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1

Multiband Images of the Barred Galaxy NGC 1097  

Microsoft Academic Search

We present B, V, R, J, H, and K broadband images of the barred galaxy NGC 1097. The optical and infrared colors maps trace the location of the major dust features. The dust lanes are relatively free of star formation and have low opacity. The depth of the dust lanes decreases as a function of wavelength so that they are

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

1995-01-01

2

MultiBand Images of the Barred Galaxy NGC 1097  

Microsoft Academic Search

We present $B,V,R,J,H,K$ broad--band images of the barred galaxy NGC 1097.\\u000aThe optical and infrared colors maps trace the location of the major dust\\u000afeatures. The dust lanes are relatively free of star formation and have low\\u000aopacity. The depth of the dust lanes decreases as a function of wavelength so\\u000athat they are deepest at $B$ and shallower at

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

1995-01-01

3

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

4

Molecular Cloud Content of Early-Type Galaxies. 4. A Molecular Bar in NGC 4691.  

National Technical Information Service (NTIS)

Observations of the (12)CO J=1-0 and J=2-1 emission in the SB0 galaxy NGC 4691 show a prominent molecular bar. Deconvolution using Lucy rectification and the method of 'Simulated Annealing' reveal that the molecular emission is distributed in several clou...

T. Wiklind, C. Henkel, L. J. Sage

1993-01-01

5

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

E-print Network

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

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

1998-12-09

6

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

NASA Astrophysics Data System (ADS)

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

Brière, É.; Cantin, S.; Spekkens, K.

2012-09-01

7

The NIR structure of the barred galaxy NGC253 from VISTA  

E-print Network

[abridged] We used J and Ks band images acquired with the VISTA telescope as part of the science verification to quantify the structures in the stellar disk of the barred Sc galaxy NGC253. 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. From the Ks image we obtain a new measure of the deprojected 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. From the deprojected length of the bar, we establish the corotation radius (R_CR=3 kpc) and bar pattern speed (Omega_b = 61.3 km /s kpc), 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 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 formatio...

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

2014-01-01

8

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

9

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

SciTech Connect

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

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

2011-06-10

10

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

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

11

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

12

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

SciTech Connect

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

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

2011-12-15

13

New insights into the X-ray properties of the nearby barred spiral galaxy NGC 1672  

E-print Network

We present some preliminary results from new Chandra and XMM-Newton X-ray observations of the nearby barred spiral galaxy NGC1672. It shows dramatic nuclear and extra-nuclear star formation activity, including starburst regions located near each end of its strong bar, both of which host ultraluminous X-ray sources (ULXs). With the new high-spatial-resolution Chandra imaging, we show for the first time that NGC1672 possesses a faint ($L(X)~10^39 erg/s), hard central X-ray source surrounded by an X-ray bright circumnuclear starburst ring that dominates the X-ray emission in the region. The central source may represent low-level AGN activity, or alternatively the emission from X-ray binaries associated with star-formation in the nucleus.

L. P. Jenkins; W. N. Brandt; E. J. M. Colbert; A. J. Levan; T. P. Roberts; M. J. Ward; A. Zezas

2008-01-15

14

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

E-print Network

We present CO(1-0) and CO(2-1) maps of the interacting barred LINER/Seyfert 2 galaxy NGC 3627 obtained with the IRAM interferometer at resolutions of 2.1" x 1.3" and 0.9" x 0.6", respectively. The molecular gas emission shows a nuclear peak, an elongated bar-like structure of ~18" (~900 pc) diameter in both CO maps and, in CO(1-0), a two-arm spiral feature from r~9" (~450 pc) to r~16" (~800 pc). The inner ~18" bar-like structure, with a north/south orientation (PA = 14{\\deg}), forms two peaks at the extremes of this elongated emission region. The kinematics of the inner molecular gas shows signatures of non-circular motions associated both with the 18" bar-like structure and the spiral feature detected beyond it. The 1.6 micron H-band 2MASS image of NGC 3627 shows a stellar bar with a PA = -21{\\deg}, different from the PA (= 14{\\deg}) of the CO bar-like structure, indicating that the gas is leading the stellar bar. The torques computed with the HST-NICMOS F160W image and our PdBI maps are negative down to the...

Casasola, V; Combes, F; Garcia-Burillo, S; Neri, R

2011-01-01

15

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

Microsoft Academic Search

We present 12CO(1-0) and 12CO(2-1) maps of the interacting barred LINER\\/Seyfert 2 galaxy NGC 3627 obtained with the IRAM interferometer at resolutions of 2.1 arcsec × 1.3 arcsec and 0.9 arcsec × 0.6 arcsec, respectively. We also present single-dish IRAM 30 m 12CO(1-0) and 12CO(2-1) observations used to compute short spacings and complete interferometric measurements. These observations are complemented by

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

2011-01-01

16

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

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

17

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

18

PHYSICAL PROPERTIES OF THE CIRCUMNUCLEAR STARBURST RING IN THE BARRED GALAXY NGC 1097  

SciTech Connect

We report high-resolution {sup 12}CO(J = 2-1), {sup 13}CO(J = 2-1), and {sup 12}CO(J = 3-2) imaging of the Seyfert 1/starburst ring galaxy NGC 1097 with the Submillimeter Array for the purpose of studying the physical and kinematic properties of the 1 kpc circumnuclear starburst ring. Individual star clusters as detected in the Hubble Space Telescope map of Pa{alpha} line emission have been used to determine the star formation rate (SFR), and are compared with the properties of the molecular gas. The molecular ring has been resolved into individual clumps at the giant molecular cloud association (GMA) scale of 200-300 pc in all three CO lines. The intersection between the dust lanes and the starburst ring, which is associated with the orbit-crowding region, is resolved into two physically/kinematically distinct features in the 1.''5 x 1.''0 (105 x 70 pc) {sup 12}CO(J = 2-1) map. The clumps associated with the dust lanes have broader line widths, higher surface gas densities, and lower SFRs, while the narrow line clumps associated with the starburst ring have opposite characteristics. A Toomre-Q value lower than unity at the radius of the ring suggests that the molecular ring is gravitationally unstable to fragmentation at GMA scale. The line widths and surface density of the gas mass of the clumps show an azimuthal variation related to the large-scale dynamics. The SFR, on the other hand, is not significantly affected by the dynamics, but has a correlation with the intensity ratio of {sup 12}CO (J = 3-2) and {sup 12}CO(J = 2-1), which traces the denser gas associated with star formation. Our resolved CO map, especially in the orbit-crowding region, observationally demonstrates for the first time that the physical/kinematic properties of GMAs are affected by the large-scale bar-potential dynamics in NGC 1097.

Hsieh, Pei-Ying [Institute of Astrophysics, National Central University, No. 300, Jhongda Road, Jhongli City, Taoyuan County 32001, Taiwan (China); Matsushita, Satoki; Ho, Paul T. P.; Wu, Ya-Lin [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan (China); Liu, Guilin [Astronomy Department, University of Massachusetts, Amherst, MA 01003 (United States); Oi, Nagisa, E-mail: pyhsieh@asiaa.sinica.edu.tw [Department of Astronomy, School of Science, Graduate University for Advanced Studies, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)

2011-08-01

19

Bars and Warps traced by the Molecular Gas in the Seyfert 2 Galaxy NGC 1068  

E-print Network

We present new interferometer observations of the 12CO(1-0) and 12CO(2-1) line emission of NGC 1068 with a resolution of 0.7''. The molecular gas in the inner 5'' is resolved into a ring with two bright knots east and west of the nuclear continuum emission. For the first time in NGC 1068, we can trace molecular gas at ~0.18'' (13pc) from the nucleus. The high velocities in this region imply an enclosed mass of ~10^8 M_solar. This value is consistent with a black hole mass of 1.7x10^7 M_solar plus a contribution from a compact nuclear stellar cluster. Perpendicular to the kinematic major axis optical images of NGC1068 show a bright, stellar, oval structure of eccentricity 0.8 and a deprojected length of 17kpc. Analysis of the rotation curve shows the CO spiral arms are at the inner Lindblad resonance of this bar-like structure. Inside the molecular spiral arms the CO kinematic axis changes direction probably in response to the 2.5kpc (deprojected) long stellar bar seen in the near infrared (NIR). The low veloc...

Schinnerer, E; Tacconi, L J; Genzel, R; Downes, D

1999-01-01

20

NGC 4340: Double Bar + Fossil Nuclear Ring  

E-print Network

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

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

2000-09-12

21

Bars and Warps traced by the Molecular Gas in the Seyfert 2 Galaxy NGC 1068  

E-print Network

We present new interferometer observations of the 12CO(1-0) and 12CO(2-1) line emission of NGC 1068 with a resolution of 0.7''. The molecular gas in the inner 5'' is resolved into a ring with two bright knots east and west of the nuclear continuum emission. For the first time in NGC 1068, we can trace molecular gas at ~0.18'' (13pc) from the nucleus. The high velocities in this region imply an enclosed mass of ~10^8 M_solar. This value is consistent with a black hole mass of 1.7x10^7 M_solar plus a contribution from a compact nuclear stellar cluster. Perpendicular to the kinematic major axis optical images of NGC1068 show a bright, stellar, oval structure of eccentricity 0.8 and a deprojected length of 17kpc. Analysis of the rotation curve shows the CO spiral arms are at the inner Lindblad resonance of this bar-like structure. Inside the molecular spiral arms the CO kinematic axis changes direction probably in response to the 2.5kpc (deprojected) long stellar bar seen in the near infrared (NIR). The low velocity dispersion indicates the molecular gas is in a disk with a thickness of 10pc in the nuclear region and 100pc in the spiral arms. We constructed kinematic models for the molecular gas using elliptical orbits caused by a ~1'' nuclear bar and using tilted rings resulting in a warp. We find that the gas motions are consistent with either the warp or the bar models. However, because there is no evidence for a 1'' nuclear bar in NIR images, we favor the warp model. A warped CO disk can also explain the obscuration of the AGN, the extinction of light from the nuclear stellar cluster, and the observed NIR and mid-IR polarization. The model predicts the warped CO disk should become edge-on at a radius of 70pc, thereby creating a cavity for the ionization cone.

E. Schinnerer; A. Eckart; L. J. Tacconi; R. Genzel; D. Downes

1999-11-27

22

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

SciTech Connect

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

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

2012-05-20

23

Galaxy NGC 55  

NASA Technical Reports Server (NTRS)

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

2003-01-01

24

Triple Bars and Complex Central Structures in Disk Galaxies  

E-print Network

We present an analysis of ground-based and HST images of three early-type barred galaxies. The first, NGC 2681, may be the clearest example yet of a galaxy with three concentric bars. The two other galaxies were previously suggested as triple-barred. Our analysis shows that while NGC 3945 is probably double-barred, NGC 4371 has only one bar; but both have intriguing central structures. NGC 3945 has a large, extremely bright disk inside its primary bar, with patchy dust lanes, a faint nuclear ring or pseudo-ring within the disk, and an apparent secondary bar crossing the ring. NGC 4371 has a bright nuclear ring only marginally bluer than the surrounding bulge and bar. There is no evidence for significant dust or star formation in either of these nuclear rings. The presence of stellar nuclear rings suggests that the centers of these galaxies are dynamically cool and disklike.

Peter Erwin; Linda S. Sparke

1999-06-16

25

Galaxy NGC 1512  

NASA Technical Reports Server (NTRS)

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

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

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

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

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

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

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

1999-01-01

26

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

SciTech Connect

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

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

2013-05-01

27

Morphology of Cold Bars in Early and Late Type Galaxies  

E-print Network

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

A. C. Quillen

1996-09-05

28

KINEMATIC AND PHOTOMETRIC EVIDENCE FOR A BAR IN NGC 2683  

SciTech Connect

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

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

2009-10-15

29

Starburst Galaxy NGC 3310  

NASA Technical Reports Server (NTRS)

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

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

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

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

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

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

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

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

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

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

1999-01-01

30

Galaxy NGC 1850  

NASA Technical Reports Server (NTRS)

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

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

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

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

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

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

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

1999-01-01

31

Galaxy NGC 4579  

NASA Technical Reports Server (NTRS)

Galaxy NGC 4579 was captured by the Spitzer Infrared Nearby Galaxy Survey, or Sings, Legacy project using the Spitzer Space Telescope's infrared array camera. In this image, the red structures are areas where gas and dust are thought to be forming new stars, while the blue light comes from mature stars. This image is a 4-channel, false-color composite, where blue indicates emission at 3.6 microns, green corresponds to 4.5 microns, and red to 5.8 and 8.0 microns. The contribution from starlight (measured at 3.6 microns) in this picture has been subtracted from the 5.8 and 8 micron images to enhance the visibility of the dust features.

2006-01-01

32

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

33

A WIYN Survey of Early-Type Barred Galaxies: Double Bars and Central Structures  

E-print Network

We present results from a preliminary analysis of a recently-completed, multicolor imaging survey of nearby, early-type barred galaxies in the field, carried out with the WIYN telescope and supplemented with archival HST images. This forms a reasonably complete sample of nearby, bright, barred S0 and Sa galaxies in the field. The excellent seeing provided by WIYN allows us to examine the galaxies for central features such as circumnuclear rings and secondary bars; we find some evidence for dust lanes within secondary bars. The most striking results is the high frequency of double bars: our analysis suggests that at least $\\sim 20%$ of barred S0-Sa galaxies possess secondary bars}. We also find an excellent candidate triply barred galaxy: NGC 2681.

Peter Erwin; Linda S. Sparke

1998-11-21

34

Resonances in barred galaxies  

NASA Astrophysics Data System (ADS)

The inner parts of many spiral galaxies are dominated by bars. These are strong non-axisymmetric features which significantly affect orbits of stars and dark matter particles. One of the main effects is the dynamical resonances between galactic material and the bar. We detect and characterize these resonances in N-body models of barred galaxies by measuring angular and radial frequencies of individual orbits. We found narrow peaks in the distribution of orbital frequencies with each peak corresponding to a specific resonance. We found five different resonances in the stellar disc and two in the dark matter. The corotation resonance (CR) and the inner and outer Lindblad resonances are the most populated. The spatial distributions of particles near resonances are wide. For example, the inner Lindblad resonance is not localized at a given radius. Particles near this resonance are mainly distributed along the bar and span a wide range of radii. On the other hand, particles near the CR are distributed in two broad areas around the two stable Lagrange points. The distribution resembles a wide ring at the corotation radius. Resonances capture disc and halo material in near-resonant orbits. Our analysis of orbits in both N-body simulations and simple analytical models indicates that resonances tend to prevent the dynamical evolution of this trapped material. Only if the bar evolves as a whole, resonances drift through the phase space. In this case particles anchored near resonant orbits track the resonance shift and evolve. The criteria to ensure a correct resonant behaviour discussed by Weinberg and Katz can be achieved with few millions particles because the regions of trapped orbits near resonances are large and evolving.

Ceverino, D.; Klypin, A.

2007-08-01

35

Galaxy Zoo: bars in disc galaxies  

NASA Astrophysics Data System (ADS)

We present first results from Galaxy Zoo 2, the second phase of the highly successful Galaxy Zoo project (). Using a volume-limited sample of 13 665 disc galaxies (0.01 < z < 0.06 and Mr < -19.38), we study the fraction of galaxies with bars as a function of global galaxy properties like colour, luminosity and bulge prominence. Overall, 29.4 ± 0.5 per cent of galaxies in our sample have a bar, in excellent agreement with previous visually classified samples of galaxies (although this overall fraction is lower than that measured by automated bar-finding methods). We see a clear increase in the bar fraction with redder (g-r) colours, decreased luminosity and in galaxies with more prominent bulges, to the extent that over half of the red, bulge-dominated disc galaxies in our sample possess a bar. We see evidence for a colour bimodality for our sample of disc galaxies, with a 'red sequence' that is both bulge and bar dominated, and a 'blue cloud' which has little, or no, evidence for a (classical) bulge or bar. These results are consistent with similar trends for barred galaxies seen recently both locally and at higher redshift, and with early studies using the RC3. We discuss these results in the context of internal (secular) galaxy evolution scenarios and the possible links to the formation of bars and bulges in disc galaxies. This publication has been made possible by the participation of more than 200 000 volunteers in the Galaxy Zoo project. Their contributions are individually acknowledged at http://www.galaxyzoo.org/Volunteers.aspx

Masters, Karen L.; Nichol, Robert C.; Hoyle, Ben; Lintott, Chris; Bamford, Steven P.; Edmondson, Edward M.; Fortson, Lucy; Keel, William C.; Schawinski, Kevin; Smith, Arfon M.; Thomas, Daniel

2011-03-01

36

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

NASA Astrophysics Data System (ADS)

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

2003-12-01

37

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

E-print Network

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

Peter Erwin; Juan Carlos Vega Beltran; John Beckman

2001-12-04

38

BVRI photometric analysis for the galaxy group NGC 4410  

NASA Astrophysics Data System (ADS)

We present a BVRI CCD (Charge Coupled Device) surface photometry analysis of the galaxy group NGC 4410, which contains four galaxies in interaction. Along with our photometric study, we show residual images (after subtracting isophotal models) and unsharp masked images to uncover any hidden structures in this system of galaxies; we have also performed a two-dimensional bulge-disk decomposition for NGC 4410C and D, and a major axis sector profile for NGC 4410A. We have calculated BVRI surface brightnesses and colors within regions such as galaxy centers, bridges, tails and optical knots in the NGC 4410 system, generating B-V color maps and color profiles. The information obtained was used to discover the predominant stellar populations. The colors of the galaxies imply ages of ~2×109 to ~2×1010 years for models using a range of metallicities. The bluer knots and H II regions have colors implying ages of a minimum of 5×108 years, but possibly as high as 3×109 years for stellar populations formed in the interaction. These results lead us to conclude that there is a moderate star formation rate and a tranquil evolving state of the system with a long timescale for interaction, much longer than the typical dynamical timescales of 108 years. Although we note that NGC 4410D has a blue nucleus (possible nuclear starburst?), bulge, bar, and short spiral arms, and may be interacting with a H I gas cloud. Some observed structures in NGC 4410A are coincident with previously studied H II regions, a tidal arm and optical/radio knots found in this galaxy. An optical knot E coincident with a radio knot may be an optical synchrotron emission or an H II region. The galaxy NGC 4410B appears to be a boxy giant elliptical with a possible dusty disk embedded (similar to Cen A?) and NGC 4410C is confirmed as a lenticular galaxy.

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

2008-07-01

39

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

40

Kinematics and photometry as complementary tools in the study of barred galaxies  

E-print Network

Recent advances in observational techniques and theoretical modelling of galaxy kinematics allow us to use more than just optical morphology to discern the structure and dynamics of galaxies. Here, we show for three barred galaxies (UGC 10205, NGC 6221 and NGC4340) that both kinematics and photometry are necessary to fully understand the properties of these galaxies. Kinematic and spectrophotometric data enable us to detect structures such as bars and gas shocks that are not directly visible in the images; conversely, imaging can be crucial for understanding the kinematic and dynamical behavior of a galaxy.

Juan Carlos Vega Beltran; Peter Erwin; John Beckman; Alessandro Pizzella; Enrico Maria Corsini; Francesco Bertola; Werner W. Zeilinger

2000-10-30

41

Magnetohydrodynamic Simulations of Barred Galaxies  

NASA Astrophysics Data System (ADS)

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

Kim, W.-T.

2013-04-01

42

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

43

The Wolf-Rayet population of the nearby barred spiral galaxy NGC 5068 uncovered by the Very Large Telescope and Gemini  

NASA Astrophysics Data System (ADS)

We present a narrow-band Very Large Telescope/Focal Reduced Low-dispersion Spectrograph #1 imaging survey of the SAB(rs)cd spiral galaxy NGC 5068, located at a distance of 5.45 Mpc, from which 160 candidate Wolf-Rayet sources have been identified, of which 59 cases possess statistically significant ?4686 excesses. Follow-up Gemini Multi-Object Spectrograph spectroscopy of 64 candidates, representing 40 per cent of the complete photometric catalogue, confirms Wolf-Rayet signatures in 30 instances, corresponding to a 47 per cent success rate. 21 out of 22 statistically significant photometric sources are spectroscopically confirmed. Nebular emission detected in 30 per cent of the Wolf-Rayet candidates spectrally observed, which enable a re-assessment of the metallicity gradient in NGC 5068. A central metallicity of log (O/H) + 12 ˜ 8.74 is obtained, declining to 8.23 at R25. We combine our spectroscopy with archival H? images of NGC 5068 to estimate a current star formation rate of ?, and provide a catalogue of the 28 brightest H II regions from our own continuum subtracted H? images, of which ˜17 qualify as giant H II regions. Spectroscopically, we identify 24 WC- and 18 WN-type Wolf-Rayet stars within 30 sources since emission-line fluxes indicate multiple Wolf-Rayet stars in several cases. We estimate an additional ˜66 Wolf-Rayet stars from the remaining photometric candidates, although sensitivity limits will lead to an incomplete census of visually faint WN stars, from which we estimate a global population of ˜170 Wolf-Rayet stars. Based on the H?-derived O star population of NGC 5068 and N(WR)/N(O) ˜ 0.03, representative of the Large Magellanic Cloud, we would expect a larger Wolf-Rayet population of 270 stars. Finally, we have compared the spatial distribution of spectroscopically confirmed WN and WC stars with Sloan Digital Sky Survey derived supernovae, and find both WN and WC stars to be most consistent with the parent population of Type Ib supernovae.

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

2012-03-01

44

Galaxy Zoo: Observing Secular Evolution Through Bars  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

45

Mon. Not. R. Astron. Soc. 420, 30913107 (2012) doi:10.1111/j.1365-2966.2011.20220.x The WolfRayet population of the nearby barred spiral galaxy NGC 5068  

E-print Network

Telescope/Focal Reduced Low-dispersion Spectro- graph #1 imaging survey of the SAB(rs)cd spiral galaxy NGC-Object Spec- trograph spectroscopy of 64 candidates, representing 40 per cent of the complete photometric.23 at R25. We combine our spectroscopy with archival H images of NGC 5068 to estimate a current star

Crowther, Paul

46

Galaxy Zoo: Observing Secular Evolution Through Bars  

E-print Network

Observations have shown that there is a connection between the presence of a bar and the properties of a galaxy. In a parallel effort, simulations have shown that this connection is consistent with the theory of bar-driven secular evolution. But observational evidence of bar-driven secular evolution has been sparse. In this paper, we use the Galaxy Zoo 2 dataset to look for evidence of this secular evolution. Our sample consists of 13,295 disk galaxies, with an overall bar fraction of 23.6 +/- 0.4%, of which 1,154 barred galaxies also have bar length measurements. These samples are the largest ever used to study the role of bars in disk galaxy evolution. We characterize bars by the bar likelihood, the likelihood a bar is present in a given galaxy, and the bar length. These two bar properties show interesting correlations with the specific star formation rate and the inner central structure of galaxies. Comparing these observations to state-of-the-art simulations of bar evolution, which include live halos and ...

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

2013-01-01

47

NGC 2442: Tidal Encounters and the Evolution of Spiral Galaxies  

E-print Network

Using imaging Fabry-Perot data, we study the star-forming properties and kinematics of the nearby barred spiral galaxy NGC 2442. The Halpha emission is very localized along the strong spiral arms of the galaxy, and shows a marked asymmetry between the sharp, well-defined northern tidal arm and the weaker southern arm. The velocity field appears highly distorted, with a rapidly rotating nuclear component. We find evidence for strong non-circular motions along the northern arm, coincident with the pronounced dust lane and regions of intense star formation. The strong asymmetries, disturbed velocity field, and presence of a perturbed companion suggest that we are witnessing a strong kinematic response to a close interaction, which has redistributed the star formation activity throughout the disk of NGC 2442. Dynamical modeling supports this hypothesis, and suggests that the regions of strongest star formation are coincident with strong shocks occurring along the perturbed northern arm. Despite this redistribution of gas on small scales, this galaxy does not show a significant departure from the Tully-Fisher relation, nor does it appear to be experiencing any strong starburst. Moreover, our models predict that in a few x 10^8 years, NGC 2442 will have recovered from this encounter and will experience another passage -- and ultimately a merger -- in a few Gyr. Given the environment of many disk galaxies, this tidal encounter cycle seems likely to be a normal phase of disk galaxy evolution.

Chris Mihos; Greg Bothun

1997-01-06

48

NGC 6872's Tidal Dwarf Galaxy  

NASA Astrophysics Data System (ADS)

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

Eufrasio, Rafael; Arendt, Richard; Dwek, Eli

2013-10-01

49

Galaxy Zoo: Observing Secular Evolution through Bars  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

50

Galaxy Zoo: Observing Secular Evolution Through Bars  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

51

How Large Are the Bars in Barred Galaxies?  

