arXiv subjects

Divya Pandey

Publications and source records attributed to Divya Pandey.

8 recordsLinked to original sources

arXiv2026

Detection and Properties of Lyman Break Galaxies at $1.6 \leq z \leq 3.0$ in GOODS-North

Lyman Break Galaxies (LBGs) are actively star-forming galaxies identified through their characteristic rest-frame ultraviolet spectral break, making them powerful probes of galaxy evolution across cosmic time. We present a search for LBGs at redshifts $1.6 \leq z \leq 3.0$ in the GOODS-North field using the dropout technique combined with color selection from the 3D-HST data. We utilize two selection criteria to identify LBG candidates at $z \sim 2.1$ and $z \sim 2.7$ via F275W- and F336W-dropouts, yielding 192 and 135 newly identified LBG candidates in the redshift ranges $1.6 \leq z \leq 2.3$ and $2.3 < z \leq 3.0$, respectively. We estimate the physical properties of the LBG candidates, including stellar age, stellar mass, and star formation rate (SFR), using spectral energy distribution (SED) fitting. Morphological analysis shows that the majority of galaxies in our sample exhibit disc-like structures. Overall, the results indicate that these LBGs are low- to intermediate-mass compact galaxies with effective half-light radii of approximately 3.5 kpc.

astro-ph.GA↗

arXiv2026

Study of Integrated Far-ultraviolet Emissions from Galactic Globular Clusters using AstroSat/UVIT observations

We used observations obtained with the Ultraviolet Imaging Telescope on board the AstroSat satellite to measure the integrated far-ultraviolet (FUV) and optical (V) magnitudes of 30 Galactic globular clusters (GCs). We classified the UV-bright evolved stellar populations of the GCs using FUV$-$V versus FUV color-magnitude diagrams (CMDs) and BaSTI-IAC isochrones and subsequently quantified their contributions to the total integrated FUV emissions. We found that the horizontal branch (HB) and post-HB (post-HB) stars contribute $\sim 40\%-45$\% to the total FUV emission of GCs, while the contribution of blue straggler stars is only $\sim$3\%. The HB stars especially dominate the UV budget of the metal-poor clusters. The observed spread in FUV-optical color in the color-color diagram supports the phenomenon that the UV upturn of early-type galaxies is due to the evolved stars. We studied for the first time the variation of integrated FUV magnitudes and colors with several cluster parameters in the core, intermediate, outer, and tidal regions, such as the fraction of second-generation stars, helium mass fraction, HB morphology, and mass of the GCs. We found that the GCs with a higher second-generation star fraction, helium mass fraction, and cluster mass are brighter in all the regions. The GCs with bluer HB morphologies also have brighter and bluer FUV magnitudes in the core and intermediate regions. Metal-poor GCs show significantly bluer FUV$-$optical colors, consistent with a stronger contribution from hot evolved stars.

astro-ph.GA↗

arXiv2024

A Comprehensive Catalog of UVIT Observations I: Catalog Description and First Release of Source Catalog (UVIT DR1)

We present the first comprehensive source catalog (UVIT DR1) of ultraviolet (UV) photometry in four far-UV (FUV $\sim$1300$-$1800 \AA) and five near-UV (NUV $\sim$2000$-$3000 \AA) filters of the Ultraviolet Imaging Telescope (UVIT) on board {\em AstroSat}. UVIT DR1 includes bright UV sources in 291 fields that UVIT detected during its first two years of pointed observation, encompassing an area of 58 square degrees. We used the {\sc ccdlab} pipeline to reduce the L1 data, source-extractor for source detection, and four photometric procedures to determine the magnitudes of the detected sources. We provided the 3$\sigma$ and 5$\sigma$ detection limits for all the filters of UVIT. We describe the details of observation, source extraction methods, and photometry procedures applied to prepare the catalog. In the final UVIT DR1 catalog, we have point sources, extended sources, clumps from nearby galaxies, There are 239,520 unique sources in the combined UVIT DR1, of which 70,488 sources have FUV magnitudes, and 211,410 have NUV magnitudes. We cross-matched and compared non-crowded sources of UVIT with the {\em Galaxy Evolution Explorer (GALEX)} and {\em Gaia} source catalogs. We provide a clean catalog of the unique sources in various UVIT filters that will help further multi-wavelength scientific analysis of the objects.

astro-ph.GA↗

arXiv2024

Star formation exists in all early-type galaxies -- evidence from ubiquitous structure in UV images

Recent surveys have demonstrated the widespread presence of UV emission in early-type galaxies (ETGs), suggesting the existence of star formation in many of these systems. However, potential UV contributions from old and young stars, together with model uncertainties, makes it challenging to confirm the presence of young stars using integrated photometry alone. This is particularly true in ETGs that are fainter in the UV and have red UV-optical colours. An unambiguous way of disentangling the source of the UV is to look for structure in UV images. Optical images of ETGs, which are dominated by old stars, are smooth and devoid of structure. If the UV is also produced by these old stars, then the UV images will share this smoothness, while, if driven by young stars, they will exhibit significant structure. We compare the UV and optical morphologies of 32 ETGs (93 per cent of which are at $z<0.03$) using quantitative parameters (concentration, asymmetry, clumpiness and the S\'ersic index), calculated via deep UV and optical images with similar resolution. Regardless of stellar mass, UV-optical colour or the presence of interactions, the asymmetry and clumpiness of ETGs is significantly larger (often by several orders of magnitudes) in the UV than in the optical, while the UV S\'ersic indices are typically lower than their optical counterparts. The ubiquitous presence of structure demonstrates that the UV flux across our entire ETG sample is dominated by young stars and indicates that star formation exists in all ETGs in the nearby Universe.

