0Assigned ID: 494
----- Attempting Submission 1 (Fri Apr 11 14:32:18 GMT 2014) -----
HST Phase I Proposal 494 (cos.apt) successfully submitted.
----- Attempting Submission 2 (Fri Apr 11 15:09:16 GMT 2014) -----
----- Attempting Submission 3 (Fri Apr 11 21:04:48 GMT 2014) -----Resubmission #3:
- Changed buffer time to more conservative values for visits 1, 4, 5, 6.
Resubmission #2:
- Changed MIRRORA acquisition and use MIRRORB instead for the following: Visit 01, exposure 2, Visit 05, exposure 2, Visit 07, exposures 1 and 2
- All exposure times modified accordingly
Resubmission #1:
- Visit 2 (He2-10) acq/image changed to MIRRORB
- Exposure times for acquisition (image+spectroscopy) adjusted accordingly-1000692992----- Attempting Submission 1 (Thu Jul 24 17:18:25 GMT 2014) -----
HST Phase II Proposal 13697 (phaseII_24_07_2014_1291.apt) successfully submitted.
----- Attempting Submission 2 (Thu Jul 24 17:47:36 GMT 2014) -----
----- Attempting Submission 3 (Thu Oct 02 14:06:56 GMT 2014) -----
----- Attempting Submission 4 (Mon Nov 03 13:39:46 GMT 2014) -----
----- Attempting Submission 5 (Tue Nov 25 16:26:46 GMT 2014) -----Does star formation proceed differently in metal-poor galaxies?The importance of molecular gas in the star-formation process has been questioned by recent theoretical studies. When metals are scarce, star formation could proceed before the molecular fraction becomes significant, making cold atomic gas the key pre-requisite for star formation. The best case studies are blue compact dwarf galaxies (BCDs), with their prominent star-formation episode and yet with little or no evidence of molecular gas. Current observations do not provide strong constraints on the presence of dense atomic gas in BCDs nor on the fraction of molecular gas.
We propose to examine the HI region of 9 nearby BCDs selected from the Herschel Dwarf Galaxy Survey. Our program relies on the synergy of Hubble and Herschel, by calculating the gas cooling rate from the fine-structure level of ionized carbon, a parameter that can be determined both in the FUV with COS (probing the diffuse gas through the 1335.7A CII* absorption) and in the FIR with Herschel (probing the denser gas through the [CII] 157um emission). This comparison allows us to constrain the volume filling factor of dense vs. diffuse gas. The program we propose will allow us to examine how this fraction varies with metallicity, star-formation rate, and total gas mass. We will also be able to quantify the mass of molecular gas and evaluate its actual importance for star formation. Finally, a secondary objective is to characterize the main gas heating mechanisms in the HI region of BCDs and in particular the validity of the photoelectric effect paradigm in sources with a low dust-to-gas ratio, with potential implications for high-redshift galaxies.Tracers
------------
The main tracers in our project are the absorption lines C II * 1335.7 and H I Ly-alpha. These lines will be used to calculate the diffuse gas cooling rate per H atom, following the method used in Damped Ly-alpha systems (Lehner et al. 2004; Wolfe et al. 2003a,b). COS is the only instrument to observe C II* in Blue Compact Dwarfs (BCDs) and to carry our research program through.
In order to calculate the gas density in the diffuse phase, we also need in principle C II 1334.5 since the C II*/C II ratio depends on the density of collision partners (free electrons or H atoms). In most cases, C II will be heavily saturated, so we will use the S II column density as a tracer, assuming that the C/S abundance ratio measured in the H II region from optical emission-lines holds in the H I region (following Bowen et al. 2005 and Lebouteiller et al. 2013).
We will also derive chemical abundances using S II , N I , O I , Si II, and Fe II lines. The metallicity of the H I region will be calculated in order to correct the comparison of cooling rates in the diffuse vs. dense gas for potential abundance inhomogeneities. Previous studies with the FUSE telescope showed that a discontinuity is often present in BCDs, implying the existence of metal-free gas in the outskirts of galaxies (results reviewed in Lebouteiller et al. 2009 and Lebouteiller et al. 2013). The greater sensitivity of COS as compared to FUSE enables access to much weaker lines, thereby avoiding possible "hidden saturation" effects that plague extragalactic absorption-line studies (Lebouteiller et al. 2013; James et al. in prep.).
