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1

The analysis of the barred galaxy NGC 6701.  

NASA Astrophysics Data System (ADS)

We present broad band and H? photometry as well as long slit spectroscopy at four different position angles for the barred Sa galaxy NGC 6701. The images show a very prominent diamond-shaped bar lying almost along the disc minor axis. The bar is especially bright along the most external regions of its major axis. The signature of star forming processes can be seen in those regions by their bluer colors and also from the H? image. Two distinct dust lanes trace the inner sides of these bright features. The spectroscopic results point to the presence of shocks along the dust lanes, in agreement with some numerical simulations of barred galaxies. In fact, the properties of NGC 6701 resemble those found in simulations quite well. The kinematical analysis of NGC 6701 shows a perturbed rotation curve. This galaxy shows many of the signs supposed to be consequences of interaction. We report the redshift of a nearby, small galaxy, which turns out to be a physical companion to NGC 6701. The redshift difference is only 145 km/s and the projected distance is 73kpc (with H_0_=75km/s/Mpc). The peculiarities in NGC 6701 could thus be produced by the interaction with this small companion.

Marquez, I.; Moles, M.; Masegosa, J.

1996-06-01

2

Molecular Gas in Candidate Double Barred Galaxies I. The Diverse Morphology and Dynamics of NGC 2273 and NGC 5728  

E-print Network

Double bars have been proposed as a means of transporting molecular gas past inner Lindblad resonances into the nuclear regions, where it can fuel active or starburst nuclei. Thus far, the existence of double bars has been determined predominantly through analysis of near infrared images, which can tell us little about the dynamics and inflow rates of these systems. We have observed two double bar galaxy candidates (NGC 2273 and NGC 5728) in CO J=1-0 with the Owens Valley Radio Observatory Millimeter Array. Despite the similarity in the near infrared images of these galaxies, we see rather different nuclear morphologies in the CO maps. NGC 2273 shows evidence of a nuclear gas bar, aligned with the nuclear stellar bar seen in the near infrared images. Both the nuclear gaseous and stellar bars are misaligned from the large scale bar by approximately 90 degrees, which also allows the possibility that both are the result of stars and gas populating the $x_2$ orbits of the primary bar. Estimates using dynamical friction arguments and star formation rates suggest significant gas inflow rates along the nuclear bar of NGC 2273. Conversely, NGC 5728 does not show any evidence for a nuclear molecular bar, but shows an arc of CO clumps that peaks just to the south-west of the dynamical center and curves to the south-east where it follows the dust lane to the south. Models of double-barred galaxies suggest that these galaxies should contain large amounts of molecular gas in their nuclei. Our calculations suggest that both galaxies contain sufficient amounts of gas in their nuclei, but only NGC 2273 shows evidence for a nuclear gas bar. This may be the result of past episodes of star formation exhausting and dispersing the nuclear gas of NGC 5728, but is more likely evidence that NGC 5728 has undergone a minor merger event.

Glen Petitpas; Christine Wilson

2002-04-24

3

The nuclear ring of the barred galaxy NGC 1326  

NASA Astrophysics Data System (ADS)

High-resolution observations are reported of the radio-continuum emission from the central region of the barred spiral galaxy NGC 1326. The observations include emissions from the central region at 1.49, 4.86, and 14.9 GHz, optical R-band continuum data, and H alpha emission. Also included are the results of near-IR broadband photometry at wavelengths of 1.25, 1.65, and 2.2 microns, as well as observations of the CO(1-0) and CO(2-1) emissions. The observations indicate a ring structure around a compact optical nucleus, and no strong radio source is identified for the compact nucleus. The typical electron density of the H II regions is given as more than 8/cu cm, and the electron density of the the ring emission is less than 100/cu cm. A mass model is employed to reproduce the observed velocities which suggests that the two observed rings are due to gravitational perturbation of the bar in the object.

Garcia-Barreto, J. A.; Dettmar, R.-J.; Combes, F.; Gerin, M.; Koribalski, B.

1991-10-01

4

A Fast Bar in the Post-Interaction Galaxy NGC 1023  

E-print Network

We measured the bar pattern speed, $\\om$, of the SB0 galaxy NGC 1023 using the Tremaine-Weinberg (1984) method with stellar-absorption slit spectroscopy. The morphology and kinematics of the \\hi gas outside NGC 1023 suggest it suffered a tidal interaction, sometime in the past, with one of its dwarf companions. At present, however, the optical disc is relaxed. If the disc had been stabilized by a massive dark matter halo and formed its bar in the interaction, then the bar would have to be slow. We found $\\om = 5.0 \\pm 1.8$ \\kmsa, so that the bar ends near its co-rotation radius. It is therefore rotating rapidly and must have a maximum disc.

Victor P. Debattista; Enrico Maria Corsini; J. A. L. Aguerri

2001-12-12

5

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

6

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

NASA Astrophysics Data System (ADS)

We have performed an X-ray study of the nearby barred spiral galaxy NGC 1672, primarily to ascertain the effect of the bar on its nuclear activity. We use both Chandra and XMM-Newton observations to investigate its X-ray properties, together with supporting high-resolution optical imaging data from the Hubble Space Telescope (HST), infrared imaging from the Spitzer Space Telescope, and Australia Telescope Compact Array ground-based radio data. We detect 28 X-ray sources within the D 25 area of the galaxy; many are spatially correlated with star formation in the bar and spiral arms, and two are identified as background galaxies in the HST images. Nine of the X-ray sources are ultraluminous X-ray sources, with the three brightest (LX > 5 × 1039 erg s-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 × 1038 erg s-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. M.; Koribalski, B.; Kuntz, K. D.; Levan, A. J.; Ojha, R.; Roberts, T. P.; Ward, M. J.; Zezas, A.

2011-06-01

7

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

8

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

9

Molecular Gasdynamics of the Young Nuclear Starburst in the Barred Galaxy NGC 3504  

NASA Astrophysics Data System (ADS)

We present CO (J = 1 ? 0) interferometry at 2".5 resolution and H? CCD observations of the circumnuclear starburst region of the barred spiral galaxy NGC 3504. The CO emission is centrally peaked, extends over a region 16" (1.6 kpc) in diameter, and is relatively azimuthally symmetric. The CO radial distribution is well fitted by an exponential with a scale length of 2".3 (220 pc). This simple distribution is surprisingly unusual for the center of a galaxy. The velocity field is consistent with purely circular motions. Gas comprises ˜40% of the dynamical mass within a radius of 100 pc (1"), if the "standard" CO-H2 relationship is assumed. If isothermal and self-gravitating, the circumnuclear gas disk has a scale height of only 5-10 pc, and a spatially averaged proton density of 104 cm-3 at radii less than 300 pc. The rotation curve and the dust-lane morphology indicate the presence of an outer inner Lindblad resonance (OILR) at a radius of ˜5", and an inner inner Lindblad resonance (IILR) at a radius of ˜2". The starburst and most of the circumnuclear gas disk seem to be located between the OILR and the IILR. The maximum value of ?-?/2 is nearly twice as large as the bar pattern speed of the large-scale bar, and the OILR and the IILR are well separated, and these may be important dynamical differences between NGC 3504 and nonstarburst barred galaxies. The rate of high-mass star formation per unit gas mass, as traced by the ratio of H? to CO emission, is uniformly high over the portion of the rotation curve which is nearly solid body, and drops by a factor of ˜4 where the rotation curve turns over and flattens out. Since the CO radial distribution is not ringlike despite the fact that gas is being consumed more rapidly in the center, we believe that the starburst in NGC 3504 is in an early phase of its evolution. The Toomre Q stability parameter is approximately constant at 0.9±0.2 throughout the circumnuclear molecular gas disk, so the simple gravitational instability theory is consistent with ongoing star formation. The radial variation in the cloud growth timescale predicted from a Toomre instability is similar to the radial variation in the gas depletion timescale derived from the H?/CO ratio, although the timescales differ by a factor of ˜103. Either star formation is surprisingly inefficient, or the cloud collapse timescale is longer than the instability growth timescale We propose that the behavior of star formation for a given value of Q is strongly influenced by the strength of tidal shear, which can help control the star formation rate via the cloud destruction rate. In the central 300 pc of NGC 3504, where the rotation curve is nearly solid body and where the starburst is most intense, a lump of gas with Q ? 1 has a density much greater than that which is susceptible to tidal shear. However, 400-600 pc from the center of NGC 3504, where the rotation curve is nearly flat, a lump of gas with Q ? 1 has a density close to the range where tidal shear can shred it. A combination of tidal shear and gravitational instability theory can explain why starbursts evolve from the inside out, why evolved starbursts have rings of gas where the rotation curve turns over, and why star formation and the gas supply are regulated to maintain Q ? 1 where rotation curves are nearly flat, but may be unregulated where rotation curves are nearly solid body.

Kenney, Jeffrey D. P.; Carlstrom, John E.; Young, Judith S.

1993-12-01

10

Star Formation Properties in Barred Galaxies(SFB). I. Ultraviolet-to-Infrared Imaging and Spectroscopic Studies of NGC 7479  

E-print Network

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 $\\sim$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 e...

Zhi-Min, Zhou; Xian-Min, Meng; Hong, Wu

2011-01-01

11

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

12

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

13

The NUGA project: The Seyfert 2 galaxy NGC3147  

E-print Network

We present CO(1-0) and CO(2-1) maps of the Seyfert 2 galaxy NGC3147 of the NUclei of GAlaxies (NUGA) sample at 1.8'' x 1.6'' and 1.4'' x 1.2'' resolution respectively. Identifying the presence of a bar in NGC3147 we also compute the gravity torques exerted from the stellar bar on the gas.

V. Casasola; F. Combes; S. Garcia-Burillo; L. K. Hunt; S. Leon; A. Baker

2007-12-03

14

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

15

Galaxy NGC 4013  

NASA Technical Reports Server (NTRS)

An amazing 'edge-on' view of a spiral galaxy 55 million light years from Earth has been captured by the Hubble Space Telescope. The image, available at http://www.jpl.nasa.gov/pictures/wfpc , reveals in great detail huge clouds of dust and gas extending along and above the galaxy's main disk.

The image was taken by Hubble's Wide Field and Planetary Camera 2, which was designed and built by NASA's Jet Propulsion Laboratory, Pasadena, Calif.

The galaxy, called NGC 4013, lies in the direction of the constellation Ursa Major. If we could see it pole-on, it would look like a nearly circular pinwheel. In this Hubble image, NGC 4013 is seen edge-on, from our vantage point. Because the galaxy is larger than Hubble's field of view, the image shows only a little more than half the object, but with unprecedented detail.

Dark clouds of interstellar dust stand out, since they absorb the light of background stars. Most of the clouds lie in the galaxy's plane and form the dark band, about 500 light years thick, that appears to cut the galaxy in two from upper right to lower left. Scientists believe that new stars form in dark interstellar clouds. NGC 4013 shows several examples of these stellar kindergartens near the center of the image, in front of the dark band along the galaxy's equator. One extremely bright star near the upper left corner is merely a nearby foreground star that lies in our Milky Way and happened to be in the line of sight.

This new picture was constructed from Hubble images taken in January 2000 by Dr. J. Christopher Howk of Johns Hopkins University, Baltimore, Md., and Dr. Blair D. Savage of the University of Wisconsin-Madison. Images taken through three different filters have been combined into a color composite covering the region of the galaxy nucleus (behind the bright foreground star at the upper left) and extending along one edge of the galaxy to the lower right.

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 available at http://www.stsci.edu . More information about the Wide Field and Planetary Camera 2 is available at http://wfpc2.jpl.nasa.gov.

1999-01-01

16

Rotations and masses of the spiral galaxies NGC 3726, NGC 3810, NGC 4559, and NGC 6118  

Microsoft Academic Search

We have observed the rotational curves and derived the masses of the spiral galaxies NGC 3726, NGC 3810, NGC 4559 and NGC 6118. The emission line radial velocities were obtained principally from plates, covering the range from 6450 Aring; to 6800 Aring;, taken with the nebular spectrograph at the Cassegrain focus of the 193 cm telescope at the Observatoire de

N. Meyssonnier

1984-01-01

17

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

18

Are bars essential for starbursts in non-interacting galaxies  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

19

ON THE BAR PATTERN SPEED DETERMINATION OF NGC 3367  

SciTech Connect

An important dynamic parameter of barred galaxies is the bar pattern speed, {omega} {sub P}. Among several methods that are used for the determination of {omega} {sub P}, the Tremaine-Weinberg method has the advantage of model independence and accuracy. In this work, we apply the method to a simulated bar including gas dynamics and study the effect of two-dimensional spectroscopy data quality on robustness of the method. We added white noise and a Gaussian random field to the data and measured the corresponding errors in {omega} {sub P}. We found that a signal to noise ratio in surface density {approx}5 introduces errors of {approx}20% for the Gaussian noise, while for the white noise the corresponding errors reach {approx}50%. At the same time, the velocity field is less sensitive to contamination. On the basis of the performed study, we applied the method to the NGC 3367 spiral galaxy using H{alpha} Fabry-Perot interferometry data. We found {omega} {sub P} = 43 {+-} 6 km s{sup -1} kpc{sup -1} for this galaxy.

Gabbasov, R. F.; Repetto, P.; Rosado, M. [Instituto de AstronomIa, Universidad Nacional Autonoma de Mexico (UNAM), A.P. 70-264, 04510, Mexico D.F. (Mexico)], E-mail: gabbasov@astroscu.unam.mx

2009-09-01

20

Secular Evolution in Barred Galaxies  

E-print Network

A strong bar rotating within a massive halo should lose angular momentum to the halo through dynamical friction, as predicted by Weinberg. We have conducted fully self-consistent, numerical simulations of barred galaxy models with a live halo population and find that bars are indeed braked very rapidly. Specifically, we find that the bar slows sufficiently within a few rotation periods that the distance from the centre to co-rotation is more than twice the semi-major axis of the bar. Observational evidence (meagre) for bar pattern speeds seems to suggest that this ratio typically lies between 1.2 to 1.5 in real galaxies. We consider, a number of possible explanations for this discrepancy between theoretical prediction and observation, and conclude that no conventional alternative seems able to account for it.

J. A. Sellwood; Victor P. Debattista

1996-02-06

21

The Superwind Galaxy NGC 4666  

NASA Astrophysics Data System (ADS)

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

2010-09-01

22

Mon. Not. R. Astron. Soc. 337, 12331244 (2002) Simulations of central structure in barred galaxies  

E-print Network

) supports the bar itself, and the per- pendicularly aligned x2 family is often identified with the nuclear structures in barred galaxies ­ nested bars, nuclear spirals and circumnuclear rings ­ by making N & Burbidge 1960) and NGC 4314 (Sandage 1961) were known before the era of CCD detectors. The observed nuclear

Salo, Heikki

23

CO Distribution and Kinematics Along the Bar in the Strongly Barred Spiral NGC 7479  

E-print Network

We report on the 2.5 arcsec (400 pc) resolution CO (J = 1 -> 0) observations covering the whole length of the bar in the strongly barred late-type spiral galaxy NGC 7479. CO emission is detected only along a dust lane that traverses the whole length of the bar, including the nucleus. The emission is strongest in the nucleus. The distribution of emission is clumpy along the bar outside the nucleus, and consists of gas complexes that are unlikely to be gravitationally bound. The CO kinematics within the bar consist of two separate components. A kinematically distinct circumnuclear disk, < 500 pc in diameter, is undergoing predominantly circular motion with a maximum rotational velocity of 245 km/s at a radius of 1 arcsec (160 pc). The CO-emitting gas in the bar outside the circumnuclear disk has substantial noncircular motions which are consistent with a large radial velocity component, directed inwards. The CO emission has a large velocity gradient across the bar dust lane, ranging from 0.5 to 1.9 km/s/pc after correcting for inclination, and the projected velocity change across the dust lane is as high as 200 km/s. This sharp velocity gradient is consistent with a shock front at the location of the bar dust lane. A comparison of H-alpha and CO kinematics across the dust lane shows that although the H-alpha emission is often observed both upstream and downstream from the dust lane, the CO emission is observed only where the velocity gradient is large. We also compare the observations with hydrodynamic models and discuss star formation along the bar.

S. Laine; J. D. P. Kenney; M. S. Yun; S. T. Gottesman

1998-08-28

24

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

NASA Technical Reports Server (NTRS)

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

2002-01-01

25

A detailed study of the ringed galaxy NGC 3344  

NASA Astrophysics Data System (ADS)

We study the relatively isolated galaxy NGC 3344, classified as SABbc, as part of our study of ringed isolated non-barred galaxies. This galaxy shows an inner and an outer ring, together with a small bar inside the inner ring. This bar is too small to relate it directly to the formation of the outer ring and we explore here its origin through HI (WSRT) line data together with broad band BR CCD-photometry and optical spectroscopy. We show that the bar is exponential and dominates the central parts, while the bulge component is small. This suggests a morphological type later than Sbc for NGC 3344, further supported by the strong abundance gradient reported in the literature for this galaxy. The inner ring defines the beginning of the spiral structure which partially wraps around this ring at small radii. Less than 1% of the HI is located in this ring which is mostly composed by a young stellar population. The outer ring shows colours similar to those of the inner ring, indicating that is actively forming stars. It is not located symmetrically with respect to the center of the galaxy, its center being shifted by about 18\\arcs. Twenty percent of the HI emission is concentrated in this ring. The atomic gas is distributed asymmetrically in NGC 3344, extending 20% farther to the SE than in the opposite direction. The outer parts of the velocity field also deviate from that of a disk in circular rotation, with a pronounced warp especially abrupt to the SE. We derive a mass model for this galaxy, but the deviations from axisymmetry prohibit a good determination of a single pattern speed explaining the location of the rings. based partially on data collected at the Observatoire de Haute Provence, France

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

2000-04-01

26

TESTING THEORIES IN BARRED-SPIRAL GALAXIES  

SciTech Connect

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

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

2012-01-10

27

The Star Clusters in the Irregular Galaxy NGC 4449  

E-print Network

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

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

2000-10-25

28

New, Faint Satellite Galaxies of NGC253  

NASA Astrophysics Data System (ADS)

As part of the Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS), we present our initial search for faint dwarf galaxies around the nearby spiral galaxy NGC253 (D~3.5 Mpc). While simulations of structure formation match observational constraints on the largest scales, they struggle to reproduce observations below that of individual galaxies. For a point of comparison, and to extend the search for faint dwarf galaxies beyond the Local Group, we have begun a search for faint dwarfs around two of our nearest galaxy neighbors: Centaurus A and NGC253. Here we present five new dwarf galaxy candidates to NGC253, all in resolved stellar light. We summarize their basic properties including their structure, star formation history and distances. When complete, the PISCeS survey will provide a complete census of dwarf satellites around NGC253 down to M_V~-8, allowing for direct comparisons with simulations and recent work around both the Milky Way and M31.

Sand, David J.; Crnojevic, Denija; Caldwell, Nelson; Guhathakurta, Puragra; McLeod, Brian A.; Seth, Anil; Simon, Joshua D.; Strader, Jay

2015-01-01

29

ON THE FRACTION OF BARRED SPIRAL GALAXIES  

SciTech Connect

We investigate the stellar masses of strongly barred spiral galaxies. Our analysis is based on a sample of {approx}14,000 visually classified nearby galaxies given by Nair and Abraham. The fraction of barred spiral galaxies is found to be a strong function of stellar mass and star formation history, with a minimum near the characteristic mass at which bimodality is seen in the stellar populations of galaxies. We also find that bar fractions are very sensitive to the central concentration of galaxies below the transition mass but not above it. This suggests that whatever process is causing the creation of the red and blue sequences is either influencing, or being influenced by, structural changes which manifest themselves in the absence of bars. As a consequence of strong bar fractions being sensitive to the mass range probed, our analysis helps resolve discrepant results on the reported evolution of bar fractions with redshift.

Nair, Preethi B.; Abraham, Roberto G., E-mail: preethi.nair@oabo.inaf.i, E-mail: abraham@astro.utoronto.c [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada)

2010-05-10

30

Structural analysis of disk galaxies of the NGC 524 group  

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

31

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.

32

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

E-print Network

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

Peter Erwin

2003-12-14

33

Observable Properties of Double-Barred Galaxies in N-Body Simulations  

E-print Network

Although at least one quarter of early-type barred galaxies host secondary stellar bars embedded in their large-scale primary counterparts, the dynamics of such double barred galaxies are still not well understood. Recently we reported success at simulating such systems in a repeatable way in collisionless systems. In order to further our understanding of double-barred galaxies, here we characterize the density and kinematics of the N-body simulations of these galaxies. This will facilitate comparison with observations and lead to a better understanding of the observed double-barred galaxies. We find the shape and size of our simulated secondary bars are quite reasonable compared to the observed ones. We demonstrate that an authentic decoupled secondary bar may produce only a weak twist of the kinematic minor axis in the stellar velocity field, due to the relatively large random motion of stars in the central region. We also find that the edge-on nuclear bars are probably not related to boxy peanut-shaped bulges which are most likely to be edge-on primary large-scale bars. Finally we demonstrate that the non-rigid rotation of the secondary bar causes its pattern speed not to be derived with great accuracy using the Tremaine-Weinberg method. We also compare with observations of NGC 2950, a prototypical double-barred early-type galaxy, which suggest that the nuclear bar may be rotating in the opposite sense as the primary.

Juntai Shen; Victor P. Debattista

2007-11-06

34

Kinematic Evidence of Minor Mergers in Normal Sa Galaxies: NGC3626, NGC3900, NGC4772 and NGC5854  

E-print Network

BVRI and H-alpha imaging and long-slit optical spectroscopic data are presented for four morphologically normal and relatively isolated Sa galaxies, NGC3626, NGC3900, NGC4772 and NGC5854. VLA HI synthesis imaging is presented for the first 3 objects. In all 4 galaxies, evidence of kinematic decoupling of ionized gas components is found; the degree and circumstances of the distinct kinematics vary from complete counterrotation of all of the gas from all of the stars (NGC3626) to nuclear gas disks decoupled from the stars (NGC5854) to anomalous velocity central gas components (NGC3900 and NGC4772). In the 3 objects mapped in HI, the neutral gas extends far beyond the optical radius, R_HI/R_25 > 2. In general, the HI surface density is very low and the outer HI is patchy and asymmetric or found in a distinct ring, exterior to the optical edge. While the overall HI velocity fields are dominated by circular motions, strong warps are suggested in the outer regions. Optical imaging is also presented for NGC 4138 previously reported by Jore et al. (1996) to show counterrotating stellar components. The multiwavelength evidence is interpreted in terms of the kinematic "memory" of past minor mergers in objects that otherwise exhibit no morphological signs of interaction.

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

2000-04-25

35

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

Microsoft Academic Search

We complement our Hubble Space Telescope (HST) observations of the inner ring of the galaxy NGC 3081 using an analytical approach and n-body simulations. We find that a gas cloud inner (r) ring forms under a rotating bar perturbation with very strong azimuthal cloud crowding where the ring crosses the bar major axis. Thus, star formation results near to and

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

2006-01-01

36

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

37

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

38

Stellar content and distances to the isolated spiral galaxies NGC 6503 and NGC 6946  

NASA Astrophysics Data System (ADS)

Based on archival Hubble Space Telescope images, we have performed stellar photometry of several fields in the isolated spiral galaxies NGC 6503 and NGC 6946 with high peculiar velocities. Based on the TRGB method, we have determined the distances to the galaxies: D = 6.30 ± 0.10 Mpc for NGC 6503 and D = 6.72 ± 0.15 Mpc for NGC 6946. The current stellar content of the galaxies does not differ from that of other similar galaxies. The metallicity for young stars in NGC 6503 is Z = 0.02 (corresponding to the solar metallicity), while the metallicity for stars in NGC 6946 reaches Z = 0.05. Very few old globular clusters have been found in NGC 6946, while they have not been found at all in NGC 6503. The number density distribution of stars with different ages in NGC 6503 does not differ from the analogous distributions in other galaxies. The large sizes of the thick disk in NGC 6503, which is clearly seen up to 6 kpc from the galactic disk plane and whose possible extension is noticeable up to 8.6 kpc from the plane, are a difference. The sizes of the region occupied by red giants of the disk in NGC 6503 are 51 × 17 kpc, which are not much larger than the sizes of this galaxy from H I radio observations.

Tikhonov, N. A.

2014-09-01

39

Near-infrared image of NGC 1068 - Bar-driven star formation and the circumnuclear composition  

NASA Astrophysics Data System (ADS)

Consideration is given to differences in images of the core of the Seyfert galaxy NGC 1068 at different wavelength regimes dominated by stellar photospheric emission. A stellar bar is observed at 1.6 and 2.2 microns, but not at shorter visual wavelength observations. Two explanations for these differences are examined: substantial stellar population variations with position and the effects of dust obscuration. The relation of the bar to active star formation is discussed. The mass of the central disk and bar is estimated at 2-3 X 10 to the 10th solar masses. It is found that the rate of star formation (100 solar masses/yr) is due to a large mass of molecular gas.

Thronson, Harley A., Jr.; Hereld, Mark; Majewski, Steven; Greenhouse, Matthew; Johnson, Paul; Spillar, Earl; Woodward, C. E.; Harper, D. A.; Rauscher, Bernard J.

1989-08-01

40

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

41

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

42

Bright Stars and Recent Star Formation in the Irregular Magellanic Galaxy NGC2366  

E-print Network

The stellar content of the Im galaxy NGC 2366 is discussed on the basis of CCD BVR photometry. The three brightest blue and red stars have been used to estimate its distance, obtaining a balue of 2.9 Mpc. The spatial distribution of the young stellar population is discussed in the light of the integrated color indices and the color-magnitude diagrams of different zones of the galaxy. A generalized star formation burst seems to have taken place about 50 Myr ago. The youngest stars are preferentially formed in the South-West part of the bar, where the giant HII complex NGC 2363 is located, being younger and bluer. The bar seems to play a role favouring star formation in one of its extremes. Self-propagation however, does not seem to be triggering star formation at large scale. A small region, populated by very young stars has also been found at the East of the galaxy.

A. Aparicio; J. Cepa; C. Gallart; H. Castaneda; C. Chiosi; G. Bertelli; C. Munoz-Tunon; Eduardo Telles; G. Tenorio-Tagle; A. I. Diaz; M. L. Garcia-Vargas; F. Garzon; R. Ma. Gonzalez-Delgado; M. Mas-Hesse; E. Perez; J. M. Rodriguez-Espinosa; E. Terlevich; R. J. Terlevich; A. M. Varela; J. M. Vilchez

1995-04-12

43

Gas flows and bars in galaxies  

E-print Network

Dynamical evolution of spiral galaxies is strongly dependent on non-axisymmetric patterns that develop from gravitational instabilities, either spontaneously or externally triggered. Some evolutionary sequences are described through which a galaxy could possibly concentrate mass and build bulges, how external gas accretion from cosmic filaments could be funneled to the galaxy disks, and intermittently driven to the galaxy center, to form nuclear starbursts and fuel an active nucleus. The frequency of both bars and lopsidedness can be used to constrain the gas accretion rate.

F. Combes

2006-08-29

44

The Central Velocity Field in NGC 253 : Possible Indication of a Bar  

E-print Network

We have investigated whether motion of gas in a bar-like potential can account for the peculiar but systematic velocity field observed in the nuclear region of the starburst galaxy NGC 253. This unusual velocity field with gradients along both major and minor axes was revealed in a high resolution ($1.8^{\\arcsec}\\times 1.0^{\\arcsec}$) H92$\\alpha$ recombination line observation by Anantharamiah and Goss (1996). A simple logarithmic potential is used to model the bar. Assuming that the bulk of the gas flows along closed and non-intersecting x1 (bar) and x2 (anti-bar) orbits of the bar potential, we have computed the expected velocity field and position-velocity diagrams and compared them with the observations. A comparison of the integrated CO intensity maps with the spatial distribution of the x1 and x2 orbits in the model indicates that the nuclear molecular gas in NGC 253 lies mainly on the x2 orbits. We also find that the velocity field observed in the central 100 pc region in the H92$\\alpha$ recombination line is well accounted for by the bar model if most of the ionized gas resides in the inner x2 orbits. However, the model is unable to explain the velocity field on a larger scale of $\\sim 500$ pc observed using the OVRO interferometer with a resolution of $5^{\\arcsec}\\times 3^{\\arcsec}$. The direction of the observed CO velocity field appears twisted compared to the model. We suggest that this perturbation in the velocity field may be due to an accretion event that could have occurred $10^7$ years ago.

Mousumi Das; K. R. Anantharamaiah; M. S. Yun

2000-10-12

45

Globular Clusters in Coma Galaxy NGC 4881  

NASA Astrophysics Data System (ADS)

We report HST-WFPC2 observations of the bright E0 galaxy NGC 4881, located about 18' north of the center of the Coma Cluster. Counts of globular clusters (GCs) were made both within the PC 1(f/28) frame and within the three WFC (f/13) frames. Attention was focused mainly on the PC1 data, in which faint GCs could be distinguished from noise spikes by the use of a PSF fitting test. Within the 34"X 34" field of the PC1 detector (minus a circle of 3" radius around the NGC 4881 nucleus), 88 GCs have been identified to a threshold of F555W = 27.6 mag~V. Noise spikes are only beginning to appear near that threshold, and they have been excluded. Extended sources, such as distant background galaxies, have also been identified and excluded. If corrected for incompleteness in the faintest bins, the numbers of GCs per 0.4 mag bin in NGC 4881 are rising monotonically to our threshold and therefore imply that we probably have not yet passed the turnover of the globular cluster luminosity function (GCLF). Alternatively, instead of applying completeness corrections, we can compare uncorrected NGC 4881 counts with a model GCLF transported to various assumed Coma Cluster distances. The relative likelihoods of various distances can then be calculated using Poisson statistics to quantify the fit. For a model we use the GCLFs of the Milky Way and M31. We find the likelihood of the GCLF fit to rise with increasing Coma distance until it crests at ~108 Mpc, and then levels off. Therefore, if the model fairly represents the GCs in NGC 4881, our estimate of the minimum Coma distance is 108 Mpc with a formal statistical error of (-11,+{infinity}) Mpc. A comparison of three independent calibrations indicates that any zero-point error in the photometry should be < 5%. Three other possible sources of systematic error include the RR Lyrae distance scale for the Milky Way GCs, the distance modulus of M31, and any intrinsic difference between NGC 4881 and the model in the M_V_ of the GCLF turnover. In all three cases, there are envisaged adjustments which, if applied, would have the effect of increasing our estimate of the minimum distance to Coma. A distance of 108(-11,+{infinity}) Mpc implies a Hubble Constant H_0_ = 67(+7, -[67]) km/s per Mpc. We cannot set an upper limit on the distance, nor a lower limit on H_0_, until observations of Coma galaxies reach deep enough to show the turnover of the GCLF, and we also caution that the results above are based on only one Coma galaxy. If the GCs detected on all four CCDs are fitted with the GCLF model and if counts are adjusted for incomplete areal coverage, the GC system in NGC 4881 is found to have a specific frequency of only about 1.0, which is lower than in the majority of bright ellipticals but not the lowest known. The GC system in NGC 4881 is also found to be only a little more spatially extended than the luminosity profile of the galaxy itself. Those findings are somewhat sensitive to any nonuniformity in the distribution of background objects in the WFC frames. Even so, the specific frequency is almost certainly less than 2.0. The low specific frequency in NGC 4881 may have implications concerning the formation, migration, and fate of GCs in a dense environment like that of Coma, where very large numbers of GCs and dwarf galaxies have been reported near the center of the cluster. There is no evidence that the GCs of NGC 4881 are abnormal: they have a mean color index (V - I) = 0.97 mag with relatively small dispersion, and the implied metallicity, [Fe/H] ~ -1.2, is within the range of GC metallicities found in the Milky Way, though a little more metal rich than the mean. Moreover, the NGC 4881 GCLF has the same slope as the bright side of the GCLF in the Milky Way.

Baum, W. A.; Hammergren, M.; Groth, E. J.; Ajhar, E. A.; Lauer, T. R.; O'Neil, E. J., Jr.; Lynds, C. R.; Faber, S. M.; Grillmair, C. J.; Holtzman, J. A.; Light, R. M.

