Malin 1, being a class of giant low surface galaxies, continues to surprise us even today. The HST/F814W observation has shown that the central region of Malin 1 is more like a normal SB0/a galaxy, while the rest of the disk has the characteristic of a low surface brightness system. The AstroSat/UVIT observations suggest scattered recent star formation activity all over the disk, especially along the spiral arms. The central 9 00 ( $ 14 kpc) region, similar to the size of the Milky Way's stellar disk, has a number of far-UV clumps-indicating recent star-formation activity. The high resolution UVIT/F154W image reveals far-UV emission within the bar region ( $ 4 kpc)-suggesting the presence of hot, young stars in the bar. These young stars from the bar region are perhaps responsible for producing the strong emission lines such as Ha, [OII] seen in the SDSS spectra. Malin 1B, a dwarf early-type galaxy, is interacting with the central region and probably responsible for inducing the recent star-formation activity in this galaxy.

We study the evolution of L* elliptical galaxies in the color-magnitude diagram in terms of their star-formation history and environment, in an attempt to learn about their quenching process. We have visually extracted 1109 L* galaxies from a sample of 36500 galaxies that were spectroscopically selected from Stripe82 of the Sloan Digital Sky Survey. From this sample we have selected 51 ellipticals based on their surface-brightness profile being well-fitted by a single S$\acute{e}$rsic profile with S$\acute{e}$rsic indices 3 < n < 6. Our sample consists of 12 blue-cloud L* ellipticals (BLE), 11 green-valley L* ellipticals (GLE), and 28 red-sequence L* ellipticals (RLE). We find that most of the RLEs and GLEs have been quenched only recently, or are still forming stars, based on their [O iii] and Hα emission, while the BLEs are forming stars vigorously. The star-formation in BLEs is found to be extended over the galaxy and not confined to their central region. In about 40 per cent of the L* ellipticals (ten BLEs, four GLEs and five RLEs), star-formation quenching seems to have started only recently, based on the lower [O iii] emission compared to the [O ii] and Hα emission, at a given metallicity. We also find that the galaxy color is correlated with the cosmic-web environment, with the BLEs tending to reside in lower-density regions, the RLEs preferring denser, clustered regions, and the GLEs found in either. One possible scenario is that as the star-forming ellipticals migrate into the clusters, their star formation is suffocated by the hot intra-cluster medium.

We present photometric properties of 183 member galaxies in the Abell 426 cluster using the Sloan Digital Sky Survey (SDSS) imaging and spectroscopic observation. Detailed morphology based on visual classification followed by multi-component image decomposition of 179 galaxies is presented in the SDSS g, r, i-bands. More than 80 per cent of the members are Early-type galaxies (ETGs), with elliptical, dwarf elliptical (dE), and lenticular morphology and follow the red-sequence in the colour-magnitude diagram (CMD). With a few dEs and spirals in the blue cloud, the cluster CMD is nearly unimodal. The dEs are ∼2-mag fainter and follow a different Sersic index and central velocity dispersion distribution than their bright counterparts. Further, we establish the Kormendy relation (KR) and the Fundamental Plane relation (FPR) for 5 different samples of ETGs constructed based on derived physical parameters such as Sersic index, concentration, central velocity dispersion in g, r, i-bands. The mean r-band slope and zero-point of the KR are 3.02 ± 0.1 and 18.65 ± 0.03 in close agreement to other cluster ellipticals in the local and higher redshift. Kinematics-based ETG sample produces the least scatter in KR with zero-point getting brighter by ∼1.3 mag from g to i band. The dEs and other low-mass ETGs follow the KR with a similar slope but with ∼1.3 mag fainter zero-point and form a parallel KR. The bright ellipticals follow an FPR with a = 1.37 ± 0.003, b = 0.35 ± 0.05 and c = −9.37 ± 0.02 in the r-band; galaxies tend to deviate from this relation at the low-mass end. A catalog with morphology and 2D structural analysis is available online.

We present Hubble Space Telescope (HST) observations of the nearby, massive, highly rotating hybrid galaxy UGC 12591, along with observations in UV to FIR bands. HST data in V, I, and H bands is used to disentangle the structural components. Surface photometry shows a dominance of the bulge over the disc with H-band B/D ratio of $69{{\%}}$. The spectral energy distribution (SED) fitting reveals an extremely low global star formation rate (SFR) of $\rm \sim 0.1\!-\!0.2\, M_\odot \, yr^{-1}$, exceptionally low for the galaxy’s huge stellar mass of $\rm 1.6\times 10^{11}M_\odot$, implying a strong quenching of its SFR with star formation efficiency of $3-5{{\%}}$. For at least the past $\rm 10^{8}$ years, the galaxy has remained in a quiescent state as a sterile, ‘red and dead’ galaxy. UGC 12591 hosts a supermassive black hole (SMBH) of $\rm 6.18\times 10^{8} \, M_\odot$ which is possibly quiescent at present, i.e. neither we see large (> 1kpc) radio jets nor is the SMBH contributing significantly to the mid-IR SED, ruling out strong radiative feedback of AGN. We obtained a detailed census of all observable baryons with a total mass of $\rm 6.46\times 10^{11} \, M_\odot$ within the virial radius, amounting to a baryonic deficiency of ${\sim }85{{\%}}$ relative to the cosmological mean. Only a small fraction of these baryons resides in a warm/hot circum-galactic X-ray halo, while the majority are still unobservable. We discussed various astrophysical scenarios for explaining its unusual properties. Our work is a major step forward in understanding the assembly history of such extremely massive, isolated galaxies.