Berkeley-Illinois-Maryland Association Research Articles

HIGH-RESOLUTION OBSERVATIONS OF MOLECULAR GAS IN THE EARLY-TYPE DWARF GALAXY NGC 404

We present Berkeley–Illinois–Maryland Association CO (1–0) observations of the nearby dwarf elliptical galaxy NGC 404. The detected CO emission is concentrated in a small feature, slightly larger than the beam size, at the center of the optical galaxy. For an assumed CO-to-H2 conversion factor of 2.3 (K km s−1)−1, the molecular gas mass is 9.0 M⊙. The velocity field suggests rotation, with a position angle ~90° different from previous single-dish observations. Both position angles are different from that of the extended H i distribution detected by del Rio et al. The lack of agreement between the postion angle of the CO velocity field and other position angles suggests an external origin for the central molecular gas clump in NGC 404.

Measurement of the cosmological distance scale using X-ray and Sunyaev–Zel'dovich effect observations of galaxy clusters

AbstractX-ray and Sunyaev–Zeldovich effect (SZE) observations of galaxy clusters can be used to measure their distances independently of the cosmic distance ladder. We have determined the distance to 38 clusters of galaxies in the redshift range 0.14 ≤ z ≤ 0.89 using X-ray data from the Chandra X-ray Observatory and SZE data from the Owens Valley Radio Observatory and the Berkeley–Illinois–Maryland Association interferometric arrays. We measure a Hubble constant of H0 = 76.9+3.9−3.4+10.0−8.0 km s−1 Mpc−1 (statistical followed by systematic uncertainties at 68% confidence) for an ΩM=0.3, ΩΛ=0.7 cosmology. Our determination of the Hubble parameter in the distant Universe agrees with measurements from the Hubble Space Telescope Key Project that probed the nearby Universe.

HCN emission from the H ii regions G75.78+0.34 and G75.77+0.34

We present images for the 3.5 mm continuum and HCN(J=1-0) hyperfine line emission from the surroundings of the HII regions G75.78+0.34 and G75.77+0.34 obtained with the Berkeley Illinois Maryland Association (BIMA) interferometer using the D configuration at a spatial resolution of 18 arcsec and spectral sampling of 0.34 km/s. The continuum emission of both objects is dominated by free-free emission from the ionized gas surrounding the exciting stars. Dust emission may contribute only a small fraction of the 3.5 mm continuum from G75.78+0.34 and is negligible for G75.77+0.34. The high spectral resolution reached by BIMA allowed us to separate the emission from each hyperfine transition (F=1-1, F=2-1 and F=0-1), as well as to construct velocity channel maps along each emission-line profile. The HCN flux distributions are similar to those observed for the CO emission, but with some knots of high intensities indicating that the HCN traces high density clouds not seen in CO. The HCN hyperfine line ratios for both HII regions differ from those predicted theoretically for Local Thermodynamic Equilibrium (LTE), probably due to scattering of radiation processes. The velocity channels shows that the HCN emission of G75.78+0.34 follows the bipolar molecular outflows previously observed in CO. For G75.77+0.34, the outflowing gas contributes only a small fraction of the HCN emission.

SIMULTANEOUS OBSERVATIONS OF COMET C/2002 T7 (LINEAR) WITH THE BERKELEY-ILLINOIS-MARYLAND ASSOCIATION AND OWENS VALLEY RADIO OBSERVATORY INTERFEROMETERS: HCN AND CH3OH

