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1

Kinematic Analysis of the Double-Barred Galaxy NGC 357  

NASA Astrophysics Data System (ADS)

We present a kinematic analysis of the double-barred early-type galaxy NGC 357. The radial velocity and velocity dispersion profiles along both the nuclear bar axis and the semi-major axis clearly reveal the presence of the two bars. The results indicate that the bulge is pressure supported whereas the |vr|/? ratio shows a plateau along the nuclear bar.

de Lorenzo-Cáceres, A.; Vazdekis, A.; Aguerri, J. A. L.

2008-06-01

2

Mass distribution and kinematics of the barred galaxy NGC2336  

Microsoft Academic Search

For the intermediate-type barred galaxy NGC2336 stationary models are\\u000aconstructed which reproduce in a consistent manner the observed distribution of\\u000athe luminous matter and the observed gas kinematics in those regions affected\\u000aby the bar. We present 2D fits to the observed NIR-band luminosity distribution\\u000athat consist of three components: a bulge, a bar, and a disk. The brightness\\u000adistribution

K. Wilke; M. Matthias

1999-01-01

3

Mass distribution and kinematics of the barred galaxy NGC 2336  

Microsoft Academic Search

For the intermediate-type barred galaxy NGC 2336 stationary models are constructed which reproduce in a consistent manner the observed distribution of the luminous matter and the observed gas kinematics in those regions affected by the bar. We present 2D fits to the observed NIR-band luminosity distribution that consist of three components: a bulge, a bar, and a disk. The brightness

K. Wilke; C. Möllenhoff; M. Matthias

1999-01-01

4

Hydrodynamical Simulations of the Barred Galaxy NGC 4314: Gas Orbits in the Bar Region  

NASA Astrophysics Data System (ADS)

We report the results of a numerical simulation of the barred galaxy NGC 4314. We start with a gaseous isothermal, non-self gravitating disk, initially in rotational equilibrium, which is perturbed by the gravitational potential of the bar estimated in Quillen, Frogel & González (1994) using near-infrared observations. We then calculate the gas orbits in the region of the bar and compare them with stellar orbits obtained by Patsis (2006).

Ramos-Martínez, M.; Gómez, G. C.

2014-03-01

5

High Resolution HI VLA Observations of the Barred Spiral Galaxies NGC 1398 and NGC 1784  

Microsoft Academic Search

Observations of the atomic hydrogen of the barred spiral galaxies NGC 1398 and NGC 1784 have been made at the C\\/D and B\\/C array configurations of the Very Large Array. After calibration, the datasets from the two configurations were combined to give a spatial resolution of 20-25\\\\char'175. The velocity resolution is 21 km s(-1) . Moment maps of the HI

E. M. Moore; S. T. Gottesman

1993-01-01

6

High Resolution HI VLA Observations of the Barred Spiral Galaxies NGC 1398 and NGC 1784  

NASA Astrophysics Data System (ADS)

Observations of the atomic hydrogen of the barred spiral galaxies NGC 1398 and NGC 1784 have been made at the C/D and B/C array configurations of the Very Large Array. After calibration, the datasets from the two configurations were combined to give a spatial resolution of 20-25\\char'175. The velocity resolution is 21 km s(-1) . Moment maps of the HI surface density and radial velocity will be presented along with rotation curves and HI radial density profiles. The radio data is compared with available surface photometry. NGC 1398 is a SBab(r)I galaxy. It is a large (6.6\\char'23), strikingly symmetric galaxy with a bright optical bar and an inner ring. In addition, thin, well defined, nearly circular spiral arms start tangent to the ring and extend out close to a full revolution, accented by bright, discrete regions. Radio observations reveal a large central depletion in the HI gas, elongated perpendicular to the optical bar. The inner ring structure found in the optical photometry is absent at this level of resolution in the radio. By convolving down the data, an upper limit on the central low density region was set at 6.4 times 10(19) cm(2) . The HI integrated flux is 51 Jy km s(-1) , corresponding to a total atomic hydrogen mass of 3.15 times 10(9) M_sun. The velocity field of NGC 1398 indicates that the motion of the galaxy appears to be regular with little noncircular motion. NGC 1784 is a SBc(rs)I-II system with a bright, narrow bar and an inner ring. Further out there are several faint, knotty arms. The arms are not clean with low level spurs and feathers seem throughout the outer disk. Radio observations show that the HI gas peaks in a narrow, high density annulus. More interesting is the evidence of a severe warp in the gas disk and noncircular motion which appears in several velocity channels. The integrated flux is 60.1 Jy km s(-1) , corresponding to a mass of 1.17 times 10(10) M_sun. This work was supported in part by NSF grants AST-9022827 and AST-9116525.

Moore, E. M.; Gottesman, S. T.

1993-05-01

7

Hydrodynamical simulations of the barred spiral galaxy NGC 1365. Dynamical interpretation of observations  

Microsoft Academic Search

We perform two-dimensional, time dependent, hydrodynamical simulations of the gas flow in a potential representing the barred spiral galaxy NGC 1365 using the FS2 code originally written by G.D. van Albada. Non-circular motions present in NGC 1365 prevent us from using an observed angle-averaged rotation curve as representative of the axisymmetric forces in the bar region. Comparing observed kinematics and

P. A. B. Lindblad; P. O. Lindblad; E. Athanassoula

1996-01-01

8

Hydrodynamical simulations of the barred spiral galaxy NGC 1300. Dynamical interpretation of observations  

Microsoft Academic Search

We perform two-dimensional time dependent hydrodynamical simulations of the barred spiral galaxy NGC 1300. The input potential is divided into an axisymmetric part mainly derived from the observed rotation curve, and a perturbing part obtained from near infrared surface photometry of the bar and spiral structure. Self-gravitation of the gas is not taken into account in our modeling. A pure

P. A. B. Lindblad; H. Kristen

1996-01-01

9

The Double-Barred Galaxy NGC 357: Kinematics and Stellar Populations  

NASA Astrophysics Data System (ADS)

We have carried out a complete analysis of the kinematics and the stellar populations of the double-barred S0 galaxy NGC 357. We have measured suitable absorption line strength indices on very high quality spectra. With the aid of stellar population models we have obtained the relative ages and metallicities for the different components to constrain the star formation history of this galaxy and test whether the nuclear bar is transporting gas to the central regions of the galaxy efficiently enough to trigger star formation. Our first results indicate that the bulk of the stellar populations of NGC 357 was completely formed in less than 1 Gyr. The old ages obtained for both the bulge and the nuclear bar indicate that the latter is not playing an important role in fueling the star formation in the center.

de Lorenzo-Cáceres, A.; Vazdekis, A.; Aguerri, J. A. L.

2007-12-01

10

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

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

11

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

12

STAR FORMATION PROPERTIES IN BARRED GALAXIES (SFB). I. ULTRAVIOLET TO INFRARED IMAGING AND SPECTROSCOPIC STUDIES OF NGC 7479  

SciTech Connect

Large-scale bars and minor mergers are important drivers for the secular evolution of galaxies. Based on ground-based optical images and spectra as well as ultraviolet data from the Galaxy Evolution Explorer and infrared data from the Spitzer Space Telescope, we present a multi-wavelength study of star formation properties in the barred galaxy NGC 7479, which also has obvious features of a minor merger. Using various tracers of star formation, we find that under the effects of both a stellar bar and a minor merger, star formation activity mainly takes place along the galactic bar and arms, while the star formation rate changes from the bar to the disk. With the help of spectral synthesis, we find that strong star formation took place in the bar region about 100 Myr ago, and the stellar bar might have been {approx}10 Gyr old. By comparing our results with the secular evolutionary scenario from Jogee et al., we suggest that NGC 7479 is possibly in a transitional stage of secular evolution at present, and it may eventually become an earlier type galaxy or a luminous infrared galaxy. We also note that the probable minor merger event happened recently in NGC 7479, and we find two candidates for minor merger remnants.

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

2011-08-15

13

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

NASA Astrophysics Data System (ADS)

We report a dynamical determination of the separate contributions of disk and dark halo masses to the rotation curve of a spiral galaxy. We use fluid-dynamical models of gas flow in the barred galaxy NGC 4123 to constrain the dynamical properties of the galaxy: disk M/L, bar pattern speed, and the central density and scale radius of the dark halo. We derive a realistic barred potential directly from the light distribution. For each model we assume a value of the stellar M/L and a bar pattern speed ?p and add a dark halo to fit the rotation curve. We then compute the gas flow velocities with a two-dimensional gasdynamical code and compare the model flow patterns to a two-dimensional velocity field derived from Fabry-Perot observations. The strong shocks and noncircular motions in the observed gas flow require a high stellar M/L and a fast-rotating bar. Models with I-band disk M/L of 2.0-2.5 h75, or 80%-100% of the maximum disk value, are highly favored. The corotation radius of the bar must be <=1.5 times the bar semimajor axis. These results contradict some recent claimed ``universal'' galaxy disk/halo relations, since NGC 4123 is of modest size (rotation curve maximum 145 km s-1 and Vflat=130 km s-1) yet quite disk-dominated. The dark halo of NGC 4123 is less concentrated than favored by current models of dark halos based on cosmological simulations. Since some 30% of bright disk galaxies are strongly barred and have dust lanes indicating shock morphology similar to that of NGC 4123, it is likely that they also have high stellar M/L and low-density halos. We suggest that luminous matter dominates inside the optical radius R25 of high surface brightness disk galaxies.

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

2001-01-01

14

A photometric and kinematic study of the barred spiral galaxy NGC 253. II - The velocity field  

Microsoft Academic Search

The velocity field of the SAB(s)c spiral galaxy NGC 253 is derived from H-alpha Fabry-Perot interferometry covering most of the main disk of H II emission. Several basic galaxy parameters are also derived and are in good agreement with previous determinations for a systemic velocity of 236 km\\/s, an inclination of 78.5 deg, and a position angle of line of

W. D. Pence

1981-01-01

15

A survey of the Wolf-Rayet population of the barred, spiral galaxy NGC 1313  

Microsoft Academic Search

We present a VLT\\/FORS1 survey of Wolf-Rayet (WR) stars in the spiral galaxy NGC 1313. In total, 94 WR candidate sources have been identified from narrow-band imaging. Of these, 82 have been spectroscopically observed, for which WR emission features are confirmed in 70 cases, one of which also exhibits strong nebular He II lambda4686 emission. We also detect strong nebular

L. J. Hadfield; P. A. Crowther

2007-01-01

16

The structure of the barred galaxy NGC253: target of the VISTA and VST Science Verification extragalactic mini-survey.  

NASA Astrophysics Data System (ADS)

The Sculptor Galaxy NGC253 is a nearby barred Sc galaxy seen nearly edge-on and it has been the target of the Science Verification (SV) for the new ESO survey telescopes VST and VISTA: SV have been defined by teams of astronomers from ESO and the community, including the Italian National Institute for Astrophysics. On the behalf of the VISTA and VST SV Team, I will present in this paper the first results on the NGC253 structure by the new NIR VISTA and optical VST images. These data have emphasized the huge potentiality of the VISTA and VST telescopes to study the structure of galaxies with a detail and accuracy comparable to higher class telescopes, i.e. VLT and HST, with the advantage of the large Field of View (FoV): i) the high angular resolution let to detect and study the sub-structures towards the nuclear regions; ii) the large FoV let to ''correlate'' the inner features to the structure of the outer galaxy disk and to map the surface brightness and colors out to the very faint outskirts.

Iodice, E.; VISTA Team; VST SV Team; Pompei, E.; Mieske, S.; Szeifert, T.; Ivanov, V.; Arnaboldi M.; Battaglia, G.; Bilbao, L.; Freudling, W.; Hatziminaoglou, E.; Hilker, M.; Hummel, W.; Melnick, J.; Misgeld, I.; Moller, P.; Neeser, M.; Nadine, N.; Nilsson, K.; Rejkuba, M.; Retzlaff, J.; Romaniello, M.; Slijkhuis, R.; Venemans, B.; Ziegler, B.; Harald, K.; Iodice E.; Greggio L.; Emerson, J.; Sutherland, W.; Irwin, M.; J., Lewis; Hodgkin, S.; Gonzalez-Solares, E.; Capaccioli, M.; Grado, A.; Limatola, L.

17

A survey of the Wolf-Rayet population of the barred, spiral galaxy NGC 1313  

NASA Astrophysics Data System (ADS)

We present a VLT/FORS1 survey of Wolf-Rayet (WR) stars in the spiral galaxy NGC 1313. In total, 94 WR candidate sources have been identified from narrow-band imaging. Of these, 82 have been spectroscopically observed, for which WR emission features are confirmed in 70 cases, one of which also exhibits strong nebular He II ?4686 emission. We also detect strong nebular He II ?4686 emission within two other regions of NGC 1313, one of which is a possible supernova remnant. Nebular properties confirm that NGC 1313 has a metal content log(O/H) + 12 = 8.23 +/- 0.06, in good agreement with previous studies. From continuum-subtracted H? images we infer a global star formation rate of 0.6 Msolar yr-1. Using template LMC WR stars, spectroscopy reveals that NGC 1313 hosts a minimum of 84 WR stars. Our census comprises 51 WN stars, including a rare WN/C transition star plus 32 WC stars. In addition, we identify one WO star which represents the first such case identified beyond the Local Group. The bright giant H II region PES 1, comparable in H? luminosity to NGC 595 in M 33, is found to host a minimum of 17 WR stars. The remaining photometric candidates generally display photometric properties consistent with WN stars, such that we expect a global WR population of ~115 stars with N(WR)/N(O) ~ 0.01 and N(WC)/N(WN) ~ 0.4. Based on observations made with ESO telescopes at the Paranal Observatory under programme ID 076.B-0071 and with archival NASA/ESA Hubble Space Telescope, obtained from the ESO/ST-ECF Science Archive Facility. E-mail: l.hadfield@shef.ac.uk

Hadfield, L. J.; Crowther, P. A.

2007-10-01

18

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

19

A survey of the Wolf-Rayet population of the barred, spiral galaxy NGC 1313  

Microsoft Academic Search

We present a VLT\\/FORS1 survey of Wolf-Rayet (WR) stars in the spiral galaxy\\u000aNGC 1313. In total, 94 WR candidate sources have been identified from\\u000anarrow-band imaging. Of these, 82 have been spectroscopically observed, for\\u000awhich WR emission features are confirmed in 70 cases, one of which also\\u000aexhibits strong nebular HeII 4686 emission. We also detect strong nebular HeII

L. J. Hadfield; P. A. Crowther

2007-01-01

20

Galaxy NGC 300  

NASA Technical Reports Server (NTRS)

This image of the nearby spiral galaxy NGC 300 was taken by Galaxy Evolution Explorer in a single orbit exposure of 27 minutes on October 10, 2003. NGC 300 lies 7 million light years from our Milky Way galaxy and is one of a group of galaxies in the constellation Sculptor. NGC 300 is often used as a prototype of a spiral galaxy because in optical images it displays flowing spiral arms and a bright central region of older (and thus redder) stars. The Galaxy Evolution Explorer image taken in ultraviolet light shows us that NGC 300 is an efficient star-forming galaxy. The bright blue regions in the Galaxy Evolution Explorer image reveal new stars forming all the way into the nucleus of NGC 300.

2003-01-01

21

Galaxy NGC 55  

NASA Technical Reports Server (NTRS)

This image of the nearby edge-on spiral galaxy NGC 55 was taken by Galaxy Evolution Explorer on September 14, 2003, during 2 orbits. This galaxy lies 5.4 million light years from our Milky Way galaxy and is a member of the 'local group' of galaxies that also includes the Andromeda galaxy (M31), the Magellanic clouds, and 40 other galaxies. The spiral disk of NGC 55 is inclined to our line of sight by approximately 80 degrees and so this galaxy looks cigar-shaped. This picture is a combination of Galaxy Evolution Explorer images taken with the far ultraviolet (colored blue) and near ultraviolet detectors, (colored red). The bright blue regions in this image are areas of active star formation detected in the ultraviolet by Galaxy Evolution Explorer. The red stars in this image are foreground stars in our own Milky Way galaxy.

2003-01-01

22

THE CENTRAL REGION OF THE BARRED SPIRAL GALAXY NGC 1097 PROBED BY AKARI NEAR-INFRARED SPECTROSCOPY  

SciTech Connect

With the Infrared Camera on board AKARI, we carried out near-infrared (2.5-5.0 {mu}m) spectroscopy of the central kiloparsec region of the barred spiral galaxy, NGC 1097, categorized as Seyfert 1 with a circumnuclear starburst ring. Our observations mapped the area of {approx}50'' Multiplication-Sign 10'' with the resolution of {approx}5'', covering about a half of the ring and the galactic center. As a result, we spatially resolve the starburst ring in the polycyclic aromatic hydrocarbon 3.3 {mu}m, the aliphatic hydrocarbon 3.4-3.6 {mu}m features, and the hydrogen Br{alpha} 4.05 {mu}m emission. They exhibit spatial distributions significantly different from each other, indicating that the environments vary considerably around the ring. In particular, the aliphatic features are enhanced near the bar connecting the ring with the nucleus, where the structure of hydrocarbon grains seems to be relatively disordered. Near the center, the continuum emission and the CO/SiO absorption features are strong, which indicates that the environments inside the ring are dominated by old stellar populations. The near-infrared spectra do not show any evidence for the presence of nuclear activity.

Kondo, Toru; Kaneda, Hidehiro; Oyabu, Shinki; Ishihara, Daisuke; Mori, Tatsuya; Yamagishi, Mitsuyoshi [Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602 (Japan); Onaka, Takashi; Sakon, Itsuki [Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan); Suzuki, Toyoaki, E-mail: kondo@u.phys.nagoya-u.ac.jp [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa 252-5210 (Japan)

2012-05-20

23

The velocity eld of the barred spiral galaxy NGC 1300 revisited?  

Microsoft Academic Search

The re-reduction, described in J¨ ors¨ ater & van Moorsel (1995), of NGC 1300 VLA Hi observations, origi- nally obtained by M. England, motivates a new analysis of the velocity eld and rotation curve. Fitting tilted ring models to the Hi velocity data, we nd the new values for the orienta- tion parameters of NGC 1300 to be PAlon =

P. A. B. Lindblad; H. Kristen

24

The velocity field of the barred spiral galaxy NGC 1300 revisited  

Microsoft Academic Search

The re-reduction, described in Joersaeter & van Moorsel (1995AJ....110.2037J), of NGC 1300 VLA HI observations, originally obtained by M. England, motivates a new analysis of the velocity field and rotation curve. Fitting tilted ring models to the HI velocity data, we find the new values for the orientation parameters of NGC 1300 to be PA_lon_=267+\\/-2deg and i=35+\\/-5deg. Subsequently, the HI

P. A. B. Lindblad; H. Kristen; S. Joersaeter; J. Hoegbom

1997-01-01

25

Galaxy NGC 1512  

NASA Technical Reports Server (NTRS)

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

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

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

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

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

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

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

1999-01-01

26

(13) CO(1-0) and (12) CO(2-1) in the center of the barred galaxy NGC 1530  

NASA Astrophysics Data System (ADS)

We present (13) CO(1-0) and (12) CO(2-1) aperture synthesis maps of the barred spiral galaxy {NGC 1530}. The angular resolutions are respectively 3''.1 and 1''.6. Both transitions show features similar to the (12) CO(1-0) map, with a nuclear feature (a ring or unresolved spiral arms) surrounded by two curved arcs. The average line ratios are (12) CO(1-0)/(13) CO(1-0)=9.3 and (12) CO(2-1)/(12) CO(1-0)=0.7. The (12) CO/(13) CO ratio is lower in the circumnuclear ring (6-8) than in the arcs (11-15). We fit the observed line ratios by escape probability models, and deduce that the gas density is probably higher in the nuclear feature (>= 5E2 cm(-3) ) than in the arcs ( =~ 2E2 cm(-3) ), confirming earlier HCN results. The kinetic temperatures are in the range 20-90 K, but are weakly constrained by the model. The average filling factor of the (12) CO(1-0) emitting gas is low, =~ 0.15. The cm-radio continuum emission also peaks in the nuclear feature, indicating a higher rate of star formation than in the arcs. We derive values for the CO luminosity to molecular gas mass conversion factor between 0.3 and 2.3 mo (K km s(-1) pc(2) )(-1), significantly lower than the standard Galactic value.

Reynaud, D.; Downes, D.

1999-07-01

27

KINEMATIC AND PHOTOMETRIC EVIDENCE FOR A BAR IN NGC 2683  

SciTech Connect

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

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

2009-10-15

28

Gas Dynamics in Barred Spirals, II: NGC 7496 and 289.  

National Technical Information Service (NTIS)

The gas velocity fields in the barred spiral galaxies NGC 7496 and 289 have been measured by means of long-slit spectra obtained with the Anglo-Australian Telescope. Pronounced deviations from circular motion of the type predicted by recent theoretical mo...

W. D. Pence C. P. Blackman

1984-01-01

29

Starburst Galaxy NGC 3310  

NASA Technical Reports Server (NTRS)

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

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

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

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

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

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

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

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

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

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

1999-01-01

30

Galaxy NGC 1850  

NASA Technical Reports Server (NTRS)

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

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

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

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

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

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

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

1999-01-01

31

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

32

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

33

The ringed X-galaxy NGC 7020  

NASA Technical Reports Server (NTRS)

The southern SO (sup +) galaxy NGC 7020 presents an unusual morphology: it includes a very regular outer ring which is completely detached and which envelops an inner ring/lens zone with a hexagon surrounding an X shape. The outer ring has a high contrast compared to those usually observed in barred galaxies, yet NGC 7020 is not obviously barred. The morphology of this galaxy poses an interesting puzzle in that the hexagonal/X zone is not a typical type of feature to find in the interior of such a regular ring. Instead, the zone bears a striking resemblance to the edge-on galaxy IC 4767, recently studied by Whitmore and Bell (1988 = WB88) and dubbed by them as the X-galaxy because its inner regions appear to be crossed by two distinct enhancements lined at plus or minus 22 deg with respect to the major axis. The observation of a similar phenomenon in NGC 7020 is interesting because of the suggestion by WB88 that X structures could be related to accretion of matter associated with a merger or tidal encounter between an SO and a small satellite galaxy. If this interpretation is correct for NGC 7020, then it has important implications for the nature of the outer ring. An alternative interpretation is that the inner hexagonal/X zone is a region where resonant periodic orbits in a weak bi-symmetric potential perturbation are influencing the morphology more strongly than might be expected. A brief summary of a more extensive paper (Buta 1990c = B90c) and a few other details concerning this interesting galaxy are given.

Buta, Ronald

1990-01-01

34

Galaxy NGC 3079  

NASA Technical Reports Server (NTRS)

A lumpy bubble of hot gas rises from a cauldron of glowing matter in a distant galaxy, as seen by NASA's Hubble Space Telescope.

The new images, taken by Hubble's Wide Field and Planetary Camera 2, are online at http://oposite.stsci.edu/pubinfo/pr/2001/28 and http://www.jpl.nasa.gov/images/wfpc. The camera was designed and built by NASA's Jet Propulsion Laboratory, Pasadena, Calif.

Galaxy NGC 3079, located 50 million light-years from Earth in the constellation Ursa Major, has a huge bubble in the center of its disc, as seen in the image on the left. The smaller photo at right shows a close-up of the bubble. The two white dots are stars.

Astronomers suspect the bubble is being blown by 'winds,' or high-speed streams of particles, released during a burst of star formation. The bubble's lumpy surface has four columns of gaseous filaments towering above the galaxy's disc. The filaments whirl around in a vortex and are expelled into space. Eventually, this gas will rain down on the disc and may collide with gas clouds, compress them and form a new generation of stars.

Theoretical models indicate the bubble formed when winds from hot stars mixed with small bubbles of hot gas from supernova explosions. Radio telescope observations indicate those processes are still active. Eventually, the hot stars will die, and the bubble's energy source will fade away.

The images, taken in 1998, show glowing gas as red and starlight as blue/green. Results appear in the July 1, 2001 issue of the Astrophysical Journal. More information about the Hubble Space Telescope is at http://www.stsci.edu. More information about the Wide Field and Planetary Camera 2 is at http://wfpc2.jpl.nasa.gov.

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

1999-01-01

35

Modeling the Gas Flow in the Bar of NGC 1365  

Microsoft Academic Search

We present new observations of the strongly-barred galaxy NGC 1365, including\\u000anew photometric images and Fabry-Perot spectroscopy, as well as a detailed\\u000are-analysis of the neutral hydrogen observations from the VLA archive. We find\\u000athe galaxy to be at once remarkably bi-symmetric in its I-band light\\u000adistribution and strongly asymmetric in the distribution of dust and in the\\u000akinematics of

R. Zanmar Sanchez; J. A. Sellwood; B. J. Weiner; T. B. Williams

2007-01-01

36

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

NASA Astrophysics Data System (ADS)

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

2003-12-01

37

Structure and kinematics of candidatedouble-barred galaxies  

NASA Astrophysics Data System (ADS)

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

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

2004-07-01

38

The O/H Distribution in the Low-Mass Galaxies NGC 2366 and NGC 4395  

NASA Astrophysics Data System (ADS)

Results of a spectrophotometric survey in the magellanic barred galaxy NGC 2366 and in the small weakly barred spiral galaxy NGC 4395, employing imaging spectrophotometry with narrow-band interference filters in the lines of H?, H?, [O III] ?5007 and [N II] ?6584, are presented. The use of [O III]/H? as an abundance indicator is assessed; it is shown that for the probable range of the physical properties of the H II regions in NGC 2366 and NGC 4395, [O III]/H? may not give reliable estimates of O/H abundances in the interstellar gas in these two low-mass galaxies. Instead we use [NII]/[O III], which is more dependable at relatively low abundances. The derived mean levels of O/H (+/-1 ? dispersion) in NGC 2366 and NGC 4395 are 12 + log O/H = 8.19 +/- 0.14 and 8.33 +/- 0.25, respectively; the global gradients of both galaxies are flat. Mechanisms which could explain the absence of abundance gradients in low-mass and irregular galaxies are explored.

Roy, Jean-Rene; Belley, Julien; Dutil, Yvan; Martin, Pierre

1996-03-01

39

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.

40

Modeling the Gas Flow in the Bar of NGC 1365  

NASA Astrophysics Data System (ADS)

We present new observations of the strongly barred galaxy NGC 1365, including new photometric images and Fabry-Perot spectroscopy, as well as a detailed reanalysis of the neutral hydrogen observations from the VLA archive. We find the galaxy to be at once remarkably bisymmetric in its I-band light distribution and strongly asymmetric in the distribution of dust and in the kinematics of the gas in the bar region. The velocity field mapped in the H? line reveals bright H II regions with velocities that differ by 60-80 km s-1 from that of the surrounding gas, which may be due to remnants of infalling material. We have attempted hydrodynamic simulations of the bar flow to estimate the separate disk and halo masses, using two different dark matter halo models and covering a wide range of mass-to-light ratios (?) and bar pattern speeds (?p). None of our models provides a compelling fit to the data, but they seem most nearly consistent with a fast bar, corotation at ~1.2rB, and ?I~=2.0+/-1.0, implying a massive, but not fully maximal, disk. The fitted dark halos are unusually concentrated, a requirement driven by the declining outer rotation curve.

Zánmar Sánchez, R.; Sellwood, J. A.; Weiner, B. J.; Williams, T. B.

2008-02-01

41

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

42

The two superposed galaxies of NGC 3314  

NASA Astrophysics Data System (ADS)

Spectroscopic observations of NGC 3314 are presented. Long-slit spectrograms clearly show two sets of emission lines stemming from the two superposed galaxies. The foreground galaxy, NGC 3314a, is a type SBbc or SBc spiral of absolute magnitude MB ? -20 and has a radial velocity cz_sun; = 2835±15 km s-1. The background galaxy, NGC 3314b, is probably an Sb of MB ? -20.5 with cz_sun; = 4641±6 km s-1. The availabe evidence suggests that at least NGC 3314a, and probably also NGC 3314b, are members of the Hydra I cluster of galaxies (cz_sun; = 3699 km s-1, ?v = 681 km s-1), although the alternative hypothesis that one of them or both are field galaxies cannot presently be ruled out.

Schweizer, F.; Thonnard, N.

1985-02-01

43

Nuclear Rings in Barred Galaxies  

NASA Astrophysics Data System (ADS)

Dust lanes, nuclear rings and nuclear spirals are typical structures in the inner region of barred galaxies. Their shapes and properties are linked to the physical parameters of galaxies. To study galaxy formation and evolution revealed by these gas features, we need to understand what conditions are responsible to the gas flow patterns. Here we use high-resolution hydrodynamical simulations to study 2D gas flows in simple barred models. We find that the location and thickness of nuclear rings are tightly correlated with galactic properties, such as the pattern speed and central mass concentration, within certain ranges. Our result may have important implications for measuring the parameters of real barred galaxies observed by IFU.

Shen, Juntai

2014-05-01

44

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

45

Galaxy Zoo: Observing Secular Evolution Through Bars  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

46

Spectropolarimetry of the Seyfert Galaxies NGC 1365 and NGC 3393  

NASA Astrophysics Data System (ADS)

We report on CTIO spectropolarimetry observations of these two Seyfert galaxies. NGC 1365 is a nearby galaxy (z=0.005) which has been variously classified as a Seyfert 2, Seyfert 1.8, NLS1, and a starburst-Seyfert. Our spectra suggests it is currently a Narrow-line Seyfert 1, with iron lines in the spectrum. It has a continuum polarization rising to about 1.5% in the blue, similar to that of other NLS1 galaxies such as IRAS 20181--2244. NGC 3393 is a luminous southern Seyfert 2 galaxy at z=0.013. Our data show it has a hidden broad line region visible in the polarized flux. Support from the NSF, NASA, the Center for Astrophysical Sciences at JHU, and FAPESP is gratefully acknowledged.

Kay, L. E.; Tran, H. D.; Magalhães, A. M.

2002-05-01

47

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

48

Bar-spheroid interaction in galaxies  

NASA Technical Reports Server (NTRS)

N-body simulation and linear analysis is employed to investigate the secular evolution of barred galaxies, with emphasis on the interaction between bars and spheroidal components of galaxies. This interaction is argued to drive secular transfer of angular momentum from bars to spheroids, primarily through resonant coupling. A moderately strong bar, having mass within corotation about 0.3 times the enclosed spheroid mass, is predicted to shed all its angular momentum typically in less than about 10 exp 9 yr. Even shorter depletion time scales are found for relatively more massive bars. It is suggested either that spheroids around barred galaxies are structured so as to inhibit strong coupling with bars, or that bars can form by unknown processes long after disks are established. The present models reinforce the notion that bars can drive secular evolution in galaxies.

Hernquist, Lars; Weinberg, Martin D.

1992-01-01

49

NGC 6872's Tidal Dwarf Galaxy  

NASA Astrophysics Data System (ADS)

Interacting galaxies are ideal laboratories to study not only star formation but also galaxy formation. We propose to observe a small system recently discovered using GALEX data just outside the interacting pair of galaxies NGC6872/IC4970. This system has the general characteristics of a young tidal dwarf galaxy (TDG), but Spitzer data is crucial for us to determine its stellar mass and thus its nature. NGC 6872 is the largest-known spiral galaxy, with its disk extending for more than 160 kpc and regions with very different Spectral Energy Distributions across the galaxy, with the TDG-candidate being one of its the bluest regions. We propose to obtain IRAC imaging to constrain the stellar mass of this TDG, complementing our studies of UV GALEX data.

Eufrasio, Rafael; Arendt, Richard; Dwek, Eli

2013-10-01

50

ASCA observation of three bright early-type galaxies: NGC 4472, NGC 4406, and NGC 4636  

NASA Technical Reports Server (NTRS)

We report Advanced Satellite for Cosmology and Astrophysics (ASCA) 0.3-10 keV and X-ray observations of three early type galaxies, NGC 4472, NGC 4406, and NGC 4636. The extended mission in these galaxies is well described by thin thermal eimssion from hot gas. The gas temperature is 0.92 +/- 0.02 keV for NGC 4472, 0.79 +/- 0.01 keV for NGC 4406, and 0.73 +/- 0.02 keV for NGC 4636. The metal abundance for NGC 4472, NGC 4406, and NGC 4636 are, under the assumption of solar ratios, 0.63 +/- 0.15, 0.45 +/- 0.10, and 0.38 +/- 0.07, respectively. Detailed analysis has allowed determination of the abundances of oxygen, silicon, sulfur, and iron. The observed abundances are consistent with the solar ratios. For NGC 4472 and NGC 4406 we also determined the mean temperature of the gas producing the Si lines from the ratio of the Si H to He-like lines and find it to be consistent with the continuum temperature. The X-ray temperature is in good agreement with the observed optical velocity dispersion, stellar density profile, and gas density profile. Our data indicates that the supernova rate should be less than one fifth of the nominal rate in early type galaxies. We derive the mass of these systems within fixed angular scales and find that M/L greater than 40, confirming that elliptical galaxies are dark matter dominated at large radii.

Awaki, Hisamitsu; Mushotzky, Richard; Tsuru, Takeshi; Fabian, Andrew C.; Fukazawa, Yasushi; Loewenstein, Michael; Makishima, Kazuo; Matsumoto, Hironori; Matsushita, Kyoko; Mihara, Tatehiro

1994-01-01

51

Diverse Group of Galaxy Types, NGC 3190 Field  

NASA Technical Reports Server (NTRS)

Ultraviolet image of a diverse group of galaxy types. NGC 3190 is a dusty edge on spiral galaxy. NGC 3187 is highly distorted. The two are separated by only 35 kilo-parsecs (about half the diameter of our own Milky Way galaxy). A ring, elliptical, and other irregular galaxies are also present.

2005-01-01

52

Extragalactic molecular line surveys: the starburst galaxy NGC253  

NASA Astrophysics Data System (ADS)

Figure 1 shows the first spectral line survey towards an extragalactic source, the starburst galaxy NGC253. The scan, carried out at the IRAM 30m telescope, covers ~86% of the observable 2mm atmospheric window from 129.1 to 175.2GHz. A total of ~ 100 spectral features have been identified as transitions from 25 different molecular species. Ten out of these 25 molecules have been detected for the first time towards a starbust galaxy. NO, NS, SO2, H2S and H2CS were reported by Martín et al.(2003), Martín et al.(2005) while C2S, CH2NH, NH2CN, HOCO+ and C3H are tentatively detected in the survey. These new detections implies an increase of ~ 40% in the 27 molecular species previosly detected outside the galaxy (Mauersberger & Henkel(1993), Mauersberger et al.(1995), Sage & Ziurys(1995), Heikkila et al.(1999).) Additionaly, DNC and N2D+, two deuterated species never obseved in the extragalactic ISM, are tentatively identified. The molecular abundances derived for each species in NGC253 have been compared with five Galactic sources known to be prototypes of different types of chemistry. The chemical complexity of NGC253 resembles closely that observed towards prototypical Galactic Center molecular clouds (SgrB2(OH) in, thought to be mainly dominated by low velocity shocks Martín-Pintado et al.(2001). This comparison certainly indicates that the chemistry of the molecular environment within the nuclear region of NGC253 and that in Galactic Center molecular clouds are driven by similar physical processes. Also a comparison has been performed with five selected prominent galaxies which clearly shows up the chemical differenciation between nuclei of galaxies. The chemical complexity of IC342, and also that of NGC4945 except for the observed lack of SiO, clearly resemble that of NGC253. On the other hand, it is remarkable the different chemical complexity observed between the starburst nuclei within NGC253 and M82. This difference has been interpreted in terms of the nuclear starburst in M82 being in a more evolved stage, dominated by photodissociation regions (PDRs) (García-Burillo et al.(2002)). This idea is fully supported by the similarity of the chemical complexity of M82 and the Orion Bar, taken as prototype of PDR.

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

53

NGC 1275 - A burgeoning elliptical galaxy  

NASA Astrophysics Data System (ADS)

Large-aperture spectrophotometry of the peculiar galaxy NGC 1275 is presented. Emission lines from H-beta and the forbidden O II, O III, and Ne III dominate this spectrum, while H-delta, H-epsilon and Na D appear in absorption. A population synthesis model for the absorption-line spectrum suggests that about 20 percent of the optical luminosity is produced by B stars. On the basis of this and the calculated H-beta emission line flux, it is estimated that the current star formation rate in NGC 1275 is about 30 solar masses per yr. This leads to a predicted supernova rate of 1 per yr. The resulting supernova heating rate is approximately one-half the cooling rate predicted by current accretion models and may thus significantly alter the accretion flow. It is proposed that in NGC 1275, the formation of an elliptical galaxy in the cluster potential may be under way.

