Spectra of Nearby Galaxies Measured with a New Very Broadband Receiver

Three-millimeter-wavelength spectra of a number of nearby galaxies have been obtained at the Five College Radio Astronomy Observatory (FCRAO) using a new, very broadband receiver. This instrument, which we call the Redshift Search Receiver, has an instantaneous bandwidth of 36 GHz and operates from 74 to 110.5 GHz. The receiver has been built at UMass/FCRAO to be part of the initial instrumentation for the Large Millimeter Telescope (LMT) and is intended primarily for determination of the redshift of distant, dust-obscured galaxies. It is being tested on the FCRAO 14m by measuring the 3mm spectra of a number of nearby galaxies. There are interesting differences in the chemistry of these galaxies.Comment: published in the Proceedings of the International Astronomical Union (2008), 4. Vol 251, pp 251-256 Cambridge University Pres

Interstellar Turbulence: II. Energy Spectra of Molecular Regions in the Outer Galaxy

The multivariate tool of Principal Component Analysis (PCA) is applied to 23 fields in the FCRAO CO Survey of the Outer Galaxy. PCA enables the identification of line profile differences which are assumed to be generated from fluctuations within a turbulent velocity field. The variation of these velocity differences with spatial scale within a molecular region is described by a singular power law, delta v= c L^alpha which can be used as a powerful diagnostic to turbulent motions. For the ensemble of 23 fields, we find a mean value alpha = 0.62 +- 0.11. From a recent calibration of this method using fractal Brownian motion simulations (Brunt & Heyer 2001), the measured velocity difference-size relationship corresponds to an energy spectrum, E(k), which varies as k^-beta, where beta = 2.17 +- 0.31. We compare our results to both decaying and forced hydrodynamic simulations of turbulence. We conclude that energy must be continually injected into the regions to replenish that lost by dissipative processes such as shocks. The absence of large, widely distributed shocks within the targeted fields suggests that the energy is injected at spatial scales less than several pc.Comment: 24 pages, 10 figures, accepted by Ap

Embedded Stellar Clusters in the W3/W4/W5 Molecular Cloud Complex

We analyze the embedded stellar content in the vicinity of the W3/W4/W5 HII regions using the FCRAO Outer Galaxy 12CO(J=1-0) Survey, the IRAS Point Source Catalog, published radio continuum surveys, and new near-infrared and molecular line observations. Thirty-four IRAS Point Sources are identified that have far-infrared colors characteristic of embedded star forming regions, and we have obtained K' mosaics and 13CO(J=1-0) maps for 32 of them. Ten of the IRAS sources are associated with an OB star and 19 with a stellar cluster, although three OB stars are not identified with a cluster. Half of the embedded stellar population identified in the K' images is found in just the 5 richest clusters, and 61% is contained in IRAS sources associated with an embedded OB star. Thus rich clusters around OB stars contribute substantially to the stellar population currently forming in the W3/W4/W5 region. Approximately 39% of the cluster population is embedded in small clouds with an average mass of ~130 Mo that are located as far as 100 pc from the W3/W4/W5 cloud complex. We speculate that these small clouds are fragments of a cloud complex dispersed by previous episodes of massive star formation. Finally, we find that 4 of the 5 known embedded massive star forming sites in the W3 molecular cloud are found along the interface with the W4 HII region despite the fact that most of the molecular mass is contained in the interior regions of the cloud. These observations are consistent with the classical notion that the W4 HII region has triggered massive star formation along the eastern edge of the W3 molecular cloud.Comment: to appear in ApJS, see http://astro.caltech.edu/~jmc/papers/w

High resolution imaging of CO outflows in OMC-2 and OMC-3

A large scale, high resolution map of CO(1-0) emission toward the OMC-2 and OMC-3 star forming regions is presented. The map is a mosaic of 46 fields using the Berkeley-Illinois-Maryland Array (BIMA) and covers $\sim 10'\times 15'$ at $\sim 10"$ resolution. These data are combined with singledish FCRAO observations and analyzed to identify and determine the properties of nine protostellar outflows. The BIMA data alone almost completely resolve out the cloud emission at central velocities and only recover 1/20 of the flux in the high velocity gas showing that outflows are generally broadly dispersed over $\sim 1'$ angular scales. All nine identified outflows emanate from known Class 0 or borderline Class 0/I sources, are associated with knots of shocked \h2\ emission, and have short dynamical times. It is suggested that only the youngest, most spatially compact, and energetic outflows have been found and that more distributed high velocity gas undetected by BIMA is due to older outflows continuing through the Class I phase of protostellar evolution. The mechanical energy injection rate into the cloud is estimated to be $\sim 1.5 L_\odot$ which is comparable to the turbulent energy dissipation rate. Outf`lows appear capable, therefore, of sustaining cloud turbulence but a high starformation rate is required implying a short cloud lifetime $\leq 5$ `Myr.Comment: Accepted for publication in v591 of the Ap

Identification of Ambient Molecular Clouds Associated with Galactic Supernova Remnant IC443