We present observations of HCN J = 1-0 and CH_3OH J(K_a, K_c) = 3(1, 3)-4(0, 4) A+ emission from comet C/2002 T7 (LINEAR) obtained simultaneously with the Owens Valley Radio Observatory (OVRO) and Berkeley-Illinois-Maryland Association (BIMA) millimeter interferometers. We combined the data from both arrays to increase the (u, v) sampling and signal to noise of the detected line emission. We also report the detection of CH_3OH J(K_a, K_c) = 8(0, 8)-7(1, 7) A^+ with OVRO data alone. Using a molecular excitation code that includes the effects of collisions with water and electrons, as well as pumping by the Solar infrared photons (for HCN alone), we find a production rate of HCN of 2.9 × 10^(26) s^(–1) and for CH_3OH of 2.2 × 10^(27) s^(–1). Compared to the adopted water production rate of 3 × 10^(29) s^(–1), this corresponds to an HCN/H_2O ratio of 0.1% and a CH_3OH/H_2O ratio of 0.7%. We critically assess the uncertainty of these values due to the noise (~10%), the uncertainties in the adopted comet model (~50%), and the uncertainties in the adopted collisional excitation rates (up to a factor of 2). Pumping by Solar infrared photons is found to be a minor effect for HCN, because our 15 synthesized beam is dominated by the region in the coma where collisions dominate. Since the uncertainties in the derived production rates are at least as large as one-third of the differences found between comets, we conclude that reliable collision rates and an accurate comet model are essential. Because the collisionally dominated region critically depends on the water production rate, using the same approximate method for different comets may introduce biases in the derived production rates. Multiline observations that directly constrain the molecular excitation provide much more reliable production rates.

THE MOLECULAR EMISSION OF THE IRRADIATED STAR-FORMING CORE AHEAD OF HH 80N

We present a Berkeley-Illinois-Maryland Association (BIMA) Array molecular survey of the star forming core ahead of HH 80N, the optically obscured northern counterpart of the Herbig-Haro objects HH 80/81. Continuum emission at 1.4 mm and 8 micron is detected at the center of the core, which confirms the presence of an embedded very young stellar object in the core. All detected molecular species arise in a ring-like structure, which is most clearly traced by CS(2-1) emission. This molecular ring suggests that strong molecular depletion occurs in the inner part of the core (at a radius of ~0.1 pc and densities higher than ~5 x 10^4 cm^{-3}). Despite of the overall morphology and kinematic similarity between the different species, there is significant molecular differentiation along the ring-like structure. The analysis of the chemistry along the core shows that part of this differentiation may be caused by the UV irradiation of the nearby HH 80N object, that illuminates the part of the core facing HH 80N, which results in an abundance enhancement of some of the detected species.

The properties of powerful radio sources at 90 GHz

We have observed a small sample of powerful double radio sources (radio galaxies and quasars) at frequencies around 90 GHz with the Berkeley Illinois Maryland Association (BIMA) millimetre array, with the intention of constraining the resolved high-frequency spectra of radio galaxies. When combined with other sources we have previously observed and with data from the BIMA archive, these observations allow us for the first time to make general statements about the high-frequency behaviour of compact components of radio galaxies – cores, jets and hotspots. We find that cores in our sample remain flat-spectrum up to 90 GHz; jets in some of our targets are detected at 90 GHz for the first time in our new observations and hotspots are found to be almost universal, but show a wide range of spectral properties. Emission from the extended lobes of radio galaxies is detected in a few cases and shows rough consistency with the expectations from standard spectral ageing models, though our ability to probe this in detail is limited by the sensitivity of BIMA. We briefly discuss the prospects for radio galaxy astrophysics with Atacama Large Millimeter Array.

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.

Dense Molecular Gas in a Young Cluster around MWC 1080: Rule of the Massive Star

We present CS -->J = 2→ 1,13CO -->J = 1→ 0, and C18O -->J = 1→ 0, observations with the 10 element Berkeley Illinois Maryland Association (BIMA) array toward the young cluster around the Be star MWC 1080. These observations reveal a biconical outflow cavity with size ~0.3 and 0.05 pc for the semimajor and semiminor axis and ~45° position angle. These transitions trace the dense gas, which is likely the swept-up gas of the outflow cavity, rather than the remaining natal gas or the outflow gas. The gas is clumpy; 32 clumps are identified. The identified clumps are approximately gravitationally bound and consistent with a standard isothermal sphere density, which suggests that they are likely collapsing protostellar cores. The gas kinematics suggests that velocity gradients exist that imply effects from the inclination of the cavity and MWC 1080. The kinematics of dense gas has also been affected by either outflows or stellar winds from MWC 1080, and lower mass clumps are possibly under stronger effects from MWC 1080 than higher mass clumps. In addition, low-mass cluster members tend to be formed in the denser and more turbulent cores, compared to isolated low-mass star-forming cores. This results from the contributions of nearby forming massive stars, such as outflows or stellar winds. Therefore, we conclude that in clusters like the MWC 1080 system, effects from massive stars dominate the star-forming environment in both the kinematics and dynamics of the natal cloud and the formation of low-mass cluster members. This study provides insights into the effects of MWC 1080 on its natal cloud, and suggests a different low-mass star-forming environment in clusters compared to isolated star formation.

