127 research outputs found
Cold Molecular Gas Along the Merger Sequence in Local Luminous Infrared Galaxies
We present an initial result from the 12CO (J=1-0) survey of 79 galaxies in
62 local luminous and ultra-luminous infrared galaxy (LIRG and ULIRG) systems
obtained using the 45 m telescope at the Nobeyama Radio Observatory. This is
the systematic 12CO (J=1-0) survey of the Great Observatories All-sky LIRGs
Survey (GOALS) sample. The molecular gas mass of the sample ranges 2.2 x 10^8 -
7.0 x 10^9 Msun within the central several kiloparsecs subtending 15" beam. A
method to estimate a size of a CO gas distribution is introduced, which is
combined with the total CO flux in the literature. The method is applied to a
part of our sample and we find that the median CO radius is 1-4 kpc. From the
early stage to the late stage of mergers, we find that the CO size decreases
while the median value of the molecular gas mass in the central several kpc
region is constant. Our results statistically support a scenario where
molecular gas inflows towards the central region from the outer disk, to
replenish gas consumed by starburst, and that such a process is common in
merging LIRGs.Comment: 25 pages, 22 figures, accepted for publication in Ap
The Diversity of Diffuse Ly Nebulae around Star-Forming Galaxies at High Redshift
We report the detection of diffuse Ly emission, or Ly halos
(LAHs), around star-forming galaxies at and in the NOAO
Deep Wide-Field Survey Bo\"otes field. Our samples consist of a total of
1400 galaxies, within two separate regions containing spectroscopically
confirmed galaxy overdensities. They provide a unique opportunity to
investigate how the LAH characteristics vary with host galaxy large-scale
environment and physical properties. We stack Ly images of different
samples defined by these properties and measure their median LAH sizes by
decomposing the stacked Ly radial profile into a compact galaxy-like
and an extended halo-like component. We find that the exponential scale-length
of LAHs depends on UV continuum and Ly luminosities, but not on
Ly equivalent widths or galaxy overdensity parameters. The full
samples, which are dominated by low UV-continuum luminosity Ly emitters
(), exhibit LAH sizes of 5kpc. However, the
most UV- or Ly-luminous galaxies have more extended halos with
scale-lengths of 7kpc. The stacked Ly radial profiles decline
more steeply than recent theoretical predictions that include the contributions
from gravitational cooling of infalling gas and from low-level star formation
in satellites. On the other hand, the LAH extent matches what one would expect
for photons produced in the galaxy and then resonantly scattered by gas in an
outflowing envelope. The observed trends of LAH sizes with host galaxy
properties suggest that the physical conditions of the circumgalactic medium
(covering fraction, HI column density, and outflow velocity) change with halo
mass and/or star-formation rates.Comment: published in ApJ, minor proof corrections applie
The FUV to Near-IR Morphologies of Luminous Infrared Galaxies in the GOALS Sample
We compare the morphologies of a sample of 20 LIRGs from the Great
Observatories All-sky LIRG Survey (GOALS) in the FUV, B, I and H bands, using
the Gini (G) and M20 parameters to quantitatively estimate the distribution and
concentration of flux as a function of wavelength. HST images provide an
average spatial resolution of ~80 pc. While our LIRGs can be reliably
classified as mergers across the entire range of wavelengths studied here,
there is a clear shift toward more negative M20 (more bulge-dominated) and a
less significant decrease in G values at longer wavelengths. We find no
correlation between the derived FUV G-M20 parameters and the global measures of
the IR to FUV flux ratio, IRX. Given the fine resolution in our HST data, this
suggests either that the UV morphology and IRX are correlated on very small
scales, or that the regions emitting the bulk of the IR emission emit almost no
FUV light. We use our multi-wavelength data to simulate how merging LIRGs would
appear from z~0.5-3 in deep optical and near-infrared images such as the HUDF,
and use these simulations to measure the G-M20 at these redshifts. Our
simulations indicate a noticeable decrease in G, which flattens at z >= 2 by as
much as 40%, resulting in mis-classifying our LIRGs as disk-like, even in the
rest-frame FUV. The higher redshift values of M20 for the GOALS sources do not
appear to change more than about 10% from the values at z~0. The change in
