Velocity Channel Maps Research Articles

Testing Velocity Kinks as a Planet Detection Method: Do Velocity Kinks in Surface Gas Emission Trace Planetary Spiral Wakes in the Midplane Continuum?

Spiral density waves generated by an embedded planet are understood to cause “kinks” in observed velocity channel maps of CO surface emission by perturbing the gas motion within the spiral arms. If velocity kinks are a reliable probe of embedded planets, we should expect to see the planet-driven spiral arms in other observational tracers. We test this prediction by searching the dust continuum for the midplane counterparts of the spirals responsible for all of the velocity kink planet candidates reported to date whose orbits lie inside the dust continuum disk. We find no clear detection of any spiral structure in current continuum observations for six of the 10 velocity kink planet candidates in our sample (DoAr 25, GW Lup, Sz 129, HD 163296 #2, P94, and HD 143006), despite the high planet masses inferred from the kink amplitude. The remaining four cases include three clear detections of two-armed dust spirals (Elias 27, IM Lup, and WaOph 6) wherein neither spiral arm aligns with a wake originating from a reported planet location, suggesting that under the planetary-origin hypothesis, an accurate method for inferring the location of the planet in the midplane may need to encompass vertical effects. The 10th case, HD 97048, is inconclusive with current knowledge of the disk geometry.

Probing Gas Kinematics and PDR Structure around O-type Stars in the Sh 2-305 H ii Region

Abstract We report an observational study of the Galactic H ii region Sh 2-305/S305 using the [C ii] 158 μm line data, which are used to examine the gas dynamics and structure of photodissociation regions. The integrated [C ii] emission map at [39.4, 49.5] km s−1 spatially traces two shell-like structures (i.e., inner and outer neutral shells) having a total mass of ∼565 M ⊙. The inner neutral shell encompasses an O9.5V star at its center and has a compact ring-like appearance. However, the outer shell is seen with more extended and diffuse [C ii] emission, hosting an O8.5V star at its center, and surrounds the inner neutral shell. The velocity channel maps and position–velocity diagrams confirm the presence of a compact [C ii] shell embedded in the diffuse outer shell, and both the shells seem to expand with v exp ∼ 1.3 km s−1. The outer shell appears to be older than the inner shell, hinting that these shells are formed sequentially. The [C ii] profiles are examined toward S305, which are either double peaked or blue skewed and have the brighter redshifted component. The redshifted and blueshifted components spatially trace the inner and outer neutral shell geometry, respectively. The ionized, neutral, and molecular zones in S305 are seen adjacent to one another around the O-type stars. The regularly spaced dense molecular and dust clumps (mass ∼10–103 M ⊙) are investigated around the neutral shells, which might have originated as a result of gravitational instability in the shell of collected materials.

Observational Signature of Tightly Wound Spirals Driven by Buoyancy Resonances in Protoplanetary Disks

Abstract Besides the spirals induced by the Lindblad resonances, planets can generate a family of tightly wound spirals through buoyancy resonances. The excitation of buoyancy resonances depends on the thermal relaxation timescale of the gas. By computing timescales of various processes associated with thermal relaxation, namely, radiation, diffusion, and gas–dust collision, we show that the thermal relaxation in protoplanetary disks’ surface layers (Z/R ≳ 0.1) and outer disks (R ≳ 100 au) is limited by infrequent gas–dust collisions. The use of the isothermal equation of state or rapid cooling, common in protoplanetary disk simulations, is therefore not justified. Using three-dimensional hydrodynamic simulations, we show that the collision-limited slow thermal relaxation provides favorable conditions for buoyancy resonances to develop. Buoyancy resonances produce predominantly vertical motions, whose magnitude at the 12CO emission surface is of the order of 100 m s−1 for Jovian-mass planets, sufficiently large to detect using molecular line observations with ALMA. We generate synthetic observations and describe characteristic features of buoyancy resonances in Keplerian-subtracted moment maps and velocity channel maps. Based on the morphology and magnitude of the perturbation, we propose that the tightly wound spirals observed in TW Hya could be driven by a (sub-)Jovian-mass planet at 90 au. We discuss how non-Keplerian motions driven by buoyancy resonances can be distinguished from those driven by other origins. We argue that observations of multiple lines tracing different heights, with sufficiently high spatial/spectral resolution and sensitivity to separate the emission arising from the near and far sides of the disk, will help constrain the origin of non-Keplerian motions.

