We present a spectroscopic analysis of Eridanus IV (Eri IV) and Centaurus I (Cen I), two ultrafaint dwarf galaxies of the Milky Way. Using IMACS/Magellan spectroscopy, we identify 28 member stars of Eri IV and 34 member stars of Cen I. For Eri IV, we measure a systemic velocity of
We use deep narrowband CaHK (F395N) imaging taken with the Hubble Space Telescope (HST) to construct the metallicity distribution function (MDF) of Local Group ultrafaint dwarf galaxy Eridanus
 NSFPAR ID:
 10361688
 Publisher / Repository:
 DOI PREFIX: 10.3847
 Date Published:
 Journal Name:
 The Astrophysical Journal
 Volume:
 925
 Issue:
 1
 ISSN:
 0004637X
 Format(s):
 Medium: X Size: Article No. 6
 Size(s):
 ["Article No. 6"]
 Sponsoring Org:
 National Science Foundation
More Like this

Abstract , and velocity dispersion ${v}_{\mathrm{sys}}={31.5}_{1.2}^{+1.3}\phantom{\rule{0.33em}{0ex}}\mathrm{km}\phantom{\rule{0.25em}{0ex}}{\mathrm{s}}^{1}$ . Additionally, we measure the metallicities of 16 member stars of Eri IV. We find a metallicity of ${\sigma}_{v}={6.1}_{0.9}^{+1.2}\phantom{\rule{0.33em}{0ex}}\mathrm{km}\phantom{\rule{0.25em}{0ex}}{\mathrm{s}}^{1}$ , and resolve a dispersion of $[\mathrm{Fe}/\mathrm{H}]={2.87}_{0.07}^{+0.08}$σ _{[Fe/H]}=0.20 ± 0.09. The mean metallicity is marginally lower than all other known ultrafaint dwarf galaxies, making it one of the most metalpoor galaxies discovered thus far. Eri IV also has a somewhat unusual rightskewed metallicity distribution. For Cen I, we find a velocityv _{sys}= 44.9 ± 0.8 km s^{−1}, and velocity dispersion . We measure the metallicities of 27 member stars of Cen I, and find a mean metallicity [Fe/H] = −2.57 ± 0.08, and metallicity dispersion ${\sigma}_{v}={4.2}_{0.5}^{+0.6}\phantom{\rule{0.33em}{0ex}}\mathrm{km}\phantom{\rule{0.25em}{0ex}}{\mathrm{s}}^{1}$ . We calculate the systemic proper motion, orbit, and the astrophysical Jfactor for each system, the latter of which indicates that Eri IV is a good target for indirect dark matter detection. We also find no strong evidence for tidal stripping of Cen I or Eri IV. Overall, our measurements confirm that Eri IV and Cen I are darkmatterdominated galaxies with properties largely consistent with other known ultrafaint dwarf galaxies. The low metallicity, rightskewed metallicity distribution, and high Jfactor make Eri IV an especially interesting candidate for further followup. ${\sigma}_{[\mathrm{Fe}/\mathrm{H}]}={0.38}_{0.05}^{+0.07}$ 
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 $\u3008\mathrm{[Fe/H]}\u3009={1.55}_{0.04}^{+0.04}$ . (ii) A metallicity gradient of −0.54 ± 0.07 dex ${\sigma}_{\mathrm{[Fe/H]}}={0.54}_{0.03}^{+0.03}$ (−2.1 ± 0.3 dex kpc^{−1}) over the extent of our imaging (∼2.5 ${R}_{e}^{1}$R _{e}), which is steeper than literature measurements. Our finding is consistent with predicted gradients from the publicly available FIRE2 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 $\u3008\mathrm{[Fe/H]}\u3009={1.78}_{0.06}^{+0.06}$ and a red RGB with ${\sigma}_{\mathrm{[Fe/H]}}={0.44}_{0.06}^{+0.07}$ and $\u3008\mathrm{[Fe/H]}\u3009={1.08}_{0.07}^{+0.07}$ . (iv) At fixed stellar mass, Tucana is more metalrich than Milky Way satellites by ∼0.4 dex, but its blue RGB is chemically comparable to the satellites. Tucana’s MDF appears consistent with starforming 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 followup. ${\sigma}_{\mathrm{[Fe/H]}}={0.42}_{0.06}^{+0.06}$ 
Abstract We present a Keck/MOSFIRE restoptical composite spectrum of 16 typical gravitationally lensed starforming dwarf galaxies at 1.7 ≲
z ≲ 2.6 (z _{mean}= 2.30), all chosen independent of emissionline strength. These galaxies have a median stellar mass of and a median star formation rate of $\mathrm{log}{({M}_{*}/{M}_{\odot})}_{\mathrm{med}}={8.29}_{0.43}^{+0.51}$ . We measure the faint electrontemperaturesensitive [O ${\mathrm{S}\mathrm{F}\mathrm{R}}_{\mathrm{H}\alpha}^{\mathrm{m}\mathrm{e}\mathrm{d}}={2.25}_{1.26}^{+2.15}\phantom{\rule{0.25em}{0ex}}{M}_{\odot}\phantom{\rule{0.25em}{0ex}}{\mathrm{y}\mathrm{r}}^{1}$iii ]λ 4363 emission line at 2.5σ (4.1σ ) significance when considering a bootstrapped (statisticalonly) uncertainty spectrum. This yields a directmethod oxygen abundance of ( $12+\mathrm{log}{(\mathrm{O}/\mathrm{H})}_{\mathrm{direct}}={7.88}_{0.22}^{+0.25}$ ). We investigate the applicability at high ${0.15}_{0.06}^{+0.12}\phantom{\rule{0.33em}{0ex}}{Z}_{\odot}$z of locally calibrated oxygenbased strongline metallicity relations, finding that the local reference calibrations of Bian et al. best reproduce (≲0.12 dex) our composite metallicity at fixed strongline ratio. At fixedM _{*}, our composite is well represented by thez ∼ 2.3 directmethod stellar mass—gasphase 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 fixed $(\mathrm{log}{({M}_{*}/{M}_{\odot})}_{\mathrm{med}}={8.92}_{0.22}^{+0.31})$M _{*}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 ( ${n}_{e}={1}_{0}^{+215}\phantom{\rule{0.33em}{0ex}}{\mathrm{cm}}^{3}$ ) when considering the bootstrapped (statisticalonly) error spectrum. This result suggests that lowermass galaxies have lower densities than highermass galaxies at ${n}_{e}={1}_{0}^{+74}\phantom{\rule{0.33em}{0ex}}{\mathrm{cm}}^{3}$z ∼ 2. 
