arXiv subjects

Zoltan Haiman

Publications and source records attributed to Zoltan Haiman.

At least 235 records · Page 13Linked to original sources

arXiv2000

Quasar Strömgren Spheres Before Cosmological Reionization

Ionizing sources embedded in the neutral intergalactic medium (IGM) before cosmological reionization generate discrete HII regions. We show that a sufficiently bright quasar (for example, one tenth as luminous as that recently discovered by Fan et al.) can ionize a large volume, allowing the transmission of a substantial fraction of the flux of its intrinsic Lyman alpha emission line on both sides of the Lyman alpha wavelength. The observed line profile is richly informative. We show that a sufficiently accurate, high spectral resolution ($R\approx 10^4$) measurement of the line profile of a bright quasar is feasible using the Next Generation Space Telescope (NGST) as well as large ground-based telescopes. Such a measurement has two potentially important applications. First, the red side of the Lyman alpha emission line provides a way to measure the quasar lifetime. Second, the blue side provides a direct measure of the density fluctuations of the intergalactic medium at the quasar redshift. The estimate of the absorption of the red side is limited by the accuracy to which the intrinsic profile of the Lyman alpha emission line is known. The blue side, however, does not sensitively depend on the intrinsic profile, because the former is much narrower than the latter.

astro-ph↗

arXiv2000

Galaxy Cluster Baryon Fractions, Cluster Surveys and Cosmology

The properties of nearby galaxy clusters limit the range of cosmological parameters consistent with our universe. We describe the limits which arise from studies of the intracluster medium (ICM) mass fraction fICM and consideration of the possible sources of systematic error: Omega_M<0.44h_{50}^{-1/2} at 95% confidence. We emphasize that independent of Type Ia supernovae (SNe Ia) observations, this cluster study, taken together with published cosmic microwave background (CMB) anisotropy studies, indicates a non-zero quintessence or dark energy component Omega_Q>0. We then discuss future galaxy cluster surveys which will probe the abundance of galaxy clusters to intermediate and high redshift. We investigate the sensitivity of these surveys to the cosmological density parameter Omega_M and the equation of state parameter w of any quintessence component. In particular, we show that cluster survey constraints from a proposed large solid angle X-ray survey are comparable in precision and complementary in nature to constraints expected from future CMB anisotropy and SNe Ia studies.

astro-ph↗

arXiv2000

Lyman Alpha Cooling Radiation from High-Redshift Halos

The baryons inside high-redshift halos with virial temperatures above T=10^4 K cool radiatively as they condense inside dark matter potential wells. We show that the release of the gravitational binding energy, over the halo assembly time-scale, results in a significant and detectable Ly alpha flux. At the limiting line flux of approximately 10^-19 erg/s/cm^2/asec^2 of the Next Generation Space Telescope, several sufficiently massive halos, with velocity dispersions above sigma=120 km/s, would be visible per 4'x4' field. The halos would have characteristic angular sizes of approximately 10 asec, would be detectable in a broad-band survey out to redshifts z=6-8, and would provide a direct probe of galaxies in the process of forming. They may be accompanied by HeII Ly alpha emission at the 10 percent level, but remain undetectable at other wavelengths. Our predictions are in good agreement with the recent finding of two Ly alpha ``blobs'' at z=3.1 by Steidel et al. (1999).

astro-ph↗

arXiv2000

The Role of H2 Molecules in Cosmological Structure Formation

We review the relevance of H2 molecules for structure formation in cosmology. Molecules are important at high redshifts, when the first collapsed structures appear with typical temperatures of a few hundred Kelvin. In these chemically pristine clouds, radiative cooling is dominated H2 molecules. As a result, H2 ``astro-chemistry'' is likely to determine the epoch when the first astrophysical objects appear. We summarize results of recent three-dimensional simulations. A discussion of the effects of feedback, and implications for the reionization of the universe is also given.

