Embedded Files
Image credits to Kees Scherer
Introduction
Introduction
Understanding how fast the universe is expanding is one of the most important questions in cosmology. Type Ia supernovae serve as standard candles that allow astronomers to measure distances across the cosmos. This project investigates a group of these supernovae in the Virgo Cluster to refine our local measurements of the Hubble Constant to help understand the universe’s expansion.
Type Ia Supernovae
Type Ia Supernovae
Fig 1: Accretion scenario
[NASA/CXC/SAO and GSFC/D. Berry]
Fig 2: Merger scenario
[NASA/CXC/SAO and GSFC/D. Berry]
Stars with a mass less than 8 times the sun's mass (M < 8M⊙) turn into white dwarfs at the end of their lives. This happens when they have exhausted the nuclear fuel in their core, and shed their outer layers.
White dwarfs are physically limited to a mass of ~1.44M⊙, but can reach the limit in binary systems, through mass accretion or merging with another white dwarf
When the white dwarf's mass approaches this limit through accretion, or when two white dwarfs merge, a runaway thermonuclear explosion occurs - a type Ia supernova (SNe Ia)
Due to their limited mass, the peak luminosities of SNe Ia are tightly correlated with their light curves This allows them to be calibrated as "standard candles", which can help us measure cosmic distances.
Light Curves and Spectra
Light Curves and Spectra
Light curves track how the brightness of a supernova changes over time. Type Ia SNe have a very distinctive light curve shape, rising rapidly and decaying slowly, which is essential for determining their intrinsic brightness.
Spectra provide a snapshot of the supernova’s composition at a given moment. At peak brightness, SNe Ia spectra show strong silicon absorption features. These features also help confirm the supernova's classification and can indicate if there are outliers or peculiar cases that might bias distance measurements.
Together, light curves and spectra allow us to use fitting algorithms like SALT2 to extract distance information and standardize the supernova brightness across the sample.
Supernova Cosmology
Supernova Cosmology
Fig 3: Hubble tension over the years
[Astrobites]
The expansion of the universe was first discovered by Edwin Hubble, who found that distant galaxies are moving away from us. This phenomenon is now measured by the Hubble constant (H₀).
The Hubble tension refers to the discrepancy between the value of H₀ derived from the early universe (using the Cosmic Microwave Background) and the value measured locally using Type Ia supernovae and Cepheids. This tension could point to new physics or unknown systematics.
By creating a consistent and well-vetted sample of Virgo Cluster SNe Ia, we can improve the reliability of local distance estimates, potentially narrowing down the sources of this discrepancy.
Purpose of Study
Purpose of Study
This research aims to create a uniform database of 38 SNe Ia in the Virgo Cluster, primarily to be used for supernova cosmology. By analyzing a large sample of spatially concentrated SNe self-consistently, we can provide precise and statistically robust distance measurements. These distances will help to refine local measurements of the Hubble constant, which could provide more data for the Hubble Tension as well as inform further models of dark energy. This work provides a valuable resource for the cosmology community by removing inconsistencies that arise from combining data across different supernova surveys. Since the Virgo Cluster is nearby (~16.5 Mpc) and densely populated with galaxies, it serves as an excellent region to focus on. This homogeneous sample can also act as a local calibration set for cosmological supernovae at higher redshifts.
Fig 4: examples of Virgo galaxies
[Atlas of the Universe: R. Powell]
Methodology
Methodology
Galaxy Membership: I used the Extended Virgo Cluster Catalog (EVCC) to identify which galaxies are part of the Virgo Cluster.
Supernova Identification: Using the Asiago Supernova Catalog, I searched for all known SNe Ia that occurred in these galaxies.
Type Verification: For each candidate, I verified its classification as a Type Ia supernova by checking available spectral data.
Data Collection: I then compiled all available photometric and spectral data, referencing original sources via the NASA ADS and scraping public databases like WISeREP and ITEP-SAI.
Homogenization: To ensure consistency, I reformatted all datasets into a uniform structure, correcting for differences in filter systems, time formats, and data presentation.
Quality Control: When multiple datasets existed, I compared them and prioritized higher-quality or more complete observations.
Visual Examples of Virgo Cluster SNe Ia
Visual Examples of Virgo Cluster SNe Ia
Here's what the actual galaxies look like! Both images mark the location of a Type Ia event used in our study.
Zoomed in version, showing light echo of 2006X
Fig 5: Virgo SNe Ia locations
[Hubble Telescope, R. Foley for making]
Compiled Spectra at Peak
Compiled Spectra at Peak
Below are spectra of Virgo SNe Ia near peak brightness. These spectra are essential for verifying supernova type and understanding any peculiarities that could affect their use as standard candles. All spectra have been normalized in flux.
Compiled Lightcurves
Compiled Lightcurves
These are standardized B (blue) and V (visible) band light curves of all pre-2000s Type Ia supernovae in the Virgo Cluster. Each plot has been aligned by peak magnitude, and normalized for easier comparison. These will later be fit using the SALT2 model to extract distance modulus values.
Lightcurves in B Filter
Lightcurves in V filter
All pre-2000s Virgo SNe light curves shown individually
Next Steps
Next Steps
Complete the collection and homogenization of post-2000s Virgo SNe Ia data
Apply SALT2 fitting to derive light curve parameters and distance moduli
Analyze the scatter and systematic offsets in the sample
Estimate the local Hubble Constant from Virgo SNe alone
Compare results to other local measurements and explore implications for the Hubble tension
Acknowledgments
Acknowledgments
I would first like to thank the Koret Foundation for their generous support of undergraduate research at UC Santa Cruz, and giving me this amazing opportunity.
I would also like to thank Professor Ryan Foley and Dr. Phil Macias for all the support and guidance they've provided me with over the past two years, enabling me to do this research.
Lastly, I would like to thank all the other members of the UCSC Transients Team and Virgo project for all the help they've given me, and providing a supportive environment to succeed in.
Page updated
Report abuse