THE EXISTENCE OF AN OLD QUASAR AT z=3.91 AND ITS IMPLICATIONS FOR Λ(t) DEFLATIONARY COSMOLOGIES

Abstract

We investigate some observational constraints on decaying vacuum cosmologies based on the recently discovered old high redshift quasar APM 08279+5255. This object is located at z = 3.91 and has an estimated age of 2-3 Gyr. The class of Λ(t) cosmologies is characterized by a positive β parameter smaller than unity which quantifies the ratio between the vacuum and the total energy density. Assuming the lower limit age (2 Gyr) and that the cold dark matter contributes with Ω M = 0.2 we show that β is constrained to be ≥ 0.07 while for an age of 3 Gyr and Ω M = 0.4 the β parameter must be greater than 0.32. Our analysis includes closed, flat and hyperbolic scenarios, and it strongly suggests that there is no age crisis for this kind of Λ(t) cosmologies. Lower limits to the redshift quasar formation are also briefly discussed to the flat case. For Ω M = 0.4 we found that the redshift formation is constrained by z f ≥ 8.0. * jvital@dfte.ufrn.br † rose@dfte.ufrn.br Recent observations from Supernovae (SNe) type Ia strongly suggest that the bulk of energy in the Universe is repulsive and appears like a dark component; an unknown form of energy with negative pressure [in addition to the ordinary dark matter] which is probably of primordial origin [1]. The most natural candidate for dark energy is the cosmological constant (Λ), or equivalently, a perfect fluid obeying the equation of state, p v = −ρ v , which is usually interpreted as the constant vacuum energy density of all fields existing in the Universe. The Λ-term is the simplest but not the unique possibility. Other candidates appearing in the literature are: a relic scalar field component (SFC) which is slowly rolling down its potencial [2], a decaying vacuum energy density, or a time varying Λ-term [3], the so-called "X-matter", an extra component [4] characterized by an equation of state p x = ωρ x(XCDM), and the Chaplygin type gas whose equation of state is p = −A/ρ α , where A and α are positive constants [5] (see also Lima [6] for a quick review). On the other hand, the existence of old high-redshift objects is one of the best methods for constraining the age of the Universe, as well the basic cosmological parameters [7]. Such objects also provide an important key for determining the first epoch of galaxy formation. In this connection, quasars are among the most luminous objects known in the universe and their prominent emission-lines contains valuable information to estimate their ages. The recently reported age estimates of the APM 08279+5255 quasar with a lower limit of 2-Gyr-old at redshift z = 3.91 is therefore a particularly interesting event [8]. In this article we investigate some cosmological implications from the existence of this quasar to a large class of decaying vacuum cosmologies proposed by Lima and collaborators [9]. Some constraints on the first epoch of quasar formation are also discussed.

Simplified gravitational collapse with an interacting vacuum energy density

“…Since the initial core surface must be non-trapped, we can also infer from (37,41) that the vacuum parameter to form a black hole satisfies the same condition previously derived in paper I (see Eq. 27 there): [73] determined by a condition involving only the values assumed by the pair of dynamical parameters (ω, β).…”

Reconciling the cosmic age problem in the $$R_\mathrm{h}=ct$$ R h = c t universe

“…The cosmic age problem is that some objects are older than the age of the universe at its redshift z. In previous literature, many cosmological models have been tested by the old quasar APM 08279+5255 with age 2.1 ± 0.3 Gyr at z = 3.91 [13,14], such as the CDM [13,15], the (t) model [16], the interacting dark energy models [12], the generalized Chaplygin gas model [17,18], the holographic dark energy model [19], braneworld models [20][21][22], and the conformal gravity model [23]. But all of these models have a serious age problem except the conformal gravity model, which can accommodate this quasar at 3σ confidence level [23].…”

Age problem in the holographic dark energy model

“…In fact, these three OHRO at z = 1.43, 1.55 and 3.91 have been used to test many dark energy models, such as the ΛCDM model [44,53,54], the dark energy models with different EoS parameterizations [49,50], the generalized Chaplygin gas [55], the Λ(t)CDM model [56], the model-independent EoS of dark energy [57], the scalar-tensor quintessence [58], the f (R) = R 2 − R 2 0 model [59], the DGP braneworld model [60,61], the power-law parameterized quintessence model [62], and so on. It is found that the two OHRO at z = 1.43 and 1.55 can be easily accommodated in most dark energy models, whereas the OHRO at z = 3.91 can not, even in the ΛCDM model.…”