Abstract
We present a new analysis of the potential power of deep, near-infrared, imaging surveys with the James Webb Space Telescope (JWST) to improve our knowledge of galaxy evolution. In this work ...we properly simulate what can be achieved with realistic survey strategies, and utilize rigorous signal-to-noise ratio calculations to calculate the resulting posterior constraints on the physical properties of galaxies. We explore a broad range of assumed input galaxy types (>20 000 models, including extremely dusty objects) across a wide redshift range (out to z ≃ 12), while at the same time considering a realistic mix of galaxy properties based on our current knowledge of the evolving population (as quantified through the Empirical Galaxy Generator). While our main focus is on imaging surveys with NIRCam, spanning $\lambda _{\mathrm{ obs}} = 0.8\!-\!5.0\, \mu$m, an important goal of this work is to quantify the impact/added-value of: (i) parallel imaging observations with MIRI at longer wavelengths, and (ii) deeper supporting optical/UV imaging with HST (potentially prior to JWST launch) in maximizing the power and robustness of a major extragalactic NIRCam survey. We show that MIRI parallel 7.7-$\mu$m imaging is of most value for better constraining the redshifts and stellar masses of the dustiest (AV > 3) galaxies, while deep B-band imaging (reaching ≃ 28.5 AB mag) with ACS on HST is vital for determining the redshifts of the large numbers of faint/low-mass, z < 5 galaxies that will be detected in a deep JWST NIRCam survey.
Aims.
We investigate the production efficiency of ionizing photons (
ξ
ion
∗
) of 1174 galaxies with secure redshift at
z
= 2 − 5 from the VANDELS survey to determine the relation between ionizing ...emission and physical properties of bright and massive sources.
Methods.
We constrained
ξ
ion
∗
and galaxy physical parameters by means of spectrophotometric fits performed with the
BEAGLE
code. The analysis exploits the multi-band photometry in the VANDELS fields and the measurement of UV rest-frame emission lines (CIII
λ
1909, HeII
λ
1640, and OIII
λ
1666) from deep VIMOS spectra.
Results.
We find no clear evolution of
ξ
ion
∗
with redshift within the probed range. The ionizing efficiency slightly increases at fainter
M
UV
and bluer UV slopes, but these trends are less evident when the analysis is restricted to a complete subsample at log(
M
star
/
M
⊙
) > 9.5. We find a significant trend of increasing
ξ
ion
∗
with increasing EW(Ly
α
), with an average log(
ξ
ion
∗
/Hz erg
−1
) > 25 at EW > 50 Å and a higher ionizing efficiency for high-EW CIII
λ
1909 and OIII
λ
1666 emitters. The most significant correlations are found with respect to stellar mass, specific star formation rate (sSFR), and SFR surface density (Σ
SFR
). The relation between
ξ
ion
∗
and sSFR increases monotonically from log(
ξ
ion
∗
/Hz erg
−1
)∼24.5 at log(sSFR) ∼ −9.5 yr
−1
to ∼25.5 at log(sSFR) ∼ −7.5 yr
−1
. This relation has a low scatter and only a weak dependence on mass. The objects above the main sequence of star formation consistently have higher than average
ξ
ion
∗
. A clear increase in
ξ
ion
∗
with Σ
SFR
is also found, with log(
ξ
ion
∗
/Hz erg
−1
) > 25 for objects at Σ
SFR
> 10
M
⊙
yr
−1
kpc
−2
.
Conclusions.
Bright (
M
UV
≲ 20) and massive (log(
M
star
/
M
⊙
)≳9.5) galaxies at
z
= 2 − 5 have a moderate ionizing efficiency. However, the correlation between
ξ
ion
∗
and sSFR, together with the known increase in the average sSFR with redshift at fixed stellar mass, suggests that similar galaxies in the epoch of reionization can be efficient sources of ionizing photons. The availability of sSFR and Σ
SFR
as proxies for
ξ
ion
∗
can be fundamentally important in determining the role of galaxy populations at
z
≳ 10 that were recently discovered by the
James Webb
Space Telescope in the onset of reionization.
