Extremely metal-poor galaxies (XMPGs) at relatively low redshift are excellent laboratories for studying galaxy formation and evolution in the early universe. Much effort has been spent on ...identifying them from large-scale spectroscopic surveys or spectroscopic follow-up observations. Previous work has identified a few hundred XMPGs. In this work, we obtain a large sample of 223 XMPGs at \(z<1\) from the early data of the Dark Energy Spectroscopic Instrument (DESI). The oxygen abundance is determined using the direct \(T_{\rm e}\) method based on the detection of the O III\(\lambda\)4363 line. The sample includes 95 confirmed XMPGs based on the oxygen abundance uncertainty; remaining 128 galaxies are regarded as XMPG candidates. These XMPGs are only 0.01% of the total DESI observed galaxies. Their coordinates and other proprieties are provided in the paper. The most XMPG has an oxygen abundance of \(\sim 1/34 Z_{\odot}\), stellar mass of about \(1.5\times10^7 M_{\odot}\) and star formation rate of 0.22 \(M_{\odot}\) yr\(^{-1}\). The two most XMPGs present distinct morphologies suggesting different formation mechanisms. The local environmental investigation shows that XMPGs preferentially reside in relatively low-density regions. Many of them fall below the stellar mass-metallicity relations (MZRs) of normal star-forming galaxies. From a comparison of the MZR with theoretical simulations, it appears that XMPGs are good analogs to high-redshift star-forming galaxies. The nature of these XMPG populations will be further investigated in detail with larger and more complete samples from the on-going DESI survey.
We present a complete structural analysis of the ellipticals (E), diffuse bulges (dB), compact bulges (cB), and disks (D) within a redshift range \(0 < z < 1\), and stellar mass ...\(\log_{10}(\mathrm{M}_*/\mathrm{M}_\odot) \geq 9.5\) volume-limited sample drawn from the combined DEVILS and HST-COSMOS region. We use the {\sc ProFit} code to profile over \(\sim35,000\) galaxies for which visual classification into single or double-component was predefined in Paper-I. Over this redshift range, we see a growth in the total stellar mass density (SMD) of a factor of 1.5. At all epochs we find that the dominant structure, contributing to the total SMD, is the disk, and holds a fairly constant share of \(\sim60\%\) of the total SMD from \(z = 0.8\) to \(z = 0.2\), dropping to \(\sim30\%\) at \(z = 0.0\) (representing \(\sim33\%\) decline in the total disk SMD). Other classes (E, dB, and cB) show steady growth in their numbers and integrated stellar mass densities. By number, the most dramatic change across the full mass range is in the growth of diffuse bulges. In terms of total SMD, the biggest gain is an increase in massive elliptical systems, rising from 20\% at \(z = 0.8\) to equal that of disks at \(z = 0.0\) (30\%) representing an absolute mass growth of a factor of 2.5. Overall we see a clear picture of the emergence and growth of all three classes of spheroids over the past 8 Gyrs, and infer that in the later half of the Universe's timeline spheroid forming-processes and pathways (secular evolution, mass-accretion, and mergers) appear to dominate mass transformation over quiescent disk growth.
We present catalogues of stellar masses, star formation rates, and ancillary stellar population parameters for galaxies spanning \(0<z<9\) from the Deep Extragalactic VIsible Legacy Survey (DEVILS). ...DEVILS is a deep spectroscopic redshift survey with very high completeness, covering several premier deep fields including COSMOS (D10). Our stellar mass and star formation rate estimates are self-consistently derived using the spectral energy distribution (SED) modelling code ProSpect, using well-motivated parameterisations for dust attenuation, star formation histories, and metallicity evolution. We show how these improvements, and especially our physically motivated assumptions about metallicity evolution, have an appreciable systematic effect on the inferred stellar masses, at the level of \(\sim\)\,0.2 dex. To illustrate the scientific value of these data, we map the evolving galaxy stellar mass function (SMF) and the SFR-\(M_\star\) relation for \(0<z<4.25\). In agreement with past studies, we find that most of the evolution in the SMF is driven by the characteristic density parameter, with little evolution in the characteristic mass and low-mass slopes. Where the SFR-\(M_\star\) relation is indistinguishable from a power-law at \(z>2.6\), we see evidence of a bend in the relation at low redshifts (\(z<0.45\)). This suggests evolution in both the normalisation and shape of the SFR-\(M_\star\) relation since cosmic noon. It is significant that we only clearly see this bend when combining our new DEVILS measurements with consistently derived values for lower redshift galaxies from the Galaxy And Mass Assembly (GAMA) survey: this shows the power of having consistent treatment for galaxies at all redshifts.
