We report a discovery of six massive galaxies with both extremely large Ly alpha equivalent widths (EWs) and evolved stellar populations at z similar to 3. These MAssive Extremely STrong Ly alpha ...emitting Objects (MAESTLOs) have been discovered in our large-volume systematic survey for strong Ly alpha emitters (LAEs) with 12 optical intermediate-band data taken with Subaru/Suprime-Cam in the COSMOS field. Based on the spectral energy distribution fitting analysis for these LAEs, it is found that these MAESTLOs have (1) large rest-frame EWs of EW0 (Ly alpha) similar to 100-300 angstrom, (2) M-star similar to 10(10.5) -10(11.1) M-circle dot, and (3) relatively low specific star formation rates of SFR/M-star similar to 0.03-1 Gyr(-1). Three of the six MAESTLOs have extended Ly alpha emission with a radius of several kiloparsecs, although they show very compact morphology in the HST/ACS images, which correspond to the rest-frame UV continuum. Since the MAESTLOs do not show any evidence for active galactic nuclei, the observed extended Ly alpha emission is likely to be caused by a star formation process including the superwind activity. We suggest that this new class of LAEs, MAESTLOs, provides a missing link from star-forming to passively evolving galaxies at the peak era of the cosmic star formation history.
We present the type-1 active galactic nuclei (AGN) sample extracted from the VIMOS VLT Deep Survey's first observations of 21 000 spectra in 1.75 deg2. This sample, which is purely magnitude-limited ...and free of morphological or color-selection biases, contains 130 broad-line AGN (BLAGN) spectra with redshift up to 5. Our data are divided into a wide ($I_{\rm AB} \le 22.5$) and a deep ($I_{\rm AB} \le 24$) subsample containing 56 and 74 objects, respectively. Because of its depth and selection criteria, this sample is uniquely suited for studying the population of faint type-1 AGN. Our measured surface density (~$472 \pm 48$ BLAGN per square degree with $I_{\rm AB} \le 24$) is significantly higher than that of any other optically selected sample of BLAGN with spectroscopic confirmation. By applying a morphological and color analysis to our AGN sample, we find that (1) ~$23 \%$ of the AGN brighter than $I_{\rm AB}=22.5$ are classified as extended, and this percentage increases to ~42% for those with $z < 1.6$; (2) a non-negligible fraction of our BLAGN are lying close to the color-space area occupied by stars in the $u^*-g'$ versus $g'-r'$ color-color diagram. This leads us to the conclusion that the classical optical-ultraviolet preselection technique, if employed at such deep magnitudes ($I_{\rm AB}=22.5$) in conjuction with a preselection of point-like sources, can miss up to ~$35\%$ of the AGN population. Finally, we present a composite spectrum of our sample of objects. While the continuum shape is very similar to that of the SDSS composite at short wavelengths, it is much redder than that of the SDSS composite at $\lambda \ge 3000$ Å. We interpret this as due to significant contamination from emission of the host galaxies, as expected from the faint absolute magnitudes sampled by our survey.
We present measurements of the stellar mass functions (SMFs) of star-forming and quiescent galaxies to z = 4 using a sample of 95,675 K sub(s)-selected galaxies in the COSMOS/UltraVISTA field. The ...SMFs of the combined population are in good agreement with previous measurements and show that the stellar mass density of the universe was only 50%, 10%, and 1% of its current value at z ~ 0.75, 2.0, and 3.5, respectively. Comparisons of the K sub(s)-selected star-forming galaxy SMFs with UV-selected SMFs at 2.5 < z < 4 show reasonable agreement and suggest that UV-selected samples are representative of the majority of the stellar mass density at z < 3.5. We estimate the average mass growth of individual galaxies by selecting galaxies at fixed cumulative number density. We examine potential sources of systematic uncertainties in the SMFs and find that those from photo-z templates, stellar population synthesis modeling, and the definition of quiescent galaxies dominate the total error budget in the SMFs.
