AbstractWe reinvestigate a claimed sample of 22 X-ray detected active galactic nuclei (AGN) at redshifts z > 4, which has reignited the debate as to whether young galaxies or AGN reionized the ...Universe. These sources lie within the Great Observatories Origins Deep Survey-South (GOODS-S)/Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) field, and we examine both the robustness of the claimed X-ray detections (within the Chandra 4Ms imaging) and perform an independent analysis of the photometric redshifts of the optical/infrared counterparts. We confirm the reality of only 15 of the 22 reported X-ray detections, and moreover find that only 12 of the 22 optical/infrared counterpart galaxies actually lie robustly at z > 4. Combining these results we find convincing evidence for only seven X-ray AGN at z > 4 in the GOODS-S field, of which only one lies at z > 5. We recalculate the evolving far-ultraviolet (1500 Å) luminosity density produced by AGN at high redshift, and find that it declines rapidly from z ≈ 4 to z ≈ 6, in agreement with several other recent studies of the evolving AGN luminosity function. The associated rapid decline in inferred hydrogen ionizing emissivity contributed by AGN falls an order-of-magnitude short of the level required to maintain hydrogen ionization at z ≈ 6. We conclude that all available evidence continues to favour a scenario in which young galaxies reionized the Universe, with AGN making, at most, a very minor contribution to cosmic hydrogen reionization.
Parametric models for galaxy star formation histories (SFHs) are widely used, though they are known to impose strong priors on physical parameters. This has consequences for measurements of the ...galaxy stellar-mass function, star formation rate density (SFRD), and star-forming main sequence (SFMS). We investigate the effects of the exponentially declining, delayed exponentially declining, lognormal, and double power-law SFH models using Bagpipes. We demonstrate that each of these models imposes strong priors on specific star formation rates (SFRs), potentially biasing the SFMS, and also imposes a strong prior preference for young stellar populations. We show that stellar mass, SFR, and mass-weighted age inferences from high-quality mock photometry vary with the choice of SFH model by at least 0.1, 0.3, and 0.2 dex, respectively. However, the biases with respect to the true values depend more on the true SFH shape than the choice of model. We also demonstrate that photometric data cannot discriminate between SFH models, meaning that it is important to perform independent tests to find well-motivated priors. We finally fit a low-redshift, volume-complete sample of galaxies from the Galaxy and Mass Assembly (GAMA) Survey with each model. We demonstrate that our stellar masses and SFRs at redshift z ∼ 0.05 are consistent with other analyses. However, our inferred cosmic SFRDs peak at z ∼ 0.4, approximately 6 Gyr later than direct observations suggest, meaning that our mass-weighted ages are significantly underestimated. This makes the use of parametric SFH models for understanding mass assembly in galaxies challenging. In a companion paper, we consider nonparametric SFH models.
Essential physics of early galaxy formation Dayal, Pratika; Ferrara, Andrea; Dunlop, James S ...
Monthly notices of the Royal Astronomical Society,
12/2014, Letnik:
445, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We present a theoretical model embedding the essential physics of early galaxy formation (z ≃ 5–12) based on the single premise that any galaxy can form stars with a maximal limiting efficiency that ...provides enough energy to expel all the remaining gas, quenching further star formation. This simple idea is implemented into a merger-tree-based semi-analytical model that utilizes two mass and redshift-independent parameters to capture the key physics of supernova feedback in ejecting gas from low-mass haloes, and tracks the resulting impact on the subsequent growth of more massive systems via halo mergers and gas accretion. Our model shows that: (i) the smallest haloes (halo mass M
h ≤ 1010 M⊙) build up their gas mass by accretion from the intergalactic medium; (ii) the bulk of the gas powering star formation in larger haloes (M
h ≥ 1011.5 M⊙) is brought in by merging progenitors; (iii) the faint-end UV luminosity function slope evolves according to α = −1.75 log z − 0.52. In addition, (iv) the stellar mass-to-light ratio is well fitted by the functional form log M
* = −0.38M
UV − 0.13 z + 2.4, which we use to build the evolving stellar mass function to compare to observations. We end with a census of the cosmic stellar mass density (SMD) across galaxies with UV magnitudes over the range −23 ≤ M
UV ≤ −11 spanning redshifts 5 < z < 12; (v) while currently detected LBGs contain ≈50 per cent (10 per cent) of the total SMD at z = 5 (8), the James Webb Space Telescope will detect up to 25 per cent of the SMD at z ≃ 9.5.
