1,721,038 research outputs found
Far infra-red emission lines in high redshift quasars
No full textWe present Plateau de Bure Interferometer observations of far infra-red
emission lines in BRI 0952-0115, a lensed quasar at z=4.4 powered by a
super-massive black hole (M_BH=2x10^9 M_sun). In this source, the resolved map
of the [CII] emission at 158 micron allows us to reveal the presence of a
companion galaxy, located at \sim 10 kpc from the quasar, undetected in optical
observations. From the CO(5-4) emission line properties we infer a stellar mass
M*<2.2x10^10 M_sun, which is significantly smaller than the one found in local
galaxies hosting black holes with similar masses (M* \sim 10^12 M_sun). The
detection of the [NII] emission at 205 micron suggests that the metallicity in
BRI 0952-0115 is consistent with solar, implying that the chemical evolution
has progressed very rapidly in this system. We also present PdBI observations
of the [CII] emission line in SDSSJ1148+5251, one of the most distant quasar
known, at z=6.4. We detect broad wings in the [CII] emission line, indicative
of gas which is outflowing from the host galaxy. In particular, the extent of
the wings, and the size of the [CII] emitting region associated to them, are
indicative of a quasar-driven massive outflow with the highest outflow rate
ever found (dM/dt>3500 M_sun/yr)
Reionization signatures in quasar absorption spectra
Full text linkOne of the most refined qualities of the human mind concerns with its natural attitude in questioning itself about the reason of everything it gets in touch with. This is a cascade process which inevitably ends up in wondering how the Universe originated and evolved into terrestrial life. In the course of ages the best approach to satisfy the human thirst of knowledge has proved to be the “scientific method”, based on the precious interplay between “tangible” (observations) and “intelligible” (theory). Cosmology is a discipline which aims, through this method, at shedding light on all the phases of the evolution of the Universe. Up to now the available technology has allowed to open and only partially come through the gates of the comprehension of the Universe..
Constraining the Reionization History with Quasar Absorption Spectra
No full textWe use a semi-analytical approach to simulate absorption spectra of QSOs at high redshifts with the aim of constraining the cosmic reionization history. We consider two physically motivated and detailed reionization histories: (i) an early reionization model (ERM) in which the intergalactic medium is reionized by Pop III stars at z≈ 14, and (ii) a more standard late reionization model (LRM) in which overlapping, induced by QSOs and normal galaxies, occurs at z≈ 6. From the analysis of current Lyα forest data at z < 6, we conclude that it is impossible to disentangle the two scenarios, which fit equally well the observed Gunn–Peterson optical depth, flux probability distribution function and dark gap width distribution. At z > 6, however, clear differences start to emerge which are best quantified by the dark gap and peak width distributions. We find that 35 (0) per cent of the lines of sight (LOS) within 5.7 < z < 6.3 show dark gaps of widths >50 Å in the rest frame of the QSO if reionization is not (is) complete at z≳ 6. Similarly, the ERM predicts peaks of width ∼1 Å in 40 per cent of the LOS in the redshift range 6.0–6.6; in the same range, LRM predicts no peaks of width >0.8 Å. We conclude that the dark gap and peak width statistics represent superb probes of cosmic reionization if about ten QSOs can be found at z > 6. We finally discuss strengths and limitations of our method
Multiscale inference of matter fields and baryon acoustic oscillations from the Lyα forest
No full textWe present a novel Bayesian method for the joint reconstruction of
cosmological matter density fields, peculiar velocities and power-spectra in
the quasi-nonlinear regime. We study its applicability to the Ly-alpha forest
based on multiple quasar absorption spectra. Our approach to this problem
includes a multiscale, nonlinear, two-step scheme since the statistics
describing the matter distribution depends on scale, being strongly
non-Gaussian on small scales (< 0.1 h^-1 Mpc) and closely lognormal on scales
>~10 h^-1 Mpc. The first step consists on performing 1D highly resolved
matter density reconstructions along the line-of-sight towards z~2-3 quasars
based on an arbitrary non-Gaussian univariate model for matter statistics. The
second step consists on Gibbs-sampling based on conditional PDFs. The matter
density field is sampled in real space with Hamiltonian-sampling using the
Poisson/Gamma-lognormal model, while redshift distortions are corrected with
linear Lagrangian perturbation theory. The power-spectrum of the lognormal
transformed variable which is Gaussian distributed (and thus close to the
linear regime) can consistently be sampled with the inverse Gamma distribution
function. We test our method through numerical N-body simulations with a
computational volume large enough (> 1 h^-3 Gpc^3) to show that the linear
power-spectra are nicely recovered over scales larger than >~20 h^-1 Mpc,
i.e. the relevant range where features imprinted by the baryon-acoustics
oscillations (BAOs) appear
The circumgalactic medium of high-redshift galaxies
No full textWe study the properties of the circumgalactic medium (CGM) of high-
galaxies in the metal enrichment simulations presented in Pallottini et al.
