Motivated by the claimed discovery of a very massive galaxy (HUDF-JD2; M≃ 5 × 1011 M⊙) at extreme redshift (z= 6.5) within the Hubble Ultra Deep Field (HUDF), we have completed a systematic search ...for comparably massive galaxies with z > 4 among the 2688 galaxies in our KS < 23.5 (AB) catalogue within the CDFS/GOODS-South field. This search was conducted using redshift estimates based on the recently completed, uniquely-deep 11-band (B, V, i, z, J, H, KS, 3.6 μ m, 4.5 μm, 5.8 μm, 8.0 μm) imaging in this 125-arcmin2 field, ≃ 25 times larger than the NICMOS HUDF. To ensure completeness, our approach places no special emphasis on the standard V-drop, i-drop or z-drop criteria commonly used to pre-select candidate high-redshift galaxies. Initial spectral fitting, based on published catalogue SExtractor photometry, led us to conclude that at least 2669 of the galaxies in our sample lie at z < 4. This list includes several galaxies for which redshifts z > 4 have been previously proposed. We carried out a detailed investigation of the 19 remaining z > 4 candidates, performing aperture photometry on all images, and including marginal detections and formal non-detections in the fitting process. This led to the rejection of a further 13 galaxies to lower redshift. Moreover, subjecting HUDF-JD2 to the same analysis, we find that it almost certainly lies at 2 < z < 3, rather than the extreme redshift favoured by Mobasher et al. The six remaining candidates appear to be credible examples of galaxies in the redshift range z= 4–6, with plausible stellar ages. However, refitting with allowance for extreme values of extinction, we find that, even for these objects, statistically acceptable solutions can be found at z < 3. In fact, only two galaxies retain formally preferred high-redshift solutions. Moreover, the recently released Spitzer MIPS imaging in GOODS-South has revealed that five out of our six final z > 4 candidates are detected at 24 μm. This was also the case for HUDF-JD2, and provides further circumstantial evidence in favour of the moderate-redshift dusty solutions. We conclude that there is no convincing evidence for any galaxy with M > 3 × 1011 M⊙ and z > 4 within the 125-arcmin2 GOODS-South field. We briefly discuss the implications of this null result, and revised expectations for the much larger (0.8 deg2), and deeper near-infrared UKIDSS Ultra Deep Survey now underway with the WFCAM on the UKIRT.
Aims.
Our aim is to estimate the intergalactic medium (IGM) transmission towards UV-selected star-forming galaxies at
z
≳ 4 and study the effect of the dust attenuation on these measurements.
...Methods.
The UV spectrum of high-redshift galaxies is a combination of their intrinsic emission and the effect of the IGM absorption along their line of sight. Using data coming from the unprecedentedly deep spectroscopy from the VANDELS ESO public survey carried out with the VIMOS instrument, we compute both the dust extinction and the mean transmission of the IGM as well as its scatter from a set of 281 galaxies at
z
> 3.87. Because of a degeneracy between the dust content of the galaxy and the IGM, we first estimate the stellar dust extinction parameter
E
(
B
−
V
) and study the result as a function of the dust prescription. Using these measurements as constraint for the spectral fit we estimate the IGM transmission Tr(Ly
α
). Both photometric and spectroscopic spectral energy distribution fits are performed using the SPectroscopy And photometRy fiTting tool for Astronomical aNalysis which is able to fit the spectral continuum of the galaxies as well as photometric data.
Results.
Using the classical Calzetti attenuation law we find that
E
(
B
−
V
) goes from 0.11 at
z
= 3.99 to 0.08 at
z
= 5.15. These results are in very close agreement with published measurements. We estimate the IGM transmission and find that the transmission is decreasing with increasing redshift from Tr(Ly
α
) = 0.53 at
z
= 3.99 to 0.28 at
z
= 5.15. We also find a large standard deviation around the average transmission that is more than 0.1 at every redshift. Our results are in very good agreement with both previous measurements from AGN studies and with theoretical models.
