More Like this

1. CLEAR: Spatially Resolved Emission Lines and Active Galactic Nuclei at 0.6 < z < 1.3

   https://doi.org/10.3847/1538-4357/aca668  

   Backhaus, Bren E. ; Bridge, Joanna S. ; Trump, Jonathan R. ; Cleri, Nikko J. ; Papovich, Casey ; Simons, Raymond C. ; Momcheva, Ivelina ; Holwerda, Benne W. ; Ji, Zhiyuan ; Jung, Intae ; et al ( January 2023 , The Astrophysical Journal)

   We investigate spatially resolved emission-line ratios in a sample of 219 galaxies (0.6 <z< 1.3) detected using the G102 grism on the Hubble Space Telescope Wide Field Camera 3 taken as part of the CANDELS LyαEmission at Reionization survey to measure ionization profiles and search for low-luminosity active galactic nuclei (AGN). We analyze [Oiii] and Hβemission-line maps, enabling us to spatially resolve the [Oiii]/Hβemission-line ratio across the galaxies in the sample. We compare the [Oiii]/Hβratio in galaxy centers and outer annular regions to measure ionization differences and investigate the potential of sources with nuclear ionization to host AGN. We investigate some of the individual galaxies that are candidates to host strong nuclear ionization and find that they often have low stellar mass and are undetected in X-rays, as expected for low-luminosity AGN in low-mass galaxies. We do not find evidence for a significant population of off-nuclear AGN or other clumps of off-nuclear ionization. We model the observed distribution of [Oiii]/Hβspatial profiles and find that most galaxies are consistent with a small or zero difference between their nuclear and off-nuclear line ratios, but 6%–16% of galaxies in the sample are likely to host nuclear [Oiii]/Hβthat is ∼0.5 dex higher thanmore »in their outer regions. This study is limited by large uncertainties in most of the measured [Oiii]/Hβspatial profiles; therefore, deeper data, e.g., from deeper HST/WFC3 programs or from JWST/NIRISS, are needed to more reliably measure the spatially resolved emission-line conditions of individual high-redshift galaxies.

   « less
2. The BPT Diagram in Cosmological Galaxy Formation Simulations: Understanding the Physics Driving Offsets at High Redshift

   https://doi.org/10.3847/1538-4357/ac43b8  

   Garg, Prerak ; Narayanan, Desika ; Byler, Nell ; Sanders, Ryan L. ; Shapley, Alice E. ; Strom, Allison L. ; Davé, Romeel ; Hirschmann, Michaela ; Lovell, Christopher C. ; Otter, Justin ; et al ( February 2022 , The Astrophysical Journal)

   The Baldwin, Philips, & Terlevich diagram of [Oiii]/Hβversus [Nii]/Hα(hereafter N2-BPT) has long been used as a tool for classifying galaxies based on the dominant source of ionizing radiation. Recent observations have demonstrated that galaxies atz∼ 2 reside offset from local galaxies in the N2-BPT space. In this paper, we conduct a series of controlled numerical experiments to understand the potential physical processes driving this offset. We model nebular line emission in a large sample of galaxies, taken from thesimbacosmological hydrodynamic galaxy formation simulation, using thecloudyphotoionization code to compute the nebular line luminosities from Hiiregions. We find that the observed shift toward higher [Oiii]/Hβand [Nii]/Hαvalues at high redshift arises from sample selection: when we consider only the most massive galaxiesM_*∼ 10^10–11M_⊙, the offset naturally appears, due to their high metallicities. We predict that deeper observations that probe lower-mass galaxies will reveal galaxies that lie on a locus comparable toz∼ 0 observations. Even when accounting for samples-selection effects, we find that there is a subtle mismatch between simulations and observations. To resolve this discrepancy, we investigate the impact of varying ionization parameters, Hiiregion densities, gas-phase abundance patterns, and increasing radiation field hardness on N2-BPT diagrams. We find that either decreasing themore »ionization parameter or increasing the N/O ratio of galaxies at fixed O/H can move galaxies along a self-similar arc in N2-BPT space that is occupied by high-redshift galaxies.

   « less
3. CLEAR: Emission-line Ratios at Cosmic High Noon

   https://doi.org/10.3847/1538-4357/ac3919  

   Backhaus, Bren E. ; Trump, Jonathan R. ; Cleri, Nikko J. ; Simons, Raymond ; Momcheva, Ivelina ; Papovich, Casey ; Estrada-Carpenter, Vicente ; Finkelstein, Steven L. ; Matharu, Jasleen ; Ji, Zhiyuan ; et al ( February 2022 , The Astrophysical Journal)