We have selected several sources with moderate metallicities (Z > 1/5 Z_solar) in which we expect to detect several H2 absorption lines, in particular at 1108AA. We will use these lines to compute the diffuse H2 column density.
The G130M grating will be used with central wavelengths 1222AA and 1291AA. Our phase I proposal used only 1222AA, but Ly-alpha falls partly in the gap between the 2 segments. Therefore, we propose to perform one set of exposures with central wavelength 1222AA to get all the tracers except Ly-alpha, and another set centered at 1291AA to get Ly-alpha. The latter observation is rather short, since the data can be heavily rebinned to measure the broad Ly-alpha damping wing profile. The G130M grating provides a larger spectral resolution and larger effective area as compared to G140L. This is extremely important to disentangle C II* to C II.
All sources in our sample have been detected in [C II] 157 um (Figure 4) and [O I] 63 um with Herschel. We also have ancillary H I 21 cm measurements to compare to our H I column density determination from Ly-alpha. The D/G ratio has been measured accurately for the first time with Herschel (Remy-Ruyer et al. 2013). Spitzer tracers (in particular PAH emission and [Si II]) are available for all sources through the Spitzer/IRS CASSIS database (Lebouteiller et al. 2011). CO(1-0) has been observed for all sources and is detected in 4/9 sources.
Sample
------------
From the initial 40 sources of the Dwarf Galaxy Survey (DGS), we first selected the most compact sources to minimize potential systematic errors in the comparison between COS (2.5 aperture) and Herschel observations (47" x 47" field-of-view, about 12 resolution). In two cases (NGC 4861 and NGC 1705), the objects are more extended than the COS aperture and we chose a pointing toward the massive stellar cluster. The contribution from the cluster to the Herschel [C II] flux is point-like and can be isolated from the extended emission.
Since we need to disentangle the BCD absorption lines from the Milky Way component, we also ignored objects with a radial velocity < 600 km s-1. Accounting for the 4 DGS compact sources already observed with G130M on COS, our initial sample was made of 24 potential targets. We have then selected a sub-sample of bright sources spanning the full range of SFR, metallicity, and H I mass of BCDs.
Our sample is deliberately not biased toward the extreme low end of the BCD metallicity range for two reasons. First, the 2 lowest-metallicity sources in our nearby Universe, I Zw 18 and SBS 0335-052, were already observed by COS/G130M, leading to a first important step (Lebouteiller et al. 2013) serving as a basis for the present program. Furthermore, although such extreme objects do provide important constraints to test theories of star formation, they are rare in the nearby Universe, and only recently with ALMA are we able to detect very high-redshift Milky-Way like sources that may harbor such low metallicities. Therefore, we also wish to include sources around 1/5 - 1/10 Z_solar that are more representative of a larger number of typical low-metallicity sources in the low-redshift Universe and that can serve as calibrators. In objects with moderate metallicities around or above 1/5 Z_solar, we expect to measure a diffuse H2 column density that we will use to calculate the molecular gas mass fraction to compare to our models. The final sample contains 9 BCDs, with distances between 5 Mpc and 50 Mpc.
Acquisition
------------------
The target coordinates have been refined since phase I mostly based on HST/STIS, WFC3, and SDSS images. We will use ACQ/SEARCH (followed by ACQ/IMAGE) for sources with uncertain coordinates (4/9 sources) either because they are somewhat extended or because several sources are located within 2-3". We will use only ACQ/IMAGE for the sources for which the coordinates are well known, mostly when the source is compact.
Exposure times
------------------------
From the 4 compact DGS sources in the MAST database, including IZw18, we have calibrated the continuum flux density estimates around 1400AA. As a starting point, we used the GALEX FUV magnitude or the FUSE (< 1200AA) spectrum when possible. In most cases, most of the FUV emission is expected to fall into the COS aperture. A correction was performed for the other cases based on the FUV extent, since GALEX (or FUSE) observations have a poorer spatial resolution and a larger field-of-view. The required signal-to-noise ratio (S/N) is driven by the C II* detection. We first estimated the C II column density by using the galaxy metallicity 12 + log(O/H) together with the C/O ratio observed in the H II region. We then estimated the column density and optical depth of C II* by assuming a typical collision partner density based on our recent study (Lebouteiller et al. 2013). Our estimates were verified by using the 4 sources in the COS database as references. We also accounted for the fact that the absorption line can be broadened if the source illuminates partially or fully the aperture. The degraded spectral resolution is always sufficient to disentangle the C II and C II* profiles. Based on our estimates, C II* is always optically thin, except in a couple of cases for which it is expected to be somewhat saturated. For such cases, we will constrain the turbulent velocity using other metallic species arising in the same phase, in the fashion of previous FUSE and COS studies.
