouds, which are thought to be dominated by low-velocity shocks. This resemblance strongly suggests that the heating in the nuclear environment of NGC 253 is dominated by the same mechanism as that in the central region of the Milky Way.

Martín, S.; Mauersberger, R.; Martín-Pintado, J.; Henkel, C.; García-Burillo, S.

2006-06-01

209

The subluminous, spectroscopically peculiar type IA supernova 1991bg in the elliptical galaxy NGC 4374  

Microsoft Academic Search

Photometric and spectroscopic observations of SN 1991bg, a very peculiar Type Ia supernova in the outskirts or the E1 galaxy NGC 4374 in the Virgo cluster, are reported. The spectra and light curves demonstrate that SN 1991bg is an intrinsically subluminous, photometrically and spectroscopically discrepant object. In some respects it is similar to the peculiar SNe Ia 1986G in Cen

Alexei V. Filippenko; Michael W. Richmond; David Branch; Martin Gaskell; William Herbst; Charles H. Ford; Richard R. Treffers; Thomas Matheson; Luis C. Ho; Arjun Dey; Wallace L. W. Sargent; Todd A. Small; Wil J. M. van Breugel

1992-01-01

210

Gemini/GMOS imaging of globular clusters in the Virgo galaxy NGC 4649 (M60)  

NASA Astrophysics Data System (ADS)

We present Sloan g and i imaging from the Gemini Multi-object Spectrograph (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 square arcmin. We detect 2151 unresolved sources. Applying colour and magnitude selection criteria to this source list gives 995 candidate GCs. Our source list is greater than 90 per cent complete to a magnitude of i= 23.6, and has little contamination from background galaxies. We find fewer than half a dozen potential ultracompact dwarf galaxies around NGC 4649. Foreground extinction from the nearby spiral NGC 4647 is limited to be AV < 0.1. We confirm the bimodality in the GC colour distribution found by earlier work using Hubble Space Telescope/WFPC2 imaging. As is commonly seen in other galaxies, the red GCs are concentrated towards the centre of the galaxy, having a steeper number density profile than the blue GC subpopulation. The varying ratio of red-to-blue GCs with radius can largely explain the overall GC system colour gradient. The underlying galaxy starlight has a similar density profile slope and colour to the red GCs. This suggests a direct connection between the galaxy field stars and the red GC subpopulation. We estimate a total GC population of 3700 +/- 900, with the uncertainty dominated by the extrapolation to larger radii than observed. This total number corresponds to a specific frequency SN= 4.1 +/- 1.0. Future work will present properties derived from GMOS spectra of the NGC 4649 GCs.

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

2004-12-01

211

NGC 404: A Rejuvenated Lenticular Galaxy on a Merger-induced, Blueward Excursion Into the Green Valley  

Microsoft Academic Search

We have discovered recent star formation in the outermost portion ((1-4) × R 25) of the nearby lenticular (S0) galaxy NGC 404 using Galaxy Evolution Explorer UV imaging. FUV-bright sources are strongly concentrated within the galaxy's H I ring (formed by a merger event according to del Río et al.), even though the average gas density is dynamically subcritical. Archival

David A. Thilker; Luciana Bianchi; David Schiminovich; Armando Gil de Paz; Mark Seibert; Barry F. Madore; Ted Wyder; R. Michael Rich; Sukyoung Yi; Tom Barlow; Tim Conrow; Karl Forster; Peter Friedman; Christopher D. Martin; Patrick Morrissey; Susan Neff; Todd Small

2010-01-01

212

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

NASA Astrophysics Data System (ADS)

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

Masters, K. L.; the Galaxy Zoo Team

213

Towards understanding the dynamics of the bar/bulge region in our Galaxy  

NASA Astrophysics Data System (ADS)

I review some of the work on bars which is closely linked to the bar/bulge system in our Galaxy. Several independent studies, using totally independent methods, come to the same results about the 3D structure of a bar, i.e., that a bar is composed of a vertically thick inner part and a vertically thin outer part. I give examples of this from simulations and substantiate the discussion with input from orbital structure analysis and from observations. The thick part has a considerably shorter radial extent than the thin part. I then see how this applies to our Galaxy, where two bars have been reported, the COBE/DIRBE bar and the Long bar. Comparing their extents and making the reasonable and necessary assumption that our Galaxy has properties similar to those of other galaxies of similar type, leads to the conclusion that these two bars can not form a standard double bar system. I then discuss arguments in favour of the two bars being simply different parts of the same bar, the COBE/DIRBE bar being the thick inner part and the Long bar being the thin outer part of this bar. I also very briefly discuss some related new results. I first consider bar formation and evolution in disc galaxies with a gaseous component - including star formation, feedback and evolution - and a triaxial halo. Then I consider bar formation in a fully cosmological context using hydrodynamical LCDM simulations, where the host galaxies grow, accrete matter and significantly evolve during the formation and evolution of the bar.

Athanassoula, E.

2012-02-01

214

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

NASA Astrophysics Data System (ADS)

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.

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

2000-09-01

215

Cold Dust but Warm Gas in the Unusual Elliptical Galaxy NGC 4125  

NASA Astrophysics Data System (ADS)

Data from the Herschel Space Observatory have revealed an unusual elliptical galaxy, NGC 4125, which has strong and extended submillimeter emission from cold dust but only very strict upper limits to its CO and H I emission. Depending on the dust emissivity, the total dust mass is 2-5 × 106 M ?. While the neutral gas-to-dust mass ratio is extremely low (<12-30), including the ionized gas traced by [C II] emission raises this limit to <39-100. The dust emission follows a similar r 1/4 profile to the stellar light and the dust to stellar mass ratio is toward the high end of what is found in nearby elliptical galaxies. We suggest that NGC 4125 is currently in an unusual phase where evolved stars produced in a merger-triggered burst of star formation are pumping large amounts of gas and dust into the interstellar medium. In this scenario, the low neutral gas-to-dust mass ratio is explained by the gas being heated to temperatures >=104 K faster than the dust is evaporated. If galaxies like NGC 4125, where the far-infrared emission does not trace neutral gas in the usual manner, are common at higher redshift, this could have significant implications for our understanding of high redshift galaxies and galaxy evolution.

Wilson, C. D.; Cridland, A.; Foyle, K.; Parkin, T. J.; Mentuch Cooper, E.; Roussel, H.; Sauvage, M.; Smith, M. W. L.; Baes, M.; Bendo, G.; Boquien, M.; Boselli, A.; Ciesla, L.; Clements, D. L.; Cooray, A.; De Looze, I.; Galametz, M.; Gear, W.; Lebouteiller, V.; Madden, S.; Pereira-Santaella, M.; Rémy-Ruyer, A.

2013-10-01

216

Photometry, kinematics and parameters of stellar population of the lenticular galaxy NGC 6340  

NASA Astrophysics Data System (ADS)

In this work a multi-aspect study of the lenticular galaxy NGC 6340 using photometry from the SDDS survey and spectroscopy obtained with the 6-m BTA telescope (Special Astrophysical Observatory of the Russian Academy of Sciences, SAO RAS). Its morphological structure is being studied; three structure components as well as weak spiral arms are found; the presence of a polar ring in the central part is confirmed. The spatial distributions of stellar population parameters and internal kimenatics are obtained, as well as conlclusions about the possible mechanisms of evolution of this galaxy and lenticular galaxies in general have been made.

Novikova, A.

2012-05-01

217

Chandra X-ray Observations of the X-ray Faint Elliptical Galaxy NGC 4697  

Microsoft Academic Search

(abridged) A Chandra ACIS S3 observation of the X-ray faint elliptical galaxy\\u000aNGC 4697 resolves much of the X-ray emission (61% of the counts from within one\\u000aeffective radius) into 90 point sources, of which ~80 are low mass X-ray\\u000abinaries (LMXBs) associated with this galaxy. The dominance of LMXBs indicates\\u000athat X-ray faint early-type galaxies have lost much of

Craig L. Sarazin; Jimmy A. Irwin; Joel N. Bregman

2001-01-01

218

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

NASA Astrophysics Data System (ADS)

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

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

2008-05-01

219

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

SciTech Connect

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

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

2012-02-15

220

Molecular gas in the early-type starburst galaxy NGC 3928  

NASA Astrophysics Data System (ADS)

Observations of (C-12)O J = 1-0, 2-1, 3-2 and (C-13)O J = 1-0 emission in the S0/a galaxy NGC 3928, which is believed to be undergoing nuclear starburst, are reported. The line ratios are consistent with optically thick (C12)O lines with molecular gas at least as warm as that in the Galactic disk. The physical conditions of the molecular gas in NGC 3928 are likely comparable to the molecular gas in the nuclear regions of spiral galaxies. The molecular gas is confined to an 11-arcsec disk with an average surface density of 400 solar masses/pc sq and is clearly associated with the miniature spiral disk, which may have been captured by an otherwise gas-poor elliptical galaxy.

Li, Jonathan G.; Seaquist, E. R.; Sage, L. J.

1993-07-01

221

Constraints on the formation history of the elliptical galaxy NGC 3923 from the colors of its globular clusters  

Microsoft Academic Search

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 T1 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

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

1995-01-01

222

A Jet Model for the Broadband Spectrum Of the Seyfert 1 Galaxy NGC 4051  

NASA Astrophysics Data System (ADS)

Recent radio very long baseline interferometry observations of the ~ parsec-scale nuclear region of the narrow line Seyfert 1 galaxy NGC 4051 hint toward the presence of outflowing plasma. From available literature we have collected high-quality, high-resolution broadband spectral energy distribution (SED) data of the nuclear region of NGC 4051 spanning from radio through X-rays, to test whether the broadband SED can be explained within the framework of a relativistically outflowing jet model. We show that once the contribution from the host galaxy is taken into account, the broadband emission from the active galactic nucleus (AGN) of NGC 4051 can be well described by the jet model. Contributions from dust and ongoing star formation in the nuclear region tend to dominate the IR emission even at the highest resolutions. In the framework of the jet model, the correlated high variability of the extreme-ultraviolet and X-rays compared to other wavelengths suggests that the emission at these wavelengths is optically thin synchrotron originating in the particle acceleration site(s) in the jet very close (few r g= GM BH/c 2) to the central supermassive black hole of mass M BH. Our conclusions support the hypothesis that narrow line Seyfert 1 galaxies (which NGC 4051 is a member of) harbor a "jetted" outflow with properties similar to what has already been seen in low-luminosity AGNs and stellar mass black holes in hard X-ray state.

Maitra, Dipankar; Miller, Jon M.; Markoff, Sera; King, Ashley

2011-07-01

223

A kinematic study of the irregular dwarf galaxy NGC 2366 using HI and H? observations  

NASA Astrophysics Data System (ADS)

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: Dwarf galaxies provide a perfect environment for studying feedback processes because their kinematics and their generally low gravitational potential support the long-term survival of shells, filaments, and holes. 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 H? 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 H? 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 escape velocities of NGC 2366. The good data quality also allowed us to discuss some peculiarities of the morphology and the dynamics in NGC 2366. Results: A large red-shifted outflow north west of the giant extragalactic HII region with an expansion velocity of up to 50 km s-1 is found in H?, but not in HI. Additionally, a blue-shifted component north of the giant extragalactic HII region was detected both in H? and HI with an expansion velocity of up to 30 km s-1. A comparison with the escape velocities of NGC 2366 reveals that the gas does not have enough kinetic energy to leave the gravitational potential. Conclusions: This result is in good agreement with hydrodynamic simulations and suggests that we need to examine even less massive galaxies (M_gas=10^6 M?).

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

2009-01-01

224

WFPC2 Narrow-Band HAlpha Imaging of the Edge-on Galaxy NGC4631  

NASA Astrophysics Data System (ADS)

Observations of nearby edge-on disk galaxies are essential to determine the role that the disk/halo interaction has in galaxy evolution. Located in a direction of exceptionally low Galactic extinction, NGC4631 is particularly suitable for a multi-wavelength investigation of extra-planar gas components. In fact, NGC4631 is one of the most well studied late-type disk galaxies. Broad-band optical, near-infrared, near-UV, and far-UV observations have been {or will be} taken with HST and FUSE. We have obtained AXAF observing time to conduct a spatially-resolved X-ray spectroscopic observation of the galaxy. Here we propose for HST WFPC2 narrow-band H-alpha imaging of the galaxy's active central region. This image will enable us to resolve various narrow filaments of warm ionized gas that extend more than 2 kpc away from the mid-plane of the galaxy. Based on the geometry, filling factor and line intensity of the filaments and their correlation with X-ray- emitting gas, we will stu dy their origins {chimney walls, b listers, condensations of cooled hot gas, shocks, etc}. The results will be invaluable for our understanding of similar extra-planar gas observed in the Milky Way and other galaxies.

Wang, Q.

1999-07-01

225

Resolving the Mystery of X-ray Faint Elliptical Galaxies: Chandra X-ray Observations of NGC 4697  

Microsoft Academic Search

Chandra observations of the X-ray faint elliptical galaxy NGC 4697 resolve most of the X-ray emission (69% within one effective radius) into ~80 point sources, of which most are low mass X-ray binaries (LMXBs). NGC 4697 is the nearest optically normal and bright but X-ray faint elliptical galaxy. Most of the emission is resolved even in the softest band, which

C. L. Sarazin; J. A. Irwin; J. N. Bregman

2000-01-01

226

The internal dynamics of the Local Group dwarf elliptical galaxies NGC 147, 185 and 205  

NASA Astrophysics Data System (ADS)

We present three-integral dynamical models for the three Local Group dwarf elliptical galaxies: NGC 147, 185 and 205. These models are fitted to the Two-Micron All-Sky Survey (2MASS) J-band surface-brightness distribution and the major-axis kinematics (mean streaming velocity and velocity dispersion) and, in the case of NGC 205, also to the minor-axis kinematics. The kinematical information extends out to 2Re in the case of NGC 205 and out to about 1Re in the case of NGC 147 and 185. It is the first time models are constructed for the Local Group dwarf ellipticals (dEs) that allow for the presence of dark matter at large radii and that are constrained by kinematics out to at least one half-light radius. The B-band mass-to-light ratios of all the three galaxies are rather similar, (M/L)B ~ 3-4Msolar/Lsolar,B. Within the inner two half-light radii, about 40-50 per cent of the mass is in the form of dark matter, so dEs contain about as much dark matter as bright ellipticals. Based on their appreciable apparent flattening, we modelled NGC 205 and 147 as being viewed edge-on. For NGC 185, having a much rounder appearance on the sky, we produced models for different inclinations. NGC 205 and 147 have a relatively isotropic velocity dispersion tensor within the region where the internal dynamics are strongly constrained by the data. Our estimated inclination for NGC 185 is i ~ 50° because in that case the model has an intrinsic flattening close to the peak of the intrinsic shape distribution of dEs and it, like the best-fitting models for NGC 147 and 205, is nearly isotropic. We also show that the dynamical properties of the bright nucleus of NGC 205 are not unlike those of a massive globular cluster. Based on observations collected at the Observatoire de Haute-Provence. E-mail: sven.derijcke@UGent.be (SDR) ‡ Postdoctoral Fellow of the Fund for Scientific Research - Flanders (Belgium)(F.W.O).

De Rijcke, S.; Prugniel, P.; Simien, F.; Dejonghe, H.

2006-07-01

227

Polar-Ring Galaxies NGC 2685 and NGC 3808B (Vv 300).  

National Technical Information Service (NTIS)

Polar-ring galaxies (PRG) are among the most interesting examples of interaction between galaxies. A PRG is a galaxy with an elongated main body surrounded by a ring (or a disk) of stars, gas, and dust rotating in a near-polar plane (Schweizer, Whitmore, ...

V. P. Reshetnikov V. A. Yakovleva

1990-01-01

228

ON A METHOD TO RESOLVE THE NUCLEAR ACTIVITY IN GALAXIES AS APPLIED TO THE SEYFERT 2 GALAXY NGC 1358  

SciTech Connect

Nuclear regions of galaxies generally host a mixture of components with different excitations, compositions, 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 modeling and knowledge of the point-spread function, may be used to resolve the differing structures. In the situation outlined above, 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 about the structure of different subcomponents 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, ending with shock and postshock cloud as revealed by the velocities, as well as a nuclear emission-line disk rotating in the potential of a stellar bulge and expressing a radial excitation gradient. The method results in a likely scenario for the nuclear structure of the Seyfert 2 galaxy NGC 1358. For definitive results, an extrapolation of the method to two dimensions combined with the use of integral field spectroscopy will be necessary.

Lindblad, Per Olof; Fathi, Kambiz; Hjelm, Maja [Stockholm Observatory, Department of Astronomy, Stockholm University, AlbaNova, 106 91 Stockholm (Sweden); Nelson, Charles H. [Physics and Astronomy Department, Drake University, 2507 University Avenue, Des Moines, IA 50311 (United States)

2010-11-01

229

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

NASA Astrophysics Data System (ADS)

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

Rubin, Vera C.

1994-01-01

230

A Radio Study of the Ultra-luminous FIR Galaxy NGC 6240  

NASA Astrophysics Data System (ADS)

A number of galaxies observed in the IRAS mission are noted to emit ~ 99% of their bolometric flux in the FIR, with FIR luminosities in excess of 10(11) Lsun. The interacting galaxy NGC 6240 has often been referred to as the ``proto-typical'' ultra-luminous (L_FIR >~ 10(12) Lsun) FIR galaxy. The origin of the FIR excess remains a disputed subject in the literature. New observations of NGC 6240 were taken with the VLA at 20cm in the B-configuration, and at 3.6cm in the A-configuration. No significant radio emission was detected from or near the possible ultra-massive ``dark core'' hypothesized by Bland-Hawthorn et. al. (1991); however, approximately 30% of Seyfert galaxies have 20 cm radio luminosities weaker than the upper limit derived from the radio maps. The non-thermal radio emission from luminous FIR galaxies is tightly correlated with the FIR emission. Previous radio observations of NGC 6240 revealed two compact, steep-spectrum nuclear sources, nearly coincident with the two nuclear sources seen in optical images. The 2 images from the new VLA observations and 5 images from previous VLA observations are used to identify the morphological and spectral features of the strong, compact components in the nuclear regions (<~ 1.5 kpc; D=100 Mpc) and of the weaker ``clumps'' of diffuse emission south and west (>~ 3 kpc) from the nucleus. Feasible explanations for the radio emission are discussed. The models that have been proposed in the literature for the FIR excess of NGC 6240 are evaluated for consistency with the observed radio emission.

Colbert, E.; Wilson, A. S.; Bland-Hawthorn, J.

1993-05-01

231

Distance and Reddening of the Isolated Dwarf Irregular Galaxy NGC 1156  

NASA Astrophysics Data System (ADS)

We present a photometric estimation of the distance and reddening values to the dwarf irregular galaxy NGC 1156, that is one of the best targets for the study of isolated dwarf galaxies in the nearby universe. We used imaging data sets of the Hubble Space Telescope (HST) Advanced Camera for Surveys, High Resolution Channel of the central region of NGC 1156 (26'' × 29'') available in the HST archive for this study. From the (U - B, B - V) color-color diagram, we first estimated the total (foreground + internal) reddening toward NGC 1156 of E (B - V) = 0.35±0.05 mag, whereas only the foreground reddening was previously known to be E (B - V) = 0.16 mag (1984, ApJS, 54, 33) or 0.24 mag (1998, ApJ, 500, 525). Based on the brightest-star method, selecting the three brightest blue supergiant (BSG) stars with a mean B magnitude of = 21.94 and the three brightest red supergiant (RSG) stars with a mean V magnitude of = 22.76, we derived the distance modulus to NGC 1156 to be (m - M)0,BSG = 29.16 mag and (m - M)0,RSG = 29.5 5 mag. By using weights of 1 for BSGs and 1.5 for RSGs, we finally obtained a weighted mean distance modulus to NGC 1156, (m - M)0 = 29.39 ± 0.20 mag (distance = 7.6 ± 0.7 Mpc), which is in agreement with previous estimates. Combining the photometry data of this study with those of Karachentsev, Musella, and Grimardi (1996, A&A, 310, 722) gives a smaller distance to NGC 1156, which is discussed together with the limits of the data.

