We present new deep ALMA and Hubble Space Telescope (HST)/WFC3 observations of MASOSA and VR7, two luminous Ly emitters (LAEs) at z = 6.5, for which the UV continuum levels differ by a factor of ...four. No IR dust continuum emission is detected in either, indicating little amounts of obscured star formation and/or high dust temperatures. MASOSA, with a UV luminosity M1500 = −20.9, compact size, and very high Ly , is undetected in C ii to a limit of LC ii < 2.2 × 107 L , implying a metallicity Z 0.07 Z . Intriguingly, our HST data indicate a red UV slope β = −1.1 0.7, at odds with the low dust content. VR7, which is a bright (M1500 = −22.4) galaxy with moderate color (β = −1.4 0.3) and Ly EW0 = 34 , is clearly detected in C ii emission (S/N = 15). VR7's rest-frame UV morphology can be described by two components separated by 1.5 kpc and is globally more compact than the C ii emission. The global C ii/UV ratio indicates Z 0.2 Z , but there are large variations in the UV/C ii ratio on kiloparsec scales. We also identify diffuse, possibly outflowing, C ii-emitting gas at 100 km s−1 with respect to the peak. VR7 appears to be assembling its components at a slightly more evolved stage than other luminous LAEs, with outflows already shaping its direct environment at z ∼ 7. Our results further indicate that the global C ii−UV relation steepens at SFR < 30 M yr−1, naturally explaining why the C ii/UV ratio is anticorrelated with Ly EW in many, but not all, observed LAEs.
Abstract
We present dynamical measurements from the KMOS (K-band multi-object spectrograph) Deep Survey (KDS), which comprises 77 typical star-forming galaxies at z ≃ 3.5 in the mass range 9.0 < log ...(M
⋆/M⊙) < 10.5. These measurements constrain the internal dynamics, the intrinsic velocity dispersions (σint) and rotation velocities (V
C) of galaxies in the high-redshift Universe. The mean velocity dispersion of the galaxies in our sample is
$\sigma _{\rm int} = 70.8^{+3.3}_{-3.1} \,\mathrm{km\,s}^{-1}$
, revealing that the increasing average σint with increasing redshift, reported for z ≲ 2, continues out to z ≃ 3.5. Only 36 ± 8 per cent of our galaxies are rotation-dominated (V
C/σint > 1), with the sample average V
C/σint value much smaller than at lower redshift. After carefully selecting comparable star-forming samples at multiple epochs, we find that the rotation-dominated fraction evolves with redshift with a z
−0.2 dependence. The rotation-dominated KDS galaxies show no clear offset from the local rotation velocity–stellar mass (i.e. V
C–M
⋆) relation, although a smaller fraction of the galaxies are on the relation due to the increase in the dispersion-dominated fraction. These observations are consistent with a simple equilibrium model picture, in which random motions are boosted in high-redshift galaxies by a combination of the increasing gas fractions, accretion efficiency, specific star formation rate and stellar feedback and which may provide significant pressure support against gravity on the galactic disc scale.
Abstract
We present dynamical measurements for 586 Hα-detected star-forming galaxies from the KMOS (K-band Multi-Object Spectrograph) Redshift One Spectroscopic Survey (KROSS). The sample represents ...typical star-forming galaxies at this redshift (z = 0.6–1.0), with a median star formation rate of ≈7 M⊙ yr−1 and a stellar mass range of log (M⋆M⊙) ≈ 9–11. We find that the rotation velocity–stellar mass relationship (the inverse of the Tully–Fisher relationship) for our rotationally dominated sources (vC/σ0 > 1) has a consistent slope and normalization as that observed for z = 0 discs. In contrast, the specific angular momentum (j⋆; angular momentum divided by stellar mass) is ≈0.2–0.3 dex lower on average compared to z = 0 discs. The specific angular momentum scales as $j_{\rm s}\propto M_{\star }^{0.6\pm 0.2}$, consistent with that expected for dark matter (i.e. $j_{\rm DM}\propto M_{\rm DM}^{2/3}$). We find that z ≈ 0.9 star-forming galaxies have decreasing specific angular momentum with increasing Sérsic index. Visually, the sources with the highest specific angular momentum, for a given mass, have the most disc-dominated morphologies. This implies that an angular momentum–mass–morphology relationship, similar to that observed in local massive galaxies, is already in place by z ≈ 1.