Disk Structure around the Class I Protostar L1489 IRS Revealed by ALMA: A Warped-disk System

Abstract We have observed the Class I protostar L1489 IRS with the Atacama Millimeter/submillimeter Array (ALMA) in Band 6. The C18O J = 2–1 line emission shows flattened and non-axisymmetric structures in the same direction as its velocity gradient due to rotation. We discovered that the C18O emission shows dips at a radius of ∼200–300 au while the 1.3 mm continuum emission extends smoothly up to r ∼ 400 au. At the radius of the C18O dips, the rotational axis of the outer portion appears to be tilted by ∼15° from that of the inner component. Both the inner and outer components with respect to the C18O dips exhibit the r −0.5 Keplerian rotation profiles until r ∼ 600 au. These results not only indicate that a Keplerian disk extends up to ∼600 au but also that the disk is warped. We constructed a three-dimensional warped-disk model rotating at the Keplerian velocity, and demonstrated that the warped-disk model reproduces main observed features in the velocity channel maps and the PV diagrams. Such a warped-disk system can form by mass accretion from a misaligned envelope. We also discuss a possible disk evolution scenario based on comparisons of disk radii and masses between Class I and Class II sources.

Templates of Binary-induced Spiral-shell Patterns around Mass-losing Post-main-sequence Stars

Abstract The morphological properties of the outflowing circumstellar envelopes surrounding mass-losing stars in eccentric binary systems are presented based upon the results from a set of three-dimensional hydrodynamical model simulations. Making use of four template models of the envelope viewed for a range of inclination angles of the systems, we implement interpretative tools for observations at high spectral/angular resolutions (as illustrated via velocity-channel maps as well as position–velocity, radius–velocity, and angle–radius diagrams). Within this framework, the image and kinematical structures can be used to place constraints on the orbital parameters of the system. Specifically, three unique characteristic patterns in the envelopes are found that distinguish these systems from those in binary systems in circular orbits. Bifurcation of the spiral pattern, asymmetry in the interarm density depression, and a concurrent spiral/ring appearance all point to a binary system with an eccentric orbit. The methodology presented in this paper is illustrated in an analysis of recent radio observations of several asymptotic giant branch stars.

H2CO and H110α Observations toward the Aquila Molecular Cloud

Abstract The formaldehyde H2CO(110–111) absorption line and H110α radio recombination line have been observed toward the Aquila Molecular Cloud using the Nanshan 25 m telescope operated by the Xinjiang Astronomical Observatory CAS. These first observations of the H2CO (110–111) absorption line determine the extent of the molecular regions that are affected by the ongoing star formation in the Aquila molecular complex and show some of the dynamic properties. The distribution of the excitation temperature T ex for H2CO identifies the two known star formation regions W40 and Serpens South as well as a smaller new region Serpens 3. The intensity and velocity distributions of H2CO and 13CO(1−0) do not agree well with each other, which confirms that the H2CO absorption structure is mostly determined by the excitation of the molecules resulting from the star formation rather than by the availability of molecular material as represented by the distribution. Some velocity-coherent linear 13CO(1−0) structures have been identified in velocity channel maps of H2CO and it is found that the three star formation regions lie on the intersect points of filaments. The H110α emission is found only at the location of the W40 H ii region and spectral profile indicates a redshifted spherical outflow structure in the outskirts of the H ii region. Sensitive mapping of H2CO absorption of the Aquila Complex has correctly identified the locations of star formation activity in complex molecular clouds and the spectral profiles reveal the dominant velocity components and may identify the presence of outflows.

Possible Counterrotation between the Disk and Protostellar Envelope around the Class I Protostar IRAS 04169+2702

