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
New JWST redshifts for the host galaxies of CDF-S XT1 and XT2: Understanding their nature
EAPPACHEN, D | Mar 26, 2025
CDF-S XT1 and XT2 are considered two “canonical” extragalactic fast X-ray transients (FXTs). In this work, we report new constraints on both FXTs, based on recent JWST NIRCam and MIRI photometry, as well as NIRspec spectroscopy for CDF-S XT2 that allow us to improve our understanding of their distances, energetics, and host galaxy properties compared to the pre-JWST era.
Methods. We use the available HST and JWST archival data to determine the host properties and constrain the energetics of each FXT based on spectral energy distribution (SED) photometric fitting.
Results. The host of CDF-S XT1 is now constrained to lie at zphot = 2.76+2.21-0.13, implying a host absolute magnitude MR = −19.14 mag, stellar mass M* ≈ 2.8 × 108 M⊙, and star formation rate SFR ≈ 0.62 M⊙ yr−1. These properties lie at the upper end of previous estimates, leaving CDF-S XT1 with a peak X-ray luminosity of LX, peak ≈ 2.8 × 1047 erg s−1. We argue that the best progenitor scenario for XT1 is a low-luminosity gamma-ray burst (GRB), although we do not fully rule out a proto-magnetar association or a jetted tidal disruption event involving a white dwarf and an intermediate-massive black hole. In the case of CDF-S XT2, JWST imaging reveals a new highly obscured component of the host galaxy, previously missed in HST images, while NIRspec spectroscopy securely places the host at zspec = 3.4598 ± 0.0022. The new redshift implies a host with MR = −21.76 mag, M* ≈ 5.5 × 1010 M⊙, SFR ≈ 160 M⊙ yr−1, and FXT LX, peak ≈ 1.4 × 1047 erg s−1. The revised energetics, similarity to X-ray flash event light curves, small host offset, and high host SFR favor a low-luminosity collapsar progenitor for CDF-S XT2. Although a magnetar model is not ruled out, it appears improbable.
Conclusions. While these HST and JWST observations shed light on the host galaxies of XT1 and XT2, and by extension, on the nature of FXTs, a unique explanation for both sources remains elusive. Rapid discovery, for instance, with the Einstein Probe satellite, and contemporaneous multiwavelength detections of FXTs remain essential for clarifying the nature of FXTs.
RESEARCH HIGHLIGHTS | IIA
An accreting supermassive black hole buried in a faint dwarf galaxy
MOUSUMI DAS | Sep 10, 2024
In the last decade, there have been several discoveries of active galactic nuclei (AGN) in dwarf galaxies including an AGN in an ultracompact dwarf galaxy with a black hole mass >106 Me. However, finding a supermassive black hole (SMBH) in a dwarf low surface brightness (LSB) galaxy is rare. We report the discovery of a Seyfert type 2 class AGN that is associated with a nuclear SMBH of mass ∼6.5 × 106 Me in a dwarf LSB galaxy (μ0,r > 23.8 mag arcsec−2) that we denote by MJ0818+2257. The galaxy was previously thought to be an outlying emission blob around the large spiral galaxy LEDA 1678924. In our current analysis, which includes the detection of the optical counterpart of MJ0818+2257, we study its ionized gas kinematics and find that the dynamical mass within the ionized gas disk is ∼5.3 × 109 Me. This is comparable to its stellar mass, which is ∼3 × 109 Me, and suggests that MJ0818+2257 is moderately dark matter dominated within the stellar disk. The SMBH-mass-togalaxy-stellar-mass ratio is MBH/M(*) > 0.022, which is high compared to disk galaxies. Our detection of an SMBH in a bulgeless LSB dwarf galaxy raises questions about the growth of SMBHs in low-luminosity galaxies and suggests the possibility of detecting heavy seed black holes from early epochs in LSB dwarf galaxies in the low-redshift Universe.