Exposure times were calculated with the COS ETC. Our results won't be affected if the spectral resolution is somewhat decreased in Cycle 22 due to the change of Lifetime Position to LP3. All the objects will be observed in a single visit, with 1 to 2 orbits, which will allow us to reach a S/N of about 15 per resolution element. We have included the overheads (guide star acquisition, target acquisition, exposure overhead) for the time calculation. Our program is a small GO program, with a total of 11 orbits.ISM IN EXTERNAL GALAXIES12falsetruefalsefalsefalseSUPPORTEDGALAXYDWARF COMPACTSTAR FORMING REGIONThis object was generated by the targetselector and retrieved from the SIMBAD database.J2000J2000GALEX_FUV=14.3, F(1400)~6.31e-14, N(CII*)~14.6GALAXYDWARF COMPACTSTAR FORMING REGIONThis object was generated by the targetselector and retrieved from the SIMBAD database.J2000J2000GALEX_FUV=13.5, F(1400)~1.88e-13, N(CII*)~15.20GALAXYDWARF COMPACTSTAR FORMING REGIONThis object was generated by the targetselector and retrieved from the SIMBAD database.J2000J2000GALEX_FUV=15.1, F(1400)~4.31e-14, N(CII*)~14.7GALAXYDWARF COMPACTSTAR FORMING REGIONThis object was generated by the targetselector and retrieved from the SIMBAD database.J2000J2000GALEX_FUV=14.0, F(1400)~4.16e-14, N(CII*)~14.3GALAXYDWARF COMPACTSTAR FORMING REGIONThis object was generated by the targetselector and retrieved from the SIMBAD database.J2000J2000GALEX_FUV=14.8, F(1400)~3.98e-14, N(CII*)~14.7GALAXYDWARF COMPACTSTAR FORMING REGIONThis object was generated by the targetselector and retrieved from the SIMBAD database.J2000J2000GALEX_FUV=15.2, F(1400)~2.75e-14, N(CII*)~14.1GALAXYDWARF COMPACTSTAR FORMING REGIONThis object was generated by the targetselector and retrieved from the SIMBAD database.J2000J2000GALEX_FUV=16.7, F(1400)=9.87e-15, N(CII*)~14.3GALAXYDWARF COMPACTSTAR FORMING REGIONThis object was generated by the targetselector and retrieved from the SIMBAD database.J2000J2000GALEX_FUV=16.9, F(1400)~5.75e-15, N(CII*)~14.3GALAXYDWARF COMPACTSTAR FORMING REGIONThis object was generated by the targetselector and retrieved from the SIMBAD database.J2000J2000GALEX_FUV=13.6, F(1400)~1.20e-13, N(CII*)~14.5COS/FUVSpectroscopicNoNoG130M1222COS/FUVSpectroscopicNoNoG130M1222COS/FUVSpectroscopicNoNoG130M1222COS/FUVSpectroscopicNoNoG130M1222COS/FUVSpectroscopicNoNoG130M1222COS/FUVSpectroscopicNoNoG130M1222COS/FUVSpectroscopicNoNoG130M1222COS/FUVSpectroscopicNoNoG130M1222COS/FUVSpectroscopicNoNoG130M1222The scheduling data was generated by CASM 22.2.CASM was run in Phase II mode./tmp/OPVisit534259625455663919.xml(Tic-Visit
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:number-of-orbits 1
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(Tic-Obset
:proposal-id 13697
:visit-id "01"
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(Tic-Orbit
:proposal-id 13697
:visit-id "01"
:orbit-number 1
:pcs-time 333
:si-vis-utilization 2893
:al-overhead-at-end 0
:internal-dur-at-end 376
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3226
:pcs-gap 0
)true10F(1400)~6.3e-14, IUE~5e-14, using 5e-15, extended sourceBuffer-time and ETC for one sub-exposureBuffer-time and ETC for one sub-exposureThe scheduling data was generated by CASM 22.2.CASM was run in Phase II mode./tmp/OPVisit3141920484705320821.xml(Tic-Visit
:proposal-id 13697
:visit-id "02"
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:trans-version "20140605"
:date "25-Nov-2014 17:12:08.0"
:trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0
:FATAL-ERRORS 0 :CONTINUABLE-FATALS 0)
:number-of-orbits 1
:saa-model "31"
:si-bright-earth-limb-angle 20.0
:data-volume 87360
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:coron NIL
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(Tic-Obset
:proposal-id 13697
:visit-id "02"
:obset-id "02"
:pcs-mode "FGS"