Kim, Sang Chul; Park, Hong Soo; Kyeong, Jaemann; Lee, Joon Hyeop; Ree, Chang Hee; Kim, Minjin

2012-04-01

232

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

233

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

NASA Astrophysics Data System (ADS)

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.

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

2010-01-01

234

Investigation of barred galaxies. vi. a comparative statistics of sb and sa galaxies. the cold gas properties  

NASA Astrophysics Data System (ADS)

The gas properties of barred and unbarred spiral galaxies are compared in two complete samples. It is found that two types of spiral galaxies do not differ from each other in atomic and molecular gas contents. On average there is 6 times more HI than H2 in spiral galaxies and the ratio MH2/MHI decreases from early to late types. The barred and unbarred spirals in general show a similar behaviors of the gas-to-luminosity relationships, but also there are certain differences between them such as correlation of two gas phases (HI and H2)for unbarred galaxies. It is suggested that different behaviors of two types galaxies are due to the higher star forming activity of barred with respect unbarred spirals. The expected values of HI and H2 gas contents have been estimated using blue and far-infrared emission.

Kandalyan, R. A.; Kalloghlian, A. T.; Naimiy, H. M. K. Ai-; Khassawneh, A. M.

2000-07-01

235

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

NASA Astrophysics Data System (ADS)

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

Vázquez, G. A.; Carigi, L.; González, J. J.

2003-03-01

236

Peanut-shaped bulges in face-on disk galaxies.  

NASA Astrophysics Data System (ADS)

We present high resolution absorption-line spectroscopy of 3 face-on galaxies, NGC 98, NGC 600, and NGC 1703 with the aim of searching for box/peanut (B/P)-shaped bulges. These observations test and confirm the prediction of \\citet{deb_etal_05} that face-on B/P-shaped bulges can be recognized by a double minimum in the profile of the fourth-order Gauss-Hermite moment h_4. In NGC 1703, which is an unbarred control galaxy, we found no evidence of a B/P bulge. In NGC 98, a clear double minimum in h_4 is present along the major axis of the bar and before the end of the bar, as predicted. In contrast, in NGC 600, which is also a barred galaxy but lacks a substantial bulge, we do not find a significant B/P shape.

Méndez-Abreu, J.; Corsini, E. M.; Debattista, V. P.; De Rijcke, S.; Aguerri, J. A. L.; Pizzella, A.

237

The large scale magnetic field structure of the spiral galaxy NGC 5775  

NASA Astrophysics Data System (ADS)

Context. The origin of large-scale magnetic fields in spiral galaxies is still a theoretical riddle and better observational constraints are required to make further progress. Aims: In order to better determine the large-scale 3D-structure of magnetic fields in spiral galaxies we present a Faraday rotation analysis of the edge-on spiral galaxy NGC 5775. Methods: Deep radio-continuum observations in total power and linear polarization were performed at 8.46 GHz with the VLA and the 100-m Effelsberg telescope. They were analyzed together with archival 4.86 and 1.49 GHz VLA-data. We thus can derive rotation measures from a comparison of three frequencies and determine the intrinsic magnetic field structure. Results: A very extended halo is detected in NGC 5775, with magnetic field lines forming an X-shaped structure. Close to the galactic disk the magnetic field is plane-parallel. The scaleheights of the radio emission esimated for NGC 5775 are comaprable with other galaxies. The rotation measure distribution varies smoothly on both sides along the major axis from positive to negative values. Conclusions: From the derived distribution of rotation measures and the plane-parallel intrinsic magnetic field orientation along the galactic midplane we conclude that NGC 5775 has an even axisymmetric large-scale magnetic field configuration in the disk as generated by an ??-dynamo which is accompanied by a quadrupolar poloidal field. The magnetic field lines of the plane-parallel component are pointing outwards. The observed X-shaped halo magnetic field, however, cannot be explained by the action of the disk's mean-field dynamo alone. It is probably due to the influence of the galactic wind together with the dynamo action.

Soida, M.; Krause, M.; Dettmar, R.-J.; Urbanik, M.

2011-07-01

238

Observations of the Galaxy NGC 3077 in the Narrow-Band [s II] and H? Filters  

NASA Astrophysics Data System (ADS)

We present observations of the H I tidal arm near a dwarf galaxy NGC 3077 (member of the M81 galaxy group) in the narrow-band [S II] and H? filters. Observations were carried out in 2011 March with the 2 m RCC telescope at the NAO Rozhen, Bulgaria. Our search for possible supernova remnant candidates (identified as sources with enhanced [S II] emission relative to their H? emission) in this region yielded no sources of this kind. Nevertheless, we found a number of objects with significant H? emission that probably represent uncatalogued, low brightness H II regions.

Andjeli?, M.; Stavrev, K.; Arbutina, B.; Ili?, D.; Uroševi?, D.

2011-08-01

239

X-ray observations of the Magellanic-type Galaxy NGC 4449  

Microsoft Academic Search

X-ray emission (L_x_~2.5x10^39^erg\\/s) from the nearby, face-on Magellanic-type irregular galaxy NGC 4449 was detected with the ROSAT PSPC and HRI. The HRI resolves seven point sources located within the D_25_ ellipse of the galaxy. The most luminous source is a supernova remnant detected with an intrinsic luminosity of L_x_=4.7x10^38^erg\\/s. Another very luminous source (L_x_=3.1x10^38^erg\\/s) is located between two Halpha shells.

A. Vogler; W. Pietsch

1997-01-01

240

Chemical abundances in starburst galaxies: M82 and NGC 253  

Microsoft Academic Search

Detailed abundances and abundance patterns of key metals like Fe, C, O and other alpha elements in starburst galaxies, as obtained from high-resolution infrared and X-ray nuclear spectra, are presented. The metals locked in stars give a picture of the galaxy metallicity prior to the last burst of star formation. The enrichment of the new generation of stars born in

L. Origlia; P. Ranalli; R. Maiolino; A. Comastri

2005-01-01

241

X-Ray and Optical Monitoring of a Gamma-Ray-Emitting Radio Galaxy, NGC 1275  

NASA Astrophysics Data System (ADS)

We performed monitoring observations of a gamma-ray-emitting radio galaxy, NGC 1275, in the X-ray and optical bands with the Suzaku/XIS, Kanata telescope, and the Okayama telescope. The X-ray flux of the nucleus was estimated by imaging spectroscopy in the hard X-ray band. In the optical band, a continuum flux, a broad H? line flux, and the polarization degree were measured. We could not find any time variability of the X-ray (2006-2011) and optical continuum (2010-2011) within 30%, regardless of the recent radio and gamma-ray variability by a factor of 3. The observed optical polarization was very small at ˜0.4% and showed little variability; it would be mostly of interstellar origin within our Galaxy. Furthermore, we confirmed with the XMM-Newton data that the X-ray spectrum of NGC 1275 in 2006 exhibited the Fe-K line, whose equivalent width was typical for other radio and Seyfert galaxies. These results indicate that the jet emission is not a major component in the optical and X-ray bands. Following these results, we discuss the jet emission of NGC 1275.

Yamazaki, Syoko; Fukazawa, Yasushi; Sasada, Mahito; Itoh, Ryosuke; Nishino, Sho; Takahashi, Hiromitsu; Takaki, Katsutoshi; Kawabata, Koji S.; Yoshida, Michitoshi; Uemura, Makoto

2013-04-01

242

C star survey of Local Group Dwarf Galaxies: The outer disc and halo of NGC 3109  

NASA Astrophysics Data System (ADS)

This proposal is part of our ongoing C star survey of Local Group dwarf galaxies. The object of this investigation is the Magellanic-type galaxy NGC 3109, located on the fringes of the Local Group. Deep color- magnitude diagrams have revealed the presence of an intermediate age population. Indeed, from its luminosity we can predict (Battinelli & Demers 2000) that NGC 3109 has at least one thousand C stars. Using R,I,CN and TiO photometry we will identify these C stars in two fields centered on the extremities of its obvious stellar disc. The size of the CCD field will allow us to obtain the spatial distribution of these C stars up to 3 kpc from the disc and up to 8 kpc along the disc, further out than the HI rotation curve. These C stars, which are among the brightest intermediate age stars, are particularly suitable to map the periphery of galaxies where the stellar density is so low that the foreground stars are more numerous. Furthermore, they can be used as kinematical probes to investigate the kinematics of the periphery of NGC 3109.

Demers, Serge; Battinelli, Paolo; Letarte, Bruno

2001-02-01

243

High Gas Fraction of Barred Spiral Galaxies at z ˜ 0.1-0.2  

NASA Astrophysics Data System (ADS)

We observed nine barred spiral galaxies at z ˜ 0.1-0.2 in CO(J=1-0) with the 45-m telescope at the Nobeyama Radio Observatory in 2010-2011 and successfully detected emissions from seven galaxies including tentative detections. The molecular gas fraction of our samples are systematically higher than the ones of local barred galaxies as well as the expected upper-limit where the bars can be formed or survive in numerical simulations. This implies that the simulations of bar formation and evolution may need a little corrections and the formation and evolution of bars must be considered in the context of the galactic disk evolution and formation, i.e., bar formation in gas-rich disks.

Matsui, K.; Sorai, K.; Baba, J.; Watanabe, Y.; Kuno, N.

2013-10-01

244

Non-circular motion estimation of the grand-design spiral galaxy NGC 628  

NASA Astrophysics Data System (ADS)

I present a harmonic decomposition analysis of the grand-design spiral galaxy NGC 628 using the H I data from The H I Nearby Galaxy Survey (THINGS), Walter et al., Astron. J. 136, 2563 (2008). The harmonic decomposition analysis allows the estimation of the peculiar motion magnitude of the galaxy not counted in the rotation of the disk. The rotation curve is obtained through a tilted ring analysis and reaches a maximum velocity not higher than 200 km s-1. The residual from the velocity field shows a morphology shift from a m = 1 to a m = 3 feature at R = 120", typical of two spiral arms perturbation of the potential. The non-circular motion have a magnitude of ~10 km s-1, in agreement with previous studies of similar Hubble type galaxies.

Colombo, D.

2013-09-01

245

A barred spiral at the centre of the giant elliptical radio galaxy Centaurus A  

Microsoft Academic Search

We report observations at mid-infrared and sub-millimeter wavelengths of Centaurus A (Cen A, NGC 5128), the giant elliptical galaxy that harbors the closest radio loud Active Galactic Nucleus (AGN) to Earth. The dust emission from the deep interior of Cen A reveals a bisymmetric structure with a diameter of 5(') (5 kpc), centred at the AGN. This structure is remarkably

I. F. Mirabel; O. Laurent; D. B. Sanders; M. Sauvage; M. Tagger; V. Charmandaris; L. Vigroux; P. Gallais; C. Cesarsky; D. L. Block

1999-01-01

246

An X-Ray, Optical, and Radio Search for Supernova Remnants in the Nearby Sculptor Group Sd Galaxy NGC 7793  

Microsoft Academic Search

This paper is the second in a series devoted to examining the multiwavelength properties of supernova remnants (SNRs) located in nearby galaxies. We consider here the resident SNRs in the nearby Sculptor group Sd galaxy NGC 7793. Using our own Very Large Array (VLA) radio observations at 6 and 20 cm, as well as archived ROSAT X-ray data, previously published

Thomas G. Pannuti; Nebojsa Duric; Christina K. Lacey; Annette M. N. Ferguson; Marcus A. Magnor; Caylin Mendelowitz

2002-01-01

247

The Holistic Evolution of Dwarf Galaxies: Internal and External Processes in NGC 6822  

NASA Astrophysics Data System (ADS)

Low-mass galaxy evolution is driven by both internal {e.g., star formation and feedback} and external {e.g., tidal interaction} processes; however, few nearby systems show evidence of both mechanisms operating in tandem. The Local Group dwarf galaxy NGC 6822 presents a unique opportunity to study important evolutionary processes because of proximity and timing: it harbors one of the largest known holes in its neutral ISM {a signpost of violent stellar feedback}, and it appears to be undergoing a tidal interaction with a very low mass companion dwarf galaxy. To capitalize on this opportunity, we propose to undertake an ACS and WFC3 imaging study of the stellar populations throughout NGC 6822. We will study the role of both internal and external processes by sampling the stellar populations associated with the main body {using archival WFPC2 data}, the giant HI hole, the companion dwarf galaxy, and the tidal material at the ends of the disk. From these data we will extract precise color magnitude diagrams; we will measure the full 13 Gyr star formation history of each field, with high time resolution {20-250 Myr} over the past 1 Gyr, and quantify the relative contributions of internal and external drivers of dwarf galaxy evolution. Specifically, we will study: 1} the nature of the companion object {differentiating between infalling gas and a genuine low-mass galaxy}; 2} the energetics of giant HI hole creation; 3} the role of interactions in the system's evolution; 4} the nature of feedback in governing the star formation process; and 5} the patterns of star formation over time. We have optimized our field placements to extract the most information possible about the competing forces that drive galaxy evolution; in only six orbits, we will gain fundamental insights into the contributions of both internal and external processes that bear on the evolution of low-mass galaxies.;

Cannon, John

2009-07-01

248

Observations of Cold and Warm CO in the Irregular Galaxy NGC 4449  

NASA Astrophysics Data System (ADS)

We present observations of cold 12CO (1-0) in H I concentrations located in and around the peculiar irregular galaxy NGC 4449. The observed positions range from the center out to 18 kpc, or nearly 4 times the Holmberg radius, but most are in the large H I complexes that encircle the optical galaxy. We have detected CO (1-0) in two positions outside the center of the galaxy, including one that has no detectable sign of star formation. No CO was detected in the H I concentrations located far from the galaxy center. In general, CO emission was detected at positions where approximately ?HI,max>=2x1021 atoms cm-2, a factor of 3 higher than expected for self-shielding for the metallicity of the galaxy, and R<=5 kpc from the center of the galaxy. In the H I complexes surrounding the galaxy, MH2/MHI,max is approximately constant. In the center of the galaxy, there is more H? emission relative to MH2 than in the outer H I complexes. Generally, there is no relationship between the presence or amount of H? emission and MH2. We have also presented observations of warm molecular 12CO (2-1) gas in the center of the galaxy where CO (1-0) had already been detected. In the center of the galaxy, the ratio ICO (2-1)/ICO (1-0) is unusually high, indicating the presence of a significant amount of hot, optically thin gas. This is generally consistent with the unusual activity that has taken place in the central regions of the galaxy, but the ratio is higher than is observed in other galaxies with high star formation rates.

Hunter, Deidre A.; Walker, Constance E.; Wilcots, Eric M.

2000-02-01

249

PARSEC-SCALE IMAGING OF THE RADIO-BUBBLE SEYFERT GALAXY NGC 6764  

SciTech Connect

We have observed the composite active galactic nucleus (AGN)-starburst galaxy NGC 6764 with the Very Long Baseline Array at 1.6 and 4.9 GHz. These observations have detected a 'core-jet' structure and a possible weak counterjet component at 1.6 GHz. The upper limits to the core and jet (1.6-4.9 GHz) spectral index are 0.6 and 0.3, respectively. Taken together with the high brightness temperature of {approx}10{sup 7} K for the core region, the radio emission appears to be coming from a synchrotron jet. At a position angle of {approx}25{sup 0}, the parsec-scale jet seems to be pointing closely toward the western edge of the southern kpc-scale bubble in NGC 6764. A real connection between the parsec- and sub-kpc-scale emission would not only suggest the presence of a curved jet, but also a close link between the AGN jet and the radio bubbles in NGC 6764. We demonstrate that a precessing jet model can explain the radio morphology from parsec to sub-kpc scales, and the model best-fit parameters of jet speed and orientation are fully consistent with the observed jet-to-counterjet surface brightness ratio. The jet however appears to be disrupted on scales of hundreds of parsecs, possibly due to interaction with and entrainment of the interstellar medium gas, which subsequently leads to the formation of bubbles. The jet energetics in NGC 6764 suggest that it would take 12-21 Myr to inflate the (southern) bubble. This timescale corresponds roughly to the starburst episode that took place in NGC 6764 about 15-50 Myr ago, and could be indicative of a close connection between jet formation and the starburst activity in this galaxy.

Kharb, P.; O'Dea, C. P.; Axon, D. J.; Robinson, A. [Department of Physics, Rochester Institute of Technology, Rochester, NY 14623 (United States); Hota, Ananda [Institute of Astronomy and Astrophysics, Academia Sinica, Taiwan (China); Croston, J. H. [School of Physics and Astronomy, University of Southampton (United Kingdom); Hardcastle, M. J. [Centre for Astrophysics Research, University of Hertfordshire (United Kingdom); Kraft, R. P., E-mail: kharb@cis.rit.ed [Harvard Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA (United States)

2010-11-01

250

Continuum Halos in Nearby Galaxies: An EVLA Survey (CHANG-ES). II. First Results on NGC 4631  

NASA Astrophysics Data System (ADS)

We present the first results from the Continuum Halos in Nearby Galaxies—an EVLA Survey (CHANG-ES), a new survey of 35 edge-on galaxies to search for both in-disk and extraplanar radio continuum emission. CHANG-ES is exploiting the new wide-band, multi-channel capabilities of the Karl G. Jansky Very Large Array (i.e., the Expanded Very Large Array or EVLA) with observations in two bands centered at 1.5 and 6 GHz in a variety of array configurations with full polarization. The motivation and science case for the survey are presented in a companion paper (Paper I). These first results are based on C-array test observations in both observing bands of the well-known radio halo galaxy, NGC 4631. In this paper, we outline the observations and the data reduction steps that are required for wide-band calibration and mapping of EVLA data, including polarization. With modest on-source observing times (30 minutes at 1.5 GHz and 75 minutes at 6 GHz for the test data), we have achieved best rms noise levels of 22 and 3.5 ?Jy beam-1 at 1.5 GHz and 6 GHz, respectively. New disk-halo features have been detected, among them two at 1.5 GHz that appear as loops in projection. We present the first 1.5 GHz spectral index map of NGC 4631 to be formed from a single wide-band observation in a single array configuration. This map represents tangent slopes to the intensities within the band centered at 1.5 GHz, rather than fits across widely separated frequencies as has been done in the past and is also the highest spatial resolution spectral index map yet presented for this galaxy. The average spectral index in the disk is \\bar{\\alpha }_{1.5 \\,GHz} =-0.84+/- 0.05 indicating that the emission is largely non-thermal, but a small global thermal contribution is sufficient to explain a positive curvature term in the spectral index over the band. Two specific star-forming regions have spectral indices that are consistent with thermal emission. Polarization results (uncorrected for internal Faraday rotation) are consistent with previous observations and also reveal some new features. On broad scales, we find strong support for the notion that magnetic fields constrain the X-ray-emitting hot gas.

Irwin, Judith; Beck, Rainer; Benjamin, R. A.; Dettmar, Ralf-Jürgen; English, Jayanne; Heald, George; Henriksen, Richard N.; Johnson, Megan; Krause, Marita; Li, Jiang-Tao; Miskolczi, Arpad; Mora, Silvia Carolina; Murphy, E. J.; Oosterloo, Tom; Porter, Troy A.; Rand, Richard J.; Saikia, D. J.; Schmidt, Philip; Strong, A. W.; Walterbos, Rene; Wang, Q. Daniel; Wiegert, Theresa

2012-08-01

251

A JET MODEL FOR THE BROADBAND SPECTRUM OF THE SEYFERT 1 GALAXY NGC 4051  

SciTech Connect

Recent radio very long baseline interferometry observations of the {approx} parsec-scale nuclear region of the narrow line Seyfert 1 galaxy NGC 4051 hint toward the presence of outflowing plasma. From available literature we have collected high-quality, high-resolution broadband spectral energy distribution (SED) data of the nuclear region of NGC 4051 spanning from radio through X-rays, to test whether the broadband SED can be explained within the framework of a relativistically outflowing jet model. We show that once the contribution from the host galaxy is taken into account, the broadband emission from the active galactic nucleus (AGN) of NGC 4051 can be well described by the jet model. Contributions from dust and ongoing star formation in the nuclear region tend to dominate the IR emission even at the highest resolutions. In the framework of the jet model, the correlated high variability of the extreme-ultraviolet and X-rays compared to other wavelengths suggests that the emission at these wavelengths is optically thin synchrotron originating in the particle acceleration site(s) in the jet very close (few r{sub g}= GM{sub BH}/c{sup 2}) to the central supermassive black hole of mass M{sub BH}. Our conclusions support the hypothesis that narrow line Seyfert 1 galaxies (which NGC 4051 is a member of) harbor a 'jetted' outflow with properties similar to what has already been seen in low-luminosity AGNs and stellar mass black holes in hard X-ray state.