A survey of SiO 5 → 4 emission towards outflows from massive young stellar objects

Results are presented of a survey of SiO 5-4 emission observed with the James Clerk Maxwell Telescope (JCMT) towards a sample of outflows from massive young stellar objects. The sample is drawn from a single-distance study by Ridge & Moore. In a sample of 12 sources, the 5-4 line was detected in 5, a detection rate of 42 per cent. This detection rate is higher than that found for a sample of low-luminosity outflow sources, although for sources of comparable luminosity, it is in good agreement with the results of a previous survey of high luminosity sources. For most of the detected sources, the 5-4 emission is compact or slightly extended along the direction of the outflow. NGC6334I shows a clear bipolar flow in the 5-4 line. Additional data were obtained for W3-IRS5, AFGL5142 and W75N for the 2-1 transition of SiO using the Berkeley-Illinois-Maryland Association (BIMA) millimetre interferometer. There is broad agreement between the appearance of the SiO emission in both lines, though there are some minor differences. The 2-1 emission in AFGL5142 is resolved into two outflow lobes which are spatially coincident on the sky, in good agreement with previous observations. In general the SiO emission is clearly associated with the outflow. The primary indicator of SiO 5-4 detectability is the outflow velocity, i.e. the presence of SiO is an indicator of a high velocity outflow. This result is consistent with the existence of a critical shock velocity required to disrupt dust grains and subsequent SiO formation in post-shock gas. There is also weak evidence that higher luminosity sources and denser outflows are more likely to be detected.

Nuclear Bar Catalyzed Star Formation:13CO, C18O, and Molecular Gas Properties in the Nucleus of Maffei 2

We present ~3 resolution maps of CO, its isotopologues, and HCN from in the center of Maffei 2. The J = 1-0 rotational lines of 12CO, 13CO, C18O and HCN, and the J = 2-1 lines of 13CO and C18O were observed with the Owens Valley Radio Observatory ( OVRO) and Berkeley-Illinois- Maryland Association (BIMA) arrays. The lower opacity CO isotopologues give more reliable constraints on H-2 column densities and physical conditions than optically thick 12CO. The J = 2-1/1-0 line ratios of the isotopologues constrain the bulk of the molecular gas to originate in low-excitation, subthermal gas. From large velocity gradient (LVG) modeling, we infer that the central giant molecular clouds (GMCs) have nH2 ~10(2.75) cm^(-3) and T-k ~30 K. Continuum emission at 3.4, 2.7, and 1.4 mm was mapped to determine the distribution and amount of H II regions and dust. Column densities derived from C18O and 1.4 mm dust continuum fluxes indicate the standard Galactic conversion factor overestimates the amount of molecular gas in the center of Maffei 2 by factors of ~2-4. Gas morphology and the clear parallelogram in the position-velocity diagram shows that molecular gas orbits within the potential of a nuclear (~220 pc) bar. The nuclear bar is distinct from the bar that governs the large-scale morphology of Maffei 2. Giant molecular clouds in the nucleus are nonspherical and have large line widths, due to tidal effects. Dense gas and star formation are concentrated at the sites of the x(1)-x(2)-orbit intersections of the nuclear bar, suggesting that the starburst is dynamically triggered.

