Mission Overview

Mapping the Escape Fraction of Ionizing Photons Using Resolved Stars (UVESCAPE)

 

Primary Investigator: Yumi Choi

HLSP Authors: Yumi Choi

Released: 2020-10-07

Updated: 2020-10-07

Primary Reference(s): Choi et al. 2020

DOI: 10.17909/t9-mraa-cd37

Citations: See ADS Statistics

Read Me

FUV Maps

Left: Comparison of the reconstructed FUV map (gray scale), derived from the BEAST SED fitting of individual stars, with actual GALEX FUV observations (contours) at the GALEX FUV angular resolution. They show an excellent agreement in their local and global morphology. Right: The predicted map of the intrinsic ionizing photon production rate at the GALEX FUV angular resolution. Red crosses denote the 73 stars with the initial masses > 100 M_solar and the effective stellar temperatures > 25,000 K. These stars produce about a quarter of the total intrinsic ionizing photons of NGC 4214 per second. Both panels have been smoothed with a 2D Gaussian filter to match GALEX FUV resolution of 4.2 arcseconds.

LyC Escape Fraction Map

Map of the LyC escape fraction. The underlying gray-scale shows the extinction-corrected H alpha emission at the full HST/WFC3 resolution. Solid lines denote the individual 13 SF regions, and are color-coded by their measured escape fractions. The local escape fraction varies from 0% to 40%. The escape fractions are high in the superbubbles, i.e., the SF regions 1 (40%) and 2 (20%), which together produce about 40% of the total ionizing photons. Morphologically, these regions have clear shell structures that indicate the presence of large low-density holes, consistent with their high escape fractions.

Overview

The UVESCAPE team has demonstrated a new method for measuring the escape fraction of ionizing photons using HST imaging of resolved stars in NGC 4214, a local analog of high-z starburst galaxies that are thought to be responsible for cosmic reionization. Specifically, they forward model the UV through near-IR spectral energy distributions of ~83,000 resolved stars to infer their individual ionizing flux outputs using the Bayesian Extinction And Stellar Tool (BEAST; Gordon et al. 2016). They constrain the local escape fraction by comparing the number of ionizing photons produced by stars to the number that are either absorbed by dust or consumed by ionizing the surrounding neutral hydrogen in individual star-forming regions. They find substantial spatial variation in the escape fraction (0-40%). Integrating over the entire galaxy yields a global escape fraction of 25% (+16% / -15%). This value is much higher than previous escape fractions of zero reported for this galaxy. They discuss sources of this apparent tension, and demonstrate that the viewing angle and the 3D ISM geometric effects are the cause. If one assumes that NGC 4214 has no internal dust, like many high-z galaxies, they find an escape fraction of 59% (an upper limit for NGC 4214). This is the first non-zero escape fraction measurement for UV-faint (M_FUV) = -15.9 galaxies at any redshift, and supports the idea that starburst UV-faint dwarf galaxies can provide a sufficient amount of ionizing photons to the intergalactic medium.  The team has made their catalog of stellar ionizing fluxes available as a High Level Science Product.

Data Products

The catalog has this file name:

hlsp_uvescape_hst_wfc3ir-wfc3uvis_ngc4214_multi_v1_catalog.fits

The catalog contains the following columns:

Column Name Units Description
RA deg Right Ascension (J2000).
DEC deg Declination (J2000).

F225W_VEGA

mag F225W Vega magnitude.

F336W_VEGA

mag F336W Vega magnitude.

F438W_VEGA

mag F438W Vega magnitude.

F814W_VEGA

mag F814W Vega magnitude.

F110W_VEGA

mag F110W Vega magnitude.

F160W_VEGA

mag F160W Vega magnitude.

LOGT_P16

K log of effective temperature (16th percentile).

LOGT_P50

K log of effective temperature (50th percentile).

LOGT_P84

K log of effective temperature (84th percentile).

LOGA_P16

yr log of stellar age (16th percentile).

LOGA_P50

yr log of stellar age (50th percentile).

LOGA_P84

yr log of stellar age (84th percentile).

LOGG_P16

cm s-2 log of stellar surface gravity (16th percentile).

LOGG_P50

cm s-2 log of stellar surface gravity (50th percentile).

LOGG_P84

cm s-2 log of stellar surface gravity (84th percentile).

M_INI_EXP

M_solar Initial stellar mass (expectation value).

M_INI_P16

M_solar Initial stellar mass (16th percentile).

M_INI_P50

M_solar Initial stellar mass (50th percentile).

M_INI_P84

M_solar Initial stellar mass (84th percentile).

AV_EXP

mag Internal extinction in V band (expectation value).

AV_P16

mag Internal extinction in V band (16th percentile).

AV_P50

mag Internal extinction in V band (50th percentile).

AV_P84

mag Internal extinction in V band (84th percentile).

LOGNION_INT_P16

# of LyC photons/s Ionizing photon production rate (16th percentile).

LOGNION_INT_P50

# of LyC photons/s Ionizing photon production rate (50th percentile).

LOGNION_INT_P84

# of LyC photons/s Ionizing photon production rate (84th percentile).

 

Data file types:

_catalog.fits Catalog of stellar ionizing sources.
_readme.txt README file describing the catalog and HLSP.

Data Access

The catalog file may be downloaded in FITS file format: hlsp_uvescape_hst_wfc3ir-wfc3uvis_ngc4214_multi_v1_catalog.fits

Citations

Please remember to cite the appropriate paper(s) below and the DOI if you use these data in a published work. 

Note: These HLSP data products are licensed for use under CC BY 4.0.

References