Shadow the Scientists (StS) offers free online public experiential learning sessions for students at all academic levels, educators, and other enthusiasts several times a month. During these sessions, the participants eavesdrop via Zoom on scientists while they are actively conducting research or related activities. We also offer dedicated sessions that can be tailored for a specific group in which participants have more opportunities for direct engagement with the scientists.
Mapping the Velocities of Stars in Distant Lensing Galaxies
Dedicated Session for Schools in Bogotá
May 8, 2 AM–4 AM Hawai’i Standard Time
May 8, 7 AM–9 AM Colombia Standard Time
The gravity from massive distant galaxies can act like magnifying lenses to blow up and distort the image of bright galaxies behind them, often showing multiple copies of the same galaxy. Astronomers use this gravitational lensing to weigh the galaxy in front. The other way we can observe the effect of gravity in distant galaxies is to measure the speeds of the stars in their orbits.
These galaxies contain billions of stars, so we measure the combined speeds of all of them together by measuring how their motions change the spectrum of light in the galaxy. Modern telescopes are capable of measuring the spectrum in different locations across the galaxy, so we can extract a map of the speeds of stars throughout the galaxy. These maps show exactly where the gravity is concentrated and tell us about the structure and evolution of these galaxies.
We have an advantage; since we are measuring this for a galaxy that acts like a gravitational lens, we can compare the measurements from lensing and from the velocities to be more precise than either can accomplish on their own. Beyond that, we can even use these galaxies to measure how fast the Universe itself is expanding, which is one of the most controversial topics in astronomy!
Raja GuhaThakurta (UC Santa Cruz), Eric Peng (NOIRLab), and Elisa Toloba (Univ. of the Pacific), members of the Next Generation Virgo Cluster Survey (NGVS) research collaboration, will be using the Keck II 10-meter telescope and KCWI+KCRM instrument to study the stellar dynamics (motion of stars) and chemical composition of an unusual class of galaxies known as ultra-diffuse galaxies (UDGs) in the Virgo cluster of galaxies, located at a distance of about 50 million light years from us.
The defining characteristic of UDGs is that they have an unusually large physical size (radius) relative to other galaxies of comparable luminosity. They appear to be found preferentially in regions of high galaxy density such as galaxy clusters. The KCWI+KCRM instrument is a pair of integral field units (IFUs). IFUs allow astronomers to obtain three-dimensional data cubes – i.e., a 1D spectrum at each (x,y) or (RA, DEC) position in the sky.
Credit: NASA, ESA, and P. van Dokkum (Yale University)
A Detailed 3D Spectroscopic Study of Enigmatic Ultra Diffuse Galaxies in the Virgo Cluster of Galaxies
Raja GuhaThakurta (UC Santa Cruz), Eric Peng (NOIRLab), and Elisa Toloba (Univ. of the Pacific), members of the Next Generation Virgo Cluster Survey (NGVS) research collaboration, will be using the Keck II 10-meter telescope and KCWI+KCRM instrument to study the stellar dynamics (motion of stars) and chemical composition of an unusual class of galaxies known as ultra-diffuse galaxies (UDGs) in the Virgo cluster of galaxies, located at a distance of about 50 million light years from us.
The defining characteristic of UDGs is that they have an unusually large physical size (radius) relative to other galaxies of comparable luminosity. They appear to be found preferentially in regions of high galaxy density such as galaxy clusters. The KCWI+KCRM instrument is a pair of integral field units (IFUs). IFUs allow astronomers to obtain three-dimensional data cubes – i.e., a 1D spectrum at each (x,y) or (RA, DEC) position in the sky.
Mapping the Velocities of Stars in Distant Lensing Galaxies
Dedicated Session for Schools in Bogotá
June 9, 2 AM–4 AM Hawai’i Standard Time
June 9, 7 AM–9 AM Colombia Standard Time
The gravity from massive distant galaxies can act like magnifying lenses to blow up and distort the image of bright galaxies behind them, often showing multiple copies of the same galaxy. Astronomers use this gravitational lensing to weigh the galaxy in front. The other way we can observe the effect of gravity in distant galaxies is to measure the speeds of the stars in their orbits.
These galaxies contain billions of stars, so we measure the combined speeds of all of them together by measuring how their motions change the spectrum of light in the galaxy. Modern telescopes are capable of measuring the spectrum in different locations across the galaxy, so we can extract a map of the speeds of stars throughout the galaxy. These maps show exactly where the gravity is concentrated and tell us about the structure and evolution of these galaxies.
We have an advantage; since we are measuring this for a galaxy that acts like a gravitational lens, we can compare the measurements from lensing and from the velocities to be more precise than either can accomplish on their own. Beyond that, we can even use these galaxies to measure how fast the Universe itself is expanding, which is one of the most controversial topics in astronomy!
Mapping the Velocities of Stars in Distant Lensing Galaxies
Dedicated Session for Schools in Bogotá
July 1, 2 AM–4 AM Hawai’i Standard Time
July 1, 7 AM–9 AM Colombia Standard Time
The gravity from massive distant galaxies can act like magnifying lenses to blow up and distort the image of bright galaxies behind them, often showing multiple copies of the same galaxy. Astronomers use this gravitational lensing to weigh the galaxy in front. The other way we can observe the effect of gravity in distant galaxies is to measure the speeds of the stars in their orbits.
These galaxies contain billions of stars, so we measure the combined speeds of all of them together by measuring how their motions change the spectrum of light in the galaxy. Modern telescopes are capable of measuring the spectrum in different locations across the galaxy, so we can extract a map of the speeds of stars throughout the galaxy. These maps show exactly where the gravity is concentrated and tell us about the structure and evolution of these galaxies.
We have an advantage; since we are measuring this for a galaxy that acts like a gravitational lens, we can compare the measurements from lensing and from the velocities to be more precise than either can accomplish on their own. Beyond that, we can even use these galaxies to measure how fast the Universe itself is expanding, which is one of the most controversial topics in astronomy!
Please read the following as it gives some insight into how the evening will be structured.
Please treat others on the Zoom call with utmost respect at all times. There is a zero tolerance policy for violations. Violators will be removed from the Zoom call and future StS sessions.
Please keep in mind at all times that the primary purpose of the StS session is for the research team (e.g., team of astronomers) to collect scientific data. Please be respectful of their time and concentration.
For the adults joining us, please try to have your Zoom name reflect your full name and school/group affiliation [e.g., Raja GuhaThakurta (UCSC)]. For minors, because this event is open to the public, please feel free to use nicknames unless you have permission from parents or guardians to use your full name.
After joining the Zoom session, you will be muted, but please feel free to type a short introduction about yourself into the chat.
Until the scientists have some down time and can directly interface with the rest of the group on the Zoom call, please feel free to type questions and comments in the chat. Once the scientists are speaking with the group, please use the “raise hand” feature in Zoom, if youʻd like to speak.
Please be aware that the StS Zoom call will be recorded, including the chat window, and both may be posted to YouTube in whole or in part for others to view. By joining the Zoom call, you are consenting to being recorded and for the recording to be posted.
Please be cognizant of your video feed. Because the focus is on the science being done, please feel free to keep your video off during the Zoom call..
