86 research outputs found
Why Are Ring Galaxies Interesting?
Compared with ordinary spirals, the ISM in ring galaxies experiences markedly
different physical conditions and evolution. As a result, ring galaxies provide
interesting perspectives on the triggering/quenching of large scale star
formation and the destructive effects of massive stars on molecular cloud
complexes. We use high resolution radio, sub-millimeter, infrared, and optical
data to investigate the role of gravitational stability in star formation
regulation, factors influencing the ISM's molecular fraction, and evidence of
peculiar star formation laws and efficiencies in two highly evolved ring
galaxies: Cartwheel and the Lindsay-Shapley ring.Comment: 6 pages with 4 figures (2 color). To appear in the conference
proceedings for "Galaxy Wars: Stellar Populations and Star Formation in
Interacting Galaxies"
Spitzer Observations of Tidal Dwarf Galaxies
We present Spitzer observations of Tidal Dwarf Galaxies (TDGs) in three interacting systems: NGC 5291, Arp 105 & Stephanâs Quintet. The spectra show bright emission from polyaromatic hydrocarbons (PAHs), nebular lines and warm molecular hydrogen, characteristic of recent episodes of star formation. The PAH emission that falls in the IRAC 8.0 ”m band leads to the TDGs having an extremely red IRAC color, with [4.5] â [8.0] \u3e 3. The emission from PAHs is characterized by a model with mainly neutral 100-C PAH atoms
Wheels of Fire. IV: Star Formation and the Neutral ISM in the Ring Galaxy AM0644-741
We combine data from the Australia Telescope National Facility and Swedish ESO Submillimeter Telescope to investigate the neutral interstellar medium (ISM) in AM0644-741, a large and robustly star-forming ring galaxy. The galaxy\u27s ISM is concentrated in the 42 kpc diameter starburst ring, but appears dominated by atomic gas, with a global molecular fraction (f mol) of only 0.062 ± 0.005. Apart from the starburst peak, the gas ring appears stable against the growth of gravitational instabilities (Q gas = 3-11). Including the stellar component lowers Q overall, but not enough to make Q \u3c 1 everywhere. High star formation efficiencies (SFEs) follow from the ring\u27s low H2 content. AM0644-741\u27s star formation law is highly peculiar: H I obeys a Schmidt law while H2 is uncorrelated with star formation rate density. Photodissociation models yield low volume densities in the ring, especially in the starburst quadrant (n 2 cmâ3), implying a warm neutral medium dominated ISM. At the same time, the ring\u27s pressure and ambient far-ultraviolet radiation field lead to the expectation of a predominantly molecular ISM. We argue that the ring\u27s high SFE, low f mol and n, and peculiar star formation law follow from the ISM\u27s 100 Myr confinement time in the starburst ring, which amplifies the destructive effects of embedded massive stars and supernovae. As a result, the ring\u27s molecular ISM becomes dominated by small clouds, causing to be significantly underestimated by 12CO line fluxes: in effect, X CO X Gal despite the ring\u27s â„solar metallicity. The observed H I is primarily a low-density photodissociation product, i.e., a tracer rather than a precursor of massive star formation. Such an over-cooked ISM may be a general characteristic of evolved starburst ring galaxies
Molecular Gas and Star Formation in the Cartwheel
Atacama Large Millimeter/submillimeter Array (ALMA) 12CO(J=1-0) observations
are used to study the cold molecular ISM of the Cartwheel ring galaxy and its
relation to HI and massive star formation (SF). CO moment maps find
M of H associated with the inner ring
(72%) and nucleus (28%) for a Galactic I(CO)-to-N(H2) conversion factor
(). The spokes and disk are not detected. Analysis of the
inner ring's CO kinematics show it to be expanding ( km
s) implying an Myr age. Stack averaging reveals CO emission
in the starburst outer ring for the first time, but only where HI surface
density () is high, representing M for a metallicity appropriate
, giving small ( M
pc), molecular fraction (), and H depletion
timescales ( Myr). Elsewhere in the outer ring
M pc,
and Myr (all ). The inner ring and
nucleus are H-dominated and are consistent with local spiral SF laws.