Barred CO emission in HE 1029-1831

We present CO(1–0) and CO(2–1) line emission maps of the barred spiral active galaxy HE 1029-1831 ($z=0.0403$) obtained with the IRAM Plateau de Bure Interferometer (PdBI) and in part by the Berkeley-Illinois-Maryland Association (BIMA) observatory. The CO emission is well associated with the optical bar and extended along it. The FWHM of the CO emission is estimated to be ~($6\pm2$) kpc. The CO emission shows a strong velocity gradient along the minor axis of the bar (${\rm PA}=90^\circ$). The molecular gas mass is estimated to be ~$1.2\times10^{10}\mathcal{M}_{\odot}$, which indicates a very gas rich host galaxy. Most of the molecular gas appears to be subthermally excited and cold but we also find weak evidence for a warmer and/or denser gas component at the southern part of the bar emission, about ~4 kpc from the galactic nucleus.

Formaldehyde in Comets C/1995 O1 (Hale‐Bopp), C/2002 T7 (LINEAR), and C/2001 Q4 (NEAT): Investigating the Cometary Origin of H2CO

Observations of formaldehyde (H2CO) have been conducted toward comets C/1995 O1 (Hale-Bopp), C/2001 Q4 (NEAT), and C/2002 T7 (LINEAR) using the Arizona Radio Observatory (ARO) 12 m telescope at 1.2 and 2 mm. Aperture synthesis maps of H2CO at 3 mm were made using the Berkeley-Illinois-Maryland Association (BIMA) interferometer toward comet Hale-Bopp. These data indicate that the production rate of H2CO is ~3.7 × 1028 s-1 at ~1 AU in comet Hale-Bopp, using a simple Monte Carlo model, if a nuclear origin for the molecule is assumed. However, maps of H2CO in Hale-Bopp, in comparison with CO, show an extended distribution (rs ~ 15,000 km) with small-scale structure oriented roughly along the comet-Sun direction. This result suggests a source of H2CO other than the comet nucleus. The extended source of formaldehyde is probably grains composed of a mixture of silicates and organic material. The production rate for H2CO increases to Q ~ 1.4 × 1029 s-1 assuming such an extended grain source. This value implies a Q/Q(H2O) ~ 1.4%, which is similar to the production rate ratio of Q/Q(H2O) ~ 4% derived from in situ measurements of H2CO in comet Halley. Production rates for H2CO toward comets C/2002 T7 (LINEAR) and C/2001 Q4 (NEAT) are 1.4 × 1027 and 5.6 × 1026 s-1, respectively, modeled using the extended grain source. The spectra of H2CO measured toward comet C/2002 T7 (LINEAR) show evidence for a second velocity component, most likely arising from comet fragmentation.

Molecular outflows from G35.2-0.74N

We present interferometric observations of the massive star-forming region associated with G35.2-0.74N using the Berkeley Illinois Maryland Association Array. With the aim of better understanding the outflow in this region we observed , and the 2.7 mm continuum. The and continuum emission peak close to the sources G35.2-0.74N (G35.2N) and G35MM2 and indicate a mass of ~ of circumstellar material associated with these sources. The 12CO traces a weak filament of emission coincident with the radio and infrared jet from G35.2N but the emission is dominated by an extended outflow with a NE-SW axis which has a total mass of ~13 . Each lobe of this extended outflow has a hollow shell structure and the location of these shells makes the source G35MM2 a more likely candidate for the source driving the outflow than G35.2N. The mass-velocity distribution is calculated for several parts of the outflow. Fitting these distributions with power laws some of the same break-points are seen as previously identified in the emission from the outflow. We conclude this indicates the temperature dependence of emissivity is not responsible for all the break-points seen and molecular dissociation is a more plausible explanation for their origin. We model the molecular outflow using the ZEUS-2D hydrodynamic code which we have augmented so that it can also track the composition of the gas. We find that a general hydromagnetic wind, without an enchanced, on axis, jet-like component, can reproduce the shape of the observed outflow. Models looking at the time evolution of the stellar wind indicate that the structure of the outflow is dominated by the initial wind conditions, rather than its later evolution. The models also show that scaling the density of the wind profile effects the apparent collimation of the resulting outflow. This may help explain some of the apparent differences between outflows from high mass and low mass young stars.

