N. Tanvir

Publications (311) View all

• Article: Dynamics in the satellite system of Triangulum: is And XXII a dwarf satellite of M33?

  S ~C Chapman, L Widrow, M ~L ~M Collins, J Dubinski, R ~A Ibata, M Rich, A ~M ~N Ferguson, M ~J Irwin, G ~F Lewis, N Martin, A McConnachie, J Peñarrubia, N Tanvir
  mnras. 03/2013; 430:37-49.
• Article: Dynamics in the satellite system of Triangulum: Is AndXXII a dwarf satellite of M33?

  S. C. Chapman, L. Widrow, M. L. M. Collins, J. Dubinski, R. A. Ibata, J. Penarrubia, M. Rich, A. M. N. Ferguson, M. J. Irwin, G. F. Lewis, N. Martin, A. McConnachie, N. Tanvir
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  ABSTRACT: We present results from a spectroscopic survey of the dwarf spheroidal And XXII and the two extended clusters EC1 and EC2. These three objects are candidate satellites of the Triangulum galaxy, M33, which itself is likely a satellite of M31. We use the DEep Imaging Multi-Object Spectrograph mounted on the Keck-II telescope to derive radial velocities for candidate member stars of these objects and thereby identify the stars that are most likely actual members. Eleven most probable stellar members (of 13 candidates) are found for AndXXII. We obtain an upper limit of sigma_v < 6.0 km s-1 for the velocity dispersion of AndXXII, [Fe/H] ~ -1.6 for its metallicity, and 255pc for the Plummer radius of its projected density profile. We construct a colour magnitude diagram for AndXXII and identify both the red giant branch and the horizontal branch. The position of the latter is used to derive a heliocentric distance to And XXII of 853 pm 26 kpc. The combination of the radial velocity, distance, and angular position of AndXXII indicates that it is a strong candidate for being the first known satellite of M33 and one of the very few examples of a galactic satellite of a satellite. N-body simulations imply that this conclusion is unchanged even if M31 and M33 had a strong encounter in the past few Gyr. We test the hypothesis that the extended clusters highlight tidally stripped galaxies by searching for an excess cloud of halo-like stars in their vicinity. We find such a cloud for the case of EC1 but not EC2. The three objects imply a dynamical mass for M33 that is consistent with previous estimates.
  06/2012;
• Article: GRB 100219A with X-shooter - abundances in a galaxy at z = 4.7

  C. C. Thoene, J. P. U. Fynbo, P. Goldoni, A. de Ugarte Postigo, S. Campana, S. D. Vergani, S. Covino, T. Kruehler, L. Kaper, N. Tanvir, [......], S. Klose, A. J. Levan, B. Milvang-Jensen, A. Nicuesa Guelbenzu, E. Palazzi, S. Piranomonte, G. Tagliaferri, D. Watson, K. Wiersema, R. A. M. J. Wijers
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  ABSTRACT: Abundances of galaxies at redshifts z > 4 are difficult to obtain from damped Ly {\alpha} (DLA) systems in the sightlines of quasars (QSOs) due to the Ly {\alpha} forest blanketing and the low number of high-redshift quasars detected. Gamma-ray bursts (GRBs) with their higher luminosity are well suited to study galaxies out to the formation of the first stars at z > 10. Its large wavelength coverage makes the X-shooter spectrograph an excellent tool to study the interstellar medium (ISM) of high redshift galaxies, in particular if the redshift is not known beforehand. Here we determine the properties of a GRB host at z = 4.66723 from a number of resonant low- and high ionization and fine-structure absorption lines. This is one of the highest redshifts where a detailed analysis with medium-resolution data has been possible. We detect one intervening system at z = 2.18. The velocity components of the absorption lines are fitted with Voigt-profiles and we determine a metallicity of [M/H] = -1.0 \pm 0.1 using S. The absorption lines show a complicated kinematic structure which could point to a merger in progress. Si II* together with the restframe UV energy release determined from GROND data gives us the distance of 0.3 to 1 kpc of the absorbing material from the GRB. We measure a low extinction of AV = 0.24 \pm 0.06 mag using X-ray spectral information and the flux calibrated X-shooter spectrum. GRB-DLAs have a shallower evolution of metallicity with redshift than QSO absorbers and no evolution in HI column density or ionization fraction. GRB hosts at high redshift might continue the trend towards lower metallicities in the LZ-relation with redshift, but the sample is still too small to draw a definite conclusion. While the detection of GRBs at z > 4 with current satellites is still difficult, they are very important for our understanding of the early epochs of star- and galaxy-formation.
  06/2012;
• Source

