Abstract
We present the results of a study investigating the dust attenuation law at z ≃ 5, based on synthetic spectral energy distributions (SEDs) calculated for a sample of N = 498 galaxies drawn ...from the First Billion Years (FiBY) simulation project. The simulated galaxies at z ≃ 5, which have M
1500 ≤ −18.0 and
$7.5 \le \rm {log(M/M}_{{\odot }}\rm {)} \le 10.2$
, display a mass-dependent α-enhancement, with a median value of
$\alpha /{\rm {Fe}}_{z=5} \simeq 4 \times \alpha /{\rm {Fe}}_{Z_{{\odot }}}$
. The median Fe/H ratio of the simulated galaxies is 0.14 ± 0.05 which produces steep intrinsic ultraviolet (UV) continuum slopes; 〈β
i
〉 = −2.4 ± 0.05. Using a set of simple dust attenuation models, in which the wavelength-dependent attenuation is assumed to be of the form A(λ) ∝ λ
n
, we explore the parameter values which best reproduce the observed z = 5 luminosity function (LF) and colour–magnitude relation (CMR). We find that a simple model in which the absolute UV attenuation is a linearly increasing function of log stellar mass (A
1500 = 0.5 × log(M/M⊙) − 3.3), and the dust attenuation slope (n) is within the range −0.7 ≤ n ≤ −0.3, can successfully reproduce the LF and CMR over a wide range of stellar population synthesis model assumptions, including the effects of massive binaries. This range of attenuation curves is consistent with a power-law fit to the Calzetti attenuation law in the UV (n = −0.55). In contrast, curves as steep as the Small Magellanic Cloud extinction curve (n = −1.24) are formally ruled out. Finally, we show that our models are consistent with recent 1.3 mm Atacama Large Millimeter Array observations of the Hubble Ultra Deep Field, and predict the form of the z ≃ 5 infrared excess (IRX)–β relation.
ABSTRACT We present 0 4 resolution extinction-independent distributions of star formation and dust in 11 star-forming galaxies (SFGs) at z = 1.3-3.0. These galaxies are selected from sensitive ...blank-field surveys of the 2′ × 2′ Hubble Ultra-Deep Field at λ = 5 cm and 1.3 mm using the Karl G. Jansky Very Large Array and Atacama Large Millimeter/submillimeter Array. They have star formation rates (SFRs), stellar masses, and dust properties representative of massive main-sequence SFGs at z ∼ 2. Morphological classification performed on spatially resolved stellar mass maps indicates a mixture of disk and morphologically disturbed systems; half of the sample harbor X-ray active galactic nuclei (AGNs), thereby representing a diversity of z ∼ 2 SFGs undergoing vigorous mass assembly. We find that their intense star formation most frequently occurs at the location of stellar-mass concentration and extends over an area comparable to their stellar-mass distribution, with a median diameter of 4.2 1.8 kpc. This provides direct evidence of galaxy-wide star formation in distant blank-field-selected main-sequence SFGs. The typical galactic-average SFR surface density is 2.5 M yr−1 kpc−2, sufficiently high to drive outflows. In X-ray-selected AGN where radio emission is enhanced over the level associated with star formation, the radio excess pinpoints the AGNs, which are found to be cospatial with star formation. The median extinction-independent size of main-sequence SFGs is two times larger than those of bright submillimeter galaxies, whose SFRs are 3-8 times larger, providing a constraint on the characteristic SFR (∼300 M yr−1) above which a significant population of more compact SFGs appears to emerge.
We present the results of a study of a large sample of luminous (z′AB < 26) Lyman-break galaxies (LBGs) in the redshift interval 4.7 < z < 6.3, selected from a contiguous 0.63 deg2 area covered by ...the UKIRT Infrared Deep Sky Survey Ultra Deep Survey and the Subaru XMM–Newton Survey. Utilizing the large area coverage and the excellent available optical+near-infrared data, we use a photometric redshift analysis to derive a new, robust, measurement of the bright end (L≥L★) of the ultraviolet-selected luminosity function at high redshift. When combined with literature studies of the fainter LBG population, our new sample provides improved constraints on the luminosity function of redshift 5 < z < 6 LBGs over the luminosity range 0.1L★≲L≲ 10L★. A maximum likelihood analysis returns best-fitting Schechter function parameters of M★1500=−20.73 ± 0.11, φ★= 0.0009 ± 0.0002 Mpc−3 and α=−1.66 ± 0.06 for the luminosity function at z= 5, and M★1500=−20.04 ± 0.12, φ★= 0.0018 ± 0.0005 Mpc−3 and α=−1.71 ± 0.11 at z= 6. In addition, an analysis of the angular clustering properties of our LBG sample demonstrates that luminous 5 < z < 6 LBGs are strongly clustered (r0= 8.1+2.1−1.5h−170 Mpc), and consistent with the occupation of dark matter haloes with masses of ≃1011.5−12 M⊙. Moreover, by stacking the available multiwavelength imaging data for the high-redshift LBGs, it is possible to place useful constraints on their typical stellar mass. The results of this analysis suggest that luminous LBGs at 5 < z < 6 have an average stellar mass of log10(M/M⊙) = 10.0+0.2−0.4, consistent with the results of the clustering analysis assuming plausible values for the ratio of stellar to dark matter. Finally, by combining our luminosity function results with those of the stacking analysis we derive estimates of ≃1 × 107 and ≃4 × 106 M⊙ Mpc−3 for the stellar mass density at z≃ 5 and 6, respectively.
