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Sample records for outer galaxy disks

  1. THE OUTER DISKS OF DWARF IRREGULAR GALAXIES

    SciTech Connect

    Hunter, Deidre A.; Massey, Philip; Wilsey, Nick; Riabokin, Malanka; Elmegreen, Bruce G.; Oh, Se-Heon; Anderson, Ed; Nordgren, Tyler E. E-mail: phil.massey@lowell.edu E-mail: riabokin@msu.edu E-mail: seheon-oh@ast.uct.ac.za E-mail: tyler_nordgren@redlands.edu

    2011-10-15

    In order to explore the properties of extreme outer stellar disks, we obtained ultra-deep V and GALEX ultraviolet (UV) images of four dwarf irregular galaxies and one blue compact dwarf galaxy, and ultra-deep B images of three of these. Our V-band surface photometry extends to 29.5 mag arcsec{sup -2}. We convert the FUV and V-band photometry, along with H{alpha} photometry obtained in a larger survey, into radial star formation rate profiles that are sensitive to timescales from 10 Myr to the lifetime of the galaxy. We also obtained H I-line emission data and compare the stellar distributions, surface brightness profiles, and star formation rate profiles to H I-line emission maps, gas surface density profiles, and gas kinematics. Our data lead us to two general observations. First, the exponential disks in these irregular galaxies are extraordinarily regular. We observe that the stellar disks continue to decline exponentially as far as our measurements extend. In spite of lumpiness in the distribution of young stars and H I distributions and kinematics that have significant unordered motions, sporadic processes that have built the disks-star formation, radial movement of stars, and perhaps even perturbations from the outside-have, nevertheless, conspired to produce standard disk profiles. Second, there is a remarkable continuity of star formation throughout these disks over time. In four out of five of our galaxies the star formation rate in the outer disk measured from the FUV tracks that determined from the V-band, to within factors of five, requiring star formation at a fairly steady rate over the galaxy's lifetime. Yet, the H I surface density profiles generally decline with radius more shallowly than the stellar light, and the gas is marginally gravitationally stable against collapse into clouds. Outer stellar disks are challenging our concepts of star formation and disk growth and provide a critical environment in which to understand processes that mold

  2. Outer Disk Star Formation in HI selected Galaxies

    NASA Astrophysics Data System (ADS)

    Meurer, G. R.

    2017-03-01

    The HI in galaxies often extends past their conventionally defined optical extent. I report results from our team which has been probing low intensity star formation in outer disks using imaging in Hα and ultraviolet. Using a sample of hundreds of HI selected galaxies, we confirm that outer disk HII regions and extended UV disks are common. Hence outer disks are not dormant but are dimly forming stars. Although the ultraviolet light in galaxies is more centrally concentrated than the HI, the UV/HI ratio (the Star Formation Efficiency) is nearly constant, with a slight dependency on surface brightness. This result is well accounted for in a model where disks maintain a constant stability parameter Q. This model also accounts for how the ISM and star formation are distributed in the bright parts of galaxies, and how HI appears to trace the distribution of dark matter in galaxy outskirts.

  3. Outer spiral structure in disk galaxies

    NASA Astrophysics Data System (ADS)

    Patsis, P. A.

    2017-03-01

    In several grand design barred-spiral galaxies it is observed a second, fainter, outer set of spiral arms. Typical examples of objects of this morphology can be considered NGC 1566 and NGC 5248. I suggest that such an overall structure can be the result of two dynamical mechanisms acting in the disc. The bar and both spiral systems rotate with the same pattern speed. The inner spiral is reinforced by regular orbits trapped around the stable, elliptical, periodic orbits of the central family, while the outer system of spiral arms is supported by chaotic orbits. Chaotic orbits are also responsible for a rhomboidal area surrounding the inner barred-spiral region. In general there is a discontinuity between the two spiral structures at the corotation region.

  4. The Red and Featureless Outer Disks of Nearby Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Watkins, Aaron E.; Mihos, J. Christopher; Harding, Paul

    2016-07-01

    We present results from deep, wide-field surface photometry of three nearby (D = 4-7 Mpc) spiral galaxies: M94 (NGC 4736), M64 (NGC 4826), and M106 (NGC 4258). Our imaging reaches a limiting surface brightness of {μ }B ˜ 28-30 mag arcsec-2 and probes colors down to {μ }B ˜ 27.5 mag arcsec-2. We compare our broadband optical data to available ultraviolet and high column density H i data to better constrain the star-forming history and stellar populations of the outermost parts of each galaxy’s disk. Each galaxy has a well-defined radius beyond which little star formation occurs and the disk light appears both azimuthally smooth and red in color, suggestive of old, well-mixed stellar populations. Given the lack of ongoing star formation or blue stellar populations in these galaxies’ outer disks, the most likely mechanisms for their formation are dynamical processes such as disk heating or radial migration, rather than inside-out growth of the disks. This is also implied by the similarity in outer disk properties despite each galaxy showing distinct levels of environmental influence, from a purely isolated galaxy (M94) to one experiencing weak tidal perturbations from its satellite galaxies (M106) to a galaxy recovering from a recent merger (M64), suggesting that a variety of evolutionary histories can yield similar outer disk structure. While this suggests a common secular mechanism for outer disk formation, the large extent of these smooth, red stellar populations—which reach several disk scale lengths beyond the galaxies’ spiral structure—may challenge models of radial migration given the lack of any nonaxisymmetric forcing at such large radii.

  5. Molecular gas in the outer disks of galaxies

    NASA Astrophysics Data System (ADS)

    Braine, Jonathan

    2017-03-01

    Molecular gas has still only been detected beyond the R25 radius in a few galaxies. Is this due to the low H2 content or to the difficulty of using Carbon Monoxide (CO) to trace H2? Similarly, star formation (SF) decreases sharply in the outer disks of spirals although HI is often plentiful; is the decrease in SF because there is little H2 or because the SF is very inefficient in the outer disk environment? Existing observations suggest that while outer disk clouds tend to be smaller (steeper mass function), their CO brightness temperature is only slightly lower than in the inner disk, at least when observed with sufficiently high angular resolution. In near-solar metallicity galaxies (Z >= 0.5Zsol ), the CO does not become intrinsically difficult to detect when H2 is present, even in the outer disk. While more observations of CO or other means of tracing H2 in the outer disks are necessary, current data tend to show that the SF rate per unit H2 remains approximately constant with galactocentric distance, indicating that the star formation proceeds normally but the transformation of HI into H2 is very slow in the outer disk.

  6. STAR CLUSTER POPULATIONS IN THE OUTER DISKS OF NEARBY GALAXIES

    SciTech Connect

    Herbert-Fort, Stephane; Zaritsky, Dennis; Di Paola, Andrea; Pogge, Richard W.; Ragazzoni, Roberto E-mail: dennis.zaritsky@gmail.com

    2012-08-01

    We present a Large Binocular Telescope imaging study that characterizes the star cluster component of nearby galaxy outer disks (beyond the optical radius R{sub 25}). Expanding on the pilot project of Herbert-Fort et al., we present deep ({approx}27.5 mag V-band point-source limiting magnitude) U- and V-band imaging of six galaxies: IC 4182, NGC 3351, NGC 4736, NGC 4826, NGC 5474, and NGC 6503. We find that the outer disk of each galaxy is populated with marginally resolved star clusters with masses {approx}10{sup 3} M{sub Sun} and ages up to {approx}1 Gyr (masses and ages are limited by the depth of our imaging and uncertainties are large given how photometry can be strongly affected by the presence or absence of a few stars in such low-mass systems), and that they are typically found out to at least 2 R{sub 25} but sometimes as far as 3-4 R{sub 25}-even beyond the apparent H I disk. The mean rate of cluster formation for 1 R{sub 25} {<=} R {<=} 1.5 R{sub 25} is at least one every {approx}2.5 Myr and the clusters are spatially correlated with the H I, most strongly with higher density gas near the periphery of the optical disk and with lower density neutral gas at the H I disk periphery. We hypothesize that the clusters near the edge of the optical disk are formed in the extension of spiral structure from the inner disk and are a fairly consistent phenomenon and that the clusters formed at the periphery of the H I disk are the result of accretion episodes.

  7. Disk Galaxies in the Outer Local Supercluster: Optical CCD Surface Photometry and Distribution of Galaxy Disk Parameter

    NASA Technical Reports Server (NTRS)

    Lu, N. Y.

    1998-01-01

    We report new B-band CCD surface photometry on a sample of 76 disk galaxies brighter than BT = 14.5 mag in the Uppsala General Catalogue of Galaxies, which are confined within a volume located in the outer part of the Local Supercluster.

  8. Cepheid variables in the flared outer disk of our galaxy.

    PubMed

    Feast, Michael W; Menzies, John W; Matsunaga, Noriyuki; Whitelock, Patricia A

    2014-05-15

    Flaring and warping of the disk of the Milky Way have been inferred from observations of atomic hydrogen but stars associated with flaring have not hitherto been reported. In the area beyond the Galactic centre the stars are largely hidden from view by dust, and the kinematic distances of the gas cannot be estimated. Thirty-two possible Cepheid stars (young pulsating variable stars) in the direction of the Galactic bulge were recently identified. With their well-calibrated period-luminosity relationships, Cepheid stars are useful distance indicators. When observations of these stars are made in two colours, so that their distance and reddening can be determined simultaneously, the problems of dust obscuration are minimized. Here we report that five of the candidates are classical Cepheid stars. These five stars are distributed from approximately one to two kiloparsecs above and below the plane of the Galaxy, at radial distances of about 13 to 22 kiloparsecs from the centre. The presence of these relatively young (less than 130 million years old) stars so far from the Galactic plane is puzzling, unless they are in the flared outer disk. If so, they may be associated with the outer molecular arm.

  9. The Stellar Populations in the Outer Banks of Massive Disk Galaxies

    NASA Astrophysics Data System (ADS)

    De Jong, Roelof; GHOSTS Team

    2006-12-01

    In recent years we have started to appreciate that the outer banks of galaxies contain valuable information about the formation process of galaxies. In hierarchical galaxy formation the stellar halos and thick disks of galaxies are formed by accretion of minor satellites, predominantly in the earlier assembly phases. The size, metallicity, and amount of substructure in current day halos are therefore directly related to issues like the small scale properties of the primordial power spectrum of density fluctuations and the suppression of star formation in small dark matter halos after reionization. We will show initial results from our ongoing HST/ACS GHOSTS (Galaxy Halos, Outer disks, Star clusters, Thick disks, and Substructure) survey of the resolved stellar populations of 14 nearby, massive disk galaxies. We will show that the smaller galaxies have no significant halo. We will present the stellar populations of a very low surface brightness stream around M83, the first such a stream resolved into stars beyond those of the Milky Way and M31. Finally, we will show that the old RGB stars of the thick disk in an edge-on galaxy truncate at the same radius as the young thin disk stars, providing insights into the formation of both disk truncations and thick disks.

  10. 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.

  11. Synthetic HI observations of spiral structure in the outer disk in galaxies

    NASA Astrophysics Data System (ADS)

    Khoperskov, Sergey A.; Bertin, Giuseppe

    2015-12-01

    > By means of 3D hydrodynamical simulations, in a separate paper we have discussed the properties of non-axisymmetric density wave trains in the outermost regions of galaxy disks, based on the picture that self-excited global spiral modes in the bright optical stellar disk are accompanied by low-amplitude short trailing wave signals outside corotation; in the gas, such wave trains can penetrate through the outer Lindblad resonance and propagate outwards, forming prominent spiral patterns. In this paper we present the synthetic 21 cm velocity maps expected from simulated models of the outer gaseous disk, focusing on the case when the disk is dominated by a two-armed spiral pattern, but considering also other more complex situations. We discuss some aspects of the spiral pattern in the gaseous periphery of galaxy disks noted in our simulations that might be interesting to compare with specific observed cases.

  12. The atomic gas in outer disks in semi-analytic models of galaxy formation†

    NASA Astrophysics Data System (ADS)

    Fu, Jian; Luo, Yu

    2017-03-01

    We use semi-analytic models of galaxy formation L-Galaxies based on ΛCDM cosmology to study the HI gas component in galaxy outskirts. We adopt the radially-resolved version of the models by Fu et al. (2013), which includes both atomic and molecular gas component in interstellar medium. This model has been recently updated by Luo et al. (2016) to include cold gas stripping in the outer disk regions of the satellite galaxies by ram pressure. In our models, we can perfectly reproduce the HI size-mass relation, which is discovered by Broeils & Rhee (1997) and confirmed by many subsequent observations. In our model, the reason for such tight correlation between HI size and mass is atomic-molecular phase conversion in high gas surface density regions while HI ionization in low gas surface density region, which leads to very narrow distribution of HI mean surface density. The models also reproduce the universal exponential HI radial profiles in galaxy outskirts found by Bluedisk (Wang et al. 2013), which arises from cold gas accretion onto the galaxy disks in exponentially profiles.

  13. THE EVOLUTION OF STELLAR POPULATIONS IN THE OUTER DISKS OF SPIRAL GALAXIES

    SciTech Connect

    Alberts, Stacey; Calzetti, Daniela; Dong Hui; Johnson, L. C.; Dale, Daniel A.; Bianchi, Luciana; Thilker, David; Chandar, Rupali; Kennicutt, Robert C.; Meurer, Gerhardt R.; Regan, Michael

    2011-04-10

    We investigate recent star formation in the extended ultraviolet (XUV) disks of five nearby galaxies (NGC 0628, NGC 2090, NGC 2841, NGC 3621, and NGC 5055) using a long wavelength baseline comprised of ultraviolet and mid-infrared imaging from the Galaxy Evolution Explorer and the Spitzer Infrared Array Camera. We identify 229 unresolved stellar complexes across targeted portions of their XUV disks and utilize spectral energy distribution fitting to measure their stellar ages and masses through comparison with Starburst99 population synthesis models of instantaneous burst populations. We find that the median age of outer-disk associations in our sample is {approx}100 Myr with a large dispersion that spans the entire range of our models (1 Myr to 1 Gyr). This relatively evolved state for most associations addresses the observed dearth of H{alpha} emission in some outer disks, as H{alpha} can only be observed in star-forming regions younger than {approx}10 Myr. The large age dispersion is robust against variations in extinction (in the range E(B - V) = 0-0.3 mag) and variations in the upper end of the stellar initial mass function (IMF). In particular, we demonstrate that the age dispersion is insensitive to steepening of the IMF, up to extreme slopes.

  14. Circumstellar disks in the outer Galaxy: the star-forming region NGC 1893

    NASA Astrophysics Data System (ADS)

    Caramazza, M.; Micela, G.; Prisinzano, L.; Rebull, L.; Sciortino, S.; Stauffer, J. R.

    2008-09-01

    Context: It is still debated whether star formation process depends on environment. In particular it is yet unclear whether star formation in the outer Galaxy, where the environmental conditions are, theoretically, less conducive, occurs in the same way as in the inner Galaxy. Aims: We investigate the population of NGC 1893, a young cluster ( 3{-}4 Myr) in the outer part of the Galaxy (RG ≥ 11 kpc), to explore the effects of environmental conditions on star forming regions. Methods: We present infrared observations acquired using the IRAC camera onboard the Spitzer Space Telescope and analyze the color-color diagrams to establish the membership of stars with excesses. We also merge this information with that obtained from Chandra ACIS-I observations, to identify the Class III population. Results: We find that the cluster is very rich, with 242 PMS Classical T Tauri stars and 7 Class 0/I stars. We identify 110 Class III candidate cluster members in the ACIS-I field of view. We estimate a disk fraction for NGC 1893 of about 67%, similar to fractions calculated for nearby star forming regions of the same age. Conclusions: Although environmental conditions are unfavorable, star formation can clearly be very successful in the outer Galaxy, allowing creation of a very rich cluster like NGC 1893.

  15. STAR FORMATION IN THE OUTER DISKS OF SPIRAL GALAXIES: ULTRAVIOLET AND H{alpha} PHOTOMETRY

    SciTech Connect

    Barnes, Kate L.; Van Zee, Liese; Skillman, Evan D. E-mail: vanzee@astro.indiana.edu

    2011-12-20

    We present an analysis of ultradeep UV and H{alpha} imaging of five nearby spiral galaxies to study the recent star formation in the outer disk. Using azimuthally averaged ellipse photometry as well as aperture photometry of individual young stellar complexes, we measure how star formation rates (SFRs) and UV and H{alpha} colors vary with radius. We detect azimuthally averaged UV flux to {approx}1.2-1.4 R{sub 25} in most galaxies; at the edge of the detected UV disk, the surface brightnesses are 28-29 mag arcsec{sup -2}, corresponding to SFR surface densities of {approx}3 Multiplication-Sign 10{sup -4} M{sub Sun} yr{sup -1} kpc{sup -2}. Additionally, we detect between 120 and 410 young stellar complexes per galaxy, with a significant number of detections out to {approx}1.5 R{sub 25}. We measure radial FUV-NUV profiles, and find that the dispersion in the UV colors of individual young stellar complexes increases with radius. We investigate how radial variations in the frequency of star formation episodes can create color gradients and increasing dispersion in the UV colors of star-forming regions, like those observed in our study. Specifically, we use recently published, high spatial and temporal resolution measurements of {Sigma}{sub SFR} throughout the disk of M33 to estimate the frequency of star formation episodes throughout the disk of a typical spiral galaxy. We use stellar synthesis models of these star formation histories (SFHs) to measure the variations in UV colors and find that we can replicate large dispersions in UV colors based on episodic SFHs.

  16. THE ACS NEARBY GALAXY SURVEY TREASURY. III. CEPHEIDS IN THE OUTER DISK OF M81

    SciTech Connect

    McCommas, Les P.; Williams, Benjamin F.; Dalcanton, Julianne J.; Davis, Matthew R.; Yoachim, Peter; Dolphin, Andrew E. E-mail: jd@astro.washington.edu E-mail: mrdavis@astro.washington.edu E-mail: adolphin@ratheon.com

    2009-06-15

    The ACS Nearby Galaxy Survey Treasury (ANGST) has acquired deep ACS imaging of a field in the outer disk of the large spiral galaxy M81. These data were obtained over a total of 20 Hubble Space Telescope orbits, providing a baseline long enough to reliably identify Cepheid variable stars in the field. Fundamental mode and first overtone types have been distinguished through comparative fits with corresponding Cepheid light curve templates derived from principal component analysis of confirmed Cepheids in the Large Magellanic Cloud (LMC), Small Magellanic Cloud, and Milky Way. A distance modulus of 27.78 {+-} 0.05 {sub r} {+-} 0.14 {sub s} with a corresponding distance of 3.60 {+-} 0.23 Mpc has been calculated from a sample of 11 fundamental mode and two first overtone Cepheids (assuming an LMC distance modulus of {mu}{sub LMC} = 18.41 {+-} 0.10 {sub r} {+-} 0.13 {sub s})

  17. The ACS Nearby Galaxy Survey Treasury. I. The Star Formation History of the M81 Outer Disk

    NASA Astrophysics Data System (ADS)

    Williams, Benjamin F.; Dalcanton, Julianne J.; Seth, Anil C.; Weisz, Daniel; Dolphin, Andrew; Skillman, Evan; Harris, Jason; Holtzman, Jon; Girardi, Léo; de Jong, Roelof S.; Olsen, Knut; Cole, Andrew; Gallart, Carme; Gogarten, Stephanie M.; Hidalgo, Sebastian L.; Mateo, Mario; Rosema, Keith; Stetson, Peter B.; Quinn, Thomas

    2009-01-01

    The Advanced Camera for Surveys (ACS) Nearby Galaxy Survey Treasury is a large Hubble Space Telescope (HST)/ACS treasury program to obtain resolved stellar photometry for a volume-limited sample of galaxies out to 4 Mpc. As part of this program, we have obtained deep ACS imaging of a field in the outer disk of the large spiral galaxy M81. The field contains the outskirts of a spiral arm as well as an area containing no current star formation. Our imaging results in a color-magnitude diagram (CMD) reaching to m F814W = 28.8 and m F606W = 29.5, one magnitude fainter than the red clump. Through detailed modeling of the full CMD, we quantify the age and metallicity distribution of the stellar populations contained in the field. The mean metallicity in the field is -1 < [M/H] < 0 and only a small fraction of stars have ages lsim 1 Gyr. The results show that most of the stars in this outer disk field were formed by z ~ 1 and that the arm structure at this radius has a lifetime of gsim 100 Myr. We discuss the measured evolution of the M81 disk in the context of surveys of high redshift disk galaxies and deep stellar photometry of other nearby galaxies. All of these indicate that massive spiral disks are mostly formed by z ~ 1 and that they have experienced rapid metal enrichment.

  18. Star formation history at the centers of lenticular galaxies with bars and purely exponential outer disks from SAURON data

    NASA Astrophysics Data System (ADS)

    Sil'Chenko, O. K.; Chilingarian, I. V.

    2011-01-01

    We have investigated the stellar population properties in the central regions of a sample of lenticular galaxies with bars and single-exponential outer stellar disks using the data from the SAURON integral-field spectrograph retrieved from the open Isaac Newton Group Archive. We have detected chemically decoupled compact stellar nuclei with a metallicity twice that of the stellar population in the bulges in seven of the eight galaxies. A starburst is currently going on at the center of the eighth galaxy and we have failed to determine the stellar population properties from its spectrum. The mean stellar ages in the chemically decoupled nuclei found range from 1 to 11 Gyr. The scenarios for the origin of both decoupled nuclei and lenticular galaxies as a whole are discussed.

  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. THE STRUCTURE AND STELLAR CONTENT OF THE OUTER DISKS OF GALAXIES: A NEW VIEW FROM THE Pan-STARRS1 MEDIUM DEEP SURVEY

    SciTech Connect

    Zheng, Zheng; Thilker, David A.; Heckman, Timothy M.; Meurer, Gerhardt R.; Burgett, W. S.; Huber, M. E.; Kaiser, N.; Magnier, E. A.; Tonry, J. L.; Wainscoat, R. J.; Waters, C.; Chambers, K. C.; Metcalfe, N.; Price, P. A.

    2015-02-20

    We present the results of an analysis of Pan-STARRS1 Medium Deep Survey multi-band (grizy) images of a sample of 698 low-redshift disk galaxies that span broad ranges in stellar mass, star-formation rate, and bulge/disk ratio. We use population synthesis spectral energy distribution fitting techniques to explore the radial distribution of the light, color, surface mass density, mass/light ratio, and age of the stellar populations. We characterize the structure and stellar content of the galaxy disks out to radii of about twice Petrosian r {sub 90}, beyond which the halo light becomes significant. We measure normalized radial profiles for sub-samples of galaxies in three bins each of stellar mass and concentration. We also fit radial profiles to each galaxy. The majority of galaxies have down-bending radial surface brightness profiles in the bluer bands with a break radius at roughly r {sub 90}. However, they typically show single unbroken exponentials in the reddest bands and in the stellar surface mass density. We find that the mass/light ratio and stellar age radial profiles have a characteristic 'U' shape. There is a good correlation between the amplitude of the down-bend in the surface brightness profile and the rate of the increase in the M/L ratio in the outer disk. As we move from late- to early-type galaxies, the amplitude of the down-bend and the radial gradient in M/L both decrease. Our results imply a combination of stellar radial migration and suppression of recent star formation can account for the stellar populations of the outer disk.

  1. Disks in elliptical galaxies

    SciTech Connect

    Rix, H.; White, S.D.M. )

    1990-10-01

    The abundance and strength of disk components in elliptical galaxies are investigated by studying the photometric properties of models containing a spheroidal r exp 1/4-law bulge and a weak exponential disk. Pointed isophotes are observed in a substantial fraction of elliptical galaxies. If these isophote distortions are interpreted in the framework of the present models, then the statistics of observed samples suggest that almost all radio-weak ellipticals could have disks containing roughly 20 percent of the light. It is shown that the E5 galaxy NGC 4660 has the photometric signatures of a disk containing a third of the light. 30 refs.

  2. Secular Evolution in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Kormendy, John

    2013-10-01

    Self-gravitating systems evolve toward the most tightly bound configuration that is reachable via the evolution processes that are available to them. They do this by spreading -- the inner parts shrink while the outer parts expand -- provided that some physical process efficiently transports energy or angular momentum outward. The reason is that self-gravitating systems have negative specific heats. As a result, the evolution of stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks and galaxy disks are fundamentally similar. How evolution proceeds then depends on the evolution processes that are available to each kind of self-gravitating system. These processes and their consequences for galaxy disks are the subjects of my lectures and of this Canary Islands Winter School. I begin with a review of the formation, growth and death of bars. Then I review the slow (`secular') rearrangement of energy, angular momentum, and mass that results from interactions between stars or gas clouds and collective phenomena such as bars, oval disks, spiral structure and triaxial dark haloes. The `existence-proof' phase of this work is largely over: we have a good heuristic understanding of how nonaxisymmetric structures rearrange disk gas into outer rings, inner rings and stuff dumped onto the centre. The results of simulations correspond closely to the morphology of barred and oval galaxies. Gas that is transported to small radii reaches high densities. Observations confirm that many barred and oval galaxies have dense central concentrations of gas and star formation. The result is to grow, on timescales of a few Gyr, dense central components that are frequently mistaken for classical (elliptical-galaxy-like) bulges but that were grown slowly out of the disk (not made rapidly by major mergers). The resulting picture of secular galaxy evolution accounts for the richness observed in galaxy structure. We can distinguish between classical and pseudo

  3. The Mass Distribution in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Courteau, Stéphane; Dutton, Aaron A.

    We present the relative fraction of baryons and dark matter at various radii in galaxies. For spiral galaxies, this fraction measured in a galaxy's inner parts is typically baryon-dominated (maximal) and dark-matter dominated (sub-maximal) in the outskirts. The transition from maximal to sub-maximal baryons occurs within the inner parts of low-mass disk galaxies (with V tot <= 200 km s-1) and in the outer disk for more massive systems. The mean mass fractions for late- and early-type galaxies vary significantly at the same fiducial radius and circular velocity, suggesting a range of galaxy formation mechanisms. A more detailed discussion, and resolution of the so-called ``maximal disk problem'', is presented in Courteau & Dutton, ApJL, 801, 20.

  4. A twisted disk equation that describes warped galaxy disks

    NASA Technical Reports Server (NTRS)

    Barker, K.

    1994-01-01

    Warped H1 gas layers in the outer regions of spiral galaxies usually display a noticeably twisted structure. This structure is thought to arise primarily as a result of differential precession in the H1 disk as it settles toward a 'preferred orientation' in an underlying dark halo potential well that is not spherically symmetric. In an attempt to better understand the structure and evolution of these twisted, warped disk structures, we have utilized the 'twist-equation' formalism. Specifically, we have generalized the twist equation to allow the treatment of non-Keplerian disks and from it have derived the steady-state structure of twisted disks that develop from free precession in a nonspherical, logarithmic halo potential. This generalized equation can also be used to examine the time-evolutionary behavior of warped galaxy disks.

  5. The ACS Nearby Galaxy Survey Treasury. II. Young Stars and their Relation to Hα and UV Emission Timescales in the M81 Outer Disk

    NASA Astrophysics Data System (ADS)

    Gogarten, Stephanie M.; Dalcanton, Julianne J.; Williams, Benjamin F.; Seth, Anil C.; Dolphin, Andrew; Weisz, Daniel; Skillman, Evan; Holtzman, Jon; Cole, Andrew; Girardi, Leo; de Jong, Roelof S.; Karachentsev, Igor D.; Olsen, Knut; Rosema, Keith

    2009-01-01

    We have obtained resolved stellar photometry from Hubble Space Telescope Advanced Camera for Surveys observations of a field in the outer disk of M81 as part of ANGST. Motivated by the recent discovery of extended UV disks around many nearby spiral galaxies, we use the observed stellar population to derive the recent star formation histories of five ~ 0.5 kpc-sized regions within this field. These regions were selected on the basis of their UV luminosity from GALEX and include two H II regions, two regions that are UV-bright but Hα-faint, and one "control" region faint in both UV and Hα. We estimate our effective star formation rate detection limit at ~2 × 10-4 M sun yr-1, which is lower than that of GALEX for regions of this size. As expected, the H II regions contain massive main-sequence stars (in the mass range 18-27 M sun, based on our best extinction estimates), while similar massive main-sequence stars are lacking in the UV-bright/Hα-faint regions. The observations are consistent with stellar ages lsim 10 Myr in the H II regions, and gsim 16 Myr in the UV-bright/Hα-faint regions. All regions but the control have formed ~ 104 M sun of stars over the past ~ 65 Myr. Thus, our results, for at least one small area in the outer disk of M81, are consistent with an age difference being sufficient to explain the observed discrepancy between star forming regions detected in Hα and those detected exclusively in UV. However, our data cannot conclusively rule out other explanations, such as a strongly truncated initial mass function.

  6. Mass distributions in disk galaxies

    NASA Astrophysics Data System (ADS)

    Martinsson, Thomas; Verheijen, Marc; Bershady, Matthew; Westfall, Kyle; Andersen, David; Swaters, Rob

    2017-03-01

    We present results on luminous and dark matter mass distributions in disk galaxies from the DiskMass Survey. As expected for normal disk galaxies, stars dominate the baryonic mass budget in the inner region of the disk; however, at about four optical scale lengths (hR ) the atomic gas starts to become the dominant contributor. Unexpectedly, we find the total baryon to dark-matter fraction within a galaxy stays nearly constant with radius from 1hR out to at least 6hR , with a baryon fraction of 15-50% among galaxies. On average, only one third of the mass within 2.2hR in a disk galaxy is baryonic and these baryons appear to have had only a minor effect on the distribution of the dark matter.

  7. The Young Outer Disk of M83

    NASA Astrophysics Data System (ADS)

    Davidge, T. J.

    2010-08-01

    Deep near-infrared images recorded with NICI on Gemini South are used to investigate the evolved stellar content in the outer southeast quadrant of the spiral galaxy M83. A diffuse population of asymptotic giant branch (AGB) stars is detected, indicating that there are stars outside of the previously identified young and intermediate age star clusters in the outer disk. The brightest AGB stars have M K >= -8, and the AGB luminosity function (LF) is well matched by model LFs that assume ages <=1 Gyr. The specific star formation rate (SFR) during the past few Gyr estimated from AGB star counts is consistent with that computed from mid-infrared observations of star clusters at similar radii, and it is concluded that the disruption timescale for star clusters in the outer disk is Lt1 Gyr. The LF and specific frequency of AGB stars vary with galactocentric radius, in a manner that is indicative of lower luminosity-weighted ages at larger radii. Modest numbers of red supergiants are also found, indicating that there has been star formation during the past 100 Myr, while the ratio of C stars to M giants is consistent with that expected for a solar metallicity system that has experienced a constant SFR for the past few Gyr. The results drawn from the properties of resolved AGB stars are broadly consistent with those deduced from integrated light observations in the UV. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a co-operative 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 of Canada (Canada), CONICYT (Chile), the Australian Research Council (Australia), the Ministerio da Ciencia e Technologia (Brazil), and the Ministerio de Ciencia, Tecnologia e Innovacion Productiva (Argentina).

  8. Diversity of Debris Disks - Constraining the Disk Outer Radii

    NASA Astrophysics Data System (ADS)

    Rieke, George; Smith, Paul; Su, Kate

    2008-03-01

    Existing Spitzer observations of debris disks show a wide range of diversity in disk morphologies and spectral energy distributions (SEDs). The majority of debris disks observed with Spitzer are not resolved, resulting in very few direct constraints on disk extent. In general, SEDs alone have little diagnostic power beyond some basic statistics. However, as demonstrated by some Spitzer observations of nearby systems (beta Leo and gamma Oph), the spectra of the excess emission in the IRS and MIPS-SED wavelength range can help to put tighter constraints on disk properties such as minimum/maximum grain sizes and inner/outer disk radii. The dust continuum slopes are very useful to differentiate between various disk structures and constrain the dust mass. We need to study sufficient numbers of disks to explore their characteristics systematically. Therefore, we propose to obtain MIPS-SED observations of 27 debris disks that already have IRS-LL spectra and MIPS 24 and 70 micron photometry.

  9. IC 1689: S0 galaxy with inner polar disk.

    NASA Astrophysics Data System (ADS)

    Hagen-Thorn, V. A.; Reshetnikov, V. P.

    1997-03-01

    The results of spectroscopic observations of the S0 galaxy IC 1689 are given. The radial velocity curves constructed from the measurements of Hα and [NII]λ6583 lines show that in the galaxy interior there is a gas disk (r=~3kpc) rotating around the axis placed in the main plane of the galaxy (polar disk). Active star formation occurs in the outer part of the disk (in the ring). Both Hα and [NII]λ6583 emission lines are observed here. Only collisionally excited [NII] radiates in the inner regions of the disk.

  10. DUSTiNGS. III. Distribution of Intermediate-age and Old Stellar Populations in Disks and Outer Extremities of Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    McQuinn, Kristen B.; Boyer, Martha; DUSTiNGS Team

    2017-06-01

    As part of the DUST in Nearby Galaxies with Spitzer (DUSTiNGS) survey, we have traced the spatial distributions of intermediate-age and old stars in nine dwarf galaxies in the distant parts of the Local Group. We find intermediate age stars are well mixed with the older populations and extend to large radii, indicating that chemical enrichment from these dust-producing stars may occur in the outer regions of galaxies with some frequency. Theories of structure formation in dwarf galaxies must account for the lack of radial gradients in intermediate-age populations and the presence of these stars in the outer extremities of dwarfs. We also identify the tip of the red giant branch (TRGB) in Spitzer IRAC 3.6 μm photometry. Unlike the constant TRGB in the I band, at 3.6 μm, the TRGB magnitude varies by ˜0.7 mag and is not a metallicity independent distance indicator.

  11. Secular evolution in disk galaxies

    NASA Astrophysics Data System (ADS)

    Knapen, J. H.

    2013-05-01

    The detailed study of the different structural components of nearby galaxies can supply vital information about the secular, or internal, evolution of these galaxies which they may have undergone since their formation. We highlight a series of new studies based on the analysis of mid-infrared images of over 2000 local galaxies which we are collecting within the Spitzer Survey of Stellar Structure in Galaxies (S^4G). In particular, we discuss new results on the thick and thin disk components of galaxies, which turn out to be roughly equally massive, and whose properties indicate that the thick disks mostly formed in situ, and to a lesser degree as a result of galaxy-galaxy interactions and secular evolution. We then briefly review recent research into rings in galaxies, which are common and closely linked to secular evolution of galaxies. Finally, we report on the research into local galaxy morphology, kinematics and stellar populations that we will perform over the coming four years within the EU-funded initial training network DAGAL (Detailed Anatomy of GALaxies).

  12. Deprojecting Edge-on Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Pohlen, M.; Zaroubi, S.; Peletier, R. F.

    2007-05-01

    We present the results of a study of the intrinsic 3 dimensional distribution of stars in a pilot sample of ˜10 edge-on disk galaxies. The reconstruction of the 3D disk structure has been obtained through a direct deprojecting of the two-dimensional images subject to the assumption of axial symmetry. The deprojection method -- which utilises the so called Fourier slice theorem -- has been tested with a large set of artificial galaxy models seen under different inclinations (80 < i <= 90) with various stellar distributions (e.g. truncated, untruncated), and with different dust distributions (spatially and with varying optical depth). For this pilot sample we are able to recover all three main classes of disk shapes (untruncated, truncated, antitruncated) recently found for complete samples of intermediate to face-on galaxies (Erwin et al. 2005, Pohlen & Trujillo 2006). The parameters (scalelength and surface brightness) of the breaks in the radial light distribution (marking the truncations) are consistent with those of face-on galaxies. Consequently, we are now able to avoid some of the problems caused by the line-of-sight integration while fitting edge-on galaxies and show that the classification introduced for face-on galaxies is indeed consistent and independent of the geometry. For the first time we present deprojection of several slices, vertically extending and parallel to the major axis. This allows to measure the thick disk component, which appear as an increasing radial scalelength (i.e. h= h(z)). Furthermore, the deprojection allows the study of the vertical distribution of the outer disk, beyond the break region, where we measure a significant increase in scalelength with vertical distance from the major axis.

  13. Galaxy Mergers and Disk Formation

    NASA Astrophysics Data System (ADS)

    Naab, Thorsten; Burkert, Andreas

    We present results from high resolution N-body/SPH simulations of merging gas-rich disk galaxies. The simulations were performed using a newly developed parallel TREE-algorithm in combination with the special purpose hardware GRAPE-5. We find that the presence of gas changes the kinematical properties of the resulting merger remnants, resulting in shapes of the velocity profiles that are in good agreement with observed boxy, non-rotating and disky, fast-rotating elltiptical galaxies. We find large scale disk-like components in unequal mass merger remnants which form by late gas infall. In addition we explore limits on gas infall and the starformation rate during the merging epoch as a function of the mass ratio and the geometry of the merging disk galaxies.

  14. The Stability of Galaxy Disks

    NASA Astrophysics Data System (ADS)

    Westfall, Kyle B.; Andersen, D. R.; Bershady, M. A.; Martinsson, T.; Swaters, R. A.; Verheijen, M. A.

    2013-01-01

    Using measurements of velocity dispersion and mass surface density for both the gas and stellar components, we calculate the multi-component stability (Q) for 30 galaxy disks observed by the DiskMass Survey. Despite their sub-maximality (Bershady et al. 2011, ApJL, 739, 47), we find all disks to be stable with roughly 85% falling in the range 1galaxy. We measure the shape of the SVE using methods developed by Westfall (2009, PhD Thesis) and Westfall et al. (2011, ApJ, 742, 18); these methods primarily hinge on asymmetric-drift measurements determined by our gas and stellar rotation curves. We find high-quality SVE measurements for a third of the galaxies in our sample. Practical (inclination) limitations and/or the requisite dynamical assumptions in these methods currently prevent satisfactory SVE solutions for the remainder of our sample; for these galaxies, we determine Q using reasonable SVE estimates based on our own high-quality results and others gathered from the literature (e.g., van der Kruit & de Grijs 1999, A&A, 352, 129; Gerssen & Shapiro Griffin 2012, MNRAS, 423, 2726). Finally, we explore correlations between disk stability and other galaxy properties such as star-formation rate, gas mass fraction, disk maximality, and Hubble type to understand their interdependencies within the context of the secular evolution of galaxy disks. We acknowledge support for this work from the National Science Foundation (AST-0307417, AST-0607516, OISE-0754437, AST-1009491), The Netherlands Organisation for Scientific Research (grant 614.000.807), the UW Graduate School (PRJ13SL, 050167, and the Vilas Associate award), the Leids Kerkhoven-Bosscha Fonds, and NASA/JPL/Spitzer (GO-30894).

  15. DUSTiNGS. III. Distribution of Intermediate-age and Old Stellar Populations in Disks and Outer Extremities of Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    McQuinn, Kristen B. W.; Boyer, Martha L.; Mitchell, Mallory B.; Skillman, Evan D.; Gehrz, R. D.; Groenewegen, Martin A. T.; McDonald, Iain; Sloan, G. C.; van Loon, Jacco Th.; Whitelock, Patricia A.; Zijlstra, Albert A.

    2017-01-01

    We have traced the spatial distributions of intermediate-age and old stars in nine dwarf galaxies in the distant parts of the Local Group, using multi-epoch 3.6 and 4.5 μm data from the DUST in Nearby Galaxies with Spitzer (DUSTiNGS) survey. Using complementary optical imaging from the Hubble Space Telescope, we identify the tip of the red giant branch (TRGB) in the 3.6 μm photometry, separating thermally pulsating asymptotic giant branch stars from the larger red giant branch populations. Unlike the constant TRGB in the I band, at 3.6 μm, the TRGB magnitude varies by ˜0.7 mag, making it unreliable as a distance indicator. The intermediate-age and old stars are well mixed in two-thirds of the sample, with no evidence of a gradient in the ratio of the intermediate-age to old stellar populations outside the central ˜1‧-2‧. Variable AGB stars are detected in the outer extremities of the galaxies, indicating that chemical enrichment from these dust-producing stars may occur in the outer regions of galaxies with some frequency. Theories of structure formation in dwarf galaxies must account for the lack of radial gradients in intermediate-age populations and the presence of these stars in the outer extremities of dwarfs. Finally, we identify unique features in individual galaxies, such as extended tidal features in Sex A and Sag DIG and a central concentration of AGB stars in the inner regions of NGC 185 and NGC 147.

  16. High velocity clouds in nearby disk galaxies

    NASA Technical Reports Server (NTRS)

    Schulman, Eric; Bregman, Joel N.; Roberts, Morton S.; Brinks, Elias

    1993-01-01

    Clouds of neutral hydrogen in our galaxy with the absolute value of v greater than 100 km/s cover approximately 10 percent of the sky to a limiting column density of 1 x 10(exp 18) cm(exp -2). These high velocity clouds (HVCs) may dominate the kinetic energy of neutral hydrogen in non-circular motion, and are an important though poorly understood component of galactic gas. It has been suggested that the HVCs can be reproduced by a combination of three phenomena: a galactic fountain driven by disk supernovae which would account for most of the HVCs, material tidally torn from the Magellanic Clouds, and an outer arm complex which is associated with the large scale structure of the warped galactic disk. We sought to detect HVCs in external galaxies in order to test the galactic fountain model.

  17. Triaxiality in disk galaxies

    SciTech Connect

    Bertola, F.; Vietri, M.; Zeilinger, W.W. Roma, Osservatorio Astronomico, Rome European Southern Observatory, Garching )

    1991-06-01

    Thirty-two bulges of nearby spirals have been observed, to detect misalignment between disk and bulge apparent major axes. Such misalignment is unequivocally present in the majority of observed objects. This may be due to the triaxiality of disks, bulges, or both. The probability distribution function for the axial ratios is derived under the two extreme hypotheses, i.e., that either only disks (case I) or only bulges (case II) are triaxial: the observational data are equally well fitted by either one. Since dynamical evidence and the internal twisting of isophotes show that bulges are triaxial, case I is unlikely, but an intermediate case cannot be ruled out. These distribution functions are compared with available constraints; in particular, that of case II is projected and compared with the distribution of apparent ellipticities of minor-axis dust-lane ellipticals and of all ellipticals. Both tests show that the observed and derived distributions are consistent. 34 refs.

  18. Properties of isolated disk galaxies

    NASA Astrophysics Data System (ADS)

    Varela, J.; Moles, M.; Márquez, I.; Galletta, G.; Masegosa, J.; Bettoni, D.

    2004-06-01

    We present a new sample of northern isolated galaxies, which are defined by the physical criterion that they were not affected by other galaxies in their evolution during the last few Gyr. To find them we used the logarithmic ratio, f, between inner and tidal forces acting upon the candidate galaxy by a possible perturber. The analysis of the distribution of the f-values for the galaxies in the Coma cluster lead us to adopt the criterion f ≤ -4.5 for isolated galaxies. The candidates were chosen from the CfA catalog of galaxies within the volume defined by cz ≤5000 km s-1, galactic latitude higher than 40o and declination ≥-2.5o. The selection of the sample, based on redshift values (when available), magnitudes and sizes of the candidate galaxies and possible perturbers present in the same field is discussed. The final list of selected isolated galaxies includes 203 objects from the initial 1706. The list contains only truly isolated galaxies in the sense defined, but it is by no means complete, since all the galaxies with possible companions under the f-criterion but with unknown redshift were discarded. We also selected a sample of perturbed galaxies comprised of all the disk galaxies from the initial list with companions (with known redshift) satisfying f ≥ -2 and \\Delta(cz) ≤500 km s-1; a total of 130 objects. The statistical comparison of both samples shows significant differences in morphology, sizes, masses, luminosities and color indices. Confirming previous results, we found that late spiral, Sc-type galaxies are, in particular, more frequent among isolated galaxies, whereas Lenticular galaxies are more abundant among perturbed galaxies. Isolated systems appear to be smaller, less luminous and bluer than interacting objects. We also found that bars are twice as frequent among perturbed galaxies compared to isolated galaxies, in particular for early Spirals and Lenticulars. The perturbed galaxies have higher LFIR/LB and Mmol/LB ratios, but the

  19. Secondary Disks and Disk Regrowth in S0 Galaxies

    NASA Astrophysics Data System (ADS)

    Moffett, Amanda; Kannappan, Sheila; Norris, Mark; Khochfar, Sadegh; Berlind, Andreas

    2010-08-01

    Early-type galaxies are predicted to regrow late-type disks in hierarchical models of galaxy formation, but the observational confirmation of this process remains largely indirect. We seek to approach this problem kinematically by searching for evidence of disk regrowth in the form of extended secondary disks in S0s (distinct from the small-scale KDCs identified in SAURON). In order to address the possible contribution of secondary disks not indicative of true disk regrowth and the expected variations of secondary disk frequency with mass, color, and environment, we propose deep spectroscopy of a broad sample of 60 S0 galaxies located in the RESOLVE Survey volume. With these data and similar data in hand for ~12 additional S0s, we aim both to resolve conflicting measurements of the frequency of secondary disks in early-type galaxies and to determine the incidence of disk regrowth.

  20. Old open clusters in the outer Galactic disk

    NASA Astrophysics Data System (ADS)

    Carraro, G.; Geisler, D.; Villanova, S.; Frinchaboy, P. M.; Majewski, S. R.

    2007-12-01

    Context: The outer parts of the Milky Way disk are believed to be one of the main arenas where the accretion of external material in the form of dwarf galaxies and subsequent formation of streams is taking place. The Monoceros stream and the Canis Major and Argo over-densities are notorious examples. Understanding whether what we detect is the signature of accretion or, more conservatively, simply the intrinsic nature of the disk, represents one of the major goals of modern Galactic astronomy. Aims: We try to shed more light on the properties of the outer disk by exploring the properties of distant anti-center old open clusters. We want to verify whether distant clusters follow the chemical and dynamical behavior of the solar vicinity disk, or whether their properties can be better explained in terms of an extra-galactic population. Methods: VLT high resolution spectra have been acquired for five distant open clusters: Ruprecht 4, Ruprecht 7, Berkeley 25, Berkeley 73 and Berkeley 75. We derive accurate radial velocities to distinguish field interlopers and cluster members. For the latter we perform a detailed abundance analysis and derive the iron abundance [Fe/H] and the abundance ratios of several α elements. Results: Our analysis confirms previous indications that the radial abundance gradient in the outer Galactic disk does not follow the expectations extrapolated from the solar vicinity, but exhibits a shallower slope. By combining the metallicity of the five program clusters with eight more clusters for which high resolution spectroscopy is available, we find that the mean metallicity in the outer disk between 12 and 21 kpc from the Galactic center is [Fe/H] ≈ -0.35, with only marginal indications for a radial variation. In addition, all the program clusters exhibit solar scaled or slightly enhanced α elements, similar to open clusters in the solar vicinity and thin disk stars. Conclusions: We investigate whether this outer disk cluster sample might

  1. Disk Galaxies : Building Blocks Of The Universe?

    NASA Astrophysics Data System (ADS)

    Bower, Richard

    2016-10-01

    In my talk I look at the origin of disk galaxies from the theoretical perspective. In particular I look at simple ways to use the properties of disk galaxies, and their evolution, to test our current paradigm for galaxy formation within the CDM scenario.

  2. FORMING DOUBLE-BARRED GALAXIES FROM DYNAMICALLY COOL INNER DISKS

    SciTech Connect

    Du, Min; Shen, Juntai; Debattista, Victor P.

    2015-05-10

    About one-third of early-type barred galaxies host small-scale secondary bars. The formation and evolution of such double-barred (S2B) galaxies remain far from being well understood. In order to understand the formation of such systems, we explore a large parameter space of isolated pure-disk simulations. We show that a dynamically cool inner disk embedded in a hotter outer disk can naturally generate a steady secondary bar while the outer disk forms a large-scale primary bar. The independent bar instabilities of inner and outer disks result in long-lived double-barred structures whose dynamical properties are comparable to those in observations. This formation scenario indicates that the secondary bar might form from the general bar instability, the same as the primary bar. Under some circumstances, the interaction of the bars and the disk leads to the two bars aligning or single, nuclear, bars only. Simulations that are cool enough of the center to experience clump instabilities may also generate steady S2B galaxies. In this case, the secondary bars are “fast,” i.e., the bar length is close to the co-rotation radius. This is the first time that S2B galaxies containing a fast secondary bar are reported. Previous orbit-based studies had suggested that fast secondary bars were not dynamically possible.

  3. Polar Disk Galaxy Found in Wall Between Voids

    NASA Astrophysics Data System (ADS)

    Stanonik, K.; Platen, E.; Aragón-Calvo, M. A.; van Gorkom, J. H.; van de Weygaert, R.; van der Hulst, J. M.; Peebles, P. J. E.

    2009-05-01

    We have found an isolated polar disk galaxy in what appears to be a cosmological wall situated between two voids. This void galaxy is unique as its polar disk was discovered serendipitously in an H I survey of SDSS void galaxies, with no optical counterpart to the H I polar disk. Yet the H I mass in the disk is comparable to the stellar mass in the galaxy. This suggests slow accretion of the H I material at a relatively recent time. There is also a hint of a warp in the outer parts of the H I disk. The central, stellar disk appears relatively blue, with faint near-UV emission, and is oriented (roughly) parallel to the surrounding wall, implying gas accretion from the voids. The considerable gas mass and apparent lack of stars in the polar disk, coupled with the general underdensity of the environment, supports recent theories of cold flow accretion as an alternate formation mechanism for polar disk galaxies.

  4. POLAR DISK GALAXY FOUND IN WALL BETWEEN VOIDS

    SciTech Connect

    Stanonik, K.; Van Gorkom, J. H.; Platen, E.; Van de Weygaert, R.; Van der Hulst, J. M.; Aragon-Calvo, M. A.; Peebles, P. J. E.

    2009-05-01

    We have found an isolated polar disk galaxy in what appears to be a cosmological wall situated between two voids. This void galaxy is unique as its polar disk was discovered serendipitously in an H I survey of SDSS void galaxies, with no optical counterpart to the H I polar disk. Yet the H I mass in the disk is comparable to the stellar mass in the galaxy. This suggests slow accretion of the H I material at a relatively recent time. There is also a hint of a warp in the outer parts of the H I disk. The central, stellar disk appears relatively blue, with faint near-UV emission, and is oriented (roughly) parallel to the surrounding wall, implying gas accretion from the voids. The considerable gas mass and apparent lack of stars in the polar disk, coupled with the general underdensity of the environment, supports recent theories of cold flow accretion as an alternate formation mechanism for polar disk galaxies.

  5. The Warped Disk of Integral-Sign Galaxy PGC 20348

    NASA Astrophysics Data System (ADS)

    Ann, H. B.

    2007-03-01

    We examine the morphology and luminosity distribution of a strongly warped spiral galaxy PGC 20348 by conducting a detailed BVI CCD surface photometry using BOAO 1.8m telescope. The radial surface brightness shows a break at warp radius (r_{w}) with a shallow gradient in the inner disk and a steeper gradient in the outer disk. The luminosity of east side of the disk is ˜ 0.5 mag fainter than the west side at r > r_{w}. The reason for the asymmetric luminosity distribution is thought to be the asymmetric flarings that result in the formation of a large diffuse region at the edge of the east disk and a smaller diffuse region at the west disk. The vertical luminosity profiles show a thick disk component whose scale heights increase with increasing galactocentric distances. The warp of PGC 20348 seems to be made by the tidal interactions with the two massive companion galaxies since the flarings and radial increase of disk scale heights are thought to be general properties of tidally perturbed disks. According to the colors of the two clumps inside the diffuse region at the edge of the east disk, they seem to be sites of active star formation triggered by tidal forces from the companion galaxies.

  6. Forming Disk Galaxies Early in the Universe

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-08-01

    What were galaxies like in the first 500 million years of the universe? According to simulations by Yu Feng (UC Berkeley) and collaborators, the earliest massive galaxies to form were mostly disk-shaped, rather than the compact clumps previously predicted. Early-Galaxy Models. Current models for galaxy formation predict that small perturbations in the distribution of matter in the early universe collapsed to form very compact, irregular, clumpy first galaxies. Observations support this: the furthest out that we've spotted disk-shaped galaxies is at z=3, whereas the galaxies we've observed from earlier times -- up to redshifts of z=8-10 -- are very compact. But could this be a selection effect, arising from the rarity of large galaxies in the early universe? Current surveys at high redshift have thus far only covered relatively small volumes of space, so it's not necessarily surprising that we haven't yet spotted any large disk galaxies. Similarly, numerical simulations of galaxy formation are limited in the size of the volume they can evolve, so resulting models of early galaxy formation also tend to favor compact clumpy galaxies over large disks. An Enormous Simulation. Pushing at these limitations, Feng and his collaborators used the Blue Waters supercomputer to carry out an enormous cosmological hydrodynamic simulation called BlueTides. In this simulation, they track 700 billion particles as they evolve in a volume of 400 comoving Mpc/h -- 40 times the volume of the largest previous simulation and 300 times the volume of the largest observational survey at these redshifts. What they find is that by z=8, a whopping 70% of the most massive galaxies (over 7 billion solar masses each) were disk-shaped, though they are more compact, gas-rich, and turbulent than present-day disk galaxies like the Milky Way. The way the most massive galaxies formed in the simulation also wasn't expected: rather than resulting from major mergers, they were built from smooth accretion

  7. An Optimal Strategy for Accurate Bulge-to-disk Decomposition of Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Gao, Hua; Ho, Luis C.

    2017-08-01

    The development of two-dimensional (2D) bulge-to-disk decomposition techniques has shown their advantages over traditional one-dimensional (1D) techniques, especially for galaxies with non-axisymmetric features. However, the full potential of 2D techniques has yet to be fully exploited. Secondary morphological features in nearby disk galaxies, such as bars, lenses, rings, disk breaks, and spiral arms, are seldom accounted for in 2D image decompositions, even though some image-fitting codes, such as GALFIT, are capable of handling them. We present detailed, 2D multi-model and multi-component decomposition of high-quality R-band images of a representative sample of nearby disk galaxies selected from the Carnegie-Irvine Galaxy Survey, using the latest version of GALFIT. The sample consists of five barred and five unbarred galaxies, spanning Hubble types from S0 to Sc. Traditional 1D decomposition is also presented for comparison. In detailed case studies of the 10 galaxies, we successfully model the secondary morphological features. Through a comparison of best-fit parameters obtained from different input surface brightness models, we identify morphological features that significantly impact bulge measurements. We show that nuclear and inner lenses/rings and disk breaks must be properly taken into account to obtain accurate bulge parameters, whereas outer lenses/rings and spiral arms have a negligible effect. We provide an optimal strategy to measure bulge parameters of typical disk galaxies, as well as prescriptions to estimate realistic uncertainties of them, which will benefit subsequent decomposition of a larger galaxy sample.

  8. Giant disk galaxies : Where environment trumps mass in galaxy evolution

    NASA Astrophysics Data System (ADS)

    Courtois, Helene M.; Zaritsky, Dennis; Sorce, Jenny G.; Pomarede, Daniel

    2015-08-01

    We identify some of the most HI massive and fastest rotating disk galaxies in the local universe with the aim of probing the processes that drive the formation of these extreme disk galaxies. By combining data from the Cosmic Flows project, which has consistently reanalyzed archival galaxy HI profiles, and 3.6 micron photometry obtained with the Spitzer Space Telescope, with which we can measure stellar mass, we use the baryonic Tully-Fisher relationship to explore whether these massive galaxies are distinct.We discuss several results, but the most striking is the systematic offset of the HI-massive sample above the baryonic Tully-Fisher. These galaxies have both more gas and more stars in their disks than the typical disk galaxy of similar rotational velocity. The ``condensed" baryon fraction, fC, the fraction of the baryons in a dark matter halo that settle either as cold gas or stars into the disk, is twice as high in the HI-massive sample than typical, and almost reaches the universal baryon fraction in some cases, suggesting that the most extreme of these galaxies have little in the way of a hot baryonic component or cold baryons distributed well outside the disk. In contrast, the star formation efficiency, measured as the ratio of the mass in stars to that in both stars and gas, shows no difference between the HI-massive sample and the typical disk galaxies. We conclude that the star formation efficiency is driven by an internal, self-regulating process, while fC is affected by external factors. Neither the morphology nor the star formation rate of these galaxies is primarily determined by either their dark or stellar mass. We also found that the most massive HI detected galaxies are located preferentially in filaments. We present the first evidence of an environmental effect on galaxy evolution using a dynamical definition of a filament.

  9. Dynamics of gas disks in triaxial galaxies

    SciTech Connect

    Steiman-Cameron, T.Y.

    1984-01-01

    Increasing evidence has accumulated since the mid 1970's arguing that many, if not all, undisturbed galaxies may have triaxial mass distributions. The steady state configurations (preferred planes) of gas disks in triaxial galaxies with static and rotating surface figures is determined. In addition, the evolution of a gas disk as it settles into the steady state is followed for both axisymmetric and triaxial galaxies. Observational tests are provided for triaxial galactic geometry and give more accurate measures of settling times than those previously published. The preferred planes for gas disks in static and tumbling triaxial galaxies are determined using an analytic method derived from celestial mechanics. The evolution of gas disks which are not in the steady state is followed using numerical methods.

  10. Numerical simulations of interacting disk galaxies

    NASA Technical Reports Server (NTRS)

    Noguchi, Masafumi

    1990-01-01

    Galaxy-galaxy interactions have long attracted many extragalactic astronomers in various aspects. A number of computer simulations performed in the 1970s have successfully reproduced the peculiar morphologies observed in interacting disk galaxies and clarified that tidal deformation explains most of the observed global peculiarities. However, most of these simulations have used test particles in modelling the disk component. Tidal response of a self-gravitating disk remains to be further clarified. Another topic which is intensely discussed at present is the relation between galaxy-galaxy interactions and activity. Many observations suggest that interactions trigger strong starbursts and possibly active galactic nuclei (AGN). However, the detailed mechanism of triggering is not yet clear. It is vital here to understand the dynamics of interstellar gas. In order to understand various phenomena related to galaxy-galaxy interactions (mainly for disk galaxies), the author performed a series of numerical simulations on close galaxy encounters which includes both interstellar gas and self-gravitating disk components. In these simulations, the galaxy model to be perturbed (target galaxy) consists of a halo and a disk. The halo was treated as a rigid spherical gravitational field which is assumed to remain fixed during the interaction. The disk is composed of stars and gas. The stellar disk was constructed by 20000 collisionless particles of the same mass. Those particles move in the halo gravitational field, interacting with each other and with the perturber. Therefore, the self-graviy of the disk is properly taken into account. Stellar particles were initially given circular velocities with small random motions required to stabilize the disk against local axisymmetric disturbances. The gravitational field of the stellar disk was calculated by the particle-mesh scheme (e.g. Hockney and Eastwood 1981). The gaseous component was modelled by the cloud-particle scheme (e

  11. Shaping Disk Galaxy Stellar Populations via Internal and External Processes

    NASA Astrophysics Data System (ADS)

    Roškar, Rok

    2015-03-01

    In recent years, effects such as the radial migration of stars in disks have been recognized as important drivers of the properties of stellar populations. Radial migration arises due to perturbative effects of disk structures such as bars and spiral arms, and can deposit stars formed in disks to regions far from their birthplaces. Migrant stars can significantly affect the demographics of their new locales, especially in low-density regions such as in the outer disks. However, in the cosmological environment, other effects such as mergers and filamentary gas accretion also influence the disk formation process. Understanding the relative importance of these processes on the detailed evolution of stellar population signatures is crucial for reconstructing the history of the Milky Way and other nearby galaxies. In the Milky Way disk in particular, the formation of the thickened component has recently attracted much attention due to its potential to serve as a diagnostic of the galaxy's early history. Some recent work suggests, however, that the vertical structure of Milky Way stellar populations is consistent with models that build up the thickened component through migration. I discuss these developments in the context of cosmological galaxy formation.

  12. Signatures Of Secular Evolution In Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Díaz-García, Simón

    2016-09-01

    In this thesis we shed light on the formation and evolution of disk galaxies, which often host a stellar bar (about 2/3 of cases). In particular, we address the bar-driven secular evolution, that is, the steady redistribution of stellar and gaseous material through the disk induced by the bar torques and resonances. We characterize the mass distribution of the disks in the Spitzer Survey of Stellar Structure in Galaxies (S4G, Sheth et al. 2010) and study the properties of the different stellar structure components and the interplay between them.We use 3.6 μm photometry for ˜1300 face-on and moderately inclined disk galaxies to analyze the frequency, dimensions, orientations and shapes of stellar bars, spiral arms, rings, (ring)lenses, and barlenses (i.e. lens-like structures embedded in the bars). We calculate the strength of the bars in the S4G via ellipse fitting, Fourier decomposition of the galaxy images, and from the gravitational tangential-to-radial forces. We also estimate the stellar contribution to the circular velocity, allowing us to analyze the coupling between non-baryonic and stellar matter within the optical disk. We average stellar density profiles (1D), the disk(+bulge) component of the rotation curve, and stellar bars (2D) as a function of fundamental galaxy parameters.We complement the study with integral-field unit kinematic data from Seidel et al. (2015b) for a subsample of 16 S4G barred galaxies. We quantify the bar-induced perturbation strengths in the stellar and gaseous disk from the kinematics, and show that they agree with the estimates obtained from the images. We also use Hα Fabry-Perot observations from Erroz-Ferrer et al. (2015) for 29 S4G disk galaxies to study the inner slope of the rotation curves.We provide possible observational evidence for the growth of bars in a Hubble time. We demonstrate the role of bars causing the spreading of the disk and the enhancement of the central stellar concentration. Our observations support

  13. OUTER-DISK POPULATIONS IN NGC 7793: EVIDENCE FOR STELLAR RADIAL MIGRATION

    SciTech Connect

    Radburn-Smith, David J.; Dalcanton, Julianne J.; Roskar, Rok; Debattista, Victor P.; Streich, David; De Jong, Roelof S.; Vlajic, Marija; Holwerda, Benne W.; Purcell, Chris W.; Dolphin, Andrew E.; Zucker, Daniel B.

    2012-07-10

    We analyzed the radial surface brightness profile of the spiral galaxy NGC 7793 using HST/ACS images from the GHOSTS survey and a new HST/WFC3 image across the disk break. We used the photometry of resolved stars to select distinct populations covering a wide range of stellar ages. We found breaks in the radial profiles of all stellar populations at 280'' ({approx}5.1 kpc). Beyond this disk break, the profiles become steeper for younger populations. This same trend is seen in numerical simulations where the outer disk is formed almost entirely by radial migration. We also found that the older stars of NGC 7793 extend significantly farther than the underlying H I disk. They are thus unlikely to have formed entirely at their current radii, unless the gas disk was substantially larger in the past. These observations thus provide evidence for substantial stellar radial migration in late-type disks.

  14. Extended Ultraviolet Disks and Ultraviolet-bright Disks in Low-mass E/S0 Galaxies

    NASA Astrophysics Data System (ADS)

    Moffett, Amanda J.; Kannappan, Sheila J.; Baker, Andrew J.; Laine, Seppo

    2012-01-01

    We have identified 15 extended ultraviolet (XUV) disks in a largely field sample of 38 E/S0 galaxies that have stellar masses primarily below ~4 × 1010 M ⊙ and comparable numbers on the red and blue sequences. We use a new purely quantitative XUV-disk definition designed with reference to the "Type 1" XUV-disk definition found in the literature, requiring UV extension relative to a UV-defined star formation threshold radius. The 39% ± 9% XUV-disk frequency for these E/S0s is roughly twice the ~20% reported for late-type galaxies (although differences in XUV-disk criteria complicate the comparison), possibly indicating that XUV disks are preferentially associated with galaxies experiencing weak or inefficient star formation. Consistent with this interpretation, we find that the XUV disks in our sample do not correlate with enhanced outer-disk star formation as traced by blue optical outer-disk colors. However, UV-Bright (UV-B) disk galaxies with blue UV colors outside their optical 50% light radii do display enhanced optical outer-disk star formation as well as enhanced atomic gas content. UV-B disks occur in our E/S0s with a 42+9 -8% frequency and need not coincide with XUV disks; thus their combined frequency is 61% ± 9%. For both XUV and UV-B disks, UV colors typically imply <1 Gyr ages, and most such disks extend beyond the optical R 25 radius. XUV disks occur over the full sample mass range and on both the red and blue sequences, suggesting an association with galaxy interactions or another similarly general evolutionary process. In contrast, UV-B disks favor the blue sequence and may also prefer low masses, perhaps reflecting the onset of cold-mode gas accretion or another mass-dependent evolutionary process. Virtually all blue E/S0s in the gas-rich regime below stellar mass M t ~ 5 × 109 M ⊙ (the "gas-richness threshold mass") display UV-B disks, supporting the previously suggested association of this population with active disk growth.

  15. EXTENDED ULTRAVIOLET DISKS AND ULTRAVIOLET-BRIGHT DISKS IN LOW-MASS E/S0 GALAXIES

    SciTech Connect

    Moffett, Amanda J.; Kannappan, Sheila J.; Baker, Andrew J.; Laine, Seppo

    2012-01-20

    We have identified 15 extended ultraviolet (XUV) disks in a largely field sample of 38 E/S0 galaxies that have stellar masses primarily below {approx}4 Multiplication-Sign 10{sup 10} M{sub Sun} and comparable numbers on the red and blue sequences. We use a new purely quantitative XUV-disk definition designed with reference to the 'Type 1' XUV-disk definition found in the literature, requiring UV extension relative to a UV-defined star formation threshold radius. The 39% {+-} 9% XUV-disk frequency for these E/S0s is roughly twice the {approx}20% reported for late-type galaxies (although differences in XUV-disk criteria complicate the comparison), possibly indicating that XUV disks are preferentially associated with galaxies experiencing weak or inefficient star formation. Consistent with this interpretation, we find that the XUV disks in our sample do not correlate with enhanced outer-disk star formation as traced by blue optical outer-disk colors. However, UV-Bright (UV-B) disk galaxies with blue UV colors outside their optical 50% light radii do display enhanced optical outer-disk star formation as well as enhanced atomic gas content. UV-B disks occur in our E/S0s with a 42{sup +9}{sub -8}% frequency and need not coincide with XUV disks; thus their combined frequency is 61% {+-} 9%. For both XUV and UV-B disks, UV colors typically imply <1 Gyr ages, and most such disks extend beyond the optical R{sub 25} radius. XUV disks occur over the full sample mass range and on both the red and blue sequences, suggesting an association with galaxy interactions or another similarly general evolutionary process. In contrast, UV-B disks favor the blue sequence and may also prefer low masses, perhaps reflecting the onset of cold-mode gas accretion or another mass-dependent evolutionary process. Virtually all blue E/S0s in the gas-rich regime below stellar mass M{sub t} {approx} 5 Multiplication-Sign 10{sup 9} M{sub Sun} (the 'gas-richness threshold mass') display UV-B disks

  16. THE STRUCTURE AND METALLICITY GRADIENT IN THE EXTREME OUTER DISK OF NGC 7793

    SciTech Connect

    Vlajic, M.; Bland-Hawthorn, J.; Freeman, K. C.

    2011-05-01

    Studies of outer regions of spirals disks are fundamental to our understanding of both the process of galaxy assembly and the subsequent secular evolution of galaxies. In an earlier series of papers, we explored the extent and abundance gradient in the outer disk of NGC 300 and found an extended purely exponential disk with a metallicity gradient which flattens off in the outermost regions. We now continue the study of outskirts of pure disk spirals with another Sculptor Group spiral, NGC 7793. Using the Gemini Multi Object Spectrograph camera at Gemini South, we trace the disk of NGC 7793 with star counts out to {approx}9 scale lengths, corresponding to 11.5 kpc at our calibrated distance of 3.61 {+-} 0.53 Mpc. The outer disk of NGC 7793 shows no evidence of a break in its light profile down to an effective surface brightness of {approx}30 mag arcsec{sup -2} ({approx}3 mag arcsec{sup -2} deeper than what has been achieved with surface photometry) and exhibits a non-negative abundance gradient within the radial extent of our data.

  17. Extended HI disks in nearby spiral galaxies

    NASA Astrophysics Data System (ADS)

    Bosma, Albert

    2017-03-01

    In this short write-up, I will concentrate on a few topics of interest. In the 1970s I found very extended HI disks in galaxies such as NGC 5055 and NGC 2841, out to 2 - 2.5 times the Holmberg radius. Since these galaxies are warped, a ``tilted ring model'' allows rotation curves to be derived, and evidence for dark matter to be found. The evaluation of the amount of dark matter is hampered by a disk-halo degeneracy, which can possibly be broken by observations of velocity dispersions in both the MgI region and the CaII region.

  18. The CALIFA connection between outer-disk reddening and gas-phase metallicities.

    NASA Astrophysics Data System (ADS)

    Marino, R. A.; Gil de Paz, A.; Sánchez, S. F.; Sánchez-Blázquez, P.; Castillo-Morales, A.; Cardiel, N.; Pascual, S.; Vílchez, J.; Califa, T.

    2017-03-01

    In Marino et al. 2016 we investigate, for the first time in a statistically significant and well- defined sample, the behavior of the colors and of the oxygen abundance from H II regions located within and beyond the break radius in the surface brightness profiles. We perform a detailed light-profile classification using Sloan Digital Sky Survey (SDSS) g'- and r'-band surface brightness, (g'- r') color, as well we characterize the ionized-gas oxygen abundance profiles for 350 galaxies within Calar Alto Legacy Integral Field Area (CALIFA) Survey. Our main results are: (i) We find that about 84% of our disks show clear down - or up-bending profiles (Type II and Type III, respectively) while the remaining 16% are well fitted by one single exponential law (Type I); (ii) The analysis of the color gradients reveals a U-shape profile for the Type II galaxies with a minimum (g'- r') color of ˜0.5 mag; (iii) We find a statistically significant signal of flattening in the outer ionized-gas metallicities, associated with the difference in the outer-to-inner disk gradient distribution. We discuss the relation between the outer-disk ionized-gas metallicity gradients and the presence of breaks in the surface brightness profiles of disk galaxies in the context of the evolution of galaxy disks and we propose different mechanism(s) that could have driven the formation and evolution of the galaxies' outskirts and, in particular, the reddening of the stellar colors found in these peripherical regions.