Giant Molecular Clouds in M31. I. Molecular Cloud Properties

We present Berkeley-Illinois-Maryland Association (BIMA) millimeter interferometer observations of giant molecular clouds (GMCs) along a spiral arm in M31. The observations consist of a survey using the compact configuration of the interferometer and follow-up, higher resolution observations on a subset of the detections in the survey. The data are processed using an analysis algorithm designed to extract GMCs and correct their derived properties for observational biases, thereby facilitating comparison with Milky Way data. The algorithm identifies 67 GMCs, of which 19 have a sufficient signal-to-noise ratio to accurately measure their properties. The GMCs in this portion of M31 are indistinguishable from those found in the Milky Way, having a similar size-line width relationship and distribution of virial parameters, confirming the results of previous, smaller studies. The velocity gradients and angular momenta of the GMCs are comparable to the values measured in M33 and the Milky Way, and in all cases are below expected values based on the local galactic shear. The studied region of M31 has an interstellar radiation field, metallicity, Toomre Q parameter, and midplane volume density similar to those of the inner Milky Way, so the similarity of GMC populations between the two systems is not surprising.

Interferometric Mapping of Magnetic Fields: NGC 2071IR

We present polarization maps of NGC 2071IR from thermal dust emission at 1.3 mm and from CO J = 2 → 1 line emission. The observations were obtained using the Berkeley-Illinois-Maryland Association (BIMA) array in the period 2002-2004. We detected dust and line polarized emission from NGC 2071IR that we used to constrain the morphology of the magnetic field. From CO J = 2 → 1 polarized emission we found evidence for a magnetic field in the powerful bipolar outflow present in this region. We calculated a visual extinction Av ≈ 26 mag from our dust observations. This result, when compared with early single-dish work, seems to show that dust grains emit polarized radiation efficiently at higher densities than previously thought. Mechanical alignment by the outflow is proposed to explain the polarization pattern observed in NGC 2071IR, which is consistent with the observed flattening in this source.

Radio linear and circular polarization from M 81*

We present results from archival Very Large Array (VLA) data and new VLA observations to investigate the long term behavior of the circular polarization of M81*, the nuclear radio source in the nearby galaxy M81. We also used the Berkeley-Illinois-Maryland Association (BIMA) array to observe M81* at 86 and 230 GHz. M81* is unpolarized in the linear sense at a frequency as high as 86 GHz and shows variable circular polarization at a frequency as high as 15 GHz. The spectrum of the fractional circular polarization is inverted in most of our observations. The sign of circular polarization is co nstant over frequency and time. The absence of linear polarization sets a lower limit to the accretion rate of 10 −7 M⊙y −1 . The polarization properties are strikingly similar to the properties of Sgr A *, the central radio source in the Milky Way. This supports the hypothesis that M81* is a scaled up version of Sgr A*. On the other hand, the broad band total intensity spectrum declines towards milimeter wavelengths which differs from previous observations of M81* and also from Sgr A*.

A BIMA Array Survey of Molecules in Comets LINEAR (C/2002 T7) and NEAT (C/2001 Q4)

We present an interferometric search for large molecules, including methanol, methyl cyanide, ethyl cyanide, ethanol, and methyl formate in comets LINEAR (C/2002 T7) and NEAT (C/2001 Q4) with the Berkeley-Illinois-Maryland Association (BIMA) array. In addition, we also searched for transitions of the simpler molecules CS, SiO, HNC, HN13C and 13CO . We detected transitions of methanol and CS around Comet LINEAR and one transition of methanol around Comet NEAT within a synthesized beam of ~20''. We calculated the total column density and production rate of each molecular species using the variable temperature and outflow velocity (VTOV) model described by Friedel et al.(2005).Considering the molecular production rate ratios with respect to water, Comet T7 LINEAR is more similar to Comet Hale-Bopp while Comet Q4 NEAT is more similar to Comet Hyakutake. It is unclear, however, due to such a small sample size, whether there is a clear distinction between a Hale-Bopp and Hyakutake class of comet or whether comets have a continuous range of molecular production rate ratios.

