We present measurements of the rest-frame UV spectral slope,
Tight binary or multiple-star systems can interact through mass transfer and follow vastly different evolutionary pathways than single stars. The star TYC 2597-735-1 is a candidate for a recent stellar merger remnant resulting from a coalescence of a low-mass companion with a primary star a few thousand years ago. This violent event is evident in a conical outflow (“Blue Ring Nebula”) emitting in UV light and surrounded by leading shock filaments observed in H
- NSF-PAR ID:
- 10364017
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astronomical Journal
- Volume:
- 163
- Issue:
- 4
- ISSN:
- 0004-6256
- Format(s):
- Medium: X Size: Article No. 173
- Size(s):
- ["Article No. 173"]
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract β , for a sample of 36 faint star-forming galaxies atz ∼ 9–16 discovered in one of the deepest JWST NIRCam surveys to date, the Next Generation Deep Extragalactic Exploratory Public Survey. We use robust photometric measurements for UV-faint galaxies (down toM UV∼ −16), originally published in Leung et al., and measure values of the UV spectral slope via photometric power-law fitting to both the observed photometry and stellar population models obtained through spectral energy distribution (SED) fitting withBagpipes . We obtain a median and 68% confidence interval forβ from photometric power-law fitting of and from SED fitting, for the full sample. We show that when only two to three photometric detections are available, SED fitting has a lower scatter and reduced biases than photometric power-law fitting. We quantify this bias and find that after correction the median . We measure physical properties for our galaxies withBagpipes and find that our faint ( ) sample is low in mass ( ), fairly dust-poor ( mag), and modestly young ( yr) with a median star formation rate of . We find no strong evidence for ultrablue UV spectral slopes (β ∼ −3) within our sample, as would be expected for exotically metal-poor (Z /Z ⊙< 10−3) stellar populations with very high Lyman continuum escape fractions. Our observations are consistent with model predictions that galaxies of these stellar masses atz ∼ 9–16 should have only modestly low metallicities (Z /Z ⊙∼ 0.1–0.2). -
Abstract We present a Keck/MOSFIRE rest-optical composite spectrum of 16 typical gravitationally lensed star-forming dwarf galaxies at 1.7 ≲
z ≲ 2.6 (z mean= 2.30), all chosen independent of emission-line strength. These galaxies have a median stellar mass of and a median star formation rate of . We measure the faint electron-temperature-sensitive [Oiii ]λ 4363 emission line at 2.5σ (4.1σ ) significance when considering a bootstrapped (statistical-only) uncertainty spectrum. This yields a direct-method oxygen abundance of ( ). We investigate the applicability at highz of locally calibrated oxygen-based strong-line metallicity relations, finding that the local reference calibrations of Bian et al. best reproduce (≲0.12 dex) our composite metallicity at fixed strong-line ratio. At fixedM *, our composite is well represented by thez ∼ 2.3 direct-method stellar mass—gas-phase metallicity relation (MZR) of Sanders et al. When comparing to predicted MZRs from the IllustrisTNG and FIRE simulations, having recalculated our stellar masses with more realistic nonparametric star formation histories , we find excellent agreement with the FIRE MZR. Our composite is consistent with no metallicity evolution, at fixedM *and SFR, of the locally defined fundamental metallicity relation. We measure the doublet ratio [Oii ]λ 3729/[Oii ]λ 3726 = 1.56 ± 0.32 (1.51 ± 0.12) and a corresponding electron density of ( ) when considering the bootstrapped (statistical-only) error spectrum. This result suggests that lower-mass galaxies have lower densities than higher-mass galaxies atz ∼ 2. -
Abstract We measure the metallicities of 374 red giant branch (RGB) stars in the isolated, quenched dwarf galaxy Tucana using Hubble Space Telescope narrowband (F395N) calcium H and K imaging. Our sample is a factor of ∼7 larger than what is available from previous studies. Our main findings are as follows. (i) A global metallicity distribution function (MDF) with
