We have examined the interactions between polymer-coated anionic (Ag–COOH) and cationic (Ag–NH) silver nanoparticles, and net-anionic lipid monolayers using dynamic surface pressure measurements. ...Monolayers composed of saturated or monounsaturated mixtures of anionic phosphatidylglycerol (PG) and zwitterionic phosphatidylcholine (PC) lipids (3:1 molar ratio) were used to determine how lipid packing and monolayer phase state influence the extent of nanoparticle binding and the monolayer response. Anionic Ag–COOH inserted into saturated dipalmitoyl-PC/PG (DPPC/DPPG) and dioleoyl-PC/PG (DOPC/DOPG) monolayers at a low initial surface pressure (10 mN m–1) and caused lipid condensation at high initial surface pressures (20 and 30 mN m–1). Hydrophobic interactions were responsible for insertion, while electrostatic and charge-dipole interactions with PCs were responsible for condensation. In contrast, cationic Ag–NH inserted only into saturated DPPC/DPPG monolayers and otherwise led to lipid condensation. For Ag–NH, adsorption was driven primarily by electrostatic interactions with PGs. Analysis of the subphase Ag and phosphorus concentrations confirmed that Ag–NH had a higher degree binding compared to Ag–COOH, and that the monolayer response was not due to lipid extraction.
GOALS: The Great Observatories All-Sky LIRG Survey Armus, L.; Mazzarella, J. M.; Evans, A. S. ...
Publications of the Astronomical Society of the Pacific,
06/2009, Volume:
121, Issue:
880
Journal Article
Peer reviewed
Open access
The Great Observatories All-Sky LIRG Survey (GOALS20) combines data from NASA’sSpitzer Space Telescope,
Chandra X-Ray Observatory,
Hubble Space Telescope(HST), andGalaxy Evolution Explorer(GALEX) ...observatories, together with ground-based data, into a comprehensive imaging and spectroscopic survey of over 200 low-redshift (
z < 0.088
z
<
0.088
), Luminous Infrared Galaxies (LIRGs). The LIRGs are a complete subset of theIRASRevised Bright Galaxy Sample (RBGS), which comprises 629 extragalactic objects with 60 μm flux densities above 5.24 Jy, and Galactic latitudes above five degrees. The LIRGs targeted in GOALS span the full range of nuclear spectral types defined via traditional optical line-ratio diagrams (type-1 and type-2 AGN, LINERs, and starbursts) as well as interaction stages (major mergers, minor mergers, and isolated galaxies). They provide an unbiased picture of the processes responsible for enhanced infrared emission in galaxies in the local Universe. As an example of the analytic power of the multiwavelength GOALS data set, we presentSpitzer, Chandra, HST,andGALEXimages and spectra for the interacting system VV 340 (IRAS
F14547 + 2449
F
14547
+
2449
). TheSpitzerMIPS imaging data indicates that between 80–95% of the total far-infrared emission (or about5 × 1011 L
⊙
5
×
10
11
L
⊙
) originates in VV 340 north. While theSpitzerIRAC colors of VV 340 north and south are consistent with star-forming galaxies, both theSpitzerIRS andChandraACIS data indicate the presence of an AGN in VV 340 north. The observed line fluxes, without correction for extinction, imply that the AGN accounts for less than 10%–20% of the observed infrared emission. The X-ray data are consistent with a heavily absorbed (
N
H
≥1024 cm-2
N
H
≥
10
24
cm
-
2
) AGN. The GALEX far and near-UV fluxes imply a extremely large infrared “excess” (IRX) for the system (FIR/Ffuv ∼ 81
F
IR
/
F
fuv
∼
81
) which is well above the correlation seen in starburst galaxies. Most of this excess is driven by VV 340 N, which has an IR excess of nearly 400. The VV 340 system seems to be comprised of two very different galaxies: an infrared luminous edge-on galaxy (VV 340 north) that dominates the long-wavelength emission from the system, which hosts a buried AGN; and a face-on starburst (VV 340 south) that dominates the short-wavelength emission.
Throughout history, observations of the motions of objects in the Universe have provided the foundation for various cosmological models. In many cases, the invoked causes of the observed motion ...appeal to mysterious elements. Indeed, the very first test motion was that of the retrograde motion of Mars, which lead to a required epicycle to save the model (e.g., Ptolemy's unmoving Earth). By the early 1840s, from approximately 50 years of orbital data (since its 1789 discovery) it was apparent that Uranus was disobeying the Newtonian rules in its orbit and speculation mounted that a "large unseen mass" was perturbing the orbit. Using Uranus as a test particle then yields the first notion of dark matter (DM). Alas, it was not DM but merely Neptune, discovered in September 1846. By 1859 enough data had been gathered to reveal that Mercury is also not obeying Newtonian physics but rather revealing curved space-time. The continuation of this history is now set in scales larger than the Solar System. Observations suggest two basic choices: (i) gravity is fully understood and Newton's second law is invariant (except in very strong gravity) and observed motions on galactic scales require the existence of DM (a currently unproven "epicycle") or (ii) Newton's second law can be modified (e.g., MOND) in certain low acceleration scale environments. In this contribution we discuss the case for and against MOND on various scales and conclude that neither MOND nor our current cosmology (ACDM) consistently explain all observed phenomena. In general, MOND works much better on small scales than ACDM but encounters difficulties on large scales. Moreover, the nature of the acoustic power spectrum of the CMB now pretty clearly shows that a fully baryonic Universe is ruled out, thus necessitating some DM component. But this should not diminish the consideration of MOND as its introduced acceleration scale; a.sub.o is fully consistent with the observed structural properties of galaxies in a way that the DM halo paradigm cannot match. Indeed, despite many attempts to falsify MOND, it has always come back from its proclaimed death to provide unique insights into the gravitational nature of galaxies, consistently raising the specter that our current understanding of gravity acting over large spatial scales may be flawed.