1995-12-01

46

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

E-print Network

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

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

2001-09-14

47

ON THE GALACTIC SPIN OF BARRED DISK GALAXIES  

SciTech Connect

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

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

2013-09-20

48

On the Galactic Spin of Barred Disk Galaxies  

NASA Astrophysics Data System (ADS)

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

Cervantes-Sodi, Bernardo; Li, Cheng; Park, Changbom; Wang, Lixin

2013-09-01

49

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

E-print Network

A common feature of hierarchical galaxy formation models is the process of "inverse" morphological transformation: a bulge dominated galaxy accretes a gas disk, dramatically reducing the system's bulge-to-disk mass ratio. During their formation, present day galaxies may execute many such cycles across the Hubble diagram. A good candidate for such a "hermaphrodite" galaxy is NGC 3108: a dust-lane early-type galaxy which has a large amount of HI gas distributed in a large scale disk. We present narrow band H_alpha and R-band imaging, and compare the results with the HI distribution. The emission is in two components: a nuclear bar and an extended disk component which coincides with the HI distribution. This suggests that a stellar disk is currently being formed out of the HI gas. The spatial distributions of the H_alpha and HI emission and the HII regions are consistent with a barred spiral structure, extending some 20 kpc in radius. We measure an extinction- corrected SFR of 0.42 Msun/yr. The luminosity function of the HII regions is similar to other spiral galaxies, with a power law index of -2.1, suggesting that the star formation mechanism is similar to other spiral galaxies. We measured the current disk mass and find that it is too massive to have been formed by the current SFR over the last few Gyr. It is likely that the SFR in NGC 3108 was higher in the past. With the current SFR, the disk in NGC 3108 will grow to be ~6.2x10^9 Msun in stellar mass within the next 5.5 Gyr. While this is substantial, the disk will be insignificant compared with the large bulge mass: the final stellar mass disk-to-bulge ratio will be ~0.02. NGC 3108 will fail to transform into anything resembling a spiral without a boost in the SFR and additional supply of gas.

George Hau; Richard Bower; Virginia Kilborn; Duncan Forbes; Michael Balogh; Tom Oosterloo

2007-11-21

50

Warm molecular gas in galaxy-galaxy merger NGC6090  

NASA Astrophysics Data System (ADS)

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

Wang, J.; SAO; ASIAA SMA Team

2003-12-01

51

FISICA observations of the starburst galaxy, NGC 1569  

NASA Astrophysics Data System (ADS)

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

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

2006-06-01

52

The Reddening law outside the local group galaxies: The case of NGC 7552 and NGC 5236  

NASA Technical Reports Server (NTRS)

The dust reddening law from the UV to the near-IR for the extended regions of galaxies is here derived from the spectral distributions of the starburst spiral galaxies NGC 7552 and NGC 5236. The centers of these galaxies have similar absorption and emission line spectra, differing only if the strength of their interstellar lines and in the continuum distribution, with NGC 7552 appearing more reddened than NGC 5236. The disk of NGC 7552 is more inclined, and there is evidence that its center is observed through additional foreground dust and gas clouds, as compared to the center of NGC 5236. While the galaxies can be expected to have similar dust content, they are known to have different dust path lengths to our line of sight. Therefore, differences in the shape of the spectra can be attributed mainly to the effects of dust, allowing us to probe for the first time the properties of the reddening law outside the local group of galaxies. We derive the reddening law based on the optical depth of the emission line of H Alpha and H Beta and also based on the continuum distribtuion. We find that the optical depth from the emission line regions are about twice the optical depth of the continuum regions. Thus, dereddening a starburst galaxy by scaling the Milky Way reddening laws to optical depths obtained from the H Alpha/H Beta line ratio overcompensates for the effect of dust.

Kinney, Anne L.; Calzetti, Daniela; Bica, Eduardo; Storchi-Bergmann, Thaisa

1994-01-01

53

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

NASA Astrophysics Data System (ADS)

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

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

2002-02-01

54

NGC 3344 - Unusual abundances for an SBC galaxy  

NASA Astrophysics Data System (ADS)

Spectrophotometry of H II regions in the Sbc galaxy NGC 3344 reveals that it has a strong radial excitation gradient, with the ratio of the log of forbidden O III to H-beta rising to +0.7 in the outermost arms. Such behavior has heretofore been observed only in Scd galaxies, and it contrasts with observations of a number of galaxies of type Sc or earlier. (The colors and gas fraction of NGC 3344 are typical for its morphological type.) If this galaxy follows the relationship between abundance and excitation that is observed in other galaxies, then it has a strong abundance gradient in which the O/H abundance ratio falls to -0.7 in the outermost arms. Alternatively, the H II regions in NGC 3344 may have normal abundances together with unusually hot ionizing stars or a low dust/gas ratio.

McCall, M. L.; Rybski, P. M.; Shields, G. A.

1981-06-01

55

Dynamical modelling of the elliptical galaxy NGC 2974  

E-print Network

In this paper we analyse the relations between a previously described oblate Jaffe model for an ellipsoidal galaxy and the observed quantities for NGC 2974, and obtain the length and velocity scales for a relevant elliptical galaxy model. We then derive the finite total mass of the model from these scales, and finally find a good fit of an isotropic oblate Jaffe model by using the Gauss-Hermite fit parameters and the observed ellipticity of the galaxy NGC 2974. The model is also used to predict the total luminous mass of NGC 2974, assuming that the influence of dark matter in this galaxy on the image, ellipticity and Gauss-Hermite fit parameters of this galaxy is negligible within the central region, of radius $0.5R_{\\rm e}.$

Zhenglu Jiang

2008-10-19

56

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

NASA Astrophysics Data System (ADS)

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

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

57

CHANDRA OBSERVATIONS OF THE COLLISIONAL RING GALAXY NGC 922  

SciTech Connect

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

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

2012-03-10

58

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

59

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

60

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

61

Detection of Infalling Hydrogen in Transfer between the Interacting Galaxies NGC 5426 and NGC 5427  

NASA Astrophysics Data System (ADS)

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

Font, Joan; Beckman, John E.; Rosado, Margarita; Epinat, Benoît; Fathi, Kambiz; Hernandez, Olivier; Carignan, Claude; Gutiérrez, Leonel; Relaño, Monica; Blasco-Herrera, Javier; Fuentes-Carrera, Isaura

2011-10-01

62

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

SciTech Connect

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

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

2011-10-10

63

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

NASA Astrophysics Data System (ADS)

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

Topal, Selcuk

2015-01-01

64

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

65

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

66

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

NASA Astrophysics Data System (ADS)

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

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

2002-08-01

67

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

NASA Astrophysics Data System (ADS)

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

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

2009-05-01

68

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

SciTech Connect

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

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

2012-11-20

69

THE STAR CLUSTER POPULATION OF THE COLLISIONAL RING GALAXY NGC 922  

SciTech Connect

We present a detailed study of the star cluster population detected in the galaxy NGC 922, one of the closest collisional ring galaxies known to date, using Hubble Space Telescope/Wide Field Planetary Camera 2 UBVI photometry, population synthesis models, and N-body/smoothed particle hydrodynamics simulations. We find that 69% of the clusters are younger than 7 Myr, and that most of them are located in the ring or along the bar, consistent with the strong H{alpha} emission. The cluster luminosity function slope of 2.1-2.3 for NGC 922 is in agreement with those of young clusters in nearby galaxies. Models of the cluster age distribution match the observations best when cluster disruption is considered. We also find clusters with ages (>50 Myr) and masses (>10{sup 5} M {sub sun}) that are excellent progenitors for faint fuzzy clusters. The images also show a tidal plume pointing toward the companion. Its stellar age from our analysis is consistent with pre-existing stars that were stripped off during the passage of the companion. Finally, a comparison of the star-forming complexes observed in NGC 922 with those of a distant ring galaxy from the GOODS field indicates very similar masses and sizes, suggesting similar origins.

Pellerin, Anne [George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, 4242 TAMU, College Station, TX 77843 (United States); Meurer, Gerhardt R. [Physics and Astronomy Department, Johns Hopkins University, 3400 Charles Street, Baltimore, MD 21218 (United States); Bekki, Kenji [Department of Astrophysics and Optics, School of Physics, University of New South Wales, NSW 2052 (Australia); Elmegreen, Debra M. [Vassar College, Department of Physics and Astronomy, Box 745, Poughkeepsie, NY 12604 (United States); Wong, O. Ivy [Astronomy Department, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Knezek, Patricia M. [WIYN Consortium Inc., P.O. Box 26732, Tucson, AZ 85726 (United States)], E-mail: pellerin@physics.tamu.edu, E-mail: Gerhardt.Meurer@icrar.org, E-mail: bekki@phys.unsw.edu.au, E-mail: elmegreen@vassar.edu, E-mail: ivy.wong@yale.edu, E-mail: knezek@noao.edu

2010-04-15

70

LENTICULAR GALAXIES AT THE OUTSKIRTS OF THE LEO II GROUP: NGC 3599 AND NGC 3626  

SciTech Connect

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

Sil'chenko, O. K.; Shulga, A. P. [Sternberg Astronomical Institute, Moscow 119992 (Russian Federation); Moiseev, A. V., E-mail: olga@sai.msu.s, E-mail: alina.shulga@gmail.co, E-mail: moisav@gmail.co [Special Astrophysical Observatory, Nizhnij Arkhyz, Karachai-Circassia 369167 (Russian Federation)

2010-11-15

71

Multi-wavelength observations of barred, flocculent galaxies  

NASA Astrophysics Data System (ADS)

Although it is generally accepted that large galaxies form through the assemblage of smaller objects, an explanation for the morphology of galaxies is not available. Any complete theory of galaxy morphology must include production and dissolution mechanisms for galactic bars, rings, nuclear bars, spiral arms, and companions. This theory does not exist because of the lack of detailed data from many types of galaxies in different environments. We have defined a new sample of galaxies which are simultaneously flocculent, barred, and isolated. We have performed optical, near-infrared, and radio (HI) observations of the galaxies in this sample. We measured properties of our galaxies including bar length, bar axis ratio, HI diameter, HI mass, and dynamical mass. We found that our sample group is heterogeneous, and compares well to a standard samples of galaxies. We found two of our galaxies to possess companions, and two others to show evidence of current interactions. This is consistent with other observations indicating that local isolated galaxies do not possess a large number of small companions. We cannot rule out the possibility of very small companions. We find that as a group our sample is slightly less luminous than normal galaxies and may be more likely to be involved in interactions. We conclude that the bar and spiral arm features in our sample are due to processes internal to the galaxies, likely involving the interaction between the galactic disk and halo. We defined a control sample of barred, grand design galaxies to further determine the acceptability of barred, flocculent galaxies as a physically meaningful subset of galaxies.

Ratay, Douglas Lee

72

The Bar-Halo Interaction in SB Galaxies  

E-print Network

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

Victor P. Debattista; J. A. Sellwood

1996-10-01

73

Star formation outside the Elliptical Galaxy NGC2865  

NASA Astrophysics Data System (ADS)

We have searched for young stellar complexes around the elliptical galaxy NGC2865. We find them in a ring of HI around the galaxy. Using the Multi-Slit Imaging Spectroscopy Technique (MSIS), we detected a total of seven H? emitters in the south part of the tidal tail of the galaxy NGC2865. These regions are young sources with stellar masses in the range 4×10^{3}M_{odot} to 2×10^{6}M_{odot}, overlapping the location of the low density intergalactic HI gas, where the probability to form stars is expected to be low. For one of the intergalactic HII regions we estimated a solar oxygen abundance, 12 + log(O/H) ˜ 8.7. Given these proprieties, the regions are considered young star forming regions, born in-situ from a pre-enriched gas which has been removed from the host galaxies in a merger event.

Urrutia-Viscarra, F.; Arnaboldi, M.; Mendes de Oliveira, C.; Torres-Flores, S.; Carrasco, E. R.; de Mello, D.

2014-10-01

74

Nonthermal Emission in the Starburst Galaxies M 82 & NGC 253  

NASA Astrophysics Data System (ADS)

Detection of high-energy ?-ray emission from the nearby starburst galaxies M 82 and NGC 253 establishes, for the first time, a direct link between leptonic and hadronic processes in an extragalactic non-AGN environment. We review the most relevant aspects of these processes and contrast theoretical predictions with available radio and ?-ray measurements in order to determine the particle spectral properties and energy densities in these galaxies.

Rephaeli, Yoel; Persic, Massimo

2014-11-01

75

NGC 5523: An Isolated Product of a Soft Galaxy Merger  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

76

The elliptical galaxies NGC 1052 and NGC 7796. Stellar populations and abundance ratio ?/Fe  

NASA Astrophysics Data System (ADS)

Context: Understanding how each early-type galaxy forms and evolves is one of the objectives of extragalactic astrophysics and cosmology. The spatial distribution of the stellar populations inside a spheroidal system and their kinematic properties supply important information about the formation process. The reconstruction of the star formation history is crucial in this context. Aims: We have performed a detailed stellar population analysis using long slit spectroscopic observations up to almost one effective radius of two different early-type galaxies of low density regions of the local Universe: NGC 1052, an E4 Liner prototype of a loose group that has a stellar rotating disc, and NGC 7796, an E1 of the field which shows a kinematically distinct core. Their mean luminosity-weighted stellar age, metallicity, and ?/Fe ratio along both photometric axes have been obtained to reconstruct the star formation history in their kinematically distinct subsystems. Methods: We have measured Lick indices and computed their radial gradients. They were compared with the predicted ones of simple stellar population models. We have also applied a stellar population synthesis. Results: The star characteristics are associated with their kinematics: they are older and ?-enhanced in the bulge of NGC 1052 and core of NGC 7796, while they show a strong spread of ?/Fe and age along the disc of NGC 1052 and an outward radial decrease outside the core of NGC 7796. The age variation is possibly connected to the ?/Fe one. Conclusions: Both galaxies were formed by processes in which the star formation occurred first at the bulge (NGC 1052) and nucleus (NGC 7796) 12-15 Gyr ago on short timescales (0.1-1 Gyr), providing an efficient chemical enrichment by SN-II. In the disc of NGC 1052, there is some spread of age and formation timescales around its stars. In NGC 7796, the star formation timescale had some outward radial increases along both axes. Based on observations made in Observatório do Pico dos Dias (OPD), which is operated by LNA (Laboratório Nacional de Astrofísica), Brazil.

Milone, A. De C.; Rickes, M. G.; Pastoriza, M. G.

2007-07-01

77

Estimating turbulent velocities in the elliptical galaxies NGC 5044 and NGC 5813  

NASA Astrophysics Data System (ADS)

Context. The interstellar and intra-cluster medium (ICM) in giant elliptical galaxies and clusters of galaxies is often assumed to be in hydrostatic equilibrium. Numerical simulations, however, show that about 5-30% of the pressure in a cluster is provided by turbulence induced by, for example, the central active galactic nucleus (AGN) and merger activity. Aims: We aim to put constraints on the turbulent velocities and the turbulent pressure in the ICM of the giant elliptical galaxies NGC 5044 and NGC 5813 using XMM-Newton reflection grating spectrometer (RGS) observations. Methods: The magnitude of the turbulence is estimated using the Fe xvii lines at 15.01 Å, 17.05 Å, and 17.10 Å in the RGS spectra. At low turbulent velocities, the gas becomes optically thick in the 15.01 Å line due to resonant scattering, while the 17 Å lines remain optically thin. By comparing the (I17.05 + I17.10)/I15.01 line ratio from RGS with simulated line ratios for different Mach numbers, the level of turbulence is constrained. The measurement is, however, limited by the systematic uncertainty in the line ratio for an optically thin plasma, which is about 20-30%. Results: We find that the (I17.05 + I17.10)/I15.01 line ratio in NGC 5813 is significantly higher than in NGC 5044. This difference can be explained by a higher level of turbulence in NGC 5044. The best estimates for the turbulent velocities using resonant scattering and upper limits from the line widths, are 320 < Vturb < 720 km s-1 for NGC 5044 and 140 < Vturb < 540 km s-1 for NGC 5813 at the 90% confidence limit. Conclusions: The high turbulent velocities and the fraction of the turbulent pressure support of >40% in NGC 5044, assuming isotropic turbulence, confirm that it is a highly disturbed system, probably due to an off-axis merger. The turbulent pressure support in NGC 5813 is more modest at 15-45%. The (I17.05 + I17.10)/I15.01 line ratio in an optically thin plasma, calculated using AtomDB v2.0.1, is 2? above the ratio measured in NGC 5044, which cannot be explained by resonant scattering. This shows that the discrepancies between theoretical, laboratory, and astrophysical data on Fe xvii lines need to be reduced to improve the accuracy of the determination of turbulent velocities using resonant scattering.

de Plaa, J.; Zhuravleva, I.; Werner, N.; Kaastra, J. S.; Churazov, E.; Smith, R. K.; Raassen, A. J. J.; Grange, Y. G.

2012-03-01

78

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

79

Evolution of bars in interacting gas-rich galaxies  

NASA Astrophysics Data System (ADS)

The evolution of disk galaxies is driven through both internal and external processes. Internal instabilities in the disk often give rise to the formation of a bar, which as many as half of all disk galaxies are now known to harbor. The presence of a bar changes both the kinematics and mass (stellar and gas) distributions within the disk. Likewise, an only recently recognized important external agent is the interaction with small companions. Since these two processes are both thought to be ubiquitous, it is a reasonable assumption that the interaction between a barred disk galaxy and a small companion would be a common event. Numerical simulations have been undertaken to investigate the effects of an interaction between an initially barred galaxy and a small spherical companion. An N-body+SPH algorithm is used to evolve the stellar and gas components of the two systems. In the models described here the small companion passes through the disk of the larger galaxy perpendicular to its plane. The impact position and time are varied with respect to the bar and evolutionary phase of the isolated barred galaxy. We describe the different features produced by the interaction like expanding ring structures, offset bars, spokes, and other asymmetries in the stars and gas. Furthermore we describe how the evolution of the bar strength, pattern speed, and gas inflow rate are affected by the interaction and its effect on the secular evolution of the disc.

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

80

Where are the massive stars of the bar of NGC 1530 forming?  

E-print Network

Aims: NGC 1530 has one of the strongest bars ever observed and recent star formation sites are distributed across its bar. Our aim is to study the photometric properties of the bar and its HII regions, to elucidate the conditions under which HII regions form and their spatial relation to the principal dynamical features of the bar. Methods: We obtained BVRKs and Halpha photometry of the HII regions of the bar in NGC 1530. Broad-band integrated colours and Halpha equivalent widths were carefully measured and analysed as a function of position with respect to the main dust-lanes of the bar. Results: We measured differences in the Halpha equivalent widths of the HII regions that are located in the trailing and leading sides of the bar dust-lane. The possible factors that could produce this difference, such as [NII] contamination, Lyman-continuum-photon dust-extinction, escape of ionizing radiation, metallicity, IMF and age, were carefully analysed. Age differences were confirmed to be the most plausible explanation. This implies that HII regions that are located further away from the bar dust-lane in its leading side, downstream from the main bar dust-lane, are older than the rest by ~1.5-2.5 Myr. In addition, a clear spatial correlation has been found between: location of HII regions, dust spurs on the trailing side of the bar dust-lane, and the loci of maximum velocity gradients parallel to the bar major axis (possibly tracing gas flow towards the main bar dust-lane). These results support the hypothesis that massive stars are forming on the trailing side of the bar dust-lane, and age as they cross the bar, on a timescale that is compatible with the bar dynamics timescale.

A. Zurita; I. Perez

2008-04-11

81

Where are the stars of the bar of NGC 1530 forming?  

NASA Astrophysics Data System (ADS)

Aims: NGC 1530 has one of the strongest bars ever observed and recent star formation sites are distributed across its bar. Our aim is to study the photometric properties of the bar and its H ii regions, to elucidate the conditions under which H ii regions form and their spatial relation to the principal dynamical features of the bar. Methods: We obtained BVRKs and H? photometry of the H ii regions of the bar in NGC 1530. Broad-band integrated colours and H? equivalent widths were carefully measured and analysed as a function of position with respect to the main dust-lanes of the bar. Results: We measured differences in the H? equivalent widths of the H ii regions that are located in the trailing and leading sides of the bar dust-lane. The possible factors that could produce this difference, such as [N ii] contamination, Lyman-continuum-photon dust-extinction, escape of ionizing radiation, metallicity, IMF and age, were carefully analysed. Age differences were confirmed to be the most plausible explanation. This implies that H ii regions that are located further away from the bar dust-lane in its leading side, downstream from the main bar dust-lane, are older than the rest by ~1.5-2.5 Myr. In addition, a clear spatial correlation has been found between: location of H ii regions, dust spurs on the trailing side of the bar dust-lane, and the loci of maximum velocity gradients parallel to the bar major axis (possibly tracing gas flow towards the main bar dust-lane).These results support the hypothesis that massive stars are forming on the trailing side of the bar dust-lane, and age as they cross the bar, on a timescale that is compatible with the bar dynamics timescale.

Zurita, A.; Pérez, I.

2008-07-01

82

Dark Matter Deprivation in Field Elliptical Galaxy NGC 7507  

E-print Network

Previous studies have shown that the kinematics of the field elliptical galaxy NGC 7507 do not necessarily require dark matter. This is troubling because, in the context of LCDM cosmologies, all galaxies should have a large dark matter component. We use penalised pixel fitting software to extract velocities and velocity dispersions from GMOS slit mask spectra. Using Jeans and MONDian modelling we produce best fit models to the velocity dispersion. We find that NGC 7507 has a two component stellar halo, with the outer halo and inner haloes counter rotating. The velocity dispersion profile exhibits an increase at ~70" (~7.9 kpc), reminiscent of several other elliptical galaxies. Our best fit models are those under mild anisotropy which include ~100 times less dark matter than predicted by LCDM, although mildly anisotropic models that are completely dark matter free fit almost equally well. Our MONDian models, both isotropic and anisotropic, systematically fail to reproduce the measured velocity dispersions at a...

Lane, Richard R; Richtler, Tom

2014-01-01

83

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

84

Chandra observations of the nearby spiral galaxy NGC6503  

E-print Network

We have observed the nearby spiral galaxy NGC6503 using Chandra. Seven discrete sources associated with the galaxy have been found, one of them coincident with its Liner-starburst nucleus. One of the sources corresponds to a ULX with Lx >~ 10e39 ergs/s. Previous ROSAT observations of the galaxy show that this source has varied by at least a factor 3 in the last 6 years. No evidence is found for strong diffuse emission in the nuclear region or the presence of a low luminosity AGN.

P. Lira; R. Johnson; A. Lawrence

2002-06-07

85

The multifrequency spectrum of the starburst galaxy NGC 2782  

NASA Technical Reports Server (NTRS)

The nuclear region of NGC 2782 has been observed at radio, millimeter, infrared, optical, ultraviolet, and X-ray frequencies to understand the ionization source that gives rise to the narrow emission lines. The continuum is probably caused by a normal galactic population plus considerable numbers of young stars and warm dust. In the ultraviolet and optical spectra, which are powerful diagnostics, no strong lines are detected in the 1200 A-3200 A region aside from L-alpha, and the optical emission lines cover only a narrow ionization range. The line and continuum properties suggest that NGC 2782 is a starburst galaxy, in which young stars photoionize the surrounding gas.

Kinney, A. L.; Bregman, J. N.; Huggins, P. J.; Glassgold, A. E.; Cohen, R. D.

1984-01-01

86

Bars and secular evolution in disk galaxies: Theoretical input  

NASA Astrophysics Data System (ADS)

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

Athanassoula, E.

2013-10-01

87

Testing MOND gravity in the shell galaxy NGC 3923  

NASA Astrophysics Data System (ADS)

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

Bílek, M.; Jungwiert, B.; Jílková, L.; Ebrová, I.; Bartošková, K.; K?ížek, M.

2013-11-01

88

Intrinsic shapes of elliptical galaxy: NGC 1052 using modified prior  

NASA Astrophysics Data System (ADS)

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

Kumar Singh, Arun; Chakraborty, D. K.

89

The Distribution of Barred Galaxies in the Virgo Cluster  

E-print Network

A study of the distribution of barred and nonbarred disk galaxies in the Virgo cluster is presented in an attempt to use the frequency and spatial distribution of galaxies with specific morphological features to study the efficiency of various environmental effects on the evolution of disk galaxies in clusters. The velocity distribution of the barred spirals in the Virgo region is clearly different than that of the nonbarred spirals, suggesting that barred spirals are more common in the main condensation of the cluster. A sample cleansed of galaxies not belonging to the main cluster condensation using the subcluster assignments of Binggeli et al. [A&AS, 98, 275 (1993)] bears this out, showing that the radial distribution of barred spirals is more centrally condensed than that of nonbarred spirals. In contrast to the spiral galaxies, the distribution of barred S0 galaxies is statistically indistinguishable from that of nonbarred S0's. Consideration of the level of tidal perturbation due to the cluster mass distribution as compared to that due to individual galaxies suggests that tidal triggering by the cluster mass distribution is the most likely source of the enhanced fraction of barred spirals in the cluster center.

Victor Andersen

1996-03-22

90

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

91

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

92

NGC 5084: A Massive Disk Galaxy Accreting its Satellites ?  

E-print Network

The spectra of 34 galaxies within 20 arcmins (\\sim 100 kpc) of the lenticular galaxy NGC 5084 have been obtained using the FOCAP system on the Anglo-Australian 3.9m telescope. Nine objects are found with projected separations \\lesssim 80 kpc and with radial velocities within \\pm 630 km/s of the parent galaxy redshift. Using various techniques, their velocity differences and projected separations are used to estimate the mass of this S0 galaxy, which ranges from 6 \\times 10^{12} M_{\\odot} to 1 \\times 10^{13} M_{\\odot}. With such a mass, NGC 5084 is one of the most massive disk galaxy known, with a M/L_B \\gtrsim 200 M_{\\odot}/L_{\\odot}. In agreement with the models' predictions of Quinn & Goodman (1986) but contrary to the results of Zaritsky et al (1993) obtained from their statistical sample, the properties of the satellites' population show no evidence for the "Holmberg effect", and a clear excess of satellites in retrograde orbits. Several signs hint that this S0 galaxy has survived the accretion of several satellites.

Claude Carignan; Stephanie Cote; Ken Freeman; Peter Quinn

1997-04-03

93

Detection of CO emission in the elliptical galaxies NGC 3265 and NGC 5666  

NASA Astrophysics Data System (ADS)

From observations of seven elliptical galaxies selected by the strength of their far-infrared (FIR) fluxes, the detection of CO (2 - 1) in the central regions of NGC 3265 and NGC 5666, classified as E4 and Ec, respectively, is reported. Observed with the FWHM beam of 17 arcsec of the IRAM telescope, the CO radial velocities and line widths agree well with H I spectra emitted from a much more extended region, caused partly by rigid rotation in their nuclear regions but also implying a contribution from extensive noncircular motions in the interstellar gas. The shapes of the CO profiles indicate velocity structure within the beam. The observational ratios of CO/H I fluxes are similar to those found in early-type galaxies. The data also imply H2 masses of 1.7 x 10 to the 8th and 3.8 x 10 to the 8th solar masses for the central regions of NGC 3265 and NGC 5666, respectively, giving for those regions H2/H I mass ratios of about three that are comparable to what is observed for the inner region of the Milky Way.

Gordon, M. A.

1991-04-01

94

Do black hole masses scale with classical bulge luminosities only? The case of the two composite pseudo-bulge galaxies NGC 3368 and NGC 3489  

NASA Astrophysics Data System (ADS)

It is now well established that all galaxies with a massive bulge component harbour a central supermassive black hole (SMBH). The mass of the SMBH correlates with bulge properties such as the bulge mass and the velocity dispersion, which implies that the bulge and the central BH of a galaxy have grown together during the formation process. As part of an investigation of the dependence of the SMBH mass on bulge types and formation mechanisms, we present measurements of SMBH masses in two pseudo-bulge galaxies. The spiral galaxy NGC 3368 is double-barred and hosts a large pseudo-bulge with a tiny classical bulge component at the very centre. The S0 galaxy NGC 3489 has only a weak large-scale bar, a small pseudo-bulge and a small classical bulge. Both galaxies show weak nuclear activity in the optical, indicative of the presence of an SMBH. We present high-resolution, adaptive-optics-assisted, near-IR integral-field data of these two galaxies, taken with SINFONI at the Very Large Telescope, and use axisymmetric orbit models to determine the masses of the SMBHs. The SMBH mass of NGC 3368, averaged over the four quadrants, is = 7.5 × 106Msolar with an error of 1.5 × 106Msolar, which mostly comes from the non-axisymmetry in the data. For NGC 3489, a solution without a BH cannot be excluded when modelling the SINFONI data alone, but can be clearly ruled out when modelling a combination of SINFONI, OASIS and SAURON data, for which we obtain M• = (6.00+0.56-0.54 |stat +/- 0.64|sys) × 106Msolar. Although both galaxies seem to be consistent with the M•-? relation, at face value they do not agree with the relation between bulge magnitude and BH mass when the total bulge magnitude (i.e. including both classical bulge and pseudo-bulge) is considered; the agreement is better when only the small classical bulge components are considered. However, taking into account the ageing of the stellar population could change this conclusion. Based on observations at the European Southern Observatory Very Large Telescope [078.B-0103(A)] and on service observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. E-mail: nnowak@mpe.mpg.de

Nowak, N.; Thomas, J.; Erwin, P.; Saglia, R. P.; Bender, R.; Davies, R. I.

2010-04-01

95

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

NASA Astrophysics Data System (ADS)

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

Smaji?, Semir; Moser, Lydia; Eckart, Andreas; Valencia-S., Mónica; Combes, Françoise; Horrobin, Matthew; García-Burillo, Santiago; García-Marín, Macarena; Fischer, Sebastian; Zuther, Jens

2014-07-01

96

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

97

Multifrequency Study of The Radio Galaxy NGC326  

E-print Network

We present the results of a multi-frequency study of the inversion symmetric radio galaxy NGC326 based on Very Large Array observations at 1.4, 1.6, 4.8, 8.5 and 14.9 GHz. The morphological, spectral and polarization properties of this peculiar object are studied at different levels of spatial resolutions. The interpretation of the data will be discussed in forthcoming papers.

M. Murgia; P. Parma; H. R. de Ruiter; M. Bondi; R. D. Ekers; R. Fanti; E. B. Fomalont

2001-10-10

98

Evidence for Secular Evolution in (non-barred) Spiral Galaxies  

E-print Network

Evidence for Secular Evolution in (non-barred) Spiral Galaxies Stéphane Courteau (Queen's) #12: Courteau, de Jong & Broeils (1996, ApJL, 457, 73) "Evidence for Secular Evolution in Spiral Galaxies" 326, Transition, Bulgeless, Truncated ... · Colour / Population Continuity · Spectroscopic Evidence for Secular

Bender, Ralf

99

The void in the Sculptor group spiral galaxy NGC 247  

NASA Astrophysics Data System (ADS)

The dwarf galaxy NGC 247, located in the Sculptor Filament, displays an apparent void on the north side of its spiral disc. The existence of the void in the disc of this dwarf galaxy has been known for some time, but the exact nature and cause of this strange feature has remained unclear. We investigate the properties of the void in the disc of NGC 247 using photometry of archival Hubble Space Telescope data to analyse the stars in and around this region. Based on a grid of isochrones from log(t) = 6.8 to 10.0, we assign ages using nearest-neighbour interpolation. Examination of the spatial variation of these ages across the galaxy reveals an age difference between stars located inside the void region and stars located outside this region. We speculate that the void in NGC 247 's stellar disc may be due to a recent interaction with a nearly dark subhalo that collided with the disc and could account for the long-lived nature of the void.

Wagner-Kaiser, R.; De Maio, T.; Sarajedini, A.; Chakrabarti, S.

2014-10-01

100

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

101

Surface photometry of the shell galaxy NGC 2865  

NASA Astrophysics Data System (ADS)

Independently calibrated charge coupled device surface photometry data were derived from 12 images of the shell galaxy NGC 2865 in the B, V, and R passbands. Short exposures were used to permit accurate sky subtraction. Mean isophotes were derived for each passband over the 3-60 second radial distance range. The isophotes are presented in the form of their best-fit ellipse parameters. The parameters for the best-fit de Vaucouleurs surface brightness law were determined for the mean profile in each passband, and deviations of the actual surface brightness profile from the r to the 1/4 power law are discussed in terms of the galaxy's shell structure. From the best-fit ellipse parameters, the amplitudes of the cosine(4 theta) component of the isophotes could be measured. It was found that they do not show the boxiness often observed in a galaxy which had experienced a recent merger. On the contrary, a peak amplitude of about +1 percent (2 sigma) over the 25-40 second interval suggests only the presence of a weak disk. If the disk is real it indicates NGC 2865 is an S0 galaxy. Both (B-V) and (B-R) color gradients were measured and show the galaxy becomes bluer with increasing radius. This may be explained in terms of a radial metallicity gradient in the sense that the metallicity decreases by about a factor of two per decade increase in distance.

