Active galactic nuclei (AGN) that show strong rest-frame optical/UVvariability in their blue continuum and broad line emission are classified as"changing-look" AGN, or at higher luminosities changing look quasars (CLQs).These surprisingly large and sometimes rapid transitions challenge acceptedmodels of quasar physics and duty cycles, offer several new avenues for studyof quasar host galaxies, and open a wider interpretation of the cause ofdifferences between broad and narrow line AGN. To better characterize extremequasar variability, we present follow-up spectroscopy as part of acomprehensive search for CLQs across the full SDSS footprint. Our primaryselection requires large-amplitude (|\Delta g|>1 mag, |\Delta r|>0.5 mag)variability over any of the available time baselines probed by the SDSS andPan-STARRS 1 surveys. We employ photometry from the Catalina Sky Survey toverify variability behavior in CLQ candidates where available, and confirm CLQsusing optical spectroscopy from the William Herschel, MMT, Magellan, andPalomar telescopes. For our adopted S/N threshold on variability of broadH\beta emission, we find 16 new CLQs, yielding a confirmation rate of >~ 20%.These candidates are at lower Eddington ratio relative to the overall quasarpopulation and support a disk-wind model for the broad line region. Amonghighly variable quasars, the CLQ fraction increases from 10% to roughly half asthe 3420 Angstrom continuum flux ratio increases from 1.5 to 6. We release acatalog of over 200 highly variable candidates to facilitate future CLQsearches.

Negative feedback from accretion onto super-massive black holes (SMBHs), thatis to remove gas and suppress star formation in galaxies, has been widelysuggested. However, for Seyfert galaxies which harbor less active, moderatelyaccreting SMBHs in the local universe, the feedback capability of their blackhole activity is elusive. We present spatially-resolved H$\alpha$ measurementsto trace ongoing star formation in Seyfert galaxies and compare their specificstar formation rate with a sample of star-forming galaxies whose global galaxyproperties are controlled to be the same as the Seyferts. From the comparisonwe find that the star formation rates within central kpc of Seyfert galaxiesare mildly suppressed as compared to the matched normal star forming galaxies.This suggests that the feedback of moderate SMBH accretion could, to someextent, regulate the ongoing star formation in these intermediate to late typegalaxies under secular evolution.

The Time Inference with MUSE in Extragalactic Rings (TIMER) project is asurvey with the VLT-MUSE integral-field spectrograph of 24 nearby barredgalaxies with prominent central structures (e.g., nuclear rings or innerdiscs). The main goals of the project are: (i) estimating the cosmic epoch whendiscs of galaxies settle, leading to the formation of bars; (ii) testing thehypothesis whereby discs in more massive galaxies are assembled first; and(iii) characterising the history of external gas accretion in disc galaxies. Wepresent details on the sample selection, observations, data reduction, andderivation of high-level data products, including stellar kinematics, ages andmetallicities. We also derive star formation histories and physical propertiesand kinematics of ionised gas. We illustrate how this dataset can be used for aplethora of scientific applications, e.g., stellar feedback, outflows, nuclearand primary bars, stellar migration and chemical enrichment, and the gaseousand stellar dynamics of nuclear spiral arms, barlenses, box/peanuts and bulges.Amongst our first results - based on a few selected galaxies -, we show thatthe dynamics of nuclear rings and inner discs is consistent with the picture inwhich they are formed by bars, that the central few hundred parsecs in massivedisc galaxies tend to show a pronounced peak in stellar metallicity, and thatnuclear rings can efficiently prevent star formation in this region. Finally,we present evidence that star-bursting nuclear rings can be fed withlow-metallicity gas from low-mass companions.