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(Tic-Orbit
:proposal-id 13697
:visit-id "02"
:orbit-number 1
:pcs-time 333
:si-vis-utilization 2868
:al-overhead-at-end 0
:internal-dur-at-end 366
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3241
:pcs-gap 0
)true10F(1400)~1.88e-13, STIS G140L (52x0.2): 3e-15; IUE Large 8e-15)
GALEX FUV = 13.5
using 5e-15
Source is neither point-source or extended, chossing exposure time in betweenBuffer-time and ETC for one sub-exposureBuffer-time and ETC for one sub-exposureThe scheduling data was generated by CASM 22.2.CASM was run in Phase II mode./tmp/OPVisit4635114671844246918.xml(Tic-Visit
:proposal-id 13697
:visit-id "03"
:proposal-version -1
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:date "25-Nov-2014 17:12:10.0"
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(Tic-Obset
:proposal-id 13697
:visit-id "03"
:obset-id "03"
:pcs-mode "FGS"
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(Tic-Orbit
:proposal-id 13697
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:orbit-number 1
:pcs-time 333
:si-vis-utilization 3076
:al-overhead-at-end 0
:internal-dur-at-end 376
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3409
:pcs-gap 0
)true10F(1400)~4.31e-14, COS G140L: 2.3e-14; STIS G140L 52x0.2: 2e-15, IUE Large: 5.5e-14
Using 3e-14
Neither extended or point-like in the FUV, taking exposure time between point-source and extendedBuffer-time and ETC for one sub-exposureBuffer-time and ETC for one sub-exposureThe scheduling data was generated by CASM 22.2.CASM was run in Phase II mode./tmp/OPVisit4195669159231533301.xml(Tic-Visit
:proposal-id 13697
:visit-id "04"
:proposal-version -1
:trans-version "20140605"
:date "25-Nov-2014 17:14:32.0"
:trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0
:FATAL-ERRORS 0 :CONTINUABLE-FATALS 0)
:number-of-orbits 1
:saa-model "31"
:si-bright-earth-limb-angle 20.0
:data-volume 191680
:tdrss-contact-duration 0
:coron NIL
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(Tic-Obset
:proposal-id 13697
:visit-id "04"
:obset-id "04"
:pcs-mode "FGS"
)
(Tic-Orbit
:proposal-id 13697
:visit-id "04"
:orbit-number 1
:pcs-time 333
:si-vis-utilization 2887
:al-overhead-at-end 0
:internal-dur-at-end 395
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3257
:pcs-gap 0
)true10F(1400)~4.16e-14, HST STIS G140L: 6e-16; IUE Large: 1e-13
Using 1e-14
Neither extended or point-like in the FUV, taking exposure time between point-source and extendedBuffer-time and ETC for one sub-exposureBuffer-time and ETC for one sub-exposureThe scheduling data was generated by CASM 22.2.CASM was run in Phase II mode./tmp/OPVisit140272320348875860.xml(Tic-Visit
:proposal-id 13697
:visit-id "05"
:proposal-version -1
:trans-version "20140605"
:date "25-Nov-2014 17:15:21.0"
:trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0
:FATAL-ERRORS 0 :CONTINUABLE-FATALS 0)
:number-of-orbits 1
:saa-model "31"
:si-bright-earth-limb-angle 20.0
:data-volume 156880
:tdrss-contact-duration 0
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(Tic-Obset
:proposal-id 13697
:visit-id "05"
:obset-id "05"
:pcs-mode "FGS"
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(Tic-Orbit
:proposal-id 13697
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:si-vis-utilization 3136
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:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3470
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)true10F(1400)~3.98e-14, COS G140L: 3e-15
Estimating 5e-15 in the peak
ExtendedBuffer-time and ETC for one sub-exposureBuffer-time and ETC for one sub-exposureThe scheduling data was generated by CASM 22.2.CASM was run in Phase II mode./tmp/OPVisit6935541096206246412.xml(Tic-Visit
:proposal-id 13697
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:date "25-Nov-2014 17:15:40.0"
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(Tic-Obset
