Existing star-forming vs. active galactic nucleus (AGN) classification schemes using optical emission-line diagnostics mostly fail for low-metallicity and/or highly star-forming galaxies, missing AGN in typical
We present the first spatially resolved maps of gas-phase metallicity for two dust-obscured star-forming galaxies at
- Award ID(s):
- 1852617
- PAR ID:
- 10518787
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- IOP
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 958
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 64
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract z ∼ 0 dwarfs. To recover AGN in dwarfs with strong emission lines (SELs), we present a classification scheme optimizing the use of existing optical diagnostics. We use Sloan Digital Sky Survey emission-line catalogs overlapping the volume- and mass-limited REsolved Spectroscopy Of a Local VolumE (RESOLVE) and Environmental COntex (ECO) surveys to determine the AGN percentage in SEL dwarfs. Our photoionization grids show that the [Oiii ]/Hβ versus [Sii ]/Hα diagram (Sii plot) and [Oiii ]/Hβ versus [Oi ]/Hα diagram (Oi plot) are less metallicity sensitive and more successful in identifying dwarf AGN than the popular [Oiii ]/Hβ versus [Nii ]/Hα diagnostic (Nii plot or “BPT diagram”). We identify a new category of “star-forming AGN” (SF-AGN) classified as star-forming by the Nii plot but as AGN by the Sii and/or Oi plots. Including SF-AGN, we find thez ∼ 0 AGN percentage in dwarfs with SELs to be ∼3%–16%, far exceeding most previous optical estimates (∼1%). The large range in our dwarf AGN percentage reflects differences in spectral fitting methodologies between catalogs. The highly complete nature of RESOLVE and ECO allows us to normalize strong emission-line galaxy statistics to the full galaxy population, reducing the dwarf AGN percentage to ∼0.6%–3.0%. The newly identified SF-AGN are mostly gas-rich dwarfs with halo mass <1011.5M ⊙, where highly efficient cosmic gas accretion is expected. Almost all SF-AGN also have low metallicities (Z ≲ 0.4Z ⊙), demonstrating the advantage of our method. -
Abstract We report the discovery of two companion sources to a strongly lensed galaxy SPT0418-47 (“ring”) at redshift 4.225, targeted by the JWST Early Release Science program. We confirm that these sources are at a similar redshift to the ring based on H
α detected in the NIRSpec spectrum and [Cii ]λ 158μ m line from the Atacama Large Millimeter/submillimeter Array (ALMA). Using multiple spectral lines detected in JWST/NIRSpec, the rest-frame optical to infrared images from NIRCam and MIRI and far-infrared dust continuum detected by ALMA, we argue that the newly discovered sources are actually lensed images of the same companion galaxy SPT0418-SE, hereafter referred to “SE,” located within 5 kpc in the source plane of the ring. The star formation rate derived using [Cii ] and the dust continuum puts a lower limit of 17M ☉yr−1, while the SFRHα is estimated to be >2 times lower, thereby confirming that SE is a dust-obscured star-forming galaxy. Analysis using optical strong line diagnostics suggests that SE has near-solar elemental abundance, while the ring appears to have supersolar metallicity O/H and N/O. We attempt to reconcile the high metallicity in this system by invoking early onset of star formation with continuous high star-forming efficiency or by suggesting that optical strong line diagnostics need revision at high redshift. We suggest that SPT0418-47 resides in a massive dark-matter halo with yet-to-be-discovered neighbors. This work highlights the importance of joint analysis of JWST and ALMA data for a deep and complete picture of the early universe. -
Abstract With ΣSFR∼ 4200
M ⊙yr−1kpc−2, SPT 0346–52 (z = 5.7) is the most intensely star-forming galaxy discovered by the South Pole Telescope. In this paper, we expand on previous spatially resolved studies, using ALMA observations of dust continuum, [Nii ] 205μ m, [Cii ] 158μ m, [Oi ] 146μ m, and undetected [Nii ] 122μ m and [Oi ] 63μ m emission to study the multiphase interstellar medium (ISM) in SPT 0346–52. We use pixelated, visibility-based lens modeling to reconstruct the source-plane emission. We also model the source-plane emission using the photoionization codecloudy and find a supersolar metallicity system. We calculateT dust= 48.3 K andλ peak= 80μ m and see line deficits in all five lines. The ionized gas is less dense than comparable galaxies, withn e < 32 cm−3, while ∼20% of the [Cii ] 158μ m emission originates from the ionized phase of the ISM. We also calculate the masses of several phases of the ISM. We find that molecular gas dominates the mass of the ISM in SPT 0346–52, with the molecular gas mass ∼4× higher than the neutral atomic gas mass and ∼100× higher than the ionized gas mass. -
Abstract We present results on the nature of extreme ejective feedback episodes and the physical conditions of a population of massive (
M *∼ 1011M ⊙), compact starburst galaxies atz = 0.4–0.7. We use data from Keck/NIRSPEC, SDSS, Gemini/GMOS, MMT, and Magellan/MagE to measure rest-frame optical and near-IR spectra of 14 starburst galaxies with extremely high star formation rate surface densities (mean ΣSFR∼ 2000M ⊙yr−1kpc−2) and powerful galactic outflows (maximum speedsv 98∼ 1000–3000 km s−1). Our unique data set includes an ensemble of both emission ([Oii] λλ 3726,3729, Hβ , [Oiii] λλ 4959,5007, Hα , [Nii] λλ 6549,6585, and [Sii] λλ 6716,6731) and absorption (Mgii λλ 2796,2803, and Feii λ 2586) lines that allow us to investigate the kinematics of the cool gas phase (T ∼ 104K) in the outflows. Employing a suite of line ratio diagnostic diagrams, we find that the central starbursts are characterized by high electron densities (mediann e ∼ 530 cm−3), and high metallicity (solar or supersolar). We show that the outflows are most likely driven by stellar feedback emerging from the extreme central starburst, rather than by an AGN. We also present multiple intriguing observational signatures suggesting that these galaxies may have substantial Lyman continuum (LyC) photon leakage, including weak [Sii] nebular emission lines. Our results imply that these galaxies may be captured in a short-lived phase of extreme star formation and feedback where much of their gas is violently blown out by powerful outflows that open up channels for LyC photons to escape. -
Abstract Deep Very Large Telescope/MUSE optical integral field spectroscopy has recently revealed an abundant population of ultra-faint galaxies (
M UV≈ −15; 0.01L ⋆) atz = 2.9−6.7 due to their strong Lyα emission with no detectable continuum. The implied Lyα equivalent widths can be in excess of 100–200 Å, challenging existing models of normal star formation and indicating extremely young ages, small stellar masses, and a very low amount of metal enrichment. We use JWST/NIRSpec’s microshutter array to follow up 45 of these galaxies (11 hr in G235M/F170LP and 7 hr in G395M/F290LP), as well as 45 lower-equivalent width Lyα emitters. Our spectroscopy covers the range 1.7−5.1 micron in order to target strong optical emission lines: Hα , [Oiii ], Hβ , and [N II]. Individual measurements as well as stacks reveal line ratios consistent with a metal-poor nature (2%−40%Z ⊙, depending on the calibration). The galaxies with the highest equivalent widths of Lyα , in excess of 90 Å, have lower [N II]/Hα (1.9σ ) and [Oiii ]/Hβ (2.2σ ) ratios than those with lower equivalent widths, implying lower gas-phase metallicities at a combined significance of 2.4σ . This implies a selection based on Lyα equivalent width is an efficient technique for identifying younger, less chemically enriched systems.