  19. Isolating the Young Stellar Population in the Outer Disk of NGC 300

    NASA Astrophysics Data System (ADS)

    Hillis, Tristan J.; Williams, Benjamin F.; Dolphin, Andrew E.; Dalcanton, Julianne J.; Skillman, Evan D.

    2016-11-01

    The recent star formation history (SFH) in the outer disk of NGC 300 is presented through the analysis of color-magnitude diagrams (CMDs). We analyze resolved stellar photometry by creating CMDs from four Hubble Space Telescope fields containing a combination of images from the Advanced Camera for Surveys and the UVIS imager aboard the Wide Field Camera 3. From the best models of these CMDs, we derive the SFH in order to extract the young stellar component for the past 200 Myr. We find that the young stellar disk of NGC 300 is unbroken out to at least ˜8 scale lengths (including an upper limit out to ˜10 scale lengths) with {r}s=1.4+/- 0.1 {kpc}, which is similar to the total stellar surface brightness profile. This unbroken profile suggests that NGC 300 is undisturbed, similar to the isolated disk galaxy NGC 2403. We compare the environments of NGC 300, NGC 2403, and M33 along with the properties of the gas and stellar disks. We find that the disturbed H i outer disk morphology is not accompanied by a break in the young stellar disk. This may indicate that processes which affect the outer H i morphology may not leave an imprint on the young stellar disk. This paper is based on Hubble Space Telescope observations.

  20. Strongly baryon-dominated disk galaxies at the peak of galaxy formation ten billion years ago.

    PubMed

    Genzel, R; Schreiber, N M Förster; Übler, H; Lang, P; Naab, T; Bender, R; Tacconi, L J; Wisnioski, E; Wuyts, S; Alexander, T; Beifiori, A; Belli, S; Brammer, G; Burkert, A; Carollo, C M; Chan, J; Davies, R; Fossati, M; Galametz, A; Genel, S; Gerhard, O; Lutz, D; Mendel, J T; Momcheva, I; Nelson, E J; Renzini, A; Saglia, R; Sternberg, A; Tacchella, S; Tadaki, K; Wilman, D

    2017-03-15

    In the cold dark matter cosmology, the baryonic components of galaxies-stars and gas-are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius-a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high

  1. Stellar evolution in the outer Galaxy

    NASA Astrophysics Data System (ADS)

    Szczerba, Ryszard; Siódmiak, Natasza; Leśniewska, Aleksandra; Karska, Agata; Sewiło, Marta

    2016-07-01

    We investigate the distribution of different classes of spectroscopically identified sources and theoretical models in the color-color diagrams (CCDs) combining the near-infrared (NIR) and mid-infrared (MIR) data to develop a method to classify Outer Galaxy sources detected with the Spitzer Space Telescope (hereafter Spitzer) SMOG survey in the IRAC 3.68.0 µm and MIPS 24 µm bands. We supplement the Spitzer data with the data from other satellite and ground-based surveys. The main goal of our study is to discover and characterize the population of intermediate- and low-mass young stellar objects (YSOs) in the Outer Galaxy and use it to study star formation in a significantly different environment than the Galaxy inside the solar circle. Since the YSOs can be confused with evolved stars in the MIR, these classes of objects need to be carefully separated. Here we present the initial results of our analysis using the Ks-[8.0] vs. Ks-[24] CCD as an example. The evolved stars separated from YSOs in the YSO selection process will be investigated in detail in the follow-up study.

  2. SPATIALLY CORRELATED CLUSTER POPULATIONS IN THE OUTER DISK OF NGC 3184

    SciTech Connect

    Herbert-Fort, Stephane; Zaritsky, Dennis; Christlein, Daniel; Wilcots, Eric; Baruffolo, Andrea; Ragazzoni, Roberto; DiPaola, Andrea; Fontana, Adriano; Giallongo, Emanuele; Pogge, Richard W.; Smareglia, Riccardo

    2009-08-01

    We use deep ({approx}27.5 mag V-band point-source limiting magnitude) V- and U-band Large Binocular Telescope imaging to study the outer disk (beyond the optical radius R {sub 25}) of the non-interacting, face-on spiral galaxy NGC 3184 (D = 11.1 Mpc; R {sub 25} = 11.1 kpc) and find that this outer disk contains >1000 objects (or marginally resolved 'knots') resembling star clusters with masses {approx}10{sup 2}-10{sup 4} M {sub sun} and ages up to {approx}1 Gyr. We find statistically significant numbers of these cluster-like knots extending to {approx}1.4 R {sub 25}, with the redder knots outnumbering bluer at the largest radii. We measure clustering among knots and find significant correlation to galactocentric radii of 1.5 R {sub 25} for knot separations <1 kpc. The effective integrated surface brightness of this outer disk cluster population ranges from 30-32 mag arcsec{sup -2} in V. We compare the H I extent to that of the correlated knots and find that the clusters extend at least to the damped Lyman-{alpha} threshold of H I column density (2 x 10{sup 20} cm{sup -2}; {approx}1.62 R {sub 25}). The blue knots are correlated with H I spiral structure to {approx}1.5 R {sub 25}, while the red knots may be correlated with the outer fringes of the H I disk to {approx}1.7 R {sub 25}. These results suggest that outer disks are well populated, common, and long-lasting features of many nearby disk galaxies.

  3. Spatially Correlated Cluster Populations in the Outer Disk of NGC 3184

    NASA Astrophysics Data System (ADS)

    Herbert-Fort, Stéphane; Zaritsky, Dennis; Moustakas, John; Christlein, Daniel; Wilcots, Eric; Baruffolo, Andrea; Di Paola, Andrea; Fontana, Adriano; Giallongo, Emanuele; Pogge, Richard W.; Ragazzoni, Roberto; Smareglia, Riccardo

    2009-08-01

    We use deep (~27.5 mag V-band point-source limiting magnitude) V- and U-band Large Binocular Telescope imaging to study the outer disk (beyond the optical radius R 25) of the non-interacting, face-on spiral galaxy NGC 3184 (D = 11.1 Mpc; R 25 = 11.1 kpc) and find that this outer disk contains >1000 objects (or marginally resolved "knots") resembling star clusters with masses ~102-104 M sun and ages up to ~1 Gyr. We find statistically significant numbers of these cluster-like knots extending to ~1.4 R 25, with the redder knots outnumbering bluer at the largest radii. We measure clustering among knots and find significant correlation to galactocentric radii of 1.5 R 25 for knot separations <1 kpc. The effective integrated surface brightness of this outer disk cluster population ranges from 30-32 mag arcsec-2 in V. We compare the H I extent to that of the correlated knots and find that the clusters extend at least to the damped Lyman-α threshold of H I column density (2 × 1020 cm-2; ~1.62 R 25). The blue knots are correlated with H I spiral structure to ~1.5 R 25, while the red knots may be correlated with the outer fringes of the H I disk to ~1.7 R 25. These results suggest that outer disks are well populated, common, and long-lasting features of many nearby disk galaxies.

  4. Outer-disk reddening and gas-phase metallicities: The CALIFA connection

    NASA Astrophysics Data System (ADS)

    Marino, R. A.; Gil de Paz, A.; Sánchez, S. F.; Sánchez-Blázquez, P.; Cardiel, N.; Castillo-Morales, A.; Pascual, S.; Vílchez, J.; Kehrig, C.; Mollá, M.; Mendez-Abreu, J.; Catalán-Torrecilla, C.; Florido, E.; Perez, I.; Ruiz-Lara, T.; Ellis, S.; López-Sánchez, A. R.; González Delgado, R. M.; de Lorenzo-Cáceres, A.; García-Benito, R.; Galbany, L.; Zibetti, S.; Cortijo, C.; Kalinova, V.; Mast, D.; Iglesias-Páramo, J.; Papaderos, P.; Walcher, C. J.; Bland-Hawthorn, J.

    2016-01-01

    We study, for the first time in a statistically significant and well-defined sample, the relation between the outer-disk ionized-gas metallicity gradients and the presence of breaks in the surface brightness profiles of disk galaxies. Sloan Digital Sky Survey (SDSS) g'- and r'-band surface brightness, (g' - r') color, and ionized-gasoxygen abundance profiles for 324 galaxies within the Calar Alto Legacy Integral Field Area (CALIFA) survey are used for this purpose. We perform a detailed light-profile classification, finding that 84% of our disks show down- or up-bending profiles (Type II and Type III, respectively), while the remaining 16% are well fitted by one single exponential (Type I). The analysis of the color gradients at both sides of this break shows a U-shaped profile for most Type II galaxies with an average minimum (g' - r') color of ~0.5 mag and an ionized-gas metallicity flattening associated with it only in the case of low-mass galaxies. Comparatively, more massive systems show a rather uniform negative metallicity gradient. The correlation between metallicity flattening and stellar mass for these systems results in p-values as low as 0.01. Independent of the mechanism having shaped the outer light profiles of these galaxies, stellar migration or a previous episode of star formation in a shrinking star-forming disk, it is clear that the imprint in their ionized-gas metallicity was different for low- and high-mass Type II galaxies. In the case of Type III disks, a positive correlation between the change in color and abundance gradient is found (the null hypothesis is ruled out with a p-value of 0.02), with the outer disks of Type III galaxies with masses ≤1010 M⊙ showing a weak color reddening or even a bluing. This is interpreted as primarily due to a mass downsizing effect on the population of Type III galaxies that recently experienced an enhanced inside-out growth.

  5. Internal and environmental secular evolution of disk galaxies

    NASA Astrophysics Data System (ADS)

    Kormendy, John

    2015-03-01

    that are available to them. They do this by spreading - the inner parts shrink while the outer parts expand. Significant changes happen only if some process efficiently transports energy or angular momentum outward. The consequences are very general: evolution by spreading happens in stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks and galaxy disks. This meeting is about disk galaxies, so the evolution most often involves the redistribution of angular momentum. We now have a good heuristic understanding of how nonaxisymmetric structures rearrange disk gas into outer rings, inner rings and stuff dumped onto the center. Numerical simulations reproduce observed morphologies very well. Gas that is transported to small radii reaches high densities that are seen in CO observations. Star formation rates measured (e.g.) in the mid-infrared show that many barred and oval galaxies grow, on timescales of a few Gyr, dense central `pseudobulges' that are frequently mistaken for classical (elliptical-galaxy-like) bulges but that were grown slowly out of the disk (not made rapidly by major mergers). Our resulting picture of secular evolution accounts for the richness observed in morphological classification schemes such as those of de Vaucouleurs (1959) and Sandage (1961). State-of-the art morphology discussions include the de Vaucouleurs Atlas of Galaxies (Buta et al. 2007) and Buta (2012, 2013). Pseudobulges as disk-grown alternatives to merger-built classical bulges are important because they impact many aspects of our understanding of galaxy evolution. For example, they are observed to contain supermassive black holes (BHs), but they do not show the well known, tight correlations between BH mass and host properties (Kormendy et al. 2011). We can distinguish between classical and pseudo bulges because the latter retain a `memory' of their disky origin. That is, they have one or more characteristics of disks: (1) flatter shapes than those of

  6. HERSCHEL OBSERVATIONS OF THE T CHA TRANSITION DISK: CONSTRAINING THE OUTER DISK PROPERTIES

    SciTech Connect

    Cieza, Lucas A.; Olofsson, Johan; Henning, Thomas; Harvey, Paul M.; Evans II, Neal J.; Pinte, Christophe; Augereau, Jean-Charles; Menard, Francois; Najita, Joan

    2011-11-10

    T Cha is a nearby (d {approx} 100 pc) transition disk known to have an optically thin gap separating optically thick inner and outer disk components. Huelamo et al. recently reported the presence of a low-mass object candidate within the gap of the T Cha disk, giving credence to the suspected planetary origin of this gap. Here we present the Herschel photometry (70, 160, 250, 350, and 500 {mu}m) of T Cha from the 'Dust, Ice, and Gas in Time' Key Program, which bridges the wavelength range between existing Spitzer and millimeter data and provide important constraints on the outer disk properties of this extraordinary system. We model the entire optical to millimeter wavelength spectral energy distribution (SED) of T Cha (19 data points between 0.36 and 3300 {mu}m without any major gaps in wavelength coverage). T Cha shows a steep spectral slope in the far-IR, which we find clearly favors models with outer disks containing little or no dust beyond {approx}40 AU. The full SED can be modeled equally well with either an outer disk that is very compact (only a few AU wide) or a much larger one that has a very steep surface density profile. That is, T Cha's outer disk seems to be either very small or very tenuous. Both scenarios suggest a highly unusual outer disk and have important but different implications for the nature of T Cha. Spatially resolved images are needed to distinguish between the two scenarios.

  7. WHEN DID ROUND DISK GALAXIES FORM?

    SciTech Connect

    Takeuchi, T. M.; Ohta, K.; Yuma, S.; Yabe, K.

    2015-03-01

    When and how galaxy morphology, such as the disk and bulge seen in the present-day universe, emerged is still not clear. In the universe at z ≳ 2, galaxies with various morphologies are seen, and star-forming galaxies at z ∼ 2 show the intrinsic shape of bar-like structures. Then, when did the round disk structure form? Here we take a simple and straightforward approach to see the epoch when a round disk galaxy population emerged by constraining the intrinsic shape statistically based on the apparent axial ratio distribution of galaxies. We derived the distributions of the apparent axial ratios in the rest-frame optical light (∼5000 Å) of star-forming main-sequence galaxies at 2.5 > z > 1.4, 1.4 > z > 0.85, and 0.85 > z > 0.5, and found that their apparent axial ratios show peaky distributions at z ≳ 0.85, while a rather flat distribution at the lower redshift. By using a tri-axial model (A > B > C) for the intrinsic shape, we found that the best-fit models give the peaks of the B/A distribution of 0.81 ± 0.04, 0.84 ± 0.04, and 0.92 ± 0.05 at 2.5 > z > 1.4, 1.4 > z > 0.85, and 0.85 > z > 0.5, respectively. The last value is close to the local value of 0.95. Thickness (C/A) is ∼0.25 at all the redshifts and is close to the local value (0.21). The results indicate that the shape of the star-forming galaxies in the main sequence changes gradually, and that the round disk is established at around z ∼ 0.9. The establishment of the round disk may be due to the cessation of a violent interaction between galaxies or the growth of a bulge and/or a supermassive black hole residing at the center of a galaxy that dissolves the bar structure.

  8. Stationary orbits of satellites of disk galaxies

    NASA Technical Reports Server (NTRS)

    Polyachenko, Valerij L.

    1990-01-01

    The satellite of an S-galaxy will experience opposing dynamical-friction forces from the stars of the disk and the halo. If these forces are in balance, the satellite may travel in a stable, near-circular orbit whose radius, for a wide range of physical parameters, should be limited to a zone 1.2 to 1.4 times the disk radius, much as is observed. The idea is very simple. The dynamical friction acting on a small satellite, moving through a stellar galactic halo, makes this satellite slow down. On the other hand, a stellar disk, rotating faster than a satellite, makes it speed up. But the density distributions in radius for disk's and halo's stars in real flat galaxies are quite different (respectively, exponential and power-law). Moreover, the observational data show that the exponential profile for disk's surface density drops abruptly at some radius (r sub d). So it is natural to expect that a stationary orbit could be near the edge of a disk (where two effects are mutually compensated).

  9. Strongly baryon-dominated disk galaxies at the peak of galaxy formation ten billion years ago

    NASA Astrophysics Data System (ADS)

    Genzel, R.; Schreiber, N. M. Förster; Übler, H.; Lang, P.; Naab, T.; Bender, R.; Tacconi, L. J.; Wisnioski, E.; Wuyts, S.; Alexander, T.; Beifiori, A.; Belli, S.; Brammer, G.; Burkert, A.; Carollo, C. M.; Chan, J.; Davies, R.; Fossati, M.; Galametz, A.; Genel, S.; Gerhard, O.; Lutz, D.; Mendel, J. T.; Momcheva, I.; Nelson, E. J.; Renzini, A.; Saglia, R.; Sternberg, A.; Tacchella, S.; Tadaki, K.; Wilman, D.

    2017-03-01

    In the cold dark matter cosmology, the baryonic components of galaxies—stars and gas—are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius—a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early

  10. Scaling Relations of Mass, Velocity, and Radius for Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Schulz, Earl

    2017-02-01

    I demonstrate four tight correlations of total baryonic mass, velocity, and radius for a set of nearby disk galaxies: the mass–velocity relation {M}{{t}}\\propto {V}4; the mass–radius relation {M}{{t}}\\propto {R}2; the radius–velocity relation R\\propto {V}2; and the mass–radius–velocity relation {M}{{t}}\\propto {{RV}}2. The mass–velocity relation is the familiar Baryonic Tully–Fisher relation, and versions of the other three relations, using magnitude rather than baryonic mass, are also well known. These four observed correlations follow from a pair of more fundamental relations. First, the centripetal acceleration at the edge of the stellar disk is proportional to the acceleration predicted by Newtonian physics, and second, this acceleration is a constant that is related to Milgrom’s constant. The two primary relations can be manipulated algebraically to generate the four observed correlations and allow little room for dark matter inside the radius of the stellar disk. The primary relations do not explain the velocity of the outer gaseous disks of spiral galaxies, which do not trace the Newtonian gravitational field of the observed matter.

  11. A Dynamical Study of Resonances in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Treuthardt, P. M.; Buta, R. J.; Salo, H.

    2005-05-01

    Resonances in disk galaxies play a fundamental role in galactic evolution because resonant stars may exchange angular momentum with a pertubation and thereby strengthen or weaken it (Athanassoula 2003, MNRAS, 341, 1179). In many disk galaxies, resonance regions are visible as distinct inner, outer, and nuclear rings of star formation. These rings act as tracers of the associated perturbation's pattern speed (Ω p). One of two ways of estimating Ω p is the direct Tremaine-Weinberg (1984, ApJ, 282, 5) method, which uses luminosity-weighted positions and velocities along strips parallel to the major axis. The second and more indirect way, is the numerical simulation method (e.g. Salo et al. 1999, AJ, 117, 778), which matches a cloud-particle model to the observed gas distribution and velocity field. This poster describes our project to use both methods on a small sample of ringed spiral galaxies in order to test the resonance idea of galactic rings (Buta and Combes 1996, Fund. Cos. Phys. 17, 95) and also to determine if the two methods give consistent results. Focusing a pattern speed study on resonance ring galaxies has the benefit of constraints, provided by the rings, on the parameters governing morphology. Our numerical analysis is based on near-infrared images which are used to infer galactic gravitational potentials.

  12. Neutral hydrogen in the outer Galaxy

    NASA Technical Reports Server (NTRS)

    Diplas, Athanassios; Savage, Blair D.

    1991-01-01

    The H I 21 cm emission-line survey data of Stark et al. (1991) have been used to study the distribution of H I in the outer Galaxy and to improve understanding of the various systematic problems which influence all studies of Galactic H I. For n(H) greater than 0.01/cu cm, the distributions are similar to those found by Burton and te Lintel Hekkert (1986) but are 'better behaved' at substantially lower values of n(H). The z distribution of gas in the H I layer is best described as complicated. The behavior of the gaseous matter is consistent with the observed distribution of H I found in external spiral galaxies. In the directions of the maximum warp the average distance of the gas away from the Galactic plane reaches about 4 kpc at R about 24 kpc, while the flaring of the layer as measured by z(rms) increases to about 3 kpc. In directions where the warp layers particularly well measured, the Galaxy is followed to R about 30 kpc. The surface density of the atomic gas decreases exponentially.

  13. Particle Trapping in the Outer Regions of Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Simon, Jacob B.; Armitage, P. J.

    2014-01-01

    I will discuss the formation and strength of axisymmetric local pressure maxima (zonal flows) in the outer regions of protoplanetary disks, where ambipolar diffusion reduces turbulent stresses driven by the magnetorotational instability. Zonal flows are a candidate mechanism for slowing the radial drift of solids and concentrating particles, a prelude to planetesimal formation. Using local numerical simulations, I will show that zonal flows in the outer disk can be strong enough to trap particles, provided that the turbulence generates enough vertically integrated stress to account for measured stellar accretion rates. In the presence of ambipolar diffusion, this requires a weak vertical magnetic field. Without such a field, particle trapping is unlikely to occur.

  14. Young circumnuclear disks in elliptical galaxies

    NASA Astrophysics Data System (ADS)

    Sil'Chenko, Olga K.

    2009-04-01

    By means of integral-field spectroscopy with the Multi-Pupil Field/Fiber Spectrograph of the Russian 6-m telescope we have studied the central parts of NGC 759 and NGC 83— regular (non-interacting, without strong nuclear activity) round red luminous ( M B =-20.8--21.6) elliptical galaxies which are however known to possess molecular gas. In both galaxies we have found central stellar disks with the extension of 1-2 kpc along the radius which are evidently being formed just now.

  15. Nonresonance Spiral Responses in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Polyachenko, V. L.; Polyachenko, E. V.

    2002-01-01

    The behavior of the gravitational potential outside the region where the main spiral arms of galaxies are located is investigated. The characteristic features of this behavior include nearly circular extensions of the main arms, which typically have an angular extent of 90°. It is natural to interpret these quarter-turn spirals as the response of the galactic disk to the gravitational potential of the main spiral arms. The theoretical models are supported by observational data for the brightness distributions in both normal (NGC 3631) and barred (NGC 1365) galaxies.

  16. The 2X-Hi disks of spiral galaxies

    NASA Astrophysics Data System (ADS)

    Koribalski, Bärbel S.

    2017-03-01

    The outskirts of galaxies - especially the very extended Hi disks of galaxies - are strongly affected by their local environment. I highlight the giant 2X-Hi disks of nearby galaxies (M 83, NGC 3621, and NGC 1512), studied as part of the Local Volume Hi Survey (LVHIS), their kinematics and relation to XUV disks, signatures of tidal interactions and accretion events, the M HI - D HI relation as well as the formation of tidal dwarf galaxies. - Using multi-wavelength data, I create 3D visualisations of the gas and stars in galaxies, with the shape of their warped disks obtained through kinematic modelling of their Hi velocity fields.

  17. DUST-DRIVEN WIND FROM DISK GALAXIES

    SciTech Connect

    Sharma, Mahavir; Nath, Biman B.; Shchekinov, Yuri E-mail: biman@rri.res.in

    2011-08-01

    We study gaseous outflows from disk galaxies driven by radiation pressure on dust grains. We include the effect of bulge and dark matter halo and show that the existence of such an outflow implies a maximum value of disk mass-to-light ratio. We show that the terminal wind speed is proportional to the disk rotation speed in the limit of a cold gaseous outflow, and that in general there is a contribution from the gas sound speed. Using the mean opacity of dust grains and the evolution of the luminosity of a simple stellar population, we then show that the ratio of the wind terminal speed (v{sub {infinity}}) to the galaxy rotation speed (v{sub c}) ranges between 2 and 3 for a period of {approx}10 Myr after a burst of star formation, after which it rapidly decays. This result is independent of any free parameter and depends only on the luminosity of the stellar population and the relation between disk and dark matter halo parameters. We briefly discuss the possible implications of our results.

  18. Inner and outer star forming regions over the discs of spiral galaxies I. Sample characterization

    NASA Astrophysics Data System (ADS)

    Rodríguez-Baras, Marina; Díaz, A. I.; Rosales-Ortega, F. F.

    2017-03-01

    This project is aimed at understanding the dependence of star formation on the environment by analysing young stellar populations in two very different positions in disk galaxies: circumnuclear and outer disk giant regions. Integral field spectroscopy (IFS) provide an ideal means to achieve these goals providing simultaneous spatial and spectral resolution. Here we present the characterization of the work sample, composed by 671 outer regions and 725 inner regions from 263 isolated spirals galaxies observed by the CALIFA survey. The wide number of regions in both samples allows us to obtain statistically relevant results about the influence of metallicity, density and environment on star formation, and how it disseminates over the galaxy, to obtain evolutionary stories for the star-forming regions and to compare our results with models of massive star formation and galactic chemical evolution.

  19. Star formation rates and abundance gradients in disk galaxies

    NASA Technical Reports Server (NTRS)

    Wyse, Rosemary F. G.; Silk, Joseph

    1989-01-01

    Analytic models for the evolution of disk galaxies are presented, placing special emphasis on the radial properties. These models are straightforward extensions of the original Schmidt (1959, 1963) models, with a dependence of star formation rate on gas density. The models provide successful descriptions of several measures of galactic disk evolution, including solar neighborhood chemical evolution, the presence and amplitude of metallicity and color gradients in disk galaxies, and the global rates of star formation in disk galaxies, and aid in the understanding of the apparent connection between young and old stellar populations in spiral galaxies.

  20. On the outer edges of protoplanetary dust disks

    SciTech Connect

    Birnstiel, Tilman; Andrews, Sean M. E-mail: sandrews@cfa.harvard.edu

    2014-01-10

    The expectation that aerodynamic drag will force the solids in a gas-rich protoplanetary disk to spiral in toward the host star on short timescales is one of the fundamental problems in planet formation theory. The nominal efficiency of this radial drift process is in conflict with observations, suggesting that an empirical calibration of solid transport mechanisms in a disk is highly desirable. However, the fact that both radial drift and grain growth produce a similar particle size segregation in a disk (such that larger particles are preferentially concentrated closer to the star) makes it difficult to disentangle a clear signature of drift alone. We highlight a new approach, by showing that radial drift leaves a distinctive 'fingerprint' in the dust surface density profile that is directly accessible to current observational facilities. Using an analytical framework for dust evolution, we demonstrate that the combined effects of drift and (viscous) gas drag naturally produce a sharp outer edge in the dust distribution (or, equivalently, a sharp decrease in the dust-to-gas mass ratio). This edge feature forms during the earliest phase in the evolution of disk solids, before grain growth in the outer disk has made much progress, and is preserved over longer timescales when both growth and transport effects are more substantial. The key features of these analytical models are reproduced in detailed numerical simulations, and are qualitatively consistent with recent millimeter-wave observations that find gas/dust size discrepancies and steep declines in dust continuum emission in the outer regions of protoplanetary disks.

  1. OUTSIDE-IN SHRINKING OF THE STAR-FORMING DISK OF DWARF IRREGULAR GALAXIES

    SciTech Connect

    Zhang Hongxin; Hunter, Deidre A.; Elmegreen, Bruce G.; Gao Yu; Schruba, Andreas E-mail: dah@lowell.edu E-mail: bge@us.ibm.com

    2012-02-15

    We have studied multi-band surface brightness profiles of a representative sample of 34 nearby dwarf irregular galaxies. Our data include Galaxy Evolution Explorer (GALEX) FUV/NUV, UBV, and H{alpha} and Spitzer 3.6 {mu}m images. These galaxies constitute the majority of the LITTLE THINGS survey (Local Irregulars That Trace Luminosity Extremes-The H I Nearby Galaxy Survey). By modeling the azimuthal averages of the spectral energy distributions with a complete library of star formation histories, we derived the stellar mass surface density distributions and the star formation rate averaged over three different timescales: the recent 0.1 Gyr, 1 Gyr, and a Hubble time. We find that, for {approx}80% (27 galaxies) of our sample galaxies, radial profiles (at least in the outer part) at shorter wavelengths, corresponding to younger stellar populations, have shorter disk scale lengths than those at longer wavelengths, corresponding to older stellar populations. This indicates that the star-forming disk has been shrinking. In addition, the radial distributions of the stellar mass surface density are well described as piece-wise exponential profiles, and {approx}80% of the galaxies have steeper mass profiles in the outer disk than in the inner region. The steep radial decline of the star formation rate in the outer parts compared to that in the inner disks gives a natural explanation for the down-bending stellar mass surface density profiles. Within the inner disks, our sample galaxies on average have constant ratios of recent star formation rate to stellar mass with radius. Nevertheless, {approx}35% (12 galaxies, among which 7 have baryonic mass {approx}<10{sup 8} M{sub Sun} ) of the sample exhibit negative slopes across the observed disk, which is in contrast with the so-called inside-out disk growth scenario suggested for luminous spiral galaxies. The tendency of star formation to become concentrated toward the inner disks in low-mass dwarf irregular galaxies is

  2. HI Gas in Disk and Dwarf Galaxies in the Semi-analytic Models of Galaxy Formation†

    NASA Astrophysics Data System (ADS)

    Fu, Jian; Wang, Jing; Luo, Yu

    We construct the radially-resolved semi-analytic models of galaxy formation based on the L-Galaxies model framework, which include both atomic and molecular gas phase in ISM. The models run on the halo outputs of ΛCDM cosmology N-body simulation. Our models can reproduce varies observations of HI gas in nearby galaxies, e.g. the HI mass function, the HI-to-star ratio vs stellar mass and stellar surface density, universal HI radial surface density profile in outer disks etc. We also give the physical origin of HI size-mass relation. Based on our model results for local dwarf galaxies, we show that the ``missing satellite problem'' also exists in the HI component, i.e., the models over-predict dwarf galaxies with low HI mass around the Milky Way. That is a shortcoming of current ΛCDM cosmology framework. Future survey for HI gas in local dwarf galaxies (e.g. MeerKAT, SKA & FAST) can help to verify the nature of dark matter (cold or warm).

  3. EXPONENTIAL GALAXY DISKS FROM STELLAR SCATTERING

    SciTech Connect

    Elmegreen, Bruce G.; Struck, Curtis E-mail: curt@iastate.edu

    2013-10-01

    Stellar scattering off of orbiting or transient clumps is shown to lead to the formation of exponential profiles in both surface density and velocity dispersion in a two-dimensional non-self gravitating stellar disk with a fixed halo potential. The exponential forms for both nearly flat rotation curves and near-solid-body rotation curves. The exponential does not depend on initial conditions, spiral arms, bars, viscosity, star formation, or strong shear. After a rapid initial development, the exponential saturates to an approximately fixed scale length. The inner exponential in a two-component profile has a break radius comparable to the initial disk radius; the outer exponential is primarily scattered stars.

  4. Far Outer Galaxy H II Regions

    NASA Technical Reports Server (NTRS)

    Rudolph, A. L.; deGues, E. J.; Brand, J.; Wouterloot, J. G. A.; Gross, Anthony R. (Technical Monitor)

    1994-01-01

    We have made a multifrequency (6, 3.6, and 2 cm), high-resolution (3"-6"), radio continuum survey of IRAS selected sources from the catalogue of Wouterloot & Brand (1989) to search for and study H II regions in the far outer Galaxy. We identified 31 sources in this catalog with well determined galactocentric distances, and with R approx.. greater than 15 kpc and L(sub FIR) approx.greater than 10(exp 4) solar luminosity, indicating the presence of high-mass star-formation. We have observed 11 of these sources with the Very Large Array (VLA). We observed the sources at 6 and 2 cm using "scaled arrays", making possible a direct and reliable comparison of the data at these two wavelengths for the determination of spectral indices. We detected a total of 12 radio sources, of which 10 have spectral indices consistent with optically-thin free-free emission from H II regions. Combined with previous VLA observations by other investigators, we have data on a total of 15 H II regions at galactocentric distances of 15 to 18.2kpc, among the most remote H II regions found in our Galaxy. The sizes of the H II regions range from approx. less than 0.10 to 2.3 pc. Using the measured fluxes and sizes, we determine the electron densities, emission measures, and excitation parameters of the H II regions, as well as the fluxes of Lyman continuum photons needed to keep the nebulae ionized. The sizes and electron densities are consistent with most of the sources detected in this survey being compact or ultracompact H II regions. Seven of the fifteen H II regions have sizes approx. less than 0.20 pc. Assuming simple pressure-driven expansion of the H II regions, these sizes indicate ages approx. less than 5 x 10(exp 4) yr, or only 1% of the lifetime of an O star, which implies an unlikely overabundance of O stars in the outer Galaxy. Thus, the large number of compact H II regions suggests that the time these regions spend in a compact phase must be much longer than their dynamical

  5. Far Outer Galaxy H II Regions

    NASA Technical Reports Server (NTRS)

    Rudolph, A. L.; deGues, E. J.; Brand, J.; Wouterloot, J. G. A.; Gross, Anthony R. (Technical Monitor)

    1994-01-01

    We have made a multifrequency (6, 3.6, and 2 cm), high-resolution (3"-6"), radio continuum survey of IRAS selected sources from the catalogue of Wouterloot & Brand (1989) to search for and study H II regions in the far outer Galaxy. We identified 31 sources in this catalog with well determined galactocentric distances, and with R approx.. greater than 15 kpc and L(sub FIR) approx.greater than 10(exp 4) solar luminosity, indicating the presence of high-mass star-formation. We have observed 11 of these sources with the Very Large Array (VLA). We observed the sources at 6 and 2 cm using "scaled arrays", making possible a direct and reliable comparison of the data at these two wavelengths for the determination of spectral indices. We detected a total of 12 radio sources, of which 10 have spectral indices consistent with optically-thin free-free emission from H II regions. Combined with previous VLA observations by other investigators, we have data on a total of 15 H II regions at galactocentric distances of 15 to 18.2kpc, among the most remote H II regions found in our Galaxy. The sizes of the H II regions range from approx. less than 0.10 to 2.3 pc. Using the measured fluxes and sizes, we determine the electron densities, emission measures, and excitation parameters of the H II regions, as well as the fluxes of Lyman continuum photons needed to keep the nebulae ionized. The sizes and electron densities are consistent with most of the sources detected in this survey being compact or ultracompact H II regions. Seven of the fifteen H II regions have sizes approx. less than 0.20 pc. Assuming simple pressure-driven expansion of the H II regions, these sizes indicate ages approx. less than 5 x 10(exp 4) yr, or only 1% of the lifetime of an O star, which implies an unlikely overabundance of O stars in the outer Galaxy. Thus, the large number of compact H II regions suggests that the time these regions spend in a compact phase must be much longer than their dynamical

  6. Stellar Populations and Radial Migrations in Virgo Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Roediger, Joel C.; Courteau, Stéphane; Sánchez-Blázquez, Patricia; McDonald, Michael

    2012-10-01

    We present new stellar age profiles, derived from well-resolved optical and near-infrared images of 64 Virgo cluster disk galaxies, whose analysis poses a challenge for current disk galaxy formation models. Our ability to break the age-metallicity degeneracy and the significant size of our sample represent key improvements over complementary studies of field disk galaxies. Our results can be summarized as follows: first, and contrary to observations of disk galaxies in the field, these cluster galaxies are distributed almost equally amongst the three main types of disk galaxy luminosity profiles (I/II/III), indicating that the formation and/or survival of Type II breaks is suppressed within the cluster environment. Second, we find examples of statistically significant inversions ("U-shapes") in the age profiles of all three disk galaxy types, reminiscent of predictions from high-resolution simulations of classically truncated Type II disks in the field. These features characterize the age profiles for only about a third (<=36%) of each disk galaxy type in our sample. An even smaller fraction of cluster disks (~11% of the total sample) exhibit age profiles that decrease outward (i.e., negative age gradients). Instead, flat and/or positive age gradients prevail (>=50%) within our Type I, II, and III subsamples. These observations thus suggest that while stellar migrations and inside-out growth can play a significant role in the evolution of all disk galaxy types, other factors contributing to the evolution of galaxies can overwhelm the predicted signatures of these processes. We interpret our observations through a scenario whereby Virgo cluster disk galaxies formed initially like their brethren in the field but which, upon falling into the cluster, were transformed into their present state through external processes linked to the environment (e.g., ram-pressure stripping and harassment). Current disk galaxy formation models, which have largely focused on field

  7. STELLAR POPULATIONS AND RADIAL MIGRATIONS IN VIRGO DISK GALAXIES

    SciTech Connect

    Roediger, Joel C.; Courteau, Stephane; Sanchez-Blazquez, Patricia; McDonald, Michael E-mail: courteau@astro.queensu.ca E-mail: mcdonald@space.mit.edu

    2012-10-10

    We present new stellar age profiles, derived from well-resolved optical and near-infrared images of 64 Virgo cluster disk galaxies, whose analysis poses a challenge for current disk galaxy formation models. Our ability to break the age-metallicity degeneracy and the significant size of our sample represent key improvements over complementary studies of field disk galaxies. Our results can be summarized as follows: first, and contrary to observations of disk galaxies in the field, these cluster galaxies are distributed almost equally amongst the three main types of disk galaxy luminosity profiles (I/II/III), indicating that the formation and/or survival of Type II breaks is suppressed within the cluster environment. Second, we find examples of statistically significant inversions ({sup U}-shapes{sup )} in the age profiles of all three disk galaxy types, reminiscent of predictions from high-resolution simulations of classically truncated Type II disks in the field. These features characterize the age profiles for only about a third ({<=}36%) of each disk galaxy type in our sample. An even smaller fraction of cluster disks ({approx}11% of the total sample) exhibit age profiles that decrease outward (i.e., negative age gradients). Instead, flat and/or positive age gradients prevail ({>=}50%) within our Type I, II, and III subsamples. These observations thus suggest that while stellar migrations and inside-out growth can play a significant role in the evolution of all disk galaxy types, other factors contributing to the evolution of galaxies can overwhelm the predicted signatures of these processes. We interpret our observations through a scenario whereby Virgo cluster disk galaxies formed initially like their brethren in the field but which, upon falling into the cluster, were transformed into their present state through external processes linked to the environment (e.g., ram-pressure stripping and harassment). Current disk galaxy formation models, which have largely

  8. Star-formation efficiency in the outer Galaxy

    NASA Astrophysics Data System (ADS)

    Izumi, Natsuko; Kobayashi, Naoto; Yasui, Chikako; Tokunaga, Alan T.; Saito, Masao; Hamano, Satoshi

    2017-03-01

    We report the results of new survey of star-forming regions in the outer Galaxy at Galactocentric radius of more than 13.5 kpc, where the environment is significantly different from that in the solar neighborhood.

  9. Constraining Galaxy Evolution With Bulge+Disk+Bar Decomposition

    NASA Astrophysics Data System (ADS)

    Weinzirl, Tim; Jogee, S.; Barazza, F.

    2007-12-01

    Structural decomposition of galaxies into bulge, disk, and bar components is important to address a number of scientific problems. Measuring bulge, disk, and bar structural parameters will set constraints on the violent and secular processes of galaxy assembly and recurrent bar formation and dissolution models. It can also help to quantify the fraction and properties of bulgeless galaxies (those systems having no bulge or only a relatively insignificant disky-pseudobulges), which defy galaxy formation paradigms requiring almost every disk galaxy to have a classical bulge at its core. We demonstrate three-component bulge+disk+bar decomposition of NIR images for a sample of 200+ galaxies, with Hubble types S0 to Sm, from the Ohio State University Bright Spiral Galaxy Survey (OSUBSGS) and the UKIRT Infrared Deep Sky Survey (UKIDSS). Unlike most early studies, which attempt two-component bulge+disk decomposition, we perform three-component bulge+disk+bar decomposition with GALFIT. We show that it is important to include the bar component, as this can lower the bulge fractional luminosity ratio (B/T), often by a factor of two or more, and effectively change the Hubble type of a galaxy from early to late. We investigate how the structure of bulges and B/T vary across the Hubble sequence for barred and unbarred galaxies. We also identify the fraction of bulgeless galaxies in our sample and characterize their properties.

  10. A FUNDAMENTAL PLANE OF SPIRAL STRUCTURE IN DISK GALAXIES

    SciTech Connect

    Davis, Benjamin L.; Kennefick, Daniel; Kennefick, Julia; Shields, Douglas W.; Flatman, Russell; Hartley, Matthew T.; Berrier, Joel C.; Martinsson, Thomas P. K.; Swaters, Rob A.

    2015-03-20

    Spiral structure is the most distinctive feature of disk galaxies and yet debate persists about which theory of spiral structure is correct. Many versions of the density wave theory demand that the pitch angle be uniquely determined by the distribution of mass in the bulge and disk of the galaxy. We present evidence that the tangent of the pitch angle of logarithmic spiral arms in disk galaxies correlates strongly with the density of neutral atomic hydrogen in the disk and with the central stellar bulge mass of the galaxy. These three quantities, when plotted against each other, form a planar relationship that we argue should be fundamental to our understanding of spiral structure in disk galaxies. We further argue that any successful theory of spiral structure must be able to explain this relationship.

  11. Nuclear-to-disk rotation curves and mass-to-luminosity ratio in galaxies

    NASA Astrophysics Data System (ADS)

    Sofue, Yoshiaki

    High-resolution nuclear-to-outer rotation curves for Sb, SBb, Sc, and SBc galaxies generally show a steep nuclear rise and flat rotation from the disk to the halo. The high-velocity central rotation indicates massive cores within bulges. Since this characteristic is common to most galaxies, the high-velocity central rotation cannot be due to a particular orientation of non-circular motion. Using these rotation curves, we derive the distributions of surface-mass density, and compare them directly with observed surface-luminosity distributions. The mass-to-luminosity ratio (ML) increases from the outer bulge to the disk, indicating that the outer disk is already dominated by dark-mass. It, then, increases more rapidly toward the outer optical edge, indicating the massive halo. In the central regions of some galaxies, the ML increases steeply toward the nucleus, reaching a value an order of magnitude greater in the central 100 pc region than that in the disk, which may indicate a massive core of radius ~ 100 parsecs and mass of ~ 109 Msolar. The core may be an object linking a bulge and a black hole at the nucleus.

  12. Massive Quiescent Disk Galaxies in the CANDELS survey

    NASA Astrophysics Data System (ADS)

    Kesseli, Aurora; McGrath, E. J.; CANDELS Collaboration

    2014-01-01

    Using data from the GOODS-S field of the CANDELS survey, we find evidence for an increasing fraction of disk-dominated galaxies at high-redshift ( 2) among the quiescent, or non-star-forming galaxy population, in agreement with a growing body of evidence from recent results in the literature. We selected all galaxies with mass M>1010 Msun within the redshift range 0.5 ≤ z ≤ 2.5, and imposed a two-color selection criteria using rest-frame U, V, and J-band flux to separate quiescent from star-forming galaxies. From this sample, we performed a qualitative visual classification and a quantitative classification using the galaxy-fitting program Galfit. Of the original 140 quiescent galaxies, 23 have a disk component that contributes 50% or more of the total integrated galaxy light, and most of these are at high-redshift. At a redshift of z ~ 2 a significant fraction of all quiescent galaxies showed strong disk components with 30% being disk-dominated. We also find that massive disk galaxies seem to live in less densely populated environments while massive ellipticals live in environments with more neighbors, which leads us to believe that there are two mechanisms for the creation of massive quiescent galaxies. For the disks, the lower density environment and the disk nature of these galaxies lead us to favor cold streams over the major merger model of galaxy formation. The ellipticals, which live in higher density environments, could be assembled through major mergers of already aged stellar populations (e.g., dry mergers). This research is supported by the Clare Boothe Luce Foundation.

  13. Gas Ejection from Spiral Galaxy Disks

    NASA Astrophysics Data System (ADS)

    Durelle, Jeremy

    We present the results of three proposed mechanisms for ejection of gas from a spiral arm into the halo. The mechanisms were modelled using magnetohydrodynamics (MHD) as a theoretical template. Each mechanism was run through simulations using a Fortran code: ZEUS-3D, an MHD equation solver. The first mechanism modelled the gas dynamics with a modified Hartmann flow which describes the fluid flow between two parallel plates. We initialized the problem based on observation of lagging halos; that is, that the rotational velocity falls to a zero at some height above the plane of the disk. When adopting a density profile which takes into account the various warm and cold H I and HII molecular clouds, the system evolves very strangely and does not reproduce the steady velocity gradient observed in edge-on galaxies. This density profile, adopted from Martos and Cox (1998), was used in the remaining models. However, when treating a system with a uniform density profile, a stable simulation can result. Next we considered supernova (SN) blasts as a possible mechanism for gas ejection. While a single SN was shown to be insufficient to promote vertical gas structures from the disk, multiple SN explosions proved to be enough to promote gas ejection from the disk. In these simulations, gas ejected to a height of 0.5 kpc at a velocity of 130 km s--1 from 500 supernovae, extending to an approximate maximum height of 1 kpc at a velocity of 6.7 x 103 km s--1 from 1500 supernovae after 0.15 Myr, the approximate time of propagation of a supernova shock wave. Finally, we simulated gas flowing into the spiral arm at such a speed to promote a jump in the disk gas, termed a hydraulic jump. The height of the jump was found to be slightly less than a kiloparsec with a flow velocity of 41 km s--1 into the halo after 167 Myr. The latter models proved to be effective mechanisms through which gas is ejected from the disk whereas the Hartmann flow (or toy model) mechanism remains unclear as the

  14. THE PARKER INSTABILITY IN DISK GALAXIES

    SciTech Connect

    Rodrigues, L. F. S.; Sarson, G. R.; Shukurov, A.; Bushby, P. J.; Fletcher, A. E-mail: graeme.sarson@newcastle.ac.uk E-mail: paul.bushby@newcastle.ac.uk

    2016-01-01

    We examine the evolution of the Parker instability in galactic disks using 3D numerical simulations. We consider a local Cartesian box section of a galactic disk, where gas, magnetic fields, and cosmic rays are all initially in a magnetohydrostatic equilibrium. This is done for different choices of initial cosmic-ray density and magnetic field. The growth rates and characteristic scales obtained from the models, as well as their dependences on the density of cosmic rays and magnetic fields, are in broad agreement with previous (linearized, ideal) analytical work. However, this nonideal instability develops a multimodal 3D structure, which cannot be quantitatively predicted from the earlier linearized studies. This 3D signature of the instability will be of importance in interpreting observations. As a preliminary step toward such interpretations, we calculate synthetic polarized intensity and Faraday rotation measure (RM) maps, and the associated structure functions of the latter, from our simulations; these suggest that the correlation scales inferred from RM maps are a possible probe for the cosmic-ray content of a given galaxy. Our calculations highlight the importance of cosmic rays in these measures, making them an essential ingredient of realistic models of the interstellar medium.

  15. THE EFFECTS OF EPISODIC STAR FORMATION ON THE FUV-NUV COLORS OF STAR FORMING REGIONS IN OUTER DISKS

    SciTech Connect

    Barnes, Kate L.; Van Zee, Liese; Dowell, Jayce D. E-mail: vanzee@astro.indiana.edu

    2013-09-20

    We run stellar population synthesis models to examine the effects of a recently episodic star formation history (SFH) on UV and Hα colors of star forming regions. Specifically, the SFHs we use are an episodic sampling of an exponentially declining star formation rate (SFR; τ model) and are intended to simulate the SFHs in the outer disks of spiral galaxies. To enable comparison between our models and observational studies of star forming regions in outer disks, we include in our models sensitivity limits that are based on recent deep UV and Hα observations in the literature. We find significant dispersion in the FUV-NUV colors of simulated star forming regions with frequencies of star formation episodes of 1 × 10{sup –8} to 4 × 10{sup –9} yr{sup –1}. The dispersion in UV colors is similar to that found in the outer disk of nearby spiral galaxies. As expected, we also find large variations in L{sub H{sub α}}/L{sub FUV}. We interpret our models within the context of inside-out disk growth, and find that a radially increasing τ and decreasing metallicity with an increasing radius will only produce modest FUV-NUV color gradients, which are significantly smaller than what is found for some nearby spiral galaxies. However, including moderate extinction gradients with our models can better match the observations with steeper UV color gradients. We estimate that the SFR at which the number of stars emitting FUV light becomes stochastic is ∼2 × 10{sup –6} M{sub ☉} yr{sup –1}, which is substantially lower than the SFR of many star forming regions in outer disks. Therefore, we conclude that stochasticity in the upper end of the initial mass function is not likely to be the dominant cause of dispersion in the FUV-NUV colors of star forming regions in outer disks. Finally, we note that if outer disks have had an episodic SFH similar to that used in this study, this should be taken into account when estimating gas depletion timescales and modeling chemical

  16. Box and peanut shaped bulges of disk galaxies

    NASA Astrophysics Data System (ADS)

    Lütticke, R.; Dettmar, R.-J.

    1998-07-01

    Our new statistics of bulges of disk galaxies reveals a high frequency of box- or peanut shaped (b/p) bulges of up to 50%. Therefore very common processes are required to explain this high fraction. In a sample of edge-on disk galaxies selected from the RC3 we characterize bulges by their degree of b/p-shape using the ``Digitized Sky Survey''. The distributions of galaxies with b/p-bulge and barred galaxies binned by morphological type show the same general dependences. In an analysis of a possible relation between this internal structure and the presence of satellite systems of isolated disk galaxies we find a possible connection between b/p bulges and galaxies with the presence of satellites. From this we conclude that b/p-bulges preferentially occur in disk galaxies with companions. Therefore the most likely reason responsible for the development of b/p-bulges is a bar originating from galaxy interaction in stable disks or by an infalling satellite.

  17. GAMA: Stellar Mass Assembly in Galaxy Bulges and Disks

    NASA Astrophysics Data System (ADS)

    Moffett, Amanda J.; Driver, Simon P.; Lange, Rebecca; Robotham, Aaron; Kelvin, Lee; GAMA Team

    2016-01-01

    The Galaxy And Mass Assembly (GAMA) survey has to date obtained spectra, redshifts, and 21-band multi-facility photometry for over 200,000 galaxies in five survey regions that total nearly 300 square degrees on sky. We consider here a low-redshift (z<0.06), volume-limited subsample of ~8,000 GAMA galaxies that have been morphologically classified by the survey team. In order to quantify the separate bulge and disk properties of these galaxies, we apply a large-scale automated procedure for fitting images with 2D, multi-component structure models, including evaluation of fit convergence using a grid of input parameter values for each galaxy. From this analysis, we calculate the total bulge and disk contributions to the local galaxy stellar mass budget and derive mass-size relations for both pure spheroid/disk systems and the separate bulge/disk components of multi-component galaxies. We further examine the fraction of total stellar mass assembled in spheroid and disk structures as a function of galaxy environment, where environment is quantified on multiple scales from membership in large-scale filaments to groups/clusters and down to local pairings. We then discuss the effect of environmental conditions on the mechanisms of stellar mass assembly, including the implied balance between merger accumulation and in situ mass growth in different environment regimes.

  18. WANDERING BLACK HOLES IN BRIGHT DISK GALAXY HALOS

    SciTech Connect

    Bellovary, Jillian M.; Governato, Fabio; Quinn, Thomas R.; Wadsley, James; Shen, Sijing; Volonteri, Marta

    2010-10-01

    We perform SPH+N-body cosmological simulations of massive disk galaxies, including a formalism for black hole (BH) seed formation and growth, and find that satellite galaxies containing supermassive BH seeds are often stripped as they merge with the primary galaxy. These events naturally create a population of 'wandering' BHs that are the remnants of stripped satellite cores; galaxies like the Milky Way may host 5-15 of these objects within their halos. The satellites that harbor BH seeds are comparable to Local Group dwarf galaxies such as the Small and Large Magellanic Clouds; these galaxies are promising candidates to host nearby intermediate-mass BHs. Provided that these wandering BHs retain a gaseous accretion disk from their host dwarf galaxy, they give a physical explanation for the origin and observed properties of some recently discovered off-nuclear ultraluminous X-ray sources such as HLX-1.

  19. Computer Model Shows a Disk Galaxy's Life History

    NASA Image and Video Library

    This cosmological simulation follows the development of a single disk galaxy over about 13.5 billion years, from shortly after the Big Bang to the present time. Colors indicate old stars (red), you...

  20. Constraining Galaxy Evolution With Bulge-Disk-Bar Decomposition

    NASA Astrophysics Data System (ADS)

    Weinzirl, T.; Jogee, S.; Barazza, F. D.

    2008-08-01

    Structural decomposition of galaxies into bulge, disk, and bar components is important to address a number of scientific problems. Measuring bulge, disk, and bar structural parameters will set constraints on the violent and secular processes of galaxy assembly and recurrent bar formation and dissolution models. It can also help to quantify the fraction and properties of bulgeless galaxies (those systems having no bulge or only a relatively insignificant disky-pseudobulges), which defy galaxy formation paradigms requiring almost every disk galaxy to have a classical bulge at its core. We demonstrate a proof of concept and show early results of our ongoing three-component bulge-disk-bar decomposition of NIR images for samples spanning different environments (field and cluster). In contrast to most early studies, which only attempt two-component bulge-disk decomposition, we fit three components using GALFIT: a bulge, a disk, and a bar. We show that it is important to include the bar component, as this can significantly lower the bulge-to-total luminosity ratio (B/T), in many cases by a factor of two or more, thus effectively changing the Hubble type of a galaxy from early to late.

  1. Revealing the structure of the outer disks of Be stars

    NASA Astrophysics Data System (ADS)

    Klement, R.; Carciofi, A. C.; Rivinius, T.; Matthews, L. D.; Vieira, R. G.; Ignace, R.; Bjorkman, J. E.; Mota, B. C.; Faes, D. M.; Bratcher, A. D.; Curé, M.; Štefl, S.

    2017-05-01

    Context. The structure of the inner parts of Be star disks (≲ 20 stellar radii) is well explained by the viscous decretion disk (VDD) model, which is able to reproduce the observable properties of most of the objects studied so far. The outer parts, on the other hand, are not observationally well-explored, as they are observable only at radio wavelengths. A steepening of the spectral slope somewhere between infrared and radio wavelengths was reported for several Be stars that were previously detected in the radio, but a convincing physical explanation for this trend has not yet been provided. Aims: We test the VDD model predictions for the extended parts of a sample of six Be disks that have been observed in the radio to address the question of whether the observed turndown in the spectral energy distribution (SED) can be explained in the framework of the VDD model, including recent theoretical development for truncated Be disks in binary systems. Methods: We combine new multi-wavelength radio observations from the Karl. G. Jansky Very Large Array (JVLA) and Atacama Pathfinder Experiment (APEX) with previously published radio data and archival SED measurements at ultraviolet, visual, and infrared wavelengths. The density structure of the disks, including their outer parts, is constrained by radiative transfer modeling of the observed spectrum using VDD model predictions. In the VDD model we include the presumed effects of possible tidal influence from faint binary companions. Results: For 5 out of 6 studied stars, the observed SED shows strong signs of SED turndown between far-IR and radio wavelengths. A VDD model that extends to large distances closely reproduces the observed SEDs up to far IR wavelengths, but fails to reproduce the radio SED. Using a truncated VDD model improves the fit, leading to a successful explanation of the SED turndown observed for the stars in our sample. The slope of the observed SEDs in the radio is however not well reproduced by

  2. The stellar mass distribution of S4G disk galaxies

    NASA Astrophysics Data System (ADS)

    Díaz-García, Simón; Salo, Heikki; Laurikainen, Eija

    2017-03-01

    We use 3.6 μm imaging from the S4G survey to characterize the typical stellar density profiles (Σ*) and bars as a function of fundamental galaxy parameters (e.g. the total stellar mass M *), providing observational constraints for galaxy simulation models to be compared with. We rescale galaxy images to a common frame determined by the size in physical units, by their disk scalelength, or by their bar size and orientation. We stack the resized images to obtain statistically representative average stellar disks and bars. For a given M * bin (>= 109 M ⊙), we find a significant difference in the stellar density profiles of barred and non-barred systems that gives evidence for bar-induced secular evolution of disk galaxies: (i) disks in barred galaxies show larger scalelengths and fainter extrapolated central surface brightnesses, (ii) the mean surface brightness profiles of barred and non-barred galaxies intersect each other slightly beyond the mean bar length, most likely at the bar corotation, and (iii) the central mass concentration of barred galaxies is larger (by almost a factor 2 when T < 5) than in their non-barred counterparts. We also show that early- and intermediate-type spirals (0 <= T < 5) host intrinsically narrower bars than the later types and S0s, whose bars are oval-shaped. We show a clear correlation between galaxy family and bar ellipticity.

  3. Clustered star formation as a natural explanation for the Halpha cut-off in disk galaxies.

    PubMed

    Pflamm-Altenburg, Jan; Kroupa, Pavel

    2008-10-02

    The rate of star formation in a galaxy is often determined by the observation of emission in the Halpha line, which is related to the presence of short-lived massive stars. Disk galaxies show a strong cut-off in Halpha radiation at a certain galactocentric distance, which has led to the conclusion that star formation is suppressed in the outer regions of disk galaxies. This is seemingly in contradiction to recent observations in the ultraviolet which imply that disk galaxies have star formation beyond the Halpha cut-off, and that the star-formation-rate surface density is linearly related to the underlying gas surface density, which is a shallower relationship than that derived from Halpha luminosities. In a galaxy-wide formulation, the clustered nature of star formation has recently led to the insight that the total galactic Halpha luminosity is nonlinearly related to the galaxy-wide star formation rate. Here we show that a local formulation of the concept of clustered star formation naturally leads to a steeper radial decrease in the Halpha surface luminosity than in the star-formation-rate surface density, in quantitative agreement with the observations, and that the observed Halpha cut-off arises naturally.

  4. The Response of Disks to Oscillatory Modes in Galaxies

    NASA Technical Reports Server (NTRS)

    Smith, Bruce F.; Gerber, R. A.; Steiman-Cameron, T. Y.; Miller, R. H.; Cuzzi, Jeff C. (Technical Monitor)

    1996-01-01

    Recent studies suggest that galaxies can oscillate in normal modes with essentially no damping over a Hubble time. These modes may play an important role in the structure and evolution of disk/halo systems. Motivated by the possibility that normal mode oscillations exist in real galaxies, we are investigating the response of galactic disks to halo oscillations. The goal of these investigations is to ascertain whether or not observational signatures exist for such oscillations. Our approach is to perform numerical experiments on the response of a self-gravitating disk to a time-varying halo potential. We assume that a significant fraction of the mass in a galaxy is in a dark halo. The halo oscillates and the luminous disk material responds to these oscillations. Preliminary results are reported for disks embedded in a radially oscillating gravitational potential. The equilibrium initial disk is represented by an exponential density profile. Considerable care was taken to build an initial disk model that was "stable" over long time scales. A control experiment was run with the disk in a static halo potential. The disk responds to the time-varying potential by developing a ring structure, which forms and disappears during each halo oscillation cycle. The density of stars becomes depressed in an annular region at the radius where the disk epicycle frequency is equal to the halo oscillation period. This pattern of response persists over time periods approaching a Hubble time. In the oscillating potential, a bar develops in the inner disk. This bar is absent when the halo remains static. Specific targets of this study include the implications for large-scale disk structure, the gas dynamical response of the interstellar medium in such systems, and the inflow of material into the central regions of the galaxy.

  5. The Warped Nuclear Disk of Radio Galaxy 3C 449

    NASA Astrophysics Data System (ADS)

    Tremblay, G. R.; Quillen, A. C.; Floyd, D. J. E.; Noel-Storr, J.; Baum, S. A.; Axon, D. J.; O'Dea, C. P.; Chiaberge, M.; Macchetto, F. D.; Sparks, W. B.; Miley, G. K.; Capetti, A.; Madrid, J. P.; Perlman, E.

    2005-12-01

    Among radio galaxies containing nuclear dust disks, the bipolar jet axis is generally expected to be perpendicular to the disk major axis. However, the FR I radio source 3C 449, possessing a nearly parallel jet/disk orientation on the sky, is an extreme example of a system that does not conform to this expectation. We examine the 600 pc dusty disk in this galaxy with images from the Hubble Space Telescope. We find that a colormap of the disk exhibits a twist in its isocolor contours (isochromes). We model the colormap by integrating galactic starlight through an absorptive disk, and find that the anomalous twist in the isochromes can be reproduced in the model with a vertically thin, warped disk. The model predicts that the disk is nearly perpendicular to the jet axis within 100 pc of the nucleus. We discuss physical mechanisms capable of causing such a warp. We show that a torque on the disk arising from a possible binary black hole in the AGN or radiation pressure from the AGN causes precession on a timescale that is too long to generate such a warp. However, we estimate that the pressure in the X-ray emitting interstellar medium is large enough to perturb the disk. The warped disk in 3C 449 may be a new manifestation of feedback from an active galactic nucleus.

  6. ECO and RESOLVE: Galaxy Disk Growth in Environmental Context

    NASA Astrophysics Data System (ADS)

    Moffett, Amanda J.; Kannappan, Sheila J.; Berlind, Andreas A.; Eckert, Kathleen D.; Stark, David V.; Hendel, David; Norris, Mark A.; Grogin, Norman A.

    2015-10-01

    We study the relationships between galaxy environments and galaxy properties related to disk (re)growth, considering two highly complete samples that are approximately baryonic mass limited into the high-mass dwarf galaxy regime, the Environmental COntext catalog (data release herein) and the B-semester region of the REsolved Spectroscopy Of a Local VolumE survey. We quantify galaxy environments using both group identification and smoothed galaxy density field methods. We use by-eye and quantitative morphological classifications plus atomic gas content measurements and estimates. We find that blue early-type (E/S0) galaxies, gas-dominated galaxies, and UV-bright disk host galaxies all become distinctly more common below group halo mass ˜ {10}11.5 {M}⊙ , implying that this low group halo mass regime may be a preferred regime for significant disk growth activity. We also find that blue early-type and blue late-type galaxies inhabit environments of similar group halo mass at fixed baryonic mass, consistent with a scenario in which blue early-types can regrow late-type disks. In fact, we find that the only significant difference in the typical group halo mass inhabited by different galaxy classes is for satellite galaxies with different colors, where at fixed baryonic mass red early- and late-types have higher typical group halo masses than blue early- and late-types. More generally, we argue that the traditional morphology-environment relation (i.e., that denser environments tend to have more early-types) can be largely attributed to the morphology-galaxy mass relation for centrals and the color-environment relation for satellites.

  7. Mass Distribution and Bar Formation in Growing Disk Galaxy Models

    NASA Astrophysics Data System (ADS)

    Berrier, Joel C.; Sellwood, J. A.

    2016-11-01

    We report idealized simulations that mimic the growth of galaxy disks embedded in responsive halos and bulges. The disks manifested an almost overwhelming tendency to form strong bars that we found very difficult to prevent. We found that fresh bars formed in growing disks after we had destroyed the original, indicating that bar formation also afflicts continued galaxy evolution, and not just the early stages of disk formation. This behavior raises still more insistently the previously unsolved question of how some galaxies avoid bars. Since our simulations included only collisionless star and halo particles, our findings may apply to gas-poor galaxies only; however, the conundrum persists for the substantial unbarred fraction of those galaxies. Our original objective was to study how internal dynamics rearranged the distribution of mass in the disk as a generalization of our earlier study with rigid spherical components. With difficulty, we were able to construct some models that were not strongly influenced by bars, and found that halo compression and angular momentum exchange with the disk did not alter our earlier conclusion that spiral activity is largely responsible for creating smooth density profiles and rotation curves.

  8. Gas accretion from the cosmic web feeding disk galaxies

    NASA Astrophysics Data System (ADS)

    Sánchez Almeida, J.; Olmo-García, A.; Elmegreen, B. G.; Muñoz-Tuñón, C.; Elmegreen, D. M.; Filho, M. E.; Pérez-Montero, E.; Amorín, R.

    2017-03-01

    Disk galaxies in cosmological numerical simulations grow by accreting gas from the cosmic web. This gas reaches the external disk, and then spirals in dragged along by tidal forces and/or disk instabilities. The importance of gas infall is as clear from numerical simulations as it is obscure to observations. Extremely metal poor (XMP) galaxies seem to be the best example we have of the gas accretion process at work. They have large off-center starbursts which show significant metallicity drop compared with the host galaxy. This observation is naturally explained as a gas accretion event caught in the act. We present preliminary results of the kinematical properties of the metal poor starbursts in XMPs, which suggest that the starbursts are kinematically decoupled entities within the host galaxy.

  9. Inner and Outer Photometric Structure of Elliptical Galaxies

    NASA Astrophysics Data System (ADS)

    Graham, Alister W.; Erwin, P.; Trujillo, I.; Asensio Ramos, A.

    The Nuker model, when applied to the inner regions of ``core'' galaxies, is shown to produce systematic biases in the determination of the core ``break-radii''. These radii can easily be (and often have been, see Trujillo et al. 2003) over-estimated by more than 100%. Moreover, due to curvature in the outer profiles of early-type galaxies (i.e., beyond the break-radius), none of the Nuker model parameters are found to be robust quantities. A new empirical model that simultaneously describes both the inner and outer light-profiles of elliptical galaxies (and bulges in general) is presented. It consists of a Sérsic function with an inner power-law and a variable transition region.

  10. Giant disk galaxies : Where environment trumps mass in galaxy evolution

    NASA Astrophysics Data System (ADS)

    Courtois, H. M.

    There is an ongoing argument regarding galaxies, like there is regarding children, of whether the final outcome is driven primarily by nature or nurture. In the case of galaxies, the total mass plays the role of genetics (nature) and the number of nearby galaxies plays the role of family life (nurture). Untangling the role of each has been particularly difficult for galaxies because the mass of a galaxy is closely tied to its environment.

  11. Tidally Induced Offset Disks in Magellanic Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Pardy, Stephen A.; D'Onghia, Elena; Athanassoula, E.; Wilcots, Eric M.; Sheth, Kartik

    2016-08-01

    Magellanic spiral galaxies are a class of one-armed systems that often exhibit an offset stellar bar and are rarely found around massive spiral galaxies. Using a set of N-body and hydrodynamic simulations, we consider a dwarf-dwarf galaxy interaction as the driving mechanism for the formation of this peculiar class of systems. We investigate here the relation between the dynamical, stellar, and gaseous disk center and the bar. In all our simulations the bar center always coincides with the dynamical center, while the stellar disk becomes highly asymmetric during the encounter, causing the photometric center of the Magellanic galaxy disk to become mismatched with both the bar and the dynamical center. The disk asymmetries persist for almost 2 Gyr, the time that it takes for the disk to be recentered with the bar, and well after the companion has passed. This explains the nature of the offset bar found in many Magellanic-type galaxies, including the Large Magellanic Cloud (LMC) and NGC 3906. In particular, these results, once applied to the LMC, suggest that the dynamical center should reside in the bar center instead of the H i center as previously assumed, pointing to a variation in the current estimate of the north component of the LMC proper motion.

  12. Metallicity evolution in mergers of disk galaxies with black holes

    NASA Astrophysics Data System (ADS)

    Rantala, Antti; Johansson, Peter H.

    2016-10-01

    We use the TreeSPH simulation code Gadget-3 including a recently improved smoothed particle hydrodynamics (SPH) module, a detailed metallicity evolution model and sophisticated subresolution feedback models for supernovae and supermassive black holes in order to study the metallicity evolution in disk galaxy mergers. In addition, we examine the simulated morphology, star formation histories, metallicity gradients and kinematic properties of merging galaxies and merger remnants. We will compare our simulation results with observations of the early-type Centaurus A galaxy and the currently colliding Antennae galaxies.

  13. On the Galactic Spin of Barred Disk Galaxies

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  14. Molecular clouds in the extreme outer galaxy

    NASA Technical Reports Server (NTRS)

    Digel, S.; De Geus, E.; Thaddeus, P.

    1994-01-01

    We present observation of 11 molecular clouds with kinematic Galactocentric distances of 18-28 kpc. The most distant is approximately 10 kpc farther from the Galactic center than any previously known and apparently lies beyond the edge of the optical disk. All are associated with much larger H I concentrations, with typical offsets of approximately 40 pc from the H I peaks. CO observations with the CfA 1.2 m and National Radio Astronomy Observatory (NRAO) 12 m telescopes indicate typical sizes of 20-40 pc, velocity widths of 1-3 km/s, and kinetic temperatures of 10-25 K. They apparently have lower CO luminosities than clouds near the solar circle with similar properties. Some may have associated infrared sources, but owing to the great distances of the clouds, the only general conclusion that can be made about star formation is that stars earlier than B1 are absent. The apparent scarcity of clouds like these indicates that their contribution to the mass of the ISM beyond R = 18 kpc is not significant.

  15. DISCOVERY OF AN EDGE-ON DEBRIS DISK WITH A DUST RING AND AN OUTER DISK WING-TILT ASYMMETRY

    SciTech Connect

    Kasper, Markus; Apai, Dániel; Wagner, Kevin; Robberto, Massimo

    2015-10-20

    Using Very Large Telescope/SPHERE near-infrared dual-band imaging and integral field spectroscopy, we discovered an edge-on debris disk around the 17 Myr old A-type member of the Scorpius–Centaurus OB association HD 110058. The edge-on disk can be traced to about 0.″6 or 65 AU projected separation. In its northern and southern wings, the disk shows at all wavelengths two prominent, bright, and symmetrically placed knots at 0.″3 or 32 AU from the star. We interpret these knots as a ring of planetesimals whose collisions may produce most of the dust observed in the disk. We find no evidence for a bow in the disk, but we identify a pair of symmetric, hooklike features in both wings. Based on similar features in the Beta Pictoris disk, we propose that this wing-tilt asymmetry traces either an outer planetesimal belt that is inclined with respect to the disk midplane or radiation-pressure-driven dust blown out from a yet unseen inner belt that is inclined with respect to the disk midplane. The misaligned inner or outer disk may be a result of interaction with a yet unseen planet. Overall, the disk geometry resembles the nearby disk around Beta Pictoris, albeit seen at smaller radial scales.

  16. Survey of Outer Galaxy Molecular Lines Associated with Water Masers

    NASA Astrophysics Data System (ADS)

    Mochizuki, N.; Hachisuka, K.; Umemoto, T.

    2009-08-01

    H_2O masers in Young stellar objects (YSOs) in our Galaxy are one of the targets of the VSOP-2 science. The advantage of VSOP-2 observation is the highest angular resolution which can detect a proper motion of H_2O masers for distant objects over short time intervals. To find candidate sources, we observed H2O maser sources in the outer Galaxy using the VLA, and we surveyed the molecular lines toward these sources to understand the environment of YSOs. Higher H2 column densities of YSOs were found for objects with active H2O masers.

  17. Supermassive Black Hole Masses and Global Properties of Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Castillo, Y. S.; Funes, J. G.; Díaz, R. J.

    2006-06-01

    Different scaling laws are known for the mass of supermassive black holes (M_{BH}): M_{BH}-σ M_{BH}-M_{Bulge}; M_{BH}-M_{DM}. We have reviewed these correlations for 17 disk galaxies and tried to find any correlation between M_{BH} and other disk properties (HI and H_2 masses, far infrared luminosity, star formation rate, etc.). The sample was taken from Marconi and Hunt (2003). For these galaxies we have done a search in the literature for the following properties: A) in the nucleus: star formation rates, and luminosities in Hα ; B) in the bulge: luminosity in B-band; C) in the disk: HI and H_2 total masses, total luminosities in X-ray, B band and far infrared, and total star formation rate. In this work we present the compiled data from the literature and the plots of M_{BH} against galaxy HI total mass, M_{BH} against galaxy H_2 total mass, and M_{BH} against disk blue luminosity. We did not find any evident correlation between the M_{BH} and the properties of the disk.