in the outer ring appears independent of ,
or . The ISM's long confinement in the
robustly star forming rings of the Cartwheel and AM0644-741 may result in
either a large diffuse H component or an abundance of CO-faint low column
density molecular clouds. The H content of evolved starburst rings may
therefore be substantially larger. Due to its lower and age
the Cartwheel's inner ring has yet to reach this state. Alternately, the outer
ring may trigger efficient SF in an HI-dominated ISM.Comment: 10-pages text; 5-figure
Development of biospecimen sample preparation techniques for molecular imaging using ultra-high resolution mass spectrometry [abstract]
Matrix assisted laser desorption ionization (MALDI) imaging is a technique which analyzes and maps the distribution of molecules in two-dimensional biospecimens, such as histological tissue sections. To-date, the classifications of molecules imaged using this technique is nearly comprehensive to those found in all tissues and include proteins, lipids, peptides, carbohydrates, nucleic acids, drugs, metabolites and other molecules. Using an imaging mass spectrometer, two-dimensional images may be produced by "staining" an optical image with an overlay of the distributions of multiple specific mass signals, elucidating the molecular architecture within the context of a biospecimen. In the future, MALDI imaging may revolutionize early-state disease diagnosis, biomarker discovery, drug development and personalized medicine
Molecular Gas and Star Formation in the Cartwheel
Atacama Large Millimeter/submillimeter Array 12CO(J = 1â0) observations are used to study the cold molecular ISM of the Cartwheel ring galaxy and its relation to H i and massive star formation (SF). CO moment maps find (2.69 ± 0.05) Ă 109 Mâ of H2 associated with the inner ring (72%) and nucleus (28%) for a Galactic ICO-to- conversion factor (αCO). The spokes and disk are not detected. Analysis of the inner ring\u27s CO kinematics shows it to be expanding (Vexp = 68.9 ± 4.9 km sâ1), implying an â70 Myr age. Stack averaging reveals CO emission in the starburst outer ring for the first time, but only where H i surface density (ÎŁH i) is high, representing Mâ for a metallicity-appropriate αCO, giving small (3.7 Mâ pcâ2), molecular fraction (fmol = 0.10), and H2 depletion timescales (Ïmol â 50â600 Myr). Elsewhere in the outer ring Mâ pcâ2, fmol 0.1 and Ïmol 140â540 Myr (all 3Ï). The inner ring and nucleus are H2 dominated and are consistent with local spiral SF laws. ÎŁSFR in the outer ring appears independent of ÎŁH i, or The ISM\u27s long confinement in the robustly star-forming rings of the Cartwheel and AM0644-741 may result in either a large diffuse H2 component or an abundance of CO-faint low column density molecular clouds. The H2 content of evolved starburst rings may therefore be substantially larger. Due to its lower ÎŁSFR and age, the Cartwheel\u27s inner ring has yet to reach this state. Alternately, the outer ring may trigger efficient SF in a H i-dominated ISM
Detection of [O III] at z~3: A Galaxy above the Main Sequence, Rapidly Assembling its Stellar Mass
We detect bright emission in the far infrared fine structure [O III] 88m
line from a strong lensing candidate galaxy, H-ATLAS J113526.3-014605,
hereafter G12v2.43, at z=3.127, using the generation Redshift (z)
and Early Universe Spectrometer (ZEUS-2) at the Atacama Pathfinder Experiment
Telescope (APEX). This is only the fifth detection of this far-IR line from a
sub-millimeter galaxy at the epoch of galaxy assembly. The observed [O III]
luminosity of likely
arises from HII regions around massive stars, and the amount of Lyman continuum
photons required to support the ionization indicate the presence of
equivalent O5.5 or higher stars;
where would be the lensing magnification factor. The observed line
luminosity also requires a minimum mass of in ionized gas, that is
of the estimated total molecular gas mass of
. We compile multi-band
photometry tracing rest-frame UV to millimeter continuum emission to further
constrain the properties of this dusty high redshift star-forming galaxy. Via
SED modeling we find G12v2.43 is forming stars at a rate of 916
and already has a stellar
mass of . We also
constrain the age of the current starburst to be 5 million years,
making G12v2.43 a gas rich galaxy lying above the star-forming main sequence at
z3, undergoing a growth spurt and, could be on the main sequence within
the derived gas depletion timescale of 66 million years.Comment: 11 pages, 3 figures, accepted for publication in The Astrophysical
Journa
Spitzer Mid-infrared Upper Limits on Anomalous X-Ray Pulsars 1E 1048.1-5937, 1RXS J170849-400910, and XTE J1810-197
We report on mid-infrared imaging observations of the anomalous X-ray pulsars (AXPs) 1E 1048.1-5937, 1RXS J170849-400910, and XTE J1810-197. The observations were carried out at 4.5 and 8.0 microns with the Infrared Array Camera and at 24 microns with the Multiband Imaging Photometer on the Spitzer Space Telescope. No mid-infrared counterparts were detected. As infrared emission from AXPs may be related to their X-ray emission either via the magnetosphere or via a dust disk, we compare the derived upper limits on the infrared/X-ray flux ratios of the AXPs to the same ratio for 4U 0142+61, an AXP previously detected in the mid-infrared range. The comparison indicates that our three non-detections are consistent with their relatively low X-ray fluxes. For XTE J1810-197, our upper limits set a constraint on its rising radio/millimeter energy spectrum, suggesting a spectral break between 1.5--6 Hz
Radio and Infrared Selected Optically Invisible Sources in the Boötes NDWFS
We have combined data from the NOAO Deep Wide-Field Survey in Bošotes and the Spitzer Space Telescope to determine basic properties for sixteen optically âinvisibleâ MIPS 24 ”m (OIMS) and thirty-five optically âinvisibleâ radio (OIRS) sources, including their spectral energy distributions (SED) and luminosities. Most OIMSs possess steep power-law SEDs over λrest = 1 â 10 ”m, indicating the presence of obscured AGN in agreement with Spitzer spectroscopy. These objects are extremely luminous at rest-frame near and mid-IR (ÎœLÎœ(5 ”m) â 1038 â 1039 W), consistent with accretion near the Eddington limit and further implying that they host buried QSOs. The majority of the IRAC detected OIRSs have flat 3.6 to 24 ”m SEDs, implying comparable emission from stellar photospheres and hot AGN illuminated dust. This may reflect relatively small amounts of dust close to the central engine or current low mass accretion rates. A small subset of OIRSs appear to be starburst dominated with photometric redshifts from 1.0 to 4.5. The OIMSs and OIRSs with significant starburst components have similar LK and stellar masses (Mâ â 1011 Mâ) assuming minimal AGN contribution. Roughly half of the OIRSs are not detected by Spitzerâs IRAC or MIPS. These are most likely z & 2 radio galaxies. The IRAC detected OIRSs are more likely than OIMSs to appear non point-like in the 3.6 ”m and 4.5 ”m images, suggesting that interactions play a role in triggering their activity. The AGN powered OIMSs may represent sub-millimeter galaxies making the transition from starburst to accretion dominance in their evolution to current epoch massive ellipticals
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