E-print Network

I present a study of the sizes (semimajor axes) of bars in disc galaxies, combining a detailed study of 65 S0-Sb galaxies with measurements of 70 Sb-Sd galaxies from Martin (1995). As has been noted before with smaller samples, bars in early-type (S0-Sb) galaxies are clearly larger than bars in late-type (Sc-Sd) galaxies; this is true both for relative sizes (bar length as fraction of isophotal radius R_25 or exponential disc scale length h) and absolute sizes (kpc). S0-Sab bars extend to ~1-10 kpc (mean ~3.3 kpc), ~0.2-0.8 R_25 (mean \\~0.38 R_25) and ~0.5-2.5 h (mean ~1.4 h). Late-type bars extend to only \\~0.5-3.5 kpc, 0.05-0.35 R_25 and 0.2-1.5 h; mean sizes are ~1.5 kpc, 0.14 R_25 and 0.6 h. Sb galaxies resemble earlier-type galaxies in terms of bar size relative to h; their smaller R_25-relative sizes may be a side effect of higher star formation, which increases R_25 but not h. For S0-Sbc galaxies, bar size correlates well with disc size (both R_25 and h); these correlations are stronger than the known correlation with M_B. All correlations appear to be weaker or absent for late-type galaxies; in particular, there seems to be no correlation between bar size and either h or M_B for Sc-Sd galaxies. I show that the bars detected in HST near-IR images at z ~ 1 by Sheth et al. (2003) have absolute sizes consistent with those in bright, nearby S0-Sb galaxies. I also compare the sizes of real bars with those produced in simulations, and discuss some possible implications for scenarios of secular evolution along the Hubble sequence. Simulations often produce bars as large as -- or larger than -- those seen in S0-Sb galaxies, but rarely any as small as those in Sc-Sd galaxies. (Abridged.)

Peter Erwin

2005-08-26

52

Galaxy Zoo: CANDELS Barred Disks and Bar Fractions  

E-print Network

The formation of bars in disk galaxies is a tracer of the dynamical maturity of the population. Previous studies have found that the incidence of bars in disks decreases from the local Universe to z ~ 1, and by z > 1 simulations predict that bar features in dynamically mature disks should be extremely rare. Here we report the discovery of strong barred structures in massive disk galaxies at z ~ 1.5 in deep rest-frame optical images from CANDELS. From within a sample of 876 disk galaxies identified by visual classification in Galaxy Zoo, we identify 123 barred galaxies. Selecting a sub-sample within the same region of the evolving galaxy luminosity function (brighter than L*), we find that the bar fraction across the redshift range 0.5< z < 2 (f_bar = 10.7 +6.3 -3.5% after correcting for incompleteness) does not significantly evolve. We discuss the implications of this discovery in the context of existing simulations and our current understanding of the way disk galaxies have evolved over the last 11 bil...

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

2014-01-01

53

Galaxy Zoo: CANDELS barred discs and bar fractions  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

54

A Galaxy Cluster Near NGC 720  

E-print Network

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

H. Arp

2005-10-06

55

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

2003-10-28

56

Double Bars, Inner Disks, and Nuclear Rings in Barred Galaxies  

E-print Network

We present results of a high-resolution imaging survey of barred S0--Sa galaxies which demonstrate that the central regions of these galaxies are surprisingly complex. We see many inner bars --- small, secondary bars (typically less than a kiloparsec in radius) located inside of, and probably rotating faster than, the large primary bars. These are present in about one quarter to one third of all our sample. In contrast to some theoretical expectations, they do not seem to enhance AGN activity significantly. A third of barred S0's appear to host kiloparsec-scale disks within their bars; but the frequency of such inner disks is much lower in our S0/a and Sa galaxies. In addition, we find one example of a triple barred galaxy, and two cases of purely stellar nuclear rings --- probably the fossil remnants of past circumnuclear starbursts. We comment briefly on results from an ongoing analysis of known double-barred systems, extending to Hubble types as late as Sbc, and discuss their characteristic sizes and orientations.

Peter Erwin; Linda S. Sparke; Juan Carlos Vega Beltran; John Beckman

2001-07-07

57

Star Formation Triggered by Galaxy Interactions--NGC 1792\\/NGC 1808  

Microsoft Academic Search

Both the level and the location of star formation (SF) in galaxy disks can be influenced by external forces, like e.g. gravitational interactions. In the interacting galaxies NGC 1792 and NGC 1808 the highest level of SF is observed at those galactocentric radii, r, where gas can accrete most easily. In NGC 1808, a starburst occurs in a ring of

Michael Dahlem

1994-01-01

58

2Cosmic Bar Graphs Galaxy Type  

E-print Network

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

59

Dark matter halos of barred disk galaxies  

E-print Network

We use a large volume-limited sample of disk galaxies drawn from the Sloan Digital Sky Survey Data Release 7 to study the dependence of the bar fraction on the stellar to halo mass ratio, making use of a group catalog we identify central and satellite galaxies in our sample. For the central galaxies in the sample we estimate the stellar to halo mass ratio (M$_{\\mathrm{*}}/$M$_{\\mathrm{h}}$) and find that the fraction of barred galaxies is a strong function of this ratio, specially for the case of strong bars. Bars are more common on galaxies with high M$_{\\mathrm{*}}/$M$_{\\mathrm{h}}$ values, as expected from early theoretical works which showed that systems with massive dark matter halos are more stable against bar instabilities. We find that the change of the bar fraction with M$_{\\mathrm{h}}$ and M$_{\\mathrm{*}}$ is stronger if we consider a relation with the form $f_{\\mathrm{bar}}=f_{\\mathrm{bar}}$(M$_{\\mathrm{*}}^{\\alpha}/$M$_{\\mathrm{h}}$) with $\\alpha=1.5$, and therefore the bar fraction is largely ind...

Sodi, Bernardo Cervantes; Park, Changbom

2014-01-01

60

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

61

Three-dimensional decomposition of galaxies with bulge and long bar  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

62

NGC 5291: Implications for the Formation of Dwarf Galaxies  

Microsoft Academic Search

The possible formation and evolution of dwarf irregular galaxies from material derived from perturbed evolved galaxies is addressed via an H I study of a likely example, the peculiar system NGC 5291. This system, located in the western outskirts of the cluster Abell 3574, contains the lenticular galaxy NGC 5291 which is in close proximity to a disturbed companion and

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

1997-01-01

63

Bar pattern speed and position of the circumnuclear ring in NGC 1097  

NASA Astrophysics Data System (ADS)

We present the first galactic-scale model of the gas dynamics of the prototype barred Seyfert 1 galaxy NGC 1097. We use large-scale FaNTOmM Fabry-Perot interferometric data covering the entire galactic disc and combine the distribution and kinematics maps with high-resolution two-dimensional spectroscopy from the Gemini telescope. We build a dynamical model for the gravitational potential by applying the analytic solution to the equations of motion, within the epicyclic approximation. Our model reproduces all the significant kinematic and structural signatures of this galaxy. We find that the primary bar is 7.9 ± 0.6 kpc long and has a pattern speed of 36 ± 2 km s-1 kpc-1. This places the corotation radius at 8.6 ± 0.5 kpc, the outer Lindblad resonance at 14.9 ± 0.9 kpc and two inner Lindblad resonances at 60 ± 5 pc and 2.9 ± 0.1 kpc. These derivations lead to a ratio of the corotation radius over bar length of 1.0-1.2, which is in agreement with the predictions of simulations for fast galaxy bars. Our model presents evidence that the circumnuclear ring in this galaxy is not located near any of the resonance radii in this galaxy. The ring might have once formed at the outer inner Lindblad resonance radius, and it has been migrating inwards, towards the centre of the galactic gravitational potential.

Piñol-Ferrer, N.; Fathi, K.; Carignan, C.; Font, J.; Hernandez, O.; Karlsson, R.; van de Ven, G.

2014-02-01

64

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

65

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

66

Imaging Carbon Monoxide Emission in the Starburst Galaxy NGC 6000  

NASA Astrophysics Data System (ADS)

We present measurements of carbon monoxide emission in the central region of the nearby starburst NGC 6000 taken with the Submillimeter Array. The J = 2-1 transition of 12CO, 13CO, and C18O were imaged at a resolution of ~3'' × 2'' (450 × 300 pc). We accurately determine the dynamical center of NGC 6000 at ?J2000.0 = 15h49m49.s5 and ?J2000.0 = -29°23'13'' which agrees with the peak of molecular emission position. The observed CO dynamics could be explained in the context of the presence of a bar potential affecting the molecular material, likely responsible for the strong nuclear concentration where more than 85% of the gas is located. We detect a kinematically detached component of dense molecular gas at relatively high velocity which might be fueling the star formation. A total nuclear dynamical mass of 7 × 109 M sun is derived and a total mass of gas of 4.6 × 108 M sun, yielding a M gas/M dyn ~ 6%, similar to other previously studied barred galaxies with central starbursts. We determined the mass of molecular gas with the optically thin isotopologue C18O and we estimate a CO-to-H2 conversion factor X CO = 0.4 × 1020 cm-2(K km s-1)-1 in agreement with that determined in other starburst galaxies.

Martín, Sergio; George, Matthew R.; Wilner, David J.; Espada, Daniel

2010-06-01

67

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

E-print Network

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

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

1999-07-07

68

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

69

Globular Clusters in Coma Galaxy NGC 4881  

Microsoft Academic Search

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

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

1995-01-01

70

Pseudobulges in Barred S0 Galaxies  

E-print Network

We present preliminary results from an ongoing study of the bulges of S0 galaxies. We show that in a subsample of 14 barred S0 galaxies, fully half the photometrically defined bulges show kinematic signatures of "pseudobulges" -- that is, their kinematics are dominated by rotation. In four of these galaxies, we identify at least two subcomponents in the photometric bulge region: flatter, disk or bar components, assocated with disklike kinematics; and rounder "inner bulges,'' which appear to be hotter systems more like classical bulges.

Peter Erwin; John E. Beckman; Juan Carlos Vega Beltran

2004-09-05

71

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

72

Supermassive black holes in the Sbc spiral galaxies NGC 3310, NGC 4303 and NGC 4258  

E-print Network

We present new Space Telescope Imaging Spectrograph (STIS) observations of three spiral galaxies, NGC 4303, NGC 3310 and NGC 4258. The bright optical emission lines H$\\alpha$ $\\lambda$ $6564 \\AA$, [NII] $\\lambda$$\\lambda$ $6549,6585 \\AA$ and [SII] $\\lambda$$\\lambda$ $ 6718,6732 \\AA$ were used to study the kinematics of the ionized gas in the nuclear region of each galaxy with a $\\sim 0.07\\arcsec$ spatial resolution. In NGC 3310, the observed gas kinematics is well matched by a circularly rotating disk model but we are only able to set an upper limit to the BH mass which, taking into account the allowed disk inclinations, varies in the range $5.0 \\times 10^{6} - 4.2 \\times 10^{7} M_{\\odot}$ at the 95% confidence level. In NGC 4303 the kinematical data require the presence of a BH with mass $M_{BH}=(5.0)^{+0.87}_{-2.26}\\times 10^{6}M_{\\odot}$ (for a disk inclination $i=70$ deg).In NGC 4258, the observed kinematics require the presence of a black hole with $M_{BH}= (7.9)^{+6.2}_{-3.5} \\times 10^{7}M_{\\odot}$ ($i=60$ deg). This result is in good agreement with the published value $(3.9 \\pm 0.1) \\times 10^{7} M_{\\odot}$, derived from $H_{2}O$-maser observations. Our attempt at measuring BH masses in these 3 late type Sbc spiral galaxies has shown that these measurements are very challenging and at the limit of the highest spatial resolution currently available. Nonetheless our estimates are in good agreement with the scaling relations between black holes and their host spheroids suggesting that (i) they are reliable and (ii) black holes in spiral galaxies follows the same scaling relations as those in more massive early-type galaxies. A crucial test for the gas kinematical method, the correct recovery of the known BH mass in NGC 4258, has been successful. [abridged

Guia Pastorini; Alessandro Marconi; Alessandro Capetti; David J. Axon; Almudena Alonso-Herrero; John Atkinson; Dan Batcheldor; C. Marcella Carollo; James Collett; Linda Dressel; Mark A. Hughes; Duccio Macchetto; Witold Maciejewski; William Sparks; Roeland van der Marel

2007-03-07

73

Gaseous Vortices in Barred Spiral Galaxies  

Microsoft Academic Search

Simulations of the gas flow in a variety of two-dimensional barred spiral galaxies have shown that vortices in the gas appear, when viewed from above, in the corotation frame of the bar. These low-density vortices generally appear at or near the L4 and L5 Lagrangian points. We show that these gas vortices in our models are the hydrodynamic analogs of

Martin N. England; J. H. Hunter Jr.; G. Contopoulos

2000-01-01

74

Complex statistics in Hamiltonian barred galaxy models  

E-print Network

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

Tassos Bountis; Thanos Manos; Chris Antonopoulos

2011-08-25

75

Barred Galaxies in the Coma Cluster  

NASA Astrophysics Data System (ADS)

We use ACS data from the HST Treasury survey of the Coma cluster (z˜0.02) to study the properties of barred galaxies in the Coma core, the densest environment in the nearby Universe. This study provides a complementary data point for studies of barred galaxies as a function of redshift and environment. From ˜470 cluster members brighter than MI = -11 mag, we select a sample of 46 disk galaxies (S0-Im) based on visual classification. The sample is dominated by S0s for which we find an optical bar fraction of 47±11% through ellipse fitting and visual inspection. Among the bars in the core of the Coma cluster, we do not find any very large (abar>2 kpc) bars. Comparison to other studies reveals that while the optical bar fraction for S0s shows only a modest variation across low-to-intermediate density environments (field to intermediate-density clusters), it can be higher by up to a factor of ˜ 2 in the very high-density environment of the rich Coma cluster core.

Marinova, I.; Jogee, S.; Trentham, N.; Ferguson, H. C.; Weinzirl, T.; Balcells, M.; Carter, D.; den Brok, M.; Erwin, P.; Graham, A. W.; Goudfrooij, P.; Guzmán, R.; Hammer, D.; Hoyos, C.; Peletier, R. F.; Peng, E.; Verdoes Kleijn, G.

2010-10-01

76

NGC 2915 -- A Galaxy with a Dark or Faded Massive Disk?  

E-print Network

NGC 2915 is a remarkable blue compact dwarf galaxy which contains an inner HI bar and strong spiral structure in its HI disk extending well beyond its optical disk. We propose here that NGC 2915 has a dark or faint (not yet observed) massive disk component. By massive we mean of the same order as the HI gas mass which ranges from 0.5 -- 10 Msol/pc^2. We present three different dynamical arguments based on bar and spiral structure that an additional disk mass component is required. The additional mass requirements from these three dynamical arguments depend upon the distance of the galaxy in the same way. If the galaxy were at a distance twice that estimated then the additional mass required would be negligible. Virgocentric models show that then its radial velocity would be 250-500 km/s below its local bulk flow value. Local flow models suggest that this is unlikely, however they also do not exclude it at high confidence levels. Detection of a quiescent or faint stellar disk population would be an exciting prospect since it would be strong evidence for a previous epoch of star formation in a previously low surface brightness galaxy. Then NGC 2915 would be an example of a galaxy which has faded and so could have been one of the faint blue galaxy population observed at moderate redshift.

A. C. Quillen

1998-01-22

77

IMAGING CARBON MONOXIDE EMISSION IN THE STARBURST GALAXY NGC 6000  

SciTech Connect

We present measurements of carbon monoxide emission in the central region of the nearby starburst NGC 6000 taken with the Submillimeter Array. The J = 2-1 transition of {sup 12}CO, {sup 13}CO, and C{sup 18}O were imaged at a resolution of {approx}3'' x 2'' (450 x 300 pc). We accurately determine the dynamical center of NGC 6000 at {alpha}{sub J2000.0} = 15{sup h}49{sup m}49.{sup s}5 and {delta}{sub J2000.0} = -29{sup 0}23'13'' which agrees with the peak of molecular emission position. The observed CO dynamics could be explained in the context of the presence of a bar potential affecting the molecular material, likely responsible for the strong nuclear concentration where more than 85% of the gas is located. We detect a kinematically detached component of dense molecular gas at relatively high velocity which might be fueling the star formation. A total nuclear dynamical mass of 7 x 10{sup 9} M{sub sun} is derived and a total mass of gas of 4.6 x 10{sup 8} M{sub sun}, yielding a M{sub gas}/M{sub dyn} {approx} 6%, similar to other previously studied barred galaxies with central starbursts. We determined the mass of molecular gas with the optically thin isotopologue C{sup 18}O and we estimate a CO-to-H{sub 2} conversion factor X{sub CO} = 0.4 x 10{sup 20} cm{sup -2}(K km s{sup -1}){sup -1} in agreement with that determined in other starburst galaxies.

Martin, Sergio [European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19 (Chile); George, Matthew R.; Wilner, David J.; Espada, Daniel, E-mail: smartin@eso.or [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2010-06-15

78

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

79

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

80

XMM-Newton observations of the interacting galaxy pairs NGC7771/0 and NGC2342/1  

E-print Network

We present XMM-Newton X-ray observations of the interacting galaxy pairs NGC7771/7770 and NGC2342/2341. In NGC7771, for the first time we are able to resolve the X-ray emission into a bright central source (L(X)~10^41 erg/s), plus two (L(X)>10^40 erg/s) ultraluminous X-ray sources (ULXs) located either end of the bar. The soft emission of the central source is well-modelled by a two-temperature thermal plasma with kT=0.4/0.7 keV. The hard emission is modelled with a flat absorbed power-law (Gamma~1.7, NH~10^22 cm^2), and this together with a low-significance (1.7 sigma) ~300 eV equivalent width emission line at ~6 keV are the first indications that NGC7771 may host a low-luminosity AGN. For the bar ULXs, a power-law fit to X-1 is improved at the 2.5 sigma level with the addition of a thermal plasma component (kT~0.3 keV), while X-2 is improved only at the 1.3 sigma level with the addition of a disc blackbody component with T(in)~0.2 keV. Both sources are variable on short time-scales implying that their emission is dominated by single accreting X-ray binaries (XRBs). The three remaining galaxies, NGC7770, NGC2342 and NGC2341, have observed X-ray luminosities of 0.2, 1.8 & 0.9x10^41 erg/s respectively (0.3-10 keV). Their integrated spectra are also well-modelled by multi-temperature thermal plasma components with kT=0.2-0.7 keV, plus power-law continua with slopes of Gamma=1.8-2.3 that are likely to represent the integrated emission of populations of XRBs as observed in other nearby merger systems. A comparison with other isolated, interacting and merging systems shows that all four galaxies follow the established correlations for starburst galaxies between X-ray, far-infrared and radio luminosities, demonstrating that their X-ray outputs are dominated by their starburst components.

L. P. Jenkins; T. P. Roberts; M. J. Ward; A. Zezas

2004-11-10

81

Molecular Gas Dynamics in NGC 6946: a Bar-driven Nuclear Starburst "Caught in the Act"  

E-print Network

We present high angular resolution ~1" and 0.6" mm-interferometric observations of the 12CO(1-0) and 12CO(2-1) line emission in the central 300pc of the late-type spiral galaxy NGC6946. The data, obtained with the IRAM Plateau de Bure Interferometer (PdBI), allow the first detection of a molecular gas spiral in the inner ~10" (270pc) with a large concentration of molecular gas (M(H_2) ~1.6x10^7M_sun) within the inner 60pc. This nuclear clump shows evidence for a ring-like geometry with a radius of ~10pc as inferred from the p-v diagrams. Both the distribution of the molecular gas as well as its kinematics can be well explained by the influence of an inner stellar bar of about 400pc length. A qualitative model of the expected gas flow shows that streaming motions along the leading sides of this bar are a plausible explanation for the high nuclear gas density. Thus, NGC6946 is a prime example of molecular gas kinematics being driven by a small-scale, secondary stellar bar.

Schinnerer, E; Emsellem, E; Lisenfeld, U

2006-01-01

82

Molecular Gas Dynamics in NGC 6946: a Bar-driven Nuclear Starburst "Caught in the Act"  

E-print Network

We present high angular resolution ~1" and 0.6" mm-interferometric observations of the 12CO(1-0) and 12CO(2-1) line emission in the central 300pc of the late-type spiral galaxy NGC6946. The data, obtained with the IRAM Plateau de Bure Interferometer (PdBI), allow the first detection of a molecular gas spiral in the inner ~10" (270pc) with a large concentration of molecular gas (M(H_2) ~1.6x10^7M_sun) within the inner 60pc. This nuclear clump shows evidence for a ring-like geometry with a radius of ~10pc as inferred from the p-v diagrams. Both the distribution of the molecular gas as well as its kinematics can be well explained by the influence of an inner stellar bar of about 400pc length. A qualitative model of the expected gas flow shows that streaming motions along the leading sides of this bar are a plausible explanation for the high nuclear gas density. Thus, NGC6946 is a prime example of molecular gas kinematics being driven by a small-scale, secondary stellar bar.

E. Schinnerer; T. Boeker; E. Emsellem; U. Lisenfeld

2006-05-29

83

SWS spectroscopy of the colliding galaxies NGC4038\\/39  

Microsoft Academic Search

We present mid-infrared spectroscopy of the prototypical interacting galaxies NGC 4038\\/39 (the `Antennae') obtained with the ISO Short Wavelength Spectrometer (SWS). Our observations focus on the interaction zone where the two galaxies overlap, providing new constraints on the properties of the young and vigorous extranuclear starburst triggered by the recent interaction of the two galaxies. We use hydrogen recombination lines

D. Kunze; D. Rigopoulou; D. Lutz; E. Egami; H. Feuchtgruber; R. Genzel; H. W. W. Spoon; E. Sturm; A. Sternberg; A. F. M. Moorwood; T. de Graauw

1996-01-01

84

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

85

The interacting galaxy pair NGC 4485 and NGC 4490 - Star formation and the interstellar medium  

NASA Technical Reports Server (NTRS)

The 100- and 160-micron continuum emission from cool dust in the interacting gas-rich pair of galaxies, NGC 4490 and NGC 4485, was mapped. Visual continuum and H-alpha images of the pair were obtained. The state of the interstellar medium and the rate and efficiency of star formation are investigated.

Thronson, Harley A., Jr.; Hunter, Deidre A.; Casey, Sean; Harper, D. A.; Latter, William B.

1989-01-01

86

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

Microsoft Academic Search

We present the results of stellar photometry of polar-ring galaxies NGC 2685\\u000aand NGC 4650A, using the archival data obtained with the Hubble Space\\u000aTelescope's Wide Field Planetary Camera 2. Polar rings of these galaxies were\\u000aresolved into ~800 and ~430 stellar objects in the B, V and Ic bands,\\u000aconsiderable part of which are blue supergiants located in the

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

2003-01-01

87

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

88

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

E-print Network

We present an analysis of the environmental dependence of bars and bulges in disc galaxies, using a volume-limited catalogue of 15810 galaxies at zZoo 2 project. We find that the likelihood of having a bar, or bulge, in disc galaxies increases when the galaxies have redder (optical) colours and larger stellar masses, and observe a transition in the bar and bulge likelihoods, such that massive disc galaxies are more likely to host bars and bulges. We use galaxy clustering methods to demonstrate statistically significant environmental correlations of barred, and bulge-dominated, galaxies, from projected separations of 150 kpc/h to 3 Mpc/h. These environmental correlations appear to be independent of each other: i.e., bulge-dominated disc galaxies exhibit a significant bar-environment correlation, and barred disc galaxies show a bulge-environment correlation. We demonstrate that approximately half (50 +/- 20%) of the bar-environm...

Skibba, Ramin A; Nichol, Robert C; Zehavi, Idit; Hoyle, Ben; Edmondson, Edward M; Bamford, Steven P; Cardamone, Carolin N; Keel, William C; Lintott, Chris; Schawinski, Kevin; Williams, Michael J

2011-01-01

89

XMM-Newton observation of the interacting galaxies NGC1512 and NGC1510  

E-print Network

The galaxy NGC1512 is interacting with the smaller galaxy NGC1510 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 NGC1512. For the first time we performed a deep X-ray observation of the galaxies NGC1512 and NGC1510 with XMM-Newton to gain information on the population of X-ray sources and diffuse emission in a system of interacting galaxies. 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. We detected 106 sources in the energy range of 0.2-12 keV, out of which 15 are located within the D_25 regions of NGC1512 and NGC1510 an...

Ducci, L; Sasaki, M; Koribalski, B S

2014-01-01

90

The Evolved Red Stellar Contents of the Sculptor Group Galaxies NGC55, NGC300, and NGC7793  

E-print Network

Deep J, H, and K images are used to probe the evolved stellar contents in the central regions of the Sculptor group galaxies NGC55, NGC300, and NGC7793. The brightest stars are massive red supergiants (RSGs) with K ~ 15 - 15.5. The peak RSG brightness is constant to within ~0.5 mag in K, suggesting that NGC55, NGC300, and NGC7793 are at comparable distances. Comparisons with bright RSGs in the Magellanic Clouds indicate that the difference in distance modulus with respect to the LMC is = 7.5. A rich population of asymptotic giant branch (AGB) stars, which isochrones indicate have ages between 0.1 and 10 Gyr, dominates the (K, J-K) color-magnitude diagram (CMD) of each galaxy. The detection of significant numbers of AGB stars with ages near 10 Gyr indicates that the disks of these galaxies contain an underlying old population. The CMDs and luminosity functions reveal significant galaxy-to-galaxy variations in stellar content. Star-forming activity in the central arcmin of NGC300 has been suppressed for the past Gyr with respect to disk fields at larger radii. Nevertheless, comparisons between fields within each galaxy indicate that star-forming activity during intermediate epochs was coherent on spatial scales of a kpc or more. A large cluster of stars, which isochrones suggest has an age near 100 Myr, is seen in one of the NGC55 fields. The luminosity function of the brightest stars in this cluster is flat, as expected if a linear luminosity-core mass relation is present.