Maitra, Dipankar; Miller, Jon M.; King, Ashley [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Markoff, Sera, E-mail: dmaitra@umich.edu [Astronomical Institute 'Anton Pannekoek', University of Amsterdam, P.O. Box 94249, 1090 GE Amsterdam (Netherlands)

2011-07-10

252

Non-Gaussian error bars in galaxy surveys - I  

NASA Astrophysics Data System (ADS)

We propose a method to estimate non-Gaussian error bars on the matter power spectrum from galaxy surveys in the presence of non-trivial survey selection functions. The estimators are often obtained from formalisms like Feldmann, Kaiser and Peacock (FKP) and pseudo-Karhunen-Loève (PKL), which rely on the assumption that the underlying field is Gaussian. The Monte Carlo method is more accurate but involves the tedious process of running and cross-correlating a large number of N-body simulations, in which the survey volume is embedded. From 200 N-body simulations, we extract a non-linear covariance matrix as a function of two scales and of the angle between two Fourier modes. All the non-Gaussian features of that matrix are then simply parametrized in terms of a few fitting functions and eigenvectors. We furthermore develop a fast and accurate strategy that combines our parametrization with a general galaxy survey selection function, and incorporate non-Gaussian Poisson uncertainty. We describe how to incorporate these two distinct non-Gaussian contributions into a typical analysis pipeline, and apply our method with the selection function from the 2dFGRS. We find that the observed Fourier modes correlate at much larger scales than that predicted by both FKP formalism or pure N-body simulations in a 'top hat' selection function. In particular, the observed Fourier modes are already 50 per cent correlated at k˜ 0.1 h Mpc-1, and the non-Gaussian fractional variance on the power spectrum [?] is about a factor of 3.0 larger than the FKP prescription. At k˜ 0.4 h Mpc-1, the deviations are an order of magnitude.

Harnois-Déraps, Joachim; Pen, Ue-Li

2012-07-01

253

Infrared array imaging and spectrophotometry of the nuclear region of the hot-spot galaxy NGC 2903  

Microsoft Academic Search

Previous studies of the hot-spot galaxy NGC 2903 at a variety of wavelengths have shown that considerable star formation is occurring within the complex hot-spot structures in this galaxy's nuclear region. A K-band (2.2 microns) image of the galaxy's nuclear region has been obtained with an infrared CCD and compared to V-band (0.55 micron) and 1-micron images of the same

D. A. Simons; D. L. Depoy; E. E. Becklin; R. W. Capps; K.-W. Hodapp; D. N. B. Hall

1988-01-01

254

Infrared array imaging and spectrophotometry of the nuclear region of the 'hot-spot' galaxy NGC 2903  

Microsoft Academic Search

Previous studies of the 'hot-spot' galaxy NGC 2903 at a variety of wavelengths have shown that considerable star formation is occurring within the complex hot-spot structures in this galaxy's nuclear region. A K-band (2.2 microns) image of the galaxy's nuclear region has been obtained with an infrared CCD and compared to V-band (0.55 micron) and 1-micron images of the same

D. A. Simons; D. L. Depoy; E. E. Becklin; R. W. Capps; K.-W. Hodapp; D. N. B. Hall

1988-01-01

255

The lenticular galaxy NGC 3607: stellar population, metallicity, and ionised gas  

NASA Astrophysics Data System (ADS)

Aims: In this work we derive clues to the formation scenario and ionisation source of the lenticular galaxy NGC 3607 by means of metallicity gradients, stellar population, and emission lines properties. Methods: We work with long-slit spectroscopy from which we (i) study the radial distribution of the equivalent widths of conspicuous metallic absorption features; (ii) make inferences about the star formation history (with a stellar population synthesis algorithm); and (iii) investigate the ionisation source responsible for a few strong emission lines. Results: Negative radial gradients are observed for most of the absorption features of NGC 3607. Compared to the external parts, the central region has a deficiency of alpha elements and higher metallicity, which implies different star formation histories in both regions. At least three star formation episodes are detected, with ages within 1-13 Gyr. The dynamical mass and the Mg2 gradient slope are consistent with mergers being important contributors to the formation mechanism of NGC 3607, a scenario consistent with the star formation episodes.. Emission-line ratios indicate a LINER at the centre of NGC 3607. Contribution of hot, old stars to the gas ionisation outside the central region is detected.

Rickes, M. G.; Pastoriza, M. G.; Bonatto, C.

2009-10-01

256

RR LYRAE VARIABLES IN THE LOCAL GROUP DWARF GALAXY NGC 147  

SciTech Connect

We investigate the RR Lyrae (RRL) population in NGC 147, a dwarf satellite galaxy of M31 (Andromeda). We used both Thuan-Gunn g-band ground-based photometry from the literature and Hubble Space Telescope Wide Field Planetary Camera 2 archival data in the F555W and F814W passbands to investigate the pulsation properties of RRL variable candidates in NGC 147. These data sets represent the two extreme cases often found in RRL studies with respect to the phase coverage of the observations and the quality of the photometric measurements. Extensive artificial variable star tests for both cases were performed. We conclude that neither data set is sufficient to confidently determine the pulsation properties of the NGC 147 RRLs. Thus, while we can assert that NGC 147 contains RRL variables, and therefore a population older than approx10 Gyr, it is not possible at this time to use the pulsation properties of these RRLs to study other aspects of this old population. Our results provide a good reference for gauging the completeness of RRL variable detection in future studies.

Yang, S-C.; Sarajedini, Ata, E-mail: sczoo@astro.ufl.ed, E-mail: ata@astro.ufl.ed [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States)

2010-01-01

257

Spectral Types of Red Supergiants in NGC 6822 and the Wolf-Lundmark-Melotte Galaxy  

NASA Astrophysics Data System (ADS)

We present moderate-resolution spectroscopic observations of red supergiants (RSGs) in the low-metallicity Local Group galaxies NGC 6822 (Z = 0.4 Z ?) and Wolf-Lundmark-Melotte (WLM; Z = 0.1 Z ?). By combining these observations with reduction techniques for multislit data reduction and flux calibration, we are able to analyze spectroscopic data of 16 RSGs in NGC 6822 and spectrophotometric data of 11 RSGs in WLM. Using these observations, we determine spectral types for these massive stars, comparing them to Milky Way and Magellanic Cloud RSGs and thus extending observational evidence of the abundance-dependent shift of RSG spectral types to lower metallicities. In addition, we have uncovered two RSGs with unusually late spectral types (J000158.14-152332.2 in WLM, with a spectral type of M3 I, and J194453.46-144552.6 in NGC 6822, with a spectral type of M4.5 I) and a third RSG (J194449.96-144333.5 in NGC 6822) whose spectral type has varied from an M2.5 in 1997 to a K5 in 2008. All three of these stars could potentially be members of a recently discovered class of extreme RSG variables. This paper is based on data gathered with the 6.5 m Magellan telescopes located at Las Campanas, Chile.

Levesque, Emily M.; Massey, Philip

2012-07-01

258

SPECTRAL TYPES OF RED SUPERGIANTS IN NGC 6822 AND THE WOLF-LUNDMARK-MELOTTE GALAXY  

SciTech Connect

We present moderate-resolution spectroscopic observations of red supergiants (RSGs) in the low-metallicity Local Group galaxies NGC 6822 (Z = 0.4 Z{sub Sun} ) and Wolf-Lundmark-Melotte (WLM; Z = 0.1 Z{sub Sun} ). By combining these observations with reduction techniques for multislit data reduction and flux calibration, we are able to analyze spectroscopic data of 16 RSGs in NGC 6822 and spectrophotometric data of 11 RSGs in WLM. Using these observations, we determine spectral types for these massive stars, comparing them to Milky Way and Magellanic Cloud RSGs and thus extending observational evidence of the abundance-dependent shift of RSG spectral types to lower metallicities. In addition, we have uncovered two RSGs with unusually late spectral types (J000158.14-152332.2 in WLM, with a spectral type of M3 I, and J194453.46-144552.6 in NGC 6822, with a spectral type of M4.5 I) and a third RSG (J194449.96-144333.5 in NGC 6822) whose spectral type has varied from an M2.5 in 1997 to a K5 in 2008. All three of these stars could potentially be members of a recently discovered class of extreme RSG variables.

Levesque, Emily M. [CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, 389-UCB, Boulder, CO 80309 (United States); Massey, Philip, E-mail: Emily.Levesque@colorado.edu [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States)

2012-07-15

259

The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey - IX. 12CO J = 3?2 observations of NGC 2976 and NGC 3351  

NASA Astrophysics Data System (ADS)

We present 12CO J = 3?2 maps of NGC 2976 and NGC 3351 obtained with the James Clerk Maxwell Telescope (JCMT), both early targets of the JCMT Nearby Galaxy Legacy Survey (NGLS). We combine the present observations with 12CO J = 1?0 data and find that the computed 12CO J = 3?2 to 12CO J = 1?0 line ratio (R31) agrees with values measured in other NGLS field galaxies. We compute the MH2 value and find that it is robust against the value of R31 used. Using H I data from The H I Nearby Galaxy Survey, we find a tight correlation between the surface density of H2 and star formation rate density for NGC 3351 when 12CO J = 3?2 data are used. Finally, we compare the 12CO J = 3?2 intensity with the polycyclic aromatic hydrocarbon (PAH) 8 ?m surface brightness and find a good correlation in the high surface brightness regions. We extend this study to include all 25 Spitzer Infrared Nearby Galaxies Survey galaxies within the NGLS sample and find a tight correlation at large spatial scales. We suggest that both PAH 8 ?m and 12CO J = 3?2 are likely to originate in regions of active star formation.

Tan, Boon-Kok; Leech, J.; Rigopoulou, D.; Warren, B. E.; Wilson, C. D.; Attewell, D.; Azimlu, M.; Bendo, G. J.; Butner, H. M.; Brinks, E.; Chanial, P.; Clements, D. L.; Heesen, V.; Israel, F.; Knapen, J. H.; Matthews, H. E.; Mortier, A. M. J.; Mühle, S.; Sánchez-Gallego, J. R.; Tilanus, R. P. J.; Usero, A.; van der Werf, P.; Zhu, M.

2013-11-01

260

The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey - IX. 12CO J = 3?2 observations of NGC 2976 and NGC 3351  

NASA Astrophysics Data System (ADS)

We present 12CO J = 3?2 maps of NGC 2976 and NGC 3351 obtained with the James Clerk Maxwell Telescope (JCMT), both early targets of the JCMT Nearby Galaxy Legacy Survey (NGLS). We combine the present observations with 12CO J = 1?0 data and find that the computed 12CO J = 3?2 to 12CO J = 1?0 line ratio (R31) agrees with values measured in other NGLS field galaxies. We compute the MH2 value and find that it is robust against the value of R31 used. Using H I data from The H I Nearby Galaxy Survey, we find a tight correlation between the surface density of H2 and star formation rate density for NGC 3351 when 12CO J = 3?2 data are used. Finally, we compare the 12CO J = 3?2 intensity with the polycyclic aromatic hydrocarbon (PAH) 8 ?m surface brightness and find a good correlation in the high surface brightness regions. We extend this study to include all 25 Spitzer Infrared Nearby Galaxies Survey galaxies within the NGLS sample and find a tight correlation at large spatial scales. We suggest that both PAH 8 ?m and 12CO J = 3?2 are likely to originate in regions of active star formation.

Tan, Boon-Kok; Leech, J.; Rigopoulou, D.; Warren, B. E.; Wilson, C. D.; Attewell, D.; Azimlu, M.; Bendo, G. J.; Butner, H. M.; Brinks, E.; Chanial, P.; Clements, D. L.; Heesen, V.; Israel, F.; Knapen, J. H.; Matthews, H. E.; Mortier, A. M. J.; Mühle, S.; Sánchez-Gallego, J. R.; Tilanus, R. P. J.; Usero, A.; van der Werf, P.; Zhu, M.

2013-09-01

261

Mapping the Resolved Stellar Population of the Dwarf Starburst Galaxy NGC 4214  

NASA Astrophysics Data System (ADS)

We present a detailed UV-optical study of the nearby dwarf galaxy NGC 4214 based on Hubble Space Telescope WFC3/UVIS observations using five filters: F225W, F336W, F438W, F547M, and F814W. We divide the central 3 kpc by 3 kpc region of NGC 4214 into a 38 box adaptive grid, and determine the age and mass distributions of the resolved stars in each grid-box by combining their color-magnitude and color-color diagrams. We also determine the ages and masses of the individual stars from the stellar spectral energy distribution (SED) fitting to a set of stellar SED models. These measurements allow us to map the recent star formation histories of the dwarf galaxy NGC 4214 in detail. We find that the young stars show strong clustering, while the old stars are more dispersed. This is consistent with a picture where stars form in star clusters and then dissipate on short timescales to form the field population. This project is based on Early Release Science observations made by the WFC3 Scientific Oversight Committee. We are grateful to the Director of the Space Telescope Science Institute for awarding Director's Discretionary time for this program. Support for program #11360 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Kim, Hwihyun; Whitmore, B. C.; Cohen, S. H.; Chandar, R.; Kaleida, C. C.; Windhorst, R. A.; WFC3 SOC Team

2013-01-01

262

A CHANDRA OBSERVATION OF THE NEARBY SCULPTOR GROUP Sd GALAXY NGC 7793  

SciTech Connect

We conducted a Chandra ACIS observation of the nearby Sculptor Group Sd galaxy NGC 7793 as part of a multiwavelength study of supernova remnants (SNRs) in nearby galaxies. At the assumed distance to NGC 7793 of 3.91 Mpc, the limiting unabsorbed luminosity of the detected discrete X-ray sources is L{sub X} (0.2-10.0 keV) {approx}3x10{sup 36} erg s{sup -1}. A total of 22 discrete sources were detected at the {approx}3{sigma} level or greater including one ultraluminous X-ray source (ULX). Based on multiwavelength comparisons, we identify X-ray sources coincident with one SNR, the candidate microquasar N7793-S26, one H II region, and two foreground Galactic stars. We also find that the X-ray counterpart to the candidate radio SNR R3 is time variable in its X-ray emission: we therefore rule out the possibility that this source is a single SNR. A marked asymmetry is seen in the distribution of the discrete sources with the majority lying in the eastern half of this galaxy. All of the sources were analyzed using quantiles to estimate spectral properties and spectra of the four brightest sources (including the ULX) were extracted and analyzed. We searched for time variability in the X-ray emission of the detected discrete sources using our measured fluxes along with fluxes measured from prior Einstein and Roentgensatellit observations. From this study, three discrete X-ray sources are established to be significantly variable. A spectral analysis of the galaxy's diffuse emission is characterized by a temperature of kT = 0.19-0.25 keV. The luminosity function of the discrete sources shows a slope with an absolute value of {Gamma} = -0.65 {+-} 0.11 if we exclude the ULX. If the ULX is included, the luminosity function has a long tail to high L{sub X} with a poor-fitting slope of {Gamma} = -0.62 {+-} 0.2. The ULX-less slope is comparable to the slopes measured for the distributions of NGC 6946 and NGC 2403 but much shallower than the slopes measured for the distributions of IC 5332 and M83. Lastly, we comment on the multiwavelength properties of the SNR population of NGC 7793.

Pannuti, Thomas G.; Staggs, Wayne D. [Space Science Center, Department of Earth and Space Sciences, Morehead State University, 235 Martindale Drive, Morehead, KY 40351 (United States); Schlegel, Eric M. [Department of Physics and Astronomy, University of Texas-San Antonio, 6900 North Loop 1604 West, San Antonio, TX, 78249-0663 (United States); Filipovic, Miroslav D.; Payne, Jeffrey L. [School of Computing and Mathematics, University of Western Sydney, Locked Bag 1797, Penrith South, DC, New South Wales, 1797 (Australia); Petre, Robert [NASA/GSFC, X-ray Astrophysics Laboratory, Code 662, Greenbelt, MD, 20771 (United States); Harrus, Ilana M. [NASA/HQ, Astrophysics Division, MS 3W39, Washington, DC 20546-0001 (United States); Lacey, Christina K., E-mail: t.pannuti@moreheadstate.edu, E-mail: wdstag01@moreheadstate.edu, E-mail: eric.schlegel@utsa.edu, E-mail: m.filipovic@uws.edu.au, E-mail: astronomer@me.com, E-mail: robert.petre-1@nasa.gov, E-mail: Ilana.M.Harrus@nasa.gov, E-mail: Christina.Lacey@hofstra.edu [Department of Physics and Astronomy, Hofstra University, 102 Berliner Hall, Hempstead, NY 11549 (United States)

2011-07-15

263

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

SciTech Connect

Using a slitless spectroscopy method with the 8.2 m Subaru telescope and its FOCAS Cassegrain spectrograph, we have increased the number of planetary nebula (PN) detections and PN velocity measurements in the flattened elliptical galaxy NGC 821. A comparison with the detections reported previously by the Planetary Nebulae Spectrograph group indicates that we have confirmed most of their detections. The velocities measured by the two groups, using different telescopes, spectrographs, and slitless techniques, are in good agreement. We have built a combined sample of 167 PNs and have confirmed the Keplerian decline of the line-of-sight velocity dispersion reported previously. We also confirm misaligned rotation from the combined sample. A dark matter halo may exist around this galaxy, but it is not needed to keep the PN velocities below the local escape velocity as calculated from the visible mass. We have measured the m(5007) magnitudes of 145 PNs and produced a statistically complete sample of 40 PNs in NGC 821. The resulting PN luminosity function (PNLF) was used to estimate a distance modulus of 31.4 mag, equivalent to 19 Mpc. We also estimated the PN formation rate. NGC 821 becomes the most distant galaxy with a PNLF distance determination. The PNLF distance modulus is smaller than the surface brightness fluctuation (SBF) distance modulus by 0.4 mag. Our kinematic information permits to rule out the idea that a shorter PNLF distance could be produced by the contamination of the PNLF by background galaxies with emission lines redshifted into the on-band filter transmission curve.

