Marc Rafelski
Johns Hopkins University, MD·Astronomy & Astrophysics
Our picture of how galaxies grew in the early universe is skewed toward the brightest ones, simply because those are the easiest to see. There is a way around the bias: when the light of a distant background source passes through a foreground galaxy's dense hydrogen gas, the gas carves a deep absorption feature into the spectrum, called a Damped Lyman-alpha system (DLA).
- Fields
Astronomy & Astrophysics
Physics
- Topics
damped Lyman-alpha systems
high-redshift galaxies
galaxy formation
- Grants
- 1 known grant, through Feb 2027
What they work on
- Directly image galaxies identified by Damped Lyman-alpha absorption, dense neutral hydrogen seen in background spectra, using the Atacama Large Millimeter Array to locate counterparts selected independently of brightness.
- Measure the luminosities, star formation rates, gas masses, and stellar masses of these HI-selected normal galaxies at high redshift.
- Determine how often DLA galaxies are rotating disks versus mergers from resolved imaging and kinematics.
- Test whether absorption-selected and emission-selected methods yield the same high-redshift galaxy population by combining far-UV to radio data from the JVLA, NOEMA, VLT, GTC, and Keck with ALMA to compare ionized gas, neutral gas, stellar, and dust diagnostics.
More about the research
Because DLAs are found by the gas that blocks light rather than by light the galaxy emits, they flag "normal" galaxies regardless of brightness. What those galaxies actually look like, and whether they are the same objects found by emission surveys, is largely unknown.
Why it matters
Measuring star formation, gas content, and structure in galaxies selected by their hydrogen gas rather than their brightness fills in the part of the early galaxy population that luminosity-limited surveys miss, giving models of galaxy formation a less biased benchmark. The Bridge program offers post-baccalaureate students research experience and preparation for astronomy graduate school.
Known grants
From NIH and NSF research grants. Labs often have other funding we can't see.
Closest labs
Karen Masters
Haverford College, PA·Astronomy & Astrophysics
Test whether atomic hydrogen (HI) depletion times in MaNGA galaxies vary with ionization and heating sources, using HI-MaNGA 21 cm data combined with MaNGA galaxy maps.
Caitlin Casey
University of California-Santa Barbara, CA·Astronomy & Astrophysics
Characterize the thermal dust emission of galaxies across cosmic time using diverse far-infrared and millimeter (FIR/mm) observational datasets.
Kate Rowlands
Johns Hopkins University, MD·Astronomy & Astrophysics
Map recent star-formation histories in nearby galaxies using full spectral fitting of KILOGAS data, and compare them with current interstellar gas to see how star formation depends on available gas.
The school
Johns Hopkins University: 100 labs on PI Pages, $4.1B a year on research, 622 research doctorates a year.
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