and . (ii) A metallicity gradient of −0.54 ± 0.07 dex (−2.1 ± 0.3 dex kpc−1) over the extent of our imaging (∼2.5R e ), which is steeper than literature measurements. Our finding is consistent with predicted gradients from the publicly available FIRE-2 simulations, in which bursty star formation creates stellar population gradients and dark matter cores. (iii) Tucana’s bifurcated RGB has distinct metallicities: a blue RGB with and and a red RGB with and . (iv) At fixed stellar mass, Tucana is more metal-rich than Milky Way satellites by ∼0.4 dex, but its blue RGB is chemically comparable to the satellites. Tucana’s MDF appears consistent with star-forming isolated dwarfs, though MDFs of the latter are not as well populated. (v) About 2% of Tucana’s stars have [Fe/H] < −3% and 20% have [Fe/H] > −1. We provide a catalog for community spectroscopic follow-up. -
Abstract We measure the CO-to-H2conversion factor (
α CO) in 37 galaxies at 2 kpc resolution, using the dust surface density inferred from far-infrared emission as a tracer of the gas surface density and assuming a constant dust-to-metal ratio. In total, we have ∼790 and ∼610 independent measurements ofα COfor CO (2–1) and (1–0), respectively. The mean values forα CO (2–1)andα CO (1–0)are and , respectively. The CO-intensity-weighted mean is 5.69 forα CO (2–1)and 3.33 forα CO (1–0). We examine howα COscales with several physical quantities, e.g., the star formation rate (SFR), stellar mass, and dust-mass-weighted average interstellar radiation field strength ( ). Among them, , ΣSFR, and the integrated CO intensity (W CO) have the strongest anticorrelation with spatially resolvedα CO. We provide linear regression results toα COfor all quantities tested. At galaxy-integrated scales, we observe significant correlations betweenα COandW CO, metallicity, , and ΣSFR. We also find thatα COin each galaxy decreases with the stellar mass surface density (Σ⋆) in high-surface-density regions (Σ⋆≥ 100M ⊙pc−2), following the power-law relations and . The power-law index is insensitive to the assumed dust-to-metal ratio. We interpret the decrease inα COwith increasing Σ⋆as a result of higher velocity dispersion compared to isolated, self-gravitating clouds due to the additional gravitational force from stellar sources, which leads to the reduction inα CO. The decrease inα COat high Σ⋆is important for accurately assessing molecular gas content and star formation efficiency in the centers of galaxies, which bridge “Milky Way–like” to “starburst-like” conversion factors. -
Abstract We present13CO(
J = 1 → 0) observations for the EDGE-CALIFA survey, which is a mapping survey of 126 nearby galaxies at a typical spatial resolution of 1.5 kpc. Using detected12CO emission as a prior, we detect13CO in 41 galaxies via integrated line flux over the entire galaxy and in 30 galaxies via integrated line intensity in resolved synthesized beams. Incorporating our CO observations and optical IFU spectroscopy, we perform a systematic comparison between the line ratio and the properties of the stars and ionized gas. Higher values are found in interacting galaxies compared to those in noninteracting galaxies. The global slightly increases with infrared colorF 60/F 100but appears insensitive to other host-galaxy properties such as morphology, stellar mass, or galaxy size. We also present azimuthally averaged profiles for our sample up to a galactocentric radius of 0.4r 25(∼6 kpc), taking into account the13CO nondetections by spectral stacking. The radial profiles of are quite flat across our sample. Within galactocentric distances of 0.2r 25, the azimuthally averaged increases with the star formation rate. However, Spearman rank correlation tests show the azimuthally averaged does not strongly correlate with any other gas or stellar properties in general, especially beyond 0.2r 25from the galaxy centers. Our findings suggest that in the complex environments in galaxy disks, is not a sensitive tracer for ISM properties. Dynamical disturbances, like galaxy interactions or the presence of a bar, also have an overall impact on , which further complicates the interpretations of variations.