129 research outputs found
Molecular gas in low-metallicity starburst galaxies: Scaling relations and the CO-to-H conversion factor
We study the molecular content and the star formation efficiency of 21 Blue
Compact Dwarfs (BCDs). We present CO(1-0) and (2-1) observations, further
supplemented with additional CO measurements and multiwavelength ancillary data
from the literature. We find the CO luminosity to be correlated with the
stellar and HI masses, SFR tracers, the size of the starburst and its
metallicity. BCDs appear offset from the Schmidt-Kennicutt (SK) law, showing
extremely low (0.1 Gyr) H2 and H2+HI depletion timescales. The
departure from the SK law is smaller when considering H2+HI rather than H2
only, and is larger for BCDs with lower metallicity and higher specific SFR.
Thus, the molecular fraction and H2 depletion timescale of BCDs is found to be
strongly correlated with metallicity. Using this and assuming that the
empirical correlation found between the specific SFR and galaxy-averaged H2
depletion timescale of more metal-rich galaxies extends to lower masses, we
derive a metallicity-dependent CO-to-H2 conversion factor , with in qualitative agreement
with previous determinations, dust-based measurements, and recent model
predictions. Our results suggest that in vigorously star-forming dwarfs the
fraction of H2 traced by CO decreases by a factor of about 40 from to , leading to a strong underestimation of
the H2 mass in metal-poor systems when a Galactic is
considered. Adopting we find that departures from the SK law
are partially resolved. Our results suggest that starbursting dwarfs have
shorter depletion gas timescales and lower molecular fractions compared to
normal late-type disc galaxies even accounting for the molecular gas not traced
by CO emission in metal-poor environments, raising additional constraints to
model predictions (Abridged).Comment: 18 pages, 14 Figures, 4 Tables: Accepted for publication in A&
Detection and Mapping of Decoupled Stellar and Ionized Gas Structures in the Ultraluminous Infrared Galaxy IRAS 12112+0305
Integral field optical spectroscopy with the INTEGRAL fiber-fed system and
HST optical imaging are used to map the complex stellar and warm ionized gas
structure in the ultraluminous infrared galaxy IRAS 12112+0305. Images
reconstructed from wavelength-delimited extractions of the integral field
spectra reveal that the observed ionized gas distribution is decoupled from the
stellar main body of the galaxy, with the dominant continuum and emission-line
regions separated by projected distances of up to 7.5 kpc. The two optical
nuclei are detected as apparently faint emission-line regions, and their
optical properties are consistent with being dust-enshrouded weak-[OI] LINERs.
The brightest emission-line region is associated with a faint (m_{I}= 20.4),
giant HII region of 600 pc diameter, where a young (about 5 Myr) massive
cluster of about 2 10 dominates the ionization.
Internal reddening towards the line-emitting regions and the optical nuclei
ranges from 1 to 8 magnitudes, in the visual. Taken the reddening into aacount,
the overall star formation in IRAS 12112+0305 is dominated by starbursts
associated with the two nuclei and corresponding to a star formation rate of 80
yr.Comment: 2 figures, accepted to Ap.J. Letter
The dusty disk around VV Ser
We have carried out observations at millimeter and centimeter wavelengths
towards VV Ser using the Plateau de Bure Interferometer and the Very Large
Array. This allows us to compute the SED from near infrared to centimeter
wavelengths. The modeling of the full SED has provided insight into the dust
properties and a more accurate value of the disk mass.
