Hai Fu's Homepage

An Introduction to Malmquist and Eddington Biases in Luminosity Relations

Posted on February 25, 2026

Astronomers often deal with a type of regression problems where the ordinate is luminosity, while the abscisca is a distance-independent observable. Such luminosity relations are some of the most useful correlations in astronomy because they enable the standard candle method to measure distances. Examples include the Leavitt (1912) law for... [Read More]

Tags: research

Mitigating Malmquist and Eddington Biases in Latent-Inclination Regression of the Tully-Fisher Relation

Posted on August 25, 2025

The Tully-Fisher relation (TFR) is an empirical correlation between luminosities and rotation velocities of disk galaxies. Since rotation velocity can be measured independent of distance, this correlation allows astronomers to use disk galaxies as standardizable candles for distance measurements. Once the correlation is calibrated using distances from Cepheid variables in... [Read More]

Tags: research

Keck Unveils a Filamentary Nebula around an Early Dusty Starburst Galaxy

Posted on June 3, 2024

Graduate student Kevin Hall and I carried out deep integral-field spectroscopic observations of a unique conjunction of an early massive dusty starburst galaxy and two quasars in its background with the 10-meter Keck telescope on Mauna Kea, Hawaii. All three massive galaxies are at redshifts greater than 2.5 (corresponding to... [Read More]

Tags: research

Building the Tully-Fisher Relation without Inclination Angles

Posted on February 23, 2024

The Lucy statistical rectification method allows one to uncover the intrinsic distribution of data from its observed distribution. In this ApJ Letter, I apply the method to build the Tully-Fisher relation of disk galaxies, where both axes of the correlation (magnitude and emission line widths) are affected by the inclination... [Read More]

Tags: research

New student papers on dual active galactic nuclei published on the Astrophysical Journal

Posted on March 8, 2023

The following papers concluded two PhD theses in Physics (Astronomy subtrack) at the University of Iowa. Congratulations, Dr. Joshua Steffen and Dr. Arran Gross! [Read More]

Tags: research

Nature paper - A fast radio burst in a complex magnetised environment and a barred galaxy

Posted on September 21, 2022

I am part of an international team who discovered the highly variable magnetised environment of an extremely active fast radio burst in a distant galaxy. I contributed to the analysis of the optical spectra of the host galaxy 1.4 billion lightyears away and the background (possibly lensed) galaxy. I also... [Read More]

Tags: research

A New Longslit Spectrograph for Undergraduate Astronomy Labs

Posted on May 6, 2022

In Fall 2021 and Spring 2022, two undergraduate students helped me commission a longslit spectrograph on the 17-in telescope (PlaneWave CDK17) at the Van Allen Observatory (VAO). The LISA Spectrograph is made by Shelyak Instruments. The spectrograph bundle includes the spectrograph optics, a small CCD camera for target acquisition, a... [Read More]

Tags: teaching

MaNGA Merger Project funded by the NSF (AST-2103251)

Posted on September 27, 2021

The important role played by collisions and mergers in galaxy evolution has been appreciated since the 1970’s. Previous spectroscopic studies of colliding/merging galaxies, while confirming several basic predictions (e.g., elevated nuclear star formation and/or black hole accretion), generally explored only their brighter inner-most regions in a largely non-uniform manner. This... [Read More]

Tags: research news

Researchers detect cold gas pipelines feeding early, massive galaxies

Posted on February 24, 2021

Using absorption lines in the spectra of two background quasars and deep ALMA observations in CO, our group discovered a cold gas stream in a massive dark matter halo. The stream is made of gas that is extremely poor in heavy elements. The detection signifies that massive starburst galaxies existed... [Read More]

Tags: research news

The gas fraction evolution of star-forming galaxies traced by the CO Tully-Fisher relation

Posted on December 10, 2018

For the first time, we used the CO Tully-Fisher relation and a Bayesian statistical method to show the dramatic evolution in gas content of star-forming galaxies, confirming previous result that galaxies were much more gaseous billions of years ago. This new method avoids correcting the inclination angles of the galaxies... [Read More]

Tags: research news