Abstract
We present the results of a new study of dust attenuation at redshifts 3 < z < 4 based on a sample of 236 star-forming galaxies from the VANDELS spectroscopic survey. Motivated by results ...from the First Billion Years (FiBY) simulation project, we argue that the intrinsic spectral energy distributions (SEDs) of star-forming galaxies at these redshifts have a self-similar shape across the mass range 8.2 ≤ log (M⋆/M⊙) ≤ 10.6 probed by our sample. Using FiBY data, we construct a set of intrinsic SED templates which incorporate both detailed star formation and chemical abundance histories, and a variety of stellar population synthesis (SPS) model assumptions. With this set of intrinsic SEDs, we present a novel approach for directly recovering the shape and normalization of the dust attenuation curve. We find, across all of the intrinsic templates considered, that the average attenuation curve for star-forming galaxies at z ≃ 3.5 is similar in shape to the commonly adopted Calzetti starburst law, with an average total-to-selective attenuation ratio of RV = 4.18 ± 0.29. In contrast, we find that an average attenuation curve as steep as the SMC extinction law is strongly disfavoured. We show that the optical attenuation (AV) versus stellar mass (M⋆) relation predicted using our method is consistent with recent ALMA observations of galaxies at 2 < z < 3 in the Hubble Ultra Deep Field (HUDF), as well as empirical AV − M⋆ relations predicted by a Calzetti-like law. In fact, our results, combined with other literature data, suggest that the AV–M⋆ relation does not evolve over the redshift range 0 < z < 5, at least for galaxies with log(M⋆/M⊙) ≳ 9.5. Finally, we present tentative evidence which suggests that the attenuation curve may become steeper at lower masses log(M⋆/M⊙) ≲ 9.0.
We discuss the structural and morphological properties of galaxies in a z = 1.62 proto-cluster using near-IR imaging data from Hubble Space Telescope Wide Field Camera 3 data of the Cosmic Assembly ...Near-IR Deep Extragalactic Legacy Survey (CANDELS). The cluster galaxies exhibit a clear color-morphology relation: galaxies with colors of quiescent stellar populations generally have morphologies consistent with spheroids, and galaxies with colors consistent with ongoing star formation have disk-like and irregular morphologies. The size distribution of the quiescent cluster galaxies shows a deficit of compact ({approx}< 1 kpc), massive galaxies compared to CANDELS field galaxies at z = 1.6. As a result, the cluster quiescent galaxies have larger average effective sizes compared to field galaxies at fixed mass at greater than 90% significance. Combined with data from the literature, the size evolution of quiescent cluster galaxies is relatively slow from z {approx_equal} 1.6 to the present, growing as (1 + z){sup -0.6{+-}0.1}. If this result is generalizable, then it implies that physical processes associated with the denser cluster region seem to have caused accelerated size growth in quiescent galaxies prior to z = 1.6 and slower subsequent growth at z < 1.6 compared to galaxies in the lower density field. The quiescent cluster galaxies at z = 1.6 have higher ellipticities compared to lower redshift samples at fixed mass, and their surface-brightness profiles suggest that they contain extended stellar disks. We argue that the cluster galaxies require dissipationless (i.e., gas-poor or 'dry') mergers to reorganize the disk material and to match the relations for ellipticity, stellar mass, size, and color of early-type galaxies in z < 1 clusters.
We present new results on the cosmological evolution of the near-infrared (near-IR) galaxy luminosity function (LF), derived from the analysis of a new sample of ∼22 000 KAB≤ 22.5 galaxies selected ...over an area of 0.6 deg2 from the Early Data Release of the UKIDSS Ultra Deep Survey (UDS). Our study has exploited the multiwavelength coverage of the UDS field provided by the new UKIDSS WFCAM K- and J-band imaging, the Subaru/XMM–Newton Deep Survey and the Spitzer Wide-Area Infrared Extragalactic survey. The unique combination of large area and depth provided by this new survey minimizes the complicating effect of cosmic variance and has allowed us, for the first time, to trace the evolution of the brightest sources out to z≃ 2 with good statistical accuracy. In agreement with previous studies, we find that the characteristic luminosity of the near-IR LF brightens by ≃1 mag between z= 0 and z≃ 2, while the total density decreases by a factor of ≃2. Using the rest-frame (U−B) colour to split the sample into red and blue galaxies, we confirm the classic luminosity-dependent colour bimodality at z≲ 1. However, the strength of the colour bimodality is found to be a decreasing function of redshift, and seems to disappear by z≳ 1.5. Due to the large size of our sample, we are able to investigate the differing cosmological evolution of the red and blue galaxy populations. It is found that the space density of the brightest red galaxies (MK≤− 23) stays approximately constant with redshift, and that these sources dominate the bright end of the LF at redshifts z≲ 1. In contrast, the brightening of the characteristic luminosity and mild decrease in space density displayed by the blue galaxy population leads them to dominate the bright end of the LF at redshifts z≳ 1.
