99 research outputs found
The molecular cloud content of early type galaxies
A survey of the CO content of early type galaxies led to 24 new detections, mostly lenticular galaxies. The galaxies, which are situated in both the Northern and Southern Hemispheres, were selected as being far-IR luminous compared to their blue luminosity, and situated at distances less than about 50 Mpc (H sub o=100 km/s Mpc(-1). Results for some early galaxies (NGC 404, NGC 3593 and NGC 4369 are given
Detection of CO (J=1-0) in the dwarf elliptical galaxy NGC 185
The detection of CO (J = 1-0) emission in the dwarf elliptical galaxy NGC 185 is reported. The presence of massive molecular clouds in this early-type galaxy supports the idea of recent or ongoing stellar formation indicated by the population of blue stars in the center. The CO was detected in two positions in the galaxy, the center, and a prominent dustcloud. The emission profile has two peaks, roughly centered around the systemic velocity. It is found that NGC 185 is overluminous in blue light for its CO luminosity compared with Sc galaxies. This might indicate a higher star-formation efficiency for NGC 185 than for the late-type galaxies
ALMA Observations of Molecular Absorption in the Gravitational Lens PMN 0134-0931
We report the detection of molecular absorption lines at z=0.7645 towards the
radio-loud QSO PMN 0134-0931. The CO J=2-1 and HCO+ J=2-1 lines are seen in
absorption along two different lines of sight to lensed images of the
background QSO. The lines of sight are separated by ~0.7", corresponding to 5
kpc in the lens plane. PMN 0134-0931 represents one out of only five known
molecular absorption line systems at cosmologically significant distances.
Moreover, it is also one of three such systems where the absorption occurs in a
galaxy acting as a gravitational lens. The absorption lines through the two
lines of sight are shifted by 215+/-8 km/s, possibly representing rotational
motion in one of the lensing galaxies. The absorption profiles are wide, ~200
km/s, suggesting that the absorption occurs in a highly inclined disk galaxy
with a flat rotation curve and a cloud-cloud velocity dispersion ~30 km/s.
Gravitational lens models require two equal mass galaxies to account for the
observed configuration of lensed images. The presence of two galaxies in close
proximity means that they might be interacting and potentially merging and the
kinematics of the molecular gas may not reflect ordered rotational motion. The
column densities of both CO and HCO+ are normal for diffuse molecular gas
towards one of the lensed images, but significantly higher towards the other.
Also, the abundance ratio N(CO)/N(HCO+) is 2-3 times higher than in typical
diffuse molecular gas. It is plausible that the second line of sight probes
denser molecular gas than what is normally the case for absorption.Comment: 17 pages, 4 figures, 4 table
The complex molecular absorption line system at z=0.886 towards PKS1830-211
New millimeter wave observations of the molecular absorption line system in
the gravitational lens to PKS1830-211 at z=0.88582 is presented.
Self-calibrated interferometer data shows unequivocally that the previously
detected absorption component is associated with the gravitationally lensed
south-west image of the background source. A second absorption line of
HCO+(2-1) at z=0.88582 is detected. This component is shifted in velocity by
-147 km/s relative to the main absorption line, and is shown to be associated
with the north-east image. These two absorption lines are used to constrain the
mass of the lensing galaxy. Upper limits to absorption and emission lines from
the possible absorption system at z=0.1927, seen in 21cm HI by Lovell et al,
are reported.Comment: 16 pages, 7 figures, Accepted for publication in Ap
Steadily Increasing Star Formation Rates in Galaxies Observed at 3 <~ z <~ 5 in the CANDELS/GOODS-S Field
We investigate the star formation histories (SFHs) of high redshift (3 <~ z
<~ 5) star-forming galaxies selected based on their rest-frame ultraviolet (UV)
colors in the CANDELS/GOODS-S field. By comparing the results from the
spectral-energy-distribution-fitting analysis with two different assumptions
about the SFHs --- i.e., exponentially declining SFHs as well as increasing
ones, we conclude that the SFHs of high-redshift star-forming galaxies increase
with time rather than exponentially decline. We also examine the correlations
between the star formation rates (SFRs) and the stellar masses. When the
galaxies are fit with rising SFRs, we find that the trend seen in the data
qualitatively matches the expectations from a semi-analytic model of galaxy
formation. The mean specific SFR is shown to increase with redshift, also in
agreement with the theoretical prediction. From the derived tight correlation
between stellar masses and SFRs, we derive the mean SFH of star-forming
galaxies in the redshift range of 3 <~ z <~ 5, which shows a steep power-law
(with power alpha = 5.85) increase with time. We also investigate the formation
timescales and the mean stellar population ages of these star-forming galaxies.
Our analysis reveals that UV-selected star-forming galaxies have a broad range
of the formation redshift. The derived stellar masses and the stellar
population ages show positive correlation in a sense that more massive galaxies
are on average older, but with significant scatter. This large scatter implies
that the galaxies' mass is not the only factor which affects the growth or star
formation of high-redshift galaxies.Comment: 31 pages, 8 figures, 2 table
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