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Sample records for ring galaxy ngc

  1. The Collisional Ring Galaxy NGC 922

    NASA Astrophysics Data System (ADS)

    Pellerin, A.; Meurer, G. R.; Bekki, K.; Elmegreen, D. M.; Wong, O. I.; Knezek, P. M.

    2010-06-01

    We present a detailed study of the star cluster population detected in the galaxy NGC 922, one of the closest collisional ring galaxies, using HST/WFPC2 UBVI photometry, population synthesis models, and N-body/SPH simulations. We find that most clusters are younger than 7 Myr, and that most of them are located in the ring or along the bar, consistent with the strong Hα emission. The observed age distribution displays a slope not consistent with the simulated star formation history of NGC 922. However our simulations match the cluster age distribution best when cluster disruption is considered. We also find clusters with ages (>50 Myr) and masses (>105 Msun) that are excellent progenitors for faint fuzzy clusters. The images also show a tidal plume pointing toward the companion. Its stellar age suggests that it consists of stars significantly older than the epoch of collision and that they were stripped off during the passage of the companion. Finally, a comparison of the star-forming complexes observed in NGC 922 with those of a distant ring galaxy from the GOODS field indicates very similar masses and sizes, suggesting similar origins.

  2. CHANDRA OBSERVATIONS OF THE COLLISIONAL RING GALAXY NGC 922

    SciTech Connect

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

    2012-03-10

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

  3. Chandra Observations of the Collisional Ring Galaxy NGC 922

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  4. Face on Barred and Ringed Spiral Galaxy NGC 3351

    NASA Technical Reports Server (NTRS)

    2005-01-01

    Ultraviolet image (left) and visual image (right) of the face on barred and ringed spiral galaxy NGC 3351 (M95). The morphological appearance of a galaxy can change dramatically between visual and ultraviolet wavelengths. In the case of M95, the nucleus and bar dominate the visual image. In the ultraviolet, the bar is not even visible and the ring and spiral arms dominate.

  5. Triggered star formation & feedback in the ring galaxy, NGC 922

    NASA Astrophysics Data System (ADS)

    Wong, O. Ivy; Koribalski, Baerbel; Meurer, Gerhardt; Zwaan, Martin; Bekki, Kenji; Garcia-Appadoo, Diego; Vlahakis, Catherine

    2013-10-01

    Star formation (and its cessation) play an integral role in galaxy evolution. However, the physical processes that govern how and when stars form in galaxies is still not fully understood. Although rare, ring galaxies provide an excellent testbed for studying two opposing compression-driven processes, namely the large-scale triggering of star formation versus the subsequent destructive feedback effects of newly-formed massive stars on nearby molecular clouds (and future star formation). Due to the simplicity of the collision, we can constrain the interaction timescales very well and hence obtain good boundary conditions for when stars can be formed within the observed ring. We propose to map the neutral gas content of NGC 922--- a recently-discovered ring galaxy that also happens to be one of the closest. We have obtained excellent observations of the stellar components from the Hubble Space Telescope for this object and we are only lacking information about its gas properties. These proposed observations will shed light on: (1) the balance between neutral and molecular gas content in the ISM of the ring galaxy; (2) the physical processes that dominate the galactic-scale triggering and suppression of star formation galaxies; (3) the kinematics and location of gas that has been disrupted and stripped from this galaxy pair; and (4) the validity of our simulated interaction model for the formation of NGC 922.

  6. Young Stellar Populations in the Collisional Ring Galaxy NGC 922

    NASA Astrophysics Data System (ADS)

    Pellerin, A.; Meurer, G. R.; Bekki, K.; Elmegreen, D. M.; Wong, O. I.; Knezek, P.

    2010-04-01

    We studied the star cluster population properties in the nearby collisional ring galaxy NGC 922 using HST/WFPC2 photometry and population synthesis modeling. We found that 69% of the detected clusters are younger than 7 Myr, and that most of them are located in the ring or along the bar, consistent with the strong Hα emission. The images also show a tidal plume pointing toward the companion. Its stellar age is consistent with pre-existing stars that were probably stripped off during the passage of the companion. We compared the star-forming complexes observed in NGC 922 with those of a distant ring galaxy from the GOODS eld. It indicates very similar masses and sizes, suggesting similar origins. Finally, we found clusters that are excellent progenitor candidates for faint fuzzy clusters.

  7. Observational study of the candidate polar-ring galaxies NGC 304 and NGC 7625

    NASA Astrophysics Data System (ADS)

    Karataeva, G. M.; Kuznetsov, A. N.

    2008-09-01

    We present the results of our photometric ( BV R) and spectroscopic CCD observations of NGC 304 and NGC 7625, candidate polar-ring galaxies, performed with the 6-m Special Astrophysical Observatory telescope. For NGC 304, such a study has been carried out for the first time. We have obtained basic integrated characteristics of the galaxies and determined their morphological types (S0 for NGC 304 and Sa for NGC 7625). The absolute magnitudes of the galaxies, M B = -20m.81 for NGC 304 and M B = -19m.34 for NGC7625, are indicative of their fairly high luminosities. The disk and bulge parameters have been determined forNGC 304 (µ0 = 20m.60, h = 3.86 kpc, µ e = 21m.59, r e = 1.26 kpc in the B band); these correspond to the parameters of S0-type objects. The rotation velocity for NGC 304 (200 km s-1) reaches its maximum at a galactocentric distance of 3.1 kpc, which yields a mass estimate for the galaxy of 2.8 × 1010 mathcal{M}_ odot . The observed photometric features at the center of NGC 304 indicate that it may have an inner ring structure, although we have failed to confirm the existence of two kinematic systems based on our spectroscopic observations. In NGC 7625, the disk makes a dominant contribution to the total brightness. The derived integrated color indices ( B-V = 0m.81 and V-R = 0m.61) agree with previous determinations of other authors. We have estimated the учештсешщт in the inner galactic regions. In the outer regions, we have detected structures with bluer colors ( B-V = 0m.60), which may be indicative of a polar ring with a minor stellar component.

  8. Weakly barred early-type ringed galaxies. IV. The double-ringed SO(+) galaxy NGC 7702

    SciTech Connect

    Buta, R. )

    1991-03-01

    UBVRI surface photometry of NGC 7702, obtained with a CCD detector on the 3.9-m Anglo-Australian Telescope and with photographic plates on the 4-m telescope at CTIO, is reported. The data are presented in tables, graphs, and contour maps and characterized in detail. NGC 7702 is found to be a true S0(+) galaxy with a bright high-contrast inner ring and a faint low-contrast outer ring; the inner ring is significantly elongated relative to typical SB inner rings and has colors which suggest a burst of star formation less than 2 Gyr ago. A small oval revealed by the bulge isophotes in the inner 4 arcsec radius is attributed to a nuclear bar. 52 refs.

  9. Hierarchical star formation across the ring galaxy NGC 6503

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    We present a detailed clustering analysis of the young stellar population across the star-forming ring galaxy NGC 6503, based on the deep Hubble Space Telescope photometry obtained with the Legacy ExtraGalactic UV Survey. We apply a contour-based map analysis technique and identify in the stellar surface density map 244 distinct star-forming structures at various levels of significance. These stellar complexes are found to be organized in a hierarchical fashion with 95 per cent being members of three dominant super-structures located along the star-forming ring. The size distribution of the identified structures and the correlation between their radii and numbers of stellar members show power-law behaviours, as expected from scale-free processes. The self-similar distribution of young stars is further quantified from their autocorrelation function, with a fractal dimension of ˜1.7 for length-scales between ˜20 pc and 2.5 kpc. The young stellar radial distribution sets the extent of the star-forming ring at radial distances between 1 and 2.5 kpc. About 60 per cent of the young stars belong to the detected stellar structures, while the remaining stars are distributed among the complexes, still inside the ring of the galaxy. The analysis of the time-dependent clustering of young populations shows a significant change from a more clustered to a more distributed behaviour in a time-scale of ˜60 Myr. The observed hierarchy in stellar clustering is consistent with star formation being regulated by turbulence across the ring. The rotational velocity difference between the edges of the ring suggests shear as the driving mechanism for this process. Our findings reveal the interesting case of an inner ring forming stars in a hierarchical fashion.

  10. The three rings of the isolated galaxy NGC 7217.

    NASA Astrophysics Data System (ADS)

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

    1995-08-01

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

  11. Weakly barred early-type ringed galaxies. III. The remarkable outer-ringed S0+ galaxy NGC 7020

    SciTech Connect

    Buta, R. )

    1990-06-01

    The southern S0+ galaxy NGC 7020 presents an unusual morphology: it includes a very regular outer ring which is completely detached and which envelops an inner ring/lens zone with an exotic hexagonal shape. The ring has a high contrast compared with those usually observed in barred galaxies, yet NGC 7020 is not obviously barred. In this paper, the structure of this galaxy is studied by means of UBVRI CCD surface photometry. The photometry reveals a complex system and shows that most of the recent star formation in the galaxy has taken place in the outer ring. Two bright knots are found on the major axis of the hexagonal zone that appear to be true enhancements of old stars rather than young associations. Between these knots and the bulge there are dips in the surface brightness and a clear zone of rectangular isophotes. 56 refs.

  12. Weakly barred early-type ringed galaxies. II. The double-ringed S0(+) galaxy NGC 7187

    SciTech Connect

    Buta, R. Alabama Univ., Tuscaloosa )

    1990-05-01

    CCD surface photometry of the southern ringed S0(+) galaxy NGC 7187, a particularly good example of a system with two bright clear rings with significantly different apparent shapes and almost no sign of a bar, is presented. The galaxy has below average luminosity and the rings are small compared to those observed in more typical (R)SB(r) type galaxies, even though the ratio of their sizes is similar to those in such galaxies. Bulge isophotes reveal the existence of two nearly orthogonal ovals, one having the same shape and position angle as isophotes of the outer disk. The central oval shows significant m = 4 deviations from elliptical isophote shapes and could be a nuclear bar. The rings are slightly blue enhancements compared to their surroundings. The mean colors of both rings do not imply exceptionally high star formation at the present time. 44 refs.

  13. The Interacting Galaxies NGC 5394/5395: A Post-Ocular Galaxy and Its Ring/Spiral Companion

    NASA Astrophysics Data System (ADS)

    Kaufman, Michele; Brinks, Elias; Elmegreen, Bruce G.; Elmegreen, Debra Meloy; Klarić , Mario; Struck, Curtis; Thomasson, Magnus; Vogel, Stuart

    1999-10-01

    H I, radio continuum, Fabry-Perot Hα, and ^12CO J=1-->0 observations and broadband optical and near infrared images are presented of the interacting spiral galaxies NGC 5395 and NGC 5394. Kinematically, there are three important, separate components to the H I gas associated with this galaxy pair: (1) the main disk of NGC 5395, (2) a long, northern tidal arm of NGC 5395 distinct in velocity from its main disk, and (3) the disk of NGC 5394. The H I northern tidal arm of NGC 5395 has a line of-sight velocity as much as 75-100 km s^-1 greater than the main disk of NGC 5395 at the same projected location and thus is not in the same plane as the disk. The velocity field of the disk of NGC 5395 is asymmetric and distorted by large-scale and small-scale noncircular motions. In NGC 5395, the encounter appears to be exciting m=1 and m=0 modes in what had been a two-armed spiral. The dominant spiral arm of NGC 5395 forms a large ring or pseudo-ring of Hα, radio continuum, and H I emission, somewhat off center with respect to the nucleus. The H I trough in the center of NGC 5395 is not filled in by molecular gas. The Hα velocity contours exhibit an organized pattern of kinks in crossing the ring and also show streaming motions in a large stellar caustic feature. The eastern side of the ring is brighter in radio continuum and Hα the western side is brighter in H I and contains massive (10^8 M_solar) H I clouds not associated with the most luminous H II regions. The smaller galaxy NGC 5394 is in an immediate post-ocular phase, with a central starburst, an intrinsically oval disk, two long, fairly symmetric, open tidal arms with high arm-interarm contrast, and very bright inner spiral arms, disjoint from the outer tidal arms. Most of the gas in NGC 5394 is in molecular form and concentrated within 3.8 kpc of the center, so is suitable for fueling the starburst. Despite the presence of H I gas, two of the three optically bright inner spiral arms of NGC 5394 show no evidence

  14. THE STAR CLUSTER POPULATION OF THE COLLISIONAL RING GALAXY NGC 922

    SciTech Connect

    Pellerin, Anne; Meurer, Gerhardt R.; Bekki, Kenji; Elmegreen, Debra M.; Wong, O. Ivy; Knezek, Patricia M. E-mail: Gerhardt.Meurer@icrar.org E-mail: elmegreen@vassar.edu E-mail: knezek@noao.edu

    2010-04-15

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

  15. The Star Cluster Population of the Collisional Ring Galaxy NGC 922

    NASA Astrophysics Data System (ADS)

    Pellerin, Anne; Meurer, Gerhardt R.; Bekki, Kenji; Elmegreen, Debra M.; Wong, O. Ivy; Knezek, Patricia M.

    2010-04-01

    We present a detailed study of the star cluster population detected in the galaxy NGC 922, one of the closest collisional ring galaxies known to date, using Hubble Space Telescope/Wide Field Planetary Camera 2 UBVI photometry, population synthesis models, and N-body/smoothed particle hydrodynamics simulations. We find that 69% of the clusters are younger than 7 Myr, and that most of them are located in the ring or along the bar, consistent with the strong Hα emission. The cluster luminosity function slope of 2.1-2.3 for NGC 922 is in agreement with those of young clusters in nearby galaxies. Models of the cluster age distribution match the observations best when cluster disruption is considered. We also find clusters with ages (>50 Myr) and masses (>105 M sun) that are excellent progenitors for faint fuzzy clusters. The images also show a tidal plume pointing toward the companion. Its stellar age from our analysis is consistent with pre-existing stars that were stripped off during the passage of the companion. Finally, a comparison of the star-forming complexes observed in NGC 922 with those of a distant ring galaxy from the GOODS field indicates very similar masses and sizes, suggesting similar origins.

  16. Compact stellar systems in the polar ring galaxies NGC 4650A and NGC 3808B: Clues to polar disk formation

    NASA Astrophysics Data System (ADS)

    Ordenes-Briceño, Yasna; Georgiev, Iskren Y.; Puzia, Thomas H.; Goudfrooij, Paul; Arnaboldi, Magda

    2016-01-01

    Context. Polar ring galaxies (PRGs) are composed of two kinematically distinct and nearly orthogonal components, a host galaxy (HG) and a polar ring/disk (PR). The HG usually contains an older stellar population than the PR. The suggested formation channel of PRGs is still poorly constrained. Suggested options are merger, gas accretion, tidal interaction, or a combination of both. Aims: To constrain the formation scenario of PRGs, we study the compact stellar systems (CSSs) in two PRGs at different evolutionary stages: NGC 4650A with well-defined PR, and NGC 3808 B, which is in the process of PR formation. Methods: We use archival HST/WFPC2 imaging in the F450W, F555W, or F606W and F814W filters. Extensive completeness tests, PSF-fitting techniques, and color selection criteria are used to select cluster candidates. Photometric analysis of the CSSs was performed to determine their ages and masses using stellar population models at a fixed metallicity. Results: Both PRGs contain young CSSs (<1 Gyr) with masses of up to 5 × 106M⊙, mostly located in the PR and along the tidal debris. The most massive CSSs may be progenitors of metal-rich globular clusters or ultra compact dwarf (UCD) galaxies. We identify one such young UCD candidate, NGC 3808 B-8, and measure its size of reff = 25.23+1.43-2.01 pc. We reconstruct the star formation history of the two PRGs and find strong peaks in the star formation rate (SFR, ≃200 M⊙/yr) in NGC 3808 B, while NGC 4650 A shows milder (declining) star formation (SFR< 10 M⊙/yr). This difference may support different evolutionary paths between these PRGs. Conclusions: The spatial distribution, masses, and peak star formation epoch of the clusters in NGC 3808 suggest for a tidally triggered star formation. Incompleteness at old ages prevents us from probing the SFR at earlier epochs of NGC 4650 A, where we observe the fading tail of CSS formation. This also impedes us from testing the formation scenarios of this PRG.

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

    NASA Astrophysics Data System (ADS)

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

    2010-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2000-05-01

    Optical imaging polarimetry has been carried out for the polar ring, starburst galaxy NGC 660. This galaxy has a highly inclined, severely tidally-disturbed disk which is surrounded by a gas-rich, polar ring. We detect scattered light from a large part of the halo and this is attributable to dust grains residing up to =~ 2.5 kpc from the stellar disk. There is evidence from emission-line imaging carried out in the past, that NGC 660 is host to an energetic outflow of hot gas along the minor axis (a `superwind'). Our results indicate that dust grains are entrained in this same outflow. Polarization due to scattering, however, is also present at positions away from the minor axis suggesting that grains may also be displaced from the stellar disk by tidal forces exerted during galactic collisions. Where the polar ring occludes the stellar disk we observe polarization due to magnetically aligned, dichroic grains. By comparing the recorded polarization with the associated optical extinction we infer that the magnetic field in the ring has a lower (but still comparable) strength to the magnetic field in the Milky Way. We also derive a dust-to-gas ratio for the ring and this is about a factor of 2-3 lower than in the solar neighbourhood (but close to the value measured in some nearby spirals). If the ring comprises the remnants of the `interloper' which collided with NGC 660, we expect that the ruptured galaxy was a massive, metal-rich spiral.

  19. Probing the X-Ray Binary Populations of the Ring Galaxy NGC 1291

    NASA Technical Reports Server (NTRS)

    Luo, B.; Fabbiano, G.; Fragos, T.; Kim, D. W.; Belczynski, K.; Brassington, N. J.; Pellegrini, S.; Tzanavaris, P.; Wang, J.; Zezas, A.

    2012-01-01

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

  20. Ultraviolet Signposts of Resonant Dynamics in the Starburst-ringed SAB Galaxy M94 (NGC 4736)

    NASA Astrophysics Data System (ADS)

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

    2001-03-01

    The dynamic orchestration of star-birth activity in the starburst-ringed galaxy M94 (NGC 4736) is investigated using images from the Ultraviolet Imaging Telescope (UIT; far-ultraviolet [FUV] band), Hubble Space Telescope (HST; near-ultraviolet [NUV] band), Kitt Peak 0.9 m telescope (Hα, R, and I bands), and Palomar 5 m telescope (B band), along with spectra from the International Ultraviolet Explorer (IUE) and the Lick 1 m telescope. The wide-field UIT image shows FUV emission from (1) an elongated nucleus, (2) a diffuse inner disk, where Hα is observed in absorption, (3) a bright inner ring of H II regions at the perimeter of the inner disk (R=48"=1.1 kpc), and (4) two 500 pc size knots of hot stars exterior to the ring on diametrically opposite sides of the nucleus (R=130"=2.9 kpc). The HST Faint Object Camera image resolves the NUV emission from the nuclear region into a bright core and a faint 20" long ``minibar'' at a position angle of 30°. Optical and IUE spectroscopy of the nucleus and diffuse inner disk indicates a ~107-108 yr old stellar population from low-level star-birth activity blended with some LINER activity. Analysis of the Hα-, FUV-, NUV-, B-, R-, and I-band emissions, along with other observed tracers of stars and gas in M94, indicates that most of the star formation is being orchestrated via ring-bar dynamics, involving the nuclear minibar, inner ring, oval disk, and outer ring. The inner starburst ring and bisymmetric knots at intermediate radius, in particular, argue for bar-mediated resonances as the primary drivers of evolution in M94 at the present epoch. Similar processes may be governing the evolution of the ``core-dominated'' galaxies that have been observed at high redshift. The gravitationally lensed ``Pretzel Galaxy'' (0024+1654) at a redshift of ~1.5 provides an important precedent in this regard.

  1. Core Kinematics in the Starburst-Ring Sab Galaxy NGC 4736

    NASA Astrophysics Data System (ADS)

    Murphy, E. J.; Waller, W. H.; Kenney, J. D. P.

    2000-05-01

    NGC 4736 (M94) is notable as the nearest early-type spiral galaxy of low inclination, and as the nearest example of a starbursting resonance-ring system. Interior to its inner star-forming ring is a luminous core containing a mix of old red stars and young UV-bright stars. Early long-slit spectroscopy revealed unusually high rotation speeds relative to the velocity dispersions, prompting Kormendy (1982) to describe the core as the innermost part of the disk, rather than the densest part of the spheroid (ie. the classic ``bulge''). Using the WIYN 3.5-m telescope, DensePak fiber array, and Bench spectrograph, we have carried out integral field spectroscopy of the central 45'' x 30'' (1.0 kpc x 0.7 kpc) in M94. Our kinematic mapping confirms the earlier claims of high rotation velocities relative to the velocity dispersions. Rotation curves of the stars and CO gas (from a recent interferometric mapping by Wong and Blitz [2000]) show the stars rotating slower by ~20--35 km/sec relative to the gas. Plans for analyzing the stellar kinematics as a function of stellar type (and corresponding age) are described.

  2. The far-infrared morphology of the double-ringed galaxy NGC 4736 (M94) - A ring surrounding an extended nucleus

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    High spatial resolution 100-micron observations of the central region of the double-ringed spiral galaxy NGC 4736 (M94) were obtained using the Kuiper Airborne Observatory. The data show a strong central peak with secondary peaks at the radius of the inner ring (50 arcsec = 1.6 kpc). The nuclear emission is extended at 100 microns, with a radius of 15 arcsec (500 pc). The far-infrared morphology is similar to that of the molecular gas, while the H I distribution shows a pronounced central depression. Since most of the hydrogen gas in the inner regions of NGC 4736 is in molecular form, it is concluded that the far-infrared emission from NGC 4736 arises mainly from dust associated with molecular gas. The H-alpha distribution differs dramatically from the far-infrared and molecular gas distributions. The ring dominates the H-alpha emission, while the total 100-micron ring emission is only slightly larger than that of the nucleus, yielding an L(FIR)/L(H-alpha) for the nucleus about 100 times that of the ring. The bolometric luminosity of the stars in the inner 1 kpc of NGC 4736 is sufficient to power the far-infrared from this region, which suggests that a significant fraction of the far-infrared emission in the nuclear region of NGC 4736 is powered by non-OB stars rather than by star formation.

  3. The Rings Survey. I. Hα and H I Velocity Maps of Galaxy NGC 2280

    NASA Astrophysics Data System (ADS)

    Mitchell, Carl J.; Williams, T. B.; Spekkens, Kristine; Lee-Waddell, K.; Kuzio de Naray, Rachel; Sellwood, J. A.

    2015-03-01

    Precise measurements of gas kinematics in the disk of a spiral galaxy can be used to estimate its mass distribution. The Southern African Large Telescope has a large collecting area and field of view, and is equipped with a Fabry-Pérot (FP) interferometer that can measure gas kinematics in a galaxy from the Hα line. To take advantage of this capability, we have constructed a sample of 19 nearby spiral galaxies, the RSS Imaging and Spectroscopy Nearby Galaxy Survey, as targets for detailed study of their mass distributions and have collected much of the needed data. In this paper, we present velocity maps produced from Hα FP interferometry and H i aperture synthesis for one of these galaxies, NGC 2280, and show that the two velocity measurements are generally in excellent agreement. Minor differences can mostly be attributed to the different spatial distributions of the excited and neutral gas in this galaxy, but we do detect some anomalous velocities in our Hα velocity map of the kind that have previously been detected in other galaxies. Models produced from our two velocity maps agree well with each other and our estimates of the systemic velocity and projection angles confirm previous measurements of these quantities for NGC 2280. Based in part on observations obtained with the Southern African Large Telescope (SALT) program 2011-3-RU-003.

  4. THE RINGS SURVEY. I. Hα AND H i VELOCITY MAPS OF GALAXY NGC 2280

    SciTech Connect

    Mitchell, Carl J.; Williams, T. B.; Sellwood, J. A.; Spekkens, Kristine; Lee-Waddell, K.; Naray, Rachel Kuzio de E-mail: williams@saao.ac.za E-mail: karen.lee-waddell@rmc.ca E-mail: sellwood@physics.rutgers.edu

    2015-03-15

    Precise measurements of gas kinematics in the disk of a spiral galaxy can be used to estimate its mass distribution. The Southern African Large Telescope has a large collecting area and field of view, and is equipped with a Fabry–Pérot (FP) interferometer that can measure gas kinematics in a galaxy from the Hα line. To take advantage of this capability, we have constructed a sample of 19 nearby spiral galaxies, the RSS Imaging and Spectroscopy Nearby Galaxy Survey, as targets for detailed study of their mass distributions and have collected much of the needed data. In this paper, we present velocity maps produced from Hα FP interferometry and H i aperture synthesis for one of these galaxies, NGC 2280, and show that the two velocity measurements are generally in excellent agreement. Minor differences can mostly be attributed to the different spatial distributions of the excited and neutral gas in this galaxy, but we do detect some anomalous velocities in our Hα velocity map of the kind that have previously been detected in other galaxies. Models produced from our two velocity maps agree well with each other and our estimates of the systemic velocity and projection angles confirm previous measurements of these quantities for NGC 2280.

  5. Circumnuclear ring of the starburst galaxy NGC 253. An Infrared view

    NASA Astrophysics Data System (ADS)

    Pérez GarcÍa, A. M.; Melo, V. P.; Acosta-Pulido, J.; Muñoz-Tuñón, C.; RodrÍguez-Espinosa, J. M.

    NGC 253 is a nearby spiral galaxy with an active starburst nucleus. Its proximity allows observation with good spatial resolution with state of the art mid and far IR facilities. Here we present preliminary results obtained from the ISO archive in 5 to 16 microns (ISOCAM-CVF) and 120 to 180 μm (ISOPHOT) ranges. The mid IR spectrum exhibits typical broad PAH features as well as weak atomic emission, which is not seen in the continuum nor in the [ArII] emission line. For the first time we present a far IR map (180 μm) as well as several profiles across the minor axis of the galaxy, showing a variation of the dust temperature. We detect an extension of the cold dust (20K) emission not seen previously in IRAS maps, which may contribute to a large fraction of the galaxy total mass.

  6. Distribution of Molecules in the Circumnuclear Disk and Surrounding Starburst Ring in the Seyfert Galaxy NGC 1068 Observed with ALMA

    NASA Astrophysics Data System (ADS)

    Takano, S.; Nakajima, T.; Kohno, K.; Harada, N.; Herbst, E.; Tamura, Y.; Izumi, T.; Taniguchi, A.; Tosaki, T.

    2015-12-01

    We report distributions of several molecular transitions including shock and dust related species (13CO and C18O J = 1-0, 13CN N = 1-0, CS J = 2-1, SO JN = 32-21, HNCO JKa,Kc = 50,5-40,4, HC3N J = 11-10, 12-11, CH3OH JK = 2K-1K, and CH3CN JK = 6K-5K) in the nearby Seyfert 2 galaxy NGC 1068 observed with ALMA. The central ˜1' (˜4.3 kpc) of this galaxy was observed in the 100 GHz region with an angular resolution of ˜4" x 2" (290 pc x 140 pc) to study the effects of an active galactic nucleus and its surrounding starburst ring on molecular abundances. We report a classification of molecular distributions into three main categories. Organic molecules such as CH3CN are found to be concentrated in the circumnuclear disk. In the starburst ring, the intensity of methanol at each clumpy region is not consistent with that of 13CO.

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

    SciTech Connect

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

    2013-05-01

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

  8. Distributions of molecules in the circumnuclear disk and surrounding starburst ring in the Seyfert galaxy NGC 1068 observed with ALMA

    NASA Astrophysics Data System (ADS)

    Takano, Shuro; Nakajima, Taku; Kohno, Kotaro; Harada, Nanase; Herbst, Eric; Tamura, Yoichi; Izumi, Takuma; Taniguchi, Akio; Tosaki, Tomoka

    2014-07-01

    Sensitive observations with the Atacama Large Millimeter/submillimeter Array (ALMA) allow astronomers to observe the detailed distributions of molecules with relatively weak intensity in nearby galaxies. In particular, we report distributions of several molecular transitions including shock and dust related species (13CO J = 1-0, C18O J = 1-0, 13CN N = 1-0, CS J = 2-1, SO JN = 32-21, HNCO JKa,Kc = 50,5-40,4, HC3N J = 11-10, 12-11, CH3OH JK = 2K-1K, and CH3CN JK = 6K-5K) in the nearby Seyfert 2 galaxy NGC 1068 observed with the ALMA early science program. The central ˜ 1'(˜ 4.3 kpc) of this galaxy was observed in the 100-GHz region covering ˜ 96-100 GHz and ˜ 108-111 GHz with an angular resolution of ˜ 4'' × 2'' (290 pc × 140 pc) to study the effects of an active galactic nucleus and its surrounding starburst ring on molecular abundances. Here, we present images and report a classification of molecular distributions into three main categories: (1) molecules concentrated in the circumnuclear disk (CND) (SO JN = 32-21, HC3N J = 11-10, 12-11, and CH3CN JK = 6K-5K), (2) molecules distributed both in the CND and the starburst ring (CS J = 2-1 and CH3OH JK = 2K-1K), and (3) molecules distributed mainly in the starburst ring (13CO J = 1-0 and C18O J = 1-0). Since most of the molecules such as HC3N observed in the CND are easily dissociated by UV photons and X-rays, our results indicate that these molecules must be effectively shielded. In the starburst ring, the relative intensity of methanol at each clumpy region is not consistent with those of 13CO, C18O, or CS. This difference is probably caused by the unique formation and destruction mechanisms of CH3OH.

  9. Galaxy NGC 1850

    NASA Technical Reports Server (NTRS)

    1999-01-01

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

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

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

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

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

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

    The Space Telescope Science Institute, Baltimore

  10. The Circumnuclear Starburst Ring in NGC 1097

    NASA Astrophysics Data System (ADS)

    Thackeray-Lacko, Beverly; Stierwalt, Sabrina; Sheth, Kartik

    2016-01-01

    The circumnuclear ring in galaxy NGC 1097 is bursting with star formation at a rate of five solar masses per year as previously measured through Hα emission. The rate of star formation drops by a factor of one thousand outside the circumnuclear ring. We characterize the behavior of the dust in this region by measuring the spectral energy distribution focused exclusively on the circumnuclear ring using a selective variety of high resolution science images spanning wavelengths from ultraviolet to infrared, and adding proprietary high resolution radio data from Atacoma Large Millimeter Array (ALMA) in Chile. High resolution radio data obtained from ALMA allows us to constrain the shape of the spectral energy distribution curve specifically at longer wavelengths, and therefore the rate of star formation within the circumnuclear ring. Comparing the spectral energy distribution of the entire galaxy with that of the circumnuclear ring indicates how starburst activity influences the galactic spectral energy distribution.

  11. Galaxy NGC 4013

    NASA Technical Reports Server (NTRS)

    1999-01-01

    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

  12. Galaxy NGC 1512

    NASA Technical Reports Server (NTRS)

    1999-01-01

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

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

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

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

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

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

  13. Hubble Space Telescope Observations of Circumnuclear Star-Forming Rings in NGC 1097 and NGC 6951

    NASA Astrophysics Data System (ADS)

    Barth, Aaron J.; Ho, Luis C.; Filippenko, Alexei V.; Sargent, Wallace L.

    1995-09-01

    We have obtained new and archival Hubble Space Telescope V-band images of kiloparsec-sized circumnuclear star-forming rings in the barred spiral galaxies NGC 1097 and NGC 6951, both of which contain active nuclei. The images resolve the rings into two-armed spirals composed of bright knots located on the outer edges of prominent dust lanes. The two-armed ring morphology seen in these two galaxies appears to be common in barred spirals and is in accord with the results of simulations of bar-driven inflow. In both galaxies, circumnuclear star formation is tightly confined to the ring: in the region between the ring and the nucleus there is an intricate spiral pattern of narrow dust lanes, but no bright knots are visible. Miniature gaseous or stellar bars interior to nuclear rings have been suggested as mechanisms for transporting gas to active nuclei, but it is not clear from the optical morphology whether either of these mechanisms may be at work in these two galaxies. The young star clusters in the rings are extremely compact, with mean effective radii of 2.5 pc in NGC 1097 and <= 4 pc in NGC 6951. Without correcting for extinction, the clusters have absolute V magnitudes of up to - 12.6 mag; with a highly uncertain extinction correction the brightest clusters have luminosities of M_v_ = - 14 to - 15 mag. Such high luminosities and small radii indicate that these objects are examples of "super star clusters" which may be newly formed globular clusters like those found recently in merging galaxies. The centers of barred galaxies may therefore be common sites for the present-day formation of globular clusters. The image of NGC 1097 also contains the type II supernova 1992bd 12 days prior to its discovery in ground-based observations.

  14. The Superwind Galaxy NGC 4666

    NASA Astrophysics Data System (ADS)

    2010-09-01

    The galaxy NGC 4666 takes pride of place at the centre of this new image, made in visible light with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile. NGC 4666 is a remarkable galaxy with very vigorous star formation and an unusual "superwind" of out-flowing gas. It had previously been observed in X-rays by the ESA XMM-Newton space telescope, and the image presented here was taken to allow further study of other objects detected in the earlier X-ray observations. The prominent galaxy NGC 4666 in the centre of the picture is a starburst galaxy, about 80 million light-years from Earth, in which particularly intense star formation is taking place. The starburst is thought to be caused by gravitational interactions between NGC 4666 and its neighbouring galaxies, including NGC 4668, visible to the lower left. These interactions often spark vigorous star-formation in the galaxies involved. A combination of supernova explosions and strong winds from massive stars in the starburst region drives a vast flow of gas from the galaxy into space - a so-called "superwind". The superwind is huge in scale, coming from the bright central region of the galaxy and extending for tens of thousands of light-years. As the superwind gas is very hot it emits radiation mostly as X-rays and in the radio part of the spectrum and cannot be seen in visible light images such as the one presented here. This image was made as part of a follow-up to observations made with the ESA XMM-Newton space telescope in X-rays. NGC 4666 was the target of the original XMM-Newton observations, but thanks to the telescope's wide field-of-view many other X-ray sources were also seen in the background. One such serendipitous detection is a faint galaxy cluster seen close to the bottom edge of the image, right of centre. This cluster is much further away from us than NGC 4666, at a distance of about three billion light-years. In order to fully understand the nature of

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

    SciTech Connect

    Sil'chenko, O. K.; Shulga, A. P.; Moiseev, A. V. E-mail: alina.shulga@gmail.co

    2010-11-15

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

  16. Near-Infrared Continuum and 3.3um PAH Imaging of the Starburst Ring in the Type I Seyfert Galaxy NGC 7469

    NASA Technical Reports Server (NTRS)

    Mazzarella, J.; Voit, G.; Soifer, B.; Matthews, K.; Graham, J.; Armus, L.; Shupe, D.

    1993-01-01

    High resolution near-infrared images of the type 1 Seyfert Galaxy NGC 7469 have been obtained to probe its dusty nuclear environment. Direct images are relatively featureless, but residual images created by subtacting a smooth model based on best-fitting elliptical isoophotes reveal a tight inner spiral whose high surface-brightness portions correspond to a previously detected 3.

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

    NASA Technical Reports Server (NTRS)

    2002-01-01

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

  18. Kinematics in irregular galaxies: NGC 4449.

    NASA Astrophysics Data System (ADS)

    Valdez, M.; Rosado, M.

    1998-11-01

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

  19. Hydrogen fluoride toward luminous nearby galaxies: NGC 253 and NGC 4945

    SciTech Connect

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

    2014-04-10

    We present the detection of hydrogen fluoride (HF) in two luminous nearby galaxies, NGC 253 and NGC 4945 using the Heterodyne Instrument for the Far-Infrared on board the Herschel Space Observatory. The HF line toward NGC 253 has a P-Cygni profile, while an asymmetric absorption profile is seen toward NGC 4945. The P-Cygni profile in NGC 253 suggests an outflow of molecular gas with a mass of M(H{sub 2}){sub out} ∼ 1 × 10{sup 7} M {sub ☉} and an outflow rate as large as M-dot ∼6.4 M {sub ☉} yr{sup –1}. In the case of NGC 4945, the axisymmetric velocity components in the HF line profile are compatible with the interpretation of a fast-rotating nuclear ring surrounding the nucleus and the presence of inflowing gas. The gas falls into the nucleus with an inflow rate of ≤1.2 M {sub ☉} yr{sup –1}, inside an inner radius of ≤200 pc. The gas accretion rate to the central active galactic nucleus is much smaller, suggesting that the inflow may be triggering a nuclear starburst. From these results, the HF J = 1-0 line is seen to provide an important probe of the kinematics of absorbing material along the sight-line to nearby galaxies with bright dust continuum and a promising new tracer of molecular gas in high-redshift galaxies.

  20. Near-infrared continuum and 3.3 micrometer(s) polycyclic aromatic hydrocarbon imaging of the starburst ring in the type 1 Seyfert galaxy NGC 7469

    NASA Technical Reports Server (NTRS)

    Mazzarella, J. M.; Voit, G. M.; Soifer, B. T.; Matthews, K.; Graham, J. R.; Armus, L.; Shupe, D.

    1994-01-01

    High resolution near-infrared images of the type 1 Seyfert galaxy NGC 7469 have been obtained to probe its dusty nuclear environment. Direct J, H, and K images are relatively featureless, but residual images created by subtracting a smooth model based on best-fitting elliptical isophotes reveal a tight inner spiral whose high surface-brightness portions correspond to a previously detected 3 sec (1 kpc) diameter ring of radio continuum emission. The inner infrared spiral arms extended approximately equal to 4 sec NW and SE from the nucleus, and the NW arm joins up with large-scale spiral structure visible in the R band. The residual images also show a bar-like structure aligned with the brightest infrared/radio hotspots at PA approximately equal to 50 deg. Three infrared hotspots are detected which align remarkably well with 6 cm radio continuum sources. The near-infrared ring and the hotspots are visible in the residual images, and in a high-resolution direct K-band image restored to an effective resolution of 0.65 sec (FWHM) using the Richardson-Lucy algorithm. The infrared hotspots have luminosities of nuL(sub nu) (2.2 micrometer(s)) approximately equal to 10(exp 8) solar luminosity (M(sub k) approximately equal to -16 mag), suggesting they are either giant H II regions or individual supernovae. The two brightest regions may be associated with enhanced star formation triggered by orbit crowding of gas where spiral arms emerge from an inner bar. Narrowband (delta lambda/lambda approximately 1.5%) imaging in the 3.28 micrometer(s) dust emission feature and surrounding continuum confirms the 3 sec diameter 3.28 micrometer(s) emission region detected previously using multiaperture photometry. The extended polycyclic aromatic hydrocarbon (PAH) emission is slightly elongated and aligned with published 1O III1 line emission and 12.5 micrometer(s) continuum emission, apparently tracing the starburst. The presence of approximately equal to 25% of the total 3.28 micrometer

  1. The molecular morphology of the SAB galaxy NGC 4736

    NASA Astrophysics Data System (ADS)

    Garman, L. E.; Young, J. S.

    1986-01-01

    The first mapping observations of molecular clouds in NGC 4736 are presented. A central hole in the molecular distribution is found, with the observed peak in CO emission at a radius of 22 arcsec from the center. If this distribution is azimuthally symmetric, the ring contains an H2 mass of 100 million solar masses, while the H I mass in the same region is 10 million solar masses. The CO peaks are coincident with the inner portion of a ring of H I. The extent of the central CO hole coincides with the region in the galaxy where the light distribution is dominated by the contribution from the nuclear bulge, as was found previously in several Sb galaxies. The fraction of mass in the ISM in this galaxy, about one percent, is lower than that found in any other galaxy in which CO has been detected. This is due to a very small amount of mass in the atomic and molecular clouds.

  2. Noncircular outer disks in unbarred S0 galaxies: NGC 502 and NGC 5485

    NASA Astrophysics Data System (ADS)

    Sil'chenko, O. K.

    2016-03-01

    Highly noncircular outer stellar disks have been detected in two SA0 (unbarred) galaxies by comparing the spectroscopic data on the rotation of stars and the photometric data on the shape and orientation of isophotes. In NGC 502, the oval distortion of the disk is manifested in the shape of the inner and outer elliptical rings occupying wide radial zones between the bulge and the disk and at the outer disk edge; such a structure can be a consequence of the so-called "dry minor merger," multiple cannibalization of gas-free satellites. In NGC 5485, the stellar kinematics is absolutely unrelated to the orientation of isophotes in the disk region, and for this galaxy the conclusion about its global triaxial structure is unavoidable.

  3. Hyperactive galaxy NGC 7673 [heic0205

    NASA Astrophysics Data System (ADS)

    2002-03-01

    Hyperactive galaxy NGC 7673 hi-res Size hi-res: 116 kb Credits: European Space Agency & Nicole Homeier (European Southern Observatory and University of Wisconsin-Madison) Hyperactive galaxy NGC 7673 The disturbed spiral galaxy NGC 7673 is ablaze with the light from millions of new stars. Each of its infant giant blue star clusters shines 100 times as brightly in the ultraviolet as similar immense star clusters in our own Galaxy. Scientists studying this object have two pressing questions: "What has triggered this enormous burst of star formation and how will this galaxy evolve in the future?" Telltale patches of blue light are signs of the formation of millions of new stars in the tangled spiral galaxy NGC 7673. Each of the bluish areas in this image consists of immense star clusters containing thousands of young stars. These clusters lie on the spiral arms of NGC 7673 and so emphasise its somewhat ragged look. This image, taken from Earth orbit by the ESA/NASA Hubble Space Telescope in 1996 and 1997, also shows two other galaxies seen in the background of the image, to the left and right of NGC 7673. These galaxies are further away and so appear redder, due to their higher redshift, an effect caused by the expansion of the Universe. The youngest blue stars in NGC 7673 are blazing with intense ultraviolet radiation. Each star cluster radiates 100 times more ultraviolet light than the famous Tarantula Nebula (30 Doradus), the largest star-forming region known in the local group of galaxies. Telltale patches of blue light are signs of the formation of millions of new stars in the tangled spiral galaxy NGC 7673. Each of the bluish areas in this image consists of immense star clusters containing thousands of young stars. These clusters lie on the spiral arms of NGC 7673 and so emphasise its somewhat ragged look. This image, taken from Earth orbit by the ESA/NASA Hubble Space Telescope in 1996 and 1997, also shows two other galaxies seen in the background of the image

  4. Erratum: ``Circumnuclear Star Formation in the Early-Type Resonance Ring Barred Spiral Galaxy NGC 1326'' [Astron. J. 120, 1289 (2000)

    NASA Astrophysics Data System (ADS)

    Buta, R.; Treuthardt, Patrick M.; Byrd, G. G.; Crocker, D. A.

    2001-11-01

    Because of a computational error, the power-law slope of the cluster luminosity function in the nuclear ring was incorrectly presented as having a value a=2.10+/-0.04. The correct value is a=3.7+/-0.1, which is not similar to other young cluster systems. This steep slope is interesting and could be interpreted in a number of ways; in particular, it suggests that many of the sources in the nuclear ring could be extreme supergiants, rather than clusters. However, as noted by D. Maoz, A. J. Barth, L. C. Ho, A. Sternberg, & A. V. Filippenko (Astron. J. 120, 1289 (2000)), individual blue supergiants that have absolute visual magnitudes up to -10 are very short-lived and may only explain a handful of the point sources seen in other nuclear rings. We cannot rule out the possibility that more of the sources in the nuclear ring of NGC 1326 than we originally thought are actually single stars, because at the distance of 19 Mpc, very compact clusters are hard to distinguish from stars. On the other hand, the analysis of two-color plots and reddening-free parameters favors the interpretations given in the paper, implying that the luminosity function is more deficient than usual in high-luminosity clusters, at least in this case. This issue will be discussed in a separate paper on the sources detected in the inner ring of NGC 3081, which presents a similar situation (R. Buta, G. G. Byrd, & T. Freeman 2001, in preparation). R. B. would like to thank B. G. Elmegreen for helpful discussions.

  5. A multispecies survey of the active galaxy NGC1068

    NASA Astrophysics Data System (ADS)

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

    2011-05-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

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

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

    SciTech Connect

    Young, Michael D.; Dowell, Jessica L.; Rhode, Katherine L. E-mail: jlwind@astro.indiana.edu

    2012-10-01

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

  9. The H I-Rich Elliptical Galaxy NGC 5266

    NASA Astrophysics Data System (ADS)

    Morganti, R.; Sadler, E. M.; Oosterloo, T.; Pizzella, A.; Bertola, F.

    1997-03-01

    We present new ion{H}{1} images of the dust-lane elliptical galaxy NGC 5266 already known from single-dish observations to contain a large amount of ion{H}{1}. Our new data confirm that NGC 5266 contains ~2.4 x 10(10) msun (for Hdeg = 50 kmsMp) of neutral hydrogen, i.e. more than most spiral galaxies of similar luminosity. The gas extends to ~8(') each side of the nucleus, or 8 times the optical half-light radius R_e. Surprisingly, most of the ion{H}{1} extends almost orthogonal to the optical dust lane. A small fraction of the ion{H}{1} is associated with the dust lane and there are some hints of a faint warp connecting the two structures. The ion{H}{1} distribution is somewhat clumpy and asymmetric, but the overall velocity field in the inner 4(') can be successfully modeled by assuming that the gas lies mainly in two perpendicular planes - in the plane of the dust lane in the central parts and orthogonal to this in the outer regions. Beyond the 4(') radius, the gas has a different structure and may be in two tidal tails, or an edge-on ring. Measurement of the ion{H}{1} rotation curve is affected by asymmetries in the gas distribution, but the rotation velocity is at least 250 kms at a radius of 4(') , and a flat rotation curve of ~270 kms is consistent with the data. This would imply a value of M / L_B ~8 at ~4 R_e. If the outermost ion{H}{1} is in an edge-on ring, we estimate M / L_B ~16 at ~8 R_e. Comparing this with the value derived from optical observations for the inner region we find an increase of M / L_B by a factor ~2.7 at r ~4 R_e, and by 5.3 at r ~8 R_e. The large amount of neutral gas observed in NGC 5266 (M_HI/L_B ~0.2) and the ion{H}{1} morphology, suggest that this object may have formed from the merger of two spiral galaxies. If so, NGC 5266 probably represents a relatively old merger remnant since most of the ion{H}{1} gas appears settled.

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

    NASA Astrophysics Data System (ADS)

    Sánchez-Gil, M. Carmen; Alfaro, Emilio J.; Pérez, Enrique

    2015-12-01

    We address the study of the H α vertical velocity field in a sample of four nearly face-on galaxies using long-slit spectroscopy taken with the Intermediate dispersion Spectrograph and Imaging System (ISIS), attached to the William Herschel Telescope (WHT) at the Roque de los Muchachos Observatory (Spain). The spatial structure of the velocity vertical component shows a radial corrugated pattern with spatial scales higher or within the order of 1 kpc. The gas is mainly ionized by high-energy photons: only in some locations of NGC 278 and NGC 1058 is there some evidence of ionization by low-velocity shocks, which, in the case of NGC 278, could be due to minor mergers. The behaviour of the gas in the neighbourhood of the spiral arms fits, in the majority of the observed cases, with that predicted by the so-called hydraulic bore mechanism, where a thick magnetized disc encounters a spiral density perturbation. The results obtained show that it is difficult to explain the H α large-scale velocity field without the presence of a magnetized, thick galactic disc. Larger samples and spatial covering of the galaxy discs are needed to provide further insight into this problem.

  11. CO observations of the SAB galaxies NGC 157, 2903, 4321, and 5248, and the Seyfert galaxy NGC 1068

    NASA Astrophysics Data System (ADS)

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

    1982-04-01

    Extragalactic carbon monoxide emission regions can, in principle, be located more precisely than the telescope beamwidth by using optically derived velocity distributions which have much higher angular resolution. Using this technique, the CO emission from five distant galaxies was analyzed. CO emission from NGC 1068 is strongest in the central region. In NGC 4321, it is strongest in the long bright spiral arms. CO emission from NGC 157 and NGC 2903 occurs more uniformly over the disk of these galaxies; the H II regions and dust clouds are more uniformly distributed in these galaxies as well. In NGC 157, the CO is brightest from the area including the NE spiral arm, which has more continuity and bright star formation than the SW arm. These results agree with the expectation that CO emission should be intensified near the H II regions and obvious dust clouds that usually concentrate near the spiral arms.

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

    NASA Astrophysics Data System (ADS)

    Carlqvist, Per

    2013-02-01

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

  13. HST/ACS DIRECT AGES OF THE DWARF ELLIPTICAL GALAXIES NGC 147 AND NGC 185

    SciTech Connect

    Geha, M.; Weisz, D.; Grocholski, A.; Dolphin, A.; Marel, R. P. van der; Guhathakurta, P.

    2015-10-01

    We present the deepest optical photometry for any dwarf elliptical (dE) galaxy based on Hubble Space Telescope Advanced Camera for Surveys (ACS) observations of the Local Group dE galaxies NGC 147 and NGC 185. Our F606W and F814W color–magnitude diagrams are the first to reach below the oldest main sequence turnoff in a dE galaxy, allowing us to determine full star formation histories in these systems. The ACS fields are located roughly ∼1.5 effective radii from the galaxy center to avoid photometric crowding. While both ACS fields show unambiguous evidence for old and intermediate age stars, the mean age of NGC 147 is ∼4–5 Gyr younger as compared to NGC 185. In NGC 147, only 40% of stars were in place 12.5 Gyr ago (z ∼ 5), with the bulk of the remaining stellar population forming between 5 to 7 Gyr. In contrast, 70% of stars were formed in NGC 185 prior to 12.5 Gyr ago with the majority of the remaining population forming between 8 to 10 Gyr ago. Star formation has ceased in both ACS fields for at least 3 Gyr. Previous observations in the central regions of NGC 185 show evidence for star formation as recent as 100 Myr ago, and a strong metallicity gradient with radius. This implies a lack of radial mixing between the center of NGC 185 and our ACS field. The lack of radial gradients in NGC 147 suggests that our inferred SFHs are more representative of its global history. We interpret the inferred differences in star formation histories to imply an earlier infall time into the M31 environment for NGC 185 as compared to NGC 147.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Smith, Beverly J.; Wallin, John F.

    1992-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    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.

  17. Velocity mapping and models of the elliptical galaxies NGC 720, NGC 1052, and NGC 4697

    NASA Technical Reports Server (NTRS)

    Binney, J. J.; Davies, Roger L.; Illingworth, Garth D.

