Gopal Narayanan

Star Formation in Bright-rimmed Clouds. I. Millimeter and Submillimeter Molecular Line Surveys

We present the results of the first detailed millimeter and submillimeter molecular line survey of bright-rimmed clouds, observed at FCRAO in the CO (J = 1 → 0), C18O (J = 1 → 0), HCO+ (J = 1 → 0), H13CO+ (J = 1 → 0), and N2H+ (J = 1 → 0) transitions, and at the Heinrich Hertz Telescope in the CO (J = 2 → 1), HCO+ (J = 3 → 2), HCO+ (J = 4 → 3), H13CO+ (J = 3 → 2), and H13CO+ (J = 4 → 3) molecular line transitions. The source list is composed of a selection of bright-rimmed clouds from the catalog of such objects compiled by Sugitani et al. We also present observations of three Bok globules done for comparison with the bright-rimmed clouds. We find that the appearance of the millimeter CO and HCO+ emission is dominated by the morphology of the shock front in the bright-rimmed clouds. The HCO+ (J = 1 → 0) emission tends to trace the swept-up gas ridge and overdense regions, which may be triggered to collapse as a result of sequential star formation. Five of the seven bright-rimmed clouds we observe seem to have an outflow; however, only one shows the spectral line blue-asymmetric signature that is indicative of infall in the optically thick HCO+ emission. We also present evidence that in bright-rimmed clouds the nearby shock front may heat the core from outside-in, thereby washing out the normally observed line infall signatures seen in isolated star-forming regions. We find that the derived core masses of these bright-rimmed clouds are similar to other low- and intermediate-mass star-forming regions.

First-Overtone CO Variability in Young Stellar Objects

We have monitored the 2.3 μm Δv = 2 CO bands toward young stellar objects that are predominantly of low luminosity (L < 10,000 L☉) and show evidence of mass loss. The CO emission can be highly variable, on timescales as short as a few days. In DG Tau, the bands have been observed to disappear and reappear and may also have a periodic modulation. For the BN object, the equivalent width has varied by a factor of 3; and for V1331 Cyg, the equivalent width doubled in 9 days. Changes in equivalent width also occurred in SSV 13, AS 353A, and 1548C27, while WL 16 and S106 have not shown variations. Of the nine CO absorption sources reobserved, only the FU Ori-type star V1057 Cyg went through a significant change in equivalent width. It also presents an unusual and variable band profile.

Entrainment Mechanisms for Outflows in the L1551 Star-forming Region

We present high sensitivity 12CO and 13CO J = 1 → 0 maps covering the full extent of the parsec-scale L1551 molecular outflow, including the redshifted east-west (EW) flow. We also present 12CO J = 3 → 2 data obtained over a good fraction of the L1551 outflow. We compare the molecular data to wide-field, narrowband optical emission in Hα. While there are multiple outflows in the L1551 cloud, the main outflow is oriented at 50° position angle and appears to be driven by an embedded source(s) in the central IRS 5 region. The J = 3 → 2 data indicate that there may be molecular emission associated with the L1551 NE jet, within the redshifted lobe of the main outflow. We have also better defined the EW flow and believe we have identified its blueshifted counterpart. We speculate that the origin of the EW outflow lies near HH 102. Velocity-dependent opacity correction is used to estimate the mass and energy of the outflow. The resulting mass spectral indices from our analysis are systematically lower (less steep) than the power-law indices obtained toward other outflows in several recent studies that use a similar opacity correction method. We show that systematic errors and biases in the mass analysis procedures could result in errors in the determination of the power-law indices. The mass spectral indices, the morphological appearance of the position-velocity plots, and integrated intensity maps of molecular data, compared with the optical, suggest that jet-driven bow shock entrainment is the best explanation for the driving mechanism of outflows in L1551. The kinetic energy of the outflows is found to be comparable to the binding energy of the cloud and sufficient to maintain the turbulence in the L1551 cloud.

Molecular outflows identified in the FCRAO CO survey of the Taurus Molecular Cloud