Wirth, A.; Kenyon, S. J.; Hunter, D. A.

1983-06-01

54

DEPENDENCE OF BARRED GALAXY FRACTION ON GALAXY PROPERTIES AND ENVIRONMENT  

SciTech Connect

We investigate the dependence of the occurrence of bars in galaxies on galaxy properties and environment. We use a volume-limited sample of 33,391 galaxies brighter than M{sub r} = -19.5 + 5logh at 0.02 {<=} z {<=} 0.05489, drawn from the Sloan Digital Sky Survey Data Release 7. We classify the galaxies into early and late types, and identify bars by visual inspection. Among 10,674 late-type galaxies with axis ratio b/a > 0.60, we find 3240 barred galaxies (f{sub bar} = 30.4%) which divide into 2542 strong bars (f{sub SB1} = 23.8%) and 698 weak bars (f{sub SB2} = 6.5%). We find that f{sub SB1} increases as u - r color becomes redder and that it has a maximum value at intermediate velocity dispersion ({sigma} {approx_equal}150 km s{sup -1}). This trend suggests that strong bars are dominantly hosted by intermediate-mass systems. Weak bars prefer bluer galaxies with lower mass and lower concentration. In the case of strong bars, their dependence on the concentration index appears only for massive galaxies with {sigma} > 150 km s{sup -1}. We also find that f{sub bar} does not directly depend on the large-scale background density when other physical parameters (u - r color or {sigma}) are fixed. We discover that f{sub SB1} decreases as the separation to the nearest neighbor galaxy becomes smaller than 0.1 times the virial radius of the neighbor regardless of neighbor's morphology. These results imply that strong bars are likely to be destroyed during strong tidal interactions and that the mechanism for this phenomenon is gravitational and not hydrodynamical. The fraction of weak bars has no correlation with environmental parameters. We do not find any direct evidence for environmental stimulation of bar formation.

Lee, Gwang-Ho; Lee, Myung Gyoon [Department of Physics and Astronomy, Seoul National University, Gwanak-gu, Seoul 151-742 (Korea, Republic of); Park, Changbom [Korea Institute for Advanced Study, Dongdaemun-gu, Seoul 130-722 (Korea, Republic of); Choi, Yun-Young, E-mail: ghlee@astro.snu.ac.kr, E-mail: mglee@astro.snu.ac.kr, E-mail: cbp@kias.re.kr, E-mail: yy.choi@khu.ac.kr [Department of Astronomy and Space Science, Kyung Hee University, Kyungki 446-701 (Korea, Republic of)

2012-02-01

55

A Multiwavelength Study of the Starburst Galaxy NGC 7771  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

56

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

Microsoft Academic Search

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.

Boyko Mihov; Lyuba Slavcheva-Mihova

2006-01-01

57

Structure and dynamics of the nuclear region of the spiral galaxy NGC 7217  

Microsoft Academic Search

The gas velocities and brightness distribution in the inner region of NGC 7217 are analyzed. This galaxy has a regular axially symmetric shape with flocullent spiral arms that have a system of three distinct rings (outer, inner, and nuclear) - a structure that is rarely observed in the absence of a bar. Observations on the 6-m telescope of the Special

A. V. Zasov; O. K. Sil'chenko

1997-01-01

58

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

59

NGC 3200 - Is this what our Galaxy is like?  

Microsoft Academic Search

Systematic dynamical properties of Sa, Sb, and Sc field galaxies are presented. The rotational properties of the Sb(r)I galaxy NGC 3200 suggest that it resembles our Galaxy. It is concluded that the general dynamical properties of our Galaxy are not yet sufficiently well known to place it accurately in the sequence of external galaxies.

V. C. Rubin

1983-01-01

60

GASEOUS STRUCTURES IN BARRED GALAXIES: EFFECTS OF THE BAR STRENGTH  

SciTech Connect

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

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

2012-10-10

61

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

SciTech Connect

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

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

2012-10-01

62

Gas flow and dark matter in the inner parts of early-type barred galaxies. I. SPH simulations and comparison with the observed kinematics  

Microsoft Academic Search

This paper presents the dynamical simulations run in the potential derived from the light distribution of 5 late-type barred spiral galaxies (IC 5186, NGC 5728, NGC 7267, NGC 7483 and NGC 5505). The aim is to determine whether the mass distribution together with the hydrodynamical simulations can reproduce the observed line-of-sight velocity curves and the gas morphology in the inner

I. Pérez; R. Fux; K. Freeman

2004-01-01

63

Longslit Spectra of the Galaxy NGC 1569  

NASA Technical Reports Server (NTRS)

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

Duenas, Ely

2000-01-01

64

The obscured circumnuclear region of the outflow galaxy NGC 3079  

NASA Astrophysics Data System (ADS)

Images of the central region of the almost edge-on Sc galaxy NGC 3079 in the J, H and K-bands and in the v=1{->}0 S(1) line of molecular hydrogen are presented. The inner few kiloparsecs of NGC 3079 exhibit a large range of near-infrared colours caused by varying contributions from direct and scattered stellar light, emission from hot dust and extinction gradients. Our results show that interpretation of the observed light distribution requires high-resolution imaging in order to separate the different effects of these contributions. The central 1'' (87 pc) of NGC 3079 suffers a peak extinction AV ~ mg 6. Its extremely red near-infrared colours require the additional presence of hot dust, radiating at temperatures close to 1000 K. The least reddened eastern parts of the bulge require either a contribution of 20% of light in the J-band from a younger population in a stellar bar or a contribution of 20-30% from scattered starlight; scattered light from a nuclear source would require a less likely emission spectrum S_?~nu for that source. The nucleus is surrounded by a disk of dense molecular material, extending out to a radius of about 300 pc and with a central cavity. Bright H_2 emission and emission from hot dust mark the hole in the CO distribution and trace the inner edge of the dense molecular disk at a radius of 120 pc. Less dense molecular gas and cooler dust extend out to radii of about 2 kpc. In the inner few hundred parsecs of NGC 3079, ion {H}i spin temperatures appear to be well below 275 K and the CO-to-H2 conversion factor has at most 5% of the Galactic value. An underabundance of H2 with respect to CO is consistent with theoretical predictions for environments subjected to dissociative shocks, where reformation of H2 is impeded by high dust grain temperatures. The overall molecular gas content of NGC 3079 is normal for a late-type galaxy.

Israel, F. P.; van der Werf, P. P.; Hawarden, T. G.; Aspin, C.

1998-08-01

65

Dust in backlit galaxies - Properties of the foreground systems in NGC 3314 and NGC 1275  

NASA Astrophysics Data System (ADS)

New digital imaging of NGC 3314 and NGC 1275 is presented. NGC 3314 consists of an Sc galaxy in front of an Sb; BVRI data are used to estimate the extinction through and between spiral arms and derive R = 3.5 for the extinction curve, with large uncertainties due to structure in the foreground galaxy. Dust lanes are identified in NGC 1275, of optical depth similar to those in NGC 3314, and occurring in association with giant H II regions; these imply a type Sc or Scd for the foreground object. This object lies outside the low-velocity filament system and is probably not interacting with the main body of NGC 1275.

Keel, W. C.

1983-11-01

66

Fabry-Pérot H? Observations of the Barred Spiral NGC 3367  

NASA Astrophysics Data System (ADS)

We report the gross properties of the velocity field of the barred spiral galaxy NGC 3367. We obtained the following values: the inclination with respect to the plane of the sky, i=30; the position angle (P.A.) of the receding semimajor axis, P.A.=51deg and the systemic velocity, Vsys=3032 km s-1. Large velocity dispersions are observed of up to 120 km s-1 in the nuclear region and of up to 70 km s-1 near the eastern bright sources just beyond the edge of the stellar bar, where three spiral arms seem to start, and in the western bright sources at about 10 kpc. Deviations from normal circular velocities are observed from the whole disk but mainly from the semicircle formed by the string of southwestern H? sources. An estimate of the dynamical mass is Mdyn=2×1011 Msolar.

García-Barreto, J. Antonio; Rosado, M.

2001-05-01

67

Using Bars as Signposts of Galaxy Evolution  

NASA Astrophysics Data System (ADS)

Recent studies of galaxy morphology with the Hubble Deep Fields have indicated a dramatic paucity of bars beyond a redshift > 0.5. This result is unexpected because the classical bar formation mechanism would predict that bars ought to be more common at higher redshifts because of dynamically colder galaxy disks and increased interactions. If the scarcity of bars is true, then serious constraints may be placed on the evolutionary stage of galactic disks. On the other hand, it is possible that the observations are misleading due to band-shifting and dust obscuration effects. While these criticisms have been suggested qualitatively, a quantitative analysis of the evolution of the bar fraction with redshift is missing. We propose to do such an analysis using the best dataset available for this type of a study, the NICMOS map of the Hubble Deep Field. For a control sample we will use a sample of spirals representative of the nearby Universe and simulate their appearance at different redshifts. From these simulated data, we will measure the bar fraction for comparison to our analysis of the NICMOS data.

Sheth, Kartik

2002-07-01

68

Using Bars as Signposts of Galaxy Evolution  

NASA Astrophysics Data System (ADS)

Recent studies of galaxy morphology with the Hubble Deep Fields have indicated a dramatic paucity of bars beyond a redshift > 0.5. This result is unexpected because the classical bar formation mechanism would predict that bars ought to be more common at higher redshifts because of dynamically colder galaxy disks and increased interactions. If the scarcity of bars is true, then serious constraints may be placed on the evolutionary stage of galactic disks. On the other hand, it is possible that the observations are misleading due to band-shifting and dust obscuration effects. While these criticisms have been suggested qualitatively, a quantitative analysis of the evolution of the bar fraction with redshift has been missing. We present preliminary results from an analysis of the bar fraction as a function of redshift using the NICMOS Deep Field, the best dataset available for such a quantitative study. For a control sample we use a sample of spirals representative of the nearby Universe and simulate their appearance at different redshifts using an IDL code developed by Strubbe et al. (discussed in poster session). This work is partially supported by grant HST-AR-09552.01-A through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555, and by NSF grant AST-9981546.

Sheth, K.; Regan, M. W.; Scoville, N. Z.; Strubbe, L. E.

2002-12-01

69

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

Microsoft Academic Search

We present preliminary results of the Johnson-Cousins (U)BVRI surface\\u000abrightness profile decompositions of the Seyfert galaxies Mrk 79 and NGC 5548.\\u000aThe profiles were modelled as a sum of a Gaussian law for the nucleus, a Sersic\\u000alaw for the bulge and an exponent law for the disk. A flat bar was added to the\\u000amodel profile of Mrk 79.

Boyko Mihov; Lyuba Slavcheva-Mihova

2007-01-01

70

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

71

Near-infrared line imaging of the circumnuclear starburst rings in the active galaxies NGC 1097 and NGC 6574  

NASA Astrophysics Data System (ADS)

We present high spatial resolution near-infrared broad-band JHK and Brgaussmma 2.166 mum and H_2 1-0 S(1) 2.121 mum emission line images of the circumnuclear star formation rings in the LINER/Seyfert 1 galaxy NGC 1097 and in the Seyfert 2 galaxy NGC 6574. We investigate the morphology, extinction, and the star formation properties and history of the rings, by comparing the observed properties with an evolutionary population synthesis model. The clumpy morphology in both galaxies varies strongly with wavelength, due to a combination of extinction, emission from hot dust and red supergiants, and the age of the stellar populations in the rings. The near-infrared and radio morphologies are in general agreement, although there are differences in the detailed morphology. From the comparison of Brgaussmma and H? fluxes, we derive average extinctions toward the hot spots A_V = 1.3 for NGC 1097 and A_V = 2.1 for NGC 6574. The observed H_2/Brgaussmma ratios indicate that in both rings the main excitation mechanism of the molecular gas is UV radiation from hot young stars, while shocks can contribute only in a few regions. The starburst rings in both galaxies exhibit small Brgaussmma equivalent widths. Assuming a constant star formation rate with M_u = 100 M_sun results in extremely long ages (up to 1 Gyr), in disagreement with the morphology and the radio spectral index of the galaxies. This situation is only slightly remedied by a reduced upper mass cutoff (M_u = 30 M_sun). We prefer a model of an instantaneous burst of star formation with M_u = 100 M_sun occurring sim6-7 Myr ago. Gaseous nuclear bars parallel to the stellar nuclear bar were detected in both galaxies, and we derive M sim100 M_sun for the mass of the excited nuclear H_2 emission. Finally, we briefly discuss the connection between the rings, bars and the fuelling of nuclear activity.

Kotilainen, J. K.; Reunanen, J.; Laine, S.; Ryder, S. D.

2000-01-01

72

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

73

Nuclear Outbursts in the Elliptical Galaxy NGC 4472  

NASA Astrophysics Data System (ADS)

We present the analysis of the Chandra ACIS observations of the giant elliptical galaxy NGC 4472. The Chandra Observatory's arcsec resolution reveals a number of new features, specifically: 1) an ~8 arcmin streamer or arm (this corresponds to a linear size of 36 kpc) extending southwest of the galaxy and an assymetrical, somewhat truncated streamer to the northeast. Smaller, morphologically similar structures are observed in NGC 4636 (Jones et al. 2001) and are explained as shocks from a nuclear outburst in the recent past. The larger size of the NGC 4472 streamers requires a correspondingly higher energy input compared to the NGC 4636 case. The asymmetry of the streamers may be due to the interaction of NGC 4472 with the ambient Virgo cluster gas. 2) A string of small, extended sources south of the nucleus. These sources may stem from an interaction of NGC 4472 with the galaxy UGC 7637. 3) X-ray cavities corresponding to radio lobes, where expanding radio plasma has evacuated the X-ray emitting gas. We also present a luminosity function for the X-ray point sources detected within NGC 4472 which we compare to that for other early type galaxies. This work was supported by CXC contract number NAS8-39073 and the Smithsonian Institution.

Biller, B.; Jones, C.; Forman, W.

2001-12-01

74

Diffuse hot gas in the NGC 4261 group of galaxies  

NASA Technical Reports Server (NTRS)

We have found diffuse X-ray gas in the group of galaxies containing the elliptical galaxy NGC 4261. This galaxy along with its associated companions are behind the Virgo cluster in the W-cloud. A recent analysis of the velocity structure in the Virgo region indicates that the W-cloud has approximately 30 members, most of which are low luminosity dwarfs. The hot X-ray emitting gas is centered about halfway between NGC 4261 and NGC 4264 and extends out to a radius of approximately 40 min(620 kpc). The spectral data for the diffuse component are well fitted with a Raymond-Smith plasma model with a temperature of 0.85(sup +0.21)(sub -0.16) keV and abundance less than 0.08 times the solar value. Under the assumption that the diffuse gas is in hydrostatic equilibrium the total mass within 40 min is 1.9 x 10(exp 13) solar mass. We estimate that the total baryonic mass of the hot gas and the galaxies is 20%-34% of the total mass in the central 40 min radius of this group. This group of galaxies contains NGC 4273 which exhibits a 'bow shock' morphology similar to that of NGC 2276. This is thought to occur when the ram pressure from the intragroup gas significantly perturbs the interstellar medium in a late-type galaxy. We show that this is unlikely in this group.

Davis, David S.; Mushotzky, Richard F.; Mulchaey, John S.; Worrall, D. M.; Birkinshaw, M.; Burstein, David

1995-01-01

75

A multispecies survey of the active galaxy NGC1068  

Microsoft Academic Search

The nearby Seyfert galaxy NGC 1068 is among the very few objects where nuclear starburst regions and Active Galactic Nuclei (AGN) can be spatially resolved with current millimeter--wavelength telescopes. We present a multispecies survey of molecular lines in this galaxy carried out with the IRAM Plateau de Bure Interferometer. Thanks to the high spatial-resolution achieved, we distinguish the circumnuclear disk

A. Usero; S. Garcia-Burillo; A. Fuente; S. Aalto; R. Neri; M. Krips

2011-01-01

76

Further observations of the elliptical galaxy NGC 5813  

Microsoft Academic Search

Measurements are given for the rotation curve and velocity dispersion profile along the major axis of the elliptical galaxy NGC 5813 which extend out to almost 90 arcsec on either side of the center of the galaxy. The peak velocity of 89 + or - 7 km\\/sec is reached at about 3 arcsec from the center, and the rotational velocity

G. Efstathiou; R. S. Ellis; D. Carter

1982-01-01

77

H I observations of the peculiar galaxy NGC 660  

NASA Technical Reports Server (NTRS)

The authors present observations of H I emission from the peculiar galaxy NGC 660. H I was detected in the companion galaxy UGC 01195 as well. Sixteen hours of observations were obtained with the VLA telescope of the National Radio Astronomy Observatory during December 1986 and March 1987.

Gottesman, Stephen T.; Mahon, Mary Elaine

1990-01-01

78

High Resolution Radio Imaging of the Merging Galaxies NGC3256 and NGC4194  

NASA Technical Reports Server (NTRS)

We present new 6cm and 4cm radio continuum images of the central regions of the merging galaxy systems NGC3256 and NGC4194. NGC3256 is imaged with a resolution of approx. 1 in. or approx. 190pc; NGC4194 is imaged with a resolution of approx. 0.3 in. or approx. 50pc. In both systems, we detect numerous compact radio sources embedded in more diffuse radio emission. We detect 65 compact sources in NGC3256 at 6cm and we detect 46 compact sources in NGC4194, both to a limiting luminosity of approx. 5 x 10(exp 18) W/ Hz or approx. 5 times the luminosity of Cas A. Most of the compact radio sources are loosely associated with active star forming regions but not with specific optical emission sources. Several compact radio sources in NGC3256 are near positions of compact X-ray sources detected by Lira et al.. In both NGC3256 and NGC4194, we are able to measure reliable spectral indices for the stronger sources. We find in NGC3256 approx. 20% have nominally flat radio spectral indices (indicating they are dominated by thermal radio emission from HII regions) while approx. 80% have nominally steep spectral indices (indicating they are dominated by nonthermal emission from supernova remnants). In NGC4194, half the compact radio sources have flat spectral indices and half have steep indices. For the flat-spectrum sources, we estimate the number of young massive stars and the associated ionized gas masses. For the steep-spectrum sources, we estimate supernova rates. We compare these results with those from other well-studied merging galaxy systems. We gratefully acknowledge use of the NRAO Very Large Array (VLA) and the VLA Archive. NRAO is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Neff, S. G.; Campion, S. D.; Ulvestad, J. S.; Fisher, Richard R. (Technical Monitor)

2001-01-01

79

A tidally distorted dwarf galaxy near NGC 4449.  

PubMed

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

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

2012-02-01

80

A tidally distorted dwarf galaxy near NGC 4449  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

81

On the Formation and Evolution of Stellar Bars in Galaxies  

Microsoft Academic Search

We have done a detailed study on the structural and kinematical properties of lenticular and early- and late-type spiral galaxies with bars, aiming to explore the formation and evolution processes of stellar bars in galaxies, and their implications on the global formation and evolution of galaxies. Using high signal-to-noise spectra obtained along the major and minor axes of the bars

D. A. Gadotti

2003-01-01

82

The lenticular NGC 3115 - A standard for galaxy photometry  

NASA Astrophysics Data System (ADS)

NGC 3115, a lenticular galaxy that is seen edge-on, is an ideal candidate for surface photometry in virtue of its proximity and absence of close prominent companions. An independent two-dimensional study of NGC 3115 has been made using the high resolution CFH telescope, as well as the ESO and UK Schmidt telescopes (for the outer regions). Light profiles along both main axes were produced for each intensity frame; the results obtained are presented in graphical form.

Capaccioli, M.; Held, E. V.; Nieto, J.-L.

83

Quantitative Spectroscopy of Blue Supergiants in Metal-poor Dwarf Galaxy NGC 3109  

NASA Astrophysics Data System (ADS)

We present a quantitative analysis of the low-resolution (~4.5 Å) spectra of 12 late-B and early-A blue supergiants (BSGs) in the metal-poor dwarf galaxy NGC 3109. A modified method of analysis is presented which does not require use of the Balmer jump as an independent T eff indicator, as used in previous studies. We determine stellar effective temperatures, gravities, metallicities, reddening, and luminosities, and combine our sample with the early-B-type BSGs analyzed by Evans et al. to derive the distance to NGC 3109 using the flux-weighted gravity-luminosity relation (FGLR). Using primarily Fe-group elements, we find an average metallicity of [\\bar{Z}] = –0.67 ± 0.13, and no evidence of a metallicity gradient in the galaxy. Our metallicities are higher than those found by Evans et al. based on the oxygen abundances of early-B supergiants ([\\bar{Z}] = –0.93 ± 0.07), suggesting a low ?/Fe ratio for the galaxy. We adjust the position of NGC 3109 on the BSG-determined galaxy mass-metallicity relation accordingly and compare it to metallicity studies of H II regions in star-forming galaxies. We derive an FGLR distance modulus of 25.55 ± 0.09 (1.27 Mpc) that compares well with Cepheid and tip of the red giant branch distances. The FGLR itself is consistent with those found in other galaxies, demonstrating the reliability of this method as a measure of extragalactic distances.

Hosek, Matthew W., Jr.; Kudritzki, Rolf-Peter; Bresolin, Fabio; Urbaneja, Miguel A.; Evans, Christopher J.; Pietrzy?ski, Grzegorz; Gieren, Wolfgang; Przybilla, Norbert; Carraro, Giovanni

2014-04-01

84

Near-infrared mapping of spiral barred galaxies  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

85

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

NASA Astrophysics Data System (ADS)

We present the detection of hydrogen fluoride (HF) in two luminous nearby galaxies, NGC 253 and NGC 4945 using the Heterodyne Instrument for the Far-Infrared on board the Herschel Space Observatory. The HF line toward NGC 253 has a P-Cygni profile, while an asymmetric absorption profile is seen toward NGC 4945. The P-Cygni profile in NGC 253 suggests an outflow of molecular gas with a mass of M(H2)out ~ 1 × 107 M ? and an outflow rate as large as dot M ~6.4 M ? yr-1. In the case of NGC 4945, the axisymmetric velocity components in the HF line profile are compatible with the interpretation of a fast-rotating nuclear ring surrounding the nucleus and the presence of inflowing gas. The gas falls into the nucleus with an inflow rate of <=1.2 M ? yr-1, inside an inner radius of <=200 pc. The gas accretion rate to the central active galactic nucleus is much smaller, suggesting that the inflow may be triggering a nuclear starburst. From these results, the HF J = 1-0 line is seen to provide an important probe of the kinematics of absorbing material along the sight-line to nearby galaxies with bright dust continuum and a promising new tracer of molecular gas in high-redshift galaxies.

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

2014-04-01

86

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

87

NGC 3928 - a highly bulge-dominated compact spiral galaxy  

SciTech Connect

Spectroscopic and surface photometric observations have been made of the blue early-type galaxy NGC 3928 (Markarian 190). This galaxy is an unusual composite system with both a miniature spiral disk (diameter about 2.4 kpc) and a spheroidal stellar envelope (diameter about 9.4 kpc). Spectroscopic properties of the nuclear emitting region are similar to those of low-excitation giant H II regions in normal spiral galaxies. This indicates that moderate star-forming activity has occurred in the central region as well as in the miniature disk and may be responsible for the relatively bluer color. Since the metallicity of the ionized gas is normal, the chemical properties of NGC 3928 are comparable to those of normal-aged or normal-sized galaxies in spite of its low luminosity (-17.6 mag). The surface photometric observations reveal that NGC 3928 is a highly bulge-dominated galaxy. NGC 3928 can be interpreted as a compact spiral disk embedded in the central region of a large spheroidal component. 51 references.

Taniguchi, Y.; Watanabe, M.

1987-02-01

88

Polar ring spiral galaxy NGC 660  

NASA Astrophysics Data System (ADS)

NGC 660 is a unique, nearby, peculiar polar ring spiral LINER galaxy with two distinct morphological and kinematic components: a spiral disk, seen almost edge on (i approximately 70 deg),with a major axis position angle of 45deg and a diameter of approximately 11 kpc (D = 13 x 60 arcsec and in the CO(1-0) and CO(2-1) lines with a 12-22 arcsec beam. B,V,I,J,H,K'-band images, and a long-slit H-alpha spectrum along the disk major axis were obtained as well. It has been morphologically classified as SBa, but our data show it has the global characteristics of a later-type (Sc?), gas-rich disk. The disk and the polar ring both have an exponential luminosity profile, with scale lengths of 1.3 and 3.9 kpc, respectively. The polar ring is blue (V - I approximately 1.0), indicating a stellar population age of a few billion years, according to our stellar population synthesis model and the nucleus is red (V-I approximately 1.8). H-alpha images show H II regions throughout the polar ring. The near-infrared images show a boxy/X shape of the bulge and 1.4 kpc long linear features along the disk major axis on both sides of the bulge. The disk was detected in radio continuum at 21 cm. It has a compact 300 mJy nuclear source and an extended (7.5 kpc diameter) component of 80 mJy. The central source has a very high radio power for a spiral galaxy, while the disk has a normal radio power. The radio spectral index is -0.57, indicating an important contribution from thermal radiation. The H I line observations show absorption against the nuclear source, and both H I and CO line data show emission from the disk and the polar ring. The H I and CO data indicate a rather flat disk rotation curve, with a rotation velocity of approximately 150 km/s. From our H-alpha spectrum, taken close to the major axis, a steeper inner gradient and a consideraably lower rotation velocity (approximately 110 kms/s) is derived in the outer parts than from that of Benvenuti et al. (l976), if one assumes the disk to be flat and in circular rotation.

van Driel, W.; Combes, F.; Casoli, F.; Gerin, M.; Nakai, N.; Miyaji, T.; Hamabe, M.; Sofue, Y.; Ichikawa, T.; Yoshida, S.; Kobayashi, Y.; Geng, F.; Minezaki, T.; Arimoto, N.; Kodama, T.; Goudfrooij, P.; Mulder, P. S.; Wakamatsu, K.; Yanagisawa, K.

1995-03-01

89

The Nature of the Optical "Jets" in the Spiral Galaxy NGC 1097  

NASA Technical Reports Server (NTRS)

We present new observations of the jet features in the barred spiral galaxy NGC 1097, including optical spectroscopy of the brightest jet features, two-color optical imagery, new VLA mapping at 327 MHz, and archival 1.4 GHz VLA data reprocessed for improved sensitivity. No optical emission lines appear to an equivalent width limit of 15-30 A (depending on the line wavelength). The jets are uniformly blue, with B - V = 0.45 for the two well-observed jets R1 and R2. No radio emission from the jets is detected at either frequency; the 327-MHz data set particularly stringent limits on "fossil" emission from aging synchrotron electrons. The morphology of the jets is shown to be inconsistent with any conical distribution of emission enhanced by edge-brightening; their combination of transverse profile and relative narrowness cannot be reproduced with cone models. The optical colors, lack of radio emission, and morphology of the features lead us to conclude that they are tidal manifestations, perhaps produced by multiple encounters of the small elliptical companion NGC 1097A with the disk of NGC 1097. We present photometric and morphological comparisons to the tail of NGC 465 1, which is similar in scale and morphology to the northeast "dogleg" feature R1 in NGC 1097.

Wehrle, Ann E.; Keel, William C.; Jones, Dayton L.

1997-01-01

90

A mid-IR comparative analysis of the Seyfert galaxies NGC 7213 and NGC 1386  

NASA Astrophysics Data System (ADS)

New Gemini mid-infrared spectroscopic observations together with Spitzer Space telescope archival data are used to study the properties of the dusty torus and circumnuclear star formation in the active galaxies NGC 7213 and NGC 1386. Our main conclusions can be summarized as follows. Polycyclic aromatic hydrocarbon (PAH) emission is absent in the Thermal-Region Camera and Spectrograph (T-ReCS) nuclear spectra but is ubiquitous in the data from Spitzer at distances above 100 pc. Star formation rates surface densities are estimated from the 12.8 ?m [Ne II] line strengths leading to values close to 0.1 M? yr-1 kpc-2. Analogous estimates based on photometric fluxes of Infrared Array Camera's 8 ?m images are higher by a factor of almost 15, which could be linked to excitation of PAH molecules by older stellar populations. T-ReCS high-spatial-resolution data reveal silicate absorption at ? 9.7 ?m in the central tens of parsecs of the Seyfert 2 NGC 1386 and silicate emission in the Seyfert 1 galaxy NGC 7213. In the case of NGC 1386, this feature is confined to the inner 20 pc, implying that the silicate might be linked to the putative dusty torus. Finally, by fitting CLUMPY models to the T-ReCS nuclear spectra, we estimate the torus physical properties for both galaxies, finding line-of-sight inclinations consistent with the AGN unified model.

Ruschel-Dutra, Daniel; Pastoriza, Miriani; Riffel, Rogério; Sales, Dinalva A.; Winge, Cláudia

2014-03-01

91

A massive BH in the edge-on E\\/SO galaxy NGC 4342  

Microsoft Academic Search

We have obtained photometric and spectroscopic data with the Hubble Space Telescope (HST) of two E\\/S0 galaxies in the Virgo cluster: NGC 4342 and NGC 4570. Both galaxies harbor, in addition to an outer disk, a very small, stellar disk in their nuclei. The kinematics of NGC 4342 reveal that the nuclear disk rotates extremely rapidly, reaching rotation velocities in

F. van den Bosch; N. Cretton

1998-01-01

92

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

93

Dwarf Galaxies in the Halo of NGC 891  

NASA Astrophysics Data System (ADS)

We report the results of a survey of the region within 40 arcmin of NGC 891, a nearby nearly perfectly edge-on spiral galaxy. Candidate "non-stars" with diameters greater than 15 arcsec were selected from the GSC 2.3.2 catalog and cross-comparison of observations in several bands using archived GALEX, DSS2, WISE, and Two Micron All Sky Survey images identified contaminating stars, artifacts, and background galaxies, all of which were excluded. The resulting 71 galaxies, many of which were previously uncataloged, comprise a size-limited survey of the region. A majority of the galaxies are in the background of NGC 891 and are for the most part members of the A347 cluster at a distance of about 75 Mpc. The new finds approximately double the known membership of A347, previously thought to be relatively sparse. We identify a total of seven dwarf galaxies, most of which are new discoveries. The newly discovered dwarf galaxies are dim and gas-poor and may be associated with the previously observed arcs of red giant branch halo stars in the halo and the prominent H I filament and the lopsided features in the disk of NGC 891. Several of the dwarfs show signs of disruption, consistent with being remnants of an ancient collision.

Schulz, Earl

2014-07-01

94

Barred S0 galaxies in the Coma cluster  

NASA Astrophysics Data System (ADS)

This study uses r-band images from the Eighth Data Release of the Sloan Digital Sky Survey (SDSS DR8) to study bars in lenticular (S0) galaxies in one of the nearest rich cluster environments, the Coma cluster. We develop techniques for bar detection and assess their success when applied to SDSS image data. To detect and characterize bars, we perform 2D bulge+disc+bar light decompositions of galaxy images with GALFIT. Using a sample of artificial galaxy images, we determine the faintest magnitude at which bars can be successfully measured at the depth and resolution of SDSS. We perform detailed decompositions of 83 S0 galaxies in Coma, 64 from a central sample, and 19 from a cluster outskirt sample. For the central sample, the S0 bar fraction is 72^{+5}_{-6} per cent. This value is significantly higher than that obtained using an ellipse-fitting method for bar detection, 48^{+6}_{-6} per cent. At a fixed luminosity, barred S0s are redder in g - r colour than unbarred S0s by 0.02 mag. The frequency and strength of bars increase towards fainter luminosities. Neither central metallicity nor stellar age distributions differ significantly between barred and unbarred S0s. There is an increase in the bar fraction towards the cluster core, but this is at a low significance level. Bars have at most a weak correlation with cluster-centric radius.

Lansbury, George B.; Lucey, John R.; Smith, Russell J.

2014-04-01

95

Kinematics of the anemic cluster galaxy NGC 4548. Is stripping still active?  

NASA Astrophysics Data System (ADS)

We present new Hi (20'' resolution) and CO observations of NGC 4548, an anemic galaxy in the Virgo cluster. The atomic gas distribution shows a ring structure which is distorted at the northern edge. The overall rotation curve is derived with a tilted ring model. We compare our rotation curve with previous ones and discuss the differences. The velocity field of the CO pointings fits very well with the one of the atomic gas where they overlap. The CO emission permits the extension of the rotation curve towards the galaxy centre. The molecular fraction is derived for the inner 120''x 120'' centered on the galaxy. We compare the Hi and CO emission to H? line and optical blue emission maps. The bar in the centre favors star formation at the outer end of the bar. The Hi intensity distribution and velocity field of the northern perturbation are deprojected with the help of a first order kinematical model. They are discussed in the framework of warps. It is concluded that the scenario of ram pressure stripping responsible for the gas removal and the northern perturbation is a very probable one. In this case the ram pressure which may have caused the galaxy's Hi deficiency is now fading after the galaxy's close passage to the cluster centre or increasing again due to a second approach of the galaxy to the cluster centre.

Vollmer, B.; Cayatte, V.; Boselli, A.; Balkowski, C.; Duschl, W. J.

1999-09-01

96

On the Formation and Evolution of Stellar Bars in Galaxies  

NASA Astrophysics Data System (ADS)

We have done a detailed study on the structural and kinematical properties of lenticular and early- and late-type spiral galaxies with bars, aiming to explore the formation and evolution processes of stellar bars in galaxies, and their implications on the global formation and evolution of galaxies. Using high signal-to-noise spectra obtained along the major and minor axes of the bars in a sample of 14 galaxies, we have determined, with an algorithm properly developed for this task, the stellar velocity distribution in the bars' vertical axis, in several points, reaching 20'' from the center. With these data, it was possible to develop a diagnostic tool that allows one to estimate the ages of bars, and distinguish between recently formed bars and evolved bars. Furthermore, we could evaluate the vertical structure of disks and bars in galaxies. Through realistic N-body simulations, we have studied the necessary conditions to the formation of bars in galaxies, as well as the time scale involved in the processes which give bars an important vertical structure. Finally, using images obtained in B, V, R, I and Ks for a sample of 19 galaxies, and images obtained in R for a sample of 51 galaxies, including elliptical galaxies, we have performed a detailed structural analysis in galaxies covering the whole Hubble morphological sequence, determining the structural parameters which describe the bulge and the disk in these galaxies, as well as obtaining residual images which reveal important sub-structures. In order to perform this analysis we have developed a specific algorithm, and built an atlas of structural analysis in galaxies. Among the main results obtained, we point out: (i) there are vertically thin and thick bars and this difference is caused by a difference in the ages of the bars; (ii) the bar thickening process, as we have determined, is slow (~ 5-10 Gyr); (iii) the current scenario for bar formation is not able to explain naturally the existence of bars in galaxies which are kinematically hot and have prominent bulges; (iv) we suggest a new mechanism for bar formation in galaxies, which can account for the serious drawbacks confronted in the current scenario, as well as explain the existence of barred galaxies in which the disk component is almost absent, a discovery which was also a product of this work; (v) bulges in lenticular and in spiral galaxies are, at least partially, formed through the secular evolutionary processes in bars; (vi) during its evolution, a bar grows stronger by capturing stars from the disk, which becomes fainter, in agreement with recent numerical and analytical results; (vii) around 1/3 of the elliptical galaxies harbor inner disks, and (viii) visual morphological classification of galaxies is wrong in nearly 1/3 of the elliptical and lenticular galaxies.

Gadotti, D. A.

