We analyze 494 main sequence turnoff and subgiant stars from the AMBRE:HARPSsurvey. These stars have accurate astrometric information from\textit{Gaia}/DR1, providing reliable age estimates with relative uncertaintiesof $\pm1-2$ Gyr and allowing precise orbital determinations. The sample issplit based on chemistry into a low-[Mg/Fe] sequence, which are oftenidentified as thin disk stellar populations, and a high-[Mg/Fe] sequence, whichare often associated with the thick disk. We find that the high-[Mg/Fe]chemical sequence has extended star formation for several Gyr and is coevalwith the oldest stars of the low-[Mg/Fe] chemical sequence: both the low- andhigh-[Mg/Fe] sequences were forming stars at the same time. The high-[Mg/Fe]stellar populations are only vertically extended for the oldest, most-metalpoor and highest [Mg/Fe] stars. When comparing vertical velocity dispersion forboth sequences, the high-[Mg/Fe] sequence has lower velocity dispersion thanthe low-[Mg/Fe] sequence for stars of similar age. Identifying either group asthin or thick disk based on chemistry is misleading. The stars belonging to thehigh-[Mg/Fe] sequence have perigalacticons that originate in the inner disk,while the perigalacticons of stars on the low-[Mg/Fe] sequence are generallyaround the solar neighborhood. From the orbital properties of the stars, thehigh-and low-[Mg/Fe] sequences are most likely a reflection of the chemicalenrichment history of the inner and outer disk populations; radial mixingcauses both populations to be observed in situ at the solar position. Based onthese results, we emphasize that it is important to be clear in defining whatpopulations are being referenced when using the terms thin and thick disk, andthat ideally the term thick disk should be reserved for purely geometricdefinitions to avoid confusion and be consistent with definitions in externalgalaxies.

We present the age-velocity dispersion relation (AVR) in three dimensions inthe solar neighbourhood using 3,564 commonly observed sub-giant/red-giantbranch stars selected from LAMOST, which gives the age and radial velocity, and\emph{Gaia}, which measures the distance and proper motion. The stars areseparated into metal-poor (${\rm [Fe/H]<-0.2}$\,dex and metal-rich (${\rm[Fe/H]>-0.2}$\,dex) groups, so that the metal-rich stars are mostly$\alpha$-poor, while the metal-poor group are mostly contributed by$\alpha$-enhanced stars. Thus, the old and metal-poor stars likely belong tothe chemically defined thick disc population, while the metal-rich sample isdominated by the thin disc. The AVR for the metal-poor sample shows an abruptincrease at $\gtrsim7$\,Gyr, which is contributed by the thick disc component.On the other hand, most of the thin disc stars with ${\rm [Fe/H]>-0.2}$\,dexdisplay a power-law like AVR with indices of about 0.3--0.4 and 0.5 for thein-plane and vertical dispersions, respectively. This is consistent with thescenario that the disc is gradually heated by the spiral arms and/or the giantmolecular clouds. Moreover, the older thin disc stars ($>7$\,Gyr) have arounder velocity ellipsoid, i.e. $\sigma_\phi/\sigma_{\rm z}$ is close to 1.0,probably due to the more efficient heating in vertical direction. Particularlyfor the old metal-poor sample located with $|z|>270$\,pc, the verticaldispersion is even larger than its azimuthal counterpart. Finally, the vertexdeviations and the tilt angles are plausibly around zero with largeuncertainties.

We examine the dynamical properties of interacting galaxies and theproperties of shocked gas produced as a result of the interaction. We observed22 galaxy mergers using the SparsePak IFU at Kitt Peak National Observatory(KPNO). The goal of the observations was to obtain the H$\alpha$ velocity mapsover the entire luminous parts of the galaxies including the faint tidal tails,and to find extended shocks and outflows. Our sample consists of major andminor galaxy mergers with mass ratios $1<\mu<8$. We fit multiple kinematiccomponents to the H$\alpha$ and [N II] emission lines, develop an MCMC code torobustly estimate the error of fit parameters, and use the F-test to determinethe best number of kinematic components for each fiber. We use [N II]/H$\alpha$and velocity dispersion of components to separate star-forming (HII) regionsfrom shocks. We use the kinematics of the H$\alpha$ emission from HII regionsand an automated modeling method to put the first ever constraints on theencounter parameters of one of the observed systems. Besides, we estimate thefraction of shocked H$\alpha$ emission, $\text{f}_\text{shocked}$, and examinethe spatial distribution of shocks. We find that close galaxy pairs have, onaverage, a higher shock fraction than wide pairs, and coalesced mergers havethe highest average $\text{f}_\text{shocked}$. In addition, galaxy pairs withmore equal mass ratio tend to have a higher $\text{f}_\text{shocked}$.Combining the dynamical models from the literature and this work, we inspecttrends between $\text{f}_\text{shocked}$ and dynamical encounter parameters.Our findings are generally consistent with shocks being produced either bydirect collision of the ISM or by the chain of events provoked by the tidalimpulse during the first passage.

