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Register a new userStellar feedback in a clumpy galaxy at $z sim$ 3.4
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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.
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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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We use numerical simulations of isolated galaxies to study the effects of stellar feedback on the formation and evolution of giant star-forming gas clumps in high-redshift, gas-rich galaxies. Such galactic disks are unstable to the formation of bound gas-rich clumps whose properties initially depend only on global disk properties, not the microphysics of feedback. In simulations without stellar feedback, clumps turn an order-unity fraction of their mass into stars and sink to the center, forming a large bulge and kicking most of the stars out into a much more extended stellar envelope. By contrast, strong radiative stellar feedback disrupts even the most massive clumps after they turn ~10-20% of their mass into stars, in a timescale of ~10-100 Myr, ejecting some material into a super-wind and recycling the rest of the gas into the diffuse ISM. This suppresses the bulge formation rate by direct clump coalescence by a factor of several. However, the galactic disks do undergo significant internal evolution in the absence of mergers: clumps form and disrupt continuously and torque gas to the galactic center. The resulting evolution is qualitatively similar to bar/spiral evolution in simulations with a more homogeneous ISM.
Every star-forming galaxy has a halo of metal-enriched gas extending out to at least 100 kpc, as revealed by the absorption lines this gas imprints on the spectra of background quasars. However, quasars are sparse and typically probe only one narrow pencil beam through the intervening galaxy. Close quasar pairs and gravitationally lensed quasars have been used to circumvent this inherently one-dimensional technique, but these objects are rare and the structure of the circum-galactic medium remains poorly constrained. As a result, our understanding of the physical processes that drive the re-cycling of baryons across the lifetime of a galaxy is limited. Here we report integral-field (tomographic) spectroscopy of an extended background source -a bright giant gravitational arc. We can thus coherently map the spatial and kinematic distribution of Mg II absorption -a standard tracer of enriched gas- in an intervening galaxy system at redshift 0.98 (i.e., ~8 Gyr ago). Our gravitational-arc tomography unveils a clumpy medium in which the absorption-strength decreases with increasing impact parameter, in good agreement with the statistics towards quasars; furthermore, we find strong evidence that the gas is not distributed isotropically. Interestingly, we detect little kinematic variation over a projected area of ~600 kpc squared, with all line-of-sight velocities confined to within a few tens of km/s of each other. These results suggest that the detected absorption originates from entrained recycled material, rather than in a galactic outflow.
Dwarf galaxies are thought to host the remnants of the early Universe seed black holes (BHs) and to be dominated by supernova feedback. However, recent studies suggest that BH feedback could also strongly impact their growth. We report the discovery of 35 dwarf galaxies hosting radio AGN out to redshift $sim$3.4, which constitutes the highest-redshift sample of AGN in dwarf galaxies. The galaxies are drawn from the VLA-COSMOS 3 GHz Large Project and all are star-forming. After removing the contribution from star formation to the radio emission, we find a range of AGN radio luminosities of $L^mathrm{AGN}_mathrm{1.4 GHz} sim 10^{37}$-$10^{40}$ erg s$^{-1}$. The bolometric luminosities derived from the fit of their spectral energy distribution are $gtrsim 10^{42}$ erg s$^{-1}$, in agreement with the presence of AGN in these dwarf galaxies. The 3 GHz radio emission of most of the sources is compact and the jet powers range from $Q_mathrm{jet} sim 10^{42}$ to 10$^{44}$ erg s$^{-1}$. These values, as well as the finding of jet efficiencies $geq 10$ % in more than 50% of the sample, indicate that dwarf galaxies can host radio jets as powerful as those of massive radio galaxies whose jet mechanical feedback can strongly affect the formation of stars in the host galaxy. We conclude that AGN feedback can also have a very strong impact on dwarf galaxies, either triggering or hampering star formation and possibly the material available for BH growth. This implies that those low-mass AGN hosted in dwarf galaxies might not be the untouched relics of the early seed BHs, which has important implications for seed BH formation models.
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