Narayanan, Gopal

Job Title

Research Assistant Professor, Department of Astronomy, College of Natural Sciences

Last Name

Narayanan

First Name

Gopal

Discipline

Astrophysics and Astronomy

Expertise

Development of advanced m\m and sub-mm receivers.
Molecular clouds and star formation
Radio astronomy

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Search Results

Now showing 1 - 10 of 13

Detection of Infall Signatures toward Serpens SMM4
(2002-01-01) Narayanan, Gopal; Moriarty-Schieven, G; Walker, CK; Butner, HM
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.
Star formation in bright-rimmed clouds. I. Millimeter and submillimeter molecular line surveys
(2002-01-01) De Vries, CH; Narayanan, Gopal; Snell, Ronald L.
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.
Entrainment Mechanisms for Outflows in the L1551 Star-Forming Region
(2006-01-01) Stojimirovív, Irena; Narayanan, Gopal; Snell, Ronald L.; Bally, John
We present high sensitivity 12/13CO(1-0) molecular line maps covering the full extent of the parsec scale L1551 molecular outflow, including the redshifted east-west (EW) flow. We also present 12CO(3-2) data that extends over a good fraction of the area mapped in the 1-0 transition. We compare the molecular data to widefield, narrow-band optical emission in Hα. While there are multiple outflows in the L1551 cloud, the main outflow is oriented at 50\arcdeg position angle and appears to be driven by embedded source(s) in the central IRS 5 region. The 3-2 data indicate that there may be molecular emission associated with the L1551 NE jet, within the redshifted lobe of main outflow. We have also better defined the previously known EW flow and believe we have identified its blueshifted counterpart. We further speculate that the origin of the EW outflow lies near HH 102. We use velocity dependent opacity correction to estimate the mass and the energy of the outflow. The resulting mass spectral indices from our analysis, are systematically lower (less steep) than the power law indices obtained towards other outflows in several recent studies that use a similar opacity correction method. We show that systematic errors and biases in the analysis procedures for deriving mass spectra 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 emission maps of the 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.
Discovery of a Molecular Outflow in the Haro 6-10 Star-forming Region
(2008-01-01) Stojimirović, Irena; Narayanan, Gopal; Snell, Ronald L.
We present high sensitivity 12CO and 13CO J=1!0 molecular line maps covering the full extent of the parsec scale Haro 6-10 Herbig-Haro (HH) flow. We report the discovery of a molecular CO outflow along the axis of parsec-scale HH flow. Previous molecular studies missed the identification of the outflow probably due to their smaller mapping area and the confusing spectral features present towards the object. Our detailed molecular line study of the full 1.6 pc extent of the optical flow shows evidence for both blueshifted and redshifted gas set in motion by Haro 6-10 activity. The molecular outflow is centered at Haro 6-10, with redshifted gas being clumpy and directed towards the northeast, while blueshifted gas is in the southwest direction. The molecular gas terminates well within the cloud, short of the most distant HH objects of the optical flow. Contamination from an unrelated cloud along the same line of sight prevents a thorough study of the blueshifted outflow lobe and the mass distribution at the lowest velocities in both lobes. The cloud core in which Haro 6-10 is embedded is filamentary and flattened in the east-west direction. The total cloud mass is calculated from 13CO J=1--0 to be ~ 200 M⊙. The lower limit of the mass associated with the outflow is ~0.25 M⊙.
THE REDSHIFT SEARCH RECEIVER 3 MM WAVELENGTH SPECTRA OF 10 GALAXIES
(2011-01-01) Snell, Ronald L.; Narayanan, Gopal; Yun, Min; Heyer, M; Chung, A; Irvine, William M.; Erickson, NR; Liu, G
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 Molecular 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 13CO/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 104 cm–3.
The Five College Radio Astronomy Observatory CO mapping survey of the Taurus molecular cloud
(2008-01-01) Narayanan, Gopal; Heyer, MH; Brunt, C; Goldsmith, PF; Snell, Ronald L.; Li, D
The FCRAO Survey of the Taurus molecular cloud observed the 12CO and 13CO J = 1–0 emission from 98 deg2 of this important, nearby, star-forming region. This set of data with 45'' resolution comprises the highest spatial dynamic range image of an individual molecular cloud constructed to date and provides valuable insights to the molecular gas distribution, kinematics, and the star formation process. In this contribution, we describe the observations, calibration, data processing, and characteristics of the noise and line emission of the survey. The angular distribution of 12CO and 13CO emission over 1 km s−1 velocity intervals and the full velocity extent of the cloud are presented. These reveal a complex, dynamic medium of cold, molecular gas.