    1990-01-01

    CCD surface photometry and extensive long-slit spectroscopy are used to construct detailed models of the flattened ellipticals NGC 720, 1052, and 4697. The models are combined with the Jeans equations to yield predicted fields of line-of-sight velocity dispersion and streaming velocity. By comparing these fields with observed velocities, it is concluded that none of these systems can have isotropic velocity dispersion tensors, and diminishing the assumed inclination of any given galaxy tends to decrease the line-of-sight velocity dispersion and, counterintuitively, to increase the line-of-sight rotation speeds. The ratio of the line-of-sight velocity dispersion along the minor axis to that along the major axis is found to be a sensitive diagnostic of the importance of a third integral for the galaxy's structure.

  18. Velocity mapping and models of the elliptical galaxies NGC 720, NGC 1052, and NGC 4697

    SciTech Connect

    Binney, J.J.; Davies, R.L.; Illingworth, G.D. Oxford Univ. National Optical Astronomy Observatories, Tucson, AZ California Univ., Santa Cruz )

    1990-09-01

    CCD surface photometry and extensive long-slit spectroscopy are used to construct detailed models of the flattened ellipticals NGC 720, 1052, and 4697. The models are combined with the Jeans equations to yield predicted fields of line-of-sight velocity dispersion and streaming velocity. By comparing these fields with observed velocities, it is concluded that none of these systems can have isotropic velocity dispersion tensors, and diminishing the assumed inclination of any given galaxy tends to decrease the line-of-sight velocity dispersion and, counterintuitively, to increase the line-of-sight rotation speeds. The ratio of the line-of-sight velocity dispersion along the minor axis to that along the major axis is found to be a sensitive diagnostic of the importance of a third integral for the galaxy's structure. 48 refs.

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

    SciTech Connect

    Hunter, D.A.; Thronson, H.A. Jr.; Casey, S.; Harper, D.A.; Wyoming Infrared Observatory, Laramie; Yerkes Observatory, Williams Bay, WI )

    1989-06-01

    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. 81 refs.

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

    NASA Astrophysics Data System (ADS)

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

    1999-04-01

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

  1. A BRIGHT RING OF STAR BIRTH AROUND A GALAXY'S CORE

    NASA Technical Reports Server (NTRS)

    2002-01-01

    n image from NASA's Hubble Space Telescope reveals clusters of infant stars that formed in a ring around the core of the barred-spiral galaxy NGC 4314. This stellar nursery, whose inhabitants were created within the past 5 million years, is the only place in the entire galaxy where new stars are being born. The Hubble image is being presented today (June 11) at the American Astronomical Society meeting in San Diego, Calif. This close-up view by Hubble also shows other interesting details in the galaxy's core: dust lanes, a smaller bar of stars, dust and gas embedded in the stellar ring, and an extra pair of spiral arms packed with young stars. These details make the center resemble a miniature version of a spiral galaxy. While it is not unusual to have dust lanes and rings of gas in the centers of galaxies, it is uncommon to have spiral arms full of young stars in the cores. NGC 4314 is one of the nearest (only 40 million light-years away in the constellation Coma Berenices) examples of a galaxy with a ring of infant stars close to the core. This stellar ring - whose radius is 1,000 light-years - is a great laboratory to study star formation in galaxies. The left-hand image, taken in February 1996 by the 30-inch telescope Prime Focus Camera at the McDonald Observatory in Texas, shows the entire galaxy, including the bar of stars bisecting the core and the outer spiral arms, which begin near the ends of this bar. The box around the galaxy's core pinpoints the focus of the Hubble image. The right-hand image shows Hubble's close-up view of the galaxy's core, taken in December 1995 by the Wide Field and Planetary Camera 2. The bluish-purple clumps that form the ring are the clusters of infant stars. Two dark, wispy lanes of dust and a pair of blue spiral arms are just outside the star-forming ring. The lanes of dust are being shepherded into the ring by the longer, primary stellar bar seen in the ground-based (left-hand) image. The gas is trapped inside the ring

  2. The Dragonfly Nearby Galaxies Survey. II. Ultra-Diffuse Galaxies near the Elliptical Galaxy NGC 5485

    NASA Astrophysics Data System (ADS)

    Merritt, Allison; van Dokkum, Pieter; Danieli, Shany; Abraham, Roberto; Zhang, Jielai; Karachentsev, I. D.; Makarova, L. N.

    2016-12-01

    We present the unexpected discovery of four ultra-diffuse galaxies (UDGs) in a group environment. We recently identified seven extremely low surface brightness galaxies in the vicinity of the spiral galaxy M101, using data from the Dragonfly Telephoto Array. The galaxies have effective radii of 10″-38″ and central surface brightnesses of 25.6-27.7 mag arcsec-2 in the g-band. We subsequently obtained follow-up observations with HST to constrain the distances to these galaxies. Four remain persistently unresolved even with the spatial resolution of HST/ACS, which implies distances of D\\gt 17.5 Mpc. We show that the galaxies are most likely associated with a background group at ˜27 Mpc containing the massive ellipticals NGC 5485 and NGC 5473. At this distance, the galaxies have sizes of 2.6-4.9 kpc, and are classified as UDGs, similar to the populations that have been revealed in clusters such as Coma, Virgo, and Fornax, yet even more diffuse. The discovery of four UDGs in a galaxy group demonstrates that the UDG phenomenon is not exclusive to cluster environments. Furthermore, their morphologies seem less regular than those of the cluster populations, which may suggest a different formation mechanism or be indicative of a threshold in surface density below which UDGs are unable to maintain stability.

  3. Dwarf galaxies in the dynamically evolved NGC 1407 Group

    NASA Astrophysics Data System (ADS)

    Trentham, Neil; Tully, R. Brent; Mahdavi, Andisheh

    2006-07-01

    The NGC 1407 Group stands out among nearby structures by its properties that suggest it is massive and evolved. It shares properties with entities that have been called fossil groups: the 1.4m differential between the dominant elliptical galaxy and the second brightest galaxy comes close to satisfying the definition that has been used to define the fossil class. There are few intermediate-luminosity galaxies, but a large number of dwarfs in the group. We estimate there are 250 group members to the depth of our survey. The slope of the faint end of the luminosity function (reaching MR = -12) is α = -1.35. Velocities for 35 galaxies demonstrate that this group with one dominant galaxy has a mass of 7 × 1013Msolar and M/LR = 340Msolar/Lsolar. Two galaxies in close proximity to NGC 1407 have very large blueshifts. The most notable is the second brightest galaxy, NGC 1400, with a velocity of -1072 km s-1 with respect to the group mean. We report the detection of X-ray emission from this galaxy and from the group.

  4. NGC 55: a disc galaxy with flat abundance gradients

    NASA Astrophysics Data System (ADS)

    Magrini, Laura; Gonçalves, Denise R.; Vajgel, Bruna

    2017-01-01

    We present new spectroscopic observations obtained with Gemini Multi-Object Spectrographs at Gemini-South of a sample of 25 H II regions located in NGC 55, a late-type galaxy in the nearby Sculptor group. We derive physical conditions and chemical composition through the Te method for 18 H II regions, and strong-line abundances for 22 H II regions. We provide abundances of He, O, N, Ne, S and Ar, finding a substantially homogeneous composition in the ionized gas of the disc of NGC 55, with no trace of radial gradients. The oxygen abundances, both derived with Te and strong-line methods, have similar mean values and similarly small dispersions: 12+log (O/H) = 8.13 ± 0.18 dex with the former and 12+log (O/H) = 8.17 ± 0.13 dex with the latter. The average metallicities and the flat gradients agree with previous studies of smaller samples of H II regions and there is a qualitative agreement with the blue supergiant radial gradient as well. We investigate the origin of such flat gradients comparing NGC 55 with NGC 300, its companion galaxy, which is also twin of NGC 55 in terms of mass and luminosity. We suggest that the differences in the metal distributions in the two galaxies might be related to the differences in their K-band surface density profile. The flatter profile of NGC 55 probably causes in this galaxy higher infall/outflow rates than in similar galaxies. This likely provokes a strong mixing of gas and a re-distribution of metals.

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

    In this work we address the study of the detection in Ha of a radial corrugation in the vertical velocity field in a sample of four nearly face-on, spiral galaxies. The geometry of the problem is a main criterion in the selection of the sample as well as of the azimuthal angle of the slits. These spatial corrugations must be equally associated with wavy vertical motions in the galactic plane with a strong large-scale consistency. Evidence of these kinematic waves were first detected in the analysis of the rotation curves of spiral galaxies (e.g. te{1963ApJ...137..363D,1965BOTT....4....8P}), but it was not until 2001 that te{2001ApJ...550..253A} analyzed in more detail the velocity corrugations in NGC 5427 and a possible physical mechanism for their origin. The aim of this study is to analyze the corrugated velocity pattern in terms of the star formation processes. We describe the geometry of the problem and establish its fundamental relationships.

  6. Radio Continuum Mapping of the Spiral Galaxy NGC 4258

    NASA Astrophysics Data System (ADS)

    Calle, Daniel; Hyman, Scott D.; Weiler, Kurt W.; van Dyk, Schuyler D.; Sramek, Richard A.

    1996-05-01

    We have combined numerous, short radio continuum observations of the Seyfert 1 galaxy NGC 4258 (M 106) made at 20 and 6 cm with the Very Large Array (VLA) to produce deep radio maps at these frequencies. These observations were originally taken for monitoring the radio supernova SN 1981K (Weiler et al. 1986, ApJ, 310, 790; Van Dyk et al. 1992, ApJ, 396, 195). The present analysis is analogous to our recent work on NGC 6946 (Hyman et al. 1993, BAAS 25, 1322) and on NGC 4321 (Hyman et al. 1994, BAAS 26, 1498) using observations taken for monitoring SN 1980K and SN 1979C, respectively. The maps we produce for NGC 4258 are of superior sensitivity (sigma ~ lt 0.02 mJy/beam at 6 cm) and spatial resolution ( ~ 0.5" at 6 cm) to those previously published by other investigators (e. g., Turner & Ho 1994, ApJ, 421, 122; Cecil et al. 1995, ApJ, 452, 613). We present preliminary measurements and analyses of the nuclear region, the anomalous arms, and of detected thermal and nonthermal sources throughout the galaxy. We also make comparisons of our radio maps with existing data at other wavelengths and with the results of our analyses of NGC 6946 and NGC 4321.

  7. Stellar Population Synthesis of the Elliptical Galaxy NGC 4649

    NASA Astrophysics Data System (ADS)

    Chun, Mun-Suk; Gim, Moon-Whan; Sohn, Young-Jong

    2001-12-01

    We investigated population of the elliptical galaxy NGC 4649 using the spectral synthesis technique based on the linear program in the spectral regions between 3160Å to 10800Å. We used the spectral data of stars obtained by Gunn & Stryker (1983), and the integrated spectrum of NGC 4649 observed by Bertola et al. (1982). Among four models with different main sequence turn-off points, G8-K0V main sequence turn-off model is best fitted to the integrated spectrum of NGC 4649. We also found that super metal rich K giants are needed to describe the absorption lines in the long wavelength regions of integrated spectrum of NGC 4649. The mass to absolute light ratio obtained from the spectral synthesis is ~20 similar to those calculated dynamically.

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    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

  9. Nuclear Star Formation in the Hot-Spot Galaxy NGC 2903

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    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.

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

    SciTech Connect

    Minchin, R. F.; Momjian, E.; Auld, R.; Davies, J. I.; Smith, M. W. L.; Taylor, R.; Valls-Gabaud, D.; Van Driel, W.; Karachentsev, I. D.; Henning, P. A.; O'Neil, K. L.

    2010-10-15

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

  11. Dwarf galaxies in the halo of NGC 891

    SciTech Connect

    Schulz, Earl

    2014-07-20

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

  12. The infrared emission from the elliptical galaxy NGC 1052

    NASA Technical Reports Server (NTRS)

    Becklin, E. E.; Tokunaga, A. T.; Wynn-Williams, C. G.

    1982-01-01

    Multi-aperture IR photometry of the elliptical galaxy NGC 1052 shows that its IR excess is confined to a region smaller than 2 arc sec (300 pc) in diameter coincident with the visible nucleus. It is suggested that the emission in the 5-20 micron range arises from dust heated by the nonthermal source seen at other wavelengths.

  13. Mapping Diffuse HI Content in MHONGOOSE Galaxies NGC 1744 and NGC 7424

    NASA Astrophysics Data System (ADS)

    Sardone, Amy; Pisano, Daniel J.; Pingel, Nickolas

    2017-01-01

    The universe contains an abundance of neutral atomic hydrogen, or HI. This HI holds the key to knowing how stars are born, how galaxies form and develop, and how dark matter halos accrete gas from the cosmic web. One of the most crucial questions regarding galaxy formation today is how galaxies accrete their gas and how accretion processes affect subsequent star formation. We are trying to answer these questions by mapping the HI content in a four square degree region around galaxies NGC 1744 and NGC 7424, galaxies to be observed as part of the MHONGOOSE survey. NGC 1744 has already been observed extensively with the VLA, so we will be able to quantify the differences in emission. To do this our GBT maps must be sensitive to column densities on the order of ~1018 cm-2. With such low column densities, we will be able to search for features of the cosmic web in the form of tidal interactions and cosmic web filaments with its relation to star-forming galaxies.

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

    NASA Astrophysics Data System (ADS)

    Colombo, D.

    2013-09-01

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

  15. Current star formation in S0 galaxies: NGC 4710

    NASA Technical Reports Server (NTRS)

    Wrobel, J. M.

    1990-01-01

    Elliptical (E) and lenticular (S0) galaxies lack the substantial interstellar medium (ISM) found in the star-forming spiral galaxies. However, significant numbers of E and S0 galaxies are known to contain detectable amounts of interstellar matter (e.g., Jura 1988). Thus, it is worth investigating whether these galaxies are currently able to form stars from their ISM, or whether they should be consigned to the dustbin of inert objects (Thronson and Bally 1987). The results strongly imply that current star formation is responsible for NGC 4710's far infrared and radio continuum properties. If this is indeed the case, then one expects this star formation to be fueled by molecular gas, which is presumably dominated by H2 and can be traced by the CO-12 J=1 to 0 line. Both Kenney and Young (1988) and Sage and Wrobel (1989) have detected such an emission line from NGC 4710, and infer the presence of more than 10(exp 8) solar mass of H2. The origin of the molecular gas in NGC 4710 remains a mystery. The galaxy is very deficient in HI (Kenney and Young, in preparation), suggesting that it originally was a spiral galaxy from which the outer, mainly atomic, gas was stripped by the ram pressure of the Virgo Cluster's intracluster medium, leaving only a central interstellar medium (ISM) rich in molecular gas. Alternatively, the CO may have originated via stellar mass loss with subsequent cooling, cooling flows, or capture from a gas-rich companion. Information on the morphology and kinematics of the CO can be compared with that of the galaxy's other gases and stars to distinguish among these various possible origins for the molecular gas. Major axis CO mapping with single dishes indicate an unresolved source. Thus, a millimeter array is currently being used to image NGC 4710 in CO to provide the needed morphological and kinematical data.

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

    NASA Astrophysics Data System (ADS)

    Smith, Beverly J.

    1998-06-01

    Using the mid-infrared camera (ISOCAM) on the Infrared Space Observatory (ISO), the Sb LINER galaxy NGC 7331 has been imaged in two broadband and four narrowband filters between 6.75 and 15 μm. These maps show a prominent circumnuclear ring of radius 0.25 arcmin × 0.75 arcmin (1.1 × 3.3 kpc) encircling an extended central source. The 7.7 and 11.3 μm dust emission features are strong in this galaxy, contributing approximately one-third of the total IRAS 12 μm broadband flux. In contrast to starburst galaxies, the 15 μm continuum is weak in NGC 7331. The mid-infrared spectrum does not vary dramatically with position in this quiescent galaxy, showing neither large-scale destruction of the carriers of the emission bands nor a large increase in the 15 μm continuum in the star-forming ring. In the bulge there is some enhancement of the LW2 (6.75 μm) flux, probably because of contributions from photospheric light; however, the 11.3 μm dust feature is also seen, showing additional emission from interstellar or circumstellar dust. Based on observations made with ISO, an ESA project with instruments funded by ESAMember States and with the participation of ISAS and NASA.

  17. Star formation in the merging Galaxy NGC3256

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

  18. Neutral hydrogen in the starburst galaxy NGC3690/IC694

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  19. Circumnuclear molecular gas in megamaser disk galaxies NGC 4388 and NGC 1194

    SciTech Connect

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

    2014-06-20

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

  20. The multifrequency spectrum of the starburst galaxy NGC 2782

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

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

    SciTech Connect

    Krienke, K.; Hodge, P. Washington, University, Seattle )

    1991-03-01

    The luminosities of the 88 H II regions of NGC 3239, very likely a merging galaxy system, were measured by digital analysis of a photographic plate (20 A bandwidth filter). Despite evidence for earlier starburst activity, the present H II luminosity function is very similar to that for the LMC, including a supergiant H II region of 0.76 the luminosity of 30 Dor. The measured H II regions of NGC 3239 have an H-alpha total luminosity of 1.3 x 10 to the 40th erg/s. 13 refs.

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

    SciTech Connect

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

    2009-05-10

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

  3. The Nature of the Peculiar Virgo Cluster Galaxies NGC 4064 and NGC 4424

    NASA Astrophysics Data System (ADS)

    Cortés, Juan R.; Kenney, Jeffrey D. P.; Hardy, Eduardo

    2006-02-01

    Using extensive kinematical and morphological data on two Virgo Cluster galaxies undergoing strong nuclear star formation, we show that ram pressure stripping and gravitational interactions can act together on galaxies that have recently fallen into clusters. We present a detailed study of the peculiar H I-deficient Virgo Cluster spiral galaxies NGC 4064 and NGC 4424 using 12CO 1-0 interferometry, optical imaging, and integral field spectroscopic observations in order to learn what type of environmental interactions have affected these galaxies. Optical imaging reveals that NGC 4424 has a strongly disturbed stellar disk, with banana-shaped isophotes and shells. NGC 4064, which lies in the cluster outskirts, possesses a relatively undisturbed outer stellar disk and a central bar. In both galaxies Hα emission is confined to the central kiloparsec and originates in barlike strings of luminous star-forming complexes surrounded by fainter filaments. Complexes of young blue stars exist beyond the present location of ongoing star formation, indicating rapidly shrinking star-forming disks. Disturbed dust lanes extend out to a radius of 2-3 kpc, much farther than the Hα and CO emission detected by us but similar to the blue stellar complexes. CO observations reveal bilobal molecular gas morphologies, with Hα emission peaking inside the CO lobes, implying a time sequence in the star formation process. Gas kinematics reveals strong barlike noncircular motions in the molecular gas in both galaxies, suggesting that the material is radially infalling. In NGC 4064 the stellar kinematics reveals strong barlike noncircular motions in the central 1 kpc and stars supported by rotation with V/σ>1 beyond a radius of 15" (1.2 kpc). On the other hand, NGC 4424 has extremely modest stellar rotation velocities (Vmax~30 km s-1), and stars are supported by random motions as far out as we can measure, with V/σ=0.6 at r=18'' (1.4 kpc). The ionized gas kinematics in the core are disturbed

  4. Extragalactic molecular line surveys: the starburst galaxy NGC253

    NASA Astrophysics Data System (ADS)

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

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

  5. The Arecibo Galaxy Environment Survey: Observations towards the NGC 7817/7798 Galaxy Pair

    NASA Astrophysics Data System (ADS)

    Harrison, Amanda; Robert Minchin

    2016-01-01

    The Arecibo Galaxy Environment Survey (AGES) examines the environment of neutral hydrogen gas in the interstellar medium. AGES uses the 305m Arecibo Radio Telescope and the Arecibo L-Band Feed Array to create a deep field neutral hydrogen survey which we used to detect galaxies in an area five square degrees around the galaxy pair NGC 7817/7798. By finding and investigating hydrogen rich galaxies we hope to gain a better understanding of how the environment affects galaxy evolution. H1 line profiles were made for the detected H1 emission and ten galaxies which had the characteristic double-horned feature were found. NGC 7798 was not detected, but NGC 7817 and the other galaxies were cross-identified in NASA/IPAC Extragalactic Database as well as in Sloan Digital Sky Survey to obtain optical data. Out of the ten, two of the sources were uncatalogued. We analyzed the hydrogen spectra and aperture photometry to learn about the characteristics of these galaxies such as their heliocentric velocity, flux, and mass of the neutral hydrogen. Furthermore, we graphed the Tully-Fisher and the Baryonic Tully-Fisher of the ten sources and found that most followed the relation. One that is the biggest outlier is suspected be a galaxy cluster while other outliers may be caused by ram pressure stripping deforming the galaxy.

  6. A survey of satellite galaxies around NGC 4258

    SciTech Connect

    Spencer, Meghin; Loebman, Sarah; Yoachim, Peter

    2014-06-20

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

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

    NASA Astrophysics Data System (ADS)

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

    2001-03-01

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

  8. Ring galaxies as the cradle for ULXs

    NASA Astrophysics Data System (ADS)

    Wolter, Anna

    2015-08-01

    Ring galaxies are unique laboratories where the effects of galaxy interactions can be studied and the final stages of stellar evolution investigated. They are characterized by high star formation rates (SFR) and low metallicity, which favours the formation of high mass remnants. The few ring galaxies for which high resolution X-ray data are available show enhanced X-ray emission, and large numbers of Ultraluminous X-ray sources (ULXs). Due to the peculiar morphology of ring galaxies, detected point sources in the ring are very likely to be physically associated with the galaxy, reducing the problem of contamination from spurious sources which affects other samples. However the evidence in the X-ray band is based on a very scanty sample of four galaxies.In order to find an unbiased sample with which to compare these findings, we have selected all the peculiar galaxies labelled as collisional rings with a spectroscopic redshift z<0.02 from the Arp & Madore `Catalogue of southern peculiar galaxies and associations'. This selection produces a sample of 12 galaxies which we have observed with Chandra and XMM-Newton. We will discuss the results of these observations and support for current models that propose low metallicity environments as the ideal cradle for ULXs. We will compare the results from this statistically selected sample with those from brighter and known ring galaxies in order to asses the likelihood to find IMBHs due to collision events. We will address the presence of other signs of interaction, from high SFR to multiwavelenght morphology and spectra (eg. IR, Halpha..).

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

    SciTech Connect

    Ludwig, Johannes; Pasquali, Anna; Grebel, Eva K.; Gallagher, John S. III

    2012-12-01

    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.

  10. EXTREMELY RAPID STAR CLUSTER DISRUPTION IN HIGH-SHEAR CIRCUMNUCLEAR STARBURST RINGS: THE UNUSUAL CASE OF NGC 7742

    SciTech Connect

    De Grijs, Richard; Anders, Peter E-mail: anders@pku.edu.cn

    2012-10-10

    All known mass distributions of recently formed star cluster populations resemble a 'universal' power-law function. Here we assess the impact of the extremely disruptive environment in NGC 7742's circumnuclear starburst ring on the early evolution of the galaxy's high-mass ({approx}10{sup 5}-10{sup 7} M{sub Sun }) star cluster population. Surprisingly, and contrary to expectations, at all ages-including the youngest, {approx}< 15 Myr-the cluster mass functions are robustly and verifiably represented by lognormal distributions that resemble those commonly found only for old, evolved globular cluster systems in the local universe. This suggests that the high-shear conditions in the NGC 7742 starburst ring may significantly speed up dynamical star cluster destruction. This enhanced mass-dependent disruption rate at very young ages might be caused by a combination of the starburst ring's high density and the shear caused by the counterrotating gas disk.

  11. Evolution of molecular clouds in the starburst galaxy NGC 1808 revealed with ALMA

    NASA Astrophysics Data System (ADS)

    Salak, D.; Nakai, N.; Miyamoto, Y.

    2015-05-01

    We present large-field CO(1-0) observations of the starburst galaxy NGC 1808 conducted with ALMA. High-resolution (˜100 pc) images reveal a high concentration of molecular gas in the nucleus, 500-pc ring, gas-rich bar, and spiral arms. We derived the bar pattern speed and found an offset between CO and Hα emission peaks in the offset ridges along the bar. The results indicate that the evolution of molecular clouds on the galactic scale is driven by bar dynamics.

  12. GMRT observations of NGC 2997 and radio detection of the circumnuclear ring

    NASA Astrophysics Data System (ADS)

    Kodilkar, J.; Kantharia, N. G.; Ananthakrishnan, S.

    2011-09-01

    We present high-resolution, high-sensitivity radio continuum observations of the nearby spiral galaxy NGC 2997 at 332, 616 and 1272 MHz using the Giant Metrewave Radio Telescope (GMRT). The integrated spectrum of this galaxy has a spectral index of -0.92 (Sν ∝ να) and we place an upper limit to the thermal fraction at 1272 MHz of ˜ 10 per cent. Our multifrequency study shows a relatively flat spectrum source (α ˜ -0.6) at the centre of the galaxy. This leads to the radio detection of a circumnuclear ring in the high-resolution map at 1272 MHz. We detect five hotspots in the ring, with an average star formation rate of ˜0.024 M⊙ yr-1, a median supernova (SN) rate of ˜0.001 yr-1 and luminosity of 1020 W Hz-1. We estimate an equipartition field in the central nuclear region of diameter ˜750 pc to be about ?G. We also report several interesting features along the spiral arms. In this paper, we present the low-frequency radio continuum maps, the spectral index distribution, the circumnuclear ring and the derived physical properties.

  13. Feeding and Feedback in the Starbust Galaxy NGC 1808 Revealed with ALMA and ASTE

    NASA Astrophysics Data System (ADS)

    Salak, D.; Nakai, N.; Miyamoto, Y.

    2015-12-01

    NGC 1808 is a nearby (10 Mpc) starburst galaxy with a superwind detected as a dust outflow from the nuclear region. In order to study the evolution of molecular clouds in the feeding and feedback processes related to the starburst activity, we have carried out observations with ALMA and ASTE telescopes. We present preliminary results of cycle 1 (12-m array) large-field CO (1-0) imaging with ALMA and 1-mm line observations with ASTE. Molecular gas was detected and resolved at a resolution of 2” (˜100 pc) throughout the galactic disk. This first high-resolution CO image of NGC 1808 reveals: a circumnuclear disk in the center, 500-pc starburst ring, indication of inflow and outflow motion, giant molecular clouds (GMCs) and associations (GMAs) in the spiral arms and bar.

  14. Gas-phase Oxygen Abundances and Radial Metallicity Gradients in the Two nearby Spiral Galaxies NGC 7793 and NGC 4945

    NASA Astrophysics Data System (ADS)

    Stanghellini, Letizia; Magrini, Laura; Casasola, Viviana

    2015-10-01

    Gas-phase abundances in H ii regions of two spiral galaxies, NGC 7793 and NGC 4945, have been studied to determine their radial metallicity gradients. We used the strong-line method to derive oxygen abundances from spectra acquired with GMOS-S, the multi-object spectrograph on the 8 m Gemini South telescope. We found that NGC 7793 has a well-defined gas-phase radial oxygen gradient of -0.321 ± 0.112 dex {R}25-1 (or -0.054 ± 0.019 dex kpc-1) in the galactocentric range 0.17 < RG/R25 < 0.82, not dissimilar from gradients calculated with direct abundance methods in galaxies of similar mass and morphology. We also determined a shallow radial oxygen gradient in NGC 4945, -0.253 ± 0.149 dex {R}25-1 (or -0.019 ± 0.011 dex kpc-1) for 0.04 < RG/R25 < 0.51, where the larger relative uncertainty derives mostly from the larger inclination of this galaxy. NGC 7793 and NGC 4945 have been selected for this study because they are similar, in mass and morphology, to M33 and the Milky Way, respectively. Since at zeroth order we expect the radial metallicity gradients to depend on mass and galaxy type, we compared our galaxies in the framework of radial metallicity models best suited for M33 and the Galaxy. We found a good agreement between M33 and NGC 7793, pointing toward similar evolution for the two galaxies. We notice instead differences between NGC 4945 and the radial metallicity gradient model that best fits the Milky Way. We found that these differences are likely related to the presence of an active galactic nucleus combined with a bar in the central regions of NGC 4945, and to its interacting environment.

  15. ISM Parameters in the Normal Galaxy NGC 5713

    NASA Technical Reports Server (NTRS)

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

    1996-01-01

    We report ISO Long Wavelength Spectrometer (LWS) observations fo the Sbc(s) pec galaxy NGC 5713. We have obtained strong detections of the fine-structure forbidden transitions [C(sub ii)] 158(micro)m, [O(sub i)]63(micro)m, and [O(sub iii)] 88(micro)m, and significant upper limits for[N(sub ii)]122(micro)m, [O(sub iii)] 52(micro)m, and [N(sub iii)] 57(micro)m. We also detect the galaxy's dust continuum emission between 43 and 197 microns.

  16. NGC 5523: An isolated product of soft galaxy mergers?

    NASA Astrophysics Data System (ADS)

    Fulmer, Leah M.; Gallagher, John S.; Kotulla, Ralf

    2017-02-01

    Multi-band images of the very isolated spiral galaxy NGC 5523 show a number of unusual features consistent with NGC 5523 having experienced a significant merger. (1) Near-infrared images from the Spitzer Space Telescope (SST) and the WIYN 3.5-m telescope reveal a nucleated bulge-like structure embedded in a spiral disk; (2) the bulge is offset by 1.8 kpc from a brightness minimum at the center of the optically bright inner disk; (3) a tidal stream, possibly associated with an ongoing satellite interaction, extends from the nucleated bulge along the disk. We interpret these properties as the results of one or more non-disruptive mergers between NGC 5523 and companion galaxies or satellites, raising the possibility that some galaxies become isolated because they have merged with former companions. The reduced images (FITS files) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/598/A119

  17. NGC 4438: Ram pressure sweeping of a tidally disrupted galaxy

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    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.

  18. Smooth dark spiral arms in the flocculent galaxy NGC2841

    NASA Astrophysics Data System (ADS)

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

    1996-06-01

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

  19. Kinematics and stellar population of the lenticular galaxy NGC 4124

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

    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).

  20. Detailed surface photometry of the cD galaxies NGC 4839 and NGC 4874

    NASA Astrophysics Data System (ADS)

    Ali, Gamal B.; Shaban, Eman A.; Amin, Magdy Y.; Rassem, M. A.

    2014-08-01

    We present a detailed photometric study of the cD galaxies NGC 4839 and NGC 4874 based on the technique of surface photometry by fitting ellipses to the isophotes of the galaxies in the u, g, r, i, and z bands using Data Release 7 (DR7) of the Sloan Digital Sky Survey (SDSS). The motivation of this paper is to study the properties (e.g. break radius and surface brightness, color gradient, etc.) of the extended envelope of the two cD galaxies. The surface brightness profile in each band is obtained and fitted to the de Vaucouleurs r 1/4 model. A deviation of the observed profile brighter than the fitted r 1/4 model is noticed especially in the outer part of each galaxy. The profiles of ellipticity, position angle, B4 and shifts with respect to the center of each isophote are also obtained. The color index profiles, u-g, g-r, r-i, and i-z are also obtained and no significant color gradients are noticed except in the outer parts of the two galaxies. The integrated magnitude in each band and color indices are obtained and found to be in good agreement with the published ones.

  1. The interstellar halo of spiral galaxies: NGC 891

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

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

    SciTech Connect

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

    2012-01-15

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

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

    NASA Technical Reports Server (NTRS)

    Stanford, S. A.; Balcells, Marc

    1991-01-01

    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.

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

    SciTech Connect

    Geha, M.; Van der Marel, R. P.; Kalirai, J.; Guhathakurta, P.; Kirby, E. N.

    2010-03-01

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

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

    NASA Technical Reports Server (NTRS)

    Jackson, James M.; Marscher, Alan M.

    1996-01-01

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

  6. A Multiwavelength Study of the Starburst Galaxy NGC 7771

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

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

  7. A census of AGB stars in Local Group galaxies. II. NGC 185 and NGC 147

    NASA Astrophysics Data System (ADS)

    Nowotny, W.; Kerschbaum, F.; Olofsson, H.; Schwarz, H. E.

    2003-05-01

    We present results of our ongoing photometric survey of Local Group galaxies, using a four filter technique based on the method of Wing (\\cite{Wing71}) to identify and characterise the late-type stellar content. Two narrow band filters centred on spectral features of TiO and CN allow us to distinguish between AGB stars of different chemistries [M-type (O-rich) and C-type (C-rich)]. The major parts of two dwarf galaxies of the M 31 subgroup - NGC 185 and NGC 147 - were observed. From photometry in V and i we estimate the tip of the RGB, and derive distance moduli respectively. With additional photometric data in the narrow band filters TiO and CN we identify 154 new AGB carbon stars in NGC 185 and 146 in NGC 147. C/M ratios are derived, as well as mean absolute magnitudes , bolometric magnitudes M_bol, luminosity functions, and the spatial/radial distributions of the C stars in both galaxies. Based on observations made with the Nordic Optical Telescope operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. Table A.1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strabg.fr/cgi-bin/qcat?J/A+A/403/93

  8. The black hole mass and the stellar ring in NGC 3706

    SciTech Connect

    Gültekin, Kayhan; Richstone, Douglas O.; Gebhardt, Karl; Kormendy, John; Lauer, Tod R.; Bender, Ralf; Tremaine, Scott

    2014-02-01

    We determine the mass of the nuclear black hole (M) in NGC 3706, an early-type galaxy with a central surface brightness minimum arising from an apparent stellar ring, which is misaligned with respect to the galaxy's major axis at larger radii. We fit new HST/STIS and archival data with axisymmetric orbit models to determine M, mass-to-light ratio (Y {sub V}), and dark matter halo profile. The best-fit model parameters with 1σ uncertainties are M=(6.0{sub −0.9}{sup +0.7})×10{sup 8} M{sub ⊙} and Υ{sub V}=6.0±0.2 M{sub ⊙} L{sub ⊙,V}{sup −1} at an assumed distance of 46 Mpc. The models are inconsistent with no black hole at a significance of Δχ{sup 2} = 15.4 and require a dark matter halo to adequately fit the kinematic data, but the fits are consistent with a large range of plausible dark matter halo parameters. The ring is inconsistent with a population of co-rotating stars on circular orbits, which would produce a narrow line-of-sight velocity distribution (LOSVD). Instead, the ring's LOSVD has a small value of |V|/σ, the ratio of mean velocity to velocity dispersion. Based on the observed low |V|/σ, our orbit modeling, and a kinematic decomposition of the ring from the bulge, we conclude that the stellar ring contains stars that orbit in both directions. We consider potential origins for this unique feature, including multiple tidal disruptions of stellar clusters, a change in the gravitational potential from triaxial to axisymmetric, resonant capture and inclining of orbits by a binary black hole, and multiple mergers leading to gas being funneled to the center of the galaxy.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    Context. Previous studies have shown that the kinematics of the field elliptical galaxy NGC 7507 do not necessarily require dark matter. This is troubling because, in the context of ΛCDM cosmologies, all galaxies should have a large dark matter component. Aims: Our aims are to determine the rotation and velocity dispersion profile out to larger radii than do previous studies, and, therefore, more accurately estimate of the dark matter content of the galaxy. Methods: We use penalised pixel-fitting software to extract velocities and velocity dispersions from GMOS slit mask spectra. Using Jeans and MONDian modelling, we then produce models with the goal of fitting the velocity dispersion data. Results: NGC 7507 has a two-component stellar halo, with the outer halo counter rotating with respect to the inner halo, with a kinematic boundary at a radius of ~110'' (~12.4 kpc). The velocity dispersion profile exhibits an increase at ~70'' (~7.9 kpc), reminiscent of several other elliptical galaxies. Our best fit models are those under mild anisotropy, which include ~100 times less dark matter than predicted by ΛCDM, although mildly anisotropic models that are completely dark matter free fit the measured dynamics almost equally well. Our MONDian models, both isotropic and anisotropic, systematically fail to reproduce the measured velocity dispersions at almost all radii. Conclusions: The counter-rotating outer halo implies a merger remnant, as does the increase in velocity dispersion at ~70''. From simulations it seems plausible that the merger that caused the increase in velocity dispersion was a spiral-spiral merger. Our Jeans models are completely consistent with a no dark matter scenario, however, some dark matter can be accommodated, although at much lower concentrations than predicted by ΛCDM simulations. This indicates that NGC 7507 may be a dark matter free elliptical galaxy. Regardless of whether NGC 7507 is completely dark matter free or very dark matter poor

  10. A multi-wavelength view of the central kiloparsec region in the luminous infrared galaxy NGC 1614

    SciTech Connect

    Herrero-Illana, Rubén; Pérez-Torres, Miguel Á.; Alberdi, Antxon; Hernández-García, Lorena; Alonso-Herrero, Almudena; Colina, Luis; Efstathiou, Andreas; Miralles-Caballero, Daniel; Väisänen, Petri; Packham, Christopher C.; Rajpaul, Vinesh; Zijlstra, Albert A.

    2014-05-10

    The Luminous Infrared Galaxy NGC 1614 hosts a prominent circumnuclear ring of star formation. However, the nature of the dominant emitting mechanism in its central ∼100 pc is still under debate. We present sub-arcsecond angular resolution radio, mid-infrared, Paα, optical, and X-ray observations of NGC 1614, aimed at studying in detail both the circumnuclear ring and the nuclear region. The 8.4 GHz continuum emission traced by the Very Large Array and the Gemini/T-ReCS 8.7 μm emission, as well as the Paα line emission, show remarkable morphological similarities within the star-forming ring, suggesting that the underlying emission mechanisms are tightly related. We used a Hubble Space Telescope/NICMOS Paα map of similar resolution to our radio maps to disentangle the thermal free-free and non-thermal synchrotron radio emission, from which we obtained the intrinsic synchrotron power law for each individual region within the central kiloparsec of NGC 1614. The radio ring surrounds a relatively faint, steep-spectrum source at the very center of the galaxy, suggesting that the central source is not powered by an active galactic nucleus (AGN), but rather by a compact (r ≲ 90 pc) starburst (SB). Chandra X-ray data also show that the central kiloparsec region is dominated by SB activity, without requiring the existence of an AGN. We also used publicly available infrared data to model-fit the spectral energy distribution of both the SB ring and a putative AGN in NGC 1614. In summary, we conclude that there is no need to invoke an AGN to explain the observed bolometric properties of the galaxy.

  11. HUBBLE SPACE TELESCOPE Imaging of Globular Clusters in the Edge-on Spiral Galaxies NGC 4565 and NGC 5907

    NASA Astrophysics Data System (ADS)

    Kissler-Patig, Markus; Ashman, Keith M.; Zepf, Stephen E.; Freeman, Kenneth C.

    1999-07-01

    We present a study of the globular cluster systems of two edge-on spiral galaxies, NGC 4565 and NGC 5907, from WFPC2 images in the F450W and F814W filters. The globular cluster systems of both galaxies appear to be similar to the Galactic globular cluster system. In particular, we derive total numbers of globular clusters of N_GC(4565)=204+/-38^+87_-53 and N_GC(5907)=170+/-41^+47_-72 (where the first are statistical, the second potential systematic errors) for NGC 4565 and NGC 5907, respectively. This determination is based on a comparison with the Milky Way system, for which we adopt a total number of globular clusters of 180+/-20. The specific frequency of both galaxies is S_N~=0.6, indistinguishable from the value for the Milky Way. The similarity in the globular cluster systems of the two galaxies is noteworthy, since they have significantly different thick disks and bulge-to-disk ratios. This would suggest that these two components do not play a major role in the building up of a globular cluster system around late-type galaxies.

  12. Mid-infrared dust in two nearby radio galaxies, NGC 1316 (Fornax A) and NGC 612 (PKS 0131-36)

    NASA Astrophysics Data System (ADS)

    Duah Asabere, B.; Horellou, C.; Jarrett, T. H.; Winkler, H.

    2016-07-01

    Context. Most radio galaxies are hosted by giant gas-poor ellipticals, but some contain significant amounts of dust, which is likely to be of external origin. Aims: In order to characterize the mid-IR properties of two of the most nearby and brightest merger-remnant radio galaxies of the Southern hemisphere, NGC 1316 (Fornax A) and NGC 612 (PKS 0131-36), we used observations with the Wide-field Infrared Survey Explorer (WISE) at wavelengths of 3.4, 4.6, 12 and 22 μm and Spitzer mid-infrared spectra. Methods: By applying a resolution-enhancement technique, new WISE images were produced at angular resolutions ranging from 2.̋6 to 5.̋5. Global measurements were performed in the four WISE bands, and stellar masses and star-formation rates were estimated using published scaling relations. Two methods were used to uncover the distribution of dust, one relying on two-dimensional fits to the 3.4 μm images to model the starlight, and the other one using a simple scaling and subtraction of the 3.4 μm images to estimate the stellar continuum contribution to the emission in the 12 and 22 μm bands. Results: The two galaxies differ markedly in their mid-IR properties. The 3.4 μm brightness distribution can be well represented by the superposition of two Sérsic models in NGC 1316 and by a Sérsic model and an exponential disk in NGC 612. The WISE colors of NGC 1316 are typical of those of early-type galaxies; those of NGC 612 are in the range found for star-forming galaxies. From the 22 μm luminosity, we infer a star-formation rate of ~0.7 M⊙ yr-1 in NGC 1316 and ~7 M⊙ yr-1 in NGC 612. Spitzer spectroscopy shows that the 7.7-to-11.3 μm PAH line ratio is significantly lower in NGC 1316 than in NGC 612. The WISE images reveal resolved emission from dust in the central 1'-2' of the galaxies. In NGC 1316, the extra-nuclear emission coincides with two dusty regions NW and SE of the nucleus seen in extinction in optical images and where molecular gas is known to reside

  13. The Arecibo Environment Galaxy Survey: The NGC 2577/UGC 4375-galaxy pair

    NASA Astrophysics Data System (ADS)

    Iguina, Ashley Ann; Minchin, Robert F.

    2017-01-01

    We searched for and catalogued galaxy candidates in an area of 5 square degrees around the NGC 2577/UGC 4375-galaxy pair via the 21-cm emission of the neutral hydrogen gas emitted by the candidates' interstellar media. The data were taken as a part of the Arecibo Galaxy Environment Survey (AGES) and consist of a data cube with the dimensions right ascension, declination, and the recessional velocity of the 21-cm line. We used the FITS viewer FRELLED to assist in visually extracting sources. We have cross identified the galaxy candidates with optical counterparts via the NASA Extragalactic Database and data from the Sloan Digital Sky Survey. We made a total of 49 HI detections in the vicinity of the galaxy pair. We did not detect the S0 galaxy, NGC 2577, but we did detect the SB galaxy, UGC 4375, and four galaxies in the region around the galaxy pair at ~2000 km/s. We detected another overdensity at 4000 km/s. Additionally, an HI detection appears in our local neighborhood at 426 km/s. The Arecibo Observatory is operated by SRI International under a cooperative agreement with the National Science Foundation and in alliance with Ana G. Méndez-Universidad Metropolitana, and the Universities Space Research Association. The Arecibo Observatory REU program is funded under grant AST-1559849 to Universidad Metropolitana.

  14. CEPHEID VARIABLES IN THE MASER-HOST GALAXY NGC 4258

    SciTech Connect

    Hoffmann, Samantha L.; Macri, Lucas M.

    2015-06-15

    We present results of a ground-based survey for Cepheid variables in NGC 4258. This galaxy plays a key role in the Extragalactic Distance Scale due to its very precise and accurate distance determination via very long baseline interferometry observations of water masers. We imaged two fields within this galaxy using the Gemini North telescope and the Gemini Multi-Object Spectrograph, obtaining 16 epochs of data in the Sloan Digital Sky Survey gri bands over 4 yr. We carried out point-spread function photometry and detected 94 Cepheids with periods between 7 and 127 days, as well as an additional 215 variables which may be Cepheids or Population II pulsators. We used the Cepheid sample to test the absolute calibration of theoretical gri Period–Luminosity relations and found good agreement with the maser distance to this galaxy. The expected data products from the Large Synoptic Survey Telescope should enable Cepheid searches out to at least 10 Mpc.

  15. NGC 4388 - A Seyfert 2 galaxy in the Virgo cluster

    NASA Astrophysics Data System (ADS)

    Phillips, M. M.; Malin, D. F.

    1982-06-01

    Direct photographic data and preliminary spectroscopy of the spiral galaxy NGC 4388 are presented. The galaxy appears to be a barred spiral of morphological class SB(s)b pec and is almost certainly a member of the Virgo cluster. The nucleus was studied with a photon-counting image intensifier/reticon scanner and was found to emit a high-excitation, narrow emission-line spectrum of relatively low luminosity. Image-tube spectrograms and spectroscopy using an image photon-counting system revealed optical, X-ray, and radio nuclear properties consistent with a classical Seyfert 2 galaxy. The radial velocity of the peaks of the asymmetric nuclear emission lines is 55 km/s less than the H I 21 cm systemic velocity.

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

    SciTech Connect

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

    1988-07-01

    The catalog of isolated galaxy pairs prepared by Karachentsev has been culled for its E-E constituents, and the results are reported. Radial variations of rotation velocity and velocity dispersion are extracted from the spectroscopic data for each of the two galaxies of a given pair. Such observations are described for two Karachentsev pairs, Nos. 99 and 564. The observed disturbances in rotation velocity and luminosity distribution are discussed in terms of the gravitational interaction hypothesis. It is argued that observational evidence of tidal friction in action is evidenced by these findings. One of the highest rotation rates known for an E2 galaxy of average luminosity is found in NGC 1587, the brighter component of K99. Because this rotation is in the same sense as the binary orbital motion, the net angular momentum in this isolated binary system is large, challenging simple tidal torque theories to identify the source of the momentum. 62 references.

  17. Reverberation Mapping of the Seyfert 1 Galaxy NGC 7469

    NASA Astrophysics Data System (ADS)

    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

    A large reverberation-mapping study of the Seyfert 1 galaxy NGC 7469 has yielded emission-line lags for Hβ λ4861 and He II λ4686 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 Hβ measurement, NGC 7469 is no longer an outlier in the relationship between the size of the Hβ-emitting broad-line region and the luminosity of the active galactic nucleus. It was necessary to detrend the continuum and Hβ and He II λ4686 line light curves and those from archival UV data for different time-series analysis methods to yield consistent results.

  18. Reverberation mapping of the Seyfert 1 galaxy NGC 7469

    SciTech Connect

    Peterson, B. M.; Grier, C. J.; Pogge, R. W.; De Rosa, G.; Denney, K. D.; Martini, Paul; Zu, Y.; Kochanek, C. S.; Shappee, B.; Araya Salvo, C.; Beatty, T. G.; Bird, J. C.; Horne, Keith; Bentz, M. C.; Sergeev, S. G.; Borman, G. A.; Minezaki, T.; Siverd, R. J.; Bord, D. J.; and others

    2014-11-10

    A large reverberation-mapping study of the Seyfert 1 galaxy NGC 7469 has yielded emission-line lags for Hβ λ4861 and He II λ4686 and a central black hole mass measurement M {sub BH} ≈ 1 × 10{sup 7} M {sub ☉}, 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 Hβ measurement, NGC 7469 is no longer an outlier in the relationship between the size of the Hβ-emitting broad-line region and the luminosity of the active galactic nucleus. It was necessary to detrend the continuum and Hβ and He II λ4686 line light curves and those from archival UV data for different time-series analysis methods to yield consistent results.

  19. Observations of CO in the Magellanic irregular galaxy NGC 55

    NASA Technical Reports Server (NTRS)

    Heithausen, Andreas; Dettmar, Ralf-Juergen

    1990-01-01

    The content of molecular gas in galaxies, mainly H2, is one of the key observations necessary for the understanding of star formation processes and history. As the CO molecule is the most widely distributed molecule after H2 and has easily observable mm lines, it is used as a tracer for the molecular gas. CO was detected towards the direction where the H alpha and 6 cm radio continuum emission is strongest (Hummel et al. 1986). Here, researchers present the Gaussian line parameters in tabular form. The distribution of CO corresponds well with the intense HI cloud near the bar of NGC 55. The extent of the CO cloud is about 975 pc perpendicular to the major axis. As the radio continuum and the H alpha emission also peaks in this region, it is most probably associated with the star forming region in NGC 55. Assuming that the molecular gas is in virial equilibrium, researchers derive a mass of about 8 times 10(exp 7) solar magnitude. The molecular mass found indicates that the conversion factor for the molecular mass in Irr galaxies as inferred from CO line emission is indeed higher by up to a factor of 20 compared to the canonical value for the Galaxy.

  20. Observations of CO in the Magellanic irregular galaxy NGC 55

    NASA Astrophysics Data System (ADS)

    Heithausen, Andreas; Dettmar, Ralf-Juergen

    1990-07-01

    The content of molecular gas in galaxies, mainly H2, is one of the key observations necessary for the understanding of star formation processes and history. As the CO molecule is the most widely distributed molecule after H2 and has easily observable mm lines, it is used as a tracer for the molecular gas. CO was detected towards the direction where the H alpha and 6 cm radio continuum emission is strongest (Hummel et al. 1986). Here, researchers present the Gaussian line parameters in tabular form. The distribution of CO corresponds well with the intense HI cloud near the bar of NGC 55. The extent of the CO cloud is about 975 pc perpendicular to the major axis. As the radio continuum and the H alpha emission also peaks in this region, it is most probably associated with the star forming region in NGC 55. Assuming that the molecular gas is in virial equilibrium, researchers derive a mass of about 8 times 107 solar magnitude. The molecular mass found indicates that the conversion factor for the molecular mass in Irr galaxies as inferred from CO line emission is indeed higher by up to a factor of 20 compared to the canonical value for the Galaxy.

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

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

    SciTech Connect

    Sheen, Yun-Kyeong; Jeong, Hyunjin; Lee, Young-Wook; 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.; Martin, D. Christopher; Morrissey, Patrick; Neff, Susan G.; Schiminovich, David; Yi, Sukyoung K.

    2009-12-15

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

  3. Nuclear Rings in Galaxies - A Kinematic Perspective

    NASA Technical Reports Server (NTRS)

    Mazzuca, Lisa M.; Swaters, Robert A.; Knapen, Johan H.; Veilleux, Sylvain

    2011-01-01

    We combine DensePak integral field unit and TAURUS Fabry-Perot observations of 13 nuclear rings to show an interconnection between the kinematic properties of the rings and their resonant origin. The nuclear rings have regular and symmetric kinematics, and lack strong non-circular motions. This symmetry, coupled with a direct relationship between the position angles and ellipticities of the rings and those of their host galaxies, indicate the rings are in the same plane as the disc and are circular. From the rotation curves derived, we have estimated the compactness (v(sup 2)/r) up to the turnover radius, which is where the nuclear rings reside. We find that there is evidence of a correlation between compactness and ring width and size. Radially wide rings are less compact, and thus have lower mass concentration. The compactness increases as the ring width decreases. We also find that the nuclear ring size is dependent on the bar strength, with weaker bars allowing rings of any size to form.