Teodorescu, A. M.; Mendez, R. H.; Kudritzki, R. P. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Bernardi, F. [Universita di Pisa, Largo B. Pontecorvo 5, 56127, Pisa (Italy); Riffeser, A., E-mail: ana@ifa.hawaii.ed, E-mail: mendez@ifa.hawaii.ed [Universitaets-Sternwarte Muenchen, Scheinerstr. 1, D-81679 Muenchen (Germany)

2010-09-20

264

The Kinematically Measured Pattern Speeds of NGC 2523 and NGC 4245  

Microsoft Academic Search

The purpose of this project is to observationally determine the bar pattern speeds (?[P]) of a mid-to-late type spiral and a unique SB0 galaxy as well as evaluate the galaxies' dark halo contributions to the inner disk regions. This was done by applying the method developed by Tremaine and Weinberg (1984, hereafter TW) to the SB(r)bc galaxy NGC 2523 and

P. Treuthardt; R. Buta

2007-01-01

265

Constraints on the Formation History of the Elliptical Galaxy NGC 3923 from the Colors of Its Globular Clusters  

Microsoft Academic Search

We present a study of the colors of globular clusters associated with the\\u000aelliptical galaxy NGC 3923. Our final sample consists of Washington system C\\u000aand T_1 photometry for 143 globular cluster candidates with an expected\\u000acontamination of no more than 10%. We find that the color distribution of the\\u000aNGC 3923 globular cluster system (GCS) is broad and appears

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

1994-01-01

266

THE ROLE OF THE MAGNETIC FIELD IN THE INTERSTELLAR MEDIUM OF THE POST-STARBURST DWARF IRREGULAR GALAXY NGC 1569  

SciTech Connect

NGC 1569 is a nearby dwarf irregular galaxy which underwent an intense burst of star formation 10-40 Myr ago. We present observations that reach surface brightnesses 2-80 times fainter than previous radio continuum observations and the first radio continuum polarization observations of this galaxy at 20 cm, 13 cm, 6 cm, and 3 cm. These observations allow us to probe the relationship of the magnetic field of NGC 1569 to the rest of its interstellar medium (ISM). We confirm the presence of an extended radio continuum halo at 20 cm and see for the first time the radio continuum feature associated with the western Halpha arm at wavelengths shorter than 20 cm. Although, in general, the spectral indices derived for this galaxy steepen as one moves into the halo of the galaxy, there are filamentary regions of flat spectral indices extending to the edge of the galaxy. The spectral index trends in this galaxy support the theory that there is a convective wind at work in this galaxy. There is strong polarized emission at 3 cm and 6 cm and weak polarized emission at 20 cm and 13 cm. We estimate that the thermal fraction is 40%-50% in the center of the galaxy and falls off rapidly with height above the disk. Using this estimate, we derive a total magnetic field strength of 38 {mu}G in the central regions and 10-15 {mu}G in the halo. The magnetic field is largely random in the center of the galaxy; the uniform field is {approx}3-9 {mu}G and is strongest in the halo. Using our total magnetic field strength estimates and the results of previous observations of NGC 1569, we find that the magnetic pressure is the same order of magnitude but, in general, a factor of a few less than the other components of the ISM in this galaxy. The uniform magnetic field in NGC 1569 is closely associated with the Halpha bubbles and filaments. We suggest that a supernova-driven dynamo may be operating in this galaxy. Based on our pressure estimates and the morphology of the magnetic field, the outflow of hot gas from NGC 1569 is clearly shaping the magnetic field, but the magnetic field in turn may be aiding the outflow by channeling gas out of the disk of the galaxy. Dwarf galaxies with extended radio continuum halos like that of NGC 1569 may play an important role in magnetizing the intergalactic medium.

Kepley, Amanda A.; Everett, John; Zweibel, Ellen G.; Wilcots, Eric M. [Department of Astronomy, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI 53706 (United States); Muehle, Stefanie [Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo (Netherlands); Klein, Uli, E-mail: kepley@astro.wisc.ed, E-mail: everett@physics.wisc.ed, E-mail: zweibel@astro.wisc.ed, E-mail: ewilcots@astro.wisc.ed, E-mail: muehle@jive.n, E-mail: uklein@astro.uni-bonn.d [Argelander Institut fuer Astronomie, Universitaet Bonn, Auf dem Huegel 71, D-53121 Bonn (Germany)

2010-03-20

267

HIERARCHICAL STELLAR STRUCTURES IN THE LOCAL GROUP DWARF GALAXY NGC 6822  

SciTech Connect

We present a comprehensive study of the star cluster population and the hierarchical structure in the clustering of blue stars with ages {approx}<500 Myr in the Local Group dwarf irregular galaxy NGC 6822. Our observational material comprises the most complete optical stellar catalog of the galaxy from imaging with the Suprime-Cam at the 8.2 m Subaru Telescope. We identify 47 distinct star clusters with the application of the nearest-neighbor density method to this catalog for a detection threshold of 3{sigma} above the average stellar density. The size distribution of the detected clusters can be very well approximated by a Gaussian with a peak at {approx}68 pc. The total stellar masses of the clusters are estimated by extrapolating the cumulative observed stellar mass function of all clusters to be in the range 10{sup 3}-10{sup 4} M{sub sun}. Their number distribution is fitted very well by a power law with index {alpha} {approx} 1.5 {+-} 0.7, which is consistent with the cluster mass functions of other Local Group galaxies and the cluster initial mass function. In addition to the detected star clusters of the galaxy, the application of the nearest-neighbor density method for various density thresholds, other than 3{sigma}, enabled the identification of stellar concentrations in various lengthscales. The stellar density maps constructed with this technique provide a direct proof of hierarchically structured stellar concentrations in NGC 6822, in the sense that smaller dense stellar concentrations are located inside larger and looser ones. We illustrate this hierarchy by the so-called dendrogram, or structure tree of the detected stellar structures, which demonstrates that most of the detected structures split up into several substructures over at least three levels. We quantify the hierarchy of these structures with the use of the minimum spanning tree method. We find that structures detected at 1, 2, and 3{sigma} density thresholds are hierarchically constructed with a fractal dimension of D {approx} 1.8. Some of the larger stellar concentrations, particularly in the northern part of the central star-forming portion of the galaxy, coincide with IR-bright complexes previously identified with Spitzer and associated with high column density neutral gas, indicating structures that currently form stars. The morphological hierarchy in stellar clustering, which we observe in NGC 6822, resembles that of the turbulent interstellar matter, suggesting that turbulence on pc and kpc scales has been probably the major agent that regulated clustered star formation in NGC 6822.

Gouliermis, Dimitrios A.; Walter, Fabian [Max Planck Institute for Astronomy, Koenigstuhl 17, 69117 Heidelberg (Germany); Schmeja, Stefan; Klessen, Ralf S. [Zentrum fuer Astronomie der Universitaet Heidelberg, Institut fuer Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg (Germany); De Blok, W. J. G., E-mail: dgoulier@mpia-hd.mpg.d, E-mail: walter@mpia-hd.mpg.d, E-mail: sschmeja@ita.uni-heidelberg.d, E-mail: rklessen@ita.uni-heidelberg.d, E-mail: edeblok@ast.uct.ac.z [University of Cape Town, Private Bag X3, Rondebosch 7701 (South Africa)

2010-12-20

268

Giant Molecular Clouds and Star Formation in the Non-Grand Design Spiral Galaxy NGC 6946  

NASA Astrophysics Data System (ADS)

Although the internal physical properties of molecular clouds have been extensively studied (Solomon et al. 1987), a more detailed understanding of their origin and evolution in different types of galaxies is needed. In order to disentangle the details of this process, we performed CO(1?0) CARMA observations of the eastern part of the multi-armed galaxy NGC 6946. Our goal was to determine if azimuthal segregation of various gas and star formation tracers occurs in this kind of spiral galaxy (Tamburro et al. 2008). Although we found no evidence of an angular offset between molecular gas, atomic gas and star formation regions in our observations, we observe a clear radial progression from regions where molecular gas dominates over atomic gas (for r ? 2.8 kpc) to regions where the gas becomes mainly atomic (5.6 kpc ? r ? 7.6 kpc) when azimuthally averaged. In addition, we found that the densest concentrations of molecular gas are located on arms, particularly where they appear to intersect. This result is in concordance with the behavior predicted by simulations of the spiral galaxies with an active potential (Clarke & Gittins 2006; Dobbs & Bonnell 2008). Since NGC 6946 is located at a distance of 5.5 Mpc, the linear resolution of the map corresponds to 140 pc. At such resolution, we were able to find CO emitting complexes with masses greater than those of typical Giant Molecular Clouds (105-106 M?). To identify GMCs individually and make a more detailed study of their physical properties, we made D array observations of CO(2?1) toward the densest concentrations of gas located in the prominent spiral arms. We achieved a linear resolution of 50 pc at 1 mm in D array, similar to GMCs sizes found in other galaxies (Bolatto et al. 2008). We present first results about possible differences in the properties of the on-arm clouds and the inter-arm clouds. While inter-arm GMAs in grand-design galaxies are thought to be formed by fragmentation of more massive on-arm GMAs, forming spur structures, in flocculent galaxies like NGC 6946 the formation of inter-arm molecular gas structures are proposed to be the result of collision between spiral arms.

Rebolledo, David; Wong, Tony; Leroy, Adam

2011-10-01

269

NGC 1365  

NASA Astrophysics Data System (ADS)

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.

Lindblad, Per Olof

270

The Massive Elliptical Galaxy NGC 4649 from the Perspective of Extended Gravity  

NASA Astrophysics Data System (ADS)

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 Re . 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 0 regime, and reduces to the Newtonian case when a > a 0. Within the MONDian a < a 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 4vprop(MGa 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.

Jiménez, M. A.; Garcia, G.; Hernandez, X.; Nasser, L.

2013-05-01

271

DEEP CHANDRA OBSERVATIONS OF EDGES AND BUBBLES IN THE NGC 5846 GALAXY GROUP  

SciTech Connect

We use a combined 120 ks Chandra exposure to analyze X-ray edges produced by non-hydrostatic gas motions (sloshing) from galaxy collisions, and cavities formed by active galactic nucleus (AGN) activity. Evidence for gas sloshing is seen in the spiral morphology and multiple cold front edges in NGC 5846's X-ray surface brightness distribution, while the lack of spiral structure in the temperature map suggests that the perturbing interaction was not in the plane of the sky. Density and spectral modeling across the edges indicate that the relative motion of gas in the cold fronts is at most transonic. Evidence for AGN activity is seen in two inner bubbles at 0.6 kpc, filled with 5 GHz and 1.5 GHz radio plasma and coincident with H{alpha} emission, and in a ghost bubble at 5.2 kpc west of NGC 5846's nucleus. The outburst energy and ages for the inner (ghost) bubbles are {approx}10{sup 55} erg and {approx}2 Myr ({approx}5 Multiplication-Sign 10{sup 55} erg and 12 Myr), respectively, implying an AGN duty cycle of 10 Myr. The inner bubble rims are threaded with nine knots, whose total 0.5-2 keV X-ray luminosity is 0.3 Multiplication-Sign 10{sup 40} erg s{sup -1}, a factor {approx}2-3 less than that of the surrounding rims, and 0.7 keV mean temperature is indistinguishable from that of the rims. We suggest that the knots may be transient clouds heated by the recent passage of a shock from the last AGN outburst. We also observe gas stripping from a cE galaxy, NGC 5846A, in a 0.5 kpc long ({approx}10{sup 5} M{sub Sun }) hot gas tail, as it falls toward NGC 5846.

Machacek, Marie E.; Jerius, Diab; Kraft, Ralph; Forman, William R.; Jones, Christine; Randall, Scott [Harvard-Smithsonian Center for Astrophysics 60 Garden Street, Cambridge, MA 02138 (United States); Giacintucci, Simona [Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States); Sun Ming, E-mail: mmachacek@cfa.harvard.edu [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22901 (United States)

2011-12-10

272

The Massive Black Hole in the Dwarf Galaxy NGC 4486B  

NASA Astrophysics Data System (ADS)

We report results from the application of a three-integral galactic dynamical model to NGC 4486B. This dwarf E1 companion to M87 has long been known to be an outlier in the Fundamental Plane. Kormendy and Magorrian et al. found a substantial central black hole mass, making it an outlier in the MBH to Lbulge relationship as well. From the modeling we are able to determine the extent to which NGC 4486B follows the MBH - sigma relation more closely than the other bulge galaxy relationships. The other unique feature NGC 4486B exhibits is a double nucleus structure, the second of only two observed. We combine the high resolution of STIS spectra with ground based data to form a more complete description of the line-of-sight velocity distributions (LOSVDs) in the nuclear region of NGC 4486B. Through the increased resolution of the dynamics and the three-integral model, we place an improved constraint on the mass-to-light ratio and black hole mass. Bender's research was supported by the NOAO/KPNO Research Experiences for Undergraduates (REU) Program which is funded by the National Science Foundation through Scientific Program Order No. 3 (AST-0243875) of the Cooperative Agreement No. AST-0132798 between the Association of Universities for Research in Astronomy (AURA) and the NSF. RG and GB were supported by NASA for the STIS Instrument Definition Team. This work is a collaboration with the STIS Instrument Definition Team galaxy nuclei group, which also includes John Hutchings, Charles Joseph, Mary Elizabeth Kaiser, Charles Nelson, Donna Weistrop, and Bruce Woodgate. This work is a collaboration with the Nuker Team, which also includes Ralf Bender, Alan Dressler, Sandra Faber, Alex Filippenko, Carl Grillmair, Luis Ho, John Magorrian, Jason Pinkney, Christos Siopis, and Scott Tremaine.

Bender, A.; Green, R. F.; Gebhardt, K.; Bower, G. A.; Kormendy, J.; Lauer, T.; Richstone, D. O.; STIS IDT Galaxy Nuclei Team; Nuker Team

2003-12-01

273

Testing for interaction between the galaxies NGC 450 and UGC 807  

NASA Astrophysics Data System (ADS)

The Sc spiral, NGC 450 (v0 = 1863 km/s) has conspicuously brighter H II regions at just the point of projected contact with the spiral UGC 807 (v0 = 11,600 km/s). New spectra and photometry are reported which show the following: (1) The rotation curve of the low-redshift spiral has asymmetries and large discontinuities. (2) The brightest H II regions show differences between them of the order of 100 km/s, and one knot shows a discrepancy of 400 km/s, well in excess of escape velocity. (3) The distribution of neutral hydrogen in NGC 450 is heavily overbalanced to the side of the bright knots and the position of UGC 807. (4) The rotation curve of the high-redshift spiral shows a shallow increase to maximum rotational velocity vmax = 171 km/s which is characteristic of lower luminosity spirals. The rotation curve is also asymmetric and shows irregularities. (5) The relative hydrogen alpha surface brightness, a distance-independent quantity, signifies currently enhanced star formation in UGC 807. The hydrogen alpha luminosity of the higher redshift spiral is unprecedentedly large if placed at its redshift distance. (6) The morphology of the higher redshift is more extended on the side toward NGC 450 than on the side away and the color index isocontour lines indicate a discontinuity where the UGC 807 image merges well that of NGC 450. The conclusion from the extensive analysis is that one would have to invoke an enormous conspiracy of accidents in order to avoid the conclusion that UGC 807 is a moderatlely low luminosity galaxy interacting with NGC 450.

Moles, Mariano; Marquez, Isabel; Masegosa, Josefa; del Olmo, Ascension; Perea, Jaime; Arp, Halton

1994-09-01

274

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

NASA Astrophysics Data System (ADS)

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.

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

2006-11-01

275

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

NASA Astrophysics Data System (ADS)

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.

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

2013-11-01

276

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

SciTech Connect

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.

Harrison, Sarah M.; /MIT /SLAC

2006-09-11

277

A New Dataset of Automatically Extracted Structure of Arms and Bars in Spiral Galaxies  

NASA Astrophysics Data System (ADS)

We present an algorithm capable of automatically extracting quantitative structure (bars and arms) from images of spiral galaxies. We have run the algorithm on 30,000 galaxies and compared the results to human classifications generously provided pre-publication by the Galaxy Zoo 2 team. In all available measures, our algorithm agrees with the humans about as well as they agree with each other. In addition we provide objective, quantitative measures not available in human classifications. We provide a preliminary analysis of this dataset to see how the properties of arms and bars vary as a function of basic variables such as environment, redshift, absolute magnitude, and color. We also show how structure can vary across wavebands as well as along and across individual arms and bars. Finally, we present preliminary results of a measurement of the total angular momentum present in our observed set of galaxies with an eye towards determining if there is a preferred "handedness" in the universe.

Hayes, Wayne B.; Davis, D.

2012-05-01

278

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

SciTech Connect

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.

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

279

UBVI Surface Photometry of the Spiral Galaxy NGC 300 in the Sculptor Group  

NASA Astrophysics Data System (ADS)

We present UBVI surface photometry over a 20.5' × 20.5' area of the late-type spiral galaxy NGC 300. We have derived isophotal maps, surface brightness profiles, ellipticity profiles, position angle profiles, and color profiles. By merging our I-band measurements with those of Böker et al. based on Hubble Space Telescope observations, we have obtained combined I-band surface brightness profiles for the region 0.02'' < r < 500'' and have decomposed the profiles into three components: a nucleus, a bulge, and an exponential disk.

Kim, Sang Chul; Sung, Hwankyung; Park, Hong Soo; Sung, Eon-Chang

2004-08-01

280

A barred spiral at the centre of the giant elliptical radio galaxy Centaurus A  

Microsoft Academic Search

We report observations at mid-infrared and sub-millimeter wavelengths of\\u000aCentaurus A (CenA, NGC 5128), the giant elliptical galaxy that harbors the\\u000aclosest radio loud Active Galactic Nucleus (AGN) to Earth. The dust emission\\u000afrom the deep interior of CenA reveals a bisymmetric structure with a diameter\\u000aof 5' (5 kpc), centred at the AGN. This structure is remarkably similar to

I. F. Mirabel; O. Laurent; D. B. Sanders; M. Sauvage; M. Tagger; V. Charmandaris; L. Vigroux; P. Gallais; C. Cesarsky; D. L. Block

1998-01-01

281

ASTROPHYSICS A barred spiral at the centre of the giant elliptical radio galaxy Centaurus A  

Microsoft Academic Search

We report observations at mid-infrared and sub-millimeter wavelengths of Centaurus A (CenA, NGC 5128), the giant elliptical galaxy that harbors the clos- est radio loud Active Galactic Nucleus (AGN) to Earth. The dust emission from the deep interior of CenA reveals a bisymmetric structure with a diameter of 5' (5 kpc), centred at the AGN. This structure is remarkably similar

I. F. Mirabel; O. Laurent; D. B. Sanders; M. Sauvage; M. Tagger; V. Charmandaris; L. Vigroux; P. Gallais; C. Cesarsky; D. L. Block

282

Optical multiband surface photometry of a sample of Seyfert galaxies: III. Global, isophotal, and bar parameters  

NASA Astrophysics Data System (ADS)

This paper is third in a series, studying the optical properties of a sample of Seyfert galaxies. Here we present a homogeneous set of global (ellipticity, position angle, inclination, and total magnitude) and isophotal (semi-major axis and colour indices at 24 V mag arcsec-2) parameters of the galaxy sample. We find the following median corrected isophotal colour indices: {(B-I_C)24(0)=1.9} mag arcsec-2 and {(V-I_C)24(0)=1.1} mag arcsec-2. A set of bar parameters (ellipticity, position angle, semi-major axis corresponding to the ellipticity maximum in the bar region, and length) are also reported; deprojection has been applied to the bar ellipticity, length, and relative length in terms of galaxy isophotal semi-major axis. Regarding bar length estimation, we use a method, based on the relation between the behaviour of the profiles and orbit analysis. The so estimated bar length tightly correlates with the semi-major axis, corresponding to the ellipticity maximum with a median ratio of the former to the latter of 1.22. The median of the deprojected bar ellipticity, length, and relative length are 0.39, 5.44 kpc, and 0.44, respectively. There is a correlation between the deprojected bar length and the corrected isophotal semi-major axis at 24 V mag arcsec-2. Three of the 17 large-scale bars appear strong, based on the deprojected bar ellipticity as a first-order approximation of bar strength. The deprojected relative bar length does not appear to correlate with the bar ellipticity. Based on observations obtained with the 2-m telescope of the Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences.

Slavcheva-Mihova, L.; Mihov, B.

2011-02-01

283

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

NASA Astrophysics Data System (ADS)

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.

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

2011-09-01

284

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

SciTech Connect

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.

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

285

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

SciTech Connect

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. 22 references.

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

1987-01-01

286

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

NASA Astrophysics Data System (ADS)

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.

