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Register a new userThe KMOS Lens-Amplified Spectroscopic Survey (KLASS): Kinematics and clumpiness of low-mass galaxies at cosmic noon
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We present results from the KMOS Lens-Amplified Spectroscopic Survey (KLASS), an ESO Very Large Telescope (VLT) large program using gravitational lensing to study the spatially resolved kinematics of 44 star-forming galaxies at 0.6<z<2.3 with a stellar mass of 8.1<log(M$_star$/M$_{odot}$)<11.0. These galaxies are located behind six galaxy clusters selected from the HST Grism Lens-Amplified Survey from Space (GLASS). We find that the majority of the galaxies show a rotating disk, but most of the rotation-dominated galaxies only have a low $upsilon_{rot}/sigma_0$ ratio (median of $upsilon_{rot}/sigma_0sim2.5$). We explore the Tully-Fisher relation by adopting the circular velocity, $V_{circ}=(upsilon_{rot}^2+3.4sigma_0^2)^{1/2}$, to account for pressure support. We find that our sample follows a Tully-Fisher relation with a positive zero-point offset of +0.18 dex compared to the local relation, consistent with more gas-rich galaxies that still have to convert most of their gas into stars. We find a strong correlation between the velocity dispersion and stellar mass in the KLASS sample. When combining our data to other surveys from the literature, we also see an increase of the velocity dispersion with stellar mass at all redshift. We obtain an increase of $upsilon_{rot}/sigma_0$ with stellar mass at 0.5<z<1.0. This could indicate that massive galaxies settle into regular rotating disks before the low-mass galaxies. For higher redshift (z>1), we find a weak increase or flat trend. We investigate the relation between the rest-frame UV clumpiness of galaxies and their global kinematic properties. We find no clear trend between the clumpiness and the velocity dispersion and $upsilon_{rot}/sigma_0$. This could suggest that the kinematic properties of galaxies evolve after the clumps formed in the galaxy disk or that the clumps can form in different physical conditions.
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We present the first results of the KMOS Lens-Amplified Spectroscopic Survey (KLASS), a new ESO Very Large Telescope (VLT) large program, doing multi-object integral field spectroscopy of galaxies gravitationally lensed behind seven galaxy clusters selected from the HST Grism Lens-Amplified Survey from Space (GLASS). Using the power of the cluster magnification we are able to reveal the kinematic structure of 25 galaxies at $0.7 lesssim z lesssim 2.3$, in four cluster fields, with stellar masses $8 lesssim log{(M_star/M_odot)} lesssim 11$. This sample includes 5 sources at $z>1$ with lower stellar masses than in any previous kinematic IFU surveys. Our sample displays a diversity in kinematic structure over this mass and redshift range. The majority of our kinematically resolved sample is rotationally supported, but with a lower ratio of rotational velocity to velocity dispersion than in the local universe, indicating the fraction of dynamically hot disks changes with cosmic time. We find no galaxies with stellar mass $<3 times 10^9 M_odot$ in our sample display regular ordered rotation. Using the enhanced spatial resolution from lensing, we resolve a lower number of dispersion dominated systems compared to field surveys, competitive with findings from surveys using adaptive optics. We find that the KMOS IFUs recover emission line flux from HST grism-selected objects more faithfully than slit spectrographs. With artificial slits we estimate slit spectrographs miss on average 60% of the total flux of emission lines, which decreases rapidly if the emission line is spatially offset from the continuum.
Detections and non-detections of Lyman alpha (Ly$alpha$) emission from $z>6$ galaxies ($<1$ Gyr after the Big Bang) can be used to measure the timeline of cosmic reionization. Of key interest to measuring reionizations mid-stages, but also increasing observational challenge, are observations at z > 7, where Ly$alpha$ redshifts to near infra-red wavelengths. Here we present a search for z > 7.2 Ly$alpha$ emission in 53 intrinsically faint Lyman Break Galaxy candidates, gravitationally lensed by massive galaxy clusters, in the KMOS Lens-Amplified Spectroscopic Survey (KLASS). With integration times of ~7-10 hours, we detect no Ly$alpha$ emission with S/N>5 in our sample. We determine our observations to be 80% complete for 5$sigma$ spatially and spectrally unresolved emission lines with integrated line flux $>5.7times10^{-18}$ erg s$^{-1}$ cm$^{-2}$. We define a photometrically selected sub-sample of 29 targets at $z=7.9pm0.6$, with a median 5$sigma$ Ly$alpha$ EW limit of 58A. We perform a Bayesian inference of the average intergalactic medium (IGM) neutral hydrogen fraction using their spectra. Our inference accounts for the wavelength sensitivity and incomplete redshift coverage of our observations, and the photometric redshift probability distribution of each target. These observations, combined with samples from the literature, enable us to place a lower limit on the average IGM neutral hydrogen fraction of $> 0.76 ; (68%), ; > 0.46 ; (95%)$ at z ~ 8, providing further evidence of rapid reionization at z~6-8. We show that this is consistent with reionization history models extending the galaxy luminosity function to $M_textrm{UV} lesssim -12$, with low ionizing photon escape fractions, $f_textrm{esc} lesssim 15%$.