T. J. Davidge

1998-03-23

91

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

92

Submillimeter Observations of Low Metallicity Galaxy NGC 4214  

E-print Network

Results of submillimeter (450 micron and 850 micron) observations of a nearby dwarf irregular galaxy NGC 4214 with SCUBA on JCMT are presented. We aimed at examining the far-infrared to submillimeter spectral energy distribution (SED) and properties of dust thermal emission in a low metallicity environment by choosing NGC 4214 of which gas metallicity (log O/H + 12) is 8.34. We found that the SED is quite similar to those of IRAS bright galaxies sample (IBGS) which are local bright star-forming galaxies with metallicity comparable to the solar abundance. A dust temperature and an emissivity index for NGC 4214 obtained by a fitting to the single temperature greybody model are T_d = 35 \\pm 0.8 K and beta = 1.4 \\pm 0.1, respectively, which are typical values for IBGS. Compiling the previous studies on similar nearby dwarf irregular galaxies, we found that NGC 1569 shows similar results to those of NGC 4214, while NGC 4449 and IC 10 SE show different SEDs and low emissivity indices. There seems to be a variety of SEDs among metal poor dwarf irregular galaxies. We examined dependence on intensity of interstellar radiation field as well as two-temperature model, but the origin of the difference is not clear. Some mechanism(s) other than metallicity and interstellar radiation field must be responsible for controlling dust emission property.

Gaku Kiuchi; Kouji Ohta; Marcin Sawicki; Michael Allen

2004-08-29

93

NGC 5291: Implications for the Formation of Dwarf Galaxies.  

National Technical Information Service (NTIS)

The possible formation and evolution of dwarf irregular galaxies from material derived from perturbed evolved galaxies is addressed via an H I study of a likely example, the peculiar system NGC 5291. This system, located in the western outskirts of the cl...

B. K. Malphrus, C. E. Simpson, S. T. Gottesman, T. G. Hawarden

1997-01-01

94

LWS observations of the colliding galaxies NGC 4038\\/39  

Microsoft Academic Search

Infrared Space Observatory (ISO) Long Wavelength Spectrometer (LWS) and ground-based Fabry-Perot imaging spectroscopic observations are used to penetrate the extinction to the powerful burst of star formation that has occurred in the extranuclear molecular cloud complex in the galaxy overlap region of the galaxies NGC 4038\\/39 (\\

J. Fischer; L. M. Shier; M. L. Luhman; S. Satyapal; H. A. Smith; G. J. Stacey; S. J. Unger; M. A. Greenhouse; L. Spinoglio; M. A. Malkan; S. D. Lord; J. W. Miles; M. A. Shure; P. E. Clegg; P. A. R. Ade; C. Armand; M. Burgdorf; S. E. Church; G. R. Davis; A. di Giorgio; D. Ewart; I. Furniss; W. M. Glencross; C. Gry; T. Lim; S. Molinari; Nguyen-Q-Rieu; M. C. Price; S. D. Sidher; A. Smith; B. M. Swinyard; D. Texier; N. R. Trams; M. G. Wolfire

1996-01-01

95

SPH Simulations of Barred Galaxies: Evolution of Nuclear Rings  

Microsoft Academic Search

Numerical simulations based on the smoothed particle hydrodynamics (SPH) is performed to investigate the dynamical properties of barred galaxies that have nuclear rings. The nuclear ring morphology depends on the relative strength of bar potentials. Nuclear rings form between the two ILRs and align perpendicular to the bars unless the bar potentials are strong enough to allow the x1 orbits

H. B. Ann

2001-01-01

96

Star formation and the interstellar medium in two peculiar, nonspiral galaxies - NGC 1569 and NGC 3593  

NASA Technical Reports Server (NTRS)

This paper discusses far-IR and optical observations aimed at investigating the far-IR energy distribution of two peculiar galaxies without spiral arms which are actively forming stars: NGC 1569, a Magellanic irregular galaxy, and NGC 3593, a dusty S0/a galaxy. The data are used to determine the characteristic temperatures of the dust and to infer dust and molecular gas masses which are combined with other data to explore the characteristics of the interstellar media. Visual-wavelength continuum and H-alpha images are presented and used to estimate current and past star formation rates and the efficiency of stellar creation.

Hunter, Deidre A.; Thronson, Harley A., Jr.; Casey, Sean; Harper, D. A.

1989-01-01

97

Submillimeter Observations of Low Metallicity Galaxy NGC 4214  

E-print Network

Results of submillimeter (450 micron and 850 micron) observations of a nearby dwarf irregular galaxy NGC 4214 with SCUBA on JCMT are presented. We aimed at examining the far-infrared to submillimeter spectral energy distribution (SED) and properties of dust thermal emission in a low metallicity environment by choosing NGC 4214 of which gas metallicity (log O/H + 12) is 8.34. We found that the SED is quite similar to those of IRAS bright galaxies sample (IBGS) which are local bright star-forming galaxies with metallicity comparable to the solar abundance. A dust temperature and an emissivity index for NGC 4214 obtained by a fitting to the single temperature greybody model are T_d = 35 \\pm 0.8 K and beta = 1.4 \\pm 0.1, respectively, which are typical values for IBGS. Compiling the previous studies on similar nearby dwarf irregular galaxies, we found that NGC 1569 shows similar results to those of NGC 4214, while NGC 4449 and IC 10 SE show different SEDs and low emissivity indices. There seems to be a variety of...

Kiuchi, G; Sawicki, M; Allen, M; Kiuchi, Gaku; Ohta, Kouji; Sawicki, Marcin; Allen, Michael

2004-01-01

98

An Infrared Portrait of the Barred Spiral Galaxy Messier 83  

NASA Astrophysics Data System (ADS)

Messier 83 (M83) is a relatively nearby spiral galaxy with a pronounced bar-like structure. It is located in the southern constellation Hydra (The Water-Snake) and is also known as NGC 5236 ; the distance is approximately 12 million light-years. Images of M83 obtained in visible light - like the VLT photo published exactly two years ago ( ESO PR 18/99 ) - show clumpy, well-defined spiral arms that are rich in young stars while the disk reveals a complex system of intricate dust lanes. This galaxy is known to be a site of vigorous star formation and no less than six supernovae (exploding stars) have been observed in M83 during the past century. It is a fairly symmetrical object and possesses no nearby companions. Gas dynamics and galaxy bars Investigations of gas motions in the nucleus and in the main disk play a key role in understanding the structure and evolution of barred spiral galaxies like M83. Inflow of gas towards the center caused by a mass distribution that is not circularly symmetric is often invoked to explain certain observed phenomena, e.g., the feeding of Active Galactic Nuclei (AGNs, see also the report about recent observations in three such galaxies in ESO PR 18/01 ), and the fueling of bursts of star formation in the nuclear region. Some astronomers think that this process may cause a change of a galaxy's (morphological) type, for instance from barred to normal spiral galaxy. It has also been suggested that the development of spiral structures in galactic disks may be due to central stellar bars. Interstellar gas that is subject to periodical perturbations by the non-circularly symmetrical gravitational field in a barred system will develop a "density wave" that attracts neighbouring stars and gas. The local density increases and once a certain ("critical") value is reached, star formation is "ignited" in this area. The mass distribution In order to better understand phenomena like these, it is essential to know in detail the distribution of matter in the galaxy disk. This is best done by means of infrared observations. Images obtained in the optical region of the spectrum mainly trace the pattern of star formation as well as young and bright stars, rather than the mass distribution in the galaxy. The regions with much dust are also well visible on such images as dark lanes and clouds, since they are very opaque to visible light. However, on infrared images, the dust absorption is much smaller and the light that is recorded mainly comes from old giant stars. Although those stars contribute little to the mass, they have the same spatial distribution as the much more numerous, smaller ("main sequence") stars. Their distribution therefore shows the mass distribution in the galaxy and hence the gravitation field that directs the motions of the interstellar gas. New infrared images of Messier 83 It is for this reason that infrared images of barred galaxies, like the ones of M83 shown here that was prepared by a group of Swedish astronomers [1], are extremely useful for the study of the dynamics of such galaxies and their development. In order to produce these (false-) colour photos, three infrared images of M83 obtained in the Ks- (wavelength 2.2 µm), J- (1.2 µm) and I-bands (0.8 µm), respectively, were combined into one colour image. The field shown in Photo 32a/01 measures 32,000 light-years across at the distance of M83. The dust lanes appear red since the emission in the longest waveband (Ks) is able to penetrate the dense gas and dust clouds. Note also how the dust lanes follow the leading edge of the bar - assuming that the arms are trailing and that the upper right area is the side of the galaxy that is nearest to us. Photo 32b/01 is an enlarged view of the galactic nucleus, processed to better show the intricate structure in this area. Here the dust lanes merge into a nuclear ring. It is obvious that the dust absorption in this region is so high that even Ks-photons have a hard time passing through. Note [1] The group includes Andreas Andersson and Hans Olo

2001-11-01

99

Submillimeter Observations of the Low-Metallicity Galaxy NGC 4214  

Microsoft Academic Search

Results of submillimeter (450 and 850 mum) observations of a nearby dwarf irregular galaxy NGC 4214 with SCUBA on JCMT are presented. We aimed at examining the far-infrared-to-submillimeter spectral energy distribution (SED) and properties of dust thermal emission in a low-metallicity environment by choosing NGC 4214, in which the gas metallicity (logO\\/H+12) is 8.34. We found that the SED is

Gaku Kiuchi; Kouji Ohta; Marcin Sawicki; Michael Allen

2004-01-01

100

Gaseous Vortices in Barred Spiral Galaxies  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

101

Magnetic fields in barred galaxies I. The atlas  

E-print Network

The total and polarized radio continuum emission of 20 barred galaxies was observed with the Very Large Array (VLA) at 3, 6, 18 and 22 cm and with the Australia Telescope Compact Array (ATCA) at 6 cm and 13 cm. Maps at 30 arcsec angular resolution are presented here. Polarized emission (and therefore a large-scale regular magnetic field) was detected in 17 galaxies. Most galaxies of our sample are similar to non-barred galaxies with respect to the radio/far-infrared flux correlation and equipartition strength of the total magnetic field. Galaxies with highly elongated bars are not always radio-bright. We discuss the correlation of radio properties with the aspect ratio of the bar and other measures of the bar strength. We introduce a new measure of the bar strength, \\Lambda, related to the quadrupole moment of the bar's gravitational potential. The radio surface brightness I of the barred galaxies in our sample is correlated with \\Lambda, I \\propto \\Lambda^0.4+/-0.1, and thus is highest in galaxies with a long bar where the velocity field is distorted by the bar over a large fraction of the disc. In these galaxies, the pattern of the regular field is significantly different from that in non-barred galaxies. In particular, field enhancements occur upstream of the dust lanes where the field lines are oriented at large angles to the bar's major axis. Polarized radio emission seems to be a good indicator of large-scale non-axisymmetric motions.

R. Beck; V. Shoutenkov; M. Ehle; J . I. Harnett; R. F. Haynes; A. Shukurov; D. D. Sokoloff; M. Thierbach

2002-07-09

102

XMM-Newton observations of the starburst merger galaxies NGC 3256 & NGC 3310  

E-print Network

We present XMM-Newton EPIC observations of the two nearby starburst merger galaxies NGC 3256 & NGC 3310. The broad-band (0.3-10 keV) integrated X-ray emission from both galaxies shows evidence of multi-phase thermal plasmas plus an underlying hard non-thermal power-law continuum. NGC 3256 is well-fit with a model comprising two MEKAL components (kT=0.6/0.9 keV) plus a hard power-law (Gamma=2), while NGC 3310 has cooler MEKAL components (kT=0.3/0.6 keV) and a harder power-law tail (Gamma=1.8). Chandra observations of these galaxies both reveal the presence of numerous discrete sources embedded in the diffuse emission, which dominate the emission above ~2 keV and are likely to be the source of the power-law emission. The thermal components show a trend of increasing absorption with higher temperature, suggesting that the hottest plasmas arise from supernova-heated gas within the disks of the galaxies, while the cooler components arise from outflowing galactic winds interacting with the ambient interstellar medium (ISM). We find no strong evidence for an active galactic nucleus (AGN) in either galaxy.

L. P. Jenkins; T. P. Roberts; M. J. Ward; A. Zezas

2004-05-14

103

Subarcsecond mid-infrared imaging of the nuclei of the infrared bright galaxies NGC 1614 and NGC 7469  

Microsoft Academic Search

The first subarcsecond resolution mid-IR images of the nuclei of two galaxies from the IRAS bright sample, NGC 1614 and NGC 7469, are described. The starburst galaxy NGC 1614 contains a double structure in the nuclear region. Most of the flux, 78 percent of 650 +\\/- 50 mJy, is emitted in two unresolved regions of 0.6 arcsec FWHM (190 pc

Eric Keto; Roger Ball; John Arens; Garrett Jernigan; Margaret Meixner

1992-01-01

104

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

105

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

106

SCUBA observations of the elliptical galaxy NGC 4374  

Microsoft Academic Search

We present SCUBA imaging and photometry of the elliptical galaxy NGC 4374. The imaging observations are used to examine the spatial distribution of thermal emission from dust and the radio-to-infrared continuum spectrum. In the SCUBA 850-mum image, the galaxy is found to be a point source, constraining the emission to a region less than 15 arcsec across (1.5kpc for a

L. L. Leeuw; A. E. Sansom; E. I. Robson

2000-01-01

107

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

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

108

A search for young optical pulsars in the galaxies NGC 4647 and NGC 4321  

NASA Astrophysics Data System (ADS)

A search has been conducted with the 6-m telescope for optical variability in supernovae that appeared in 1979 in the galaxies NGC 4647 and NGC 4321. The MANIA (Multichannel Analysis of Nanosecond Intensity Alterations) instrumentation system was used. Throughout the time-scale range investigated, 10 to the -6th to 10 to the 2nd sec, variability is found to be absent. Any pulsar with a period of 0.001-0.1 sec that may correspond to the NGC 4647 supernova had an optical luminosity below 3 x 10 to the 40th erg sec; for the NGC 4321 supernova, below 2 x 10 to the 39th erg/sec (on the 60th and 300th day after maximum light, respectively). Some possible interpretations of the negative results of this search for extragalactic pulsars are discussed.

Beskin, G. M.; Lebedev, V. S.; Neizvestnyj, S. I.; Plakhotnichenko, V. L.; Shvartsman, V. F.

1981-10-01

109

RXTE observations of the Seyfert 2 galaxy NGC4507:  

NASA Astrophysics Data System (ADS)

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

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

110

Deep H I Survey of the Spiral Galaxy NGC 2403  

Microsoft Academic Search

High-sensitivity H I observations of the nearby spiral galaxy NGC 2403 obtained with the VLA are presented and discussed. The properties of the extended, differentially rotating H I layer with its H I holes, spiral structure, and outer warp are described. In addition, these new data reveal the presence of a faint, extended, and kinematically anomalous component. This shows up

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

2002-01-01

111

Nobeyama CO Atlas of Nearby Spiral Galaxies: Distribution of Molecular Gas in Barred and Non-barred Spiral Galaxies  

E-print Network

The data from a CO(1 - 0) mapping survey of 40 nearby spiral galaxies performed with the Nobeyama 45-m telescope are presented. The criteria of the sample selection were (1) RC3 morphological type in the range Sa to Scd, (2) distance less than 25 Mpc, (3) inclination angle less than 79deg (RC3), (4) flux at 100 um higher than ~ 10 Jy, (5) spiral structure is not destroyed by interaction. The maps of CO cover most of the optical disk of the galaxies. We investigated the influence of bar on the distribution of molecular gas in spiral galaxies using these data. We confirmed that the degree of central concentration is higher in barred spirals than in non-barred spirals as shown by the previous works. Furthermore, we present an observational evidence that bars are efficient in driving molecular gas that lies within the bar length toward the center, while the role in bringing gas in from the outer parts of the disks is small. The transported gas accounts for about half of molecular gas within the central region in barred spiral galaxies. We found a correlation between the degree of central concentration and bar strength. Galaxies with stronger bars tend to have higher central concentration. The correlation implies that stronger bars accumulate molecular gas toward the center more efficiently. These results are consistent with long-lived bars.

N. Kuno; N. Sato; H. Nakanishi; A. Hirota; T. Tosaki; Y. Shioya; K. Sorai; N. Nakai; K. Nishiyama; B. Vila-Vilaro

2007-05-18

112

NGC 1291  

NASA Technical Reports Server (NTRS)

This image from NASA's Galaxy Evolution Explorer shows the galaxy NGC 1291, located about 33 million light-years away in the constellation Eridanus. NGC 1291 is notable for its unusual inner bar and outer ring structure.

Blue represents ultraviolet light captured by the telescope's long-wavelength detector. Green shows ultraviolet light from the short-wavelength detector, and red shows red visible light from the Cerro Tololo Inter-American Observatory, Chile.

The Galaxy Evolution Explorer data was taken in December 2003.

2007-01-01

113

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

114

H{\\alpha} Kinematics of S4G spiral galaxies I. NGC 864  

E-print Network

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

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

2012-01-01

115

Kinematics and ionization of extended gas in active galaxies. VI - The Seyfert 2 galaxy NGC 1386  

NASA Technical Reports Server (NTRS)

Results are presented of direct imaging with a CCD detector and long-slit medium- and low-dispersion spectroscopy of the spatially extended narrow-line-emitting gas in the nearby Seyfert 2 galaxy NGC 1386. The distribution, kinematics, and ionization structure of the excited gas were examined in the regions surrounding the nucleus out to a distance of about 1.0. Results present evidence for a spiral structure in this galaxy and for the presence of H II regions in the disk (supporting the classification of NGC 1386 as a Sa galaxy).

Weaver, K. A.; Wilson, A. S.; Baldwin, J. A.

1991-01-01

116

Dust properties of external galaxies; NGC 891 revisited  

E-print Network

We compare 850um SCUBA images of NGC 891 with the corresponding V-band optical depth predicted from radiation transfer simulations. These two tracers of dust show a very similar distribution along the minor axis and a reasonable agreement along the major axis. Assuming that the grains responsible for optical extinction are also the source of 850um emission we derive a submillimeter emissivity (emission efficiency) for dust in the NGC 891 disk. This quantity is found to be a factor of 2-3 higher than the generally-accepted (but highly uncertain) values adopted for the Milky Way. It should be stated, however, that if a substantial fraction of dust in NGC 891 is clumped, the emissivity in the two galaxies may be quite similar. We use our newly-acquired emissivity to convert our 850um images into detailed maps of dust mass and, utilizing 21cm and CO-emission data for NGC 891, derive the gas-to-dust ratio along the disk. We compute an average ratio of 260 -- a value consistent with the Milky Way and external spirals within the uncertainties in deriving both the dust mass and the quantity of molecular gas. The bulk of dust in NGC 891 appears to be closely associated with the molecular gas phase although it may start to follow the distribution of atomic hydrogen at radii >9 kpc (i.e. >0.5 R_25). Using the optical depth of the NGC 891 disk, we quantify how light emitted at high redshift is attenuated by dust residing in foreground spirals. For B-band observations of galaxies typically found in the Hubble Deep Field, the amount of light lost is expected to be small (~ 5%). This value depends critically on the maximum radial extent of cold dust in spiral disks (which is poorly known). It may also represent a lower limit if galaxies expel dust over time into the intergalactic medium.

P. B. Alton; E. M. Xilouris; S. Bianchi; J. Davies; N. Kylafis

2000-03-20

117

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

E-print Network

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

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

1997-08-22

118

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

E-print Network

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

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

2014-01-01

119

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 functi...

Hau, George; Kilborn, Virginia; Forbes, Duncan; Balogh, Michael; Oosterloo, Tom

2007-01-01

120

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.

121

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

122

NGC 5291: Implications for the Formation of Dwarf Galaxies  

NASA Astrophysics Data System (ADS)

The possible formation and evolution of dwarf irregular galaxies from material derived from perturbed evolved galaxies is addressed via an H I study of a likely example, the peculiar system NGC 5291. This system, located in the western outskirts of the cluster Abell 3574, contains the lenticular galaxy NGC 5291 which is in close proximity to a disturbed companion and is flanked by an extensive complex of numerous knots extending roughly 4 min north and 4 min south of the galaxy. In an initial optical and radio study, Longmore et al. (1979, MNRAS, 188, 285) showed that these knots have the spectra of vigorous star-forming regions, and suggested that some may in fact be young dwarf irregular galaxies. High resolution 21-cm line observations taken with the VLA are presented here and reveal that the H I distribution associated with this system encompasses not only the entire N-S complex of optical knots, but also forms an incomplete ring or tail that extends approximately 3 min to the west. The H I associated with NGC 5291 itself shows a high velocity range; the Seashell is not detected. The formation mechanism for this unusual system is unclear and two models - a large, low-luminosity ram-swept disk, and a ram-swept interaction-are discussed. The H I in the system contains numerous concentrations, mostly along the N-S arc of the star-forming complexes, which generally coincide with one or more optical knots; the larger H I features contain several x 109 solar mass of gas. Each of the knots is compared to a set of criteria designed to determine if these objects are bound against their own internal kinetic energy and are tidally stable relative to the host galaxy. An analysis of the properties of the H I concentrations surrounding the optical star-forming complexes indicates that at least the largest of these is a bound system; it also possesses a stellar component. It is suggested that this object is a genuinely young dwarf irregular galaxy that has evolved from the material associated with the system and that this entire complex contains several proto- or young dwarf irregular galaxies in various stages of development. We are therefore witnessing the early evolution of a number of genuinely young galaxies. Given the evident importance of the NGC 5291 system as a 'nursery' for young galaxies, careful modeling is required if we are to understand this remarkable galaxy.

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

1997-10-01

123

NGC 5291: Implications for the Formation of Dwarf Galaxies  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

124

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

NASA Astrophysics Data System (ADS)

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

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

2001-12-01

125

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

126

Bars, Spiral Structure, and Secular Evolution in Disk Galaxies  

E-print Network

Simulations and observations of galactic bars suggest they do not commonly evolve into bulges, although it is possible that the earliest bars formed bulges long ago, when galaxies were smaller, denser, and had more gas. The most highly evolved of today's bars may become lenses over a Hubble time. Most galaxies in the early Universe are extremely clumpy, with 10^8-10^9 Msun blue clumps that resemble in color and magnitude the isolated field objects nearby. The presence of blue and irregular bars at high redshift suggests that some bars formed primarily in the gas phase accompanied by giant starbursts, rather than in pure stellar disks like most models. Secular and non-secular processes that cause galaxies to evolve are summarized.

Bruce G. Elmegreen

2005-10-09

127

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

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

128

Secular Evolution of Barred Galaxies with Massive Central Black Holes  

E-print Network

The influence of central black holes on the dynamical evolution of bars in disk galaxies is examined. In particular, we use numerical simulation to estimate the minimum mass black hole (BH) needed to destroy a bar. Initially, bars form in the disks via dynamical instability. Thereafter, once a bar is fully developed, a BH is adiabatically added at the center of the disk. To mitigate the global effects of gravitational softening, Poisson's equation for the disk is solved by expanding the density and potential of the galaxy in a set of basis functions. Our results indicate that a bar can be completely destroyed in a time much smaller than a Hubble time if the central mass exceeds about 0.5% of the disk mass. Since the implied minimum BH mass for bar destruction is of order 10^{8.5} solar masses for a typical disk galaxy, this process should not be a rare phenomenon. The bar amplitude decreases gradually with time after the BH is added, and the rate at which the bar is destroyed increases with increasing BH mass. This suggests that bar destruction arises from scattering of stars that support the bar as they pass close to the center.

Shunsuke Hozumi; Lars Hernquist

1998-05-30

129

A Survey of Satellite Galaxies around NGC 4258  

E-print Network

We conduct a survey of satellite galaxies around the nearby spiral NGC 4258 by combining spectroscopic observations from the Apache Point Observatory 3.5-meter telescope with SDSS spectra. New spectroscopy is obtained for 15 galaxies. Of the 47 observed objects, we categorize 8 of them as probable satellites, 8 as possible satellites, and 17 as unlikely to be satellites. We do not speculate on the membership of the remaining 14 galaxies due to a lack of velocity and distance information. Radially integrating our best fit NFW profile for NGC 4258 yields a total mass of 1.8e12 Msun within 200 kpc. We find that the angular distribution of the satellites appears to be random, and not preferentially aligned with the disk of NGC 4258. In addition, many of the probable satellite galaxies have blue u-r colors and appear to be star-forming irregulars in SDSS images; this stands in contrast to the low number of blue satellites in the Milky Way and M31 systems at comparable distances.