Results of observations with the Spitzer, Hubble, GALEX, Chandra, and XMM-Newton space telescopes are presented for the luminous infrared galaxy (LIRG) merger Markarian 266. The SW (Seyfert 2) and NE ...(LINER) nuclei reside in galaxies with Hubble types SBb (pec) and S0/a (pec), respectively. Optical knots embedded in an arc with aligned radio continuum radiation, combined with luminous H sub(2) line emission, provide evidence for a radiative bow shock in an AGN-driven outflow surrounding the NE nucleus. A soft X-ray emission feature modeled as shock-heated plasma with T ~ 10 super(7) K is cospatial with radio continuum emission between the galaxies. Mid-infrared diagnostics provide mixed results, but overall suggest a composite system with roughly equal contributions of AGN and starburst radiation powering the bolometric luminosity. An evolutionary sequence is proposed representing a progression from dual to binary AGNs, accompanied by an increase in observed L sub(x)/L sub(ir) ratios by over two orders of magnitude.
The Baryonic Tully-Fisher Relation McGaugh, S. S; Schombert, J. M; Bothun, G. D ...
Astrophysical journal/The Astrophysical journal,
04/2000, Volume:
533, Issue:
2
Journal Article
Peer reviewed
Open access
We explore the Tully-Fisher relation over five decades in stellar mass in galaxies with circular velocities ranging over 30 less, similarVc less, similar300 km s-1. We find a clear break in the ...optical Tully-Fisher relation: field galaxies with Vc less, similar90 km s-1 fall below the relation defined by brighter galaxies. These faint galaxies, however, are very rich in gas; adding in the gas mass and plotting the baryonic disk mass Md=M*+Mgas in place of luminosity restores the single linear relation. The Tully-Fisher relation thus appears fundamentally to be a relation between rotation velocity and total baryonic mass of the form Md~V4c.
We present an analysis of the extended mid-infrared (MIR) emission of the Great Observatories All-Sky LIRG Survey sample based on 5-15 Delta *mm low-resolution spectra obtained with the Infrared ...Spectrograph on Spitzer. We calculate the fraction of extended emission (FEE) as a function of wavelength for the galaxies in the sample, FEE Delta *l, defined as the fraction of the emission which originates outside of the unresolved component of a source at a given distance. We find that the FEE Delta *l varies from one galaxy to another, but we can identify three general types of FEE Delta *l: one where FEE Delta *l is constant, one where features due to emission lines and polycyclic aromatic hydrocarbons appear more extended than the continuum, and a third which is characteristic of sources with deep silicate absorption at 9.7 Delta *mm. More than 30% of the galaxies have a median FEE Delta *l larger than 0.5, implying that at least half of their MIR emission is extended. Luminous Infrared Galaxies (LIRGs) display a wide range of FEE in their warm dust continuum (0 FEE13.2 Delta *mm 0.85). The large values of FEE13.2 Delta *mm that we find in many LIRGs suggest that the extended component of their MIR continuum emission originates in scales up to 10 kpc and may contribute as much as the nuclear region to their total MIR luminosity. The mean size of the LIRG cores at 13.2 Delta *mm is 2.6 kpc. However, once the IR luminosity of the systems reaches the threshold of L IR ~ 1011.8 L , slightly below the regime of Ultra-luminous Infrared Galaxies (ULIRGs), all sources become clearly more compact, with FEE13.2 Delta *mm 0.2, and their cores are unresolved. Our estimated upper limit for the core size of ULIRGs is less than 1.5 kpc. Furthermore, our analysis indicates that the compactness of systems with L IR 1011.25 L strongly increases in those classified as mergers in their final stage of interaction. The FEE13.2 Delta *mm is also related to the contribution of an active galactic nucleus (AGN) to the MIR emission. Galaxies which are more AGN dominated are less extended, independently of their L IR. We finally find that the extent of the MIR continuum emission is correlated with the far-IR IRAS log(f 60 Delta *mm/f 100 Delta *mm) color. This enables us to place a lower limit to the area in a galaxy from where the cold dust emission may originate, a prediction which can be tested soon with the Herschel Space Telescope.
