Large Velocity Widths Research Articles

A Galactic Center 50-kms$^{-1}$ Molecular Cloud with an Expanding Shell

We performed high-resolution observations of a Galactic Center 50-km s$^{-1}$ molecular cloud in the CS $J$$=$ 1–0 line using the Nobeyama Millimeter Array (NMA). The molecular cloud mainly has three different spatial components with large velocity widths of up to 60 kms$^{-1}$. The northwest component is located at an apparent contact point to the Sgr A east shell, and elongated along the boundary of the shell. The large velocity width of the component is responsible for interaction with the Sgr A east shell. The molecular gas distribution in CS line emission is dissimilar to that observed previously in NH$_3$ line emissions. The appearance shows presumably the area of CS line emission enhanced by shock. The central and southwest components are located just out of the Sgr A east shell and far from it, respectively. However, these components have large velocity widths. We found a well-shaped circular molecular shell with expanding motion in the 50-km s$^{-1}$ molecular cloud. This is responsible for the large velocity width. The continuum source in the expanding molecular shell has a steep spectrum in mm-wavelengths, although this was not identified in a previous 5-GHz map. This source may be an SNR with an ionized sheath. From the aspect ratio of an expanding molecular shell of 1.1, the magnetic field in/around the shell is estimated to be smaller than 100$\mu$Gauss. This weak magnetic field is consistent with on-going active star formation in the 50-km s$^{-1}$ molecular cloud. A comparison among CS line emission, low-frequency continuum, and millimeter continuum toward the 50-km s$^{-1}$ molecular cloud suggests a face-on view of the Sgr A region. The molecular cloud is located in the Sgr A halo region.

A Large-Scale 13CO Mapping of the W 49 A Molecular Cloud Complex

Abstract We present $^{13}$CO ($J$$=$ 1-0) and C$^{18}$O ($J$$=$ 1-0) maps of the W 49 A molecular cloud complex observed at a resolution of 17$''$ (HPBW). Fourteen features (MHH-1 to MHH-14) were identified in the $^{13}$CO velocity channel maps, most of them distributed within an area of 6$'$ (20 pc) in diameter with their total mass amounting to 1.7 $\times$ 10$^{6}M_\odot$. The features have a three-dimensional velocity dispersion of 8 km s$^{-1}$, which leads to a mean free time per feature of 10$^{6}$yr. This suggests that they are interacting one another in a region of $\sim$20 pc in diameter. The feature MHH-1, which corresponds to W 49 N, is unique in that it exhibits a large velocity width (15 km s$^{-1}$ FWHM) and is compact in size (2.3 pc $\times$ 3.0 pc FWHM), while containing a large mass of 2.4 $\times$ 10$^{5}M_\odot$. This indicates that the free-fall time of MHH-1 is on the order of 10$^{5}$yr, an order of magnitude smaller than that of the entire complex. It has turned out that MHH-1 has a smaller spatial width at $V_{\rm LSR}$$\lesssim$ 8 km s$^{-1}$ than at $\gtrsim$8 km s$^{-1}$. This result, together with the line-profile characteristics of various optically thin lines, suggests that at least two massive clouds with different radial velocities exist toward MHH-1. The massive compact feature may have been produced by the interaction of the two different velocity clouds.

A SURVEY OF DENSE CORES IN THE ORION B CLOUD

We have carried out an H13CO+(J = 1-0) core survey in a large area of 1.5° × 0.5°, covering the whole region of the Orion A molecular cloud, using the Nobeyama 45 m radio telescope with the 25 Beam Array Receiver System (BEARS). This survey is unique in that a large area (~48 pc2) of the cloud was covered with a high spatial resolution of 21'' (0.05 pc) and with a deep integration (1 σ ~ 0.1 K in T), resulting in a core mass detection of 1.6 M☉. The morphology of the H13CO+(J = 1-0) emission is very similar to that of the 850 μm continuum emission. We identified 236 dense cores from our data with the clumpfind algorithm. The cores are close to virial equilibrium, independent of whether they are thermal or turbulent. We predict an initial mass function (IMF) from the core mass function, considering binary formation and confusion along the line of sight, and find that this IMF agrees well with the Orion Nebula cluster IMF for a star formation efficiency of ~40%. Therefore, we suggest that the IMF is determined at the time of the dense core formation. Furthermore, we discovered three cores with large velocity widths, significantly wider than those of the other cores, only toward the M42 H II region, suggesting that the energy input from the H II region increases the velocity width. Since the three cores can produce the most massive stars, owing to their large mass accretion rates, massive star formation in the next generation in the Orion A cloud is likely to be caused by nearby stellar activity.

