Observational constraints on the physical nature of submillimetre source multiplicity : chance projections are common

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2018 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.Interferometric observations have demonstrated that a significant fraction of single-dish submillimetre (submm) sources are blends of multiple submm galaxies (SMGs), but the nature of this multiplicity, i.e. whether the galaxies are physically associated or chance projections, has not been determined.We performed spectroscopy of 11 SMGs in six multicomponent submm sources, obtaining spectroscopic redshifts for nine of them. For an additional two component SMGs, we detected continuum emission but no obvious features.We supplement our observed sources with four single-dish submm sources from the literature. This sample allows us to statistically constrain the physical nature of single-dish submm source multiplicity for the first time. In three (3/7, or 43 -33 +39 per cent at 95 per cent confidence) of the single-dish sources for which the nature of the blending is unambiguous, the components for which spectroscopic redshifts are available are physically associated, whereas 4/7 (57 -39 +33 per cent) have at least one unassociated component. When components whose spectra exhibit continuum but no features and for which the photometric redshift is significantly different from the spectroscopic redshift of the other component are also considered, 6/9 (67 -37 +26 per cent) of the single-dish sources are comprised of at least one unassociated component SMG. The nature of the multiplicity of one single-dish source is ambiguous. We conclude that physically associated systems and chance projections both contribute to the multicomponent single-dish submm source population. This result contradicts the conventional wisdom that bright submm sources are solely a result of merger-induced starbursts, as blending of unassociated galaxies is also important.Peer reviewe

Blue BX galaxies breaking bad : allegations of a 2175Å feature at z ~ 2.2 in violation of the Calzetti dust law

vii, 84 leaves : ill. (chiefly col.) ; 29 cm.Includes abstract.Includes bibliographical references (leaves 81-84).The dust properties of star forming galaxies at z ~ 2 are examined using a sample of BX objects selected from the Keck Deep Fields (KDF) using colour-colour selection criteria. Spectral energy distribution (SED) fitting is used to infer physical properties of these galaxies from UnGRIHKs photometric data. Results suggest that the spectra of many of the BX objects with blue rest-frame UV colours include a 2175Å absorption feature not conventionally considered in high redshift analyses. The redshift ranges over which SEDs exhibiting the feature satisfy the BX selection criteria are computed and found to vary significantly between models including different dust laws. Clustering analyses are shown to be sensitive to the assumed dust attenuation law. Inappropriate dust model choices may lead to factor-of-two overestimates of spatial correlation lengths. The possibility of using the 2175Å feature as a redshift indicator is investigated through tests on synthetic galaxy photometry with promising results

LARgE Survey – I. Dead monsters: the massive end of the passive galaxy stellar mass function at cosmic noon

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LARgE Survey – I. Dead monsters: the massive end of the passive galaxy stellar mass function at cosmic noon

Published VersionWe introduce the largest to date survey of massive quiescent galaxies at redshift z ∼ 1.6. With these data, which cover 27.6 deg2, we can find significant numbers of very rare objects such as ultra-massive quiescent galaxies that populate the extreme massive end of the galaxy mass function, or dense environments that are likely to become present-day massive galaxy clusters. In this paper, the first in a series, we apply our gzKs adaptation of the BzK technique to select our z ∼ 1.6 galaxy catalogue and then study the quiescent galaxy stellar mass function with good statistics over M⋆ ∼ 1010.2–1011.7 M⊙ – a factor of 30 in mass – including 60 ultra-massive z ∼ 1.6 quiescent galaxies with M⋆ > 1011.5 M⊙. We find that the stellar mass function of quiescent galaxies at z ∼ 1.6 is well represented by the Schechter function over this large mass range. This suggests that the mass-quenching mechanism observed at lower redshifts must have already been well established by this epoch, and that it is likely due to a single physical mechanism over a wide range of mass. This close adherence to the Schechter shape also suggests that neither merging nor gravitational lensing significantly affects the observed quenched population. Finally, comparing measurements of M∗ parameters for quiescent and star-forming populations (ours and from the literature), we find hints of an offset (⁠M∗SF>M∗PE⁠), which could suggest that the efficiency of the quenching process evolves with time

LARgE survey – III. Environments of ultra-massive passive galaxies at cosmic noon: BCG progenitors growing through mergers

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LARgE Survey – II. The dark matter haloes and the progenitors and descendants of ultramassive passive galaxies at cosmic noon

International audienceWe use a 27.6 deg^2 survey to measure the clustering of -selected quiescent galaxies at z ∼ 1.6, focusing on ultramassive quiescent galaxies. We find that z ∼ 1.6 Ultra-Massive Passively Evolving Galaxies (UMPEGs), which have K_s(AB)  = 10^11.5 M_⊙), cluster more strongly than any other known galaxy population at high redshift. Comparing their correlation length, r_0 = 29.77 ± 2.75h^−1Mpc, with the clustering of dark matter (DM) haloes in the Millennium XXL N-body simulation suggests that these z ∼ 1.6 UMPEGs reside in DM haloes of mass M_h ∼ 10^14.1h^−1M_⊙. Such very massive z ∼ 1.6 haloes are associated with the ancestors of z ∼ 0 massive galaxy clusters such as the Virgo and Coma clusters. Given their extreme stellar masses and lack of companions with comparable mass, we surmise that these UMPEGs could be the already-quenched central massive galaxies of their (proto)clusters. We conclude that with only a modest amount of further growth in their stellar mass, z ∼ 1.6 UMPEGs could be the progenitors of some of the massive central galaxies of present-day massive galaxy clusters observed to be already very massive and quiescent near the peak epoch of the cosmic star formation

On the fast quenching of young low-mass galaxies up to z ∼ 0.6: new spotlight on the lead role of environment

14 pages, 5 figures, accepted for publication in MNRAS; published versionInternational audienceWe investigate the connection between environment and the different quenching channels that galaxies are prone to follow in the rest-frame NUVrK colour diagram, as identified by Moutard et al. (2016b). Namely, the fast quenching channel followed by $young$ low-mass galaxies and the slow quenching channel followed by $old$ high-mass ones. We make use of the >22 deg$^2$ covered the VIPERS Multi-Lambda Survey (VIPERS-MLS) to select a galaxy sample complete down to stellar masses of $M_* > 10^{9.4} M_\odot$ at $z 10^{8.8} M_\odot$ at $z < 0.5$) and including 33,500 (43,000) quiescent galaxies properly selected at $0.2 < z < 0.65$, while being characterized by reliable photometric redshifts ($\sigma_{\delta z/(1+z)} \leq 0.04$) that we use to measure galaxy local densities. We find that (1) the quiescence of low-mass [$M_* \leq 10^{9.7} M_\odot$] galaxies requires a strong increase of the local density, which confirms the lead role played by environment in their fast quenching and, therefore, confirms that the low-mass upturn observed in the stellar mass function of quiescent galaxies is due to $environmental$ $quenching$. We also observe that (2) the reservoir of low-mass star-forming galaxies located in very dense regions (prone to environmental quenching) has grown between $z \sim 0.6$ and $z \sim 0.4$ whilst the share of low-mass quiescent galaxies (expected to being environmentally quenched) may have simultaneously increased, which would plead for a rising importance of $environmental$ $quenching$ with cosmic time, compared to $mass$ $quenching$. We finally discuss the composite picture of such environmental quenching of low-mass galaxies and, in particular, how this picture may be consistent with a $delayed$-$then$-$rapid$ quenching scenario

UV and U-band luminosity functions from CLAUDS and HSC-SSP – I. Using four million galaxies to simultaneously constrain the very faint and bright regimes to z ∼ 3

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