astro-ph.GA↗

arXiv2024

Exploring filament galaxies using {\em AstroSat}/ UVIT

We present results from our deep Far-ultraviolet (FUV) survey using {\em AstroSat}/UVIT of a filamentary structure at $z$ $\sim$ $0.072$. A total of four filaments comprising 58 galaxies were probed in our study. We detect 18 filament galaxies in our FUV observation. All filament galaxies are further classified based on their photometric color, nuclear activity, and morphology. The filaments contain galaxies with mixed stellar population types and structures. We do not detect galaxies in our UVIT survey up to a distance of 0.4~Mpc $h^{-1}$ from the filament axis, implying a lack of recent star formation in the inner region of filaments. The FUV star formation rate (SFR) for star-forming galaxies agrees well with the SFR$_{\rm 144 MHz}$ calculated using Low-Frequency Array (LOFAR) radio-continuum observations. We witness an increase in FUV specific-SFR (sSFR) of filament galaxies with increasing distance from the filament spine (D$_{\rm fil}$). The intermediate-to-high stellar mass filament galaxies were more star-forming than cluster galaxies in a fixed stellar mass bin. The FUV morphology of some filament galaxies detected in the filament outskirts (D$_{\rm fil}$ $\gtrsim$ 0.7~Mpc $h^{-1}$) is comparable to or slightly extended than their optical counterpart. The mass assembly of galaxies examined by estimating $(FUV-r)$ color gradients show that more `red-cored' galaxies reside in the outer region of the filaments. Our results prove that the likelihood of merger interaction and gas starvation increases when approaching the filament spine. We report a definitive and in-homogeneous impact of filaments on the galaxies residing inside them.

astro-ph.GA↗

arXiv2022

Witnessing the star-formation quenching in $L_{*}$ ellipticals

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\sc{iii}}] and H$\alpha$ 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\% 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\sc{iii}}] emission compared to the [{O\sc{ii}}] and H$\alpha$ 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.

astro-ph.GA↗

arXiv2022

Central star formation in an early-type galaxy I~Zw~81 in the Bootes void

The origin of star-formation in customarily passively evolving early-type massive galaxies is poorly understood. We present a case study of a massive galaxy, I~Zw~81, inside the Bootes void. The void galaxy is known to host an active galactic nuclei (AGN). Our detailed 2D decomposition of the surface brightness distribution in the $Canada$ $France$ $Hawaii$ $Telescope$ ($CFHT$) g- and r-bands revealed multiple structural components such as a nuclear point source, a bar, a ring, and an inner exponential disk followed by an outer low surface brightness (LSB) disk. I~Zw~81 turns out to be a disk-dominated galaxy with lenticular morphology. The modelling of the multi-wavelength spectral energy distribution (SED) shows that the galaxy is star-forming (SF), and belongs to the blue cloud. We find that the optical (g$-$r) color of the bar is bluer than the disks, and the far- and near-ultraviolet emission inside the galaxy observed with Ultraviolet Imaging Telescope (UVIT) onboard {\em AstroSat} is concentrated in the central few kpc region enclosing the bar. The strong bar might be playing a pivotal role in driving the gas inflow and causing SF activity in tandem with the minor merger-like interactions as evident from the deep $CFHT$ data. The low-luminosity AGN is insufficient to quench the central SF. The results are peculiar from the standpoint of a massive barred lenticular galaxy.

astro-ph.GA↗

arXiv2021

The Ultraviolet Deep Imaging Survey of Galaxies in the Bootes Void I: catalog, color-magnitude relations and star formation

We present a deep far and near-ultraviolet (FUV and NUV) wide-field imaging survey of galaxies in the Bootes Void using Ultra-Violet Imaging Telescope onboard {\em AstroSat}. Our data reach $5\sigma$ limiting magnitudes for point sources at 23.0 and 24.0 AB mag in FUV and NUV respectively. We report a total of six star-forming galaxies residing in the Bootes Void alongside the full catalog, and of these, three are newly detected in our FUV observation. Our void galaxy sample spans a range of UV colors $(-0.35\, \leq$ FUV$-$NUV $\leq\, 0.68)$ and absolute magnitudes $(-14.16\, \leq\, \mathrm{M_{NUV}}\, \leq\, -18.65)$. In addition, {\em Sloan Digital Sky Survey} and {\em Two-micron All Sky Survey} archival data are being used to study UV, optical, and infrared color-magnitude relations for our galaxies in the void. We investigate the nature of bi-modal color distribution, morphologies, and star formation of the void galaxies. Most of the galaxies in our sample are fainter and less massive than L$^{\ast}$ galaxies, with M$_\mathrm{r} > -20$. Our analysis reveals a dominant fraction of bluer galaxies over the red ones in the void region probed. The internal and Galactic extinction corrected FUV star formation rates (SFRs) in our void galaxy catalog varies in a large range of $0.05$ to $51.01$ M$_{\odot} yr^{-1}$, with a median $3.96$ M$_{\odot} yr^{-1}$. We find a weak effect of the environment on the SFRs of galaxies. Implications of our findings are discussed.

astro-ph.GA↗