   We use Hubble Space Telescope Wide Field Camera 3 G102 and G141 grism spectroscopy to measure rest-frame optical emission-line ratios of 533 galaxies atz∼ 1.5 in the CANDELS LyαEmission at Reionization survey. We compare [Oiii]/Hβversus [Sii]/(Hα+ [Nii]) as an “unVO87” diagram for 461 galaxies and [Oiii]/Hβversus [Neiii]/[Oii] as an “OHNO” diagram for 91 galaxies. The unVO87 diagram does not effectively separate active galactic nuclei (AGN) and [Nev] sources from star-forming galaxies, indicating that the unVO87 properties of star-forming galaxies evolve with redshift and overlap with AGN emission-line signatures atz> 1. The OHNO diagram does effectively separate X-ray AGN and [Nev]-emitting galaxies from the rest of the population. We find that the [Oiii]/Hβline ratios are significantly anticorrelated with stellar mass and significantly correlated with$\log (L_{\mathrm{H}\beta })$, while [Sii]/(Hα+ [Nii]) is significantly anticorrelated with$\log (L_{\mathrm{H}\beta })$. Comparison with MAPPINGS V photoionization models indicates that these trends are consistent with lower metallicity and higher ionization in low-mass and high-star formation rate (SFR) galaxies. We do not find evidence for redshift evolution of the emission-line ratios outside of the correlations with mass and SFR. Our results suggest that the OHNO diagram of [Oiii]/Hβversus [Neiii]/[Oii] willmore »be a useful indicator of AGN content and gas conditions in very high-redshift galaxies to be observed by the James Webb Space Telescope.

   « less
4. Galaxy Zoo: Clump Scout: Surveying the Local Universe for Giant Star-forming Clumps

   https://doi.org/10.3847/1538-4357/ac6512  

   Adams, Dominic ; Mehta, Vihang ; Dickinson, Hugh ; Scarlata, Claudia ; Fortson, Lucy ; Kruk, Sandor ; Simmons, Brooke ; Lintott, Chris ( May 2022 , The Astrophysical Journal)

   Massive, star-forming clumps are a common feature of high-redshift star-forming galaxies. How they formed, and why they are so rare at low redshift, remains unclear. In this paper we identify the largest sample yet of clumpy galaxies (7050) at low redshift using data from the citizen science project Galaxy Zoo: Clump Scout, in which volunteers classified 58,550 Sloan Digital Sky Survey (SDSS) galaxies spanning redshift 0.02 <z< 0.15. We apply a robust completeness correction by comparing with simulated clumps identified by the same method. Requiring that the ratio of clump to galaxy flux in the SDSSuband be greater than 8% (similar to clump definitions used by other works), we estimate the fraction of local star-forming galaxies hosting at least one clump (f_clumpy) to be${3.22}_{-0.34}^{+0.38}\%$. We also compute the same fraction with a less stringent relative flux cut of 3% (${12.68}_{-0.88}^{+1.38}\%$), as the higher number count and lower statistical noise of this fraction permit finer comparison with future low-redshift clumpy galaxy studies. Our results reveal a sharp decline inf_clumpyover 0 <z< 0.5. The minor merger rate remains roughly constant over the same span, so we suggest that minor mergers are unlikely to be themore »primary driver of clump formation. Instead, the rate of galaxy turbulence is a better tracer forf_clumpyover 0 <z< 1.5 for galaxies of all masses, which supports the idea that clump formation is primarily driven by violent disk instability for all galaxy populations during this period.

   « less
5. Molecular gas cloud properties at z ≃ 1 revealed by the superb angular resolution achieved with ALMA and gravitational lensing

   https://doi.org/10.1093/mnras/stad113  

   Dessauges-Zavadsky, Miroslava ; Richard, Johan ; Combes, Françoise ; Messa, Matteo ; Nagy, David ; Mayer, Lucio ; Schaerer, Daniel ; Egami, Eiichi ; Adamo, Angela ( January 2023 , Monthly Notices of the Royal Astronomical Society)

   Current observations favour that the massive ultraviolet-bright clumps with a median stellar mass of $\sim 10^7\, {\rm M}_{\odot }$, ubiquitously observed in z ∼ 1–3 galaxies, are star-forming regions formed in situ in galaxies. It has been proposed that they result from gas fragmentation due to gravitational instability of gas-rich, turbulent, and high-redshift discs. We bring support to this scenario by reporting the new discovery of giant molecular clouds (GMCs) in the strongly lensed, clumpy, main-sequence galaxy, A521-sys1, at z = 1.043. Its CO(4–3) emission was mapped with the Atacama Large Millimetre/submillimetre Array (ALMA) at an angular resolution of 0.19 × 0.16 arcsec2, reading down to 30 pc, thanks to gravitational lensing. We identified 14 GMCs, most being virialized, with $10^{5.9}-10^{7.9}\, {\rm M}_{\odot }$ masses and a median $800\, {\rm M}_{\odot }~\mathrm{pc}^{-2}$ molecular gas mass surface density, that are, respectively, 100 and 10 times higher than for nearby GMCs. They are also characterized by 10 times higher supersonic turbulence with a median Mach number of 60. They end up to fall above the Larson scaling relations, similarly to the GMCs in another clumpy z ≃ 1 galaxy, the Cosmic Snake, although differences between the two sets of high-redshift GMCs exist. Altogether theymore »support that GMCs form with properties that adjust to the ambient interstellar medium conditions prevalent in the host galaxy whatever its redshift. The detected A521-sys1 GMCs are massive enough to be the parent gas clouds of stellar clumps, with a relatively high star formation efficiency per free-fall time of ∼11 per cent.

   « less