A new technique is presented for determining the black hole masses of high-redshift quasars from optical spectroscopy. The new method utilizes the full-width at half-maximum (FWHM) of the ...low-ionization Mg ii emission line and the correlation between the broad-line region (BLR) radius and the continuum luminosity at 3000 Å. Using archival ultraviolet (UV) spectra it is found that the correlation between BLR radius and 3000-Å luminosity is tighter than the established correlation with 5100-Å luminosity. Furthermore, it is found that the correlation between BLR radius and 3000-Å continuum luminosity is consistent with a relation of the form RBLR∝λL1/2λ, as expected for a constant ionization parameter. Using a sample of objects with broad-line radii determined from reverberation mapping it is shown that the FWHM of Mg ii and Hβ are consistent with following an exact one-to-one relation, as expected if both Hβ and Mg ii are emitted at the same radius from the central ionizing source. The resulting virial black hole mass estimator based on rest-frame UV observables is shown to reproduce black hole mass measurements based on reverberation mapping to within a factor of 2.5 (1σ). Finally, the new UV black hole mass estimator is shown to produce identical results to the established optical (Hβ) estimator when applied to 128 intermediate-redshift (0.3 < z < 0.9) quasars drawn from the Large Bright Quasar Survey and the radio-selected Molonglo quasar sample. We therefore conclude that the new UV virial black hole mass estimator can be reliably used to estimate the black hole masses of quasars from z∼ 0.25 through to the peak epoch of quasar activity at z∼ 2.5 via optical spectroscopy alone.
We use the new ultra-deep, near-infrared imaging of the Hubble Ultra-Deep Field (HUDF) provided by our UDF12 Hubble Space Telescope (HST) Wide Field Camera 3/IR campaign to explore the rest-frame ...ultraviolet (UV) properties of galaxies at redshifts z > 6.5. We present the first unbiased measurement of the average UV power-law index, 〈β〉, (f
λ ∝ λβ) for faint galaxies at z 7, the first meaningful measurements of 〈β〉 at z 8, and tentative estimates for a new sample of galaxies at z 9. Utilizing galaxy selection in the new F140W (J
140) imaging to minimize colour bias, and applying both colour and power-law estimators of β, we find 〈β〉 = −2.1 ± 0.2 at z 7 for galaxies with M
UV −18. This means that the faintest galaxies uncovered at this epoch have, on average, UV colours no more extreme than those displayed by the bluest star-forming galaxies at low redshift. At z 8 we find a similar value, 〈β〉 = −1.9 ± 0.3. At z 9, we find 〈β〉 = −1.8 ± 0.6, essentially unchanged from z 6 to 7 (albeit highly uncertain). Finally, we show that there is as yet no evidence for a significant intrinsic scatter in β within our new, robust z 7 galaxy sample. Our results are most easily explained by a population of steadily star-forming galaxies with either solar metallicity and zero dust, or moderately sub-solar ( 10-20 per cent) metallicity with modest dust obscuration (A
V
0.1-0.2). This latter interpretation is consistent with the predictions of a state-of-the-art galaxy-formation simulation, which also suggests that a significant population of very-low metallicity, dust-free galaxies with β −2.5 may not emerge until M
UV > −16, a regime likely to remain inaccessible until the James Webb Space Telescope.
Aims. We present the first public release of photometric redshifts, galaxy rest frame properties and associated magnification values in the cluster and parallel pointings of the first two Frontier ...Fields, Abell-2744 and MACS-J0416. The released catalogues aim to provide a reference for future investigations of extragalactic populations in these legacy fields: from lensed high-redshift galaxies to cluster members themselves. Methods. We exploit a multiwavelength catalogue, ranging from Hubble Space Telescope (HST) to ground-based K and Spitzer IRAC, which is specifically designed to enable detection and measurement of accurate fluxes in crowded cluster regions. The multiband information is used to derive photometric redshifts and physical properties of sources detected either in the H-band image alone, or from a stack of four WFC3 bands. To minimize systematics, median photometric redshifts are assembled from six different approaches to photo-z estimates. Their reliability is assessed through a comparison with available spectroscopic samples. State-of-the-art lensing models are used to derive magnification values on an object-by-object basis by taking into account sources positions and redshifts. Results. We show that photometric redshifts reach a remarkable ~3-5% accuracy. After accounting for magnification, the H-band number counts are found to be in agreement at bright magnitudes with number counts from the CANDELS fields, while extending the presently available samples to galaxies that, intrinsically, are as faint as H~ 32-33, thanks to strong gravitational lensing. The Frontier Fields allow the galaxy stellar mass distribution to be probed, depending on magnification, at 0.5-1.5 dex lower masses with respect to extragalactic wide fields, including sources at M sub(star)~ 10 super(7)-10 super(8)M sub(middot in circle) at z> 5. Similarly, they allow the detection of objects with intrinsic star formation rates (SFRs) >1 dex lower than in the CANDELS fields reaching 0.1-1 M sub(middot in circle)/yr at z~ 6-10.