Automated detection of contaminated radar image pixels in mountain areas

In mountain areas, radar observations are often contaminated (1) by echoes from high-speed moving vehicles and (2) by point-wise ground clutter under either normal propagation (NP) or anomalous propagation (AP) conditions. Level II data are collected from KMTX (Salt Lake City, Utah) radar to analyze these two types of contamination in the mountain area around the Great Salt Lake. Human experts provide the “ground truth” for possible contamination of either type on each individual pixel. Common features are then extracted for contaminated pixels of each type. For example, pixels contaminated by echoes from high-speed moving vehicles are characterized by large radial velocity and spectrum width. Echoes from a moving train tend to have larger velocity and reflectivity but smaller spectrum width than those from moving vehicles on highways. These contaminated pixels are only seen in areas of large terrain gradient (in the radial direction along the radar beam). The same is true for the second type of contamination-point-wise ground clutters. Six quality control (QC) parameters are selected to quantify the extracted features. Histograms are computed for each QC parameter and grouped for contaminated pixels of each type and also for non-contaminated pixels. Based on the computed histograms, a fuzzy logical algorithm is developed for automated detection of contaminated pixels. The algorithm is tested with KMTX radar data under different (clear and rainy) weather conditions.

Dynamical Properties ofz∼ 2 Star‐forming Galaxies and a Universal Star Formation Relation

We present the first comparison of the dynamical properties of different samples of z ~ 1.4-3.4 star-forming galaxies from spatially resolved imaging spectroscopy from SINFONI/VLT integral field spectroscopy and IRAM CO millimeter interferometry. Our samples include 16 rest-frame UV-selected, 16 rest-frame optically selected, and 13 submillimeter galaxies (SMGs). We find that rest-frame UV and optically bright (K < 20) z ~ 2 star forming galaxies are dynamically similar, and follow the same velocity-size relation as disk galaxies at z ~ 0. In the theoretical framework of rotating disks forming from dissipative collapse in dark matter halos, the two samples require a spin parameter ranging from 0.06 to 0.2. In contrast, bright SMGs (S850 μm ⩾ 5 mJy) have larger velocity widths and are much more compact. Hence, SMGs have lower angular momenta and higher matter densities than either the UV or optically selected populations. This indicates that dissipative major mergers may dominate the SMGs population, resulting in early spheroids, and that a significant fraction of the UV/optically bright galaxies have evolved less violently, either in a series of minor mergers, or in rapid dissipative collapse from the halo, given that either process may leads to the formation of early disks. These early disks may later evolve into spheroids via disk instabilities or mergers. Because of their small sizes and large densities, SMGs lie at the high surface density end of a universal (out to z = 2.5) "Schmidt-Kennicutt" relation between gas surface density and star formation rate surface density. The best-fit relation suggests that the star formation rate per unit area scales as the surface gas density to a power of ~1.7, and that the star formation efficiency increases by a factor of 4 between non-starbursts and strong starbursts.

