arXiv subjects

Divakara Mayya

Publications and source records attributed to Divakara Mayya.

11 recordsLinked to original sources

arXiv2026

Ages of the resolved stellar populations inside the JWST/MIRI bubbles in NGC 628

JWST images in the MIRI filters are characterized by prominent interstellar bubbles, most of which are expected to be created by mechanical energy injected into the interstellar medium by dying massive stars. In this work, we use resolved stellar populations (RSPs) in JWST/NIRCam images of NGC 628 from the JWST-FEAST dataset to determine the demography of stellar populations within these bubbles by comparing them with PARSEC+COLIBRI isochrones using a Bayesian framework. Our analysis reveals the presence of multiple stellar populations younger than 100 Myr within the bubbles, suggesting secondary star formation following the first generation of stars that formed the bubble. We find a clear preference for the most recently formed stars to lie closer to the bubble shell. In contrast, relatively older stars are distributed throughout the bubble interior, consistent with a scenario in which stars formed in dense shells are left behind as the shell expands. We also examine PHANGS-HST cluster candidates within large bubbles and find no convincing progenitor clusters responsible for the initial trigger, indicating that low-mass clusters or OB associations may be sufficient to drive the initial expansion. However, the cluster may dissolve as it co-evolves with the bubble, producing the dispersed stellar distributions observed in larger bubbles. We establish a fundamental plane relation for stellar feedback-driven bubbles that involves the stellar population mass, age, bubble size, gas density, and feedback efficiency, highlighting the ability of JWST/NIRCam CMDs to characterize stellar populations driving interstellar bubble expansion in nearby galaxies

astro-ph.GA↗

arXiv2026

Bulgeless Evolution And the Rise of Discs (BEARD) II. The role of mergers in shaping the Milky Way analogues in TNG50

We study the formation and evolution of bulgeless galaxies within the Milky Way-Andromeda analogue sample of the TNG50 simulation. Through kinematic decomposition with Mordor, we identified bulgeless galaxies with a bulge-to-disc mass ratio of B/D<0.08, in line with the Bulgeless Evolution And the Rise of Discs (BEARD) survey and Milky Way constraints. We compared them to bulge-dominated galaxies (B/D>1). We find that 74% of bulgeless galaxies experience at least one major merger (stellar mass ratio 1:4) over their lifetime. Bulgeless galaxies form later ($z_{50}\sim 0.7$) than bulge-dominated counterparts ($z_{50}\sim1.2$). Bulgeless galaxies have lower-mass haloes and higher specific stellar angular momentum, compatible with Milky Way observations. However, specific star formation rates and hydrogen gas fractions are slightly higher than Milky Way observations. Our analysis of the redshift evolution of stellar components reveals that bulgeless galaxies have gradual disc growth with high thin disc-to-total mass ratios (D/T>0.5) since $z\sim 1$ and minimal bulge growth (B/T<0.1) since $z\sim1.5$. In contrast, bulge-dominated galaxies have earlier disc formation, which is disrupted, resulting in higher morphology evolution. Bulgeless galaxies are more likely to undergo gas-rich, coplanar, and corotating mergers, promoting disc survival, compared to bulge-dominated galaxies that encounter a broader spectrum of mergers. We also observed differences in galaxy structure between bulgeless and bulge-dominated galaxies without major mergers, suggesting the relevance of early gas accretion and alignment. Bulgeless galaxies have younger stellar populations and more extended star formation histories than bulge-dominated galaxies, which rapidly quench and have older stellar populations. These findings elucidate the distinct merger-driven and secular pathways that give rise to Milky Way galaxies.

astro-ph.GA↗

arXiv2026

Bulgeless Evolution And the Rise of Discs (BEARD) III. A numerical simulation view of satellites around Milky-Way analogues

