Dr Aayush Saxena

Abstract:

The unexpectedly high abundance of galaxies at $z>11$ revealed by JWST has sparked a debate on the nature of early galaxies and the physical mechanisms regulating their formation. The Atacama Large Millimeter/submillimeter Array (ALMA) has begun to provide vital insights on their gas and dust content, but so far only for extreme ‘blue monsters’. Here we present new, deep ALMA observations of JADES-GS-z11-0, a more typical (sub- $L^{*}$ ) $z>11$ galaxy that bridges the discovery space of JWST and the Hubble Space Telescope. These data confirm the presence of the [O III] 88 $\mu$ m line at $4.5\sigma$ significance, precisely at the redshift of several faint emission lines previously seen with JWST/NIRSpec, while the underlying dust continuum remains undetected ( $F_{\nu }<9.0\mathrm{\mu }\mathrm{J}\mathrm{y}$ ), implying an obscured star formation rate (SFR) of ${\mathrm{\text{SFR}}}_{\mathrm{\text{IR}}}\lesssim 6{\mathrm{M}}_{\mathrm{\odot }}\mathrm{y}{\mathrm{r}}^{\mathrm{-}\mathrm{1}}$ and dust mass of $M_{\mathrm{\text{dust}}}\lesssim 1.0\times {10}^6{\mathrm{M}}_{\mathrm{\odot }}$ (all $3\sigma$ ). The accurate ALMA redshift of $z_{\mathrm{\text{[O III]}}}=11.1221\pm 0.0006$ ( $\gtrsim 5\times$ refined over NIRSpec) helps confirm that redshifts measured purely from the Lyman- $\alpha$ break, even spectroscopically, should properly take into account the effects of potential damped Lyman- $\alpha$ absorption (DLA) systems to avoid systematic overestimates of up to $\Delta z\approx 0.5$ . The [O III] 88 $\mu$ m luminosity of $L_{\mathrm{\text{[O III]}}}=(1.1\pm 0.3)\times {10}^8{\mathrm{L}}_{\mathrm{\odot }}$ , meanwhile, agrees well with the scaling relation for local metal-poor dwarfs given the SFR measured by NIRCam, NIRSpec, and MIRI. The spatially resolved MIRI and ALMA emission also underscores that JADES-GS-z11-0 is likely to consist of two low-mass components that are undergoing strong bursts of star formation yet are already pre-enriched in oxygen ( $\sim 30\%$ solar), only 400 Myr after the Big Bang.

Abstract:

We summarize the properties and initial data release of the JADES Origins Field (JOF), the longest single pointing yet imaged with the James Webb Space Telescope (JWST). This field falls within the GOODS-S region about 8′ southwest of the Hubble Ultra Deep Field (HUDF), where it was formed initially in Cycle 1 as a parallel field of HUDF spectroscopic observations within the JWST Advanced Deep Extragalactic Survey (JADES). This imaging was greatly extended in Cycle 2 program 3215, which observed the JOF for 5 days in six medium-band filters, seeking robust candidates for z > 15 galaxies. This program also includes ultradeep parallel NIRSpec spectroscopy (up to 91 hr on source, summing over the dispersion modes) on the HUDF. Cycle 3 observations from program 4540 added 20 hr of NIRCam slitless spectroscopy and F070W imaging to the JOF. With these three campaigns, the JOF was observed for 380 open-shutter hours with NIRCam using 15 imaging filters and two grism bandpasses. Further, parts of the JOF have deep 43 hr MIRI observations in F770W. Taken together, the JOF is one of the most compelling deep fields available with JWST and a powerful window into the early Universe. This paper presents the second data release from JADES, featuring the imaging and catalogs from the year 1 JOF observations.

Abstract:

The James Webb Space Telescope has ushered in an era of abundant high-redshift observations of young stellar populations characterized by strong emission lines, motivating us to integrate nebular emission into the new Maraston stellar population model which incorporates the latest Geneva stellar evolutionary tracks for massive stars with rotation. We use the photoionization code Cloudy to obtain the emergent nebular continuum and line emission for a range of modelling parameters, then compare our results to observations on various emission line diagnostic diagrams. We carry out a detailed comparison with several other models in the literature assuming different input physics, including modified prescriptions for stellar evolution and the inclusion of binary stars, and find close agreement in the H , H , [N ii], and [S ii] luminosities between the models. However, we find significant differences in lines with high ionization energies, such as He ii1640 and [O iii], due to large variations in the hard ionizing photon production rates. The models differ by a maximum of , where these differences are mostly caused by the assumed stellar rotation and effective temperatures for the Wolf Rayet phase. Interestingly, rotation and uncorrected effective temperatures in our single star population models alone generate [O iii] ionizing photon production rates higher than models including binary stars with ages between 1 to 6 Myr. These differences highlight the dependence of derived properties from SED fitting on the assumed model, as well as the sensitivity of predictions from cosmological simulations.

Abstract:

Understanding the origin and evolution of supermassive black holes (SMBHs) stands as one of the most important challenges in astrophysics and cosmology, with little current theoretical consensus. Improved observational constraints on the cosmological evolution of SMBH demographics are needed. Here we report results of a search via photometric variability for SMBHs appearing as active galactic nuclei (AGN) in the cosmological volume defined by the Hubble Ultra Deep Field. This work includes particular focus on a new observation carried out in 2023 with the Hubble Space Telescope using the WFC3/IR/F140W, which is compared directly to equivalent data taken 11 yr earlier in 2012. Two earlier pairs of observations from 2009 to 2012 with WFC3/IR/F105W and WFC3/IR/F160W are also analyzed. We identify 521, 188, and 109 AGN candidates as nuclear sources that exhibit photometric variability at a level of 2σ, 2.5σ, and 3σ, respectively, in at least one filter. This sample includes 13, 3, and 2 AGN candidates at redshifts z > 6, when the Universe was ≲900 Myr old. After variability and luminosity function (down to MUV = −17 mag) completeness corrections, we estimate the comoving number density of SMBHs, nSMBH(z). At z ≳ 6, nSMBH ≳ 6 × 10−3 cMpc−3. At low z our observations are sensitive to AGN fainter than MUV = −17 mag, and we estimate nSMBH ≳ 10−2 cMpc−3. We discuss how these results place strong constraints on a variety of SMBH seeding theories.

Abstract:

Early JWST photometric studies discovered a population of UV-faint ( 700 Å) exclude the most metal-poor efficient ionizers and favor (1) more chemically enriched systems with comparable extreme radiation fields and (2) older starbursting systems. In contrast, metallicity degeneracies are reduced in Hα space, enabling the identification of these metal-poor efficient ionizers by their specific star formation rate.