New abundance determinations in z &lt; 1.5 QSO absorbers: seven sub-DLAs and one DLA

We present chemical abundance measurements from high resolution observations of 7 subdamped Lyman-� absorbers and 1 damped Lyman-� system at z < 1.5. Three of these objects have high metallicity, with near or super-solar Zn abundance. Grids of Cloudy models for each system were constructed to look for possible ionization effects in these systems. For the systems in which we could constrain the ionization parameter, we find that the ionization corrections as predicted by the Cloudy models are generally small and within the typical error bars (� 0.15 dex), in general agreement with previous studies. The Al III to Al II ratio for these and other absorbers from the literature are compared, and we find that while the subDLAs have a larger scatter in the Al III to Al II ratios than the DLAs, there appears to be little correlation between the ratio and NH I. The relationship between the metallicity and the velocity width of the profile for these systems is investigat ed. We show that the sub-DLAs that have been observed to date follow a similar trend as DLA absorbers, with the more metal rich systems exhibiting large velocity widths. We also find that t he systems at the upper edge of this relationship with high metallicities and large velocity wi dths are more likely to be sub-DLAs than DLA absorbers, perhaps implying that the sub-DLA absorbers are more representative of massive galaxies.

Positional coincidence between an H2O maser and a plasma torus in NGC 1052

AbstractWe present VLBA observation towards the nucleus of a nearby radio galaxy NGC 1052. In NGC 1052, two-sided jet structure and a dense plasma circumnuclear torus with a radius of 0.7 pc have been found around the central mass. It emits a H2O megamaser, which is redshifted with respect to the systemic velocity of the galaxy (1491 kms−1) with a large velocity width of 100 kms−1 (FWHM). The maser gas is found at the inner jet components of both the approaching and receding jets. The maser gas is positionally coincident with a plasma torus. The maser gas in NGC 1052 could be explained as a circumnuclear torus or disk, as found for the nucleus of NGC 4258.

A CO J = 3–2 Survey of the Galactic Center

Abstract We have surveyed the central molecular zone (CMZ) of our Galaxy in the CO J$=$3–2 line with the Atacama Submillimeter-wave Telescope Experiment (ASTE). Molecular gas in the Galactic center shows a high J$= 3-2/J = 1-0$ intensity ratio ($\sim 0.9$), while gas in the spiral arms of the Galactic disk shows a lower ratio ($\sim 0.5$). The high-velocity compact cloud CO $0.02-0.02$ and the hyperenergetic shell CO 1.27$+$0.01, as well as gas in the Sgr A region, exhibit high J$=$3–2$/J=$1–0 intensity ratios exceeding 1.5. We also found a number of small spots of high-ratio gas. Some of these high-ratio spots have large velocity widths and some seem to be associated with nonthermal threads or filaments. These could be spots of hot molecular gas shocked by unidentified supernovae, which may be abundant in the CMZ.

A Large-scale CO J = 3-2 Survey of the Galactic Center

We have surveyed the central molecular zone (CMZ) of our Galaxy in the CO J = 3-2 line with the Atacama Submillimeter-wave Telescope Experiment (ASTE). Molecular gas in the Galactic center shows high J = 3-2/J = 1-0 intensity ratio (∼ 0.9) while gas in the Galactic disk shows the lower ratio (∼ 0.5). The high-velocity compact cloud CO 0.02-0.02 and the hyperenergetic shell CO 1.27+0.01, as well as gas in the Sgr A region exhibit high J = 3-2/J = 1-0 intensity ratio exceeding 1.5. We also found a number of small spots of high ratio gas. Some of these high ratio spots have large velocity widths and some seem to associate with nonthermal ‘threads’ or filaments. These could be spots of hot molecular gas shocked by unidentified supernovae which may be abundant in the CMZ.

Supersolar Super-Lyman Limit Systems

We present abundance measurements for two super Lyman Limit systems (SLLS; quasar absorption line systems with 10^19 cm^-2 < N_HI < 10^20.3 cm^-2) selected from a set of metal-strong absorbers in the Sloan Digital Sky Survey quasar database. After applying estimate corrections for photoionization effects, we derive gas-phase metallicities of [M/H]=+0.7 +/- 0.2 dex for the SLLS at z=1.7749 toward SDSS0927+5621 and [M/H]=+0.05 +/- 0.1 dex for the SLLS at z=1.7678 toward SDSS0953+5230. The former exhibits among the highest gas metallicity of any astrophysical environment and its total metal surface density exceeds that of nearly every known damped Lya system. The properties of these absorbers -- high metallicity and large velocity width (> 300 km/s) -- resemble those of gas observed in absorption in the spectra of bright, star-forming galaxies at high redshift. We discuss the metal mass density of the SLLS based on these observations and our ongoing SLLS survey and argue that a conservative estimate to the total metal budget at z=2 is greater than 15% of the total, suggesting that the metal-rich LLS may represent the dominant metal reservoir in the young universe.