2003-12-01

97

Current star formation in S0 galaxies: NGC 4710  

NASA Astrophysics Data System (ADS)

Elliptical (E) and lenticular (S0) galaxies lack the substantial interstellar medium (ISM) found in the star-forming spiral galaxies. However, significant numbers of E and S0 galaxies are known to contain detectable amounts of interstellar matter (e.g., Jura 1988). Thus, it is worth investigating whether these galaxies are currently able to form stars from their ISM, or whether they should be consigned to the dustbin of inert objects (Thronson and Bally 1987). The results strongly imply that current star formation is responsible for NGC 4710's far infrared and radio continuum properties. If this is indeed the case, then one expects this star formation to be fueled by molecular gas, which is presumably dominated by H2 and can be traced by the CO-12 J=1 to 0 line. Both Kenney and Young (1988) and Sage and Wrobel (1989) have detected such an emission line from NGC 4710, and infer the presence of more than 108 solar mass of H2. The origin of the molecular gas in NGC 4710 remains a mystery. The galaxy is very deficient in HI (Kenney and Young, in preparation), suggesting that it originally was a spiral galaxy from which the outer, mainly atomic, gas was stripped by the ram pressure of the Virgo Cluster's intracluster medium, leaving only a central interstellar medium (ISM) rich in molecular gas. Alternatively, the CO may have originated via stellar mass loss with subsequent cooling, cooling flows, or capture from a gas-rich companion. Information on the morphology and kinematics of the CO can be compared with that of the galaxy's other gases and stars to distinguish among these various possible origins for the molecular gas. Major axis CO mapping with single dishes indicate an unresolved source. Thus, a millimeter array is currently being used to image NGC 4710 in CO to provide the needed morphological and kinematical data.

Wrobel, J. M.

1990-07-01

98

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

99

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

100

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

NASA Technical Reports Server (NTRS)

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

Simpson, C.; Meadows, V.

1998-01-01

101

Neutral hydrogen in the starburst galaxy NGC3690/IC694  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

102

Star formation in the merging Galaxy NGC3256  

NASA Technical Reports Server (NTRS)

The central 5 kpc of the ultra-luminous merging galaxy NGC 3256 was mapped at J, H, K, L, and 10 micrometer, and a 2 micrometer spectra of the nuclear region was obtained. This data was used to identify and characterize the super starburst which has apparently been triggered and fuelled by the merger of two gas rich galaxies. It is also shown that the old stellar population has relaxed into a single spheroidal system, and that a supernova driven wind might eventually drive any remaining gas from the system to leave a relic which will be indistinguishable from an elliptical galaxy.

Graham, James R.; Wright, G. S.; Joseph, R. D.; Frogel, J. A.; Phillips, M. M.; Meikle, W. P. S.

1987-01-01

103

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

NASA Astrophysics Data System (ADS)

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

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

2008-06-01

104

Circumnuclear Molecular Gas in Megamaser Disk Galaxies NGC 4388 and NGC 1194  

NASA Astrophysics Data System (ADS)

We explore the warm molecular and ionized gas in the centers of two megamaser disk galaxies using K-band spectroscopy. Our ultimate goal is to determine how gas is funneled onto the accretion disk, here traced by megamaser spots on sub-parsec scales. We present NIR IFU data with a resolution of ~50 pc for two galaxies: NGC 4388 with VLT/SINFONI and NGC 1194 with Keck/OSIRIS+AO. The high spatial resolution and rich spectral diagnostics allow us to study both the stellar and gas kinematics as well as gas excitation on scales only an order of magnitude larger than the maser disk. We find a drop in the stellar velocity dispersion in the inner ~100 pc of NGC 4388, a common signature of a dynamically cold central component seen in many active nuclei. We also see evidence for noncircular gas motions in the molecular hydrogen on similar scales, with the gas kinematics on 100 parsec scales aligned with the megamaser disk. In contrast, the high ionization lines and Br? trace outflow along the 100 parsec-scale jet. In NGC 1194, the continuum from the accreting black hole is very strong, making it difficult to measure robust two-dimensional kinematics, but the spatial distribution and line ratios of the molecular hydrogen and Br? have consistent properties between the two galaxies.

Greene, Jenny E.; Seth, Anil; Lyubenova, Mariya; Walsh, Jonelle; van de Ven, Glenn; Läsker, Ronald

2014-06-01

105

3D spectroscopy of candidate double-barred lenticular galaxies  

NASA Astrophysics Data System (ADS)

A significant fraction of barred galaxies hosts secondary bar-like structures on optical and NIR images. The circumnuclear dynamics of double-barred objects are still not well understood, while observational data concerning kinematics are incomplete and inconsistent. In order to compare the simulations results with observations, we have started a new spectroscopic study of the stellar kinematics in lenticular galaxies from Peter Erwin's catalog of secondary bars. We present first results concerning their stellar kinematics based on the observations performed with the integral-field spectrograph MPFS at the Russian 6-m telescope.

Moiseev, A. V.

106

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

107

A Survey of Satellite Galaxies around NGC 4258  

NASA Astrophysics Data System (ADS)

We conduct a survey of satellite galaxies around the nearby spiral NGC 4258 by combining spectroscopic observations from the Apache Point Observatory 3.5 m telescope with Sloan Digital Sky Survey (SDSS) spectra. New spectroscopy is obtained for 15 galaxies. Of the 47 observed objects, we categorize 8 of them as probable satellites, 8 as possible satellites, and 17 as unlikely to be satellites. We do not speculate on the membership of the remaining 14 galaxies due to a lack of velocity and distance information. Radially integrating our best-fit NFW profile for NGC 4258 yields a total mass of 1.8 × 1012 M ? within 200 kpc. We find that the angular distribution of the satellites appears to be random, and not preferentially aligned with the disk of NGC 4258. In addition, many of the probable satellite galaxies have blue u–r colors and appear to be star-forming irregulars in SDSS images; this stands in contrast to the low number of blue satellites in the Milky Way and M31 systems at comparable distances.

Spencer, Meghin; Loebman, Sarah; Yoachim, Peter

2014-06-01

108

Ultraviolet imaging of the AGN+starburst galaxy NGC 1068  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

109

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

110

A multispecies survey of the active galaxy NGC1068  

NASA Astrophysics Data System (ADS)

The nearby Seyfert galaxy NGC 1068 is among the very few objects where nuclear starburst regions and Active Galactic Nuclei (AGN) can be spatially resolved with current millimeter--wavelength telescopes. We present a multispecies survey of molecular lines in this galaxy carried out with the IRAM Plateau de Bure Interferometer. Thanks to the high spatial-resolution achieved, we distinguish the circumnuclear disk (CND) that surrounds the active nucleus of the galaxy from the outer starburst ring. We mapped the line emission of the most common tracers of UV-ray- X-ray- and shock-driven molecular chemistry in external galaxies (e.g., HCN, HCO^+, HNC, CN, SiO). This help us assess the importance of the main mechanisms whereby massive star formation and AGN may inject energy into the interstellar medium. We measure line ratios that evidence chemical/excitation differences between the AGN- and starburst-dominated environments in NGC 1068. Gradients of several line ratios within the CND support a complex picture of this region, where energy might be radiatively and mechanically injected at different locations. We consider the implications of our results for diagnostics of AGN- and starburst-driven feedback based on molecular lines. We also discuss whether molecular lines can fairly trace molecular mass in AGN and starburst galaxies, as commonly assumed in studies of star-forming laws in galaxies.

Usero, A.; Garcia-Burillo, S.; Fuente, A.; Aalto, S.; Neri, R.; Krips, M.

2011-05-01

111

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

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

112

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

SciTech Connect

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

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

2013-03-15

113

Dynamics of the Polar Disk Galaxy NGC 4650A  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

114

Gas flow and dark matter in the inner parts of early-type barred galaxies. I. SPH simulations and comparison with the observed kinematics  

NASA Astrophysics Data System (ADS)

This paper presents the dynamical simulations run in the potential derived from the light distribution of 5 late-type barred spiral galaxies (IC 5186, NGC 5728, NGC 7267, NGC 7483 and NGC 5505). The aim is to determine whether the mass distribution together with the hydrodynamical simulations can reproduce the observed line-of-sight velocity curves and the gas morphology in the inner regions of these barred galaxies. The light distribution is obtained from the H-band and the I-band combined. The M/L is determined using population synthesis models. The observations and the methodology of the mass distribution modelling are presented in a companion paper. The SPH models using the stellar mass models obtained directly from the H-band light distributions give a good representation of the gas distribution and dynamics of the modelled galaxies, supporting the maximum disk assumption. This result indicates that the gravitational field in the inner region is mostly provided by the stellar luminous component. When 40% of the total mass is transferred to an axisymmetric dark halo, the modelled kinematics clearly depart from the observed kinematics, whereas the departures are negligible for dark mass halos of 5% and 20% of the total mass. This result sets a lower limit for the contribution of the luminous component of about 80%, which is in agreement with the maximum disk definition of the stellar mass contribution to the rotation curve (about 85% ± 10). This result is in agreement with the results found by \\citet{weiner01} for NGC 4123 using a similar methodology. For two galaxies, NGC 7483 and IC 5186, a very good agreement with the observed data is found. In these cases the non-circular motions can help to break the disk-halo degeneracy. For the other three galaxies (NGC 5728, NGC 7267 and NGC 5505) no definite results are found: for NGC 7267 and NGC 5505 no steady state is reached in the simulations and for NGC 5728 there is no good agreement with the observed kinematics, possibly due to the presence of a secondary bar decoupled from the primary. However, for this latter galaxy the M/L ratio used gives the right amplitude of the rotation curve, in further support of the M/L calculation method used throughout this work. Fast bars give the best fit to the observed kinematics for NGC 7483 and IC 5186 with corotation at the end of the bar for NGC 7483 and at 1.4× Rbar for IC 5186. For NGC 5505 for which no steady state configuration is found, the addition of a rigid halo stabilises the gas flows but the derived kinematics does not fit well the observations. Figures \\ref{fig:vel1}-\\ref{fig:Lz_IC5186}, \\ref{fig:mask_height}, \\ref{fig:height_rc}, \\ref{fig:rc_NGC5728}, \\ref{fig:pv_NGC7483}, \\ref{fig:substract_NGC7483}, \\ref{fig:mask_dm}, \\ref{fig:dm_rc} and \\ref{fig:ngc5505_dm_rc} are only available in electronic form at http://www.edpsciences.org}

Pérez, I.; Fux, R.; Freeman, K.

2004-09-01

115

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

NASA Astrophysics Data System (ADS)

We study the observed correlation between atomic gas content and the likelihood of hosting a large-scale bar in a sample of 2090 disc galaxies. Such a test has never been done before on this scale. We use data on morphologies from the Galaxy Zoo project and information on the galaxies' H I content from the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) blind H I survey. Our main result is that the bar fraction is significantly lower among gas-rich disc galaxies than gas-poor ones. This is not explained by known trends for more massive (stellar) and redder disc galaxies to host more bars and have lower gas fractions: we still see at fixed stellar mass a residual correlation between gas content and bar fraction. We discuss three possible causal explanations: (1) bars in disc galaxies cause atomic gas to be used up more quickly, (2) increasing the atomic gas content in a disc galaxy inhibits bar formation and (3) bar fraction and gas content are both driven by correlation with environmental effects (e.g. tidal triggering of bars, combined with strangulation removing gas). All three explanations are consistent with the observed correlations. In addition our observations suggest bars may reduce or halt star formation in the outer parts of discs by holding back the infall of external gas beyond bar co-rotation, reddening the global colours of barred disc galaxies. This suggests that secular evolution driven by the exchange of angular momentum between stars in the bar, and gas in the disc, acts as a feedback mechanism to regulate star formation in intermediate-mass disc galaxies. This publication has been made possible by the participation of more than 200 000 volunteers in the Galaxy Zoo project. Their contributions are individually acknowledged at South East Physics Network, E-mail: karen.masters@port.ac.ukEinstein fellow.

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

2012-08-01

116

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

117

Study of stellar populations in the bulges of barred galaxies  

NASA Astrophysics Data System (ADS)

Aims: We wish to determine the influence of bars on the building of galaxy bulges through analysis of ages and metallicities derived from stellar absorption line-strength indices. Methods: Long-slit spectroscopy was obtained for a sample of 20 early-type barred galaxies. Line-strength indices were measured and used to derive age and metallicity gradients in the bulge region by comparing them with stellar population models. The same analysis was carried out with similar data for unbarred galaxies taken from the literature. Results: The bulges of barred galaxies seem to be more metal rich, at a given velocity dispersion (?), than the bulges of unbarred galaxies, as measured by a few metallicity sensitive indices. There are indications that the ratio of relative abundance of alpha elements with respect to iron, [E/Fe], derived for the bulges of barred galaxies tend to lie above the values of the unbarred galaxies at a given ?. The metallicity gradients for the majority of the bulges are negative so less metal-rich towards the end of the bulge. The gradient values show a large scatter for galaxies with ? below 150 km s-1. The age distribution is related to the presence of a bulge substructure, such as a nuclear ring or an inner disk. The metallicity of both the bulge and the bar are very well correlated, indicating a close link between the enrichment histories of both components. Conclusions: Bulges of barred early type galaxies might have experienced a different chemical enrichment than do the bulges of unbarred galaxies of the same morphological type, the same central velocity dispersion, and low inclination angles. The hinted stellar populations differences separating the bulges of barred and unbarred galaxies and the strong link between the metallicity of the bulge and the presence of a bar points to scenarios where they both form simultaneously in processes that lead to rapid and massive episodes of star formation, possibly linked to the bar formation. To confirm and generalise the results found here, it would be useful to extend the data set to a larger number of unbarred galaxies and a wider range of morphological types Based on observations obtained at Siding Spring Observatory (RSAA, ANU, Australia) and the INT telescope at the ING, La Palma, Spain.Appendix A is only available in electronic form at http://www.aanda.org

Pérez, I.; Sánchez-Blázquez, P.

2011-05-01

118

The Formation of Nuclear Rings in Barred Spiral Galaxies  

Microsoft Academic Search

Although nuclear rings of gas and star formation are common in barred spiral galaxies, current theories of why and how they form do not provide the level of detail needed to quantify the effect that these rings can have on the fueling of active galactic nuclei and on the evolution of their host galaxy. In this paper we use detailed

Michael W. Regan; Peter J. Teuben

2003-01-01

119

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

120

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

SciTech Connect

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

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

2012-01-15

121

An X-ray and Radio Study of the Seyfert 2 Nucleus in the LSB galaxy NGC~5905  

NASA Astrophysics Data System (ADS)

We present an x-ray and radio study of the barred spiral galaxy NGC5905. This is a low surface brightness galaxy that has a Seyfert2 type nucleus associated with a compact bulge. Not much is known about the x-ray or radio properties of this class of low luminosity, dark matter dominated systems. NGC5905 is interacting with a nearby companion galaxy NGC5908. We used Chandra archival data and GMRT 1280 MHz radio observations to study the x-ray and radio properties of the AGN. The X-ray image shows evidence of an AGN; it has a x-ray luminosity of Log Lx 40. The x-ray spectrum shows significant absorption. We detected diffuse x-ray emission associated with the bulge and inner disk. The radio image shows a compact core associated with the AGN and some extended disk emission due to star formation. We used the x-ray radio fundamental plane correlation to constrain the black hole mass of the AGN. Our results show that though LSB galaxies are usually poorly evolved systems, they can be triggered into nuclear activity through interactions with nearby companion galaxies.

Das, Mousumi; Shastri, Prajval; Alonso-Herrero, Almudena; Raichur, Harsha; Kantharia, Niimisha

2012-07-01

122

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

123

NGC 7217: A Spheroid-dominated, Early-Type Resonance Ring Spiral Galaxy  

NASA Astrophysics Data System (ADS)

NGC 7217 is a well-known northern spiral galaxy which is characterized by flocculent spiral structure and a series of three optical ringlike zones: a nuclear ring 21" in diameter, a weak inner ring 63" in diameter, and a striking outer ring 2'.6 in diameter. The rings all have nearly the same shape and position angle in projection. The appearance of the galaxy suggests that it may be more axisymmetric than the typical spiral galaxy, since there is little evidence for the presence of a bar, oval, or stellar density wave. This makes the origin of the ring features uncertain. In an effort to understand this kind of ringed galaxy, which is by no means typical, we have obtained multicolor CCD BVRI images, accurate surface photometry, mappings of the CO and H I gas distributions, and rotational velocities from H? and H I spectral line data. Our deep surface photometry has revealed an important feature of NGC 7217 that was missed in previous studies: The region occupied by the rings of the galaxy is surrounded by an extensive, nearly circular luminous halo. This halo cannot be merely an extension of the disk component because it is much rounder than the inner regions. Instead, we believe the light represents either the outer regions of the bulge or a separate stellar halo component. We are able to successfully model the luminosity profile in terms of an r114 "spheroid" and an exponential disk with a spheroid-to-total disk (including rings) luminosity ratio of 2.3-2.4. This makes NGC 7217 one of the most spheroid-dominated spirals known, and the finding has important implications for the recent discovery by Merrifield and Kuijken of a significant population of counter-rotating stars in the galaxy. Although the spiral structure of NGC 7217 is flocculent in blue light, there is a definite two-armed stellar spiral in the region of the outer ring. This ring includes about 4.4% of the total blue luminosity and is the locus of most of the recent star formation in the galaxy. The ring is also where we find the H I gas to be concentrated. The galaxy is very gas poor (MH I/L0B = 0.024 Msun/Lsun, B for its morphological type. The H I rotational velocities agree well with published and our new H?-values. Fourier analysis reveals a very weak possible oval distortion in the stellar mass distribution. Using the I-band light distribution to define the potential, we carried out simulations of gas streaming with no self- gravity. A model with a bulge-to-disk mass ratio of 2.4 reproduces the observed optical ring morphology very well. This suggests to us that in spite of the extreme weakness of the observed nonaxisymmetry of this galaxy, this nonaxisymmetry is still sufficient to torque the gas into the usual resonance rings identified in other, more obviously barred galaxies. An additional noteworthy feature that we have identified in a B - I color index map is a symmetric, nuclear dust ring 17" in angular diameter. Other dust lanes are seen mainly on the near side of the galaxy.

Buta, R.; van Driel, W.; Braine, J.; Combes, F.; Wakamatsu, K.; Sofue, Y.; Tomita, A.

1995-09-01

124

Hard Gamma Ray Emission from the Starburst Galaxy NGC 253  

NASA Technical Reports Server (NTRS)

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

Jackson, James M.; Marscher, Alan M.

1996-01-01

125

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

NASA Astrophysics Data System (ADS)

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

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

1995-07-01

126

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

NASA Astrophysics Data System (ADS)

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

Carignan, C.; Puche, D.

1995-08-01

127

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

NASA Astrophysics Data System (ADS)

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

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

1995-07-01

128

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

NASA Astrophysics Data System (ADS)

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

Carignan, C.; Puche, D.

1995-07-01

129

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

NASA Astrophysics Data System (ADS)

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

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

1995-07-01

130

Testing the gravitational field in elliptical galaxies - NGC 5077  

SciTech Connect

The intrinsic shape and the mass distribution of the underlying galaxy of NGC 5077, a southern elliptical galaxy with a disk of ionized gas along its minor axis, are investigated on the basis of observations of the structure and kinematics of this gas disk. It is shown that it is possible to construct realistic triaxial mass models for early-type galaxies. These models suggest that NGC 5077 has a constant M/L of about 4-5 in solar units throughout the central 5-10 kpc. The velocity fields of the triaxial models offer three advantages: they can explain the observed position angle differnce of 23 degrees between the gas rotation axis and the apparent major axis of the stars as being due to a projection effect; they provide a natural explanation for the observed increase in the gas velocity dispersion in the central 2-3 arcsec; and the associated density distributions have small cores, so they do not require M/L to drop to low values in the center. Equilibrium and polar ring models and other galaxies are discussed as well. 71 refs.

Bertola, F.; Bettoni, D.; Danziger, J.; Sadler, E.; Sparke, L. (Padova, Universita, Padua (Italy) Padova, Osservatorio Astronomico, Padua (Italy) European Southern Observatory, Garching (Federal Republic of Germany) Anglo-Australian Observatory, Epping (Australia) Kapteyn Laboratorium, Groningen (Netherlands))

1991-06-01

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

The distance to the giant elliptical galaxy NGC 5128  

NASA Astrophysics Data System (ADS)

The distance to NGC 5128, the central galaxy of the Centaurus group and the nearest giant elliptical to us, has been determined using two independent distance indicators: the Mira period-luminosity (PL) relation and the luminosity of the tip of the red giant branch (RGB). The data were taken at two different locations in the halo of NGC 5128 with the ISAAC near-IR array on ESO VLT. From more than 20 hours of observations with ISAAC a very deep Ks-band luminosity function was constructed. The tip of the RGB is detected at Ks=21.24 ± 0.05 mag. Using an empirical calibration of the K-band RGB tip magnitude, and assuming a mean metallicity of [M/ H]=-0.4 dex and reddening of E(B-V)=0.11, a distance modulus of NGC 5128 of (m-M)0=27.87 ± 0.16 was derived. The comparison of the H-band RGB tip magnitude in NGC 5128 and the Galactic Bulge implies a distance modulus of NGC 5128 of (m-M)0=27.9 ± 0.2 in good agreement with the K-band RGB tip measurement. The inner halo field has larger photometric errors, brighter completeness limits and a larger number of blends. Thus the RGB tip feature is not as sharp as in the outer halo field. The population of stars above the tip of the RGB amounts to 2176 stars in the outer halo field (Field 1) and 6072 stars in the inner halo field (Field 2). The large majority of these sources belong to the asymptotic giant branch (AGB) population in NGC 5128 with numerous long period variables. Mira variables were used to determine the distance of NGC 5128 from a period-luminosity relation calibrated using the Hipparcos parallaxes and LMC Mira period-luminosity relation in the K-band. This is the first Mira period-luminosity relation outside the Local Group. A distance modulus of 27.96 ± 0.11 was derived, adopting the LMC distance modulus of 18.50 ± 0.04. The mean of the two methods yields a distance modulus to NGC 5128 of 27.92 ± 0.19 corresponding to D=3.84 ± 0.35 Mpc. Based on observations collected at the European Southern Observatory, Paranal, Chile, within the Observing Programmes 63.N-0229, 65.N-0164, 67.N-503, 68.B-0129 and 69.B-0292 and at La Silla Observatory, Chile, within the Observing Programme 64.N-0176(B).

Rejkuba, M.

2004-01-01

133

Magnetic Fields in Irregular Galaxies: NGC 4214  

Microsoft Academic Search

Magnetic fields are an important component of the interstellar medium of galaxies. They provide support, transfer energy from supernovae, provide a possible heating mechanism, and channel gas flows (Beck 2004). Despite the importance of magnetic fields in the ISM, it is not well known what generates and sustains galactic magnetic fields or how magnetic fields, gas, and stars interact in

Amanda A. Kepley; E. M. Wilcots; T. Robishaw; C. Heiles; E. Zweibel

2006-01-01

134

Two-micron spectrophotometry of the galaxy NGC 253  

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

135

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

NSDL National Science Digital Library

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

136

The ULX Population in the Starburst Galaxy NGC 253  

NASA Technical Reports Server (NTRS)

Optimism is mounting for the existence of intermediate mass black holes (IMBH), which occupy the mass spectrum somewhere between the stellar-mass and supermassive varieties. IMBH are naturally predicted by theoretical stellar and black hole evolution models, but the strong attention to them began only recently with the discovery of ultraluminous x-ray sources (ULX). If isotropic and accreting normally, ULX have luminosities tens to thousands of times greater than the Eddington luminosity of a neutron star or stellar-mass black hole. A standard interpretation of their x-ray flux implies that they are powered by IMBH. On the other hand, they may be stellar-mass black holes that are beamed or emit anisotropically. Therefore, the exact nature of ULX is highly controversial. ULX are common in starburst galaxies. At a distance of only 3 Mpc, NGC 253 is bright, nearby, and one of the best-studied starburst galaxies. Approximately 50 distinct x-ray point sources are detected in or near the plane of the galaxy. At least six of these are ULX, with luminosities greater than 10 times that expected for a stellar-mass, accreting compact object. We present new Chandra data from an 80 ksec observation of NGC 253 obtained in 2003 that provides high quality spectra of these sources. Comparing the 1999 and 2003 Chandra observations, the sources have varied significantly over the course of four years, with one of the ULX disappearing completely. The ULX spectra are similar to black-hole XRBs and at least one appears to possess an iron K line. We will discuss what insight these data provide for the nature of ULX in NGC 253 .

Weaver, K. A.; Heckman, T. M.; Strickland, D. K.

2004-01-01

137

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

NASA Astrophysics Data System (ADS)

High resolution near infrared array images of the nuclear regions of two merging galaxy systems, NGC 1614 and NGC 520, are presented. The broadband photometric images at 1.25, 1.65, and 2.23 micron wavelengths and the CO bandhead (2.3 microns) absorption index measurements are used to investigate the spatial distribution of starburst activity and extinction in the central regions of these merging systems. The broadband near infrared colors of each of these objects indicate an anomalously red composition, even when corrected for extinction using extinction models ranging from a uniform foreground screen of absorbing material to a distribution of absorbing material fully mixed with the infrared emission sources. This red color may indicate the presence of substantial amounts of hot dust (1000 K) in the merger cores; in the case of NGC 1614, 3 micron continuum measurements by Mizutani, et al. (1994) allow us to estimate the contribution of such hot dust grains to the shorter wavelength near infrared colors. Once that contribution, negligible at 1.25 and 1.65 microns but not at 2.23 microns, is subtracted, the nuclear colors are consistent, within the photometric uncertainties, with red giant and supergiant colors. This, along with the strong CO bandhead index measured for the nuclei of these galaxies, indicates that starbursts containing large numbers of red supergiant stars are responsible for the near infrared emission in these merger cores. No indication of an underlying unresolved central engine is seen from the near infrared broadband emission in either galaxy.

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

1997-05-01

138

Peculiarities in the optical variability of the galaxy NGC 4151  

SciTech Connect

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

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

1981-11-01

139

Photodissociation Chemistry Footprints in the Starburst Galaxy NGC 253  

NASA Astrophysics Data System (ADS)

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+ and CO+, 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+ detection suffers from significant blending to a group of transitions of 13CH3OH, 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.

Martín, Sergio; Martín-Pintado, J.; Viti, S.

2009-12-01

140

The Formation of Nuclear Rings in Barred Spiral Galaxies  

NASA Astrophysics Data System (ADS)

Although nuclear rings of gas and star formation are common in barred spiral galaxies, current theories of why and how they form do not provide the level of detail needed to quantify the effect that these rings can have on the fueling of active galactic nuclei and on the evolution of their host galaxy. In this paper we use detailed modeling to show that existence of nuclear rings is directly related to the existence of the orbit family whose major axis is perpendicular to the major axis of the bar (x2). We explore a large range of barred galaxy potentials, and for each potential we use a two-dimensional hydrodynamic simulation to determine whether and at what radius a nuclear ring forms. We compare the results of the hydrodynamic simulations to numerical integrations of periodic orbits in a barred potential and show that the rings only form when a minimum number of x2 orbits exist. Because the rings migrate inward with time as they accumulate gas, the radius at which a nuclear ring is seen does not give direct information on the shape of the rotation curve. We also show that the common assumption that nuclear rings are related to an inner Lindblad resonance is incorrect. In fact, we show that there is no resonance at the inner Lindblad resonance in barred galaxies. We also compare the predictions of this theory to Hubble Space Telescope observations and show that it correctly predicts the observed gas and star formation morphology of nuclear rings.

Regan, Michael W.; Teuben, Peter

2003-01-01

141

Arecibo Galaxy Environment Survey: Visualizing the Volumes of Isolated Galaxies NGC 5523 & UGC 2082  

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 analyzed the isolated NGC 5523 & UGC 2082 regions, two 5 square degrees fields obtained with the Wideband Arecibo Pulsar Processor (WAPP) correlators covering a redshift range of z ~ 0 - 0.06. A number of possibly interacting galactic systems were identified by their HI structure. Particularly, a lack of companions to NGC 5523 was found to a lower limit of 9*10^6 solar masses (NGC 5523 is at a distance of approximately 20 Mpc). Additionally, I studied the reliability and completeness of automated source extraction techniques. Finally, I employed novel forms of data visualisation in order to investigate the volume behind these two isolated galaxies, which resulted in the production a catalogue containing measured parameters such as flux, HI mass, velocity width, position fitting, mass-to-light ratios and gas deficiencies for the detected sources.

Rodriguez, Roberto A.; Minchin, R. F.; Taylor, R.

2014-01-01

142

Bars, Ovals, and Lenses in Early-Type Disk Galaxies: Probes of Galaxy Evolution  

NASA Astrophysics Data System (ADS)

The origin of S0 galaxies is discussed in the framework of early mergers in a cold dark matter cosmology, and in a scenario where S0s are assumed to be former spirals stripped of gas. From an analysis of 127 early-type disk galaxies (S0-Sa), we find a clear correlation between the scale parameters of the bulge (r eff) and the disk (h R), a correlation which is difficult to explain if these galaxies were formed in mergers of disk galaxies. However, the stripping hypothesis, including quiescent star formation, is not sufficient to explain the origin of S0s either, because it is not compatible with our finding that S0s have a significantly smaller fraction of bars (46% ± 6%) than their assumed progenitors, S0/a galaxies (93% ± 5%) or spirals (64%-69%). Our conclusion is that even if a large majority of S0s were descendants of spiral galaxies, bars and ovals must play an important role in their evolution. The smaller fraction particularly of strong bars in S0 galaxies is compensated by a larger fraction of ovals/lenses (97% ± 2% compared to 82%-83% in spirals), many of which might be weakened bars. We also found massive disklike bulges in nine of the S0 galaxies, which might have formed at an early gas-rich stage of galaxy evolution.

Laurikainen, E.; Salo, H.; Buta, R.; Knapen, J. H.

2009-02-01

143

Genesis of the ring galaxy Arp 144 (NGC 7828/29)  

SciTech Connect

Multicolor near-infrared images have been obtained for the folded ring galaxy Arp 144 (NGC 7828/29). About 10 to the 10th solar mass stellar nuclei associated with both NGC 7828 and NGC 7829 are found, indicating that this system is the result of an interaction between two similarly massive galaxies. The galaxy/intergalactic H I cloud collision model proposed by Freeman and de Vaucouleurs (1974) appears to be untenable, since it unequivocally predicts the existence of a single evolved stellar nucleus. 18 references.

Joy, M.; Ellis, H.B. Jr.; Tollestrup, E.V.; Brock, D.; Higdon, J.L.

1988-07-01

144

The genesis of the ring galaxy Arp 144 (NGC 7828/29)  

NASA Technical Reports Server (NTRS)

Multicolor near-infrared images have been obtained for the 'folded ring' galaxy Arp 144 (NGC 7828/29). About 10 to the 10th solar mass stellar nuclei associated with both NGC 7828 and NGC 7829 are found, indicating that this system is the result of an interaction between two similarly massive galaxies. The galaxy/intergalactic H I cloud collision model proposed by Freeman and de Vaucouleurs (1974) appears to be untenable, since it unequivocally predicts the existence of a single evolved stellar nucleus.

Joy, Marshall; Ellis, H. B., Jr.; Tollestrup, E. V.; Brock, D.; Higdon, J. L.

1988-01-01

145

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

146

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.

2013-12-01

147

Local Group Dwarf Elliptical Galaxies. I. Mapping the Dynamics of NGC 205 Beyond the Tidal Radius  

NASA Astrophysics Data System (ADS)

NGC 205 is the nearest example of a dwarf elliptical galaxy and the prototype of this enigmatic galaxy class. Photometric evidence suggests that NGC 205, a close satellite of the M31 galaxy, is tidally interacting with its parent galaxy. We present stellar radial velocity measurements out to a projected radius of 20' (5 kpc) in NGC 205 based on Keck DEIMOS multislit spectroscopic observations of 725 individual red giant branch stars. Our kinematic measurements extend from the center out to 6 times the effective radius of NGC 205, well past the expected tidal radius. The contamination in our kinematic sample from M31 field stars is estimated to be a few percent based on maximum likelihood fits to the distribution of stars in position-velocity space. We measure a maximum major-axis rotation speed for the body of NGC 205 of 11+/-5 km s-1 and note that this is based on observing a definite turnover in the rotation curve; this is the first dE galaxy in which the maximum rotation velocity has been measured. Combined with the velocity dispersion, we conclude that NGC 205 is supported by a combination of rotation and anisotropic velocity dispersion. At a major-axis distance of 4.5 arcmin (1 kpc), the velocity profile of NGC 205 turns over; stars beyond this radius are moving counter to the rotation of the inner part of the galaxy. The turnover radius is coincident with the onset of isophotal twisting and the estimated tidal radius, suggesting that the outer kinematics of NGC 205 is dominated by gravitational interactions with the nearby M31 galaxy. The motion of stars beyond a radius of ~4.5 arcmin implies that NGC 205 is in a prograde encounter with its parent galaxy, M31.

Geha, M.; Guhathakurta, P.; Rich, R. M.; Cooper, M. C.

2006-01-01

148

The complex nature of the Seyfert galaxy NGC 7592  

NASA Technical Reports Server (NTRS)

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

Rafanelli, Piero; Marziani, Paolo

1990-01-01

149

Hubble Space Telescope Pixel Analysis of the Interacting S0 Galaxy NGC 5195 (M51B)  

NASA Astrophysics Data System (ADS)

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 < ?? 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

2012-08-01

150

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

151

Aperture Synthesis Study of Neutral Hydrogen in the Galaxies NGC 6946 and IC 342.  

National Technical Information Service (NTIS)

Synthesis observations of netural hydrogen emission in the two spiral galaxies NGC 6946 and IC 342 are presented. The velocity resolution is 21 km/s and the angular resolution is 2 and 4 min of arc for NGC 6946 and IC 342 respectively. Results are present...

D. H. Rogstad, G. S. Shostak, A. H. Rots

1972-01-01

152

Seeing Galaxies through Thick and Thin. IV. The Superposed Spiral Galaxies of NGC 3314  

NASA Astrophysics Data System (ADS)

The superposed pair of spiral galaxies making up NGC 3314 offers a unique opportunity to trace the dust properties in a spiral galaxy. We analyze multicolor Hubble Space Telescope imaging, supported by ground-based near-IR imaging and fiber-array spectroscopy, to measure dust extinction in the foreground Sc galaxy NGC 3314A, which is backlit by the Sb system NGC 3314B. The superposition allows us to measure extinctions over a wide range of galactocentric radii in the foreground galaxy from 0.4-4.5 kpc. In the outer half of the disk, the extinction is strongly localized in discrete dust lanes, including some patches whose galactic setting is clear only because of associated H? emission at the foreground velocity. These dust features show an extinction curve with a slope close to the Galactic mean (R=3.5+/-0.3) over a range in galactocentric radius from 1.6 to 3.8 kpc, with no radial trend. Using the I-K color of the background nucleus, we derive an extinction of AI=3.3 through the disk at a projected distance of 400 pc from the nucleus of NGC 3314A. The extinction in even the inner disk of NGC 3314A is quite patchy, since background H? emission is detected from all parts of the system. Local anticorrelations between foreground and background line emission demonstrate that the dust is concentrated in star-forming regions, as has been found for the blue light in several systems. The colors of the dust lanes in NGC 3314A that are projected only partially against the background disk indicate that the dust scale height in the foreground disk is substantially smaller than that of the stars. The color-intensity behavior of the net light in these regions tracks the predictions of a thin-layer model closely. Based on observations 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.

Keel, William C.; White, Raymond E., III

2001-09-01

153

Inclined Gas Disks in the Lenticular Seyfert Galaxy NGC 5252  

NASA Astrophysics Data System (ADS)

We discuss the morphology and kinematics of the extended gas in the type 2 Seyfert galaxy NGC 5252 based on Hubble Space Telescope (HST) WFPC2 continuum and emission-line images (including a new [O III] ?5007 image) and a ground-based Fabry-Perot (F-P) velocity map of the ionized gas. The fine-scale morphology of the ionized gas in this galaxy's very extended (~40 kpc) ionization bicone consists of a complex network of filamentary strands. The new WFPC2 [O III] image also reveals more detail in the circumnuclear (~3 kpc) gas disk than is seen in the H? + [N II] image presented previously by Tsvetanov and coworkers. The F-P velocity map shows an obvious antisymmetry of the velocity field of the ionized gas across the nucleus. We conclude that there are three dynamical components to the extended gas in NGC 5252. Two of these components are gas disks aligned with the stellar disk, one rotating with the stars and the other counterrotating. The third component is the circumnuclear gas disk seen in the HST observations and its extension to larger scales; this disk has an inclination of ~40° and a kinematic major axis in P.A. ~ 90°-135°, some 80°-125° from the major axis of the stellar disk. This simple model of two inclined rotating disks, superposed along the line of sight, describes well the seemingly complex kinematics observed in the optical emission lines and the H I 21 cm radio maps. The large misalignment between the second disk and the stellar disk suggests that the gas distribution, and possibly the nuclear activity, in NGC 5252 may have resulted from a galaxy merger event. The absence of significant radial motions, together with the well-defined ionization cones, strongly suggests that the gas is photoionized by a compact nuclear source rather than being ionized in situ by shock waves in a large-scale outflow. Based in part on observations with the NASA ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

Morse, Jon A.; Cecil, Gerald; Wilson, Andrew S.; Tsvetanov, Zlatan I.