  Available from: Glenn J. White

  Article: The JCMT Nearby Galaxies Legacy Survey VIII. CO data and the L(CO3-2)-L(FIR) correlation in the SINGS sample

  C. D. Wilson, B. E. Warren, F. P. Israel, S. Serjeant, D. Attewell, G. J. Bendo, H. M. Butner, P. Chanial, D. L. Clements, J. Golding, [......], E. Rosolowsky, E. R. Seaquist, K. Spekkens, N. Tanvir, J. M. van der Hulst, P. van der Werf, C. Vlahakis, T. M. Webb, B. Weferling, G. J. White
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  ABSTRACT: The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey (NGLS) comprises an HI-selected sample of 155 galaxies spanning all morphological types with distances less than 25 Mpc. We describe the scientific goals of the survey, the sample selection, and the observing strategy. We also present an atlas and analysis of the CO J=3-2 maps for the 47 galaxies in the NGLS which are also part of the Spitzer Infrared Nearby Galaxies Survey. We find a wide range of molecular gas mass fractions in the galaxies in this sample and explore the correlation of the far-infrared luminosity, which traces star formation, with the CO luminosity, which traces the molecular gas mass. By comparing the NGLS data with merging galaxies at low and high redshift which have also been observed in the CO J=3-2 line, we show that the correlation of far-infrared and CO luminosity shows a significant trend with luminosity. This trend is consistent with a molecular gas depletion time which is more than an order of magnitude faster in the merger galaxies than in nearby normal galaxies. We also find a strong correlation of the L(FIR)/L(CO3-2) ratio with the atomic to molecular gas mass ratio. This correlation suggests that some of the far-infrared emission originates from dust associated with atomic gas and that its contribution is particularly important in galaxies where most of the gas is in the atomic phase.
  06/2012;
• Source

  Available from: Eleonora Troja

  Article: ORIGIN: metal creation and evolution from the cosmic dawn

  Jan-Willem den Herder, Luigi Piro, Takaya Ohashi, Chryssa Kouveliotou, Dieter H. Hartmann, Jelle S. Kaastra, L. Amati, M. I. Andersen, M. Arnaud, J. -L. Attéia, [......], S. Wachter, D. Watson, M. Weisskopf, N. Werner, N. White, R. Willingale, R. Wijers, N. Yamasaki, K. Yoshikawa, S. Zane
  [show abstract] [hide abstract]
  ABSTRACT: ORIGIN is a proposal for the M3 mission call of ESA aimed at the study of metal creation from the epoch of cosmic dawn. Using high-spectral resolution in the soft X-ray band, ORIGIN will be able to identify the physical conditions of all abundant elements between C and Ni to red-shifts of z = 10, and beyond. The mission will answer questions such as: When were the first metals created? How does the cosmic metal content evolve? Where do most of the metals reside in the Universe? What is the role of metals in structure formation and evolution? To reach out to the early Universe ORIGIN will use Gamma-Ray Bursts (GRBs) to study their local environments in their host galaxies. This requires the capability to slew the satellite in less than a minute to the GRB location. By studying the chemical composition and properties of clusters of galaxies we can extend the range of exploration to lower redshifts (z ∼0.2). For this task we need a high-resolution spectral imaging instrument with a large field of view. Using the same instrument, we can also study the so far only partially detected baryons in the Warm-Hot Intergalactic Medium (WHIM). The less dense part of the WHIM will be studied using absorption lines at low redshift in the spectra for GRBs. The ORIGIN mission includes a Transient Event Detector (coded mask with a sensitivity of 0.4 photon/cm2/s in 10s in the 5–150keV band) to identify and localize 2000GRBs over a five year mission, of which ∼65GRBs have a redshift >7. The Cryogenic Imaging Spectrometer, with a spectral resolution of 2.5eV, a field of view of 30arcmin and large effective area below 1keV has the sensitivity to study clusters up to a significant fraction of the virial radius and to map the denser parts of the WHIM (factor 30 higher than achievable with current instruments). The payload is complemented by a Burst InfraRed Telescope to enable onboard red-shift determination of GRBs (hence securing proper follow up of high-z bursts) and also probes the mildly ionized state of the gas. Fast repointing is achieved by a dedicated Controlled Momentum Gyro and a low background is achieved by the selected low Earth orbit. KeywordsX-ray–Mission–Gamma-ray bursts–Clusters of galaxies–Warm-hot intergalactic medium–Chemical evolution
  Experimental Astronomy 04/2012; · 1.82 Impact Factor