ABSTRACT: The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey (NGLS)
comprises an HI-selected sample of 155 galaxies spanning all morphological
types with distances less than 25 Mpc. We describe the scientific goals of the
survey, the sample selection, and the observing strategy. We also present an
atlas and analysis of the CO J=3-2 maps for the 47 galaxies in the NGLS which
are also part of the Spitzer Infrared Nearby Galaxies Survey. We find a wide
range of molecular gas mass fractions in the galaxies in this sample and
explore the correlation of the far-infrared luminosity, which traces star
formation, with the CO luminosity, which traces the molecular gas mass. By
comparing the NGLS data with merging galaxies at low and high redshift which
have also been observed in the CO J=3-2 line, we show that the correlation of
far-infrared and CO luminosity shows a significant trend with luminosity. This
trend is consistent with a molecular gas depletion time which is more than an
order of magnitude faster in the merger galaxies than in nearby normal
galaxies. We also find a strong correlation of the L(FIR)/L(CO3-2) ratio with
the atomic to molecular gas mass ratio. This correlation suggests that some of
the far-infrared emission originates from dust associated with atomic gas and
that its contribution is particularly important in galaxies where most of the
gas is in the atomic phase.
ABSTRACT: The question whether or not the initial mass function is universal, i.e. the
same in all kinds of environments, is of critical importance for the theory of
star formation and still intensely debated. A top-heavy initial mass function
may be the result of star formation out of dense molecular clouds with a
temperature of ~ 100 K. Such a molecular gas phase is not commonly found in the
Galactic plane, but may be present in active environments like cores of
starburst galaxies or AGN. Unfortunately, the kinetic temperature of the
molecular gas in external galaxies is often not well constrained. Having proven
the diagnostic power of selected formaldehyde lines as tracers of the
properties of the molecular gas in external galaxies, we have engaged in
observing these diagnostic lines in a number of starburst galaxies or near AGN.
This contribution presents the latest results of these studies.
ABSTRACT: There is growing evidence that the properties of the molecular gas in the nuclei of starburst galaxies and in AGN may be very different from those seen in Galactic star forming regions and that a high kinetic temperature in the molecular gas may lead to a non-standard initial mass function in the next generation of stars. Unfortunately, among the fundamental parameters derived from molecular line observations, the kinetic temperature of the molecular gas in external galaxies is often not well determined due to a lack of suitable tracer molecules. We discuss the diagnostic power of selected transition lines of formaldehyde (H_2CO), which can be used as a molecular thermometer as well as an excellent tracer of the molecular gas density. As a proof of concept, we present the results of our multi-transition line study of the H_2CO emission from the prototypical starburst galaxy M82. Using our large velocity gradient model, we tightly constrain the physical properties of the dense gas in the prominent molecular lobes, completely independent of the standard "cloud thermometer" ammonia (NH_3) or other molecular tracers. Our results agree well with the properties of the high-excitation molecular gas component found in the most comprehensive CO studies. Our observations also indicate that there may be an asymmetry between the two molecular lobes.
ABSTRACT: Using the IRAM 30 m telescope and the 15 m JCMT, we explore the value of paraformaldehyde (p-H2CO) as a tracer of density and temperature of the molecular gas in external galaxies. The target of our observations are the lobes of the molecular ring around the center of the nearby prototypical starburst galaxy M82. It is shown that p-H2CO provides one of the rare direct molecular thermometers. Reproducing the measured line intensities with a large velocity gradient (LVG) model, we find densities of nH2 ~ 7 × 103 cm −3 and kinetic temperatures of Tkin ~ 200 K. The derived kinetic temperature is significantly higher than the dust temperature or the temperature deduced from ammonia (NH3) lines, but our results agree well with the properties of the high-excitation component seen in CO. We also present the serendipitous discovery of the 42→ 31 line of methanol (CH3OH) in the northeastern lobe, which shows—unlike CO and H2CO—significantly different line intensities in the two lobes.
The Astrophysical Journal 12/2008; 671(2):1579. · 6.02 Impact Factor
ABSTRACT: We demonstrate the diagnostic value of para-formaldehyde (p-H2CO) as a tracer of the density and the temperature of the molecular gas in external galaxies using the prototypical starburst galaxy M 82 as an example. We also report the discovery of the methanol line CH3OH(42 to 3_1,E) from M 82.
EAS Publications Series 01/2008; 31:189-190.