The continuous culture of Clostridium thermocellum, a thermophilic bacterium capable of producing ethanol from cellulosic material, is demonstrated at elevated hydrostatic pressure (7.0 MPa, 17.3 ...MPa) and compared with cultures at atmospheric pressure. A commercial limitation of ethanol production by C. thermocellum is low ethanol yield due to the formation of organic acids (acetate, lactate). At elevated hydrostatic pressure, ethanol:acetate (E/A) ratios increased >10(2) relative to atmospheric pressure. Cell growth was inhibited by approximately 40% and 60% for incubations at 7.0 MPa and 17.3 MPa, respectively, relative to continuous culture at atmospheric pressure. A decrease in the theoretical maximum growth yield and an increase in the maintenance coefficient indicated that more cellobiose and ATP are channeled towards maintaining cellular function in pressurized cultures. Shifts in product selectivity toward ethanol are consistent with previous observations of hydrostatic pressure effects in batch cultures. The results are partially attributed to the increasing concentration of dissolved product gases (H2, CO2) with increasing pressure; and they highlight the utility of continuous culture experiments for the quantification of the complex role of dissolved gas and pressure effects on metabolic activity.
We present 21 cm H i line observations of 5 × 1 deg2 centred on the local Abell cluster 1367 obtained as part of the Arecibo Galaxy Environment Survey. One hundred sources are detected (79 new H i ...measurements and 50 new redshifts), more than half belonging to the cluster core and its infalling region. Combining the H i data with Sloan Digital Sky Survey (SDSS) optical imaging, we show that our H i selected sample follows scaling relations similar to the ones usually observed in optically selected samples. Interestingly, all galaxies in our sample appear to have nearly the same baryon fraction independently of their size, surface brightness and luminosity. The most striking difference between H i and optically selected samples resides in their large-scale distribution: whereas optical and X-ray observations trace the cluster core very well, in H i there is almost no evidence of the presence of the cluster. Some implications on the determination of the cluster luminosity function and H i distribution for samples selected at different wavelength are also discussed.
We present UBVRIJHK photometry and optical spectroscopy of the so-called peculiar Type Ia supernova 1999by in NGC 2841. The observations began 1 week before visual maximum light, which is well ...defined by daily observations. The light curves and spectra are similar to those of the prototypical subluminous event SN 1991bg. We find that maximum light in B occurred on 1999 May 10.3 UT (JD 2,451,308.8 plus or minus 0.3) with B = 13.66 plus or minus 0.02 and a color of B sub(max) - V sub(max) = 0.51 plus or minus 0.03. The late-time color implies minimal dust extinction from the host galaxy. Our photometry, when combined with the recent Cepheid distance to NGC 2841, gives a peak absolute magnitude of M sub(B) = -17.15 plus or minus 0.23, making SN 1999by one of the least luminous Type Ia events ever observed. We estimate a decline rate parameter of Delta m sub(15)(B) = 1.90 mag, versus 1.93 for SN 1991bg, for which 1.10 is typical for so-called normal events. We compare SN 1999by with other subluminous events and find that the B sub(max) - V sub(max) color correlates strongly with the decline rate and may be a more sensitive indicator of luminosity than the fading rate for these objects. We find a good correlation between luminosity and the depth of the spectral feature at 580 nm, which had been attributed solely to Si II. We show that in cooler photospheres the 580 nm feature is dominated by Ti II, which provides a simple physical explanation for the correlation. Using only subluminous Type Ia supernovae, we derive a Hubble parameter of H sub(0) = 75 super(+) sub(-) super(1) sub(1) super(2) sub(1) km s super(-1) Mpc super(-1), consistent with values found from brighter events.
An analysis of data from the Spitzer Space Telescope, Hubble Space Telescope, Chandra X-ray Observatory, and AKARI Infrared Astronomy Satellite is presented for the z = 0.036 merging galaxy system II ...Zw 096 (CGCG 448-020). Because II Zw 096 has an infrared luminosity of log(L IR/L ) = 11.94, it is classified as a Luminous Infrared Galaxy (LIRG), and was observed as part of the Great Observatories All-sky LIRG Survey (GOALS). The Spitzer data suggest that 80% of the total infrared luminosity comes from an extremely compact, red source not associated with the nuclei of the merging galaxies. The Spitzer mid-infrared spectra indicate no high-ionization lines from a buried active galactic nucleus in this source. The strong detection of the 3.3 Delta *mm and 6.2 Delta *mm polycyclic aromatic hydrocarbon emission features in the AKARI and Spitzer spectra also implies that the energy source of II Zw 096 is a starburst. Based on Spitzer infrared imaging and AKARI near-infrared spectroscopy, the star formation rate is estimated to be 120 M yr-1 and >45 M yr-1, respectively. Finally, the high-resolution B-, I-, and H-band images show many star clusters in the interacting system. The colors of these clusters suggest at least two populations--one with an age of 1-5 Myr and one with an age of 20-500 Myr, reddened by 0-2 mag of visual extinction. The masses of these clusters span a range between 106 and 108 M . This starburst source is reminiscent of the extranuclear starburst seen in NGC 4038/9 (the Antennae Galaxies) and Arp 299 but approximately an order of magnitude more luminous than the Antennae. The source is remarkable in that the off-nuclear infrared luminosity dominates the entire system.
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