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

    NASA Astrophysics Data System (ADS)

    2004-11-01

    Star formation is one of the most basic phenomena in the Universe. Inside stars, primordial material from the Big Bang is processed into heavier elements that we observe today. In the extended atmospheres of certain types of stars, these elements combine into more complex systems like molecules and dust grains, the building blocks for new planets, stars and galaxies and, ultimately, for life. Violent star-forming processes let otherwise dull galaxies shine in the darkness of deep space and make them visible to us over large distances. Star formation begins with the collapse of the densest parts of interstellar clouds, regions that are characterized by comparatively high concentration of molecular gas and dust like the Orion complex (ESO PR Photo 20/04) and the Galactic Centre region (ESO Press Release 26/03). Since this gas and dust are products of earlier star formation, there must have been an early epoch when they did not yet exist. But how did the first stars then form? Indeed, to describe and explain "primordial star formation" - without molecular gas and dust - is a major challenge in modern Astrophysics. A particular class of relatively small galaxies, known as "Blue Dwarf Galaxies", possibly provide nearby and contemporary examples of what may have occurred in the early Universe during the formation of the first stars. These galaxies are poor in dust and heavier elements. They contain interstellar clouds which, in some cases, appear to be quite similar to those primordial clouds from which the first stars were formed. And yet, despite the relative lack of the dust and molecular gas that form the basic ingredients for star formation as we know it from the Milky Way, those Blue Dwarf Galaxies sometimes harbour very active star-forming regions. Thus, by studying those areas, we may hope to better understand the star-forming processes in the early Universe. Very active star formation in NGC 5253 NGC 5253 is one of the nearest of the known Blue Dwarf Galaxies

  5. The ULX Population in the Starburst Galaxy NGC 253

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  6. Analysis of the structure of disk galaxies in the NGC 2300 group

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    Data from the 6-m telescope of the Special Astrophysical Observatory obtained using the SCORPIO instrument in imaging mode are used to study member galaxies of the NGC 2300 group. Surface photometry has been carried out for the five largest galaxies in the group, whose isophotal parameters and the parameters of their large-scale structural components (disks and bulges) have been determined. The morphological type of the central galaxy in the group has been refined, and shown to be elliptical. Studies of structural features in non-central disk galaxies have revealed an enhanced percent of bars: bars were found in all disk galaxies of this group, with all of these being compact structures. The similarity of the structural features of the disks of the group galaxies suggests that these disksmay be being restructured in the process of the current merger of the two X-ray subgroups comprising NGC 2300: the group NGC 2300 itself and the group NGC 2276.

  7. Peculiarities in the optical variability of the galaxy NGC 4151

    SciTech Connect

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

    1981-11-01

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

  8. The circumnuclear environment of the Seyfert 1 galaxy NGC 3516

    SciTech Connect

    Pogge, R.W.; McDonald Observatory, Austin, TX )

    1989-07-01

    Results of an emission-line imaging and spectrophotometric study of the ionized gas in the circumnuclear regions of the Seyfert 1 galaxy NGC 3516 are reported. The morphology and ionization of the gas are consistent with excitation by the power law continuum from the active nucleus. The optical emission-line gas is well aligned with the extended 6 cm radio-continuum emission. The ionization, structure, and published kinematical data are strongly suggestive of an outflow origin for the circumnuclear gas, although important details are missing to firmly establish outflow as the origin of all of the ionized gas. 31 refs.

  9. Exploring the mass assembly of the early-type disc galaxy NGC 3115 with MUSE

    NASA Astrophysics Data System (ADS)

    Guérou, A.; Emsellem, E.; Krajnović, D.; McDermid, R. M.; Contini, T.; Weilbacher, P. M.

    2016-07-01

    We present MUSE integral field spectroscopic data of the S0 galaxy NGC 3115 obtained during the instrument commissioning at the ESO Very Large Telescope (VLT). We analyse the galaxy stellar kinematics and stellar populations and present two-dimensional maps of their associated quantities. We thus illustrate the capacity of MUSE to map extra-galactic sources to large radii in an efficient manner, i.e. ~4 Re, and provide relevant constraints on its mass assembly. We probe the well-known set of substructures of NGC 3115 (nuclear disc, stellar rings, outer kpc-scale stellar disc, and spheroid) and show their individual associated signatures in the MUSE stellar kinematics and stellar populations maps. In particular, we confirm that NGC 3115 has a thin fast-rotating stellar disc embedded in a fast-rotating spheroid, and that these two structures show clear differences in their stellar age and metallicity properties. We emphasise an observed correlation between the radial stellar velocity, V, and the Gauss-Hermite moment, h3, which creates a butterfly shape in the central 15'' of the h3 map. We further detect the previously reported weak spiral- and ring-like structures, and find evidence that these features can be associated with regions of younger mean stellar ages. We provide tentative evidence for the presence of a bar, although the V-h3 correlation can be reproduced by a simple axisymmetric dynamical model. Finally, we present a reconstruction of the two-dimensional star formation history of NGC 3115 and find that most of its current stellar mass was formed at early epochs (>12 Gyr ago), while star formation continued in the outer (kpc-scale) stellar disc until recently. Since z ~2 and within ~4 Re, we suggest that NGC 3115 has been mainly shaped by secular processes. The images of the derived parameters in FITS format and the reduced datacube are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc

  10. The flaring Hi disk of the nearby spiral galaxy NGC 2683

    NASA Astrophysics Data System (ADS)

    Vollmer, B.; Nehlig, F.; Ibata, R.

    2016-02-01

    New deep VLA D array Hi observations of the highly inclined nearby spiral galaxy NGC 2683 are presented. Archival C array data were processed and added to the new observations. To investigate the 3D structure of the atomic gas disk, we made different 3D models for which we produced model Hi data cubes. The main ingredients of our best-fit model are (i) a thin disk inclined by 80°; (ii) a crude approximation of a spiral and/or bar structure by an elliptical surface density distribution of the gas disk; (iii) a slight warp in inclination between 10 kpc ≤ R ≤ 20 kpc (decreasing by 10°); (iv) an exponential flare that rises from 0.5 kpc at R = 9 kpc to 4 kpc at R = 15 kpc, stays constant until R = 22 kpc, and decreases its height for R> 22 kpc; and (v) a low surface-density gas ring with a vertical offset of 1.3 kpc. The slope of NGC 2683's flare is comparable, but somewhat steeper than those of other spiral galaxies. NGC 2683's maximum height of the flare is also comparable to those of other galaxies. On the other hand, a saturation of the flare is only observed in NGC 2683. Based on the comparison between the high resolution model and observations, we exclude the existence of an extended atomic gas halo around the optical and thin gas disk. Under the assumption of vertical hydrostatic equilibrium we derive the vertical velocity dispersion of the gas. The high turbulent velocity dispersion in the flare can be explained by energy injection by (i) supernovae; (ii) magneto-rotational instabilities; (iii) interstellar medium stirring by dark matter substructure; or (iv) external gas accretion. The existence of the complex large-scale warping and asymmetries favors external gas accretion as one of the major energy sources that drives turbulence in the outer gas disk. We propose a scenario where this external accretion leads to turbulent adiabatic compression that enhances the turbulent velocity dispersion and might quench star formation in the outer gas disk of NGC

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

    SciTech Connect

    Saha, A.; Hoessel, J.G.; Mossman, A.E. Space Telescope Science Institute, Baltimore, MD Washburn Observatory, Madison, WI )

    1990-07-01

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

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

    NASA Technical Reports Server (NTRS)

    2000-01-01

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

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

    SciTech Connect

    Tang, Qing-Wen; Wang, Xiang-Yu; Thomas Tam, Pak-Hin E-mail: phtam@phys.nthu.edu.tw

    2014-10-10

    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 ∼5.5σ 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.

  14. AKARI observations of dust processing in merger galaxies: NGC2782 and NGC7727

    NASA Astrophysics Data System (ADS)

    Onaka, Takashi; Nakamura, Tomohiko; Sakon, Itsuki; Ohsawa, Ryou; Mori, Tamami; Wu, Ronin; Kaneda, Hidehiro

    2015-08-01

    Dust grains are the major reservoir of heavy elements and play significant roles in the thermal balance and chemistry in the interstellar medium. Where dust grains are formed and how they evolve in the ISM are one of the key issues for the understanding of the material evolution in the Universe. Although theoretical studies have been made, very little is so far known observationally about the lifecycle of dust grains in the ISM and that associated with Galactic scale events. The lifecycle of very small carbonaceous grains that contain polycyclic aromatic hydrocarbons (PAHs) or PAH-like atomic groups are of particular interest because they emit distinct band emission in the near- to mid-infrared region and they are thought to be most vulnerable to environmental conditions. PAHs may be formed in carbon-rich stars, while recent AKARI observations suggest that they may be formed by fragmentation of large carbonaceous grains in shocks in a supernova remnant or a galactic wind (Onaka et al. 2010, A&A, 514, 15; Seok et al. 2012, ApJ, 744, 160).Here we report results of AKARI observations of two mergers. NGC2782 (Arp 215) and NGC7727 (Arp 222). NGC2782 is a merger of 200Myr old. It shows a very long western tail of HI gas by a tidal interaction and the eastern tail that consists mainly of stellar components without an appreciable amount of gas and is thought to be a relic of the colliding low-mass galaxy whose gas component has been stripped off Smith 1994, AJ, 107, 1695. We found significant emission at the 7 μm band of the IRC onboard AKARI, which must come from PAH 6.2 and 7.7 μm bands, in the eastern tail. Based on dust model fitting, we found a low abundance of ~10nm size dust despite of the presence of PAHs, suggesting that PAHs may be formed from fragmentation of ~10nm carbonaceous dust grains. NGC7727 is a 1.2Gyr old merger and shows a SED similar to the NGC2782 tail in the northern tail of the merger event product, suggesting also the formation of PAHs from

  15. ISOCAM view of the starburst galaxies M 82, NGC 253 and NGC 1808

    NASA Astrophysics Data System (ADS)

    Förster Schreiber, N. M.; Sauvage, M.; Charmandaris, V.; Laurent, O.; Gallais, P.; Mirabel, I. F.; Vigroux, L.

    2003-03-01

    We present results of mid-infrared lambda = 5.0-16.5 μm spectrophotometric imaging of the starburst galaxies M 82, NGC 253, and NGC 1808 from the ISOCAM instrument on board the Infrared Space Observatory. The mid-infrared spectra of the three galaxies are very similar in terms of features present. The lambda >~ 11 μm continuum attributed to very small dust grains (VSGs) exhibits a large spread in intensity relative to the short-wavelength emission. We find that the 15 mu m dust continuum flux density correlates well with the fine-structure [Ar Ii] 6.99 mu m line flux and thus provides a good quantitative indicator of the level of star formation activity. By contrast, the lambda = 5-11 μm region dominated by emission from polycyclic aromatic hydrocarbons (PAHs) has a nearly invariant shape. Variations in the relative intensities of the PAH features are nevertheless observed, at the 20%-100% level. We illustrate extinction effects on the shape of the mid-infrared spectrum of obscured starbursts, emphasizing the differences depending on the applicable extinction law and the consequences for the interpretation of PAH ratios and extinction estimates. The relative spatial distributions of the PAH, VSG, and [Ar Ii] 6.99 mu m emission between the three galaxies exhibit remarkable differences. The la 1 kpc size of the mid-infrared source is much smaller than the optical extent of our sample galaxies and 70%-100% of the IRAS 12 mu m flux is recovered within the ISOCAM <= 1.5 arcmin2 field of view, indicating that the nuclear starburst dominates the total mid-infrared emission while diffuse light from quiescent disk star formation contributes little. Based on observations with ISO, an ESA project with instruments funded by ESA member states (especially the PI countries: France, Germany, The Netherlands, and the UK), and with participation of ISAS and NASA.

  16. Near-Infrared Photometric Properties of Red Supergiant Stars in Neaby Galaxies: NGC 4214, NGC 4736 and M51

    NASA Astrophysics Data System (ADS)

    Jung, DooSeok; Chun, Sang-Hyun; Choudhury, Samyaday; Sohn, Young-Jong

    2017-01-01

    Red supergiant stars (RSGs) are post-main sequence phase of massive stars which can be easily resolved in nearby galaxies due to their bright luminosity as compared to the low-mass stars. RSGs are cool, and hence have a dominant light output at near-infrared (NIR) wavelengths. To investigate the photometric properties of RSGs in a few nearby galaxies, we observed NGC 4214, NGC 4736 and M51 by using the WFCAM detector mounted on the UKIRT telescope at Hawaii, and obtained the NIR (JHK bands) imaging data. After carrying out the photometry, the age ranges of RSGs in each galaxy were estimated by over-plotting PARSEC isochrones to the (J-K, K) colour-magnitude diagram: log(tyr) = 6.9 - 7.3 for NGC 4214; log(tyr) = 7.0 - 8.0 for NGC 4736; and log(tyr) = 6.7 - 6.9 for M51. The effective temperatures and luminosities of RSGs were calculated using MARCS synthetic fluxes, and these results were used to compare the properties of RSGs in Hertzsprung-Russell (H-R) diagram of dominant H II regions within each galaxy, over-plotted with PARSEC evolutionary tracks. The RSGs in NGC 4214 and NGC 4736 are found to have a mass of 9 M⊙ - 30 M⊙, and the maximum luminosities found to be almost constant with log(L/L⊙) = 5.6 - 5.7. However, the location of the RSGs in the H-R diagram are not consistent with the evolutionary tracks for M51.(Key Words: stars: massive - supergiants - galaxies: photometry - galaxies: stellar content - infrared: stars)

  17. Gas Dynamics and Outflow in the Barred Starburst Galaxy NGC 1808 Revealed with ALMA

    NASA Astrophysics Data System (ADS)

    Salak, Dragan; Nakai, Naomasa; Hatakeyama, Takuya; Miyamoto, Yusuke

    2016-05-01

    NGC 1808 is a nearby barred starburst galaxy with an outflow from the nuclear region. To study the inflow and outflow processes related to star formation and dynamical evolution of the galaxy, we have carried out 12CO (J=1-0) mapping observations of the central r ˜ 4 kpc of NGC 1808 using the Atacama Large Millimeter/submillimeter Array. Four distinct components of molecular gas are revealed at high spatial resolution of 2″ (˜100 pc): (1) a compact (r < 200 pc) circumnuclear disk (CND), (2) r ˜ 500 pc ring, (3) gas-rich galactic bar, and (4) spiral arms. Basic geometric and kinematic parameters are derived for the central 1 kpc region using tilted-ring modeling. The derived rotation curve reveals multiple mass components that include (1) a stellar bulge, (2) a nuclear bar and molecular CND, and (3) an unresolved massive (˜107 M ⊙) core. Two systemic velocities, 998 km s-1 for the CND and 964 km s-1 for the 500 pc ring, are revealed, indicating a kinematic offset. The pattern speed of the primary bar, derived by using a cloud-orbit model, is 56 ± 11 km s-1 kpc-1. Noncircular motions are detected associated with a nuclear spiral pattern and outflow in the central 1 kpc region. The ratio of the mass outflow rate to the star formation rate is {\\dot{M}}{out}/{SFR}˜ 0.2 in the case of optically thin CO (1-0) emission in the outflow, suggesting low efficiency of star formation quenching.

  18. AN IONIZATION CONE IN THE DWARF STARBURST GALAXY NGC 5253

    SciTech Connect

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

    2011-11-01

    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.

  19. Globular Cluster Systems in Brightest Cluster Galaxies. II. NGC 6166

    NASA Astrophysics Data System (ADS)

    Harris, William E.; Blakeslee, John P.; Whitmore, Bradley C.; Gnedin, Oleg Y.; Geisler, Douglas; Rothberg, Barry

    2016-01-01

    We present new deep photometry of the globular cluster system (GCS) around NGC 6166, the central supergiant galaxy in Abell 2199. Hubble Space Telescope data from the Advanced Camera for Surveys and WFC3 cameras in F475W and F814W are used to determine the spatial distribution of the GCS, its metallicity distribution function (MDF), and the dependence of the MDF on galactocentric radius and on GC luminosity. The MDF is extremely broad, with the classic red and blue subpopulations heavily overlapped, but a double-Gaussian model can still formally match the MDF closely. The spatial distribution follows a Sérsic-like profile detectably to a projected radius of at least Rgc = 250 kpc. To that radius, the total number of clusters in the system is NGC = 39000 ± 2000, the global specific frequency is SN = 11.2 ± 0.6, and 57% of the total are blue, metal-poor clusters. The GCS may fade smoothly into the intracluster medium (ICM) of A2199; we see no clear transition from the core of the galaxy to the cD halo or the ICM. The radial distribution, projected ellipticity, and mean metallicity of the red (metal-richer) clusters match the halo light extremely well for {R}{gc}≳ 15 {{kpc}}, both of them varying as {σ }{MRGC}∼ {σ }{light}∼ {R}-1.8. By comparison, the blue (metal-poor) GC component has a much shallower falloff {σ }{MPGC}∼ {R}-1.0 and a more nearly spherical distribution. This strong difference in their density distributions produces a net metallicity gradient in the GCS as a whole that is primarily generated by the population gradient. With NGC 6166 we appear to be penetrating into a regime of high enough galaxy mass and rich enough environment that the bimodal two-phase description of GC formation is no longer as clear or effective as it has been in smaller galaxies.

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

    SciTech Connect

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

    2010-11-01

    We present a detailed investigation of the morphological distribution and level of star formation and dust obscuration in the nearby tidally distorted galaxy NGC 2442. Spitzer images in the IR at 3.6, 4.5, 5.8, 8.0, and 24 {mu}m and GALEX images at 1500 A and 2300 A allow us to resolve the galaxy on scales between {approx}240 and 600 pc. We supplement these with archival data in the B, J, H, and K bands. We use the 8 {mu}m, 24 {mu}m, and FUV (1500 A) emission to study the star formation rate (SFR). We find that, globally, these tracers of star formation give a range of results of {approx}6-11 M{sub sun} yr{sup -1}, with the dust-corrected FUV giving the highest value of SFR. We can reconcile the UV- and IR-based estimates by adopting a steeper UV extinction curve that lies in between the starburst (Calzetti) and Small Magellanic Cloud extinction curves. However, the regions of the highest SFR intensity along the spiral arms are consistent with a starburst-like extinction. Overall, the level of star formation we find is higher than previously published for this galaxy, by about a factor of 2, which, contrary to previous conclusions, implies that the interaction that caused the distorted morphology of NGC 2442 likely also triggered increased levels of star formation activity. We also find marked asymmetry in that the north spiral arm has a noticeably higher SFR than the southern arm. The tip of the southern spiral arm shows a likely tidally distorted peculiar morphology. It is UV bright and shows unusual IRAC colors, consistent with other published tidal features IRAC data. Outside of the spiral arms, we discover what appears to be a superbubble, {approx}1.7 kpc across, which is seen most clearly in the IRAC images. Significant H{alpha}, UV, and IR emission in the area also suggest vigorous ongoing star formation. A known, recent supernova (SN 1999ga) is located at the edge of this superbubble. Although speculative at this stage, this area suggests a large star

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  2. The complex nature of the Seyfert galaxy NGC 7592

    NASA Technical Reports Server (NTRS)

    Rafanelli, Piero; Marziani, Paolo

    1990-01-01

    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

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

    SciTech Connect

    Lee, Joon Hyeop; Kim, Sang Chul; Ree, Chang Hee; Kim, Minjin; Jeong, Hyunjin; Lee, Jong Chul; Kyeong, Jaemann E-mail: sckim@kasi.re.kr E-mail: mkim@kasi.re.kr E-mail: jclee@kasi.re.kr

    2012-08-01

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

  4. 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)

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

    1985-01-01

    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.

  5. 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

    SciTech Connect

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

    1985-04-01

    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. 63 references.

  6. ROSAT PSPC observations of the early-type galaxies NGC 507 and NGC 499: Central cooling and mass determination

    NASA Technical Reports Server (NTRS)

    Kim, Dong-Woo; Fabbiano, G.

    1995-01-01

    We present the results of a deep observation of NGC 507 and NGC 499 with the ROSAT Position Sensitive Proportional Counter (PSPC). The X-ray emission of NGC 507 is extended at least out to 1000 sec (458 kpc at a distance of 94.5 Mpc). The radial profile of X-ray surface brightness goes as Sigma(sub x) is approximately r(exp -1.8) outside the core region. The radial profile is a function of energy such that the softer X-rays have a smaller core radius and a flatter slope. Spectral analysis reveals that the emission temperature, with an average of 1 keV, peaks at an intermediate radius of 2-3 min and falls toward the center (possibly decreases outward as well). The absorption column density is consistent with the Galactic line-of-sight value. The X-ray emission of NGC 499 is extended to 300 sec and suggests a similarly cooler core. The cooler cores of NGC 507 and NGC 499 are strong evidence of the presence of cooling flows in these galaxies. Assuming hydrostatic equilibrium outside the cooling radius, the estimated mass-to-light ratio of NGC 507 is 97 +/- 16 within 458 kpc, indicative of the presence of a heavy halo. Similarly, the mass-to-light ratio of NGC 499 is 89 +/- 14 within 137 kpc. Near the edge of the X-ray-emitting region of NGC 507 we detect 19 soft, unresolved sources. These sources do not have optical counterparts and are significantly in excess of the expected number of background serendipitous sources. We speculate that they may represent cooling clumps in the halo of NGC 507. If there are many undetected cooling clumps distributed at large radii, then the radial profile of the X-ray surface brightness does not directly reflect the potential, adding uncertainty to the measurement of the binding mass; the gas mass could also be overestimated.

  7. NGC 5044-N50: a link between blue compact galaxies and dwarf ellipticals

    NASA Astrophysics Data System (ADS)

    Cellone, Sergio A.; Buzzoni, Alberto

    We present new optical observations of the dwarf galaxy N50 in the NGC 5044 Group, showing that this object is probably at an intermediate BCD→dE evolutionary stage, after a realtively recent burst of star formation.

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

    SciTech Connect

    Momose, Rieko; Okumura, Sachiko K.; Sawada, Tsuyoshi; Koda, Jin E-mail: sokumura@nro.nao.ac.j E-mail: Jin.Koda@stonybrook.ed

    2010-09-20

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

  9. Vertical motions in the gaseous disk of the spiral galaxy NGC 3631

    NASA Astrophysics Data System (ADS)

    Fridman, A. M.; Koruzhii, O. V.; Zasov, A. V.; Sil'chenko, O. K.; Moiseev, A. V.; Burlak, A. N.; Afanas'ev, V. L.; Dodonov, S. N.; Knapen, J.

    1998-11-01

    The velocity field of the nearly face-on galaxy NGC 3631 is derived from observations in the Hα line on the 6-m telescope of the Special Astrophysical Observatory. These optical data are compared with radio observations of this galaxy (Knapen 1997). It is argued that the two-armed spiral structure of NGC 3631 has a wave nature, and that the observed vertical gas motions represent motions in a spiral density wave.

  10. The VIRUS-P Exploration of Nearby Galaxies (VENGA): Radial Gas Inflow and Shock Excitation in NGC 1042

    NASA Astrophysics Data System (ADS)

    Luo, Rongxin; Hao, Lei; Blanc, Guillermo A.; Jogee, Shardha; van den Bosch, Remco C. E.; Weinzirl, Tim

    2016-06-01

    NGC 1042 is a late-type bulgeless disk galaxy that hosts low-luminosity active galactic nuclei (AGNs) coincident with a massive nuclear star cluster. In this paper, we present the integral field spectroscopy studies of this galaxy, based on the data obtained with the Mitchell spectrograph on the 2.7 m Harlan J. Smith telescope. In the central 100-300 pc region of NGC 1042, we find a circumnuclear ring structure of gas with enhanced ionization, which we suggest is mainly induced by shocks. Combining this with the harmonic decomposition analysis of the velocity field of the ionized gas, we propose that the shocked gas is the result of gas inflow driven by the inner spiral arms. The inflow velocity is ˜ 32+/- 10 {km} {{{s}}}-1, and the estimated mass-inflow rate is ˜ 1.1+/- 0.3× {10}-3 {M}⊙ {{yr}}-1. The mass-inflow rate is about one hundred times the black hole’s mass-accretion rate (˜ 1.4× {10}-5 {M}⊙ {{yr}}-1) and slightly larger than the star-formation rate in the nuclear star cluster (7.94× {10}-4 {M}⊙ {{yr}}-1), implying that the inflow material is enough to feed both the AGN activity and star formation in the nuclear star cluster. Our study highlights that secular evolution can be important in late-type unbarred galaxies like NGC 1042.

  11. Distribution and motions of H I and H_2_ in the peculiar spiral galaxy NGC 3310.

    NASA Astrophysics Data System (ADS)

    Mulder, P. S.; van Driel, W.; Braine, J.

    1995-08-01

    The peculiar Sbc-type starburst galaxy NGC 3310 was mapped in the 21 cm H i line at Westerbork with an angular resolution of 12.2"x15.1" (αxδ) and a velocity resolution of 33km/s. The galaxy was also partially mapped in the CO(1-0) and (2-1) lines at IRAM with resolutions of ~23" and ~12", respectively. In the H i line, an extension of the optical jet-like feature in the Northwestern outer parts (the "arrow") is observed, extending outward to ~6.5' (38kpc) from the centre in data degraded to a resolution of 60". A region of H I emission is found some 9' to the South of NGC 3310 at radial velocities around 1040km/s, i.e. just above systemic, which may be connected to the "main body" H I by a weak bridge. At higher resolutions, the H I shows a central "hole" and two ridges partially coincident with the inner arms seen in Hα and continuing outwards as an extension of these, bending strongly just beyond their optical extent. The central hole is centered on the Southeastern side of the optical inner ring, not on the optical nucleus. The Northern ridge seems to connect its Hα counterpart in the inner regions to the "arrow" in the outer parts. Going from the optical disc to the outer regions, radial velocities measured in the H I gas generally change gradually, with the notable exception of the region of the optical "arrow". The receding half of the galaxy shows rather normal kinematics, as do the inner ~70" of radius of the half with velocities below systemic. Severely disturbed H I kinematics are found in the approaching half beyond that radius, which corresponds to the domain of the optical "bow and arrow" feature. Fits of a circular rotation model to the apparently undisturbed parts of the observed H I velocity field yield a kinematic inclination of 52deg+/-2deg and major axis position angle of 167deg+/-1deg. Subtraction of a model velocity field based on these results from that observed in H I confirms that the gas in the Northwestern (disturbed) half of the

  12. IUE and Einstein observations of the LINER galaxy NGC 4579

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    2002-01-01

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

  14. Line asymmetry in the Seyfert Galaxy NGC 3783

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

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

    SciTech Connect

    Saha, A.; Hoessel, J.G. Space Telescope Science Institute, Baltimore, MD Washburn Observatory, Madison, WI )

    1990-01-01

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

  16. Discovery of a deep Seyfert-2 galaxy at z = 0.222 behind NGC 300

    NASA Astrophysics Data System (ADS)

    Combi, J. A.; García, F.; Rodríguez, M. J.; Gamen, R.; Cellone, S. A.

    2016-08-01

    We report on the unveiling of the nature of the unidentified X-ray source 3XMM J005450.3-373849 as a Seyfert-2 galaxy located behind the spiral galaxy NGC 300 using Hubble Space Telescope data, new spectroscopic Gemini observations and available XMM-Newton and Chandra data. We show that the X-ray source is positionally coincident with an extended optical source, composed of a marginally resolved nucleus/bulge, surrounded by an elliptical disc-like feature and two symmetrical outer rings. The optical spectrum is typical of a Seyfert-2 galaxy redshifted to z = 0.222 ± 0.001, which confirms that the source is not physically related to NGC 300. At this redshift the source would be located at 909 ± 4 Mpc (comoving distance in the standard model). The X-ray spectra of the source are well fitted by an absorbed power-law model. By tying NH between the six available spectra, we found a variable index Γ running from ˜2 in 2000-2001 to 1.4-1.6 in the 2005-2014 period. Alternatively, by tying Γ, we found variable absorption columns of NH ˜ 0.34 × 10-22 cm-2 in 2000-2001, and 0.54-0.75 × 10-22 cm-2 in the 2005-2014 period. Although we cannot distinguish between a spectral or absorption origin, from the derived unabsorbed X-ray fluxes, we are able to assure the presence of long-term X-ray variability. Furthermore, the unabsorbed X-ray luminosities of 0.8-2 × 1043 erg s-1 derived in the X-ray band are in agreement with a weakly obscured Seyfert-2 AGN at z ≈ 0.22.

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

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

    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.

  18. How Does Dense Molecular Gas Contribute to Star Formation in the Starburst Galaxy NGC 2146?

    NASA Astrophysics Data System (ADS)

    Wofford, Alia

    2017-01-01

    The starburst galaxy NGC 2146 is believed to have been formed approximately 800 Myr ago, when two galaxies collided with each other possibly leading to a burst of star formation. NGC 2146 is known as a starburst galaxy for the high frequency of star formation going on in its molecular clouds. These clouds serve as nurseries for star formation to occur. Hydrogen Cyanide (HCN) and Carbon monoxide (CO) are molecules found in molecular gas clouds. HCN molecules are tracers for high density star forming gas. Whereas, CO molecules are tracers for low density star forming gas. In this project, we are observing these two molecules and their proximity to where the stars are forming in the galaxy to determine if the star formation is occurring in the same area as the high and low density molecular gas areas in starburst galaxy NGC 2146.

  19. Statistical Correlations Between Near-Infrared Luminosities and Ring Sizes in Field Ringed Galaxies

    NASA Astrophysics Data System (ADS)

    Wu, Wentao

    2008-01-01

    Statistically complete samples of inner-pseudo-, inner-, and outer-ringed galaxies can be extracted from the Catalog of Southern Ringed Galaxies. Redshifts and near-infrared (NIR) photometric data are available for the samples, allowing the derivation of the statistical correlations between the total NIR luminosities (L NIR) and the projected ring major axes in the physical scale (D) for these galaxies. For any of the three types of rings, the correlations are approximately L NIR vprop D 1.2 among the early-type ringed galaxies (the most commonly observed ringed galaxies). The correlations among late-type ringed galaxies appear significantly different. The results contradict the previous suggestion by Kormendy (1979, ApJ, 227, 714), who gave LB vprop D 2 (LB : B-band galaxy luminosity). The relations can be used in future to test theoretical simulations of dynamical structures of ringed galaxies as well as those of ring formation under the framework of cosmological models. Currently the results indicate at most small differences in the relative contributions of disk components to total galaxy masses and in the initial disk velocity dispersions between commonly observed ringed galaxies of similar type. The correlations also suggest a new approach to effectively use ring sizes as tertiary cosmological distance indicators, to help enhance the reliability of the measurement of the Hubble Constant.

  20. VIBRATIONALLY EXCITED HCN IN THE LUMINOUS INFRARED GALAXY NGC 4418

    SciTech Connect

    Sakamoto, Kazushi; Aalto, Susanne; Evans, Aaron S.; Wiedner, Martina C.; Wilner, David J.

    2010-12-20

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

  1. ALMA CO Observations of Shocks and Star Formation in the Interacting Galaxies IC 2163 and NGC 2207

    NASA Astrophysics Data System (ADS)

    Elmegreen, Debra M.; Elmegreen, Bruce; Kaufman, Michele; Brinks, Elias; Struck, Curtis; Bournaud, Frederic; Sheth, Kartik; Juneau, Stephanie

    2017-01-01

    The spiral galaxies IC 2163 and NGC 2207 are a well-studied pair undergoing a grazing collision. ALMA CO observations of masses, column densities, and velocities are combined with HI, Hα, optical, and 24 micron data to study the star formation rates and efficiencies. The close encounter of the galaxies produced in-plane tidal forces in IC 2163, resulting in a large shock with high molecular velocity gradients and both radial and azimuthal streaming (100 km/s) that formed a pile-up of molecular gas in the resulting cuspy-oval or ``eyelid'' structure at mid-radius. The encounter also produced forces nearly orthogonal to the plane of NGC 2207, resulting in a warp. By comparing with the Kennicutt-Schmidt relation for star formation, we find that some regions of NGC 2207 with unusually high turbulent speeds (40-50 km/s) and high star formation rates (>0.01 Mo/pc2/Myr) have gas that is predominantly atomic with high density cores. Half of the CO mass is in 300 clouds each more massive than 4.0x105 Mo. The mass distribution functions for the CO clouds and star complexes in the eyelid in IC 2163 both have a slope similar to what is observed in Milky Way clouds; the CO slope is steeper in NGC 2207. The CO distribution in NGC 2207 also includes a nuclear ring, a mini-bar, and a mini-starburst region that dominates the 24 micron, radio, and Hα emission in both galaxies. Dust extinction, molecular column densities, and slightly negative molecular velocities indicate the mini-starburst region has ejected a jet of molecular gas nearly perpendicular to the plane of NGC 2207 on the near side with a kinetic energy of 1052 ergs. The large scale star formation efficiency, measured as the ratio of the summed masses of the star complexes near molecular clouds to the combined star complex and cloud masses, is 7% overall; it is 23% in the mini-starburst. The maximum age of star complexes in the galactic-scale shock front at the eyelid is about the same as the time since closest

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

    NASA Astrophysics Data System (ADS)

    Moiseev, Alexei; Karachentsev, Igor; Kaisin, Serafim

    2010-04-01

    We used integral-field and long-slit spectroscopy to study a bright extended nebulosity recently discovered in the isolated lenticular galaxy NGC 4460 during an Hα 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

  3. The Resolved Stellar Population of the Poststarburst Galaxy NGC 1569

    NASA Astrophysics Data System (ADS)

    Greggio, Laura; Tosi, Monica; Clampin, Mark; De Marchi, Guido; Leitherer, Claus; Nota, Antonella; Sirianni, Marco

    1998-09-01

    We present Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC2) photometry of the resolved stellar population in the poststarburst galaxy NGC 1569. The color-magnitude diagram (CMD) derived in the F439W and F555W photometric bands contains ~2800 stars with a photometric error of <=0.2 mag down to mF439, mF555 ~= 26 and is complete for mF555 <~ 23. Adopting the literature-distance modulus and reddening, our CMD samples stars more massive than ~4 M⊙, allowing us to study the star formation (SF) history over the last ~0.15 Gyr. The data are interpreted using theoretical simulations based on stellar evolutionary models. The synthetic diagrams include photometric errors and incompleteness factors. Testing various sets of tracks, we find that the ability of the models to reproduce the observed features in the CMD is strictly related to the shape of the blue loops of the sequences with masses around 5 M⊙. The field of NGC 1569 experienced a global SF burst of >~0.1 Gyr duration, ending ~5-10 Myr ago. During the burst, the SF rate was approximately constant, and, if quiescent periods occurred, they lasted less than ~10 Myr. The level of the SF rate was very high; for a single-slope initial mass function (IMF) ranging from 0.1 to 120 M⊙, we find values of 3, 1, and 0.5 M⊙ yr-1 for α = 3, 2.6, and 2.35 (Salpeter), respectively. When scaled for the surveyed area, these rates are approximately 100 times larger than found in the most active dwarf irregulars in the Local Group. The data are consistent with a Salpeter IMF, though our best models indicate slightly steeper exponents. We discuss the implications of our results in the general context of the evolution of dwarf galaxies. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA for NASA under contract NAS 5-26555.

  4. A GIANT STAR FACTORY IN NEIGHBORING GALAXY NGC 6822

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Resembling curling flames from a campfire, this magnificent nebula in a neighboring galaxy is giving astronomers new insight into the fierce birth of stars as it may have more commonly happened in the early universe. The glowing gas cloud, called Hubble-V, has a diameter of about 200 light-years. A faint tail of nebulosity trailing off the top of the image sits opposite a dense cluster of bright stars at the bottom of the irregularly shaped nebula. NASA's Hubble Space Telescope's resolution and ultraviolet sensitivity reveals a dense knot of dozens of ultra-hot stars nestled in the nebula, each glowing 100,000 times brighter than our Sun. These youthful 4-million-year-old stars are too distant and crowded together to be resolved from ground-based telescopes. The small, irregular host galaxy, called NGC 6822, is one of the Milky Way's closest neighbors and is considered prototypical of the earliest fragmentary galaxies that inhabited the young universe. The galaxy is 1.6 million light-years away in the constellation Sagittarius. The Hubble-V image data was taken with Hubble's Wide Field Planetary Camera 2 (WFPC2) by two science teams: C. Robert O'Dell of Vanderbilt University and collaborators, and Luciana Bianchi of Johns Hopkins University and Osservatorio Astronomico, Torinese, Italy, and collaborators. This color image was produced by The Hubble Heritage Team (STScI). A Hubble image of Hubble-X, another intense star-forming region in NGC 6822, was released by The Heritage Team in January 2001. Credits: NASA, ESA and The Hubble Heritage Team (STScI/AURA) Acknowledgment: C. R. O'Dell (Vanderbilt University) and L. Bianchi (Johns Hopkins University and Osservatorio Astronomico, Torinese, Italy) NOTE TO EDITORS: For additional information, please contact C. R. O'Dell, Vanderbilt University, Physics and Astronomy Dept., Box 1807 Station B, Nashville, TN 37235, (phone) 615-343-1779, (fax) 615-343-7263, (e-mail) cr.odell@vanderbilt.edu or Luciana Bianchi, Johns Hopkins

  5. Globular Clusters and Spur Clusters in NGC 4921, the Brightest Spiral Galaxy in the Coma Cluster

    NASA Astrophysics Data System (ADS)

    Lee, Myung Gyoon; Jang, In Sung

    2016-03-01

    We resolve a significant fraction of globular clusters (GCs) in NGC 4921, the brightest spiral galaxy in the Coma cluster. We also find a number of extended bright star clusters (star complexes) in the spur region of the arms. The latter are much brighter and bluer than those in the normal star-forming region, being as massive as 3 × 105 M⊙. The color distribution of the GCs in this galaxy is found to be bimodal. The turnover magnitudes of the luminosity functions of the blue (metal-poor) GCs (0.70 < (V - I) ≤ 1.05) in the halo are estimated V(max) = 27.11 ± 0.09 mag and I(max) = 26.21 ± 0.11 mag. We obtain similar values for NGC 4923, a companion S0 galaxy, and two Coma cD galaxies (NGC 4874 and NGC 4889). The mean value for the turnover magnitudes of these four galaxies is I(max) = 26.25 ± 0.03 mag. Adopting MI (max) = -8.56 ± 0.09 mag for the metal-poor GCs, we determine the mean distance to the four Coma galaxies to be 91 ± 4 Mpc. Combining this with the Coma radial velocity, we derive a value of the Hubble constant, H0 = 77.9 ± 3.6 km s-1 Mpc-1. We estimate the GC specific frequency of NGC 4921 to be SN = 1.29 ± 0.25, close to the values for early-type galaxies. This indicates that NGC 4921 is in the transition phase to S0s.

  6. Deep Fabry-Perot Hα observations of two Sculptor group galaxies, NGC 247 and 300

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

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

  7. Spatial environment of polar-ring galaxies from the SDSS

    NASA Astrophysics Data System (ADS)

    Savchenko, S. S.; Reshetnikov, V. P.

    2017-03-01

    Based on SDSS data, we have considered the spatial environment of galaxies with extended polar rings. We used two approaches: estimating the projected distance to the nearest companion and counting the number of companions as a function of the distance to the galaxy. Both approaches have shown that the spatial environment of polar-ring galaxies on scales of hundreds of kiloparsecs is, on average, less dense than that of galaxies without polar structures. Apparently, one of the main causes of this effect is that the polar structures in a denser environment are destroyed more often during encounters and mergers with other galaxies.

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Johnson, Megan

    2013-06-01

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

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

    SciTech Connect

    Williams, Benjamin F.; Dalcanton, Julianne J.; Stilp, Adrienne; Radburn-Smith, David; Dolphin, Andrew; Skillman, Evan D. E-mail: jd@astro.washington.edu E-mail: dolphin@raytheon.com

    2013-03-10

    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.

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

    SciTech Connect

    Johnson, Megan

    2013-06-15

    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.

  12. Atomic hydrogen in the spiral galaxy NGC 3631

    NASA Astrophysics Data System (ADS)

    Knapen, J. H.

    1997-04-01

    New high-resolution, high-sensitivity Westerbork Synthesis Radio Telescope Hi synthesis observations of the spiral galaxy NGC 3631 are presented. In the total atomic hydrogen map, the spiral arms are well distinguished from the interarm regions, while the sensitivity allows detection of Hi in all but a few isolated regions of the areas between the spiral arms. Most of the atomic hydrogen is located within the optical disc, but the Hi extends to some 1.5R_opt. The Hi follows the spiral arms, and streaming motions of up to ~15 km s^-1 (projected) can be identified from the velocity field. Assuming a constant inclination angle of 17 deg, a rotation curve is derived which is declining slightly in the outer parts of the disc. An analysis of a residual velocity field, obtained after the subtraction of an axisymmetric model based on the rotation curve, confirms the existence of streaming motions near the spiral arms in an otherwise undisturbed disc.

  13. NICMOS FINDS A GOLDEN RING AT THE HEART OF A GALAXY

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The revived Near Infrared Camera and Multi-Object Spectrometer (NICMOS) aboard NASA's Hubble Space Telescope has pierced the dusty disk of the 'edge-on' galaxy NGC 4013 and peered all the way to the galactic core. To the surprise of astronomers, NICMOS found a brilliant band-like structure, that may be a ring of newly formed stars [yellow band in middle photo] seen edge-on. In the visible-light view of the galaxy [top photo], the star-forming ring cannot be seen because it is embedded in dust. The most prominent feature in the visible-light image -- taken by the Wide Field and Planetary Camera 2 (WFPC2) -- is the thin, dark band of gas and dust, which is about 500 light-years thick. NICMOS enables the Hubble telescope to see in near-infrared wavelengths of light, so that it can penetrate the dust that obscures the inner hub of the galaxy. The ring-like structure spied by NICMOS encircles the core and is about 720 light-years wide, which is the typical size of most star-forming rings found in disk galaxies. The small ring is churning out stars at a torrid pace. The Milky Way Galaxy, for example, is more than 10,000 times larger than the ring. If the Milky Way produced stars at the same rate, it would be making 1,000 times more stars a year. The human eye cannot see infrared light, so colors have been assigned to correspond with near-infrared wavelengths. The blue light represents shorter near-infrared wavelengths and the red light corresponds to longer wavelengths. The ring-like structure is seen more clearly in the photo at bottom. This picture, taken with a filter sensitive to hydrogen, shows the glow of stars and gas. Astronomers used this information to calculate the rate of star formation in the ring-like structure. The extremely bright star near the center of each picture is a nearby foreground star belonging to our own Milky Way. Rings of developing stars are common in barred spiral galaxies, which have 'bars' of stars and gas slicing across their disks. The

  14. VLA Discovers Giant Rings Around Galaxy Cluster

    NASA Astrophysics Data System (ADS)

    2006-11-01

    Astronomers using the National Science Foundation's Very Large Array (VLA) radio telescope have discovered giant, ring-like structures around a cluster of galaxies. The discovery provides tantalizing new information about how such galaxy clusters are assembled, about magnetic fields in the vast spaces between galaxy clusters, and possibly about the origin of cosmic rays. Radio-Optical Image of Cluster Galaxy Cluster Abell 3376 (Radio/Optical) CREDIT: Joydeep Bagchi, IUCAA, NRAO/AUI/NSF Above, a combined radio/optical image shows the galaxy cluster Abell 3376 in visible light (blue) and radio (red) images. The giant radio arcs surrounding the cluster were discovered using the Very Large Array. The visible-light image is from the Digitized Sky survey. Below, an X-ray image of Abell 3376 made using the European Space Agency's XMM-Newton telescope shows a spectacular, bullet-shaped region of X-rays coming from gas heated to 60 million degrees Kelvin. The bullet shape results from the supersonic collision of a smaller smaller galaxy subcluster with the main body of the larger cluster. Click on images for larger version. X-Ray Image of Cluster Galaxy Cluster Abell 3376 (X-Ray) CREDIT: Joydeep Bagchi, IUCAA, ESA "These giant, radio-emitting rings probably are the result of shock waves caused by violent collisions of smaller groups of galaxies within the cluster," said Joydeep Bagchi, of the Inter-University Centre for Astronomy and Astrophysics in Pune, India, who led an international research team. The scientists reported their findings in the November 3 edition of the journal Science. The newly-discovered ring segments, some 6 million light-years across, surround a galaxy cluster called Abell 3376, more than 600 million light-years from Earth. They were revealed because fast-moving electrons emitted radio waves as they spiraled around magnetic field lines in intergalactic space. "Even from this large distance, the feeble radio waves were easily picked up by the VLA

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  17. Triple Scoop from Galaxy Hunter

    NASA Technical Reports Server (NTRS)

    2006-01-01

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

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

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

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

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

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

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

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

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

  1. Shaken, not Stirred: the Ancestry of the Starburst Galaxy NGC 253

    NASA Astrophysics Data System (ADS)

    Davidge, T. J.

    2011-12-01

    Near-infrared images obtained with WIRCam are used to investigate the recent history of the starburst galaxy NGC 253. The distribution of stars in the disk is lopsided, with the projected density of young and intermediate age stars in the north east portion of the disk higher than on the opposite side of the galaxy. Bright AGB stars are also detected out to 15 kpc above the disk plane. Comparisons with models suggest that the extraplanar stars formed over a broad range of ages, suggesting that the disk of NGC 253 was disrupted by a tidal encounter.

  2. Rings in Radio Galaxies: a Multiwavelength Approach

    NASA Astrophysics Data System (ADS)

    Gizani, Nectaria A.; Garrett, M. A.; Morganti, R.; Cohen, A.; Kassim, N.; Gonzales-Serrano, I.; Leahy, J. P.

    We are studying the two powerful radio galaxies Hercules A and 3C310 and their clusters. They present many essential and atypical similarities with the striking one being the presence of large-scale rings instead of hotspots. Employing a multiwavelength observational campaign from radio to Gamma-ray wavelengths we are trying to determine the origin of their unusual structure and tenue (compared with the common AGN) and to disentagle the physical mechanisms taking place interior to them and in their clusters. For example: -In the RADIO we probe the pc- and kpc-scale environment. -In the (Near-)INFRARED we try to constrain the nature of the acceleration mechanism in the rings with the corresponding in the usual hotspots investigate the ISM shed light in their evolution. -In the OPTICAL we study of the ionized gas in the accretion disk fuelling the massive black hole. -In the ULTRAVIOLET we explore the nuclear region the ISM and its interaction with the jets. -In the X-RAYS we probe the intracluster medium identify possible interactions between the X-ray and radio emission measure cluster magnetic fields. -In the GAMMA-RAYS we study the intergalactic medium.

  3. The `shook up' galaxy NGC 3079: the complex interplay between H I, activity and environment

    NASA Astrophysics Data System (ADS)

    Shafi, N.; Oosterloo, T. A.; Morganti, R.; Colafrancesco, S.; Booth, R.

    2015-12-01

    We present deep neutral hydrogen (H I) observations of the starburst/Seyfert galaxy NGC 3079 and its environment, obtained with the Westerbork Synthesis Radio Telescope. Our observations reveal previously unknown components, both in H I emission and in absorption, that show that NGC 3079 is going through a hectic phase in its evolution. The H I disc appears much more extended than previously observed and is morphologically and kinematically lopsided on all scales with evidence for strong non-circular motions in the central regions. Our data reveal prominent gas streams encircling the entire galaxy suggesting strong interaction with its neighbours. A 33 kpc long H I bridge is detected between NGC 3079 and MCG 9-17-9, likely caused by ram-pressure stripping of MGC 9-17-9 by the halo of hot gas of NGC 3079. The cometary H I tail of the companion NGC 3073, earlier discovered by Irwin et al., extends about twice as long in our data, while a shorter, second tail is also found. This tail is likely caused by ram-pressure stripping by the strong, starburst-driven wind coming from NGC 3079. We also detect, in absorption, a nuclear H I outflow extending to velocities well outside what expected for gravitational motion. This is likely an atomic counterpart of the well-studied outflow of ionized gas present in this galaxy. This may indicate that also large amounts of cold gas are blown out of NGC 3079 by the starburst/AGN. Our estimates of the jet energy and kinetic power suggest that both the AGN and the starburst in NGC 3079 are powerful enough to drive the atomic outflow.

  4. The star formation history of low-mass disk galaxies: A case study of NGC 300

    NASA Astrophysics Data System (ADS)

    Kang, Xiaoyu; Zhang, Fenghui; Chang, Ruixiang; Wang, Lang; Cheng, Liantao

    2016-01-01

    Context. Since NGC 300 is a bulgeless, isolated low-mass galaxy and it has not experienced radial migration during its evolution history, it can be treated as an ideal laboratory to test the simple galactic chemical evolution model. Aims: Our main aim is to investigate the main properties of the star formation history (SFH) of NGC 300 and compare its SFH with that of M 33 to explore the common properties and differences between these two nearby low-mass systems. Methods: We construct a simple chemical evolution model for NGC 300, assuming its disk forms gradually from continuous accretion of primordial gas and including the gas-outflow process. The model allows us to build a bridge between the SFH and observed data of NGC 300, in particular, the present-day radial profiles and global observed properties (e.g., cold gas mass, star formation rate, and metallicity). By means of comparing the model predictions with the corresponding observations, we adopt the classical χ2 methodology to find out the best combination of free parameters a, b, and bout. Results: Our results show that by assuming an inside-out formation scenario and an appropriate outflow rate, our model reproduces well most of the present-day observational values. The model not only reproduces well the radial profiles, but also the global observational data for the NGC 300 disk. Our results suggest that NGC 300 may experience a rapid growth of its disk. Through comparing the best-fitting, model-predicted SFH of NGC 300 with that of M 33, we find that the mean stellar age of NGC 300 is older than that of M 33 and there is a recent lack of primordial gas infall onto the disk of NGC 300. Our results also imply that the local environment may play a key role in the secular evolution of galaxy disks.