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

2013-05-01

287

Effect of Central Mass Concentration on the Formation of Nuclear Spirals in Barred Galaxies  

NASA Astrophysics Data System (ADS)

We have performed smoothed particle hydrodynamics simulations to study the response of the central kiloparsec region of a gaseous disk to the imposition of nonaxisymmetric bar potentials. The model galaxies are composed of three axisymmetric components (halo, disk, and bulge) and a nonaxisymmetric bar. These components are assumed to be invariant in time in the frame corotating with the bar. The potential of spherical ?-models of Dehnen is adopted for the bulge component whose density varies as r -? near the center and r -4 at larger radii and, hence, possesses a central density core for ? = 0 and cusps for ?>0. Since the central mass concentration of the model galaxies increases with the cusp parameter ?, we have examined here the effect of the central mass concentration by varying the cusp parameter ? on the mechanism responsible for the formation of the symmetric two-armed nuclear spirals in barred galaxies. Our simulations show that the symmetric two-armed nuclear spirals are formed by hydrodynamic spiral shocks driven by the gravitational torque of the bar for the models with ? = 0 and 0.5. On the other hand, the symmetric two-armed nuclear spirals in the models with ? = 1 and 1.5 are explained by gas density waves. Thus, we conclude that the mechanism responsible for the formation of symmetric two-armed nuclear spirals in barred galaxies changes from hydrodynamic shocks to gas density waves as the central mass concentration increases from ? = 0 to 1.5.

Thakur, Parijat; Ann, H. B.; Jiang, Ing-Guey

2009-03-01

288

Toward a New Geometric Distance to the Active Galaxy NGC 4258. III. Final Results and the Hubble Constant  

NASA Astrophysics Data System (ADS)

We report a new geometric maser distance estimate to the active galaxy NGC 4258. The data for the new model are maser line-of-sight (LOS) velocities and sky positions from 18 epochs of very long baseline interferometry observations, and LOS accelerations measured from a 10 yr monitoring program of the 22 GHz maser emission of NGC 4258. The new model includes both disk warping and confocal elliptical maser orbits with differential precession. The distance to NGC 4258 is 7.60 ± 0.17 ± 0.15 Mpc, a 3% uncertainty including formal fitting and systematic terms. The resulting Hubble constant, based on the use of the Cepheid variables in NGC 4258 to recalibrate the Cepheid distance scale, is H 0 = 72.0 ± 3.0 km s–1 Mpc–1.

Humphreys, E. M. L.; Reid, M. J.; Moran, J. M.; Greenhill, L. J.; Argon, A. L.

2013-09-01

289

The Stellar and Gas Kinematics of the LITTLE THINGS Dwarf Irregular Galaxy NGC 1569  

NASA Astrophysics Data System (ADS)

In order to understand the formation and evolution of Magellanic-type dwarf irregular (dIm) galaxies, one needs to understand their three-dimensional structure. We present measurements of the stellar velocity dispersion in NGC 1569, a nearby post-starburst dIm galaxy. The stellar vertical velocity dispersion, ?z, coupled with the maximum rotational velocity derived from H I observations, V max, gives a measure of how kinematically hot the galaxy is, and, therefore, indicates its structure. We conclude that the stars in NGC 1569 are in a thick disk with a V max/?z = 2.4 ± 0.7. In addition to the structure, we analyze the ionized gas kinematics from O III observations along the morphological major axis. These data show evidence for outflow from the inner starburst region and a potential expanding shell near supermassive star cluster (SSC) A. When compared to the stellar kinematics, the velocity dispersion of the stars increases in the region of SSC A supporting the hypothesis of an expanding shell. The stellar kinematics closely follow the motion of the gas. Analysis of high-resolution H I data clearly reveals the presence of an H I cloud that appears to be impacting the eastern edge of NGC 1569. Also, an ultra-dense H I cloud can be seen extending to the west of the impacting H I cloud. This dense cloud is likely the remains of a dense H I bridge that extended through what is now the central starburst area. The impacting H I cloud was the catalyst for the starburst, thus turning the dense gas into stars over a short timescale, ~1 Gyr. We performed a careful study of the spectral energy distribution using infrared, optical, and ultraviolet photometry, producing a state-of-the-art mass model for the stellar disk. This mass modeling shows that stars dominate the gravitational potential in the inner 1 kpc. The dynamical mass of NGC 1569, derived from V max, shows that the disk may be dark matter deficient in the inner region, although, when compared to the expected virial mass determined from halo abundance matching techniques, the dark matter profile seems to agree with the observed mass profile at a radius of 2.2 kpc.

Johnson, Megan; Hunter, Deidre A.; Oh, Se-Heon; Zhang, Hong-Xin; Elmegreen, Bruce; Brinks, Elias; Tollerud, Erik; Herrmann, Kimberly

2012-11-01

290

THE STELLAR AND GAS KINEMATICS OF THE LITTLE THINGS DWARF IRREGULAR GALAXY NGC 1569  

SciTech Connect

In order to understand the formation and evolution of Magellanic-type dwarf irregular (dIm) galaxies, one needs to understand their three-dimensional structure. We present measurements of the stellar velocity dispersion in NGC 1569, a nearby post-starburst dIm galaxy. The stellar vertical velocity dispersion, {sigma}{sub z}, coupled with the maximum rotational velocity derived from H I observations, V{sub max}, gives a measure of how kinematically hot the galaxy is, and, therefore, indicates its structure. We conclude that the stars in NGC 1569 are in a thick disk with a V{sub max}/{sigma}{sub z} = 2.4 {+-} 0.7. In addition to the structure, we analyze the ionized gas kinematics from O III observations along the morphological major axis. These data show evidence for outflow from the inner starburst region and a potential expanding shell near supermassive star cluster (SSC) A. When compared to the stellar kinematics, the velocity dispersion of the stars increases in the region of SSC A supporting the hypothesis of an expanding shell. The stellar kinematics closely follow the motion of the gas. Analysis of high-resolution H I data clearly reveals the presence of an H I cloud that appears to be impacting the eastern edge of NGC 1569. Also, an ultra-dense H I cloud can be seen extending to the west of the impacting H I cloud. This dense cloud is likely the remains of a dense H I bridge that extended through what is now the central starburst area. The impacting H I cloud was the catalyst for the starburst, thus turning the dense gas into stars over a short timescale, {approx}1 Gyr. We performed a careful study of the spectral energy distribution using infrared, optical, and ultraviolet photometry, producing a state-of-the-art mass model for the stellar disk. This mass modeling shows that stars dominate the gravitational potential in the inner 1 kpc. The dynamical mass of NGC 1569, derived from V{sub max}, shows that the disk may be dark matter deficient in the inner region, although, when compared to the expected virial mass determined from halo abundance matching techniques, the dark matter profile seems to agree with the observed mass profile at a radius of 2.2 kpc.

Johnson, Megan [National Radio Astronomy Observatory, P.O. Box 2, Green Bank, WV 24944 (United States); Hunter, Deidre A.; Zhang, Hong-Xin; Herrmann, Kimberly [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Oh, Se-Heon [International Centre for Radio Astronomy Research (ICRAR), University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia); Elmegreen, Bruce [IBM T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Hts., NY 10598 (United States); Brinks, Elias [Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, AL10 9AB (United Kingdom); Tollerud, Erik, E-mail: mjohnson@nrao.edu, E-mail: dah@lowell.edu, E-mail: hxzhang@lowell.edu, E-mail: herrmann@lowell.edu, E-mail: se-heon.oh@uwa.edu.au, E-mail: bge@us.ibm.com, E-mail: E.Brinks@herts.ac.uk, E-mail: etolleru@uci.edu [Center For Cosmology, Department of Physics and Astronomy, 4129 Frederick Reines Hall, University of California, Irvine, CA 92697 (United States)

2012-11-01

291

Galactic dynamics and magnetic fields. 2: Magnetic fields in barred galaxies  

NASA Astrophysics Data System (ADS)

We present a magnetic-field amplification process in galaxies in conjunction with bar dynamics. Our model considers especially the observed non-circular gas velocities in barred spiral galaxies. The bar drives the spirally-falling gas flow toward the center, which consists of a net radial flow (referred to as flow b) and an elliptically elongated flow rotating in the azimuth (flow a). The induced radial flow by a bar (flow b) produces a magnetic field, whose exponential growth is closely related with the angular-momentum transport by the non-axisymmetric bar perturbation. Furthermore, the non-axisymmetric gas flow (flow a) also leads to the exponential and oscillatory growth of magnetic fields by driving a growing magnetic wave. The interplay of both flows in a bar hence induces an oscillatory amplification of magnetic fields, and the resulting magnetic field pattern rotates with a bar and holds the azimuthal wavenumber m = 1 or 2, depending on the strength of velocity disturbances. This model naturally explains the characteristic radio features observed in M83, where the m = 1 magnetic field is aligned with the bar, and the bar ends are dominated by the vertical component Bz, giving the holes in polarized intensity map. It is emphasized that the evolution of galactic magnetic fields is closely related with galactic dynamics and evolution.

Chiba, M.; Lesch, H.

1994-04-01

292

Dust and molecules in the Local Group galaxy NGC 6822. II. CO and molecular hydrogen.  

NASA Astrophysics Data System (ADS)

Emission from the J=1-0 ^12^CO transition was detected unambiguously at 4 out of 17 observed positions in the Magellanic irregular galaxy NGC 6822; two more positions yielded marginal 3? detections. These positions include the HII region complexes Hubble V and Hubble I/III, and two IRAS far-infrared emission peaks not associated with bright HII regions. The bright HII region Hubble X was not detected. The CO emission detected is rather weak, typically 0.4-0.8 K.km/s in a 105 pc beam. It is well-correlated with infrared brightness, but not with that of HI emission. The sum of all observed spectra yields an integrated CO signal I_CO_=6.4+/-1.2K.km/s, 70% greater than the sum of the individual detected components. This implies the presence of more widespread weak CO emission not detected in individual pointings. The total CO content of NGC 6822 is argued to be 1.2(+1.2,-0.6)x10^5^K.km/s/pc^2^, nominally twice the amount detected. The available HI, infrared and CO data have been used to estimate the magnitude of the empirical conversion factor X=N(H_2_)/I_CO_ in NGC 6822, resulting in X_N6822_=8+/-3x10^21^cm^-2^(K.km/s)^-1^, or 40+/-15 times higher than the Galactic conversion factor. Even with this factor, the total H_2_ mass of NGC 6822 is estimated at only M(H_2_)=1.5(+3, -1)x10^7^Msun_, roughly 15 per cent of the HI mass. In the Galactic foreground, CO emission from a diffuse cloud was detected with a narrow linewidth of about 1km/s at V_LSR_=+5 km/s.

Israel, F. P.

1997-01-01

293

Oxygen and Neon Abundances of Planetary Nebulae in the Elliptical Galaxy NGC 4697  

NASA Astrophysics Data System (ADS)

This paper presents deep spectra of 14 planetary nebulae (PNs) at a variety of angular distances from the center of the flattened elliptical galaxy NGC 4697, which is located at ~11 Mpc from us. Both near the center and among the most outlying PNs, we have found several examples of very strong [O III] ?5007, about 20 times brighter than H?. This, together with strong [Ne III] lines, implies a lower limit for O and Ne abundances near solar at the center and also at more than 2 effective radii from the center of NGC 4697. Thus we have found, for the first time from individual stars, direct evidence of the existence of a metal-rich population in elliptical galaxies, confirming metallicities derived from absorption-line indices and extending the information to angular distances where the stellar surface brightness is too low for absorption-line studies. A comparison with abundances obtained closer to the center of NGC 4697 from integrated absorption-line spectra indicates that the metallicity gradient, which is quite steep within 1 effective radius, becomes much less pronounced beyond 1 effective radius. The only alternative to this interpretation would be the presence of a very metal-poor PN population with [Z/H] below -1, which we cannot rule out, but it would require an extremely bimodal metallicity distribution with almost no intermediate metallicities. Part of the data presented herein were obtained at the European Southern Observatory, Chile, Program ESO 69.B-0124. Part of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Méndez, R. H.; Thomas, D.; Saglia, R. P.; Maraston, C.; Kudritzki, R. P.; Bender, R.

2005-07-01

294

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

NASA Astrophysics Data System (ADS)

Near-infrared images are useful for analyzing the stellar backbone of disk galaxies, and in particular can be used to derive gravitational potentials (Quillen, Frogel, and Gonzalez 1994, ApJ, 437, 162). We have shown (Buta and Block 2001, ApJ, 550, 243) that from such potentials, the maximum value of the ratio of the tangential force to the mean radial force in the bar region is an easily derived quantity that can represent the most reliable measure of "bar strength" in disk galaxies. However, such maximum relative torques could also be affected by spirals emanating from the ends of bars. In this poster, we describe a Fourier-based method of separating bars from spirals in near-infrared images, such that the maximum torques due to each of these features alone can be derived. The method takes advantage of the fact that a bar is typically a feature with a relatively fixed position angle, and uses a simple assumption to extrapolate the relative Fourier amplitudes of the bar into the spiral region. We outline the complete procedure for a single, representative example, and summarize the main uncertainties in the technique. We also present the first results of application of the technique to a sample of 17 spiral galaxies, and find that the strongest spirals tend to be associated with strong bars. This work was supported by NSF Grant AST-0205143 to the University of Alabama and the Anglo-American Chairman's Fund, University of the Witwatersrand.

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

2003-05-01

295

AN X-RAY, OPTICAL, AND RADIO SEARCH FOR SUPERNOVA REMNANTS IN THE NEARBY SCULPTOR GROUP Sd GALAXY NGC 300  

Microsoft Academic Search

We have conducted a multiwavelength (X-ray, optical, and radio) search for supernova remnants (SNRs) in the nearby Sculptor Group Sd galaxy NGC 300. Our Very Large Array (VLA) radio obser- vations at 6 cm and 20 cm have been combined with previously published optical results, our own optical image, and archived ROSAT X-ray data to search for new SNR candidates.

THOMAS G. PANNUTI; NEBOJSA DURIC; Yale Boulevard; CHRISTINA K. LACEY; W. M. GOSS; CHARLES G. HOOPES; N. Charles; A. M. WALTERBOS; MARCUS A. MAGNOR

2000-01-01

296

An X-Ray, Optical, and Radio Search for Supernova Remnants in the Nearby Sculptor Group Sd Galaxy NGC 300  

Microsoft Academic Search

We have conducted a multiwavelength (X-ray, optical, and radio) search for supernova remnants (SNRs) in the nearby Sculptor Group Sd galaxy NGC 300. Our Very Large Array (VLA) radio observations at 6 cm and 20 cm have been combined with previously published optical results, our own optical image, and archived ROSAT X-ray data to search for new SNR candidates. Of

Thomas G. Pannuti; Nebojsa Duric; Christina K. Lacey; W. M. Goss; Charles G. Hoopes; René A. M. Walterbos; Marcus A. Magnor

2000-01-01

297

Reflection of Bulge Light from a 2 Kiloparsec Segment of Dust Lane in the Galaxy NGC 2841  

Microsoft Academic Search

The highly inclined galaxy NGC 2841 shows an amorphous linear strip transverse to the nearside minor axis that is bright in the optical but coincident with a dark dust lane at 2.1 mum. Spectra of this strip obtained with the Low-Resolution Imaging Spectrometer on the Keck II telescope are essentially identical to spectra of the bulge, indicating that the emission

David L. Block; Alan Stockton; Bruce G. Elmegreen; Jon Willis

1999-01-01

298

Ionized gas characteristics in the cavities of the gas and dust disc of the spiral galaxy NGC 6946  

NASA Astrophysics Data System (ADS)

The parameters of the ionized gas in NGC 6946 (in the [NII] ??6548, 6583, H ? and [SII] ??6717, 6731 lines) are investigated with the SAO RAS BTA telescope along three positions of the long slit of the SCORPIO focal reducer, passing through a number of large and small cavities of the gaseous disc of the galaxy. These cavities correspond exactly to the cavities in warm dust, visible at 5 - 8µm. We found that everywhere in the direction of NGC 6946 the lines of ionized gas are decomposed into two Gaussians, one of which shows almost constant [SII]/H ? and [NII]/H ? ratios, as well as an almost constant radial velocity within the measurement errors (about -35… - 50 km/s). This component is in fact the foreground radiation from the diffuse ionized gas of our Galaxy, which is not surprising, given the low (12°) latitude of NGC 6946; a similar component is also present in the emission of neutral hydrogen. The analysis of the component of ionized gas, occurring inNGC 6946, has revealed that it shows signs of shock excitation in the cavities of the gaseous disc of the galaxy. This shock excitation is as well typical for the extraplanar diffuse ionized gas (EDIG), observed in a number of spiral galaxies at their high Z-coordinates. This can most likely be explained by low density of the gas in the NGC 6946 disc (with the usual photoionization) inside the cavities, due to what we see the spectral features of the EDIG gas of NGC 6946, projected onto them, and located outside the plane of the galaxy. In the absence of separation of ionized gas into two components by radial velocities, there is an increasing contribution to the integral line parameters by the EDIG of our Galaxy when the gas density in NGC 6946 decreases, which explains some strange results, obtained in the previous studies. Themorphology of warmdust, visible in the infrared range and HI is almost the same (except for the peripheral parts of the galaxy, where there are no sources of dust heating).Moreover, the shock excitation of the ionized gas is detected in the smallest holes, distinguishable only in the IR images.

Efremov, Yu. N.; Afanasiev, V. L.; Egorov, O. V.

2011-07-01

299

Global properties of 'ordinary' early-type galaxies: photometry and spectroscopy of stars and globular clusters in NGC 4494  

NASA Astrophysics Data System (ADS)

We present a comprehensive analysis of the spatial, kinematic and chemical properties of stars and globular clusters (GCs) in the 'ordinary' elliptical galaxy NGC 4494 using data from the Keck and Subaru telescopes. We derive galaxy surface brightness and colour profiles out to large galactocentric radii. We compare the latter to metallicities derived using the near-infrared Calcium Triplet. We obtain stellar kinematics out to ˜3.5 effective radii. The latter appear flattened or elongated beyond ˜1.8 effective radii in contrast to the relatively round photometric isophotes. In fact, NGC 4494 may be a flattened galaxy, possibly even an S0, seen at an inclination of ˜45°. We publish a catalogue of 431 GC candidates brighter than i0= 24 based on the photometry, of which 109 are confirmed spectroscopically and 54 have measured spectroscopic metallicities. We also report the discovery of three spectroscopically confirmed ultra-compact dwarfs around NGC 4494 with measured metallicities of -0.4 ?[Fe/H]?-0.3. Based on their properties, we conclude that they are simply bright GCs. The metal-poor GCs are found to be rotating with similar amplitude as the galaxy stars, while the metal-rich GCs show marginal rotation. We supplement our analysis with available literature data and results. Using model predictions of galaxy formation, and a suite of merger simulations, we find that many of the observational properties of NGC 4494 may be explained by formation in a relatively recent gas-rich major merger. Complete studies of individual galaxies incorporating a range of observational avenues and methods such as the one presented here will be an invaluable tool for constraining the fine details of galaxy formation models, especially at large galactocentric radii.

Foster, Caroline; Spitler, Lee R.; Romanowsky, Aaron J.; Forbes, Duncan A.; Pota, Vincenzo; Bekki, Kenji; Strader, Jay; Proctor, Robert N.; Arnold, Jacob A.; Brodie, Jean P.

2011-08-01

300

Evolutionary properties of the low-luminosity galaxy population in the NGC 5044 Group  

NASA Astrophysics Data System (ADS)

In this third paper of a series we present Johnson-Gunn B, g, V, r, i, z multicolour photometry for 79 objects, including a significant fraction of the faintest galaxies around NGC 5044, assessing group membership on the basis of apparent morphology (through accurate Sérsic-profile fitting) and low-resolution (R= 500-1000) optical spectroscopy to estimate the redshift for 21 objects. Early- and late-type systems are found to be clearly separate in Sérsic parameter space, with the well-known luminosity versus shape relation being mostly traced by different morphological types spanning different ranges in the shape parameter n. A significantly blue colour is confirmed for Magellanic irregulars (Sm/Ims), while a drift toward bluer integrated colours is also an issue for dwarf ellipticals (dEs). Both features point to moderate but pervasive star-formation activity even among nominally 'quiescent' stellar systems. Together, dEs and Ims provide the bulk of the galaxy luminosity function, around M(g) ?-18.0 ± 1.5, while the S0 and dwarf spheroidal (dSph) components dominate the bright and faint-end tails of the distribution respectively. This special mix places the NGC 5044 Group just 'midway' between the high-density cosmic aggregation scale typical of galaxy clusters and the low-density environment of looser galaxy clumps like our Local Group. The bright mass of the 136 member galaxies with available photometry and morphological classification, as inferred from appropriate M/L model fitting, amounts to a total of 2.3 × 1012 M?. This is one seventh of the total dynamical mass of the group, according to its X-ray emission. The current star-formation rate within the group turns to be about 23 M? yr-1, a figure that may however be slightly increased as a result of the evident activity among dwarf ellipticals, as shown by enhanced H? emission in their spectra. Lick narrow-band indices have been computed for 17 galaxies, probing all the relevant atomic and molecular features in the 4300-5800 Å wavelength range. Dwarf ellipticals are found to share a subsolar metallicity (-1.0 ? [Fe/H] ?- 0.5), with a clear decoupling between iron and ? elements, as already established for high-mass systems. Both dEs and dS0s are consistent with a high age, about one Hubble time, although a possible bias towards higher values of age may be induced by the gas emission affecting the H? strength.

