Anowar J. Shajib

I am a KICP Fellow at the University of Chicago. My principal research interest is gravitational lensing and observational cosmology. I work with galaxy-galaxy strong lenses and strongly lensed quasar/supernova systems to measure cosmological parameters such as the Hubble constant and to study properties of elliptical galaxies at the intermediate redshift (\(z\sim0.5\)).

I am the co-convener of the strong lensing topical team within the Rubin Observatory LSST's Dark Energy Science Collaboration. I am a co-PI of the STRIDES collaboration that aims to discover strongly lensed quasars from the Dark Energy Survey and other large-area sky-surveys.

Research Highlights

Time-delay cosmography

In a strong lens creating multiple images of a time-variable background source (quasar or SN), photons from the source that appear in different lensed images travel different cosmological distances around the foreground galaxy. Therefore, the measured time delay between the photon arrivals of the different images allows us to constrain a combination of these cosmological distances, which then provides a direct measurement of \(H_0\). The TDCOSMO collaboration has measured \(H_0\) by analyzing seven lensed quasar systems. Among them, I led the analysis for the system DES J0408\(-\)5354 (left picture) measuring \(H_0\) with 3.9% precision, the most precise single-system measurement of \(H_0\) to date (Shajib et al. 2020).

Evolving Dark Energy

We have proposed a simple \(w(z)\) function in Shajib & Frieman (2025) that is based on the scalar field model (i.e., quintessence) of evolving dark energy. This new model avoids going into the phantom regime (invoking exotic physics by having negative kinetic energy), that the widely-used \(w_0 w_a\) parametrization does by crossing the null energy condition (NEC) line. I have made the most complete compilation of cosmological datasets to date (figure on the left), to which I fit this new model. I find that the scalar-field model for dark energy is substantially preferred by the Baysian evidence ratio over the \(\Lambda\)CDM model, with a 2.7\(\sigma\) discrepancy between the two.

Improving \(H_0\) precison with resolved kinematics

The seven time-delay analyses from the TDCOSMO collaboration have assumed simple parametric forms for the mass profile, such as the power law, which is a potential systematic if the true mass profile in elliptical galaxies deviates from this assumption. We have developed a methodology to relax this assumption of simply-parametrized mass profiles in the lens galaxy and constrain \(H_0\) and the galaxy mass profile simultaneously using stellar kinematics. Relaxing this assumption increases the \(H_0\) uncertainty from 2% to ~8%. To improve the precision back to \(<\)2%, spatially resolved stellar kinematics is key. Using IFU data from Keck/KCWI (left picture), I have demonstrated for the first time that spatially resolved kinematics provide about seven-fold improvement in \(H_0\) precision over unresolved kinematics (Shajib et al. 2023). I am co-PI of a Cycle 2 JWST program to collect higher-\(S/N\) IFU data for TDCOSMO systems.

Project Dinos: studying galaxy evolution with the largest lens sample

To study the impact of baryonic feedback on elliptical galaxy evolution in the last 7 billion years (\(0.2 \lesssim z \lesssim 1\)) with strong lensing, a large statistical sample is necessary. To achieve this goal, I have formed Project Dinos, a HST archival program. Paper-I from this project (Tan, Shajib, et al. 2024) present the lens models of \(\sim\)80 galaxy-galaxy lens systems, the largest such sample to date with uniform, power-law mass models. Paper-II (Sheu, Shajib, et al. 2025) has extended the lens sample from Paper-I and provided the tightest constraint to-date on the inner slope of the dark matter halo of massive elliptical galaxies and its evolution at \(z \lesssim 1\). Data and model products from this project are publicly released at the project's dedicated webite.

First general solution to a 30-year-old problem: Efficient lensing computation for any elliptical mass distribution

The 2D integral to compute the deflection angle for an elliptical mass profile is non-analytical in the general case, which lacked an efficient solution for more than three decades. I proposed an efficient method that solves this problem (Shajib 2019). My proposed framework self-consistently unifies the lensing and kinematic analyses of a general elliptical mass distribution.

Integrated Sachs-Wolfe effect

In a dark-energy-dominated universe, the large-scale potential well decays with time. CMB photons gain a little amount of energy after crossing such a decaying potential well, which is the integrated Sachs-Wolfe (ISW) effect. I analyzed WISE and WMAP data to detect the ISW effect signal at \(3.4\sigma\) confidence level (left picture, Shajib & Wright 2016). This was the highest-significance detection of the ISW effect from a single dataset at the time of publication (2016).

Scinetific software development

I have developed several software packages (Github GitHub profile), all of which are open source for the benefit of the scientific community. These include:

Outreach

I am the creator of the Astro Bridge program, an initiative aimed at offering research experience to undergraduate students who come from communities or countries with limited access to such opportunities. By providing fully online programs, Astro Bridge aims to engage multiple students in a single collaborative project, ensuring access for a large number of participants. So far, four Bangladeshi students from this bridge program have been accepted to Physics and Astronomy graduate programs in the US.

In the pilot project within this program, I have mentored 19 undergraduate students from Bangladesh. Our project focuses on analyzing strong lensing systems, utilizing data obtained from the Hubble Space Telescope. We have submitted a journal article from this project ( Adnan et al. 2025 ) that is currently under peer review. This single paper has roughly tripled the number of published astronomers from Bangladesh, the eighth largest population in the world.
All the notebooks and codes used in this research project are released on GitHub here, and my tutorial for undergraduate+ students to self-learn strong lens modeling is here.

Please contact me if you are interested in creating such a project with the Astro Bridge template that faciliates efficient mentoring of a large number of students in the same research project.

Publications

Total 51 refereed/under-review papers with 13 first-author ones.

1. Evolving dark energy models: Current and forecast constraints. Submitted to Phys. Rev. D.
2. Strong gravitational lenses from the Vera C. Rubin Observatory. Accepted by Phil. Trans. A.
3. Strong Lensing by Galaxies. Invited Review in Space Science Reviews, 2024.
4. TDCOSMO. XII. Improved Hubble constant measurement from lensing time delays using spatially resolved stellar kinematics of the lens galaxy. A&A, 673, A9, 2023.
5. LensingETC: a tool to optimize multi-filter imaging campaigns of galaxy-scale strong lensing systems. ApJ, 938, 141, 2022.
6. TDCOSMO. IX. Systematic comparison between lens modelling software programs: time delay prediction for WGD 2038\(-\)4008. A&A, 667, A123, 2022.
7. Dark matter haloes of massive elliptical galaxies at \(z\sim0.2\) are well described by the Navarro-Frenk-White profile. MNRAS, 503, 2, 2380-2405, 2021.
8. High-resolution imaging follow-up of doubly imaged quasars. MNRAS, 503, 2, 1557-1567, 2021.
9. STRIDES: A 3.9 per cent measurement of the Hubble constant from the strong lens system DES J0408\(-\)5354. MNRAS, 494, 6072--6102, 2020
10. Unified lensing and kinematic analysis for any elliptical mass profile. MNRAS, stz1796, 2019.
11. Is every strong lens model unhappy in its own way? Uniform modelling of a sample of 13 quadruply+ imaged quasars. MNRAS, 483, 5649-5671, 2019.
12. Improving time-delay cosmography with spatially resolved kinematics. MNRAS, 473, 210-226, 2018.
13. Measurement of the integrated Sachs-Wolfe effect using the AllWISE data release. ApJ, 827:116, 2016.

CV

Find my CV here.