astro-ph↗

arXiv2000

Probing the Cosmic Dark Age in X-rays

Empirical studies of the first generation of stars and quasars will likely become feasible within the next decade in several different wavelength bands. Microwave anisotropy experiments, such as MAP or Planck, will set constraints on the ionization history of the intergalactic medium due to these sources. In the infrared, the Next Generation Space Telescope (NGST) will be able to directly detect sub-galactic objects at redshifts z>10. In the optical, data from the Hubble Deep Field already places a constraint on the abundance of high-redshift quasars. However, the epoch of the first quasars might be first probed in X-ray bands, by instruments such as the Chandra X-ray Observatory (CXO) and the X-ray Multi-mirror Mission (XMM). In a 500 Ksec integration, CXO reaches a sensitivity of 2x10-16 erg/s cm^2. Based on simple hierarchical CDM models, we find that at this flux threshold approx. 100 quasars might be detectable from redshifts z>5, and approx. 1 quasar at z=10, in each 17x17 arcmin field. Measurement of the power spectrum of the unresolved soft X-ray background will further constrain models of faint, high-redshift quasars.

astro-ph↗

arXiv1999

Cosmological Constant or Intergalactic Dust? Constraints from the Cosmic Far Infrared Background

Recent observations of Type Ia SNe at redshifts 0 < z <1 reveal a progressive dimming which has been interpreted as evidence for a cosmological constant of Omega_Lambda ~ 0.7. An alternative explanation of the SN results is an open universe with Omega_Lambda=0 and the presence of > 0.1 micron dust grains with a mass density of Omega_dust ~ (few) * 10^{-5} in the intergalactic (IG) medium. The same dust that dims the SNe absorbs the cosmic UV/optical background radiation around ~ 1 micron, and re-emits it at far infrared (FIR) wavelengths. Here we compare the FIR emission from IG dust with observations of the cosmic microwave (CMB) and cosmic far infrared backgrounds (FIRB) by the DIRBE/FIRAS instruments. We find that the emission would not lead to measurable distortion to the CMB, but would represent a substantial fraction (> 75%) of the measured value of the FIRB in the 300-1000 micron range. This contribution would be marginally consistent with the present unresolved fraction of the observed FIRB in an open universe. However, we find that IG dust probably could not reconcile the standard Omega=1 CDM model with the SN observations, even if the necessary quantity of dust existed. Future observations able to reliably resolve the FIRB to a flux limit of ~0.5 mJy, along with a more precise measure of the coarse-grained FIRB, will provide a definitive test of the IG dust hypothesis in all cosmologies.

astro-ph↗

arXiv1999

On the Cosmological Evolution of the Luminosity Function and the Accretion Rate of Quasars

We consider a class of models for the redshift evolution (between $0\lsim z \lsim 4$) of the observed optical and X-ray quasar luminosity functions (LFs), with the following assumptions: (i) the mass-function of dark matter halos follows the Press-Schechter theory, (ii) the black hole (BH) mass scales linearly with the halo mass, (iii) quasars have a constant universal lifetime, and (iv) a thin accretion disk provides the optical luminosity of quasars, while the X-ray/optical flux ratio is calibrated from a sample of observed quasars. The mass accretion rate $\dot{M}$ onto quasar BHs is a free parameter of the models, that we constrain using the observed LFs. The accretion rate $\dot M$ inferred from either the optical or X-ray data under these assumptions generally decreases as a function of cosmic time from $z \simeq 4$ to $z \simeq 0$. We find that a comparable accretion rate is inferred from the X-ray and optical LF only if the X-ray/optical flux ratio decreases with BH mass. Near $z\simeq 0$, $\dot M$ drops to substantially sub-Eddington values at which advection-dominated accretion flows (ADAFs) exist. Such a decline of $\dot M$, possibly followed by a transition to radiatively inefficient ADAFs, could explain both the absence of bright quasars in the local universe and the faintness of accreting BHs at the centers of nearby galaxies. We argue that a decline of the accretion rate of the quasar population is indeed expected in cosmological structure formation models.

astro-ph↗

arXiv1999

Correlations in the Far Infrared Background

We compute the expected angular power spectrum of the cosmic Far Infrared Background (FIRB). We find that the signal due to source correlations dominates the shot--noise for $\ell \la 1000$ and results in anisotropies with rms amplitudes $(\sqrt{\ell(\ell+1)C_\ell/2π})$ between 5% and 10% of the mean for $l \ga 150$. The angular power spectrum depends on several unknown quantities, such as the UV flux density evolution, optical properties of the dust, biasing of the sources of the FIRB, and cosmological parameters. However, when we require our models to reproduce the observed DC level of the FIRB, we find that the anisotropy is at least a few percent in all cases. This anisotropy is detectable with proposed instruments, and its measurement will provide strong constraints on models of galaxy evolution and large-scale structure at redshifts up to at least $z \sim5$.