Abstract
We present a MUSE (Multi-Unit Spectroscopic Explorer) and KMOS (K-band Multi-Object Spectrograph) dynamical study 405 star-forming galaxies
at redshift z = 0.28–1.65 (median redshift
...$\bar{z}$
= 0.84). Our sample is representative of the star-forming ‘main sequence’, with star formation rates of SFR = 0.1–30 M⊙ yr−1 and stellar masses M
⋆ = 108–1011 M⊙. For 49 ± 4 per cent of our sample, the dynamics suggest rotational support, 24 ± 3 per cent are unresolved systems and 5 ± 2 per cent appear to be early-stage major mergers with components on 8–30 kpc scales. The remaining 22 ± 5 per cent appear to be dynamically complex, irregular (or face-on systems). For galaxies whose dynamics suggest rotational support, we derive inclination-corrected rotational velocities and show that these systems lie on a similar scaling between stellar mass and specific angular momentum as local spirals with j
⋆ = J/
$M_\star \propto M_\star ^{2/3}$
but with a redshift evolution that scales as j
⋆ ∝ M
$_\star ^{2/3}(1+z)^{-1}$
. We also identify a correlation between specific angular momentum and disc stability such that galaxies with the highest specific angular momentum (log(j
⋆/M
$_\star ^{2/3}$
) > 2.5) are the most stable, with Toomre Q = 1.10 ± 0.18, compared to Q = 0.53 ± 0.22 for galaxies with log(j
⋆/M
$_\star ^{2/3}$
) < 2.5. At a fixed mass, the Hubble Space Telescope morphologies of galaxies with the highest specific angular momentum resemble spiral galaxies, whilst those with low specific angular momentum are morphologically complex and dominated by several bright star-forming regions. This suggests that angular momentum plays a major role in defining the stability of gas discs: at z ∼ 1, massive galaxies that have discs with low specific angular momentum are globally unstable, clumpy and turbulent systems. In contrast, galaxies with high specific angular momentum have evolved into stable discs with spiral structure where star formation is a local (rather than global) process.
We present spectroscopic follow-up observations of CR7 with ALMA, targeted at constraining the infrared (IR) continuum and C ii line-emission at high spatial resolution matched to the HST/WFC3 ...imaging. CR7 is a luminous Ly emitting galaxy at z = 6.6 that consists of three separated UV-continuum components. Our observations reveal several well-separated components of C ii emission. The two most luminous components in C ii coincide with the brightest UV components (A and B), blueshifted by km s−1 with respect to the peak of Ly emission. Other C ii components are observed close to UV clumps B and C and are blueshifted by and 80 km s−1 with respect to the systemic redshift. We do not detect FIR continuum emission due to dust with a 3 limiting luminosity . This allows us to mitigate uncertainties in the dust-corrected SFR and derive SFRs for the three UV clumps A, B, and C of 28, 5, and 7 yr−1. All clumps have C ii luminosities consistent within the scatter observed in the local relation between SFR and , implying that strong Ly emission does not necessarily anti-correlate with C ii luminosity. Combining our measurements with the literature, we show that galaxies with blue UV slopes have weaker C ii emission at fixed SFR, potentially due to their lower metallicities and/or higher photoionization. Comparison with hydrodynamical simulations suggests that CR7's clumps have metallicities of . The observed ISM structure of CR7 indicates that we are likely witnessing the build up of a central galaxy in the early universe through complex accretion of satellites.
Golovich et al. present an optical imaging and spectroscopic survey of 29 radio relic merging galaxy clusters. In this paper, we study this survey to identify substructure and quantify the dynamics ...of the mergers. Using a combined photometric and spectroscopic approach, we identify the minimum number of substructures in each system to describe the galaxy populations and estimate the line-of-sight velocity difference between likely merging subclusters. We find that the line-of-sight velocity components of the mergers are typically small compared with the maximum 3D relative velocity (usually <1000 km s−1 and often consistent with zero). We also compare our systems to n-body simulation analogs and estimate the viewing angle of the clean mergers in our ensemble. We find that the median system's separation vector lies within 40° (17°) at a 90% (50%) confidence level. This suggests that the merger axes of these systems are generally in or near the plane of the sky, matching findings in magnetohydrodynamical simulations. In 28 of the 29 systems we identify substructures in the galaxy population aligned with the radio relic(s) and presumed associated merger-induced shock. From this ensemble, we identify eight systems to include in a "gold" sample that is prime for further observation, modeling, and simulation study. Additional papers will present weak-lensing mass maps and dynamical modeling for each merging system, ultimately leading to new insight into a wide range of astrophysical phenomena at some of the largest scales in the universe.