Wing, David Lee

1990-07-01

102

Age dating Star Clusters in Starburst Galaxy Merger NGC3256  

NASA Astrophysics Data System (ADS)

Luminous infrared galaxies are systems undergoing rapid bursts of star formation triggered by the merging of molecular gas-rich galaxies. These galaxies can form more than 100 solar masses of stars per year. Here, an HST ACS/WFC study of optically-visible star formation in the late-stage merger NGC3256 is presented. This galaxy is clearly undergoing a starburst, with many young clusters visible in the HST far-ultraviolet and optical (F140LP, F435W and F814W) images of the merger. Estimates of optically-visible star cluster ages are summarized. These broad-band photometric age estimates are compared with those determined spectroscopically with Keck LRIS.

Lambert-Brown, Tamar

2015-01-01

103

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

E-print Network

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

Aguerri, J A L; Falcón-Barroso, J; Amorin, A; Barrera-Ballesteros, J; Fernandes, R Cid; García-Benito, R; García-Lorenzo, B; Delgado, R M González; Husemann, B; Kalinova, V; Lyubenova, M; Marino, R A; Márquez, I; Mast, D; Pérez, E; Sánchez, S F; van de Ven, G; Walcher, C J; Backsmann, N; Cortijo-Ferrero, C; Bland-Hawthorn, J; del Olmo, A; Iglesias-Páramo, J; Pérez, I; Sánchez-Blázquez, P; Wisotzki, L; Ziegler, B

2015-01-01

104

The interstellar halo of spiral galaxies: NGC 891  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

105

Dense cloud formation and star formation in a barred galaxy  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

106

The Fueling of Nuclear Activity: II. The Bar Properties of Seyfert and Normal Galaxies  

E-print Network

We use a recent near-infrared imaging survey of samples of Seyfert and normal galaxies to study the role of bars in the fueling of nuclear activity. The active galaxy sample includes Seyfert galaxies in the Revised Shapely-Ames (RSA) and Sandage & Tammann's (1987) extension to this catalog. The normal galaxies were selected to match the Seyfert sample in Hubble type, redshift, inclination and blue luminosity. All the galaxies in both samples classified as barred in the RSA catalog are also barred in the near-infrared. In addition, ~55% of the galaxies classified as non-barred in the RSA show evidence for bars at 2.1 microns. Overall, ~70% of the galaxies observed show evidence for bar structures. The incidence of bars in the Seyfert and normal galaxies is similar, suggesting Seyfert nuclei do not occur preferentially in barred systems. Furthermore, a slightly higher percentage of normal galaxies have multiple-bar structures.

John S. Mulchaey; Michael W. Regan

1997-04-11

107

Dark matter deprivation in the field elliptical galaxy NGC 7507  

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

108

Far-infrared observations of Circinus and NGC 4945 galaxies  

NASA Technical Reports Server (NTRS)

Circinus and NGC 4945 are two galaxies luminous in the infrared and are characterized by compact non thermal radio nuclei, deep silicate absorption features and unusually strong water vapor maser luminosities. Moorwood and Glass (1984) have observed these galaxies extensively in the 1 to 20 micron range. In the far-infrared, observations up to 100 microns are available from the Infrared Astronomy Satellite (IRAS). In order to study the cool dust component of these galaxies, researchers observed them at 150 microns using the Tata Institute of Fundamental Research (TIFR) 100 cm balloon-borne telescope. Here, they report observations along with deconvolved maps at 50 and 100 microns obtained from the Chopped Photometric Channel (CPC) on board IRAS.

Bisht, R. S.; Ghosh, S. K.; Iyengar, K. V. K.; Rengarajan, T. N.; Tandon, S. N.; Verma, R. P.

1990-01-01

109

Star Formation Color-Time Sequence and ``Anti-Spiral" Wagon-Spoke Perturbation in Resonance Ring Galaxies: NGC3081  

NASA Astrophysics Data System (ADS)

Byrd, Ousley, and Dalla Piazza(1998a, MNRAS, 298, 78) described a hybrid analytic/computer formulation of periodic interstellar cloud orbits which explains morphologies of resonance rings in SB galaxies. Byrd, Ousley, Dalla Piazza, and Domingue (1998b, Dynamics of Galaxies conf.) applied the formulation to NGC 3081 to show how ring morphology and rotation curve can give the two-fold perturbation strength and pattern speed plus the disk inclination and line of nodes. Using the perturbation in Poisson's equation with the outer disk isophote ellipticity gives the disk surface mass density as a function of radius. Within errors, the density is sufficient to explain the NGC 3081 rotation curve i.e. no halo is required. Disk density/surface brightness at each radius gives the NGC 3081 M/L, indicating a large amount of dark matter in its outer disk plane possibly eliminating certain galaxy dark matter candidates. In this poster, we study how star formation in inner resonance rings occurs where gas clouds are crowded near the end of the bar of NGC 3081. As these orbit in position angle away from the end, they age and their B-I colors change. Using the above formulation, color indexes of stellar associations can thus be empirically calibrated in years, to serve in age estimates of associations in other galaxies and as an observational test of association models. Our morphological match for NGC 3081 is excellent from the nuclear ring through the outer rings. The perturbation potential must also be valid indicating it is the radial ``wagon-spoke" type descried by Shu (1970) with two spokes. Thus NGC 3081's disk must be non-dissipational (stellar) with a stabilizing velocity dispersion. Globally, gas must be gravitationally unimportant. We explore the possibility that the elongated ``bar" of NGC3081 may only be a minority of luminous resonance ring stars superposed on a gentler global old disk star perturbation. Ousley was supported by a McWane Undergraduate Research Fellowship. We thank R. Buta and G. Purcell for use of figures.

Ousley, D.; Byrd, G. G.

1998-12-01

110

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

E-print Network

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

William C. Keel; Raymond E. White III

2001-06-04

111

Reverberation Mapping of the Seyfert 1 Galaxy NGC 7469  

E-print Network

A large reverberation mapping study of the Seyfert 1 galaxy NGC 7469 has yielded emission-line lags for Hbeta 4861 and He II 4686 and a central black hole mass measurement of about 10 million solar masses, consistent with previous measurements. A very low level of variability during the monitoring campaign precluded meeting our original goal of recovering velocity-delay maps from the data, but with the new Hbeta measurement, NGC 7469 is no longer an outlier in the relationship between the size of the Hbeta-emitting broad-line region and the AGN luminosity. It was necessary to detrend the continuum and Hbeta and He II 4686 line light curves and those from archival UV data for different time-series analysis methods to yield consistent results.

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

2014-01-01

112

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

NASA Astrophysics Data System (ADS)

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

Erwin, Peter; Debattista, Victor P.

2013-06-01

113

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

NASA Astrophysics Data System (ADS)

NGC 7619 and NGC 7626 are the two dominant elliptical galaxies in the Pegasus I group (~50 Mpc). This group includes about 13 members and firm evidence that it hosts an ongoing merger. This kind of event is one of the most powerful ways of modifying the galaxies and group structure, morphologies and contents. The globular clusters (GCs) are known to be good tracers of the galaxies formation and evolution. In this context, we present the first complete analysis of the GC system (GCS) surrounding the NGC 7619/7626 pair, based on recently obtained deep Gemini+GMOS images in the g', r' and i' bands. A mosaic of four fields has been taken along the line that joins both galaxies and high quality psf photometry has been achieved. We characterize the GC integrated colour distribution, studying the presence of bimodality, as well as the spatial projected distribution. The likely existence of some Ultra Compact Dwarf candidates is also considered.

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

2011-06-01

114

Interstellar Gas in the NGC 4410 Galaxy Group  

E-print Network

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

Beverly J. Smith

2000-05-04

115

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

116

New SNR candidates in nearby spiral galaxy NGC 3344  

NASA Astrophysics Data System (ADS)

We present a SNR survey using optical imaging in the nearby spiral galaxy NGC3344.Observations have been carried out with the 1.5m telescope at TUG (Tubitak National Observatory, Antalya-Turkey). We identified new SNR candidates using basic criterion [SII]/H? ¿= 0.4. We also present spectral follow up observations of the new set of SNR candidates. In addition, we dis-cuss a search for the X-ray counterparts to these new SNRs using archival Chandra Observatory data.

Akyuz, Aysun

117

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

SciTech Connect

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

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

2009-12-15

118

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.

119

Gas Dynamics in the LINER Galaxy NGC 5005: Episodic Fueling of a Nuclear Disk  

E-print Network

We report high-resolution CO(1-0) observations in the central 6 kpc of the LINER galaxy NGC 5005 with the Owens Valley Radio Observatory millimeter array. Molecular gas is distributed in three components - a ring at a radius of about 3 kpc, a strong central condensation, and a stream to the northwest of the nucleus but inside the 3 kpc ring. The central condensation is a disk of about 1 kpc radius with a molecular gas mass of 2 x 10^9 M_sun. The stream between the 3 kpc ring and the nuclear disk lies on a straight dust lane seen in the optical. If this material moves in the plane of the galaxy, it has a velocity offset by up to ~ 150 km/s from galactic rotation. We suggest that an optically inconspicuous stellar bar lying within the 3 kpc ring can explain the observed gas dynamics. This bar is expected to connect the nuclear disk and the ring along the position angle of the northwest stream. A position-velocity cut in this direction reveals features which match the characteristic motions of gas in a barred potential. Our model indicates that gas in the northwest stream is on an x_1 orbit at the bar's leading edge; it is falling into the nucleus with a large noncircular velocity, and will eventually contribute about 2 x 10^8 M_sun to the nuclear disk. If most of this material merges with the disk on its first passage of pericenter, the gas accretion rate during the collision will be 50 M_sun/yr. We associate the nuclear disk with an inner 2:1 Lindblad resonance, and the 3 kpc ring with an inner 4:1 Lindblad resonance. The high rate of bar-driven inflow and the irregular appearance of the northwest stream suggest that a major fueling event is in progress in NGC 5005. Such episodic (rather than continuous) gas supply can regulate the triggering of starburst and accretion activity in galactic nuclei. (abridged)

Kazushi Sakamoto; Andrew J. Baker; Nick Z. Scoville

1999-10-01

120

A Compton thick AGN in the barred spiral NGC 4785  

E-print Network

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

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

2014-01-01

121

Australia Telescope Compact Array H I observations of the NGC 6845 galaxy group  

NASA Astrophysics Data System (ADS)

We present the results of Australia Telescope Compact Array (ATCA) HI line and 20-cm radio continuum observations of the galaxy quartet NGC 6845. The HI emission extends over all four galaxies but can only be associated clearly with the two spiral galaxies, NGC 6845A and B, which show signs of strong tidal interaction. We derive a total HI mass of at least 1.8 × 1010 Msolar, most of which is associated with NGC 6845A, the largest galaxy of the group. We investigate the tidal interaction between NGC 6845A and B by studying the kinematics of distinct HI components and their relation to the known HII regions. No HI emission is detected from the two lenticular galaxies, NGC 6845C and D. A previously uncatalogued dwarf galaxy, ATCA J2001-4659, was detected 4.4 arcmin NE from NGC 6845B and has an HI mass of ~5 × 108 Msolar. No HI bridge is visible between the group and its newly detected companion. Extended 20-cm radio continuum emission is detected in NGC 6845A and B as well as in the tidal bridge between the two galaxies. We derive star formation rates of 15-40 Msolar yr-1.

Gordon, Scott; Koribalski, Bärbel; Jones, Keith

2003-07-01

122

Wind and Reflections From Black Hole in Galaxy NGC 1068  

NASA Technical Reports Server (NTRS)

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

2000-01-01

123

Resolving Molecular Clouds in the Nearby Galaxy NGC 300  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

124

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

NASA Astrophysics Data System (ADS)

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

Diwakar, Arun Kumar

125

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

126

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

127

Bar-Halo Friction in Galaxies II: Metastability  

E-print Network

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

J. A. Sellwood; Victor P. Debattista

2005-11-05

128

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

129

Low-Luminosity Early-Type Galaxies in the NGC 128 Group  

E-print Network

We present spatially resolved kinematics and stellar population parameters for three low-luminosity galaxies in the NGC128 group obtained by means of 3D spectroscopy. We briefly discuss their evolutionary scenarii.

Igor Chilingarian; Olga Sil'chenko; Victor Afanasiev; Philippe Prugniel

2007-11-14

130

Kinematics and ionization of extended gas in active galaxies. IV - The Seyfert 2 galaxy NGC 4388  

NASA Technical Reports Server (NTRS)

The results of direct CCD imaging and long-slit medium-dispersion spectroscopy of the extended narrow-line-emitting gas in the nearby Seyfert 2 galaxy NGC 4388 are presented. The spectra are used to investigate the distribution, kinematics, and ionization structure of the excited gas in the regions surrounding the nucleus out to a distance of about 4.8 kpc. The data support earlier suggestions that the galaxy, which appears to lie near the core of the Virgo cluster, has been tidally distorted, possibly by the nearby cluster core galaxies M84 or IC 3303. Much of the highly ionized gas in the galaxy appears to be distributed in two wide cones originating from the nucleus and extending above and below the disk. Explanations are offered for the distribution of this gas and for the remainder of the gas above and below the disk.

Corbin, Michael R.; Baldwin, J. A.; Wilson, A. S.

1988-01-01

131

Kinematics and ionization of extended gas in active galaxies. I. The Seyfert 2 galaxy NGC 4388  

SciTech Connect

The results of direct CCD imaging and long-slit medium-dispersion spectroscopy of the extended narrow-line-emitting gas in the nearby Seyfert 2 galaxy NGC 4388 are presented. The spectra are used to investigate the distribution, kinematics, and ionization structure of the excited gas in the regions surrounding the nucleus out to a distance of about 4.8 kpc. The data support earlier suggestions that the galaxy, which appears to lie near the core of the Virgo cluster, has been tidally distorted, possibly by the nearby cluster core galaxies M84 or IC 3303. Much of the highly ionized gas in the galaxy appears to be distributed in two wide cones originating from the nucleus and extending above and below the disk. Explanations are offered for the distribution of this gas and for the remainder of the gas above and below the disk. 47 references.

Corbin, M.R.; Baldwin, J.A.; Wilson, A.S.

1988-11-01

132

Star Formation Properties in Barred Galaxies. III. Statistical Study of Bar-Driven Secular Evolution Using a Sample of Nearby Barred Spirals  

NASA Astrophysics Data System (ADS)

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

Zhou, Zhi-Min; Cao, Chen; Wu, Hong

2015-01-01

133

Physical Conditions in the Seyfert Galaxy NGC 2992  

E-print Network

This paper presents long slit spectral maps of the bi-cone shaped extended narrow line region (ENLR) in the Seyfert galaxy NGC 2992. We investigate the physical properties of the ENLR via emission line diagnostics, and compare the observations to shock and photoionization models for the excitation mechanism of the gas. The line ratios vary as a function of position in the ENLR, and the loci of the observed points on line ratio diagrams are shown to be most consistent with shock+precursor model grids. We consider the energetics of a nuclear ionizing source for the ENLR, and perform the q-test in which the rate of ionizing photons from the nucleus is inferred from measurements of the density and ionization parameter. The q-test is shown to be invalid in the case of NGC 2992 because of the limitations of the [S II]6717/6731 density diagnostic. The excitation of the gas is shown to be broadly consistent with the kinematics, with higher [N II]6583/H-alpha present in the more dynamically active region. We also show that the pressure associated with the X-ray emitting plasma may provide a large fraction of the pressure required to power the ENLR via shocks.

Mark G. Allen; Michael A. Dopita; Zlatan I. Tsvetanov; Ralph S. Sutherland

1998-09-10

134

Streaming Circumnuclear Gas of the Seyfert 2 Galaxy NGC 5728  

NASA Astrophysics Data System (ADS)

We investigated the circumnuclear region of the Seyfert 2 galaxy NGC 5728, using the CFHT 3.6 m OASIS S II, O III, & H?, spectral images complemented with the IUE spectra. The physical condition of the circumnuclear zone has been derived: the gas density (indicated by S II6716/31 ratio) around the C core is generally similar to that around the NW core, i.e., ˜ 500 cm^{-3}. However, there appears to be evidence of a higher density shell in front of the NW core, ˜10^{4} cm ^{-3} at -250 kms. The IUE ssi 1892/ç1909 ratio implies a possible presence of a broad emission region of gas densities of ˜10^{10} cm^{-3}. The SE cone and surrounding area show several prominent features, while the NW cone does not show any particular structure: we identified three prominent blobs in the SE cone and one possible candidate in the NW cone. The outflow activities exist within the relatively large conic opening angle. We discussed the possibility of inflow or outflow activities of blobs found in the circumnuclear region of NGC 5728. The gas around two cores, two cones, and several blobs, is likely to be excited by the AGN hot source(s).

Son, Dong-Hoon; Hyung, Siek; Lee, Seong-Jae; Ferruit, Pierre

2009-10-01

135

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

136

Spitzer Infrared Nearby Galaxies Survey (SINGS) Imaging of NGC 7331: A Panchromatic View of a Ringed Galaxy  

NASA Astrophysics Data System (ADS)

Well-resolved infrared observations of nearby galaxies are of fundamental importance to the study of the processes that affect galactic evolution. In this paper we report on the first imaging results from the Spitzer Infrared Nearby Galaxies Survey (SINGS) using observations of the Sb galaxy NGC 7331. We present images of NGC 7331 over a large range of wavelengths that allow us to compare the distributions of gas, stars, and dust in unprecedented detail. As an example of the types of information that the full SINGS will provide, we use three methods to determine that the interstellar medium mass in the ring of NGC 7331 is ~5×109 Msolar. We also present the first images showing emission from small hot (~1000 K) dust grains, but we show that these dust grains contribute only a small fraction of the integrated 4.5 ?m emission from NGC 7331.

Regan, Michael W.; Thornley, Michele D.; Bendo, George J.; Draine, Bruce T.; Li, Aigen; Dale, Daniel A.; Engelbracht, Charles W.; Kennicutt, Robert C., Jr.; Armus, Lee; Calzetti, Daniela; Gordon, Karl D.; Helou, George; Hollenbach, David J.; Jarrett, Thomas H.; Kewley, Lisa J.; Leitherer, Claus; Malhotra, Sangeeta; Meyer, Martin; Misselt, Karl A.; Morrison, Jane E.; Murphy, Eric J.; Muzerolle, James; Rieke, George H.; Rieke, Marcia J.; Roussel, Hélène; Smith, John-David T.; Walter, Fabian

2004-09-01

137

Atomic hydrogen in the spiral galaxy NGC 3631  

E-print Network

New high resolution, high sensitivity WSRT HI synthesis observations of the spiral galaxy NGC 3631 are presented. In the total atomic hydrogen map, the spiral arms are well distinguished from the interarm regions, while the sensitivity allows detection of HI in all but a few isolated regions of the areas between the spiral arms. Most of the atomic hydrogen is located within the optical disc, but the HI extends to some 1.5R_opt. The HI follows the spiral arms, and streaming motions of up to ~15 kms (projected) can be identified from the velocity field. Assuming a constant inclination angle of 17 deg, a rotation curve is derived which is slightly falling in the outer parts of the disc. Analysis of a residual velocity field, obtained after subtraction of an axisymmetric model based on the rotation curve, confirms the existence of streaming motions near the spiral arms in an otherwise undisturbed disc.

J. H. Knapen

1996-12-13

138

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

139

Stellar Clusters Forming in the Blue Dwarf Galaxy NGC 5253  

NASA Astrophysics Data System (ADS)

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

2004-11-01

140

Multimolecule ALMA observations toward the Seyfert 1 galaxy NGC 1097  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

141

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

SciTech Connect

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

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

2011-12-10

142

Bar-halo Friction in Galaxies I: Scaling Laws  

E-print Network

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

J. A. Sellwood

2005-09-28

143

STAR FORMATION IN NUCLEAR RINGS OF BARRED GALAXIES  

SciTech Connect

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

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

2013-06-01

144

Star Formation in Nuclear Rings of Barred Galaxies  

NASA Astrophysics Data System (ADS)

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

Seo, Woo-Young; Kim, Woong-Tae

2013-06-01

145

The elliptical galaxy NGC 720: An unequal-mass galaxy merger remnant  

NASA Astrophysics Data System (ADS)

The stellar population of the central region of the galaxy NGC 720 has been investigated through longslit optical spectroscopy. The velocity dispersion and 13 Lick indices were obtained as a function of the radius along the semimajor axis of the galaxy. The Mg2 index presents a gradient of d Mg2 / d log r=-0.079 which behaves similarly to the Fe I lines, indicating no enhancement of Mg2 in relation to Fe I. The stellar population ages and metallicities were derived by a population synthesis method using available evolutive spectrophotometric models. The synthesis indicates a strong age gradient along the semimajor axis of NGC 720. In the central region a 13 Gyr and solar metallicity stellar population dominates the flux at 5870 Å; the contribution of this component vanishes at a radius of 0.73 kpc, where the total flux is accounted for by a younger, 5 Gyr and solar metallicity stellar population. For distances larger than 1 kpc a 2.5 Gyr component becomes very important. Moreover, NGC 720 is probably overabundant in CN in the center with respect to the solar abundance. The estimated total mass (3.29×1011~M_?) and the Mg2 gradient values suggest that this galaxy might have undergone a merger event. The correspondence between the J-band brightness profile decomposition and the result of the spectral synthesis shows that this galaxy is formed by an old (13-5 Gyr), bulge-like, small-scale and massive spheroid and a younger (5-2.5 Gyr), large-scale disk component. We discuss our results in comparison with available numerical simulations and propose that the merger event must have occurred about 4 Gyr ago.

Rembold, S. B.; Pastoriza, M. G.; Bruzual, G.

2005-06-01

146

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

147

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

148

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

149

CO Observations of the Interacting Galaxy Pair NGC 5394/95  

E-print Network

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

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

2001-11-13

150

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

151

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

NASA Astrophysics Data System (ADS)

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

Carlqvist, Per

2013-02-01

152

Ultraviolet Signposts of Resonant Dynamics in the Starburst-Ringed Sab Galaxy, M94 (NGC 4736)  

E-print Network

M94 (NGC 4736) is investigated using images from the Ultraviolet Imaging Telescope (FUV-band), Hubble Space Telescope (NUV-band), Kitt Peak 0.9-m telescope (H-alpha, R, and I bands), and Palomar 5-m telescope (B-band), along with spectra from the International Ultraviolet Explorer and Lick 1-m telescopes. The wide-field UIT image shows FUV emission from (a) an elongated nucleus, (b) a diffuse inner disk, where H-alpha is observed in absorption, (c) a bright inner ring of H II regions at the perimeter of the inner disk (R = 48 arcsec. = 1.1 kpc), and (d) two 500-pc size knots of hot stars exterior to the ring on diametrically opposite sides of the nucleus (R= 130 arcsec. = 2.9 kpc). The HST/FOC image resolves the NUV emission from the nuclear region into a bright core and a faint 20 arcsec. long ``mini-bar'' at a position angle of 30 deg. Optical and IUE spectroscopy of the nucleus and diffuse inner disk indicates an approximately 10^7 or 10^8 yr-old stellar population from low-level starbirth activity blended with some LINER activity. Analysis of the H-alpha, FUV, NUV, B, R, and I-band emission along with other observed tracers of stars and gas in M94 indicates that most of the star formation is being orchestrated via ring-bar dynamics involving the nuclear mini-bar, inner ring, oval disk, and outer ring. The inner starburst ring and bi-symmetric knots at intermediate radius, in particular, argue for bar-mediated resonances as the primary drivers of evolution in M94 at the present epoch. Similar processes may be governing the evolution of the ``core-dominated'' galaxies that have been observed at high redshift. The gravitationally-lensed ``Pretzel Galaxy'' (0024+1654) at a redshift of approximately 1.5 provides an important precedent in this regard.

William H. Waller; Michael N. Fanelli; William C. Keel; Ralph Bohlin; Nicholas R. Collins; Barry F. Madore; Pamela M. Marcum; Susan G. Neff; Robert W. O'Connell; Joel D. Offenberg; Morton S. Roberts; Andrew M. Smith; Theodore P. Stecher

2000-11-04

153

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

154

Dynamical Friction and the Distribution of Dark Matter in Barred Galaxies  

E-print Network

We use fully self-consistent N-body simulations of barred galaxies to show that dynamical friction from a dense dark matter halo dramatically slows the rotation rate of bars. Our result supports previous theoretical predictions for a bar rotating within a massive halo. On the other hand, low density halos, such as those required for maximum disks, allow the bar to continue to rotate at a high rate. There is somewhat meager observational evidence indicating that bars in real galaxies do rotate rapidly and we use our result to argue that dark matter halos must have a low central density in all high surface brightness disk galaxies, including the Milky Way. Bars in galaxies that have larger fractions of dark matter should rotate slowly, and we suggest that a promising place to look for such candidate objects is among galaxies of intermediate surface brightness.

Victor P. Debattista; J. A. Sellwood

1997-10-03

155

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

Microsoft Academic Search

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

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

2006-01-01

156

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

157

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

158

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

SciTech Connect

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

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

2013-03-10

159

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

E-print Network

With a Chandra ACIS-S3 observation, we detect 42 X-ray point sources in the elliptical galaxy NGC 720, including a possible central source. Most of these sources will be low-mass X-ray binaries (LMXBs), and 12 are located within 2" of globular cluster candidates. We investigate both the hardness ratios and combined spectra of the sources. They exhibit a distribution of X-ray colors similar to those seen in other early-type galaxies. We find that there is a population of highly absorbed sources located at large distances from the center of the galaxy. The overall spatial distribution of sources is consistent with the ellipticity and position angle of the galaxy, but the sources appear to form several arcs. NGC 720 contains nine ultraluminous sources (L_x >= 10^39 ergs/s). This number is more than have previously been detected in an early-type galaxy but similar to the number seen in the Antennae merger system. The ratio L_ULX/L_B for NGC 720 is more than double the ratio for the S0 galaxy NGC 1553 and a factor of seven higher than for the elliptical galaxy NGC 4697, although uncertainties in the distance and the source spectral properties could bring these ratios into agreement. The X-ray source luminosity function is also nearly as flat as those seen in disk and merger systems. The large number of ULXs in NGC 720 and its relatively flat XLF may provide evidence against the association of all ULXs with young stars. We also see a possible high luminosity break in the luminosity function at 2x10^39 h_50^-2 ergs/s.

Tesla E. Jeltema; Claude R. Canizares; David A. Buote; Gordon P. Garmire

2002-11-10

160

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

161

A Local Group Polar Ring Galaxy: NGC 6822  

E-print Network

Star counts, obtained from a 2 x 2 degree area centered on NGC 6822 have revealed an optical image of this galaxy composed of two components: in addition to the well-known HI disk with its young stellar component, there is a spheroidal stellar structure as extensive as its HI disk but with its major axis at roughly right angles to it which we traced to at least 36 arcmin. Radial velocities of over 100 intermediate-age carbon stars found within this structure display kinematics contrasting strongly with those of the HI disk. These C stars belong to the spheroid. Although devoid of gas, the spheroid rotation is consistent with the I-band Tully-Fisher relation. The orientation of the rotation axis which minimizes the stellar velocity dispersion coincides with the minor axis of the stellar population ellipsoid, lying very nearly in the plane of the HI disk. We conclude: that the HI disk is a polar ring and the spheroidal component an erstwhile disk, a fossil remainder of a past close encounter episode.

Serge Demers; Paolo Battinelli; William E. Kunkel

2005-12-05

162

The Nuclear Ring in the Barred Spiral Galaxy IC 4933  

NASA Astrophysics Data System (ADS)

We present infrared imaging from IRIS2 on the Anglo-Australian Telescope that shows the barred spiral galaxy IC 4933 has not just an inner ring encircling the bar, but also a star-forming nuclear ring 1.5 kpc in diameter. Imaging in the u' band with GMOS on Gemini South confirms that this ring is not purely an artifact due to dust. Optical and near-infrared colours alone however cannot break the degeneracy between age, extinction, and burst duration that would allow the star formation history of the ring to be unraveled. Integral field spectroscopy with the GNIRS spectrograph on Gemini South shows the equivalent width of the Pa? line to peak in the north and south quadrants of the ring, indicative of a bipolar azimuthal age gradient around the ring. The youngest star-forming regions do not appear to correspond to where we expect to find the contact points between the offset dust lanes and the nuclear ring unless the nuclear ring is oval in shape, causing the contact points to lead the bar by more than 90°.

Ryder, Stuart D.; Illingworth, Samuel M.; Sharp, Robert G.; Farage, Catherine L.

2010-03-01

163

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

164

The Globular Cluster System of the Elliptical Galaxy NGC 2937 as a Marker of its Evolutionary History  

NASA Astrophysics Data System (ADS)

Using imaging data from the Hubble Space Telescope archive, we examine the rich globular cluster population of the giant elliptical galaxy NGC 2937, located at a distance of 70 Mpc. We present a color-magnitude diagram and two-color diagram of the galaxy’s globular cluster system and discuss their possible implications for the evolutionary history of the galaxy.

Observatory, Michael West Maria Mitchell, Dr.; Harris McMaster University, William, Dr.

2015-01-01

165

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

166

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

SciTech Connect

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

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

2012-07-20

167

96Calculating Black Hole Power This image shows the large galaxy, NGC-6872, interacting with a smaller galaxy,  

E-print Network

96Calculating Black Hole Power This image shows the large galaxy, NGC-6872, interacting output! When black holes 'digest' gas, stars and other forms of matter that enter their event horizons' that surrounds a black hole. The amount of heat energy that is emitted by the matter each second (power) can

168

The Star Clusters in the Starburst Irregular Galaxy NGC 1569  

E-print Network

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

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

2000-09-18

169

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

170

NICMOS Observations of Interaction Triggered Star Formation in the Luminous Infrared Galaxy NGC 6090  

E-print Network

High resolution, 1.1, 1.6, and 2.2 micron imaging of the luminous infrared galaxy NGC 6090 obtained with NICMOS of the Hubble Space Telescope are presented. These new observations are centered on the two nuclei of the merger, and reveal the spiral structure of the eastern galaxy and the amorphous nature of the western galaxy. The nuclear separation of 3.2 kpc (H_0 = 75 km/s/Mpc) indicates that NGC 6090 is at an intermediate stage of merging. Bright knots/clusters are also visible in the region overlapping the merging galaxies; four of these knots appear bluer than the underlying galaxies and have colors consistent with young (<~ 10^7 yr) star clusters. The spatial coincidence of the knots with the molecular gas in NGC 6090 indicates that much of the present star formation is occuring outside of the nuclear region of merging galaxies, consistent with recent studies of other double nuclei luminous infrared galaxies.

N. Dinshaw; A. S. Evans; H. Epps; N. Z. Scoville; M. Rieke

1999-07-28

171

The Nuclear Disk in the Dwarf Elliptical Galaxy NGC 4486A  

E-print Network

Many ellipticals contain nuclear disks of dust and gas. Some ellipticals contain nuclear disks of stars that are distinct from the rest of the galaxy. We show that the dwarf E2 galaxy NGC 4486A contains both -- it is a "Rosetta stone" object that tells us how nuclear disks evolve. Its properties suggest that, as accreted gas dissipates and settles toward the center, it forms stars and builds a stellar disk. Secular growth may explain not only the most distinct nuclear disks such as those in NGC 4486A but also some of the disky distortions that are commonly seen in elliptical galaxies. That is, density distributions may grow secularly cuspier. This would result in chaotic mixing of stellar orbits in phase space and would tend to make an elliptical galaxy evolve toward a more nearly axisymmetric shape.

John Kormendy; Karl Gebhardt; F. Duccio Macchetto; W. B. Sparks

2001-07-12

172

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

SciTech Connect

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

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

2013-05-10

173

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

NASA Astrophysics Data System (ADS)

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

NuSTAR Starburst Team

2015-01-01

174

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

175

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

NASA Astrophysics Data System (ADS)

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

Samurovic, S.; Cirkovic, M. M.

2008-12-01

176

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

177

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

178

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

E-print Network

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

Canizares, Claude R.