  18. Disk heating and bending instability in galaxies with counterrotation

    NASA Astrophysics Data System (ADS)

    Khoperskov, Sergey; Bertin, Giuseppe

    2017-01-01

    With the help of high-resolution long-slit and integral-field spectroscopy observations, the number of confirmed cases of galaxies with counterrotation is increasing rapidly. The evolution of such counterrotating galaxies remains far from being well understood. In this paper we study the dynamics of counterrotating collisionless stellar disks by means of N-body simulations. We show that, in the presence of counterrotation, an otherwise gravitationally stable disk can naturally generate bending waves accompanied by strong disk heating across the disk plane, that is in the vertical direction. Such a conclusion is found to hold even for dynamically warm systems with typical values of the initial vertical-to-radial velocity dispersion ratio σz/σR ≈ 0.5, for which the role of pressure anisotropy should be unimportant. We note that, during evolution, the σz/σR ratio tends to rise up to values close to unity in the case of locally Jeans-stable disks, whereas in disks that are initially Jeans-unstable it may reach even higher values, especially in the innermost regions. This unusual behavior of the σz/σR ratio in galaxies with counterrotation appears not to have been noticed earlier. Our investigations of systems made of two counterrotating components with different mass-ratios suggest that even apparently normal disk galaxies (i.e., with a minor counterrotating component so as to escape detection in current observations) might be subject to significant disk heating especially in the vertical direction.

  19. 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.

  20. Elemental Abundance Ratios in Stars of the Outer Galactic Disk. III. Cepheids

    NASA Astrophysics Data System (ADS)

    Yong, David; Carney, Bruce W.; Teixera de Almeida, Maria Luísa; Pohl, Brian L.

    2006-04-01

    We present metallicities, [Fe/H], and elemental abundance ratios, [X/Fe], for a sample of 24 Cepheids in the outer Galactic disk based on high-resolution echelle spectra. The sample members have galactocentric distances covering 12 kpc<=RGC<=17.2 kpc, making them the most distant Galactic Cepheids upon which detailed abundance analyses have been performed. We find subsolar ratios of [Fe/H] and overabundances of [α/Fe], [La/Fe], and [Eu/Fe] in the program stars. All abundance ratios exhibit a dispersion that exceeds the measurement uncertainties. As seen in our previous studies of old open clusters and field giants, enhanced ratios of [α/Fe] and [Eu/Fe] reveal that recent star formation has taken place in the outer disk with Type II supernovae preferentially contributing ejecta to the interstellar medium and with Type Ia supernovae playing only a minor role. The enhancements for La suggest that asymptotic giant branch stars have contributed to the chemical evolution of the outer Galactic disk. Some of the young Cepheids are more metal-poor than the older open clusters and field stars at comparable galactocentric distances. This demonstrates that the outer disk is not the end result of the isolated evolution of an ensemble of gas and stars. We showed previously that the older open clusters and field stars reached a basement metallicity at about 10-11 kpc. The younger Cepheids reach the same metallicity but at larger galactocentric distances, roughly 14 kpc. This suggests that the Galactic disk has been growing with time, as predicted from numerical simulations. The outer disk Cepheids appear to exhibit a bimodal distribution for [Fe/H] and [α/Fe]. Most of the Cepheids continue the trends with galactocentric distance exhibited by S. M. Andrievsky's larger Cepheid sample, and we refer to these stars as the ``Galactic Cepheids.'' A minority of the Cepheids show considerably lower [Fe/H] and higher [α/Fe], and we refer to these stars as the ``Merger Cepheids.'' One

  1. A massive, dead disk galaxy in the early Universe.

    PubMed

    Toft, Sune; Zabl, Johannes; Richard, Johan; Gallazzi, Anna; Zibetti, Stefano; Prescott, Moire; Grillo, Claudio; Man, Allison W S; Lee, Nicholas Y; Gómez-Guijarro, Carlos; Stockmann, Mikkel; Magdis, Georgios; Steinhardt, Charles L

    2017-06-21

    At redshift z = 2, when the Universe was just three billion years old, half of the most massive galaxies were extremely compact and had already exhausted their fuel for star formation. It is believed that they were formed in intense nuclear starbursts and that they ultimately grew into the most massive local elliptical galaxies seen today, through mergers with minor companions, but validating this picture requires higher-resolution observations of their centres than is currently possible. Magnification from gravitational lensing offers an opportunity to resolve the inner regions of galaxies. Here we report an analysis of the stellar populations and kinematics of a lensed z = 2.1478 compact galaxy, which-surprisingly-turns out to be a fast-spinning, rotationally supported disk galaxy. Its stars must have formed in a disk, rather than in a merger-driven nuclear starburst. The galaxy was probably fed by streams of cold gas, which were able to penetrate the hot halo gas until they were cut off by shock heating from the dark matter halo. This result confirms previous indirect indications that the first galaxies to cease star formation must have gone through major changes not just in their structure, but also in their kinematics, to evolve into present-day elliptical galaxies.

  2. A massive, dead disk galaxy in the early Universe

    NASA Astrophysics Data System (ADS)

    Toft, Sune; Zabl, Johannes; Richard, Johan; Gallazzi, Anna; Zibetti, Stefano; Prescott, Moire; Grillo, Claudio; Man, Allison W. S.; Lee, Nicholas Y.; Gómez-Guijarro, Carlos; Stockmann, Mikkel; Magdis, Georgios; Steinhardt, Charles L.

    2017-06-01

    At redshift z = 2, when the Universe was just three billion years old, half of the most massive galaxies were extremely compact and had already exhausted their fuel for star formation. It is believed that they were formed in intense nuclear starbursts and that they ultimately grew into the most massive local elliptical galaxies seen today, through mergers with minor companions, but validating this picture requires higher-resolution observations of their centres than is currently possible. Magnification from gravitational lensing offers an opportunity to resolve the inner regions of galaxies. Here we report an analysis of the stellar populations and kinematics of a lensed z = 2.1478 compact galaxy, which—surprisingly—turns out to be a fast-spinning, rotationally supported disk galaxy. Its stars must have formed in a disk, rather than in a merger-driven nuclear starburst. The galaxy was probably fed by streams of cold gas, which were able to penetrate the hot halo gas until they were cut off by shock heating from the dark matter halo. This result confirms previous indirect indications that the first galaxies to cease star formation must have gone through major changes not just in their structure, but also in their kinematics, to evolve into present-day elliptical galaxies.

  3. Theory of bending waves with applications to disk galaxies

    SciTech Connect

    Mark, J.W.K.

    1982-01-01

    A theory of bending waves is surveyed which provides an explanation for the required amplification of the warp in the Milky Way. It also provides for self-generated warps in isolated external galaxies. The shape of observed warps and partly their existence in isolated galaxies are indicative of substantial spheroidal components. The theory also provides a plausible explanation for the bending of the inner disk (<2 kpc) of the Milky Way.

  4. Connecting Clump Sizes in Turbulent Disk Galaxies to Instability Theory

    NASA Astrophysics Data System (ADS)

    Fisher, David B.; Glazebrook, Karl; Abraham, Roberto G.; Damjanov, Ivana; White, Heidi A.; Obreschkow, Danail; Basset, Robert; Bekiaris, Georgios; Wisnioski, Emily; Green, Andy; Bolatto, Alberto D.

    2017-04-01

    In this letter we study the mean sizes of Hα clumps in turbulent disk galaxies relative to kinematics, gas fractions, and Toomre Q. We use ∼100 pc resolution HST images, IFU kinematics, and gas fractions of a sample of rare, nearby turbulent disks with properties closely matched to z∼ 1.5{--}2 main-sequence galaxies (the DYNAMO sample). We find linear correlations of normalized mean clump sizes with both the gas fraction and the velocity dispersion-to-rotation velocity ratio of the host galaxy. We show that these correlations are consistent with predictions derived from a model of instabilities in a self-gravitating disk (the so-called “violent disk instability model”). We also observe, using a two-fluid model for Q, a correlation between the size of clumps and self-gravity-driven unstable regions. These results are most consistent with the hypothesis that massive star-forming clumps in turbulent disks are the result of instabilities in self-gravitating gas-rich disks, and therefore provide a direct connection between resolved clump sizes and this in situ mechanism.

  5. The Peculiar Velocities of Satellites of External Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Azzaro, Marco; Zentner, Andrew R.; Prada, Francisco; Klypin, Anatoly A.

    2006-07-01

    We analyze the angular distribution and the orbital rotation directions of a sample of carefully selected satellite galaxies about disk galaxy primaries extracted from the Sloan Digital Sky Survey (SDSS). We complement this analysis with a theoretical study of these statistics in an N-body simulation of cosmological structure formation set within the ΛCDM paradigm under various assumptions for the orientations of disk angular momenta. Under the assumption that the angular momenta of the disks are aligned with the angular momenta of the inner regions of their host dark matter halos, we find that the fraction of simulated satellite halos that exhibit prograde motion is fprog~0.55-0.60, with larger satellites more likely to be prograde. In our observational sample, approximately 60% of the satellites exhibit prograde motion, a result that is broadly consistent with the simulated sample. Our observational sample of satellite galaxies shows no evidence for an anisotropic satellite distribution relative to disk primaries; however, the small sample size does not yet support a statistically significant comparison to previous studies of satellite anisotropy. Again, this result is broadly consistent with our simulated sample of satellites under the assumption that disk and halo angular momenta are aligned. However, the small size of our observational sample does not yet allow us to distinguish between various assumptions regarding the orientations of disks in their halos. Finally, we present an assessment of the importance of contamination by interlopers on the measured prograde and retrograde statistics.

  6. Large scale structure and galaxy disks as Lyman-alpha clouds

    NASA Astrophysics Data System (ADS)

    Salpeter, Edwin E.

    1993-10-01

    Large-scale structure in the universe is enriched by two morphological categories, expanding 'clouds' of bound 'local groups' of galaxies and superclusters. Part of the complexity is due to a 'category overlap' in length scales, e.g., some galaxy pairs have a larger separation than the size of some rich compact groups. This essay includes conjectures on (presently unseen) galaxies, located in the Voids between superclusters, with highly extended gas disks (out to about 250 kpc) providing most of the Ly-alpha 'forest' absorption systems. The main postulate is a small central peak value N(max) of the mass surface density for the protodisks of these galaxies, which delays not only the recombination of hydrogen but also the phase transition from warm to cold neutral hydrogen. On this model, star formation starts only when the cold phase is reached, but then results in a violent starburst. If conditions are favorable, this burst results in a mild galactic wind (or a galactic fountain) which removes much of the inner gas disk, but leaves most of the outer disk intact; the ratio of the number of 'damped wing' to the number of forest lines is predicted to be much smaller at low redshifts than for z above 2.

  7. The luminous and dark matter content of disk galaxies

    NASA Astrophysics Data System (ADS)

    Zavala, J.; Avila-Reese, V.; Hernández-Toledo, H.; Firmani, C.

    2003-12-01

    We have compiled a sample of disk galaxies with available photometry in the B and K bands, velocity line-widths and HI integral fluxes. Several parameters that trace the luminous, baryonic and dark matter contents were inferred. We investigated how these parameters vary with different galaxy properties, and compared the results with predictions of galaxy evolutionary models in the context of the Λ Cold Dark Matter (ΛCDM) cosmogony. The ratio of disk-to-total maximum circular velocity, (Vd,m/Vt,m), depends mainly on the central disk surface density Σd,0 (or surface brightness, SB), increasing roughly as Σd,00.15. While a fraction of high SB galaxies have a (Vd,m/Vt,m) ratio corresponding to the maximum disk solution, the low SB are completely dark matter dominated. The trend is similar for the models, although they have slightly smaller (Vd,m/Vt,m) ratios than observations, in particular at the highest SBs and when small baryon fractions are used. The scatter in the (Vd,m/Vt,m)- Σd,0 plot is large. An analysis of residuals shows that (Vd,m/Vt,m) tends to decrease as the galaxy is redder, more luminous (massive), and of earlier type. The models allow us to explain the physics of these results, which imply a connexion between halo structure and luminous properties. The dynamical-to-baryon mass and dynamical mass-to-light (B and K) ratios at a given radius were also estimated. All these ratios, for observations and models, decrease with Σd,0; (or SB) and do not correlate significantly with the galaxy scale, contrary to what has been reported in previous works, based on the analysis of rotation curve shapes. We discuss this difference and state the importance of solving the controversy of whether the dark and luminous contents in disk galaxies depend on SB or luminosity. The broad agreement between the models and observations presented here regarding the trends of the dynamical-to-baryon matter and mass-to-light ratios with several galaxy properties favors the

  8. Understanding the Structure and Evolution of Nearby Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Zheng, Zheng

    2014-01-01

    In order to understand the structure and evolution of disk galaxies, we studied the stellar and gaseous components as well as the star formation rate in nearby disk galaxies. We used PS1 medium deep survey images to derive five-band (grizy) surface brightness profiles down to 30 ABmag/arcsec^2 for about 700 galaxies. From these stellar mass and mass-to-light ratio radial profiles are derived. The stellar mass radial profiles tend to bend-up at large radii, this often traces an extended old stellar population. The mass-to-light ratio profiles tend to rise outside the r25 radii. We also find a larger fraction of up-bending surface brightness profiles than Polen & Trujillo (2006). This may be because their sample is biased towards low surface brightness galaxies. We used HIPASS data as well as VLA HI 21cm data to study the gas component and dynamics of disk galaxies. We used the GALEX UV images to study the star formation of a HI-selected star-forming sample of about 400 galaxies, compiling a database of FUV and NUV radial profiles and related parameters. We used this to study the star forming efficiency (SFE, star formation rate per unit area divided by gas surface mass density) of the sample galaxies. We found that the UV based SFE has a tighter relationship with HI mass than an H_alpha based SFE as typically used in previous studies and the UV SFE is flat across wide range of stellar mass. We constructed a simple model to predict the distribution of interstellar medium and star formation rate in an equilibrium disk with constant two-fluid Toomre Q. This model can reproduces the SFE relations we derived.

  9. HI Disks In Nearby Galaxies From The HALOGAS Survey

    NASA Astrophysics Data System (ADS)

    Jozsa, Gyula I. G.

    2016-09-01

    The HALOGAS (Hydrogen Accretion in LOcal GAlaxieS) survey with the Westerbork Synthesis Radio Telescope is the most sensitive systematic survey of the diffuse neutral hydrogen component in nearby spiral galaxies so far. The 5-sigma column density sensitivity reached for the sample of 22 galaxies is 10^19 atoms cm^-2 over the typical line width of the neutral gas in our target galaxies. The 3D observations are sensitive enough to perform detailed kinematical and dynamical analyses of the extended (vertical) disk structure of our targets. Additionally, we are able to provide a census of the complete cold neutral cloud population above the mass detection limit for individual objects of 10^5 solar masses on average. Our results are relevant in the context of theories describing star formation feedback on the gaseous interface of the galaxy disks with their surroundings, as well as gas accretion from the intergalactic medium. Most notably, we find that the presence of anomalous, slowly rotating extraplanar gas is related to the star formation surface density. I will present the consequences of our observations for the current accretion in local galaxies, and discuss the implied constraints on the accretion process more generally.

  10. A scaling law of radial gas distribution in disk galaxies

    NASA Technical Reports Server (NTRS)

    Wang, Zhong

    1990-01-01

    Based on the idea that local conditions within a galactic disk largely determine the region's evolution time scale, researchers built a theoretical model to take into account molecular cloud and star formations in the disk evolution process. Despite some variations that may be caused by spiral arms and central bulge masses, they found that many late-type galaxies show consistency with the model in their radial atomic and molecular gas profiles. In particular, researchers propose that a scaling law be used to generalize the gas distribution characteristics. This scaling law may be useful in helping to understand the observed gas contents in many galaxies. Their model assumes an exponential mass distribution with disk radius. Most of the mass are in atomic gas state at the beginning of the evolution. Molecular clouds form through a modified Schmidt Law which takes into account gravitational instabilities in a possible three-phase structure of diffuse interstellar medium (McKee and Ostriker, 1977; Balbus and Cowie, 1985); whereas star formation proceeds presumably unaffected by the environmental conditions outside of molecular clouds (Young, 1987). In such a model both atomic and molecular gas profiles in a typical galactic disk (as a result of the evolution) can be fitted simultaneously by adjusting the efficiency constants. Galaxies of different sizes and masses, on the other hand, can be compared with the model by simply scaling their characteristic length scales and shifting their radial ranges to match the assumed disk total mass profile sigma tot(r).

  11. The catalog of edge-on disk galaxies from SDSS. I. The catalog and the structural parameters of stellar disks

    SciTech Connect

    Bizyaev, D. V.; Kautsch, S. J.; Mosenkov, A. V.; Reshetnikov, V. P.; Sotnikova, N. Ya.; Yablokova, N. V.; Hillyer, R. W.

    2014-05-20

    We present a catalog of true edge-on disk galaxies automatically selected from the Seventh Data Release of the Sloan Digital Sky Survey (SDSS). A visual inspection of the g, r, and i images of about 15,000 galaxies allowed us to split the initial sample of edge-on galaxy candidates into 4768 (31.8% of the initial sample) genuine edge-on galaxies, 8350 (55.7%) non-edge-on galaxies, and 1865 (12.5%) edge-on galaxies not suitable for simple automatic analysis because these objects either show signs of interaction and warps, or nearby bright stars project on it. We added more candidate galaxies from RFGC, EFIGI, RC3, and Galaxy Zoo catalogs found in the SDSS footprints. Our final sample consists of 5747 genuine edge-on galaxies. We estimate the structural parameters of the stellar disks (the stellar disk thickness, radial scale length, and central surface brightness) in the galaxies by analyzing photometric profiles in each of the g, r, and i images. We also perform simplified three-dimensional modeling of the light distribution in the stellar disks of edge-on galaxies from our sample. Our large sample is intended to be used for studying scaling relations in the stellar disks and bulges and for estimating parameters of the thick disks in different types of galaxies via the image stacking. In this paper, we present the sample selection procedure and general description of the sample.

  12. Star formation and accretion in the circumnuclear disks of active galaxies

    NASA Astrophysics Data System (ADS)

    Wutschik, Stephanie; Schleicher, Dominik R. G.; Palmer, Thomas S.

    2013-12-01

    Aims: We explore the evolution of supermassive black holes (SMBH) centered in a circumnuclear disk (CND) as a function of the mass supply from the host galaxy and considering different star formation laws, which may give rise to a self-regulation via the injection of supernova-driven turbulence. Methods: A system of equations describing star formation, black hole accretion and angular momentum transport in the disk was solved self-consistently for an axisymmetric disk in which the gravitational potential includes contributions from the black hole, the disk and the hosting galaxy. Our model extends the framework provided by Kawakatu & Wada (2008, ApJ, 681, 73), by separately considering the inner and outer part of the disk, and by introducing a potentially non-linear dependence of the star formation rate on the gas surface density and the turbulent velocity. The star formation recipes are calibrated using observational data for NGC 1097, while the accretion model is based on turbulent viscosity as a source of angular momentum transport in a thin viscous accretion disk. Results: We find that current data provide no strong constraint on the star formation recipe, and can in particular not distinguish between models entirely regulated by the surface density, and models including a dependence on the turbulent velocity. The evolution of the black hole mass, on the other hand, strongly depends on the applied star formation law, as well as the mass supply from the host galaxy. We suggest to explore the star formation process in local AGN with high-resolution ALMA observations to break the degeneracy between different star formation models.

  13. Disk mass densities in edge-on spiral galaxies

    NASA Technical Reports Server (NTRS)

    Rupen, Michael P.

    1990-01-01

    Very Large Array (VLA) observations of the neutral hydrogen (HI) gas in two nearby edge-on spirals (NGC 4565 and NGC 891) successfully resolve the thickness of the gas layers in both disks over a wide range in radii. The combination of B, C, and D array data produces a 4 arcsec (approx. 200 pc) beam and 21 km s(exp -1) velocity resolution, combined with sensitivity to structures as large as 18 arcmin (approx. 54 kpc). These observations directly constrain the mid-plane disk mass densities, under the assumption of an equilibrium between the thermal pressure of the gas and the gravitational attraction of the disk. The results of a preliminary analysis are given regarding the z-velocity dispersion of the gas, the mass-to-light ratio of the disk in NGC 4565, and the roles of atomic and molecular gases. The data also allow a detailed study of the HI in these galaxies; in general their brightness temperature distributions seem similar to that in the Milky Way. Both galaxies show asymmetric HI extensions beyond the optical disk. In NGC 4565 the extension is a surprisingly abrupt warp, which may bend back to parallel the galactic plane; the velocity structure implies the warp is continuous around the disk.

  14. Dynamical Evolution of Galaxy Disks in CDM models

    NASA Astrophysics Data System (ADS)

    Font, A.; Navarro, J.; Quinn, T.; Stadel, J.

    2002-12-01

    A long lasting problem in our understanding of the evolution of disk galaxies is the question of how stellar disks respond to encounters with the numerous dark matter sub-halos predicted by the Cold Dark Matter cosmology. We address this issue through a set of high resolution numerical simulations that include a realistic distribution of satellites (with masses and orbital parameters as predicted by CDM models), orbiting around a typical stellar disk, like the Milky Way's. This is the first numerical study to account for the interactions of multiple satellites with a disk within the full cosmological context. The primary conclusion of our study is that the disk is able to survive in this violent environment for several Gyrs, thus weakening the argument calling for a revision of the CDM paradigm. The only visible adjustments made by the disk to the incoming satellites are through the (angular momentum conserving) tilting, and through changes in the kinematical properties of the stars: minor vertical disk heating, flaring and warping. Changes in the disk structure are driven mainly by a few massive satellites rather than by the cumulative effect of many minor mergers.

  15. Dynamical experiments on models of colliding disk galaxies

    NASA Technical Reports Server (NTRS)

    Gerber, Richard A.; Balsara, Dinshaw S.; Lamb, Susan A.

    1990-01-01

    Collisions between galaxies can induce large morphological changes in the participants and, in the case of colliding disk galaxies, bridges and tails are often formed. Observations of such systems indicate a wide variation in color (see Larson and Tinsley, 1978) and that some of the particpants are experiencing enhanced rates of star formation, especially in their central regions (Bushouse 1986, 1987; Kennicutt et al., 1987, Bushouse, Lamb, and Werner, 1988). Here the authors describe progress made in understanding some of the dynamics of interacting galaxies using N-body stellar dynamical computer experiments, with the goal of extending these models to include a hydrodynamical treatment of the gas so that a better understanding of globally enhanced star formation will eventually be forthcoming. It was concluded that close interactions between galaxies can produce large perturbations in both density and velocity fields. The authors measured, via computational experiments that represent a galaxy's stars, average radial velocity flows as large as 100 km/sec and 400 percent density increases. These can occur in rings that move outwards through the disk of a galaxy, in roughly homologous inflows toward the nucleus, and in off center, non-axisymmetric regions. Here the authors illustrate where the gas is likely to flow during the early stages of interaction and in future work they plan to investigate the fate of the gas more realistically by using an N-body/Smoothed Particle Hydrodynamics code to model both the stellar and gaseous components of a disk galaxy during a collision. Specifically, they will determine the locations of enhanced gas density and the strength and location of shock fronts that form during the interaction.

  16. Simple Models for Turbulent Self-Regulation in Galaxy Disks

    NASA Astrophysics Data System (ADS)

    Struck, Curtis; Smith, Daniel C.

    1999-12-01

    Supernova explosions and winds and energetic photon fluxes from young star clusters drive outflows and supersonic turbulence in the interstellar medium in galaxy disks and provide broad-spectrum heating, which generates a wide range of thermal phases in the gas. Star formation, the source of the energy inputs, is itself regulated by heating and phase exchanges in the gas. However, thermohydrodynamic self-regulation cannot be a strictly local process in the interstellar gas since galaxy disks also have a nearly universal structure on large scales. We propose that turbulent heating, wave pressure, and gas exchanges between different regions of disks play a dominant role in determining the preferred, quasi-equilibrium, self-similar states of gas disks on large scales. This paper presents simple families of analytic, thermohydrodynamic models for these global states, which include terms for turbulent pressure and Reynolds stresses. In these model disks, star formation rates, phase balances, and hydrodynamic forces are all tightly coupled and balanced. The models have stratified radial flows, with the cold gas slowly flowing inward in the midplane of the disk and with the warm/hot phases that surround the midplane flowing outward. The models suggest a number of results that are in accord with observations, as well as some novel predictions, including the following. (1) The large-scale gas-density and thermal-phase distributions in galaxy disks can be explained as the result of turbulent heating and spatial couplings. (2) The turbulent pressures and stresses that drive radial outflows in the warm gas above and below the disk midplane also allow a reduced circular velocity there. This effect was observed by Swaters, Sancisi, & van der Hulst in NGC 891, a particularly turbulent edge-on disk. The models predict that the effect should be universal in such disks. (3) Since dissipative processes generally depend on the square of the gas density, the heating and cooling balance

  17. UV-IR color profiles of the outer regions of 2K nearby S4G galaxies

    NASA Astrophysics Data System (ADS)

    Bouquin, Alexandre Y. K.; Gil de Paz, Armando

    2017-03-01

    We present our new, spatially-resolved, photometry in FUV and NUV from images obtained by GALEX, and IRAC1 (3.6 μm) photometry obtained by the Spitzer Space Telescope. We analyzed the surface brightness profiles μFUV, μNUV, μ[3.6], as well as the radial evolution of the (FUV-NUV), (FUV - [3.6]), and (NUV - [3.6]) colors in the Spitzer Survey of Stellar Structures in Galaxies (S4G) galaxies (d < 40 Mpc) sample. We defined the GALEX Blue Sequence (GBS) and GALEX Red Sequence (GBR) from the (FUV - NUV) versus (NUV - [3.6]) color-color diagram, populated by late-type star forming galaxies and quiescent early-type galaxies respectively. While most disk becomes radially bluer for GBS galaxies, and stay constant for GRS galaxies, a large fraction ( > 50%) of intermediary GALEX Green Valley (GGV) galaxies' outer disks are becoming redder. An outside-in quenching mechanism such as environmentally-related mechanisms such as starvation or ram-pressure-stripping could explain our results.

  18. The Upside Down Construction of a Simulated Disk Galaxy

    NASA Astrophysics Data System (ADS)

    Bird, J. C.; Kazantzidis, S.; Weinberg, D. H.; Guedes, J.; Callegari, S.; Mayer, L.; Madau, P.

    2014-03-01

    We analyze the dynamical evolution of stellar age cohorts, groups of stars with similar formation times, to determine the detailed structure formation history of the cosmological simulation of the formation of a disk galaxy similar to the Milky Way (the “Eris” simulation). There is a remarkably smooth correlation between structure and stellar age at z = 0, going from spheroidal distributions for the oldest stars to long, thin disks for the youngest populations. We find the velocity dispersion of a cohort increases monotonically with age. The smooth relationships between stellar age, structure, and dynamics seen at z = 0, which agree nicely with the observed properties of mono-abundance populations in the Milky Way, are largely established by the disk formation process. Stars continuously form as the initially spheroidal gas reservoir cools and contracts, increasing its rotational support and becomingly progressively longer and vertically thinner. Thus, the stellar disk forms “inside-out” radially and “upside-down” vertically.

  19. The Upside Down Assembly of Simulated Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Bird, Jonathan C.; Kazantzidis, S.; Weinberg, D. H.; Guedes, J.; Callegari, S.; Mayer, L.; Madau, P.

    2014-01-01

    The puzzle of disk galaxy formation, and the formation of the Milky Way itself, remains unsolved. We analyze the present-day structure and assembly history of a high resolution hydrodynamic simulation of the formation of a Milky Way-like disk galaxy, from the ``Eris'' simulation suite, dissecting it into cohorts of stars formed at different epochs of cosmic history. The oldest disk cohorts form in structures that are radially compact and relatively thick, while subsequent cohorts form in progressively larger, thinner, colder configurations from gas with increasing levels of rotational support. The disk thus forms ``inside-out'' in a radial sense and ``upside-down'' in a vertical sense. While secular heating and radial migration may influence the final state of each age cohort, the dynamics of each co-eval population generically exhibit only minor evolution since formation. This assembly history is largely responsible for the galaxy's present-day correlations of stellar age with spatial and kinematic structure, which themselves are a good qualitative match to the observed correlations for mono-abundance stellar populations in the Milky Way.

  20. Low Angular Momentum in Clumpy, Turbulent Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Obreschkow, Danail; Glazebrook, Karl; Bassett, Robert; Fisher, David B.; Abraham, Roberto G.; Wisnioski, Emily; Green, Andrew W.; McGregor, Peter J.; Damjanov, Ivana; Popping, Attila; Jørgensen, Inger

    2015-12-01

    We measure the stellar specific angular momentum {j}s={J}s/{M}s in four nearby (z ≈ 0.1) disk galaxies that have stellar masses {M}s near the break {M}s* of the galaxy mass function but look like typical star-forming disks at z ≈ 2 in terms of their low stability (Q ≈ 1), clumpiness, high ionized gas dispersion (40-50 {km} {{{s}}}-1), high molecular gas fraction (20%-30%), and rapid star formation (˜ 20{M}⊙ {{yr}}-1). Combining high-resolution (Keck-OSIRIS) and large-radius (Gemini-GMOS) spectroscopic maps, only available at low z, we discover that these targets have ˜ 3 times less stellar angular momentum than typical local spiral galaxies of equal stellar mass and bulge fraction. Theoretical considerations show that this deficiency in angular momentum is the main cause of their low stability, while the high gas fraction plays a complementary role. Interestingly, the low {j}s values of our targets are similar to those expected in the {M}s* population at higher z from the approximate theoretical scaling {j}s\\propto {(1+z)}-1/2 at fixed {M}s. This suggests that a change in angular momentum, driven by cosmic expansion, is the main cause for the remarkable difference between clumpy {M}s* disks at high z (which likely evolve into early-type galaxies) and mass-matched local spirals.

  1. Stellar Nuclei and Inner Polar Disks in Lenticular Galaxies

    NASA Astrophysics Data System (ADS)

    Sil'chenko, Olga K.

    2016-09-01

    I analyze statistics of the stellar population properties for stellar nuclei and bulges of nearby lenticular galaxies in different environments by using panoramic spectral data of the integral-field spectrograph SAURON retrieved from the open archive of the Isaac Newton Group. I also estimate the fraction of nearby lenticular galaxies having inner polar gaseous disks by exploring the volume-limited sample of early-type galaxies of the ATLAS-3D survey. By inspecting the two-dimensional velocity fields of the stellar and gaseous components with the running tilted-ring technique, I have found seven new cases of inner polar disks. Together with those, the frequency of inner polar disks in nearby S0 galaxies reaches 10%, which is much higher than the frequency of large-scale polar rings. Interestingly, the properties of the nuclear stellar populations in the inner polar ring hosts are statistically the same as those in the whole S0 sample, implying similar histories of multiple gas-accretion events from various directions.

  2. OUR MILKY WAY AS A PURE-DISK GALAXY-A CHALLENGE FOR GALAXY FORMATION

    SciTech Connect

    Shen Juntai; Rich, R. Michael; Howard, Christian D.; Kormendy, John; De Propris, Roberto; Kunder, Andrea

    2010-09-01

    Bulges are commonly believed to form in the dynamical violence of galaxy collisions and mergers. Here, we model the stellar kinematics of the Bulge Radial Velocity Assay (BRAVA) and find no sign that the Milky Way contains a classical bulge formed by scrambling pre-existing disks of stars in major mergers. Rather, the bulge appears to be a bar seen somewhat end-on, as hinted from its asymmetric boxy shape. We construct a simple but realistic N-body model of the Galaxy that self-consistently develops a bar. The bar immediately buckles and thickens in the vertical direction. As seen from the Sun, the result resembles the boxy bulge of our Galaxy. The model fits the BRAVA stellar kinematic data covering the whole bulge strikingly well with no need for a merger-made classical bulge. The bar in our best-fit model has a half-length of {approx}4 kpc and extends 20{sup 0} from the Sun-Galactic center line. We use the new kinematic constraints to show that any classical bulge contribution cannot be larger than {approx}8% of the disk mass. Thus, the Galactic bulge is a part of the disk and not a separate component made in a prior merger. Giant, pure-disk galaxies like our own present a major challenge to the standard picture in which galaxy formation is dominated by hierarchical clustering and galaxy mergers.

  3. Shocked Outflows and Gas Disks in Local Merging Galaxies

    NASA Astrophysics Data System (ADS)

    Soto, Kurt; Martin, C. L.; Prescott, M. K. M.; Armus, L.

    2012-01-01

    We have mapped the kinematic and physical properties of gas emitting optical emission lines across 39 gas-rich mergers, which were previously shown to host tidally-induced gas inflows, with deep ESI spectroscopy. In our unique analysis of these longslit spectra, we fitted multiple kinematic components to forbidden lines and recombination lines simultaneously, enabling an examination of the excitation mechanism in different kinematic components. We identify many rotating gas disks in systems whose stellar component is no longer a disk due to the merger. Many of these disks present gas excited by hot stars, but some of the disks present shock-like ratios of diagnostic emission lines, an observation we attribute to the collision of the two galaxies. In another subset of galaxies, we find very broad (sigma > 150 km/s) emission components that also present shock-like emission-line ratios. The large spatial extent of this emission favors shocks over the narrow-line region of a hidden AGN as the excitation mechanism. The high star formation rate, high dust content, and blueshift of the broad emission further suggest an origin in a galactic outflow. If this interpretation is correct, then our study of these nearby galaxies provides important insight for interpreting the broad emission lines associated with giant star-forming clumps in z 2 galaxies. It also shows that galactic outflows can be recognized via resolved emission lines, in addition to absorption lines, even in integrated spectra; and this technique could prove very powerful for studying galactic outflows in infrared spectra of high-redshift galaxies in the future. This work was supported by the National Science Foundation under contract 0808161.

  4. Radio continuum of galaxies with H2O megamaser disks: 33 GHz VLA data

    NASA Astrophysics Data System (ADS)

    Kamali, F.; Henkel, C.; Brunthaler, A.; Impellizzeri, C. M. V.; Menten, K. M.; Braatz, J. A.; Greene, J. E.; Reid, M. J.; Condon, J. J.; Lo, K. Y.; Kuo, C. Y.; Litzinger, E.; Kadler, M.

    2017-09-01

    sources. Whenever possible, central positions with accuracies of 20-280 mas are provided. A correlation analysis shows that the 33 GHz luminosity weakly correlates with the infrared luminosity. The 33 GHz luminosity is anticorrelated with the circular velocity of the galaxy. The black hole masses show stronger correlations with H2O maser luminosity than with 1.4 GHz, 33 GHz, or hard X-ray luminosities. Furthermore, the inner radii of the disks show stronger correlations with 1.4 GHz, 33 GHz, and hard X-ray luminosities than their outer radii, suggesting that the outer radii may be affected by disk warping, star formation, or peculiar density distributions.

  5. Semi-analytic models for HI gas in disk and local dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Fu, Jian

    2015-08-01

    We construct the radially-resolved semi-analytic models of galaxy formation based on the L-Galaxies model framework, which include both atomic and molecular gas phase in ISM. The models adopt the ΛCDM cosmology simulation Millennium, Millennium II and Aquarius. Our models can reproduce varies properties of HI gas in nearby galaxies, e.g. the HI mass function, the HI-to-star ratio vs stellar mass and stellar surface density, universal HI radial surface density profile in outer disks etc. We can also give some physical origins of HI size mass relation in many observations.Based on our model results for local dwarf galaxies, we show that the "missing satellite problem" also exists in the HI component, i.e., the models over predict dwarf galaxies with low HI mass. That is a shortcoming of current ΛCDM cosmology framework. Future survey for HI gas in dwarf galaxies (e.g. SKA or FAST) in local group can help to verify the correctness of cold dark matter.

  6. Significant Enhancement of H2 Formation in Disk Galaxies under Strong Ram Pressure

    NASA Astrophysics Data System (ADS)

    Henderson, Benjamin; Bekki, Kenji

    2016-05-01

    We show for the first time that H2 formation on dust grains can be enhanced in disk galaxies under strong ram pressure (RP). We numerically investigate how the time evolution of H i and H2 components in disk galaxies orbiting a group/cluster of galaxies can be influenced by the hydrodynamical interaction between the gaseous components of the galaxies and the hot intracluster medium. We find that compression of H i caused by RP increases H2 formation in disk galaxies before RP rapidly strips H i, cutting off the fuel supply and causing a drop in H2 density. We also find that the level of this H2 formation enhancement in a disk galaxy under RP depends on the mass of its host cluster dark matter halo, the initial positions and velocities of the disk galaxy, and the disk inclination angle with respect to the orbital plane. We demonstrate that dust growth is a key factor in the evolution of the H i and H2 mass in disk galaxies under strong RP. We discuss how the correlation between H2 fractions and surface gas densities of disk galaxies evolves with time in the galaxies under RP. We also discuss whether galaxy-wide star formation rates (SFRs) in cluster disk galaxies can be enhanced by RP if the SFRs depend on H2 densities.

  7. Hall Effect Controlled Gas Dynamics in Protoplanetary Disks. II. Full 3D Simulations toward the Outer Disk

    NASA Astrophysics Data System (ADS)

    Bai, Xue-Ning

    2015-01-01

    We perform three-dimensional stratified shearing-box magnetohydrodynamic (MHD) simulations on the gas dynamics of protoplanetary disks with a net vertical magnetic flux of B z0. All three nonideal MHD effects, Ohmic resistivity, the Hall effect, and ambipolar diffusion, are included in a self-consistent manner based on equilibrium chemistry. We focus on regions toward outer disk radii, from 5 to 60 AU, where Ohmic resistivity tends to become negligible, ambipolar diffusion dominates over an extended region across the disk height, and the Hall effect largely controls the dynamics near the disk midplane. We find that at around R = 5 AU the system launches a laminar or weakly turbulent magnetocentrifugal wind when the net vertical field B z0 is not too weak. Moreover, the wind is able to achieve and maintain a configuration with reflection symmetry at the disk midplane. The case with anti-aligned field polarity ({\\boldsymbol{Ω }}\\cdot {\\boldsymbol{B}}z0<0) is more susceptible to the magnetorotational instability (MRI) when B z0 decreases, leading to an outflow oscillating in radial directions and very inefficient angular momentum transport. At the outer disk around and beyond R = 30 AU, the system shows vigorous MRI turbulence in the surface layer due to far-UV ionization, which efficiently drives disk accretion. The Hall effect affects the stability of the midplane region to the MRI, leading to strong/weak Maxwell stress for aligned/anti-aligned field polarities. Nevertheless, the midplane region is only very weakly turbulent in both cases. Overall, the basic picture is analogous to the conventional layered accretion scenario applied to the outer disk. In addition, we find that the vertical magnetic flux is strongly concentrated into thin, azimuthally extended shells in most of our simulations beyond 15 AU, leading to enhanced radial density variations know as zonal flows. Theoretical implications and observational consequences are briefly discussed.

  8. Double DCO+ Rings Reveal CO Ice Desorption in the Outer Disk Around IM Lup

    NASA Astrophysics Data System (ADS)

    Öberg, Karin I.; Furuya, Kenji; Loomis, Ryan; Aikawa, Yuri; Andrews, Sean M.; Qi, Chunhua; van Dishoeck, Ewine F.; Wilner, David J.

    2015-09-01

    In a protoplanetary disk, a combination of thermal and non-thermal desorption processes regulate where volatiles are liberated from icy grain mantles into the gas phase. Non-thermal desorption should result in volatile-enriched gas in disk-regions where complete freeze-out is otherwise expected. We present Atacama Large Millimeter/Submillimeter Array observations of the disk around the young star IM Lup in 1.4 mm continuum, C18O 2-1, H13CO+ 3-2 and DCO+ 3-2 emission at ˜0.″5 resolution. The images of these dust and gas tracers are clearly resolved. The DCO+ line exhibits a striking pair of concentric rings of emission that peak at radii of ˜0.″6 and 2″ (˜90 and 300 AU, respectively). Based on disk chemistry model comparison, the inner DCO+ ring is associated with the balance of CO freeze-out and thermal desorption due to a radial decrease in disk temperature. The outer DCO+ ring is explained by non-thermal desorption of CO ice in the low-column-density outer disk, repopulating the disk midplane with cold CO gas. The CO gas then reacts with abundant H2D+ to form the observed DCO+ outer ring. These observations demonstrate that spatially resolved DCO+ emission can be used to trace otherwise hidden cold gas reservoirs in the outmost disk regions, opening a new window onto their chemistry and kinematics.

  9. 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:

  10. The magnetic field in the disk of our Galaxy

    NASA Astrophysics Data System (ADS)

    Han, J. L.; Qiao, G. J.

    1994-08-01

    The magnetic field in the disk of our Galaxy is investigated by using the Rotation Measures (RMs) of pulsars and Extragalactic Radio Sources (ERSes). Through analyses of the RMs of carefully selected pulsar samples, it is found that the Galaxy has a global field of BiSymmetric Spiral (BSS) configuration, rather than a concentric ring or an AxiSymmetric Spiral (ASS) configuration. The Galactic magnetic field of BSS structure is supposed to be of primordial origin. The pitch angle of the BSS structure is -8.2deg+/-0.5deg. The field geometry shows that the field goes along the Carina-Sagittarius arm, which is delineated by Giant Molecular Clouds (GMCs). The amplitude of the BSS field is 1.8+/-0.3μG. The first field strength maximum is at r_0_=11.9+/-0.15 kpc in the direction of l=180deg. The field is strong in the interarm regions and it reverses in the arm regions. In the vicinity of the Sun, it has a strength of ~1.4μG and reverses at 0.2-0.3kpc in the direction of l=0deg. Because of the unknown electron distribution of the Galaxy and other difficulties, it is impossible to derive the galactic field from the RMs of ERSes very quantitatively. Nevertheless, the RMs of ERSes located in the region of the two galactic poles are used to estimate the vertical component of the local galactic field, which is found to have a strength of 0.2-0.3μG and is directed from the south galactic pole to the north galactic pole. The scale height of the magnetic disk of the Galaxy is estimated from the RMs of all-sky distributed ERSes, being about 1.2+/-0.4pc. The regular magnetic field of our Galaxy, which is probably similar to that of M81, extends far from the optical disk.

  11. The Outer Halo -- Halo Origins and Mass of the Galaxy

    NASA Astrophysics Data System (ADS)

    Morrison, Heather; Arabadjis, John; Dohm-Palmer, Robbie; Freeman, Ken; Harding, Paul; Mateo, Mario; Norris, John; Olszewski, Ed; Sneden, Chris

    2000-02-01

    Through our detection of distant halo stars, we are now well placed to map the regions of the Galactic halo where previously only satellite galaxies and a few globular clusters were known. Mapping this region is crucial for answering questions like: How and over what timescales was the Milky Way's stellar halo assembled? What is the total mass and shape of its dark halo? The Sagittarius dwarf has demonstrated that at least some of the stellar halo was accreted. But, HOW MUCH of the halo was accreted? Our previous efforts have proven that the Washington photometric system, in conjuction with spectroscopy, is capable of efficiently and unambiguously identifying halo stars out to 100 kpc or more. We require followup spectroscopy to map velocity substructure, which is more likely visible in the outer halo because of the long dynamical timescales, and to identify the rare objects in the extreme outer halo which will constrain the shape and size of its dark halo. We are applying for 4m/RCSP time at both CTIO and KPNO to observe faint outer-halo giant and BHB candidates.

  12. Star Formation of Merging Disk Galaxies with AGN Feedback Effects

    NASA Astrophysics Data System (ADS)

    Park, Jongwon; Smith, Rory; Yi, Sukyoung K.

    2017-08-01

    Using a numerical hydrodynamics code, we perform various idealized galaxy merger simulations to study the star formation (SF) of two merging disk galaxies. Our simulations include gas accretion onto supermassive black holes and active galactic nucleus (AGN) feedback. By comparing AGN simulations with those without AGNs, we attempt to understand when the AGN feedback effect is significant. Using ∼70 simulations, we investigate SF with the AGN effect in mergers with a variety of mass ratios, inclinations, orbits, galaxy structures, and morphologies. Using these merger simulations with AGN feedback, we measure merger-driven SF using the burst efficiency parameter introduced by Cox et al. We confirm previous studies which demonstrated that, in galaxy mergers, AGN suppresses SF more efficiently than in isolated galaxies. However, we also find that the effect of AGNs on SF is larger in major than in minor mergers. In minor merger simulations with different primary bulge-to-total ratios, the effect of bulge fraction on the merger-driven SF decreases due to AGN feedback. We create models of Sa-, Sb-, and Sc-type galaxies and compare their SF properties while undergoing mergers. With the current AGN prescriptions, the difference in merger-driven SF is not as pronounced as in the recent observational study of Kaviraj. We discuss the implications of this discrepancy.

  13. Environment Dependence of Disk Morphology of Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Ann, Hong Bae

    2014-02-01

    We analyze the dependence of disk morphology (arm class, Hubble type, bar type) of nearby spiral galaxies on the galaxy environment by using local background density (Σ_{n}), project distance (r_{p}), and tidal index (TI) as measures of the environment. There is a strong dependence of arm class and Hubble type on the galaxy environment, while the bar type exhibits a weak dependence with a high frequency of SB galaxies in high density regions. Grand design fractions and early-type fractions increase with increasing Σ_{n}, 1/r_{p}, and TI, while fractions of flocculent spirals and late-type spirals decrease. Multiple-arm and intermediate-type spirals exhibit nearly constant fractions with weak trends similar to grand design and early-type spirals. While bar types show only a marginal dependence on Σ_{n}, they show a fairly clear dependence on r_{p} with a high frequency of SB galaxies at small r_{p}. The arm class also exhibits a stronger correlation with r_{p} than Σ_{n} and TI, whereas the Hubble type exhibits similar correlations with Σ_{n} and r_{p}. This suggests that the arm class is mostly affected by the nearest neighbor while the Hubble type is affected by the local densities contributed by neighboring galaxies as well as the nearest neighbor.

  14. Radial Velocities, Metallicities, and Improved Fundamental Parameters of Outer Disk Open Clusters

    NASA Astrophysics Data System (ADS)

    Zasowski, Gail; Hamm, K.; Beaton, R.; Damke, G.; Carlberg, J. K.; Majewski, S. R.; Frinchaboy, P. M.

    2014-01-01

    Open stellar clusters have proven to be powerful tools for understanding the structure and stellar evolution of our Galaxy. Using photometry from 2MASS and the new Spitzer-IRAC GLIMPSE-360 surveys, Zasowski et al. (2013) identified and characterized more than a dozen new or poorly studied, heavily reddened open clusters in the outer Galactic disk. Here, we present follow-up spectroscopy for 11 of the clusters. Low resolution optical spectra were obtained with the DIS spectrograph on the Apache Point Observatory 3.5-meter telescope (R˜1200) for candidate members of seven clusters (GLM-CYGX 16, GLM-G360 18, GLM-G360 105, SAI 24, Berkeley 14, Berkeley 14a, and Czernik 20), and with the B&C spectrograph on the Las Campanas Observatory duPont telescope (R˜5400) for three clusters (GLM-G360 50, GLM-G360 75, and GLM-G360 79). High resolution (R˜22,500) infrared (H-band) spectra were also obtained for one cluster (GLM-G360 90) as part of an ancillary program for the SDSS-III/APOGEE survey. We use the mean chemical abundances and radial velocities (RVs) to identify likely cluster members and then revisit our previous isochrone fits. With reddening constrained by the Rayleigh-Jeans Color Excess method and mean metallicities by spectroscopy, the cluster distances and ages are estimated from improved isochrone fits to the stellar overdensity, weighted by confirmed RV and/or abundance members.

  15. Ejection of Supernova-Enriched Gas From Dwarf Disk Galaxies

    SciTech Connect

    Fragile, P C; Murray, S D; Lin, D C

    2004-06-15

    We examine the efficiency with which supernova-enriched gas may be ejected from dwarf disk galaxies, using a methodology previously employed to study the self-enrichment efficiency of dwarf spheroidal systems. Unlike previous studies that focused on highly concentrated starbursts, in the current work we consider discrete supernova events spread throughout various fractions of the disk. We model disk systems having gas masses of 10{sup 8} and 10{sup 9} M{sub {circle_dot}} with supernova rates of 30, 300, and 3000 Myr{sup -1}. The supernova events are confined to the midplane of the disk, but distributed over radii of 0, 30, and 80% of the disk radius, consistent with expectations for Type II supernovae. In agreement with earlier studies, we find that the enriched material from supernovae is largely lost when the supernovae are concentrated near the nucleus, as expected for a starburst event. In contrast, we find the loss of enriched material to be much less efficient (as low as 21%) when the supernovae occur over even a relatively small fraction of the disk. The difference is due to the ability of the system to relax following supernova events that occur over more extended regions. Larger physical separations also reduce the likelihood of supernovae going off within low-density ''chimneys'' swept out by previous supernovae. We also find that, for the most distributed systems, significant metal loss is more likely to be accompanied by significant mass loss. A comparison with theoretical predications indicates that, when undergoing self-regulated star formation, galaxies in the mass range considered shall efficiently retain the products of Type II supernovae.

  16. THE THICK DISKS OF SPIRAL GALAXIES AS RELICS FROM GAS-RICH, TURBULENT, CLUMPY DISKS AT HIGH REDSHIFT

    SciTech Connect

    Bournaud, Frederic; Martig, Marie; Elmegreen, Bruce G.

    2009-12-10

    The formation of thick stellar disks in spiral galaxies is studied. Simulations of gas-rich young galaxies show formation of internal clumps by gravitational instabilities, clump coalescence into a bulge, and disk thickening by strong stellar scattering. The bulge and thick disks of modern galaxies may form this way. Simulations of minor mergers make thick disks too, but there is an important difference. Thick disks made by internal processes have a constant scale height with galactocentric radius, but thick disks made by mergers flare. The difference arises because in the first case, perpendicular forcing and disk-gravity resistance are both proportional to the disk column density, so the resulting scale height is independent of this density. In the case of mergers, perpendicular forcing is independent of the column density and the low-density regions get thicker; the resulting flaring is inconsistent with observations. Late-stage gas accretion and thin-disk growth are shown to preserve the constant scale heights of thick disks formed by internal evolution. These results reinforce the idea that disk galaxies accrete most of their mass smoothly and acquire their structure by internal processes, in particular through turbulent and clumpy phases at high redshift.

  17. 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

  18. Misaligned Disks as Obscurers in Active Galaxies

    SciTech Connect

    Lawrence, A.; Elvis, M.; /Edinburgh U., Inst. Astron. /Harvard-Smithsonian Ctr. Astrophys.

    2010-06-02

    We review critically the evidence concerning the fraction of Active Galactic Nuclei (AGN) which appear as Type 2 AGN, carefully distinguishing strict Type 2 AGN from both more lightly reddened Type 1 AGN, and from low excitation narrow line AGN, which may represent a different mode of activity. Low excitation AGN occur predominantly at low luminosities; after removing these, true Type 2 AGN represent 58{-+}5% of all AGN, and lightly reddened Type 1 AGN a further {approx}15%. Radio, IR, and volume-limited samples all agree in showing no change of Type 2 fraction with luminosity. X-ray samples do show a change with luminosity; we discuss possible reasons for this discrepancy. We test a very simple picture which produces this Type 2 fraction with minimal assumptions. In this picture, infall from large scales occurs in random directions, but must eventually align with the inner accretion flow, producing a severely warped disk on parsec scales. If the re-alignment is dominated by tilt, with minimal twist, a wide range of covering factors is predicted in individual objects, but with an expected mean fraction of Type 2 AGN of exactly 50%. This 'tilted disc' picture predicts reasonable alignment of observed nuclear structures on average, but with distinct misalignments in individual cases. Initial case studies of the few well resolved objects show that such misalignments are indeed present.

  19. Tomographic Sounding of Protoplanetary and Transitional Disks: Using Inner Disk Variability at Near to Mid-IR Wavelengths to Probe Conditions in the Outer Disk

    NASA Technical Reports Server (NTRS)

    Grady, C. A.; Sitko, M.L.

    2013-01-01

    Spitzer synoptic monitoring of young stellar associations has demonstrated that variability among young stars and their disks is ubiquitous. The Spitzer studies have been limited by target visibility windows and cover only a short temporal baseline in years. A complementary approach is to focus on stars chosen for high-value observations (e.g. high-contrast imaging, interferometry, or access to wavelengths which are difficult to achieve from the ground) where the synoptic data can augment the imagery or interferometry as well as probing disk structure. In this talk, we discuss how synoptic data for two protoplanetary disks, MWC 480 and HD 163296, constrain the dust disk scale height, account for variable disk illumination, and can be used to locate emission features, such as the IR bands commonly associated with PAHs in the disk, as part of our SOFIA cycle 1 study. Similar variability is now known for several pre-transitional disks, where synoptic data can be used to identify inner disks which are not coplanar with the outer disk, and which may be relicts of giant planet-giant planet scattering events. Despite the logistical difficulties in arranging supporting, coordinated observations in tandem with high-value observations, such data have allowed us to place imagery in context, constrained structures in inner disks not accessible to direct imagery, and may be a tool for identifying systems where planet scattering events have occurred.

  20. Galactic evolution. II - Disk galaxies with massive halos

    NASA Technical Reports Server (NTRS)

    Ostriker, J. P.; Thuan, T. X.

    1975-01-01

    Models of galactic evolution are computed in which matter shed by dying halo stars accumulates in a smaller, more rapidly rotating disk. The models are simpler and more successful than one-zone (pure disk) models in that (1) the observed absence of low-metal-abundance low-mass dwarfs is expected, not anomalous and (2) the relative birthrate function (or IMF) need not be a strongly variable function of time in agreement with recent interpretations of observed stellar populations and neutral hydrogen in our own and other galaxies. Even a simple 'Salpeter' IMF for both disk and halo will produce an acceptable model. The model with a halo 'Salpeter' IMF, roughly one-quarter of the mass in the secondary disk, and approximately half the metals produced in the halo seems most compatible with observations of the metal abundance in low-mass stars, the deuterium abundance, halo planetary nebulae, and light from Population II stars, as well as with arguments on the stability of the disk.

  1. Caustic waves in galaxy disks produced in collisions with low mass companions

    NASA Technical Reports Server (NTRS)

    Struck-Marcell, Curtis

    1990-01-01

    The author lists a few reasons for studying collisions with relatively low mass companions, specifically those that are less than about one third of the mass of the target galaxy. The primary effect of such collisions on a target galaxy with a 'cold' disk component is the generation of waves in the disk. The focus here is on the purely stellar waves in such disks. The example of a ring galaxy case is examined.

  2. The Evolution of Luminous Compact Blue Galaxies: Disks or Spheroids?

    NASA Astrophysics Data System (ADS)

    Pisano, D. J.; Rabidoux, K.; Garland, C. A.; Guzmán, R.; Castander, F. J.; Pérez-Gallego, J.

    2011-12-01

    Luminous compact blue galaxies (LCBGs) are a diverse class of galaxies characterized by high luminosity, blue color, and high surface brightness that sit at the critical juncture of galaxies evolving from the blue to the red sequence. As part of our multi-wavelength survey of local LCBGs, we have been studying the HI content of these galaxies using both single-dish telescopes and interferometers. Our goals are to determine if single-dish HI observations represent a true measure of the dynamical mass of LCBGs and to look for signatures of recent interactions that may be triggering star formation in LCBGs. Our data show that while some LCBGs are undergoing interactions, many appear isolated. While all LCBGs contain HI and show signatures of rotation, the population does not lie on the Tully-Fisher relation nor can it evolve onto it. Furthermore, the HI maps of many LCBGs show signatures of dynamically hot components, suggesting that we are seeing the formation of a thick disk or spheroid in at least some LCBGs. There is good agreement between the HI and Hα kinematics for LCBGs, and both are similar in appearance to the Hα kinematics of high redshift star-forming galaxies. Our combined data suggest that star formation in LCBGs is primarily quenched by virial heating, consistent with model predictions.

  3. Simulations of Disk Galaxies with Cosmic Ray Driven Galactic Winds

    NASA Astrophysics Data System (ADS)

    Booth, C. M.; Agertz, Oscar; Kravtsov, Andrey V.; Gnedin, Nickolay Y.

    2013-11-01

    We present results from high-resolution hydrodynamic simulations of isolated Small Magellanic Cloud (SMC)- and Milky-Way-sized galaxies that include a model for feedback from galactic cosmic rays (CRs). We find that CRs are naturally able to drive winds with mass loading factors of up to ~10 in dwarf systems. The scaling of the mass loading factor with circular velocity between the two simulated systems is consistent with \\eta \\propto v_circ^{1-2} required to reproduce the faint end of the galaxy luminosity function. In addition, simulations with CR feedback reproduce both the normalization and the slope of the observed trend of wind velocity with galaxy circular velocity. We find that winds in simulations with CR feedback exhibit qualitatively different properties compared to supernova-driven winds, where most of acceleration happens violently in situ near star forming sites. The CR-driven winds are accelerated gently by the large-scale pressure gradient established by CRs diffusing from the star-forming galaxy disk out into the halo. The CR-driven winds also exhibit much cooler temperatures and, in the SMC-sized system, warm (T ~ 104 K) gas dominates the outflow. The prevalence of warm gas in such outflows may provide a clue as to the origin of ubiquitous warm gas in the gaseous halos of galaxies detected via absorption lines in quasar spectra.

  4. SIMULATIONS OF DISK GALAXIES WITH COSMIC RAY DRIVEN GALACTIC WINDS

    SciTech Connect

    Booth, C. M.; Agertz, Oscar; Kravtsov, Andrey V.; Gnedin, Nickolay Y.

    2013-11-01

    We present results from high-resolution hydrodynamic simulations of isolated Small Magellanic Cloud (SMC)- and Milky-Way-sized galaxies that include a model for feedback from galactic cosmic rays (CRs). We find that CRs are naturally able to drive winds with mass loading factors of up to ∼10 in dwarf systems. The scaling of the mass loading factor with circular velocity between the two simulated systems is consistent with η∝v{sub circ}{sup 1-2} required to reproduce the faint end of the galaxy luminosity function. In addition, simulations with CR feedback reproduce both the normalization and the slope of the observed trend of wind velocity with galaxy circular velocity. We find that winds in simulations with CR feedback exhibit qualitatively different properties compared to supernova-driven winds, where most of acceleration happens violently in situ near star forming sites. The CR-driven winds are accelerated gently by the large-scale pressure gradient established by CRs diffusing from the star-forming galaxy disk out into the halo. The CR-driven winds also exhibit much cooler temperatures and, in the SMC-sized system, warm (T ∼ 10{sup 4} K) gas dominates the outflow. The prevalence of warm gas in such outflows may provide a clue as to the origin of ubiquitous warm gas in the gaseous halos of galaxies detected via absorption lines in quasar spectra.

  5. Merger Histories of Galaxy Halos and Implications for Disk Survival

    SciTech Connect

    Stewart, Kyle R.; Bullock, James S.; Wechsler, Risa H.; Maller, Ariyeh H.; Zentner, Andrew R.

    2008-05-16

    The authors study the merger histories of galaxy dark matter halos using a high resolution {Lambda}CDM N-body simulation. The merger trees follow {approx} 17,000 halos with masses M{sub 0} = (10{sup 11} - 10{sup 13})h{sup -1}M{sub {circle_dot}} at z = 0 and track accretion events involving objects as small as m {approx_equal} 10{sup 10} h{sup -1}M{sub {circle_dot}}. They find that mass assembly is remarkably self-similar in m/M{sub 0}, and dominated by mergers that are {approx}10% of the final halo mass. While very large mergers, m {approx}> 0.4 M{sub 0}, are quite rare, sizeable accretion events, m {approx} 0.1 M{sub 0}, are common. Over the last {approx} 10 Gyr, an overwhelming majority ({approx} 95%) of Milky Way-sized halos with M{sub 0} = 10{sup 12} h{sup -1}M{sub {circle_dot}} have accreted at least one object with greater total mass than the Milky Way disk (m > 5 x 10{sup 10} h{sup -1}M{sub {circle_dot}}), and approximately 70% have accreted an object with more than twice that mass (m > 10{sup 11} h{sup -1}M{sub {circle_dot}}). The results raise serious concerns about the survival of thin-disk dominated galaxies within the current paradigm for galaxy formation in a {Lambda}CDM universe. in order to achieve a {approx} 70% disk-dominated fraction in Milky Way-sized {Lambda}CDM halos, mergers involving m {approx_equal} 2 x 10{sup 11} h{sup -1}M{sub {circle_dot}} objects must not destroy disks. Considering that most thick disks and bulges contain old stellar populations, the situation is even more restrictive: these mergers must not heat disks or drive gas into their centers to create young bulges.

  6. Near-infrared Structure of Fast and Slow-rotating Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Schechtman-Rook, Andrew; Bershady, Matthew A.

    2014-11-01

    We investigate the stellar disk structure of six nearby edge-on spiral galaxies using high-resolution JHK s-band images and three-dimensional radiative transfer models. To explore how mass and environment shape spiral disks, we selected galaxies with rotational velocities between 69 km s-1 disk structure. Of the fast-rotating (V rot > 150 km s-1) galaxies, only NGC 4013 has the super-thin+thin+thick nested disk structure seen in NGC 891 and the Milky Way, albeit with decreased oblateness, while NGC 1055, a disturbed massive spiral galaxy, contains disks with hz <~ 200 pc. NGC 4565, another fast-rotator, contains a prominent ring at a radius ~5 kpc but no super-thin disk. Despite these differences, all fast-rotating galaxies in our sample have inner truncations in at least one of their disks. These truncations lead to Freeman Type II profiles when projected face-on. Slow-rotating galaxies are less complex, lacking inner disk truncations and requiring fewer disk components to reproduce their light distributions. Super-thin disk components in undisturbed disks contribute ~25% of the total K s-band light, up to that of the thin-disk contribution. The presence of super-thin disks correlates with infrared flux ratios; galaxies with super-thin disks have f{K_s}/f60 μ m ≤ 0.12 for integrated light, consistent with super-thin disks being regions of ongoing star-formation. Attenuation-corrected vertical color gradients in (J - K s) correlate with the observed disk structure and are consistent with population gradients with young-to-intermediate ages closer to the mid-plane, indicating that disk heating—or cooling—is a ubiquitous phenomenon.

  7. Black Hole Growth in Disk Galaxies Mediated by the Secular Evolution of Short Bars

    NASA Astrophysics Data System (ADS)

    Du, Min; Debattista, Victor P.; Shen, Juntai; Ho, Luis C.; Erwin, Peter

    2017-08-01

    The growth of black holes (BHs) in disk galaxies lacking classical bulges, which implies an absence of significant mergers, appears to be driven by secular processes. Short bars of sub-kiloparsec radius have been hypothesized to be an important mechanism for driving gas inflows to small scale, feeding central BHs. In order to quantify the maximum BH mass allowed by this mechanism, we examine the robustness of short bars to the dynamical influence of BHs. Large-scale bars are expected to be robust, long-lived structures; extremely massive BHs, which are rare, are needed to completely destroy such bars. However, we find that short bars, which are generally embedded in large-scale outer bars, can be destroyed quickly when BHs of mass {M}{bh}∼ 0.05 % {--}0.2 % of the total stellar mass ({M}\\star ) are present. In agreement with this prediction, all galaxies observed to host short bars have BHs with a mass fraction less than 0.2 % {M}\\star . Thus, the dissolution of short inner bars is possible, perhaps even frequent, in the universe. An important implication of this result is that inner-bar-driven gas inflows may be terminated when BHs grow to ∼ 0.1 % {M}\\star . We predict that 0.2 % {M}\\star is the maximum mass of BHs allowed if they are fed predominately via inner bars. This value matches well the maximum ratio of BH-to-host-galaxy stellar mass observed in galaxies with pseudo-bulges and most nearby active galactic nucleus host galaxies. This hypothesis provides a novel explanation for the lower {M}{bh}/{M}\\star in galaxies that have avoided significant mergers compared with galaxies with classical bulges.

  8. 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

  9. Observational and Numerical Diagnostics of Galaxy Cluster Outer Regions

    NASA Technical Reports Server (NTRS)

    Eckert, D.; Vazza, F.; Ettori, S.; Molendi, S.; Nagai, D.; Lau, E.; Roncarelli, M.; Rossetti, M.; Snowden, S. L.; Gastaldello, F.

    2011-01-01

    Aims. We present the analysis of a local (z = 0.04 - 0.2) sample of 31 galaxy clusters with the aim of measuring the density of the X-ray emitting gas in cluster outskirts. We compare our results with numerical simulations to set constraints on the azimuthal symmetry and gas clumping in the outer regions of galaxy clusters. Methods. We exploit the large field-of-view and low instrumental background of ROSAT/PSPC to trace the density of the intracluster gas out to the virial radius. We perform a stacking of the density profiles to detect a signal beyond r(sub 200) and measure the typical density and scatter in cluster outskirts. We also compute the azimuthal scatter of the profiles with respect to the mean value to look for deviations from spherical symmetry. Finally, we compare our average density and scatter profiles with the results of numerical simulations. Results. As opposed to several recent results, we observe a steepening of the density profiles beyond approximately 0.3r(sub 500). Comparing our density profiles with simulations, we find that non-radiative runs predict too steep density profiles, whereas runs including additional physics and/or gas clumping are in better agreement with the observed gas distribution. We note a systematic difference between cool-core and non-cool core clusters beyond approximately 0.3r(sub 200), which we explain by a different distribution of the gas in the two classes. Beyond approximately r(sub 500), galaxy clusters deviate significantly from spherical symmetry, with only little differences between relaxed and disturbed systems. We find good agreement between the observed and predicted scatter profiles, but only when the 1% densest clumps are filtered out in the simulations. Conclusions. The general trend of steepening density around the virial radius indicates that the shallow density profiles found in several recent works were probably obtained along particular directions (e.g., filaments) and are not representative of the

  10. The Gas Distribution in the Outer Regions of Galaxy Clusters

    NASA Technical Reports Server (NTRS)

    Eckert, D.; Vazza, F.; Ettori, S.; Molendi, S.; Nagai, D.; Lau, E. T.; Roncarelli, M.; Rossetti, M.; Snowden, L.; Gastaldello, F.

    2012-01-01

    Aims. We present our analysis of a local (z = 0.04 - 0.2) sample of 31 galaxy clusters with the aim of measuring the density of the X-ray emitting gas in cluster outskirts. We compare our results with numerical simulations to set constraints on the azimuthal symmetry and gas clumping in the outer regions of galaxy clusters. Methods. We have exploited the large field-of-view and low instrumental background of ROSAT/PSPC to trace the density of the intracluster gas out to the virial radius, We stacked the density profiles to detect a signal beyond T200 and measured the typical density and scatter in cluster outskirts. We also computed the azimuthal scatter of the profiles with respect to the mean value to look for deviations from spherical symmetry. Finally, we compared our average density and scatter profiles with the results of numerical simulations. Results. As opposed to some recent Suzaku results, and confirming previous evidence from ROSAT and Chandra, we observe a steepening of the density profiles beyond approximately r(sub 500). Comparing our density profiles with simulations, we find that non-radiative runs predict density profiles that are too steep, whereas runs including additional physics and/ or treating gas clumping agree better with the observed gas distribution. We report high-confidence detection of a systematic difference between cool-core and non cool-core clusters beyond approximately 0.3r(sub 200), which we explain by a different distribution of the gas in the two classes. Beyond approximately r(sub 500), galaxy clusters deviate significantly from spherical symmetry, with only small differences between relaxed and disturbed systems. We find good agreement between the observed and predicted scatter profiles, but only when the 1% densest clumps are filtered out in the ENZO simulations. Conclusions. Comparing our results with numerical simulations, we find that non-radiative simulations fail to reproduce the gas distribution, even well outside

  11. The Gas Distribution in Galaxy Cluster Outer Regions

    NASA Technical Reports Server (NTRS)

    Eckert, D.; Vazza, F.; Ettori, S.; Molendi, S.; Nagai, D.; Laue, E. T.; Roncarelli, M.; Rossetti, M.; Snowden, S. L.; Gastaldello, F.

    2012-01-01

    Aims. We present the analysis of a local (z = 0.04 - 0.2) sample of 31 galaxy clusters with the aim of measuring the density of the X-ray emitting gas in cluster outskirts. We compare our results with numerical simulations to set constraints on the azimuthal symmetry and gas clumping in the outer regions of galaxy clusters. Methods. We exploit the large field-of-view and low instrumental background of ROSAT/PSPC to trace the density of the intracluster gas out to the virial radius. We perform a stacking of the density profiles to detect a signal beyond r200 and measure the typical density and scatter in cluster outskirts. We also compute the azimuthal scatter of the profiles with respect to the mean value to look for deviations from spherical symmetry. Finally, we compare our average density and scatter profiles with the results of numerical simulations. Results. As opposed to some recent Suzaku results, and confirming previous evidence from ROSAT and Chandra, we observe a steepening of the density profiles beyond approximately r(sub 500). Comparing our density profiles with simulations, we find that non-radiative runs predict too steep density profiles, whereas runs including additional physics and/or treating gas clumping are in better agreement with the observed gas distribution. We report for the first time the high-confidence detection of a systematic difference between cool-core and non-cool core clusters beyond 0.3r(sub 200), which we explain by a different distribution of the gas in the two classes. Beyond r(sub 500), galaxy clusters deviate significantly from spherical symmetry, with only little differences between relaxed and disturbed systems. We find good agreement between the observed and predicted scatter profiles, but only when the 1% densest clumps are filtered out in the simulations. Conclusions. Comparing our results with numerical simulations, we find that non-radiative simulations fail to reproduce the gas distribution, even well outside cluster

  12. Observational and Numerical Diagnostics of Galaxy Cluster Outer Regions

    NASA Technical Reports Server (NTRS)

    Eckert, D.; Vazza, F.; Ettori, S.; Molendi, S.; Nagai, D.; Lau, E.; Roncarelli, M.; Rossetti, M.; Snowden, S. L.; Gastaldello, F.