Jets and outflows are an integral part of the star formation process. While there are many detailed studies of molecular outflows towards individual star-forming sites, few studies have surveyed an entire star-forming molecular cloud for this phenomenon. The 100-deg2 Five College Radio Astronomy Observatory CO survey of the Taurus Molecular Cloud provides an excellent opportunity to undertake an unbiased survey of a large, nearby, molecular cloud complex for molecular outflow activity. Our study provides information on the extent, energetics and frequency of outflows in this region, which are then used to assess the impact of outflows on the parent molecular cloud. The search identified 20 outflows in the Taurus region, eight of which were previously unknown. Both 12CO and 13CO data cubes from the Taurus molecular map were used, and dynamical properties of the outflows are derived. Even for previously known outflows, our large-scale maps indicate that many of the outflows are much larger than previously suspected, with eight of the outflows (40 per cent) being more than a parsec long. The mass, momentum and kinetic energy from the 20 outflows are compared to the repository of turbulent energy in Taurus. Comparing the energy deposition rate from outflows to the dissipation rate of turbulence, we conclude that outflows by themselves cannot sustain the observed turbulence seen in the entire cloud. However, when the impact of outflows is studied in selected regions of Taurus, it is seen that locally outflows can provide a significant source of turbulence and feedback. The L1551 dark cloud which is just south of the main Taurus complex was not covered by this survey, but the outflows in L1551 have much higher energies compared to the outflows in the main Taurus cloud. In the L1551 cloud, outflows can not only account for the turbulent energy present, but are probably also disrupting their parent cloud. We conclude that for a molecular cloud like Taurus, an L1551-like episode occurring once every 105 years is sufficient to sustain the turbulence observed. Five of the eight newly discovered outflows have no known associated stellar source, indicating that they may be embedded Class 0 sources. In Taurus, 30 per cent of Class I sources and 12 per cent of flat-spectrum sources from the Spitzer young stellar object (YSO) catalogue have outflows, while 75 per cent of known Class 0 objects have outflows. Overall, the paucity of outflows in Taurus compared to the embedded population of Class I and flat-spectrum YSOs indicates that molecular outflows are a short-lived stage marking the youngest phase of protostellar life. The current generation of outflows in Taurus highlight an ongoing period of active star formation, while a large fraction of YSOs in Taurus have evolved well past the Class I stage.

The Redshift Search Receiver 3 mm Wavelength Spectra of 10 Galaxies

The 3 mm wavelength spectra of 10 galaxies have been obtained at the Five College Radio Astronomy Observatory using a new, very broadband receiver and spectrometer, called the Redshift Search Receiver (RSR). The RSR has an instantaneous bandwidth of 37 GHz covering frequencies from 74 to 111 GHz, and has a spectral resolution of 31 MHz (�100 km s −1 ). During tests of the RSR on the FCRAO 14 m telescope the complete 3 mm spectra of the central regions of NGC 253, Maffei 2, NGC1068, IC 342, M82, NGC 3079, NGC 3690, NGC 4258, Arp 220 and NGC 6240 were obtained. Within the wavelength band covered by the RSR, 20 spectral lines from 14 different atomic and molecular species were detected. Based on simultaneous fits to the spectrum of each galaxy, a number of key molecular line ratios are derived. A simple model which assumes the emission arises from an ensemble of Milky Way-like Giant Nolecular Cloud cores can adequately fit the observed line ratios using molecular abundances based on Galactic molecular cloud cores. Variations seen in some line ratios, such as 13 CO/HCN and HCO + /HCN, can be explained if the mean density of the molecular gas varies from galaxy to galaxy. However, NGC 3690, NGC 4258 and NGC 6240 show very large HCO + /HCN ratios and require significant abundance enhancement of HCO + over HCN, possible due to the proximity to active galactic nucleus activity. Finally, the mass of dense molecular gas is estimated and we infer that 25-85% of the total molecular gas in the central regions of these galaxies must have densities greater than 10 4 cm −3 . Subject headings: galaxies: ISM —ISM: Molecules — ISM: Abundances — Radio Lines: galaxies

Detection of Infall Signatures toward Serpens SMM4

We present the detection of kinematic infall signatures toward the Class 0 protostellar system SMM4 in the Serpens cloud core. We have observed the dense molecular gas toward the embedded source using millimeter and submillimeter line transitions of density sensitive molecular tracers. High signal-to-noise ratio maps obtained in HCO+ J = 1 → 0, J = 3 → 2, and J = 4 → 3, and CS J = 2 → 1 show the blue-bulge infall signature. The blue-bulge infall signature can be observed in the centroid velocity maps of protostellar objects when infall dominates over rotation. The line profiles of HCO+ and CS exhibit the characteristic blue asymmetric line profile signature consistent with infall. In addition, HCO+ and CS optical depth profiles obtained using isotopic observations show a red asymmetry also consistent with an infall interpretation. Using three-dimensional radiative transfer models based on the rotating, collapse model of Terebey, Shu, & Cassen, we derive infall parameters of the source. To determine the direction and orientation of molecular outflows in the larger Serpens cluster, wide-field mapping of CO J = 1 → 0 emission was also performed.

The Intrinsic Shape of Sagittarius A* at 3.5-mm Wavelength

The radio emission from Sgr A

Early Science with the Large Millimeter Telescope: COOL BUDHIES I - a pilot study of molecular and atomic gas at z ≃ 0.2

^\ast

The Red Radio Ring: a gravitationally lensed hyperluminous infrared radio galaxy at z = 2.553 discovered through the citizen science project Space Warps

is thought to be powered by accretion onto a supermassive black hole of

Early Science with the Large Millimeter Telescope: Observations of Extremely Luminous High-z Sources Identified by Planck

\sim\! 4\times10^6~ \rm{M}_\odot