We present a simple, redshift-independent analytic model that explains the local fundamental metallicity relation (FMR), taking into account the physical processes of star formation, inflow of ...metal-poor intergalactic medium (IGM) gas, and the outflow of metal-rich interstellar medium (ISM) gas. We show that the physics of the FMR can be summarized as follows: for massive galaxies with stellar mass M
* ≥ 1011 M, ISM metal enrichment due to star formation is compensated by inflow of metal-poor IGM gas, leading to a constant value of the gas metallicity with star formation rate (SFR); outflows are rendered negligible as a result of the large potential wells of these galaxies. On the other hand, as a result of their smaller SFR, less massive galaxies produce less heavy elements that are also more efficiently ejected due to their shallow potential wells; as a result, for a given M
*, the gas metallicity decreases with SFR. For such galaxies, the outflow efficiency determines both the slope and the knee of the metallicity-SFR relation. Without changing any parameters, this simple model is also successfully matched to the gas fraction-gas metallicity relation observed for a sample of about 260 nearby galaxies.
We present a new, robust measurement of the evolving rest-frame ultraviolet (UV) galaxy luminosity function (LF) over the key redshift range from z ... 2 to z ... 4. Our results are based on the high ...dynamic range provided by combining the Hubble Ultra Deep Field (HUDF), CANDELS/GOODS-South, and UltraVISTA/COSMOS surveys. We utilize the unparalleled multifrequency photometry available in this survey 'wedding cake' to compile complete galaxy samples at z ... 2, 3, 4 via photometric redshifts (calibrated against the latest spectroscopy) rather than colour-colour selection, and to determine accurate rest-frame UV absolute magnitudes (M sub( 1500)) from spectral energy distribution (SED) fitting. Our new determinations of the UV LF extend from M sub( 1500) ... -22 (AB mag) down to M sub( 1500) = -14.5, -15.5 and -16 at z ... 2, 3 and 4, respectively (thus, reaching ... 3-4 mag fainter than previous blank-field studies at z ... 2,3). At z ... 2, 3, we find a much shallower faint-end slope (... = -1.32 plus or minus 0.03) than reported in some previous studies (... -1.7), and demonstrate that this new measurement is robust. By z ... 4, the faint-end slope has steepened slightly, to ... = -1.43 plus or minus 0.04, and we show that these measurements are consistent with the overall evolutionary trend from z = 0 to 8. Finally, we find that while characteristic number density (...*) drops from z ... 2 to z ... 4, characteristic luminosity (M*) brightens by ... 1 mag. This, combined with the new flatter faint-end slopes, has the consequence that UV luminosity density (and hence unobscured star formation density) peaks at z ... 2.5-3, when the Universe was ... 2.5 Gyr old. (ProQuest: ... denotes formulae/symbols omitted.)
Submillimetre galaxies (SMGs) are among the most luminous dusty galaxies in the Universe, but their true nature remains unclear; are SMGs the progenitors of the massive elliptical galaxies we see in ...the local Universe, or are they just a short-lived phase among more typical star-forming galaxies? To explore this problem further, we investigate the clustering of SMGs identified in the SCUBA-2 Cosmology Legacy Survey. We use a catalogue of submillimetre (850 mu m) source identifications derived using a combination of radio counterparts and colour/infrared selection to analyse a sample of 610 SMG counterparts in the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Survey (UKIDSS) Ultra Deep Survey (UDS), making this the largest high-redshift sample of these galaxies to date. Using angular cross-correlation techniques, we estimate the halo masses for this large sample of SMGs and compare them with passive and star-forming galaxies selected in the same field. We find that SMGs, on average, occupy high-mass dark matter haloes ... at redshifts z > 2.5, consistent with being the progenitors of massive quiescent galaxies in present-day galaxy clusters. We also find evidence of downsizing, in which SMG activity shifts to lower mass haloes at lower redshifts. In terms of their clustering and halo masses, SMGs appear to be consistent with other star-forming galaxies at a given redshift. (ProQuest: ... denotes formulae/symbols omitted.)
