NIR/Optical Selected Local Mergers --- Spatial Density and sSFR Enhancement

Mergers play important roles in triggering the most active objects in the universe, including (U)LIRGs and QSOs. However, whether they are also important for the total stellar mass build-up in galaxies in general is unclear and controversial. The answer to that question depends on the merger rate and the average strength of merger induced star formation. In this talk, I will review studies on spatial density and sSFR enhancement of local mergers found in NIR/optical selected pair samples. In line with the current literature on galaxy formation/evolution, special attention will be paid to the dependence of the local merger rate and of the sSFR enhancement on four fundamental observables: (1) stellar mass, (2) mass ratio, (3) separation, and (4) environment.Comment: A review talk; 8 pages; to appear on the Conference Proceedings for "Galaxy Mergers in an Evolving Universe", held in Hualien, Taiwan (October 2011

ALMA Explorations of Warm Dense Molecular Gas in Nearby LIRGs

We present results of ALMA (Cycle-0) observations of the CO (6-5) line emission and the 435μm continuum of two nearby luminous infrared galaxies (LIRGs) NGC 34 (a major merger with an AGN) and NGC 1614 (a minor merger with a circum-nuclear starburst). Using receivers in the highest frequency ALMA band available (Band-9), these observations achieved the best angular resolutions (∼0″.25) for ALMA Cycle-0 observations and resolved for the first time distributions of warm dense molecular gas (n > 10^5 cm^(−3), T > 100 K) in LIRGs with spatial resolutions better than 100 pc. Our ALMA data show a very tight correlation between the CO (6-5) line emission and the 435μm dust continuum emission, suggesting the warm dense molecular gas dominates the ISM in the central kpc of LIRGs, and gas heating and dust heating in the warm dense gas cores are strongly coupled. On the other hand, we saw very different spatial distributions and kinematic properties of warm dense gas in the two LIRGs, indicating that physical conditions in the ISM can be very different in different LIRGs

N-body simulation of the Stephan's Quintet

The evolution of compact groups of galaxies may represent one of the few places in the nearby universe in which massive galaxies are being forged through a complex set of processes involving tidal interaction, ram-pressure stripping, and perhaps finally "dry-mergers" of galaxies stripped of their cool gas. Using collisionless N-body simulations, we propose a possible scenario for the formation of one of the best studied compact groups: Stephan's Quintet. We define a serial approach which allows us to consider the history of the group as sequence of galaxy-galaxy interactions seen as relatively separate events in time, but chained together in such a way as to provide a plausible scenario that ends in the current configuration of the galaxies. By covering a large set of parameters, we claim that it is very unlikely that both major tidal tails of the group have been created by the interaction between the main galaxy and a single intruder. We propose instead a scenario based on two satellites orbiting the main disk, plus the recent involvement of an additional interloper, coming from the background at high speed. This purely N-body study of the quintet will provide a parameter-space exploration of the basic dynamics of the group that can be used as a basis for a more sophisticated N-body/hydrodynamic study of the group that is necessary to explain the giant shock structure and other purely gaseous phenomena observed in both the cold, warm and hot gas in the group.Comment: 13 pages, 13 figures. Accepted for publication in Ap

SPIRE Map-Making Test Report

The photometer section of SPIRE is one of the key instruments on board of Herschel. Its legacy depends very much on how well the scanmap observations that it carried out during the Herschel mission can be converted to high quality maps. In order to have a comprehensive assessment on the current status of SPIRE map-making, as well as to provide guidance for future development of the SPIRE scan-map data reduction pipeline, we carried out a test campaign on SPIRE map-making. In this report, we present results of the tests in this campaign.Comment: This document has an executive summary, 6 chapters, and 102 pages. More information can be found at: https://nhscsci.ipac.caltech.edu/sc/index.php/Spire/SPIREMap-MakingTest201

ALMA Maps of Dust and Warm Dense Gas Emission in the Starburst Galaxy IC 5179⋆^\star