ABSTRACT
We present a comparative analysis of the properties of active galactic nuclei (AGNs) emitting at radio and X-ray wavelengths. The study is performed on 907 X-ray AGNs and 100 radio AGNs ...selected on the CDFS and UDS fields and makes use of new and ancillary data available to the VANDELS collaboration. Our results indicate that the mass of the host galaxy is a fundamental quantity that determines the level of AGN activity at the various wavelengths. Indeed, large stellar masses are found to be connected with AGN radio emission, as virtually all radio-active AGNs reside within galaxies of M* > 1010 M⊙. Large stellar masses also seem to favour AGN activity in the X-ray, even though X-ray AGNs present a mass distribution that is more spread out and with a non-negligible tail at M* ≲ 109 M⊙. Stellar mass alone is also observed to play a fundamental role in simultaneous radio and X-ray emission: the percentage of AGNs active at both wavelengths increases from around 1 per cent of all X-ray AGNs residing within hosts of M* < 1011 M⊙ to ∼13 per cent in more massive galaxies. In the case of radio-selected AGNs, such a percentage moves from ∼15 per cent to ∼45 per cent (but up to ∼80 per cent in the deepest fields). Neither cosmic epoch, nor radio luminosity, X-ray luminosity, Eddington ratio or star formation rate of the hosts are found to be connected to an enhanced probability for joint radio + X-ray emission of AGN origin. Furthermore, only a loose relation is observed between X-ray and radio luminosity in those AGNs that are simultaneously active at both frequencies.
We investigate the environments of both X-ray and radio-loud active galactic nuclei (AGN) within the UK Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) Ultra-deep Survey (UDS) using deep ...infrared selection to sample the galaxy density field in the redshift range 1.0 ≤z≤ 1.5. Using angular cross-correlation techniques we find that both X-ray and radio-loud AGN preferentially reside in overdense environments. We also find that both types of AGN cluster more strongly with those galaxies classified as 'passive' rather than those that are actively star forming. We infer clustering scalelengths comparable to those of passive red galaxies, suggesting that typical AGN at these epochs reside in dark matter haloes of mass M≳ 1013 M⊙. A closer look at the small-scale environments of the AGN reveals that the neighbouring galaxies of radio-loud AGN have U−B colours more skewed towards the 'green valley' and the red sequence, whereas the neighbours of X-ray AGN show no difference to the general galaxy population. This suggests that although both AGN types live in overdense environments, the radio-loud AGN may be preferentially located in more evolved cluster cores, in a similar environment to low-powered radio AGN in the local Universe.
Aims.
We aim to derive a new constraint on the expansion history of the Universe by applying the cosmic chronometers method in the VANDELS survey, studying the age evolution of high-redshift galaxies ...with a full-spectral-fitting approach.
Methods.
We selected a sample of 39 massive (log(
M
⋆
/
M
⊙
) > 10.8) and passive (log(sSFR/yr
−1
) < −11) galaxies from the fourth data release of the VANDELS survey at 1 <
z
< 1.5. To minimise the potential contamination by star-forming outliers, we selected our sample by combining different selection criteria, considering both photometric and spectroscopic information. The analysis of the observed spectral features provides direct evidence of an age evolution with redshift and of mass-downsizing, with more massive galaxies presenting stronger age-related features. To estimate the physical properties of the sample, we performed full spectral fitting with the code
BAGPIPES
, jointly analysing spectra and photometry of our sources without any cosmological assumption regarding the age of the population.
Results.
The derived physical properties of the selected galaxies are characteristic of a passive population, with short star formation timescales (⟨
τ
⟩ = 0.28 ± 0.02 Gyr), low dust extinction (⟨
A
V
, dust
⟩ = 0.43 ± 0.02 mag), and sub-solar metallicities (⟨
Z
/
Z
⊙
⟩ = 0.44 ± 0.01) compatible with other measurements of similar galaxies in this redshift range. The stellar ages, even if no cosmological constraint is assumed in the fit, show a decreasing trend compatible with a standard cosmological model, proving the robustness of the method in measuring the ageing of the population. Moreover, they show a distinctive mass-downsizing pattern, with more massive galaxies (⟨log(
M
⋆
/
M
⊙
)⟩ = 11.4) being older than less massive ones (⟨log(
M
⋆
/
M
⊙
)⟩ = 11.15) by ∼0.8 Gyr. We thoroughly tested the dependence of our results on the assumed SFH, finding a maximum 2% fluctuation on median results using models with significantly different functional forms. The derived ages are combined to build a median age–redshift relation, which we used to perform our cosmological analysis.