ABSTRACT We discuss new constraints on the epoch of cosmic reionization and test the assumption that most of the ionizing photons responsible arose from high-redshift star-forming galaxies. Good ...progress has been made in charting the end of reionization through spectroscopic studies of 6-8 QSOs, gamma-ray bursts, and galaxies expected to host Ly emission. However, the most stringent constraints on its duration have come from the integrated optical depth, τ, of Thomson scattering to the cosmic microwave background. Using the latest data on the abundance and luminosity distribution of distant galaxies from Hubble Space Telescope imaging, we simultaneously match the reduced value recently reported by the Planck collaboration and the evolving neutrality of the intergalactic medium with a reionization history within , thereby reducing the requirement for a significant population of very high redshift ( ) galaxies. Our analysis strengthens the conclusion that star-forming galaxies dominated the reionization process and has important implications for upcoming 21 cm experiments and searches for early galaxies with the James Webb Space Telescope.
We investigate the relation between star formation rate (SFR) and stellar mass (M), i.e., the main sequence (MS) relation of star-forming galaxies, at in the first four Hubble Space Telescope (HST) ...Frontier Fields, on the basis of rest-frame UV observations. Gravitational lensing combined with deep HST observations allows us to extend the analysis of the MS down to at and at higher redshifts, a factor of ∼10 below most previous results. We perform an accurate simulation to take into account the effect of observational uncertainties and correct for the Eddington bias. This step allows us to reliably measure the MS and in particular its slope. While the normalization increases with redshift, we fit an unevolving and approximately linear slope. We nicely extend to lower masses the results of brighter surveys. Thanks to the large dynamic range in mass and by making use of the simulation, we analyzed any possible mass dependence of the dispersion around the MS. We find tentative evidence that the scatter decreases with increasing mass, suggesting a larger variety of star formation histories in low-mass galaxies. This trend agrees with theoretical predictions and is explained as either a consequence of the smaller number of progenitors of low-mass galaxies in a hierarchical scenario and/or of the efficient but intermittent stellar feedback processes in low-mass halos. Finally, we observe an increase in the SFR per unit stellar mass with redshift milder than predicted by theoretical models, implying a still incomplete understanding of the processes responsible for galaxy growth.
Abstract
We investigate the relationship between the quenching of star formation and the structural transformation of massive galaxies, using a large sample of photometrically selected post-starburst ...galaxies in the UKIDSS Ultra-Deep Survey field. We find that post-starburst galaxies at high redshift (z > 1) show high Sérsic indices, significantly higher than those of active star-forming galaxies, but with a distribution that is indistinguishable from the old quiescent population. We conclude that the morphological transformation occurs before (or during) the quenching of star formation. Recently quenched galaxies are also the most compact; we find evidence that massive post-starburst galaxies (M* > 1010.5 M⊙) at high redshift (z > 1) are on average smaller than comparable quiescent galaxies at the same epoch. Our findings are consistent with a scenario in which massive passive galaxies are formed from three distinct phases: (1) gas-rich dissipative collapse to very high densities, forming the proto-spheroid, (2) rapid quenching of star formation to create the ‘red nugget’ with post-starburst features and (3) a gradual growth in size as the population ages, perhaps as a result of minor mergers.
We present the results of the deepest search to date for star-forming galaxies beyond a redshift z Asymptotically = to 8.5 utilizing a new sequence of near-infrared Wide-Field Camera 3 (WFC3/IR) ...images of the Hubble Ultra Deep Field (UDF). This "UDF12" campaign completed in 2012 September doubles the earlier exposures with WFC3/IR in this field and quadruples the exposure in the key F105W filter used to locate such distant galaxies. Combined with additional imaging in the F140W filter, the fidelity of high-redshift candidates is greatly improved. Using spectral energy distribution fitting techniques on objects selected from a deep multi-band near-infrared stack, we find seven promising z > 8.5 candidates. As none of the previously claimed UDF candidates with 8.5 < z < 10 are confirmed by our deeper multi-band imaging, our campaign has transformed the measured abundance of galaxies in this redshift range. Although we recover the candidate UDFj-39546284 (previously proposed at z = 10.3), it is undetected in the newly added F140W image, implying that it lies at z = 11.9 or is an intense emission line galaxy at z Asymptotically = to 2.4. Although no physically plausible model can explain the required line intensity given the lack of Ly? or broadband UV signal, without an infrared spectrum we cannot rule out an exotic interloper. Regardless, our robust z Asymptotically = to 8.5-10 sample demonstrates a luminosity density that continues the smooth decline observed over 6 < z < 8. Such continuity has important implications for models of cosmic reionization and future searches for z > 10 galaxies with James Webb Space Telescope.
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