An Unbiased Survey for Molecular Clouds in the Southern Galactic Warp

We have made an unbiased survey for molecular clouds in the Galactic Warp. This survey, covering an area of 56 square degrees at l = 252 deg to 266 deg and b = -5 deg to -1 deg, has revealed 70 molecular clouds, while only 6 clouds were previously known in the region. The number of molecular clouds is, then, an order of magnitude greater than previously known in this sector at R > 14.5 kpc. The mass of the clouds is in a range from 7.8x10(2) Mo to 8.4x10(4) Mo, significantly less than the most massive giant molecular clouds in the inner disk, ~10(6) Mo, while the cloud mass spectrum characterized by a power law is basically similar to other parts of the Galaxy. The X factor, N(H2)/Wco(12CO), derived from the molecular clouds in the Warp is estimated to be 3.5(+/-1.8) times larger than that in the inner disk. The total molecular mass in the Warp is estimated as 7.3x10(5) Mo, and total mass in the far-outer Galaxy (R > 14.5 kpc) can be estimated as 2x10(7) Mo. The spatial correlation between the CO and HI distribution appears fairly good, and the mass of the molecular gas is about 1% of that of the atomic gas in the far-outer Galaxy. This ratio is similar to that in the interarm but is ten times smaller than those of the spiral arms. Only 6 of the 70 Warp clouds show signs of star formation at the IRAS sensitivity and star formation efficiency for high-mass stars in the Warp is found to be smaller than those in other molecular clouds in the Galaxy.Comment: 29 pages, including 12 (pages of) figures, accepted for PASJ, and will be published in PASJ Vol.57, No.6. Tables and color-figures are available on-line: http://www.a.phys.nagoya-u.ac.jp/~masa/study/nakagawa_etal2005_warp.pd

Aligned Molecular Clouds towards SS433 and L=348.5 degrees; Possible Evidence for Galactic "Vapor Trail" Created by Relativistic Jet

We have carried out a detailed analysis of the NANTEN 12CO(J=1-0) dataset in two large areas of ~25 square degrees towards SS433 (l~40 degree) and of ~18 square degrees towards l~348.5 degree, respectively. We have discovered two groups of remarkably aligned molecular clouds at |b|~1--5 degree in the two regions. In SS433, we have detected 10 clouds in total, which are well aligned nearly along the axis of the X-ray jet emanating from SS433. These clouds have similar line-of-sight velocities of 42--56 km s^-1 and the total projected length of the feature is ~300 pc, three times larger than that of the X-ray jet, at a distance of 3 kpc. Towards l~348.5 degree, we have detected four clouds named as MJG348.5 at line-of-sight velocities of -80 -- -95 km s^-1 in V_LSR, which also show alignment nearly perpendicular to the Galactic plane. The total length of the feature is ~400 pc at a kinematic distance of 6 kpc. In the both cases, the CO clouds are distributed at high galactic latitudes where such clouds are very rare. In addition, their alignments and coincidence in velocity should be even rarer, suggesting that they are physically associated. We tested a few possibilities to explain these clouds, including protostellar outflows, supershells, and interactions with energetic jets. Among them, a favorable scenario is that the interaction between relativistic jet and the interstellar medium induced the formation of molecular clouds over the last ~10^5-6 yrs. It is suggested that the timescale of the relativistic jet may be considerably larger, in the order of 10^5-6 yrs, than previously thought in SS433. The driving engine of the jet is obviously SS433 itself in SS433, although the engine is not yet identified in MJG348.5 among possible several candidates detected in the X-rays and TeV gamma rays.Comment: 29 pages, 10 figures, already published in PASJ, 2008,60, 71