$Aims$. The existence of massive disc galaxies with little or no bulge challenges conventional $\Lambda$ cold dark matter model, which typically favours dynamically hot central structures due to early collapse and mergers. The study of these bulgeless disc galaxies is the aim of the Bulgeless Evolution And the Rise of Discs (BEARD) survey, as they offer a unique opportunity to investigate the link between galaxy morphology and the properties of their satellite systems. $Methods$. Using the high-resolution cosmological hydrodynamical simulation TNG50-1, we studied the satellite populations of 135 bulgeless galaxies. We compared their satellite properties to those of a bulge-dominated control sample with matched stellar masses. Our analysis focuses on satellite abundance, luminosity functions, spatial distribution, orbital alignment, and infall histories. $Results$. We find that satellite abundance is largely independent of host galaxy morphology. However, satellites around bulgeless galaxies exhibit luminosity functions with a steeper faint-end slope, are more centrally concentrated, and show stronger orbital alignment with the host disc plane. The orbital alignment originates from coherent post-infall dynamical evolution that depends on host galaxy morphology. The infall of more massive satellites can additionally perturb this process, contributing to a weakening or temporary stalling of the secular alignment. $Conclusions$. Due to the co-evolution of the host galaxy and the satellite system, the morphology of the central galaxy leaves a clear imprint on its satellite system. Bulgeless galaxies tend to have dynamically colder, more aligned, and more centrally concentrated satellite populations. These trends reflect a more quiet merger history and support the use of satellite properties as tracers of host galaxy formation pathways.

astro-ph.GA↗

arXiv2026

Multi-phase AGN-driven outflow in the NLSy1 IRAS 17020+4544. Unveiling dual-feedback and an energy-conserving ionized outflow with MEGARA/GTC integral field spectroscopy

The narrow-line Seyfert 1 (NLSy1) galaxy IRAS~17020+4544 is one of the few known sources exhibiting a multi-phase outflow detected in both highly ionized and molecular gas, consistent with AGN feedback operating in an `energy-conserving' regime. We investigate the properties and kinematics of the warm ionized gas using new optical seeing-limited integral-field spectroscopic observations obtained with MEGARA at the Gran Telescopio Canarias in both low- (R$\sim$6000) and medium-resolution (R$\sim$12000) modes. The H$\alpha$ and [OIII]$\lambda$5007 emission lines are modeled with multi-Gaussian fitting to characterize the ionized gas kinematics and derive the energetics of the outflow, which we compare with those of the X-ray and molecular phases. Ionization diagnostic diagrams (WHAN, WHaD, and BPT) are used to investigate the dominant ionization mechanism. We detect a fast ionized outflow traced by both H$\alpha$ and [OIII] emission lines, with similar spatial extensions (R$_\mathrm{out}\sim$1 kpc and $\sim$0.5 kpc) and velocities (v$_\mathrm{out}\sim$1460 and 1240 km s$^{-1}$, respectively), as well as a slower ionized outflow (v$_\mathrm{out}\sim$450 km s$^{-1}$) detected in the secondary component of the [OIII] line. The fast outflow follows an `energy-conserving' regime, while the slower component is consistent with a `momentum-driven' regime. The ionized outflows are enclosed within the molecular outflow detected with NOEMA (R$_\mathrm{CO}$=2.8$\pm$0.3 kpc), and the large momentum boosts derived in both phases suggest efficient AGN feedback, likely dominated by radiatively driven winds (quasar-mode) rather than kinetic (jet-driven) processes. Ionization diagnostics suggest that the outflow is mainly AGN-driven, with potential contributions from star formation and shocks. The molecular outflow dominates, with the ionized phase contributing less to the mass and feedback efficiency.

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arXiv2025

Peculiar galaxies I: A Catalog of Polar-Ring Galaxies from the TNG50 Simulation

The hydrodynamic cosmological simulation, TNG50, is employed to conduct an analysis of multi-spin galaxies that exhibit ringed structures composed of gas and stars that orbit nearly perpendicular around a host galaxy, known as polar ring galaxies (PRG). To ensure a robust sample, we select subhalos based on the angle subtended by the angular momentum profiles, as well as on a visual inspection. The analysis is focused on galaxies with stellar masses greater than 10$^{9}$ M$_\odot$. In addition, a dynamic decomposition is employed to separate the stellar and gaseous ring from the host galaxy. This results in a sample of 32 subhalos with PRGs. This sample exhibits properties similar to those observed. These include colours typical of early-type galaxies (ETGs) or those transitioning toward blue systems. Most host galaxies are classified as ETGs, with 37.5\% exhibiting a disk-dominated morphology. The mean bulge-to-total (B/T) ratio is 0.64. Rings have average radii that are 2.36 and 3.41 times larger than their effective radii for the stellar and gaseous components, respectively, with star formation occurring predominantly within the rings. In contrast with observations, rings in the simulation tend to be less massive and slightly less perpendicular. The obtained sample displays a variety of host galaxy morphologies, including wide and narrow rings, providing a robust framework for studying the varied structural characteristics of PRG variants.

