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B. E. Warren,
C. D. Wilson,
F. P. Israel,
S. Serjeant,
G. J. Bendo,
E. Brinks,
D. L. Clements, J. A. Irwin,
J. H. Knapen,
J. Leech, [......],
G. Petitpas,
E. Sinukoff,
K. Spekkens,
B. K. Tan,
R. P. J. Tilanus,
A. Usero,
P. P. van der Werf,
C. Vlahakis,
T. Wiegert,
and M. Zhu
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ABSTRACT: We present the results of large-area 12CO J = 3-2 emission mapping of three nearby field galaxies, NGC 628, NGC 3521, and NGC 3627, completed at the James Clerk Maxwell Telescope as part of the Nearby Galaxies Legacy Survey. These galaxies all have moderate to strong 12CO J = 3-2 detections over large areas of the fields observed by the survey, showing resolved structure and dynamics in their warm/dense molecular gas disks. All three galaxies were part of the Spitzer Infrared Nearby Galaxies Survey sample, and as such have excellent published multiwavelength ancillary data. These data sets allow us to examine the star formation properties, gas content, and dynamics of these galaxies on sub-kiloparsec scales. We find that the global gas depletion time for dense/warm molecular gas in these galaxies is consistent with other results for nearby spiral galaxies, indicating this may be independent of galaxy properties such as structures, gas compositions, and environments. Similar to the results from The H I Nearby Galaxy Survey, we do not see a correlation of the star formation efficiency with the gas surface density consistent with the Schmidt-Kennicutt law. Finally, we find that the star formation efficiency of the dense molecular gas traced by 12CO J = 3-2 is potentially flat or slightly declining as a function of molecular gas density, the 12CO J = 3-2/J = 1-0 ratio (in contrast to the correlation found in a previous study into the starburst galaxy M83), and the fraction of total gas in molecular form.
The Astrophysical Journal 04/2010; 714(1):571. · 6.02 Impact Factor
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ABSTRACT: We present a multiwavlength infrared (IR) study of the nearby, edge-on, spiral galaxy NGC 891. We have examined 20 independent, spatially resolved IR images of this galaxy, 14 of which are newly reduced and/or previously unpublished images. These images span a wavelength regime from λ 1.2 μm in which the emission is dominated by cool stars, through the mid-IR, in which emission is dominated by polycyclic aromatic hydrocarbons (PAHs), to λ 850 μm, in which emission is dominated by cold dust in thermal equilibrium with the radiation field. The changing morphology of the galaxy with wavelength illustrates the changing dominant components. We detect extraplanar dust emission in this galaxy, consistent with previously published results, but now show that PAH emission is also in the halo, to a vertical distance of z≥ 2.5 kpc. We compare the vertical extents of various components and find that the PAHs (from λ 7.7 and 8 μm data) and warm dust (λ 24 μm) extend to smaller z heights than the cool dust (λ 450 μm). For six locations in the galaxy for which the signal-to-noise ratio was sufficient, we present spectral energy distributions (SEDs) of the IR emission, including two in the halo – the first time a halo SED in an external galaxy has been presented. We have modelled these SEDs and find that the PAH fraction, fPAH, is similar to Galactic values (within a factor of 2), with the lowest value at the galaxy's centre, consistent with independent results of other galaxies. In the halo environment, the fraction of dust exposed to a colder radiation field, fcold, is of the order of unity, consistent with an environment in which there is no star formation. The source of excitation is likely from photons escaping from the disc.
Monthly Notices of the Royal Astronomical Society 04/2009; 395(1):97 - 113. · 4.90 Impact Factor
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J. A. Irwin,
G. L. Hoffman,
K. Spekkens,
M. P. Haynes,
R. Giovanelli,
S. M. Linder,
B. Catinella,
E. Momjian,
B. S. Koribalski,
J Davies,
E. Brinks,
W. J. G. de Blok,
M. E. Putman,
W. van Driel
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ABSTRACT: We have conducted a deep, complete HI survey, using Arecibo/ALFA, of a field
centered on the nearby, isolated galaxy, NGC 2903, which is similar to the
Milky Way in its properties. The field size was 150 kpc x 260 kpc and the final
velocity range spanned from 100 to 1133 km/s. The ALFA beams have been mapped
as a function of azimuth and cleaned from each azimuth-specific cube prior to
forming final cubes. The final HI data are sensitive down to an HI mass of 2 x
10^5 Mo and column density of 2 x 10^{17} cm^{-2} at the 3sigma x 2deltaV
level, where sigma is the rms noise level and deltaV is the velocity
resolution. NGC 2903 is found to have an HI envelope that is larger than
previously known, extending to at least 3 times the optical diameter of the
galaxy. Our search for companions yields one new discovery with an HI mass of
2.6 x 10^6 Mo. The companion is 64 kpc from NGC 2903 in projection, is likely
associated with a small optical galaxy of similar total stellar mass, and is
dark matter dominated, with a total mass >10^8 Mo. In the region surveyed,
there are now two known companions: our new discovery and a previously known
system that is likely a dwarf spheroidal, lacking HI content. If HI constitutes
1% of the total mass in all possible companions, then we should have detected
230 companions, according to LCDM predictions. Consequently, if this number of
dark matter clumps are indeed present, then they contain less than 1% HI
content, possibly existing as very faint dwarf spheroidals or as starless,
gasless dark matter clumps.