1998-09-01

154

Magnetic spiral arms in the galaxy NGC6946  

NASA Astrophysics Data System (ADS)

MAGNETIC fields pervade spiral galaxies1-at least all those searched so far; these fields have a substantial energy density, and hence could play an important role in galaxy evolution. Dynamo theory has been used for many years to explain the presence and overall structure of galactic magnetic fields, through the amplification of a weak seed field2,3. Here we report the observation of two 'magnetic spiral arms' in the nearby galaxy NGC6946, lying between the optical spiral arms. This is surprising because dynamo action is thought to be related to star formation activity4, which is concentrated within or in the leading edges of the optical spiral arms. The magnetic spiral arms are about 500-1,000 parsecs wide and more than 12 kiloparsecs long, and have greater symmetry than the optical arms. This organized structure probably reflects the signature of some global mechanism relating to magnetic field generation, but no current theory-in particular dynamo theory in its present form-is able to explain this phenomenon.

Beck, R.; Hoernes, P.

1996-01-01

155

Diffuse Ionized Gas inside the Dwarf Irregular Galaxy NGC 6822  

NASA Astrophysics Data System (ADS)

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

Hidalgo-Gámez, A. M.; Peimbert, A.

2007-05-01

156

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

Microsoft Academic Search

A few nearby interacting galaxies are known that host elevated numbers of ultraluminous X-ray sources. Here we report the results of a multiwavelength study of the X-ray source population in the field of the interacting pair of galaxies NGC 5774\\/5775. A total of 49 discrete sources are detected, including 12 ultraluminous X-ray source candidates with luminosities above 1039 erg s-1

Kajal K. Ghosh; Lakshmi Saripalli; Poshak Gandhi; Cédric Foellmi; Carlos M. Gutiérrez; Martin López-Corredoira

2009-01-01

157

IUE and Einstein observations of the LINER galaxy NGC 4579  

NASA Technical Reports Server (NTRS)

Results of International Ultraviolet Explorer (IUE) and Einstein observations of the LINER galaxy NGC 4579 are reported. Spatial profiles of the long wavelength IUE emission show a two component structure, with an unresolved core superimposed on broader underlying emission. The core spectrum shows strong C II lambda 2326 and broad Mg II lambda 2800 emission, and perhaps emission due to blends of Fe II multiplets (2300 to 23600 angstrom). The short wavelength emission is spatially unresolved, and shows C II lambda 1335, C III lambda 1909 broad C IV lambda 1550 emission, and a broad feature at approximately 1360 angstrom which may be due to 0.1 lambda 1356. Contrary to previous reports no evidence for He II lambda 1640 is found in the spectrum. An unresolved x ray source is detected at the location of the nucleus; its spectrum is well fitted by a power law of energy slope alpha approximately -0.5. These results further support the idea that NGC 4579 may contain a dwarf Seyfert nucleus.

Reichert, G. A.; Puchnarewicz, E. M.; Mason, K. O.

1990-01-01

158

Line asymmetry in the Seyfert Galaxy NGC 3783  

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

159

Structure of the nucleus of the Seyfert galaxy NGC 1275  

SciTech Connect

The nucleus of the Seyfert galaxy NGC 1275 has been surveyed at 1.35-cm wavelength with the Haystack--Green Bank--Effelsberg--Onsala--Crimea radio-interferometer network. Its structure comprises eastern and western systems of features, separated by 0.7 pc. The eastern system has a core embedded in an absorbing medium whose electron density depends on distance L as N/sub e/approx. =4 x 10/sup 45/ L/sup -2.3plus-or-minus0.5/. The compact components, which measure approx. =0''.0001 across, have a magnetic field strength Happrox. =0.3 gauss. All fine-structure components maintain stable positions, but their brightness is variable. The radio brightness distribution is probably governed by the magnetic field structure.

Matveenko, L.I.; Kellermann, K.I.; Pauliny-Toth, I.I.K.; Kostenko, V.I.; Moiseev, I.G.; Kogan, L.R.; Witzel, A.; Roennaeng, B.O.; Shaffer, D.B.; Preuss, E.

1980-01-01

160

Clumpy metal concentrations in elliptical galaxies NGC 4374 and NGC 4636  

NASA Astrophysics Data System (ADS)

We present a high spatial resolution study of metal distributions in the nearby, gas-rich elliptical galaxies NGC 4374 and NGC 4636 with the Chandra ACIS archive data. We define the hardness ratio HRFeL as the ratio of the emission in 0.65-1.4 keV to that in 0.3-0.6 keV and 1.4-3.5 keV (after the magnesium and silicon lines are excluded), and HRcont as the ratio of the emission in 1.4-3.5 keV to that in 0.3-0.6 keV, so that the HRFeL and HRcont maps can be used to trace the iron abundance and gas temperature distributions, respectively. By applying the à Trous wavelet algorithm to the obtained emission hardness ratio maps, we reveal that the HRFeL distributions are highly irregular, exhibiting strong spatial variations on 0.1-1 Re scales, which do not follow the HRcont distributions. Since the effect of temperature variation is small, we conclude that most of the high-HRFeL regions are very likely to possess higher abundances than the ambient gas. We also find that these high-HRFeL substructures are not associated with either the LMXB or globular cluster populations, thus their origins should be related to AGN activity or mergers.

Xu, Hai-Guang; Gu, Jun-Hua; Gu, Li-Yi; Zhang, Zhong-Li; Wang, Yu; An, Tao

2010-03-01

161

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

162

Superassociations at the ends of the bars in spiral Markarian galaxies  

Microsoft Academic Search

A sample of 130 barred spiral Markarian galaxies has been compiled on the basis of large-scale photographs. It is shown that 51 of the galaxies do not contain superassociations (SAs) at the end of the bars, 31 contain SAs at one end of the bar, and 48 have SAs at both ends. Factors affecting the frequency of SA occurrence at

A. R. Petrosian; K. A. Sahakian

1990-01-01

163

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

164

Bar-driven spiral waves in disk galaxies  

NASA Technical Reports Server (NTRS)

The response of rotating disks of gas to barlike perturbations in galactic gravitational fields is investigated. In particular, two-dimensional time-dependent numerical hydrodynamical calculations have been performed in order to determine the steady-state response of disks of gas to rotating barlike perturbations. Two types of barlike perturbations are considered: oval distortions in the axisymmetric gravitational field of the disk, and heterogeneous prolate spheroids. The calculations reveal that in the absence of gaseous self-gravity, a viscous differentially rotating disk of gas responds to a rotating barlike perturbation by forming a central gas bar with two trailing spiral waves. The local phase of the gas response is primarily a function of the number and spacing of the principal resonances in the disk. This result may be understood in terms of particle orbit theory. The gas response to barlike perturbations also depends on the relative strength and the effective axial ratio of the bar. In these calculations strong narrow bars produce offset shocks in the central gas bar. These shocks correspond in position to the long narrow dust lanes observed in many barred spiral galaxies.

Huntley, J. M.; Sanders, R. H.; Roberts, W. W., Jr.

1978-01-01

165

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

166

Pre-peak ram pressure stripping in the Virgo cluster spiral galaxy NGC 4501  

Microsoft Academic Search

VIVA Hi observations of the Virgo spiral galaxy NGC 4501 are presented. The Hi disk is sharply truncated to the southwest, well within the stellar disk. A region of low surface-density gas, which is more extended than the main Hi disk, is discovered northeast of the galaxy center. These data are compared to existing 6 cm polarized radio continuum emission,

B. Vollmer; M. Soida; A. Chung; J. H. van Gorkom; K. Otmianowska-Mazur; R. Beck; M. Urbanik; J. D. P. Kenney

2008-01-01

167

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

168

Triple Scoop from Galaxy Hunter  

NASA Technical Reports Server (NTRS)

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

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

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

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

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

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

2006-01-01

169

NGC 4656UV: A UV-SELECTED TIDAL DWARF GALAXY CANDIDATE  

SciTech Connect

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{sub Sun} yr{sup -1} from the far-ultraviolet flux and measure a total H I mass of 3.8 Multiplication-Sign 10{sup 8} M{sub Sun} 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 {approx}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.

Schechtman-Rook, Andrew; Hess, Kelley M., E-mail: andrew@astro.wisc.edu, E-mail: hess@ast.uct.ac.za [Department of Astronomy, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI 53706 (United States)

2012-05-10

170

Structure of the galaxies of the NGC 80 group: Two-tiered disks  

NASA Astrophysics Data System (ADS)

Two-color photometric data obtained on the 6-m telescope of the Special Astrophysical Observatory are used to analyze the structure of 13 large disk galaxies in the NGC 80 group. Nine of the 13 studied galaxies are classified as lenticular galaxies. The stellar populations in the galaxies are very diverse, from old stars with ages of T > 10 billion years (IC 1541) to relatively young stars with ages of T ˜ 1-3 billion years (IC 1548, NGC 85); in one case, star formation is ongoing (UCM 0018+2216). In most of the studied galaxies, more precisely in all of them brighter than M B ˜ -18, two-tiered stellar disks are detected, whose radial surface-brightness profiles can be described by two exponential segments with different characteristic scales—shorter near the center and longer at the periphery. All of the dwarf S0 galaxies with single-tiered disks are close companions to larger galaxies. Except for this fact, no dependence of the properties of S0 galaxies on distance from the center of the group is found. Morphological signs of a "minor merger" are found in the lenticular galaxy NGC 85. Based on these last two results, it is concluded that the most probable mechanism for their transformation of spiral into lenticular galaxies in groups is gravitational (minor mergers and tidal interactions).

Startseva, M. A.; Sil'Chenko, O. K.; Moiseev, A. V.

2009-12-01

171

Spatially-resolved 3 Micron Spectroscopy of NGC 7027 and the Orion Bar  

NASA Astrophysics Data System (ADS)

We have obtained moderate resolution (R 2000) spatially-resolved spectroscopy of NGC 7027 and the Orion Bar in order to investigate the spatial evolution of the 3.3 micron polycyclic aromatic hydrocarbon (PAH) emission band and its associated bands at 3.4, 3.46, 3.51, and 3.56 microns. These observations were performed at the Keck Observatory with the NIRSPEC instrument by systematically stepping the entrance slit across the extended, obtaining 3.0-3.8 micron spectra at each position. This procedure creates a data cube for each object with two spatial dimensions and one spectral dimension. Spectra at each spatial position were fitted with a series of gaussians to measure the central wavelength, FWHM and total flux of each feature. Spatial distribution and spatial variation of hydrocarbon features was examined and compared to that of HeII, Pfund delta and Pfund gamma atomic emission. We find that the hydrocarbon bands show a different spatial distribution than that of the atomic emission. In NGC 7027 hydrocarbon distribution was bi-polar in nature, while atomic emission was ring-like. In the Orion Bar hydrocarbon emission was offset from atomic emission by 2-3 arcseconds. Although similar in overall spatial distribution, individual hydrocarbon features exhibited correlations, most significantly between the 3.4 and 3.51 micron features, suggesting a common carrier.

Smith, Erin C.; McLean, I.

2009-01-01

172

A GIANT STAR FACTORY IN NEIGHBORING GALAXY NGC 6822  

NASA Technical Reports Server (NTRS)

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

2002-01-01

173

Dynamical model of the grand-design spiral galaxy NGC 157  

Microsoft Academic Search

Numerical simulations of the interstellar medium under the action of a density wave provide an accurate method for determining the positions of the main resonances in grand-design spiral galaxies. Barred spiral galaxies are among the best candidates for a single and well defined wave mode, because bars are standing waves which may share the same pattern speed as the spiral

M. J. Sempere; M. Rozas

1997-01-01

174

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

175

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

176

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

Microsoft Academic Search

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

Bradley C. Whitmore; Francois Schweizer

1995-01-01

177

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

178

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

179

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

Microsoft Academic Search

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

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

1994-01-01

180

First Observations of Individual Molecular Clouds in the Irregular Galaxy NGC 6822  

Microsoft Academic Search

Three molecular clouds have been mapped in the nearby metal-poor dwarf\\u000airregular galaxy NGC 6822 using the Owens Valley Millimeter-Wave\\u000aInterferometer. Based on upper limits to the virial masses of the clouds, the\\u000aCO-to-H2 conversion factor in NGC 6822 is <2.2+\\/-1.3 times larger than the\\u000aGalactic value. Conversion factors obtained for Galactic molecular clouds,\\u000a NGC 6822, and the SMC are

Christine D. Wilson

1994-01-01

181

Gravitational Microlensing in the NGC 3314A-B Galaxy Pair  

NASA Astrophysics Data System (ADS)

Determining the composition of the dark matter that dominates the masses of galaxies is an important unsolved problem, and the results of the MACHO Collaboration suggest that some of Milky Way's dark matter may be in the form of very old white dwarfs. However, some have argued that the excess of microlensing events seen by MACHO are due to a larger than expected microlensing rate for lens stars in the LMC itself or its tidal debris. We propose to address this question by detecting microlensing events in the line-of-sight galaxy pair NGC 3314 A & B. The large line-of-sight distance between these galaxies gives an optical depth that is 3-4 orders of magnitude larger than if the source stars and lenses were in the same galaxy, and the fact that the background galaxy is a spiral ensures that there will be a sufficient number of bright, non-variable source stars. Our proposed observations should have the sensitivity to detect microlensing by both ordinary stars and dark matter in NGC 3314A {the foreground galaxy}. If there are dark matter microlensing events to be found, they can be clearly distinguished from stellar microlensing events because they will occur outside the visible disk of NGC 3314A. If baryonic dark matter is detected in NGC 3314A, we will be able to map its radial density variation.

Bennett, David

2002-07-01

182

Gravitational Microlensing in the NGC 3314A-B Galaxy Pair  

NASA Astrophysics Data System (ADS)

Determining the composition of the dark matter that dominates the masses of galaxies is an important unsolved problem, and the results of the MACHO Collaboration suggest that some of Milky Way's dark matter may be in the form of very old white dwarfs. However, some have argued that the excess of microlensing events seen by MACHO are due to a larger than expected microlensing rate for lens stars in the LMC itself or its tidal debris. We propose to address this question by detecting microlensing events in the line-of-sight galaxy pair NGC 3314 A & B. The large line-of-sight distance between these galaxies gives an optical depth that is 3-4 orders of magnitude larger than if the source stars and lenses were in the same galaxy, and the fact that the background galaxy is a spiral ensures that there will be a sufficient number of bright, non-variable source stars. Our proposed observations should have the sensitivity to detect microlensing by both ordinary stars and dark matter in NGC 3314A {the foreground galaxy}. If there are dark matter microlensing events to be found, they can be clearly distinguished from stellar microlensing events because they will occur outside the visible disk of NGC 3314A. If baryonic dark matter is detected in NGC 3314A, we will be able to map its radial density variation.

Bennett, David

2003-07-01

183

New Cepheid distances to nearby galaxies based on BVRI CCD photometry. III - NGC 300  

NASA Technical Reports Server (NTRS)

A true distance modulus of (m - M) sub 0 = 26.66 +/- 0.10 mag (corresponding to 2.1 +/- 0.1 Mpc) has been determined for the Sculptor Group spiral galaxy NGC 300. New CCD data have been obtained for a sample of known Cepheids in this galaxy from which apparent distance moduli at B, V, R, and I wavelengths are determined. Combining the data available at different wavelenghts, and assuming a true distance modulus to the LMC of 18.5 mag, a true distance modulus is obtained for NGC 300, corrected for the effects of interstellar reddening. The availability of a new distance to NGC 300 brings to five the total number of galaxies with new CCD photometry of Cepheids, useful for calibration of the Hubble constant.

Freedman, Wendy L.; Madore, Barry F.; Hawley, S. L.; Horowitz, Irwin K.; Mould, Jeremy; Navarrete, Mauricio; Sallmen, Shauna

1992-01-01

184

The filaments of NGC 1275 - A collision between a galaxy and an accretion flow?  

NASA Technical Reports Server (NTRS)

Morphological evidence is presented (in the form of 3-A-bandpass Fabry-Perot images made with a CCD camera) that the two bright emission-line systems seen toward the galaxy NGC 1275 arise from a high-velocity impact of a foreground galaxy upon the accretion flow of gas cooling in the center of the Perseus cluster. The uniquely high optical-line luminosity of NGC 1275, in comparison with other central galaxies in clusters observed to have cooling flows, may be explained by energy deposited during the collision. Using additional information from 21-cm and extinction measurements, a rough model of the interaction is developed. Problems remain with this model - such as the likelihood of a gas-rich system penetrating to the cluster center. The kinematic structure of the optically emitting gas shows additional complex structure near the nucleus of NGC 1275.

Kaaret, P.; York, D. G.; Roesler, F. L.; Hu, E. M.; Cowie, L. L.; Jenkins, E. B.

1983-01-01

185

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

NASA Astrophysics Data System (ADS)

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

Pfrommer, C.; Jones, T. W.

2011-03-01

186

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

187

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

188

Ongoing Mass Transfer in the Interacting Galaxy Pair NGC 1409/1410  

NASA Astrophysics Data System (ADS)

I present two-band Hubble Space Telescope (HST) STIS imaging and WIYN spectral mapping of ongoing mass transfer in the interacting galaxy pair NGC 1409/1410 (where NGC 1410 is the Seyfert galaxy also cataloged as III Zw 55). Archival snapshot WFPC2 imaging from the survey by Malkan and coworkers showed a dust feature stretching between the galaxies, apparently being captured by NGC 1409. The new images allow estimates of the mass being transferred and the rate of transfer. An absorption lane typically 0.25" (100 pc) wide, with a representative optical depth ?B=0.2, cuts across the spiral structure of NGC 1410, crosses the 7 kpc projected space between the nuclei, wraps in front of and, at the limits of detection, behind NGC 1409 and becomes a denser (?B=0.4) polar feature around the core of NGC 1409. The combination of extinction data in two passbands allows a crude three-dimensional recovery of the dust structure, supporting the front/back geometry derived from colors and extinction estimates. The whole feature contains on the order of 2×106 Msolar in dust, implying about 3×108 Msolar of gas and requiring a mass transfer rate averaging ~1 Msolar yr-1, unless we are particularly unlucky in viewing angle. Curiously, this demonstrable case of mass transfer seems to be independent of the occurrence of a Seyfert nucleus, since the Seyfert galaxy in this pair is the donor of the material. Likewise, the recipient shows no signs of recent star formation from incoming gas, although NGC 1410 has numerous luminous young star clusters and widespread H? emission. Based on observations 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 (AURA), Inc., under NASA contract NAS 5-26555.

Keel, William C.

2004-03-01

189

Kinematics and dynamics of the M 51-type galaxy pair NGC 3893/96 (KPG 302)  

NASA Astrophysics Data System (ADS)

Aims:We study the kinematics and dynamics of the M 51-type interacting galaxy pair KPG 302 (NGC 3893/96). We analyze the perturbations induced by the encounter on each member of the pair, as well as the distribution of the dark matter (DM) halo of the main galaxy in order to explore possible differences between DM halos of "isolated" galaxies and those of galaxies belonging to a pair. Methods: The velocity field of each galaxy was obtained using scanning Fabry-Perot interferometry. A two-dimensional kinematic and dynamical analysis of each galaxy and the pair as a whole are done emphasizing the contribution of circular and non-circular velocities. Non-circular motions can be traced on the rotation curves of each galaxy allowing us to differentiate between motions associated to particular features and motions that reflect the global mass distribution of the galaxy. For the main galaxy of the pair, NGC 3893, optical kinematic information is complemented with HI observations from the literature to build a multi-wavelength rotation curve. We try to fit this curve with a mass-distribution model using different DM halos. Results: Non-circular motions are detected on the velocity fields of both galaxies. These motions can be associated to perturbations due to the encounter and, in the case of the main galaxy, to the presence of a structure such as spiral arms. The location of the corotation radius of this galaxy is also explored. We find that the multi-wavelength rotation curve of NGC 3893, "cleaned" from the effect of non-circular motions, cannot be fitted whether by a pseudo-isothermal or by a NFW DM halo.

Fuentes-Carrera, I.; Rosado, M.; Amram, P.; Salo, H.; Laurikainen, E.

2007-05-01

190

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

191

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

NASA Technical Reports Server (NTRS)

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

Smith, Beverly J.; Wallin, John F.

1992-01-01

192

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

193

The influence of bars in the star formation history and chemical evolution of disk galaxies  

NASA Astrophysics Data System (ADS)

This is a pilot study part of a larger program devoted to understand the influence of bars in the evolution of galaxy disks. Some of the goals of this observational program are to compare the stellar metallicity gradients of galaxies with and without bars, the role of bars in the redistribution of mass and angular momentum and to study the evolution of the metallicity gradients with time. Some promising results are presented as well as some words of caution.

Sánchez-Blázquez, Patricia

2010-04-01

194

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

SciTech Connect

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

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

2011-09-01

195

The Nuclear Stellar Dynamics of the S0 Galaxy NGC7332  

Microsoft Academic Search

STIS near-IR longslit spectroscopy of the nearby S0 galaxy NGC 7332 was obtained of the Ca II triplet absorption lines at ~ 8600 Angstroms. We use the Fourier correlation quotient method (Bender 1990, A&Ap, 229, 441) to extract the line-of-sight velocity distribution in the inner 4'' of the galaxy. Combined with ground-based imaging and spectroscopy (Fisher, Illingworth & Franx 1994,

C. H. Nelson; D. Weistrop; G. A. Bower; R. F. Green

2000-01-01

196

VERITAS Upper Limit on the Very High Energy Emission from the Radio Galaxy NGC 1275  

NASA Astrophysics Data System (ADS)

The recent detection by the Fermi ?-ray space telescope of high-energy ?-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 ?-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.; Aliu, E.; Arlen, T.; Aune, T.; Bautista, M.; Beilicke, M.; Benbow, W.; Boltuch, D.; Bradbury, S. M.; Buckley, J. H.; Bugaev, V.; Byrum, K.; Cannon, A.; Celik, O.; Cesarini, A.; Ciupik, L.; Cogan, P.; Cui, W.; Dickherber, R.; Duke, C.; Fegan, S. J.; Finley, J. P.; Fortin, P.; Fortson, L.; Furniss, A.; Galante, N.; Gall, D.; Gibbs, K.; Gillanders, G. H.; Godambe, S.; Grube, J.; Guenette, R.; Gyuk, G.; Hanna, D.; Holder, J.; Horan, D.; Hui, C. M.; Humensky, T. B.; Imran, A.; Kaaret, P.; Karlsson, N.; Kertzman, M.; Kieda, D.; Konopelko, A.; Krawczynski, H.; Krennrich, F.; Lang, M. J.; Le Bohec, S.; Maier, G.; McCann, A.; McCutcheon, M.; Millis, J.; Moriarty, P.; Mukherjee, R.; Ong, R. A.; Otte, A. N.; Pandel, D.; Perkins, J. S.; Pohl, M.; Quinn, J.; Ragan, K.; Reynolds, P. T.; Roache, E.; Rose, H. J.; Schroedter, M.; Sembroski, G. H.; Smith, A. W.; Steele, D.; Swordy, S. P.; Theiling, M.; Toner, J. A.; Varlotta, A.; Vassiliev, V. V.; Vincent, S.; Wagner, R. G.; Wakely, S. P.; Ward, J. E.; Weekes, T. C.; Weinstein, A.; Weisgarber, T.; Williams, D. A.; Wissel, S.; Wood, M.; Zitzer, B.; Kataoka, J.; Cavazzuti, E.; Cheung, C. C.; Lott, B.; Thompson, D. J.; Tosti, G.

2009-12-01

197

The Hubble Heritage Image of the Polar-Ring Galaxy NGC 4650A  

Microsoft Academic Search

The Hubble Heritage Project has the aim of providing the public with pictorially striking images of celestial objects obtained with the Hubble Space Telescope. As part of the Heritage Project, we have used HST to obtain a multi-color image of the peculiar galaxy NGC 4650A. This was the first Heritage observation for which the public joined in the target selection.

A. L. Kinney; J. Gallagher; L. Matthews; L. Sparke; H. E. Bond; C. A. Christian; J. English; L. Frattare; Z. Levay; K. Noll

1999-01-01

198

The Nuclear Stellar Dynamics of the S0 Galaxy NGC7332  

Microsoft Academic Search

STIS longslit spectroscopy of the nearby S0 galaxy NGC 7332 was obtained for the purpose of modeling the nuclear stellar dynamics and to search for evidence of a massive black hole. The primary stellar absorption features are the strong Ca II triplet lines at 8600 Angstroms. Stellar kinematical measurements characterizing the line-of-sight velocity distribution were extracted using the Fourier correlation

C. H. Nelson; D. Weistrop; G. A. Bower; R. F. Green

1999-01-01

199

The Frequency of Barred Spiral Galaxies in the Near-Infrared  

NASA Astrophysics Data System (ADS)

We have determined the fraction of barred galaxies in the H-band for a statistically well-defined sample of 186 spirals drawn from the Ohio State University Bright Spiral Galaxy Survey. We find 56% of our sample to be strongly barred in the H band while another 16% is weakly barred. Only 27% of our sample is unbarred in the near-infrared. The RC3 and the Carnegie Atlas of Galaxies both classify only about 30% of our sample as strongly barred. Thus strong bars are nearly twice as prevalent in the near-infrared as in the optical. The frequency of genuine optically hidden bars is significant but lower than many claims in the literature: 40% of the galaxies in our sample that are classified as unbarred in the RC3 show evidence for a bar in the H band while the Carnegie Atlas lists this fraction as 66%. Our data reveal no significant trend in bar fraction as a function of morphology in either the optical or H band. Optical surveys of high-redshift galaxies may be strongly biased against finding bars, as bars are increasingly difficult to detect at bluer rest wavelengths. Based partially on observations obtained at the Cerro Tololo Inter-American Observatory, operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.

Eskridge, Paul B.; Frogel, Jay A.; Pogge, Richard W.; Quillen, Alice C.; Davies, Roger L.; DePoy, D. L.; Houdashelt, Mark L.; Kuchinski, Leslie E.; Ramírez, Solange V.; Sellgren, K.; Terndrup, Donald M.; Tiede, Glenn P.

2000-02-01

200

NGC 1277: A Massive Compact Relic Galaxy in the Nearby Universe  

NASA Astrophysics Data System (ADS)

As early as 10 Gyr ago, galaxies with more than 1011 M ? of stars already existed. While most of these massive galaxies must have subsequently transformed through on-going star formation and mergers with other galaxies, a small fraction (lsim0.1%) may have survived untouched until today. Searches for such relic galaxies, useful windows to explore the early universe, have been inconclusive to date: galaxies with masses and sizes like those observed at high redshift (M sstarf >~ 1011 M ? Re <~ 1.5 kpc) have been found in the local universe, but their stars are far too young for the galaxy to be a relic galaxy. This paper explores the first case of a nearby galaxy, NGC 1277 (at a distance of 73 Mpc in the Perseus galaxy cluster), which fulfills many criteria to be considered a relic galaxy. Using deep optical spectroscopy, we derive the star formation history along the structure of the galaxy: the stellar populations are uniformly old (>10 Gyr) with no evidence for more recent star formation episodes. The metallicity of their stars is super-solar ([Fe/H] = 0.20 ± 0.04 with a smooth decline toward the outer regions) and ?-enriched ([?/Fe] = 0.4 ± 0.1). This suggests a very short formation time scale for the bulk of the stars in this galaxy. This object also rotates very fast (V rot ~ 300 km s-1) and has a large central velocity dispersion (? > 300 km s-1). NGC 1277 allows the exploration in full detail of properties such as the structure, internal dynamics, metallicity, and initial mass function as they were at ~10-12 Gyr ago when the first massive galaxies were built.

Trujillo, Ignacio; Ferré-Mateu, Anna; Balcells, Marc; Vazdekis, Alexandre; Sánchez-Blázquez, Patricia

2014-01-01

201

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

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

202

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

203

On the Offset of Barred Galaxies from the Black Hole M BH-? Relationship  

NASA Astrophysics Data System (ADS)

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

Brown, Jonathan S.; Valluri, Monica; Shen, Juntai; Debattista, Victor P.

2013-12-01

204

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

SciTech Connect

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

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

2013-10-20

205

Stellar populations in local group dwarf elliptical galaxies. II - NGC 205  

NASA Technical Reports Server (NTRS)

NGC 205, a dwarf elliptical companion of M31, was studied using deep CCD photometry on the VRI system. Consideration is given to a comparison between the giant branch and the Galactic globular clusters, the degree of chemical enrichment in the outer parts of NGC 204, and the setting of constraints on the stellar population of NGC 205. Should the distance of the galaxy be that of M31, this field's stellar population is extremely old. If star formation in NGC 205 is a recurring phenomenon, it is confined to the interior of the galaxy. Should the stellar population of NGC 205 be as old as Galactic globular clusters, its distance modulus is 24.3 + or - 0.2. The giant branch location corresponds to a mean metallicity greater than or equal to -0.9 + or - 0.2, and a metallicity dispersion is determined to be sigma greater than or equal to 0.5 dex. Also noted is that the color distribution at a given luminosity appears to be positively skewed.

Mould, J.; Kristian, J.; Da Costa, G. S.

1984-01-01

206

The Ghost of a Dwarf Galaxy: Fossils of the Hierarchical Formation of the Nearby Spiral Galaxy NGC 5907  

NASA Astrophysics Data System (ADS)

We present an extragalactic perspective of an extended stellar tidal stream wrapping around the edge-on spiral galaxy NGC 5907. Our deep images reveal for the first time a large-scale complex of arcing loops that is an excellent example of how low-mass satellite accretion can produce an interwoven, rosette-like structure of debris dispersed in the halo of its host galaxy. The existence of this structure, which has probably formed and survived for several gigayears, confirms that halos of spiral galaxies in the local universe may still contain a significant number of galactic fossils from their hierarchical formation. To examine the validity of the external accretion scenario, we present N-body simulations of the tidal disruption of a dwarf galaxy-like system in a disk galaxy plus dark halo potential that demonstrate that most of the tidal features observed in NGC 5907 can be explained by a single accretion event. Unfortunately, with no kinematic data and only the projected geometry of the stream as a constraint, the parameters of our model are considerably degenerate and, for now, must be considered illustrative only. Interestingly, NGC 5907 has long been considered a prototypical example of a warped spiral in relative isolation. The presence of an extended tidal stream challenges this picture and suggests that the gravitational perturbations induced by the stream progenitor must be considered as a possible cause for the warp. The detection of an old, complex tidal stream in a nearby galaxy with rather modest instrumentation points to the viability of surveys to find extragalactic tidal substructures around spiral galaxies in the Local Volume (<15 Mpc), with the prospect of obtaining a census with enough statistical significance to be compared with cosmological simulations.

Martínez-Delgado, David; Peñarrubia, Jorge; Gabany, R. Jay; Trujillo, Ignacio; Majewski, Steven R.; Pohlen, M.

2008-12-01

207

The core of the nearby S0 galaxy NGC 7457 imaged with the HST planetary camera  

NASA Technical Reports Server (NTRS)

A brief analysis is presented of images of the nearby S0 galaxy NGC 7457 obtained with the HST Planetary Camera. While the galaxy remains unresolved with the HST, the images reveal that any core most likely has r(c) less than 0.052 arcsec. The light distribution is consistent with a gamma = -1.0 power law inward to the resolution limit, with a possible stellar nucleus with luminosity of 10 million solar. This result represents the first observation outside the Local Group of a galaxy nucleus at this spatial resolution, and it suggests that such small, high surface brightness cores may be common.

Lauer, Tod R.; Faber, S. M.; Holtzman, Jon A.; Baum, William A.; Currie, Douglas G.; Ewald, S. P.; Groth, Edward J.; Hester, J. Jeff; Kelsall, T.

1991-01-01

208

A Bar Fuels a Supermassive Black Hole?: Host Galaxies of Narrow-Line Seyfert 1 Galaxies  

NASA Astrophysics Data System (ADS)

We present optical images of nearby 50 narrow-line Seyfert 1 galaxies (NLS1s) that cover all the NLS1s at z<0.0666 and ?>=-25deg known in 2001. Among the 50 NLS1s, 40 images are newly obtained by our observations and 10 images are taken from archive data. Motivated by the hypothesis that NLS1s are in an early phase of a supermassive black hole (BH) evolution, we present a study of NLS1 host galaxy morphology to examine trigger mechanism(s) of active galactic nuclei (AGNs) by seeing the early phase of AGN. With these images, we made morphological classification by visual inspection and by quantitative method, and found a high bar frequency of the NLS1s in the optical band; the bar frequency is 85%+/-7% among disk galaxies (64%-71% in total sample) which is more frequent than that (40%-70%) of broad-line Seyfert 1 galaxies (BLS1s) and normal disk galaxies, although the significance is marginal. Our results confirm the claim by Crenshaw and coworkers with a similar analysis for 19 NLS1s. The frequency is comparable to that of H II/starburst galaxies. We also examined the bar frequency against width of the broad H? emission line, Eddington ratio, and BH mass, but no clear trend is seen. Possible implications, such as an evolutionary sequence from NLS1s to BLS1s, are discussed briefly. Based on data collected at University of Hawaii 88 inch telescope, Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, Kitt Peak National Observatory 2.1 m telescope, which is operated by the National Optical Astronomy Observatory (NOAO), operated by AURA, Inc., under contract with the National Science Foundation; and the Canada-France-Hawaii Telescope with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at 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.

Ohta, Kouji; Aoki, Kentaro; Kawaguchi, Toshihiro; Kiuchi, Gaku

2007-03-01

209

Near-infrared properties of asymptotic giant branch stars in nearby dwarf elliptical galaxy NGC 205  

NASA Astrophysics Data System (ADS)

Aims: We investigated the distribution of resolved asymptotic giant branch (AGB) stars over a much larger area than covered by previous near-infrared studies in the nearby dwarf elliptical galaxy NGC 205. Methods: Using data obtained with the WIRCam near-infrared imager of the CFHT, we selected the AGB stars in the JHKs color - magnitude diagrams, and separated the C stars from M-giant stars in the JHKs color - color diagram. Results: We identified 1,550 C stars in NGC 205 with a mean absolute magnitude of ? MKs ? = -7.49 ± 0.54, and colors of ? (J - Ks)0 ? = 1.81 ± 0.41 and ? (H - Ks)0 ? = 0.76 ± 0.24. The ratio of C stars to M-giant stars was estimated to be 0.15 ± 0.01 in NGC 205, and the local C/M ratios for the southern region are somewhat lower than those for the northern region. The (J - Ks) color distributions of AGB stars contain the main peak of the M-giant stars and the red tail of the C stars. A comparison of the theoretical isochrone models with the observed color distribution indicates that most of the bright M-giant stars in NGC 205 were formed at log (tyr) ~ 9.0-9.7. The logarithmic slope of the MKs luminosity function for M-giant stars was estimated to be 0.84 ± 0.01, which is comparable with dwarf elliptical galaxies NGC 147 and NGC 185. Furthermore, we found that the logarithmic slopes of the MKs luminosity function for C and M-giant stars are different to places, implying a different star formation history within NGC 205. The bolometric luminosity function for M-giant stars extends to Mbol = -6.0 mag, and that for C stars spans -5.6 < Mbol < -3.0. The bolometric luminosity function of C stars is unlikely to be a Gaussian distribution and the mean bolometric magnitude of C stars is estimated to be Mbol = -4.24 ± 0.55, which is consistent with our results for dwarf elliptical galaxies NGC 147 and NGC 185. Based on observations carried out at the Canada-France-Hawaii Telescope, operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique de France, and the University of Hawaii.Calibrated photometry is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/543/A35

Jung, M. Y.; Ko, J.; Kim, J.-W.; Chun, S.-H.; Kim, H.-I.; Sohn, Y.-J.

2012-07-01

210

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

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

211

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

NASA Astrophysics Data System (ADS)

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

Wang, Xilu; Fields, Brian D.