Buzzoni, A.; Cellone, S. A.; Saracco, P.; Zucca, E.

2012-03-01

301

Morphology of 15 Southern Early-Type Disk Galaxies  

NASA Astrophysics Data System (ADS)

Structural analysis has been performed for a sample of 15 southern early-type disk galaxies, mainly S0 galaxies, using high-resolution Ks-band images. The galaxies are mostly barred, and many of them show multiple structures including bars and ovals, typical for S0 galaxies. The new images are of sufficient quality to reveal new detail of the morphology of the galaxies. For example, we report a hitherto undetected nuclear ring in NGC 1387, a nuclear bar in NGC 1326, and in the residual image a weak primary bar in NGC 1317. For the galaxies we (1) measure the radial profiles of the orientation parameters derived from the elliptical isophotes, (2) apply Fourier methods for calculating tangential forces, and, in particular, (3) apply structural decomposition methods. For galaxies with multiple structures a two-dimensional method is found to be superior to a one-dimensional method but only if in addition to the bulge and the disk at least one other component is taken into account. We find strong evidence of pseudobulges in S0 galaxies: 10 of the galaxies have a shape parameter of the bulge near n=2, indicating that the bulges are more disklike than following the R1/4 law. Also, six of the galaxies have either nuclear rings, nuclear bars, or nuclear disks. In all nonelliptical galaxies in our sample the bulge-to-total (B/T) flux ratio is less than 0.4, as is typically found in galaxies having pseudobulges. In two of the galaxies the B/T flux ratio is as small as in typical Sc-type spiral galaxies. This might be the hitherto undiscovered link in the scenario in which spiral galaxies are transformed into S0 galaxies. Also, bars in S0 systems are found to be shorter and less massive and to have smaller bar torques than bars in S0/a-type galaxies.

Laurikainen, Eija; Salo, Heikki; Buta, Ronald; Knapen, Johan; Speltincx, Tom; Block, David

2006-12-01

302

The 'sleeping beauty' galaxy NGC 4826: an almost textbook example of the Abelian Higgs vorto-source (-sink)  

NASA Astrophysics Data System (ADS)

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.

Saniga, Metod

1995-03-01

303

CHANDRA OBSERVATIONS OF NGC 4342, AN OPTICALLY FAINT, X-RAY GAS-RICH EARLY-TYPE GALAXY  

SciTech Connect

Chandra x-ray observations of NGC 4342, a low-stellar mass (M{sub K} = -22.79 mag) early-type galaxy, show luminous, diffuse x-ray emission originating from hot gas with temperature of kT {approx} 0.6 keV. The observed 0.5-2 keV band luminosity of the diffuse x-ray emission within the D{sub 25} ellipse is L{sub 0.5-2keV} = 2.7 Multiplication-Sign 10{sup 39} erg s{sup -1}. The hot gas has a significantly broader distribution than the stellar light, and shows strong hydrodynamic disturbances with a sharp surface brightness edge to the northeast and a trailing tail. We identify the edge as a cold front and conclude that the distorted morphology of the hot gas is produced by ram pressure as NGC 4342 moves through external gas. From the thermal pressure ratios inside and outside the cold front, we estimate the velocity of NGC 4342 and find that it moves supersonically (M {approx} 2.6) toward the northeast. Outside the optical extent of the galaxy, we detect {approx}17 bright (L{sub 0.5-8keV} > or approx. 3 x 10{sup 37} erg s{sup -1}) excess x-ray point sources. The excess sources are presumably LMXBs located in metal-poor globular clusters (GCs) in the extended dark matter halo of NGC 4342. Based on the number of excess sources and the average frequency of bright LMXBs in GCs, we estimate that NGC 4342 may host roughly 850-1700 GCs. In good agreement with this, optical observations hint that NGC 4342 may harbor 1200 {+-} 500 GCs. This number corresponds to a GC specific frequency of S{sub N} = 19.9 {+-} 8.3, which is among the largest values observed in full-size galaxies.

Bogdan, Akos; Forman, William R.; Kraft, Ralph P.; Jones, Christine; Randall, Scott W.; Li Zhiyuan; Nulsen, Paul E. J.; Vikhlinin, Alexey [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Blom, Christina [Centre for Astrophysics and Supercomputing, Swinburne University, Hawthorn, VIC 3122 (Australia); Zhang Zhongli; Zhuravleva, Irina; Churazov, Eugene [Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-str. 1, 85748 Garching (Germany); Schindler, Sabine, E-mail: abogdan@cfa.harvard.edu [Institut fuer Astrophysik, Leopold-Franzens Universitaet Innsbruck, Technikerstrasse 25, 6020 Innsbruck (Austria)

2012-08-10

304

STAR FORMATION AND DUST OBSCURATION IN THE TIDALLY DISTORTED GALAXY NGC 2442  

SciTech Connect

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.

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

305

X-Ray Nuclear Activity in S4G Barred Galaxies: No Link between Bar Strength and Co-occurrent Supermassive Black Hole Fueling  

NASA Astrophysics Data System (ADS)

Stellar bars can lead to gas inflow toward the center of a galaxy and stimulate nuclear star formation. However, there is no compelling evidence on whether they also feed a central supermassive black hole: by measuring the fractions of barred active and inactive galaxies, previous studies have yielded conflicting results. In this paper, we aim to understand the lack of observational evidence for bar-driven active galactic nucleus (AGN) activity by studying a sample of 41 nearby (d < 35 Mpc) barred galaxies from the Spitzer Survey for Stellar Structure in Galaxies. We use Chandra observations to measure nuclear 2-10 keV X-ray luminosities and estimate Eddington ratios, together with Spitzer 3.6 ?m imaging to quantify the strength of the stellar bar in two independent ways: (1) from its structure, as traced by its ellipticity and boxiness, and (2) from its gravitational torque Qb , taken as the maximum ratio of the tangential force to the mean background radial force. In this way, rather than discretizing the presence of both stellar bars and nuclear activity, we are able to account for the continuum of bar strengths and degrees of AGN activity. We find nuclear X-ray sources in 31 out of 41 galaxies with median X-ray luminosity and Eddington ratio of L X = 4.3 × 1038 erg s-1 and L bol/L Edd = 6.9 × 10-6, respectively, consistent with low-luminosity AGN activity. Including upper limits for those galaxies without nuclear detections, we find no significant correlation between any of the bar strength indicators and the degree of nuclear activity, irrespective of galaxy luminosity, stellar mass, Hubble type, or bulge size. Strong bars do not favor brighter or more efficient nuclear activity, implying that at least for the low-luminosity regime, supermassive black hole fueling is not closely connected to large-scale features.

Cisternas, Mauricio; Gadotti, Dimitri A.; Knapen, Johan H.; Kim, Taehyun; Díaz-García, Simón; Laurikainen, Eija; Salo, Heikki; González-Martín, Omaira; Ho, Luis C.; Elmegreen, Bruce G.; Zaritsky, Dennis; Sheth, Kartik; Athanassoula, E.; Bosma, Albert; Comerón, Sébastien; Erroz-Ferrer, Santiago; Gil de Paz, Armando; Hinz, Joannah L.; Holwerda, Benne W.; Laine, Jarkko; Meidt, Sharon; Menéndez-Delmestre, Karín; Mizusawa, Trisha; Muñoz-Mateos, Juan Carlos; Regan, Michael W.; Seibert, Mark

2013-10-01

306

The Planetary Nebula Spectrograph elliptical galaxy survey: the dark matter in NGC 4494  

NASA Astrophysics Data System (ADS)

We present new Planetary Nebula Spectrograph observations of the ordinary elliptical galaxy NGC 4494, resulting in positions and velocities of 255 planetary nebulae out to seven effective radii (25 kpc). We also present new wide-field surface photometry from MMT/Megacam, and long-slit stellar kinematics from VLT/FORS2. The spatial and kinematical distributions of the planetary nebulae agree with the field stars in the region of overlap. The mean rotation is relatively low, with a possible kinematic axis twist outside 1Re. The velocity dispersion profile declines with radius, though not very steeply, down to ~70kms-1 at the last data point. We have constructed spherical dynamical models of the system, including Jeans analyses with multi-component ? cold dark matter (CDM) motivated galaxies as well as logarithmic potentials. These models include special attention to orbital anisotropy, which we constrain using fourth-order velocity moments. Given several different sets of modelling methods and assumptions, we find consistent results for the mass profile within the radial range constrained by the data. Some dark matter (DM) is required by the data; our best-fitting solution has a radially anisotropic stellar halo, a plausible stellar mass-to-light ratio and a DM halo with an unexpectedly low central density. We find that this result does not substantially change with a flattened axisymmetric model. Taken together with other results for galaxy halo masses, we find suggestions for a puzzling pattern wherein most intermediate-luminosity galaxies have very low concentration haloes, while some high-mass ellipticals have very high concentrations. We discuss some possible implications of these results for DM and galaxy formation.

Napolitano, N. R.; Romanowsky, A. J.; Coccato, L.; Capaccioli, M.; Douglas, N. G.; Noordermeer, E.; Gerhard, O.; Arnaboldi, M.; de Lorenzi, F.; Kuijken, K.; Merrifield, M. R.; O'Sullivan, E.; Cortesi, A.; Das, P.; Freeman, K. C.

2009-02-01

307

HALOGAS: H I OBSERVATIONS AND MODELING OF THE NEARBY EDGE-ON SPIRAL GALAXY NGC 4244  

SciTech Connect

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.

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

308

Deriving the pattern speed using dynamical modelling of gas flows in barred galaxies .  

NASA Astrophysics Data System (ADS)

In this paper we analyse the methodology to derive the bar pattern speed from dynamical simulations. The results are robust to the changes in the vertical-scale height and in the mass-to-light (M/L) ratios. There is a small range of parameters for which the kinematics can be fitted. We have also taken into account the use of different type of dynamical modelling and the effect of using 2-D vs 1-D models in deriving the pattern speeds. We conclude that the derivation of the bar streaming motions and strength and position of shocks is not greatly affected by the fluid dynamical model used. We show new results on the derivation of the pattern speed for NGC 1530. The best fit pattern speed is around 10 km s-1 kpc-1 , which corresponds to a R_cor/R_bar = 1.4, implying a slower bar than previously derived from more indirect assumptions. With this pattern speed, the global and most local kinematic features are beautifully reproduced. However, the simulations fail to reproduce the velocity gradients close to some bright HII regions in the bar. We have shown from the study of the H{alpha } equivalent widths that the HII regions that are located further away from the bar dust-lane in its leading side, downstream from the main bar dust-lane, are older than the rest by 1.5-2.5 Myr. In addition, a clear spatial correlation was found between the location of HII regions, dust spurs on the trailing side of the bar dust-lane, and the loci of maximum velocity gradients parallel to the bar major axis.

Pérez, I.; Freeman, K. C.; Fux, R.; Zurita, A.

309

Fraction of Strong Barred Galaxies (SB) in the Nearby Universe, 0 ? z ? 0.066 as a function of redshift  

NASA Astrophysics Data System (ADS)

An analysis of 913 groups of galaxies and 56 clusters of galaxies from the literature has been made in order to find the mean of the fraction of barred galaxies (SB/[S+SB]) and (SB/N) in the redshift interval 0 ? z ? 0.066.

García-Barreto, J. A.

2011-10-01

310

Photometric and spectroscopic study of the S0 galaxy, NGC 1266  

NASA Astrophysics Data System (ADS)

We present the results from a photometric and spectroscopic study of the S0 galaxy, NGC 1266, in the optical wavelengths. This project was carried out as part of the IGO observational training school, held during 20 December, 2010 to 15 January, 2011, at IUCAA (Pune). Surface photometry was performed in the BVR wide band and H-alpha narrow band filters. We used ellipse fitting to the isophotes, to measure the surface-brightness profile, the radial variation of position angle, ellipticity, and the B4 (boxyness/diskyness) parameter. We created colour maps and H-alpha emission line maps to identify the spatial distribution of dust features and ionized gas. We report the identification of extended cone of ionized gas outflow in the central 2 kiloparsec region of NGC 1266. Follow-up spectroscopy shows that the narrow-band emission is dominated by the [N II] emission, which is stronger than H-alpha emission. We detect outflow velocity of approximately 500 km s^{-1} from the wavelength shifts of the emission lines. Our results from the spectroscopic study include emission line identification, flux measurements of the emission lines, and physical parameters of the ionized gas.

Sahu, Sheetal Kumar

311

Giant H II regions in the interacting galaxies NGC 4038--4039  

SciTech Connect

Photographic determinations of the absolute H..cap alpha.. intensity of giant H II regions in NGC 4038--4039 are compared with other authors' photographic and spectroscopic measurements. The results can be reconciled only if the internal absorption in this system exceeds 3/sup m/ in the H..beta.. line. Much of the absorbing matter would then be concentrated within and near the H II regions. Their combined H..cap alpha.. luminosity would be approx. =3x10/sup 42/ erg/sec; their mass, approx. =10/sup 8/Msun; and the absolute magnitude of individual superassociations of hot stars and accompanying H II regions would average M/sub V/<-18/sup m/. Such parameters appear to be admissible either for a model of two interacting galaxies with a large amount of gas or for an isolated object undergoing fragmentation.

Metlov, V.G.

1978-11-01

312

Discovery of a population of compact radio sources in the spiral galaxy NGC 4736  

SciTech Connect

The discovery of 19 compact radio sources in the near-nuclear region of the spiral galaxy NGC 4736 is reported. Nine are found to have thermal bremsstrahlung spectra. Their small sizes of 1-2 arcsec (20-40 pc at a distance of 4 Mpc), combined with typical flux densities of 0.3-1.0 mJy at 20 cm, suggest high gas densities of 60-270/cu cm. It is proposed that these are H II regions associated with recently formed stars. The remaining 10 sources are all unresolved to 1 arcsec (20 pc) and have synchrotron spectra. Equipartition calculations show that the limits on the relativistic particle energies and magnetic field strengths are consistent with values found for Galactic SNRs. Furthermore, the radio luminosities and small sizes of these sources suggest that these are young SNRs. 20 references.

Duric, N.; Dittmar, M.R.

1988-09-01

313

PLANETARY NEBULAE IN THE ELLIPTICAL GALAXY NGC 4649 (M 60): KINEMATICS AND DISTANCE REDETERMINATION  

SciTech Connect

Using a slitless spectroscopy method with (1) the 8.2 m Subaru telescope and its FOCAS Cassegrain spectrograph and (2) the ESO Very Large Telescope unit 1 (Antu) and its FORS2 Cassegrain spectrograph, we have detected 326 planetary nebulae (PNs) in the giant Virgo elliptical galaxy NGC 4649 (M 60) and measured their radial velocities. After rejecting some PNs more likely to belong to the companion galaxy NGC 4647, we have built a catalog with kinematic information for 298 PNs in M 60. Using these radial velocities, we have concluded that they support the presence of a dark matter halo around M 60. Based on an isotropic, two-component Hernquist model, we estimate the dark matter halo mass within 3R{sub e} to be 4 x 10{sup 11} M{sub sun}, which is almost one-half of the total mass of about 10{sup 12} M{sub sun} within 3R{sub e}. This total mass is similar to that estimated from globular cluster, XMM-Newton, and Chandra observations. The dark matter becomes dominant outside. More detailed dynamical modeling of the PN data is being published in a companion paper. We have also measured the m(5007) magnitudes of many of these PNs and built a statistically complete sample of 218 PNs. The resulting PN luminosity function (PNLF) was used to estimate a distance modulus of 30.7 {+-} 0.2 mag, equivalent to 14 {+-} 1 Mpc. This confirms an earlier PNLF distance measurement based on a much smaller sample. The PNLF distance modulus remains smaller than the surface brightness fluctuation distance modulus by 0.4 mag.

Teodorescu, A. M.; Mendez, R. H. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Bernardi, F. [Dipartimento di Matematica, Universita di Pisa, Largo B. Pontecorvo 5, 56127 Pisa (Italy); Thomas, J.; Das, P.; Gerhard, O., E-mail: ana@ifa.hawaii.edu, E-mail: mendez@ifa.hawaii.edu [Max Planck Institut fuer Extraterrestrische Physik, P.O. Box 1603, D-85740 Garching bei Muenchen (Germany)

2011-07-20

314

The composite starburst/AGN nature of the superwind galaxy NGC 4666  

NASA Astrophysics Data System (ADS)

We report the discovery of a Compton-thick AGN and of intense star-formation activity in the nucleus and disk, respectively, of the nearly edge-on superwind galaxy NGC 4666. Spatially unresolved emission is detected by BeppoSAX only at energies <10 keV, whereas spatially resolved emission from the whole disk is detected by XMM-Newton. A prominent (EW ˜ 1-2 keV) emission line at ˜ 6.4 keV is detected by both instruments. From the XMM-Newton data alone the line is spectrally localized at E ? 6.42 ± 0.03 keV, and seems to be spatially concentrated in the nuclear region of NGC 4666. This, together with the presence of a flat (? ˜ 1.3) continuum in the nuclear region, suggests the existence of a strongly absorbed (i.e., Compton-thick) AGN, whose intrinsic 2-10 keV luminosity is estimated to be L2-10 ? 2 × 1041 erg s-1. At energies ?1 keV the integrated (BeppoSAX) spectrum is dominated by a ˜ 0.25 keV thermal gas component distributed throughout the disk (resolved by XMM-Newton). At energies ˜ 2-10 keV, the integrated spectrum is dominated by a steep (? ? 2) power-law (PL) component. The latter emission is likely due to unresolved sources with luminosity L ˜ 1038-1039 erg s-1 that are most likely accreting binaries (with BH masses ?8 M?). Such binaries, which are known to dominate the X-ray point-source luminosity in nearby star-forming galaxies, have ? ˜ 2 PL spectra in the relevant energy range. A ? ˜ 1.8 PL contribution from Compton scattering of (the radio-emitting) relativistic electrons by the ambient FIR photons may add a truly diffuse component to the 2-10 keV emission.

Persic, M.; Cappi, M.; Rephaeli, Y.; Bassani, L.; Della Ceca, R.; Franceschini, A.; Hunt, L.; Malaguti, G.; Palazzi, E.

2004-11-01

315

Molecular Cloud-Scale Star Formation in External Galaxies: NGC 300  

NASA Astrophysics Data System (ADS)

We have completed a CO (J=2-1) survey of previously identified H II regions in the nearby spiral galaxy NGC 300 with the goal of assessing their molecular gas properties and star formation activity. Our sample comprises a fairly uniform set of massive star-forming regions at a single distance, making it ideal for testing the connections between the dense ISM and star formation in galaxies. We detect CO at 34 of 76 positions targeted with the APEX 12m telescope, reaching typical sensitivities of ~30 mK (3?). The APEX angular resolution of 27” corresponds to a physical resolution of ~250 pc at the distance of NGC 300, and our CO-detected sources have masses of 0.4 - 3.2 x 105 M?, suggesting that they likely correspond to Giant Molecular Clouds or cloud complexes. We have also utilized publicly available Spitzer 24?m, GALEX far-UV, and H? data to investigate ongoing star formation in these clouds, and see in general strong morphological similarities between the structures observed in each of these star formation tracers. There is a clear correlation (albeit with significant scatter) between these tracers and the CO integrated intensity. Although the origin of the scatter is not entirely clear, it may be related to the fact that we are probing spatial scales small enough that the ability of integrated measures to trace star formation is starting to break down. Applying prescriptions from the literature, we compute star formation rates (SFRs) of 10-5 - 10-3 M?/yr for individual sources. We caution, however, that existing SFR recipes may not be appropriate for the spatial scales probed by our observations, and explore some possible calibrations that can be made to more appropriately measure SFRs in regions consisting of one or few stellar populations.