G-M20 is caused by the surface brightness dimming of extended tidal features
and asymmetries, and also the decreased spatial resolution which reduced the
number of individual clumps identified. This effect, seen as early as z~0.5,
could easily lead to an underestimate of the number of merging galaxies at
high-redshift in the rest-frame FUV.Comment: Accepted for publication in the Astronomical Journal. The total page
count is 15 pages with 13 figures and 1 Tabl
ALMA [NII] 205 micron Imaging Spectroscopy of the Interacting Galaxy System BRI 1202-0725 at Redshift 4.7
We present the results from Atacama Large Millimeter/submillimeter Array
(ALMA) imaging in the [NII] 205 micron fine-structure line (hereafter [NII])
and the underlying continuum of BRI 1202-0725, an interacting galaxy system at
4.7, consisting of an optical QSO, a sub-millimeter galaxy (SMG) and two
Lyman- emitters (LAEs), all within 25 kpc of the QSO. We detect
the QSO and SMG in both [NII] and continuum. At the (or 6.6 kpc)
resolution, both QSO and SMG are resolved in [NII], with the de-convolved major
axes of 9 and 14 kpc, respectively. In contrast, their continuum
emissions are much more compact and unresolved even at an enhanced resolution
of . The ratio of the [NII] flux to the existing CO (76) flux is
used to constrain the dust temperature () for a more accurate
determination of the FIR luminosity . Our best estimated equals K for both galaxies (assuming an emissivity index
). The resulting ratios are
statistically consistent with that of local luminous infrared galaxies,
confirming that traces the star formation (SF) rate (SFR) in
these galaxies. We estimate that the on-going SF of the QSO (SMG) has a SFR of
5.1 yr ( 30%) assuming Chabrier
initial mass function, takes place within a diameter (at half maximum) of 1.3
(1.5) kpc, and shall consume the existing 5 of
molecular gas in 10 years.Comment: 4 pages, 1 table, 4 figures; accepted for publication in the ApJ
Letter
ALMA Observation of NGC5135: The Circumnuclear CO(6-5) and Dust Continuum Emission at 45 Parsec Resolution[]
We present high-resolution (0.17\arcsec 0.14\arcsec) Atacama Large
Millimeter/submillimeter Array (ALMA) observations of the CO\,(6-5) line, and
435\um\ dust continuum emission within a 9\arcsec 9\arcsec\ area
centered on the nucleus of the galaxy NGC\,5135. NGC\,5135 is a well-studied
luminous infrared galaxy that also harbors a Compton-thick active galactic
nucleus (AGN). At the achieved resolution of 48 40\,pc, the CO\,(6-5)
and dust emissions are resolved into gas "clumps" along the symmetrical dust
lanes associated with the inner stellar bar. The clumps have radii between
45-180\,pc and CO\,(6-5) line widths of 60-88\,\kms. The CO\,(6-5)
to dust continuum flux ratios vary among the clumps and show an increasing
trend with the \FeII/Br- ratios, which we interpret as evidence for
supernova-driven shocked gas providing a significant contribution to the \co65\
emission. The central AGN is undetected in continuum, nor in CO\,(6-5) if its
line velocity width is no less than \,40\,\kms. We estimate that the AGN
contributes at most 1\% of the integrated CO\,(6-5) flux of 512
24Jy\kms\ within the ALMA field of view, which in turn accounts for
32\% of the CO\,(6-5) flux of the whole galaxy.Comment: 21 pages, 12 figures, Accepted for publication in Ap
A broadband millimeter-wave spectrometer Z-Spec: sensitivity and ULIRGs
Z-Spec is a cryogenic, broadband, millimeter-wave grating spectrometer. It is capable of obtaining many spectral lines simultaneously because of its unprecedented broad bandwidth (185-305GHz). The bandpass covers the 1mm atmospheric transmission window with a resolving power of 250-400. Z-Spec uses 160 silicon nitride micromesh bolometers cooled down to less than 100mK for background-limited performance. The unique capability of Z-Spec to detect multiple lines simultaneously allows us to obtain information efficiently on the physical and chemical conditions of nearby Ultra-luminous Infrared Galaxies (ULIRGs) powered by starbursts or Active Galactic Nuclei. Here we report on new millimeter-wave broadband data for ULIRGs acquired with Z-Spec and the noise performance and achieved sensitivity in observations with the CSO. We found that during the observations the noise scales with the atmospheric opacity and can be explained well by our sensitivity model, considering the photon noise originating from the sky and the telescope, as well as the detector and electronics noise. The photon noise is found to dominate the total noise
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