  5. The Far-Infrared Emission Line and Continuum Spectrum of the Seyfert Galaxy NGC 1068

    NASA Astrophysics Data System (ADS)

    Spinoglio, Luigi; Malkan, Matthew A.; Smith, Howard A.; González-Alfonso, Eduardo; Fischer, Jacqueline

    2005-04-01

    We report on the analysis of the first complete far-infrared spectrum (43-197 μm) of the Seyfert 2 galaxy NGC 1068 as observed with the Long Wavelength Spectrometer (LWS) on board the Infrared Space Observatory (ISO). In addition to the seven expected ionic fine-structure emission lines, the OH rotational lines at 79, 119, and 163 μm were all detected in emission, which is unique among galaxies with full LWS spectra, where the 119 μm line, when detected, is always in absorption. The observed line intensities were modeled together with ISOShort Wavelength Spectrometer (SWS) and optical and ultraviolet line intensities from the literature, considering two independent emission components: the active galactic nucleus (AGN) component and the starburst component in the circumnuclear ring of ~3 kpc in size. Using the UV to mid-IR emission line spectrum to constrain the nuclear ionizing continuum, we have confirmed previous results: a canonical power-law ionizing spectrum is a poorer fit than one with a deep absorption trough, while the presence of a `` big blue bump'' is ruled out. Based on the instantaneous starburst age of 5 Myr constrained by the Brγ equivalent width in the starburst ring, and starburst synthesis models of the mid- and far-infrared fine-structure line emission, a low-ionization parameter (U=10-3.5) and low densities (n=100 cm-3) are derived. Combining the AGN and starburst components, we succeeded in modeling the overall UV to far-IR atomic spectrum of NGC 1068, reproducing the line fluxes to within a factor of 2.0 on average with a standard deviation of 1.3, and the overall continuum as the sum of the contribution of the thermal dust emission in the ionized and neutral components. The OH 119 μm emission indicates that the line is collisionally excited and arises in a warm and dense region. The OH emission has been modeled using spherically symmetric, nonlocal, non-LTE radiative transfer models. The models indicate that the bulk of the emission

  6. AM 2217-490: A polar ring galaxy under construction

    NASA Astrophysics Data System (ADS)

    Freitas-Lemes, P.; Rodrigues, I.; Faúndez-Abans, M.; Dors, O.

    2014-10-01

    This work is part of a series of case studies of Polar Ring Galaxies (PRGs) (see also Posters GAL-1: 163, GAL-2: 178). A PRG is formed by an early type host galaxy (e.g. lenticular or elliptical), surrounded by a ring of gas and stars orbiting approximately at the polar plane of the host galaxy. AM2217-490 is an interesting case of PRG in formation, with a still asymmetrical ring that surrounds the host galaxy. Apparently, this bluish structure (characteristic of the rings of PRGs), is not yet in equilibrium with the host galaxy. This study is based on spectra on the range 6250-7250 Å obtained with the CTIO 1.5 m telescope - Chile. From them, we measure a heliocentric radial velocity of 9152± 18 km/s. The value of the ionization parameter (log U = -3.5) is similar to that in interacting galaxies (Freitas-Lemes et al. 2013, submitted to MNRAS; and Krabbe et al. 2013, MNRAS Accepted), and lower than that of isolated ones. The electron density shows little variation along the major axis of the host galaxy, and a mean value typical of interacting galaxies. Diagnostic diagrams show that the nuclear region harbors an AGN, following a trend among polar ring galaxies. The low-resolution images of the SDSS show no tails or bridges connecting the galaxy to other objects, however, in a radius of 5 arcmin there are three other galaxies with similar speeds, featuring a group. A plausible hypothesis is that one of these galaxies may have interacted with AM2217-490, donating material to form the ring.

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

    NASA Astrophysics Data System (ADS)

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

    2004-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Tully, R. Brent; Trentham, Neil

    2008-04-01

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

  9. GALEX Ultraviolet Observations of the Interacting Galaxy NGC 4438 in the Virgo Cluster

    NASA Astrophysics Data System (ADS)

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

    2005-04-01

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

  10. First confirmed ultra-compact dwarf galaxy in the NGC 5044 group

    NASA Astrophysics Data System (ADS)

    Faifer, Favio R.; Escudero, Carlos G.; Scalia, María C.; Smith Castelli, Analía V.; Norris, Mark; De Rossi, María E.; Forte, Juan C.; Cellone, Sergio A.

    2017-03-01

    Context. Ultra-compact dwarfs (UCDs) are stellar systems displaying colours and metallicities between those of globular clusters (GCs) and early-type dwarf galaxies, as well as sizes of Reff ≲ 100 pc and luminosities in the range -13.5 galaxies. Aims: NGC 5044 is the central massive elliptical galaxy of the NGC 5044 group. Its GC/UCD system is completely unexplored. Methods: In Gemini+GMOS deep images of several fields around NGC 5044 and in spectroscopic multi-object data of one of these fields, we detected an unresolved source with g' 20.6 mag, compatible with being an UCD. Its radial velocity was obtained with FXCOR and the penalized pixel-fitting (pPXF) code. To study its stellar population content, we measured the Lick/IDS indices and compared them with predictions of single stellar population models, and we used the full spectral fitting technique. Results: The spectroscopic analysis of the UCD revealed a radial velocity that agrees with the velocity of the elliptical galaxy NGC 5044. From the Lick/IDS indices, we have obtained a luminosity-weighted age and metallicity of 11.7+ 1.4-1.2 Gyr and [Z/H] = -0.79 ± 0.04 dex, respectively, as well as [α/ Fe] = 0.30 ± 0.06. From the full spectral fitting technique, we measured a lower age (8.52 Gyr) and a similar total metallicity ([Z/H] = -0.86 dex). Conclusions: Our results indicate that NGC 5044-UCD1 is most likely an extreme GC (MV -12.5 mag) belonging to the GC system of the elliptical galaxy NGC 5044.

  11. UBVRI Photometry of Stellar Structures throughout the Disk of the Barred Galaxy NGC 3367

    NASA Astrophysics Data System (ADS)

    García-Barreto, J. Antonio; Hernández-Toledo, Héctor; Moreno-Díaz, Edmundo; Bernal-Marín, Tula; Villarreal-Castillo, A. Lucía

    2007-07-01

    We report new detailed surface U, B, V, R, and I photometry of 81 stellar structures in the disk of the barred galaxy NGC 3367. The images show many different structures, indicating that star formation is going on in most parts of the disk. NGC 3367 is known to have a very high concentration of molecular gas distribution in the central regions of the galaxy and bipolar synchrotron emission from the nucleus, with two lobes (at 6 kpc) forming a triple structure similar to a radio galaxy. We have determined the U, B, V, R, and I magnitudes and U-B, B-V, U-V, and V-I colors for the central region (nucleus), a region which includes supernova 2003 AA, and 79 star associations throughout NGC 3367. The estimation of ages of star associations is very difficult due to several factors, among them the filling factor, metallicity, spatial distribution of each structure, and the fact that we estimated the magnitudes with a circular aperture of 16 pixels in diameter, equivalent to 6.8''~1.4 kpc. However, even though the colors derived for NGC 3367 were similar to the colors expected of star clusters with theoretical evolutionary star tracks developed for the LMC and had a similar metallicity, NGC 3367 shows 56% of the observed structures with age type SWB I (a few tens of megayears), with seven sources outside the high surface brightness visible disk.

  12. The low-luminosity galaxy population in the NGC5044 Group

    NASA Astrophysics Data System (ADS)

    Cellone, Sergio A.; Buzzoni, Alberto

    2005-01-01

    We present multicolour imaging for a sample of 33 dwarf and intermediate-luminosity galaxies in the field of the NGC5044 Group, complemented with mid-resolution spectroscopy for a subsample of 13 objects. With these data, a revised membership and morphological classification is made for the galaxies in the sample. We were able to confirm all but one of the `definite members' included in the spectroscopic subsample, galaxies which were originally classified based on morphological criteria. An important fraction of background galaxies, however, is probably present among `likely' and `possible' members. The presence of a nucleus could be detected in just five out of the nine galaxies originally classified as dE,N, confirming the intrinsic difficulty of photographic-plate morphological classification for this kind of object. Our deep surface photometry provided clear evidence for disc structure in at least three galaxies previously catalogued as dE or dS0. Their transition-type properties are also evident from the colour-magnitude diagram, where they lie near the late-type galaxy locus, suggesting an evolutionary connection between a parent disc-galaxy population and at least some present-day dEs. Six new dSph candidates were also found, most of them at small projected distances from NGC5044, the central galaxy of the group. The NGC5044 Group appears clearly defined in redshift space, with a mean heliocentric radial velocity of = 2461 +/- 84km s-1 (z= 0.0082), and a moderate dispersion of σvr= 431 km s-1. Our kinematical data show no luminosity segregation for early-type galaxies: both dwarf and bright E/S0 systems show very similar velocity distributions (σvr~ 290 km s-1). This is in contrast to late-type galaxies, which seem to display a broader distribution (σvr~ 680 km s-1).

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

    SciTech Connect

    Acciari, V. A.; Benbow, W.; Aliu, E.; Boltuch, D.; Arlen, T.; Celik, O.; Aune, T.; Bautista, M.; Cogan, P.; Beilicke, M.; Buckley, J. H.; Bugaev, V.; Dickherber, R.; Bradbury, S. M.; Byrum, K.; Cannon, A.; Cesarini, A.; Ciupik, L.; Cui, W.; Duke, C.

    2009-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2006-06-01

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

  15. Measuring the Stellar Kinematics of the S0 Galaxy NGC 4203

    NASA Astrophysics Data System (ADS)

    Calbo, Zuzana Isabelle; Walsh, Jonelle; Barth, Aaron J.; van den Bosch, Remco; Shields, Joseph C.; Sarzi, Marc

    2017-01-01

    Black holes lie at the centers of every large galaxy, and their masses can be measured in two ways, by modeling the motions of stars or gas. Both methods suffer from different systematic effects, therefore comparisons between the two are important for assessing the consistency of the methods and the effects on the black hole - host galaxy relations. However, there are only a few cases in which a galaxy's black hole mass has been determined using both stellar and gas-dynamical methods. The nearby, S0 galaxy NGC 4203 provides the opportunity to conduct this necessary cross-check. Here we present near infrared adaptive optics observations of NGC 4203 taken with the integral field spectrograph OSIRIS on the Keck II telescope. We measure the velocity, velocity dispersion, and higher-order velocity moments, h_3 and h_4, within ~100 pc of the galaxy's center. We find that the galaxy is rotating, and that there is a drop in velocity dispersion at the nucleus. The stellar kinematics on these small spatial scales are essential for a robust determination of the NGC 4203 black hole mass, which can then be compared to a gas-dynamical determination from existing Hubble Space Telescope observations.

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

    NASA Technical Reports Server (NTRS)

    Lester, Dan F.; Gaffney, Niall I.

    1994-01-01

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

  17. The Low-luminosity Galaxy Population in the NGC 5044 Group

    NASA Astrophysics Data System (ADS)

    Cellone, S. A.; Buzzoni, A.

    Detailed surface photometry for 79 (mostly dwarf) galaxies in the NGC5044 Group area is analysed, revealing the existence of different morphologies among objects originally classified as early-type dwarfs. Particularly, a significant fraction of bright dwarf "ellipticals" show a distinct bulge+disc structure; we thus re-classify these objects as dwarf lenticulars (dS0).

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

    NASA Astrophysics Data System (ADS)

    Gusev, A. S.

    2006-03-01

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

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

    SciTech Connect

    Marino, R. A.; Gil de Paz, A.; Castillo-Morales, A.; Perez-Gonzalez, P. G.; Gallego, J.; Zamorano, J.; Sanchez, S. F.

    2012-07-20

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

  20. The potential role of NGC 205 in generating Andromeda's vast thin corotating plane of satellite galaxies

    NASA Astrophysics Data System (ADS)

    Angus, Garry W.; Coppin, Paul; Gentile, Gianfranco; Diaferio, Antonaldo

    2016-11-01

    The Andromeda galaxy is observed to have a system of two large dwarf ellipticals and ˜13 smaller satellite galaxies that are currently corotating in a thin plane, in addition to 2 counter-rotating satellite galaxies. We explored the consistency of those observations with a scenario where the majority of the corotating satellite galaxies originated from a subhalo group, where NGC 205 was the host and the satellite galaxies occupied dark matter sub-subhaloes. We ran N-body simulations of a close encounter between NGC 205 and M31. In the simulations, NGC 205 was surrounded by massless particles to statistically sample the distribution of the sub-subhaloes expected in a subhalo that has a mass similar to NGC 205. We made Monte Carlo samplings and found that, using a set of reference parameters, the probability of producing a thinner distribution of sub-subhaloes than the observed NGC 205 + 15 smaller satellites (thus including the two counter-rotators, but excluding M32) increased from <10-8 for the initial distribution to ˜10-2 at pericentre. The probability of the simulated sub-subhaloes occupying the locations of the observed corotating satellites in the line-of-sight velocity versus projected on-sky distance plane is at most 2 × 10-3 for 11 out of 13 satellites. Increasing the mass of M31 and the extent of the initial distribution of sub-subhaloes gives a maximum probability of 4 × 10-3 for all 13 corotating satellites, but the probability of producing the thinness would drop to ˜10-3.

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

    NASA Astrophysics Data System (ADS)

    Bird, Sarah A.; Flynn, Chris; Harris, William E.; Valtonen, Mauri

    2015-03-01

    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±0.08), 65 kpc from the galaxy's center and along the major axis. The stellar population has been resolved to I0 ≈ 27 with a 50% completeness limit of I0 = 24.7, well below the tip of the red-giant branch (TRGB), which is seen at I0 ≈ 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 ≈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. We found both metal-rich and metal-poor stellar populations and found that the falloff of the two follows the same de Vaucouleurs' law profiles from ≈8 kpc out to ≈70 kpc. The metallicity distribution function (MDF) and the density falloff agree with the results of two recent studies of similar outermost halo fields in NGC 5128. We found no evidence of a "transition" in the radial profile of the halo, in which the metal-rich halo density would drop rapidly, leaving the underlying metal-poor halo to dominate by default out to greater radial extent, as has been seen in the outer halo of two other large galaxies. If NGC 5128 has such a transition, it must lie at larger galactocentric distances.

  2. Fine structure of the nucleus of the galaxy NGC 1275

    NASA Astrophysics Data System (ADS)

    Matveyenko, L. I.; Seleznev, S. V.

    2016-04-01

    The fine structure of the nucleus of the Seyfert galaxy NGC 1275 was investigated in 2005-2010 at a wavelength of 2 cm with a resolution as high as 50 μas. The structure consists of two parallel identical systems, eastern and western, spaced 0.5 pc apart in the plane of the sky. Each of them contains an ejector and a bipolar outflow. There are extended regions, lobes, at the extension of the bipolar outflows in the -10° and 170° directions at distances of 5 pc northward and 6.5 pc southward of the active zone. The observed difference between the jet and counterjet sizes by a factor of ~3 and between the distances to the lobes by a factor of 0.8 is determined by the difference between their velocities and by the change of sign of the outflow acceleration in the period of silence. The high-velocity bipolar outflows are surrounded by three pairs of low-velocity components. The diameters of the low-velocity coaxial outflows and the third component are Ø1 ≈ 0.3 pc, Ø2 ≈ 0.8 pc, and Ø3 ≈ 1.4 pc at the detection limit. The outer low-velocity components of the outflows encompass both high-velocity outflows. The velocities of the outflows and their brightness temperatures increase exponentially as the center of the high-velocity outflows is approached. The brightness temperatures of the high-velocity outflows at the ejector exit are T b > 1012 K. The spectral line velocities in the nuclear region differ by ~600 km s-1 due to the velocity difference between the two systems. In the case of Keplerian motion, the revolution period is ~5 × 103 yr, and the mass of the central massive bodies, black holes, is M ≈ 107M⊙. The fine structure suggests a vortical nature of the formation. In the case under consideration, two parallel vortices spaced ~0.5 pc apart and shifted by ~0.5 pc relative to each other were formed. The surrounding material inflows onto the disk of each system, is transferred in a spiral to the center, and is ejected in the -10° and 170

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

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

  5. The ring galaxy HRG 54 103: a first study

    NASA Astrophysics Data System (ADS)

    Faúndez-Abans, M.; Fernandes, I. F.; de Oliveira-Abans, M.; Poppe, P. C. R.; Martin, V. A. F.

    2009-12-01

    Aims: We report the first study of the peculiar ring galaxy HRG 54103 which was previously classified as a Saturn-like type galaxy. Methods: The study is based on low resolution spectroscopy and photometric observations in the optical band to highlight the characteristics of this almost isolated galaxy. The colour distribution of HRG 54103 was examined through direct CCD BVRI Kron-Cousins system imagery. Color-color diagrams of the bulge and ring are displayed and further compared with the star-forming ring galaxy HRG 2302. Results: The results of image enhancement of the morphological structure of this galaxy are discussed. The nuclear emission-line spectrum resembles that of a Seyfert2/LINER object, with z = 0.022 and heliocentric V = 6483 ± 18 km s-1, in agreement with the literature. The nuclear, bulge and ring section radial velocities along the ring major axis show a peculiar distribution, which together with the [N ii]/Hα and [S ii]/Hα ratios and image enhancement suggest an offset nucleus and an internal tilted ring or shell. Conclusions: HRG 54103 is a peculiar galaxy with an intermediate activity region, probably due to a residual excitation effect through the central AGN phenomenon. The individual sections of the color-color map are redder than a typical star-forming ring galaxy, in agreement with the behavior of the [S ii]/Hα versus [N ii]/Hα diagnostic diagram. The two bulge satellites, the plume-like appendix, and the disk-ring asymmetry suggest a possible merger event in the recent past of this object, which could also have caused its formation. Based on observations made at: (a) Observatório do Pico dos Dias, operated by MCT/Laboratório Nacional de Astrofísica, Brazil, and (b) Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatories, which are operated by AURA, Inc., under contract to the National Science Foundation.

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

    SciTech Connect

    Wilson, C. D.; Cridland, A.; Foyle, K.; Parkin, T. J.; Cooper, E. Mentuch; Roussel, H.; Sauvage, M.; Lebouteiller, V.; Madden, S.; Baes, M.; De Looze, I.; Bendo, G.; Boquien, M.; Boselli, A.; Ciesla, L.; Clements, D. L.; Cooray, A.; Galametz, M.; and others

    2013-10-20

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2008-05-01

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

  8. Carbon star survey in the Local Group. VII. NGC 3109 a galaxy without a stellar halo

    NASA Astrophysics Data System (ADS)

    Demers, S.; Battinelli, P.; Letarte, B.

    2003-11-01

    We present a CFH12K wide field survey of the carbon star population in and around NGC 3109. Carbon stars, the brightest members of the intermediate-age population, were found nearly exclusively in and near the disk of NGC 3109, ruling out the existence of an extensive intermediate-age halo like the one found in NGC 6822. Over 400 carbon stars identified have = -4.71, confirming the nearly universality of mean magnitude of C star populations in Local Group galaxies. Star counts over the field reveal that NGC 3109 is a truncated disk shaped galaxy without an extensive stellar halo. The minor axis star counts reach the foreground density between 4' and 5', a distance that can be explained by an inclined disk rather than a spheroidal halo. We calculate a global C/M ratio of 1.75 +/- 0.20, a value expected for such a metal poor galaxy. The complete Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/410/795

  9. A neutral hydrogen study of the barred spiral galaxy NGC 3319

    NASA Astrophysics Data System (ADS)

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

    1998-03-01

    Neutral hydrogen line observations of the late-type barred spiral galaxy NGC 3319 are presented. The distribution and kinematics of the galaxy are studied using the Very Large Array, with spatial resolutions between 11 and 50 arcsec and a channel separation of 10.33 km/s. As is typical for late-type galaxies, NGC 3319 is rich in H I, with a gaseous bar and spiral features. Several large, low-density regions are present, and the H I spiral structure is distorted, especially in the south. The gas distribution is asymmetric and extends significantly further to the southeast due to a long, off-center tail. Noncircular motions caused by the bar, spiral structure, and low-density regions are present in the radial velocity field, complicating the rotation curve analysis. These nonaxisymmetric structures cause the values of the position angle and inclination derived from the velocity field to vary across the disk. In addition, beyond a radius of 180 arcsec, the velocity field is severely perturbed on the approaching (southern) side of the galaxy, and the disk becomes nonplanar. However, the galaxy does not show the typical 'integral sign' shape of a warped system. We detect a small system approximately 11 arcmin south of the center of NGC 3319. It is seen in eight velocity channels and is coincident with a small, resolved object in the Palomar Sky Survey. A tidal interaction between this object and NGC 3319 is the most likely cause of the distorted spiral structure, the H I tail, and the velocity perturbations found in the southern half of the galaxy. Infalling tidal debris from such an event may account for the large, low-density regions found in the disk, several of which show kinematic evidence that suggest they are expanding superstructures.

  10. GLOBULAR CLUSTERS AND SPUR CLUSTERS IN NGC 4921, THE BRIGHTEST SPIRAL GALAXY IN THE COMA CLUSTER

    SciTech Connect

    Lee, Myung Gyoon; Jang, In Sung E-mail: isjang@astro.snu.ac.kr

    2016-03-01

    We resolve a significant fraction of globular clusters (GCs) in NGC 4921, the brightest spiral galaxy in the Coma cluster. We also find a number of extended bright star clusters (star complexes) in the spur region of the arms. The latter are much brighter and bluer than those in the normal star-forming region, being as massive as 3 × 10{sup 5} M{sub ⊙}. The color distribution of the GCs in this galaxy is found to be bimodal. The turnover magnitudes of the luminosity functions of the blue (metal-poor) GCs (0.70 < (V − I) ≤ 1.05) in the halo are estimated V(max) = 27.11 ± 0.09 mag and I(max) = 26.21 ± 0.11 mag. We obtain similar values for NGC 4923, a companion S0 galaxy, and two Coma cD galaxies (NGC 4874 and NGC 4889). The mean value for the turnover magnitudes of these four galaxies is I(max) = 26.25 ± 0.03 mag. Adopting M{sub I} (max) = −8.56 ± 0.09 mag for the metal-poor GCs, we determine the mean distance to the four Coma galaxies to be 91 ± 4 Mpc. Combining this with the Coma radial velocity, we derive a value of the Hubble constant, H{sub 0} = 77.9 ± 3.6 km s{sup −1} Mpc{sup −1}. We estimate the GC specific frequency of NGC 4921 to be S{sub N} = 1.29 ± 0.25, close to the values for early-type galaxies. This indicates that NGC 4921 is in the transition phase to S0s.

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

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

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

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

    SciTech Connect

    Wang, Xilu; Fields, Brian D.

    2014-05-09

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

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

    NASA Technical Reports Server (NTRS)

    Merrifield, Michael R.; Kuijken, Konrad

    1994-01-01

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

  14. Counterrotating stars in the disk of the SAB galaxy NGC 7217

    NASA Astrophysics Data System (ADS)

    Merrifield, Michael R.; Kuijken, Konrad

    1994-09-01

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

  15. Evidence for a Merger in the Peculiar Virgo Cluster SA Galaxy NGC 4424

    NASA Astrophysics Data System (ADS)

    Kenney, Jeffrey D. P.; Koopmann, Rebecca A.; Rubin, Vera C.; Young, Judith S.

    1996-01-01

    We present R-band and Hα images and Hα long-slit spectroscopy of the peculiar Virgo cluster Sa galaxy NGC 4424. The broadband R image reveals banana-shaped isophotes, shell-like features, and other complex structure generally associated with mergers and significant accretion events. The only Hα emission arises from a few bright H II complexes located within 500 pc of the nucleus and inside the bulge- dominated region. Although the main stellar body of NGC 4424 is highly elongated in projection, and the outer part of the galaxy has a disk-like exponential light profile, gas velocities are remarkably low in the central kpc, indicating strong non-circular motions or complex geometry for the inner gas. The peculiar properties are consistent with an intermediate mass ratio (0.1-0.5) merger, making NGC 4424 one of the best cases among spiral galaxies in the nearby Virgo cluster for a significant and recent merger. The degree of morphological peculiarities suggest that the merger is recent, and we propose that the galaxy will become a small- bulge S0 within ~1 Gyr. We discuss the possibility that the banana-shaped stellar distribution is the result of a merger-induced bending instability.

  16. Satellite accretion in action: a tidally disrupting dwarf spheroidal around the nearby spiral galaxy NGC 253

    NASA Astrophysics Data System (ADS)

    Romanowsky, Aaron J.; Martínez-Delgado, David; Martin, Nicolas F.; Morales, Gustavo; Jennings, Zachary G.; GaBany, R. Jay; Brodie, Jean P.; Grebel, Eva K.; Schedler, Johannes; Sidonio, Michael

    2016-03-01

    We report the discovery of NGC 253-dw2, a dwarf spheroidal (dSph) galaxy candidate undergoing tidal disruption around a nearby spiral galaxy, NGC 253 in the Sculptor group: the first such event identified beyond the Local Group. The dwarf was found using small-aperture amateur telescopes, and followed up with Suprime-Cam on the 8 m Subaru Telescope in order to resolve its brightest stars. Using g- and Rc-band photometry, we detect a red giant branch consistent with an old, metal-poor stellar population at a distance of ˜3.5 Mpc. From the distribution of likely member stars, we infer a highly elongated shape with a semimajor axis half-light radius of (2 ± 0.4) kpc. Star counts also yield a luminosity estimate of ˜2 × 106 L⊙,V (MV ˜ -10.7). The morphological properties of NGC 253-dw2 mark it as distinct from normal dSphs and imply ongoing disruption at a projected distance of ˜50 kpc from the main galaxy. Our observations support the hierarchical paradigm wherein massive galaxies continuously accrete less massive ones, and provide a new case study for dSph infall and dissolution dynamics. We also note the continued efficacy of small telescopes for making big discoveries.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Rubin, Vera C.

    1994-01-01

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

  19. Star Formation in NGC4532/DDO 137'S Tidal Dwarf Galaxies and 500 KPC HI Stream

    NASA Astrophysics Data System (ADS)

    Higdon, Sarah

    Mergers and close-passages between gas rich galaxies can result in the formation of long HI/stellar streams. The tidally induced star formation and gas concentrations can result in the creation of tidal dwarf galaxies (TDGs). TDGs may contribute significantly to the dwarf galaxy population, by far the most common galaxy type in the current epoch. We have discovered one of the longest known tidal streams (500 kpc) in the NGC 4535/DDO 137 system. We propose 3 ksec FUV/NUV images centered on the stream and its five TDGs. We will readily detect faint/low mass star forming regions (~2E-17 erg s-1 cm-2 A-1) to 5-sigma. The GALEX observations are a unique opportunity to undertake a sensitive and comprehensive study of tidally induced star formation, dwarf galaxy formation and inter-galactic enrichment in this system.

  20. Abundance ratios and IMF slopes in the dwarf elliptical galaxy NGC 1396 with MUSE

    NASA Astrophysics Data System (ADS)

    Mentz, J. J.; La Barbera, F.; Peletier, R. F.; Falcón-Barroso, J.; Lisker, T.; van de Ven, G.; Loubser, S. I.; Hilker, M.; Sánchez-Janssen, R.; Napolitano, N.; Cantiello, M.; Capaccioli, M.; Norris, M.; Paolillo, M.; Smith, R.; Beasley, M. A.; Lyubenova, M.; Munoz, R.; Puzia, T.

    2016-12-01

    Deep observations of the dwarf elliptical (dE) galaxy NGC 1396 (MV = -16.60, Mass ˜4 × 108 M⊙), located in the Fornax cluster, have been performed with the Very Large Telescope/Multi Unit Spectroscopic Explorer spectrograph in the wavelength region from 4750 to 9350 Å. In this paper, we present a stellar population analysis studying chemical abundances, the star formation history (SFH) and the stellar initial mass function (IMF) as a function of galactocentric distance. Different, independent ways to analyse the stellar populations result in a luminosity-weighted age of ˜6 Gyr and a metallicity [Fe/H]˜ -0.4, similar to other dEs of similar mass. We find unusually overabundant values of [Ca/Fe] ˜+ 0.1, and underabundant Sodium, with [Na/Fe] values around -0.1, while [Mg/Fe] is overabundant at all radii, increasing from ˜+ 0.1 in the centre to ˜+ 0.2 dex. We notice a significant metallicity and age gradient within this dwarf galaxy. To constrain the stellar IMF of NGC 1396, we find that the IMF of NGC 1396 is consistent with either a Kroupa-like or a top-heavy distribution, while a bottom-heavy IMF is firmly ruled out. An analysis of the abundance ratios, and a comparison with galaxies in the Local Group, shows that the chemical enrichment history of NGC 1396 is similar to the Galactic disc, with an extended SFH. This would be the case if the galaxy originated from a Large Magellanic Cloud-sized dwarf galaxy progenitor, which would lose its gas while falling into the Fornax cluster.

  1. The Far-Infrared Emission Line and Continuum Spectrum of the Seyfert Galaxy NGC 1068

    NASA Technical Reports Server (NTRS)

    Spinoglio, Luigi; Smith, Howard A.; Gonzalez-Alfonso, Eduardo; Fisher, Jacqueline

    2005-01-01

    We report on the analysis of the first complete far-infrared spectrum (43-197 microns) of the Seyfert 2 galaxy NGC 1068 as observed with the Long Wavelength Spectrometer (LWS) onboard the Infrared Space Observatory (ISO). In addition to the 7 expected ionic fine structure emission lines, the OH rotational lines at 79, 119 and 163 microns were all detected in emission, which is unique among galaxies with full LWS spectra, where the 119 micron line, where detected, is always in absorption. The observed line intensities were modelled together with IS0 Short Wavelength Spectrometer (SWS) and optical and ultraviolet line intensities from the literature, considering two independent emission components: the AGN component and the starburst component in the circumnuclear ring of approximately 3kpc in size. Using the UV to mid-IR emission line spectrum to constrain the nuclear ionizing continuum, we have confirmed previous results: a canonical power-law ionizing spectrum is a poorer fit than one with a deep absorption trough, while the presence of a big blue bump is ruled out. Based on the instantaneous starburst age of 5 Myr constrained by the Br gamma equivalent width in the starburst ring, and starburst synthesis models of the mid- and far-infrared fine-structure line emission, a low ionization parameter (U=10(exp -3.5)) and low densities (n=100 cm (exp -3)) are derived. Combining the AGN and starburst components, we succeed in modeling the overall UV to far-IR atomic spectrum of SGC 1068, reproducing the line fluxes to within a factor 2.0 on average with a standard deviation of 1.4. The OH 119 micron emission indicates that the line is collisionally excited, and arises in a warm and dense region. The OH emission has been modeled using spherically symmetric, non-local, non-LTE radiative transfer models. The models indicate that the bulk of the emission arises from the nuclear region, although some extended contribution from the starburst is not ruled out. The OH abundance

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

    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.

  3. Globular Clusters as Tracers of Fine Structure in the Dramatic Shell Galaxy NGC 474

    NASA Astrophysics Data System (ADS)

    Lim, Sungsoon; Peng, Eric W.; Duc, Pierre-Alain; Fensch, Jérémy; Durrell, Patrick R.; Harris, William E.; Cuillandre, Jean-Charles; Gwyn, Stephen; Lançon, Ariane; Sánchez-Janssen, Rúben

    2017-02-01

    Globular clusters (GCs) are some of the most visible tracers of the merging and accretion histories of galaxy halos. Metal-poor GCs, in particular, are thought to arrive in massive galaxies largely through dry, minor merging events, but it is rare to see a direct connection between GCs and visible stellar streams. NGC 474 is a post-merger early-type galaxy with dramatic fine structures made of concentric shells and radial streams that have been more clearly revealed by deep imaging. We present a study of GCs in NGC 474 to better establish the relationship between merger-induced fine structure and the GC system. We find that many GCs are superimposed on visible streams and shells, and about 35% of GCs outside 3{R}{{e},{galaxy}} are located in regions of fine structure. The spatial correlation between GCs and fine structure is significant at the 99.9% level, which shows that this correlation is not coincidental. The colors of GCs on fine structures are mostly blue, and we also find an intermediate-color population that is dominant in the central region and that will likely passively evolve to have colors consistent with a traditional metal-rich GC population. The association of the blue GCs with fine structures is direct confirmation that many metal-poor GCs are accreted onto massive galaxy halos through merging events and that the progenitors of these mergers are sub-{L}\\star galaxies.

  4. The Structure of the Circumgalactic Medium of Galaxies: Cool Accretion Inflow Around NGC 1097

    NASA Astrophysics Data System (ADS)

    Bowen, David V.; Chelouche, Doron; Jenkins, Edward B.; Tripp, Todd M.; Pettini, Max; York, Donald G.; Frye, Brenda L.

    2016-07-01

    We present Hubble Space Telescope far-UV spectra of four QSOs whose sightlines pass through the halo of NGC 1097 at impact parameters of ρ = 48-165 kpc. NGC 1097 is a nearby spiral galaxy that has undergone at least two minor merger events, but no apparent major mergers, and is relatively isolated with respect to other nearby bright galaxies. This makes NGC 1097 a good case study for exploring baryons in a paradigmatic bright-galaxy halo. Lyα absorption is detected along all sightlines and Si iii λ1206 is found along the three sightlines with the smallest ρ metal lines of C ii, Si ii, and Si iv are only found with certainty toward the innermost sightline. The kinematics of the absorption lines are best replicated by a model with a disk-like distribution of gas approximately planar to the observed 21 cm H i disk, which is rotating more slowly than the inner disk, and into which gas is infalling from the intergalactic medium. Some part of the absorption toward the innermost sightline may arise either from a small-scale outflow or from tidal debris associated with the minor merger that gives rise to the well known “dog-leg” stellar stream that projects from NGC 1097. When compared to other studies, NGC 1097 appears to be a “typical” absorber, although the large dispersion in absorption line column density and equivalent width in a single halo goes perhaps some way toward explaining the wide range of these values seen in higher-z studies. Based on observations with the NASA/ESA Hubble Space Telescope (HST) obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  5. The mass of the central black hole in the nearby Seyfert galaxy NGC 5273

    SciTech Connect

    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

    2014-11-20

    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 {sub BH} = (4.7 ± 1.6) × 10{sup 6} M {sub ☉}. 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.

  6. NGC 3310 and Its Stellar Debris: the Remnants of Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Wehner, Elizabeth H.; Gallagher, J. S.; Papaderos, P.; Fritze-von Alvensleben, U.; Westfall, K. B.

    2006-06-01

    NGC 3310 is a local (d = 14 Mpc) starburst galaxy that shows signs of a recent and complex merging history. Its most well-known debris features are the "bow and arrow" which extend to the northwest and are strong sources of H-alpha emission. NGC 3310 is also surrounded by a radially symmetric network of shell-like stellar debris, and a large closed stellar loop emanates from the eastern side of the galaxy and rejoins in the north. It has an H I disk and two massive H I tails. One tail begins in the northwest and coincides with the bow and arrow, and the other extends to the south. We present deep UBV and R photometry of this debris network and a compare these results to spectral synthesis models used to examine the origins of these debris. We find that the shell-like debris are not consistent with having originated in NGC 3310's disk and that the underlying disk in this system is extremely blue. We also examine the surface brightness profiles of this system and will discuss the implications of our results for the merging history of NGC 3310.

  7. The Nonbarred Double-Ringed Galaxy, PGC 1000714

    NASA Astrophysics Data System (ADS)

    Seigar, Marc; Mutlu Pakdil, Burcin; Mangedarage, Mithila; Treuthardt, Patrick M.

    2017-01-01

    Hoag-type galaxies are rare peculiar systems which bear strong resemblance to Hoag's Object with an elliptical-like core, a detached outer ring, and no signs of a bar or stellar disk. They represent extreme cases and help us understand the formation of galaxies in general by providing clues on formation mechanisms. The nature of outer rings in Hoag-type galaxies is still debated and may be related either to slow secular evolution, such as dissolution of a barlike structure or to environmental processes, such as galaxy-galaxy interactions or gas infall. Due to a fairly superficial resemblance to Hoag's Object, PGC 1000714 is a good target for detailed study of the peculiar structure of this type. We present the first photometric study of PGC 1000714 that has not yet been described in the literature. Our aim is to evaluate its structure and properties as well as understand the origin of outer rings in such galaxies. Surface photometry of the central body is performed using near-UV, BVRI and JHK images. Based on the photometric data, the nearly round central body follows a de Vaucouleurs profile almost all the way to the center. The detailed photometry reveals a reddish inner ring-shaped structure that shares the same center as the central body. However, no sign of a bar or stellar disk is detected. The outer ring appears as a bump in the surface brightness profile with a peak brightness of 25.8 mag/arcsec^{2} in the B-band and shows no sharp outer boundary. By reconstructing the observed SED for the central body and the rings, we recover the stellar population properties of the galaxy components. Our work suggests different formation histories for the inner and outer rings. We rule out the secular evolution model as being a formation mechanism for the outer ring. The colors of the outer ring are consistent with a feature that may have experienced a burst of star formation due to a possible recent accretion event. In addition, our work supports that the central body

  8. Measuring the Mass of the Central Black Hole in the Bulgeless Galaxy NGC 4395 from Gas Dynamical Modeling

    NASA Astrophysics Data System (ADS)

    den Brok, Mark; Seth, Anil C.; Barth, Aaron J.; Carson, Daniel J.; Neumayer, Nadine; Cappellari, Michele; Debattista, Victor P.; Ho, Luis C.; Hood, Carol E.; McDermid, Richard M.

    2015-08-01

    NGC 4395 is a bulgeless spiral galaxy, harboring one of the nearest known type 1 Seyfert nuclei. Although there is no consensus on the mass of its central engine, several estimates suggest it is one of the lightest massive black holes (MBHs) known. We present the first direct dynamical measurement of the mass of this MBH from a combination of two-dimensional gas kinematic data, obtained with the adaptive optics assisted near-infrared integral field spectrograph Gemini/NIFS and high-resolution multiband photometric data from Hubble Space Telescope's Wide Field Camera 3. We use the photometric data to model the shape and stellar mass-to-light ratio of the nuclear star cluster (NSC). From the Gemini/NIFS observations, we derive the kinematics of warm molecular hydrogen gas as traced by emission through the H2 1-0 S(1) transition. These kinematics show a clear rotational signal, with a position angle orthogonal to NGC 4395's radio jet. Our best-fitting tilted ring models of the kinematics of the molecular hydrogen gas contain a black hole with mass M={4}-3+8× {10}5 M⊙ (3σ uncertainties) embedded in an NSC of mass M=2× {10}6 M⊙. Our black hole mass measurement is in excellent agreement with the reverberation mapping mass estimate of Peterson et al. but shows some tension with other mass measurement methods based on accretion signals.

  9. Multi-long-slit Spectroscopy For Kinematic Studies. II. Initial Results For The Edge-on Galaxies NGC891 And NGC4244

    NASA Astrophysics Data System (ADS)

    Choi, Jiehae; Cisneros, S.; Wu, C.; Patterson, M.; Walterbos, R.

    2007-12-01

    We present results of observations of the edge-on galaxies NGC891 and NGC4244 using a multi-long-slit setup on the DIS spectrograph on the ARC 3.5m telescope. In combination with a 25A H-alpha filter, 16 slits of 2" by 4.5' could be observed simultaneously over a 4' by 4.5' field of view. The spectral resolution is 4 Anstrom. In the case of NGC891 we have obtained a deep spectrum of the Northern half of the halo, while for NGC4244 we obtained spectra with the slits oriented parallel to the major axis and a second exposure with the slits perpendicular to the major axis. In the case of NGC 891, the data were obtained to test the accuracy of our velocity measurements by comparison with previous observations, although we also do expand on the spatial coverage of ionized gas in the halo. For NGC4244, deep optical imaging has not shown a very extended diffuse ionized gas halo, and here our goal is to use the spectroscopic data to improve upon the limits set in the imaging studies. We present the results of these tests and discuss other implementations of the multi-long-slit setup. One of these is the possibility to perform deep spectroscopic searches for detection of ionized gas in galaxy halos through use of up to 45 slits when using a lower resolution grating. This research was supported by an award from Research Corporation.

  10. Quantitative spectroscopy of blue supergiants in metal-poor dwarf galaxy NGC 3109

    SciTech Connect

    Hosek, Matthew W. Jr.; Kudritzki, Rolf-Peter; Bresolin, Fabio; Urbaneja, Miguel A.; Przybilla, Norbert; Evans, Christopher J.; Pietrzyński, Grzegorz; Gieren, Wolfgang; Carraro, Giovanni E-mail: kud@ifa.hawaii.edu E-mail: Miguel.Urbaneja-Perez@uibk.ac.at E-mail: chris.evans@stfc.ac.uk E-mail: wgieren@astro-udec.cl

    2014-04-20

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

  11. Evidence for a triaxial bulge in the spiral galaxy NGC 4845

    SciTech Connect

    Bertola, F.; Zeilinger, W.W.; Rubin, V.C. Carnegie Institution of Washington, Washington, DC )

    1989-10-01

    Spectroscopic observations for the Sa galaxy NGC 4845 in five position angles reveal a regular but nonaxisymmetric velocity field for the gas at r of 1.5 kpc or less. Photometry indicates a possible slight twisting between the disk and bulge isophotes. These phenomena are interpreted as a manifestation of a triaxial bulge, and estimates of the ranges of b/a and c/a are obtained. 20 refs.

  12. The dynamics and structure of the S0 galaxy NGC 7332

    NASA Technical Reports Server (NTRS)

    Fisher, David; Illingworth, Garth; Franx, Marijn

    1994-01-01

    Spectroscopic and photometric observations of the edge-on S0 galaxy NGC 7332 are presented. The spectra show the galaxy to possess a rapidly counter-rotating extended gas disk as detected from both (O III) 5007 A and H alpha emission. Multiple slit orientations at a variety of position angles clearly show the decoupling of the angular momenta between the stellar and gaseous components. The gas is distributed asymmetrically and displays noncircular motions indicating that it has not reached equilibrium. These observations are strong evidence in support of an accretion process having occurred in NGC 7332. Broad R and B band CCD images show the boxy isophotes that NGC 7332 has long been known to possess while offset spectra taken parallel to the major and minor axes display the cylindrical rotation common to galaxies with box-shaped bulges. The bulge of NGC 7332 is well described by an r(exp 1/4)-law on both the major and minor axes while the outer disk is exponential. The B-R color of the disk is uniform; the only indication of a trend to blue colors is a Delta(B-R(sub c))/Delta log r= -0.04 +/- 0.01 gradient seen perpendicular to the bulge and disk. There exists a 10 sec long region of nearly constant surface brightness along the major axis between the bulge and disk components. Not likely due to absorbing material, the relation of this feature to the already complicated structure of the galaxy is considered.

  13. LWS Observations of the Colliding Galaxies NGC 4038/39

    DTIC Science & Technology

    1996-01-01

    cor- related ( Luhman & Jaffe 1996). If the H2 emission in NGC 4038/39 arises in UV exposed gas (PDRs), then applying this correlation to the ISO far...Leitherer, C., Heckman, T.M. 1995, ApJS, 96, 9 Lord, S.D., Hollenbach, D.J., et al. 1996, ApJ, 465, 703 Luhman , M.L., Jaffe, D.T. 1996, ApJ, 463, 191

  14. STAR FORMATION IN NUCLEAR RINGS OF BARRED GALAXIES

    SciTech Connect

    Seo, Woo-Young; Kim, Woong-Tae E-mail: wkim@astro.snu.ac.kr

    2013-06-01

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

  15. Star Formation in Nuclear Rings of Barred Galaxies

    NASA Astrophysics Data System (ADS)

    Seo, Woo-Young; Kim, Woong-Tae

    2013-06-01

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

  16. THE 0.3–30 keV SPECTRA OF POWERFUL STARBURST GALAXIES: NuSTAR AND CHANDRA OBSERVATIONS OF NGC 3256 AND NGC 3310

    SciTech Connect

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

    2015-06-10

    We present nearly simultaneous Chandra and NuSTAR observations of two actively star-forming galaxies within 50 Mpc: NGC 3256 and NGC 3310. Both galaxies are significantly detected by both Chandra and NuSTAR, which together provide the first-ever spectra of these two galaxies spanning 0.3–30 keV. The X-ray emission from both galaxies is spatially resolved by Chandra; we find that hot gas dominates the E < 1–3 keV emission while ultraluminous X-ray sources (ULXs) provide majority contributions to the emission at E > 1–3 keV. The NuSTAR galaxy-wide spectra of both galaxies follow steep power-law distributions with Γ ≈ 2.6 at E > 5–7 keV. Using new and archival Chandra data, we search for signatures of heavily obscured or low luminosity active galactic nuclei (AGNs). We find that both NGC 3256 and NGC 3310 have X-ray detected sources coincident with nuclear regions; however, the steep NuSTAR spectra of both galaxies restricts these sources to be either low luminosity AGNs (L{sub 2−10} {sub keV}/L{sub Edd} ≲ 10{sup −5}) or non-AGNs in nature (e.g., ULXs or crowded X-ray sources that reach L{sub 2−10} {sub keV} ∼ 10{sup 40} erg s{sup −1} cannot be ruled out). Combining our constraints on the 0.3–30 keV spectra of NGC 3256 and NGC 3310 with equivalent measurements for nearby star-forming galaxies M83 and NGC 253, we analyze the star formation rate (SFR) normalized spectra of these starburst galaxies. The spectra of all four galaxies show sharply declining power-law slopes at energies above 3–6 keV primarily due to ULX populations. Our observations therefore constrain the average spectral shape of galaxy-wide populations of luminous accreting binaries (i.e., ULXs). Interestingly, despite a completely different galaxy sample selection, emphasizing here a range of SFRs and stellar masses, these properties are similar to those of super-Eddington accreting ULXs that have been studied individually in a targeted NuSTAR ULX program. We also find that

  17. HST Observations of Star Formation in Interacting Galaxies: NGC 4194, the "Medusa"

    NASA Technical Reports Server (NTRS)

    Weistrop, D.; Eggers, D.; Nelson, C. H.; Kaiser, M. E.

    2001-01-01

    Ultraviolet and visible imaging of the blue compact galaxy NGC4194 was obtained to survey the star-forming knots in the center of this galaxy. Photometry and image analysis were performed on these regions. Comparison with evolutionary tracks indicates many of the knots are reddened with a typical E(B-V)approx.0.3. The knot ages range from 10(exp 6-10(exp 8)years. Some of the knots may have masses 3-5x10(exp 5) solar mass. The FUV fluxes correspond to the flux from 60-3.8x10(exp 3) O5V stars.

  18. A Supermassive Black Hole in the Seyfert 1 Galaxy NGC 3783

    NASA Technical Reports Server (NTRS)

    Onken, C. A.; Peterson, B. M.

    2004-01-01

    Updated analysis techniques and recalibrated archival monitoring data for the Seyfert 1 galaxy NGC 3783 indicated the presence of a supermassive black hole in this galaxy. Using UV data from the International Ultraviolet Explorer satellite and ground-based optical spectra, we have measured more precise emission line reverberation in response to continuum variations. The stratification of the broad line region (BLR) suggested by our results, combined with estimates of the line velocity widths, is consistent with a gravitationally-dominated BLR and allows us to derive a mass for the central black hole.

  19. Gas inflows towards the nucleus of the Seyfert 2 galaxy NGC 1667

    NASA Astrophysics Data System (ADS)

    Schnorr-Müller, Allan; Storchi-Bergmann, Thaisa; Ferrari, Fabricio; Nagar, Neil M.

    2017-01-01

    We use optical spectra from the inner 2 × 3 kpc2 of the Seyfert 2 galaxy NGC 1667, obtained with the GMOS integral field spectrograph on the Gemini South telescope at a spatial resolution of ≈ 240 pc, to assess the feeding and feedback processes in this nearby AGN. We have identified two gaseous kinematical components in the emission line profiles: a broader component (σ ≈ 400 km s-1) which is observed in the inner 1-2″ and a narrower component (σ ≈ 200 km s-1) which is present over the entire field-of-view. We identify the broader component as due to an unresolved nuclear outflow. The narrower component velocity field shows strong isovelocity twists relative to a rotation pattern, implying the presence of strong non-circular motions. The subtraction of a rotational model reveals that these twists are caused by outflowing gas in the inner ≈ 1″, and by inflows associated with two spiral arms at larger radii. We calculate an ionized gas mass outflow rate of dot{M}_{out} ≈ 0.16 M⊙ yr-1. We calculate the net gas mass flow rate across a series of concentric rings, obtaining a maximum mass inflow rate in ionized gas of ≈ 2.8 M⊙ year-1 at 800 pc from the nucleus, which is two orders of magnitude larger than the accretion rate necessary to power this AGN. However, as the mass inflow rate decreases at smaller radii, most of the gas probably will not reach the AGN, but accumulate in the inner few hundred parsecs. This will create a reservoir of gas that can trigger the formation of new stars.

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

    NASA Technical Reports Server (NTRS)

    2002-01-01

    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

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  2. ``A Beautiful Galaxy :" Further HST Evidence and Mechanisms for Two Leading Arms in NGC 4622

    NASA Astrophysics Data System (ADS)

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

    2002-05-01

    Shu (1982) noted the galaxy NGC4622's ``beautiful spiral pattern composed of two trailing spiral arms." which E. M. Burbidge (1982) described as ``extraordinarily symmetric." Besides the two arms which wind outward clockwise (CW), Byrd et al. (1989) pointed out a weaker, single, inner arm which winds outward counterclockwise (CCW). Byrd et al. suspected the single arm must lead, a very rare configuration. Buta, Crocker, and Byrd (1992)'s BVI photometry showed the inner arm is a mostly stellar disk feature. Byrd, Freeman, and Howard (1993) simulated creation of a single leading and outer trailing pair via a plunging low-mass perturber. At the Jan. `02 AAS meeting, we discussed new HST WFPC2 BVI images of NGC4622 (http://bama.ua.edu/ ~ rbuta/ngc4622/). Despite the low inclination i=26o+/-4o, sharp dust lanes are silhouetted on the east side of NGC4622's kinematic line of nodes (p.a. 22o) but not the west, indicating the east is nearer. In a ground-based Hα velocity field, the north half of the galaxy is receding. Therefore, the disk rotates CW. The two CW-opening arms thus lead, NOT the single inner CCW-opening arm. At the June `02 AAS meeting, we will discuss further the silhouetted dust lanes and show they are also found west of the line of nodes, but these are less sharp and less red because they are on the far side, viewed through the bright bulge. We will show via a model galaxy with an r1/4 bulge and an exponential disk, that a measurable reddening and dust asymmetry across the line of nodes results even with i=20o-30o, if the bulge is nearly spherical and is a significant fraction of the total luminosity. The HST images reveal a globular cluster system in NGC4622 which we will discuss. Despite previous descriptions, this beautiful galaxy apparently has a pattern far from a classical trailing density wave. We will discuss how a pair of leading arms in NGC4622 may originate via tidal perturbation and/or a merger. Supported by Grants NASA/STScI GO 8707 and by

  3. A survey of ring galaxies in search of IMBHs

    NASA Astrophysics Data System (ADS)

    Wolter, Anna

    2015-08-01

    Recent results support the notion that the majority of Ultra Luminous X-ray sources are X-ray binary systems. In particular, the higher luminosity sources are the main reservoir in which to look for Intermediate Mass Black Holes (IMBH). IMBH have fundamental cosmological implications, as they are deemed to be the seeds of SuperMassive BHs, sources of pre-heating of the intergalactic medium and of fluctuation in the Near IR Cosmic Background. Although a few hundred ULXs and candidates are now known, there has never been a specific survey tailored to find these sources. Most of the host galaxies that contain a large number of ULXs have been selected because they are bright and famous, such e.g. the Cartwheel. The collection of ULXs in various catalogs is based on detections without assessment of non-detections. As a first step towards creating a statistical significant sample of ULXs, we have started a small but focused project to observe a sample of Ring Galaxies. Ring galaxies are particularly suitable for this study, as they generally have high SFR and are expected to host a relatively large number of ULXs. Due to the peculiar morphology of ring galaxies, detected point sources in the ring are very likely to be physically associated with the galaxy, reducing the problem of contamination from spurious sources. From formation model we expect them to have a low metallicity content, which favours the formation of high mass remnants, possibly from direct collapse.We have selected all the peculiar galaxies labelled as collisional rings with a spectroscopic redshift z<0.02 from the Arp & Madore `Catalogue of southern peculiar galaxies and associations'. This selection produces a sample of 12 galaxies which we have observed with Chandra and XMM-Newton. We will discuss the results of these observations and support for current models that propose low metallicity environments as the ideal cradle for ULXs. We will compare the results from this statistically selected sample

  4. Escape fraction of ionizing photons from a dwarf galaxy NGC 4214

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

    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

    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 μm) 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 μm 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.

