भारतीय खगोलभौतिकी संस्थान
Indian Institute of Astrophysics
Exploring the Universe since 1786
An Autonomous Institute under the
Department of Science & Technology
Government of India
Research Highlights
RESEARCH HIGHLIGHTS | IIA
Candidate ram-pressure stripped galaxies in six low-redshift clusters revealed from ultraviolet imaging
ANNAPURNI SUBRAMANIAM | Oct 22, 2024
The assembly of galaxy clusters is understood to be a hierarchical process with a continuous accretion of galaxies over time, which increases the cluster size and mass. Late-type galaxies that fall into clusters can undergo ram-pressure stripping, forming extended gas tails within which star formation can happen. The number, location, and tail orientations of such galaxies provide clues about the galaxy infall process, the assembly of the cluster over time, and the consequences of infall for galaxy evolution. Here, we utilise the ∼0.5-degree diameter circular field of the Ultraviolet Imaging Telescope to image six galaxy clusters at z < 0.06 that are known to contain ‘jellyfish’ galaxies. We searched for stripping candidates in the ultraviolet images of these clusters, which revealed 54 candidates showing signs of unilateral extra-planar emission, due to ram pressure stripping. Seven candidates had already been identified as likely stripping based on optical B-band imaging. We identified 47 new candidates through UV imaging. Spectroscopic redshift information is available for 39 of these candidate galaxies, of which 19 are associated with six clusters. The galaxies with spectroscopic redshifts that are not part of the clusters appear to be within structures at different redshifts identified as additional peaks in the redshift distribution of galaxies, indicating that they might be ram-pressure stripped or disturbed galaxies in other structures along the line of sight. We examine the orbital history of these galaxies based on their location in the position-velocity phase-space diagram and explore a possible connection to the orientation of the tail direction among cluster member candidates. There are limitations due to different integration times and imaging different regions with respect to the cluster centre. The tails of confirmed cluster member galaxies are found to be oriented away from the cluster centre.
RESEARCH HIGHLIGHTS | IIA
Mining the GALAH Data. I. Study of Five Super Lithium-rich Metal-poor Giants
SUSMITHA, A | May 01, 2024
The presence of a large amount of Li in giants is still a mystery. Most of the super Li-rich (SLR) giants reported in recent studies are in the solar metallicity regime. Here, we study the five metal-poor SLRs from the Galactic Archeology with HERMES Data Release 3, with their [Fe/H] ranging from −1.35 to −2.38 with lithium abundance of A(Li) 3.4 dex. The asteroseismic analysis reveals that none are on the red giant branch. The average period spacing (ΔP ) values indicate giants are in the core He-burning phase. All of them are low-mass giants (M < 1.5 Me). Their location in the Hertzsprung–Russell diagram suggests one of them is in the red clump (RC) phase, and interestingly, the other four are much brighter and coincide with the early asymptotic giant branch phase. The analysis of the abundance reveals that C, O, Na, Ba, and Eu are normal in giants of respective metallicities and evolutionary phases. Further, we did not find any strong evidence of the presence of dust in the form of infrared excess or binarity from the available radial velocity data. We discuss a few scenarios for the existence of SLRs at higher luminosity, including past merger events. Our findings will help in understanding the production and evolution of Li among giants, in particular, during the RC phase and the post-RC phase.
RESEARCH HIGHLIGHTS | IIA
The stellar bar–dark matter halo connection in the TNG50 simulations
MOUSUMI DAS | Nov 10, 2024
Stellar bars in disk galaxies grow as stars in near-circular orbits lose angular momentum to their environments, including their dark matter (DM) halo, and transform into elongated bar orbits. This angular momentum exchange during galaxy evolution hints at a connection between bar properties and the DM halo spin λ, the dimensionless form of DM angular momentum. We investigate the connection between halo spin λ and galaxy properties in the presence/absence of stellar bars, using the cosmological magnetohydrodynamic TNG50 simulations at multiple redshifts (0 < zr < 1). We determine the bar strength (or bar amplitude, A2/A0), using Fourier decomposition of the face-on stellar density distribution. We determine the halo spin for barred and unbarred galaxies (0 < A2/A0 < 0.7) in the center of the DM halo, close to the galaxy's stellar disk. At zr = 0, there is an anticorrelation between halo spin and bar strength. Strongly barred galaxies (A2/A0 > 0.4) reside in DM halos with low spin and low specific angular momentum at their centers. In contrast, unbarred/weakly barred galaxies (A2/A0 < 0.2) exist in halos with higher central spin and higher specific angular momentum. The anticorrelation is due to the barred galaxies' higher DM mass and lower angular momentum than the unbarred galaxies at zr = 0, as a result of galaxy evolution. At high redshifts (zr = 1), all galaxies have higher halo spin compared to those at lower redshifts (zr = 0), with a weak anticorrelation for galaxies having A2/A0 > 0.2. The formation of DM bars in strongly barred systems highlights how angular momentum transfer to the halo can influence its central spin.