astro-ph↗

arXiv1999

X-Ray Emission from the First Quasars

It is currently unknown whether the Universe was reionized by quasars or stars at z>5. We point out that quasars can be best distinguished from stellar systems by their X-ray emission. Based on a simple hierarchical CDM model, we predict the number counts and X-ray fluxes of quasars at high redshifts. The model is consistent with available data on the luminosity function of high-redshift quasars in the optical and soft X-ray bands. The cumulative contribution of faint, undetected quasars in our model is consistent with the unresolved fraction of the X-ray background. We find that the Chandra X-ray Observatory might detect approximately 100 quasars from redshifts z>5 per its 17'x17' field of view at the flux threshold of 2x10^-16 erg/s/cm^2. The redshifts of these faint point-sources could be identified by follow-up infrared observations from the ground or with the Next Generation Space Telescope.

astro-ph↗

arXiv1999

Reionization of the Intergalactic Medium and its Effect on the CMB

The bulk of the hydrogen in the universe transformed from neutral to ionized somewhere in the redshift interval 5 < z < 40, most likely due to ionizing photons produced by an early generation of stars or mini-quasars. The resulting free electrons, interacting with the CMB photons via Thomson scattering, are a mixed blessing, providing both a probe of the epoch of the first stars and a contaminant to the pristine primary anisotropy. Here we review our current knowledge of reionization with emphasis on inhomogeneities and describe the possible connections to CMB anisotropy.

astro-ph↗

arXiv1999

The Radiative Feedback of the First Cosmological Objects

In hierarchical models of structure formation, an early cosmic UV background (UVB) is produced by the small (T_vir < 10^4 K) halos that collapse before reionization. The UVB at energies below 13.6eV suppresses the formation of stars or black holes inside small halos, by photo-dissociating their only cooling agent, molecular H2. We self-consistently compute the buildup of the early UVB in Press-Schechter models, coupled with H2 photo-dissociation both in the intergalactic medium (IGM), and inside virialized halos. We find that the intergalactic H2 has a negligible effect on the UVB, both because its initial optical depth is small (tau<0.1), and because it is photo-dissociated at an early stage. If the UV sources in the first collapsed halos are stars, then their UV flux suppresses further star-formation inside small halos. This results in a pause in the buildup of the UVB, and reionization is delayed until larger halos (T_vir> 10^4 K) collapse. If the small halos host mini-quasars with hard spectra extending to approximately 1 keV, then their X-rays balance the effects of the UVB, the negative feedback does not occur, and reionization can be caused by the small halos.

astro-ph↗

arXiv1998

Empirical Constraints on the First Stars and Quasars

Empirical studies of the first generation of stars and quasars in the Universe will likely become feasible over the next decade. The Next Generation Space Telescope will provide direct imaging and photometry of sub-galactic objects at redshifts above z=10, while microwave anisotropy experiments, such as MAP or Planck, will set constraints on the ionization history of the intergalactic medium due to these sources. We describe the expected signals that will be detectable with these future instruments.

astro-ph↗

arXiv1998

Models for High-Redshift Lyman Alpha Emitters

We present models for dusty high-redshift Lyman alpha emitting galaxies by combining the Press-Schechter formalism with a treatment of inhomogeneous dust distribution inside galaxies. These models reproduce the surface density of emitters inferred from recent observations, and also agree with previous non-detections. Although a detailed determination of the individual model parameters is precluded by uncertainties, we find that (i) the dust content of primordial galaxies builds up in no more than 5x10^8 years, (ii) the galactic HII regions are inhomogeneous with a cloud covering factor of order unity, and (iii) the overall star formation efficiency is at least 5 percent. Future observations should be able to detect Lyman alpha galaxies upto redshifts of about z=8. If the universe is reionized at z(reion)<8, the corresponding decline in the number of Lyman alpha emitters at z>z(reion) could prove to be a useful probe of the reionization epoch.

astro-ph↗

arXiv1998

Formation of the First Stars and Quasars

We review observable signatures of the first generation of stars and low-luminosity quasars, including the metal enrichment, radiation background, and dust opacity/emission that they produce. We compute the formation history of collapsed baryonic halos based on an extension of the Press-Schechter formalism, incorporating the effects of pressure and H2-dissociation, and calibrate this history to observational data at redshifts z<5. To be consistent with the lack of faint point-sources in the Hubble Deep Field, we introduce a lower limit of 75 km/s for the circular velocities of halos harboring central black holes. Based on our models, we predict that future satellite instruments such as MAP, Planck, and NGST will be able to detect the signatures small star clusters and low-luminosity quasars at redshifts exceeding z=10.