2014-05-01

212

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

213

The vertical disk structure of the edge-on spiral galaxy NGC 3079  

NASA Technical Reports Server (NTRS)

NGC 3079 is an edge-on SB(s)c galaxy at a redshift of 1225 km/s relative to the Local Group. Earlier researchers found a spectacular 'figure-eight' radio structure aligned along the minor axis of the galaxy, centered on the nucleus, and extending 3 kpc above and below the plane. The geometry of this structure and the evidence of unusually high nuclear gas velocities suggest that a wind-type outflow from the nucleus is taking place. The disk of NGC 3079 is also remarkable: it is extremely rich in H 2 regions and is the only unambiguous example of a galaxy outside M31 and our own Galaxy to exhibit 'Heiles-like' shells. Other researchers have also identified a nebulosity with a ragged X-shaped morphology formed by a system of lumpy filaments with individual lengths of 3 - 5 kpc. They suggest that this material is ambient halo gas entrained into the boundary layers of the nuclear outflow. The complex structure of the line emission in NGC 3079 makes this object an ideal target for an imaging spectroscopic study. The present paper reports the preliminary results of such a study.

Veilleux, S.; Bland-Hawthorn, Jonathan; Cecil, G.; Tully, R. B.

1993-01-01

214

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

215

An X-ray Study of the Nearby Massive Early-Type Galaxy NGC 4472  

NASA Astrophysics Data System (ADS)

We present results from a deep archival XMM-Newton observation of the nearby massive early-type galaxy NGC 4472. This galaxy is in the early stages of merging with the Virgo cluster (1.35 Mpc from M87), and is the most optically luminous galaxy in the local Universe. Our earlier Chandra observations (Biller et al. 2004) showed a complex morphology in the X-ray emitting gas including cavities associated with twin radio lobes, a surface brightness discontinuity presumable due to an interaction with the Virgo cluster gas, and a filamentary arm similar to structures seen in M87. The deep XMM-Newton observation clearly demonstrates the existence of a ram pressure stripped tail anti-coincident to M87 and a surface brightness discontinuity, presumably the contact discontinuity between two moving fluids, between the core of NGC 4472 and the Virgo cluster gas. A temperature map of the NGC 4472 gas shows complex temperature variations in the core, perhaps indicative of non-azimuthally symmetric gas motions induced by the merger. Such motions have been predicted in various hydrodynamic simulations of galaxy/cluster mergers (Heinz et al. 2003). We also detect four filaments of cold gas in the temperature map extending roughly 25 kpc from the nucleus, one of which is coincident with the feature seen in the short Chandra observation. We discuss the implications of these results in terms of our understanding of group/cluster merger dynamics.

Kraft, Ralph; Forman, W. R.; Jones, C.; Nulsen, P. E. J.; Hardcastle, M. J.; Evans, D. A.; Raychaudhury, S.; Sivakoff, G.; Sarazin, C.; Murray, S. S.

2009-09-01

216

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

217

On a Method to Resolve the Nuclear Activity in Galaxies as Applied to the Seyfert 2 Galaxy NGC 1358  

NASA Astrophysics Data System (ADS)

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. Based on observations at the European Southern Observatory.

Lindblad, Per Olof; Fathi, Kambiz; Hjelm, Maja; Nelson, Charles H.

2010-11-01

218

The star cluster system of the luminous elliptical galaxy NGC 1600  

NASA Astrophysics Data System (ADS)

Context: Luminous elliptical galaxies generally display a rich star cluster system, whose properties provide strong constraints on the physics of galaxy formation and evolution. Star cluster system studies, however, concentrate on galaxies located in nearby or rich galaxy clusters. Aims: We acquired deep B and I images of NGC 1600, a luminous elliptical in a galaxy group to study its star cluster system. The images were obtained with the Optical Imager at the Southern Telescope for Astrophysical Research for an exposure time of 1.66 h in each filter. Methods: The sample selection incompleteness was assessed as a function of magnitude and image background level. Source counts were measured for different elliptical annuli from the centre of NGC 1600, background subtracted, and fitted with a Gaussian function. Colour distributions were derived as a function of galactocentric distance for sources measured successfully in both filters. Typical ages and metallicities were estimated based on single stellar population models. Results: A clear excess of point sources around NGC 1600 was found in relation to the nearby field. The source counts were consistent with a Gaussian distribution typical of other luminous ellipticals. The luminosity function fits provided an estimate of the density of clusters at the different annuli that could be integrated in solid angle, resulting in an estimated total population of N_GC ? 2850 star clusters. This yielded a specific frequency of SN ? 1.6. The colour distributions show a hint of bimodality, especially at ?20 kpc from the centre. Clusters in this region may be associated with a ring or shell perturbation. Finally, the star cluster candidates were cross-correlated to discrete X-ray sources and a coincidence rate of ?40% was found. These are likely to be globular clusters harboring low-mass X-ray binaries.

Santiago, B. X.

2008-12-01

219

Characterizing Barred Galaxies in the Abell 901/902 Supercluster from STAGES  

NASA Astrophysics Data System (ADS)

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

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

2008-08-01

220

The Inner Size of the Dust Torus in the Seyfert 1 Galaxy NGC 4151  

NASA Astrophysics Data System (ADS)

The most intense optical and near-infrared monitoring observations yet made were carried out on the Seyfert 1 galaxy NGC 4151 using the multi-color imaging photometer (MIP) mounted on the MAGNUM telescope. The lag time between the V and K light curves at the flux minimum in 2001 was precisely 48^{+2}_{-3} days using a cross-correlation analysis. The correlation between the optical luminosity of an active galactic nucleus (AGN) and the lag time between the UV/optical and the near-infrared light curves is presented for NGC 4151 in combination with previous lag-time measurements of NGC 4151 and other AGNs in the literature. The correlation is interpreted as thermal dust reverberation in the AGNs tep{mine04}.

Minezaki, T.; Yoshii, Y.; Aoki, T.; Kobayashi, Y.; Suganuma, M.; Enya, K.; Tomita, H.; Peterson, B. A.

2006-12-01

221

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.

222

A HST Study of the Stellar Populations in the Cometary Dwarf Irregular Galaxy NGC 2366  

NASA Astrophysics Data System (ADS)

We present V and I photometry of the resolved stars in the cometary dwarf irregular galaxy NGC 2366, using Wide Field Planetary Camera 2 images obtained with the Hubble Space Telescope. The resulting color-magnitude diagram reaches down to I~26.0 mag. It reveals not only a young population of blue main-sequence stars (age <~30 Myr) but also an intermediate-age population of blue and red supergiants (20 Myr <~ age <~100 Myr) and older evolved populations of asymptotic giant branch (AGB) stars (age >~100 Myr) and red giant branch (RGB) stars (age >~1 Gyr). The measured magnitude I=23.65+/-0.10 mag of the RGB tip results in a distance modulus m-M=27.67+/-0.10, which corresponds to a distance of 3.42+/-0.15 Mpc, in agreement with previous distance determinations. The youngest stars are associated with the bright complex of H II regions NGC 2363 (=Mrk 71) in the southwest extremity of the galaxy. As a consequence of the diffusion and relaxation processes of stellar ensembles, the older the stellar population is, the smoother and more extended is its spatial distribution. An underlying population of older stars is found throughout the body of NGC 2366. The most notable feature of this older population is the presence of numerous relatively bright AGB stars. The number ratio of AGB to RGB stars and the average absolute brightness of AGB stars in NGC 2366 are appreciably higher than in the BCD VII Zw 403, indicating a younger age of the AGB stars in NGC 2366. In addition to the present burst of age <~100 Myr, there has been strong star formation activity in the past of NGC 2366, from ~100 Myr to <~3 Gyr ago. Based on observations obtained with the NASA/ESA Hubble Space Telescope through the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555.

Thuan, Trinh X.; Izotov, Yuri I.

2005-07-01

223

Low Dark Matter Content of the Nearby Early-Type Galaxy NGC 821  

NASA Astrophysics Data System (ADS)

In this paper we analyze the kinematics and dynamics of the nearby early-type galaxy NGC~821 based on its globular clusters (GCs) and planetary nebulae (PNe). We use PNe and GCs to extract the kinematics of NGC~821 which is then used for the dynamical modelling based on the Jeans equation. We apply the Jeans equation using the Newtonian mass-follows-light approach assuming constant mass-to-light ratio and find that using such an approach we can successfully fit the kinematic data. The inferred constant mass-to-light ratio, 4.2galaxy, implies the lack of significant amount of dark matter. We also used three different MOND approaches and found that we can fit the kinematic data without the need for additional, dark, component.

Samurovic, S.; Vudragovic, A.; Jovanovic, M.; Cirkovic, M. M.

2014-06-01

224

The Narrow-Line Region in the Seyfert 2 Galaxy NGC 3393  

Microsoft Academic Search

The narrow-line region (NLR) of the Seyfert 2 galaxy NGC 3393 is dominated by a symmetric structure which appears as S-shaped arms in Hubble Space Telescope (HST) images. These arms, which occupy the central few arcseconds of the nucleus, border a linear, triple-lobed radio source. We use HST imaging and spectra, ground-based optical images, long-slit spectra, Fabry-Perot imaging spectroscopy, and

Andrew J. Cooke; J. A. Baldwin; G. J. Ferland; Hagai Netzer; Andrew S. Wilson

2000-01-01

225

The Flattened Dark Halo of Polar Ring Galaxy NGC 4650A: A Conspiracy of Shapes?  

Microsoft Academic Search

Kinematics and photometry of the polar ring galaxy NGC 4650A, including new\\u000aobservations of the rotation and velocity dispersion of its central stellar\\u000adisk, are used to infer the presence of a dark matter halo and to measure its\\u000ashape. Fits to the observed disk and polar ring rotation curves from detailed\\u000amass and photometric modeling rule out a spherical

Penny D. Sackett; Hans-Walter Rix; Brian J. Jarvis; Kenneth C. Freeman

1994-01-01

226

Spitzer\\/IRS Imaging and Spectroscopy of the luminous infrared galaxy NGC 6052 (Mrk 297)  

Microsoft Academic Search

We present photometric and spectroscopic data of the interacting starburst\\u000agalaxy NGC 6052 obtained with the Spitzer Space Telescope. The mid-infrared\\u000a(MIR) spectra of the three brightest spatially resolved regions in the galaxy\\u000aare remarkably similar and are consistent with dust emission from young nearly\\u000acoeval stellar populations. Analysis of the brightest infrared region of the\\u000asystem, which contributes ~18.5

D. G. Whelan; D. Devost; V. Charmandaris; J. A. Marshall; J. R. Houck

2007-01-01

227

Nuclear Star Formation in the Hot-Spot Galaxy NGC 2903  

NASA Technical Reports Server (NTRS)

We present high-resolution near-infrared imaging obtained using adaptive optics and HST/NICMOS and ground-based spectroscopy of the hot-spot galaxy NGC 2903. Our near-infrared resolution imaging enables us to resolve the infrared hot spots into individual young stellar clusters or groups of these. The spatial distribution of the stellar clusters is not coincident with that of the bright H II regions, as revealed by the HST/NICMOS Pace image. Overall, the circumnuclear star formation in NGC 2903 shows a ring-like morphology with an approximate diameter of 625 pc. The SF properties of the stellar clusters and H II regions have been studied using the photometric and spectroscopic information in conjunction with evolutionary synthesis models. The population of bright stellar clusters shows a very narrow range of ages, 4 to 7 x 10(exp 6) yr after the peak of star formation, or absolute ages 6.5 to 9.5 x 10(exp 6) yr (for the assumed short-duration Gaussian bursts), and luminosities similar to the clusters found in the Antennae interacting galaxy. This population of young stellar clusters accounts for some 7 - 12% of the total stellar mass in the central 625 pc of NGC 2903. The H II regions in the ring of star formation have luminosities close to that of the super-giant H II region 30 Doradus, they are younger than the stellar clusters, and will probably evolve into bright infrared stellar clusters similar to those observed today. We find that the star formation efficiency in the central regions of NGC 2903 is higher than in normal galaxies, approaching the lower end of infrared luminous galaxies.

Alonso-Herrero, A.; Ryder, S. D.; Knapen, J. H.

1994-01-01

228

Detection of Molecular Clouds in the Interarm of the Flocculent Galaxy NGC 5055  

Microsoft Academic Search

We present high-resolution (˜ 4'') 12CO(J = 1-0) mapping observations with high-velocity resolution (˜ 2.6 km s-1) toward the disk of flocculent galaxy NGC 5055, using the Nobeyama Millimeter Array in order to study the physical properties of the molecular clouds in the arm and the interarm. The map shows clumpy structures. Although these are mainly distributed along an arm

Tomoka Tosaki; Yasuhiro Shioya; Nario Kuno; Kouichiro Nakanishi; Takashi Hasegawa

2003-01-01

229

Continuum emission at 1 millimeter from the elliptical galaxy NGC 205  

SciTech Connect

The nucleus of NGC 205 has been detected in the continuum at 1.1 mm with a flux of 21 + or - 5 mJy within the central 18 arcsec of the galaxy. This is the first detection of thermal emission from dust grains at millimeter wavelengths from an elliptical galaxy. Combining this measurement with IRAS and optical fluxes suggests that the dust temperature lies between 19 and 26 K and the dust mass between 1 solar mass and 3000 solar masses. These limits depend strongly on the dust emissivity. 26 refs.

Fich, M.; Hodge, P. (Waterloo, University (Canada) Washington, University, Seattle (USA))

1991-06-01

230

Diffuse Gamma-Ray Emission from the Starburst Galaxy NGC 253  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

231

Results from the NGC 7448 cube of the Arecibo Galaxy Environment Survey  

NASA Astrophysics Data System (ADS)

The Arecibo Galaxy Environment Survey is an ongoing neutral hydrogen galaxy survey with higher sensitivity and better spatial and velocity resolution than previous 21cm multi-beam surveys. Here, we present results from the AGES 7448 cube, a 5x4 sq deg field including the NGC 7448 galaxy group and the surrounding volume out to 19,000 km/sec. In the cube, we identify a total of 376 HI sources, including 217 new detections. A wedge plot of the detections shows clear filamentary structure throughout the volume of the cube. Within the NGC 7448 group, we detect an HI tidal bridge connecting NGC 7448 to the rest of the group members. A preliminary search for optical counterparts was performed using SDSS; of our 376 sources, we find 4 sources with early type counterparts and 12 sources with no obvious SDSS counterpart that will require follow up. Our source catalogue includes fitted positions, velocities, velocity widths, flux and HI mass measurements for each of the 376 sources.

Herbst, Hanna; Taylor, R.; Minchin, R.

2012-01-01

232

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

233

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

NASA Technical Reports Server (NTRS)

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

2002-01-01

234

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

235

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

236

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

SciTech Connect

Hot gaseous halos are predicted around all large galaxies and are critically important for our understanding of galaxy formation, but they have never been detected at distances beyond a few kpc around a spiral galaxy. We used the ACIS-I instrument on board Chandra to search for diffuse X-ray emission around an ideal candidate galaxy: the isolated giant spiral NGC 1961. We observed four quadrants around the galaxy for 30 ks each, carefully subtracting background and point-source emission, and found diffuse emission that appears to extend to 40-50 kpc. We fit {beta}-models to the emission and estimate a hot halo mass within 50 kpc of 5 x 10{sup 9} M{sub sun}. When this profile is extrapolated to 500 kpc (the approximate virial radius), the implied hot halo mass is 1-3 x 10{sup 11} M{sub sun}. These mass estimates assume a gas metallicity of Z = 0.5 Z{sub sun}. This galaxy's hot halo is a large reservoir of gas, but falls significantly below observational upper limits set by pervious searches, and suggests that NGC 1961 is missing 75% of its baryons relative to the cosmic mean, which would tentatively place it below an extrapolation of the baryon Tully-Fisher relationship of less massive galaxies. The cooling rate of the gas is no more than 0.4 M{sub sun} yr{sup -1}, more than an order of magnitude below the gas consumption rate through star formation. We discuss the implications of this halo for galaxy formation models.

Anderson, Michael E.; Bregman, Joel N., E-mail: michevan@umich.edu, E-mail: jbregman@umich.edu [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States)

2011-08-10

237

MOND prediction of a new giant shell in the elliptical galaxy NGC 3923  

NASA Astrophysics Data System (ADS)

Context. Stellar shells, which form axially symmetric systems of arcs in some elliptical galaxies, are most likely remnants of radial minor mergers. They are observed up a radius of ~100 kpc. The stars in them oscillate in radial orbits. The radius of a shell depends on the free-fall time at the position of the shell and on the time since the merger. We previously verified the consistency of shell radii in the elliptical galaxy NGC 3923 with its most probable MOND potential. Our results implied that an as yet undiscovered shell exists at the outskirts of the galaxy. Aims: We here extend our study by assuming more general models for the gravitational potential to verify the prediction of the new shell and to estimate its position. Methods: We tested the consistency of the shell radial distribution observed in NGC 3923 with a wide variety of MOND potentials of the galaxy. The potentials differed in the mass-to-light ratio and in distance to the galaxy. We considered different MOND interpolation functions, values of the acceleration constant a0, and density profiles of the galaxy. We verified the functionality of our code on a Newtonian self-consistent simulation of the formation of a shell galaxy. Results: Our method reliably predicts that exactly one new outermost shell exists at a galactocentric radius of about 1900'' (~210 kpc) on the southwestern side of the galaxy. Its estimated surface brightness is about 28 mag arcsec-2 in B - a value accessible by current instruments. This prediction enables a rare test of MOND in an elliptical down to an acceleration of a0/ 10. The predictive power of our method is verified by reconstructing the position of the largest known shell from the distribution of the remaining shells.

Bílek, M.; Bartošková, K.; Ebrová, I.; Jungwiert, B.

2014-06-01

238

The Westerbork Hydrogen Accretion in Local Galaxies (HALOGAS) Survey: NGC 3198 and Its Extraplanar H I Gas  

NASA Astrophysics Data System (ADS)

I am showing a selection of results of the Westerbork Hydrogen Accretion in Local Galaxies survey, concentrating on the galaxy NGC 3198. The goal of the survey is to investigate the presence, morphology and kinematics of extraplanar neutral hydrogen gas. The presence of extraplanar gas in the spiral galaxy NGC 3198 is revealed for the first time, by making models of the observations. The extraplanar gas has a lower rotation velocity with increasing height from the midplane, with a vertical gradient of ˜10 km s-1 kpc-1. Global (but preliminary) results of the survey sample are also briefly mentioned.

Gentile, G.; Halogas Team

2014-05-01

239

CONTINUUM HALOS IN NEARBY GALAXIES: AN EVLA SURVEY (CHANG-ES). II. FIRST RESULTS ON NGC 4631  

SciTech Connect

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 {mu}Jy beam{sup -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 {alpha}-bar{sub 1.5GHz} = -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; Henriksen, Richard N. [Department of Physics, Engineering Physics and Astronomy, Queen's University, Kingston, ON K7L 3N6 (Canada); Beck, Rainer; Krause, Marita; Mora, Silvia Carolina; Schmidt, Philip [Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, 53121, Bonn (Germany); Benjamin, R. A. [Department of Physics, University of Wisconsin at Whitewater, 800 West Main St., Whitewater, WI 53190 (United States); Dettmar, Ralf-Juergen; Miskolczi, Arpad [Astronomisches Institut, Ruhr-Universitaet Bochum, 44780 Bochum (Germany); English, Jayanne [Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada); Heald, George; Oosterloo, Tom [Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA, Dwingeloo (Netherlands); Johnson, Megan [National Radio Astronomy Observatory, P.O. Box 2, Greenbank, WV 24944 (United States); Li, Jiang-Tao [Department of Astronomy, University of Massachusetts, 710 North Pleasant St., Amherst, MA 01003 (United States); Murphy, E. J. [Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Porter, Troy A. [Hansen Experimental Physics Laboratory, Stanford University, 452 Lomita Mall, Stanford, CA 94305 (United States); Rand, Richard J. [Department of Physics and Astronomy, University of New Mexico, 800 Yale Boulevard, NE, Albuquerque, NM 87131 (United States); Saikia, D. J. [National Centre for Radio Astrophysics, TIFR, Pune University Campus, Post Bag 3, Pune 411 007 (India); Strong, A. W. [Max-Planck-Institut fuer extraterrestrische Physik, Garching bei Muenchen (Germany); Walterbos, Rene, E-mail: irwin@astro.queensu.ca, E-mail: henriksn@astro.queensu.ca, E-mail: twiegert@astro.queensu.ca, E-mail: rbeck@mpifr-bonn.mpg.de, E-mail: mkrause@mpifr-bonn.mpg.de, E-mail: cmora@mpifr-bonn.mpg.de [Department of Astronomy, New Mexico State University, P.O. Box 30001, MSC 4500, Las Cruces, NM 88003 (United States); and others

2012-08-15

240

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

241

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

242

UBVRI Light Curves of the Seyfert Galaxy NGC 7469 During 1990-1998: Microvariability  

NASA Astrophysics Data System (ADS)

Observations of the nuclear region of the Seyfert galaxy NGC 7469 obtained at Crimean Astrophysical Observatory with the 1.25 m telescope are presented. During 64 nights on nine observational runs between 1990 September 24 and 1998 October 22 in each spectral band of the Johnson UBVRI system, about 1500 measurements have been performed simultaneously through the round aperture 20" in diameter using differential photometry techniques. The estimated accuracy of each measurement is about 0.01 mag. During the observing period 1990-1996 the mean luminosity of the nucleus was almost constant; only overlapping brightness fluctuations were observed. The mean luminosity level has been raised in 1996 October. The peak amplitude (maximum flux/minimum flux) Fmax/Fmin=2.09 on the light curves was observed in the U band, while the minimum amplitude Fmax/Fmin=1.32 was in the I band for the entire observation period. Using structure function (SF) analysis, the following conclusions have been made: (1) Long-term variability is caused by the same processes in the optical, because the slope b of the SF is approximately equal for all wave bands, except for the I band the slope is appreciably distinguished from the others. This would be an indication of the presence of an independent IR energy source in NGC 7469. (2) Considering the same time interval (from 6 minutes to 2 hr) for intranight variability on SFs at different wave bands, one can conclude that flicker noise causes variations observed on the light curve at the UV region (U and B bands), while at the near-IR region the light curve is formed by mixed shot noise and flicker noise-the greater the wavelength, the more the contribution of shot noise processes. (3) On intranight light curves of the NGC 7469 there exist rapid flares with durations ~25 minutes at U band, ~55 minutes at B, V bands, and ~2 hr at R, I bands-a typical timescale of intranight variability increasing with the increasing wavelength. In order to examine the intranight variations of the nucleus of NGC 7469, standard deviations (SDs) of the nightly averaged flux, F, and a measure of intranight variability, SD/F, were calculated for each night of observations. The ratios P=Ni/Ntot of number of nights with SD/F>=1%, 2%, 3%, and so forth (Ni) to all 64 observational nights (Ntot) were expressed as a percentage of probability to detect variability at a given level; they were plotted versus the appropriate parameter SD/F. It is interesting that a probability to detect intranight variability at a level given by a parameter SD/F may be fitted well by a ``probability curve'' for a given galaxy. The homogeneity of data obtained with the same telescope using the same technique has made statistical comparisons possible among different galaxies and different wave bands. Therefore, analogous curves for the Seyfert galaxies NGC 1275 and NGC 4151 were plotted and were averaged by bands. Probability curves for the two galaxies of the same type (Seyfert 1; NGC 4151 and NGC 7469) coincided well. The probability curve for the galaxy NGC 1275 of BL Lacertae type shows more nights with variations of amplitude less than 7%. The probability to observe intranight variations with an amplitude of more than 7% is approximately equal for both types of objects. An excess of nights with intranight variability parameter SD/F in the range of ~4%-8% is a common characteristic of the two Seyfert 1 galaxies (NGC 4151 and NGC 7469) and of the BL Lac object (NGC 1275) studied in this paper. This excess may be connected with a specific type of intranight galaxy variability. All probability curves are fitted best by the second-order exponential decay. As a result, one can conclude that intranight variability is really transient in character and has manifested itself with different probabilities for different galaxies. The efficiency of the energy source for every galaxy to produce intranight variability on a given level (duty cycle of the central energy engine) was estimated using these probability curves. For a given threshold of detection estim

Merkulova, N. I.

2000-02-01

243

A close nuclear black-hole pair in the spiral galaxy NGC 3393.  

PubMed

The current picture of galaxy evolution advocates co-evolution of galaxies and their nuclear massive black holes, through accretion and galactic merging. Pairs of quasars, each with a massive black hole at the centre of its galaxy, have separations of 6,000 to 300,000 light years (refs 2 and 3; 1 parsec = 3.26 light years) and exemplify the first stages of this gravitational interaction. The final stages of the black-hole merging process, through binary black holes and final collapse into a single black hole with gravitational wave emission, are consistent with the sub-light-year separation inferred from the optical spectra and light-variability of two such quasars. The double active nuclei of a few nearby galaxies with disrupted morphology and intense star formation (such as NGC 6240 with a separation of about 2,600 light years and Mrk 463 with a separation of about 13,000 light years between the nuclei) demonstrate the importance of major mergers of equal-mass spiral galaxies in this evolution; such mergers lead to an elliptical galaxy, as in the case of the double-radio-nucleus elliptical galaxy 0402+379 (with a separation of about 24 light years between the nuclei). Minor mergers of a spiral galaxy with a smaller companion should be a more common occurrence, evolving into spiral galaxies with active massive black-hole pairs, but have hitherto not been seen. Here we report the presence of two active massive black holes, separated by about 490 light years, in the Seyfert galaxy NGC 3393 (50 Mpc, about 160 million light years). The regular spiral morphology and predominantly old circum-nuclear stellar population of this galaxy, and the closeness of the black holes embedded in the bulge, provide a hitherto missing observational point to the study of galaxy/black hole evolution. Comparison of our observations with current theoretical models of mergers suggests that they are the result of minor merger evolution. PMID:21881560

Fabbiano, G; Wang, Junfeng; Elvis, M; Risaliti, G

2011-09-22

244

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

NASA Astrophysics Data System (ADS)

The steeply declining bar fraction from 65% in the local Universe to <20% 7 Gyr ago allowed us to constrain the detailed mass assembly of disk galaxies from the COSMOS survey. We showed that the most massive galaxies formed their bars first and by z˜1, >50% of massive disks already had bars. The low mass galaxies evolved to acquire their bars only very recently. Now using the Spitzer Survey of Stellar Structure in Galaxies (S4G) we show that this mass-dependent trend is extremely clear in the 2300+ galaxy sample. Galaxies with masses log M > 9.5 have bar fractions of 65% whereas galaxies masses log M < 9 have almost no bars -- in direct contrast to other studies that have claimed an increase in bars at the low mass end. We show that elongations due to poor quality imaging and blurring of nearby star forming regions likely lead to a mis-classification of bars in late type, low mass galaxies. At log M ˜9.2 there is a increase in the bar fraction indicating that the bar formation is occurring at the fastest rate in these systems - that is now the epoch of mature disk building.

Sheth, Kartik; S4G Team

2014-01-01

245

NGC 5128 - a nearby laboratory for planetary nebulae in a giant early-type galaxy  

NASA Astrophysics Data System (ADS)

NGC 5128 at 3.8 Mpc is the nearest large elliptical galaxy and is ideally suited to a detailed study of its planetary nebula population. Two spectroscopic programmes are summarised. More than 1200 PNe candidates are known from imaging campaigns in NGC 5128 and accurate radial velocities of 1070 have been measured with the VLT FLAMES/Giraffe spectrometer. From these data a variety of studies of the galaxy kinematics are enabled, such as search for PN sub-groups, representing the relics of accretion of small galaxies. Emission line spectra were observed with VLT FORS and the light element abundances determined for 40 PNe through photoionization modelling. A spread in O abundance of about 0.9 dex is found but no obvious radial gradient out to 19 kpc. Comparison of the O abundance from these PN with the metallicity for the stellar population in the neighbourhood of the PN will probe the star formation and enrichment history of the galaxy. Full results from this analysis will be presented in a forthcoming paper.

Walsh, Jeremy R.; Jacoby, George H.; Kuntschner, Harald; Peletier, Reynier F.; Rejkuba, Marina; Walton, Nicholas A.; Woodley, Kristin A.

2012-08-01

246

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

247

Stellar populations in local group dwarf elliptical galaxies. I - NGC 147  

NASA Technical Reports Server (NTRS)

A color-magnitude diagram of NGC 147 to an I magnitude of 23 is presented. The stellar population in the outer parts of this elliptical galaxy resembles that of the globular clusters of the Milky Way. Quantitative comparison of the giant branch with those of globular clusters yields a mean metallicity of -1.2 + or - 0.2, making NGC 147 a part of the general correlation between mass and metallicity seen in ellipticals. The giant branch appears to be broad, which suggests a metallicity dispersion. The absence of asymptotic giant branch stars at luminosities above that of the red giant branch tip sets an upper limit of 10 percent for the fraction of stars in this NGC 147 field that have ages less than 12 Gyr. This result contrasts with the situation in some of the related, but less massive, dwarf spheroidal systems. If the choice is made to assume, rather than determine the stellar content of NGC 147, a distance of 630 + or - 50 kpc is derived, similar to that of M31.

Mould, J. R.; Kristian, J.; Da Costa, G. S.

1983-01-01

248

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

249

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

250

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

NASA Astrophysics Data System (ADS)

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

Lindblad, Per-Olof; Fathi, Kambiz

2011-12-01

251

BIMA CO (1-0) Observations of the Dwarf Elliptical Galaxy NGC 404  

NASA Astrophysics Data System (ADS)

We present high resolution observations of the CO emission in NGC 404, a nearby dwarf elliptical (dE) galaxy (D = 3.3 Mpc). NGC 404 is only the third dwarf elliptical to have its CO emission mapped by interferometric observations, and is the first outside the Local Group. Our observations show a very concentrated, marginally resolved structure about 9 × 9 arcseconds in diameter. This corresponds to a very small cloud at the center of a much larger distribution of stars. NGC 404 is surrounded by a doughnut shaped distribution of HI gas centered on the stellar component. The CO and HI appear to be kinematically distinct components, suggesting that the HI may be part of the galaxy's original gas distribution, while the CO may be recycled from the products of stellar evolution. C.L.T. has been supported by CSU Sacramento via a Research and Creative Activity Award. G.R.P. has been supported by the Laboratory for Millimeter-Wave Astronomy through NSF grant AST 99-81289

Taylor, C. L.; Petitpas, G. R.

2004-12-01

252

The Interplay between Bulge-Disk-Bar Photometric Measures in the Most Isolated Spiral Galaxies  

NASA Astrophysics Data System (ADS)

We perform bulge-disk-bar decomposition using the BUDDA code (de Souza, Gadotti, dos Anjos 2004) on i-band SDSS images for a sample isolated galaxies from the AMIGA sample (Verdes-Montenegro et al. 2004). We studied 100 of the isolated galaxies classified Sb-Sc that were also included in SDSS. This appears to be the dominant population of isolated galaxies representing 2/3 of the reasonably complete AMIGA sample. We report a series of correlations and scaling relations between the photometrically derived parameters describing the three main structural components i.e. bulges, disks and bars. We illustrate how various measures that quantify the structure of galaxies evolve along the Sb-Sbc-Sc morphological sequence. Comparison with other studies seems to suggest that both the frecquency of barred galaxies and the bar sizes are sensitive to environment. Additionally our results suggest that most galaxies in our sample host pseudobulges rather than classical bulges, consistent with the idea that classical bulges are environmentally formed and fostered.

Durbala, Adriana; Sulentic, J. W.; Verdes-Montenegro, L.

2008-05-01

253

X-ray emission from galaxies - ULXs in the bright spiral NGC 2276  

NASA Astrophysics Data System (ADS)

ULXs are now found almost ubiquitously in star-forming galaxies. Their presence is linked to the enhancement of the star formation rate, but their formation process is not completely understood. As part of our study of ULXs and their environment, we present a bright spiral, NGC 2276, belonging to a poor group of galaxies well known to have a bright extended hot gaseous halo. We have already shown, by using Chandra data, that the brightest ULX detected by XMM-Newton is instead a combination of various sources, most of which bright enough to be classified as ULXs. We present here the source properties and Luminosity Function and discuss possible formation mechanism by applying different scenarios and numerical simulations to explain the presence of ULXs and the distorted morphology of the galaxy.

Wolter, Anna; Villani, Mattia; Pizzolato, Fabio; Mapelli, Michela; Ripamonti, Emanuele

2012-09-01

254

The Mass of the Central Black Hole in the Seyfert Galaxy NGC 3783  

NASA Technical Reports Server (NTRS)

Improved analysis of ultraviolet and optical monitoring data on the Seyfert 1 galaxy NGC 3783 provides evidence for the existence of a supermassive, (8.7 +/- 1.1) x 10(exp 6) solar mass, black hole in this galaxy. By using recalibrated spectra from the International Ultraviolet Explorer satellite and ground-based optical data, as well as refined techniques of reverberation mapping analysis, we have reduced the statistical uncertainties in the response of the emission lines to variations in the ionizing continuum. The different time lags in the emission-line responses indicate a stratification in the ionization structure of the broad-line region and are consistent with the virial relationship suggested by the analysis of similar active galaxies.

Onken, Christopher A.; Peterson, Bradley M.

2004-01-01

255

Chandra Observation of the Edge-on Galaxy NGC 3556 (M108): Violent Galactic Disk-Halo Interaction Revealed  

NASA Astrophysics Data System (ADS)

We present a 60 ks Chandra ACIS-S observation of the isolated edge-on spiral galaxy NGC 3556, together with a multiwavelength analysis of various discrete X-ray sources and diffuse X-ray features. Among 33 discrete X-ray sources detected within the IB=25 mag arcsec-2 isophote ellipse of the galaxy, we identify a candidate for the galactic nucleus, an ultraluminous X-ray source that might be an accreting intermediate-mass black hole, a possible X-ray binary with a radio counterpart, and two radio-bright giant H II regions. We detect large amounts of extraplanar diffuse X-ray emission, which extend about 10 kpc radially in the disk and >~4 kpc away from the galactic plane. The diffuse X-ray emission exhibits significant substructures, possibly representing various blown-out superbubbles or chimneys of hot gas heated in massive star-forming regions. This X-ray-emitting gas has temperatures in the range of ~(2-7)×106 K and has a total cooling rate of ~2×1040 ergs s-1. The energy can be easily supplied by supernova blast waves in the galaxy. These results show NGC 3556 to be a galaxy undergoing vigorous disk-halo interaction. The halo in NGC 3556 is considerably less extended, however, than that of NGC 4631, in spite of many similarities between the two galaxies. This may be due to the fact that NGC 3556 is isolated, whereas NGC 4631 is interacting. Thus, NGC 3556 presents a more pristine environment for studying the disk-halo interaction.

Wang, Q. Daniel; Chaves, Tara; Irwin, Judith A.

2003-12-01

256

Atomic hydrogen in the disturbed edge-on galaxy NGC 4631  

NASA Technical Reports Server (NTRS)

We present WSRT HI observations of the nearby, disturbed, edge-on galaxy NGC 4631. A low-resolution (45 in. x 87 in.) map shows previously unknown tidal debris at large distances from the plane, and two dwarf companions. A high resolution (12 in. x 22 in.) map reveals a very disturbed gas layer in NGC 4631, with a wealth of small-scale structure. The most striking discovery is a supershell in the eastern half of the disk with a diameter of about 3 kpc, a mass of approximately 10 exp 8 solar mass and a tentative expansion velocity of 45 km/s. If the expansion is real, the energy which must have been injected by supernovae to explain the shell's current parameters is roughly 4 x 10(exp 55) ergs. Such a high energy requirement suggests an alternative formation mechanism, such as a collision with a small companion.

Rand, Richard J.; Vanderhulst, J. M.

1993-01-01

257

The radio source and bipolar nebulosity in the Seyfert galaxy NGC 3516  

NASA Technical Reports Server (NTRS)

Results of radio continuum and optical emission-line observations of the type 1 Seyfert galaxy NGC 3516 are presented. The radio maps reveal an elongated one-sided curved structure, which comprises a series of small-scale 'blobs' and extends up to 4 kpc from the nucleus. This radio structure is aligned and cospatial with one side of the double-sided and highly symmetric Z-shaped emission-line structure. It is argued that these morphological features are associated with a bipolar gaseous outflow from the nucleus of NGC 3516. The radio 'blobs' are elongated roughly perpendicular to the apparent local direction of the outflow, a result which is interpreted in terms of synchrotron emission from outflow-driven shock waves.