New black hole mass estimates are presented for a sample of 72 active galactic nuclei (AGNs) covering three decades in optical luminosity. Using a subsample of Seyfert galaxies, which have black hole ...mass estimates from both reverberation mapping and stellar velocity dispersions, we investigate the geometry of the AGNs’ broad-line region. It is demonstrated that a model in which the orbits of the line-emitting material have a flattened geometry is favoured over randomly-orientated orbits. Using this model we investigate the Mbh-Lbulge relation for a combined 90-object sample consisting of the AGNs plus a sample of 18 nearby inactive elliptical galaxies with dynamical black hole mass measurements. It is found that, for all reasonable mass-to-light ratios, the Mbh-Lbulge relation is equivalent to a linear scaling between bulge and black hole mass. The best-fitting normalization of the Mbh-Mbulge relation is found to be Mbh=0.0012Mbulge, in agreement with recent black hole mass studies based on stellar velocity dispersions. Furthermore, the scatter around the Mbh-Lbulge relation for the full sample is found to be significantly smaller than has been previously reported (Δlog Mbh=0.39 dex). Finally, using the nearby inactive elliptical galaxy sample alone, it is shown that the scatter in the Mbh-Lbulge relation is only 0.33 dex, comparable with that of the Mbh-σ relation. These results indicate that reliable black hole mass estimates can be obtained for high redshift galaxies.
We use the United Kingdom Infrared Telescope Deep Sky Survey (UKIDSS) Ultra Deep Survey (UDS), the deepest degree-scale near-infrared survey to date, to investigate the clustering of star-forming and ...passive galaxies to z ∼ 3.5. Our new measurements include the first determination of the clustering for passive galaxies at z > 2, which we achieve using a cross-correlation technique. We find that passive galaxies are the most strongly clustered, typically hosted by massive dark matter haloes with M
halo > 5 × 1012 M irrespective of redshift or stellar mass. Our findings are consistent with models in which a critical halo mass determines the transition from star-forming to passive galaxies. Star-forming galaxies show no strong correlation between stellar mass and halo mass, but passive galaxies show evidence for an anticorrelation; low-mass passive galaxies appear, on average, to be located in the most massive haloes. These results can be understood if the termination of star formation is most efficient for galaxies of low stellar mass in very dense environments.
Following the discovery of the first significant samples of galaxies at z > 6.5 with Wide Field Camera 3/Infra-Red (WFC3/IR) on board Hubble Space Telescope (HST), it has been claimed that the ...faintest high-redshift galaxies display extremely blue ultraviolet (UV) continuum slopes, with a UV power-law index β≃−3 (where f
λ∝λβ). Such slopes are bluer than previously reported for any other galaxy population, and are most readily explained theoretically by extinction-free, young and very low metallicity stellar populations with a high ionizing photon escape fraction. Here we undertake a critical study of the evidence for such extreme values of β, combining three new WFC3/IR-selected samples of galaxies spanning nearly two decades in UV luminosity over the redshift range z≃ 4.5-8. We explore the impact of inclusion/exclusion of less robust high-redshift candidates and use the varying depths of the samples to explore the effects of noise and selection bias at a given UV luminosity. Simple data-consistency arguments suggest that artificially blue average values of β can result when the analysis is extended into the deepest ≃0.5 mag bin of these WFC3/IR-selected galaxy samples, regardless of the actual luminosity or redshift range probed. By confining attention to robust high-redshift galaxy candidates, with at least one 8σ detection in the WFC3/IR imaging, we find that the average value of β is consistent with 〈β〉=−2.05 ± 0.10 over the redshift range z= 5-7 and the UV absolute magnitude range −22 < M
UV,AB < − 18, and that 〈β〉 shows no significant trend with either redshift or M
UV. We create and analyse a set of simple end-to-end simulations based on the WFC3/IR+ACS Hubble Ultra Deep Field (HUDF) and Early Release Science data sets which demonstrate that a bias towards artificially low/blue average values of β is indeed 'expected' when the UV slope analysis is extended towards the source detection threshold, and conclude that there is as yet no clear evidence for UV slopes significantly bluer than β≃−2, the typical value displayed by the bluest star-forming galaxies at more modest redshifts. A robust measurement of 〈β〉 for the faintest galaxies at z≃ 7 (and indeed z≃ 8) remains a key observational goal, as it provides a fundamental test for high escape fractions from a potentially abundant source of re-ionizing photons. This goal is achievable with HST, but requires still deeper WFC3/IR imaging in the HUDF.
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