2014. At , we find that the simulated CGM gas density profiles are
self-similar, once scaled with the virial radius of the parent dark matter
halo. We also find a simple analytical expression relating the neutral hydrogen
equivalent width (\rm EW_\rm HI) of CGM absorbers as a function of the
line of sight impact parameter (). We test our predictions against mock
spectra extracted from the simulations, and show that the model reproduces the
\rm EW_\rm HI(b) profile extracted from the synthetic spectra analysis.
When compared with available data, our CGM model nicely predicts the observed
\rm EW_\rm HI(b) in galaxies, and supports the idea that the
CGM profile does not evolve with redshift
Inferring physical properties of galaxies from their emission-line spectra
No full textWe present a new approach based on Supervised Machine Learning algorithms to infer key physical properties of galaxies (density, metallicity, column density and ionization parameter) from their emission-line spectra. We introduce a numerical code (called GAME, GAlaxy Machine learning for Emission lines) implementing this method and test it extensively. GAME delivers excellent predictive performances, especially for estimates of metallicity and column densities. We compare GAME with the most widely used diagnostics (e.g. R23, [NII] λ6584/Hα indicators) showing that it provides much better accuracy and wider applicability range. GAME is particularly suitable for use in combination with Integral Field Unit spectroscopy, both for rest-frame optical/UV nebular lines and far-infrared/sub-millimeter lines arising from photodissociation regions. Finally, GAME can also be applied to the analysis of synthetic galaxy maps built from numerical simulations
ON THE [C ii]–SFR RELATION IN HIGH REDSHIFT GALAXIES
Full text linkAfter two Atacama Large Millimeter/submillimeter Array (ALMA) observing cycles, only a handful of [C II] 158 μm emission line searches in z > 6 galaxies have reported a positive detection, questioning the applicability of the local [C II]-star formation rate (SFR) relation to high-z systems. To investigate this issue we use the Vallini et al. (V13) model,based on high-resolution, radiative transfer cosmological simulations to predict the [C II] emission from the interstellar medium of a z ≈ 7 (halo mass Mh = 1.17 × 1011 Mo) galaxy. We improve the V13 model by including (a) a physically motivated metallicity (Z) distribution of the gas, (b) the contribution of photodissociation regions (PDRs), and (c) the effects of cosmic microwave background (CMB) on the [C II] line luminosity. We study the relative contribution of diffuse neutral gas to the total [C II] emission (Fdiff/Ftot) for different SFR and Z values. We find that the [C II] emission arises predominantly from PDRs: regardless of the galaxy properties, Fdiff/Ftot ≤ 10%, since at these early epochs the CMB temperature approaches the spin temperature of the [C II] transition in the cold neutral medium (TCMB ∼ TCNMs ∼ 20 K). Our model predicts a high-z [C II]-SFR relation, consistent with observations of local dwarf galaxies (0.02 < Z/Zo < 0.5). The [C II] deficit suggested by actual data (LCii < 2.0 × 107 Lo in BDF3299 at z ≈ 7.1) if confirmed by deeper ALMA observations, can be ascribed to negative stellar feedback disrupting molecular clouds around star formation sites. The deviation from the local [C II]-SFR would then imply a modified Kennicutt-Schmidt relation in z > 6 galaxies. Alternatively/in addition, the deficit might be explained by low gas metallicities (Z < 0.1 Zo)
Intensity mapping of [C II] emission from early galaxies
Full text linkThe intensity mapping of the [CII] 157.7 m fine-structure emission
line represents an ideal experiment to probe star formation activity in
galaxies, especially in those that are too faint to be individually detected.
Here, we investigate the feasibility of such an experiment for
galaxies. We construct the L_\rm CII - M_\rm h relation from observations
and simulations, then generate mock [CII] intensity maps by applying this
relation to halo catalogs built from large scale N-body simulations. Maps of
the extragalactic far-infrared (FIR) continuum, referred to as "foreground",
and CO rotational transition lines and [CI] fine-structure lines referred to as
"contamination", are produced as well. We find that, at 316 GHz (corresponding
to z_\rm CII = 5), the mean intensities of the extragalactic FIR continuum,
[CII] signal, all CO lines from to 13 and two [CI] lines are Jy sr, Jy sr, Jy sr
and Jy sr, respectively. We discuss a method that allows us
to subtract the FIR continuum foreground by removing a spectrally smooth
component from each line of sight, and to suppress the CO/[CI] contamination by
discarding pixels that are bright in contamination emission. The [CII]
signal comes mainly from halos in the mass range ; as
this mass range is narrow, intensity mapping is an ideal experiment to
investigate these early galaxies. In principle such signal is accessible to a
ground-based telescope with a 6 m aperture, 150 K system temperature, a
pixels FIR camera in 5000 hr total integration time, however it
is difficult to perform such an experiment by using currently available
telescopes
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