GRB 050408: A Bright Gamma‐Ray Burst Probing an Atypical Galactic Environment

The bright ORB 050408 was localized by HETE-2 near local midnight in the Western Hemisphere, enabling an impressive ground-based follow-up effort, as well as space-based follow-up from Swift. The Swift data from the XRT and our own optical photometry and spectrum of the afterglow provide the cornerstone for our analysis. Under the traditional assumption that the visible wave band was above the peak synchrotron frequency and below the cooling frequency, the optical photometry of 0.03-5.03 days shows an afterglow decay corresponding to an electron energy index of plc = 2.05±0.04, without a jet break as suggested by others. A break is seen in the X-ray data at early times (at ∼ 12,600 s after the GRB). The spectral slope of the optical spectrum is consistent with plc assuming a host galaxy extinction of A v = 1.18 mag. The optical-NIR broadband spectrum is also consistent with p = 2.05 but prefers Av = 0.57 mag. The X-ray afterglow shows a break at 1.26×104 s, which may be the result of a refreshed shock. This burst stands out in that the optical and X-ray data suggest a large H I column density of NH I ≈ 1022 cm-2; it is very likely a damped Lyα system, so the faintness of the host galaxy (Mv > -18 mag) is noteworthy. Moreover, we detect extraordinarily strong Ti II absorption lines with a column density through the GRB host that exceeds the largest values observed for the Milky Way by 1 order of magnitude. Furthermore, the Ti II equivalent width is in the top 1% of Mg II absorption-selected QSOs. This suggests that the large-scale environment of GRB 050408 has significantly lower Ti depletion than our Galaxy and a large velocity width (δv > 150 km s-1). © 2006. The American Astronomical Society. All rights reserved.

A Keck/DEIMOS Spectroscopy of Lyα Blobs at Redshift z = 3.1

We present the results of intermediate-resolution (~2 ?) spectroscopy of a sample of 37 candidate Ly? blobs and emitters at redshift z = 3.1 using the DEIMOS spectrograph on the 10 m Keck telescope. The emission lines are detected for all 37 objects and show variety in their line profiles. The Ly? velocity widths (FWHM) of the 28 objects with higher quality spectra, measured by fitting a single Gaussian profile, are in the range of 150-1700 km s-1 and correlate with the Ly? spatial extents. All 12 Ly? blobs (?16 arcsec2) have large velocity widths of 500 km s-1. While there are several possible physical interpretations of the Ly? velocity widths (the motion of gravitationally bound gas clouds, inflows, the merging of clumps, or outflows from superwinds), the large velocity widths of the Ly? blobs suggest that they are the sites of massive galaxy formation. If we assume gravitationally bound gas clouds, the dynamical masses of the Ly? blobs are estimated to be ~1012-1013 M?. Even for the case of outflows, the outflow velocities are likely to be comparable to the rotation velocities as inferred from the observational evidence for local starburst galaxies.

Molecular Superbubbles in the Starburst Galaxy NGC 253

The central 2x1 kpc of the starburst galaxy NGC 253 has been imaged using the Submillimeter Array at a 60 pc resolution in the J=2-1 transitions of 12CO, 13CO, and C18O as well as in the 1.3 mm continuum. Molecular gas and dust are mainly in the circumnuclear disk of ~500 pc radius, with warm (~40 K) and high area-filling factor gas in its central part. Two gas shells or cavities have been discovered in the circumnuclear disk. They have ~100 pc diameters and have large velocity widths of 80-100 km/s, suggestive of expansion at ~50 km/s. Modeled as an expanding bubble, each shell has an age of ~0.5 Myr and needed kinetic energy of ~1E46 J as well as mean mechanical luminosity of ~1E33 W for its formation. The large energy allows each to be called a superbubble. A ~10^6 Msun super star cluster can provide the luminosity, and could be a building block of the nuclear starburst in NGC 253. Alternatively, a hypernova can also be the main source of energy for each superbubble, not only because it can provide the mechanical energy and luminosity but also because the estimated rate of superbubble formation and that of hypernova explosions are comparable. Our observations indicate that the circumnuclear molecular disk harboring the starburst is highly disturbed on 100 pc or smaller scales, presumably by individual young clusters and stellar explosions, in addition to globally disturbed in the form of the well-known superwind.

