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We have analysed optical, near-, and mid-IR images of the bright planetary nebula (PN) IC 418. These images probe unambiguously for the first time a number of low surface brightness structures and shells around the bright main nebula,…
We report on the study of an intriguing active galaxy that was selected as a potential multiple supermassive black hole merger in the early-type host SDSS J151709.20+335324.7 (z=0.135). Ground-based SDSS imaging reveals two blue structures…
The Owl Nebula is a triple-shell planetary nebula with the outermost shell being a faint bow-shaped halo. We have obtained deep narrow-band images and high-dispersion echelle spectra in the H-alpha, [O III], and [N II] emission lines to…
The possible association of the supernova remnant (SNR) G 343.1-2.3 with the pulsar PSR B 1706-44 (superposed on the arclike "shell" of the SNR) has been questioned by some authors on the basis of an inconsistency between the implied and…
We present the results of optical spectroscopic observations of 54 candidate evolved massive stars revealed through the detection of mid-infrared nebulae of various shapes surrounding them with the {\it Spitzer Space Telescope} and {\it…
Double-peaked narrow emission lines in active galactic nucleus (AGN) spectra can be produced by AGN outflows, rotation, or dual AGNs, which are AGN pairs in ongoing galaxy mergers. Consequently, double-peaked narrow AGN emission lines are…
Stellar shells are low surface brightness features, created during nearly head-on galaxy mergers from the debris of the tidally disrupted satellite. Here, we investigate the formation and evolution mechanism of shells in six dimensions (3d…
Many of the properties of massive stars in external galaxies, such as chemical compositions, mass functions, and ionizing fluxes, can be derived from the study of the associated clouds of ionized gas. Moreover, the signatures of Wolf-Rayet…
We present a strong-lensing (SL) analysis of the galaxy cluster MACS J1319.9+7003 ($z=0.33$, also known as Abell 1722), as part of our ongoing effort to analyze massive clusters with archival {\it HST} imaging. We spectroscopically measured…
We present a high spatial resolution optical and infrared study of the circumnuclear region in Arp 220, a late-stage galaxy merger. Narrowband imaging using HST/WFC3 has resolved the previously observed peak in H$\alpha$+[NII] emission into…
We present the first detailed spatio-kinematical analysis and modelling of the planetary nebula Abell 65, which is known to host a post-common envelope, binary, central star system. As such, this object is of great interest in studying the…
LBQS 0302-0019 is a blue quasar (QSO) at z ~ 3.3, hosting powerful outflows, and residing in a complex environment consisting of an obscured AGN candidate, and multiple companions, all within 30 kpc in projection. We use JWST NIRSpec IFS…
Investigation of spectra from the Sloan Digital Sky Survey reveals the presence of a region of ionized gas of >2 degrees diameter centered approximately at alpha = 10^h 37^m delta = -00^o 18' (J2000) (Galactic coordinates l=248, b=+48).…
As massive stars evolve, their winds change. This causes a series of hydrodynamical interactions in the surrounding medium. Whenever a fast wind follows a slow wind phase, the fast wind sweeps up the slow wind in a shell, which can be…
We report results from an ASCA X-ray study of DEM L316, an emission nebula in the Large Magellanic Cloud (LMC) consisting of two closely-spaced supernova remnants (SNRs). The SIS image shows separate X-ray sources located at the positions…
Although thousands of galaxy mergers are known, only a handful of sub-kiloparsec-scale supermassive black hole (SMBH) pairs have been confirmed so far, leaving a huge gap between the observed and predicted numbers of such objects. In this…
We present photometric observations of two shell galaxies, NGC 474 and NGC 7600. We examine the photometric colours and surface brightnesses of the shells and their host galaxies, and the isophotal parameters of each galaxy. In the case of…
We report Chandra X-ray observations and optical weak-lensing measurements from Subaru/Suprime-Cam images of the double galaxy cluster Abell 2465 (z=0.245). The X-ray brightness data are fit to a beta-model to obtain the radial gas density…
Based on ROSAT PSPC pointed observations, we have determined the aggregate X-ray shapes of 10 distant (z = 0.17-0.54) rich clusters: A2397, A222, A520, A1689, A223B, A1758, A2218, A2111, A2125, and CL0016+16. Four of the clusters have…
We study the nucleosynthesis and the induced mixing during the merging of massive stars inside a common envelope. The systems of interest are close binaries, initially consisting of a massive red supergiant and a main-sequence companion of…