D. Narayanan

The University of Arizona, Tucson, Arizona, United States

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Publications (13)35.19 Total impact

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    ABSTRACT: We present observational evidence for forming a molecular gas disk in merging galaxies using new and archival interferometric CO maps of 37 optically selected merger remnants in the local universe. We found that 65% (24/37) of the merger remnants sample shows kinematical signatures of a rotating disk in the interferometer maps. The sources with an extended CO disk have high FIR luminosities (˜ 1011 L⊙), which suggests that active star formation takes place in the extended CO disks and stellar disks will be possibly formed. The molecular gas-to-stellar mass ratio for merger remnants is larger than that of the stellar mass matched early-type galaxies. However, there is no significant evidence suggesting that the high gas mass ratio leads to a more efficient formation of a molecular gas disk.
    10/2013;
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    ABSTRACT: We present preliminary results from our ongoing single-dish and interferometric molecular gas survey toward a sample of optically selected merger remnants. We show structural and kinematical evidence that a significant fraction of merger remnants form rotating molecular disks around their central remnants, and that the size of the resultant disks in some of the galaxies are larger compared to the central bulge size inferred from the Sersic radius. The high occurrence of disks in merger remnants may support the evolutionary scenario where major mergers can evolve into a variety of Hubble types.
    10/2013;
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    ABSTRACT: Panchromatic observations of the best candidate HyLIRG from the widest Herschel extragalactic imaging survey have led to the discovery of at least four intrinsically luminous z=2.41 galaxies across a ~100-kpc region - a cluster of starbursting proto-ellipticals. Via sub-arcsecond interferometric imaging we have measured accurate gas and star-formation surface densities. The two brightest galaxies span ~3 kpc FWHM in submm/radio continuum and CO J=4-3, and double that in CO J=1-0. The broad CO line is due partly to the multitude of constituent galaxies and partly to large rotational velocities in two counter-rotating gas disks -- a scenario predicted to lead to the most intense starbursts, which will therefore come in pairs. The disks have M(dyn) of several x 10^11 Msun, and gas fractions of ~40%. Velocity dispersions are modest so the disks are unstable, potentially on scales commensurate with their radii: these galaxies are undergoing extreme bursts of star formation, not confined to their nuclei, at close to the Eddington limit. Their specific star-formation rates place them ~>5x above the main sequence, which supposedly comprises large gas disks like these. Their high star-formation efficiencies are difficult to reconcile with a simple volumetric star-formation law. N-body and dark matter simulations suggest this system is the progenitor of a B(inary)-type ~10^14.6-Msun cluster.
    The Astrophysical Journal 02/2013; 772(2):137. DOI:10.1088/0004-637X/772/2/137 · 6.28 Impact Factor
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    ABSTRACT: Huge amounts of far-infrared (FIR) emitting warm dust and molecular gas have been discovered in the host galaxies of ~30% of the quasars at 6, indicating the presence of massive star formation coeval with rapid supermassive black hole (SMBH) accretion in these earliest quasar host galaxies close to end of cosmic reionization. We present our recent ALMA observations of the [C II] 158 micron fine structure line emission from the host galaxies of four millimeter bright quasars at 6. The detections of [C II] line emission provide strong evidence of active star formation and SMBH-galaxy coevolution in the most distant universe. The line velocity maps of three of them at ~0.6" spatial resolution show indications of velocity gradient along the major axis direction, which suggests the presence of a nuclear star-forming disk over the central a few kpc region of the quasar hosts. These results reveal important constraints on the distributions of nuclear star formation and dynamical properties of the cool atomic gas in the young quasar host galaxies. They are the keys to understand the growth of the first SMBHs and their host galaxies close to the cosmic reionization epoch.
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    ABSTRACT: We present 2D, integral field spectroscopy covering the rest-frame wavelengths of strong optical emission lines in nine submillimetre luminous galaxies (SMGs) at 2.0 < z < 2.7. The Gemini-North/Near-Infrared Integral Field Spectrograph (NIFS) and Very Large Telescope (VLT) Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) imaging spectroscopy allow the mapping of the gas morphologies and dynamics within the sources, and we measure an average Hα velocity dispersion of 〈σ〉 = 220 ± 80 km s−1 and an average half-light radius of 〈r1/2〉 = 3.7 ± 0.8 kpc. The dynamical measure, 〈Vobs/2σ〉 = 0.9 ± 0.1, for the SMGs is higher than in more quiescent star-forming galaxies at the same redshift, highlighting a difference in the dynamics of the two populations. The far-infrared star formation rates (SFRs) of the SMGs, measured using Herschel-SPIRE† far-infrared photometry, are on average 370 ± 90 M⊙ yr−1, which is ∼2 times higher than the extinction-corrected SFRs of the more quiescent star-forming galaxies. Six of the SMGs in our sample show strong evidence for kinematically distinct multiple components with average velocity offsets of 200 ± 100 km s−1 and average projected spatial offsets of 8 ± 2 kpc, which we attribute to systems in the early stages of major mergers. Indeed, all SMGs are classified as mergers from a kinemetry analysis of the velocity and dispersion field asymmetry. We bring together our sample with the seven other SMGs with integral field unit observations to describe the ionized gas morphologies and kinematics in a sample of 16 SMGs. By comparing the velocity and spatial offsets of the SMG Hα components with subhalo offsets in the Millennium Simulation data base, we infer an average halo mass for SMGs in the range of 13 < log (M[h−1 M⊙]) < 14. Finally, we explore the relationship between the velocity dispersion and star formation intensity within the SMGs, finding that the gas motions are consistent with the Kennicutt–Schmidt law and a range of extinction corrections, although they might also be driven by the tidal torques from merging or even the star formation itself.