Miyaji, Takamitsu; Wilson, Andrew S.; Perez-Fournon, Ismael

1992-01-01

258

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

259

Old Populations and the Star Formation History of the Local Group Dwarf Irregular Galaxy NGC 6822  

NASA Astrophysics Data System (ADS)

A method for studying the star formation history (SFH) of nearby galaxies, as a function of time, has been developped and implemented. For the first time, the full SFH of a nearby dwarf irregular galaxy (DIG) has been retrieved from the photometry of its resolved stars. In the [(V-I),I] colour-magnitude diagram (CMD) of about 18000 stars in NGC 6822, two structures, the red-tangle and the red-tail, are the locus of the old and intermediate-age RGB and AGB stars. The tool used to retrieve the SFH is the comparison of the observed CMD with a set of model CMDs, computed assuming different evolutionary scenarios. The model CMDs have been computed in collaboration with the Padova Group if stellar evolution. Their reliability is a result of three main components : i) a reliable set of stellar evolutionary models covering the needed range of ages and metallicities, ii) the interpolation of the stellar evolutionary tracks of fixed mass and metallicity to determine the smooth distribution of stars of any age, mass, and metallicity on the CMD, and iii) a realistic simulation of the observational effects on the synthetic CMD. The following constraints have been put on the SFH of NGC 6822: --Star formation beginning in NGC 6822 at T_i<= 6 Gyr can be ruled out. It has most likely begun at a very early epoch (about 15-12 Gyr ago), from low metallicity gas. --An SFR close to constant or declining in the last few Gyr of the galaxy's lifetime seems best to reproduce the observations. -- An overall enhancement of the star formation activity has occurred in the last 100-200 Myr. The strength of this enhancement has been different in different regions of the galaxy. The fundamentals of the method can be applied to galaxies of any morphological type, provided that deep enough photometry is available. This can be achieved, from the ground, for all Local Group galaxies, and using HST, for galaxies within 4--5 Mpc.

Gallart, C.; Aparicio, Antonio

1997-05-01

260

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

NASA Astrophysics Data System (ADS)

Context. The galaxy NGC 4418 contains one of the most compact obscured nuclei within a luminous infrared galaxy (LIRG) in the nearby Universe. This nucleus contains a rich molecular gas environment and an unusually high ratio of infrared-to-radio luminosity (q-factor). The compact nucleus is powered by either a compact starburst or an active galactic nucleus (AGN). Aims: The aim of this study is to constrain the nature of the nuclear region (starburst or AGN) within NGC 4418 via very-high-resolution radio imaging. Methods: Archival data from radio observations using the European Very Long Baseline Interferometry Network (EVN) and Multi-Element Radio Linked Interferometer Network (MERLIN) interferometers are imaged. Sizes and flux densities are obtained by fitting Gaussian intensity distributions to the image. The average spectral index of the compact radio emission is estimated from measurements at 1.4 GHz and 5.0 GHz. Results: The nuclear structure of NGC 4418 visible with EVN and MERLIN consists of eight compact (<49 mas i.e. <8 pc) features spread within a region of 250 mas, i.e. 41 pc. We derive an inverted spectral index ? ? 0.7 (S? ? ??) for the compact radio emission. Conclusions: Brightness temperatures >104.8 K indicate that these compact features cannot be HII-regions. The complex morphology and inverted spectrum of the eight detected compact features is evidence against the hypothesis that an AGN alone is powering the nucleus of NGC 4418. The compact features could be super star clusters with intense star formation, and their associated free-free absorption could then naturally explain both their inverted radio spectrum and the low radio-to-IR ratio of the nucleus. The required star formation area density is extreme, however, and close to the limit of what can be observed in a well-mixed thermal/non-thermal plasma produced by star formation, and is also close to the limit of what can be physically sustained.

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

2014-06-01

261

THE YOUNG STELLAR POPULATION OF THE NEARBY LATE-TYPE GALAXY NGC 1311  

SciTech Connect

We have extracted point-spread-function-fitted stellar photometry from near-ultraviolet, optical, and near-infrared images, obtained with the Hubble Space Telescope, of the nearby (D {approx} 5.5 Mpc) SBm galaxy NGC 1311. The ultraviolet and optical data reveal a population of hot main-sequence (MS) stars with ages of 2-10 Myr. We also find populations of blue supergiants with ages between 10 and 40 Myr and red supergiants with ages between 10 and 100 Myr. Our near-infrared data show evidence of star formation going back {approx}1 Gyr, in agreement with previous work. Fits to isochrones indicate a metallicity of Z {approx} 0.004. The ratio of blue to red supergiants is consistent with this metallicity. This indicates that NGC 1311 follows the well-known luminosity-metallicity relation for late-type dwarf galaxies. About half of the hot MS stars and blue supergiants are found in two regions in the inner part of NGC 1311. These two regions are each about 200 pc across, and thus have crossing times roughly equal to the 10 Myr age we find for the dominant young population. The luminosity functions of the supergiants indicate a slowly rising star formation rate ({approx}10{sup -3} M{sub sun} yr{sup -1}) from {approx}100 Myr ago until {approx}15 Myr ago, followed by a strong enhancement ({approx}10{sup -2} M{sub sun} yr{sup -1}) at {approx}10 Myr ago. We see no compelling evidence for gaps in the star-forming history of NGC 1311 over the last 100 Myr, and, with lower significance, none over the last Gyr. This argues against a bursting mode, and in favor of a gasping or breathing mode for the recent star formation history.

Eskridge, Paul B. [Department of Physics and Astronomy, Minnesota State University, Mankato, MN 56001 (United States); Windhorst, Rogier A.; Jansen, Rolf A. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States); Mager, Violet A., E-mail: paul.eskridge@mnsu.ed [Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287 (United States)

2010-11-15

262

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

263

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

SciTech Connect

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

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

2013-05-10

264

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

265

Evidence of merging in the Seyfert galaxy NGC 3393, revealed by modelling the spectra  

NASA Astrophysics Data System (ADS)

The discovery (Fabbiano et al. 2001) of two active black holes in the Seyfert galaxy NGC 3393, which are separated by about 490 light years, has revealed a merging event. This has led us to look for other evidence of galaxy collision and merging, using an analysis of the observed spectra in different frequency ranges. In the narrow-line region (NLR) of NGC 3393, we have found pre-shock densities that are higher by a factor of about 10 than in other active galactic nuclei, and we have found patches of ionized matter beyond the observed NLR bulk. These can be explained by the compression and heating of the gas downstream of the shock waves created by the collision. Metallicity, in terms of the O/H relative abundance, is about 0.78 solar. The Mg/H depletion by a factor of about 3, compared with solar, cannot be explained by Mg trapping into dust grains, as a result of high shock velocities. The low O/H and Mg/H abundances indicate mixing with external matter during the collision. Twice solar N/H is predicted by modelling the spectra of high-shock-velocity clouds reached by a T* ? 105 K blackbody flux. This suggests that Wolf-Rayet stars could be created by galaxy collision in the central region.

Contini, M.

2012-09-01

266

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

267

High-density Molecular Gas Properties of the Starburst Galaxy NGC 1614 Revealed with ALMA  

NASA Astrophysics Data System (ADS)

We present the results of HCN/HCO+/HNC J = 4-3 transition line observations of the nearby starburst galaxy NGC 1614, obtained with ALMA Cycle 0. We find that high density molecular gas traced with these lines shows a velocity structure such that the northern (southern) side of the nucleus is redshifted (blueshifted) with respect to the nuclear velocity of this galaxy. The redshifted and blueshifted emission peaks are offset by ~0.''6 at the northern and southern sides of the nucleus, respectively. At these offset positions, observations at infrared >3 ?m indicate the presence of active dusty starbursts, supporting the picture that high-density molecular gas is the site of active starbursts. The enclosed dynamical mass within the central ~2'' in radius, derived from the dynamics of the high-density molecular gas, is ~109 M ?, which is similar to previous estimates. Finally, the HCN emission is weaker than HCO+ but stronger than HNC for J = 4-3 for all starburst regions of NGC 1614, as seen for J = 1-0 transition lines in starburst-dominated galaxies.

Imanishi, Masatoshi; Nakanishi, Kouichiro

2013-09-01

268

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

269

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

270

The Properties of Local Barred Disks in the Field and Dense Environments: Implications for Galaxy Evolution  

NASA Astrophysics Data System (ADS)

Stellar bars are the most efficient internal drivers of disk evolution because they redistribute material and angular momentum within the galaxy and dark matter halo. Mounting evidence suggests that processes other than major mergers, such as minor mergers, secular processes driven by bars, and clump coalescence, as well as smooth accretion, play an important role in galaxy evolution since z = 2. As a key step toward characterizing this evolution and constraining theoretical models, we determine the frequency and properties of bars in the local Universe in both field and cluster environment, based on three of our studies: Marinova & Jogee (2007), Barazza, Jogee, & Marinova (2008) and Marinova et al. (2009). Among field spirals of intermediate Hubble types in the OSU survey, we find using ellipse fitting that the bar fraction is 44% in the optical and 60% in the NIR, giving an extinction correction factor of approximately 1.4 at z ˜ 0. Using data from the Abell 901/902 cluster system at z ˜ 0.165 from the HST ACS survey STAGES, we find that the optical bar fraction is a strong trend of both absolute magnitude and host bulge-to-total ratio, increasing for galaxies that are brighter and/or more disk-dominated. The latter trend is also found in the field from SDSS. For bright early types and faint late types the optical bar fraction in the cluster is similar to that in the field. We find that between the core region and the virial radii of the clusters the optical bar fraction is not a strong function of local environment density. We discuss the implications of our results in the context of theoretical models of the impact of bars on galaxy evolution.

Marinova, I.; Jogee, S.; Barazza, F. D.; Heiderman, A.; Gray, M. E.; Barden, M.; Wolf, C.; Peng, C. Y.; Bacon, D.; Balogh, M.; Bell, E. F.; Böhm, A.; Caldwell, J. A. R.; Häußler, B.; Heymans, C.; Jahnke, K.; van Kampen, E.; Lane, K.; McIntosh, D. H.; Meisenheimer, K.; Sánchez, S. F.; Sommerville, R. S.; Taylor, A.; Wisotzki, L.; Zheng, X.

2009-12-01

271

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

272

The Globular Cluster System of NGC 4636 and Formation of Globular Clusters in Giant Elliptical Galaxies  

NASA Astrophysics Data System (ADS)

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 & Huchra method, and [Z/H], age, and [?/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(? = 0.32) and -0.35(? = 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 [?/Fe] of the GCs shows a broad distribution with a mean value [?/Fe] ?0.14 dex. The dependence of these chemical properties on the galactocentric radius is weak. We also derive the metallicities, ages, and [?/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 [?/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. Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Park, Hong Soo; Lee, Myung Gyoon; Hwang, Ho Seong; Kim, Sang Chul; Arimoto, Nobuo; Yamada, Yoshihiko; Tamura, Naoyuki; Onodera, Masato

2012-11-01

273

Stellar Populations in NGC 4038/39 (the Antennae): Exploring a Galaxy Merger Pixel by Pixel  

NASA Astrophysics Data System (ADS)

We present deep, photometrically calibrated BVRJHK images of the nearby interacting galaxy pair NGC 4038/39 (the Antennae). Color maps of the images are derived, and those using the B, V, and K bands are analyzed with techniques developed for examining the colors of stars. From these data we derive pixel-by-pixel maps of the distributions of stellar populations and dust extinction for the galaxies. Analysis of the stellar population map reveals two distinct episodes of recent star formation: one currently in progress and a second that occurred ~600 Myr ago. A roughly 15 Gyr old population is found which traces the old disks of the galaxies and the bulge of NGC 4038. The models used successfully reproduce the locations of clusters, and the ages we derive are consistent with those found from previous Hubble Space Telescope observations of individual star clusters. We also find five luminous ``super-star clusters'' in our K-band images that do not appear in the B- or V-band images. These clusters are located in the overlap region between the two galaxies, and are hidden by dust with visual extinctions of AV>~3 mag. The techniques we describe in this paper should be generally applicable to the study of stellar populations in galaxies for which detailed spatial resolution with HST is not possible. Based in part on observations obtained at the Cerro Tololo Inter-American Observatory (CTIO), operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the National Science Foundation.

Kassin, Susan A.; Frogel, Jay A.; Pogge, Richard W.; Tiede, Glenn P.; Sellgren, K.

2003-09-01

274

Planetary Camera imaging of the counter-rotating core galaxy NGC 4365  

NASA Technical Reports Server (NTRS)

We analyze F555W(V) band Planetary Camera images of NGC 4365, for which ground-based spectroscopy has revealed a misaligned, counter-rotating core. Line profile analysis by Surma indicates that the counter-rotating component has a disk structure. After deconvolution and galaxy modeling, we find photometric evidence, at small radii to support this claim. There is no indication of a central point source or dust lane. The surface brightness profile reveals a steep outer profile and shallow, by not flat, inner profile with the inflection radius occurring at 1.8 sec. The inner profile is consistent with a cusp.

Forbes, Duncan A.

1994-01-01

275

Perseus I and the NGC 3109 association in the context of the Local Group dwarf galaxy structures  

NASA Astrophysics Data System (ADS)

The recently discovered dwarf galaxy Perseus I appears to be associated with the dominant plane of non-satellite galaxies in the Local Group (LG). We predict its velocity dispersion and those of the other isolated dwarf spheroidals Cetus and Tucana to be 6.5, 8.2 and 5.5 km s-1, respectively. The NGC 3109 association, including the recently discovered dwarf galaxy Leo P, aligns with the dwarf galaxy structures in the LG such that all known nearby non-satellite galaxies in the northern Galactic hemisphere lie in a common thin plane (rms height 53 kpc; diameter 1.2 Mpc). This plane has an orientation similar to the preferred orbital plane of the Milky Way (MW) satellites in the vast polar structure. Five of seven of these northern galaxies were identified as possible backsplash objects, even though only about one is expected from cosmological simulations. This may pose a problem, or instead the search for local backsplash galaxies might be identifying ancient tidal dwarf galaxies expelled in a past major galaxy encounter. The NGC 3109 association supports the notion that material preferentially falls towards the MW from the Galactic south and recedes towards the north, as if the MW were moving through a stream of dwarf galaxies.

Pawlowski, Marcel S.; McGaugh, Stacy S.

2014-05-01

276

Barred Galaxies in the Abell 901/2 Supercluster with Stages  

NASA Astrophysics Data System (ADS)

We present a study of bar and host disk evolution in a dense cluster environment, based on a sample of ~800 bright (M V <= -18) galaxies in the Abell 901/2 supercluster at z~ 0.165. We use Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) F606W imaging from the STAGES survey, and data from Spitzer, XMM-Newton, and COMBO-17. We identify and characterize bars through ellipse-fitting, and other morphological features through visual classification. We find the following results. (1) To define the optical fraction of barred disk galaxies, we explore three commonly used methods for selecting disk galaxies. We find 625, 485, and 353 disk galaxies, respectively, via visual classification, a single component Sérsic cut (n <= 2.5), and a blue-cloud cut. In cluster environments, the latter two methods suffer from serious limitations, and miss 31% and 51%, respectively, of visually identified disks, particularly the many red, bulge-dominated disk galaxies in clusters. (2) For moderately inclined disks, the three methods of disk selection, however, yield a similar global optical bar fraction (f bar-opt) of 34%+10% -3% (115/340), 31%+10% -3% (58/189), and 30%+10% -3% (72/241), respectively. (3) We explore f bar-opt as a function of host galaxy properties and find that it rises in brighter galaxies and those which appear to have no significant bulge component. Within a given absolute magnitude bin, f bar-opt is higher in visually selected disk galaxies that have no bulge as opposed to those with bulges. Conversely, for a given visual morphological class, f bar-opt rises at higher luminosities. Both results are similar to trends found in the field. (4) For bright early-types, as well as faint late-type systems with no evident bulge, the optical bar fraction in the Abell 901/2 clusters is comparable within a factor of 1.1-1.4 to that of field galaxies at lower redshifts (z < 0.04). (5) Between the core and the virial radius of the cluster (R~ 0.25-1.2 Mpc) at intermediate environmental densities (log(?10) ~ 1.7-2.3), the optical bar fraction does not appear to depend strongly on the local environment density tracers (?, ?10, and intracluster medium (ICM) density), and varies at most by a factor of ~1.3. Inside the cluster core, we are limited by number statistics, projection effects, and different trends from different indicators, but overall f bar-opt does not show evidence for a variation larger than a factor of 1.5. We discuss the implications of our results for the evolution of bars and disks in dense environments.

Marinova, Irina; Jogee, Shardha; Heiderman, Amanda; Barazza, Fabio D.; Gray, Meghan E.; Barden, Marco; Wolf, Christian; Peng, Chien Y.; Bacon, David; Balogh, Michael; Bell, Eric F.; Böhm, Asmus; Caldwell, John A. R.; Häußler, Boris; Heymans, Catherine; Jahnke, Knud; van Kampen, Eelco; Lane, Kyle; McIntosh, Daniel H.; Meisenheimer, Klaus; Sánchez, Sebastian F.; Somerville, Rachel; Taylor, Andy; Wisotzki, Lutz; Zheng, Xianzhong

2009-06-01

277

Initial Results from a Very Deep Chandra Observation of the Galaxy Group NGC 5813  

NASA Astrophysics Data System (ADS)

I will present initial results from a deep (650 ks) Chandra observation of the galaxy group NGC 5813, the deepest Chandra observation of a galaxy group core to date. This unique system shows three pairs of collinear cavities in the intragroup medium (IGM), with each pair associated with an elliptical outburst shock front with a measured temperature jump. It is therefore ideal for studying AGN feedback and the outburst history of the central AGN. Measurements of the shock heating at each shock front show that shocks alone are enough to offset radiative cooling of the gas indefinitely, within least the central 26 kpc. The internal energy of the cavities is not required, and is likely deposited in the IGM at larger radii. This demonstrates that shock heating can play an important role in the AGN feedback process, particularly at smaller radii, close to the central AGN.

Randall, Scott; Nulsen, P.; Forman, W.; Clarke, T.; Donahue, M.; Giacintucci, S.; Jones, C.; Sun, M.; Churazov, E.; David, L.; Kraft, R.; Blanton, E.; Simionescu, A.; Werner, N.

2012-09-01

278

NuSTAR observations of the starburst galaxy NGC 253: constraints on diffuse inverse Compton emission  

NASA Astrophysics Data System (ADS)

The nearby starburst galaxy NGC 253 has been detected at GeV and TeV energies, however, the dominant emission mechanism responsible for the gamma-ray luminosity is challenging to determine from the Fermi-LAT and H.E.S.S. data alone. Understanding what fraction of the gamma-ray signal comes from hadronic processes has implications for the non-thermal energy density in actively star-forming regions in both cosmic rays and magnetic fields. The focusing hard X-ray optics of NuSTAR have enabled the most sensitive search to date for diffuse inverse Compton emission in the 10-30 keV energy range in a starburst galaxy. We discuss NuSTAR upper limits on the diffuse inverse Compton component in the context of broadband spectral models.

Bechtol, Keith

2014-08-01

279

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

SciTech Connect

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 {approx}<10{sup 3} M{sub Sun }. 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{alpha} luminosities, which needs to be taken into account when conducting this type of analysis.

Andrews, J. E.; Calzetti, D. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)] [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Chandar, R. [Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606 (United States)] [Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606 (United States); Lee, J. C.; Whitmore, B. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)] [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Elmegreen, B. G. [IBM T. J. Watson Research Center, Yorktown Heights, NY (United States)] [IBM T. J. Watson Research Center, Yorktown Heights, NY (United States); Kennicutt, R. C. [Institute of Astronomy, Cambridge University, Cambridge (United Kingdom)] [Institute of Astronomy, Cambridge University, Cambridge (United Kingdom); Kissel, J. S. [Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)] [Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Da Silva, Robert L.; Krumholz, Mark R. [Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)] [Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States); O'Connell, R. W. [Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903 (United States)] [Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903 (United States); Dopita, M. A. [Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston, ACT 2611 (Australia)] [Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston, ACT 2611 (Australia); Frogel, Jay A. [Galaxies Unlimited, 1 Tremblant Court, Lutherville, MD (United States)] [Galaxies Unlimited, 1 Tremblant Court, Lutherville, MD (United States); Kim, Hwihyun, E-mail: jandrews@astro.umass.edu, E-mail: callzetti@astro.umass.edu [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404 (United States)] [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404 (United States)

2013-04-10

280

Identification of an Extensive Luminous Halo Around the Ringed Spiral Galaxy NGC 7217  

NASA Astrophysics Data System (ADS)

The isolated spiral galaxy NGC 7217 is characterized by flocculent spiral structure and three optical ring-like zones: a stellar nuclear ring, a weak inner pseudoring, and a bright patchy outer ring. The rings all have nearly the same shape and position angle in projection. To understand this kind of ringed galaxy, we have obtained deep CCD BVRI surface photometry and mapping of the CO and HI gas distributions and kinematics. Our images reveal something that was missed in previous studies: a large, nearly round halo of light extending far beyond the outer ring. We interpret this as bulge light which comes back to dominate the luminosity distribution at large radii. Ellipse fits to isophotes out to 240('') radius reveal a minimum axis ratio of 0.83 just outside the outer ring at 90('') , and then a rise to 0.96 at about 140('') . The luminosity profiles are well-fitted by a combined r({1/) 4} bulge and exponential disk model. In all filters, the bulge dominates at all radii, and the bulge-to-total disk ratio is about 2.3 (B). If the minimum axis ratio of 0.83 approximates the apparent flattening of the disk, then NGC 7217 is remarkably axisymmetric. Nevertheless, the I-band image reveals a tightly-wrapped, two-armed spiral pattern in the outer ring region. The outer ring includes 4.5% of the total B luminosity and is the locus of most of the recent star formation in the galaxy; it is also where the HI gas is concentrated. An additional noteworthy feature is a circumnuclear dust ring 1.2 kpc in diameter. Other dust lanes are seen only on the near side of the galaxy. The rings of NGC 7217 could be resonances with a very weak internal perturbation. We are attempting to simulate the structure using the I-band light distribution to help define the potential. But most interesting is the recent discovery of a substantial population of counter-rotating stars in the galaxy (Kuijken 1993, PASP, 105, 1016). One possible explanation for these stars is that the bulge is more important than previous studies indicated. Our surface photometry tentatively supports this idea.

Buta, R.; van Driel, W.; Braine, J.; Combes, F.

1993-12-01

281

Interstellar Absorption Lines in the Spectrum of the Starburst Galaxy NGC 1705  

NASA Astrophysics Data System (ADS)

I present the results of a GHRS archival study of the interstellar absorption lines in the line-of-sight to the H i-rich, starburst dwarf galaxy NGC 1705 in the 1170 to 1740 Angstroms \\ range at ~ 120 km s(-1) resolution. In an earlier study using the same data, Sahu & Blades (1997) identified the interstellar component at --20 km s(-1) (LSR velocities) with Milky Way disk/halo gas and the 260 km s(-1) component with a small, isolated high-velocity cloud HVC 487, located ~ 10(deg) from the H i gas which envelops the Magellanic Clouds and the Magellanic Stream (MS). The 540 km s(-1) absorption component seen in the GHRS spectra was identified with the front side of a kpc-scale expanding, ionized supershell centred on the central superstar cluster NGC 1705-1 and has a low Fe/Al abundance ratio. I report a low N/Si abundance ratio for the 540 km s(-1) component. Massive stars (> 10 M_sun) evolve on time scales <= 2 x 10(7) years and return elements like Si into the ISM through Type II SNe while the main contributors to nitrogen are intermediate stars (1 to 10 M_sun) through He shell burning. The N/Si ratio of the supershell component of NGC 1705 is a good indicator of the age of the dwarf galaxy: the N/Si is expected to decrease because of the increase in Si through Type II SNe due to the massive stars, until the onset of He shell burning in intermediate mass stars which occurs on time scales of 10(8) -- 10(9) years. The data point to nucleosythetic enrichment of the supershell component by the first generation of massive stars in NGC 1705-1 over a time scale of < 10(8) years. This time scale for the supershell component is consistent the age estimate of 10 -- 20 x 10(6) years for NGC 1705-1 (Heckman and Leitherer, 1997) and with the low Fe/Al abundance reported by Sahu and Blades.

Sahu, Meena S.

1998-05-01

282

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

283

Gaseous-phase metallicities and stellar populations in the centres of barred galaxies  

NASA Astrophysics Data System (ADS)

Numerical simulations predict that bars represent a very important agent for triggering gas inflows, which in turn could lead to central star formation. Bars thus are thought to contribute to the formation of the bulge. This process changes both the gaseous-phase and the stellar-phase metallicities in the centres of galaxies. With the aim of quantifying the importance of this process, we present a comparative study of the gaseous-phase and stellar-phase metallicities in the centres of members of a sample of barred and unbarred galaxies from SDSS. We do not find a significant difference in the metallicity (neither gaseous nor stellar) between barred and unbarred galaxies, but we find different trends in the metallicities of early- and late-type galaxies, with larger differences in the metallicity in the early-type subsample. Our results contradict some previous research in this field, but we find a possible origin of the discrepancies between previous works and our results.

Cacho, R.; Sánchez-Blázquez, P.; Gorgas, J.; Pérez, I.

2014-08-01

284

Detection of Molecular Clouds in the Interarm of the Flocculent Galaxy NGC 5055  

NASA Astrophysics Data System (ADS)

We present high-resolution (˜ 4'') 12CO(J = 1-0) mapping observations with high-velocity resolution (˜ 2.6 km s-1) toward the disk of flocculent galaxy NGC 5055, using the Nobeyama Millimeter Array in order to study the physical properties of the molecular clouds in the arm and the interarm. The map shows clumpy structures. Although these are mainly distributed along an arm seen in NIR, some are located in the interarm. These clouds in the arm and the interarm have a typical size and mass of a few 100pc and a few 106Msolar. These correspond to the largest Giant Molecular Cloud (GMC) in our Galaxy, and are slightly smaller than Giant Molecular Associations (GMAs) in the grand design spiral M 51. Their CO flux-based masses show good agreement with their virial masses. A size-velocity dispersion relation is plotted on an extension of the relation for the Galactic GMCs. It suggest that the properties of these clouds are similar to that of the Galactic GMCs. We found no clear systematic offset between the molecular gas and H II regions unlike M 51. This and no existense of GMAs suggest that, in NGC 5055, cloud formation and star formation in the arm and the interarm are due to enhancement of gas by local fluctuation; while, in grand design spiral galaxies, such as M 51, GMA formations may occur only in the arm due to a strong density wave and enhanced star formation in GMA formation may occur. These may control the optical morphology of spiral arms in spiral galaxies.

Tosaki, Tomoka; Shioya, Yasuhiro; Kuno, Nario; Nakanishi, Kouichiro; Hasegawa, Takashi

2003-06-01

285

New Kinematics for the Central Spheroid in Polar Disk Galaxy NGC4650A  

NASA Astrophysics Data System (ADS)

NGC4650A is the prototype for Polar Ring Galaxies (PRGs). Its luminous components, inner spheroid and polar structure, have been studied with optical and near-infrared photometry, optical spectroscopy and in the radio. The central spheroid is an exponential thick disk, characterized by a very bright nucleus; the polar structure has been shown to be a disk, rather than a ring. The question about the shape of the dark halo of NGC4650A is still open: the biggest uncertainties in the mass models proposed until 1996 for the dark halo shape were maily related to the difficulty in measuring velocity dispersion profiles along the major axis of the central spheroid. In order to constraint the dark halo shape, we have obtained high resolution spectra (with FORS2@UT4 on the ESO VLT) of the Calcium triplet absorption lines on the photometric axes of the stellar spheroid in NGC4650A. The new CaT spectra are better tracers of the kinematics for the NGC4650A spheroid than was available before. Along the major axis, the observed rotation and velocity dispersion measurements show the presence of a kinematically decoupled nucleus, and a flat velocity dispersion profile. The minor axis kinematics is determined for the first time: along this direction some rotation is measured, and the velocity dispersion is nearly constant and slightly increases at larger distances from the center. The new high resolution kinematic data suggest that the stellar component in NGC4650A resembles a nearly-exponential oblate spheroid supported by rotation. The main implications of these results on the previous mass models for NGC4650A concern the law adopted to fit the velocity dispersion profile: the measured flat velocity dispersion profile along the spheroid major axis shows that both the linear decreasing fit and the exponential empirical law adopted in the previous mass models do not reproduce the observed trend with radius and previous conclusions on the halo flattening are no longer valid. Moreover, the new kinematic data set constraints on current models for the formation scenarios of PRG, supporting a slow accretion rather then a secondary strong dissipative event.

Iodice, E.; Arnaboldi, M.; Saglia, R.; Sparke, L.; Gerhard, O.

2007-05-01

286

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

287

TOWARD A NEW GEOMETRIC DISTANCE TO THE ACTIVE GALAXY NGC 4258. III. FINAL RESULTS AND THE HUBBLE CONSTANT  

SciTech Connect

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{sub 0} = 72.0 {+-} 3.0 km s{sup -1} Mpc{sup -1}.

Humphreys, E. M. L. [European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei Muenchen (Germany); Reid, M. J.; Moran, J. M.; Greenhill, L. J.; Argon, A. L., E-mail: ehumphre@eso.org [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2013-09-20

288

Observations of Sy2 galaxy NGC 3281 by XMM-Newton and INTEGRAL satellites  

NASA Astrophysics Data System (ADS)

We present the results of the analysis of X-ray properties of the Seyfert 2 galaxy NGC 3281, based on the observational data obtained by XMM-Newton and INTEGRAL within the energy ranges 0.2-12 keV and 20-150 keV, respectively. The XMM-Newton spectrum of this object is presented for the first time. We show that fitting the X-ray spectrum of this galaxy with models based on the reflection from the disc with infinite column density yields non-physical results. A more appropriate fit takes into account both transmitted and reflected emission, passed through a gas-dust torus-like structure. Keeping this in mind, to model the inhomogeneous clumpy torus, we used the MYTorus model. Hence, we conclude that the torus of NGC 3281 is not a continuous structure, but rather consists of separate clouds, which is in a good agreement with the results of near-IR observations. Using this assumption, we found that the torus inclination angle and the hydrogen column density are 66.98^{+2.63}_{-1.34} degrees and 2.08^{+0.35}_{-0.18}×10^{24} cm^{-2}, respectively. Also, emissions of hot diffuse gases with temperature ˜590 eV, and warm absorption, were detected.

Vasylenko, A. A.; Fedorova, E.; Zhdanov, V. I.

2013-12-01

289

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

290

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

SciTech Connect

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

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

2011-01-20

291

Spitzer Space Telescope IRAC and MIPS Observations of the Interacting Galaxies IC2163 and NGC2207: Clumpy Emission  

Microsoft Academic Search

IC 2163 and NGC 2207 are interacting galaxies that have been well studied at optical and radio wavelengths and simulated in numerical models to reproduce the observed kinematics and morphological features. Spitzer IRAC and MIPS observations reported here show over 200 bright clumps from young star complexes. The brightest IR clump is a morphologically peculiar region of star formation in

D. M. Elmegreen; B. G. Elmegreen; M. Kaufman; K. Sheth; C. Struck; M. Thomasson; E. Brinks

2005-01-01

292

Spitzer Space Telescope IRAC and MIPS Observations of the Interacting Galaxies IC 2163 and NGC 2207: Clumpy Emission  

Microsoft Academic Search

IC 2163 and NGC 2207 are interacting galaxies that have been well studied at optical and radio wavelengths and simulated in numerical models to reproduce the observed kinematics and morphological features. Spitzer IRAC and MIPS observations reported here show over 200 bright clumps from young star complexes. The brightest IR clump is a morphologically peculiar region of star formation in

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

2006-01-01

293

Hubble Space Telescope First Observations of the Brightest Stars in the Virgo Galaxy M100 = NGC 4321  

NASA Technical Reports Server (NTRS)

As part of both the Early Release Observations fromthe Hubble Space Telescope and the Key PRoject on the Extragalctic Distance Scale, we have obtained multi-wavelength BVR WFPC2 images for the face-on Virgo cluster spiral galaxy M11 = NGC 4321.

Freedman, W. L.; Madore, B. F.; Stetson, P. B.; Hughes, S. M. G.; Holtzman, J. A.; Mould, J. R.; Trauger, J. T.; Gallagher, J. S., III; Ballester, G. E.; Burrows, C. J.; Casertano, S.; Clarke, J. T; Crisp, D.; Ferrarese, L.; Ford, H.; Graham, J. A.; Griffiths, R. E.; Hester, J. J.; Hill, R.; Hoessel, J. G.; Huchra, J.; Kennicutt, R. C.; Scowen, P. A.; Sparks, B.; Stapelfeldt, K. R.

1994-01-01

294

Understanding the Puzzling X-Ray Spectrum of the SO Galaxy NGC 4382; NGC 43819: Spectral Analysis of the Prototypical Early Merger and ASCA Observations of a Dynamically Young Elliptical: NGC 4125  

NASA Technical Reports Server (NTRS)

We have analyzed the ASCA observations of NGC 4382, NGC 4038/9, NGC 4125 and produced papers for publication. NGC 4382 is one of the E and SO galaxies detected with the lowest X-ray to optical luminosity ratio. These galaxies have a peculiar X-ray (0.1-3 keV) spectrum, with a significant excess of counts in the lowest spectral channels (less than 1 keV) relative to the spectral count distributions of X-ray brihter E and SO galaxies. Analyzing the ROSAT PSPC observation of NGC 4382 it was unclear whether this soft excess was due to a real very soft component in a multi-component spectrum, or reflected an extremely low metal abundance in an isothermal hot gas. Our ASCA observations show that the low-abundance single-temperature model does not fit well to the X-ray spectrum, in agreement with our previous suggestions. A better explanation is a composite spectrum with a very soft component (0.3 keV) in addition to a harder (5 keV) component from X-ray binaries. In this model, the abundance cannot be constrained. More complex spectral models are also possible. The ASCA observations of The Antennae - (NGC4038/9) show that at least two spectral components are required to describe the emission-thermal emission from a plasma at 0.8 keV, and a component at higher energies. The hot gas contributes about half of the flux in the 0.5 to 6 keV band. If the column density to the higher energy component is greater than 2 x 10 (exp 21) per square centimeter, then the fitted abundance in the hot gas component is less than 0.2 solar. This low abundance is not expected for the hot interstellar medium in NGC4038/9 in which supernovae and star formation (expected to enrich and heat the gas) are ongoing. We do not detect any spatial variations in the spectrum. We relate these findings to data obtained by other satellites (Einstein, ROSAT) for this interacting galaxy pair. NGC4125's ASCA data was analyzed jointly with its Beppo-SAX observation. A hard component (kT /sim 4-10 keV) is observed together with a thermal component with line emission.

Fabbiano, Giuseppina

2001-01-01

295

The construction of barred galaxy models using non-linear extensions of linear modes  

NASA Astrophysics Data System (ADS)

We present a new method for the construction of quasi-self-consistent dynamical models for the stellar component of barred or spiral galaxies, based on the non-linear extension of linear modes. Just like N-body simulations, these barred models are guaranteed to be physical, since they are based on the presence of a global instability in an initially axisymmetric system. In addition, the full distribution function is obtained with very high accuracy and resolution, making this method particularly well suited for the interpretation of high quality observational data, such as line-of-sight velocity distributions (LOSVDs). We show that such a model produces distribution functions, and hence LOSVDs, that are different from models based on purely linear modes. We created a barred galaxy model using this method, and calculated observable kinematics: velocity fields, dispersion fields, vertex deviations and LOSVDs. The behaviour of the stellar component turns out to be qualitatively very similar to the gaseous component, but the kinematic signature of the bar is not so well pronounced, as a result of the presence of velocity dispersion. However, we show that LOSVDs can show a very clear signature of the bar, and may even become double-peaked in some places. This indicates that the comparison of observed stellar line profiles with detailed models may provide important information, such as bar masses and eccentricities, pattern speeds, etc.

Vauterin, P.; Dejonghe, H.