We present results from our SMA observations and data analyses of the SMA archival data of the Class I protostar IRAS 04169+2702. The high-resolution (~0.5") $^{13}$CO (3-2) image cube shows a compact ($r$ ~< 100 au) structure with a northwest (blue) to southeast (red) velocity gradient, centered on the 0.9-mm dust-continuum emission. The direction of the velocity gradient is orthogonal to the axis of the molecular outflow as seen in the SMA $^{12}$CO (2-1) data. A similar gas component is seen in the SO (6$_5$-5$_4$) line. On the other hand, the C$^{18}$O (2-1) emission traces a more extended ($r$ ~400 au) component with the opposite, northwest (red) to southeast (blue) velocity gradient. Such opposite velocity gradients in the different molecular lines are also confirmed from direct fitting to the visibility data. We have constructed models of a forward-rotating and counter-rotating Keplerian disk and a protostellar envelope, including the SMA imaging simulations. The counter-rotating model could better reproduce the observed velocity channel maps, although we could not obtain statistically significant fitting results. The derived model parameters are; Keplerian radius of 200 au, central stellar mass of 0.1 $M_{solar}$, and envelope rotational and infalling velocities of 0.20 km s$^{-1}$ and 0.16 km s$^{-1}$, respectively. One possible interpretation for these results is the effect of the magnetic field in the process of disk formation around protostars, $i.e.$, Hall effect.

New Insights in the Mid-infrared Bubble N49 Site: A Clue of Collision of Filamentary Molecular Clouds

Abstract We investigate the star formation processes operating in a mid-infrared bubble N49 site that harbors an O-type star in its interior, an ultracompact H ii region, and a 6.7 GHz methanol maser at its edges. The 13CO line data reveal two velocity components (at velocity peaks ∼88 and ∼95 km s−1) in the direction of the bubble. An elongated filamentary feature (length &gt;15 pc) is investigated in each molecular cloud component, and the bubble is found at the interface of these two filamentary molecular clouds. The Herschel temperature map traces all these structures in a temperature range of ∼16–24 K. In the velocity space of 13CO, the two molecular clouds are separated by ∼7 km s−1, and are interconnected by a lower-intensity intermediate velocity emission (i.e., a broad bridge feature). A possible complementary molecular pair at [87, 88] km s−1 and [95, 96] km s−1 is also observed in the velocity channel maps. These observational signatures are in agreement with the outcomes of simulations of the cloud–cloud collision process. There are also noticeable embedded protostars and Herschel clumps distributed toward the filamentary features including the intersection zone of the two molecular clouds. In the bubble site, different early evolutionary stages of massive star formation are also present. Together, these observational results suggest that in the bubble N49 site, the collision of the filamentary molecular clouds appears to be operated about 0.7 Myr ago, and may have triggered the formation of embedded protostars and massive stars.

Observational Signatures of Cloud–Cloud Collision in the Extended Star-forming Region S235

Abstract We present a multi-wavelength data analysis of the extended star-forming region S235 (hereafter E-S235), where two molecular clouds are present. In E-S235, using the 12CO (1–0) and 13CO (1–0) line data, a molecular cloud linked with the site “S235main” is traced in a velocity range [−24, −18] km s−1, while the other one containing the sites S235A, S235B, and S235C (hereafter “S235ABC”) is depicted in a velocity range [−18, −13] km s−1. In the velocity space, these two clouds are separated by ∼4 km s−1, and are interconnected by a lower-intensity intermediate velocity emission, tracing a broad bridge feature. In the velocity channel maps, a possible complementary molecular pair at [−21, −20] km s−1 and [−16, −15] km s−1 is also evident. The sites, “S235ABC,” east 1, and south–west, are spatially seen in the interface of two clouds. Together, these observed features are consistent with the predictions of numerical models of the cloud–cloud collision (CCC) process, favoring the onset of the CCC in E-S235 about 0.5 Myr ago. Deep UKIDSS near-infrared photometric analysis of point-like sources reveals significant clustering of young stellar populations toward the sites located at the junction, and the “S235main.” The sites “S235ABC” harbor young compact H ii regions with dynamical ages of ∼0.06–0.22 Myr, and these sites (including south–west and east 1) also contain dust clumps (having M clump ∼ 40 to 635 M ⊙ ). Our observational findings suggest that the star formation activities (including massive stars) appear to be influenced by the CCC mechanism at the junction.