Faesi, Christopher; Lada, C. J.; Forbrich, J.; Menten, K.

2013-01-01

316

COMPARING X-RAY AND DYNAMICAL MASS PROFILES IN THE EARLY-TYPE GALAXY NGC 4636  

SciTech Connect

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 approx10 kpc, which we interpret as the result of non-thermal pressure support or a local inflow. However, over the radial range approx10-30 kpc, the mass profiles agree within the 1sigma 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.

Johnson, Ria; Raychaudhury, Somak [School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Chakrabarty, Dalia [School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom); O'Sullivan, Ewan, E-mail: ria@star.sr.bham.ac.u, E-mail: D.Chakrabarty@warwick.ac.u [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2009-12-01

317

Simulations of Barred Galaxies in Triaxial Dark Matter Haloes: The Effects of Gas  

NASA Astrophysics Data System (ADS)

The baryonic discs of galaxies are believed to alter the shapes of the dark matter haloes in which they reside. We perform a set of hydrodynamical N-body simulations of disc galaxies with triaxial dark matter haloes, using elliptical discs with a gaseous component as initial conditions. We explore models of different halo triaxiality and also of different initial gas fractions, which allows us to evaluate how each affects the formations of the bar. Due to star formation, models of all halo shapes and of all initial gas fractions reach approximately the same gas content at the end of the simulation. Nevertheless, we find that the presence of gas in the early phases has important effects on the subsequent evolution. Bars are generally weaker for larger initial gas content and for larger halo triaxiality. The presence of gas, however, is a more efficient factor in inhibiting the formation of a strong bar than halo triaxiality is.

Machado, R. E. G.; Athanassoula, E.; Rodionov, S.

2012-07-01

318

Two modes of gas flow in a single barred galaxy  

Microsoft Academic Search

We investigate stationary gas flows in a fixed, rotating barred potential. The gas is assumed to be isothermal with an effective sound speed c_s, and the equations of motion are solved with smoothed particle hydrodynamics (SPH). Since the thermal energy in cloud random motions is negligible compared with the orbital kinetic energy, no dependence of the flow on c_s is

Peter Englmaier; Ortwin Gerhard

1997-01-01

319

Cold gas in massive early-type galaxies: the case of NGC 1167  

NASA Astrophysics Data System (ADS)

We present a study of the morphology and kinematics of the neutral hydrogen in the gas-rich (MHI = 1.5 × 1010 M?), massive early-type galaxy NGC 1167, which was observed with the Westerbork Synthesis Radio Telescope (WSRT). The H i is located in a 160 kpc disk (? 3 × D25) and has low surface density (? 2 M? pc-2). The disk shows regular rotation for r < 65 kpc but several signs of recent and ongoing interaction and merging with fairly massive companions are observed. No population of cold gas clouds is observed - in contrast to what is found in some spiral galaxies. This suggests that currently the main mechanism bringing in cold gas to the disk is the accretion of fairly massive satellite galaxies, rather than the accretion of a large number of small gas clumps. NGC 1167 is located in a (gas-) rich environment: we detect eight companions with a total H i mass of ~ 6 × 109 M? within a projected distance of 350 kpc. Deep optical images show a disrupted satellite at the northern edge of the H i disk. The observed rotation curve shows a prominent bump of about 50 km s-1 (in the plane of the disk) at r ? 1.3 × R25. This feature in the rotation curve occurs at the radius where the H i surface density drops significantly and may be due to large-scale streaming motions in the disk. We suspect that both the streaming motions and the H i density distribution are the result of the interaction/accretion with the disrupted satellite. Like in other galaxies with wiggles and bumps in the rotation curve, H i scaling describes the observed rotation curve best. We suggest that interactions create streaming motions and features in the H i density distribution and that this is the reason for the success of H i scaling in fitting such rotation curves. Appendices are only available in electronic form at http://www.aanda.org

Struve, C.; Oosterloo, T.; Sancisi, R.; Morganti, R.; Emonts, B. H. C.

2010-11-01

320

Disclosing the true nature of the Sy 2 galaxy NGC 3281: One more Compton-thick source  

NASA Astrophysics Data System (ADS)

We present the BeppoSAX broad-band X-ray spectrum of the Seyfert 2 galaxy NGC 3281. The source high-energy spectrum is characterized by the nuclear transmitted component, with an absorbing column density of ~2x1024 cm-2, while the MECS spectrum is reflection-dominated, with a prominent (EW~0.5-1.2 keV) iron K? emission line. The source is detected at only the 5sigma significance level in the LECS band, because of the strong obscuration which hampers at low energies the direct view of the active nucleus harbored in NGC 3281. BeppoSAX results are consistent with the scenario where NGC 3281 is inclined more than 60deg with respect to the line-of-sight. Combining the NH value obtained from the present X-ray analysis with the AV measurement, a NH/AV about 50 times the Galactic value is derived.

Vignali, C.; Comastri, A.

2002-01-01

321

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

NASA Astrophysics Data System (ADS)

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 system is remarkably similar to those of the ``chain galaxies'' evident at high redshift, thus suggesting a similar interpretation for at least some of those distant objects. FUV, U, B, and V magnitudes, measured for 48 star-forming regions, along with corresponding H? and H? measurements are used to construct diagnostic color-color diagrams. Although there are significant exceptions, most of the star-forming regions are less massive and older than 30 Doradus. Comparison with the expectations from two star formation models yields ages of 2.7 to 10 Myr for the instantaneous burst (IB) model and star formation cutoff ages of 0 to 9 Myr for the continuous star formation (CSF) model. Interpreted in terms of the IB model the photometry implies a total created mass in the 48 star-forming regions of 2.5×107 Msolar. When viewed as resulting from constant star formation the photometry implies a star formation rate of 0.33 Msolar yr-1. These results are compared to those derived from FIR and radio observations. Corrections for FUV emission reprocessed by interstellar grains are estimated. A large ring, ~3 kpc in diameter, of 14 star-forming regions is concentrically located with an expanding H I shell toward the eastern end of the galaxy. Our observations imply that the shell may have been generated primarily by supernovae arising from 5.3×104 OB stars in a massive star-forming region beginning about 20 Myr ago, and that the presently observed FUV bright emission is due to second generation stars.

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

2001-01-01

322

Giant Molecular Clouds and Star Formation in the Non-Grand Design Spiral Galaxy NGC 6946  

NASA Astrophysics Data System (ADS)

Although the internal physical properties of molecular clouds have been extensively studied (Solomon et al. 1987), a more detailed understanding of their origin and evolution in different types of galaxies is needed. In order to disentangle the details of this process, we performed CO(1-0) CARMA observations of the eastern part of the multi-armed galaxy NGC 6946. Although we found no evidence of an angular offset between molecular gas, atomic gas and star formation regions in our observations (Tamburro et al. 2008), we observe a clear radial progression from regions where molecular gas dominates over atomic gas (for r ? 2.8 kpc) to regions where the gas becomes mainly atomic (5.6 kpc ? r ? 7.6 kpc) when azimuthally averaged. In addition, we found that the densest concentrations of molecular gas are located on arms, particularly where they appear to intersect, which is in concordance with the predictions by simulations of the spiral galaxies with an active potential (Clarke & Gittins 2006; Dobbs & Bonnell 2008). At CO(1-0) resolution (140 pc), we were able to find CO emitting complexes with masses greater than those of typical Giant Molecular Clouds (105-106 M?). To identify GMCs individually and make a more detailed study of their physical properties, we made D array observations of CO(2-1) toward the densest concentrations of gas, achieving a resolution similar to GMCs sizes found in other galaxies (Bolatto et al. 2008). We present first results about differences in properties of the on-arm clouds and inter-arm clouds. We found that, in general, on-arm clouds present broader line widths, are more massive and more active in star formation than inter-arm clouds. We investigated if the velocity dispersion observed in CO(1-0) emitting complexes reflects velocity differences between unresolved smaller clouds, or if it corresponds to actual internal turbulence of the gas observed.

Rebolledo, David; Wong, T.; Leroy, A.

2012-01-01

323

What produces the extended LINER-type emission in the NUGA galaxy NGC 5850?  

NASA Astrophysics Data System (ADS)

Context. The role of low ionization nuclear emission region (LINER) galaxies within the picture of active galactic nuclei (AGN) has been controversial. It is still not clear whether they host an AGN in a low accretion mode or whether they are not active at all but are instead dominated by alternative ionization mechanisms, namely shocks, winds/outflows, or photoionization by a post-asymptotic giant branch (p-AGB) stellar population. The detection of extended LINER-like emission was often taken as evidence of ionization by stellar components, but this has not been undisputed. Aims: Using optical spectroscopy, we examine the possible ionization mechanisms responsible for the extended LINER-like emission in the central ~4 kpc of NGC 5850. Methods: We performed integral field spectroscopic observations using VIMOS at the VLT, which provides spatially-resolved spectra for the gas emission and the stellar continuum. We subtract the underlying stellar continuum from the galaxy spectra and fit the emission lines. With these methods, we derive and analyze emission line and kinematic maps. Emission line ratio maps are examined by means of diagnostic diagrams. Results: The central few kpc of NGC 5850 are dominated by extended LINER-like emission. The emission-line ratios that are sensitive to the ionization parameter increase with radial distance to the nucleus. The LINER-like region is surrounded by emission that is classed as "composite" in terms of diagnostic diagrams. Two star-forming (SF) regions are present in the 21? × 19? field of view. One of them is located approximately in the ring, surrounding the kinematically decoupled core. The second one is close to the nucleus and is the origin of a region of decreased emission line ratios oriented radially outwards. We find the interstellar gas to have a complex kinematic morphology and to have areas of steep velocity gradients. Conclusions: The extended LINER-like emission in NGC 5850 is dominated by ionization from distributed ionization sources, probably by stars on the p-AGB. The extended "composite" emission is likely due to a mixture of a LINER-like ionization pattern and photoionization by low-level star formation. With the extended region of decreased emission line ratios, we possibly observe enhanced SF or a region that is shielded from the central LINER-like emission by the central H ii-region. The peculiar gas kinematics are probably caused by the lopsided (m = 1) distribution of the gas and make the inflow of gas toward the center appear possible. Based on observations obtained with VIMOS at ESO VLT under program ID 083.B-0906(A).

Bremer, M.; Scharwächter, J.; Eckart, A.; Valencia-S., M.; Zuther, J.; Combes, F.; Garcia-Burillo, S.; Fischer, S.

2013-10-01

324

Molecular distribution and kinematics in nearby galaxies. II. Sub-mm observations of NGC4945.  

NASA Astrophysics Data System (ADS)

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%.

Mauersberger, R.; Henkel, C.; Whiteoak, J. B.; Chin, Y.-N.; Tieftrunk, A. R.

1996-05-01

325

High-Resolution X-ray and UV Spectra of the Seyfert 1 galaxy NGC High-Resolution X-ray and UV Spectra of the Seyfert 1 galaxy NGC 4151. I. Physical Conditions in the X-ray Absorbers  

Microsoft Academic Search

We present a detailed analysis of the intrinsic X-ray absorption in the Seyfert 1 galaxy NGC 4151 using Chandra\\/High Energy Transmission Grating Spectrometer data obtained 2002 May as part of a program which included simultaneous ultraviolet (UV) spectra using the Hubble Space Telescope\\/Space Telescope Imaging Spectrograph and the Far Ultraviolet Spectrographic Explorer. Previous studies, most recently using ASCA spectra, revealed

S. B. Kraemer; D. M. Crenshaw; I. M. George; J. R. Gabel

2005-01-01

326

Azimuthal and Kinematic Segregation of Neutral and Molecular Gas in Arp 118: The Yin-Yang Galaxy NGC 1144  

NASA Astrophysics Data System (ADS)

We present new high-resolution H I observations of the disk of the collisional infrared luminous (LIR=2.2×1011Lsolar) galaxy NGC 1144, which reveal an apparent large-scale azimuthal and kinematic segregation of neutral hydrogen relative to the molecular gas distribution. Even among violently collisional galaxies, the CO/H I asymmetry in NGC 1144 is unusual, both in the inner regions and in the outer disk. We suggest that we are observing Arp 118 at a special moment, shortly after a high-speed collision between NGC 1144 and its elliptical companion NGC 1143. H I emission with an average molecular fraction fmol<0.5 is observed on one side (northwest) of the rotating disk of NGC 1144, while the other side (southeast) is dominated by dense molecular complexes in which fmol is almost unity. The interface region between the warm- and cool-cloud dominated regions lies on a deep spiral-like dust lane that we identify as a shock wave responsible for the relative shift in the dominance of H I and H2 gas. A strong shock being fed by diffuse H I clouds with unusually large (>400 km s-1) rotational velocities can explain (1) the CO/H I asymmetries, (2) a large velocity jump (185 km s-1) across the arm as measured by H I absorption against a radio bright continuum source that straddles the arm, and (3) the asymmetric distribution of star formation and off-nuclear molecular gas resulting from likely streaming motions associated with the strong shock. The new results provide for the first time a coherent picture of Arp 118's many peculiarities and underline the potentially complex changes in the gas phase that can accompany large gravitational perturbations of gas-rich galaxies.

Appleton, P. N.; Charmandaris, V.; Gao, Yu; Jarrett, Tom; Bransford, M. A.

2003-03-01

327

Dust and molecules in the Local Group galaxy NGC 6822. I. Dust, star formation and the origin of infrared emission.  

NASA Astrophysics Data System (ADS)

High-resolution (about 1') maps of the irregular galaxy NGC 6822 show that about half the far-infrared emission arises in discrete sources with sizes less than 400 pc, three of which are associated with the brightest HII regions. Two equally bright infrared sources have no such counterpart. Dust temperatures of both types of discrete sources as well as the extended emission are in a narrow range T_d_=29-32K. The dust-to-gas ratio is 1.4x10^-4^, uncertain by a factor of two. The far-infrared luminosity L_FIR_=2.5x10^7^Lsun_ of NGC 6822 is only 10% of the bolometric stellar luminosity. The ratio of the far-infrared to thermal radio continuum emission of the bright HII regions implies that the fraction of stellar photons absorbed by the dust is very similar to the fraction of Lyman continuum photons absorbed by the gas. A comparison of the nonthermal radio emission from NGC 6822 with its infrared emission suggests that previously found correlations between these quantities are not causal in nature. They appear to be critically dependent on the cosmic ray production rate and the degree of retention, which may vary, especially in dwarf galaxies. In NGC 6822, about half of the infrared emission orginates from dust heated by nonionizing stars. As it is thus not associated with recent star formation, it follows that far-infrared emission from galaxies by itself is not a good measure of recent star formation rates. In NGC 6822, recent star formation rates are dM/dt=0.04Msun_/yr and dM/(dt.dA)=0.04Msun_/yr/kpc^2^ respectively. The global star formation efficiency is 3(+7,-2)%.

Israel, F. P.; Bontekoe, T. R.; Kester, D. J. M.

1996-04-01

328

Two modes of gas flow in a single barred galaxy  

Microsoft Academic Search

We investigate stationary gas flows in a fixed, rotating barred potential.\\u000aThe gas is assumed to be isothermal with an effective sound speed c_s, and the\\u000aequations of motion are solved with smoothed particle hydrodynamics (SPH).\\u000aSince the thermal energy in cloud random motions is negligible compared to the\\u000aorbital kinetic energy, no dependence of the flow on c_s is

Peter Englmaier; Ortwin Gerhard

1996-01-01

329

Ultraviolet morphologies of nearby barred and unbarred spiral galaxies  

Microsoft Academic Search

Deep high-resolution imaging of galaxies at high-redshift has revealed a remarkable diversity of emission structures in the restframe ultraviolet. To better understand these remote and primeval realms, it is important to compare them with UV-emitting counterparts in the local universe. As part of two Spacelab\\/Astro missions, the Ultraviolet Imaging Telescope (UIT) has obtained wide-field (40-arcmin), well-resolved (3 arcsec) images of

William H. Waller; Michael N. Fanelli; Nicholas R. Collins; Robert H. Cornett; Joel Offenberg; Pamela M. Marcum; Theodore P. Stecher

1997-01-01

330

THE SUZAKU VIEW OF THE DISK-JET CONNECTION IN THE LOW-EXCITATION RADIO GALAXY NGC 6251  

SciTech Connect

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.

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

331

ROSAT detection of diffuse hot gas in the edge-on galaxy NGC 4631  

NASA Astrophysics Data System (ADS)

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, NH approximately 1.4 x 1020cm-2, this observation is sensitive to gas of temperature greater than or equal to a few times 105 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 106 K and a radiative cooling rate of approximately 8 x 1039 ergs s-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 105 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-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 Lchi(0.1 - 2 keV) approximately 5 x 1039 ergs s-1, which makes it a stellar mass black hole candidate.

Wang, Q. David; Walterbos, Rene A. M.; Steakley, Michael F.; Norman, Colin A.; Braun, Robert

332

ROSAT detection of diffuse hot gas in the edge-on galaxy NGC 4631  

NASA Astrophysics Data System (ADS)

We present our ROSAT observation 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, NHI approximately = 1.4 x 1020/sq cm, this observation is sensitive to gas of temperature greater than or approximately = a few x 105 K. We detected soft (approximately 0.25 keV) X-ray radiation out to more than 8 kpc above the midplane of the galaxy. The stongest 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. We also found diffuse X-ray emission from hot gas in the galaxy's disk. The spectrum of the radiation can be characterized by a thermal plasma with a temperature of 3 x 106 K and a radiative cooling rate of approximately 8 x 1039 ergs/sec. 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 105 K) halo gas component that could consume a much larger fraction of the supernova energy. We found strong evidence 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. 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. We have identified a strong X-ray source which coincides spatially with an H I supershell. However, the source is likely an extremely luminous X-ray binary with Lx(0.1-2 keV) approximately = 5 x 1039 ergs/sec, which makes it a stellar mass black hole candidate.

Wang, Q. Daniel; Walterbos, Rene A. M.; Steakley, Michael F.; Norman, Colin A.; Braun, Robert

1995-01-01

333

Quantifying the faint structure of galaxies: the late-type spiral NGC 2403  

NASA Astrophysics Data System (ADS)

Ground-based surveys have mapped the stellar outskirts of Local Group disc galaxies in unprecedented detail, but extending this work to other galaxies is necessary in order to overcome stochastic variations in evolutionary history and provide more stringent constraints on cosmological galaxy formation models. As part of our continuing programme of ultra-deep imagery of galaxies beyond the Local Group, we present a wide-field analysis of the isolated late-type spiral NGC 2403 using data obtained with Suprime-Cam on the Subaru telescope. The surveyed area reaches a maximum projected radius of 30 kpc or a deprojected radius of Rdp˜ 60 kpc. The colour-magnitude diagram reaches 1.5 mag below the tip of the metal-poor red giant branch (RGB) at a completeness rate >50 per cent for Rdp > rsim 12 kpc. Using the combination of diffuse light photometry and resolved star counts, we are able to trace the radial surface brightness (SB) profile over a much larger range of radii and SB than is possible with either technique alone. The exponential disc as traced by RGB stars dominates the SB profile out to ?8 disc scalelengths, or Rdp˜ 18 kpc, and reaches a V-band SB of ?V˜ 29 mag arcsec-2. Beyond this radius, we find evidence for an extended structural component with a significantly flatter SB profile than the inner disc and which we trace to Rdp˜ 40 kpc and ?V˜ 32 mag arcsec-2. This component can be fit with a power-law index of ?˜ 3, has an axial ratio consistent with that of the inner disc and has a V-band luminosity integrated over all radii of 1-7 per cent that of the whole galaxy. At Rdp˜ 20 - 30 kpc, we estimate a peak metallicity [M/H] =-1.0 ± 0.3 assuming an age of 10 Gyr and zero ?-element enhancement. Although the extant data are unable to discriminate between stellar halo or thick disc interpretations of this component, our results support the notion that faint, extended stellar structures are a common feature of all disc galaxies, even isolated, low-mass systems.