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arXiv2024

JWST Observations of Starbursts: Massive Star Clusters in the Central Starburst of M82

We present a near infrared (NIR) candidate star cluster catalog for the central kiloparsec of M82 based on new JWST NIRCam images. We identify star cluster candidates using the F250M filter, finding 1357 star cluster candidates with stellar masses $>10^4$ M$_\odot$. Compared to previous optical catalogs, nearly all (87%) of the candidates we identify are new. The star cluster candidates have a median intrinsic cluster radius of $\approx$1 pc and have stellar masses up to $10^6$ M$_\odot$. By comparing the color-color diagram to dust-free yggdrasil stellar population models, we estimate that the star cluster candidates have A$_{\rm V}\sim3-24$ mag, corresponding to A$_{\rm 2.5μm}\sim0.3-2.1$ mag. There is still appreciable dust extinction towards these clusters into the NIR. We measure the stellar masses of the star cluster candidates, assuming ages of 0 and 8 Myr. The slope of the resulting cluster mass function is $β=1.9\pm0.2$, in excellent agreement with studies of star clusters in other galaxies.

astro-ph.GA↗

arXiv2024

JWST Observations of Starbursts: Cold Clouds and Plumes Launching in the M82 Outflow

In this paper we study the filamentary substructure of 3.3 $μ$m PAH emission from JWST/NIRCam observations in the base of the M82 star-burst driven wind. We identify plume-like substructure within the PAH emission with widths of $\sim$50 pc. Several of the plumes extend to the edge of the field-of-view, and thus are at least 200-300 pc in length. In this region of the outflow, the vast majority ($\sim$70\%) of PAH emission is associated with the plumes. We show that those structures contain smaller scale "clouds" with widths that are $\sim$5-15 pc, and they are morphologically similar to the results of "cloud-crushing" simulations. We estimate the cloud-crushing time-scales of $\sim$0.5-3 Myr, depending on assumptions. We show this time scale is consistent with a picture in which these observed PAH clouds survived break-out from the disk rather than being destroyed by the hot wind. The PAH emission in both the midplane and the outflow is shown to tightly correlate with that of Pa$α$ emission (from HST/NICMOS data), at the scale of both plumes and clouds, though the ratio of PAH-to-Pa$α$ increases at further distances from the midplane. Finally, we show that the outflow PAH emission is suppressed in regions of the M82 wind that are bright in X-ray emission. Overall, our results are broadly consistent with a picture in which cold gas in galactic outflows is launched via hierarchically structured plumes, and those small scale clouds are more likely to survive the wind environment when collected into the larger plume structure.

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arXiv2023

The cluster initial mass function of the M82 disk Super Star Clusters

The presence of a population of a large number ($\sim$400) of almost coeval (100--300 Myr) super star clusters (SSCs) in the disk of M82 offers an opportunity to construct the Cluster Initial Mass Function (CIMF) from the observed present-day Cluster Mass Function (CMF). We carry out the dynamical and photometric evolution of the CMF assuming the clusters move in circular orbits under the gravitational potential of the host galaxy using the semi-analytical simulation code EMACSS. We explore power-law and log-normal functions for the CIMFs, and populate the clusters in the disk assuming uniform, power-law, and exponential radial distribution functions. We find that the observed CMF is best produced by a CIMF that is power-law in form with an index of 1.8, for a power-law radial distribution function. More importantly, we establish that the observed turn-over in the present-day CMF is the result of observational incompleteness rather than due to dynamically induced effects, or an intrinsically log-normal CIMF, as was proposed for the fossil starburst region B of this galaxy. Our simulations naturally reproduce the mass-radius relation observed for a sub-sample of M82 SSCs.