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

    SciTech Connect

    Hernandez-Toledo, H. M.; Cano-Diaz, M.; Valenzuela, O.; Garcia-Barreto, J. A; Moreno-Diaz, E.; Puerari, I.; Bravo-Alfaro, H.

    2011-12-15

    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

  7. Deep WIYN Imaging of the Globular Cluster System of the Lenticular Galaxy NGC 3607

    NASA Astrophysics Data System (ADS)

    Carr, Derrick; Rhode, Katherine L.; Jorgenson, Regina

    2017-01-01

    Globular clusters serve as relics of a galaxy’s past history, because they are thought to be among the first objects to form in a galaxy. Measuring the properties of the globular cluster population of a galaxy — in particular the total number, spatial distribution, and color distribution of the clusters — can provide important clues about the formation and evolution of that galaxy. Here we present results from the analysis of the globular cluster population of NGC 3607, an S0 galaxy with M_V = -21.9 that is ~23 Mpc away and is the brightest member of the Leo II group. We used images from the Minimosaic camera on the WIYN 3.5-m telescope with total exposure times of 6300, 6000, and 5400 seconds in the B, V, and R filters, respectively, to image the globular cluster system of NGC 3607 well past its apparent radial extent of 6.3’ (41 kpc). Point-source globular clusters are selected with three-filter photometry to help eliminate foreground stars and background galaxies. The excellent seeing in our WIYN images (0.6” to 0.9”) also helped reduce contamination in the globular cluster candidate sample. Artificial star tests yielded 50% completeness levels of B = 25.4, V=25.2, and R=24.1 and we observed approximately 41% of the galaxy’s Globular Cluster Luminosity Function. We estimate the total number of globular clusters in NGC 3607 is 1000+/-50, which translates to specific frequency values of S_N = 1.7+/-0.3 and T = 2.6+/-0.3 for this galaxy’s luminosity and stellar mass. This research was supported in part by NSF REU grant AST-1358980 and the Nantucket Maria Mitchell Association.

  8. NGC 3105: A Young Cluster in the Outer Galaxy

    NASA Astrophysics Data System (ADS)

    Davidge, T. J.

    2017-03-01

    Images and spectra of the open cluster NGC 3105 have been obtained with the Gemini Multi-Object Spectrograph on Gemini South. The (i\\prime ,g\\prime -i\\prime ) color–magnitude diagram (CMD) constructed from these data extends from the brightest cluster members to g\\prime ∼ 23. This is ∼ 4{--}5 mag fainter than previous CMDs at visible wavelengths and allowing cluster members with sub-solar masses to be sampled. Assuming a half-solar metallicity, comparisons with isochrones yield a distance of 6.6 ± 0.3 kpc. An age of at least 32 Myr is found based on the photometric properties of the brightest stars, coupled with the apparent absence of pre-main-sequence stars in the lower regions of the CMD. The luminosity function of stars between 50 and 70 arcsec from the cluster center is consistent with a Chabrier lognormal mass function. However, at radii smaller than 50 arcsec there is a higher specific frequency of the most massive main-sequence (MS) stars than at larger radii. Photometry obtained from archival SPITZER images reveals that some of the brightest stars near NGC 3105 have excess infrared emission, presumably from warm dust envelopes. Hα emission is detected in a few early-type stars in and around the cluster, building upon previous spectroscopic observations that found Be stars near NGC 3105. The equivalent width of the NaD lines in the spectra of early-type stars is consistent with the reddening found from comparisons with isochrones. Stars with i\\prime ∼ 18.5 that fall near the cluster MS have a spectral-type A5V, and a distance modulus that is consistent with that obtained by comparing isochrones with the CMD is found assuming solar neighborhood intrinsic brightnesses for these stars.

  9. Spectroscopic study of extended star clusters in dwarf galaxy NGC 6822

    SciTech Connect

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

    2014-03-01

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

  10. Dense Molecular Gas Tracers in the Outflow of the Starburst Galaxy NGC 253

    NASA Astrophysics Data System (ADS)

    Walter, Fabian; Bolatto, Alberto D.; Leroy, Adam K.; Veilleux, Sylvain; Warren, Steven R.; Hodge, Jacqueline; Levy, Rebecca C.; Meier, David S.; Ostriker, Eve C.; Ott, Jürgen; Rosolowsky, Erik; Scoville, Nick; Weiss, Axel; Zschaechner, Laura; Zwaan, Martin

    2017-02-01

    We present a detailed study of a molecular outflow feature in the nearby starburst galaxy NGC 253 using ALMA. We find that this feature is clearly associated with the edge of NGC 253's prominent ionized outflow, has a projected length of ∼300 pc, with a width of ∼50 pc, and a velocity dispersion of ∼40 km s‑1, which is consistent with an ejection from the disk about 1 Myr ago. The kinematics of the molecular gas in this feature can be interpreted (albeit not uniquely) as accelerating at a rate of 1 km s‑1 pc‑1. In this scenario, the gas is approaching an escape velocity at the last measured point. Strikingly, bright tracers of dense molecular gas (HCN, CN, HCO+, CS) are also detected in the molecular outflow: we measure an HCN(1–0)/CO(1–0) line ratio of ∼ 1/10 in the outflow, similar to that in the central starburst region of NGC 253 and other starburst galaxies. By contrast, the HCN/CO line ratio in the NGC 253 disk is significantly lower (∼ 1/30), similar to other nearby galaxy disks. This strongly suggests that the streamer gas originates from the starburst, and that its physical state does not change significantly over timescales of ∼1 Myr during its entrainment in the outflow. Simple calculations indicate that radiation pressure is not the main mechanism for driving the outflow. The presence of such dense material in molecular outflows needs to be accounted for in simulations of galactic outflows.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    We present observations in the optical lines of Hα and [S II] (λλ6717, 6731 Å) and in X-rays of the irregular galaxy, NGC 1569. The observations in Hα and [S II] were made with the UNAM scanning Fabry-Perot interferometer (PUMA) and the X-ray data were obtained from the Chandra data archive. We detected several superbubbles, filaments, and supershells in NGC 1569 for which we determined size as well as their kinematic properties. We present a catalog of expansion velocities of 12 superbubbles, listing their positions, diameters, and physical parameters. Likewise, we present a catalog of 15 filaments and 4 supershells. In order to identify possible X-ray emission from the superbubbles in this galaxy, we analyzed the X-ray emission of NGC 1569 in two energy bands: 0.2-2.0 keV (soft X-rays) and 2.0-8.0 keV (hard X-rays). Based on X-ray images, we detected X-ray emission that could possibly be related to some of the superbubbles. The spectrum of the X-ray superbubbles can be described by an optically thin thermal plasma model. In order to identify the possible coexistence of galactic super winds and superbubbles we have performed adiabatic three-dimensional N-body/smoothed particle hydrodynamics simulations to follow the evolution of the most important stellar clusters in this galaxy, SSC A and SSC B, using the GADGET-2 code. Those simulations demonstrate that depending on the specific initial conditions, the formation of superbubbles or a galactic superwind can result in NGC 1569.

  12. The Hydra I cluster core. I. Stellar populations in the cD galaxy NGC 3311

    NASA Astrophysics Data System (ADS)

    Barbosa, C. E.; Arnaboldi, M.; Coccato, L.; Hilker, M.; Mendes de Oliveira, C.; Richtler, T.

    2016-05-01

    Context. The history of the mass assembly of brightest cluster galaxies may be studied by mapping the stellar populations at large radial distances from the galaxy centre, where the dynamical times are long and preserve the chemodynamical signatures of the accretion events. Aims: We provide extended and robust measurements of the stellar population parameters in NGC 3311, the cD galaxy at the centre of the Hydra I cluster, and out to three effective radii. We wish to characterize the processes that drove the build-up of the stellar light at all these radii. Methods: We obtained the spectra from several regions in NGC 3311 covering an area of ~3 arcmin2 in the wavelength range 4800 ≲ λ(Å) ≲ 5800, using the FORS2 spectrograph at the Very Large Telescope in the MXU mode. We measured the equivalent widths of seven absorption-features defined in the Lick/IDS system, which were modelled by single stellar populations, to provide luminosity-weighted ages, metallicities, and alpha element abundances. Results: The trends in the Lick indices and the distribution of the stellar population parameters indicate that the stars of NGC 3311 may be divided in two radial regimes, one within and the another beyond one effective radius, Re = 8.4 kpc, similar to the distinction between the inner galaxy and the external halo derived from the NGC 3311 velocity dispersion profile. The inner galaxy (R ≤ Re) is old (age ~14 Gyr), has negative metallicity gradients and positive alpha element gradients. The external halo is also very old, but has a negative age gradient. The metal and element abundances of the external halo both have a large scatter, indicating that stars from a variety of satellites with different masses have been accreted. The region in the extended halo associated with the off-centred envelope at 0°< PA < 90° has higher metallicity with respect to the symmetric external halo. Conclusions: The different stellar populations in the inner galaxy and extended halo

  13. Star formation and gas flows in the centre of the NUGA galaxy NGC 1808 observed with SINFONI

    NASA Astrophysics Data System (ADS)

    Busch, Gerold; Eckart, Andreas; Valencia-S., Mónica; Fazeli, Nastaran; Scharwächter, Julia; Combes, Françoise; García-Burillo, Santiago

    2017-02-01

    NGC 1808 is a nearby barred spiral galaxy which hosts young stellar clusters in a patchy circumnuclear ring with a radius of 240 pc. In order to study the gaseous and stellar kinematics and the star formation properties of the clusters, we perform seeing-limited H + K-band near-infrared integral-field spectroscopy with SINFONI of the inner 600 pc. From the MBH-σ∗ relation, we find a black hole mass of a few 107M⊙. We estimate the age of the young stellar clusters in the circumnuclear ring to be ≲10 Myr. No age gradient along the ring is visible. However, the starburst age is comparable to the travel time along the ring, indicating that the clusters almost completed a full orbit along the ring during their lifetime. In the central 600 pc, we find a hot molecular gas mass of 730 M⊙ which, with standard conversion factors, corresponds to a large cold molecular gas reservoir of several 108M⊙, in agreement with CO measurements from the literature. The gaseous and stellar kinematics show several deviations from pure disc motion, including a circumnuclear disc and signs of a nuclear bar potential. In addition, we confirm streaming motions on the 200 pc scale that have recently been detected in CO(1-0) emission. Thanks to the enhanced angular resolution of <1″, we find further streaming motion within the inner arcsecond that had not been detected until now. Despite the flow of gas towards the centre, no signs of significant AGN activity are found. This raises the question: will the infalling gas fuel an AGN or star formation? Based on observations with ESO-VLT, STS-Cologne GTO proposal ID 094.B-0009(A) and ESO archival data, proposal nos 074.A-9011(A) and 075.B-0648(A).

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

    PubMed

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

    2011-08-31

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  16. GIANT MOLECULAR CLOUDS IN THE EARLY-TYPE GALAXY NGC 4526

    SciTech Connect

    Utomo, Dyas; Blitz, Leo; Davis, Timothy; Rosolowsky, Erik; Bureau, Martin; Cappellari, Michele; Sarzi, Marc

    2015-04-10

    We present a high spatial resolution (≈20 pc) of {sup 12}CO(2 −1) observations of the lenticular galaxy NGC 4526. We identify 103 resolved giant molecular clouds (GMCs) and measure their properties: size R, velocity dispersion σ{sub v}, and luminosity L. This is the first GMC catalog of an early-type galaxy. We find that the GMC population in NGC 4526 is gravitationally bound, with a virial parameter α ∼ 1. The mass distribution, dN/dM ∝ M{sup −2.39±0.03}, is steeper than that for GMCs in the inner Milky Way, but comparable to that found in some late-type galaxies. We find no size–line width correlation for the NGC 4526 clouds, in contradiction to the expectation from Larson’s relation. In general, the GMCs in NGC 4526 are more luminous, denser, and have a higher velocity dispersion than equal-size GMCs in the Milky Way and other galaxies in the Local Group. These may be due to higher interstellar radiation field than in the Milky Way disk and weaker external pressure than in the Galactic center. In addition, a kinematic measurement of cloud rotation shows that the rotation is driven by the galactic shear. For the vast majority of the clouds, the rotational energy is less than the turbulent and gravitational energy, while the four innermost clouds are unbound and will likely be torn apart by the strong shear at the galactic center. We combine our data with the archival data of other galaxies to show that the surface density Σ of GMCs is not approximately constant, as previously believed, but varies by ∼3 orders of magnitude. We also show that the size and velocity dispersion of the GMC population across galaxies are related to the surface density, as expected from the gravitational and pressure equilibrium, i.e., σ{sub v} R{sup −1/2} ∝ Σ{sup 1/2}.

  17. Detailed photometric analysis of young star groups in the galaxy NGC 300

    NASA Astrophysics Data System (ADS)

    Rodríguez, M. J.; Baume, G.; Feinstein, C.

    2016-10-01

    Aims: The purpose of this work is to understand the global characteristics of the stellar populations in NGC 300. In particular, we focused our attention on searching young star groups and study their hierarchical organization. The proximity and orientation of this Sculptor Group galaxy make it an ideal candidate for this study. Methods: The research was conducted using archival point spread function (PSF) fitting photometry measured from images in multiple bands obtained with the Advanced Camera for Surveys of the Hubble Space Telescope (ACS/HST). Using the path linkage criterion (PLC), we cataloged young star groups and analyzed them from the observation of individual stars in the galaxy NGC 300. We also built stellar density maps from the bluest stars and applied the SExtractor code to identify overdensities. This method provided an additional tool for the detection of young stellar structures. By plotting isocontours over the density maps and comparing the two methods, we could infer and delineate the hierarchical structure of the blue population in the galaxy. For each region of a detected young star group, we estimated the size and derived the radial surface density profiles for stellar populations of different color (blue and red). A statistical decontamination of field stars was performed for each region. In this way it was possible to build the color-magnitude diagrams (CMD) and compare them with theoretical evolutionary models. We also constrained the present-day mass function (PDMF) per group by estimating a value for its slope. Results: The blue population distribution in NGC 300 clearly follows the spiral arms of the galaxy, showing a hierarchical behavior in which the larger and loosely distributed structures split into more compact and denser ones over several density levels. We created a catalog of 1147 young star groups in six fields of the galaxy NGC 300, in which we present their fundamental characteristics. The mean and the mode radius values

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

    SciTech Connect

    Levesque, Emily M.; Massey, Philip

    2012-07-15

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

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

    NASA Technical Reports Server (NTRS)

    Engargiola, G.; Harper, D. A.

    1992-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

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

    SciTech Connect

    Pannuti, Thomas G.; Staggs, Wayne D.; Schlegel, Eric M.; Filipovic, Miroslav D.; Payne, Jeffrey L.; Petre, Robert

    2011-07-15

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

  2. A Search for Triggered Star Formation in the Compact Group of Galaxies NGC 5851, NGC 5852 and CGCG 077-007

    NASA Astrophysics Data System (ADS)

    Olsen, Charlotte Alexandra; Basu-Zych, Antara; Hornschemeier, Ann E.; NASA / GSFC X-ray Galaxies Group

    2017-01-01

    Galaxy interactions provide ideal conditions for triggering star formation, and impact galaxy evolution and the structure of the universe. The aim of this research is to study the key factors during galaxy interactions that influence star formation events by studying close pairs of galaxies to find the relationship between interaction properties (e.g. relative velocities and distances, mass ratios, orientation, and merger stage) and star formation rate (SFR). We present our analysis on one compact group of star-forming galaxies CGCG 077-007, NGC 5851, and their quiescent companion NGC 5852. Within this group we investigate the conditions where galaxy interactions cause higher SFR or supermassive black hole accretion (i.e. AGN activity), which might rather quench SFR. Areas of increased star formation are classified by the identification of the most UV bright regions within the galaxies. We find these areas by taking the Swift UVOT W2 filter and subtracting from it the Sloan Digital Sky Survey (SDSS) z-band image in order to remove the underlying stellar population. The regions identified by this process allow us to conduct a multi-wavelength study of stellar populations within this compact group. We use Spectral Energy Distribution models to fit ultraviolet to mid-infrared photometry from Swift UVOT, SDSS, 2MASS and WISE and measure global star formation histories for the galaxies and for the identified star forming regions within the galaxies. In the future we will include analysis of Swift XRT data to place constraints on AGN activity, and relate to the star formation history. This group serves as a pilot study and we will apply these methods to a sample of 30 galaxy groups and close pairs in order to investigate the relationship between galaxy interactions, SFR, and AGN activity and gain deeper insight into how mergers drive galaxy evolution.

  3. Planetary Nebulae in the Elliptical Galaxy NGC 821: Kinematics and Distance Determination

    NASA Astrophysics Data System (ADS)

    Teodorescu, A. M.; Méndez, R. H.; Bernardi, F.; Riffeser, A.; Kudritzki, R. P.

    2010-09-01

    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. Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

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

    NASA Astrophysics Data System (ADS)

    Brière, É.; Cantin, S.; Spekkens, K.

    2012-09-01

    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 Hα and [N II]λ6584 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.

  5. A search for Wolf-Rayet stars in active star forming regions of low mass galaxies - GR8, NGC 2366, IC 2574, and NGC 1569

    NASA Astrophysics Data System (ADS)

    Drissen, Laurent; Roy, Jean-Rene; Moffat, Anthony F. J.

    1993-10-01

    We report the detection, via narrow-band 4686 A filter imagery, of possible new Wolf-Rayet stars in the most massive giant H II regions of the irregular galaxies NGC 2366 and IC 2574. One stellar knot in the post-starburst galaxy NGC 1569 also appears to contain a weak excess of light at 4686 A. A similar search yielded negative results in the very low mass galaxy GR8. The strongest 4686 A excess is located close to the secondary eastern knot in the core of NGC 2366-I (NGC 2363). If this excess is of stellar origin, about five Wolf-Rayet stars of the luminous late-type can account for the excess emission. Nebular emission wraps around this cluster in the form of a shell. The putative Wolf-Rayet stars appear to be close to the center of the large expanding H II bubble discovered by Roy et al. (1991). A possible nebular origin of the 4686 A excess is also discussed.

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

    NASA Technical Reports Server (NTRS)

    Onken, Christopher A.; Peterson, Bradley M.

    2004-01-01

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

  7. The extent of CO in the early-type galaxy NGC 4472

    NASA Technical Reports Server (NTRS)

    Hutchtmeier, W. K.; Bregman, J. N.; Hogg, D. E.; Roberts, M. S.

    1994-01-01

    NGC 4472, and E/SO system, is the earliest type normal galaxy with detected CO emission, and here we present additional radio observations in the lines of CO(1-0) and CO(2-1) to determine the distribution and internal properties of this gas. The original detection is reconfirmed, but observations at five surrounding locations and at two other locations in the galaxy do not show the gas to be extended; the total H2 gas mass is estimated to be 4 x 10(exp 7) solar mass. A high CO(1-0)/CO(2-1) brightness temperature ratio is found (greater than 3), which is indicative of subthermal excitation of the CO(2-1) line that can occur at low gas temperatures and low gas densities. Also, upper limits are given for the CO(2-1) fluxes in four other early-type galaxies.

  8. Untangling the magnetic fields in spiral galaxy NGC 6946 with wide-band polarimetry

    NASA Astrophysics Data System (ADS)

    Williams, Anna; Heald, George; Wilcots, Eric M.; Gould Zweibel, Ellen

    2017-01-01

    We present 13 cm polarization observations of nearby spiral galaxy NGC 6946. These data provide a new perspective into the magnetic field structure of this galaxy. Previous observations show strong depolarization between 6 cm and 22 cm, and we show that the morphology of the 13 cm polarization bridges this gap. We combine all available high resolution polarization observations to fit models of the line of sight magnetic field structure across the disk. We find simple screens of Faraday rotation, differential Faraday rotation, and internal Faraday dispersion are insufficient to explain the observed depolarization, and present the results of the best fit models. We discuss how future broadband observations and improved models will help reconstruct the full 3D model of the magnetic field structure in the disks and haloes of galaxies.

  9. Applying the analytic theory of colliding ring galaxies

    NASA Astrophysics Data System (ADS)

    Struck, Curtis

    2010-04-01

    An analytic theory of the waves in colliding ring galaxies was presented some years ago, but the observations were not of sufficient quality then to make quantitative comparisons. Well-resolved observations of a few systems are now available to make such comparisons, and structure imaged in several dozen systems, derived from the recent compilation of Madore, Nelson and Petrillo and the Galaxy Zoo project, can further constrain the theory. Systems with two rings are especially useful for deriving such constraints. After examining the implications of recent observations of ring sizes and structure, I extend the analytic theory, investigate limiting cases and present several levels of approximation. The theory is especially simple in the case of nearly flat rotation curves. I present observational comparisons for a few systems, including Arp 10, the Cartwheel and AM 2136-492. The fit is quite good over a large range of cases. For the Cartwheel there are discrepancies, but the areas of disagreement are suggestive of additional factors, such as multiple collisions. A specific prediction of the theory in the case of nearly flat rotation curves is that the ratio of the outward velocities of successive rings approximately equals the ratio of ring sizes. Ring velocities are also shown to scale simply with local circular velocities in this limit.

  10. Distribution and kinematics of H I in the active elliptical galaxy NGC 1052

    SciTech Connect

    van Gorkom, J.H.; Knapp, G.R.; Raimond, E.; Faber, S.M.; Gallagher, J.S.

    1986-04-01

    The H I distribution in the active elliptical galaxy NGC 1052 has been mapped at a resolution of 1 arcmin with the VLA. The H I structure is about three times the size of the optical galaxy and is roughly perpendicular to its major axis. The H I has a circular velocity of approx.200 km/s, roughly constant with radius; the mass of the galaxy is 1.5 x 10/sup 11/ M/sub sun/ at a radius of 16 kpc (D = 13.4 Mpc), and the mass to blue luminosity ratio at this radius is M/L/sub B/ approx.15 M/sub sun//L/sub sun/. H I absorption is seen against the central radio continuum source, at both the systemic velocity and at redshifted velocities. The gas in NGC 1052, as in other ellipticals, has a rotation axis that is not aligned with the stellar rotation axis (the difference is 63/sup 0/) and a mean specific angular momentum that is considerably larger than that of the stars. The H I distribution is unusually irregular. In the southwest region of the galaxy, the distribution shows what appears to be a tidal tail, suggesting that the H I may have been acquired about 10/sup 9/ years ago. The presence of dust associated with the H I and the distribution and kinematics of the H I are consistent with capture of gas from a gas-rich dwarf or spiral. In the inner regions of the galaxy (r<5 kpc) the H I velocity field shows evidence of noncircular orbits and therefore possibly of a triaxial mass distribution for the galaxy. Alternatively the gas could be falling in toward the center.

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

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  13. The trace of the CNO cycle in the ring nebula NGC 6888

    SciTech Connect

    Mesa-Delgado, A.; Esteban, C.; García-Rojas, J.; Reyes-Pérez, J.; Morisset, C.; Bresolin, F.

    2014-04-20

    We present new results on the chemical composition of the Galactic ring nebula NGC 6888 surrounding the WN6(h) star WR136. The data are based on deep spectroscopical observations taken with the High Dispersion Spectrograph at the 8.2 m Subaru Telescope. The spectra cover the optical range from 3700 to 7400 Å. The effect of the CNO cycle is well-identified in the abundances of He, N, and O, while elements not involved in the synthesis such as Ar, S, and Fe present values consistent with the solar vicinity and the ambient gas. The major achievement of this work is the first detection of the faint C II λ4267 recombination line in a Wolf-Rayet nebula. This allows us to estimate the C abundance in NGC 6888 and therefore investigate for the first time the trace of the CNO cycle in a ring nebula around a Wolf-Rayet star. Although the detection of the C II line has a low signal-to-noise ratio, the C abundance seems to be higher than the predictions of recent stellar evolution models of massive stars. The Ne abundance also shows a puzzling pattern with an abundance of about 0.5 dex lower than the solar vicinity, which may be related to the action of the NeNa cycle. Attending to the constraints imposed by the dynamical timescale and the He/H and N/O ratios of the nebula, the comparison with stellar evolution models indicates that the initial mass of the stellar progenitor of NGC 6888 is between 25 M {sub ☉} and 40 M {sub ☉}.

  14. The Trace of the CNO Cycle in the Ring Nebula NGC 6888

    NASA Astrophysics Data System (ADS)

    Mesa-Delgado, A.; Esteban, C.; García-Rojas, J.; Reyes-Pérez, J.; Morisset, C.; Bresolin, F.

    2014-04-01

    We present new results on the chemical composition of the Galactic ring nebula NGC 6888 surrounding the WN6(h) star WR136. The data are based on deep spectroscopical observations taken with the High Dispersion Spectrograph at the 8.2 m Subaru Telescope. The spectra cover the optical range from 3700 to 7400 Å. The effect of the CNO cycle is well-identified in the abundances of He, N, and O, while elements not involved in the synthesis such as Ar, S, and Fe present values consistent with the solar vicinity and the ambient gas. The major achievement of this work is the first detection of the faint C II λ4267 recombination line in a Wolf-Rayet nebula. This allows us to estimate the C abundance in NGC 6888 and therefore investigate for the first time the trace of the CNO cycle in a ring nebula around a Wolf-Rayet star. Although the detection of the C II line has a low signal-to-noise ratio, the C abundance seems to be higher than the predictions of recent stellar evolution models of massive stars. The Ne abundance also shows a puzzling pattern with an abundance of about 0.5 dex lower than the solar vicinity, which may be related to the action of the NeNa cycle. Attending to the constraints imposed by the dynamical timescale and the He/H and N/O ratios of the nebula, the comparison with stellar evolution models indicates that the initial mass of the stellar progenitor of NGC 6888 is between 25 M ⊙ and 40 M ⊙. Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

  15. Molecular hydrogen maps of extended planetary nebulae - the Dumbbell, the Ring, and NGC 2346

    SciTech Connect

    Zuckerman, B.; Gatley, I.

    1988-01-01

    The 3.8-m United Kingdom Infrared Telecsope at Mauna Kea was used to obtain complete H2 maps of three extended planetary nebulae (PNs) that are representative of two of the most common PN morphologies, bow tie and bipolar ring: the Dumbbell (NGC 6853), the Ring (NGC 6720), and the NG 2346, are discussed. The results of map analysis indicates that the S(1) emission from H2 closely follows the optical morphology of the three nebulae. The H2 emission is more extended than the main emitting mass of ionized gas and, in NGCC 2346, there is evidence for a dense torus of hot H2 surrounding the central star. The H2 emissionl appears to be shock-excited. Examinations of existing H2 measurements indicate that strong H2 emission is preferentially present in PNs that lie at small galactic latitude, implying that massive main-sequence stars produce ionization-bounded PNs, whereas low-mass stars produce density-bounded PNs. Thus, maps of H2 emission may not only be used to determine whether a given PN is ionization-bounded or density-bounded, but also to estimate the mass of the progenitor star. 83 references.

  16. The Massive Black Hole in the Dwarf Galaxy NGC 4486B

    NASA Astrophysics Data System (ADS)

    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

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    Context. Rich globular cluster systems, particularly the metal-poor part of them, are thought to be the visible manifestations of long-term accretion processes. The invisible part is the dark matter halo, which may show some correspondence to the globular cluster system. It is therefore interesting to investigate the globular cluster systems of isolated elliptical galaxies, which supposedly have not experienced extended accretion. Aims: We investigate the globular cluster system of the isolated elliptical NGC 7796, present new photometry of the galaxy, and use published kinematical data to constrain the dark matter content. Methods: Deep images in B and R, obtained with the VIsible MultiObject Spectrograph (VIMOS) at the VLT, form the data base. We performed photometry with DAOPHOT and constructed a spherical photometric model. We present isotropic and anisotropic Jeans-models and give a morphological description of the companion dwarf galaxy. Results: The globular cluster system has about 2000 members, so it is not as rich as those of giant ellipticals in galaxy clusters with a comparable stellar mass, but richer than many cluster systems of other isolated ellipticals. The colour distribution of globular clusters is bimodal, which does not necessarily mean a metallicity bimodality. The kinematic literature data are somewhat inconclusive. The velocity dispersion in the inner parts can be reproduced without dark matter under isotropy. Radially anisotropic models need a low stellar mass-to-light ratio, which would contrast with the old age of the galaxy. A MONDian model is supported by X-ray analysis and previous dynamical modelling, but better data are necessary for a confirmation. The dwarf companion galaxy NGC 7796-1 exhibits tidal tails, multiple nuclei, and very boxy isophotes. Conclusions: NGC 7796 is an old, massive isolated elliptical galaxy with no indications of later major star formation events as seen frequently in other isolated ellipticals. Its

  18. Star formation histories across the interacting galaxy NGC 6872, the largest-known spiral

    SciTech Connect

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

    2014-11-01

    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 μm) 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.

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

    NASA Astrophysics Data System (ADS)

    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

    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 μm) 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.

  20. STAR Formation Histories Across the Interacting Galaxy NGC 6872, the Largest-Known Spiral

    NASA Technical Reports Server (NTRS)

    Eufrasio, Rafael T.; Dwek, E.; Arendt, RIchard G.; deMello, Duilia F.; Gadotti, DImitri A.; Urrutia-Viscarra, Fernanda; deOliveira, CLaudia Mendes; Benford, Dominic J.

    2014-01-01

    NGC6872, 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 micrometer) 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

     Hobby-Eberly Telescope (HET) spectroscopy is used to measure the velocity dispersion profile of the nearest prototypical cD galaxy, NGC 6166 in the cluster Abell 2199. We also present composite surface photometry from many telescopes. We confirm the defining feature of a cD galaxy; i.e., (we suggest), a halo of stars that fills the cluster center and that is controlled dynamically by cluster gravity, not by the central galaxy. Our HET spectroscopy shows that the velocity dispersion of NGC 6166 rises from σ ≃ 300 km s-1 in the inner r˜ 10\\prime\\prime to σ =865+/- 58 km s-1 at r ˜ 100″ in the cD halo. This extends published observations of an outward σ increase and shows for the first time that σ rises all the way to the cluster velocity dispersion of 819 ± 32 km s-1. We also observe that the main body of NGC 6166 moves at +206 ± 39 km s-1 with respect to the cluster mean velocity, but the velocity of the inner cD halo is ˜70 km s-1 closer to the cluster velocity. These results support our picture that cD halos consist of stars that were stripped from individual cluster galaxies by fast tidal encounters.  However, our photometry does not confirm the widespread view that cD halos are identifiable as an extra, low-surface-brightness component that is photometrically distinct from the inner, steep-Sérsic-function main body of an otherwise-normal giant elliptical galaxy. Instead, all of the brightness profile of NGC 6166 outside its core is described to ±0.037 V mag arcsec-2 by a single Sérsic function with index n≃ 8.3. The cD halo is not recognizable from photometry alone. This blurs the distinction between cluster-dominated cD halos and the similarly-large-Sérsic-index halos of giant, core-boxy-nonrotating ellipticals. These halos are believed to be accreted onto compact, high-redshift progenitors (“red nuggets”) by large numbers of minor mergers. They belong dynamically to their central galaxies. Still, cDs and core-boxy-nonrotating Es

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

    SciTech Connect

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

    2013-11-10

    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.

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

    SciTech Connect

    Imanishi, Masatoshi; Nakanishi, Kouichiro

    2013-09-15

    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.

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

    SciTech Connect

    Harrison, Sarah M.; /MIT /SLAC

    2006-09-11

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

  5. CHANG-ES. VII. Magnetic Outflows from the Virgo Cluster Galaxy NGC 4388

    NASA Astrophysics Data System (ADS)

    Damas-Segovia, A.; Beck, R.; Vollmer, B.; Wiegert, T.; Krause, M.; Irwin, J.; Weżgowiec, M.; Li, J.; Dettmar, R.-J.; English, J.; Wang, Q. D.

    2016-06-01

    We investigate the effects of ram pressure on the ordered magnetic field of a galaxy hosting a radio halo and strong nuclear outflows. New radio images in total and polarized intensity of the edge-on Virgo galaxy NGC 4388 were obtained within the CHANG-ES EVLA project. The unprecedented noise level reached allows us to detect striking new features of the ordered magnetic field. The nuclear outflow extends far into the halo to about 5 kpc from the center and is spatially correlated with the {{H}}α and X-ray emission. For the first time, the southern outflow is detected. Above and below both spiral arms we find extended blobs of polarized emission with an ordered field oriented perpendicular to the disk. The synchrotron lifetime of the cosmic-ray electrons (CREs) in these regions yields a mean outflow velocity of 270+/- 70 {km} {{{s}}}-1, in agreement with a galactic wind scenario. The observed symmetry of the polarized halo features in NGC 4388 excludes a compression of the halo gas by the ram pressure of the intracluster medium (ICM). The assumption of equilibrium between the halo pressure and the ICM ram pressure yields an estimate of the ICM density that is consistent with both the ICM density derived from X-ray observations and the recent Planck Sunyaev-Zel’dovich measurements. The detection of a faint radio halo around cluster galaxies could thus be used for an estimate of ICM ram pressure.

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

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

    SciTech Connect

    Park, Hong Soo; Lee, Myung Gyoon; Hwang, Ho Seong; Kim, Sang Chul; Arimoto, Nobuo; Yamada, Yoshihiko; Tamura, Naoyuki; Onodera, Masato E-mail: mglee@astro.snu.ac.kr E-mail: sckim@kasi.re.kr E-mail: yoshihiko.yamada@nao.ac.jp E-mail: monodera@phys.ethz.ch

    2012-11-10

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  9. Revisiting the Abundance Gradient in the Maser Host Galaxy NGC 4258

    NASA Astrophysics Data System (ADS)

    Bresolin, Fabio

    2011-03-01

    New spectroscopic observations of 36 H II regions in NGC 4258 obtained with the Gemini telescope are combined with existing data from the literature to measure the radial oxygen abundance gradient in this galaxy. The [O III]λ4363 auroral line was detected in four of the outermost targets (17-22 kpc from the galaxy center), allowing a determination of the electron temperature Te of the ionized gas. From the use of different calibrations of the R 23 abundance indicator, an oxygen abundance gradient of approximately -0.012 ± 0.002 dex kpc-1 is derived. Such a shallow gradient, combined with the difference in the distance moduli measured from the Cepheid period-luminosity relation by Macri et al. between two distinct fields in NGC 4258, would yield an unrealistically strong effect of metallicity on the Cepheid distances. This strengthens the suggestion that systematic biases might affect the Cepheid distance of the outer field. Evidence for a similar effect in the differential study of M33 by Scowcroft et al. is presented. A revision of the transformation between strong-line and Te -based abundances in Cepheid-host galaxies is discussed. In the Te abundance scale, the oxygen abundance of the inner field of NGC 4258 is found to be comparable with the LMC value. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência e Tecnologia (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).

  10. The extremely populated globular cluster system of the lenticular galaxy NGC 6861

    NASA Astrophysics Data System (ADS)

    Escudero, Carlos G.; Faifer, Favio R.; Bassino, Lilia P.; Calderón, Juan Pablo; Caso, Juan Pablo

    2015-05-01

    We present a photometric study of the globular cluster (GC) system associated with the lenticular galaxy (S0) NGC 6861, which is located in a relatively low density environment. It is based on Gemini/GMOS images in the filters g', r', i' of three fields, obtained under good seeing conditions. Analysing the colour-magnitude and colour-colour diagrams, we find a large number of GC candidates, which extend out to 100 kpc, and we estimate a total population of 3000 ± 300 GCs. Besides the well-known blue and red subpopulations, the colour distribution shows signs of the possible existence of a third subpopulation with intermediate colours. This could be interpreted as evidence of a past interaction or fusion event. Other signs of interactions presented by the galaxy are the non-concentric isophotes and the asymmetric spatial distribution of GC candidates with colours (g' - i')0 > 1.16. As observed in other galaxies, the red GCs show a steeper radial distribution than the blue GCs. In addition, the spatial distribution of these candidates exhibits strong signs of elongation. This feature is also detected in the intermediate subpopulation. On the other hand, the blue candidates show an excellent agreement with the X-ray surface brightness profile, outside 10 kpc. They also show a colour-luminosity relation (blue tilt), similar to that observed in other galaxies. A new distance modulus has been estimated through the blue subpopulation, which is in good agreement with the previous value obtained through the surface brightness fluctuation method. The specific frequency of NGC 6861 (S N = 10.6 ± 2.1) is probably one of the highest values obtained for an S0 galaxy so far.

  11. H I maps of S0 galaxies with polar rings

    SciTech Connect

    Van gorkom, J.H.; Schechter, P.L.; Kristian, J.

    1987-03-01

    VLA maps in the 21 cm line of neutral hydrogen have been obtained for three S0 galaxies with polar rings, and an upper limit on H I has been obtained for a fourth system. Polar rings span a continuum, ranging from those in which the H I seems to be in a relatively stable configuration, producing stars throughout its extent, to those in which the H I is very asymmetric, with stars forming only at the inner edge of an H I disk. A deep CCD image of MGC -5-7-1 shows arcs and filaments, some of which coincide with the likewise chaotic H I. If the system formed as the result of the merger of a gas-rich system with an S0 galaxy, the gas-rich system must have included considerable numbers of stars. 25 references.

  12. On the emission-line response to continuum variations in the Seyfert galaxy NGC 5548

    NASA Astrophysics Data System (ADS)

    Netzer, Hagai; Maoz, Dan

    1990-12-01

    The two optical monitoring groups which have recently attempted to ascertain the continuum and emission-line variations in the Seyfert galaxy NGC 5548 have reported apparently contradictory results for the delay of H-beta variations with respect to the continuum. The measurements of Clavel et al. (1991) are presently used to demonstrate that the emission-line lag behind continuum variations depends on the continuum variability time-scale in this object, in the sense that continuum variations with larger time-scales yield larger emission-line lags. Monte Carlo simulations are used to show that there is at least one possible model which can reproduce the two differing delays.

  13. Gravitational Instability of Nuclear Rings in Barred Galaxies

    NASA Astrophysics Data System (ADS)

    Kim, Woong-Tae; Moon, Sanghyuk

    2017-01-01

    Nuclear rings at centers of barred galaxies exhibit strong star formation activities. They are thought to undergo gravitational instability when sufficiently massive. We approximate them as rigidly-rotating isothermal objects and investigate their gravitational instability. Using a self-consistent field method, we first construct their equilibrium sequences specified by two parameters: alpha corresponding to the thermal energy relative to gravitational potential energy, and R_B measuring the ellipticity or ring thickness. The density distributions in the meridional plane are steeper for smaller alpha, and well approximated by those of infinite cylinders for slender rings. We also calculate the dispersion relations of nonaxisymmetric modes in rigidly-rotating slender rings with angular frequency Omega and central density rho_c. Rings with smaller are found more unstable with a larger unstable range of the azimuthal mode number. The instability is completely suppressed by rotation when Omega exceeds the critical value. The critical angular frequency is found to be almost constant at 0.7(G rho_c)^0.5 for alph > 0.01 and increases rapidly for smaller alpha . We apply our results to a sample of observed star-forming rings and confirm that rings without a noticeable azimuthal age gradient of young star clusters are indeed gravitationally unstable.

  14. A kinematic determination of the structure of the double ring planetary nebula NGC 2392, the Eskimo

    NASA Technical Reports Server (NTRS)

    O'Dell, C. R.; Weiner, Larry D.; Chu, You-Hua

    1990-01-01

    Slit spectra and existing 'velocity cube' data have been used to determine the structure of the double ring PN NGC 2392. The inner shell is a stellar wind-sculpted prolate spheroid with a ratio of axes of 2:1 and the approaching end of the long axis pointed 20 deg from the line of sight in P.A. = 200 deg. The outer ring is caused by an outer disk with density dropping off with distance from the central star and with distance from its plane, which is the same as the equatorial band of high density in the inner shell. The outer disk contains a ring of higher density knots at a distance of 16 arcsec and is losing material through free expansion, forming an outer envelope of increasing velocity. Forbidden S II spectra are used to determine the densities in all of the major regions of the nebula. It is argued that the filamentary cores at the centers of the knots seen in the outer ring originate in the sublimation of bodies formed at the same time as the parent star.

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

    NASA Astrophysics Data System (ADS)

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

    2009-10-01

    Aims: We aim to derive the chemical behavior of a significant sample of PNe and HII regions in the irregular galaxy NGC 6822. The selected objects are distributed in different zones of the galaxy. Our purpose is to obtain the chemical abundances of the present interstellar medium (ISM), represented by H ii regions, and the corresponding values at the time of formation of PNe. With these data the chemical homogeneity of NGC 6822 were tested and the abundance pattern given by H ii regions and PNe used as an observational constraint for computing chemical evolution models to infer the chemical history of NGC 6822. Methods: Due to the faintness of PNe and H ii regions in NGC 6822, to gather spectroscopic data with large telescopes is necessary. We obtained a well suited sample of spectra by employing VLT-FORS 2 and Gemini-GMOS spectrographs. Ionic and total abundances were calculated for the objects where electron temperatures could determined through the detection of [O iii] λ4363 or/and [N ii] λ5755 lines. A “simple” chemical evolution model was developed and the observed data were used to compute a model for NGC 6822 in order to infer a preliminary chemical history in this galaxy. Results: Confident determinations of He, O, N, Ne, S and Ar abundances were derived for a sample of 11 PNe and one H ii region. We confirm that the present ISM is chemically homogeneous, at least in the central 2 kpc of the galaxy, showing a value 12 + log O/H = 8.06 ± 0.04. From the abundance pattern of PNe, we identified two populations: a group of young PNe with abundances similar to H ii regions and a group of older objects with abundances a factor of two lower. A pair of extreme Type I PNe were found. No third dredge-up O enrichement was detected in PNe of this galaxy. The abundance determinations allow us to discuss the chemical behavior of the present and past ISM in NGC 6822. Our preliminary chemical evolution model predicts that an important gas-mass loss occurred during

  16. The old globular cluster system of the dIrr galaxy NGC 1427A in the Fornax cluster

    NASA Astrophysics Data System (ADS)

    Georgiev, I. Y.; Hilker, M.; Puzia, T. H.; Chanamé, J.; Mieske, S.; Goudfrooij, P.; Reisenegger, A.; Infante, L.

    2006-06-01

    We present a study of the old globular cluster (GC) population of the dwarf irregular galaxy NGC 1427A using multi-wavelength VLT observations in U,B,V,I, Hα and J bands under excellent observing conditions. We applied color and size selection criteria to select old GC candidates and made use of archival ACS images taken with the Hubble Space Telescope to reject contaminating background sources and blended objects from the GC candidates' list. The Hα observations were used to check for contamination due to compact, highly reddened young star clusters whose colors and sizes could mimic those of old GCs. After accounting for contamination we obtain a total number of 38±8 GC candidates with colors consistent with an old (~10 Gyr) and metal-poor (Z<0.4× Z⊙) population as judged by simple stellar population models. Our contamination analysis indicates that the density distribution of GCs in the outskirts of the Fornax central cD galaxy NGC 1399 may not be spherically symmetric. We derive a present-day specific frequency SN of 1.6 for NGC 1427A, a value significantly larger than what is observed in the Local Group dwarf irregular galaxies and comparable with the values found for the same galaxy types in the Virgo and Fornax clusters. Assuming a universal globular cluster luminosity function turnover magnitude, we derive a distance modulus to NGC 1427A of 31.01±0.21 mag which places it ˜3.2±2.5 (statistic)±1.6 (systematic) Mpc in front of the Fornax central cD galaxy NGC 1399. The implications of this result for the relationship between NGC 1427A and the cluster environment are briefly discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

    for heavier elements, confirm the deficiency of the interstellar medium (gas+dust) in the inner regions of NGC 205, which is predicted to contain at least >107 M⊙ of gas if we assume a reasonable star formation efficiency of 10 per cent and account for the mass return from planetary nebulae. In an attempt to explain the missing interstellar medium mass problem, we claim that efficient supernova feedback capable of expelling gas from the inner, star-forming regions to the outer regions and/or tidal interactions with M31 stripping the gas component from the galaxy provide the best explanation for the removal of a significant amount of gas and dust from NGC 205.

  18. Deep Photometry of Galaxies in the VEGAS Survey: The Case of NGC 4472

    NASA Astrophysics Data System (ADS)

    Spavone, M.

    The VST-VEGAS project is aimed at observing and studying a rich sample of nearby early-type galaxies in order to systematically characterize their properties over a wide baseline of sizes and out to the faint outskirts where data are rather scarce so far. The external regions of galaxies more easily retain signatures about the formation and evolution mechanisms which shaped them, as their relaxation time are longer, and they are more weakly influenced by processes such as mergers, secular evolution, central black hole activity, and supernova feedback on the ISM, which tend to level age and metallicity gradients. The collection of a wide photometric dataset of a large number of galaxies in various environmental conditions, may help to shed light on these questions. To this end VEGAS exploits the potential of the VLT Survey Telescope (VST) which provides high quality images of 1 deg2 field of view in order to satisfy both the requirement of high resolution data and the need of studying nearby, and thus large, objects. We present a detailed study of the surface photometry of the elliptical galaxy NGC4472 and of smaller ETGs in its field, performed by using new g and i bands images to constrain the formation history of this nearby giant galaxy, and to investigate the presence of very faint substructures in its surroundings.

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

    SciTech Connect

    Okuda, Takeshi; Iguchi, Satoru; Kohno, Kotaro

    2013-05-01

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

  20. X-ray observations of the Compton-thick Seyfert 2 galaxy, NGC 5643

    NASA Astrophysics Data System (ADS)

    Matt, G.; Bianchi, S.; Marinucci, A.; Guainazzi, M.; Iwawasa, K.; Jimenez Bailon, E.

    2013-08-01

    We present results from a ~55 ks long XMM-Newton observation of the obscured AGN, NGC 5643, performed in July 2009. A previous, shorter (about 10 ks) XMM-Newton observation in February 2003 had left two major issues open, the nature of the hard X-ray emission (Compton-thin vs. Compton-thick) and of the soft X-ray excess (photoionized vs. collisionally ionized matter). The new observation shows that the source is Compton-thick and that the dominant contribution to the soft X-ray emission is by photoionized matter (even if it is still unclear whether collisionally ionized matter may contribute as well). We also studied three bright X-ray sources that are in the field of NGC 5643. The ULX NGC 5643 X-1 was confirmed to be very luminous, even if more than a factor 2 fainter than in 2003. We then provided the first high-quality spectrum of the cluster of galaxies Abell 3602. The last source, CXOJ143244.5-442020, is likely an unobscured AGN, possibly belonging to Abell 3602.

  1. Stellar and ionized gas kinematics of the interacting Seyfert 1.9 galaxy NGC 2992

    NASA Astrophysics Data System (ADS)

    García-Lorenzo, B.; Arribas, S.; Mediavilla, E.

    2001-11-01

    Integral field spectroscopy in the central 16''x 12'' (2.4 kpc x 1.8 kpc, if H0 = 75 km s-1 Mpc-1) of the Seyfert 1.9 galaxy NGC 2992 has been obtained using the fibre system INTEGRAL. The data are mainly used to study the stellar and ionized gas kinematics. In spite of the photometric disruptions in the outer parts (r > 6 kpc) produced by the interaction with its close companion (NGC 2993), the present stellar velocity field shows regular rotation. The ionized gas presents several kinematically distinct components. Apart from the outflowing component already reported by other authors, we found an additional (high ionization) kinematic component which seems to be associated with the boundaries of the figure-of-eight-shaped emission detected in the 6 cm radio map. We locate the hidden nucleus in the apex of the biconical structure defined by the [O iii] emission, coincident with the outflow origin and with the center of the dust lane. We do not find any clear evidence of direct influence of the interaction in the kinematics of the stars or the ionized gas in the circumnuclear region of NGC 2992.

  2. Dust in the nuclei of the Seyfert galaxies Markarian 231 and NGC 4151

    SciTech Connect

    Jones, B.; Worrall, D.M.; Rodriguez-Espinosa, J.M.; Stein, W.A.

    1984-09-01

    Observations carried out with a 8-13 micron grating-spectrometer of Mrk 231 and NGC 4151 are reported. The Mrk 231 data can be fitted to various thermal dust emission models or a single power law, with dust extinction. In all the model fits, except for that of graphite and silicon carbide grain emission, a component of silicate absorption of optical depth of not more than 0.7 is required. Confirming published work, the absorption being at the redshift of the low-redshift absorption-line system is ruled out. The high values of silicate optical depth absorption do not give ratios to the galaxy's visual extinction which are comparable to those of galactic H II regions. Weak evidence for a 10-micron absorption feature in NGC 4151 is also reported. This is somewhat contrary to expectation, since the visual extinction of NGC 4151 is lower than that of Mrk 231, and since there is evidence to support a nonthermal rather than thermal dust origin for the infrared continuum emission. 46 references.

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

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Davidge, T. J.

    2010-12-01

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

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

    SciTech Connect

    Davidge, T. J.

    2010-12-10

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

  6. A New High Resolution JVLA Survey of the Fireworks Galaxy, NGC 6946

    NASA Astrophysics Data System (ADS)

    Lacey, Christina K.; Calbo, Zuzana Isabelle; Pannuti, Thomas; Stockdale, Christopher; Fries, Kelly E.