ABSTRACT: Using the IRAM 30-m telescope and the 15-m JCMT, we explore the value of para-formaldehyde (p-H_2CO) as a tracer of density and temperature of the molecular gas in external galaxies. The target of our observations are the lobes of the molecular ring around the center of the nearby prototypical starburst galaxy M 82. It is shown that p-H_2CO provides one of the rare direct molecular thermometers. Reproducing the measured line intensities with a large velocity gradient (LVG) model, we find densities of n_H2 ~ 7 10^3 cm^-3 and kinetic temperatures of T_kin ~ 200 K. The derived kinetic temperature is significantly higher than the dust temperature or the temperature deduced from ammonia (NH_3) lines, but our results agree well with the properties of the high-excitation component seen in CO. We also present the serendipitous discovery of the 4_2 - 3_1 line of methanol (CH_3OH) in the northeastern lobe, which shows -- unlike CO and H_2CO -- significantly different line intensities in the two lobes. Comment: 32 pages, 6 figures, accepted for publication by the Astrophysical Journal, for a pdf version with color figures, see http://www.astro.utoronto.ca/~muehle/papers/h2co1.pdf
ABSTRACT: The radical CN, through the CN/HCN ratio, has proven to be an exceptionally good tool to study the photodissociation regions (PDRs) dominated by FUV radiation. Our region of interest, the circumnuclear disk (CND) surrounding Sgr A*, is exposed to the strong UV radiation field originating from the central stellar cluster. It contains potentially star forming cores recently elucidated by interferometric HCN observations with OVRO by Christopher et al. (2005). We present the results of preliminary observations of CN (N = 2-l) transitions with the IRAM 30-m telescope and report, for the first time, detection of CN emission in the GC region indicative of PDR, activity. This work motivates the further investigation of the role of PDRs in the clumpy medium of the Galactic center (GC) environment in global photodissociation and in promoting or inhibiting star formation in the CND.
Journal of Physics Conference Series 12/2006; 54(1):81.
ABSTRACT: We report millimetre-wave continuum observations of symbiotic stars
obtained using the Swedish-ESO Submillimetre Telescope, the James Clerk
Maxwell Telescope and the Owens Valley Radio Observatory millimetre
array. Complementary centimetre-wave observations from the Very Large
Array and the Australia Telescope Compact Array, often obtained within
weeks of the millimetre-wave data, are also described. As a result of
these measurements, the number of symbiotics observed at millimetre
wavelengths has increased from 6 to 32, adding He2-38, BICru, He2-104,
He2-106 (= V835Cen), He2-171, He2-176, AS210, H1-36, AS289, K3-9, CHCyg,
RRTel and ZAnd to the list of those detected. We note that several
sources are variable at millimetre wavelengths and we discuss these
objects individually. Additionally, we report 0.45-mm upper limits for
HMSge and V1016Cyg - dusty symbiotics previously detected at 0.8-2.0mm.
We demonstrate that most of the symbiotics detected at centimetre
wavelengths, including several with known binary periods, will fall
above the detection threshold of new millimetre-wave bolometer arrays,
thus allowing us more stringently to test the standard binary models for
symbiotic radio emission. In Paper II we shall describe our fits to the
data presented here, concentrating on prototypical systems such as ZAnd
Monthly Notices of the Royal Astronomical Society 02/1995; 273:517-527. · 4.90 Impact Factor
ABSTRACT: K3-9 ranks among the most intense symbiotic radio sources, and most of
those that are brighter have experienced very slow nova outbursts within
the last century. The intruiging combination of extreme visual faintness
and high radio flux density led us to obtain multi-frequency coverage in
order to determine physical parameters of the source. We report
measurements of K3-9 covering five orders of magnitude in wavelength,
including the first IR, millimetre and radio data. Near-IR spectra and
photometry clearly demonstrate that the system contains a late-type
giant (a Mira or OH/IR star such as those found in D-type symbiotics)
which is probably shrouded in a dusty circumbinary envelope. This
reconciles the level of radio and IR emission with the visual magnitude
and the high Balmer decrement. The radio spectrum is similar to that of
other symbiotic Miras and is best represented by a single power law with
spectral index alpha=0.81+/-0.02 it flattens at a frequency of
approximately 8 GHz, before steepening again beyond 90 GHz. This
submillimetre flux excess is probably due to emission from dust
(possibly material lost by the hot star, or by one or more symbiotic
nova outbursts) and it is reminiscent of R Aqr which also has its
spectral turnover hidden by dust emission. The implied dust mass is
0.01-0.15 M_solar for 30<T_d<300 K, respectively. The ionized
region in K3-9 has been slightly resolved (FWHM~0.1 arcsec~750au) by the
A configuration of the Very Large Array at 8.44 GHz and by the BnA
configuration at 22.5 GHz. We have determined the systemic distance and
made model-dependent estimates of the Mira's mass-loss rate, the binary
separation and the Lyman continuum luminosity.
Monthly Notices of the Royal Astronomical Society 01/1995; 272:878-884. · 4.90 Impact Factor