179

Are Galaxies Optically Thin to Their Own Lyman Continuum Radiation? II. NGC 6822  

E-print Network

Halpha and UBV photometry of NGC 6822 are used to study the distribution of OB stars and HII regions in the galaxy and to determine whether individual regions of the galaxy are in a state of ionization balance. Four distinct components of the Halpha emission (bright, halo, diffuse and field) differentiated by their surface brightnesses are identified. We find that approximately 1/2 of all OB stars in NGC 6822 are located in the field while only 1/4 are found in the combined bright and halo regions, suggesting that OB stars spend roughly 3/4 of their lifetimes outside ``classical'' H II regions. Comparing the observed Halpha emission with that predicted from stellar ionizing flux models, we find that although the bright, halo and diffuse regions are probably in ionization balance, the field region is producing at least 6 times as much ionizing flux as is observed. The ionization balance results in NGC 6822 suggest that star formation rates obtained from Halpha luminosities must underestimate the true star formation rate in this galaxy by about 50%. Comparing our results for NGC 6822 with previous results for the spiral galaxy M33, we find that the inner kiloparsec of M33 is in a more serious state of ionization imbalance, perhaps due to its higher surface density of blue stars.

K. Patel; C. D. Wilson

1995-06-20

180

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

E-print Network

Three molecular clouds have been mapped in the nearby metal-poor dwarf irregular galaxy NGC 6822 using the Owens Valley Millimeter-Wave Interferometer. Based on upper limits to the virial masses of the clouds, the CO-to-H2 conversion factor in NGC 6822 is <2.2+/-1.3 times larger than the Galactic value. Conversion factors obtained for Galactic molecular clouds, NGC 6822, and the SMC are consistent with the variation in the CO-to-H2 conversion factor being linearly proportional to the oxygen abundance of the galaxy. However, the uncertainties are sufficiently large that equal conversion factors in NGC 6822 and the Galaxy cannot be ruled out. The gas depletion time obtained for the HII region Hubble V is comparable to those of giant HII regions in M33. Thus high-efficiency star formation is not limited to the giant HII regions seen spiral galaxies, but can also occur in a small group of relatively low-mass molecular clouds.

C. D. Wilson

1994-07-22

181

Chandra Evidence of a Flattened, Triaxial Dark Matter Halo in the Elliptical Galaxy NGC 720  

E-print Network

We present an analysis of a Chandra ACIS-S observation of the elliptical galaxy NGC 720, to verify the existence of a dark matter halo and to measure its ellipticity. The ACIS-S3 image reveals over 60 point sources distributed ...

Jeltema, Tesla E.

182

DECREASED FREQUENCY OF STRONG BARS IN S0 GALAXIES: EVIDENCE FOR SECULAR EVOLUTION?  

SciTech Connect

Using data from the Near-Infrared S0 Survey of nearby, early-type galaxies, we examine the distribution of bar strengths in S0 galaxies as compared to S0/a and Sa galaxies, and as compared to previously published bar strength data for Ohio State University Bright Spiral Galaxy Survey spiral galaxies. Bar strengths based on the gravitational torque method are derived from 2.2 {mu}m K{sub s} -band images for a statistical sample of 138 (98 S0, 40 S0/a,Sa) galaxies having a mean total blue magnitude (B{sub T}) {<=} 12.5 and generally inclined less than 65{sup 0}. We find that S0 galaxies have weaker bars on average than spiral galaxies in general, even compared to their closest spiral counterparts, S0/a and Sa galaxies. The differences are significant and cannot be entirely due to uncertainties in the assumed vertical scale heights or in the assumption of constant mass-to-light ratios. Part of the difference is likely simply due to the dilution of the bar torques by the higher mass bulges seen in S0s. If spiral galaxies accrete external gas, as advocated by Bournaud and Combes, then the fewer strong bars found among S0s imply a lack of gas accretion according to this theory. If S0s are stripped former spirals, or else are evolved from former spirals due to internal secular dynamical processes which deplete the gas as well as grow the bulges, then the weaker bars and the prevalence of lenses in S0 galaxies could further indicate that bar evolution continues to proceed during and even after gas depletion.

Buta, R. [Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487 (United States); Laurikainen, E.; Salo, H. [Department of Physics/Astronomy Division, University of Oulu, FIN-90014 (Finland); Knapen, J. H. [Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife (Spain)

2010-09-20

183

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

184

Bar-driven Galaxy Evolution and Time-scales to Feed AGN  

E-print Network

Recent progress in the understanding of the role of bars and gravitational instabilities in galaxy disks is reviewed. It has been proposed that bars can produce mass transfer towards the center, and progressively metamorphose late-type galaxies in early-types, along the Hubble sequence. Through this mass transfer, bars are self-destroyed, and can act only during a certain "duty-cycle" in the galaxy life. After sufficient gas infall, another bar-phase can spontaneously occur. This recurrent evolution is strongly dependent on environment. A scenario is proposed, based on N-body simulations time-scales of the bar-life events, to explain the observed bar frequency, gas mass fraction, bulge and possible black hole mass growth, in a typical spiral.

F. Combes

1999-08-13

185

The low-luminosity galaxy population in the NGC 5044 Group  

E-print Network

We present multicolour imaging for 33 dwarf and intermediate-luminosity galaxies in the field of the NGC 5044 Group, complemented with mid-resolution spectroscopy for a subsample of 13 objects. With these data, a revised membership and morphological classification is made for the galaxies in the sample. We were able to confirm all but one of the "definite members" included in the spectroscopic subsample, which were originally classified based on morphological criteria; however, an important fraction of background galaxies is probably present among "likely" and "possible" members. The presence of a nucleus could be detected in just five out of the nine galaxies originally classified as dE,N, thus confirming the intrisic difficulty of photographic-plate morphological classification for this kind of object. Our deep surface photometry provided clear evidences for disc structure in at least three galaxies previously catalogued as dE or dS0. Their transition-type properties are also evident from the colour-magnitude diagram, where they lie near the late-type galaxies locus, suggesting an evolutionary connection between a parent disc-galaxy population and at least part of present-day dEs. Six new dSph candidates were also found, most of them at small projected distances from NGC 5044, the central galaxy of the Group. The NGC 5044 Group appears clearly defined in redshift space, with a mean heliocentric radial velocity, =2461 +/- 84 km/s (z=0.0082), and a moderate dispersion, \\sigma_{v_r}=431 km/s. Our data show no luminosity segregation for early-type galaxies: both dwarf and bright E/S0 systems show very similar velocity distributions (\\sigma_{v_r} ~ 290 km/s), in contrast to late-type galaxies that seem to display a broader distribution (\\sigma_{v_r} ~ 680 km/s).

Sergio A. Cellone; Alberto Buzzoni

2004-10-19

186

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

187

The Mass Profile and Shape of Bars in the Spitzer Survey of Stellar Structure in Galaxies (S4G): Search for an Age Indicator for Bars  

NASA Astrophysics Data System (ADS)

We have measured the radial light profiles and global shapes of bars using two-dimensional 3.6 ?m image decompositions for 144 face-on barred galaxies from the Spitzer Survey of Stellar Structure in Galaxies. The bar surface brightness profile is correlated with the stellar mass and bulge-to-total (B/T) ratio of their host galaxies. Bars in massive and bulge-dominated galaxies (B/T > 0.2) show a flat profile, while bars in less massive, disk-dominated galaxies (B/T ~ 0) show an exponential, disk-like profile with a wider spread in the radial profile than in the bulge-dominated galaxies. The global two-dimensional shapes of bars, however, are rectangular/boxy, independent of the bulge or disk properties. We speculate that because bars are formed out of disks, bars initially have an exponential (disk-like) profile that evolves over time, trapping more disk stars to boxy bar orbits. This leads bars to become stronger and have flatter profiles. The narrow spread of bar radial profiles in more massive disks suggests that these bars formed earlier (z > 1), while the disk-like profiles and a larger spread in the radial profile in less massive systems imply a later and more gradual evolution, consistent with the cosmological evolution of bars inferred from observational studies. Therefore, we expect that the flatness of the bar profile can be used as a dynamical age indicator of the bar to measure the time elapsed since the bar formation. We argue that cosmic gas accretion is required to explain our results on bar profile and the presence of gas within the bar region.

Kim, Taehyun; Sheth, Kartik; Gadotti, Dimitri A.; Lee, Myung Gyoon; Zaritsky, Dennis; Elmegreen, Bruce G.; Athanassoula, E.; Bosma, Albert; Holwerda, Benne; Ho, Luis C.; Comerón, Sébastien; Knapen, Johan H.; Hinz, Joannah L.; Muñoz-Mateos, Juan-Carlos; Erroz-Ferrer, Santiago; Buta, Ronald J.; Kim, Minjin; Laurikainen, Eija; Salo, Heikki; Madore, Barry F.; Laine, Jarkko; Menéndez-Delmestre, Karín; Regan, Michael W.; de Swardt, Bonita; Gil de Paz, Armando; Seibert, Mark; Mizusawa, Trisha

2015-01-01

188

The Globular Cluster System of the Elliptical Galaxy NGC 2937 as a Marker of its Evolutionary History  

NASA Astrophysics Data System (ADS)

Using imaging data from the Hubble Space Telescope archive, we examine the rich globular cluster population of the giant elliptical galaxy NGC 2937, located at a distance of 70 Mpc. We present a color-magnitude diagram and two-color diagram of the galaxy's globular cluster system and discuss their possible implications for the evolutionary history of the galaxy.

Longley, Emily; Michael West Maria Mitchell Observatory, Dr. _William Harris McMaster University, Dr.

2015-01-01

189

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

190

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

NASA Astrophysics Data System (ADS)

We find that NGC 6789 is the most nearby example of a blue compact dwarf galaxy known to date. With the help of the Wide Field Planetary Camera 2 aboard the Hubble Space Telescope, we resolve NGC 6789 into over 15,000 point sources in the V and I bands. The young stars of NGC 6789 are found exclusively near the center of the galaxy. The red giant population identified at large galactocentric radii yields a distance of about 3.6 Mpc, a stellar metallicity [Fe/H] of about -2, and a minimum age of about 1 Gyr. Despite its isolated location in the Local Void, its low metallicity, and its active star formation, the properties of NGC 6789 are clearly not those of a galaxy in formation. Based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

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

2001-04-01

191

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

192

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

193

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

SciTech Connect

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

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

2014-05-09

194

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

E-print Network

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

Victor P. Debattista; J. A. Sellwood

2000-06-20

195

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.

196

Peanut-shaped bulges in face-on disk galaxies  

E-print Network

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

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

2010-01-01

197

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

E-print Network

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

Paul B. Eskridge; Raymond E. White, III

1997-06-17

198

Chemical behavior of the Dwarf Irregular Galaxy NGC 6822. Its PN and HII region abundances  

E-print Network

We aim to derive the chemical behavior of a significant sample of PNe and HII regions in the irregular galaxy NGC 6822 The selected objects are distributed in different zones of the galaxy. Due to the faintness of PNe and HII regions in NGC 6822, to gather spectroscopic data with large telescopes is necessary. We obtained a well suited sample of spectra by employing VLT-FORS 2 and Gemini-GMOS spectrographs. Ionic and total abundances are calculated for the objects where electron temperatures can be determined through the detection of [OIII] \\lambda 4363 or/and [NII] \\lambda 5755 lines. A "simple" chemical evolution model has been developed and the observed data are used to compute a model for NGC 6822 in order to infer a preliminary chemical history in this galaxy. Confident determinations of He, O, N, Ne, S and Ar abundances were derived for a sample of 11 PNe and one HII region. We confirm that the present ISM is chemically homogeneous, at least in the central 2 kpc of the galaxy, showing a value 12+log O/H...

Hernandez-Martinez, Liliana; Carigi, Leticia; Garcia-Rojas, Jorge

2009-01-01

199

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

NASA Technical Reports Server (NTRS)

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

Rubin, Vera C.

1994-01-01

200

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

201

Discovery of a New Faint Dwarf Galaxy Associated with NGC 253  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

202

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

203

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

E-print Network

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

H. Jerjen; B. Bingelli; Narae Hwang; Myung Gyoon Lee; Jong Chul Lee; Won-kee Park; Hong Soo Park Jang-hyun Park; Sang-gak Lee; Hyung Mok Lee; Mun-suk Chun; Young-wook Lee; Young-jong Sohn; In-soo Yuk; Sang Chul Kim; Ho-il Kim; Wonyong Han

2005-01-01

204

Hubble Space Telescope Imaging of Bipolar Nuclear Shells in the Disturbed Virgo Cluster Galaxy NGC 4438  

E-print Network

We present broadband and narrowband Hubble Space Telescope images of the central region of the heavily disturbed Virgo cluster galaxy NGC 4438 (Arp120), whose nucleus has been described as a type 1 LINER or dwarf Seyfert. Narrowband H-alpha and [NII] HST images reveal striking bipolar shell features, 1 kpc in projected length from end-to-end, which are likely the result of an outflow from the nuclear region experiencing a strong interaction with the ISM. While these outflow shells share similarities with those in some other starburst or AGN galaxies, these in NGC 4438 are notable because NGC 4438 harbors neither a luminous circumnuclear starburst nor a luminous AGN. The shells appear to be closed at their outer ends, suggesting that the outflow in NGC 4438 is dynamically younger than those in some other galaxies. The radio continuum emission is strongly enhanced near the outer ends of the shells, suggesting working surfaces arising from collimated nuclear outflows which have impacted and shocked the surrounding ISM. The 2 shells are quite different, as the northwestern (NW) shell is luminous and compact, while the southeastern (SE) shell is 2.5 times longer and much fainter, in both optical emission lines and the non-thermal radio continuum. The differences between the 2 shells may be attributed to a difference in ISM density on the 2 sides of the nuclear disk. Such an ISM asymmetry exists on larger scales in this heavily disturbed galaxy. At the base of the outflow is a nuclear source, which is the highest surface brightness source in the galaxy at optical wavelengths, We discuss whether the outflow is powered by a low luminosity AGN or a compact nuclear starburst.

Jeffrey D. P. Kenney; Elizabeth E. Yale

2001-12-04

205

Barred galaxy resonance rings: analytically explaining morphology and predicting dissipative misalignment  

Microsoft Academic Search

Many barred disc galaxies show rings of gas clouds and young stars thought to be in periodic orbits near the two-fold inner and outer Lindblad resonances (ILR and OLR) plus a four-fold ultraharmonic resonance (UHR) of the turning bar with oscillations about the disc orbital motion. To confirm and extend simulations by Schwarz and by Byrd et al. of resonance

Gene G. Byrd; Derrick Ousley; Chris dalla Piazza

1998-01-01

206

HDI in Action: Comparison Imaging of the Interacting Starburst Galaxy NGC 3310  

NASA Astrophysics Data System (ADS)

NGC 3310 is an interacting starburst galaxy located approximately 18 Mpc away. Previous studies reveal a circumnuclear starburst, substantial star formation in its spiral arms, and an extensive system of tidal debris likely induced from the collision with and subsequent merger of a now-destroyed companion galaxy. A study by Wehner et al. in 2006 revealed the presence of a previously undetected tidal loop in the Northeast quadrant of the system. We have obtained follow up observations of this system using the newly-built Half Degree Imager (HDI) recently mounted on the WIYN 0.9m telescope in Kitt Peak, Arizaon. We present a comparison of deep imaging of NGC 3310 from HDI and from S2KB, the former primary CCD camera on the 0.9m. We present our results for comparison of image depth and image quality in order to assess the new HDI camera for future low surface brightness observations.

Wehner, Elizabeth

2015-01-01

207

Building the intra-group medium from shock heated HI in the NGC 5903 galaxy group  

NASA Astrophysics Data System (ADS)

Observations of the famous shock in Stephan's Quintet suggest that low-mass galaxy groups may form a significant part of their IGM via shock heating of tidally stripped HI. Stephan's Quintet is, to date, unique, but we may have found a second nearby example. The NGC 5903 group hosts a 65kpc diameter diffuse ultra-steep spectrum radio source suggestive of shock emission, and a short XMM observation shows a strong correlation between a 100kpc HI filament and bright ridges of X-ray emission, indicating that the HI has been partially shock heated by a collision with the nearby elliptical NGC 5898. XMM lacks the spatial resolution to examine these complex structures, and we request a 155ks ACIS-S pointing to investigate what may be a key example of early IGM formation in a galaxy group.

O'Sullivan, Ewan

2014-09-01

208

Narrowband imaging and spectroscopy close to the nucleus of the Seyfert galaxy NGC 7682  

NASA Technical Reports Server (NTRS)

Keel's (1985) report of a jet-like optical feature emanating from the nucleus of NGC 7682 is investigated. Deep CCD images of NGC 7682 were taken with narrowband filters centered on the redshifted wavelength of H-alpha + forbidden N II and on a nearby continuum region. The continuum-subtracted line images show no evidence of the jet feature, although numerous H II regions appear clearly, both close to the nucleus and in the extended spiral arm structure. Spectra were taken at various dispersions and position angles, including the supposed position angle of the jet. These data were used to obtain background-subtracted spectra at the precise location of the jet. No excess emission was detected above the background-galaxy contribution. The highest-resolution spectra were used to determine the redshift of the galaxy to high precision.

Brodie, Jean; Willick, Jeffrey A.; Bowyer, Stuart; Henry, J. Patrick

1987-01-01

209

NIRSPEC Observations of Brackett Lines in the Dwarf Starburst Galaxy NGC 5253  

Microsoft Academic Search

We present high spectral (R ~25,000) and spatial resolution near-infrared spectra of the starburst in the dwarf galaxy NGC 5253. The data were obtained with the NIRSPEC spectrometer on the Keck Telescope. The spectra confirm the presence of the bright IR and radio ``supernebula'' discovered by Beck et al. (1996 ApJ, 457, 610) and Turner et al. (1998, AJ, 116,

J. L. Turner; L. P. Crosthwaite; D. S. Meier; S. C. Beck

2001-01-01

210

Radio jets and high velocity gas in the Seyfert Galaxy NGC 1068  

Microsoft Academic Search

New, high sensitivity VLA maps of the central regions of NGC 1068 at 4.9 GHz (total intensity and linear polarization) and 15.0 GHz (total intensity only) are presented. As found by van der Hulst, Hummel, and Dickey (1982), the bright radio emission coincident with the galaxy nucleus is resolved into a bent triple of total extent 0.7 arcsec, with the

A. S. Wilson; J. S. Ulvestad

1983-01-01

211

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

NASA Astrophysics Data System (ADS)

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, H?, and optical broad band images. We observe a coincidence between the western Hi and polarized emission edges, on the one hand, and a faint H? emission ridge, on the other. The polarized emission maxima are located within the gaps between the spiral arms and the faint H? ridge. Based on the comparison of these observations with a sample of dynamical simulations with different values for maximum ram pressure and different inclination angles between the disk and the orbital plane, we conclude that ram pressure stripping can account for the main observed characteristics. NGC 4501 is stripped nearly edge-on, is heading southwest, and is 200{-}300 Myr before peak ram pressure, i.e. its closest approach to M 87. The southwestern ridge of enhanced gas surface density and enhanced polarized radio-continuum emission is due to ram pressure compression. It is argued that the faint western H? emission ridge is induced by nearly edge-on ram pressure stripping. NGC 4501 represents an especially clear example of early stage ram pressure stripping of a large cluster-spiral galaxy.

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

2008-05-01

212

The Halo Dynamics of NGC 3379: A Normal Elliptical Galaxy with No Dark Matter  

NASA Astrophysics Data System (ADS)

We present the results of a radial velocity survey of planetary nebulae in the normal, non-interacting, elliptical galaxy NGC 3379. In two half-nights with the Kitt Peak 4-m telescope and the NESSIE multifiber spectrograph, we measured the velocities of 29 PNe with projected galactocentric distances between 0.4 and 3.8 effective radii (1 kpc < R < 10 kpc). These data, which have an observational uncertainty of ~ 7 km s(-1) , extend 3 times further into the halo than any previous absorption line study, and allow us for the first time, to examine the kinematics of halo stars in a normal E0 galaxy. The observed velocity dispersion and photometric profile of NGC 3379 agrees extremely well with that expected from a constant mass-to-light, isotropic orbit Jaffe model with a mass-to-light ratio M/L_B ~ 7. A simple c = 2.33 King model with M/L_B ~ 7 also fits the data reasonably well, but models with purely radial or circular orbits are ruled out. The data strongly suggest that NGC 3379 is a galaxy with little or no dark matter within 3.5 effective radii of its nucleus.

Ciardullo, R.; Jacoby, G. H.

1993-05-01

213

The association between water kilomasers and compact radio sources in the starburst galaxy NGC2146  

E-print Network

We report the detection of 22 GHz water vapor emission toward the starburst galaxy NGC2146, made using the Effelsberg 100-m telescope. Interferometric observations with the Very Large Array (VLA) show that a part of the emission originates from two prominent sites of star formation that are associated with compact radio continuum sources, likely ultra-compact HII regions. It is concluded that the emission arises from the most luminous and distant water `kilomasers' detected so far. Our data increase the number of water maser detections in northern galaxies (Dec > -30 deg) with 100 micron IRAS point source fluxes > 50 Jy to 18%.

A. Tarchi; C. Henkel; A. B. Peck; K. M. Menten

2002-05-16

214

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

215

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

216

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

NASA Technical Reports Server (NTRS)

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

Ikebe, Y.; Ohashi, T.; Makishima, K.; Tsuru, T.; Fabbiano, G.; Kim, D.-W.; Trinchieri, G.; Hatsukade, I.; Yamashita, K.; Kondo, H.

1992-01-01

217

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

218

Escape fraction of ionizing photons from a dwarf galaxy NGC 4214  

NASA Astrophysics Data System (ADS)

Recent studies suggest that starburst dwarf galaxies played an important role in the early universe. Because these galaxies dominate by number, their leaked ionizing photons are likely main contributors to the reionization of the intergalactic medium (IGM). However, the complex structure of the interstellar medium (ISM) even at the pc scale makes it hard to predict the escape fraction of ionizing photons from high-redshift galaxies accurately. Analogues to their high-redshift counterparts, nearby starburst dwarf galaxies provide excellent laboratories to study the impact of star formation on the surrounding ISM and IGM in detail. Thanks to its proximity, the dwarf galaxy, NGC 4214, has been imaged with the high-resolution of WFC3 on HST from the near-UV to the near-IR (F225W, F336W, F438W, F814W, F110W, and F160W). These observations yielded measurements of the broad spectral energy distributions (SEDs) for ?36,000 resolved stars within this galaxy. We developed a probabilistic tool (Bayesian Extinction and Stellar Tool, a.k.a. BEAST) to simultaneously infer from their SEDs the stellar properties of individual stars and the intervening dust properties along the line of sight to each star. With the aid of BEAST, we are able to infer the intrinsic ionizing flux produced by individual stars. By comparing this intrinsic ionizing flux with the flux that is used to ionize the ISM in the galaxy, derived based on the extinction-corrected H? emission, we can estimate the escape fraction and its local variation within the galaxy. Our preliminary results show that the global UV leakage of NGC 4214 is ?10%.

Choi, Yumi; Fouesneau, Morgan; Gordon, Karl D.; Williams, Benjamin F.; Dalcanton, Julianne; Weisz, Daniel R.; Arab, Heddy; Sandstrom, Karin; Dolphin, Andrew E.

2015-01-01

219

The dust energy balance in the edge-on spiral galaxy NGC 4565  

NASA Astrophysics Data System (ADS)

We combine new dust continuum observations of the edge-on spiral galaxy NGC 4565 in all Herschel/Spectral and Photometric Imaging Receiver (250, 350 and 500 ?m) wavebands, obtained as part of the Herschel Reference Survey, and a large set of ancillary data (Spitzer, Sloan Digital Sky Survey, Galaxy Evolution Explorer) to analyse its dust energy balance. We fit a radiative transfer model for the stars and dust to the optical maps with the fitting algorithm FITSKIRT. To account for the observed ultraviolet and mid-infrared emission, this initial model was supplemented with both obscured and unobscured star-forming regions. Even though these star-forming complexes provide an additional heating source for the dust, the far-infrared/submillimetre emission long wards of 100 ?m is underestimated by a factor of 3-4. This inconsistency in the dust energy budget of NGC 4565 suggests that a sizable fraction (two-thirds) of the total dust reservoir (Md ˜ 2.9 × 108 M?) consists of a clumpy distribution with no associated young stellar sources. The distribution of those dense dust clouds would be in such a way that they remain unresolved in current far-infrared/submillimetre observations and hardly contribute to the attenuation at optical wavelengths. More than two-thirds of the dust heating in NGC 4565 is powered by the old stellar population, with localized embedded sources supplying the remaining dust heating in NGC 4565. The results from this detailed dust energy balance study in NGC 4565 are consistent with that of similar analyses of other edge-on spirals.

de Looze, Ilse; Baes, Maarten; Bendo, George J.; Ciesla, Laure; Cortese, Luca; de Geyter, Gert; Groves, Brent; Boquien, Médéric; Boselli, Alessandro; Brondeel, Lena; Cooray, Asantha; Eales, Steve; Fritz, Jacopo; Galliano, Frédéric; Gentile, Gianfranco; Gordon, Karl D.; Hony, Sacha; Law, Ka-Hei; Madden, Suzanne C.; Sauvage, Marc; Smith, Matthew W. L.; Spinoglio, Luigi; Verstappen, Joris

2012-12-01

220

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

E-print Network

We present a comprehensive multi-wavelength study of the nearby interacting dwarf galaxy NGC3077 (member of the M81 triplet). High resolution VLA HI observations show that most of the atomic gas (~90%) around NGC3077 is situated in a prominent tidal arm with a complex velocity structure. Little HI (~5 x 10^7 M_sun) is associated with NGC3077 itself. High resolution OVRO observations of the molecular component (CO) reveal the presence of 16 molecular complexes near the center of NGC3077 (total mass: ~1.6 x 10^6 M_sun). A virial mass analysis of the individual complexes yields a lower CO-to-H_2 conversion factor in NGC3077 than the Galactic value - a surprising result for a dwarf galaxy. The total (atomic and molecular) gas content in the centre of NGC3077 is displaced from the stellar component of NGC3077 -- this implies that not only the gas at large galactocentric radii is affected by the interaction within the triplet but also the center. We speculate that the starburst activity of NGC3077 was triggered by this redistribution of gas in the center. Some of these supershells are surrounded by neutral hydrogen. In a few cases, the rims of the ionized supershells are associated with dust absorption. The most prominent star forming region in NGC3077 as probed by Pa-alpha observations is hidden behind a dust cloud which is traced by the molecular complexes. Correcting for extinction we derive a star forming rate of 0.05 M_sun year^-1, i.e. given the reservoir in atomic and molecular gas in NGC3077, star formation may proceed at a similar rate for a few 10^8 years. The efficiency to form stars out of molecular gas in NGC3077 is similar to that in M82.

F. Walter; A. Weiss; C. Martin; N. Scoville

2001-10-27

221

Kinematics of Superbubbles and Supershells in the Irregular Galaxy, NGC 1569  

NASA Astrophysics Data System (ADS)

We present observations in the optical lines of H? and [S II] (??6717, 6731 Å) and in X-rays of the irregular galaxy, NGC 1569. The observations in H? and [S II] were made with the UNAM scanning Fabry-Perot interferometer (PUMA) and the X-ray data were obtained from the Chandra data archive. We detected several superbubbles, filaments, and supershells in NGC 1569 for which we determined size as well as their kinematic properties. We present a catalog of expansion velocities of 12 superbubbles, listing their positions, diameters, and physical parameters. Likewise, we present a catalog of 15 filaments and 4 supershells. In order to identify possible X-ray emission from the superbubbles in this galaxy, we analyzed the X-ray emission of NGC 1569 in two energy bands: 0.2-2.0 keV (soft X-rays) and 2.0-8.0 keV (hard X-rays). Based on X-ray images, we detected X-ray emission that could possibly be related to some of the superbubbles. The spectrum of the X-ray superbubbles can be described by an optically thin thermal plasma model. In order to identify the possible coexistence of galactic super winds and superbubbles we have performed adiabatic three-dimensional N-body/smoothed particle hydrodynamics simulations to follow the evolution of the most important stellar clusters in this galaxy, SSC A and SSC B, using the GADGET-2 code. Those simulations demonstrate that depending on the specific initial conditions, the formation of superbubbles or a galactic superwind can result in NGC 1569.

Sánchez-Cruces, M.; Rosado, M.; Rodríguez-González, A.; Reyes-Iturbide, J.

2015-02-01

222

Evolution of Structure in Late-type Spiral Galaxies I: Ionized Gas Kinematics in NGC 628  

E-print Network

We study two dimensional Fabry-Perot interferometric observations of the nearby face-on late-type spiral galaxy, NGC 628, in order to analyse the ionized gas component of the interstellar medium. Covering the galaxy out to a radius larger than 12 kpc, and with a spatial sampling of 1.6 arcsec, we investigate the large-scale dynamics as well as feedback from individual HII regions into their surrounding medium. We study the role of gravitational perturbations along with that of external triggers which can disturb the kinematics and morphology of NGC 628. We verify the presence of an inner rapidly rotating disc-like component in NGC 628, which we interpret as caused by slow secular evolution of the large-scale spiral arms and oval structure. In combination with auxiliary data, we find indication for that gas is falling in from the outer parts towards the central regions, where a nuclear ring has formed at the location of the inner Lindblad resonance radius of an m=2 perturbation which could help build a pseudo-bulge in NGC 628. Moreover, we calculate radial profiles of the emission-line velocity dispersion which we use to study the role of feedback from individual HII regions. The mean velocity dispersion for the ionized gas (even when excluding pixels belonging to individual HII regions) is almost constant out to 12 kpc, although it varies from 14 to 20 km/s, with a steady decline in the outer parts. The current paper demonstrates a number of tools that we have developed for building a solid frame work for studying the evolution of structure in spiral galaxies using two dimensional kinematic observations.

Kambiz Fathi; John E. Beckman; Almudena Zurita; Monica Relano; Johan H. Knapen; Olivier Daigle; Olivier Hernandez; Claude Carignan

2007-03-01

223

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

NASA Astrophysics Data System (ADS)

Recent observations with the Murchison Widefield Array at 185 MHz have serendipitously unveiled a heretofore unknown giant and relatively nearby (z = 0.0178) radio galaxy associated with NGC 1534. The diffuse emission presented here is the first indication that NGC 1534 is one of a rare class of objects (along with NGC 5128 and NGC 612) in which a galaxy with a prominent dust lane hosts radio emission on scales of ˜700 kpc. We present details of the radio emission along with a detailed comparison with other radio galaxies with discs. NGC 1534 is the lowest surface brightness radio galaxy known with an estimated scaled 1.4-GHz surface brightness of just 0.2 mJy arcmin-2. The radio lobes have one of the steepest spectral indices yet observed: ? = -2.1 ± 0.1, and the core to lobe luminosity ratio is <0.1 per cent. We estimate the space density of this low brightness (dying) phase of radio galaxy evolution as 7 × 10-7 Mpc-3 and argue that normal AGN cannot spend more than 6 per cent of their lifetime in this phase if they all go through the same cycle.

Hurley-Walker, Natasha; Johnston-Hollitt, Melanie; Ekers, Ron; Hunstead, Richard; Sadler, Elaine M.; Hindson, Luke; Hancock, Paul; Bernardi, Gianni; Bowman, Judd D.; Briggs, Frank; Cappallo, Roger; Corey, Brian; Deshpande, Avinash A.; Emrich, David; Gaensler, Bryan M.; Goeke, Robert; Greenhill, Lincoln; Hazelton, Bryna J.; Hewitt, Jacqueline; Kaplan, David L.; Kasper, Justin; Kratzenberg, Eric; Lonsdale, Colin; Lynch, Mervyn; Mitchell, Daniel; McWhirter, Russell; Morales, Miguel; Morgan, Edward; Oberoi, Divya; Offringa, André; Ord, Stephen; Prabu, Thiagaraj; Rogers, Alan; Roshi, Anish; Shankar, Udaya; Srivani, K.; Subrahmanyan, Ravi; Tingay, Steven; Waterson, Mark; Wayth, Randall B.; Webster, Rachel; Whitney, Alan; Williams, Andrew; Williams, Chris

2015-03-01

224

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

225

Reverberation Mapping Analysis of the Broad-Line Region in Seyfert Galaxy NGC 4151  

NASA Astrophysics Data System (ADS)

By careful and intensive monitoring the continuum variations and the resulting emission-line response in AGN, it is possible to determine the physical conditions and the structure of the BLR through the process of "reverberation mapping (RM)". We have applied such a technique to Seyfert galaxy NGC 4151 by using the optical monitoring data obtained in a recent international AGN watch campaign in 1993. In order to tackle the issue revealed by the preliminary analysis of this watch campaign, i.e. the BLR size is very different from the result determined several years ago, we carried out the following two kinds of RM analysis: a) Test how a specific continuum variation can affect the delay of the emission-lines by use of Mone-Carlo simulations. b) Solve the BLR transfer function, which describes the size and the structure of the BLR in NGC 4151, by use of the regularized linear-inversion method. We find that the transfer function of NGC 4151 was drastically changed from the shape in 1988, and this naturally explains the size problem of NGC 4151.

