The Dwarf Galaxy Population at z ∼ 0.7: A Catalog of Emission Lines and Redshifts from Deep Keck Observations

Abstract

We present a catalog of spectroscopically measured redshifts over 0 < z < 2 and emission-line fluxes for 1440 galaxies. The majority (∼65%) of the galaxies come from the HALO7D survey, with the remainder from the DEEPwinds program. This catalog includes redshifts for 646 dwarf galaxies with log ( M ⋆ / M ⊙ ) < 9.5 . Eight-hundred and ten catalog galaxies did not have previously published spectroscopic redshifts, including 454 dwarf galaxies. HALO7D used the DEIMOS spectrograph on the Keck II telescope to take very deep (up to 32 hr exposure, with a median of ∼7 hr) optical spectroscopy in the COSMOS, EGS, GOODS-North, and GOODS-South CANDELS fields, and in some areas outside CANDELS. We compare our redshift results to existing spectroscopic and photometric redshifts in these fields, finding only a 1% rate of discrepancy with other spectroscopic redshifts. We measure a small increase in median photometric redshift error (from 1.0% to 1.3%) and catastrophic outlier rate (from 3.5% to 8%) with decreasing stellar mass. We obtained successful redshift fits for 75% of massive galaxies, and demonstrate a similar 70%–75% successful redshift measurement rate in 8.5 < log ( M ⋆ / M ⊙ ) < 9.5 galaxies, suggesting similar survey sensitivity in this low-mass range. We describe the redshift, mass, and color–magnitude distributions of the catalog galaxies, finding HALO7D galaxies representative of CANDELS galaxies up to i-band magnitudes of 25. The catalogs presented will enable studies of star formation, the mass–metallicity relation, star formation–morphology relations, and other properties of the z ∼ 0.7 dwarf galaxy population.

The Neon Gap: Probing Ionization with Dwarf Galaxies at z ∼ 1

“…The coadded spectra were then flux-scaled to best-fit photometric spectral energy distributions(SEDs). For more details on the coaddition and flux calibration of the spectra, see Pharo et al (2022).…”

“…To obtain redshift measurements from the coadded 1D galaxy spectra, we developed a routine to fit strong emission lines in a 0 < z < 2 redshift window, selected to encapsulate the region where strong line emitters were likely to be found. This procedure is described in detail in Pharo et al (2022). In Figure 1, we show an example HALO7D spectrum for a dwarf emission-line galaxy, demonstrating many of these features.…”

“…For this stacking procedure, we limit our sample to dwarf galaxies with a significant [OII]3727,3729 ÅÅ detection in Pharo et al (2022), so as to avoid including quiescent massive galaxies from the HALO7D sample (Tacchella et al 2020). This should not bias the sample since [OII]3727,3729 ÅÅ is typically one of the brightest emission lines detected, and it is close in wavelength to [NeIII]3869, so the redshift range will not be artificially restricted.…”

“…The distribution of the stacked sample in Figure 2 shows that the stacking sample is composed of the vast majority of HALO7D emission-line galaxies in the given redshift range. Pharo et al (2022) investigated the star formation and colormagnitude properties of HALO7D emission-line galaxies relative to CANDELS photometric catalogs, finding them comparable to CANDELS on the star-forming main sequence at similar redshift and with similar color properties. This indicates our stacking sample ought to be representative of the general galaxy population.…”

“…For each bin, we then combine the individual spectra with the following procedure. First, the continuum is estimated and subtracted using the median-filter method described in Section 3.2 of Pharo et al (2022), and the residual fluxes are normalized to the [OII]λλ3727,3729 line flux. We choose to initially remove the continuum from all galaxies in order to avoid difficulties with particularly low-mass galaxies, where the continuum is often not well detected.…”