Barker, Michael K.; Ferguson, Annette M. N.; Irwin, M. J.; Arimoto, N.; Jablonka, P.

2012-01-01

334

Structure of the Galactic Bulge: Is the Milky Way a Double-barred Galaxy?  

NASA Astrophysics Data System (ADS)

Using the data of the IRSF/SIRIUS infrared survey along the Galactic plane (| l | <= 10.°5 at b = +1°), we find a distinct structure, which is probably a secondary bar, inside the primary bar of our Galaxy. The apparent magnitude peak of Bulge red clump stars changes continuously from KS ~ 13.5 (l = -10°) to KS ~ 12.3 (l = +10°), and this can be explained by the bar structure of the Galactic Bulge. However, the apparent magnitude changes by only ~ 0.1 mag over the central 8°, and this indicates that there is a distinct structure inside the primary bar. In the process of the distance derivation, we have used the infrared extinction law in the J, H, and KS bands toward the Galactic center newly determined from our survey.

Nishiyama, Shogo; Nagata, Tetsuya; IRSF/SIRIUS Team

2006-12-01

335

The Study of Barred Spiral Galaxies with Integral-Field Units  

NASA Astrophysics Data System (ADS)

Integral-Field Units have been used to describe the morphology in numerous continuum and line wavebands of a sample of barred spirals galaxies (some of which known as starbursts and LINERs) and to characterize their gas and stellar populations. The central region of eight galaxies was studied with OASIS and an iterative technique developed to separate superposed stellar populations. Young populations, responsible for nebular emission lines, are found in nuclear structures. Older stellar components are mostly uniformly distributed. The mass distribution of the different populations indicates a long sequence of burst events over the whole galaxy history. An activity of the type composite/transition region is often seen over the whole central region. SpIOMM was also used to map the emission lines over the entire disk of one of these galaxies. Among other results, it confirms the peculiar line ratio.

Robert, Carmelle; Cantin, Simon; Brière, Élaine; Rousseau-Nepton, Laurie; Drissen, Laurent

2011-12-01

336

NGC 404: A REJUVENATED LENTICULAR GALAXY ON A MERGER-INDUCED, BLUEWARD EXCURSION INTO THE GREEN VALLEY  

SciTech Connect

We have discovered recent star formation in the outermost portion ((1-4) x R {sub 25}) of the nearby lenticular (S0) galaxy NGC 404 using Galaxy Evolution Explorer UV imaging. FUV-bright sources are strongly concentrated within the galaxy's H I ring (formed by a merger event according to del RIo et al.), even though the average gas density is dynamically subcritical. Archival Hubble Space Telescope imaging reveals resolved upper main-sequence stars and conclusively demonstrates that the UV light originates from recent star formation activity. We present FUV, NUV radial surface brightness profiles, and integrated magnitudes for NGC 404. Within the ring, the average star formation rate (SFR) surface density ({Sigma}{sub SFR}) is {approx}2.2 x 10{sup -5} M {sub sun} yr{sup -1} kpc{sup -2}. Of the total FUV flux, 70% comes from the H I ring which is forming stars at a rate of 2.5 x 10{sup -3} M {sub sun} yr{sup -1}. The gas consumption timescale, assuming a constant SFR and no gas recycling, is several times the age of the universe. In the context of the UV-optical galaxy color-magnitude diagram, the presence of the star-forming H I ring places NGC 404 in the green valley separating the red and blue sequences. The rejuvenated lenticular galaxy has experienced a merger-induced, disk-building excursion away from the red sequence toward bluer colors, where it may evolve quiescently or (if appropriately triggered) experience a burst capable of placing it on the blue/star-forming sequence for up to {approx}1 Gyr. The green valley galaxy population is heterogeneous, with most systems transitioning from blue to red but others evolving in the opposite sense due to acquisition of fresh gas through various channels.

Thilker, David A.; Bianchi, Luciana [Center for Astrophysical Sciences, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218 (United States); Schiminovich, David [Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States); Gil de Paz, Armando [Departamento de AstrofIsica y CC. de la Atmosfera, Universidad Complutense de Madrid, Avda. de la Complutense, s/n, E-28040 Madrid (Spain); Seibert, Mark; Madore, Barry F. [Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Wyder, Ted; Barlow, Tom; Conrow, Tim; Forster, Karl; Friedman, Peter; Martin, Chris; Morrissey, Patrick; Small, Todd [California Institute of Technology, MC 405-47, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Rich, R. Michael [Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1547 (United States); Yi, Sukyoung [Department of Astronomy, Yonsei University, Seoul 120-749 (Korea, Republic of); Neff, Susan, E-mail: dthilker@pha.jhu.ed [Laboratory for Astronomy and Solar Physics, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2010-05-01

337

An Initial Mass Function Study of the Dwarf Starburst Galaxy NGC 4214  

NASA Astrophysics Data System (ADS)

The production rate of ionizing photons in young (<=8 Myr), unresolved stellar clusters in the nearby irregular galaxy NGC 4214 is probed using multi-wavelength Hubble Space Telescope WFC3 data. We normalize the ionizing photon rate by the cluster mass to investigate the upper end of the stellar initial mass function (IMF). We have found that within the uncertainties the upper end of the stellar IMF appears to be universal in this galaxy, and that deviations from a universal IMF can be attributed to stochastic sampling of stars in clusters with masses lap103 M ?. Furthermore, we have found that there does not seem to be a dependence of the maximum stellar mass on the cluster mass. We have also found that for massive clusters, feedback may cause an underrepresentation in H? luminosities, which needs to be taken into account when conducting this type of analysis. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-11360.

Andrews, J. E.; Calzetti, D.; Chandar, R.; Lee, J. C.; Elmegreen, B. G.; Kennicutt, R. C.; Whitmore, B.; Kissel, J. S.; da Silva, Robert L.; Krumholz, Mark R.; O'Connell, R. W.; Dopita, M. A.; Frogel, Jay A.; Kim, Hwihyun

2013-04-01

338

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

NASA Astrophysics Data System (ADS)

We have characterized the energy-dependent X-ray variability properties of the Seyfert 1 galaxy NGC 3783 using archival XMM-Newton and Rossi X-Ray Timing Explorer data. The high-frequency fluctuation power spectral density function (PSD) slope is consistent with flattening toward higher energies. Light-curve cross-correlation functions yield no significant lags, but peak coefficients generally decrease as energy separation of the bands increases on both short and long timescales. We have measured the coherence between various X-ray bands over the temporal frequency range of 6×10-8-1×10-4 Hz; this range includes the temporal frequency of the low-frequency PSD break tentatively detected by Markowitz et al. and includes the lowest temporal frequency over which coherence has been measured in any active galactic nucleus to date. Coherence is generally near unity at these temporal frequencies, although it decreases slightly as energy separation of the bands increases. Temporal frequency-dependent phase lags are detected on short timescales; 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.

Markowitz, A.

2005-12-01

339

Dark mammoth trunks in the merging galaxy NGC 1316 and a mechanism of cosmic double helices  

NASA Astrophysics Data System (ADS)

NGC 1316 is a giant, elliptical galaxy containing a complex network of dark, dust features. The morphology of these features has been examined in some detail using a Hubble Space Telescope, Advanced Camera for Surveys image. It is found that most of the features are constituted of long filaments. There also exist a great number of dark structures protruding inwards from the filaments. Many of these structures are strikingly similar to elephant trunks in H ii regions in the Milky Way Galaxy, although much larger. The structures, termed mammoth trunks, generally are filamentary and often have shapes resembling the letters V or Y. In some of the mammoth trunks the stem of the Y can be resolved into two or more filaments, many of which showing signs of being intertwined. A model of the mammoth trunks, related to a recent theory of elephant trunks, is proposed. Based on magnetized filaments, the model is capable of giving an account of the various shapes of the mammoth trunks observed, including the twined structures.

Carlqvist, Per

2010-06-01

340

Disentangling the stellar populations in the counter-rotating disc galaxy NGC 4550  

NASA Astrophysics Data System (ADS)

In order to try and understand its origins, we present high-quality long-slit spectral observations of the counter-rotating stellar discs in the strange S0 galaxy NGC 4550. We kinematically decompose the spectra into two counter-rotating stellar components (plus a gaseous component), in order to study both their kinematics and their populations. The derived kinematics largely confirm what was known previously about the stellar discs, but trace them to larger radii with smaller errors; the fitted gaseous component allows us to trace the hydrogen emission lines for the first time, which are found to follow the same rather strange kinematics previously seen in the [O iii] line. Analysis of the populations of the two separate stellar components shows that the secondary disc has a significantly younger mean age than the primary disc, consistent with later star formation from the associated gaseous material. In addition, the secondary disc is somewhat brighter, also consistent with such additional star formation. However, these measurements cannot be self-consistently modelled by a scenario in which extra stars have been added to initially identical counter-rotating stellar discs, which rules out the Evans & Collett's elegant `separatrix-crossing' model for the formation of such massive counter-rotating discs from a single galaxy, leaving some form of unusual gas accretion history as the most likely formation mechanism.

Johnston, Evelyn J.; Merrifield, Michael R.; Aragón-Salamanca, Alfonso; Cappellari, Michele

2013-01-01

341

The Multicolored Hot Interstellar Medium of ``the Antennae'' Galaxies (NGC 4038/4039)  

NASA Astrophysics Data System (ADS)

We report the results of the analysis of the extended soft emission discovered in the Chandra ACIS pointing at the merging system NGC 4038/4039 (``the Antennae''). We present a multicolor X-ray image that suggests both extensive absorption by the dust in this system, peaking in the contact region, as well as variations in the temperature of different emitting regions of the hot interstellar medium (ISM). Spectral fits to multicomponent thermal emission models confirm this picture and give a first evaluation of the parameters of the hot plasma. We compare the diffuse X-ray emission with radio continuum (6 cm), H I, CO, and H? images to take a first look at the multiphase ISM of ``the Antennae'' galaxies. We find that the hot (X-ray) and cold (CO) gas have comparable thermal pressures in the two nuclear regions. We also conclude that the displacement between the peak of the diffuse X-ray emission in the north of the galaxy system, toward the inner regions of the northern spiral arm (as defined by H?, radio continuum, and H I), could result from ram pressure of infalling H I clouds.

Fabbiano, G.; Krauss, M.; Zezas, A.; Rots, A.; Neff, S.

2003-11-01

342

The interstellar disk-halo connection in the spiral galaxy NGC 3079  

NASA Astrophysics Data System (ADS)

We discuss the morphology and excitation of ionized gas in the nearby Sc galaxy NGC 3079. The almost edge-on orientation is ideal for studying the vertical structure of the gaseous disk, and especially the diffuse ionized medium (DIM) found between the bright H II regions. We used the Hawaii Imaging Fabry-Perot Interferometer (HIFI) to map 150,000 H-alpha + (N II) lambda lambda 6548, 6583 emission-line profiles across the entire disk, with resolution 70 km/s at subarcsecond steps, down to a flux level of approximately 10-17 ergs/s/sq cm (EM approximately equal to 4 cm-6 pc). The DIM contributes approximately 30% of the total disk H-alpha emission within a radius of 10 kpc. The DIM has broader emission lines and larger (N II) H-alpha flux ratios than the adjacent H II regions. Within a radius of 5 kpc, we find that the X-shaped filaments reported in previous studies emerge from the inner (R approximately equal to 1.5 kpc) disk, and rise more than 4 kpc above the disk plane. The morphology, kinematics, and excitation of the filaments suggest that they form a biconic interface between the undisturbed disk gas, and gas entrained in the wide-angle outflow. The DIM beyond 5 kpc radius is more vertically extended than the thick ionized disk detected in our Galaxy and in a few nearby edge-on systems. After correcting for dust, the vertical profile of this DIM has an exponential scale height of about 1.1 kpc, similar to that of the H I disk. The (N II) lambda 6538/H-alpha flux ratio of the DIM increases monotonically with vertical height, reaching unity for absolute value of z greater than or approximately equal to 2.5 kpc. The flux required to keep the DIM ionized at R = 8 kpc is similar to that near the solar circle of our Galaxy. Highly dilute radiation from O stars in the galactic plane probably maintains the DIM. The total mass of the DIM is of order 108 - 109 solar mass, representing less than 1% of the total dynamical mass of NGC 3079. Mechanical energy from intense star formation in the disk probably lifts the DIM above the disk. The several bubbles and filaments within 1 kpc of the disk plane is direct evidence for gas flow between the disk and halo.

Veilleux, Sylvain; Cecil, Gerald; Bland-Hawthorn, J.

1995-05-01

343

Dynamics of stars around spiral arms in an N-body/SPH simulated barred spiral galaxy  

NASA Astrophysics Data System (ADS)

We run N-body smoothed particle hydrodynamics (SPH) simulations of a Milky Way-sized galaxy. The code takes into account hydrodynamics, self-gravity, star formation, supernova and stellar wind feedback, radiative cooling and metal enrichment. The simulated galaxy is a barred spiral galaxy consisting of a stellar and gas disc, enveloped in a static dark matter halo. Similar to what is found in our pure N-body simulation of a non-barred galaxy in Grand et al., we find that the spiral arms are transient features whose pattern speeds decrease with radius, in such a way that the pattern speed is similar to the rotation of star particles. Compared to the non-barred case, we find that the spiral arm pattern speed is slightly faster than the rotation speed of star particles: the bar appears to boost the pattern speed ahead of the rotational velocity. We trace particle motion around the spiral arms at different radii, and demonstrate that there are star particles that are drawn towards and join the arm from behind (in front of) the arm and migrate towards the outer (inner) regions of the disc until the arm disappears as a result of their transient nature. We see this migration over the entire radial range analysed, which is a consequence of the spiral arm rotating at similar speeds to star particles at all radii, which is inconsistent with the prediction of classical density wave theory. The bar does not prevent this systematic radial migration, which is shown to largely preserve circular orbits. We also demonstrate that there is no significant offset of different star-forming tracers across the spiral arm, which is also inconsistent with the prediction of classical density wave theory.

Grand, Robert J. J.; Kawata, Daisuke; Cropper, Mark

2012-10-01

344

The Star Formation History of the Local Group Dwarf Elliptical Galaxy NGC 185. II. Gradients in the Stellar Population  

NASA Astrophysics Data System (ADS)

The star formation history of the dwarf elliptical galaxy NGC 185, together with its spatial variations, has been investigated for old, intermediate-age, and young stars, using new ground-based H? and BVI photometry and synthetic color-magnitude diagrams (CMDs). We find that the bulk of the stars were formed in NGC 185 at an early epoch of its evolution. After that, star formation proceeded at a low rate until the recent past, the age of the most recent traces of star formation activity detected in the galaxy being some 100 Myr. As for the spatial variations, the star formation rates, ?(t), for old and intermediate-age stars show a gradient, in the sense of exhibiting lower values for higher galactocentric radii. Moreover, recent star formation is detected in the central 150x90 pc2 only, where the youngest, 100 Myr old, population is found. No traces of stars born more recently than 1 Gyr ago are found outside this central region. Since the larger concentration of stars of any age lies in the central part of a galaxy, it could be the case that the youngest stars originate from material ejected from dying stars and that this process would only be efficient enough in the center of the galaxy. The luminous ``blue stars'' discovered by W. Baade in 1951 in the center of NGC 185 are discussed using new CCD images in B and Baade's original photographic plates. Considering their fuzzy, unresolved appearance and that a conspicuous main sequence is lacking in the CMD at our limiting magnitude, we reach the conclusion that most of Baade's blue objects are in fact star clusters. These clusters, as well as the other stellar populations, are young (a few times 100 Myr) but not as young as they would be if they were individual stars (a few times 10 Myr). A supernova remnant (SNR) close to the center of NGC 185 has been analyzed from H? images. The fact that a conspicuous main sequence is lacking in our CMD implies that the supernova (SN) had originated from a white dwarf progenitor. A consistent picture arises in which the gas observed in the central region of NGC 185 would have an internal origin. The rate at which evolved stars return gas to the interstellar medium is enough to seed the recent star formation observed in the center of the galaxy, and the SN rate is probably low enough to allow the galaxy to retain the gas not used in the new stellar generations. Further support is found in the similar kinematic properties of gas and stars.

Martínez-Delgado, D.; Aparicio, A.; Gallart, C.

1999-11-01

345

Fermi LAT detection of renewed gamma-ray flaring activity from the radio galaxy NGC 1275 (Perseus A)  

NASA Astrophysics Data System (ADS)

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed GeV gamma-ray flaring activity from a source positionally consistent with NGC 1275 (also known as 2FGL J0319.8+4130, Nolan et al. 2012, ApJS, 199, 31, as Perseus A and 3C 84) a radio galaxy located at the center of the Perseus galaxy cluster (see also Abdo et al. 2009, ApJ, 699, 31).

Ciprini, Stefano

2013-01-01

346

Starbursts in barred spiral galaxies. VI. HI observations and the K-band Tully-Fisher relation  

NASA Astrophysics Data System (ADS)

This paper reports a study of the effect of a bar on the neutral hydrogen (HI) content of starburst and Seyfert galaxies. We also make comparisons with a sample of ``normal'' galaxies and investigate how well starburst and Seyfert galaxies follow the fundamental scaling Tully-Fisher (TF) relation defined for normal galaxies. 111 Markarian (Mrk) IRAS galaxies were observed with the Nançay radiotelescope, and HI data were obtained for 80 galaxies, of which 64 are new detections. We determined the (20 and 50%) linewidths, the maximum velocity of rotation and total HI flux for each galaxy. These measurements are complemented by data from the literature to form a sample of Mrk IRAS (74% starburst, 23% Seyfert and 3% unknown) galaxies containing 105 unbarred and 113 barred ones. Barred galaxies have lower total and bias-corrected HI masses than unbarred galaxies, and this is true for both Mrk IRAS and normal galaxies. This robust result suggests that bars funnel the HI gas toward the center of the galaxy where it becomes molecular before forming new stars. The Mrk IRAS galaxies have higher bias-corrected HI masses than normal galaxies. They also show significant departures from the TF relation, both in the B and K bands. The most deviant points from the TF relation tend to have a strong far-infrared luminosity and a low oxygen abundance. These results suggest that a fraction of our Mrk IRAS galaxies are still in the process of formation, and that their neutral HI gas, partly of external origin, has not yet reached a stationary state. Based on observations obtained at the large radiotelescope of Observatoire de Nançay, operated by Observatoire de Paris. Tables 5 and 6 are only (and Table 4 also) available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/515

Davoust, E.; Contini, T.

2004-03-01

347

THE INTERSTELLAR MEDIUM AND STAR FORMATION IN EDGE-ON GALAXIES. I. NGC 891  

SciTech Connect

We analyze images of BIMA {sup 12}CO (J = 1 {yields} 0) , Very Large Array H I, and Spitzer 3.6 and 24 {mu}m emission toward the edge-on galaxy NGC 891 and derive the radial and vertical distributions of gas and the radial distributions of stellar mass and recent star formation. We describe our method of deriving radial profiles for edge-on galaxies, assuming circular motion, and verify basic relationships between star formation rate (SFR) and gas and stellar content, and between the molecular-to-atomic ratio and hydrostatic midplane pressure that have been found in other galaxy samples. The Schmidt law index we find for the total gas (H{sub 2} + H I) is 0.85 {+-} 0.55, but the Schmidt law provides a poor description of the SFR in comparison to a model that includes the influence of the stellar disk. Using our measurements of the thickness of th