Context: Hierarchical models of galaxy formation predict that the properties of a dark matter halo depend on the large-scale environment surrounding the halo. As a result of this correlation, we ...expect massive haloes to be present in larger number in overdense regions than in underdense ones. Given that a correlation exists between a galaxy stellar mass and the hosting dark matter halo mass, the segregation in dark matter halo mass should then result in a segregation in the distribution of stellar mass in the galaxy population. Aims: In this work we study the distribution of galaxy stellar mass and rest-frame optical color as a function of the large-scale galaxy distribution using the VLT VIMOS Deep Survey sample, in order to verify the presence of segregation in the properties of the galaxy population. Methods: We use VVDS redshift measurements and multi-band photometric data to derive estimates of the stellar mass, rest-frame optical color, and of the large-scale galaxy density, on a scale of approximately 8 Mpc, for a sample of 5619 galaxies in the redshift range 0.2
We report the discovery of a galaxy at a redshift $z = 6.17$ identified from deep narrow band imaging and spectroscopic follow-up in one of the CFHT-VIRMOS deep survey fields at 0226-04. In addition ...to the existing deep BVRI images of this field, we obtained a very deep narrow band image at 920 nm with the aim of detecting Lyα emission at redshift ~6.5. Spectroscopic follow-up of some of the candidates selected on the basis of their excess flux in the NB920 filter was performed at the VLT-UT4 with the FORS2 instrument. For one object a strong and asymmetric emission line associated with a strong break in continuum emission is identified as Lyα at $z = 6.17$. This galaxy was selected from its continuum emission in the 920 nm filter and not from its Lyα emission, in effect performing a Lyman Break detection at $z = 6.17$. We estimate a star formation rate of several tens of $M_\odot$ yr-1 for this object, with a velocity dispersion ~400 km s-1. The spectroscopic follow-up of other high z galaxy candidates is on-going.
ABSTRACT We report a discovery of six massive galaxies with both extremely large Ly equivalent widths (EWs) and evolved stellar populations at z ∼ 3. These MAssive Extremely STrong Ly emitting ...Objects (MAESTLOs) have been discovered in our large-volume systematic survey for strong Ly emitters (LAEs) with 12 optical intermediate-band data taken with Subaru/Suprime-Cam in the COSMOS field. Based on the spectral energy distribution fitting analysis for these LAEs, it is found that these MAESTLOs have (1) large rest-frame EWs of EW0 (Ly ) ∼ 100-300 , (2) M ∼ 1010.5-1011.1 M , and (3) relatively low specific star formation rates of SFR/M ∼ 0.03-1 Gyr−1. Three of the six MAESTLOs have extended Ly emission with a radius of several kiloparsecs, although they show very compact morphology in the HST/ACS images, which correspond to the rest-frame UV continuum. Since the MAESTLOs do not show any evidence for active galactic nuclei, the observed extended Ly emission is likely to be caused by a star formation process including the superwind activity. We suggest that this new class of LAEs, MAESTLOs, provides a missing link from star-forming to passively evolving galaxies at the peak era of the cosmic star formation history.
Several ‘great walls’ are clearly visible in the Durham/UKST Galaxy Redshift Survey (DURS). We make a statistical study of this superlarge-scale structure (SLSS) by applying our core sampling, ...cluster, inertia tensor and minimal-spanning-tree analyses to the DURS. The results in the main support similar results from the complementary Las Campañas Redshift Survey (LCRS); the DURS is a fully three-dimensional, though shallower, survey, whilst the LCRS was carried out in six thin wedges of space. Because of the one-in-three sparse sampling used for DURS, the galaxy filaments of large-scale structure (LSS) are less clear here; the mean separation of ∼25 h−1 Mpc for the richer filaments is consistent with the LCRS result, but the poorer filaments are not seen in the DURS. In contrast, the analysis clearly picks out SLSS and we find, as with the LCRS, that ∼50 per cent of the galaxies lie within the SLSS in regions with overdensities of 5-10 times the mean galaxy density. It quantitatively demonstrates that SLSS is a major component of large-scale structure in the Universe. The SLSS is also confirmed as having statistical parameters similar to those for a sheet-like object, albeit a very irregular one with a highly inhomogeneous inner structure. The ‘mean-free path’, or average separation between SLSS structures, is found to be Ds≈50 h−1 Mpc. The inertia tensor analysis gives mean lengths, widths and thicknesses of ∼20-40, 10 and 5 h−1 Mpc, respectively, for the clusters of SLSS. In particular, the largest great wall in the DURS is found to have a length of ∼75 h−1 Mpc. Unlike the LCRS, the cluster mass function for the three-dimensional DURS has a high mass ‘tail’; such a ‘tail’ would constitute a quantitative signature for the presence of great walls. Finally, theoretical considerations would suggest that the results support arguments for the large-scale biasing of galaxies with respect to dark matter.
