Red giant stars as standard candles

Event Date:
2022-06-07T12:30:00
2022-06-07T15:00:00
Event Location:
room 203 of the graduate student centre
Speaker:
Javiera Fernanda Parada Torres
Related Upcoming Events:
Grad Theses
Intended Audience:
Public
Event Information:

This thesis introduces two new extragalactic distance determination

methods; the first uses the median magnitude of carbon-rich asymptotic

giant branch stars (CS), while the second uses the combined luminosity

function of the red-giant branch (RGB) and oxygen-rich asymptotic giant

branch stars (AGB). The sample of CS and RGB+AGB stars are selected from

near-infrared JHK_s-bands colour-magnitude diagrams (CMD), as in these

filters RGs are bright and easy to identify. Both methods use the

Magellanic Clouds as the fundamental calibrators and are tested in four

Magellanic type galaxies: NGC 6822, IC 1613, WLM and NGC 3109, these

target galaxies are all members of the Local Group.

 

For the CS method, the CS J-band luminosity function is fitted using a

Lorentzian distribution modified to allow the distribution to be

asymmetric. The parameters of the best-fit distribution are then used to

determine if the CS luminosity function of a given galaxy resembles that

of the Large or Small Magellanic Clouds (LMC or SMC). Based on this

resemblance, either the LMC or SMC is used as the calibrator and the

distance to the given galaxy is estimated using the median J magnitude

of the CS samples.

 

The second method uses an un-binned maximum likelihood estimator to find

the distance modulus that minimizes the difference between the

luminosity function of the RGB+AGB stars in a target galaxy and the

model distribution given by the luminosity function of the RGB+AGB stars

in the LMC and SMC. The model luminosity function can be given by the

LMC and SMC individually or as a linear combination (LC) of both. The LC

includes a "shape" parameters that quantifies how "LMC-" or "SMC-like" a

target galaxy is. Except for the NGC 3109 K_s luminosity function, the

LC "shape" results agree with the CS "LMC/SMC-like" classification.

 

Estimations of the distances through the tip of the RGB method are also

included to test the performance and compare the results when the three

different methods are applied to the same data set. The distance

estimates for the target galaxies from the three different methods

presented in this thesis are in good agreement within the error bars.

Add to Calendar 2022-06-07T12:30:00 2022-06-07T15:00:00 Red giant stars as standard candles Event Information: This thesis introduces two new extragalactic distance determination methods; the first uses the median magnitude of carbon-rich asymptotic giant branch stars (CS), while the second uses the combined luminosity function of the red-giant branch (RGB) and oxygen-rich asymptotic giant branch stars (AGB). The sample of CS and RGB+AGB stars are selected from near-infrared JHK_s-bands colour-magnitude diagrams (CMD), as in these filters RGs are bright and easy to identify. Both methods use the Magellanic Clouds as the fundamental calibrators and are tested in four Magellanic type galaxies: NGC 6822, IC 1613, WLM and NGC 3109, these target galaxies are all members of the Local Group.   For the CS method, the CS J-band luminosity function is fitted using a Lorentzian distribution modified to allow the distribution to be asymmetric. The parameters of the best-fit distribution are then used to determine if the CS luminosity function of a given galaxy resembles that of the Large or Small Magellanic Clouds (LMC or SMC). Based on this resemblance, either the LMC or SMC is used as the calibrator and the distance to the given galaxy is estimated using the median J magnitude of the CS samples.   The second method uses an un-binned maximum likelihood estimator to find the distance modulus that minimizes the difference between the luminosity function of the RGB+AGB stars in a target galaxy and the model distribution given by the luminosity function of the RGB+AGB stars in the LMC and SMC. The model luminosity function can be given by the LMC and SMC individually or as a linear combination (LC) of both. The LC includes a "shape" parameters that quantifies how "LMC-" or "SMC-like" a target galaxy is. Except for the NGC 3109 K_s luminosity function, the LC "shape" results agree with the CS "LMC/SMC-like" classification.   Estimations of the distances through the tip of the RGB method are also included to test the performance and compare the results when the three different methods are applied to the same data set. The distance estimates for the target galaxies from the three different methods presented in this thesis are in good agreement within the error bars. Event Location: room 203 of the graduate student centre