arXiv subjects

Joy Bhattacharyya

Publications and source records attributed to Joy Bhattacharyya.

9 recordsLinked to original sources

arXiv2026

Morphologies of SAGAbg low-mass galaxies in Legacy Survey multi-band imaging: dependence on stellar masses, star-formation rates and low-redshift evolution

The optical morphologies of low-mass galaxies can be used to directly trace their assembly and constrain models of galaxy evolution. We select a sample of 6211 low-mass ($7\lesssim {\rm log}(M_{\ast}/M_{\odot})\lesssim 10$) star-forming galaxies from the SAGAbg catalog that has high-completeness at low-redshifts ($z<0.1$). We obtain their galaxy maps in the $griz$ - bands of the Legacy Surveys and apply STATMORPH to calculate non-parametric morphological measures including the Gini index, $M_{20}$ measure, and CAS parameters. We study how resolution and signal-to-noise affect the morphology measures and find that the bulge strength measurements are the most reliable. The sequence in Gini$-M_{20}$ space is directly linked to the star-forming sequence of galaxies and is dominated by Sb/Sc/Ir morphologies. The $g$-band light distributions are the least concentrated among all the bands. The systematic trends of $M_{20}$ with respect to stellar mass and GALEX NUV-derived specific star formation rate (sSFR) strongly indicate that the galaxies with flatter light profiles are less massive with higher sSFR and vice-versa. We statistically infer that star-forming low-mass galaxies predominantly have disk morphologies with bulges becoming more prominent in quenched systems at higher masses (${\rm log}(M_{\ast}/M_{\odot})\gtrsim 9$).

astro-ph.GA↗

arXiv2025

The Merian Survey: A Statistical Census of Bright Satellites of Milky Way Analogs

We present a statistical census of bright, star-forming satellite galaxies around Milky Way (MW) analogs using the first data release of the Merian Survey. Our sample consists of 393 MW analogs with stellar masses $10^{10.5} < M_{\star, \rm host} < 10^{10.9} M_\odot$ at redshifts $0.07 < z < 0.09$, all central galaxies of their own dark matter halos. Using photometric selection -- including magnitude, color, angular size, photometric redshift, and size-mass cuts -- we identify 793 satellite candidates around these 393 hosts. Our selection leverages two medium-band filters targeting H$α$ and [O \textsc{iii}] emission, enabling a nearly complete sample of star-forming, Magellanic Clouds-like satellites with $M_{\star, \rm sat} \gtrsim 10^{8} M_\odot$. We find that $\sim80\%$ of hosts have 0-3 massive satellites, and $13\pm4\%$ have two satellites (similar to the MW). Satellite abundance correlates with total stellar mass, and we provide significantly improved statistics for the most massive satellites at $\log_{10}[M_{\star, \rm sat}/M_{\odot}] \gtrsim 10$. The completeness-corrected radial distribution is less centrally concentrated than an NFW profile. In contrast, the Milky Way satellites are more centrally concentrated than the 50\% richest Merian systems, but are broadly consistent with the 50\% most centrally concentrated Merian systems. Our results highlight the power of medium-band photometry for satellite identification and provide a key benchmark for studying satellite quenching, environmental effects, and hierarchical galaxy formation.

astro-ph.GA↗

arXiv2025

Dwarf Galaxies in the TNG50 Field: connecting their Star-formation Rates with their Environments

The dwarf galaxies comparable to the LMC and SMC, with stellar masses $7.5 <{\rm log}(M_{\ast}/M_{\odot})<9.5$, are found in a diversity of environments and have long quenching timescales. We need to understand how this phenomenon is connected to the dwarfs' halo properties and their locations in the large-scale structure of the universe. We study the star-formation rates of dwarfs in the TNG50 simulation of the IllustrisTNG project across different environments, focusing on field dwarfs in host halos with virial masses of $9 < {\rm log}(M_{200}/M_{\odot}) < 11.5$, in contrast to dwarf satellites in hosts with ${\rm log}(M_{200}/M_{\odot}) \geq 11.5$. Our field dwarf sample is heterogeneous, consisting of primary (central) galaxies, with smaller numbers of secondaries and dwarf galaxies that are on backsplash orbits around massive galaxies. We study how the quenched fraction and star-formation histories depend on the dwarfs' large-scale environment and find that only $\sim 1\%$ of the most isolated dwarfs are quenched. The vast majority of the quenched field dwarfs are backsplash dwarfs located in the neighborhood of cluster-scale halos. We discover a two-halo galactic conformity signal that arises from the tendency of the quenched dwarfs, particularly the backsplash sample, to have a quenched massive galaxy as a neighbor. We attribute the low quenched fractions of the simulated LMC/SMC analogs in the field to the locations of their low-mass hosts in the sparse large-scale environment, which predominate over the relatively small number of backsplash and quenched primary dwarfs in denser environments.