Spencer, Meghin; Yoachim, Peter

2014-01-01

130

A Survey of Satellite Galaxies around NGC 4258  

NASA Astrophysics Data System (ADS)

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

Spencer, Meghin; Loebman, Sarah; Yoachim, Peter

2014-06-01

131

An Imaging Survey of Early-Type Barred Galaxies  

E-print Network

This paper presents the results of a high-resolution imaging survey, using both ground-based and Hubble Space Telescope images, of a complete sample of nearby barred S0--Sa galaxies in the field, with a particular emphasis on identifying and measuring central structures within the bars: secondary bars, inner disks, nuclear rings and spirals, and off-plane dust. A discussion of the frequency and statistical properties of the various types of inner structures has already been published. Here, we present the data for the individual galaxies and measurements of their bars and inner structures. We set out the methods we use to find and measure these structures, and how we discriminate between them. In particular, we discuss some of the deficiencies of ellipse fitting of the isophotes, which by itself cannot always distinguish between bars, rings, spirals, and dust, and which can produce erroneous measurements of bar sizes and orientations.

Peter Erwin; Linda S. Sparke

2002-12-04

132

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

SciTech Connect

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

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

2012-12-01

133

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 in the southern constellation Pavo, and about 300 million light years from the Sun. From tip to tip, NGC-6872 is a composite made by NASA's Spitzer and Chandra satellites, and a ground-based telescope. Although NGC-6872

134

ROSAT and ASCA Observations of X-ray Luminous starburst Galaxies : NGC3310 and NGC3690  

E-print Network

We present ROSAT (HRI and PSPC) and ASCA observations of the two luminous (L_x ~10^{41-42} erg s^{-1}) star-forming galaxies NGC3310 and NGC3690. The HRI shows clearly that the sources are extended with the X-ray emission in NGC3690 coming from at least three regions. The combined 0.1-10 keV spectrum of NGC3310 can be described by two components, a Raymond-Smith plasma with temperature kT=0.81^{+0.09}_{-0.12} keV and a hard power-law, Gamma=1.44^{+0.20}_{-0.11}, (or alternatively a harder Raymond-Smith plasma with kT ~15 keV), while there is no substantial excess absorption above the Galactic. The soft component emission is probably due to a super-wind while the nature of the hard emission is more uncertain with likely origins, X-ray binaries, inverse Compton scattering of IR photons, an AGN or a very hot gas component (~10^8 K). The spectrum of NGC3690 is similar, with kT=0.83^{+0.02}_{-0.04} keV and Gamma=1.56^{+0.11}_{-0.11}. We also employ more complicated models such as a multi-temperature thermal plasma, a non-equilibrium ionization code or the addition of a third softer component which improve the fit but not at a statistically significant level (<2sigma). These results are similar to recent results on the archetypal star-forming galaxies M82 and NGC253.

A. L. Zezas; I. Georgantopoulos; M. J. Ward

1998-07-24

135

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, Transition, Bulgeless, Truncated ... · Colour / Population Continuity · Spectroscopic Evidence for Secular: Courteau, de Jong & Broeils (1996, ApJL, 457, 73) "Evidence for Secular Evolution in Spiral Galaxies" 326

Bender, Ralf

136

A spectroscopic study of NGC 6251 and its companion galaxies  

E-print Network

Measurements of the velocities of galaxies thought to be associated with the giant radio galaxy NGC 6251 confirm the presence of a poor cluster with a systemic redshift of z= 0.0244 +/- 0.0004 and a line-of-sight velocity dispersion of sigma_{z}= 283 (+109, -52) km/s. This suggests a cluster atmosphere temperature of T = 0.7 (+0.6, -0.2) keV, which is not enough to confine the radio jet by gas pressure. The core of NGC 6251 shows strong emission lines of [O III] and H alpha + [N II], but there is no evidence for line emission from the jet (detected in optical continuum by Keel (1988)).

P. N. Werner; D. M. Worrall; M. Birkinshaw

2000-05-03

137

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

138

Dynamics of the Polar Disk Galaxy NGC 4650A  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

139

H I in the Shell Elliptical Galaxy NGC 3656  

Microsoft Academic Search

Very Large Array7 neutral hydrogen observations of the shell elliptical galaxy NGC 3656 reveal an edge-on, warped minor-axis gaseous disk (MHI~2×109 Msolar) extending 7 kpc. H I is also found outside the optical image, on two complexes to the northeast and northwest that seem to trace one or two tidal tails, or possibly an outer broken H I disk or

Marc Balcells; J. H. van Gorkom; Renzo Sancisi; Carlos del Burgo

2001-01-01

140

Submillimetre maps of the edge-on galaxy NGC 891  

Microsoft Academic Search

Broadband continuum images of the edge-on galaxy NGC 891 at 850 and 450\\u000amicrons are presented. These images are qualitatively very similar to the 1300\\u000amicron and CO images obtained by others. With respect to the 850 micron\\u000acontinuum, CO is strongest in the socalled `molecular ring', and weakest at the\\u000alargest radii sampled. Inside the molecular ring, the CO\\/850

F. P. Israel; P. P. van der Werf; R. P. J. Tilanus

1998-01-01

141

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

142

Orbital Structure and Asymptotic Orbits in Barred-Spiral Galaxies  

NASA Astrophysics Data System (ADS)

Using frequency analysis we find the orbital structure of a self-consistent N-body configuration simulating a rotating barred-spiral galaxy. We detect the main families of the regular orbits and of the chaotic ones, separately. Chaotic orbits play a major role in supporting the outer envelope of the bar as well as the ring and the spiral arms. The explanation is given by studying the unstable asymptotic curves of the main unstable periodic orbits of the system. A new type of stickiness phenomenon near the main unstable asymptotic curves on the phase space seems to be responsible for the galaxy’s shape outside corotation.

Harsoula, M.; Kalapotharakos, C.; Contopoulos, G.

2010-07-01

143

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

144

Star Formation Properties in Barred Galaxies(SFB). III. Statistical Study of Bar-driven Secular Evolution using a sample of nearby barred spirals  

E-print Network

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 to be 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 towards 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 ...

Zhou, Zhi-Min; Wu, Hong

2014-01-01

145

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

146

The Evolutionary History of the Elliptical Galaxy NGC 1052  

E-print Network

We have obtained Keck spectra for 16 globular clusters (GCs) associated with the merger remnant elliptical NGC 1052, as well as a long-slit spectrum of the galaxy. We derive ages, metallicities and abundance ratios from simple stellar population models using the methods of Proctor & Sansom (2002), applied to extragalactic GCs for the first time. We find all of the GCs to be ~13 Gyr old according to simple stellar populations, with a large range of metallicities. From the galaxy spectrum we find NGC 1052 to have a luminosity-weighted central age of ~2 Gyr and metallicity of [Fe/H]~+0.6. No strong gradients in either age or metallicity were found to the maximum radius measured (~1 kpc). However, we do find a strong radial gradient in alpha-element abundance, which reaches a very high central value. The young central starburst age is consistent with the age inferred from the HI tidal tails and infalling gas of \\~1 Gyr. Thus, although NGC 1052 shows substantial evidence for a recent merger and an associated starburst, it appears that the merger did not induce the formation of new GCs, perhaps suggesting that little recent star formation occurred. This interpretation is consistent with ``frosting'' models for early-type galaxy formation. (Abridged)

Michael Pierce; Jean P. Brodie; Duncan A. Forbes; Michael A. Beasley; Robert Proctor; Jay Strader

2005-01-05

147

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

148

The Void in the Sculptor Group Spiral Galaxy NGC 247  

E-print Network

The dwarf galaxy NGC 247, located in the Sculptor Filament, displays an apparent void on the north side of its spiral disk. The existence of the void in the disk 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 disk of NGC 247 using photometry of archival Hubble Space Telescope data to analyze the stars in and around this region. Based on a grid of isochrones from log(t)=6.8 to log(t)=10.0, we assign ages using nearest-neighbor 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 disk may be due to a recent interaction with a nearly dark sub-halo that collided with the disk and could account for the long-lived nature of the void.

Wagner-Kaiser, R; Sarajedini, A; Chakrabarti, S

2014-01-01

149

NGC 4438: Ram pressure sweeping of a tidally disrupted galaxy  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

150

Kinematics and stellar population of the lenticular galaxy NGC 4124  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

151

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

152

The ratio of pattern speeds in double-barred galaxies  

NASA Astrophysics Data System (ADS)

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

Font, Joan; Beckman, John E.; Zaragoza-Cardiel, Javier; Fathi, Kambiz; Epinat, Benoit; Amram, Philippe

2014-10-01

153

LUMINOSITIES OF BARRED AND UNBARRED S0 GALAXIES  

SciTech Connect

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

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

2012-07-20

154

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

NASA Astrophysics Data System (ADS)

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

Stanford, S. A.; Balcells, Marc

1991-03-01

155

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

SciTech Connect

Numerical simulations of the interacting galaxies in the NGC 520/UGC 957 system are presented. Two sets of models were produced to investigate the postulated three-galaxy system of two colliding disk galaxies within NGC 520 and the dwarf galaxy UGC 957. The first set of models simulated a dwarf perturbing one-disk galaxy, which tested the possibility that NGC 520 contains only one galaxy disturbed by the passage of UGC 957. The resulting morphology of the perturbed single disk in the simulation fails to reproduce the observed tidal tails and northwest mass condensation of NGC 520. A second set of models simulated two colliding disks, which tested the hypothesis that NGC 520 itself contains two galaxies in a strong collision and UGC 957 is unimportant to the interaction. These disk-disk models produced a good match to the morphology of the present NGC 520. It is concluded that (1) NGC 520 contains two colliding disk galaxies which have produced the brighter southern half of the long tidal tail and (2) UGC 957, which may originally have been a satellite of one of the disk galaxies, formed the diffuse northern tail as it orbited NGC 520. 27 refs.

Stanford, S.A.; Balcells, M. (Wisconsin Univ., Madison (USA) Groningen State Univ. (Netherlands))

1991-03-01

156

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

NASA Technical Reports Server (NTRS)

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

Stanford, S. A.; Balcells, Marc

1991-01-01

157

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

E-print Network

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

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

2012-01-01

158

Hard Gamma Ray Emission from the Starburst Galaxy NGC 253  

NASA Technical Reports Server (NTRS)

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

Jackson, James M.; Marscher, Alan M.

1996-01-01

159

Cosmic evolution of bars in simulations of galaxy formation  

E-print Network

We investigate the evolution of two bars formed in fully self-consistent hydrodynamical simulations of the formation of Milky Way-mass galaxies. One galaxy shows higher central mass concentration and has a longer and stronger bar than the other at $z = 0$. The stronger bar evolves by transferring its angular momentum mainly to the dark halo. Consequently the rotation speed of the bar decreases with time, while the amplitude of the bar increases with time. While these features qualitatively agree with the results obtained by idealized simulations, our bars show some unusual behaviors. The pattern speed of the stronger bar largely goes up and down within a half revolution in its early evolutionary stage. This unsteady rotation occurs when the bar is misaligned with the $m = 4$ mode Fourier component. The amplitude of the weaker bar does not increase despite the fact that its rotation slows down with time. This result contradicts what is expected from idealized simulations and is caused by the decline of the cen...

Okamoto, Takashi; Habe, Asao

2014-01-01

160

Enormous disc of cool gas surrounding the nearby powerful radio galaxy NGC 612 (PKS 0131-36)  

E-print Network

We present the detection of an enormous disc of cool neutral hydrogen (HI) gas surrounding the S0 galaxy NGC 612, which hosts one of the nearest powerful radio sources (PKS 0131-36). Using the Australia Telescope Compact Array, we detect M_HI = 1.8 x 10^9 M_sun of HI emission-line gas that is distributed in a 140 kpc wide disc-like structure along the optical disc and dust-lane of NGC 612. The bulk of the gas in the disc appears to be settled in regular rotation with a total velocity range of 850 km/s, although asymmetries in this disc indicate that perturbations are being exerted on part of the gas, possibly by a number of nearby companions. The HI disc in NGC 612 suggests that the total mass enclosed by the system is M_enc ~ 2.9 x 10^12 sin^-2(i) M_sun, implying that this early-type galaxy contains a massive dark matter halo. We also discuss an earlier study by Holt et al. that revealed the presence of a prominent young stellar population at various locations throughout the disc of NGC 612, indicating that this is a rare example of an extended radio source that is hosted by a galaxy with a large-scale star-forming disc. In addition, we map a faint HI bridge along a distance of 400 kpc in between NGC 612 and the gas-rich (M_HI = 8.9 x 10^9 M_sun) barred galaxy NGC 619, indicating that likely an interaction between both systems occurred. From the unusual amounts of HI gas and young stars in this early-type galaxy, in combination with the detection of a faint optical shell and the system's high infra-red luminosity, we argue that either ongoing or past galaxy interactions or a major merger event are a likely mechanism for the triggering of the radio source in NGC 612. This paper is part of an ongoing study to map the large-scale neutral hydrogen properties of nearby radio galaxies. --abridged--

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

2008-05-22

161

Globular Clusters in the Sombrero Galaxy (NGC 4594)  

E-print Network

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

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

1997-01-20

162

The Initial Mass Function in the Outer Galaxy: The star forming region NGC 1893  

Microsoft Academic Search

We will explore the effects of environmental conditions, which change dramatically between the inner and outer regions of the Galaxy, on the initial mass function (IMF) of the star forming region NGC 1893. Our proposed 450 ksec observation of NGC 1893, a SFR of ~3 Myr in the outer part of the Galaxy, joint with two hours of Spitzer data,

Giuseppina Micela

2005-01-01

163

Variable stars as tracers of stellar populations in Local Group galaxies: Leo I and NGC 6822  

Microsoft Academic Search

Results are presented of a study of the variable star populations in the dwarf spheroidal galaxy Leo I and in the dwarf irregular galaxy NGC 6822, based on time series photometry obtained with the Wide Field Imager of the 2.2 m ESO\\/MPI telescope (Leo I) and the Very Large Telescope (NGC 6822). We found about 250 (lower limit) variables in

L. Baldacci; F. Matonti; L. Rizzi; G. Clementini; E. V. Held; Y. Momany; L. Di Fabrizio; I. Saviane

2004-01-01

164

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

SciTech Connect

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

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

2010-09-15

165

SN 1978K: an Extraordinary Supernova in the Nearby Galaxy NGC 1313  

NASA Astrophysics Data System (ADS)

We have identified an extremely luminous radio and X-ray source with an optically variable emission-line object in the outskirts of the nearby barred spiral galaxy NGC 1313. Archival data show that the object (officially designated SN 1978K) had a major optical outburst (MB < -12.3) in mid-1978 and that a radio and X-ray outburst followed this event. The light curve, optical spectra, radio data, and the X-ray data all indicate that the event was a very unusual Type II supernova, with many similar properties to the so-called Type V supernovae SN 1961V in NGC 1058 and SN 1986J in NGC 891. The currently bright Doppler-broadened Balmer lines, the forbidden lines and the extremely high radio and X-ray luminosities (among the brightest of known supernovae in both regimes) are believed to be powered by the shock driving through a dense circumstellar medium created by extreme mass-loss (˜4 × 10-5 Msun yr-1) from a massive progenitor. Some of the optical properties may be explained by the super outburst of an ?I Carinae-type object, but such an event would fail to explain the radio and X-ray luminosity. The closeness, low extinction and low confusion toward SN 1978K will allow for a detailed study of a class of peculiar supernovae which is possibly much more common than previously supposed.

Ryder, Stuart; Staveley-Smith, Lister; Dopita, Michael; Petre, Robert; Colbert, Edward; Malin, David; Schlegel, Eric

1993-10-01

166

NGC 625: An Intriguing Nearby Dwarf Starburst Galaxy  

NASA Astrophysics Data System (ADS)

NGC 625 is a dwarf irregular galaxy in the nearby Sculptor group which is experiencing a strong burst of star formation. Its close proximity and high galactic latitude make it a very desirable target to help us to understand the starburst phase of dwarf galaxies. WFPC2 observations are needed to combine with existing HI synthesis imaging, ground based optical imaging and spectroscopy, and x-ray imaging in order to construct a coherent model for this starburst. Specifically, we need high resolution optical imaging at V and I in order to reconstruct the recent star formation history. This will allow us to assess the impact of the burst on the HI and the development of the x-ray emission in a self-consistent way. Our ultimate goal is a better understanding of the average duration of bursts of star formation and the duty cycle for bursting star formation in dwarf galaxies through comparative studies of nearby systems.

Skillman, Evan

2000-07-01

167

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

168

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

169

Reverberation Mapping of the Seyfert 1 Galaxy NGC 7469  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

170

Submillimetre maps of the edge-on galaxy NGC 891  

E-print Network

Broadband continuum images of the edge-on galaxy NGC 891 at 850 and 450 microns are presented. These images are qualitatively very similar to the 1300 micron and CO images obtained by others. With respect to the 850 micron continuum, CO is strongest in the socalled `molecular ring', and weakest at the largest radii sampled. Inside the molecular ring, the CO/850 micron ratio is somewhat less than in the ring, but higher than in the remainder of the disk. The integrated far-infrared emission from NGC 891 is dominated by small particles shortwards of 100 microns. Longwards of 100 micron, the emission can be equally well fitted by a single population of large dust grains at 21 K, or a bimodal population of grains at temperatures of 18 K and 27 K. The circumnuclear disk is at a temperature of at least 50 K, and probably much higher.

F. P. Israel; P. P. van der Werf; R. P. J. Tilanus

1998-06-19

171

Submillimetre maps of the edge-on galaxy NGC 891  

E-print Network

Broadband continuum images of the edge-on galaxy NGC 891 at 850 and 450 microns are presented. These images are qualitatively very similar to the 1300 micron and CO images obtained by others. With respect to the 850 micron continuum, CO is strongest in the socalled `molecular ring', and weakest at the largest radii sampled. Inside the molecular ring, the CO/850 micron ratio is somewhat less than in the ring, but higher than in the remainder of the disk. The integrated far-infrared emission from NGC 891 is dominated by small particles shortwards of 100 microns. Longwards of 100 micron, the emission can be equally well fitted by a single population of large dust grains at 21 K, or a bimodal population of grains at temperatures of 18 K and 27 K. The circumnuclear disk is at a temperature of at least 50 K, and probably much higher.

Israel, F P; Tilanus, R P J

1999-01-01

172

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

173

Multiphase Observations of the Dwarf Starburst Galaxy NGC 625  

NASA Astrophysics Data System (ADS)

Nearby dwarf galaxies offer an unique opportunity to study the multiphase ISM at high resolution. Of special interest are those galaxies which exhibit starburst activity, as they may represent nearby analogs to the star-forming galaxies seen in large numbers at higher redshifts. These objects display a complicated interplay of ISM phases, with molecular, neutral, ionized and coronal gases each tracing a different component or consequence of the star formation process. The high spectral resolution of FUSE in the vacuum UV provides the unique opportunity to study each of these phases simultaneously in relatively nearby galaxies. We therefore propose a deep FUSE integration of the Sculptor Group dwarf starburst galaxy NGC625. In particular we will study the coronal gas content and kinematics using the OVI 1032, 1038 Angstrom doublet in absorption, and the diffuse molecular component using the absorption lines of H_2 in the Lyman-Werner bands. These data will be compared with ground-based and HST optical imaging, XMM-NEWTON x-ray imaging and spectroscopy, high-resolution radio data, and forthcoming SIRTF mid-IR spectroscopy in a detailed multiwavelength study of this paradigm starburst galaxy.

Skillman, E.

174

Tidal Dwarf Galaxies Around a Post-merger Galaxy, NGC 4922  

NASA Astrophysics Data System (ADS)

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 ~106-7 M sun, typical for dwarf galaxies.

Sheen, Yun-Kyeong; Jeong, Hyunjin; Yi, Sukyoung K.; Ferreras, Ignacio; Lotz, Jennifer M.; Olsen, Knut A. G.; Dickinson, Mark; Barnes, Sydney; Park, Jang-Hyun; Ree, Chang H.; Madore, Barry F.; Barlow, Tom A.; Conrow, Tim; Foster, Karl; Friendman, Peter G.; Lee, Young-Wook; Martin, D. Christopher; Morrissey, Patrick; Neff, Susan G.; Schiminovich, David; Seibert, Mark; Small, Todd; Wyder, Ted K.

2009-12-01

175

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

176

SCUBA Observations of the Elliptical Galaxy NGC 4374  

E-print Network

We present SCUBA imaging and photometry of the elliptical galaxy NGC 4374. The imaging observations are used to examine the spatial distribution of thermal emission from dust and the radio to infrared continuum spectrum. In the SCUBA 850 um image, the galaxy is found to be a point source, constraining the emission to less than 15'' (1.5 kpc for a distance of 20.74 Mpc). The simplest interpretation is that the 2000 um to 850 um SCUBA emission is synchroton from a compact core or inner-jet, and most unlikely thermal emission from cold diffuse dust. We cannot exclude free-free emission, but this would be very unexpected. The thermal emission from dust is shown in IRAS data and these along with the 450 um SCUBA datum give a dust temperature of 35 K, corresponding to a dust mass of 0.12 million solar masses. These are pilot observations in a program to look for cold, diffusely distributed dust in elliptical galaxies, however much deeper 450 um imaging is required to investigate this in NGC 4374.

Leeuw, L L; Robson, E I

1999-01-01

177

SCUBA Observations of the Elliptical Galaxy NGC 4374  

E-print Network

We present SCUBA imaging and photometry of the elliptical galaxy NGC 4374. The imaging observations are used to examine the spatial distribution of thermal emission from dust and the radio to infrared continuum spectrum. In the SCUBA 850 um image, the galaxy is found to be a point source, constraining the emission to less than 15'' (1.5 kpc for a distance of 20.74 Mpc). The simplest interpretation is that the 2000 um to 850 um SCUBA emission is synchroton from a compact core or inner-jet, and most unlikely thermal emission from cold diffuse dust. We cannot exclude free-free emission, but this would be very unexpected. The thermal emission from dust is shown in IRAS data and these along with the 450 um SCUBA datum give a dust temperature of 35 K, corresponding to a dust mass of 0.12 million solar masses. These are pilot observations in a program to look for cold, diffusely distributed dust in elliptical galaxies, however much deeper 450 um imaging is required to investigate this in NGC 4374.

L. L. Leeuw; A. E. Sansom; E. I. Robson

1999-11-06

178

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

179

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.

180

Secular- and merger-built bulges in barred galaxies  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

181

THE MAGNETIC FIELD OF THE IRREGULAR GALAXY NGC 4214  

SciTech Connect

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

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

2011-08-01

182

Barred Galaxies at z > 0.7: NICMOS HDFN Observations  

E-print Network

Previous optical studies found an unexpected deficit of bars at z > 0.7. To investigate the effects of bandshifting, we have studied the fraction of barred spirals in the NICMOS Deep Field North. At z > 0.7 we find at least four barred spirals, doubling the number previously detected. The number of barred galaxies is small because these (and previous) data lack adequate spatial resolution. A typical 5 kpc bar at z > 0.7 is only marginally detectable for WFPC2 at 0.8microns; the NICMOS data have even lower resolution and can only find the largest bars. The average size of the four bars seen at z > 0.7 is 12 kpc. The fraction of such large bars (4/95) is higher than that seen in nearby spirals (1/44); all known selection effects suggest that the observed fraction is a lower limit. However, important caveats such as small numbers and difficulties in defining comparable samples at high and low redshifts should be noted. We conclude that there is no significant evidence for a decrease in the fraction of barred spirals beyond z ~ 0.7.

Kartik Sheth; Michael W. Regan; Nick Scoville; Linda Strubbe

2003-05-29

183

On the nature of the barlens component in barred galaxies  

E-print Network

Barred galaxies have very interesting morphological features. Here we examine the barlens, a lens-like component whose extent along the bar major axis is shorter than that of the bar and whose outline is oval or circular. We show that such a component can also be found in a number of N-body plus SPH simulations. We analyse its properties by converting simulation snapshots into images, which we then analyse in the same way as images of observed galaxies. We make extensive comparisons with galaxies from the NIRS0S (Near Infrared S0 Survey) and the S$^4$G (Spitzer Stellar Structure Survey of Galaxies) samples and find very good agreement. These comparisons include morphology, radial projected density profiles, shapes, sizes and fluxes. We observe the barlens component in our simulations from different viewing angles. This reveals that {\\it barlenses are the vertically thick part of the bar seen face-on, i.e. that a barlens seen edge-on is a boxy/peanut/X bulge}. This finding makes it possible to follow barlens d...

Athanassoula, E; Salo, H; Bosma, A

2014-01-01

184

GMOS Spectroscopy of the S0 galaxy NGC 3115  

E-print Network

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

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

2006-01-10

185

Discovery of GeV Emission from the Direction of the Luminous Infrared Galaxy NGC 2146  

NASA Astrophysics Data System (ADS)

Recent detections of high-energy gamma-ray emission from starburst galaxies M82 and NGC 253 suggest that starburst galaxies are huge reservoirs of cosmic rays and these cosmic rays convert a significant fraction of their energy into gamma-rays by colliding with the dense interstellar medium. In this paper, we report the search for high-energy gamma-ray emission from several nearby star-forming and starburst galaxies using the 68 month data obtained with the Fermi Large Area Telescope. We found a ~5.5? detection of gamma-ray emission above 200 MeV from a source spatially coincident with the location of the luminous infrared galaxy NGC 2146. Also taking into account the temporal and spectral properties of the gamma-ray emission, we suggest that the gamma-ray source is likely to be the counterpart of NGC 2146. The gamma-ray luminosity suggests that cosmic rays in NGC 2146 convert most of their energy into secondary pions, so NGC 2146 is a "proton calorimeter." It is also found that NGC 2146 obeys the quasi-linear scaling relation between gamma-ray luminosity and total infrared luminosity for star-forming galaxies, strengthening the connection between massive star formation and gamma-ray emission of star-forming galaxies. Possible TeV emission from NGC 2146 is predicted and the implications for high-energy neutrino emission from starburst galaxies are discussed.