Xue, S. J.; Cheng, F. Z.

226

Probing The Multiphase Interstellar Medium Of The Dwarf Starburst Galaxy NGC 625 With FUSE Spectroscopy  

E-print Network

We present new FUSE spectroscopy of the dwarf starburst galaxy NGC 625. These observations probe multiple phases of the interstellar medium, including the coronal, ionized, neutral and molecular gas. This nearby (D = 3.9 +/- 0.2 Mpc) system shows a clear detection of outflowing coronal gas as traced by OVI 1032 Angstrom absorption. The centroid of the OVI profile is blueshifted with respect to the galaxy systemic velocity by ~ 30 km/sec, suggesting a low-velocity outflow. The implied OVI velocity extent is found to be 100 +/- 20 km/sec, which is fully consistent with the detected HI outflow velocity found in radio synthesis observations. We detect multiple lines of diffuse H2 absorption from the ISM of NGC 625; this is one of only a few extragalactic systems with FUSE detections of H2 lines in the Lyman and Werner bands. We find a potential abundance offset between the neutral and nebular gas that exceeds the errors on the derived column densities. Since such an offset has been found in multiple dwarf galaxies, we discuss the implications of a lower-metallicity halo surrounding the central star forming regions of dwarf galaxies. The apparent offset may be due to saturation of the observed OI line, and higher S/N observations are required to resolve this issue.

John M. Cannon; Evan D. Skillman; Kenneth R. Sembach; Dominik J. Bomans

2004-09-14

227

Chandra Observations of Nuclear Outflows in the Elliptical Galaxy NGC 4552 in the Virgo Cluster  

NASA Astrophysics Data System (ADS)

We use a 54.4 ks Chandra observation to study nuclear outflow activity in NGC 4552 (M89), an elliptical galaxy in the Virgo Cluster. Chandra images in the 0.5-2 keV band show two ringlike features ~1.7 kpc in diameter in the core of NGC 4552, as reported previously by Filho et al. We use spherically symmetric point explosion shock models to argue that the shape of the surface brightness profile across the rims of the rings and the temperature of hot gas in the rings are consistent with a Mach 1.7 shock carrying mean mechanical power Lshock~3×1041 ergs s-1 produced by a ~1.4×1055 ergs nuclear outburst ~1-2 Myr ago. We find the gas temperature in the central ~100 pc of the galaxy to be 1.0+/-0.2 keV, hotter than elsewhere in the galaxy, suggesting that we may be directly observing the reheating of the galaxy ISM by the outburst.

Machacek, M.; Nulsen, P. E. J.; Jones, C.; Forman, W. R.

2006-09-01

228

The chemical content of nearby galaxies from planetary nebulae: NGC 147  

NASA Astrophysics Data System (ADS)

We report the results of spectroscopic observations, obtained with the Gemini Multi-Object Spectrograph, of eight planetary nebulae (PNe) in the dwarf spheroidal (dSph) galaxy NGC 147, a companion of M31. The physico-chemical properties of the six brightest PNe were derived using both the empirical ICF method and photoionization modelling with CLOUDY. Different aspects of the evolution of low- and intermediate-mass stars in a low-metallicity environment are analysed using relationships between chemical abundances. In addition, certain features of the chemical evolution of NGC 147 were examined. In particular, the mean metallicity of PNe, O/H = 8.06+0.09-0.12 (corresponding to [Fe/H]PNe ~ -0.97), is close to the metallicity of the old stellar population, [Fe/H] = -1.0, suggesting a negligible chemical enrichment during a substantial amount of time. Finally, the luminosity-metallicity relationship for the dwarf galaxies of the Local Group is discussed. The location in the luminosity-metallicity diagram of dSphs does not exclude their formation from old dwarf irregular (dIr) galaxies, but it does exclude their formation from the present time dIrs, since the differences between their metallicities are already present in their older populations. The offset in the luminosity-metallicity relationship indicates a faster enrichment of dSphs and, together with the different average abundance ratio [O/Fe ]demonstrates the different star formation histories for these two types of galaxies.

Gonçalves, D. R.; Magrini, L.; Leisy, P.; Corradi, R. L. M.

2007-02-01

229

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

230

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

231

Far-Infrared Spectroscopy with ISO: The Physical Conditions of the ISM in the Normal Spiral Galaxy NGC 5713  

Microsoft Academic Search

We report new ISO Long Wavelength Spectrometer (LWS) observations of the SAB(rs)bc galaxy NGC 5713. These are the first LWS results from our ``US Key Project'' on normal galaxies (Helou et al. 1996) which uses ISO LWS, CAM, and PHOT observations to study ISM properties in normal galaxies. We have obtained strong detections of the fine-structure forbidden transitions of [CII

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

1996-01-01

232

The structure and dynamics of ringed galaxies. III - Surface photometry and kinematics of the ringed nonbarred spiral NGC 7531  

Microsoft Academic Search

The photometric and kinematic properties of the southern galaxy NGC 7531, a large example of a nonbarred spiral possessing a very bright inner ring, are explored via UVBRI surface photometry and emission-line spectroscopy. The galaxy is a global, two-armed spiral galaxy possessing a bright inner ring with a radius of 2.3 kpc. The ring has an average surface brightness in

R. Buta

1987-01-01

233

ROSAT PSPC observation of the X-ray faint early-type galaxy NGC5866  

E-print Network

We present the results of the analysis of the ROSAT PSPC pointed observation of the S0 galaxy NGC5866. Previous Einstein observations had revealed that this galaxy has a low X-ray to optical ratio Lx/Lb. Theoretical models of the X-ra emission of early-type galaxies had suggested that in objects of this kind the emission is not dominated by the presence of a hot diffuse gas, but should originate in stellar sources. We discuss the evidence in favor of this hypothesis following from the results of the analysis of the ROSAT PSPC data. The X-ray spectrum shows properties similar to those of the other two low Lx/Lb early-type galaxies observed by ROSAT so far, including the presence of very soft emission. So, these galaxies can be recognized as a group with homogeneous properties, and a more exhaustive picture of the nature of the X-ray emission across the Lx/Lb plane of early-type galaxies can be outlined. We also discuss the importance of rotation in the X-ray emission of S0 galaxies, and suggest that it could explain why on average S0s are less X-ray luminous than ellipticals.

S. Pellegrini

1994-07-03

234

Stellar population and the origin of intra-cluster stars around brightest cluster galaxies: the case of NGC 3311  

NASA Astrophysics Data System (ADS)

Context. We investigate the stellar population and the origin of diffuse light around brightest cluster galaxies. Aims: We study the stellar population of the dynamically hot stellar halo of NGC 3311, the brightest galaxy in the Hydra I cluster, and that of photometric substructures in the diffuse light to constrain the origin of these components. Methods: We analyze absorption lines in medium-resolution, long-slit spectra in the wavelength range 4800-5800 Å obtained with FORS2 at the Very Large Telescope. We measure the equivalent width of Lick indices out to 20 kpc from the center of NGC 3311 and fit them with stellar population models that account for the [?/Fe] overabundance. Results: Stars in the dynamically hot halo of NGC 3311 are old (age >13 Gyr), metal-poor ([Z/H] ~ -0.35), and alpha-enhanced ([?/Fe] ~ 0.48). Together with the high velocity dispersion, these measurements indicate that the stars in the halo were accreted from the outskirts of other early-type galaxies, with a possible contribution from dwarf galaxies. We identify a region in the halo of NGC 3311 associated with a photometric substructure where the stellar population is even more metal-poor ([Z/H] ~ -0.73). In this region, our measurements are consistent with a composite stellar population superposed along the line of sight, consisting of stars from the dynamically hot halo of NGC 3311 and stars stripped from dwarf galaxies. The latter component contributes ?28% to the local surface brightness. Conclusions: The build-up of diffuse light around NGC 3311 is on-going. Based on the observed stellar population properties, the dominant part of these stars may have come from the outskirts of bright early-type galaxies, while stars from stripped dwarf galaxies are presently being added. Based on observations collected at the European Southern Observatory for the program 082.A-0255(A).

Coccato, L.; Gerhard, O.; Arnaboldi, M.; Ventimiglia, G.

2011-09-01

235

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

SciTech Connect

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

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

2010-09-20

236

The low-luminosity galaxy population in the NGC 5044 Group (Conference proceeding)  

E-print Network

Detailed surface photometry for 79 (mostly dwarf) galaxies in the NGC 5044 Group area is analysed, revealing the existence of different morphologies among objects originally classified as early-type dwarfs. Particularly, a significant fraction of bright dwarf "ellipticals" show a distinct bulge+disc structure; we thus re-classify these objects as dwarf lenticulars (dS0). Our finding points at a possible scenario where these systems are the remnants of "harassed" disc galaxies. This is emphasized by the discovery of a few objects with hints for very low-surface brightness spiral-like structure. The colours, structure, and spatial distribution of the different galaxy types suggest that our classification may indeed be separating objects with different origins and/or evolutionary paths.

Sergio A. Cellone; Alberto Buzzoni

2006-03-27

237

Intrinsic UV Absorption in the Seyfert 1 Galaxy NGC 3783: FUSE and HST/STIS Results  

NASA Astrophysics Data System (ADS)

We present results in the UV and far-UV, as part of an intensive multiwavelength monitoring campaign designed to study the intrinsic absorption in the Seyfert 1 galaxy, NGC 3783. We have combined 18 HST/STIS echelle grating observations and 5 FUSE observations to produce a high signal-to-noise averaged spectrum that samples numerous lines spanning a large range in ionization states. Analysis of the Lyman lines reveals a complex absorption geometry in the UV absorption. The individual covering factors of the continuum and broad line region emission sources are deconvolved. We find evidence for variable covering factor with velocity in the individual absorption components, with a decrease in the wings of the profiles. The H I covering factor profiles are used to derive ionic column densities for all available lines. These results are used to constrain the physical conditions in the absorbers and investigate the complex absorption geometry in NGC 3783.

Gabel, J. R.; Kraemer, S. B.; Crenshaw, D. M.

238

NGC300 X-1: an extraordinary black hole binary in a normal galaxy  

NASA Astrophysics Data System (ADS)

NGC300 X-1 is one of only 2 confirmed black hole + Wolf-Rayet binaries, and one of only ~20 high inclination X-ray binaries known in the Universe. It has a ~32 hr period, discovered in X-rays from periodic intensity dips. We believe that these dips originate in the outer accretion disc, meaning that we can use the ingress time to estimate the corona size. We request a 130 ks observation that guarantees dip coverage. Furthermore, NGC300 is an appealing galaxy for further study, as it fills most of the XMM field of view, with ~100 known X-ray sources. We will better characterize the X-ray population with improved spectral and timing analysis. We will identify black hole binaries with high luminosity low states, and weed out AGN interlopers with long term variability.

Barnard, Robin

2011-10-01

239

Deep Fabry-Perot imaging of NGC 6240: Kinematic evidence for merging galaxies  

NASA Technical Reports Server (NTRS)

The authors have observed the superluminous, infrared galaxy NGC 6240 (z = 0.025) at H alpha with the Hawaii Imaging Fabry-Perot Interferometer (HIFI - Bland and Tully 1989). During the past decade, observational evidence from all wavebands indicates that the unusual appearance of NGC 6240 has resulted from a collision between two gas-rich systems, a view which is supported by our spectrophotometric data. However, the origin of the enormous infrared luminosity (4 times 10(exp 11) solar luminosity) detected by the Infrared Astronomy Satellite (IRAS) remains highly controversial, where opinions differ on the relative roles of large-scale shocks, massive star formation or a buried 'active' nucleus. These mechanisms are discussed in the light of the author's Fabry-Perot observations.

Hawthorn, J. Bland; Wilson, A. S.; Tully, R. B.

1990-01-01

240

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

Microsoft Academic Search

We show that bars in galaxy models having halos of moderate density and a\\u000avariety of velocity distributions all experience a strong drag from dynamical\\u000afriction unless the halo has large angular momentum in the same sense as the\\u000adisk. The frictional drag decreases the bar pattern speed, driving the\\u000acorotation point out to distances well in excess of those

Victor P. Debattista; J. A. Sellwood

2000-01-01

241

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

242

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

243

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

244

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

SciTech Connect

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

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

2010-03-20

245

Isolated elliptical galaxies and their globular cluster systems. II. NGC 7796 - globular clusters, dynamics, companion  

NASA Astrophysics Data System (ADS)

Context. Rich globular cluster systems, particularly the metal-poor part of them, are thought to be the visible manifestations of long-term accretion processes. The invisible part is the dark matter halo, which may show some correspondence to the globular cluster system. It is therefore interesting to investigate the globular cluster systems of isolated elliptical galaxies, which supposedly have not experienced extended accretion. Aims: We investigate the globular cluster system of the isolated elliptical NGC 7796, present new photometry of the galaxy, and use published kinematical data to constrain the dark matter content. Methods: Deep images in B and R, obtained with the VIsible MultiObject Spectrograph (VIMOS) at the VLT, form the data base. We performed photometry with DAOPHOT and constructed a spherical photometric model. We present isotropic and anisotropic Jeans-models and give a morphological description of the companion dwarf galaxy. Results: The globular cluster system has about 2000 members, so it is not as rich as those of giant ellipticals in galaxy clusters with a comparable stellar mass, but richer than many cluster systems of other isolated ellipticals. The colour distribution of globular clusters is bimodal, which does not necessarily mean a metallicity bimodality. The kinematic literature data are somewhat inconclusive. The velocity dispersion in the inner parts can be reproduced without dark matter under isotropy. Radially anisotropic models need a low stellar mass-to-light ratio, which would contrast with the old age of the galaxy. A MONDian model is supported by X-ray analysis and previous dynamical modelling, but better data are necessary for a confirmation. The dwarf companion galaxy NGC 7796-1 exhibits tidal tails, multiple nuclei, and very boxy isophotes. Conclusions: NGC 7796 is an old, massive isolated elliptical galaxy with no indications of later major star formation events as seen frequently in other isolated ellipticals. Its relatively rich globular cluster system shows that isolation does not always mean a poor cluster system. The properties of the dwarf companion might indicate a dwarf-dwarf merger. Based on observations taken at the European Southern Observatory, Cerro Paranal, Chile, under the programme 089.B-0457. Partly based on observations taken at the Las Campanas Observatory and the Gemini observatory (GS-2011B-Q83).The catalogue of the photometry is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/574/A21

Richtler, T.; Salinas, R.; Lane, R. R.; Hilker, M.; Schirmer, M.

2015-02-01

246

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

NASA Astrophysics Data System (ADS)

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

Wiita, Paul; Gopal-Krishna; Mhaskey, Mukul

2012-03-01

247

X-RAY NUCLEAR ACTIVITY IN S{sup 4}G BARRED GALAXIES: NO LINK BETWEEN BAR STRENGTH AND CO-OCCURRENT SUPERMASSIVE BLACK HOLE FUELING  

SciTech Connect

Stellar bars can lead to gas inflow toward the center of a galaxy and stimulate nuclear star formation. However, there is no compelling evidence on whether they also feed a central supermassive black hole: by measuring the fractions of barred active and inactive galaxies, previous studies have yielded conflicting results. In this paper, we aim to understand the lack of observational evidence for bar-driven active galactic nucleus (AGN) activity by studying a sample of 41 nearby (d < 35 Mpc) barred galaxies from the Spitzer Survey for Stellar Structure in Galaxies. We use Chandra observations to measure nuclear 2-10 keV X-ray luminosities and estimate Eddington ratios, together with Spitzer 3.6 ?m imaging to quantify the strength of the stellar bar in two independent ways: (1) from its structure, as traced by its ellipticity and boxiness, and (2) from its gravitational torque Q{sub b} , taken as the maximum ratio of the tangential force to the mean background radial force. In this way, rather than discretizing the presence of both stellar bars and nuclear activity, we are able to account for the continuum of bar strengths and degrees of AGN activity. We find nuclear X-ray sources in 31 out of 41 galaxies with median X-ray luminosity and Eddington ratio of L{sub X} = 4.3 × 10{sup 38} erg s{sup –1} and L{sub bol}/L{sub Edd} = 6.9 × 10{sup –6}, respectively, consistent with low-luminosity AGN activity. Including upper limits for those galaxies without nuclear detections, we find no significant correlation between any of the bar strength indicators and the degree of nuclear activity, irrespective of galaxy luminosity, stellar mass, Hubble type, or bulge size. Strong bars do not favor brighter or more efficient nuclear activity, implying that at least for the low-luminosity regime, supermassive black hole fueling is not closely connected to large-scale features.

Cisternas, Mauricio; Knapen, Johan H.; González-Martín, Omaira; Erroz-Ferrer, Santiago [Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife (Spain); Gadotti, Dimitri A.; Kim, Taehyun [European Southern Observatory, Casilla 19001, Santiago 19 (Chile); Díaz-García, Simón; Laurikainen, Eija; Salo, Heikki; Comerón, Sébastien; Laine, Jarkko [Division of Astronomy, Department of Physical Sciences, University of Oulu, Oulu FI-90014 (Finland); Ho, Luis C. [The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Elmegreen, Bruce G. [IBM T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598 (United States); Zaritsky, Dennis; Hinz, Joannah L. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Sheth, Kartik [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Athanassoula, E.; Bosma, Albert [Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, F-13388 Marseille (France); Gil de Paz, Armando [Departamento de Astrofísica, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Holwerda, Benne W., E-mail: mauricio@iac.es [European Space Agency, ESTEC, Keplerlaan 1, 2200 AG Noordwijk (Netherlands); and others

2013-10-10

248

Star Formation Histories across the Interacting Galaxy NGC 6872, the Largest-known Spiral  

NASA Astrophysics Data System (ADS)

NGC 6872, hereafter the Condor, is a large spiral galaxy that is interacting with its closest companion, the S0 galaxy IC 4970. The extent of the Condor provides an opportunity for detailed investigation of the impact of the interaction on the current star formation rate and its history across the galaxy, on the age and spatial distribution of its stellar population, and on the mechanism that drives the star formation activity. To address these issues we analyzed the far-ultraviolet (FUV) to near-infrared (near-IR) spectral energy distribution of seventeen 10 kpc diameter regions across the galaxy, and derived their star formation history, current star formation rate, and stellar population and mass. We find that most of the star formation takes place in the extended arms, with very little star formation in the central 5 kpc of the galaxy, in contrast to what was predicted from previous numerical simulations. There is a trend of increasing star formation activity with distance from the nucleus of the galaxy, and no evidence for a recent increase in the current star formation rate due to the interaction. The nucleus itself shows no significant current star formation activity. The extent of the Condor also provides an opportunity to test the applicability of a single standard prescription for conversion of the FUV + IR (22 ?m) intensities to a star formation rate for all regions. We find that the conversion factor differs from region to region, arising from regional differences in the stellar populations.

Eufrasio, Rafael T.; Dwek, Eli; Arendt, Richard G.; de Mello, Duilia F.; Gadotti, Dimitri A.; Urrutia-Viscarra, Fernanda; Mendes de Oliveira, Claudia; Benford, Dominic J.

2014-11-01

249

Infrared photometry of the inner regions of the dwarf irregular galaxy NGC 3109  

NASA Astrophysics Data System (ADS)

We present VIJHK photometry for stars in a 0.8x2.0 kpc(2) inner field of the dwarf irregular galaxy NGC 3109. The infrared photometry reaches 3 magnitudes fainter than previous work. Optical and infrared color-color and color-magnitude diagrams, and a bolometric luminosity function are constructed, confirming the presence of an intermediate-age stellar population. We also present a log{L/Lsun} vs log{Teff} diagram of the galaxy and compare the results with the theoretical isochrones of Bertelli et al. ( te{bertelli}) for Z=0.004 and Y=0.24. The comparison suggests that most of the stars detected in the IR are 10(9) yr or younger. We compare the infrared color-magnitude diagrams of NGC 3109 with the composite color-magnitude diagrams of LMC clusters and of the outer disk of the Scd galaxy M33. They show similar stellar content in these late-type systems. Based on observations collected at La Silla Observatory

Alonso, M. Victoria; Minniti, Dante; Zijlstra, Albert A.; Tolstoy, Eline

1999-06-01

250

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

251

Star formation and nuclear activity in the blue early-type galaxy NGC 5373  

NASA Astrophysics Data System (ADS)

We present new optical and X-ray observations of NGC 5373, an isolated star-forming elliptical that has a stellar mass of 7e10 solar and lies at a distance of 175 Mpc. Our B and R band Magellan IMACS imaging substantially improves on SDSS resolution and sensitivity, enabling accurate modeling of the galaxy surface brightness profile. As expected from its mass, NGC 5373 is a core galaxy with a best-fit Sersic profile of n~3.8; no prominent tidal tails or shells are found, although there are slight residual asymmetries. The H-alpha emission in the SDSS spectrum is narrow, and the line ratios confirm a star-forming classification in the BPT diagram, near the transition/composite line. The star formation rate is about 6 solar masses per year, making NGC 5373 an extreme outlier relative to typical local early-type galaxies of similar mass. Our 50 ks Chandra ACIS-S exposure provides a clear detection of a central X-ray source, with a hardness ratio consistent with a power-law photon index of 2.0+/-0.5. The unabsorbed luminosity is Lx = 2e40 erg/s over 0.3-8 keV. Comparison with a MARX simulated point spread function suggests the central source may be extended, for example due to contributions from one or more unresolved high-mass X-ray binaries, as might be present given the high star formation rate. For a black hole of 1.6e8 solar masses as predicted from scaling relations, Lx/Ledd is then around 1e-6 (or potentially lower).

Zaidi, Tayeb; Miller, Brendan P.; Gallo, Elena; Alfvin, Erik; Martinkus, Charlotte; Molter, Edward

2015-01-01

252

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

E-print Network

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

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

2006-04-28

253

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

254

Luminous clusters of Wolf-Rayet stars in the SBmIII galaxy NGC 4214  

NASA Technical Reports Server (NTRS)

Observations are reported of strong broad emission lines attributed to WR stars in the spectra of several bright knots in the nearby Magellanic irregular galaxy NGC 4214 (classified as type SBmIII), in addition to the emission produced by the more prevalent WN stars). Data are presented on measurements of the line fluxes, the line equivalent widths, and continuum flux densities in the four observed knots, showing that the strongest WR lines generally appear in knots having the most luminous stellar continuum. The significance of this observation is discussed.

Sargent, Wallace L. W.; Filippenko, Alexei V.

1991-01-01

255

Chemical behavior of the dwarf irregular galaxy NGC6822. Its PN and HII region abundances  

NASA Astrophysics Data System (ADS)

Aims: We aim to derive the chemical behavior of a significant sample of PNe and HII regions in the irregular galaxy NGC 6822. The selected objects are distributed in different zones of the galaxy. Our purpose is to obtain the chemical abundances of the present interstellar medium (ISM), represented by H ii regions, and the corresponding values at the time of formation of PNe. With these data the chemical homogeneity of NGC 6822 were tested and the abundance pattern given by H ii regions and PNe used as an observational constraint for computing chemical evolution models to infer the chemical history of NGC 6822. Methods: Due to the faintness of PNe and H ii regions in NGC 6822, to gather spectroscopic data with large telescopes is necessary. We obtained a well suited sample of spectra by employing VLT-FORS 2 and Gemini-GMOS spectrographs. Ionic and total abundances were calculated for the objects where electron temperatures could determined through the detection of [O iii] ?4363 or/and [N ii] ?5755 lines. A “simple” chemical evolution model was developed and the observed data were used to compute a model for NGC 6822 in order to infer a preliminary chemical history in this galaxy. Results: Confident determinations of He, O, N, Ne, S and Ar abundances were derived for a sample of 11 PNe and one H ii region. We confirm that the present ISM is chemically homogeneous, at least in the central 2 kpc of the galaxy, showing a value 12 + log O/H = 8.06 ± 0.04. From the abundance pattern of PNe, we identified two populations: a group of young PNe with abundances similar to H ii regions and a group of older objects with abundances a factor of two lower. A pair of extreme Type I PNe were found. No third dredge-up O enrichement was detected in PNe of this galaxy. The abundance determinations allow us to discuss the chemical behavior of the present and past ISM in NGC 6822. Our preliminary chemical evolution model predicts that an important gas-mass loss occurred during the first 5.3 Gyr, that no star higher than 40 M_? was formed, and that 1% of all 3-15 M_? stars became binary system progenitors of SNIa. Based on observations collected at the European Southern Observatory, VLT, Paranal, Chile, program ID 077.B-0430. Based on observations obtained at the Gemini Observatory (program ID G-2005B-56), which is operated by AURA, Inc. under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (USA), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciencia e Tecnologia (Brazil) and SECYT (Argentina).

Hernández-Martínez, L.; Peña, M.; Carigi, L.; García-Rojas, J.

2009-10-01

256

Herschel and JCMT observations of the early-type dwarf galaxy NGC 205  

NASA Astrophysics Data System (ADS)

We present Herschel dust continuum, James Clerk Maxwell Telescope CO (3-2) observations and a search for [C II] 158 ?m and [O I] 63 ?m spectral line emission for the brightest early-type dwarf satellite of Andromeda, NGC 205. While direct gas measurements [Mg˜ 1.5 × 106 M?, H I+ CO (1-0)] have proven to be inconsistent with theoretical predictions of the current gas reservoir in NGC 205 (>107 M?), we revise the missing interstellar medium mass problem based on new gas mass estimates (CO (3-2), [C II], [O I]) and indirect measurements of the interstellar medium content through dust continuum emission. Based on Herschel observations, covering a wide wavelength range from 70 to 500 ?m, we are able to probe the entire dust content in NGC 205 (? M? at Td˜ 18-22 K) and rule out the presence of a massive cold dust component (? M?, Td˜ 12 K), which was suggested based on millimetre observations from the inner 18.4 arcsec. Assuming a reasonable gas-to-dust ratio of ˜400, the dust mass in NGC 205 translates into a gas mass Mg˜ 4-7 × 106 M?. The non-detection of [O I] and the low L[C II]-to-LCO(1-0) line intensity ratio (˜1850) imply that the molecular gas phase is well traced by CO molecules in NGC 205. We estimate an atomic gas mass of 1.5 × 104 M? associated with the [C II] emitting photodissociation regions in NGC 205. From the partial CO (3-2) map of the northern region in NGC 205, we derive a molecular gas mass of ? M?. Upon comparison with the molecular gas mass estimated from CO (1-0) observations (? M?), we find most of the H2 gas in NGC 205 to be locked in diffuse regions of low density and/or temperature, characteristic for an interstellar medium with little star formation activity. New total gas mass estimates from Herschel dust continuum (4-7 × 106 M?), Herschel [C II] line spectroscopic mapping (1.5 × 104 M?) and James Clerk Maxwell Telescope CO (3-2) observations (7 × 105 M?), including the H I mass (? M?) and a correction for heavier elements, confirm the deficiency of the interstellar medium (gas+dust) in the inner regions of NGC 205, which is predicted to contain at least >107 M? of gas if we assume a reasonable star formation efficiency of 10 per cent and account for the mass return from planetary nebulae. In an attempt to explain the missing interstellar medium mass problem, we claim that efficient supernova feedback capable of expelling gas from the inner, star-forming regions to the outer regions and/or tidal interactions with M31 stripping the gas component from the galaxy provide the best explanation for the removal of a significant amount of gas and dust from NGC 205.

De Looze, I.; Baes, M.; Parkin, T. J.; Wilson, C. D.; Bendo, G. J.; Boquien, M.; Boselli, A.; Cooray, A.; Cormier, D.; Fritz, J.; Galliano, F.; Gear, W.; Gentile, G.; Lebouteiller, V.; Madden, S. C.; Roussel, H.; Sauvage, M.; Smith, M. W. L.; Spinoglio, L.; Verstappen, J.; Young, L.

2012-07-01

257

Peanuts at an Angle: The Three-Dimensional Structure of Bars in Moderately Inclined Galaxies  

NASA Astrophysics Data System (ADS)

We show that direct detection of the vertically thickened parts of bars ("boxy" or "peanut-shaped" bulges) is possible not only for edge-on galaxies but also for galaxies with moderate inclinations (i < 70 degrees), and that examples are relatively common in the nearby universe. Comparison with n-body simulations indicates that detection of the box/peanut structure is maximized when the bar's position is close to the apparent major axis of the projected disk, and minimized when it lies along the minor axis. Analysis of a sample of nearby, moderately inclined (i < 65 degrees) early-type (S0-Sb) disk galaxies shows that this signature can be detected for inclinations as low as 40 degrees -- and in rare cases down to 30 degrees. Detection of box/peanut structures in moderately inclined galaxies makes it possible to directly compare vertical and in-plane structures of disks in ways that are difficult or impossible for edge-on systems; for example, we can compare the linear size of the box/peanut structure with the size of the bar itself, and directly determine what fraction of bars have box/peanut structures.

Erwin, Peter; Debattista, V.

2010-01-01

258

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

SciTech Connect

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

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

2013-05-01

259

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

SciTech Connect

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

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

2010-12-10

260

NGC 1266: Characterization of the Nuclear Molecular Gas in an Unusual SB0 Galaxy  

E-print Network

With a substantial nuclear molecular gas reservoir and broad, high-velocity CO molecular line wings previously interpreted as an outflow, NGC 1266 is a rare SB$0$ galaxy. Previous analyses of interferometry, spectrally resolved low-$J$ CO emission lines, and unresolved high-$J$ emission lines have established basic properties of the molecular gas and the likely presence of an AGN. Here, new spectrally resolved CO $J = 5 - 4$ to $J = 8 - 7$ lines from {\\it Herschel Space Observatory} HIFI observations are combined with ground-based observations and high-$J$ {\\it Herschel} SPIRE observations to decompose the nuclear and putative outflow velocity components and to model the molecular gas to quantify its properties. Details of the modeling and results are described, with comparisons to previous results and exploration of the implications for the gas excitation mechanisms. Among the findings, like for other galaxies, the nuclear and putative outflow molecular gas are well represented by components that are cool ($...

Glenn, Jason; Maloney, Philip R; Kamenetzky, Julia R

2015-01-01

261

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

262

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

263

Spectroscopic Study of Extended Star Clusters in Dwarf Galaxy NGC 6822  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

264

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

E-print Network

We present $^{12}$CO \\textit{J=3$\\rightarrow$2} maps of NGC 2976 and NGC 3351 obtained with the James Clerk Maxwell Telescope (JCMT), both early targets of the JCMT Nearby Galaxy Legacy Survey (NGLS). We combine the present observations with $^{12}$CO \\textit{J=1$\\rightarrow$0} data and find that the computed $^{12}$CO \\textit{J=3$\\rightarrow$2} to $^{12}$CO \\textit{J=1$\\rightarrow$0} line ratio ($R_{31}$) agrees with values measured in other NGLS field galaxies. We compute the M$_{\\rm{H_2}}$ value and find that it is robust against the value of $R_{31}$ used. Using \\textsc{Hi} data from the The \\textsc{Hi} Nearby Galaxy Survey (THINGS) survey, we find a tight correlation between surface density of H$_2$ and star formation rate density for NGC 3351 when $^{12}$CO \\textit{J=3$\\rightarrow$2} data are used. Finally, we compare the $^{12}$CO \\textit{J=3$\\rightarrow$2} intensity with the PAH 8 $\\mu$m surface brightness and find a good correlation in the high surface brightness regions. We extend this study to incl...

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

2013-01-01

265

On the origin of the Z-shaped narrow-line region in the Seyfert galaxy NGC 3516  

NASA Technical Reports Server (NTRS)

A kinematic study has been carried out of the line-emitting gas in the Seyfert galaxy NGC 3516. The existence of two curved filaments in the central 2.5 kpc of this galaxy, which give Z-shaped appearance to its NLR. A precessing twin-jet model in which the line-emitting material is entrained by a precessing radio jet and kept ionized by the nuclear ionization field can explain the kinematic data of the brightest emission rather well. If this model is valid, this would make NGC 3516 the least luminous known active galaxy with a precessing jet. An alternative scenario assumes that the curved inner filaments represent gas entrained by a radio jet which is deflected by ram pressure from the rotation interstellar medium of the galaxy.