The Galactic supernova remnant (SNR) IC443 is one of the most studied core-collapse SNRs for its interaction with molecular clouds. However, the ambient molecular clouds with which IC443 is interacting have not been thoroughly studied and remain poorly understood. Using Five College Radio Astronomy Observatory 14m telescope, we obtained fully sampled maps of ~ 1{\deg} \times 1{\deg} region toward IC443 in the 12CO J=1-0 and HCO+ J=1-0 lines. In addition to the previously known molecular clouds in the velocity range v_lsr = -6 to -1 km/s (-3 km/s clouds), our observations reveal two new ambient molecular cloud components: small (~ 1') bright clouds in v_lsr = -8 to -3 km/s (SCs), and diffuse clouds in v_lsr = +3 to +10 km/s (+5 km/s clouds). Our data also reveal the detailed kinematics of the shocked molecular gas in IC443, however the focus of this paper is the physical relationship between the shocked clumps and the ambient cloud components. We find strong evidence that the SCs are associated with the shocked clumps. This is supported by the positional coincidence of the SCs with shocked clumps and other tracers of shocks. Furthermore, the kinematic features of some shocked clumps suggest that these are the ablated material from the SCs upon the impact of the SNR shock. The SCs are interpreted as dense cores of parental molecular clouds that survived the destruction by the pre-supernova evolution of the progenitor star or its nearby stars. We propose that the expanding SNR shock is now impacting some of the remaining cores and the gas is being ablated and accelerated producing the shocked molecular gas. The morphology of the +5 km/s clouds suggests an association with IC443. On the other hand, the -3 km/s clouds show no evidence for interaction.Comment: Accepted for publication in ApJ. 15 pages (with emulateapj.cls), 17 figures, and 2 table

The COMPLETE Survey of Star-Forming Regions: Phase I Data

We present an overview of data available for the Ophiuchus and Perseus molecular clouds from ``Phase I'' of the COMPLETE Survey of Star-Forming Regions. This survey provides a range of data complementary to the Spitzer Legacy Program ``From Molecular Cores to Planet Forming Disks.'' Phase I includes: Extinction maps derived from 2MASS near-infrared data using the NICER algorithm; extinction and temperature maps derived from IRAS 60 and 100um emission; HI maps of atomic gas; 12CO and 13CO maps of molecular gas; and submillimetre continuum images of emission from dust in dense cores. Not unexpectedly, the morphology of the regions appears quite different depending on the column-density tracer which is used, with IRAS tracing mainly warmer dust and CO being biased by chemical, excitation and optical depth effects. Histograms of column-density distribution are presented, showing that extinction as derived from 2MASS/NICER gives the closest match to a log-normal distribution as is predicted by numerical simulations. All the data presented in this paper, and links to more detailed publications on their implications are publically available at the COMPLETE website.Comment: Accepted by AJ. Full resolution version available from: http://www.cfa.harvard.edu/COMPLETE/papers/complete_phase1.pd

The Equilibrium State of Molecular Regions in the Outer Galaxy

A summary of global properties and an evaluation of the equilibrium state of molecular regions in the outer Galaxy are presented from the decomposition of the FCRAO Outer Galaxy Survey and targeted 12CO and 13CO observations of four giant molecular cloud complexes. The ensemble of identified objects includes both small, isolated clouds and clumps within larger cloud complexes. 12CO velocity dispersions show little variation with cloud sizes for radii less than 10 pc. It is demonstrated that the internal motions of regions with molecular masses greater than 10**4 msuns are bound by self gravity, yet, the constituent clumps of cloud complexes and isolated molecular clouds with M < 10**3 msuns are not in self gravitational equilibrium. The required external pressures to maintain the equilibrium of this population are (1-2)x10**4 cm-3-K.Comment: To appear in ApJ, 32 pages, 13 figures, 2 table

Turbulent Gas Flows in the Rosette and G216-2.5 Molecular Clouds: Assessing Turbulent Fragmentation Descriptions of Star Formation

The role of turbulent fragmentation in regulating the efficiency of star formation in interstellar clouds is examined from new wide field imaging of 12CO and 13CO J=1-0 emission from the Rosette and G216-2.5 molecular clouds. The Rosette molecular cloud is a typical star forming giant molecular cloud and G215-2.5 is a massive molecular cloud with no OB stars and very little low mass star formation. The properties of the turbulent gas flow are derived from the set of eigenvectors and eigenimages generated by Principal Component Analysis of the spectroscopic data cubes. While the two clouds represent quite divergent states of star formation activity, the velocity structure functions for both clouds are similar. The sonic scale, lambda_S, defined as the spatial scale at which turbulent velocity fluctuations are equivalent to the local sound speed, and the turbulent Mach number evaluated at 1 pc, M_{1pc}, are derived for an ensemble of clouds including the Rosette and, G216-2.5 regions that span a large range in star formation activity. We find no evidence for the positive correlations between these quantities and the star formation efficiency, that are predicted by turbulent fragmentation models. A correlation does exist between the star formation efficiency and the sonic scale for a subset of clouds with L_{FIR}/M(H_2) > 1 that are generating young stellar clusters. Turbulent fragmentation must play a limited and non-exclusive role in determining the yield of stellar masses within interstellar clouds.Comment: Accepted by ApJ, 22 pages, 7 figure