Tang, Qing-Wen; Wang, Xiang-Yu; Tam, Pak-Hin Thomas

2014-10-01

186

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

187

Infrared observations of the spiral galaxy NGC 891  

NASA Astrophysics Data System (ADS)

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

Whaley, Cynthia

2007-08-01

188

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

189

Dynamic S0 Galaxies: A Case Study of NGC 5866  

NASA Astrophysics Data System (ADS)

S0 galaxies are often thought to be passively evolved from spirals after star formation is quenched. To explore what is actually occurring in such galaxies, we present a multi-wavelength case study of NGC 5866—a nearby edge-on S0 galaxy in a relatively isolated environment. This study shows strong evidence for dynamic activities in the interstellar medium, which are most likely driven by supernova explosions in the galactic disk and bulge. Understanding these activities can have strong implications for studying the evolution of such galaxies. We utilize Chandra, Hubble Space Telescope, and Spitzer data as well as ground-based observations to characterize the content, structure, and physical state of the medium and its interplay with the stellar component in NGC 5866. A cold gas disk is detected with an exponential scale height of ~102 pc. Numerous distinct off-disk dusty spurs are also clearly present: prominent ones can extend as far as ~3 × 102 pc from the galactic plane and are probably produced by individual SNe, whereas faint filaments can have ~kpc scale and are likely produced by SNe collectively in the disk/bulge. We also detect substantial amounts of diffuse H?- and P?-emitting gas with a comparable scale height as the cold gas. We find that the heating of the dust and warm ionized gas cannot be explained by the radiation from evolved stars alone, strongly indicating the presence of young stars in the galactic disk, though at a slow formation rate of ~0.05 M sun yr-1. We further reveal the presence of diffuse X-ray-emitting hot gas, which extends as far as 3.5 kpc away from the galactic plane and can be heated easily by Type Ia SNe in the bulge. However, the mean temperature of this gas is ~0.2 keV, substantially lower than what might be expected from the mass loss of evolved stars and Type Ia SNe heating alone in the galaxy, indicating that the mass loading from the cool gas is important. The total masses of the cold, warm ionized, and hot gases are ~5 × 108 M sun, 4 × 104 M sun, and 3 × 107 M sun, respectively. The relative richness of the gases, apparently undergoing circulations between the disk and halo of the galaxy, is perhaps a result of its relative isolation.

Li, Jiang-Tao; Wang, Q. Daniel; Li, Zhiyuan; Chen, Yang

2009-11-01

190

Double barred galaxies at intermediate redshifts: A feasibility study  

E-print Network

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

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

2005-09-20

191

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

192

The complex nature of the Seyfert galaxy NGC 7592  

NASA Technical Reports Server (NTRS)

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

Rafanelli, Piero; Marziani, Paolo

1990-01-01

193

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

194

The Nuclear Spectral Energy Distribution of NGC 4395, the Least Luminous Type 1 Seyfert Galaxy  

Microsoft Academic Search

We present X-ray (ROSAT), infrared, and radio observations of NGC 4395, which harbors the optically least luminous type 1 Seyfert nucleus discovered thus far. In combination with published optical and ultraviolet spectra, we have used these data to assemble the broadband spectral energy distribution (SED) of the galaxy's nucleus. Interestingly, the SED of NGC 4395 differs markedly from the SEDs

Edward C. Moran; Alexei V. Filippenko; Luis C. Ho; Joseph C. Shields; Tomaso Belloni; Andrea Comastri; Steven L. Snowden; Richard A. Sramek

1999-01-01

195

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

196

Large-scale shocks in the starburst galaxy NGC 253 Interferometer mapping of a 600 pc SiO\\/H13CO+ circumnuclear disk  

Microsoft Academic Search

This paper presents the first high-resolution SiO map made in an external galaxy. The nucleus of the nearby barred spiral NGC 253 has been observed simultaneously in the v=0, J=2-1 line of SiO and in the J=1-0 line of H13CO+ with the IRAM interferometer, with a resolution of 7.5002.600. Emission from SiO and H13CO+ is extended in the nu- cleus

S. Garc ´ ia-Burillo; J. Mart ´ in-Pintado; A. Fuente; R. Neri

197

Variable stars as tracers of stellar populations in Local Group galaxies: Leo I and NGC 6822  

Microsoft Academic Search

Results are presented of a study of the variable star populations in the\\u000adwarf spheroidal galaxy Leo I and in the dwarf irregular galaxy NGC 6822, based\\u000aon time series photometry obtained with the Wide Field Imager of the 2.2 m\\u000aESO\\/MPI telescope (Leo I) and the Very Large Telescope (NGC 6822). We found\\u000aabout 250 (lower limit) variables in

L. Baldacci; F. Matonti; L. Rizzi; G. Clementini; E. V. Held; Y. Momany; L. Di Fabrizio; I. Saviane

2003-01-01

198

Kinematics of the narrow-line regions in the Seyfert galaxies NGC 4151 and NGC 1068  

NASA Astrophysics Data System (ADS)

We present a study of high-resolution long-slit spectra of the narrow-line regions (NLRs) of NGC 4151 (a Seyfert 1 galaxy) and NGC 1068 (a Seyfert 2 galaxy) obtained with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST). The spectra were retrieved from the Multimission Archive at Space Telescope (MAST) and were obtained from five and seven orbits of HST time resulting in five and seven parallel slit configurations at position angles of 52° and 38° for NGC 4151 and NGC 1068 respectively. The spectra have a spatial resolution of 0?.2 across and 0?.1 along each slit. Observations of [O III] emission from the NLRs were made using the medium resolution G430M grating aboard HST. The spectral resolving power of the grating, R=lDl?90 00 , resulted in the detection of multiple kinematic components of the [O III] emission line gas along each slit. Radial velocities of the components were measured using a Gaussian fitting procedure. Biconical outflow models were generated to match the data and for comparison to previous models done with lower dispersion observations. The general trend is an increase in radial velocity roughly proportional to distance from the nucleus, followed by a linear decrease after roughly 100 pc. This is similar to that seen in other Seyfert galaxies, indicating common acceleration and deceleration mechanisms. The full-width at half-maximum (FWHM) of the emission lines reaches a maximum of 1000 kms-1 near the nucleus, and generally decreases with increasing distance to about 100 kms-1 in the extended narrow-line region (ENLR), starting at about 400 pc from the nucleus. In addition to the bright emission knots, which generally fit our model, there are faint high velocity clouds that do not fit the biconical outflow pattern of our kinematic model. A comparison of our observations with high-resolution radio maps shows that the kinematics of the faint NLR clouds may be affected by the radio lobes that comprise the inner jet. However, the bright NLR clouds show a smooth transition across the radio knots in radial velocity and velocity dispersion plots and remain essentially undisturbed in their vicinity, indicating that the radio jet is not the principal driving force on the outflowing NLR clouds. A dynamical model was developed for NGC 1068; it includes forces of radiation pressure, gravity, and drag due an ambient medium, simultaneously acting on the NLR clouds. The velocity profile from this model was too steep to fit the data, which show a more slowly increasing velocity profile. Gravity alone was not able to slow down the clouds but with the drag forces included, the clouds could slow down, reaching systemic velocities at distances that depend on the column densities of the NLR gas and density of the intercloud medium. A biconical model using the geometric parameters from our kinematic fit, and the velocity law from the dynamic fit, was used to match the data. The resulting dynamic model represented a poor fit to the data, indicating the need for additional dynamical considerations.

Das, Varendra

199

Nuclear outflows in the Seyfert 2 galaxy NGC 5929  

NASA Astrophysics Data System (ADS)

We present two-dimensional (2D) near-infrared spectra of the inner 3^{"}× 3^{"} of the Seyfert 2 galaxy NGC 5929 at a spatial resolution of ˜ 20 pc obtained with the Gemini NIFS. We report the discovery of a linear structure ˜ 300 pc in extent and of ˜ 50 pc in width oriented perpendicular to the radio jet, showing broadened emission-line profiles. While over most of the field the emission-line profiles have full-widths-at -half-maximum (FWHM) of ? 200km s^{-1}, at the linear structure perpendicular do the radio jet the emission-line FWHMs are twice this value, and are due to two velocity components, one blueshifted and the other redshifted relative to the systemic velocity. We attribute these velocities to an outflow from the nucleus which is launched perpendicular to the radio jet. This means that: (1) both ionizing radiation and relativistic particles are escaping through holes in the torus perpendicular to the radio jet; and/or (2) the torus is also outflowing, as proposed by recent models of tori as winds from the outer parts of an accretion flow; or (3) the torus is absent in NGC 5929.

Riffel, R. A.; Storchi-Bergmmann, T.; Riffel, R.

2014-10-01

200

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

201

Dynamic S0 Galaxies: a Case Study of NGC 5866  

E-print Network

S0 galaxies are often thought to be passively evolved from spirals after star formation is quenched. To explore what is occurring in S0s, we present a multi-wavelength study of NGC5866--an isolated nearby edge-on S0. This study shows strong evidence for dynamic activities in the interstellar medium, which are most likely driven by supernova explosions in the galactic disk and bulge. We utilize Chandra, HST, and Spitzer data as well as ground-based observations to characterize the content, structure, and physical state of the medium and its interplay with stars in NGC5866. A cold gas disk is detected with an exponential scale height of 100pc. Numerous off-disk dusty spurs are clearly present: prominent ones can extend as far as 300pc from the galactic plane and are probably produced by individual SNe, whereas faint filaments can have ~ kpc scale and are likely produced by SNe collectively in disk/bulge. We also detect substantial amounts of diffuse Ha- and Pa-emitting gas with a comparable scale height as the ...

Li, Jiang-Tao; Li, Zhiyuan; Chen, Yang

2009-01-01

202

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

203

Monitoring the long term variable Seyfert 2 galaxy NGC 2992  

NASA Astrophysics Data System (ADS)

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

Matt, Giorgio

2005-10-01

204

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

205

XMM-Newton observations of the late-stage merger-remnant galaxies NGC 3921 and NGC 7252  

E-print Network

Using the high sensitivity of XMM, we have studied the X-ray emission of the two proto-typical late-stage merger remnants, NGC 3921 and NGC 7252. In the case of NGC 7252, this is complemented by archival Chandra data. We investigate the nature of the discrete X-ray point source populations and the hot diffuse gas components in these two galaxies, and compare them in the light of their different merger ages and histories. We detect 3 candidate ultra-luminous X-ray point sources in NGC 3921 and at least 6 in NGC 7252, for which we have high spatial resolution Chandra data. These have luminosities ranging from \\~1.4x10^39-10^40 erg s^-1 (for H_0= 75 km s-1 Mpc^-1). We expect these ULXs to be high mass X-ray binaries, associated with the recent star formation in these two galaxies. Extended hot gas is observed in both galaxies. We have sufficient counts in the XMM data to fit two-component hot plasma models to their X-ray spectra and estimate the X-ray luminosities of the hot diffuse gas components to be 2.75x10^40 erg s^-1 and 2.09x10^40 erg s^-1 in NGC 3921 and NGC 7252, respectively. These luminosities are low compared with the luminosities observed in typical mature elliptical galaxies LX ~10^(41-42) erg s^-1), into which these merger remnants are expected to evolve. We do not see evidence that the X-ray halos of these galaxies are currently being regenerated to the masses and luminosities seen in typical elliptical galaxies. The mass of atomic gas available to fall back into the main bodies of these galaxies and shock-heat to X-ray temperatures is insufficient for this to be the sole halo regeneration mechanism. We conclude that halo regeneration is most likely a long-term (>10 Gyr) process, occurring predominantly via mass loss from evolving stars, in a sub-sonic outflow stage commencing ~2 Gyr after the merging event.

L. A. Nolan; T. J. Ponman; A. M. Read; Francois Schweizer

2004-05-27

206

Variable stars as tracers of stellar populations in Local Group galaxies: Leo I and NGC 6822  

E-print Network

Results are presented of a study of the variable star populations in the dwarf spheroidal galaxy Leo I and in the dwarf irregular galaxy NGC 6822, based on time series photometry obtained with the Wide Field Imager of the 2.2 m ESO/MPI telescope (Leo I) and the Very Large Telescope (NGC 6822). We found about 250 (lower limit) variables in Leo I most of which are RR Lyrae stars. In NGC 6822 we identified 450 candidate variables among which about 20 are RR Lyrae stars, and many are low-luminosity, small-amplitude Cepheids.

L. Baldacci; F. Matonti; L. Rizzi; G. Clementini; E. V. Held; Y. Momany; L. Di Fabrizio; I. Saviane

2003-05-27

207

The thick disk in the galaxy NGC 4244 from S4G imaging  

Microsoft Academic Search

If thick disks are ubiquitous and a natural product of disk galaxy formation\\u000aand\\/or evolution processes, all undisturbed galaxies which have evolved during\\u000aa significant fraction of a Hubble time should have a thick disk. The late-type\\u000aspiral galaxy NGC 4244 has been reported as the only nearby edge-on galaxy\\u000awithout a confirmed thick disk. Using data from the Spitzer

Sébastien Comerón; Johan H. Knapen; Kartik Sheth; Michael W. Regan; Joannah L. Hinz; Armando Gil de Paz; Karín Menéndez-Delmestre; Juan-Carlos Muñoz-Mateos; Mark Seibert; Taehyun Kim; E. Athanassoula; Albert Bosma; Ronald J. Buta; Bruce G. Elmegreen; Luis C. Ho; Benne W. Holwerda; Eija Laurikainen; Heikki Salo; Eva Schinnerer

2010-01-01

208

The Thick Disk in the Galaxy NGC 4244 from S4G Imaging  

Microsoft Academic Search

If thick disks are ubiquitous and a natural product of disk galaxy formation and\\/or evolution processes, all undisturbed galaxies that have evolved during a significant fraction of a Hubble time should have a thick disk. The late-type spiral galaxy NGC 4244 has been reported as the only nearby edge-on galaxy without a confirmed thick disk. Using data from the Spitzer

Sébastien Comerón; Johan H. Knapen; Kartik Sheth; Michael W. Regan; Joannah L. Hinz; Armando Gil de Paz; Karín Menéndez-Delmestre; Juan-Carlos Muñoz-Mateos; Mark Seibert; Taehyun Kim; E. Athanassoula; Albert Bosma; Ronald J. Buta; Bruce G. Elmegreen; Luis C. Ho; Benne W. Holwerda; Eija Laurikainen; Heikki Salo; Eva Schinnerer

2011-01-01

209

The impact of gas inflows on star formation rates and metallicities in barred galaxies  

NASA Astrophysics Data System (ADS)

The star formation rates (SFRs) and metallicities of a sample of 294 galaxies with visually classified, strong, large-scale bars are compared to a control sample of unbarred disc galaxies selected from the Sloan Digital Sky Survey Data Release 4. The fibre (inner few kpc) metallicities of barred galaxies are uniformly higher (at a given mass) than the unbarred sample by ˜0.06 dex. However, the fibre SFRs of the visually classified barred galaxies are higher by about 60 per cent only in the galaxies with total stellar mass M? > 1010 M?. The metal enhancement at M? < 1010 M? without an accompanying increase in the SFR may be due to a short-lived phase of early bar-triggered star formation in the past, compared to on-going SFR enhancements in higher mass barred galaxies. There is no correlation between bar length or bar axial ratio with the enhancement of the SFR. In order to assess the relative importance of star formation triggered by bars and galaxy-galaxy interactions, SFRs are also determined for a sample of close galaxy pairs. Both mechanisms appear to be similarly effective at triggering central star formation for galaxies with M? > 1010 M?. However, due to the much lower fraction of pairs than bars, bars account for ˜3.5 times more triggered central star formation than interactions.

Ellison, Sara L.; Nair, Preethi; Patton, David R.; Scudder, Jillian M.; Mendel, J. Trevor; Simard, Luc

2011-09-01

210

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

E-print Network

Mon. Not. R. Astron. Soc. 337, 1233­1244 (2002) Simulations of central structure in barred galaxies structures in barred galaxies ­ nested bars, nuclear spirals and circumnuclear rings ­ by making N-body simulations, which include the gas component as inelastically colliding particles. Our models suggest

Salo, Heikki

211

Near-infrared spectrophotometry of four Seyfert 1 galaxies and NGC 1275  

NASA Technical Reports Server (NTRS)

Low-resolution spectrophotometry from 2 to 4 microns is reported for the four Seyfert 1 galaxies Mrk 335, 3C 120, Mrk 509, NGC 7469, and the peculiar emission-line galaxy NGC 1275. The spectrum of NGC 7469 exhibits a strong 3.3-micron dust feature, indicating a thermal origin for the bulk of its considerable nonstellar infrared emission. NGC 1275 has a large stellar contribution to its infrared flux at wavelengths shortward of 3 microns. The spectrum from 3 to 4 microns fits a power law which fits the 10-micron and 20-micron broad bands, as well. A thermal model which can explain the spectrum of NGC 1275 is discussed. Mrk 335 displays a complex spectrum suggestive of thermal dust emission. 3C 120 and Mrk 509 have nonstellar infrared emission shortward of 2 microns, but the data are ambiguous as to whether this emission is thermal or nonthermal in origin.

Rudy, R. J.; Jones, B.; Levan, P. D.; Puetter, R. C.; Smith, H. E.; Willner, S. P.; Tokunaga, A. T.

1982-01-01

212

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

213

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

NASA Astrophysics Data System (ADS)

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

Sellwood, J. A.

2008-05-01

214

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

E-print Network

We find that NGC6789 is the most nearby example of a Blue Compact Dwarf galaxy known to date. With the help of WFPC2 aboard the Hubble Space Telescope, we resolve NGC6789 into over 15,000 point sources in the V and I bands. The young stars of NGC6789 are found exclusively near the center of the galaxy. The red giant population identified at large galacticentric 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 NGC6789 are clearly not those of a galaxy in formation.

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

2001-02-26

215

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

E-print Network

We present Sloan g and i imaging from the GMOS instrument on the Gemini North telescope for the globular cluster (GC) system around the Virgo galaxy NGC 4649 (M60). Our three pointings, taken in good seeing conditions, cover an area of about 90 sq. arcmins. We detect 2,151 unresolved sources. Applying colour and magnitude selection criteria to this source list gives 995 candidate GCs that is greater than 90% complete to a magnitude of i = 23.6, with little contamination from background galaxies. We find fewer than half a dozen potential Ultra Compact Dwarf galaxies around NGC 4649. Foreground extinction from the nearby spiral NGC 4647 is limited to be A_V GMOS spectra of the NGC 4649 GCs.

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

2004-08-23

216

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

NASA Astrophysics Data System (ADS)

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

Schechtman-Rook, Andrew; Hess, Kelley M.

2012-05-01

217

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

E-print Network

We present a detailed photometric study of the dwarf irregular galaxy NGC 6822 aimed at investigating the properties of its stellar populations and, in particular, the presence of stellar radial gradients. Our goal is to analyse the stellar populations in six fields, which cover the whole bar of this dwarf galaxy. We derived the quantitative star formation history (SFH) of the six fields using the IAC method, involving IAC-pop/MinnIAC codes. The solutions we derived show an enhanced star formation rate (SFR) in Fields 1 and 3 during the past 500 Myr. The SFRs of the other fields are almost extinguished at very recent epochs and. We study the radial gradients of the SFR and consider the total mass converted into stars in two time intervals (between 0 and 0.5 Gyr ago and between 0.5 and 13.5 Gyr ago). We find that the scale lengths of the young and intermediate-to-old populations are perfectly compatible, with the exception of the young populations in Fields 1 and 3. The recent SF in these two fields is greater...

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

2014-01-01

218

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

NASA Astrophysics Data System (ADS)

We used deep, long-slit spectra and integral-field spectral data to study the stars, ionized gas kinematics, and stellar population properties in the lenticular barred galaxy NGC 7743. We show that ionized gas at distances larger than 1.5 kpc from the nucleus settles in the disk, which is significantly inclined toward the stellar disk of the galaxy. Making different assumptions about the geometry of the disks and including different sets of emission lines in the fitting, under the assumption of thin, flat-disk circular rotation, we obtain the full possible range of angles between the disks to be 34° ± 9° or 77° ± 9°. The most probable origin of the inclined disk is the external gas accretion from a satellite orbiting the host galaxy, with a corresponding angular momentum direction. The published data on the H I distribution around NGC 7743 suggest that the galaxy has a gas-rich environment. The emission-line ratio diagrams imply the domination of shock waves in the ionization state of the gaseous disk, whereas the contribution of photoionization from recent star formation seems to be negligible. In some parts of the disk, a difference between the velocities of the gas emitting from the forbidden lines and Balmer lines is detected. This may be caused by the mainly shock-excited inclined disk, whereas some fraction of the Balmer-line emission is produced by a small amount of gas excited by young stars in the main stellar disk of NGC 7743. In the circumnuclear region (R < 200 pc), some evidence of the active galactic nucleus jet's interaction with an ambient interstellar medium was found. Based on the observations collected with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences, which is operated under the financial support of the Science Department of Russia (registration number 01-43).

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

2011-10-01

219

Secular- and merger-built bulges in barred galaxies  

E-print Network

(Abridged) We study the incidence, as well as the nature, of composite bulges in a sample of 10 face-on barred galaxies to constrain the formation and evolutionary processes of the central regions of disk galaxies. We analyze the morphological, photometric, and kinematic properties of each bulge. Then, by using a case-by-case analysis we identify composite bulges and classify every component into a classical or pseudobulge. In addition, bar-related boxy/peanut (B/P) structures were also identified and characterised. We find only three galaxies hosting a single-component bulge (two pseudobulges and one classical bulge). We find evidence of composite bulges coming in two main types based on their formation: secular-built and merger- and secular-built. We call secular-built to composite bulges made of entirely by structures associated with secular processes such as pseudo bulges, central disks, or B/P bulges. We find four composite bulges of this kind in our sample. On the other hand, merger- and secular-built b...

Mendez-Abreu, J; Corsini, E M; Aguerri, J A L

2014-01-01

220

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

221

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

222

A Galaxy in Transition: Structure, Globular Clusters, and Distance of the Star-Forming S0 Galaxy NGC 1533 in Dorado  

E-print Network

We use two-band imaging data from the Advanced Camera for Surveys on board the Hubble Space Telescope for a detailed study of NGC1533, an SB0 galaxy in the Dorado group surrounded by a ring of HI. NGC1533 appears to be completing a transition from late to early type: it is red, but not quite dead. Faint spiral structure becomes visible following galaxy subtraction, and luminous blue stars can be seen in isolated areas of the disk. Dust is visible in the color map in the region around the bar, and there is a linear color gradient throughout the disk. We determine an accurate distance from the surface brightness fluctuations (SBF) method, finding m-M = 31.44\\pm0.12 mag, or d = 19.4\\pm1.1 Mpc. We then study the globular cluster (GC) colors, sizes, and luminosity function (GCLF). Estimates of the distance from the median of the GC half-light radii and from the peak of the GCLF both agree well with the SBF distance. The GC specific frequency is S_N=1.3\\pm0.2, typical for an early-type disk galaxy. The color distribution is bimodal, as commonly observed for bright galaxies. There is a suggestion of the redder GCs having smaller sizes, but the trend is not significant. The sizes do increase significantly with galactocentric radius, in a manner more similar to the Milky Way GC system than to those in Virgo. This difference may be an effect of the steeper density gradients in loose groups as compared to galaxy clusters. Additional studies of early-type galaxies in low density regions can help determine if this is indeed a general environmental trend.