Multiple parsec-scale outflows in the NGC 2071 cluster
(2008-01-01) Stojimirovic, I; Snell, Ronald L.; Narayanan, Gopal
We present high-sensitivity large-scale mapping results of the NGC 2071 cluster in Orion and its surrounding environment in 12CO and 13CO J = 1→ 0 molecular line tracers. The data were obtained at the FCRAO 14 m telescope with an angular resolution of ~45''. We show that the known outflow in NGC 2071 has a larger extent than previously reported, reaching 1.7 pc at its lowest velocities. We also report the discovery of two new outflows: the bipolar north outflow, located approximately 4' north of the main outflow, and the southeast outflow, which originates near the main outflow and has only a redshifted component. We compare our molecular-line data to the H2 data of Eislöffel and find a morphological match between the CO and H2 outflows. We also identify possible driving sources for the two new outflows from the SCUBA image of this region. We use multiple lines of evidence, including the mass-velocity relation, position-velocity maps, and the morphological relationship between the H2 and CO emission, to distinguish between entrainment models for each of these flows. Jet entrainment is the dominant entrainment mechanism in the three outflows observed in NGC 2071. The mass of the main outflow, over velocities where the outflow dominates, is 14.8 M. Likewise, the mass of the southeast redshifted-only outflow is 7.6 M, suggesting that it may also be driven by a luminous YSO. The mass of the north outflow is much smaller (1.4 M) and is more consistent with outflows driven by low-mass stars.
Kinematics of Protostellar Objects in the ρ Ophiuchus A Region
(2006-01-01) Narayanan, Gopal; Logan, DW
We present the detection of infall, rotation, and outflow kinematic signatures toward both a protostellar source, VLA 1623, and what was initially thought to be a pre-protostellar core, SM 1N, in the ρ Ophiuchus A region. The kinematic signatures of early star formation were detected in the dense molecular gas surrounding the embedded sources using high signal-to-noise ratio millimeter and submillimeter data. Centroid velocity maps made with HCO+ J = 4 → 3 and J = 1 → 0 line emission exhibit the blue bulge signature of infall, which is predicted to be seen when infall motion dominates over rotational motion. Further evidence for infalling gas is found in the HCO+ blue asymmetric line profiles and red asymmetric opacity profiles. We also performed CO J = 3 → 2 and J = 1 → 0 observations to determine the direction, orientation, and extent of molecular outflows, and we report the discovery of a new bipolar outflow possibly driven by SM 1N.
Large-scale structure of the molecular gas in Taurus revealed by high linear dynamic range spectral line mapping
(2008-01-01) Goldsmith, PF; Heyer, M; Narayanan, Gopal; Snell, Ronald L.; Li, D; Brunt, C
We report the results of a 100 deg2 survey of the Taurus molecular cloud region in 12CO and 13CO J = 1→ 0. The image of the cloud in each velocity channel includes 3 × 106 Nyquist-sampled pixels on a 20'' grid. The high sensitivity and large spatial dynamic range of the maps reveal a very complex, highly structured cloud morphology, including filaments, cavities, and rings. The axes of the striations seen in the 12CO emission from relatively diffuse gas are aligned with the direction of the magnetic field. We have developed a statistical method for analyzing the pixels in which 12CO but not 13CO is detected, which allows us to determine the CO column in the diffuse portion of the cloud, as well as in the denser regions in which we detect both isotopologues. Using a column-density-dependent model for the CO fractional abundance, we derive the mass of the region mapped to be 2.4 × 104 M, more than twice as large as would be obtained using a canonical fixed fractional abundance of 13CO, and a factor of 3 greater than would be obtained considering only the high column density regions. We determine that half the mass of the cloud is in regions having column density below 2.1 × 1021 cm−2. The distribution of young stars in the region covered is highly nonuniform, with the probability of finding a star in a pixel with a specified column density rising sharply for N(H2) = 6 × 1021 cm−2. We determine a relatively low star formation efficiency (mass of young stars/mass of molecular gas), between 0.3% and 1.2%, and an average star formation rate during the past 3 Myr of 8 × 10−5 s
Spectra of Nearby Galaxies Measured with a New Very Broadband Receiver
(2008-01-01) Narayanan, Gopal; Snell, Ronald L.; Erickson, NR; Chung, Aeree; Heyer, Mark H.; Yun, Min; Irvine, William M.
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 14 m by measuring the 3 mm spectra of a number of nearby galaxies. There are interesting differences in the chemistry of these galaxies.