ABSTRACT
We use multi-object near-infrared spectroscopy with VLT/KMOS to investigate the role of the environment in the evolution of the ionized gas properties of narrow-band-selected H α emitters ...(HAEs) in the Spiderweb protocluster at z = 2.16. Based on rest-frame optical emission lines, H α and N iiλ6584, we confirm the cluster membership of 39 of our targets (i.e. 93 per cent success rate), and measure their star formation rates (SFR), gas-phase oxygen abundances, and effective radius. We parametrize the environment where our targets reside using local and global density indicators based on previous samples of spectroscopic and narrow-band cluster members. We find that star-forming galaxies embedded in the Spiderweb protocluster display SFRs compatible with those of the main sequence and morphologies comparable to those of late-type galaxies at z = 2.2 in the field. We also report a mild gas-phase metallicity enhancement (0.06 ± 0.03 dex) at intermediate stellar masses. Furthermore, we identify two UVJ-selected quiescent galaxies with residual H α-based star formation and find signs of extreme dust obscuration in a small sample of starbursty submillimetre galaxies based on their FIR and H α emission. Interestingly, the spatial distribution of these objects differs from the rest of HAEs, avoiding the protocluster core. Finally, we explore the gas fraction–gas metallicity diagram for seven galaxies with molecular gas masses measured by ATCA using CO(1−0). In the context of the gas-regulator model, our objects are consistent with relatively low mass-loading factors, suggesting lower outflow activity than field samples at the cosmic noon and thus, hinting at the onset of environmental effects in this massive protocluster.
ABSTRACT
We explore deep rest-frame UV to FIR data in the COSMOS field to measure the individual spectral energy distributions (SED) of the ∼4000 SC4K (Sobral et al.) Lyman α (Ly α) emitters (LAEs) ...at z ∼ 2–6. We find typical stellar masses of 109.3 ± 0.6 M⊙ and star formation rates (SFR) of SFR$_{\rm SED}=4.4^{+10.5}_{-2.4}$ M⊙ yr−1 and SFR$_{\rm Ly\,\alpha }=5.9^{+6.3}_{-2.6}$ M⊙ yr−1, combined with very blue UV slopes of $\beta =-2.1^{+0.5}_{-0.4}$, but with significant variations within the population. MUV and β are correlated in a similar way to UV-selected sources, but LAEs are consistently bluer. This suggests that LAEs are the youngest and/or most dust-poor subset of the UV-selected population. We also study the Ly α rest-frame equivalent width (EW0) and find 45 ‘extreme’ LAEs with EW0 > 240 Å (3σ), implying a low number density of (7 ± 1) × 10−7 Mpc−3. Overall, we measure little to no evolution of the Ly α EW0 and scale length parameter (w0), which are consistently high (EW$_0=140^{+280}_{-70}$ Å, $w_0=129^{+11}_{-11}$ Å) from z ∼ 6 to z ∼ 2 and below. However, w0 is anticorrelated with MUV and stellar mass. Our results imply that sources selected as LAEs have a high Ly α escape fraction (fesc,Ly α) irrespective of cosmic time, but fesc,Ly α is still higher for UV-fainter and lower mass LAEs. The least massive LAEs (<109.5 M⊙) are typically located above the star formation ‘main sequence’ (MS), but the offset from the MS decreases towards z ∼ 6 and towards 1010 M⊙. Our results imply a lack of evolution in the properties of LAEs across time and reveals the increasing overlap in properties of LAEs and UV-continuum selected galaxies as typical star-forming galaxies at high redshift effectively become LAEs.
![Resolved UV and [C ii] Stru...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-637X/small "Resolved UV and [C ii] Structures of Luminous Galaxies within the Epoch of Reionization")
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