1997-04-01

296

Supernova Remnants in the Most Fertile Galaxy: NGC 6946  

NASA Astrophysics Data System (ADS)

As the host to more recorded supernovae (nine in the past century) than any other galaxy, ngal is a unique venue for studying young (and old) supernova remnants (SNRs). Using deep emission-line images of ngal we obtained from WIYN, we have identified 148 new emission nebulae through their high S II:H? ratios, indicating that they are strong SNR candidates. This is over 5 times as many as have previously been identified; yet of the 175 total objects, only 6 have been spectroscopically confirmed. We propose multislit spectroscopy from GMOS-N to study the majority of those with no spectra to date. Some 26 are essentially unresolved in our images (diameters ? 1 arcsec=27 pc at ngal) and hence probably are relatively young. Several are also coincident with soft X-ray sources (a further indicator of youthful vigor) and have strong O III emission. Some may be rare, ejecta- dominated core-collapse SNRs akin to Cas A, where ``fresh" nucleosynthesis products can be seen. Only spectroscopy, to look for broad emission lines from fast-moving ejecta, can confirm this. We will include spectra of two of the nine recorded SNe in ngal-the first late-time spectrum of SN 2004et, and the first of SN 1980K with high signal-to-noise-adding to the extremely small number of spectra for SNRs only a few decades old. Finally we will use the H II:H? ratio in a large number of ISM-dominated SNRs to map the N abundance and its gradient across the disk of ngal, and we will use archival HST images to identify the stellar environments that produced the SNe whose remnants we see today.

Winkler, P. Frank; Long, Knox S.; Blair, William P.

2014-08-01

297

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

298

DISCOVERY OF AN ACTIVE SUPERMASSIVE BLACK HOLE IN THE BULGELESS GALAXY NGC 4561  

SciTech Connect

We present XMM-Newton observations of the Chandra-detected nuclear X-ray source in NGC 4561. The hard X-ray spectrum can be described by a model composed of an absorbed power law with {Gamma} = 2.5{sup +0.4}{sub -0.3} and column density N{sub H} = 1.9{sup +0.1}{sub -0.2} Multiplication-Sign 10{sup 22} atoms cm{sup -2}. The absorption-corrected luminosity of the source is L(0.2-10.0 keV) =2.5 Multiplication-Sign 10{sup 41} erg s{sup -1}, with bolometric luminosity over 3 Multiplication-Sign 10{sup 42} erg s{sup -1}. Based on the spectrum and the luminosity, we identify the nuclear X-ray source in NGC 4561 to be an active galactic nucleus (AGN), with a black hole (BH) of mass M{sub BH} >2 Multiplication-Sign 10{sup 4} M{sub Sun }. The presence of a supermassive black hole at the center of this bulgeless galaxy shows that BH masses are not necessarily related to bulge properties, contrary to general belief. Observations such as these call into question several theoretical models of BH-galaxy coevolution that are based on merger-driven BH growth; secular processes clearly play an important role. Several emission lines are detected in the soft X-ray spectrum of the source which can be well parameterized by an absorbed diffuse thermal plasma with non-solar abundances of some heavy elements. Similar soft X-ray emission is observed in spectra of Seyfert 2 galaxies and low-luminosity AGNs, suggesting an origin in the circumnuclear plasma.

Salvo, C. Araya; Mathur, S. [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Ghosh, H. [CNRS/CEA-Saclay, F-91911 Gif-sur-Yvette (France); Fiore, F. [Osservatorio Astronomico di Roma, Via Frascati 33, I-100040 Monteporzio Catone (Italy); Ferrarese, L., E-mail: araya@astronomy.ohio-state.edu [Hertzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)

2012-10-01

299

OUTFLOW VERSUS INFALL IN SPIRAL GALAXIES: METAL ABSORPTION IN THE HALO OF NGC 891  

SciTech Connect

Gas accreting onto a galaxy will be of low metallicity while halo gas due to a galactic fountain will be of near-solar metallicity. We test these predictions by measuring the metal absorption line properties of halo gas 5 kpc above the plane of the edge-on galaxy NGC 891, using observations taken with HST/STIS toward a bright background quasar. Metal absorption lines of Fe II, Mg II, and Mg I in the halo of NGC 891 are clearly seen, and when combined with recent deep H I observations, we are able to place constraints on the metallicity of the halo gas for the first time. The H I line width defines the line broadening, from which we model opacity effects in these metal lines, assuming that the absorbing gas is continuously distributed in the halo. The gas-phase metallicities are [Fe/H] = -1.18 {+-} 0.07 and [Mg/H] = -0.23 + 0.36/ - 0.27 (statistical errors) and this difference is probably due to differential depletion onto grains. When corrected for such depletion using Galactic gas as a guide, both elements have approximately solar or even supersolar abundances. This suggests that the gas is from the galaxy disk, probably expelled into the halo by a galactic fountain, rather than from accretion of intergalactic gas, which would have a low metallicity. The abundances would be raised by significant amounts if the absorbing gas lies in a few clouds with thermal widths smaller than the rotational velocity of the halo. If this is the case, both the abundances and [Mg/Fe] would be supersolar.

Bregman, Joel N.; Seitzer, Patrick; Cowley, C. R.; Miller, Matthew J. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48105 (United States)] [Department of Astronomy, University of Michigan, Ann Arbor, MI 48105 (United States); Miller, Eric D., E-mail: jbregman@umich.edu [Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)

2013-03-20

300

Dissecting the star formation history of starburst galaxies: the case of NGC 7673  

NASA Astrophysics Data System (ADS)

We have collected archival data on NGC 7673 to constrain the star formation history that produced the young star clusters and the field stellar population in this galaxy during the last 2 Gyr. We have considered the sample of 50 star clusters detected by Hubble Space Telescope/WFPC2 in the UV,V and I bands and estimated their age, intrinsic reddening and mass via comparison of their colours with STARBURST99 models. We have found two prominent epochs of cluster formation occurred about 20 and 2 Myr ago, with somewhat minor events between 3 and 6 Myr ago. The star clusters are characterized by an intrinsic reddening E(B - V) < 0.4 mag and a mass lower than 2 × 106Msolar. Out of the 50 star clusters, we have selected 31 located within the boundaries of the (IUE) large slit that was employed to obtain the spectrum of NGC 7673 between 1150 and 3350 Å. For each cluster, we have built a synthetic spectrum corresponding to the age, mass and intrinsic reddening derived from the cluster colours, properly redshifted to NGC 7673. The spectra have then been added together in a final, clusters integrated spectrum. This and the IUE, FUSE spectra of NGC 7673 have allowed us to describe the star formation history of the unresolved stars in the field as either exponentially decaying or multiburst. In the first case, we have derived an e-folding time of 700 (900) Myr and an initial star formation rate of 16 (13) Msolaryr-1 when the Fitzpatrick's (Calzetti's) extinction law is used. In the case of a multiburst star formation history, we have assumed that the same bursts which produced the star clusters built up also the field population. In this way, the field population turns out to be composed by a young (<40 Myr) component three (two) times brighter than the star clusters, and a component as old as ~850 (450) Myr, about 200 (100) times more massive than the star clusters together. These star formation histories fit equally well the observed UV spectrum of NGC 7673.

Pasquali, A.; Castangia, P.

2008-03-01

301

Hubble Space Telescope/Faint Object Spectrograph Spectroscopy of Spatially Resolved Narrow-Line Regions in the Seyfert 2 Galaxies NGC 2110 and NGC 5929  

NASA Astrophysics Data System (ADS)

We present the results of UV and optical Hubble Space Telescope/Faint Object Spectrograph spectroscopy of bright, extranuclear regions of line emission in the Seyfert galaxies NGC 2110 and NGC 5929. We have obtained spectra of the brightest region of the ``nuclear jet'' of NGC 2110 (75 pc from the nucleus) and of the southwest emission-line cloud of NGC 5929 (90 pc from the nucleus), in the G130H (1090-1605 Å), G190H (1570-2310 Å), G400H (3235-4780 Å), and G570H (4570-6820 Å) configurations. The observed line ratios are compared with the predictions of the two component (matter- and ionization-bounded, MB-IB), central source photoionization models of Binette, Wilson, & Storchi-Bergmann and of the fast, photoionizing (``autoionizing'') shock models of Dopita & Sutherland. In both objects, the significant reddening inferred from the Balmer line ratios and/or its uncertainty limit the utility of the ultraviolet carbon lines C IV ?1549 and C III] ?1909 for discrimination between the central source and shock-induced photoionization mechanisms. In NGC 2110, shock+precursor models with a shock velocity of ~=400 km s-1 provide a better match to the data than the MB-IB models. However, given the simplifying assumptions made in the latter models, photoionization by a central source cannot be ruled out. We investigate whether photoionizing shocks in the emission-line region of NGC 2110 can power the extended, soft X-ray emission north of the nucleus and find that shock velocities higher than 500 km s-1 are required. In NGC 5929, the MB-IB models have problems reproducing the strengths of the neon lines, while shock+precursor models with a velocity ~=300 km s-1 provide a good match to the data. For both galaxies, the emission-line powers and volumes of the ionized gas inferred from observations imply that both the preshock density (n0) and magnetic parameter (B0/n1/20) must be relatively high (n0>10 cm-3 B0/n1/20~=4 ?G cm3/2) for the photoionizing shock models to be viable. Based on observations 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.

Ferruit, Pierre; Wilson, Andrew S.; Whittle, Mark; Simpson, Chris; Mulchaey, John S.; Ferland, Gary J.

1999-09-01

302

NGC 4654: polarized radio continuum emission as a diagnostic tool for a galaxy-cluster interaction. Models versus observations  

NASA Astrophysics Data System (ADS)

Context: .A recent comparison between deep VLA Hi observations and dynamical models of the Virgo cluster spiral galaxy NGC 4654 has shown that only a model involving a combination of a tidal interaction and ram pressure can reproduce the data. Aims: .Deep radio polarization studies, together with detailed MHD modeling, can independently verify those conclusions, that are based on Hi observations and dynamical models. Methods: .We performed deep polarized radio-continuum observations of the Virgo cluster spiral galaxy NGC 4654 with the Effelsberg 100 m telescope at 8.35 GHz and the VLA at 4.85 GHz. Detailed 3D MHD simulations were made to determine the large-scale magnetic field and the emission distribution of the polarized radio continuum in the model, during the galaxy evolution within the cluster environment. Results: .This direct comparison between the observed and simulated polarized radio continuum emission corroborates the earlier results, that the galaxy had a recent rapid close encounter with NGC 4639 and is undergoing weak ram pressure by the intracluster medium. Conclusions: .This combination of deep radio polarization studies and detailed MHD modeling thus gives us unique insight into the interactions of a galaxy with its cluster environment. It represents a diagnostic tool that is complementary to deep Hi observations.

Soida, M.; Otmianowska-Mazur, K.; Chy?y, K.; Vollmer, B.

2006-11-01

303

Cosmic Evolution of Barred Spiral Galaxies in the COSMOS 2degree field  

NASA Astrophysics Data System (ADS)

Challenging nearly a decade of observational results, several recent studies have suggested that the fraction of bars does not decline with redshift. The first of these studies (Sheth et al. 2003) pointed out that a measurement of the bar fraction at any epoch must take into account the bar length. With the improved pixel size of the ACS, surveys such as COSMOS, GOODS and GEMS have begun to adequately resolve bars. Our preliminary analysis with the COSMOS data, consistent with other recent studies (Elmegreen et al. 2004, Jogee et al. 2004), suggests that the bar fraction is constant with redshift. This is difficult to reconcile with earlier studies which concluded that bars have undergone two or more epochs of destruction and reformation. To better understand these different evolutionary scenarios we present preliminary results from an analysis of the 2-square degree COSMOS ACS field. With this unique data we compare the evolution of the bar properties (length, ellipticity) and the properties of the host galaxies to a well-studied local sample from 2MASS (Menendez-Delmestre et al. 2004) and GALEX (Gil de Paz et al. 2004).

Sheth, K.; Schinnerer, E.; Mobasher, B.; Scoville, N. Z.; Menendez-Delmestre, K.; Gil de Paz, A.; Koda, J.; Capak, P.; COSMOS Team

2004-12-01

304

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

305

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

306

ON THE MASS-LOSS RATE OF MASSIVE STARS IN THE LOW-METALLICITY GALAXIES IC 1613, WLM, AND NGC 3109  

SciTech Connect

We present a spectroscopic analysis of Very Large Telescope/X-Shooter observations of six O-type stars in the low-metallicity (Z {approx} 1/7 Z {sub sun}) galaxies IC 1613, WLM, and NGC 3109. The stellar and wind parameters of these sources allow us, for the first time, to probe the mass loss versus metallicity dependence of stellar winds at metallicities below that of the Small Magellanic Cloud (at Z {approx} 1/5 Z {sub sun}) by means of a modified wind momentum versus luminosity diagram. The wind strengths that we obtain for the objects in WLM and NGC 3109 are unexpectedly high and do not agree with theoretical predictions. The objects in IC 1613 tend toward a higher than expected mass-loss rate, but remain consistent with predictions within their error bars. We discuss potential systematic uncertainties in the mass-loss determinations to explain our results. However, if further scrutinization of these findings point towards an intrinsic cause for this unexpected sub-SMC mass-loss behavior, implications would include a higher than anticipated number of Wolf-Rayet stars and Ib/Ic supernovae in low-metallicity environments, but a reduced number of long-duration gamma-ray bursts produced through a single-star evolutionary channel.

Tramper, F.; Sana, H.; De Koter, A.; Kaper, L., E-mail: F.Tramper@uva.nl [Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands)

2011-11-01

307

A Novel Approach to Constrain the Mass Ratio of Minor Mergers in Elliptical Galaxies: Application to NGC 4889, the Brightest Cluster Galaxy in Coma  

NASA Astrophysics Data System (ADS)

Minor mergers are thought to be important for the buildup and structural evolution of massive elliptical galaxies. In this work, we report the discovery of a system of four shell features in NGC 4889, one of the brightest members of the Coma cluster, using optical images taken with the Hubble Space Telescope and the Sloan Digital Sky Survey. The shells are well aligned with the major axis of the host and are likely to have been formed by the accretion of a small satellite galaxy. We have performed a detailed two-dimensional photometric decomposition of NGC 4889 and of the many overlapping nearby galaxies in its vicinity. This comprehensive model allows us not only to firmly detect the low-surface brightness shells, but, crucially, also to accurately measure their luminosities and colors. The shells are bluer than the underlying stars at the same radius in the main galaxy. We make use of the colors of the shells and the color-magnitude relation of the Coma cluster to infer the luminosity (or mass) of the progenitor galaxy. The shells in NGC 4889 appear to have been produced by the minor merger of a moderate-luminosity (MI ? -18.7 mag) disk (S0 or spiral) galaxy with a luminosity (mass) ratio of ~90:1 with respect to the primary galaxy. The novel methodology presented in this work can be exploited to decode the fossil record imprinted in the photometric substructure of other nearby early-type galaxies. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555.

Gu, Meng; Ho, Luis C.; Peng, Chien Y.; Huang, Song

2013-08-01

308

A NOVEL APPROACH TO CONSTRAIN THE MASS RATIO OF MINOR MERGERS IN ELLIPTICAL GALAXIES: APPLICATION TO NGC 4889, THE BRIGHTEST CLUSTER GALAXY IN COMA  

SciTech Connect

Minor mergers are thought to be important for the buildup and structural evolution of massive elliptical galaxies. In this work, we report the discovery of a system of four shell features in NGC 4889, one of the brightest members of the Coma cluster, using optical images taken with the Hubble Space Telescope and the Sloan Digital Sky Survey. The shells are well aligned with the major axis of the host and are likely to have been formed by the accretion of a small satellite galaxy. We have performed a detailed two-dimensional photometric decomposition of NGC 4889 and of the many overlapping nearby galaxies in its vicinity. This comprehensive model allows us not only to firmly detect the low-surface brightness shells, but, crucially, also to accurately measure their luminosities and colors. The shells are bluer than the underlying stars at the same radius in the main galaxy. We make use of the colors of the shells and the color-magnitude relation of the Coma cluster to infer the luminosity (or mass) of the progenitor galaxy. The shells in NGC 4889 appear to have been produced by the minor merger of a moderate-luminosity (M{sub I} Almost-Equal-To -18.7 mag) disk (S0 or spiral) galaxy with a luminosity (mass) ratio of {approx}90:1 with respect to the primary galaxy. The novel methodology presented in this work can be exploited to decode the fossil record imprinted in the photometric substructure of other nearby early-type galaxies.

Gu Meng; Huang Song [School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China); Ho, Luis C. [Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Peng, Chien Y. [Giant Magellan Telescope Organization, 251 South Lake Avenue, Suite 300, Pasadena, CA 91101 (United States)

2013-08-10

309

Resolving the nuclear dust distribution of the Seyfert 2 galaxy NGC 3081  

NASA Astrophysics Data System (ADS)

We report far-infrared (FIR) imaging of the Seyfert 2 galaxy NGC 3081 in the range 70-500 ?m, obtained with an unprecedented angular resolution, using the Herschel Space Observatory instruments PACS and SPIRE. The 11 kpc (˜70 arcsec) diameter star-forming ring of the galaxy appears resolved up to 250 ?m. We extracted IR (1.6-500 ?m) nuclear fluxes, that is active nucleus-dominated fluxes, and fitted them with clumpy torus models, which successfully reproduce the FIR emission with small torus sizes. Adding the FIR data to the near- and mid-IR spectral energy distribution (SED) results in a torus radial extent of Ro= 4+2- 1 pc, as well as in a flat radial distribution of the clouds (i.e. the q parameter). At wavelengths beyond 200 ?m, cold dust emission at T= 28 ± 1 K from the circumnuclear star-forming ring of 2.3 kpc (˜15 arcsec) in diameter starts making a contribution to the nuclear emission. The dust in the outer parts of the galaxy is heated by the interstellar radiation field (19 ± 3 K).

Ramos Almeida, C.; Sánchez-Portal, M.; Pérez García, A. M.; Acosta-Pulido, J. A.; Castillo, M.; Asensio Ramos, A.; González-Serrano, J. I.; Alonso-Herrero, A.; Rodríguez Espinosa, J. M.; Hatziminaoglou, E.; Coia, D.; Valtchanov, I.; Povi?, M.; Esquej, P.; Packham, C.; Altieri, B.

2011-10-01

310

Hierarchy and size distribution function of star formation regions in the spiral galaxy NGC 628  

NASA Astrophysics Data System (ADS)

Hierarchical structures and the size distribution of star formation regions in the nearby spiral galaxy NGC 628 are studied over a range of scales from 50 to 1000 pc using optical images obtained with the 1.5-m telescope of the Maidanak Observatory. We have found hierarchically structured concentrations of star formation regions in the galaxy, and smaller regions with a higher surface brightness are located inside larger complexes that have a lower surface brightness. We illustrate this hierarchy using a dendrogram, or structure tree, of the detected star formation regions, which demonstrates that most of these regions are combined into larger structures over several levels. We have found three characteristic sizes of young star groups: ?65 pc (OB associations), ?240 pc (stellar aggregates) and ?600 pc (star complexes). The cumulative size distribution function of star formation regions is found to be a power law with a slope of approximately -1.5 on scales appropriate to diameters of associations, aggregates and complexes. This slope is close to the slope found earlier by B. Elmegreen et al. for star formation regions in the galaxy on scales from 2 to 100 pc.

Gusev, Alexander S.

2014-08-01

311

Galaxy shells and the structure of radio galaxies: Clues from Centaurus A (NGC 5128)  

NASA Astrophysics Data System (ADS)

We show that the northern middle radio lobe of Cen A, an intriguing and much debated manifestation of radio lobe asymmetry, can be understood in terms of a direct interaction of the northern jet with a gaseous cloud associated with a stellar shell. This same basic mechanism was proposed earlier for the northern inner lobe, but new data allows a more detailed case to be made for the northern middle lobe. Although such an interaction can presently be demonstrated only for Cen A, the nearest radio galaxy, it is likely to be a fairly common occurrence and it provides an alternative to models invoking episodic nuclear activity, possibly accompanied with jet precession, for radio galaxies with multiple lobes and S-shapes. This proposed scenario may also play a key role in the origin of prominent radio galaxy morphological classes, such as the Wide-Angle-Tail sources and the Z-symmetric X-shaped radio sources. The strong tendency for radio lobes to be more distorted in double radio sources with jets that are in closer alignment with the optical major axis of the host elliptical galaxy can likewise be understood in terms of jet-shell interactions. In the frequent cases when jet activity is triggered by mergers of a large elliptical galaxy with a disk galaxy containing cold gas the impact of the gas associated with stellar shells upon the jets is likely to have significant manifestations.

Gopal-Krishna; Wiita, Paul J.

2010-01-01

312

Old Populations and the Star Formation History of the Local Group Dwarf Irregular Galaxy NGC 6822  

NASA Astrophysics Data System (ADS)

A method for studying the full star formation history (SFH) of nearby galaxies,as a function of time, has been developped and implemented. For the first time, the full SFH of a nearby dwarf irregular galaxy (DIG) has been retrieved from the photometry of its resolved stars. NGC~6822 has been observed in $UBVRI$ at the 2.5m INT telescope, at the Roque de los Muchachos Observatory and photometry of the resolved stellar content has been obtained [1]. The $VRI$ frames are very deep and contain about 18000 well measured stars. Most of them are old stars populating the red-giant branch (RGB) and the asymptotic giant branch (AGB) phase, which has been well sampled. Using the new $BVRI$ magnitudes for the Cepheids, the first self-consistent $BVRI$ multi-wavelength Cepheid distance and reddening has been derived for NGC~6822 [1]. The values obtained are $(m-M)_0=23.49\\pm 0.08$ and $E(B-V)=0.24\\pm0.03$, respectively. The comparison of the $[(V-I),I]$ and $[(V-R),V]$ colour-magnitude (CM) diagrams with theoretical isochrones allowed the qualitative understanding of the stellar populations present in NGC~6822 ([1] and [4]). Two structures, the red-tangle and the red-tail ({\\it tocho} and {\\it colita}, as we originally called them) have been identified as the locus of the old and intermediate-age stars (age $>1$ Gyr), and therefore, as the structures to be studied to retrieve information of the old and intermediate-age SFH. Since stars older and younger than 1 Gyr are situated in clearly distinct areas of the CM diagram, and because of the different time-resolution on which these populations can be studied, the old and intermediate-age SFH and the young SFH have been derived separately ([2] and [3]). Nevertheless, the tool has been in both cases the same: the comparison of the observed $[(V-I),I]$ CM diagram with a set of model CM diagrams, computed assuming different evolutionary scenarios. This is the main core of this thesis. The comparison has been performed through a number of indicators relative to the stars' distribution over the CM diagram. The model CM diagrams have been computed in collaboration with the Padova Group of stellar evolution. The reliability of the model CM diagrams computed is a result of three main components : i) a reliable set of stellar evolutionary models covering the needed range of ages and metallicities, ii) the interpolation of the stellar evolutionary tracks of fixed mass and metallicity to determine the precise, {\\it smooth} distribution of stars of any age, mass, and metallicity on the CM diagram, and iii) a realistic simulation of the observational effects on the synthetic CM diagram. Significant constraints have been put on the SFH of NGC~6822. The main conclusions reached are the following: --Star formation beginning at $T_i\\le$ 6 Gyr can be ruled out. Star formation beginning at $T_i\\simeq$ 6 Gyr would only be possible if the galaxy started its early star formation from gas already enriched, or if a prompt metal enrichment occurred in the galaxy. --NGC~6822 has most likely begun forming stars at a very early epoch (about 15-12 Gyr ago), from low metallicity gas. --An SFR close to constant or declining in the last few Gyr of the galaxy's lifetime seems best to reproduce the observations. Short-time and small-amplitude fluctuations of the SFR may have occurred. -- An overall enhancement of the star formation activity has occurred in the last 100-200 Myr. The strength of this enhancement has been somewhat different from one region of the galaxy to another. Although applied to the case of a DIG, the fundamentals of the method developed in this thesis can be applied to galaxies of any morphological type, provided that deep enough photometry is available. This can be achieved, from the ground, for all Local Group galaxies, and using Hubble Space Telescope, for galaxies within 4--5 Mp. (SECTION: Dissertation Summaries)

Gallart, C.

1997-05-01

313

Reverberation Mapping of the Least Luminous Seyfert 1 Galaxy NGC 4395  

NASA Astrophysics Data System (ADS)

We propose to make a short UV and optical reverberation mapping monitoring of NGC 4395, by far the least luminous Seyfert 1 galaxy known {M_B -10}, where the Broad Line Region {BLR} is most likely between a fraction of a light hour to a few light hours across. This program will: 1. extend by a factor of 100 the range of R_BLR probed by RM, 2. allow to test models for AGN continuum emission and BLR structure at very low L and M_BH. 3. provide significantly more reliable estimates of its M_BH than currently available, 4. allow to probe the M_BH-sigma_* relation in AGN at very low M_BH, which cannot be probed by other methods. Existing archival FOS observations indicate significant {up to 30-40%} line and continuum variations within one orbit, suggesting that the proposed RM is likely to succeed. The unusually small R_BLR in NGC 4395 implies that RM can be performed here at only a fraction of the cost required in typical AGN.

Laor, Ari

2003-07-01

314

A BIMA CO (J=1-0) survey of seven barred galaxies  

NASA Astrophysics Data System (ADS)

We present observations of seven barred galaxies observed with BIMA (Berkeley-Illinois-Maryland Array) in the CO (J=1-0) line emission. In all seven galaxies, CO spectra show the presence of high velocity (higher than circular velocity) streaming gas; this gas appears to be confined to the dust lanes and flows from the galactic disk towards the center. At least some of the high velocity gas overshoots the central concentration of CO and sprays back into the bar. The presence of this phenomenon is consistent with the predictions of Regan et al.(1997). In addition to the high velocity, dust lane gas, spectra reveal the presence of lower velocity gas which may be identified with gas on circular orbits inside the inner Lindblad resonance (ILR).

Sheth, K.; Regan, M. W.; Vogel, S. N.

1997-12-01

315

Archival HST study of novae. I. The Seyfert galaxy NGC 3627  

NASA Astrophysics Data System (ADS)

A V-band nova search was carried out in NGC 3627 with archival Hubble Space Telescope WFPC2 data which was obtained in the period between November 1997 and January 1998. A total of four novae candidates were discovered which corresponds to a global nova rate of R = 83.65 ± 7.58 yr -1. Taking into account the K-band luminosity obtained from 2MASS ( Jarrett et al., 2003) yielded a luminosity specific nova rate (LSNR) of ?K = 9.60 ± 1.64 novae per year per 10 10L?, K. Excluding one of the candidates which may be a long-period variable leads to a LSNR of ?K = 7.20 ± 1.23 novae per year per 10 10L?, K. These values are higher than other known nova rates for external galaxies except the Magellanic Clouds.

Alis, S.; Saygaç, A. T.

2012-02-01

316

On the H 2 Line Emission from NGC 6240 and Other Starburst Galaxies: Erratum  

NASA Astrophysics Data System (ADS)

In the paper "On the H2 Line Emission from NGC 6240 and Other Starburst Galaxies" by B. T. Draine and D. T. Woods (ApJ, 363,464 [1990]), there is an error in Table 1. The reported efficiencies for production of H Ly? are incorrect, owing to a factor of 10 error in estimation of the Ly? emission due to nonthermal excitation. The tabulated efficiencies for h = 1, 10, and 62.3 eV should instead be ?(H Ly?) = 8.8 x 10^-3^, 3.2 x 10^-2^, and 8.8 x 10^-2^. This error does not affect any of the other results in the paper, nor any of the conclusions. The authors thank Dr. Frank Bertoldi for bringing this error to their attention.

Draine, B. T.; Woods, D. T.

1992-03-01

317

Ultraviolet Imaging Telescope observations of the ScI galaxy NGC 628 (M74)  

NASA Technical Reports Server (NTRS)

Ultraviolet images of NGC 628 at 1520 and 2490 A show that the nucleus has an oblong appearance and that the arms and disk exhibit features not seen in blue or H-alpha images. Aperture photometry of the nucleus gives results that are compatible with observations in other bandpasses and with models. The spiral arms appear more symmetrical in the UV than in other colors; in particular, two gaps are seen on either side of the nucleus. Combined UV and radio data appear to support a large-scale collective phenomenon, perhaps a quasi-static spiral structure mechanism, as being the dominant mode of spiral formation in this galaxy. We report the detection of a low surface brightness object at a distance of 7.6 arcmin southwest of the nucleus.

Chen, Peter C.; Cornett, Robert H.; Roberts, Morton S.; Bohlin, Ralph C.; Neff, Susan G.; O'Connell, Robert W.; Parise, Ronald A.; Smith, Andrew M.; Stecher, Theodore P.

1992-01-01

318

Near-infrared Polarimetry of the Edge-on Galaxy NGC 891  

NASA Astrophysics Data System (ADS)

The edge-on galaxy NGC 891 was probed using near-infrared (NIR) imaging polarimetry in the H band (1.6 ?m) with the Mimir instrument on the 1.8 m Perkins Telescope. Polarization was detected with a signal-to-noise ratio greater than three out to a surface brightness of 18.8 mag arcsec–2. The unweighted average and dispersion in polarization percentage (P) across the full disk were 0.7% and 0.3%, respectively, and the same quantities for polarization position angle (P.A.) were 12° and 19°, respectively. At least one polarization null point, where P falls nearly to zero, was detected in the northeast disk but not the southwest disk. Several other asymmetries in P between the northern and southern disk were found and may be related to spiral structure. Profiles of P and P.A. along the minor axis of NGC 891 suggest a transition from magnetic (B) field tracing dichroic polarization near the disk mid-plane to scattering dominated polarization off the disk mid-plane. A comparison between NIR P.A. and radio (3.6 cm) synchrotron polarization P.A. values revealed similar B-field orientations in the central-northeast region, which suggests that the hot plasma and cold, star-forming interstellar medium may share a common B-field. Disk-perpendicular polarizations previously seen at optical wavelengths are likely caused by scattered light from the bright galaxy center and are unlikely to be tracing poloidal B-fields in the outer disk.

Montgomery, J. D.; Clemens, D. P.

2014-05-01

319

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

PubMed

The under-abundance of very massive galaxies in the Universe is frequently attributed to the effect of galactic winds. Although ionized galactic winds are readily observable, most of the expelled mass (that is, the total mass flowing out from the nuclear region) is likely to be in atomic and molecular phases that are cooler than the ionized phases. Expanding molecular shells observed in starburst systems such as NGC 253 (ref. 12) and M 82 (refs 13, 14) may facilitate the entrainment of molecular gas in the wind. Although shell properties are well constrained, determining the amount of outflowing gas emerging from such shells and the connection between this gas and the ionized wind requires spatial resolution better than 100?parsecs coupled with sensitivity to a wide range of spatial scales, a combination hitherto not available. Here we report observations of NGC 253, a nearby starburst galaxy (distance ??3.4 megaparsecs) known to possess a wind, that trace the cool molecular wind at 50-parsec resolution. At this resolution, the extraplanar molecular gas closely tracks the H? filaments, and it appears to be connected to expanding molecular shells located in the starburst region. These observations allow us to determine that the molecular outflow rate is greater than 3 solar masses per year and probably about 9 solar masses per year. This implies a ratio of mass-outflow rate to star-formation rate of at least 1, and probably ?3, indicating that the starburst-driven wind limits the star-formation activity and the final stellar content. PMID:23887428

Bolatto, Alberto D; Warren, Steven R; Leroy, Adam K; Walter, Fabian; Veilleux, Sylvain; Ostriker, Eve C; Ott, Jürgen; Zwaan, Martin; Fisher, David B; Weiss, Axel; Rosolowsky, Erik; Hodge, Jacqueline

2013-07-25

320

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

321

Planetary Nebulae in the Elliptical Galaxy NGC 4649 (M 60): Kinematics and Distance Redetermination  

NASA Astrophysics Data System (ADS)

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 e to be 4 × 1011 M sun, which is almost one-half of the total mass of about 1012 M sun within 3R 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. Based partly on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. Based partly on data collected at the European Southern Observatory, Chile, ESO Program 079.B-0577(A).

Teodorescu, A. M.; Méndez, R. H.; Bernardi, F.; Thomas, J.; Das, P.; Gerhard, O.

2011-07-01

322

The diffusion of chaotic orbits in 3D barred spiral galaxies  

NASA Astrophysics Data System (ADS)

We study the way in which the 3D chaotic orbits, initially belonging to the bar of an N-body model simulating a barred spiral galaxy, are getting diffused outwards. An important percentage of these orbits stay trapped for very long time inside the corotation radius and behave as regular orbits. In the 4D phase space these orbits seem to be trapped close to rotational tori of stable periodic orbits, or close to simply unstable periodic orbits, supporting the shape of the bar. After they get diffused outwards, they get trapped along the asymptotic manifolds of the simply unstable periodic orbits of the region outside corotation and support the shape of the spiral structure for approximately 100 half mass crossing times of the system (Thmct), before escape from it. This phenomenon of diffusion through the 3rd dimension is known as "Arnold Diffusion".

Harsoula, M.

2013-09-01

323

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

324

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

325

The Detection of Circumnuclear X-Ray Emission from the Seyfert Galaxy NGC 3516  

NASA Technical Reports Server (NTRS)

We present the first high-resolution, X-ray image of the circumnuclear regions of the Seyfert 1 galaxy NGC 3516, using the Chandra X-ray Observatory (CXO). All three of the CXO observations reported were performed with one of the two grating assemblies in place, and here we restrict our analysis to undispersed photons (i.e. those detected in the zeroth-order). A previously-unknown X-ray source is detected approximately 6 arcsec (1.1h(sub 75)(exp -1) kpc) NNE of the nucleus (position angle approximately 29 degrees) which we designate CXOU 110648.1 + 723412. Its spectrum can be characterized as a power law with a photon index (Gamma) approximately 1.8 - 2.6, or as thermal emission with a temperature kT approximately 0.7 - 3 keV. Assuming a location within NGC 3516, isotropic emission implies a luminosity L approximately 2 - 8 x 10(exp 39)h(sub 75)(exp-2) erg s(exp -1) in the 0.4 - 2 keV band. If due to a single point source, the object is super-Eddington for a 1.4 solar mass neutron star. However, multiple sources or a small, extended source cannot be excluded using the current data. Large-scale extended S-ray emission is also detected out to approximately 10 arcsec (approximately 2h(sub 75)(exp -1) kpc) from the nucleus to the NE and SW, and is approximately aligned with the morphologies of the radio emission and extended narrow emission line region (ENLR). The mean luminosity of this emission is 1 - 5 x 10(exp 37)h(sub 75)(exp -2) erg s(exp -1) arcsec(exp -2), in the 0.4 - 2 keV band. Unfortunately the current data cannot usefully constrain its spectrum. These results are consistent with earlier suggestions of circumnuclear X-ray emissi in NGC 3516 based on ROSAT observations, and thus provide the first clear detection of extended X-ray emission in a Seyfert 1.0 galaxy. If the extended emission is due to scattering of the nuclear X-ray continuum, then the pressure in the X-ray emitting gas is at least two orders of magnitude too small to provide the confining medium for the ENLR clouds.

George, I. M.; Turner, T. J.; Netzer, H.; Kraemer, S. B.; Ruiz, J.; Chelouche, D.; Crenshaw, D. M.; Yaqoob, T.; Nandra, K.; Mushotzky, R. F.; White, Nicholas E. (Technical Monitor)

2001-01-01

326

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

327

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

NASA Technical Reports Server (NTRS)

We present a study of the colors of globular clusters associated with the elliptical galaxy NGC 3923. Our final sample consists of Wasington system C and T(sub 1) photometry for 143 globular cluster candidates with an expected contamination of no more than 10%. We find that the color distribution of the NGC 3923 globular cluster system (GCS) is broad and appears to have at least two peaks. A mixture modeling analysis of the color distribution indicates that a two-component model is favored over a single-component one at a high level of confidence (greater than 99%). This evidence for more than one population in the GCS of NGC 3923 is similar to that previously noted for the four other elliptical galaxies for which similar data have been published. Furthermore, we find that the NGC 3923 GCS is redder than the GCSs of previously studed elliptical galaxies of similar luminosity. The median metallicity inferred from our (C-(T(sub 1)))(sub 0) colors is (Fe/H)(sub med) = -0.56, with an uncertainty of 0.14 dex arising from all sources of uncertainty in the mean color. This is more metal rich than the median metallicity found for the GCS of M87 using the same method, (Fe/H)(sub med) = -0.94. Since M87 is more luminous than NGC 3923, this result points to significant scatter about any trend of higher GCS metallicity with increasing galaxy luminosity. We also show that there is a color gradient in the NGC 3923 GCS corresponding to about -0.5 dex in Delta(Fe/H)/Delta(log r). We conclude that the shape of the color distribution of individual GCSs and the variation in mean color among the GCSs of ellipticals are difficult to understand if elliptical galaxies are formed in a single protogalactic collapse. Models in which ellipticals and their globular clusters are formed in more than one event, such as a merger scenario, are more successful in accounting for these observations.

