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Register a new userResolved Multi-element Stellar Chemical Abundances in the Brightest Quiescent Galaxy at z $sim$ 2
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Marziye Jafariyazani
Publication date
2020
fields
Physics
and research's language is
English
Authors
Marziye Jafariyazani
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Measuring the chemical composition of galaxies is crucial to our understanding of galaxy formation and evolution models. However, such measurements are extremely challenging for quiescent galaxies at high redshifts, which have faint stellar continua and compact sizes, making it difficult to detect absorption lines and nearly impossible to spatially resolve them. Gravitational lensing offers the opportunity to study these galaxies with detailed spectroscopy that can be spatially resolved. In this work, we analyze deep spectra of MRG-M0138, a lensed quiescent galaxy at z = 1.98 which is the brightest of its kind, with an H-band magnitude of 17.1. Taking advantage of full spectral fitting, we measure $[{rm Mg/Fe}]=0.51pm0.05$, $[rm{Fe/H}]=0.26pm0.04$, and, for the first time, the stellar abundances of 6 other elements in this galaxy. We further constrained, also for the first time in a $zsim2$ galaxy, radial gradients in stellar age, [Fe/H], and [Mg/Fe]. We detect no gradient in age or [Mg/Fe] and a slightly negative gradient in [Fe/H], which has a slope comparable to that seen in local early-type galaxies. Our measurements show that not only is MRG-M0138 very Mg-enhanced compared to the centers of local massive early-type galaxies, it is also very iron rich. These dissimilar abundances suggest that even the inner regions of massive galaxies have experienced significant mixing of stars in mergers, in contrast to a purely inside-out growth model. The abundance pattern observed in MRG-M0138 challenges simple galactic chemical evolution models that vary only the star formation timescale and shows the need for more elaborate models.
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Element abundances in high-redshift quasar absorbers offer excellent probes of the chemical enrichment of distant galaxies, and can constrain models for population III and early population II stars. Recent observations indicate that the sub-damped Lyman-alpha (sub-DLA) absorbers are more metal-rich than DLA absorbers at redshifts 0$<$$z$$<$3. It has also been suggested that the DLA metallicity drops suddenly at $z$$>$4.7. However, only 3 DLAs at $z$$>$4.5 and none at $z$$>$3.5 have dust-free metallicity measurements of undepleted elements. We report the first quasar sub-DLA metallicity measurement at $z$$>$3.5, from detections of undepleted elements in high-resolution data for a sub-DLA at $z$=5.0. We obtain fairly robust abundances of C, O, Si, and Fe, using lines outside the Lyman-alpha forest. This absorber is metal-poor, with O/H]=-2.00$pm$0.12, which is $gtrsim$4$sigma$ below the level expected from extrapolation of the trend for $z$$<$3.5 sub-DLAs. The C/O ratio is 1.8$^{+0.4}_{-0.3}$ times lower than in the Sun. More strikingly, Si/O is 3.2$^{+0.6}_{-0.5}$ times lower than in the Sun, while Si/Fe is nearly (1.2$^{+0.4}_{-0.3}$ times) solar. This absorber does not display a clear alpha/Fe enhancement. Dust depletion may have removed more Si from the gas phase than is common in the Milky Way interstellar medium, which may be expected if high-redshift supernovae form more silicate-rich dust. C/O and Si/O vary substantially between different velocity components, indicating spatial variations in dust depletion and/or early stellar nucleosynethesis (e.g., population III star initial mass function). The higher velocity gas may trace an outflow enriched by early stars.
Giant star-forming regions (clumps) are widespread features of galaxies at $z approx 1-4$. Theory predicts that they can play a crucial role in galaxy evolution if they survive to stellar feedback for > 50 Myr. Numerical simulations show that clumps survival depends on the stellar feedback recipes that are adopted. Up to date, observational constraints on both clumps outflows strength and gas removal timescale are still uncertain. In this context, we study a line-emitting galaxy at redshift $z simeq 3.4$ lensed by the foreground galaxy cluster Abell 2895. Four compact clumps with sizes $lesssim$ 280 pc and representative of the low-mass end of clumps mass distribution (stellar masses $lesssim 2times10^8 {rm M}_odot$) dominate the galaxy morphology. The clumps are likely forming stars in a starbursting mode and have a young stellar population ($sim$ 10 Myr). The properties of the Lyman-$alpha$ (Ly$alpha$) emission and nebular far-ultraviolet absorption lines indicate the presence of ejected material with global outflowing velocities of $sim$ 200-300 km/s. Assuming that the detected outflows are the consequence of star formation feedback, we infer an average mass loading factor ($eta$) for the clumps of $sim$ 1.8 - 2.4 consistent with results obtained from hydro-dynamical simulations of clumpy galaxies that assume relatively strong stellar feedback. Assuming no gas inflows (semi-closed box model), the estimates of $eta$ suggest that the timescale over which the outflows expel the molecular gas reservoir ($simeq 7times 10^8 text{M}_odot$) of the four detected low-mass clumps is $lesssim$ 50 Myr.