Using data from the COSMOS survey, we perform the first joint analysis of galaxy-galaxy weak lensing, galaxy spatial clustering, and galaxy number densities. Carefully accounting for sample variance ...and for scatter between stellar and halo mass, we model all three observables simultaneously using a novel and self-consistent theoretical framework. Our results provide strong constraints on the shape and redshift evolution of the stellar-to-halo mass relation (SHMR) from z = 0.2 to z = 1. At low stellar mass, we find that halo mass scales as M-h proportional to M-*(0.46) and that this scaling does not evolve significantly with redshift from z = 0.2 to z = 1. The slope of the SHMR rises sharply at M-* \textgreater 5 x 10(10)M(circle dot) and as a consequence, the stellar mass of a central galaxy becomes a poor tracer of its parent halo mass. We show that the dark-to-stellar ratio, Mh/M*, varies from low to high masses, reaching a minimum of Mh/M-* similar to 27 at M-* = 4.5 x 10(10) M-circle dot and M-h = 1.2 x 10(12) M-circle dot. This minimum is important for models of galaxy formation because it marks the mass at which the accumulated stellar growth of the central galaxy has been themost efficient. We describe the SHMR at this minimum in terms of the “ pivot stellarmass,” M-*(piv) the “pivot halo mass,” M-h(piv), and the “pivot ratio,” (M-h/M-*)(piv). Thanks to a homogeneous analysis of a single data set spanning a large redshift range, we report the first detection of mass downsizing trends for both M-h(piv) and M-*(piv) The pivot stellar mass decreases from M-*(piv) = 5.75 +/- 0.13x10(10) M-circle dot at z = 0.88 to M-*(piv) = 3.55 +/- 0.17x10(10) M-circle dot at z = 0.37. Intriguingly, however, the corresponding evolution of M-h(piv) leaves the pivot ratio constant with redshift at (M-h/M-*)(piv) similar to 27. We use simple arguments to show how this result raises the possibility that star formation quenching may ultimately depend on M-h/M-* and not simply onMh, as is commonly assumed. We show that simple models with such a dependence naturally lead to downsizing in the sites of star formation. Finally, we discuss the implications of our results in the context of popular quenching models, including disk instabilities and active galactic nucleus feedback.
Abstract
The variation of galaxy stellar masses and colour types with the distance to projected cosmic filaments are quantified using the precise photometric redshifts of the COSMOS2015 catalogue ...extracted from Cosmological Evolution Survey (COSMOS) field (2 deg2). Realistic mock catalogues are also extracted from the lightcone of the cosmological hydrodynamical simulation Horizon-AGN. They show that the photometric redshift accuracy of the observed catalogue (σz < 0.015 at M* > 1010M⊙ and z < 0.9) is sufficient to provide two-dimensional (2D) filaments that closely match their projected three-dimensional (3D) counterparts. Transverse stellar mass gradients are measured in projected slices of thickness 75 Mpc between 0.5 < z < 0.9, showing that the most massive galaxies are statistically closer to their neighbouring filament. At fixed stellar mass, passive galaxies are also found closer to their filament, while active star-forming galaxies statistically lie further away. The contributions of nodes and local density are removed from these gradients to highlight the specific role played by the geometry of the filaments. We find that the measured signal does persist after this removal, clearly demonstrating that proximity to a filament is not equivalent to proximity to an overdensity. These findings are in agreement with gradients measured in both 2D and 3D in the Horizon-AGN simulation and those observed in the spectroscopic surveys VIPERS and GAMA (which both rely on the identification of 3D filaments). They are consistent with a picture in which the influence of the geometry of the large-scale environment drives anisotropic tides that impact the assembly history of galaxies, and hence their observed properties.
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