Tracing planet-induced structures in circumstellar disks using molecular lines

Circumstellar disks are considered to be the birthplace of planets. Specific structures like spiral arms, gaps, and cavities are characteristic indicators of planet-disk interaction. Investigating these structures can provide insights into the growth of protoplanets and the physical properties of the disk. We investigate the feasibility of using molecular lines to trace planet-induced structures in circumstellar disks. Based on 3D hydrodynamic simulations of planet-disk interactions, we perform self-consistent temperature calculations and produce N-LTE molecular line velocity-channel maps and spectra of these disks using our new N-LTE line radiative transfer code Mol3D. Subsequently, we simulate ALMA observations using the CASA simulator. We consider two nearly face-on inclinations, 5 disk masses, 7 disk radii, and 2 different typical pre-main-sequence host stars (T Tauri, Herbig Ae). We calculate up to 141 individual velocity-channel maps for five molecules/isotopoloques in a total of 32 rotational transitions to investigate the frequency dependence of the structures indicated above. We find that the majority of protoplanetary disks in our parameter space could be detected in the molecular lines considered. However, unlike the continuum case, gap detection is not straightforward in lines. For example, gaps are not seen in symmetric rings but are masked by the pattern caused by the global (Keplerian) velocity field. We identify specific regions in the velocity-channel maps that are characteristic of planet-induced structures. Simulations of high angular resolution molecular line observations demonstrate the potential of ALMA to provide complementary information about the planet-disk interaction as compared to continuum observations. In particular, the detection of planet-induced gaps is possible under certain conditions.(abridged)

CO GAS INSIDE THE PROTOPLANETARY DISK CAVITY IN HD 142527: DISK STRUCTURE FROM ALMA

Inner cavities and annular gaps in circumstellar disks are possible signposts of giant planet formation. The young star HD 142527 hosts a massive protoplanetary disk with a large cavity that extends up to 140 AU from the central star, as seen in continuum images at infrared and millimeter wavelengths. Estimates of the survival of gas inside disk cavities are needed to discriminate between clearing scenarios. We present a spatially and spectrally resolved carbon monoxide isotopologue observations of the gas-rich disk HD 142527, in the J = 2–1 line of 12CO, 13CO, and C18O obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). We detect emission coming from inside the dust-depleted cavity in all three isotopologues. Based on our analysis of the gas in the dust cavity, the 12CO emission is optically thick, while 13CO and C18O emissions are both optically thin. The total mass of residual gas inside the cavity is ∼1.5–2 MJup. We model the gas with an axisymmetric disk model. Our best-fit model shows that the cavity radius is much smaller in CO than it is in millimeter continuum and scattered light observations, with a gas cavity that does not extend beyond 105 AU (at 3σ). The gap wall at its outer edge is diffuse and smooth in the gas distribution, while in dust continuum it is manifestly sharper. The inclination angle, as estimated from the high velocity channel maps, is 28 ± 0.5 deg, higher than in previous estimates, assuming a fix central star mass of 2.2 M☉.

Signatures of infall motions in the images of the molecular emission of G31.41+0.31 hot molecular core

Although gravitational collapse is supposed to play an essential role in the star formation process, infall motions have been always elusive to detect. So far, only a few observational signatures have been commonly used to claim for the presence of infall. Often these features consist in either "blue-asymmetries" or absorption at red-shifted velocities (e.g., inverse P-Cygni profiles). Both signatures are based only on the shape of the line profile and they do not guarantee by themselves the presence of dominant infall motions. More robust "mapping signatures" can be obtained from images that angularly resolve the infalling gas. Here we present VLA observations of the ammonia inversion transitions (2,2), (3,3), (4,4), (5,5), and (6,6) towards the hot molecular core (HMC) near G31.41+0.31 that show the signatures of protostellar infall theoretically predicted by Anglada et al. (1991). The intensity of the ammonia emission is compact and sharply increases towards the centre in the blue-shifted velocity channel maps, while it shows a more flattened distribution in the red-shifted velocity channels. Additionally, the emission becomes more compact with increasing (relative) velocity for both red and blue-shifted channels. We introduce a new infall signature, the "central blue spot", easily identifiable in the first-order moment maps. We show that rotation produces an additional, independent signature, making the distribution of the emission in the channel maps asymmetric with respect to the central position, but without masking the infall signatures. All these mapping signatures, which are identified here for the first time, are present in the observed ammonia transitions of G31 HMC.

