Properties of the KISS Green Pea Galaxies

Green peas (GPs) are a class of extreme star-forming galaxies (SFGs) at intermediate redshifts, originally discovered via color selection using multifilter, wide-field survey imaging data. They are commonly thought of as being analogs of high-redshift Lyα-emitting galaxies. The defining characteristic of GP galaxies is a high-excitation nebular spectrum with very large equivalent width lines, leading to the recognition that GP-like galaxies can also be identified in samples of emission-line galaxies. Here we compare the properties a sample of [O iii]-selected SFGs (z = 0.29–0.41) from the KPNO International Spectroscopic Survey (KISS) with the color-selected GPs. We find that the KISS [O iii]-selected galaxies overlap with the parameter space defined by the color-selected GPs; the two samples appear to be drawn from the same population of objects. We compare the KISS GPs with the full Hα-selected KISS SFG sample (z < 0.1) and find that they are extreme systems. Many appear to be young systems at their observed look-back times (3–4 Gyr), with more than 90% of their rest-frame B-band luminosity coming from the starburst population. We compute the volume density of the KISS red (KISSR) GPs at z = 0.29–0.41 and find that they are extremely rare objects. We do not see galaxies as extreme as the KISSR GPs in the local universe, although we recognize several lower-luminosity systems at z < 0.1

Properties of the KISS Green Pea Galaxies

Green Peas are a class of extreme star-forming galaxies at intermediate redshifts, originally discovered via color-selection using multi-filter, wide-field survey imaging data (Cardamone et al. 2009). They are commonly thought of as being analogs of high-redshift Ly$\alpha$-emitting galaxies. The defining characteristic of Green Pea galaxies is a high-excitation nebular spectrum with very large equivalent width lines, leading to the recognition that Green Pea-like galaxies can also be identified in samples of emission-line galaxies. Here we compare the properties a sample of [O III]-selected star-forming galaxies (z = 0.29-0.41) from the KPNO International Spectroscopic Survey (KISS) with the color-selected Green Peas. We find that the KISS [O III]-selected galaxies overlap with the parameter space defined by the color-selected Green Peas; the two samples appear to be drawn from the same population of objects. We compare the KISS Green Peas with the full H$\alpha$-selected KISS star-forming galaxy sample (z $<$ 0.1) and find that they are extreme systems. Many appear to be young systems at their observed look-back times (3-4 Gyr), with more than 90% of their rest-frame B-band luminosity coming from the starburst population. We compute the volume density of the KISSR Green Peas at z = 0.29-0.41 and find that they are extremely rare objects. We don't see galaxies as extreme as the KISSR Green Peas in the local Universe, although we recognize several lower-luminosity systems at z $<$ 0.1.Comment: 21 pages, 12 figures. Accepted for publication in the Astrophysical Journa

The Star Formation Across Cosmic Time (SFACT) Survey. III. Spectroscopy of the Initial Catalog of Emission-Line Objects

The Star Formation Across Cosmic Time (SFACT) survey is a new narrowband survey designed to detect emission-line galaxies (ELGs) and quasi-stellar objects (QSOs) over a wide range of redshifts in discrete redshift windows. The survey utilizes the WIYN 3.5m telescope and the Hydra multifiber positioner to perform efficient follow-up spectroscopy on galaxies identified in the imaging part of the survey. Since the objects in the SFACT survey are selected by their strong emission lines, it is possible to obtain useful spectra for even the faintest of our sources (r ~ 25). Here we present the 453 objects that have spectroscopic data from the three SFACT pilot-study fields, 415 of which are confirmed ELGs. The methodology for processing and measuring these data is outlined in this paper and example spectra are displayed for each of the three primary emission lines used to detect objects in the survey (H-alpha, [O III]5007, and [O II]3727). Spectra of additional QSOs and non-primary emission-line detections are also shown as examples. The redshift distribution of the pilot-study sample is examined and the ELGs are placed in different emission-line diagnostic diagrams in order to distinguish the star-forming galaxies from the active galactic nuclei.Comment: 20 pages, 10 figures. Accepted for publication in the Astronomical Journa

The Star Formation Across Cosmic Time (SFACT) Survey. I. Survey Description and Early Results from a New Narrow-Band Emission-Line Galaxy Survey

We introduce the Star Formation Across Cosmic Time (SFACT) survey. SFACT is a new narrow-band survey for emission-line galaxies (ELGs) and QSOs being carried out using the wide-field imager on the WIYN 3.5 m telescope. Because of the superior depth and excellent image quality afforded by WIYN, we routinely detect ELGs to r = 25.0. Our survey observations are made using three custom narrow-band filters centered on 6590 A, 6950 A, and 7460 A. Due to the sensitivity of the survey, we are able to simultaneously detect sources via a number of different emission lines over a wide range of redshifts. The principal lines detected in SFACT are H-alpha (redshifts up to 0.144), [O III]5007 (redshifts up to 0.500) and [O II]3727 (redshifts up to 1.015). In this paper we detail the properties of the survey as well as present initial results obtained by analyzing our three pilot-study fields. These fields have yielded a total of 533 ELG candidates in an area of 1.50 square degrees (surface density of 355 ELGs per square degree). Follow-up spectra for a subset of the ELG candidates are also presented. One of the key attributes of the SFACT survey is that the ELGs are detected in discrete redshift windows that will allow us to robustly quantify the properties of the star-forming and AGN populations as a function of redshift to z = 1 and beyond. The planned acquisition of additional narrow-band filters will allow us to expand our survey to substantially higher redshifts.Comment: 27 pages, 13 figures. Accepted for publication in the Astronomical Journa

