arXiv subjects

Chandan Watts

Publications and source records attributed to Chandan Watts.

4 recordsLinked to original sources

arXiv2026

Cluster-centric trends in bar size and pattern speed: the case of Abell 2199

We investigate how the environment of a dynamically unrelaxed galaxy cluster influences the structure and dynamics of stellar bars. In particular, we examine cluster-centric variations in normalised bar size and bar pattern speed in Abell 2199. Our analysis is based on 578 spectroscopically confirmed members of Abell 2199, including a master sample of 325 galaxies with homogeneous stellar mass and star formation rate measurements. We identify 39 barred galaxies and measure their structural properties using isophotal ellipse fitting and three-component (bulge+disc+bar) photometric decompositions. For 22 barred galaxies with MaNGA integral-field spectroscopy, we estimate bar pattern speeds using the Tremaine-Weinberg method, obtaining robust measurements for 12 galaxies. Stellar population age and projected specific angular momentum are analysed using $D4000_{R_{\mathrm{e}}}$ and $\lambda_{R_{\mathrm{e}}}$ from the MaNGA Pipe3D catalogue. Abell2199 exhibits star formation-density and morphology-density relations despite its non-relaxed dynamical state. Early-type spiral (ETS) barred galaxies show systematic cluster-centric variations in normalised bar size, with relatively larger bars towards the cluster centre and smaller bars at intermediate radii. A corresponding variation in bar pattern speed with cluster-centric distance is also observed. These trends motivate a division at $\sim$0.5$R_{\mathrm{vir}}$, within which morphology-dependent environmental signatures become clearer, as barred galaxies in the inner region tend to host older stellar populations and lower projected angular momentum than those in the outskirts, with ETS+Bar galaxies retaining higher angular momentum compared to S0+Bar galaxies at comparable radii.

astro-ph.GA↗

arXiv2026

Dwarf and Intermediate-Mass Galaxies in MaNGA: Evidence for Different Evolutionary Trends

We investigate the interplay between morphology, specific star formation rate (sSFR), and local environment using a sample of 7,408 galaxies from the SDSS-IV MaNGA survey. Our analysis spans stellar masses from dwarf to massive galaxies, enabling a unified view of how stellar mass and environment regulate galaxy evolution. Galaxies are classified by morphology (ellipticals (E), lenticulars (S0s), early-type spirals (ETS), and late-type spirals (LTS)) and local environmental density, with star formation activity traced using sSFR. Low-mass galaxies ($\log (M_{\star}/M_{\odot}) < 10$) are predominantly star-forming and dominated by LTS, whereas high-mass galaxies ($\log (M_{\star}/M_{\odot}) \geq 10$) are dominated by ETS and are largely quenched. By separating dwarf ($\log (M_{\star}/M_{\odot}) \leq 9.5$) and intermediate-mass galaxies ($9.5 < \log (M_{\star}/M_{\odot}) < 10$), we find that dwarf galaxies remain predominantly star-forming with only weak environmental dependence, whereas intermediate-mass galaxies exhibit clearer environmental trends toward quenching. Using the D4000 index as a tracer of long-term stellar population aging, we further show that dwarf E and S0s host systematically younger stellar populations than their intermediate-mass counterparts, implying reduced quenching efficiency and more gradual environmental processing in the dwarf regime. This distinction is not evident among spiral galaxies, whose stellar population properties are comparatively insensitive to the dwarf versus non-dwarf classification. Overall, these results indicate that the commonly defined low-mass galaxy population is not homogeneous and that dwarf and intermediate-mass galaxies show systematically different evolutionary trends. Treating them separately is therefore essential for interpreting galaxy evolution in the low-mass regime.

astro-ph.GA↗

arXiv2024

A Tale of NGC 3785: The Formation of an Ultra-Diffuse Galaxy at the end of the Longest Tidal Tail

We present the discovery of an extended and faint tail observed in the isolated environment associated with galaxy NGC 3785. This study additionally provides observational evidence supporting the formation of ultra-diffuse galaxies at the end of the tail. We utilized the Gnuastro software to detect and analyse the low surface brightness structures in the optical $g$, and $r$ bands using data from the Dark Energy Camera Legacy Survey. We created a detection map to identify the faint tail, and measured its length using cubic spline fitting. Additionally, we found 84 star-forming clumps along the tail and performed photometric analysis on the tail portion after applying a significance threshold on the signal-to-noise ratio. We have measured the projected length of the tail, which is $\sim$390 kpc. We propose that this tail arises from the interaction of the NGC 3785 with a gas-rich galaxy, which ends up as ultra-diffuse galaxy at the end of the tail.

astro-ph.GA↗

arXiv2024

Anatomy of the Star-formation in a Tidally Disturbed Disk galaxy: NGC 3718

We present a UV, optical and near-infrared (near-IR) study of the star-forming complexes in the nearby peculiar galaxy NGC 3718, using UVIT, GALEX, Spitzer and DECaLS imaging data. The galaxy has a disturbed optical morphology due to the multiple tidal arms, the warped disk and the prominent curved dust lanes, but in the near-IR, it appears to be a bulge-dominated galaxy. Its disturbed morphology makes it an excellent case to study star formation in a tidally disturbed galaxy that may have undergone a recent minor merger. To study the distribution and properties of the star-forming clumps (SFCs), we divided the galaxy within the R$_{25}$ (B band) radius into three parts --the upper, central and lower regions. Using the UV band images, we investigated the warped star-forming disk, the extended tidal arms, and the distribution and sizes of the 182 SFCs. Their distribution is 49, 60 and 73 in the galaxy's upper, central and lower regions, respectively. We determined the UV color, star-formation rates (SFRs), star-formation density ($\Sigma_{SFR}$) and ages of the SFCs.The central disk of the galaxy has a larger mean $\Sigma_{SFR}$ which is $\sim$3.3 and $\sim$1.6 times higher than the upper and lower regions, respectively. We also find that the SFCs in the central disk are older than those in the tidal arms. Our study thus shows that minor mergers can trigger the inside-out growth of galaxy disks, where the younger SFCs are in outer tidal arms and not in the inner disk.

astro-ph.GA↗