astro-ph.GA↗

arXiv2024

Merian: A Wide-Field Imaging Survey of Dwarf Galaxies at z~0.06-0.10

We present the Merian Survey, an optical imaging survey optimized for studying the physical properties of bright star-forming dwarf galaxies. Merian is carried out with two medium-band filters ($N708$ and $N540$, centered at $708$ and $540$ nm), custom-built for the Dark Energy Camera (DECam) on the Blanco telescope. Merian covers $\sim 750\,\mathrm{deg}^2$ of equatorial fields, overlapping with the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) wide, deep, and ultra-deep fields. When combined with the HSC-SSP imaging data ($grizy$), the new Merian DECam medium-band imaging allows for photometric redshift measurements via the detection of H$\rmα$ and [OIII] line emission flux excess in the $N708$ and $N540$ filters, respectively, at $0.06<z<0.10$. We present an overview of the survey design, observations taken to date, data reduction using the LSST Science Pipelines, including aperture-matched photometry for accurate galaxy colors, and a description of the data included in the first data release (DR1). The key science goals of Merian include: probing the dark matter halos of dwarf galaxies out to their virial radii using high signal-to-noise weak lensing profile measurements, decoupling the effects of baryonic processes from dark matter, and understanding the role of black holes in dwarf galaxy evolution. This rich dataset will also offer unique opportunities for studying extremely metal-poor galaxies via their strong [OIII] emission and H$\rmα$ lines, as well as [OIII] emitters at $z\sim 0.4$, and Ly$\rmα$ emitters at $z\sim 3.3$ and $z\sim 4.8$. Merian showcases the power of utilizing narrow and medium-band filters alongside broad-band filters for sky imaging, demonstrating their synergistic capacity to unveil astrophysical insights across diverse astrophysical phenomena.

astro-ph.GA↗

arXiv2024

A Nonparametric Morphological Analysis of H$α$ Emission in Bright Dwarfs Using the Merian Survey

Using medium-band imaging from the newly released Merian Survey, we conduct a nonparametric morphological analysis of H$α$ emission maps and stellar continua for a sample of galaxies with $8\lesssim\log (M_\star/M_\odot) < 10.3$ at $0.064<z<0.1$. We present a novel method for estimating the stellar continuum emission through the Merian Survey's N708 medium-band filter, which we use to measure H$α$ emission and produce H$α$ maps for our sample of galaxies with seven-band Merian photometry and available spectroscopy. We measure nonparametric morphological statistics for the H$α$ and stellar continuum images, explore how the morphology of the H$α$ differs from the continuum, and investigate how the parameters evolve with the galaxies' physical properties. In agreement with previous results for more massive galaxies, we find that the asymmetry of the stellar continuum increases with specific star formation rate (SSFR) and we extend the trend to lower masses, also showing that it holds for the asymmetry of the H$α$ emission. We find that the lowest-mass galaxies with the highest SSFR have H$α$ emission that is consistently heterogeneous and compact, while the less active galaxies in this mass range have H$α$ emission that appears diffuse. At higher masses, our data do not span a sufficient range in SSFR to evaluate whether similar trends apply. We conclude that high SSFRs in low-mass galaxies likely result from dynamical instabilities that compress a galaxy's molecular gas to a dense region near the center.

astro-ph.GA↗

arXiv2024

The Merian Survey: Design, Construction, and Characterization of a Filter Set Optimized to Find Dwarf Galaxies and Measure their Dark Matter Halo Properties with Weak Lensing

The Merian survey is mapping $\sim$ 850 degrees$^2$ of the Hyper Suprime-Cam Strategic Survey Program (HSC-SSP) wide layer with two medium-band filters on the 4-meter Victor M. Blanco telescope at the Cerro Tololo Inter-American Observatory, with the goal of carrying the first high signal-to-noise (S/N) measurements of weak gravitational lensing around dwarf galaxies. This paper presents the design of the Merian filter set: N708 ($λ_c = 7080 \unicode{x212B}$, $Δλ= 275\unicode{x212B}$) and N540 ($λ_c = 5400\unicode{x212B}$, $Δλ= 210\unicode{x212B}$). The central wavelengths and filter widths of N708 and N540 were designed to detect the $\rm Hα$ and $\rm [OIII]$ emission lines of galaxies in the mass range $8<\rm \log M_*/M_\odot<9$ by comparing Merian fluxes with HSC broad-band fluxes. Our filter design takes into account the weak lensing S/N and photometric redshift performance. Our simulations predict that Merian will yield a sample of $\sim$ 85,000 star-forming dwarf galaxies with a photometric redshift accuracy of $σ_{Δz/(1+z)}\sim 0.01$ and an outlier fraction of $η=2.8\%$ over the redshift range $0.058<z<0.10$. With 60 full nights on the Blanco/Dark Energy Camera (DECam), the Merian survey is predicted to measure the average weak lensing profile around dwarf galaxies with lensing $\rm S/N \sim 32$ within $r<0.5$ Mpc and lensing $\rm S/N \sim 90$ within $r<1.0$ Mpc. This unprecedented sample of star-forming dwarf galaxies will allow for studies of the interplay between dark matter and stellar feedback and their roles in the evolution of dwarf galaxies.

