Diagnosing Ionization Mechanisms in Blue Compact Dwarfs, the Local Analogues to Primordial Galaxies

0 Assigned ID: 670 ----- Attempting Submission 1 (Fri Feb 24 20:31:10 GMT 2012) ----- This should be the final submission of Phase II, with newly distributed exposure times. Previous issues regarding readout times have been addressed. 1144252557 ----- Attempting Submission 1 (Mon Jul 09 14:40:41 GMT 2012) ----- ----- Attempting Submission 2 (Thu Dec 13 13:48:57 GMT 2012) ----- ----- Attempting Submission 3 (Mon Dec 17 12:17:58 GMT 2012) ----- Waiting for feedback from PC/CS regarding this warning. Diagnosing Ionization Mechanisms in Blue Compact Dwarfs, the Local Analogues to Primordial Galaxies Nearby Blue Compact Dwarf (BCD) galaxies are excellent laboratories for studying star-formation (SF) and feedback in relatively pristine, low-metallicity environments analogous to those thought to exist in the early Universe. Until recently, the dominant ISM energy source in BCDs was assumed to be photoionization from the young starburst. However, recent spectroscopic evidence suggests that energy input from shocks or AGN may also play a significant role, particularly on local scales. Distinguishing between these mechanisms/sources is key to understanding the evolution and composition of the ISM, and requires spatially resolving the structure and physical properties of the BCD's ISM, particularly the spatially narrow shock fronts (~10 pc ~ 0.4" at 5 Mpc). This can only be achieved with the unrivalled angular-resolution, sensitivity and FoV of WFC3. Here we propose to take advantage of the extensive filter set available on WFC3 to diagnose the ionization mechanisms within 2 nearby (D<5 Mpc) BCDs via narrow-band imaging. These observations will allow us to 1) distinguish between ionization mechanisms on ~1pc scales using diagnostic emission line ratios (e.g. [SII]/Ha and [OIII]/Hb; BPT diagram method); 2) locate WR stars from HeII4686 emission and correlate WR activity with shock and feedback activity; 3) investigate the electron density and metallicity (O/H) variations within these systems, via [OII] and [SII] doublet imaging. This study will provide significant insight into the role of feedback in the energetics, structure and SF history of dwarf galaxies and essentially, primordial galaxies in the early Universe. 1) Targets. Our sample consists of two BCDs; Mrk 71 and Mrk 209. Both BCDs lie at 4.3-5Mpc (taken from NED) and are thus the only two BCDs capable of meeting our science goals and maximally exploiting the high angular resolution of WFC3/UVIS (1 pixel =1 pc at 5Mpc). They are also at comparable distances, in order to minimize differences in the physical size resolved by HST. 2) Emission Line Filters. Imaging will be performed in a total of eleven filters, covering seven emission lines and four continuum regions. The narrow band images F487N and F656N will map the ionized gas via the Halpha(4861) and Hbeta(6563) emission, respectively. The [O ii] (3727; 29), [O iii] (5007) and He ii (4686) emission will be mapped with the F373N, F502N and F469N filters, respectively. Separated [S ii] doublet emission at 6716A and 6731A will be imaged using the FQ672N and FQ674N filters, respectively, and will map the electron density of the ionized gas via the ratio of these two lters. Each emission line lies within the wavelength range of its respective filter at the redshift of the galaxies and filter bandpasses are wide enough to accommodate the width of the broad component emission. The largest spatial dimension of the two proposed targets is ~64"x38", that can be covered by WFC3 quad filters (FoV of 80"^2). 3) Continuum Filters. Four continuum filters (F336W, F438W, F547M and F814W) have been chosen to sample the continuum at suitable wavelength intervals. These images will be used to accurately measure the continuum level at each emission line image and allow for its subtraction. Breakdown of exposure times (in seconds) per galaxy and filter: Filter Line Mrk 71 Mrk 209 F336W Continuum 350 350 F373N [O ii] 3727, 3729 1200 800 F438W Continuum 200 200 F469N He ii 4686 7000 3800 F487N Ha 1000 250 F502N [O iii] 5007 550 60 F547M Continuum 100 100 F656N H 850 200 FQ672N [S ii] 6717 2250 1300 FQ674N [S ii] 6731 5 300 2300 F814W Continuum 4 50 450 Total exp time 19250 9810 No. Orbits (inc. overheads) 5.0a 5.0 a = object in CVZ ISM IN EXTERNAL GALAXIES 12 false 0.0 0.0 false false false false SUPPORTED GALAXY DWARF COMPACT This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 GALAXY DWARF COMPACT This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F469N WFC3/UVIS Imaging No No F502N WFC3/UVIS Imaging No No F547M WFC3/UVIS Imaging No No F656N WFC3/UVIS Imaging No No FQ672N WFC3/UVIS Imaging No No FQ674N WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F373N WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F469N WFC3/UVIS Imaging No No F502N WFC3/UVIS Imaging No No F547M WFC3/UVIS Imaging No No F656N WFC3/UVIS Imaging No No FQ672N WFC3/UVIS Imaging No No FQ674N WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F373N WFC3/UVIS Imaging No No F336W POS-TARG DITHER 0.135 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 1

false

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