    2017-01-01

    A Jansky Very Large Array high resolution survey was undertaken at three wavelengths: 20 cm, 6 cm, and 3.6 cm of the Fireworks Galaxy, NGC 6946, which is a nearby, grand design spiral galaxy with a distance of ~5 Mpc. This new radio survey has a sensitivity of two - three times previous high resolution surveys. Analysis of the radio maps allow us to identify many new compact sources. We will present a preliminary analysis of the radio maps and discuss the nature of the identified compact sources, which are expected to be supernova remnants (SNRs), HII regions, and background sources. We will compare our source lists to a previous survey conducted in 1994.

  7. A Multiwavelength Study of Face-On Spiral Galaxy NGC 3631

    NASA Astrophysics Data System (ADS)

    Keddie-Hill, Crystal; Chomiuk, L.; Freeland, E.; Wilcots, E.

    2007-12-01

    We have undertaken a multiwavelength study of nearby face-on spiral galaxy NGC 3631. Data sets include 21 cm line data from the VLA with 14" resolution, radio continuum data at 6cm and 20 cm with 4" resolution, optical data from the WIYN 3.5m, and Chandra X-ray data. Preliminary results are interesting, including what appears to be a hole in the center of the galaxy in both the Hα and radio continuum images. There is also evidence of tidally removed HI near the edge of the disk. The research is ongoing and was supported in part by the REU and ASSURE programs through NSF award AST-0453442.

  8. Globular cluster clustering around ultra compact dwarf galaxies in the halo of NGC 1399

    NASA Astrophysics Data System (ADS)

    Voggel, Karina; Hilker, Michael; Richtler, Tom

    2016-08-01

    We tested the spatial distribution of UCDs and GCs in the halo of NGC 1399 in the Fornax cluster. In particular we tried to find out if globular clusters are more abundant in the vicinity of UCDs than what is expected from their global distribution. A local overabundance of globular clusters was found around UCDs on a scale of 1 kpc compared to what is expected from the large scale distribution of globulars in the host galaxy. This effect is stronger for the metal-poor blue GCs and weaker for the red GCs. An explanation for these clustered globulars is either that they are the remains of a GC system of an ancestor dwarf galaxy before it was stripped to its nucleus, which appears as UCD today. Alternatively these clustered GCs could have been originally part of a super star cluster complex.

  9. RED SUPERGIANTS AS COSMIC ABUNDANCE PROBES: THE SCULPTOR GALAXY NGC 300

    SciTech Connect

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

    2015-06-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

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

    SciTech Connect

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

    2013-09-20

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  13. TRANSIENT X-RAY SOURCE POPULATION IN THE MAGELLANIC-TYPE GALAXY NGC 55

    SciTech Connect

    Jithesh, V.; Wang, Zhongxiang

    2016-04-10

    We present the spectral and temporal properties of 15 candidate transient X-ray sources detected in archival XMM-Newton and Chandra observations of the nearby Magellanic-type, SB(s)m galaxy NGC 55. Based on an X-ray color classification scheme, the majority of the sources may be identified as X-ray binaries (XRBs), and six sources are soft, including a likely supernova remnant. We perform a detailed spectral and variability analysis of the data for two bright candidate XRBs. Both sources displayed strong short-term X-ray variability, and their X-ray spectra and hardness ratios are consistent with those of XRBs. These results, combined with their high X-ray luminosities (∼10{sup 38} erg s{sup −1}), strongly suggest that they are black hole (BH) binaries. Seven less luminous sources have spectral properties consistent with those of neutron star or BH XRBs in both normal and high-rate accretion modes, but one of them is the likely counterpart to a background galaxy (because of positional coincidence). From our spectral analysis, we find that the six soft sources are candidate super soft sources (SSSs) with dominant emission in the soft (0.3–2 keV) X-ray band. Archival Hubble Space Telescope optical images for seven sources are available, and the data suggest that most of them are likely to be high-mass XRBs. Our analysis has revealed the heterogeneous nature of the transient population in NGC 55 (six high-mass XRBs, one low-mass XRBs, six SSSs, one active galactic nucleus), helping establish the similarity of the X-ray properties of this galaxy to those of other Magellanic-type galaxies.

  14. The nature of the UV halo around the spiral galaxy NGC 3628

    NASA Astrophysics Data System (ADS)

    Baes, Maarten; Viaene, Sébastien

    2016-03-01

    Thanks to deep UV observations with GALEX and Swift, diffuse UV haloes have recently been discovered around galaxies. Based on UV-optical colours, it has been advocated that the UV haloes around spiral galaxies are due to UV radiation emitted from the disc and scattered off dust grains at high latitudes. Detailed UV radiative transfer models that take into account scattering and absorption can explain the morphology of the UV haloes, and they require the presence of an additional thick dust disc next the to traditional thin disc for half of the galaxies in their sample. We test whether such an additional thick dust disc agrees with the observed infrared emission in NGC 3628, an edge-on galaxy with a clear signature of a thick dust disc. We extend the far-ultraviolet radiative transfer models to full-scale panchromatic models. Our model, which contains no fine-tuning, can almost perfectly reproduce the observed spectral energy distribution from UV to mm wavelengths. These results corroborate the interpretation of the extended UV emission in NGC 3628 as scattering off dust grains, and hence of the presence of a substantial amount of diffuse extra-planar dust. A significant caveat, however, is the geometrical simplicity and non-uniqueness of our model: other models with a different geometrical setting could lead to a similar spectral energy distribution. More detailed radiative transfer simulations that compare the model results to images from UV to submm wavelengths are a way to break this degeneracy, as are UV polarisation measurements.

  15. Chemical abundances of the WR-ring nebulae NGC 2359 and RCW 78

    NASA Astrophysics Data System (ADS)

    Esteban, C.; Vilchez, J. M.; Manchado, A.; Edmunds, M. G.

    1989-07-01

    This paper reports on extensive spectroscopic observations of the WR-ring nebulae NGC 2359 and RCW 78, respectively, excited by the WN5 stars HD 56925 and WN8 HD 117688. For the first object, abundances were determined for O/H, Ne/H, N/H, and He/H in many different positions, including the ionized gas in the bubble, inside the optical shell structure, and the outermost zones associated with the S 298 H II region. No significant difference in the N/H and O/H abundances was found over the entire nebula. The O/H and N/H abundances expected are close to those for a normal H II region located at similar distance. In the case of He/H, indication is found of local enhancements which sum to the abundance of metal-rich galactic H II regions like M17. RCW 78 appears to show slight overabundances of He/H and N/H in the two observed positions. The ionizing temperature for the WN central star (HD 56925) of NGC 2359 is determined from the observed H II region spectrum giving a value of 50,000 K, appropriate to its spectral type.

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

    SciTech Connect

    Johnson, Megan; Hunter, Deidre A.; Zhang, Hong-Xin; Herrmann, Kimberly; Oh, Se-Heon; Elmegreen, Bruce; Brinks, Elias; Tollerud, Erik E-mail: dah@lowell.edu E-mail: herrmann@lowell.edu E-mail: bge@us.ibm.com E-mail: etolleru@uci.edu

    2012-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

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

  18. Discovery of a fast transient outflow in the Seyfert 1 galaxy NGC 985

    NASA Astrophysics Data System (ADS)

    Ebrero, J.; Kriss, J.; Kaastra, J.; Domcek, V.

    2016-06-01

    Obscuration events in active galaxies are key to understand the physical conditions and the dynamics of the gas in the vicinity of their central super-massive black hole. Using recent joint observations with XMM-Newton and the Hubble Space Telescope of the nearby Seyfert 1 galaxy NGC 985, we have monitored the pass-by of obscuring material across our line of sight, traveling at 6000 km/s. This kind of event has been recorded previously in only a handful of cases. The properties of this transient absorber suggest that it may originate very close to the broad line region, possibly in an accretion disk wind. Moreover, by analyzing past archival observations of NGC 985, we found evidence that this obscuration process is recurrent. The analysis of the RGS spectra of this source at different epochs reveals that some of the components of the persistent warm absorber vary in response to the changes in the ionizing flux caused by this transient obscurer. In this way, we are able to derive stringent upper limits on the location of the warm absorber.

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

    NASA Astrophysics Data System (ADS)

    Filippenko, Alex

    2010-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Filippenko, Alexei

    2010-09-01

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

  1. The Nuclear Stellar Dynamics of the S0 Galaxy NGC7332

    NASA Astrophysics Data System (ADS)

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

    1999-12-01

    STIS longslit spectroscopy of the nearby S0 galaxy NGC 7332 was obtained for the purpose of modeling the nuclear stellar dynamics and to search for evidence of a massive black hole. The primary stellar absorption features are the strong Ca II triplet lines at 8600 Angstroms. Stellar kinematical measurements characterizing the line-of-sight velocity distribution were extracted using the Fourier correlation quotient method (Bender 1990, A&Ap, 229, 441). Combined with ground-based imaging and spectroscopy (Fisher, Illingworth & Franx 1994, AJ, 107, 160) and HST WF/PC-1 imaging (Lauer et al. 1995, AJ, 110, 2622) these data were fitted with dynamical models developed by K. Gebhardt which included a compact massive dark object (MDO). We will discuss our results in the context of the relationship for spheroidal stellar systems between spheroid mass and the mass of the MDO, M, (see e.g. Kormendy & Richstone 1995, ARA&A, 33, 581). NGC 7332 is of particular interest since Magorrian et al. (1998, AJ, 115, 2285) find that of all the galaxies in their survey this one is most consistent with M=0 with an upper limit M<7*E6 Msun.

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  3. Ring Galaxy AM 0644-741 Captured by Hubble Space Telescope

    NASA Technical Reports Server (NTRS)

    2004-01-01

    Released to commemorate the 14th anniversary of NASA's Hubble Space Telescope (HST) is the image of a galaxy cataloged as AM 0644-741. Resembling a diamond encrusted bracelet, the ring of brilliant blue star clusters wraps around a yellowish nucleus of what was once a normal spiral galaxy. Located 300 million light years away in the direction of the southern constellation Dorado, the sparkling blue ring is 150,000 light years in diameter, making it larger than our entire home galaxy, the Milky Way. Ring galaxies are a striking example of how collisions between galaxies can dramatically change their structure, while triggering the formation of new stars. Typically one galaxy plunges directly into the disk of another one. The ring that pierced through this galaxy's ring is out of the image but is visible in larger-field images. The soft galaxy visible to the left of the ring galaxy is a coincidental background galaxy which is not interacting with the ring. Rampant star formation explains why the ring is so blue. It is continuously forming massive, young, hot stars. Another sign of robust star formation is the pink regions along the ring. These are rare clouds of glowing hydrogen gas, fluorescing because of the strong ultraviolet light from the newly formed stars. The Hubble Heritage Team used the Hubble Advanced Camera for Surveys to take this image using a combination of four separate filters that isolate blue, green, red, and near-infrared light to create the color image.

  4. Chandra Evidence for AGN Feedback in the Spiral Galaxy NGC 6764

    NASA Astrophysics Data System (ADS)

    Croston, J. H.; Hardcastle, M. J.; Kharb, P.; Kraft, R. P.; Hota, A.

    2008-11-01

    We report the Chandra detection of X-ray emission spatially coincident with the kiloparsec-scale radio bubbles in the nearby (DL ~ 31 Mpc) AGN-starburst galaxy NGC 6764. The X-ray emission originates in hot gas (kT ~ 0.75 keV), which may either be contained within the radio bubbles, or in a shell of hot gas surrounding them. We consider three models for the origin of the hot gas: (1) a starburst-driven galactic wind, (2) shocked gas associated with the expanding radio bubbles, and (3) gas heated and entrained into the bubbles by jet/ISM interactions in the inner AGN outflow. We rule out a galactic wind based on significant differences from known galactic wind systems. The tight correspondence between the brightest X-ray emission and the radio emission in the inner outflow from the Seyfert nucleus, as well as a correlation between X-ray and radio spectral features suggestive of shocks and particle acceleration, lead us to favor the third model; however, we cannot firmly rule out a model in which the bubbles are driving large-scale shocks into the galaxy ISM. In either AGN-driven heating scenario, the total energy stored in the hot gas is high, ~1056 ergs, comparable to the energetic impact of low-power radio galaxies such as Centaurus A, and will have a dramatic impact on the galaxy and its surroundings.

  5. Gas motions in the plane of the spiral galaxy NGC 3631

    NASA Astrophysics Data System (ADS)

    Fridman, A. M.; Khoruzhii, O. V.; Polyachenko, E. V.; Zasov, A. V.; Sil'chenko, O. K.; Moiseev, A. V.; Burlak, A. N.; Afanasiev, V. L.; Dodonov, S. N.; Knapen, J. H.

    2001-05-01

    The velocity field of the nearly face-on galaxy NGC 3631, derived from observations in the Hα line and Hi radio line, is analysed to study perturbations related to the spiral structure of the galaxy. We confirm our previous conclusion that the line-of-sight velocity field gives evidence of the wave nature of the observed two-armed spiral structure. Fourier analysis of the observed velocity field is used to determine the location of corotation of the spiral structure of this galaxy, and the radius of corotation Rc is found to be about 42arcsec, or 3.2kpc. The vector velocity field of the gas in the plane of the disc is restored, and, taking into account that we previously investigated vertical motions, we now have a full three-dimensional gaseous velocity field of the galaxy. We show clear evidence of the existence of two anticyclonic and four cyclonic vortices near corotation in a frame of reference rotating with the spiral pattern. The centres of the anticyclones lie between the observed spiral arms. The cyclones lie close to the observed spirals, but their centres are shifted from the maxima in brightness.

  6. Supernova Remnants in the Most Fertile Galaxy: NGC 6946

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  8. HUBBLE SERVES UP A GALAXY

    NASA Technical Reports Server (NTRS)

    2002-01-01

    What may first appear as a sunny side up egg is actually NASA Hubble Space Telescope's face-on snapshot of the small spiral galaxy NGC 7742. But NGC 7742 is not a run-of-the-mill spiral galaxy. In fact, this spiral is known to be a Seyfert 2 active galaxy, a type of galaxy that is probably powered by a black hole residing in its core. The core of NGC 7742 is the large yellow 'yolk' in the center of the image. The lumpy, thick ring around this core is an area of active starbirth. The ring is about 3,000 light-years from the core. Tightly wound spiral arms also are faintly visible. Surrounding the inner ring is a wispy band of material, which is probably the remains of a once very active stellar breeding ground. Credit: Hubble Heritage Team (AURA/STScI/NASA)

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

    SciTech Connect

    Bregman, Joel N.; Seitzer, Patrick; Cowley, C. R.; Miller, Matthew J.; Miller, Eric D.

    2013-03-20

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

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

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    Context. The galaxy NGC 4418 contains one of the most compact obscured nuclei within a luminous infrared galaxy (LIRG) in the nearby Universe. This nucleus contains a rich molecular gas environment and an unusually high ratio of infrared-to-radio luminosity (q-factor). The compact nucleus is powered by either a compact starburst or an active galactic nucleus (AGN). Aims: The aim of this study is to constrain the nature of the nuclear region (starburst or AGN) within NGC 4418 via very-high-resolution radio imaging. Methods: Archival data from radio observations using the European Very Long Baseline Interferometry Network (EVN) and Multi-Element Radio Linked Interferometer Network (MERLIN) interferometers are imaged. Sizes and flux densities are obtained by fitting Gaussian intensity distributions to the image. The average spectral index of the compact radio emission is estimated from measurements at 1.4 GHz and 5.0 GHz. Results: The nuclear structure of NGC 4418 visible with EVN and MERLIN consists of eight compact (<49 mas i.e. <8 pc) features spread within a region of 250 mas, i.e. 41 pc. We derive an inverted spectral index α ≥ 0.7 (Sν ∝ να) 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.

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

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The Space Telescope Imaging Spectrograph (STIS) simultaneously records, in unprecedented detail, the velocities of hundreds of gas knots streaming at hundreds of thousands of miles per hour from the nucleus of NGC 4151, thought to house a supermassive black hole. This is the first time the velocity structure in the heart of this object, or similar objects, has been mapped so vividly this close to its central black hole. The twin cones of gas emission are powered by the energy released from the supermassive black hole believed to reside at the heart of this Seyfert galaxy. The STIS data clearly show that the gas knots illuminated by one of these cones is rapidly moving towards us, while the gas knots illuminated by the other cone are rapidly receding. The images have been rotated to show the same orientation of NGC 4151. The figures show: WFPC2 (upper left) -- A Hubble Wide Field Planetary Camera 2 image of the oxygen emission (5007 Angstroms) from the gas at the heart of NGC 4151. Though the twin cone structure can be seen, the image does not provide any information about the motion of the oxygen gas. STIS OPTICAL (upper right) -- In this STIS spectral image of the oxygen gas, the velocities of the knots are determined by comparing the knots of gas in the stationary WFPC2 image to the horizontal location of the knots in the STIS image. STIS OPTICAL (lower right) -- In this false color image the two emission lines of oxygen gas (the weaker one at 4959 Angstroms and the stronger one at 5007 Angstroms) are clearly visible. The horizontal line passing through the image is from the light generated by the powerful black hole at the center of NGC 4151. STIS ULTRAVIOLET (lower left) -- This STIS spectral image shows the velocity distribution of the carbon emission from the gas in the core of NGC 4151. It requires more energy to make the carbon gas glow (CIV at 1549 Angstroms) than it does to ionize the oxygen gas seen in the other images. This means we expect that the

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

    NASA Technical Reports Server (NTRS)

    Whitmore, Bradley C.; Schweizer, Francois

    1995-01-01

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

  14. The Tip of the Red Giant Branch Distances to Typa Ia Supernova Host Galaxies. V. NGC 3021, NGC 3370, and NGC 1309 and the Value of the Hubble Constant

    NASA Astrophysics Data System (ADS)

    Jang, In Sung; Lee, Myung Gyoon

    2017-02-01

    We present final results of a program for the determination of the Hubble constant based on the calibration of the Type Ia supernovae (SNe Ia) using the Tip of the Red Giant Branch (TRGB). We report TRGB distances to three SN Ia host galaxies, NGC 3021, NGC 3370, and NGC 1309. We obtain F555W and F814W photometry of resolved stars from the archival Hubble Space Telescope data. Luminosity functions of red giant stars in the outer regions of these galaxies show the TRGB to be at F814W ≈ QT = 28.2 ∼ 28.5 mag. From these TRGB magnitudes and the revised TRGB calibration based on two distance anchors (NGC 4258 and the LMC) in Jang & Lee (2017; Paper IV), we derive the distances: {(m-M)}0=32.178+/- 0.033 for NGC 3021, 32.253 ± 0.041 for NGC 3370, and 32.471 ± 0.040 for NGC 1309. We update our previous results on the TRGB distances to five SN Ia host galaxies using the revised TRGB calibration. By combining the TRGB distance estimates to SN Ia host galaxies in this study with the SN Ia calibration provided by Riess et al. (2011), we obtain a value of the Hubble constant: H 0 = 71.66 ± 1.80(random) ± 1.88(systematic) km s‑1 Mpc‑1 (a 3.6% uncertainty including systematics) from all eight SNe, and H 0 = 73.72 ± 2.03 ± 1.94 km s‑1 Mpc‑1 (a 3.8% uncertainty) from six low-reddened SNe. We present our best estimate, H 0 = 71.17 ± 1.66 ± 1.87 km s‑1 Mpc‑1 (a 3.5% uncertainty) from six low-reddened SNe with the recent SN Ia calibration in Riess et al. (2016). This value is between those from the Cepheid calibrated SNe Ia and those from the Cosmic Microwave Background analysis, lowering the Hubble tension.

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Saniga, Metod

    1995-03-01

    It is demonstrated that the kinematic 'peculiarity' of the early Sab galaxy NGC 4826 can easily be understood in terms of the Abelian Higgs (AH) model of spiral galaxies. A cylindrically symmetric AH vorto-source (-sink) with a disk-to-bulge ratio Omega greater than 1 is discussed and the distributions of the diagonal components of the corresponding stress-energy tensor Tmu,nu are presented. It is argued that the sign-changing component Tphiphi could account for the existence of two counter-rotating gas disks while negative values of Trr imply inward gas motions as observed in the outer and transition regions of the galaxy.

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

    SciTech Connect

    Bogdan, Akos; Forman, William R.; Kraft, Ralph P.; Jones, Christine; Randall, Scott W.; Li Zhiyuan; Nulsen, Paul E. J.; Vikhlinin, Alexey; Blom, Christina; Zhang Zhongli; Zhuravleva, Irina; Churazov, Eugene; Schindler, Sabine

    2012-08-10

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  19. Deep Chandra Observations of NGC 1404: Cluster Plasma Physics Revealed by an Infalling Early-type Galaxy

    NASA Astrophysics Data System (ADS)

    Su, Yuanyuan; Kraft, Ralph P.; Roediger, Elke; Nulsen, Paul; Forman, William R.; Churazov, Eugene; Randall, Scott W.; Jones, Christine; Machacek, Marie E.

    2017-01-01

    The intracluster medium (ICM), as a magnetized and highly ionized fluid, provides an ideal laboratory to study plasma physics under extreme conditions that cannot be achieved on Earth. NGC 1404 is a bright elliptical galaxy that is being gas stripped as it falls through the ICM of the Fornax Cluster. We use the new Chandra X-ray observations of NGC 1404 to study ICM microphysics. The interstellar medium of NGC 1404 is characterized by a sharp leading edge, 8 kpc from the Galaxy center, and a short downstream gaseous tail. Contact discontinuities are resolved on unprecedented spatial scales (0.″5 = 45 pc) due to the combination of the proximity of NGC 1404, the superb spatial resolution of Chandra, and the very deep (670 ks) exposure. At the leading edge, we observe sub-kiloparsec-scale eddies generated by Kelvin–Helmholtz instability (KHI) and put an upper limit of 5% Spitzer on the isotropic viscosity of the hot cluster plasma. We also observe mixing between the hot cluster gas and the cooler galaxy gas in the downstream stripped tail, which provides further evidence of a low viscosity plasma. The assumed ordered magnetic fields in the ICM ought to be smaller than 5 μG to allow KHI to develop. The lack of an evident magnetic draping layer just outside the contact edge is consistent with such an upper limit.

  20. The Sérsic-Pastoriza galaxy NGC 1808. I. Radio-continuum, optical and H I observations.

    NASA Astrophysics Data System (ADS)

    Saikia, D. J.; Unger, S. W.; Pedlar, A.; Yates, G. J.; Axon, D. J.; Wolstencroft, R. D.; Taylor, K.; Gyldenkerne, K.

    1990-08-01

    The authors present radio-continuum observations made at high angular resolution with the VLA at 20, 6 and 2 cm of the central region of the Sérsic-Pastoriza galaxy NGC 1808. These observations reveal a population of compact radio sources, reminiscent of those found in the archetypal starburst galaxies M82 and NGC 253. The bulk of these compact features are not coincident with the optical hot-spots and are likely to be individual or unresolved groups of SNRs. The authors have also made H I observations of NGC 1808 with the VLA. Although this was primarily to search for unusual motions which may enable the authors to understand the nuclear activity, they also obtained information on the large-scale distribution and dynamics of gas in this system. The neutral hydrogen is largely concentrated in a central bar, with weak emission from the spiral arms. An absorption profile against the radio emission from the nuclear region shows two features straddling the systemic velocity. The velocity field of the galaxy is largely consistent with rotation although there is evidence of significant non-circular motions in the bar. The authors discuss any possible relationship between these non-circular motions and the starburst/nuclear activity in the central region of NGC 1808.

  1. A massive dense gas cloud close to the nucleus of the Seyfert galaxy NGC 1068

    NASA Astrophysics Data System (ADS)

    Furuya, Ray S.; Taniguchi, Yoshiaki

    2016-12-01

    Using the ALMA archival data of both 12CO (6-5) line and 689-GHz continuum emission towards the archetypical Seyfert galaxy, NGC 1068, we identified a distinct continuum peak separated by 15 pc from the nuclear radio component S1 in projection. The continuum flux gives a gas mass of ˜2 × 105 M⊙ and bolometric luminosity of ˜108 L⊙, leading to a star formation rate of ˜0.1 M⊙ yr-1. Subsequent analysis on the line data suggest that the gas cloud has a size of ˜10 pc, yielding to a mean H2 number density of ˜105 cm-3. We therefore refer to the gas as a "massive dense gas cloud": the gas density is high enough to form a "protostar cluster" with a stellar mass of ˜104 M⊙. We found that the gas stands at a unique position between galactic and extraglactic clouds in the diagrams of start formation rate (SFR) vs. gas mass proposed by Lada et al. (2012, ApJ, 745, 190) and surface density of gas vs. SFR density by Krumholz and McKee (2005, ApJ, 630, 250). All the gaseous and star-formation properties may be understood in terms of the turbulence-regulated star formation scenario. Since there are two stellar populations with ages of 300 Myr and 30 Myr in the 100 pc scale circumnulear region, we discuss that NGC 1068 has experienced at least three episodic star-formation events with the likelihood that the inner star-forming region is the younger. Together with several lines of evidence that the dynamics of the nuclear region is decoupled from that of the entire galactic disk, we discuss that the gas inflow towards the nuclear region of NGC 1068 may be driven by a past minor merger.

  2. The Spatial Distribution of the Young Stellar Clusters in the Star-forming Galaxy NGC 628

    NASA Astrophysics Data System (ADS)

    Grasha, K.; Calzetti, D.; Adamo, A.; Kim, H.; Elmegreen, B. G.; Gouliermis, D. A.; Aloisi, A.; Bright, S. N.; Christian, C.; Cignoni, M.; Dale, D. A.; Dobbs, C.; Elmegreen, D. M.; Fumagalli, M.; Gallagher, J. S., III; Grebel, E. K.; Johnson, K. E.; Lee, J. C.; Messa, M.; Smith, L. J.; Ryon, J. E.; Thilker, D.; Ubeda, L.; Wofford, A.

    2015-12-01

    We present a study of the spatial distribution of the stellar cluster populations in the star-forming galaxy NGC 628. Using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey), we have identified 1392 potential young (≲ 100 Myr) stellar clusters within the galaxy using a combination of visual inspection and automatic selection. We investigate the clustering of these young stellar clusters and quantify the strength and change of clustering strength with scale using the two-point correlation function. We also investigate how image boundary conditions and dust lanes affect the observed clustering. The distribution of the clusters is well fit by a broken power law with negative exponent α. We recover a weighted mean index of α ∼ -0.8 for all spatial scales below the break at 3.″3 (158 pc at a distance of 9.9 Mpc) and an index of α ∼ -0.18 above 158 pc for the accumulation of all cluster types. The strength of the clustering increases with decreasing age and clusters older than 40 Myr lose their clustered structure very rapidly and tend to be randomly distributed in this galaxy, whereas the mass of the star cluster has little effect on the clustering strength. This is consistent with results from other studies that the morphological hierarchy in stellar clustering resembles the same hierarchy as the turbulent interstellar medium.

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

    SciTech Connect

    Zschaechner, Laura K.; Rand, Richard J.; Heald, George H.; Gentile, Gianfranco; Kamphuis, Peter E-mail: rjr@phys.unm.edu E-mail: Gianfranco.Gentile@ugent.be

    2011-10-10

    We present 21 cm observations and models of the H I kinematics and distribution of NGC 4244, a nearby edge-on Scd galaxy observed as part of the Westerbork HALOGAS (Hydrogen Accretion in LOcal GAlaxieS) survey. Our models give insight into the H I kinematics and distribution with an emphasis on the potential existence of extraplanar gas as well as a negative gradient in rotational velocity with height above the plane of the disk (a lag). Our models yield strong evidence against a significantly extended halo and instead favor a warp component along the line of sight as an explanation for most of the observed thickening of the disk. Based on these models, we detect a lag of -9{sup +3}{sub -2} km s{sup -1} kpc{sup -1} in the approaching half and -9 {+-} 2 km s{sup -1} kpc{sup -1} in the receding half. This lag decreases in magnitude to -5 {+-} 2 km s{sup -1} kpc{sup -1} and -4 {+-} 2 km s{sup -1} kpc{sup -1} near a radius of 10 kpc in the approaching and receding halves, respectively. Additionally, we detect several distinct morphological and kinematic features including a shell that is probably driven by star formation within the disk.

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

    PubMed

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

    1999-09-23

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

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

    SciTech Connect

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

    2013-08-10

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

  6. CO(J = 3-2) on-the-fly mapping of the nearby spiral galaxies NGC 628 and NGC 7793: Spatially resolved CO(J = 3-2) star-formation law

    NASA Astrophysics Data System (ADS)

    Muraoka, Kazuyuki; Takeda, Miho; Yanagitani, Kazuki; Kaneko, Hiroyuki; Nakanishi, Kouichiro; Kuno, Nario; Sorai, Kazuo; Tosaki, Tomoka; Kohno, Kotaro

    2016-04-01

    We present the results of CO(J = 3-2) on-the-fly mappings of two nearby non-barred spiral galaxies, NGC 628 and NGC 7793, with the Atacama Submillimeter Telescope Experiment at an effective angular resolution of 25″. We successfully obtained global distributions of CO(J = 3-2) emission over the entire disks at a sub-kpc resolution for both galaxies. We examined the spatially resolved (sub-kpc) relationship between CO(J = 3-2) luminosities (L^' }_CO(3-2)) and infrared (IR) luminosities (LIR) for NGC 628, NGC 7793, and M 83, and compared it with global luminosities of a JCMT (James Clerk Maxwell Telescope) Nearby Galaxy Legacy Survey sample. We found a striking linear L^' }_CO(3-2)-LIR correlation over the four orders of magnitude, and the correlation is consistent even with that for ultraluminous IR galaxies and submillimeter-selected galaxies. In addition, we examined the spatially resolved relationship between CO(J = 3-2) intensities (ICO(3-2)) and extinction-corrected star formation rates (SFRs) for NGC 628, NGC 7793, and M 83, and compared it with that for Giant Molecular Clouds in M 33 and 14 nearby galaxy centers. We found a linear ICO(3-2)-SFR correlation with ˜1 dex scatter. We conclude that the CO(J = 3-2) star-formation law (i.e., linear L^' }_CO(3-2)-LIR and ICO(3-2)-SFR correlations) is universally applicable to various types and spatial scales of galaxies; from spatially resolved nearby galaxy disks to distant IR-luminous galaxies, within ˜1 dex scatter.

  7. NGC 4051 and the Nature of Narrow-Line Seyfert I Galaxies

    NASA Technical Reports Server (NTRS)

    Peterson, B. M.; McHardy, I. M.; Wilkes, B. J.

    2004-01-01

    We report on the results of a three-year program of coordinated X-ray and optical monitoring of the narrow-line Seyfert 1 galaxy NGC 4051. The principal results of this program are: (1) The H-beta emission line time lag and Doppler width yield a virial mass estimate of about 1.1 mission solar masses, at the extreme low end of AGN masses. A plausible adjustment for inclination effects increases this mass slightly to about 1.4 mission solar masses. (2) During the third year of this campaign, both the X-ray continuum and the He II 4686 line went into extremely low states, although the optical continuum and the H-beta broad line were both still present and variable. We suggest that the inner part of the accretion disk may have gone into an advection-dominated state, yielding little radiation from the hotter inner disk. (3) The He II 4686 line is almost five times as broad as H-beta, and it is strongly blueward asymmetric, as are the high-ionization UV lines recorded in archive spectra of NGC 4051. The data are consistent with the Balmer lines arising in a low-inclination disk-like configuration, and the high-ionization lines arising in an outflowing wind, of which we observe preferentially the near side.

  8. 12 and 20 micron imaging of the starburst galaxy NGC 253

    NASA Technical Reports Server (NTRS)

    Pina, R. K.; Jones, B.; Puetter, R. C.; Stein, W. A.

    1992-01-01

    The study presents 12- and 20-micron imaging of the starburst galaxy NGC 253 with a spatial resolution of 0.8 arcsec. A positional uncertainty of 1.6 arcsec in these images is estimated on the basis of previous ground-based mid-IR studies to determine the absolute position of the images. It is concluded that the proposed 'nucleus' of NGC 253, i.e., the dominant, bright, flat-spectrum radio source identified by Turner & Ho (1985) (TH 2), is not associated with the mid-IR peak, but rather is located 2.2 arcsec to the northeast. The mid-IR peak, IRS 1, is placed midway between TH 6 and TH 7. Several coincidences with the present 12-micron image are found: IRS 1 falls within 1 arcsec of the 2-micron peak; a second significantly weaker IR source, IRS 2, coincides with TH 2; and the brightest steep-spectrum 6-cm radio source, TH 9, coincides with a 'tongue' of emission extending to the southwest of IRS 1.

  9. Observational Manifestation of Chaos in the Gaseous Disk of the Grand Design Spiral Galaxy NGC 3631

    NASA Astrophysics Data System (ADS)

    Fridman, A. M.; Khoruzhii, O. V.; Polyachenko, E. V.

    2002-10-01

    The main goal of the paper is to demonstrate the presence of chaotic trajectories in the gaseous disk of a real spiral galaxy. As an example we have chosen NGC 3631. First, we show the stationarity of the 3-D velocity field restored from the observed line-of-sight velocity field of the gaseous disk. That allows to analyse behaviour of the trajectories of the fluid particles (gas clouds) in the disk, calculating the corresponding observed streamlines. We estimate the Lyapunov characteristic numbers using their independence of the metrics and show the existence of chaotic trajectories outside the vortices which are present in the velocity field, and in the vicinity of the saddle point. Related spectra of the stretching numbers for some trajectories are also calculated.

  10. EVN VLBI Imaging of the Jet in the Nucleus of the Barred Spiral Galaxy NGC 7479

    NASA Astrophysics Data System (ADS)

    Laine, Seppo J.; Momjian, Emmanuel; Krichbaum, Thomas; Beck, Rainer; Komossa, S.

    2017-01-01

    The nearby (D = 32 Mpc) barred spiral galaxy NGC 7479 hosts a remarkable jet-like radio continuum feature: bright, 12-kpc long in projection, and hosting an S-shaped, aligned magnetic field. The bending of the jet in 3-D is most easily explained by precession, with a jet age less than a million years. We have imaged the nucleus with European VLBI Network (EVN) observations at 6 and 18 cm. Here we report our tentative results on the search for nuclear jet emission on sub-arcsecond scales, including its alignment with the outer kpc-scale jet. We also describe the nature of the nucleus with the help of spectral index determination, brightness temperature limit and variability of the nucleus.

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

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  12. Hard X-Ray Emission of the Luminous Infrared Galaxy NGC 6240 as Observed by Nustar

    NASA Technical Reports Server (NTRS)

    Puccetti, S.; Comastri, A.; Bauer, F. E.; Brandt, W. N.; Fiore, F.; Harrison, F. A.; Luo, B.; Stern, D.; Urry, C. M.; Alexander, D. M.; Annuar, A.; Arévalo, P.; Balokovic, M.; Boggs, S. E.; Brightman, M.; Christensen, F. E.; Craig, W. W.; Gandhi, P.; Hailey, C. J.; Koss, M. J.; La Massa, S.; Marinucci, A.; Ricci, C.; Walton, D. J.; Zappacosta, L.; Zhang, W.

    2016-01-01

    We present a broadband (approx.0.3-70 keV) spectral and temporal analysis of NuSTAR observations of the luminous infrared galaxy NGC 6240 combined with archival Chandra, XMM-Newton, and BeppoSAX data. NGC 6240 is a galaxy in a relatively early merger state with two distinct nuclei separated by approx.1.5. Previous Chandra observations resolved the two nuclei and showed that they are both active and obscured by Compton-thick material. Although they cannot be resolved by NuSTAR, we were able to clearly detect, for the first time, both the primary and the reflection continuum components thanks to the unprecedented quality of the NuSTAR data at energies >10 keV. The NuSTAR hard X-ray spectrum is dominated by the primary continuum piercing through an absorbing column density which is mildly optically thick to Compton scattering (tau approx. = 1.2, NH approx. 1.5×10(exp 24)/sq cm. We detect moderately hard X-ray (>10 keV) flux variability up to 20% on short (15-20 ks) timescales. The amplitude of the variability is largest at approx..30 keV and is likely to originate from the primary continuum of the southern nucleus. Nevertheless, the mean hard X-ray flux on longer timescales (years) is relatively constant. Moreover, the two nuclei remain Compton-thick, although we find evidence of variability in the material along the line of sight with column densities NH < or = 2×10(exp 23)/sq cm over long (approx.3-15 yr) timescales. The observed X-ray emission in the NuSTAR energy range is fully consistent with the sum of the best-fit models of the spatially resolved Chandra spectra of the two nuclei.

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

    SciTech Connect

    Teodorescu, A. M.; Mendez, R. H.; Bernardi, F.; Thomas, J.; Das, P.; Gerhard, O. E-mail: mendez@ifa.hawaii.edu

    2011-07-20

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

  14. Transient X-Ray Sources in the Magellanic-type Galaxy NGC 4449

    NASA Astrophysics Data System (ADS)

    Jithesh, V.; Wang, Zhongxiang

    2017-02-01

    We report the identification of seven transient X-ray sources in the nearby Magellanic-type galaxy NGC 4449 using archival multi-epoch X-ray observations conducted with the Chandra, XMM-Newton, and Swift telescopes over the years 2001–2013. Among them, two sources are classified as supersoft X-ray sources (SSSs) because of their soft X-ray color; the rest of the sources are X-ray binaries (XRBs). Transient SSSs’ spectra can be fitted with a blackbody of effective temperature ∼80–105 eV, and luminosities were ≃ {10}37{--}{10}38 {erg} {{{s}}}-1 in 0.3–8 keV. These properties are consistent with the widely accepted model for SSSs, an accreting white dwarf with steady nuclear burning on its surface, and the SSS emission has also been observed in many post-nova systems. Detailed analysis of one sufficiently bright SSS revealed strong short-term variability, possibly showing a 2.3-hr periodic modulation, and long-term variability, detectable over 23 years with different X-ray telescopes before the year 2003. The X-ray properties of four other transients are consistent with neutron star or black hole binaries in their hard state, whereas the remaining source is most likely an XRB with a quasi-soft X-ray spectrum. Analysis of archival Hubble Space Telescope image data was also conducted, and multiple massive stars were found as possible counterparts. We conclude that the X-ray transient properties in NGC 4449 are similar to those in other Magellanic-type galaxies.

  15. Near-infrared polarimetry of the edge-on galaxy NGC 891

    SciTech Connect

    Montgomery, J. D.; Clemens, D. P. E-mail: clemens@bu.edu

    2014-05-01

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

  16. Chandra Reveals Heavy Obscuration and Circumnuclear Star Formation in Seyfert 2 Galaxy NGC 4968

    NASA Astrophysics Data System (ADS)

    LaMassa, Stephanie M.; Yaqoob, Tahir; Levenson, N. A.; Boorman, Peter; Heckman, Timothy M.; Gandhi, Poshak; Rigby, Jane R.; Urry, C. Megan; Ptak, Andrew F.

    2017-01-01

    We present the Chandra imaging and spectral analysis of NGC 4968, a nearby (z = 0.00986) Seyfert 2 galaxy. We discover extended (∼1 kpc) X-ray emission in the soft band (0.5–2 keV) that is neither coincident with the narrow line region nor the extended radio emission. Based on spectral modeling, it is linked to on-going star formation (∼2.6–4 M⊙ yr‑1). The soft emission at circumnuclear scales (inner ∼400 pc) originates from hot gas, with kT ∼ 0.7 keV, while the most extended thermal emission is cooler (kT ∼ 0.3 keV). We refine previous measurements of the extreme Fe Kα equivalent width in this source ({EW}={2.5}-1.0+2.6 {keV}), which suggests the central engine is completely embedded within Compton-thick levels of obscuration. Using physically motivated models fit to the Chandra spectrum, we derive a Compton-thick column density (NH > 1.25 × 1024 cm‑2) and an intrinsic hard (2–10 keV) X-ray luminosity of ∼3–8 × 1042 erg s‑1 (depending on the presumed geometry of the obscurer), which is over two orders of magnitude larger than that observed. The large Fe Kα EW suggests a spherical covering geometry, which could be confirmed with X-ray measurements above 10 keV. NGC 4968 is similar to other active galaxies that exhibit extreme Fe Kα EWs (i.e., >2 keV) in that they also contain on-going star formation. This work supports the idea that gas associated with nuclear star formation may increase the covering factor of the enshrouding gas and play a role in obscuring active galactic nuclei.

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

    PubMed

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

    2013-07-25

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

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

    SciTech Connect

    Johnson, Ria; Raychaudhury, Somak; Chakrabarty, Dalia; O'Sullivan, Ewan E-mail: D.Chakrabarty@warwick.ac.u

    2009-12-01

    We present the results of an X-ray mass analysis of the early-type galaxy NGC 4636, using Chandra data. We have compared the X-ray mass density profile with that derived from a dynamical analysis of the system's globular clusters (GCs). Given the observed interaction between the central active galactic nucleus and the X-ray emitting gas in NGC 4636, we would expect to see a discrepancy in the masses recovered by the two methods. Such a discrepancy exists within the central approx10 kpc, which we interpret as the result of non-thermal pressure support or a local inflow. However, over the radial range approx10-30 kpc, the mass profiles agree within the 1sigma errors, indicating that even in this highly disturbed system, agreement can be sought at an acceptable level of significance over intermediate radii, with both methods also indicating the need for a dark matter halo. However, at radii larger than 30 kpc, the X-ray mass exceeds the dynamical mass, by a factor of 4-5 at the largest disagreement. A Fully Bayesian Significance Test finds no statistical reason to reject our assumption of velocity isotropy, and an analysis of X-ray mass profiles in different directions from the galaxy center suggests that local disturbances at large radius are not the cause of the discrepancy. We instead attribute the discrepancy to the paucity of GC kinematics at large radius, coupled with not knowing the overall state of the gas at the radius where we are reaching the group regime (>30 kpc), or a combination of the two.

  19. NGC 6340: an old S0 galaxy with a young polar disc. Clues from morphology, internal kinematics, and stellar populations

    NASA Astrophysics Data System (ADS)

    Chilingarian, I. V.; Novikova, A. P.; Cayatte, V.; Combes, F.; Di Matteo, P.; Zasov, A. V.

    2009-09-01

    Context: Lenticular galaxies are believed to form by a combination of environmental effects and secular evolution. Aims: We study the nearby disc-dominated S0 galaxy NGC 6340 photometrically and spectroscopically to understand the mechanisms of S0 formation and evolution in groups. Methods: We use SDSS images to build colour maps and the light profile of NGC 6340, which we decompose using a three-component model including Sérsic and two exponential profiles. We also use Spitzer Space Telescope archival near-infrared images to study the morphology of regions containing warm interstellar medium and dust. Then, we re-process and re-analyse deep long-slit spectroscopic data for NGC 6340, applying a novel sky subtraction technique and recover its stellar and gas kinematics, distribution of age and metallicity with the NBursts full spectral fitting. Results: We obtain the profiles of internal kinematics, age, and metallicity out to >2 half-light radii. The three structural components of NGC 6340 are found to have distinct kinematic and stellar population properties. We see a kinematic misalignment between inner and outer regions of the galaxy. We confirm the old metal-rich centre and a wrapped inner gaseous polar disc (r˜ 1 kpc) having weak ongoing star formation, counter-rotating in projection with respect to the stars. The central compact pseudo-bulge of NGC 6340 looks very similar to compact elliptical galaxies. Conclusions: In accordance with the results of numerical simulations, we conclude that the properties of NGC 6340 can be explained as the result of a major merger of an early-type galaxy and a spiral galaxy that occurred about 12 Gyr ago. The intermediate exponential structure might be a triaxial pseudo-bulge formed by a past bar structure. The inner compact bulge could be the result of a nuclear starburst triggered by the merger. The inner polar disc appeared recently, 1/3-1/2 Gyr ago, as a result of another minor merger or cold gas accretion. Data points

  20. An extremely low gas-to-dust ratio in the dust-lane lenticular galaxy NGC 5485

    NASA Astrophysics Data System (ADS)

    Baes, Maarten; Allaert, Flor; Sarzi, Marc; De Looze, Ilse; Fritz, Jacopo; Gentile, Gianfranco; Hughes, Thomas M.; Puerari, Ivânio; Smith, Matthew W. L.; Viaene, Sébastien

    2014-10-01

    Evidence is mounting that a significant fraction of the early-type galaxy population contains substantial reservoirs of cold interstellar gas and dust. We investigate the gas and dust in NGC 5485, an early-type galaxy with a prominent minor-axis dust lane. Using new Herschel PACS and SPIRE imaging data, we detect 3.8 × 106 M⊙ of cool interstellar dust in NGC 5485, which is in stark contrast with the non-detection of the galaxy in sensitive H I and CO observations from the ATLAS3D consortium. The resulting gas-to-dust ratio upper limit is Mgas/Md < 14.5, almost an order of magnitude lower than the canonical value for the Milky Way. We scrutinize the reliability of the dust, atomic gas and molecular gas mass estimates, but these do not show systematic uncertainties that can explain the extreme gas-to-dust ratio. Also a warm or hot ionized gas medium does not offer an explanation. A possible scenario could be that NGC 5485 merged with an SMC-type metal-poor galaxy with a substantial CO-dark molecular gas component and that the bulk of atomic gas was lost during the interaction, but it remains to be investigated whether such a scenario is possible.

  1. Globular clusters as tracers of stellar bimodality in elliptical galaxies: the case of NGC 1399

    NASA Astrophysics Data System (ADS)

    Forte, Juan C.; Faifer, Favio; Geisler, Doug

    2005-02-01

    Globular cluster systems (GCSs) frequently show a bimodal distribution of cluster integrated colours. This work explores the arguments to support the idea that the same feature is shared by the diffuse stellar population of the galaxy they are associated with. The particular case of NGC 1399, one of the dominant central galaxies in the Fornax cluster, for which a new B surface brightness profile and (B-RKC) colours are presented, is discussed taking advantage of a recently published wide-field study of its GCS. The results show that the galaxy brightness profile and colour gradient, as well as the behaviour of the cumulative globular cluster specific frequency, are compatible with the presence of two dominant stellar populations, associated with the so-called `blue' and `red' globular cluster families. These globular families are characterized by different intrinsic specific frequencies (defined in terms of each stellar population): Sn= 3.3 +/- 0.3 in the case of the red globulars and Sn= 14.3 +/- 2.5 for the blue ones. We stress that this result does not necessarily conflict with recent works that point out a clear difference between the metallicity distribution of (resolved) halo stars and globulars when comparing their number statistics. The region within 0.5arcmin of the centre shows a deviation from the model profile (in both surface brightness and colour) that may be explained in terms of the presence of a bulge-like high-metallicity component. Otherwise, the model gives an excellent fit up to 12arcmin (or 66.5Kpc) from the centre, the galactocentric limit of our blue brightness profile. The inferred specific frequencies imply that, in terms of their associated stellar populations, the formation of the blue globulars took place with an efficiency about six times higher than that corresponding to their red counterparts. The similarity of the spatial distribution of the blue globulars with that inferred for dark matter, as well as with that of the X

  2. Starbursts in dwarf galaxies: A multiwavelength case study of NGC 625

    NASA Astrophysics Data System (ADS)

    Cannon, John Michael

    The results of a multiwavelength case study of the nearby dwarf starburst galaxy NGC 625 are presented. This low- mass galaxy hosts a massive starburst comparable in luminosity to 30 Doradus in the Large Magellanic Cloud; its proximity and high galactic latitude provide an ideal opportunity to investigate the starburst phenomenon and its impact on the ISM and IGM. We use Chandra, FUSE, HST, CTIO, ATCA, and VLA data to investigate the nature of the stellar population and multi-phase ISM. Our principal findings are summarized as follows: (1)Ground-based optical spectroscopy finds a prominent Wolf-Rayet (W-R) feature arising from the major starburst region, implying a brief burst duration (4 6 Myr); (2)A spatially resolved star formation history analysis using HST/WFPC2 data shows that the duration of the burst is actually much longer than the W-R features would imply (duration ≳ 50 Myr), and that the star formation has been widespread throughout the disk over this interval; (3)This extended starburst has input sufficient kinetic energy into the ISM to create a large-scale outflow; (4)H I observations from the ATCA show complex kinematics that are consistent with a minor-axis outflow of large amounts of neutral gas; (5)This outflow is verified by FUSE spectroscopy, where strong O VI coronal gas absorption is blueshifted with respect to the neutral and diffuse H2 absorption lines; (6)FUSE spectra also reveal an abundance offset between the neutral and nebular gas regions that may be a common component of the ISM of low-metallicity dwarf galaxies; (7)The ROSAT detection of diffuse soft x-ray emission is verified by new Chandra imaging of NGC 625; (8)VLA radio continuum data shows a thermal global spectral index and a mix of thermal and nonthermal indices for the individual major star formation regions, suggesting vigorous and (temporally and spatially) extended star formation throughout the disk. We interpret these results in the context of low-mass galaxy evolution

  3. Kinematic and stellar population properties of the counter-rotating components in the S0 galaxy NGC 1366

    NASA Astrophysics Data System (ADS)

    Morelli, L.; Pizzella, A.; Coccato, L.; Corsini, E. M.; Dalla Bontà, E.; Buson, L. M.; Ivanov, V. D.; Pagotto, I.; Pompei, E.; Rocco, M.

    2017-04-01

    Context. Many disk galaxies host two extended stellar components that rotate in opposite directions. The analysis of the stellar populations of the counter-rotating components provides constraints on the environmental and internal processes that drive their formation. Aims: The S0 NGC 1366 in the Fornax cluster is known to host a stellar component that is kinematically decoupled from the main body of the galaxy. Here we successfully separated the two counter-rotating stellar components to independently measure the kinematics and properties of their stellar populations. Methods: We performed a spectroscopic decomposition of the spectrum obtained along the galaxy major axis and separated the relative contribution of the two counter-rotating stellar components and of the ionized-gas component. We measured the line-strength indices of the two counter-rotating stellar components and modeled each of them with single stellar population models that account for the α/Fe overabundance. Results: We found that the counter-rotating stellar component is younger, has nearly the same metallicity, and is less α/Fe enhanced than the corotating component. Unlike most of the counter-rotating galaxies, the ionized gas detected in NGC 1366 is neither associated with the counter-rotating stellar component nor with the main galaxy body. On the contrary, it has a disordered distribution and a disturbed kinematics with multiple velocity components observed along the minor axis of the galaxy. Conclusions: The different properties of the counter-rotating stellar components and the kinematic peculiarities of the ionized gas suggest that NGC 1366 is at an intermediate stage of the acquisition process, building the counter-rotating components with some gas clouds still falling onto the galaxy. Based on observations made with ESO Telescopes at the La Silla-Paranal Observatory under programmes 075.B-0794 and 077.B-0767.