    Monthly Notices of the Royal Astronomical Society 08/2012; 424(3). · 5.52 Impact Factor
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    ABSTRACT: We present 2D, integral field spectroscopy covering the rest-frame wavelengths of strong optical emission lines in nine submillimetre luminous galaxies (SMGs) at 2.0 < z < 2.7. The Gemini-North/Near-Infrared Integral Field Spectrograph (NIFS) and Very Large Telescope (VLT) Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) imaging spectroscopy allow the mapping of the gas morphologies and dynamics within the sources, and we measure an average Hα velocity dispersion of <σ> = 220 ± 80 km s-1 and an average half-light radius of <r1/2> = 3.7 ± 0.8 kpc. The dynamical measure, <Vobs/2σ> = 0.9 ± 0.1, for the SMGs is higher than in more quiescent star-forming galaxies at the same redshift, highlighting a difference in the dynamics of the two populations. The far-infrared star formation rates (SFRs) of the SMGs, measured using Herschel-SPIRE† far-infrared photometry, are on average 370 ± 90 M⊙ yr-1, which is ˜2 times higher than the extinction-corrected SFRs of the more quiescent star-forming galaxies. Six of the SMGs in our sample show strong evidence for kinematically distinct multiple components with average velocity offsets of 200 ± 100 km s-1 and average projected spatial offsets of 8 ± 2 kpc, which we attribute to systems in the early stages of major mergers. Indeed, all SMGs are classified as mergers from a kinemetry analysis of the velocity and dispersion field asymmetry. We bring together our sample with the seven other SMGs with integral field unit observations to describe the ionized gas morphologies and kinematics in a sample of 16 SMGs. By comparing the velocity and spatial offsets of the SMG Hα components with subhalo offsets in the Millennium Simulation data base, we infer an average halo mass for SMGs in the range of 13 < log (M[h-1 M⊙]) < 14. Finally, we explore the relationship between the velocity dispersion and star formation intensity within the SMGs, finding that the gas motions are consistent with the Kennicutt-Schmidt law and a range of extinction corrections, although they might also be driven by the tidal torques from merging or even the star formation itself.
    Monthly Notices of the Royal Astronomical Society 08/2012; 424(3):2232-2248. DOI:10.1111/j.1365-2966.2012.21386.x · 5.23 Impact Factor
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    ABSTRACT: We present two-dimensional, integral field spectroscopy covering the rest-frame wavelengths of strong optical emission lines in nine sub-mm-luminous galaxies (SMGs) at 2.0<z<2.7. The GEMINI-NIFS and VLT-SINFONI imaging spectroscopy allows the mapping of the gas morphologies and dynamics within the sources, and we measure an average Halpha velocity dispersion of sigma=220+-80km/s and an average half light radius of r=3.7+-0.8kpc. The average dynamical measure, V_obs/2sigma=0.9+-0.1 for the SMGs, is higher than in more quiescent star-forming galaxies at the same redshift, highlighting a difference in the dynamics of the two populations. The SMGs' far-infrared SFRs, measured using Herschel-SPIRE far-infrared photometry, are on average 370+-90Mo/yr which is ~2 times higher than the extinction corrected SFRs of the more quiescent star-forming galaxies. Six of the SMGs in our sample show strong evidence for kinematically distinct multiple components with average velocity offsets of 200+-100km/s and average projected spatial offsets of 8+-2kpc, which we attribute to systems in the early stages of major mergers. Indeed all SMGs are classified as mergers from a kinemetry analysis of the velocity and dispersion field asymmetry. We bring together our sample with seven other SMGs with IFU observations to describe the ionized gas morphologies and kinematics in a sample of 16 SMGs. By comparing the velocity and spatial offsets of the SMG Halpha components with sub-halo offsets in the Millennium simulation database we infer an average halo mass for SMGs of 13<log(M[h^-1Mo])<14. Finally we explore the relationship between the velocity dispersion and star formation intensity within the SMGs, finding the gas motions are consistent with the Kennicutt-Schmidt law and a range of extinction corrections, although might also be driven by the tidal torques from merging or even the star formation itself.