We present the results of a multiwavelength survey of HI-excess galaxies, anintriguing population with large HI reservoirs associated with little currentstar formation. These galaxies have stellar masses $M_{\star} >10^{10}$M$_{\odot}$, and were identified as outliers in the gas fraction vs. NUV$-r$color and stellar mass surface density scaling relations based on the GALEXArecibo SDSS Survey (GASS). We obtained HI interferometry with the GMRT, Keckoptical long-slit spectroscopy and deep optical imaging (where available) forfour galaxies. Our analysis reveals multiple possible reasons for the HI excessin these systems. One galaxy, AGC 10111, shows an HI disk that iscounter-rotating with respect to the stellar bulge, a clear indication ofexternal origin of the gas. Another galaxy appears to host a Malin 1-type disk,where a large specific angular momentum has to be invoked to explain theextreme $M_{\rm HI}$/$M_{\star}$ ratio of 166$\%$. The other two galaxies haveearly-type morphology with very high gas fractions. The lack of mergersignatures (unsettled gas, stellar shells and streams) in these systemssuggests that these gas-rich disks have been built several Gyr-s ago, but itremains unclear how the gas reservoirs were assembled. Numerical simulations oflarge cosmological volumes are needed to gain insight into the formation ofthese rare and interesting systems.

We present new high-resolution HI spectral line imaging of Coma P, thebrightest HI source in the system HI 1232$+$20. This extremely low surfacebrightness galaxy was first identified in the ALFALFA survey as an "(Almost)Dark" object: a clearly extragalactic HI source with no obvious opticalcounterpart in existing optical survey data (although faint ultravioletemission was detected in archival GALEX imaging). Using a combination of datafrom the Westerbork Synthesis Radio Telescope and the Karl G. Jansky Very LargeArray, we investigate the HI morphology and kinematics at a variety of physicalscales. The HI morphology is irregular, reaching only moderate maxima in masssurface density (peak $\sigma_{\rm HI}\sim 10$ $M_{\odot}$ pc$^{-2}$). Gas oflower surface brightness extends to large radial distances, with the HIdiameter measured at 4.0$\pm$0.2 kpc inside the 1 $M_{\odot}$ pc$^{-2}$ level.We quantify the relationships between HI gas mass surface density and varioustypes of star formation by considering GALEX far ultraviolet observations andH$\alpha$ nondetections. We describe Coma P's complex HI kinematics usingspatially resolved position-velocity analysis and three-dimensional modeling.Both methods of analysis suggest that Coma P's kinematics show signatures ofeither the collision of two HI disks or a significant infall event. Coma P isjust consistent (within 3$\sigma$) with the known M$_{\rm HI}$ -- D$_{\rm HI}$scaling relation. It is either too large for its HI mass, has too low an HImass for its HI size, or the two HI components artificially extend its HI size.Coma P lies within the empirical scatter at the faint end of the baryonicTully--Fisher relation, although the complexity of the HI dynamics complicatesthe interpretation. The collective HI characteristics of Coma P make it unusualamong known galaxies in the nearby universe. [Abridged]

Gas-rich minor mergers contribute significantly to the gas reservoir ofearly-type galaxies (ETGs) at low redshift, yet the star formation efficiency(SFE; the star formation rate divided by the molecular gas mass) appears to bestrongly suppressed following some of these events, in contrast to the morewell-known merger-driven starbursts. We present observations with the AtacamaLarge Millimeter/submillimeter Array (ALMA) of six ETGs, which have eachrecently undergone a gas-rich minor merger, as evidenced by their disturbedstellar morphologies. These galaxies were selected because they exhibitextremely low SFEs. We use the resolving power of ALMA to study the morphologyand kinematics of the molecular gas. The majority of our galaxies exhibitspatial and kinematical irregularities, such as detached gas clouds, warps, andother asymmetries. These asymmetries support the interpretation that thesuppression of the SFE is caused by dynamical effects stabilizing the gasagainst gravitational collapse. Through kinematic modelling we derive highvelocity dispersions and Toomre Q stability parameters for the gas, but cautionthat such measurements in edge-on galaxies suffer from degeneracies. Weestimate merger ages to be about 100~Myr based on the observed disturbances inthe gas distribution. Furthermore, we determine that these galaxies lie, onaverage, two orders of magnitude below the Kennicutt-Schmidt relation forstar-forming galaxies as well as below the relation for relaxed ETGs. Wediscuss potential dynamical processes responsible for this strong suppressionof star formation surface density at fixed molecular gas surface density.

We present the results of our ALMA Cycle 4 high-spatial-resolution(0.04-0.07") observations, at HCN J=3-2 and HCO+ J=3-2 lines, of the nucleus ofNGC 1068, the nearby prototypical type 2 active galactic nucleus (AGN). Ourprevious ALMA observations identified the compact emission of these lines atthe putative location of the torus around a mass-accreting supermassive blackhole. We now report that we have detected the rotation of this compactemission, with the eastern and western sides being redshifted and blueshifted,respectively. Unlike the previously reported CO J=6-5 emission, both themorphological and dynamical alignments of the HCN J=3-2 and HCO+ J=3-2 emissionare roughly aligned along the east-west direction (i.e., the expected torusdirection), suggesting that these molecular lines are better probes of arotating dense molecular gas component in the torus. The western part of thetorus exhibits larger velocity dispersion and stronger emission in the HCNJ=3-2 and HCO+ J=3-2 lines than the eastern part, revealing a highlyinhomogeneous molecular torus. The dense molecular gas in the torus and that ofthe host galaxy at 0.5-2.0" from the AGN along the torus direction are found tobe counter-rotating, suggesting an external process happened in the past at theNGC 1068 nucleus.