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This target is not used in this proposal.0Assigned ID: 2638
----- Attempting Submission 1 (Thu Nov 11 15:08:18 GMT 2021) -----Joint NRAO/HST0----- Attempting Submission 1 (Thu Dec 09 17:12:18 GMT 2021) -----The molecular gas mass of high-redshift HI-selected galaxiesHI-absorption-selected galaxies associated with damped Ly-alpha absorbers (DLAs) provide a unique opportunity to study the gas in 'typical' galaxies at high redshifts, without a luminosity bias. We have used ALMA and NOEMA to detect [CII]-158 micron or CO emission from 13 DLA galaxies at z ~ 2-4, and the JVLA to detect CO(2-1) or CO(1-0) emission from three of these galaxies. We propose to continue this successful ALMA+JVLA project, with (1) a JVLA search for CO(1-0) or CO(2-1) emission from five DLA galaxies at z~2-4 with ALMA/NOEMA detections of CO or [CII]-158 micron emission, and (2) an HST ACS/WFC3 imaging of 3 of the 5 DLA galaxies, covering the rest-frame near-UV continuum. The JVLA observations will yield molecular gas masses for all five galaxies, and CO excitation information for four systems, while the HST observations will measure the dust-unobscured star formation rates; the combination of ALMA/NOEMA, JVLA and HST data will allow us to obtain the most complete picture of high-z DLA galaxies to date, and to directly test whether such galaxies might have been missed in emission-selected samples due to dust obscuration. We request 36.5 hours of JVLA time and 3 orbits of HST time.We aim to image 2 galaxies associated with z~4 and z~2 DLAs in the near-infrared and optical wavebands with the WFC3 and ACS cameras. The primary goal of the HST observations is a measurement of the rest-frame NUV flux from the galaxies in order to determine the unobscured SFR. The two targets were selected from a sample of DLA host galaxies which have been detected with the Atacama Large Millimeter/sub-millimeter Array, in either [CII] or CO line emission, and in the far-infrared (FIR) or sub-mm continuum. This is a joint proposal with the Very Large Array (VLA); the VLA observations will provide information on the molecular content of each DLA host through the observation of CO(2-1) or CO(1-0) emission. The goal of the HST proposal is to identify the stellar counterparts of the host galaxies, determine the morphology of the star-forming regions, quantify the dust characteristics of the galaxies by comparing the unobscured SFR with the SFR inferred from the FIR or sub-mm continuum, and directly test whether the stellar continuum, the FIR continuum, the CO emission, and the [CII] emission are co-spatial, or arise from different parts of the galaxy.
We plan to sample the rest-frame NUV of these 4 DLA galaxies with the following filters:
QSO z_DLA Filter
J1626+2751 4.311 WFC3/F140W
J2225+0527 2.131 ACS/F814W
For each galaxy, the filter was chosen to cover the rest-frame near-ultraviolet (NUV) emission of the galaxies, i.e. just blueward of the [OII] 3727A line and the beginning of the Balmer break at 3650 A (thus providing clean measurements of the rest-frame NUV emission of the galaxies). These measurements can be converted into reliable UV-SFR estimates using well-calibrated scaling relations (Kennicutt & Evans, 2012), and will provide precise measurements of the morphology of the star-forming regions, i.e. size, spatial distribution, signatures of clumps.
For ACS/WFC we multiply the standard four point dither position by a factor of 5 to sample different parts of the detector while maintaining the optimal sub-pixel sampling. We also place the target close to the readout to minimize CTE, and place the target on Chip 1 which has reduced read noise over Chip 2. We note that we do not want to place the target in the corner of the chip with WFC-1 CTE, as we want to have more space around the target in case there is another galaxy nearby of interest associated with the absorber. We therefore place the target on the center of Chip 1, which has reduced read noise over Chip 2.
For the WFC3/IR dither pattern, we use the WIDE-7 pattern increased by a factor of 3 on page 17 from ISR 2016-14 by implementing POS-TARGs. For the NIR observations, we wish to stay in the linear regime and minimize persistence with our bright targets, and therefore will use SPAR25 with NSAMP of 14.
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