(Abridged) The Maunakea Spectroscopic Explorer (MSE) is an end-to-end science platform for the design, execution and scientific exploitation of spectroscopic surveys. It will unveil the composition ...and dynamics of the faint Universe and impact nearly every field of astrophysics across all spatial scales, from individual stars to the largest scale structures in the Universe. Major pillars in the science program for MSE include (i) the ultimate Gaia follow-up facility for understanding the chemistry and dynamics of the distant Milky Way, including the outer disk and faint stellar halo at high spectral resolution (ii) galaxy formation and evolution at cosmic noon, via the type of revolutionary surveys that have occurred in the nearby Universe, but now conducted at the peak of the star formation history of the Universe (iii) derivation of the mass of the neutrino and insights into inflationary physics through a cosmological redshift survey that probes a large volume of the Universe with a high galaxy density. MSE is positioned to become a critical hub in the emerging international network of front-line astronomical facilities, with scientific capabilities that naturally complement and extend the scientific power of Gaia, the Large Synoptic Survey Telescope, the Square Kilometer Array, Euclid, WFIRST, the 30m telescopes and many more.
Using high-resolution Hubble Space Telescope imaging data, we perform a visual morphological classification of \(\sim 36,000\) galaxies at \(z < 1\) in the DEVILS/COSMOS region. As the main goal of ...this study, we derive the stellar mass function (SMF) and stellar mass density (SMD) sub-divided by morphological types. We find that visual morphological classification using optical imaging is increasingly difficult at \(z > 1\) as the fraction of irregular galaxies and merger systems (when observed at rest-frame UV/blue wavelengths) dramatically increases. We determine that roughly two-thirds of the total stellar mass of the Universe today was in place by \(z \sim 1\). Double-component galaxies dominate the SMD at all epochs and increase in their contribution to the stellar mass budget to the present day. Elliptical galaxies are the second most dominant morphological type and increase their SMD by \(\sim 2.5\) times, while by contrast, the pure-disk population significantly decreases by \(\sim 85\%\). According to the evolution of both high- and low-mass ends of the SMF, we find that mergers and in-situ evolution in disks are both present at \(z < 1\), and conclude that double-component galaxies are predominantly being built by the in-situ evolution in disks (apparent as the growth of the low-mass end with time), while mergers are likely responsible for the growth of ellipticals (apparent as the increase of intermediate/high-mass end).
We present -- and make publicly available -- accurate and precise photometric redshifts in the ACS footprint from the COSMOS field for objects with \(i_{\mathrm{AB}}\leq 23\). The redshifts are ...computed using a combination of narrow band photometry from PAUS, a survey with 40 narrow bands spaced at \(100Å\) intervals covering the range from \(4500Å\) to \(8500Å\), and 26 broad, intermediate, and narrow bands covering the UV, visible and near infrared spectrum from the COSMOS2015 catalogue. We introduce a new method that models the spectral energy distributions (SEDs) as a linear combination of continuum and emission line templates and computes its Bayes evidence, integrating over the linear combinations. The correlation between the UV luminosity and the OII line is measured using the 66 available bands with the zCOSMOS spectroscopic sample, and used as a prior which constrains the relative flux between continuum and emission line templates. The flux ratios between the OII line and \(\mathrm{H}_{\alpha}\), \(\mathrm{H}_{\beta}\) and \(\mathrm{OIII}\) are similarly measured and used to generate the emission line templates. Comparing to public spectroscopic surveys via the quantity \(\Delta_z\equiv(z_{\mathrm{photo}}-z_{\mathrm{spec}})/(1+z_{\mathrm{spec}})\), we find the photometric redshifts to be more precise than previous estimates, with \(\sigma_{68}(\Delta_z) \approx (0.003, 0.009)\) for galaxies at magnitude \(i_{\mathrm{AB}}\sim18\) and \(i_{\mathrm{AB}}\sim23\), respectively, which is \(3\times\) and \(1.66\times\) tighter than COSMOS2015. Additionally, we find the redshifts to be very accurate on average, yielding a median of the \(\Delta_z\) distribution compatible with \(|\mathrm{median}(\Delta_z)|\leq0.001\) at all redshifts and magnitudes considered. Both the added PAUS data and new methodology contribute significantly to the improved results.