astro-ph.GA↗

arXiv2022

The hot circumgalactic medium of the Milky-Way: new insights from XMM-Newton observations

We present XMM-Newton observations around the sightline of Mrk 421. The emission spectrum of the Milky Way circumgalactic medium (CGM) shows that a two phase model is a better fit to the data compared to a single phase model; in addition to the warm-hot virial phase at log ($T/$K) = $6.33_{-0.02}^{+0.03}$, a hot super-virial phase at log ($T/$K) = $6.88_{-0.07}^{+0.08}$ is required. Furthermore, we present observations of five fields within 5 degrees of the primary field. Their spectra also require a two-phase model at warm-hot and hot temperatures. The hot phase, first discovered in Das et al. 2019, appears to be widespread. By chemical tagging we show that emission from the supevirial phase comes from the L-shell transitions of Fe XVIII-FeXXII, and that the range of temperatures probed in emission is distinct from that in absorption. We detect scatter in temperature and emission measure (EM) in both the phases, and deduce that there is small-scale density inhomogeneity in the MW CGM. The emitting gas likely has higher density, possibly from regions close to the disk of the MW, while the absorption in the virial phase may arise from low-density gas extended out to the virial radius of the MW. The presence of the super-virial phase far from the regions around the Galactic center implicates physical processes unrelated to the activity at the Galactic center. Hot outflows resulting from star-formation activity throughout the Galactic disk are likely responsible for producing this phase.

astro-ph.GA↗

arXiv2021

The Signatures of Self-Interacting Dark Matter and Subhalo Disruption on Cluster Substructure

The abundance, distribution and inner structure of satellites of galaxy clusters can be sensitive probes of the properties of dark matter. We run 30 cosmological zoom-in simulations with self-interacting dark matter (SIDM), with a velocity-dependent cross-section, to study the properties of subhalos within cluster-mass hosts. We find that the abundance of subhalos that survive in the SIDM simulations are suppressed relative to their cold dark matter (CDM) counterparts. Once the population of disrupted subhalos -- which may host orphan galaxies -- are taken into account, satellite galaxy populations in CDM and SIDM models can be reconciled. However, even in this case, the inner structure of subhalos are significantly different in the two dark matter models. We study the feasibility of using the weak lensing signal from the subhalo density profiles to distinguish between the cold and self-interacting dark matter while accounting for the potential contribution of orphan galaxies. We find that the effects of self-interactions on the density profile of subhalos can appear degenerate with subhalo disruption in CDM, when orphans are accounted for. With current error bars from the Subaru Hyper Suprime-Cam Strategic Program, we find that subhalos in the outskirts of clusters (where disruption is less prevalent) can be used to constrain dark matter physics. In the future, the Vera C. Rubin Observatory Legacy Survey of Space and Time will give precise measurements of the weak lensing profile and can be used to constrain $σ_T/m$ at the $\sim 1$ cm$^2$ g$^{-1}$ level at $v\sim 2000$ km s$^{-1}$.

astro-ph.CO↗

arXiv2020

Blazar Variability: A Study of Non-stationarity and the Flux-RMS Relation

We analyze X-ray light curves of the blazars Mrk 421, PKS 2155-304, and 3C 273 using observations by the Soft X-ray Telescope on board AstroSat and archival XMM-Newton data. We use light curves of length 30-90 ks each from 3-4 epochs for all three blazars. We apply the autoregressive integrated moving average (ARIMA) model which indicates the variability is consistent with short memory processes for most of the epochs. We show that the power spectral density (PSD) of the X-ray variability of the individual blazars are consistent within uncertainties across the epochs. This implies that the construction of broadband PSD using light curves from different epochs is accurate. However, using certain properties of the variance of the light curves and its segments, we show that the blazars exhibit hints of non-stationarity beyond that due to their characteristic red noise nature in some of those observations. We find a linear relationship between the root-mean-squared amplitude of variability at shorter timescales and the mean flux level at longer timescales for light curves of Mrk 421 across epochs separated by decades as well as light curves spanning 5 days and $\sim$10 yr. The presence of flux-rms relation over very different timescales may imply that, similar to the X-ray binaries and Seyfert galaxies, longer and shorter timescale variability are connected in blazars.

astro-ph.HE↗