We introduce the OSIRIS Lens-Amplified Survey (OLAS), a kinematic survey of gravitationally lensed galaxies at cosmic noon taken with Keck adaptive optics. In this paper we present spatially resolved spectroscopy and nebular emission kinematic maps for 17 star forming galaxies with stellar masses 8 < log($M_*$/$M_{odot}$) < 9.8 and redshifts 1.2 < z < 2.3. OLAS is designed to probe the stellar mass ($M_*$) and specific star formation rate (sSFR) range where simulations suggest that stellar feedback is most effective at driving gaseous outflows that create galaxy-wide potential fluctuations which can generate dark matter cores. We compare our kinematic data with the trend between sSFR, $M_*$ and H$alpha$ velocity dispersion, $sigma$, from the Feedback In Realistic Environments (FIRE) simulations. Our observations reveal a correlation between sSFR and sigma at fixed $M_*$ that is similar to the trend predicted by simulations: feedback from star formation drives star-forming gas and newly formed stars into more dispersion dominated orbits. The observed magnitude of this effect is in good agreement with the FIRE simulations, in which feedback alters the central density profiles of low mass galaxies, converting dark matter cusps into cores over time. Our data support the scenario that stellar feedback drives gaseous outflows and potential fluctuations, which in turn drive dark matter core formation in dwarf galaxies.
The MAMMOTH-Grism slitless spectroscopic survey is a Hubble Space Telescope (HST) cycle-28 medium program, which is obtaining 45 orbits of WFC3/IR grism spectroscopy in the density peak regions of three massive galaxy protoclusters at $z=2-3$ discovered using the MAMMOTH technique. We introduce this survey by presenting the first measurement of mass-metallicity relation (MZR) at high redshift in overdense environments via grism spectroscopy. From the completed MAMMOTH-Grism observation in the field of the BOSS1244 protocluster at $z=2.24pm0.02$, We secure a sample of 36 protocluster member galaxies at $zsim2.24$, showing strong nebular emission lines ([O III], H$beta$ and [O II]) in their G141 spectra. Using the multi-wavelength broad-band deep imaging from HST and ground-based telescopes, we measure their stellar masses in the range of $[10^{9},10^{10.4}]M_odot$, instantaneous star formation rates (SFR) from 10 to 240$M_odot yr^{-1}$, and global gas-phase metallicities [1/3,1] of solar. Compared with similarly selected field galaxy sample at the same redshift, our galaxies show on average increased SFRs by ~0.06dex and ~0.18dex at ~10$^{10.1}M_odot$ and ~10$^{9.8}M_odot$, respectively. Using the stacked spectra of our sample galaxies, we derive the MZR in the BOSS1244 protocluster core as $12+log({rm O/H})=(0.136pm0.018)timeslog(M_ast/M_odot)+(7.082pm0.175)$, showing significantly shallower slope than that in the field. This shallow MZR slope is likely caused by the combined effects of efficient recycling of feedback-driven winds and cold-mode gas accretion in protocluster environments. The former effect helps low-mass galaxies residing in overdensities retain their metal production, whereas the latter effect dilutes the metal content of high-mass galaxies, making them more metal poor than their coeval field counterparts.
(Abridged) We combine deep HST grism spectroscopy with a new Bayesian method to derive maps of gas-phase metallicity, nebular dust extinction, and star-formation rate for 10 star-forming galaxies at high redshift ($1.2<z<2.3$). Exploiting lensing magnification by the foreground cluster MACS1149.6+2223, we reach sub-kpc spatial resolution and push the stellar mass limit associated with such high-z spatially resolved measurements below $10^8M_odot$ for the first time. Our maps exhibit diverse morphologies, indicative of various effects such as efficient radial mixing from tidal torques, rapid accretion of low-metallicity gas, etc., which can affect the gas and metallicity distributions in individual galaxies. Based upon an exhaustive sample of all existing sub-kpc metallicity gradients at high-z, we find that predictions given by analytical chemical evolution models assuming a relatively extended star-formation profile in the early disk formation phase can explain the majority of observed gradients, without involving galactic feedback or radial outflows. We observe a tentative correlation between stellar mass and metallicity gradient, consistent with the downsizing galaxy formation picture that more massive galaxies are more evolved into a later phase of disk growth, where they experience more coherent mass assembly at all radii and thus show shallower metallicity gradients. In addition, we compile a sample of homogeneously cross-calibrated integrated metallicity measurements spanning three orders of magnitude in stellar mass at $zsim1.8$. We use this sample to study the mass-metallicity relation (MZR) and test the fundamental metallicity relation (FMR). The slope of the observed MZR can rule out the momentum-driven wind model at 3-$sigma$ confidence level. We find no significant offset with respect to the FMR, taking into account the intrinsic scatter and measurement uncertainties.
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