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Register a new userA clumpy and anisotropic galaxy halo at z=1 from gravitational-arc tomography
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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.
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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.
In this review, I discuss the use of galaxy-galaxy weak lensing measurements to study the masses of dark matter halos in which galaxies reside. After summarizing how weak gravitational lensing measurements can be interpreted in terms of halo mass, I review measurements that were used to derive the relationship between optical galaxy mass tracers, such as stellar mass or luminosity, and dark matter halo mass. Measurements of galaxy-galaxy lensing from the past decade have led to increasingly tight constraints on the connection between dark matter halo mass and optical mass tracers, including both the mean relationships between these quantities and the intrinsic scatter between them. I also review some of the factors that can complicate analysis, such as the choice of modeling procedure, and choices made when dividing up samples of lens galaxies.
Lyman- and Werner-band absorption of molecular hydrogen (H$_2$) is detected in $sim$50% of low redshift ($z<1$) DLAs/sub-DLAs with $N$(H$_2$) > 10$^{14.4}$ cm$^{-2}$. However the true origin(s) of the H$_2$ bearing gas remain elusive. Here we report a new detection of an H$_{2}$ absorber at $z=$ 0.4298 in the HST/COS spectra of quasar PKS 2128-123. The total $N$(HI) of 10$^{19.50pm0.15}$ cm$^{-2}$ classifies the absorber as a sub-DLA. H$_{2}$ absorption is detected up to the $J=3$ rotational level with a total $log N$(H$_{2}$) = 16.36$pm$0.08 corresponding to a molecular fraction of log $f$(H$_{2}$) = $-$2.84$pm$0.17. The excitation temperature of $T_{ex}$ = 206$pm$6K indicates the presence of cold gas. Using detailed ionization modelling we obtain a near-solar metallicity (i.e., [O/H]= $-$0.26$pm$0.19) and a dust-to-gas ratio of $log kappa sim -0.45$ for the H$_{2}$ absorbing gas. The host-galaxy of the sub-DLA is detected at an impact parameter of $rho sim$ 48 kpc with an inclination angle of $i sim$ 48 degree and an azimuthal angle of $Phi sim$ 15 degree with respect to the QSO sightline. We show that co-rotating gas in an extended disk cannot explain the observed kinematics of Mg II absorption. Moreover, the inferred high metallicity is not consistent with the scenario of gas accretion. An outflow from the central region of the host-galaxy, on the other hand, would require a large opening angle (i.e., 2$theta>$150 degree), much larger than the observed outflow opening angles in Seyfert galaxies, in order to intercept the QSO sightline. We thus favor a scenario in which the H$_2$ bearing gas is stemming from a dwarf-satellite galaxy, presumably via tidal and/or ram-pressure stripping. Detection of a dwarf galaxy candidate in the HST/WFPC2 image at an impact parameter of $sim$12 kpc reinforces such an idea.
We use photometric redshifts and statistical background subtraction to measure stellar mass functions in galaxy group-mass ($4.5-8times10^{13}~mathrm{M}_odot$) haloes at $1<z<1.5$. Groups are selected from COSMOS and SXDF, based on X-ray imaging and sparse spectroscopy. Stellar mass ($M_{mathrm{stellar}}$) functions are computed for quiescent and star-forming galaxies separately, based on their rest-frame $UVJ$ colours. From these we compute the quiescent fraction and quiescent fraction excess (QFE) relative to the field as a function of $M_{mathrm{stellar}}$. QFE increases with $M_{mathrm{stellar}}$, similar to more massive clusters at $1<z<1.5$. This contrasts with the apparent separability of $M_{mathrm{stellar}}$ and environmental factors on galaxy quiescent fractions at $zsim 0$. We then compare our results with higher mass clusters at $1<z<1.5$ and lower redshifts. We find a strong QFE dependence on halo mass at fixed $M_{mathrm{stellar}}$; well fit by a logarithmic slope of $mathrm{d}(mathrm{QFE})/mathrm{d}log (M_{mathrm{halo}}) sim 0.24 pm 0.04$ for all $M_{mathrm{stellar}}$ and redshift bins. This dependence is in remarkably good qualitative agreement with the hydrodynamic simulation BAHAMAS, but contradicts the observed dependence of QFE on $M_{mathrm{stellar}}$. We interpret the results using two toy models: one where a time delay until rapid (instantaneous) quenching begins upon accretion to the main progenitor (no pre-processing) and one where it starts upon first becoming a satellite (pre-processing). Delay times appear to be halo mass dependent, with a significantly stronger dependence required without pre-processing. We conclude that our results support models in which environmental quenching begins in low-mass ($<10^{14}M_odot$) haloes at $z>1$.
We report the discovery of eMACSJ1341-QG-1, a quiescent galaxy at $z=1.594$ located behind the massive galaxy cluster eMACSJ1341.9$-$2442 ($z=0.835$). The system was identified as a gravitationally lensed triple image in Hubble Space Telescope images obtained as part of a snapshot survey of the most X-ray luminous galaxy clusters at $z>0.5$ and spectroscopically confirmed in ground-based follow-up observations with the ESO/X-Shooter spectrograph. From the constraints provided by the triple image, we derive a first, crude model of the mass distribution of the cluster lens, which predicts a gravitational amplification of a factor of $sim$30 for the primary image and a factor of $sim$6 for the remaining two images of the source, making eMACSJ1341-QG-1 by far the most strongly amplified quiescent galaxy discovered to date. Our discovery underlines the power of SNAPshot observations of massive, X-ray selected galaxy clusters for lensing-assisted studies of faint background populations.
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