01/06/2008 213th Meeting of the AAS, Session - Starburst Galaxies I., Poster - 445.10

Abstract: We present preliminary results from an HST program to search for Ly! escaping from galaxies previously identified as good candidates to search for Lyman continuum (LyC) emission using FUSE. The selection criteria

required redshifts high enough for LyC emission to avoid the HI absorption shadow of the Milky-way (z > 0.02), and objects bright enough for FUSE to detect if the escape fraction > 5%. The LyC flux was estimated from extrapolations

of GALEX FUV and NUV photometry. The candidates span a variety of morphological types, including face-on spirals, interacting systems, irregulars and compact blue objects. Unfortunately the FUSE mission ended before the LyC

observations could be secured. Nevertheless, ACS-SBC three color images of these objects, composed of synthetic bandpass filters centered on 1316, 1413 and 1617 Angstroms, constructed by subtracting the nested set of F125LP,

F140LP and F150LP long pass filter images, do show tantalizing hints of diffuse and concentrated Ly! escape. If the recent installation of the Cosmic Origins Spectrograph (COS) on HST proves successful and if the telescope's MgF2

overcoated Al mirrors have maintained a good portion of their original reflectivity of ~ 15% below 1150 Angstroms, then it may be possible to use this instrument to fulfill the original goals of the FUSE program. At the very least it will

be possible to verify the existence and investigate the dynamics of Ly! escape in these objects. Support for this work was provided by NASA through grant number 11110 from the Space Telescope Science Institute, which is operated

by AURA, Inc., under NASA contract NAS 5-26555.

ACS-SBC Search for Lyman ! Emission from FUSE Lyman Continuum CandidatesStephan R. McCandliss1, B. Fleming1, R. Lupu1, K. France2, E. B. Burgh2, G. R. Meurer1, E. Leitet3, J. Kruk1, B. Andersson4, N. Bergvall3, J. Deharveng5, P. D. Feldman1, T. M. Heckman1, P. Friedman6, M. Kaiser1

1Johns Hopkins Univ., 2University of Colorado, 3Uppsala Astronomical Observatory, Sweden, 4NASA Ames Research Center, 5Observatoire Astronomique de Marseille-Provence, France, 6California Institute of Technology.

New Ultraviolet

Photometric System

Project BalmerSlope Luminosity Histograms Ly! EscapeTarget Summary

Open Questions

• 14 UV bright galaxies

• LyC leak candidates

• Morphologically diverse

• Range of surface brightness

• 0.02 < z < 0.043

• 10 pc < pixel < 22 pc

• Super star clusters (~ R136) unresolved!

• How does Ly! escape?

• Ly! - LyC escape proxy?

• JWST reionization calibration?

Instantaneous Continuous

Images acquired from the set of nested ACS/SBC

longpass filters F125LP (CaF2), F140LP (BaF2)

are subtracted to form bandpass filters. F150Lp

(Quartz) serves as its own bandpass filter.

• C = F125LP - F140LP " Blue

• B = F140LP - F150LP " Green

• Q = F150LP " Red

Redshifted H II region spectra are overplotted on

the figure below. The target images are depicted

in the three colors further below.

We find large numbers of pixels that are

•“Impossibly Blue” (#bg< -4) " Ly! emission

•“Impossibly Red” (#gr > 4) " CIV-III, OIII?

In general each pixel contains the integrated

light from the UV bright stars and nebula, for a

variety of ages and attenuation by dust. For

each triplet of pixels we determine power law

slopes (blue/green, green/red, blue/red)

e.g. #bg = log[f131/f141]/log[1314./1412.]

and form the luminosity histograms shown

under each three color image below.

Spectral Synthesis EvolutionWe compare these histograms to the expected

evolution of these parameters calculated from

Starburst99 population synthesis models.

Balmer line emission can be used to estimate the

total ionizing radiation and assess the escape

fraction of Ly!. Ultimately we wish to close the

loop by observations of LyC escape.

We are acquiring Balmer emission line images

of our targets using the Nordic Optical

Telescope (NOT, E. Leiter - PI). Apache Point

Observatory Dual Imaging Spectrograph slit

scanned line images (shown below) allow

determination of the [NII] contamination in the

NOT H! images.

After filtering for ”Impossibly Blue” and

subtracting the “green” continuum we find

the ”Impossibly Red” is located near the stars

surrounded by diffuse Ly!.

We find before dust corrections

• FLy! = 9.92 x 10-13 ergs cm-2 s-1

• FH! = 6.00 x 10-13 ergs cm-2 s-1

• R = 1.65 compared to case b of 8.7