The gas temperature in the surface layers of protoplanetary disks

Models for the structure of protoplanetary disks have so far been based on the assumption that the gas and the dust temperature are equal. The gas temperature, an essential ingredient in the equations of hydrostatic equilibrium of the disk, is then determined from a continuum radiative transfer calculation, in which the continuum opacity is provided by the dust. It has been long debated whether this assumption still holds in the surface layers of the disk, where the dust infrared emission features are produced. In this paper we compute the temperature of the gas in the surface layers of the disk in a self-consistent manner. The gas temperature is determined from a heating-cooling balance equation in which processes such as photoelectric heating, dissociative heating, dust-gas thermal heat exchange and line cooling are included. The abundances of the dominant cooling species such as CO, C, C+ and O are determined from a chemical network based on the atomic species H, He, C, O, S, Mg, Si, Fe (Kamp & Bertoldi 2000). The underlying disk models to our calculations are the models of Dullemond, van Zadelhoff & Natta (2002). We find that in general the dust and gas temperature are equal to withing 10% for A_V >~ 0.1, which is above the location of the `super-heated surface layer' in which the dust emission features are produced (e.g. Chiang & Goldreich 1997). High above the disk surface the gas temperature exceeds the dust temperature and can can become -- in the presence of polycyclic aromatic hydrocarbons -- as high as 600 K at a radius of 100 AU. This is a region where CO has fully dissociated, but a significant fraction of hydrogen is still in molecular form. The densities are still high enough for non-negligible H_2 emission to be produced.....(see paper for full abstract)Comment: 28 pages, 8 figures, accepted for publication in Ap

A New Method for Measuring Tail Exponents of Firm Size Distributions

We propose a new method for estimating the power-law exponents of firm size variables. Our focus is on how to empirically identify a range in which a firm size variable follows a power-law distribution. As is well known, a firm size variable follows a power-law distribution only beyond some threshold. On the other hand, in almost all empirical exercises, the right end part of a distribution deviates from a power-law due to finite size effect. We modify the method proposed by Malevergne et al. (2011) so that we can identify both of the lower and the upper thresholds and then estimate the power-law exponent using observations only in the range defined by the two thresholds. We apply this new method to various firm size variables, including annual sales, the number of workers, and tangible fixed assets for firms in more than thirty countries.Econophysics, power-law distributions, power-law exponents, firm size variables, finite size effect

Anatomy of helical relativistic jets: The case of S5 0836+710

Helical structures are common in extragalactic jets. They are usually attributed in the literature to periodical phenomena in the source (e.g., precession). In this work, we use VLBI data of the radio-jet in the quasar S5 0836+710 and hypothesize that the ridge-line of helical jets like this corresponds to a pressure maximum in the jet and assume that the helically twisted pressure maximum is the result of a helical wave pattern. For our study, we use observations of the jet in S5 0836+710 at different frequencies and epochs. The results show that the structures observed are physical and not generated artificially by the observing arrays. Our hypothesis that the observed intensity ridge-line can correspond to a helically twisted pressure maximum is confirmed by our observational tests. This interpretation allows us to explain jet misalignment between parsec and kiloparsec scales when the viewing angle is small, and also brings us to the conclusion that high-frequency observations may show only a small region of the jet flow concentrated around the maximum pressure ridge-line observed at low frequencies. Our work provides a potential explanation for the apparent transversal superluminal speeds observed in several extragalactic jets by means of transversal shift of an apparent core position with time.Comment: Accepted for publication in the Astrophysical Journa

Catalogue of 12CO(J=1-0) and 13CO(J=1-0) Molecular Clouds in the Carina Flare Supershell

We present a catalogue of 12CO(J=1-0) and 13CO(J=1-0) molecular clouds in the spatio-velocity range of the Carina Flare supershell, GSH 287+04-17. The data cover a region of ~66 square degrees and were taken with the NANTEN 4m telescope, at spatial and velocity resolutions of 2.6' and 0.1 km/s. Decomposition of the emission results in the identification of 156 12CO clouds and 60 13CO clouds, for which we provide observational and physical parameters. Previous work suggests the majority of the detected mass forms part of a comoving molecular cloud complex that is physically associated with the expanding shell. The cloud internal velocity dispersions, degree of virialization and size-linewidth relations are found to be consistent with those of other Galactic samples. However, the vertical distribution is heavily skewed towards high-altitudes. The robust association of high-z molecular clouds with a known supershell provides some observational backing for the theory that expanding shells contribute to the support of a high-altitude molecular layer.Comment: To be published in PASJ Vol. 60, No. 6. (Issued on December 25th 2008). 35 pages (including 13 pages of tables), 7 figures. Please note that formatting problems with the journal macro result in loss of rightmost data columns in some long tables. These will be fixed in the final published issue. In the meantime, please contact the authors for missing dat