    2011-01-01

    Aims. We present the analysis of a local (z = 0.04 - 0.2) sample of 31 galaxy clusters with the aim of measuring the density of the X-ray emitting gas in cluster outskirts. We compare our results with numerical simulations to set constraints on the azimuthal symmetry and gas clumping in the outer regions of galaxy clusters. Methods. We exploit the large field-of-view and low instrumental background of ROSAT/PSPC to trace the density of the intracluster gas out to the virial radius. We perform a stacking of the density profiles to detect a signal beyond r(sub 200) and measure the typical density and scatter in cluster outskirts. We also compute the azimuthal scatter of the profiles with respect to the mean value to look for deviations from spherical symmetry. Finally, we compare our average density and scatter profiles with the results of numerical simulations. Results. As opposed to several recent results, we observe a steepening of the density profiles beyond approximately 0.3r(sub 500). Comparing our density profiles with simulations, we find that non-radiative runs predict too steep density profiles, whereas runs including additional physics and/or gas clumping are in better agreement with the observed gas distribution. We note a systematic difference between cool-core and non-cool core clusters beyond approximately 0.3r(sub 200), which we explain by a different distribution of the gas in the two classes. Beyond approximately r(sub 500), galaxy clusters deviate significantly from spherical symmetry, with only little differences between relaxed and disturbed systems. We find good agreement between the observed and predicted scatter profiles, but only when the 1% densest clumps are filtered out in the simulations. Conclusions. The general trend of steepening density around the virial radius indicates that the shallow density profiles found in several recent works were probably obtained along particular directions (e.g., filaments) and are not representative of the

  13. Unveiling the structure of barred galaxies at 3.6 μm with the Spitzer survey of stellar structure in galaxies (S{sup 4}G). I. Disk breaks

    SciTech Connect

    Kim, Taehyun; Lee, Myung Gyoon; Gadotti, Dimitri A.; Muñoz-Mateos, Juan-Carlos; Sheth, Kartik; Madore, Barry F.; Ho, Luis C.; Elmegreen, Bruce; Knapen, Johan H.; Cisternas, Mauricio; Erroz-Ferrer, Santiago; Zaritsky, Dennis; Comerón, Sébastien; Laurikainen, Eija; Salo, Heikki; Holwerda, Benne; Hinz, Joannah L.; Buta, Ron; and others

    2014-02-20

    We have performed two-dimensional multicomponent decomposition of 144 local barred spiral galaxies using 3.6 μm images from the Spitzer Survey of Stellar Structure in Galaxies. Our model fit includes up to four components (bulge, disk, bar, and a point source) and, most importantly, takes into account disk breaks. We find that ignoring the disk break and using a single disk scale length in the model fit for Type II (down-bending) disk galaxies can lead to differences of 40% in the disk scale length, 10% in bulge-to-total luminosity ratio (B/T), and 25% in bar-to-total luminosity ratios. We find that for galaxies with B/T ≥ 0.1, the break radius to bar radius, r {sub br}/R {sub bar}, varies between 1 and 3, but as a function of B/T the ratio remains roughly constant. This suggests that in bulge-dominated galaxies the disk break is likely related to the outer Lindblad resonance of the bar and thus moves outward as the bar grows. For galaxies with small bulges, B/T < 0.1, r {sub br}/R {sub bar} spans a wide range from 1 to 6. This suggests that the mechanism that produces the break in these galaxies may be different from that in galaxies with more massive bulges. Consistent with previous studies, we conclude that disk breaks in galaxies with small bulges may originate from bar resonances that may be also coupled with the spiral arms, or be related to star formation thresholds.

  14. SELF-PERPETUATING SPIRAL ARMS IN DISK GALAXIES

    SciTech Connect

    D'Onghia, Elena; Vogelsberger, Mark; Hernquist, Lars

    2013-03-20

    The causes of spiral structure in galaxies remain uncertain. Leaving aside the grand bisymmetric spirals with their own well-known complications, here we consider the possibility that multi-armed spiral features originate from density inhomogeneities orbiting within disks. Using high-resolution N-body simulations, we follow the motions of stars under the influence of gravity, and show that mass concentrations with properties similar to those of giant molecular clouds can induce the development of spiral arms through a process termed swing amplification. However, unlike in earlier work, we demonstrate that the eventual response of the disk can be highly non-linear, significantly modifying the formation and longevity of the resulting patterns. Contrary to expectations, ragged spiral structures can thus survive at least in a statistical sense long after the original perturbing influence has been removed.

  15. Self-perpetuating Spiral Arms in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    D'Onghia, Elena; Vogelsberger, Mark; Hernquist, Lars

    2013-03-01

    The causes of spiral structure in galaxies remain uncertain. Leaving aside the grand bisymmetric spirals with their own well-known complications, here we consider the possibility that multi-armed spiral features originate from density inhomogeneities orbiting within disks. Using high-resolution N-body simulations, we follow the motions of stars under the influence of gravity, and show that mass concentrations with properties similar to those of giant molecular clouds can induce the development of spiral arms through a process termed swing amplification. However, unlike in earlier work, we demonstrate that the eventual response of the disk can be highly non-linear, significantly modifying the formation and longevity of the resulting patterns. Contrary to expectations, ragged spiral structures can thus survive at least in a statistical sense long after the original perturbing influence has been removed.

  16. Neutral Gas Outside the Disks of Local Group Galaxies

    NASA Astrophysics Data System (ADS)

    Lockman, Felix J.

    2017-03-01

    Of the three kinds of neutral gas found outside the stellar disks of Local Group galaxies, only the products of interaction, like the Magellanic Stream, have a clearly understandable origin. Both the high-velocity clouds and the faint H I between M31 and M33 remain a mystery. New observations of the region between M31 and M33 with the Green Bank Telescope show that the H I there resides in clouds with a size and mass similar to that of dwarf galaxies, but without stars. These clouds might be products of an interaction, or condensations in the hot circumgalactic medium of M31, but both these models have difficulties. The prevalence of clouds like this in the Local Group remains to be determined.

  17. Dying Young: Massive Dead Disk Galaxy Challenges the Picture of How Galaxies Evolve

    NASA Image and Video Library

    2017-06-21

    By combining the power of a “natural lens” in space with the capability of NASA’s Hubble Space Telescope, astronomers made a surprising discovery—the first example of very compact yet massive disk-shaped and rotating galaxy that stopped making stars only a few billion years after the big bang. Finding a galaxy that is pancake-shaped—much like our own Milky Way—so early in the history of the universe challenges the current understanding of how massive galaxies form and evolve, say researchers. The galaxy, called MACS 2129-1, is considered “dead” because it is no longer making stars. The existence of dead galaxies so early—when the universe was just one-quarter its current age—has long been a puzzle, as the Universe at that time was full of gas and at the peak of the cosmic star formation history. The leading theory has been that they formed in galaxy collisions that efficiently drove all the gas into the center of the collision and turned it into stars. “Perhaps we have been blind to the fact that early “dead” galaxies could in fact be disks, simply because we haven’t been able to resolve them,” said study leader Sune Toft of the Dark Cosmology Centre at the Niels Bohr Institute, University of Copenhagen. “This new insight may force us to rethink the whole cosmological context of how galaxies burn out early on and evolve into local elliptical-shaped galaxies.” When the universe was just 3 billion years old, half of the most massive galaxies were extremely compact and had already completed their star formation. Astronomers believe that they ultimately grew into the most massive elliptical galaxies seen in the nearby universe today. Scientists theorize they did this through mergers with small companion galaxies, which added to the stars on the galaxy’s outskirts. Confirming this scenario requires more powerful telescopes than are currently available, whether on Earth or in space. However, through the phenomenon known as

  18. Statistical-mechanical selection of the shapes of disk galaxies

    NASA Technical Reports Server (NTRS)

    Montgomery, David; Lee, Y. C.

    1991-01-01

    A new method is proposed for selecting steady state shapes of disk galaxies as 'most probable states' of a large number of stars, given only the total energy and total angular momentum. A partial differential equation is derived for the mean gravitational potential; it is closely related to the 'sinh-Poisson' equation for the mean-field description of a line vortex system or electrostatic guiding-center plasma. A 'water bag' approximation to the distribution function for bound stars renders the equation analytically tractable, but accurate solution of it may require numerical integration, in view of its general nonlinearity.

  19. DOUBLE DCO{sup +} RINGS REVEAL CO ICE DESORPTION IN THE OUTER DISK AROUND IM LUP

    SciTech Connect

    Öberg, Karin I.; Loomis, Ryan; Andrews, Sean M.; Qi, Chunhua; Wilner, David J.; Furuya, Kenji; Dishoeck, Ewine F. van; Aikawa, Yuri

    2015-09-10

    In a protoplanetary disk, a combination of thermal and non-thermal desorption processes regulate where volatiles are liberated from icy grain mantles into the gas phase. Non-thermal desorption should result in volatile-enriched gas in disk-regions where complete freeze-out is otherwise expected. We present Atacama Large Millimeter/Submillimeter Array observations of the disk around the young star IM Lup in 1.4 mm continuum, C{sup 18}O 2–1, H{sup 13}CO{sup +} 3–2 and DCO{sup +} 3–2 emission at ∼0.″5 resolution. The images of these dust and gas tracers are clearly resolved. The DCO{sup +} line exhibits a striking pair of concentric rings of emission that peak at radii of ∼0.″6 and 2″ (∼90 and 300 AU, respectively). Based on disk chemistry model comparison, the inner DCO{sup +} ring is associated with the balance of CO freeze-out and thermal desorption due to a radial decrease in disk temperature. The outer DCO{sup +} ring is explained by non-thermal desorption of CO ice in the low-column-density outer disk, repopulating the disk midplane with cold CO gas. The CO gas then reacts with abundant H{sub 2}D{sup +} to form the observed DCO{sup +} outer ring. These observations demonstrate that spatially resolved DCO{sup +} emission can be used to trace otherwise hidden cold gas reservoirs in the outmost disk regions, opening a new window onto their chemistry and kinematics.

  20. Not a galaxy: IRAS 04186+5143, a new young stellar cluster in the outer Galaxy

    NASA Astrophysics Data System (ADS)

    Yun, J. L.; Elia, Davide; Djupvik, A. A.; Torrelles, J. M.; Molinari, S.

    2015-09-01

    We report the discovery of a new young stellar cluster in the outer Galaxy located at the position of an IRAS Point Source Catalog source that has been previously misidentified as an external galaxy. The cluster is seen in our near-infrared imaging towards IRAS 04186+5143 and in archive Spitzer images confirming the young stellar nature of the sources detected. There is also evidence of subclustering seen in the spatial distributions of young stars and of gas and dust. Near- and mid-infrared photometry indicates that the stars exhibit colours compatible with reddening by interstellar and circumstellar dust and are likely to be low- and intermediate-mass young stellar objects (YSOs) with a large proportion of Class I YSOs. Ammonia and CO lines were detected, with the CO emission well centred near the position of the richest part of the cluster. The velocity of the CO and NH3 lines indicates that the gas is Galactic and located at a distance of about 5.5 kpc, in the outer Galaxy. Herschel data of this region characterize the dust environment of this molecular cloud core where the young cluster is embedded. We derive masses, luminosities, and temperatures of the molecular clumps where the young stars reside and discuss their evolutionary stages.

  1. Control of Ca2+ in rod outer segment disks by light and cyclic GMP.

    PubMed

    George, J S; Hagins, W A

    1983-05-26

    Photons absorbed in vertebrate rods and cones probably cause electrochemical changes at the photoreceptor plasma membrane by changing the cytoplasmic concentration of a diffusible transmitter substance, reducing the Na+ current flowing into the outer segment of the cell in the dark, to produce the observed membrane hyperpolarization that is the initial excitatory response. Cyclic GMP has been proposed as the transmitter because a light-activated cyclic GMP phosphodiesterase (PDE) has been found in rod disk membranes and because intracellularly injected cyclic GMP reduces rod membrane potentials. Free Ca2+ has also been proposed because increasing external [Ca2+] quickly and reversibly reduces the dark current and divalent cationophores increase the Ca2+ sensitivity. Ca2+ efflux from rod outer segments (ROS) of intact retinas occurs simultaneously with light responses. Vesicles prepared from ROS disk membranes become more permeable on illumination, releasing trapped ions or molecules, but intact outer segment disks have not previously been found to store sufficient Ca2+ in darkness and to release enough in light to meet the theoretical requirements for control of the dark current by varying cytoplasmic Ca2+ (refs 14-18). We now report experiments that show the required Ca2+ storage and release from rod disk membranes suspended in media containing high-energy phosphate esters and electrolytes approximating the cytoplasmic composition of live rod cells. Cyclic GMP stimulates Ca2+ uptake by ROS disks in such media.

  2. Time evolution of interstellar dust and far-infrared luminosity of disk galaxies

    NASA Technical Reports Server (NTRS)

    Wang, Boqi

    1991-01-01

    The evolution of interstellar dust in disk galaxies is modeled, assuming that dust forms predominantly in molecular clouds associated with star formation. Analytical solutions for the dust abundance in disk galaxies as a function of galaxy age are obtained for the prompt initial enrichment and accretion models of chemical evolution, consistent with observations of the heavy element abundance in the Galaxy. Star formation rates in the disks of galaxies are taken as either constant or decreasing exponentially with time. It is found that the total amount of dust in the early history of galaxies can be up to 4 times the value observed today. The total emission from dust in galaxies is calculated, using an average dust temperature derived from IRAS observations. In the strongly evolving models, the far-infrared luminosity from galaxies can be roughly two orders of magnitude larger than the current value.

  3. Growth of Bulges in Disk Galaxies Since z ˜ 1

    NASA Astrophysics Data System (ADS)

    Sachdeva, Sonali; Saha, Kanak; Singh, Harinder P.

    2017-05-01

    We investigate the growth of bulges in bright ({M}B< -20) disk galaxies since z˜ 1, in rest-frame B and I-band, using images from HST ACS and WFC3 in GOODS-South for high redshifts (0.4< z< 1.0) and SDSS for local (0.02< z< 0.05). The growth history has been traced by performing two-component bulge-disk decomposition and further classifying the bulges into pseudos and classicals using the Kormendy relation. We have about 27% pseudo and 40% classical bulges in our sample. Classical bulges are brighter than pseudo, in both rest-bands, at all redshifts probed here; in fact since z˜ 0.77, classicals are about ˜1 mag brighter than pseudo bulges. Both bulges have witnessed substantial growth, more than half of their present-day stellar mass has been gained since z˜ 1. Their host disks have grown concurrently, becoming progressively brighter in rest-frame I-band. The high-redshift host disks of both pseudo and classical bulges are found to be equally clumpy in rest-frame B-band. In the same band, we found that the growth of classical bulges is accompanied by fading of their host disks—which might be an indication of secular processes in action. However, both host disk as well as the bulge have grown substantially in terms of stellar mass. Our analysis suggests that clump migration and secular processes alone cannot account for the bulge growth, since z˜ 1, accretion, and minor mergers would be required.

  4. STABILITY OF THE OUTER PLANETS IN MULTIRESONANT CONFIGURATIONS WITH A SELF-GRAVITATING PLANETESIMAL DISK

    SciTech Connect

    Reyes-Ruiz, M.; Aceves, H.; Chavez, C. E.

    2015-05-10

    We study the effect of a massive planetesimal disk on the dynamical stability of the outer planets in a system representing the early solar system assuming, as has been suggested recently, that these planets were initially locked in a compact and multiresonant configuration as a result of gas-driven migration in a protoplanetary disk. The planetesimal disk is represented by an ensemble of 2000 lunar mass bodies for which the gravitational interaction is calculated self-consistently using the Mercury6.5 code. Several initial multiresonant configurations and planetesimal disk models are considered. Under such conditions a strong dynamical instability, manifested as a rapid giant planet migration and planetesimal disk dispersal, develops on a timescale of less than 40 Myr in most cases. Dynamical disk heating due to the gravitational interactions among planetesimals leads to more frequent interactions between the planetesimals and the ice giants, in comparison to models in which planetesimal–planetesimal interactions are neglected. The number of particles used to represent the planetesimal disk has implications for our results, and although our studies represent the first self-consistent calculations of unstable planetesimal-driven migration, our results point toward the need for using more realistic treatments of the planetesimal disk. Finally, in the framework of our model, we discuss the possible implications of our results on the early evolution of the solar system.

  5. ROSAT Observations of Low Mass Disk Galaxies: No Evidence of Baryonic Blow Out

    NASA Technical Reports Server (NTRS)

    Bothun, Gregory D.; Eriksen, James

    1994-01-01

    To test the hypothesis that galctic winds associated with star formation in low mass disk galaxies can be an effective means of relocating cold disk gas to a warm tenuous halo, we have obtained long exposure ROSAT PSPC observations of three such galaxies.

  6. ROSAT Observations of Low Mass Disk Galaxies: No Evidence of Baryonic Blow Out

    NASA Technical Reports Server (NTRS)

    Bothun, Gregory D.; Eriksen, James

    1994-01-01

    To test the hypothesis that galctic winds associated with star formation in low mass disk galaxies can be an effective means of relocating cold disk gas to a warm tenuous halo, we have obtained long exposure ROSAT PSPC observations of three such galaxies.

  7. How surface density of galaxy disks affects metallicity? Outflow and Accretion

    NASA Astrophysics Data System (ADS)

    Wu, Po-Feng; Kudritzki, Rolf-Peter; Tully, R. Brent; Neill, J. D.

    2015-08-01

    The surface density of disk is considered as a second parameter affecting the evolution of disk galaxies other than mass. Several physical and chemical properties of galaxies are found to be correlated with surface density of disk galaxies. However, the surface density, or surface brightness, is also strongly correlated with mass. It's not clear whether surface density really plays a role, or those correlations simply reflect the effect from stellar mass. To ask the question properly, one should take away the dependence on mass of galaxies, i.e., compare galaxies with the same mass but different surface densities.In this study, we ask, besides stellar mass, whether the surface density of disks also affects chemical evolution of galaxies. We demonstrate that, after removing the dependence on stellar mass and gas mass, the metallicity of galaxy still correlates with surface density of the galaxy disk. At the same stellar and gas mass, higher surface brightness galaxies on average possess both higher stellar and gas-phase metallicity, inferred from broadband color and spectrosopy of HII regions, respectively.We use an analytical model of chemical evolution involving gas outflow and accretion to explore possible reasons causing the difference in metallicity. Accroding to the model, at the same mass, lower metallicity galaxies should have experienced severer mass loss during star-formation events, and/or be inert to gas accretion. Both scenarios are consistent with general expections from properties of low surface density disks of shallow potential wells and dynamical stability.

  8. Falling outer rotation curves of star-forming galaxies at 0.7 < z < 2.6 probed with KMOS3D and SINS/zC-SINF

    NASA Astrophysics Data System (ADS)

    Lang, Philipp; Schreiber, Natascha M. Förster; Genzel, Reinhard; Burkert, Andreas; Lutz, Dieter; Tacconi, Linda; Wisnioski, Emily; Wuyts, Stijn; KMOS 3D Team

    2017-03-01

    We exploit the deep Hα IFU kinematic data from the KMOS3D and SINS/zC-SINF surveys to explore the so far unconstrained outer rotation curves of star-forming disk galaxies at high redshift. Through stacking the signal of ~ 100 massive disks at 0.7 < z < 2.6, we construct a representative rotation curve reaching out to several effective radii. Our stacked rotation curve exhibits a turnover with a steep falloff in the outer regions, significantly strengthening the tantalizing evidence previously hinted at in a handful only of individual disks among the sample with the deepest data. This finding confirms the high baryon fractions found by comparing the stellar, gas and dynamical masses of high redshift galaxies independently of assumptions on the light-to-mass conversion and Initial stellar Mass Function (IMF). The rapid falloff of the stacked rotation curve is most naturally explained by the effects of pressure gradients, which are significant in the gas-rich, turbulent high-z disks and which would imply a possible pressure-driven truncation of the outer disk.

  9. 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.

  10. Color-mass-to-light-ratio relations for disk galaxies

    SciTech Connect

    McGaugh, Stacy S.; Schombert, James M. E-mail: jschombe@uoregon.edu

    2014-11-01

    We combine Spitzer 3.6 μm observations of a sample of disk galaxies spanning over 10 mag in luminosity with optical luminosities and colors to test population synthesis prescriptions for computing stellar mass. Many commonly employed models fail to provide self-consistent results: the stellar mass estimated from the luminosity in one band can differ grossly from that of another band for the same galaxy. Independent models agree closely in the optical (V band), but diverge at longer wavelengths. This effect is particularly pronounced in recent models with substantial contributions from TP-AGB stars. We provide revised color-mass-to-light ratio relations that yield self-consistent stellar masses when applied to real galaxies. The B – V color is a good indicator of the mass-to-light ratio. Some additional information is provided by V – I, but neither it nor J – K{sub s} are particularly useful for constraining the mass-to-light ratio on their own. In the near-infrared, the mass-to-light ratio depends weakly on color, with typical values of 0.6 M {sub ☉}/L {sub ☉} in the K{sub s} band and 0.47 M {sub ☉}/L {sub ☉} at 3.6 μm.

  11. Color-Mass-to-light-ratio Relations for Disk Galaxies

    NASA Astrophysics Data System (ADS)

    McGaugh, Stacy S.; Schombert, James M.

    2014-11-01

    We combine Spitzer 3.6 μm observations of a sample of disk galaxies spanning over 10 mag in luminosity with optical luminosities and colors to test population synthesis prescriptions for computing stellar mass. Many commonly employed models fail to provide self-consistent results: the stellar mass estimated from the luminosity in one band can differ grossly from that of another band for the same galaxy. Independent models agree closely in the optical (V band), but diverge at longer wavelengths. This effect is particularly pronounced in recent models with substantial contributions from TP-AGB stars. We provide revised color-mass-to-light ratio relations that yield self-consistent stellar masses when applied to real galaxies. The B - V color is a good indicator of the mass-to-light ratio. Some additional information is provided by V - I, but neither it nor J - Ks are particularly useful for constraining the mass-to-light ratio on their own. In the near-infrared, the mass-to-light ratio depends weakly on color, with typical values of 0.6 M ⊙/L ⊙ in the Ks band and 0.47 M ⊙/L ⊙ at 3.6 μm.

  12. Properties of the outer regions of spiral disks: abundances, colors and ages

    NASA Astrophysics Data System (ADS)

    Mollá, Mercedes; Díaz, Angeles I.; Gibson, Brad K.; Cavichia, Oscar; López-Sánchez, Ángel-R.

    2017-03-01

    We summarize the results obtained from our suite of chemical evolution models for spiral disks, computed for different total masses and star formation efficiencies. Once the gas, stars and star formation radial distributions are reproduced, we analyze the Oxygen abundances radial profiles for gas and stars, in addition to stellar averaged ages and global metallicity. We examine scenarios for the potential origin of the apparent flattening of abundance gradients in the outskirts of disk galaxies, in particular the role of molecular gas formation prescriptions.

  13. 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.

  14. Excess C/O and C/H in Outer Protoplanetary Disk Gas

    NASA Astrophysics Data System (ADS)

    Öberg, Karin I.; Bergin, Edwin A.

    2016-11-01

    The compositions of nascent planets depend on the compositions of their birth disks. In particular, the elemental compositions of gas giant gaseous envelopes depend on the elemental compositions of the disk gas from which the envelopes are accreted. Previous models have demonstrated that sequential freeze-out of O- and C-bearing volatiles in disks will result in supersolar C/O ratios and subsolar C/H ratios in the gas between water and CO snowlines. However, this result does not take into account the expected grain growth and radial drift of pebbles in disks, and the accompanying redistribution of volatiles from the outer to the inner disk. Using a toy model we demonstrate that when drift is considered, CO is enhanced between the water and CO snowline, resulting in both supersolar C/O and C/H ratios in the disk gas in the gas giant formation zone. This result appears to be robust for the disk model as long as there is substantial pebble drift across the CO snowline, and the efficiency of CO vapor diffusion is limited. Gas giants that accrete their gaseous envelopes exterior to the water snowline and do not experience substantial core-envelope mixing may thus feature both superstellar C/O and C/H ratios in their atmospheres. Pebble drift will also affect the nitrogen and noble gas abundances in the planet-forming zones, which may explain some of Jupiter’s peculiar abundance patterns.

  15. 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.

  16. 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.

  17. Galaxy Zoo Hubble: First results of the redshift evolution of disk fraction in the red sequence

    NASA Astrophysics Data System (ADS)

    Galloway, Melanie; Willett, Kyle; Fortson, Lucy; Scarlata, Claudia; Beck, Melanie; Masters, Karen; Melvin, Tom

    2016-01-01

    The transition of galaxies from the blue cloud to the red sequence is commonly linked to a morphological transformation from disk to elliptical structure. However, the correlation between color and morphology is not one-to-one, as evidenced by the existence of a significant population of red disks. As this stage in a galaxy's evolution is likely to be transitory, the mechanism by which red disks are formed offers insight to the processes that trigger quenching of star formation and the galaxy's position on the star-forming sequence. To study the population of disk galaxies in the red sequence as a function of cosmic time, we utilize data from the Galaxy Zoo: Hubble project, which uses crowdsourced visual classifications of images of galaxies selected from the AEGIS, COSMOS, GEMS, and GOODS surveys. We construct a large sample of over 10,000 disk galaxies spanning a wide (0 < z < 1.0) redshift range. We use this sample to examine the change in the fraction of disks in the red sequence with respect to all disks from z˜1 to the present day. Preliminary results confirm that the fraction of disks in the red sequence decreases as the Universe evolves. We discuss the quenching processes which may explain this trend, and which morphological transformations are most affected by it.

  18. Local Turbulent Disks: analogs of high-redshift vigorously star-forming disks and laboratories for galaxy assembly?

    NASA Astrophysics Data System (ADS)

    Damjanov, Ivana

    2012-10-01

    Kinematical investigations at redshifts 1galaxies exhibit very high internal velocity dispersions. Dynamical data collected with integral field spectrographs {IFS} suggest that the level of rotational support in these systems follows a trend in mass, with compact dispersion-dominated Lyman Break Galaxies at lower stelar masses and large dynamically unstable turbulent disks at stellar masses larger than 10^10 solar masses. The high velocity dispersion of these young disks results in a large characteristic scale for star-forming clusters thereby also explaining their 'clump cluster' morphology. Galaxies like these were thought to be absent from the local Universe. As part of a IFS campaign to observe the most H-alpha luminous galaxies in SDSS, we have discovered a sample of very rare objects seemingly identical to these high-z turbulent disks. In this proposal we seek imaging in H-alpha of thirteen local disk galaxies in our sample, using the ACS tunable-wavelength ramp filters. Our goal is to measure the size distribution of the star-forming complexes in these objects, with ten times the typical physical resolution of HST observations of high-z galaxies, in order to test the idea that they are indeed dynamically unstable turbulent disks caught in the process of formation. In synergy with existing high resolution HST imaging of the local analogs of low-mass dispersion-dominated galaxies at high redshift {Lyman Break Analogs}, our proposed observations of the local counterparts to large turbulent disks at high redshift will help to paint a complete picture of local analogs of high-z star-forming galaxies.

  19. Detection of Prominent Stellar Disks in the Progenitors of Present-day Massive Elliptical Galaxies

    NASA Astrophysics Data System (ADS)

    Davari, Roozbeh H.; Ho, Luis C.; Mobasher, Bahram; Canalizo, Gabriela

    2017-02-01

    Massive galaxies at high redshifts (z > 2) show different characteristics from their local counterparts: they are compact and most likely have a disk. In this study, we trace the evolution of local massive galaxies by performing a detailed morphological analysis, namely, fitting single Sérsic profiles and performing bulge+disk decompositions. We analyze ∼250 massive galaxies selected from all CANDELS fields (COSMOS, UDS, EGS, GOODS-South, and GOODS-North). We confirm that both star-forming and quiescent galaxies increase their sizes significantly from z ≈ 2.5 to the present day. The global Sérsic index of quiescent galaxies increases over time (from n ≈ 2.5 to n > 4), while that of star-forming galaxies remains roughly constant (n ≈ 2.5). By decomposing galaxy profiles into bulge+disk components, we find that massive galaxies at high redshift have prominent stellar disks, which are also evident from visual inspection of the images. By z ≈ 0.5, the majority of the disks disappear and massive quiescent galaxies begin to resemble the local elliptical galaxies. Star-forming galaxies have lower bulge-to-total ratios (B/T) than their quiescent counterparts in each redshift bin. The bulges of star-forming and quiescent galaxies follow different evolutionary histories, while their disks evolve similarly. Based on our morphological analysis and previous cosmological simulations, we argue that major mergers, along with minor mergers, have played a crucial role in the significant increase in size of high-z galaxies and the destruction of their massive and large-scale disks.

  20. The Chemistry of Multiply Deuterated Molecules in Protoplanetary Disks: I. The Outer Disk

    NASA Technical Reports Server (NTRS)

    Willacy, K.

    2007-01-01

    We present new models of the deuterium chemistry in protoplanetary disks, including, for the first time, multiply deuterated species. We use these models to explore whether observations in combination with models can give us clues as to which desorption processes occur in disks.We find, in common with other authors, that photodesorption can allow strongly bound molecules such as HDO to exist in the gas phase in a layer above the midplane. Models including this process give the best agreement with the observations. In the midplane, cosmic-ray heating can desorb weakly bound molecules such as CO and N2. We find the observations suggest that N2 is gaseous in this region, but that CO must be retained on the grains to account for the observed DCO+/HCO+. This could be achieved by CO having a higher binding energy than N2 (as may be the case when these molecules are accreted onto water ice) or by a smaller cosmic-ray desorption rate for CO than assumed here, as suggested by recent theoretical work. For gaseous molecules the calculated deuteration can be greatly changed by chemical processing in the disk from the input molecular cloud values. On the grains singly deuterated species tend to retain the D/H ratio set in the molecular cloud, whereas multiply deuterated species are more affected by the disk chemistry. Consequently, the D/H ratios observed in comets may be partly set in the parent cloud and partly in the disk, depending on the molecule.

  1. The Chemistry of Multiply Deuterated Molecules in Protoplanetary Disks: I. The Outer Disk

    NASA Technical Reports Server (NTRS)

    Willacy, K.

    2007-01-01

    We present new models of the deuterium chemistry in protoplanetary disks, including, for the first time, multiply deuterated species. We use these models to explore whether observations in combination with models can give us clues as to which desorption processes occur in disks.We find, in common with other authors, that photodesorption can allow strongly bound molecules such as HDO to exist in the gas phase in a layer above the midplane. Models including this process give the best agreement with the observations. In the midplane, cosmic-ray heating can desorb weakly bound molecules such as CO and N2. We find the observations suggest that N2 is gaseous in this region, but that CO must be retained on the grains to account for the observed DCO+/HCO+. This could be achieved by CO having a higher binding energy than N2 (as may be the case when these molecules are accreted onto water ice) or by a smaller cosmic-ray desorption rate for CO than assumed here, as suggested by recent theoretical work. For gaseous molecules the calculated deuteration can be greatly changed by chemical processing in the disk from the input molecular cloud values. On the grains singly deuterated species tend to retain the D/H ratio set in the molecular cloud, whereas multiply deuterated species are more affected by the disk chemistry. Consequently, the D/H ratios observed in comets may be partly set in the parent cloud and partly in the disk, depending on the molecule.

  2. Efficiency of particle trapping in the outer regions of protoplanetary disks

    SciTech Connect

    Simon, Jacob B.; Armitage, Philip J.

    2014-03-20

    We investigate the strength of axisymmetric local pressure maxima (zonal flows) in the outer regions of protoplanetary disks, where ambipolar diffusion reduces turbulent stresses driven by the magnetorotational instability. Using local numerical simulations we show that in the absence of net vertical magnetic fields, the strength of turbulence in the ambipolar dominated region of the disk is low and any zonal flows that are present are weak. For net fields strong enough to yield observed protostellar accretion rates, however, zonal flows with a density amplitude of 10%-20% are formed. These strengths are comparable to those seen in simulations of ideal MHD disk turbulence. We investigate whether these zonal flows are able to reverse the inward radial drift of solids, leading to prolonged and enhanced concentration as a prelude to planetesimal formation. For commonly assumed mean surface density profiles (surface density Σ∝r {sup –1/2} or steeper) we find that the predicted perturbations to the background disk profile do not correspond to local pressure maxima. This is a consequence of radial width of the simulated zonal flows, which is larger than was assumed in prior analytic models of particle trapping. These larger scale flows would only trap particles for higher amplitude fluctuations than observed. We conclude that zonal flows are likely to be present in the outer regions of protoplanetary disks and are potentially large enough to be observable, but are unlikely to lead to strong particle trapping.

  3. Efficiency of Particle Trapping in the Outer Regions of Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Simon, Jacob B.; Armitage, Philip J.

    2014-03-01

    We investigate the strength of axisymmetric local pressure maxima (zonal flows) in the outer regions of protoplanetary disks, where ambipolar diffusion reduces turbulent stresses driven by the magnetorotational instability. Using local numerical simulations we show that in the absence of net vertical magnetic fields, the strength of turbulence in the ambipolar dominated region of the disk is low and any zonal flows that are present are weak. For net fields strong enough to yield observed protostellar accretion rates, however, zonal flows with a density amplitude of 10%-20% are formed. These strengths are comparable to those seen in simulations of ideal MHD disk turbulence. We investigate whether these zonal flows are able to reverse the inward radial drift of solids, leading to prolonged and enhanced concentration as a prelude to planetesimal formation. For commonly assumed mean surface density profiles (surface density Σvpropr -1/2 or steeper) we find that the predicted perturbations to the background disk profile do not correspond to local pressure maxima. This is a consequence of radial width of the simulated zonal flows, which is larger than was assumed in prior analytic models of particle trapping. These larger scale flows would only trap particles for higher amplitude fluctuations than observed. We conclude that zonal flows are likely to be present in the outer regions of protoplanetary disks and are potentially large enough to be observable, but are unlikely to lead to strong particle trapping.

  4. Gas disks and supermassive black holes in nearby radio galaxies

    NASA Astrophysics Data System (ADS)

    Noel-Storr, Jacob

    2004-12-01

    We present a detailed analysis of a set of medium- resolution spectra, obtained by the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, of the emission-line gas present in the nuclei of a complete sample of 21 nearby, early-type galaxies with radio jets. For each galaxy nucleus we present spectroscopic data in the region of hydrogen-alpha and the kinematics derived therefrom. We find in 67% of the nuclei the gas appears to be rotating and, with one exception, the cases where rotation is not seen are either face on or have complex morphologies. We find that in 62% of the nuclei the fit to the central spectrum is improved by inclusion of a broad emission-line component. These broad components have a mean velocity dispersion of 1349 kilometers per second (with a standard deviation of 345 kilometers per second) and are redshifted from the narrow-line components (assuming an origin in hydrogen-alpha) by 486 kilometers per second (with a standard deviation of 443 kilometers per second). We generated model velocity profiles including no black hole, a one hundred million solar mass black hole and a nine hundred million solar mass black hole. We compared the predicted profiles to the observed velocity profiles from the above spectra, finding kinematic signatures compatible with black holes greater than one hundred million solar masses in 53% of the sample. We suspect that hydrodynamic flow of the gas is a significant factor in the nucleus of NGC 2329. We found hints of jet-disk interaction in 24% of the sample nuclei and signs of twists or warps in 19%. Twenty-four percent of the velocity profiles show signs of multiple kinematic components. We suggest that the gas disks in these galaxies are generally not well-settled systems. We characterize the kinematic state of the nuclear gas through three weighted mean parameters, and find that again the disks appear not to be well-settled. We show evidence of a connection between the stellar and gas velocity

  5. A `Universal' Density Profile for the Outer Stellar Halos of Galaxies

    NASA Astrophysics Data System (ADS)

    Remus, Rhea-Silvia; Burkert, Andreas; Dolag, Klaus

    2017-03-01

    The outer stellar halos of galaxies contain vital information about the formation history of galaxies, since the relaxation timescales in the outskirts are long enough to keep the memory, while the information about individual formation events in the central parts has long been lost due to mixing, star formation and relaxation. To unveil some of the information encoded in these faint outer halo regions, we study the stellar outskirts of galaxies selected from a fully hydrodynamical high-resolution cosmological simulation, called Magneticum. We find that the density profiles of the outer stellar halos of galaxies over a broad mass range can be well described by an Einasto profile. For a fixed total mass range, the free parameters of the Einasto fits are closely correlated. Galaxies which had more (dry) merger events tend to have lesser curved outer stellar halos, however, we find no indication that the amount of curvature is correlated with galaxy morphology. The Einasto-like shape of the outer stellar halo densities can also explain the observed differences between the Milky Way and Andromeda outer stellar halos.

  6. THE MILKY WAY AS A HIGH-REDSHIFT GALAXY: THE IMPORTANCE OF THICK DISK FORMATION IN GALAXIES

    SciTech Connect

    Lehnert, Matthew D.; Di Matteo, Paola; Haywood, Misha; Snaith, Owain N.

    2014-07-10

    We compare the star formation history and dynamics of the Milky Way (MW) with the properties of distant disk galaxies. During the first ∼4 Gyr of its evolution, the MW formed stars with a high star formation intensity (SFI), Σ{sub SFR} ≈ 0.6 M {sub ☉} yr{sup –1} kpc{sup –2} and as a result, generated outflows and high turbulence in its interstellar medium (ISM). This intense phase of star formation corresponds to the formation of the thick disk. The formation of the thick disk is a crucial phase that enables the MW to have formed approximately half of its total stellar mass by z ∼ 1 which is similar to ''MW progenitor galaxies'' selected by abundance matching. This agreement suggests that the formation of the thick disk may be a generic evolutionary phase in disk galaxies. Using a simple energy injection-kinetic energy relationship between the one-dimensional velocity dispersion and SFI, we can reproduce the average perpendicular dispersion in stellar velocities of the MW with age. This relationship, its inferred evolution, and required efficiency are consistent with observations of galaxies from z ≈ 0-3. The high turbulence generated by intense star formation naturally resulted in a thick disk, a chemically well-mixed ISM, and is the mechanism that links the evolution of MW to the observed characteristics of distant disk galaxies.

  7. A dynamo in a torus as an explanation of magnetic fields in the outer rings of galaxies

    NASA Astrophysics Data System (ADS)

    Mikhailov, E. A.

    2017-09-01

    It is currently generally believed that magnetic fields in the disks of spiral galaxies are generated by the dynamo mechanism, which is based on the joint action of differential rotation and the alpha effect, associated with turbulent motions in the interstellar gas. Together with their disks, outer rings are also encountered in galaxies, where magnetic fields may be present. In earlier studies, the generation of magnetic fields has been described in a planar approximation, whose essence is that the size of rings perpendicular to the plane of the galaxy is much smaller than their size in the radial direction. However, it is plausible that these sizesmay sometimes be comparable, so that it would be more logical to suppose that a ring has a toroidal form. A model for a dynamo in a toroidal ring is constructed in this study. This model describes the magnetic field using two functions, corresponding to the toroidal component of the field and the part of the vector potential characterizing its poloidal component. The possible generation of magnetic field in various cases is shown, with both quadrupolar symmetry (close to the fields obtained in the planar approximation) and dipolar symmetry (when two layers with oppositely directed magnetic fields form in the ring). The parameter values for which the generation of fields with one or the other type of symmetry is possible are estimated. The results can also be used to describe the evolution of the magnetic fields in other toroidal astrophysical objects.

  8. Extreme Gas Fractions in Clumpy, Turbulent Disk Galaxies at z ~ 0.1

    NASA Astrophysics Data System (ADS)

    Fisher, David B.; Glazebrook, Karl; Bolatto, Alberto; Obreschkow, Danail; Mentuch Cooper, Erin; Wisnioski, Emily; Bassett, Robert; Abraham, Roberto G.; Damjanov, Ivana; Green, Andy; McGregor, Peter

    2014-08-01

    In this Letter, we report the discovery of CO fluxes, suggesting very high gas fractions in three disk galaxies seen in the nearby universe (z ~ 0.1). These galaxies were investigated as part of the DYnamics of Newly Assembled Massive Objects (DYNAMO) survey. High-resolution Hubble Space Telescope imaging of these objects reveals the presence of large star forming clumps in the bodies of the galaxies, while spatially resolved spectroscopy of redshifted Hα reveals the presence of high dispersion rotating disks. The internal dynamical state of these galaxies resembles that of disk systems seen at much higher redshifts (1 < z < 3). Using CO(1-0) observations made with the Plateau de Bure Interferometer, we find gas fractions of 20%-30% and depletion times of t dep ~ 0.5 Gyr (assuming a Milky-Way-like αCO). These properties are unlike those expected for low-redshift galaxies of comparable specific star formation rate, but they are normal for their high-z counterparts. DYNAMO galaxies break the degeneracy between gas fraction and redshift, and we show that the depletion time per specific star formation rate for galaxies is closely tied to gas fraction, independent of redshift. We also show that the gas dynamics of two of our local targets corresponds to those expected from unstable disks, again resembling the dynamics of high-z disks. These results provide evidence that DYNAMO galaxies are local analogs to the clumpy, turbulent disks, which are often found at high redshift.

  9. PLANET-PLANET SCATTERING IN PLANETESIMAL DISKS. II. PREDICTIONS FOR OUTER EXTRASOLAR PLANETARY SYSTEMS

    SciTech Connect

    Raymond, Sean N.; Armitage, Philip J.; Gorelick, Noel

    2010-03-10

    We develop an idealized dynamical model to predict the typical properties of outer extrasolar planetary systems, at radii comparable to the Jupiter-to-Neptune region of the solar system. The model is based upon the hypothesis that dynamical evolution in outer planetary systems is controlled by a combination of planet-planet scattering and planetary interactions with an exterior disk of small bodies ('planetesimals'). Our results are based on 5000 long duration N-body simulations that follow the evolution of three planets from a few to 10 AU, together with a planetesimal disk containing 50 M{sub +} from 10 to 20 AU. For large planet masses (M {approx}> M{sub Sat}), the model recovers the observed eccentricity distribution of extrasolar planets. For lower-mass planets, the range of outcomes in models with disks is far greater than that which is seen in isolated planet-planet scattering. Common outcomes include strong scattering among massive planets, sudden jumps in eccentricity due to resonance crossings driven by divergent migration, and re-circularization of scattered low-mass planets in the outer disk. We present the distributions of the eccentricity and inclination that result, and discuss how they vary with planet mass and initial system architecture. In agreement with other studies, we find that the currently observed eccentricity distribution (derived primarily from planets at a {approx}< 3 AU) is consistent with isolated planet-planet scattering. We explain the observed mass dependence-which is in the opposite sense from that predicted by the simplest scattering models-as a consequence of strong correlations between planet masses in the same system. At somewhat larger radii, initial planetary mass correlations and disk effects can yield similar modest changes to the eccentricity distribution. Nonetheless, strong damping of eccentricity for low-mass planets at large radii appears to be a secure signature of the dynamical influence of disks. Radial velocity

  10. A Test of Star Formation Laws in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Tan, Jonathan C.

    2010-02-01

    We use observations of the radial profiles of the mass surface density of total, Σ g , and molecular, ΣH2, gas rotation velocity and star formation rate surface density, Σsfr, of the molecular dominated regions of 12 disk galaxies from Leroy et al. to test several star formation laws: a "Kennicutt-Schmidt power law," Σsfr = Ag Σ1.5 g,2; a "constant molecular law," Σsfr = A H2ΣH2,2 the "turbulence-regulated laws" of Krumholz & McKee (KM) and Krumholz, McKee, & Tumlinson (KMT), a "gas-Ω law," Σsfr = B ΩΣ g Ω and a shear-driven "giant molecular cloud (GMC) collisions law," Σsfr = B CCΣ g Ω(1 - 0.7β), where β ≡ d ln v circ/d ln r. We find the constant molecular law, KMT turbulence law, and GMC collision law are the most accurate, with an rms error of a factor of 1.5 if the normalization constants are allowed to vary between galaxies. Of these three laws, the GMC collision law does not require a change in physics to account for the full range of star formation activity seen from normal galaxies to circumnuclear starbursts. A single global GMC collision law with B CC = 8.0 × 10-3, i.e., a gas consumption time of 20 orbital times for β = 0, yields an rms error of a factor of 1.8.

  11. A TEST OF STAR FORMATION LAWS IN DISK GALAXIES

    SciTech Connect

    Tan, Jonathan C.

    2010-02-10

    We use observations of the radial profiles of the mass surface density of total, {sigma} {sub g}, and molecular, {sigma}{sub H2}, gas rotation velocity and star formation rate surface density, {sigma}{sub sfr}, of the molecular dominated regions of 12 disk galaxies from Leroy et al. to test several star formation laws: a 'Kennicutt-Schmidt power law', {sigma}{sub sfr} = A{sub g} {sigma}{sup 1.5} {sub g,2}; a 'constant molecular law', {sigma}{sub sfr} = A {sub H2}{sigma}{sub H2,2}; the 'turbulence-regulated laws' of Krumholz and McKee (KM) and Krumholz, McKee, and Tumlinson (KMT), a 'gas-{omega} law', {sigma}{sub sfr} = B {sub {omega}}{sigma} {sub g}{omega}; and a shear-driven 'giant molecular cloud (GMC) collisions law', {sigma}{sub sfr} = B {sub CC}{sigma} {sub g}{omega}(1 - 0.7{beta}), where {beta} {identical_to} d ln v {sub circ}/d ln r. We find the constant molecular law, KMT turbulence law, and GMC collision law are the most accurate, with an rms error of a factor of 1.5 if the normalization constants are allowed to vary between galaxies. Of these three laws, the GMC collision law does not require a change in physics to account for the full range of star formation activity seen from normal galaxies to circumnuclear starbursts. A single global GMC collision law with B {sub CC} = 8.0 x 10{sup -3}, i.e., a gas consumption time of 20 orbital times for {beta} = 0, yields an rms error of a factor of 1.8.

  12. An Investigation of the Cold Interstellar Medium of the Outer Galaxy

    NASA Technical Reports Server (NTRS)

    Heyer, Mark H.

    1997-01-01

    The primary objective of this proposal was to determine the relationship between the molecular gas and dust components of the interstellar medium of the Outer Galaxy. It made use of the High Resolution IRAS Galaxy Atlas and the FCRAO CO Survey of the Outer Galaxy. These HIRES images greatly augment the spatial dynamic range of the IRAS Survey data and the ability to discriminate multiple point sources within a compact region. Additionally, the HIRES far infrared images allow for more direct comparisons with molecular line data observed at 45 sec resolution. From funding of this proposal, we have completed two papers for publication in a refereed journal.

  13. Measuring the Metallicity Gradient in the Outer Disk of the Milky Way

    NASA Astrophysics Data System (ADS)

    Bernard-Salas, Jeronimo; Guiles, Shannon; Houck, James R.; Morris, Patrick, W.; Pottasch, Stuart, R.

    2007-05-01

    It has been known for many years that there is an abundance gradient in the Galaxy. This has been verified by studies of HII regions, young stars and Cepheid variables. While the gradient is well characterised in the solar neighborhood its behavior is more uncertain in the bulge and in the anti-galactic center regions. For instance, results from HII regions indicate that the gradient in the outer part of the Galaxy decreases, but this is not supported from the works on early type stars, and Cepheid results suggest a flattened gradient in the solar vicinity. Planetary Nebulae (PNe) are ideal objects to solve these discrepancies because their abundances can be accurately determined. Certain elements, like sulfur, neon and argon are neither produced nor destroyed in the course of evolution of low- and intermediate-mass stars and therefore represent the composition at the time of star formation. These elements emit many lines in the infrared part of the electromagnetic spectrum and thus, infrared observations are essential to derive their abundances. Infrared observations of PNe have recently been used by Pottasch & Bernard-Salas (2006) to study the Galactic gradient in the solar vicinity using data from the Infrared Space Observatory (ISO). The gradient found reproduces exactly the solar metallicity at 8kpc. The enhanced sensitivity of Spitzer enables one to extend this study to the outer regions of the Galaxy. The study of bulge PNe using the IRS instrument on board Spitzer is the subject of an earlier proposal. With the present proposal we want to study a selection of 24 PNe in the outer part of the Galaxy to fully characterise the gradient in the Galaxy. In addition, we include in this proposal observations of four (extended) PNe. These four PNe have well known distances and will anchor these relations.

  14. Increased H2CO production in the outer disk around HD 163296

    NASA Astrophysics Data System (ADS)

    Carney, M. T.; Hogerheijde, M. R.; Loomis, R. A.; Salinas, V. N.; Öberg, K. I.; Qi, C.; Wilner, D. J.

    2017-09-01

    Context. The gas and dust in circumstellar disks provide the raw materials to form planets. The study of organic molecules and their building blocks in such disks offers insight into the origin of the prebiotic environment of terrestrial planets. Aims: We aim to determine the distribution of formaldehyde, H2CO, in the disk around HD 163296 to assess the contribution of gas- and solid-phase formation routes of this simple organic. Methods: Three formaldehyde lines were observed (H2CO 303-202, H2CO 322-221, and H2CO 321-220) in the protoplanetary disk around the Herbig Ae star HD 163296 with ALMA at 0.5″ (60 AU) spatial resolution. Different parameterizations of the H2CO abundance were compared to the observed visibilities, using either a characteristic temperature, a characteristic radius or a radial power law index to describe the H2CO chemistry. Similar models were applied to ALMA Science Verification data of C18O. In each scenario, χ2 minimization on the visibilities was used to determine the best-fit model in each scenario. Results: H2CO 303-202 was readily detected via imaging, while the weaker H2CO 322-221 and H2CO 321-220 lines required matched filter analysis to detect. H2CO is present throughout most of the gaseous disk, extending out to 550 AU. An apparent 50 AU inner radius of the H2CO emission is likely caused by an optically thick dust continuum. The H2CO radial intensity profile shows a peak at 100 AU and a secondary bump at 300 AU, suggesting increased production in the outer disk. In all modeling scenarios, fits to the H2CO data show an increased abundance in the outer disk. The overall best-fit H2CO model shows a factor of two enhancement beyond a radius of 270 ± 20 AU, with an inner abundance (relative to H2) of 2 - 5 × 10-12. The H2CO emitting region has a lower limit on the kinetic temperature of T> 20 K. The C18O modeling suggests an order of magnitude depletion of C18O in the outer disk and an abundance of 4 - 12 × 10-8 in the inner disk

  15. A High-Velocity Collision With Our Galaxy's Disk

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-08-01

    What caused the newly discovered supershell in the outskirts of our galaxy? A new study finds evidence that a high-velocity cloud may have smashed into the Milky Ways disk millions of years ago.Mysterious Gas ShellsA single velocity-channel map of the supershell GS040.2+00.670, with red contours marking the high-velocity cloud at its center. [Adapted from Park et al. 2016]The neutral hydrogen gas that fills interstellar space is organized into structures like filaments, loops, and shells. Supershells are enormous shells of hydrogen gas that can have radii of a thousand light-years or more; weve spotted about 20 of these in our own galaxy, and more in nearby dwarfs and spiral galaxies.How do these structures form? One theory is that they result from several supernovae explosions occurring in the same area. But the energy needed to create a supershell is more than 3 x 1052 erg, which corresponds to over 30 supernovae quite a lot to have exploding in the same region.Theres an interesting alternative scenario: the supershells might instead be caused by the impacts of high-velocity clouds that fall into the galactic disk.Velocity data for the compact high-velocity cloud CHVC040. The cloud is moving fast enough to create the supershell observed. [Adapted from Park et al. 2016]The Milky Ways Speeding CloudsHigh-velocity clouds are clouds of mostly hydrogen that speed through the Milky Way with radial velocities that are very different from the material in the galactic disk. The origins of these clouds are unknown, but its proposed that they come from outside the galaxy they might be fragments of a nearby, disrupting galaxy, or they might have originated from flows of accreting gas in the space in between galaxies.Though high-velocity clouds have long been on the list of things that might cause supershells, weve yet to find conclusive evidence of this. But that might have just changed, with a recent discovery by a team of scientists led by Geumsook Park (Seoul National

  16. The spectacular 200 kpc-wide disk of the Malin 1 giant low surface brightness galaxy

    NASA Astrophysics Data System (ADS)

    Boissier, Samuel

    2017-03-01

    Malin 1 is the best example among giant low surface brightness galaxies. New observations of this object in 6 broad-bands allow us for the first time to perform a pan-chromatic study of the stellar population in its 200 kpc wide disk. We observe a spiral structure revealing a star forming disk. The colors indicate a long history with a low efficiency of star formation. It is well reproduced by a model of disk galaxy making it similar to the disk of the Milky Way or other nearby spirals, except for its extremely large angular momentum.

  17. Near-infrared structure of fast and slow-rotating disk galaxies

    SciTech Connect

    Schechtman-Rook, Andrew; Bershady, Matthew A.

    2014-11-10

    We investigate the stellar disk structure of six nearby edge-on spiral galaxies using high-resolution JHK {sub s}-band images and three-dimensional radiative transfer models. To explore how mass and environment shape spiral disks, we selected galaxies with rotational velocities between 69 km s{sup –1} disk structure. Of the fast-rotating (V {sub rot} > 150 km s{sup –1}) galaxies, only NGC 4013 has the super-thin+thin+thick nested disk structure seen in NGC 891 and the Milky Way, albeit with decreased oblateness, while NGC 1055, a disturbed massive spiral galaxy, contains disks with h{sub z} ≲ 200 pc. NGC 4565, another fast-rotator, contains a prominent ring at a radius ∼5 kpc but no super-thin disk. Despite these differences, all fast-rotating galaxies in our sample have inner truncations in at least one of their disks. These truncations lead to Freeman Type II profiles when projected face-on. Slow-rotating galaxies are less complex, lacking inner disk truncations and requiring fewer disk components to reproduce their light distributions. Super-thin disk components in undisturbed disks contribute ∼25% of the total K {sub s}-band light, up to that of the thin-disk contribution. The presence of super-thin disks correlates with infrared flux ratios; galaxies with super-thin disks have f{sub K{sub s}}/f{sub 60} {sub μm}≤0.12 for integrated light, consistent with super-thin disks being regions of ongoing star-formation. Attenuation-corrected vertical color gradients in (J – K {sub s}) correlate with the observed disk structure and are consistent with population gradients with young-to-intermediate ages closer to the mid-plane, indicating that disk heating—or cooling—is a ubiquitous phenomenon.

  18. 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.

  19. MOLECULAR GAS AND STAR FORMATION IN NEARBY DISK GALAXIES

    SciTech Connect

    Leroy, Adam K.; Munoz-Mateos, Juan-Carlos; Walter, Fabian; Sandstrom, Karin; Meidt, Sharon; Rix, Hans-Walter; Schinnerer, Eva; Schruba, Andreas; Bigiel, Frank; Bolatto, Alberto; Brinks, Elias; De Blok, W. J. G.; Rosolowsky, Erik; Schuster, Karl-Friedrich; Usero, Antonio

    2013-08-01

    We compare molecular gas traced by {sup 12}CO (2-1) maps from the HERACLES survey, with tracers of the recent star formation rate (SFR) across 30 nearby disk galaxies. We demonstrate a first-order linear correspondence between {Sigma}{sub mol} and {Sigma}{sub SFR} but also find important second-order systematic variations in the apparent molecular gas depletion time, {tau}{sub dep}{sup mol}={Sigma}{sub mol}/{Sigma}{sub SFR}. At the 1 kpc common resolution of HERACLES, CO emission correlates closely with many tracers of the recent SFR. Weighting each line of sight equally, using a fixed {alpha}{sub CO} equivalent to the Milky Way value, our data yield a molecular gas depletion time, {tau}{sub dep}{sup mol}={Sigma}{sub mol}/{Sigma}{sub SFR}{approx}2.2 Gyr with 0.3 dex 1{sigma} scatter, in very good agreement with recent literature data. We apply a forward-modeling approach to constrain the power-law index, N, that relates the SFR surface density and the molecular gas surface density, {Sigma}{sub SFR}{proportional_to}{Sigma}{sub mol}{sup N}. We find N = 1 {+-} 0.15 for our full data set with some scatter from galaxy to galaxy. This also agrees with recent work, but we caution that a power-law treatment oversimplifies the topic given that we observe correlations between {tau}{sub dep}{sup mol} and other local and global quantities. The strongest of these are a decreased {tau}{sub dep}{sup mol} in low-mass, low-metallicity galaxies and a correlation of the kpc-scale {tau}{sub dep}{sup mol} with dust-to-gas ratio, D/G. These correlations can be explained by a CO-to-H{sub 2} conversion factor ({alpha}{sub CO}) that depends on dust shielding, and thus D/G, in the theoretically expected way. This is not a unique interpretation, but external evidence of conversion factor variations makes this the most conservative explanation of the strongest observed {tau}{sub dep}{sup mol} trends. After applying a D/G-dependent {alpha}{sub CO}, some weak correlations between {tau}{sub dep

  20. Extragalactic SETI: The Tully-Fisher Relation as a Probe of Dysonian Astroengineering in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Zackrisson, Erik; Calissendorff, Per; Asadi, Saghar; Nyholm, Anders

    2015-09-01

    If advanced extraterrestrial civilizations choose to construct vast numbers of Dyson spheres to harvest radiation energy, this could affect the characteristics of their host galaxies. Potential signatures of such astroengineering projects include reduced optical luminosity, boosted infrared luminosity, and morphological anomalies. Here, we apply a technique pioneered by Annis to search for Kardashev type III civilizations in disk galaxies, based on the predicted offset of these galaxies from the optical Tully-Fisher (TF) relation. By analyzing a sample of 1359 disk galaxies, we are able to set a conservative upper limit of ≲ 3% on the fraction of local disks subject to Dysonian astroengineering on galaxy-wide scales. However, the available data suggests that a small subset of disk galaxies actually may be underluminous with respect to the TF relation in the way expected for Kardashev type III objects. Based on the optical morphologies and infrared-to-optical luminosity ratios of such galaxies in our sample, we conclude that none of them stand out as strong Kardashev type III candidates and that their inferred properties likely have mundane explanations. This allows us to set a tentative upper limit at ≲ 0.3% on the fraction of Karashev type III disk galaxies in the local universe.

  1. Supermassive black holes do not correlate with galaxy disks or pseudobulges.

    PubMed

    Kormendy, John; Bender, R; Cornell, M E

    2011-01-20

    The masses of supermassive black holes are known to correlate with the properties of the bulge components of their host galaxies. In contrast, they seem not to correlate with galaxy disks. Disk-grown 'pseudobulges' are intermediate in properties between bulges and disks; it has been unclear whether they do or do not correlate with black holes in the same way that bulges do. At stake in this issue are conclusions about which parts of galaxies coevolve with black holes, possibly by being regulated by energy feedback from black holes. Here we report pseudobulge classifications for galaxies with dynamically detected black holes and combine them with recent measurements of velocity dispersions in the biggest bulgeless galaxies. These data confirm that black holes do not correlate with disks and show that they correlate little or not at all with pseudobulges. We suggest that there are two different modes of black-hole feeding. Black holes in bulges grow rapidly to high masses when mergers drive gas infall that feeds quasar-like events. In contrast, small black holes in bulgeless galaxies and in galaxies with pseudobulges grow as low-level Seyfert galaxies. Growth of the former is driven by global processes, so the biggest black holes coevolve with bulges, but growth of the latter is driven locally and stochastically, and they do not coevolve with disks and pseudobulges.

  2. The Stability Of Disk Barred Galaxies Over the Past 7 Billion Years

    NASA Astrophysics Data System (ADS)

    Tapia, Amauri; Simmons, Brooke

    2017-01-01

    A recently released model of interacting disk galaxies provides a hypothesis for the origins of off center bars in disks. No systematic search for offset bars in the early universe has yet been undertaken. The Galaxy Zoo project has produced data regarding the large-scale bars of many galaxies. Using this data alongside images collected by the Hubble Space Telescope and other sources, we have examined 5190 galaxies for signatures of off-centered bars. Less than 5 percent of the sample shows clear signs of an offset bar. We describe their overall properties of this sub-sample and compare the properties of galaxies with offset bars to those with centered bars. We assess the feasibility of the proposed model and place these galaxies in the context of the overall evolution of galaxies.

  3. A barrier to lateral diffusion of porphyropsin in Necturus rod outer segment disks.

    PubMed Central

    Drzymala, R E; Weiner, H L; Dearry, C A; Liebman, P A

    1984-01-01

    Microspectrophotometry was used to study lateral diffusion of the visual pigment, porphyropsin , in the disk membrane in intact mudpuppy (Necturus maculosus) rod outer segments (ROS), isolated in frog Ringer's solution. A concentration gradient of unbleached visual pigment was produced on the disks by rapidly photobleaching 40% of the pigment in an area spanning 1/4 or 1/2 of the cell's width. The change in optical density of the cells at 580 nm was then followed with time on either the bleached or unbleached side. The temperature dependence of porphyropsin diffusion yielded a Q10 of 2.5 between 10 and 20 degrees C with an activation energy of 12 +/- 2 kcal. At completion of pigment diffusion, the center and edge of the disk had, respectively, attained only 90 and 55% of the concentration expected. Computed diffusion coefficients (5.4 X 10(-9) cm2/s) were similar at the center and periphery of the disk immediately after the flash, however, an additional slow component for diffusion was detected at the periphery. A comparison of optical density at 525 nm along the diameter of ROS before and after the flash showed a persistent (20 min) postbleach concentration gradient of unbleached porphyropsin . This suggests that 15% of the prophyropsins may be sequestered into distinct areas on a mudpuppy disk and are not free to diffuse over the whole surface. This argument is supported by the observation that mudpuppy disks are separated into petal -shaped regions by incisures, some of which penetrate nearly to the disk center. Images FIGURE 7 FIGURE 8 PMID:6722262

  4. The structure of the stellar disks of southern S0 galaxies in sparse environments

    NASA Astrophysics Data System (ADS)

    Sil'chenko, O. K.; Kniazev, A. Yu.; Chudakova, E. M.

    2016-01-01

    Surface photometry data are presented for 12 southern lenticular galaxies located in regions of low density. Digital images in the gri bands were obtained on the LCOGT network of meter-class telescopes. Structural parameters of the global stellar disks of the galaxies are calculated—the exponential scale and relative thickness. The presence of substructure in the disks is noted; in particular, more than half the studied galaxies possess ring structures, sometimes more than one. The color maps presented indicate complex evolution of the substructure of the disks of lenticular galaxies: they can be classified as blue (ongoing star formation) or red (concentration of dust). The rings do not always lie in the main plane of the disk; there are cases of clearly inclined, or even polar, compact rings.

  5. Self-regulating galaxy formation. Part 1: HII disk and Lyman alpha pressure

    NASA Technical Reports Server (NTRS)

    Cox, D. P.

    1983-01-01

    Assuming a simple but physically based prototype for behavior of interstellar material during formation of a disk galaxy, coupled with the lowest order description of infall, a scenario is developed for self-regulated disk galaxy formation. Radiation pressure, particularly that of Lyman depha (from fluorescence conversion Lyman continuum), is an essential component, maintaining an inflated disk and stopping infall when only a small fraction of the overall perturbation has joined the disk. The resulting galaxies consist of a two dimensional family whose typical scales and surface density are expressable in terms of fundamental constants. The model leads naturally to galaxies with a rich circumgalactic environment and flat rotation curves (but is weak in its analysis of the subsequent evolution of halo material).

  6. The faint outer regions of the Pegasus dwarf irregular galaxy: a much larger and undisturbed galaxy

    NASA Astrophysics Data System (ADS)

    Kniazev, Alexei Y.; Brosch, Noah; Hoffman, G. Lyle; Grebel, Eva K.; Zucker, Daniel B.; Pustilnik, Simon A.

    2009-12-01

    We investigate the spatial extent and structure of the Pegasus dwarf irregular galaxy (PegDIG) using deep, wide-field, multicolour CCD photometry from the Sloan Digital Sky Survey (SDSS) and new deep HI observations. We study an area of ~0.6 deg2 centred on the Pegasus dwarf that was imaged by the SDSS. Using effective filtering in colour-magnitude space, we reduce the contamination by foreground Galactic field stars and significantly increase the contrast in the outer regions of the Pegasus dwarf. Our extended surface photometry reaches down to a surface brightness magnitude μr ~= 32 mag arcsec-2. It reveals a stellar body with a diameter of ~8 kpc that follows a Sérsic surface brightness distribution law, which is composed of a significantly older stellar population than that observed in the ~2 kpc main body. The galaxy is at least five times more extended than listed in the NASA/IPAC Extragalactic Database. The faint extensions of the galaxy are not equally distributed around its circumference; the north-west end is more jagged than the south-east end. We also identified a number of stellar concentrations, possibly stellar associations, arranged in a ring around the main luminous body. New HI observations were collected at the Arecibo Observatory as part of the Arecibo Legacy Fast ALFA survey. They reveal an HI distribution somewhat elongated in RA and about wide, with the region of highest column density coincident with the luminous galaxy. The HI rotation curve shows a solid-body rotation behaviour, with opposite ends differing by 15 kms-1. There is a stream to lower velocities about 5 arcmin from the centre of the galaxy. We were able to measure ugriz colours in a number of apertures using the SDSS data and compared these with predictions of evolutionary synthesis models. The results indicate that the outermost regions of the PegDIG are 5-10 Gyr old, while the inner kpc contains stars ~1 Gyr old and younger. The colours correspond to K stars; earlier

  7. MCMC Analysis of biases in the interpretation of disk galaxy kinematics

    NASA Astrophysics Data System (ADS)

    Aquino-Ortíz, E.; Valenzuela, O.; Cano-Díaz, M.; Sánchez-Sánchez, S. F.; Hernández-Toledo, H.

    2016-06-01

    The new generation of galaxy surveys like SAMI, CALIFA and MaNGA opens up the possibility of studying simultaneously properties of galaxies such as spiral arms, bars, disk geometry and orientation, stellar and gas mass distribution, 2D kinematics, etc. The previous task involves exploring a complicated multi-dimensional parameter space. Puglielli et al. (2010) introduced Bayesian statistics and MCMC (Monte Carlo Markov Chain) techniques to construct dynamical models of spiral galaxies. In our study we used synthetic velocity fields that include non-circular motions and assume different disk orientations in order to produce mock observations. We apply popular reconstruction techniques in order to estimate the geometrical disk parameters, systemic velocities, rotation curve shape and maximum circular velocity which are crucial to construct the scaling relations. We conclude that a detailed analysis of kinematics in galaxies using MCMC technique will be reflected in accurate estimations of galaxy properties and more robust scalings relations, otherwise physical conclusions may be importantly biased.

  8. HALO ORBITS IN COSMOLOGICAL DISK GALAXIES: TRACERS OF FORMATION HISTORY

    SciTech Connect

    Valluri, Monica; Debattista, Victor P.; Stinson, Gregory S.; Bailin, Jeremy; Quinn, Thomas R.; Couchman, H. M. P.; Wadsley, James

    2013-04-10

    We analyze the orbits of stars and dark matter particles in the halo of a disk galaxy formed in a cosmological hydrodynamical simulation. The halo is oblate within the inner {approx}20 kpc and triaxial beyond this radius. About 43% of orbits are short axis tubes-the rest belong to orbit families that characterize triaxial potentials (boxes, long-axis tubes and chaotic orbits), but their shapes are close to axisymmetric. We find no evidence that the self-consistent distribution function of the nearly oblate inner halo is comprised primarily of axisymmetric short-axis tube orbits. Orbits of all families and both types of particles are highly eccentric, with mean eccentricity {approx}> 0.6. We find that randomly selected samples of halo stars show no substructure in 'integrals of motion' space. However, individual accretion events can clearly be identified in plots of metallicity versus formation time. Dynamically young tidal debris is found primarily on a single type of orbit. However, stars associated with older satellites become chaotically mixed during the formation process (possibly due to scattering by the central bulge and disk, and baryonic processes), and appear on all four types of orbits. We find that the tidal debris in cosmological hydrodynamical simulations experiences significantly more chaotic evolution than in collisionless simulations, making it much harder to identify individual progenitors using phase space coordinates alone. However, by combining information on stellar ages and chemical abundances with the orbital properties of halo stars in the underlying self-consistent potential, the identification of progenitors is likely to be possible.

  9. Detailed Structure of the Outer Disk Around HD 169142 with Polarized Light in H-band

    NASA Technical Reports Server (NTRS)

    Momose, Munetake; Morita, Ayaka; Fukagawa, Misato; Muto, Takayuki; Takeuchi, Taku; Hashimoto, Jun; Honda, Mitsuhiko; Kudo, Tomoyuki; Okamoto, Yoshiko K.; Kanagawa, Kazuhiro D.; Tanaka, Hidekazu; Grady, Carol A.; Sitko, Michael L.; Akiyama, Eiji; Currie, Thayne; Follette, Katherine B.; Mayama, Satoshi; Kusakabe, Nobuhiko; Abe, Lyu; Brandner, Wolfgang; Brandt, Timothy D.; Carson, Joseph C.; Egner, Sebastian; Feldt, Markus; McElwain, Michael W.

    2015-01-01

    Coronagraphic imagery of the circumstellar disk around HD 169142 in H-band polarized intensity (PI) with Subaru/HiCIAO is presented. The emission scattered by dust particles at the disk surface in 0.''2=r=1.''2, or 29=r=174 AU, is successfully detected. The azimuthally-averaged radial profile of the PI shows a double power-law distribution, in which the PIs in r = 29-52 AU and r = 81.2-145 AU respectively show r-3-dependence. These two power-law regions are connected smoothly with a transition zone (TZ), exhibiting an apparent gap in r = 40-70 AU. The PI in the inner power-law region shows a deep minimum whose location seems to coincide with the point source at lambda = 7 mm. This can be regarded as another sign of a protoplanet in TZ. The observed radial profile of the PI is reproduced by a minimally flaring disk with an irregular surface density distribution or with an irregular temperature distribution or with the combination of both. The depletion factor of surface density in the inner power-law region (r <50 AU) is derived to be =0.16 from a simple model calculation. The obtained PI image also shows small scale asymmetries in the outer power-law region. Possible origins for these asymmetries include corrugation of the scattering surface in the outer region, and shadowing effect by a puffed up structure in the inner power-law region.