Veilleux, Sylvain; Tully, R. B.; Bland-Hawthorn, Jonathan

1993-01-01

266

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

E-print Network

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

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

2008-11-11

267

Long-Lived Triaxiality in the Dynamically Old Elliptical Galaxy NGC 4365: A Limit on Chaos and Black Hole Mass  

Microsoft Academic Search

Supermassive black holes in the centres of giant elliptical galaxies are\\u000athought to induce chaos and eliminate triaxiality in their hosts. We address\\u000awhether this process operates in real systems, by modeling the stellar\\u000akinematics of the old elliptical NGC 4365. This galaxy has a mean stellar\\u000apopulation age > 12 Gyr and is known for its kinematically decoupled core

Thomas S. Statler; Eric Emsellem; Reynier F. Peletier; Roland Bacon

2004-01-01

268

Accurate Parameters of the Mass Distribution in Spiral Galaxies: 1. Fabry - Perot Observations of NGC 5585  

E-print Network

Using the example of the Sd galaxy NGC 5585, it is shown that high resolution 2-D HII kinematical data are necessary to determine accurately the parameters of the mass distribution in spirals. New CFHT Fabry-Perot Halpha observations are combined with low resolution (20") Westerbork HI data to study its mass distribution. Using the combined rotation curve and best fit models, it can be seen that M/L of the luminous disk goes from 0.3 using only the HI rotation curve, to 0.8 using both the optical and the radio data. This reduces the dark-to-luminous mass ratio in NGC 5585 by ~30% through increasing the dark matter halo core radius by nearly the same amount. This shows the importance of the inner, rising part of the rotation curve for the accurate determination of the parameters of the global mass (luminous & dark) distribution and suggests that such a fine tuning of the rotation velocities using high resolution 2-D HII kinematics is necessary to look at correlations between the parameters of the dark matter component and other properties of galaxies.

Sebastien Blais-Ouellette; Claude Carignan; Philippe Amram; Stephanie Cote

1999-11-12

269

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

NASA Astrophysics Data System (ADS)

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

Filippenko, Alex

2010-09-01

270

Accretion onto nearby supermassive black holes: Chandra constraints on the dominant cluster galaxy NGC 6166  

E-print Network

Chandra observations of low-luminosity supermassive black holes in nearby elliptical galaxies provide tight limits on both their nuclear luminosities and on their Bondi accretion rates. We examine Chandra constraints on NGC 6166, the dominant galaxy in the cluster Abell 2199, which hosts a \\sim 10^9 \\Msun black hole. We measure a nuclear X-ray luminosity L_{x} \\sim 10^{40} erg/s and show that the density and temperature profiles of the hot interstellar medium imply a Bondi accretion rate of Mdot_{Bondi} \\sim 3 10^{-2} Msun/yr. This accretion rate predicts a nuclear luminosity of \\sim 10^{44} erg/s for a canonical radiative efficiency of 10%. Unless the Bondi estimate is inappropriate and/or the accretion rate onto the black hole is significantly reduced, the observed nuclear flux constrains the radiative efficiency of the accretion flow to be \\eta \\sim 10^{-5}. We show that low-radiative efficiency accretion flows with radial density profiles \\rho \\approxpropto r^{-3/2} (and not significantly flatter) can explain the observed nuclear X-ray luminosity but that the power output from the jets in NGC 6166 is also important to the energetics of the system.

T. Di Matteo; R. M. Johnstone; S. W. Allen; A. C. Fabian

2000-12-09

271

A multi-wavelength study of the peculiar galaxy NGC 2976  

NASA Technical Reports Server (NTRS)

Researchers are currently studying NGC 2976 at many wavelengths to investigate the extent to which an interaction with M81 may have affected the star formation history of this galaxy. Here, researchers present observations of NGC 2976 made at 50 microns with the high resolution (CPC) instrument onboard Infrared Astronomy Satellite (IRAS) at 21-cm (both HI line and radio continuum) with the Westerbork Synthesis Radio Telescope (WSRT) and in the H alpha line with the Kitt Peak National Observatory (KPNO) 36 inch telescope. The far infrared emission is not centrally peaked as in other spirals (e.g., Wainscoat et al. 1987), but has obvious intensity peaks near the ends of the disk. The ionized gas as inferred from the H alpha observations, is largely confined to two large, symmetrically placed emission regions near the ends of the disk. Finally, the HI and 21-cm radio continuum emission also exhibit this strongly double-peaked structure. At all of the above wavelengths the emission peaks are roughly coincident and lie approx. 1.2 minutes to the NW and approx. 1.1 minutes to the SE of the optical center of this galaxy.

Tacconi, L. J.; Vanderhulst, J. M.; Wesselius, P. R.

1990-01-01

272

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

273

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

NASA Astrophysics Data System (ADS)

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

SAMI Galaxy Survey Team; GAMA Survey Team

2015-01-01

274

Circumnuclear Regions In Barred Spiral Galaxies. 1; Near-Infrared Imaging  

NASA Technical Reports Server (NTRS)

We present sub-arcsecond resolution ground-based near-infrared images of the central regions of a sample of twelve barred galaxies with circumnuclear star formation activity, which is organized in ring-like regions typically one kiloparsec in diameter. We also present Hubble Space Telescope near-infrared images of ten of our sample galaxies, and compare them with our ground-based data. Although our sample galaxies were selected for the presence of circumnuclear star formation activity, our broad-band near-infrared images are heterogeneous, showing a substantial amount of small-scale structure in some galaxies, and practically none in others. We argue that, where it exists, this structure is caused by young stars, which also cause the characteristic bumps or changes in slope in the radial profiles of ellipticity, major axis position angle, surface brightness and colour at the radius of the circumnuclear ring in most of our sample galaxies. In 7 out of 10 HST images, star formation in the nuclear ring is clearly visible as a large number of small emitting regions, organised into spiral arm fragments, which are accompanied by dust lanes. NIR colour index maps show much more clearly the location of dust lanes and, in certain cases, regions of star formation than single broad-band images. Circumnuclear spiral structure thus outlined appears to be common in barred spiral galaxies with circumnuclear star formation.

Perez-Ramirez, D.; Knapen, J. H.; Peletier, R. F.; Laine, S.; Doyon, R.; Nadeau, D.

2000-01-01

275

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

276

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

NASA Astrophysics Data System (ADS)

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

Galaxy Zoo; AEGIS; COSMOS; GOODS

2015-01-01

277

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

278

Survey of Water and Ammonia in Nearby galaxies (SWAN): Physical Conditions in NGC 253  

NASA Astrophysics Data System (ADS)

Nearby galaxies provide the vital link between local Galactic findings and integrated, galaxy-wide properties of star formation. We have observed four nearby star forming galaxies with the VLA in K and Ka bands, yielding a resolution on order of a few tens of parsecs. The sample spans a range of star formation rates and galactic environments. We present the first results from the nearby, prototypical starburst galaxy NGC 253. The K band observations cover ammonia inversion transitions from (1,1) to (5,5) in addition to the 22.3GHz water maser line with a resolution of ?63pc. Ammonia is a known temperature probe and traces gas densities greater than 102 cm-3. We observe relatively warm and uniform temperature distribution in the inner 0.5 kpc. The (3,3) line appears to be masing in the innermost 200 pc. Furthermore, we see indications of extended H20 maser components in the direction of the galactic outflow.

Gorski, Mark; Ott, Jüergen; Rand, Richard J.; Meier, David S.; Momjian, Emmanuel; Walter, Fabian

2015-01-01

279

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

NASA Technical Reports Server (NTRS)

Near- and far-IR data and mm-wave CO observations are used to study the star-forming properties of the Magellanic irregular galaxy NGC 4214 and its interstellar medium. The galaxy is forming stars at present at about 0.5-1 solar mass/yr in its central few arcmin, if the new stars follow the Salpeter initial mass function from 0.1 to 100 solar masses. This has been maintained for around a Hubble time, although some regions of the galaxy may undergo periods of enhanced and depressed star formation. Based on the mass of dust in emission at 160 microns, a plausible star formation efficiency of about 1.5 percent is estimated, if the H I gas does not take part in forming stars. Molecular masses derived using the H + 1 - 0 line and a conversion to M(H2) appropriate to spiral galaxies produces a mass estimate that is too low by a factor of five to ten.

Thronson, Harley A., Jr.; Greenhouse, Matthew; Hunter, Deidre A.; Telesco, C. M.; Harper, D. A.

1988-01-01

280

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

NASA Astrophysics Data System (ADS)

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

Davidge, T. J.

2015-01-01

281

Evidence of a Supermassive Black Hole in the Galaxy NGC 1023 From The Nuclear Stellar Dynamics  

NASA Technical Reports Server (NTRS)

We analyze the nuclear stellar dynamics of the SBO galaxy NGC 1023, utilizing observational data both from the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope and from the ground. The stellar kinematics measured from these long-slit spectra show rapid rotation (V equals approx. 70 km/s at a distance of O.1 deg = 4.9 pc from the nucleus) and increasing velocity dispersion toward the nucleus (where sigma = 295 +/- 30 km/s). We model the observed stellar kinematics assuming an axisymmetric mass distribution with both two and three integrals of motion. Both modeling techniques point to the presence of a central dark compact mass (which presumably is a supermassive black hole) with confidence > 99%. The isotropic two-integral models yield a best-fitting black hole mass of (6.0 +/- 0.4) x 10(exp 7) solar masses and mass-to-light ratio (M/L(sub v)) of 5.38 +/- 0.08, and the goodness-of-fit (CHI(exp 2)) is insensitive to reasonable values for the galaxy's inclination. The three-integral models, which non-parametrically fit the observed line-of-sight velocity distribution as a function of position in the galaxy, suggest a black hole mass of (3.9 +/- 0.4) x 10(exp 7) solar masses and M/L(sub v) of 5.56 +/- 0.02 (internal errors), and the edge-on models are vastly superior fits over models at other inclinations. The internal dynamics in NGC 1023 as suggested by our best-fit three-integral model shows that the velocity distribution function at the nucleus is tangentially anisotropic, suggesting the presence of a nuclear stellar disk. The nuclear line of sight velocity distribution has enhanced wings at velocities >= 600 km/s from systemic, suggesting that perhaps we have detected a group of stars very close to the central dark mass.

Bower, G. A.; Green, R. F.; Bender, R.; Gebhardt, K.; Lauer, T. R.; Magorrian, J.; Richstone, D. O.; Danks, A.; Gull, T.; Hutchings, J.

2000-01-01

282

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

283

FIREWORKS NEAR A BLACK HOLE IN THE CORE OF SEYFERT GALAXY NGC 4151  

NASA Technical Reports Server (NTRS)

The Space Telescope Imaging Spectrograph (STIS) simultaneously records, in unprecedented detail, the velocities of hundreds of gas knots streaming at hundreds of thousands of miles per hour from the nucleus of NGC 4151, thought to house a supermassive black hole. This is the first time the velocity structure in the heart of this object, or similar objects, has been mapped so vividly this close to its central black hole. The twin cones of gas emission are powered by the energy released from the supermassive black hole believed to reside at the heart of this Seyfert galaxy. The STIS data clearly show that the gas knots illuminated by one of these cones is rapidly moving towards us, while the gas knots illuminated by the other cone are rapidly receding. The images have been rotated to show the same orientation of NGC 4151. The figures show: WFPC2 (upper left) -- A Hubble Wide Field Planetary Camera 2 image of the oxygen emission (5007 Angstroms) from the gas at the heart of NGC 4151. Though the twin cone structure can be seen, the image does not provide any information about the motion of the oxygen gas. STIS OPTICAL (upper right) -- In this STIS spectral image of the oxygen gas, the velocities of the knots are determined by comparing the knots of gas in the stationary WFPC2 image to the horizontal location of the knots in the STIS image. STIS OPTICAL (lower right) -- In this false color image the two emission lines of oxygen gas (the weaker one at 4959 Angstroms and the stronger one at 5007 Angstroms) are clearly visible. The horizontal line passing through the image is from the light generated by the powerful black hole at the center of NGC 4151. STIS ULTRAVIOLET (lower left) -- This STIS spectral image shows the velocity distribution of the carbon emission from the gas in the core of NGC 4151. It requires more energy to make the carbon gas glow (CIV at 1549 Angstroms) than it does to ionize the oxygen gas seen in the other images. This means we expect that the carbon emitting gas is closer to the heart of the energy source. Credit: John Hutchings (Dominion Astrophysical Observatory), Bruce Woodgate (GSFC/NASA), Mary Beth Kaiser (Johns Hopkins University), Steven Kraemer (Catholic University of America), and the STIS Team. Image files in GIF and JPEG format and captions may be accessed on the Internet via anonymous ftp from ftp.stsci.edu in /pubinfo.

2002-01-01

284

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

285

Hubble space telescope observations of young star clusters in NGC-4038/4039, 'the antennae' galaxies  

NASA Technical Reports Server (NTRS)

New, high-resolution images of the disks of NGC 4038/4039 obtained with the Wide Field Camera of the Hubble Space Telescope (HST) are presented. NGC 4038/4039, nicknamed The Antennae, is a prototypical example of a pair of colliding galaxies believed to be at an early stage of a merger. Down to the limiting magnitude of V approximately 23 mag, the HST images reveal a population of over 700 blue pointlike objects within the disks. The mean absolute magnitude of these objects is M(sub V) = -11 mag, with the brightest objects reaching M(sub V) approximately -15. Their mean apparent color indices ar U - V = -0.7 mag and V - 1 = 0.8 mag on the Johnson UVI passband system, while their mean indices corrected for internal reddening are (u - v)(sub 0) = -1.0 mag and (V - I(sub 0) = 0.5. Their mean effective radius, determined from slightly resolved images, is 18 pc (for H(sub 0) = 50 km/s /Mpc). Based on their luminosities and resolution, most of these objects cannot be individual stars, but are likely young compact star clusters. The brighter ones are similar to the objects found in NGC 1275 and NGC 7252, which appear to be young globular clusters formed during recent galazy mergers. Based on their U - V and V - I colors, the brightest, bluest clusters of NGC 4038/4039 appear to be less than 10 Myr old. Most of these bright clusters are relatively tightly clustered themselves, with typically a dozen individual clusters belonging to a complex identified as a giant H II region from ground-based observations. The cluster luminosity function (LF) is approximately a power law, phi(L)dL proportional to L(exp -1.78+/-0.05)dL, with no hint of a turnover at fainter magnitudes. This power-law shape agrees with the LF of Magellanic Cloud clusters and Galactic open clusters, but differs from the LF of old globular cluster systems that is typically Gaussian with a Full Width at Half Maximum (FWHM) of approximately 3 mag. Besides the blue clusters, we also find about a dozen extremely red objects with V - I greater than 3.0. The highest number density of these red objects is found in the SE quadrant, where star formation appears to be most recent. We propose that these objects may be very young star clusters still embedded in their placental dust cocoons.

Whitmore, Bradley C.; Schweizer, Francois

1995-01-01

286

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

287

Circumnuclear Dust in Nearby Active and Inactive Galaxies. II. Bars, Nuclear Spirals, and the Fueling of Active Galactic Nuclei  

E-print Network

(Abridged) We present a detailed study of the relation between circumnuclear dust morphology, host galaxy properties, and nuclear activity in nearby galaxies. We use our sample of 123 nearby galaxies with visible--near-infrared colormaps from the Hubble Space Telescope to create well-matched, "paired" samples of 28 active and 28 inactive galaxies, as well as 19 barred and 19 unbarred galaxies, that have the same host galaxy properties. Comparison of the barred and unbarred galaxies shows that grand design nuclear dust spirals are only found in galaxies with a large-scale bar. Tightly wound nuclear dust spirals, in contrast, show a strong tendency to avoid galaxies with large-scale bars. Comparison of the AGN and inactive samples shows that nuclear dust spirals, which may trace shocks and angular momentum dissipation in the ISM, occur with comparable frequency in both active and inactive galaxies. The only difference between the active and inactive galaxies is that several inactive galaxies appear to completely lack dust structure in their circumnuclear region, while none of the AGN lack this structure. The comparable frequency of nuclear spirals in active and inactive galaxies, combined with previous work that finds no significant differences in the frequency of bars or interactions between well-matched active and inactive galaxies, suggests that no universal fueling mechanism for low-luminosity AGN operates at spatial scales greater than ~100 pc radius from the galactic nuclei. The similarities instead suggest that the lifetime of nuclear activity is less than the characteristic inflow time from these spatial scales. An order-of-magnitude estimate of this inflow time is the dynamical timescale. This sets an upper limit of several million years to the lifetime of an individual episode of nuclear activity.

Paul Martini; Michael W. Regan; John S. Mulchaey; Richard W. Pogge

2002-12-17

288

Regrowth of stellar disks in mature galaxies: The two component nature of NGC 7217 revisited with VIRUS-W† ?  

NASA Astrophysics Data System (ADS)

We have obtained high spectral resolution (R ~ 9000), integral field observations of the three spiral galaxies NGC 3521, NGC 7217 and NGC 7331 using the new fiber-based Integral Field Unit instrument VIRUS-W at the 2.7 m telescope of the McDonald Observatory in Texas. Our data allow us to revisit previous claims of counter rotation in these objects. A detailed kinematic decomposition of NGC 7217 shows that no counter rotating stellar component is present. We find that NGC 7217 hosts a low dispersion, rotating disk that is embedded in a high velocity dispersion stellar halo or bulge that is co-rotating with the disk. Due to the very different velocity dispersions (~ 20 km s-1 vs. 150 km s-1) , we are further able to perform a Lick index analysis on both components separately which indicates that the two stellar populations are clearly separated in (Mgb,) space. The velocities and dispersions of the faster component are very similar to those of the interstellar gas as measured from the [O iii] emission. Morphological evidence of active star formation in this component further suggests that NGC 7217 may be in the process of (re)growing a disk inside a more massive and higher dispersion stellar halo.

Fabricius, Maximilian H.; Coccato, Lodovico; Bender, Ralf; Drory, Niv; Gössl, Claus; Landriau, Martin; Saglia, Roberto P.; Thomas, Jens; Williams, Michael J.

2015-02-01

289

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

SciTech Connect

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

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

2012-08-10

290

Fabry-Perot Absorption-Line Spectroscopy of NGC 7079  

E-print Network

We report on absorption-line Fabry-Perot spectroscopy of the SB0 galaxy NGC 7079. Our data allow us to determine velocity and dispersion maps, which compare well with the results of slit observations. Our goals are to obtain a bar pattern speed and to determine the velocity ellipsoid as a function of radius; this is work in progress.

Victor P. Debattista; T. B. Williams

1999-09-17

291

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

292

HOT AND COLD GALACTIC GAS IN THE NGC 2563 GALAXY GROUP  

SciTech Connect

The role of environmentally induced gas stripping in driving galaxy evolution in groups remains poorly understood. Here we present extensive Chandra and Very Large Array mosaic observations of the hot and cold interstellar medium within the members of the nearby, X-ray bright NGC 2563 group, a prime target for studies of the role of gas stripping and interactions in relatively small host halos. Our observations cover nearly all group members within a projected radius of 1.15 Mpc ({approx}1.4 R{sub vir}) of the group center, down to a limiting X-ray luminosity and H I mass of 3 Multiplication-Sign 10{sup 39} erg s{sup -1} and 2 Multiplication-Sign 10{sup 8} M{sub Sun }, respectively. The X-ray data are consistent with efficient ram pressure stripping of the hot gas halos of early-type galaxies near the group core, but no X-ray tails are seen and the limited statistics preclude strong conclusions. The H I results suggest moderate H I mass loss from the group members when compared to similar field galaxies. Six of the 20 H I-detected group members show H I evidence of ongoing interactions with other galaxies or with the intragroup medium. Suggestive evidence is further seen for galaxies with close neighbors in position-velocity space to show relatively low H I content, consistent with tidal removal of H I. The results thus indicate removal of both hot and cold gas from the group members via a combination of ram pressure stripping and tidal interactions. We also find that 16 of the 20 H I detections occur on one side of the group, reflecting an unusual morphological segregation whose origin remains unclear.

Rasmussen, Jesper [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark); Bai, Xue-Ning [Department of Astrophysical Sciences, Peyton Hall, Princeton University, NJ 08544 (United States); Mulchaey, John S. [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Van Gorkom, J. H.; Lee, Duane [Department of Astronomy, Columbia University, Mail Code 5246, 550 West 120th Street, New York, NY 10027 (United States); Jeltema, Tesla E. [UCO/Lick Observatories, 1156 High Street, Santa Cruz, CA 95064 (United States); Zabludoff, Ann I. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Wilcots, Eric [Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter St., Madison, WI 53706 (United States); Martini, Paul [Department of Astronomy, 4055 McPherson Laboratory, Ohio State University, 140 West 18th Avenue, Columbus, OH (United States); Roberts, Timothy P., E-mail: jr@dark-cosmology.dk [Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom)

2012-03-01

293

Spitzer and JCMT Observations of the Active Galactic Nucleus in the Sombrero Galaxy (NGC 4594)  

E-print Network

We present Spitzer 3.6-160 micron images, Spitzer mid-infrared spectra, and JCMT SCUBA 850 micron images of the Sombrero Galaxy (NGC 4594), an Sa galaxy with a 10^9 M_solar low luminosity active galactic nucleus (AGN). The brightest infrared sources in the galaxy are the nucleus and the dust ring. The spectral energy distribution of the AGN demonstrates that, while the environment around the AGN is a prominent source of mid-infrared emission, it is a relatively weak source of far-infrared emission, as had been inferred for AGN in previous research. The weak nuclear 160 micron emission and the negligible polycyclic aromatic hydrocarbon emission from the nucleus also implies that the nucleus is a site of only weak star formation activity and the nucleus contains relatively little cool interstellar gas needed to fuel such activity. We propose that this galaxy may be representative of a subset of low ionization nuclear emission region galaxies that are in a quiescent AGN phase because of the lack of gas needed to fuel circumnuclear star formation and Seyfert-like AGN activity. Surprisingly, the AGN is the predominant source of 850 micron emission. We examine the possible emission mechanisms that could give rise to the 850 micron emission and find that neither thermal dust emission, CO line emission, bremsstrahlung emission, nor the synchrotron emission observed at radio wavelengths can adequately explain the measured 850 micron flux density by themselves. The remaining possibilities for the source of the 850 micron emission include a combination of known emission mechanisms, synchrotron emission that is self-absorbed at wavelengths longer than 850 microns, or unidentified spectral lines in the 850 micron band.

G. J. Bendo; B. A. Buckalew; D. A. Dale; B. T. Draine; R. D. Joseph; R. C. Kennicutt, Jr.; K. Sheth; J. -D. T. Smith; F. Walter; D. Calzetti; J. M. Cannon; C. W. Engelbracht; K. D. Gordon; G. Helou; D. Hollenbach; E. J. Murphy; H. Roussel

2006-03-07

294

A distance to the galaxy NGC4258 from observations of Cepheid variable stars.  

PubMed

Cepheid variable stars pulsate in a way that is correlated with their intrinsic luminosity, making them useful as 'standard candles' for determining distances to galaxies; the potential systematic uncertainties in the resulting distances have been estimated to be only 8-10%. They have played a crucial role in establishing the extragalactic distance scale and hence the value of the Hubble constant. Here we report observations of Cepheids in the nearby galaxy NGC4258; the distance calculated from the Cepheids is 8.1 +/- 0.4 Mpc, where the uncertainty does not include possible systematic errors. There is an independently determined geometric distance to this galaxy of 7.2 +/- 0.5 Mpc, based on the observed proper motions of water masers orbiting the central black hole; the distances differ by 1.3sigma. If the maser-based distance is adopted and the Cepheid distance scale revised accordingly, the derived value of the Hubble constant would increase by 12 +/- 9%, while the expansion age of the Universe would decrease by the same amount. PMID:16862105

Maoz, E; Newman, J A; Ferrarese, L; Stetson, P B; Zepf, S E; Davis, M; Freedman, W L; Madore, B F

1999-09-23

295

Advectively dominated flows in the cores of giant elliptical galaxies: application to M60 (NGC 4649)  

E-print Network

It has been suggested that the final stages of accretion in present--day giant elliptical galaxies occur in an advection-dominated mode. The poor radiative efficiency of this accretion solution accounts for the fact that massive black holes, which are believed to reside in the centres of these galaxies, do not have the luminosities expected if accretion from the hot interstellar medium occurs at the Bondi rate. We discuss the advection-dominated solution for the nucleus of M60 (NGC 4649) and show that accretion at the Bondi rate is consistent with the core flux from radio to X-ray. This solution allows for a black hole mass of ~ 10^9 solar masses as required by independent arguments. The successful application of this model to both M60, and previously to the well known nucleus of M87, suggests that accretion of hot gas in an elliptical galaxy creates the ideal circumstances for advection-dominated accretion flows to operate.

T. Di Matteo; A. C. Fabian

1997-03-12

296

H i observations of interacting galaxy pair NGC 4038/9  

NASA Astrophysics Data System (ADS)

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

Gordon, Scott; Koribalski, Bärbel; Jones, Keith

2001-09-01

297

Star Bursts in the UV Bright Interacting Galaxies NGC 3395 & 3396  

NASA Astrophysics Data System (ADS)

We have obtained ultraviolet and visible wavelength images for the interacting galaxies, NGC 3395 and 3396, using the Space Telescope Imaging Spectrograph on Hubble Space Telescope. IUE observations (Kinney et al. 1993) indicate that both of these galaxies have strong UV emission. Ground based spectra display evidence of extensive star formation. The visible images were obtained using the CCD detector and filter F28X50LP (central wavelength ~ 7230 Angstroms , FWHM ~ 1998 Angstroms). The ultraviolet images were obtained using the F25QTZ filter with the far-UV MAMA detector (central wavelength ~ 1595 Angstroms , FWHM ~ 206 Angstroms), and the F25CN182 filter with the near-UV MAMA detector (central wavelength ~ 2010 Angstroms, FWHM ~ 681 Angstroms). The data were reduced and analyzed using standard IRAF and STSDAS packages and customized software routines. This work has been supported in part by NASA, under contract NAS5-31231. We will present luminosities, luminosity functions, sizes and colors for the UV bright star forming regions. Stellar populations and ages of these knots will be constrained by comparison with star burst models (Leitherer et al. 1999). We will discuss the dependence of the characteristics of the knots on position in the galaxies and the possible relationship to the tidal interaction.

Hancock, M.; Weistrop, D.; Nelson, C. H.

2000-05-01

298

The structure of spiral galaxies - I. Near-infrared properties of bulges, discs and bars  

Microsoft Academic Search

We present data for a sample of 45 spiral galaxies over a range of Hubble types, imaged in the near-IR JK bands. Parameters are calculated describing the bulge, disc and bar K-band light distributions, and we look for correlations showing the interrelation between these components. We find that bulge profiles are not well-fitted by the classic de Vaucouleurs profile, and

M. S. Seigar; P. A. James

1998-01-01

299

Efficient star cluster formation in the core of a galaxy cluster: The dwarf irregular NGC 1427A in Fornax  

E-print Network

Gas-rich galaxies in dense environments such as galaxy clusters and massive groups are affected by a number of possible types of interactions with the cluster environment, which make their evolution radically different than that of field galaxies. The dIrr galaxy NGC 1427A, presently infalling towards the core of the Fornax galaxy cluster, offers a unique opportunity to study those processes in a level of detail not possible to achieve for galaxies at higher redshits. Using HST/ACS and auxiliary VLT/FORS ground-based observations, we study the properties of the most recent episodes of star formation in this gas-rich galaxy, the only one of its type near the core of the Fornax cluster. We study the structural and photometric properties of young star cluster complexes in NGC 1427A, identifying 12 bright such complexes with exceptionally blue colors. The comparison of our broadband near-UV/optical photometry with simple stellar population models yields ages below ~4x10^6 yr and stellar masses from a few thousand...

Mora, Marcelo D; Puzia, Thomas H

2014-01-01

300

On the Anomalous Silicate Absorption Feature of the Prototypical Seyfert 2 Galaxy NGC 1068  

E-print Network

The first detection of the silicate absorption feature in AGNs was made at 9.7 micrometer for the prototypical Seyfert 2 galaxy NGC 1068 over 30 years ago, indicating the presence of a large column of silicate dust in the line-of-sight to the nucleus. It is now well recognized that type 2 AGNs exhibit prominent silicate absorption bands, while the silicate bands of type 1 AGNs appear in emission. More recently, using the Mid-Infrared Interferometric Instrument on the Very Large Telescope Interferometer, Jaffe et al. (2004) by the first time spatially resolved the parsec-sized dust torus around NGC 1068 and found that the 10 micrometer silicate absorption feature of the innermost hot component exhibits an anomalous profile differing from that of the interstellar medium and that of common olivine-type silicate dust. While they ascribed the anomalous absorption profile to gehlenite (Ca_2Al_2SiO_7, a calcium aluminum silicate species), we propose a physical dust model and argue that, although the presence of gehl...

Koehler, Melanie

2012-01-01

301

Discovery of an obscured low luminosity active nucleus in the spiral galaxy NGC 4258  

NASA Technical Reports Server (NTRS)

The spectra and images of the nearby jet galaxy NGC 4258 (M106) obtained with ASCA indicate presence of several distinct X-ray emission components. The emission above 3 keV is pointlike and coincident in position with the optical nucleus, exhibiting a hard (photon index approximately 1.78) and absorbed N(sub H) approximately 1.5 x 10(exp 23) cm(exp -2) spectrum. This provides clear evidence that NGC 4258 hosts an obscured active nucleus of low luminosity, about 4 x 10(exp 40) ergs s(exp -1) in 2-10 keV after removing the absorption. Iron K-line emission with an equivalent width 0.25 +/- 0.10 keV was detected. The emission below 1 keV is dominated by an extended approximately 4 min thin-thermal component with a temperature approximately 0.5 keV exhibiting atomic emission lines, possibly associated with the jet. There exists a third continuum component with an intermediate spectral hardness, which is brightest at approximately 1 min south-east of the nucleus.

Makishima, Kazuo; Fujimoto, Ryuichi; Ishisaki, Yoshitaka; Kii, Tsuneo; Loewenstein, Michael; Mushotzky, Richard; Serlemitsos, Peter; Sonobe, Takashi; Tashiro, Makoto; Yaqoob, Tahir

1994-01-01

302

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

303

Chandra Observations of the Evening Core of the Starburst Galaxy NGC 253  

NASA Technical Reports Server (NTRS)

Chandra observations of the core of the nearby starburst galaxy NGC 253 reveal a heavily absorbed source of hard X-rays embedded within the nuclear starburst region. The source has an unabsorbed, 2 to 10 keV luminosity of greater than or equal to 10(exp 39) erg per s and photoionizes the surrounding gas. We observe this source through a dusty torus with a neutral absorbing column density of N(sub eta) approximately 2 x 10(exp 23)cm (exp -2). The torus is hundreds of pc across and collimates the starburst-driven nuclear outflow. We suggest that the ionizing source is an intermediate-mass black hole or a weakly accreting supermassive black hole, which may signal the beginnings or endings of AGN (active galactic nuclei) activity.

Weaver, K. A.; Heckman, T. M.; Dahlem, M.; White, Nicholas E. (Technical Monitor)

2002-01-01

304

Search for Obscured Nucleus in a Luminous IRAS Galaxy NGC 6240  

NASA Technical Reports Server (NTRS)

IRAS discovered very luminous objects which emit the vast majority of their radiation in the infrared wavelength. The energy source of such a tremendous amount of emission is not understood. Starburst and active galactic nuclei (AGN) are thought to be the origin of their power. X-ray observations are expected to be able to reveal the characteristics of the AGN component. However, some are very X-ray quiet, because the AGN is thought to be obscured by a large column density. In order to determine the primary luminosity of the nucleus, we need an X-ray observation with a wide energy band at least up to several tens of keV. We propose to observe NGC 6240, one of the luminous IRAS galaxies, to investigate the characteristics of its AGN, which must be obscured by large column density.

Leighly, Karen

1999-01-01

305

The dust SED in the dwarf galaxy NGC 1569: Indications for an altered dust composition?  

E-print Network

We discuss the interpretation of the dust SED from the mid-infrared to the millimeter range of NGC 1569. The model developed by D\\'esert et al. (1990) including three dust components (Polyaromatic Hydrocarbons, Very Small Grains and big grains) can explain the data using a realistic interstellar radiation field and adopting an enhanced abundance of VSGs. A simple three-temperature model is also able to reproduce the data but requires a very low dust temperature which is considered to be unlikely in this low-metallicity starburst galaxy. The high abundance of Very Small Grains might be due to large grain destruction in supernova shocks. This possibility is supported by ISO data showing that the emission at 14.3 $\\mu$m, tracing VSGs, is enhanced with respect to the emission at 6.7 $\\mu$m and 850 $\\mu$m in regions of high star formation.