Unusual high-redshift radio broad absorption-line quasar 1624+3758

We present observations of the most radio-luminous broad absorption-line (BAL) quasar known, 1624+3758, at redshift z = 3.377. The quasar has several unusual properties. (1) The Fe II UV191 1787-A emission line is very prominent. (2) The BAL trough (BALnicity index 2990 km s −1 )i sdetached by 21 000 km s −1 and extends to velocity v =− 29 000 km s −1 . There are additional intrinsic absorbers at −1900 and −2800 km s −1 . (3) The radio rotation measure of the quasar, 18 350 rad m −2 ,i sthe second highest known. The radio luminosity is P 1.4 GHz = 4.3 × 10 27 WH z −1 (H 0 = 50 km s −1 Mpc −1 , q 0 = 0.5) and the radio loudness is R ∗ = 260. The radio source is compact ( ∼ 2.8 kpc) and the radio spectrum is GHz-peaked, consistent with it being relatively young. The width of the C IV emission line, in conjunction with the total optical luminosity, implies a black hole mass M BH ∼ 10 9 M� , L/L Eddington ≈ 2. The high Eddington ratio and the radio-loudness place this quasar in one corner of Boroson’s two-component scheme for the classification of active galactic nuclei, implying a very high accretion rate, and this may account for some of the unusual observed properties. The v = −1900 km s −1 absorber is a possible Lyman-limit system, with N (H I) = 4 × 10 18 cm −2 , and a covering factor of 0.7. A complex mini-BAL absorber at v =− 2200 to −3400 km s −1 is detected in each of C IV ,N V and O VI. The blue and red components of the C IV doublet happen to be unblended, allowing both the covering factor and optical depth to be determined as a function of velocity. Variation of the covering factor with velocity dominates the form of the mini-BAL, with the absorption being saturated (e −τ ≈ 0) over most of the velocity range. The velocity dependence of the covering factor and the large velocity width imply that the mini-BAL is intrinsic to the quasar. There is some evidence of line-locking between velocity components in the C IV mini-BAL, suggesting that radiation pressure plays a role in accelerating the outflow. Ke yw ords: galaxies: high-redshift ‐ intergalactic medium ‐ quasars: absorption lines ‐ quasars: emission lines ‐ quasars: general ‐ early Universe.

A homogeneous sample of sub-damped Lyman alpha systems - II. Statistical, kinematic and chemical properties