We present our high-resolution ($0^{\prime\prime}.15\times0^{\prime\prime}.13$, $\sim$34 pc) observations of the CO(6-5) line emission, which probes the warm and dense molecular gas, and the 434 $\mu$m dust continuum emission in the nuclear region of the starburst galaxy IC 5179, conducted with the Atacama Large Millimeter Array (ALMA). The CO(6-5) emission is spatially distributed in filamentary structures with many dense cores and shows a velocity field that is characteristic of a circum-nuclear rotating gas disk, with 90% of the rotation speed arising within a radius of $\lesssim150$ pc. At the scale of our spatial resolution, the CO(6-5) and dust emission peaks do not always coincide, with their surface brightness ratio varying by a factor of $\sim$10. This result suggests that their excitation mechanisms are likely different, as further evidenced by the Southwest to Northeast spatial gradient of both CO-to-dust continuum ratio and Pa-$\alpha$ equivalent width. Within the nuclear region (radius$\sim$300 pc) and with a resolution of $\sim$34 pc, the CO line flux (dust flux density) detected in our ALMA observations is $180\pm18$ Jy km/s ($71\pm7$ mJy), which account for 22% (2.4%) of the total value measured by Herschel.Comment: Accepted for publication in Ap

Mechanism of glycan receptor recognition and specificity switch for avian, swine, and human adapted influenza virus hemagglutinins: a molecular dynamics perspective.

Hemagglutinins (HA's) from duck, swine, and human influenza viruses have previously been shown to prefer avian and human glycan receptor analogues with distinct topological profiles, pentasaccharides LSTa (alpha-2,3 linkage) and LSTc (alpha-2,6 linkage), in comparative molecular dynamics studies. On the basis of detailed analyses of the dynamic motions of the receptor binding domains (RBDs) and interaction energy profiles with individual glycan residues, we have identified approximately 30 residue positions in the RBD that present distinct profiles with the receptor analogues. Glycan binding constrained the conformational space sampling by the HA. Electrostatic steering appeared to play a key role in glycan binding specificity. The complex dynamic behaviors of the major SSE and trimeric interfaces with or without bound glycans suggested that networks of interactions might account for species specificity in these low affinity and high avidity (multivalent) interactions between different HA and glycans. Contact frequency, energetic decomposition, and H-bond analyses revealed species-specific differences in HA-glycan interaction profiles, not readily discernible from crystal structures alone. Interaction energy profiles indicated that mutation events at the set of residues such as 145, 156, 158, and 222 would favor human or avian receptor analogues, often through interactions with distal asialo-residues. These results correlate well with existing experimental evidence, and suggest new opportunities for simulation-based vaccine and drug development

Shotgun ion mobility mass spectrometry sequencing of heparan sulfate saccharides

Despite evident regulatory roles of heparan sulfate (HS) saccharides in numerous biological processes, definitive information on the bioactive sequences of these polymers is lacking, with only a handful of natural structures sequenced to date. Here, we develop a “Shotgun” Ion Mobility Mass Spectrometry Sequencing (SIMMS2) method in which intact HS saccharides are dissociated in an ion mobility mass spectrometer and collision cross section values of fragments measured. Matching of data for intact and fragment ions against known values for 36 fully defined HS saccharide structures (from di- to decasaccharides) permits unambiguous sequence determination of validated standards and unknown natural saccharides, notably including variants with 3O-sulfate groups. SIMMS2 analysis of two fibroblast growth factor-inhibiting hexasaccharides identified from a HS oligosaccharide library screen demonstrates that the approach allows elucidation of structure-activity relationships. SIMMS2 thus overcomes the bottleneck for decoding the informational content of functional HS motifs which is crucial for their future biomedical exploitation

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 $z =$ 4.7, consisting of an optical QSO, a sub-millimeter galaxy (SMG) and two Lyman-$\alpha$ emitters (LAEs), all within $\sim$25 kpc of the QSO. We detect the QSO and SMG in both [NII] and continuum. At the $\sim$$1"$ (or 6.6 kpc) resolution, both QSO and SMG are resolved in [NII], with the de-convolved major axes of $\sim$9 and $\sim$14 kpc, respectively. In contrast, their continuum emissions are much more compact and unresolved even at an enhanced resolution of $\sim$$0.7"$. The ratio of the [NII] flux to the existing CO (7$-$6) flux is used to constrain the dust temperature ($T_{\rm dust}$) for a more accurate determination of the FIR luminosity $L_{\rm FIR}$. Our best estimated $T_{\rm dust}$ equals $43 (\pm 2)$ K for both galaxies (assuming an emissivity index $\beta = 1.8$). The resulting $L_{\rm CO(7-6)}/L_{\rm FIR}$ ratios are statistically consistent with that of local luminous infrared galaxies, confirming that $L_{\rm CO(7-6)}$ 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 $(6.9) \times 10^3 M_{\odot}$ yr$^{-1}$ ($\pm$ 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 $(5) \times 10^{11} M_{\odot}$ of molecular gas in 10 $(7) \times 10^7$ years.Comment: 4 pages, 1 table, 4 figures; accepted for publication in the ApJ Letter