We report the results of a study exploring the stellar populations of 13 luminous (L > 1.2L*), spectroscopically confirmed, galaxies in the redshift interval 5.5 < z < 6.5, all with Hubble Space ...Telescope (HST) Wide Field Camera 3/infrared and Spitzer Infrared Array Camera imaging from the HST/Cosmic Assembly Near-infrared Deep Survey and Spitzer Extended Deep Survey. Based on fitting the observed photometry with galaxy spectral energy distribution (SED) templates covering a wide range of different star formation histories, including exponentially increasing star formation rates and a self-consistent treatment of Lyα emission, we find that the derived stellar masses lie within the range of 109< M
* < 1010 M and are robust to within a factor of 2. In contrast, we confirm previous reports that the ages of the stellar populations are poorly constrained. Although the best-fitting models for 3/13 of the sample have ages of 300 Myr, the degeneracies introduced by dust extinction mean that only two of these objects actually require a 300 Myr old stellar population to reproduce the observed photometry. We also explore SED fitting with more general, two-component models (burst plus ongoing star formation), thereby relaxing the requirement that the current star formation rate and assembled stellar mass must be coupled, and allow for nebular line+continuum emission. On average, the inclusion of nebular emission leads to lower stellar mass estimates (median offset 0.18 dex), moderately higher specific star formation rates, and allows for a wider range of plausible stellar ages. However, based on our SED modelling, we find no strong evidence for extremely young ages in our sample (i.e. <50 Myr). Finally, considering all of the different star formation histories explored, we find that the median best-fitting ages are of the order of 200-300 Myr and that the objects with the tightest constraints indicate ages in the range of 50-200 Myr.
We have studied the μJy radio properties of K-selected galaxy populations detected in the Ultra-Deep Survey (UDS) portion of the United Kingdom Infrared Telescope (UKIRT) Deep Sky Survey using 610- ...and 1400-MHz images from the Very Large Array and the Giant Metre-wave Telescope. These deep radio mosaics, combined with the largest and deepest K-band image currently available, allow high signal-to-noise ratio (S/N) detections of many K-selected subpopulations, including sBzK and pBzK star-forming and passive galaxies. We find a strong correlation between the radio and K-band fluxes and a linear relationship between star formation rate (SFR) and K-band luminosity. We find no evidence, either from radio spectral indices or a comparison with submm-derived SFRs, that the full sample is strongly contaminated by active galactic nuclei (AGN) at these low flux densities, though this is very difficult to determine from this data set. The photometric redshift distributions for the BzK galaxies place 37 (29) per cent of pBzK (sBzK) galaxies at z < 1.4, implying that location on the BzK diagram alone is not sufficient to select samples at 1.4 < z < 2.5. The sBzK and pBzK galaxies have similar levels of radio flux density, SFR and specific SFR (SSFR – SFR per unit stellar mass) at z < 1.4, suggesting there is strong contamination of the pBzK sample by star-forming galaxies. At z > 1.4, the pBzK galaxies become difficult to detect in the radio stack, though the implied SFRs are still much higher than expected for passively evolving galaxies. It may be that their radio emission comes from low-luminosity AGN. Extremely red objects (EROs) straddle the passive and star-forming regions of the BzK diagram and also straddle the two groups in terms of their radio properties. We find that K-bright ERO samples are dominated by passive galaxies and faint ERO samples contain more star-forming galaxies. The star formation history (SFH) from stacking all K-band sources in the UDS agrees well with that derived for other wavebands and other radio surveys, at least out to z∼ 2. The radio-derived SFH then appears to fall more steeply than that measured at other wavelengths. The SSFR for K-selected sources rises strongly with redshift at all stellar masses, and shows a weak dependence on stellar mass. High- and low-mass galaxies show a similar decline in SSFR since z∼ 2.