RESEARCH HIGHLIGHTS | IIA
Changing-look active galactic nuclei: a study of optical/uv and the highly ionized fe kα x-ray line flux variations using photoionization simulations
SANTANU MONDAL | Jul 20, 2025
Significant variability in broad emission line strengths of active galactic nuclei (AGN) over months to years has been observed, often accompanied by intrinsic continuum changes. Such spectral variability challenges the traditional AGN classification scheme, which attributes differences between type 1 and type 2 to geometrical effects, as transitions between these types occur on timescales shorter than viscous ones. In this work, using the cloudy photoionization simulations, we investigated the response of the major emission line fluxes, in the optical/UV and hard X-ray bands, to changes in the intensity and shape of the continuum emission of the AGN under two scenarios: (i) changes in the X-ray power law while keeping disk emission fixed, and (ii) broadband continuum variations. We demonstrate that broad-line region (BLR) line fluxes are insensitive to X-ray power-law changes alone. Considering a well-studied case of the changing-look (CL) AGN Mrk 1018, which exhibits variations in the intrinsic disk emission, as well as the X-ray power law, our simulations reproduce observed brightening and dimming trends of the BLR emission. Moreover, we show that the highly ionized Fe Kα X-ray flux, primarily produced by the H-like and He-like ions of Fe, strongly depends on the X-ray strength of the intrinsic spectral energy distribution. These findings suggest that the origin of highly ionized Fe Kα emission is in the coronal part of the accretion disk and that the CL phenomenon can be triggered by intrinsic changes in the accretion properties of AGN.
Press Releases
PRESS RELEASES | SCOPE
Astronomers unveil observational evidence of how cosmic dust grains line up with the Galaxy’s magnetic field
SCOPE | Sep 03, 2025
Scientists have long believed that just like dust particles dancing in a ray of light, tiny cosmic particles floating between stars in the Milky Way act as storytellers of the universe. Now a team of astronomers, has just uncovered the strongest observational evidence yet of how these interstellar dust grains align themselves with magnetic fields in our Galaxy.
This is based on the paper titled "B-fields and Dust in Interstellar Filaments Using Dust Polarization (BALLAD-POL). III. Grain Alignment and Disruption Mechanisms in G34.43+0.24 Using Polarization Observations from JCMT/POL-2", by Saikhom Pravash, Archana Soam, Pham Ngoc Diep, Thiem Hoang, Nguyen Bich Ngoc, and Le Ngoc Tram, The Astrophysical Journal, 2025, 981, 128.
Press release by DST published here.
Press release by PIB published here.
Download the paper here.
PRESS RELEASES | SCOPE
Hanle Dark Sky Reserve star party brings together astronomy enthusiasts for the third year
SCOPE | Sep 26, 2025
Astronomy enthusiasts from across the country participated in amateur astronomy and astrophotography related activities at the third edition of the HDSR Star Party that was jointly organised by the Indian Institute of Astrophysics (IIA), Department of Wildlife Protection of UT Ladakh, and Bhabha Atomic Research Centre (BARC) between 18 and 23 September.
The PIB press release is here.
The DST press release is here.
PRESS RELEASES | SCOPE
Black holes and cosmic jets join forces to shape galaxies
SCOPE | Oct 21, 2025
Black hole activities suppress the birth of new stars around it, shows a new study that can help in a deeper understanding of how galaxies evolve and may provide answers to why some have very low star-formation rates.
This study was published in the Astrophysical Journal, titled “Warm Ionized Gas Outflows in Active Galactic Nuclei: What Causes Them?”, and is authored by Payel Nandi and C.S. Stalin from IIA and D.J. Saikia from IUCAA.
The PIB press release is here.
The DST press release is here.
The paper can be downloaded from here.
Upcoming Events
Study at IIA
PhD Programme
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.
Admissions
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. .
Research Fields
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.
Notice Board
Tenders, Technically Qualified Vendors & e-Auction Notices | GSTIN: 29AABTI0567R1ZZ
Job Opportunities
Galleries
VIGILANCE PLEDGE | 2025
Vigilance pledge
VIGILANCE PLEDGE | 2025
Vigilance pledge
INDEPENDENCE DAY | 2025
Independence Day celebrations at IIA Bengaluru
INDEPENDENCE DAY | 2025
Independence Day celebrations at IIA Bengaluru
INDEPENDENCE DAY | 2025
Independence Day celebrations at IIA Bengaluru
INDEPENDENCE DAY | 2025
Independence Day celebrations at GRO
INDEPENDENCE DAY | 2025
Independence Day celebrations at KSO
INDEPENDENCE DAY | 2025
Independence Day celebrations at VBO
INDEPENDENCE DAY | 2025
Independence Day celebrations at VBO
INDEPENDENCE DAY | 2025
Independence Day celebrations at GRO
INDEPENDENCE DAY | 2025
Independence Day celebrations at IAO Leh
INDEPENDENCE DAY | 2025
Independence Day celebrations at IAO Hanle
INDEPENDENCE DAY | 2025
Independence Day celebrations at Merak
INDEPENDENCE DAY | 2025