U. Lisenfeld; F. P. Israel; J. Stil; A. Sievers; M. Haas

2004-12-17

306

Simulations of Bar-driven Evolution of Self-gravitating Gas Disks in Normal Galaxies  

NASA Astrophysics Data System (ADS)

In this report, we will show the results of our numerical simulations of a self-gravitating disk subject to a rotating bar force. Normally, spiral density waves are excited at three resonances in the disk, namely, the outer Lindblad resonance (OLR), the outer inner Lindblad resonance (OILR), and the inner inner Lindblad resonances (IILR). Associated with these waves are the angular momentum transports between the disk and the bar, and gas in the disk will redistribute accordingly. Gas accumulated near the OLR often becomes unstable and develops into chaos. Waves at different resonances can interact to form spiral-ring patterns. We will present the following simulations: (1) disk with the presence of all three resonances. (2) interaction between leading spirals excited at IILR and trailing spirals at OILR, (3) the chaotic pattern at OLR and the stable disk with high surface density near the center (OILR), and (4) simulation of waves driven a major bar, such as NGC5248. We use the high-order Godunov codes we developed, with FFT Poisson solver. The work is supported in parts by a Key Project of Academia Sinica and National Science Council grant 91-2112-M-011-070.

Yuan, C.; Yen, D. C. C.

2003-12-01

307

Chandra Evidence for a Flattened, Triaxial Dark Matter Halo in the Elliptical Galaxy NGC 720  

E-print Network

(Abridged) We present an analysis of a Chandra ACIS-S observation of the elliptical galaxy NGC 720 to verify the existence of a dark matter (DM) halo and to measure its ellipticity. The ACIS-S3 image reveals over 60 point sources. For semi-major axes a<~150" (18.2h_{70}^{-1} kpc) the ellipticity of the diffuse emission is ex ~0.15, which is less than the values 0.2-0.3 obtained from ROSAT because the point sources contaminated the ROSAT values. The Chandra data confirm the ~20 deg position angle (PA) twist discovered by ROSAT, but the Chandra twist is more gradual also because of the point sources contaminating the ROSAT values. Overall the ex and PA values for a<~150" can be explained by the triaxial model of NGC 720 published by Romanowsky & Kochanek. Since the optical image displays no substantial isophote twisting, the X-ray PA twist requires a massive DM halo if the hot gas is in hydrostatic equilibrium. The mass-follows-light hypothesis is also inconsistent with the Chandra ellipticities at the 96% (98%) level for oblate (prolate) symmetry. Thus, both the PA twist and the ellipticities of the Chandra image imply a DM halo independent of the gas T profile -- evidence that cannot be obviated by alternative gravity theories such as MOND. The DM density model, rho ~a^{-2}, provides the best fit and gives ellipticities of 0.37 +/- 0.03 (0.36 +/- 0.02) for oblate (prolate) models. These moderate ellipticities for the DM halo are inconsistent with both the nearly spherical halos predicted if the DM is self-interacting and with the highly flattened halos predicted if the DM is cold molecular gas. These ellipticities may also be too large to be explained by warm DM, but are consistent with galaxy-sized halos formed in the Lambda-CDM paradigm.

David A. Buote; Tesla E. Jeltema; Claude R. Canizares; Gordon P. Garmire

2002-05-28

308

Probing the Ionization Structure of the Narrow Line Region in the Seyfert 1 Galaxy NGC 4151  

E-print Network

We present a study of the distribution of [O III] $\\lambda$5007 and [O II] $\\lambda$3727 emission in the Narrow Line Region (NLR) of the Seyfert 1 galaxy NGC 4151. While the NLR of NGC 4151 exhibits an overall structure consistent with the unified model of Seyfert galaxies, narrow-band [O III] and [O II] images obtained with the Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope reveal significant emission from outside the the emission-line bi-cone. The [O III]/[O II] ratios are lower in these regions, consistent with a weaker ionizing flux. We performed a photoionization modeling analysis of the emission-line gas within a series of annuli, centered on the the central continuum source, with inner radii from 13 to 90 pc. The gas is ionized by radiation that has been attenuated by a relatively highly-ionized absorber (HABS), which completely covers the central source, and a lower-ionization absorber (LABS), which has a covering factor ranging from 0 to 1. We found that the [O III]/[O II] ratios are well fit by assuming that, within each segment of an annulus, some fraction of the NLR gas is completely within the shadow of LABS, while the rest is irradiated by the continuum filtered only by HABS. This suggests that the structure of the NLR is due to filtering of the ionizing radiation by ionized gas, consistent with disk-wind models. One possible scenario is that the low-ionization absorbers are dense knots of gas swept up by a wind.

S. B. Kraemer; H. R. Schmitt; D. M. Crenshaw

2008-02-22

309

Interaction between the intergalactic medium and central radio source in the NGC 4261 group of galaxies  

NASA Astrophysics Data System (ADS)

Using observations from the Chandra and XMM-Newton X-ray observatories, we examine the interaction between the intragroup medium and central radio source in the nearby NGC 4261 galaxy group. We confirm the presence of cavities associated with the radio lobes and estimate their enthalpy to be ˜2.4 × 1058 erg. The mechanical power output of the jets is ?1043 erg s-1, at least a factor of 60 greater than the cooling luminosity in the region the lobes inhabit. We identify rims of compressed gas enclosing the lobes, but find no statistically significant temperature difference between them and their surroundings, suggesting that the lobe expansion velocity is approximately sonic (?). The apparent pressure of the radio lobes, based on the synchrotron minimum energy density argument, is a factor of 5 lower than that of the intragroup medium. Pressure balance could be achieved if the entrainment of thermal gas provided additional non-radiating particles in the lobe plasma, but the energy required to heat these particles would be ˜20 per cent of the mechanical energy output of the radio source. NGC 4261 has a relatively compact cool core, which should probably be categorized as a galactic corona. The corona is capable of fuelling the active nucleus for considerably longer than the inferred source lifetime, but can be only inefficiently heated by the active galactic nucleus (AGN) or conduction. The expansion of the radio lobes has affected the structure of the gas in the galaxy, compressing and moving the material of the corona without causing significant shock heating, and expelling gas from the immediate neighbourhood of the jets. We discuss the possible implications of this environment for the duration of the AGN outburst and consider mechanisms which might lead to the cessation of nuclear activity.

O'Sullivan, E.; Worrall, D. M.; Birkinshaw, M.; Trinchieri, G.; Wolter, A.; Zezas, A.; Giacintucci, S.

2011-10-01

310

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

311

Dense gas in nearby galaxies: XV. Hot ammonia in NGC253, Maffei2 and IC342  

E-print Network

The detection of NH3 inversion lines up to the (J,K)=(6,6) level is reported toward the central regions of the nearby galaxies NGC253, Maffei2, and IC342. The observed lines are up to 406K (for (J,K)=(6,6)) and 848K (for the (9,9) transition) above the ground state and reveal a warm (T_kin= 100 - 140 K) molecular component toward all galaxies studied. The tentatively detected (J,K)=(9,9) line is evidence for an even warmer (>400K) component toward IC342. Toward NGC253, IC342 and Maffei2 the global beam averaged NH3 abundances are 1-2 10^-8, while the abundance relative to warm H2 is around 10^-7. The temperatures and NH3 abundances are similar to values found for the Galactic central region. C-shocks produced in cloud-cloud collisions can explain kinetic temperatures and chemical abundances. In the central region of M82, however, the NH3 emitting gas component is comparatively cool (~ 30K). It must be dense (to provide sufficient NH3 excitation) and well shielded from dissociating photons and comprises only a small fraction of the molecular gas mass in M82. An important molecular component, which is warm and tenuous and characterized by a low ammonia abundance, can be seen mainly in CO. Photon dominated regions (PDRs) can explain both the high fraction of warm H_2 in M82 and the observed chemical abundances.

R. Mauersberger; C. Henkel; A. Weiss; A. B. Peck; Y. Hagiwara

2003-03-12

312

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

313

Size and Properties of the NLR in the Seyfert-2 Galaxy NGC 1386  

E-print Network

We study the narrow-line region (NLR) of the Seyfert-2 galaxy NGC 1386 by means of long-slit spectroscopy obtained with FORS1 at the VLT. We use the galaxy itself for subtracting the stellar template, applying reddening corrections to fit the stellar template to the spectra of the NLR. The continuum gets steadily redder towards the nucleus. The spatial distribution of the reddening derived from the Balmer decrement differs from the continuum reddening, indicating dust within the NLR with a varying column density along the line of sight. Using spatially resolved spectral diagnostics, we find a transition between central line ratios falling into the AGN regime and outer ones in the HII-region regime, occuring at a radius of ~6 arcsec (310 pc) in all three diagnostic diagrams. Applying CLOUDY photoionisation models, we show that the observed distinction between HII-like and AGN-like ratios in NGC 1386 represents a true difference in ionisation source and cannot be explained by variations of physical parameters such as ionisation parameter, electron density or metallicity. We interpret it as a real border between the NLR, i.e. the central AGN-photoionised region and surrounding HII regions. We derive surface brightness, electron density, and ionisation parameter as a function of distance from the nucleus. Both the electron density and the ionisation parameter decrease with radius. We discuss the consequences of these observations for the interpretation of the empirical NLR size-luminosity relation. In the outer part of the NLR, we find evidence for shocks, resulting in a secondary peak of the electron-density and ionisation-parameter distribution north of the nucleus. We compare the NLR velocity curve with the stellar one and discuss the differences.

Nicola Bennert; Bruno Jungwiert; Stefanie Komossa; Martin Haas; Rolf Chini

2005-11-09

314

Models for Low-Mass X-Ray Binaries in the Elliptical Galaxies NGC 3379 and NGC 4278: Comparison with Observations  

NASA Astrophysics Data System (ADS)

We present theoretical models for the formation and evolution of populations of low-mass X-ray binaries (LMXBs) in the two elliptical galaxies NGC 3379 and NGC 4278. The models are calculated with the recently updated StarTrack code, assuming only a primordial galactic field LMXB population. StarTrack is an advanced population synthesis code that has been tested and calibrated using detailed binary star calculations and incorporates all the important physical processes of binary evolution. The simulations are targeted to modeling and understanding the origin of the X-ray luminosity functions (XLFs) of point sources in these galaxies. For the first time we explore the population XLF in luminosities below 1037 ergs s-1, as probed by the most recent observational results. We consider models for the formation and evolution of LMXBs in galactic fields with different CE efficiencies, stellar wind prescriptions, magnetic braking laws, and IMFs. We identify models that produce XLFs consistent with the observations both in shape and absolute normalization, suggesting that a primordial galactic field LMXB population can make a significant contribution to the total population of an elliptical galaxy. We also find that the treatment of the outburst luminosity of transient systems remains a crucial factor for the determination of the XLF, since the modeled populations are dominated by transient X-ray systems.

Fragos, T.; Kalogera, V.; Belczynski, K.; Fabbiano, G.; Kim, D.-W.; Brassington, N. J.; Angelini, L.; Davies, R. L.; Gallagher, J. S.; King, A. R.; Pellegrini, S.; Trinchieri, G.; Zepf, S. E.; Kundu, A.; Zezas, A.

2008-08-01

315

Dynamical studies of two common features in spiral galaxies: Bars and warps  

NASA Astrophysics Data System (ADS)

This thesis presents two new studies of different aspects of disk galaxy dynamics using high-quality N -body simulations. The first part of the thesis is a systematic study of the effects of central mass concentrations (CMCs) on bars. We find that bars are more robust than previously thought; the central mass has to be as large as several percent of the disk mass to completely destroy the bar on a short timescale. For a given mass, dense objects cause the greatest reduction in bar amplitude, while significantly more diffuse objects have a lesser effect. The bar is generally weakened by a CMC in two phases---the first phase of bar-weakening is due to the destruction by the CMC of lower-energy, bar-supporting orbits, while the second phase is a consequence of secular changes to the global potential which further diminish the number of bar-supporting orbits. We provide detailed phase-space and orbit analysis to support this suggestion. Our findings show that neither typical supermassive black holes in spirals nor typical central molecular gas concentrations should weaken the bar significantly within a Hubble time. In the second part of the thesis, we study galactic warps formed through an idealized form of cosmic infall onto a disk galaxy. We find warps that closely resemble those observed and are in agreement with Briggs (1990)'s rules. The inner disk tilts remarkably rigidly, indicating strong cohesion due to self- gravity. The line of nodes of the warp inside R 26.5 ~ 4.5 R d is straight, while that beyond R 26.5 generally forms a loosely-wound, leading spiral in agreement with Briggs's rules. We focus on the mechanism of the warp and show that the leading spiral arises from the torques from the misaligned inner disk and its associated inner oblate halo. The warp is not strongly damped by the halo because the precession rate of the inner disk is slow and the inner halo generally remains aligned with the inner disk. Thus warps formed this way can persist for a few Gyrs, by which time another infall event can be expected.

Shen, Juntai

2005-11-01

316

Contemporaneous observations of the radio galaxy NGC 1275 from radio to very high energy ?-rays  

NASA Astrophysics Data System (ADS)

Aims: The radio galaxy NGC 1275, recently identified as a very high energy (VHE, >100 GeV) ?-ray emitter by MAGIC, is one of the few non-blazar active galactic nuclei detected in the VHE regime. The purpose of this work is to better understand the origin of the ?-ray emission and locate it within the galaxy. Methods: We studied contemporaneous multifrequency observations of NGC 1275 and modeled the overall spectral energy distribution. We analyzed unpublished MAGIC observations carried out between October 2009 and February 2010, and the previously published observations taken between August 2010 and February 2011. We studied the multiband variability and correlations by analyzing data of Fermi-LAT in the 100 MeV-100 GeV energy band, as well as Chandra (X-ray), KVA (optical), and MOJAVE (radio) data taken during the same period. Results: Using customized Monte Carlo simulations corresponding to early MAGIC stereoscopic data, we detect NGC 1275 also in the earlier MAGIC campaign. The flux level and energy spectra are similar to the results of the second campaign. The monthly light curve above 100 GeV shows a hint of variability at the 3.6? level. In the Fermi-LAT band, both flux and spectral shape variabilities are reported. The optical light curve is also variable and shows a clear correlation with the ?-ray flux above 100 MeV. In radio, three compact components are resolved in the innermost part of the jet. One of these components shows a similar trend as the Fermi-LAT and KVA light curves. The ?-ray spectra measured simultaneously with MAGIC and Fermi-LAT from 100 MeV to 650 GeV can be well fitted either by a log-parabola or by a power-law with a subexponential cutoff for the two observation campaigns. A single-zone synchrotron-self-Compton model, with an electron spectrum following a power-law with an exponential cutoff, can explain the broadband spectral energy distribution and the multifrequency behavior of the source. However, this model suggests an untypical low bulk-Lorentz factor or a velocity alignment closer to the line of sight than the parsec-scale radio jet.

Aleksi?, J.; Ansoldi, S.; Antonelli, L. A.; Antoranz, P.; Babic, A.; Bangale, P.; Barres de Almeida, U.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Berger, K.; Bernardini, E.; Biland, A.; Blanch, O.; Bock, R. K.; Bonnefoy, S.; Bonnoli, G.; Borracci, F.; Bretz, T.; Carmona, E.; Carosi, A.; Carreto Fidalgo, D.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Caneva, G.; De Lotto, B.; Delgado Mendez, C.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Eisenacher, D.; Elsaesser, D.; Farina, E.; Ferenc, D.; Fonseca, M. V.; Font, L.; Frantzen, K.; Fruck, C.; García López, R. J.; Garczarczyk, M.; Garrido Terrats, D.; Gaug, M.; Giavitto, G.; Godinovi?, N.; González Muñoz, A.; Gozzini, S. R.; Hadamek, A.; Hadasch, D.; Herrero, A.; Hildebrand, D.; Hose, J.; Hrupec, D.; Idec, W.; Kadenius, V.; Kellermann, H.; Knoetig, M. L.; Krause, J.; Kushida, J.; La Barbera, A.; Lelas, D.; Lewandowska, N.; Lindfors, E.; Lombardi, S.; López, M.; López-Coto, R.; López-Oramas, A.; Lorenz, E.; Lozano, I.; Makariev, M.; Mallot, K.; Maneva, G.; Mankuzhiyil, N.; Mannheim, K.; Maraschi, L.; Marcote, B.; Mariotti, M.; Martínez, M.; Mazin, D.; Menzel, U.; Meucci, M.; Miranda, J. M.; Mirzoyan, R.; Moralejo, A.; Munar-Adrover, P.; Nakajima, D.; Niedzwiecki, A.; Nilsson, K.; Nowak, N.; Orito, R.; Overkemping, A.; Paiano, S.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Paredes-Fortuny, X.; Partini, S.; Persic, M.; Prada, F.; Prada Moroni, P. G.; Prandini, E.; Preziuso, S.; Puljak, I.; Reinthal, R.; Rhode, W.; Ribó, M.; Rico, J.; Rodriguez Garcia, J.; Rügamer, S.; Saggion, A.; Saito, T.; Saito, K.; Salvati, M.; Satalecka, K.; Scalzotto, V.; Scapin, V.; Schultz, C.; Schweizer, T.; Shore, S. N.; Sillanpää, A.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Spanier, F.; Stamatescu, V.; Stamerra, A.; Steinbring, T.; Storz, J.; Sun, S.; Suri?, T.; Takalo, L.; Tavecchio, F.; Terzi?, T.; Tescaro, D.; Teshima, M.; Thaele, J.; Tibolla, O.; Torres, D. F.; Toyama, T.; Treves, A.; Uellenbeck, M.; Vogler, P.; Wagner, R. M.; Zandanel, F.; Zanin, R.; MAGIC Collaboration; Balmaverde, B.; Kataoka, J.; Rekola, R.; Takahashi, Y.

2014-04-01

317

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

318

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

319

DETECTION OF A PSEUDOBULGE HIDDEN INSIDE THE 'BOX-SHAPED BULGE' OF NGC 4565  

SciTech Connect

Numerical simulations show that box-shaped bulges of edge-on galaxies are not bulges: they are bars seen side-on. Therefore, the two components that are seen in edge-on Sb galaxies such as NGC 4565 are a disk and a bar. But face-on SBb galaxies always show a disk, a bar, and a (pseudo)bulge. Where is the (pseudo)bulge in NGC 4565? We use archival Hubble Space Telescope H-band images and Spitzer Space Telescope 3.6 {mu}m wavelength images, both calibrated to Two Micron All Sky Survey K{sub s} band, to penetrate the prominent dust lane in NGC 4565. We find a high surface brightness, central stellar component that is clearly distinct from the boxy bar and from the disk. Its brightness profile is a Sersic function with index n = 1.55 {+-} 0.07 along the major axis and 1.33 {+-} 0.12 along the minor axis. Therefore, it is a pseudobulge. It is much less luminous than the boxy bar, so the true pseudobulge-to-total luminosity ratio of the galaxy is PB/T = 0.06 {+-} 0.01, much less than the previously believed value of B/T = 0.4 for the 'boxy bulge'. We infer that published B/T luminosity ratios of edge-on galaxies with boxy bulges have been overestimated. Therefore, more galaxies than we thought contain little or no evidence of a merger-built classical bulge. From a formation point of view, NGC 4565 is a giant, pure-disk galaxy. This presents a challenge to our picture of galaxy formation by hierarchical clustering: it is difficult to grow galaxies as big as NGC 4565 without also making big classical bulges.

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

2010-06-01

320

DWARFS GOBBLING DWARFS: A STELLAR TIDAL STREAM AROUND NGC 4449 AND HIERARCHICAL GALAXY FORMATION ON SMALL SCALES  

SciTech Connect

A candidate diffuse stellar substructure was previously reported in the halo of the nearby dwarf starburst galaxy NGC 4449 by Karachentsev et al. We map and analyze this feature using a unique combination of deep integrated-light images from the BlackBird 0.5 m telescope, and high-resolution wide-field images from the 8 m Subaru Telescope, which resolve the nebulosity into a stream of red giant branch stars, and confirm its physical association with NGC 4449. The properties of the stream imply a massive dwarf spheroidal progenitor, which after complete disruption will deposit an amount of stellar mass that is comparable to the existing stellar halo of the main galaxy. The stellar mass ratio between the two galaxies is {approx}1:50, while the indirectly measured dynamical mass ratio, when including dark matter, may be {approx}1:10-1:5. This system may thus represent a 'stealth' merger, where an infalling satellite galaxy is nearly undetectable by conventional means, yet has a substantial dynamical influence on its host galaxy. This singular discovery also suggests that satellite accretion can play a significant role in building up the stellar halos of low-mass galaxies, and possibly in triggering their starbursts.

Martinez-Delgado, David; Rix, Hans-Walter; Maccio, Andrea V. [Max-Planck-Institut fuer Astronomy, Heidelberg (Germany); Romanowsky, Aaron J.; Arnold, Jacob A.; Brodie, Jean P. [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Jay Gabany, R. [Black Bird Observatory, Mayhill, New Mexico (United States); Annibali, Francesca [Osservatorio Astronomico di Bologna, INAF, Via Ranzani 1, I-40127 Bologna (Italy); Fliri, Juergen [LERMA, CNRS UMR 8112, Observatoire de Paris, 61 Avenue de l'Observatoire, F-75014 Paris (France); Zibetti, Stefano [Dark Cosmology Centre, Niels Bohr Institute-University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark); Van der Marel, Roeland P.; Aloisi, Alessandra [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Chonis, Taylor S. [Department of Astronomy, University of Texas at Austin, Texas (United States); Carballo-Bello, Julio A. [Instituto de Astrofisica de Canarias, Tenerife (Spain); Gallego-Laborda, J. [Fosca Nit Observatory, Montsec Astronomical Park, Ager (Spain); Merrifield, Michael R. [School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom)

2012-04-01

321

Evidence of a Supermassive Black Hole in the Galaxy NGC 1023 from the Nuclear Stellar Dynamics  

E-print Network

We analyze the nuclear stellar dynamics of the SB0 galaxy NGC 1023, utilizing observational data both from the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope and from the ground. The stellar kinematics measured from these long-slit spectra show rapid rotation (V = 70 km/s at a distance of 0.1 arcsec = 4.9 pc from the nucleus) and increasing velocity dispersion toward the nucleus (where sigma = 295 +/- 30 km/s). We model the observed stellar kinematics assuming an axisymmetric mass distribution with both two and three integrals of motion. Both modeling techniques point to the presence of a central dark compact mass (which presumably is a supermassive black hole) with confidence > 99%. The isotropic two-integral models yield a best-fitting black hole mass of (6.0 +/- 1.4) x 10^7 M_sun and mass-to-light ratio (M/L_V) of 5.38 +/- 0.08, and the goodness-of-fit (chi^2) is insensitive to reasonable values for the galaxy's inclination. The three-integral models, which non-parametrically fit th...

Bower, G A; Bender, R; Gebhardt, K; Lauer, T R; Magorrian, J; Richstone, D O; Danks, A C; Gull, T R; Hutchings, J B; Joseph, C L; Kaiser, M E; Weistrop, D; Woodgate, B; Nelson, C; Malumuth, E M

2001-01-01

322

Star formation and dust obscuration in the tidally distorted galaxy NGC 2442  

E-print Network

Abridged: We present a detailed investigation of the morphological distribution and level of star formation and dust obscuration in the nearby tidally distorted galaxy NGC2442. Spitzer images in the IR at 3.6, 4.5, 5.8, 8.0um, and 24um and GALEX images at 1500\\AA{} and 2300\\AA{} allow us to resolve the galaxy on scales between 240-600pc. We supplement these with archival data in the B, J, H, and K bands. We use the 8um, 24um and FUV (1500\\AA) emission to study the star formation rate (SFR). We find that globally, these tracers of star formation give a range of results of ~6-11\\msun/yr, 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 SMC extinction curves. However, the regions of 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 g...

Pancoast, Anna; Lacy, Mark; Noriega-Crespo, Alberto; Rho, Jeonghee

2010-01-01

323

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

324

The dynamics of the bulge dominated galaxy NGC 7814 in MOND  

NASA Astrophysics Data System (ADS)

Context. The bulge dominated galaxy NGC 7814 provides one of the strongest dynamical tests possible for MOdified Newtonian Dynamics (MOND). Spitzer 3.6 ?m photometry fixes the bulge parameterisation and strongly constrains the properties of the subdominant stellar disk. Furthermore, the distance is known to better than 5%, virtually eliminating it as a free parameter. The rotation curve is easily measured, since the H I (and stellar) disks are edge on, and both the receding and approaching sides agree very well. Aims: We explore the agreement between the model and observed rotation curves in MOND given that the only two free parameters available are the mass-to-light ratios of the bulge and disk. Methods: We use a grid based MOND Poisson solver that accurately solves for the MOND gravity and produces our model rotation curves from a given mass distribtion. The input to the Poisson solver is a 3D distribution of N particles which is generated from modelling the observed distribution of stars and gas in the galaxy. Results: By ensuring a superior fit to the radial surface brightness profile than previous works, by virtue of a double Sérsic fit to the bulge, we were able to produce excellent fits to the rotation curve with typical values for both mass-to-light ratios. Conclusions: The model rotation curve of a mass distribution in MOND is extremely sensitive to the bulge-disk decomposition and even slight deviation from the observed mass distribution can produce large differences in the model rotation curve.

Angus, G. W.; van der Heyden, K. J.; Diaferio, A.

2012-07-01

325

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

326

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

NASA Technical Reports Server (NTRS)

We discuss the morphology and excitation of ionized gas in the nearby Sc galaxy NGC 3079. The almost edge-on orientation is ideal for studying the vertical structure of the gaseous disk, and especially the diffuse ionized medium (DIM) found between the bright H II regions. We used the Hawaii Imaging Fabry-Perot Interferometer (HIFI) to map 150,000 H-alpha + (N II) lambda lambda 6548, 6583 emission-line profiles across the entire disk, with resolution 70 km/s at subarcsecond steps, down to a flux level of approximately 10(exp -17) ergs/s/sq cm (EM approximately equal to 4 cm(exp -6) pc). The DIM contributes approximately 30% of the total disk H-alpha emission within a radius of 10 kpc. The DIM has broader emission lines and larger (N II) H-alpha flux ratios than the adjacent H II regions. Within a radius of 5 kpc, we find that the X-shaped filaments reported in previous studies emerge from the inner (R approximately equal to 1.5 kpc) disk, and rise more than 4 kpc above the disk plane. The morphology, kinematics, and excitation of the filaments suggest that they form a biconic interface between the undisturbed disk gas, and gas entrained in the wide-angle outflow. The DIM beyond 5 kpc radius is more vertically extended than the thick ionized disk detected in our Galaxy and in a few nearby edge-on systems. After correcting for dust, the vertical profile of this DIM has an exponential scale height of about 1.1 kpc, similar to that of the H I disk. The (N II) lambda 6538/H-alpha flux ratio of the DIM increases monotonically with vertical height, reaching unity for absolute value of z greater than or approximately equal to 2.5 kpc. The flux required to keep the DIM ionized at R = 8 kpc is similar to that near the solar circle of our Galaxy. Highly dilute radiation from O stars in the galactic plane probably maintains the DIM. The total mass of the DIM is of order 10(exp 8) - 10(exp 9) solar mass, representing less than 1% of the total dynamical mass of NGC 3079. Mechanical energy from intense star formation in the disk probably lifts the DIM above the disk. The several bubbles and filaments within 1 kpc of the disk plane is direct evidence for gas flow between the disk and halo.

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

1995-01-01

327

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

328

Accretion-Inhibited Star Formation in the Warm Molecular Disk of the Green-valley Elliptical Galaxy NGC 3226?  

NASA Astrophysics Data System (ADS)

We present archival Spitzer photometry and spectroscopy and Herschel photometry of the peculiar "Green Valley" elliptical galaxy NGC 3226. The galaxy, which contains a low-luminosity active galactic nucleus (AGN), forms a pair with NGC 3227 and is shown to lie in a complex web of stellar and H I filaments. Imaging at 8 and 16 ?m reveals a curved plume structure 3 kpc in extent, embedded within the core of the galaxy and coincident with the termination of a 30 kpc long H I tail. In situ star formation associated with the infrared (IR) plume is identified from narrowband Hubble Space Telescope (HST) imaging. The end of the IR plume coincides with a warm molecular hydrogen disk and dusty ring containing 0.7-1.1 × 107 M ? detected within the central kiloparsec. Sensitive upper limits to the detection of cold molecular gas may indicate that a large fraction of the H2 is in a warm state. Photometry derived from the ultraviolet (UV) to the far-IR shows evidence for a low star-formation rate of ~0.04 M ? yr–1 averaged over the last 100 Myr. A mid-IR component to the spectral energy distribution (SED) contributes ~20% of the IR luminosity of the galaxy, and is consistent with emission associated with the AGN. The current measured star formation rate is insufficient to explain NGC 3226's global UV-optical "green" colors via the resurgence of star formation in a "red and dead" galaxy. This form of "cold accretion" from a tidal stream would appear to be an inefficient way to rejuvenate early-type galaxies and may actually inhibit star formation.

Appleton, P. N.; Mundell, C.; Bitsakis, T.; Lacy, M.; Alatalo, K.; Armus, L.; Charmandaris, V.; Duc, P.-A.; Lisenfeld, U.; Ogle, P.

2014-12-01

329

Molecular Gas in Candidate Double-Barred Galaxies II. Cooler, Less Dense Gas Associated with Stronger Central Concentrations  

E-print Network

We have performed a multi-transition CO study of the centers of seven double-barred galaxies that exhibit a variety of molecular gas morphologies to determine if the molecular gas properties are correlated with the nuclear morphology and star forming activity. Near infrared galaxy surveys have revealed the existence of nuclear stellar bars in a large number of barred or lenticular galaxies. High resolution CO maps of these galaxies exhibit a wide range of morphologies. Recent simulations of double-barred galaxies suggest that variations in the gas properties may allow it to respond differently to similar gravitational potentials. We find that the 12CO J=3-2/J=2-1 line ratio is lower in galaxies with centrally concentrated gas distributions and higher in galaxies with CO emission dispersed around the galactic center in rings and peaks. The 13CO/12CO J=2-1 line ratios are similar for all galaxies, which indicates that the J=3-2/J=2-1 line ratio is tracing variations in gas temperature and density, rather than variations in optical depth. There is evidence that the galaxies which contain more centralized CO distributions are comprised of molecular gas that is cooler and less dense. Observations suggest that the star formation rates are higher in the galaxies containing the warmer, denser, less centrally concentrated gas. It is possible that either the bar dynamics are responsible for the variety of gas distributions and densities (and hence the star formation rates) or that the star formation alone is responsible for modifying the gas properties.

Glen Petitpas; Christine Wilson

2003-01-07

330

Triggering and Feedback: The Relation between the HI Gas and the Starburst in the Dwarf Galaxy NGC 1569  

E-print Network

As part of our study on the impact of violent star formation on the interstellar medium (ISM) of dwarf galaxies, we report observations of neutral atomic hydrogen (HI) in the post-starburst dwarf galaxy NGC 1569. High-resolution measurements with the VLA (B-, C- and D-array) are aimed at identifying morphological and kinematical signatures in the HI caused by the starburst. Our kinematical data suggest a huge hole in the HI distribution, probably due to the large number of supernovae explosions in the center of the galaxy over the past 20 Myr. Investigating the large-scale HI structure, we confirm the existence of a possible HI companion and a so-called HI bridge east of NGC 1569. Furthermore, we report the detection of additional low-intensity HI halo emission, which leads us to suggest a revised halo structure. Based on the new picture, we discuss the origin of the halo gas and possible implications for the evolution of the starburst in NGC 1569.