We investigate the stellar populations for a sample of 24 quiescent galaxiesat 1.5 < z < 2.5 using deep rest-frame optical spectra obtained with KeckMOSFIRE. By fitting templates simultaneously to the spectroscopic andphotometric data, and exploring a variety of star formation histories, weobtain robust measurements of median stellar ages and residual levels of starformation. After subtracting the stellar templates, the stacked spectrumreveals the H-alpha and [NII] emission lines, providing an upper limit on theongoing star formation rate of 0.9 +/- 0.1 Msun/yr, thus confirming thequiescence of this population. By combining the MOSFIRE data to our sample ofKeck LRIS spectra at lower redshift, we analyze in a consistent manner thequiescent population at 1 < z < 2.5, finding a tight relation between thestellar age and the rest-frame U-V and V-J colors, with a scatter of only 0.13dex. Using this combined dataset of 79 spectroscopically studied galaxies, wedetermine an empirical calibration that can be used to estimate the age ofquiescent galaxies given their UVJ colors. Applying this age - color relationto large, photometric samples, the number density of quiescent galaxies ofvarious ages can be determined. We model the number density evolution and findevidence for two distinct quenching paths: a fast quenching that producescompact, spheroidal post-starburst systems residing in overdense regions; and aslow quenching of larger galaxies. Fast quenching accounts for about a fifth ofthe growth of the red sequence at z~1.4, and half at z~2.2. We conclude thatfast quenching is triggered by dramatic events such as gas-rich mergers, whileslow quenching is likely caused by a different physical mechanism.

We use both photometric and spectroscopic data from the {\it Hubble SpaceTelescope} to explore the relationships among 4000 \AA\ break (D4000) strength,colors, stellar masses, and morphology, in a sample of 352 galaxies withlog$(M_{*}/M_{\odot}) > 9.44$ at 0.6 $\lesssim z \lesssim$ 1.2. We haveidentified authentically quiescent galaxies in the $UVJ$ diagram based on theirD4000 strengths. This spectroscopic identification is in good agreement withtheir photometrically-derived specific star formation rates (sSFR).Morphologically, most (that is, 66 out of 68 galaxies, $\sim$ 97 \%) of thesenewly identified quiescent galaxies have a prominent bulge component. However,not all of the bulge-dominated galaxies are quenched. We found thatbulge-dominated galaxies show positive correlations among the D4000 strength,stellar mass, and the S\'ersic index, while late-type disks do not show suchstrong positive correlations. Also, bulge-dominated galaxies are clearlyseparated into two main groups in the parameter space of sSFR vs. stellar massand stellar surface density within the effective radius, $\Sigma_{\rm e}$,while late-type disks and irregulars only show high sSFR. This split isdirectly linked to the `blue cloud' and the `red sequence' populations, andcorrelates with the associated central compactness indicated by $\Sigma_{\rme}$. While star-forming massive late-type disks and irregulars (with D4000 $<$1.5 and log$(M_{*}/M_{\odot}) \gtrsim 10.5$) span a stellar mass rangecomparable to bulge-dominated galaxies, most have systematically lower$\Sigma_{\rm e}$ $\lesssim$ $10^{9}M_{\odot}\rm{kpc^{-2}}$. This suggests thatthe presence of a bulge is a necessary but not sufficient requirement forquenching at intermediate redshifts.

The observed present-day stellar mass function (PDMF) of the solarneighborhood is a mixture of stellar populations born in star-forming eventsthat occurred over the life-time of the thin disk of the Galaxy. Assuming starsform in embedded clusters which have stellar initial mass functions (IMFs)which depend on the metallicity and density of the star-forming gas clumps, theintegrated galaxy-wide IMF (IGIMF) can be calculated. The shape of the IGIMFthus depends on the SFR and metallicity. Here, the shape of the PDMF for starsmore massive than $1\,M_\odot$ in combination with the mass density in low-massstars is used to constrain the current star-formation rate (SFR), the starformation history (SFH) and the current stellar plus remnant mass ($M_*$) inthe Galactic thin disk. This yields the current SFR, $\dot{M}_*=4.1^{+3.1}_{-2.8}~M_\odot$yr$^{-1}$, a declining SFH and$M_*=2.1^{+3.0}_{-1.5}\times 10^{11}M_\odot$, respectively, with a V-bandstellar mass-to-light ratio of $M_*/L_V=2.79^{+0.48}_{-0.38}$.These values areconsistent with independent measurements. We also quantify the surface densityof black holes and neutron stars in the Galactic thin disk. The invariantcanonical IMF can reproduce the PDMF of the Galaxy as well as the IGIMF, but inthe universal IMF framework it is not possible to constrain any of the aboveGalactic properties. Assuming the IGMF theory is the correct framework and incombination with the vertical velocity dispersion data of stars, it followsthat the Milky Way would have appeared as a chain galaxy at high redshift.