KINEMATICS AND PHYSICAL CONDITIONS OF THE INNERMOST ENVELOPE IN B335

We made C18O (2-1) and CS (7-6) images of the protostellar envelope around B335 with a high spatial dynamic range from ~10000 to ~400 AU, by combining the Submillimeter Array and single-dish data. The C18O emission shows an extended (~10000 AU) structure as well as a compact (~1500 AU) component concentrated at the protostellar position. The CS emission shows a compact (~900 AU) component surrounding the protostar, plus a halo-like (~3000 AU) structure elongated along the east-west direction. At higher velocities (|dV| >~0.3 km s^-1), the CS emission is stronger and more extended than the C18O emission. Physical conditions of the envelope were examined through an LVG model. At |dV| >~0.3 km s^-1, the gas temperature is higher (>40 K) than that at |dV| <~0.3 km s^-1, whereas the gas density is lower (<10^6 cm^-3). We consider that the higher-temperature and lower-density gas at |dV| >~0.3 km s^-1 is related to the associated outflow, while the lower-temperature and higher-density gas at |dV| <~0.3 km s^-1 is the envelope component. From the inspection of the positional offsets in the velocity channel maps, the radial profile of the specific angular momentum of the envelope rotation in B335 was revealed at radii from ~10^4 down to ~10^2 AU. The specific angular momentum decreases down to the radius of ~370 AU, and then appears to be conserved within that radius. A possible scenario of the evolution of envelope rotation is discussed.

A survey of the Galactic center region in HCO+, H13CO+, and SiO

Aims: A large scale survey of the Galactic center region in he 3 mm rotational transitions of SiO, HCO+ and H13CO+ (beamsize ~ 3. 6 arcmin) was conducted to provide an estimate of cloud conditions, heating mechanisms, chemistry and other properties. Methods: Using the NANTEN 4m telescope from Nagoya University, a region between -5.75<l<5.6 (degree) and -0.68<b<1.3 (degree) was mapped in the J=1-0 lines of HCO+ and H13CO+ and in the J=2-1 line of SiO with a spacing of 3.75 arcmin (HCO+) and 1.875 arcmin (SiO and H13CO+). Results: Velocity channel maps, longitude-velocity maps and latitude-velocity maps are presented. We identify 51 molecular clouds; 33 of them belong to the Galactic center, and 18 to disk gas. We derive an average of the luminosity ratio of SiO(J=2-1)/CO(J=1-0) in clouds belonging to the Galactic center of 4.9x10^{-3} and for disk clouds of 3.4x 10^{-3}. The luminosity ratio of HCO^+(J=1-0)/CO(J=1\to0) in the Galactic Center is 3.5x 10^{-2}, and for disk clouds is 1.5x 10^{-2}. We can distinguish clearly between regions where the SiO or HCO+ are dominating.

EMISSION FROM A YOUNG PROTOSTELLAR OBJECT. I. SIGNATURES OF YOUNG EMBEDDED OUTFLOWS

We examine emission from a young protostellar object (YPO) with three-dimensional ideal MHD simulations and three-dimensional non-local thermodynamic equilibrium (non-LTE) line transfer calculations, and show the first results. To calculate the emission field, we employed a snapshot result of an MHD simulation having young bipolar outflows and a dense protostellar disk (a young circumstellar disk) embedded in an infalling envelope. Synthesized line emission of two molecular species (CO and SiO) show that subthermally excited SiO lines as a high density tracer can provide a better probe of the complex velocity field of a YPO, compared to fully thermalized CO lines. In a YPO at the earliest stage when the outflows are still embedded in the collapsing envelope, infall, rotation and outflow motions have similar speeds. We find that the combined velocity field of these components introduces a great complexity in the line emissions through varying optical thickness and emissivity, such as asymmetric double-horn profiles. We show that the rotation of the outflows, one of the features that characterizes an outflow driven by magneto-centrifugal forces, appears clearly in velocity channel maps and intensity-weighted mean velocity (first moment of velocity) maps. The somewhat irregular morphology of the line emission at this youngest stage is dissimilar to a more evolved object such as young Class 0. High angular resolution observation by e.g., the Atacama Large Millimeter/submillimeter Array (ALMA) telescope can reveal these features.

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.