Damped Lyman α systems (DLAs), with N(H i) > 2 × 1020 atom cm−2, observed in the spectra of quasars have allowed us to quantify the chemical content of the Universe over cosmological scales. Such studies can be extended to lower column densities, in the sub-DLA range [1019 < N(H i) < 2 × 1020 atom cm−2], which are systems believed to contain a large fraction of the neutral hydrogen at z > 3.5. In this paper, we use a homogeneous sample of sub-DLAs from the European Southern Oberservatory (ESO) Ultraviolet–Visual Echelle Spectrograph (UVES) archives presented in Paper I, to determine observationally for the first time the shape of the column density distribution, ƒ(N), down to N(H i) = 1019 atom cm−2. The results are in good agreement with the predictions from Péroux et al. We also present the kinematic and clustering properties of this survey of sub-DLAs, which appear to be marginally different from the DLAs. We compare low- and high-ionization transition widths and find that the properties of the sub-DLAs span roughly the parameter space of DLAs. We also find hints of an increase of metallicity in systems with larger velocity widths in the metal lines, although the statistical significance of this result is low. Then we analyse the chemical content of this sample in conjunction with a compilation of abundances from 72 DLAs taken from the literature. As previously reported, the individual metallicities traced by [Fe/H] of these systems evolve mildly with redshift. Moreover, we analyse the H i column-density-weighted mean abundance, which is believed to be an indicator of the metallicity of the Universe. Although the number statistics is limited in the current sample, the results suggest a slightly stronger evolution of this quantity in the sub-DLA range. The effect is predominant at z < 2 and most of the evolution observed lies in this redshift range. Observational arguments support the hypothesis that the evolution we probe in the sub-DLA range is not due to their lower dust content. Therefore, these systems might be associated with a different class of objects, which better trace the overall chemical evolution of the Universe. Finally, we present abundance ratios of [Si/Fe], [O/Fe], [C/Fe] and [Al/Fe] for sub-DLAs in conjunction with DLA measurements from the literature. The elemental ratios in sub-DLAs are comparable with those from DLAs. It is difficult to decipher whether the observed values are the effect of nucleosynthesis or are due to differential dust depletion. The metallicities are compared with two different sets of models of galaxy evolution in order to provide constraints on the morphology of quasar absorbers.

HiAbsorption in the Gigamaser Galaxy TXS 2226−184 and the Relation between HiAbsorption and Water Emission

We report on the discovery of H I in absorption toward the gigamaser galaxy TXS 2226-184 using the Very Large Array. The absorption appears to consist of two components—one with a width of 125 km s-1 and one broader (420 km s-1)—both toward the compact radio source in the nucleus of the galaxy. Based on these large velocity widths, we suggest that the H I absorption is produced in the central parsecs of the galaxy, on a scale similar to that which gives rise to the water maser emission. This brings to eight the number of galaxies known to exhibit both water masers and H I absorption. We explore the relationship between these two phenomena and present a physically motivated (but unfruitful) search for water maser emission in five radio galaxies known to exhibit strong H I absorption.

Statistical Properties of Molecular Clouds in the Galactic Center

The data from the Nobeyama Radio Observatory 45 m telescope Galactic Center CO survey have been analyzed to generate a compilation of molecular clouds with intense CO emission in this region. Clouds are identified in an automated manner through the main part of the survey data for all CO emission peaks exceeding 10 K (T). The measured parameters of identified clouds are analyzed and cross-correlated to compare with those of clouds in the Galactic disk. For the clouds in the Galactic center (GC), we find the scaling laws of the type σV S0.40 and MVT (LCO)0.88, which are similar to those of clouds in the Galactic disk. All the GC clouds identified have larger velocity widths and virial theorem masses each above the σV-S and LCO-MVT lines of the disk clouds. We diagnosed gravitational stabilities of identified clouds assuming that the disk clouds are nearly at the onset of gravitational instability. All the clouds and cloud complexes in the GC are gravitationally stable, indicating they are in equilibrium with high pressure in the GC environment. Gravitationally less stable clouds follow the main ridge of intense CO emission, part of which define two rigidly rotating molecular arms. The velocity dispersion of a cloud correlates inversely with the degree of gravitational instability. It is concluded that mechanisms such as orbit crowding at the inner Lindblad resonance may promote gravitational instability and subsequent star formation.

Infrared spectroscopy of cataclysmic variables -- III. Dwarf novae below the period gap and nova-like variables