Context. The exploration of the relation between galaxy sizes and other physical parameters (luminosity, mass, star formation rate) has provided important clues for understanding galaxy formation, ...but such exploration has until recently been limited to intermediate redshift objects. Aims. We use the currently available CANDELS Deep+Wide surveys in the GOODS-South, UDS and EGS fields, complemented by data from the HUDF09 program, to address the relation between size and luminosity at z ~ 7. Methods. The six different fields used for this study are characterized by a wide combination of depth and areal coverage, well suited for reducing the biases on the observed size-magnitude plane. From these fields, we select 153 z-band dropout galaxies. Detailed simulations have been carried out for each of these six fields, inserting simulated galaxies at different magnitudes and half light radius in the two dimensional images for all the Hubble Space Telescope (HST) bands available and recovering them as carried out for the real galaxies. These simulations allow us to derive precisely the completeness as a function of size and magnitude and to quantify measurements errors/biases, under the assumption that the 2D profile of z = 7 galaxies is well represented by an exponential disk function. Results. We find in a rather robust way that the half light radius distribution function of z ~ 7 galaxies fainter than J = 26.6 is peaked at ≤ 0.1 arcsec (or equivalently 0.5 kpc proper), while at brighter magnitudes high-z galaxies are typically larger than ~0.15 arcsec. We also find a well defined size-luminosity relation, Rh ∝ L1/2. We compute the luminosity function (LF) in the HUDF and P12HUDF fields, finding large spatial variation on the number density of faint galaxies. Adopting the size distribution and the size-luminosity relation found for faint galaxies at z = 7, we derive a mean slope of −1.7 ± 0.1 for the LF of LBGs at this redshift. Conclusions. Using this LF, we find that the number of ionizing photons emitted from galaxies at z ~ 7 cannot keep the Universe re-ionized if the IGM is clumpy (CHII ≥ 3) and the Lyman continuum escape fraction of high-z LBGs is relatively low (fesc ≤ 0.3). If these results are confirmed and strengthened by future CANDELS data, in particular by the forthcoming deep observations in GOODS-South and North and the wide field COSMOS, we can put severe limits to the role of galaxies in the reionization of the Universe.
We present a study of galaxy environments to z∼ 2, based on a sample of over 33 000 K-band-selected galaxies detected in the UKIDSS Ultra Deep Survey (UDS). The combination of infrared depth and area ...in the UDS allows us to extend previous studies of galaxy environment to z > 1 without the strong biases associated with optical galaxy selection. We study the environments of galaxies divided by rest-frame (U−B) colours, in addition to 'passive' and 'star-forming' subsets based on template fitting. We find that galaxy colour is strongly correlated with galaxy overdensity on small scales (<1-Mpc diameter), with red/passive galaxies residing in significantly denser environments than blue/star-forming galaxies to z∼ 1.5. On smaller scales (<0.5-Mpc diameter) we also find a relationship between galaxy luminosity and environment, with the most luminous blue galaxies at z∼ 1 inhabiting environments comparable to red, passive systems at the same redshift. Monte Carlo simulations demonstrate that these conclusions are robust to the uncertainties introduced by photometric redshift errors.
Abstract
We present a new measurement of the evolving galaxy far-IR luminosity function (LF) extending out to redshifts z ≃ 5, with resulting implications for the level of dust-obscured star ...formation density in the young Universe. To achieve this, we have exploited recent advances in sub-mm/mm imaging with SCUBA-2 on the James Clerk Maxwell Telescope and the Atacama Large Millimeter/Submillimeter Array, which together provide unconfused imaging with sufficient dynamic range to provide meaningful coverage of the luminosity-redshift plane out to z > 4. Our results support previous indications that the faint-end slope of the far-IR LF is sufficiently flat that comoving luminosity density is dominated by bright objects (≃L*). However, we find that the number density/luminosity of such sources at high redshifts has been severely overestimated by studies that have attempted to push the highly confused Herschel SPIRE surveys beyond z ≃ 2. Consequently, we confirm recent reports that cosmic star formation density is dominated by UV-visible star formation at z > 4. Using both direct (1/V
max) and maximum likelihood determinations of the LF, we find that its high-redshift evolution is well characterized by continued positive luminosity evolution coupled with negative density evolution (with increasing redshift). This explains why bright sub-mm sources continue to be found at z > 5, even though their integrated contribution to cosmic star formation density at such early times is very small. The evolution of the far-IR galaxy LF thus appears similar in form to that already established for active galactic nuclei, possibly reflecting a similar dependence on the growth of galaxy mass.
