We present the first results of the Subaru/Hyper Suprime-Cam (HSC) survey ofthe interacting galaxy system, NGC4631 and NGC4656. From the maps of resolvedstellar populations, we identify 11 dwarf galaxies (including already-knowndwarfs) in the outer region of NGC4631 and the two tidal stellar streams aroundNGC4631, named Stream SE and Stream NW, respectively. This paper describes thefundamental properties of these tidal streams. Based on the tip of red giantbranch method and the Bayesian statistics, we find that StreamSE (7.10 Mpc inExpected a posteriori, EAP, with the 90% credible intervals of [6.22, 7.29]Mpc) and StreamNW (7.91 Mpc in EAP with the 90% credible intervals of [6.44,7.97] Mpc) are located in front of and behind NGC4631, respectively. We alsocalculate the metallicity distribution of stellar streams by comparing themember stars with theoretical isochrones on the color-magnitude diagram. Wefind that both streams have the same stellar population based on the Bayesianmodel selection method, suggesting that they originated from a tidalinteraction between NGC4631 and a single dwarf satellite. The expectedprogenitor has a positively skewed metallicity distribution function with[M/H]_EAP=-0.92 with the 90% credible intervals of [-1.46, -0.51]. The stellarmass of the progenitor is estimated as 3.7 x 10e+8 Msun with the 90% credibleintervals of [5.8 x 10e+6, 8.6 x 10e+9] Msun based on the mass-metallicityrelation for Local group dwarf galaxies. This is in good agreement with aninitial stellar mass of the progenitor presumed in the previous N-bodysimulation.

Holes and clumps in the interstellar gas of dwarf irregular galaxies aregravitational scattering centers that heat field stars and change their radialand vertical distributions. Because the gas structures are extended and eachstellar scattering is relatively weak, the stellar orbits remain nearlycircular and the net effect accumulates slowly over time. We calculate theradial profile of scattered stars with an idealized model and find that itapproaches an equilibrium shape that is exponential, similar to the observedshapes of galaxy discs. Our models treat only scattering and have no bars orspiral arms, so the results apply mostly to dwarf irregular galaxies wherethere are no other obvious scattering processes. Stellar scattering by gaseousperturbations slows down when the stellar population gets thicker than the gaslayer. An accreting galaxy with a growing thin gas layer can form multiplestellar exponential profiles from the inside-out, preserving the remnants ofeach Gyr interval in a sequence of ever-lengthening and thinning stellarsubdiscs.

We investigate the growth of bulges in bright ($M_B<-20$) disc galaxies since$z\sim1$, in rest-frame B and I-band, using images from HST ACS and WFC3 inGOODS-South for high redshifts ($0.4<z<1.0$) and SDSS for local($0.02<z<0.05$). The growth history has been traced by performing two-componentbulge-disc decomposition and further classifying the bulges into pseudos andclassicals using Kormendy relation. We have about $27\%$ pseudo and $40\%$classical bulges in our sample. Classical bulges are brighter than pseudo, inboth rest-bands, at all redshifts probed here; in fact since $z\sim0.77$,classical are about $\sim1$ mag brighter than pseudo bulges. Both bulges havewitnessed substantial growth, more than half of their present day stellar masshas been gained since $z\sim1$. Their host discs have grown concurrently,becoming progressively brighter in rest-frame I-band. The high redshift host discs of both pseudo and classical bulges are found tobe equally clumpy in rest-frame B-band. In the same band, we found that thegrowth of classical bulges is accompanied by fading of their host discs - whichmight be an indication of secular processes in action. However, both host discas well as the bulge have grown substantially in terms of stellar mass. Ouranalysis suggests that, clump migration and secular processes alone can notaccount for the bulge growth, since $z\sim1$, accretion and minor mergers wouldbe required.

We present results from the EDGE survey, a spatially resolved CO(1-0)follow-up to CALIFA, an optical Integral Field Unit (IFU) survey of localgalaxies. By combining the data products of EDGE and CALIFA, we study thevariation of molecular gas depletion time ($\tau_{\rm dep}$) on kiloparsecscales in 52 galaxies. We divide each galaxy into two parts: the center,defined as the region within $0.1 \ R_{25}$, and the disk, defined as theregion between $0.1$ and $0.7 \ R_{25}$. We find that 13 galaxies show ashorter $\tau_{\rm dep}$ ($\sim 1$ Gyr) in the center relative to the disk($\tau_{\rm dep} \sim 2.4$ Gyrs), which means the central region in thosegalaxies is more efficient at forming stars per unit molecular gas mass. Thisfinding implies that the centers with shorter $\tau_{\rm dep}$ resemble theintermediate regime between galactic disks and starburst galaxies. Furthermore,the central drop in $\tau_{\rm dep}$ is correlated with a central increase inthe stellar surface density, suggesting that a shorter $\tau_{\rm dep}$ isassociated with molecular gas compression by the stellar gravitationalpotential. We argue that varying the CO-to-H$_2$ conversion factor onlyexaggerates the central drop of $\tau_{\rm dep}$.

Motivated by theoretical expectations that Nuclear Star Clusters (NSCs) ingalactic centers may provide a favorable environment for super-massive blackholes to form and/or efficiently grow, we set out to measure the fraction ofnearby nucleated galaxies that also host an Active Galactic Nucleus (AGN). Wetargeted a distance-limited sample of 98 objects with the Chandra X-rayTelescope, down to a uniform X-ray luminosity threshold of $\sim$10$^{38}$ ergs$^{-1}$. The sample is composed of 47 late-types and 51 early-types, enablingus to further investigate the active fraction as a function of galacticmorphology. After correcting for contamination to the nuclear X-ray signal frombright X-ray binaries, we measure an active fraction $f$=11.2$\%^{+7.4}_{-4.9}$(1$\sigma$ C.L.) across the whole sample, in agreement with previous estimatesbased on an heterogeneous combination of optical, X-ray and radio diagnostics,by Seth et al. (2008). After accounting for the different stellar massdistributions in our samples, we find no statistically significant differencein the active fraction of early- vs. late-type nucleated galaxies, with$f$=10.6$\%^{+11.9}_{-4.9}$ and 10.8$\%^{+11.3}_{-6.3}$, respectively. For theearly-type nucleated galaxies, we are able to carry out a controlled comparisonwith a parent sample of non-nucleated galaxies covering the same stellar massrange, finding again no statistically significant difference in the activefraction. Taken at face value, our findings suggest that the presence of a NSCdoes not facilitate nor enhance accretion-powered emission from a nuclearsuper-massive black hole. This is true even for late-type nucleated galaxies,home to bluer NSCs and arguably larger gas reservoirs.