The Enigmatic (Almost) Dark Galaxy Coma P: Distance Measurement and Stellar Populations from HST Imaging

We present Hubble Space Telescope (HST) observations of the low surface brightness (SB) galaxy Coma P. This system was first discovered in the Arecibo Legacy Fast ALFA HI survey and was cataloged as an (almost) dark galaxy because it did not exhibit any obvious optical counterpart in the available survey data (e.g., Sloan Digital Sky Survey). Subsequent WIYN pODI imaging revealed an ultra-low SB stellar component located at the center of the HI detection. We use the HST images to produce a deep color-magnitude diagram (CMD) of the resolved stellar population present in Coma P. We clearly detect a red stellar sequence that we interpret to be a red giant branch, and use it to infer a tip of the red giant branch (TRGB) distance of 5.50$^{+0.28}_{-0.53}$ Mpc. The new distance is substantially lower than earlier estimates and shows that Coma P is an extreme dwarf galaxy. Our derived stellar mass is only 4.3 $\times$ 10$^5$ $M_\odot$, meaning that Coma P has an extreme HI-to-stellar mass ratio of 81. We present a detailed analysis of the galaxy environment within which Coma P resides. We hypothesize that Coma P formed within a local void and has spent most of its lifetime in a low-density environment. Over time, the gravitational attraction of the galaxies located in the void wall has moved it to the edge, where it had a recent "fly-by" interaction with M64. We investigate the possibility that Coma P is at a farther distance and conclude that the available data are best fit by a distance of 5.5 Mpc.Comment: 22 pages, 11 figures. Accepted for publication in the Astronomical Journa

The Physical Conditions of Emission-Line Galaxies at Cosmic Dawn from JWST/NIRSpec Spectroscopy in the SMACS 0723 Early Release Observations

We present rest-frame optical emission-line flux ratio measurements for five $z>5$ galaxies observed by the JWST Near-Infared Spectrograph (NIRSpec) in the SMACS 0723 Early Release Observations. We add several quality-control and post-processing steps to the NIRSpec pipeline reduction products in order to ensure reliable relative flux calibration of emission lines that are closely separated in wavelength, despite the uncertain \textit{absolute} spectrophotometry of the current version of the reductions. Compared to $z\sim3$ galaxies in the literature, the $z>5$ galaxies have similar [OIII]$\lambda$5008/H$\beta$ ratios, similar [OIII]$\lambda$4364/H$\gamma$ ratios, and higher ($\sim$0.5 dex) [NeIII]$\lambda$3870/[OII]$\lambda$3728 ratios. We compare the observations to MAPPINGS V photoionization models and find that the measured [NeIII]$\lambda$3870/[OII]$\lambda$3728, [OIII]$\lambda$4364/H$\gamma$, and [OIII]$\lambda$5008/H$\beta$ emission-line ratios are consistent with an interstellar medium that has very high ionization ($\log(Q) \simeq 8-9$, units of cm~s$^{-1}$), low metallicity ($Z/Z_\odot \lesssim 0.2$), and very high pressure ($\log(P/k) \simeq 8-9$, units of cm$^{-3}$). The combination of [OIII]$\lambda$4364/H$\gamma$ and [OIII]$\lambda$(4960+5008)/H$\beta$ line ratios indicate very high electron temperatures of $4.1<\log(T_e/{\rm K})<4.4$, further implying metallicities of $Z/Z_\odot \lesssim 0.2$ with the application of low-redshift calibrations for ``$T_e$-based'' metallicities. These observations represent a tantalizing new view of the physical conditions of the interstellar medium in galaxies at cosmic dawn.Comment: Accepted for publication in AAS Journals. 14 pages, 6 figures, 3 table

Evaluating the Effects of SARS-CoV-2 Spike Mutation D614G on Transmissibility and Pathogenicity.

Global dispersal and increasing frequency of the SARS-CoV-2 spike protein variant D614G are suggestive of a selective advantage but may also be due to a random founder effect. We investigate the hypothesis for positive selection of spike D614G in the United Kingdom using more than 25,000 whole genome SARS-CoV-2 sequences. Despite the availability of a large dataset, well represented by both spike 614 variants, not all approaches showed a conclusive signal of positive selection. Population genetic analysis indicates that 614G increases in frequency relative to 614D in a manner consistent with a selective advantage. We do not find any indication that patients infected with the spike 614G variant have higher COVID-19 mortality or clinical severity, but 614G is associated with higher viral load and younger age of patients. Significant differences in growth and size of 614G phylogenetic clusters indicate a need for continued study of this variant

Evaluating the Effects of SARS-CoV-2 Spike Mutation D614G on Transmissibility and Pathogenicity

Global dispersal and increasing frequency of the SARS-CoV-2 spike protein variant D614G are suggestive of a selective advantage but may also be due to a random founder effect. We investigate the hypothesis for positive selection of spike D614G in the United Kingdom using more than 25,000 whole genome SARS-CoV-2 sequences. Despite the availability of a large dataset, well represented by both spike 614 variants, not all approaches showed a conclusive signal of positive selection. Population genetic analysis indicates that 614G increases in frequency relative to 614D in a manner consistent with a selective advantage. We do not find any indication that patients infected with the spike 614G variant have higher COVID-19 mortality or clinical severity, but 614G is associated with higher viral load and younger age of patients. Significant differences in growth and size of 614G phylogenetic clusters indicate a need for continued study of this variant