Regina Barber DeGraaff; John P. Blakeslee; Gerhardt R. Meurer; Mary E. Putman

2007-10-03

223

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

Microsoft Academic Search

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

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

1998-01-01

224

The Formation of Dwarf Irregular Galaxies from Tidally Removed Debris and the Peculiar System NGC 5291  

Microsoft Academic Search

The formation and evolution of dwarf irregular galaxies from tidally removed material in interacting systems are discussed via a case study of the peculiar system NGC 5291. This system contains an S0 galaxy interacting with a disturbed companion known as the Seashell. The pair is located in the western outskirts of the IC 4329 cluster. Initial observations indicated a complex

B. K. Malphrus; C. E. Simpson; S. T. Gottesman; T. G. Hawarden

1995-01-01

225

The Formation of Dwarf Irregular Galaxies from Tidally Removed Debris and the Peculiar System NGC 5291  

Microsoft Academic Search

The formation and evolution of dwarf irregular galaxies from tidally removed material in interacting systems are discussed via a case study of the peculiar system NGC 5291. This system contains an S0 galaxy interacting with a disturbed companion known as the Seashell. The pair is located in the western outskirts of the IC 4329 cluster. Initial observations indicated a complex

Benjamin Malphrus

1998-01-01

226

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

Microsoft Academic Search

We present broadband and narrowband Hubble Space Telescope (HST) images of the central region of the heavily disturbed Virgo cluster galaxy NGC 4438 (Arp 120), whose nucleus has been described as a type 1 LINER or dwarf Seyfert galaxy. Narrowband Halpha and [N II] HST images reveal striking bipolar shell features, 1 kpc in projected length from end to end,

Jeffrey D. P. Kenney; Elizabeth E. Yale

2002-01-01

227

The cold dust concentrations in the colliding galaxies NGC 4038\\/39  

Microsoft Academic Search

SCUBA 450 and 850 mu m maps of the Antennae Galaxy resolve the nuclei of NGC 4038\\/39 and two prominent regions in the overlap area of the galaxy disks. They coincide excellently with bright emission peaks seen on 15 mu m, 6 cm and CO maps. ISOPHOT 60 and 100 mu m maps reveal that the overlap area and the

M. Haas; U. Klaas; I. Coulson; E. Thommes; C. Xu

2000-01-01

228

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

Microsoft Academic Search

Context. An important open question is the relation between intracluster light and the halos of central galaxies in galaxy clusters. Aims: Here we report results from an on going project with the aim to characterize the dynamical state in the core of the Hydra I (Abell 1060) cluster around NGC 3311. Methods: We analyze deep long-slit absorption line spectra reaching

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

2010-01-01

229

Near-infrared mapping of ARP 299 (IC 694NGC 3690) - Colliding galaxies unveiled  

Microsoft Academic Search

Near-infrared maps and multicolor photometry of the interacting galaxies IC 694 and NGC 3690 which form Arp 299 (= Markarian 171) are presented. These data reveal for the first time the distribution of nuclei and old red stars in a cataclysmically interacting system. The nuclei are considerably offset from the visual centroids of the galaxies but not from the mass

C. M. Telesco; R. Decher; I. Gatley

1985-01-01

230

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

SciTech Connect

We report the discovery of a UV-bright tidal dwarf galaxy (TDG) candidate in the NGC 4631/4656 galaxy group, which we designate NGC 4656UV. Using survey and archival data spanning from 1.4 GHz to the ultraviolet, we investigate the gas kinematics and stellar properties of this system. The H I morphologies of NGC 4656UV and its parent galaxy NGC 4656 are extremely disturbed, with significant amounts of counterrotating and extraplanar gas. From UV-FIR photometry, computed using a new method to correct for surface gradients on faint objects, we find that NGC 4656UV has no significant dust opacity and a blue spectral energy distribution. We compute a star formation rate of 0.027 M{sub Sun} yr{sup -1} from the far-ultraviolet flux and measure a total H I mass of 3.8 Multiplication-Sign 10{sup 8} M{sub Sun} for the object. Evolutionary synthesis modeling indicates that NGC 4656UV is a low-metallicity system whose only major burst of star formation occurred within the last {approx}260-290 Myr. The age of the stellar population is consistent with a rough timescale for a recent tidal interaction between NGC 4656 and NGC 4631, although we discuss the true nature of the object-whether it is tidal or pre-existing in origin-in the context of its metallicity being a factor of 10 lower than its parent galaxy. We estimate that NGC 4656UV is either marginally bound or unbound. If bound, it contains relatively low amounts of dark matter. The abundance of archival data allows for a deeper investigation into this dynamic system than is currently possible for most TDG candidates.

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

2012-05-10

231

The Environment of Barred Galaxies in the Low-redshift Universe  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

232

Starbursts in barred spiral galaxies. I. Mrk 712: a new Wolf-Rayet galaxy  

E-print Network

We report the discovery of emission from Wolf-Rayet stars in a giant HII region 4.5 arcsec South of the nucleus of the IRAS barred spiral galaxy Mrk 712. The ratio of WNL to OV stars, estimated from the luminosity of the HeII 4686 line, is 0.2. By comparison with starburst and stellar evolution models, we find that this high value is only compatible with a very young starburst episode (3 - 4 Myr) and a flat initial mass function (Gamma = -1). The presence of the [ArV] line reveals that the HII region is strongly ionized by the hot Wolf-Rayet stars. The comparison with other barred Wolf-Rayet galaxies suggests that the detection of Wolf-Rayet stars depends on the dust content and orientation of the galaxy.

Thierry Contini; Emmanuel Davoust; Suzanne Considere

1995-05-10

233

Bar slowdown and the distribution of dark matter in barred galaxies  

NASA Astrophysics Data System (ADS)

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

Athanassoula, E.

2014-02-01

234

The PN.S Elliptical Galaxy Survey: a standard LCDM halo around NGC 4374?  

Microsoft Academic Search

As part of our current programme to test LCDM predictions for dark matter\\u000a(DM) haloes using extended kinematical observations of early-type galaxies, we\\u000apresent a dynamical analysis of the bright elliptical galaxy NGC 4374 (M84)\\u000abased on ~450 Planetary Nebulae (PNe) velocities from the PN.Spectrograph,\\u000aalong with extended long-slit stellar kinematics. This is the first such\\u000aanalysis of a galaxy

N. R. Napolitano; A. J. Romanowsky; M. Capaccioli; N. G. Douglas; M. Arnaboldi; L. Coccato; O. Gerhard; K. Kuijken; M. R. Merrifield; S. P. Bamford; A. Cortesi; P. Das; K. C. Freeman

2010-01-01

235

Signs of gas flows in the variable Balmer line profiles of the Seyfert galaxy nuclei NGC 3227 and NGC 7469  

NASA Astrophysics Data System (ADS)

The data on the variable Balmer line profiles obtained by us for the Seyfert galaxy NGC 3227 and NGC 7469 nuclei and published separately during 1975-2006, were combined with the data compiled from literature, and reviewed in this paper. We hypothesize that the profile variations are connected with three independent regions of different physical conditions: 1) Classical broad line region (BLR) of size ~4.5 × 1016 cm is ionized and excited by the central source radiation. The central source brightness variations in 1971-1972 produced gas parameter variations of 109 cm-3 ? ne ? 108 cm-3 and 2 × 104 K ? Te ? 4 × 104 K. 2) The profiles of the Balmer lines contain narrow components that have retained their positions (radial velocities) over 25 and 17 years in NGC 3227 and NGC 7469, respectively. These components are supposed to be caused by long-lived gas flows in the nuclei of the galaxies. Observational data acquired by Rubin and Ford allow us to assume that gas in the flows can be explained by models of collision ionization and excitation of gas with self-absorption. It is dense and hot plasma with ne = 108-1012 cm-3 and Te = (1-2.5) × 104 K. 3) Broad blue bumps of radial velocities between -4000 km s-1 and -5000 km s-1 were detected in the H? profile during a several day flare twice in NGC 3227 nucleus and once in NGC 7469. One can speculate that the flares are connected with short-lived ejections. The gas in the ejections was ionized and excited by collision processes with ne ~ 1014 cm-3 and Te ~ 25 000 K.

Pronik, I. I.

2009-03-01

236

Metal-rich globular clusters in the Galaxy. III - The 'X-ray' globular cluster NGC 6441. IV - A color-magnitude diagram for NGC 6304  

Microsoft Academic Search

Results are reported for UBV photoelectric and photographic observations of about 700 stars in the southern globular cluster NGC 6441 and of about 385 stars in or near the G2 globular cluster NGC 6304. Features in the color-magnitude diagrams of the clusters are found which indicate that NGC 6441 is one of the most metal-rich clusters known in the Galaxy

J. E. Hesser; F. D. A. Hartwick

1976-01-01

237

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

238

The thick disk in the galaxy NGC 4244 from S4G imaging  

E-print Network

If thick disks are ubiquitous and a natural product of disk galaxy formation and/or evolution processes, all undisturbed galaxies which have evolved during a significant fraction of a Hubble time should have a thick disk. The late-type spiral galaxy NGC 4244 has been reported as the only nearby edge-on galaxy without a confirmed thick disk. Using data from the Spitzer Survey of Stellar Structure in Galaxies (S4G) we have identified signs of two disk components in this galaxy. The asymmetries between the light profiles on both sides of the mid-plane of NGC 4244 can be explained by a combination of the galaxy not being perfectly edge-on and a certain degree of opacity of the thin disk. We argue that the subtlety of the thick disk is a consequence of either a limited secular evolution in NGC 4244, a small fraction of stellar material in the fragments which built the galaxy, or a high amount of gaseous accretion after the formation of the galaxy.

Comerón, Sébastien; Sheth, Kartik; Regan, Michael W; Hinz, Joannah L; de Paz, Armando Gil; Menéndez-Delmestre, Karín; Muñoz-Mateos, Juan-Carlos; Seibert, Mark; Kim, Taehyun; Athanassoula, E; Bosma, Albert; Buta, Ronald J; Elmegreen, Bruce G; Ho, Luis C; Holwerda, Benne W; Laurikainen, Eija; Salo, Heikki; Schinnerer, Eva

2010-01-01

239

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

240

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

241

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

242

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

SciTech Connect

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

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

2013-06-15

243

Gas and Stellar Kinematics in the Galaxy NGC 1961  

NASA Astrophysics Data System (ADS)

Long-slit spectroscopy and CCD imaging from the Hubble Space Telescope and the MDM Observatory is presented for the massive spiral galaxy NGC 1961. We intend to measure the mass of the central supermassive black hole (SMBH). We developed our own software for spectral extraction, and for the fitting of absorption and emission lines. The program subtracts the absorption-line (stellar) portion from the emission-line spectra using a shifted template star. This improves the measurements of the residual emission lines. We present our measurements of the line centroids (velocities), widths (velocity dispersions), and strengths for the most prominent emission lines (H?, [NII], and [SII]). The rotation curve from the ground-based data is in good agreement with previous work by Rubin (1979); its asymmetric appearance suggests a possible merger. The emission lines near the nucleus broaden indicating some intrinsic dispersion. The central gas rotation curve at HST resolution is more complex than that expected for a cold, gas disk, confounding the measurement of a central black hole.

Sacash, Brian; Pinkney, Jason

2007-10-01

244

Stellar content of the interacting galaxies IC 1727 and NGC 672  

NASA Astrophysics Data System (ADS)

Based on archival Hubble Space Telescope ACS/WFC images, we have performed stellar photometry for an isolated pair of interacting galaxies, IC 1727 and NGC 672, and constructed their Hertzsprung-Russell diagrams. The galaxy IC 1727 exhibits a strong asymmetry in the apparent distribution of young stars. The distribution of old stars is smoother and less asymmetric. In the galaxy NGC672, there is no noticeable asymmetry in the distribution of stars of different ages. Based on the TRGB method, we have determined an accurate distance to each galaxy for the first time: D = 7.14 ± 0.10 Mpc for IC 1727 and D = 7.22 ± 0.10 Mpc for NGC 672, confirming that these galaxies are closely spaced. The luminosity functions of red supergiants and peripheral AGB stars in both galaxies have positionally coincident local maxima, suggesting the simultaneous enhancement of star formation in the two galaxies occurred in the intervals 20-30 and 450-700 Myr ago. The results obtained point to an enhancement of star formation processes in the interacting galaxies.

Tikhonov, N. A.; Galazutdinova, O. A.; Lebedev, V. S.

2014-01-01

245

Discovery of GeV emission from the direction of the luminous infrared galaxy NGC 2146  

E-print Network

Recent detection of high-energy gamma-ray emission from starburst galaxies M82 and NGC 253 suggests that starburst galaxies are huge revisors of cosmic rays and these cosmic rays convert a significant fraction of their energy into gamma-rays by colliding with the dense interstellar medium. In this {\\it Letter}, we report the search for high-energy gamma-ray emission from several nearby star-forming and starburst galaxies using the 68 month data obtained with the Fermi Large Area Telescope. We found a $\\sim5.5\\sigma$ detection of gamma-ray emission above 200{\\rm MeV} from a source spatially coincident with the location of the luminous infrared galaxy NGC~2146. Taking into account also the temporal and spectral properties of the gamma-ray emission, we suggest that the gamma-ray source is likely to be the counterpart of NGC~2146. The gamma-ray luminosity suggests that cosmic rays in NGC~2146 convert nearly half of their energy into secondary pions, so NGC~2146 is approximately a "proton calorimeter". It is also ...

Tang, Qing-Wen; Tam, Pak-Hin Thomas

2014-01-01

246

Discovery of a stellar tidal stream around the Whale galaxy, NGC 4631  

E-print Network

We report the discovery of a giant stellar tidal stream in the halo of NGC 4631, a nearby edge-on spiral galaxy interacting with the spiral NGC 4656, in deep images taken with a 40-cm aperture robotic telescope. The stream has two components: a bridge-like feature extended between NGC 4631 and NGC 4656 (stream_SE) and an overdensity with extended features on the opposite side of the NGC 4631 disk (stream_NW). Together, these features extend more than 85 kpc and display a clear (g-r) colour gradient. The orientation of stream_SE relative to the orientations of NGC 4631 and NGC 4656 is not consistent with an origin from interaction between these two spirals, and is more likely debris from a satellite encounter. The stellar tidal features can be qualitatively reproduced in an N-body model of the tidal disruption of a single, massive dwarf satellite on a moderately eccentric orbit (e=0.6) around NGC 4631 over $\\sim$ 3.5 Gyr, with a dynamical mass ratio (m1:m2) of ~40. Both modelling and inferences from the morpho...

Martinez-Delgado, David; Chonis, Taylor S; Beaton, Rachael L; Teuwen, Karel; GaBany, R Jay; Grebel, Eva K; Morales, Gustavo

2014-01-01

247

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

Microsoft Academic Search

We present an extragalactic perspective of an extended stellar tidal stream wrapping around the edge-on spiral galaxy NGC 5907. Our deep images reveal for the first time a large-scale complex of arcing loops that is an excellent example of how low-mass satellite accretion can produce an interwoven, rosette-like structure of debris dispersed in the halo of its host galaxy. The

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

2008-01-01

248

Non-Gaussian error bars in galaxy surveys - II  

NASA Astrophysics Data System (ADS)

Estimating the uncertainty on the matter power spectrum internally (i.e. directly from the data) is made challenging by the simple fact that galaxy surveys offer at most a few independent samples. In addition, surveys have non-trivial geometries, which make the interpretation of the observations even trickier, but the uncertainty can nevertheless be worked out within the Gaussian approximation. With the recent realization that Gaussian treatments of the power spectrum lead to biased error bars about the dilation of the baryonic acoustic oscillation scale, efforts are being directed towards developing non-Gaussian analyses, mainly from N-body simulations so far. Unfortunately, there is currently no way to tell how the non-Gaussian features observed in the simulations compare to those of the real Universe, and it is generally hard to tell at what level of accuracy the N-body simulations can model complicated non-linear effects such as mode coupling and galaxy bias. We propose in this paper a novel method that aims at measuring non-Gaussian error bars on the matter power spectrum directly from galaxy survey data. We utilize known symmetries of the four-point function, Wiener filtering and principal component analysis to estimate the full covariance matrix from only four independent fields with minimal prior assumptions. We assess the quality of the estimated covariance matrix with a measurement of the Fisher information content in the amplitude of the power spectrum. With the noise filtering techniques and only four fields, we are able to recover the results obtained from a large N = 200 sample to within 20 per cent, for k ? 1.0 h Mpc-1. We further provide error bars on Fisher information and on the best-fitting parameters, and identify which parts of the non-Gaussian features are the hardest to extract. Finally, we provide a prescription to extract a noise-filtered, non-Gaussian, covariance matrix from a handful of fields in the presence of a survey selection function.

Harnois-Déraps, Joachim; Pen, Ue-Li

2013-06-01

249

Colliding and merging galaxies. I - Evidence for the recent merging of two disk galaxies in NGC 7252  

Microsoft Academic Search

Results from a photographic, spectroscopic, and photometric study of the 'Atoms-for-Peace' galaxy are presented. The observations reveal that NGC 7252 possesses a single nucleus, a nearly round main body marked by delicate ripples, faint surrounding loops, and two slender tails that project to 80 kpc and 130 kpc from the center. The principal body itself shows a spectrum indicative of

F. Schweizer

1982-01-01

250

Ongoing Mass Transfer in the Interacting Galaxy Pair NGC 1409/10  

E-print Network

I present two-band HST STIS imaging, and WIYN spectral mapping, of ongoing mass transfer in the interacting galaxy pair NGC 1409/10 (where NGC 1410 is the Seyfert galaxy also catalogued as III Zw 55). Archival snapshot WFPC2 imaging from the survey by Malkan et al. showed a dust feature stretching between the galaxies, apparently being captured by NGC 1409. The new images allow estimates of the mass being transferred and rate of transfer. An absorption lane typically 0.25" (100 pc) wide with a representative optical depth tau_B = 0.2 cuts across the spiral structure of NGC 1410, crosses the 7-kpc projected space between the nuclei, wraps in front of and, at the limits of detection, behind NGC 1409, and becomes a denser (tau_B = 0.4) polar feature around the core of NGC 1409. Combination of extinction data in two passbands allows a crude three-dimensional recovery of the dust structure, supporting the front/back geometry derived from colors and extinction estimates. The whole feature contains of order $10^6$ solar masses in dust, implying about 2x10^7 solar masses of gas, requiring a mass transfer rate averaging ~1 solar mass per year unless we are particularly unlucky in viewing angle. Curiously, this demonstrable case of mass transfer seems to be independent of the occurrence of a Seyfert nucleus, since the Seyfert galaxy in this pair is the donor of the material. Likewise, the recipient shows no signs of recent star formation from incoming gas, although NGC 1410 has numerous luminous young star clusters and widespread H-alpha emission.

W. C. Keel

2003-11-28

251

The Outer Disks of Early-Type Galaxies. I. Surface-Brightness Profiles of Barred Galaxies  

E-print Network

We present a study of 66 barred, early-type (S0-Sb) disk galaxies, focused on the disk surface brightness profile outside the bar region and the nature of Freeman Type I and II profiles, their origins, and their possible relation to disk truncations. This paper discusses the data and their reduction, outlines our classification system, and presents $R$-band profiles and classifications for all galaxies in the sample. The profiles are derived from a variety of different sources, including the Sloan Digital Sky Survey (Data Release 5). For about half of the galaxies, we have profiles derived from more than one telescope; this allows us to check the stability and repeatability of our profile extraction and classification. The vast majority of the profiles are reliable down to levels of mu_R ~ 27 mag arcsec^-2; in exceptional cases, we can trace profiles down to mu_R > 28. We can typically follow disk profiles out to at least 1.5 times the traditional optical radius R_25; for some galaxies, we find light extending to ~ 3 R_25. We classify the profiles into three main groups: Type I (single-exponential), Type II (down-bending), and Type III (up-bending). The frequencies of these types are approximately 27%, 42%, and 24%, respectively, plus another 6% which are combinations of Types II and III. We further classify Type II profiles by where the break falls in relation to the bar length, and in terms of the postulated mechanisms for breaks at large radii ("classical trunction" of star formation versus the influence of the Outer Lindblad Resonance of the bar). We also classify the Type III profiles by the probable morphology of the outer light (disk or spheroid). Illustrations are given for all cases. (Abridged)

Peter Erwin; Michael Pohlen; John E. Beckman

2007-09-21

252

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

NASA Astrophysics Data System (ADS)

Context. An important open question is the relation between intracluster light and the halos of central galaxies in galaxy clusters. Aims: Here we report results from an on going project with the aim to characterize the dynamical state in the core of the Hydra I (Abell 1060) cluster around NGC 3311. Methods: We analyze deep long-slit absorption line spectra reaching out to ~25 kpc in the halo of NGC 3311. Results: We find a very steep increase in the velocity dispersion profile from a central ?0 = 150 km s-1 to ?out ? 450 km s-1 at R ? 12 kpc. Farther out, to ~25 kpc, ? appears to be constant at this value, which is ~60% of the velocity dispersion of the Hydra I galaxies. With its dynamically hot halo kinematics, NGC 3311 is unlike other normal early-type galaxies. Conclusions: These results and the large amount of dark matter inferred from X-rays around NGC 3311 suggest that the stellar halo of this galaxy is dominated by the central intracluster stars of the cluster, and that the transition from predominantly galaxy-bound stars to cluster stars occurs in the radial range 4 to 12 kpc from the center of NGC 3311. We comment on the wide range of halo kinematics observed in cluster central galaxies, depending on the evolutionary state of their host clusters. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, during the observing program 082.A-0255(A) on 2009 March 25.Table 1 is only available in electronic form at http://www.aanda.org

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

2010-09-01

253

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

E-print Network

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

Ventimiglia, G; Arnaboldi, M; Coccato, L

2010-01-01

254

Double Bars, Inner Disks, and Nuclear Rings in Early-Type Disk Galaxies  

E-print Network

We present results from an imaging survey of an unbiased sample of thirty-eight early-type (S0--Sa), low-inclination, optically barred galaxies in the field. Our goal was to find and characterize central stellar and gaseous structures: secondary bars, inner disks, and nuclear rings. Bars inside bars are surprisingly common: at least one quarter of the sample galaxies (possibly as many as 40%) are double-barred, with no preference for Hubble type or the strength of the primary bar. A typical secondary bar is ~12% of the size of its primary bar and 240--750 pc in radius. We see no significant effect of secondary bars on nuclear activity. We also find kiloparsec-scale inner disks in at least 20% of our sample, almost exclusively in S0 galaxies. These disks are on average 20% the size of their host bar, and show a wider range of relative sizes than do secondary bars. Nuclear rings are present in about a third of our sample. Most are dusty, sites of current or recent star formation, or both; such rings are preferentially found in Sa galaxies. Three S0 galaxies (15% of the S0's) appear to have purely stellar nuclear rings, with no evidence for dust or recent star formation. The fact that these central stellar structures are so common indicates that the inner regions of early-type barred galaxies typically contain dynamically cool and disklike structures. This is especially true for S0 galaxies, where secondary bars, inner disks, and/or stellar nuclear rings are present at least two thirds of the time. (abridged)

Peter Erwin; Linda S. Sparke

2002-03-29

255

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

256

NGC 5253 and ESO 269-G058: Dwarf Galaxies with a Past  

E-print Network

Deep r' and i' images obtained with GMOS on Gemini South are used to probe the bright stellar content in the outer regions of NGC 5253 and ESO269-G058. Red giant branch (RGB) stars are traced out to a distance of 8 kpc along the major axis of NGC 5253, and 6 kpc in ESO269-G058. The outer regions of both galaxies are metal-poor; RGB stars located between projected major axis distances of 2 and 4 kpc in NGC 5253 have [Fe/H] ~ -1, whereas RGB stars in the corresponding portion of ESO269-G058 have [Fe/H] ~ -1.8. Stars with metallicities that differ from the mean by more than a few tenths of a dex make only a modest contribution to the stellar content in the outer regions of both galaxies. A population of bright asymptotic giant branch (AGB) stars is seen in both galaxies. Roughly 1 - 10% of the stellar mass of NGC 5253 may have formed during the past few hundred million years, and it is suggested that the progenitors of the two recent SN Ia in this galaxy may have formed at this time. It is argued that the current episodes of star formation in NGC 5253 and ESO269-G058 may have been triggered up to ~ 1 Gyr in the past. Finally, a distance modulus is computed for each galaxy based on the brightness of the RGB-tip, and the results are 27.48 +/- 0.14 for NGC 5253, and 27.93 +/- 0.18 for ESO269-G058.

T. J. Davidge

2007-09-24

257

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

NASA Astrophysics Data System (ADS)

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

Salak, Dragan; Nakai, Naomasa; Kitamoto, Shoko

2014-10-01

258

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

NASA Astrophysics Data System (ADS)

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

Salak, Dragan; Nakai, Naomasa; Kitamoto, Shoko

2014-09-01

259

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

260

ALFALFA HI and Star Formation Properties of the NGC 5846 Galaxy Group  

NASA Astrophysics Data System (ADS)

The Undergraduate ALFALFA (Arecibo Legacy Fast ALFA) Team Groups Project is a collaborative undertaking of faculty and undergraduates at 11 institutions, aimed at investigating properties of galaxy groups surveyed by the ALFALFA blind HI survey. The Union College team is analyzing a 9x7 degree region surrounding the galaxy group NGC 5846. We present HI and star formation properties based on analysis of data from the ALFALFA survey, KPNO MOSAIC and CTIO SMARTS 0.9m Halpha imaging, and Sloan Digital Sky Survey spectra. 34% of NGC 5846 group members are detected in HI compared to 60% of galaxies in the environment. Preliminary results indicate that star formation rates are lower in group galaxies. This work has been supported by NSF grants AST-0724918, AST-0725267, and AST-0725380.

Darling, Halley; Smith, W.; Viani, L.; Koopmann, R. A.; ALFALFA Team

2012-01-01

261

The kinematics and morphology of NGC 520: One, two, or three galaxies  

NASA Technical Reports Server (NTRS)

The peculiar galaxy NGC 520 (Arp 157) is often interpreted as an interacting pair of galaxies. The identification of the two bulges and overall morphology of the two galaxies has long been a puzzle which the authors attempt to solve here. New longslit optical spectroscopy and near-infrared images of NGC 520 are presented. These data suggest that the northwest peak is the bulge of one of two galaxies in the system. The other larger bulge is clearly evident in the K band image in the middle of the dust lane. The stellar radial velocity profile in the central 10 seconds of the larger bulge is consistent with counterrotation seen in the molecular gas component. This kinematic subsystem could be the remains of a merged gas-rich irregular.