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    X. Xu, D. Narayanan, C. Walker
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    ABSTRACT: We study the simulated CO emission from elliptical galaxies formed in the mergers of gas-rich disk galaxies. The cold gas not consumed in the merger-driven starburst quickly resettles into a disk-like configuration. By analyzing a variety of arbitrary merger orbits that produce a range of fast to slow-rotating remnants, we find that molecular disk formation is a fairly common consequence of gas-rich galaxy mergers. Hence, if a molecular disk is observed in an early-type merger remnant, it is likely the result of a "wet merger" rather than a "dry merger". We compare the physical properties from our simulated disks (e.g. size and mass) and find reasonably good agreement with recent observations. Finally, we discuss the detectability of these disks as an aid to future observations. Comment: 6 pages, 3 figures, ApJL accepted
    The Astrophysical Journal Letters 08/2010; 721(2). DOI:10.1088/2041-8205/721/2/L112 · 5.60 Impact Factor
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    ABSTRACT: In the coming years the Atacama Large Millimeter Array (ALMA) will provide a new window into the physics of protoplanetary disks and Gas Giant Planet (GGP) formation. We use a 3D, non-LTE, microturbulent radiative transfer code coupled with recent 3D hydrodynamic simulations of gravitationally unstable protoplanetary disks to predict spectral signatures of disk dynamics and planet formation detectable with ALMA. The radiative transfer code can rotate the hydrodynamic protoplanetary disk model and simulate line-of-sight spectra for different viewing geometries. By using the high density tracer HCO+ J=7-6, we find that ALMA will be able to detect massive, infalling protoplanetary clumps and disentangle motions associated with spiral density waves within a protoplanetary disk. In our talk we will present results from the simulations and further discuss the sensitivity of ALMA to these features.
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    ABSTRACT: We present a detailed analysis of the relation between infrared luminosity and molecular line luminosity, for a variety of molecular transitions, using a sample of 34 nearby galaxies spanning a broad range of infrared luminosities (1010 L ☉ < L IR < 1012.5 L ☉). We show that the power-law index of the relation is sensitive to the critical density of the molecular gas tracer used, and that the dominant driver in observed molecular line ratios in galaxies is the gas density. As most nearby ultraluminous infrared galaxies (ULIRGs) exhibit strong signatures of active galactic nuclei (AGNs) in their center, we revisit previous claims questioning the reliability of HCN as a probe of the dense gas responsible for star formation in the presence of AGNs. We find that the enhanced HCN(1-0)/CO(1-0) luminosity ratio observed in ULIRGs can be successfully reproduced using numerical models with fixed chemical abundances and without AGN-induced chemistry effects. We extend this analysis to a total of 10 molecular line ratios by combining the following transitions: CO(1-0), HCO+(1-0), HCO+(3-2), HCN(1-0), and HCN(3-2). Our results suggest that AGNs reside in systems with higher dense gas fraction, and that chemistry or other effects associated with their hard radiation field may not dominate (NGC 1068 is one exception). Galaxy merger could be the underlying cause of increased dense gas fraction, and the evolutionary stage of such mergers may be another determinant of the HCN/CO luminosity ratio.
    The Astrophysical Journal 12/2009; 707(2):1217. DOI:10.1088/0004-637X/707/2/1217 · 6.28 Impact Factor
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    ABSTRACT: When, and how, did the first galaxies and supermassive black holes (SMBH) form, and how did they reionization the Universe? First galaxy formation and cosmic reionization are among the last frontiers in studies of cosmic structure formation. We delineate the detailed astrophysical probes of early galaxy and SMBH formation afforded by observations at centimeter through submillimeter wavelengths. These observations include studies of the molecular gas (= the fuel for star formation in galaxies), atomic fine structure lines (= the dominant ISM gas coolant), thermal dust continuum emission (= an ideal star formation rate estimator), and radio continuum emission from star formation and relativistic jets. High resolution spectroscopic imaging can be used to study galaxy dynamics and star formation on sub-kpc scales. These cm and mm observations are the necessary compliment to near-IR observations, which probe the stars and ionized gas, and X-ray observations, which reveal the AGN. Together, a suite of revolutionary observatories planned for the next decade from centimeter to X-ray wavelengths will provide the requisite panchromatic view of the complex processes involved in the formation of the first generation of galaxies and SMBHs, and cosmic reionization.
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    ABSTRACT: We present observations made with the 10m Heinrich Hertz Sub-Millimeter Telescope of HCN (3-2) emission from a sample of 30 nearby galaxies ranging in infrared luminosity from 10^10 - 10^12.5 L_sun and HCN (3-2) luminosity from 10^6 - 10^9 K km s^-1 pc^2. We examine the correlation between the infrared luminosity and HCN (3-2) luminosity and find that the best fit linear regression has a slope (in log-log space) of 0.74+/-0.12. Including recently published data from Gracia-Carpio et al. tightens the constraints on the best-fit slope to 0.79+/-0.09. This slope below unity suggests that the HCN (3-2) molecular line luminosity is not linearly tracing the amount of dense gas. Our results are consistent with predictions from recent theoretical models that find slopes below unity when the line luminosity depends upon the average gas density with a power-law index greater than a Kennicutt-Schmidt index of 1.5. Comment: 4 pages, 1 table, 2 figures; accepted to the ApJL
    The Astrophysical Journal 05/2008; 681(2). DOI:10.1086/590181 · 6.28 Impact Factor
  • D. Narayanan, C. Kulesa, A. Boss, C. K. Walker