astro-ph↗

arXiv1998

Models for Dusty Lyman alpha Emitters at High Redshift

Models are presented for the Lyman alpha emission of dusty high-redshift galaxies by combining the Press-Schechter formalism with a treatment of the inhomogeneous dust distribution inside galaxies. It is found that the amount of Lyman alpha radiation escaping from the galaxies strongly depends on the time over which the dust is produced through stellar activity, and on the ambient inhomogeneity of the HII regions that surround the ionizing OB stars. Good agreement is found with recent observations, as well as previous non-detections. Our models indicate that the dust content builds up in no more than approximately 5x10^8 yr, the galactic HII regions are inhomogeneous with a cloud covering factor of order unity, and the overall star formation efficiency is at least about 5%. It is predicted that future observations can detect these Lyman alpha galaxies upto redshifts of about 8.

astro-ph↗

arXiv1998

Determining the Redshift of Reionization From the Spectra of High-Redshift Sources

The redshift at which the universe was reionized is currently unknown. We examine the optimal strategy for extracting this redshift, z_{reion}, from the spectra of early sources. For a source located at a redshift z_s beyond but close to reionization, 1<[(1+z_s)/(1+z_{reion})]<(32/27), the Gunn-Peterson trough splits into disjoint Lyman-alpha, beta, and possibly higher Lyman series troughs, with some transmitted flux in between these troughs. We show that although the transmitted flux is suppressed considerably by the dense Lyman-alpha forest after reionization, it is still detectable for sufficiently bright sources and can be used to infer the reionization redshift. The Next Generation Space Telescope will reach the spectroscopic sensitivity required for the detection of such sources.

astro-ph↗

arXiv1998

Constraints from the Hubble Deep Field on High Redshift Quasar Models

High resolution, deep imaging surveys are instrumental in setting constraints on semi-analytical structure formation models in Cold Dark Matter (CDM) cosmologies. We show here that the lack of unresolved B-band ``dropouts'' with V > 25 mag in the Hubble Deep Field (HDF) appears to be inconsistent with the expected number of quasars if massive black holes form with a constant universal efficiency in all CDM halos. To reconcile the models with the data, a mechanism is needed that suppresses the formation of quasars in halos with circular velocities v(circ) < 50-75 km/s. This feedback naturally arises due to the photoionization heating of the gas by the UV background. We consider several alternative effects that would help reduce the quasar number counts, and find that these can not alone account for the observed lack of detections. If reddening by dust can be neglected at early epochs, consistency with the optical data also requires that the luminous extent of dwarf galaxies at high redshifts be larger than a few percent of the virial radii of their dark matter halos, in order not to overpredict the number of point-like B-band dropouts. Future deep observations in the J and H bands with NICMOS might reveal several z > 5 objects per field or provide even stronger constraints on the models than existing B, V, and I data.

astro-ph↗

arXiv1997

Observational Signatures of the First Quasars

We study the observational signatures of a potential population of low-luminosity quasars at high redshifts in a LambdaCDM cosmology. We derive the evolution of the quasar luminosity function at fainter luminosities and higher redshifts than currently detected, based on three assumptions: (1) the formation of dark-matter halos follows the Press-Schechter theory, (2) the ratio of central black hole mass to halo mass is the same for all halos, and (3) the light-curve of quasars, in Eddington units, is universal. We show that a universal light-curve provides an excellent fit to the observed quasar luminosity function at redshifts 2.6 < z < 4.5. By extrapolating the evolution of this luminosity function to higher redshifts (4.5 < z < 20), we find that the associated early population of low-luminosity quasars reionizes the universe around redshift z=12. The reprocessing of the UV light of these quasars by dust from early type II supernovae, distorts the microwave background spectrum by a Compton y-parameter, y = 1e-5, comparable to the upper limit set by COBE. The Next Generation Space Telescope could detect tens of quasars from redshifts z > 10 per square arcminute, with its proposed 1nJy sensitivity at 1-3.5 microns. Absorption spectra of several such quasars would reveal the reionization history of the universe.

astro-ph↗