Measurements of [Fe/H] and [$alpha$/Fe] can probe the minor merging history of a galaxy, providing a direct way to test the hierarchical assembly paradigm. While measurements of [$alpha$/Fe] have been made in the stellar halo of the Milky Way, little is known about detailed chemical abundances in the stellar halo of M31. To make progress with existing telescopes, we apply spectral synthesis to low-resolution DEIMOS spectroscopy (R $sim$ 2500 at 7000 Angstroms) across a wide spectral range (4500 Angstroms $<$ $lambda$ $<$ 9100 Angstroms). By applying our technique to low-resolution spectra of 170 giant stars in 5 MW globular clusters, we demonstrate that our technique reproduces previous measurements from higher resolution spectroscopy. Based on the intrinsic dispersion in [Fe/H] and [$alpha$/Fe] of individual stars in our combined cluster sample, we estimate systematic uncertainties of $sim$0.11 dex and $sim$0.09 dex in [Fe/H] and [$alpha$/Fe], respectively. We apply our method to deep, low-resolution spectra of 11 red giant branch stars in the smooth halo of M31, resulting in higher signal-to-noise per spectral resolution element compared to DEIMOS medium-resolution spectroscopy, given the same exposure time and conditions. We find $langle$[$alpha$/Fe]$rangle$ = 0.49 $pm$ 0.29 dex and $langle$[Fe/H]$rangle$ = 1.59 $pm$ 0.56 dex for our sample. This implies that---much like the Milky Way---the smooth halo of M31 is likely composed of disrupted dwarf galaxies with truncated star formation histories that were accreted early in the halos formation.
We aim at constraining the stellar population properties of quiescent galaxies. These properties reveal how these galaxies evolved and assembled since $zsim1$ up to the present time. Combining the ALHAMBRA multi-filter photo-spectra with the SED-fitting code MUFFIT, we build a complete catalogue of quiescent galaxies via the dust-corrected stellar mass vs colour diagram. This catalogue includes stellar population properties, such as age, metallicity, extinction, stellar mass and photometric redshift, retrieved from the analysis of composited populations based on two independent sets of SSP models. We develop and apply a novel methodology to provide, for the first time, the analytic probability distribution functions (PDFs) of mass-weighted age, metallicity, and extinction of quiescent galaxies as a function of redshift and stellar mass. We adopt different star formation histories to discard potential systematics in the analysis. The number density of quiescent galaxies is found to increase since $zsim1$, with a more substantial variation at lower mass. Quiescent galaxies feature extinction $A_V<0.6$, with median values in the range $A_V = 0.15mathrm{-}0.3$. At increasing stellar mass, quiescent galaxies are older and more metal rich since $zsim1$. A detailed analysis of the PDFs reveals that the evolution of quiescent galaxies is not compatible with passive evolution and a slight decrease is hinted at median metallicity $0.1mathrm{-}0.2$~dex. The intrinsic dispersion of the age and metallicity PDFs show a dependence with stellar mass and/or redshift. These results are consistent with both sets of SSP models and the alternative SFH assumptions explored. Consequently, the quiescent population must undergo an evolutive pathway including mergers and/or remnants of star formation to reconcile the observed trends, where the `progenitor bias should also be taken into account.
We examine the Fundamental Plane (FP) and mass-to-light ratio ($M/L$) scaling relations using the largest sample of massive quiescent galaxies at $1.5<z<2.5$ to date. The FP ($r_{e}, sigma_{e}, I_{e}$) is established using $19$ $UVJ$ quiescent galaxies from COSMOS with $Hubble$ $Space$ $Telescope$ $(HST)$ $H_{F160W}$ rest-frame optical sizes and X-shooter absorption line measured stellar velocity dispersions. For a very massive, ${rm{log}}(M_{ast}/M_{odot})>11.26$, subset of 8 quiescent galaxies at $z>2$, from Stockmann et al. (2020), we show that they cannot passively evolve to the local Coma cluster relation alone and must undergo significant structural evolution to mimic the sizes of local massive galaxies. The evolution of the FP and $M/L$ scaling relations, from $z=2$ to present-day, for this subset are consistent with passive aging of the stellar population and minor merger structural evolution into the most massive galaxies in the Coma cluster and other massive elliptical galaxies from the MASSIVE Survey. Modeling the luminosity evolution from minor merger added stellar populations favors a history of merging with dry quiescent galaxies.
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