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(Tic-Orbit
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:si-vis-utilization 3040
:al-overhead-at-end 0
:internal-dur-at-end 376
:dark-offset NIL
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:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3409
:pcs-gap 0
)true10F(1400)~2.75e-14, IUE Large: 3.6e-14; FUSE: 2.0e-14
Using 1e-14
Neither extended or point-like in the FUV, taking exposure time between point-source and extendedBuffer-time and ETC for one sub-exposureBuffer-time and ETC for one sub-exposureThe scheduling data was generated by CASM 22.2.CASM was run in Phase II mode.(Tic-Visit
:proposal-id 13697
:visit-id "07"
:proposal-version -1
:trans-version "20140605"
:date "03-Nov-2014 14:06:46.0"
:trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0
:FATAL-ERRORS 0 :CONTINUABLE-FATALS 0)
:number-of-orbits 2
:saa-model "31"
:si-bright-earth-limb-angle 20.0
:data-volume 122128
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:coron NIL
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(Tic-Obset
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:visit-id "07"
:obset-id "07"
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(Tic-Orbit
:proposal-id 13697
:visit-id "07"
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:si-vis-utilization 3136
:al-overhead-at-end 0
:internal-dur-at-end 48
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3470
:pcs-gap 0
)
(Tic-Orbit
:proposal-id 13697
:visit-id "07"
:orbit-number 2
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:si-vis-utilization 3246
:al-overhead-at-end 0
:internal-dur-at-end 376
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3470
:pcs-gap 0
)true20F(1400)=9.87e-15, FUSE: 8e-15
Using 5e-15
Neither extended or point-like in the FUV, taking exposure time between point-source and extendedBuffer-time and ETC for one sub-exposureBuffer-time and ETC for one sub-exposureThe scheduling data was generated by CASM 22.2.CASM was run in Phase II mode./tmp/OPVisit1905104225859572035.xml(Tic-Visit
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:trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0
:FATAL-ERRORS 0 :CONTINUABLE-FATALS 0)
:number-of-orbits 2
:saa-model "31"
:si-bright-earth-limb-angle 20.0
:data-volume 122112
:tdrss-contact-duration 0
:coron NIL
)
(Tic-Obset
:proposal-id 13697
:visit-id "08"
:obset-id "08"
:pcs-mode "FGS"
)
(Tic-Orbit
:proposal-id 13697
:visit-id "08"
:orbit-number 1
:pcs-time 333
:si-vis-utilization 3103
:al-overhead-at-end 0
:internal-dur-at-end 48
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3470
:pcs-gap 0
)
(Tic-Orbit
:proposal-id 13697
:visit-id "08"
:orbit-number 2
:pcs-time 222
:si-vis-utilization 3246
:al-overhead-at-end 0
:internal-dur-at-end 376
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3470
:pcs-gap 0
)true20F(1400)~5.75e-15, only GALEX
Point-sourceBuffer-time and ETC for one sub-exposureBuffer-time and ETC for one sub-exposureThe scheduling data was generated by CASM 22.2.CASM was run in Phase II mode./tmp/OPVisit6175196966270455746.xml(Tic-Visit
:proposal-id 13697
:visit-id "09"
:proposal-version -1
:trans-version "20140605"
:date "25-Nov-2014 17:12:20.0"
:trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0
:FATAL-ERRORS 0 :CONTINUABLE-FATALS 0)
:number-of-orbits 1
:saa-model "31"
:si-bright-earth-limb-angle 20.0
:data-volume 191616
:tdrss-contact-duration 0
:coron NIL
)
(Tic-Obset
:proposal-id 13697
:visit-id "09"
:obset-id "09"
:pcs-mode "FGS"
)
(Tic-Orbit
:proposal-id 13697
:visit-id "09"
:orbit-number 1
:pcs-time 333
:si-vis-utilization 3041
:al-overhead-at-end 0
:internal-dur-at-end 385
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3409
:pcs-gap 0
)true10F(1400)~1.20e-13, 7.1e-14
Using 5e-14
Point-sourceBuffer-time and ETC for one sub-exposureBuffer-time and ETC for one sub-exposure