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

1995-01-01

328

Detection of CO(J = 1-0) Emission from Barred Spiral Galaxies at z ˜ 0.1.  

NASA Astrophysics Data System (ADS)

We present the results of CO (J = 1-0) observations toward nine barred spiral galaxies at z = 0.08-0.25 using the 45 m telescope at Nobeyama Radio Observatory. This survey is the first one specializing in barred spiral galaxies in this redshift range. We detected CO emission in six galaxies out of nine, whose CO luminosities (L"CO) ranged (1.09-10.8) × 109K km s-1 pc2. These six are the infrared dimmest galaxies that have ever been detected in CO at z ˜ 0.1 to date. They follow the L"CO-LIR (IR luminosity) relation among such galaxies as local spiral galaxies, luminous infrared galaxies, ultra-luminous infrared galaxies, and submillimeter galaxies. Their L"CO and LIR are higher than those of local spiral galaxies, which have been detected in CO so far; LIR/L"CO, which is a measure of the star-formation efficiency, is comparable to, or slightly higher than, that of local ones. This result suggests that these six galaxies are forming stars more actively than local spiral galaxies simply because they have more fuel.

Matsui, Kana; Sorai, Kazuo; Watanabe, Yoshimasa; Kuno, Nario

2012-06-01

329

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

NASA Technical Reports Server (NTRS)

ROSAT observation is presented of the edge-on spiral galaxy NGC 4631, a nearby Sc/SBd galaxy best known for its extended radio halo. Because of the low foreground Galactic X-ray-absorbing gas column density, N(sub H) approximately 1.4 x 10(exp 20)cm(exp -2), this observation is sensitive to gas of temperature greater than or equal to a few times 10(exp 5) K. A soft (approximately 0.25 keV) X-ray radiation out to more than 8 kpc above the midplane of the galaxy was detected. The strongest X-ray emission in the halo is above the central disk, a region of about 3 kpc radius which shows high star formation activity. The X-ray emission in the halo is bordered by two extended filaments of radio continuum emission. Diffuse X-ray emission from hot gas in the galaxy's disk was found. The spectrum of the radiation can be characterized by a thermal plasma with a temperature of 3 x 10(exp 6) K and a radiative cooling rate of approximately 8 x 10(exp 39) ergs s(exp -1). This rate is only a few percent of the estimated supernova energy release in the interstellar medium of the galaxy. Analysis of the X-ray spectrum shows evidence for the presence of a cooler (several times 10(exp 5) K) halo gas component that could consume a much larger fraction of the supernova energy. Strong evidence was found for disk/halo interaction. Hot gas apparently blows out from supershells in the galaxy's disk at a rate of approximately 1 solar mass yr(exp -1). This outflow of hot gas drags magnetic field lines up in the halo and forms a magnetized gaseous halo. If the magnetic field lines are still anchored to the disk gas at large disk radii, the outflowing gas may be confined high above the disk by magnetic pressure. A strong X-ray source which coincides spatially with an H I supershell has been identified. However, the source is likely an extremely luminous X-ray binary with L(sub chi)(0.1 - 2 keV) approximately 5 x 10(exp 39) ergs s(exp -1), which makes it a stellar mass black hole candidate.

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

1994-01-01

330

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

331

STAR CLUSTERS IN THE NEARBY LATE-TYPE GALAXY NGC 1311  

SciTech Connect

Ultraviolet, optical and near-infrared images of the nearby (D {approx} 5.5 Mpc) SBm galaxy NGC 1311, obtained with the Hubble Space Telescope, reveal a small population of 13 candidate star clusters. We identify candidate star clusters based on a combination of their luminosity, extent, and spectral energy distribution. The masses of the cluster candidates range from {approx}10{sup 3} M{sub sun} up to {approx}10{sup 5} M{sub sun}, and show a strong positive trend of larger mass with increasing with cluster age. Such a trend follows from the fading and dissolution of old, low-mass clusters, and the lack of any young super-star clusters of the sort often formed in strong starbursts. The cluster age distribution is consistent with a bursting mode of cluster formation, with active episodes of age {approx}10 Myr, {approx}100 Myr, and {approx}>Gyr. The ranges of age and mass we probe are consistent with those of the star clusters found in quiescent Local Group dwarf galaxies.

Eskridge, Paul B. [Department of Physics and Astronomy, Minnesota State University, Mankato, MN 56001 (United States); Grijs, Richard de [Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH (United Kingdom); Anders, Peter [Sterrenkundig Instituut, Universiteit Utrecht, NL-3508 TA Utrecht (Netherlands); Windhorst, Rogier A.; Jansen, Rolf A. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States); Mager, Violet A., E-mail: paul.eskridge@mnsu.edu [Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287 (United States)

2008-01-15

332

A detailed X-ray variability study of the Seyfert galaxy NGC 4051  

NASA Astrophysics Data System (ADS)

We present a detailed and rigorous examination of the X-ray variability characteristics of the Seyfert galaxy NGC 4051, using the 1985 EXOSAT observation and our improved power spectrum modelling techniques. The Medium Energy (ME) power spectrum is adequately fitted by a power-law model, but the Low Energy (LE) spectrum is not. We find an excellent fit by adding a broad quasi-periodic oscillation (QPO) feature on a time-scale of ~1h, which contains 1/4 of the overall variance. A similar, but much weaker, feature may exist in the ME power spectrum as well. The LE power spectrum is also clearly steeper than the ME spectrum. There is no significant lag between the ME and LE data (at most 60 s), but the cross-correlation function is noticeably asymmetric. We confirm earlier claims of a correlation between softness and flux, and show that this is essentially caused by the presence of high peaks present in the LE but not in the ME light curve. We discuss various generic models for X-ray variability. In particular, several features (especially the softness effect and the cross-correlation asymmetry) are suggestive of thermal Comptonization models. We examined one of these models in detail, with parameters suggested by recent fits to the OSSE energy spectra of Seyfert galaxies. However, this model predicts that the ME spectrum should be much steeper, in contradiction with the observed facts.

Papadakis, I. E.; Lawrence, A.

1995-01-01

333

The optical and UV spectrum of the Seyfert type 2 galaxy NGC 3393  

NASA Astrophysics Data System (ADS)

The combined UV and optical spectrum of the Seyfert type 2 galaxy NGC 3393 is presented and analyzed together with published IR and IRAS data. The conditions in the narrow-line gas strongly suggest that the high-ionization material is in a zone of higher density (Ne = 100,000/cu cm) while the low-ionization material is at Ne = 1000/cu cm. No evidence is found for internal reddening. Most of the optical and NIR flux is of stellar origin, and the IRAS fluxes can be adequately described by dust emission with two components at temperatures of about 30 K and 130 K, respectively. This dust would probably be located in the regions surrounding the Seyfert nucleus. The flux distribution of the nonstellar component can be fitted by a power law with index alpha = -0.60. This power law is closer to that observed in quasars and Seyfert type 1 galaxies than to the commonly derived for Seyfert types 2 (alpha = -1.5).

Diaz, A. I.; Prieto, M. A.; Wamsteker, W.

1988-04-01

334

THE DETECTION OF ANOMALOUS DUST EMISSION IN THE NEARBY GALAXY NGC 6946  

SciTech Connect

We report on the Ka-band (26-40 GHz) emission properties for 10 star-forming regions in the nearby galaxy NGC 6946. From a radio spectral decomposition, we find that the 33 GHz flux densities are typically dominated by thermal (free-free) radiation. However, we also detect excess Ka-band emission for an outer-disk star-forming region relative to what is expected given existing radio, submillimeter, and infrared data. Among the 10 targeted regions, measurable excess emission at 33 GHz is detected for half of them, but in only one region is the excess found to be statistically significant ({approx}7{sigma}). We interpret this as the first likely detection of so-called 'anomalous' dust emission outside of the Milky Way. We find that models explaining this feature as the result of dipole emission from rapidly rotating ultrasmall grains are able to reproduce the observations for reasonable interstellar medium conditions. While these results suggest that the use of Ka-band data as a measure of star formation activity in external galaxies may be complicated by the presence of anomalous dust, it is unclear how significant a factor this will be for globally integrated measurements as the excess emission accounts for {approx}<10% of the total Ka-band flux density from all 10 regions.

Murphy, E. J.; Chary, R.-R.; Armus, L. [Spitzer Science Center, California Institute of Technology, MC 314-6, Pasadena, CA 91125 (United States); Helou, G. [California Institute of Technology, MC 314-6, Pasadena, CA 91125 (United States); Condon, J. J.; Mason, B. S. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Schinnerer, E. [Max Planck Institut fuer Astronomie, Koenigstuhl 17, Heidelberg D-69117 (Germany); Turner, J. L. [Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095 (United States); Beck, R. [Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel, Bonn (Germany)], E-mail: emurphy@ipac.caltech.edu

2010-02-01

335

Two extreme H I supershells in the disturbed edge-on galaxy NGC 4631  

NASA Astrophysics Data System (ADS)

Using Westerbork Synthesis Radio Telescope maps of 21 cm emission from NGC 4631, we have discovered two very large supershells of atomic gas in the disk of this nearby, disturbed edge-on galaxy. The larger shell has a diameter of about 3 kpc and a swept up mass of roughly 1-2 x 10 exp 8 solar masses. There is some evidence for expansion, with a velocity of 45 km/s. Above a break at the top of the shell, there is a prominent 'worm' of mass about 4 x 10 exp 7 solar masses. The smaller shell has a diameter of 1.8 kpc and shows better evidence for expansion, at 35 km/s, and has a mass of about 5-10 x 10 exp 7 solar masses. The kinetic energy of the larger shell is roughly 2-5 x 10 exp 54 erg, and the necessary input energy from supernovae and stellar winds to explain its current parameters is 2-5 x 10 exp 55 erg, implying an association containing 10,000-35,000 supernova-producing OB stars. A more attractive explanation as far as energetics are concerned is that small companions or massive gas clouds hit the disk of the galaxy and formed the shells. Unfortunately, there is no clear independent evidence for such collisions, and the near-complete ringlike appearance of the shells may be a problem for this explanation.

Rand, Richard J.; van der Hulst, J. M.

1993-06-01

336

Secular bar formation in galaxies with a significant amount of dark matter  

NASA Astrophysics Data System (ADS)

Using high-resolution N-body simulations of stellar discs embedded in cosmologically motivated dark matter haloes, we study the evolution of bars and the transfer of angular momentum between haloes and bars. We find that dynamical friction results in some transfer of angular momentum to the halo, but the effect is much smaller than previously found in low-resolution simulations and is incompatible with early analytical estimates. After 5 Gyr of evolution the stellar component loses only 5-7 per cent of its initial angular momentum. Mass and force resolutions are crucial for the modelling of bar dynamics. In low-resolution (300-500 pc) simulations we find that the bar slows down and angular momentum is lost relatively fast. In simulations with millions of particles reaching a resolution of 20-40 pc, the pattern speed may not change over billions of years. Our high-resolution models produce bars that are fast rotators, where the ratio of the corotation radius to the bar semi-major axis lies in the range , marginally compatible with observational results. In contrast to many previous simulations, we find that bars are relatively short. As in many observed cases, the bar semi-major axis is close to the exponential length of the disc. The transfer of angular momentum between inner and outer parts of the disc plays a very important role in the secular evolution of the disc and the bar. The bar formation increases the exponential length of the disc by a factor of 1.2-1.5. The transfer substantially increases the stellar mass in the centre of the galaxy and decreases the dark matter to baryon ratio. As the result, the central 2-kpc region is always strongly dominated by the baryonic component. At intermediate (3-10 kpc) scales the disc is sub-dominant. These models demonstrate that the efficiency of angular momentum transfer to the dark matter has been greatly overestimated. More realistic models produce bar structure in striking agreement with observational results.

Valenzuela, Octavio; Klypin, Anatoly

2003-10-01

337

CO(1-0) observations of the cooling flow galaxy NGC 1275 with the IRAM interferometer.  

NASA Astrophysics Data System (ADS)

High resolution ^12^CO(1-0) interferometric observations are presented of NGC 1275 (3C84, Perseus A), which is the dominant galaxy of the Perseus cluster (Abell 426) and is believed to have a strong cooling flow. No CO absorption was detected towards the powerful point-like nucleus although CO emission may have been detected in an area surrounding the nucleus. The constraints placed by these observations and existing data on the massive cooling flow scenario are examined. Contrary to some claims, the covering fraction of neutral gas has been found to be much less than unity in all cooling flows where the necessary data are available. As the cooling gas presumably forms low-mass stars or sub-stellar objects, the possibility of large masses of neutral gas escaping detection is investigated in detail. The gas, with or without dust, should not cool down to T_gas_=~3K as has been claimed but should remain >8K through X-ray heating at column densities up to N_H2_=~5x10^22^/cm2. Greater column densities may be physically reasonable if the magnetic field is strong enough to support the cloud against fragmentation. In this case, ambi-polar diffusion or magnetic slip-ion heating becomes important and should maintain the temperature T_gas_>10K. If the clouds contain dust, then although the dust radiates away most of the energy, the absorbed starlight keeps the temperature T_dust_>10K. Lack of CO or very broad lines do not appear to be feasible means of reconciling large molecular (or atomic) gas masses with the global lack of detections and tight upper limits. The primary conclusion is that the real mass inflow rates must be much lower that frequently claimed. It should then be noted that present-day cooling flows, if not so massive, lose much of their cosmological importance. The FIR and CO emission from NGC 1275 correspond exactly to what is found in gas-rich spirals. Rather than a massive cooling flow, the gas may come from accretion of one or more gas-rich galaxies. Since, however, at least 14 other central galaxies would have been detected in CO if they contained similar quantities of gas, such events must be quite rare, very roughly 1/15Gyr^-1^ if the time required for a large fraction of the gas to disappear is 10^9^yr.

Braine, J.; Wyrowski, F.; Radford, S. J. E.; Henkel, C.; Lesch, H.

1995-01-01

338

High-Resolution Observations of the Elliptical Galaxy NGC 4636 with the Reflection Grating Spectrometer on Board XMM-Newton  

Microsoft Academic Search

We present the first high spectral resolution X-ray observation of the giant elliptical galaxy NGC 4636, obtained with the reflection grating spectrometer on board the XMM-Newton Observatory. The resulting spectrum contains a wealth of emission lines from various charge states of oxygen, neon, magnesium, and iron. Examination of the cross-dispersion profiles of several of these lines provides clear, unambiguous evidence

H. Xu; S. M. Kahn; J. R. Peterson; E. Behar; F. B. S. Paerels; R. F. Mushotzky; J. G. Jernigan; A. C. Brinkman; K. Makishima

2002-01-01

339

The Nature of Dark Matter in Elliptical Galaxies: Chandra X-ray Observatory Observations of NGC 4636  

Microsoft Academic Search

We determine the total enclosed mass profile from 0.7 to 35 kpc in the elliptical galaxy NGC 4636 based on the hot interstellar medium temperature profile measured using the Chandra X-ray Observatory, and other X-ray and optical data. The total mass increases as radius to the power 1.2 to a good approximation over this range in radii, attaining a total

Michael Loewenstein; Richard F. Mushotzky

2002-01-01

340

The Effect of Star Formation on Molecular Clouds in Dwarf Irregular Galaxies: IC 10 and NGC 6822  

Microsoft Academic Search

We have observed the 13CO J=2-1, 12CO J=2-1 and 12CO J=3-2 lines at a few\\u000alocations in the dwarf irregular galaxies IC 10 and NGC 6822 using the James\\u000aClerk Maxwell Telescope. In addition, we report the first detection of the 13CO\\u000aJ=3-2 transition in a Local Group galaxy. These low metallicity environments\\u000aappear to be porous to UV radiation

Glen R. Petitpas; Christine D. Wilson

1997-01-01

341

An Investigation of the Dust Content in the Galaxy Pair NGC 1512/1510 from Near-Infrared to Millimeter Wavelengths  

NASA Astrophysics Data System (ADS)

We combine new ASTE/AzTEC 1.1 mm maps of the galaxy pair NGC 1512/1510 with archival Spitzer IRAC and MIPS images covering the wavelength range 3.6-160 ?m from the SINGS project. The availability of the 1.1 mm map enables us to measure the long-wavelength tail of the dust emission in each galaxy, and in sub-galactic regions in NGC 1512, and to derive accurate dust masses. The two galaxies form a pair consisting of a large, high-metallicity spiral (NGC 1512) and a low-metallicity, blue compact dwarf (NGC 1510), which we use to compare similarities and contrast differences. Using the models of Draine and Li, the derived total dust masses are (2.4 ± 0.6) × 107 M sun and (1.7 ± 3.6) × 105 M sun for NGC 1512 and NGC 1510, respectively. The derived ratio of dust mass to H I gas mass for the galaxy pair, M_d/M_H I ˜ 0.0034, is much lower (by at least a factor of 3) than expected, as previously found by Draine et al. In contrast, regions within NGC 1512, specifically the central region and the arms, do not show such unusually low M_d/M_H I ratios; furthermore, the dust-to-gas ratio is within expectations for NGC 1510. These results suggest that a fraction of the H I included in the determination of the M_d/M_H I ratio of the NGC 1512/NGC 1510 pair is not associated with the star-forming disks/regions of either galaxy. Using the dust masses derived from the models of Draine & Li as references, we perform simple two-temperature modified blackbody fits to the far-infrared/millimeter data of the two galaxies and the sub-regions of NGC 1512, in order to derive and compare the dust masses associated with warm and cool dust temperature components. As generally expected, the warm dust temperature of the low-metallicity, low-mass NGC 1510 (Tw ~ 36 K) is substantially higher than the corresponding warm temperature of the high-metallicity spiral NGC 1512 (Tw ~ 24 K). In both galaxies (albeit with a large uncertainty for NGC 1510), our fits indicate that a substantial fraction (>93%) of the total dust mass is in a cool dust component, with temperatures ~14-16 K for NGC 1512 and ~15-24 K for NGC 1510. This result is similar to what is determined for a few other nearby galaxies. In contrast, the warm dust component in the sub-galactic regions of NGC 1512 represents a much larger fraction of the total dust content, in agreement with the fact that all three regions have higher specific star formation rates than the average in the galaxy; in the center, the warm dust represents about 40% of the total, while in the arms the fractions are close to ~20%.

Liu, Guilin; Calzetti, Daniela; Yun, Min S.; Wilson, Grant W.; Draine, Bruce T.; Scott, Kimberly; Austermann, Jason; Perera, Thushara; Hughes, David; Aretxaga, Itziar; Kohno, Kotaro; Kawabe, Ryohei; Ezawa, Hajime

2010-03-01

342

Optical imaging and high spatial resolution 21 cm H I observations of the peculiar galaxy NGC 2782 (Arp 215)  

NASA Technical Reports Server (NTRS)

We have used the Very Large Array (VLA) B and C Arrays to make 21 cm H I observations of the peculiar galaxy NGC 2782 (Arp 215). These observations are complementary to previously published D Array VLA data, which revealed the presence of a long (5 min to 54 kpc) H I plume near the western side of this galaxy. We have also obtained BVRI H alpha images of the main body of this galaxy using the McDonald Observatory 30 inch telescope. The optical images of this galaxy show a strong stellar tail extending to the east, opposite the H I plume. Within the disk of NGC 2782, unsharp masking of the optical images at all 4 broadband wavelengths reveals three bright 'ripples', separated by approximately 15 sec. The light profiles across these ripples are symmetric, without a sharp outer edge. H alpha is strong at the starburst nucleus and along the northern and western sections of the inner ripple. The new higher resolution H I data show that the atomic gas is very clumpy. We have identified ten H I clumps in the long western plume, with H I masses of approximately 10(exp 8) solar mass, similar to those of dwarf galaxies, and column densities of approximately 10(exp 21) cm(exp -2) over surface areas of approximately 10 kpc(exp 2). No CO (1-0) emission has been detected from this plume, suggesting that it is material stripped from the outer edge of a disk galaxy. The H alpha peaks, in contrast, are generally not coincident with H I peaks. No H I is seen at the tip of the eastern extension. The H I distribution near this structure is ring-like rather than tail-like as in the optical data. We have detected redshifted H I absorption toward the central continuum source, indicating gas infall into the nuclear region. Using a restricted 3-body dynamical model, we have successfully reproduced the basic properties of NGC 2782 with an off-center collision between two galaxies, where a lower mass disk companion (M(sub 2)/M(sub 1) approximately 0.25) collides almost head-on with a larger disk galaxy. In this scenario, the companion becomes the eastern extension, and the long western tail is material pulled out from the larger galaxy. The lack of H I at the tip of the eastern tail may be due to stripping during the collision. Alternative formation scenarios include a merger or interaction between two disk galaxies, where the ripples may be due to a disturbed spiral density wave or galactic winds due to the central starburst.

Smith, Beverly J.

1994-01-01

343

Interstellar Absorption Lines in the Spectrum of the Starburst Galaxy NGC 1705  

NASA Astrophysics Data System (ADS)

A Goddard High Resolution Spectrograph archival study of the interstellar absorption lines in the line of sight to the H i-rich, starburst dwarf galaxy NGC 1705 in the 1170 to 1740 Å range at ~120 km s^-1 resolution is presented. The absorption features arising because of photospheric lines are distinctly different from the interstellar lines: the photospheric lines are weak, broad (equivalent widths >1 Å), asymmetric, and centered around the systemic LSR velocity of NGC 1705 (~610 km s^-1). The interstellar lines consist of three relatively narrow components at LSR velocities of -20, 260, and 540 km s^-1, and include absorption by neutral atoms (N i lambda1200 triplet and O i lambda1302), singly ionized atoms (Si ii lambdalambda1190, 1193, 1260, 1304, and 1526, S ii lambda1253, C ii lambda1334, C ii^* lambda1336, Fe ii lambda1608, and Al ii lambda1670), and atoms in higher ionization states (Si iii lambda1206, Si iv lambdalambda1393, 1402, and C iv lambdalambda1548, 1550). The Si iv and C iv absorption features have both interstellar and photospheric contributions. In an earlier study, Sahu & Blades identified the absorption system at -20 km s^-1 with Milky Way disk/halo gas, and the 260 km s^-1 system with a small, isolated high-velocity cloud HVC 487, which is probably associated with Magellanic Stream gas. The 540 km s^-1 absorption system is associated with a kiloparsec-scale expanding, ionized supershell centered on the super-star cluster NGC 1705-1. The analysis presented in this paper consists of (1) a list of all interstellar absorption features with greater than 3 sigma significance and their measured equivalent widths, (2) plots of the lines in the various atomic species together with the results of nonlinear least-squares fit profiles to the observed data, and (3) unpublished 21 cm maps from the Wakker & van Woerden survey showing the large-scale H i distribution in the region near the NGC 1705 sight line and HVC 487. Furthermore, weak N i lambda1200 triplet absorption for the supershell component is reported, which in the absence of dust depletion and ionization corrections implies a low N abundance. A low N abundance for the supershell is consistent with an interpretation of nucleosynthetic enrichment by time-delayed primary nitrogen production, the age estimate of (10-20) x 10^6 yr for the central super-star cluster NGC 1705-1 of Heckman & Leitherer, and the underabundance of Fe reported by Sahu & Blades. However, using the N i lambda1200 triplet alone to estimate the total N abundance could result in a severe underestimation of this quantity: although N does not deplete onto interstellar dust grains, photoionization and collisional ionization effects could increase the fraction of N found in higher ionization stages. Uncertainties in the total N abundance caused by photoionization and collisional ionization effects can only be addressed by future observations of the higher ionization lines, namely, N ii lambda1084 and N iii lambda989. Based on observations 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.

Sahu, M. S.

1998-09-01

344

Formation of nuclear rings of barred galaxies and star formation therein  

NASA Astrophysics Data System (ADS)

Barred galaxies contain substructures such as a pair of dust lanes and nuclear rings, with the latter being sites of intense star formation. We study the substructure formation as well as star formation in nuclear rings using numerical simulations. We find that nuclear rings form not by the Lindblad resonances, as previously thought, but by the centrifugal barrier that inflowing gas along dust lanes cannot overcome. This predicts a smaller ring in a more strongly barred galaxy, consistent with observations. Star formation rate (SFR) in a nuclear ring is determined primarily by the mass inflow rate to the ring. In our models, the SFR typically shows a short strong burst associated with the rapid gas infall and stays very small for the rest of the evolution. When the SFR is low, ages of young star clusters exhibit an azimuthal gradient along the ring since star formation takes place mostly near the contact points between the dust lanes and the nuclear ring. When the SFR is large, on the other hand, star formation is widely distributed throughout the whole length of the ring, with no apparent age gradient of star clusters. Since observed ring star formation appears long-lived with episodic bursts, our results suggest that the bar region should be replenished continually with fresh gas from outside.

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

2014-05-01

345

Circumnuclear Star Clusters in the Galaxy Merger NGC 6240, Observed with Keck Adaptive Optics and HST  

SciTech Connect

We discuss images of the central {approx} 10 kpc (in projection) of the galaxy merger NGC 6240 at H and K{prime} bands, taken with the NIRC2 narrow camera on Keck II using natural guide star adaptive optics. We detect 28 star clusters in the NIRC2 images, of which only 7 can be seen in the similar-spatial-resolution, archival WFPC2 Planetary Camera data at either B or I bands. Combining the NIRC2 narrow camera pointings with wider NICMOS NIC2 images taken with the F110W, F160W, and F222M filters, we identify a total of 32 clusters that are detected in at least one of these 5 infrared ({lambda}{sub c} > 1 {micro}m) bandpasses. By comparing to instantaneous burst, stellar population synthesis models (Bruzual & Charlot 2003), we estimate that most of the clusters are consistent with being {approx} 15 Myr old and have photometric masses ranging from 7 x 10{sup 5} M{sub {circle_dot}} to 4 x 10{sup 7}M{sub {circle_dot}}. The total contribution to the star formation rate (SFR) from these clusters is approximately 10M{sub {circle_dot}} yr{sup -1}, or {approx} 10% of the total SFR in the nuclear region. We use these newly discovered clusters to estimate the extinction toward NGC 6240's double nuclei, and find values of A{sub v} as high as 14 magnitudes along some sightlines, with an average extinction of A{sub v} {approx} 7 mag toward sightlines within {approx} 3-inches of the double nuclei.

Pollack, L K; Max, C E; Schneider, G

2007-02-12

346

The Narrow-Line Region in the Seyfert 2 Galaxy NGC 3393  

NASA Astrophysics Data System (ADS)

The narrow-line region (NLR) of the Seyfert 2 galaxy NGC 3393 is dominated by a symmetric structure which appears as S-shaped arms in Hubble Space Telescope (HST) images. These arms, which occupy the central few arcseconds of the nucleus, border a linear, triple-lobed radio source. We use HST imaging and spectra, ground-based optical images, long-slit spectra, Fabry-Perot imaging spectroscopy, and VLA radio data to perform a detailed investigation of the kinematics and ionization of the line-emitting gas in NGC 3393 and of its relationship with the relativistic gas responsible for the radio emission. The excitation map [O III] ?5007/(H?+[N II] ??6548, 6584) shows a biconical structure, consistent with the anisotropic nuclear ionizing radiation expected in the unified scheme. Extrapolation to ionizing frequencies of our upper limit to the 2100 Å flux of the nuclear source provides a factor >=3×104 too few ionizing photons to account for the recombination line emission, which also suggests that the nuclear ionizing source radiates anisotropically. However, the kinetic energy of the outflow is sufficient to power the line emission via photoionizing shocks, and a tentative detection of extended UV emission is consistent with this model. Furthermore, the broad component of the emission lines has a similar orientation and spatial extent as the triple radio source. Nevertheless, other tests are inconsistent with the photoionizing shock model--there is no correlation between local velocity dispersion, surface brightness, and excitation, and the gaseous abundances of [Ca II], Al II], and Mg II are much lower than expected if these species have been liberated into the gas phase through grain destruction by shocks. We conclude that the radio lobes appear to have created denser regions of gas on their leading edges, thus forming the S-shaped arms, but that the ionization is most likely due to photoionization by an obscured central source.

Cooke, Andrew J.; Baldwin, J. A.; Ferland, G. J.; Netzer, Hagai; Wilson, Andrew S.

2000-08-01

347

Physical Condition of Molecular Gas at the Centre of the active galaxy NGC 1097  

NASA Astrophysics Data System (ADS)

We have used the Xco conversion factor, Local Thermal Equilibrium and Large Velocity Gradient approximation to parametrize the cold and warm phase of the interstellar medium from five different low transitions of the CO molecule in the central 21 arcsec (kpc) region of NGC 1097. We have applied a one-component model and derived a typical kinetic temperature of about 33 K, a molecular Hydrogen density of 4.9×103 M? pc-3 and a CO column density of 1.2× 10-2 M? pc-2. A two-component model results in 85% cold-to-total gas fraction in the presence of a 90 K warm counterpart. Furthermore, we ``resolve" the spatially unresolved single dish observations by selecting velocity channels that in an interferometric velocity map correspond to specific regions. We have selected five such regions and found that the physical properties in these regions are comparable to those derived from the full line profile. This implies that the central kpc of NGC 1097 is rather homogeneous in nature, and, although the regions are not uniquely located within the ring, the star formation along the ring is homogeneously distributed (in agreement with recent Herschel observations). We have further revised the mass inflow rate onto the Supermassive Black Hole in this prototype LINER/Sy1 galaxy and found that, accounting for the total interstellar medium and applying a careful contribution of the disc thickness and corresponding stability criterion, increases the previous estimations by a factor 10. Finally we have calculated the Xco conversion factor for the centre of NGC 1097 using an independent estimation of the surface density to the CO emission, and obtained Xco=(2.8%B m0.5)× 1020 cm-2 (K km s-1)-1 at radius 10.5 arcsec and Xco=(5.0%B m0.5)×1020 cm-2 (K km s-1)-1 at radius 7.5 arcsec. With the approach and analysis described in here we have demonstrated that important physical properties can be derived to a resolution beyond the single dish resolution element, however, caution is necessary for interpreting the results. To obtain a more accurate description of the molecular gas at the nuclear region, observations of higher transitions with ALMA will help overcome most of the limitations that we have faced in the current work.

Piñol Ferrer, N.; Fathi, K.; Lundgren, A.; van de Ven, G.

2011-05-01

348

Interplay between chaotic and regular motion in a time-dependent barred galaxy model  

NASA Astrophysics Data System (ADS)

We study the distinction and quantification of chaotic and regular motion in a time-dependent Hamiltonian barred galaxy model. Recently, a strong correlation was found between the strength of the bar and the presence of chaotic motion in this system, as models with relatively strong bars were shown to exhibit stronger chaotic behavior compared to those having a weaker bar component. Here, we attempt to further explore this connection by studying the interplay between chaotic and regular behavior of star orbits when the parameters of the model evolve in time. This happens for example when one introduces linear time dependence in the mass parameters of the model to mimic, in some general sense, the effect of self-consistent interactions of the actual N-body problem. We thus observe, in this simple time-dependent model also, that the increase of the bar’s mass leads to an increase of the system’s chaoticity. We propose a new way of using the generalized alignment index (GALI) method as a reliable criterion to estimate the relative fraction of chaotic versus regular orbits in such time-dependent potentials, which proves to be much more efficient than the computation of Lyapunov exponents. In particular, GALI is able to capture subtle changes in the nature of an orbit (or ensemble of orbits) even for relatively small time intervals, which makes it ideal for detecting dynamical transitions in time-dependent systems. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Lyapunov analysis: from dynamical systems theory to applications’.

Manos, T.; Bountis, T.; Skokos, Ch

2013-06-01

349

PROBING THE X-RAY BINARY POPULATIONS OF THE RING GALAXY NGC 1291  

SciTech Connect

We present Chandra studies of the X-ray binary (XRB) populations in the bulge and ring regions of the ring galaxy NGC 1291. We detect 169 X-ray point sources in the galaxy, 75 in the bulge and 71 in the ring, utilizing the four available Chandra observations totaling an effective exposure of 179 ks. We report photometric properties of these sources in a point-source catalog. There are Almost-Equal-To 40% of the bulge sources and Almost-Equal-To 25% of the ring sources showing >3{sigma} long-term variability in their X-ray count rate. The X-ray colors suggest that a significant fraction of the bulge ( Almost-Equal-To 75%) and ring ( Almost-Equal-To 65%) sources are likely low-mass X-ray binaries (LMXBs). The spectra of the nuclear source indicate that it is a low-luminosity active galactic nucleus (AGN) with moderate obscuration; spectral variability is observed between individual observations. We construct 0.3-8.0 keV X-ray luminosity functions (XLFs) for the bulge and ring XRB populations, taking into account the detection incompleteness and background AGN contamination. We reach 90% completeness limits of Almost-Equal-To 1.5 Multiplication-Sign 10{sup 37} and Almost-Equal-To 2.2 Multiplication-Sign 10{sup 37} erg s{sup -1} for the bulge and ring populations, respectively. Both XLFs can be fit with a broken power-law model, and the shapes are consistent with those expected for populations dominated by LMXBs. We perform detailed population synthesis modeling of the XRB populations in NGC 1291, which suggests that the observed combined XLF is dominated by an old LMXB population. We compare the bulge and ring XRB populations, and argue that the ring XRBs are associated with a younger stellar population than the bulge sources, based on the relative overdensity of X-ray sources in the ring, the generally harder X-ray color of the ring sources, the overabundance of luminous sources in the combined XLF, and the flatter shape of the ring XLF.

Luo, B.; Fabbiano, G.; Fragos, T.; Kim, D.-W.; Wang Junfeng [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Belczynski, K. [Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warsaw (Poland); Brassington, N. J. [School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB (United Kingdom); Pellegrini, S. [Dipartimento di Astronomia, Universita di Bologna, Via Ranzani 1, 40127 Bologna (Italy); Tzanavaris, P. [Laboratory for X-ray Astrophysics, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Zezas, A. [Physics Department, University of Crete, P.O. Box 2208, GR-710 03, Heraklion, Crete (Greece)

2012-04-20

350

Wide Field Planetary Camera 2 Observations of the Polar Ring Galaxy NGC 4650A  

NASA Astrophysics Data System (ADS)

We present multicolor Wide Field Planetary Camera 2 images of the polar ring galaxy NGC 4650A (D=35 Mpc), taken with the Hubble Space Telescope. These data allow a detailed examination of the morphology of the central S0 component and the surrounding ``polar ring'' of stars, gas, and dust, which are spatially extended and form a ``polar disk.'' The nuclear complex, located near the common center of the two components, consists of an unresolved compact source less than 20 pc across, embedded in a more extended light distribution about 60 pc in radius. A complicated pattern of dust lanes crosses the high surface brightness central region of the S0, where dust features appear to extend inward to small radii. In areas of the S0 exterior to the projected polar disk, the light distribution is relatively smooth on small spatial scales, with few candidates for old star clusters or signs of internal dust features. Outer regions of the S0 galaxy have uniformly red colors of a stellar population where major star formation ceased ~3-5 Gyr in the past. The polar disk appears to be warped, with a complex morphology. On small spatial scales, features are produced mainly by dust and clumps of star formation; gas seems to be piling up in a dusty ring that encircles the central S0 at a radius of ~1 kpc (6"). The polar disk is inclined by about 63° near its center, twists toward edge-on at intermediate radii, and again becomes more nearly face-on further out, where two spiral arms are marked by young stars. We do not detect any regions with a prominent ``Baade sheet'' of older red stars in the polar disk; most of the optical light is supplied by moderately young stars, with lifetimes of ~1 Gyr. The polar material appears relatively unevolved, especially when compared to the S0 component of NGC 4650A. Either the polar disk is a late addition to the system or the outer gas has formed very few stars until recently. Observations obtained 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 (AURA), Inc., under NASA contract NAS5-26555.

Gallagher, J. S.; Sparke, L. S.; Matthews, L. D.; Frattare, L. M.; English, J.; Kinney, A. L.; Iodice, E.; Arnaboldi, M.

2002-03-01

351