Stanford, S. A.; Balcells, M.

1990-01-01

262

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

E-print Network

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

Draine, Bruce T.

263

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

NASA Astrophysics Data System (ADS)

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

Bianchi, Stefano; Matt, Giorgio

264

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

Microsoft Academic Search

We studied the colliding galaxy NGC 7714 with two XMM-Newton observations, six months apart. The galaxy contains two bright X-ray sources: we show that they have different physical nature. The off-nuclear source is an accreting compact object, one of the brightest ultraluminous X-ray sources (ULXs) found to date. It showed spectral and luminosity changes between the two observations, from a

Roberto Soria; Christian Motch

2004-01-01

265

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

Microsoft Academic Search

We present an analysis of the nearby interacting galaxies NGC 6621\\/22 (Arp 81), comparing the results of a combined N-body\\/SPH simulation of the collision between two suitable disk galaxy models with multi-wavelength observations. Arp 81 is undergoing a strong collision that has triggered periods of intense star formation in the pair. We use archived IRAC and HST images to identify

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

2005-01-01

266

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

NASA Astrophysics Data System (ADS)

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

Bianchi, Stefano; Matt, Giorgio; Iwasawa, Kazushi

2001-04-01

267

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

E-print Network

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

Low, Steven H.

268

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

269

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

270

The Initial Mass Function in the Outer Galaxy: The star forming region NGC 1893  

NASA Astrophysics Data System (ADS)

We will explore the effects of environmental conditions, which change dramatically between the inner and outer regions of the Galaxy, on the initial mass function (IMF) of the star forming region NGC 1893. Our proposed 450 ksec observation of NGC 1893, a SFR of ~3 Myr in the outer part of the Galaxy, joint with two hours of Spitzer data, will permit us to identify members down to 0.5 Msun and enable a comparison of NGC 1893's IMF with those derived for SFRs in the solar neighborhood. Our observations will help in determining, particularly in the low mass regime, how the IMF depends on galactic environment. With its spatial resolution and sensitivity, Chandra, with the support of Spitzer, is uniquely suited to achieve our objectives.

Micela, Giuseppina

2005-09-01

271

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

272

Hubble Space Telescope (HST) imagery of galaxy NGC 7457 and Supernova 1987A  

NASA Technical Reports Server (NTRS)

Hubble Space Telescope (HST) imagery of galaxy NGC 7457 (47925 BW) and Supernova 1987A (47926 CN) released 08/29/90. HST view of galaxy NGC 7457 (47925) was taken on 08/17/90 with the Wide Field and Planetary Camera (WFPC). The picture on the left with high contrast shows the central portion of the galaxy. The picture on the right is of the same galaxy, but the contrast has been adjusted to reveal a suprisingly high concentration of stars pinpointed exactly at the galaxy's core. The nucleus is so compact it is beyond HST's.1 arc resolution. Forty million light-years away NGC 7457 is one of the first 'normal' galaxies that HST has observed. The gaseous ring seen around Supernova 1987A (47926) was taken with the European Space Agency's (ESA) Faint Object Camera (FOC), 08/23/90. The ring appears as a yellow ellipse and tightly knotted debris from the stellar expolsion appears as a red blob near the center of the ring. The blue stars to the left and right of the ring are not associated wit

1990-01-01

273

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

274

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.

275

WARM DUST AND SPATIALLY VARIABLE POLYCYCLIC AROMATIC HYDROCARBON EMISSION IN THE DWARF STARBURST GALAXY NGC 1705  

E-print Network

Thomas H. Jarrett,16 Aigen Li,17 Martin J. Meyer,18 Eric J. Murphy,19 Michael W. Regan,20 George H. Rieke GALAXY NGC 1705 John M. Cannon,1 John-David T. Smith,2 Fabian Walter,3 George J. Bendo,4 Daniela Calzetti,5 Daniel A. Dale,6 Bruce T. Draine,7 Charles W. Engelbracht,8 Karl D. Gordon,9 George Helou,10

Draine, Bruce T.

276

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.

277

Cold dust and its relation to molecular gas in the dwarf irregular galaxy NGC 4449  

Microsoft Academic Search

We present observations of the dwarf irregular galaxy NGC 4449 at 850 mu m and 450 mu m obtained with SCUBA at the JCMT. The distribution of the cold dust agrees well with that of the CO and Halpha emission. To explain the integrated mm- through far-infrared continuum spectrum three dust components are required, with temperatures of 16 K, 39

C. Böttner; U. Klein; A. Heithausen

2003-01-01

278

Rotation and mass of the inner 5 kiloparsecs of the S0 galaxy NGC 3115  

Microsoft Academic Search

NGC 3115 is an isolated field galaxy of type S0. It has a small disk embedded in a large flattened halo. Observed velocities rise steeply to 200 km\\/s at r = 450 pc and then are flat at 267 km\\/s from r = 700 to r = 4.7 kpc. Based on a simple spheroid model, the mass is greater than

V. C. Rubin; C. J. Peterson; W. K. Ford Jr.

1980-01-01

279

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

280

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

281

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

NASA Astrophysics Data System (ADS)

NGC 5291 is an early type galaxy at the edge of the cluster Abell 3574 which drew the attention because of the unusual high amount of atomic gas ( ~ 5 x 10(10) {M_{\\odot}}) found associated to it. The HI is distributed along a huge and fragmented ring, possibly formed after a tidal interaction with a companion galaxy. We present multi-slit optical spectroscopic observations and optical/near-infrared images of the system. We show that NGC 5291 is a LINER galaxy exhibiting several remnants of previous merging events, in particular a curved dust lane and a counter-rotation of the gas with respect to the stars. The atomic hydrogen has undoubtly an external origin and was probably accreted by the galaxy from a gas-rich object in the cluster. It is unlikely that the HI comes from the closest companion of NGC 5291, the so-called ``Seashell'' galaxy, which appears to be a fly-by object at a velocity greater than 400 km s(-1) . We have analyzed the properties of 11 optical counterparts to the clumps observed in the HI ring. The brightest knots show strong similarities with classical blue compact dwarf galaxies. They are dominated by active star forming regions; their most recent starburst is younger than 5 Myr; we did not find evidences for the presence of an old underlying stellar population. NGC 5291 appears to be a maternity of extremely young objects most probably forming their first generation of stars. Born in pre-enriched gas clouds, these recycled galaxies have an oxygen abundance which is higher than BCDGs ({Z_{\\odot}}/3 on average) and which departs from the luminosity-metallicity relation observed for typical dwarf and giant galaxies. We propose this property as a tool to identify tidal dwarf galaxies (TDGs) among the dwarf galaxy population. Several TDGs in NGC 5291 exhibit strong velocity gradients in their ionized gas and may already be dynamically independent galaxies. Based on observations collected at the European Southern Observatory, La Silla, Chile. ESO N$^{o

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

1998-05-01

282

Imaging Carbon Monoxide Emission in the Starburst Galaxy NGC 6000  

Microsoft Academic Search

We present measurements of carbon monoxide emission in the central region of the nearby starburst NGC 6000 taken with the Submillimeter Array. The J = 2-1 transition of 12CO, 13CO, and C18O were imaged at a resolution of ~3'' × 2'' (450 × 300 pc). We accurately determine the dynamical center of NGC 6000 at alphaJ2000.0 = 15h49m49.s5 and deltaJ2000.0

Sergio Martín; Matthew R. George; David J. Wilner; Daniel Espada

2010-01-01

283

IMAGING CARBON MONOXIDE EMISSION IN THE STARBURST GALAXY NGC 6000  

Microsoft Academic Search

We present measurements of carbon monoxide emission in the central region of the nearby starburst NGC 6000 taken with the Submillimeter Array. The J = 2-1 transition of ¹²CO, ¹³CO, and C¹O were imaged at a resolution of 3'' x 2'' (450 x 300 pc). We accurately determine the dynamical center of NGC 6000 at {sub J2000.0} = 15{sup h}49{sup

Sergio Martin; Matthew R. George; David J. Wilner; Daniel Espada

2010-01-01

284

CIRCUMNUCLEAR STAR CLUSTERS IN THE GALAXY MERGER NGC 6240, OBSERVED WITH KECK ADAPTIVE OPTICS AND THE HUBBLE SPACE TELESCOPE  

E-print Network

that they represent a short-lived yet common phase of galactic evolution, namely, when spiral galaxies collide to formCIRCUMNUCLEAR STAR CLUSTERS IN THE GALAXY MERGER NGC 6240, OBSERVED WITH KECK ADAPTIVE OPTICS 2007 January 15 ABSTRACT We discuss images of the central $10 kpc (in projection) of the galaxy merger

Schneider, Glenn

285

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

286

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

NASA Astrophysics Data System (ADS)

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

Valluri, Monica

2014-10-01

287

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

288

The ghost of a dwarf galaxy: fossils of the hierarchical formation of the nearby spiral galaxy NGC 5907  

E-print Network

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

David Martinez-Delgado; Jorge Penarrubia; R. Jay Gabany; Ignacio Trujillo; Steven R. Majewski; Michael Pohlen

2008-05-08

289

The role of bars in AGN fueling in disk galaxies over the last seven billion years  

E-print Network

We present empirical constraints on the influence of stellar bars on the fueling of active galactic nuclei (AGN) out to z=0.84 using a sample of X-ray-selected AGN hosted in luminous face-on disk galaxies from the Chandra COSMOS survey. Using high-resolution Hubble Space Telescope imaging to identify bars, we find that the fraction of barred active galaxies displays a similar behavior as that of inactive spirals, declining with redshift from 71% at z~0.3, to 35% at z~0.8. With active galaxies being typically massive, we compare them against a mass-matched sample of inactive spirals and find that the AGN bar fraction is higher, with this enhancement being marginal at z>0.4, but becoming more pronounced at low redshift. The presence of a bar has no influence on the AGN strength, with barred and unbarred active galaxies showing equivalent X-ray luminosity distributions, though barred galaxies on average seem to show higher levels of central star formation. From our results, we conclude that the role of bars is r...

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

2014-01-01

290

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

SciTech Connect

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

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

2012-02-15

291

On the distance and reddening of the Local Group dwarf irregular galaxy NGC 6822  

E-print Network

On the basis of a new photometric analysis of the Local Group Dwarf Irregular Galaxy NCG 6822 based on observations obtained with Advanced Camera for Surveys on board of the the Hubble Space Telescope, we have obtained a new estimate of the extinction of two fields located in the southeast region of the galaxy. Due to the presence of significant differences in the distance estimates to NGC 6822 available in literature, we have decided to provide an independent determination of the distance to this galaxy based on an updated and self-consistent theoretical calibration of the tip of the Red Giant Branch (TRGB) brightness. As a result we have obtained a new determination of the distance to NGC 6822 equal to ${\\rm(m-M)}_0=23.54\\pm 0.05$, and compared our measurement with the most recent determinations of this distance.

Fusco, F; Bono, G; Cassisi, S; Monelli, M; Pietrinferni, A

2012-01-01

292

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

SciTech Connect

A brief analysis is presented of images of the nearby S0 galaxy NGC 7457 obtained with the HST Planetary Camera. While the galaxy remains unresolved with the HST, the images reveal that any core most likely has r(c) less than 0.052 arcsec. The light distribution is consistent with a gamma = -1.0 power law inward to the resolution limit, with a possible stellar nucleus with luminosity of 10 million solar. This result represents the first observation outside the Local Group of a galaxy nucleus at this spatial resolution, and it suggests that such small, high surface brightness cores may be common. 20 refs.

Lauer, T.R.; Faber, S.M.; Holtzman, J.A.; Baum, W.A.; Currie, D.G.; Ewald, S.P.; Groth, E.J.; Hester, J.J.; Kelsall, T. (Kitt Peak National Observatory, Tucson, AZ (USA) Lick Observatory, Santa Cruz, CA (USA) Lowell Observatory, Flagstaff, AZ (USA) Washington Univ., Seattle (USA) Maryland Univ., College Park (USA) Space Telescope Science Institute, Baltimore, MD (USA) Princeton Univ., NJ (USA) California Institute of Technology, Pasadena (USA) NASA, Goddard Space Flight Center, Greenbelt, MD (USA))

1991-03-01

293

Near-infrared mapping of ARP 299 (IC 694-NGC 3690) - Colliding galaxies unveiled  

NASA Technical Reports Server (NTRS)

Near-infrared maps and multicolor photometry of the interacting galaxies IC 694 and NGC 3690 which form Arp 299 (= Markarian 171) are presented. These data reveal for the first time the distribution of nuclei and old red stars in a cataclysmically interacting system. The nuclei are considerably offset from the visual centroids of the galaxies but not from the mass centroids. The near-infrared colors of the most active regions are strongly affected by extinction, emission form hot dust, and bremsstrahlung. Near-infrared emission is also identified with secondary regions of star formation, probably resulting from the galaxies' interaction.

Telesco, C. M.; Decher, R.; Gatley, I.

1985-01-01

294

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

E-print Network

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

Cacho, Raúl; Gorgas, Javier; Pérez, Isabel

2014-01-01

295

Redshift and velocity dispersion of the cluster of galaxies around NGC 326  

E-print Network

Redshifts of several galaxies thought to be associated with NGC 326 are determined. The results confirm the presence of a cluster and find a mean redshift of z = 0.0477 +/- 0.0007 and a line-of-sight velocity dispersion sigma_{z} = 599 (+230, -110) km/s. The velocity dispersion and previously measured X-ray gas temperature of kT ~ 1.9 keV are consistent with the cluster sigma_{z}/kT relation, and NGC 326 is seen to be a slowly-moving member of the cluster.

P. N. Werner; D. M. Worrall; M. Birkinshaw

1999-06-25

296

The Infall of the MCG+10+24-117 Into the NGC 6338 Galaxy Cluster  

NASA Astrophysics Data System (ADS)

We present preliminary results of an X-ray analysis of 47 ksec with the Chandra satellite aimed at the cluster NGC 6338. The hot ISM density profile of MCG+10+24-117 shows a sharp edge at about 6 kpc from its center in the direction of NGC 6338. The discontinuity is consistent with a cold front, where gradient factors of about 1.7 both in density and in gas temperature are measured with no significant radial pressure gradient. We argue that the front is due to an ram pressure stripping of the galaxy gas, caused by its subsonic motion through the surrounding intracluster medium.

Dupke, Renato A.; Martins, S.

2013-04-01

297

A multi-wavelength study of the starburst galaxy NGC 7673  

E-print Network

HST/WFPC2 images resolved NGC 7673 into a large number of star clusters. Among these, 31 fall inside the IUE large aperture, which was used to acquire an integrated ultraviolet spectrum of the galaxy. We have fitted Starburst99 evolutionary synthesis models to the observed colours of these clusters and derived ages, reddenings, and masses of the clusters. Then a simple sum of the clusters synthetic UV spectra has been compared to the observed IUE spectrum, in order to investigate the star formation history of NGC 7673.

Paola Castangia; Anna Pasquali; Piero Benvenuti

2004-11-16

298

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

299

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

E-print Network

Context. The prototype of Polar Ring Galaxies NGC 4650A contains two main structural components, a central spheroid, which is the host galaxy, and an extended polar disk. Both photometric and kinematic studies revealed that these two components co-exist on two different planes within the central regions of the galaxy. Aims. The aim of this work is to study the spectroscopic and kinematic properties of the host galaxy and the polar disk in the central regions of NGC 4650A by disentangling their contributions to the observed galaxy spectrum. Methods. We applied the spectral decomposition technique introduced in previous works to long-slit spectroscopic observations in the CaII triplet region. We focused the analysis along the PA = 152 that corresponds to the photometric minor axis of the host galaxy, where the superimposition of the two components is more relevant and the spectral decomposition is necessary. We aim to disentangle the stars that move in the equatorial plane of the host galaxy from those that mov...

Coccato, L; Arnaboldi, M

2014-01-01

300

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

301

The Recent Evolution Of The Dwarf Starburst Galaxy NGC 625 From Hubble Space Telescope Imaging  

NASA Astrophysics Data System (ADS)

We present new HST/WFPC2 imaging of the nearby dwarf starburst galaxy NGC 625. Deep images in V and I reach limiting magnitudes of 26.5 and 26, respectively. Narrow band images in H? and H Beta allow us to address the internal extinction within the starburst regions. We derive a tip of the red giant branch (TRGB) distance of 3.89 +/- 0.22 Mpc, in excellent agreement with the value derived from the empirical distance-velocity relation within the Sculptor Group. We find an older stellar population that is relatively smoothly distributed throughout the galaxy, and we also detect a very red, extended AGB branch, similar to that found in the Local Group dIrr NGC 6822. From the young stars, we derive the recent star formation history of NGC 625; it is found that the recent level of star formation has been significantly elevated compared to the average value over much of the galaxy's history. We speculate on the possible causes of the present burst of star formation in this apparently isolated galaxy. This research was supported, in part, by NASA through grants GO-8708, NAG5-9221 and NGT 5-50345.

Cannon, J. M.; Dohm-Palmer, R. C.; Skillman, E. D.; Bomans, D. J.; Cote, S.; Miller, B. W.

2002-12-01

302

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

303

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

E-print Network

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

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

2014-01-01

304

Discovery of a new faint dwarf galaxy associated with NGC 253  

E-print Network

We report the discovery of a new faint dwarf galaxy, which we dub Scl-MM-Dw1, at a projected distance of $\\sim$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$\\pm$0.5 Mpc, consistent with that of NGC 253, making their association likely. The new dwarf's stellar population is complex, with an old, metal poor red giant branch ($\\gtrsim$10 Gyr, [Fe/H]$\\sim$$-$2), and an asymptotic giant branch with an age of $\\sim$500 Myr. Scl-MM-Dw1 has a half-light radius of $r_{h}$=340$\\pm$50 pc and an absolute magnitude of $M_{V}$=$-$10.3$\\pm$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 ...

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

2014-01-01

305

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

306

Distance and Reddening of the Isolated Dwarf Irregular Galaxy NGC 1156  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

307

The Mass of the Central Black Hole in the Nearby Seyfert Galaxy NGC5273  

E-print Network

We present the results of a reverberation-mapping program targeting NGC5273, a nearby early-type galaxy with a broad-lined active galactic nucleus. Over the course of the monitoring program, NGC5273 showed strong variability that allowed us to measure time delays in the responses of the broad optical recombination lines to changes in the continuum flux. A weighted average of these measurements results in a black hole mass determination of $M_{\\rm BH} = (4.7 \\pm 1.6) \\times 10^6$ M$_{\\odot}$. An estimate of the size of the black hole sphere of influence in NGC5273 puts it just at the limit of the resolution achievable with current ground-based large aperture telescopes. NGC5273 is therefore an important future target for a black hole mass determination from stellar dynamical modeling, especially because it is the only nearby early-type galaxy hosting an AGN with a reverberation-based mass, allowing the best comparison for the masses determined from these two techniques.

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

2014-01-01

308

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

309

The Nature Of X-Ray Emission In Nearby Dwarf Galaxies: The Case Of NGC 625  

NASA Astrophysics Data System (ADS)

We propose to add a 60 ksec ACIS-S observation to a multi-wavelength (XMM, FUSE, HST, CTIO, JCMT, ATCA) study of NGC 625, a nearby dwarf starburst galaxy showing coincident diffuse X-ray and H-alpha emission indicative of an active outflow from the starburst region. Chandra observations will allow us to isolate point sources and determine the distribution and temperature of the diffuse X-ray emission. We can then study the energetics of the X-ray superbubble and compare NGC 625 with the few other well-studied low-mass systems harboring active galactic winds, furthering our understanding of the impact of star formation on galaxy evolution.

Skillman, Evan

2003-09-01

310

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

311

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

NASA Astrophysics Data System (ADS)

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

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

2008-03-01

312

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

313

The Dwarf Irregular/Wolf-Rayet Galaxy NGC4214: I. A New Distance, Stellar Content, and Global Parameters  

E-print Network

We present the results of a detailed optical and near-IR study of the nearby star-forming dwarf galaxy NGC4214. We discuss the stellar content, drawing particular attention to the intermediate-age and/or old field stars, which are used as a distance indicator. On images obtained with the Hubble Space Telescope WFPC2 and NICMOS instruments in the equivalents of the V, R, I, J and H bands, the galaxy is well resolved into stars. We achieve limiting magnitudes of F814W ~27 in the WF chips and F110W ~25 in the NIC2. The optical and near-infrared color-magnitude diagrams confirm a core-halo galaxy morphology: an inner high surface-brightness young population within ~1.5' (~1 kpc) from the center of the galaxy, where the stars are concentrated in bright complexes along a bar-like structure; and a relatively low-surface-brightness, field-star population extending out to at least 8' (7 kpc). The color-magnitude diagrams of the core region show evidence of blue and red supergiants, main-sequence stars, asymptotic giant branch stars and blue loop stars. We identify some candidate carbon stars from their extreme near-IR color. The field-star population is dominated by the "red tangle", which contains the red giant branch. We use the I-band luminosity function to determine the distance based on the tip-of-the-red-giant-branch method: 2.7\\pm0.3 Mpc. This is much closer than the values usually assumed in the literature, and we provide revised distance dependent parameters such as physical size, luminosity, HI mass and star-formation rate.

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

2002-05-02

314

Extended Gas in Seyfert Galaxies: Near Infrared Observations of NGC 2110 and Circinus  

E-print Network

We present results of near--IR long-slit spectroscopy in the J and K bands of the Seyfert 2 galaxies NGC 2110 and Circinus, investigating the gaseous distribution, excitation, reddening and kinematics. In NGC 2110, the emission line ratio [FeII]/Pa beta increases towards the nucleus (to ~ 7). The nuclear [Fe II]1.257 (microns) and Pa beta lines are broader (FWHM ~ 500 km/s) than the H2 (2.121) line (FWHM ~ 300 km/s). Both these results suggest that shocks, driven by the radio jet, are an important source of excitation of [Fe II]. The H2 excitation appears to be dominated by X-rays from the nucleus. In Circinus, both [FeII]/Pa beta and H2/Br gamma decrease from ~ 2 at 4 arcsec from the nucleus to nuclear values of ~ 0.6 and ~ 1, respectively, suggesting that the starburst dominates the nuclear excitation, while the AGN dominates the excitation further out (r > 2 arcsec). For both galaxies, the gaseous kinematics are consistent with circular rotation in the plane of the disk. Our rotation curves suggest that the nucleus (identified with the peak of the IR continuum) is displaced from the kinematic centre of the galaxies. This effect has been observed previously in NGC 2110 based on the kinematics of optical emission lines, but the displacement is smaller in the infrared, suggesting the effect is related to obscuration. The continuum J-K colours of the nuclear region indicate a red stellar population in NGC 2110 and a reddened young stellar population in Circinus. Right at the nucleus of both galaxies, the colours are redder, apparently a result of hot dust emission from the inner edge of a circumnuclear torus.

T. Storchi-Bergmann; C. Winge; Martin J. Ward; A. S. Wilson

1998-12-11

315

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

NASA Astrophysics Data System (ADS)

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

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

1997-02-01

316

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

Microsoft Academic Search

We present broadband and narrowband Hubble Space Telescope images of the\\u000acentral region of the heavily disturbed Virgo cluster galaxy NGC 4438 (Arp120),\\u000awhose nucleus has been described as a type 1 LINER or dwarf Seyfert. Narrowband\\u000aH-alpha and [NII] HST images reveal striking bipolar shell features, 1 kpc in\\u000aprojected length from end-to-end, which are likely the result of

Jeffrey D. P. Kenney; Elizabeth E. Yale

2000-01-01

317

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

NASA Astrophysics Data System (ADS)

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

Barth, Aaron

2014-10-01

318

MASS DISTRIBUTION OF THE E0 GALAXY NGC 6703 FROM ABSORPTION LINE PROFILE KINEMATICS  

E-print Network

). 2. Data and Analysis NGC 6703 is an E0 galaxy at a distance D=36h \\Gamma1 50 Mpc (h 50 j H 0 =50km of the data, where fi = \\Gamma0:5 \\Gamma +0:5, depending on variations of the potential in the allowed range=s = Mpc). From a Jaffe profile fit, its absorption--corrected magnitude is MB = \\Gamma21:07, or luminosity

Saglia, Roberto P.