10/2008;
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Judith A Irwin,
C D Wilson,
T Wiegert,
G J Bendo,
B E Warren,
Q D Wang,
F P Israel,
S Serjeant,
J H Knapen,
E Brinks,
R P J Tilanus,
P Van Der Werf,
S Mühle, J A Irwin
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ABSTRACT: Accepted year month day. Received year month day; in original form year month day ABSTRACT We have made the first map of CO(J=3-2) emission covering the disk of the edge-on galaxy, NGC 4631, which is known for its spectacular gaseous halo. The strongest emission, which we model with a Gaussian ring, occurs within a radius of 5 kpc. Weaker disk emission is detected out to radii of 12 kpc, the most extensive molecular component yet seen in this galaxy. From comparisons with infrared data, we find that CO(J=3-2) emission more closely follows the hot dust component, rather than the cold dust, consistent with it being a good tracer of star formation. The first maps of R 3−2/1−0 , H 2 mass surface density and SFE have been made for the inner 2.4 kpc radius region. Only 20% of the SF occurs in this region and excitation conditions are typical of galaxy disks, rather than of central starbursts. The SFE suggests long gas consumption timescales (> 10 9 yr). The velocity field is dominated by a steeply rising rotation curve in the region of the central molecular ring followed by a flatter curve in the disk. A very steep gradient in the rotation curve is observed at the nucleus, providing the first evidence for a central concentration of mass: M dyn = 5 × 10 7 M ⊙ within a radius of 282 pc. The velocity field shows anomalous features indicating the presence of molecular outflows; one of them is associated with a previously observed CO(J=1-0) expanding shell. Consistent with these outflows is the presence of a thick (z up to 1.4 kpc) CO(J=3-2) disk. We suggest that the interaction between NGC 4631 and its companion(s) has agitated the disk and also initiated star formation which was likely higher in the past than it is now. These may be necessary conditions for seeing prominent halos.
Mon. Not. R. Astron. Soc. 09/2008; 000:1-21.
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ABSTRACT: We study the edge-on galaxy NGC 5775, utilizing a 58.2 ks {\sl Chandra} ACIS-S observation together with complementary {\sl HST} ACS, {\sl Spitzer} IRAC and other multi-wavelength data sets. This edge-on galaxy, with its disk-wide active star formation, is particularly well-suited for studying the disk/halo interaction on sub-galactic scales. We detect 27 discrete X-ray sources within the $D_{25}$ region of the galaxy, including an ultra-luminous source with a 0.3-7 keV luminosity of $\sim7\times10^{40}\rm ergs s^{-1}$. The source-removed diffuse X-ray emission shows several prominent extraplanar features, including a $\sim10\rm kpc$ diameter ``shell-like'' feature and a ``blob'' reaching a projected distance of $\sim25\rm kpc$ from the galactic disk. The bulk of the X-ray emission in the halo has a scale height of $\sim$1.5 kpc and can be characterized by a two-temperature optically thin thermal plasma with temperatures of $\sim$ 0.2 and 0.6 keV and a total 0.3-2 keV luminosity of $\sim3.5\times10^{39}\rm ergs s^{-1}$. The high-resolution, multi-wavelength data reveal the presence of several extraplanar features around the disk, which appear to be associated with the in-disk star formation. We suggest that hot gas produced with different levels of mass loading can have different temperatures, which may explain the characteristic temperatures of hot gas in the halo. We have obtained a sub-galactic scale X-ray-intensity-star formation relation, which is consistent with the integrated version in other star forming galaxies.
08/2008;
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ABSTRACT: We present the first high-resolution study of the disk-halo interface in an edge-on galaxy (NGC 5775) in which every component of the interstellar medium is represented and resolved. New single-dish CO J=2-1 and CO J=1-0 data, ROSAT X-ray data, and HIRES IRAS data are presented along with HI data which emphasizes the high latitude features. In conjunction with previously published radio continuum (6 and 20 cm) and H alpha data, we find spatial correlations between various ISM components in that all components of the ISM are present in the disk-halo features (except for CO for which there is insufficient spatial coverage). The HI features extend to about 7 kpc above the plane. In one case, a loop is detected in position-velocity space, and are also observed over a large velocity range. This implies that the disk-halo features represent expanding supershells. However, the shells may be incomplete and partially open-topped, suggesting that we are observing the breakup of the supershells as they traverse the disk-halo interface. There is some evidence for acceleration with z height and both redshifted and blueshifted velocities are present, although the gas which is lagging with respect to galactic rotation dominates. The radio continuum spectral index is flatter around the shell rims, suggesting that shocks may be important in these regions (thermal contribution can not account for this flattening). The H alpha emission is located interior to the HI. For feature F3, the H alpha emission forms the interior "skin" of the HI shell, yet there appears to be a minimum of in-disk star formation immediately below the feature. We present a picture of a "typical" HI supershell which accelerates and breaks up through the disk-halo interface. Such a feature is likely internally generated via an energetic event in the disk. Comment: 14 pages plus 12 jpg figures, accepted for publication by the Astron. & Astrophy. Journal
08/2001;
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The Journal of the Royal Astronomical Society of Canada. Royal Astronomical Society of Canada 11/1998; 92:26.
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ABSTRACT: We present a multi-wavelength study of the disk-halo interface of the
edge-on galaxy, NGC 5775. This interacting galaxy is known to host a
number of high-latitude, kpc-scale HI supershells. Based on the
observations, we offer a likely anatomy of the supershells and propose
that the supershells are most probably internally generated rather than
results of external cloud impacts.
240:396.