FRACTAL DIMENSIONS OF INTERSTELLAR MEDIUM: II. THE MOLECULAR CLOUDS ASSOCIATED WITH THE HII REGION SH 156

We have estimated the fractal dimension of the molecular clouds associated with the Hii region Sh 156 in the Outer Galaxy. We selected the <TEX>$^{12}CO$</TEX> cube data from the FCRAO CO Survey of the Outer Galaxy. Using a developed code within IRAF, we identified slice-clouds (2-dimensional clouds in velocity-channel maps) with two threshold temperatures to estimate the fractal dimension. With the threshold temperatures of 1.8 K, and 3 K, we identified 317 slice-clouds and 217 slice-clouds, respectively. There seems to be a turn-over location in fractional dimension slope around NP (area; number of pixel) = 40. The fractal dimensions was estimated to be D = <TEX>$1.5\;{\sim}\;1.53$</TEX> for <TEX>$NP\;{\geq}\;40$</TEX>, where <TEX>$P\;{\propto}\;A^{D/2}$</TEX> (P is perimeter and A is area), which is slightly larger than other results. The sampling rate (spatial resolution) of observed data must be an important parameter when estimating fractal dimension. Fractal dimension is apparently invariant when varying the threshold temperatures applied to slice-clouds identification.

Interferometric Mapping of Magnetic Fields: The Massive Star‐forming Region G34.4+0.23 MM

We report millimeter interferometric observations of polarized continuum and line emission from the massive star-forming region G34.4. Polarized thermal dust emission at 3 mm wavelength and CO J = 1→ 0 line emission were observed using the Berkeley-Illinois-Maryland Association (BIMA) array. Our results show a remarkably uniform polarization pattern in both dust and in CO J = 1→ 0 emission. In addition, the line emission presents a consistent uniform polarization pattern over most of the velocity channel maps. These uniform polarization patterns are aligned with the north-south main axis of the filament between the main millimeter source (MM) and the ultracompact H II region, which are the central sources in G34.4, suggesting a magnetic field orthogonal to this axis. This morphology is consistent with a magnetically supported disk seen roughly edge-on.

Hydrodynamic simulations of rotating molecular jets

Molecular outflows and the jets which may drive them can be expected to display signatures associated with rotation if they are the channels through which angular momentum is extracted from material accreting on to protostars. Here, we determine some basic signatures of rapidly rotating flows through three-dimensional numerical simulations of hydrodynamic jets with molecular cooling and chemistry. We find that these rotating jets generate a broad advancing interface which is unstable and develops into a large swarm of small bow features. In comparison to precessing jets, there is no stagnation point along the axis. The greater the rotation rate, the greater the instability. On the other hand, velocity signatures are only significant close to the jet inlet since jet expansion rapidly reduces the rotation speed. We present predictions for atomic, H-2 and CO submillimetre images and spectroscopy including velocity channel maps and position-velocity diagrams. We also include simulated images corresponding to Spitzer IRAC band images and CO emission, relevant for APEX and eventual ALMA observations. We conclude that protostellar jets often show signs of slow precession but only a few sources display properties which could indicate jet rotation.

A KOSMA 7 deg$\mathsf{^{2}}$ $\mathsf{^{13}}$CO 2–1 and $\mathsf{^{12}}$CO 3–2 survey of the Perseus cloud

Context. Characterizing the spatial and velocity structure of molecular clouds is a first step towards a better understanding of interstellar turbulence and its link to star formation. Aims. We present observations and structure analysis results for a large-scale (∼7.10 deg 2 ) 13 CO J = 2–1 and 12 CO J = 3–2 survey towards the nearby Perseus molecular cloud observed with the KOSMA 3 m telescope. Methods. We study the spatial structure of line-integrated and velocity channel maps, measuring the ∆-variance as a function of size scale. We determine the spectral index β of the corresponding power spectrum and study its variation across the cloud and across the lines. Results. We find that the spectra of all CO line-integrated maps of the whole complex show the same index, β ≈ 3.1, for scales between about 0.2 and 3 pc, independent of isotopomer and rotational transition. A complementary 2MASS map of optical extinction shows a noticeably smaller index of 2.6. In contrast to the overall region, the CO maps of individual subregions show a significant variation of β .T he 12 CO 3–2 data provide e.g. a spread of indices between 2.9 in L 1455 and 3.5 in NGC 1333. In general, active star forming regions show a larger power-law exponent. We find that the ∆-variance spectra of individual velocity channel maps are very sensitive to optical depth effects clearly indicating self-absorption in the densest regions. When studying the dependence of the channel-map spectra as a function of the velocity channel width, the expected systematic increase of the spectral index with channel width is only detected in the blue line wings. This could be explained by a filamentary, pillar-like structure which is left at low velocities while the overall molecular gas is swept up by a supernova shock wave.