Conclusions.
By fitting the median age–redshift relation with a flat ΛCDM model, assuming a Gaussian prior on Ω
M, 0
= 0.3 ± 0.02 from late-Universe cosmological probes, we obtain a new estimate of the Hubble constant
H
0
= 67
−15
+14
km s
−1
Mpc
−1
. In the end, we derive a new estimate of the Hubble parameter by applying the cosmic chronometers method to this sample, deriving a value of
H
(
z
= 1.26) = 135 ± 65 km s
−1
Mpc
−1
considering both statistical and systematic errors. While the error budget in this analysis is dominated by the scarcity of the sample, this work demonstrates the potential strength of the cosmic chronometers approach up to
z
> 1, especially in view of the next incoming large spectroscopic surveys such as
Euclid
.
ABSTRACT
We investigate the degree of dust obscured star formation in 49 massive (log10(M⋆/M⊙) > 9) Lyman-break galaxies (LBGs) at z = 6.5–8 observed as part of the Atacama Large ...Millimeter/submillimeter Array (ALMA) Reionization Era Bright Emission Line Survey (REBELS) large program. By creating deep stacks of the photometric data and the REBELS ALMA measurements we determine the average rest-frame ultraviolet (UV), optical, and far-infrared (FIR) properties which reveal a significant fraction (fobs = 0.4–0.7) of obscured star formation, consistent with previous studies. From measurements of the rest-frame UV slope, we find that the brightest LBGs at these redshifts show bluer (β ≃ −2.2) colours than expected from an extrapolation of the colour–magnitude relation found at fainter magnitudes. Assuming a modified blackbody spectral energy distribution (SED) in the FIR (with dust temperature of $T_{\rm d} = 46\, {\rm K}$ and βd = 2.0), we find that the REBELS sources are in agreement with the local ‘Calzetti-like’ starburst Infrared-excess (IRX)–β relation. By re-analysing the data available for 108 galaxies at z ≃ 4–6 from the ALMA Large Program to Investigate C+ at Early Times (ALPINE) using a consistent methodology and assumed FIR SED, we show that from z ≃ 4–8, massive galaxies selected in the rest-frame UV have no appreciable evolution in their derived IRX–β relation. When comparing the IRX–M⋆ relation derived from the combined ALPINE and REBELS sample to relations established at z < 4, we find a deficit in the IRX, indicating that at z > 4 the proportion of obscured star formation is lower by a factor of ≳ 3 at a given a M⋆. Our IRX–β results are in good agreement with the high-redshift predictions of simulations and semi-analytic models for z ≃ 7 galaxies with similar stellar masses and star formation rates.
We present the first results from a major HST WFPC2 imaging study aimed at providing the first statistically meaningful comparison of the morphologies, luminosities, scalelengths and colours of the ...host galaxies of radio-quiet quasars, radio-loud quasars and radio galaxies. We describe the design of this study and present the images that have been obtained for the first half of our 33-source sample. We find that the hosts of all three classes of luminous AGN are massive elliptical galaxies, with scalelengths ≃10 kpc, and R−K colours consistent with mature stellar populations. Most importantly, this is first unambiguous evidence that, just like radio-loud quasars, essentially all radio-quiet quasars brighter than MR=−24 reside in massive ellipticals. This result removes the possibility that radio ‘loudness’ is directly linked to host galaxy morphology, but is however in excellent accord with the black hole/spheroid mass correlation recently highlighted by Magorrian et al. We apply the relations given by Magorrian et al. to infer the expected Eddington luminosity of the putative black hole at the centre of each of the spheroidal host galaxies we have uncovered. Comparison with the actual nuclear R-band luminosities suggests that the black holes in most of these galaxies are radiating at a few per cent of the Eddington luminosity; the brightest host galaxies in our low-z sample are capable of hosting quasars with MR≃−28, comparable to the most luminous quasars at z≃3. Finally, we discuss our host-derived black hole masses in the context of the radio luminosity:black hole mass correlation recently uncovered for nearby galaxies by Franceschini et al., and consider the resulting implications for the physical origin of radio loudness.
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