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

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2003-03-01

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

  7. NUSTAR Unveils a Heavily Obscured Low-luminosity Active Galactic Nucleus in the Luminous Infrared Galaxy NGC 6286

    NASA Astrophysics Data System (ADS)

    Ricci, C.; Bauer, F. E.; Treister, E.; Romero-Cañizales, C.; Arevalo, P.; Iwasawa, K.; Privon, G. C.; Sanders, D. B.; Schawinski, K.; Stern, D.; Imanishi, M.

    2016-03-01

    We report the detection of a heavily obscured active galactic nucleus (AGN) in the luminous infrared galaxy (LIRG) NGC 6286 identified in a 17.5 ks Nuclear Spectroscopic Telescope Array observation. The source is in an early merging stage and was targeted as part of our ongoing NuSTAR campaign observing local luminous and ultra-luminous infrared galaxies in different merger stages. NGC 6286 is clearly detected above 10 keV and by including the quasi-simultaneous Swift/XRT and archival XMM-Newton and Chandra data, we find that the source is heavily obscured (NH ≃(0.95-1.32) × 1024 cm-2) with a column density consistent with being Compton-thick (CT, {log}({N}{{H}}/{{cm}}-2)≥slant 24). The AGN in NGC 6286 has a low absorption-corrected luminosity (L2-10 keV ˜ 3-20 × 1041 erg s-1) and contributes ≲1% to the energetics of the system. Because of its low luminosity, previous observations carried out in the soft X-ray band (<10 keV) and in the infrared did not notice the presence of a buried AGN. NGC 6286 has multiwavelength characteristics typical of objects with the same infrared luminosity and in the same merger stage, which might imply that there is a significant population of obscured low-luminosity AGNs in LIRGs that can only be detected by sensitive hard X-ray observations.

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  9. High-Resolution Imaging in 3-mm and 0.8-mm Bands and Abundances of Shock/Dust Related Molecules Toward the Seyfert Galaxy NGC 1068 Observed with ALMA

    NASA Astrophysics Data System (ADS)

    Nakajima, T.; Takano, S.; Kohno, K.; Harada, N.; Herbst, E.; Tamura, Y.; Izumi, T.; Taniguchi, A.; Tosaki, T.

    2015-12-01

    We present the results of high-angular-resolution in 3-mm and 0.8-mm band observations with ALMA in cycle-0 toward one of the nearest galaxies with an active galactic nucleus (AGN), NGC 1068. The physical properties of CO isotopic species, CS, CN, and shock and dust related molecules such as HNCO, CH3CN, SO, and CH3OH were estimated using rotation diagrams. We discuss the chemistry of each species, and compare the fractional abundances in the circumnuclear disk (CND) and starburst ring with those of Galactic sources in order to study the overall characteristics.

  10. Monitoring the Remarkable Radio Spectral-Line/Continuum Outburst in Galaxy NGC 660

    NASA Astrophysics Data System (ADS)

    Salter, Christopher J.; Ghosh, Tapasi; Minchin, Robert F.; Momjian, Emmanuel

    2017-01-01

    A radio continuum and spectral-line outburst in galaxy NGC660 was serendipitously discovered by us at Arecibo in 2007/8. From Feb. 2013, roughly bi-monthly Arecibo spectral-line and continuum monitoring of this remarkable event has been performed, with 28 observing epochs completed to Auguast 2016. Variability of the continuum spectrum, and of the detailed OH emission/absorption spectra at 4660, 4750, and 4765 MHz have been followed over this period. The rapid changes seen in the molecular emission from the nuclear region of this galaxy are unprecedented. To delineate the physical model of this complicated starburst system further, we have supplemented this Arecibo monitoring by two epochs of milliarcsecond-resolution HSA line and continuum imaging, (with Arecibo in this VLBI array). The VLBI images reveal jet structure consistent with a recent nuclear outburst. The OH features show association with the outburst hotspots. Both the continuum and OH maser intensities have been steadily declining since peaking at mid-2011.

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

    NASA Astrophysics Data System (ADS)

    Carlqvist, Per

    2010-06-01

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

  12. Gas and Stellar Kinematics in the Giant Spiral Galaxy NGC 1961

    NASA Astrophysics Data System (ADS)

    Sacash, Brian; Pinkney, Jason

    2009-04-01

    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 aimed to measure the mass of the central supermassive black hole (SMBH). We have developed our own software for spectral extraction and for the fitting of absorption and emission lines. The program subtracts the absorption-line (stellar) component from the emission-line spectra to improve the fidelity of our emission line measurements. We present our line centroids (velocities), widths (velocity dispersions), and strengths for the most prominent emission lines (Hα, [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 tidal interaction or merger. We use the rotation curve and surface photometry to estimate the enclosed mass profile of the galaxy. The emission lines near the nucleus broaden indicating more intrinsic dispersion than expected for a cold, gas disk. We estimate the BH mass using simple gas disk models. However, the high dispersion and the asymmetry in its inner rotation curve suggest that this approach is unreliable.

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

    NASA Astrophysics Data System (ADS)

    Papadakis, I. E.; Lawrence, A.

    1995-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  15. SUBMILLIMETER LINE SPECTRUM OF THE SEYFERT GALAXY NGC 1068 FROM THE HERSCHEL-SPIRE FOURIER TRANSFORM SPECTROMETER

    SciTech Connect

    Spinoglio, Luigi; Pereira-Santaella, Miguel; Busquet, Gemma; Schirm, Maximilien R. P.; Wilson, Christine D.; Parkin, Tara J.; Glenn, Jason; Kamenetzky, Julia; Rangwala, Naseem; Maloney, Philip R.; Bendo, George J.; Madden, Suzanne C.; Boselli, Alessandro; Cooray, Asantha; Page, Mathew J.

    2012-10-20

    The first complete submillimeter spectrum (190-670 {mu}m) of the Seyfert 2 galaxy NGC 1068 has been observed with the SPIRE Fourier transform spectrometer on board the Herschel Space Observatory. The sequence of CO lines (J {sub up} = 4-13), lines from H{sub 2}O, the fundamental rotational transition of hydrogen fluoride, two o-H{sub 2}O{sup +} lines, and one line each from CH{sup +} and OH{sup +} have been detected, together with the two [C I] lines and the [N II] 205 {mu}m line. The observations in both single pointing mode with sparse image sampling and in mapping mode with full image sampling allow us to disentangle two molecular emission components, one due to the compact circumnuclear disk (CND) and one from the extended region encompassing the star-forming ring (SF-ring). Radiative transfer models show that the two CO components are characterized by densities of n(H{sub 2}) = 10{sup 4.5} and 10{sup 2.9} cm{sup -3} and temperatures of T {sub kin} = 100 K and 127 K, respectively. A comparison of the CO line intensities with the photodissociation region (PDR) and X-ray-dominated region (XDR) models, together with the other observational constraints, such as the observed CO surface brightness and the radiation field, indicates that the best explanation for the CO excitation of the CND is an XDR with a density of n(H{sub 2}) {approx} 10{sup 4} cm{sup -3} and an X-ray flux of 9 erg s{sup -1} cm{sup -2}, consistent with illumination by the active galactic nucleus, while the CO lines in the SF-ring are better modeled by a PDR. The detected water transitions, together with those observed with the Herschel PACS spectrometer, can be modeled by a large velocity gradient model with low temperature (T {sub kin} {approx} 40 K) and high density (n(H{sub 2}) in the range 10{sup 6.7}-10{sup 7.9} cm{sup -3}). The emission of H{sub 2}O{sup +} and OH{sup +} are in agreement with PDR models with cosmic-ray ionization. The diffuse ionized atomic component observed through the [N

  16. Submillimeter Line Spectrum of the Seyfert Galaxy NGC 1068 from the Herschel-SPIRE Fourier Transform Spectrometer

    NASA Astrophysics Data System (ADS)

    Spinoglio, Luigi; Pereira-Santaella, Miguel; Busquet, Gemma; Schirm, Maximilien R. P.; Wilson, Christine D.; Glenn, Jason; Kamenetzky, Julia; Rangwala, Naseem; Maloney, Philip R.; Parkin, Tara J.; Bendo, George J.; Madden, Suzanne C.; Wolfire, Mark G.; Boselli, Alessandro; Cooray, Asantha; Page, Mathew J.

    2012-10-01

    The first complete submillimeter spectrum (190-670 μm) of the Seyfert 2 galaxy NGC 1068 has been observed with the SPIRE Fourier transform spectrometer on board the Herschel Space Observatory. The sequence of CO lines (J up = 4-13), lines from H2O, the fundamental rotational transition of hydrogen fluoride, two o-H2O+ lines, and one line each from CH+ and OH+ have been detected, together with the two [C I] lines and the [N II] 205 μm line. The observations in both single pointing mode with sparse image sampling and in mapping mode with full image sampling allow us to disentangle two molecular emission components, one due to the compact circumnuclear disk (CND) and one from the extended region encompassing the star-forming ring (SF-ring). Radiative transfer models show that the two CO components are characterized by densities of n(H2) = 104.5 and 102.9 cm-3 and temperatures of T kin = 100 K and 127 K, respectively. A comparison of the CO line intensities with the photodissociation region (PDR) and X-ray-dominated region (XDR) models, together with the other observational constraints, such as the observed CO surface brightness and the radiation field, indicates that the best explanation for the CO excitation of the CND is an XDR with a density of n(H2) ~ 104 cm-3 and an X-ray flux of 9 erg s-1 cm-2, consistent with illumination by the active galactic nucleus, while the CO lines in the SF-ring are better modeled by a PDR. The detected water transitions, together with those observed with the Herschel PACS spectrometer, can be modeled by a large velocity gradient model with low temperature (T kin ~ 40 K) and high density (n(H2) in the range 106.7-107.9 cm-3). The emission of H2O+ and OH+ are in agreement with PDR models with cosmic-ray ionization. The diffuse ionized atomic component observed through the [N II] 205 μm line is consistent with previous photoionization models of the starburst. Herschel is an ESA space observatory with science instruments provided by

  17. Effects of environmental gas compression on the multiphase ISM and star formation . The Virgo spiral galaxies NGC 4501 and NGC 4567/68

    NASA Astrophysics Data System (ADS)

    Nehlig, F.; Vollmer, B.; Braine, J.

    2016-03-01

    The cluster environment can affect galaxy evolution in different ways: via ram pressure stripping or by gravitational perturbations caused by galactic encounters. Both kinds of interactions can lead to the compression of the interstellar medium (ISM) and its associated magnetic fields, causing an increase in the gas surface density and the appearance of asymmetric ridges of polarized radio continuum emission. New IRAM 30m HERA CO(2-1) data of NGC 4501, a Virgo spiral galaxy currently experiencing ram pressure stripping, and NGC 4567/68, an interacting pair of galaxies in the Virgo cluster, are presented. We find an increase in the molecular fraction where the ISM is compressed. The gas is close to self-gravitation in compressed regions. This leads to an increase in gas pressure and a decrease in the ratio between the molecular fraction and total ISM pressure. The overall Kennicutt Schmidt relation based on a pixel-by-pixel analysis at ~1.5 kpc resolution is not significantly modified by compression. However, we detected continuous regions of low molecular star formation efficiencies in the compressed parts of the galactic gas disks. The data suggest that a relation between the molecular star formation efficiency SFEH2 = SFR/M(H2) and gas self-gravitation (Rmol/Ptot and Toomre Q parameter) exists. Both systems show spatial variations in the star formation efficiency with respect to the molecular gas that can be related to environmental compression of the ISM. An analytical model was used to investigate the dependence of SFEH2 on self-gravitation. The model correctly reproduces the correlations between Rmol/Ptot, SFEH2, and Q if different global turbulent velocity dispersions are assumed for the three galaxies. We found that variations in the NH2/ICO conversion factor can mask most of the correlation between SFEH2 and the Toomre Q parameter. Dynamical simulations were used to compare the effects of ram pressure and tidal ISM compression. These models give direct

  18. Scale Lengths in Disk Surface Brightness as Probes of Dust Extinction in Three Spiral Galaxies: M51, NGC 3631, and NGC 4321

    NASA Astrophysics Data System (ADS)

    Beckman, J. E.; Peletier, R. F.; Knapen, J. H.; Corradi, R. L. M.; Gentet, L. J.

    1996-08-01

    We have measured the radial brightness distributions in the disks of three nearby face-on spiral galaxies, M51, NGC 3631, and NGC 4321 (M100), in the photometric bands B through I, with the addition of the K band for M51 only. The measurements were made by averaging azimuthally, in three modes, the two-dimensional surface brightness over the disks in photometric images of the objects in each band: (1) over each disk as a whole, (2) over the spiral arms alone, and (3) over the interarm zones alone. From these profiles, scale lengths were derived for comparison with schematic exponential disk models that incorporate interstellar dust. These models include both absorption and scattering in their treatment of radiative transfer. The model fits show that the arms exhibit greater optical depth in dust than the interarm zones. The average fraction of emitted stellar light in V that is extinguished by dust within 3 scale lengths of the center of each galaxy does not rise above 20% in any of them. We show that this conclusion is also valid for models with similar overall quantities of dust but in which this is concentrated in lanes. These can also account for the observed scale lengths and their variations.

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

    NASA Astrophysics Data System (ADS)

    Sahu, M. S.

    1998-09-01

    A Goddard High Resolution Spectrograph archival study of the interstellar absorption lines in the line of sight to the H i-rich, starburst dwarf galaxy NGC 1705 in the 1170 to 1740 Å range at ~120 km s^-1 resolution is presented. The absorption features arising because of photospheric lines are distinctly different from the interstellar lines: the photospheric lines are weak, broad (equivalent widths >1 Å), asymmetric, and centered around the systemic LSR velocity of NGC 1705 (~610 km s^-1). The interstellar lines consist of three relatively narrow components at LSR velocities of -20, 260, and 540 km s^-1, and include absorption by neutral atoms (N i lambda1200 triplet and O i lambda1302), singly ionized atoms (Si ii lambdalambda1190, 1193, 1260, 1304, and 1526, S ii lambda1253, C ii lambda1334, C ii^* lambda1336, Fe ii lambda1608, and Al ii lambda1670), and atoms in higher ionization states (Si iii lambda1206, Si iv lambdalambda1393, 1402, and C iv lambdalambda1548, 1550). The Si iv and C iv absorption features have both interstellar and photospheric contributions. In an earlier study, Sahu & Blades identified the absorption system at -20 km s^-1 with Milky Way disk/halo gas, and the 260 km s^-1 system with a small, isolated high-velocity cloud HVC 487, which is probably associated with Magellanic Stream gas. The 540 km s^-1 absorption system is associated with a kiloparsec-scale expanding, ionized supershell centered on the super-star cluster NGC 1705-1. The analysis presented in this paper consists of (1) a list of all interstellar absorption features with greater than 3 sigma significance and their measured equivalent widths, (2) plots of the lines in the various atomic species together with the results of nonlinear least-squares fit profiles to the observed data, and (3) unpublished 21 cm maps from the Wakker & van Woerden survey showing the large-scale H i distribution in the region near the NGC 1705 sight line and HVC 487. Furthermore, weak N i lambda1200

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  1. H I observations of the nearest starburst galaxy NGC 253 with the SKA precursor KAT-7

    NASA Astrophysics Data System (ADS)

    Lucero, D. M.; Carignan, C.; Elson, E. C.; Randriamampandry, T. H.; Jarrett, T. H.; Oosterloo, T. A.; Heald, G. H.

    2015-07-01

    We present H I observations of the Sculptor group starburst spiral galaxy NGC 253, obtained with the Karoo Array Telescope (KAT-7). KAT-7 is a pathfinder for the Square Kilometre Array precursor MeerKAT, under construction. The short baselines and low system temperature of the telescope make it very sensitive to large-scale, low-surface-brightness emission. The KAT-7 observations detected 33 per cent more flux than previous Very Large Array observations, mainly in the outer parts and in the halo for a total H I mass of 2.1 ± 0.1 × 109 M⊙. H I can be found at large distances perpendicular to the plane out to projected distances of ˜9-10 kpc away from the nucleus and ˜13-14 kpc at the edge of the disc. A novel technique, based on interactive profile fitting, was used to separate the main disc gas from the anomalous (halo) gas. The rotation curve (RC) derived for the H I disc confirms that it is declining in the outer parts, as seen in previous optical Fabry-Perot measurements. As for the anomalous component, its RC has a very shallow gradient in the inner parts and turns over at the same radius as the disc, kinematically lagging by 100 km s-1. The kinematics of the observed extra-planar gas is compatible with an outflow due to the central starburst and galactic fountains in the outer parts. However, the gas kinematics shows no evidence for inflow. Analysis of the near-IR WISE data, shows clearly that the star formation rate is compatible with the starburst nature of NGC 253.

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

    SciTech Connect

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

    2007-02-12

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

  3. A remarkable double-ring galaxy in the cluster Abell 2199

    SciTech Connect

    Pence, W.D.; Oegerle, W.; Borne, K.D. )

    1990-12-01

    B and R CCD images have been obtained of the morphologically peculiar galaxy A1627 + 39, which lies near the center of the rich cluster of galaxies A2199. The galaxy is determined to be a nearly face-on barred S0 galaxy containing two nonconcentric rings. The rings are quite unusual in that they are displaced in opposite directions from the galactic center. There is no color difference across the rings, indicating no recent burst of star formation. Two hypotheses for the origin of the rings have been investigated: (1) a resonance effect with the central bar, and (2) the result of an off-axis, deeply penetrating collision with another cluster member. Models of such a collision are presented, which can reproduce the observed rings. However, neither hypothesis can provide a completely satisfactory explanation of all the observations reported here. 32 refs.

  4. The SLUGGS survey: multipopulation dynamical modelling of the elliptical galaxy NGC 1407 from stars and globular clusters

    NASA Astrophysics Data System (ADS)

    Pota, Vincenzo; Romanowsky, Aaron J.; Brodie, Jean P.; Peñarrubia, Jorge; Forbes, Duncan A.; Napolitano, Nicola R.; Foster, Caroline; Walker, Matthew G.; Strader, Jay; Roediger, Joel C.

    2015-07-01

    We perform in-depth dynamical modelling of the luminous and dark matter (DM) content of the elliptical galaxy NGC 1407. Our strategy consists of solving the spherical Jeans equations for three independent dynamical tracers: stars, blue globular clusters (GCs) and red GCs in a self-consistent manner. We adopt a maximum-likelihood Markov Chain Monte Carlo fitting technique in the attempt to constrain the inner slope of the DM density profile (the cusp/core problem), and the stellar initial mass function (IMF) of the galaxy. We find the inner logarithmic slope of the DM density profiles to be γ = 0.6 ± 0.4, which is consistent with either a DM cusp (γ = 1) or with a DM core (γ = 0). Our findings are consistent with a Salpeter IMF, and marginally consistent with a Kroupa IMF. We infer tangential orbits for the blue GCs, and radial anisotropy for red GCs and stars. The modelling results are consistent with the virial mass-concentration relation predicted by Λ cold dark matter (CDM) simulations. The virial mass of NGC 1407 is log Mvir = 13.3 ± 0.2M⊙, whereas the stellar mass is log M* = 11.8 ± 0.1 M⊙. The overall uncertainties on the mass of NGC 1407 are only 5 per cent at the projected stellar effective radius. We attribute the disagreement between our results and previous X-ray results to the gas not being in hydrostatic equilibrium in the central regions of the galaxy. The halo of NGC 1407 is found be DM-dominated, with a dynamical mass-to-light ratio of M/L=260_{-100} ^{+174} M_{⊙}/L_{⊙, B}. However, this value can be larger up to a factor of 3 depending on the assumed prior on the DM scale radius.

  5. Dynamics of the NGC 4636 globular cluster system. An extremely dark matter dominated galaxy?

    NASA Astrophysics Data System (ADS)

    Schuberth, Y.; Richtler, T.; Dirsch, B.; Hilker, M.; Larsen, S. S.; Kissler-Patig, M.; Mebold, U.

    2006-11-01

    Context: .We present the first dynamical study of the globular cluster system of NGC 4636. It is the southernmost giant elliptical galaxy of the Virgo cluster and is claimed to be extremely dark matter dominated, according to X-ray observations. Aims: .Globular clusters are used as dynamical tracers to investigate, by stellar dynamical means, the dark matter content of this galaxy. Methods: .Several hundred medium resolution spectra were acquired at the VLT with FORS 2/MXU. We obtained velocities for 174 globular clusters in the radial range 0.90 arcmin < R < 15.5 arcmin, or 0.5-9~Re in units of effective radius. Assuming a distance of 15 Mpc, the clusters are found at projected galactocentric distances in the range 4 to 70 kpc, the overwhelming majority within 30 kpc. The measured line-of-sight velocity dispersions are compared to Jeans-models. Results: .We find some indication of a rotation of the red (metal-rich) clusters about the minor axis. Out to a radius of 30 kpc, we find a roughly constant projected velocity dispersion for the blue clusters of σ ≈ 200~km s-1. The red clusters are found to have a distinctly different behavior: at a radius of about 3', the velocity dispersion drops by ~50~km s-1 to about 170~km s-1, which then remains constant out to a radius of 7'. The cause might be the steepening of the number density profile at ~3' observed for the red clusters. Using only the blue clusters as dynamical tracers, we perform Jeans-analyses for different assumptions of the orbital anisotropy. Enforcing the model dark halos to be of the NFW type, we determine their structural parameters. Depending on the anisotropy and the adopted M/L-values, we find that the dark matter fraction within one effective radius can vary between 20% and 50%, with most a probable range between 20% and 30%. The ambiguity of the velocity dispersion in the outermost bin is a main source of uncertainty. A comparison with cosmological N-body simulations reveals no striking

  6. MRK 1216 and NGC 1277 - an orbit-based dynamical analysis of compact, high-velocity dispersion galaxies

    NASA Astrophysics Data System (ADS)

    Yıldırım, Akın; van den Bosch, Remco C. E.; van de Ven, Glenn; Husemann, Bernd; Lyubenova, Mariya; Walsh, Jonelle L.; Gebhardt, Karl; Gültekin, Kayhan

    2015-09-01

    We present a dynamical analysis to infer the structural parameters and properties of the two nearby, compact, high-velocity dispersion galaxies MRK 1216 and NGC 1277. Combining deep Hubble Space Telescope imaging, wide-field integral field unit stellar kinematics, and complementary long-slit spectroscopic data out to three effective radii, we construct orbit-based models to constrain their black hole masses, dark matter content and stellar mass-to-light ratios. We obtain a black hole mass of log(M•/M⊙) = 10.1_{-0.2}^{+0.1} for NGC 1277 and an upper limit of log(M•/M⊙) = 10.0 for MRK 1216, within 99.7 per cent (3σ) confidence. The stellar mass-to-light ratios span a range of ΥV = 6.5_{-1.5}^{+1.5} in NGC 1277 and ΥH = 1.8_{-0.8}^{+0.5} in MRK 1216 and are in good agreement with single stellar population models of a single power-law Salpeter initial mass function. Even though our models do not place strong constraints on the dark halo parameters, they suggest that dark matter is a necessary ingredient in MRK 1216, with a dark matter contribution of 22^{+30}_{-20} per cent to the total mass budget within one effective radius. NGC 1277, on the other hand, can be reproduced without the need for a dark halo, and a maximal dark matter fraction of 13 per cent within the same radial extent. In addition, we investigate the orbital structures of both galaxies, which are rotationally supported and consistent with photometric multi-Sérsic decompositions, indicating that these compact objects do not host classical, non-rotating bulges formed during recent (z ≤ 2) dissipative events or through violent relaxation. Finally, both MRK 1216 and NGC 1277 are anisotropic, with a global anisotropy parameter δ of 0.33 and 0.58, respectively. While MRK 1216 follows the trend of fast-rotating, oblate galaxies with a flattened velocity dispersion tensor in the meridional plane of the order of βz ˜ δ, NGC 1277 is highly tangentially anisotropic and seems to belong

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

    NASA Astrophysics Data System (ADS)

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

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

  8. Multi-Wavelength Observations of the Supernova Remnant Populations in the Nearby Spiral Galaxies IC 342 and NGC 4258

    NASA Astrophysics Data System (ADS)

    Pannuti, Thomas; Chomiuk, L.; Grimes, C. K.; Staggs, W. D.; Tussey, J. M.; Laine, S.; Schlegel, E.

    2011-01-01

    Supernova remnants (SNRs) are intimately tied to many crucial processes associated with the interstellar medium of galaxies, such as the acceleration of cosmic-ray particles and the deposition of vast amounts of kinetic energy and chemically-enriched material. Well-known observational challenges in the study of SNRs located in the Milky Way Galaxy (for example, formidable extinction along Galactic lines of sight and considerable uncertainties in the distances to these sources) have motivated searches for SNRs in nearby galaxies at such characteristic wavelengths as X-ray, optical and radio. These searches have revealed a considerable number of SNRs and led to new insights into their properties, but the SNR populations in only a handful of nearby galaxies have been adequately surveyed at multiple wavelengths. To help remedy this situation, we are conducting a multi-wavelength study of the SNR population of selected nearby galaxies. To illustrate our work, we present the results of studies of the SNR population in two nearby spiral galaxies, IC 342 and NGC 4258. Our results draw upon the analysis of pointed archival radio and X-ray observations of these two galaxies. Initial results will be presented and discussed.

  9. SN 2006gy: An Extremely Luminous Supernova in the Galaxy NGC 1260

    NASA Astrophysics Data System (ADS)

    Ofek, E. O.; Cameron, P. B.; Kasliwal, M. M.; Gal-Yam, A.; Rau, A.; Kulkarni, S. R.; Frail, D. A.; Chandra, P.; Cenko, S. B.; Soderberg, A. M.; Immler, S.

    2007-04-01

    With an extinction-corrected V-band peak absolute magnitude of about -22, supernova SN 2006gy is probably the brightest SN ever observed. We report on multiwavelength observations of this SN and its environment. Our spectroscopy shows an Hα emission line as well as absorption features that may be identified as Si II lines at low expansion velocity. The slow brightening, the peak luminosity, and the Hα emission line resemble those observed in hybrid Type IIn/Ia SNe (also known as Type IIa) and may suggest that SN 2006gy is related to the Type IIa SNe class. The host galaxy, NGC 1260, is dominated by an old stellar population with solar metallicity. However, our high-resolution adaptive optics images reveal a dust lane in this galaxy, and there appears to be an H II region in the vicinity of the SN. The extraordinarily large peak luminosity, ~3 × 1044 ergs s-1, demands a dense circumstellar medium, regardless of the mass of the progenitor star. The inferred mass-loss rate of the progenitor is ~0.1 Msolar yr-1 over a period of ~10 yr prior to explosion. Such an high mass-loss rate may be the result of a binary star common envelope ejection. The total radiated energy in the first 2 months is about 1.1 × 1051 ergs, which is only a factor of 2 less than that available from a super-Chandrasekhar Type Ia explosion. Therefore, given the presence of a star-forming region in the vicinity of the SN and the high-energy requirements, a plausible scenario is that SN 2006gy is related to the death of a massive star.

  10. A non-thermal study of the brightest cluster galaxy NGC 1275 - the Gamma-Radio connection over four decades

    NASA Astrophysics Data System (ADS)

    Dutson, K. L.; Edge, A. C.; Hinton, J. A.; Hogan, M. T.; Gurwell, M. A.; Alston, W. N.

    2014-08-01

    Emission from the active nucleus in the core of the brightest cluster galaxy of the Perseus cluster, NGC 1275, has varied dramatically over the past four decades. Prompted by the Fermi detection of flaring in the γ-ray band, we present the recent increased activity of this source in the context of its past radio and γ-ray output. The broad correspondence between the high-frequency radio data and the high-energy (HE) emission is striking. However, on short time-scales this correlation breaks down and the 1.3 mm Submillimeter Array flux is apparently unaffected during Fermi -detected flaring activity. The fact that NGC 1275 is also detected at TeV energies during the periods of HE γ-ray flaring suggests that the short-time-scale variation might be primarily related to changes in the inverse Compton scattering of photons by the electron population in the jet. The longer-time-scale changes suggest a 30-40 year variation in the fuelling of the black hole that affects the power of the inner jet. NCG 1275 is a laboratory for the class of brightest cluster galaxies, and its variability on these time-scales has implications for our understanding of massive galaxies in cooling-core clusters. The case of NGC 1275 highlights the need for wide coverage across the radio band to correctly account for the contribution to emission from a synchrotron self-absorbed core (for example when considering contamination of Sunyaev-Zel'dovich effect observations), and the danger of variability biases in radio surveys of galaxies.

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

    NASA Technical Reports Server (NTRS)

    Bregman, Joel N.; Pidis, Rachel A.

    1994-01-01

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

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

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This is an illustration of how the night sky might look to a dweller in the core of galaxy NGC 4261, which harbors an 800-light-year-wide disk of dust and 1.2 billion-solar-mass black hole. This imaginary view is from a hypothetical planet inside the dust dusk, looking toward the black hole. The black hole's white-hot glow from super-heated gas is reddened by intervening dust. A 'lighthouse beam' from the hot accretion disk around the black hole, along with invisible radio jets, radiates above and below the hole at right angles to the dark dust disk encircling the hole. This dark, dusty disk bisects the sky, blocking out light from the star behind it, and reddening starlight traveling near it by optical scattering - much in the same way the sunlight turns red at sunset by scatter from dust in our atmosphere. The imaginary planet, and surrounding stars, are destined to be swallowed by the black hole, and material in the disk spirals into its gravitational abyss. Illustration by J. Gitlin (Space Telescope Science Institute)

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1983-12-01

    New, high sensitivity VLA maps of the central regions of NGC 1068 at 4.9 GHz (total intensity and linear polarization) and 15.0 GHz (total intensity only) are presented. As found by van der Hulst, Hummel, and Dickey (1982), the bright radio emission coincident with the galaxy nucleus is resolved into a bent triple of total extent 0.7 arcsec, with the central source apparently associated with the nucleus proper. It is found that the 13 arcsec scale linear source comprises oppositely directed radio jets feeding a 'hot spot' and radio lobes. The radio emission of the NE lobe seems to be concentrated near the surface of a conically shaped region, which is also closely associated with some of the high velocity, optical line emitting clouds, and may relate to a bow shock, blast wave, or cocoon of material shed by the jet as it propagates through the interstellar medium. Two models for the ionization of the optical clouds are discussed either ionizing photons eacape preferentially along the rotation axis of the disk which collimates the radio jets, or the excitation is effected by the kinetic energy of the jets or lobes themselves.

  15. Kinematics and ionization of extended gas in active galaxies. III. The extranuclear properties of NGC 1068

    SciTech Connect

    Baldwin, J.A.; Wilson, A.S.; Whittle, M.

    1987-08-01

    The kinematic and ionization structure of the extranuclear gas of the Seyfert 2 galaxy NGC 1068 has been investigated using a grid of 28 high- and seven low-dispersion long-slit spectra. The velocity field of most of the gas more than 15 arcsec from the nucleus is well described by a rotating disk with an approximately flat rotation curve. The kinematic line of nodes coincides with the major axis of the outermost continuum light, and the disk inclination derived from the axial ratio of the outer isophotes and the kinematic fit are broadly consistent. The progressive change of the position angle of the major axes of the brighter isophotes are evidently due to a superposition of oval or barlike distortions in the galactic plane. The observed ionization structure of the gas can be understood as a mixture of two disk components projected on top of each other. Much of the ionization pattern in the other disk may result from partial beaming of the ionizing continuum radiation as it escapes from the nucleus. 60 references.

  16. Evidence for a supermassive black hole in the nucleus of the Seyfert galaxy NGC 5548

    NASA Technical Reports Server (NTRS)

    Crenshaw, D. Michael; Blackwell, James H., Jr.

    1990-01-01

    The international campaign to monitor the variable Seyfert 1 galaxy NGC 5548 with the IUE has provided an extensive and well-sampled set of spectroscopic observations. These observations are used to study the response of the C IV 1550 A emission-line profile to changes in the photoionizing continuum. Near the end of the IUE campaign, the continuum flux at 1440 A and the total C IV flux dopped by factors of 2.9 and 1.8, respectively, in 16 days. The red wing of the C IV profile responded more rapidly to the sharp continuum drop than the blue wing, indicating that clouds in the inner broad-line region (BLR) are undergoing gravitational infall. These results provide direct evidence that the central engine is a supermassive object, presumably a black hole, with a mass on the order of 10 to the 7th solar masses. Analysis of the profile variations also demonstrates that excess emission in the blue wing of C IV is from a component that is physically distinct from the bulk of the BLR.

  17. Stellar metallicity of the extended disk and distance of the spiral galaxy NGC 3621

    SciTech Connect

    Kudritzki, Rolf-Peter; Bresolin, Fabio; Hosek, Matthew W. Jr.; Urbaneja, Miguel A.; Przybilla, Norbert E-mail: bresolin@ifa.hawaii.edu E-mail: Miguel.Urbaneja-Perez@uibk.ac.at

    2014-06-10

    Low resolution (∼4.5 Å) ESO VLT/FORS spectra of blue supergiant stars are analyzed to determine stellar metallicities (based on elements such as iron, titanium, and magnesium) in the extended disk of the spiral galaxy, NGC 3621. Mildly subsolar metallicity (–0.30 dex) is found for the outer objects beyond 7 kpc, independent of galactocentric radius and compatible with the absence of a metallicity gradient, confirming the results of a recent investigation of interstellar medium H II region gas oxygen abundances. The stellar metallicities are slightly higher than those from the H II regions when based on measurements of the weak forbidden auroral oxygen line at 4363 Å but lower than the ones obtained with the R {sub 23} strong line method. It is shown that the present level of metallicity in the extended disk cannot be the result of chemical evolution over the age of the disk with the present rate of in situ star formation. Additional mechanisms must be involved. In addition to metallicity, stellar effective temperatures, gravities, interstellar reddening, and bolometric magnitudes are determined. After the application of individual reddening corrections for each target, the flux-weighted gravity-luminosity relationship of blue supergiant stars is used to obtain a distance modulus of 29.07 ± 0.09 mag (distance D = 6.52 ± 0.28 Mpc). This new distance is discussed in relation to Cepheid and the tip of the red giant branch distances.

  18. Distributions, equivalent widths and metallicities of the H II regions in the spiral galaxies NGC 5457 and NGC 4395

    NASA Astrophysics Data System (ADS)

    Cedrés, B.; Cepa, J.

    2002-09-01

    Using CCD observations in the narrow band filters in Hα , Hβ , [O Ii], [O Iii], [S Ii] and [S Iii] lines we have compiled a catalogue of 338 H Ii regions for the inner parts of NGC 5457 and 158 for NGC 4395. The extinction, equivalent widths, distributions, excitations, ionization hardness, ionization parameters and metallicities for these regions, a distinction being made between arm and inter-arm zones, are presented here with the first results of a study of stellar formation. Tables 3 to 8 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/391/809

  19. CLUES ON THE REJUVENATION OF THE S0 GALAXY NGC 404 FROM THE CHEMICAL ABUNDANCE OF ITS OUTER DISK

    SciTech Connect

    Bresolin, Fabio

    2013-08-01

    The oxygen abundance of the outer disk of the nearby S0 galaxy NGC 404, a prototypical early-type galaxy with extended star formation, has been derived from the analysis of H II region spectra. The high mean value found, 12 + log(O/H) = 8.6 {+-} 0.1, equivalent to approximately 80% of the solar value, argues against both the previously proposed cold accretion and recent merger scenarios as viable mechanisms for the assembly of the star-forming gas. The combination of the present-day gas metallicity with the published star formation history of this galaxy favors a model in which the recent star forming activity represents the declining tail of the original one.

  20. Stellar populations in the edge-on spiral galaxy NGC 4565. I - Surface brightness and color distributions

    NASA Technical Reports Server (NTRS)

    Jensen, E. B.; Thuan, T. X.

    1982-01-01

    Results are presented for photographic and photoelectric photometry of the edge-on Sb galaxy NGC 4565. Major-axis, minor-axis, and perpendicular surface brightness profiles are determined, along with color gradients parallel and perpendicular to the plane of the galaxy. It is found that the galaxy's light can be deconvolved naturally into five components: (1) a starlike nucleus located at the center of the bulge and the edge of the dust lane; (2) a thin disk containing the gas and dust, the young OB stars, and the spiral arms; (3) a thick disk that may be a locally isothermal sheet of old Population I metal-rich stars; (4) a bulge that merges smoothly into the thick disk at a radial distance of about 2.9 kpc; and (5) a corona whose light dominates the perpendicular profiles from about 2.9 to at least 8.2 kpc above the galactic plane.

  1. A new catalogue of polar-ring galaxies selected from the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Moiseev, Alexei V.; Smirnova, Ksenia I.; Smirnova, Aleksandrina A.; Reshetnikov, Vladimir P.

    2011-11-01

    Galaxies with polar rings (PRGs) are a unique class of extragalactic objects. Using these, we can investigate a wide range of problems, linked to the formation and evolution of galaxies, and we can study the properties of their dark haloes. The progress that has been made in the study of PRGs has been constrained by the small number of known objects of this type. The Polar Ring Catalogue (PRC) by Whitmore et al. and their photographic atlas of PRGs and related objects includes 157 galaxies. At present, there are only about two dozen kinematically confirmed galaxies in this PRG class, mostly from the PRC. We present a new catalogue of PRGs, supplementing the PRC and significantly increasing the number of known candidate PRGs. The catalogue is based on the results of the original Galaxy Zoo project. Within this project, volunteers performed visual classifications of nearly a million galaxies from the Sloan Digital Sky Survey (SDSS). Based on the preliminary classifications of the Galaxy Zoo, we viewed more than 40 000 images of the SDSS and selected 275 galaxies to include in our catalogue. Our SDSS-based Polar Ring Catalogue (SPRC) contains 70 galaxies that we have classified as 'the best candidates'. Among these, we expect to have a very high proportion of true PRGs, and 115 good PRG candidates. There are 53 galaxies classified as PRG-related objects (mostly galaxies with strongly warped discs, and mergers). In addition, we have identified 37 galaxies that have their presumed polar rings strongly inclined to the line of sight (seen almost face-on). The SPRC objects are, on average, fainter and are located further away than the galaxies from the PRC, although our catalogue does include dozens of new nearby candidate PRGs. The SPRC significantly increases the number of genuine PRG candidates. It might serve as a good basis for both a further detailed study of individual galaxies and a statistical analysis of PRGs as a separate class of objects. We have performed

  2. The Advanced Camera for Surveys Nearby Galaxy Survey Treasury. IV. The Star Formation History of NGC 2976

    NASA Astrophysics Data System (ADS)

    Williams, Benjamin F.; Dalcanton, Julianne J.; Stilp, Adrienne; Gilbert, Karoline M.; Roškar, Rok; Seth, Anil C.; Weisz, Daniel; Dolphin, Andrew; Gogarten, Stephanie M.; Skillman, Evan; Holtzman, Jon

    2010-01-01

    We present resolved stellar photometry of NGC 2976 obtained with the Advanced Camera for Surveys (ACS) as part of the ACS Nearby Galaxy Survey Treasury (ANGST) program. The data cover the radial extent of the major axis of the disk out to 6 kpc, or ~6 scale lengths. The outer disk was imaged to a depth of M F606W ~ 1, and an inner field was imaged to the crowding limit at a depth of M F606W ~ -1. Through detailed analysis and modeling of the resulting color-magnitude diagrams, we have reconstructed the star formation history (SFH) of the stellar populations currently residing in these portions of the galaxy, finding similar ancient populations at all radii but significantly different young populations at increasing radii. In particular, outside of the well-measured break in the disk surface brightness profile, the age of the youngest population increases with distance from the galaxy center, suggesting that star formation is shutting down from the outside-in. We use our measured SFH, along with H I surface density measurements, to reconstruct the surface density profile of the disk during previous epochs. Comparisons between the recovered star formation rates and reconstructed gas densities at previous epochs are consistent with star formation following the Schmidt law during the past 0.5 Gyr, but with a drop in star formation efficiency at low gas densities, as seen in local galaxies at the present day. The current rate and gas density suggest that rapid star formation in NGC 2976 is currently in the process of ceasing from the outside-in due to gas depletion. This process of outer disk gas depletion and inner disk star formation was likely triggered by an interaction with the core of the M81 group gsim1 Gyr ago that stripped the gas from the galaxy halo and/or triggered gas inflow from the outer disk toward the galaxy center.

  3. THE ADVANCED CAMERA FOR SURVEYS NEARBY GALAXY SURVEY TREASURY. IV. THE STAR FORMATION HISTORY OF NGC 2976

    SciTech Connect

    Williams, Benjamin F.; Dalcanton, Julianne J.; Stilp, Adrienne; Gilbert, Karoline M.; Roskar, Rok; Gogarten, Stephanie M.; Seth, Anil C.; Weisz, Daniel; Skillman, Evan; Dolphin, Andrew; Holtzman, Jon E-mail: jd@astro.washington.ed E-mail: stephanie@astro.washington.ed E-mail: dweisz@astro.umn.ed E-mail: dolphin@raytheon.co

    2010-01-20

    We present resolved stellar photometry of NGC 2976 obtained with the Advanced Camera for Surveys (ACS) as part of the ACS Nearby Galaxy Survey Treasury (ANGST) program. The data cover the radial extent of the major axis of the disk out to 6 kpc, or approx6 scale lengths. The outer disk was imaged to a depth of M{sub F606W} approx 1, and an inner field was imaged to the crowding limit at a depth of M{sub F606W} approx -1. Through detailed analysis and modeling of the resulting color-magnitude diagrams, we have reconstructed the star formation history (SFH) of the stellar populations currently residing in these portions of the galaxy, finding similar ancient populations at all radii but significantly different young populations at increasing radii. In particular, outside of the well-measured break in the disk surface brightness profile, the age of the youngest population increases with distance from the galaxy center, suggesting that star formation is shutting down from the outside-in. We use our measured SFH, along with H I surface density measurements, to reconstruct the surface density profile of the disk during previous epochs. Comparisons between the recovered star formation rates and reconstructed gas densities at previous epochs are consistent with star formation following the Schmidt law during the past 0.5 Gyr, but with a drop in star formation efficiency at low gas densities, as seen in local galaxies at the present day. The current rate and gas density suggest that rapid star formation in NGC 2976 is currently in the process of ceasing from the outside-in due to gas depletion. This process of outer disk gas depletion and inner disk star formation was likely triggered by an interaction with the core of the M81 group approx>1 Gyr ago that stripped the gas from the galaxy halo and/or triggered gas inflow from the outer disk toward the galaxy center.

  4. Bridging the Gap from Galactic to Extragalactic: Star Formation and Giant Molecular Clouds within the Nearby Spiral Galaxy NGC 300

    NASA Astrophysics Data System (ADS)

    Faesi, Christopher

    2017-01-01

    The questions surrounding the origins of stars are of key importance in astrophysics across a huge range in physical scales. However, until recently, investigations have been restricted to either detailed studies targeting a few nearby regions in the Milky Way, or kpc- or larger-scale studies of entire galaxies. Between these two scales lies a crucial gap in understanding. In this thesis work, I have taken steps in bridging this gap between Galactic and extragalactic star formation. I will present the results of a campaign of observations and modeling targeting the nearby spiral galaxy NGC 300. Using an extensive suite of multi-wavelength data I have characterized the star formation activity and molecular gas in a large sample of star-forming regions within this galaxy. Additionally, I have assembled an extensive (300 clouds) and high resolution (10 pc) catalog of Giant Molecular Clouds (GMCs) based on ALMA CO observations. This unprecedented look at the population of GMCs in a nearby spiral galaxy reveals an astonishing range of morphologies and properties in the Molecular Gas as well as providing a key testbed for comparison with GMCs in the Milky Way and other nearby galaxies. The GMCs in NGC 300 appear to have similar global properties and show scaling relations consistent with those seen in the Milky Way. Furthermore, the star formation rate appears to correlate with the mass of molecular gas with approximately 250 Gyr depletion time, extending the relation discovered in the Milky Way linearly to larger scales. These results suggest a level of universality in the star formation process within spiral galaxy disks like our own Milky Way.

  5. Structural Transition in the NGC 6251 Jet: an Interplay with the Supermassive Black Hole and Its Host Galaxy

    NASA Astrophysics Data System (ADS)

    Tseng, Chih-Yin; Asada, Keiichi; Nakamura, Masanori; Pu, Hung-Yi; Algaba, Juan-Carlos; Lo, Wen-Ping

    2016-12-01

    The structure of the NGC 6251 jet on the milliarcsecond scale is investigated using images taken with the European VLBI Network and the Very Long Baseline Array. We detect a structural transition of the jet from a parabolic to a conical shape at a distance of (1-2) × 105 times the Schwarzschild radius from the central engine, which is close to the sphere of gravitational influence of the supermassive black hole (SMBH). We also examine the jet pressure profiles with the synchrotron minimum energy assumption to discuss the physical origin of the structural transition. The NGC 6251 jet, together with the M87 jet, suggests a fundamental process of structural transition in the jets of active galactic nuclei (AGNs). Collimated AGN jets are characterized by their external galactic medium, showing that AGN jets interplay with the SMBH and its host galaxy.

  6. Elliptical galaxies with rapidly decreasing velocity dispersion profiles: NMAGIC models and dark halo parameter estimates for NGC 4494

    NASA Astrophysics Data System (ADS)

    Morganti, Lucia; Gerhard, Ortwin; Coccato, Lodovico; Martinez-Valpuesta, Inma; Arnaboldi, Magda

    2013-06-01

    NGC 4494 is one of several intermediate-luminosity elliptical galaxies inferred to have an unusually diffuse dark matter halo. We use the χ2-made-to-measure particle code NMAGIC to construct axisymmetric models of NGC 4494 from photometric and various kinematic data. The extended kinematics include light spectra in multiple slitlets out to 3.5Re, and hundreds of planetary nebula velocities out to ≃7Re, thus allowing us to probe the dark matter content and orbital structure in the halo. We use Monte Carlo simulations to estimate confidence boundaries for the halo parameters, given our data and modelling set-up. We find that the true potential of the dark matter halo is recovered within ΔG (merit function) ≲ 26 (Δχ2 ≲ 59) at the 70 per cent confidence level (CL), and within ΔG ≲ 32 (Δχ2 ≲ 70) at the 90 per cent CL. These numbers are much larger than the usually assumed Δχ2 = 2.3 (4.6) for the 70 per cent (90 per cent) CL for two free parameters, perhaps case dependent, but calling into question the general validity of the standard assumptions used for halo and black hole mass determinations. The best-fitting models for NGC 4494 have a dark matter fraction of about 0.6 ± 0.1 at 5Re (70 per cent CL) and are embedded in a dark matter halo with circular velocity ˜200 km s-1. The total circular velocity curve (CVC) is approximately flat at vc = 220 km s-1 outside ˜0.5Re. The orbital anisotropy of the stars is moderately radial. These results are independent of the assumed inclination of the galaxy, and edge-on models are preferred. Comparing with the haloes of NGC 3379 and NGC 4697, whose velocity dispersion profiles also decrease rapidly from the centre outwards, the outer CVCs and dark matter haloes are quite similar. NGC 4494 shows a particularly high dark matter fraction inside ˜ 3Re, and a strong concentration of baryons in the centre.

  7. Surface Photometry of NGC 4656/4657

    SciTech Connect

    Stayton, L.C.; Angione, R.J.; Talbert, F.D.

    1983-05-01

    An analysis by surface photometry of the galaxy system NGC 4656/4657 yields the following results. First, NGC 4656 and NGC 4657 appear to be parts of the same galaxy. Second, the system bears a strong resemblance to both the SMC and NGC 55. Third, although the outermost isophotes in B and G light show coincidences with radio continuum, we found no conclusive optical indications of an interaction with the galaxy NGC 4631.

  8. VLBI observations of a complete sample of radio galaxies. 4: The radio galaxies NGC 2484, 3C 109, and 3C 382

    NASA Technical Reports Server (NTRS)

    Giovannini, G.; Feretti, L.; Venturi, T.; Lara, L.; Marcaide, J.; Rioja, M.; Spangler, S. R.; Wehrle, A. E.

    1994-01-01

    We present here new Very Long Base Interferometry (VLBI) observations of one Fanaroff and Riley (F-R) I radio galaxy (NGC 2484) and two broad-line F-R II radio galaxies (3C 109 and 3C 382). For 3C 109 new Very Large Array (VLA) maps are also shown. These sources belong to a complete sample of radio galaxies under study for a better knowledge of their structures at parsec resolution. The parsec structure of these three objects is very similar: asymmetric emission, which we interpret as the core plus a one-side jet. The parsec-scale jet is always on the same side of the main kiloparsec-scale jet. The limit on the jet to counterjet brightness ratio, the ratio of the core radio power to the total radio power and the synchrotron-self Compton model allow us to derive some constraints on the jet velocity and orientation with respect to the line of sight. From these data and from those published on two other sources of our sample, we suggest that parsec-scale jets are relativistic in both F-R I and F-R II radio galaxies and that parsec scale properties in F-R I and F-R II radio galaxies are very similar despite the large difference between these two classes of radio galaxies on the kiloparsec scale.

  9. HIGH-RESOLUTION IMAGING OF WATER MASER EMISSION IN THE ACTIVE GALAXIES NGC 6240 AND M51

    SciTech Connect

    Hagiwara, Yoshiaki; Edwards, Philip G. E-mail: Philip.Edwards@csiro.au

    2015-12-20

    We present the results of observations of 22 GHz H{sub 2}O maser emission in NGC 6240 and M51 made with the Karl G. Jansky Very Large Array. Two major H{sub 2}O maser features and several minor features are detected toward the southern nucleus of NGC 6240. These features are redshifted by about 300 km s{sup −1} from the galaxy’s systemic velocity and remain unresolved at the synthesized beam size. A combination of our two-epoch observations and published data reveals an apparent correlation between the strength of the maser and the 22 GHz radio continuum emission, implying that the maser excitation relates to the activity of an active galactic nucleus in the southern nucleus rather than star-forming activity. The star-forming galaxy M51 hosts H{sub 2}O maser emission in the center of the galaxy; however, the origin of the maser has been an open question. We report the first detection of 22 GHz nuclear radio continuum emission in M51. The continuum emission is co-located with the maser position, which indicates that the maser arises from nuclear active galactic nucleus-activity and not from star-forming activity in the galaxy.

  10. UIT: Ultraviolet surface photometry of the spiral galaxy M74 (NGC 628)

    NASA Technical Reports Server (NTRS)

    Cornett, Robert H.; O'Connell, Robert W.; Greason, Michael R.; Offenberg, Joel D.; Angione, Ronald J.; Bohlin, Ralph C.; Cheng, K. P.; Roberts, Morton S.; Smith, Andrew M.; Smith, Eric P.