The mass of dust in the disk around VV Ser is found to be about 4 10^(-5)
Msun, i.e. 400 times larger than previous estimates. Moreoever, the SED can
only be accounted for assuming dust stratification in the vertical direction
across the disk. The existence of small grains (0.25--1 micron) in the disk
surface is required to explain the emission at near- and mid-infrared
wavelengths. The fluxes measured at millimeter wavelengths imply that the dust
grains in the midplane have grown up to very large sizes, at least to some
centimeters.Comment: To appear in Ap
The First CO Map of a Low Surface Brightness Galaxy
Using the Owens Valley Radio Observatory Millimeter-Wavelength Array (OVRO)
we have obtained the first CO map of a low surface brightness (LSB) galaxy. The
studied galaxy, UGC 01922, was chosen for these observations because both of
its previous CO detection with the IRAM 30m telescope and its classification as
a Malin 1 `cousin' - an LSB galaxy with M_HI > 10^10 Msol. The OVRO map
detected approximately 65% of the CO(1-0) flux found earlier with the single
dish measurements, giving a detected gas mass equivalent to M_H2 = 1.1X10^9
Msol. The integrated gas peak lies at the center of the galaxy and coincides
with both the optical and 1.4 GHz continuum emission peaks. The molecular gas
extends well beyond the OVRO beam size (~4'' or 3 kpc), covering ~25% of the
optical bulge. In all, perhaps the most remarkable aspect of this map is its
unexceptional appearance. Given that it took over ten years to successfully
detect molecular gas in any low surface brightness system, it is surprising
that the appearance and distribution of UGC 01922's CO is similar to what would
be expected for a high surface brightness galaxy in the same morphological
class.Comment: 5 pages, including 3 figures and 3 tables. also available online at
http://www.gb.nrao.edu/~koneil. Accepted by ApJ
A CO Survey of Young Planetary Nebulae
We report the results of a sensitive survey of young planetary nebulae in the
CO J=2-1 line that significantly increases the available data on warm, dense,
molecular gas in the early phases of planetary nebula formation. The
observations were made using the IRAM 30 m telescope with the 3 by 3 pixel
Heterodyne Receiver Array (HERA). The array provides an effective means of
discriminating the CO emission of planetary nebulae in the galactic plane from
contaminating emission of interstellar clouds along the line of sight. 110
planetary nebulae were observed in the survey and 40 were detected. The results
increase the number of young planetary nebulae with known CO emission by
approximately a factor of two. The CO spectra yield radial velocities for the
detected nebulae, about half of which have uncertain or no velocity
measurements at optical wavelengths. The CO profiles range from parabolic to
double-peaked, tracing the evolution of structure in the molecular gas. The
line widths are significantly larger than on the Asymptotic Giant Branch, and
many of the lines show extended wings, which probably result from the effects
on the envelopes of high velocity jets.Comment: 29 pages, 2 figures (with multiple panels), to be published in
Astrophysical Journal Supplement Serie
Sub-arcsecond CO(1-0) and CO(2-1) observations of the ultraluminous infrared galaxy IRAS 10190+1322
We present the results of high resolution mapping of the CO(1-0) and CO(2-1)
emission of the ultraluminous infrared galaxy (ULIRG) IRAS 10190+1322, with the
IRAM interferometer, down to an angular resolution of ~0.3 arcsec. This object
is composed of two interacting galaxies with a projected nuclear separation of
6 kpc, and was selected to analyze the physical and dynamical properties of the
molecular gas in each galaxy in order to study the conditions that lead a
galaxy pair to become ultraluminous in the infrared. With the exception of Arp
220, the closest ULIRG, this is the first time that the CO emission is
morphologically and kinematically resolved in the two interacting galaxies of a
ULIRG system. In one of the galaxies the molecular gas is highly concentrated,
distributed in a circumnuclear disk of 1.7 kpc in size. The molecular gas in
the presumably less infrared luminous galaxy is distributed in a more extended
disk of 7.4 kpc. The molecular gas mass accounts for ~10% of the dynamical mass
in each galaxy. Both objects are rich enough in molecular gas, Mgas ~ 4 10^9
Msun, as to experience an infrared ultraluminous phase.Comment: 4 pages, 3 figures. Accepted for publication in A&A Letters Special
Issue for the new extended configuration of the Plateau de Bure
Interferomete
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