  10. THICK DISKS OF EDGE-ON GALAXIES SEEN THROUGH THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S{sup 4}G): LAIR OF MISSING BARYONS?

    SciTech Connect

    Comeron, Sebastien; Elmegreen, Bruce G.; Knapen, Johan H.; Salo, Heikki; Laine, Jarkko; Laurikainen, Eija; Athanassoula, E.; Bosma, Albert; Hinz, Joannah L.; De Paz, Armando Gil; Menendez-Delmestre, KarIn; Seibert, Mark; Ho, Luis C.; Elmegreen, Debra M.; Gadotti, Dimitri A.

    2011-11-01

    Most, if not all, disk galaxies have a thin (classical) disk and a thick disk. In most models thick disks are thought to be a necessary consequence of the disk formation and/or evolution of the galaxy. We present the results of a study of the thick disk properties in a sample of carefully selected edge-on galaxies with types ranging from T = 3 to T = 8. We fitted one-dimensional luminosity profiles with physically motivated functions-the solutions of two stellar and one gaseous isothermal coupled disks in equilibrium-which are likely to yield more accurate results than other functions used in previous studies. The images used for the fits come from the Spitzer Survey of Stellar Structure in Galaxies (S{sup 4}G). We found that thick disks are on average more massive than previously reported, mostly due to the selected fitting function. Typically, the thin and thick disks have similar masses. We also found that thick disks do not flare significantly within the observed range in galactocentric radii and that the ratio of thick-to-thin disk scale heights is higher for galaxies of earlier types. Our results tend to favor an in situ origin for most of the stars in the thick disk. In addition, the thick disk may contain a significant amount of stars coming from satellites accreted after the initial buildup of the galaxy and an extra fraction of stars coming from the secular heating of the thin disk by its own overdensities. Assigning thick disk light to the thin disk component may lead to an underestimate of the overall stellar mass in galaxies because of different mass-to-light ratios in the two disk components. On the basis of our new results, we estimate that disk stellar masses are between 10% and 50% higher than previously thought and we suggest that thick disks are a reservoir of 'local missing baryons'.

  11. Discovery of Giant X-Ray Disk Sheds Light on Elliptical Galaxies

    NASA Astrophysics Data System (ADS)

    2002-12-01

    Ohio University astronomers have discovered the largest disk of hot, X-ray emitting gas ever observed in the universe: At 90,000 light years in diameter, it's about 100,000 times the size of any comparable object. The disk, spinning through a distant galaxy, is more than just an interstellar oddity, the researchers say. The object could offer new information about the way certain galaxies form and evolve. About 20 percent of all galaxies are elliptical, the largest of the three types of galaxies in the universe. They differ from spiral galaxies like the Milky Way, as they lack new stars and spiral "arms." Scientists once believed that elliptical galaxies were ancient, simple systems that contained only old stars and formed in the early days of the universe. But new research suggests elliptical galaxies are more complex and dynamic. "It used to be thought that galaxies form and then sit there and age quietly over time. But now we understand that galaxies live, in the sense that there's an interplay of gas and stars," said Thomas Statler, an associate professor of physics and astronomy and lead author of the study, published in the Dec. 20 issue of the Astrophysical Journal. The newly discovered X-ray disk offers more evidence for that argument. Using NASA's Chandra X-ray Observatory, an orbiting spacecraft that houses the most powerful X-ray telescope in existence, the astronomers discovered the disk while analyzing data collected from NGC 1700, a young elliptical galaxy about 160 million light years from Earth. Giant in size and about 8 million degrees in temperature, the disk was an unexpected find for Statler and colleague Brian McNamara. But while its gargantuan scale is striking, the disk also yielded another surprise: The hot gas is not in calm balance with the gravitational forces as expected, but spinning through the galaxy. In fact, the giant, rotating X-ray disk suggests that this elliptical galaxy and perhaps others like it wasn't created by the merger of

  12. SUSTAINING STAR FORMATION RATES IN SPIRAL GALAXIES: SUPERNOVA-DRIVEN TURBULENT ACCRETION DISK MODELS APPLIED TO THINGS GALAXIES

    SciTech Connect

    Vollmer, Bernd; Leroy, Adam K.

    2011-01-15

    Gas disks of spiral galaxies can be described as clumpy accretion disks without a coupling of viscosity to the actual thermal state of the gas. The model description of a turbulent disk consisting of emerging and spreading clumps contains free parameters, which can be constrained by observations of molecular gas, atomic gas, and the star formation rate for individual galaxies. Radial profiles of 18 nearby spiral galaxies from THINGS, HERACLES, SINGS, and GALEX data are used to compare the observed star formation efficiency, molecular fraction, and velocity dispersion to the model. The observed radially decreasing velocity dispersion can be reproduced by the model. In the framework of this model, the decrease in the inner disk is due to the stellar mass distribution which dominates the gravitational potential. Introducing a radial break in the star formation efficiency into the model improves the fits significantly. This change in the star formation regime is realized by replacing the free-fall time in the prescription of the star formation rate with the molecule formation timescale. Depending on the star formation prescription, the break radius is located near the transition region between the molecular-gas-dominated and atomic-gas-dominated parts of the galactic disk or closer to the optical radius. It is found that only less massive galaxies (log M(M{sub sun}) {approx}< 10) can balance gas loss via star formation by radial gas accretion within the disk. These galaxies can thus access their gas reservoirs with large angular momentum. On the other hand, the star formation of massive galaxies is determined by the external gas mass accretion rate from a putative spherical halo of ionized gas or from satellite accretion. In the absence of this external accretion, star formation slowly exhausts the gas within the optical disk within the star formation timescale.

  13. WITNESSING THE DIFFERENTIAL EVOLUTION OF DISK GALAXIES IN LUMINOSITY AND SIZE VIA GRAVITATIONAL LENSING

    SciTech Connect

    Bandara, Kaushala; Crampton, David; Peng, Chien; Simard, Luc

    2013-11-01

    We take advantage of the magnification in size and flux of a galaxy provided by gravitational lensing to analyze the properties of 62 strongly lensed galaxies from the Sloan Lens ACS (SLACS) Survey. The sample of lensed galaxies spans a redshift range of 0.20 ≤ z ≤ 1.20 with a median redshift of z = 0.61. We use the lens modeling code LENSFIT to derive the luminosities, sizes, and Sérsic indices of the lensed galaxies. The measured properties of the lensed galaxies show a primarily compact, {sup d}isk{sup -}like population with the peaks of the size and Sérsic index distributions corresponding to ∼1.50 kpc and n ∼ 1, respectively. Comparison of the SLACS galaxies to a non-lensing, broadband imaging survey shows that a lensing survey allows us to probe a galaxy population that reaches ∼2 mag fainter. Our analysis allows us to compare the (z) = 0.61 disk galaxy sample (n ≤ 2.5) to an unprecedented local galaxy sample of ∼670, 000 SDSS galaxies at z ∼ 0.1; this analysis indicates that the evolution of the luminosity-size relation since z ∼ 1 may not be fully explained by a pure-size or pure-luminosity evolution but may instead require a combination of both. Our observations are also in agreement with recent numerical simulations of disk galaxies that show evidence of a mass-dependent evolution since z ∼ 1, where high-mass disk galaxies (M{sub *} > 10{sup 9} M{sub ☉}) evolve more in size and low-mass disk galaxies (M{sub *} ≤ 10{sup 9} M{sub ☉}) evolve more in luminosity.

  14. Self-regulating galaxy formation. I - H II disk and Lyman-alpha pressure

    NASA Technical Reports Server (NTRS)

    Cox, D. P.

    1985-01-01

    The nascent interstellar medium and star formation model are incorporated into a scenario for the formation epoch of spiral galaxies. The structure, star formation time scale, and luminosity of a self-gravitating isothermal disk are evaluated as functions of the disk surface density. The importance of radiation pressure, particularly that of Lyman-alpha, in maintaining an inflated disk and halting infall is discussed. The Lyman-alpha pressure also supports a considerable halo of material in the vicinity of the disk. A first-order infall scenario and the time-dependent properties of the system it constructs are presented. Disk properties are evaluated at the epoch at which further material is supportable against infall by Lyman-alpha pressure. The two-dimensional family of disk galaxies whose scales and surface density are expressible in terms of fundamental constants and which arise from the three parameter sets of perturbations in the Hubble flow are determined.

  15. Catalytic properties of the retinal rod outer segment disk ADP-ribosyl cyclase.

    PubMed

    Fabiano, Andrea; Panfoli, Isabella; Calzia, Daniela; Bruschi, Maurizio; Ravera, Silvia; Bachi, Angela; Cattaneo, Angela; Morelli, Alessandro; Candiano, Giovanni

    2011-03-01

    Cyclic ADP-ribose (cADPR) is a second messenger modulating intracellular calcium levels. We have previously described a cADPR-dependent calcium signaling pathway in bovine rod outer segments (ROS), where calcium ions play a pivotal role. ROS ADP-ribosyl cyclase (ADPR-cyclase) was localized in the membrane fraction. In the present work, we examined the properties of the disk ADPR-cyclase through the production of cyclic GDP-ribose from the NAD(+) analogue NGD(+). The enzyme displayed an estimated K(m) for NGD(+) of 12.5 ± 0.3 μM, a V(max) of 26.50 ± 0.70 pmol cyclic GDP-ribose synthesized/min/mg, and optimal pH of 6.5. The effect of divalent cations (Zn(2+), Cu(2+), and Ca(2+)) was also tested. Micromolar Zn(2+) and Cu(2+) inhibited the disk ADPR-cyclase activity (half maximal inhibitory concentration, IC50=1.1 and 3.6 μM, respectively). By contrast, Ca(2+) ions had no effect. Interestingly, the properties of the intracellular membrane-associated ROS disk ADPR-cyclase are more similar to those of the ADPR-cyclase found in CD38-deficient mouse brain, than to those of CD38 or CD157. The novel intracellular mammalian ADPR-cyclase would elicit Ca(2+) release from the disks at various rates in response to change in free Ca(2+) concentrations, caused by light versus dark adaptation, in fact there was no difference in disk ADPR-cyclase activity in light or dark conditions. Data suggest that disk ADPR-cyclase may be a potential target of retinal toxicity of Zn(2+) and may shed light to the role of Cu(2+) and Zn(2+) deficiency in retina. Copyright © Cambridge University Press, 2011

  16. Galactic Behavior for the Outer B Ring

    NASA Image and Video Library

    2010-11-01

    Keeping a close watch on the outer portion of Saturn B ring, NASA Cassini spacecraft records the complex inward and outward movement of the edge of the ring. This ring movement resembles the suspected behavior of spiral disk galaxies.

  17. Galactic Structure in the Outer Disk: The Field in the Line of Sight to the Intermediate-age Open Cluster Tombaugh 1

    NASA Astrophysics Data System (ADS)

    Carraro, Giovanni; Sales Silva, Joao Victor; Moni Bidin, Christian; Vazquez, Ruben A.

    2017-03-01

    We employ optical photometry and high-resolution spectroscopy to study a field toward the open cluster Tombaugh 1, where we identify a complex population mixture that we describe in terms of young and old Galactic thin disks. Of particular interest is the spatial distribution of the young population, which consists of dwarfs with spectral types as early as B6 and is distributed in a blue plume feature in the color–magnitude diagram. For the first time, we confirm spectroscopically that most of these stars are early-type stars and not blue stragglers or halo/thick-disk subdwarfs. Moreover, they are not evenly distributed along the line of sight but crowd at heliocentric distances between 6.6 and 8.2 kpc. We compare these results with present-day understanding of the spiral structure of the Galaxy and suggest that they trace the outer arm. This range of distances challenges current Galactic models adopting a disk cutoff at 14 kpc from the Galactic center. The young dwarfs overlap in space with an older component, which is identified as an old Galactic thin disk. Both young and old populations are confined in space since the disk is warped at the latitude and longitude of Tombaugh 1. The main effects of the warp are that the line of sight intersects the disk and entirely crosses it at the outer arm distance and that there are no traces of the closer Perseus arm, which would then be either unimportant in this sector or located much closer to the formal Galactic plane. Finally, we analyze a group of giant stars, which turn out to be located at very different distances and to possess very different chemical properties, with no obvious relation to the other populations. Based on observations carried out at Las Campanas Observatory, Chile (program ID CN009B-042), and Cerro Tololo Inter-American Observatory.

  18. Why do disk galaxies present a common gas-phase metallicity gradient?

    NASA Astrophysics Data System (ADS)

    Chang, R.; Zhang, Shuhui; Shen, Shiyin; Yin, Jun; Hou, Jinliang

    2017-03-01

    CALIFA data show that isolated disk galaxies present a common gas-phase metallicity gradient, with a characteristic slope of -0.1dex/re between 0.3 and 2 disk effective radius re (Sanchez et al. 2014). Here we construct a simple model to investigate which processes regulate the formation and evolution.

  19. The dynamical settling of warped disks and angular momentum transport in galaxies

    NASA Technical Reports Server (NTRS)

    Fisher, P.

    1994-01-01

    We present results of three-dimensional, hydrodynamic models of gaseous disks settling in a nonspherical potential. As the gas settles, differential precession creates a warped disk similar to the warps seen in spiral galaxies. A logarithmic potential, indicative of a massive halo, seems to induce warps more extreme than those produced by a l/r potential with a quadrupole distortion.

  20. Disk and Halo Globular Clusters in the Edge-On Spiral Galaxy NGC 5170

    NASA Astrophysics Data System (ADS)

    Van Der Kruit, Pieter

    1991-07-01

    The system of globular clusters of our Galaxy is known to consist of two sub-systems, the disk and halo sub-systems. The halo sub-system has metal-poor globular clusters, is at most moderately flattened and and is slowly rotating. Ths disk sub-system has more metal-rich globulars, is much flatter and has significant rotation. The latter resembles the ``thick disk' of Gilmore and Wyse. These sub-systems relate to different phases in the formation of the Galaxy; the halo sub-system to the very early phases of Population II formation and the disk-system probably to a stage much later related to disk formation or satellite capture. The structure of the globular cluster system thus contains much information about disk galaxy formation. In this project we will determine how common this phenomenon is. By mapping with WPC the distribution in an edge-on spiral we can uniquely determine the spatial relation of any disk sub-system to the thin disk, which is not possible in our Galaxy or moderately inclined systems (e.g. M31). We will use colors to discriminate between the two sub-systems, since metallicity differences predict a color-index difference in our proposed system of at least 0.6 mag. We will make parallel observations with the FOC to search for outlying clusters and dwarf companions.

  1. The intricate Galaxy disk: velocity asymmetries in Gaia-TGAS

    NASA Astrophysics Data System (ADS)

    Antoja, T.; de Bruijne, J.; Figueras, F.; Mor, R.; Prusti, T.; Roca-Fàbrega, S.

    2017-06-01

    We use Gaia-TGAS data to compare the transverse velocities in Galactic longitude (coming from proper motions and parallaxes) in the Milky Way disk for negative and positive longitudes as a function of distance. The transverse velocities are strongly asymmetric and deviate significantly from the expectations for an axisymmetric galaxy. The value and sign of the asymmetry changes at spatial scales of several tens of degrees in Galactic longitude and about 0.5 kpc in distance. The asymmetry is statistically significant at 95% confidence level for 57% of the region probed, which extends up to 1.2 kpc. A percentage of 24% of the region shows absolute differences at this confidence level larger than 5 km s-1 and 7% larger than 10 km s-1. The asymmetry pattern shows mild variations in the vertical direction and with stellar type. A first qualitative comparison with spiral arm models indicates that the arms are probably not the main source of the asymmetry. We briefly discuss alternative origins. This is the first time that global all-sky asymmetries are detected in the Milky Way kinematics beyond the local neighbourhood and with a purely astrometric sample.

  2. N-body Simulation of Disk Galaxy Parameters -- Revisited

    NASA Astrophysics Data System (ADS)

    Comins, N. F.; Rivers, A. J.; Shorey, P.

    1993-05-01

    Although two dimensional N-body simulations of disk galaxies have been done for over thirty years, we feel that the interactions between various free parameters deserve further study. As a preliminary step in validating a computer code with collisionless particles representing star clusters, colliding particles representing giant molecular clouds, and a gravitating hydrodynamic component representing the intercloud medium, we study the effects of the number of particles (10k-400k), the softening of the gravitational potential (.25-1.0 cell widths), and the grid size (64(2) and 128(2) ) on the changes of Toomre's Q and the bar-mode (m=2) instability for the collisionless N-body component. We use a Cartesian grid with a time-centered leap frog integration scheme and a fast Fourier transform potential calculator. We find that the growth of Q and the bar mode depend sensitively on both N and the softening factor. We also find that as N increases, the amount of softening required to maintain cool systems decreases. Judicious selection of parameters can minimize growth rates of various instabilities, thereby increasing relaxation times.

  3. ABUNDANCES OF PLANETARY NEBULAE IN THE OUTER DISK OF M31

    SciTech Connect

    Kwitter, Karen B.; Lehman, Emma M. M.; Balick, Bruce; Henry, R. B. C. E-mail: emmalehman@gmail.com E-mail: rhenry@ou.edu

    2012-07-01

    We present spectroscopic observations and chemical abundances of 16 planetary nebulae (PNe) in the outer disk of M31. The [O III] {lambda}4363 line is detected in all objects, allowing a direct measurement of the nebular temperature essential for accurate abundance determinations. Our results show that the abundances in these M31 PNe display the same correlations and general behaviors as Type II PNe in the Milky Way. We also calculate photoionization models to derive estimates of central star properties. From these we infer that our sample PNe, all near the bright-end cutoff of the planetary nebula luminosity function, originated from stars near 2 M{sub Sun }. Finally, under the assumption that these PNe are located in M31's disk, we plot the oxygen abundance gradient, which appears shallower than the gradient in the Milky Way.

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

    NASA Astrophysics Data System (ADS)

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

    1992-12-01

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

  5. Herschel-Resolved Outer Belts of Two-Belt Debris Disks--Evidence of Icy Grains

    NASA Astrophysics Data System (ADS)

    Morales, Farisa Y.; Bryden, Geoffrey; Werner, Michael W.; Stapelfeldt, Karl

    2015-12-01

    We present dual-band Herschel/PACS imaging for 57 main sequence stars (42 A-type and 15 solar-type) with previously known warm dust (Twarm ~200K) detected and characterized by Spitzer. About half of the star-disk systems in our sample have spectral energy distributions (SEDs) that suggest two-ring disk architectures that mirror that of the asteroid-Kuiper belt geometry of our own solar system. The Herschel observations at 70 and/or 100 micron spatially resolve the cold/outer dust component for 18 two-belt debris systems (15 for the first time; 10 are also resolved at 160 micron), finding evidence of planetesimals at >100 AU, i.e. larger size than assumed from a simple blackbody fit to the SED. By breaking the degeneracy between the grain properties and the dust's radial location, the resolved images help constrain the grain size distribution and hint at the dust's composition for each system. Based on the combined Spitzer/IRS+MIPS (5 to 70 micron), the Herschel/PACS (70 and/or 100 and 160 micron) dataset, and under the assumption of idealized spherical grains, we find that the majority of resolved cold/outer belts of star+disk systems are well fit with a mixed ice/rock composition, rather than pure rocky grains. In the absence of spectral features for ice, we find that the behavior of the continuum can help constrain the composition of the grains well (of icy nature and not pure rocky material) given the Herschel-resolved locations of the cold/outer dust belts. We have also begin to identify the presence of candidate companions via Keck direct imaging, which may be interacting with the observed dust.

  6. THE 21 cm 'OUTER ARM' AND THE OUTER-GALAXY HIGH-VELOCITY CLOUDS: CONNECTED BY KINEMATICS, METALLICITY, AND DISTANCE

    SciTech Connect

    Tripp, Todd M.; Song Limin

    2012-02-20

    Using high-resolution ultraviolet spectra obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph and the Far Ultraviolet Spectroscopic Explorer, we study the metallicity, kinematics, and distance of the gaseous 'outer arm' (OA) and the high-velocity clouds (HVCs) in the outer Galaxy. We detect the OA in a variety of absorption lines toward two QSOs, H1821+643 and HS0624+6907. We search for OA absorption toward eight Galactic stars and detect it in one case, which constrains the OA Galactocentric radius to 9 kpc outer-Galaxy HVCs, including high velocities that are not consistent with Galactic rotation, suggests that the OA and outer-Galaxy HVCs could have a common origin.

  7. Distant encounters between disk galaxies and the origin of S 0 spirals

    NASA Astrophysics Data System (ADS)

    Icke, V.

    1985-03-01

    Numerical calculations of the hydrodynamics of a gaseous disk in a galaxy perturbed by an intruder flying in a hyperbolic orbit are presented. It is shown that if the pericenter of the distance between the galaxy and the intruder object becomes so large that stellar bridges and tails become unimportant, gravitational shocks may occur. It is suggested that the theoretical calculations may help explain the physical mechanisms of S 0 spiral galaxy formation. Computer-generated illustrations of the numerical results are provided.

  8. Variations in the Star Formation Efficiency of the Dense Molecular Gas across the Disks of Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Usero, Antonio; Leroy, Adam K.; Walter, Fabian; Schruba, Andreas; García-Burillo, Santiago; Sandstrom, Karin; Bigiel, Frank; Brinks, Elias; Kramer, Carsten; Rosolowsky, Erik; Schuster, Karl-Friedrich; de Blok, W. J. G.

    2015-10-01

    same parameters and is ˜6-8 times lower near galaxy centers than in the outer regions of the galaxy disks. For fixed conversion factors, these results are incompatible with a simple model in which star formation depends only on the amount of gas mass above some density threshold. Moreover, only a very specific set of environment-dependent conversion factors can render our observations compatible with such a model. Whole cloud models, such as the theory of turbulence regulated star formation, do a better job of matching our observations. We explore one such model in which variations in the Mach number drive many of the trends within galaxy disks, while density contrasts drive the differences between disk and merging galaxies. Based on observations with the IRAM 30 m telescope. IRAM is supported by CNRS/INSU (France), the MPG (Germany), and the IGN (Spain).

  9. Outskirts of spiral galaxies

    NASA Astrophysics Data System (ADS)

    Bresolin, Fabio

    2017-03-01

    I present an overview of the recent star formation activity in the outer disks of spiral galaxies, from the observational standpoint, with emphasis on the gas content, the star formation law, the metallicity and the stellar populations.

  10. A spatially-resolved study of initial mass function in the outer Galaxy

    NASA Astrophysics Data System (ADS)

    Yasui, Chikako; Izumi, Natsuko; Saito, Masao; Kobayashi, Naoto

    2017-03-01

    Outskirts of spiral galaxies, including our own, and dwarf irregular galaxies are known to have a different environment from the solar neighborhood, e.g., low metallicities ( ~ - 1 dex). Among them, the outer Galaxy is the closest and hence is so far the only site suitable for population studies of resolved stars on the same basis as solar neighborhood. We have obtained NIR images of young clusters in the outer Galaxy, using the Subaru 8.2-m telescope, and clearly resolved cluster members with mass detection limits of ~ 0.1 M ⊙. Based on the fitting of K-band luminosity functions (KLFs) for four clusters, we found that the initial mass function (IMF) in the outer Galaxy is consistent with that in the solar neighborhood in terms of the high-mass slope and IMF peak. Upcoming observations with a higher spatial resolution and sensitivity, using JWST, TMT, etc., will allow us to extend spatially-resolved studies of the IMF to Local Group galaxies.

  11. Nebular and Stellar Dust Extinction Across the Disk of Emission-line Galaxies on Kiloparsec Scales

    NASA Astrophysics Data System (ADS)

    Hemmati, Shoubaneh; Mobasher, Bahram; Darvish, Behnam; Nayyeri, Hooshang; Sobral, David; Miller, Sarah

    2015-11-01

    We investigate the resolved kiloparsec-scale stellar and nebular dust distribution in eight star-forming galaxies at z ∼ 0.4 in the Great Observatories Origins Deep Survey fields. This is to get a better understanding of the effect of dust attenuation on measurements of physical properties and its variation with redshift. Constructing the observed spectral energy distributions (SEDs) per pixel, based on seven bands of photometric data from Hubble Space Telescope/Advanced Camera for Surveys and WFC3, we performed pixel-by-pixel SED fits to population synthesis models and estimated the small-scale distribution of stellar dust extinction. We use Hα/Hβ nebular emission line ratios from Keck/DEIMOS high-resolution spectra at each spatial resolution element to measure the amount of attenuation faced by ionized gas at different radii from the centers of galaxies. We find a good agreement between the integrated and median of resolved color excess measurements in our galaxies. The ratio of integrated nebular to stellar dust extinction is always greater than unity, but does not show any trend with stellar mass or star formation rate (SFR). We find that inclination plays an important role in the variation of the nebular to stellar excess ratio. The stellar color excess profiles are found to have higher values at the center compared to outer parts of the disk. However, for lower mass galaxies, a similar trend is not found for the nebular color excess. We find that the nebular color excess increases with stellar mass surface density. This explains the absence of radial trend in the nebular color excess in lower mass galaxies which lack a large radial variation of stellar mass surface density. Using standard conversions of SFR surface density to gas mass surface density, and the relation between dust mass surface density and color excess, we find no significant variation in the dust-to-gas ratio in regions with high gas mass surface densities over the scales probed in this

  12. NEBULAR AND STELLAR DUST EXTINCTION ACROSS THE DISK OF EMISSION-LINE GALAXIES ON KILOPARSEC SCALES

    SciTech Connect

    Hemmati, Shoubaneh; Mobasher, Bahram; Darvish, Behnam; Nayyeri, Hooshang; Miller, Sarah; Sobral, David

    2015-11-20

    We investigate the resolved kiloparsec-scale stellar and nebular dust distribution in eight star-forming galaxies at z ∼ 0.4 in the Great Observatories Origins Deep Survey fields. This is to get a better understanding of the effect of dust attenuation on measurements of physical properties and its variation with redshift. Constructing the observed spectral energy distributions (SEDs) per pixel, based on seven bands of photometric data from Hubble Space Telescope/Advanced Camera for Surveys and WFC3, we performed pixel-by-pixel SED fits to population synthesis models and estimated the small-scale distribution of stellar dust extinction. We use Hα/Hβ nebular emission line ratios from Keck/DEIMOS high-resolution spectra at each spatial resolution element to measure the amount of attenuation faced by ionized gas at different radii from the centers of galaxies. We find a good agreement between the integrated and median of resolved color excess measurements in our galaxies. The ratio of integrated nebular to stellar dust extinction is always greater than unity, but does not show any trend with stellar mass or star formation rate (SFR). We find that inclination plays an important role in the variation of the nebular to stellar excess ratio. The stellar color excess profiles are found to have higher values at the center compared to outer parts of the disk. However, for lower mass galaxies, a similar trend is not found for the nebular color excess. We find that the nebular color excess increases with stellar mass surface density. This explains the absence of radial trend in the nebular color excess in lower mass galaxies which lack a large radial variation of stellar mass surface density. Using standard conversions of SFR surface density to gas mass surface density, and the relation between dust mass surface density and color excess, we find no significant variation in the dust-to-gas ratio in regions with high gas mass surface densities over the scales probed in this

  13. EXTREME GAS FRACTIONS IN CLUMPY, TURBULENT DISK GALAXIES AT z ∼ 0.1

    SciTech Connect

    Fisher, David B.; Glazebrook, Karl; Bassett, Robert; Bolatto, Alberto; Obreschkow, Danail; Cooper, Erin Mentuch; Wisnioski, Emily; Abraham, Roberto G.; Damjanov, Ivana; Green, Andy; McGregor, Peter

    2014-08-01

    In this Letter, we report the discovery of CO fluxes, suggesting very high gas fractions in three disk galaxies seen in the nearby universe (z ∼ 0.1). These galaxies were investigated as part of the DYnamics of Newly Assembled Massive Objects (DYNAMO) survey. High-resolution Hubble Space Telescope imaging of these objects reveals the presence of large star forming clumps in the bodies of the galaxies, while spatially resolved spectroscopy of redshifted Hα reveals the presence of high dispersion rotating disks. The internal dynamical state of these galaxies resembles that of disk systems seen at much higher redshifts (1 < z < 3). Using CO(1-0) observations made with the Plateau de Bure Interferometer, we find gas fractions of 20%-30% and depletion times of t {sub dep} ∼ 0.5 Gyr (assuming a Milky-Way-like α{sub CO}). These properties are unlike those expected for low-redshift galaxies of comparable specific star formation rate, but they are normal for their high-z counterparts. DYNAMO galaxies break the degeneracy between gas fraction and redshift, and we show that the depletion time per specific star formation rate for galaxies is closely tied to gas fraction, independent of redshift. We also show that the gas dynamics of two of our local targets corresponds to those expected from unstable disks, again resembling the dynamics of high-z disks. These results provide evidence that DYNAMO galaxies are local analogs to the clumpy, turbulent disks, which are often found at high redshift.

  14. The outer stellar populations and environments of unusually H I-rich galaxies

    NASA Astrophysics Data System (ADS)

    Kauffmann, Guinevere

    2015-06-01

    We investigate the nature of H I-rich galaxies, which are defined as the 10 per cent of galaxies with the highest atomic gas fractions at a given stellar mass and morphological type. We analyse outer (R > 1.5Re) stellar populations for a subset of face-on systems using optical g - r versus r - z colour/colour diagrams. The results are compared with those from control samples that are defined without regard to atomic gas content, but are matched in redshift, stellar mass and structural parameters. When compared to the control sample, the outer stellar populations of H I-rich early-type galaxies are shifted along a locus consistent with younger stellar ages, but similar metallicities. The outer colours of H I-rich late-type galaxies are much bluer in r - z than the H I-rich early types, and we infer that they have outer discs which are both younger and more metal-poor. We also analyse the environments of H I-rich galaxies within a projected radius of 500 kpc. Low-mass (log M* < 10.5) H I-rich early types are more likely to be central rather than satellite systems. Their satellites are less massive and have younger stellar populations. Similar, but weaker effects are found for low-mass H I-rich late-type galaxies. The satellites of H I-rich late types are also more likely to align along the major axis of the primary. No environmental differences are found for massive (log M* > 10.5) H I-rich galaxies, regardless of type.

  15. Photoelectric signals generated by bovine rod outer segment disk membranes attached to a lecithin bilayer.

    PubMed Central

    Bauer, P J; Bamberg, E; Fahr, A

    1984-01-01

    Purified bovine rod outer segment disk membranes were attached to a lecithin bilayer membrane. After photoexcitation with a 500-nm flash delivered by a dye laser, a negative photovoltage was observed on the bilayer under normal ionic strengths (100 mM KCl), which had a rise phase of 1-3 ms at 20 degrees C. The photoresponse was obviously due to bleaching of rhodopsin as it decreased for successive flashes of light. It originated most probably during the metarhodopsin-I metarhodopsin-II (meta-I-II) transition of rhodopsin because it was pH dependent at 2 degrees C but not at 20 degrees C. At 10 mM KCl, i.e., under hypotonic conditions, a positive photovoltage with slower kinetics than at high salt was observed. As the disk membranes were merely attached to the bilayer membrane, the photovoltage was apparently due to a light-induced transmembrane potential change in the disk membranes. Possible electrogenic mechanisms underlying the photosignal will be discussed. PMID:6743754

  16. Detailed structure of the outer disk around HD 169142 with polarized light in H-band

    NASA Astrophysics Data System (ADS)

    Momose, Munetake; Morita, Ayaka; Fukagawa, Misato; Muto, Takayuki; Takeuchi, Taku; Hashimoto, Jun; Honda, Mitsuhiko; Kudo, Tomoyuki; Okamoto, Yoshiko K.; Kanagawa, Kazuhiro D.; Tanaka, Hidekazu; Grady, Carol A.; Sitko, Michael L.; Akiyama, Eiji; Currie, Thayne; Follette, Katherine B.; Mayama, Satoshi; Kusakabe, Nobuhiko; Abe, Lyu; Brandner, Wolfgang; Brandt, Timothy D.; Carson, Joseph C.; Egner, Sebastian; Feldt, Markus; Goto, Miwa; Guyon, Olivier; Hayano, Yutaka; Hayashi, Masahiko; Hayashi, Saeko S.; Henning, Thomas; Hodapp, Klaus W.; Ishii, Miki; Iye, Masanori; Janson, Markus; Kandori, Ryo; Knapp, Gillian R.; Kuzuhara, Masayuki; Kwon, Jungmi; Matsuo, Taro; McElwain, Michael W.; Miyama, Shoken; Morino, Jun-Ichi; Moro-Martin, Amaya; Nishimura, Tetsuo; Pyo, Tae-Soo; Serabyn, Eugene; Suenaga, Takuya; Suto, Hiroshi; Suzuki, Ryuji; Takahashi, Yasuhiro H.; Takami, Michihiro; Takato, Naruhisa; Terada, Hiroshi; Thalmann, Christian; Tomono, Daigo; Turner, Edwin L.; Watanabe, Makoto; Wisniewski, John; Yamada, Toru; Takami, Hideki; Usuda, Tomonori; Tamura, Motohide

    2015-10-01

    Coronagraphic imagery of the circumstellar disk around HD 169142 in H-band polarized intensity (PI) with Subaru/HiCIAO is presented. The emission scattered by dust particles at the disk surface in 0{^''.}2 ≤ r ≤ 1{^''.}2, or 29 ≤ r ≤ 174 au, is successfully detected. The azimuthally averaged radial profile of the PI shows a double power-law distribution, in which the PIs in r = 29-52 au and r = 81.2-145 au respectively show r-3 dependence. These two power-law regions are connected smoothly with a transition zone (TZ), exhibiting an apparent gap in r = 40-70 au. The PI in the inner power-law region shows a deep minimum whose location seems to coincide with the point source at λ = 7 mm. This can be regarded as another sign of a protoplanet in the TZ. The observed radial profile of the PI is reproduced by a minimally flaring disk with an irregular surface density distribution, an irregular temperature distribution, or with a combination of both. The depletion factor of surface density in the inner power-law region (r < 50 au) is derived to be ≥ 0.16 from a simple model calculation. The obtained PI image also shows small-scale asymmetries in the outer power-law region. Possible origins for these asymmetries include corrugation of the scattering surface in the outer region, and a shadowing effect by a puffed-up structure in the inner power-law region.

  17. The Star Formation Histories of Disk Galaxies: The Live, the Dead, and the Undead

    NASA Astrophysics Data System (ADS)

    Oemler, Augustus, Jr.; Abramson, Louis E.; Gladders, Michael D.; Dressler, Alan; Poggianti, Bianca M.; Vulcani, Benedetta

    2017-07-01

    We reexamine the properties of local galaxy populations using published surveys of star formation, structure, and gas content. After recalibrating star formation measures, we are able to reliably measure specific star formation rates well below that of the so-called “main sequence” of star formation versus mass. We find an unexpectedly large population of quiescent galaxies with star formation rates intermediate between the main sequence and passive populations and with disproportionately high star formation rates. We demonstrate that a tight main sequence is a natural outcome of most histories of star formation and has little astrophysical significance but that the quiescent population requires additional astrophysics to explain its properties. Using a simple model for disk evolution based on the observed dependence of star formation on gas content in local galaxies, and assuming simple histories of cold gas inflow, we show that the evolution of galaxies away from the main sequence can be attributed to the depletion of gas due to star formation after a cutoff of gas inflow. The quiescent population is composed of galaxies in which the density of disk gas has fallen below a threshold for star formation probably set by disk stability. The evolution of galaxies beyond the quiescent state to gas exhaustion and the end of star formation requires another process, probably wind-driven mass loss. The environmental dependence of the three galaxy populations is consistent with recent numerical modeling, which indicates that cold gas inflows into galaxies are truncated at earlier epochs in denser environments.

  18. LOW-METALLICITY YOUNG CLUSTERS IN THE OUTER GALAXY. I. Sh 2-207

    SciTech Connect

    Yasui, Chikako; Kobayashi, Naoto; Izumi, Natsuko; Tokunaga, Alan T.; Saito, Masao

    2016-03-15

    To study star formation in low-metallicity environments ([M/H] ∼ −1 dex), we obtained deep near-infrared (NIR) images of Sh 2-207 (S207), which is an H ii region in the outer Galaxy with a spectroscopically determined metallicity of [O/H] ≃ −0.8 dex. We identified a young cluster in the western region of S207 with a limiting magnitude of K{sub S} = 19.0 mag (10σ) that corresponds to a mass detection limit of ≲0.1 M{sub ⊙} and enables the comparison of star-forming properties under low metallicity with those of the solar neighborhood. From the fitting of the K-band luminosity function (KLF), the age and distance of the S207 cluster are estimated at 2–3 Myr and ∼4 kpc, respectively. The estimated age is consistent with the suggestion of small extinctions of stars in the cluster (A{sub V} ∼ 3 mag) and the non-detection of molecular clouds. The reasonably good fit between the observed KLF and the model KLF suggests that the underlying initial mass function (IMF) of the cluster down to the detection limit is not significantly different from the typical IMFs in the solar metallicity. From the fraction of stars with NIR excesses, a low disk fraction (<10%) in the cluster with a relatively young age is suggested, as we had previously proposed.

  19. BREAKS IN THIN AND THICK DISKS OF EDGE-ON GALAXIES IMAGED IN THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S{sup 4}G)

    SciTech Connect

    Comeron, Sebastien; Salo, Heikki; Laurikainen, Eija; Laine, Jarkko; Elmegreen, Bruce G.; Athanassoula, E.; Bosma, Albert; Knapen, Johan H.; Gadotti, Dimitri A.; Sheth, Kartik; Munoz-Mateos, Juan Carlos; Kim, Taehyun; Hinz, Joannah L.; Regan, Michael W.; Gil de Paz, Armando; Menendez-Delmestre, Karin; Seibert, Mark; Ho, Luis C.; Mizusawa, Trisha; Holwerda, Benne

    2012-11-10

    Breaks in the radial luminosity profiles of galaxies have until now been mostly studied averaged over disks. Here, we study separately breaks in thin and thick disks in 70 edge-on galaxies using imaging from the Spitzer Survey of Stellar Structure in Galaxies. We built luminosity profiles of the thin and thick disks parallel to midplanes and we found that thin disks often truncate (77%). Thick disks truncate less often (31%), but when they do, their break radius is comparable with that in the thin disk. This suggests either two different truncation mechanisms-one of dynamical origin affecting both disks simultaneously and another one only affecting the thin disk-or a single mechanism that creates a truncation in one disk or in both depending on some galaxy property. Thin disks apparently antitruncate in around 40% of galaxies. However, in many cases, these antitruncations are an artifact caused by the superposition of a thin disk and a thick disk, with the latter having a longer scale length. We estimate the real thin disk antitruncation fraction to be less than 15%. We found that the ratio of the thick and thin stellar disk mass is roughly constant (0.2 < M{sub T} /M{sub t} < 0.7) for circular velocities v{sub c} > 120 km s{sup -1}, but becomes much larger at smaller velocities. We hypothesize that this is due to a combination of a high efficiency of supernova feedback and a slower dynamical evolution in lower-mass galaxies causing stellar thin disks to be younger and less massive than in higher-mass galaxies.

  20. Clumpy Disks as a Testbed for Feedback-regulated Galaxy Formation

    NASA Astrophysics Data System (ADS)

    Mayer, Lucio; Tamburello, Valentina; Lupi, Alessandro; Keller, Ben; Wadsley, James; Madau, Piero

    2016-10-01

    We study the dependence of fragmentation in massive gas-rich galaxy disks at z > 1 on stellar feedback schemes and hydrodynamical solvers, employing the GASOLINE2 SPH code and the lagrangian mesh-less code GIZMO in finite mass mode. Non-cosmological galaxy disk runs with the standard delayed-cooling blastwave feedback are compared with runs adopting a new superbubble feedback, which produces winds by modeling the detailed physics of supernova-driven bubbles and leads to efficient self-regulation of star formation. We find that, with blastwave feedback, massive star-forming clumps form in comparable number and with very similar masses in GASOLINE2 and GIZMO. Typical clump masses are in the range 107-108 M ⊙, lower than in most previous works, while giant clumps with masses above 109 M ⊙ are exceedingly rare. By contrast, superbubble feedback does not produce massive star-forming bound clumps as galaxies never undergo a phase of violent disk instability. In this scheme, only sporadic, unbound star-forming overdensities lasting a few tens of Myr can arise, triggered by non-linear perturbations from massive satellite companions. We conclude that there is severe tension between explaining massive star-forming clumps observed at z > 1 primarily as the result of disk fragmentation driven by gravitational instability and the prevailing view of feedback-regulated galaxy formation. The link between disk stability and star formation efficiency should thus be regarded as a key testing ground for galaxy formation theory.

  1. High star formation rates as the origin of turbulence in early and modern disk galaxies.

    PubMed

    Green, Andrew W; Glazebrook, Karl; McGregor, Peter J; Abraham, Roberto G; Poole, Gregory B; Damjanov, Ivana; McCarthy, Patrick J; Colless, Matthew; Sharp, Robert G

    2010-10-07

    Observations of star formation and kinematics in early galaxies at high spatial and spectral resolution have shown that two-thirds are massive rotating disk galaxies, with the remainder being less massive non-rotating objects. The line-of-sight-averaged velocity dispersions are typically five times higher than in today's disk galaxies. This suggests that gravitationally unstable, gas-rich disks in the early Universe are fuelled by cold, dense accreting gas flowing along cosmic filaments and penetrating hot galactic gas halos. These accreting flows, however, have not been observed, and cosmic accretion cannot power the observed level of turbulence. Here we report observations of a sample of rare, high-velocity-dispersion disk galaxies in the nearby Universe where cold accretion is unlikely to drive their high star formation rates. We find that their velocity dispersions are correlated with their star formation rates, but not their masses or gas fractions, which suggests that star formation is the energetic driver of galaxy disk turbulence at all cosmic epochs.

  2. The power spectra of non-circular motions in disk galaxies

    NASA Astrophysics Data System (ADS)

    Westfall, Kyle; Laws, Anna S. E.; MaNGA Team

    2016-01-01

    Using data from the first year of the SDSS-IV/MaNGA survey, we present a preliminary study of the amplitude of non-circular motions in a sample of disk galaxies. We select galaxies that have either a visual classification as a spiral galaxy by the Galaxy Zoo project (Lintott et al. 2011) and/or a measured Sersic index of less than 2.5 from the NASA-Sloan Atlas (nsatlas.org). We also remove high-inclination systems by selecting galaxies with isophotal ellipticity measurements of less than 0.6, implying an inclination of less than 65 degrees. For each galaxy, we fit a tilted-disk model to the observed line-of-sight velocities (Andersen & Bershady 2013). The geometric projection of the circularly rotating disk is simultaneously fit to both the ionized-gas (H-alpha) and stellar kinematics, whereas the rotation curves of the two dynamical tracers are allowed to be independent. We deproject the residuals of the velocity-field fit to the disk-plane polar coordinates and select a radial region that is fully covered in aziumuth, yet not undersampled by the on-sky spaxel. Similar to the approach taken by Bovy et al. (2015) for the Milky Way, we then compute the two-dimensional power spectrum of this velocity-residual map, which provides the amplitude of non-circular motions at all modes probed by the data. Our preliminary analysis reveals disk-plane non-circular motions in both the stars and ionized-gas with typical peak amplitudes of approximately 20 km/s. Additionally, our initial findings appear to demonstrate that non-circular motions in barred galaxies are stronger in the ionized gas than in the stars, a trend not seen in unbarred galaxies.

  3. Simulating the Growth of a Disk Galaxy and its Supermassive Black Hole in a Cosmological Simulating the Growth of a Disk Galaxy and its Supermassive Black Hole in a Cosmological Context

    SciTech Connect

    Levine, Robyn Deborah

    2008-01-01

    Supermassive black holes (SMBHs) are ubiquitous in the centers of galaxies. Their formation and subsequent evolution is inextricably linked to that of their host galaxies, and the study of galaxy formation is incomplete without the inclusion of SMBHs. The present work seeks to understand the growth and evolution of SMBHs through their interaction with the host galaxy and its environment. In the first part of the thesis (Chap. 2 and 3), we combine a simple semi-analytic model of outflows from active galactic nuclei (AGN) with a simulated dark matter density distribution to study the impact of SMBH feedback on cosmological scales. We find that constraints can be placed on the kinetic efficiency of such feedback using observations of the filling fraction of the Lyα forest. We also find that AGN feedback is energetic enough to redistribute baryons over cosmological distances, having potentially significant effects on the interpretation of cosmological data which are sensitive to the total matter density distribution (e.g. weak lensing). However, truly assessing the impact of AGN feedback in the universe necessitates large-dynamic range simulations with extensive treatment of baryonic physics to first model the fueling of SMBHs. In the second part of the thesis (Chap. 4-6) we use a hydrodynamic adaptive mesh refinement simulation to follow the growth and evolution of a typical disk galaxy hosting a SMBH, in a cosmological context. The simulation covers a dynamical range of 10 million allowing us to study the transport of matter and angular momentum from super-galactic scales all the way down to the outer edge of the accretion disk around the SMBH. Focusing our attention on the central few hundred parsecs of the galaxy, we find the presence of a cold, self-gravitating, molecular gas disk which is globally unstable. The global instabilities drive super-sonic turbulence, which maintains local stability and allows gas to fuel a SMBH without first fragmenting completely

  4. The Angular Momentum of Disk Galaxies: A Multi-Wavelength Study Using the Virtual Observatory

    NASA Astrophysics Data System (ADS)

    Cortese, Luca; Catinella, B.; Springob, C. M.

    2006-12-01

    The determination of the angular momentum distribution of disk galaxies and its dependence on other galaxy properties and environment is essential in order to develop an accurate picture of galaxy formation and evolution. N-body simulations and semi-analytic models of galaxy formation within the standard cosmological framework identify the spin parameter of the dark matter halos as one of the main drivers of galaxy evolution and yield insights into its properties and distribution in present-day galaxies. Various relations have been proposed to link the halo spin parameter to observational data. In this work, we exploit such relations to obtain observational constraints for theoretical models of galaxy formation. To this extent, we used the Virtual Observatory to create a multi-wavelength database for the study of the properties of the angular momentum distribution of disk galaxies. Our sample builds upon the SFI++ database, which includes the largest collection of long-slit optical galaxy rotation curves currently available. Preliminary results of our analysis will be presented. This work is partially funded by PPARC under grant PPA/G/O/2002/00497. The Arecibo Observatory is part of the National Astronomy and Ionosphere Center, which is operated by Cornell University under a cooperative agreement with the National Science Foundation.

  5. ROSAT observations of quiescent low mass disk galaxies: No evidence of baryonic blow out

    NASA Technical Reports Server (NTRS)

    Bothun, Gregory D.; Eriksen, James; Schombert, James M.

    1994-01-01

    To test the hypothesis that galactic winds associated with star formation in low mass disk galaxies can be an effective means of relocating cold disk gas to a warm tenuous halo, we have obtained long exposure ROSAT Position Sensitive Proportional Counter (PSPC) observations of three such galaxies. The sensitivity of the PSPC to the presence of an extended, approximately 0.15 KEV halo of 10(exp 9) solar mass of gas, is quite high for the exposure times we used. We failed to detect this halo in all three cases and the observed x-ray luminosity of the galaxy is two orders of magnitude less than the hypothetical case in which the mass of gas that has been expelled by previous generations of star formation is equal to the stellar mass of the galaxy itself. This limit is much less than the actual mass of cold gas in these galaxies. Thus, we were unable to verify directly the presence of significant galactic winds in these three galaxies either because they are not operative, because their halos are not sufficiently massive to aid in the retention of this gas, or because the amount of injected gas is just a small percentage of the cold disk gas. If the latter reason is emblematic of low mass galaxies then we would not expect the detection of halos. We also report here the serendipitous detection of Abell 1560, a distance class 7 cluster of unknown redshift.

  6. ROSAT observations of quiescent low mass disk galaxies: No evidence of baryonic blow out

    NASA Technical Reports Server (NTRS)

    Bothun, Gregory D.; Eriksen, James; Schombert, James M.

    1994-01-01

    To test the hypothesis that galactic winds associated with star formation in low mass disk galaxies can be an effective means of relocating cold disk gas to a warm tenuous halo, we have obtained long exposure ROSAT Position Sensitive Proportional Counter (PSPC) observations of three such galaxies. The sensitivity of the PSPC to the presence of an extended, approximately 0.15 KEV halo of 10(exp 9) solar mass of gas, is quite high for the exposure times we used. We failed to detect this halo in all three cases and the observed x-ray luminosity of the galaxy is two orders of magnitude less than the hypothetical case in which the mass of gas that has been expelled by previous generations of star formation is equal to the stellar mass of the galaxy itself. This limit is much less than the actual mass of cold gas in these galaxies. Thus, we were unable to verify directly the presence of significant galactic winds in these three galaxies either because they are not operative, because their halos are not sufficiently massive to aid in the retention of this gas, or because the amount of injected gas is just a small percentage of the cold disk gas. If the latter reason is emblematic of low mass galaxies then we would not expect the detection of halos. We also report here the serendipitous detection of Abell 1560, a distance class 7 cluster of unknown redshift.

  7. A Study of Bar Strengths in Early-Type Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Buta, Ronald J.; Laurikainen, Eija; Salo, Heikki; Knapen, Johan H.

    2009-02-01

    Angular momentum exchange between a bar and a massive halo is thought to be responsible for producing strong bars in disk galaxies (Athanassoula, 2003), while gas transport to the center is believed to weaken or even dissolve bars (Bournaud and Combes 2002). We are carrying out a systematic survey of early-type disk galaxies with the main emphasis to derive the distribution of their bar strengths and to examine their Fourier amplitude properties. We propose to use FLAMINGOS with the KPNO 2.1m to obtain 2.2(micron) K_s-band observations of 16 galaxies for the ``Near-Infrared S0 Survey", a project already in progress to measure the bulge, disk, and bar properties of a statistically well-defined sample of 184 galaxies in the type range S0^- to Sa, including some possibly mis-classified elliptical galaxies. The principal goals of the survey, which was started 5 years ago and is now 90% completed, are to allow us to (1) compare relative Fourier near- IR intensity profiles of observed early-type galaxy bars with equivalent Fourier mass profiles of various Athanassoula models; (2) derive the distribution of bar strengths for the early-type sample and compare it with the known distribution for spirals; and (3) examine the properties of bulges and disks in early-type galaxies in order to better understand the origin of bulges (classical verus pseudo) in such galaxies. Our study is the first attempt to quantify bar strength in S0 galaxies. We are asking for enough KPNO 2.1m time to help complete our survey.

  8. Evolution of Warped Accretion Disks in Active Galactic Nuclei. I. Roles of Feeding at the Outer Boundaries

    NASA Astrophysics Data System (ADS)

    Li, Yan-Rong; Wang, Jian-Min; Cheng, Cheng; Qiu, Jie

    2013-02-01

    We investigate the alignment processes of spinning black holes and their surrounding warped accretion disks in a frame of two different types of feeding at the outer boundaries. We consider (1) fixed flows in which gas is continually fed with a preferred angular momentum, and (2) free flows in which there is no gas supply and the disks diffuse freely at their outer edges. As expected, we find that for the cases of fixed flows the black hole disk systems always align on timescales of several 106 yr, irrespective of the initial inclinations. If the initial inclination angles are larger than π/2, the black hole accretion transits from retrograde to prograde fashion, and the accreted mass onto the black holes during these two phases is comparable. On the other hand, for the cases of free flows, both alignments and anti-alignments can occur, depending on the initial inclinations and the ratios of the angular momentum of the disks to that of the black holes. In such cases, the disks will be consumed within timescales of 106 yr by black holes accreting at the Eddington limit. We propose that there is a close connection between the black hole spin and the lifetime for which the feeding persists, which determines the observable episodic lifetimes of active galactic nuclei. We conclude that careful inclusion of the disk feeding at the outer boundaries is crucial for modeling the evolution of the black hole spin.

  9. Downsizing among disk galaxies and the role of the environment

    NASA Astrophysics Data System (ADS)

    Gavazzi, G.

    2009-11-01

    The study of PopI and PopII indicators in galaxies has a profound impact on our understanding of galaxy evolution. Their present (z = 0) ratio suggests that the star formation history of galaxies was primarily dictated by their global mass. Since 1989 Luis Carrasco and I spent most of our sleepless nights gathering H α and near infrared surface photometry of galaxies in the local Universe and focused most of our scientific career on these two indicators trying to convince the community that the mass was the key parameter to their evolution. We were unsuccessful, until in 2004 the Sloan team rediscovered this phenomenon and named it ``downsizing''.

  10. THE INCIDENCE OF ACTIVE GALACTIC NUCLEI IN PURE DISK GALAXIES: THE SPITZER VIEW

    SciTech Connect

    Satyapal, S.; Mcalpine, W.; Gliozzi, M.; Boeker, T.; Heckman, T.

    2009-10-10

    Using the Spitzer telescope, we have conducted a high-resolution spectroscopic study of 18 bulgeless (Hubble type of Sd or Sdm) galaxies that show no definitive signatures of nuclear activity in their optical spectra. This is the first systematic mid-infrared (MIR) search for weak or hidden active galactic nuclei (AGNs) in a statistically significant sample of bulgeless (Sd/Sdm) disk galaxies. Based on the detection of the high-ionization [Ne V] 14.3 mum line, we report the discovery of an AGN in 1 out of the 18 galaxies in the sample. This galaxy, NGC 4178, is a nearby edge-on Sd galaxy, which likely hosts a prominent nuclear star cluster (NSC). The bolometric luminosity of the AGN inferred from the [Ne V] line luminosity is approx8 x 10{sup 41} ergs s{sup -1}. This is almost 2 orders of magnitude greater than the luminosity of the AGN in NGC 4395, the best studied AGN in a bulgeless disk galaxy. Assuming that the AGN in NGC 4178 is radiating below the Eddington limit, the lower mass limit for the black hole is approx6 x 10{sup 3} M {sub sun}. The fact that none of the other galaxies in the sample shows any evidence for an AGN demonstrates that while the AGN detection rate based on MIR diagnostics is high (30%-40%) in optically quiescent galaxies with pseudobulges or weak classical bulges (Hubble type Sbc and Sc), it drops drastically in Sd/Sdm galaxies. Our observations, therefore, confirm that AGNs in completely bulgeless disk galaxies are not hidden in the optical but truly are rare. Of the three Sd galaxies with AGNs known so far, all have prominent NSCs, suggesting that in the absence of a well-defined bulge, the galaxy must possess an NSC in order to host an AGN. On the other hand, while the presence of an NSC appears to be a requirement for hosting an AGN in bulgeless galaxies, neither the properties of the NSC nor those of the host galaxy appear exceptional in late-type AGN host galaxies. The recipe for forming and growing a central black hole in a

  11. Three-dimensional distribution of the ISM in the Milky Way galaxy. III. The total neutral gas disk

    NASA Astrophysics Data System (ADS)

    Nakanishi, Hiroyuki; Sofue, Yoshiaki

    2016-02-01

    We present newly obtained three-dimensional gaseous maps of the Milky Way Galaxy: H I, H2, and total-gas (H I plus H2) maps, which were derived from the H I and 12CO(J = 1-0) survey data and rotation curves based on the kinematic distance. The H I and H2 face-on maps show that the H I disk is extended to a radius of 15-20 kpc and its outskirts are asymmetric to the Galactic center, while most of the H2 gas is distributed inside the solar circle. The total gas mass within a radius of 30 kpc amounts to 8.0 × 109 M⊙, 89% and 11% of which are H I and H2, respectively. The vertical slices show that the outer H I disk is strongly warped and the inner H I and H2 disks are corrugated. The total gas map is advantageous for tracing spiral structures from the inner to outer disk. Spiral structures such as the Norma-Cygnus, the Perseus, the Sagittarius-Carina, the Scutum-Crux, and the Orion arms are more clearly traced in the total gas map than ever. All the spiral arms are well explained by logarithmic spiral arms with pitch angles of 11°-15°. The molecular fraction of the total gas is high near the Galactic center and decreases with Galactocentric distance. The molecular fraction is also locally enhanced at the spiral arms compared with the inter-arm regions.

  12. The role of interactions in triggering bars, spiral arms and AGN in disk galaxies

    NASA Astrophysics Data System (ADS)

    Nair, Preethi; Ellison, Sara L.; Patton, David R.

    2016-01-01

    The role of secular structures like bars, rings and spiral arms in triggering star formation and AGN activity in disk galaxies are not well understood. In addition, the mechanisms which create and destroy these structures are not well characterized. Mergers are considered to be one of the main mechanisms which can trigger bars in massive disk galaxies. Using a sample of ~8000 close pair galaxies at 0.02 < z < 0.06 from the Sloan Digital Sky Survey, I will present results illustrating the role of mergers in triggering bars, rings, spiral arms and AGN as a function of close pair separation and merger ratios as well as their dependence on morphology and other physical properties of the galaxies. Time permitting, I will show how resolved IFU observations from SDSS MaNGA will help to place stronger constraints on the role of these structures in triggering star formation and AGN.

  13. Observations of extended and counterrotating disks of ionized gas in S0 galaxies

    NASA Technical Reports Server (NTRS)

    Dettmar, Ralf-Juergen; Jullien-Dettmar, Marlies; Barteldrees, Andreas

    1990-01-01

    While many E/S0 galaxies have been found to show emission line spectra in their nuclear regions, the question of the presence and nature of extended disks of ionized gas in these galaxies has been addressed only in recent years. Typically the ionized gas is detected in the inner region on a scale of approx. 1 kpc (e.g., Phillips et al. 1986, Caldwell 1984). Here researchers present evidence that the disks of ionized gas of at least some S0 galaxies are much more extended than previously believed. In addition, with the detection of the counterrotation of gas and stars in NGC 7007 they strengthen the basis for arguments that the source of gas in S0 galaxies is external

  14. Inner polar ionized-gas disks and properties of their host galaxies

    NASA Astrophysics Data System (ADS)

    Sil'chenko, Olga K.

    2015-02-01

    I have analyzed line-of-sight velocity fields of the stellar and ionized-gas components for the volume-limited sample of nearby lenticular galaxies by using the raw data of the ATLAS-3D survey undertaken with the integral-field spectrograph SAURON. Among 200 nearby lenticular galaxies, I distinguish 20 cases of nearly orthogonal rotation of the inner ionized gas with respect to the central stellar components; so I estimate a frequency of the inner polar disks in nearby S0 galaxies as 10%. Properties of the central stellar populations - mean ages, metallicities, magnesium-to-iron ratios - are derived through the Lick indices. The typical stellar population properties of the polar-disk host galaxies are exactly the same as the stellar population properties of the complete sample.

  15. A Citizen-Science-enabled Comprehensive Search for XUV-disk Galaxies

    NASA Astrophysics Data System (ADS)

    Thilker, David A.

    2017-03-01

    Initial efforts to identify extended UV disk (XUV-disk) galaxies were confined to nearby targets using image products from early in the GALEX mission. We developed a beta Zooniverse-based citizen science project to address this issue, specifically (1) allowing a dramatically larger galaxy sample by crowd-sourcing blink comparison UV-optical image inspection to volunteers, and (2) incorporating all archived GALEX data for each target considered. We aim to widely deploy this project to the public within the upcoming year.

  16. The Evolution of the Number Density of Large Disk Galaxies in COSMOS

    NASA Astrophysics Data System (ADS)

    Sargent, M. T.; Carollo, C. M.; Lilly, S. J.; Scarlata, C.; Feldmann, R.; Kampczyk, P.; Koekemoer, A. M.; Scoville, N.; Kneib, J.-P.; Leauthaud, A.; Massey, R.; Rhodes, J.; Tasca, L. A. M.; Capak, P.; McCracken, H. J.; Porciani, C.; Renzini, A.; Taniguchi, Y.; Thompson, D. J.; Sheth, K.

    2007-09-01

    We study a sample of approximately 16,500 galaxies with IACS,AB<=22.5 in the central 38% of the COSMOS field, which are extracted from a catalog constructed from the Cycle 12 ACS F814W COSMOS data set. Structural information on the galaxies is derived by fitting single Sérsic models to their two-dimensional surface brightness distributions. In this paper we focus on the disk galaxy population (as classified by the Zurich Estimator of Structural Types), and investigate the evolution of the number density of disk galaxies larger than approximately 5 kpc between redshift z~1 and the present epoch. Specifically, we use the measurements of the half-light radii derived from the Sérsic fits to construct, as a function of redshift, the size function Φ(r1/2, z) of both the total disk galaxy population and of disk galaxies split in four bins of bulge-to-disk ratio. In each redshift bin, the size function specifies the number of galaxies per unit comoving volume and per unit half-light radius r1/2. Furthermore, we use a selected sample of roughly 1800 SDSS galaxies to calibrate our results with respect to the local universe. We find the following: (1) The number density of disk galaxies with intermediate sizes (r1/2~5-7 kpc) remains nearly constant from z~1 to today. Unless the growth and destruction of such systems exactly balanced in the last eight billion years, they must have neither grown nor been destroyed over this period. (2) The number density of the largest disks (r1/2>7 kpc) decreases by a factor of about 2 out to z~1. (3) There is a constancy-or even slight increase-in the number density of large bulgeless disks out to z~1 the deficit of large disks at early epochs seems to arise from a smaller number of bulged disks. Our results indicate that the bulk of the large disk galaxy population has completed its growth by z~1 and support the theory that secular evolution processes produce-or at least add stellar mass to-the bulge components of disk galaxies. Based on

  17. The Bilayer Enhances Rhodopsin Kinetic Stability in Bovine Rod Outer Segment Disk Membranes

    PubMed Central

    Corley, Scott C.; Sprangers, Peter; Albert, Arlene D.

    2011-01-01

    Rhodopsin is a kinetically stable protein constituting >90% of rod outer segment disk membrane protein. To investigate the bilayer contribution to rhodopsin kinetic stability, disk membranes were systematically disrupted by octyl-β-D-glucopyranoside. Rhodopsin kinetic stability was examined under subsolubilizing (rhodopsin in a bilayer environment perturbed by octyl-β-D-glucopyranoside) and under fully solubilizing conditions (rhodopsin in a micelle with cosolubilized phospholipids). As determined by DSC, rhodopsin exhibited a scan-rate-dependent irreversible endothermic transition at all stages of solubilization. The transition temperature (Tm) decreased in the subsolubilizing stage. However, once the rhodopsin was in a micelle environment there was little change of the Tm as the phospholipid/rhodopsin ratio in the mixed micelles decreased during the fully solubilized stage. Rhodopsin thermal denaturation is consistent with the two-state irreversible model at all stages of solubilization. The activation energy of denaturation (Eact) was calculated from the scan rate dependence of the Tm and from the rate of rhodopsin thermal bleaching at all stages of solubilization. The Eact as determined by both techniques decreased in the subsolubilizing stage, but remained constant once fully solubilized. These results indicate the bilayer structure increases the Eact to rhodopsin denaturation. PMID:21689528

  18. Abundances of Planetary Nebulae in the Outer Disk of M31

    NASA Astrophysics Data System (ADS)

    Kwitter, Karen B.; Lehman, Emma M. M.; Balick, Bruce; Henry, R. B. C.

    2012-07-01

    We present spectroscopic observations and chemical abundances of 16 planetary nebulae (PNe) in the outer disk of M31. The [O III] λ4363 line is detected in all objects, allowing a direct measurement of the nebular temperature essential for accurate abundance determinations. Our results show that the abundances in these M31 PNe display the same correlations and general behaviors as Type II PNe in the Milky Way. We also calculate photoionization models to derive estimates of central star properties. From these we infer that our sample PNe, all near the bright-end cutoff of the planetary nebula luminosity function, originated from stars near 2 M ⊙. Finally, under the assumption that these PNe are located in M31's disk, we plot the oxygen abundance gradient, which appears shallower than the gradient in the Milky Way. Partially based on observations obtained with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium; and 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), Ministerio da Ciencia e Tecnologia (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).

  19. Dual effect of local anesthetics on the function of excitable rod outer segment disk membrane

    SciTech Connect

    Mashimo, T.; Abe, K.; Yoshiya, I.

    1986-04-01

    The effects of local anesthetics and a divalent cation, Ca2+, on the function of rhodopsin were estimated from the measurements of light-induced proton uptake. The light-induced proton uptake by rhodopsin in the rod outer segment disk membrane was enhanced at lower pH (4) but depressed at higher pHs (6 to 8) by the tertiary amine local anesthetics lidocaine, bupivacaine, tetracaine, and dibucaine. The order of local anesthetic-induced depression of the proton uptake followed that of their clinical anesthetic potencies. The depression of the proton uptake versus the concentration of the uncharged form of local anesthetic nearly describes the same curve for small and large dose of added anesthetic. Furthermore, a neutral local anesthetic, benzocaine, depressed the proton uptake at all pHs between 4 and 7. These results indicate that the depression of the proton uptake is due to the effect of only the uncharged form. It is hypothesized that the uncharged form of local anesthetics interacts hydrophobically with the rhodopsin in the disk membrane. The dual effect of local anesthetics on the proton uptake, on the other hand, suggests that the activation of the function of rhodopsin may be caused by the charged form. There was no significant change in the light-induced proton uptake by rhodopsin when 1 mM of Ca2+ was introduced into the disk membrane at varying pHs in the absence or presence of local anesthetics. This fact indicates that Ca2+ ion does not influence the diprotonating process of metarhodopsin; neither does it interfere with the local anesthetic-induced changes in the rhodopsin molecule.

  20. Recent star formation in the Hi dominated outer regions of early-type galaxies

    NASA Astrophysics Data System (ADS)

    Yıldız, Mustafa K.; Serra, Paolo; Peletier, Reynier F.; Oosterloo, Tom A.; Duc, Pierre-Alain

    2017-03-01

    Context According to the ATLAS3D project, about 20 percent of all nearby early-type galaxies (D < 42 Mpc; M K < -21.5 mag; stellar mass M stars >~ 6 × 109 M⊙) outside clusters are surrounded by a disc or ring of low-column-density neutral hydrogen (Hi) gas with typical radii of tens of kpc, much larger than the stellar body. Aims Our aim is to understand the impact of these gas systems on the host galaxies, in particular, whether there is any recent star formation related to the Hi and effect of recent star formation on the host early-type galaxies. Methods and sample We analyse the distribution of star formation out to large radii by using resolved Hi images together with UV and optical images. We calculate the UV-UV and UV-optical colours in two apertures, 1-3 and 3-10 R eff. Using FUV emission as a proxy for star formation, we also estimate the integrated star formation rate in the outer regions. Our sample consists of 18 Hi-rich galaxies as well as 55 control galaxies where no Hi has been detected. We select the control sample galaxies to match the Hi-rich galaxies in stellar mass, environment, distance and stellar kinematics. Results In half of the Hi-rich galaxies the radial UV profile changes slope at the position of the Hi radial profile peak. We find that the FUV-NUV and UV-optical colours in the first and second apertures of the Hi-rich galaxies are on average 0.5 and 0.8 mag bluer than the Hi-poor ones, respectively. We also find that the Hi-rich early-type galaxies have colour gradients that are almost 2 times stronger than the Hi-poor ones. we estimate the integrated star formation rate in the outer regions (R > 1 R eff) to be on average ~ 6.1×10-3 M⊙ yr-1 for the Hi-rich galaxies. We find that the gas depletion time in the outermost region (3-10 R eff) is ~ 80 Gyrs, which is similar to that estimated for the outskirts of spirals. Conclusions Studying the stellar populations in early type galaxies with and without Hi, we find that galaxies with

  1. Discovery of star formation in the extreme outer galaxy possibly induced by a high-velocity cloud impact

    SciTech Connect

    Izumi, Natsuko; Kobayashi, Naoto; Hamano, Satoshi; Yasui, Chikako; Tokunaga, Alan T.; Saito, Masao

    2014-11-01

    We report the discovery of star formation activity in perhaps the most distant molecular cloud in the extreme outer galaxy. We performed deep near-infrared imaging with the Subaru 8.2 m telescope, and found two young embedded clusters at two CO peaks of 'Digel Cloud 1' at the kinematic distance of D = 16 kpc (Galactocentric radius R {sub G} = 22 kpc). We identified 18 and 45 cluster members in the two peaks, and the estimated stellar densities are ∼5 and ∼3 pc{sup –2}, respectively. The observed K-band luminosity function suggests that the age of the clusters is less than 1 Myr and also that the distance to the clusters is consistent with the kinematic distance. On the sky, Cloud 1 is located very close to the H I peak of high-velocity cloud Complex H, and there are some H I intermediate velocity structures between the Complex H and the Galactic disk, which could indicate an interaction between them. We suggest the possibility that Complex H impacting on the Galactic disk has triggered star formation in Cloud 1 as well as the formation of the Cloud 1 molecular cloud.

  2. Antitruncated stellar light profiles in the outer regions of STAGES spiral galaxies: bulge or disc related?

    NASA Astrophysics Data System (ADS)

    Maltby, David T.; Hoyos, Carlos; Gray, Meghan E.; Aragón-Salamanca, Alfonso; Wolf, Christian

    2012-03-01

    We present a comparison of azimuthally averaged radial surface brightness μ(r) profiles and analytical bulge-disc decompositions (de Vaucouleurs, r1/4 bulge plus exponential disc) for spiral galaxies using Hubble Space Telescope/Advanced Camera for Surveys V-band imaging from the Space Telescope A901/2 Galaxy Evolution Survey (STAGES). In the established classification scheme, antitruncated μ(r) profiles (Type III) have a broken exponential disc with a shallower region beyond the break radius rbrk. The excess light at large radii (r > rbrk) can either be caused by an outer exponential disc (Type III-d) or an extended spheroidal component (Type III-s). Using our comparisons, we determine the contribution of bulge light at r > rbrk for a large sample of 78 (barred/unbarred, Sa-Sd) spiral galaxies with outer disc antitruncations (?). In the majority of cases (˜85 per cent), evidence indicates that excess light at r > rbrk is related to an outer shallow disc (Type III-d). Here, the contribution of bulge light at r > rbrk is either negligible (˜70 per cent) or too little to explain the antitruncation (˜15 per cent). However in the latter cases, bulge light can affect the measured disc properties (e.g. μbrk, outer scalelength). In the remaining cases (˜15 per cent), light at r > rbrk is dominated by the bulge (Type III-s). Here, for most cases the bulge profile dominates at all radii and only occasionally (? galaxies, ˜5 per cent) extends beyond that of a dominant disc and explains the excess light at r > rbrk. We thus conclude that in the vast majority of cases antitruncated outer discs cannot be explained by bulge light and thus remain a pure disc phenomenon.