Radio Linear and Circular Polarization from M81*

We present results from archival Very Large Array (VLA) data and new VLA observations to investigate the long term behavior of the circular polarization of M81*, the nuclear radio source in the nearby galaxy M81. We also used the Berkeley-Illinois-Maryland Association (BIMA) array to observe M81* at 86 and 230 GHz. M81* is unpolarized in the linear sense at a frequency as high as 86 GHz and shows variable circular polarization at a frequency as high as 15 GHz. The spectrum of the fractional circular polarization is inverted in most of our observations. The sign of circular polarization is constant over frequency and time. The absence of linear polarization sets a lower limit to the accretion rate of 10−7 M⊙y−1. The polarization properties are strikingly similar to the properties of Sgr A*, the central radio source in the Milky Way. This supports the hypothesis that M81* is a scaled up version of Sgr A*. On the other hand, the broad band total intensity spectrum declines towards milimeter wavelengths which differs from previous observations of M81* and also from Sgr A*.

Interstellar Isomers: The Importance of Bonding Energy Differences

We present strong detections of methyl cyanide (CH3CN), vinyl cyanide (CH2CHCN), ethyl cyanide (CH3CH2CN) and cyanodiacetylene (HC4CN) molecules with the Green Bank Telescope (GBT) toward the Sgr B2(N) molecular cloud. Attempts to detect the corresponding isocyanide isomers were only successful in the case of methyl isocyanide (CH3NC) for its J(sub K) = 1(sub 0) - 0(sub 0) transition, which is the first interstellar report of this line. To determine the spatial distribution of CH3NC, we used archival Berkeley-Illinois-Maryland Association (BIMA) array data for the J(sub K) = 1(sub 0) - 0(sub 0) transitions but no emission was detected. From ab initio calculations, the bonding energy difference between the cyanide and isocyanide molecules is greater than 8500 per centimeter (greater than 12,000 K). Thus, cyanides are the more stable isomers and would likely be formed more preferentially over their isocyanide counterparts. That we detect CH3NC emission with a single antenna (Gaussian beamsize(omega(sub B))=1723 arcsec(sup 2)) but not with an interferometer (omega(sub b)=192 arcsec(sup 2)), strongly suggests that CH3NC has a widespread spatial distribution toward the Sgr B2(N) region. Other investigators have shown that CH3CN is present both in the LMH hot core of Sgr B2(N) and in the surrounding medium, while we have shown that CH3NC appears to be deficient in the LMH hot core. Thus, largescale, non-thermal processes in the surrounding medium may account for the conversion of CH3CN to CH3NC while the LMH hot core, which is dominated by thermal processes, does not produce a significant amount of CH3NC. Ice analog experiments by other investigators have shown that radiation bombardment of CH3CN can produce CH3NC, thus supporting our observations. We conclude that isomers separated by such large bonding energy differences are distributed in different interstellar environments, making the evaluation of column density ratios between such isomers irrelevant unless it can be independently shown that these species are co-spatial.

BIMA Array Detections of HCN in Comets LINEAR (C/2002 T7) and NEAT (C/2001 Q4)

We present interferometric detections of HCN in comets LINEAR (C/2002 T7) and NEAT (C/2001 Q4) with the Berkeley-Illinois-Maryland Association (BIMA) Array. With a 25.4x20.3 synthesized beam around Comet LINEAR and using a variable temperature and outflow velocity (VTOV) model, we found an HCN column density of N_T=6.4+-2.1x10^12 cm^-2, and a production rate of Q(HCN)=6.5+-2.2x10^26 s^-1, giving a production rate ratio of HCN relative to H_2O of ~3.3+-1.1x10^-3 and relative to CN of ~4.6+-1.5. With a 21.3x17.5 synthesized beam around Comet NEAT and using a VTOV model, we found an HCN column density of N_T=8.5+-4.5x10^11 cm^-2, and a production rate of Q(HCN)=8.9+-4.7x10^25 s^-1, giving a production rate ratio of HCN relative to H_2O of ~7.4+-3.9x10^-4 and relative to CN of ~0.3+-0.2. For both comets, the production rates relative to H_2O are similar to those found in previous comet observations. For Comet LINEAR the production rate relative to CN is consistent with HCN being the primary parent species of CN, while for Comet NEAT it is too low for this to be the case.