ABSTRACT
The results of analysis of HST I‐band imaging of a sample of 41 radio galaxies spanning three orders of magnitude in radio luminosity at redshift z≃ 0.5 are presented. These results ...represent the first stage in a coordinated programme to study the connection between radio luminosity and host galaxy properties, black hole masses and cluster environments in radio galaxies spanning a wide range in radio luminosity over a restricted range in redshift. The full sample is comprised of objects drawn from four complete, low‐frequency selected radio samples with progressively fainter flux‐density limits (3CRR, 6CE, 7CRS and the new TexOx‐1000 sample). Modelling of the HST imaging data shows that the host galaxies have surface‐brightness distributions consistent with those expected for classic ellipticals (Sérsic parameter, β≃ 0.25), with β in the range 0.17 < β < 0.30, and a mean of 〈β〉= 0.23 ± 0.01. The luminosities of the host galaxies are found to be comparable with those of galaxies drawn from the bright end of the local cluster galaxy luminosity function, spanning the range 0.7L★ < L < 10 L★, with a mean of 3.2 ± 0.3L★, after correcting for the effects of passive evolution. In addition, the radio galaxies are shown to follow a Kormendy (μe−re) relation indistinguishable from that of both powerful low‐redshift radio galaxies and local Abell brightest cluster galaxies (BCGs). Combining our new results with those in the literature it is found that the scalelengths and Kormendy relations of 3C‐class radio galaxies do not vary significantly over the redshift range 0.0 < z < 0.8, providing no evidence for dynamical evolution of this class of host galaxy within this redshift interval. Converting the host galaxy luminosities into black hole mass estimates, using the local Mbh−Mbulge correlation, predicts that the radio galaxies harbour central black holes with masses in the range 108.1 M⊙ < Mbh < 109.5 M⊙, with a geometric mean of 〈Mbh〉= 108.87±0.04 M⊙. Finally, a significant (≃ 3σ) correlation is found between black hole mass and 151‐MHz radio luminosity for those objects in the sample with either high‐excitation nuclear spectra or classical double radio structures.
ABSTRACT
We have selected and analysed the properties of a sample of 2905 Ks < 21.5 galaxies in ∼131 arcmin2 of the Great Observatories Origins Deep Survey (GOODS) Chandra Deep Field South (CDFS), to ...obtain further constraints on the evolution of Ks‐selected galaxies with respect to the results already obtained in previous studies. We made use of the public deep multiwavelength imaging from the optical B through the infrared (IR) 4.5‐μm bands, in conjunction with available spectroscopic and COMBO17 data in the CDFS, to construct an optimized redshift catalogue for our galaxy sample. We computed the Ks‐band luminosity function and determined that its characteristic magnitude has a substantial brightening and a decreasing total density from z= 0 to 〈z〉= 2.5. We also analysed the colours and number density evolution of galaxies with different stellar masses. Within our sample, and in contrast to what is observed for less massive systems, the vast majority (∼85–90 per cent) of the most massive (M > 2.5 × 1011 M⊙) local galaxies appear to be in place before redshift z∼ 1. Around 65–70 per cent of the total assemble between redshifts z= 1 and 3 and most of them display extremely red colours, suggesting that plausible star formation in these very massive systems should mainly proceed in obscured, short‐time‐scale bursts. The remaining fraction (up to ∼20 per cent) could be in place at even higher redshifts z= 3–4, pushing the first epoch of formation of massive galaxies beyond the limits of current near‐IR surveys.
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