    1994-01-01

    Ultraviolet photometry, obtained from Ultraviolet Imaging Telescope (UIT) images at 1520 A (far-UV; magnitudes m(152)) and 2490 A (near-UV; magnitudes m(249)), of the spiral galaxy M74 (NGC 628) is compared with H-alpha, R, V, and B surface photometry and with models. M74's surface brightness profiles have a central peak with an exponential falloff; the exponential scale lengths of the profiles increase with decreasing wavelength for the broad-band images. The slope of the continuum-subtracted H-alpha profile is intermediate between those of far-UV and near-UV profiles, consistent with the related origins of H-alpha and UV emission in extreme Population I material. M74's color profiles all become bluer with increasing radius. The (m(152) - m(249)) color as measured by UIT averages near 0.0 (the color of an A0 star) over the central 20 sec radius and decreases from approximately -0.2 to approximately -0.4 from 20 sec to 200 sec. The spiral arms are the dominant component of the surface photometry colors; interarm regions are slightly redder. In the UV, M74's nuclear region resembles its disk/spiral arm material in colors and morphology, unlike galaxies such as M81. No UV 'bulge' is apparent. The m(152) - m(249) colors and models of M74's central region clearly demonstrate that there is no significant population of O or B stars present in the central 10 sec. M74's UV morphology and (m(152) - m(249)) color profiles are similar to those of M33, although M74 is approximately 0.5 mag redder. M81 has a smooth UV bulge which is much redder than the nuclear regions of M74 and M33. M74 is approximately 0.4 mag bluer than M81 in its outer disk, although M81 has bright UV sources only in spiral arms more than 5 kpc from its center. We investigate possible explanations for the color profiles of the galaxies and the differences among the galaxies: abundances; reddening due to internal dust; interplanetary magnetic field (IMF) variations, and the history of formation of the

  11. Hubble space telescope absolute proper motions of NGC 6681 (M70) and the sagittarius dwarf spheroidal galaxy

    SciTech Connect

    Massari, D.; Ferraro, F. R.; Dalessandro, E.; Lanzoni, B.

    2013-12-10

    We have measured absolute proper motions for the three populations intercepted in the direction of the Galactic globular cluster NGC 6681: the cluster itself, the Sagittarius dwarf spheroidal galaxy, and the field. For this, we used Hubble Space Telescope ACS/WFC and WFC3/UVIS optical imaging data separated by a temporal baseline of 5.464 yr. Five background galaxies were used to determine the zero point of the absolute-motion reference frame. The resulting absolute proper motion of NGC 6681 is (μ{sub α}cos δ, μ{sub δ}) = (1.58 ± 0.18, –4.57 ± 0.16) mas yr{sup –1}. This is the first estimate ever made for this cluster. For the Sgr dSph we obtain (μ{sub α}cos δ, μ{sub δ}) = –2.54 ± 0.18, –1.19 ± 0.16) mas yr{sup –1}, consistent with previous measurements and with the values predicted by theoretical models. The absolute proper motion of the Galaxy population in our field of view is (μ{sub α}cos δ, μ{sub δ}) = (– 1.21 ± 0.27, –4.39 ± 0.26) mas yr{sup –1}. In this study we also use background Sagittarius Dwarf Spheroidal stars to determine the rotation of the globular cluster in the plane of the sky and find that NGC 6681 is not rotating significantly: v {sub rot} = 0.82 ± 1.02 km s{sup –1} at a distance of 1' from the cluster center.

  12. Probing the interstellar medium of external galaxies using quasar absortion lines: The 3C 232/NGC 3067 system

    NASA Technical Reports Server (NTRS)

    Stocke, John T.; Case, James; Donahue, Megan; Shull, J. Michael; Snow, Theodore P.

    1990-01-01

    Quasar absorption lines offer unique opportunities to probe the interstellar medium of external galaxies. Researchers present new optical and UV absorption line spectroscopy of the quasar 3C232 (z=0.55) revealing new detail in the foreground absorption system due to the bright, spiral galaxy NGC 3067 (cz=1420 km/s). Specifically, the spectra show evidence for two and possibly three separate absorption components in CaII and Na I spanning approx. 150 km/s. The original HI detection of Haschick and Burke (1975) corresponds to the strongest of these metal systems which exhibits doublet ratios consistent with saturation in both CaII and Na I. Due to the recent detection in HI emission of a tidal tail or finger of HI extending from the western edge of NGC 3067 through the position of 3C 232 (Carilli, van Gorkom and Stocke, 1989), the morphology of the HI absorber is now known and is not either a warped disk nor a spherical halo as had been proposed. New deep continuum and H alpha imaging provides a sensitive upper limit on the the ionizing continuum impinging upon this cloud (and thus a limit on the intensity of the extragalactic ionizing radiation field). Together with the observed UV spectrum of 3C 232, the optical emission line ratios and the deep H alpha imaging set a minimum distance between the quasar and the HI cloud disregarding redshift information. This limit strains the non-cosmological redshift interpretation for 3C 232 -- and this quasar is one of the original 5 3C quasars found to be too close to NGC galaxies as if by chance (Burbidge, Burbidge, Solomon and Strittmatter, 1972).

  13. The Advanced Camera for Surveys Nearby Galaxy Survey Treasury. V. Radial Star Formation History of NGC 300

    NASA Astrophysics Data System (ADS)

    Gogarten, Stephanie M.; Dalcanton, Julianne J.; Williams, Benjamin F.; Roškar, Rok; Holtzman, Jon; Seth, Anil C.; Dolphin, Andrew; Weisz, Daniel; Cole, Andrew; Debattista, Victor P.; Gilbert, Karoline M.; Olsen, Knut; Skillman, Evan; de Jong, Roelof S.; Karachentsev, Igor D.; Quinn, Thomas R.

    2010-04-01

    We present new Hubble Space Telescope (HST) observations of NGC 300 taken as part of the Advanced Camera for Surveys Nearby Galaxy Survey Treasury (ANGST). Individual stars are resolved in these images down to an absolute magnitude of M F814W = 1.0 (below the red clump). We determine the star formation history of the galaxy in six radial bins by comparing our observed color-magnitude diagrams (CMDs) with synthetic CMDs based on theoretical isochrones. We find that the stellar disk out to 5.4 kpc is primarily old, in contrast with the outwardly similar galaxy M33. We determine the scale length as a function of age and find evidence for inside-out growth of the stellar disk: the scale length has increased from 1.1 ± 0.1 kpc 10 Gyr ago to 1.3 ± 0.1 kpc at present, indicating a buildup in the fraction of young stars at larger radii. As the scale length of M33 has recently been shown to have increased much more dramatically with time, our results demonstrate that two galaxies with similar sizes and morphologies can have very different histories. With an N-body simulation of a galaxy designed to be similar to NGC 300, we determine that the effects of radial migration should be minimal. We trace the metallicity gradient as a function of time and find a present-day metallicity gradient consistent with that seen in previous studies. Consistent results are obtained from archival images covering the same radial extent but differing in placement and filter combination.

  14. THE ADVANCED CAMERA FOR SURVEYS NEARBY GALAXY SURVEY TREASURY. V. RADIAL STAR FORMATION HISTORY OF NGC 300

    SciTech Connect

    Gogarten, Stephanie M.; Dalcanton, Julianne J.; Williams, Benjamin F.; Roskar, Rok; Gilbert, Karoline M.; Quinn, Thomas R.; Holtzman, Jon; Seth, Anil C.; Dolphin, Andrew; Weisz, Daniel; Skillman, Evan; Cole, Andrew; Debattista, Victor P.; Olsen, Knut; De Jong, Roelof S.; Karachentsev, Igor D.

    2010-04-01

    We present new Hubble Space Telescope (HST) observations of NGC 300 taken as part of the Advanced Camera for Surveys Nearby Galaxy Survey Treasury (ANGST). Individual stars are resolved in these images down to an absolute magnitude of M{sub F814W} = 1.0 (below the red clump). We determine the star formation history of the galaxy in six radial bins by comparing our observed color-magnitude diagrams (CMDs) with synthetic CMDs based on theoretical isochrones. We find that the stellar disk out to 5.4 kpc is primarily old, in contrast with the outwardly similar galaxy M33. We determine the scale length as a function of age and find evidence for inside-out growth of the stellar disk: the scale length has increased from 1.1 +- 0.1 kpc 10 Gyr ago to 1.3 +- 0.1 kpc at present, indicating a buildup in the fraction of young stars at larger radii. As the scale length of M33 has recently been shown to have increased much more dramatically with time, our results demonstrate that two galaxies with similar sizes and morphologies can have very different histories. With an N-body simulation of a galaxy designed to be similar to NGC 300, we determine that the effects of radial migration should be minimal. We trace the metallicity gradient as a function of time and find a present-day metallicity gradient consistent with that seen in previous studies. Consistent results are obtained from archival images covering the same radial extent but differing in placement and filter combination.

  15. Does the inner broad-line region dim down when the power turns up?. [Seyfert 1 galaxy NGC 5548

    NASA Technical Reports Server (NTRS)

    Sparke, Linda S.

    1993-01-01

    The temporal correlations of continuum and broad emission-line fluxes from the Seyfert galaxy NGC 5548 as measured during the 1989 monitoring campaign show two related peculiarities: first, some of the crosscorrelations of line and continuum flux appear steeper on the negative time lag side than the continuum autocorrelation itself; then, the autocorrelation of the line flux is sometimes more sharply peaked than the continuum autocorrelation function. These are here interpreted as evidence that conditions in the inner part of the broad-line region are such that some emission lines decrease in intensity as the continuum strengthens.

  16. THE ADVANCED CAMERA FOR SURVEYS NEARBY GALAXY SURVEY TREASURY. VI. THE ANCIENT STAR-FORMING DISK OF NGC 404

    SciTech Connect

    Williams, Benjamin F.; Dalcanton, Julianne J.; Gilbert, Karoline M.; Stilp, Adrienne; Dolphin, Andrew; Seth, Anil C.; Weisz, Daniel; Skillman, Evan E-mail: jd@astro.washington.ed E-mail: roskar@astro.washington.ed E-mail: aseth@cfa.harvard.ed E-mail: skillman@astro.umn.ed

    2010-06-10

    We present HST/WFPC2 observations across the disk of the nearby isolated dwarf S0 galaxy NGC 404, which hosts an extended gas disk. The locations of our fields contain a roughly equal mixture of bulge and disk stars. All of our resolved stellar photometry reaches m {sub F814W} = 26 (M {sub F814W} = -1.4), which covers 2.5 mag of the red giant branch and main-sequence stars with ages <300 Myr. Our deepest field reaches m {sub F814W} = 27.2 (M {sub F814W} = -0.2), sufficient to resolve the red clump and main-sequence stars with ages <500 Myr. Although we detect trace amounts of star formation at times more recent than 10 Gyr ago for all fields, the proportion of red giant stars to asymptotic giants and main-sequence stars suggests that the disk is dominated by an ancient (>10 Gyr) population. Detailed modeling of the color-magnitude diagram suggests that {approx}70% of the stellar mass in the NGC 404 disk formed by z {approx} 2 (10 Gyr ago) and at least {approx}90% formed prior to z {approx} 1 (8 Gyr ago). These results indicate that the stellar populations of the NGC 404 disk are on average significantly older than those of other nearby disk galaxies, suggesting that early- and late-type disks may have different long-term evolutionary histories, not simply differences in their recent star formation rates. Comparisons of the spatial distribution of the young stellar mass and FUV emission in Galaxy Evolution Explorer images show that the brightest FUV regions contain the youngest stars, but that some young stars (<160 Myr) lie outside of these regions. FUV luminosity appears to be strongly affected by both age and stellar mass within individual regions. Finally, we use our measurements to infer the relationship between the star formation rate and the gas density of the disk at previous epochs. We find that most of the history of the NGC 404 disk is consistent with star formation that has decreased with the gas density according to the Schmidt law. However, {approx} 0

  17. Time Variability and Luminosity of X-ray Sources of Face-on Spiral Galaxy NGC 1232

    NASA Astrophysics Data System (ADS)

    Cantua, Oscar; Rucas, Tyler; Singh, Pranjal; Schlegel, Eric M.

    2017-01-01

    The ACIS detector (Advanced CCD Imaging Spectrometer) onboard the Chandra X-ray Observatory has imaged the face-on spiral NGC 1232 over six epochs for a total exposure of ~250 ksec. We describe each observation as well as the merged data set. Each exposure contains ~50 individual sources. We focus on the time variability and luminosity distributions of the sources. We also describe our search for diffuse emission as well as our search for evidence for a reported collision with a dwarf galaxy. Finally, we compare the merged data set and the detected sources with other wavebands.

  18. NGC 3801 caught in the act: a post-merger star-forming early-type galaxy with AGN-jet feedback

    NASA Astrophysics Data System (ADS)

    Hota, Ananda; Rey, Soo-Chang; Kang, Yongbeom; Kim, Suk; Matsushita, Satoki; Chung, Jiwon

    2012-05-01

    In the current models of galaxy formation and evolution, AGN feedback is crucial to reproduce galaxy luminosity function, colour-magnitude relation and M•-σ relation. However, whether AGN feedback can indeed expel and heat up significant amount of cool molecular gas and consequently quench star formation is yet to be demonstrated observationally. Only in four cases so far (Cen A, NGC 3801, NGC 6764 and Mrk 6), X-ray observations have found evidences of jet-driven shocks heating the ISM. We chose the least explored galaxy NGC 3801, and present the first ultraviolet imaging and stellar population analysis of this galaxy from GALEX data. We find this merger-remnant early-type galaxy to have an intriguing spiral wisp of young star-forming regions (age ranging from 100 to 500 Myr). Taking clues from dust/PAH, H I and CO emission images, we interpret NGC 3801 to have a kinematically decoupled core or an extremely warped gas disc. From the HST data, we also show evidence of ionized gas outflow similar to that observed in H I and molecular gas (CO) data, which may have caused the decline of star formation leading to the red optical colour of the galaxy. However, from these panchromatic data, we interpret that the expanding shock shells from the young (˜2.4 Myr) radio jets are yet to reach the outer gaseous regions of the galaxy. It seems we observe this galaxy at a rare stage of its evolutionary sequence where post-merger star formation has already declined and new powerful jet feedback is about to affect the gaseous star-forming outer disc within the next 10 Myr, to further transform it into a red-and-dead early-type galaxy.

  19. Spitzer Space Telescope Measurements of Dust Reverberation Lags in the Seyfert 1 Galaxy NGC 6418

    NASA Astrophysics Data System (ADS)

    Vazquez, Billy; Galianni, Pasquale; Richmond, Michael; Robinson, Andrew; Axon, David J.; Horne, Keith; Almeyda, Triana; Fausnaugh, Michael; Peterson, Bradley M.; Bottorff, Mark; Gallimore, Jack; Eltizur, Moshe; Netzer, Hagai; Storchi-Bergmann, Thaisa; Marconi, Alessandro; Capetti, Alessandro; Batcheldor, Dan; Buchanan, Catherine; Stirpe, Giovanna; Kishimoto, Makoto; Packham, Christopher; Perez, Enrique; Tadhunter, Clive; Upton, John; Estrada-Carpenter, Vicente

    2015-03-01

    We present results from a 15 month campaign of high-cadence (˜3 days) mid-infrared Spitzer and optical (B and V) monitoring of the Seyfert 1 galaxy NGC 6418, with the objective of determining the characteristic size of the dusty torus in this active galactic nucleus (AGN). We find that the 3.6 and 4.5 μm flux variations lag behind those of the optical continuum by 37.2-2.2+2.4 days and 47.1-3.1+3.1 days, respectively. We report a cross-correlation time lag between the 4.5 and 3.6 μm flux of 13.9-0.1+0.5 days. The lags indicate that the dust emitting at 3.6 and 4.5 μm is located at a distance ≈ 1 light-month (≈ 0.03 pc) from the source of the AGN UV-optical continuum. The reverberation radii are consistent with the inferred lower limit to the sublimation radius for pure graphite grains at 1800 K, but smaller by a factor of ˜2 than the corresponding lower limit for silicate grains; this is similar to what has been found for near-infrared (K-band) lags in other AGNs. The 3.6 and 4.5 μm reverberation radii fall above the K-band τ \\propto {{L}0.5} size-luminosity relationship by factors ≲ 2.7 and ≲ 3.4, respectively, while the 4.5 μm reverberation radius is only 27% larger than the 3.6 μm radius. This is broadly consistent with clumpy torus models, in which individual optically thick clouds emit strongly over a broad wavelength range.

  20. The VIRUS-P Exploration of Nearby Galaxies (VENGA): The X CO Gradient in NGC 628

    NASA Astrophysics Data System (ADS)

    Blanc, Guillermo A.; Schruba, Andreas; Evans, Neal J., II; Jogee, Shardha; Bolatto, Alberto; Leroy, Adam K.; Song, Mimi; van den Bosch, Remco C. E.; Drory, Niv; Fabricius, Maximilian; Fisher, David; Gebhardt, Karl; Heiderman, Amanda; Marinova, Irina; Vogel, Stuart; Weinzirl, Tim

    2013-02-01

    We measure the radial profile of the 12CO(1-0) to H2 conversion factor (X CO) in NGC 628. The Hα emission from the VENGA integral field spectroscopy is used to map the star formation rate (SFR) surface density (ΣSFR). We estimate the molecular gas surface density (ΣH2) from ΣSFR by inverting the molecular star formation law (SFL), and compare it to the CO intensity to measure X CO. We study the impact of systematic uncertainties by changing the slope of the SFL, using different SFR tracers (Hα versus far-UV plus 24 μm), and CO maps from different telescopes (single-dish and interferometers). The observed X CO profile is robust against these systematics, drops by a factor of two from R ~ 7 kpc to the center of the galaxy, and is well fit by a gradient Δlog(X CO) = 0.06 ± 0.02 dex kpc-1. We study how changes in X CO follow changes in metallicity, gas density, and ionization parameter. Theoretical models show that the gradient in X CO can be explained by a combination of decreasing metallicity, and decreasing ΣH2 with radius. Photoelectric heating from the local UV radiation field appears to contribute to the decrease of X CO in higher density regions. Our results show that galactic environment plays an important role at setting the physical conditions in star-forming regions, in particular the chemistry of carbon in molecular complexes, and the radiative transfer of CO emission. We caution against adopting a single X CO value when large changes in gas surface density or metallicity are present.

  1. A CHANDRA STUDY OF THE RADIO GALAXY NGC 326: WINGS, OUTBURST HISTORY, AND ACTIVE GALACTIC NUCLEUS FEEDBACK

    SciTech Connect

    Hodges-Kluck, Edmund J.; Reynolds, Christopher S.

    2012-02-20

    NGC 326 is one of the most prominent 'X'- or 'Z'-shaped radio galaxies (XRGs/ZRGs) and has been the subject of several studies attempting to explain its morphology through either fluid motions or reorientation of the jet axis. We examine a 100 ks Chandra X-Ray Observatory exposure and find several features associated with the radio galaxy: a high-temperature front that may indicate a shock, high-temperature knots around the rim of the radio emission, and a cavity associated with the eastern wing of the radio galaxy. A reasonable interpretation of these features in light of the radio data allows us to reconstruct the history of the active galactic nucleus (AGN) outbursts. The active outburst was likely once a powerful radio source which has since decayed, and circumstantial evidence favors reorientation as the means to produce the wings. Because of the obvious interaction between the radio galaxy and the intracluster medium and the wide separation between the active lobes and wings, we conclude that XRGs are excellent sources in which to study AGN feedback in galaxy groups by measuring the heating rates associated with both active and passive heating mechanisms.

  2. A MONTE CARLO MARKOV CHAIN BASED INVESTIGATION OF BLACK HOLE SPIN IN THE ACTIVE GALAXY NGC 3783

    SciTech Connect

    Reynolds, Christopher S.; Lohfink, Anne M.; Trippe, Margaret L.; Brenneman, Laura W.; Miller, Jon M.; Fabian, Andrew C.; Nowak, Michael A. E-mail: alohfink@astro.umd.edu

    2012-08-20

    The analysis of relativistically broadened X-ray spectral features from the inner accretion disk provides a powerful tool for measuring the spin of supermassive black holes in active galactic nuclei (AGNs). However, AGN spectra are often complex and careful analysis employing appropriate and self-consistent models is required if one has to obtain robust results. In this paper, we revisit the deep 2009 July Suzaku observation of the Seyfert galaxy NGC 3783 in order to study in a rigorous manner the robustness of the inferred black hole spin parameter. Using Monte Carlo Markov chain techniques, we identify a (partial) modeling degeneracy between the iron abundance of the disk and the black hole spin parameter. We show that the data for NGC 3783 strongly require both supersolar iron abundance (Z{sub Fe} = 2-4 Z{sub Sun }) and a rapidly spinning black hole (a > 0.89). We discuss various astrophysical considerations that can affect the measured abundance. We note that, while the abundance enhancement inferred in NGC 3783 is modest, the X-ray analysis of some other objects has found extreme iron abundances. We introduce the hypothesis that the radiative levitation of iron ions in the innermost regions of radiation-dominated AGN disks can enhance the photospheric abundance of iron. We show that radiative levitation is a plausible mechanism in the very inner regions of high accretion rate AGN disks.

  3. Discovery of a 3.6-hr Eclipsing Luminous X-Ray Binary in the Galaxy NGC 4214

    NASA Technical Reports Server (NTRS)

    Ghosh, Kajal K.; Rappaport, Saul; Tennant, Allyn F.; Swartz, Douglas A.; Pooley, David; Madhusudhan, N.

    2006-01-01

    We report the discovery of an eclipsing X-ray binary with a 3.62-hr period within 24 arcsec of the center of the dwarf starburst galaxy NGC 4214. The orbital period places interesting constraints on the nature of the binary, and allows for a few very different interpretations. The most likely possibility is that the source lies within NGC 4214 and has an X-ray luminosity of up to 7e38. In this case the binary may well be comprised of a naked He-burning donor star with a neutron-star accretor, though a stellar-mass black-hole accretor cannot be completely excluded. There is no obvious evidence for a strong stellar wind in the X-ray orbital light curve that would be expected from a massive He star; thus, the mass of the He star should be <3-4 solar masses. If correct, this would represent a new class of very luminous X-ray binary----perhaps related to Cyg X-3. Other less likely possibilities include a conventional low-mass X-ray binary that somehow manages to produce such a high X-ray luminosity and is apparently persistent over an interval of years; or a foreground AM Her binary of much lower luminosity that fortuitously lies in the direction of NGC 4214. Any model for this system must accommodate the lack of an optical counterpart down to a limiting magnitude of 22.6 in the visible.

  4. HUBBLE SPACE TELESCOPE PIXEL ANALYSIS OF THE INTERACTING FACE-ON SPIRAL GALAXY NGC 5194 (M51A)

    SciTech Connect

    Lee, Joon Hyeop; Kim, Sang Chul; Park, Hong Soo; Ree, Chang Hee; Kyeong, Jaemann; Chung, Jiwon E-mail: sckim@kasi.re.kr E-mail: chr@kasi.re.kr E-mail: jiwon@kasi.re.kr

    2011-10-10

    A pixel analysis is carried out on the interacting face-on spiral galaxy NGC 5194 (M51A), using the Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) images in the F435W, F555W, and F814W (BVI) bands. After 4 x 4 binning of the HST/ACS images to secure a sufficient signal-to-noise ratio for each pixel, we derive several quantities describing the pixel color-magnitude diagram (pCMD) of NGC 5194: blue/red color cut, red pixel sequence parameters, blue pixel sequence parameters, and blue-to-red pixel ratio. The red sequence pixels are mostly older than 1 Gyr, while the blue sequence pixels are mostly younger than 1 Gyr, in their luminosity-weighted mean stellar ages. The color variation in the red pixel sequence from V = 20 mag arcsec{sup -2} to V = 17 mag arcsec{sup -2} corresponds to a metallicity variation of {Delta}[Fe/H] {approx}2 or an optical depth variation of {Delta}{tau}{sub V} {approx} 4 by dust, but the actual sequence is thought to originate from the combination of those two effects. At V < 20 mag arcsec{sup -2}, the color variation in the blue pixel sequence corresponds to an age variation from 5 Myr to 300 Myr under the assumption of solar metallicity and {tau}{sub V} = 1. To investigate the spatial distributions of stellar populations, we divide pixel stellar populations using the pixel color-color diagram and population synthesis models. As a result, we find that the pixel population distributions across the spiral arms agree with a compressing process by spiral density waves: dense dust {yields} newly formed stars. The tidal interaction between NGC 5194 and NGC 5195 appears to enhance the star formation at the tidal bridge connecting the two galaxies. We find that the pixels corresponding to the central active galactic nucleus (AGN) area of NGC 5194 show a tight sequence at the bright-end of the pCMD, which are in the region of R {approx} 100 pc and may be a photometric indicator of AGN properties.

  5. Active galaxies. A fast and long-lived outflow from the supermassive black hole in NGC 5548.

    PubMed

    Kaastra, J S; Kriss, G A; Cappi, M; Mehdipour, M; Petrucci, P-O; Steenbrugge, K C; Arav, N; Behar, E; Bianchi, S; Boissay, R; Branduardi-Raymont, G; Chamberlain, C; Costantini, E; Ely, J C; Ebrero, J; Di Gesu, L; Harrison, F A; Kaspi, S; Malzac, J; De Marco, B; Matt, G; Nandra, K; Paltani, S; Person, R; Peterson, B M; Pinto, C; Ponti, G; Pozo Nuñez, F; De Rosa, A; Seta, H; Ursini, F; de Vries, C P; Walton, D J; Whewell, M

    2014-07-04

    Supermassive black holes in the nuclei of active galaxies expel large amounts of matter through powerful winds of ionized gas. The archetypal active galaxy NGC 5548 has been studied for decades, and high-resolution x-ray and ultraviolet (UV) observations have previously shown a persistent ionized outflow. An observing campaign in 2013 with six space observatories shows the nucleus to be obscured by a long-lasting, clumpy stream of ionized gas not seen before. It blocks 90% of the soft x-ray emission and causes simultaneous deep, broad UV absorption troughs. The outflow velocities of this gas are up to five times faster than those in the persistent outflow, and, at a distance of only a few light days from the nucleus, it may likely originate from the accretion disk.

  6. TWO EPOCHS OF VERY LARGE ARRAY OBSERVATIONS OF WATER MASER EMISSION IN THE ACTIVE GALAXY NGC 6240

    SciTech Connect

    Hagiwara, Yoshiaki

    2010-12-15

    Studies of 22 GHz H{sub 2}O maser emission from the merging galaxy NGC 6240 with double nuclei are presented. Two epochs of Very Large Array (VLA) observations in the A-configuration in spectral-line mode were carried out at 0.1 arcsec resolution by covering the redshifted velocity range of {approx}300 km s{sup -1} with respect to the systemic velocity of the galaxy. The purpose of these new observations is twofold: to detect an H{sub 2}O maser that an earlier VLA observation pinpointed in the southern nucleus in the northern nucleus as well to clarify the kinematics of the double nuclei, and to understand the origin of the maser in the galaxy. In the second epoch, one velocity feature peaking at V{sub LSR} = 7491.1 km s{sup -1}, redshifted by {approx}200 km s{sup -1} relative to the systemic velocity, was detected only toward the southern nucleus. The detection of an H{sub 2}O maser feature at or near this velocity had never been reported in earlier observations. However, including the known velocity features at redshifted velocities, no other velocity features were observed toward either nuclei throughout these epochs. The maser remains unresolved at an angular resolution of {approx}0.''1, corresponding to a linear size of less than about 45 pc. The two epochs of VLA observations show that the maser intensity is variable on timescales of at least three months, while the correlation between the maser intensity and the radio continuum intensity is not certain from our data. It is plausible that the maser in NGC 6240 is associated with the activity of an active galactic nucleus in the southern nucleus. Alternatively, the maser can be explained by star-forming activity at the site of massive star formation in the galaxy.

  7. ALMA observations of the dense and shocked gas in the nuclear region of NGC 4038 (Antennae galaxies)

    NASA Astrophysics Data System (ADS)

    Ueda, Junko; Watanabe, Yoshimasa; Iono, Daisuke; Wilner, David J.; Fazio, Giovanni G.; Ohashi, Satoshi; Kawabe, Ryohei; Saito, Toshiki; Komugi, Shinya

    2017-02-01

    We present 1″(<100 pc) resolution maps of millimeter emission from five molecules-CN, HCN, HCO+, CH3OH, and HNCO-obtained towards NGC 4038, which is the northern galaxy of the mid-stage merger, Antennae galaxies, with the Atacama Large Millimeter/submillimeter Array. Three molecules (CN, CH3OH, and HNCO) were detected for the first time in the nuclear region of NGC 4038. High-resolution mapping reveals a systematic difference in distributions of different molecular species and continuum emission. Active star-forming regions identified by the 3 mm and 850 μm continuum emission are offset from the gas-rich region associated with the HCN (1-0) and CO (3-2) peaks. The CN (1-0)/HCN (1-0) line ratios are enhanced (CN/HCN ≃ 0.8-1.2) in the star-forming regions, suggesting that the regions are photon dominated. The large molecular gas mass (108 M⊙) within a 0{^''.}6 (˜60 pc) radius of the CO (3-2) peak and a high dense gas fraction (>20%) suggested by the HCN (1-0)/CO (3-2) line ratio may signify a future burst of intense star formation there. The shocked gas traced in the CH3OH and HNCO emission indicates sub-kpc-scale molecular shocks. We suggest that the molecular shocks may be driven by collisions between inflowing gas and the central massive molecular complex.

  8. Detection of faint BLR components in the starburst/Seyfert galaxy NGC 6221 and measure of the central BH mass

    NASA Astrophysics Data System (ADS)

    La Franca, Fabio; Onori, Francesca; Ricci, Federica; Bianchi, Stefano; Marconi, Alessandro; Sani, Eleonora; Vignali, Cristian

    2016-04-01

    In the last decade, using single epoch virial based techniques in the optical band, it has been possible to measure the central black hole mass on large type 1 Active Galactive Nuclei (AGN) samples. However these measurements use the width of the broad line region as a proxy of the virial velocities and are therefore difficult to be carried out on those obscured (type 2) or low luminosity AGN where the nuclear component does not dominate in the optical. Here we present the optical and near infrared spectrum of the starburst/Seyfert galaxy NGC 6221, observed with X-shooter/VLT. Previous observations of NGC 6221 in the X-ray band shows an absorbed (N_H=8.5 +/- 0.4 x 10^21 cm^-2) spectrum typical of a type 2 AGN with luminosity log(L_14-195/ erg s^-1) = 42.05, while in the optical band its spectrum is typical of a reddened (A_V=3) starburst. Our deep X-shooter/VLT observations have allowed us to detect faint broad emission in the H_alpha, HeI and Pa_beta lines (FWHM=1400-2300 km s^-1) confirming previous studies indicating that NGC 6221 is a reddened starbust galaxy which hosts an AGN. We use the measure of the broad components to provide a first estimate of its central black hole mass (M_BH = 10^6.6+/-0.3 Msol, lambda_Edd=0.01-0.03), obtained using recently calibrated virial relations suitable for moderately obscured (N_H<10^24 cm^-2) AGN.

  9. DISCOVERY OF AN ACTIVE GALACTIC NUCLEUS DRIVEN MOLECULAR OUTFLOW IN THE LOCAL EARLY-TYPE GALAXY NGC 1266

    SciTech Connect

    Alatalo, K.; Blitz, L.; Young, L. M.; Davis, T. A.; Bureau, M.; Cappellari, M.; Scott, N.; Davies, R. L.; Lopez, L. A.; Shapiro, K. L.; Crocker, A. F.; MartIn, S.; Bois, M.; Emsellem, E.; Bournaud, F.; Duc, P.-A.; Falcon-Barroso, J.

    2011-07-10

    We report the discovery of a powerful molecular wind from the nucleus of the non-interacting nearby S0 field galaxy NGC 1266. The single-dish CO profile exhibits emission to {+-}400 km s{sup -1} and requires a nested Gaussian fit to be properly described. Interferometric observations reveal a massive, centrally concentrated molecular component with a mass of 1.1 x 10{sup 9} M{sub sun} and a molecular outflow with a molecular mass of {approx}2.4 x 10{sup 7} M{sub sun}. The molecular gas close to the systemic velocity consists of a rotating, compact nucleus with a mass of about 4.1 x 10{sup 8} M{sub sun} within a radius of {approx}60 pc. This compact molecular nucleus has a surface density of {approx}2.7 x 10{sup 4} M{sub sun} pc{sup -2}, more than two orders of magnitude larger than that of giant molecular clouds in the disk of the Milky Way, and it appears to sit on the Kennicutt-Schmidt relation despite its extreme kinematics and energetic activity. We interpret this nucleus as a disk that confines the outflowing wind. A mass outflow rate of {approx}13 M{sub sun} yr{sup -1} leads to a depletion timescale of {approx}<85 Myr. The star formation in NGC 1266 is insufficient to drive the outflow, and thus it is likely driven by the active galactic nucleus. The concentration of the majority of the molecular gas in the central 100 pc requires an extraordinary loss of angular momentum, but no obvious companion or interacting galaxy is present to enable the transfer. NGC 1266 is the first known outflowing molecular system that does not show any evidence of a recent interaction.

  10. Polar Ring Galaxies Favor Milgromian Dynamics over Standard Dark-Matter-Based Models

    NASA Astrophysics Data System (ADS)

    Lüghausen, F.; Famaey, B.; Kroupa, P.

    2014-05-01

    Polar ring galaxies are ideal objects with which to study the 3-dimensional shapes of galactic gravitational potentials since two rotation curves can be measured in two perpendicular planes. Observational studies have uncovered systematically larger rotation velocities in the extended polar rings than in the associated host galaxies. In the dark matter context, this can only be explained through dark halos that are systematically flattened along the polar rings. Here, we point out that these objects can also be used as very effective tests of gravity theories, such as those based on Milgromian dynamics. We run a set of polar ring models using both Milgromian and Newtonian dynamics to predict the expected shapes of the rotation curves in both planes, varying the total mass of the system, the mass of the ring with respect to the host, as well as the size of the hole at the center of the ring. We find that Milgromian dynamics not only naturally leads to rotation velocities being typically higher in the extended polar rings than in the hosts, as would be the case in Newtonian dynamics without dark matter, but that it also gets the shape and amplitude of velocities correct. Observational data on polar ring galaxies thus favour Milgromian dynamics over Newtonian dynamics plus dark matter.

  11. Interacting binary galaxies. IV. Simulations, masses, and spatial orientations for NGC 1587/1588 and NGC 7236/7237

    SciTech Connect

    Borne, K.D.

    1988-07-01

    Successful efforts to match interaction models to all of the available data for two pairs of interacting binary galaxies, Nos. 99 and 564 in the Karachentsev catalog of isolated pairs, are described. The results validate simple Newtonian gravity on the 10 kpc scale. The dynamical orbital status of both K99 and K564 is uniquely determined, and the masses and spatial orientations of the pairs are tightly constrained. Total masses for the pairs are derived which are quite reasonable and yield M/L values near 10. It is concluded that the observed disturbances in rotation velocity and luminosity distribution for these binary galaxies are entirely consistent with the merger hypothesis. Distortions including U-shaped rotation profiles and one-sided luminosity disturbances provide solid observational evidence of tidal friction in action. 18 references.

  12. Thickness determination of three-dimensional spiral galaxies.

    NASA Astrophysics Data System (ADS)

    Zhao, Shanghui; Bao, Mengxian; Zhang, Wenyuan; Peng, Qiuhe

    1992-12-01

    CCD images of some spiral galaxies were obtained with the 1-m telescope of Yunnan Observatory. After processing and measuring the images, the authors get the morphological parameters, thickness and their relative errors of seven spiral galaxies (NGC 2608, NGC 2713, NGC 2776, NGC 3631, NGC 5669, NGC 5985 and NGC 7156) by fitting their spiral arms with logarithmic spirals.

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

    NASA Astrophysics Data System (ADS)

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

    2002-02-01

    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 optical results, and our own Hα image, we have searched for X-ray and radio counterparts to previously known optically identified SNRs and for new previously unidentified SNRs at these two wavelength regimes. Consistent with our prior results for NGC 300, only a tiny minority of the optically identified SNRs have been found at another wavelength. The most noteworthy source in our study is N7793-S26, which is the only SNR in this galaxy that is detected at all three wavelengths (X-ray, optical, and radio). It features a long (~450 pc) filamentary morphology that is clearly seen in both the optical and the radio images. N7793-S26's radio luminosity exceeds that of the Galactic SNR Cas A, and based on equipartition calculations we determine that an energy of at least 1052 ergs is required to maintain this source. Such a result argues for the source being created by multiple supernova explosions rather than by a single supernova event. A second optically identified SNR, N7793-S11, has detectable radio emission but no detectable X-ray emission. A radio-selected sample of candidate SNRs has also been prepared by searching for coincidences between nonthermal radio sources and regions of Hα emission in this galaxy. This search has produced five new candidate radio SNRs to be added to the 28 SNRs that have already been detected by optical methods. A complementary search for new candidate X-ray SNRs has also been conducted by searching for soft-spectrum sources (kT<1 keV) that are coincident with regions of Hα emission. That search has yielded a candidate X-ray SNR that is coincident with one (and possibly two) of the

  14. SPECTRAL ANALYSIS AND INTERPRETATION OF THE {gamma}-RAY EMISSION FROM THE STARBURST GALAXY NGC 253

    SciTech Connect

    Abramowski, A.; Acero, F.; Akhperjanian, A. G.; Anton, G.; Balzer, A.; Brucker, J.; Barnacka, A.; Becherini, Y.; Birsin, E.; Biteau, J.; Brun, F.; Bolmont, J.; Brun, P.; Collaboration: H.E.S.S. Collaboration; and others

    2012-10-01

    Very high energy (VHE; E {>=} 100 GeV) and high-energy (HE; 100 MeV {<=} E {<=} 100 GeV) data from {gamma}-ray observations performed with the H.E.S.S. telescope array and the Fermi-LAT instrument, respectively, are analyzed in order to investigate the non-thermal processes in the starburst galaxy NGC 253. The VHE {gamma}-ray data can be described by a power law in energy with differential photon index {Gamma} = 2.14 {+-} 0.18{sub stat} {+-} 0.30{sub sys} and differential flux normalization at 1 TeV of F{sub 0} = (9.6 {+-} 1.5{sub stat}(+ 5.7, -2.9){sub sys}) Multiplication-Sign 10{sup -14} TeV{sup -1} cm{sup -2} s{sup -1}. A power-law fit to the differential HE {gamma}-ray spectrum reveals a photon index of {Gamma} 2.24 {+-} 0.14{sub stat} {+-} 0.03{sub sys} and an integral flux between 200 MeV and 200 GeV of F(0.2-200 GeV) = (4.9 {+-} 1.0{sub stat} {+-} 0.3{sub sys}) Multiplication-Sign 10{sup -9} cm{sup -2} s{sup -1}. No evidence for a spectral break or turnover is found over the dynamic range of both the LAT instrument and the H.E.S.S. experiment: a combined fit of a power law to the HE and VHE {gamma}-ray data results in a differential photon index {Gamma} = 2.34 {+-} 0.03 with a p-value of 30%. The {gamma}-ray observations indicate that at least about 20% of the energy of the cosmic rays (CRs) capable of producing hadronic interactions is channeled into pion production. The smooth alignment between the spectra in the HE and VHE {gamma}-ray domain suggests that the same transport processes dominate in the entire energy range. Advection is most likely responsible for charged particle removal from the starburst nucleus from GeV to multiple TeV energies. In a hadronic scenario for the {gamma}-ray production, the single overall power-law spectrum observed would therefore correspond to the mean energy spectrum produced by the ensemble of CR sources in the starburst region.

  15. Winds of change - a molecular outflow in NGC 1377?. The anatomy of an extreme FIR-excess galaxy

    NASA Astrophysics Data System (ADS)

    Aalto, S.; Muller, S.; Sakamoto, K.; Gallagher, J. S.; Martín, S.; Costagliola, F.

    2012-10-01

    Aims: Our goal was to investigate the molecular gas distribution and kinematics in the extreme far-infrared (FIR) excess galaxy NGC 1377 and to address the nature and evolutionary status of the buried source. Methods: We used high- (0''65 × 0''52, (65 × 52 pc)) and low- (4''88 × 2''93) resolution SubMillimeter Array (SMA) observations to image the 12CO and 13CO 2-1 line emission. Results: We find bright, complex 12CO 2-1 line emission in the inner 400 pc of NGC 1377. The 12CO 2-1 line has wings that are tracing a kinematical component that appears to be perpendicular to the component traced by the line core. Together with an intriguing X-shape of the integrated intensity and dispersion maps, this suggests that the molecular emission of NGC 1377 consists of a disk-outflow system. Lower limits to the molecular mass and outflow rate are Mout(H2) > 1 × 107 M⊙ and Ṁ > 8 M⊙ yr-1. The age of the proposed outflow is estimated to be 1.4 Myr, the extent to be 200 pc and the outflow speed to be Vout = 140 km s-1. The total molecular mass in the SMA map is estimated to Mtot(H2) = 1.5 × 108 M⊙ (on a scale of 400 pc) while in the inner r = 29 pc the molecular mass is Mcore(H2) = 1.7 × 107 M⊙ with a corresponding H2 column density of N(H2) = 3.4 × 1023 cm-2 and an average 12CO 2-1 brightness temperature of 19 K. 13CO 2-1 emission is found at a factor 10 fainter than 12CO in the low-resolution map while C18O 2-1 remains undetected. We find weak 1 mm continuum emission of 2.4 mJy with spatial extent less than 400 pc. Conclusions: Observing the molecular properties of the FIR-excess galaxy NGC 1377 allows us to probe the early stages of nuclear activity and the onset of feedback in active galaxies. The age of the outflow supports the notion that the current nuclear activity is young - a few Myr. The outflow may be powered by radiation pressure from a compact, dust enshrouded nucleus, but other driving mechanisms are possible. The buried source may be an active

  16. Young star clusters in circumnuclear starburst rings

    NASA Astrophysics Data System (ADS)

    de Grijs, Richard; Ma, Chao; Jia, Siyao; Ho, Luis C.; Anders, Peter

    2017-03-01

    We analyse the cluster luminosity functions (CLFs) of the youngest star clusters in two galaxies exhibiting prominent circumnuclear starburst rings. We focus specifically on NGC 1512 and NGC 6951, for which we have access to Hα data that allow us to unambiguously identify the youngest sample clusters. To place our results on a firm statistical footing, we first explore in detail a number of important technical issues affecting the process from converting the observational data into the spectral energy distributions of the objects in our final catalogues. The CLFs of the young clusters in both galaxies exhibit approximate power-law behaviour down to the 90 per cent observational completeness limits, thus showing that star cluster formation in the violent environments of starburst rings appears to proceed similarly as that elsewhere in the local Universe. We discuss this result in the context of the density of the interstellar medium in our starburst-ring galaxies.

  17. A 300-parsec-long jet-inflated bubble around a powerful microquasar in the galaxy NGC 7793.

    PubMed

    Pakull, Manfred W; Soria, Roberto; Motch, Christian

    2010-07-08

    Black-hole accretion states near or above the Eddington luminosity (the point at which radiation force outwards overcomes gravity) are still poorly known because of the rarity of such sources. Ultraluminous X-ray sources are the most luminous class of black hole (L(X) approximately 10(40) erg s(-1)) located outside the nuclei of active galaxies. They are likely to be accreting at super-Eddington rates, if they are powered by black holes with masses less than 100 solar masses. They are often associated with shock-ionized nebulae, though with no evidence of collimated jets. Microquasars with steady jets are much less luminous. Here we report that the large nebula S26 (ref. 4) in the nearby galaxy NGC 7793 is powered by a black hole with a pair of collimated jets. It is similar to the famous Galactic source SS433 (ref. 5), but twice as large and a few times more powerful. We determine a mechanical power of around a few 10(40) erg s(-1). The jets therefore seem 10(4) times more energetic than the X-ray emission from the core. S26 has the structure of a Fanaroff-Riley type II (FRII-type) active galaxy: X-ray and optical core, X-ray hot spots, radio lobes and an optical and X-ray cocoon. It is a microquasar where most of the jet power is dissipated in thermal particles in the lobes rather than relativistic electrons.

  18. Physical conditions in the x-ray emission-line gas in the Seyfert 2 galaxy NGC 1068

    NASA Astrophysics Data System (ADS)

    Sharma, Neetika

    2016-08-01

    Active Galactic Nuclei (AGN) reside in the centers of many (10%) galaxies. The nuclear spectra exhibit a broad (from radio to gamma-rays) non-stellar continuum which exceeds the luminosity of the host. AGN are thought to be powered by accretion of matter onto a supermassive black hole (BH~10 6--109 times the mass of the Sun). Since this activity takes place in a relatively small region (<< 3 light years), the central engine of even the closest AGN cannot be imaged directly with current technology. Nevertheless, spectroscopic observations can help us constrain the conditions of the gas very close to the BH. The scientific goal of my thesis is to examine the physical conditions in the circumnuclear regions of the Seyfert 2 galaxy NGC 1068. The soft X-ray spectrum comprises a multitude of emission lines including those of C, N, O, Ne, Mg, that arise in gas that is spatially extended over ~1000 light years. Radiative recombination continuum widths indicate the gas is photoionized and I model it finding a two-zone solution with unusual abundances attributed to the star formation history of the galaxy. Also of interest are the Fe K complex of em.

  19. Imaging and two-dimensional spectra of the IR-bright galaxy NGC 2146 - A recent low-energy merger?

    NASA Technical Reports Server (NTRS)

    Hutchings, J. B.; Lo, E.; Neff, S. G.; Stanford, S. A.; Unger, S. W.

    1990-01-01

    New data are presented on the IR-luminous galaxy NGC 2146 from several sources: direct imaging in B, R, and H-alpha; IR imaging in the J, H, and K bands; long-slit spectroscopy at optical and IR wavelengths; and scanning etalon observations in H-alpha. The results allow measurement of the interstellar extinction in the dust lane, and estimation of the true luminosity of the galaxy and nuclear regions. The spectra indicate that there is no active nucleus, and measure the changing ratio of forbidden to permitted lines across the galaxy. IR images and colors indicate the existence of a significant population of hot young stars in the central regions of the system. The H-alpha velocity maps show the full radial-velocity pattern, and suggest that the system consists of a disturbed disk and a merging or interacting arm which connects to the inner dust and radio structures. Outer H-alpha and H I structures appear to be the earlier remnants of this spiraling merger.

  20. LACK OF INTERACTION BETWEEN THE DUST GRAINS AND THE ANOMALOUS RADIO JET IN THE NEARBY SPIRAL GALAXY NGC 4258

    SciTech Connect

    Laine, Seppo; Krause, Marita; Tabatabaei, Fatemeh S.; Siopis, Christos E-mail: mkrause@mpifr-bonn.mpg.d E-mail: christos.siopis@ulb.ac.b

    2010-10-15

    We obtained Spitzer/IRAC 3.6-8 {mu}m images of the nearby spiral galaxy NGC 4258 to study possible interactions between dust and the radio jet. In our analysis, we also included high-resolution radio continuum, H{alpha}, CO, and X-ray data. Our data reveal that the 8 {mu}m emission, believed to originate largely from polycyclic aromatic hydrocarbon molecules and hot dust, is an excellent tracer of the normal spiral structure in NGC 4258, and hence it originates from the galactic plane. We investigated the possibility of dust destruction by the radio jet by calculating correlation coefficients between the 8 {mu}m and radio continuum emissions along the jet in two independent ways, namely, (1) from wavelet-transformed maps of the original images at different spatial scales and (2) from one-dimensional intensity cuts perpendicular to the projected path of the radio jet on the sky. No definitive sign of a correlation (or anticorrelation) was detected on relevant spatial scales with either approach, implying that any dust destruction must take place at spatial scales that are not resolved by our observations.

  1. X-ray Variability of the Magnetic Cataclysmic Variable V1432 Aql and the Seyfert Galaxy NGC 6814

    NASA Technical Reports Server (NTRS)

    Mukai, K.; Hellier, C.; Madejski, G.; Patterson, J.; Skillman, D. R.

    2003-01-01

    V1432 Aquilae (=RX J1940.2-1025) is the X-ray bright, eclipsing magnetic cataclysmic variable approximately 37 (sup) away from the Seyfert galaxy, NGC 6814. Due to a 0.3% difference between the orbital (12116.3 s) and the spin (12150 s) periods: the accretion geometry changes over the approximately 50 day beat period. Here we report the results of an RXTE campaign to observe the eclipse 25 times, as well as of archival observations with ASCA and BeppoSAX. Having confirmed that the eclipse is indeed caused by the secondary, we use the eclipse timings and profiles to map the accretion geometry as a function of the beat phase. We find that the accretion region is compact, and that it moves relative to the center of white dwarf on the beat period. The amplitude of this movement suggest a low-mass white dwarf, in contrast to the high mass previously estimated from its X-ray spectrum. The size of the X-ray emission region appears to be larger than in other eclipsing magnetic CVs. We also report on the RXTE data as well as the long-term behavior of NGC 6814, indicating flux variability by a factor of at least 10 on time scales of years.

  2. Gas kinematics in the inner kiloparsec of NGC 1386: a new clue to the torus-galaxy connection?

    NASA Astrophysics Data System (ADS)

    Lena, D.

    2015-09-01

    We used the GMOS integral field unit on the Gemini South telescope to investigate the kinematics of the circum-nuclear ionized gas in the Seyfert 2 galaxy NGC 1386. We found that the dominant kinematic components can be explained as a combination of rotation in the large-scale galactic disk and a compact bipolar outflow along the axis of the AGN 'radiation cone'. However, there is also compelling evidence for an additional kinematic component which is consistent with outflow and/or rotation in a plane that is approximately perpendicular to the axis of the AGN radiation cone. We speculate that this is a wind which is both outfowing in the equatorial plane of the torus, and rotating about the axis of the radiation cones. From the emission line surface brightness distribution, we infer the torus inclination and opening angle.

  3. Investigation of the Activity of the Nucleus of Seyfert Galaxy NGC 7469 during the Observation Period from 1990 TO 2008

    NASA Astrophysics Data System (ADS)

    Ugolkova, L. S.; Artamonov, B. P.

    We combine many published photometrical observations of the Seyfert Galaxy (SG) NGC 7469 and also new results from Hubble Space Telescope which can be used for future research of some properties of the activity of the nuclear of the SG. A drift of the activity maximum from 1997 to 1998 is observed with an increased of the wave length similarly to some blazars in radio range. Analyzing the surface photometry according to data obtained both at the Maidanak observatory and HST data an intensity asymmetry at the SG central region image is observed at different periods. The existence of a second compone