449 research outputs found
ASTE Simultaneous HCN(4-3) and HCO+(4-3) Observations of the Two Luminous Infrared Galaxies NGC 4418 and Arp 220
We report the results of HCN(J=4-3) and HCO+(J=4-3) observations of two
luminous infrared galaxies (LIRGs), NGC 4418 and Arp 220, made using the
Atacama Submillimeter Telescope Experiment (ASTE). The ASTE wide-band
correlator provided simultaneous observations of HCN(4-3) and HCO+(4-3) lines,
and a precise determination of their flux ratios. Both galaxies showed high
HCN(4-3) to HCO+(4-3) flux ratios of >2, possibly due to AGN-related phenomena.
The J = 4-3 to J = 1-0 transition flux ratios for HCN (HCO+) are similar to
those expected for fully thermalized (sub-thermally excited) gas in both
sources, in spite of HCN's higher critical density. If we assume collisional
excitation and neglect an infrared radiative pumping process, our non-LTE
analysis suggests that HCN traces gas with significantly higher density than
HCO+. In Arp 220, we separated the double-peaked HCN(4-3) emission into the
eastern and western nuclei, based on velocity information. We confirmed that
the eastern nucleus showed a higher HCN(4-3) to HCN(1-0) flux ratio, and thus
contained a larger amount of highly excited molecular gas than the western
nucleus.Comment: 21 pages, 4 figures, accepted for publication in PASJ (Vol.62, No.1,
2010 Feb 25 issue
Sequential Formation of Low-Mass Stars in the BRC 14 Region
We have carried out a deep near-infrared survey of a bright-rimmed molecular
cloud, BRC 14 (IC 1848A). The 10 sigma limiting magnitude of the survey is 17.7
mag at the K-band. Seventy-four sources are classified as young stellar object
(YSO) candidates based on the near-infrared color-color diagram. The faintest
YSO candidates may have masses of an order of tenths of the solar mass,
assuming the age of 1 Myr. We examined three values as indicators of star
formation; fraction of the YSO candidates, extinctions of all sources, and
near-infrared excesses of the YSO candidates. All indicators increase from
outside of the rim to the center of the molecular cloud, which suggests that
the formation of the low-mass stars in the BRC 14 region proceeds from outside
to the center of the cloud.Comment: 12 pages, 5 figures, 1 table, PASJ accepte
ALMA Observations of the Gravitational Lens SDP.9
We present long-baseline ALMA observations of the strong gravitational lens
H-ATLAS J090740.0-004200 (SDP.9), which consists of an elliptical galaxy at
lensing a background submillimeter galaxy into two
extended arcs. The data include Band 6 continuum observations, as well as CO
=65 molecular line observations, from which we measure an updated source
redshift of . The image morphology in the ALMA data is
different from that of the HST data, indicating a spatial offset between the
stellar, gas, and dust component of the source galaxy. We model the lens as an
elliptical power law density profile with external shear using a combination of
archival HST data and conjugate points identified in the ALMA data. Our best
model has an Einstein radius of and a
slightly steeper than isothermal mass profile slope. We search for the central
image of the lens, which can be used constrain the inner mass distribution of
the lens galaxy including the central supermassive black hole, but do not
detect it in the integrated CO image at a 3 rms level of 0.0471 Jy km
s.Comment: Accepted for publication in ApJL; 6 pages, 2 figures, 3 table
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