  3. The Elaboration of Disk in Spiral Galaxies: Analyses of their Progenitors, 6 Gyrs Ago

    NASA Astrophysics Data System (ADS)

    Hammer, F.; Images Team

    2010-10-01

    The Large program (Intermediate MAss Galaxy Evolution Sequence, IMAGES) aims at measuring the velocity fields of a representative sample of 100 massive galaxies at z=0.4-0.75, taken from the CDFS, the CFRS and the HDFS fields. It uses the unique mode of multiple integral field units of FLAMES/GIRAFFE at VLT. The resolved kinematics data allow to sample the large scale motions at few kpc scale for each individual galaxy. They have been combined with the deepest HST/ACS, Spitzer (MIPS and IRAC) and VLT/FORS2 ever achieved observations. Most intermediate redshift galaxies show anomalous velocity fields implying that, 6 Gyrs ago, half of the present day spirals were out of equilibrium and have peculiar morphologies. The wealth of data in these fields allows to modelize the physical processes in each galaxy with an accuracy almost similar to what is done in the local Universe. These detailed analyses reveal the importance of merger processes, including their remnant phases. It points out the importance of disk survival and it supports the disk rebuilding scenario, suggesting that the hierarchical scenario may apply to the elaboration of disk galaxies as well as it does for ellipticals.

  4. The opacity of spiral galaxy disks: IX. Dust and gas surface densities

    NASA Astrophysics Data System (ADS)

    Holwerda, B. W.; Allen, R. J.; de Blok, W. J. G.; Bouchard, A.; González-Lópezlira, R. A.; van der Kruit, P. C.; Leroy, A.

    2013-03-01

    Our aim is to explore the relation between gas, atomic and molecular, and dust in spiral galaxies. Gas surface densities are from atomic hydrogen and CO line emission maps. To estimate the dust content, we use the disk opacity as inferred from the number of distant galaxies identified in twelve HST/WFPC2 fields of ten nearby spiral galaxies. The observed number of distant galaxies is calibrated for source confusion and crowding with artificial galaxy counts and here we verify our results with sub-mm surface brightnesses from archival Herschel-SPIRE data. We find that the opacity of the spiral disk does not correlate well with the surface density of atomic (H I) or molecular hydrogen (H_2) alone implying that dust is not only associated with the molecular clouds but also the diffuse atomic disk in these galaxies. Our result is a typical dust-to-gas ratio of 0.04, with some evidence that this ratio declines with galactocentric radius, consistent with recent Herschel results. We discuss the possible causes of this high dust-to-gas ratio; an over-estimate of the dust surface-density, an under-estimate of the molecular hydrogen density from CO maps or a combination of both. We note that while our value of the mean dust-to-gas ratio is high, it is consistent with the metallicity at the measured radii if one assumes the Pilyugin & Thuan (2005) calibration of gas metallicity.

  5. WHICH GALAXIES HOST BARS AND DISKS? A STUDY OF THE COMA CLUSTER

    SciTech Connect

    Mendez-Abreu, J.; Aguerri, J. A. L. E-mail: jalfonso@iac.es

    2010-03-10

    We present a study of the bar fraction in the Coma Cluster galaxies based on a sample of {approx}190 galaxies selected from the Sloan Digital Sky Survey Data Release 6 and observed with the Hubble Space Telescope (HST) Advanced Camera for Survey (ACS). The unprecedented resolution of the HST-ACS images allows us to explore the presence of bars, detected by visual classification, throughout a luminosity range of 9 mag (-23 {approx}< M{sub r} {approx}< -14), permitting us to study the poor known region of dwarf galaxies. We find that bars are hosted by galaxies in a tight range of both luminosities (-22 {approx}< M{sub r} {approx}< -17) and masses (10{sup 9}{approx}galaxies. In addition, we find that the bar fraction does not vary significantly when going from the center to the cluster outskirts, implying that cluster environment plays a second-order role in bar formation/evolution. The shape of the bar fraction distribution with respect to both luminosity and mass is well matched by the luminosity distribution of disk galaxies in Coma, indicating that bars are good tracers of cold stellar disks. We discuss the implications of our results for the formation and evolution scenarios of bars and disks.

  6. Forming Disk Galaxies in Wet Major Mergers. I. Three Fiducial Examples

    NASA Astrophysics Data System (ADS)

    Athanassoula, E.; Rodionov, S. A.; Peschken, N.; Lambert, J. C.

    2016-04-01

    Using three fiducial N-body+SPH simulations, we follow the merging of two disk galaxies that each have a hot gaseous halo component, and examine whether the merger remnant can be a spiral galaxy. The stellar progenitor disks are destroyed by violent relaxation during the merging and most of their stars form a classical bulge, while the remaining stars, as well as stars born during the merging times, form a thick disk and its bar. A new stellar disk forms subsequently and gradually in the remnant from the gas accreted mainly from the halo. It is vertically thin and well extended in its equatorial plane. A bar starts forming before the disk is fully in place, which is contrary to what is assumed in idealized simulations of isolated bar-forming galaxies, and has morphological features such as ansae and boxy/peanut bulges. Stars of different ages populate different parts of the box/peanut. A disky pseudobulge also forms, so that by the end of the simulation all three types of bulges coexist. The oldest stars are found in the classical bulge, followed by those of the thick disk, then by those in the thin disk. The youngest stars are in the spiral arms and the disky pseudobulge. The disk surface density profiles are of type II (exponential with downbending); the circular velocity curves are flat and show that the disks are submaximum in these examples: two clearly so and one near-borderline between maximum and submaximum. On average, only roughly between 10% and 20% of the stellar mass is in the classical bulge of the final models, i.e., much less than in previous simulations.

  7. Falling Outer Rotation Curves of Star-forming Galaxies at 0.6 ≲ z ≲ 2.6 Probed with KMOS3D and SINS/zC-SINF

    NASA Astrophysics Data System (ADS)

    Lang, Philipp; Förster Schreiber, Natascha M.; Genzel, Reinhard; Wuyts, Stijn; Wisnioski, Emily; Beifiori, Alessandra; Belli, Sirio; Bender, Ralf; Brammer, Gabe; Burkert, Andreas; Chan, Jeffrey; Davies, Ric; Fossati, Matteo; Galametz, Audrey; Kulkarni, Sandesh K.; Lutz, Dieter; Mendel, J. Trevor; Momcheva, Ivelina G.; Naab, Thorsten; Nelson, Erica J.; Saglia, Roberto P.; Seitz, Stella; Tacchella, Sandro; Tacconi, Linda J.; Tadaki, Ken-ichi; Übler, Hannah; van Dokkum, Pieter G.; Wilman, David J.

    2017-05-01

    We exploit the deep, resolved, Hα kinematic data from the KMOS3D and SINS/zC-SINF surveys to examine the largely unexplored outer-disk kinematics of star-forming galaxies (SFGs), out to the peak of cosmic star formation. Our sample contains 101 SFGs, representative of the more massive (9.3≲ {log}{M}* /{M}⊙ ≲ 11.5) main sequence population at 0.6 ≤ z ≤ 2.6. Through a novel stacking approach, we are able to constrain a representative rotation curve extending out to ˜4 effective radii. This average rotation curve exhibits a significant drop in rotation velocity beyond the turnover, with a slope of {{Δ }}V/{{Δ }}R=-{0.26}-0.09+0.10 in units of normalized coordinates V/V max and R/R turn. This result confirms that the fall-off seen in some individual galaxies is a common feature of our sample of high-z disks. The outer fall-off strikingly deviates from the flat or mildly rising rotation curves of local spiral galaxies that have similar masses. Through a comparison with models that include baryons and dark matter, we demonstrate that the falling stacked rotation curve is consistent with a high mass fraction of baryons, relative to the total dark matter halo (m d ≳ 0.05), in combination with a sizeable level of pressure support in the outer disk. These findings agree with recent studies demonstrating that high-z star-forming disks are strongly baryon-dominated within the disk scale, and furthermore suggest that pressure gradients caused by large, turbulent gas motions are present even in their outer disks. These results are largely independent of our model assumptions, such as the presence of stellar bulges, the effect of adiabatic contraction, and variations in halo concentration.

  8. Survival of Pure Disk Galaxies over the Last 8 Billion Years

    NASA Astrophysics Data System (ADS)

    Sachdeva, Sonali; Saha, Kanak

    2016-03-01

    Pure disk galaxies without any bulge component, i.e., bulges that are neither classical nor pseudo, seem to have escaped the effects of merger activity that are inherent to hierarchical galaxy formation models as well as strong internal secular evolution. We discover that a significant fraction (˜15%-18%) of disk galaxies in the Hubble Deep Field (0.4\\lt z\\lt 1.0) and in the local universe (0.02\\lt z\\lt 0.05) are such pure disk systems (PDSs). The spatial distribution of light in these PDSs is well-described by a single exponential function from the outskirts to the center and appears to have remained intact over the last 8 billion years, keeping the mean central surface brightness and scale-length nearly constant. These two disk parameters of PDSs are brighter and shorter, respectively, than those of disks which are part of disk galaxies with bulges. Since the fraction of PDSs, as well as their profile-defining parameters, do not change, this indicates that these galaxies have not witnessed either major mergers or multiple minor mergers since z˜ 1. However, there is a substantial increase in their total stellar mass and total size over the same time range. This suggests that smooth accretion of cold gas via cosmic filaments is the most probable mode of their evolutions. We speculate that PDSs are dynamically hotter and cushioned in massive dark matter halos, which may prevent them from undergoing strong secular evolution.

  9. Wind from the black-hole accretion disk driving a molecular outflow in an active galaxy.

    PubMed

    Tombesi, F; Meléndez, M; Veilleux, S; Reeves, J N; González-Alfonso, E; Reynolds, C S

    2015-03-26

    Powerful winds driven by active galactic nuclei are often thought to affect the evolution of both supermassive black holes and their host galaxies, quenching star formation and explaining the close relationship between black holes and galaxies. Recent observations of large-scale molecular outflows in ultraluminous infrared galaxies support this quasar-feedback idea, because they directly trace the gas from which stars form. Theoretical models suggest that these outflows originate as energy-conserving flows driven by fast accretion-disk winds. Proposed connections between large-scale molecular outflows and accretion-disk activity in ultraluminous galaxies were incomplete because no accretion-disk wind had been detected. Conversely, studies of powerful accretion-disk winds have until now focused only on X-ray observations of local Seyfert galaxies and a few higher-redshift quasars. Here we report observations of a powerful accretion-disk wind with a mildly relativistic velocity (a quarter that of light) in the X-ray spectrum of IRAS F11119+3257, a nearby (redshift 0.189) optically classified type 1 ultraluminous infrared galaxy hosting a powerful molecular outflow. The active galactic nucleus is responsible for about 80 per cent of the emission, with a quasar-like luminosity of 1.5 × 10(46) ergs per second. The energetics of these two types of wide-angle outflows is consistent with the energy-conserving mechanism that is the basis of the quasar feedback in active galactic nuclei that lack powerful radio jets (such jets are an alternative way to drive molecular outflows).

  10. A characteristic oxygen abundance gradient in galaxy disks unveiled with CALIFA

    NASA Astrophysics Data System (ADS)

    Sánchez, S. F.; Rosales-Ortega, F. F.; Iglesias-Páramo, J.; Mollá, M.; Barrera-Ballesteros, J.; Marino, R. A.; Pérez, E.; Sánchez-Blazquez, P.; González Delgado, R.; Cid Fernandes, R.; de Lorenzo-Cáceres, A.; Mendez-Abreu, J.; Galbany, L.; Falcon-Barroso, J.; Miralles-Caballero, D.; Husemann, B.; García-Benito, R.; Mast, D.; Walcher, C. J.; Gil de Paz, A.; García-Lorenzo, B.; Jungwiert, B.; Vílchez, J. M.; Jílková, Lucie; Lyubenova, M.; Cortijo-Ferrero, C.; Díaz, A. I.; Wisotzki, L.; Márquez, I.; Bland-Hawthorn, J.; Ellis, S.; van de Ven, G.; Jahnke, K.; Papaderos, P.; Gomes, J. M.; Mendoza, M. A.; López-Sánchez, Á. R.

    2014-03-01

    We present the largest and most homogeneous catalog of H ii regions and associations compiled so far. The catalog comprises more than 7000 ionized regions, extracted from 306 galaxies observed by the CALIFA survey. We describe the procedures used to detect, select, and analyze the spectroscopic properties of these ionized regions. In the current study we focus on characterizing of the radial gradient of the oxygen abundance in the ionized gas, based on the study of the deprojecteddistribution of H ii regions. We found that all galaxies without clear evidence of an interaction present a common gradient in the oxygen abundance, with a characteristic slope of αO/H = -0.1 dex/re between 0.3 and 2 disk effective radii (re), and a scatter compatible with random fluctuations around this value, when the gradient is normalized to the disk effective radius. The slope is independent of morphology, the incidence of bars, absolute magnitude, or mass. Only those galaxies with evidence of interactions and/or clear merging systems present a significantly shallower gradient, consistent with previous results. The majority of the 94 galaxies with H ii regions detected beyond two disk effective radii present a flattening in the oxygen abundance. The flattening is statistically significant. We cannot provide a conclusive answer regarding the origin of this flattening. However, our results indicate that its origin is most probably related to the secular evolution of galaxies. Finally, we find a drop/truncation of the oxygen abundance in the inner regions for 26 of the galaxies. All of them are non-interacting, mostly unbarred Sb/Sbc galaxies. This feature is associated with a central star-forming ring, which suggests that both features are produced by radial gas flows induced by resonance processes. Our result suggests that galaxy disks grow inside-out, with metal enrichment driven by the local star formation history and with a small variation galaxy-by-galaxy. At a certain

  11. The Size-Luminosity Relation of Disk Galaxies in EDisCS Clusters

    NASA Astrophysics Data System (ADS)

    Gogarten, Stephanie M.; Dalcanton, J. J.; Simard, L.; Rudnick, G.; Desai, V.; EDisCS Collaboration

    2006-12-01

    We present the size-luminosity relation (SLR) for disk galaxies observed in eight clusters from the ESO Distant Cluster Survey (EDisCS). These clusters, at redshifts 0.4 < z < 0.8, were observed with the Hubble Space Telescope's Advanced Camera for Surveys. While we observe a change in the SLR with redshift, namely that there is an absence of low surface brightness galaxies at high redshift, we demonstrate that this could be a product of selection effects and thus is not a confirmation of evolution. We also compare the SLR for cluster and field galaxies in each redshift bin and see no significant effects of environment on the SLR.

  12. Generation and maintenance of bisymmetric spiral magnetic fields in disk galaxies in differential rotation

    NASA Astrophysics Data System (ADS)

    Sawa, Takeyasu; Fujimoto, M.

    1993-05-01

    The approximate dynamo equation, which yields asymptotic solutions for the large scale bisymmetric spiral (BSS) magnetic fields rotating rigidly over a large area of the galactic disk, is derived. The vertical thickness and the dynamo strength of the gaseous disk which are necessary to generate and sustain the BSS magnetic fields is determined. The globally BSS magnetic fields which propagate over the disk as a wave without being twisted more tightly are reproduced. A poloidal field configuration is theoretically predicted in the halo around the disk, and is observed in the edge-on galaxy NGC4631. Mathematical methods for the galactic dynamo are shown to be equivalent. Those methods give different growth rates between the BSS and the axisymmetric spiral (ASS) magnetic fields in the disk. Magnetohydrodynamical excitation is discussed between the BSS magnetic fields and the two armed spiral density waves.

  13. Tidal disruption events from eccentric nuclear disks in post-merger galaxies

    NASA Astrophysics Data System (ADS)

    Madigan, Ann-Marie

    Surprisingly, in more than twenty percent of nearby elliptical galaxies, the distribution of stars orbiting the central supermassive black hole is strongly asymmetric. In these galaxies, the stars are on apsidally-aligned orbits in an eccentric nuclear disk. Long thought to be exotic, this configuration is quite common in our local universe. Despite the prevalence of eccentric disks however, their dynamics have been largely overlooked. Naively, one might expect that packing orbits so closely together would make them violently unstable to gravitational scattering, or that differential precession would wipe out their large-scale apsidal-alignment. We have recently identified a new dynamical mechanism which stabilizes eccentric nuclear disks (Madigan et al., 2016), thus explaining their observed ubiquity. The stabilizing mechanism produces oscillations of orbital eccentricities of stars in the disk, pushing many stars extremely close to the black hole. If these disks form in gas-rich mergers, as is found in cosmological simulations, there will be an enhanced rate of stellar tidal disruption events (TDEs) following the merger. In a preliminary calculation, we show the TDE rate is initially so high that the nucleus would appear as an AGN, or as a changing-look-quasar. We therefore suggest that accretion of dense stellar material may contribute significantly to the growth of supermassive black holes; if so, this could explain the presence of supermassive black holes in the extremely early universe, z>7, as well as the peaking of quasar activity around z 2, when the galaxy merger rate peaks. Our model can also explain the recently observed preference of TDEs in post-merger, post-starburst (K+A) galaxies. Here we propose to quantify these calculations. We will also undertake a statistical analysis of the literature to determine the true occurrence rate of eccentric nuclear disks. Long after the merger and the K+A phase, eccentric disks no longer directly produce TDEs

  14. Molecular disks in radio galaxies. The pathway to ALMA

    NASA Astrophysics Data System (ADS)

    Prandoni, I.; Laing, R. A.; de Ruiter, H. R.; Parma, P.

    2010-11-01

    Context. It has recently been proposed that the jets of low-luminosity radio galaxies are powered by direct accretion of the hot phase of the IGM onto the central black hole. Cold gas remains a plausible alternative fuel supply, however. The most compelling evidence that cold gas plays a role in fueling radio galaxies is that dust is detected more commonly and/or in larger quantities in (elliptical) radio galaxies compared with radio-quiet elliptical galaxies. On the other hand, only small numbers of radio galaxies have yet been detected in CO (and even fewer imaged), and whether or not all radio galaxies have enough cold gas to fuel their jets remains an open question. If so, then the dynamics of the cold gas in the nuclei of radio galaxies may provide important clues to the fuelling mechanism. Aims: The only instrument capable of imaging the molecular component on scales relevant to the accretion process is ALMA, but very little is yet known about CO in southern radio galaxies. Our aim is to measure the CO content in a complete volume-limited sample of southern radio galaxies, in order to create a well-defined list of nearby targets to be imaged in the near future with ALMA. Methods: APEX [This publication is based on data acquired with the Atacama Pathfinder Experiment (APEX). APEX is a collaboration between the Max-Planck-Institut fur Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory.] has recently been equipped with a receiver (APEX-1) able to observe the 230 GHz waveband. This allows us to search for CO(2-1) line emission in our target galaxies. Results: Here we present the results for our first three southern targets, proposed for APEX-1 spectroscopy during science verification: NGC 3557, IC 4296 and NGC 1399. The experiment was successful with two targets detected, and possible indications for a double-horned CO line profile, consistent with ordered rotation. These early results are encouraging, demonstrating that APEX can

  15. Megamaser Disks Reveal a Broad Distribution of Black Hole Mass in Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Greene, J. E.; Seth, A.; Kim, M.; Läsker, R.; Goulding, A.; Gao, F.; Braatz, J. A.; Henkel, C.; Condon, J.; Lo, K. Y.; Zhao, W.

    2016-08-01

    We use new precision measurements of black hole (BH) masses from water megamaser disks to investigate scaling relations between macroscopic galaxy properties and supermassive BH mass. The megamaser-derived BH masses span 106-108 {M}⊙ , while all the galaxy properties that we examine (including total stellar mass, central mass density, and central velocity dispersion) lie within a narrower range. Thus, no galaxy property correlates tightly with {M}{BH} in ˜L* spiral galaxies as traced by megamaser disks. Of them all, stellar velocity dispersion provides the tightest relation, but at fixed {σ }* the mean megamaser {M}{BH} are offset by -0.6 ± 0.1 dex relative to early-type galaxies. Spiral galaxies with non-maser dynamical BH masses do not appear to show this offset. At low mass, we do not yet know the full distribution of BH mass at fixed galaxy property; the non-maser dynamical measurements may miss the low-mass end of the BH distribution due to an inability to resolve their spheres of influence and/or megamasers may preferentially occur in lower-mass BHs.

  16. Studying nearby disk galaxies with the CALIFA survey.

    NASA Astrophysics Data System (ADS)

    Marino, R. A.; Gil de Paz, A.; Sánchez, S. F.; Castillo-Morales, A.; CALIFA Team

    CALIFA, the Calar Alto Legacy Integral Field Area survey, will provide the largest and most comprehensive wide-field IFU survey of galaxies carried out to date, addressing several fundamental issues in galactic structure and evolution. We will observe a statistically well-defined sample of ˜ 600 galaxies in the local universe using 210 observing nights already awarded with the PMAS/PPAK integral field spectrophotometer, mounted on the Calar Alto 3.5m telescope. The definining science drivers for the project are: a) star formation and chemical history of galaxies, b) the physical state of the interstellar medium, c) stellar and gas kinematics in galaxies, and d) the influence of the AGNs on galaxy evolution. The CALIFA project comprises researchers from a large number of institutions worldwide: 8 institutions in Spain, 4 in Germany (CAHA funding countries) and 11 elsewhere, and includes a total of 56 researchers. CALIFA will provide a valuable bridge between large single-aperture surveys such as SDSS and more detailed studies of individual galaxies with PPAK (e.g. PINGS), SAURON, VIRUS-P, and other instruments.

  17. The complex structure of stars in the outer galactic disk as revealed by Pan-STARRS1

    SciTech Connect

    Slater, Colin T.; Bell, Eric F.; Schlafly, Edward F.; Martin, Nicolas F.; Rix, Hans-Walter; Morganson, Eric; Peñarrubia, Jorge; Bernard, Edouard J.; Ferguson, Annette M. N.; Martinez-Delgado, David; Wyse, Rosemary F. G.; Burgett, William S.; Chambers, Kenneth C.; Hodapp, Klaus W.; Kaiser, Nicholas; Magnier, Eugene A.; Tonry, John L.; Draper, Peter W.; Metcalfe, Nigel; Price, Paul A.; and others

    2014-08-10

    We present a panoptic view of the stellar structure in the Galactic disk's outer reaches commonly known as the Monoceros Ring, based on data from Pan-STARRS1. These observations clearly show the large extent of the stellar overdensities on both sides of the Galactic disk, extending between b = –25° and b = +35° and covering over 130° in Galactic longitude. The structure exhibits a complex morphology with both stream-like features and a sharp edge to the structure in both the north and the south. We compare this map to mock observations of two published simulations aimed at explaining such structures in the outer stellar disk, one postulating an origin as a tidal stream and the other demonstrating a scenario where the disk is strongly distorted by the accretion of a satellite. These morphological comparisons of simulations can link formation scenarios to observed structures, such as demonstrating that the distorted-disk model can produce thin density features resembling tidal streams. Although neither model produces perfect agreement with the observations—the tidal stream predicts material at larger distances that is not detected while in the distorted disk model, the midplane is warped to an excessive degree—future tuning of the models to accommodate these latest data may yield better agreement.

  18. Interaction of the stream from L 1 with the outer edge of the accretion disk in a cataclysmic variable

    NASA Astrophysics Data System (ADS)

    Kaigorodov, P. V.; Bisikalo, D. V.; Kurbatov, E. P.

    2017-08-01

    Vertical oscillations of the gas at the outer edge of the accretion disk in a semi-detached binary due to interaction with the stream of matter from the inner Lagrangian point L 1 are considered. Mixing of the matter from the stream from L 1 with matter of the disk halo results in the formation of a system of two diverging shocks and a contact discontinuity, or so-called "hot line". The passage of matter through the region of the hot line leads to an increase in its vertical velocity and a thickening of the disk at phases 0.7-0.8. Subsequently, the matter moving along the outer edge of the disk also experiences vertical oscillations, forming secondary maxima at phases 0.2-0.4. It is shown that, for systems with component mass ratios of 0.6, these oscillations will be amplified with each passage of the matter through the hotline zone, while the observations will be quenched in systems with component mass ratios 0.07 and 7. The most favorable conditions for the flow of matter from the stream through the edge of the disk arise for component mass ratios 0.62. A theoretical relation between the phases of disk thickenings and the component mass ratio of the system is derived.

  19. Galactic Winds Driven by Isotropic and Anisotropic Cosmic-Ray Diffusion in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Pakmor, R.; Pfrommer, C.; Simpson, C. M.; Springel, V.

    2016-06-01

    The physics of cosmic rays (CRs) is a promising candidate for explaining the driving of galactic winds and outflows. Recent galaxy formation simulations have demonstrated the need for active CR transport either in the form of diffusion or streaming to successfully launch winds in galaxies. However, due to computational limitations, most previous simulations have modeled CR transport isotropically. Here, we discuss high-resolution simulations of isolated disk galaxies in a 1011 M ⊙ halo with the moving-mesh code Arepo that include injection of CRs from supernovae, advective transport, CR cooling, and CR transport through isotropic or anisotropic diffusion. We show that either mode of diffusion leads to the formation of strong bipolar outflows. However, they develop significantly later in the simulation with anisotropic diffusion compared to the simulation with isotropic diffusion. Moreover, we find that isotropic diffusion allows most of the CRs to quickly diffuse out of the disk, while in the simulation with anisotropic diffusion, most CRs remain in the disk once the magnetic field becomes dominated by its azimuthal component, which occurs after ˜300 Myr. This has important consequences for the gas dynamics in the disk. In particular, we show that isotropic diffusion strongly suppresses the amplification of the magnetic field in the disk compared to anisotropic or no diffusion models. We therefore conclude that reliable simulations which include CR transport inevitably need to account for anisotropic diffusion.

  20. Studying nearby disk galaxies with the CALIFA survey

    NASA Astrophysics Data System (ADS)

    Marino, R. A.; Gil de Paz, A.; Sánchez, S. F.; Castillo-Morales, A.

    2011-11-01

    CALIFA, the Calar Alto Legacy Integral Field Area survey, will provide the largest and most comprehensive wide-field IFU survey of galaxies carried out to date, combining the advantages of imaging and spectroscopy we will able to understand the origin for the observed diversity of galaxies, and the physical mechanisms -intrinsic and environmental- that are responsible for the differences as well as similarities between them. We will observe a statistically well-defined sample of ˜ 600 galaxies in the local universe (0.005 < z < 0.03) using 210 observing nights already awarded with the PMAS/PPAK integral field spectrophotometer, mounted on the Calar Alto 3.5 m telescope. PPAK offers a combination of extremely wide field-of-view (> 1 arcmin^2) with a high filling factor in one single pointing (65%), good spectral resolution, and wavelength sensitivity across the optical spectrum. The spectra will be covering the range 3700-7000 Å in two overlapping setups, one in the red (4300-7000 Å) at a spectral resolution of R ˜ 1000 and one in the blue (3700-5000 Å) at R ˜ 2000. The fully reduced and flux calibrated data of this legacy survey will be made available to the public. Some of definining science drivers for the CALIFA project are the star formation and the chemical history of galaxies; the study of the physical state of the interstellar medium; improve our knowledge on the stellar and gas kinematics in galaxies, and understand the influence of the AGNs on galaxy evolution. The CALIFA project comprises researchers from a large number of institutions worldwide: 8 institutions in Spain, 4 in Germany (CAHA funding countries) and 11 elsewhere, and includes a total of 56 researchers. CALIFA will provide a valuable bridge between large single-aperture surveys such as SDSS and more detailed studies of individual galaxies with PPAK (e.g. PINGS), SAURON, VIRUS-P, and other instruments.

  1. Spatially-resolved SFR in nearby disk galaxies using IFS data

    NASA Astrophysics Data System (ADS)

    Catalán-Torrecilla, C.; Gil de Paz, A.; Castillo-Morales, A.; Méndez-Abreu, J.; Pascual, S.; Ruiz-Lara, T.; de Lorenzo-Cáceres, A.; Sánchez-Menguiano, L.

    2017-03-01

    Exploring the spatial distribution of the star formation rate (SFR) in nearby galaxies is essential to understand their evolution through cosmic time. With this aim in mind, we use a representative sample that contains a variety of morphological types, the CALIFA Integral Field Spectroscopy (IFS) sample. Previous to this work, we have verified that our extinction-corrected Hα measurements successfully reproduce the values derived from other SFR tracers such as Hα obs + IR or UV obs + IR (Catalán-Torrecilla et al. 2015). Now, we go one step further applying 2-dimensional photometric decompositions (Méndez-Abreu et al. (2008), Méndez-Abreu et al. (2014)) over these datacubes. This method allows us to obtain the amount of SFR in the central part (bulge or nuclear source), the bar and the disk, separately. First, we determine the light coming from each component as the ratio between the luminosity in every component (bulge, bar or disk) and the total luminosity of the galaxy. Then, for each galaxy we multiply the IFS datacubes by these previous factors to recover the luminosity in each component. Finally, we derive the spectrum associated to each galaxy component integrating the spatial information in the weighted datacube using an elliptical aperture covering the whole galaxy. 2D photometric decomposition applied over 3D datacubes will give us a more detailed understanding of the role that disks play in more massive galaxies. Knowing if the disks in more massive SF galaxies have on average a lower or higher level of star formation activity and how these results are affected by the presence of nuclear bars are still open questions that we can now solve. We describe the behavior of these components in the SFR vs. stellar mass diagram. In particular, we highlight the role of the disks and their contribution to both the integrated SFR for the whole galaxy and the SFR in the disk at different stellar masses in the SFR vs. stellar mass diagram together with their

  2. AN OBSERVED LINK BETWEEN ACTIVE GALACTIC NUCLEI AND VIOLENT DISK INSTABILITIES IN HIGH-REDSHIFT GALAXIES

    SciTech Connect

    Bournaud, Frederic; Juneau, Stephanie; Le Floc'h, Emeric; Mullaney, James; Daddi, Emanuele; Duc, Pierre-Alain; Elbaz, David; Salmi, Fadia; Dekel, Avishai; Dickinson, Mark

    2012-09-20

    We provide evidence for a correlation between the presence of giant clumps and the occurrence of active galactic nuclei (AGNs) in disk galaxies. Giant clumps of 10{sup 8}-10{sup 9} M{sub Sun} arise from violent gravitational instability in gas-rich galaxies, and it has been proposed that this instability could feed supermassive black holes (BHs). We use emission line diagnostics to compare a sample of 14 clumpy (unstable) disks and a sample of 13 smoother (stable) disks at redshift z {approx} 0.7. The majority of clumpy disks in our sample have a high probability of containing AGNs. Their [O III] {lambda}5007 emission line is strongly excited, inconsistent with low-metallicity star formation (SF) alone. [Ne III] {lambda}3869 excitation is also higher. Stable disks rarely have such properties. Stacking ultra sensitive Chandra observations (4 Ms) reveals an X-ray excess in clumpy galaxies, which confirms the presence of AGNs. The clumpy galaxies in our intermediate-redshift sample have properties typical of gas-rich disk galaxies rather than mergers, being in particular on the main sequence of SF. This suggests that our findings apply to the physically similar and numerous gas-rich unstable disks at z > 1. Using the observed [O III] and X-ray luminosities, we conservatively estimate that AGNs hosted by clumpy disks have typical bolometric luminosities of the order of a few 10{sup 43} erg s{sup -1}, BH growth rates m-dot{sub BH}{approx}10{sup -2} M{sub Sun} yr{sup -1}, and that these AGNs are substantially obscured in X-rays. This moderate-luminosity mode could provide a large fraction of today's BH mass with a high duty cycle (>10%), accretion bursts with higher luminosities being possible over shorter phases. Violent instabilities at high redshift (giant clumps) are a much more efficient driver of BH growth than the weak instabilities in nearby spirals (bars), and the evolution of disk instabilities with mass and redshift could explain the simultaneous downsizing of

  3. 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

  4. 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

  5. Magnetohydrodynamic Simulations of Disk GalaxyFormation: the Magnetization of The Cold and Warm Medium

    SciTech Connect

    Wang, Peng; Abel, Tom; /KIPAC, Menlo Park /Santa Barbara, KITP

    2007-12-18

    Using magnetohydrodynamic (MHD) adaptive mesh refinement simulations, we study the formation and early evolution of disk galaxies with a magnetized interstellar medium. For a 10{sup 10} M{sub {circle_dot}} halo with initial NFW dark matter and gas profiles, we impose a uniform 10{sup -9} G magnetic field and follow its collapse, disk formation and evolution up to 1 Gyr. Comparing to a purely hydrodynamic simulation with the same initial condition, we find that a protogalactic field of this strength does not significantly influence the global disk properties. At the same time, the initial magnetic fields are quickly amplified by the differentially rotating turbulent disk. After the initial rapid amplification lasting {approx} 500 Myr, subsequent field amplification appears self-regulated. As a result, highly magnetized material begin to form above and below the disk. Interestingly, the field strengths in the self-regulated regime agrees well with the observed fields in the Milky Way galaxy both in the warm and the cold HI phase and do not change appreciably with time. Most of the cold phase shows a dispersion of order ten in the magnetic field strength. The global azimuthal magnetic fields reverse at different radii and the amplitude declines as a function of radius of the disk. By comparing the estimated star formation rate (SFR) in hydrodynamic and MHD simulations, we find that after the magnetic field strength saturates, magnetic forces provide further support in the cold gas and lead to a decline of the SFR.

  6. Circumnuclear Disks in Early-type Galaxies: 12CO(2-1) and Continuum Properties

    NASA Astrophysics Data System (ADS)

    Boizelle, Benjamin; Barth, Aaron J.; Baker, Andrew J.; Darling, Jeremiah K.; Ho, Luis; Walsh, Jonelle; Buote, David A.

    2017-01-01

    Black hole masses in early-type galaxies (ETGs) can be precisely measured using the kinematics of circumnuclear gas. About 10% of nearby ETGs possess round, morphologically regular nuclear dust disks. The accompanying molecular gas is expected to be in uniform, circular rotation and therefore be a good dynamical tracer of the inner galaxy potential. Using ALMA, we have obtained 0.3”-resolution observations of thirteen ETGs which were selected based on the presence of nuclear dust disks seen in HST images. Most are detected in CO(2-1), and we find that these molecular gas disks are in dynamically cold rotation with a few showing clear evidence of rapid central rotation. We present the gas distributions and kinematics of these molecular disks, as well as the continuum properties of the dusty disks and the prevalence of low-luminosity active galactic nuclei at their centers. We discuss the suitability of molecular gas disks in ETGs for making precision measurements of black hole masses.

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

    NASA Astrophysics Data System (ADS)

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

    2008-05-01

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

  8. KINEMATIC CLASSIFICATIONS OF LOCAL INTERACTING GALAXIES: IMPLICATIONS FOR THE MERGER/DISK CLASSIFICATIONS AT HIGH-z

    SciTech Connect

    Hung, Chao-Ling; Larson, Kirsten L.; Sanders, D. B.; Rich, Jeffrey A.; Yuan, Tiantian; Kewley, Lisa J.; Casey, Caitlin M.; Smith, Howard A.; Hayward, Christopher C.

    2015-04-20

    The classification of galaxy mergers and isolated disks is key for understanding the relative importance of galaxy interactions and secular evolution during the assembly of galaxies. Galaxy kinematics as traced by emission lines have been used to suggest the existence of a significant population of high-z star-forming galaxies consistent with isolated rotating disks. However, recent studies have cautioned that post-coalescence mergers may also display disk-like kinematics. To further investigate the robustness of merger/disk classifications based on kinematic properties, we carry out a systematic classification of 24 local (U)LIRGs spanning a range of morphologies: from isolated spiral galaxies, ongoing interacting systems, to fully merged remnants. We artificially redshift the Wide Field Spectrograph observations of these local (U)LIRGs to z = 1.5 to make a realistic comparison with observations at high-z, and also to ensure that all galaxies have the same spatial sampling of ∼900 pc. Using both kinemetry-based and visual classifications, we find that the reliability of kinematic classification shows a strong trend with the interaction stage of galaxies. Mergers with two nuclei and tidal tails have the most distinct kinematics compared to isolated disks, whereas a significant population of the interacting disks and merger remnants are indistinguishable from isolated disks. The high fraction of mergers displaying disk-like kinematics reflects the complexity of the dynamics during galaxy interactions. Additional merger indicators such as morphological properties traced by stars or molecular gas are required to further constrain the merger/disk classifications at high-z.

  9. Calorimetric studies of bovine rod outer segment disk membranes support a monomeric unit for both rhodopsin and opsin.

    PubMed

    Edrington, Thomas C; Bennett, Michael; Albert, Arlene D

    2008-09-15

    The photoreceptor rhodopsin is a G-protein coupled receptor that has recently been proposed to exist as a dimer or higher order oligomer, in contrast to the previously described monomer, in retinal rod outer segment disk membranes. Rhodopsin exhibits considerably greater thermal stability than opsin (the bleached form of the receptor), which is reflected in an approximately 15 degrees C difference in the thermal denaturation temperatures (T(m)) of rhodopsin and opsin as measured by differential scanning calorimetry. Here we use differential scanning calorimetry to investigate the effect of partial bleaching of disk membranes on the T(m) of rhodopsin and of opsin in native disk membranes, as well as in cross-linked disk membranes in which rhodopsin dimers are known to be present. The T(m)s of rhodopsin and opsin are expected to be perturbed if mixed oligomers are present. The T(m) remained constant for rhodopsin and opsin in native disks regardless of the level of bleaching. In contrast, the T(m) of cross-linked rhodopsin in disk membranes was dependent on the extent of bleaching. The energy of activation for denaturation of rhodopsin and cross-linked rhodopsin was calculated. Cross-linking rhodopsin significantly decreased the energy of activation. We conclude that in native disk membranes, rhodopsin behaves predominantly as a monomer.

  10. GAS INFLOW AND OUTFLOW HISTORIES IN DISK GALAXIES AS REVEALED FROM OBSERVATIONS OF DISTANT STAR-FORMING GALAXIES

    SciTech Connect

    Toyouchi, Daisuke; Chiba, Masashi

    2015-09-01

    We investigate gas inflow and outflow histories in Milky Way-like disk galaxies, to get new insights into the baryonic processes in galaxy formation and evolution. For this purpose, we solve the equations for the evolution of the surface mass densities of gas and metals at each radius in a galactic disk, based on the observed structural properties of distant star-forming galaxies, including the redshift evolution of their stellar mass distribution, their scaling relation between the mass of baryonic components, star formation rate (SFR), and chemical abundance, as well as the supposed evolution of their radial metallicity gradients (RMGs). We find that the efficiency of gas inflow for a given SFR decreases with time and that the inflow rate is always nearly proportional to the SFR. For gas outflow, although its efficiency for a given SFR is a decreasing function of time, similar to gas inflow, the outflow rate is not necessarily proportional to the SFR and the relation between the outflow rate and SFR strongly depends on the evolution of the adopted RMG. We also find that the results on the outflow rate can be reproduced in the framework of a momentum-driven (energy-driven) wind mechanism if the RMG is steepening (flattening) with time. Therefore if the well-measured RMGs and their evolution for Milky Way-like galaxies are obtained from future observations, then our results will be useful to constrain the main driving mechanism for their galactic outflows.

  11. Bulge-forming Galaxies with an Extended Rotating Disk at z ~ 2

    NASA Astrophysics Data System (ADS)

    Tadaki, Ken-ichi; Genzel, Reinhard; Kodama, Tadayuki; Wuyts, Stijn; Wisnioski, Emily; Förster Schreiber, Natascha M.; Burkert, Andreas; Lang, Philipp; Tacconi, Linda J.; Lutz, Dieter; Belli, Sirio; Davies, Richard I.; Hatsukade, Bunyo; Hayashi, Masao; Herrera-Camus, Rodrigo; Ikarashi, Soh; Inoue, Shigeki; Kohno, Kotaro; Koyama, Yusei; Mendel, J. Trevor; Nakanishi, Kouichiro; Shimakawa, Rhythm; Suzuki, Tomoko L.; Tamura, Yoichi; Tanaka, Ichi; Übler, Hannah; Wilman, Dave J.

    2017-01-01

    We present 0.″2-resolution Atacama Large Millimeter/submillimeter Array observations at 870 μm for 25 Hα-seleced star-forming galaxies around the main sequence at z = 2.2-2.5. We detect significant 870 μm continuum emission in 16 (64%) of these galaxies. The high-resolution maps reveal that the dust emission is mostly radiated from a single region close to the galaxy center. Exploiting the visibility data taken over a wide uv distance range, we measure the half-light radii of the rest-frame far-infrared emission for the best sample of 12 massive galaxies with log(M*/M⊙) > 11. We find nine galaxies to be associated with extremely compact dust emission with R1/2,870 μm < 1.5 kpc, which is more than a factor of 2 smaller than their rest-optical sizes, < {R}1/2,1.6μ {{m}}> =3.2 {kpc}, and is comparable with optical sizes of massive quiescent galaxies at similar redshifts. As they have an exponential disk with Sérsic index of < {n}1.6μ {{m}}> =1.2 in the rest-optical, they are likely to be in the transition phase from extended disks to compact spheroids. Given their high star formation rate surface densities within the central 1 kpc of < {{Σ }}{{SFR}}1{kpc}> =40 M⊙ yr-1 kpc-2, the intense circumnuclear starbursts can rapidly build up a central bulge with ΣM*,1 kpc > 1010 M⊙ kpc-2 in several hundred megayears, i.e., by z ˜ 2. Moreover, ionized gas kinematics reveal that they are rotation supported with an angular momentum as large as that of typical star-forming galaxies at z = 1-3. Our results suggest that bulges are commonly formed in extended rotating disks by internal processes, not involving major mergers.

  12. On the Effective Oxygen Yield in the Disks of Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Zasov, A.; Saburova, A.; Abramova, O.

    2015-12-01

    The factors that influence the chemical evolution of galaxies are poorly understood. Both gas inflow and gas outflow reduce the gas-phase abundance of heavy elements (metallicity), whereas ongoing star formation continuously increases it. To exclude the stellar nucleosynthesis from consideration, we analyze for a sample of 14 spiral galaxies the radial distribution of the effective yield of oxygen yeff, which would be identical to the true stellar yield (per stellar generation) yo if the evolution followed the closed-box model. As the initial data for gas-phase abundance, we used the O/H radial profiles from Moustakas et al., based on two different calibrations (the PT2005 and KK2004 methods). In most of the galaxies with the PT2005 calibration, which we consider the preferred one, the yield yeff in the main disk (R≥slant 0.2 {R}25, where R25 is the optical radius) increases with radius, remaining lower than the empirically found true stellar yield yo. This may indicate the inflow of less-enriched gas predominantly to the inner disk regions, which reduces yeff. We show that the maximal values of the effective yield in the main disks of galaxies, {y}{eff,{max}}, anticorrelate with the total mass of galaxies and with the mass of their dark halos enclosed within R25. It allows us to propose the greater role of gas accretion for galaxies with massive halos. We also found that the radial gradient of oxygen abundance normalized to R25 has a tendency to be shallower in the systems with lower dark halo to stellar mass ratio within the optical radius, which, if confirmed, gives evidence of the effective radial mixing of gas in galaxies with a relatively light dark matter halo.

  13. SPARC: Mass Models for 175 Disk Galaxies with Spitzer Photometry and Accurate Rotation Curves

    NASA Astrophysics Data System (ADS)

    Lelli, Federico; McGaugh, Stacy S.; Schombert, James M.

    2016-12-01

    We introduce SPARC (Spitzer Photometry and Accurate Rotation Curves): a sample of 175 nearby galaxies with new surface photometry at 3.6 μm and high-quality rotation curves from previous H i/Hα studies. SPARC spans a broad range of morphologies (S0 to Irr), luminosities (∼5 dex), and surface brightnesses (∼4 dex). We derive [3.6] surface photometry and study structural relations of stellar and gas disks. We find that both the stellar mass–H i mass relation and the stellar radius–H i radius relation have significant intrinsic scatter, while the H i mass–radius relation is extremely tight. We build detailed mass models and quantify the ratio of baryonic to observed velocity (V bar/V obs) for different characteristic radii and values of the stellar mass-to-light ratio (ϒ⋆) at [3.6]. Assuming ϒ⋆ ≃ 0.5 M ⊙/L ⊙ (as suggested by stellar population models), we find that (i) the gas fraction linearly correlates with total luminosity (ii) the transition from star-dominated to gas-dominated galaxies roughly corresponds to the transition from spiral galaxies to dwarf irregulars, in line with density wave theory; and (iii) V bar/V obs varies with luminosity and surface brightness: high-mass, high-surface-brightness galaxies are nearly maximal, while low-mass, low-surface-brightness galaxies are submaximal. These basic properties are lost for low values of ϒ⋆ ≃ 0.2 M ⊙/L ⊙ as suggested by the DiskMass survey. The mean maximum-disk limit in bright galaxies is ϒ⋆ ≃ 0.7 M ⊙/L ⊙ at [3.6]. The SPARC data are publicly available and represent an ideal test bed for models of galaxy formation.

  14. The rapid formation of a large rotating disk galaxy three billion years after the Big Bang.

    PubMed

    Genzel, R; Tacconi, L J; Eisenhauer, F; Schreiber, N M Förster; Cimatti, A; Daddi, E; Bouché, N; Davies, R; Lehnert, M D; Lutz, D; Nesvadba, N; Verma, A; Abuter, R; Shapiro, K; Sternberg, A; Renzini, A; Kong, X; Arimoto, N; Mignoli, M

    2006-08-17

    Observations and theoretical simulations have established a framework for galaxy formation and evolution in the young Universe. Galaxies formed as baryonic gas cooled at the centres of collapsing dark-matter haloes; mergers of haloes and galaxies then led to the hierarchical build-up of galaxy mass. It remains unclear, however, over what timescales galaxies were assembled and when and how bulges and disks--the primary components of present-day galaxies--were formed. It is also puzzling that the most massive galaxies were more abundant and were forming stars more rapidly at early epochs than expected from models. Here we report high-angular-resolution observations of a representative luminous star-forming galaxy when the Universe was only 20% of its current age. A large and massive rotating protodisk is channelling gas towards a growing central stellar bulge hosting an accreting massive black hole. The high surface densities of gas, the high rate of star formation and the moderately young stellar ages suggest rapid assembly, fragmentation and conversion to stars of an initially very gas-rich protodisk, with no obvious evidence for a major merger.

  15. A Universal Coupling Relation between Luminous and Dark Matter Surface Densities in Disk Rotating Galaxies

    NASA Astrophysics Data System (ADS)

    Giraud, Edmond

    2000-03-01

    The mutual dynamical evolution of visible and dark matter in spiral galaxies may have resulted in some kind of coupling between the distributions of visible and dark matter today. This conjecture is empirically explored in the present paper, where rotation curves of 60 spiral galaxies and universal rotation curves are fitted using dark halo models with a distribution that depends on the luminous mass distribution. It is shown that the dark matter profiles of any universal rotation curve can be decomposed into two components: (1) a main component, called ``coupled halo,'' and (2) a component having a gaslike distribution, negligible in bright galaxies, but of increasing significance toward faint galaxies. Once the disk component (stars, gas, and gaslike component) is subtracted, the dark halo integrated surface densities, σd(r), are in a plane (in log scale) σ2d(r)=σγσ(r), where the fundamental parameters are the disk integrated surface density, σ(r), and a surface density, σγ, which depends on the galaxy system only and characterizes the relative importance of the dark halo to the disk mass. This is the coupled halo. In the case of an exponential disk, the coupled halo has a central profile of the form ρ~r-1 and a flat curve at r>=ropt. The fact that the gaslike component decreases with luminosity suggests that it may be transformed into stars, and therefore could be dark baryons, possibly cold gas in the disk. In these models, the baryonic fraction (stars, gas, and gaslike component) is almost a constant over a range of 5 mag, that is, ~30% at 1.5 optical radii. The stellar fraction of baryonic matter increases with luminosity. The model predicts a large fraction of gaslike baryonic dark matter in faint spiral galaxies, i.e., in H I gas-rich systems. The mass fraction of this gaslike component is negligible in a galaxy like the Milky Way, and reaches half the halo mass in the faint, low surface brightness galaxy DDO 154. Some fine-tuning relations, which

  16. Impact of magnetic fields on ram pressure stripping in disk galaxies

    SciTech Connect

    Ruszkowski, M.; Brüggen, M.; Lee, D.; Shin, M.-S.

    2014-03-20

    Ram pressure stripping can remove significant amounts of gas from galaxies in clusters and massive groups and thus has a large impact on the evolution of cluster galaxies. Recent observations have shown that key properties of ram-pressure-stripped tails of galaxies, such as their width and structure, are in conflict with predictions by simulations. To increase the realism of existing simulations, we simulated for the first time a disk galaxy exposed to a uniformly magnetized wind including radiative cooling and self-gravity of the gas. We find that magnetic fields have a strong effect on the morphology of the gas in the tail of the galaxy. While in the purely hydrodynamical case the tail is very clumpy, the magnetohydrodynamical case shows very filamentary structures in the tail. The filaments can be strongly supported by magnetic pressure and, wherever this is the case, the magnetic fields vectors tend to be aligned with the filaments. The ram pressure stripping process may lead to the formation of magnetized density tails that appear as bifurcated in the plane of the sky and resemble the double tails observed in ESO 137-001 and ESO 137-002. Such tails can be formed under a variety of situations, both for the disks oriented face-on with respect to the intracluster medium (ICM) wind and for the tilted ones. While this bifurcation is the consequence of the generic tendency for the magnetic fields to produce very filamentary tail morphology, the tail properties are further shaped by the combination of the magnetic field orientation and the sliding of the field past the disk surface exposed to the wind. Despite the fact that the effect of the magnetic field on the morphology of the tail is strong, magnetic draping does not strongly change the rate of gas stripping. For a face-on galaxy, the field tends to reduce the amount of gas stripping compared to the pure hydrodynamical case, and is associated with the formation of a stable magnetic draping layer on the side of

  17. Fueling nuclear activity in disk galaxies: Starbursts and monsters

    NASA Astrophysics Data System (ADS)

    Heller, Clayton H.; Shlosman, Isaac

    1994-03-01

    We study the evolution of the gas distribution in a globally unstable galactic disk with a particular emphasis on the gasdynamics in the central kiloparsec and the fueling activity there. The two-component self-gravitating disk is embedded in a responsive halo of comparable mass. The gas and stars are evolved using a three-dimensional hybrid smoothed particle hydrodynamics/N-body code and the gravitational interactions are calculated using a hierarchical TREE algorithm. A massive 'star formation' is introduced when the gas becomes Jeans unstable and locally exceeds the critical density of approximately 100 solar mass pc-3. The newly formed OB stars deposit energy in the gas by means of radiation-driven winds and supernovae. This energy is partially thermalized (efficiency of a few percent); the rest is radiated away. Models without star formation are evolved for a comparison. The effect of a massive object at the disk center is studied by placing a 'seed' black hole (BH) of 5 x 107 solar mass with an accretion radius of 20 pc. The tendency of the system to form a massive object 'spontaneously' is tested in models without the BH. We find that for models without star formation the bar- or dynamical friction-driven inflows lead to (1) domination of the central kpc by a few massive clouds that evolve into a single object probably via a cloud binary system, with and without a 'seed' BH, (2) accretion onto the BH which has a sporadic character, and (3) formation of remnant disks around the BH with a radius of 60-80 pc which result from the capture and digestion of clouds. For models with star formation, we find that (1) the enrgy input into the gas induces angular momentum loss and inflow rates by a factor less than 3, (2) the star formation is concentrated mainly at the apocenters of the gaseous circulation in the stellar bar and in the nuclear region, (3) the nuclear starburst phase appears to be very luminous approximately 1045-1046 erg/s and episodic with a typical

  18. Broad iron emission lines in Seyfert galaxies - re-condensation of gas onto an inner disk below the ADAF?

    NASA Astrophysics Data System (ADS)

    Meyer-Hofmeister, E.; Meyer, F.

    2011-03-01

    Context. The number of strong iron Kα line detections in Seyfert AGN is clearly growing in the Chandra, XMM-Newton and Suzaku era. The iron emission lines are broad, some are relativistically blurred. These relativistic disk lines have also been observed for galactic black hole X-ray binaries. Thermal components found in hard spectra were interpreted as an indication for a weak inner cool accretion disk underneath a hot corona. Aims: Accretion in low-mass X-ray binaries (LMXB) occurs during phases of high and low mass accretion rate, outburst and quiescence, soft and hard spectral state, respectively. After the soft/hard transition for some sources a thermal component is found, which can be interpreted as sustained by re-condensation of gas from an advection-dominated flow (ADAF) onto the disk. In view of the similarity of accretion flows around stellar mass and supermassive black holes we discuss whether the broad iron emission lines in Seyfert 1 AGN (active galactic nuclei) can be understood as arising from a similar accretion flow geometry as in X-ray binaries. Methods: We derive accretion rates for those Seyfert galaxies for which broad iron emission lines were observed, the "best candidates" in the investigations of Miller (2007, ARA&A, 45, 441) and Nandra et al. (2007, MNRAS, 382, 194). For the evaluation of the Eddington-scaled rates we use the observed X-ray luminosity, bolometric corrections and black hole masses from the literature. Results: The accretion rates derived for the Seyfert galaxies in our sample are less than 0.1 of the Eddington rate for more than half of the sources. For 107 to 108M⊙ black holes in Seyfert 1 AGN this limit corresponds to 0.01 to 0.2 M⊙/yr. This documents that the sources probably are in a hard spectral state and iron emission lines can arise from an inner weak accretion disk surrounded by an ADAF as predicted by the re-condensation model. Some of the remaining sources with higher accretion rates may be in a spectral

  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. Super Massive Black Holes in Disk Galaxies: HST/STIS Observations for 3 new Objects

    NASA Astrophysics Data System (ADS)

    Coccato, L.; Sarzi, M.; Corsini, E. M.; Pizzella, A.; Bertola, F.

    We present long-slit HST/STIS measurements of the ionized-gas kinematics in the nucleus of three disk galaxies, namely NGC 2179, NGC 4343, NGC 4435. The sample galaxies have been selected on the basis of their ground-based spectroscopy, for displaying a strong central velocity gradient for the ionized gas, which is consistent with the presence of a circumnuclear Keplerian disk (CNKD, Bertola et al. 1998; Funes et al. 2002) rotating around a super massive black hole (SMBH). For each target galaxy we obtained the Hα and [NII] 6583A kinematics along the major axis and two 0.25'' parallel offset positions. Out of three objects only NGC 4435 turned out to have a disk of ionized gas in regular motion and a regular dust-lane morphology. Preliminary modeling indicates a SMBH mass (MBH) one order of magnitude lower than the one expected from the MBH - αc relation for galaxies (Ferrarese & Merritt 2000; Gebhardt et al. 2000).

  1. KK 246: A DWARF GALAXY WITH AN EXTENDED H I DISK IN THE LOCAL VOID

    SciTech Connect

    Kreckel, K.; Van Gorkom, J. H.; Peebles, P. J. E.; Van de Weygaert, R.; Van der Hulst, J. M.

    2011-06-15

    We have found that KK 246, the only confirmed galaxy located within the nearby Tully Void, is a dwarf galaxy with an extremely extended H I disk and signs of an H I cloud with anomalous velocity. It also exhibits clear misalignment between the kinematical major and minor axes, indicative of an oval distortion, and a general misalignment between the H I and optical major axes. We measure an H I mass of (1.05 {+-} 0.08) x 10{sup 8} M{sub sun}, and an H I extent five times that of the stellar disk, one of the most extended H I disks known. We estimate a dynamical mass of 4.1 x 10{sup 9} M{sub sun}, making this also one of the darkest galaxies known, with a mass-to-light ratio of 89. The relative isolation and extreme underdense environment make this an interesting case for examining the role of gas accretion in galaxy evolution.

  2. Do Disk Galaxies Have Different Central Velocity Dispersions At A Given Rotation Velocity?

    NASA Astrophysics Data System (ADS)

    Danilovich, Taissa; Jones, H.; Mould, J.; Taylor, E.; Tonini, C.; Webster, R.

    2011-05-01

    Hubble's classification of spiral galaxies was one dimensional. Actually it was 1.5 dimensional, as he distinguished barred spirals. Van den Bergh's was two dimensional: spirals had luminosity classes too. Other schemes are summarized at http://www.daviddarling.info/encyclopedia/G/galaxyclassification.html A more quantitative approach is to classify spiral galaxies by rotation velocity. Their central velocity dispersion (bulge) tends to be roughly one half of their rotation velocity (disk). There is a trend from σ/W = 0.8 to σ/W = 0.2 as one goes from W = 100 to 500 km/s, where W is twice the rotation velocity. But some fraction of spirals have a velocity dispersion up to a factor of two larger than that. In hierarchical galaxy formation models, the relative contributions of σ and W depend on the mass accretion history of the galaxy, which determines the mass distribution of the dynamical components such as disk, bulge and dark matter halo. The wide variety of histories that originate in the hierarchical mass assembly produce at any value of W a wide range of σ/W, that reaches high values in more bulge- dominated systems. In a sense the two classifiers were both right: spirals are mostly one dimensional, but σ/W (bulge to disk ratio) is often larger than average. Is this a signature of merger history?

  3. DISSECTING THE STELLAR-MASS-SFR CORRELATION IN z = 1 STAR-FORMING DISK GALAXIES

    SciTech Connect

    Salmi, F.; Daddi, E.; Elbaz, D.; Sargent, M. T.; Bethermin, M.; Renzini, A.; Le Borgne, D. E-mail: edaddi@cea.fr

    2012-07-20

    Using a mass-limited sample of 24 {mu}m detected, star-forming galaxies at 0.5 < z < 1.3, we study the mass-star formation rate (SFR) correlation and its tightness. The correlation is well defined ({sigma} = 0.28 dex) for disk galaxies (n{sub Sersic} < 1.5), while more bulge-dominated objects often have lower specific SFRs (sSFRs). For disk galaxies, a much tighter correlation ({sigma} = 0.19 dex) is obtained if the rest-frame H-band luminosity is used instead of stellar mass derived from multi-color photometry. The sSFR correlates strongly with rest-frame optical colors (hence luminosity-weighted stellar age) and also with clumpiness (which likely reflects the molecular gas fraction). This implies that most of the observed scatter is real, despite its low level, and not dominated by random measurement errors. After correcting for these differential effects a remarkably small dispersion remains ({sigma} = 0.14 dex), suggesting that measurement errors in mass or SFR are {approx}< 0.10 dex, excluding systematic uncertainties. Measurement errors in stellar masses, the thickening of the correlation due to real sSFR variations, and varying completeness with stellar mass, can spuriously bias the derived slope to lower values due to the finite range over which observables (mass and SFR) are available. When accounting for these effects, the intrinsic slope for the main sequence for disk galaxies gets closer to unity.

  4. The Size-Luminosity Relation of Disk Galaxies in EDisCS Clusters

    NASA Astrophysics Data System (ADS)

    Gogarten, Stephanie M.; Dalcanton, Julianne J.; Simard, Luc; Rudnick, Gregory; Desai, Vandana

    2007-05-01

    We present the size-luminosity relation (SLR) for disk galaxies observed in eight clusters from the ESO Distant Cluster Survey (EDisCS). These clusters, at redshifts 0.4 < z < 0.8, were observed with the Hubble Space Telescope's Advanced Camera for Surveys. We describe the evolution of the size-luminosity relation with redshift. Previous studies have yielded conflicting opinions over whether or not there has been evolution in the SLR since z˜1, mostly hinging on the proper characterization of selection effects. Additionally, we compare the SLR for cluster and field galaxies to see if the cluster environment has an effect on the evolution of the average size and/or surface brightness. We also derive a theoretical SLR from a simple model of galaxy formation and empirical distribution functions for mass and angular momentum. Comparing this model to our observations provides constraints for galaxy evolution models, particularly models of star formation.

  5. VizieR Online Data Catalog: Black hole masses in megamaser disk galaxies (Greene+, 2016)

    NASA Astrophysics Data System (ADS)

    Greene, J. E.; Seth, A.; Kim, M.; Lasker, R.; Goulding, A.; Gao, F.; Braatz, J. A.; Henkel, C.; Condon, J.; Lo, K. Y.; Zhao, W.

    2016-11-01

    The velocity dispersion (σ*) presented here for megamaser disk galaxies are measured from three data sets. Two galaxies (NGC1320, NGC5495) were observed with the B&C spectrograph on the Dupont telescope at the Las Campanas Observatory. These spectra have an instrumental resolution of σr~120km/s and a wavelength range of 3400-6000Å. Two galaxies (Mrk1029, ESO558-G009) have σ* measurements from the cross-dispersed near-infrared spectrograph Triplespec on the 3.5m telescope at Apache Point. Triplespec has a wavelength range of 0.9-2.4um with a spectral resolution of σr~37km/s. Finally, three galaxies (J0437+2456, NGC5765b, UGC6093) have spectra from the SDSS. They have a spectral resolution of σr~65km/s and cover a range of 3800-9200Å. (1 data file).

  6. OBSERVATIONAL EVIDENCE FOR YOUNG RADIO GALAXIES IS TRIGGERED BY ACCRETION DISK INSTABILITY

    SciTech Connect

    Wu Qingwen

    2009-08-20

    Bolometric luminosities and black hole (BH) masses are estimated by various methods for a sample of young radio galaxies with known ages. We find that the ages are positively correlated with the bolometric luminosities in these young radio galaxies. This positive correlation is consistent with the theoretical prediction based on the radiation pressure instability of accretion disks in Czerny et al. The ages of young radio galaxies are also found to be consistent with the theoretical durations of outbursts in BH mass and accretion rate (in Eddington unit) plane, where the outbursts are assumed to be triggered by the radiation pressure instabilities. Our results provide observational evidence for the radiation pressure instability, which causes limit-cycle behavior, as a physical mechanism that may be responsible for these short-lived young radio galaxies.

  7. Kinematical Modeling of WARPS in the H i Disks of Galaxies

    NASA Astrophysics Data System (ADS)

    Christodoulou, Dimitris M.; Tohline, Joel E.; Steiman-Cameron, Thomas Y.

    1993-10-01

    In order to gain an appreciation for the general structure of warped gas layers in galaxies, we have constructed kinematical, tilted-ring models of 21 galaxies for which detailed H I observations already exist in the literature. In this paper we present results for the 15 normal spiral galaxies of this sample that are not viewed edge-on. A comparison between our models and tilted-ring models of the same galaxies previously constructed by other authors shows that there is generally good agreement. We make an attempt to unify the notation of diff&rent authors who have published radio observations and/or kinematical models of individual galaxies in this sample. We also suggest how, in future work of this nature, model parameters should be presented and referenced in order to maintain a reasonable degree of consistency in the literature. When viewed in the perspective of dynamical models, a twisted warped gas layer can be understood as arising from orbiting gas which is in the process of settling to a preferred orientation in the nonspherical, gravitational potential well of the galaxy. Hence, detailed kinematical modeling of a specific galaxy disk can provide not only information regarding the orientation and structure of its warp but also information about the shape (whether oblate or prolate) of the dark halo in which the disk is embedded. By examining a large number of galaxies in a consistent manner, we have deduced some general characteristics of warped disks that have heretofore gone unnoticed. We have also identified uniqueness problems that can arise in this type of modeling procedure which can considerably cloud one's ability to completely decipher an individual disk's structure. For 14 out of 15 spiral galaxies modeled here, we have been able to determine the local kinematical structure of the warp. Gas layers do not appear to warp more than ˜40° out of the plane defined by the central disk of the galaxy, but they can twist through angles as large as ˜170

  8. Hydrodynamic vortices in the gaseous disks of galaxies

    NASA Astrophysics Data System (ADS)

    Antonov, V. A.; Zhelezniak, O. A.

    1989-08-01

    A two-dimensional gas stream with a velocity field vx proportional to y is considered which is assumed to be stationary with respect to a rotating coordinate system. This stream can serve as a model of the local kinematic of a galactic gaseous disk. It is shown the local uniform stream cannot develop into a soliton if self-gravitation, dissipation, and the nonuniformity of the vortex are neglected.

  9. The Imprint of Radial Migration on the Vertical Structure of Galaxy Disks

    NASA Astrophysics Data System (ADS)

    Vera-Ciro, Carlos; D'Onghia, Elena; Navarro, Julio F.

    2016-12-01

    We use numerical simulations to examine the effects of radial migration on the vertical structure of galaxy disks. The simulations follow three exponential disks of different mass but similar circular velocity, radial scalelength, and (constant) scale height. The disks develop different non-axisymmetric patterns, ranging from feeble, long-lived multiple arms to strong, rapidly evolving few-armed spirals. These fluctuations induce radial migration through secular changes in the angular momentum of disk particles, mixing the disk radially and blurring pre-existing gradients. Migration primarily affects stars with small vertical excursions, regardless of spiral pattern. This “provenance bias” largely determines the vertical structure of migrating stars: inward migrators thin down as they move in, whereas outward migrators do not thicken up but rather preserve the disk scale height at their destination. Migrators of equal birth radius thus develop a strong scale-height gradient, not by flaring out as commonly assumed, but by thinning down as they spread inward. Similar gradients have been observed for low-[α/Fe] mono-abundance populations (MAPs) in the Galaxy, but our results argue against interpreting them as a consequence of radial migration. This is because outward migration does not lead to thickening, implying that the maximum scale height of any population should reflect its value at birth. In contrast, Galactic MAPs have scale heights that increase monotonically outward, reaching values that greatly exceed those at their presumed birth radii. Given the strong vertical bias affecting migration, a proper assessment of the importance of radial migration in the Galaxy should take carefully into account the strong radial dependence of the scale heights of the various stellar populations.

  10. Star Formation in the Extended Gaseous Disk of the Isolated Galaxy CIG 96

    NASA Astrophysics Data System (ADS)

    Espada, D.; Muñoz-Mateos, J. C.; Gil de Paz, A.; Sabater, J.; Boissier, S.; Verley, S.; Athanassoula, E.; Bosma, A.; Leon, S.; Verdes-Montenegro, L.; Yun, M.; Sulentic, J.

    2011-07-01

    We study the Kennicutt-Schmidt star formation law and efficiency in the gaseous disk of the isolated galaxy CIG 96 (NGC 864), with special emphasis on its unusually large atomic gas (H I) disk (r H mathsci/r 25 = 3.5, r 25 = 1farcm85). We present deep Galaxy Evolution Explorer near- and far-UV observations, used as a recent star formation tracer, and we compare them with new, high-resolution (16''or 1.6 kpc) Very Large Array H I observations. The UV and H I maps show good spatial correlation outside the inner 1', where the H I phase dominates over H2. Star-forming regions in the extended gaseous disk are mainly located along the enhanced H I emission within two (relatively) symmetric, giant gaseous spiral arm-like features, which emulate an H I pseudo-ring at r ~= 3'. Inside this structure, two smaller gaseous spiral arms extend from the northeast and southwest of the optical disk and connect to the previously mentioned H I pseudo-ring. Interestingly, we find that the (atomic) Kennicutt-Schmidt power-law index systematically decreases with radius, from N ~= 3.0 ± 0.3 in the inner disk (0farcm8-1farcm7) to N = 1.6 ± 0.5 in the outskirts of the gaseous disk (3farcm3-4farcm2). Although the star formation efficiency (SFE), the star formation rate per unit of gas, decreases with radius where the H I component dominates as is common in galaxies, we find that there is a break of the correlation at r = 1.5r 25. At radii 1.5r 25 < r < 3.5r 25, mostly within the H I pseudo-ring structure, regions exist whose SFE remains nearly constant, SFE ~= 10-11 yr-1. We discuss possible mechanisms that might be triggering the star formation in the outskirts of this galaxy, and we suggest that the constant SFE for such large radii (r > 2r 25) and at such low surface densities might be a common characteristic in extended UV disk galaxies.

  11. STAR FORMATION IN THE EXTENDED GASEOUS DISK OF THE ISOLATED GALAXY CIG 96

    SciTech Connect

    Espada, D.; Sabater, J.; Verdes-Montenegro, L.; Sulentic, J.; Munoz-Mateos, J. C.; Gil de Paz, A.; Verley, S.; Leon, S.

    2011-07-20

    We study the Kennicutt-Schmidt star formation law and efficiency in the gaseous disk of the isolated galaxy CIG 96 (NGC 864), with special emphasis on its unusually large atomic gas (H I) disk (r{sub Hmathsci}/r{sub 25} = 3.5, r{sub 25} = 1.'85). We present deep Galaxy Evolution Explorer near- and far-UV observations, used as a recent star formation tracer, and we compare them with new, high-resolution (16''or 1.6 kpc) Very Large Array H I observations. The UV and H I maps show good spatial correlation outside the inner 1', where the H I phase dominates over H{sub 2}. Star-forming regions in the extended gaseous disk are mainly located along the enhanced H I emission within two (relatively) symmetric, giant gaseous spiral arm-like features, which emulate an H I pseudo-ring at r {approx_equal} 3'. Inside this structure, two smaller gaseous spiral arms extend from the northeast and southwest of the optical disk and connect to the previously mentioned H I pseudo-ring. Interestingly, we find that the (atomic) Kennicutt-Schmidt power-law index systematically decreases with radius, from N {approx_equal} 3.0 {+-} 0.3 in the inner disk (0.'8-1.'7) to N = 1.6 {+-} 0.5 in the outskirts of the gaseous disk (3.'3-4.'2). Although the star formation efficiency (SFE), the star formation rate per unit of gas, decreases with radius where the H I component dominates as is common in galaxies, we find that there is a break of the correlation at r = 1.5r{sub 25}. At radii 1.5r{sub 25} < r < 3.5r{sub 25}, mostly within the H I pseudo-ring structure, regions exist whose SFE remains nearly constant, SFE {approx_equal} 10{sup -11} yr{sup -1}. We discuss possible mechanisms that might be triggering the star formation in the outskirts of this galaxy, and we suggest that the constant SFE for such large radii (r > 2r{sub 25}) and at such low surface densities might be a common characteristic in extended UV disk galaxies.