We present K-band spectra of the short-period dwarf novae YZ Cnc, LY Hya, BK Lyn, T Leo, SW UMa and WZ Sge, the nova-like variables DW UMa, V1315 Aql, RW Tri, VY Scl, UU Aqr and GP Com, and a series of field dwarf stars with spectral types ranging from K2 to M6. The spectra of the dwarf novae are dominated by emission lines of H i and He i. The large velocity and equivalent widths of these lines, in conjunction with the fact that the lines are double-peaked in the highest inclination systems, indicate an accretion disc origin. In the case of YZ Cnc and T Leo, for which we obtained time-resolved data covering a complete orbital cycle, the emission lines show modulations in their equivalent widths that are most probably associated with the bright spot (the region where the gas stream collides with the accretion disc). There are no clear detections of the secondary star in any of the dwarf novae below the period gap, yielding upper limits of 10–30 per cent for the contribution of the secondary star to the observed K-band flux. In conjunction with the K-band magnitudes of the dwarf novae, we use the derived secondary star contributions to calculate lower limits to the distances to these systems. The spectra of the nova-like variables are dominated by broad, single-peaked emission lines of H i and He i– even the eclipsing systems we observed do not show the double-peaked profiles predicted by standard accretion disc theory. With the exception of RW Tri, which exhibits Na i, Ca i and 12CO absorption features consistent with a M0V secondary contributing 65 per cent of the observed K-band flux, we find no evidence for the secondary star in any of the nova-like variables. The implications of this result are discussed.

CO (4–3) and Dust Emission in Two Powerful High‐zRadio Galaxies, and CO Lines at High Redshifts

We report the detection of sub-mm emission from dust at 850 microns and of the 12CO J=4-3 line in the two distant powerful radio galaxies 4C 60.07 (z=3.79) and 6C 1909+722 (z=3.53). In the case of 4C 60.07 the dust emission is also detected at 1.25 mm. The estimated molecular gas masses are large, of the order of ~(0.5-1)x10^{11} Solar. The large FIR luminosities (L_fir ~ 10^{13} Solar) suggest that we are witnessing two major starburst phenomena, while the observed large velocity widths (FWHM > 500 km/sec) are characteristic of mergers. In the case of 4C 60.07 the CO emission extends over ~30 kpc and spans a velocity range of >1000 km/sec. It consists of two distinct features with FWHM of >= 550 km/sec and ~150 km/sec and line centers separated by >=700 km/sec The least massive of these components is probably very gas-rich with potentially >=60% of its dynamical mass in the form of molecular gas. The extraordinary morphology of the CO emission in this object suggests that it is not just a scaled-up version of a local Ultra Luminous Infrared Galaxy, and it may be a formative stage of the elliptical host of the residing radio-loud AGN. Finally we briefly explore the effects of the wide range of gas excitation conditions expected for starburst environments on the luminosity of high-J CO lines. We conclude that in unlensed objects, CO (J+1-->J), J+1>3 lines can be significantly weak with respect to CO J=1-0 and this can hinder their detection even in the presence of substantial molecular gas masses.

13CO ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $J=1- 0$ \end{document} ) Depression in Luminous Starburst Mergers, Revisited

It is known that merging galaxies with luminous starbursts and high far-infrared luminosities tend to have higher R1-0 = 12CO (J = 1-0)/13CO (J = 1-0) integrated line intensity ratios (R1-0 ≃ 20-50) than normal spiral galaxies (R1-0 ≃ 5-15). Comparing far-infrared luminosities [L(FIR)] with those of 12CO (J = 1-0) and 13CO (J = 1-0) for a sample of normal and starburst galaxies, Taniguchi & Ohyama found that the observed high R1-0 values for the luminous starburst mergers are attributed to their lower (by a factor of 3 on average) 13CO line intensities. They suggested the following two possibilities: in the luminous starburst mergers (1) 13CO is underabundant with respect to 12CO, or (2) exitation and/or optical depth effects are responsible for the change in R1-0. In this paper, we investigate the second possibility, using higher transition data of both 12CO and 13CO emission lines. Applying the same method proposed by Taniguchi & Ohyama to both 12CO (J = 2-1) and 13CO (J = 2-1), we find that 13CO (J = 2-1) is also depressed with respect to 12CO (J = 2-1). This suggests that the 13CO gas may be underabundant in the high-R1-0 starburst mergers, although we cannot rule out the possibility that excitation and optical depth effects are still affecting R2-1, for example, as a result of the large velocity widths in the CO emission lines. Additional observations of both 12CO and 13CO lines at J ≥ 3 are required to better constrain the conditions of the molecular gas in luminous starburst galaxies.