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arXiv2022

Nebular abundance gradient in the Cartwheel galaxy using MUSE data

We here present the results from a detailed analysis of nebular abundances of commonly observed ions in the collisional ring galaxy Cartwheel using the Very Large Telescope (VLT) Multi-Unit Spectroscopic Explorer (MUSE) dataset. The analysis includes 221 HII regions in the star-forming ring, in addition to 40 relatively fainter H$α$ emitting regions in the spokes, disk and the inner ring. The ionic abundances of He, N, O and Fe are obtained using the direct method (DM) for 9, 20, 20, and 17 ring HII regions, respectively, where the S$^{++}$ temperature-sensitive line is detected. For the rest of the regions, including all the nebulae between the inner and the outer ring, we obtained O abundances using the strong-line method (SLM). The ring regions have a median $12+\log\rm{\frac{O}{H}}$=8.19$\pm$0.15, $\log\rm{\frac{N}{O}}=-$1.57$\pm$0.09 and $\log\rm{\frac{Fe}{O}}=-$2.24$\pm$0.09 using the DM. Within the range of O abundances seen in the Cartwheel, the N/O and Fe/O values decrease proportionately with increasing O, suggesting local enrichment of O without corresponding enrichment of primary N and Fe. The O abundances of the disk HII regions obtained using the SLM show a well-defined radial gradient. The mean O abundance of the ring HII regions is lower by $\sim$0.1 dex as compared to the extrapolation of the radial gradient. The observed trends suggest the preservation of the pre-collisional abundance gradient, displacement of most of the processed elements to the ring, as predicted by the recent simulation by Renaud et al. (2018), and post-collisional infall of metal-poor gas in the ring.

astro-ph.GA↗

arXiv2019

Detection of the self-regulation of star formation in galaxy discs

Stellar feedback has a notable influence on the formation and evolution of galaxies. However, direct observational evidence is scarce. We have performed stellar population analysis using MUSE optical spectra of the spiral galaxy NGC 628 and find that current maximum star formation in spatially resolved regions is regulated according to the level of star formation in the recent past. We propose a model based on the self-regulator or "bathtub" models, but for spatially resolved regions of the galaxy. We name it the "resolved self-regulator model" and show that the predictions of this model are in agreement with the presented observations. We observe star formation self-regulation and estimate the mass-loading factor, $η=2.5 \pm 0.5$, consistent with values predicted by galaxy formation models. The method described here will help provide better constraints on those models.

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arXiv2009

The Synoptic All-Sky Infrared (SASIR) Survey

We are proposing to conduct a multicolor, synoptic infrared (IR) imaging survey of the Northern sky with a new, dedicated 6.5-meter telescope at San Pedro Mártir (SPM) Observatory. This initiative is being developed in partnership with astronomy institutions in Mexico and the University of California. The 4-year, dedicated survey, planned to begin in 2017, will reach more than 100 times deeper than 2MASS. The Synoptic All-Sky Infrared (SASIR) Survey will reveal the missing sample of faint red dwarf stars in the local solar neighborhood, and the unprecedented sensitivity over such a wide field will result in the discovery of thousands of z ~ 7 quasars (and reaching to z > 10), allowing detailed study (in concert with JWST and Giant Segmented Mirror Telescopes) of the timing and the origin(s) of reionization. As a time-domain survey, SASIR will reveal the dynamic infrared universe, opening new phase space for discovery. Synoptic observations of over 10^6 supernovae and variable stars will provide better distance measures than optical studies alone. SASIR also provides significant synergy with other major Astro2010 facilities, improving the overall scientific return of community investments. Compared to optical-only measurements, IR colors vastly improve photometric redshifts to z ~ 4, enhancing dark energy and dark matter surveys based on weak lensing and baryon oscillations. The wide field and ToO capabilities will enable a connection of the gravitational wave and neutrino universe - with events otherwise poorly localized on the sky - to transient electromagnetic phenomena.

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