Cosmological Dynamics of a Dirac-Born-Infeld field

We analyze the dynamics of a Dirac-Born-Infeld (DBI) field in a cosmological set-up which includes a perfect fluid. Introducing convenient dynamical variables, we show the evolution equations form an autonomous system when the potential and the brane tension of the DBI field are arbitrary power-law or exponential functions of the DBI field. In particular we find scaling solutions can exist when powers of the field in the potential and warp-factor satisfy specific relations. A new class of fixed-point solutions are obtained corresponding to points which initially appear singular in the evolution equations, but on closer inspection are actually well defined. In all cases, we perform a phase-space analysis and obtain the late-time attractor structure of the system. Of particular note when considering cosmological perturbations in DBI inflation is a fixed-point solution where the Lorentz factor is a finite large constant and the equation of state parameter of the DBI field is $w=-1$. Since in this case the speed of sound $c_s$ becomes constant, the solution can be thought to serve as a good background to perturb about.Comment: 24 pages, 7 figures, minor corrections, references adde

Temperature and Density Distribution in the Molecular Gas Toward Westerlund 2: Further Evidence for Physical Association

Furukawa et al. 2009 reported the existence of a large mass of molecular gas associated with the super star cluster Westerlund 2 and the surrounding HII region RCW49, based on a strong morphological correspondence between NANTEN2 12CO(J=2-1) emission and Spitzer IRAC images of the HII region. We here present temperature and density distributions in the associated molecular gas at 3.5 pc resolution, as derived from an LVG analysis of the 12CO(J=2-1), 12CO(J=1-0) and 13CO(J=2-1) transitions. The kinetic temperature is as high as 60-150 K within a projected distance of 5-10 pc from Westerlund 2 and decreases to as low as 10 K away from the cluster. The high temperature provides robust verification that the molecular gas is indeed physically associated with the HII region, supporting Furukawa et al.'s conclusion. The derived temperature is also roughly consistent with theoretical calculations of photo dissociation regions (PDRs), while the low spatial resolution of the present study does not warrant a more detailed comparison with PDR models. We suggest that the molecular clouds presented here will serve as an ideal laboratory to test theories on PDRs in future higher resolution studies.Comment: 23 pages, 5 figures, accepted for publication in Ap

ASCA observations of the nearby galaxies Dwingeloo 1 and Maffei 1

We present ASCA observations of the nearby galaxies Dwingeloo 1 (Dw1) and Maffei 1 (Mf1). X-ray sources are clearly detected within 3 arcminutes of the optical nuclei of both galaxies. Despite the low Galactic latitude of these fields (|b|<1\degmark) we conclude, on probability and spectral grounds, that the detected sources are intrinsic to these galaxies rather than foreground or background interlopers. The Dw1 source, designated Dw1-X1, is interpreted as being either a hyper-luminous X-ray binary (with a 0.5--10\,keV luminosity of more than 10^{39}\ergps) or an X-ray bright supernova. The Mf1 emission is hard and extended, suggesting that it originates from a population of X-ray binaries. Prompted by the Dw1-X1 results, we discuss the nature of hyper-luminous X-ray binary systems. Such sources are commonly seen in nearby galaxies with a frequency of approximately one per galaxy. We present a possible connection between these luminous systems and Galactic superluminal sources.Comment: 9 pages (4 ps figures included). Accepted for publication in MNRAS. Higher quality reproductions of Figure 1 available upon reques