The aim is to generate "expected" flux from a system (defined as a starburst model redshifted to the target redshift) by simulating an HST observation. This is done by convolving the chosen model with the relevant HST filter's transmission curve. The redshift-corrected bandpass-convolved model SED can then be used to compute the (predicted) integrated flux in the given filter bandpass (i.e., effective stimulus).
Ingredients:
- Evolutionary models from the stellar population synthesis code Starburst99
- synphot and stsynphot packages
These artificial fluxes synthesized from starburst models can then be directly compared with the extinction-corrected observed photometry, to estimate star formation parameters- rates of star formation (SFRs) in case of continuous starbursts or initial starburst masses (Mburst) in the instantaneous burst scenario.
The code and results in this repository were produced from the analysis of HST/UV imaging of 6 radio galaxies, a part of a study newly published in ApJ, Duggal et al. 2024.
The target sample consists of 6 radio galaxies, with their redshifts, luminosity distances and HST imaging filters required as input. HST imaging for this sample was obtained with WFC3/UVIS in Cycle 25 GO program 15245 (PI: C. O’Dea).
There are 6 models each for continuous and instantantaneous star formation in the original 1999 dataset (hosted here). See starburst_models_info.txt for details. Each Starburst99 model (example_model.txt) is a set of spectral energy distributions, associated with 36 epochs between the stellar ages of 1 Myr to 1 Gyr, on a wavelength range of 10 to 1000 nm.
Also used in this analysis is the Starburst99 "far-UV properties" model, i.e. the number of (ionizing) photons produced with wavelength below 912 Å vs. time, for continuous and single-burst star formation.
Observed_SFR_calc| Script to calculate SFRs from various indicators (UV, Halpha, far-IR, etc.) using observed flux from target sources in these bands.10myr_Epoch.ipynb| A basic script that computes the (simulated) UV photomtery, in units of flux and AB mags, at a chosen stellar age of 10 Myr. This is done iteratively for all target galaxies, considering each of the 12 starburst models.SFR_Mburst_AllEpochs.ipynb| Automated computation of "expected" SFRs and Mburst values for all targets in each model scenario. Observed flux from HST observations is used to scale the model-produced fluxes. This can be used to check for "best fit" models by comparing with observed SFRs.SFR+IonizingPhotons_3Models_3Epochs.ipynb| This script includes the calculation of ionizing photons from the hot, massive stars, along with SFRs and starburst masses (continuous and instantaneous burst cases) at the young ages of 1 Myr, 10 Myr and 100 Myr. This is done with only those models that include nebular continuum with stellar UV emission.Obs_vs_Syn_plots| Plotting the comparison of "expected" SFRs and initial burst masses in the 6 radio galaxies, with the values deduced from observations. The best-fit model/epoch is highlighted.