S. Muehle; U. Klein; E. M. Wilcots; S. Huettemeister

2005-04-10

331

THE TWO-PHASE FORMATION HISTORY OF SPIRAL GALAXIES TRACED BY THE COSMIC EVOLUTION OF THE BAR FRACTION  

SciTech Connect

We study the evolution of galactic bars and the link with disk and spheroid formation in a sample of zoom-in cosmological simulations. Our simulation sample focuses on galaxies with present-day stellar masses in the 10{sup 10}-10{sup 11} M{sub Sun} range, in field and loose group environments, with a broad variety of mass growth histories. In our models, bars are almost absent from the progenitors of present-day spirals at z > 1.5, and they remain rare and generally too weak to be observable down to z Almost-Equal-To 1. After this characteristic epoch, the fractions of observable and strong bars rise rapidly, bars being present in 80% of spiral galaxies and easily observable in two thirds of these at z {<=} 0.5. This is quantitatively consistent with the redshift evolution of the observed bar fraction, although the latter is presently known up to z Almost-Equal-To 0.8 because of band-shifting and resolution effects. Our models hence predict that the decrease in the bar fraction with increasing redshift should continue with a fraction of observable bars not larger than 10%-15% in disk galaxies at z > 1. Our models also predict later bar formation in lower-mass galaxies, in agreement with existing data. We find that the characteristic epoch of bar formation, namely redshift z Almost-Equal-To 0.8-1 in the studied mass range, corresponds to the epoch at which today's spirals acquire their disk-dominated morphology. At higher redshift, disks tend to be rapidly destroyed by mergers and gravitational instabilities and rarely develop significant bars. We hence suggest that the bar formation epoch corresponds to the transition between an early 'violent' phase of spiral galaxy formation at z {>=} 1 and a late 'secular' phase at z {<=} 0.8. In the secular phase, the presence of bars substantially contributes to the growth of the (pseudo-)bulge, but the bulge mass budget remains statistically dominated by the contribution of mergers, interactions, and disk instabilities at high redshift. Early bars at z > 1 are often short-lived, while most of the bars formed at z {<=} 1 persist down to z = 0, late cosmological gas infall being necessary to maintain some of them.

Kraljic, Katarina; Bournaud, Frederic [Laboratoire AIM Paris-Saclay, CEA/IRFU/SAp, CNRS/INSU, Universite Paris Diderot, 91191 Gif-sur-Yvette Cedex (France); Martig, Marie [Centre for Astrophysics and Supercomputing, Swinburne University of Technology, P.O. Box 218, Hawthorn, VIC 3122 (Australia)

2012-09-20

332

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

333

The radio emission from the ultraluminous far-infrared galaxy NGC 6240  

NASA Technical Reports Server (NTRS)

We present new radio observations of the 'prototypical' ultraluminous far-infrared galaxy NGC 6240, obtained using the Very Large Array (VLA) at lambda = 20 cm in B-configuration and at lambda = 3.6 cm in A-configuration. These data, along with those from four previous VLA observations, are used to perform a comprehensive study of the radio emission from NGC 6240. Approximately 70% (approximately 3 x 10(exp 23) W/Hz) of the total radio power at 20 cm originates from the nuclear region (approximately less than 1.5 kpc), of which half is emitted by two unresolved (R approximately less than 36 pc) cores and half by a diffuse component. The radio spectrum of the nuclear emission is relatively flat (alpha approximately equals 0.6; S(sub nu) proportional to nu(exp -alpha). The supernova rate required to power the diffuse component is consistent with that predicted by the stellar evolution models of Rieke et al. (1985). If the radio emission from the two compact cores is powered by supernova remnants, then either the remnants overlap and form hot bubbles in the cores, or they are very young (approximately less than 100 yr.) Nearly all of the remaining 30% of the total radio power comes from an 'armlike' region extending westward from the nuclear region. The western arm emission has a steep spectrum (alpha approximately equals 1.0), suggestive of aging effects from synchrotron or inverse-Compton losses, and is not correlated with starlight; we suggest that it is synchrotron emission from a shell of material driven by a galactic superwind. Inverse Compton scattering of far-infrared photons in the radio sources is expected to produce an X-ray flux of approximately 2 - 6 x 10(exp -14) ergs/s/sq cm in the 2 - 10 keV band. No significant radio emission is detected from or near the possible ultramassive 'dark core'.

Colbert, Edward J. M.; Wilson, Andrew S.; Bland-Hawthorn, Jonathan

1994-01-01

334

Can Spiral Arms Affect Star Formation in Nuclear Rings of Barred-spiral Galaxies?  

NASA Astrophysics Data System (ADS)

We use hydrodynamic simulations to study star formation occurring in nuclear rings of barred-spiral galaxies in the presence of outer spiral arms. We find that spiral arms can drive gas toward the bar region from outside only if the arms rotate more slowly than the bar. The inflowing gas enhances the surface density in dust lanes as well as the star formation rate (SFR) in the nuclear ring at late time. The enhanced ring-SFR is larger by a factor of ?3–20 than in no-arm counterpart. The total stellar mass formed is larger for models with stonger and/or slower-rotating arms. On the other hand, spiral arms rotating faster than the bar do not affect the ring star formation much. When the SFR is large, star formation is distributed throughout the ring, with no appreciable age gradient of star clusters in the azimuthal direction. When the SFR is low, on the other hand, star formation occurs preferentially in the the contact points between the dust lanes and the ring, exhibiting an azimuthal age gradient.

Seo, Woo-Young; Kim, Woong-Tae

2015-01-01

335

THE HST/ACS COMA CLUSTER SURVEY. VIII. BARRED DISK GALAXIES IN THE CORE OF THE COMA CLUSTER  

SciTech Connect

We use high-resolution ({approx}0.''1) F814W Advanced Camera for Surveys (ACS) images from the Hubble Space Telescope ACS Treasury survey of the Coma cluster at z {approx} 0.02 to study bars in massive disk galaxies (S0s), as well as low-mass dwarf galaxies in the core of the Coma cluster, the densest environment in the nearby universe. Our study helps to constrain the evolution of bars and disks in dense environments and provides a comparison point for studies in lower density environments and at higher redshifts. Our results are: (1) we characterize the fraction and properties of bars in a sample of 32 bright (M{sub V} {approx}< -18, M{sub *} > 10{sup 9.5} M{sub Sun }) S0 galaxies, which dominate the population of massive disk galaxies in the Coma core. We find that the measurement of a bar fraction among S0 galaxies must be handled with special care due to the difficulty in separating unbarred S0s from ellipticals, and the potential dilution of the bar signature by light from a relatively large, bright bulge. The results depend sensitively on the method used: the bar fraction for bright S0s in the Coma core is 50% {+-} 11%, 65% {+-} 11%, and 60% {+-} 11% based on three methods of bar detection, namely, strict ellipse fit criteria, relaxed ellipse fit criteria, and visual classification. (2) We compare the S0 bar fraction across different environments (the Coma core, A901/902, and Virgo) adopting the critical step of using matched samples and matched methods in order to ensure robust comparisons. We find that the bar fraction among bright S0 galaxies does not show a statistically significant variation (within the error bars of {+-}11%) across environments which span two orders of magnitude in galaxy number density (n {approx} 300-10,000 galaxies Mpc{sup -3}) and include rich and poor clusters, such as the core of Coma, the A901/902 cluster, and Virgo. We speculate that the bar fraction among S0s is not significantly enhanced in rich clusters compared to low-density environments for two reasons. First, S0s in rich clusters are less prone to bar instabilities as they are dynamically heated by harassment and are gas poor as a result of ram pressure stripping and accelerated star formation. Second, high-speed encounters in rich clusters may be less effective than slow, strong encounters in inducing bars. (3) We also take advantage of the high resolution of the ACS ({approx}50 pc) to analyze a sample of 333 faint (M{sub V} > -18) dwarf galaxies in the Coma core. Using visual inspection of unsharp-masked images, we find only 13 galaxies with bar and/or spiral structure. An additional eight galaxies show evidence for an inclined disk. The paucity of disk structures in Coma dwarfs suggests that either disks are not common in these galaxies or that any disks present are too hot to develop instabilities.

Marinova, Irina; Jogee, Shardha; Weinzirl, Tim [Department of Astronomy, University of Texas at Austin, Austin, TX (United States); Erwin, Peter [Max-Planck-Insitut fuer extraterrestrische Physik, Giessenbachstrasse, 85748 Garching (Germany); Trentham, Neil [Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA (United Kingdom); Ferguson, Henry C.; Goudfrooij, Paul [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Hammer, Derek [Department of Physics and Astronomy, Johns Hopkins, Baltimore, MD 21218 (United States); Den Brok, Mark; Peletier, Reynier F.; Kleijn, Gijs V. [Kapteyn Astronomical Institute, University of Groningen, Groningen (Netherlands); Graham, Alister W. [Centre for Astrophysics and Supercomputing, Swinburne University, Hawthorn (Australia); Carter, David; Mouhcine, Mustapha [Astrophysics Research Institute, Liverpool John Moores University, Birkenhead (United Kingdom); Balcells, Marc [Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife (Spain); Guzman, Rafael; Hoyos, Carlos [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Mobasher, Bahram [Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States); Peng, Eric W., E-mail: marinova@astro.as.utexas.edu, E-mail: sj@astro.as.utexas.edu [Department of Astronomy, Peking University, Beijing 100871 (China)

2012-02-20

336

Formation of young boxy/peanut bulges in ringed barred galaxies  

NASA Astrophysics Data System (ADS)

Aims: We investigate whether the formation mechanism of boxy and peanut-shaped (B/PS) bulges could depend on the gas content of the galaxy. Methods: We have performed N-body simulations with and without a gaseous component. In the second case star formation/feedback recipes have also been implemented to create new stellar populations. Results: As in many previous studies, in our N-body collisionless simulation, the B/PS is due to the classical break in the z mirror symmetry lasting roughly 200 Myr. When a gaseous component and star formation recipes are added to the simulation, the bulge-growing mechanism is quite different. The young stellar population that is born in the thin gaseous disc rapidly populates vertical resonant orbits triggered by the combined effects of the linear horizontal and vertical ILRs. This leads to a B/PS bulge mainly made of stellar material younger than the surrounding population. The non-linear analysis of the orbital structure shows that the main orbit family responsible for the B/PS is not the same in the two cases. The 2:2:1 orbits prevail in the collisionless simulation whereas additional asymmetrical families contribute to the B/PS if a dissipative component is present and can form new stars. We found that 2:3:1 and 2:5:1 orbits trap a significant fraction of the mass. A flat ringed discy stellar component also appears simultaneously with the thickening of the young population. It is due to the star formation in a nuclear gaseous disc located in the central kpc, inside the ILR, and accumulated there by the torques exerted by the large-scale bar. Remarkably, it remains flat throughout the simulation although it develops a nuclear bar, leading to a double-barred galaxy. Conclusions: We predict that two populations of B/PS bulges could exist and even coexist in the same galaxy.

Wozniak, H.; Michel-Dansac, L.

2009-01-01

337

The Nature of Infrared Emission in the Local Group Dwarf Galaxy NGC 6822 as Revealed by Spitzer  

NASA Astrophysics Data System (ADS)

We present Spitzer imaging of the metal-deficient (Z~=30% Zsolar) Local Group dwarf galaxy NGC 6822. On spatial scales of ~130 pc, we study the nature of IR, H?, H I, and radio continuum emission. Nebular emission strength correlates with IR surface brightness; however, roughly half of the IR emission is associated with diffuse regions not luminous at H? (as found in previous studies). The global ratio of dust to H I gas in the ISM, while uncertain at the factor of ~2 level, is ~25 times lower than the global values derived for spiral galaxies using similar modeling techniques; localized ratios of dust to H I gas are about a factor of 5 higher than the global value in NGC 6822. There are strong variations (factors of ~10) in the relative ratios of H? and IR flux throughout the central disk; the low dust content of NGC 6822 is likely responsible for the different H?/IR ratios compared to those found in more metal-rich environments. The H? and IR emission is associated with high column density (>~1021 cm-2) neutral gas. Increases in IR surface brightness appear to be affected by both increased radiation field strength and increased local gas density. Individual regions and the galaxy as a whole fall within the observed scatter of recent high-resolution studies of the radio-far-IR correlation in nearby spiral galaxies; this is likely the result of depleted radio and far-IR emission strengths in the ISM of this dwarf galaxy.

Cannon, John M.; Walter, Fabian; Armus, Lee; Bendo, George J.; Calzetti, Daniela; Draine, Bruce T.; Engelbracht, Charles W.; Helou, George; Kennicutt, Robert C., Jr.; Leitherer, Claus; Roussel, Hélène; Bot, Caroline; Buckalew, Brent A.; Dale, Daniel A.; de Blok, W. J. G.; Gordon, Karl D.; Hollenbach, David J.; Jarrett, Thomas H.; Meyer, Martin J.; Murphy, Eric J.; Sheth, Kartik; Thornley, Michele D.

2006-12-01

338

The Nature of Infrared Emission in the Local Group Dwarf Galaxy NGC 6822 As Revealed by Spitzer  

E-print Network

We present Spitzer imaging of the metal-deficient (Z ~30% Z_sun) Local Group dwarf galaxy NGC 6822. On spatial scales of ~130 pc, we study the nature of IR, H alpha, HI, and radio continuum emission. Nebular emission strength correlates with IR surface brightness; however, roughly half of the IR emission is associated with diffuse regions not luminous at H alpha (as found in previous studies). The global ratio of dust to HI gas in the ISM, while uncertain at the factor of ~2 level, is ~25 times lower than the global values derived for spiral galaxies using similar modeling techniques; localized ratios of dust to HI gas are about a factor of five higher than the global value in NGC 6822. There are strong variations (factors of ~10) in the relative ratios of H alpha and IR flux throughout the central disk; the low dust content of NGC 6822 is likely responsible for the different H alpha/IR ratios compared to those found in more metal-rich environments. The H alpha and IR emission is associated with high-column density (> ~1E21 cm^-2) neutral gas. Increases in IR surface brightness appear to be affected by both increased radiation field strength and increased local gas density. Individual regions and the galaxy as a whole fall within the observed scatter of recent high-resolution studies of the radio-far IR correlation in nearby spiral galaxies; this is likely the result of depleted radio and far-IR emission strengths in the ISM of this dwarf galaxy.

John M. Cannon; Fabian Walter; Lee Armus; George J. Bendo; Daniela Calzetti; Bruce T. Draine; Charles W. Engelbracht; George Helou; Robert C. Kennicutt Jr.; Claus Leitherer; Helene Roussel; Caroline Bot; Brent Buckalew; Daniel A. Dale; W. J. G. de Blok; Karl D. Gordon; David J. Hollenbach; Thomas H. Jarrett; Martin J. Meyer; Eric J. Murphy; Kartik Sheth; Michele D. Thornley

2006-08-11

339

Establishing the connection between peanut-shaped bulges and galactic bars  

NASA Technical Reports Server (NTRS)

It has been suggested that the peanut-shaped bulges seen in some edge-on disk galaxies are due to the presence of a central bar. Although bars cannot be detected photometrically in edge-on galaxies, we show that barred potentials produce a strong kinematic signature in the form of double-peaked line-of-sight velocity distributions with a characteristic 'figure-of-eight' variation with radius. We have obtained spectroscopic observations of two edge-on galaxies with peanut-shaped bulges (NGC 5746 and NGC 5965), and they reveal exactly such line-of-sight velocity distributions in both their gaseous (emission line) and their stellar (absorption line) components. These observations provide strong observational evidence that peanut-shaped bulges are a by-product of bar formation.

Kuijken, Konrad; Merrifield, Michael R.

1995-01-01

340

Box/Peanut and Bar structures in edge-on and face-on SDSS nearby galaxies I. Catalogue  

E-print Network

We investigate Box/Peanut and bar structures in image data of edge-on and face-on nearby galaxies taken from SDSS (Sloan Digital Sky Survey) to present catalogues containing the surface brightness parameters and the morphology classification. About 1700 edge-on galaxies and 2600 face-on galaxies are selected from SDSS DR7 in g, r and i-band. The images of each galaxy are fitted with the model of 2-dimensional surface brightness of S\\'{e}rsic bulge and exponential disk. After removing some irregular data, Box/Peanut, bar and other structures are easily distinguished by eye using residual (observed minus model) images. We find 292 Box/Peanut structures in the 1329 edge-on samples and 630 bar structures in 1890 face-on samples in i-band, after removing some irregular data. Then the fraction of Box/Peanut galaxies is about 22 percent against the edge-on samples, and that of bar is about 33 percent (about 50 percent if 629 elliptical galaxies are removed) against the face-on samples. Furthermore the strengths of t...

Yoshino, Akira

2014-01-01

341

The Cepheid distance to the maser-host galaxy NGC 4258: Studying systematics with the Large Binocular Telescope  

E-print Network

We identify and phase a sample of 81 Cepheids in the maser-host galaxy NGC 4258 using the Large Binocular Telescope (LBT), and obtain calibrated mean magnitudes in up to 4 filters for a subset of 43 Cepheids using archival HST data. We employ 3 models to study the systematic effects of extinction, the assumed extinction law, and metallicity on the Cepheid distance to NGC 4258. We find a correction to the Cepheid colors consistent with a grayer extinction law in NGC 4258 compared to the Milky Way ($R_V =4.9$), although we believe this is indicative of other systematic effects. If we combine our Cepheid sample with previously known Cepheids, we find a significant metallicity adjustment to the distance modulus of $\\gamma_1 = -0.60 \\pm 0.21$ mag/dex, for the Zaritsky et al. (1994) metallicity scale, as well as a weak trend of Cepheid colors with metallicity. Conclusions about the absolute effect of metallicity on Cepheid mean magnitudes appear to be limited by the available data on the metallicity gradient in NGC...

Fausnaugh, M M; Gerke, J R; Macri, L M; Riess, A G; Stanek, K Z

2014-01-01

342

Co Observations of Edge-on Galaxies. IV, NGC 4565: Radial Variation of the H2-to-Hi Ratio  

E-print Network

The edge-on galaxy NGC 4565 has been observed in the 12CO(J=1-0)-line emission using the Nobeyama 45-m telescope with an angular resolution of 15". We obtained a scan along the major axis for +/-5' (+/- 15 kpc) about the galactic center, and some scans perpendicular to the galactic plane. The radial density distribution shows a dense molecular gas ring of 5 kpc radius, which is associated with an HI ring. The molecular disk comprises two components: an unresolved thin and dense disk, and a thick disk (or a halo) extending to a height greater than 1.4 kpc. The position-velocity diagram shows that the general rotation of the entire galaxy is circular with a flat rotation curve. However, the radial distribution of molecular gas is asymmetric with respect to the galaxy center in the sense that the molecular gas is much richer in the NW side. We derived a radial variation of \\htwo-to-(HI+ \\htwo) density ratio, and found that int erstellar gas in the central 4 kpc region is almost entirely H2, while HI is dominant beyond 10 kpc. A similar HI-vs-\\htwo\\ behavior was found in the edge-on galaxy NGC 891.

Y. Sofue; N. Nakai

1993-08-31

343

Contemporaneous observations of the radio galaxy NGC 1275 from radio to very high energy gamma-rays  

E-print Network

The radio galaxy NGC 1275, recently identified as a very high energy (VHE, >100 GeV) gamma-ray emitter by MAGIC, is one of the few non-blazar AGN detected in the VHE regime. In order to better understand the origin of the gamma-ray emission and locate it within the galaxy, we study contemporaneous multi-frequency observations of NGC 1275 and model the overall spectral energy distribution (SED). We analyze unpublished MAGIC observations carried out between Oct. 2009 and Feb. 2010, and the already published ones taken between Aug. 2010 and Feb. 2011. We study the multi-band variability and correlations analyzing data of Fermi-LAT (0.1 - 100 GeV), Chandra (X-ray), KVA (optical) and MOJAVE (radio) taken during the same period. Using custom Monte Carlo simulations corresponding to early MAGIC stereo data, we detect NGC 1275 also in the earlier MAGIC campaign. The flux level and energy spectra are similar to the results of the second campaign. The monthly light curve above 100 GeV shows a hint of variability at the...

Aleksi?, J; Antonelli, L A; Antoranz, P; Babic, A; Bangale, P; de Almeida, U Barres; Barrio, J A; González, J Becerra; Bednarek, W; Berger, K; Bernardini, E; Biland, A; Blanch, O; Bock, R K; Bonnefoy, S; Bonnoli, G; Borracci, F; Bretz, T; Carmona, E; Carosi, A; Fidalgo, D Carreto; Colin, P; Colombo, E; Contreras, J L; Cortina, J; Covino, S; Da Vela, P; Dazzi, F; De Angelis, A; De Caneva, G; De Lotto, B; Mendez, C Delgado; Doert, M; Domínguez, A; Prester, D Dominis; Dorner, D; Doro, M; Einecke, S; Eisenacher, D; Elsaesser, D; Farina, E; Ferenc, D; Fonseca, M V; Font, L; Frantzen, K; Fruck, C; López, R J García; Garczarczyk, M; Terrats, D Garrido; Gaug, M; Giavitto, G; Godinovi?, N; Muñoz, A González; Gozzini, S R; Hadamek, A; Hadasch, D; Herrero, A; Hildebrand, D; Hose, J; Hrupec, D; Idec, W; Kadenius, V; Kellermann, H; Knoetig, M L; Krause, J; Kushida, J; La Barbera, A; Lelas, D; Lewandowska, N; Lindfors, E; Lombardi, S; López, M; López-Coto, R; López-Oramas, A; Lorenz, E; Lozano, I; Makariev, M; Mallot, K; Maneva, G; Mankuzhiyil, N; Mannheim, K; Maraschi, L; Marcote, B; Mariotti, M; Martínez, M; Mazin, D; Menzel, U; Meucci, M; Miranda, J M; Mirzoyan, R; Moralejo, A; Munar-Adrover, P; Nakajima, D; Niedzwiecki, A; Nilsson, K; Nowak, N; Orito, R; Overkemping, A; Paiano, S; Palatiello, M; Paneque, D; Paoletti, R; Paredes, J M; Paredes-Fortuny, X; Partini, S; Persic, M; Prada, F; Moroni, P G Prada; Prandini, E; Preziuso, S; Puljak, I; Reinthal, R; Rhode, W; Ribó, M; Rico, J; Garcia, J Rodriguez; Rügamer, S; Saggion, A; Saito, K; Salvati, M; Satalecka, K; Scalzotto, V; Scapin, V; Schultz, C; Schweizer, T; Shore, S N; Sillanpää, A; Sitarek, J; Snidaric, I; Sobczynska, D; Spanier, F; Stamatescu, V; Stamerra, A; Steinbring, T; Storz, J; Sun, S; Suri?, T; Takalo, L; Tavecchio, F; Temnikov, P; Terzi?, T; Tescaro, D; Teshima, M; Thaele, J; Tibolla, O; Torres, D F; Toyama, T; Treves, A; Uellenbeck, M; Vogler, P; Wagner, R M; Zandanel, F; Zanin, R; Balmaverde, B; Kataoka, J; Rekola, R; Takahashi, Y; .,

2013-01-01

344

Witness of gas infall and outflow in the young starburst dwarf galaxy NGC 5253  

NASA Astrophysics Data System (ADS)

We present 12CO(2-1) observations towards the dwarf galaxy NGC 5253 using the Submillimeter Array. The data shows that a large amount of molecular gas is located in the central ˜ 200 pc starburst region, physically associated with two young super stellar clusters (SSCs). The molecular gas traced by 12CO(2-1) is elongated along the minor axis (dust lane) of the galaxy and its kinematics suggest that there is an inflow of molecular gas to the direction of the central SSCs, as is also observed in H I gas at a larger scale. Due to their correlation in spatial and velocity domains, the central SSCs were likely formed from molecular gas in the nucleus. We compare the 12CO(2-1) with available H2 1-0 S(1) data, and show that while the relatively cold gas traced by 12CO(2-1) is distributed around the central starburst region but also along the dust lane, the warm gas traced by H2 1-0 S(1) is associated with the central H II region and other star-forming regions. Interestingly, a cavity in the H2 1-0 S(1) emission is found to be spatially correlated with a H? shell. This H? shell may trace a bipolar outflow from the central SSCs and the H2 1-0 S(1) gas, the gas shocked by the outflow encountering the surrounding quiescent gas. We calculate a molecular gas inflow rate of ˜ 2 M? yr-1, a star formation rate of 0.3-0.5 M? yr-1, and an ionized gas outflow being emitted from the SSCs with a rate of (5-25)× 10-3 f M? yr-1, where f is a volume filling factor.

Miura, Rie E.; Espada, Daniel; Sugai, Hajime; Nakanishi, Kouichiro; Hirota, Akihiko

2014-12-01

345

Variations of the ultraviolet Fe II and Balmer continuum emission in the Seyfert galaxy NGC 5548  

NASA Technical Reports Server (NTRS)

We present measurements of the Balmer continuum/Fe II emission blend between 2160 and 4130 A in the Seyfert galaxy NGC 5548. The measurements are from spectra obtained as part of the combined space-based and ground-based monitoring program of this object in 1988-1989. An iterative scheme is used to determine and subtract the continuum emission underlying the emission blend so as to obtain a light curve sampled once every four days. The small blue bump is an important component of the emission-line cooling, constituting about one third of the line flux in this object. Its flux varies with an amplitude of approximately +/- 20 percent about the mean, similar to the amplitude of the Balmer line variations during the same period. Its light curve resembles that of Ly-alpha, with a lag of about 10 days behind the continuum variations. The bump variation amplitude is independent of the wavelength interval where it is measured, which indicates that both the Balmer continuum and Fe II emission have comparable variation amplitudes. These results suggest that the Fe II UV multiplets and the Balmer continuum are emitted in the same parts of the broad-line region as most other broad emission lines in this object.

Maoz, D.; Netzer, H.; Peterson, B. M.; Bechtold, J.; Bertram, R.; Bochkarev, N. G.; Carone, T. E.; Dietrich, M.; Filippenko, A. V.; Kollatschny, W.

1993-01-01

346

The Twisting X-ray Isophotes of the Elliptical Galaxy NGC 720  

E-print Network

We present spatial analysis of the deep (57ks) ROSAT HRI X-ray image of the E4 galaxy NGC 720. The orientation of the HRI surface brightness is consistent with the optical position angle $(PA)$ interior to semi-major axis $a\\sim 60\\arcsec$ (optical $R_e\\sim 50\\arcsec$). For larger $a$ the isophotes twist and eventually $(a\\gtrsim 100\\arcsec)$ orient along a direction consistent with the $PA$ measured with the PSPC data (Buote & Canizares 1994) -- the $\\sim 30\\arcdeg$ twist is significant at an estimated 99% confidence level. We argue that this twist is not the result of projected foreground and background sources, ram pressure effects, or tidal distortions. If spheroidal symmetry and a nearly isothermal hot gas are assumed, then the azimuthally averaged radial profile displays features which, when combined with the observed $PA$ twist, are inconsistent with the simple assumptions that the X-ray emission is due either entirely to hot gas or to the combined emission from hot gas and discrete sources. We discuss possible origins of the $PA$ twist and radial profile features (e.g., triaxiality).

David A. Buote; Claude R. Canizares

1996-01-10

347

X-ray-emitting gas surrounding the spiral galaxy NGC 891  

NASA Technical Reports Server (NTRS)

We observed the edge-on spiral galaxy NGC 891 with the Position Sensitive Proportional Counter (PSPC) on Roentgen Satellite (ROSAT) to search for how extraplanar gas expected in the galactic fountain model. Diffuse X-ray emission surrounds the disk with a Half Width at Half Maximum (HWHM) for the surface brightness perpendicular to the disk of 50 sec (2.4 kpc) and a radial extent of approximately 6.5 kpc, both of which are similar in extent to the extended H(alpha) and radio halo component; the implied density scale height for the hot gas is 7 kpc. The spectrum is best fitted with a hard stellar component and a soft diffuse gas component of temperature 3.6 x 10(exp 6) K. The density of this gas is 2 x 10(exp -3)/cu cm, the luminosity is 4.4 x 10(exp 39) ergs/s, the mass is 1 x 10(exp 8) solar mass, and the pressure (P/k) is 1.4 10(exp 4) K/cu cm. These data are consistent with this gas participating in a galactic fountain, where the material approaches hydrostatic equilibrium before cooling at a rate of 0.12 solar mass/yr. The cooled material may be responsible for some of the H(alpha) emission.

Bregman, Joel N.; Pidis, Rachel A.

1994-01-01

348

Kinematics of the Nuclear Ionized Gas in the Radio Galaxy M84 (NGC 4374)  

E-print Network

We present optical long-slit spectroscopy of the nucleus of the nearby radio galaxy M84 (NGC 4374 = 3C 272.1) obtained with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST). Our spectra reveal that the nuclear gas disk seen in WFPC2 imaging by Bower et al. (1997, ApJ, 483, L33) is rotating rapidly. The velocity curve has an S-shape with a peak amplitude of 400 km/s at 0.1" = 8 pc from the nucleus. To model the observed gas kinematics, we construct a thin Keplerian disk model that fits the data well if the rotation axis of the gas disk is aligned with the radio jet axis. These models indicate that the gas dynamics are driven by a nuclear compact mass of 1.5 x 10^9 Msun with an uncertainty range of (0.9 - 2.6) x 10^9 Msun and that the inclination of the disk with respect to the plane of the sky is 75 - 85 degrees. Of this nuclear mass, only <= 2 x 10^7 Msun can possibly be attributed to luminous mass. Thus, we conclude that a dark compact mass (most likely a supermassive black hole) resides in the nucleus of M84.

G. A. Bower; R. F. Green

1997-10-23

349

Inconsistencies of the photoionized model for the broad line region in the Seyfert galaxy NGC 7469  

NASA Astrophysics Data System (ADS)

We present a study of ultraviolet and optical spectra of the active galaxy NGC 7469 taken as part of the International AGN Watch database. We have measured the CIV/L?, L?/H? and H?/H? line ratios across the line profiles. The modeling of the observed line ratios has been done with the photoionization code CLOUDY in two variants, with and without taking into account the turbulence in the Broad Line Region (BLR).The comparison of the observed and theoretical emission shows that there are problems with both variants. The observed line ratios can be accounted for by two systems of clouds without turbulence. One corresponds to the high-ionization line (HIL) zone with an electron density n_{e} ? 10^{9-11} cm^{-3}. It is presumably located above the accretion disk. The other system corresponds to the low-ionization line (LIL) zone which is probably the inner part of the accretion disk and which has a high electron density, n_{e}?10^{12.5 - 13} cm^{-3}

Nazarova, L. S.; Bochkarev, N. G.

350

Beryllium in turnoff stars of NGC6397: early Galaxy spallation, cosmochronology and cluster formation  

E-print Network

We present the first detection of beryllium in two turnoff stars of the old, metal-poor globular cluster NGC 6397. The beryllium lines are clearly detected and we determine a mean beryllium abundance of log(Be/H)=-12.35 +/- 0.2. The beryllium abundance is very similar to that of field stars of similar Fe content. We interpret the beryllium abundance observed as the result of primary spallation of cosmic rays acting on a Galactic scale, showing that beryllium can be used as a powerful cosmochronometer for the first stellar generations. With this method, we estimate that the cluster formed 0.2-0.3 Gyr after the onset of star formation in the Galaxy, in excellent agreement with the age derived from main sequence fitting. From the same spectra we also find low O (noticeably different for the two stars) and high N abundances, suggesting that the original gas was enriched in CNO processed material. Our beryllium results, together with the N, O, and Li abundances, provide insights on the formation of this globular cluster, showing that any CNO processing of the gas must have occurred in the protocluster cloud before the formation of the stars we observe now. We encounter, however, difficulties in giving a fully consistent picture of the cluster formation, able to explain the complex overall abundance pattern.

L. Pasquini; P. Bonifacio; S. Randich; D. Galli; R. G. Gratton

2004-07-26

351

Sub-arcsecond Radio Observations of the Dwarf Starburst Galaxy NGC 3077  

E-print Network

We present the first sub-arcsecond radio observations of the nearby dwarf starburst galaxy NGC 3077 obtained with the MERLIN interferometer. We have detected two resolved sources which are coincident with the positions of two discrete X-ray sources detected by Chandra. One of the radio sources is associated with a supernova remnant and the observed radio flux is consistent with having a non-thermal origin. The age of the SNRs of about 760 years is between the average age of the SNRs detected in M82 and those detected in the Milky Way and the Large Magellanic Cloud. We use this detection to calculate a star formation rate (SFR) of 0.28 M_sun year-1 which is similar to the SFR calculated by using far infrared and millimeter observations but larger than the SFR given by optical recombination lines corrected for extinction. The other compact radio source detected by MERLIN which is coincident with the position of an X-ray binary, has the properties of an HII region with a flux density of about 747 microJy which corresponds to an ionizing flux of 6.8x10^50 s-1. A young massive stellar cluster with a mass of about 2x10^5 M_sun, detected by the Hubble Space Telescope could be the responsible for the production of the ionizing flux.

Daniel Rosa-Gonzalez

2005-10-04

352

THE NEAR VICINITY OF THE BLACK HOLE AT THE CORE OF GALAXY NGC 4261 - ARTIST CONCEPT  

NASA Technical Reports Server (NTRS)

This is an illustration of how the night sky might look to a dweller in the core of galaxy NGC 4261, which harbors an 800-light-year-wide disk of dust and 1.2 billion-solar-mass black hole. This imaginary view is from a hypothetical pl