  12. Shrinking galaxy disks with fountain-driven accretion from the halo

    SciTech Connect

    Elmegreen, Bruce G.; Struck, Curtis; Hunter, Deidre A. E-mail: curt@iastate.edu

    2014-12-01

    Star formation in most galaxies requires cosmic gas accretion because the gas consumption time is short compared to the Hubble time. This accretion presumably comes from a combination of infalling satellite debris, cold flows, and condensation of hot halo gas at the cool disk interface, perhaps aided by a galactic fountain. In general, the accretion will have a different specific angular momentum than the part of the disk that receives it, even if the gas comes from the nearby halo. The gas disk then expands or shrinks over time. Here we show that condensation of halo gas at a rate proportional to the star formation rate in the fountain model will preserve an initial shape, such as an exponential, with a shrinking scale length, leaving behind a stellar disk with a slightly steeper profile of younger stars near the center. This process is slow for most galaxies, producing imperceptible radial speeds, and it may be dominated by other torques, but it could be important for blue compact dwarfs, which tend to have large, irregular gas reservoirs and steep blue profiles in their inner stellar disks.

  13. THE DISTANCE TO A STAR-FORMING REGION IN THE OUTER ARM OF THE GALAXY

    SciTech Connect

    Hachisuka, K.; Brunthaler, A.; Menten, K. M.; Reid, M. J.; Hagiwara, Y.; Mochizuki, N.

    2009-05-10

    We performed astrometric observations with the Very Long Baseline Army of WB89-437, an H{sub 2}O maser source in the Outer spiral arm of the Galaxy. We measure an annual parallax of 0.167 {+-} 0.006 mas, corresponding to a heliocentric distance of 6.0 {+-} 0.2 kpc or a Galactocentric distance of 13.4 {+-} 0.2 kpc. This value for the heliocentric distance is considerably smaller than the kinematic distance of 8.6 kpc. This confirms the presence of a faint Outer arm toward l = 135 deg. We also measured the full space motion of the object and find a large peculiar motion of {approx}20 km s{sup -1} toward the Galactic center. This peculiar motion explains the large error in the kinematic distance estimate. We also find that WB89-437 has the same rotation speed as the LSR, providing more evidence for a flat rotation curve and thus the presence of dark matter in the outer Galaxy.

  14. Stellar haloes in Milky Way mass galaxies: from the inner to the outer haloes

    NASA Astrophysics Data System (ADS)

    Tissera, Patricia B.; Beers, Timothy C.; Carollo, Daniela; Scannapieco, Cecilia

    2014-04-01

    We present a comprehensive study of the chemical properties of the stellar haloes of Milky Way mass galaxies, analysing the transition between the inner to the outer haloes. We find the transition radius between the relative dominance of the inner-halo and outer-halo stellar populations to be ˜15-20 kpc for most of our haloes, similar to that inferred for the Milky Way from recent observations. While the number density of stars in the simulated inner-halo populations decreases rapidly with distance, the outer-halo populations contribute about 20-40 per cent in the fiducial solar neighbourhood, in particular at the lowest metallicities. We have determined [Fe/H] profiles for our simulated haloes; they exhibit flat or mild gradients, in the range [-0.002, -0.01] dex kpc-1. The metallicity distribution functions exhibit different features, reflecting the different assembly history of the individual stellar haloes. We find that stellar haloes formed with larger contributions from massive subgalactic systems have steeper metallicity gradients. Very metal-poor stars are mainly contributed to the halo systems by lower mass satellites. There is a clear trend among the predicted metallicity distribution functions that a higher fraction of low-metallicity stars are found with increasing radius. These properties are consistent with the range of behaviours observed for stellar haloes of nearby galaxies.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  16. EXTINCTION IN STAR-FORMING DISK GALAXIES FROM INCLINATION-DEPENDENT COMPOSITE SPECTRA

    SciTech Connect

    Yip, Ching-Wa; Szalay, Alex S.; Wyse, Rosemary F. G.; Budavari, Tamas; Dobos, Laszlo; Csabai, Istvan E-mail: szalay@pha.jhu.ed

    2010-02-01

    Extinction in galaxies affects their observed properties. In scenarios describing the distribution of dust and stars in individual disk galaxies, the amplitude of the extinction can be modulated by the inclination of the galaxies. In this work, we investigate the inclination dependency in composite spectra of star-forming disk galaxies from the Sloan Digital Sky Survey Data Release 5. In a volume-limited sample within a redshift range 0.065-0.075 and a r-band Petrosian absolute magnitude range -19.5 to -22 mag which exhibits a flat distribution of inclination, the inclined relative to face-on extinction in the stellar continuum is found empirically to increase with inclination in the g, r, and i bands. Within the central 0.5 intrinsic half-light radius of the galaxies, the g-band relative extinction in the stellar continuum for the highly inclined objects (axis ratio b/a = 0.1) is 1.2 mag, agreeing with previous studies. The extinction curve of the disk galaxies is given in the rest-frame wavelengths 3700-8000 A, identified with major optical emission and absorption lines in diagnostics. The Balmer decrement, Halpha/Hbeta, remains constant with inclination, suggesting a different kind of dust configuration and/or reddening mechanism in the H II region from that in the stellar continuum. One factor is shown to be the presence of spatially non-uniform interstellar extinction, presumably caused by clumped dust in the vicinity of the H II region.

  17. Spitzer/Infrared Array Camera near-infrared features in the outer parts of S4G galaxies

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    We present a catalogue and images of visually detected features, such as asymmetries, extensions, warps, shells, tidal tails, polar rings, and obvious signs of mergers or interactions, in the faint outer regions (at and outside of R25) of nearby galaxies. This catalogue can be used in future quantitative studies that examine galaxy evolution due to internal and external factors. We are able to reliably detect outer region features down to a brightness level of 0.03 MJy sr-1 pixel-1 at 3.6 μm in the Spitzer Survey of Stellar Structure in Galaxies (S4G). We also tabulate companion galaxies. We find asymmetries in the outer isophotes in 22 ± 1 per cent of the sample. The asymmetry fraction does not correlate with galaxy classification as an interacting galaxy or merger remnant, or with the presence of companions. We also compare the detected features to similar features in galaxies taken from cosmological zoom re-simulations. The simulated images have a higher fraction (33 per cent) of outer disc asymmetries, which may be due to selection effects and an uncertain star formation threshold in the models. The asymmetries may have either an internal (e.g. lopsidedness due to dark halo asymmetry) or external origin.

  18. VizieR Online Data Catalog: Central surface densities in SPARC disk galaxies (Lelli+, 2016)

    NASA Astrophysics Data System (ADS)

    Lelli, F.; McGaugh, S. S.; Schombert, J. M.; Pawlowski, M. S.

    2017-02-01

    We use galaxies from the Spitzer Photometry and Accurate Rotation Curves (SPARC) database (Paper I; Lelli et al. 2016, Cat. J/AJ/152/157). SPARC spans the widest possible range for disk galaxies: morphologies from S0 to dIrr, luminosities from ~107 to ~1012L{Sun}, effective surface brightnesses from ~5 to ~5000L{Sun}/pc2, effective radii from ~0.3 to ~15kpc, rotation velocities from ~20 to ~300km/s, and gas fractions from ~0.01 to 0.95. In Paper I, we describe the analysis of [3.6] images and the rotation curve data. We also define a quality flag: Q=1 indicates galaxies with high-quality HI data or hybrid HI/Hα rotation curves (99 objects), Q=2 indicates galaxies with minor asymmetries or HI data of lower quality (64 objects), and Q=3 indicates galaxies with major asymmetries, strong non-circular motions, or off-sets between stellar and HI distributions (12 objects). We exclude objects with Q=3 since the rotation curves do not necessarily trace the equilibrium gravitational potential. We also exclude face-on (i<30°) and edge-on (i>85°) galaxies due to uncertain corrections on the rotation velocities and central surface brightnesses, respectively. Our final sample consists of 135 galaxies. (1 data file).

  19. The Outer Regions of the Nearby Sc Galaxies NGC 2403 and M33: Evidence for an Intermediate-Age Population at Large Radii

    NASA Astrophysics Data System (ADS)

    Davidge, T. J.

    2003-06-01

    Deep g'r'i'z' images obtained with the Gemini Multiobject Spectrograph (GMOS) on Gemini North are used to investigate the stellar content in the outer regions of the nearby Sc galaxies NGC 2403 and M33. The field observed in NGC 2403 covers galactocentric distances between 5 and 11 kpc perpendicular to the line of sight (RLOSGC) and 7 and 19 kpc along the plane of the disk (RdiskGC). The red giant branch (RGB) tip occurs at i'=23.6+/-0.1, and the Cepheid and RGB-tip distance scales for NGC 2403 are in good agreement. The number density of bright main-sequence stars in this field experiences a steep cutoff at RdiskGC~10 kpc, which is consistent with the expected truncation radius of the disk predicted from studies of edge-on spiral galaxies. While very young stars are restricted to RdiskGC<10 kpc, a population of bright asymptotic giant branch (AGB) stars is present throughout the entire GMOS field, indicating that star formation occurred outside of the present-day star-forming disk of NGC 2403 during intermediate epochs. The AGB stars are not in a tidal stream; in fact, the ratio of AGB stars above the RGB tip to those below the RGB tip does not change with radius, indicating that the bright AGB stars are uniformly mixed with the fainter stellar content throughout the field. The AGB luminosity function (LF) scales with r-band surface brightness over a wide range of radii throughout the main body of NGC 2403, indicating that the age distribution of stars in the outer regions of the present-day star-forming disk is not skewed to younger values than in the inner disk. Based on the color of stars on the upper portions of the RGB, it is concluded that metallicity changes across the field, with [Fe/H]=-0.8+/-0.1(random)+/-0.3(systematic) at RLOSGC=5 kpc, and [Fe/H]=-2.2+/-0.2(random)+/-0.8(systematic) at RLOSGC=11 kpc. The M33 field samples RLOSGC between 8 and 10 kpc and RdiskGC between 14 and 17 kpc. Bright AGB stars are detected in this field, and the ratio of bright

  20. A comprehensive study of the spatially-resolved SFR in nearby disk galaxies using CALIFA IF data

    NASA Astrophysics Data System (ADS)

    Catalán-Torrecilla, C.; Gil de Paz, A.; Castillo-Morales, A.; Méndez-Abreu, J.; Califa Team

    2017-03-01

    A detailed analysis of the Star Formation Rate (SFR) distribution in nearby galaxies is essential to understand the mechanisms that drive the formation and evolution of galaxies. Although measurements of the integrated SFR in galaxies as a whole are also required to fulfill this goal, we focus here on the relative contribution of the SFR in the different components that shape galaxies (bulges, bars and disks). With this aim in mind, we combine for the first time in a large sample of nearby galaxies from the CALIFA survey, 2D multicomponent photometric decomposition with Integral Field Spectroscopy (IFS) data to enable measurements of the SFR in the different galaxy components. We find that not only more massive galaxies are being quenched more efficiently but also more massive disks tend to exhibit lower SFRs for a fixed value of their disk stellar masses in the SFR-M_* plane. We show that type-2 AGN host galaxies are mostly found in galaxies with the higher values of their stellar masses and that they contribute to decrease the specific SFR for bulges and disks, being this effect more important for the case of the bulges.

  1. Ly-alpha emission from disk absorption systems at high redshift - Star formation in young galaxy disks

    NASA Technical Reports Server (NTRS)

    Smith, Harding E.; Cohen, Ross D.; Burns, Joseph E.; Moore, David J.; Uchida, Barbara A.

    1989-01-01

    Narrow-band imaging observations are reported which were made in an attempt to detect Ly-alpha emission from high-redshift candidate galaxy disk systems discovered as high column density absorbers of background QSOs. For four systems with z = 2.3-2.8, no emission is detected to a limit of about 10 to the -16th ergs/sq cm/s, corresponding to luminosity limits of about 10 exp 42-43 ergs/s for the material producing the absorption. The inferred Ly-alpha luminosities lie one to two orders of magnitude below estimates of the Ly-alpha luminosities for active star-forming epochs of many prescriptions for galaxy formation and also considerably below measured Ly-alpha luminosities for other candidate young galaxies detected in radio surveys. A limiting star-formation rate in these systems of about 2-7 solar masses/yr is set; the limit may be about 10 times larger with small but observationally allowable amounts of dust.

  2. IMAGING THE INNER AND OUTER GAPS OF THE PRE-TRANSITIONAL DISK OF HD 169142 AT 7 mm

    SciTech Connect

    Osorio, Mayra; Anglada, Guillem; Macías, Enrique; Gómez, José F.; Mayen-Gijon, Juan M.; Torrelles, José M.; Nagel, Erick; Dent, William R. F.; Quanz, Sascha P.; Reggiani, Maddalena

    2014-08-20

    We present Very Large Array observations at 7 mm that trace the thermal emission of large dust grains in the HD 169142 protoplanetary disk. Our images show a ring of enhanced emission of radius ∼25-30 AU, whose inner region is devoid of detectable 7 mm emission. We interpret this ring as tracing the rim of an inner cavity or gap, possibly created by a planet or a substellar companion. The ring appears asymmetric, with the western part significantly brighter than the eastern one. This azimuthal asymmetry is reminiscent of the lopsided structures that are expected to be produced as a consequence of trapping of large dust grains. Our observations also reveal an outer annular gap at radii from ∼40 to ∼70 AU. Unlike other sources, the radii of the inner cavity, the ring, and the outer gap observed in the 7 mm images, which trace preferentially the distribution of large (millimeter/centimeter sized) dust grains, coincide with those obtained from a previous near-infrared polarimetric image, which traces scattered light from small (micron-sized) dust grains. We model the broadband spectral energy distribution and the 7 mm images to constrain the disk physical structure. From this modeling we infer the presence of a small (radius ∼0.6 AU) residual disk inside the central cavity, indicating that the HD 169142 disk is a pre-transitional disk. The distribution of dust in three annuli with gaps in between them suggests that the disk in HD 169142 is being disrupted by at least two planets or substellar objects.

  3. A NEARBY ANALOG OF z {approx} 2 COMPACT QUIESCENT GALAXIES WITH A ROTATING DISK

    SciTech Connect

    Jiang, Fangzhou; Van Dokkum, Pieter; Bezanson, Rachel; Franx, Marijn

    2012-04-10

    Recent studies have identified a population of compact quiescent galaxies at z {approx} 2. These galaxies are very rare today and establishing the existence of a nearby analog could allow us to study its structure in greater detail than is possible at high redshift. Here we present such a local analog, NGC 5845, which has a dynamical mass of M{sub dyn} = 4.3 {+-} 0.6 Multiplication-Sign 10{sup 10} M{sub Sun} and an effective radius of only r{sub e} 0.45 {+-} 0.05 kpc. We study the structure and kinematics with HST/WFPC2 data and previously published spatially resolved kinematics. We find that NGC 5845 is similar to compact quiescent galaxies at z {approx} 2 in terms of size versus dynamical mass (r{sub e}-M{sub dyn}), effective velocity dispersion versus size ({sigma}{sub e}-r{sub e}), and effective velocity dispersion versus dynamical mass ({sigma}{sub e}-M{sub dyn}). The galaxy has a prominent rotating disk evident in both the photometry and the kinematics: it extends to well beyond {approx}> 1/3 effective radius and contribute to {approx}> 1/4 of the total light of the galaxy. Our results lend support to the idea that a fraction of z {approx} 2 compact galaxies have prominent disks and positive mass-to-light ratio gradients, although we caution that NGC 5845 may have had a different formation history than the more massive compact quiescent galaxies at z {approx} 2.

  4. THE FIRST GALAXIES: ASSEMBLY OF DISKS AND PROSPECTS FOR DIRECT DETECTION

    SciTech Connect

    Pawlik, Andreas H.; Milosavljevic, Milos; Bromm, Volker

    2011-04-10

    The James Webb Space Telescope (JWST) will enable observations of galaxies at redshifts z {approx}> 10 and hence allow us to test our current understanding of structure formation at very early times. Previous work has shown that the very first galaxies inside halos with virial temperatures T{sub vir} {approx}< 10{sup 4} K and masses M{sub vir} {approx}< 10{sup 8} M{sub sun} at z {approx}> 10 are probably too faint, by at least one order of magnitude, to be detected even in deep exposures with JWST. The light collected with JWST may therefore be dominated by radiation from galaxies inside 10 times more massive halos. We use cosmological zoomed smoothed particle hydrodynamics simulations to investigate the assembly of such galaxies and assess their observability with JWST. We compare two simulations that are identical except for the inclusion of non-equilibrium H/D chemistry and radiative cooling by molecular hydrogen. In both simulations a large fraction of the halo gas settles in two nested, extended gas disks which surround a compact massive gas core. The presence of molecular hydrogen allows the disk gas to reach low temperatures and to develop marked spiral structure but does not qualitatively change its stability against fragmentation. We post-process the simulated galaxies by combining idealized models for star formation with stellar population synthesis models to estimate the luminosities in nebular recombination lines as well as in the ultraviolet continuum. We demonstrate that JWST will be able to constrain the nature of the stellar populations in galaxies such as simulated here based on the detection of the He1640 recombination line. Extrapolation of our results to halos with masses both lower and higher than those simulated shows that JWST may find up to a thousand star-bursting galaxies in future deep exposures of the z {approx}> 10 universe.

  5. The X-ray halo of an extremely luminous LSB disk galaxy

    NASA Technical Reports Server (NTRS)

    Weiner, Benjamin J.

    2004-01-01

    We are continuing to refine our upper limit on emission from halo gas in Malin 2. The upper limit is, of course, below the detected flux, but is made more difficult to quantify by the disk and possible AGN sources. We are also exploring spectral and spatial-size constraints to help separate the sources of emission. On the theory side, more recent work on the X-ray halo luminosity from halo gas leftover from galaxy formation has lowered the prediction for disk galaxies (e.g. Toft et al. 2002, MNRAS, 335, 799). While our upper limit is well below the original prediction, refinements in model have moved the theoretical goalposts, so that the observation may be consistent with newer models. A recent theoretical development, which our observations of Malin 2 appear to support, is that a substantial amount of mass can be accreted onto galaxies without being heated at a virial shock. The previous standard theory was that gas accreting into a halo hits a virial shock and is heated to high temperatures, which could produce X-ray halos in massive galaxies. Recent models show that "smooth accretion" of matter bypasses the virial shocking (Murali e t al. 2002, ApJ, 571, 1; Birnboim & Dekel 2003, MNRAS, 345, 349). Additionally, new hydrodynamical simulations of galaxy mergers by UCSC graduate student T. J. Cox show that hot gas halos can be created by gas blown out from the merger, taking up orbital energy of the merging galaxies (Cox et al. 2004, ApJ, 607, L87). If mergers rather than virial shocking are the origin of hot gas halos, the existence of an X-ray halo should depend more on past merger activity than halo mass. Then it makes sense that elliptical galaxies and poor groups with ellipticals, which are probably formed in mergers, have X-ray gas halos; while a giant, quiescent LSB disk galaxy like Malin 2, which has never suffered a major merger, does not have an X-ray halo. While both the observational expectations and theoretical models have changed since we began this

  6. 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

  7. 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

  8. The Formation of a Milky Way-sized Disk Galaxy. I. A Comparison of Numerical Methods

    NASA Astrophysics Data System (ADS)

    Zhu, Qirong; Li, Yuexing

    2016-11-01

    The long-standing challenge of creating a Milky Way- (MW-) like disk galaxy from cosmological simulations has motivated significant developments in both numerical methods and physical models. We investigate these two fundamental aspects in a new comparison project using a set of cosmological hydrodynamic simulations of an MW-sized galaxy. In this study, we focus on the comparison of two particle-based hydrodynamics methods: an improved smoothed particle hydrodynamics (SPH) code Gadget, and a Lagrangian Meshless Finite-Mass (MFM) code Gizmo. All the simulations in this paper use the same initial conditions and physical models, which include star formation, “energy-driven” outflows, metal-dependent cooling, stellar evolution, and metal enrichment. We find that both numerical schemes produce a late-type galaxy with extended gaseous and stellar disks. However, notable differences are present in a wide range of galaxy properties and their evolution, including star-formation history, gas content, disk structure, and kinematics. Compared to Gizmo, the Gadget simulation produced a larger fraction of cold, dense gas at high redshift which fuels rapid star formation and results in a higher stellar mass by 20% and a lower gas fraction by 10% at z = 0, and the resulting gas disk is smoother and more coherent in rotation due to damping of turbulent motion by the numerical viscosity in SPH, in contrast to the Gizmo simulation, which shows a more prominent spiral structure. Given its better convergence properties and lower computational cost, we argue that the MFM method is a promising alternative to SPH in cosmological hydrodynamic simulations.

  9. High-resolution Velocity Fields of Low-mass Disk Galaxies. I. CO Observations

    NASA Astrophysics Data System (ADS)

    Truong, Phuongmai N.; Newman, Andrew B.; Simon, Joshua D.; Blitz, Leo; Ellis, Richard; Bolatto, Alberto

    2017-07-01

    This paper is the first in a series whose aim is to examine the relative distributions of dark and baryonic matter as a function of star formation history in a representative sample of low-mass disk galaxies. In this paper, we present high-resolution 12CO(J=1\\to 0) interferometry for a sample of 26 nearby dwarf galaxies that were obtained from the Combined Array for Research in Millimeter-wave Astronomy (CARMA). Among these 26 galaxies, 14 have good CO detections, including 6 galaxies previously detected in single-dish CO measurements and 8 newly detected ones. We find a linear correlation between the CO flux and the mid- and far-IR flux from the WISE and IRAS catalogs. Compared to the far-IR flux, the mid-IR flux may be a better indication of whether a galaxy contains sufficient CO for detection at the level of instrument sensitivity of CARMA. This correlation might prove to be useful in future studies to help choosing other CO targets for observation. The median molecular mass (including helium) of our galaxies is 2.8× {10}8 {M}⊙ , which is consistent with past observations for dwarf galaxies. The molecular content is weakly correlated with the dynamical mass, r-band luminosity and size of the galaxies. The median ratios of molecular mass versus dynamical mass and molecular mass versus r-band luminosity are {M}{mol}/{M}{dyn}≈ 0.035 and {M}{mol}/{L}r≈ 0.078 {M}⊙ /{L}r,⊙ , respectively, which are also consistent with past observations for dwarf galaxies.

  10. 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.

  11. Determination of Disk Thickness of Face-on Spiral Galaxies and Its Image Processing Method

    NASA Astrophysics Data System (ADS)

    Hu, T.; Peng, Q. H.

    2014-11-01

    It is uneasy to obtain the disk thickness of face-on spiral galaxies by measuring the galactic light distributions. Here we obtain the spiral galactic disk thickness based on an asymptotic expression of Poisson's equation for a logarithmic perturbation of matter density in spiral galaxies. For measuring the key parameter of the innermost position of the spiral arm (forbidden radius r_0) freed from the contamination by the light of bulge, an improved image processing method is used in this study by subtracting a decomposition brightness model from the galactic observed image. On the basis of measuring some fundamental parameters of spiral structures, we obtain the disk thickness and some other parameters of two (types S and SB) face-on spiral galaxies, and their ratio parameters (r_{b}/r_{d} and r_{d}/H) are also derived. By using this improved subtracted-method, it is easy to measure the forbidden radius r_0, which is smaller than that obtained from unsubtracted-method.

  12. 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.

  13. Measurement of a Rotation Velocity of the Outer Galaxy with VERA: Mass Distribution of the Galaxy

    NASA Astrophysics Data System (ADS)

    Sakai, N.; Honma, M.; Nakanishi, H.; Sakanoue, H.; Kurayama, T.; VERA project member

    2012-08-01

    We report measurement of trigonometric parallax of IRAS 05168+3634 with VERA. The parallax is 0.532±0.053 mas, corresponding to a distance of 1.88±0.210.17 kpc. This result is significantly smaller than the previous distance estimate based on kinematic distance, being 6 kpc. This drastic change in the source distance revises location of the source, placing it in the Perseus arm rather than the Outer arm. We also measure the proper motions of the source. Combination of the distance and the proper motions with the systemic velocity yields rotation velocity (Θ) of 227±911 km s-1 at the source (Θ0=240 km s-1 assumed). This indicates that a part of the outer rotation at Galacto-centric distance of ˜ 10 kpc is smaller than the galactic rotation at the LSR, which is consistent with previous VERA and VLBA results. The lower rotation velocity may be caused in inner edge of the Perseus arm where shock front predicted by the density-wave theory occurs.

  14. High-Resolution Velocity Fields of Low-Mass Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Truong, Phuongmai N.

    This study aims to examine the relative distributions of dark and baryonic matter as a function of star formation history in a representative sample of low mass disk galaxies. In this study, we present the high-resolution 12CO(J=1 → 0) interferometry for a sample of 26 nearby dwarf galaxies, which were obtained from the Combined Array for Research in Millimeter-wave Astronomy (CARMA). Among these 26 galaxies, 14 have good CO detections, including 6 galaxies previously detected in single-dish CO measurements and 8 newly detected ones. We find a linear correlation between the CO flux and the mid- and far-IR flux from the WISE and IRAS catalogs. Compared to the far-IR flux, the mid-IR flux may be a better indication of whether a galaxy contains sufficient CO for detection at the level of instrument sensitivity of CARMA. This correlation might prove to be useful in future studies to help choosing other CO targets for observation. The median molecular mass (including helium and H2) of our galaxies is 2.8 x 108 M., which is consistent with past observations for dwarf galaxies. The molecular content is weakly correlated with the dynamical mass, r-band luminosity and size of the galaxies. The median ratios of molecular mass vs. dynamical mass and molecular mass vs. r-band luminosity are Mmol/Mdyn ≈ 0.035 and Mmol/Lr ≈ 0.078M./Lr,., respectively, which are also consistent with past observations for dwarf galaxies. In addition, we present the rotation curves of these 14 galaxies. To examine the dark matter distribution in their central regions, the reduced CO data were fitted with simple kinematic models using two different algorithms. For all 14 galaxies, despite inhomogeneous distribution of molecular gas in some of the sources, robust kinematic results were obtained for all sources. Most galaxies show approximately zero or small noncircular motions, particularly the ones with smooth spatial distributions of CO emission. Furthermore, consistent rotation curves are

  15. Disk and Bulge Morphology of WFPC2 Galaxies: The HUBBLE SPACE TELESCOPE Medium Deep Survey

    NASA Astrophysics Data System (ADS)

    Ratnatunga, Kavan U.; Griffiths, Richard E.; Ostrander, Eric J.

    1999-07-01

    Quantitative morphological and structural parameters are estimated for galaxies detected in Hubble Space Telescope observations of WFPC2 survey fields. A modeling approach based on maximum likelihood has been developed for two-dimensional decomposition of faint undersampled galaxy images into components of disk and bulge morphology. Decomposition can be achieved for images down to F814W(I)~23.0, F606W(V)~23.8, and F450W(B)~23.3 mag in WFPC2 exposures of 1 hr. We discuss details of the fitting procedure and present the observed distributions of magnitude, color, effective half-light radius, disk and bulge axis ratios, bulge-to-(disk+bulge) flux ratio, bulge-to-disk half-light radius ratio, and surface brightness. We also discuss the various selection limits on the measured parameters. The Medium Deep Survey catalogs and images of random pure parallel fields and other similar archival primary WFPC2 fields have been made available via the Internet with a searchable browser interface to the database.

  16. The effects of interactions on spiral galaxies. II - Disk star-formation rates

    NASA Technical Reports Server (NTRS)

    Kennicutt, Robert C., Jr.; Roettiger, Kurt A.; Keel, William C.; Van Der Hulst, J. M.; Hummel, E.

    1987-01-01

    H-alpha emission-line and IRAS far-IR observations of interacting spiral and irregular galaxies are here used to assess the influence of interactions on their global star-formation rates. Two samples of interacting galaxies were observed: a complete sample of close pairs, and an Arp atlas sample of peculiar systems. When compared to a control sample of single galaxies, both samples of interacting systems exhibit systematically higher levels of H-alpha and infrared emission on average, and a larger dispersion in emission properties. Emission levels in the very active system are much more strongly correlated with the properties of the interaction than with the internal properties of the galaxies themselves. Strong disk emission is almost always accompanied by unusually strong nuclear activity. Simple star-formation burst models can reproduce the observed H-alpha equivalent widths and broadband colors of most of the galaxies. The bursts are relatively short (few times 10 million yr) and rarely involve more than 1-2 percent of a galaxy's total mass.

  17. The dynamics and excitation of circumnuclear disks in radio-active galaxies

    NASA Astrophysics Data System (ADS)

    Mould, Jeremy; Brown, Michael; Jannuzi, Buell; McGregor, Peter; Floyd, David; Jones, Heath; Ferrarese, Laura

    2011-08-01

    Powerful radio-active galaxies may harbor a heavily obscured Active Galactic Nucleus (AGN), where the black hole is hidden by an optically and geometrically thick dust "torus". Near-IR spectroscopy with Adaptive Optics (AO) has shown that the ratio of atomic to molecular hydrogen varies greatly across the nuclear regions, thus allowing one to set limits of the size of the torus. AO IFU observations with Gemini and Keck will enable a study of a complete sample of early-type galaxies harboring radio AGNs, resulting in a complete picture of the kinematics and distribution of the gas around the nucleus, and trace the 2-D structure of the torus in these galaxies. The time is right to survey a complete sample of nearby radio-active galaxies to (1) characterize the dynamics of these circumnuclear disks as a function of galaxy mass and (2) outline the ecology of the gas flows that support them. %First we must see which of Brown et al's %complete sample of nearby radiogalaxies have emission As a first step, we need to determine which of our selected sample of 23 nearby radio-active galaxies have emission lines in J & H and are thus amenable to NIR IFU observations. This we propose to do with FLAMINGOS. To survey our sample for suitable objects for the Keck/Gemini follow-up will require approximately 22 nights distributed evenly over the next four observing semesters.%It will take 11 nights in 11B & 12B and

  18. 13CO/C18O Gradients across the Disks of Nearby Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Jiménez-Donaire, María J.; Cormier, Diane; Bigiel, Frank; Leroy, Adam K.; Gallagher, Molly; Krumholz, Mark R.; Usero, Antonio; Hughes, Annie; Kramer, Carsten; Meier, David; Murphy, Eric; Pety, Jérôme; Schinnerer, Eva; Schruba, Andreas; Schuster, Karl; Sliwa, Kazimierz; Tomicic, Neven

    2017-02-01

    We use the IRAM Large Program EMPIRE and new high-resolution ALMA data to measure 13CO(1-0)/C18O(1-0) intensity ratios across nine nearby spiral galaxies. These isotopologues of 12CO are typically optically thin across most of the area in galaxy disks, and this ratio allows us to gauge their relative abundance due to chemistry or stellar nucleosynthesis effects. Resolved 13CO/C18O gradients across normal galaxies have been rare due to the faintness of these lines. We find a mean 13CO/C18O ratio of 6.0 ± 0.9 for the central regions of our galaxies. This agrees well with results in the Milky Way, but differs from results for starburst galaxies (3.4 ± 0.9) and ultraluminous infrared galaxies (1.1 ± 0.4). In our sample, the 13CO/C18O ratio consistently increases with increasing galactocentric radius and decreases with increasing star formation rate surface density. These trends could be explained if the isotopic abundances are altered by fractionation; the sense of the trends also agrees with those expected for carbon and oxygen isotopic abundance variations due to selective enrichment by massive stars.

  19. 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.

  20. A Disk Galaxy of Old Stars at z~2.5

    NASA Astrophysics Data System (ADS)

    Stockton, Alan; Canalizo, Gabriela; Maihara, Toshinori

    2004-04-01

    We describe observations of a galaxy in the field of the z=2.483 radio galaxy 4C 23.56, photometrically selected to have a spectral energy distribution consistent with an old stellar population at the redshift of the radio galaxy. Exploration of redshift-stellar-population-reddening constraints from the photometry indicates that the galaxy is indeed at a redshift close to that of 4C 23.56, that the age of the most recent significant star formation is roughly >~2 Gyr, and that reddening is fairly modest, with more reddening required for the younger end of stellar age range. From analysis of a deep adaptive optics image of the galaxy, we find that an r1/4-law profile, common for local spheroidal galaxies, can be excluded quite strongly. On the other hand, a pure exponential profile fits remarkably well, while the best fit is given by a Sérsic profile with index n=1.49. Reconstruction of the two-dimensional form of the galaxy from the best-fit model is consistent with a disk galaxy with neither a significant bulge component nor gross azimuthal structure. The assembly of roughly 2L* of old stars into such a configuration this early in the history of the universe is not easily explainable by any of the currently popular scenarios for galaxy formation. A galaxy with these properties would seem to require smooth but rapid infall of the large mass of gas involved, followed by a burst of extremely vigorous and efficient star formation in the resulting disk. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  1. HOW WELL CAN WE MEASURE THE INTRINSIC VELOCITY DISPERSION OF DISTANT DISK GALAXIES?

    SciTech Connect

    Davies, R.; Schreiber, N. M. Foerster; Genzel, R.; Burkert, A.; Buschkamp, P.; Genel, S.; Kurk, J.; Lutz, D.; Tacconi, L. J.; Wuyts, S.; Cresci, G.; Bouche, N.; Hicks, E.; Newman, S.; Shapiro, K.; Sternberg, A.

    2011-11-10

    The kinematics of distant galaxies from z = 0.1 to z > 2 play a key role in our understanding of galaxy evolution from early times to the present. One of the important parameters is the intrinsic, or local, velocity dispersion of a galaxy, which allows one to quantify the degree of non-circular motions such as pressure support. However, this is difficult to measure because the observed dispersion includes the effects of (often severe) beam smearing on the velocity gradient. Here we investigate four methods of measuring the dispersion that have been used in the literature, to assess their effectiveness at recovering the intrinsic dispersion. We discuss the biases inherent in each method, and apply them to model disk galaxies in order to determine which methods yield meaningful quantities and under what conditions. All the mean-weighted dispersion estimators are affected by (residual) beam smearing. In contrast, the dispersion recovered by fitting a spatially and spectrally convolved disk model to the data is unbiased by the beam smearing it is trying to compensate. Because of this, and because the bias it does exhibit depends only on the signal-to-noise ratio (S/N), it can be considered reliable. However, at very low S/N, all methods should be used with caution.

  2. Puzzling outer-density profile of the dark matter halo in the Andromeda galaxy

    NASA Astrophysics Data System (ADS)

    Kirihara, Takanobu; Miki, Yohei; Mori, Masao

    2014-12-01

    The cold dark matter (CDM) cosmology, which is the standard theory of the structure formation in the universe, predicts that the outer density profile of dark matter halos decreases with the cube of distance from the center. However, so far not much effort has been expended in examining this hypothesis. In the halo of the Andromeda galaxy (M 31), large-scale stellar structures detected by the recent observations provide a potentially suitable window to investigate the mass-density distribution of the dark matter halo. We explore the density structure of the dark matter halo in M 31 using an N-body simulation of the interaction between an accreting satellite galaxy and M 31. To reproduce the Andromeda Giant Southern Stream and the stellar shells at the east and west sides of M 31, we find the sufficient condition for the power-law index α of the outer density distribution of the dark matter halo. The best-fitting parameter is α = -3.7, which is steeper than the CDM prediction.

  3. The Evolution of Massive Morphological Spheroid and Disk Galaxies in CANDELS from 11 to 6 Billion Years Ago

    NASA Astrophysics Data System (ADS)

    McIntosh, Daniel H.; CANDELS Collaboration

    2017-01-01

    The premiere HST/WFC3 Treasury program CANDELS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey) has produced detailed visual classifications for statistically useful samples of bright (H>24.5mag) galaxies during and after z~2, the epoch of peak galaxy development. By averaging multiple classifications per galaxy that encompass spheroid-only, bulge-dominated, disk-dominated, disk-only, and irregular/peculiar appearances at visible rest-frame wavelengths, we find that 90% of massive (>1e10 Msun) galaxies at 0.6disk morphologies. Morphological spheroids are physically distinct from disks in terms of Sersic indices, half-light sizes, and axial ratios from GALFIT measurements, and quenched (Q) vs. active star formation (SF) based on either specific SFR or rest-frame UVJ analyses. At all redshifts probed, disks with/without subdominant central mass concentrations are flat, larger and mostly SF, compared to spheroids and dominant 'bulges' which are round, smaller and evolving from 50% SF at z>2 to mostly Q at later times. Combining morphologies, structural properties, and SF nature, we find clear differences in the histories of spheroid and disk populations that are robust to selections based on visual or Sersic selection, and to either Q/SF divisor. Massive spheroids experience strong number density growth, substantial size growth, and rapid changes in SF fraction suggesting quenching processes that act on <0.5 Gyr timescales. In contrast, the massive disk population undergoes a steady addition of similar-size disks and a mild decline in average sSFR. Our results indicate that active SF in disks appears to slowly build up their inner mass (or bulge), which subsequently quenches these galaxies. Data-theory comparison is needed to better constrain which physical processes drive the transformation and quenching of massive galaxies.

  4. Development of Realistic Simulations of the Interactions between Stars and the Interstellar Medium in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Zeltwanger, T.

    1999-12-01

    We have developed a self-consistent N-body plus hydrodynamic computer program to model and study the behavior of disk galaxies like our Milky Way. Our goal is to better understand how such galaxies maintain their spiral structure for billions of years. The program utilizes a gravitating N-body code to simulate the collisionless star particles in the galaxy, and a gravitating hydrodynamic portion of the code to simulate the interstellar medium in the form of gas and clouds. Additionally, the potential due to a static spherical halo and a central black hole interacts gravitationally with the other components of the model galaxy. All components interchange mass, energy, and momentum through various evolution processes and gravity. The research for this thesis primarily studies the interaction between stars and the interstellar medium. These interactions include cloud formation from gas by Jeans instability, star formation by cloud collision, star formation from clouds by Jeans instability, star formation by snowplow effects, gas infall from the halo, and energy and mass transfer due to supernovae. The simulations done for this thesis produced results that are in agreement with observations of spiral galaxies, and they can be used to make predictions about the properties and behavior of disk galaxies, such as the formation of spiral arms, or the formation of a central bar. These predictions can then be tested against observations. This work was made possible by a generous donation of SUN and HP workstations by EDS (Electronic Data Systems), and a Graduate Teaching Assistantship from the University of Maine.

  5. Molecular gas and a new young stellar cluster in the far outer Galaxy

    NASA Astrophysics Data System (ADS)

    Yun, J. L.; Elia, D.; Palmeirim, P. M.; Gomes, J. I.; Martins, A. M.

    2009-06-01

    Aims: We investigate the star-formation ocurring in the region towards IRAS 07527-3446 in the molecular cloud [MAB97]250.63-3.63, in the far outer Galaxy. We report the discovery of a new young stellar cluster, and describe its properties and those of its parent molecular cloud. Methods: Near-infrared JHKS images were obtained with VLT/ISAAC, and millimetre line CO spectra were obtained with the SEST telescope. VLA archive date were also used. Results: The cloud and cluster are located at a distance of 10.3 kpc and a Galactocentric distance of 15.4 kpc, in the far outer Galaxy. Morphologically, IRAS 07527-3446 appears as a young embedded cluster of a few hundred stars seen towards the position of the IRAS source, extending for about 2-4 pc and exhibiting sub-clustering. The cluster contains low and intermediate-mass young reddened stars, a large fraction having cleared the inner regions of their circumstellar discs responsible for (H-K_S) colour excess. The observations are compatible with a ≤5 Myr cluster with variable spatial extinction of between A_V=5 and A_V=11. Decomposition of CO emission in clumps, reveals a clump clearly associated with the cluster position, of mass 3.3 × 103 M_⊙. Estimates of the slopes of the K_S-band luminosity function and of the star-formation efficiency yield values similar to those seen in nearby star-formation sites. These findings reinforce previous results that the distant outer Galaxy continues to be active in the production of new and rich stellar clusters, with the physical conditions required for the formation of rich clusters continuing to be met in the very distant environment of the outer Galactic disc. Based on observations collected at the ESO 8.2-m VLT-UT1 Antu telescope (program 66.C-0015A). Table 2 is only available in electonic form at http://www.aanda.org

  6. HERSCHEL's ''COLD DEBRIS DISKS'': BACKGROUND GALAXIES OR QUIESCENT RIMS OF PLANETARY SYSTEMS?

    SciTech Connect

    Krivov, A. V.; Loehne, T.; Mutschke, H.; Neuhaeuser, R.; Eiroa, C.; Marshall, J. P.; Mustill, A. J.; Montesinos, B.; Del Burgo, C.; Absil, O.; Ardila, D.; Augereau, J.-C.; Ertel, S.; Lebreton, J.; Bryden, G.; Danchi, W.; Liseau, R.; Mora, A.; Pilbratt, G. L. [ESA Astrophysics and Fundamental Physics Missions Division, ESTEC and others

    2013-07-20

    than a few kilometers in size. If larger planetesimals were present, then they would stir the disk, triggering a collisional cascade and thus causing production of small debris, which is not seen. Thus, planetesimal formation, at least in the outer regions of the systems, has stopped before 'cometary' or 'asteroidal' sizes were reached.

  7. Herschel's "Cold Debris Disks": Background Galaxies or Quiescent Rims of Planetary Systems?

    NASA Technical Reports Server (NTRS)

    Krivov, A. V.; Eiroa, C.; Loehne, T.; Marshall, J. P.; Montesinos, B.; DelBurgo, C.; Absil, O.; Ardila, D.; Augereau, J.-C.; Bayo, A.; hide

    2013-01-01

    smaller than a few kilometers in size. If larger planetesimals were present, then they would stir the disk, triggering a collisional cascade and thus causing production of small debris, which is not seen. Thus, planetesimal formation, at least in the outer regions of the systems, has stopped before "cometary" or "asteroidal" sizes were reached.

  8. Herschel's "Cold Debris Disks": Background Galaxies or Quiescent Rims of Planetary Systems?

    NASA Astrophysics Data System (ADS)

    Krivov, A. V.; Eiroa, C.; Löhne, T.; Marshall, J. P.; Montesinos, B.; del Burgo, C.; Absil, O.; Ardila, D.; Augereau, J.-C.; Bayo, A.; Bryden, G.; Danchi, W.; Ertel, S.; Lebreton, J.; Liseau, R.; Mora, A.; Mustill, A. J.; Mutschke, H.; Neuhäuser, R.; Pilbratt, G. L.; Roberge, A.; Schmidt, T. O. B.; Stapelfeldt, K. R.; Thébault, Ph.; Vitense, Ch.; White, G. J.; Wolf, S.

    2013-07-01

    kilometers in size. If larger planetesimals were present, then they would stir the disk, triggering a collisional cascade and thus causing production of small debris, which is not seen. Thus, planetesimal formation, at least in the outer regions of the systems, has stopped before "cometary" or "asteroidal" sizes were reached.

  9. SHAPE EVOLUTION OF MASSIVE EARLY-TYPE GALAXIES: CONFIRMATION OF INCREASED DISK PREVALENCE AT z > 1

    SciTech Connect

    Chang, Yu-Yen; Van der Wel, Arjen; Rix, Hans-Walter; Ramkumar, Balasubramanian; Wuyts, Stijn; Zibetti, Stefano; Holden, Bradford

    2013-01-10

    We use high-resolution K-band VLT/HAWK-I imaging over 0.25 deg{sup 2} to study the structural evolution of massive early-type galaxies since z {approx} 2. Mass-selected samples, complete down to log(M/M {sub Sun }) {approx} 10.7 such that 'typical' (L*) galaxies are included at all redshifts, are drawn from pre-existing photometric redshift surveys. We then separate the samples into different redshift slices and classify them as late- or early-type galaxies on the basis of their specific star formation rate. Axis-ratio measurements for the {approx}400 early-type galaxies in the redshift range 0.6 < z < 1.8 are accurate to 0.1 or better. The projected axis-ratio distributions are then compared with lower redshift samples. We find strong evidence for evolution of the population properties: early-type galaxies at z > 1 are, on average, flatter than at z < 1 and the median projected axis ratio at a fixed mass decreases with redshift. However, we also find that at all epochs z {approx}< 2, the most massive early-type galaxies (log(M/M {sub Sun }) > 11.3) are the roundest, with a pronounced lack of galaxies that are flat in projection. Merging is a plausible mechanism that can explain both results: at all epochs, merging is required for early-type galaxies to grow beyond log(M/M {sub Sun }) {approx} 11.3, and all early types over time gradually and partially lose their disk-like characteristics.

  10. Shape Evolution of Massive Early-type Galaxies: Confirmation of Increased Disk Prevalence at z > 1

    NASA Astrophysics Data System (ADS)

    Chang, Yu-Yen; van der Wel, Arjen; Rix, Hans-Walter; Wuyts, Stijn; Zibetti, Stefano; Ramkumar, Balasubramanian; Holden, Bradford

    2013-01-01

    We use high-resolution K-band VLT/HAWK-I imaging over 0.25 deg2 to study the structural evolution of massive early-type galaxies since z ~ 2. Mass-selected samples, complete down to log(M/M ⊙) ~ 10.7 such that "typical" (L*) galaxies are included at all redshifts, are drawn from pre-existing photometric redshift surveys. We then separate the samples into different redshift slices and classify them as late- or early-type galaxies on the basis of their specific star formation rate. Axis-ratio measurements for the ~400 early-type galaxies in the redshift range 0.6 < z < 1.8 are accurate to 0.1 or better. The projected axis-ratio distributions are then compared with lower redshift samples. We find strong evidence for evolution of the population properties: early-type galaxies at z > 1 are, on average, flatter than at z < 1 and the median projected axis ratio at a fixed mass decreases with redshift. However, we also find that at all epochs z <~ 2, the most massive early-type galaxies (log(M/M ⊙) > 11.3) are the roundest, with a pronounced lack of galaxies that are flat in projection. Merging is a plausible mechanism that can explain both results: at all epochs, merging is required for early-type galaxies to grow beyond log(M/M ⊙) ~ 11.3, and all early types over time gradually and partially lose their disk-like characteristics.

  11. The Outer Disks of Herbig Stars From the UV to NIR

    NASA Technical Reports Server (NTRS)

    Grady, C.; Fukagawa, M.; Maruta, Y.; Ohta, Y.; Wisniewski, J.; Hashimoto, J.; Okamoto, Y.; Momose, M.; Currie, T.; Mcelwain, M.; hide

    2014-01-01

    Spatially-resolved imaging of Herbig stars and related objects began with HST, but intensified with commissioning of high-contrast imagers on 8-m class telescopes. The bulk of the data taken from the ground have been polarized intensity imagery at H-band, with the majority of the sources observed as part of the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) survey. Sufficiently many systems have been imaged that we discuss disk properties in scattered, polarized light in terms of groups defined by the IR spectral energy distribution. We find novel phenomena in many of the disks, including spiral density waves, and discuss the disks in terms of clearing mechanisms. Some of the disks have sufficient data to map the dust and gas components, including water ice dissociation products.

  12. The Outer Disks of Herbig Stars From the UV to NIR

    NASA Technical Reports Server (NTRS)

    Grady, C.; Fukagawa, M.; Maruta, Y.; Ohta, Y.; Wisniewski, J.; Hashimoto, J.; Okamoto, Y.; Momose, M.; Currie, T.; Mcelwain, M.; Muto, T.; Kotani, T.; Kusakabe, N.; Kudo, T.; Hayashi, M.; Ishii, M.; Iye, M.; Morino, J.-I.; Suenaga, T.; Suto, H.; Suzuki, R.; Takahashi, Y. H.; Takami, H.; Usuda, T.; Tamura, M.

    2014-01-01

    Spatially-resolved imaging of Herbig stars and related objects began with HST, but intensified with commissioning of high-contrast imagers on 8-m class telescopes. The bulk of the data taken from the ground have been polarized intensity imagery at H-band, with the majority of the sources observed as part of the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) survey. Sufficiently many systems have been imaged that we discuss disk properties in scattered, polarized light in terms of groups defined by the IR spectral energy distribution. We find novel phenomena in many of the disks, including spiral density waves, and discuss the disks in terms of clearing mechanisms. Some of the disks have sufficient data to map the dust and gas components, including water ice dissociation products.

  13. Gas-Rich Mergers in LCDM: Disk Survivability and the Baryonic Assembly of Galaxies

    SciTech Connect

    Stewart, Kyle R.; Bullock, James S.; Wechsler, Risa H.; Maller, Ariyeh H.; /New York City Coll. Tech.

    2009-08-03

    We use N-body simulations and observationally-normalized relations between dark matter halo mass, stellar mass, and cold gas mass to derive robust expectations about the baryonic content of major mergers out to redshift z {approx} 2. First, we find that the majority of major mergers (m/M > 0.3) experienced by Milky Way size dark matter halos should have been gas-rich, and that gas-rich mergers are increasingly common at high redshift. Though the frequency of major mergers into galaxy halos in our simulations greatly exceeds the observed late-type galaxy fraction, the frequency of gas-poor major mergers is consistent with the observed fraction of bulge-dominated galaxies across the halo mass range M{sub DM} {approx} 10{sup 11} - 10{sup 13} M{sub {circle_dot}}. These results lend support to the conjecture that mergers with high baryonic gas fractions play an important role in building and/or preserving disk galaxies in the universe. Secondly, we find that there is a transition mass below which a galaxy's past major mergers were primarily gas-rich and above which they were gas poor. The associated stellar mass scale corresponds closely to that marking the observed bimodal division between blue, star-forming, disk-dominated systems and red, bulge-dominated systems with old populations. Finally, we find that the overall fraction of a galaxy's cold baryons deposited directly via major mergers is substantial. Approximately 30% of the cold baryonic material in M{sub star} {approx} 10{sup 10} M{sub {circle_dot}} (M{sub DM} {approx} 10{sup 11.5} M{sub {circle_dot}}) galaxies is accreted as cold gas in major mergers. For more massive galaxies with M{sub star} {approx} 10{sup 11} M{sub {circle_dot}} (M{sub DM} {approx} 10{sup 13} M{sub {circle_dot}} the fraction of baryons amassed in mergers is even higher, {approx} 50%, but most of these accreted baryons are delivered directly in the form of stars. This baryonic mass deposition is almost unavoidable, and provides a limit on

  14. Density wave formation in differentially rotating disk galaxies: Hydrodynamic simulation of the linear regime

    NASA Astrophysics Data System (ADS)

    Griv, Evgeny; Wang, Hsiang-Hsu

    2014-07-01

    Most rapidly and differentially rotating disk galaxies, in which the sound speed (thermal velocity dispersion) is smaller than the orbital velocity, display graceful spiral patterns. Yet, over almost 240 yr after their discovery in M51 by Charles Messier, we still do not fully understand how they originate. In this first paper of a series, the dynamical behavior of a rotating galactic disk is examined numerically by a high-order Godunov hydrodynamic code. The code is implemented to simulate a two-dimensional flow driven by an internal Jeans gravitational instability in a nonresonant wave-“fluid” interaction in an infinitesimally thin disk composed of stars or gas clouds. A goal of this work is to explore the local and linear regimes of density wave formation, employed by Lin, Shu, Yuan and many others in connection with the problem of spiral pattern of rotationally supported galaxies, by means of computer-generated models and to compare those numerical results with the generalized fluid-dynamical wave theory. The focus is on a statistical analysis of time-evolution of density wave structures seen in the simulations. The leading role of collective processes in the formation of both the circular and spiral density waves (“heavy sound”) is emphasized. The main new result is that the disk evolution in the initial, quasilinear stage of the instability in our global simulations is fairly well described using the local approximation of the generalized wave theory. Certain applications of the simulation to actual gas-rich spiral galaxies are also explored.

  15. 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.

  16. THE LINK BETWEEN LIGHT AND MASS IN LATE-TYPE SPIRAL GALAXY DISKS

    SciTech Connect

    Swaters, Robert A.; Bershady, Matthew A.; Martinsson, Thomas P. K.; Westfall, Kyle B.; Andersen, David R.; Verheijen, Marc A. W.

    2014-12-20

    We present the correlation between the extrapolated central disk surface brightness (μ) and extrapolated central surface mass density (Σ) for galaxies in the DiskMass sample. This μ-Σ relation has a small scatter of 30% at the high surface brightness (HSB) end. At the low surface brightness (LSB) end, galaxies fall above the μ-Σ relation, which we attribute to their higher dark matter content. After correcting for the dark matter as well as for the contribution of gas and the effects of radial gradients in the disk, the LSB end falls back on the linear μ-Σ relation. The resulting scatter around the corrected μ-Σ relation is 25% at the HSB end and about 50% at the LSB end. The intrinsic scatter in the μ-Σ relation is estimated to be 10%-20%. Thus, if μ {sub K,} {sub 0} is known, the stellar surface mass density is known to within 10%-20% (random error). Assuming disks have an exponential vertical distribution of mass, the average Υ{sub ∗}{sup K} is 0.24 M {sub ☉}/L {sub ☉}, with an intrinsic scatter around the mean of at most 0.05 M {sub ☉}/L {sub ☉}. This value for Υ{sub ∗}{sup K} is 20% smaller than we found in Martinsson et al., mainly due to the correction for dark matter applied here. This small scatter means that among the galaxies in our sample, variations in scale height, vertical density profile shape, and/or the ratio of vertical over radial velocity dispersion must be small.

  17. COSMIC RAYS CAN DRIVE STRONG OUTFLOWS FROM GAS-RICH HIGH-REDSHIFT DISK GALAXIES

    SciTech Connect

    Hanasz, M.; Kowalik, K.; Wóltański, D.; Lesch, H.; Naab, T.; Gawryszczak, A.

    2013-11-10

    We present simulations of the magnetized interstellar medium (ISM) in models of massive star-forming (40 M {sub ☉} yr{sup –1}) disk galaxies with high gas surface densities (Σ{sub gas} ∼ 100 M {sub ☉} pc{sup –2}) similar to observed star-forming high-redshift disks. We assume that type II supernovae deposit 10% of their energy into the ISM as cosmic rays (CRs) and neglect the additional deposition of thermal energy or momentum. With a typical Galactic diffusion coefficient for CRs (3 × 10{sup 28} cm{sup 2} s{sup –1}), we demonstrate that this process alone can trigger the local formation of a strong low-density galactic wind maintaining vertically open field lines. Driven by the additional pressure gradient of the relativistic fluid, the wind speed can exceed 10{sup 3} km s{sup –1}, much higher than the escape velocity of the galaxy. The global mass loading, i.e., the ratio of the gas mass leaving the galactic disk in a wind to the star formation rate, becomes of order unity once the system has settled into an equilibrium. We conclude that relativistic particles accelerated in supernova remnants alone provide a natural and efficient mechanism to trigger winds similar to observed mass-loaded galactic winds in high-redshift galaxies. These winds also help in explaining the low efficiencies for the conversion of gas into stars in galaxies, as well as the early enrichment of the intergalactic medium with metals. This mechanism may be at least of similar importance to the traditionally considered momentum feedback from massive stars and thermal and kinetic feedback from supernova explosions.

  18. A determination of the thick disk chemical abundance distribution: Implications for galaxy evolution

    NASA Technical Reports Server (NTRS)

    Gilmore, Gerard; Wyse, Rosemary F. G.; Jones, Bryn J.

    1995-01-01

    We present a determination of the thick disk iron abundance distribution obtained from an in situ sample of F/G stars. These stars are faint, 15 less than or approximately = V less than or approximately = 18, selected on the basis of color, being a subset of the larger survey of Gilmore and Wyse designed to determine the properties of the stellar populations several kiloparsecs from the Sun. The fields studied in the present paper probe the iron abundance distribution of the stellar populations of the galaxy at 500-3000 pc above the plane, at the solar Galactocentric distance. The derived chemical abundance distributions are consistent with no metallicity gradients in the thick disk over this range of vertical distance, and with an iron abundance distribution for the thick disk that has a peak at -0.7 dex. The lack of a vertical gradient argues against slow, dissipational settling as a mechanism for the formation of the thick disk. The photometric and metallicity data support a turn-off of the thick disk that is comparable in age to the metal-rich globular clusters, or greater than or approximately = 12 Gyr, and are consistent with a spread to older ages.

  19. A determination of the thick disk chemical abundance distribution: Implications for galaxy evolution

    NASA Technical Reports Server (NTRS)

    Gilmore, Gerard; Wyse, Rosemary F. G.; Jones, Bryn J.

    1995-01-01

    We present a determination of the thick disk iron abundance distribution obtained from an in situ sample of F/G stars. These stars are faint, 15 less than or approximately = V less than or approximately = 18, selected on the basis of color, being a subset of the larger survey of Gilmore and Wyse designed to determine the properties of the stellar populations several kiloparsecs from the Sun. The fields studied in the present paper probe the iron abundance distribution of the stellar populations of the galaxy at 500-3000 pc above the plane, at the solar Galactocentric distance. The derived chemical abundance distributions are consistent with no metallicity gradients in the thick disk over this range of vertical distance, and with an iron abundance distribution for the thick disk that has a peak at -0.7 dex. The lack of a vertical gradient argues against slow, dissipational settling as a mechanism for the formation of the thick disk. The photometric and metallicity data support a turn-off of the thick disk that is comparable in age to the metal-rich globular clusters, or greater than or approximately = 12 Gyr, and are consistent with a spread to older ages.

  20. Dusty Acoustic Turbulence in the Nuclear Disks of Two LINER Galaxies NGC 4450 and NGC 4736

    NASA Astrophysics Data System (ADS)

    Elmegreen, Debra Meloy; Elmegreen, Bruce G.; Eberwein, Kate S.

    2002-01-01

    The structure of dust spirals in the nuclei of the SAab-type LINER galaxies NGC 4450 and NGC 4736 is studied using archival Hubble Space Telescope Planetary Camera images. The spirals are typically only several hundredths of a magnitude fainter than the neighboring disks, so unsharp-mask techniques are used to highlight them. The ambient extinction is estimated to be less than 0.1 mag from the intensity decrements of the dust features and from the spiral surface filling factor, which is about constant for all radii and sizes. The nuclear dust spirals differ from main disk spirals in several respects: the nuclear spirals have no associated star formation, they are very irregular with both trailing and leading components that often cross, they become darker as they approach the center, they completely fill the inner disks with a constant areal density, making the number of distinct spirals (the azimuthal wavenumber m) increase linearly with radius, and their number decreases with increasing arm width as a power law. Fourier transform power spectra of the spirals, taken in the azimuthal direction, show a power-law behavior with a slope of -5/3 over the range of frequencies where the power stands above the pixel noise. This is the same slope as that found for the one-dimensional power spectra of H I emission in the Large Magellanic Cloud and also the slope expected for a thin turbulent disk. All of these properties suggest that the dust spirals are a manifestation of acoustic turbulence in the inner gas disks of these galaxies. Such turbulence should dissipate orbital energy and transfer angular momentum outward, leading to a steady accretion of gas toward the nucleus.

  1. 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.

  2. DISK GALAXY SCALING RELATIONS IN THE SFI++: INTRINSIC SCATTER AND APPLICATIONS

    SciTech Connect

    Saintonge, Amelie; Spekkens, Kristine E-mail: kristine.spekkens@rmc.ca

    2011-01-10

    We study the scaling relations between the luminosities, sizes, and rotation velocities of disk galaxies in the SFI++, with a focus on the size-luminosity (RL) and size-rotation velocity (RV) relations. Using isophotal radii instead of disk scale lengths as a size indicator, we find relations that are significantly tighter than previously reported: the correlation coefficients of the template RL and RV relations are r = 0.97 and r= 0.85, respectively, which rival that of the more widely studied LV (Tully-Fisher) relation. The scatter in the SFI++ RL relation is 2.5-4 times smaller than previously reported for various samples, which we attribute to the reliability of isophotal radii relative to disk scale lengths. After carefully accounting for all measurement errors, our scaling relation error budgets are consistent with a constant intrinsic scatter in the LV and RV relations for velocity widths log W {approx}> 2.4, with evidence for increasing intrinsic scatter below this threshold. The scatter in the RL relation is consistent with constant intrinsic scatter that is biased by incompleteness at the low-L end. Possible applications of the unprecedentedly tight SFI++ RV and RL relations are investigated. Just like the Tully-Fisher relation, the RV relation can be used as a distance indicator: we derive distances to galaxies with primary Cepheid distances that are accurate to 25%, and reverse the problem to measure a Hubble constant H{sub 0} = 72 {+-} 7 km s{sup -1} Mpc{sup -1}. Combining the small intrinsic scatter of our RL relation ({epsilon}{sub int} = 0.034 {+-} 0.001log [h{sup -1} kpc]) with a simple model for disk galaxy formation, we find an upper limit in the range of disk spin parameters that is a factor of {approx}7 smaller than that of the halo spin parameters predicted by cosmological simulations. This likely implies that the halos hosting Sc galaxies have a much narrower distribution of spin parameters than previously thought.

  3. Angular Momentum Distribution of Hot Gas and Implications for Disk Galaxy Formation

    NASA Astrophysics Data System (ADS)

    Chen, D. N.; Jing, Y. P.; Yoshikaw, Kohji

    2003-11-01

    We study the angular momentum profiles both for dark matter and for gas within virialized halos using a statistical sample of halos drawn from cosmological hydrodynamics simulations. Three simulations have been analyzed: one is the nonradiative simulation and the other two have radiative cooling. We find that the gas component, on average, has a larger spin and contains a smaller fraction of mass with negative angular momentum than its dark matter counterpart in the nonradiative model. As to the cooling models, the gas component shares approximately the same spin parameter as its dark matter counterpart, but the hot gas has a higher spin and is more aligned in angular momentum than dark matter, while the opposite holds for the cold gas. After the mass of negative angular momentum is excluded, the angular momentum profile of the hot gas component approximately follows the universal function originally proposed by Bullock et al. for dark matter, though the shape parameter μ is much larger for hot gas and is comfortably in the range required by observations of disk galaxies. Since disk formation is related to the distribution of hot gas that will cool, our study may explain the fact that the disk component of observed galaxies contains a smaller fraction of low angular momentum material than dark matter in halos.

  4. Ab Initio Simulations of a Supernova-driven Galactic Dynamo in an Isolated Disk Galaxy

    DOE PAGES

    Butsky, Iryna; Zrake, Jonathan; Kim, Ji-hoon; ...

    2017-07-10

    Here, we study the magnetic field evolution of an isolated spiral galaxy, using isolated Milky Way–mass galaxy formation simulations and a novel prescription for magnetohydrodynamic (MHD) supernova feedback. Our main result is that a galactic dynamo can be seeded and driven by supernova explosions, resulting in magnetic fields whose strength and morphology are consistent with observations. In our model, supernovae supply thermal energy and a low-level magnetic field along with their ejecta. The thermal expansion drives turbulence, which serves a dual role by efficiently mixing the magnetic field into the interstellar medium and amplifying it by means of a turbulentmore » dynamo. The computational prescription for MHD supernova feedback has been implemented within the publicly available ENZO code and is fully described in this paper. This improves upon ENZO's existing modules for hydrodynamic feedback from stars and active galaxies. We find that the field attains microgauss levels over gigayear timescales throughout the disk. The field also develops a large-scale structure, which appears to be correlated with the disk's spiral arm density structure. We find that seeding of the galactic dynamo by supernova ejecta predicts a persistent correlation between gas metallicity and magnetic field strength. We also generate all-sky maps of the Faraday rotation measure from the simulation-predicted magnetic field, and we present a direct comparison with observations.« less

  5. MISSING LENSED IMAGES AND THE GALAXY DISK MASS IN CXOCY J220132.8-320144

    SciTech Connect

    Chen, Jacqueline; Lee, Samuel K.; Schechter, Paul L.; Castander, Francisco-Javier; Maza, Jose

    2013-05-20

    The CXOCY J220132.8-320144 system consists of an edge-on spiral galaxy lensing a background quasar into two bright images. Previous efforts to constrain the mass distribution in the galaxy have suggested that at least one additional image must be present. These extra images may be hidden behind the disk which features a prominent dust lane. We present and analyze Hubble Space Telescope observations of the system. We do not detect any extra images, but the observations further narrow the observable parameters of the lens system. We explore a range of models to describe the mass distribution in the system and find that a variety of acceptable model fits exist. All plausible models require 2 mag of dust extinction in order to obscure extra images from detection, and some models may require an offset between the center of the galaxy and the center of the dark matter halo of 1 kpc. Currently unobserved images will be detectable by future James Webb Space Telescope observations and will provide strict constraints on the fraction of mass in the disk.

  6. Barred Ring Galaxy NGC 1291

    NASA Image and Video Library

    2005-05-05

    This ultraviolet image left and visual image right from NASA Galaxy Evolution Explorer is of the barred ring galaxy NGC 1291. The VIS image is dominated by the inner disk and bar. The UV image is dominated by the low surface brightness outer arms.

  7. FORMATION OF LATE-TYPE SPIRAL GALAXIES: GAS RETURN FROM STELLAR POPULATIONS REGULATES DISK DESTRUCTION AND BULGE GROWTH

    SciTech Connect

    Martig, Marie; Bournaud, Frederic

    2010-05-10

    Spiral galaxies have most of their stellar mass in a large rotating disk, and only a modest fraction in a central spheroidal bulge. This challenges present models of galaxy formation: galaxies form at the center of dark matter halos through a combination of hierarchical merging and gas accretion along cold streams. Cosmological simulations thus predict that galaxies rapidly grow their bulge through mergers and instabilities and end up with most of their mass in the bulge and an angular momentum much below the observed level, except in dwarf galaxies. We propose that the continuous return of gas by stellar populations over cosmic times could help to solve this issue. A population of stars formed at a given instant typically returns half of its initial mass in the form of gas over 10 billion years, and the process is not dominated by supernovae explosions but by the long-term mass-loss from low- and intermediate-mass stars. Using simulations of galaxy formation, we show that this gas recycling can strongly affect the structural evolution of massive galaxies, potentially solving the bulge fraction issue, as the bulge-to-disk ratio of a massive galaxy can be divided by a factor of 3. The continuous recycling of baryons through star formation and stellar mass loss helps the growth of disks and their survival to interactions and mergers. Instead of forming only early-type, spheroid-dominated galaxies (S0 and ellipticals), the standard cosmological model can successfully account for massive late-type, disk-dominated spiral galaxies (Sb-Sc).

  8. Galactic Angular Momentum in Cosmological Zoom-in Simulations. I. Disk and Bulge Components and the Galaxy-Halo Connection

    NASA Astrophysics Data System (ADS)

    Sokołowska, Aleksandra; Capelo, Pedro R.; Fall, S. Michael; Mayer, Lucio; Shen, Sijing; Bonoli, Silvia

    2017-02-01

    We investigate the angular momentum evolution of four disk galaxies residing in Milky-Way-sized halos formed in cosmological zoom-in simulations with various sub-grid physics and merging histories. We decompose these galaxies, kinematically and photometrically, into their disk and bulge components. The simulated galaxies and their components lie on the observed sequences in the j *-M * diagram, relating the specific angular momentum and mass of the stellar component. We find that galaxies in low-density environments follow the relation {j}* \\propto {M}* α past major mergers, with α ˜ 0.6 in the case of strong feedback, when bulge-to-disk ratios are relatively constant, and α ˜ 1.4 in the other cases, when secular processes operate on shorter timescales. We compute the retention factors (i.e., the ratio of the specific angular momenta of stars and dark matter) for both disks and bulges and show that they vary relatively slowly after averaging over numerous but brief fluctuations. For disks, the retention factors are usually close to unity, while for bulges, they are a few times smaller. Our simulations therefore indicate that galaxies and their halos grow in a quasi-homologous way.

  9. At the cradle of the Milky Way: Formation of the most massive field disk galaxies at z>1

    NASA Astrophysics Data System (ADS)

    Noeske, Kai

    2007-07-01

    We propose to obtain 2 orbit WFPC2 F814W images of a sample of the 15 most massive galaxies found at 1 < z < 1.3. These were culled from over 20,000 Keck spectra collected as part of DEEP and are unique among high redshift massive galaxy samples in being kinematically selected. Through a recent HST NICMOS-2 imaging program {GO-10532}, we have confirmed that these galaxies have regular stellar disks, and their emission line kinematics are not due to gradients from merging components. These potentially very young galaxies are likely precursors to massive local disks, assuming no further merging. The proposed WFPC2 and existing NIC-2 data provide colors, stellar masses, and ages of bulge and disk subcomponents, to assess whether old stellar bulges and disks are in place at that time or still being built, and constrain their formation epochs. Finally, this sample will yield the first statistically significant results on the z > 1 evolution of the size-velocity-luminosity scaling relations, for massive galaxies at different wavelengths, and constrain whether this evolution reflects stellar mass growth, or passive evolution, of either bulge or disk components.

  10. An X-Ray Reprocessing Model of Disk Thermal Emission in Type 1 Seyfert Galaxies

    NASA Technical Reports Server (NTRS)

    Chiang, James; White, Nicholas E. (Technical Monitor)

    2002-01-01

    Using a geometry consisting of a hot central Comptonizing plasma surrounded by a thin accretion disk, we model the optical through hard X-ray spectral energy distributions of the type 1 Seyfert. galaxies NGC 3516 and NGC 7469. As in the model proposed by Poutanen, Krolik, and Ryde for the X-ray binary Cygnus X-1 and later applied to Seyfert galaxies by Zdziarski, Lubifiski, and Smith, feedback between the radiation reprocessed by the disk and the thermal Comptonization emission from the hot central plasma plays a pivotal role in determining the X-ray spectrum, and as we show, the optical and ultraviolet spectra as well. Seemingly uncorrelated optical/UV and X-ray light curves, similar to those which have been observed from these objects can, in principle, be explained by variations in the size, shape, and temperature of the Comptonizing plasma. Furthermore, by positing a disk mass accretion rate which satisfies a condition for global energy balance between the thermal Comptonization luminosity and the power available from accretion, one can predict the spectral properties of the heretofore poorly measured hard X-ray continuum above approximately 50 keV in type 1 Seyfert galaxies. Conversely, forthcoming measurements of the hard X-ray continuum by more sensitive hard X-ray and soft gamma-ray telescopes, such as those aboard the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) in conjunction with simultaneous optical, UV, and soft X-ray monitoring, will allow the mass accretion rates to be directly constrained for these sources in the context of this model.