Abstract We present and confirm TOI1751 b, a transiting subNeptune orbiting a slightly evolved, solartype, metalpoor star (
T _{eff}= 5996 ± 110 K, , $\mathrm{log}(g)=4.2\pm 0.1$V = 9.3 mag, [Fe/H] = −0.40 ± 0.06 dex) every 37.47 days. We use TESS photometry to measure a planet radius of . We also use both Keck/HIRES and APF/Levy radial velocities (RV) to derive a planet mass of ${2.77}_{0.07}^{+0.15}\phantom{\rule{0.25em}{0ex}}{R}_{\oplus}$ , and thus a planet density of 3.6 ± 0.9 g cm^{−3}. There is also a longperiod (∼400 days) signal that is observed in only the Keck/HIRES data. We conclude that this longperiod signal is not planetary in nature and is likely due to the window function of the Keck/HIRES observations. This highlights the role of complementary observations from multiple observatories to identify and exclude aliases in RV data. Finally, we investigate the potential compositions of this planet, including rocky and waterrich solutions, as well as theoretical irradiated ocean models. TOI1751 b is a warm subNeptune with an equilibrium temperature of ∼820 K. As TOI1751 is a metalpoor star, TOI1751 b may have formed in a waterenriched formation environment. We thus favor a volatilerich interior composition for this planet. ${14.5}_{3.14}^{+3.15}\phantom{\rule{0.25em}{0ex}}{M}_{\oplus}$ 
Abstract We present the
z ≈ 6 type1 quasar luminosity function (QLF), based on the PanSTARRS1 (PS1) quasar survey. The PS1 sample includes 125 quasars atz ≈ 5.7–6.2, with −28 ≲M _{1450}≲ −25. With the addition of 48 fainter quasars from the SHELLQs survey, we evaluate thez ≈ 6 QLF over −28 ≲M _{1450}≲ −22. Adopting a double power law with an exponential evolution of the quasar density (Φ(z ) ∝ 10^{k(z−6)};k = −0.7), we use a maximum likelihood method to model our data. We find a break magnitude of , a faintend slope of ${M}^{*}={26.38}_{0.60}^{+0.79}\phantom{\rule{0.25em}{0ex}}\mathrm{mag}$ , and a steep brightend slope of $\alpha ={1.70}_{0.19}^{+0.29}$ . Based on our new QLF model, we determine the quasar comoving spatial density at $\beta ={3.84}_{1.21}^{+0.63}$z ≈ 6 to be . In comparison with the literature, we find the quasar density to evolve with a constant value of $n({M}_{1450}<26)={1.16}_{0.12}^{+0.13}\phantom{\rule{0.25em}{0ex}}{\mathrm{cGpc}}^{3}$k ≈ −0.7, fromz ≈ 7 toz ≈ 4. Additionally, we derive an ionizing emissivity of , based on the QLF measurement. Given standard assumptions, and the recent measurement of the mean free path by Becker et al. at ${\u03f5}_{912}(z=6)={7.23}_{1.02}^{+1.65}\times {10}^{22}\phantom{\rule{0.25em}{0ex}}\mathrm{erg}\phantom{\rule{0.25em}{0ex}}{\mathrm{s}}^{1}\phantom{\rule{0.25em}{0ex}}{\mathrm{Hz}}^{1}\phantom{\rule{0.25em}{0ex}}{\mathrm{cMpc}}^{3}$z ≈ 6, we calculate an Hi photoionizing rate of Γ_{H I}(z = 6) ≈ 6 × 10^{−16}s^{−1}, strongly disfavoring a dominant role of quasars in hydrogen reionization.