Press Releases
PRESS RELEASES | SCOPE
International solar conference celebrates 125 years of solar physics research in India
SCOPE | Jan 24, 2025
More than 200 solar physicists from India and abroad have come together in Bengaluru this week for an international conference on “Sun, Space Weather, and Solar-Stellar Connections”. The conference is being organised by the Indian Institute of Astrophysics to commemorate the 125th anniversary of the Kodaikanal Solar Observatory and the birth of solar astrophysics in the country (conference webpage)
Download the PIB press release from here.
PRESS RELEASES | SCOPE
Thermal structure of solar coronal holes and their magnetic fields unveiled
SCOPE | Feb 18, 2025
A new study has accurately estimated the physical parameters of thermal and magnetic field structures of solar coronal holes which have significant influence on space weather. They found that there is no latitudinal variation of temperature structure of coronal holes, suggesting that coronal holes are likely to originate from the deep interior, and also that there is a latitudinal variation of strength of magnetic field structure of coronal holes that increases from the solar equator to the pole suggesting that coronal holes might have formed from the superposition of Alfven wave perturbations.
This is based on the paper titled "Thermal and magnetic field structure of near-equatorial coronal holes", by Hegde, M. and K.M. Hiremath, 688, A35, 2024, Astronomy & Astrophysics, 279, 7.
Press release by PIB published here.
Press release issued by DST here.
Download the paper from here.
PRESS RELEASES | SCOPE
Scientists Chart the Sun's Subsurface Weather Patterns Tied to Its 11-Year Activity Cycle
SCOPE | Apr 29, 2025
An international team of solar physicists has unveiled new insights into the dynamic "inner weather" of the Sun—plasma currents just beneath its surface that pulse in step with its 11-year sunspot cycle. In a study published on the 22nd of April 2025, in the The Astrophysical Journal Letters, researchers from the Indian Institute of Astrophysics (IIA), Stanford University (USA), and the National Solar Observatory (NSO, USA) have traced how these hidden flows shift over time, potentially reshaping our understanding of how the Sun's interior connects to its outer magnetic behavior, which has far-reaching influence on space weather and Earth.
This is based on the paper titled "Solar Cycle Variations in Meridional Flows and Rotational Shear within the Sun's Near-surface Shear Layer", by Anisha Sen, S. P. Rajaguru, Abhinav Govindan Iyer, Ruizhu Chen, Junwei Zhao, and Shukur Kholikov, 2025, Astrophysical Journal Letters, 984, 1.
Press release by PIB published here.
Press release issued by DST here.
Download the paper from here.
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IIA offers a vigorous programme of graduate studies that forms a vital component of research & training. The programme is overseen by the board of graduate studies. The Institute is also a major partner in the Joint Astronomy Programme (JAP), organized by the Indian Institute of Science.
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PhD applications may be submitted through the IIA PhD online applications portal in May. After the initial screening, shortlisted candidates will be interviewed in June. The final list of selected candidates will be announced in July, followed by the commencement of the programme in August. .
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Solar Studies
Studies of the Sun and solar system have been the longest pursued discipline at IIA. Members of the group conduct theoretical, numerical modeling, and observational studies in solar physics.
Stars & Galaxies
Research interests of the group members range from exoplanets, star formation, stellar evolution, end states of stars, Interstellar medium, the milky way Galaxy, nearby galaxies, active galaxies and time domain astronomy.
Theory
Members of the theoretical Astrophysics group work on a broad range of topics such as black hole astrophysics, pulsars, exoplanets, astrophysical turbulence & magnetic fields, MHD, cosmology and early universe.
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