319

Nuclear Star Formation in the Hot-Spot Galaxy NGC 2903  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

320

Hubble Space Telescope Observations of the Seyfert Galaxy NGC 3783: Discovery of Variable C IV Absorption  

Microsoft Academic Search

We have discovered variable absorption lines in HST spectra of the Seyfert 1 galaxy NGC 3783. C IV lambdalambda1548.2, 1550.8 absorption is present in an FOS spectrum on 1992 July 27 and a GHRS spectrum on 1994 January 16 at a radial velocity of -450 km s^-1^ relative to the emission-line peak, but there is no evidence for absorption in

Stephen P. Maran; D. Michael Crenshaw; Richard F. Mushotzky; Gail A. Reichert; Kenneth G. Carpenter; Andrew M. Smith; John B. Hutchings; Ray J. Weymann

1996-01-01

321

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

Microsoft Academic Search

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

A. Pasquali; P. Castangia

2008-01-01

322

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

Microsoft Academic Search

We present here a general numerical simulation algorithm for ballistic radio jets. The evolution of the jets is determined by their response to mechanical forces (i.e., gravity and ram pressure). Using a previously derived collision model for the interacting pair of elliptical galaxies NGC 4782\\/4783, we have used this algorithm to simulate the specific two-sided jet morphology seen in the

Kirk D. Borne; Luis Colina

1993-01-01

323

Colliding and Merging Galaxies. III. The Dynamically Young Merger Remnant NGC 3921  

Microsoft Academic Search

This paper presents imaging, photometric, and spectroscopic observations of NGC 3921 = Mrk 430 gathered over many years with five optical telescopes. This luminous galaxy (M_V_= -22.8 for H_0_ = 50) at cz_hel_=5926 +\\/- 15 km s^-1^ features a single nucleus, a main body with complex fine structure (ripples, loops, fan-shaped protrusions), and a pair of ~100 kpc long, crossed

Francois Schweizer

1996-01-01

324

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

325

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

E-print Network

We determine the mass of the black hole at the center of the spiral galaxy NGC 4258 by constructing axisymmetric dynamical models of the galaxy. These models are constrained by high spatial resolution imaging and long-slit spectroscopy of the nuclear region obtained with the {\\em Hubble Space Telescope}, complemented by ground-based observations extending to larger radii. Our best mass estimate is $\\MBH = (3.3 \\pm 0.2) \\times 10^7 \\MSun $ for a distance of 7.28 Mpc (statistical errors only). This is within 15% of $ (3.82\\pm 0.01) \\times 10^7 \\MSun$, the mass determined from the kinematics of water masers (rescaled to the same distance) assuming they are in Keplerian rotation in a warped disk. The construction of accurate dynamical models of NGC 4258 is somewhat compromised by an unresolved active nucleus and color gradients, the latter caused by variations in the stellar population and/or obscuring dust. These problems are not present in the $\\sim 30$ other black hole mass determinations from stellar dynamics that have been published by us and other groups; thus, the relatively close agreement between the stellar dynamical mass and the maser mass in NGC 4258 enhances our confidence in the black hole masses determined in other galaxies from stellar dynamics using similar methods and data of comparable quality.

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

2008-08-28

326

Accurate and Robust Calibration of the Extragalactic Distance Scale with the Maser Galaxy NGC4258  

NASA Astrophysics Data System (ADS)

The extragalactic distance scale {EDS} is defined by a comparison of Cepheid Period-Luminosity {PL} relations for nearby galaxies and the LMC, whose uncertain distance is thereby the SOLE anchor. Studies of maser sources orbiting the central black hole in the galaxy NGC4258 have provided the most accurate extragalactic distance ever {7.2+/- 0.5Mpc}. Since this distance is well determined and based on GEOMETRIC arguments, NGC4258 can provide a much needed new anchor for the EDS. We propose multi-epoch BVIH observations of NGC4258 in order to discover about 100 Cepheids and to characterize their light curves with 2-3 times greater accuracy than was previously possible with WFPC2. At 90 orbits {48 in Cycle 12; 42 in Cycle 13}, this is a relatively large program. However, the result will have a major impact on the EDS, and substantial attention must be paid to characterization and minimization of systematic errors, as from metallicity, crowding, and blending. The resulting dataset will be the most complete for Cepheids in any galaxy yet studied with HST. In an ongoing NASA-funded program {OSS-SARA}, we are using new analysis techniques and radio data to reduce uncertainty in the geometric distance to < 3% {0.07 mag}. With this improved geometric distance and the BVIH data, we will be able to calculate the zero point of the PL relation ROBUSTLY to <4% {0.09 mag}.

Greenhill, Lincoln

2003-07-01

327

Diffuse Gamma-Ray Emission from the Starburst Galaxy NGC 253  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

328

A MOND prediction of a new giant shell in the elliptical galaxy NGC3923  

E-print Network

Context. Stellar shells, forming axially symmetric systems of arcs in some elliptical galaxies, are likely remnants of radial minor mergers. They are observed up the radius of ~100 kpc. The stars in them oscillate in radial orbits. The radius of a shell depends on the free-fall time at the position of the shell and on the time since the merger. In B\\'ilek et al. (2013), we verified the consistency of shell radii in the elliptical galaxy NGC 3923 with its most probable MOND potential. Our results implied that a yet undiscovered shell exists at the outskirts of the galaxy. Aims. In the present paper, we extend our study assuming more general models for gravitational potential to verify the prediction of the new shell and to estimate its position. Methods. We test the consistency of the shell radial distribution observed in NGC 3923 with a wide variety of MOND potentials of the galaxy. The potentials differ in the mass-to-light ratio and the distance of the galaxy. We consider different MOND interpolation functi...

Bílek, M; Ebrová, I; Jungwiert, B

2014-01-01

329

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

330

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

331

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

Microsoft Academic Search

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

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

2002-01-01

332

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

333

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

334

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

335

Globular Clusters as Dynamical Probes of the s0 Galaxy NGC 3115  

NASA Astrophysics Data System (ADS)

This thesis presents a photometric and spectroscopic investigation of the globular cluster system (GCS) of the S0 galaxy NGC 3115. Photometric observations, obtained at the CFHT, were made in V and I. The limiting magnitude in both filters is approximately at the level of the peak of the globular cluster luminosity function, determined to be mVTO = 22.8 ± 0.2. This turnover value, when compared with that of the Milky Way, implies a distance modulus of (m - M)VTO = 30.2 ± 0.3 which is consistent with distance estimates based on the magnitude of the red giant branch tip. Analysis of the integrated V - I colours of the clusters indicates that the GCS contains multiple population components. The red clusters appear more concentrated towards the plane of NGC 3115 than do the blue clusters. From the spectroscopic observations, obtained at the WHT using the LDSS, we find that the cluster system is rapidly rotating and that the velocity dispersion of the cluster system implies M/L = 19-3+10 at a distance of R = 15kpc from the center of NGC 3115. This value of M/L is larger than that found at smaller radii suggesting that NGC 3115 possesses a dark matter halo. By combining the spectral and photometric data we find very strong evidence that NGC 3115 possesses two separate and distinct cluster populations, one a metal-rich thick disk system and the other a metal-poor halo system. This is the first detection of a disk system of clusters in a non-Local Group galaxy.

Kavelaars, J. J.

336

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

337

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

PubMed

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

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

2011-09-22

338

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

NASA Astrophysics Data System (ADS)

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 O VI ? 1032 Å absorption. The centroid of the O VI profile is blueshifted with respect to the galaxy systemic velocity by ˜ 30 km s-1, suggesting a low-velocity outflow. The implied O VI velocity extent is found to be 100 ± 20 km s-1, which is fully consistent with the detected H I 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 O I line, and higher S/N observations are required to resolve this issue.

Cannon, J. M.; Skillman, E. D.; Sembach, K. R.; Bomans, D. J.

2006-06-01

339

Gemini Spectroscopic Survey of Young Star Clusters in Merging/Interacting Galaxies. II. NGC 3256 Clusters  

E-print Network

We present Gemini optical spectroscopy of 23 young star clusters in NGC3256. We find that the cluster ages range are from few Myr to ~150 Myr. All these clusters are relatively massive (2--40)x 10^{5} \\msun$ and appear to be of roughly 1.5 \\zo metallicity. The majority of the clusters in our sample follow the same rotation curve as the gas and hence were presumably formed in the molecular-gas disk. However, a western subsample of five clusters has velocities that deviate significantly from the gas rotation curve. These clusters may either belong to the second spiral galaxy of the merger or may have formed in tidal-tail gas falling back into the system. We discuss our observations in light of other known cluster populations in merging galaxies, and suggest that NGC 3256 is similar to Arp 220, and hence may become an Ultra-luminous Infrared Galaxy as the merger progresses and the star-formation rate increases. Some of the clusters which appeared as isolated in our ground-based images are clearly resolved into multiple sub-components in the HST-ACS images. The same effect has been observed in the Antennae galaxies, showing that clusters are often not formed in isolation, but instead tend to form in larger groups or cluster complexes.

Gelys Trancho; Nate Bastian; Bryan W. Miller; François Schweizer

2007-04-19

340

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

341

THE SPECTRAL ENERGY DISTRIBUTION OF DUST EMISSION IN THE EDGE-ON SPIRAL GALAXY NGC 4631 AS SEEN WITH SPITZER AND THE JAMES CLERK MAXWELL TELESCOPE  

E-print Network

-on Sd spiral galaxy NGC 4631 using 3.6Y160 m Spitzer Space Telescope data and 450Y850 m JCMT dataTHE SPECTRAL ENERGY DISTRIBUTION OF DUST EMISSION IN THE EDGE-ON SPIRAL GALAXY NGC 4631 AS SEEN of radius. The 70 m/160 m and 160 m/450 m flux density ratios are remarkably constant even though

Draine, Bruce T.

342

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

NASA Technical Reports Server (NTRS)

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

Borne, Kirk D.; Colina, Luis

1993-01-01

343

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

344

The structure of NGC at 100, 160, and 200 microns - Continuum dust emission in a quiescent Sb galaxy  

NASA Technical Reports Server (NTRS)

Observations of NGC 4565 at 100, 160, and 200 microns with the University of Chicago Far-Infrared Camera and the NASA-Kuiper Airborne Observatory are reported. In order to examine the dependence of FIR emission on spiral structure and star formation activity, these observations of NGC 4565, a quiescent Sb galaxy, are compared with observations of NGC 6946, an active Sc galaxy, made by Engargiola (1991) using the same instruments. Warm dust (30 K) in a bisymmetric spiral pattern superposed on an exponential disk of cool dust (20 K) can account for the FIR morphology of NGC 4565. Optical and IR data suggest that there are more embedded sources heating dust locally in the southeast arm region and more UV radiation from unobscured young stellar associations heating the cool, neutral medium in the northeast arm region.

Engargiola, G.; Harper, D. A.

1992-01-01

345

Nuclear structure & merger-starburst relation in the ultraluminous IRAS galaxy NGC 6240  

NASA Astrophysics Data System (ADS)

The ultraluminous IRAS galaxy NGC 6240 has been studied extensively from the ground at all accessible wavelengths. Loops, tidal tails and a double nucleus {separation approximately 1.5 arcsec = 0.7 kpc} suggest an ongoing merger. The far-IR luminosity is generally attributed to dust-heating by a nuclear starburst. This is supported by most, but not all data. In particular, the nuclear stellar velocity dispersion {approximately 350 kms} indicates too high an M/L for a starburst and the UV field strength appears to be too low. Alternative models for the dust heating, e.g. invoking an AGN, therefore remain viable. Of equal interest has been a claim for the presence of a 10^11 solar mass black hole {BH} at 12 arcsec from the double nucleus, from a decomposition of the ionized gas velocity field into that of two disks, presumed to be the merging progenitors. We will obtain broad- and narrow-band WFPC2 images of NGC 6240 to study the nuclear distributions of stars, dust and ionized gas. We will search for an AGN component. We will construct dissipational {tree+SPH} N-body models, to interpret the data, test the starburst hypothesis, and study whether equilibrium kinematics can be used to infer M/L values and BH masses for a merging galaxy like NGC 6240.

van der Marel, Roeland

1996-07-01

346

The Nature of Radio Continuum Emission in the Dwarf Starburst Galaxy NGC 625  

NASA Astrophysics Data System (ADS)

We present new multifrequency radio continuum imaging of the dwarf starburst galaxy NGC 625 obtained with the Very Large Array. Data at 20, 6, and 3.6 cm reveal global continuum emission dominated by free-free emission, with only mild synchrotron components. Each of the major H II regions is detected; the individual spectral indices are thermal for the youngest regions (showing largest H? emission) and nonthermal for the oldest. We do not detect any sources that appear to be associated with deeply embedded, dense, young clusters, although we have discovered one low-luminosity, obscured source that has no luminous optical counterpart and resides in the region of highest optical extinction. Since NGC 625 is a Wolf-Rayet galaxy with strong recent star formation, these radio properties suggest that the youngest star formation complexes have not yet evolved to the point where their thermal spectra are significantly contaminated by synchrotron emission. The nonthermal components are associated with regions of older star formation that have smaller ionized gas components. These results imply a range of ages for the H II regions and radio components that agrees with our previous resolved stellar population analysis, where an extended burst of star formation has pervaded the disk of NGC 625 over the last ~50 Myr. We compare the nature of radio continuum emission in selected nearby dwarf starburst and Wolf-Rayet galaxies, demonstrating that thermal radio continuum emission appears to be more common in these systems than in typical H II galaxies with less recent star formation and more evolved stellar clusters.

Cannon, John M.; Skillman, Evan D.

2004-08-01

347

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

348

Hubble Space Telescope images of the Seyfert galaxies NGC 5929 and MCG 8-11-11  

NASA Technical Reports Server (NTRS)

We present the initial results of a program to obtain high resolution images of Seyfert galaxies with the Planetary Camera aboard the Hubble Space Telescope (HST). In this paper we discuss the images of the type 2 Seyfert NGC 5929 and the type 1.5 Seyfert MCG 8-11-11 (= UGC 3374). The images were obtained in the emission lines of (O III) lambda lambda 4959 and 5007 A and H alpha + (N II) lambda lambda 6548 and 6583 A and their adjacent continua. The high-excitation gas in the narrow line region (NLR) of NGC 5929 is resolved into individual clouds in the central 1 sec .5. Although the (O III) emission is clearly not spherically symmetric with respect to the nucleus, it does not define a distinct 'bicone' morphology, as observed by the HST in a few other Seyfert galaxies. We find no direct evidence for the reddening and/or obscuration effects characteristic of a dusty torus, which, in the context of 'unified models', is expected to obscure the active galactic nucleus (AGN) in type 2 Seyfert galaxies. The correspondence between the emission line gas and the radio morphology suggests that the structure of the NLR in NGC 5929 is governed by matter ejected from the AGN. A comparison of the recombination rate of hydrogen in the brightest emission line cloud with an upper limit on the ionizing luminosity emitted toward Earth provides no evidence that the central ionizing source radiates anisotropically. The images of MCG 8-11-11 show only an unresolved nuclear source. No emission line gas associated with the extended radio source is detected. We estimate upper limits on the intensity of extended line emission in this galaxy and examine their significance.

Bower, Gary A.; Wilson, Andrew S.; Mulchaey, John S.; Miley, George K.; Heckman, Timothy M.; Krolik, Julian H.

1994-01-01

349

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

350

Destructible Bars in Disk Galaxies under the Dynamical Influence of a Massive Central Black Hole  

NASA Astrophysics Data System (ADS)

The characteristics of the galactic bars that are prone to suffer a damaging impact from a massive central black hole are examined using flat stellar disks. We construct three disk model groups that consist of exponential disks with one type of velocity distribution and Kuzmin-Toomre disks with two different types of exact equilibrium distribution functions. For each disk model group, three disks that have different typical Toomre's Q values are evolved to form bars through dynamical instability. Once a bar is fully developed, a black hole (BH), whose mass is 1% of the disk mass, is adiabatically added at the center of the disk. Our results show that lower-amplitude bars, that is weaker bars, are dissolved more easily by that BH. We have found that this destructibility is rooted in the characteristic feature that the bar formed spontaneously becomes shorter in length and rounder in shape with decreasing bar amplitude. Since such weaker bars are found to originate from colder disks in each disk model group, it follows that for a given form of velocity structure, the coldness of an initial disk determines whether the bar produced in that disk is favorable to dissolution induced by a massive central BH. In addition, the existence of bar-dissolved galaxies of the kind studied here is also discussed.

Hozumi, Shunsuke

2012-02-01

351

Invariant manifolds as building blocks for the formation of spiral arms and rings in barred galaxies  

E-print Network

We propose a theory to explain the formation of spiral arms and of all types of outer rings in barred galaxies, extending and applying the technique used in celestial mechanics to compute transfer orbits. Thus, our theory is based on the chaotic orbital motion driven by the invariant manifolds associated to the periodic orbits around the hyperbolic equilibrium points. In particular, spiral arms and outer rings are related to the presence of heteroclinic or homoclinic orbits. Thus, R1 rings are associated to the presence of heteroclinic orbits, while R1R2 rings are associated to the presence of homoclinic orbits. Spiral arms and R2 rings, however, appear when there exist neither heteroclinic nor homoclinic orbits. We examine the parameter space of three realistic, yet simple, barred galaxy models and discuss the formation of the different morphologies according to the properties of the galaxy model. The different morphologies arise from differences in the dynamical parameters of the galaxy.

M. Romero-Gomez; E. Athanassoula; J. J. Masdemont; C. Garcia-Gomez

2008-01-22

352

The Formation of Dwarf Irregular Galaxies from Tidally Removed Debris and the Peculiar System NGC 5291  

NASA Astrophysics Data System (ADS)

The formation and evolution of dwarf irregular galaxies from tidally removed material in interacting systems are discussed via a case study of the peculiar system NGC 5291. This system contains an S0 galaxy interacting with a disturbed companion known as the Seashell. The pair is located in the western outskirts of the IC 4329 cluster. Initial observations indicated a complex of star-formation knots extending roughly 4’ north and 4’ south of the galaxy, and a large HI extent apparently offset to the west. High resolution atomic hydrogen observations taken with the VLA are presented here and confirm that the HI is offset, but also reveal that it forms an incomplete ring, or tail, to the west. NGC 5291 shows a high velocity gradient in HI; the Seashell was not detected and is presumably stripped of gas by the interaction. Several of the optical knots coincide with large concentrations (10 EXP 9 solar masses) of HI. Each of the knots is compared to a set of criteria designed to determine if these objects are bound against their own internal kinetic energy and are tidally stable relative to the host galaxies. A large star-forming knot located in the north part of the ring is shown to meet the established criteria, is self-gravitating, and possesses a stellar component. It is suggested that this object is a genuinely young dwarf irregular galaxy that has evolved from the interaction and that this entire complex contains several proto or young dwarf irregular galaxies in various stages of development. More detailed information is avaible via the Internet at the NRAO VLA press release web site note

Malphrus, Benjamin

1998-11-01

353

The Formation of Dwarf Irregular Galaxies from Tidally Removed Debris and the Peculiar System NGC 5291  

NASA Astrophysics Data System (ADS)

The formation and evolution of dwarf irregular galaxies from tidally removed material in interacting systems are discussed via a case study of the peculiar system NGC 5291. This system contains an S0 galaxy interacting with a disturbed companion known as the Seashell. The pair is located in the western outskirts of the IC 4329 cluster. Initial observations indicated a complex of star-formation knots extending roughly 4' north and 4' south of the galaxy, and a large HI extent apparently offset to the west. High resolution atomic hydrogen observations taken with the VLA are presented here and confirm that the HI is offset, but also reveal that it forms an incomplete ring, or tail, to the west. NGC 5291 shows a high velocity gradient in HI; the Seashell was not detected and is presumably stripped of gas by the interaction. Several of the optical knots coincide with large concentrations (10 EXP 9 solar masses) of HI. Each of the knots is compared to a set of criteria designed to determine if these objects are bound against their own internal kinetic energy and are tidally stable relative to the host galaxies. A large star-forming knot located in the north part of the ring is shown to meet the established criteria, is self-gravitating, and possesses a stellar component. It is suggested that this object is a genuinely young dwarf irregular galaxy that has evolved from the interaction and that this entire complex contains several proto or young dwarf irregular galaxies in various stages of development.

Malphrus, B. K.; Simpson, C. E.; Gottesman, S. T.; Hawarden, T. G.

1995-12-01

354

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

NASA Astrophysics Data System (ADS)

We report on simultaneous optical and X-ray observations of the Seyfert galaxy, NGC3147. The XMM-Newton spectrum shows that the source is unabsorbed in the X-rays ( N_H < 5 10^20 cm ^-2 ). On the other hand, no broad lines are present in the optical spectrum. The origin of this optical/X-rays misclassification (with respect to the Unification Model) cannot be attributed to variability, since the observations in the two bands are simultaneous. Moreover, a Compton-thick nature of the object can be rejected on the basis of the low equivalent width of the iron K alpha line ( ~eq 130 eV) and the large ratio between the 2-10 keV and the [OIII] fluxes. It seems therefore inescapable to conclude that NGC3147 intrinsically lacks the Broad Line Region (BLR), making it the first 'true' Seyfert 2.

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

2008-10-01

355

The X-ray spectrum and variability of the Seyfert 2 galaxy NGC 7172  

NASA Astrophysics Data System (ADS)

We present evidence of flux variability, on both short (hours) and long (months) time-scales, of the Seyfert 2 galaxy NGC 7172. These results are based on the ASCA observation of NGC 7172 performed in 1996 May. The source was detected at a rather low flux level, about 3 times fainter than its usual state (including 1 yr before, when it was also observed by ASCA). The source also varied by about 30 per cent during the observation, confirming the presence of a type 1 nucleus in its centre. However, its spectrum appears to be flatter than the typical Seyfert 1 spectrum (in agreement with findings on other Seyfert 2s), posing problems for the unification model unless complex absorption is invoked.

Guainazzi, M.; Matt, G.; Antonelli, L. A.; Fiore, F.; Piro, L.; Ueno, S.

1998-08-01

356

Model for the variable continuum of the Seyfert 1 galaxy NGC 5548  

SciTech Connect

The variations of NGC 5548 as observed by IUE are analyzed. The results indicate that the amplitude of the variation is largest at the shorter UV wavelengths. The implications of this wavelength dependence are of importance for the continuum modeling. A fit to a simultaneously obtained UV and optical spectra based on the Fe II fluorescence model of Netzer and Wills is shown to give an extremely good match with the data. The results presented show that the spectrum of the Seyfert I galaxy NGC 5548 can be fairly well represented by a combination of a single power law continuum, Fe II lines, Balmer lines, and continuum and stellar variability data suggest that the variations in the strength of the power law spectrum are not accompanied by large changes in the spectral index. Apparent spectral index variations can occur due to the difference in relative importance of individual components at different wavelengths.

Wamsteker, W.; Benvenuti, P.

1984-12-01

357

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

358

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

359

Properties of bars in spiral galaxies from COSMOS  

NASA Astrophysics Data System (ADS)

In this work we present the analysis of 760 spiral galaxies from COSMOS using both visual inspection and analysis of the radial profiles. In this way we have determined some criteria for a semiautomatic classification.

Hernández-López, I.; Recillas, E.; Mújica-García, R.; Athanassoula, E.

2011-10-01

360

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

361

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

362

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

363

Star Formation Histories Across the Interacting Galaxy NGC 6872, the Largest-Known Spiral  

E-print Network

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 drive the star formation activity. To address these issues we analyzed the far-ultraviolet (FUV) to near-infrared (near-IR) spectral energy distribution (SED) of 17, 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, ...

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

2014-01-01

364

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

SciTech Connect

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

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

2013-05-10

365

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

366

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

367

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

NASA Astrophysics Data System (ADS)

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

Contini, M.

2012-09-01

368

A MULTI-WAVELENGTH ANALYSIS OF NGC 4178: A BULGELESS GALAXY WITH AN ACTIVE GALACTIC NUCLEUS  

SciTech Connect

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

Secrest, N. J.; Satyapal, S.; Gliozzi, M. [Department of Physics and Astronomy, George Mason University, MS 3F3, 4400 University Drive, Fairfax, VA 22030 (United States); Moran, S. M. [Department of Physics and Astronomy, Johns Hopkins University, 366 Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218 (United States); Cheung, C. C. [Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352 (United States); Giroletti, M. [INAF Istituto di Radioastronomia, I-40129 Bologna (Italy); Bergmann, M. P. [NOAO Gemini Science Center, P.O. Box 26732, Tucson, AZ 85726 (United States); Seth, A. C. [Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112 (United States)

2013-11-10

369

HIGH-DENSITY MOLECULAR GAS PROPERTIES OF THE STARBURST GALAXY NGC 1614 REVEALED WITH ALMA  

SciTech Connect

We present the results of HCN/HCO{sup +}/HNC J = 4-3 transition line observations of the nearby starburst galaxy NGC 1614, obtained with ALMA Cycle 0. We find that high density molecular gas traced with these lines shows a velocity structure such that the northern (southern) side of the nucleus is redshifted (blueshifted) with respect to the nuclear velocity of this galaxy. The redshifted and blueshifted emission peaks are offset by {approx}0.''6 at the northern and southern sides of the nucleus, respectively. At these offset positions, observations at infrared >3 {mu}m indicate the presence of active dusty starbursts, supporting the picture that high-density molecular gas is the site of active starbursts. The enclosed dynamical mass within the central {approx}2'' in radius, derived from the dynamics of the high-density molecular gas, is {approx}10{sup 9} M{sub Sun }, which is similar to previous estimates. Finally, the HCN emission is weaker than HCO{sup +} but stronger than HNC for J = 4-3 for all starburst regions of NGC 1614, as seen for J = 1-0 transition lines in starburst-dominated galaxies.

Imanishi, Masatoshi [Subaru Telescope, 650 North A'ohoku Place, Hilo, HI 96720 (United States); Nakanishi, Kouichiro, E-mail: masa.imanishi@nao.ac.jp [Joint ALMA Observatory, Alonso de Cordova 3107, Vitacura 763-0355, Santiago (Chile)

2013-09-15

370

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

SciTech Connect

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

Harrison, Sarah M.; /MIT /SLAC