  11. The AGORA High-resolution Galaxy Simulations Comparison Project. II. Isolated Disk Test

    NASA Astrophysics Data System (ADS)

    Kim, Ji-hoon; Agertz, Oscar; Teyssier, Romain; Butler, Michael J.; Ceverino, Daniel; Choi, Jun-Hwan; Feldmann, Robert; Keller, Ben W.; Lupi, Alessandro; Quinn, Thomas; Revaz, Yves; Wallace, Spencer; Gnedin, Nickolay Y.; Leitner, Samuel N.; Shen, Sijing; Smith, Britton D.; Thompson, Robert; Turk, Matthew J.; Abel, Tom; Arraki, Kenza S.; Benincasa, Samantha M.; Chakrabarti, Sukanya; DeGraf, Colin; Dekel, Avishai; Goldbaum, Nathan J.; Hopkins, Philip F.; Hummels, Cameron B.; Klypin, Anatoly; Li, Hui; Madau, Piero; Mandelker, Nir; Mayer, Lucio; Nagamine, Kentaro; Nickerson, Sarah; O'Shea, Brian W.; Primack, Joel R.; Roca-Fàbrega, Santi; Semenov, Vadim; Shimizu, Ikkoh; Simpson, Christine M.; Todoroki, Keita; Wadsley, James W.; Wise, John H.; AGORA Collaboration

    2016-12-01

    Using an isolated Milky Way-mass galaxy simulation, we compare results from nine state-of-the-art gravito-hydrodynamics codes widely used in the numerical community. We utilize the infrastructure we have built for the AGORA High-resolution Galaxy Simulations Comparison Project. This includes the common disk initial conditions, common physics models (e.g., radiative cooling and UV background by the standardized package Grackle) and common analysis toolkit yt, all of which are publicly available. Subgrid physics models such as Jeans pressure floor, star formation, supernova feedback energy, and metal production are carefully constrained across code platforms. With numerical accuracy that resolves the disk scale height, we find that the codes overall agree well with one another in many dimensions including: gas and stellar surface densities, rotation curves, velocity dispersions, density and temperature distribution functions, disk vertical heights, stellar clumps, star formation rates, and Kennicutt-Schmidt relations. Quantities such as velocity dispersions are very robust (agreement within a few tens of percent at all radii) while measures like newly formed stellar clump mass functions show more significant variation (difference by up to a factor of ˜3). Systematic differences exist, for example, between mesh-based and particle-based codes in the low-density region, and between more diffusive and less diffusive schemes in the high-density tail of the density distribution. Yet intrinsic code differences are generally small compared to the variations in numerical implementations of the common subgrid physics such as supernova feedback. Our experiment reassures that, if adequately designed in accordance with our proposed common parameters, results of a modern high-resolution galaxy formation simulation are more sensitive to input physics than to intrinsic differences in numerical schemes.

  12. The AGORA High-resolution Galaxy Simulations Comparison Project II: Isolated disk test

    DOE PAGES

    Kim, Ji-hoon; Agertz, Oscar; Teyssier, Romain; ...

    2016-12-20

    Using an isolated Milky Way-mass galaxy simulation, we compare results from 9 state-of-the-art gravito-hydrodynamics codes widely used in the numerical community. We utilize the infrastructure we have built for the AGORA High-resolution Galaxy Simulations Comparison Project. This includes the common disk initial conditions, common physics models (e.g., radiative cooling and UV background by the standardized package Grackle) and common analysis toolkit yt, all of which are publicly available. Subgrid physics models such as Jeans pressure floor, star formation, supernova feedback energy, and metal production are carefully constrained across code platforms. With numerical accuracy that resolves the disk scale height, wemore » find that the codes overall agree well with one another in many dimensions including: gas and stellar surface densities, rotation curves, velocity dispersions, density and temperature distribution functions, disk vertical heights, stellar clumps, star formation rates, and Kennicutt-Schmidt relations. Quantities such as velocity dispersions are very robust (agreement within a few tens of percent at all radii) while measures like newly-formed stellar clump mass functions show more significant variation (difference by up to a factor of ~3). Systematic differences exist, for example, between mesh-based and particle-based codes in the low density region, and between more diffusive and less diffusive schemes in the high density tail of the density distribution. Yet intrinsic code differences are generally small compared to the variations in numerical implementations of the common subgrid physics such as supernova feedback. Lastly, our experiment reassures that, if adequately designed in accordance with our proposed common parameters, results of a modern high-resolution galaxy formation simulation are more sensitive to input physics than to intrinsic differences in numerical schemes.« less

  13. The AGORA High-resolution Galaxy Simulations Comparison Project II: Isolated disk test

    SciTech Connect

    Kim, Ji-hoon; Agertz, Oscar; Teyssier, Romain; Butler, Michael J.; Ceverino, Daniel; Choi, Jun-Hwan; Feldmann, Robert; Keller, Ben W.; Lupi, Alessandro; Quinn, Thomas; Revaz, Yves; Wallace, Spencer; Gnedin, Nickolay Y.; Leitner, Samuel N.; Shen, Sijing; Smith, Britton D.; Thompson, Robert; Turk, Matthew J.; Abel, Tom; Arraki, Kenza S.; Benincasa, Samantha M.; Chakrabarti, Sukanya; DeGraf, Colin; Dekel, Avishai; Goldbaum, Nathan J.; Hopkins, Philip F.; Hummels, Cameron B.; Klypin, Anatoly; Li, Hui; Madau, Piero; Mandelker, Nir; Mayer, Lucio; Nagamine, Kentaro; Nickerson, Sarah; O’Shea, Brian W.; Primack, Joel R.; Roca-Fàbrega, Santi; Semenov, Vadim; Shimizu, Ikkoh; Simpson, Christine M.; Todoroki, Keita; Wadsley, James W.; Wise, John H.

    2016-12-20

    Using an isolated Milky Way-mass galaxy simulation, we compare results from 9 state-of-the-art gravito-hydrodynamics codes widely used in the numerical community. We utilize the infrastructure we have built for the AGORA High-resolution Galaxy Simulations Comparison Project. This includes the common disk initial conditions, common physics models (e.g., radiative cooling and UV background by the standardized package Grackle) and common analysis toolkit yt, all of which are publicly available. Subgrid physics models such as Jeans pressure floor, star formation, supernova feedback energy, and metal production are carefully constrained across code platforms. With numerical accuracy that resolves the disk scale height, we find that the codes overall agree well with one another in many dimensions including: gas and stellar surface densities, rotation curves, velocity dispersions, density and temperature distribution functions, disk vertical heights, stellar clumps, star formation rates, and Kennicutt-Schmidt relations. Quantities such as velocity dispersions are very robust (agreement within a few tens of percent at all radii) while measures like newly-formed stellar clump mass functions show more significant variation (difference by up to a factor of ~3). Systematic differences exist, for example, between mesh-based and particle-based codes in the low density region, and between more diffusive and less diffusive schemes in the high density tail of the density distribution. Yet intrinsic code differences are generally small compared to the variations in numerical implementations of the common subgrid physics such as supernova feedback. Lastly, our experiment reassures that, if adequately designed in accordance with our proposed common parameters, results of a modern high-resolution galaxy formation simulation are more sensitive to input physics than to intrinsic differences in numerical schemes.

  14. Sporadic mass loss, spin-down, and element redistribution in young disk galaxies

    NASA Astrophysics Data System (ADS)

    Charlton, Jane C.; Salpeter, Edwin E.

    1989-11-01

    Violent conditions in young spiral disks may be conducive to the high-velocity ejection of large 'blobs' of material powered by the concerted action of supernovae. Using explicit numerical Monte Carlo models, treating ejected 'bobs' as 'galactic cannonballs' traveling with little interaction through the corona, several important consequences for galactic evolution are found. Preferential escape from the galaxy or objects with high specific angular momenta lead to a significant spin-down of the disk. In addition, this process may contribute to the production of an exponential column density distribution, and a metallicity gradient. The models predict a reversal in the sign of the metallicity gradient at large radii because the metal-rich objects that return to such a low column density region suffer relatively little dilution.

  15. METALLICITIES, AGE-METALLICITY RELATIONSHIPS, AND KINEMATICS OF RED GIANT BRANCH STARS IN THE OUTER DISK OF THE LARGE MAGELLANIC CLOUD

    SciTech Connect

    Carrera, R.; Gallart, C.; Aparicio, A.; Hardy, E.

    2011-08-15

    The outer disk of the Large Magellanic Cloud (LMC) is studied in order to unveil clues about its formation and evolution. Complementing our previous studies in innermost fields (3 kpc {approx}< R {approx}< 7 kpc), we obtained deep color-magnitude diagrams in six fields with galactocentric distances from 5.2 kpc to 9.2 kpc and different azimuths. The comparison with isochrones shows that while the oldest population is approximately coeval in all fields, the age of the youngest populations increases with increasing radius. This agrees with the results obtained in the innermost fields. Low-resolution spectroscopy in the infrared Ca II triplet region has been obtained for about 150 stars near the tip of the red giant branch in the same fields. Radial velocities and stellar metallicities have been obtained from these spectra. The metallicity distribution of each field has been analyzed together with those previously studied. The metal content of the most metal-poor objects, which are also the oldest according to the derived age-metallicity relationships, is similar in all fields independently of the galactocentric distance. However, while the metallicity of the most metal-rich objects measured, which are the youngest ones, remains constant in the inner 6 kpc, it decreases with increasing radius from there on. The same is true for the mean metallicity. According to the derived age-metallicity relationships, which are consistent with being the same in all fields, this result may be interpreted as an outside-in formation scheme in opposition with the inside-out scenario predicted by {Lambda}CDM cosmology for a galaxy like the LMC. The analysis of the radial velocities of our sample of giants shows that they follow a rotational cold disk kinematics. The velocity dispersion increases as metallicity decreases indicating that the most metal-poor/oldest objects are distributed in a thicker disk than the most metal-rich/youngest ones in agreement with the findings in other disks

  16. Computer experiments on the effect of retrograde stars in disk galaxies

    NASA Technical Reports Server (NTRS)

    Zang, T. A.; Hohl, F.

    1978-01-01

    Using large-scale N-body calculations for flat disk galaxies, we examine the effect of reversing the angular momentum for various fractions of the stars upon the global bar-forming mode. The initial conditions for these simulations are based on stationary states of two classes of models: the isochrones studied recently by Kalnajs by means of linear theory, and a model resembling the Schmidt model of our own Galaxy. In both cases, as the fraction of retrograde stars is increased, the growth of the bar-forming mode is inhibited (although not eliminated). These N-body results for the isochrones agree with the predictions of linear theory, quantitatively as well as qualitatively.

  17. Low-redshift Lyman-alpha absorption lines and the dark matter halos of disk galaxies

    NASA Technical Reports Server (NTRS)

    Maloney, Philip

    1992-01-01

    Ultraviolet observations of the low-redshift quasar 3C 273 using the Hubble Space Telescope have revealed many more Lyman-alpha absorption lines than would be expected from extrapolation of the absorption systems seen toward QSOs at z about 2. It is shown here that these absorption lines can plausibly be produced by gas at large radii in the disks of spiral and irregular galaxies; the gas is confined by the dark matter halos and ionized and heated by the extragalactic radiation field. This scenario does not require the extragalactic ionizing radiation field to decline as rapidly with decreasing z as the QSO emissivity. Observations of Ly-alpha absorption through the halos of known galaxies at low redshift will constrain both the extragalactic background and the properties of galactic halos.

  18. Sharp edges to neutral hydrogen disks in galaxies and the extragalactic radiation field

    NASA Astrophysics Data System (ADS)

    Maloney, Philip

    1993-09-01

    It is shown that the very sharp truncation of the neutral hydrogen distribution seen in NGC 3198 (and probably M33) is well modeled as the result of ionization of the atomic gas by the extragalactic radiation field. Below a critical column density of about a few times 10 exp 19/sq cm the gas is dominantly ionized and undetectable in the 21-cm line. It is inferred from the photoionization models that the total disk gas distribution in NGC 3198 is actually fairly axisymmetric. The critical column density for ionization is not a strong function of galaxy mass or mass distribution; thus, all galaxies should show a cutoff at approximately the same column density. Specific models of 3198 suggest that the extragalactic ionizing photon flux is 5000-10,000 photons/sq cm s.

  19. Sharp edges to neutral hydrogen disks in galaxies and the extragalactic radiation field

    NASA Technical Reports Server (NTRS)

    Maloney, Philip

    1993-01-01

    It is shown that the very sharp truncation of the neutral hydrogen distribution seen in NGC 3198 (and probably M33) is well modeled as the result of ionization of the atomic gas by the extragalactic radiation field. Below a critical column density of about a few times 10 exp 19/sq cm the gas is dominantly ionized and undetectable in the 21-cm line. It is inferred from the photoionization models that the total disk gas distribution in NGC 3198 is actually fairly axisymmetric. The critical column density for ionization is not a strong function of galaxy mass or mass distribution; thus, all galaxies should show a cutoff at approximately the same column density. Specific models of 3198 suggest that the extragalactic ionizing photon flux is 5000-10,000 photons/sq cm s.

  20. Low-redshift Lyman-alpha absorption lines and the dark matter halos of disk galaxies

    NASA Technical Reports Server (NTRS)

    Maloney, Philip

    1992-01-01

    Ultraviolet observations of the low-redshift quasar 3C 273 using the Hubble Space Telescope have revealed many more Lyman-alpha absorption lines than would be expected from extrapolation of the absorption systems seen toward QSOs at z about 2. It is shown here that these absorption lines can plausibly be produced by gas at large radii in the disks of spiral and irregular galaxies; the gas is confined by the dark matter halos and ionized and heated by the extragalactic radiation field. This scenario does not require the extragalactic ionizing radiation field to decline as rapidly with decreasing z as the QSO emissivity. Observations of Ly-alpha absorption through the halos of known galaxies at low redshift will constrain both the extragalactic background and the properties of galactic halos.

  1. A Green Bank Telescope Search for Highly Extended HI Disks Around Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Ford, H. Alyson; Bregman, Joel

    2015-08-01

    Recent UV absorption line studies suggest that a large fraction of missing baryons are in the warm ionized and neutral phases, with about half of Milky Way-mass galaxies containing absorption systems with HI column densities of 10^18 cm^-2 or greater. This HI gas, which would have been difficult to detect with previous instruments, could have enough mass to account for the missing baryons. The Green Bank Telescope (GBT) presents a unique opportunity to detect this emission. We present GBT results from a sample of ten nearby optically luminous spirals in search of these extended disks of low column density HI.

  2. Molecular clouds associated with luminous far-infrared sources in the outer Galaxy

    NASA Technical Reports Server (NTRS)

    Carpenter, John M.; Snell, Ronald L.; Schloerb, F. Peter

    1990-01-01

    The stellar content and physical properties of the molecular clouds associated with 21 bright far-IR sources in the outer Galaxy have been determined through C-12O, C-13O, 6-cm radio continuum, and IRAS observations. The molecular cloud masses range from 200 to about 10,000 solar masses. The far-IR luminosity-to-mass ratio for these clouds has a mean value of 6.8 solar luminosity/solar masses and shows no correlation with the cloud mass, a result similar to that found for more massive clouds in the inner Galaxy. The radio continuum survey of the 21 bright far-IR sources indicates that most of these regions probably have a single, massive star providing most of the ionization. The cloud masses derived from virial and LTE analyses are in agreement, supporting the assumptions commonly made in their calculations, and a tight, near-linear correlation is found between the C-12O luminosity and the cloud mass. The H2 column density and integrated C-12O intensity are also correlated on a point-by-point basis, although the scatter is larger than the C-12O luminosity-cloud mass relation.

  3. The outer limits of galaxy clusters: Observations to the virial radius with Suzaku, XMM, and Chandra

    NASA Astrophysics Data System (ADS)

    Miller, Eric D.; Bautz, Marshall; George, Jithin; Mushotzky, Richard; Davis, David; Henry, J. Patrick

    2012-03-01

    The outskirts of galaxy clusters, near the virial radius, remain relatively unexplored territory and yet are vital to our understanding of cluster growth, structure, and mass. In this presentation, we show the first results from a program to constrain the state of the outer intra-cluster medium (ICM) in a large sample of galaxy clusters, exploiting the strengths of three complementary X-ray observatories: Suzaku (low, stable background), XMM-Newton (high sensitivity), and Chandra (good spatial resolution). By carefully combining observations from the cluster core to beyond r200, we are able to identify and reduce systematic uncertainties that would impede our spatial and spectral analysis using a single telescope. Our sample comprises nine clusters at z ~ 0.1-0.2 fully covered in azimuth to beyond r200, and our analysis indicates that the ICMis not in hydrostatic equilibrium in the cluster outskirts, where we see clear azimuthal variations in temperature and surface brightness. In one of the clusters, we are able to measure the diffuse X-ray emission well beyond r200, and we find that the entropy profile and the gas fraction are consistent with expectations from theory and numerical simulations. These results stands in contrast to recent studies which point to gas clumping in the outskirts; the extent to which differences of cluster environment or instrumental effects factor in this difference remains unclear. From a broader perspective, this project will produce a sizeable fiducial data set for detailed comparison with high-resolution numerical simulations.

  4. 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.

  5. VizieR Online Data Catalog: Mass models for 175 disk galaxies with SPARC (Lelli+, 2016)

    NASA Astrophysics Data System (ADS)

    Lelli, F.; McGaugh, S. S.; Schombert, J. M.

    2017-02-01

    Created by team leaders Federico Lelli and Stacy McGaugh (CWRU Astronomy) and Jim Schombert (UOregon Physics), SPARC (Spitzer Photometry and Accurate Rotation Curves) is a sample of 175 disk galaxies covering a broad range of morphologies (S0 to Irr), luminosities (107 to 1012Lsun), and sizes (0.3 to 15kpc). We collected more than 200 extended HI rotation curves from previous compilations, large surveys, and individual studies. This kinematic data set is the result of ~30yr of interferometric HI observations using the Westerbork Synthesis Radio Telescope (WSRT), Very Large Array (VLA), Australia Telescope Compact Array (ATCA), and Giant Metrewave Radio Telescope (GMRT). Subsequently, we searched the Spitzer archive and found useful [3.6] images for 175 galaxies. Most of these objects are part of the Spitzer Survey for Stellar Structure in Galaxies (S4G; Sheth et al. 2010, Cat. J/PASP/122/1397). We also used [3.6] images from Schombert & McGaugh 2014PASA...31...11S for low-surface-brightness (LSB) galaxies (3 data files).

  6. Automated bar detection in local disk galaxies from the SDSS. The colors of bars

    NASA Astrophysics Data System (ADS)

    Consolandi, G.

    2016-10-01

    This paper describes an automatic isophotal fitting procedure that succeeds, without the support of any visual inspection of either the images or the ellipticity/position-angle radial profiles, to extract a fairly pure sample of barred late-type galaxies (LTGs) among thousands of optical images from the Sloan Digital Sky Survey (SDSS). The procedure relies on previous methods to robustly extract the photometrical properties of a large sample of local SDSS galaxies and is tailored to extract bars on the basis of their well-known peculiarities in their position angle and ellipticity profiles. This procedure was run on a sample of 5853 galaxies in the Coma and Local superclusters. The procedure extracted a color, an ellipticity and a position angle radial profile of the ellipses fitted to the isophotes for each galaxy. Examining the profiles of 922 face-on LTGs (B/A > 0.7) automatically, the procedure found that 36% are barred. The local bar fraction strongly increases with stellar mass. The sample of barred galaxies is used to construct a set of template radial color profiles to test the impact of the barred galaxy population on the average color profiles as previously shown in the literature and to test the bar-quenching scenario. The radial color profile of barred galaxy shows that bars are on average redder than their surrounding disk producing an outside-in gradient toward red in correspondence with their corotation radius. The distribution of the extension of the deprojected length of the bar suggests that bars have strong impact on the gradients of averaged color profiles. The dependence of the profiles on the mass is consistent with the bar-quenching scenario, i.e. more massive barred galaxies have redder colors (hence older stellar population and suppressed star formation) inside their corotation radius with respect to their lower mass counterparts. Tables of the barred and non-barred galaxies are only available at the CDS via anonymous ftp to http

  7. The History of Star Formation in Galaxy Disks in the Local Volume as Measured by the Advanced Camera for Surveys Nearby Galaxy Survey Treasury

    NASA Astrophysics Data System (ADS)

    Williams, Benjamin F.; Dalcanton, Julianne J.; Johnson, L. C.; Weisz, Daniel R.; Seth, Anil C.; Dolphin, Andrew; Gilbert, Karoline M.; Skillman, Evan; Rosema, Keith; Gogarten, Stephanie M.; Holtzman, Jon; de Jong, Roelof S.

    2011-06-01

    We present a measurement of the age distribution of stars residing in spiral disks and dwarf galaxies. We derive a complete star formation history of the ~140 Mpc3 covered by the volume-limited sample of galaxies in the Advanced Camera for Surveys (ACS) Nearby Galaxy Survey Treasury (ANGST). The total star formation rate density history (ρSFR(t)) is dominated by the large spirals in the volume, although the sample consists mainly of dwarf galaxies. Our ρSFR(t) shows a factor of ~3 drop at z ~ 2, in approximate agreement with results from other measurement techniques. While our results show that the overall ρSFR(t) has decreased since z ~ 1, the measured rates during this epoch are higher than those obtained from other measurement techniques. This enhanced recent star formation rate appears to be largely due to an increase in the fraction of star formation contained in low-mass disks at recent times. Finally, our results indicate that despite the differences at recent times, the epoch of formation of ~50% of the stellar mass in dwarf galaxies was similar to that of ~50% of the stellar mass in large spiral galaxies (z >~ 2), despite the observed galaxy-to-galaxy diversity among the dwarfs.

  8. OPEN CLUSTERS IN THE MILKY WAY OUTER DISK: NEWLY DISCOVERED AND UNSTUDIED CLUSTERS IN THE SPITZER GLIMPSE-360, CYG-X, AND SMOG SURVEYS

    SciTech Connect

    Zasowski, G.; Beaton, R. L.; Hamm, K. K.; Majewski, S. R.; Patterson, R. J.; Babler, B.; Churchwell, E.; Meade, M.; Whitney, B. A.; Benjamin, R. A.; Watson, C.

    2013-09-15

    Open stellar clusters are extremely valuable probes of Galactic structure, star formation, kinematics, and chemical abundance patterns. Near-infrared (NIR) data have enabled the detection of hundreds of clusters hidden from optical surveys, and mid-infrared (MIR) data are poised to offer an even clearer view into the most heavily obscured parts of the Milky Way. We use new MIR images from the Spitzer GLIMPSE-360, Cyg-X, and SMOG surveys to visually identify a large number of open cluster candidates in the outer disk of the Milky Way (65 Degree-Sign < l < 265 Degree-Sign ). Using NIR color-magnitude diagrams, stellar isochrones, and stellar reddening estimates, we derive cluster parameters (metallicity, distance, reddening) for those objects without previous identification and/or parameters in the literature. In total, we present coordinates and sizes of 20 previously unknown open cluster candidates; for 7 of these we also present metallicity, distance, and reddening values. In addition, we provide the first estimates of these values for nine clusters that had been previously cataloged. We compare our cluster sizes and other derived parameters to those in the open cluster catalog of Dias et al. and find strong similarities except for a higher mean reddening for our objects, which signifies our increased detection sensitivity in regions of high extinction. The results of this cluster search and analysis demonstrate the ability of MIR imaging and photometry to augment significantly the current census of open clusters in the Galaxy.

  9. A detailed view of a molecular cloud in the far outer disk of M 33. Molecular cloud formation in M 33

    NASA Astrophysics Data System (ADS)

    Braine, J.; Gratier, P.; Contreras, Y.; Schuster, K. F.; Brouillet, N.

    2012-12-01

    The amount of H2 present in spiral galaxies remains uncertain, particularly in the dim outer regions and in low-metallicity environments. We present high-resolution CO(1-0) observations with the Plateau de Bure interferometer of the most distant molecular cloud in the local group galaxy M 33. The cloud is a single entity rather than a set of smaller clouds within the broad beam of the original single-dish observations. The interferometer and single-dish fluxes are very similar and the line widths are indistinguishable, despite the difference in beamsize. At a spatial resolution of 10 pc, beyond the optical radius of the M 33, the CO brightness temperature reaches 2.4 Kelvins. A virial mass estimate for the cloud yields a mass of 4.3 × 104 M⊙ and a ratio N(H2)/ICO(1-0) ≃ 3.5 × 1020 cm-2/(K km s-1). While no velocity gradient is seen where the emission is strong, the velocity is redshifted to the extreme SW and blue-shifted to the far NE. If the orientation of the cloud is along the plane of the disk (i.e. not perpendicular), then these velocities correspond to slow infall or accretion. The rather modest infall rate would be about 2 × 10-4 M⊙ yr-1. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).Data cube in FITS files is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/548/A52

  10. The outer regions of galaxy clusters: Chandra constraints on the X-ray surface brightness

    NASA Astrophysics Data System (ADS)

    Ettori, S.; Balestra, I.

    2009-03-01

    Context: We study the properties of the X-ray surface brightness profiles in a sample of galaxy clusters that were observed with Chandra and have emission detectable with a signal-to-noise ratio higher than 2 per radial bin at a radius beyond R500 ≈ 0.7 × R200. Aims: Our study aims to measure the slopes in both the X-ray surface brightness and gas density profiles in the outskirts of massive clusters. These constraints are compared with similar results obtained from observations and numerical simulations of the temperature and dark-matter density profiles with the intention of presenting a consistent picture of the outer regions of galaxy clusters. Methods: We extract the surface brightness profiles S_b(r) of 52 X-ray luminous galaxy clusters at z>0.3 from X-ray exposures obtained with Chandra. These objects, which are of both high X-ray surface brightness and high redshift, allow us to use Chandra either in ACIS-I or even ACIS-S configuration to survey the cluster outskirts. We estimate R200 using both a β-model that reproduces the surface brightness profiles and scaling relations from the literature. The two methods converge to comparable values. We determine the radius, R_S2N, at which the signal-to-noise ratio is higher than 2, and select the objects in the sample that satisfy the criterion R_S2N/R200 > 0.7. For the eleven selected objects, we model by a power-law function the behaviour of S_b(r) to estimate the slope at several characteristic radii expressed as a fraction of R200. Results: We measure a consistent steepening of the S_b(r) profile moving outward from 0.4R200, where an average slope of -3.6 (σ = 0.8) is estimated. At R200, we evaluate a slope of -4.3 (σ = 0.9) that implies a slope in the gas density profile of ≈-2.6 and a predicted mean value of the surface brightness in the 0.5-2 keV band of 2 × 10-12 erg s-1 cm-2 deg-2. Conclusions: Combined with estimates of the outer slope of the gas temperature profile and expectations about the

  11. No more active galactic nuclei in clumpy disks than in smooth galaxies at z ∼ 2 in CANDELS/3D-HST

    SciTech Connect

    Trump, Jonathan R.; Luo, Bin; Brandt, W. N.; Barro, Guillermo; Guo, Yicheng; Koo, David C.; Faber, S. M.; Brammer, Gabriel B.; Ferguson, Henry C.; Grogin, Norman A.; Kartaltepe, Jeyhan; Koekemoer, Anton M.; Bell, Eric F.; Dekel, Avishai; Hopkins, Philip F.; Kocevski, Dale D.; McIntosh, Daniel H.; Momcheva, Ivelina; and others

    2014-10-01

    We use CANDELS imaging, 3D-HST spectroscopy, and Chandra X-ray data to investigate if active galactic nuclei (AGNs) are preferentially fueled by violent disk instabilities funneling gas into galaxy centers at 1.3 < z < 2.4. We select galaxies undergoing gravitational instabilities using the number of clumps and degree of patchiness as proxies. The CANDELS visual classification system is used to identify 44 clumpy disk galaxies, along with mass-matched comparison samples of smooth and intermediate morphology galaxies. We note that despite being mass-matched and having similar star formation rates, the smoother galaxies tend to be smaller disks with more prominent bulges compared to the clumpy galaxies. The lack of smooth extended disks is probably a general feature of the z ∼ 2 galaxy population, and means we cannot directly compare with the clumpy and smooth extended disks observed at lower redshift. We find that z ∼ 2 clumpy galaxies have slightly enhanced AGN fractions selected by integrated line ratios (in the mass-excitation method), but the spatially resolved line ratios indicate this is likely due to extended phenomena rather than nuclear AGNs. Meanwhile, the X-ray data show that clumpy, smooth, and intermediate galaxies have nearly indistinguishable AGN fractions derived from both individual detections and stacked non-detections. The data demonstrate that AGN fueling modes at z ∼ 1.85—whether violent disk instabilities or secular processes—are as efficient in smooth galaxies as they are in clumpy galaxies.

  12. Electron Heating in Magnetorotational Instability: Implications for Turbulence Strength in the Outer Regions of Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Mori, Shoji; Okuzumi, Satoshi

    2016-01-01

    The magnetorotational instability (MRI) drives vigorous turbulence in a region of protoplanetary disks where the ionization fraction is sufficiently high. It has recently been shown that the electric field induced by the MRI can heat up electrons and thereby affect the ionization balance in the gas. In particular, in a disk where abundant dust grains are present, the electron heating causes a reduction of the electron abundance, thereby preventing further growth of the MRI. By using the nonlinear Ohm's law that takes into account electron heating, we investigate where in protoplanetary disks this negative feedback between the MRI and ionization chemistry becomes important. We find that the “e-heating zone,” the region where the electron heating limits the saturation of the MRI, extends out up to 80 AU in the minimum-mass solar nebula with abundant submicron-sized grains. This region is considerably larger than the conventional dead zone whose radial extent is ∼20 AU in the same disk model. Scaling arguments show that the MRI turbulence in the e-heating zone should have a significantly lower saturation level. Submicron-sized grains in the e-heating zone are so negatively charged that their collisional growth is unlikely to occur. Our present model neglects ambipolar and Hall diffusion, but our estimate shows that ambipolar diffusion would also affect the MRI in the e-heating zone.

  13. ELECTRON HEATING IN MAGNETOROTATIONAL INSTABILITY: IMPLICATIONS FOR TURBULENCE STRENGTH IN THE OUTER REGIONS OF PROTOPLANETARY DISKS

    SciTech Connect

    Mori, Shoji; Okuzumi, Satoshi

    2016-01-20

    The magnetorotational instability (MRI) drives vigorous turbulence in a region of protoplanetary disks where the ionization fraction is sufficiently high. It has recently been shown that the electric field induced by the MRI can heat up electrons and thereby affect the ionization balance in the gas. In particular, in a disk where abundant dust grains are present, the electron heating causes a reduction of the electron abundance, thereby preventing further growth of the MRI. By using the nonlinear Ohm's law that takes into account electron heating, we investigate where in protoplanetary disks this negative feedback between the MRI and ionization chemistry becomes important. We find that the “e-heating zone,” the region where the electron heating limits the saturation of the MRI, extends out up to 80 AU in the minimum-mass solar nebula with abundant submicron-sized grains. This region is considerably larger than the conventional dead zone whose radial extent is ∼20 AU in the same disk model. Scaling arguments show that the MRI turbulence in the e-heating zone should have a significantly lower saturation level. Submicron-sized grains in the e-heating zone are so negatively charged that their collisional growth is unlikely to occur. Our present model neglects ambipolar and Hall diffusion, but our estimate shows that ambipolar diffusion would also affect the MRI in the e-heating zone.

  14. GRAVITATIONAL INSTABILITIES IN TWO-COMPONENT GALAXY DISKS WITH GAS DISSIPATION

    SciTech Connect

    Elmegreen, Bruce G.

    2011-08-10

    Growth rates for gravitational instabilities in a thick disk of gas and stars are determined for a turbulent gas that dissipates on the local crossing time. The scale heights are derived from vertical equilibrium. The accuracy of the usual thickness correction, (1 + kH){sup -1}, is better than 6% in the growth rate when compared to exact integrations for the gravitational acceleration in the disk. Gas dissipation extends the instability to small scales, removing the minimum Jeans length. This makes infinitesimally thin disks unstable for all Toomre-Q values and reasonably thick disks stable at high Q primarily because of thickness effects. The conventional gas+star threshold, Q{sub tot}, increases from {approx}1 without dissipation to 2 or 3 when dissipation has a rate equal to the crossing rate over a perturbation scale. Observations of Q{sub tot} {approx} 2-3 and the presence of supersonic turbulence suggest that disks are unstable over a wide range of scales. Such instabilities drive spiral structure if there is shear and clumpy structure if shear is weak; they may dominate the generation of turbulence. Feedback regulation of Q{sub tot} is complex because the stellar component does not cool; the range of spiral strengths from multiple arm to flocculent galaxies suggests that feedback is weak. Gravitational instabilities may have a connection to star formation even when the star formation rate scales directly with the molecular mass because the instabilities return dispersed gas to molecular clouds and complete the cycle of cloud formation and destruction. The mass flow to dense clouds by instabilities can be 10 times larger than the star formation rate.

  15. HALO GAS AND GALAXY DISK KINEMATICS DERIVED FROM OBSERVATIONS AND LAMBDACDM SIMULATIONS OF Mg II ABSORPTION-SELECTED GALAXIES AT INTERMEDIATE REDSHIFT

    SciTech Connect

    Kacprzak, Glenn G.; Murphy, Michael T.; Churchill, Christopher W.; Ceverino, Daniel; Klypin, Anatoly; Steidel, Charles C. E-mail: mmurphy@astro.swin.edu.a E-mail: ceverino@nmsu.ed E-mail: ceverino@phys.huji.ac.i

    2010-03-10

    We obtained ESI/Keck rotation curves of 10 Mg II absorption-selected galaxies (0.3 <= z <= 1.0) for which we have WFPC-2/HST images and high-resolution HIRES/Keck and UVES/VLT quasar spectra of the Mg II absorption profiles. We perform a kinematic comparison of these galaxies and their associated halo Mg II absorption. For all 10 galaxies, the majority of the absorption velocities lie in the range of the observed galaxy rotation velocities. In 7/10 cases, the absorption velocities reside fully to one side of the galaxy systemic velocity and usually align with one arm of the rotation curve. In all cases, a constant rotating thick-disk model poorly reproduces the full spread of observed Mg II absorption velocities when reasonably realistic parameters are employed. In 2/10 cases, the galaxy kinematics, star formation surface densities, and absorption kinematics have a resemblance to those of high-redshift galaxies showing strong outflows. We find that Mg II absorption velocity spread and optical depth distribution may be dependent on galaxy inclination. To further aid in the spatial-kinematic relationships of the data, we apply quasar absorption-line techniques to a galaxy (v{sub c} = 180 km s{sup -1}) embedded in LAMBDACDM simulations. In the simulations, Mg II absorption selects metal-enriched 'halo' gas out to {approx}100 kpc from the galaxy, tidal streams, filaments, and small satellite galaxies. Within the limitations inherent in the simulations, the majority of the simulated Mg II absorption arises in the filaments and tidal streams and is infalling toward the galaxy with velocities between -200 km s{sup -1} <= v{sub r} <= -180 km s{sup -1}. The Mg II absorption velocity offset distribution (relative to the simulated galaxy) spans {approx}200 km s{sup -1} with the lowest frequency of detecting Mg II at the galaxy systematic velocity.

  16. GALAXY FORMATION IN HEAVILY OVERDENSE REGIONS AT z {approx} 10: THE PREVALENCE OF DISKS IN MASSIVE HALOS

    SciTech Connect

    Romano-Diaz, Emilio; Choi, Jun-Hwan; Shlosman, Isaac; Trenti, Michele

    2011-09-10

    Using a high-resolution cosmological numerical simulation, we have analyzed the evolution of galaxies at z {approx} 10 in a highly overdense region of the universe. These objects could represent the high-redshift galaxies recently observed by the Hubble's Wide Field Camera 3 and could as well be possible precursors of QSOs at z {approx} 6-7. To overcome the sampling and resolution problems in cosmological simulations of these rare regions, we have used the constrained realizations method. Our main result for z {approx} 10 shows the high-resolution central region of 3.5 h {sup -1} Mpc radius in comoving coordinates being completely dominated by disk galaxies in the total mass range of {approx}> 10{sup 9} h {sup -1} M{sub sun}. We have verified that the gaseous and stellar disks we identify are robust morphological features, capable of surviving the ongoing merger process at these redshifts. Below this mass range, we find a sharp decline in the disk fraction to negligible numbers. At this redshift, the disks appear to be gas-rich compared to z = 0, and the dark matter halos baryon-rich, by a factor of {approx}2-3 above the average fraction of baryons in the universe. The dominance of disk galaxies in the high-density peaks during the epoch of re-ionization is contrary to the morphology-density trend observed at low redshifts.

  17. Observational evidence for the accretion-disk origin for a radio jet in an active galaxy.

    PubMed

    Marscher, Alan P; Jorstad, Svetlana G; Gómez, José-Luis; Aller, Margo F; Teräsranta, Harri; Lister, Matthew L; Stirling, Alastair M

    2002-06-06

    Accretion of gas onto black holes is thought to power the relativistic jets of material ejected from active galactic nuclei (AGN) and the 'microquasars' located in our Galaxy. In microquasars, superluminal radio-emitting features appear and propagate along the jet shortly after sudden decreases in the X-ray fluxes. This establishes a direct observational link between the black hole and the jet: the X-ray dip is probably caused by the disappearance of a section of the inner accretion disk as it falls past the event horizon, while the remainder of the disk section is ejected into the jet, creating the appearance of a superluminal bright spot. No such connection has hitherto been established for AGN, because of insufficient multi-frequency data. Here we report the results of three years of monitoring the X-ray and radio emission of the galaxy 3C120. As has been observed for microquasars, we find that dips in the X-ray emission are followed by ejections of bright superluminal knots in the radio jet. The mean time between X-ray dips appears to scale roughly with the mass of the black hole, although there are at present only a few data points.

  18. Low-metallicity Young Clusters in the Outer Galaxy. II. Sh 2-208

    NASA Astrophysics Data System (ADS)

    Yasui, Chikako; Kobayashi, Naoto; Saito, Masao; Izumi, Natsuko

    2016-05-01

    We obtained deep near-infrared images of Sh 2-208, one of the lowest-metallicity H ii regions in the Galaxy, [O/H] = -0.8 dex. We detected a young cluster in the center of the H ii region with a limiting magnitude of K = 18.0 mag (10σ), which corresponds to a mass detection limit of ˜0.2 M⊙. This enables the comparison of star-forming properties under low metallicity with those of the solar neighborhood. We identified 89 cluster members. From the fitting of the K-band luminosity function (KLF), the age and distance of the cluster are estimated to be ˜0.5 Myr and ˜4 kpc, respectively. The estimated young age is consistent with the detection of strong CO emission in the cluster region and the estimated large extinction of cluster members (AV ˜ 4-25 mag). The observed KLF suggests that the underlying initial mass function (IMF) of the low-metallicity cluster is not significantly different from canonical IMFs in the solar neighborhood in terms of both high-mass slope and IMF peak (characteristic mass). Despite the very young age, the disk fraction of the cluster is estimated at only 27% ± 6%, which is significantly lower than those in the solar metallicity. Those results are similar to Sh 2-207, which is another star-forming region close to Sh 2-208 with a separation of 12 pc, suggesting that their star-forming activities in low-metallicity environments are essentially identical to those in the solar neighborhood, except for the disk dispersal timescale. From large-scale mid-infrared images, we suggest that sequential star formation is taking place in Sh 2-207, Sh 2-208, and the surrounding region, triggered by an expanding bubble with a ˜30 pc radius.

  19. Kiloparsec-scale Dust Disks in High-redshift Luminous Submillimeter Galaxies

    NASA Astrophysics Data System (ADS)

    Hodge, J. A.; Swinbank, A. M.; Simpson, J. M.; Smail, I.; Walter, F.; Alexander, D. M.; Bertoldi, F.; Biggs, A. D.; Brandt, W. N.; Chapman, S. C.; Chen, C. C.; Coppin, K. E. K.; Cox, P.; Dannerbauer, H.; Edge, A. C.; Greve, T. R.; Ivison, R. J.; Karim, A.; Knudsen, K. K.; Menten, K. M.; Rix, H.-W.; Schinnerer, E.; Wardlow, J. L.; Weiss, A.; van der Werf, P.

    2016-12-01

    We present high-resolution (0.″16) 870 μm Atacama Large Millimeter/submillimeter Array (ALMA) imaging of 16 luminous ({L}{IR}˜ 4× {10}12 {L}⊙ ) submillimeter galaxies (SMGs) from the ALESS survey of the Extended Chandra Deep Field South. This dust imaging traces the dust-obscured star formation in these z˜ 2.5 galaxies on ˜1.3 kpc scales. The emission has a median effective radius of R e = 0.″24 ± 0.″02, corresponding to a typical physical size of {R}e= 1.8 ± 0.2 kpc. We derive a median Sérsic index of n = 0.9 ± 0.2, implying that the dust emission is remarkably disk-like at the current resolution and sensitivity. We use different weighting schemes with the visibilities to search for clumps on 0.″12 (˜1.0 kpc) scales, but we find no significant evidence for clumping in the majority of cases. Indeed, we demonstrate using simulations that the observed morphologies are generally consistent with smooth exponential disks, suggesting that caution should be exercised when identifying candidate clumps in even moderate signal-to-noise ratio interferometric data. We compare our maps to comparable-resolution Hubble Space Telescope {H}160-band images, finding that the stellar morphologies appear significantly more extended and disturbed, and suggesting that major mergers may be responsible for driving the formation of the compact dust disks we observe. The stark contrast between the obscured and unobscured morphologies may also have implications for SED fitting routines that assume the dust is co-located with the optical/near-IR continuum emission. Finally, we discuss the potential of the current bursts of star formation to transform the observed galaxy sizes and light profiles, showing that the z˜ 0 descendants of these SMGs are expected to have stellar masses, effective radii, and gas surface densities consistent with the most compact massive ({M}* ˜ 1-2 × 1011 {M}⊙ ) early-type galaxies observed locally.

  20. HST WFC3/IR OBSERVATIONS OF ACTIVE GALACTIC NUCLEUS HOST GALAXIES AT z {approx} 2: SUPERMASSIVE BLACK HOLES GROW IN DISK GALAXIES

    SciTech Connect

    Schawinski, Kevin; Urry, C. Megan; Treister, Ezequiel; Cardamone, Carolin N.; Simmons, Brooke; Yi, Sukyoung K.

    2011-02-01

    We present the rest-frame optical morphologies of active galactic nucleus (AGN) host galaxies at 1.5 < z < 3, using near-infrared imaging from the Hubble Space Telescope Wide Field Camera 3, the first such study of AGN host galaxies at these redshifts. The AGNs are X-ray-selected from the Chandra Deep Field South and have typical luminosities of 10{sup 42} erg s{sup -1}galaxies of these AGNs have low Sersic indices indicative of disk-dominated light profiles, suggesting that secular processes govern a significant fraction of the cosmic growth of black holes. That is, many black holes in the present-day universe grew much of their mass in disk-dominated galaxies and not in early-type galaxies or major mergers. The properties of the AGN host galaxies are furthermore indistinguishable from their parent galaxy population and we find no strong evolution in either effective radii or morphological mix between z {approx} 2 and z {approx} 0.05.

  1. LATE ORBITAL INSTABILITIES IN THE OUTER PLANETS INDUCED BY INTERACTION WITH A SELF-GRAVITATING PLANETESIMAL DISK

    SciTech Connect

    Levison, Harold F.; Nesvorny, David; Morbidelli, Alessandro; Tsiganis, Kleomenis; Gomes, Rodney

    2011-11-15

    We revisit the issue of the cause of the dynamical instability during the so-called Nice model, which describes the early dynamical evolution of the giant planets. In particular, we address the problem of the interaction of planets with a distant planetesimal disk in the time interval between the dispersal of the proto-solar nebula and the instability. In contrast to previous works, we assume that the inner edge of the planetesimal disk is several AUs beyond the orbit of the outermost planet, so that no close encounters between planets and planetesimals occur. Moreover, we model the disk's viscous stirring, induced by the presence of embedded Pluto-sized objects. The four outer planets are assumed to be initially locked in a multi-resonant state that most likely resulted from a preceding phase of gas-driven migration. We show that viscous stirring leads to an irreversible exchange of energy between a planet and a planetesimal disk even in the absence of close encounters between the planet and disk particles. The process is mainly driven by the most eccentric planet, which is the inner ice giant in the case studied here. In isolation, this would cause this ice giant to migrate inward. However, because it is locked in resonance with Saturn, its eccentricity increases due to adiabatic invariance. During this process, the system crosses many weak secular resonances-many of which can disrupt the mean motion resonance and make the planetary system unstable. We argue that this basic dynamical process would work in many generic multi-resonant systems-forcing a good fraction of them to become unstable. Because the energy exchange proceeds at a very slow pace, the instability manifests itself late, on a timescale consistent with the epoch of the late heavy bombardment ({approx}700 Myr). In the migration mechanism presented here, the instability time is much less sensitive to the properties of the planetesimal disk (particularly the location of its inner edge) than in the

  2. EVIDENCE FOR A CLUMPY, ROTATING GAS DISK IN A SUBMILLIMETER GALAXY AT z = 4

    SciTech Connect

    Hodge, J. A.; Walter, F.; Carilli, C. L.; De Blok, W. J. G.; Riechers, D.; Daddi, E.

    2012-11-20

    We present Karl G. Jansky Very Large Array observations of the CO(2-1) emission in the z = 4.05 submillimeter galaxy (SMG) GN20. These high-resolution data allow us to image the molecular gas at 1.3 kpc resolution just 1.6 Gyr after the big bang. The data reveal a clumpy, extended gas reservoir, 14 {+-} 4 kpc in diameter, in unprecedented detail. A dynamical analysis shows that the data are consistent with a rotating disk of total dynamical mass 5.4 {+-} 2.4 Multiplication-Sign 10{sup 11} M {sub Sun }. We use this dynamical mass estimate to constrain the CO-to-H{sub 2} mass conversion factor ({alpha}{sub CO}), finding {alpha}{sub CO} = 1.1 {+-} 0.6 M {sub Sun }(K km s{sup -1} pc{sup 2}){sup -1}. We identify five distinct molecular gas clumps in the disk of GN20 with masses a few percent of the total gas mass, brightness temperatures of 16-31K, and surface densities of >3200-4500 Multiplication-Sign ({alpha}{sub CO}/0.8) M {sub Sun} pc{sup -2}. Virial mass estimates indicate they could be self-gravitating, and we constrain their CO-to-H{sub 2} mass conversion factor to be <0.2-0.7 M {sub Sun }(K km s{sup -1} pc{sup 2}){sup -1}. A multiwavelength comparison demonstrates that the molecular gas is concentrated in a region of the galaxy that is heavily obscured in the rest-frame UV/optical. We investigate the spatially resolved gas excitation and find that the CO(6-5)/CO(2-1) ratio is constant with radius, consistent with star formation occurring over a large portion of the disk. We discuss the implications of our results in the context of different fueling scenarios for SMGs.

  3. Indications of M-Dwarf Deficits in the Halo and Thick Disk of the Galaxy

    NASA Technical Reports Server (NTRS)

    Konishi, Mihoko; Shibai, Hiroshi; Sumi, Takahiro; Fukagawa, Misato; Matsuo, Taro; Samland, Matthias S.; Yamamoto, Kodai; Sudo, Jun; Itoh, Yoichi; Arimoto, Nubuo; hide

    2014-01-01

    We compared the number of faint stars detected in deep survey fields with the current stellar distribution model of the Galaxy and found that the detected number in the H band is significantly smaller than the predicted number. This indicates that M-dwarfs, the major component, are fewer in the halo and the thick disk. We used archived data of several surveys in both the north and south field of GOODS (Great Observatories Origins Deep Survey), MODS in GOODS-N, and ERS and CANDELS in GOODS-S. The number density of M-dwarfs in the halo has to be 20 +/- 13% relative to that in the solar vicinity, in order for the detected number of stars fainter than 20.5 mag in the H band to match with the predicted value from the model. In the thick disk, the number density of M-dwarfs must be reduced (52 +/- 13%) or the scale height must be decreased (approximately 600 pc). Alternatively, overall fractions of the halo and thick disks can be significantly reduced to achieve the same effect, because our sample mainly consists of faint M-dwarfs. Our results imply that the M-dwarf population in regions distant from the Galactic plane is significantly smaller than previously thought. We then discussed the implications this has on the suitability of the model predictions for the prediction of non-companion faint stars in direct imaging extrasolar planet surveys by using the best-fit number densities.

  4. Indications of M-Dwarf Deficits in the Halo and Thick Disk of the Galaxy

    NASA Technical Reports Server (NTRS)

    Konishi, Mihoko; Shibai, Hiroshi; Sumi, Takahiro; Fukagawa, Misato; Matsuo, Taro; Samland, Matthias S.; Yamamoto, Kodai; Sudo, Jun; Itoh, Yoichi; Arimoto, Nobuo; hide

    2014-01-01

    We compared the number of faint stars detected in deep survey fields with the current stellar distribution model of the Galaxy and found that the detected number in the H band is significantly smaller than the predicted number. This indicates that M-dwarfs, the major component, are fewer in the halo and the thick disk. We used archived data of several surveys in both the north and south field of GOODS (Great Observatories Origins Deep Survey), MODS in GOODS-N, and ERS and CANDELS in GOODS-S. The number density of M-dwarfs in the halo has to be 20+/-13% relative to that in the solar vicinity, in order for the detected number of stars fainter than 20.5 mag in the H band to match with the predicted value from the model. In the thick disk, the number density of M-dwarfs must be reduced (52+/-13%) or the scale height must be decreased ( approx. 600 pc). Alternatively, overall fractions of the halo and thick disks can be significantly reduced to achieve the same effect, because our sample mainly consists of faint M-dwarfs. Our results imply that the M-dwarf population in regions distant from the Galactic plane is significantly smaller than previously thought. We then discussed the implications this has on the suitability of the model predictions for the prediction of non-companion faint stars in direct imaging extrasolar planet surveys by using the best-fit number densities.

  5. Metallicity and Age of the Stellar Stream around the Disk Galaxy NGC 5907

    NASA Astrophysics Data System (ADS)

    Laine, Seppo; Grillmair, Carl J.; Capak, Peter; Arendt, Richard G.; Romanowsky, Aaron J.; Martínez-Delgado, David; Ashby, Matthew L. N.; Davies, James E.; Majewski, Stephen R.; Brodie, Jean P.; GaBany, R. Jay; Arnold, Jacob A.

    2016-09-01

    Stellar streams have become central to studies of the interaction histories of nearby galaxies. To characterize the most prominent parts of the stellar stream around the well-known nearby (d = 17 Mpc) edge-on disk galaxy NGC 5907, we have obtained and analyzed new, deep gri Subaru/Suprime-Cam and 3.6 μm Spitzer/Infrared Array Camera observations. Combining the near-infrared 3.6 μm data with visible-light images allows us to use a long wavelength baseline to estimate the metallicity and age of the stellar population along an ˜60 kpc long segment of the stream. We have fitted the stellar spectral energy distribution with a single-burst stellar population synthesis model and we use it to distinguish between the proposed satellite accretion and minor/major merger formation models of the stellar stream around this galaxy. We conclude that a massive minor merger (stellar mass ratio of at least 1:8) can best account for the metallicity of -0.3 inferred along the brightest parts of the stream.

  6. Ab Initio Simulations of a Supernova-driven Galactic Dynamo in an Isolated Disk Galaxy

    NASA Astrophysics Data System (ADS)

    Butsky, Iryna; Zrake, Jonathan; Kim, Ji-hoon; Yang, Hung-I.; Abel, Tom

    2017-07-01

    We study the magnetic field evolution of an isolated spiral galaxy, using isolated Milky Way-mass galaxy formation simulations and a novel prescription for magnetohydrodynamic (MHD) supernova feedback. Our main result is that a galactic dynamo can be seeded and driven by supernova explosions, resulting in magnetic fields whose strength and morphology are consistent with observations. In our model, supernovae supply thermal energy and a low-level magnetic field along with their ejecta. The thermal expansion drives turbulence, which serves a dual role by efficiently mixing the magnetic field into the interstellar medium and amplifying it by means of a turbulent dynamo. The computational prescription for MHD supernova feedback has been implemented within the publicly available ENZO code and is fully described in this paper. This improves upon ENZO's existing modules for hydrodynamic feedback from stars and active galaxies. We find that the field attains microgauss levels over gigayear timescales throughout the disk. The field also develops a large-scale structure, which appears to be correlated with the disk’s spiral arm density structure. We find that seeding of the galactic dynamo by supernova ejecta predicts a persistent correlation between gas metallicity and magnetic field strength. We also generate all-sky maps of the Faraday rotation measure from the simulation-predicted magnetic field, and we present a direct comparison with observations.

  7. Star formation activity in spiral galaxy disks and the properties of radio halos: Observational evidence for a direct dependence

    NASA Technical Reports Server (NTRS)

    Dahlem, Michael; Lisenfeld, Ute; Golla, Gotz

    1995-01-01

    In this article we address observationally the questions: how does star formation (SF) in the disks of galaxies lead to the creation of radio halos, and what minimum energy input into the interstellar medium (ISM) is needed to facilitate this? For the investigation we use a sample of five edge-on galaxies exhibiting radio continuum emmission in their halos and enhanced SF spread over large parts of their disks. In a detailed study of the two galaxies in our sample for which we have the best data, NGC 891 and NGC 4631, we show that the radio halos cut off abruptly at galactocentric radii smaller than those of the underlying thin radio disks. Our most important result is that the halo cutoffs are spatially coincident with the radii where the SF activity in the underlying disks drops sharply. The difference in radius of the emission distributions tracing ongoing SF in the disks (IRAS 50 micrometers, H alpha) versus that of the nonthermal radio continuum thin disks (tracing the distribution of cosmic-ray (CR) electrons) is typically a few kpc. This difference in extent is caused by CR diffusion. We have measured the CR diffusion coefficients in the thin disks of both NGC 891 and NGC 4631. For radial diffusion of CR electrons within the galactic disks the values are D(sub r) = 1.1-2.5 x 10 (exp 29) sq cm/s (NGC 4631) and D(sub r) = 1.2 x 10(exp 29) sq cm/s (NGC 891). For motions in the z-direction in areas within the thin disks where no outflows occur, we derive a firm upper limit of D(sub z) less than or equal to 0.2 x 10(exp 28) sq cm/s for NGC 891. The value for NGC 4631 is D(sub z = 1.4 x 10 (exp 28) sq cm/s. The other three galaxies in our sample, NGC 3044, NGC 4666, and NGC 5775 show (at the sensitivity of our data) less extended, more filamentary radio halos. Isolates spurs or filaments of nonthermal radio continuum emission in their halos are traced only above the most actively star-forming regions in the disks. This, in conjuction with the results obtained for

  8. H I line studies of galaxies. III - Distance moduli of 822 disk galaxies

    NASA Astrophysics Data System (ADS)

    Bottinelli, L.; Gouguenheim, L.; Paturel, G.; de Vaucouleurs, G.

    1984-06-01

    The distance scale established on the basis of a distance moduli catalog (for 822 galaxies) that was derived from 21-cm line widths via the B-band Tully-Fisher relation is compared with several independent scales having a common zero point, that are based on the indicators for luminosity index, redshift, ring diameters, brightest superassociations, and effective diameters. These are in excellent systematic agreement, and confirm the linearity of the H I scale in the 24-35 modulus interval, but indicate a small systematic zero point difference of about 0.2 mag, which must be added to the H I moduli to place them on the same 'short' distance scale defined by the others.

  9. Properties of compact HII regions and their host clumps in the inner vs outer Galaxy - early results from SASSy

    NASA Astrophysics Data System (ADS)

    Djordjevic, Julie; Thompson, Mark; Urquhart, James S.

    2017-01-01

    We present a catalog of compact and ultracompact HII regions for all Galactocentric radii. Previous catalogs focus on the inner Galaxy (Rgal ≤ 8 kpc) but the recent SASSy 870 µm survey allows us to identify regions out to ~20 kpc. Early samples are also filled with false classifications leading to uncertainty when deriving star formation efficiencies in Galactic models. These objects have similar mid-IR colours to HII regions. Urquhart et al. (2013) found that they could use mid-IR, submm, and radio data to identify the genuine compact HII regions, avoiding confusion. They used this method on a small portion of the Galaxy (10 < l < 60), identifying 213 HII regions embedded in 170 clumps. We use ATLASGAL and SASSy, crossmatched with RMS, to sample the remaining galactic longitudes out to Rgal = 20 kpc. We derive the properties of the identified compact HII regions and their host clumps while addressing the implications for recent massive star formation in the outer Galaxy. Observations towards nearby galaxies are biased towards massive stars, affecting simulations and overestimating models for galactic evolution and star formation rates. The Milky Way provides the ideal template for studying factors affecting massive star formation rates and efficiencies at high resolution, thus fine-tuning those models. We find that there is no significant change in the rate of massive star formation in the outer vs inner Galaxy. Despite some peaks in known complexes and possible correlation with spiral arms, the outer Galaxy appears to produce massive stars as efficiently as the inner regions. However, many of the potential star forming SASSy clumps have no available radio counterpart to confirm the presence of an HII region or other star formation tracer. Follow-up observations will be required to verify this conclusion and are currently in progress.

  10. Detail studies of the physical properties in the outer regions of galaxy clusters using Suzaku observations

    NASA Astrophysics Data System (ADS)

    Babyk, Yu. V.

    2016-06-01

    A detailed physical analysis of five nearby galaxy clusters using Suzaku observationsis presented. The low and stable level of the instrumental background at large radii facilitate the determination of the main physical characteristics in clusters at the virial radius. The temperatures, metal abundances, and entropy profiles have been constructed out to the outskirts of the clusters. The temperature profiles all display the same shape, with a negative gradient towards to the center and a flat outer plateau. The strong temperature gradients in the central parts of the clusters are usually associated with strong peaks of the surface brightness profiles. The temperature systematically decrease outward from the central regions, by a factor of three at and slightly beyond the cluster outskirts. The temperature profiles are compared with profiles predicted by N-body and hydrodynamical simulations obtained using several numerical algorithms. The slopes in the observed and simulated temperature profiles are consistent with each other in the cluster outskirts. The central regions of the clusters are characterized by low entropy and high metallicity. The possible influence of cool cores on the cluster outskirts is also discussed. The total mass profiles were determined using the observed gas-density and temperature profiles, assuming hydrostatic equilibriumand spherical symmetry. The gas-density profiles were fitted using an improved three-dimensional model to fit the inner and outer regions of the cluster independently. The total mass profiles were described using an NFW model out to R 200. The measurements show clear evidence for universality of the total mass distribution. The scaled mass profiles in units of R 200 and M 200 display a dispersion of ~15% at 0.1 R 200. The fraction of gas out to R 200 was also found.

  11. Two-dimensional rhodopsin crystals from disk membranes of frog retinal rod outer segments.

    PubMed Central

    Corless, J M; McCaslin, D R; Scott, B L

    1982-01-01

    Two-dimensional crystals of rhodopsin have been prepared from purified frog disk membranes by using the detergent Tween 80. The space group of the orthorhombic crystals is p22121; the unit cell dimensions are 47 X 151 A. Projection maps of negatively stained preparations have been calculated to a resolution of approximately 22 A. The rhodopsin molecules are associated as dimers that appear to be slightly sigmoidal and are 20-25 A in width and 70-80 A in length. Images PMID:6175962

  12. rab8 in retinal photoreceptors may participate in rhodopsin transport and in rod outer segment disk morphogenesis.

    PubMed

    Deretic, D; Huber, L A; Ransom, N; Mancini, M; Simons, K; Papermaster, D S

    1995-01-01

    Small GTP-binding protein rab8 regulates transport from the TGN to the basolateral plasma membrane in epithelial cells and to the dendritic plasma membrane in cultured hippocampal neurons. In our approach to identify proteins involved in rhodopsin transport and sorting in retinal photoreceptors, we have found, using [32P]GTP overlays of 2D gel blots, that six small GTP-binding proteins are tightly bound to the post-Golgi membranes immunoisolated with a mAb to the cytoplasmic domain of frog rhodopsin. We report here that one of these proteins is rab8. About 50% of photoreceptor rab8 is membrane associated and approximately 13% is tightly bound to the post-Golgi vesicles. By confocal microscopy, antibody to rab8 specifically labels calycal processes and the actin bundles of the photoreceptor inner segment that extend inward to the junctional complexes that comprise the outer limiting membrane. Anti-rab8 shows a striking periodicity of high density labeling at 1 +/- 0.12 microns intervals along the actin bundles. Rhodopsin-bearing post-Golgi membranes cluster around the base of the cilium where rab8 and actin are also co-localized, as revealed by confocal microscopy of retinal sections double labeled with anti-rab8 and phalloidin. Microfilaments have been implicated in rod outer segment (ROS) disk morphogenesis. Our data suggest that rab6, which we have previously localized to the post-Golgi compartment, and rab8 associate with the post-Golgi membranes sequentially at different stages of transport. rab8 may mediate later steps that involve interaction of transport membranes with actin filaments and may participate in microfilament-dependent ROS disk morphogenesis.

  13. A New Perspective on Galaxy Evolution from the Low Density Outskirts of Galaxies

    NASA Astrophysics Data System (ADS)

    Emery Watkins, Aaron

    2017-01-01

    In order to investigate the nature of galaxy outskirts, we carried out a deep imaging campaign of several nearby ($D\\lesssim$10Mpc) galaxies, across a range of environments. We found that most of the galaxies we imaged show red and non-star-forming outer disks, implying evolved stellar populations. Such populations in outer disks are expected as the result of radial migration, yet through Fourier analysis we found no evidence of extended spiral structure in these galaxies. Without star formation or outer spiral structure, it is difficult to determine how these outer disks formed. To investigate the effects of interactions on outer disks, we also observed the Leo I Group; however, while group environments are expected to promote frequent interactions, we found only three extremely faint tidal streams, implying a calm interaction history. As Leo I is fairly low density, this implies that loose groups are ineffective at producing intragroup light (IGL). In the famous interacting system M51, we found that its extended tidal features show similarly red colors as the typical outer disks we observed, implying that M51 had a similar outer disk prior to the interaction, and that the interaction induced no extended star formation, including in the system's HI tail. Therefore, to investigate the nature of star formation in low-density environments, we carried out deep narrow-band H$\\alpha$ imaging of M101 and M51.

  14. DGSAT: Dwarf Galaxy Survey with Amateur Telescopes. II. A catalogue of isolated nearby edge-on disk galaxies and the discovery of new low surface brightness systems

    NASA Astrophysics Data System (ADS)

    Henkel, C.; Javanmardi, B.; Martínez-Delgado, D.; Kroupa, P.; Teuwen, K.

    2017-07-01

    The connection between the bulge mass or bulge luminosity in disk galaxies and the number, spatial and phase space distribution of associated dwarf galaxies is a discriminator between cosmological simulations related to galaxy formation in cold dark matter and generalised gravity models. Here, a nearby sample of isolated Milky Way-class edge-on galaxies is introduced, to facilitate observational campaigns to detect the associated families of dwarf galaxies at low surface brightness. Three galaxy pairs with at least one of the targets being edge-on are also introduced. Approximately 60% of the catalogued isolated galaxies contain bulges of different size, while the remaining objects appear to be bulgeless. Deep images of NGC 3669 (small bulge, with NGC 3625 at the edge of the image) and NGC 7814 (prominent bulge), obtained with a 0.4 m aperture, are also presented, resulting in the discovery of two new dwarf galaxy candidates, NGC 3669-DGSAT-3 and NGC 7814-DGSAT-7. Eleven additional low surface brightness galaxies are identified, previously notified with low quality measurement flags in the Sloan Digital Sky Survey (SDSS). Integrated magnitudes, surface brightnesses, effective radii, Sersic indices, axis ratios, and projected distances to their putative major hosts are displayed. At least one of the galaxies, NGC 3625-DGSAT-4, belongs with a surface brightness of μr ≈ 26 mag arcsec-2 and effective radius >1.5 kpc to the class of ultra-diffuse galaxies (UDGs). NGC 3669-DGSAT-3, the galaxy with the lowest surface brightness in our sample, may also be an UDG.

  15. The Interaction of Hot and Cold Gas in the Disk and Halo of Galaxies

    NASA Technical Reports Server (NTRS)

    Slavin, Jonathan; Salamon, Michael (Technical Monitor)

    2004-01-01

    Most of the thermal energy in the Galaxy and perhaps most of the baryons in the Universe are found in hot (log T approximately 5.5 - 7) gas. Hot gas is detected in the local interstellar medium, in supernova remnants (SNR), the Galactic halo, galaxy clusters and the intergalactic medium (IGM). In our own Galaxy, hot gas exists in large superbubbles up to several hundred pc in diameter that locally dominate the interstellar medium (ISM) and determine its thermal and dynamic evolution. While X-ray observations using ROSAT, Chandra and XMM have allowed us to make dramatic progress in mapping out the morphology of the hot gas and in understanding some of its spectral characteristics, there remain fundamental questions that are unanswered. Chief among these questions is the way that hot gas interacts with cooler phase gas and the effects these interactions have on hot gas energetics. The theoretical investigations we proposed in this grant aim to explore these interactions and to develop observational diagnostics that will allow us to gain much improved information on the evolution of hot gas in the disk and halo of galaxies. The first of the series of investigations that we proposed was a thorough exploration of turbulent mixing layers and cloud evaporation. We proposed to employ a multi-dimensional hydrodynamical code that includes non-equilibrium ionization (NEI), radiative cooling and thermal conduction. These models are to be applied to high velocity clouds in our galactic halo that are seen to have O VI by FUSE (Sembach et ai. 2000) and other clouds for which sufficient constraining observations exist.

  16. The Interaction of Hot and Cold Gas in the Disk and Halo of Galaxies

    NASA Technical Reports Server (NTRS)

    Slavin, Jonathan; Salamon, Michael (Technical Monitor)

    2004-01-01

    Most of the thermal energy in the Galaxy and perhaps most of the baryons in the Universe are found in hot (log T approximately 5.5 - 7) gas. Hot gas is detected in the local interstellar medium, in supernova remnants (SNR), the Galactic halo, galaxy clusters and the intergalactic medium (IGM). In our own Galaxy, hot gas exists in large superbubbles up to several hundred pc in diameter that locally dominate the interstellar medium (ISM) and determine its thermal and dynamic evolution. While X-ray observations using ROSAT, Chandra and XMM have allowed us to make dramatic progress in mapping out the morphology of the hot gas and in understanding some of its spectral characteristics, there remain fundamental questions that are unanswered. Chief among these questions is the way that hot gas interacts with cooler phase gas and the effects these interactions have on hot gas energetics. The theoretical investigations we proposed in this grant aim to explore these interactions and to develop observational diagnostics that will allow us to gain much improved information on the evolution of hot gas in the disk and halo of galaxies. The first of the series of investigations that we proposed was a thorough exploration of turbulent mixing layers and cloud evaporation. We proposed to employ a multi-dimensional hydrodynamical code that includes non-equilibrium ionization (NEI), radiative cooling and thermal conduction. These models are to be applied to high velocity clouds in our galactic halo that are seen to have O VI by FUSE (Sembach et ai. 2000) and other clouds for which sufficient constraining observations exist.

  17. A test of star formation laws in disk galaxies. II. Dependence on dynamical properties

    SciTech Connect

    Suwannajak, Chutipong; Tan, Jonathan C.; Leroy, Adam K.

    2014-05-20

    We use the observed radial profiles of the mass surface densities of total, Σ {sub g}, and molecular, Σ{sub H2}, gas, rotation velocity, and star formation rate (SFR) surface density, Σ{sub sfr}, of the molecular-rich (Σ{sub H2} ≥ Σ{sub HI}/2) regions of 16 nearby disk galaxies to test several star formation (SF) laws: a 'Kennicutt-Schmidt (K-S)' law, Σ{sub sfr}=A{sub g}Σ{sub g,2}{sup 1.5}; a 'Constant Molecular' law, Σ{sub sfr} = A {sub H2}Σ{sub H2,2}; the turbulence-regulated laws of Krumholz and McKee (KM05) and Krumholz, McKee, and Tumlinson (KMT09); a 'Gas-Ω' law, Σ{sub sfr}=B{sub Ω}Σ{sub g}Ω; and a shear-driven 'giant molecular cloud (GMC) Collision' law, Σ{sub sfr} = B {sub CC}Σ {sub g}Ω(1-0.7β), where β ≡ d ln v {sub circ}/d ln r. If allowed one free normalization parameter for each galaxy, these laws predict the SFR with rms errors of factors of 1.4-1.8. If a single normalization parameter is used by each law for the entire galaxy sample, then rms errors range from factors of 1.5-2.1. Although the Constant Molecular law gives the smallest rms errors, the improvement over the KMT, K-S, and GMC Collision laws is not especially significant, particularly given the different observational inputs that the laws utilize and the scope of included physics, which ranges from empirical relations to detailed treatment of interstellar medium processes. We next search for systematic variation of SF law parameters with local and global galactic dynamical properties of disk shear rate (related to β), rotation speed, and presence of a bar. We demonstrate with high significance that higher shear rates enhance SF efficiency per local orbital time. Such a trend is expected if GMC collisions play an important role in SF, while an opposite trend would be expected if the development of disk gravitational instabilities is the controlling physics.

  18. A Test of Star Formation Laws in Disk Galaxies. II. Dependence on Dynamical Properties

    NASA Astrophysics Data System (ADS)

    Suwannajak, Chutipong; Tan, Jonathan C.; Leroy, Adam K.

    2014-05-01

    We use the observed radial profiles of the mass surface densities of total, Σ g , and molecular, ΣH2, gas, rotation velocity, and star formation rate (SFR) surface density, Σsfr, of the molecular-rich (ΣH2 >= ΣHI/2) regions of 16 nearby disk galaxies to test several star formation (SF) laws: a "Kennicutt-Schmidt (K-S)" law, \\Sigma _{sfr}=A_g\\Sigma _{g,2}^{1.5}; a "Constant Molecular" law, Σsfr = A H2ΣH2, 2; the turbulence-regulated laws of Krumholz & McKee (KM05) and Krumholz, McKee, & Tumlinson (KMT09); a "Gas-Ω" law, \\Sigma _{sfr}=B_\\Omega \\Sigma _g\\Omega; and a shear-driven "giant molecular cloud (GMC) Collision" law, Σsfr = B CCΣ g Ω(1-0.7β